Posttranslational regulation of CYP2J2 by nitric oxide

CYP2J2-mediated metabolism of arachidonic acid in heart: A review of its kinetics, inhibition and role in heart rhythm control

Cytochrome P450 2 J2 (CYP2J2) is primarily expressed extrahepatically and is the predominant epoxygenase in human cardiac tissues. This highlights its key role in the metabolism of endogenous substrates. Significant scientific interest lies in cardiac CYP2J2 metabolism of arachidonic acid (AA), an omega-6 polyunsaturated fatty acid, to regioisomeric bioactive epoxyeicosatrienoic acid (EET) metabolites that show cardioprotective effects including regulation of cardiac electrophysiology. From an in vitro perspective, the accurate characterization of the kinetics of CYP2J2 metabolism of AA including its inhibition and inactivation by drugs could be useful in facilitating in vitro-in vivo extrapolations to predict drug-AA interactions in drug discovery and development. In this review, background information on the structure, regulation and expression of CYP2J2 in human heart is presented alongside AA and EETs as its endogenous substrate and metabolites. The in vitro and in vivo implications of the kinetics of this endogenous metabolic pathway as well as its perturbation via inhibition and inactivation by drugs are elaborated. Additionally, the role of CYP2J2-mediated metabolism of AA to EETs in cardiac electrophysiology will be expounded.

Cardiomyocyte-specific CYP2J2 and its therapeutic implications

INTRODUCTION

Cytochrome P450s (CYPs) are a superfamily of monooxygenases with diverse biological roles. CYP2J2 is an isozyme highly expressed in the heart where it metabolizes endogenous substrates such as N-3/N-6 polyunsaturated fatty acids (PUFA) to produce lipid mediators involved in homeostasis and cardioprotective responses. Expanding our knowledge of the role CYP2J2 has within the heart is important for understanding its impact on cardiac health and disease.

AREAS COVERED

The objective of this review was to assess the state of knowledge regarding cardiac CYP2J2. A literature search was conducted using PubMed-MEDLINE (from 2022 and earlier) to evaluate relevant studies regarding CYP2J2 mediated cardioprotection, small molecule modulators, effects of CYP2J2 substrates toward biologically relevant effects and implications of CYP2J2 polymorphisms and sexual dimorphism in the heart.

EXPERT OPINION

Cardiac CYP2J2-mediated metabolism of endogenous and exogenous substrates have been shown to impact cardiac function. Identifying individual factors, like sex and age, that affect CYP2J2 require further elucidation to better understand CYP2J2's clinical relevance. Resolving the biological targets and activities of CYP2J2-derived PUFA metabolites will be necessary to safely target CYP2J2 and design novel analogues. Targeting CYP2J2 for therapeutic aims offers a potential novel approach to regulating cardiac homeostasis, drug metabolism and cardioprotection.

Regulation of cytochrome P450 enzyme activity and expression by nitric oxide in the context of inflammatory disease

Many hepatic cytochrome P450 enzymes and their associated drug metabolizing activities are down-regulated in disease states, and much of this has been associated with inflammatory cytokines and their signaling pathways. One such pathway is the induction of inducible nitric oxide synthase (NOS2) and generation of nitric oxide (NO) in many tissues and cells including the liver and hepatocytes. Experiments in the 1990s demonstrated that NO could bind to and inhibit P450 enzymes, and suggested that inhibition of NOS could attenuate, and NO generation could mimic, the down-regulation by inflammatory stimuli of not only P450 catalytic activities but also of mRNA expression and protein levels of certain P450 enzymes. This review will summarize and examine the evidence that NO functionally inhibits and down-regulates P450 enzymes in vivo and in vitro, with a particular focus on the mechanisms by which these effects are achieved.

Tyrosine Nitration Contributes to Nitric Oxide-Stimulated Degradation of CYP2B6

Human cytochrome P450 (P450) CYP2B6 undergoes nitric oxide (NO)-dependent proteasomal degradation in response to the NO donor dipropylenetriamine NONOate (DPTA) and biologic NO in HeLa and HuH7 cell lines. CYP2B6 is also downregulated by NO in primary human hepatocytes. We hypothesized that NO or derivative reactive nitrogen species may generate adducts of tyrosine and/or cysteine residues, causing CYP2B6 downregulation, and selected Tyr and Cys residues for mutation based on predicted solvent accessibility. CYP2B6V5-Y317A, -Y380A, and -Y190A mutant proteins expressed in HuH7 cells were less sensitive than wild-type (WT) enzyme to degradation evoked by DPTA, suggesting that these tyrosines are targets for NO-dependent downregulation. The Y317A or Y380A mutants did not show increases in high molecular mass (HMM) species after treatment with DPTA or bortezomib + DPTA, in contrast to the WT enzyme. Carbon monoxide-releasing molecule 2 treatment caused rapid suppression of 2B6 enzyme activity, significant HMM species generation, and ubiquitination of CYP2B6 protein but did not stimulate CYP2B6 degradation. The CYP2B6 inhibitor 4-(4-chlorophenyl)imidazole blocked NO-dependent CYP2B6 degradation, suggesting that NO access to the active site is important. Molecular dynamics simulations predicted that tyrosine nitrations of CYP2B6 would cause significant destabilizing perturbations of secondary structure and remove correlated motions likely required for enzyme function. We propose that cumulative nitrations of Y190, Y317, and Y380 by reactive nitrogen species cause destabilization of CYP2B6, which may act synergistically with heme nitrosylation to target the enzyme for degradation. SIGNIFICANCE STATEMENT: This work provides novel insight into the mechanisms by which nitric oxide, which is produced in hepatocytes in response to inflammation, triggers the ubiquitin-dependent proteasomal degradation of the cytochrome P450 (P450) enzyme CYP2B6. Our data demonstrate that both nitration of specific tyrosine residues and interaction of nitric oxide (NO) with the P450 heme are necessary for NO to trigger ubiquitination and protein degradation.

The Role of Arachidonic Acid Metabolism in Myocardial Ischemia-Reperfusion Injury

Patients with myocardial ischemic diseases or who are undergoing one of various heart treatments, such as open heart surgery, coronary artery bypass grafting, percutaneous coronary artery intervention or drug thrombolysis, face myocardial ischemia-reperfusion injury (MIRI). However, no effective treatment is currently available for MIRI. To improve the prognosis of people with cardiovascular disease, it is important to research the mechanism of MIRI. Arachidonic acid (AA) is one of the focuses of current research. The various metabolic pathways of AA are closely related to the development of cardiovascular disease, and the roles of various metabolites in ischemia-reperfusion injury have gradually been confirmed. AA is mainly metabolized in the cyclooxygenase (COX) pathway, lipoxygenase (LOX) pathway, and cytochrome P450 monooxygenase (CYP) pathway. This paper summarizes the progress of research on these three major AA metabolic pathways with respect to MIRI.

Nitric Oxide Mediated Degradation of CYP2A6 via the Ubiquitin-Proteasome Pathway in Human Hepatoma Cells

Several cytochrome P450 enzymes are known to be down-regulated by nitric oxide (NO). CYP2A6 is responsible for the metabolism of nicotine and several other xenobiotics, but its susceptibility to down-regulation by NO has not been reported. To address this question, we used Huh7 human hepatoma cell lines to express CYP2A6 with a C-terminal V5 tag (CYP2A6V5). NO donor treatment [dipropylenetriamine NONOate (DPTA)] down-regulated CYP2A6 protein to approximately 40% of control levels in 4 hours. An NO scavenging agent protected CYP2A6 from down-regulation by DPTA in a concentration-dependent manner, demonstrating that the down-regulation is NO-dependent. Experiments with the protein synthesis inhibitor cycloheximide showed that CYP2A6 protein down-regulation occurs posttranslationally. In the presence of proteasome inhibitors MG132 or bortezomib, NO-treated cells showed an accumulation of a high molecular mass signal, whereas autophagy inhibitors chloroquine and 3-methyladenine and the lysosomal and calpain inhibitor E64d had no effect. Immunoprecipitation of CYP2A6 followed by Western blotting with an antiubiquitin antibody showed that the high molecular mass species contain polyubiquitinated CYP2A6 protein. This suggests that NO led to the degradation of protein via the ubiquitin-proteasome pathway. The down-regulation by NO was blocked by the reversible CYP2A6 inhibitor pilocarpine but not by the suicide inhibitor methoxsalen, demonstrating that down-regulation requires NO access to the active site but does not require catalytic activity of the enzyme. These findings provide novel insights toward the regulation of CYP2A6 in a human cell line and can influence our understanding of CYP2A6-related drug metabolism. SIGNIFICANCE STATEMENT: This study demonstrates that the nicotine metabolizing enzyme CYP2A6 is down-regulated by nitric oxide, a molecule produced in large amounts in the context of inflammation and that is also inhaled from cigarette smoke. This occurs via ubiquitination and proteasomal degradation, and does not require catalytic activity of the enzyme. This work adds to the growing knowledge of the selective effect and mechanism of action of nitric oxide (NO) on cytochrome P450 enzymes and suggests a possible novel mode of interaction between nicotine and NO in cigarette smokers.

NF-κB-mediated regulation of rat CYP2E1 by two independent signaling pathways

Cytochrome P450 2E1 (CYP2E1) plays an important role in both alcohol-induced and immune-mediated liver injury. However, the mechanism underlying CYP2E1 transcriptional regulation has not been clarified. This study focused on the NF-κB-mediated transcriptional regulation of rat CYP2E1 by two independent signaling pathways in alcohol-induced and immune-mediated liver injury rat models. Male Sprague-Dawley rats were used in pharmacokinetic, molecular pharmacology, and morphology experiments. A rat model of alcohol-induced liver injury (AL) was established by feeding an ethanol-containing diet (42 g/kg/day) for 5 weeks as indicated. A rat immune-mediated liver injury (IM) model was established by the sequential injection of bacillus Calmette-Guérin (BCG, 125 mg/kg, once) via the tail vein after test day 21 and 10 μg/kg LPS 13 days later. HPLC, real-time PCR, western blot and ELISA analyses were performed. CYP2E1 expression was enhanced during the process of alcohol-induced liver injury (increased by 56%, P < 0.05) and significantly reduced during that of immune-mediated liver injury (reducedby52%, P < 0.05). NF-κB was activated in both the AL and IM groups (increased by 56% and76%, respectively, P < 0.05). Compared to those in the livers of AL model rats, the interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and iNOS levels in IM model rat livers were increased (increased by 26%, 21% and 101%, respectively, P < 0.05). The differential changes in CYP2E1 in the processes of alcohol-induced and immune-mediated liver injury may result from the differential expression of inflammatory cytokines and iNOS after NF-κB activation, leading to the NF-κB-mediated transcriptional regulation of rat CYP2E1 by two independent signaling pathways.