Renal lesions in spontaneous insulin-dependent diabetes mellitus in the nonobese diabetic mouse: acute phase of diabetes

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.

Consequences of Both Coxsackievirus B4 and Type 1 Diabetes on Female Non-Obese Diabetic Mouse Kidneys

Despite the 2019 Executive Order on Advancing American Kidney Health Initiative, kidney disease has moved up in rank from the 9th to the 8th leading cause of death in the United States. A recent push in the field of nephrology has been to identify molecular markers and/or molecular profiles involved in kidney disease process or injury that can help identify the cause of injury and predict patient outcomes. While these studies have had moderate success, they have not yet considered that many of the health conditions that cause kidney disease (diabetes, hypertension, etc.) can also be caused by environmental factors (such as viruses), which in and of themselves can cause kidney disease. Thus, the goal of this study was to identify molecular and phenotypic profiles that can differentiate kidney injury caused by diabetes (a health condition resulting in kidney disease) and coxsackievirus B4 (CVB4) exposure (which can cause diabetes and/or kidney disease), both alone and together. Non-obese diabetic (NOD) mice were used for this study due to their susceptibility to both type 1 diabetes (T1D)- and CVB4-mediated kidney injury, in order to glean a better understanding of how hyperglycemia and viral exposure, when occurring on their own and in combination, may alter the kidneys’ molecular and phenotypic profiles. While no changes in kidney function were observed, molecular biomarkers of kidney injury were significantly up- and downregulated based on T1D and CVB4 exposure, both alone and together, but not in a predictable pattern. By combining individual biomarkers with function and phenotypic measurements (i.e., urinary albumin creatinine ratio, serum creatinine, kidney weight, and body weight), we were able to perform an unbiased separation of injury group based on the type of injury. This study provides evidence that unique kidney injury profiles within a kidney disease health condition are identifiable, and will help us to identify the causes of kidney injury in the future.

Tolerogenic Iron Oxide Nanoparticles in Type 1 Diabetes: Biodistribution and Pharmacokinetics Studies in Nonobese Diabetic Mice

Nanoparticle (NP) administration is among the most attractive approaches to exploit the synergy of different copackaged molecules for the same target. In this work, iron oxide NPs are surface-engineered for the copackaging of the autoantigen proinsulin, a major target of adaptive immunity in type 1 diabetes (T1D), and 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methylester (ITE), a small drug conditioning a tolerogenic environment. Magnetic resonance imaging (MRI) combined with magnetic quantification are used to investigate NP biokinetics in nonobese diabetic (NOD) mice and control mice in different organs. Different NP biodistribution, with in particular enhanced kidney elimination and a stronger accumulation in the pancreas for prediabetic NOD mice, is observed. This is related to preferential NP accumulation in the pancreatic inflammatory zone and to enhancement of renal elimination by diabetic nephropathy. For both mouse strains, an MRI T2 contrast enhancement at 72 h in the liver, pancreas, and kidneys, and indicating recirculating NPs, is also found. This unexpected result is confirmed by magnetic quantification at different time points as well as by histological evaluation. Besides, such NPs are potential MRI contrast agents for early diagnosis of T1D.

Diabetes and pregnancy in Wistar rats: renal effects for mothers in the postpartum period

In this study, diabetes mellitus (DM) was induced in Wistar rats during pregnancy and maintained in the postpartum period (PP) and we evaluated systolic blood pressure (SBP), glomerular filtration rate (GFR) and renal immunohistochemical and morphometric studies from different groups: G1 (non-pregnant control rats), G2 (non-pregnant diabetic rats), G3 (control mothers) and G4 (diabetic mothers). We found that there were no differences in relation to SBP, but there was a tendency for reduction in GFR from G4 compared with the other groups (G). There was increased total kidney weight/body weight ratio of G4 compared with other G. There were increase in glomerular tuft area in G3 and G4 compared with G1 and G2. G2 and G4 showed even higher percentage of cortical collagen. G3 showed increased glomerular proliferating cells compared with G1 and G2, while in G4 this number was smaller than G3. Cell proliferation was higher in the tubulointerstitial (TBI) compartment from G4. Glomerular and TBI α-smooth muscle actin expression was increased in G4 compared with other G. The glomerular p-p38 expression showed a pattern similar to proliferation cell nuclear antigen, with a reduction of p-p38 in G4 relative to other G. The immunoreactivity of p-JNK was higher in both the glomeruli and TBI compartment in G4 compared with G1, G2 and G3. The DM induced during pregnancy and maintained in the PP resulted in renal structural and functional changes to mothers. In addition, altered mitogen-activated protein kinase expression in association with these changes may play an important role in renal damage observed in the present investigation.

Antioxidant diet and sex interact to regulate NOS isoform expression and glomerular mesangium proliferation in Zucker diabetic rat kidney

Oxidative stress contributes substantially to the pathophysiology of diabetic nephropathy (DN). Consumption of an antioxidant-fortified (AO) diet from an early age prevents or delays later development of DN in the Zucker rat female with type 2 diabetes. We hypothesize this is due to effects on mesangial matrix and renal nitric oxide synthase (NOS) distribution and to sex-specific differences in NOS responses in the diabetic kidney. Total glomerular tuft area (GTA) and PAS-positive tuft area (PTA), endothelial (e), neuronal (n) and inducible (i) NOS were quantified in males and females on AO or regular (REG) diet at 6 and 20 weeks of age. eNOS was observed in glomeruli and tubules. nNOS predominantly localized to tubular epithelium in both cortex and medulla. iNOS was expressed in proximal and distal tubules and collecting ducts. Sex, diabetes duration and AO diet affected the distribution of the three isoforms. GTA and PTA increased with duration of hyperglycemia and showed a negative correlation with renal levels of all NOS isoforms. AO diet in both genders was associated with less PAS-positive staining and less mesangial expansion than the REG diet, an early increase in cortical iNOS in males, and sex-specific changes in cortical eNOS at 20 weeks. These effects of AO diet may contribute to sex-specific preservation of renal function in females.

A Long-Term High-Fat/High-Sucrose Diet Promotes Kidney Lipid Deposition and Causes Apoptosis and Glomerular Hypertrophy in Bama Minipigs

Metabolic syndrome can induce chronic renal injury in humans. In the present study, Bama minipigs were fed a high-fat/high-sucrose diet (HFHSD) for 23 months, which caused them to develop the pathological characteristics of metabolic syndrome, including obesity, hyperinsulinemia, and hyperlipidemia, and resulted in kidney tissue damage. In the HFHSD group, the ratio of the glomus areas to the glomerulus area and the glomerular density inside the renal cortex both decreased. Lipid deposition in the renal tubules was detected in the HFHSD group, and up-regulated expression levels of SREBP-1, FABP3 and LEPR promoted lipid deposition. The decreased levels of SOD, T-AOC and GSH-PX indicated that the antioxidant capacity of the renal tissues was diminished in the HFHSD group compared with MDA, which increased. The renal tissue in the HFHSD group exhibited clear signs of inflammation as well as significantly elevated expression of key genes associated with inflammation, including tumor necrosis factor-α (TNF-α) and macrophage migration inhibitory factor (MIF), compared with the control group. The tubular epithelial cells in the HFHSD group displayed significantly greater numbers of apoptotic cells, and the expression of proliferating cell nuclear antigen (PCNA) in the renal tubules decreased. Caspase-3 expression increased significantly, and the transcription factor nuclear factor κB (NF-κB) was activated and translocated into the nucleus. In conclusion, long-term HFHSDs cause metabolic syndrome and chronic renal tissue injury in Bama minipigs. These findings provide a foundation for further studies investigating metabolic syndrome and nephropathy.

Understanding type 1 diabetes: etiology and models

Type 1 diabetes is a complex disease involving a combination of factors, such as genetic susceptibility, immunologic dysregulation and exposure to environmental triggers. Animal models serve an important function both in elucidating the pathophysiology and preliminary screening of antidiabetic molecules. Hence, the development of models for type 1 diabetes can be broadly divided into 3 categories, namely: identification of spontaneously developing type 1 diabetes mellitus strains, creating diabetes-prone species through gene transfer techniques and forced destruction of islet cells through chemical or surgical means. This review discusses the models used to study type 1 diabetes with special emphasis on genetics.

Development of hyperglycemia and diabetes in captive Polish bank voles

Diabetes has been detected in Danish and Swedish bank voles (Myodes glareolus). There are no data, however, concerning the prevalence of diabetes in populations from other geographic regions. We investigated the frequency and physiological effects of glucose metabolism disorders in captive bank voles from Poland. Single measurement of fasting blood glucose concentration performed in the 3-4month old captive-born bank Polish voles without any disease symptoms showed that 8% of individuals (22/284) displayed an impaired fasting glucose (IFG, blood glucose (BG) ≥100mg/dL) and 1% (4/284) showed hyperglycemia (BG ≥126mg/dL) which could suggest diabetes. Next, we analyzed blood glucose in samples taken once a month from an additional cohort of bank voles with (FHD), or without (H), a family history of diabetes. The prevalence of IFG at age six months was 26% (16/62) among bank voles from the H group. In the FHD group the prevalence increased to 49% (43/88), and additional 12% (11/88) became diabetic (DB, BG ≥126mg/dL at two time points). Postnatal stress (three maternal deprivations before weaning) did not affect the risk of developing IFG or DB in H voles, but significantly reduced the frequency of glucose metabolism disorders (IFG and DB combined) in FHD voles. IFG was associated with hyperinsulinemia, but not with other biochemical disturbances. Diabetic animals displayed a progressive malformation and vacuolization of β-cells in the pancreas, without visible leukocytic infiltrations. In summary, our results indicate that Polish captive bank voles can develop diabetes, which shows features of both type 1 and type 2 diabetes in humans. Risk of diabetes is higher in animal with FHD.

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.

Kidney Injury Biomarkers in Hypertensive, Diabetic, and Nephropathy Rat Models Treated with Contrast Media

Contrast-induced nephropathy (CIN) refers to a decline in renal function following exposure to iodinated contrast media (CM). The present study was initiated to explore the role of known human risk factors (spontaneous hypertension, diabetes, protein-losing nephropathy) on CIN development in rodent models and to determine the effect of CM administration on kidney injury biomarkers in the face of preexisting kidney injury. Spontaneously hypertensive rats (hypertension), streptozotocin-treated Sprague Dawley rats (diabetes), and Dahl salt-sensitive rats (protein-losing nephropathy) were given single intravenous injections of the nonionic, low osmolar contrast medium, iohexol. Blood urea nitrogen (BUN), serum creatinine (sCr), and urinary biomarkers; albumin, lipocalin 2 (Lcn-2), osteopontin (Opn), kidney injury molecule 1 (Kim-1), renal papillary antigen 1 (Rpa-1), α-glutathione S-transferase (α-Gst), µ-glutathione S-transferase (µ-Gst), and beta-2 microglobulin (β2m) were measured in disease models and appropriate controls to determine the response of these biomarkers to CM administration. Each disease model produced elevated biomarkers of kidney injury without CM. Preexisting histopathology was exacerbated by CM but little or no significant increases in biomarkers were observed. When 1.5-fold or greater sCr increases from pre-CM were used to define true positives, receiver–operating characteristic curve analysis of biomarker performance showed sCr was the best predictor of CIN across disease models. β2m, Lcn-2, and BUN were the best predictors of histopathology defined kidney injury.

Knockout of toll-like receptor-2 attenuates both the proinflammatory state of diabetes and incipient diabetic nephropathy

OBJECTIVE

Type 1 diabetes (T1DM) is a proinflammatory state and confers an increased risk for vascular complications. Toll-like receptors (TLR) could participate in diabetic vasculopathies. Whether TLR activation contributes to the proinflammatory state of T1DM and the pathogenesis of diabetic nephropathy remains unknown.

METHODS AND RESULTS

We induced T1DM in TLR2 knockout mice (TLR2-/-) and wild-type littermates (C57BL/6J-WT) using streptozotocin (STZ). Fasting blood, peritoneal macrophages, and kidneys were obtained for flow cytometry, Western blot, microscopy, and cytokine assays at 6 and 14 weeks after induction of diabetes. Macrophage TLR2 expression and MyD88-dependent signaling were increased in diabetic mice (WT+STZ) compared with nondiabetic WT mice. These biomarkers were attenuated in diabetic TLR2-/- macrophages. WT+STZ mice showed increased kidney:body weight ratio due to cell hypertrophy, increased albuminuria, decreased kidney nephrin, podocin, and podocyte number and increased transforming growth factor-β and laminin compared with WT mice. Nephrin, podocin, and podocyte number and effacement were restored, and transforming growth factor-β and laminin levels were decreased in TLR2-/-+ STZ mice kidneys versus WT+STZ. Peritoneal and kidney macrophages were predominantly M1 phenotype in WT+STZ mice; this was attenuated in TLR2-/-+STZ mice.

CONCLUSIONS

These data support a role for TLR2 in promoting inflammation and early changes of incipient diabetic nephropathy, in addition to albuminuria and podocyte loss.

Renin-angiotensin system may trigger kidney damage in NOD mice

Diabetic nephropathy is a complication of diabetes and one of the main causes of end-stage renal disease. A possible causal link between renin-angiotensin aldosterone system (RAAS) and diabetes is widely recognized but the mechanisms by which the RAAS may lead to this complication remains unclear. The aim of this study was to evaluate angiotensin-I converting enzyme (ACE) activity and expression in numerous tissues, especially kidney, of non-obese diabetic mouse. Kidney, lung, pancreas, heart, liver and adrenal tissues from diabetic and control female NOD mice were homogenized for measurement of ACE activity, SDS-PAGE and Western blotting for ACE and ACE2, immunohistochemistry for ACE and angiotensins I, II and 1-7 and bradykinin quantification. ACE activity was higher in kidney, lung and adrenal tissue of diabetic mice compared with control mice. In pancreas, activity was decreased in the diabetic group. Western blotting analysis indicated that both groups presented ACE isoforms with molecular weights of 142 and 69 kDa and a decrease in ACE2 protein expression. Angiotensin concentrations were not altered within groups, although bradykinin levels were higher in diabetic mice. The immunohistochemical study in kidney showed an increase in tubular ACE expression. Our results show that the RAAS is affected by diabetes and the elevated ACE/ACE2 ratio may contribute to renal damage.

Diabetic kidney lesions of GIPRdn transgenic mice: podocyte hypertrophy and thickening of the GBM precede glomerular hypertrophy and glomerulosclerosis

Diabetic nephropathy is the leading cause of end-stage renal disease and the largest contributor to the total cost of diabetes care. Rodent models are excellent tools to gain more insight into the pathogenesis of diabetic nephropathy. In the present study, we characterize the age-related sequence of diabetes-associated kidney lesions in GIPRdn transgenic mice, a novel mouse model of early-onset diabetes mellitus. Clinical-chemical analyses as well as qualitative and quantitative morphological analyses of the kidneys of GIPRdn transgenic animals and nontransgenic littermate controls were performed at 3, 8, 20, and 28 wk of age. Early renal changes of transgenic mice consisted of podocyte hypertrophy, reduced numerical volume density of podocytes in glomeruli, and homogenous thickening of the glomerular basement membrane, followed by renal and glomerular hypertrophy as well as mesangial expansion and matrix accumulation. At 28 wk of age, glomerular damage was most prominent, including advanced glomerulosclerosis, tubulointerstitial lesions, and proteinuria. Real-time PCR demonstrated increased glomerular expression of Col4a1, Fn1, and Tgfb1. Immunohistochemistry revealed increased mesangial deposition of collagen type IV, fibronectin, and laminin. The present study shows that GIPRdn transgenic mice exhibit renal changes that closely resemble diabetes-associated kidney alterations in humans. Data particularly from male transgenic mice indicate that podocyte hypertrophy is directly linked to hyperglycemia, without the influence of mechanical stress. GIPRdn transgenic mice are considered an excellent new tool to study the mechanisms involved in onset and progression of diabetic nephropathy.

Cellular and humoral immune responses in the early stages of diabetic nephropathy in NOD mice

This study was designed to examine immunopathology of diabetic nephropathy in non-obese diabetic (NOD) mice and to investigate the involvement of cellular and humoral immunity at various time points after diabetes onset. We found that the glomeruli of diabetic NOD mice were infiltrated with T and B cells, as well as CD11c+ dendritic cells, which had close contact with CD4+ and CD8+ T cells in the infiltrates. We also found that IgG deposits in the glomeruli of diabetic NOD mice were accompanied by the presence of complement C3. Moreover, the serum from diabetic mice contained autoantibodies directed towards components of the glomeruli and these antibodies were not present in non-diabetic NOD mice. The immune changes in the kidney occurred together with increasing kidney weight and urinary albumin excretion along with duration of diabetes. We provide evidence that infiltrating lymphocytes and anti-kidney autoantibodies may be involved in diabetic nephropathy in autoimmune diabetes in the NOD mouse. Understanding the role that the immune system plays in the pathogenesis of diabetic nephropathy could lead to identification of new strategies and/or additional therapeutic targets for prevention and treatment of diabetic nephropathy.

Insulin therapy in renal disease

Diabetes mellitus (DM) is the main cause of end-stage renal disease (ESRD). Conversely, chronic renal failure (CRF) is also associated with diverse alterations in carbohydrate and insulin metabolism. CRF-induced metabolic disorders should be borne in mind when treating diabetic patients, to ensure the introduction of adequate therapy adjustments that are in line with the onset of renal function decline. Moreover, several specific therapies employed in CRF may also influence pharmacological therapy of DM in uraemic patients. Adequate glycaemic control has also been associated with a reduction in the onset and progression of diabetic nephropathy as well as in the morbidity and mortality in uraemic diabetic patients during dialysis. Intensive insulin therapy can notably improve glycemic control and it should be considered part of the management of insulin-treated CRF diabetic patients. Insulin analogues have been recently evaluated in CRF diabetic patients, with encouraging results. In this study, we review the more relevant aspects related to insulin therapy in diabetic patients with different degrees of renal failure and in patients with ESRD, both in conservative therapy and dialysis.

Can rodent models of diabetic kidney disease clarify the significance of early hyperfiltration?: recognizing clinical and experimental uncertainties

In the past, hyperfiltration and increased glomerular capillary pressure have been identified as important determinants of the development of DN (diabetic nephropathy). Recently, some basic research and clinical reviews on DN have omitted identifying hyperfiltration as an important risk factor. At the same time, different rodent models of DN have been described without and with documented hyperfiltration. In the present review, the importance of hyperfiltration is reassessed, reviewing key clinical and research studies, including the first single nephron studies in a mouse model of DN. From clinical studies of Type 1 and Type 2 diabetes mellitus, it is clear that many patients do not have early hyperfiltration and, even when present, its contribution to subsequent DN remains uncertain. Key mechanisms underlying hyperfiltration in rodent models are reviewed. Findings on intrarenal NO metabolism and the control of single-nephron GFR (glomerular filtration rate) in rodent models of DN are also presented. Characterization of valid experimental models of DN should include a careful delineation of the absence or presence of early hyperfiltration, with special efforts made to establish the specific role hyperfiltration may play in the emergence of DN.

Genistein and daidzein prevent diabetes onset by elevating insulin level and altering hepatic gluconeogenic and lipogenic enzyme activities in non-obese diabetic (NOD) mice

BACKGROUND

Non-obese diabetic (NOD) mice are regarded as being excellent animal models of human type 1 diabetes or insulin dependent diabetes (IDDM). This study investigated the beneficial effects of genistein and daidzein on IDDM, an autoimmune disease.

METHODS

Female NOD mice were divided into control, genistein (0.02%, w/w) and daidzein (0.02%, w/w) groups. Blood glucose level, plasma biomarkers, hepatic glucose and lipid regulating enzyme activities and pancreas immunohistochemistry analysis were examined after a 9-week experimental period.

RESULTS

Blood glucose levels of genistein and daidzein groups were 40 and 36% of control value at the end of study (9th week). The genistein and daidzein supplements increased insulin/glucagon ratio and C-peptide level with preservation of insulin staining beta-cell of pancreas in the NOD mice. In the liver, genistein and daidzein supplements resulted in lowering glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) activities, while increasing two lipogenic enzymes activities, malic enzyme and glucose-6-phosphate dehydrogenase (G6PD), compared to the control group. Significantly, genistein and daidzein supplementation lowered the activities of fatty acid beta-oxidation and carnitine palmitoyltransferase (CPT) in these mice. Genistein and daidzein also improved plasma triglyceride and free fatty acid (FFA) concentrations compared to the control group.

CONCLUSIONS

These results suggest that genistein and daidzein play important roles in regulation of glucose homeostasis in type 1 diabetic mice by down-regulating G6Pase, PEPCK, fatty acid beta-oxidation and CPT activities, while up-regulating malic enzyme and G6PD activities in liver with preservation of pancreatic beta-cells. The supplementation of genistein and daidzein are seemingly helpful for preventing IDDM onset.

Hormonal status affects the progression of STZ-induced diabetes and diabetic renal damage in the VCD mouse model of menopause

Changes in the estrogen/testosterone balance at menopause may negatively influence the development of diabetic kidney disease. Furthermore, recent studies suggest that changes in hormone levels during perimenopause may influence disease development. Injection of 4-vinylcyclohexene diepoxide (VCD) in B(6)C(3)F(1) mice induces gradual ovarian failure, preserving both the perimenopausal (peri-ovarian failure) and menopausal (post-ovarian failure) periods. To address the impact of the transition into menopause on the development of diabetes and diabetic kidney damage, we used streptozotocin (STZ)-induced diabetes in the VCD model of menopause. After 6 wk of STZ-induced diabetes, blood glucose was significantly increased in post-ovarian failure (post-OF) diabetic mice compared with cycling diabetic mice. In peri-ovarian failure (peri-OF) diabetic mice, blood glucose levels trended higher but were not significantly different from cycling diabetic mice, suggesting a continuum of worsening blood glucose across the menopausal transition. Cell proliferation, an early marker of damage in the kidney, was increased in post-OF diabetic mice compared with cycling diabetic mice, as measured by PCNA immunohistochemistry. In post-OF diabetic mice, mRNA abundance of early growth response-1 (Egr-1), collagen-4alpha1, and matrix metalloproteinase-9 were increased and 3beta-hydroxysteroid dehydrogenase 4 (3beta-HSD4) and transforming growth factor-beta(2) (TGF-beta(2)) were decreased compared with cycling diabetic mice. In peri-OF diabetic mice, mRNA abundance of Egr-1 and 3beta-HSD4 were increased, and TGF-beta(2) was decreased compared with cycling diabetic mice. This study highlights the importance and utility of the VCD model of menopause, as it provides a physiologically relevant system for determining the impact of the menopausal transition on diabetes and diabetic kidney damage.

Functional and molecular alterations of the glomerular barrier in long-term diabetes in mice

AIMS/HYPOTHESIS

Despite the fact that diabetic nephropathy is an increasingly common disorder that may lead to uraemia, the underlying mechanisms are still poorly understood and there is no specific therapy. To clarify whether long-term diabetes alters glomerular size- or charge-selectivity or both, we studied non-obese diabetic mice for up to 40 weeks.

MATERIALS AND METHODS

During the study period, spot urine was collected and blood pressure measured. At weeks 10 and 40, the right kidney was isolated and perfused at 8 degrees C to inhibit tubular function, allowing for analysis of glomerular selectivity with albumin and Ficoll clearance. The left kidney was removed for further investigation using electron microscopy and molecular biology. Real-time PCR with low-density arrays was done to evaluate renal cortex mRNA expression of proteoglycans and other components in the glomerular barrier. After 40 weeks of diabetes, kidneys showed morphological changes typical of diabetic complications.

RESULTS

At 40 weeks, the fractional clearance for negatively charged albumin was three times higher in the diabetic animals (0.0160) than in controls (0.0051, p<0.001), while fractional clearance for neutral Ficoll 35.5 A with a Stokes Einstein radius similar to that of albumin was unaffected. In addition, protein and mRNA levels for versican and decorin were downregulated after 40 weeks of diabetes.

CONCLUSIONS/INTERPRETATION

We conclude that glomerular charge- but not size-selectivity was impaired in the diabetic animals with proteinuria. Also, glomerular components such as versican, decorin and fibromodulin were found to be downregulated after 40 weeks of diabetes.

The use of lysosomal enzymuria in the early detection and monitoring of the progression of diabetic nephropathy

Recent acquisitions on the early detection and monitoring of the progression of diabetic complications (nephropathy) using the techniques of enzymology (lysosomal enzymes) are reviewed. it appears that the kidney is the principal source of urinary lysosomal enzymes. Urinary samples for lysosomal enzyme determination can be either 24-hour or spot-collection. The use of synthetic substrates (4-methylumbelliferyl substrates) provides an easy, inexpensive, sensitive and highly reproducible method of lysosomal enzyme assay. It is recommended that more than one enzyme be assayed in the process. The use of fractional enzyme excretion (FEE) ratios is further recommended. The urinary lysosomal glycosidases investigated and found to be of particular diagnostic value in the early detection of diabetic nephropathy include N-acetyl-β-D-glucosaminidase (β-hexosaminidase, NAG), β-glucuronidase and β-galactosidase, with NAG being the most useful indicator. Urinary NAG can be used in monitoring the progression of diabetic nephropathy. The fluorimetric assay of lysosomal glycosidases is particuarly recommended in developing countries since it is simple, sensitive and inexpensive.

Pioglitazone mitigates renal glomerular vascular changes in high-fat, high-calorie-induced type 2 diabetes mellitus

Our hypothesis is that impairment of peroxisome proliferator-activated receptor-gamma (PPARgamma) initiates renal dysfunction by increasing renal glomerular matrix metalloproteinase-2 (MMP-2) activity because of increased renal homocysteine (Hcy) and decreased nitric oxide (NO) levels. C57BL/6J mice were made diabetic (D) by being fed a high-fat-calorie diet, and an increase in PPARgamma activity was induced by adding pioglitazone (Pi) to the diet. Mice were grouped as follows: normal calorie diet (N), D, N+Pi, and D+Pi (n = 6/group). The glomerular filtration rate (GFR), renal artery blood flow and pressure, and plasma glucose were measured. Renal glomeruli and preglomerular arterioles were isolated. Plasma and glomerular levels of NO, Hcy, and MMP activity were measured. The contractile response to phenylephrine and the dilatation response to acetylcholine in renal arteriolar rings were measured in a tissue myobath. In N, D, N+Pi, and D+Pi groups, respectively, GFR was 9.4 +/- 1.2, 3.9 +/- 1.1, 9.2 +/- 1.6, and 8.4 +/- 1.4 microl x min(-1) x g body wt(-1). Renovascular resistance was 140 +/- 3, 367 +/- 21, 161 +/- 9, and 153 +/- 10 mmHg x ml x min(-1). Levels of Hcy were increased from 5.8 +/- 1.5 in the N to 18.0 +/- 4.0 micromol/l in the D group. Glomerular levels of MMP-2 were increased in D mice compared with N mice, and there was no change in levels of MMP-9. Treatment with Pi ameliorated glomerular levels of MMP-2 and Hcy in the D group. Renal artery ring contraction and relaxation by phenylephrine and acetylcholine, respectively, were attenuated in the D groups compared with the N groups. Results suggest that a PPARgamma agonist ameliorates preglomerular arteriole remodeling in diabetes by decreasing tissue levels of Hcy and MMP-2 activity and increasing NO.

Leukocyte recruitment and vascular injury in diabetic nephropathy

Different types of activated leukocytes play a crucial role in the pathogenesis of most kidney diseases from acute to chronic stages; however, diabetic nephropathy was not considered an inflammatory disease in the past. This view is changing now because there is a growing body of evidence implicating inflammatory cells at every stage of diabetic nephropathy. Renal tissue macrophages, T cells, and neutrophils produce various reactive oxygen species, proinflammatory cytokines, metalloproteinases, and growth factors, which modulate the local response and increase inflammation within the diabetic kidney. Although the precise mechanisms that direct leukocyte homing into renal tissues are not fully identified, it has been reported that intercellular adhesion molecule-1 and the chemokines CCL2 and CX3CL1 probably are involved in leukocyte migration in diabetic nephropathy. This review focuses on the molecular mechanisms of leukocyte recruitment into the diabetic kidney and the involvement of immigrated immune cells in the damage to renal tissues.

Tubular changes in early diabetic nephropathy

Far from being bystanders in diabetic nephropathy, changes in the proximal tubule are important for the development of progressive diabetic kidney disease. The proximal tubule is uniquely susceptible to a variety of metabolic and hemodynamic factors associated with diabetes. Renal function and prognosis correlate better with structural lesions in the tubuli and cortical interstitium than with classical glomerular changes of diabetic nephropathy. The proximal tubules show a variety of poorly characterized changes, which have led to the notion that tubular damage represents a "final common pathway" for proteinuric renal injury. However, tubular hypertrophy, reduced organic ion transport, and other tubular changes reviewed in this paper, are already apparent before the onset of proteinuria in diabetes. Indeed, increased tubuloglomerular feedback and defective uptake and lysosomal processing may independently contribute to hyperfiltration and urinary protein loss, respectively. This finding does not mean that glomerular or vascular dysfunction do not contribute to progressive nephropathy. However, although subdividing the nephron for the purposes of analysis and scientific discovery may be useful, the interactions between tubule, glomerulus, and interstitium are likely key to the understanding of complex disorders such as diabetic nephropathy. From this "holonephric" point of view, an understanding of the changes in the diabetic tubule forms an important component to the understanding of kidney disease in diabetes.

Use of genetic mouse models in the study of diabetic nephropathy

The study of experimental diabetic nephropathy in rodent models has led to many changes in the clinical management of human diabetic nephropathy. With the development of technology to generate knockout and transgenic animals, the mouse has become a favored species in medical research. There are several genetic mouse models of diabetes, with the majority being models of type 2 diabetes mellitus. These include the hypoinsulinemic nonobese diabetic mouse, the KKAy mouse, the New Zealand obese mouse, the hyperinsulinemic ob/ob mouse, and the different strains of obese hyperinsulinemic db/db mouse. Each of these models displays some renal changes, but by far the best model of renal disease and the one that is the most studied is the db/db mouse. The db/db mouse displays substantial glomerular pathology, including mesangial matrix expansion and modest albuminuria. It has been reported that the db/db mouse has a decline in creatinine clearance after 5 months of age, but more specific approaches are warranted to confirm these findings. A number of intervention studies show renoprotection in this model. Although mice have many advantages, such as being able to be crossbred with genetically manipulated animals, in many ways they are not very similar to humans, and in some respects the rat may be a better choice, particularly in relation to some features of end-organ injury.

Mouse models of diabetic nephropathy

Mice provide an experimental model of unparalleled flexibility for studying mammalian diseases. Inbred strains of mice exhibit substantial differences in their susceptibility to the renal complications of diabetes. Much remains to be established regarding the course of diabetic nephropathy (DN) in mice as well as defining those strains and/or mutants that are most susceptible to renal injury from diabetes. Through the use of the unique genetic reagents available in mice (including knockouts and transgenics), the validation of a mouse model reproducing human DN should significantly facilitate the understanding of the underlying genetic mechanisms that contribute to the development of DN. Establishment of an authentic mouse model of DN will undoubtedly facilitate testing of translational diagnostic and therapeutic interventions in mice before testing in humans.

Morphometrical analysis of the kidney from nonobese diabetic (NOD) mice in the non-diabetic stage

The kidneys of non-diabetic NOD and wild type ICR mice were examined morphometrically at 3 and 6 months of age. Kidney weights and diameter of renal corpuscles of non-diabetic NOD mice were less than those of ICR mice. No lesions were observed in glomeruli or uriniferous tubules. Renin-positive areas were more common in NOD mice than in ICR mice, but no differences were detected in the Western blot analyses.

Use of genetic mouse models in the study of diabetic nephropathy

The study of experimental diabetic nephropathy in rodent models has led to many changes in the clinical management of human diabetic nephropathy. With the development of technology to generate knockout and transgenic animals, the mouse has become a favored species in medical research. There are several genetic mouse models of diabetes, with the majority being models of type 2 diabetes mellitus. These include the hypoinsulinemic non-obese diabetic mouse, the Kkay mouse, the New Zealand obese mouse, the hyperinsulinemic ob/ob mouse, and the different strains of obese hyperinsulinemic db/db mouse. Each of these models displays some renal changes, but by far the best model of renal disease and the one that is the most studied is the db/db mouse. The db/db mouse displays substantial glomerular pathology, including mesangial matrix expansion and modest albuminuria. It has been reported that the db/db mouse has a decline in creatinine clearance after 5 months of age, but more specific approaches are warranted to confirm these findings. A number of intervention studies show renoprotection in this model. Although mice have many advantages, such as being able to be cross-bred with genetically manipulated animals, in many ways they are not very similar to humans, and in some respects the rat may be a better choice, particularly in relation to some features of end-organ injury.

Utility of endogenous creatinine clearance as a measure of renal function in mice

BACKGROUND

The use of endogenous plasma creatinine levels and creatinine clearance as a tool to evaluate renal function in mice has come under scrutiny as prior studies have reported that the Jaffé alkaline picrate method grossly overestimates true plasma creatinine in mice. As members of the NIDDK Animal Models of Diabetic Complications Consortium (AMDCC), we evaluated the performance and feasibility of an alternative high-performance liquid chromatography (HPLC)-based method for standard determination of plasma creatinine and creatinine clearance in mice. Our purpose was to develop a simple method that provides a reliable, reproducible, and sensitive assay for small volumes (<25 microL) of mouse plasma and sera.

METHODS

We compared creatinine clearance measured by HPLC with the Jaffé method and HPLC creatinine clearance with inulin clearance [fluoroscein isothiocyanate (FITC) inulin in an osmotic pump implanted in mouse] in C57BL/6J mice. Different groups of mice underwent either one of two protocols. Protocol A included dietary intervention with normal, low salt plus enalapril, or high salt. Protocol B induced diabetes using streptozotocin.

RESULTS

First, mean plasma creatinine levels were significantly lower (P < 0.0001) by HPLC (0.128 +/- 0.026 mg/dL) vs. Jaffé (0.4 +/- 0.12 mg/dL) for mice on a normal diet. Urine creatinine concentrations measured by HPLC were 10% lower than by Jaffé (P < 0.01). Second, mean creatinine clearance by HPLC for mice on a normal diet was 255 +/- 68 microL/min. Mice on low salt diet plus enalapril had reduced creatinine clearance (72.8 +/- 24.2 microL/min) while mice on high salt diet had an elevated creatinine clearance (355 +/- 105 microL/min). Third, diabetic mice (19 to 24 weeks of diabetes) exhibited hyperfiltration as creatinine clearance was 524 +/- 214 microL/min whereas nondiabetic age/gender-matched mice showed a mean creatinine clearance of 206 +/- 41 microL/min. Finally, significant correlation was demonstrated for creatinine clearance by HPLC vs. inulin clearance (R= 0.643; P < 0.001).

CONCLUSION

HPLC is highly accurate, much more sensitive and specific than the Jaffé method for plasma creatinine measurements in mice. Creatinine clearance in mice measured by HPLC reflects changes in renal function induced by diet and diabetes.