Effects of homocysteine on murine splenic B lymphocyte proliferation and its signal transduction mechanism

Objective: Elevated plasma homocysteine (Hey) levels have been defined as an increased risk of atherosclerosis, However, the mechanisms that Hey induces the development of atherosclerosis a-re not fully understood. Therefore, effect of Hey on B lymphocyte proliferation and its cellular mechanism were examined in normal and hyperhomocysteinemia ApoE-knockout mice. Methods: Mouse B lymphocytes were incubated with Hey, related compounds and/or antioxidants and/or inhibitors of PKC, p38 MAPK, NF-kappaB in the presence or absence of lipopolysaccharide. DNA synthesis, production of reactive oxygen species was measured. Results: Hey (0.1-3.0 mM) and other compounds with thiol (-SH), such as cysteine and glutathione significantly increased resting and lipopolysaccharide-induced B lymphocyte proliferation. ApoE-knockout mice with hypercysteinemia (plasma Hey levels were 20.3+/-2.9 vs. 2.6+/-0.6 muM in control, P<0.05) had a significant promotion of B cell proliferation in response to lipopolysaccharide. Hey also increased intracellular reactive oxygen species production, Radical scavengers reduced Hcy-induced B lymphocyte proliferation. The promotion of Hcy was significantly inhibited by inhibitors of PKC (calphostin C and RO-31-82201), p39 MAPK (SB 202190 and PD 169316) and NF-kappaB (pyrrolidine dithiocarbamate). Conclusions: The reactive oxygen species generated by thiol (-SH) auto-oxidation of Hey are essential, and PKC, p38 MAPK and NF-kappaB are involved in the Hey-induced B lymphocyte proliferation. Hyperhomocysteinemia may increase B lymphocyte susceptibility to inflammatory progression of atherosclerotic lesions. (C) 2001 Elsevier Science B.V. All rights reserved.