Deprenyl in Parkinson disease: personal experience

The new generation of monoamine oxidase inhibitors

Irreversible and unspecific inhibitors of MAO were the first modern antidepressants, but after an initial success they fell into discredit due to adverse side effects. In the past two decades interest in MAO inhibitors has been renewed because of progress in basic research, a milestone being the finding that there are two subtypes of MAO, MAO-A and MAO-B. These are distinct proteins with high amino acid homology, coded by separate genes both located on the short arm of the human chromosome X. The enzyme subforms show different substrate specificities in vitro and different distributions within the central nervous system and in peripheral organs. In the central nervous system of man MAO-A seems to be mainly involved in the metabolism of 5 HT and noradrenaline, whereas 2-phenylethylamine and probably dopamine are predominantly deaminated by MAO-B. In the intestinal tract tyramine is mainly metabolized by MAO-A. These characteristics indicate distinct physiological functions of the two MAO-subforms. Several irreversible and reversible non-hydrazine inhibitors with relative selectivities for one of the MAO-subforms have been developed. They belong to various chemical classes with different modes of enzyme inhibition. These range from covalent mechanism based interaction (e.g. by propargyl- and allylamine derivatives) to pseudosubstrate inhibition (e.g. by 2-aminoethyl-carboxamides) and non-covalent interaction (e.g. by brofaromine, toloxatone and possibly moclobemide). The most important pharmacological effects of the new types of MAO inhibitors are those observed in neuropsychiatric disorders. The inhibitors of MAO-A show a favorable action in various forms of mental depression. The drugs seem to have about the same activity as other types of antidepressants, including tricyclic and related compounds as well as classical MAO inhibitors. The onset of action of the MAO-A inhibitors is claimed to be relatively fast. Other possible indications of these drugs include disorders with cognitive impairment, e.g. dementia of the Alzheimer type. In subjects with Parkinson's disease the MAO-B inhibitor L-deprenyl exerts a L-dopa-sparing effect, prolongs L-dopa action and seems to have a favorable influence regarding on-off disabilities. The action is in general transitory (months to several years). In addition L-deprenyl has been shown to delay the necessity for L-dopa treatment in patients with early parkinsonism. Whether the drug influence the progression of the disease is still a matter of debate. L-deprenyl also appears to have some antidepressant effect (especially in higher doses) and to exert a beneficial influence in other disorders, e.g. dementia of the Alzheimer type.(ABSTRACT TRUNCATED AT 400 WORDS)

Selegiline. A review of its pharmacology, symptomatic benefits and protective potential in Parkinson's disease

Selegiline (deprenyl) is a selective inhibitor of cerebral monoamine oxidase type B at the dosage (10 mg/day) used in patients with Parkinson's disease. Through this activity, the drug increases nigrostriatal dopamine levels, and may protect neurons against damage by free radicals and possibly exogenous neurotoxins. Selegiline also inhibits dopamine reuptake from the synaptic cleft. Because of its selectivity, selegiline 10mg daily does not prevent the breakdown and exacerbate the indirect pressor effects of dietary amines such as tyramine; it is devoid of the 'cheese' effect. Following oral administration, selegiline is rapidly metabolised to L-methamphetamine and L-amphetamine, which may account for the euphoria and insomnia seen in many patients, although potentiation of dopaminergic activity with concurrent levodopa appears more likely. The drug is a useful adjunct to levodopa in Parkinsonism, improving 'end-of-dose' fluctuations, producing modest improvements in motor function, and allowing a reduction in levodopa dosage. Indeed, if levodopa dosages are not decreased when selegiline is added to the therapeutic regimen, peak concentration dyskinesias due to levodopa are often exacerbated. However, symptomatic benefits are rarely maintained for more than a year and selegiline is relatively ineffective in allaying the abrupt swings in response to levodopa ('on/off' effects). When used alone in patients with mild disease, selegiline appears to slow the rate of symptom progression and may extend survival, through either neuroprotection or symptom relief. Whichever mechanism(s) is responsible, there is strong evidence to suggest that selegiline should be considered both in patients newly diagnosed with Parkinson's disease in an attempt to delay symptom progression, and in those experiencing dose-dependent fluctuations in response to levodopa.

Selegiline in the treatment of Parkinson's disease

Selegiline is a selective, irreversible inhibitor of monoamine oxidase type B (MAO-B). It also inhibits the reuptake of catecholamines into the presynaptic nerve and enhances the synthesis of dopamine by blocking the presynaptic dopamine autoreceptors. Thanks to these properties it potentiates and prolongs the duration of action of levodopa. Several clinical trials have shown its efficacy as an adjuvant to levodopa therapy. Improvement in parkinsonian disability and reduction of fluctuations in disability can be achieved by adding selegiline to the prevailing levodopa therapy. End-of-dose type fluctuations, in particular, react favourably to selegiline. Side-effects of the therapy can be managed by reducing the dose of levodopa. According to preliminary studies selegiline may also have some benefit as monotherapy in de novo parkinsonian patients. High doses of selegiline have been found to have some antidepressant efficacy, especially in patients with nonendogenous depression. It may also have an effect on bradyphrenia and some symptoms of cognitive dysfunction and dementia. In animal models selegiline has been shown to prevent parkinsonism caused by MPTP and also to increase the life span of rats. Whether selegiline slows down the progression of Parkinson's disease needs further examination.