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Fulltext Awareness and knowledge of nurses towards hepatitis b virus infection at a tertiary hospital in Selangor, Malaysia

Chieng, Jin Yu, Yasotha Sugumaran, Pan Yan

Borneo Journal of Medical Sciences, 2021;15(1):11-20.
MyJurnal

Hepatitis B is a well-recognized occupational risk for healthcare workers. This self-administered questionnaire study was designed to assess awareness and knowledge towards hepatitis B virus infection among 140 nurses at Serdang Hospital, Selangor, Malaysia from the period of 1st April to 30th September 2017. The response rate was 97.2% (n = 140/144). A total of 71.4% of participants showed adequate awareness of hepatitis B. Most participants had heard hepatitis B with the predominant sources receiving from friends, media and education. Majority of them did serology blood test of hepatitis B before. A total of 84.3% of participants were aware of vaccine available for hepatitis B, although 78.6% got vaccinated in the past. Antiviral treatment of hepatitis B was not well noticed by most of them. Education qualification determines the awareness of hepatitis B. Regarding the knowledge, 73.6% of participants showed poor knowledge of hepatitis B. Most participants understood that hepatitis B was caused by a virus infection and the organ most affected was the liver. Surprisingly, 77.9% of them failed to recognize that cancer could be caused by hepatitis B. Majority of participants were aware that transmission of hepatitis B could be mediated via sexual intercourse, as well as childbirth. Nevertheless, 14.3% of them believed that hepatitis B was able to spread by cough and sneeze. Older age, Chinese ethnicity, and having high educational qualification were factors leading to adequate knowledge of hepatitis B. Additional attention should be emphasized to strengthen knowledge towards hepatitis B among nurses and perhaps other healthcare workers in Malaysia.
Fulltext Prevalence of helicobacter pylori infection among patients attending gastroenterology endoscopy unit at Serdang Hospital

Chieng, Jin Yu, Pan, Yan, Loong, Yik Yee

Malaysian Journal of Medicine and Health Sciences, 2015;11(1):11-17.
MyJurnal

To study the prevalence of Helicobacter Pylori (H. pylori) infection, according to ethnicity, gender and endoscopic findings among the patients underwent the oesophago-gastro-duodenoscopes (OGDS) at gastroenterology endoscopy unit, Hospital Serdang, Selangor, Malaysia. The database of all whom underwent OGDS at the gastroenterology endoscopy unit, Hospital Serdang from 1st August 2010 to 31st July 2012 was collected and assessed, retrospectively. A total of 924 patients who underwent OGDS were analyzed for the H. pylori infection by using Campylobacter-like organism (CLO) test. 130 (14.07%) tested positive, and their data were further studied according to gender, ethnicity, age group, initial indication for OGDS and endoscopic finding. The prevalence rate among males was 15.15% (70/462), while it was 12.99% (60/462) among females. In terms of ethnics, H. pylori infection was commonly found among Indian and Chinese with prevalence rate of 25.13% (50/199) and 17.41% (51/293) respectively. These figures are significantly higher than the 6.01% (25/416) for Malays. The age group (31-50 years old) had the highest prevalence rate of H. Pylori infection, which is of 18.55% (41/221). No significant difference was observed among initial indications for OGDS. Erosions were the commonest finding in H. pylori positive group with rate of 51.54% (67/130). However, erosions were not uncommon in H. pylori negative group as well with the rate of 48.61% (386/794). H. pylori infection rate among Malaysians was generally low, with the highest rate in Indians, followed by Chinese and relatively low in Malays. No significant difference between the prevalence rate of H. pylori infection in male and that in female was found. Erosions were equally common in either H. pylori positive or H. pylori negative group.
Fulltext Transient unilateral parotid gland swelling following upper endoscopy

Chieng Jin Yu, Then Ru Fah, Sharifah Intan Safura Shahabudin, Pan Yan

Journal of Clinical and Health Sciences, 2021;6(1):50-52.
MyJurnal

Transient parotid gland swelling could happen as complication after per oral endoscopy or
intubation. We reported a 53-year-old man who developed transient unilateral parotid gland
swelling following esophagogastroduodenoscopy (OGDS) with dilatation of achalasia cardia.
The swelling of the parotid gland was transient and resolved completely without any
intervention.
Cytochrome P450 2W1 (CYP2W1) - ready for use as the biomarker and drug target for cancer?

Pan Y, Ong EC

Xenobiotica, 2017 Oct;47(10):923-932.
PMID: 27690753 DOI: 10.1080/00498254.2016.1244370

1. This article aims to evaluate the potentials of using cytochrome P450 2W1 (CYP2W1) as a biomarker and a drug target of cancer because of its characteristic cancer-specific expression. 2. Discrepant findings comparing the expression levels of CYP2W1 in cancer and non-cancer samples were reported. In general, the expression followed a developmental pattern. The demethylation status of CpG island and the expression levels of CYP2W1 genes was positively correlated. 3. CYP2W1 was able to activate several procarcinogens, anticancer pro-drugs and to metabolise many endogenous substances including fatty acids and lysophospholipids. 4. CYP2W1 expression level was suggested to serve as an independent prognostic biomarker in colorectal cancer and hepatocellular carcinoma. The correlation of genetic polymorphisms of CYP2W1 and cancer risk was uncertain. 5. Further characterisation of CYP2W1 structure is suggested to link to its functions. More studies are warranted to reveal the true status and the regulation of CYP2W1 expression across normal and cancer tissues. Catalytic activity of CYP2W1 should be tested on a wider spectrum of endogenous and exogenous substances before its use as the drug target. Larger size of clinical samples can be included to verify the potential of CYP2W1 as the prognostic or cancer risk biomarker.
Heterologous expression of human cytochrome P450 (CYP) 2C19 in Escherichia coli and establishment of RP-HPLC method to serve as activity marker

Pan Y, Mak JW, Ong CE

Biomed Chromatogr, 2013 Jul;27(7):859-65.
PMID: 23386533 DOI: 10.1002/bmc.2872

In this study, a simple and reliable reverse-phase high-performance liquid chromatography (RP-HPLC) method was established and validated to analyze S-mephenytoin 4-hydroxylase activity of a recombinant CYP2C19 system. This system was obtained by co-expressing CYP2C19 and NADPH-CYP oxidoreductase (OxR) proteins in Escherichia coli (E. coli) cells. In addition to RP-HPLC, the expressed proteins were evaluated by immunoblotting and reduced CO difference spectral scanning. The RP-HPLC assay showed good linearity (r(2) = 1.00) with 4-hydroxymephenytoin concentration from 0.100 to 50.0 μm and the limit of detection was 5.00 × 10(-2) μm. Intraday and interday precisions determined were from 1.90 to 8.19% and from 2.20 to 14.9%, respectively. Recovery and accuracy of the assay were from 83.5 to 85.8% and from 95.0 to 105%. Enzyme kinetic parameters (Km , Vmax and Ki ) were comparable to reported values. The presence of CYP2C19 in bacterial membranes was confirmed by immunoblotting and the characteristic absorbance peak at 450 nm was determined in the reduced CO difference spectral assay. Moreover, the activity level of co-expressed OxR was found to be comparable to that of the literature. As a conclusion, the procedures described here have generated catalytically active CYP2C19 and the RP-HPLC assay developed is able to serve as CYP2C19 activity marker for pharmacokinetic drug interaction study in vitro.
Unveiling the Role of Cytochrome P450 (2E1) in Human Brain Specifically in Parkinson's Disease - Literature Review

Shah A, Ong CE, Pan Y

Curr Drug Metab, 2021;22(9):698-708.
PMID: 34325630 DOI: 10.2174/1389200222666210729115151

BACKGROUND: In recent years, the significance of cytochrome P450 enzymes (CYPs) has expanded beyond their role in the liver. Factors such as genetics, environmental toxins, drug biotransformation and underlying diseases mediate the expression of these enzymes. Among the CYP enzymes, CYP2E1, a well-recognized monooxygenase enzyme involved in the metabolism of various endogenous and exogenous substances, plays a crucial role in the brain concerning the development of Parkinson's disease. The expression of CYP2E1 varies in different brain regions making certain regions more vulnerable than others. CYP2E1 expression is inducible which generates tissuedamaging radicals leading to oxidative stress, mitochondrial dysfunction and ultimately neurodegeneration.
OBJECTIVE: Less is understood about the role of CYP2E1 in the central nervous system, therefore the purpose of the study was to investigate the relationship between the expression and activity of CYP2E1 enzyme relevant to Parkinson's disease and to identify whether an increase in the expression of CYP2E1 is associated with neurodegeneration.
METHODS: The objectives of the study were achieved by implicating an unsystematic integrative literature review approach in which the literature was qualitatively analysed, critically evaluated and a new theory with an overall view of the mechanism was presented.
RESULTS: The contribution of CYP2E1 in the development of Parkinson's disease was found to be significant as the negative effects of CYP2E1 overshadowed its protective detoxifying role.
CONCLUSION: Overexpression of CYP2E1 seems detrimental to dopaminergic neurons, therefore, to overcome this, a synthetic biochemical is required, which paves the way for further research and development of valuable biomolecules.
In vitro approaches to investigate cytochrome P450 activities: update on current status and their applicability

Ong CE, Pan Y, Mak JW, Ismail R

Expert Opin Drug Metab Toxicol, 2013 Sep;9(9):1097-113.
PMID: 23682848 DOI: 10.1517/17425255.2013.800482

Cytochromes P450 (CYPs) play a central role in the Phase I metabolism of drugs and other xenobiotics. It is estimated that CYPs can metabolize up to two-thirds of drugs present in humans. Over the past two decades, there have been numerous advances in in vitro methodologies to characterize drug metabolism and interaction involving CYPs.
Cytochrome P450 genotype-guided drug therapies: An update on current states

Dong AN, Tan BH, Pan Y, Ong CE

Clin Exp Pharmacol Physiol, 2018 10;45(10):991-1001.
PMID: 29858511 DOI: 10.1111/1440-1681.12978

Over the past 2 decades, knowledge of the role and clinical value of pharmacogenetic markers has expanded so that individualized pre-emptive therapy based on genetic background of patients could be within reach for clinical implementation. This is evidenced from the frequent updating of drug labels that incorporates pharmacogenetic information (where compelling data become available) by the regulatory agencies (such as the US FDA), and the periodical publication of guidelines of specific therapeutic recommendations based on the results of pharmacogenetic tests by the pharmacogenetics working groups or consortiums of professional bodies. Clinical relevance of the cytochrome P450 (CYP) polymorphism related to dose, effectiveness and/or toxicity of key drugs are presented in this review, including that of warfarin, clopidogrel, tricyclic antidepressants, and proton pump inhibitors. Prospect for routine clinical application of CYP genotyping before prescribing drugs is still currently unclear due to challenges and barriers associated with availability of well-defined and validated pharmacogenetic studies, the interpretation, result reporting and potential error of genotype testing, involvement of non-genetic factors, and other patient's demographic and disease conditions. Further studies to provide additional supporting clinical data and acceleration of pharmacogenetic testing standards and techniques should help improve the evidence base needed for clinical utility and hence move the implementation of genotype-guided therapy in clinical practice a step closer to reality.
Fulltext The CYP2R1 Enzyme: Structure, Function, Enzymatic Properties and Genetic Polymorphism

Dong AN, Tan BH, Pan Y, Ong CE

J Pharm Pharm Sci, 2021;24:94-112.
PMID: 33626316 DOI: 10.18433/jpps31305

Since the discovery of its role in vitamin D metabolism, significant progress has been made in the understanding of gene organisation, protein structure, catalytic function, and genetic polymorphism of cytochrome P450 2R1 (CYP2R1). Located on chromosome 11p15.2, CYP2R1 possesses five exons, unlike most other CYP isoforms that carry nine exons. CYP2R1 crystal structure displays a fold pattern typical of a CYP protein, with 12 a-helices as its structural core, and b-sheets mostly arranged on one side, and the heme buried in the interior part of the protein. Overall, CYP2R1 structure adopts a closed conformation with the B' helix serving as a gate covering the substrate access channel, with the substrate vitamin D3 occupying a position with the side chain pointing toward the heme group. In liver, CYP2R1 25-hydroxylates vitamin D and serves as an important determinant of 25(OH)D level in the tissue and in circulation. While substrate profile has been well studied, inhibitor specificity for CYP2R1 requires further investigation. Both exonic and non-exonic single nucleotide polymorphisms (SNPs) have been reported in CYP2R1, including the CYP2R1*2 carrying Leu99Pro exchange, and a number of non-exonic SNPs with variable functional consequences in gene regulation. A non-exonic SNP, rs10741657, has its causal relationship with diseases established, including that of rickets, ovarian cancer, and multiple sclerosis. The role of other CYP2R1 SNPs in vitamin D deficiency and their causal link to other traits however remain uncertain currently and more studies are warranted to help identify possible physiological mechanisms underlying those complex traits.
Fulltext In vitro and in silico Approaches to Study Cytochrome P450-Mediated Interactions

Tan BH, Pan Y, Dong AN, Ong CE

J Pharm Pharm Sci, 2017;20(1):319-328.
PMID: 29145931 DOI: 10.18433/J3434R

In vitro and in silico models of drug metabolism are utilized regularly in the drug research and development as tools for assessing pharmacokinetic variability and drug-drug interaction risk. The use of in vitro and in silico predictive approaches offers advantages including guiding rational design of clinical drug-drug interaction studies, minimization of human risk in the clinical trials, as well as cost and time savings due to lesser attrition during compound development process. This article gives a review of some of the current in vitro and in silico methods used to characterize cytochrome P450(CYP)-mediated drug metabolism for estimating pharmacokinetic variability and the magnitude of drug-drug interactions. Examples demonstrating the predictive applicability of specific in vitro and in silico approaches are described. Commonly encountered confounding factors and sources of bias and error in these approaches are presented. With the advent of technological advancement in high throughput screening and computer power, the in vitro and in silico methods are becoming more efficient and reliable and will continue to contribute to the process of drug discovery, development and ultimately safer and more effective pharmacotherapy. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.
Mechanism-based inactivation of cytochromes P450: implications in drug interactions and pharmacotherapy

Tan BH, Ahemad N, Pan Y, Ong CE

Xenobiotica, 2024 Aug 28.
PMID: 39175333 DOI: 10.1080/00498254.2024.2395557

Cytochrome P40 (CYP) enzymes dominate the metabolism of numerous endogenous and xenobiotic substances. While it is commonly believed that CYP-catalysed reactions result in the detoxication of foreign substances, these reactions can also yield reactive intermediates that can bind to cellular macromolecules to cause cytotoxicity or irreversibly inactivate CYPs that create them.Mechanism-based inactivation (MBI) produces either irreversible or quasi-irreversible inactivation and is commonly caused by CYP metabolic bioactivation to an electrophilic reactive intermediate. Many drugs that have been known to cause MBI in CYPs have been discovered as perpetrators in drug-drug interactions throughout the last 20-30 years.This review will highlight the key findings from the recent literature about the mechanisms of CYP enzyme inhibition, with a focus on the broad mechanistic elements of MBI for widely used drugs linked to the phenomenon. There will also be a brief discussion of the clinical or pharmacokinetic consequences of CYP inactivation with regard to drug interaction and toxicity risk.Gaining knowledge about the selective inactivation of CYPs by common therapeutic drugs helps with the assessment of factors that affect the systemic clearance of co-administered drugs and improves comprehension of anticipated interactions with other drugs or xenobiotics.
The current understanding of the interactions between nanoparticles and cytochrome P450 enzymes - a literature-based review

Pan Y, Ong CE, Pung YF, Chieng JY

Xenobiotica, 2019 Jul;49(7):863-876.
PMID: 30028220 DOI: 10.1080/00498254.2018.1503360

Nanoparticles (NPs) have wide spectrum applications in the areas of industry and biomedicine. However, concerns about their toxic and negative impacts on the environments as well as human health have been raised. Cytochrome P450s (CYPs) are involved in endogenous and exogenous metabolism. Modulations of CYP can adversely damage drug metabolism, detoxification of xenobiotics and animal physiology functions. This article focused on NPs-CYP interactions for humans and animals available in the literature. It was found that different NPs process specific inhibitory potencies against CYPs involved in drug metabolism. Moreover, NPs were able to modify the expression of CYPs genes or protein in humans and other animals, which highlighted their detoxification functions. Nonetheless, changes of CYPs responsible for hormone synthesis and metabolism resulted in endocrine disturbances. Hence, there is a need to screen newly developed NPs to evaluate their interactions with CYPs. The future studies should further strategize the in vitro approaches to reveal the molecular mechanisms behind interactions by taking full considerations of the interference of co-factors, buffers, substrates and metabolites with NPs. Moreover, in vivo studies should compare the influences of NPs via different administration routes and different duration of treatments to reveal the physiological significance.
In vitro effect of important herbal active constituents on human cytochrome P450 1A2 (CYP1A2) activity

Pan Y, Tiong KH, Abd-Rashid BA, Ismail Z, Ismail R, Mak JW, et al.

Phytomedicine, 2014 Oct 15;21(12):1645-50.
PMID: 25442272 DOI: 10.1016/j.phymed.2014.08.003

This study was designed to investigate eight herbal active constituents (andrographolide, asiaticoside, asiatic acid, madecassic acid, eupatorin, sinensetin, caffeic acid, and rosmarinic acid) on their potential inhibitory effects on human cytochrome P450 1A2 (CYP1A2) activity. A fluorescence-based enzyme assay was performed by co-incubating human cDNA-expressed CYP1A2 with its selective probe substrate, 3-cyano-7-ethoxycoumarin (CEC), in the absence or presence of various concentrations of herbal active constituents. The metabolite (cyano-hydroxycoumarin) formed was subsequently measured in order to obtain IC50 values. The results indicated that only eupatorin and sinensetin moderately inhibited CYP1A2 with IC50 values of 50.8 and 40.2 μM, while the other active compounds did not significantly affect CYP1A2 activity with IC50 values more than 100 μM. Ki values further determined for eupatorin and sinensetin were 46.4 and 35.2 μM, respectively. Our data indicated that most of the investigated herbal constituents have negligible CYP1A2 inhibitory effect. In vivo studies however may be warranted to ascertain the inhibitory effect of eupatorin and sinensetin on CYP1A2 activity in clinical situations.
Effect of eurycomanone on cytochrome P450 isoforms CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2E1 and CYP3A4 in vitro

Pan Y, Tiong KH, Abd-Rashid BA, Ismail Z, Ismail R, Mak JW, et al.

J Nat Med, 2014 Apr;68(2):402-6.
PMID: 23881640 DOI: 10.1007/s11418-013-0794-8

Eurycomanone, an active constituent isolated from Eurycoma longifolia Jack, was examined for modulatory effects on cytochrome P450 (CYP) isoforms CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2E1 and CYP3A4 using in vitro assays. The IC50 value was determined to assess the potencies of modulation for each CYP isoform. Our results indicated that eurycomanone did not potently inhibit any of the CYP isoforms investigated, with IC50 values greater than 250 μg/ml. Hence there appears to be little likelihood of drug-herb interaction between eurycomanone or herbal products with high content of this compound and CYP drug substrates via CYP inhibition.
Inhibitory effects of cytochrome P450 enzymes CYP2C8, CYP2C9, CYP2C19 and CYP3A4 by Labisia pumila extracts

Pan Y, Tiong KH, Abd-Rashid BA, Ismail Z, Ismail R, Mak JW, et al.

J Ethnopharmacol, 2012 Sep 28;143(2):586-91.
PMID: 22885070 DOI: 10.1016/j.jep.2012.07.024

Labisa pumila (LP), popularly known with its local name, Kacip Fatimah, is a well known herb grown in Indochina and Southeast Asia and is traditionally used to regain energy after giving birth in women. The propensity of LP to cause drug-herb interaction via cytochrome P450 (CYP) enzyme system has not been investigated.
Functional role of Ile264 in CYP2C8: mutations affect haem incorporation and catalytic activity

Singh R, Ting JG, Pan Y, Teh LK, Ismail R, Ong CE

Drug Metab. Pharmacokinet., 2008;23(3):165-74.
PMID: 18574320

The work described in this study aimed to express CYP2C8 wild-type and mutant proteins in bacterial expression system and to use the expressed proteins to investigate the structural and functional consequences of a reported allele CYP2C8(*)4 (carrying Ile264Met substitution) on protein activity. Ile264 was replaced by three different amino acids resulting in three mutant constructs, 2C8I264M, 2C8I264R and 2C8I264D. The presence of isoleucine at position 264 in CYP2C8 was found to be important for proper haem insertion and protein folding; whereas bulkier or charged residues were highly disruptive resulting in inactive proteins with minimum spectral and catalytic activities. This was evidenced from the low levels of Soret peak at 450 nm and negligible levels of tolbutamide methylhydroxylase activity. Kinetic study using paclitaxel indicated that all three mutants exhibited only 9.7 to 35.4% of the activity level observed in the wild-type. In addition, the mutants were more sensitive to proteinase K digestion, indicating a possible alteration of conformation. The combined effects of protein instability and compromised catalytic activity resulted in defective CYP2C8 protein which may have clinical implications in carriers of CYP2C8*4, particularly in terms of their capacity to clear potent drugs and their susceptibility to adverse drug reactions.
Heterologous expression of human cytochromes P450 2D6 and CYP3A4 in Escherichia coli and their functional characterization

Pan Y, Abd-Rashid BA, Ismail Z, Ismail R, Mak JW, Ong CE

Protein J, 2011 Dec;30(8):581-91.
PMID: 22001938 DOI: 10.1007/s10930-011-9365-6

This study aimed to express two major drug-metabolizing human hepatic cytochromes P450 (CYPs), CYP2D6 and CYP3A4, together with NADPH-cytochrome P450 oxidoreductase (OxR) in Escherichia coli and to evaluate their catalytic activities. Full length cDNA clones of both isoforms in which the N-terminus was modified to incorporate bovine CYP17α sequence were inserted into a pCWori(+) vector. The modified CYP cDNAs were subsequently expressed individually, each together with OxR by means of separate, compatible plasmids with different antibiotic selection markers. The expressed proteins were evaluated by immunoblotting and reduced CO difference spectral scanning. Enzyme activities were examined using high performance liquid chromatography (HPLC) assays with probe substrates dextromethorphan and testosterone for CYP2D6 and CYP3A4, respectively. Results from immunoblotting demonstrated the presence of both CYP proteins in bacterial membranes and reduced CO difference spectra of the cell preparations exhibited the characteristic absorbance peak at 450 nm. Co-expressed OxR also demonstrated an activity level comparable to literature values. Kinetic parameters, K(m) and V(max) values determined from the HPLC assays also agreed well with literature values. As a conclusion, the procedures described in this study provide a relatively convenient and reliable means of producing catalytically active CYP isoforms suitable for drug metabolism and interaction studies.
Functional and structural characterisation of common cytochrome P450 2D6 allelic variants-roles of Pro34 and Thr107 in catalysis and inhibition

Dong AN, Ahemad N, Pan Y, Palanisamy UD, Yiap BC, Ong CE

Naunyn Schmiedebergs Arch Pharmacol, 2019 08;392(8):1015-1029.
PMID: 31025144 DOI: 10.1007/s00210-019-01651-0

One major source of inter-individual variability in drug pharmacokinetics is genetic polymorphism of the cytochrome P450 (CYP) genes. This study aimed to elucidate the enzyme kinetic and molecular basis for altered activity in three major alleles of CYP2D6, namely CYP2D6*2, CYP2D6*10 and CYP2D6*17. The E. coli-expressed allelic variants were examined using substrate (venlafaxine and 3-cyano-7-ethoxycoumarin[CEC]) and inhibitor (quinidine, fluoxetine, paroxetine, terbinafine) probes in enzyme assays as well as molecular docking. The kinetics data indicated that R296C and S486T mutations in CYP2D6*2 have caused enhanced ligand binding (enhanced intrinsic clearance for venlafaxine and reduced IC50 for quinidine, paroxetine and terbinafine), suggesting morphological changes within the active site cavity that favoured ligand docking and binding. Mutations in CYP2D6*10 and CYP2D6*17 tended to cause deleterious effect on catalysis, with reduced clearance for venlafaxine and CEC. Molecular docking indicated that P34S and T107I, the unique mutations in the alleles, have negatively impacted activity by affecting ligand access and binding due to alteration of the substrate access channel and active site morphology. IC50 values however were quite variable for quinidine, fluoxetine and terbinafine, and a general decrease in IC50 was observed for paroxetine, suggesting ligand-specific altered susceptibility to inhibition in the alleles. This study indicates that CYP2D6 allele selectivity for ligands was not solely governed by changes in the active site architecture induced by the mutations, but that the intrinsic properties of the substrates and inhibitors also played vital role.
The Molecular and Enzyme Kinetic Basis for Altered Activity of Three Cytochrome P450 2C19 Variants Found in the Chinese Population

Dong AN, Ahemad N, Pan Y, Palanisamy UD, Yiap BC, Ong CE

Curr Mol Pharmacol, 2020;13(3):233-244.
PMID: 31713493 DOI: 10.2174/1874467212666191111110429

BACKGROUND: There is a large inter-individual variation in cytochrome P450 2C19 (CYP2C19) activity. The variability can be caused by the genetic polymorphism of CYP2C19 gene. This study aimed to investigate the molecular and kinetics basis for activity changes in three alleles including CYP2C19*23, CYP2C19*24 and CYP2C19*25found in the Chinese population.
METHODS: The three variants expressed by bacteria were investigated using substrate (omeprazole and 3- cyano-7-ethoxycoumarin[CEC]) and inhibitor (ketoconazole, fluoxetine, sertraline and loratadine) probes in enzyme assays along with molecular docking.
RESULTS: All alleles exhibited very low enzyme activity and affinity towards omeprazole and CEC (6.1% or less in intrinsic clearance). The inhibition studies with the four inhibitors, however, suggested that mutations in different variants have a tendency to cause enhanced binding (reduced IC50 values). The enhanced binding could partially be explained by the lower polar solvent accessible surface area of the inhibitors relative to the substrates. Molecular docking indicated that G91R, R335Q and F448L, the unique mutations in the alleles, have caused slight alteration in the substrate access channel morphology and a more compact active site cavity hence affecting ligand access and binding. It is likely that these structural alterations in CYP2C19 proteins have caused ligand-specific alteration in catalytic and inhibitory specificities as observed in the in vitro assays.
CONCLUSION: This study indicates that CYP2C19 variant selectivity for ligands was not solely governed by mutation-induced modifications in the active site architecture, but the intrinsic properties of the probe compounds also played a vital role.
In Vitro Functional Characterisation of Cytochrome P450 (CYP) 2C19 Allelic Variants CYP2C19*23 and CYP2C19*24

Lau PS, Leong KV, Ong CE, Dong AN, Pan Y

Biochem Genet, 2017 Feb;55(1):48-62.
PMID: 27578295 DOI: 10.1007/s10528-016-9771-8

Cytochrome P450 (CYP) 2C19 is essential for the metabolism of clinically used drugs including omeprazole, proguanil, and S-mephenytoin. This hepatic enzyme exhibits genetic polymorphism with inter-individual variability in catalytic activity. This study aimed to characterise the functional consequences of CYP2C19*23 (271 G>C, 991 A>G) and CYP2C19*24 (991 A>G, 1004 G>A) in vitro. Mutations in CYP2C19 cDNA were introduced by site-directed mutagenesis, and the CYP2C19 wild type (WT) as well as variants proteins were subsequently expressed using Escherichia coli cells. Catalytic activities of CYP2C19 WT and those of variants were determined by high performance liquid chromatography-based essay employing S-mephenytoin and omeprazole as probe substrates. Results showed that the level of S-mephenytoin 4'-hydroxylation activity of CYP2C19*23 (V max 111.5 ± 16.0 pmol/min/mg, K m 158.3 ± 88.0 μM) protein relative to CYP2C19 WT (V max 101.6 + 12.4 pmol/min/mg, K m 123.0 ± 19.2 μM) protein had no significant difference. In contrast, the K m of CYP2C19*24 (270.1 ± 57.2 μM) increased significantly as compared to CYP2C19 WT (123.0 ± 19.2 μM) and V max of CYP2C19*24 (23.6 ± 2.6 pmol/min/mg) protein was significantly lower than that of the WT protein (101.6 ± 12.4 pmol/min/mg). In vitro intrinsic clearance (CLint = V max/K m) for CYP2C19*23 protein was 85.4 % of that of CYP2C19 WT protein. The corresponding CLint value for CYP2C19*24 protein reduced to 11.0 % of that of WT protein. These findings suggested that catalytic activity of CYP2C19 was not affected by the corresponding amino acid substitutions in CYP2C19*23 protein; and the reverse was true for CYP2C19*24 protein. When omeprazole was employed as the substrate, K m of CYP2C19*23 (1911 ± 244.73 μM) was at least 100 times higher than that of CYP2C19 WT (18.37 ± 1.64 μM) and V max of CYP2C19*23 (3.87 ± 0.74 pmol/min/mg) dropped to 13.4 % of the CYP2C19 WT (28.84 ± 0.61 pmol/min/mg) level. Derived from V max/K m, the CLint value of CYP2C19 WT was 785 folds of CYP2C19*23. K m and V max values could not be determined for CYP2C19*24 due to its low catalytic activity towards omeprazole 5'-hydroxylation. Therefore, both CYP2C19*23 and CYP2C19*24 showed marked reduced activities of metabolising omeprazole to 5-hydroxyomeprazole. Hence, carriers of CYP2C19*23 and CYP2C19*24 allele are potentially poor metabolisers of CYP2C19-mediated substrates.

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