anti-hypertensive Azelnidipine-induced improvement of insulin sensitivity in 3T3-L1 adipocutes*
Azelnidipine (AZE), one of dihydropridine calcium channel blockers has besides its blood-pressure-lowering effects, actions to improve whole body insulin sensitivity and increase circulating adiponectin levels in human and experimental animal models. However, the molecular mechanisms underlying such metabolic actions remain unknown. In this study, we investigated the effect of AZE upon insulin sensitivity and adiponectin secretion in cultured 3T3-L1 adipocytes to see whether AZE showed direct effects in adipocytes and to analyze the molecular mechanisms involved in the metabolic actions in adipocytes. We found that AZE (3.55 x by insulin, p<0.05 vs. control), but not nifedipine (NIF) (2.30 x), significantly increased the magnitude of insulin-stimulated glucose transport activity in 3T3-L1 adipocytes, compared with control (2.46 x), suggesting that AZE enhanced insulin sensitivity through its direct action in adipocytes. Furthermore, incubation of cells with AZE (1.30 x, p<0.05 vs. control), but not NIF (1.01 x), over a 24 hour period significantly stimulated adiponectin secretion from 3T3-L1 adipocytes. This was associated with significant increases in adiponectin mRNA expression (1.21 x, p<0.05 vs. control), measured by real-time RT-PCR, in 3T3-L1 adipocytes. Nevertheless, unlike the extremely potent actions of thiazolidinediones upon adipocytes, AZEinduced increase in adiponectin secretion was not associated with acceleration of adipocyte differentiation, and normally along with the activation of peroxisome proliferator-activated receptor (PPAR)γ, and the resultant downsizing of adipocytes, which were demonstrated by morphological analysis of adipose differentiation process in the presence of AZE or pioglitazone. The expression of other metabolic adipocytokines including leptin, resistin, interleukin-6, tumor necrosis factor-α, and monocyte chemoattractant protein-1 were also neither affected by AZE stimulation. These results suggested that AZE enhanced insulin sensitivity and increased adiponectin secretion in 3T3-L1 adipocytes independently of activation of PPARγ. Finally, we investigated the antioxidative effect of AZE in 3T3-L1 adipocytes and found that expression of p22 phox and p67 phox , NADPH oxidase subunits, were significantly decreased, in contrast to upregulation of antioxidative enzymes, such as SOD1 and catalase , by stimulation of 3T3-L1 adipocytes with AZE for 24 hours. In conclusion, these results demonstrated that AZE significantly enhanced insulin sensitivity and increased adiponectin secretion in 3T3-L1 adipocytes, independently of PPARγ activation, which were unique characteristics of AZE and not a class effect of dihydropridine calcium channel blockers. In addition to this, we suggest the possibility that antioxidative effects of AZE would be involved in its metabolically preferable actions in adipocytes. (Accepted on October 24, 2011)
