ASCORBATE AFFECTS PROLIFERATION OF GUINEA-PIG VASCULAR SMOOTH-MUSCLE CELLS BY DIRECT AND EXTRACELLULAR-MATRIX MEDIATED EFFECTS

Proliferation of smooth muscle cells and deposition of extracellular m atrix proteins are important events in the formation of atheroscleroti c plaques, Mie have investigated the direct and matrix-mediated effect s of ascorbate on the proliferation rate of vascular smooth muscle cel ls (VSMC) isolated from the guinea-pig aorta, In the presence of ascor bate, cells showed a bi-phasic growth pattern, At 125 mu M ascorbate, [H-3]-thymidine incorporation was stimulated 25%. However, higher conc entrations of ascorbate gradually decreased cell-incorporated radioact ivity up to 50% at 2 mM ascorbate. These effects of ascorbate on DNA s ynthesis in VSMC were paralleled by the changes in cell number and wer e not due to ascorbate cytotoxicity, Alpha-tocopherol (0.1 mM), indivi dually and in combinations with 1 mM ascorbate, also inhibited DNA syn thesis in VSMC. Ascorbate also influenced proliferation of smooth musc le cells through matrix-mediated effect. New VSMC culture plated on ex tracellular matrices deposited by smooth muscle cells in the presence of 0.1-1 mM ascorbate had up to 50% lower proliferation rate than on m atrices from ascorbate-deficient cells, as assessed by [H-3]-thymidine incorporation. This effect was independent from alpha-tocopherol and specific inhibitors of collagen synthesis: L-azetidine-2-carboxylic ac id and pyridine-2,4-dicarboxylic acid. An ascorbate-dependent matrix e ffect was specific for smooth muscle cells grown on VSMC and human ski n fibroblast-originated matrices, but not for human vascular endotheli al cells. The possible involvement of ascorbate in the regulation of s mooth muscle cells proliferation by its antioxidant/pro-oxidant effect s and regulation of extracellular matrix composition are discussed. (C ) 1997 Academic Press Limited.