Alternatives to Levodopa in the Initial??Treatment of Early Parkinson???s Disease

Dual-target-directed drugs that block monoamine oxidase B and adenosine A(2A) receptors for Parkinson's disease

Inadequacies of the current pharmacotherapies to treat Parkinson's disease (PD) have prompted efforts to identify novel drug targets. The adenosine A(2A) receptor is one such target. Antagonists of this receptor (A(2A) antagonists) are considered promising agents for the symptomatic treatment of PD. Evidence suggests that A(2A) antagonists may also have neuroprotective properties that may prevent the development of the dyskinesia that often complicates levodopa treatment. Because the therapeutic benefits of A(2A) antagonists are additive to that of dopamine replacement therapy, it may be possible to reduce the dose of the dopaminergic drugs and therefore the occurrence of side effects. Inhibitors of monoamine oxidase (MAO)-B also are considered useful tools for the treatment of PD. When used in combination with levodopa, inhibitors of MAO-B may enhance the elevation of dopamine levels after levodopa treatment, particularly when used in early stages of the disease when dopamine production may not be so severely compromised. Furthermore, MAO-B inhibitors may also possess neuroprotective properties in part by reducing the damaging effect of dopamine turnover in the brain. These effects of MAO-B inhibitors are especially relevant when considering that the brain shows an age-related increase in MAO-B activity. Based on these observations, dual-target-directed drugs, compounds that inhibit MAO-B and antagonize A(2A) receptors, may have value in the management of PD. This review summarizes recent efforts to develop such dual-acting drugs using caffeine as the lead compound.

Rotigotine transdermal patch: a review of its use in the management of Parkinson's disease

A transdermal patch formulation of the non-ergolinic dopamine agonist rotigotine (Neupro) is indicated for use as monotherapy in the treatment of early-stage Parkinson's disease or, in the EU, as an adjunct to levodopa across all disease stages. Transdermal rotigotine is an effective and generally well tolerated addition to the armamentarium for the control of Parkinson's disease, with the once-daily transdermal patch system offering several practical advantages and the possible benefits of avoiding pulsatile dopaminergic stimulation. Transdermal rotigotine was superior to placebo in patients with early-stage and advanced Parkinson's disease, although noninferiority to the oral dopamine agonists ropinirole or pramipexole was not consistently demonstrated. Additional active comparator trials would be of interest. In the meantime, transdermal rotigotine offers a convenient new treatment option for patients with Parkinson's disease.

COMT inhibition with tolcapone in the treatment algorithm of patients with Parkinson's disease (PD): relevance for motor and non-motor features

Levodopa is the most effective treatment in Parkinson's disease and the association with COMT inhibitors widens its plasma bioavailability and effectiveness. Tolcapone is a potent COMT inhibitor whose utilization in PD is limited due to safety concerns on liver toxicity. However, recent data indicate that if liver function is actively monitored, tolerability is no worse than other currently available therapies. By contrast, administration of tolcapone is associated with significant clinical improvement and benefit involves also non-motor features. In this review we discuss the rationale for the use of tolcapone in association with levodopa and other treatments in PD, and we provide an indirect comparison of current strategies to reduce "off" time. We propose that future guidelines include a trial with tolcapone in all PD patients who continue to complain about motor fluctuations despite treatment with entacapone and/or MAO-B inhibitors. Moreover, we suggest that tolcapone should be considered before surgical or infusional strategies are applied.

Role of calcium-independent phospholipase A2 in cortex striatum thalamus cortex circuitry-enzyme inhibition causes vacuous chewing movements in rats

RATIONALE

High levels of calcium independent phospholipase A2 (iPLA2) are present in certain regions of the brain, including the cerebral cortex, striatum, and cerebellum (Ong et al. 2005).

OBJECTIVES

The present study was carried out to elucidate a possible role of the enzyme in the motor system.

METHODS

The selective iPLA2 inhibitor bromoenol lactone (BEL), the nonselective PLA2 inhibitor methyl arachidonyl fluorophosphonate (MAFP), and an antisense oligonucleotide were used to interfere with iPLA2 activity in various components of the motor system. Control animals received injections of carrier (phosphate buffered saline, PBS) at the same locations. The number of vacuous chewing movements (VCM) was counted from 1 to 14 days after injection.

RESULTS

Rats that received BEL and high-dose MAFP injections in the striatum, thalamus, and motor cortex, but not the cerebellum, showed significant increase in VCM, compared to those injected with PBS at these locations. BEL-induced VCM were blocked by intramuscular injections of the anticholinergic drug, benztropine. Increased VCM was also observed after intrastriatal injection of antisense oligonucleotide to iPLA2. The latter caused a decrease in striatal iPLA2 levels, confirming a role of decreased enzyme activity in the appearance of VCM.

CONCLUSIONS

These results suggest an important role for iPLA2 in the cortex-striatum-thalamus-cortex circuitry. It is postulated that VCM induced by iPLA2 inhibition may be a model of human parkinsonian tremor.

Rasagiline (TVP-1012): a new selective monoamine oxidase inhibitor for Parkinson's disease

OBJECTIVE

This article reviews the chemistry, pharmacodynamics, pharmacokinetics, clinical efficacy, tolerability, drug-interaction potential, indications, dosing, and potential role of rasagiline mesylate, a new selective monoamine oxidase (MAO) type B (MAO-B) inhibitor, in the treatment of Parkinson's disease.

METHODS

A MEDLINE/PUBMED search (1986 through September 2006) was conducted to identify studies involving rasagiline written in English. Additional references were obtained from the bibliographies of these studies. All studies evaluating any aspect of rasagiline, including in vitro, in vivo (animal), and human studies, were reviewed.

RESULTS

Rasagiline mesylate was developed with the goal of producing a selective MAO-B inhibitor that is not metabolized to (presumed) toxic metabolites (eg, amphetamine and methamphetamine, which are byproducts of the metabolism of selegiline, another selective MAO-B inhibitor). In vitro and in vivo data have confirmed the drug's selectivity for MAO-B. Rasagiline is almost completely eliminated by oxidative metabolism (catalyzed by cytochrome P-450 [CYP] isozyme 1A2) followed by renal excretion of conjugated parent compound and metabolites. Drug clearance is sufficiently slow to allow once-daily dosing. Several studies have documented its efficacy as monotherapy for early-stage disease and as adjunctive therapy in L-dopa recipients with motor fluctuations. As monotherapy, rasagiline is well tolerated with an adverse-effect profile similar to that of placebo. As adjunctive therapy, it exhibits the expected adverse effects of dopamine excess, which can be ameliorated by reducing the L-dopa dosage. CYP1A2 inhibitors slow the elimination of rasagiline and mandate dosage reduction. Hepatic impairment has an analogous effect. The recommended dosage regimens for monotherapy and adjunctive therapy are 1 and 0.5 mg PO QD, respectively.

CONCLUSIONS

Despite the well-documented selectivity of rasagiline, the manufacturer recommends virtually all of the dietary (vis-à-vis tyramine) and drug restrictions of the nonselective MAO inhibitors. Although useful, selective MAO-B inhibitors have a limited role in Parkinson's disease. Of greater interest is the potential neuroprotective effect of rasagiline and its major metabolite, 1(R)-aminoindan, which may have great utility in a wide variety of neurodegenerative disorders of aging. In addition, bifunctional molecules combining selective MAO-B inhibition (based on the active moiety of rasagiline) with acetylcholinesterase inhibition or iron chelation may eventually be useful in Alzheimer's disease.

Cell repair in Parkinson’s disease

Parkinson’s disease (PD) is a progressive neurodegenerative movement disorder with the cardinal clinical features of muscular rigidity, resting tremor and bradykinesia. The prevalence of this disease is approximately 2% of those aged over 65 years, thus causing significant morbidity. The disease is characterized by degeneration of dopaminergic cells in the substantia nigra pars compacta, resulting in reduced dopaminergic input to the striatum. Significant clinical benefit can be achieved through the restoration of dopamine levels in this system with pharmacological interventions, although these therapies are only symptomatic and the disease progresses. Indeed, with disease progression other features often appear, including autonomic, affective and cognitive dysfunction, reflecting pathology at non-nigral sites. The occurrence of neural stem cells (NSCs) in the adult CNS, which, under certain conditions, are able to proliferate and renew neuronal numbers, has raised great expectations for alternative therapeutic applications in the treatment of PD. Indeed, it is potentially possible to harness this capacity either directly (increase of local proliferation, directed migration and differentiation) or indirectly (in vitro expansion before their transplantation), to facilitate the generation of specific cell types in order to replace missing neurons in neurodegenerative diseases. The manipulation of embryonic stem cells or their derivatives also offers a promising alternative as extensive proliferation may be achieved and, most importantly, directed differentiation to a dopaminergic phenotype is possible. Nevertheless, neuronal replacement will only be possible if proliferating or transplanted NSCs and their progeny can be harnessed at sites of pathology. It is the manipulation of stem cells both in vivo and in vitro, in the context of repairing the core pathological hallmark of PD, that is the main focus of this report.

Community and Long-Term Care Management of Parkinson???s Disease in the Elderly

Parkinson's disease affects up to 1 million people in the US, most of them elderly. Motor and non-motor symptoms can be significantly disabling to the point of necessitating institutionalisation. Age-related changes in drug absorption, distribution, metabolism and excretion complicate the treatment of elderly patients with Parkinson's disease. General management principles include initiation of medication at low doses with gradual titration based on clinical effects, avoidance of certain classes of drugs (e.g. anticholinergics), and attention to polypharmacy and its risk for potentially toxic drug interactions. Levodopa remains the most efficacious anti-Parkinson's disease medication and should be the cornerstone of therapy in the elderly Parkinson's disease patient. Use of dopamine receptor agonists, amantadine and anticholinergic drugs in the elderly is limited by high risk for psychotoxicity. Catechol-O-methyltransferase inhibitors may be used to augment levodopa in the setting of 'wearing off' (i.e. motor fluctuations). Monoamine oxidase type B (MAO-B) inhibitors can be used across the spectrum of disease severity, but selegiline (deprenyl), the prototype in this class, is characterised by low and erratic bioavailability of the parent drug and conversion to amphetamine metabolites that may increase the risk of adverse events. A new orally disintegrating tablet formulation overcomes some of these limitations. Rasagiline is a new, selective, second-generation MAO-B inhibitor that is chemically and metabolically distinct from selegiline. The favourable safety profile of rasagiline in the elderly and its once-daily formulation may maximise drug adherence and improve outcomes.

Epidemiological, clinical, and genetic characteristics of early-onset parkinsonism

In this review we discuss the epidemiological, clinical, and genetic characteristics of early-onset parkinsonism, defined as parkinsonism starting before age 40 (sometimes 50) years. Juvenile parkinsonism is very rare and is the result of various secondary or genetic causes. In patients with onset at or above age 21 years, secondary causes require exclusion but are rare; most cases with a fairly pure parkinsonian syndrome (eg, young-onset Parkinson's disease; YOPD) are due to typical Lewy-body Parkinson's disease or, less commonly, genetic causes. In comparison with patients with late-onset disease, most patients with YOPD progress more slowly in terms of motor features and have a longer disease course with preservation of cognitive function, but typically develop motor fluctuations and dyskinesias earlier. Patients with YOPD generally experience a greater effect in their lives than those with late onset, with poorer social adjustment, higher rates of depression, and lower quality of life. Management of YOPD must therefore aim to maintain occupational, social, and daily functioning, while delaying or ameliorating motor complications of treatment, providing psychological support, and, where possible, preventing psychiatric complications including depression.