Symptomatic anti-parkinsonian effects of monoamine oxidase-B inhibition: comparison of selegiline and lazabemide

Efficacy and safety of selegiline for the treatment of Parkinson's disease: A systematic review and meta-analysis

Background

Drug efficacy generally varies with different durations. There is no systematic review analyzing the effect of selegiline for Parkinson's disease (PD) on different treatment duration. This study aims to analyze how the efficacy and safety of selegiline changes for PD over time.

Methods

PubMed, the Cochrane Library, Embase, China National Knowledge Infrastructure and Wanfang Database were systematically retrieved for randomized controlled trials (RCTs) and observational studies of selegiline for PD. The search period was from inception to January 18th, 2022. The efficacy outcomes were measured by the mean change from baseline in the total and sub Unified Parkinson's Disease Rating Scale (UPDRS), Hamilton Depression Rating Scale (HAMD) and Webster Rating Scale (WRS) scores. The safety outcomes were measured by the proportion of participants having any adverse events overall and that in different system organ classes.

Results

Among the 3,786 studies obtained, 27 RCTs and 11 observational studies met the inclusion criteria. Twenty-three studies reported an outcome which was also reported in at least one other study, and were included in meta-analyses. Compared with placebo, selegiline was found with a stronger reduction of total UPDRS score with increasing treatment duration [mean difference and 95% CIs in 1 month: -3.56 (-6.67, -0.45); 3 months: -3.32 (-3.75, -2.89); 6 months: -7.46 (-12.60, -2.32); 12 months: -5.07 (-6.74, -3.41); 48 months: -8.78 (-13.75, -3.80); 60 months: -11.06 (-16.19, -5.94)]. A similar trend was also found from the point estimates in UPDRS I, II, III, HAMD and WRS score. The results of observational studies on efficacy were not entirely consistent. As for safety, compared with placebo, selegiline had higher risk of incurring any adverse events [rate: 54.7% vs. 62.1%; odd ratio and 95% CIs: 1.58 (1.02, 2.44)], with the excess adverse events mainly manifested as neuropsychiatric disorders [26.7% vs. 31.6%; 1.36 (1.06, 1.75)] and no significant change over time. The statistically difference in overall adverse event between selegiline and active controls was not found.

Conclusion

Selegiline was effective in improving total UPDRS score with increasing treatment duration, and had a higher risk of incurring adverse events, especially the adverse events in the neuropsychiatric system.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier: PROSPERO CRD42021233145.

MAO-B inhibitors: multiple roles in the therapy of neurodegenerative disorders?

Monoamine oxidases play a central role in catecholamine catabolism in the central nervous system. The biochemical and pharmacological properties of inhibitors of the monoamine oxidase type B are reviewed. The evidence for biochemical activities distinct from their ability to inhibit MAO-B is discussed, including possible antioxidative and antiapoptotic activities of these agents. The significance of these properties for the pharmacological management of Parkinson's disease and the evidence for a neuroprotective effect of one such agent (selegiline) is also discussed.

Investigational agents in the treatment of Parkinson's disease: focus on safinamide

The authors review management issues in Parkinson's disease (PD) and provide an overview of the current pharmacological management strategies, with a specific focus on safinamide. Current therapeutic management of PD largely involves strategies to optimize the replacement of deficient dopamine, using levodopa, dopamine agonists, and inhibitors of dopamine-metabolizing enzymes. Currently under investigation for use in the treatment of PD, safinamide has multiple modes of action including monoamine oxidase B inhibition. It is well absorbed orally, has a long plasma half-life, and does not have liver enzyme-inducing or liver enzyme-inhibiting activity. Peak plasma concentration occurs 2-4 hours after single oral doses. Safinamide as monotherapy and as an adjunct to dopamine agonists improves Unified Parkinson's Disease Rating Scale motor scores. One randomized, placebo-controlled trial involving 168 patients given a median safinamide dose of 70 mg/day (range 40-90 mg/day) significantly increased the proportion of responders - defined as patients improving their Unified Parkinson's Disease Rating Scale motor scores by 30% or more from baseline - after 3 months (37.5% for safinamide versus 21.4% for placebo; P < 0.05). Safinamide increased "on" time with no or minor dyskinesia compared with the placebo in another trial, but dyskinesia severity was not reduced. Safinamide was well tolerated, with an adverse effect profile similar to that of the placebo. Further Phase III trial data for safinamide efficacy is awaited, and will be of interest in a comparison with other developments in PD therapeutics: modified formulations of available compounds, new drug classes such as adenosine receptor antagonists, and gene-based therapies.

Oxidative stress in neurodegenerative diseases: mechanisms and therapeutic perspectives

The incidence and prevalence of neurodegenerative diseases (ND) increase with life expectancy. This paper reviews the role of oxidative stress (OS) in ND and pharmacological attempts to fight against reactive oxygen species (ROS)-induced neurodegeneration. Several mechanisms involved in ROS generation in neurodegeneration have been proposed. Recent articles about molecular pathways involved in ROS generation were reviewed. The progress in the development of neuroprotective therapies has been hampered because it is difficult to define targets for treatment and determine what should be considered as neuroprotective. Therefore, the attention was focused on researches about pharmacological targets that could protect neurons against OS. Since it is necessary to look for genes as the ultimate controllers of all biological processes, this paper also tried to identify gerontogenes involved in OS and neurodegeneration. Since neurons depend on glial cells to survive, recent articles about the functioning of these cells in aging and ND were also reviewed. Finally, clinical trials testing potential neuroprotective agents were critically reviewed. Although several potential drugs have been screened in in vitro and in vivo models of ND, these results were not translated in benefit of patients, and disappointing results were obtained in the majority of clinical trials.

Protection against Parkinson's disease progression: clinical experience

Treatments with potential neuroprotective capability for Parkinson's disease (PD) have been investigated in randomized, controlled, clinical trials and other studies since the mid-1980s. Although promising leads have arisen, no therapy has been proven to halt or slow disease progression. Several large-scale studies have highlighted progress in methodology, as well as the frustrations of translating laboratory science to practical applications. This review summarizes findings from clinical trials with several classes of compounds, including monoamine oxidase-B inhibitors (selegiline, lazabemide, rasagiline), dopaminergic drugs (ropinirole, pramipexole, levodopa), antioxidant strategies (alpha-tocopherol), mitochondrial energy enhancers (coenzyme Q(10), creatine), antiapoptotic agents (TCH346, minocycline, CEP-1347), and antiglutamatergic compounds (riluzole). Beyond small-molecule pharmacology, gene therapy approaches, such as delivering neurotrophic substances (e.g., neurturin) by viral vector, are the next generation of treatment options.

Neuroprotection in Parkinson's disease: clinical trials

Advances in our understanding of the cause and pathogenesis of Parkinson's disease (PD) have permitted the rational selection of putative neuroprotective agents for study in PD. However, the list of agents that might provide neuroprotective effects derived from laboratory studies is daunting, and we face the challenge of determining which agents to bring to the clinic and how to find the resources (patients and funds) to properly study so many promising therapeutic opportunities.1 Appropriate outcome variables that are not confounded by any symptomatic effect of the drug and are acceptable to clinicians and regulatory authorities also remain to be defined. The first clinical trials designed to test the capacity of putative neuroprotective agents to alter the natural history of PD have now been performed and illustrate some of these problems. The DATATOP (Deprenyl and Tocopherol Antioxidant Therapy of PD) study used the time to reach a disease milestone in untreated PD patients (ie, need for levodopa) as the primary end point. However, interpretation of results was confounded by the drug's symptomatic effect. The SINDEPAR (Sinemet-Deprenyl-Parlodel) study used the change in motor score between initial visit and final visit after washout of all study medications as the primary end point. However, here too there were concerns about confounding symptomatic effects, because antiparkinsonian medications have now been shown to have a long duration response that can persist for weeks and perhaps even months after withdrawal. More recent studies have used surrogate markers of the integrity of nigrostriatal function such as striatal uptake of fluorodopa on positron emission tomography (PET) or beta-CIT-on single-photon emission computerized tomography (SPECT) as primary outcome measures. However, it has not yet been confirmed that striatal uptake of these isotopes does in fact correlate with the remaining number of dopamine neurons or terminals, and the possibility of a confounding pharmacological effect has not yet been completely excluded. To date, no drug has been established to have a neuroprotective effect in PD, and none has been approved for a neuroprotective indication. Furthermore, regulatory agencies have not yet agreed that any of the outcome measures currently used will be acceptable for approval of a new drug. Resolution of these issues is of critical importance to convince pharmaceutical companies to expend the hundreds of millions of dollars necessary to bring a new drug to market. Drugs that already have been approved in PD for their symptomatic effects, such as dopamine agonists or propargylamines (eg, selegiline), offer the best opportunity for establishing that a drug is neuroprotective in PD in the immediate future, but herein also lies the difficulty of establishing that any benefits observed are not solely because of the drug's symptomatic properties. Currently, this will most likely entail demonstrating that the drug provides benefit for PD patients for both imaging and clinical markers of disease progression.

In vivo properties of N-(2-aminoethyl)-5-halogeno-2-pyridinecarboxamide 18F- and 123I-labelled reversible inhibitors of monoamine oxidase B

The reversible and highly selective monoamine oxidase B (MAO-B) inhibitor Ro 19-6327, a picolinic acid derivative, was selected for the development of new radiopharmaceuticals, whereby in place of Cl either 123I or 18F was introduced. The respective labelling procedures have been described earlier. In this study, some metabolic properties were investigated. Blood and urine samples were analysed, and halogenated picolinylglycine, a more hydrophilic compound, was identified as the main metabolite. This shows that the amine is oxidised to the respective carboxylate, but the intermediate imine or aldehyde that was proposed earlier could not be detected. First experiments with single photon emission tomography and positron emission tomography (PET) showed that the iodo compound can be used to investigate MAO-B in vivo while the fluoro compound is accumulated in the brain to such a low degree that no PET studies can be performed. We conclude that the main reason for the poor uptake of the fluoro compound is its lower lipophilicity as compared to the iodo compound and, to a lesser degree, its metabolism, which is similar for both compounds.

The extraneuronal transporter for monoamine transmitters exists in cells derived from human central nervous system glia

From studies on sympathetically innervated peripheral tissues it is well known that both neuronal and non-neuronal transport systems contribute to the inactivation of released monoamine transmitters. The close proximity between synapses and glia cell processes in the CNS leads to the so far unresolved question whether non-neuronal transporters are involved in the inactivation of centrally released monamine transmitters such as noradrenaline, dopamine and 5-hydroxytryptamine. 1-Methyl-4-phenylpyridinium (MPP+) is a prototypical substrate of the extraneuronal monoamine transporter (uptake2). [3H]MPP+ was found to accumulate in various human glioma cell lines. [3H]MPP+ transport was characterized in more detail in HTZ146 human glioma cells. The Ki values of various compounds for the inhibition of initial rates of [3H]MPP+ transport into HTZ146 cells were closely correlated with known Ki values for the inhibition of the extraneuronal monoamine transporter (P < 0.01, r = 0.991, n = 7). The rank order of inhibitory potencies was decynium 22 > corticosterone > cyanine 863 > O-methylisoprenaline > quinine > clonidine > quinidine. [3H]MPP+ accumulation was investigated not only in various CNS tumour cell lines but also in primary cultures of human astrocytes and rat cerebral cortex slices. In all tested experimental systems, accumulation was sensitive to cyanine-related inhibitors of the extraneuronal monamine transporter. These findings suggest that the extraneuronal monamine transporter exists in glia cells. Furthermore, it was shown that MPP+ is able to make use of the extraneuronal monoamine transporter not only to enter but also to leave glia cells. This finding suggests that the extraneuronal monoamine transporter may play a key role in the mechanism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity.

In vitro effects on monoamine uptake and release by the reversible monoamine oxidase-B inhibitors lazabemide and N-(2-aminoethyl)-p-chlorobenzamide: a comparison with L-deprenyl

To investigate whether the reversible monoamine oxidase-B (MAO-B) inhibitors lazabemide and Ro 16-6491 have any additional effect on monoamine uptake and release, in vitro experiments were performed on rat forebrain synaptosomes and blood platelets. The effects of the two drugs were compared with those of L-deprenyl, the well-known irreversible MAO-B inhibitor which is reported to affect amine uptake. Both lazabemide and Ro 16-6491 behaved as weak inhibitors of [3H]monoamine uptake by synaptosomes, with a similar rank order of potency for amine uptake inhibition (noradrenaline (NA) > or = 5-hydroxytryptamine (5 HT) > dopamine (DA)). The IC50 values for lazabemide and Ro 16-6491, respectively, were: 86 microM and 90 microM for NA uptake; 123 microM and 90 microM for 5HT uptake; > 500 microM and > 1000 microM for DA uptake. L-Deprenyl (rank order of inhibitory potency: NA > DA > 5 HT) was four to 10 times more potent than either compound in inhibiting [3H]catecholamine uptake (IC50 = NA 23 microM, DA 109 microM), and two to three times less potent in inhibiting 5 HT uptake (IC50 233 microM). Lazabemide and Ro 16-6491 also differed from L-deprenyl in their ability to induce release of endogenous monoamines from synaptosomes. Thus, Ro 16-6491 (500 microM) induced a greater 5 HT release than did L-deprenyl, but was less effective than L-deprenyl in releasing DA. On the contrary, lazabemide was almost completely inactive on either 5 HT and DA release. The differential effect of the three MAO-B inhibitors on synaptosome 5 HT uptake and release was confirmed by [14C]5HT uptake and liberation experiments with isolated rat platelets. The data indicate that the reversible MAO-B inhibitors lazabemide and Ro 16-6491 at relatively high concentrations possess amine uptake-inhibiting properties. With regard to the effects examined, lazabemide markedly differs from L-deprenyl since it does not interfere with DA uptake nor induce amine release from synaptosomes.