Metabolic Stability and Metabolite Identification of CYP450 Probe Substrates in Ferret Hepatocytes.

BACKGROUND: Ferrets exhibit similar lung physiology to humans and display similar clinical signs following influenza infection, making them a valuable model for studying high susceptibility and infection patterns. However, the metabolic fate of several common human CYP450 probe substrates in ferrets is still unknown and has not been studied. OBJECTIVE: The purpose of this study was to investigate the metabolism of nine human CYP450 probe substrates in ferret hepatocytes and explore their metabolic rate differences between ferrets and other species. METHOD: Nine substrates were individually incubated in ferret hepatocytes for up to 120 min. At each time point, 30 µL mixtures were extracted for stability analysis using LC-MS/MS methods. After a 120-minute incubation period, 400 µL of the mixtures were extracted for metabolite identification using UHPLC-QExactive Plus. RESULTS: The metabolic clearance was determined as follows: diclofenac > taxol > chlorzoxazone > dextromethorphan > midazolam > omeprazole > bupropion > phenacetin > testosterone. Seven metabolites were identified from phenacetin. Deethylation was found to be the major pathway, and the major metabolite was matched with acetaminophen as probed with the CYP1A2 enzyme. Six metabolites were identified from diclofenac. Glucuronidation was the primary pathway, and a metabolite was found to match 4-OH-diclofenac as probed with the CYP2C9 enzyme. Twenty-two metabolites were identified from omeprazole. The major metabolic pathways included mono-oxygenation and sulfoxide to thioether conversion. No metabolite was found to match with the 5-OH-omeprazole as probed with the CYP2C19 enzyme. Twenty-two metabolites were identified from dextromethorphan. Demethylation was found to be the major metabolic pathway, and one demethylation metabolite was matched with dextrorphan as probed with CYP2D6. Fourteen metabolites were identified from midazolam. Mono-oxygenation was found to be the primary metabolic pathway, and one of the mono-oxygenation metabolites was matched with 1-OH-midazolam as probed with the CYP3A4 enzyme. Eight metabolites were identified from testosterone. Mono-oxygenation and glucuronidation were identified as the major metabolic pathways. One mono-oxygenation was matched with 6-ß-testosterone as probed with CYP3A4 enzyme. Six metabolites were identified from taxol. Hydrolysis and mono-oxygenation were the top two metabolic pathways. No metabolite was matched with 6-α-OH-taxol as probed with the CYP2C8 enzyme. Ten metabolites were identified from bupropion. Mono-oxygenation and hydrogenation were identified as the top two metabolic pathways. No mono-oxygenation metabolite was matched with hydroxy-bupropion as probed with the CYP2B6 enzyme. Nine metabolites were identified from chlorzoxazone. Monooxygenation and sulfation were the top two metabolic pathways. One mono-oxygenation metabolite was matched with 6-OH-chlorzoxazone as probed with the CYP2E1 enzyme. CONCLUSION: Nine human CYP probe substrates were clearly metabolized in ferret hepatocytes, demonstrating substrate-dependent metabolic rates in ferret hepatocytes and species-dependent metabolic rates in mouse, rat, dog, monkey, and human hepatocytes. Except for 6-a-5-OH-omeprazole, 6-α-OH-taxol, and hydroxy-bupropion, specific metabolites of other six probe substrates in ferret hepatocytes were detected and identified as probed with six human CYP enzymes, respectively.

Functional significance of CYP2B6 gene rare allelic variants identified in Japanese individuals.

Cytochrome P450 2B6 (CYP2B6) catalyzes the metabolism of many drugs, including efavirenz and propofol. Genetic polymorphisms in CYP2B6 alter its enzymatic activity and substantially affect its pharmacokinetics. High-frequency variants, such as CYP2B6*6, are associated with the risk of developing side effects due to reduced CYP2B6 activity. However, the impact of rare alterations on enzyme function remains unknown, and some of these variants may significantly decrease the CYP2B6 activity. Therefore, in this study, we evaluated in vitro the functional alterations in 29 missense variants of the CYP2B6 gene identified in 8,380 Japanese individuals. Wild-type CYP2B6 and 29 rare CYP2B6 variants were transiently expressed in mammalian cells. The expression levels of variant CYP2B6 proteins in the microsomal fractions extracted from 293FT cells were assessed using western blotting and reduced-carbon monoxide difference spectroscopy, and a specific peak at 450 nm was detected in the wild-type and 19 variants. Furthermore, kinetic parameters were determined by assaying the reactions with efavirenz and propofol and quantifying the metabolite concentrations. We found that 12 variants had significantly lower or abolished enzymatic activity with both the substrates. In silico three-dimensional docking and molecular-dynamics simulations suggested that these functional changes were due to conformational changes in essential regions, such as the heme-binding site and ligand channels involved in transporting substrates to the active site. These findings have implications for predicting the plasma concentrations of CYP2B6 substrates and controlling their side effects.

Effect of protein binding on the pharmacokinetics of the six substrates in the Basel phenotyping cocktail in healthy subjects and patients with liver cirrhosis.

Phenotyping serves to estimate enzyme activities in healthy persons and patients in vivo. Low doses of enzyme-specific substrates are administered, and activities estimated using metabolic ratios (MR, calculated as AUCmetabolite/AUCparent). We administered the Basel phenotyping cocktail containing caffeine (CYP1A2 substrate), efavirenz (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), metoprolol (CYP2D6) and midazolam (CYP3A) to 36 patients with liver cirrhosis and 12 control subjects and determined free and total plasma concentrations over 24 h. Aims were to assess whether MRs reflect CYP activities in patients with liver cirrhosis and whether MRs calculated with free plasma concentrations (MRfree) provide better estimates than with total concentrations (MRtotal). The correlation of MRtotal with MRfree was excellent (R2 >0.910) for substrates with low (<30 %, caffeine and metoprolol) and intermediate protein binding (≥30 and <99 %, midazolam and omeprazole) but weak (R2 <0.30) for substrates with high protein binding (≥99 %, efavirenz and flurbiprofen). The correlations between MRtotal and MRfree with CYP activities were good (R2 >0.820) for CYP1A2, CYP2C19 and CYP2D6. CYP3A4 activity was reflected better by midazolam elimination than by midazolam MRtotal or MRfree. The correlation between MRtotal and MRfree with CYP activity was not significant or weak for CYP2B6 and CYP2C9. In conclusion, MRs of substrates with an extensive protein binding (>99 %) show high inter-patient variabilities and do not accurately reflect CYP activity in patients with liver cirrhosis. Protein binding of the probe drugs has a high impact on the precision of CYP activity estimates and probe drugs with low or intermediate protein binding should be preferred.

Impact of steroid hormone levels on estradiol-mediated regulation of cytochrome P450 2B6 compared to 1B1 in breast cancer cells.

Pharmacogenetic variants of the steroid hormone-metabolizing enzyme cytochrome P450 2B6 (CYP2B6) were reported to be associated with breast cancer (BC) risk and prognosis. CYP2B6 expression is inducible by estradiol (E2) but induction was demonstrated only under steroid hormone-deprived medium conditions. Physiological conditions, however, even under endocrinological BC treatment, do not correspond to complete steroid hormone depletion. The aim of this study was to investigate the E2-mediated CYP2B6 and CYP1B1 regulation under various steroid hormone conditions, including physiological concentrations, in human oestrogen receptor positive (T47D, MCF-7) and negative (MDA-MB-231) BC cell lines. We confirm that steroid-deprived pre-cultivation led to CYP2B6 upregulation in T47D, but not in MCF-7. However, when pre-cultivated with steroid-containing medium CYP2B6 was downregulated in T47D and MCF-7, while the addition of physiological E2 concentrations to steroid-deprived medium resulted in a downregulation in T47D. In contrast, CYP1B1 was never downregulated in any culture condition. Thus, we show that E2-mediated CYP2B6 regulation in BC cells depends on steroid hormone exposure in a cell line-specific manner. Our data indicates the importance of being careful with conclusions drawn from CYP2B6 induction findings in vitro, as we demonstrate potential influences of hormonal changes on CYP2B6 expression, which could impact steroid hormone homeostasis and, consequently, BC risk.

The Influence of CYP2B6 Variants and Administration of Propofol on Patient Outcomes after Traumatic Brain Injury.

Management of severe traumatic brain injury (sTBI) typically involves the use of sedation, which inherently results in benefits and risks. The cytochrome P450 enzyme CYP2B6 is involved in the biotransformation of particular drug classes, including many intravenous sedatives. Variants of the CYP2B6 gene can lead to decreased systemic clearance of some sedatives, including propofol. This study aimed to investigate the relationship of CYP2B6 gene variation and patient outcomes after TBI while also considering propofol administration. Patients who sustained a non-penetrating sTBI and admitted to a single-center Level 1 trauma hospital were included in this study (n = 440). The *6 functional allele of CYP2B6 that leads to reduced enzyme expression and activity required genotyping two single nucleotide polymorphisms, rs3745274 and rs2279343. Patient outcomes were evaluated using the Glasgow Outcome Scale (GOS) and Disability Rating Scale (DRS) at 3 and 6 months post-injury. Data on sedative administration were abstracted from medical records. Individuals homozygous for the alleles coding for the reduced enzyme expression and activity were more likely to have worse outcomes. A relationship between propofol administration and 3-month GOS and 6-month DRS was noted when controlling for CYP2B6 genotype. These findings suggest that genetic variation in CYP2B6 may influence the impact of intravenous sedation on patient outcomes after TBI and warrants further investigation.

CYP2B6 and ABCB1 genotypes predict methadone plasma exposure among patients on maintenance therapy against opioid addictions in Tanzania.

AIMS: Methadone maintenance therapy (MMT) exhibits significant variability in pharmacokinetics and clinical response, partly due to genetic variations. However, data from sub-Saharan African populations are lacking. We examined plasma methadone variability and pharmacogenetic influences among opioid-addicted Tanzanian patients. METHODS: Patients attending MMT clinics (n = 119) in Tanzania were genotyped for common functional variants of the CYP3A4, CYP3A5, CYP2A6, CYP2B6, CYP2C19, CYP2D6, ABCB1, UGT2B7 and SLCO1B1 genotypes. Trough plasma concentrations of total methadone, S-methadone (S-MTD) and R-methadone (R-MTD), with their respective metabolites, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The methadone-to-EDDP metabolic ratio (MMR) was used to categorize the phenotype. RESULTS: The proportions of MMR-predicted ultrarapid, extensive, intermediate and slow methadone metabolizer phenotypes were 2.5%, 58.2%, 23.7% and 15.6%, respectively. CYP2B6 genotype significantly correlated with S-methadone (P = .006), total methadone (P = .03), and dose-normalized methadone plasma concentrations (P = .001). Metabolic ratios of R-methadone (R-MTD/R-EDDP), S-methadone (S-MTD/S-EDDP), and total methadone (MMR) were significantly higher among patients homozygous for defective variants (*6 or *18) than heterozygous or CYP2B6*1/*1 genotypes (P < .001). The metabolic ratio for S-MTD and total methadone was significantly higher among ABCB1c.3435T/T than in the C/C genotype. No significant effect of CYP2D6, CYP2C19, CYP3A4, CYP3A5, CYP2A6, UGT2B7 and SLCO1B1 genotypes on S-methadone, R-methadone, or total methadone was observed. CONCLUSIONS: Approximately one in six opioid-addicted Tanzanian patients are methadone slow metabolizers, influenced by genetic factors. Both the CYP2B6 and ABCB1 genotypes are strong predictors of methadone metabolic capacity and plasma exposure. Further investigation is needed to determine their predictive value for methadone treatment outcomes and to develop genotype-based dosing algorithms for safe and effective therapy.

Genetic variants, haplotype determination, and function of novel alleles of CYP2B6 in a Han Chinese population.

Amino acid variants in protein may result in deleterious effects on enzymatic activity. In this study we investigate the DNA variants on activity of CYP2B6 gene in a Chinese Han population for potential use in precision medicine. All exons in CYP2B6 gene from 1483 Chinese Han adults (Zhejiang province) were sequenced using Sanger sequencing. The effects of nonsynonymous variants on recombinant protein catalytic activity were investigated in vitro with Sf12 system. The haplotype of novel nonsynonymous variants with other single nucleotide variants in the same allele was determined using Nanopore sequencing. Of 38 alleles listed on the Pharmacogene Variation Consortium, we detected 7 previously reported alleles and 18 novel variants, of which 11 nonsynonymous variants showed lower catalytic activity (0.00-0.60) on bupropion compared to CYP2B6*1. Further, these 11 novel star-alleles (CYP2B6*39-49) were assigned by the Pharmacogene Variation Consortium, which may be valuable for pharmacogenetic research and personalized medicine.

Therapeutic efficacy of generic artemether-lumefantrine in the treatment of uncomplicated malaria in Ghana: assessing anti-malarial efficacy amidst pharmacogenetic variations.

BACKGROUND: Despite efforts made to reduce morbidity and mortality associated with malaria, especially in sub-Saharan Africa, malaria continues to be a public health concern that requires innovative efforts to reach the WHO-set zero malaria agenda. Among the innovations is the use of artemisinin-based combination therapy (ACT) that is effective against Plasmodium falciparum. Generic artemether-lumefantrine (AL) is used to treat uncomplicated malaria after appropriate diagnosis. AL is metabolized by the cytochrome P450 family of enzymes, such as CYP2B6, CYP3A4 and CYP3A5, which can be under pharmacogenetic influence. Pharmacogenetics affecting AL metabolism, significantly influence the overall anti-malarial activity leading to variable therapeutic efficacy. This study focused on generic AL drugs used in malarial treatment as prescribed at health facilities and evaluated pharmacogenomic influences on their efficacy. METHODS: Patients who have been diagnosed with malaria and confirmed through RDT and microscopy were recruited in this study. Blood samples were taken on days 1, 2, 3 and 7 for parasite count and blood levels of lumefantrine, artemisinin, desbutyl-lumefantrine (DBL), and dihydroartemisinin (DHA), the active metabolites of lumefantrine and artemether, respectively, were analysed using established methods. Pharmacogene variation analysis was undertaken using iPLEX microarray and PCR-RFLP. RESULTS: A total of 52 patients completed the study. Median parasite density from day 1 to 7 ranged from 0-2666/µL of blood, with days 3 and 7 recording 0 parasite density. Highest median plasma concentration for lumefantrine and desbutyl lumefantrine, which are the long-acting components of artemisinin-based combinations, was 4123.75 ng/mL and 35.87 ng/mL, respectively. Day 7 plasma lumefantrine concentration across all generic ACT brands was ≥ 200 ng/mL which potentially accounted for the parasitaemia profile observed. Monomorphism was observed for CYP3A4 variants, while there were observed variations in CYP2B6 and CYP3A5 alleles. Among the CYP3A5 genotypes, significant differences in genotypes and plasma concentration for DBL were seen on day 3 between 1/*1 versus *1/*6 (p = 0.002), *1/*3 versus *1/*6 (p = 0.006) and *1/*7 versus *1/*6 (p = 0.008). Day 7 plasma DBL concentrations showed a significant difference between *1/*6 and *1/*3 (p = 0.026) expressors. CONCLUSIONS: The study findings show that CYP2B6 and CYP3A5 pharmacogenetic variations may lead to higher plasma exposure of AL metabolites.

The role of polymorphic cytochrome P450 gene (CYP2B6) in B-chronic lymphocytic leukemia (B-CLL) incidence and outcome among Egyptian patients.

Cytochromes P450 (CYPs) play a prominent role in catalyzing phase I xenobiotic biotransformation and account for about 75% of the total metabolism of commercially available drugs, including chemotherapeutics. The gene expression and enzyme activity of CYPs are variable between individuals, which subsequently leads to different patterns of susceptibility to carcinogenesis by genotoxic xenobiotics, as well as differences in the efficacy and toxicity of clinically used drugs. This research aimed to examine the presence of the CYP2B6*9 polymorphism and its possible association with the incidence of B-CLL in Egyptian patients, as well as the clinical outcome after receiving cyclophosphamide chemotherapy. DNA was isolated from whole blood samples of 100 de novo B-CLL cases and also from 100 sex- and age-matched healthy individuals. The presence of the CYP2B6*9 (G516T) polymorphism was examined by PCR-based allele specific amplification (ASA). Patients were further indicated for receiving chemotherapy, and then they were followed up. The CYP2B6*9 variant indicated a statistically significant higher risk of B-CLL under different genetic models, comprising allelic (T-allele vs. G-allele, OR = 4.8, p < 0.001) and dominant (GT + TT vs. GG, OR = 5.4, p < 0.001) models. Following cyclophosphamide chemotherapy, we found that the patients with variant genotypes (GT + TT) were less likely to achieve remission compared to those with the wild-type genotype (GG), with a response percentage of (37.5% vs. 83%, respectively). In conclusion, our findings showed that the CYP2B6*9 (G516T) polymorphism is associated with B-CLL susceptibility among Egyptian patients. This variant greatly affected the clinical outcome and can serve as a good therapeutic marker in predicting response to cyclophosphamide treatment.

Uncoupling of Cytochrome P450 2B6 and stimulation of reactive oxygen species production in pharmacogenomic alleles affected by interethnic variability.

Cytochrome P450 mediated substrate metabolism is generally characterized by the formation of reactive intermediates. In vitro and in vivo reaction uncoupling, results in the accumulation and dissociation of reactive intermediates, leading to increased ROS formation. The susceptibility towards uncoupling and altered metabolic activity is partly modulated by pharmacogenomic alleles resulting in amino acid substitutions. A large variability in the prevalence of these alleles has been demonstrated in CYP2B6, with some being predominantly unique to African populations. The aim of this study is to characterize the uncoupling potential of recombinant CYP2B6*1, CYP2B6*6 and CYP2B6*34 metabolism of specific substrates. Therefore, functional effects of these alterations on enzyme activity were determined by quantification of bupropion, efavirenz and ketamine biotransformation using HPLC-MS/MS. Determination of H2O2 levels was performed by the AmplexRed/horseradish peroxidase assay. Our studies of the amino acid substitutions Q172H, K262R and R487S revealed an exclusive use of the peroxide shunt for the metabolism of bupropion and ketamine by CYP2B6*K262R. Ketamine was also identified as a trigger for the peroxide shunt in CYP2B6*1 and all variants. Concurrently, ketamine acted as an uncoupler for all enzymes. We further showed that the expressed CYP2B6*34 allele results in the highest H2O2 formation. We therefore conclude that the reaction uncoupling and peroxide shunt are directly linked and can be substrate specifically induced with K262R carriers being most likely to use the peroxide shunt and R487S carrier being most prone to reaction uncoupling. This elucidates the functional diversity of pharmacogenomics in drug metabolism and safety.

Genetic polymorphisms of CYP2B6 is a risk of metabolic associated fatty liver disease in Chinese population.

BACKGROUND: The expression and activity of cytochrome P450 2B6 (CYP2B6) may be related to the metabolic associated fat liver disease (MAFLD). Since constitutive androstane receptor (CAR) is a classic transcriptional regulator of CYP2B6, and the single nucleotide polymorphisms (SNPs) of CYP2B6 and CAR are both associated with adverse reactions of efavirenz, we hypothesized that genetic polymorphisms of CAR might also result in additional interindividual variability in CYP2B6. This study was devoted to explore the association between CYP2B6 and CAR SNPs and susceptibility to MAFLD. MATERIALS AND METHODS: A total of 590 objects of study (118 with MAFLD and 472 healthy control) between December 2014 and April 2018 were retrospectively enrolled. Twenty-two selected SNPs in CYP2B6 and CAR were genotyped with a custom-designed 48-plex SNP Scan TM® Kit. The frequencies of the alleles, genotypes and genetic models of the variants were compared between the two groups. The odds ratios (ORs) and the corresponding 95% confidence intervals (CIs) were calculated. RESULTS: The T allele of rs3745274 in CYP2B6 was associated with a decreased risk for MAFLD (OR 0.610; 95% CI: 0.451-0.825, p = 0.001) which was still statistically significant after adjusting with Bonferroni method(p = 0.014) The allele, genotype and genetic model frequencies were similar in the two groups for the other twenty-one SNPs (all P > 0.05). There were no multiplicative or additive interactions between the SNPs. CONCLUSION: Our study revealed that rs3745274 variants in CYP2B6 is associated with susceptibility to MAFLD in the Han Chinese population.

The Impact of Certain Pharmacogenetic Differences on the Metabolism of Antiretroviral Drugs Used in A Black South African Population.

BACKGROUND: Genetic polymorphism of drug-metabolising enzymes and transporters may influence the effect and toxicity of antiretroviral drugs. OBJECTIVES: To determine and compare the minimum allele frequency of 20 single nucleotide polymorphisms (SNPs) with possible involvement in the metabolism of the antiretroviral drugs with other populations. To investigate the influence of these variants on Reverse transcriptase, Protease and Integrase strand transfer inhibitor drugs. METHOD: DNA samples were collected from 1489 subjects. All SNPs with a gene call score of > 0.6 were selected for genotyping. The R package calculated call rates, MAF and Hardy-Weinberg equilibrium (HWE), test p-values, and Chi-squared analysis were performed on the data. The Fisher's exact test compared the allele frequencies between the populations. RESULTS: The highest similarities in minimum allele frequency (MAF) were between the Prospective Urban and Rural Epidemiological group (PURE), a Black population in South Africa, and the Yoruba and Luhya populations in Africa. The following SNPs were identified with a possible effect on metabolism: CYP2B6 rs28399494 (MAF 11%) is indicated in the toxicity of Efavirenz and Nevirapine. CYP3A5 rs776746 (MAF 17%) and CYP3A4 rs2749674 (MAF 23%) both cause an increase in the metabolism of the protease inhibitors. The very low MAF values for both SCL01B1 rs4149056 (MAF 0.6%) and ABCC rs717620 (MAF 2.8%) are indications that OATP1B1 transport function and glomerular filtration tempo will not be compromised. The high MAF value of 30% for UGTA1 rs10929302 can result in hyperbilirubinemia, which can decrease the clearance of Dolutegravir. CONCLUSION: These results show a possibility of kidney protection and an increase in bilirubin in this population.

Association of CYP3A5*3, CYP3A4*18 & CYP2B6*6 polymorphisms with imatinib treatment outcome in Azerbaijani chronic myeloid leukaemia patients.

Background & objectives: Imatinib mesylate (IM) is a reliable first line treatment for chronic myeloid leukaemia (CML). Nevertheless, despite promising results, a considerable proportion of patients develop resistance to the drug. Cytochrome P450 (CYP) enzymes play a crucial role in IM metabolism. Thus, point mutations in CYP genes may modify IM enzyme activity resulting in insufficient treatment response. This investigation was aimed to identify the functional impact of CYP3A5*3, CYP3A4*18 and CYP2B6*6 polymorphisms on the IM response in patients with CML in Azerbaijan. Methods: Genotyping of CYP3A5*3, CYP3A4*18 and CYP2B6*6 was performed in 153 patients (102 IM non-responders and 51 IM responders) with CML by the PCR-restriction fragment length polymorphism (RFLP) assays. The odds ratios (ORs) with 95 per cent confidence intervals (CIs) were applied to assess the association between allelic variants and IM therapy outcome. The results were validated by sequencing. Results: The frequency of the CYP3A4*18 allele was considerably lower in the responder's group (97.1 vs. 100%; P=0.036). For CYP3A5*3, the allelic frequency was slightly higher among the IM responders (100 vs. 99.02%) with no significant difference. Although patients heterozygous (TC) for CYP2B6*6 demonstrated a higher risk of acquiring resistance (OR 1.04; 95% CI: 0.492-2.218), differences were not significant (P=0.909). In addition, the homozygous genotype (TT) demonstrated a lower risk of unresponsiveness (OR 0.72; 95% CI: 0.283-1.836), but associations were not significant (P=0.491). Interpretation & conclusions: Our results demonstrated that CYP3A4*18 was significantly associated with IM treatment response in patients with CML in Azerbaijan, whereas rather common CYP3A5*3 was identified to have no such association.

METTL3 exacerbates insulin resistance in hepatocytes by regulating m6A modification of cytochrome P450 2B6.

BACKGROUND: Insulin resistance (IR) in hepatocytes endangers human health, and frequently results in the development of non-alcoholic fatty liver disease (NAFLD). Research on m6A methylation of RNA molecules has gained popularity in recent years; however, the molecular mechanisms regulating the processes of m6A modification and IR are not known. The cytochrome P450 (CYP450) enzyme system, which is mainly found in the liver, is associated with the pathogenesis of NAFLD. However, few studies have been conducted on CYP450 related m6A methylation. Here, we investigated the role of the methyltransferase METTL3 in exacerbating IR in hepatocytes, mainly focusing on the regulation of m6A modifications in CYP2B6. METHODS AND RESULTS: Analysis using dot blot and epitranscriptomic chips revealed that the m6A modification pattern of the transcriptome in high-fat diet (HFD)-induced fatty liver and free fatty acid (FFA)-induced fatty hepatocytes showed significant changes. CYP450 family members, especially Cyp2b10, whose homolog in humans is CYP2B6, led to a noticeable increase in m6A levels in HFD-induced mice livers. Application of the METTL3 methyltransferase inhibitor, STM2457, increased the level of insulin sensitivity in hepatocytes. We then analyzed the role of METTL3 in regulating m6A modification of CYP2B6 in hepatocytes. METTL3 regulated the m6A modification of CYP2B6, and a positive correlation was found between the levels of CYP2B6 translation and m6A modifications. Furthermore, interference with METTL3 expression and exposure to STM2457 inhibited METTL3 activity, which in turn interfered with the phosphorylated insulin receptor substrate (pIRS)-glucose transporter 2 (GLUT2) insulin signaling pathway; overexpression of CYP2B6 hindered IRS phosphorylation and translocation of GLUT2 to membranes, which ultimately exacerbated IR. CONCLUSION: These findings offer unique insights into the role that METTL3-mediated m6A modifications of CYP2B6 play in regulating insulin sensitivity in hepatocytes and provide key information for the development of strategies to induce m6A modifications for the clinical treatment of NAFLD.

High-Throughput Assay of Cytochrome P450-Dependent Drug Demethylation Reactions and Its Use to Re-Evaluate the Pathways of Ketamine Metabolism.

In a search for a reliable, inexpensive, and versatile technique for high-throughput kinetic assays of drug metabolism, we elected to rehire an old-school approach based on the determination of formaldehyde (FA) formed in cytochrome P450-dependent demethylation reactions. After evaluating several fluorometric techniques for FA detection, we chose the method based on the Hantzsch reaction with acetoacetanilide as the most sensitive, robust, and adaptable to high-throughput implementation. Here we provide a detailed protocol for using our new technique for automatized assays of cytochrome P450-dependent drug demethylations and discuss its applicability for high-throughput scanning of drug metabolism pathways in the human liver. To probe our method further, we applied it to re-evaluating the pathways of metabolism of ketamine, a dissociative anesthetic and potent antidepressant increasingly used in the treatment of alcohol withdrawal syndrome. Probing the kinetic parameters of ketamine demethylation by ten major cytochrome P450 (CYP) enzymes, we demonstrate that in addition to CYP2B6 and CYP3A enzymes, which were initially recognized as the primary metabolizers of ketamine, an important role is also played by CYP2C19 and CYP2D6. At the same time, the involvement of CYP2C9 suggested in the previous reports was deemed insignificant.

Metabolic ratios and SNPs implicated in tramadol-related deaths.

Tramadol (TR) metabolism is performed by polymorphic enzymes that are influenced by genetic polymorphisms. Within this scope, the study presented here aimed to describe 41 genetic variants within CYP2D6, CYP2B6, and CYP3A4 genes in 48 cases of TR-related death that may be involved in the response to TR and to assess whether there is a correlation between these genetic variants and metabolic ratios (MRs). Blood samples from 48 victims of a TR-related death were analyzed to determine the concentrations of TR and its metabolites [O-desmethyltramadol (M1) & N-desmethyltramadol (M2)] using a LC-MS/MS method. All the samples were also genotyped for 41 common CYP2D6, CYP2B6, and CYP3A4 single nucleotide polymorphisms (SNPs) using the HaloPlex Target Enrichment system. Cases with the T/- genotype (rs35742686 in CYP2D6) had significantly higher M2/M1 ratio than cases with T/T genotype and cases with the G/A genotype (rs35599367 in CYP3A4) had significantly higher MR2 (TR/M2) ratio than cases with G/G genotype. The frequency of tested SNPs which belong to CYP2D6, CYP2B6, and CYP3A4 revealed the over-presentation of 2 SNPs (rs1058172 in CYP2D6 and rs4803419 in CYP2B6) in TR overdose group, which could have toxicological implications. These results indicate these polymorphisms in CYP2D6, CYP2B6, and CYP3A4 might influence the function and could increase the risk of toxicity. However, these findings should be supported in future studies with larger groups of cases.

Expression of CYP2B6 Enzyme in Human Liver Tissue of HIV and HCV Patients.

Background and Objectives: Hepatitis C virus (HCV) and human immunodeficiency virus (HIV) infections present significant public health challenges worldwide. The management of these infections is complicated by the need for antiviral and antiretroviral therapies, which are influenced by drug metabolism mediated by metabolic enzymes and transporters. This study focuses on the gene expression of CYP2B6, CYP3A4, and ABCB1 transporters in patients with HIV, HCV, and HIV/HCV co-infection, aiming to assess their potential association with the choice of therapy, patohistological and clinical parameters of liver damage such as the stage of liver fibrosis, serum levels of ALT and AST, as well as the grade of liver inflammation and other available biochemical parameters. Materials and Methods: The study included 54 patients who underwent liver biopsy, divided into HIV-infected, HCV-infected, and co-infected groups. The mRNA levels of CYP2B6, CYP3A4, and ABCB1 was quantified and compared between the groups, along with the analysis of liver fibrosis and inflammation levels. Results: The results indicated a significant increase in CYP2B6 mRNA levels in co-infected patients, a significant association with the presence of HIV infection with an increase in CYP3A4 mRNA levels. A trend towards downregulation of ABCB1 expression was observed in patients using lamivudine. Conclusions: This study provides insight into gene expression of CYP2B6 CYP3A4, and ABCB1 in HIV, HCV, and HIV/HCV co-infected patients. The absence of correlation with liver damage, inflammation, and specific treatment interventions emphasises the need for additional research to elucidate the complex interplay between gene expression, viral co-infection, liver pathology, and therapeutic responses in these particular patients population.

Association Between CYP2B6 Polymorphisms and Efficacy of Clopidogrel in Minor Stroke or Transient Ischemic Attack.

BACKGROUND: CYP2B6 (cytochrome P450 subfamily IIB polypeptide 6), encoded by the CYP2B6 gene, is a critical enzyme involved in clopidogrel metabolism. However, the association between CYP2B6 polymorphisms and the efficacy of clopidogrel in minor stroke or transient ischemic attack for secondary stroke prevention remains unclear. METHODS: Based on CHANCE (Clopidogrel in High-Risk Patients With Acute Nondisabling Cerebrovascular Events) randomized clinical trial of aspirin plus clopidogrel versus aspirin alone, we investigated the role of CYP2B6 polymorphisms and the efficacy of clopidogrel in patients with minor stroke or transient ischemic attack in China from October 2009 to July 2012. A total of 2853 patients were successfully genotyped for CYP2B6-516G>T, rs3745274 and CYP2B6-1456 T>C, rs2054675. The primary efficacy and safety outcomes were new stroke and any bleeding within 90 days. RESULTS: Among the 2853 patients, 32.8% were identified as the carriers of the CYP2B6-516 GT/TT or -1456 TC/CC genotype. The incidences of 90-day new stroke in aspirin plus clopidogrel and aspirin alone groups were 7.1% versus 11.3% among noncarriers, respectively; and 9.7% versus 12.2% among carriers, respectively. The efficacy of aspirin plus clopidogrel versus aspirin alone was not significantly different (P interaction=0.29) in noncarriers (adjusted hazard ratio, 0.61 [95% CI, 0.45-0.83]) compared to carriers (adjusted hazard ratio, 0.80 [95% CI, 0.54-1.18]). The incidence (n=51) of 90-day any bleeding in aspirin plus clopidogrel and aspirin alone groups were 2.2% (21 bleeds) versus 1.9% (18 bleeds) among noncarriers (adjusted hazard ratio, 1.11 [95% CI, 0.59-2.09]) and 1.9% (9 bleeds) versus 0.7% (3 bleeds) among carriers (adjusted hazard ratio, 3.23 [95% CI, 0.86-12.12]). Similar findings were observed during the 1-year follow-up. CONCLUSIONS: In this post hoc analysis of the CHANCE trial, we did not observe a significant difference in the efficacy of aspirin plus clopidogrel compared with aspirin in carriers versus noncarriers of CYP2B6-516 GT/TT or -1456 TC/CC genotype. Our results suggest that both carriers and noncarriers suffering from a minor stroke are likely to benefit from aspirin plus clopidogrel treatment over aspirin monotherapy for secondary prevention. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: NCT00979589.

Tratamiento del tabaquismo guiado por marcadores genéticos

Introducción: Entre las adicciones por drogas, el tabaquismo ocupa el primer lugar como causa de morbimortalidad y es factor de riesgo para seis de las ocho principales causas de muerte en el mundo. La nicotina es el principal componente adictivo del tabaco. En la terapia de reemplazo con nicotina (TRN), la vareniclina y el bupropion son los medicamentos aprobados para tratamiento del tabaquismo, pero los resultados de las clínicas de dejación del tabaquismo sugieren que aún se desconoce muchas variables influyentes en la respuesta al tratamiento. Objetivo: Determinar la adherencia, la tolerabilidad y la efectividad de un programa de dejación de tabaquismo basado en nicotina o bupropion, en pacientes con dependencia al tabaco, seleccionados según los genotipos de las enzimas que metabolizan los dos fármacos. Hallazgos clínicos: Se incluyeron en esta serie 21 fumadores, 67% hombres, con edad promedio de 46,2±11,7 años. Su tabaquismo comenzó a los 17,8±6 años y llevaban fumando 28±13 años. Al inicio del estudio fumaban 17±12 cigarrillos por día (CPD), habían hecho 3,7±2 intentos de dejar de fumar y el puntaje NDSS (escala breve de evaluación de dependencia de la nicotina, por sus siglas en inglés) fue de 22±5 (punto de corte para dependencia a nicotina: 11 o más puntos). Tratamiento: Los pacientes tenían libre acceso telefónico al médico tratante y, cada semana, una consulta consistente en consejería y control del tratamiento farmacológico prescrito según los genotipos CYP2A6 (que codifica la enzima que metaboliza la nicotina) y CYP2B6 (que codifica la enzima que metaboliza el bupropion). Se empleó nicotina en parches transdérmicos de 14 mg el primer mes y luego de 7 mg el segundo mes, complementados con chicles para manejo del síndrome de abstinencia y bupropion en forma de liberación regulada por 300 mg, 1-2 veces al día. Resultados: Después de 8 semanas de tratamiento y 4 de observación, 15 sujetos (71,4%) respondieron en forma parcial/total. El consumo de CPD bajó de 17±12 al inicio del estudio, a 2,2±3,5 al final del estudio, que corresponde a una reducción de 195 cigarrillos/día. Siete de ocho pacientes tratados con bupropion (87,5%) y siete de trece tratados con nicotina (54%) tuvieron respuesta parcial/total. Solo un paciente formulado con nicotina suspendió el medicamento por intolerancia gastrointestinal (náusea y vómito). La tasa de recaídas, evaluada un mes después del tratamiento farmacológico, fue de cero. Se encontró buena correlación genotipo-fenotipo en los individuos tratados con bupropion, pero no en los tratados con nicotina. Relevancia clínica: La inclusión de marcadores farmacogenéticos para la elección de nicotina o bupropion en un programa de dejación de tabaquismo puede mejorar la adherencia, la tolerabilidad al fármaco y la efectividad del tratamiento.

Introduction: Among drug addictions, smoking ranks first as a cause of morbidity and mortality and is a risk factor for six of the eight leading causes of death in the world. Nicotine is the main addictive component of tobacco. In nicotine replacement therapy (NRT), varenicline and bupropion are the approved medications for smoking cessation, but results from smoking cessation clinics suggest that many variables influencing response to treatment remain unknown. Objective: To determine the adherence, tolerability and effectiveness of a smoking cessation program based on nicotine or bupropion, in patients with tobacco dependence, selected according to the genotypes of the enzymes that metabolize the two drugs. Clinical findings: Twenty-one smokers were included in this series, 67% men, with a mean age of 46.2 ± 11.7 years. Their smoking began at 17.8±6 years and they had been smoking for 28±13 years. At baseline, they smoked 17±12 cigarettes per day (CPD), had made 3.7±2 quit attempts, and the NDSS score it was 22±5 (cut-off point for nicotine dependence: 11 or more points). Treatment: The patients had free telephone access to the treating physician and, every week, a consultation consisting of counseling and control of the pharmacological treatment prescribed according to the CYP2A6 genotypes (encoding the enzyme that metabolizes nicotine) and CYP2B6 (coding for the enzyme that metabolizes bupropion). Nicotine was used in transdermal patches of 14 mg the first month and then 7 mg the second month, supplemented with gum to manage the withdrawal syndrome and bupropion in the form of controlled release 300 mg, 1-2 times a day. Results: After 8 weeks of treatment and 4 weeks of observation, 15 subjects (71.4%) responded partially/totally. CPD consumption dropped from 17±12 at the beginning of the study to 2.2±3.5 at the end of the study, which corresponds to a reduction of 195 cigarettes/day. Seven of eight patients treated with bupropion (87.5%) and seven of thirteen treated with nicotine (54%) had a partial/total response. Only one patient receiving nicotine discontinued the medication due to gastrointestinal intolerance (nausea and vomiting). The relapse rate, assessed one month after drug treatment, was zero. Good genotype-phenotype correlation was found in individuals treated with bupropion, but not in those treated with nicotine. Clinical relevance: The inclusion of pharmacogenetic markers for the choice of nicotine or bupropion in a smoking cessation program may improve adherence, drug tolerability, and treatment effectiveness.

Influence of CYP2B6 Genotype on Methadone Dosage in Patients from the Methadone Maintenance Treatment (MMT) Program in Pereira, Colombia.

Methadone treatment reduces the use of heroin and withdrawal symptoms; however, methadone is an expensive medication with a narrow safety margin. We compared the retention rates, persistence of heroin use, and quality of life of a group of patients undergoing conventional Methadone Maintenance Treatment (MMT) with a group for whom the CYP2B6 516G>T polymorphism was used in addition to the MMT to calculate the required methadone dose. Over 12 weeks, the retention rate, heroin usage, and quality of life of patients under conventional treatment (n = 34) were compared with those of patients for whom we used genetic markers to calculate methadone dosage (n = 38). At the end of the study, 26.4% of patients abandoned the program, and neither demographic nor clinical variables were associated with treatment adherence. Of the remaining patients, 16% of the control group and 8% of patients in the pharmacogenetic group reported heroin use, while both groups showed a 64% reduction in the use of cocaine/crack (no significant differences between the groups were found). Starting in the second week, the methadone dosage was lower among the patients for whom methadone was prescribed based on genotype. Although there were six individuals in the control group and three in the pharmacogenetic group with QTc intervals > 450 ms (a threshold that is considered dangerous), we did not find a relationship between the QTc interval and methadone dosage. There were no differences in the perception of quality of life between the two groups. The results of this pilot study suggest that concerning methadone therapy, the CYP2B6 genotype contributes to reduced effective doses and treatment costs.