The glucose tolerance test is commonly used to assess the ability of standardized glucose bolus to induce hyperglycaemia. Alterations in insulin sensitivity (resistance or hypersensitivity) can be revealed on the basis of an insulin sensitivity test.
Science, Technology and Medicine open access publisher.Publish, read and share novel research. Glucose Tolerance Factor – Insulin Mimeticand Potentiating Agent – A Source for a Novel Anti Diabetic MedicationNitsa Mirsky[1] Department of Biology, University of Haifa at Oranim, Tivon, Israel1. P Zhang, X Zhang, J Brown, D Vistisen, R Sicree, J Shaw, G Nichols, 2010Global healthcare expenditure on diabetes for 2010 and 2030 Diab. An oral glucose tolerance test (OGTT) or intra-peritoneal glucose tolerance test (IPGTT) is used to assess the body’s ability to metabolize glucose. Traditional methods of glucose tolerance tests consist of the following basic steps: Fast the subject for 6-16 hours, depending on the protocol and IACUC considerations.
If doing manual sampling to use as a reference or for calibration purposes, follow guidelines in DSI technical note related to appropriate timing and entry of values into software.
Tamer Coskun1, Libbey O’Farrell1, Robert Brockway2, Paul Haefner2, Kimberly White2, Richard G. The current standard for routine glucose measurements in preclinical research is often glucometers and test strips.
Presently, few continuous monitoring glucose options are available for preclinical research.
Robert Brockway1, Tamer Coskun2, Libbey O’Farrell2, Paul Haefner1, Kimberly White1, Charles V. Background and aims: The current standard for routine glucose measurements in preclinical research is often glucometers and test strips.
Results: The glucose sensors provided high resolution data and demonstrated the ability to accurately assess chronic diurnal patterns matching with the feeding pattern of rats from 3 days up to 7 weeks after surgery.
Scott Tiesma1, Robert Brockway1, Tamer Coskun2, Libbey O’Farrell2, M Dodson Michael2, Amy L Cox2. Continuous glucose monitoring options have been very limited for research applications in pre-clinical models. The effect of a high-fat diet on glucose and food intake (FI) in pre-diabetic ZDSD male rats was assessed using continuous glucose (CG) telemetry (DSI, model HD-XG) and the BioDAQ FI monitoring system (Research Diets). The goal of this study was to assess the effect of a high-fat diet on glucose and food intake (FI) in pre-diabetic ZDSD male rats using continuous glucose (CG) telemetry (DSI, model HD-XG) and the BioDAQ FI monitoring system (Research Diets). Chronic cervical vagal nerve stimulation (VNS) causes weight loss in obese patients and in experimental animal models of obesity. The gene encoding for the catalytic subunit of the phosphatidylinositol-3-kinase (PI3K), p110a (PIK3CA) is the most frequently mutated kinase in cancer. However until now, continuous glucose monitoring options have been very limited in biomedical research. The present study evaluates the use of a new radio-telemetry device (HD-XG, Data Sciences International) incorporating an implantable glucose sensor (Nova Biomedical, Waltham, MA) for chronic continuous (every minute) glucose measurements in the arterial blood of brown Norway (BN) rats. Continuous glucose monitoring (CGM) systems are becoming more prevalent providing real-time measures of blood glucose in humans but may also prove invaluable in diabetes research.
Background: Chronic continuous glucose monitoring options for animal research have been very limited due to various technical and biological challenges. Methods: In vivo testing in rats including oral glucose tolerance tests (OGTTs) and intraperitoneal glucose tolerance tests (IPGTTs) and ex vivo waterbath testing were performed to evaluate acute and chronic sensor performance.
Results: Results demonstrated the ability to record continuous measurements for 75 days or longer.
Conclusions: This device provides significant advantages in the quality and quantity of data that can be obtained relative to existing alternatives such as intermittent blood sampling.
Metabolic syndrome is a cluster of abnormalities often associated with obesity and diabetes. There are numerous sex differences in metabolic parameters and blood pressure (BP), although many fewer studies have examined the molecular mechanisms driving high-fat (HF)-induced increases in BP and metabolic disorders in males vs. Historically, diabetes, obesity and metabolism research has focused on acute metabolic testing characterized by infrequent sampling methods.
In this exclusive webinar sponsored by Data Sciences International, we present a new method of continuously monitoring blood glucose via implantable telemetry. Six male Sprague Dawley rats were simultaneously implanted with a telemetry device measuring continuous arterial blood glucose (HD-XG) transmitting at 455KHz, and an second telemetry device measuring arterial blood pressure and a biopotential (ECG) operating at 18MHz (HD-S11-F2). Insulin-resistant diabetes (Type 2 diabetes mellitus, T2DM) is the most common form of diabetes. New technology was employed in a novel way to monitor the effect of diet change on continuous blood glucose in addition to standard hemodynamic parameters. The HD-XG glucose telemetry implant from DSI provides the ability to obtain continuous, real-time, blood glucose measurements in rodents.
Non-Obese Type2 Diabetes Animals ModelsYukihito Ishii, Takeshi Ohta and Tomohiko Sasase[1] Japan Tobacco Inc., Central Pharmaceutical Research Institute, Murasaki-cho, Takatsuki, Osaka, Japan1. Y Goto, K-I Suzuki, M Sasaki, T Ono, S Abe, GK rats as amodel of nonobese, noninsulin-dependent diabetes.
Y Goto, M Kakizaki, N Masaki, Spontaneous diabetes produced by selective breeding of normal Wistar rats. Y Tsuura, H Ishida, Y Okamoto, S Kato, K Sakamoto, M Horie, et alGlucose sensitivity of ATP-sensitive K+ channels is impaired in beta-cells of the GK rat.
K Ueta, T Ishihara, Y Matsumoto, A Oku, M Nawano, T Fujita, et alLong-term treatment with the Na+-glucose cotransporter inhibitor T-1095 causes sustained improvement in hyperglycemia and prevents diabetic neuropathy in Goto-Kakizaki Rats.
H Yamamoto, Y Uchigata, H Okamoto, Streptozotocin and alloxan induce DNA strand breaks and poly(ADP-ribose) synthetase in pancreatic islets. M Kergoat, B Portha, In vivo hepatic and peripheral insulin sensitivity in rats with non-insulin-dependent diabetes induced by streptozocin.
However a more reliable quantitative analysis is performed using the Euglycaemic Hyperinsulinemic clamp technique. IntroductionDiabetes is the world’s most common metabolic disease and one of the leading causes of morbidity and mortality.
S Holdsworth, E Neville, 1990Effects of extracts of high- and low-chromium brewer’s yeast on metabolism of glucose by hepatocytes from rats fed on high- or low-Cr dietsBr.
V Mantha, K Prasad, 1995Lipid peroxidation and activity of antioxidant enzymes in diabetic rats.Mol. I Varga, L Szabo, H Witas, 1983The effect of diabetes on the activities of the peroxides metabolizing enzymes. These pose significant limitations in terms of accuracy, animal stress, and frequency of sampling.
This study compares the performance of an existing interstitial system (Medtronic MiniMed) with a fully implantable direct blood monitoring prototype (Data Sciences International). Investigators have used periodic sampling of blood glucose to provide a coarse assessment of the efficacy of novel anti-diabetic therapies.
Ten male rats, 14 weeks old, were housed singly for 3 days prior to aseptic surgery to acclimate them to the FI system on control diet (Purina #5008). When rats were switched to D12468 their glucose excursion was significantly greater, even though their FI was similar to 5008. Ten male rats, 14 weeks old, were housed singly for three days prior to aseptic surgery to acclimate them to the FI system on control diet (Purina #5008).
Furthermore, parasympathetic activity directed to the liver has been demonstrated to reduce hepatic glucose release.
To assess whether bitter taste also decreases blood glucose after a glucose load, we took advantage of a new technology that continuously monitors changes in blood glucose – the DSI HD-XG glucose sensor. This discovery triggered the development of small molecule anti-PI3K inhibitors, such as NVP-BYL719. Investigators have used periodic sampling of blood glucose using a glucometer and test strips approach to provide a snap-shot assessment of the effect of PI3K inhibitors to glucose metabolism.
Aging nonhuman primates (NHPs) develop insulin resistance and high blood glucose in a way similar to the progression and onset of type 2 diabetes in humans, which makes them an excellent model for diabetes research.
We provide an evaluation of a novel telemetry device for continuous monitoring of temperature, activity, and plasma glucose levels in the arterial blood of rats for up to 2 months. Animal studies were in accordance with the guidelines for the care and use of laboratory animals and approved by the corresponding animal care and use committees (Data Sciences International, Eli Lilly). These devices provide the opportunity to expand the understanding of both glucose metabolism and homeostasis and to work toward improved therapies and cures for diabetes.
The hallmark of diabetes is insulin resistance, an impairment of insulin action within tissues at the level of the insulin receptor and subsequent cellular events. This research contributes critical information regarding glucose metabolism and homeostasis; however, the acute approach and low sampling frequency leaves critical gaps in glucose metabolism research findings.
Using case studies, we explore how a complete glucose profile can be observed while also reducing animal stress and associated labor for the scientist.
The HD-XG sensor was placed in the descending abdominal aorta and the device body was located IP. Nonhuman primates (NHPs) can naturally develop to insulin resistance and diabetes in a way similar to the progression and onset of T2DM in humans, which makes them as an excellent model for diabetes research.
A new telemetry implant (HD-S11-F2, DSI) enables researchers to collect and transmit data at a different radio-frequency (18MHz) than the traditional 455KHz implants. The goal of the current study was to compare spot blood glucose measurements with values obtained using telemetry in male and female DSS. Effect of DPPIV-i on blood glucose (A) and insulin (B) levels in glucose-loaded SDT fatty rats.
IntroductionDiabetes mellitus has become a global health problem, and the incidence of the disease is increasing rapidly in all regions of the world. H Giroix, B Portha, M Kergoat, D Bailbe, L Picon, Glucose insensitivity and amino-acid hypersensitivity of insulin release in rats with non-insulin-dependent diabetes. In this procedure insulin is administrated to raise plasma insulin concentration while glucose is infused to maintain euglycaemia. The medications currently in use are limited in their potency, have many side effects, and cannot be tolerated by many patients. T Dean, 1987Glucose autoxidation and protein modification: the potential role of autoxidative glycosylation in diabetes.
C Gutteridge, 1984Lipid peroxidation, oxygen radicals, cell damage and antioxidant therapy. Prototype sensors were surgically implanted in the abdominal aorta of 10 weight matched Sprague Dawley rats at 8 weeks of age. Each animal was surgically instrumented with glucose sensors in the abdominal aorta and the telemetry device placed in the intraperitoneal (ip) cavity. All rats under isofluorane anesthesia were implanted with a glucose sensor in the abdominal aorta and transmitter in the peritoneum. All rats were implanted with a glucose sensor in the abdominal aorta and transmitter in the peritoneum.
Thus, chronic cervical VNS may be particularly beneficial in obese type 2 diabetic patients. The HD-XG sensor was inserted into the abdominal aorta of a Sprague Dawley rat and a telemetry transponder was implanted into the peritoneal cavity.
The conventional tests of blood glucose are by handheld glucometer, clinical chemistry analyzer or analox analyzer. Type 2 diabetes arises from a combination of insulin resistance and a relative impairment of insulin secretion in response to meal ingestion. The HD-S11-F2 catheter was inserted in the femoral artery and routed to the abdominal aorta (just proximal to the iliac bifurcation and distal to the glucose sensor. The conventional tests of blood glucose are by handheld glucometer, clinical chemistry analyzer or Analox analyzer. While a second frequency allows for social housing and tighter density of research subjects, in this experiment the 18MHz device was paired with a continuous glucose telemetry implant (HD-XG, DSI) in the same animal.
Male and female rats were implanted with glucose telemeters at 11 weeks of age, and allowed 1 week to recover before being placed on receivers. The glucose infusion rate needed to maintain euglycaemia is a reflection of insulin action in the whole body when both glycemia and hyperinsulinemia are set at constant.
As a result of the global epidemic of diabetes, the need for new diabetes therapies is expected to grow dramatically during the next decade. The present study evaluates the use of a novel prototype device (Data Sciences International) for acute and chronic glucose measurements in rats.
The implantable device is 1.4 cc and provides continuous temperature, activity, and arterial blood glucose readings for 4 wks or longer. The animals were maintained on 5008 for 2 weeks and switched to a high-fat diet (Research Diets #D12468) for an additional 2 weeks. Here we tested the hypothesis that acute cervical VNS reduces blood glucose concentration in anesthetized rats. These methods require periodical blood sampling with potential subject stress and ethical volume limitation, especially during research. The glucose tolerance test (GTT) is vital for the characterization of metabolic syndrome, the natural progression of type 2 diabetes. Ralf Dechend (Max Delbruck Center for Molecular Medicine) presents a method of glucose monitoring in a novel pregnant rat model of type 2 diabetes and shares realized advantages pertaining to this new continuous approach. These methods require sampling blood periodically and may miss some critical information during monitoring. Implantation of two devices in a single animal allowed us to measure blood pressure, ECG, arterial blood glucose, body temperature and activity in a single rat. The glucose and the insulin levels were examined at immediately before glucose-loading, 30, 60, and 120 min after glucose-loading.
The glucose (A) and the insulin (B) levels were examined at immediately before glucose-loading, 30, 60, and 120 min after glucose-loading.
For example, prevalence of diabetes across the world is forecast to increase from 171 million in 2000 to 366 million in 2030 [1].Diabetes mellitus is classified into two categories, type 1 and type 2. An intense research has been conducted to identify new therapeutic targets and pharmacologic compounds that might correct the impaired glucose tolerance.
The device is 1.4cc and provides temperature, activity, and direct continuous blood glucose readings for 4 weeks or longer.
Daily and GTT reference values were recorded with a StatStrip Xpress glucometer (Nova Biomedical).
Continuous assessment of blood glucose was performed in 12 Sprague Dawley rats in which diabetes was induced with streptozotocin (STZ). Animals were then switched to a high-fat diet (Research Diets #D12468) for an additional 2 weeks at which time another OGTT was performed.
CG monitoring allowed for visualization of the circadian pattern that was not seen with FI and would not have been detected to the same degree using twice daily blood glucose sampling.
Sprague Dawley rats were instrumented with catheters in the left carotid artery, bipolar electrodes on the right cervical vagus nerve, and a novel telemetric glucose sensor (HD-XG, DSI) in the abdominal aorta, that allows for continuous monitoring of blood glucose concentration.
The rat was then returned to its home cage and remained undisturbed while blood glucose levels were monitored every 10 sec for several hours.
These data validate this platform technology against standard methods of glucose monitoring and demonstrate the utility of this technology in drug discovery and diabetes research.
This study investigated HD-XG transmitter, a Data Sciences International implantable device, for continuous monitoring of blood glucose in conscious NHPs. In metabolic syndrome research, routine glucose measurements, including GTT, are often accomplished using glucometers and test strips.
In addition, Christian Schnell (Novartis) discusses the value of continuous glucose data in the application of pharmacokinetics and pharmacodynamics while testing an oncology compound. After recovery from surgery, data were collected for several days to observe changes in normal circadian rhythm.
This study investigated the changes of blood glucose during circadian, meal, stress procedure and drug exposure monitored continuously by implanted HD-XG transmitter device (Data Sciences International, Inc) in conscious Macaca fascicularis. Six male Sprague Dawley rats were implanted with 2 telemetry implants that each required an arterial site for sensor placement. Additional rats without telemeter implants were maintained on normal-salt, normal-fat diet for the duration of the experiment. Type 1 diabetes mellitus (T1D or IDDM; Insulin Dependent Diabetes Mellitus) is characterized by a loss of insulin secretion due to pancreatic ?-cell degeneration, leading to autoimmune attack. Materials that mimic insulin action or augment the effect of residual endogenous insulin are likely to be beneficial for both type 1 and 2 diabetic patients.
V Arkhipenko, 1982The role of lipid peroxidation in pathogenesis of ischemic damage and antioxidant protection in the heart. Sensors were calibrated via an interpolated one point calibration method utilizing daily readings. The rise, peak, and duration of the elevation in blood glucose produced by the glucose load were similar after the rat tasted water or saccharin.
The glucose sensor was implanted into a femoral artery and the reference electrode plus its device body was implanted subcutaneously nearby. This method has significant limitations, as it is inaccurate, is timeconsuming, requires frequent sampling, and induces animal stress. To demonstrate rapid changes in blood glucose while monitoring blood pressure and heart rate, animals were enrolled in a simple cross-over designed study to compare the response to high carbohydrate (marshmallows and fruit) with low carbohydrate treats (cheese cubes) after a 12 hour fast.
The glucose sensor was implanted into the femoral artery and its reference electrode plus the device body was implanted subcutaneously nearby. During the recent years many investigators have shown that natural products are a potential source for new drug candidates for many diseases in general, and diabetes in particular. A relative absolute difference was calculated for each sensor, on both GTT’s and daily readings. Daily reference glucose values were measured from tail vein blood samples using the Nova StatStrip Xpress glucometer. CG monitoring allowed for visualization of the circadian pattern that was not seen with FI and would not have been detected using twice daily sampling. However, tasting quinine significantly delayed the return of blood glucose concentrations to their nadir.
However, with newly developed implantable continuous glucose telemetry, we now are able to obtain continuous, real-time, blood glucose measurements in conscious laboratory animals without disturbing them. The HD-S11-F2 was inserted in the femoral artery and the catheter tip was advanced to the abdominal aorta (just cranial to the iliac bifurcation), not overlapping the glucose sensor. A research aimed at revealing new natural sources to treat diabetes is of high importance.A variety of traditional anti diabetic plants are known in the folk medicine. Following STZ administration, the rats experienced a transient period of hyperglycemia followed by a hypoglycemic period. The combination of CG and FI monitoring offers the ability to detect subtle and comprehensive diet-related changes in glycemic level and variability not practical with infrequent manual blood samples. Thus, stimulation of bitter taste receptors can influence blood glucose levels after a glucose load. Blood glucose, body temperature and physical activity were monitored wirelessly and recorded continuously for over a month. The present study evaluates the use and the performance of this system in hyperglycemic Goto-Kakizaki (GK) rats and Zucker Diabetic Fatty (ZDF) rats. Monitoring hemodynamic parameters in addition to blood glucose allowed us to separate excitement responses due to room entry or offering food, and actual changes in blood glucose due to the composition of the food. Blood glucose, body temperature and physical activity were simultaneously monitored wirelessly and recorded continuously for more than 6 weeks. Development of T2D is usually caused by several factors, which are combined with lifestyle, genetic defects, virus infection, and drugs [3, 4]. Although some of them have been studied for their anti diabetic effects, the knowledge on their efficacy and mechanism of action is very limited. Two of 10 interstitial sensors and 2 of 10 blood monitoring sensors (improperly implanted) failed to perform correctly. Over the next 24 hrs, blood glucose steadily increased, and hyperglycemia stabilized with a distinct diurnal fluctuation. This work highlights the advantages of the HD-XG glucose sensor, which allows monitoring of blood glucose with 10-sec temporal resolution without the stress of repeated blood draws.
Many classical diabetes assays, such as ivGTT, oGTT, ITT, clamp, were tested with this remote method and compared with the conventional glucometer assay (Fig. Glucose telemetry was implanted in the abdominal aorta and the transmitter body in the peritoneum via an aseptic surgery. Room entry had minimal effect on the blood pressure and heart rate following the 12 hour fast, and no observed effect on blood glucose. After recovery from surgery, animals were enrolled in a cross-over designed study to compare the physiologic effects of offering high carbohydrate or low carbohydrate treats after a 12 hour fast. Sustained hyperglycemia causes severe diabetic microvascular complications, such as retinopathy, peripheral neuropathy, and nephropathy. The Glucose Tolerance Factor (GTF) is a dietary agent first extracted from Brewer’s yeast [1]. A similar increase in blood glucose concentration was observed with efferent VNS after sectioning the vagus nerve cranial to the stimulation electrode. The system enabled monitoring of disease progression over time as well as repeatedly glucose tolerance test on same animal.


Addition of a food offering caused an immediate increase in blood glucose that was related to the carbohydrate load offered by the food.
Their blood glucose levels showed circadian oscillations and kept at low levels during 12 am to 9 am (housing light circle = 7pm off to 7am on). In the diabetic states, multiple mechanisms have been implicated in glucose-mediated vascular damage and contribute to diabetic microvascular complications.
These devices hold great potential for comparing physiologic processes associated with glucose regulation in normal and disease condition rats; monitoring diabetes progression and developing preventive treatments for type II diabetes.
In summary, acute cervical VNS at an intensity that reduces heart rate elicits a glucogenic effect in anesthetized rats. Our data demonstrate the 1st success of remote, continuous monitoring of blood glucose in conscious, stress-free NHPs and its potential advantages bringing to diabetes research and drug discovery.
Two weeks after postsurgical recovery, detectable differences of treatment effects on prandial and fasting blood glucose levels were evident. Animals offered marshmallows and fruit had an immediate increase in blood glucose while those offered cheese had a blunted glucose response. There was no obvious postprandial hyperglycemia after morning feeding, but blood glucose increased by 20 to 30% after afternoon feeding.
Marshmallows and mangos were offered as high carbohydrate treats while cheese cubes were offered as the low carbohydrate treat. Baseline blood glucose levels in male and female DSS measured by HD-XG were comparable (109±2 vs. In addition, postprandial state is also an important factor in the development of macroangiopathy.
In vitro studies with GTF showed remarkable increase in glucose transport into adipocytes, and cardiomyocytes.
The implanted glucose sensors provided unprecedented time resolution of the glucose response for each insulin dose. Further studies are needed to understand the mechanisms by which acute and potentially also chronic cervical VNS may increase blood glucose. Telemetry glucose monitoring data, in parallel with measurements of food intake, body weight, and locomotor activity validated this platform technology as a refinement in aiding our understanding of anti-diabetic therapeutic agents.
However, 1 hour after the treats were offered, the normal rat chow was restored to the feeders.
Grabbing out a monkey from its housing cage for sitting in a monkey chair caused a transient increase in blood glucose by 30 to 40% in both normoglycemic and diabetic monkeys, but took 30 min for returning to its baseline in normoglycemic animals and almost 2 hrs in diabetic monkeys.
Approximately 1 hour after the treat offering, the standard rat chow was restored to the cage feeders. In diabetes, the postprandial phase is characterized by an exaggerated rise in blood glucose levels. An increase in glucose incorporation into glycogen in rat hepatocytes was also found for GTF preparations [2].
These prototype devices provide a promising alternative for chronic preclinical continuous glucose monitoring in a free roaming type 1 rat model.
These profiles will provide a reference against which to compare novel drugs under development.
When the normal rat chow was restored, the rats in the marshmallow and fruit group showed little additional increase in blood glucose, while the cheese group had an immediate increase in blood glucose that was even greater than the group that had received the marshmallows and fruit. The stress-induced hyperglycemia by oral gavage was similar to grabbing monkey from hosing cage. The excitement from the technician opening the cage was evident in HR and BP changes associated with that activity. It has recently been shown that postprandial hyperglycemia is relevant to onset of cardiovascular complications.
Despite the high anti diabetic activity of this natural compound, GTF has not been fully characterized or identified, mainly due to the instability of the purified fractions. Additionally, average weekly glucose for both sexes were statistically identical whether analyzed over 24 hour periods or limited to only the light or dark periods. From this evidence, treatment of diabetes has become a part of the strategies for the prevention of diabetic vascular complications.To help develop new diabetic treatments, it is important to reveal the complex mechanisms of diabetes.
Our laboratory succeeded in extraction and partial purification of an active and stable GTF preparation from brewer’s yeast.
These experiments demonstrate the value of using two implants to get a more complete picture of whole animal metabolic and cardiovascular physiology. From this study we can conclude the following: 1) glucose telemeters are a reliable methods to obtain continuous measurements of blood glucose in male and female rats, 2) there are no sex differences in blood glucose following a 4 week HF diet in DSS, and 3) DSS are able to tolerate a HF diet with minimal alterations in body weight or blood glucose. In particular, studies using diabetic animal models are essential to aid in clarification of the pathogenesis and progression in human disease course. We examined GTF effects in animal models for both types of diabetes, and found high and rapid anti diabetic activity. The results demonstrate that compared with nighttime, blood glucose during daytime is higher in the experimental monkeys. We also examined GTF effects on the cellular level and found high insulin mimetic and insulin potentiating activity for GTF. It is interesting that housed monkeys only showed afternoon post-prandial hyperglycemia after feeding. These experiments demonstrate a successful surgical approach using two implants to get a more comprehensive picture of whole animal cardiovascular and metabolic physiology. In this chapter, we review these three types of T2D animal models with respect to characteristic features, including impaired glucose tolerance.2. Non-obese type 2 diabetic animal modelsCertain non-obese diabetic models are used in the investigation of T2D in humans.
Prevalence of diabetes mellitus Diabetes is the world’s most common metabolic disease and one of the leading causes of morbidity and mortality. Stress-related hormones, such as norepinephrine and angiotensin, can also cause hyperglycemia. According to WHO (World Health Organization) report [3], 346 million people worldwide are diabetic. Therefore, remote and continuous monitor of blood glucose via telemetry device in conscious NHPs may provide a sophisticated approach to investigate neurological regulation of blood glucose due to behavior and hormonal changes. The number is expected to grow to 438 million until 2030 [8% of the world population!) [4]. Diabetes imposes an increasing economic burden on national health care systems worldwide [5].
The global health expenditure on diabetes in 2010 was 376$ billion and is expected to grow to 490$ billion by 2030 [6]. Since the GK rat is generally considered as one of the best models of T2D, many researchers have used this animal model to study the physiology of diabetes and its complications, and to evaluate anti-diabetes drugs.
In 1973, Goto and Kakizaki of Tohoku University (Japan) started selection of this substrain from Wistar rats by mating pairs with glucose intolerance. Diabetes mellitus and its complications Diabetes mellitus is a complex syndrome involving severe insulin dysfunction along with gross abnormalities in glucose homeostasis and lipid and protein metabolism. Since F8, sister-brother mating has been repeated, and were established as an SPF animal at F29. The disease is generally divided into two major types: Insulin Dependent Diabetes Mellitus (IDDM, or type 1], and Non Insulin Dependent Diabetes Mellitus (NIDDM, or type 2 DM). Today, many colonies of the GK rat exist and the rats are available for purchase from several breeders.The major quantitative trait locus (QTL) for impaired glucose tolerance is Niddm1, identified in chromosome 1. Several loci linked to pathophysiologic characteristics was observed on chromosomes 2, 4, 5, 8, 10, and 17, indicating that the diabetic features in GK rats are inherited as polygenic traits and that GK rats would provide insights into genetics of human T2D [7]. People with diabetes have a 25-fold increase in the risk of blindness, a 20-fold increase in the risk of renal failure, a 20-fold increase in the risk of amputation as a result of gangrene and a 2 to 6-fold increase in the risk of coronary heart disease and ischemic brain damage. Glucose tolerance and insulin sensitivityNon-fasting blood insulin levels in GK rats are slightly higher than in age-matched Wistar rats. Impaired glucose-stimulated insulin secretion has been reported in GK rat in vivo [8], in the isolated pancreas [9], and in isolated pancreatic islets [10]. Diabetes mellitus and oxidative stress Oxidative stress and non enzymatic glycation play a major role in the pathogenesis of diabetes mellitus [7, 8]. Perfusion experiments using isolated pancreas showed that the first phase of insulin secretion by glucose stimulation was impaired in GK rats, although the response to arginine was preserved [9].“Starfish-shaped” islets are a morphological feature of GK rat. During diabetes, persistent high concentrations of blood glucose increase the production of oxygen free radicals – OFRs.
The number of enlarged islets with irregular shape, ill-defined borders, and fibrous strands of endocrine cells is increased in aged GK rats.
These islets showed similar or moderately decreased insulin content compared with control rats.
Pancreatic glucagon content is at almost the same level as in Wistar rats, and somatostatin content is slightly higher in GK rats [11].
Lipid peroxide levels, and especially oxidized LDL, are significantly higher in diabetic patients than in healthy individuals. The defective insulin response to glucose in ?-cells is due to abnormalities in the function of K+ATP channels and L-type Ca2+ channels [12].The GK rats show mild insulin resistance, mainly considered to be due to increased hepatic glucose production [8].
These Major changes in lipid metabolism cause lipid peroxidation in plasma and cellular membranes which lead to micro and macro vascular pathologies [15]. Drug treatment and diabetic complicationsGK rats have been widely used for evaluating anti-diabetic drugs.
The natural protective system of antioxidant enzymes like superoxide dismutase, glutathione peroxidase and catalase that provides the detoxification steps for the oxidative products, cannot overcome massive production of free radicals to prevent oxidative damage. Almost all types of such drugs have been tested with GK rats, including sulfonylureas [13], an ?-glucosidase inhibitor [14], a thiazolidinedione derivative (troglitazone) [15], a biguanide (metformin) and a gluconeogenesis inhibitor [16], a GLP-1 analog and a dipeptidyl peptidase-4 inhibitor (DPPIV-i) [17], and an SGLT2 inhibitor [18].In addition to its useful features as a T2D model, GK rat has been used as model of diabetic complications. Reduced motor nerve conduction velocity (MNCV) in the caudal nerve is reported in 2-month-old GK rats [19]. It was shown that the activity of the antioxidant systems is decreased in diabetic patients. Diabetes mellitus and aldose reductase The reduction of glucose by the aldose reductase (AR) catalyzed polyol pathway has been linked to the development of secondary diabetic complications like cataract, nephropathy, retinopathy and neuropathy. BackgroundStreptozotocin (STZ) is an antibiotic derived from Streptomyces achromogenes that has selective toxicity to pancreatic ?-cells. Accumulation of sorbitol in the organs, due to AR-catalyzed reduction of glucose, causes osmotic swelling resulting in ionic imbalance and protein insolubilization leading to diabetes complications.
STZ induces DNA strand breaks and a consequent excess activation of poly (ADP-ribose) synthetase, an enzyme that repairs DNA, depleting NAD in cells, which leads to energy depletion and finally causes ?-cell death [22]. Although treatment with AR inhibitors has been shown to prevent tissue injury in animal models of diabetes, the clinical efficacy of these drugs remains to be established. Neonatal rats treated with STZ at birth (nSTZ rat) revealed acute insulin deficient diabetes at 3-5 days after birth [23]. Their pancreatic insulin contents reduced to 7% that of normal rats, and showed hyperglycemia in this period. However, after this period, blood glucose and insulin levels in nSTZ rats were almost the same as in control rats at 3 weeks of age. Treatment of diabetes mellitusDaily injections of insulin are the only treatment for type 1 diabetes.
At eight weeks of age, nSTZ rats showed mild hyperglycemia and impaired glucose tolerance with a 50% decrease in pancreatic insulin content [24].Recently, Masiello et al. The treatment for type 2 ranges from diet, to classical oral drugs (Sulfonyl urea and biguanides), and to Thiazolidinediones and the new GLP1 analogues. Although the pathogenesis of diabetes and its long-term complications are well known, optimal treatment remains elusive.
When given a calorie-controlled high fat diet, hyperlipidemia and insulin resistance without obesity were observed [26]. Only half of the patients achieve the recommended hemoglobin A1c target using conventional treatment [21]. Glucose toleranceThe reduction of ?-cell number and insulin content in the pancreas leads to defective insulin response in vivo. As a result of the global epidemic of diabetes, the need for new diabetes therapies is expected to grow dramatically during the next years.
An isolated pancreas perfusion study using adult nSTZ rats showed lack of insulin response to glucose stimulation, indicating loss of ?-cell function [27].
Pharmaceutical research conducted over the past decades has shown that natural sources like herbs, medicinal plants and yeast extract, are potential sources for new drug candidates for many diseases in general [23], and diabetes in particular [24]. Reduction of GLUT2 expression in ?-cells may attribute to impaired glucose entry into ?-cells and the following insulin secretion [28].
Reduced sensitivity of KATP channel to extracellular glucose has also been suggested by the patch-clamp technique [29]. Anti diabetic medicinal plantsSeveral reviews published in recent years screen many plant sources with anti-diabetic properties [24, 25, 26, 27, 28, 29]. Furthermore, an in vivo study has indicated that the hepatic glucose production (HGP) in the basal state is higher in adult nSTZ rats than in control animals [30]. Ghrelin, the hunger-stimulating peptide produced in stomach, also promotes regeneration of ?-cells in nSTZ rats. Garlic has been reported to possess a variety of medicinal properties including hypoglycemic, hypocholesterolemic and hypolipidemic activities [32]. Treatment with ghrelin increased pancreatic expression of insulin and Pdx1 mRNA with a consequent improvement of hyperglycemia in nSTZ rats [38].3.
Raw garlic extract reversed proteinuria in diabetic rats in addition to reducing blood glucose, cholesterol and triglyceride in diabetic rats [33].
Obese type 2 diabetes animal modelsObesity is a well-established risk factor for many chronic disorders, such as T2D [39]. Silybum Extract (Silybum Marianum) increases the cellular sensitivity to insulin and thus reduces blood glucose total cholesterol and LDL levels in diabetic patients [34]. To understand the complicated features of the disease, spontaneously T2D models provide important knowledge.
Bitter cucumber plant fruit (Mamordica Charantia) reduced blood glucose in patients with type 1 diabetes [35]. In particular, the development of diabetic animal models and pathophysiological analyses of the models are very important to aid in clarification of the pathogenesis and the patterns of progression in the human disease course.
Studies show that the consumption of one and a half gram dry powder of green tea, improved the metabolism of blood sugar in diabetic patients [36]. Ginkgo biloba plant is capable of lowering glucose, fat, and lipid peroxide in diabetic patients [37]. BackgroundZucker diabetic fatty (ZDF) rat is an obese animal associated with hyperphagia, hyperglycemia, hyperinsulinemia, and hyperlipidemia. The ethanolic extract of Allium porrum leaves had hypoglycemic effects on diabetic animals probably through the increase of insulin release [38].
Insulin resistance is caused by age-dependent degeneration in pancreatic ?-cells that trigger hyperglycemia. Some nutritional factors, such as polyphenols, counteract insulin resistance and therefore may be beneficial for patients with type 2 diabetes mellitus through their insulin-potentiating, antioxidant, and anti-inflammatory properties. Thus, ZDF rat is a widely studied model of obesity and insulin resistance and is used for evaluation of anti-diabetic drugs.
The common cinnamon (CN) has a long history of use as a spice, preservative, and pharmacological agent; CN is also a source of polyphenols. ZDF rat was discovered in a colony of outbred Zucker fatty (ZF) rat in the laboratory of Dr. Several studies demonstrated that in animals and humans, CN and aqueous extracts of cinnamon improved the level of blood glucose, lipids and insulin, and may be beneficial to counteract the features of insulin resistance, metabolic syndrome, and the onset of type 2 diabetes mellitus [39, 40, 41, 42]. Yeast as a natural source for anti diabetic materialBrewers' yeast is also included among the anti diabetic natural sources [46, 47]. Schwartz and Mertz were the first to discover the natural anti diabetic agent present in yeast and called it "Glucose Tolerance Factor" (GTF) [1]. Richard Peterson at Indiana University Medical School (IUMS) started selection of this rederivation, and established an inbred line of ZDF rat in 1985.
It is well known that sexual differences exist in the incidence and progression of diabetes mellitus in ZDF rat [41]. Glucose Tolerance Factor (GTF) a natural anti diabetic agent The Glucose Tolerance Factor (GTF) is a dietary agent first extracted from Brewer’s yeast [1].
Diabetes mellitus has developed in more 90% of the males, whereas the blood glucose level remains normal in most females. This natural compound reversed the impaired glucose tolerance of diabetic rats [48, 49], and of diabetic patients [50]. However, female ZDF rat became diabetic on high-fat diet, and it was shown that the dietary fat content affected development of diabetes in females [41]. GTF can be extracted from several sources, among them: liver [51], black pepper, and kidneys. Glucose tolerance and insulin sensitivitySerum glucose levels in ZDF rat are usually elevated from 7-10 weeks of age. Addition of partially purified GTF to the diet of glucose intolerant rats rapidly returned them to normal [56]. Doisy and his group found an improvement in glucose tolerance in elderly people who were treated for two months with GTF. ZDF rats showed hyperinsulinemia from 6 to 12 weeks, but after about 14 weeks of age their insulin levels showed a tendency to decrease.
Glucose intolerance at 12 weeks becomes more severe than that at 5-7 weeks of age [42, 43].
Offenbacher and Pi Sunyer [46], examined 24 elderly subjects, who were fed daily for 8 weeks with brewers’ yeast as a sorce for GTF. Age-dependent degenerative changes of pancreatic islets showed decreased production and secretion of insulin, and atrophy of islets. They found a considerable improvement in glucose tolerance and insulin sensitivity, and a reduction of total lipids in these patients.
Early pathological changes of the pancreatic islets, such as hypertrophy, disarray of islet architecture, and irregular islet boundaries, were observed by 10-12 weeks of age [44, 45].
Grant and McMullen [50] treated 37 type 2 diabetics for 7 weeks, in a double blind study, with either brewers’ yeast as a source of GTF, or placebo.
The specific factor that causes deterioration of pancreatic ?-cells has not been identified, but changes in ?-cell structure and function have been well studied. Supplementation of brewers’ yeast significantly decreased HbA1c and increased HDL cholesterol in the treated group. It was reported that lipotoxicity based on high plasma free fatty acid could attribute to ?-cell dysfunction [46]. Elwood [58] supplemented 11 normolipidemic and 16 hyperlipidemic subjects with brewers’ yeast.
Reduction of islet mRNAs in ?-cells, such as those for insulin, GLUT2, and glucokinase, contributes to the ?-cell deterioration [42]. They found that total circulating cholesterol was significantly reduced and the HDL levels were significantly increased in both the normo and hyperlipidemic subjects supplemented with brewers’ yeast. Furthermore, decrease in GLUT4 expression is also observed in skeletal muscle and adipose tissue of ZDF rat [47]. Riales [59] reported that human subjects receiving 7g of brewers’ yeast for 6 weeks had a significant decrease in serum LDL and an increase in HDL cholesterol. In vitro studies with partially purified preparations of GTF, showed stimulation of glucose metabolism in several tissues. Drug treatment and diabetic complicationsIt is well known that ZDF rat is a useful model for evaluating anti-diabetic compounds.
GTF potentiated glucose oxidation to CO2 in adipose tissue [54, 60], or adipocytes [53, 61]. In those studies the enhancement was shown only in the presence of insulin, and the stimulation of CO2 production by GTF in the absence of insulin was negligible [53, 54, 60, 61]. Other compounds also have been evaluated in ZDF rat, including a sulfonylurea [48], ?-glucosidase inhibitors [49], a thiazolidinedione (pioglitazone) [50], a biguanide (metformin) [51], a GLP-1 analog [52], an SGLT2 inhibitor [53], a ?3-andrenergic receptor agonist [54], and a variety of other compounds [55-58].A number of studies demonstrated that ZDF rat can be used as model of diabetic complications. In contrast to the findings above, showing GTF activity only in the presence of insulin, other groups found an increase of glucose metabolism by adding GTF in the absence of insulin. Blood urea nitrogen (BUN) levels and urinary protein excretion in ZDF rat were elevated from about 40-50 weeks of age.
Tokuda et al, [62] examined GTF obtained from yeast extract powder on glucose uptake in adipocytes.
They found a stimulation of glucose uptake (5.6 times greater than the basal level) in the absence of insulin. Our group also showed an increase in glucose transport both to yeast cells [63, 64], and to animal cells [65].Since GTF is supposed to be essential for normal glucose tolerance in mammals, and as muscle tissue consumes a major part of blood glucose in the post prandial state, it is most important to assess the effect of GTF on muscle tissue.
Reduced MNCV in the sciatic nerve is observed from 12–14 weeks of age in ZDF rats, and endoneurial blood flow (EBF) in the sciatic nerve is also decreased after 24 weeks of age [60]. Fischer and his group [66] examined the effect of GTF obtained by partial purification of yeast extract, on glucose transport in isolated cardiomyocytes. They found that GTF samples increased the rate of glucose transport in the isolated cells, 2 to 2.5 fold, in the absence of insulin. The degeneration and swelling of fibrae lentis, formation of Morgagnian globules, and stratification of epithelium lentis cells is observed in ZDF rat at 21 weeks of age [61, 62].


Hwang et al [67] showed enhancement of 14C -glucose oxidation into CO2 in rat adipocytes by the addition of several fractions extracted from yeast.
The authors found only insulin like activity and not insulin potentiating activity for the fractions examined.The exact composition and structure of GTF are still obscure.
Mertz and his group suggested that GTF is probably a small organic molecule comprising one trivalent chromium ion, two molecules of nicotinic acid, and three amino acids: glycine, cystein and glutamic acid [54, 68, 69].
BackgroundOtsuka-Long-Evans-Tokushima-Fatty (OLETF) rat is a mildly obese animal associated with polydipsia, polyuria, polyphagia, hyperglycemia, and hyperlipidemia. Its molecular weight is estimated to be around 500 daltons [54, 69], It is cationic, soluble in water, and stable in physiological solutions [54, 68].
Several groups who tried to identify the active components present in brewers' yeast, claimed that they are quinoline derivatives [70], or phosphatidylinositol glycans [71].
OLETF rat is considered to be a suitable model for understanding the properties of T2D with mild obesity.
Other investigators tried to further purify and identify the exact structure and composition of GTF. The spontaneously obese rat with T2D was obtained from a colony of outbred Long-Evans rat, available for purchase from Charles River, in 1984 at laboratory of Otsuka pharmaceuticals, Tokushima [63]. There is no standard accepted method to isolate GTF, and this fact can probably explain the diversity of the results reported in the literature.
A strain of this rat was established by sister-brother mating with obesity and glucose intolerance.
In addition, a major problem related to GTF purification, is the instability of the partially purified fractions. According to the results of a study by Takiguchi [64, 65], a disrupted cholecystokinin-A (CCK-A) receptor gene in peripheral tissues and central nervous system is found in the OLETF rats [64].
This lability, can partially explain the complexity of the subject, and the fact that in spite of the long time since the material was discovered, its exact composition and structure have not been determined.Tuman [48] who presented the activity of GTF and several synthetic complexes on lowering blood glucose found that in 10 days both the natural compound and the synthetic complexes lost their activity.
Mertz reported that highly purified preparations of GTF from yeast or pork kidney tend to be unstable, and lost their activity very quickly [52]. Meanwhile, in peripheral tissues, CCK-A also controls satiety signals through the vagal afferent neurons [67]. Yamamoto [51] found that GTF like activity of the purified LMCr (low molecular weight chromium binding substance) reduced gradually, and finally there could not be detected any activity. Thus, dysfunctional signal of CCK may cause obese T2D, leading to hyperphagia in OLETF rats. We can explain the instability of the purified fractions of GTF by a loss of a co-factor(s) which is probably responsible for the stability of the complex.Most of the groups who tried to purify GTF from brewers' yeast agree that the GTF is a cationic compound. Glucose tolerance and insulin sensitivityNon-fasting plasma glucose levels in OLETF rats were elevated from 18 weeks of age, and the increase was sustained until 40 weeks of age.
Only several researchers claimed that the GTF is an anionic compound: Votava and his group [72] reported that GTF is an anionic chromium complex of molecular weight 400-600, containing at least six amino acids.
Diabetes mellitus developed in about 90% of OLETF rats at 30 weeks of age, whereas the plasma glucose level remained normal in most females at 24 weeks of age [63, 68]. Since the authors measured only the absorption of the complex by rats, and no biological activity assay was done on it, it is hard to compare Votava’s compound to other extracts exhibiting GTF activity.A low molecular weight chromium binding substance (LMCr), was isolated from mouse or rabbit liver and bovine colostrum by Yamamoto and his group [51, 73]. Sexual differences exit in the incidence and progression of diabetes mellitus in OLETF rats [69]. LMCr appears as anionic organic Cr compound, with a relative molecular mass of 1500 daltons.
In glucose tolerance test, marked elevation of plasma glucose and insulin level responses to glucose are observed at 24 weeks of age [63].
The purified LMCr enhanced glucose conversion to CO2 in rat epididymal adipocytes in the presence of insulin. Age-dependent degenerative changes of pancreatic islets are observed from 16 weeks of age [70]. The rate of glucose incorporation into lipid was stimulated by 30-40% with insulin, or by 15-23% without insulin [51]. The pathological changes of the pancreatic islets, such as hypertrophy, atrophy of insulin positive-?-cells, fibrosis, and indistinct, irregular islet boundaries, were observed by 30 weeks of age [71]. Yamamoto and his colleagues were not able to detect nicotinic acid in the extract of LMCr, but some UV absorption was present [73]. These dysfunctions of ?-cells seem to cause the development of glucose intolerance in OLETF rats. Insulin resistance has been reported in OLETF rats at 16 weeks of age, as measured by hyperinsulinemic euglycemic clamp technique [70].
In adipocytes, the GLUT4 protein expression considerably decreased in OLETF rats at 30 weeks of age. Urumow & Wieland [74], suggested that GTF activity in stimulating 14C-glucose oxidation is attributable to the combined action of certain amino acids (aspartate, cystein) and nucleosides (adenosine).
The decrease in GLUT4 protein in muscles is also observed in OLETF rats at 30 weeks of age [72]. Fischer [66] came to a conclusion that GTF activity is attributed to the presence of alanine. Hwang and his group [70] suggested that the GTF obtained was a quinoline derivative, which easily binds chromium.While many research groups in the past agreed with the concept suggested by Mertz that GTF contains chromium [51, 55, 73, 75], accumulating data during the years indicates that there is no chromium present in the GTF preparation. Drug treatment and diabetic complicationsOLETF rats have been widely used for pharmacological evaluation while testing for many anti-diabetic drugs, including a Ca2+ antagonist [73], sulfonylureas [74], an ?-glucosidase inhibitor [75], a thiazolidinedione [76], a biguanide (metformin) and a gluconeogenesis inhibitor [77], and a GLP-1 analog [78].OLETF rats are also used as a model for assessment of diabetic complications.
Haylock and his group, who tried to purify and identify GTF for many years, did not find a correlation between chromium content and the biologic activity. It was reported that histopathological changes in the kidney were observed after 23 weeks of age. They came to the conclusion that: "GTF from brewers' yeast can no longer be regarded as a chromium complex" [76].
OLETF rats at 55 weeks of age showed an expansion of the mesangial matrix and aneurismal dilatation of intraglomerular vessels [63]. Stearns [78] summarized the purification research that had been done on GTF and discussed the relation of the active component to chromium. It is known that lenticular sorbitol level increases in OLETF rats from 40 weeks of age [79]. OLETF rats show swelling and liquefaction of lens fibers in the subcapsular and supranuclear region at 60 weeks of age.
Stearns also investigated the issue of the essentiality of chromium to human health, and found that "no chromium-containing glucose tolerance factor has been characterized, the purpose of the low-molecular-weight chromium-binding protein is questionable, and no direct interaction between chromium and insulin has been found" [79]. Moreover, she criticized the dietary supplementation of chromium: "Chromium+3 may act clinically by decreasing the iron stores that are linked to diabetes and heart disease.
BackgroundWistar fatty rat develops obesity with hyperphagia, hyperglycemia, hyperinsulinemia, hyperlipidemia, and glucose intolerance.
Eddens and his colleagues [47], isolated three separate fractions by eluting yeast extract from C18 column and found diverse activities in increasing glucose metabolism and inhibiting lipolysis for the different fractions, not connected to their chromium content.
Wistar fatty rat is a good model for studying obesity and insulin resistance, and for evaluation of anti-diabetic drugs. Wistar fatty rat was established as a congenic line of the insulin resistance of the Wistar Kyoto strain (WKY) rat by introducing the fa allele of the ZF rat for obesity into the WKY rat genome in the laboratory of Dr. We used several separation techniques including membranes with different molecular cut off, ion exchange columns and reversed phase HPLC. At 5th generation of backcrossing, male obese animals exhibit hyperglycemia, and were established as Wistar fatty rat at 10th generation. It was found to be very stable: it is stable to high and low pH and it keeps its activity up to 12 months in 4°C.
This finding enables an oral treatment with GTF, in contrast to insulin, which is a protein and has to be injected [49, 80, 81].
Glucose tolerance and insulin sensitivityNonfasting plasma glucose levels in Wistar fatty rats were elevated until 8 weeks of age, and this level was sustained until 24 weeks of age. In the following paragraphs we shall present several of our findings on GTF both in vivo and in vitro. We examined GTF effects in animal models for both types of diabetes, and found high and rapid anti diabetic, hypolipidemic and antioxidant activity. Wistar fatty rat is a widely studied model used to investigate the pathogenesis of obesity and insulin resistance, and for evaluation of anti-diabetic drugs. We also found a remarkable reduction in the complications of diabetes: nephropathy and retinopathy, by treating the diabetic animals with oral doses of GTF [81]. In glucose tolerance test conducted at 12 weeks of age, Wistar fatty rat showed higher serum glucose and insulin levels after glucose loading compared with WKY rat, and glucose intolerance became more severe age-dependently. In vitro studies done in our laboratory showed insulin mimetic and insulin potentiating activity for GTF [65].9. Hypertrophied pancreatic islets in Wistar fatty rat were increased in pancreas compared with WKY rat [80]. GTF decreases blood glucose in diabetic rat modelsA single oral dose of GTF, orally administered to both types of diabetic animals, decreased immediately and remarkably glucose and lipid levels in their blood [49, 80]. Insulin resistance has been reported in Wistar fatty rats, confirmed by glucose clamp technique [82]. Glucose reduction appeared immediately after the administration of GTF, reached a maximum within 2 hours, and lasted for several hours. Decreased insulin-stimulated glycogen synthesis and glycolysis in the isolated soleus muscles, and insulin-stimulated glucose oxidation and lipogenesis in adipocytes were observed in Wistar fatty rats [83].
When GTF was administered in concert with marginal insulin doses, the reduction in blood glucose was much higher than for each agent alone, demonstrating a synergy between GTF and insulin [80]. Drug treatment and diabetic complicationsWistar fatty rats have been used as a good model for evaluation of a number of anti-diabetic drugs, including a biguanide [84], an ?-glucosidase inhibitor [75], a thiazolidinedione [85], and an DPPIV-i [86].Wistar fatty rats are also used as a model of diabetic complications. It was reported that age-related increases in urinary NAG (N-acetyl-beta-D-glucosaminidase) and urinary protein and albumin excretion in Wistar fatty rat were elevated from 5-11 weeks of age. Wistar fatty rats at 26 weeks of age showed an expansion of the glomerular mesangial matrix and local formation of a nodular-like lesion. Insulin secretion in response to glucose stimulation did not change significantly in GTF treated hyp-CDs rats (From Wexler-Zangen et al, [65], indicating that the glucose lowering effect of GTF is not related to stimulation of insulin secretion. Reduced MNCV in the fibula nerve and histopathological changes, such as demyelination and axonal degeneration, were observed in Wistar fatty rats [88]. BackgroundThe Spontaneously Diabetic Torii (SDT) rat is a new inbred strain of Sprague-Dawley (SD) rat established as a non-obese model of type 2 diabetes mellitus. The cumulative incidence of diabetes was 100% by 32 weeks in male SDT rats, while it was only 33% in females even at 65 weeks. GTF reduces postprandial blood glucose concentration in diabetic ratsPost prandial (PP) blood glucose level is very high in both hyp-CDs and STZ diabetic rats. In the vehicle treated hyp-CDs and STZ rats, the markedly elevated BG concentrations remained high for more than 120 min (Figs 2A and B).
As a result of chronic severe hyperglycemia, the SDT rats developed severe complications in eyes, peripheral nerves, and kidneys.
Especially, ocular complications including the diabetic retinopathy in SDT rats is noteworthy [90].
Of many diabetic ocular complications, cataract, retinopathy, and neovascular glaucoma (hemorrhagic glaucoma) are the most important clinically. Glucose tolerance and insulin sensitivityIn SDT rats, development of hyperglycemia may be more dependent on decreased insulin secretion than insulin resistance, as shown by the fact that the blood insulin concentration tended to be lower than in normal SD rats even before the onset of diabetes, and marked hypoinsulinemia developed after the onset of hyperglycemia [91-93], indicating that this strain of rat is a model of non-obese T2D associated with impaired insulin secretion.
In oral glucose tolerance test in SDT rats, glucose tolerance markedly decreased at least 3 months before manifestation of hyperglycemia (around 16 weeks old), and the rate of rise in blood glucose level after glucose-loading increased with age.
We examined the glucose tolerance periodically at 5, 9, and 13 weeks of age in SDT rats (Figure 1.). Figure 1.Glucose tolerance test (GTT) at 5, 9, and 13 weeks of age in SD rats and SDT rats. GTF decreases tri glyceride and LDL cholesterol and increases HDL cholesterolA remarkable decrease in triglyceride level was observed in diabetic animals administered with 5 daily oral doses of GTF (Figure 3).
The treatment with GTF also remarkably decreased the level of LDL cholesterol (Figure 4A), and increased the level of HDL cholesterol (Figure 4B), (Ampel et al., unpublished data). GTF reduces lipid peroxidation in the plasma, both in vivo and in vitroGTF can inhibit the deleterious elevation in lipid peroxides induced by diabetes.
The blood glucose level before glucose-loading and the level at 120 min after glucose-loading in SDT rats significantly decreased as compared with those in SD rats. The animals were killed and the levels of lipid peroxidation products - malondialdehyde (measured as TBARS – thiobarbituric acid reactive substances), in healthy, diabetic and diabetic rats treated with GTF were determined. The blood insulin level at 30 min after glucose-loading was not different from that in SD rats, but the insulin levels at the other points significantly decreased as compared with those in SD rats (Figure 1B.). Figure 5 demonstrates the level of lipid peroxidation products detected in the plasma of healthy, diabetic, and diabetic rats treated with GTF, showing a major decrease in the level of plasma peroxides in diabetic animals treated with GTF. The insulin levels at points except for 120 min after glucose-loading in SDT rats was comparable with those in SD rats (Figure 1D.), but the insulinogenic index showed a lower level than SD rats (Figure. In male rats, the severity of impaired glucose tolerance before the onset of diabetes was closely correlated with the age. In addition, the insulin secretion level in pancreatic islets of Langerhans from SDT rats after glucose treatment markedly decreased at 12 weeks of age and thereafter compared with normal SD rats. Likewise, the mRNA expression levels for GLUT2 and glucokinase (GK) in the isolated pancreatic islets of Langerhans markedly decreased at 12 weeks and thereafter in SDT rats [94].
In female rats, glucose tolerance also decreased, at 25 weeks and thereafter, but insulin was secreted after glucose-loading, indicating that some factors cause insulin resistance or insulin requirement in the females, unlike in the males [95].It is reported that the pancreatic insulin content in SDT rats at 7 weeks of age decreased as compared with that in SD rats [96]. In human, ? cell mass in impaired fasting glucose (IFG) subjects significantly decreased as compared with that in nondiabetic subjects [97].
The value of lipid peroxides in untreated diabetic rats was significantly higher than the value detected for healthy animals. The level of lipid peroxides in the hearts of diabetic rats treated with 5 oral doses of GTF was very low - a higher effect seen for the higher dose of GTF, similar to the level found in healthy animals. Other non-obese type 2 diabetic models, such as GK rats and the nSTZ rats, did not show a pre-diabetic state.
A remarkable decrease in lipid peroxidation level is shown also in kidneys removed from diabetic rats treated with GTF (Figure 7). Peroxide values found in the animals treated with GTF were very similar to those found in healthy controls.
Drug treatmentIn previous study, ?-glucosidase inhibitor voglibose was administered to male SDT rats in a pre-diabetic stage, and the effects of voglibose on the glucose intolerance and the development of diabetes were investigated [98]. GTF decreases aldose reductase activityElevated activity of aldose reductase (AR) in the organs is one of the events occurring in hyperglycemic conditions. Moreover, voglibose was administered as a dietary mixture to SDT rats from 10 to 20 weeks of age. We measured aldose reductase activity in the hearts of healthy, diabetic and diabetic treated with GTF (Figure 8). AR activity in the hearts of diabetic rats was much higher than that found in healthy rats. In clinical study, ?-glucosidase inhibitor, such as voglibose and acarbose, showed a prevention of type 2 diabetes mellitus [99, 100]. The results showed that pharmacological intervention with voglibose in SDT rats with IGT can delay progression to T2D. The decreased sensitivity to insulin leads to an increased requirement for insulin, and is often associated with obesity in which metabolic disturbances are marked in insulin-target organs, such as the liver, muscle and adipose tissues [102].
Obesity plays key roles in the pathophysiology of several metabolic diseases and is a risk factor for diabetes mellitus and dyslipidemia. Products of lipid peroxidation were measured in the presence (induced) and absence (non-induced) of FeSO4.
Based on the above concept, a novel model of obesity-related diabetes was established by Masuyama et al.
They established a congenic line of the Spontaneously Diabetic Torii (SDT) rat by introducing the fa allele of the ZF rat into the SDT rat genome via the Speed Congenic Method using a PCR technique with DNA markers.
This congenic strain has been maintained by inter-crossing between fa-heterozygous littermates. Glucose tolerance, insulin sensitivity and drug treatmentMetabolic disorder in SDT fatty rats was obviously promoted as compared with SDT rats [104, 105]. Serum glucose levels in SDT fatty rats of both sexes were elevated from 6 weeks, and lipid parameters such as serum triglyceride and total cholesterol levels in the rats were elevated from 4 weeks of age. With early incidence of diabetes mellitus, diabetes-associated complications in SDT fatty rats were seen at younger ages than those in the SDT rats.
SDT fatty rats did not almost show a pre-diabetic state, since the rats showed a hyperglycemia from a young age.
Decreased urine volume and urine protein in diabetic rats treated with GTFWe measured the urine volume and urine protein of healthy, diabetic, and diabetic rats treated for two weeks with oral doses of GTF.
However, the glucose intolerance in SDT fatty rats is considered to exist with the progression of diabetes mellitus.We evaluated the pharmacological effects of an anti-diabetic drug, DPPIV-i on SDT fatty rats.
The group of diabetic animals treated with GTF received daily doses of GTF mixed in their food immediately with the induction of diabetes. GFAP expression in healthy, diabetic and Diabetic rats treated with GTF Glial Fibrillary Acidic Protein (GFAP) is normally expressed in retinal astrocytes.
Under pathologic conditions like hyperglycemia or ischemia, GFAP can be detected in other retina's areas like Muller cells layer. DPPIV-i is expected to control postprandial hyperglycemia in patients with type 2 diabetes mellitus without increasing body weight. SDT fatty rats at 9 weeks of age showed a prominent hyperglycemia after glucose-loading (Figure 4A.). The glucose levels at 30 and 60 min after glucose-loading in the SDT fatty rats significantly increased as compared with those in SD rats. Moreover, the insulin levels at 30 and 120 min after glucose-loading in the SDT fatty rats increased as compared with those in SD rats (Figure 4B.).
The GSIS in SDT fatty rats was accelerated as compared with SD rats, suggesting that hyperinsulinemia (insulin resistance) exists in the SDT fatty rats at 9 weeks of age. Glucose intolerance in SDT fatty rats is considered to be related with both the insulin resistance and the impaired insulin secretion.
A prevention of the damage could be detected in retinas isolated from diabetic animals treated for two weeks with GTF, where the activity of the pump is similar to the activity shown for healthy controls.
Each of these models has different features as described above (Table 1.), and each model acts as an important tool for revealing the complex mechanisms of diabetes and developing new anti-diabetic drugs. Studies using diabetic animal models are especially essential to aid in clarification of the pathogenetic development in human T2D.
Mechanism of action of GTF: Insulin mimetic activity Binding of insulin to its receptor initiates a cascade of phosphorylations of several substrates, including insulin receptor substrate (IRS) proteins.
IRS-1 is widely expressed in insulin-sensitive tissues, and it transmits the signal from insulin receptor to biological endpoints, such as glucose transport, protein, lipid, and glycogen synthesis.
Studies done in our laboratory on L6 myoblasts and 3T3-L1 adipocytes presented a marked increase in 2-deoxy-glucose [2-DG) uptake induced by GTF, in a rate similar to insulin, indicating a high positive effect on glucose uptake (Figure 13) (From Weksler-Zangen et al., [65]. Cells were dissolved in 1N NaOH, and aliquots were taken for scintillation counting and protein determination.
We also found that the increased glucose transport induced by GTF is dose dependent (Weksler-Zangen et al., [65]. A similar synergy between GTF and insulin that was demonstrated in diabetic animals in vivo was also found in vitro: The increase in 2-DG transport detected for the combination of GTF and insulin was much higher than for each agent alone. The rate of 2-DG transport found for the combined treatment exceeded the sum of the two separate treatments, indicating a synergy between GTF and insulin (Weksler-Zangen et al., [65]. We also found increased phosphorylation of key proteins along insulin signaling pathway, like IRS1, AKT, ccbl and MAPK, by the addition of GTF to the medium (Figures 14-16). However, we did not find any augmented phosphorylation of the insulin receptor following GTF addition, indicating a possible "by pass" of the insulin receptor by GTF.
Cells were lysed and western blot analysis was performed with antibodies for phosphotyrosine followed by stripping and reblotting with antibodies for total IRS1 as a loading control. Cells were lysed and western blot analysis was performed with antibodies for phospho-Akt followed by stripping and reblotting with antibodies for total Akt as a loading control. ConclusionsIn a search for new and effective medications for diabetes mellitus, there is a growing interest in natural derived hypoglycemic agents such as medicinal plants, herbs, and yeast. The Glucose Tolerance Factor (GTF), which is an active anti diabetic material extracted from yeast, is presented in the current manuscript.GTF effectively decreased the elevated blood glucose in diabetic animals and humans. It also decreased triglycerides and LDL cholestrerol and increased HDL cholesterol in diabetic subjects.
GTF treatment also prevented diabetes complications like nephropathy and retinopathy.Not being a protein, GTF can be taken orally. These results demonstrate GTF as a potential natural source for a novel oral anti diabetic drug in the future.



Ground cinnamon lower blood sugar
Blood sugar levels after glucose tolerance test values


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