The role of visfatin in intermittent hypoxia-induced inflammation and endothelial dysfunction

Abstract

RATIONALE: Intermittent hypoxia (IH), a hallmark feature in obstructive sleep apnea (OSA) associated with transient cessation of breathing during sleep, may be the main culprit underlying endothelial dysfunction, a risk factor for atherosclerosis. Visfatin is a multifaceted adipokine, the extracellular form of which can exert various effects on the vascular endothelium including inflammation, proliferation and endothelium-dependent relaxation. However, little is known about the role of visfatin in inflammation and endothelial dysfunction induced by IH. This study is aimed to compare the effects of visfatin on inflammation and endothelial function between IH and normoxia in endothelial cells. METHODS: IH exposure was performed in the hypoxic chamber in which O2 levels were alternated between 1% for 10 min and 21% for 5 min in one complete cycle and CO2 levels were maintained at 5%. Intermittent normoxia (IN;21% O2 and 5% CO2) exposure was carried out simultaneously in control cell cultures. Endothelial EA.hy926 cells were exposed to IN or IH for 96 cycles with two concentrations of visfatin (10ng/ml and 100ng/ml). Supernatants were collected after treatment to measure the levels of inflammatory markers, interleukin (IL)-8 and monocyte chemoattractant protein (MCP)-1, using commercial ELISA kits. Cellular proteins were extracted to determine the expression ofa key enzyme regulating endothelial function, nitric oxide synthase (eNOS) and its activity in terms of phosphorylation at ser1177 [p-eNOS (Ser1177)] using Western blot. RESULTS: IH exposure induced elevation of IL-8 and MCP-1 levels (p<0.05). Visfatin attenuated IH-induced elevation of IL-8 and MCP-1 levels in a dose-dependent manner. Visfatin alone had no effects on basal levels of IL-8 and MCP-1. Western blot analysis revealed that IH exposure significantly suppressed p-eNOS expression but not eNOS expression in EA.hy926 cells. In the presence of visfatin, no differences were found in the basal expression of p-eNOS and eNOS or in IH-induced suppression of p-eNOS. CONCLUSION: These results provided evidence that visfatin might play a pivotal role in IH-induced endothelial inflammation but not in reversing endothelial dysfunction in OSA.