Effect of food restriction on adipose tissue in spontaneously diabetic Torii 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.

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.

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.

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.

The influence of dietary restriction on the development of diabetes and pancreatitis in female WBN/Kob-fatty rats

Original WBN/Kob male rats commonly develop chronic pancreatitis by the age of 3 months, while diabetes mellitus occurs at 9 months. In contrast, female rats of this strain do not show pancreatitis or diabetes. The WBN/Kob-fatty rat is a homozygous (fa/fa) congenic strain for the fa allele of the leptin receptor gene (Lepr). In WBN/Kob-fatty rats, both females and males provide a model of non-insulin-dependent diabetes with obesity. The leptin receptor fatty gene (Lepr(fa)) induces obesity and hyperphagia. In the present study, we examined the effect of dietary restriction on pancreatitis and diabetes in female WBN/Kob-fatty rats. Five female fatty rats comprised a restricted feeding group with paired-feeding from 3 to 13 weeks of age, and five female lean rats comprised a control group with paired-feeding. At 13 weeks of age, two of the five female fatty rats of the control group developed diabetes mellitus, while no female fatty rats of the restricted feeding group developed diabetes mellitus. At this stage, pathological changes of the pancreas were observed in female fatty rats. All female fatty rats showed severe interlobular, intra-lobular and intra-islet fibrosis. In female fatty rats of the restricted feeding group, pathological changes of the pancreas were milder those of the free-feeding fatty group. Although dietary restriction could not completely prevent pancreatitis in female fatty rats, the development of diabetes was inhibited by its reduction of the severity of pancreatitis.

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.

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.

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.