title: The effect of bicarbonate on menadione-induced redox cycling and cytotoxicity: potential involvement of the carbonate radical.
abstract: We have investigated the effect of NaHCO3 on menadione redox cycling and cytotoxicity. A cell-free system utilized menadione and ascorbic acid to catalyze a redox cycle, and we utilized murine hepatoma (Hepa 1c1c7) cells for in vitro experiments. Experiments were performed using low (2 mmol/L) and physiological (25 mmol/L) levels of NaHCO3 in buffer equilibrated to physiological pH. Using oximetry, ascorbic acid oxidation, and ascorbyl radical detection, we found that menadione redox cycling was enhanced by NaHCO3. Furthermore, Hepa 1c1c7 cells treated with menadione demonstrated cytotoxicity that was significantly increased with physiological concentrations of NaHCO3 in the media, compared with low levels of NaHCO3. Interestingly, the inhibition of superoxide dismutase (SOD) with 2 different metal chelators was associated with a protective effect against menadione cytotoxicity. Using isolated protein, we found a significant increase in protein carbonyls with menadione-ascorbate-SOD with physiological NaHCO3 levels; low NaHCO3 or SOD-free reactions produced lower levels of protein carbonyls. In conclusion, these findings suggest that the hydrogen peroxide generated by menadione redox cycling together with NaHCO3-CO2 are potential substrates for SOD peroxidase activity that can lead to carbonate-radical-enhanced cytotoxicity. These findings demonstrate the importance of NaHCO3 in menadione redox cycling and cytotoxicity.
authors.affiliation: a University of Alberta, Faculty of Pharmacy and Pharmaceutical Sciences, Edmonton, AB T6G 2E1, Canada.
authors.forename: Naif
authors.initials: N
authors.lastname: Aljuhani
authors.forename: Karim
authors.initials: K
authors.lastname: Michail
authors.forename: Zubeida
authors.initials: Z
authors.lastname: Karapetyan
authors.forename: Arno G
authors.initials: AG
authors.lastname: Siraki
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D002021:Buffers; D045744:Cell Line, Tumor; D002474:Cell-Free System; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D051379:Mice; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects*; D050050:Protein Carbonylation; D017693:Sodium Bicarbonate / Q000633:toxicity*; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000378:metabolism; D024483:Vitamin K 3 / Q000633:toxicity*
chemical_list: D002021:Buffers; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005609:Free Radicals; D024483:Vitamin K 3; D017693:Sodium Bicarbonate; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; D001205:Ascorbic Acid