914-74 Estradiol 17βProtects Against Homocysteine-induced Vascular Injury in Rat Thoracic Aorta

Abstract

Hyperhomocysteinemia produces atherosclerotic lesions with characteristic endothelial desquamation and intimal smooth muscle cell (VSMC) proliferation. In vitro , homocysteine is cytotoxic to endothelial cells and recent observations suggest that it may directly stimulate VSMC proliferation. Estrogen, on the other hand, inhibits VSMC proliferation both in vivo and in vitro . We evaluated the effect of estradiol 17 β (E 2 β ) on homocysteine-induced VSMC proliferation in arterial segments from the rat thoracic aorta. Segments were placed overnight in Dulbecco's Minimum Essential Medium, supplemented with gentamycin (25 μg/ml), glutamine (2 mM) and 0.4% fatal bovine serum, before incubation for 30 hours with DL-homocysteine thiolactone (0.1–5.0 mM). Radiolabelled thymidine uptake was assessed in intact and deendothelialized arterial segments, in presence of E 2 β (30 nM) or vehicle (1% ethanol). In deendothelialized segments homocysteine elicited a concentration-dependent increase in 3 H-thymidine uptake, expressed as cpm/mg protein. Thymidine uptake increased from a basal value of 8694 ± 1465 to 36338 ± 2025, at 5 mM homocysteine concentration (p < 0.01). Intact arterial segments showed a significantly attenuated response to homocysteine stimulation. On the other hand, incubation of deendothelialized segments with E 2 β (30 nM) caused a significant inhibition of homocysteinestimulated response, without affecting basal 3 H-thymidine incorporation. These results provide evidence for a direct stimulatory effect of homocysteine on VSMC proliferation in rat aortic segments. Further, our data show estradiol 17 β protects against homocysteine-induced vascular injury, possibly via a direct effect on VSMC.