Development of a PC12 Cell Based Assay for Screening Catechol-O-methyltransferase Inhibitors

Hinokinin Decreases Methamphetamine-Induced Hyperlocomotion via the Regulatory Effects on Dopamine Levels

The global abuse of stimulant methamphetamine (METH) imposes a significant social burden. Despite this, effective therapeutic interventions for mitigating the harmful effects associated with METH-induced central nervous system (CNS) stimulation remain elusive. Chamaecyparis obtusa (hinoki), containing hinokinin as its active constituent, has been identified to exhibit CNS depressant properties. Here, we explored the potential of the hinoki extract and hinokinin in modulating METH-induced hyperlocomotion through the regulation of dopaminergic neuronal activity. We discovered that pretreatment with hinokinin significantly attenuates METH-induced locomotor activity, indicative of reduced CNS stimulation. Furthermore, treatment with hinokinin was observed to inhibit the METH-induced elevation in dopamine levels and the concomitant decrease in dopamine transporter (DAT) function within striatal brain slices of mice. In silico analysis coupled with pull-down assays and the dose-response curve substantiated the direct binding of hinokinin to DAT. We propose that hinokinin mitigates METH-induced hyperlocomotion via the inhibition of dopaminergic neurotransmission, with allosteric modulation of DAT playing a critical role in this regulatory mechanism. Collectively, our research suggests the potential of hinokinin to mitigate dopamine-mediated central nervous system excitation.

Natural products from Odontonema strictum promote neurite outgrowth in neuronal PC12 cells

The leaves of Odontonema strictum, a tropical plant used for its antihypertensive properties, are rich in nutrients and biologically active phytochemicals, such as β-sitosterol, stigmasterol, umuravumbolide, deacetylumuravumbolide, dideacetylboronolide, deacetylboronolide, verbascoside, and isoverbascoside. In addition, its roots are rich in β-sitosterol, stigmasterol, and the iridoid glycoside β-O-methyl-unedoside. Ingestion of the roots was reported to have a sedative effect in a dog was previously reported on a dog eating the roots of this plant. In the present study, we report for the first time the cell proliferation- and neurite outgrowth-promoting effects in PC12 neuronal cells of the isolated organic compounds and crude extracts from O. strictum. Pituitary adenylate cyclase-activating peptide (PACAP) and quercetin were used as positive controls. At the concentration of 0.2 μg/mL, β-sitosterol was more potent than quercetin and displayed the same activity (>45 μm/cell) as PACAP (100 nM). At a low concentration (0.04 μg/mL), verbascoside and isoverbascoside showed the strongest neurite outgrowth-promoting effect (neurite length of 30 to 35 μm/cell). Our results indicate that phytomedicines made from O. strictum may be useful in preventing neurodegenerative diseases.

Nitrophenols disrupt the expression and activity of biotransformation enzymes (CYP3A and COMT) in chicken ovarian follicles in vivo and in vitro

Nitrophenols are environmental pollutants and xenobiotics, the main sources of which are diesel exhaust fumes and pesticides. The biotransformation processes that take place in the liver are defence mechanisms against xenobiotics, such as nitrophenols. Our previous study showed that the chicken ovary is an additional xenobiotic detoxification place and that nitrophenols disrupt steroidogenesis in chicken ovarian follicles. Therefore, the present study aimed to determine the in vivo and in vitro effects of 4-nitrophenol (PNP) and 3-methyl-4-nitrophenol (PNMC) on the expression and activity of phase I (CYP3A) and phase II (COMT) biotransformation enzymes in chicken ovary. In an in vivo study, hens were treated with a vehicle or 10 mg PNP or PNMC/kg b.wt. per day for 6 days. In an in vitro study, prehierarchical white and yellowish follicles, as well as the granulosa and theca layers of the three largest preovulatory follicles (F3, F2 and F1), were isolated and then incubated in a control medium or medium supplemented with PNP (10-6 M) or PNMC (10-6 M) for 24 or 48 h. Both in vivo and in vitro studies showed that nitrophenols exert tissue- and compound-dependent (PNP or PNMC) effects on CYP3A and COMT gene (real-time PCR) protein (Western blot) expression and their activity (colorimetric methods). The inhibitory effect of nitrophenols in vivo on the activity of biotransformation enzymes suggest that the ovary has the capacity to metabolise PNP and PNMC.

3D printing of customized bioceramics for promoting bone tissue regeneration by regulating sympathetic nerve behavior

Numerous studies have shown that there are multiple neural activities involved in the process of bone resorption and bone regeneration, and promoting osteogenesis by promoting neural network reconstruction is an effective strategy for repairing critical size bone defects. However, traumatic bone defects often cause activation of the sympathetic nervous system (SNS) in the damaged area, releasing excess catecholamines (CAs), resulting in a decrease in the rate of bone formation. Herein, a 3D-printed scaffold loaded with propranolol (PRN) is proposed to reduce CA concentrations in bone defect areas and promote bone regeneration through drug release. For this purpose, PRN-loaded methacrylated gelatin (GelMA) microspheres were mixed with low-concentration GelMA and perfused into a 3D-printed porous hydroxyapatite (HAp) scaffold. By releasing PRN, which can block β-adrenergic receptors, it hinders the activation of sympathetic nerves and inhibits the release of excess CA by the SNS. At the same time, the composite scaffold recruits bone marrow mesenchymal stem cells (BMSCs) and promotes the differentiation of BMSCs in the direction of osteoblasts, which effectively promotes bone regeneration in the rabbit femoral condyle defect model. The results of the study showed that the release of PRN from the composite scaffold could effectively hinder the activation of sympathetic nerves and promote bone regeneration, providing a new strategy for the treatment of bone defects.

Antagonising a novel toxin "T14" in Alzheimer's disease: Comparison of receptor blocker versus antibody effects in vitro

A 14mer peptide, T14, is a possible signaling molecule driving neurodegeneration. Its levels are doubled in the Alzheimer brain, but its effects can be blocked at the target alpha-7 receptor by a cyclised variant, 'NBP14', which has beneficial effects, in a transgenic mouse model, on the behavioral and histochemical profile. Since the antagonism of T14 has evident therapeutic potential, we explore here an alternative method of preventing its action by comparing the efficacy of NBP14 with a proprietorial polyclonal antibody against T14, 'Ab-19', at inhibiting three distinct effects of the peptide in PC12 cells: calcium influx, cell viability and compensatory acetylcholinesterase (AChE) release. None of these three parameters was affected by either blocking agent when applied alone. However, both NBP14 and the Ab-19 exhibited a dose-dependent profile against the actions of T14 in all three scenarios: the least sensitive effect observed was in the lower dose range, for both the antibody and the receptor blocker, in antagonizing T14-triggered release of AChE: this parameter is interpreted as indirect compensation for the T14-induced compromise of cell viability, triggered by the enhanced influx of calcium through the initial binding of the peptide to an allosteric site on the alpha-7 receptor. As such, it is the most delayed and indirect index of T14 action and thus the least relatively impacted by lowest doses of either NBP14 or Ab-19. In all three scenarios however the effects of T14 are successfully offset by either agent and thus offer two potentially very different therapies against Alzheimer's disease.

Pharmacokinetic and Permeation Studies in Rat Brain of Natural Compounds Led to Investigate Eugenol as Direct Activator of Dopamine Release in PC12 Cells

Eugenol, cinnamaldehyde and D-limonene, the main components of natural essential oils, are endowed with antioxidant and anti-inflammatory properties which allow them to induce beneficial effects on intestinal, cardiac and neuronal levels. In order to characterize their pharmacokinetic profiles and aptitude to permeate in the central nervous system after intravenous and oral administration to rats, new analytical procedures, easily achievable with HPLC-UV techniques, were developed. The terminal half-lives of these compounds range from 12.4 ± 0.9 (D-limonene) and 23.1 ± 1.6 min (cinnamaldehyde); their oral bioavailability appears relatively poor, ranging from 4.25 ± 0.11% (eugenol) to 7.33 ± 0.37% (cinnamaldehyde). Eugenol evidences a marked aptitude to permeate in the cerebrospinal fluid (CSF) of rats following both intravenous and oral administrations, whereas cinnamaldehyde appears able to reach the CSF only after intravenous administration; limonene is totally unable to permeate in the CSF. Eugenol was therefore recruited for in vitro studies of viability and time-/dose-dependent dopamine release in neuronal differentiated PC12 cells (a recognized cellular model mimicking dopaminergic neurons), evidencing its ability to increase cell viability and to induce dopamine release according to a U-shaped time-course curve. Moreover, concentration-response data suggest that eugenol may induce beneficial effects against Parkinson's disease after oral administration.

Identification of minimum essential therapeutic mixtures from cannabis plant extracts by screening in cell and animal models of Parkinson's disease

Medicinal cannabis has shown promise for the symptomatic treatment of Parkinson's disease (PD), but patient exposure to whole plant mixtures may be undesirable due to concerns around safety, consistency, regulatory issues, and psychoactivity. Identification of a subset of components responsible for the potential therapeutic effects within cannabis represents a direct path forward for the generation of anti-PD drugs. Using an in silico database, literature reviews, and cell based assays, GB Sciences previously identified and patented a subset of five cannabinoids and five terpenes that could potentially recapitulate the anti-PD attributes of cannabis. While this work represents a critical step towards harnessing the anti-PD capabilities of cannabis, polypharmaceutical drugs of this complexity may not be feasible as therapeutics. In this paper, we utilize a reductionist approach to identify minimal essential mixtures (MEMs) of these components that are amenable to pharmacological formulation. In the first phase, cell-based models revealed that the cannabinoids had the most significant positive effects on neuroprotection and dopamine secretion. We then evaluated the ability of combinations of these cannabinoids to ameliorate a 6-hydroxydopmamine (OHDA)-induced change in locomotion in larval zebrafish, which has become a well-established PD disease model. Equimolar mixtures that each contained three cannabinoids were able to significantly reverse the OHDA mediated changes in locomotion and other advanced metrics of behavior. Additional screening of sixty-three variations of the original cannabinoid mixtures identified five highly efficacious mixtures that outperformed the original equimolar cannabinoid MEMs and represent the most attractive candidates for therapeutic development. This work highlights the strength of the reductionist approach for the development of ratio-controlled, cannabis mixture-based therapeutics for the treatment of Parkinson's disease.

Alleviating Effects of Black Soybean Peptide on Oxidative Stress Injury Induced by Lead in PC12 Cells via Keap1/Nrf2/TXNIP Signaling Pathway

Many researchers have found that Pb exposure can cause oxidative stress damage to the body’s tissue. Black soybean peptide (BSP) has a variety of physiological functions, especially in terms of oxidative stress. Nevertheless, the mitigation function of BSPs on Pb-induced oxidative stress damage in PC12 cells has not been clearly defined. In this study, cell viability was detected by CCK8. Oxidative stress indicators, such as ROS, GSH/GSSG, MDA, SOD, CAT, GPx, and GR, were tested with biochemical kit. Protein expression of Keap1, Nrf2, and TXNIP was measured by Western blot. Compared with the control group, Pb reduced the cell viability of PC12 cells. However, BSP treatment significantly increased the viability of PC12 cells induced by lead exposure (p < 0.05). Lead can enrich the contents of MDA and ROS, but decrease the amount of CAT, SOD, GR, GPx, and GSH/GSSG in PC12 cells, while BSP can alleviate it (p < 0.05). Lead can enhance the expression of Keap1 and TXNIP proteins, but reduce Nrf2 expression. In contrast, BSPs reversed this phenomenon (p < 0.05). BSPs can alleviate oxidative stress injury induced by lead in PC12 cells through the Keap1/Nrf2/TXNIP signaling pathway.

Differential analyte derivatization enables unbiased MALDI-TOF-based high-throughput screening: A proof-of-concept study for the discovery of catechol-o-methyltransferase inhibitors

Recent advances in label-free high-throughput screening via matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) offer unprecedented opportunities for the identification of novel chemical starting points in target-based drug discovery. A clear advantage of the technology is the possibility for label-free, direct quantification of analytes with high precision and robustness. Here we have expanded the range of analytes and biology that can be addressed via MALDI-TOF HTS, by developing a method based on post-reaction pyrylium-based derivatization to detect 3-methoxytyramine, the physiological enzyme product of the catechol-O-methyltransferase (COMT) enzyme. The introduction of pyrylium-type reagents as universal derivatization strategy under aqueous conditions for molecules containing primary amines represents a valuable addition to the toolbox of MALDI-TOF assay development. Characterization of COMT's enzymatic activity and inhibition by reference inhibitors, and comparison of the results obtained in our assay with data from previous mechanistic studies validated the performance of this new method. To address the problem of isobaric interference, a source of false results in MALDI-TOF assays measuring low molecular weight analytes, we devised a differential derivatization workflow which can potentially replace other counter- or orthogonal assays in future screening campaigns. Finally, we report on the first label-free HTS campaign for the identification of COMT inhibitors performed in miniaturized 1536-well microtiter plate format via MALDI-TOF MS analysis.

Highly Potent, Selective, and Competitive Indole-Based MAO-B Inhibitors Protect PC12 Cells against 6-Hydroxydopamine- and Rotenone-Induced Oxidative Stress

Monoamine oxidase B (MAO-B) is responsible for dopamine metabolism and plays a key role in oxidative stress by changing the redox state of neuronal and glial cells. To date, no disease-modifying therapy for Parkinson's disease (PD) has been identified. However, MAO-B inhibitors have emerged as a viable therapeutic strategy for PD patients. Herein, a novel series of indole-based small molecules was synthesized as new MAO-B inhibitors with the potential to counteract the induced oxidative stress in PC12 cells. At a single dose concentration of 10 µM, 10 compounds out of 30 were able to inhibit MAO-B with more than 50%. Among them, compounds 7b, 8a, 8b, and 8e showed 84.1, 99.3, 99.4, and 89.6% inhibition over MAO-B and IC50 values of 0.33, 0.02, 0.03, and 0.45 µM, respectively. When compared to the modest selectivity index of rasagiline (II, a well-known MAO-B inhibitor, SI > 50), compounds 7b, 8a, 8b and 8e showed remarkable selectivity indices (SI > 305, 3649, 3278, and 220, respectively). A further kinetic study displayed a competitive mode of action for 8a and 8b over MAO-B with Ki values of 10.34 and 6.63 nM. Molecular docking studies of the enzyme-inhibitor binding complexes in MAO-B revealed that free NH and substituted indole derivatives share a common favorable binding mode: H-bonding with a crucial water "anchor" and Tyr326. Whereas in MAO-A the compounds failed to form favorable interactions, which explained their high selectivity. In addition, compounds 7b, 8a, 8b, and 8e exhibited safe neurotoxicity profiles in PC12 cells and partially reversed 6-hydroxydopamine- and rotenone-induced cell death. Accordingly, we report compounds 7b, 8a, 8b, and 8e as novel promising leads that could be further exploited for their multi-targeted role in the development of a new oxidative stress-related PD therapy.

Melatonin Analogues Potently Inhibit MAO-B and Protect PC12 Cells against Oxidative Stress

Monoamine oxidase B (MAO-B) metabolizes dopamine and plays an important role in oxidative stress by altering the redox state of neuronal and glial cells. MAO-B inhibitors are a promising therapeutical approach for Parkinson’s disease (PD). Herein, 24 melatonin analogues (3a–x) were synthesized as novel MAO-B inhibitors with the potential to counteract oxidative stress in neuronal PC12 cells. Structure elucidation, characterization, and purity of the synthesized compounds were performed using ¹H-NMR, ¹³C-NMR, HRMS, and HPLC. At 10 µM, 12 compounds showed >50% MAO-B inhibition. Among them, compounds 3n, 3r, and 3u–w showed >70% inhibition of MAO-B and IC₅₀ values of 1.41, 0.91, 1.20, 0.66, and 2.41 µM, respectively. When compared with the modest selectivity index of rasagiline (II, a well-known MAO-B inhibitor, SI > 50), compounds 3n, 3r, 3u, and 3v demonstrated better selectivity indices (SI > 71, 109, 83, and 151, respectively). Furthermore, compounds 3n and 3r exhibited safe neurotoxicity profiles in PC12 cells and reversed 6-OHDA- and rotenone-induced neuronal oxidative stress. Both compounds significantly up-regulated the expression of the anti-oxidant enzyme, heme oxygenase (HO)-1. Treatment with Zn(II)-protoporphyrin IX (ZnPP), a selective HO-1 inhibitor, abolished the neuroprotective effects of the tested compounds, suggesting a critical role of HO-1 up-regulation. Both compounds increased the nuclear translocation of Nrf2, which is a key regulator of the antioxidative response. Taken together, these data show that compounds 3n and 3r could be further exploited for their multi-targeted role in oxidative stress-related PD therapy.

Analytical methodologies for sensing catechol-O-methyltransferase activity and their applications

Mammalian catechol-O-methyltransferases (COMT) are an important class of conjugative enzymes, which play a key role in the metabolism and inactivation of catechol neurotransmitters, catechol estrogens and a wide range of endobiotics and xenobiotics that bear the catechol group. Currently, COMT inhibitors are used in combination with levodopa for the treatment of Parkinson's disease in clinical practice. The crucial role of COMT in human health has raised great interest in the development of more practical assays for highly selective and sensitive detection of COMT activity in real samples, as well as for rapid screening and characterization of COMT inhibitors as drug candidates. This review summarizes recent advances in analytical methodologies for sensing COMT activity and their applications. Several lists of biochemical assays for measuring COMT activity, including the probe substrates, along with their analytical conditions and kinetic parameters, are presented. Finally, the challenges and future perspectives in the field, such as visualization of COMT activity in vivo and in situ, are highlighted. Collectively, this review article overviews the practical assays for measuring COMT activities in complex biological samples, which will strongly facilitate the investigations on the relevance of COMT to human diseases and promote the discovery of COMT inhibitors via high-throughput screening.

Membrane bound catechol-O-methytransferase is the dominant isoform for dopamine metabolism in PC12 cells and rat brain

Impaired dopamine activity in the dorsolateral prefrontal cortex (DLPFC) is thought to contribute to cognitive deficits in diseases such as schizophrenia, attention deficit hyperactivity disorder (ADHD) and traumatic brain injury. Catechol-O-methyltransfease (COMT) metabolizes dopamine and is an important regulator of dopamine signaling in the DLPFC. In mammalian species, two isoforms of COMT protein, membrane-bound COMT (MB-COMT) and soluble COMT (S-COMT), are encoded by one COMT gene and expressed widely. While S-COMT is thought to play a dominant role in the peripheral tissues, MB-COMT is suggested to have a greater role in dopamine metabolism in the brain. However, whether a selective inhibitor for MB-COMT may effectively block dopamine metabolism remains unknown. We generated a knockout of MB-COMT in PC12 cells using CRISPR-cas9 technology to evaluate the effect of both MB and S-COMT on dopamine metabolism. Deletion of MB-COMT in PC12 cells significantly decreased homovanillic acid (HVA), completely depleted 3-methyoxytyramine (3-MT), and significantly increased 3,4-dihydroxyphenylacetic acid (DOPAC) levels. Comparison of the effect of a MB-COMT selective inhibitor LI-1141 on dopamine metabolism in wild type and MB-COMT knockout PC12 cells allowed us to confirm the selectivity of LI-1141 with respect to MB-COMT in cells. Under conditions in which LI-1141 was shown to inhibit only MB-COMT but not S-COMT, it effectively changed dopamine metabolites similar to the effect induced by tolcapone, a non-selective COMT inhibitor, suggesting that selective inhibition of MB-COMT will be effective in blocking dopamine metabolism, providing an attractive therapeutic approach in improving cognition for patients.

Novel, non-nitrocatechol catechol-O-methyltransferase inhibitors modulate dopamine neurotransmission in the frontal cortex and improve cognitive flexibility

RATIONALE

Cognitive impairment is a primary feature of many neuropsychiatric disorders and there is a need for new therapeutic options. Catechol-O-methyltransferase (COMT) inhibitors modulate cortical dopaminergic function and have been proposed as potential cognitive enhancers. Unfortunately, currently available COMT inhibitors are not good candidates due to either poor blood-brain barrier penetration or severe toxicity.

OBJECTIVES

To address the need for safe, brain-penetrant COMT inhibitors, we tested multiple novel compounds in a set of preclinical in vivo efficacy assays in rats to determine their ability to inhibit COMT function and viability as potential clinical candidates.

METHODS

We measured the change in concentration of dopamine (DA) metabolites in cerebrospinal fluid (CSF) from the cisterna magna and extracellular fluid (ECF) from the frontal cortex produced by our novel compounds. Additionally, we tested the effects of our brain-penetrant COMT inhibitors in an attentional set-shifting assay (ASST). We benchmarked the performance of the novel COMT inhibitors to the effects produced by the known COMT inhibitor tolcapone.

RESULTS

We found that multiple COMT inhibitors, exemplified by LIBD-1 and LIBD-3, significantly modulated dopaminergic function measured as decreases in homovanillic acid (HVA) and increases in 3,4-Dihydroxyphenylacetic acid (DOPAC), two DA metabolites, in CSF and the frontal cortex. Additionally, we found that LIBD-1 significantly improved cognitive flexibility in the ASST, an effect previously reported following tolcapone administration.

CONCLUSIONS

These results demonstrate that LIBD-1 is a novel COMT inhibitor with promising in vivo activity and the potential to serve as a new therapy for cognitive impairment.