Nicotine inhibition of apoptosis in murine immune cells

Nicotine, the addictive component of tobacco, is thought to be at least par tially responsible for the deleterious effects of smoking such as heart dis ease and cancer. Evidence shows that nicotine is an immunomodulator and tha t one of its possible mechanisms is regulation of apoptosis, or programmed cell death, in immune cells. This study examined the effects and the mechan isms of action of nicotine on dexamethasone (DEX)-induced apoptosis in muri ne immune cells by examining the expression of levels of the 17-kDa active caspase-3, a marker of apoptosis. Thymocytes and splenocytes from adult BAL B/c female mice were incubated with concentrations, of nicotine correlating to those found in the blood and tissue of smokers (0.01 mug/ml [0.022 muM] and 1 mug/ml [2.2 muM]), concurrently with 100 nM DEX, to induce apoptosis . Cytosolic protein fractions were analyzed by Western blotting with polycl onal antibodies that recognize the active form of caspase-3. The data showe d that nicotine significantly blocked the formation of the DEX-induced 17-k Da caspase-3 subunit expression. This downregulation ranged from 65% to 100 % of the active caspase-3 expressed in cultures treated with DEX alone. Add ition of d-tubocurarine chloride (dTC), a general nicotinic receptor antago nist, inhibited nicotine downregulation of the DEX-induced active caspase-3 expression, providing evidence that this action of nicotine was receptor-m ediated. These data support that nicotine is an important immunomodulator a t the level of immune cell apoptosis, a process thought to be a contributor y mechanism of autoimmunity, cardiovascular disease, and carcinogenesis.