l-Deprenyl metabolism by the cytochrome P450 system in monkey (Cercopithecus aethiops) liver microsomes

β-Naphtoflavone and Ethanol Induce Cytochrome P450 and Protect towards MPP⁺ Toxicity in Human Neuroblastoma SH-SY5Y Cells

Cytochrome P450 (CYP) isozymes vary their expression depending on the brain area, the cell type, and the presence of drugs. Some isoforms are involved in detoxification and/or toxic activation of xenobiotics in central nervous system. However, their role in brain metabolism and neurodegeneration is still a subject of debate. We have studied the inducibility of CYP isozymes in human neuroblastoma SH-SY5Y cells, treated with β-naphtoflavone (β-NF) or ethanol (EtOH) as inducers, by qRT-PCR, Western blot (WB), and metabolic activity assays. Immunohistochemistry was used to localize the isoforms in mitochondria and/or endoplasmic reticulum (ER). Tetrazolium (MTT) assay was performed to study the role of CYPs during methylphenyl pyridine (MPP⁺) exposure. EtOH increased mRNA and protein levels of CYP2D6 by 73% and 60% respectively. Both β-NF and EtOH increased CYP2E1 mRNA (4- and 1.4-fold, respectively) and protein levels (64% both). The 7-ethoxycoumarin O-deethylation and dextromethorphan O-demethylation was greater in treatment samples than in controls. Furthermore, both treatments increased by 22% and 18%, respectively, the cell viability in MPP⁺-treated cells. Finally, CYP2D6 localized at mitochondria and ER. These data indicate that CYP is inducible in SH-SY5Y cells and underline this in vitro system for studying the role of CYPs in neurodegeneration.

Key Targets for Multi-Target Ligands Designed to Combat Neurodegeneration

HIGHLIGHTS Compounds that interact with multiple targets but minimally with the cytochrome P450 system (CYP) address the many factors leading to neurodegeneration.Acetyl- and Butyryl-cholineEsterases (AChE, BChE) and Monoamine Oxidases A/B (MAO A, MAO B) are targets for Multi-Target Designed Ligands (MTDL).ASS234 is an irreversible inhibitor of MAO A >MAO B and has micromolar potency against the cholinesterases.ASS234 is a poor CYP substrate in human liver, yielding the depropargylated metabolite.SMe1EC2, a stobadine derivative, showed high radical scavenging property, in vitro and in vivo giving protection in head trauma and diabetic damage of endothelium.Control of mitochondrial function and morphology by manipulating fission and fusion is emerging as a target area for therapeutic strategies to decrease the pathological outcome of neurodegenerative diseases. Growing evidence supports the view that neurodegenerative diseases have multiple and common mechanisms in their aetiologies. These multifactorial aspects have changed the broadly common assumption that selective drugs are superior to "dirty drugs" for use in therapy. This drives the research in studies of novel compounds that might have multiple action mechanisms. In neurodegeneration, loss of neuronal signaling is a major cause of the symptoms, so preservation of neurotransmitters by inhibiting the breakdown enzymes is a first approach. Acetylcholinesterase (AChE) inhibitors are the drugs preferentially used in AD and that one of these, rivastigmine, is licensed also for PD. Several studies have shown that monoamine oxidase (MAO) B, located mainly in glial cells, increases with age and is elevated in Alzheimer (AD) and Parkinson's Disease's (PD). Deprenyl, a MAO B inhibitor, significantly delays the initiation of levodopa treatment in PD patients. These indications underline that AChE and MAO are considered a necessary part of multi-target designed ligands (MTDL). However, both of these targets are simply symptomatic treatment so if new drugs are to prevent degeneration rather than compensate for loss of neurotransmitters, then oxidative stress and mitochondrial events must also be targeted. MAO inhibitors can protect neurons from apoptosis by mechanisms unrelated to enzyme inhibition. Understanding the involvement of MAO and other proteins in the induction and regulation of the apoptosis in mitochondria will aid progress toward strategies to prevent the loss of neurons. In general, the oxidative stress observed both in PD and AD indicate that antioxidant properties are a desirable part of MTDL molecules. After two or more properties are incorporated into one molecule, the passage from a lead compound to a therapeutic tool is strictly linked to its pharmacokinetic and toxicity. In this context the interaction of any new molecules with cytochrome P450 and other xenobiotic metabolic processes is a crucial point. The present review covers the biochemistry of enzymes targeted in the design of drugs against neurodegeneration and the cytochrome P450-dependent metabolism of MTDLs.

Metabolism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine by mitochondrion-targeted cytochrome P450 2D6: implications in Parkinson disease

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxic side product formed in the chemical synthesis of desmethylprodine opioid analgesic, which induces Parkinson disease. Monoamine oxidase B, present in the mitochondrial outer membrane of glial cells, catalyzes the oxidation of MPTP to the toxic 1-methyl-4-phenylpyridinium ion (MPP(+)), which then targets the dopaminergic neurons causing neuronal death. Here, we demonstrate that mitochondrion-targeted human cytochrome P450 2D6 (CYP2D6), supported by mitochondrial adrenodoxin and adrenodoxin reductase, can efficiently catalyze the metabolism of MPTP to MPP(+), as shown with purified enzymes and also in cells expressing mitochondrial CYP2D6. Neuro-2A cells stably expressing predominantly mitochondrion-targeted CYP2D6 were more sensitive to MPTP-mediated mitochondrial respiratory dysfunction and complex I inhibition than cells expressing predominantly endoplasmic reticulum-targeted CYP2D6. Mitochondrial CYP2D6 expressing Neuro-2A cells produced higher levels of reactive oxygen species and showed abnormal mitochondrial structures. MPTP treatment also induced mitochondrial translocation of an autophagic marker, Parkin, and a mitochondrial fission marker, Drp1, in differentiated neurons expressing mitochondrial CYP2D6. MPTP-mediated toxicity in primary dopaminergic neurons was attenuated by CYP2D6 inhibitor, quinidine, and also partly by monoamine oxidase B inhibitors deprenyl and pargyline. These studies show for the first time that dopaminergic neurons expressing mitochondrial CYP2D6 are fully capable of activating the pro-neurotoxin MPTP and inducing neuronal damage, which is effectively prevented by the CYP2D6 inhibitor quinidine.

The pharmacology of selegiline

Selegiline, the R-optical enantiomer of deprenyl (phenyl-isopropyl-methyl-propargylamine), was almost exclusively used MAO-B inhibitor during the past decades to treat Parkinson's disease. Oral treatment prolongs the need of levodopa administration. Selegiline is rapidly metabolized by the microsomal enzymes to amphetamine, methamphetamine, and desmethyl-deprenyl. In addition, the flavin-containing monooxigenase is synthesizing deprenyl-N-oxide. Selegiline in rather low concentrations (10⁻⁹-10⁻¹³ M), does not influence MAO-B, but it has an antiapoptotic activity in tissue culture. The neuroprotective effect of selegiline has a biphasic character. In higher concentrations than 10⁻⁷ M increases the rate of apoptosis (proapoptotic activity). The metabolites are also taking part in the complex pharmacological activity of selegiline. The simultaneous presence of the pro- and antiapoptotic effects of selegiline and its metabolites frequently hindered its clinical usage. During the past years rasagiline has been introduced to replace selegiline in clinical application. MAO-B inhibitors beside their effect on the enzyme MAO-B could hold different spectrum of pharmacological activities. Selegiline is administered orally and it possesses an intensive "first pass" metabolism. To circumvent the "first pass" metabolism, parenteral administration of the drug might lead to different distribution and pharmacological activity of selegiline.

R-deprenyl: pharmacological spectrum of its activity

Deprenyl has been discovered by Knoll and co-workers. The R-enantiomer of deprenyl (selegiline) is a selective and irreversible inhibitor of the B-isoform of monoamine oxidase (MAO-B) enzyme. Due to its dopamine potentiating and possible neuroprotective properties it has an established role in the treatment of parkinsonian patients. By inhibiting MAO-B enzyme, R-deprenyl decreases the formation of hydrogen peroxide, alleviating the oxidative stress also reduced by increased expression of antioxidant enzymes (superoxide dismutases and catalase) reported during chronic treatment. It was shown to prevent the detrimental effects of neurotoxins like MPTP and DSP-4. R-Deprenyl elicits neuroprotective and neuronal rescue activities in concentrations too low to inhibit MAO-B. It is extensively metabolized and some of the metabolites possess pharmacological activities, thus their contribution to neuroprotective properties was also suggested. The recently identified deprenyl-N-oxide is extensively studied in our laboratory. Effects other than neuroprotection, like influencing cell adhesion and proliferation cannot be neglected.

No Regional Differences of Cytochrome P450 Expression in the Liver of Cynomolgus Monkeys (Macaca fascicularis)

Non-human primates are frequently used in toxicological studies the result of which are extrapolated to humans, but background data on drug metabolism ability among monkeys derived from different countries has not been published, especially on the key enzyme, cytochrome P450 (CYP450). We assessed the amounts of hepatic CYP450 obtained from cynomolgus monkeys of different ages and from different countries in this study. There were no regional differences of total P450 content, as well as major CYP450 isozymes (CYP 1A, 2A, 2B, 2C, 2D, 2E1 and 3A4) in cynomolgus monkeys by westernblot analysis. Similarly, there were no significant differences with hybrid cynomolgus monkeys, but variations in individual values were large. As for aging, total P450 contents declined in old cynomolgus monkeys (12-32 years of age). These results indicate the usefulness of basic data of hepatic CYP450 obtained from cynomolgus monkeys of different ages and from different countries.

Cytochrome P450-dependent metabolism of l-deprenyl in monkey (Cercopithecus aethiops) and C57BL/6 mouse brain microsomal preparations

The aim of the present investigation was to characterize the cytochrome P450 (CYP)-dependent metabolism of l-deprenyl by brain microsomal preparations obtained from two different animal models that have been extensively used in Parkinson's disease studies, namely monkey (Cercopithecus aethiops) and C57BL/6 mouse. In monkey brain microsomal fractions, the apparent Km values for methamphetamine formation from l-deprenyl were 67.8 +/- 1.0 and 72.0 +/- 1.6 microm, in the cortex and striatum, respectively. Similarly, for nordeprenyl formation from l-deprenyl, Km values in cortex and striatum were 21.3 +/- 3.2 and 27.3 +/- 4.0 microm, respectively. Both metabolic pathways appear to be more efficient in the cortex than in the striatum as the Vmax for microsomal preparation was lower in the striatum for the formation of both metabolites. The formation rate of l-methamphetamine was up to one order of magnitude greater than that of nordeprenyl. Inhibition analysis of both pathways in monkey brain suggested that l-methamphetamine formation is catalysed by CYP2A and CYP3A, whereas only CYP3A appears to be involved in nordeprenyl formation. With microsomal preparations from whole brain of C57BL/6 mice, the only l-deprenyl metabolite that could be detected was methamphetamine and the Km and Vmax values were similar to those determined in monkey cortex (53.6 +/- 2.9 microm and 33.9 +/- 0.4 pmol/min/mg protein, respectively). 4-Methylpyrazole selectively inhibited methamphetamine formation, suggesting the involvement of CYP2E1. In conclusion, the present study indicates that l-deprenyl is effectively metabolised by CYP-dependent oxidases in the brain, giving rise mainly to the formation of methamphetamine, which has been suggested to play a role in the pharmacological effects of the parent drug. The results also demonstrate that there are differences between species in CYP-dependent metabolism of l-deprenyl.