Free Radical Generation as Induced by Ochratoxin A and Its Analogs in Bacteria (Bacillus brevis)

Abstract

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 O␣; and four synthetic analogs, d-OA, the ethylamide of OA (OE-OA), O-methylated OA (OM-OA), and the lactoneopened 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 ␣-(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 Ca 2؉ , 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 ␣-hydroxyethyl radicals resulting from generated hydroxyl radicals, which are trapped by ␣-(4-pyridyl-1-oxide)-N-tertbutyl nitrone. The results further suggest that OA induces free radical production in this model system by enhancing the permeability of the cellular membrane to Ca 2؉ .

Ochratoxin A induces oxidative DNA damage in liver and kidney after oral dosing to rats

“…Changes in renal enzyme activities were also observed in these cotreatment experiments [30,31]. The hypothesis of oxidative stress being involved in OTA-mediated genetic damage is further strengthened by evidence from studies revealing OTA-dependent lipid peroxidation and free radical formation in mammalian cells and other systems as well as in rats [32][33][34][35]. Decreased concentrations of vitamin E in plasma of rats [30], and of glutathione in liver of mice, in primary hepatocytes and in CV-1 cells have also been reported after OTA treatment [22,36,37].…”

Ochratoxin A: The Continuing Enigma

“…In contrast, Hoehler et al 135 demonstrated vitamin E but not vitamin C to ameliorate the prooxidative effects of OTA in the chick model. The same group also demonstrated the generation of free radicals and malondialdehyde formation in Bacillus brevis 136 and in hepatocytes 137 following exposure to OTA and several of its analogs. Interestingly, the impact of OTB on free radical production in the B. brevis system was far less than that observed for OTA, which correlates with their relative in vivo and in vitro potencies.…”

Toxicity of Ochratoxin A and Its Modulation by Antioxidants: A Review

“…According to the authors, it is not yet clear whether the predominant toxic mechanism of OTA is of a genotoxic or epigenetic nature, such as induced cytotoxicity, oxidative cell stress or increased cell proliferation, due to an imbalance between proliferative and antiproliferative intracellular signal pathways. However, both the carcinogenicity and cytotoxicity of OTA have been related to free radical-mediated oxidative cell damage [42,43,44,45,46,47,48,49,50,51]. Schaaf et al .…”

“…Using a Bacillus brevis model, Hoehler’s et al . showed that OTA behaved as a cell pro-oxidant through mobilization of the Fe 2+ and Ca 2+ pathways, leading to uncoupling oxidative phosphorylation and increased production of hydroxyl radical via the Fenton reaction [45]. However, in other studies using OTA and structural analogs, a direct correlation between toxicity and iron chelating capacity was only partially supported [57].…”