Evaluation of the antioxidant activity of tetracycline antibiotics in vitro

Tetracyclines are the second most common antibiotic family in medicine usage. These antibiotics exhibit antioxidant potential; however, the exact mechanism remains unclear. The antiradical activity of the seven tetracyclines (TCs; tetracycline, chlortetracycline, oxytetracycline, doxocycline, methacycline, demeclocycline, minocycline) was determined using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals (HO) generated in a Fenton reaction. Electron spin resonance (ESR), ESR spin-trapping, chemiluminescence and spectrophotometry techniques were applied. It was found that the TCs showed high DPPH antiradical activity in the range 2696% at 2.5?mmol/L concentration. The second-order rate constants for the reaction between HO and TCs were calculated, in the range (3.69.6) x 109?L/mol/s. The tetracycline compounds also exhibited a strong decrease in light emission (range 6185% at concentration of 1?mmol/L). This study also showed that TCs promote the generation of singlet oxygen in the presence of H2O2 and Fe(II)/Fe(III) ions. Our findings suggest direct scavenging activity of the examined tetracyclines towards free radicals, and may be relevant to therapeutic strategy. Copyright (c) 2011 John Wiley & Sons, Ltd.