Unsaturated free fatty acids inhibit Ca2+ mobilization and NO release in endothelial cells

Circulating free fatty acids (FFAs) are elevated in various disorders like states of insulin resistance, and an increase of FFAs has been reported to be associated with endothelial dysfunction. To investigate the effect of FFAs on vascular endothelial cells, we measured nitric oxide (NO) release and intracellular free calcium concentration ([Ca2+]i ) in cultured bovine aortic endothelial cells (BAECs). Monounsaturated FFAs such as oleic acid (OA) and polyunsaturated FFAs such as linoleic acid (LA) dose-dependently (10-100 Emol/L) inhibited NO release from BAECs stimulated by adenosine 5'-(3-O-thio)triphosphate (ATP AS) whereas saturated FFAs such as palmitic acid had no effect on NO release. ATP AS induced a biphasic increase in [Ca2+]i, which consisted of a rapid increase followed by a sustained increase. OA and LA inhibited ATP AS-induced Ca2+ release from intracellular Ca2+ stores and increase in Ca2+ influx from extracellular space. In addition, OA and LA rapidly decreased sustained increase in [Ca2+]i induced by ATP AS when OA or LA was added after stimulation with ATP AS. Impaired Ca2+ mobilization by unsaturated FFAs (UFFAs) was completely reversed by treatment with bovine serum albumin (1 mg/ml) indicating that inhibitory effect of FFAs was not caused by cytotoxic effect. In spite of this inhibitory effect of UFFAs, neither OA nor LA had any effect on phosphoinositide hydrolysis evoked by ATP AS. From these results, elevated UFFA may contribute to impaired NO production through inhibition of receptor-mediated Ca2+ mobilization and Ca2+ influx in pathological conditions such as multiple risk factor syndrome and insulin resistance.