The Metabolism of Tyramine by Monoamine Oxidase A/B Causes Oxidative Damage to Mitochondrial DNA
摘要
Monoamine oxidases A/B (EC 1.4.3.4, MAO), flavoenzymes located on the outer mitochondrial membrane, catalyze the oxidative deamination of biogenic amines, such as dopamine, serotonin, and norepinephrine. In this study, we examined whether the H2O2formed during the two-electron oxidation of tyramine [4-(2-aminoethyl)phenol] (a substrate for monoamine oxidases A/B) may contribute to the intramitochondrial steady-state concentration of H2O2([H2O2]ss) and, thus, be involved in the oxidative impairment of mitochondrial matrix components. Supplementation of intact, coupled rat brain mitochondria with benzylamine, β-phenylethylamine, or tyramine showed initial rates of H2O2production ranging from 0.4- to 1.6 nmol H2O2/min/mg protein. ESR analysis of the oxidative deamination of tyramine by intact rat brain mitochondria revealed the formation of hydroxyl (HO) and carbon-centered radical adducts—the latter probably originating by the HO-mediated oxidation of mannitol. The signals were substantially enhanced upon addition of FeSO4and were abolished by catalase. The intramitochondrial [H2O2]sscalculated in terms of glutathione peroxidase activity during the metabolism of tyramine was 48-fold higher (7.71 ± 0.25 × 10−7M) than that obtained during the oxidation of succinate via complex II in the presence of antimycin A (1.64 ± 0.2 × 10−8M). Oxidative damage to the brain mtDNA was assessed by single strand breakage. The ratio of nicked DNA for the preparations treated with tyramine and those without the amine was 1.5 ± 0.29 (n