Chronic homocysteine exposure upregulates endothelial adhesion molecules and mediates leukocyte: endothelial cell interactions under flow conditions.

Abstract

Homocysteine upregulates expression of adhesion molecules on endothelial cells which recruits leukocytes and initiates atherosclerosis. Endothelial cells in hyperhomocysteinemic patients are continuously exposed to high levels of homocysteine. This study exposed adult endothelial cells and endothelial cells from immune naïve foetal tissue to homocysteine chronically and studied effects on cellular adhesion molecule expression under static and flow conditions. Human umbilical vein endothelial cells (HUVEC) and human saphenous vein endothelial cells (HSVEC) were cultured in medium containing 1 mM dl-homocysteine or l-cysteine for 5-9 days. Proliferation was assessed. Cells were subjected to flowing neutrophils and numbers of tethered, rolled fixed and transmigrated neutrophils on endothelial cells were counted and compared to controls. Immunofluorescence staining with antibodies against Intercellular adhesion molecule-1 (ICAM-1), E-selectin and P-selectin were used to quantify expression. Chronic treatment with 1 mM homocysteine inhibited proliferation of HUVEC and HSVEC. Homocysteine treated cells showed significantly increased expression of ICAM-1, E-selectin and to a lesser extent P-selectin. In both cell types, homocysteine significantly increased interactions between neutrophils and endothelial cells under flow conditions (p < 0.05) while cysteine had no effect. Endothelial cells from adult and immune naïve foetal tissue showed similar responses to chronic treatment with homocysteine.