Genetic analysis for diabetes in a new rat model of nonobese type 2 diabetes, Spontaneously Diabetic Torii rat

The dichloromethane fraction from Calotropis gigantea (L.) dryand. Stem bark extract prevents liver cancer in SDT rats with insulin-independent diabetes mellitus

ETHNOPHARMACOLOGICAL RELEVANCE

Calotropis gigantea (L.) Dryand. (C. gigantea) is a traditional medicinal plant, recognized for its effectiveness in managing diabetes, along with its notable antioxidant, anti-inflammatory, and anticancer properties. Type II diabetes mellitus (T2DM) is characterized by chronic metabolic disorders associated with an elevated risk of hepatocellular carcinoma (HCC) due to hyperglycemia and impaired insulin response. The scientific validation of C. gigantea's ethnopharmacological efficacy offers advantages in alleviating cancer progression in T2DM complications, enriching existing knowledge and potentially aiding future clinical cancer treatments.

AIM

This study aimed to investigate the preventive potential of the dichloromethane fraction of C. gigantea stem bark extract (CGDCM) against diethylnitrosamine (DEN)-induced HCC in T2DM rats, aiming to reduce cancer incidence associated with diabetes while validating C. gigantea's ethnopharmacological efficacy.

MATERIALS AND METHODS

Spontaneously Diabetic Torii (SDT) rats were administered DEN to induce HCC (SDT-DEN-VEH), followed by treatment with CGDCM. Metformin was used as a positive control (SDT-DEN-MET). All the treatments were administered for 10 weeks after the initial DEN injection. Diabetes-related parameters, including serum levels of glucose, insulin, and glycosylated hemoglobin (HbA1c), as well as liver function enzymes (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and gamma-glutamyl transferase), were quantified. Serum inflammation biomarkers interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were evaluated. Liver tissue samples were analyzed for inflammation protein expression (IL-6, TNF-α, transforming growth factor-β1 (TGF-β1), and α-smooth muscle actin (α-SMA)). Histopathological evaluation was performed to assess hepatic necrosis, inflammation, and fibrosis. Liver cell proliferation was determined using immunohistochemistry for Ki-67 expression.

RESULTS

Rats with SDT-DEN-induced HCC treated with CGDCM exhibited reduced serum glucose levels, elevated insulin levels, and decreased HbA1c levels. CGDCM treatment also reduced elevated hepatic IL-6, TNF-α, TGF-β1, and α-SMA levels in SDT-DEN-VEH rats. Additionally, CGDCM treatment prevented hepatocyte damage, fibrosis, and cell proliferation. No adverse effects on normal organs were observed with CGDCM treatment, suggesting its safety for the treatment of HCC complications associated with diabetes. Additionally, the absence of adverse effects in SD rats treated with CGDCM at 2.5 mg/kg further supports the notion of its safe usage.

CONCLUSIONS

These findings suggest that C. gigantea stem bark extract exerts preventive effects against the development of HCC complications in patients with T2DM, expanding the potential benefits of its ethnopharmacological advantages.

Contribution of animal models to diabetes research: Its history, significance, and translation to humans

Diabetes mellitus is still expanding globally and is epidemic in developing countries. The combat of this plague has caused enormous economic and social burdens related to a lowered quality of life in people with diabetes. Despite recent significant improvements of life expectancy in patients with diabetes, there is still a need for efforts to elucidate the complexities and mechanisms of the disease processes to overcome this difficult disorder. To this end, the use of appropriate animal models in diabetes studies is invaluable for translation to humans and for the development of effective treatment. In this review, a variety of animal models of diabetes with spontaneous onset in particular will be introduced and discussed for their implication in diabetes research.

Pathophysiological features in the brains of female Spontaneously Diabetic Torii (SDT) fatty rats

Diabetes mellitus (DM) and obesity are associated with neurodegenerative diseases such as Alzheimer's disease and psychiatric disorders such as major depression. In this study, we investigated pathophysiological changes in the brains of female Spontaneously Diabetic Torii (SDT) fatty rats with diabetes and obesity. Brains of Sprague-Dawley (SD), SDT and SDT fatty rats were collected at 58 weeks of age. The parietal cortical thickness was measured and the number of pyramidal cells in the hippocampal cornu ammonis 1 and 3 (CA1 and CA3) and the number of granule cells in the dentate gyrus (DG) regions were counted. The area of glial fibrillary acidic protein (GFAP) positivity in CA1, CA3 and DG regions were measured. The parietal cortical thickness and the number of cells in CA3 and DG regions of SDT and SDT fatty rats did not show obvious changes. On the other hand, in the CA1 region, the number of cells in SDT rats and SDT fatty rats was significantly lower than that in SD rats, and that in SDT fatty rats was significantly lower than that in SDT rats. The GFAP-positive area in SDT fatty rats was significantly reduced compared to that in SD rats only in the DG region. Preliminarily result showed that the expression of S100a9, an inflammation-related gene, was increased in the brains of SDT fatty rats. These results suggest that female SDT fatty rat may exhibit central nervous system diseases due to obesity and DM.

Protective effects of low-intensity exercise on metabolic oxidative capacity and capillarization in skeletal muscle of non-obese diabetic rats

Diabetes mellitus induces skeletal muscle dysfunction, such as decreased metabolic activity and capillarization. This study aimed to investigate the effects of aerobic low intensity exercise training on metabolic oxidative capacity and capillarization in skeletal muscle of non-obese diabetic rats. Eleven to twenty-five week-old male non-obese Spontaneous Diabetic Torii (SDT) rats (n = 11) and age-matched healthy male Sprague-Dawley SD rats (n = 11) were randomly assigned to either exercise or sedentary groups. The exercise training was performed on a low-speed motorized treadmill (15 m min^-1) for 60 min per session, 5 sessions per week for 14 weeks in exercised groups. Sedentary SDT rats resulted in hyperglycemia, reduction of metabolic oxidative enzyme, and low percentage of oxidative fibers in the skeletal muscles. The low-intensity exercise training inhibited the growth-related increase in glucose level, and increased the muscle oxidative enzyme in exercised SDT rats compared with sedentary SDT rats. In addition, the exercise program prevented capillary regression in the skeletal muscle of diabetic rats. These results suggest that low-intensity exercise training may be an effective treatment to counter the detrimental effects of type 2 diabetes mellitus on the oxidative capacity and the capillary network of skeletal muscles.

Animal models of diabetic retinopathy

The retina is the posterior neuro-integrated layer of the eye that conducts impulses induced by light to the optic nerve for human vision. Diseases of the retina often leads to diminished vision and in some cases blindness. Diabetes mellitus (DM) is a worldwide public health issue and globally, there is an estimated 463 million people that are affected by DM and its consequences. Diabetic retinopathy (DR) is a blinding complication of chronic uncontrolled DM and is the most common cause of blindness in the United States between the ages 24-75. It is estimated that the global prevalence of DR will increase to 191.0 million by 2030, of those 56.3 million possessing vision-threatening diabetic retinopathy (VTDR). For the most part, current treatment modalities control the complications of DR without addressing the underlying pathophysiology of the disease. Therefore, there is an unmet need for new therapeutics that not only repair the damaged retinal tissue, but also reverse the course of DR. The key element in developing these treatments is expanding our basic knowledge by studying DR pathogenesis in animal models of proliferative and non-proliferative DR (PDR and NPDR). There are numerous models available for the research of both PDR and NPDR with substantial overlap. Animal models available include those with genetic backgrounds prone to hyperglycemic states, immunologic etiologies, or environmentally induced disease. In this review we aimed to comprehensively summarize the available animal models for DR while also providing insight to each model's ocular therapeutic potential for drug discovery.

Prolonged Hyperglycemia Reduces Elasticity of Type II Diabetic Rat Bone

An increase in bone fracture risk has been reported in patients with diabetes. To evaluate an early effect of glucose intolerance on bone homeostasis, we have characterized bones from spontaneously diabetic torii (SDT) rats, an animal model of type 2 diabetes in comparison with Sprague Dawley (SD) rats as healthy control. Focusing on early effects of diabetes on bone elasticity, longitudinal wave velocities of animal bones were first determined by a micro-Brillouin scattering technique in a non-destructive way. Wave velocities in the cortical and cancellous bones in the tibias of the SDT and SD rats were compared. In a pre-diabetic stage at approximately 10 weeks of age, there seems no significant difference in wave velocities in bones from age-matched SDT and SD rats. By contrast, after the onset of diabetes at approximately 20 weeks of age, the mean velocities of bones from SDT rats were lower than those of SD rat. In addition, the X-ray CT showed that the bone amounts of SDT rats were smaller than those of SD rats in an early diabetic stage at 20 weeks of age. The current study demonstrated that the wave velocity decreased in bones of SDT rats in the early stages of diabetes. While a decrease of bone strength in an early stage of diabetes can be partially explained from decreases in bone amount as well as bone elasticity, further studies will be needed in understanding a detailed mechanism of bone deterioration due to diabetes.

Urothelial hyperplasia with calculi (papillomatosis) in the urinary bladder of a male spontaneous diabetic Torii rat

A 40-week-old male spontaneous diabetic Torii rat, an animal model of type 2 diabetes mellitus, was found to have marked urinary calculi with hematuria in the urinary bladder on necropsy. Histological findings in the urinary bladder included a papillary growth pattern with a fibrovascular stroma without atypia. Fine granular materials in the bladder lumen were positive for Von Kossa staining but negative for periodic acid-Schiff or Gram staining, indicating no apparent bacterial infection in the urinary bladder. Scanning electron microscopy revealed that the urinary calculi were magnesium ammonium phosphate crystals (struvite). On the basis of the results, the lesion was diagnosed as urothelial hyperplasia with calculi (papillomatosis). Chronic inciting stimuli by struvite crystals were considered the primary cause of the bladder findings.

Rat Models of Metabolic Syndrome

Metabolic syndrome is a complex disorder that comprises several other complex disorders, including obesity, hypertension, dyslipidemia, and diabetes. There are several rat models that encompass component features of MetS. Some models are inbred strains selected for one or more traits underlying MetS; others are population models with genetic risk for MetS traits, are induced by environmental stressors such as diet, are spontaneous monogenic mutant models, or are congenic strains derived from a combination of these models. Together they can be studied to identify the genetic and physiological underpinnings of MetS to identify candidate genes or mechanisms for study in human MetS subjects.

A deletion in the Ctns gene causes renal tubular dysfunction and cystine accumulation in LEA/Tohm rats

The Long-Evans Agouti (LEA/Tohm) rat has recently been established as a new rat model of type 2 diabetes. The onset of diabetes mellitus was observed only in male LEA/Tohm rats; however, urinary glucose appeared before the onset of diabetes. To clarify the genetic basis of urinary glucose, we performed genetic linkage analysis using (BN × LEA) F₂ intercross progeny. A recessively acting locus responsible for urinary glucose excretion (ugl) was mapped to a 7.9 Mb region of chromosome 10, which contains the cystinosin (Ctns) gene. The Ctns gene encodes the cystine transporter, which transports cystine out of the lysosome and is responsible for nephropathic cystinosis in humans. Sequence analysis identified a 13-bp deletion in the Ctns gene, leading to a truncated and loss-of-function protein, which cause cystine accumulation in various tissues. We also developed a novel congenic rat strain harboring the Ctns^ugl mutation on the F344 genetic background. Phenotypic analysis of F344-Ctns^ugl rats indicated that the incidence of urinary glucose was 100% in both males and females at around 40 weeks of age, and marked cystine accumulation was observed in the tissues, as well as remarkable renal lesions and cystine crystals in the lysosomes of the renal cortex. Furthermore, treatment with cysteamine depleted the cystine contents in F344-Ctns^ugl rat embryonic fibroblasts. These results indicated that the F344-Ctns^ugl rat provides a novel rat model of cystinosis, which allows not only a better understanding of the pathogenesis and pathophysiology of cystinosis but will also contribute to the development of new therapies.

Novel High-Fat Diet Formulation and Streptozotocin Treatment for Induction of Prediabetes and Type 2 Diabetes in Rats

Background:

The previously established methods for type 2 diabetes (T2D) have mainly concentrated on overt diabetes model development. Here, our intention was to create an animal model passing through distinct phases such as obesity with insulin resistance, prediabetes, and gradual progress to the overt diabetes stage. A high-fat high-carbohydrate diet formulation was prescribed combined with multiple low-dose streptozotocin (STZ) injections after obesity establishment.

Materials and Methods:

Sixteen male Wistar rats were separated randomly into two groups and fed a normal diet for 1 week after which the body weight and biochemical indices of each rat were measured and recorded. Subsequently, one group (n = 8) switched to the high-fat high-carbohydrate diet formulated by us for 10 weeks, whereas the other group (n = 8) continued with the normal diet. Body weight and biochemical indices of the rats in the high-fat diet (HFD) group were measured at the end of 10 weeks, and each rat received 30 mg/kg intraperitoneal STZ injections with 1-week intervals in two steps and was continued on a high-fat high-carbohydrate diet. The differences between the groups were analyzed using the Student's t-test or one-way analysis of variance and by post hoc multiple comparisons.

Results:

A significant change in weight, fasting blood glucose, and triglyceride was observed in rats fed with a HFD after 10 weeks. The HFD rats showed typical characteristics of T2D mellitus (T2DM) such as insulin resistance and hyperglycemia following 30 mg/kg STZ.

Conclusions:

The novel high-fat high-carbohydrate formulation we used, along with multiple low doses of STZ, can mimic peculiar characteristics of T2DM development.

High fructose diet feeding accelerates diabetic nephropathy in Spontaneously Diabetic Torii (SDT) rats

Diabetic nephropathy (DN) is one of the complications of diabetes and is now the most common cause of end-stage renal disease. Fructose is a simple carbohydrate that is present in fruits and honey and is used as a sweetener because of its sweet taste. Fructose has been reported to have the potential to progress diabetes and DN in humans even though fructose itself does not increase postprandial plasma glucose levels. In this study, we investigated the effects of high fructose intake on the kidney of the Spontaneously Diabetic Torii (SDT) rats which have renal lesions similar to those in DN patients and compared these with the effects in normal SD rats. This study revealed that a 4-week feeding of the high fructose diet increased urinary excretion of kidney injury makers for tubular injury and accelerated mainly renal tubular and interstitial lesions in the SDT rats but not in normal rats. The progression of the nephropathy in the SDT rats was considered to be related to increased internal uric acid and blood glucose levels due to the high fructose intake. In conclusion, high fructose intake exaggerated the renal lesions in the SDT rats probably due to effects on the tubules and interstitium through metabolic implications for uric acid and glucose.

The Nile Rat (Arvicanthis niloticus) as a Superior Carbohydrate-Sensitive Model for Type 2 Diabetes Mellitus (T2DM)

Type II diabetes mellitus (T2DM) is a multifactorial disease involving complex genetic and environmental interactions. No single animal model has so far mirrored all the characteristics or complications of diabetes in humans. Since this disease represents a chronic nutritional insult based on a diet bearing a high glycemic load, the ideal model should recapitulate the underlying dietary issues. Most rodent models have three shortcomings: (1) they are genetically or chemically modified to produce diabetes; (2) unlike humans, most require high-fat feeding; (3) and they take too long to develop diabetes. By contrast, Nile rats develop diabetes rapidly (8-10 weeks) with high-carbohydrate (hiCHO) diets, similar to humans, and are protected by high fat (with low glycemic load) intake. This review describes diabetes progression in the Nile rat, including various aspects of breeding, feeding, and handling for best experimental outcomes. The diabetes is characterized by a striking genetic permissiveness influencing hyperphagia and hyperinsulinemia; random blood glucose is the best index of disease progression; and kidney failure with chronic morbidity and death are outcomes, all of which mimic uncontrolled T2DM in humans. Non-alcoholic fatty liver disease (NAFLD), also described in diabetic humans, results from hepatic triglyceride and cholesterol accumulation associated with rising blood glucose. Protection is afforded by low glycemic load diets rich in certain fibers or polyphenols. Accordingly, the Nile rat provides a unique opportunity to identify the nutritional factors and underlying genetic and molecular mechanisms that characterize human T2DM.

Animal Models of Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is one of the most common complications associated with chronic hyperglycemia seen in patients with diabetes mellitus. While many facets of DR are still not fully understood, animal studies have contributed significantly to understanding the etiology and progression of human DR. This review provides a comprehensive discussion of the induced and genetic DR models in different species and the advantages and disadvantages of each model.

RECENT FINDINGS

Rodents are the most commonly used models, though dogs develop the most similar morphological retinal lesions as those seen in humans, and pigs and zebrafish have similar vasculature and retinal structures to humans. Nonhuman primates can also develop diabetes mellitus spontaneously or have focal lesions induced to simulate retinal neovascular disease observed in individuals with DR. DR results in vascular changes and dysfunction of the neural, glial, and pancreatic β cells. Currently, no model completely recapitulates the full pathophysiology of neuronal and vascular changes that occur at each stage of diabetic retinopathy; however, each model recapitulates many of the disease phenotypes.

Neuropeptides, trophic factors, and other substances providing morphofunctional and metabolic protection in experimental models of diabetic retinopathy

Vision is the most important sensory modality for many species, including humans. Damage to the retina results in vision loss or even blindness. One of the most serious complications of diabetes, a disease that has seen a worldwide increase in prevalence, is diabetic retinopathy. This condition stems from consequences of pathological metabolism and develops in 75% of patients with type 1 and 50% with type 2 diabetes. The development of novel protective drugs is essential. In this review we provide a description of the disease and conclude that type 1 diabetes and type 2 diabetes lead to the same retinopathy. We evaluate existing experimental models and recent developments in finding effective compounds against this disorder. In our opinion, the best models are the long-term streptozotocin-induced diabetes and Otsuka Long-Evans Tokushima Fatty and spontaneously diabetic Torii rats, while the most promising substances are topically administered somatostatin and pigment epithelium-derived factor analogs, antivasculogenic substances, and systemic antioxidants. Future drug development should focus on these.

Spontaneous type 2 diabetic rodent models

Diabetes mellitus, especially type 2 diabetes (T2DM), is one of the most common chronic diseases and continues to increase in numbers with large proportion of health care budget being used. Many animal models have been established in order to investigate the mechanisms and pathophysiologic progress of T2DM and find effective treatments for its complications. On the basis of their strains, features, advantages, and disadvantages, various types of animal models of T2DM can be divided into spontaneously diabetic models, artificially induced diabetic models, and transgenic/knockout diabetic models. Among these models, the spontaneous rodent models are used more frequently because many of them can closely describe the characteristic features of T2DM, especially obesity and insulin resistance. In this paper, we aim to investigate the current available spontaneous rodent models for T2DM with regard to their characteristic features, advantages, and disadvantages, and especially to describe appropriate selection and usefulness of different spontaneous rodent models in testing of various new antidiabetic drugs for the treatment of type 2 diabetes.

The spontaneously diabetic torii rat: an animal model of nonobese type 2 diabetes with severe diabetic complications

The Spontaneously Diabetic Torii (SDT) rat is an inbred strain of Sprague-Dawley rat and recently is established as a nonobese model of type 2 diabetes (T2D). Male SDT rats show high plasma glucose levels (over 700 mg/dL) by 20 weeks. Male SDT rats show pancreatic islet histopathology, including hemorrhage in pancreatic islets and inflammatory cell infiltration with fibroblasts. Prior to the onset of diabetes, glucose intolerance with hypoinsulinemia is also observed. As a result of chronic severe hyperglycemia, the SDT rats develop profound complications. In eyes, retinopathy, cataract, and neovascular glaucoma are observed. Proliferative retinopathy, especially, resulting from retinal neovascular vessels is a unique characteristic of this model. In kidney, mesangial proliferation and nodular lesion are observed. Both peripheral neuropathy such as decreased nerve conduction velocity and thermal hypoalgesia and autonomic neuropathy such as diabetic diarrhea and voiding dysfunction have been reported. Osteoporosis is another complication characterized in SDT rat. Decreased bone density and low-turnover bone lesions are observed. Taking advantage of these features, SDT rat has been used for evaluating antidiabetic drugs and drugs/gene therapy for diabetic complications. In conclusion, the SDT rat is potentially a useful T2D model for studies on pathogenesis and treatment of diabetic complications in humans.

Phenotypic Characterization of LEA Rat: A New Rat Model of Nonobese Type 2 Diabetes

Animal models have provided important information for the genetics and pathophysiology of diabetes. Here we have established a novel, nonobese rat strain with spontaneous diabetes, Long-Evans Agouti (LEA) rat derived from Long-Evans (LE) strain. The incidence of diabetes in the males was 10% at 6 months of age and 86% at 14 months, while none of the females developed diabetes. The blood glucose level in LEA male rats was between 200 and 300 mg/dl at 120 min according to OGTT. The glucose intolerance in correspondence with the impairment of insulin secretion was observed in male rats, which was the main cause of diabetes in LEA rats. Histological examination revealed that the reduction of β-cell mass was caused by progressive fibrosis in pancreatic islets in age-dependent manner. The intracytoplasmic hyaline droplet accumulation and the disappearance of tubular epithelial cell layer associated with thickening of basement membrane were evident in renal proximal tubules. The body mass index and glycaemic response to exogenous insulin were comparable to those of control rats. The unique characteristics of LEA rat are a great advantage not only to analyze the progression of diabetes, but also to disclose the genes involved in type 2 diabetes mellitus.

The hyperglycemia stimulated myocardial endoplasmic reticulum (ER) stress contributes to diabetic cardiomyopathy in the transgenic non-obese type 2 diabetic rats: a differential role of unfolded protein response (UPR) signaling proteins

It has been well demonstrated that excessive blood glucose level could be detrimental to the myocardial function through the variety of mechanisms, of which endoplasmic reticulum stress (ERS) could play an unprecedented role through the activation of unfolded protein response (UPR). Recently, reports are coming out with the evidences that UPR signaling proteins are regulated differentially depend on the experimental conditions and cell types. In addition, ERS has been proposed to be closely associated with the regulation of lipogenesis. Therefore, in this study we tried to find out the expressions of myocardial UPR signaling proteins as well as proteins involved in lipid and glucose metabolism in non-obese type 2 diabetic mellitus (DM) condition using Spontaneous Diabetic Torii (SDT) rat. We have found the significant up-regulation of oxidative, nitrosative and ERS marker proteins in the myocardium of the SDT rats, in comparison to its normal (Sprague-Dawley - SD) rats. In addition, the sub-arm of UPR signaling proteins, such as p-PERK, p-eIF2α, ATF6, CHOP/GADD153, TRAF2, apoptotic signaling proteins, such as BAD, cytochrome C, cleaved caspase-7 and -12, were significantly up-regulated in the SDT rats, in comparison to the SD rats. Interestingly, there were no significant changes in the phosphorylation of IRE-1α, and XBP-1 protein expression. In addition, the proteins involved in lipid and glucose metabolisms, such as PPARα, PPARγ, CPT1, PGC-1α except GLUT4, and the proteins involved in insulin signaling, such as p-Akt and p-PI3K were shown significant attenuation in its expressions in the SDT rats, when compared with the SD rats. Taken together, it is suggested that the activation of PERK and ATF6 pathway are the major determinant rather than the IRE-1α-XBP1 pathway for the ERS-mediated metabolic dysfunction, which might eventually leads to diabetic cardiomyopathy in non-obese type 2 DM.

Characteristics of bone turnover, bone mass and bone strength in Spontaneously Diabetic Torii-Lepr fa rats

The Spontaneously Diabetic Torii-Lepr (fa) (SDT-fa/fa) rat is a new model of obese type 2 diabetes. The SDT-fa/fa rat shows obesity and hyperglycemia at a young age compared to the Spontaneously Diabetic Torii (SDT-+/+) rat; however, bone abnormalities in the SDT-fa/fa rat have not been investigated. The objective of the present study was to investigate the effects of obese type 2 diabetes on bone turnover, bone mass, and bone strength in the SDT-fa/fa rat. Sprague-Dawley rats were used as control animals, and SDT-+/+ rats were used as non-obese type 2 diabetic rats. Serum osteocalcin and urine deoxypyridinoline levels were decreased in SDT-fa/fa rats compared to control rats at a young age. SDT-fa/fa rats showed decreases in bone mineral density and bone mineral content of the whole tibia, and shortening of the tibia and femur compared to control and SDT-+/+ rats. Deterioration in bone geometrical properties of the femur midshaft such as cortical thickness and minimum moment of inertia, was observed in SDT-fa/fa rats compared to control and SDT-+/+ rats. Furthermore, trabecular bone volume of the distal femur was decreased in SDT-fa/fa rats compared to control rats. These negative effects on bone in SDT-fa/fa rats caused severe decreases in maximum load, stiffness, and energy absorption of the femur. In addition, serum levels of homocysteine, a candidate for bone fragility markers, were elevated in SDT-fa/fa rats compared to control and SDT-+/+ rats. In conclusion, the SDT-fa/fa rat may be a useful model to investigate bone abnormalities in obese type 2 diabetes.

A high-fat diet inhibits the progression of diabetes mellitus in type 2 diabetic rats

It is well known that rats and mice, when fed a high-fat diet, develop obesity associated with abnormal glycolipid metabolism. In this study, we investigated the effects of a high-fat diet on a diabetic rat model, Spontaneously Diabetic Torii (SDT), which develops diabetes due to decreased insulin production and secretion with age. We hypothesized that a high-fat diet would accelerate the induction of diabetes in this model. The SDT rats were divided into 2 groups, which were fed a high-fat diet or standard diet for 16 weeks. The group fed a high-fat diet developed obesity, hyperinsulinemia, and hyperlipidemia until 16 weeks of age. Before 16 weeks of age, hyperglycemia accompanied by hypoinsulinemia developed in the group on a standard diet, but serum glucose levels were comparable in both groups. After 16 weeks of age, the group on a standard diet showed an increase in serum glucose levels and a decrease in serum insulin levels. Unexpectedly, in the group on the high-fat diet, we observed a suppressed of the progression of hyperglycemia/hypoinsulinemia. Histopathological observation revealed more pancreatic beta cells in the group on the high-fat diet. This study suggests that feeding SDT rats a high-fat diet induces obesity, hyperinsulinemia, and hyperlipidemia, but not hyperglycemia, until 16 weeks of age. Thereafter, age-dependent progress of hyperglycemia and hypoinsulinemia was delayed by a high-fat diet. The hyperfunction of pancreatic beta cells induced by a high-fat diet before the onset of hyperglycemia appears to suppress development of hyperglycemia/hypoinsulinemia.

Effects of food restriction on pancreatic islets in Spontaneously Diabetic Torii fatty rats

The Spontaneously Diabetic Torii (SDT) fatty rat, established by introducing the fa allele of the Zucker fatty rat into the SDT rat genome, is a new model of obesity/type 2 diabetes. The present study investigated effects of food restriction on metabolic and endocrinological function in SDT fatty rats. SDT fatty rats were pair-fed with SDT rats from 7 to 21 weeks of age. The SDT fatty rats were already hyperinsulinemic and hyperlipidemic at 7 weeks of age. After 7 weeks of age, SDT fatty rats showed age-dependently increasing serum glucose levels associated with decreasing serum insulin levels. However, in pair-fed SDT fatty rats, hyperglycemia and hyperinsulinemia were attenuated at 9 weeks of age. After 9 weeks of age, the serum insulin levels unexpectedly increased in the pair-fed SDT fatty rats. Glucose tolerance was also improved, and the pancreatic insulin contents were increased in these rats. Pancreatic islets were hypertrophied in pair-fed SDT fatty rats compared with ad lib-fed SDT fatty rats, which were comparable to SDT rats. This study showed that, in SDT fatty rats, calorie restriction by paired-feeding with SDT rats attenuated hyperglycemia and hyperinsulinemia for the first 2 weeks. Thereafter, the serum insulin levels and pancreatic insulin contents were increased, though the restriction was continued. Hypertrophic pancreatic islets were also remarkable, indicating increased beta cell proliferation. The activated pancreatic beta cell functions might be due to rapid food ingestion, a change of feeding behavior resulting form increasing the fasting period, which was indispensable for calorie restriction.

Pathophysiological characteristics of diabetic ocular complications in spontaneously diabetic torii rat

The Spontaneously Diabetic Torii (SDT) rat, a nonobese type 2 diabetes model, develops severe diabetic retinopathy as result of chronic severe hyperglycemia. Although existing diabetes animal models also develop ocular complications, severe retinal lesions frequently observed in human diabetes patients such as preretinal neovascularization or retinal detachment are not found. Distinctive features in SDT rat are hypermature cataract, tractional retinal detachment with fibrous proliferation, and massive hemorrhaging in the anterior chamber. These pathophysiological changes are caused by sustained hyperglycemic condition and subsequent increased expression of vascular endothelial growth factor (VEGF) in retina, iris, and ciliary body. Although some differences in diabetic retinopathy exist between SDT rats and humans (e.g., a low incidence of neovascular formation and poor development of nonperfused area are found in this animal), SDT rat will be a useful model in studies of the pathogenesis and treatment of diabetic retinopathy.

Effect of food restriction on adipose tissue in spontaneously diabetic Torii fatty rats

Spontaneously Diabetic Torii-fa/fa (SDT fatty) rat is a new model of obese type 2 diabetes. SDT fatty rat exhibits obesity associated with hyperphagia. In this study, SDT fatty rats were subjected to pair-feeding with SDT-+/+ (SDT) rats from 6 to 22 weeks of age. The ratio of visceral fat weight to subcutaneous fat weight (V/S) decreased at 12 weeks of age in the pair-feeding rats. The intraperitoneal fat weight such as epididymal and retroperitoneal fat weight decreased, whereas mesenteric fat weight had no change. Cell size of the epididymal fat in the pair-feeding rats tended to decrease. Glucose oxidation level in epididymal fat in the pair-feeding rats at 12 weeks of age was recovered to a similar level with that in SDT rats. These results indicated that SDT fatty rat is a useful model to evaluate the functional or the morphological features in adipose tissue and develop a novel drug for antiobesity.

Linkage disequilibrium mapping of the replicated type 2 diabetes linkage signal on chromosome 1q

OBJECTIVE

Linkage of the chromosome 1q21-25 region to type 2 diabetes has been demonstrated in multiple ethnic groups. We performed common variant fine-mapping across a 23-Mb interval in a multiethnic sample to search for variants responsible for this linkage signal.

RESEARCH DESIGN AND METHODS

In all, 5,290 single nucleotide polymorphisms (SNPs) were successfully genotyped in 3,179 type 2 diabetes case and control subjects from eight populations with evidence of 1q linkage. Samples were ascertained using strategies designed to enhance power to detect variants causal for 1q linkage. After imputation, we estimate approximately 80% coverage of common variation across the region (r (2) > 0.8, Europeans). Association signals of interest were evaluated through in silico replication and de novo genotyping in approximately 8,500 case subjects and 12,400 control subjects.

RESULTS

Association mapping of the 23-Mb region identified two strong signals, both of which were restricted to the subset of European-descent samples. The first mapped to the NOS1AP (CAPON) gene region (lead SNP: rs7538490, odds ratio 1.38 [95% CI 1.21-1.57], P = 1.4 x 10(-6), in 999 case subjects and 1,190 control subjects); the second mapped within an extensive region of linkage disequilibrium that includes the ASH1L and PKLR genes (lead SNP: rs11264371, odds ratio 1.48 [1.18-1.76], P = 1.0 x 10(-5), under a dominant model). However, there was no evidence for association at either signal on replication, and, across all data (>24,000 subjects), there was no indication that these variants were causally related to type 2 diabetes status.

CONCLUSIONS

Detailed fine-mapping of the 23-Mb region of replicated linkage has failed to identify common variant signals contributing to the observed signal. Future studies should focus on identification of causal alleles of lower frequency and higher penetrance.

Long-term angiotensin II blockade may improve not only hyperglycemia but also age-associated cardiac fibrosis

In the present study, the effects of long-term angiotensin (Ang) II antagonism on the development of cardiac and endothelial disorders were examined in Spontaneously Diabetic Torii (SDT) rats. Blood glucose concentration started to increase markedly in the untreated SDT rats from 20 weeks of age, while the blood glucose concentrations of candesartan cilexetil-treated SDT rats were significantly lower until 30 weeks of age. Cardiac function deteriorated in SDT rats and was accompanied by severe cardiac fibrosis, cardiac hypertrophy, and microstructural pathologic change in cardiomyocytes. Cardiac function was very well preserved in the age-matched Sprague Dawley (SD) rats, but cardiac fibrosis developed with aging. Candesartan cilexetil treatment improved cardiac structural remodeling and cardiac function in SDT rats. Surprisingly, the degree of cardiac fibrosis in candesartan cilexetil-treated SDT rats was less than that of SD rats. Immunohistological staining confirmed that in addition to collagen deposition, fibroblasts and myofibroblasts were the main cellular components in the cardiac fibrotic areas. The diabetic hearts showed positive staining for ACE, Ang II, and AT(1) receptors. SDT rats also showed decreased endothelial function, which was improved with candesartan cilexetil treatment. These findings indicate that Ang II is involved in the development of cardiac dysfunction by accelerating cardiac remodeling and cardiomyocyte damage in the presence of hyperglycemia. On the other hand, although the mechanisms responsible for the cardiac fibrosis that occurs under normal conditions may differ greatly from those responsible for cardiac fibrosis with hyperglycemia, Ang II seems to play an important role in both.

Telmisartan, an angiotensin II type 1 receptor blocker, prevents the development of diabetes in male Spontaneously Diabetic Torii rats

To assess the beneficial effects of the angiotensin II type 1 receptor blocker telmisartan on a non-obese animal model of reduced function and mass of islet beta-cells prior to the development of diabetes, Spontaneously Diabetic Torii (SDT) rats were treated with telmisartan at 8 weeks of age. At 24 weeks of age, the treatment with telmisartan dose-dependently ameliorated hyperglycemia and hypoinsulinemia, and high-dose (5 mg/kg/day) treated SDT rats did not developed diabetes. Real-time RT-PCR analysis revealed that treatment with high-dose telmisartan reduced mRNA expression of local renin-angiotensin system (RAS) components, components of NAD(P)H oxidase, transforming growth factor-beta1 and vascular endothelial growth factor in the pancreas of male SDT rats. Immunohistochemical and Western blot analyses revealed that treatment with telmisartan also reduced expression of p47(phox). These results suggest that treatment with telmisartan reduces oxidative stress by local RAS activation and protects against islet beta-cell damage and dysfunction. These findings provide at least a partial explanation for the reduced incidence of new-onset diabetes that has been observed in several clinical trials involving angiotensin II type 1 receptor blockers and ACE inhibitors.

Characterization of hepatic glucose metabolism disorder with the progress of diabetes in male Spontaneously Diabetic Torii rats

The Spontaneously Diabetic Torii (SDT) rat has recently been established as a new model of non-obese type 2 diabetes. In this study, we examined changes in hepatic glucose metabolism in prediabetic and diabetic SDT rats compared with age-matched control rats. The prediabetic state was confirmed at 16 weeks of age, and the diabetic state was confirmed at 24 and 32 weeks of age. Decreases in glucokinase mRNA levels and activity were observed in the prediabetic state. In this state, glycogen synthase activity and glycogen content were also decreased in the SDT rat. In addition to the above changes, glycogen phosphorylase mRNA and activity were decreased and gluconeogenetic enzyme mRNA levels were significantly increased in the diabetic state. These results indicate there is a great potential that abnormalities in hepatic glucose metabolism play a role in the progression to onset of diabetes. We suggest that the SDT rat is a valuable diabetic model for investigations into mechanisms or causes of progression to diabetes.

Electroretinographic study of spontaneously diabetic Torii rats

Spontaneously diabetic Torii (SDT) rats are an inbred strain of rats with a non-obese type 2 diabetes mellitus that were isolated from an outbred colony of Sprague-Dawley (SD) rats. Electroretinograms (ERGs) were recorded from SDT and SD (controls) rats at 10- and 44-weeks-of-age to determine their retinal function. The amplitudes and implicit times of the ERGs of the right and left eyes were not significantly different indicating that the intra-individual variation was small. Both amplitudes and implicit times of the ERGs in the SDT rats were not significantly different from those of SD rats at 10-weeks-of-age. At 44-weeks-of-age, however, the a- and b-waves and the oscillatory potentials were significantly reduced with prolonged implicit times in the SDT rats compared to SD rats. These depressed ERGs may reflect vascular and neuronal damage throughout the retina as are seen in the advanced stages of human diabetic retinopathy. Thus, the SDT rat can be used to study the retinal physiology of diabetic retinopathy.

Quantitative trait loci for impaired glucose tolerance in nondiabetic SM/J and A/J mice

The SMXA-5 recombinant inbred strain, which was established from nondiabetic parental SM/J and A/J mice, develops diabetic phenotypes such as impaired glucose tolerance. The combination of diabetogenic genes in the SM/J and A/J genomes impairs glucose tolerance in SMXA-5 mice. Using (SM/J x SMXA-5)F2 mice fed a high-fat diet, we previously detected a diabetogenic locus, T2dm2sa, on chromosome (Chr) 2. The A/J allele at this locus is diabetogenic. The SM.A-T2dm2sa congenic mouse, in which the Chr 2 region of A/J including T2dm2sa was introgressed into SM/J, showed obviously impaired glucose tolerance. These results indicate that SM.A-T2dm2sa mice develop diabetogenic traits due to T2dm2sa with the A/J allele and unknown diabetogenic loci with the SM/J allele. The aim of this study was to dissect these unknown loci, using quantitative trait locus (QTL) analysis in the (A/J x SM.A-T2dm2sa) F2 intercross fed a high-fat diet. The results revealed a highly significant QTL, T2dm4sa, for glucose tolerance on Chr 6 and a significant QTL, T2dm5sa, for glucose tolerance on Chr 11. These loci with the SM/J allele were diabetogenic. The diabetogenic effect of T2dm4sa or T2dm5sa was verified by the impairment of glucose tolerance in the A/J-6(SM) or A/J-11(SM) consomic strain, in which Chr 6 or Chr 11 of SM/J is introgressed into A/J, respectively. These results demonstrate that diabetogenic loci exist in the genomes of nondiabetic A/J and SM/J mice and suggest that T2dm2sa with the A/J allele and T2dm4sa and/or T2dm5sa with the SM/J allele elicit impaired glucose tolerance in SM.A-T2dm2sa mice.

Diabetes-associated complications in Spontaneously Diabetic Torii fatty rats

The Spontaneously Diabetic Torii (SDT) fatty rat, established by introducing the fa allele of the Zucker fatty rat into the SDT rat genome, is a new model of obese type 2 diabetes. The SDT-fa/fa (SDT fatty) rat shows overt obesity, and hyperglycemia and hyperlipidemia are observed at a young age as compared with the SDT-+/+ (SDT normal) rat. However, the features of the diabetic complications in the SDT fatty rat have not been reported. In the present study, the incidence and the progression of diabetic complications in the SDT fatty rat were examined, and compared with those of the SDT normal rat. Renal function parameters, such as blood urea nitrogen, urine volume and urinary protein, increased from 4 weeks of age in the SDT fatty rat, and pathological findings in the renal tubule were observed from 8 weeks. Furthermore, cataract was observed in the SDT fatty rat from 8 weeks of age, and prolongation of peak latencies on electroretinograms was observed at 16 and 24 weeks of age. On the other hand, in the SDT normal rat, renal or ocular changes were observed from 24 weeks of age. With early incidence of diabetes mellitus, diabetes-associated complications in the SDT fatty rat were seen at younger ages than those in the SDT normal rat. In conclusion, the SDT fatty rat is expected to be a useful model for the analysis of diabetic complications and the evaluation of drugs related to metabolic diseases.

Identification of a major locus for islet inflammation and fibrosis in the spontaneously diabetic Torii rat

The pathogenesis of inflammation and fibrosis in the pancreatic islets in diabetes is largely unknown. Spontaneously diabetic Torii (SDT) rats exhibit inflammation and fibrosis in and around the islets during the development of the disease. We investigated genetic factors for diabetes, islet inflammation, and fibrosis in the SDT rat. We produced F1 and F2 rats by intercross between SDT and F344 rats, examined the onset of diabetes, glucose tolerance, and histology of the pancreas, and performed genetic analysis of these traits. We then established a congenic strain carrying the SDT allele at the strongest diabetogenic locus on the F344 genetic background and characterized glucose tolerance and histology of the pancreas. F1 rats showed glucose intolerance and inflammatory changes mainly in the islets. Genetic analysis of diabetes identified a major locus on chromosome 3, designated Dmsdt1, at which a dominantly acting SDT allele was involved. Quantitative trait locus (QTL) analysis of glucose tolerance revealed, in addition to Dmsdt1 [logarithm of odds (LOD) 5.3 near D3Mit12], three other loci, designated Dmsdt2 (LOD 4.2 at D8Rat46), Dmsdt3 (LOD 3.8 near D13Arb5), and Dmsdt4 (LOD 5.8 at D14Arb18). Analysis of a congenic strain for Dmsdt1 indicates that the dominantly acting SDT allele induces islet inflammation and fibrosis. Thus we have found a major locus on chromosome 3 for islet inflammation and fibrosis in the SDT rat. Identification of the genes responsible should provide insight into the pathogenesis of diabetes.

A meta-analysis of QTL for diabetes-related traits in rodents

Crossbreeding studies in rodents have identified numerous quantitative trait loci (QTL) that are linked to diabetes-related component traits. To identify genetic consensus regions implicated in insulin action and glucose homeostasis, we have performed a meta-analysis of genomewide linkage scans for diabetes-related traits. From a total of 43 published genomewide scans we assembled a nonredundant collection of 153 QTL for glucose levels, insulin levels, and glucose tolerance. Collectively, these studies include data from 48 different parental strains and >11,000 individual animals. The results of the studies were analyzed by the truncated product method (TPM). The analysis revealed significant evidence for linkage of glucose levels, insulin levels, and glucose tolerance to 27 different segments of the mouse genome. The most prominent consensus regions [localized to chromosomes 2, 4, 7, 9, 11, 13, and 19; logarithm of odds (LOD) scores 10.5-17.4] cover approximately 11% of the mouse genome and collectively contain the peak markers for 47 QTL. Approximately half of these genomic segments also show significant linkage to body weight and adiposity, indicating the presence of multiple obesity-dependent and -independent consensus regions for diabetes-related traits. At least 84 human genetic markers from genomewide scans and >80 candidate genes from human and rodent studies map into the mouse consensus regions for diabetes-related traits, indicating a substantial overlap between the species. Our results provide guidance for the identification of novel candidate genes and demonstrate the presence of numerous distinct consensus QTL regions with highly significant LOD scores that control glucose homeostasis. An interactive physical map of the QTL is available online at http://www.diabesitygenes.org.

The genetic landscape of type 2 diabetes in mice

Inbred mouse strains provide genetic diversity comparable to that of the human population. Like humans, mice have a wide range of diabetes-related phenotypes. The inbred mouse strains differ in the response of their critical physiological functions, such as insulin sensitivity, insulin secretion, beta-cell proliferation and survival, and fuel partitioning, to diet and obesity. Most of the critical genes underlying these differences have not been identified, although many loci have been mapped. The dramatic improvements in genomic and bioinformatics resources are accelerating the pace of gene discovery. This review describes how mouse genetics can be used to discover diabetes-related genes, summarizes how the mouse strains differ in their diabetes-related phenotypes, and describes several examples of how loci identified in the mouse may directly relate to human diabetes.

The spontaneously diabetic Torii rat with gastroenteropathy

The spontaneously diabetic Torii (SDT) rat was recently recognized as a new animal model of non-obese type 2 diabetes. As the severe diabetic ocular complications seen in SDT rats already have been investigated, we examined another common diabetic complication, gastroenteropathy. Male SDT rats developed diabetes at 20 weeks and diarrhea at 28 weeks of age. Gastrointestinal motility was evaluated at 28 weeks by measuring the distance of small intestinal transit by oral administration of the non-absorbed marker, arabic gum. SDT rats exhibited greater intestinal transit distance than control SD rats (54.1+/-2.6% versus 43.0+/-1.2%). Insulin treatment of SDT rats begun at 20 weeks of age produced improved stool and reduced intestinal transit distance (41.4+/-0.3%). Morphologically, the SDT rats exhibited longer villi and heavier weight of intestine compared to control SD rats. These results suggest that the SDT rat may be a useful animal model for studies of diabetic gastroenteropathy.

Identifying susceptibility variants for type 2 diabetes

The etiology of type 2 diabetes (T2D) is complex and remains poorly understood. Differences in individual susceptibility to this condition reflect the action of multiple variants, each of which confers a modest effect, and their interactions with a variety of environmental exposures. Several complementary approaches to the identification of the etiological variants have been adopted, though, for all, association analyses provide the final common pathway. The genes and/or chromosomal regions studied have been selected on the basis of their presumed biological relevance to diabetes, known involvement in monogenic forms, or animal models of the condition and/or signals arising from whole-genome linkage scans. These association studies have featured a wide variety of designs and analytical approaches, but reliable biological insights have been few, largely because of difficulties in obtaining reproducible findings. However, in recent years, several examples of robustly replicated associations have emerged, largely as a result of an emphasis on the need for improved power and more appropriate analysis and interpretation. New strategies for the large-scale identification of T2D susceptibility variants are now becoming possible, including the prospect of genuine genome-wide association scans, but caution in their design, analysis, and interpretation remains essential.

Antidiabetic activity of lipophilic (−)-epigallocatechin-3-gallate derivative under its role of α-glucosidase inhibition

(-)-Epigallocatechin-3-gallate (EGCG), a component of catechins, has been shown to reduce blood glucose levels. In the present study, we investigated the antidiabetic activity and its mechanism of lipophilic EGCG derivative (L-EGCGd) in streptozotocin (STZ)-induced diabetic rats. L-EGCGd was chemically modified from traditional hydrophilic EGCG. After 30 days treatment, plasma levels of glucose were significantly reduced by 40.5+/-7.0% and 17.0+/-2.8% in groups administered 50 or 25 mg kg(-1)d(-1) L-EGCGd, respectively, as compared with that in the diabetic control group. Lipid metabolites, such as total cholesterol (TC), triglyceride (TG) and low-density lipoprotein cholesterol (LDLC) were effectively attenuated by L-EGCGd administration, but plasma HDLC levels did not change significantly. The oral glucose tolerance test (OGTT) greatly revealed the improved ability of glucose tolerance with treatment of L-EGCGd. L-EGCGd only retarded the postprandial rise in blood glucose with sucrose loading but not glucose loading. And activity of alpha-glucosidase was inhibited by 50% at the concentration of 246.6 microg ml(-1) L-EGCGd. As a result, we first demonstrated that the purified form of compound L-EGCGd possessed the hypoglycemic effect under its role of alpha-glucosidase inhibition, and therefore should be possibly accepted as an alternative oral medication protecting patients against postprandial hyperglycemic toxicity on the treatment of diabetes and its complications.

Characteristics of diabetic retinopathy in SDT rats

BACKGROUND

We previously reported a new diabetic strain of the Sprague-Dawley rat, named the Spontaneously Diabetic Torii (SDT) rat. The purpose of the present study was to report the histologic and ultrastructural characteristics of diabetic retinopathy (DR) in a new animal model, the SDT rat.

METHODS

Fifty-three eyes of 43 SDT rats of various ages (35-82 weeks) were examined, of which 33 underwent histopathologic examination, 15 eyes fluorescein-dextran microscopy, and five eyes the trypsin digestion method.

RESULTS

Of the 33 eyes examined histopathologically, DR was identified in 20 eyes (61%). Large retinal folds mimicking diabetic tractional retinal detachment were observed in 20 eyes (61%). Retinal hemorrhages were seen in four eyes (12%). A neovascular fibrous membrane around the iris developed in five eyes (15%), of which two eyes had a massive anterior chamber hemorrhage. Of the 15 eyes examined by fluorescein-dextran microscopy, an area of nonperfusion and/or extensive hyperfluorescence was observed in 12 eyes (80%). Of the five eyes examined using the trypsin digestion method, acellular capillaries and pericyte loss were observed in four eyes (80%). Of the 53 eyes, the previously mentioned retinal changes of DR were observed in 36 eyes (68%). The rats with DR (49-82 weeks; mean, 60 weeks) were older than the rats without DR (35-55 weeks; mean, 40 weeks) (p < 0.001).

CONCLUSION

Large retinal folds mimicking tractional retinal detachment with extensive leakage of fluorescein around the optic disk was the most prominent finding of DR in SDT rats.

Diabetic modifier QTLs identified in F2 intercrosses between Akita and A/J mice

To identify novel genetic modifiers of type 2 diabetes (T2D), we performed quantitative trait loci (QTL) analysis on F(2) progeny of hypoinsulinemic diabetic Akita mice, heterozygous for the Ins2 gene Cys96Tyr mutation, and nondiabetic A/J mice. We generated 625 heterozygous (F(2)-Hetero) and 338 wild-type (F(2)-Wild) mice with regard to the Ins2 mutation in F(2) intercross progeny. We measured quantitative traits, including plasma glucose and insulin concentrations during the intraperitoneal glucose tolerance test (IPGTT), and body weight (BW). We observed three significant QTLs in hypoinsulinemic hyperglycemic male F(2)-Hetero mice, designated Dbm1, Dbm3, and Dbm4 on Chromosomes 6, 14, and 15, respectively. They showed linkage to plasma glucose concentrations, with significant maximum logarithm of odds (LOD) scores of 4.12, 4.17, and 6.17, respectively, all exceeding threshold values by permutation tests. In normoinsulinemic normoglycemic male F(2)-Wild mice, Dbm1 on Chromosome 6 showed linkage to both plasma insulin concentrations and BW, and Dbm2 on Chromosome 11 showed linkage to plasma glucose concentrations only, with LOD scores of 4.52 and 6.32, and 5.78, respectively. Based on these results, we concluded that Dbm1, Dbm2, Dbm3, and Dbm4 represent four major modifier QTLs specifically affecting T2D-related traits and that these diabetic modifier QTLs are conditional on the heterozygous Ins2 gene mutation and sex to exert their modifier functions. Identification of the genes responsible for these QTLs would provide new drug development targets for human T2D.

Preventive effects of glycaemic control on ocular complications of Spontaneously Diabetic Torii rat

AIM

Spontaneously Diabetic Torii (SDT) rat is a new model of non-obese type 2 diabetes. SDT rats show severe ocular complications such as cataracts, tractional retinal detachment with fibrous proliferation and massive haemorrhaging in the anterior chamber. In the present study, blood glucose levels of SDT rats were controlled in order to examine whether these ocular complications are caused by hyperglycaemia.

METHODS

SDT rats were treated with an insulin implant to control blood glucose. To evaluate retinal function, we used electroretinograms (ERG) and measured vascular endothelial growth factor (VEGF) concentrations within the aqueous humour. Finally, we studied retinal flat-mounts and trypsin digestion to evaluate vascular abnormalities in SDT rats.

RESULTS

Forty-four-week-old SDT rats displayed an increase in VEGF concentrations within the aqueous humour and significant prolongation of the peak latencies in ERG (Sigma(OP(1)-OP(4)); Sprague-Dawley (SD): 146.2 +/- 1.06 ms; SDT: 166.3 +/- 2.38 ms; SDT + insulin: 149.2 +/- 1.83 ms). Retinal flat-mounts of SDT rats showed venous dilation and meandering vascular networks. Furthermore, acellular capillaries were observed in the retinal trypsin digestion. Insulin treatment prevented these ocular abnormalities in SDT rats.

CONCLUSIONS

These findings indicate that ocular complications of SDT rats are caused by hyperglycaemia. The features of SDT rats indicate their usefulness for the future study of diabetic retinopathy.

Genetic determinants of metabolic syndrome components in the stroke-prone spontaneously hypertensive rat

OBJECTIVE

The metabolic syndrome is a complex multifactorial disease, which results from interactions between genes on multiple chromosomes and environmental factors. Animal models may facilitate genetic analysis of complex phenotypes by allowing complete control of environmental conditions and the ability to produce designer strains.

METHODS

Stroke-prone spontaneously hypertensive (SHRSP) and Wistar-Kyoto (WKY) rat strains were used to construct congenic (SP.WKYGla2a), consomic (SP.WKYGlaYw, WKY.SPGlaYs) and double-introgressed (SP.WKYGla2aYw) strains, which were characterized for metabolic syndrome phenotypes (systolic blood pressure, glucose tolerance and lipid profile) after feeding a 60% fructose diet for 14 days.

RESULTS

The Y consomic strain (SP.WKYGlaYw) demonstrated that the WKY Y chromosome significantly lowered triglyceride levels (3.77 +/- 0.60 versus 9.09 +/- 1.47 mmol/l; P < 0.001) and improved glucose tolerance [area under the curve (AUC): 26.93 +/- 0.81 versus 31.47 +/- 0.89; P < 0.05] compared with SHRSP. The chromosome 2 congenic strain (SP.WKYGla2a) exhibited significantly improved glucose tolerance (AUC: 28.19 +/- 1.17 versus 31.47 +/- 0.89; P < 0.05) and lower systolic blood pressure (161.2 +/- 6.2 versus 179.7 +/- 3.9 mmHg; P < 0.05) compared with SHRSP. 2 x 2 factorial ANOVA identified a significant interaction for glucose metabolism (P = 0.004) in the double-introgressed strain (SP.WKYGla2aYw) between chromosome 2 and Y.

CONCLUSIONS

These results identify novel interacting regions on chromosome 2 and the Y chromosome influencing a cluster of metabolic and cardiovascular phenotypes. Translation to clinical studies will facilitate genetic dissection of human metabolic syndrome.

Major quantitative trait locus on chromosome 2 for glucose tolerance in diabetic SMXA-5 mouse established from non-diabetic SM/J and A/J strains

AIMS/HYPOTHESIS

The SMXA-5 mouse is one of the SMXA recombinant inbred substrains established from the non-diabetic SM/J and A/J strains, and is a model for polygenic type 2 diabetes, characterised by moderately impaired glucose tolerance and hyperinsulinaemia. These diabetic traits are worsened by feeding a high-fat diet. The aim of this study was to dissect the diabetogenic loci in the A/J regions of the SMXA-5 genome that contribute to diabetes-related traits.

MATERIALS AND METHODS

We analysed the quantitative trait loci (QTL) for diabetes-related traits and obesity in (SM/JxSMXA-5)F(2) intercross mice fed a high-fat diet. To verify the function of the responsible locus that was mapped in the present study, we constructed a congenic strain and characterised its diabetes-related traits.

RESULTS

A major QTL for glucose tolerance, free-fed blood glucose concentration and BMI was mapped on chromosome 2. This locus existed near D2Mit15, with the highest logarithm of the odds score (12.6) for glucose concentration at 120 min in a glucose tolerance test, and was designated T2dm2sa. The diabetogenic allele of T2dm2sa originated in the A/J strain. SM.A-T2dm2sa, a congenic strain that introgressed the T2dm2sa region of A/J genome into SM/J, exhibited overt impaired glucose tolerance and hyperinsulinaemia.

CONCLUSIONS/INTERPRETATION

The development of impaired glucose tolerance in SM.A-T2dm2sa mice confirmed the results of QTL analysis for diabetes-related traits in F(2) intercross mice. The present results suggest that there are latent diabetogenic loci in the genomes of non-diabetic A/J and SM/J mice, and that the coexistence of these loci, including T2dm2sa, causes impaired glucose tolerance in SMXA-5 and SM.A-T2dm2sa mice.

High levels of pigment epithelium-derived factor in the retina of a rat model of type 2 diabetes

Spontaneously diabetic Torii (SDT) rats are a new animal model of diabetes. To investigate the mechanisms controlling diabetic retinopathy, we examined the retinal changes in SDT rats and determined the molecular balance between pigment epithelium-derived factor (PEDF), an angiogenic inhibitor, and vascular endothelial growth factor (VEGF), a major angiogenic stimulator. The retinopathy in SDT rats was characterized by a low incidence of neovascular formation and absence of non-perfused areas, and high levels of both PEDF and VEGF. Proliferative neovascular membranes, that are similar to that in human eyes with proliferative diabetic retinopathy, were found in the eyes of some of the SDT rats at >50-weeks-of-age, Immunoreactivity for VEGF was detected in the retina of SDT rats and the level of VEGF increased with the duration of diabetes. More importantly, immunoreactivity for PEDF was also increased in the retina of diabetic SDT rats. Western blot analysis showed that the level of VEGF in the retina was increased by 2.4 fold at 20-week-old, and by 6.8 fold at >40-week-old compared to that of 10-weeks old SDT rats. The levels of PEDF in the retina at 20-week- and at >40-week-old were significantly higher than that of 10-weeks old SDT rats (20-week-old; 13.5-fold increase, > 40-week-old; 10.3-fold increase). Earlier studies showed that the level of PEDF was decreased and VEGF was increased in proliferative diabetic retinopathy in human eyes. The high levels of PEDF in the retina of SDT rats may contribute to the low incidence of neovascular formation and absence of non-perfused areas that do not match the typical diabetic retinopathy in humans.

Development of islet-like cell clusters after pancreas transplantation in the spontaneously diabetic Torri rat

Pancreas transplantation (PTx) has evolved as a clinical therapy to achieve sustained euglycemia. However, it remains unclear if naive diseased islets of the pancreas benefit from the avoidance of glucose toxicity by PTx. In the present study, using an animal model of type 2 diabetes, the Spontaneously Diabetic Torii (SDT; RT1a) rat, we syngeneically transplanted nondiabetic 10-week-old pancreaticduodenal grafts into diabetic 25-week-old recipients. In the control SDT rats that received no treatment, hyperglycemia developed with a mean onset time of 25 +/- 3.9 weeks of age. Few normal islet cells were found from 25 weeks and none at 40 weeks. However, in the PTx rats, the onset age (graft age) of diabetes was significantly prolonged (47 +/- 18.2 weeks). Moreover, we found that the beta-cell mass was significantly increased in the naive pancreases of 40-week-old PTx recipients (PTx40-naive). Interestingly, islet-like cell clusters of varying size were found close to ductal structures of PTx40-naive pancreases, suggesting that these cells are derived from ductal cells. Furthermore, pancreatic and duodenal homeobox factor-1 (PDX-1) was more clearly expressed in the nuclei of PTx40-naive pancreatic islet-like cell clusters. Our results demonstrate the development of duct-derived beta cells in the pancreas of type 2 diabetic recipients after PTx.

A novel model of obesity-related diabetes: introgression of the Lepr(fa) allele of the Zucker fatty rat into nonobese Spontaneously Diabetic Torii (SDT) rats

An fa allele of the leptin receptor gene (Lepr(fa)) of the Zucker fatty rat was introduced into the genome of the Spontaneously Diabetic Torii (SDT) rat, an inbred model of nonobese type 2 diabetes mellitus, through the 'Speed congenic method'. The newly established congenic strain of a SDT rat for Lepr(fa) was maintained by intercrossing between fa-heterozygous littermates, and the phenotypes related to obesity and diabetes were investigated till 32 wks of age. SDT fa/fa rats of both sexes exhibited obesity, adiposity and insulin resistance associated with hyperphagia from the loss of leptin action. Interestingly, they developed diabetes from 5 wks of age in males and 8 wks in females with the incidences reaching 100% at 16 wks in males and 73% at 32 wks in females. In contrast, heterozygous (+/fa) and wild-type (+/+) rats developed spontaneous nonobese diabetes in males from approximately 20 wks, but not in females, as with the original SDT rats. These results indicate that the fa gene accelerates the onset of diabetes in SDT rats by making adiposity and/or insulin resistance as potent risk factors for development of their diabetes. The SDT.Lepr(fa) congenic rat strain is expected to be a novel model of obesity-related diabetes and could be a useful tool for studies of the genetic backgrounds of diabetes in response to fa-induced obesity.