NICOTINE AND ITS METABOLITE COTININE ARE MITOGENIC FOR HUMAN VASCULARSMOOTH-MUSCLE CELLS

Purpose: Intimal hyperplasia caused by smooth muscle cell (SMC) prolif eration is the major cause of infrainguinal graft failure within the f irst 12 months, Tobacco smoking is associated with a twofold increase in graft failure within the first year of extremity bypass surgery, bu t the mechanism is not clearly understood. This study evaluated the ef fect of nicotine and its major stable metabolite cotinine on vascular SMC proliferation in vitro. Methods: SMC were harvested from human art eries and grown in culture with standard methods. Cells were seeded at a density of 1.8 x 10(4) cells/well in 24 multiwell dishes and cell c ircle-synchronized. Subsequently the SMC were incubated with media con taining 0.1% or 15% fetal bovine serum and nicotine or cotinine at con centrations ranging from 10(-9) mol/L to 10(-6) mol/L. Control samples mere incubated with corresponding media but without the drugs. SMC pr oliferation was determined at 4 daps with a cell counter. DNA synthesi s was assessed at 24 hours with H-3-thymidine uptake. The results were expressed as a percentage change compared with the control samples (m ean +/- SEM). Results were analyzed by analysis of variance and t test s. Results: In the presence of serum both nicotine and cotinine at con centrations of 10(-7) and 10(-8) mol/L were mitogenic for SMC in vitro (p < 0.05). A weak mitogenic effect was observed at a low serum conce ntration for cotinine but not nicotine. Cotinine at a concentration of 10(-9) mol/L, a level seen among passive smokers, was a statistically significant stimulus for DNA synthesis in both minimum serum and seru m-supplemented media. At high concentrations both substances were toxi c for the cells. Conclusion: We have demonstrated a potential role for nicotine and cotinine in the development of intimal hyperplasia and u ltimately failure of the vascular reconstruction.