Metabolic dysfunction in familial, but not sporadic, amyotrophic lateral sclerosis

Autosomal dominant familial amyotrophic lateral sclerosis (FALS) is associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Previous studies have implicated the involvement of metabolic dysfunction in ALS pathogenesis. To further investigate the biochemical features of FALS and sporadic ALS (SALS), we examined SOD activity and mitochondrial oxidative phosphorylation enzyme activities in motor cortex (Brodmann area 4), parietal cortex (Brodmann area 40), and cerebellum from control subjects, FALS patients with and without known SOD mutations, SALS patients, and disease controls (Pick's disease, progressive supranuclear palsy, diffuse Lewy body disease). Cytosolic SOD activity, predominantly Cu/Zn SOD, was decreased approximately 50% in all regions in FALS patients with SOD mutations but was not significantly altered in other patient groups. Marked increases in complex I and II-III activities were seen in FALS patients with SOD mutations but not in SALS patients. We also measured electron transport chain enzyme activities in a transgenic mouse model of FALS. Complex I activity was significantly increased in the forebrain of 60-day-old G93A transgenic mice overexpressing human mutant SOD1, relative to levels in transgenic wild-type animals, supporting the hypothesis that the motor neuron disorder associated with SOD1 mutations involves a defect in mitochondrial energy metabolism.

Evidence of increased oxidative damage in both sporadic and familial amyotrophic lateral sclerosis

Some cases of autosomal dominant familial amyotrophic lateral sclerosis (FALS) are associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1), suggesting that oxidative damage may play a role in ALS pathogenesis. To further investigate the biochemical features of FALS and sporadic ALS (SALS), we examined markers of oxidative damage to protein, lipids, and DNA in motor cortex (Brodmann area 4), parietal cortex (Brodmann area 40), and cerebellum from control subjects, FALS patients with and without known SOD mutations, SALS patients, and disease controls (Pick's disease, progressive supranuclear palsy, diffuse Lewy body disease). Protein carbonyl and nuclear DNA 8-hydroxy-2'-deoxyguanosine (OH8dG) levels were increased in SALS motor cortex but not in FALS patients. Malondialdehyde levels showed no significant changes. Immunohistochemical studies showed increased neuronal staining for hemeoxygenase-1, malondialdehyde-modified protein, and OH8dG in both SALS and FALS spinal cord. These studies therefore provide further evidence that oxidative damage may play a role in the pathogenesis of neuronal degeneration in both SALS and FALS.

Oxidative damage and metabolic dysfunction in Huntington's disease: selective vulnerability of the basal ganglia

The etiology of the selective neuronal death that occurs in Huntington's disease (HD) is unknown. Several lines of evidence implicate the involvement of energetic defects and oxidative damage in the disease process, including a recent study that demonstrated an interaction between huntingtin protein and the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Using spectrophotometric assays in postmortem brain tissue, we found evidence of impaired oxidative phosphorylation enzyme activities restricted to the basal ganglia in HD brain, while enzyme activities were unaltered in three regions relatively spared by HD pathology (frontal cortex, parietal cortex, and cerebellum). Citrate synthase-corrected complex II-III activity was markedly reduced in both HD caudate (-29%) and putamen (-67%), and complex IV activity was reduced in HD putamen (-62%). Complex I and GAPDH activities were unaltered in all regions examined. We also measured levels of the oxidative damage product 8-hydroxydeoxyguanosine (OH8dG) in nuclear DNA, and superoxide dismutase (SOD) activity. OH8dG levels were significantly increased in HD caudate. Cytosolic SOD activity was slightly reduced in HD parietal cortex and cerebellum, whereas particulate SOD activity was unaltered in these regions. These results further support a role for metabolic dysfunction and oxidative damage in the pathogenesis of HD.