Dopamine neurotoxicity: inhibition of mitochondrial respiration.
Level 5 - mechanism / opinion, no new human data
Preclinical animal and in vitro biochemical study
PubMed 7830065 · doi:10.1046/j.1471-4159.1995.64020718.x
What was done
Rats pretreated with the nonselective monoamine oxidase inhibitor pargyline received intracerebroventricular injections of dopamine or norepinephrine to evaluate mortality, with or without co-treatment using the iron chelator desferrioxamine. Brain tissue from the frontal cortex and striatum of rats receiving lethal doses of dopamine was analyzed for lipid peroxidation, protein peroxidation, and glutathione reductase and peroxidase activities. In vitro assays evaluated iron-induced malondialdehyde formation and mitochondrial NADH dehydrogenase activity in the presence of catecholamines, desferrioxamine, and ADP.
What was found
Intracerebroventricular dopamine caused dose-dependent mortality in pargyline-pretreated rats with an LD50 of 90 micrograms, compared to an LD50 of 141 micrograms for norepinephrine. Desferrioxamine completely protected against dopamine-induced mortality, and survival increased in the absence of pargyline. Brain tissue from lethally dosed rats showed no differences in lipid or protein peroxidation or glutathione enzyme activities compared to controls. In vitro, dopamine reduced iron-induced malondialdehyde formation and inhibited mitochondrial NADH dehydrogenase activity with an IC50 of 8 microM (norepinephrine IC50 = 15 microM). NADH dehydrogenase inhibition was partially reversed by desferrioxamine and reversed dose-dependently by ADP.
Why it matters
The findings demonstrate that dopamine toxicity can occur via direct inhibition of the mitochondrial electron transport chain (NADH dehydrogenase) rather than exclusively through enzymatic oxidation products or generalized oxidative stress.
Limits
Findings are limited to acute rodent and in vitro assays; the abstract does not report the number of animals or replicate samples used. High-dose intracerebroventricular bolus injections do not fully replicate chronic endogenous human neurodegenerative processes.
Cited by
- contradicts Dopamine binds to monoamine oxidase on the outer surface of mitochondria to initiate electron transport and increase ATP availability.