Cytotoxicity of lawsone and cytoprotective activity of antioxidants in catalase mutant Escherichia coli

Lawsone is an active naphthoquinone derivative isolated from henna (Lawsonia inermis L.), a widely used hair dye. Previous study on the toxicity of lawsone remains unclear since the involvement of oxidative stress and the kind of ROS (reactive oxygen species) involved have not been fully resolved yet. This present study reports the cytotoxic effects of lawsone and henna. We carried out CAT assay (a zone of inhibition test of bacterial growth and colony-forming efficiency test of transformant Escherichia coli strains that express mammalian catalase gene derived from normal catalase mice (Csa) and catalase-deficient mutant mice (Csb)), Ames mutagenicity assay and H2O2 generation assay. Lawsone generated H2O2 slightly in phosphate buffer system and was not mutagenic in Ames assay using TA 98, TA 100 and TA 102, both in the absence and presence of metabolic activation. Lawsone exposure inhibited the growth of both Csa and Csb strains in a dose-dependent manner. Mean zone diameter for Csa was 9.75 ± 0.96 mm and 12.75 ± 1.5 mm for Csb. Natural henna leaves did not show toxic effects, whereas two out of four samples of marketed henna products were shown toxicity effects. Catalase abolished zone of inhibition (ZOI) of marketed henna products, eliminated ZOI of lawsone in a dose-dependent manner and low concentration of exogenous MnSOD and Cu/ZnSOD eliminated the toxicity. Histidine and DTPA, the metal chelator; BHA and low concentration of capsaicin, the inducer of NADH-quinone reductase, effectively protected Csa and Csb against lawsone in this study. We suggest that lawsone cytotoxicity is probably mediated, at least in part, by the release of O2−, H2O2 and OH−.