Passive smoking induces atherogenic changes in low-density lipoprotein

Background-According to the American Heart Association, passive smoking is an important risk factor for coronary heart disease (CHD), but the mechanisms underlying this association are not fully understood. We studied the acute effect of passive smoking on the factors that influence the development of CHD: the antioxidant defense of human serum, the extent of lipid peroxidation, and the accumulation of LDL cholesterol in cultured human macrophages, the precursors of foam cells in atherosclerotic lesions. Methods and Results-Blood samples were collected during 2 ordinary working days from healthy, nonsmoking subjects (n=10) before and after (up to 5.5 hours) spending half an hour in a smoke-free area (day 1) or in a room for smokers (day 2). Passive smoking caused an acute decrease (1.5 hours after exposure) in serum ascorbic acid (P<.001) and in serum antioxidant defense (P<.001), a decreased capacity of LDL to resist oxidation (P<.01), and the appearance of increased amounts of lipid peroxidation end products in serum (P<.01). Finally, LDL isolated from subjects after passive smoking was taken up by cultured macrophages at an increased rate (P<.05). Conclusions-Exposure of nonsmoking subjects to secondhand smoke breaks down the serum antioxidant defense, leading to accelerated lipid peroxidation, LDL modification, and accumulation of LDL cholesterol in human macrophages. These data provide the pathophysiological background for the recent epidemiological evidence about the increased CHD risk among passive smokers.