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

Immune Disorders and Sex Differences in Spontaneously Diabetic Torii Rats, Type 2 Diabetic Model

Type 2 diabetes (T2D) is believed to be a non-autoimmune metabolic disorder. However, there are increasing reports that some T2D patients have immune abnormalities. In addition, it is known that there are sex differences in the onset of diabetes and immune responses in humans. Spontaneously Diabetic Torii (SDT) rats, a non-obese T2D model, also have sex differences in the onset of diabetes, but the involvement of immune abnormalities in diabetes is unknown. In this study, we investigated immune abnormalities in SDT rats. Immune cell subset analysis was performed in male and female SDT rats and control Sprague-Dawley (SD) rats at 5, 11, and 17 weeks of age. Male and female SDT rats had swelling of the spleen and lymph nodes and a higher number of T cells and B cells in the blood, spleen, and lymph nodes than SD rats. Only male SDT rats developed diabetes at 17 weeks of age, and the number of classical and non-classical monocytes in the blood and spleen of male SDT rats was higher than that in male SD rats and female SDT rats that did not develop diabetes. Most of these findings were observed before the onset of diabetes (~11 weeks of age), suggesting that classical and non-classical monocytes may contribute to the development of diabetes in male SDT rats. In conclusion, SDT rats may be a useful T2D model involved in immune abnormalities, and further research will help elucidate the pathophysiology of T2D with immune abnormalities and develop new therapeutic agents.

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.

The sphingosine-1-phosphate receptor modulator, FTY720, prevents the incidence of diabetes in Spontaneously Diabetic Torii rats

The sphingosine-1-phosphate (S1P) receptor modulator regulates lymphocyte trafficking, resulting in its depletion from circulation, which ultimately causes immunosuppression. In this study, we investigated the preventive effect of fingolimod (FTY720) in the non-obese type 2 diabetic model, Spontaneously Diabetic Torii (SDT) rats. The S1P receptor modulator, FTY720 (0.3 mg/kg p.o.), was administered for 12 weeks to SDT rats from 5 to 17 weeks of age. Based on our findings, FTY720 could suppress the incidence of diabetes in SDT rats. Further, glucose intolerance was improved in FTY720-treated SDT rats at 14 weeks of age. Based on the haematological and histological analyses performed at 17 to 18 weeks of age, a decrease in lymphocytes and monocytes in the peripheral blood and a decrease in lymphocyte and atrophy in spleen occurred in the FTY720-treated SDT rats. Furthermore, the pancreatic changes, such as inflammation, atrophy, and fibrosis in islets observed in SDT rats were improved by FTY720 treatment. These findings suggest that the immunomodulatory effects of FTY720 reduced the pancreatic lesion in SDT rats, thereby demonstrating its preventive effect against diabetes. The development of diabetes in SDT rats is related to disorders of the immune system. However, the S1P receptor modulator may be useful for treating type 2 diabetes.

Improvement in Diabetic Retinopathy through Protection against Retinal Apoptosis in Spontaneously Diabetic Torii Rats Mediated by Ethanol Extract of Osteomeles schwerinae C.K. Schneid

Retinal apoptosis plays a critical role in the progression of diabetic retinopathy (DR), a common diabetic complication. Currently, the tight control of blood glucose levels is the standard approach to prevent or delay the progression of DR. However, prevalence of DR among diabetic patients remains high. Focusing on natural nutrients or herbal medicines that can prevent or delay the onset of diabetic complications, we administered an ethanol extract of the aerial portion of Osteomeles schwerinae (OSSCE), a Chinese herbal medicine, over a period of 17 weeks to spontaneously diabetic Torii (SDT) rats. OSSCE was found to ameliorate retinal apoptosis through the regulation of advanced glycation end product (AGE) accumulation, oxidative stress, and mitochondrial function via the inhibition of NF-κB activity, in turn, through the downregulation of PKCδ, P47phox, and ERK1/2. We further demonstrated in 25 mM glucose-treated human retinal microvascular endothelial cells (HRMECs) that hyperoside (3-O-galactoside-quercetin), quercitrin (3-O-rhamnoside-quercetin), and 2″-O-acetylvitexin (8-C-(2″-O-acetyl-glucoside)-apigenin) were the active components of OSSCE that mediated its pharmacological action. Our results provide evidence that OSSCE is a powerful agent that may directly mediate a delay in the development or disease improvement in patients of DR.

Pathological Features of Diabetic Retinopathy in Spontaneously Diabetic Torii Fatty Rats

OBJECTIVE

The Spontaneously Diabetic Torii (SDT) fatty rat, established by introducing the fa allele (obesity gene) of the Zucker fatty rat into the SDT rat genome, is a new model of obese type 2 diabetes. We studied the pathologic features of diabetic retinopathy (DR) in this animal.

METHODS

The eyes of SDT fatty, SDT (controls), and Sprague Dawley (SD) rats (normal controls) were enucleated at 8, 16, 24, 32, and 40 weeks of age (n = 5-6 for each rat type at each age). The retinal thicknesses, numbers of retinal folds, and choroidal thicknesses were evaluated. Immunostaining for glial fibrillary acidic protein (GFAP) and vascular endothelial growth factor (VEGF) was performed. Quantitative analyses of the immunopositive regions were performed using a cell-counting algorithm.

RESULTS

The retinas tended to be thicker in the SDT fatty rats and SDT rats than in the SD rats; the choroids tended to be thicker in the SDT fatty rats than in the SD rats. The retinal folds in the SDT fatty rats developed earlier and were more severe than in the SDT rats. Quantitative analyses showed that the GFAP- and VEGF-positive regions in the retinas of the SDT fatty rats were significantly larger than those of the SDT rats.

CONCLUSIONS

SDT fatty rats developed more severe DR earlier than the SDT rats. The SDT fatty rats might be useful as a type 2 diabetes animal model to study DR.

Aster koraiensis extract prevents diabetes-induced retinal vascular dysfunction in spontaneously diabetic Torii rats

BACKGROUND

Aster koraiensis extract (AKE) is a standard dietary herbal supplement. The aim of this study is to investigate the inhibitory effects of AKE on diabetes-induced retinal vascular dysfunction in Spontaneously Diabetic Torii (SDT) rats.

METHODS

AKE (50 and 100 mg/kg body weight/day) was administered for 16 weeks. The effects of orally administered AKE on blood glucose levels, retinal vascular leakage, apoptosis, and accumulation of advanced glycation end products (AGEs) in the retina were evaluated.

RESULTS

SDT rats exhibited hyperglycemia and retinal vascular leakage, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was clearly detected apoptosis in the retinal microvasculature. Immunofluorescence staining revealed the accumulation of AGEs in the retinal vasculature of the SDT rats. However, oral administration of AKE for 16 weeks blocked diabetes-induced blood-retinal barrier (BRB) breakdown and the loss of occludin, which is an important tight junction protein. Apoptosis of retinal vascular cells and AGE accumulation were significantly inhibited after AKE treatment.

CONCLUSION

These results indicate that, as a dietary herbal supplement, AKE may have beneficial effects on patients with diabetic retinopathy.

Differential expression of breast cancer-resistance protein, lung resistance protein, and multidrug resistance protein 1 in retinas of streptozotocin-induced diabetic mice

AIM

To investigate the altering expression profiles of efflux transporters such as breast cancer-resistance protein (BCRP), lung resistance protein (LRP), and multidrug resistance protein 1 (MDR1) at the inner blood-retinal barrier (BRB) during the development of early diabetic retinopathy (DR) and/or aging in mice.

METHODS

Relative mRNA and protein expression profiles of these three efflux transporters in the retina during the development of early DR and/or aging in mice were examined. The differing expression profiles of Zonula occludens 1 (ZO-1) and vascular endothelial growth factor-A (VEGFA) in the retina as well as the perfusion characterization of fluorescein isothiocyanate (FITC)-dextran and Evans blue were examined to evaluate the integrity of the inner BRB.

RESULTS

There were significant alterations in these three efflux transporters' expression profiles in the mRNA and protein levels of the retina during the development of diabetes mellitus and/or aging. The development of early DR was confirmed by the expression profiles of ZO-1 and VEGFA in the retina as well as the compromised integrity of the inner BRB.

CONCLUSION

The expression profiles of some efflux transporters such as BCRP, LRP, and MDR1 in mice retina during diabetic and/or aging conditions are tested, and the attenuated expression of BCRP, LRP, and MDR1 along with the breakdown of the inner BRB is found, which may be linked to the pathogenesis of early DR.

Methylglyoxal-derived hydroimidazolone residue of plasma protein can behave as a predictor of prediabetes in Spontaneously Diabetic Torii rats

Prediabetes, typically defined as impaired glucose tolerance and/or impaired fasting blood glucose, is a high-risk state of developing diabetes. The association of diabetes-related metabolites with prediabetes has not been investigated intensively. This study aimed to get insights into the metabolic behaviors of some typical diabetes-related metabolites in plasma of male Spontaneously Diabetic Torii (SDT) rats during pathogenic progress of diabetes and to assess in vivo if the variation in these metabolites related to the progression of prediabetic stage. To address this question, SDT rats and Sprague Dawley (SD) rats as control were maintained from the age of 7 to 25 weeks. Five typical advanced glycation end products (AGEs) residue of plasma protein and their free adducts were determined by liquid chromatography with tandem mass detection over the duration of the investigation. The SDT rats exhibited impaired glucose tolerance since the age of 12 weeks and developed diabetes with significantly elevated fasting glucose levels after 22 weeks. At the prediabetic stage (12–21 weeks), no significant differences were observed on AGE-free adducts levels of SDT rats compared with SD rats. However, methylglyoxal-derived hydroimidazolone (MG-H1) residue contents of plasma protein were significantly elevated in SDT rats at the age of 16 weeks, whereas other AGE residues of plasma protein did not show marked difference. The present study has revealed significant increase in MG-H1 residue content of plasma protein at the prediabetic stage of a spontaneously diabetic rat model, irrespective of unaltered fasting blood glucose and constant plasma levels of other AGEs.

Contribution of hyperglycemia on diabetic complications in obese type 2 diabetic SDT fatty rats: effects of SGLT inhibitor phlorizin

The spontaneously diabetic torii (SDT) fatty rat is a new model of type 2 diabetes showing overt obesity, hyperglycemia and hyperlipidemia. With early onset of diabetes mellitus, diabetic microvascular complications, including nephropathy, peripheral neuropathy and retinopathy, are observed at young ages. In the present study, blood glucose levels of female SDT fatty rats were controlled with phlorizin, a non-selective SGLT inhibitor, to examine whether and how these complications are caused by hyperglycemia. Phlorizin treatment adequately controlled plasma glucose levels during the experiment. At 29 weeks of age, urinary albumin excretion considerably increased in SDT fatty rats. Glomerulosclerosis and tubular pathological findings also indicate diabetic nephropathy. These renal parameters tended to decrease with phlorizin; however, effects were partial. Sciatic nerve conduction velocities were significantly delayed in SDT fatty rats compared with Sprague-Dawley (SD) rats. Intraepidermal nerve fiber density, an indicator of subclinical small nerve fiber neuropathy, significantly decreased in SDT fatty rats. Retinal dysfunction (prolongation of peak latency for oscillatory potential in electroretinograms) and histopathological eye abnormalities, including retinal folding and mature cataracts were also observed. Both nerve and eye disorders were prevented with phlorizin. These findings indicate that severe hyperglycemia mainly causes diabetic complications in SDT fatty rats. However, other factors, such as hyperlipidemia and hypertension, may affect diabetic nephropathy. These characteristics of diabetic complications will become helpful in evaluating new drugs for diabetic complications using SDT fatty rats.

Retinopathy in a novel model of metabolic syndrome and type 2 diabetes: new insight on the inflammatory paradigm

The pathogenesis of diabetic retinopathy (DR) in metabolic syndrome (MetS) and type 2 diabetes (T2D) is not well studied, partly because an appropriate model has not been developed. Recently, we introduced a novel model of spontaneous T2D and MetS that replicates the relevant features of the human disease. In the current study, we investigated the retinal vascular changes in these animals. Experimental DR in streptozotocin (STZ)-injected rodents is described as an inflammatory disease, in which intercellular adhesion molecule 1 (ICAM-1) plays a key role. In comparison, advanced diabetes (HbA1c>10%) in the Nile grass rat (NGR) was associated with lower ICAM-1 protein expression when compared with that in normal or moderately diabetic animals. Vascular cell adhesion molecule 1 (VCAM-1) expression, however, was unaffected by the disease state. As opposed to the STZ-induced model of DR, in diabetic NGRs, most leukocytes accumulated in the retinal arteries. Consistent with the ICAM-1 reduction, leukocyte accumulation was significantly reduced in advanced disease. Similarly, leukocyte adhesions were significantly lower, with elevated plasma triglycerides (>200 mg/dl), and cholesterol (>240 mg/dl). However, these adhesions were significantly higher in animals with higher plasma insulin (>5 μIU/ml) and leptin (>20 ng/ml), suggesting a role for these hormones in diabetic retinal leukostasis. Diabetic NGRs showed substantial retinal endothelial injury, primarily in the microvessels, including vascular tortuosity, obliterated acellular capillaries, and pericyte ghosts. The NGR provides a convenient and realistic model for investigation of retinal changes in MetS/T2D with convincing advantages over the commonly used STZ-induced T1D.

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.

Renal podocyte injury in a rat model of type 2 diabetes is prevented by metformin

Hyperglycemia promotes oxidative stress and hence generation of reactive oxygen species (ROS), which is known to play a crucial role in the pathogenesis of diabetic nephropathy. Metformin, an oral hypoglycemic drug, possesses antioxidant effects. The aim of this paper is to investigate the protective effects of metformin on the injury of renal podocytes in spontaneously diabetic Torii (SDT) rats, a new model for nonobese type 2 diabetes. Metformin (350 mg/kg/day) was given to SDT rats for 17 weeks. Blood glucose, glycated haemoglobin (HbA1c), and albuminuria were examined. Kidney histopathology, renal 8-hydroxydeoxyguanosine (8-OHdG) levels and apoptosis were examined. In 43-week-old SDT rats, severe hyperglycemia was developed, and albuminuria was markedly increased. Diabetes induced significant alterations in renal glomerular structure. In addition, urinary and renal 8-OHdG levels were highly increased, and podocyte loss was shown through application of the TUNEL and synaptopodin staining. However, treatment of SDT rats with metformin restored all these renal changes. Our data suggested that diabetes-induced podocyte loss in diabetic nephropathy could be suppressed by the antidiabetes drug, metformin, through the repression of oxidative injury.

Diabetic peripheral neuropathy in Spontaneously Diabetic Torii-Lepr(fa) (SDT fatty) rats

Spontaneously Diabetic Torii (SDT) rat is a hereditary model of diabetes. Although the SDT rat shows severe diabetic complications, the onset of hyperglycemia is late. SDT fatty rat, established by introducing the fa allele of the Zucker fatty rat to SDT rat, develops diabetes much faster than SDT rat. In the present study, diabetic peripheral neuropathy (DPN) was evaluated to show the further usefulness of this animal model. Motor nerve conduction velocity (MNCV) was delayed, and the number of sural nerve fibers was decreased in SDT fatty rat. Treatment of pioglitazone lowered blood glucose level and prevented delay of MNCV in SDT fatty rats. SDT fatty rat is a useful animal model for studies of DPN in 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.

Blood pressure characteristics of female spontaneously diabetic Torii-Lepr(fa) rats

Blood pressure in female SDT-fa/fa rats was periodically investigated at ages 8, 16, and 24 weeks. Furthermore, an insulin therapy was performed for 5 weeks in the female rats at age 11 weeks, and the change of blood pressure was examined. In addition to obesity, hyperglycemia, hyperinsulinemia, and hyperlipidemia, hyperleptinemia and increased urinary angiotensinogen level were observed during the experimental period. Blood pressure was elevated at ages 8 and 16 weeks, but that at 24 weeks was comparable to that in Sprague-Dawley (SD) rats. Heart rate was decreased from age 8 to 24 weeks. Insulin therapy induced good glycemic control and improvement of hyperlipidemia, but the blood pressure was not reduced. Blood pressure in female SDT-fa/fa rats was elevated temporarily. The blood pressure was not decreased by insulin treatment. SDT-fa/fa rat is a useful model to investigate the relation between diabetes mellitus and hypertension.

Pathophysiological analysis of female Spontaneously Diabetic Torii fatty rats

Obesity, hyperglycemia, hyperlipidemia, and diabetes-associated complications appear at younger ages (6-8 weeks) in the male Spontaneously Diabetic Torii-Lepr(fa) (SDT-fa/fa) rat than in the male original SDT (SDT-+/+) rat. However, the incidence and progression of diabetes mellitus and diabetic complications in the female SDT-fa/fa rat have not been reported in detail. In the present study, the pathophysiological features of the female SDT-fa/fa rat were examined, and compared with those of the female SDT-+/+ rat. Female SDT-fa/fa rats showed hyperphagia, obesity, hyperglycemia, and hyperlipidemia from 5 or 6 weeks of age, and hyperinsulinemia was observed from 5 to 12 weeks. Pathological changes pancreatic islets were observed from 8 weeks. Renal function parameters, such as urine volume and urinary protein, increased from 16 weeks, and pathological findings in the renal tubule, and cataracts were also observed from 16 weeks. Increases of visceral and subcutaneous fats were obvious during the observation period. In pair-feeding with SDT-+/+ rats, SDT-fa/fa rats showed improved hyperglycemia and hypertriglycemia, but hypercholesterolemia was not entirely improved during the study period. Female SDT-fa/fa rats showed diabetes mellitus and diabetes-associated complications at young ages, and fat accumulation was remarkable. Suppression of hyperphagia in SDT-fa/fa rats was effective at improving hyperglycemia and hypertriglycemia. In conclusion, the female SDT-fa/fa rat has the potential to become an important animal model of type 2 diabetes mellitus with obesity, especially for women, for which few models currently exist.

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.

Protein kinase C beta inhibitor prevents diabetic peripheral neuropathy, but not histopathological abnormalities of retina in Spontaneously Diabetic Torii rat

Spontaneously Diabetic Torii (SDT) rat shows severe ocular complications such as tractional retinal detachment. In the present study, effect of protein kinase C beta (PKCbeta) inhibitor JTT-010 was evaluated to clarify the involvement of PKCbeta in complications of SDT rat. SDT rats were administered JTT-010 (10 or 50 mg/kg/day) for 48 weeks. SDT rats showed delayed oscillatory potentials in electroretinogram. Delayed motor nerve conduction velocity, decreased coefficients of variation of R-R intervals in electrocardiogram and thermal hypoalgesia were also observed. These functional disorders were prevented by administration of JTT-010. Abnormal retinal vascular was formed and the optic disc was protruded in SDT rat; however, JTT-010 did not prevent these hyperglycaemia-induced retinal abnormalities. These findings indicate that PKCbeta is intimately involved in diabetic complications; however, it seems that other factor(s) are primary contributors to histopathological abnormalities in retina. Therefore, PKCbeta inhibitors require concurrent administration of antihyperglycaemic drugs to achieve maximum effect on diabetic complications.

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.

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.

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.

Effect of insulin therapy on renal changes in spontaneously diabetic Torii rats

The spontaneously diabetic Torii (SDT) rat has recently been established as an animal model of non-obese type 2 diabetes, in which ocular complications severe occur. However, the function and morphological features of the diabetic renal lesions in SDT rats have not been reported in detail. Therefore, we evaluated changes over time in renal lesions in SDT rats. In addition, SDT rats were treated with insulin to observe whether these renal complications are caused by hyperglycemia. Renal functional parameters and renal lesions were monitored in SDT rats from 8 to 68 weeks of age. Sprague-Dawley (SD) rats of similar age were used as control animals. In the insulin-treated group of SDT rats, insulin pellets were implanted at 24 weeks of age to compare the development of renal lesions. The SDT rats began to develop hyperglycemia at 20 weeks of age. In the histopathological examination of the kidney, glycogen deposition of the renal tubular epithelium and renal tubular dilation were observed from 24 weeks of age in the untreated SDT rats, and the changes in the renal tubules markedly progressed with aging. Moreover, thickening of the glomerular basement membrane was observed from 32 weeks of age. At 50 weeks of age, the glomeruli showed increase of mesangial matrix, with predominantly diffuse lesions showing by 68 weeks of age. The mesangial proliferation gradually progressed. In the SD rats, no renal lesions were present at 50 and 68 weeks of age. SDT rats with insulin treatment remained normoglycemic throughout observation and their renal functional parameters were normal. Glycemic control in SDT rats prevented the development of renal lesions. The features of SDT rats indicate their usefulness as an animal model for investigating diabetic nephropathy.

Increased fat absorption and impaired fat clearance cause postprandial hypertriglyceridemia in Spontaneously Diabetic Torii rat

In diabetes, postprandial hyperlipidemia is recognized as a risk factor for premature atherosclerosis and following cardiovascular disease. In the present study, features of fat absorption and clearance were examined to clarify the lipid metabolism of Spontaneously Diabetic Torii (SDT) rats. Olive oil was orally administered to evaluate increase of blood triglyceride (TG) level. Mesenteric lymph chylomicron TG was also measured. mRNAs of enzymes and transfer protein related to TG metabolism and histopathological changes were evaluated. In an oil loading test, elevation of TG in plasma and lymph chylomicron was increased in SDT rats. Interestingly, SDT rats showed elevation of plasma TG after oil loading and relatively low epididymal fat lipoprotein lipase (LPL) mRNA expression even at the pre-diabetic state without increase of TG absorption from intestine. In the diabetic state, intestines of SDT rats were hypertrophic and expressed mRNAs of enzymes and transfer protein related to TG absorption highly. From these results, it seems that intestinal abnormalities related to hypoinsulinemia/hyperglycemia cause postprandial hypertriglyceridemia in SDT rats. In addition, our findings suggest that SDT rats have impaired lipid catabolism antecedent to hypoinsulinemia/hyperglycemia. These characteristics of SDT rats can be useful in studies of diabetic hypertriglyceridemia and TG metabolism.

Angiotensin II receptor blocker inhibits abnormal accumulation of advanced glycation end products and retinal damage in a rat model of type 2 diabetes

The effects of an angiotensin II receptor blocker (ARB) on the accumulation of one of advanced glycation end products (AGEs), pentosidine, expression of vascular endothelial growth factor (VEGF) and retinal function were investigated in Spontaneously Diabetic Torii (SDT) rats. Candesartan, an ARB, was administered to SDT rats from 10 to 44 weeks of age and the results compared with untreated SDT rats and SD rats. Electroretinograms (ERGs) were recorded to evaluate retinal function. At 44 weeks of age, pentosidine was quantified in the vitreous, lens and plasma using high-performance liquid chromatography (HPLC). Real-time reverse transcription-PCR (RT-PCR) analysis was also performed in order to measure VEGF mRNA expression in the retina. Histological changes were examined and immunohistochemistry for pentosidine performed on the retina and retinal microvasculature. In untreated SDT rats, the amplitudes of a- and b-waves, oscillatory potentials were reduced significantly at 44 weeks of age compared with the 10-week levels, whereas they remained unchanged in SDT rats treated with candesartan. The concentration of pentosidine in the vitreous and lens did not change in treated SDT rats but increased in untreated SDT rats. Retinal VEGF mRNA expression was inhibited in treated SDT rats. Histologically, proliferative tissue was detected around the optic disc, with pentosidine being detected only in untreated SDT rats. Our findings indicate the ARB may inhibit the development of diabetic retinopathy by reducing the accumulation of pentosidine, one of AGEs and expression of VEGF in the retina.