Methanol is an important industrial solvent and is being developed as an alternative fuel and energy source. Blindness or serious visual impairment is a well known effect of human methanol poisoning, however, the mechanisms responsible for the toxic actions of this agent are not understood. The increased use an availability of methanol expands the potential for methanol exposure and underscores the importance of understanding its toxicity. The objective of this research is to investigate the mechanisms of methanol-induced retinal and optic nerve toxicity using a methanol-sensitive nonprimate animal model developed in my laboratory. These studies will test the hypothesis that formic acid, the toxic metabolite in methanol poisoning, inhibits the activity of the mitochondrial enzyme cytochrome oxidase resulting in depletion of high energy phosphates and disruption of ATP dependent processes followed by retinal dysfunctional and retinal damage. (1) Studies will conducted to define the relationship between the bioenergetic, neurofunctional and morphologic alterations produced in the retina during methanol- intoxication. The activity of cytochrome oxidase and the concentrations of energy metabolites will be measured in the retinas of methanol- intoxicated rats to determine if formate inhibits cytochrome oxidase activity in vivo resulting in decreased ATP production and a shift to and a shift to anaerobic metabolism. Detailed electroretinographic investigations will be conducted to define the development, nature and extent of formate-induced alterations in rod and one mediated responses and to correlate these changes with alterations in retinal energy metabolism and morphology. Morphologic studies coupled with cytochrome oxidase histochemistry will determine if reductions in cytochrome oxidase activity precede the onset of visual disturbances and histopathologic changes in the retina and optic nerve. (2) Experiments will be performed to characterized the effects of direct formate exposure on retinal energy metabolism, function and structure. To further substantiate the role of formate in methanol-induced retinal toxicity, we will compare the effects of intravitreal formate administration with those of methanol- intoxication on retinal cytochrome oxidase activity, energy metabolites electroretinographic responses and cytochrome oxidase histochemistry. (3) Studies will be conducted to investigate the involvement of excitatory amino acids as mediators of retinal damage secondary to formate induced energy depletion in methanol-intoxication. These studies will determine if therapeutic interventions designed to attenuate the neurotoxic actions of excitatory amino acids will ameliorate formate retinotoxicity in methanol-intoxicated rats. Successful completion of the studies outlined in this proposal will improve our understanding of the mechanism of action of this important environmental neurotoxin at a cellular and molecular level. Furthermore, this information will enhance our understanding of mitochondrial function and dysfunction and may be a first step in the development and testing of effective treatments for mitochondrial toxicities.
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