Free radical generation as induced by ochratoxin A and its analogs in bacteria (Bacillus brevis)

Lipid peroxidation is considered as one of the manifestations of cellular damage in the toxicity of ochratoxin A (OA). OA; its three natural analogs, OB, OC, and Oalpha; and four synthetic analogs, d-OA, the ethylamide of OA (OE-OA), O-methylated OA (OM-OA), and the lactone-opened OA (OP-OA) were used to study free radical generation in bacteria with Bacillus brevis as a model system. The uptake of the different ochratoxins by B. brevis varied substantially depending on the molecular structures. Electron paramagnetic resonance spectroscopy using alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone as a spin trapping agent showed an enhanced free radical generation due to the addition of OA and most of the analogs. The EPR signals could be further enhanced by the addition of Ca2+, a calcium ionophore and an ATPase uncoupler, whereas they were eliminated by incubating the growing cells with vitamin E. The spin adduct hyperfine splitting constants indicate the presence of alpha-hydroxyethyl radicals resulting from generated hydroxyl radicals, which are trapped by alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone. The results further suggest that OA induces free radical production in this model system by enhancing the permeability of the cellular membrane to Ca2+.