Association of prolonged hyperglycemia with glomerular hypertrophy and renal basement membrane thickening in the Goto Kakizaki model of non-insulin-dependent diabetes mellitus

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

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

Rodent models to study type 1 and type 2 diabetes induced human diabetic nephropathy

INTRODUCTION

Diabetic nephropathy (DN), an outcome of prolonged diabetes, has affected millions of people worldwide and every year the incidence and prevalence increase substantially. The symptoms may start with mild manifestations of the disease such as increased albuminuria, serum creatinine levels, thickening of glomerular basement membrane, expansion of mesangial matrix to severe pathological symptoms such as glomerular lesions and tubulointerstitial fibrosis which may further proceed to cardiovascular dysfunction or end-stage renal disease.

PERSPECTIVE

Numerous therapeutic interventions are being explored for the management of DN, however, these interventions do not completely halt the progression of this disease and hence animal models are being explored to identify critical genetic and molecular parameters which could help in tackling the disease. Rodent models which mostly include mice and rats are commonly used experimental animals which provide a wide range of advantages in understanding the onset and progression of disease in humans and also their response to a wide range of interventions helps in the development of effective therapeutics. Rodent models of type 1 and type 2 diabetes induced DN have been developed utilizing different platforms and interventions during the last few decades some of which mimic various stages of diabetes ranging from early to later stages. However, a rodent model which replicates all the features of human DN is still lacking. This review tries to evaluate the rodent models that are currently available and understand their features and limitations which may help in further development of more robust models of human DN.

CONCLUSION

Using these rodent models can help to understand different aspects of human DN although further research is required to develop more robust models utilizing diverse genetic platforms which may, in turn, assist in developing effective interventions to target the disease at different levels.

Translation Animal Models of Diabetic Kidney Disease: Biochemical and Histological Phenotypes, Advantages and Limitations

Animal models play a crucial role in studying the pathogenesis of diseases, developing new drugs, identifying disease risk markers, and improving means of prevention and treatment. However, modeling diabetic kidney disease (DKD) has posed a challenge for scientists. Although numerous models have been successfully developed, none of them can encompass all the key characteristics of human DKD. It is essential to choose the appropriate model according to the research needs, as different models develop different phenotypes and have their limitations. This paper provides a comprehensive overview of biochemical and histological phenotypes, modeling mechanisms, advantages and limitations of DKD animal models, in order to update relevant model information and provide insights and references for generating or selecting the appropriate animal models to fit different experimental needs.

Selectively bred rodent models for studying the etiology of type 2 diabetes: Goto-Kakizaki rats and Oikawa-Nagao mice

Type 2 diabetes (T2D) is a polygenic disease and studies to understand the etiology of the disease have required selectively bred animal models with polygenic background. In this review, we present two models; the Goto-Kakizaki (GK) rat and the Oikawa-Nagao Diabetes-Prone (ON-DP) and Diabetes-Resistant (ON-DR) mouse. The GK rat was developed by continuous selective breeding for glucose tolerance from the outbred Wistar rat around 50 years ago. The main cause of spontaneous hyperglycemia in this model is insulin secretion deficiency from pancreatic β-cells and mild insulin resistance in insulin target organs. A disadvantage of the GK rat is that environmental factors have not been considered in the selective breeding. Hence, the GK rat may not be suitable for elucidating predisposition to diabetes under certain environmental conditions, such as a high-fat diet. Therefore, we recently established two mouse lines with different susceptibilities to diet-induced diabetes, which are prone and resistant to the development of diabetes, designated as the ON-DP and ON-DR mouse, respectively. The two ON mouse lines were established by continuous selective breeding for inferior and superior glucose tolerance after high-fat diet feeding in hybrid mice of three inbred strains. Studies of phenotypic differences between ON-DP and ON-DR mice and their underlying molecular mechanisms will shed light on predisposing factors for the development of T2D in the modern obesogenic environment. This review summarizes the background and the phenotypic differences and similarities of GK rats and ON mice and highlights the advantages of using selectively bred rodent models in diabetes research.

Assessment of Physiological Rat Kidney Ageing—Implications for the Evaluation of Allograft Quality Prior to Renal Transplantation

Due to organ shortage and rising life expectancy the age of organ donors and recipients is increasing. Reliable biomarkers of organ quality that predict successful long-term transplantation outcomes are poorly defined. The aim of this study was the identification of age-related markers of kidney function that might accurately reflect donor organ quality. Histomorphometric, biochemical and molecular parameters were measured in young (3-month-old) and old (24-month-old) male Sprague Dawley rats. In addition to conventional methods, we used urine metabolomics by NMR spectroscopy and gene expression analysis by quantitative RT-PCR to identify markers of ageing relevant to allograft survival. Beside known markers of kidney ageing like albuminuria, changes in the concentration of urine metabolites such as trimethylamine-N-oxide, trigonelline, 2-oxoglutarate, citrate, hippurate, glutamine, acetoacetate, valine and 1-methyl-histidine were identified in association with ageing. In addition, expression of several genes of the toll-like receptor (TLR) pathway, known for their implication in inflammaging, were upregulated in the kidneys of old rats. This study led to the identification of age-related markers of biological allograft age potentially relevant for allograft survival in the future. Among those, urine metabolites and markers of immunity and inflammation, which are highly relevant to immunosuppression in transplant recipients, are promising and deserve further investigation in humans.

The effect of etanercept and anakinra on experimental type 2 diabetes pathology in rats

In this study, the effects of etanercept, anakinra, and their combination on streptozotocin-induced type 2 diabetes in rats were pathologically evaluated. A total of 30 rats were separated into 5 groups as control (C), diabetes (D), diabetes + anakinra (DA), diabetes + etanercept (DE), and diabetes + anakinra + etanercept (DAE). Anakinra (10 mg/kg/day, s.c.) and etanercept (10 mg/kg, twice weekly, s.c.) were administered to the DA and DE groups, respectively, and the DAE group received both anakinra and etanercept for 21 days. Histopathologically, pathological changes related to diabetes in internal organs occurred in the diabetes group, and there was a significant decrease (improvement) in these changes in the treatment groups (P < 0.05). There was no significant difference (P > 0.05) between the treatment groups, but some changes in the liver and kidneys were higher in the combined group which should be taken into account for longer use. Although there was no significant difference, etanercept was more effective on pancreatic lesion scores and anakinra was more effective on testicular changes. As a result, the single or combined use of IL-1 and TNF-α antagonists anakinra and etanercept were effective in the treatment of type 2 diabetes in rats without any toxic-pathological effect.

Animal models of diabetic microvascular complications: Relevance to clinical features

Diabetes has become more common in recent years worldwide, and this growth is projected to continue in the future. The primary concern with diabetes is developing various complications, which significantly contribute to the disease's mortality and morbidity. Over time, the condition progresses from the pre-diabetic to the diabetic stage and then to the development of complications. Years and enormous resources are required to evaluate pharmacological interventions to prevent or delay the progression of disease or complications in humans. Appropriate screening models are required to gain a better understanding of both pathogenesis and potential therapeutic agents. Different species of animals are used to evaluate the pharmacological potentials and study the pathogenesis of the disease. Animal models are essential for research because they represent most of the structural, functional, and biochemical characteristics of human diseases. An ideal screening model should mimic the pathogenesis of the disease with identifiable characteristics. A thorough understanding of animal models is required for the experimental design to select an appropriate model. Each animal model has certain advantages and limitations. The present manuscript describes the animal models and their diagnostic characteristics to evaluate microvascular diabetic complications.

A Review on Cellular and Molecular Mechanisms Linked to the Development of Diabetes Complications

Modern lifestyle, changing eating habits and reduced physical work have been known to culminate into making diabetes a global pandemic. Hyperglycemia during the course of diabetes is an important causative factor for the development of both microvascular (retinopathy, nephropathy and neuropathy) and macrovascular (coronary artery disease, stroke and peripheral artery disease) complications. In this article, we summarize several mechanisms accountable for the development of both microvascular and macrovascular complications of diabetes. Several metabolic and cellular events are linked to the augmentation of oxidative stress like the activation of advanced glycation end products (AGE) pathway, polyol pathway, Protein Kinase C (PKC) pathway, Poly-ADP Ribose Polymerase (PARP) and hexosamine pathway. Oxidative stress also leads to the production of reactive oxygen species (ROS) like hydroxyl radical, superoxide anion and peroxides. Enhanced levels of ROS rescind the anti-oxidant defence mechanisms associated with superoxide dismutase, glutathione and ascorbic acid. Moreover, ROS triggers oxidative damages at the level of DNA, protein and lipids, which eventually cause cell necrosis or apoptosis. These physiological insults may be related to the microvascular complications of diabetes by negatively impacting the eyes, kidneys and the brain. While underlying pathomechanism of the macrovascular complications is quite complex, hyperglycemia associated atherosclerotic abnormalities like changes in the coagulation system, thrombin formation, fibrinolysis, platelet and endothelial function and vascular smooth muscle are well proven. Since hyperglycemia also modulates the vascular inflammation, cytokines, macrophage activation and gene expression of growth factors, elevated blood glucose level may play a central role in the development of macrovascular complications of diabetes. Taken collectively, chronic hyperglycemia and increased production of ROS are the miscreants for the development of microvascular and macrovascular complications of diabetes.

Oral Health Messiers: Diabetes Mellitus Relevance

This article aims to narrate the various oral complications in individuals suffering from diabetes mellitus. Google search for "diabetes mellitus and oral complications" was done. The search was also carried out for "diabetes mellitus" and its oral complications individually. Diabetes mellitus is a chronic metabolic disorder that is a global epidemic and a common cause of morbidity and mortality in the world today. Currently, there are about 422 million cases of diabetes mellitus worldwide. Diabetic patients can develop different complications in the body such as retinopathy, neuropathy, nephropathy, cardiovascular disease. Complications in the oral cavity have been observed in individuals suffering from diabetes mellitus. A study noted that more than 90% of diabetic patients suffered from oral complications. Another research has shown a greater prevalence of oral mucosal disorders in patients with diabetes mellitus than non-diabetic population: 45-88% in patients with type 2 diabetes compared to 38.3-45% in non-diabetic subjects and 44.7% in type 1 diabetic individuals compared to 25% in the non-diabetic population. Oral complications in people with diabetes are periodontal disease, dental caries, oral infections, salivary dysfunction, taste dysfunction, delayed wound healing, tongue abnormalities, halitosis, and lichen planus. The high glucose level in saliva, poor neutrophil function, neuropathy, and small vessel damage contribute to oral complications in individuals with uncontrolled diabetes. Good oral health is imperative for healthy living. Oral complications cause deterioration to the quality of life in diabetic patients. Complications like periodontal disease having a bidirectional relationship with diabetes mellitus even contribute to increased blood glucose levels in people with diabetes. This article intends to promote awareness regarding the oral health of diabetics and to stress the importance of maintaining proper oral hygiene, taking preventive measures, early detection, and appropriate management of oral complications of these patients through a multidisciplinary approach.

Time series changes in pseudo-R2 values regarding maximum glomerular diameter and the Oxford MEST-C score in patients with IgA nephropathy: A long-term follow-up study

There is no effectual pathological factor to predict the long-term renal prognosis of IgA nephropathy. Glomerular hypertrophy plays a crucial role in kidney disease outcomes in both experimental models and humans. This study aimed to 1) confirm the long-term prognostic significance of a maximal glomerular diameter (Max GD) ≥ 242.3 μm, 2) test a renal prognosis prediction model adding Max GD ≥ 242.3 μm to the Oxford classification (MEST-C), and 3) examine the time series changes in the long-term renal prognosis of patients with IgA nephropathy. The study included 43 patients diagnosed with IgA nephropathy from 1993 to 1998 at Kameda General Hospital. Renal prognosis with the endpoint of a 50% reduction in estimated glomerular filtration rate (eGFR) or the development of end-stage renal disease requiring dialysis was examined using logistic regression analysis, Cox regression analysis, and the Kaplan-Meier method. Pathological evaluation was performed using MEST-C and Max GD, and the validity of the prediction model was evaluated. Patients with Max GD ≥ 242.3 μm had significantly poor renal prognosis with multivariate Cox analysis (P = 0.0293). The results of the Kaplan-Meier analysis showed that kidney survival rates in the high-Max GD group were significantly lower than those in the low-Max GD group (log rank, P = 0.0043), which was confirmed in propensity score-matched models (log rank, P = 0.0426). Adding Max GD ≥ 242.3 μm to MEST-C improved diagnostic power of the renal prognosis prediction model by renal pathology tissue examination (R²: 3.3 to 14.5%, AICc: 71.8 to 68.0, C statistic: 0.657 to 0.772). We confirm that glomerular hypertrophy is useful as a long-term renal prognostic factor.

Using Genetic and Species Diversity to Tackle Kidney Disease

Progress in the identification of causal genes and understanding of the mechanism underlying kidney disease is hindered by the almost exclusive use of a few animal models with restrictive monogenic backgrounds that may be more resistant to kidney disease compared with humans and, therefore, poor models. Exploring the large genetic diversity in classical animal models, such as mice and rats, and leveraging species diversity will allow us to use the genetic advantages of zebrafish, Drosophila, and other species, to develop both new animal models that are more relevant to the study of human kidney disease and potential therapies.

Effects of ATRA on diabetic rats with renal ischemia-reperfusion injury

Purpose

To explore the role of all-trans retinoic acid (ATRA) in renal ischemia/reperfusion injury of diabetic rats.

Methods

Sixty adult male rats were randomly divided into 6 groups, including sham group (S group), ischemia-reperfusion group (I/R group), ischemia-reperfusion+ATRA group (A group), diabetic group (D group), diabetic ischemia-reperfusion group (DI/R group), diabetic ischemia-reperfusion +ATRA group (DA group). The levels of creatinine (Cr), cystatin C (Cys-C) and β2-microglobulin (β2-MG) were measured. Morphology of renal tissue was observed under light microscope.

Results

DJ-1, Nrf2, HO-1 and caspase-3 were detected by western blot. DJ-1, Nrf2, HO-1 and caspase-3 in I/R group, D group and DI/R group was higher than that in S group. Compared with I/R group, Nrf2 and HO-1 in A group was decreased, but caspase-3 was increased. However, Nrf2 in DA group was higher than that in DI/R group, HO-1 and caspase-3 in DA group were lower than that in DI/R group. Compared with group S, Cr, Cys-C and β2-MG in I/R group, A group, D group, and DI/R group were higher. Whereas the levels of Cr, Cys-C, β2-MG and renal injury score in DA group were lower than those in DI/R group.

Conclusion

ATRA has a protective effect on renal ischemia-reperfusion injury in diabetic rats, maybe relating to DJ/Nrf2 pathway.

Genomic Research in Rat Models of Kidney Disease

Current understanding of the mechanisms underlying renal disease in humans is incomplete. Consequently, our ability to prevent the occurrence of renal disease or treat established kidney disease is limited. Investigating kidney disease directly in humans poses objective difficulties, which has led investigators to seek experimental animal models that simulate renal disease in humans. Animal models have thus become a tool of major importance in the study of renal physiology and have been crucial in shedding light on the complex mechanisms involved in kidney function and in our current understanding of the pathophysiology of renal disease. Among animal models, the rat has been the preferred and most commonly used species for the investigation of renal disease. This chapter reviews what has been achieved over the years, using the rat as a tool for the investigation of renal disease in humans, focusing on the contribution of rat genetics and genomics to the elucidation of the mechanisms underlying the pathophysiology of the major types of renal disease, including primary and secondary renal diseases.

Aerobic interval exercise improves renal functionality and affects mineral metabolism in obese Zucker rats

Obesity, metabolic syndrome, and renal injury are considered risk factors for type 2 diabetes, as well as kidney disease. Functional and structural changes in the kidney as consequence of obesity and metabolic syndrome may lead to impaired mineral metabolism in what is known as chronic kidney disease-mineral and bone disorder. Lifestyle interventions such as physical activity are good strategies to manage these pathologies and therefore, prevent the loss of kidney functionality and related complications in mineral metabolism. In this study, we have used 40 male Zucker rats that were randomly allocated into four different experimental groups, two of them (an obese and a lean one) performed an aerobic interval training protocol, and the other two groups were sedentary. At the end of the experimental period (8 wk), urine, plasma, and femur were collected for biochemical and mineral composition analysis, whereas the kidney was processed for histological studies. The obese rats exhibited albuminuria, glomerulosclerosis, and hypertrophy in glomeruli and renal tubule in some areas, together with alterations in mineral content of plasma but not of femur. The training protocol prevented the generation of albuminuria and glomerulosclerosis, showing a significant action on plasma and bone mineral levels. Therefore, the specific training protocol used in this study was able to prevent the development of diabetic nephropathy and affected the metabolism of certain minerals.

Calcium Signaling in the Ventricular Myocardium of the Goto-Kakizaki Type 2 Diabetic Rat

The association between diabetes mellitus (DM) and high mortality linked to cardiovascular disease (CVD) is a major concern worldwide. Clinical and preclinical studies have demonstrated a variety of diastolic and systolic dysfunctions in patients with type 2 diabetes mellitus (T2DM) with the severity of abnormalities depending on the patients' age and duration of diabetes. The cellular basis of hemodynamic dysfunction in a type 2 diabetic heart is still not well understood. The aim of this review is to evaluate our current understanding of contractile dysfunction and disturbances of Ca²⁺ transport in the Goto-Kakizaki (GK) diabetic rat heart. The GK rat is a widely used nonobese, nonhypertensive genetic model of T2DM which is characterized by insulin resistance, elevated blood glucose, alterations in blood lipid profile, and cardiac dysfunction.

Diabetic aggravation of stroke and animal models

Cerebral ischemia in diabetics results in severe brain damage. Different animal models of cerebral ischemia have been used to study the aggravation of ischemic brain damage in the diabetic condition. Since different disease conditions such as diabetes differently affect outcome following cerebral ischemia, the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines recommends use of diseased animals for evaluating neuroprotective therapies targeted to reduce cerebral ischemic damage. The goal of this review is to discuss the technicalities and pros/cons of various animal models of cerebral ischemia currently being employed to study diabetes-related ischemic brain damage. The rational use of such animal systems in studying the disease condition may better help evaluate novel therapeutic approaches for diabetes related exacerbation of ischemic brain damage.

All-Trans Retinoic Acid Has a Potential Therapeutic Role for Diabetic Nephropathy

PURPOSE

The aim of this study was to examine the effects of all-trans retinoic acid (ATRA) on diabetic nephropathy.

MATERIALS AND METHODS

We measured amounts of urinary albumin excretion (UAE) after administrating ATRA to Otsuka Long-Evans Tokushima Fatty (OLETF) rats. In order to understand the mechanism of action for ATRA, we administrated ATRA to examine its inhibitory action on the production of transforming growth factor-β₁ (TGF-β₁), protein kinase C (PKC), and reactive oxidative stress (ROS) in cultured rat mesangial cells (RMCs).

RESULTS

After 16 weeks of treatment, UAE was lower in the ATRA-treated OLETF rats than in the non-treated OLETF rats (0.07±0.03 mg/mgCr vs. 0.17±0.15 mg/mgCr, p<0.01). After incubation of RMCs in media containing 30 or 5 mM of glucose, treatment with ATRA showed time- and dose-dependent decreases in TGF-β₁ levels and ROS. Moreover, ATRA treatment showed a dose-dependent decrease in PKC expression.

CONCLUSION

ATRA treatment suppressed UAE and TGF-β₁ synthesis, which was mediated by significant reductions in PKC activity and ROS production. Our results suggest that ATRA has a potential therapeutic role for diabetic nephropathy.

Kidney glycosphingolipids are elevated early in diabetic nephropathy and mediate hypertrophy of mesangial cells

Glycosphingolipids (GSLs) play a role in insulin resistance and diabetes, but their role in diabetic nephropathy (DN) has received limited attention. We used 9- and 17-wk-old nondiabetic db/m and diabetic db/db mice to examine the role of GSLs in DN. Cerebrosides or monoglycosylated GSLs [hexosylceramides (HexCers); glucosyl- and galactosylceramides] and lactosylceramide (LacCers) were elevated in db/db mouse kidney cortices, specifically in glomeruli, and also in urine. In our recent paper (25), we observed that the kidneys exhibited glomerular hypertrophy and proximal tubular vacuolization and increased fibrosis markers at these time points. Mesangial cells contribute to hyperglycemia-induced glomerular hypertrophy in DN. Hyperglycemic culture conditions, similar to that present in diabetes, were sufficient to elevate mesangial cell HexCers and increase markers of fibrosis, extracellular matrix proteins, and cellular hypertrophy. Inhibition of glucosylceramide synthase or lowering glucose levels decreased markers of fibrosis and extracellular matrix proteins and reversed mesangial cell hypertrophy. Hyperglycemia increased phosphorylated (p)SMAD3 and pAkt levels and reduced phosphatase and tensin homolog levels, which were reversed with glucosylceramide synthase inhibition. These data suggest that inhibition of glucosylceramide synthase reversed mesangial cell hypertrophy through decreased pAkt and pSmad3 and increased pathways responsible for protein degradation. Importantly, urinary GSL levels were higher in patients with DN compared with healthy control subjects, implicating a role for these lipids in human DN. Thus, hyperglycemia in type II diabetes leads to renal dysfunction at least in part by inducing accumulation of HexCers and LacCers in mesangial cells, resulting in fibrosis, extracellular matrix production, and hypertrophy.

Relationships among protein tyrosine phosphatase 1B, angiotensin II, and insulin-mediated aortic responses in type 2 diabetic Goto-Kakizaki rats

OBJECTIVE

We investigated the relationships among protein tyrosine phosphatase 1B (PTP1B), angiotensin II (Ang II), and insulin signaling in the presence of endothelial dysfunction in type 2 diabetic Goto-Kakizaki (GK) rat aortas.

METHODS AND RESULTS

Aortas isolated from GK or control Wistar rats were examined in the presence or absence of Ang II with or without a selective antagonist of the Ang II type 1 (AT1) receptor or a PTP1B inhibitor to evaluate vascular functional and molecular mechanisms, such as insulin-induced relaxation, nitric oxide (NO) production, phosphorylation of insulin receptor substrate (IRS)-1, endothelial NO synthase (eNOS), and phosphorylation, and the subcellular localization of PTP1B. GK aortas exhibited reductions of: 1) insulin-induced relaxation, 2) NO production, 3) Ser(1177)-p-eNOS, and 4) Tyr(612)-p-IRS-1. Pre-incubation with a PTP1B inhibitor normalized these reductions. In Wistar aortas, the four above-mentioned parameters were reduced by Ang II, but were completely inhibited by co-treatment with the PTP1B inhibitor. The membrane expression of PTP1B was greater in GK than in Wistar aortas, and it was increased by Ang II in Wistar rats. The membrane PTP1B expression in the presence of insulin + Ang II was reduced by the PTP1B inhibitor or AT1-receptor antagonist.

CONCLUSIONS

These results suggest that the membrane PTP1B suppressed insulin-mediated aortic relaxation, and this was due to the Ang II-AT1-receptor signaling pathway. The inhibition of PTP1B warrants further investigation as a potential therapeutic target for endothelial dysfunction in type 2 diabetes.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Rice protein ameliorates the progression of diabetic nephropathy in Goto–Kakizaki rats with high-sucrose feeding

The effect of rice protein (RP) on diabetic nephropathy in non-obese, spontaneous type 2 diabetic Goto–Kakizaki (GK) rats was investigated. GK rats at 7 weeks of age were fed 20 % RP or casein (C) in standard or high-sucrose diets for 10 weeks. Plasma total cholesterol, TAG, alkaline phosphatase (ALP), adiponectin, creatinine and urinary albumin excretion (UAE) were measured and renal histology was evaluated. Compared with C, RP lowered plasma TAG and improved plasma adiponectin levels in GK rats fed the standard diet (P< 0·05), and also lowered total cholesterol and ALP in high-sucrose-fed GK rats (P< 0·05). RP markedly suppressed the sharp increase in UAE when GK rats were fed high-sucrose diets (P< 0·05), and prevented glomerular mesangial matrix expansion in the deep renal cortex near the corticomedullary junction (P< 0·05). These results strongly indicate that dietary RP can ameliorate the progression of diabetic nephropathy at an early stage compared with C.

Type II diabetes increases mitochondrial DNA mutations in the left ventricle of the Goto-Kakizaki diabetic rat

Mitochondrial dysfunction has a significant role in the development of diabetic cardiomyopathy. Mitochondrial oxidant stress has been accepted as the singular cause of mitochondrial DNA (mtDNA) damage as an underlying cause of mitochondrial dysfunction. However, separate from a direct effect on mtDNA integrity, diabetic-induced increases in oxidant stress alter mitochondrial topoisomerase function to propagate mtDNA mutations as a contributor to mitochondrial dysfunction. Both glucose-challenged neonatal cardiomyocytes and the diabetic Goto-Kakizaki (GK) rat were studied. In both the GK left ventricle (LV) and in cardiomyocytes, chronically elevated glucose presentation induced a significant increase in mtDNA damage that was accompanied by decreased mitochondrial function. TTGE analysis revealed a number of base pair substitutions in the 3' end of COX3 from GK LV mtDNA that significantly altered the protein sequence. Mitochondrial topoisomerase DNA cleavage activity in isolated mitochondria was significantly increased in the GK LV compared with Wistar controls. Both hydroxycamptothecin, a topoisomerase type 1 inhibitor, and doxorubicin, a topoisomerase type 2 inhibitor, significantly exacerbated the DNA cleavage activity of isolated mitochondrial extracts indicating the presence of multiple functional topoisomerases in the mitochondria. Mitochondrial topoisomerase function was significantly altered in the presence of H2O2 suggesting that separate from a direct effect on mtDNA, oxidant stress mediated type II diabetes-induced alterations of mitochondrial topoisomerase function. These findings are significant in that the activation/inhibition state of the mitochondrial topoisomerases will have important consequences for mtDNA integrity and the well being of the diabetic myocardium.

Comparison of the Development Diabetic Induced Renal Disease in Strains of Goto-Kakizaki Rats

This study compared temporal changes in renal hemodynamics, proteinuria and the development of renal disease in Goto-Kakizaki (GK) type II diabetic rats that are resistant to the development of diabetic nephropathy and a genetically modified GK substrain (T2DN) carrying the mitochondrial genome and other alleles from Fawn hooded-hypertensive (FHH) rats is more susceptible to the development of renal injury. Both GK and T2DN rats were diabetic (>250 mg/ dL) and blood glucose levels were not significantly different at 3, 6 and 18 months of age. Blood pressure was also similar in both strains at all 3 ages. Renal blood flow (RBF) was 45% higher in 3 month old T2DN rats than GK rats but glomerular filtration rate (GFR) was similar. T2DN rats exhibited a progressive increase in proteinuria from 41 ± 2 to 524 ± 50 mg/day and 57% fall in GFR as they aged from 3 to 18 months of age. In contrast, proteinuria only increased to 162 ± 31 mg/day in GK rats and GFR remained unaltered. The kidneys from 18 month old T2DN rats exhibited severe glomerulosclerosis, interstitial fibrosis and tubular necrosis while kidneys from GK rats did not. Plasma creatinine levels were 2.4 fold higher in 18 month old T2DN than in GK rats. These data demonstrate that T2DN rats develop most of the features of diabetic nephropathy including progressive proteinuria and chronic kidney disease whereas the closely related GK strain does not, even though blood pressure and the level of hyperglycemia are similar.

Advances in murine models of diabetic nephropathy

Diabetic nephropathy (DN) is one of the microvascular complications of both type 1 and type 2 diabetes, which is also associated with a poor life expectancy of diabetic patients. However, the pathogenesis of DN is still unclear. Thus, it is of great use to establish appropriate animal models of DN for doing research on pathogenesis and developing novel therapeutic strategies. Although a large number of murine models of DN including artificially induced, spontaneous, and genetically engineered (knockout and transgenic) animal models have been developed, none of them develops renal changes sufficiently reflecting those seen in humans. Here we review the identified murine models of DN from the aspects of genetic background, type of diabetes, method of induction, gene deficiency, animal age and gender, kidney histopathology, and phenotypic alterations in the hope of enhancing our comprehension of genetic susceptibility and molecular mechanisms responsible for this disease and providing new clues as to how to choose appropriate animal models of DN.

Fibrates: therapeutic potential for diabetic nephropathy?

Despite intensive glucose-lowering treatment and advanced therapies for cardiovascular risk factors, such as hypertension and dyslipidaemia, diabetes mellitus with its macro- and microvascular complications remains a major health problem. Especially diabetic nephropathy is a leading cause of morbidity and mortality, and its prevalence is increasing. Peroxisome proliferator-activated receptor-α (PPAR-α), a member of a large nuclear receptor superfamily, is expressed in several tissues including the kidney. Recently, experimental data have suggested that PPAR-α activation plays a pivotal role in the regulation of fatty acid oxidation, lipid metabolism, inflammatory and vascular responses, and might regulate various metabolic and intracellular signalling pathways that lead to diabetic microvascular complications. This review examines the role of PPAR-α activation in diabetic nephropathy and summarises data from experimental and clinical studies on the emerging therapeutic potential of fibrates in diabetic nephropathy.

The GK rat: a prototype for the study of non-overweight type 2 diabetes

Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of β-cell secretory dysfunction and/or decreased β-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK abnormalities so far identified is proposed in this perspective, together with their time-course and interactions. A special focus is given toward the pathogenesis of defective β-cell number and function in the GK model. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (1) several susceptibility loci containing genes responsible for some diabetic traits; (2) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas and the major insulin target tissues; and (3) environmentally induced loss of β-cell differentiation due to chronic exposure to hyperglycemia/hyperlipidemia, inflammation, and oxidative stress.

Reduced aldehyde dehydrogenase activity and arginine vasopressin receptor 2 expression in the kidneys of male TALLYHO/JngJ mice of prediabetic age

The TALLYHO/JngJ (TH) mouse is a novel polygenic model of type 2 diabetes and exhibits obesity, hyperglycemia (males), hyperinsulinemia, hyperlipidemia, and enlarged pancreatic islets. Since the kidney is damaged by hyperglycemia in other animal models, the present study aimed to determine the kidney phenotype of TH mice using immunoblot and histological analyses of the kidneys of 6-week-old (prediabetic) and 16-week-old TH mice. Interestingly, even 6-week-old male TH mice showed significant increases in kidney weight, compared to C57BL/B6 (B6) mice. Cuboidal parietal epithelium was observed in the Bowman's capsule in male TH mice at the prediabetic age. Water accumulated inside the kidneys of male TH mice in an age-dependent manner, but not in B6 mice. Since Swr/J mice are reported to develop diabetes insipidus and share 86.8% genotype homology with TH mice, the expression level of arginine vasopressin receptor 2 (AVPR2), a candidate protein for diabetes insipidus, was examined and determined to be significantly reduced in the kidneys of prediabetic male TH mice, compared to B6 mice. Aldehyde dehydrogenase (ALDH) activity in the kidneys of prediabetic male TH mice was significantly lower than that in age-matched male B6 mice, while there were no differences between female TH and B6 mice. These results suggest that the kidney phenotype of prediabetic TH mice occurs only in males, accompanied by a reduction in ALDH activity and AVPR2 expression. The kidney phenotype of male TH mice at a prediabetic age becomes evident before the onset of diabetes.

Anti-diabetic effect of pyroglutamic acid in type 2 diabetic Goto-Kakizaki rats and KK-Ay mice

With the rapidly increasing prevalence of type 2 diabetes mellitus (T2DM), specific dietary components with anti-diabetic efficacy could be one strategy with therapeutic potential. In the present study, the anti-diabetic effects of an amino acid, pyroglutamic acid (PA), found in vegetables and fruits were investigated in T2DM models using Goto-Kakizaki (GK) rats and KK-Ay mice by measuring glucose tolerance and other markers of diabetes. Moreover, the effect of PA on gene expression in GK rats was measured by DNA microarray analysis. Oral glucose tolerance and serum insulin levels were reduced by PA in both animal models. Serum and liver total cholesterol levels were also improved by PA. Expression of genes involved with gluconeogenesis and those involved with its related transcription factor were down-regulated by feeding PA. In KK-Ay mice, the glucokinase:glucose-6-phosphatase (G6Pase) activity ratio increased. From these results, it is suggested that dietary PA beneficially modifies glucose and lipid metabolism in diabetic animals, and can potentially contribute to the mitigation of T2DM.

Role of NAD(P)H oxidase in superoxide generation and endothelial dysfunction in Goto-Kakizaki (GK) rats as a model of nonobese NIDDM

Background

Cardiovascular disease is the leading cause of mortality in diabetics, and it has a complex etiology that operates on several levels. Endothelial dysfunction and increased generation of reactive oxygen species are believed to be an underlying cause of vascular dysfunction and coronary artery disease in diabetes. This impairment is likely the result of decreased bioavailability of nitric oxide (NO) within the vasculature. However, it is unclear whether hyperglycemia per se stimulates NADPH oxidase-derived superoxide generation in vascular tissue.

Methods and Results

This study focused on whether NADPH oxidase-derived superoxide is elevated in vasculature tissue evoking endothelial/smooth muscle dysfunction in the hyperglycemic (169±4 mg%) Goto-Kakizaki (GK) rat. By dihydroethidine fluorescence staining, we determined that aorta superoxide levels were significantly elevated in 9 month-old GK compared with age matched Wistar (GK; 195±6%, Wistar; 100±3.5%). Consistent with these findings, 10⁻⁶ mol/L acetylcholine-induced relaxation of the carotid artery was significantly reduced in GK rats compared with age matched Wistar (GK; 41±7%, Wistar; 100±5%) and measurements in the aorta showed a similar trend (p = .08). In contrast, relaxation to the NO donor SNAP was unaltered in GK compared to Wistar. Endothelial dysfunction was reversed by lowering of superoxide with apocynin, a specific Nox inhibitor.

Conclusions

The major findings from this study are that chronic hyperglycemia induces significant vascular dysfunction in both the aorta and small arteries. Hyperglycemic induced increases in NAD(P)H oxidase activity that did not come from an increase in the expression of the NAD(P)H oxidase subunits, but more likely as a result of chronic activation via intracellular signaling pathways.

Genomic research in rat models of kidney disease

Current understanding of the mechanisms underlying renal disease in humans is incomplete. Consequently, our ability to prevent the occurrence of renal disease or treat kidney disease once it develops is limited. There are objective difficulties in investigating kidney disease directly in humans, leading investigators to resort to experimental animal models that simulate renal disease in humans. Animal models have thus been a tool of major importance in the study of normal renal physiology and have been crucial in shedding light on the complex mechanisms involved in normal kidney function and in our current understanding of and ability to treat renal disease. Among the animal models, rat has been the preferred and most commonly used species for the investigation of renal disease. This chapter reviews what has been achieved over the years, using rat as a tool for the investigation of renal disease in humans, focusing on the contribution of rat genetics and genomics to the elucidation of the mechanisms underlying the pathophysiology of the major types of renal disease, including primary and secondary renal diseases.

Hyperglycemia induces elevated expression of thyroid hormone binding protein in vivo in kidney and heart and in vitro in mesangial cells

During a search for glucose-regulated abundant mRNAs in the diabetic rat kidney, we cloned thyroid hormone binding protein (THBP), also known as mu-crystallin or CRYM. The aim of this study was to investigate the effect of hyperglycemia/high glucose on the expression of THBP. THBP mRNA copy numbers were determined in kidneys and hearts of diabetic GK rats vs normoglycemic Wistar rats, and in human mesangial cells (HMCs) exposed to high glucose using real-time qPCR, and THBP protein levels were measured by Western blotting and immunofluorescence. Intracellular ROS was measured in THBP transfected cells using DCF fluorescence. Hyperglycemia significantly increased THBP mRNA in GK rat kidneys (326+/-50 vs 147+/-54, p<0.05), and hearts (1583+/-277 vs 191+/-63, p<0.05). Moreover, the levels of THBP mRNA increased with age and hyperglycemia in GK rat kidneys, whereas in normoglycemic Wistar rat kidneys there was a decline with age. High glucose significantly increased THBP mRNA (92+/-37 vs 18+/-4, p<0.005), and protein in HMCs. The expression of THBP as a fusion protein in transfected HMCs resulted in reduction of glucose-induced intracellular ROS. We have shown that THBP mRNA is increased in diabetic kidney and heart, is regulated by high glucose in renal cells, and appears to attenuate glucose-induced intracellular ROS. These data suggest that THBP may be involved in the cellular pathways activated in response to glucose. This is the first report linking hyperglycemia with THBP and suggests that the role of THBP in diabetic complications should be further investigated.

Regular moderate exercise reduces advanced glycation and ameliorates early diabetic nephropathy in obese Zucker rats

Advanced glycation end products (AGEs) play a key role in the pathogenesis of diabetes and its complications, including the diabetic nephropathy. The renoprotective effects of exercise are well known; however, the mechanisms remain elusive. Here we examined whether a regular moderate exercise in obese Zucker rats (OZR), a model of diabetes- and obesity-associated nephropathy, will affect the development of early renal injury in OZR possibly via alteration of AGEs formation. The OZR were left without exercise (sedentary) or subjected to 10 weeks intermittent treadmill running of moderate intensity. Compared with sedentary OZR, kidneys of running OZR had significantly less glomerular mesangial expansion and tubulointerstitial fibrosis. Running OZR had significantly lower plasma AGEs-associated fluorescence and N(epsilon)-carboxymethyllysine. Correspondingly, renal AGEs and N(epsilon)-carboxymethyllysine content were lower in running OZR. Systemically, exercise increased aerobic metabolism, as apparent from urinary metabolite profiling. No differences in plasma glucose, insulin, or lipid profile were found between the 2 groups. Apart from lower advanced oxidation protein products (a marker of myeloperoxidase activity), no other marker of inflammation was altered by exercise, either systemically or locally in kidneys. No indication of changed oxidative status was revealed between the groups. Exercise in OZR decreased advanced glycation. This might represent the early event of exercise-induced renoprotection in diabetic nephropathy in OZR. If confirmed in clinical studies, regular moderate exercise could represent an easy and effective nonpharmacologic approach to reduce advanced glycation.

Functional annotations of diabetes nephropathy susceptibility loci through analysis of genome-wide renal gene expression in rat models of diabetes mellitus

Background

Hyperglycaemia in diabetes mellitus (DM) alters gene expression regulation in various organs and contributes to long term vascular and renal complications. We aimed to generate novel renal genome-wide gene transcription data in rat models of diabetes in order to test the responsiveness to hyperglycaemia and renal structural changes of positional candidate genes at selected diabetic nephropathy (DN) susceptibility loci.

Methods

Both Affymetrix and Illumina technologies were used to identify significant quantitative changes in the abundance of over 15,000 transcripts in kidney of models of spontaneous (genetically determined) mild hyperglycaemia and insulin resistance (Goto-Kakizaki-GK) and experimentally induced severe hyperglycaemia (Wistar-Kyoto-WKY rats injected with streptozotocin [STZ]).

Results

Different patterns of transcription regulation in the two rat models of diabetes likely underlie the roles of genetic variants and hyperglycaemia severity. The impact of prolonged hyperglycaemia on gene expression changes was more profound in STZ-WKY rats than in GK rats and involved largely different sets of genes. These included genes already tested in genetic studies of DN and a large number of protein coding sequences of unknown function which can be considered as functional and, when they map to DN loci, positional candidates for DN. Further expression analysis of rat orthologs of human DN positional candidate genes provided functional annotations of known and novel genes that are responsive to hyperglycaemia and may contribute to renal functional and/or structural alterations.

Conclusion

Combining transcriptomics in animal models and comparative genomics provides important information to improve functional annotations of disease susceptibility loci in humans and experimental support for testing candidate genes in human genetics.

Distinct genetic regulation of progression of diabetes and renal disease in the Goto-Kakizaki rat

Goto-Kakizaki (GK) rats develop early-onset type 2 diabetes (T2D) symptoms, with signs of diabetic nephropathy becoming apparent with aging. To determine whether T2D and renal disease share similar genetic architecture, we ran a quantitative trait locus (QTL) analysis in the F2 progeny of a GK x Brown Norway (BN) rat cross. Further, to determine whether genetic components change over time, we ran the QTL analysis on phenotypes collected longitudinally, at 3, 6, 9 and 12 mo, from the same animals. We confirmed three chromosomal regions that are linked to early diabetes phenotypes (chromosomes 1, 5, and 10) and a single region involved in the late progression of the disorder (chromosome 4). A single region was identified for the onset of the renal phenotype proteinuria (chromosome 5). This region overlaps the diabetic QTL, although it is not certain whether similar genes are involved in both phenotypes. A second QTL linked to the progression of the renal phenotype was found on chromosome 7. Linkage for triglyceride and cholesterol levels were also identified (chromosomes 7 and 8, respectively). These results demonstrate that, in general, different genetic components control diabetic and renal phenotypes in a diabetic nephropathy model. Furthermore, these results demonstrate that, over time, different genetic components are involved in progression of disease from those that were involved in disease onset. This observation would suggest that clinical studies collecting participants over a wide age distribution may be diluting genetic effects and reducing power to detect true effects.

Exercise training enhanced myocardial endothelial nitric oxide synthase (eNOS) function in diabetic Goto-Kakizaki (GK) rats

BACKGROUND

Different mechanisms of diabetic-induced NO dysfunction have been proposed and central to most of them are significant changes in eNOS function as the rate-limiting step in NO bioavailability. eNOS exists in both monomeric and dimeric conformations, with the dimeric form catalyzing the synthesis of nitric oxide, while the monomeric form catalyzes the synthesis of superoxide (O2-). Diabetic-induced shifts to decrease the dimer:monomer ratio is thought to contribute to the degradation of nitric oxide (NO) bioavailability. Exercise has long been useful in the management of diabetes. Although exercise-induced increases expression of eNOS has been reported, it is unclear if exercise may alter the functional coupling of eNOS.

METHODS

To investigate this question, Goto-Kakizaki rats (a model of type II diabetes) were randomly assigned to a 9-week running program (train) or sedentary (sed) groups.

RESULTS

Exercise training significantly (p < .05) increased plantaris muscle cytochrome oxidase, significantly improved glycosylated hemoglobin (sed: 7.33 +/- 0.56%; train: 6.1 +/- 0.18%), ad improved insulin sensitivity. Exercise increased both total eNOS expression and the dimer:monomer ratio in the left ventricle LV (sed: 11.7 +/- 3.2%; train: 41.4 +/- 4.7%). Functional analysis of eNOS indicated that exercise induced significant increases in nitric oxide (+28%) production and concomitant decreases in eNOS-dependent superoxide (-12%) production. This effect was observed in the absence of tetrahydrobiopterin (BH4), but not in the presence of exogenous BH4. Exercise training also significantly decreased NADPH-dependent O2- activity.

CONCLUSION

Exercise-induced increased eNOS dimerization resulted in an increased coupling of the enzyme to facilitate production of NO at the expense of ROS generation. This shift that could serve to decrease diabetic-related oxidative stress, which should serve to lessen diabetic-related complications.

Chromium supplementation improves glucose tolerance in diabetic Goto-Kakizaki rats

Chromium supplementation (Cr) may be useful in the management of diabetes and appears to improve some aspects of glucose handling. However, several studies have used either high doses of Cr supplementation or have placed control animals on a Cr-deficient diet. We therefore wanted to test whether Cr dosages in the ranges that more closely approximate recommended levels of supplementation in humans are efficacious in glycemic control under normal dietary conditions. Euglycemic Wistar or diabetic Goto-Kakizaki (GK) rats (a model of nonobese NIDDM) were assigned to water (control) or chromium picolinate (Cr-P) supplementation (1 or 10 mg/kg/day) groups for up to 32 weeks. Glucose tolerance was tested following an overnight fast by injecting sterile glucose (1.0 g/kg, i.p.) and then measuring blood glucose at select times to determine the sensitivity to glucose by calculation of the area under the curve. Cr-P did not significantly alter the growth of the animals. In the euglycemic Wistar rats, Cr-P supplementation did not alter the response to a glucose tolerance test. In the GK rats, Cr-P supplementation significantly improved glucose tolerance at both levels of Cr-P supplementation (1 mg/kg/day: H20; 100 +/- 11%; Cr-P 70 +/- 8%; 10 mg/kg/day: H(2)0; 100 +/- 10%; Cr-P 66 +/- 9 %). Cr-P supplementation produced a small improvement in some indices of glycemic control. There were no differences observed for the two levels of Cr-P supplementation suggested that we did not identify a threshold for Cr-P effects, and future studies may use lower doses to find a threshold effect for improving glucose tolerance in diabetics.

Upregulation of AT2 receptor and iNOS impairs angiotensin II-induced contraction without endothelium influence in young normotensive diabetic rats

Diabetes and insulin resistance are associated with an increased risk of hypertension and cardiovascular disease. Recent evidence demonstrates that AT2 receptors (AT2R) play an important role in the hemodynamic control of hypertension by vasodilation. The quantitative significance of AT2R in the establishment of diabetic vascular dysfunction, however, is not well defined and needs further investigation. Goto-Kakizaki (GK) rats, a polygenic model of spontaneous normotensive type 2 diabetes, were used to examine any abnormalities in cardiovascular function associated with AT2R at the early stage of the disease without endothelium influence. Using a myograph to measure the isometric force, we observed that ANG II-induced contraction was impaired in denuded GK aorta compared with control Wistar-Kyoto (WKY) aorta and exhibited a retarded AT1R antagonist response and enhanced Rho kinase signaling. When AT1R were blocked, ANG II induced a significant vasodilation of precontracted GK aorta via AT2R. The protein and mRNA of AT2R were increased in diabetic GK denuded aorta. Blocking AT2R restored the ANG II-induced contraction in the GK vasculature to control levels, demonstrating a counteractive role for AT2R in AT1R-induced contraction. Inhibition of inducible nitric oxide synthase (iNOS) by NG-monomethyl-L-arginine mimicked AT2R inhibition in denuded GK aorta, suggesting that AT2R-induced vasodilation was dependent on iNOS/NO generation. The protein and mRNA of iNOS were also increased in GK aorta. In conclusion, these results clearly demonstrate that enhanced AT2R and iNOS-induced, NO-mediated vasodilation impair ANG II-induced contraction in an endothelium-independent manner at the early stage of type 2 diabetes.

Immunohistochemical and electron-microscopic observation of beta-cells in pancreatic islets of spontaneously diabetic Goto-Kakizaki rats

The Goto-Kakizaki (GK) rat offers a genetic model of type 2 diabetes and displays profoundly defective insulin secretion leading to basal hyperglycemia. This animal is widely used for studying type 2 diabetes. However, the morphological characteristics of the pancreatic islets of Langerhans in GK rats are not fully understood. The present study sought to clarify this issue using immunohistochemical and electron microscopic techniques. GK rats were killed at 7, 14, 21, and 35 weeks of age. Structural islet changes were not observed at 7 weeks old. At 14 and 21 weeks of age, GK rats displayed histopathological islet changes. The general shape of islets became irregular, and immunoreaction of beta-cells against antiinsulin appeared diffusely weakened. Electron microscopy revealed that the numbers of so-called beta-granules decreased and the numbers of immature granules increased. The Golgi apparatus of beta-cells was developed and the cisternae of rough endoplasmic reticulum were often dilated, indicating hyperfunction of the cells. However, at 35 weeks old, immunoreactivities of dispersed beta-cells into the exocrine portion recovered, and numbers of secretory granules increased again and features of the cell organelles did not display hyperfunction. These results suggest that insulin deficiency in GK rats is not caused by simple dysfunction and/or degeneration of beta-cells but rather by more complicated events within cells.

High-fat diet in low-dose-streptozotocin-treated heminephrectomized rats induces all features of human type 2 diabetic nephropathy: a new rat model of diabetic nephropathy

BACKGROUND AND AIM

We have developed a new rat model that mimics the natural course of diabetic nephropathy seen in type 2 diabetes.

METHODS

Nine days after intravenous injection of streptozotocin (STZ) (40 mg/kg) or vehicle to 8-week-old male Sprague-Dawley rats, the animals' right kidneys were surgically removed. Two weeks after surgery, the STZ-injected rats were fed on either a high-fat (ST+HF) or a normal (ST) diet, while the vehicle-injected rats were fed on the high-fat diet (HF).

RESULTS

Baseline biochemical markers did not differ between the three groups. Only the ST+HF group showed a significant increase in plasma glucose levels after 15 weeks, and simultaneously plasma insulin levels started to decrease, followed by an increase in plasma total cholesterol and triglyceride levels at 25 weeks and slightly later by an increase in blood pressure. In the ST+HF group, significant microalbuminuria was detected at 15 weeks followed by overt proteinuria, both of which were absent in the other two groups. Also in ST+HF, the creatinine clearance rate increased until week 15, and then gradually decreased. Histologically, ST+HF rats showed mesangial expansion at week 25, and diffuse glomerular sclerosis at the end of the experiments.

CONCLUSION

The chronological changes in biochemical, physiological and histological markers in ST+HF rats are reminiscent of human type 2 diabetes and nephropathy. Our new model of type 2 diabetic nephropathy should help us to understand the pathophysiology of the disease and serve to explore measures to prevent and treat diabetic nephropathy.

Renoprotective effect of a dopamine D3 receptor antagonist in experimental type II diabetes

Diabetic nephropathy is the leading cause of end-stage renal disease. Dopamine receptors are involved in the regulation of renal hemodynamics and may play a role in diabetes-induced hyperfiltration. To test this hypothesis, we investigated the renal effect of a dopamine D3 receptor antagonist (D3-RA) in hypertensive type II diabetic SHR/N-cp rats. Lean and obese SHR/N-cp rats were randomly assigned to D3-RA, angiotensin-converting enzyme inhibitor (ACE-i), or D3-RA+ACE-i treatment or control conditions. Treated animals were given the D3-RA A-437203 (10 mg/kg/body weight (BW)/day) or the ACE-i trandolapril (0.3 mg/kg BW/day) or a combination of both. At 6 months following perfusion, fixed kidneys were analyzed by morphological and stereological methods. Indices of renal damage (glomerulosclerosis, glomerulosclerosis damage index (GSI), tubulointerstitial and vascular damage), glomerular geometry and functional variables such as urinary albumin excretion, glomerular filtration rate, blood pressure, blood chemistry and BW were determined. The GSI (score 0-4) was significantly higher (P<0.05) in untreated diabetic animals (1.62+/-0.3) compared to nondiabetic controls (0.4+/-0.2) and the treatment groups (D3-RA: 0.31+/-0.12; ACE-i: 0.29+/-0.1; combination treatment: 0.12+/-0.01). Urinary albumin excretion (mg/24 h) was higher in untreated diabetic controls (102+/-19) compared to nondiabetic controls (31+/-12) and the treatment groups (D3-RA: 44+/-15; ACE-i: 41+/-13; combination treatment: 15+/-8). Mean glomerular volume was higher in untreated diabetic animals compared to nondiabetic controls and to the treatment groups. Desmin expression, a marker of podocyte damage, was elevated in untreated diabetic controls and diminished in all treatment groups. These data suggest that in a model of type II diabetes, the dopamine D3-RA had a beneficial effect on renal morphology and albuminuria, which was comparable in magnitude to that of ACE-i treatment.

Protein Kinase C β Inhibitor LY333531 Attenuates Intercellular Adhesion Molecule-1 and Monocyte Chemotactic Protein-1 Expression in the Kidney in Diabetic Rats

In vitro studies have shown that activation of protein kinase C (PKC) is a key mediator of intercellular adhesion molecule-1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1) in a range of cell types and in response to high glucose, however, its role in the in vivo setting has not been clearly delineated. Streptozotocin-induced diabetic rats were treated with the PKC-beta isoform inhibitor LY333531 for 8 weeks. LY333531 treatment significantly attenuated increased urinary albumin excretion rate and glomerular volume and tubulointerstitial injury index as well as elevated PKC activity and PKC-beta protein expression in the kidney. Level of malondialdehyde was markedly higher and antioxidant enzyme activity such as superoxide diamutase and catalase as well as glutathione peroxidase were significantly lower in the kidney from diabetic rats than that of the control group. LY333531 administration could remit these changes. Increased macrophages recruitment as well as ICAM-1 and MCP-1 protein expression in the kidney were significantly inhibited by LY333531 in diabetic rats. It is concluded that mechanism of renoprotection of LY333531 may be correlated, at least partly, with suppression of increased macrophages recruitment and overexpression of ICAM-1 and MCP-1 in diabetic rats.