OBJECTIVETo investigate the effect of homocysteine (HCY) on activation of nuclear factor (NF-kappaB) and inhibitory factor IkappaB-alpha in human monocyte cell line THP-1, as well as its association with macrophage inflammatory protein (MIP-1alpha) upregulation.

METHODSTHP-1 monocytes were incubated with HCY, with and without NF-kappaB inhibitor pyrolidine dithiocarbamate (PDTC) pretreatment. Northern blot analysis and flow cytometry were used to detect MIP-1alpha mRNA and protein respectively. The nuclear protein NF-kappaB P65 subunit and the inhibitory protein IkappaB-alpha were analyzed by Western blotting.

RESULTSCompared with controls, HCY, at a concentration of 0.1 mmol/L, was able to enhance the expression of MIP-1alpha mRNA (up to 3.69-fold) and protein (1.16-fold) in THP-1 monocytes, as well as enhance NF-kappaB P65 transcription to nuclear proteins. These actions were significantly suppressed after pretreatment with 100 micromol/L PDTC for 30 minutes before HCY incubation; whereas incubation of THP-1 monocytes with PDTC only had no effect on both the expression of MIP-1alpha and nuclear transcription of NF-kappaB P65. Moreover, the level of IkappaB-alpha protein in THP-1 monocytes decreased after a 30-minute incubation with HCY, which gradually increased after 120 minutes.

CONCLUSIONSHomocysteine at a pathologic concentration stimulates MIP-1alpha expression in THP-1 monocytes, probably via NF-kappaB activation. Such activation may be caused by enhanced phosphorylation and degradation of the inhibitor protein IkappaB-alpha.