Homocysteinaemia is an independent risk factor for atherosclerosis. The development of atherosclerosis involves monocyte chemoattractant protein 1 (MCP-1)-mediated monocyte recruitment to the lesion site. The action of MCP-1 is mostly via its interaction with MCP-1 receptor (CCR2), which is the major receptor for MCP-1 on the surface of monocytes. The objective of the present study was to investigate the effect of homocysteine on CCR2 expression in human THP-1 monocytes. Cells were incubated with various concentrations of homocysteine for 6, 12, 24 and 48h. The expression of CCR2 mRNA was determined by nuclease protection assay and the CCR2 protein was measured by Western immunoblotting analysis. The binding of MCP-1 to CCR2 as a functional receptor on the monocyte surface was determined by flow cytometry. Homocysteine (0.05–0.2mM) significantly enhanced the expression of CCR2 mRNA (129–209% of the control) and CCR2 protein (up to 183% of control) in these cells after 24h of incubation. Stimulation of CCR2 expression was associated with a parallel increase in the binding activity of CCR2 (129–191% of control) as well as an enhanced chemotactic response of homocysteine-treated monocytes. Further investigation revealed that the levels of superoxide were significantly elevated in cells incubated with homocysteine for 12–48h. The addition of superoxide dismutase, a scavenger of superoxide, to the culture medium abolished the stimulatory effect of homocysteine on CCR2 expression as well as the binding activity of the receptor. The stimulatory effect of homocysteine on the expression of CCR2 mRNA and the levels of CCR2 protein was also observed in human peripheral blood monocytes. In conclusion, the present study has clearly demonstrated that homocysteine stimulates CCR2 expression in monocytes, leading to an enhanced binding activity and chemotatic response. Homocysteine-induced superoxide formation might serve as one of the underlying mechanisms for this effect.

Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that stimulates the migration of monocytes into the intima of arterial walls. Although many factors that induce MCP-1 expression have been identified, the effect of homocysteine on the expression of MCP-1 in atherogenesis and the underlying mechanisms are not entirely clear. The objective of the present study was to investigate the role of homocysteine in MCP-1 expression in human aorta vascular smooth-muscle cells (VSMCs). After VSMCs were incubated with homocysteine for various time periods, a nuclease protection assay and ELISA were performed. Homocysteine (0.05Ő0.2mM) significantly increased the expression of MCP-1 mRNA (up to 2.7-fold) and protein (up to 3.3-fold) in these cells. The increase in MCP-1 expression was associated with the activation of protein kinase C (PKC) as well as nuclear factor κB (NF-κB). Further investigation demonstrated that the activation of NF-κB was the result of a PKC-mediated reduction in the expression of inhibitory protein (IκBα) mRNA and protein in homocysteine-treated cells. Oxidative stress might also be involved in the activation of NF-κB by homocysteine in VSMCs. In conclusion, the present study has clearly demonstrated that the activation of PKC as well as superoxide production followed by activation of NF-κB is responsible for homocysteine-induced MCP-1 expression in VSMCs. These results suggest that homocysteine-stimulated MCP-1 expression via NF-κB activation may play an important role in atherogenesis.