Pioglitazone reduces tumor necrosis factor-alpha serum concentration and mRNA expression of adipose tissue in hypercholesterolemic rabbits.

BACKGROUND: Tumor necrosis factor-alpha (TNF-alpha) is an inflammatory cytokine involved in atherogenesis. Adipose tissue is an important source of endogenous TNF-alpha production. Pioglitazone, a member of the thiazolidinediones (TZDs), has anti-inflammatory and anti-atherogenic properties, while underlying mechanism has not been fully elucidated. The aim of this study was to evaluate the effect of pioglitazone on TNF-alpha serum concentration and mRNA expressions of subcutaneous adipose tissue in hypercholesterolemic rabbits. METHODS: Ten rabbits fed with high-cholesterol diet for 8 weeks were randomly divided into two groups: (1) high cholesterol group (n=5): maintained high cholesterol diet for 4 weeks; (2) pioglitazone group (n=5): the same cholesterol diet plus pioglitazone (3 mg/kg/day) for 4 weeks. Control group (n=5) was fed with normal diet for 12 weeks. Subcutaneous adipose tissue was collected for RNA analysis. The direct effect of pioglitazone on TNF-alpha release was assayed in primary rabbit adipocytes. TNF-alpha levels in serum and adipocytes culture supernatant were measured by ELISA. RT-PCR was used to evaluate TNF-alpha mRNA expressions in adipose tissue and adipocytes. RESULTS: Compared with control group, rabbits fed with high cholesterol diet showed significantly higher levels of serum total cholesterol (TC), low density lipoprotein cholesterol (LDL-C) and TNF-alpha. Though having no effect on serum glucose level and lipid profile, pioglitazone administration significantly reduced circulating TNF-alpha concentrations, which were positively correlated with TNF-alpha mRNA expressions of adipose tissue (r=0.53, P<0.01). Pioglitazone dose-dependently inhibited lipopolysaccharide (LPS)-induced TNF-alpha secretion and mRNA expression in cultured adipocytes. CONCLUSION: Pioglitazone significantly reduced serum TNF-alpha level in hypercholesterolemic rabbits independent of its metabolic actions, which may at least partly be due to its direct inhibition of TNF-alpha expression and secretion of adipocytes. This may help to explain the mechanism by which pioglitazone exert anti-atherosclerotic effects.

Pioglitazone decreased CD40/CD40L expression on human umbilical vein endothelial cells induced by oxidized low-density lipoprotein.

BACKGROUND: The CD40/CD40 ligand pathway mediated inflammatory processes are important in atherogenesis and the formation of the intraplaque lipid pool. We tested the hypothesis that pioglitazone could decrease lectin-like oxLDL receptor-1 (LOX-1) and CD40/CD40L expression on human umbilical vein endothelial cells (HUVECs) induced by oxidized low-density lipoprotein (oxLDL). METHODS: HUVECs were incubated with oxLDL for 24h with or without pretreated by pioglitazone. Expression of CD40/CD40L on the cell surface was detected by flow cytometry. CD40/CD40L and LOX-1 mRNA expression were evaluated by RT-PCR. The expression of LOX-1 on HUVECs was determined by cell immunohistochemistry. RESULTS: OxLDL increased the expression of CD40 and CD40L in a dose- and time-dependent manner. Pretreatment of HUVECs with pioglitazone (1 and 10 micromol/l) for 60 min decreased the expression of CD40 mRNA induced by oxLDL by 16% and 52%, respectively (both P<0.05). Pretreatment of HUVECs with pioglitazone (1 and 10 micromol/l) for 60 min decreased the expression of CD40L mRNA induced by oxLDL by 16% and 43% (both P<0.05). Also, pretreatment of HUVECs with pioglitazone (1 and 10 micromol/l) for 60 min also significantly decreased CD40 and CD40L expression on HUVECs induced by oxLDL in a concentration-dependent manner. Pretreatment of HUVECs with pioglitazone (1 and 10 micromol/l) decreased oxLDL induced upregulation mRNA of LOX-1 by 11% and 28%, respectively. Furthermore, through immunohistochemistry, we found that pioglitazone could decrease the LOX-1 expression on HUVECs induced by oxLDL. CONCLUSION: Pioglitazone inhibited the upregulation of LOX-1 on HUVECs elicited by oxLDL and subsequently decreased HUVECs CD40/CD40L expression induced by oxLDL. These observations provided novel insight into a potential novel anti-inflammatory pathway of thiazolidinediones.