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Genetic or nutritional deficiencies in homocysteine (Hcy) metabolism lead to hyperhomocysteinemia (HHcy) and cause endothelial dysfunction, a hallmark of atherosclerosis. In addition to Hcy, related metabolites accumulate in HHcy but their role in endothelial dysfunction is unknown. Here, we examine how Hcy-thiolactone, N-Hcy-protein, and Hcy affect gene expression and molecular pathways in human umbilical vein endothelial cells. We used microarray technology, real-time quantitative polymerase chain reaction, and bioinformatic analysis with PANTHER, DAVID, and Ingenuity Pathway Analysis (IPA) resources. We identified 47, 113, and 30 mRNAs regulated by N-Hcy-protein, Hcy-thiolactone, and Hcy, respectively, and found that each metabolite induced a unique pattern of gene expression. Top molecular pathways affected by Hcy-thiolactone were chromatin organization, one-carbon metabolism, and lipid-related processes [-log(P value) = 20-31]. Top pathways affected by N-Hcy-protein and Hcy were blood coagulation, sulfur amino acid metabolism, and lipid metabolism [-log(P value)] = 4-11; also affected by Hcy-thiolactone, [-log(P value) = 8-14]. Top disease related to Hcy-thiolactone, N-Hcy-protein, and Hcy was 'atherosclerosis, coronary heart disease' [-log(P value) = 9-16]. Top-scored biological networks affected by Hcy-thiolactone (score = 34-40) were cardiovascular disease and function; those affected by N-Hcy-protein (score = 24-35) were 'small molecule biochemistry, neurological disease,' and 'cardiovascular system development and function'; and those affected by Hcy (score = 25-37) were 'amino acid metabolism, lipid metabolism,' 'cellular movement, and cardiovascular and nervous system development and function.' These results indicate that each Hcy metabolite uniquely modulates gene expression in pathways important for vascular homeostasis and identify new genes and pathways that are linked to HHcy-induced endothelial dysfunction and vascular disease.