Antimutagenic effects of vitamin C against oxidative changes induced by quinolones

Quinolones are broad-spectrum antibiotics effective against both Gram-positive and Gram-negative bacteria. Reactive oxygen species (ROS) generated by quinolones may damage cell structures and could be a risk to health. The use of vitamin C to reduce such risks may have the opposite effects: vitamin C in the presence of divalent metal ions can induce the Fenton reaction, leading to hydroxyl radical (HO^̇) generation and oxidative damage. The purpose of this study is to evaluate the antioxidant and prooxidant properties of vitamin C by measuring its effects on both lipid peroxidation and mutagenesis induced by quinolones nalidixic acid (NLX) or norfloxacin (NOR) in Salmonella typhimurium TA102. Mutagenicity was evaluated by the Ames test and the results were expressed as (histidine⁺ revertants/ng of quinolone), while lipoperoxidation was measured as thiobarbituric acid reactive substances (umol malondialdehyde/(mL·h)). The effects of different concentrations of nalidixic acid (10-1000 ng) or norfloxacin (7-700 ng) on S. typhimurium TA102 were studied, employing the S9 mix (liver homogenate from rats pre-treated with Arochlor 1254) in the presence of 10-1000 ng of ascorbic acid (AA) with 0.1 mM FeCl₃ or EDTA. Minimal inhibitory concentrations of NOR and NLX against 25 uropathogenic Escherichia coli strains were obtained using the plate dilution method in the presence of vitamin C. Vitamin C (1 mg) together with 0.1 mM FeCl₃ showed a prooxidant effect in the S9 mix and enhanced the lipoperoxidation induced by either NOR or NLX. Mutagenic potency was also increased for both NOR and NLX. When metal ions were chelated with EDTA, ascorbate showed both antimutagenic and antioxidant properties. Mutagenic potency and lipoperoxidation were reduced for both NOR and NLX. The addition of vitamin C did not change the minimal in vitro inhibitory concentrations of NLX or NOR against the 25 uropathogenic E. coli strains. The antimutagenic and antioxidant effects of vitamin C were especially marked when the Salmonella strain was exposed to NOR or NLX in the presence of EDTA. In contrast, the vitamin C in the presence of FeCl₃ increased ROS generation, enhancing both the mutagenic effect of the quinolones and malondialdehyde production from lipoperoxidation induced in the bacterial membranes. Therapeutic use of quinolones together with vitamin C and divalent cations might induce the Fenton reaction involving norfloxacin and nalidixic acid. However, our results suggest that vitamin C could be a good alternative for reducing the genotoxic risk of these therapeutic drugs if it is carefully handled.