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

Obesity, inflammation, and the potential application of pharmaconutrition

Obesity is an emerging problem worldwide. Hospitalized obese patients often have a worse outcome than patients of normal weight, particularly in the setting of trauma and critical care. Obesity creates a low-grade systemic inflammatory response syndrome (SIRS) that is similar (but on a much smaller scale) to gram-negative sepsis. This process involves up-regulation of systemic immunity, is characterized clinically by insulin resistance and the metabolic syndrome, and puts the patient at increased risk for organ failure, infectious morbidity, and mortality. Through lipotoxicity and cytokine dysregulation, obesity may act to prime the immune system, predisposing to an exaggerated subsequent immune response when a second clinical insult occurs (such as trauma, burns, or myocardial infarction). Specialized nutrition therapy for such patients currently consists of a hypocaloric, high-protein diet. However, this approach does not address the putative pathophysiologic mechanisms of inflammation and altered metabolism associated with obesity. A number of dietary agents such as arginine, fish oil, and carnitine may correct these problems at the molecular level. Pharmaconutrition formulas may provide exciting innovations for the nutrition therapy of the obese patient.

Pioglitazone attenuates diabetic nephropathy through an anti-inflammatory mechanism in type 2 diabetic rats

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors that play a role in insulin sensitivity, lipid metabolism and inflammation. However, the effects of PPARgamma agonist on renal inflammation have not been fully examined in type 2 diabetic nephropathy.

METHODS

In the present study, we investigated the effect and molecular mechanism of the PPARgamma agonist, pioglitazone, on the progression of diabetic nephropathy in type 2 diabetic rats. Inflammatory markers including NF-kappaB, MCP-1 and pro-fibrotic cytokines were determined by RT-PCR, western blot, immunohistochemical staining and EMSA. In addition, to evaluate the direct anti-inflammatory effect of PPARgamma agonist, we performed an in vitro study using mesangial cells.

RESULTS

Treatment of OLETF rats with pioglitazone improved insulin sensitivity and kidney/body weight, but had a little effect on blood pressure. Pioglitazone treatment markedly reduced urinary albumin and MCP-1 excretion, and ameliorated glomerulosclerosis. In cDNA microarray analysis using renal cortical tissues, several inflammatory and profibrotic genes were significantly down-regulated by pioglitazone including NF-kappaB, CCL2, TGFbeta1, PAI-1 and VEGF. In renal tissues, pioglitazone treatment significantly reduced macrophage infiltration and NF-kappaB activation in association with a decrease in type IV collagen, PAI-1, and TGFbeta1 expression. In cultured mesangial cells, pioglitazone-activated endogenous PPARgamma transcriptional activity and abolished high glucose-induced collagen production. In addition, pioglitazone treatment also markedly suppressed high glucose-induced MCP-1 synthesis and NF-kappaB activation.

CONCLUSIONS

These data suggest that pioglitazone not only improves insulin resistance, glycaemic control and lipid profile, but also ameliorates renal injury through an anti-inflammatory mechanism in type 2 diabetic rats.

Pioglitazone ameliorates endothelial dysfunction in obese rats with nephropathy

Endothelial dysfunction is a key event in the development of renovascular complications in the metabolic syndrome. The aim of this study was to elucidate the pathogenetic mechanisms involved in renovascular injuries in the Zucker obese rat, a model of the metabolic syndrome, and to examine the therapeutic effects of pioglitazone, a thiazolidinedione. Obese rats fed high-protein diet (OHP) for 12 weeks exhibited nephropathy and endothelial dysfunction, which were improved by pioglitazone. Accumulation of nitrotyrosine, a tracer of nitrative stress, was increased in aorta of the OHP group. The mRNA expressions of NADPH oxidase components and inducible nitric oxide synthase in the aorta were enhanced in the OHP group. Pioglitazone reduced nitrotyrosine in the aorta of the OHP group, inhibiting the augmented expression levels of both. These results suggest that nitrative stress could cause endothelial dysfunction in the rat model of metabolic syndrome with nephropathy, and that pioglitazone ameliorates these injuries, presumably by reducing nitrative stress.