Does selegiline monotherapy in Parkinson's disease act by symptomatic or protective mechanisms?

Selegiline monotherapy has been clearly demonstrated to delay the development of disability in early, otherwise untreated Parkinson's disease patients. It remains uncertain, however, whether this benefit is due to protective effects on residual neurons or to symptomatic effects that mask the detection of underlying disability. This paper examines the evidence and theory supporting the hypotheses that selegiline acts by protective or symptomatic mechanisms and considers what future studies might help clarify these issues.

Aging of the brain and vitamin E

Using a recently-developed membrane lipid peroxidation (MLP) system, we demonstrated the important role of vitamin E in the prevention of MLP and the possible relationship between MLP and pathogenesis of Parkinson's disease.

Initiating treatment of Parkinson's disease

Treatment of Parkinson's disease (PD) can be divided into two categories: symptomatic therapy (restoring dopamine levels toward normal and reversing functional disability) and preventive therapy (interfering with the pathophysiologic mechanism of PD to prevent or decrease the rate of progression of the disease). Regarding symptomatic treatment, although anticholinergic preparations generally are considered effective for the symptoms of tremor and rigidity without altering bradykinesia, their effectiveness is limited and adverse reactions are common; their role should be restricted to use as adjuvants to levodopa therapy. Amantadine has been shown to be as effective as anticholinergics, but it lacks long-term efficacy. Dopamine agonists--bromocriptine, pergolide mesylate and lisuride in Europe--are not as effective as levodopa and therefore rarely are used as initial therapy; their proposed role, too, is as adjuvants to levodopa therapy. Levodopa is the most effective drug presently available for the treatment of PD; its introduction is accompanied by rapid and dramatic reduction of symptoms and signs. Initial adverse reactions are not usually a major problem; and although there is speculation that initiation of therapy should be delayed because of possible long-term complications, clinically distinguishing these from problems related to disease progression itself is difficult. The possibility that nigral cell death is mediated by oxidative mechanisms provides the basis for considering antioxidant therapy as protective treatment; selegiline, an antioxidant, has been found to delay the need for symptomatic therapy. It is suggested that initial treatment of Parkinson's disease begin with both preventive therapy with selegiline and symptomatic treatment with the sustained-release preparation of levodopa, which may be associated with fewer long-term complications.

Smoker's melanosis may explain the lower hearing loss and lower frequency of Parkinson's disease found among tobacco smokers--a new hypothesis

A new hypothesis is presented explaining the preventive effect of tobacco smoking found on noise induced hearing loss and on the frequency of Parkinson's disease. The hypothesis is based on the finding of a melanocyte stimulation of tobacco smoking in the human oral mucosa, resulting in a higher melanin content in the epithelial cells, and a higher frequency of visible oral melanin pigmentation--smoker's melanosis. The preventive influence of smoking found in the cochlea and substantia nigra may also be due to a higher melanin content and to the ability of melanin to strongly bind specific chemical agents for a long time. Melanin may in this way act as a scavenger against cell toxic factors in these organs.

MPTP-induced neurotoxicity and the quest for a preventative therapy for Parkinson's disease

Less than 10 years have passed since the discovery that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is capable of producing parkinsonism in both humans and non-human primates. In that time, there has been considerable interest in the possibility that the pathogenesis of idiopathic Parkinson's disease (PD) might involve a process analogous to that of MPTP toxicity. One hypothesis holds that PD might arise, at least in part, from exposure to an MPTP-like environmental toxin. Rapid progress has been made towards elucidating the precise mechanism by which MPTP exerts toxicity, and clarifying the relationship of MPTP toxicity to idiopathic PD. The goal of these efforts is to develop a therapy that inhibits the underlying disease process in PD.

A screening and alerting questionnaire for parkinsonism

A self-administered eight-symptom questionnaire on parkinsonism was completed by 35 patients known to have parkinsonism and 88 controls independently selected by a local general practice. The presence of shaking and difficulty opening things/doing small buttons were the commonest positive responses among the cases (27/35). While a shuffling walk and difficulty turning in bed were the least frequent positive responses among the cases, they were also the two questions least likely to be positive in the control group. The question on shaking was the most discriminating between cases and controls. When the question on a shuffling walk was added, a positive answer to questions correctly identified 91% of cases and 92% of controls. These questions can form the basis of an alerting/screening questionnaire for parkinsonism and could be useful in screening smaller targeted populations such as a general practice list.

Nicotine exposure and Parkinson disease

The observed inverse relationship between smoking and Parkinson disease has prompted suggestions that nicotine, a centrally active agent, might protect against the disease. In this case-control study, cases were found to have ever regularly smoked cigarettes significantly less frequently than sex-, race-, and age-matched neighbors. This report analyzes the detailed smoking histories of cases and neighbors to see if these histories support the nicotine protection hypothesis. Estimated nicotine exposure before age at onset of symptoms for smoking cases was 186.1 g; for smoking controls it was 208.3 g (p = 0.34). Among the cases, severity of disease was not related to the extent of nicotine exposure before disease onset. Age at onset of symptoms for smoking cases (52.7 years) was not delayed (57.8 years for nonsmoking cases). Since the study was unable th find further support for the nicotine protection hypothesis, it is concluded that the observed inverse relationship between smoking and Parkinson disease is likely explainable by other factors, such as selective mortality or pre-morbid behavioral and/or constitutional changes.