thapsigargin and alpha-naphthoflavone

Previous studies in this laboratory have shown that polycyclic aromatic hydrocarbons (PAHs) alter Ca2+ homeostasis and inhibit activation of both B and T lymphocytes obtained from rodents and humans. In the present studies, we demonstrate that alpha-naphthoflavone (ANF), an inhibitor of cytochrome P4501A activity, reduced the Ca2+ elevation produced by BaP in human peripheral blood mononuclear cell (HPBMC) lymphocytes. These results suggested that BaP metabolites may play a role in intracellular Ca2+ homeostasis in human lymphocytes. Reactive oxidative intermediates of BaP produced in HPMBC are known to be highly carcinogenic and have also been shown to be immunosuppressive. We examined the effects of benzo(a)pyrene (BaP), 7,12-dimethylbenz(a)anthracene (DMBA), benzo(e)pyrene (BeP), and anthracene, as well as certain BaP metabolites, on the levels of intracellular Ca2+ and glutathione in HPBMC. While BaP, DMBA, BeP, and anthracene did not cause a statistically significant decrease in GSH in HPBMC at concentrations of 1 or 10 microM following a 6-, 48-, or 72-hr exposure, reactive BaP metabolites including 4,5-epoxide BaP and 7,8-diol-9,10-epoxide BaP consistently produced a 20-30% depletion of glutathione in HPBMC following a 6-hr treatment period. These BaP metabolites also elevated intracellular Ca2+ in HPBMC during a 6-hr incubation. Results of these experiments suggest that metabolism of BaP to certain epoxide metabolites may be responsible for sulfhydryl damage leading to transient GSH depletion and Ca2+ elevation. These results are consistent with the hypothesis that sulfhydryl damage by certain PAH metabolites may lead to altered Ca2+ homeostasis, leading to inhibition of cell activation and proliferation in HPBMC.

Topics: Benzo(a)pyrene; Benzoflavones; Calcium; Enzyme Activation; Glutathione; Humans; Ionomycin; Lymphocytes; Protein Kinase C; Tetradecanoylphorbol Acetate; Thapsigargin