Free fatty acid overload attenuates Ca2+ signaling and NO production in endothelial cells

Hyperlipidemia represents a major risk factor for development of vascular dysfunction and atherosclerosis. Although the unfortunate role of low-density lipoprotein has been clearly demonstrated, the mechanistic pathways through which triglyceride-derived free fatty acids (FFAs) contribute to vascular disorders are not completely understood. Thus, the present study was designed to elucidate the effects of FFAs on cultured endothelial cells. The Ca2+ signaling, endothelial nitric oxide synthase (eNOS) activity, and production of superoxide anions (.O-2-) were monitored in cells treated with bovine serum albumin-conjugated FFA. FFA-loaded cells showed enhanced intracellular Ca2+ release in response to ATP, histamine, or the SERCA inhibitor thapsigargin. This effect corresponded to an overall increase in intracellularly stored Ca2+. In contrast, autacoid-triggered elevation of cytosolic free Ca2+ concentration was blunted in FFA-loaded cells due to inhibition of capacitative Ca2+ entry. In agreement with the reduced Ca2+ signaling, the Ca2+-dependent activity of eNOS was reduced under basal conditions and if cells were stimulated with ATP, histamine, or thapsigargin. The attenuated eNOS activity was associated with .O-2- release in FFA-loaded cells. These data indicate that FFAs significantly affect endothelial Ca2+ signaling, eNOS activity, and .O-2- release and, thus, might contribute to vascular dysfunction in atherogenesis.