Dipeptidyl peptidase-4 inhibitor ameliorates early renal injury through its anti-inflammatory action in a rat model of type 1 diabetes.

INTRODUCTION: Dipeptidyl peptidase-4 (DPP-4) inhibitors are incretin-based drugs in patients with type 2 diabetes. In our previous study, we showed that glucagon-like peptide-1 (GLP-1) receptor agonist has reno-protective effects through anti-inflammatory action. The mechanism of action of DPP-4 inhibitor is different from that of GLP-1 receptor agonists. It is not obvious whether DPP-4 inhibitor prevents the exacerbation of diabetic nephropathy through anti-inflammatory effects besides lowering blood glucose or not. The purpose of this study is to clarify the reno-protective effects of DPP-4 inhibitor through anti-inflammatory actions in the early diabetic nephropathy. MATERIALS AND METHODS: Five-week-old male Sprague-Dawley (SD) rats were divided into three groups; non-diabetes, diabetes and diabetes treated with DPP-4 inhibitor (PKF275-055; 3 mg/kg/day). PKF275-055 was administered orally for 8 weeks. RESULTS: PKF275-055 increased the serum active GLP-1 concentration and the production of urinary cyclic AMP. PKF275-055 decreased urinary albumin excretion and ameliorated histological change of diabetic nephropathy. Macrophage infiltration was inhibited, and inflammatory molecules were down-regulated by PKF275-055 in the glomeruli. In addition, nuclear factor-κB (NF-κB) activity was suppressed in the kidney. CONCLUSIONS: These results indicate that DPP-4 inhibitor, PKF275-055, have reno-protective effects through anti-inflammatory action in the early stage of diabetic nephropathy. The endogenous biological active GLP-1 might be beneficial on diabetic nephropathy besides lowering blood glucose.

Adiponectin regulates albuminuria and podocyte function in mice.

Increased albuminuria is associated with obesity and diabetes and is a risk factor for cardiovascular and renal disease. However, the link between early albuminuria and adiposity remains unclear. To determine whether adiponectin, an adipocyte-derived hormone, is a communication signal between adipocytes and the kidney, we performed studies in a cohort of patients at high risk for diabetes and kidney disease as well as in adiponectin-knockout (Ad(-/-)) mice. Albuminuria had a negative correlation with plasma adiponectin in obese patients, and Ad(-/-) mice exhibited increased albuminuria and fusion of podocyte foot processes. In cultured podocytes, adiponectin administration was associated with increased activity of AMPK, and both adiponectin and AMPK activation reduced podocyte permeability to albumin and podocyte dysfunction, as evidenced by zona occludens-1 translocation to the membrane. These effects seemed to be caused by reduction of oxidative stress, as adiponectin and AMPK activation both reduced protein levels of the NADPH oxidase Nox4 in podocytes. Ad(-/-) mice treated with adiponectin exhibited normalization of albuminuria, improvement of podocyte foot process effacement, increased glomerular AMPK activation, and reduced urinary and glomerular markers of oxidant stress. These results suggest that adiponectin is a key regulator of albuminuria, likely acting through the AMPK pathway to modulate oxidant stress in podocytes.

Macrophage scavenger receptor-a-deficient mice are resistant against diabetic nephropathy through amelioration of microinflammation.

Microinflammation is a common major mechanism in the pathogenesis of diabetic vascular complications, including diabetic nephropathy. Macrophage scavenger receptor-A (SR-A) is a multifunctional receptor expressed on macrophages. This study aimed to determine the role of SR-A in diabetic nephropathy using SR-A-deficient (SR-A(-/-)) mice. Diabetes was induced in SR-A(-/-) and wild-type (SR-A(+/+)) mice by streptozotocin injection. Diabetic SR-A(+/+) mice presented characteristic features of diabetic nephropathy: albuminuria, glomerular hypertrophy, mesangial matrix expansion, and overexpression of transforming growth factor-beta at 6 months after induction of diabetes. These changes were markedly diminished in diabetic SR-A(-/-) mice, without differences in blood glucose and blood pressure levels. Interestingly, macrophage infiltration in the kidneys was dramatically decreased in diabetic SR-A(-/-) mice compared with diabetic SR-A(+/+) mice. DNA microarray revealed that proinflammatory genes were overexpressed in renal cortex of diabetic SR-A(+/+) mice and suppressed in diabetic SR-A(-/-) mice. Moreover, anti-SR-A antibody blocked the attachment of monocytes to type IV collagen substratum but not to endothelial cells. Our results suggest that SR-A promotes macrophage migration into diabetic kidneys by accelerating the attachment to renal extracellular matrices. SR-A may be a key molecule for the inflammatory process in pathogenesis of diabetic nephropathy and a novel therapeutic target for diabetic vascular complications.

Regulation of transforming growth factor beta in diabetic nephropathy: implications for treatment.

The recognition that the drivers of matrix accumulation is an appropriate therapeutic target for diabetic nephropathy is now accepted by the nephrology and pharmaceutical communities. Interventions focused around transforming growth factor-beta (TGF-beta) likely will be an important area of clinical investigation in the near future. Understanding the various pathways involved in stimulating TGF-beta in the diabetic kidney is of paramount importance in devising strategies to combat the development and progression of diabetic nephropathy. In this review we highlight the major pathways involved in stimulating TGF-beta production by increased glucose levels and discuss the therapeutic implications thereof.

Changes of gene expression profiles in macrophages stimulated by angiotensin II--angiotensin II induces MCP-2 through AT1-receptor.

INTRODUCTION: Macrophages play critical roles in the development of atherosclerosis and diabetic nephropathy as well as many inflammatory diseases. Angiotensin II type 1 receptor antagonists (AIIA) are beneficial for the prevention of atherosclerosis and diabetic nephropathy suggesting that angiotensin II (Ang II) promotes the development of these diseases. It has recently been reported that Ang II exerts proinflammatory actions in vivo and in vitro. This study was aimed to clarify the direct effects of Ang II on monocytes/macrophages. MATERIALS AND METHODS: PMA-treated THP-1 cells, a human monocytic leukaemia cell line, were treated with Ang II (10-6 mol/L) for 24 hours with or without AIIA (CV11974). We evaluated gene expression profiles of these cells using DNA microarray system and quantified them by real-time RT-PCR. RESULTS: DNA microarray revealed that in total 19 genes, including monocyte chemoattractant protein (MCP)-2, were up-regulated by Ang II and down-regulated by AIIA. Real-time RT-PCR showed that up-regulation of MCP-2 with Ang II is blocked by the AIIA (CV11974) but not by an AT2-receptor antagonist. CONCLUSIONS: These results suggest that Ang II directly stimulates MCP-2 expression through AT1-receptors in activated macrophages. Ang II may contribute to the persistence or amplification of microinflammation in vessel walls, heart and kidney. Vasculoprotective or renoprotective effects of AIIA might partly depend on direct anti-inflammatory effects on macrophages.

Intercellular adhesion molecule-1-deficient mice are resistant against renal injury after induction of diabetes.

Diabetic nephropathy is a leading cause of end-stage renal failure. Several mechanisms, including activation of protein kinase C, advanced glycation end products, and overexpression of transforming growth factor (TGF)-beta, are believed to be involved in the pathogenesis of diabetic nephropathy. However, the significance of inflammatory processes in the pathogenesis of diabetic microvascular complications is poorly understood. Accumulation of macrophages and overexpression of leukocyte adhesion molecules and chemokines are prominent in diabetic human kidney tissues. We previously demonstrated that intercellular adhesion molecule (ICAM)-1 mediates macrophage infiltration into the diabetic kidney. In the present study, to investigate the role of ICAM-1 in diabetic nephropathy, we induced diabetes in ICAM-1-deficient (ICAM-1(-/-)) mice and ICAM-1(+/+) mice with streptozotocin and examined the renal pathology over a period of 6 months. The infiltration of macrophages was markedly suppressed in diabetic ICAM-1(-/-) mice compared with that of ICAM-1(+/+) mice. Urinary albumin excretion, glomerular hypertrophy, and mesangial matrix expansion were significantly lower in diabetic ICAM-1(-/-) mice than in diabetic ICAM-1(+/+) mice. Moreover, expressions of TGF-beta and type IV collagen in glomeruli were also suppressed in diabetic ICAM-1(-/-) mice. These results suggest that ICAM-1 is critically involved in the pathogenesis of diabetic nephropathy.

Pathological roles of advanced glycation end product receptors SR-A and CD36.

The pathological significance of advanced glycation end product (AGE)-modified proteins deposited in several lesions is generally accounted for by their cellular interaction via the AGE receptors and subsequent acceleration of the inflammatory process. In this study, we focused on two AGE receptors-specifically, the role of SR-A in pathogenesis of diabetic nephropathy and the role of CD36 in AGE-induced downregulation of leptin by adipocytes. In terms of SR-A, diabetic wild-type mice exhibited increased urinary albumin excretion, glomerular hypertrophy, and mesangial matrix expansion, whereas SR-A-knockout mice showed reduced glomerular size and mesangial matrix area. In these diabetic SR-A-knockout mice, the number of macrophages that infiltrated into glomeruli was remarkably reduced (P < 0.05), suggesting that SR-A-dependent glomerular migration of macrophages plays an important role in the pathogenesis of diabetic nephropathy. In terms of CD36, incubation of glycolaldehyde-modified bovine serum albumin (GA-BSA) with 3T3-L1 adipocytes reduced leptin secretion by these cells. The binding of GA-BSA to these cells and subsequent endocytic degradation were effectively inhibited by a neutralizing anti-CD36 antibody. AGE-induced downregulation of leptin was protected by N-acetyl-cysteine, an antioxidant. These results indicate that the interaction of AGE ligands with 3T3-L1 adipocytes via CD36 induces oxidative stress and leads to inhibition of leptin expression by these cells, suggesting a potential link of this phenomenon to exacerbation of the insulin sensitivity in metabolic syndrome.

Clinical features of non-diabetic renal diseases in patients with type 2 diabetes.

Although persistent proteinuria is characteristic of diabetic nephropathy (DN), it is important to differentiate non-diabetic renal diseases (NDRD) in diabetic patients with proteinuria. In order to re-evaluate the indications for renal biopsy in the diabetic patients, we retrospectively analyzed the relationship between clinical features and histological diagnosis in 97 Japanese patients with type 2 diabetes manifesting overt proteinuria. Renal biopsy was performed because they were clinically suspected to have NDRD. Patients were divided into three groups according to the histological diagnosis: (1) the DN group (n=35) had only diabetic lesions, (2) the complicated group (n=16) had histological changes of NDRD superimposed on DN and (3) the non-DN group (n=46) had NDRD without diabetic lesions. We evaluated the specificity and sensitivity of four clinical parameters (duration of diabetes, presence or absence of diabetic retinopathy, microscopic hematuria and granular casts as urinary sediments) for the prediction of NDRD. Short duration of diabetes (<5 years) showed high sensitivity (75%) and specificity (70%). Diabetic retinopathy showed the highest sensitivity (87%) and specificity (93%). The sensitivity and specificity of microscopic hematuria (56 and 58%) and granular casts (68 and 47%) were lower. Our study confirmed that the absence of retinopathy and short duration of diabetes are useful clinical indications for renal biopsy in diabetic patients with overt proteinuria.

[A case of minimal change nephrotic syndrome manifesting acute renal failure in the course of systemic lupus erythematosus].

A 51-year-old woman with systematic lupus erythematosus(SLE) associated with minimal change nephrotic syndrome(MCNS) is described. The patient was diagnosed as SLE at 33 years of age. After steroid therapy for two years, the patient's course was uneventful without therapy until June 2000, when facial erythema and facial, pretibial edema developed. On admission, proteinuria and renal dysfunction were detected. Subsequently, oliguric acute renal failure developed and hemodialysis was started. Laboratory examination showed no significant change in complements and anti ds-DNA antibody levels. Renal biopsy revealed minor glomerular abnormalities without the deposition of immune complexes. Electron microscopic examination showed foot process fusion and a vacuolar change in glomerular epithelial cells. The diagnosis of MCNS was made and administration of steroid(40 mg/day) was started. Urine volume and renal function improved after 2 weeks, and nephrotic syndrome remitted completely after 5 weeks. Although the association of SLE and MCNS is rare, the findings suggest that in the course of SLE manifesting acute ranal failure, not only lupus nephritis, but also the complication of MCNS should be considered.

Thiazolidinedione ameliorates renal injury in experimental diabetic rats through anti-inflammatory effects mediated by inhibition of NF-kappaB activation.

Thiazolidinedione (TZD), a ligand for peroxisome proliferator-activated receptor-gamma (PPAR-gamma), exerts anti-inflammatory effects independently of the insulin-sensitizing effect. In the present study, we tested the hypothesis that TZD prevents the progression of diabetic nephropathy by modulating the inflammatory process. Five-week-old Sprague-Dawley rats were divided into three groups: 1) nondiabetic control rats (non-DM), 2) diabetic rats (DM), and 3) diabetic rats treated with pioglitazone (DM+pio). Diabetes was induced by injection with streptozotocin (STZ). The DM+pio group received 0.0002% pioglitazone mixed in chow for 8 wk after induction of diabetes. Blood glucose and HbA1c were elevated in diabetic rats but did not change by treatment with pioglitazone. Pioglitazone reduced urinary albumin excretion and glomerular hypertrophy, suppressed the expression of transforming growth factor (TGF)-beta, type IV collagen, and ICAM-1, and infiltration of macrophages in the kidneys of diabetic rats. Furthermore, renal NF-kappaB activity was increased in diabetic rats and reduced by pioglitazone. PPAR-gamma was expressed in glomerular endothelial cells in the diabetic kidney and in cultured glomerular endothelial cells. High-glucose conditions increased the expression of ICAM-1 and the activation of NF-kappaB in cultured glomerular endothelial cells. These changes were reduced by pioglitazone, ciglitazone, and pyrrolidine dithiocarbamate, an inhibitor of NF-kappaB. However, pioglitazone did not show the changes in the presence of PPAR-gamma antagonist GW9662. Our results suggest that the preventive effects of pioglitazone may be mediated by its anti-inflammatory actions, including inhibition of NF-kappaB activation, ICAM-1 expression, and macrophage infiltration in the diabetic kidney.

Decorin deficiency enhances progressive nephropathy in diabetic mice.

Decorin, a proteoglycan that inhibits active transforming growth factor-beta, is increased in diabetic nephropathy; however, its functional significance is unclear. In this study, we used low-dose streptozotocin to induce type 1 diabetes in wild-type (C57BL/6J Dcn(+/+)), Dcn(-/-), and Dcn(+/-) mice and studied the mice for up to 1 year of diabetes. Decorin gene dose had no effect on severity of diabetes; however, the Dcn(-/-) diabetic mice died significantly earlier than nondiabetic controls (57 versus 7.3% mortality). In contrast to wild-type diabetic mice, which failed to develop significant nephropathy, the Dcn(-/-) diabetic mice developed a significant increase in albuminuria and plasma creatinine and a concurrent decrease in circulating adiponectin levels. Interestingly, adiponectin levels at 6 months of diabetes were predictive of mortality in diabetic mice. Dcn(-/-) diabetic mice exhibited advanced glomerular lesions, including diffuse mesangial matrix accumulation and fibrin cap formation. By immunohistochemistry, Dcn(-/-) diabetic mice exhibited significant increases in glomerular transforming growth factor-beta, type I collagen, macrophage infiltration, and Nox4. We conclude that decorin is a natural protective factor against diabetic nephropathy and that the Dcn(-/-) diabetic mouse is a useful new model of progressive diabetic nephropathy.

Methotrexate prevents renal injury in experimental diabetic rats via anti-inflammatory actions.

Recent studies suggested the involvement of inflammatory processes in the pathogenesis of diabetic nephropathy. Methotrexate (MTX), a folic acid antagonist, is widely used for the treatment of inflammatory diseases. Recently, it has been shown that treatment with low-dose MTX reduces the cardiovascular mortality in patients with rheumatoid arthritis, suggesting that MTX has anti-atherosclerotic effects via its anti-inflammatory actions. This study was designed to determine the anti-inflammatory effects of this agent on diabetic nephropathy. Diabetes was induced in Sprague-Dawley rats with streptozotocin, and MTX (0.5 or 1.0 mg/kg) was administered once a week for 8 wk. Treatment with MTX reduced urinary albumin excretion, mesangial matrix expansion, macrophage infiltration, expression of TGF-beta and type IV collagen, and intercellular adhesion molecule-1 in glomeruli. MTX also reduced the high glucose-induced NF-kappaB activation in vitro and in vivo. The results indicate that intermittent administration of MTX prevented renal injuries without changes in blood glucose level and BP in experimental diabetic rats. The protective effects of MTX are suggested to be mediated by its anti-inflammatory actions through inhibition of NF-kappaB activation and consequent reduction of intercellular adhesion molecule-1 expression and macrophage infiltration. The results suggest that anti-inflammatory agents might be beneficial for the treatment of diabetic nephropathy.

Protective effect of a novel and selective inhibitor of inducible nitric oxide synthase on experimental crescentic glomerulonephritis in WKY rats.

BACKGROUND: Nitric oxide (NO) plays important roles in a variety of pathophysiological processes. It has been reported that inducible NO synthase (iNOS) is upregulated in the glomeruli of patients with glomerulonephritis, although there has been no direct evidence that NO generated by iNOS contributes to the progression of glomerulonephritis. ONO-1714, a novel cyclic amidine analog, is a selective inhibitor of iNOS. To elucidate the role of iNOS in the pathogenesis of experimental crescentic glomerulonephritis, we examined the effect of ONO-1714 given to rats with nephrotoxic serum (NTS) nephritis. METHODS: We induced NTS nephritis in Wistar-Kyoto (WKY) rats. These rats were given ONO-1714 or physiological saline intraperitoneally for 14 days using an osmotic pump after intraperitoneal injection with NTS. RESULTS: Glomerular expression of iNOS and urinary excretion of NO metabolites (nitrite/nitrate) were increased in rats after injection of NTS. As compared with the control group, ONO-1714 significantly reduced proteinuria, crescent formation, glomerular infiltration of macrophages and urinary excretion of nitrite/nitrate. CONCLUSION: The present results suggest that NO radicals generated by iNOS contribute to the progression of experimental crescentic glomerulonephritis in WKY rats. The selective iNOS inhibitor ONO-1714 may be beneficial for the treatment of crescentic glomerulonephritis.

HMG-CoA reductase inhibitor ameliorates diabetic nephropathy by its pleiotropic effects in rats.

BACKGROUND: An inflammatory process may be one of the critical factors that contribute to the development of diabetic nephropathy (DN). We reported previously that intercellular adhesion molecule-1 (ICAM-1) is up-regulated and promotes macrophage infiltration in the glomeruli of diabetic rats. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have recently been emphasized to have anti-inflammatory effects; inhibition of leukocyte adhesion and migration, independent of the cholesterol-lowering effect. The present study was designed to test the hypothesis that statins prevent the development of DN by pleiotropic effects. METHODS: Streptozotocin-induced diabetic rats were treated with cerivastatin (0.5 mg/kg body weight) or vehicle for 4 weeks. We analysed glomerular macrophage infiltration and ICAM-1 expression. We also evaluated major regulators of ICAM-1, activation of nuclear factor-kappa B (NF-kappaB) using electrophoretic mobility shift assay, and oxidative stress. RESULTS: Statin treatment reduced urinary albumin excretion (UAE) (2.96+/-0.18 vs 2.38+/-0.06; log(10) UAE, P<0.05), glomerular size (12 150+/-329 vs 9963+/-307 micro m(2), P<0.05), and lowered blood pressure, compared with untreated diabetic rats. Immunohistochemistry revealed that macrophage infiltration and ICAM-1 expression in glomeruli were increased in diabetic rats and were inhibited by statin treatment. Renal NF-kappaB activity, urinary excretion and renal deposition of 8-OHdG were increased in diabetic rats, and reduced by statin treatment. CONCLUSION: Statin treatment prevented glomerular injury, independent of the cholesterol-lowering effects. Our findings suggest that the beneficial effect might be mediated by pleiotropic effects including an anti-inflammatory action through a reduction of oxidative stress, NF-kappaB activation, ICAM-1 expression and macrophage infiltration in the early phase of DN.

Cerebroside sulfotransferase deficiency ameliorates L-selectin-dependent monocyte infiltration in the kidney after ureteral obstruction.

Mononuclear cells infiltrating the interstitium are involved in renal tubulointerstitial injury. The unilateral ureteral obstruction (UUO) is an established experimental model of renal interstitial inflammation. In our previous study, we postulated that L-selectin on monocytes is involved in their infiltration into the interstitium by UUO and that a sulfated glycolipid, sulfatide, is the physiological L-selectin ligand in the kidney. Here we tested the above hypothesis using sulfatide- and L-selectin-deficient mice. Sulfatide-deficient mice were generated by gene targeting of the cerebroside sulfotransferase (Cst) gene. Although the L-selectin-IgG chimera protein specifically bound to sulfatide fraction in acidic lipids from wild-type kidney, it did not show such binding in fractions of Cst(-/-) mice kidney, indicating that sulfatide is the major L-selectin-binding glycolipid in the kidney. The distribution of L-selectin ligand in wild-type mice changed after UUO; sulfatide was relocated from the distal tubules to the peritubular capillaries where monocytes infiltrate, suggesting that sulfatide relocated to the endothelium after UUO interacted with L-selectin on monocytes. In contrast, L-selectin ligand was not detected in Cst(-/-) mice irrespective of UUO treatment. Compared with wild-type mice, Cst(-/-) mice showed a considerable reduction in the number of monocytes/macrophages that infiltrated the interstitium after UUO. The number of monocytes/macrophages was also reduced to a similar extent in L-selectin(-/-) mice. Our results suggest that sulfatide is a major L-selectin-binding molecule in the kidney and that the interaction between L-selectin and sulfatide plays a critical role in monocyte infiltration into the kidney interstitium.