Diabetes-associated complications in Spontaneously Diabetic Torii fatty rats

Correlation of diabetic renal hypoperfusion with microvascular responses of the skeletal muscle: a rat model study using diffuse correlation spectroscopy

Using diffuse correlation spectroscopy, we assessed the renal blood flow and thigh muscle microvascular responses in a rat model of type 2 diabetes. The blood flow index at the renal surface decreased significantly with arterial clamping, cardiac extirpation, and the progression of diabetic endothelial dysfunction. Renal blood flow measured in diabetic and nondiabetic rats also showed a significant correlation with the reactive hyperemic response of the thigh muscle. These results suggest shared microcirculatory dysfunction in the kidney and skeletal muscle and support endothelial responses in the skeletal muscle as a potential noninvasive biomarker of renal hypoperfusion.

Glycation promotes pulp calcification in Type 2 diabetes rat model

OBJECTIVES

Intrapulpal calcifications can occur in the dental pulp of patients with diabetes. We focused on the association between ectopic calcifications in the dental pulp and advanced glycation end products (AGEs) in Spontaneously Diabetic Torii (SDT)-fatty rats, an obese type 2 diabetic rat model, to determine the mechanism of calcification with pulp stone in the dental pulp.

MATERIALS AND METHODS

Pathologic calcification in the dental pulp of SDT-fatty rats was observed using electron microscopy and immunohistochemical analysis. Moreover, mechanical analysis of periapical region of molar tooth against occlusal force was performed.

RESULTS

In SDT-fatty rats, pathogenic pulpal calcifications occurred during blood glucose elevation after 6 weeks, and granular calcification was observed in the dental pulp after 11 weeks. Pentosidine, a major AGE, and the receptor for AGEs were strongly expressed in the dental pulp of SDT-fatty rats. S100A8, TNF-α, and IL-6 also showed positive response in the dental pulp of the SDT-fatty rat, which indicated pulpal inflammation. Blood flow disorder and hypoxic dental pulp cells were also observed. In silico simulation, strain from occlusal force concentrates on the root apex.

CONCLUSIONS

Glycation makes blood vessels fragile, and occlusal forces damage the vessels mechanically. These are factors for intrapulpal calcification of diabetes.

Protective Effect of Pemafibrate Treatment against Diabetic Retinopathy in Spontaneously Diabetic Torii Fatty Rats

Diabetic retinopathy (DR) can cause visual impairment and blindness, and the increasing global prevalence of diabetes underscores the need for effective therapies to prevent and treat DR. Therefore, this study aimed to evaluate the protective effect of pemafibrate treatment against DR, using a Spontaneously Diabetic Torii (SDT) fatty rat model of obese type 2 diabetes. SDT fatty rats were fed either a diet supplemented with pemafibrate (0.3 mg/kg/day) for 16 weeks, starting at 8 weeks of age (Pf SDT fatty: study group), or normal chow (SDT fatty: controls). Normal chow was provided to Sprague-Dawley (SD) rats (SD: normal controls). Electroretinography (ERG) was performed at 8 and 24 weeks of age to evaluate the retinal neural function. After sacrifice, retinal thickness, number of retinal folds, and choroidal thickness were evaluated, and immunostaining was performed for aquaporin-4 (AQP4). No significant differences were noted in food consumption, body weight, or blood glucose level after pemafibrate administration. Triglyceride levels were reduced, and high-density lipoprotein cholesterol levels were increased. Extension of oscillatory potential (OP)1 and OP3 waves on ERG was suppressed in the Pf SDT fatty group. Retinal thickness at 1,500 microns from the optic disc improved in the Pf SDT fatty group. No significant improvements were noted in choroidal thickness or number of retinal folds. Quantitative analyses showed that AQP4-positive regions in the retinas were significantly larger in the Pf SDT fatty group than in the SDT fatty group. The findings suggest that pemafibrate treatment can exert protective effects against DR.

Animal Models of Type 2 Diabetes Complications: A Review

Diabetes mellitus is a multifactorial metabolic disease, of which type 2 diabetes (T2D) is one of the most common. The complications of diabetes are far more harmful than diabetes itself. Type 2 diabetes complications include diabetic nephropathy (DN), diabetic heart disease, diabetic foot ulcers (DFU), diabetic peripheral neuropathy (DPN), and diabetic retinopathy (DR) et al. Many animal models have been developed to study the pathogenesis of T2D and discover an effective strategy to treat its consequences. In this sense, it is crucial to choose the right animal model for the corresponding diabetic complication. This paper summarizes and classifies the animal modeling approaches to T2D complications and provides a comprehensive review of their advantages and disadvantages. It is hopeful that this paper will provide theoretical support for animal trials of diabetic complications.

Glucagon-like peptide-1 receptor agonist, liraglutide, attenuated retinal thickening in spontaneously diabetic Torii fatty rats

BACKGROUND

This study aims to investigate the effect of the glucagon-like peptide-1 (GLP-1) receptor agonist (GLP-1RA) liraglutide on retinal pathological findings as compared with insulin and hydralazine using an animal model of type 2 diabetes with obesity, hypertension, and hyperlipidemia.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats at 8 weeks of age were randomly assigned to three groups: the liraglutide group (SDT-lira, n = 6) received a subcutaneous injection of liraglutide from the age of 8 to 16 weeks, the SDT-ins-hyd group (n = 6) was provided both insulin against hyperglycemia and hydralazine against hypertension to match levels of both blood glucose and blood pressure to those of the liraglutide group, and the control group of SDT fatty rats (SDT-vehicle, n = 7) and a nondiabetic control group of Sprague-Dawley rats (SD, n = 7) were injected with vehicle only. Both eyeballs of all groups were collected at the age of 16 weeks.

RESULTS

Retinal thickness, which was found in the SDT-vehicle group, was significantly prevented to similar levels in both the SDT-lira and SDT-ins-hyd groups. Immunohistological analysis revealed that GLP-1 receptor was not expressed in the retina of all rats. The ocular protein expression of monocyte chemoattractant protein-1, which causes a proinflammatory situation, was significantly upregulated in all SDT fatty rats as compared to SD rats, but the expression levels were similar between all SDT fatty rats. With regard to neovascularization in the eyes, there were no significant differences in protein expressions of vascular endothelial growth factor, CD31, or endothelial nitric oxide synthase in all rats.

CONCLUSIONS

The present study indicates that liraglutide prevents retinal thickening, dependent on blood glucose and blood pressure levels in SDT fatty rats without ocular neovascularization. However, the effects did not improve the ocular proinflammatory state.

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.

Effects of excessive sodium chloride loading in the spontaneously diabetic torii (SDT) fatty rats, a preclinical model of type 2 diabetes mellitus

Type 2 diabetes mellitus represents an international health concern with its growing number of patients worldwide. At the same time, excessive salt consumption is also seen as a major cause of diseases such as hypertension and may expedite renal complications in diabetic patients. In this study, we investigated the effects of excessive sodium chloride supplementation on the kidney of the Spontaneously Diabetic Torii-Lepr^fa (SDT fatty) rat, an obese type 2 diabetes model. Male and female SDT fatty rats and normal Sprague-Dawley (SD) rats at 5 weeks of age were loaded with 0.3% sodium chloride (NaCl) in drinking water for 13 weeks. Blood serum and urinary parameters were observed throughout the experiment and kidney samples were examined in histopathological and genetical analyses. Significant changes on the body weight, blood pressure, urine volume, creatinine clearance, blood urea nitrogen (BUN), relative gene expressions of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1) and transforming growth factor-β (TGF-β) were observed in the salt-loaded male SDT fatty rats. Urinary L-type fatty acid-binding protein (L-FABP) and albumin levels were higher observed in the salt-loaded male SDT fatty rats throughout the period, but urinary albumin levels in the female SDT fatty rats remain unchanged. In the kidney, slight Armani-Ebstein changes, tubular degeneration, hyaline cast, and inflammatory cell infiltration were observed in female SDT fatty rats while the levels of some changes were higher in the salt-loaded group. The kidney of the salt-loaded male SDT fatty rats demonstrated a higher degree of lesions compared to the female group and the male unloaded group. Histopathological changes in salt-loaded SDT fatty rats show that excessive salt consumption may act as a diabetic pathology exacerbation factor, but the pathology may be influenced by gender difference. Urinary L-FABP levels may act as a useful biomarker to detect slight tubular damages in the kidney. Excessive salt loading was shown to exacerbate the renal injury in SDT fatty rats.

Lysophosphatidylcholine mediates fast decline in kidney function in diabetic kidney disease

Some patients with diabetic kidney disease (DKD) show a fast progression of kidney dysfunction and are known as a "fast decliner" (FD). Therefore, it is critical to understand pathomechanisms specific for fast decline. Here, we performed a comprehensive metabolomic analysis of patients with stage G3 DKD and identified increased urinary lysophosphatidylcholine (LPC) in fast decline. This was confirmed by quantification of urinary LPC using mass spectrometry and identified urinary LPC containing saturated fatty acids palmitic (16:0) and stearic (18:0) acids was increased in FDs. The upsurge in urinary LPC levels was correlated with a decline in estimated glomerular filtration rate after 2.5 years. To clarify a pathogenic role of LPC in FD, we studied an accelerated rat model of DKD and observed an increase in LPC (16:0) and (18:0) levels in the urine and kidney tubulointerstitium as the disease progressed. These findings suggested that local dysregulation of lipid metabolism resulted in excessive accumulation of this LPC species in the kidney. Our in vitro studies also confirmed LPC-mediated lipotoxicity in cultured proximal tubular cells. LPC induced accumulation of lipid droplets via activation of peroxisome proliferator-activated receptor-δ followed by upregulation of the lipid droplet membrane protein perilipin 2 and decreased autophagic flux, thereby inducing organelle stress and subsequent apoptosis. Thus, LPC (16:0) and (18:0) may mediate a fast progression of DKD and may serve as a target for novel therapeutic approaches.

Renoprotective effect of GLP-1 receptor agonist, liraglutide, in early-phase diabetic kidney disease in spontaneously diabetic Torii fatty rats

BACKGROUND

The aim of this study is to investigate the renoprotective effect of the GLP-1 receptor agonist, liraglutide, in early-phase diabetic kidney disease (DKD) using an animal model of type 2 diabetes with several metabolic disorders.

METHODS

Male 8-week-old spontaneously diabetic Torii (SDT) fatty rats (n = 19) were randomly assigned to three groups. The liraglutide group (n = 6) was injected subcutaneously with liraglutide. Another treatment group (n = 6) received subcutaneous insulin against hyperglycemia and hydralazine against hypertension for matching blood glucose levels and blood pressure with the liraglutide group. The control groups of SDT fatty (n = 7) and non-diabetic Sprague-Dawley rats (n = 7) were injected only with a vehicle.

RESULTS

The control group of SDT fatty rats exhibited hyperglycemia, obesity, hypertension, hyperlipidemia, glomerular sclerosis, and tubulointerstitial injury with high urinary albumin and L-FABP levels. Liraglutide treatment reduced body weight, food intake, blood glucose and blood pressure levels, as well as ameliorated renal pathologic findings with lower urinary albumin and L-FABP levels. Liraglutide increased expressions of phosphorylated (p)-eNOS and p-AMPK in glomeruli, downregulated renal expression of p-mTOR, and increased renal expressions of LC3B-II, suggesting activation of autophagy. However, these effects were not caused by the treatments with insulin and hydralazine, despite comparable levels of hyperglycemia and hypertension to those achieved with liraglutide treatment.

CONCLUSIONS

Liraglutide may exert a renoprotective effect via prevention of glomerular endothelial abnormality and preservation of autophagy in early-phase DKD, independent of blood glucose, and blood pressure levels.

Glomerular hyperfiltration with hyperglycemia in the spontaneously diabetic Torii (SDT) fatty rat, an obese type 2 diabetic model

Glomerular hyperfiltration is observed in an early stage of kidney diseases including diabetic nephropathy. A better understanding of pathophysiological changes in glomerular hyperfiltration is essential for development of new therapies to prevent kidney disease progression. In this study, we investigated glomerular changes including glomerular filtration rate (GFR) and glomerular size in the Spontaneously Diabetic Torii (SDT) fatty rat, an obese type 2 diabetic model, and we also evaluated pharmacological effects of the sodium glucose cotransporter 2 inhibitor dapagliflozin on the renal lesions. Dapagliflozin was administered to SDT fatty rats from 5 to 17 weeks of age. Blood and urinary biochemical parameters were periodically measured. GFR was determined by transdermal GFR monitor at 16 weeks of age and histopathological analysis was performed at 17 weeks of age. SDT fatty rat developed severe hyperglycemia and exhibited pathophysiological abnormalities in the kidney, such as an increased GFR, glomerular hypertrophy and tissue lesions. Dapagliflozin achieved good glycemic control during the experimental period, inhibited the increase in GFR, and improved histopathological abnormalities in tubules. These results suggest that the SDT fatty rat is a useful model for analyzing the pathogenesis of diabetic nephropathy during its early stage and dapagliflozin improves not only hyperglycemia but also glomerular hyperfiltration and tubule lesions in SDT fatty rat.

Relationship between Urinary Liver-Type Fatty Acid-Binding Protein (L-FABP) and Sarcopenia in Spontaneously Diabetic Torii Fatty Rats

BACKGROUND

Type 2 diabetes (T2D) is a known risk factor for diabetic kidney disease (DKD) and sarcopenia in older patients. Because there may be an interaction between DKD and sarcopenia, the aim of the present study is to investigate the relationship between urinary levels of liver-type fatty acid-binding protein (L-FABP) and sarcopenia using a novel rat model of T2D.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats (n = 5) at 16 weeks of age were used as an animal model of T2D. Age- and sex-matched Sprague-Dawley (SD) rats (n = 7) were used as controls. Urine samples were obtained from the rats, and muscle strength was evaluated with the use of the forelimb grip test at 16, 20, and 24 weeks of age. Serum, kidney, soleus, and extensor digitorum longus (EDL) muscle samples were collected at 24 weeks of age. Urinary L-FABP levels were measured using dedicated enzyme-linked immunosorbent assays.

RESULTS

Increased urinary L-FABP levels, focal glomerular sclerosis, moderate interstitial inflammation and fibrosis, and accumulation of renal oxidative proteins were significantly observed in the SDT fatty rats, compared to the SD rats. Muscle weight, muscle strength, cross-sectional areas of both type I and type IIb muscle fibers, and increasing rate of muscle strength were significantly decreased in the SDT fatty rats compared to the SD rats at 24 weeks. Urinary L-FABP levels at 20 and 24 weeks were significantly negatively correlated with muscle strength. Urinary L-FABP levels at 16 weeks were significantly negatively correlated with the increasing rate of muscle strength.

CONCLUSIONS

Urinary L-FABP reflects the degree of muscle strength and weight, as well as cross-sectional areas of muscle fibers. Although further clinical study is needed, urinary L-FABP may be useful to monitor the progression of sarcopenia and DKD in T2D patients.

Diabetic Cataract in Spontaneously Diabetic Torii Fatty Rats

Spontaneously Diabetic Torii (SDT) fatty rat is a novel animal model of type 2 diabetes with obesity. SDT fatty rats develop hyperglycemia, dyslipidemia, and other diabetic complications including ocular disorders; however, diabetic cataract formation in SDT fatty rats has not been fully investigated. The aim of the current study was to investigate the characteristics of cataract in the SDT fatty rats. The mean body weight of SDT fatty rats is larger than that of age-matched Sprague-Dawley (SD) rats and control animals until 8 weeks of age, and thereafter the growing speed decreased until the end of observation at 16 weeks of age. Blood glucose levels in SDT fatty rats were significantly higher than those in SD rats throughout the observational period. Slit-lamp examination revealed that no rats showed cataract formation at 5 weeks of age; however, SDT fatty rats gradually developed cortical cataract and posterior subcapsular cataract, both of which are the common types of cataract in patients with type 2 diabetes. The levels of glucose, sorbitol, and fructose were higher in the lens tissues of SDT fatty rats in comparison with that of SD rats. Furthermore, the level of 4-hydroxynonenal (4-HNE) was higher in the lens of SDT fatty rats than in that of SD rats. By contrast, total glutathione (GSH) concentration was lower in the lens of SDT fatty rats than in that of SD rats. The present study demonstrated that the cataractogenesis in SDT fatty rats resembled human diabetic cataract formation, indicating that SDT fatty rats serve as a potential animal model in researches on human cataract associated with type 2 diabetes and obesity.

The Possibility of Urinary Liver-Type Fatty Acid-Binding Protein as a Biomarker of Renal Hypoxia in Spontaneously Diabetic Torii Fatty Rats

BACKGROUND

Renal hypoxia is an aggravating factor for tubulointerstitial damage, which is strongly associated with renal prognosis in diabetic kidney disease (DKD). Therefore, urinary markers that can detect renal hypoxia are useful for monitoring DKD.

OBJECTIVE

To determine the correlation between urinary liver-type fatty acid-binding protein (L-FABP) and renal hypoxia using a novel animal model of type 2 diabetes.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats (n = 6) were used as an animal model of type 2 diabetes. Age- and sex-matched Sprague-Dawley (SD) rats (n = 8) were used as controls. Body weight, systolic blood pressure, and blood glucose levels were measured at 8, 12, 16, and 24 weeks of age. Urine samples and serum and kidney tissues were collected at 24 weeks of age. Microvascular blood flow index (BFI) was measured using diffuse correlation spectroscopy before sampling both the serum and kidneys for the evaluation of renal microcirculation at the corticomedullary junction.

RESULTS

Obesity, hyperglycemia, and hypertension were observed in the SDT fatty rats. Focal glomerular sclerosis, moderate interstitial inflammation, and fibrosis were significantly more frequent in SDT fatty rats than in SD rats. While the frequency of peritubular endothelial cells and phosphoendothelial nitric oxide synthase levels were similar in both types of rats, the degree of renal hypoxia-inducible factor-1α (HIF-1α) expression was significantly higher (and with no change in renal vascular endothelial growth factor expression levels) in the SDT fatty rats. Urinary L-FABP levels were significantly higher and renal microvascular BFI was significantly lower in the SDT fatty rats than in the SD rats. Urinary L-FABP levels exhibited a significant positive correlation with renal HIF-1α expression and a significant negative correlation with renal microvascular BFI.

CONCLUSIONS

Urinary L-FABP levels reflect the degree of renal hypoxia in DKD in a type 2 diabetic animal model. Urinary L-FABP may thus prove useful as a renal hypoxia marker for monitoring DKD in patients with type 2 diabetes in clinical practice.

Estimation of potential risk of allyl alcohol induced liver injury in diabetic patients using type 2 diabetes spontaneously diabetic Torii-Leprfa (SDT fatty) rats

In order to estimate the potential risk of chemicals including drug in patients with type 2 diabetes mellitus (T2DM), we investigated allyl alcohol induced liver injury using SD rats and Spontaneously Diabetic Torii-Lepr^fa (SDT fatty) rats as a model for human T2DM. The diabetic state is one of the risk factors for chemically induced liver injury because of lower levels of glutathione for detoxification by conjugation with chemicals and environmental pollutants and their reactive metabolites. Allyl alcohol is metabolized to a highly reactive unsaturated aldehyde, acrolein, which is detoxified by conjugation with glutathione. Therefore, we used allyl alcohol as a model compound. Our investigations showed that SDT fatty rats appropriately mimic the diabetic state in humans. The profiles of glucose metabolism, hepatic function tests and glutathione synthesis in the SDT fatty rats were similar to those in patients with T2DM. Five-week oral dosing with allyl alcohol to the SDT fatty rats revealed that the allyl alcohol induced liver injury was markedly enhanced in the SDT fatty rats when compared with the SD rats and the difference was considered to be due to lower hepatic detoxification of acrolein, the reactive metabolite of allyl alcohol, by depleted hepatic glutathione synthesis. Taking all the results of the present study into consideration, the potential for allyl alcohol to induce liver injury is considered to be higher in diabetic patients than in healthy humans.

Acute and Direct Effects of Sodium-Glucose Cotransporter 2 Inhibition on Glomerular Filtration Rate in Spontaneously Diabetic Torii Fatty Rats

Recent clinical studies indicate that sodium-glucose cotransporter 2 (SGLT2) inhibitors exhibit a renoprotective effect. While studies at the single nephron level suggest that direct effects of SGLT2 inhibitors on renal hemodynamics may be a possible mechanism underlying their renoprotective effect, few studies have focused on such direct effects at the whole-kidney level. In the present study, we investigated the acute and direct effect of SGLT2 inhibition on creatinine clearance, an index of whole-kidney glomerular filtration rate (GFR), in a rat model of type 2 diabetes. Twelve to fifteen-week-old male Spontaneously Diabetic Torii (SDT) fatty rats and Sprague-Dawley rats were used as diabetic animals and non-diabetic controls, respectively. Under general anesthesia, baseline urine samples were collected from the left and right ureters for 1 h. The selective SGLT2 inhibitor ipragliflozin or vehicle was subsequently administered intravenously and post-drug urine was collected for 1 h. Baseline and post-drug blood samples were collected immediately before baseline urine collection and immediately after post-drug urine collection, respectively. Plasma glucose, urine volume, urinary glucose and albumin excretion were measured, and creatinine clearance was calculated. Blood pressure and heart rate were monitored continuously throughout the experiment. A single intravenous injection of ipragliflozin increased both urine output and glucose excretion, but reduced creatinine clearance without affecting systemic blood pressure. These results suggest that SGLT2 inhibition directly reduced whole-kidney GFR, most likely due to a reduction in intraglomerular pressure, by altering local renal hemodynamics, which may contribute to the renoprotective effects demonstrated in clinical studies.

Teriparatide Improves Bone and Lipid Metabolism in a Male Rat Model of Type 2 Diabetes Mellitus

Osteoporosis is a complication of diabetes mellitus (DM). The pathology of diabetic osteoporosis is distinct from postmenopausal osteoporosis, and there are no specific treatment guidelines for diabetic osteoporosis. In the current study, this issue was addressed by evaluating the effect of osteoporosis medications, such as the anabolic agent PTH [teriparatide (TPTD)] and the antiresorptive agents calcitonin [elcatonin (ECT)] and bisphosphonate [risedronate (RIS)], on bone metabolism as well as on glucose and lipid metabolism in spontaneously diabetic Torii (SDT) fatty rats, which are a model of type 2 DM (T2DM). The medicines were injected subcutaneously into 8-week-old male SDT fatty rats three times weekly for 8 weeks. TPTD treatment in SDT fatty rats increased the osteoblast number and function on trabecular bone in vertebrae, and increased the trabecular bone mass, bone mineral density (BMD), and mechanical strength of vertebrae. Additionally, TPTD improved cortical bone structure and increased BMD. RIS decreased the osteoclast number and function, which led to an increase in vertebral bone mineral content and BMD in the femoral diaphysis, and mechanical strength was increased in the vertebrae. ECT showed no clear effects on bone mass or metabolism. Similar to diabetic lesions, all of the drugs had no effects on hyperglycemia, pancreas morphology, or serum insulin and glucagon levels. However, triglyceride levels and lipid droplets in fatty liver were decreased in the TPTD group. These results suggest that TPTD may be useful for treating fatty liver in addition to osteoporosis in T2DM.

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.

First-dose effect of the SGLT2 inhibitor ipragliflozin on cardiovascular activity in spontaneously diabetic Torii fatty rats

The first dose of a sodium-dependent glucose cotransporter 2 (SGLT2) inhibitor induces osmotic diuresis and can thereby affect cardiovascular activity in hyperglycemic patients. We aimed to determine whether the first dose of the selective SGLT2 inhibitor ipragliflozin affects cardiovascular activity in non-diabetic Sprague-Dawley (SD) rats and Spontaneously Diabetic Torii (SDT) fatty rats in two studies, a urine collection study and a telemetry study. In the former study, urine was collected for 24 hours after a single oral dose of ipragliflozin. In the latter study, systolic blood pressure (SBP) and heart rate (HR) were continuously monitored for 24 hours under conscious and unrestrained conditions from immediately before the administration of ipragliflozin. The telemetry study was conducted in a crossover design at successive 1 week intervals. Cardiovascular autonomic nerve activity was calculated from the SBP and HR. SDT fatty rats exhibited polyuria, glucosuria and hyperglycemia. In addition, the mean and standard deviation of SBP were higher, while the coefficient of variance of HR was lower than the respective parameters in SD rats. Ipragliflozin increased both urine output and urinary glucose excretion, and the increases were more pronounced in SDT fatty rats than in SD rats. In contrast, ipragliflozin had no effect on SBP, the standard deviation of SBP, HR, and the coefficient of variance of HR, or on autonomic nerve activity in either rat strain. These results suggest that the first dose of the SGLT2 inhibitor ipragliflozin has little impact on cardiovascular activity despite causing glucosuria with osmotic diuresis.

Effects on Glycemic Control in Impaired Wound Healing in Spontaneously Diabetic Torii (SDT) Fatty Rats

Introduction

Impaired diabetic wound healing is an important issue in diabetic complications. The present study aims to evaluate the protective effect on glycemic control against impaired diabetic wound healing using a diabetic rat model. We investigated the wound healing process and effect on the impaired wound repair by glycemic control in the Spontaneously Diabetic Torii (SDT) fatty rat, which is a new animal model of obese type 2 diabetes and may be a good model for study impaired wound healing.

Material and methods

Male SDT fatty rats at 15 weeks of age were administered orally with sodium glucose co-transporter (SGLT) 2 inhibitor for 3 weeks. Wounds were induced at 2 weeks after SGLT 2 inhibitor treatment, and the wound areas were periodically examined in morphological and histological analyses.

Results

The SDT fatty rats showed a delayed wound healing as compared with the normal rats, but a glycemic control improved the impaired wound healing. In histological analysis in the skin of SDT fatty rats showed severe infiltration of inflammatory cell, hemorrhage and many bacterial masses in the remaining and slight fibrosis of crust on skin tissue. Thought that this results skin performance to be a delay of crust formation and regeneration of epithelium; however, these findings were ameliorated in the SGLT 2 inhibitor treated group.

Conclusion

Glycemic control is effective for treatment in diabetic wounds and the SDT fatty rat may be useful to investigate pathophysiological changes in impaired diabetic wound healing.

Assessment of Pharmacological Responses to an Anti-diabetic Drug in a New Obese Type 2 Diabetic Rat Model

Introduction

The number of diabetic patients has recently been increasing worldwide, and numerous anti-diabetic drugs have been developed to induce good glycemic control. In particular, metformin, which exhibits glucose-lowering effects by suppressing gluconeogenesis in the liver, is widely used as a first line oral anti-diabetic drug for type 2 diabetes mellitus.

Material and Methods

In this study, the pharmacological effects of metformin were investigated using female and male Spontaneously Diabetic Torii (SDT) fatty rats, a new obese type 2 diabetic model.

Results

Two experiments were performed: an assessment of repeated treatment with metformin in female SDT fatty rats 5 to 13 weeks of age (experiment 1), and an assessment of repeated treatment with metformin in male SDT fatty rats 6 to 10 weeks of age (experiment 2). In female SDT fatty rats, metformin treatment led to good glycemic control, increases in sensory nerve conduction velocity, and improvements in pancreatic abnormalities such as irregular boundaries and vacuole form of islets. In male SDT fatty rats, metformin decreased blood glucose levels 4 weeks after treatment.

Conclusion

Metformin treatment led to maintained good glycemic control and improved neuropathy and pancreatic lesions in female SDT fatty rats. The SDT fatty rat is useful for the development of novel anti-diabetic agents that show potential to improve glucose metabolic disorders in the liver.

Pathophysiological abnormalities in the brains of Spontaneously Diabetic Torii-Lepr fa (SDT fatty) rats, a novel type 2 diabetic model

In recent years, a relationship between diabetes and neurodegenerative diseases, such as Parkinson's disease, Alzheimer disease or depression, has been proposed. In this study, pathophysiological changes in the brain, especially in the hippocampus, of male SDT fatty rats with obesity and hyperglycemia were investigated. Brains of SD rats and SDT fatty rats were collected at 32 and 58 weeks of age, and parietal cortical thickness and number of pyramidal cells in the hippocampal cornu ammonis 1 and 3 (CA1 and CA3) regions were measured. At 58 weeks of age, the parietal cortical thickness and number of pyramidal cells in the hippocampal CA1 and CA3 regions were lower in SDT fatty rats than in age-matched SD rats. Measurements of mRNA in rat brains at 58 weeks of age showed that the expression of genes related to inflammatory responses (S100a9, TNFα, NF-κB) was elevated in SDT fatty rats. From the aforementioned results, changes suggestive of brain atrophy and impairment in cognitive function were observed in male SDT fatty rat brains.

Osteomeles schwerinae Extract Prevents Diabetes-Induced Renal Injury in Spontaneously Diabetic Torii Rats

Mesangial cell proliferation contributes to the development of glomerulosclerosis in diabetic nephropathy. This study was aimed at determining whether Osteomeles schwerinae (OSSC) extract can ameliorate renal damage in Spontaneously Diabetic Torii (SDT) rats. OSSC extract (100 and 250 mg/kg/day) was administered to the SDT rats through oral gavage for 17 weeks. At the end of the experiment, glucose, HbA1c, and albuminuria were measured. In addition, the levels of mesangial proliferation-related proteins were determined by western blotting and immunohistochemistry. Our results show that albuminuria, accumulation of the extracellular matrix (ECM), and renal expansion were markedly restored by OSSC extract administration. The OSSC treatment also inhibited α-smooth muscle actin and transforming growth factor-β1 protein expression. In addition, OSSC and its bioactive compounds hyperoside and quercitrin inhibited the platelet-derived growth factor-BB (PDGF-BB)/platelet-derived growth factor-B receptor (PDGFR-β) ligand binding in an in vitro assay. Taken together, these results indicate that OSSC inhibits ECM accumulation and mesangial proliferation of the glomeruli in SDT rats through inhibition of the interaction between PDGF-BB and PDGFR-β. OSSC has ameliorating effects on the initiation and progression of diabetes complications and can be used for the treatment of early diabetic renal dysfunction.

Investigation of pharmacological responses to anti-diabetic drugs in female Spontaneously Diabetic Torii (SDT) fatty rats, a new nonalcoholic steatohepatitis (NASH) model

Nonalcoholic steatohepatitis (NASH) is a progressive liver disease, and some patients develop hepatic cirrhosis/carcinoma. Animal models play key roles in the development of new therapies for NASH. In this study, the pharmacological effects of metformin and pioglitazone were investigated in female Spontaneously Diabetic Torii (SDT) fatty rats to verify the utility of this model. The anti-diabetic drugs were administered to SDT fatty rats fed a cholesterol-enriched diet from 4 to 25 weeks, and changes in food intake, body weight, and blood chemistry parameters were evaluated every 4 weeks. The hepatic lipid content, mRNA expression in relation to lipid synthesis, inflammation, and fibrosis, and histopathological analyses were performed at 25 weeks. Pioglitazone improved hyperglycemia, hyperlipidemia, and abnormalities in hepatic parameters. The insulin levels were lower than those in the control rats before 16 weeks. Plasma glucose levels in the metformin-treated rats were lower than those in the control rats, and plasma alanine aminotransferase levels temporarily decreased. The lipid content and some mRNA expression in relation to fibrosis in the liver decreased with pioglitazone treatment, and the mRNA expression of microsomal triglyceride transfer protein increased. Hepatic fibrosis observed in the SDT fatty rats improved with pioglitazone treatment; however, the effect with metformin treatment was partial. These results in both drugs are in line with results in the human study, suggesting that the SDT fatty rat is useful for developing new anti-NASH drugs that show potential to regulate glucose/lipid metabolism.

Diabetic macular edema-like ocular lesions in male spontaneously diabetic torii fatty rats

Diabetic macular edema (DME) is a major factor contributing to visual disabilities in diabetic patients, and the number of patients is increasing. Animal models play a key role in the development of novel therapies. In this study, pathophysiological analyses of ocular lesions in Spontaneously Diabetic Torii (SDT) fatty rats were performed. First, vascular endothelial growth factor (VEGF) concentrations in vitreous humor, retinal vascular permeability and retinal thickness were measured in SDT fatty rats (Experiment 1). Furthermore, the pharmacological effects of two anti-diabetic drugs, phlorizin and pioglitazone, on retinal lesions were evaluated (Experiment 2). As results, the SDT fatty rats exhibited VEGF increase in vitreous humor at 8 and 16 weeks of age, and both retinal vascular hyperpermeability and retinal thickening at 16 weeks of age. In particular, the layers between the retinal internal limiting membrane and the outer nuclear layer were thickened. Phlorizin treatment from 4 to 16 weeks of age improved hyperglycemia and normalized retinal thickness; however, the effect of pioglitazone on retinal thickness was not strong despite the normalization of hyperglycemia. These data demonstrate that the male SDT fatty rat is a useful model for developing new therapeutic approaches in DME.

Pathophysiological analyses of skeletal muscle in obese type 2 diabetes SDT fatty rats

Sarcopenia is the age-related decrease of muscle mass and function. Diabetes and obesity are known to be risk factors that exacerbate sarcopenia, but the underlying mechanism of diabetes-related sarcopenia is still unknown. Obese type 2 diabetes SDT fatty rats show early onset of severe diabetes and there have been no reports on the characteristics of their skeletal muscle. Therefore, pathophysiological analyses were performed for the skeletal muscle in these rats. Diabetic male SDT fatty rats were sacrificed at 8, 16, 24, 32 and 40 weeks of age. Age-matched Sprague Dawley (SD) rats were used as the normal control. In addition to biological blood parameters, the soleus and the extensor digitorum longus muscles were examined for muscle weight, histopathology, and protein synthesis and degradation. Muscle grip strength was also examined. These results revealed that the muscle weights of the SDT fatty rats were significantly decreased from 16 weeks of age. The mean cross-sectional area of muscle fibers in the SDT fatty rats decreased from 24 weeks of age. Increased intramyocellular lipid accumulation, identified by immunohistochemistry for adipophilin and TEM, was observed in the SDT fatty rats from 8 weeks of age. Plasma insulin-like growth factor (IGF)-1 levels and muscle strength in the SDT fatty rats decreased at 24 weeks of age and thereafter. These pathophysiological findings have been reported both in sarcopenia in aged humans and in patients with diabetes. In conclusion, the SDT fatty rat was considered to be a useful model for analysis of diabetes-related sarcopenia.

Bone morphological analyses in Spontaneously Diabetic Torii (SDT) fatty rats

The Spontaneously Diabetic Torii (SDT) fatty rat, a model for obese type 2 diabetes, shows bone quantitative abnormalities, namely low bone mineral density (BMD). The objective of this study was to evaluate bone morphological changes, in particular identifying the bone qualitative abnormalities, in the SDT fatty rat. Male SDT fatty rats showed increases in total trabecular area and trabecular number and decreases in trabecular thickness in cancellous bones of the proximal tibia, indicating trabecular miniaturization. The SDT fatty rat is useful for investigation of pathophysiological changes in bone quality in diabetic osteoporosis.

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.

Diabetic complications in obese type 2 diabetic rat models

We overviewed the pathophysiological features of diabetes and its complications in obese type 2 diabetic rat models: Otsuka Long-Evans Tokushima fatty (OLETF) rat, Wistar fatty rat, Zucker diabetic fatty (ZDF) rat and Spontaneously diabetic Torii (SDT) fatty rat. Pancreatic changes with progression of diabetes were classified into early changes, such as islet hypertrophy and degranulation of β cells, and degenerative changes, such as islet atrophy and fibrosis of islet with infiltration of inflammatory cells. Renal lesions in tubuli and glomeruli were observed, and nodular lesions in glomeruli were notable changes in OLETF and SDT fatty rats. Among retinal changes, folding and thickening were interesting findings in SDT fatty rats. A decrease of motor nerve conduction velocity with progression of diabetes was presented in obese diabetic rats. Other diabetic complications, osteoporosis and sexual dysfunction, were also observed. Observation of bone metabolic abnormalities, including decrease of osteogenesis and bone mineral density, and sexual dysfunction, including hypotestosteronemia and erectile dysfunction, in obese type 2 diabetic rats have been reported.

Physiological changes induced by salt intake in female Spontaneously Diabetic Torii-Lepr(fa) (SDT fatty) rat, a novel obese type 2 diabetic model

Salt plays an important role in the control of blood pressure in obesity and diabetes mellitus. In this study, we investigated physiological changes such as blood pressure and renal function in salt-loaded female Spontaneously Diabetic Torii-Lepr(fa) (SDT fatty) rats. SDT fatty rats were given 1% NaCl in drinking water for 14 weeks, from 4 to 18 weeks of age. Significant salt-sensitive hypertension was observed in the salt-loaded SDT fatty rats. Moreover, the salt-loaded rats showed a decrease of creatinine clearance and deterioration on pathological renal findings, including glomerulosclerosis and tubular and interstitial lesions. Female SDT fatty rat is a useful model for investigating the mechanisms of high salt sensitivity in obesity and diabetes mellitus.

Gender differences in metabolic disorders and related diseases in Spontaneously Diabetic Torii-Lepr(fa) rats

The Spontaneously Diabetic Torii Lepr(fa) (SDT fatty) rat is a novel type 2 diabetic model wherein both male and female rats develop glucose and lipid abnormalities from a young age. In this study, we investigated gender differences in abnormalities and related complications in SDT fatty rats. Food intake was higher in males compared to female rats; however, body weight was not different between genders. Progression of diabetes, including increases in blood glucose and declines in blood insulin, was observed earlier in male rats than in females, and diabetic grade was more critical in male rats. Blood lipids tended to increase in female rats. Gonadal dysfunction was observed in both male and female rats with aging. Microangiopathies, such as nephropathy, retinopathy, neuropathy, and osteoporosis, were seen in both genders, and pathological grade and progression were more significant in males. Qualitative and quantitative changes were observed for metabolic disease gender differences in SDT fatty rats. The SDT fatty rat is a useful model for researching gender differences in metabolic disorders and related diseases in diabetes with obesity.

Ocular inflammation in uveal tract in aged obese type 2 diabetic rats (Spontaneously Diabetic Torii fatty rats)

We report uveitis observed in an obese type 2 diabetes rat model, Spontaneously Diabetic Torii Lepr(fa) (SDT fatty) rats aged over 50 weeks. The eyes of SDT fatty rats (16 animals: 7 males and 9 females with 50 or 60 weeks of age) were examined histopathologically. Infiltration of inflammatory cells in the uveal tract was observed in 13 of 16 animals. One female showed severe inflammation affecting the entire uveal tract including the iris, ciliary body, and choroid with a variety of inflammatory cells (neutrophils, lymphocytes, and macrophages). Those changes clinically mimic the findings of diabetic iridocyclitis in diabetic patients. Uveitis associated with diabetes can occur in diabetic patients but the pathogenesis still remains unknown. Since increased extramedullary hematopoiesis in the spleen and abscess in the genital and lower urinary tracts were observed in some SDT fatty rats, increased susceptibility to infection, prolongation of inflammatory states, and disorders of the immune system were considered to be possible factors of the uveitis in aged SDT fatty rats. There have been few reports on how diabetes has influence on the development of uveitis associated with bacterial infection. The SDT fatty rat can be an animal model to investigate diabetes-associated uveitis.

Effects of unilateral nephrectomy on renal function in male Spontaneously Diabetic Torii fatty rats: a novel obese type 2 diabetic model

The Spontaneously Diabetic Torii (SDT) fatty rat is a new model for obese type 2 diabetes. The aim of the present study was to investigate the effect of 1/2 nephrectomy (Nx) on renal function and morphology and on blood pressure in SDT fatty rats. Male SDT fatty rats underwent 1/2 Nx or a sham operation (Sham). Subsequently, animals were studied with respect to renal function and histological alterations. Induction of 1/2 Nx in SDT fatty rats led to functional and morphological damage to the remnant kidney and to hypertension, which are considered main characteristics of chronic kidney disease, at a younger age compared with the sham group. In conclusion, the SDT fatty rat is useful in investigations to elucidate the pathogenesis of human diabetic nephropathy and in new drug discovery.

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.

Metabolic Disorders and Diabetic Complications in Spontaneously Diabetic Torii Lepr (fa) Rat: A New Obese Type 2 Diabetic Model

Spontaneously Diabetic Torii Lepr (fa) (SDT fatty) rat, established by introducing the fa allele of the Zucker fatty rat into SDT rat genome, is a new model of obese type 2 diabetes. Both male and female SDT fatty rats show overt obesity, and hyperglycemia and hyperlipidemia are observed at a young age as compared with SDT rats. With early incidence of diabetes mellitus, diabetic complications, such as nephropathy, retinopathy, and neuropathy, in SDT fatty rats were seen at younger ages compared to those in the SDT rats. In this paper, we overview pathophysiological features in SDT fatty rats and also describe new insights regarding the hematology, blood pressure, renal complications, and sexual dysfunction. The SDT fatty rats showed an increase of leukocytes, especially the monocyte count, prominent hypertension associated with salt drinking, end-stage renal disease with aging, and hypogonadism. Unlike other diabetic models, the characteristic of SDT fatty rat is to present an incidence of diabetes in females, hypertension, and retinopathy. SDT fatty rat is a useful model for analysis of various metabolic disorders and the evaluation of drugs related to metabolic disease.

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.

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.

Retinal changes in an experimental model of early type 2 diabetes in rats characterized by non-fasting hyperglycemia

Diabetic retinopathy is a leading cause of acquired blindness in young, but also in elder adults, mostly affected by type 2 diabetes mellitus (T2DM). The aim of this work was to develop an experimental model of early human T2DM in adult rats, and to analyze retinal functional, morphological, and biochemical changes arising during the early stages of the moderate metabolic derangement. For this purpose, animals were divided in four groups: adult male Wistar rats receiving: tap water and citrate buffer i.p. (group 1), tap water with 30% sucrose and citrate buffer i.p. (group 2), tap water and 25mg/kg i.p streptozotocin (STZ, group 3), or 30% sucrose and STZ (group 4). Fasting and postprandial glycemia, fructosamine and serum insulin levels were assessed. In addition, i.p. glucose and insulin tolerance tests were performed. Retinal function (electroretinogram, ERG) and morphology (optical microscopy), retinal nitric oxide synthase (NOS) activity (using (3)H-arginine), lipid peroxidation (thiobarbituric acid reactive substances, TBARS), and TNFα levels (ELISA) were evaluated. At 6 and 12 weeks of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in most metabolic tests, as compared with the other groups. At 12 weeks of treatment, a significant decrease in the ERG a- and b- wave and oscillatory potential amplitudes, and a significant increase in retinal NOS activity, TBARS, TNFα, glial fibrillary acidic protein in Müller cells, and vascular endothelial growth factor levels were observed. These results indicate that the combination of diet-induced insulin resistance and a slight secretory impairment resulting from a low-dose STZ treatment mimics some features of human T2DM at its initial stages, and provokes significant retinal alterations.

Parathyroid hormone (1-34) improves bone mineral density and glucose metabolism in Spontaneously Diabetic Torii-Lepr(fa) rats

The Spontaneously Diabetic Torii-Lepr(fa) (SDT-fa/fa) rat, a model of obese type 2 diabetes, shows obesity, hyperglycaemia and low bone mineral density (BMD). The objective of this study is to evaluate the effects of parathyroid hormone (1-34) [PTH(1-34)] on BMD and glucose metabolism in the SDT-fa/fa rat. SDT-fa/fa rats showed obesity with hyperglycaemia and decreased serum osteocalcin levels and the tibial BMD. A 4-week treatment of PTH(1-34) (20 µg/kg/day) increased the serum osteocalcin levels and the tibial BMD, and decreased the serum glucose levels without changing the serum insulin levels. These findings indicate that PTH(1-34) improved not only BMD but also glucose metabolism in SDT-fa/fa rats. This study suggests that PTH(1-34) is a novel agent for the treatment of diabetic osteoporosis.

Effects of ovariectomy on bone metabolism and bone mineral density 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 female SDT-fa/fa rat shows obesity, hyperglycemia and hyperlipidemia from a young age. However, it is not known whether diabetes and estrogen deficiency can lead to bone abnormalities in the female SDT-fa/fa rat. The objective of the present study was to investigate the effects of ovariectomy (OVX) on bone metabolism and bone mineral density (BMD) in the female SDT-fa/fa rat. Female Sprague-Dawley rats were used as control animals. The BMDs of the whole tibia and fifth lumbar (L5) vertebral body were analyzed at 30 weeks after OVX. Serum osteocalcin, a bone formation marker, and urine deoxypyridinoline (DPD), a bone resorption marker, were sequentially analyzed before and at 5, 15 and 30 weeks after OVX. Serum osteocalcin and urine DPD levels were lower in SDT-fa/fa rats than in control rats before OVX. Both serum osteocalcin and urine DPD levels were elevated in control rats 5-30 weeks after OVX, but only the urine DPD levels were elevated in SDT-fa/fa rats 5-30 weeks after OVX. SDT-fa/fa rats showed a decrease in the BMDs of the whole tibia and L5 vertebral body compared with control rats. OVX decreased the BMDs of the whole tibia and L5 vertebral body in control rats, but not in SDT-fa/fa rats. These data suggest that estrogen deficiency is not a risk factor for bone loss in type 2 diabetes mellitus.

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.

Evaluation of blood pressure in Spontaneously Diabetic Torii-Lepr(fa) rats

The Spontaneously Diabetic Torii-Lepr(fa) (SDT-fa/fa) rat, a new model of obese type 2 diabetes, shows obesity, hyperglycemia, and hyperlipidemia from 6 weeks of age. Diabetic complications such as nephropathy and cataract are observed with aging; however, blood pressure change with age has not previously been examined. In this study, blood pressure was periodically measured and the change was investigated. Blood pressure in male SDT-fa/fa rats was elevated at 8, 16, and 24 weeks of age, whereas the heart rate was not changed. In addition to hyperglycemia, hyperlipidemia, and proteinuria, hyperleptinemia and increased urine angiotensinogen were observed in SDT-fa/fa rats. Blood pressure and heart rate in the male original SDT (SDT-+/+) rat did not significantly change. In conclusion, the SDT-fa/fa rat is a promising model, showing significant hypertension with diabetes mellitus.

Microangiopathy and visual deficits characterize the retinopathy of a spontaneously hypertensive rat model with type 2 diabetes and metabolic syndrome

Retinopathy has been increasing in prevalence as a consequence of type 2 diabetes and a cluster of coexisting risk factors characterized as the metabolic syndrome. However, the combined effects of these conditions on the retina are poorly understood. Therefore, we focused on the spontaneously hypertensive corpulent rat (SHR/N-cp), a model with type 2 diabetes, obesity and features of the metabolic syndrome to characterize retinal changes at a structural and functional level. SHR/N-cp males at 4 and 8 months of age were used in this study. Metabolic parameters and blood pressure were measured by standard methods. Morphology was investigated by histological techniques supplemented by nicotinamide adenine dinucleotide phosphate-diaphorase staining of whole mounts and fluorescein angiography to analyze the retinal vasculature. The in vivo function of the retina was examined by electroretinography (ERG). Obese SHR/N-cp rats were hypertensive and showed significant increases in body weight, serum levels of glucose, triglycerides, total cholesterol and urinary glucose excretion compared with lean controls (P < 0.01 for each). Histology indicated an overall intact integrity of the retina and aspects of microangiopathy in obese SHR/N-cp rats. ERG revealed intact processing of light signals but significantly decreased amplitudes of b-waves for all (P < 0.01) and of a-waves for some examined light intensities (P < 0.05). Oscillatory potentials were significantly protracted (P < 0.01), whereas amplitudes were not reduced. Microangiopathy and electroretinographic deficits combine to produce an early non-proliferative retinopathy phenotype in the obese SHR/N-cp rats. Thus, this model represents a valuable experimental tool to obtain further insights into the mechanisms of retinopathy in the context of obesity, type 2 diabetes and metabolic syndrome.

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 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.