MONOCYTE-VASCULAR SMOOTH-MUSCLE CELL-INTERACTION ENHANCES NITRIC-OXIDE PRODUCTION

Objective: The adhesive interaction of monocytes and vascular smooth m uscle cells (VSMCs) has been suggested to be a regulatory signal in th e cellular activation that is involved in the pathogenesis of atherosc lerosis. We investigated the effects of monocyte-VSMC interaction on i nducible nitric oxide (NO) synthase expression. Methods: NO production by the cultured cells was determined by measuring the nitrite content of the culture media using the Griess reagent. The expression of indu cible NO synthase protein was assayed by Western blotting. Results: In terleukin-1 beta (IL-1 beta) induced nitrite production by VSMCs in a time-dependent manner. The addition of the mouse monocyte cell line J7 74 to IL-1 beta-stimulated VSMCs further increased nitrite production in a monocyte number-dependent manner. Enhanced nitrite production by coculture was accompanied by increased inducible NO synthase protein a ccumulation. Addition of tumor necrosis factor-alpha (TNF-alpha) also enhanced IL-1 beta-induced nitrite production by VSMCs, but TNF-alpha showed no effect in the presence of monocytes. Coculture of monocytes and VSMCs in the presence of IL-1 beta secreted substantial amounts of TNF-alpha. The production of nitrite by coculture was markedly inhibi ted by an anti-TNF-alpha antibody. Conclusions: The present study reve aled that direct cell-to-cell interaction between monocytes and VSMCs enhances NO production, suggesting an important role for their interac tion in the pathogenesis of atherosclerosis. (C) 1998 Elsevier Science B.V.