Exposure to Cigarette Smoke is Linked to Platelet‐Activating Factor Accumulation in Myocardial Tissue

Abstract

Smoking is a lifestyle risk factor for heart disease and is responsible for one‐third of all cardiovascular deaths. Although many studies have investigated the correlation between smoking and coronary artery disease, there are few studies examining the direct effect of smoking on the myocardium. In this study, we examined the effect of smoking on myocardial accumulation of platelet‐activating factor (PAF), a phospholipid mediator that causes a negative inotropic effect, arrhythmias, apoptosis and is involved in inflammation and atherosclerosis. Ventricular samples from mice exposed up to six months of cigarette smoke (48 min/day, 5 days/week), and human right atrial samples from smokers and nonsmokers scheduled for coronary artery bypass graft surgery were analyzed for biochemical and histochemical changes using activity assays, ELISA, immunoblot, and immunohistochemistry. Mice exposed to cigarette smoke showed a decrease in PAF‐acetylhydrolase (PAF‐AH, the enzyme responsible for PAF metabolism) activity that was significant after 1 month and decreased progressively over the 6 month period (5.8 ± 0.3 to 3.2 ± 0.5 nmol/mg protein/min, p<0.01, n=6). This inhibition in PAF‐AH activity was accompanied by increased myocardial PAF content (0.23 ± 0.04 to 0.35 ± 0.03 at 6 months smoking, p<0.05, n=6). In humans, smoking was associated with an increase in PAF content (3.19 ± 0.28 vs 4.29 ± 0.37 nmol/mg protein, p<0.05, n=18) and inhibition of PAF‐AH activity (30.7 ± 2.0 vs 23.2 ± 1.8 nmol/mg protein/min, p<0.01, n=18) when comparing atrial tissue from never smokers to current smokers. We did not detect a change in phospholipase A2 activity (the enzyme responsible for PAF production) in human or mouse myocardium exposed to cigarette smoke or room air. Thus, we hypothesize that the increase in PAF content in the myocardium is likely a result of smoking‐induced inhibition of PAF‐AH activity. The inhibition of PAF‐AH and subsequent accumulation of PAF in the myocardium of cigarette smokers may play a role in the pathogenesis of heart disease in this population. Support or Funding Information Lottie Caroline Hardy Foundation (to J.McH.)