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Hydrogen peroxide production by monoamine oxidase during ischemia-reperfusion in the rat brain
S G Simonson1, J Zhang, A T Canada
1Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
Abstract:
Monoamine oxidase (MAO) as a source of hydrogen peroxide (H2O2) was evaluated during ischemia-reperfusion in vivo in the rat brain. H2O2 production was assessed with and without inhibition of MAO during and after 15 min of ischemia. Metabolism of H2O2 by catalase during ischemia and reperfusion was measured in forebrain homogenates using aminotriazole (ATZ), an irreversible H2O2-dependent inhibitor of catalase. Catecholamine and glutathione concentrations in forebrain were measured with and without MAO inhibitors. During ischemia, forebrain blood flow was reduced to 8% of baseline and H2O2 production decreased as measured at the microperoxisome. During reperfusion, a rapid increase in H2O2 generation occurred within 5 min as measured by a threefold increase in oxidized glutathione (GSSG). The H2O2-dependent rates of ATZ inactivation of catalase between control and ischemia-reperfusion were similar, indicating that H2O2 was more available to glutathione peroxidase than to catalase in this model. MAO inhibitors eliminated the biochemical indications of increased H2O2 production and increased the catecholamine concentrations. Mortality was 67% at 48 h after ischemia-reperfusion, and there was no improvement in survival after inhibition of MAO. We conclude that MAO is an important source of H2O2 generation early in brain reperfusion, but inhibition of the enzyme does not improve survival in this model despite ablating H2O2 production.
Insights
Monoamine oxidase (MAO) generates hydrogen peroxide (H2O2) during brain reperfusion after ischemia. Inhibiting MAO reduced H2O2 but did not improve survival rates in rats.
Area of Science:
- Neuroscience
- Biochemistry
- Pathophysiology
Background:
- Ischemia-reperfusion injury is a significant cause of brain damage.
- Hydrogen peroxide (H2O2) plays a role in cellular damage during reperfusion.
- Monoamine oxidase (MAO) is an enzyme involved in neurotransmitter metabolism and can produce H2O2.
Purpose of the Study:
- To investigate the role of MAO as a source of H2O2 during in vivo rat brain ischemia-reperfusion.
- To assess the impact of MAO inhibition on H2O2 production, catecholamine levels, and survival.
Main Methods:
- In vivo rat model of 15-minute forebrain ischemia followed by reperfusion.
- Measurement of H2O2 production using microperoxisomes and assessment of catalase activity.
- Quantification of oxidized glutathione (GSSG), catecholamines, and glutathione concentrations.
- Administration of MAO inhibitors and aminotriazole (ATZ).
Main Results:
- During ischemia, H2O2 production decreased, but rapidly increased upon reperfusion, indicated by a threefold rise in GSSG.
- MAO inhibition abolished the increase in H2O2 production and elevated catecholamine levels.
- Catalase activity was similar between control and ischemia-reperfusion groups, suggesting H2O2 preferentially engaged glutathione peroxidase.
- MAO inhibition did not improve the 67% mortality rate at 48 hours post-reperfusion.
Conclusions:
- MAO is a significant contributor to H2O2 generation during early brain reperfusion.
- Despite mitigating H2O2 production, MAO inhibition does not enhance survival in this specific ischemia-reperfusion model.
- Further research is needed to explore therapeutic strategies targeting MAO or H2O2 pathways in brain injury.