One aspect of homocysteine (Hcy) action is the impairment of endothelial cell function due to an impairment of endothelial nitric oxide (NO) production. The activity of the endothelial isoform of NO synthase (eNOS) is regulated by its interaction with caveolin-1 (Cav-1). The aim of this study was to determine whether Hcy may alter the levels of Cav-1 and eNOS in endothelial caveolae. We isolated caveolae-enriched membrane fractions from Hcy-treated human coronary artery endothelial cells. We found that treatment with 500 microM Hcy for 6h significantly reduced the levels of Cav-1 and eNOS in caveolae compared to untreated control by 47+/-7% and by 38+/-14%, respectively. Similarly, long-term incubation (96h) of HCAEC with 100 microM Hcy led to a comparable effect. The decreased Cav-1 abundance in endothelial caveolae in response to Hcy resulted from a decrease in Cav-1 expression at the transcriptional level. The reduced levels of eNOS in caveolae were caused by a translocation of eNOS from the caveolar fractions to noncaveolar fractions. The effects of Hcy were associated with an impairment of stimulated release of NO. These results suggest that Hcy induced impairment of NO production through a modulation of Cav-1 expression associated with a loss of eNOS in caveolae.