Pharmacokinetics and pharmacodynamics of entacapone and tolcapone after acute and repeated administration: a comparative study in the rat

A systematic review of the cognitive effects of the COMT inhibitor, tolcapone, in adult humans

OBJECTIVE

The catechol-o-methyltransferase (COMT) inhibitor tolcapone constitutes a potentially useful probe of frontal cortical dopaminergic function. The aim of this systematic review was to examine what is known of effects of tolcapone on human cognition in randomized controlled studies.

METHODS

The study protocol was preregistered on the Open Science Framework. A systematic review was conducted using PubMed to identify relevant randomized controlled trials examining the effects of tolcapone on human cognition. Identified articles were then screened against inclusion and exclusion criteria.

RESULTS

Of the 22 full-text papers identified, 13 randomized control trials were found to fit the pre-specified criteria. The most consistent finding was that tolcapone modulated working memory; however, the direction of effect appeared to be contingent on the COMT polymorphism (more consistent evidence of improvement in Val-Val participants). There were insufficient nature and number of studies for meta-analysis.

CONCLUSION

The cognitive improvements identified upon tolcapone administration, in some studies, are likely to be due to the level of dopamine in the prefrontal cortex being shifted closer to its optimum, per an inverted U model of prefrontal function. However, the results should be interpreted cautiously due to the small numbers of studies. Given the centrality of cortical dopamine to understanding human cognition, studies using tolcapone in larger samples and across a broader set of cognitive domains would be valuable. It would also be useful to explore the effects of different dosing regimens (different doses; and single versus repeated administration).

Identification of New Modulators and Inhibitors of Palmitoyl-Protein Thioesterase 1 for CLN1 Batten Disease and Cancer

Palmitoyl-protein thioesterase 1 (PPT1) is an understudied enzyme that is gaining attention due to its role in the depalmitoylation of several proteins involved in neurodegenerative diseases and cancer. PPT1 is overexpressed in several cancers, specifically cholangiocarcinoma and esophageal cancers. Inhibitors of PPT1 lead to cell death and have been shown to enhance the killing of tumor cells alongside known chemotherapeutics. PPT1 is hence a viable target for anticancer drug development. Furthermore, mutations in PPT1 cause a lysosomal storage disorder called infantile neuronal ceroid lipofuscinosis (CLN1 disease). Molecules that can inhibit, stabilize, or modulate the activity of this target are needed to address these diseases. We used PPT1 enzymatic assays to identify molecules that were subsequently tested by using differential scanning fluorimetry and microscale thermophoresis. Selected compounds were also tested in neuroblastoma cell lines. The resulting PPT1 screening data was used for building machine learning models to help select additional compounds for testing. We discovered two of the most potent PPT1 inhibitors reported to date, orlistat (IC50 178.8 nM) and palmostatin B (IC50 11.8 nM). When tested in HepG2 cells, it was found that these molecules had decreased activity, indicating that they were likely not penetrating the cells. The combination of in vitro enzymatic and biophysical assays enabled the identification of several molecules that can bind or inhibit PPT1 and may aid in the discovery of modulators or chaperones. The molecules identified could be used as a starting point for further optimization as treatments for other potential therapeutic applications outside CLN1 disease, such as cancer and neurological diseases.

Effects of a New Natural Catechol-O-methyl Transferase Inhibitor on Two In Vivo Models of Parkinson's Disease

A tetrahydroisoquinoline identified in Mucuna pruriens ((1R,3S)-6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline-1,3-dicarboxylic acid, compound 4) was synthesized and assessed for its in vitro pharmacological profile and in vivo effects in two animal models of Parkinson's disease. Compound 4 inhibits catechol-O-methyltransferase (COMT) with no affinity for the dopaminergic receptors or the dopamine transporter. It restores dopamine-mediated motor behavior when it is co-administered with L-DOPA to C. elegans worms with 1-methyl-4-phenylpyridinium-damaged dopaminergic neurons. In a 6-hydroxydopamine rat model of Parkinson's disease, its co-administration at 30 mg/kg with L-DOPA enhances the effect of L-DOPA with an intensity similar to that of tolcapone 1 at 30 mg/kg but for a shorter duration. The effect is not dose-dependent. Compound 4 seems not to cross the blood-brain barrier and thus acts as a peripheral COMT inhibitor. COMT inhibition by compound 4 further validates the traditional use of M. pruriens for the treatment of Parkinson's disease, and compound 4 can thus be considered as a promising drug candidate for the development of safe, peripheral COMT inhibitors.

Unveiling the biopathway for the design of novel COMT inhibitors

Catechol-O-methyltransferase (COMT) is an enzyme responsible for the O-methylation of biologically active catechol-based molecules. It has been associated with several neurological disorders, especially Parkinson's disease (PD), because of its involvement in catecholamine metabolism, and has been considered an important therapeutic target for central nervous system disorders. In this review, we summarize the biophysical, structural, and therapeutical relevance of COMT; the medicinal chemistry behind the development of COMT inhibitors and the application of computer-aided design to support the design of novel molecules; current methodologies for the biosynthesis, isolation, and purification of COMT; and revise existing bioanalytical approaches for the assessment of enzymatic activity in several biological matrices.

1-Hydroxy-2(1H)-pyridinone-Based Chelators with Potential Catechol O-Methyl Transferase Inhibition and Neurorescue Dual Action against Parkinson's Disease

Two analogues of tolcapone where the nitrocatechol group has been replaced by a 1-hydroxy-2(1H)-pyridinone have been designed and synthesised. These compounds are expected to have a dual mode of action both beneficial against Parkinson’s disease: they are designed to be inhibitors of catechol O-methyl transferase, which contribute to the reduction of dopamine in the brain, and to protect neurons against oxidative damage. To assess whether these compounds are worthy of biological assessment to demonstrate these effects, measurement of their pKa and stability constants for Fe(III), in silico modelling of their potential to inhibit COMT and blood–brain barrier scoring were performed. These results demonstrate that the compounds may indeed have the desired properties, indicating they are indeed promising candidates for further evaluation.

In vitro and in vivo characterization of Entacapone-loaded nanostructured lipid carriers developed by quality-by-design approach

Entacapone, a reversible catechol-o-methyl transferase inhibitor, is used to enhance the action of dopamine agonists by reducing their metabolism and the 'Wearing-off' effects associated with long-term use in the treatment of Parkinson's disease. It is used as an adjunct to levodopa/Carbidopa therapy. Due to limited dissolution and first-pass clearance, it suffers low and variable bioavailability issues. To overcome this problem, the present study aims to explore the potential of nanostructured lipid carriers (NLCs) for the delivery of Entacapone. The Quality by Design (QbD) approach was used for the systematic development of NLCs. The 2³ full factorial designs were investigated using Design-Expert®11 software. The three independent variables namely content of total lipid (X1), surfactant (X2), and sonication time (X3) were optimized against two responses namely particle size and entrapment efficiency. The optimized NLCs were characterized for their size, surface morphology, entrapment efficiency, drug release, thermal and crystallographic studies. In-vivo pharmacokinetic studies in Entacapone-loaded NLCs showed an increase in t_1/2, AUC_0-∞, MRT compared to free drug. The reduction in elimination (Kel) depicts the prolonged action of Entacapone by loading in NLCs. The results displayed Entacapone-loaded NLCs have promising potential for oral delivery and enhanced therapeutic effect which otherwise was a major issue.

The inhibition of catechol O-methyltransferase and monoamine oxidase by tetralone and indanone derivatives substituted with the nitrocatechol moiety

The enzymes, catechol O-methyltransferase (COMT) and monoamine oxidase (MAO) are important drug targets, and inhibitors of these enzymes are established therapy for symptomatic Parkinson's disease (PD). COMT inhibitors enhance the bioavailability of levodopa to the brain, and therefore are combined with levodopa for the treatment of motor fluctuations in PD. Inhibitors of the MAO-B isoform, in turn, are used as monotherapy or in conjunction with levodopa in PD, and function by reducing the central degradation of dopamine. It has been reported that 1-tetralone and 1-indanone derivatives are potent and specific inhibitors of MAO-B, while compounds containing the nitrocatechol moiety (e.g. tolcapone and entacapone) are often potent COMT inhibitors. The present study attempted to discover compounds that exhibit dual COMT and MAO-B inhibition by synthesizing series of 1-tetralone, 1-indanone and related derivatives substituted with the nitrocatechol moiety. These compounds are structurally related to series of nitrocatechol derivatives of chalcone that have recently been investigated as potential dual COMT/MAO inhibitors. The results show that 4-chromanone derivative (7) is the most promising dual inhibitor with IC₅₀ values of 0.57 and 7.26 μM for COMT and MAO-B, respectively, followed by 1-tetralone derivative (4d) with IC₅₀ values of 0.42 and 7.83 μM for COMT and MAO-B, respectively. Based on their potent inhibition of COMT, it may be concluded that nitrocatechol compounds investigated in this study are appropriate for peripheral COMT inhibition, which represents an important strategy in the treatment of PD.

Tissue and interspecies comparison of catechol-O-methyltransferase mediated catalysis of 6-O-methylation of esculetin to scopoletin and its inhibition by entacapone and tolcapone

Catechol-O-methyltransferase (COMT) methylates both endogenous and exogenous catechol compounds to inactive and safe metabolites. We first optimised conditions for a convenient and sensitive continuous fluorescence-based 6-O-methylation assay of esculetin, which we used for investigating the COMT activity in human, mouse, rat, dog, rabbit, and sheep liver cytosols and microsomes and in ten different rat tissues. Furthermore, we compared the inhibition potencies and mechanisms of two clinically used COMT inhibitors, entacapone and tolcapone, in these species. In most tissues, the COMT activity was at least three times higher in cytosol than in microsomes. In the rat, the highest COMT activity was found in the liver, followed by kidney, ileum, thymus, spleen, lung, pancreas, heart, brain, and finally, skeletal muscle. Entacapone and tolcapone were characterised as highly potent mixed type tight-binding inhibitors. The competitive inhibition type dominated over the uncompetitive inhibition with entacapone, whereas uncompetitive inhibition dominated with tolcapone. Rats, dogs, pigs, and sheep are high COMT activity species, in contrast to humans, mice, and rabbits; COMT activity is highest in the liver. Both entacapone and tolcapone are potent COMT inhibitors, but their inhibition mechanisms differ.

Structure-Based Drug Design of Bisubstrate Inhibitors of Phenylethanolamine N-Methyltransferase Possessing Low Nanomolar Affinity at Both Substrate Binding Domains1

The enzyme phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) catalyzes the final step in the biosynthesis of epinephrine and is a potential drug target, primarily for the control of hypertension. Unfortunately, many potent PNMT inhibitors also possess significant affinity for the a₂-adrenoceptor, which complicates the interpretation of their pharmacology. A bisubstrate analogue approach offers the potential for development of highly selective inhibitors of PNMT. This paper documents the design, synthesis, and evaluation of such analogues, several of which were found to possess human PNMT (hPNMT) inhibitory potency <5 nM versus AdoMet. Site-directed mutagenesis studies were consistent with bisubstrate binding. Two of these compounds (19 and 29) were co-crystallized with hPNMT and the resulting structures revealed both compounds bound as predicted, simultaneously occupying both substrate binding domains. This bisubstrate inhibitor approach has resulted in one of the most potent (20) and selective (vs the a_2-adrenoceptor) inhibitors of hPNMT yet reported.

Voltammetric Behaviour of Drug Molecules as a Predictor of Metabolic Liabilities

Electron transfer plays a vital role in drug metabolism and underlying toxicity mechanisms. Currently, pharmaceutical research relies on pharmacokinetics (PK) and absorption, distribution, metabolism, elimination and toxicity (ADMET) measurements to understand and predict drug reactions in the body. Metabolic stability (and toxicity) prediction in the early phases of the drug discovery and development process is key in identifying a suitable lead compound for optimisation. Voltammetric methods have the potential to overcome the significant barrier of new drug failure rates, by giving insight into phase I metabolism events which can have a direct bearing on the stability and toxicity of the parent drug being dosed. Herein, we report for the first time a data-mining investigation into the voltammetric behaviour of reported drug molecules and their correlation with metabolic stability (indirectly measured via t½), as a potential predictor of drug stability/toxicity in vivo. We observed an inverse relationship between oxidation potential and drug stability. Furthermore, we selected and prepared short- (<10 min) and longer-circulation (>2 h) drug molecules to prospectively survey the relationship between oxidation potential and stability.

General Aggregation-Induced Emission Probes for Amyloid Inhibitors with Dual Inhibition Capacity against Amyloid β-Protein and α-Synuclein

Amyloid self-assembly is pathologically linked to many neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). While many inhibitors have been developed individually for specific amyloid proteins, there are a few effective platforms to screen on a large scale general amyloid inhibitors against different amyloid proteins. Herein, we developed a new class of amyloid inhibitor probes by site-specific conjugation of aggregation-induced emission (AIE) molecules with amyloid proteins (i.e., AIE@amyloid probes) to realize a high-throughput screening of small-molecule inhibitors. Optimization of site-specific AIE conjugation with two amyloid proteins, amyloid-β protein (Aβ) and α-synuclein (αSN), enabled us to retain their high amyloidogenic properties; i.e., AIE-amyloid probes alone exhibited strong fluorescence due to amyloid-like aggregation, but they showed no fluorescence in the presence of amyloid inhibitors to prevent amyloid aggregation. From integration of AIE@amyloid probes and computational virtual screening from a large drug database, it was found that tolcapone possessed a dual inhibition against the aggregation and cytotoxicity of both Aβ and αSN. More importantly, tolcapone significantly improved the spatial cognition and recognition of Aβ-treated mice. This work represents an innovative attempt to design an AIE-based anti-amyloid drug platform for identifying new small-molecule inhibitors against amyloidogenesis in both AD and PD or other amyloid diseases.

Are There Benefits in Adding Catechol-O Methyltransferase Inhibitors in the Pharmacotherapy of Parkinson's Disease Patients? A Systematic Review

BACKGROUND

A qualified consensus suggests that a combination of levodopa with a peripherally acting dopa decarboxylase inhibitor continues to present the gold standard treatment of Parkinson's disease (PD). However, as the disease progresses the therapeutic window of levodopa becomes narrowed. Pharmacological strategies for motor fluctuations are focused on providing less pulsatile and more continuous dopaminergic stimulation. Peripheral catechol-O-methyltransferase (COMT) inhibition improves the bioavailability of levodopa and results in a prolonged response.

OBJECTIVE

The primary aim of this study was to investigate the efficacy and safety of the two available COMT inhibitors; entacapone and tolcapone and the recently introduced opicapone.

METHODS

Electronic databases were systematically searched for original studies published within the last 37 years. In addition, lists of identified studies, reviews and their references were examined.

RESULTS

Twelve studies fulfilled the inclusion criteria. 3701 patients with PD were included in this systematic review.

CONCLUSIONS

Adjuvant treatment of PD patients experiencing motor fluctuations with entacapone resulted in improvement of motor function and was well tolerated. Therefore, entacapone presented an acceptable benefit to risk ratio. Tolcapone appeared to result in a greater therapeutic effect. However, this was not consistent across all motor variables and studies, and thus would not support its use, given the current onerous monitoring that is required. Opicapone was not associated with adverse reactions in a phase III trial but did not present a greater efficacy than entacapone, and thus further studies are required in order to illustrate its cost effectiveness.

Drug repurposing for antimicrobial discovery

Antimicrobial resistance continues to be a public threat on a global scale. The ongoing need to develop new antimicrobial drugs that are effective against multi-drug-resistant pathogens has spurred the research community to invest in various drug discovery strategies, one of which is drug repurposing-the process of finding new uses for existing drugs. While still nascent in the antimicrobial field, the approach is gaining traction in both the public and private sector. While the approach has particular promise in fast-tracking compounds into clinical studies, it nevertheless has substantial obstacles to success. This Review covers the art of repurposing existing drugs for antimicrobial purposes. We discuss enabling screening platforms for antimicrobial discovery and present encouraging findings of novel antimicrobial therapeutic strategies. Also covered are general advantages of repurposing over de novo drug development and challenges of the strategy, including scientific, intellectual property and regulatory issues.

Editor's Highlight: An Impaired Immune Tolerance Animal Model Distinguishes the Potential of Troglitazone/Pioglitazone and Tolcapone/Entacapone to Cause IDILI

We have developed an animal model of amodiaquine-induced liver injury that has characteristics very similar to idiosyncratic drug-induced liver injury (IDILI) in humans by impairing immune tolerance using a PD1-/- mouse and cotreatment with anti-CTLA-4. In order to test the usefulness of this model as a general model for human IDILI risk, pairs of drugs with similar structures were tested, one of which is associated with a relatively high risk of IDILI and the other not. One such pair is troglitazone and pioglitazone; troglitazone has caused fatal cases of IDILI while pioglitazone is quite safe. Another pair is tolcapone and entacapone; tolcapone can cause serious IDILI; in contrast, although entacapone has been reported to cause liver injury, it is relatively safe. PD1-/- mice treated with anti-CTLA-4 and troglitazone or tolcapone displayed liver injury as determined by ALT levels and histology, while pioglitazone and entacapone showed less signs of liver injury. One possible mechanism by which drugs could induce an immune response leading to IDILI is by causing the release of danger-associated molecular pattern molecules that activate inflammasomes. We found that the supernatants from incubations of troglitazone, tolcapone, or entacapone with hepatocytes were also able to activate inflammasomes in macrophages, while the supernatant from pioglitazone incubations did not. These results are consistent with an immune mechanism for troglitazone- and tolcapone-induced IDILI and add to the evidence that this may be a general model for IDILI.

Elucidation of the Impact of P-glycoprotein and Breast Cancer Resistance Protein on the Brain Distribution of Catechol-O-Methyltransferase Inhibitors

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are clinically important efflux transporters that act cooperatively at the blood-brain barrier, limiting the entry of several drugs into the central nervous system (CNS) and affecting their pharmacokinetics, therapeutic efficacy, and safety. In the present study, the interactions of catechol-O-methyltransferase (COMT) inhibitors (BIA 9-1059, BIA 9-1079, entacapone, nebicapone, opicapone, and tolcapone) with P-gp and BCRP were investigated to determine the contribution of these transporters in their access to the brain. In vitro cellular accumulation and bidirectional transport assays were conducted in Madin-Darby canine kidney (MDCK) II, MDCK-MDR1, and MDCK-BCRP cells. In vivo pharmacokinetic studies were carried out for tolcapone and BIA 9-1079 in rats, with and without elacridar, a well-known P-gp and BCRP modulator. The results suggest that BIA 9-1079, nebicapone, and tolcapone inhibit BCRP in a concentration-dependent manner. Moreover, with net flux ratios higher than 2 and decreased over 50% in the presence of verapamil or Ko143, BIA 9-1079 was identified as a P-gp substrate while BIA 9-1059, entacapone, opicapone, and nebicapone were revealed to be BCRP substrates. In vivo, brain exposure was limited for tolcapone and BIA 9-1079, although tolcapone crossed the blood-brain barrier at a greater rate and to a greater extent than BIA 9-1079. The extent of brain distribution of both compounds was significantly increased in the presence of elacridar, attesting to the involvement of efflux transporters. These findings provide relevant information and improve the understanding of the mechanisms that govern the access of these COMT inhibitors to the CNS.

Deficiency in catechol-o-methyltransferase is linked to a disruption of glucose homeostasis in mice

2-methoxyestradiol (2-ME), an estrogen metabolite generated via catechol-o-methyltransferase (COMT), is multifunctional methoxy-catechol. Here, we report that COMT deficiency leads to glucose intolerance and 2-ME rescues COMT-deficient-associated metabolic defects. Liver COMT protein was suppressed in high fat diet (HFD)-fed or in pregnant mice. COMT suppression, by Ro41-0960 or siRNA, in HFD fed mice or in pregnant mice exacerbated glucose intolerance; 2-ME intervention ameliorated these defects. 2-ME effects on glucose tolerance were associated with AMPK phosphorylation in the liver and in islet cells. Metformin restored liver COMT protein levels, and metformin-induced liver AMPK phosphorylation was abolished by COMT inhibition. The amelioration in glucose tolerance by 2-ME was associated with biphasic insulin secretion in an environment-dependent manner. 2-ME-induced insulin secretion was associated with the AMPK phosphorylation, PDX-1 phosphorylation, and MST-1 suppression in MIN-6 cells. Furthermore 2-ME displayed PPARγ agonist-like activity. These results suggest that COMT is an enzyme to maintain glucose homeostasis and 2-ME is a potential endogenous multi-target anti-diabetic candidate.

Theranostic Biomarkers for Schizophrenia

Schizophrenia is a highly heritable, chronic, severe, disabling neurodevelopmental brain disorder with a heterogeneous genetic and neurobiological background, which is still poorly understood. To allow better diagnostic procedures and therapeutic strategies in schizophrenia patients, use of easy accessible biomarkers is suggested. The most frequently used biomarkers in schizophrenia are those associated with the neuroimmune and neuroendocrine system, metabolism, different neurotransmitter systems and neurotrophic factors. However, there are still no validated and reliable biomarkers in clinical use for schizophrenia. This review will address potential biomarkers in schizophrenia. It will discuss biomarkers in schizophrenia and propose the use of specific blood-based panels that will include a set of markers associated with immune processes, metabolic disorders, and neuroendocrine/neurotrophin/neurotransmitter alterations. The combination of different markers, or complex multi-marker panels, might help in the discrimination of patients with different underlying pathologies and in the better classification of the more homogenous groups. Therefore, the development of the diagnostic, prognostic and theranostic biomarkers is an urgent and an unmet need in psychiatry, with the aim of improving diagnosis, therapy monitoring, prediction of treatment outcome and focus on the personal medicine approach in order to improve the quality of life in patients with schizophrenia and decrease health costs worldwide.

Novel Dopamine Therapeutics for Cognitive Deficits in Schizophrenia

Schizophrenia is characterized by profound cognitive deficits that are not alleviated by currently available medications. Many of these cognitive deficits involve dysfunction of the newly evolved, dorsolateral prefrontal cortex (dlPFC). The brains of patients with schizophrenia show evidence of dlPFC pyramidal cell dendritic atrophy, likely reductions in cortical dopamine, and possible changes in dopamine D1 receptors (D1R). It has been appreciated for decades that optimal levels of dopamine are essential for dlPFC working memory function, with many beneficial actions arising from D1R stimulation. D1R are concentrated on dendritic spines in the primate dlPFC, where their stimulation produces an inverted-U dose response on dlPFC neuronal firing and cognitive performance during working memory tasks. Research in both academia and the pharmaceutical industry has led to the development of selective D1 agonists, e.g., the first full D1 agonist, dihydrexidine, which at low doses improved working memory in monkeys. Dihydrexidine has begun to be tested in patients with schizophrenia or schizotypal disorder. Initial results are encouraging, but studies are limited by the pharmacokinetics of the drug. These data, however, have spurred efforts toward the discovery and development of improved or novel new compounds, including D1 agonists with better pharmacokinetics, functionally selective D1 ligands, and D1R positive allosteric modulators. One or several of these approaches should allow optimization of the beneficial effects of D1R stimulation in the dlPFC that can be translated into clinical practice.

Design of Potent and Druglike Nonphenolic Inhibitors for Catechol O-Methyltransferase Derived from a Fragment Screening Approach Targeting the S-Adenosyl-l-methionine Pocket

A fragment screening approach designed to target specifically the S-adenosyl-l-methionine pocket of catechol O-methyl transferase allowed the identification of structurally related fragments of high ligand efficiency and with activity on the described orthogonal assays. By use of a reliable enzymatic assay together with X-ray crystallography as guidance, a series of fragment modifications revealed an SAR and, after several expansions, potent lead compounds could be obtained. For the first time nonphenolic and small low nanomolar potent, SAM competitive COMT inhibitors are reported. These compounds represent a novel series of potent COMT inhibitors that might be further optimized to new drugs useful for the treatment of Parkinson's disease, as adjuncts in levodopa based therapy, or for the treatment of schizophrenia.

3-O-Methyldopa inhibits astrocyte-mediated dopaminergic neuroprotective effects of L-DOPA

BACKGROUND

We evaluated the effects of 3-O-methyldopa (3-OMD), a metabolite of L-DOPA which is formed by catechol-O-methyltransferase (COMT), on the uptake, metabolism, and neuroprotective effects of L-DOPA in striatal astrocytes. We examined changes in the numbers of dopaminergic neurons after treatment with L-DOPA and 3-OMD or entacapone, a peripheral COMT inhibitor, using primary cultured mesencephalic neurons and striatal astrocytes.

RESULTS

The number of tyrosine hydroxylase-positive dopaminergic neurons was not affected by L-DOPA treatment in mesencephalic neurons alone. However, the increase in viability of dopaminergic neurons in the presence of astrocytes was further enhanced after methyl-L-DOPA treatment (25 µM) in mixed cultured mesencephalic neurons and striatal astrocytes. The neuroprotective effect of 25 µM L-DOPA was almost completely inhibited by simultaneous treatment with 3-OMD (10 or 100 µM), and was enhanced by concomitant treatment with entacapone (0.3 µM). The uptake of L-DOPA into and the release of glutathione from striatal astrocytes after L-DOPA treatment (100 µM) were inhibited by simultaneous exposure to 3-OMD (100 µM).

CONCLUSIONS

These data suggest that L-DOPA exerts its neuroprotective effect on dopaminergic neurons via astrocytes and that 3-OMD competes with L-DOPA by acting on target molecule(s) (possibly including glutathione) released from astrocytes. Since some amount of entacapone can cross the blood-brain barrier, this reagent may enhance L-DOPA transportation by inhibiting COMT and increase the astrocyte-mediated neuroprotective effects of L-DOPA on dopaminergic neurons.

Novel DOT1L ReceptorNatural Inhibitors Involved in Mixed Lineage Leukemia: a Virtual Screening, Molecular Docking and Dynamics Simulation Study

BACKGROUND

The human protein methyl-transferase DOT1L catalyzes the methylation of histone H3 on lysine 79 (H3K79) at homeobox genes and is also involved in a number of significant processes ranging from gene expression to DNA-damage response and cell cycle progression. Inhibition of DOT1L activity by shRNA or small-molecule inhibitors has been established to prevent proliferation of various MLL-rearranged leukemia cells in vitro, establishing DOT1L an attractive therapeutic target for mixed lineage leukemia (MLL). Most of the drugs currently in use for the MLL treatment are reported to have low efficacy, hence this study focused on various natural compounds which exhibit minimal toxic effects and high efficacy for the target receptor.

MATERIALS AND METHODS

Structures of human protein methyl-transferase DOT1L and natural compound databases were downloaded from various sources. Virtual screening, molecular docking, dynamics simulation and drug likeness studies were performed for those natural compounds to evaluate and analyze their anti-cancer activity.

RESULTS

The top five screened compounds possessing good binding affinity were identified as potential high affinity inhibitors against DOT1L's active site. The top ranking molecule amongst the screened ligands had a Glide g-score of -10.940 kcal/mol and Glide e-model score of -86.011 with 5 hydrogen bonds and 12 hydrophobic contacts. This ligand's behaviour also showed consistency during the simulation of protein-ligand complex for 20000 ps, which is indicative of its stability in the receptor pocket.

CONCLUSIONS

The ligand obtained out of this screening study can be considered as a potential inhibitor for DOT1L and further can be treated as a lead for the drug designing pipeline.

A new PAMPA model using an in-house brain lipid extract for screening the blood-brain barrier permeability of drug candidates

The determination of the permeability of drug candidates across the blood-brain barrier (BBB) is a fundamental step during drug discovery programs. The parallel artificial membrane permeability assay (PAMPA) is a high throughput screening tool applied to evaluate the passive permeability and adapted to predict BBB penetration. Herein, a new PAMPA model was developed using an in-house brain lipid extract capable of discriminating BBB permeable from non-permeable compounds. The apparent permeability (Papp) of 18 reference molecules and 10 test compounds was assessed and compared with phosphatidylcholine and commercial porcine polar brain lipid (PBL). The physicochemical selectivity of the in-house brain lipid extract was demonstrated by correlating Papp values with physicochemical properties and its predictive capacity estimated by establishing in vitro-in vivo correlations. The strong correlations achieved between 2% (w/v) in-house lipid extract and PBL for reference (r(2)=0.77) and test compounds (r(2)=0.94) support an equivalent discriminatory capacity and validate the presented model. Moreover, PAMPA studies performed with PBL and in-house lipid extract exhibited a higher correlation with the in vivo parameter logBB (r(2)=0.76 and r(2)=0.72, respectively) than phosphatidylcholine (r(2)=0.51). Overall, the applied lipid extraction process was reproducible, economical and provided lipid extracts that can be used to reliably assess BBB permeation.

Dopamine bioavailability in the mPFC modulates operant learning performance in rats: an experimental study with a computational interpretation

Dopamine encodes reward and its prediction in reinforcement learning. Catechol-O-methyltransferase (COMT) activity in the medial prefrontal cortex (mPFC) has been shown to influence cognitive abilities by modifying dopamine clearance. Nevertheless, it is unknown how COMT in the mPFC influences operant learning. Systemic entacapone (50mg/kg), as well as local entacapone (3 pg) and recombinant COMT (17 μg) in the mPFC were administered to male Long Evans rats prior to training in an operant conditioning task. We found that systemic and local administration of the COMT inhibitor entacapone significantly improves learning performance. Conversely, recombinant COMT administration totally impaired learning. These data have been interpreted through a computational model where the phasic firing of dopaminergic neurons was computed by means of a temporal difference algorithm and dopamine bioavailability in the mPFC was simulated with a gating window. The duration of this window was selected to simulate the effects of inhibited or enhanced COMT activity (by entacapone or recombinant COMT respectively). The model accounts for an improved performance reproducing the entacapone effects, and a detrimental impact on learning when the clearance is increased reproducing the recombinant COMT effects. The experimental and computational results show that learning performance can be deeply influenced by COMT manipulations in the mPFC.

Tolcapone, COMT polymorphisms and pharmacogenomic treatment of schizophrenia

It is widely accepted that abnormal prefrontal cortex biology resulting in deficient cognition is a primary problem in schizophrenia and that all currently available antipsychotics fail to improve cognitive and negative symptoms originating from this deficit. Evidence from basic science has revealed the importance of prefrontal dopamine signaling for optimal prefrontal function. This article describes succinctly the progress made so far, taking into account the mechanisms involved in catechol-O-methyltransferase (COMT)-induced modulation of prefrontal dopamine signaling, the impact of COMT on cognitive function and the role of COMT gene polymorphisms. The potential role of the COMT inhibitor tolcapone to improve cognitive function in health and disease is also presented here. It will soon be understood if tolcapone represents one of the first hypothesis-driven, biology-based, genotype-specific, targeted treatments of cognitive and negative symptoms of schizophrenia.

Systemic catechol-O-methyl transferase inhibition enables the D1 agonist radiotracer R-[11C]SKF 82957

INTRODUCTION

R-[(11)C]-SKF 82957 is a high-affinity and potent dopamine D(1) receptor agonist radioligand, which gives rise to a brain-penetrant lipophilic metabolite. In this study, we demonstrate that systemic administration of catechol-O-methyl transferase (COMT) inhibitors blocks this metabolic pathway, facilitating the use of R-[(11)C]-SKF 82957 to image the high-affinity state of the dopamine D(1) receptor with PET.

METHODS

R-[(11)C]SKF 82957 was administered to untreated and COMT inhibitor-treated conscious rats, and the radioactive metabolites present in the brain and plasma were quantified by HPLC. Under optimal conditions, cerebral uptake and dopamine D(1) binding of R-[(11)C]SKF 82957 were measured ex vivo. In addition, pharmacological challenges with the receptor antagonist SCH 23390, amphetamine, the dopamine reuptake inhibitor RTI-32 and the dopamine hydroxylase inhibitor α-methyl-p-tyrosine were performed to study the specificity and sensitivity of R-[(11)C]-SKF 82957 dopamine D(1) binding in COMT-inhibited animals.

RESULTS

Treatment with the COMT inhibitor tolcapone was associated with a dose-dependent (EC(90) 5.3 ± 4.3 mg/kg) reduction in the lipophilic metabolite. Tolcapone treatment (20 mg/kg) also resulted in a significant increase in the striatum/cerebellum ratio of R-[(11)C]SKF 82957, from 15 (controls) to 24. Treatment with the dopamine D(1) antagonist SCH 23390 reduced the striatal binding to the levels of the cerebellum, demonstrating a high specificity and selectivity of R-[(11)C]SKF 82957 binding.

CONCLUSIONS

Pre-treatment with the COMT inhibitor tolcapone inhibits formation of an interfering metabolite of R-[(11)C]SKF 82957. Under such conditions, R-[(11)C]SKF 82957 demonstrates high potential as the first agonist radiotracer for imaging the dopamine D(1) receptor by PET.

Entacapone and tolcapone, two catechol O-methyltransferase inhibitors, block fibril formation of alpha-synuclein and beta-amyloid and protect against amyloid-induced toxicity

Parkinson disease (PD) is the second most common neurodegenerative disorder after Alzheimer disease (AD). There is considerable consensus that the increased production and/or aggregation of alpha-synuclein (alpha-syn) plays a central role in the pathogenesis of PD and related synucleinopathies. Current therapeutic strategies for treating PD offer mainly transient symptomatic relief and aim at the restitution of dopamine levels to counterbalance the loss of dopaminergic neurons. Therefore, the identification and development of drug-like molecules that block alpha-synuclein aggregation and prevent the loss of dopaminergic neurons are desperately needed to treat or slow the progression of PD. Here, we show that entacapone and tolcapone are potent inhibitors of alpha-syn and beta-amyloid (Abeta) oligomerization and fibrillogenesis, and they also protect against extracellular toxicity induced by the aggregation of both proteins. Comparison of the anti-aggregation properties of entacapone and tolcapone with the effect of five other catechol-containing compounds, dopamine, pyrogallol, gallic acid, caffeic acid, and quercetin on the oligomerization and fibrillization of alpha-syn and Abeta, demonstrate that the catechol moiety is essential for the anti-amyloidogenic activity. Our findings present the first characterization of the anti-amyloidogenic properties of tolcapone and entacapone against both alpha-synuclein and Abeta42 and highlight the potential of this class of nitro-catechol compounds as anti-amyloidogenic agents. Their inhibitory properties, mode of action, and structural properties suggest that they constitute promising lead compounds for further optimization.

Levodopa/carbidopa and entacapone in the treatment of Parkinson's disease: efficacy, safety and patient preference

Levodopa (LD) is the oldest, most efficacious and best-tolerated drug for dopaminergic substitution of patients with Parkinson's disease (PD). Its main drawback is its short half-life, which supports onset of motor complications in the long term. Therefore well-informed PD patients mostly accept LD therapy as late as possible. Recent LD trials indicate that a combination of LD with carbidopa (CD) and the catechol-O-methyltransferase (COMT) inhibitor entacapone (EN) may reduce the onset of these motor complications to a certain extent. This observation is further supported by pharmacokinetic trials and experimental research, but there is still a need to confirm this in a clinical trial, which is under way. Additionally, combined LD/CD/EN was superior to LD/CD administration regarding cognition, muscle behavior and gastrointestinal function in small clinical trials. Moreover there is accumulating evidence that combined COMT inhibition with LD administration reduces homocysteine synthesis. In the long term, homocysteine elevation supports onset of arteriosclerosis-related disorders, which are more frequent in PD patients according to epidemiological studies than in the normal healthy population. The introduction of LD/CD/EN in one tablet supported patients' preference of COMT inhibition as an essential component of LD/DDI therapy, as this combination reduced number and size of tablets.

Evidence-based efficacy comparison of tolcapone and entacapone as adjunctive therapy in Parkinson's disease

The relative efficacy has not been adequately established for the two catechol-O-methyltransferase (COMT) inhibitors that are currently available for adjunctive therapy in Parkinson's disease; tolcapone and entacapone. A recent Cochrane meta-analysis of 14 studies in 2566 patients, conducted to assess the efficacy and safety of tolcapone and entacapone, found both to be statistically superior to placebo in increasing ON time and decreasing OFF time. The meta-analysis also showed that the weighted mean difference from baseline to endpoint in tolcapone-treated patients was twice that in entacapone-treated patients for both placebo-corrected ON time and OFF time. Withdrawal rates were generally lower for tolcapone. Two additional studies have examined the switch between tolcapone and entacapone. In 40 Parkinson's disease patients with fluctuations who were switched from tolcapone to entacapone, improvements in ON time and reductions in OFF time were approximately twice the magnitude for tolcapone than for entacapone. In a second study examining the switch from entacapone to tolcapone, the results for several exploratory variables also suggested that tolcapone has greater efficacy than entacapone. These findings indicate that tolcapone should be considered in all patients with entacapone-refractory motor fluctuations.

Novel screening assay for antioxidant protection against peroxyl radical‐induced loss of protein function

Oxidative damage to proteins, implicated amongst other in the etiology and progression of Parkinson's disease (PD) and Alzheimer's disease (AD), results in the loss of specific biological protein function. A simple, sensitive, and cost-effective fluorimetric test to assess the antioxidant capacity of new chemical entities to protect proteins from loss of activity caused by reactive oxygen species (ROS) was developed using alkaline phosphatase (ALP) as model protein. Protein oxidation was induced by 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH) and the decrease in catalytic activity of ALP to hydrolyze 4-methylumbelliferyl phosphate (4-MUP) to fluorescent 4-methylumbelliferone (4-MU) was monitored as a marker of protein degradation. According to their capacity to protect ALP from peroxyl radical-induced activity loss, ten reference antioxidants were divided into three classes, namely efficient (pIC(50) > 5 for quercetin, chlorogenic acid, caffeic acid, mangiferin, and resveratrol), intermediate (4 < pIC(50) < or = 5 for melatonin, trolox, and ascorbic acid), and poor antioxidants (pIC(50) < 4 for glutathione and D-mannitol). Multifunctional drugs, having the ability to interact with several disease-related targets are of interest in PD. Therefore, the capacity of three catechol-O-methyltransferase (COMT) inhibitors, entacapone, nitecapone, and tolcapone to protect ALP from oxidative damage was also investigated and found to be very similar to the most potent reference antioxidants.

Treatment of cognitive deficits associated with schizophrenia: potential role of catechol-O-methyltransferase inhibitors

In the last two decades, understanding of the dynamics of dopamine function in the prefrontal cortex and its role in prefrontal cortex physiology has opened up new avenues for therapeutic interventions in conditions in which prefrontal cortex function is compromised. Neuropsychological and imaging studies of prefrontal information processing have confirmed specific cognitive and neurophysiological abnormalities in individuals with schizophrenia. Because such findings are also observed in the healthy siblings of patients with schizophrenia, they may represent intermediate phenotypes related to schizophrenia susceptibility genes.Catechol-O-methyltransferase (COMT) represents an important candidate as a susceptibility gene for cognitive dysfunction in schizophrenia because of the unique role this enzyme plays in regulating prefrontal dopaminergic function. A functional COMT polymorphism (Val158Met) predicts performance in tasks of prefrontal executive function and the neurophysiological response measured with electroencephalography and functional magnetic resonance imaging in tasks assessing working memory. In fact, individuals with the Val/Val genotype, which encodes for the high-activity enzyme resulting in lower dopamine concentrations in the prefrontal cortex, perform less well and are less efficient physiologically than Met/Met individuals. These findings raise the possibility of new pharmacological interventions for the treatment of prefrontal cortex dysfunction and of predicting outcome based on COMT genotype. One strategy consists of the use of CNS-penetrant COMT inhibitors such as tolcapone. A second strategy is to increase extracellular dopamine concentrations in the frontal cortex by blocking the noradrenaline (norepinephrine) reuptake system, a secondary mechanism responsible for the disposal of dopamine from synaptic clefts in the prefrontal cortex. A third possibility involves the use of modafinil, a drug with an unclear mechanism of action but with positive effects on working memory in rodents. The potential of these drugs to improve executive cognitive function by selectively increasing dopamine load in the frontal cortex but not in subcortical territories, and the possibility that response to them may be modified by a COMT polymorphism, provides a novel genotype-based targeted pharmacological approach without abuse potential for the treatment of cognitive disorder in schizophrenia and in other conditions involving prefrontal cortex dysfunction.

Increased catechol-O-methyltransferase activity and protein expression in OX-42-positive cells in the substantia nigra after lipopolysaccharide microinfusion

Activated microglial cells are found in the substantia nigra and the striatum of Parkinson's disease patients. These cells have been shown to express catechol-O-methyltransferase activity which may increase during pathological conditions. Lipopolysaccharides are potent activators of microglial cells. After paranigral lipopolysaccharide infusion to rats we observed intense microglial activation around the lesion area followed by a delayed injury in nigrostriatal pathway in 2 weeks. Simultaneously, catechol-O-methyltransferase activity in the substantia nigra was gradually increased up to 213%. In the Western blot the amount of soluble COMT and membrane bound COMT proteins were increased by 255% and 86%, respectively. Increased catechol-O-methyltransferase immunoreactivity was located primarily into the activated microglial cells in the lesion area. Interestingly, catechol-O-methyltransferase and OX-42 stained also intensively microglia/macrophage-like cells which surrounded the adjacent blood vessels. Inhibition of catechol-O-methyltransferase activity by tolcapone or entacapone did not increase lipopolysaccharide-induced neurotoxicity. We conclude that catechol-O-methyltransferase activity and protein expression were increased in the substantia nigra after inflammation induced by lipopolysaccharides. These changes in glial and perivascular catechol-O-methyltransferase activity may have clinical relevance for Parkinson's disease drug treatment due to increased metabolism of levodopa in the brain.

Tolcapone improves cognition and cortical information processing in normal human subjects

Prefrontal cortical dopamine (DA) regulates various executive cognitive functions, including attention and working memory. Efforts to enhance prefrontal-related cognition, which have focused on catecholaminergic stimulant drugs, have been unsatisfactory. Recently, the demonstration that a functional polymorphism in the catecholamine-O-methyltransferase (COMT) gene impacts prefrontal cognition raises the possibility of a novel pharmacological approach for the treatment of prefrontal lobe executive dysfunction. To explore in a proof of concept study the effects of tolcapone, a CNS penetrant specific COMT inhibitor, we performed a randomized, double blind, placebo controlled, and crossover design of this drug in normal subjects stratified by COMT (val158met) genotype. COMT enzyme activity was determined in peripheral blood. Forty-seven normal volunteers with no family history of psychiatric disorders underwent neuropsychological testing and 34 of those subjects underwent physiological measurement of prefrontal information processing assessed by blood oxygen level-dependent functional magnetic resonance imaging (fMRI). We found significant drug effects on measures of executive function and verbal episodic memory and a significant drug by genotype interaction on the latter, such that individuals with val/val genotypes improved, whereas individuals with met/met genotypes worsened on tolcapone. fMRI revealed a significant tolcapone-induced improvement in the efficiency of information processing in prefrontal cortex during a working memory test. This study demonstrates enhancement of prefrontal cortical function in normal human subjects with a nonstimulant drug having COMT inhibitory activity. Our results are consistent with data from animal studies and from computational models of the effects of selective enhancement of DA signaling in the prefrontal cortex.

Advances in the delivery of treatments for Parkinson's disease

Innovative drug delivery in Parkinson's disease (PD) has the potential to reduce or avoid many side effects of current treatment, such as wearing-off type fluctuations, dyskinesia, on-off phenomena or bouts of motor freezing. The traditional orally administered formulations of l-dihydroxyphenylalanine combined with a peripheral aromatic acid decarboxylase inhibitor remain the mainstay of treatments for PD. However, such combination therapies have been further formulated to extend their duration of action by including a catechol-O-methyltransferase inhibitor. Preventing the breakdown of dopamine has also been achieved by monoamine oxidase-B inhibition; this approach now having been formulated for sublingual use (Zelapar, Valeant Pharmaceuticals). An alternative approach bypasses the oral route of administration and instead relies on continuous duodenal infusion (Duodopa, Solvay, NeoPharma AB) for better therapeutic effect. The clinical use of dopamine agonists as antiparkinsonian drugs now incorporates a variety of delivery techniques. For example, apomorphine, which relies on parenteral administration for maximum bioavailability, may be delivered via rectal, intranasal, sublingual and subcutaneous (e.g., Apokyn, Mylan Bertek) routes. Meanwhile, rotigotine and lisuride have both been formulated for delivery via skin patches. Finally, the authors examine more experimental delivery techniques, including the delivery of genes via viral vectors or liposomes, intracranial transplant of a variety of cells and of L-dihydroxyphenylalanine by prodrug-dispensing liposomes or pulmonary delivery (AIR, Alkermes). The advent and application of these varied technologies will help encourage patient-specific means of treatment for PD.

The role of physicochemical properties of entacapone and tolcapone on their efficacy during local intrastriatal administration

Aqueous solubility, apparent partition coefficient (logPapp) and catechol-O-methyltransferase (COMT, EC 2.1.1.6) inhibiting potency of entacapone and tolcapone were compared in vitro. Both drugs (at 10 and 100 microM) were also delivered directly into rat striatum via a microdialysis probe. Extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations were measured to evaluate the inhibition of striatal COMT in vivo. Although entacapone had 15-fold better aqueous solubility than tolcapone at pH 7.4, also tolcapone had sufficient aqueous solubility to remain in solution at 100 microM. The logPapp of tolcapone was higher than that reported for entacapone in the pH range from 5.0 to 7.4. Entacapone and tolcapone inhibited equally rat striatal COMT in vitro with Ki values of 1.86 and 2.50 nM, respectively. Both drugs had similar outflow from the microdialysis probe in vitro. Perfusion of 100 microM entacapone increased significantly extracellular DOPAC levels compared to the control group. Both entacapone and tolcapone (at 10 and 100 microM) decreased significantly HVA levels, but entacapone was significantly more effective than tolcapone at 100 microM. In conclusion, entacapone and tolcapone are equally potent COMT inhibitors against rat striatal COMT in vitro. After local intrastriatal administration, entacapone appeared to inhibit COMT faster and more effectively than the more lipophilic tolcapone. Thus, intrastriatal administration led to opposite results compared to those reported in the brain after systemic administration. The present results also suggest that the local distribution of entacapone and tolcapone differ when the drugs are delivered directly into the brain.

The COMT inhibitor, entacapone, reduces levodopa-induced elevations in plasma homocysteine in healthy adult rats

Levodopa treatment has been shown to increase plasma homocysteine levels in Parkinson's disease (PD) patients and this may lead to an increased risk for coronary arterial diseases. Levodopa is metabolised via O-methylation by catechol-O-methyltransferase (COMT) using S-adenosyl-L-methionine (SAM) as the methyl donor, this leading to the subsequent formation of homocysteine. In this study, the effects of the COMT inhibitor, entacapone, on levodopa-induced hyperhomocysteinaemia were studied in rats. Using a single dose acute treatment paradigm, entacapone (10 or 30 mg/kg) prevented the levodopa (30 or 100 mg/kg) induced rise in plasma homocysteine levels in a dose-dependent manner. Five-day sub-chronic treatment with levodopa (3 x 100 mg/kg per day) resulted in a marked rise in plasma homocysteine levels when measured 2 hours post-treatment on Day 5. These levels fell but remained greater than baseline at 8 hours post-treatment on Day 5. Consistent with findings in the acute treatment test paradigm, the co-administration of entacapone (30 mg/kg) significantly (p<0.001) reduced levodopa-induced hyperhomocysteinaemia for up to 2 hours post-treatment on Day 5 of the sub-chronic study. These results suggest that entacapone may reduce levodopa-induced hyperhomocysteinaemia in PD patients.