Parkinsonism Treatment: Part III—Update

Mitochondrial dysfunction and oxidative stress in aging and neurodegenerative disease

A major risk factor for neurodegenerative diseases such as Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) is aging. Two processes that have been implicated in aging are free radical-induced oxidative damage and mitochondrial dysfunction. A progressive impairment of mitochondrial function and/or increased oxidative damage has been suggested to play critical roles in the pathogenesis of these neurodegenerative diseases. For example, decreased complex I activity, increased oxidative damage and altered activities of antioxidant defense enzymes have been demonstrated in PD. In AD, decrements in complex IV activity and increased oxidative damage have been reported. Reductions in complex II activity, increased cortical lactate levels and oxidative damage have been described in HD. Some familial ALS cases are associated with mutations in the gene for Cu,Zn superoxide dismutase (SOD1) while increased oxidative damage is observed in sporadic ALS. Studies in PSP have demonstrated regionally specific reductions in brain and muscle mitochondrial function, hypofrontality and increased oxidative damage. Altogether, the age-dependent onset and progressive course of these neurodegenerative diseases may ultimately highlight an association between aging, mitochondrial impairment and oxidative stress.

Vitamin E in extrapyramidal disorders

In this article the effect of vitamin E on two extrapyramidal disorders, tardive dyskinesia and Parkinson's disease, is reviewed. After a brief description of the symptoms, the current hypotheses for the pathogenesis of these diseases are described. A summary of the clinical research that has been done to establish the effectiveness of vitamin E is given. In tardive dyskinesia four clinical trials (double-blind, placebo-controlled) showed improvement in the symptoms with vitamin E in doses of up to 1,600 IU/day. Preliminary studies concerning Parkinson's disease suggested that vitamin E (2,000 IU/day) probably cannot prevent the development of the disease. It was suggested that vitamin E is able to slow the progression of the illness. The results from a large double-blind, placebo-controlled clinical trial, however, did not show any beneficial effect of vitamin E in Parkinson's disease.