Selegiline and Parkinson's disease. Protective and symptomatic considerations

The Effects of Two New Amphetamine-like Derivatives on the Phagocytic Ability of the Protozoan, Tetrahymena pyriformis

Six new amphetamine-like molecules (2-[2,3-dihydro-4 H-1,4-benzoxazine-4-yl]-1-methyl-2-[l-methyl-2-phenylethylamino] ethanamines) were synthesised and their physico-chemical behaviour was studied. The log P values (index of lipophilicity) of the derivatives were calculated according to Rekker's fragmental system. One derivative representative of each series (C-5508 and C-5512) was selected, and their biological effects on the phagocytic ability of the protozoan, Tetrahymena pyriformis, were studied as a basic functional test for an amphetamine-like action. Furthermore, the action of both derivatives when administered concomitantly with haloperidol was also investigated. The data indicate that both derivatives significantly increased the phagocytic ability of the protozoan (p < 0.001), presumably via an alternative pathway to that of one of the dopamine monoaminergic pools. The administration of haloperidol significantly suppressed phagocytosis (p < 0.001). However, cultures exposed to the derivatives and to haloperidol indicated quantitatively different reactions. The lipophilic behaviours of the derivatives provide & possible explanation for such distinct effects.

Time to change the blind men and the elephant approach to Parkinson disease?

Parkinson disease (PD) is a progressive neurodegenerative disease that is associated with substantial morbidity and early mortality. Disease-related costs exceed $10 billion, not including medications, out-of-pocket expenses, or societal costs. Symptomatic treatment with levodopa, which has been available for over 30 years, and advanced therapies such as deep brain stimulation improve outcomes. Yet most new medications for PD provide a therapeutic benefit that is relatively modest compared to the benefits from levodopa. Despite dozens of neuroprotective clinical trials, there are no medications proven to slow the progression of the disease. Given these limitations, we provide evidence of the potential public health impact of a research agenda that emphasizes identification of risk factors to reduce disease burden through exposure mitigation. In addition, we emphasize health care policy that focuses on increasing health care expenditures for neurologic evaluation and management services to increase access to specialists to improve disease outcomes and reduce costs through better disease management.

Does selegiline modify the progression of early Parkinson's disease? Results from a five-year study. The Norwegian-Danish Study Group

The objective of this study was to examine the effect of long-term treatment with selegiline on the progression of Parkinson's disease (PD). One hundred and sixty-three patients with early PD were treated with levodopa and benserazide, combined with selegiline or placebo in a five-year randomized, placebo-controlled, double-blind, parallel group study followed by a one-month wash-out of selegiline or placebo. The main outcome measures were assessments of the severity of parkinsonism, levodopa requirements and the development of end-of-dose motor fluctuations over time and after wash-out at the end of the study period. Results indicated that patients treated with the combination of selegiline and levodopa developed markedly less severe parkinsonism and required lower doses of levodopa during the five-year study period than patients treated with levodopa and placebo. There was no trend towards worsening during wash-out among patients previously treated with selegiline. The results cannot easily be explained by a symptomatic effect of selegiline.

Nigrostriatal monoamine oxidase A and B in aging squirrel monkeys and C57BL/6 mice

In this study we assessed the two forms of monoamine oxidase (MAO) in the caudate, putamen, and substantia nigra of young (4-year-old), intermediate-aged (11-year-old), and aged (20-year-old) squirrel monkeys and in the striata of young (2-month-old) and older (10-month-old) C57Bl/6 mice. MAO A and B activities were determined by measuring the rate of oxidation of the specific substrates phenethylamine and serotonin. In squirrel monkey, the vast majority of MAO activity was MAO B with activity of this isoform 10 times greater than of MAO A, while in mice the activity of the two forms was approximately equivalent. Although mice demonstrated nearly twofold selective increases in striatal MAO B between 2 and 10 months of age, neither MAO B nor A showed statistically significant changes with age in squirrel monkeys. These results document the marked differences between nonhuman primates and rodents with respect to the relative activities and the effects of age on MAO A and B, and indicate that increased MAO is not an inevitable feature of aging.

The effects of early selegiline therapy on long-term levodopa treatment and parkinsonian disability: an interim analysis of a Norwegian--Danish 5-year study. Norwegian-Danish Study Group

In this study, we investigated the effects of selegiline on levodopa treatment and parkinsonian disability over several years of treatment in patients with early Parkinson's disease (PD). The 163 patients were randomized to receive either selegiline or placebo in addition to levodopa in a double-blind, parallel-group study design, and the patients were to be followed up until a defined termination point or for 5 years. All patients had previously either never (two thirds) or for < 6 months (one third) received levodopa. After 1 year of treatment or at withdrawal from study or both, the patients were divided according to specified diagnostic criteria into groups of definite, probable, possible, or unlikely PD. The efficacy parameters were levodopa therapy, Unified Parkinson's Disease Rating Scale (UPDRS) with subscales, and the time to develop wearing-off fluctuations or reaching the termination point. Evaluation of efficacy was performed for all patients with PD and for patients with a definite and probable disease. The results of this study are based on an interim analysis when 80% of the 163 randomized patients had been followed up for > or = 3 years. Nine patients were excluded from the study because of protocol violations or because the patients were diagnosed as unlikely PD. At the time of interim analysis, 39 patients had been withdrawn from the study because of adverse effects or their own wish. Eighteen patients had reached the termination point, and 97 patients (observation time, 30-54 months) were still in the study. Among the patients receiving selegiline, we found a rather stable daily levodopa dose during 54 months of therapy, compared with an anticipated increase among patients with levodopa monotherapy. Concurrently, patients in the selegiline group showed a trend to develop less severe parkinsonian disability and a lower frequency of motor fluctuations and need for additional antiparkinsonian medication. The results of this study indicate that early combination therapy of selegiline and levodopa compared with levodopa monotherapy has an increasingly favorable impact on the long-term daily levodopa dose and may possibly delay the development of disability in PD.

Oxidative stress and antioxidant therapy in Parkinson's disease

Parkinson's disease, known also as striatal dopamine deficiency syndrome, is a degenerative disorder of the central nervous system characterized by akinesia, muscular rigidity, tremor at rest, and postural abnormalities. In early stages of parkinsonism, there appears to be a compensatory increase in the number of dopamine receptors to accommodate the initial loss of dopamine neurons. As the disease progresses, the number of dopamine receptors decreases, apparently due to the concomitant degeneration of dopamine target sites on striatal neurons. The loss of dopaminergic neurons in Parkinson's disease results in enhanced metabolism of dopamine, augmenting the formation of H2O2, thus leading to generation of highly neurotoxic hydroxyl radicals (OH.). The generation of free radicals can also be produced by 6-hydroxydopamine or MPTP which destroys striatal dopaminergic neurons causing parkinsonism in experimental animals as well as human beings. Studies of the substantia nigra after death in Parkinson's disease have suggested the presence of oxidative stress and depletion of reduced glutathione; a high level of total iron with reduced level of ferritin; and deficiency of mitochondrial complex I. New approaches designed to attenuate the effects of oxidative stress and to provide neuroprotection of striatal dopaminergic neurons in Parkinson's disease include blocking dopamine transporter by mazindol, blocking NMDA receptors by dizocilpine maleate, enhancing the survival of neurons by giving brain-derived neurotrophic factors, providing antioxidants such as vitamin E, or inhibiting monoamine oxidase B (MAO-B) by selegiline. Among all of these experimental therapeutic refinements, the use of selegiline has been most successful in that it has been shown that selegiline may have a neurotrophic factor-like action rescuing striatal neurons and prolonging the survival of patients with Parkinson's disease.

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.

Diagnostic and pharmacological approaches in Alzheimer's disease

Alzheimer's disease is a chronic progressive disease affecting higher intellectual functioning. The clinical diagnosis is made when the onset of illness is insidious, the course slowly progressive and all the treatable causes of dementia have been ruled out. The use of more stringent criteria has improved clinical diagnosis, but at best only 80% of patients are accurately diagnosed. Ultimately the diagnosis depends upon pathological confirmation. The neuritic plaques and neurofibrillary tangles described by Alzheimer, although not pathognomonic for the disease, continue to be the basis for pathological diagnosis. The aetiology and pathophysiology of Alzheimer's disease are presently unknown. Epidemiological studies have suggested a genetic basis for the disorder, and many biochemical studies have linked it to degeneration of central cholinergic neurons, and possibly to abnormalities of other neurotransmitter systems. A marker which would permit accurate diagnosis early in the course of disease would be of major importance to researchers and clinicians alike. No marker has been found to date, although recent research results are promising. Various pharmacological strategies have been employed in the treatment of Alzheimer's disease. More recently attempts have focused on enhancing central cholinergic transmission. Despite the well-founded rationale for these studies, results have been modest.