Microsomal cytochrome P450 as a target for drug discovery and repurposing

Cadmium causes spleen toxicity in chickens by regulating mitochondrial unfolded protein response and nuclear receptors response

Cadmium (Cd) is a heavy metal that pollutes the environment and threatens human and animal health via the food chain. The spleen is one of the target organs affected by Cd toxicity. However, the mechanism of Cd toxicity is not fully understood. In this study, 80 chicks were allocated into 4 groups (n = 20) and exposed to different doses of CdCl2 (0 mg/kg, 35 mg/kg, 70 mg/kg and 140 mg/kg) for 90 d. The pathological changes in the spleen, mitochondrial dynamics-related factors, cytochrome P450 (CYP450) enzyme system contents, activities, transcription levels, nuclear receptors (NRs) response molecule levels, and mitochondrial unfolded protein-related factors were detected. The findings indicate that exposure to Cd significantly leads to spleen injury. In Cd groups, the total contents of CYP450 and cytochrome b5 (Cyt b5) increased, and the activities of the CYP450 enzyme system (APND, ERND, AH, and NCR) changed. The NRs response was induced, and the gene levels of AHR/CAR and corresponding CYP450 isoforms (CYP1B1, CYP1A5, CYP1A1, CYP2C18, CYP2D6 and CYP3A4) were found altered. The study found that Cd exposure altered the mRNA expression levels of mitochondrial dynamics-related factors, such as OPA1, Fis1, MFF, Mfn1, and Mfn2, breaking mitochondrial fusion and cleavage and ultimately leading to mitochondrial dysfunction. Changes were detected in the gene levels of several mitochondrial unfolded protein response (mtUPR)-related factors, namely (SIRT1, PGC-1α, NRF1, TFAM, SOD2, and HtrA2). Cd also altered the gene levels of mitochondrial function-related factors (VDAC1, Cyt-C, COA6, PRDX3, RAF and SIRT3). It is showed that Cd can initiate the NRs response, influence the homeostasis of the CPY450 enzyme system, trigger the mtUPR, impair mitochondrial function, and ultimately lead to Cd toxicity in the spleen of chickens.

Effect of Cannabistilbene I in Attenuating Angiotensin II-Induced Cardiac Hypertrophy: Insights into Cytochrome P450s and Arachidonic Acid Metabolites Modulation

Introduction: This research investigated the impact of Cannabistilbene I on Angiotensin II (Ang II)-induced cardiac hypertrophy and its potential role in cytochrome P450 (CYP) enzymes and arachidonic acid (AA) metabolic pathways. Cardiac hypertrophy, a response to increased stress on the heart, can lead to severe cardiovascular diseases if not managed effectively. CYP enzymes and AA metabolites play critical roles in cardiac function and hypertrophy, making them important targets for therapeutic intervention. Methods: Adult human ventricular cardiomyocyte cell line (AC16) was cultured and treated with Cannabistilbene I in the presence and absence of Ang II. The effects on mRNA expression related to cardiac hypertrophic markers and CYP were analyzed using real-time polymerase chain reaction, while CYP protein levels were measured by Western blot analysis. AA metabolites were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Results: Results showed that Ang II triggered hypertrophy, as evidenced by the increase in hypertrophic marker expression, and enlarged the cell surface area, effects that were alleviated by Cannabistilbene I. Gene expression analysis indicated that Cannabistilbene I upregulated CYP1A1, leading to increased enzymatic activity, as evidenced by 7-ethoxyresorufin-O-deethylase assay. Furthermore, LC-MS/MS analysis of AA metabolites revealed that Ang II elevated midchain (R/S)-hydroxyeicosatetraenoic acid (HETE) concentrations, which were reduced by Cannabistilbene I. Notably, Cannabistilbene I selectively increased 19(S)-HETE concentration and reversed the Ang II-induced decline in 19(S)-HETE, suggesting a unique protective role. Conclusion: This study provides new insights into the potential of Cannabistilbene I in modulating AA metabolites and reducing Ang II-induced cardiac hypertrophy, revealing a new candidate as a therapeutic agent for cardiac hypertrophy.

Cytochrome P450 1B1 is critical in the development of TNF-α, IL-6, and LPS-induced cellular hypertrophy

Heart failure (HF) is preceded by cellular hypertrophy (CeH) which alters expression of cytochrome P450 enzymes (CYPs) and arachidonic acid (AA) metabolism. Inflammation is involved in CeH pathophysiology, but mechanisms remain elusive. This study investigates the impacts of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and lipopolysaccharides (LPS) on the development of CeH and the role of CYP1B1. AC16 cells were treated with TNF-α, IL-6, and LPS in the presence and absence of CYP1B1-siRNA or resveratrol. mRNA and protein expression levels of CYP1B1 and hypertrophic markers were determined using PCR and Western blot analysis, respectively. CYP1B1 enzyme activity was determined, and AA metabolites were analyzed using liquid chromatography-tandem mass spectrometry. Our results show that TNF-α, IL-6, and LPS induce expression of hypertrophic markers, induce CYP1B1 expression, and enantioselectively modulate CYP1B1-mediated AA metabolism in favor of mid-chain HETEs. CYP1B1-siRNA or resveratrol ameliorated these effects. In conclusion, our results demonstrate the crucial role of CYP1B1 in TNF-α, IL-6, and LPS-induced CeH.

Effects of Inducible Nitric Oxide Synthase (iNOS) Gene Knockout on the Diversity, Composition, and Function of Gut Microbiota in Adult Zebrafish

The gut microbiota constitutes a complex ecosystem that has an important impact on host health. In this study, genetically engineered zebrafish with inducible nitric oxide synthase (iNOS or NOS2) knockout were used as a model to investigate the effects of nos2a/nos2b gene single knockout and nos2 gene double knockout on intestinal microbiome composition and function. Extensive 16S rRNA sequencing revealed substantial changes in microbial diversity and specific taxonomic abundances, yet it did not affect the functional structure of the intestinal tissues. Notably, iNOS-deficient zebrafish demonstrated a decrease in Vibrio species and an increase in Aeromonas species, with more pronounced effects observed in double knockouts. Further transcriptomic analysis of the gut in double iNOS knockout zebrafish indicated significant alterations in immune-related and metabolic pathways, including the complement and PPAR signaling pathways. These findings underscore the crucial interplay between host genetics and gut microbiota, indicating that iNOS plays a key role in modulating the gut microbial ecology, host immune system, and metabolic responses.

Alteration of Hepatic Cytochrome P450 Expression and Arachidonic Acid Metabolism by Arsenic Trioxide (ATO) in C57BL/6 Mice

The success of arsenic trioxide (ATO) in acute promyelocytic leukemia has driven a plethora studies to investigate its efficacy in other malignancies. However, the inherent toxicity of ATO limits the expansion of its clinical applications. Such toxicity may be linked to ATO-induced metabolic derangements of endogenous substrates. Therefore, the primary objective of this study was to investigate the effect of ATO on the hepatic formation of arachidonic acid (AA) metabolites, hydroxyeicosatetraenoic acids (HETEs), as well as their most notable producing machinery, cytochrome P450 (CYP) enzymes. For this purpose, C57BL/6 mice were intraperitoneally injected with 8 mg/kg ATO for 6 and 24 h. Total RNA was extracted from harvested liver tissues for qPCR analysis of target genes. Hepatic microsomal proteins underwent incubation with AA, followed by identification/quantification of the produced HETEs. ATO downregulated Cyp2e1, while induced Cyp2j9 and most of Cyp4a and Cyp4f, and this has resulted in a significant increase in 17(S)-HETE and 18(R)-HETE, while significantly decreased 18(S)-HETE. Additionally, ATO induced Cyp4a10, Cyp4a14, Cyp4f13, Cyp4f16, and Cyp4f18, resulting in a significant elevation in 20-HETE formation. In conclusion, ATO altered hepatic AA metabolites formation through modulating the underlying network of CYP enzymes. Modifying the homeostatic production of bioactive AA metabolites, such as HETEs, may entail toxic events that can, at least partly, explain ATO-induced hepatotoxicity. Such modification can also compromise the overall body tolerability to ATO treatment in cancer patients.

17-(R/S)-hydroxyeicosatetraenoic acid (HETE) induces cardiac hypertrophy through the CYP1B1 in enantioselective manners

Cardiac cellular hypertrophy is the increase in the size of individual cardiac cells. Cytochrome P450 1B1 (CYP1B1) is an extrahepatic inducible enzyme that is associated with toxicity, including cardiotoxicity. We previously reported that 19-hydroxyeicosatetraenoic acid (19-HETE) inhibited CYP1B1 and prevented cardiac hypertrophy in enantioselective manner. Therefore, our aim is to investigate the effect of 17-HETE enantiomers on cardiac hypertrophy and CYP1B1. Human adult cardiomyocyte (AC16) cells were treated with 17-HETE enantiomers (20 µM); cellular hypertrophy was evaluated by cell surface area and cardiac hypertrophy markers. In addition, CYP1B1 gene, protein and activity were assessed. Human recombinant CYP1B1 and heart microsomes of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-treated rats were incubated with 17-HETE enantiomers (10-80 nM). Our results demonstrated that 17-HETE induced cellular hypertrophy, which is manifested by increase in cell surface area and cardiac hypertrophy markers. 17-HETE enantiomers allosterically activated CYP1B1 and selectively upregulated CYP1B1 gene and protein expression in AC16 cells at uM range. In addition, CYP1B1 was allosterically activated by 17-HETE enantiomers at nM range in recombinant CYP1B1 and heart microsomes. In conclusion, 17-HETE acts as an autocrine mediator, leading to the cardiac hypertrophy through induction of CYP1B1 activity in the heart.

Sex- and enantiospecific differences in the formation rate of hydroxyeicosatetraenoic acids in rat organs

Hydroxyeicosatetraenoic acids (HETEs) are hydroxylated arachidonic acid (AA) metabolites that are classified into midchain, subterminal, and terminal HETEs. Hydroxylation results in the formation of R and S enantiomers for each HETE, except for 20-HETE. HETEs have multiple physiological and pathological effects. Several studies have demonstrated sex-specific differences in AA metabolism in different organs. In this study, microsomes from the heart, liver, kidney, lung, intestine, and brain of adult male and female Sprague-Dawley rats were isolated and incubated with AA. Thereafter, the enantiomers of all HETEs were analyzed by liquid chromatography-tandem mass spectrometry. We found significant sex- and enantiospecific differences in the formation levels of different HETEs in all organs. The majority of HETEs, especially midchain HETEs and 20-HETE, showed significantly higher formation rates in male organs. In the liver, the R enantiomer of several HETEs showed a higher formation rate than the corresponding S enantiomer (e.g., 8-, 9-, and 16-HETE). On the other hand, the brain and small intestine demonstrated a higher abundance of the S enantiomer. 19(S)-HETE was more abundant than 19(R)-HETE in all organs except the kidney. Elucidating sex-specific differences in HETE levels provides interesting insights into their physiological and pathophysiological roles and their possible implications for different diseases.

Biochemical characterisation of Cytochrome P450 oxidoreductase from the cattle tick, Rhipicephalus microplus, highlights potential new acaricide target

Management of the cattle tick, Rhipicephalus microplus, presents a challenge because some populations of this cosmopolitan and economically important ectoparasite are resistant to multiple classes of acaricides. Cytochrome P450 oxidoreductase (CPR) is part of the cytochrome P450 (CYP450) monooxygenases that are involved in metabolic resistance by their ability to detoxify acaricides. Inhibiting CPR, the sole redox partner that transfers electrons to CYP450s, could overcome this type of metabolic resistance. This report represents the biochemical characterisation of a CPR from ticks. Recombinant CPR of R. microplus (RmCPR), minus its N-terminal transmembrane domain, was produced in a bacterial expression system and subjected to biochemical analyses. RmCPR displayed a characteristic dual flavin oxidoreductase spectrum. Incubation with nicotinamide adenine dinucleotide phosphate (NADPH) lead to an increase in absorbance between 500 and 600 nm with a corresponding appearance of a peak absorbance at 340-350 nm indicating functional transfer of electrons between NADPH and the bound flavin cofactors. Using the pseudoredox partner, kinetic parameters for both cytochrome c and NADPH binding were calculated as 26.6 ± 11.4 µM and 7.03 ± 1.8 µM, respectively. The turnover, K_cat, for RmCPR for cytochrome c was calculated as 0.08 s^-1 which is significantly lower than the CPR homologues of other species. IC₅₀ (Half maximal Inhibitory Concentration) values obtained for the adenosine analogues 2', 5' ADP, 2'- AMP, NADP⁺and the reductase inhibitor diphenyliodonium were: 140, 82.2, 24.5, and 75.3 µM, respectively. Biochemically, RmCPR resembles CPRs of hematophagous arthropods more so than mammalian CPRs. These findings highlight the potential of RmCPR as a target for the rational design of safer and potent acaricides against R. microplus.

The enantioselective separation and quantitation of the hydroxy-metabolites of arachidonic acid by liquid chromatography - tandem mass spectrometry

Arachidonic acid (AA) is a polyunsaturated fatty acid with a structure of 20:4(ω-6). Cytochrome P450s (CYPs) metabolize AA to several regioisomers and enantiomers of hydroxyeicosatetraenoic acids (HETEs). The hydroxy-metabolites (HETEs) exist as enantiomers in the biological system. The chiral assays developed for HETEs are so far limited to a few assays reported for midchain HETEs. The developed method is capable of quantitative analysis for midchain, subterminal HETE enantiomers, and terminal HETEs in microsomes. The peak area or height ratios were linear over concentrations ranging (0.01 -0.6 µg/ml) with r2 > 0.99. The intra-run percent error and coefficient of variation (CV) were ≤ ± 12 %. The inter-run percent error and coefficient of variation (CV)were ≤ ± 13 %, and ≤ 15 %, respectively. The matrix effect for the assay was also within the acceptable limit (≤ ± 15 %). The recovery of HETE metabolites ranged from 70 % to 115 %. The method showed a reliable and robust performance for chiral analysis of cytochrome P450-mediated HETE metabolites.

Nanosystems, Drug Molecule Functionalization and Intranasal Delivery: An Update on the Most Promising Strategies for Increasing the Therapeutic Efficacy of Antidepressant and Anxiolytic Drugs

Depression and anxiety are high incidence and debilitating psychiatric disorders, usually treated by antidepressant or anxiolytic drug administration, respectively. Nevertheless, treatment is usually given through the oral route, but the low permeability of the blood-brain barrier reduces the amount of drug that will be able to reach it, thus consequently reducing the therapeutic efficacy. Which is why it is imperative to find new solutions to make these treatments more effective, safer, and faster. To overcome this obstacle, three main strategies have been used to improve brain drug targeting: the intranasal route of administration, which allows the drug to be directly transported to the brain by neuronal pathways, bypassing the blood-brain barrier and avoiding the hepatic and gastrointestinal metabolism; the use of nanosystems for drug encapsulation, including polymeric and lipidic nanoparticles, nanometric emulsions, and nanogels; and drug molecule functionalization by ligand attachment, such as peptides and polymers. Pharmacokinetic and pharmacodynamic in vivo studies' results have shown that intranasal administration can be more efficient in brain targeting than other administration routes, and that the use of nanoformulations and drug functionalization can be quite advantageous in increasing brain-drug bioavailability. These strategies could be the key to future improved therapies for depressive and anxiety disorders.

Sexual Dimorphism in the Expression of Cytochrome P450 Enzymes in Rat Heart, Liver, Kidney, Lung, Brain, and Small Intestine

Cytochrome P450 (P450) enzymes are monooxygenases that are expressed hepatically and extrahepatically and play an essential role in xenobiotic metabolism. Substantial scientific evidence indicates sex-specific differences between males and females in disease patterns and drug responses, which could be attributed, even partly, to differences in the expression and/or activity levels of P450 enzymes in different organs. In this study, we compared the mRNA and protein expression of P450 enzymes in different organs of male and female Sprague-Dawley rats by real-time polymerase chain reaction and western blot techniques. We found significant sex- and organ-specific differences in several enzymes. Hepatic Cyp2c11, Cyp2c13, and Cyp4a2 showed male-specific expression, whereas Cyp2c12 showed female-specific expression. Cyp2e1 and Cyp4f enzymes demonstrated higher expression in the female heart and kidneys compared with males; however, they showed no significant sexual dimorphism in the liver. Male rats showed higher hepatic and renal Cyp1b1 levels. All assessed enzymes were found in the liver, but some were not expressed in other organs. At the protein expression level, CYP1A2, CYP3A, and CYP4A1 demonstrated higher expression levels in the females in several organs, including the liver. Elucidating sex-specific differences in P450 enzyme levels could help better understand differences in disease pathogeneses and drug responses between males and females and thus improve treatment strategies. SIGNIFICANCE STATEMENT: This study characterized the differences in the mRNA and protein expression levels of different cytochrome P450 (P450) enzymes between male and female rats in the heart, liver, lung, kidney, brain, and small intestine. It demonstrated unique sex-specific differences in the different organs. This study is considered a big step towards elucidating sex-specific differences in P450 enzyme levels, which is largely important for achieving a better understanding of the differences between males and females in the disease's processes and treatment outcomes.

Effect of inflammation on cytochrome P450-mediated arachidonic acid metabolism and the consequences on cardiac hypertrophy

The incidence of heart failure (HF) is generally preceded by cardiac hypertrophy (CH), which is the enlargement of cardiac myocytes in response to stress. During CH, the metabolism of arachidonic acid (AA), which is present in the cell membrane phospholipids, is modulated. Metabolism of AA gives rise to hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs) via cytochrome P450 (CYP) ω-hydroxylases and CYP epoxygenases, respectively. A plethora of studies demonstrated the involvement of CYP-mediated AA metabolites in the pathogenesis of CH. Also, inflammation is known to be a characteristic hallmark of CH. In this review, our aim is to highlight the impact of inflammation on CYP-derived AA metabolites and CH. Inflammation is shown to modulate the expression of various CYP ω-hydroxylases and CYP epoxygenases and their respective metabolites in the heart. In general, HETEs such as 20-HETE and mid-chain HETEs are pro-inflammatory, while EETs are characterized by their anti-inflammatory and cardioprotective properties. Several mechanisms are implicated in inflammation-induced CH, including the modulation of NF-κB and MAPK. This review demonstrated the inflammatory modulation of cardiac CYPs and their metabolites in the context of CH and the anti-inflammatory strategies that can be employed in the treatment of CH and HF.

Sex differences in eicosanoid formation and metabolism: A possible mediator of sex discrepancies in cardiovascular diseases

Arachidonic acid is metabolized by cyclooxygenase, lipoxygenase, and cytochrome P450 enzymes to produce prostaglandins, leukotrienes, epoxyeicosatrienoic acids (EETs), and hydroxyeicosatetraenoic acids (HETEs), along with other eicosanoids. Eicosanoids have important physiological and pathological roles in the body, including the cardiovascular system. Evidence from several experimental and clinical studies indicates differences in eicosanoid levels, as well as in the activity or expression levels of their synthesizing and metabolizing enzymes between males and females. In addition, there is a clear state of gender specificity in cardiovascular diseases (CVD), which tend to be more common in men compared to women, and their risk increases significantly in postmenopausal women compared to younger women. This could be largely attributed to sex hormones, as androgens exert detrimental effects on the heart and blood vessels, whereas estrogen exhibits cardioprotective effects. Many of androgen and estrogen effects on the cardiovascular system are mediated by eicosanoids. For example, androgens increase the levels of cardiotoxic eicosanoids like 20-HETE, while estrogens increase the levels of cardioprotective EETs. Thus, sex differences in eicosanoid levels in the cardiovascular system could be an important underlying mechanism for the different effects of sex hormones and the differences in CVD between males and females. Understanding the role of eicosanoids in these differences can help improve the management of CVD.

Insights into oral bioavailability enhancement of therapeutic herbal constituents by cytochrome P450 3A inhibition

Herbal plants typically have complex compositions and diverse mechanisms. Among them, bioactive constituents with relatively high exposure in vivo are likely to exhibit therapeutic efficacy. On the other hand, their bioavailability may be influenced by the synergistic effects of different bioactive components. Cytochrome P450 3A (CYP3A) is one of the most abundant CYP enzymes, responsible for the metabolism of 50% of approved drugs. In recent years, many therapeutic herbal constituents have been identified as CYP3A substrates. It is more evident that CYP3A inhibition derived from the herbal formula plays a critical role in improving the oral bioavailability of therapeutic constituents. CYP3A inhibition may be the mechanism of the synergism of herbal formula. In this review, we explored the multiplicity of CYP3A, summarized herbal monomers with CYP3A inhibitory effects, and evaluated herb-mediated CYP3A inhibition, thereby providing new insights into the mechanisms of CYP3A inhibition-mediated oral herb bioavailability.

Fluconazole Represses Cytochrome P450 1B1 and Its Associated Arachidonic Acid Metabolites in the Heart and Protects Against Angiotensin II-Induced Cardiac Hypertrophy

Cytochrome P450 1B1 (CYP1B1) has been reported to have a major role in metabolizing arachidonic acid (AA) into cardiotoxic metabolites, mid-chain hydroxyeicosatetraenoic acids (HETEs). Recently, we have shown that fluconazole decreases the level of mid-chain HETEs in human liver microsomes. Therefore, the objectives of this study were to investigate the effect of fluconazole on CYP1B1 mediated mid-chain HETEs and to explore its potential protective effect against angiotensin II- (Ang II)-induced cellular hypertrophy. To do this, Sprague Dawley rats were injected intraperitoneally with a single dose of fluconazole (20 mg/kg) for 24 h. Also, H9c2 and RL-14 cells were treated with 10 μM Ang II in the presence and absence of 50 μM fluconazole for 24 h. Our results demonstrated that treatment of rats with fluconazole significantly decreased the expression of CYP1B1 enzyme and the level of mid-chain HETEs in the heart. Furthermore, fluconazole was able to attenuate Ang-II-induced cellular hypertrophy as evidenced by a significant down-regulation of hypertrophic markers; β-myosin heavy chain (MHC)/α-MHC and brain natriuretic peptide (BNP) as well as cell surface area. In conclusion, our findings indicate that fluconazole protects against Ang II-induced cellular hypertrophy by repressing CYP1B1 and its associated mid-chain HETEs.

Subterminal hydroxyeicosatetraenoic acids: Crucial lipid mediators in normal physiology and disease states

Cytochrome P450 (P450) enzymes are superfamily of monooxygenases that hold the utmost diversity of substrate structures and catalytic reaction forms amongst all other enzymes. P450 enzymes metabolize arachidonic acid (AA) to a wide array of biologically active lipid mediators. P450-mediated AA metabolites have a significant role in normal physiological and pathophysiological conditions, hence they could be promising therapeutic targets in different disease states. P450 monooxygenases mediate the (ω-n)-hydroxylation reactions, which involve the introduction of a hydroxyl group to the carbon skeleton of AA, forming subterminal hydroxyeicosatetraenoic acids (HETEs). In the current review, we specified different P450 isozymes implicated in the formation of subterminal HETEs in varied tissues. In addition, we focused on the role of subterminal HETEs namely 19-HETE, 16-HETE, 17-HETE and 18-HETE in different organs, importantly the kidneys, heart, liver and brain. Furthermore, we highlighted their role in hypertension, acute coronary syndrome, diabetic retinopathy, non-alcoholic fatty liver disease, ischemic stroke as well as inflammatory diseases. Since each member of subterminal HETEs exist as R and S enantiomer, we addressed the issue of stereoselectivity related to the formation and differential effects of these enantiomers. In conclusion, elucidation of different roles of subterminal HETEs in normal and disease states leads to identification of novel therapeutic targets and development of new therapeutic modalities in different disease states.

A UHPLC-MS/MS method coupled with liquid-liquid extraction for the quantitation of phenacetin, omeprazole, metoprolol, midazolam and their metabolites in rat plasma and its application to the study of four CYP450 activities

Drug-drug interactions (DDIs) are thought to be associated with the inhibition of cytochrome P450 activities. The cocktail method with analysis of the metabolism of two or more probe drugs is used to determine CYP450 activities. In this study, we established a UHPLC-MS/MS method for simultaneous quantitation of four CYP450 probe drugs (phenacetin, omeprazole, metoprolol and midazolam) and their metabolites (acetaminophen, 5'-hydroxy omeprazole, α-hydroxy metoprolol and 1'-hydroxy midazolam) in rat plasma. Sample preparation by plasma protein precipitation was combined with a liquid-liquid extraction method. The separation was carried out on a ZORBAX Eclipse Plus C18 Rapid Resolution High Definition column with a gradient elution, using water containing 0.1% formic acid (A) and acetonitrile (B) in a run time of only 3.0 min. Detection was conducted with a 6420 series triple-quadrupole tandem mass spectrometer, using ESI in positive ion mode with multiple reaction monitoring (MRM). The calibration curves were linear over the concentration range 10-5000 ng/mL for phenacetin, omeprazole, metoprolol and midazolam, and 1-500 ng/mL for their metabolites. Intra- and inter-day precisions were within 15%, and the accuracies were in the range of 87-112%. The method was successfully applied to the pharmacokinetic study of probe drugs/metabolites and DDIs with 3-n-butylphthalide (NBP) after administration of a single oral dose of phenacetin, omeprazole, metoprolol and midazolam in rats.

Exploring the structure characteristics and major channels of cytochrome P450 2A6, 2A13, and 2E1 with pilocarpine

The majority of cytochromes P450 play a critical role in metabolism of endogenous and exogenous substrates, some of its products are carcinogens. Therefore, inhibition of P450 enzymes activity can promote the detoxification and elimination of chemical carcinogens. In this study, molecular dynamics (MD) simulations and adaptive steered molecular dynamics (ASMD) simulations were performed to explore the structure features and channel dynamics of three P450 isoforms 2A6, 2A13, and 2E1 bound with the common inhibitor pilocarpine. The binding free energy results combined with the PMF calculations give a reasonable ranking of binding affinity, which are consistent with the experimental data. Our results uncover how a sequence divergence of different CYP2 enzymes causes individual variations in major channel selections. On the basis of channel bottleneck and energy decomposition analysis, we propose a gating mechanism of their respective major channels in three enzymes, which may be attributed to a reversal of Phe209 in CYP2A6/2A13, as well as the rotation of Phe116 and Phe298 in CYP2E1. The hydrophobic residues not only make strong hydrophobic interactions with inhibitor, but also act as gatekeeper to regulate the opening of channel. The present study provides important insights into the structure-function relationships of three cytochrome P450s and the molecular basis for development of potent inhibitors.