Cigarette smoke causes follicle loss in mice ovaries at concentrations representative of human exposure

Cigarette smoke is a documented reproductive toxicant associated with infertility and ovarian failure. However, the underlying mechanism(s) regulating the toxic effects of cigarette smoke are unknown. Therefore, we tested the hypothesis that mainstream cigarette smoke and a cigarette smoke constituent, benzo[a]pyrene (BaP), induce apoptosis in ovarian follicles. Mice were exposed to mainstream cigarette smoke and the ovaries were analysed for follicle loss and markers of apoptosis (TUNEL, Caspase 3, Caspase 8, Bax, Bcl-2, Fas and FasL). Isolated ovaries from female pups were cultured in media containing increasing concentrations of BaP (1-10 000 ng ml(-1)), and markers of apoptosis were quantified. Cigarette smoke exposure induced a significant reduction in the number of primordial follicles, but not growing or antral follicles compared with controls. Mainstream cigarette smoke exposure had no effect on any marker of apoptosis measured. Exposure of ovaries to BaP in vitro resulted in an increase in the pro-survival marker Bcl-2, but no change in apoptosis. Our data suggest that cigarette smoke-induced follicle loss is not mediated via BaP-induced apoptosis.