Homocysteine decreases endothelin‐1 production by cultured human endothelial cells

Hyperhomocysteinemia is believed to be responsible for the development of vascular disease via several mechanisms, including the impairment of endothelial‐cell functionality. In‐vitro studies have demonstrated that homocysteine decreases the production or bioavailability of vasodilator autacoids, such as prostacyclin and NO. Here, we show that the treatment of human endothelial cells with noncytotoxic homocysteine concentrations leads to a dose‐dependent decrease in both the secretion of the vasoconstrictor agent endothelin‐1 (ET‐1) and the level of its mRNA. Homocysteine had an inhibitory effect at pathophysiological (0.1 and 0.5 mmol·L−1) and pharmacological noncytotoxic (1.0 and 2.0 mmol·L−1) concentrations. Mean percentage variation from control for ET‐1 production was −36.2 ± 18.9% for 0.5 mmol·L−1 homocysteine and −41.5 ± 26.8% for 1.0 mmol·L−1 homocysteine, after incubation for 8 h. Mean percentage variation from control for steady‐state mRNA was −17.3 ± 7.1% for 0.5 mmol·L−1 homocysteine and −46.0 ± 10.1 for 1.0 mmol·L−1 homocysteine, after an incubation time of 2 h. ET‐1 production was also reduced by incubation with various other thiol compounds containing free thiol groups, but not by incubation with thiol compounds with no free thiol group. Co‐incubation of cells with homocysteine and the sulfhydryl inhibitor N‐ethylmaleimide prevented the effect of homocysteine on ET‐1 production, confirming a sulfhydryl‐dependent mechanism. Based on the reciprocal feedback mechanism controlling the synthesis of vasoactive mediators, these preliminary data suggest a mechanism by which homocysteine may selectively impair endothelium‐dependent vasodilation by primary inhibition of ET‐1 production.