Nitroindazole compounds inhibit the oxidative activation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxin to neurotoxic pyridinium cations by human monoamine oxidase (MAO)

β-Carboline Alkaloids in Soy Sauce and Inhibition of Monoamine Oxidase (MAO)

Monoamine oxidase (MAO) oxidizes neurotransmitters and xenobiotic amines, including vasopressor and neurotoxic amines such as the MPTP neurotoxin. Its inhibitors are useful as antidepressants and neuroprotectants. This work shows that diluted soy sauce (1/3) and soy sauce extracts inhibited human MAO-A and -B isozymes in vitro, which were measured with a chromatographic assay to avoid interferences, and it suggests the presence of MAO inhibitors. Chromatographic and spectrometric studies showed the occurrence of the β-carboline alkaloids harman and norharman in soy sauce extracts inhibiting MAO-A. Harman was isolated from soy sauce, and it was a potent and competitive inhibitor of MAO-A (0.4 µM, 44 % inhibition). The concentrations of harman and norharman were determined in commercial soy sauces, reaching 243 and 52 μg/L, respectively. Subsequently, the alkaloids 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (THCA) and 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCA) were identified and analyzed in soy sauces reaching concentrations of 69 and 448 mg/L, respectively. The results show that MTCA was a precursor of harman under oxidative and heating conditions, and soy sauces increased the amount of harman under those conditions. This work shows that soy sauce contains bioactive β-carbolines and constitutes a dietary source of MAO-A and -B inhibitors.

Assay of MAO Inhibition by Chromatographic Techniques (HPLC/HPLC-MS)

Monoamine oxidase (MAO) enzymes (MAO A and B) catalyze the oxidative deamination of biogenic amines, neurotransmitters, and xenobiotic amines and contribute to the regulation of the content of these active substances in mammalian organisms. The oxidation of biogenic amines by MAO produces hydrogen peroxide (H₂O₂) and aldehydes that represent risk factors for oxidative injury. The inhibitors of MAO are useful as antidepressants and neuroprotective agents. Usually, the assays of MAO determine amine deamination products or measure the H₂O₂ released by using direct spectrophotometric or fluorimetric methods. Direct methods are more prone to interferences and can afford inaccurate results. Those limitations can be avoided by using chromatographic techniques. This work describes a chromatographic method to assay MAO A and MAO B activity by using kynuramine as a nonselective substrate and the subsequent analysis of 4-hydroxyquinoline by RP-HPLC-DAD-fluorescence and mass spectrometry (MS). Alternatively, the assay uses the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxin as a substrate of MAO that is oxidized (bioactivated) to neurotoxic pyridinium cations which are analyzed by HPLC. These methods are applied to assess the inhibition of MAO by bioactive β-carboline alkaloids occurring in foods, plants, and biological systems.

Protective effects of a new glutamic acid derivative against stress after nNOS blockade

We studied the effects of a new glutamic acid derivative, glufimet, on oxidative stress, activity of antioxidant enzymes, mitochondrial respiration, endothelial vasodilation and anti-platelet activity in female rats after exposure to 24-hour immobilization pain stress and 7-nitroindazole, a neuronal nitric oxide synthase (nNOS) inhibitor. A single dose administration of glufimet (29 mg/kg intraperitoneally) 10 minutes before stress exposure caused a decrease of NO metabolites in serum (by 27.2%) and heart homogenate (33.5% (p£0.05), respectively, compared with the control group. Administration of 7-nitroindazole with glufimet also decreased the studied parameters by 14.3% in the heart homogenate and by 30,3% in the brain (p£0.05) compared with stress exposed rats receiving only the nNOS inhibitor. Glufimet decreased the levels of primary and secondary products of lipid peroxidation (LPO), conjugated dienes by 20% (p£0.05) and 17.3% (p£0.05), ketodienes by 16% and 13.7%, malondialdehyde by 15% (p£0.05) and 26.6% (p£0.05) in the heart and brain mitochondria of stress exposed rats, respectively, compared with the control group. Glufimet administration also increased SOD activity (by 14.4% and 13.1%, respectively), catalase (by 19% and 26.8%, respectively) and glutathione peroxidase (GPx) activity (by 45.5% (p£0.05) and 7.3%, respectively). The antioxidant effect of glufimet may be also attributed to increased coupling between the processes of mitochondria respiration and oxidative phosphorylation. This was evidenced by an increase in the respiratory control ratio (RCR) (by 46.0% (p£0.05) for malate/glutamate and by 49,7% (p£0.05) for succinate) in the heart mitochondria. A statistically significant increase in RCR (by 37.3% (p£0.05)) was observed in stress exposed female rat brain mitochondria for succinate. RCRs differed significantly for succinate in the heart and brain of rats receiving glufimet after nNOS blockade. RCR increased by 62.3% (p£0.05) in the heart mitochondria and by 72.2% (p£0.05) in the brain mitochondria compared with the RCRs in stress exposed rats receiving 7-nitroindazole.

Evaluation of a New Molecular Entity as a Victim of Metabolic Drug-Drug Interactions-an Industry Perspective

Under the guidance of the International Consortium for Innovation and Quality in Pharmaceutical Development (IQ), scientists from 20 pharmaceutical companies formed a Victim Drug-Drug Interactions Working Group. This working group has conducted a review of the literature and the practices of each company on the approaches to clearance pathway identification (fCL), estimation of fractional contribution of metabolizing enzyme toward metabolism (fm), along with modeling and simulation-aided strategy in predicting the victim drug-drug interaction (DDI) liability due to modulation of drug metabolizing enzymes. Presented in this perspective are the recommendations from this working group on: 1) strategic and experimental approaches to identify fCL and fm, 2) whether those assessments may be quantitative for certain enzymes (e.g., cytochrome P450, P450, and limited uridine diphosphoglucuronosyltransferase, UGT enzymes) or qualitative (for most of other drug metabolism enzymes), and the impact due to the lack of quantitative information on the latter. Multiple decision trees are presented with stepwise approaches to identify specific enzymes that are involved in the metabolism of a given drug and to aid the prediction and risk assessment of drug as a victim in DDI. Modeling and simulation approaches are also discussed to better predict DDI risk in humans. Variability and parameter sensitivity analysis were emphasized when applying modeling and simulation to capture the differences within the population used and to characterize the parameters that have the most influence on the prediction outcome.

The anti-cancer agent SU4312 unexpectedly protects against MPP(+) -induced neurotoxicity via selective and direct inhibition of neuronal NOS

BACKGROUND AND PURPOSE

SU4312, a potent and selective inhibitor of VEGF receptor-2 (VEGFR-2), has been designed to treat cancer. Recent studies have suggested that SU4312 can also be useful in treating neurodegenerative disorders. In this study, we assessed neuroprotection by SU4312 against 1-methyl-4-phenylpyridinium ion (MPP(+) )-induced neurotoxicity and further explored the underlying mechanisms.

EXPERIMENTAL APPROACH

MPP(+) -treated neurons and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated zebrafish were used to study neuroprotection by SU4312. NOS activity was assayed in vitro to examine direct interactions between SU4312 and NOS isoforms.

KEY RESULTS

SU4312 unexpectedly prevented MPP(+) -induced neuronal apoptosis in vitro and decreased MPTP-induced loss of dopaminergic neurons, reduced expression of mRNA for tyrosine hydroxylase and impaired swimming behaviour in zebrafish. In contrast, PTK787/ZK222584, a well-studied VEGFR-2 inhibitor, failed to prevent neurotoxicity, suggesting that the neuroprotective actions of SU4312 were independent of its anti-angiogenic action. Furthermore, SU4312 exhibited non-competitive inhibition of purified neuronal NOS (nNOS) with an IC(50) value of 19.0 μM but showed little or no effects on inducible and endothelial NOS. Molecular docking simulations suggested an interaction between SU4312 and the haem group within the active centre of nNOS.

CONCLUSIONS AND IMPLICATION

SU4312 exhibited neuroprotection against MPP(+) at least partly via selective and direct inhibition of nNOS. Because SU4312 could reach the brain in rats, our study also offered a support for further development of SU4312 to treat neurodegenerative disorders, particularly those associated with NO-mediated neurotoxicity.

Nitric oxide synthase inhibitors protect against rotenone-induced, oxidative stress mediated parkinsonism in rats

Rotenone is known to cause progressive dopaminergic neuronal loss in rodents, but it remains unclear how this mitochondrial complex-I inhibitor mediates neurodegeneration specific to substantia nigra pars compacta (SNpc). One of the proposed mechanisms is increased free radical generation owing to mitochondrial electron transport chain dysfunction following complex-I inhibition. The present study examined the role of nitric oxide (NO) and hydroxyl radicals (OH) in mediating rotenone-induced dopaminergic neurotoxicity. Indications of NO involvement are evidenced by inducible nitric oxide synthase (NOS) over-expression, and increased NADPH-diaphorase staining in SNpc neurons 96h following rotenone administration. Treatment of these animals with specific neuronal NOS inhibitor, 7-nitroindazole (7-NI) and non-specific NOS inhibitor, N-ω-nitro-l-argenine methyl ester (l-NAME) caused reversal of rotenone-induced striatal dopamine depletion, and attenuation of the neurotoxin-induced decrease in the number of tyrosine hydroxylase immunoreactive neurons in SNpc, as well as in apomorphine and amphetamine-induced unilateral rotations. Interestingly, the study also demonstrated the contribution of OH in mediating rotenone nigral toxicity since there appeared a significant generation of the reactive oxygen species in vivo 24h following rotenone administration, a copious loss of reduced and oxidized glutathione, and increased superoxide dismutase and catalase activities in the cytosolic fractions of the ipsilateral SNpc area on the 5th day. An OH scavenging capacity of 7-NI and l-NAME in a Fenton-like reaction, as well as complete reversal of the rotenone-induced increases in the antioxidant enzyme activities, and the loss in reduced and oxidized glutathione contents in the SNpc supported OH involvement in rotenone-induced dopaminergic neurotoxicity. While these results strongly suggest the contribution of both OH and NO, resulting in acute oxidative stress culminating in dopaminergic neurodegeneration caused by rotenone, the course of events indicated generation of OH as the primary event in the neurotoxic processes.

Evaluation of the oxidation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to toxic pyridinium cations by monoamine oxidase (MAO) enzymes and its use to search for new MAO inhibitors and protective agents

Monoamine oxidase (MAO) enzymes catalyze the oxidative deamination of amines and neurotransmitters and inhibitors of MAO are useful as neuroprotectants. This work evaluates the human MAO-catalyzed oxidation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a dopaminergic neurotoxin, to the directly-acting neurotoxic metabolites, 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP(+)) and 1-methyl-4-phenylpyridinium (MPP(+)) measured by High-Performance Liquid Chromatography (HPLC), and this approach is subsequently used as a new method for screening of MAO inhibitors and protective agents. Oxidation of MPTP by human MAO-B was more efficient than by MAO-A. R-Deprenyl, a known neuroprotectant, norharman (β-carboline), 5-nitroindazole and menadione (vitamin K3) inhibited MAO-B and reduced the formation of toxic pyridinium cations. Clorgyline and the β-carbolines, harman and norharman, inhibited the oxidation of MPTP by MAO-A. Cigarette smoke, as well as the naturally occurring β-carbolines (norharman and harman) isolated from smoke and coffee inhibited the oxidation of MPTP by MAO-B and/or MAO-A, suggesting protective effects against MPTP. The results show the suitability of the approach used to search for new MAO inhibitors with eventual neuroprotective activity.

beta-Carboline alkaloids in Peganum harmala and inhibition of human monoamine oxidase (MAO)

Peganum harmala L. is a multipurpose medicinal plant increasingly used for psychoactive recreational purposes (Ayahuasca analog). Harmaline, harmine, harmalol, harmol and tetrahydroharmine were identified and quantified as the main beta-carboline alkaloids in P. harmala extracts. Seeds and roots contained the highest levels of alkaloids with low levels in stems and leaves, and absence in flowers. Harmine and harmaline accumulated in dry seeds at 4.3% and 5.6% (w/w), respectively, harmalol at 0.6%, and tetrahydroharmine at 0.1% (w/w). Roots contained harmine and harmol with 2.0% and 1.4% (w/w), respectively. Seed extracts were potent reversible and competitive inhibitors of human monoamine oxidase (MAO-A) with an IC(50) of 27 microg/l whereas root extracts strongly inhibited MAO-A with an IC(50) of 159 microg/l. In contrast, they were poor inhibitors of MAO-B. Inhibition of MAO-A by seed extracts was quantitatively attributed to harmaline and harmine whereas inhibition by root extracts came from harmine with no additional interferences. Stems and leaves extracts were poor inhibitors of MAO. The potent inhibition of MAO-A by seed and root extracts of P. harmala containing beta-carbolines should contribute to the psychopharmacological and toxicological effects of this plant and could be the basis for its purported antidepressant actions.