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Armstrong SJ, King K, Steventon G. Precision medicine for Defence? BMJ Mil Health 2024:e002721. [PMID: 39181566 DOI: 10.1136/military-2024-002721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Accepted: 06/28/2024] [Indexed: 08/27/2024]
Abstract
Proteins control individual patient's response to pharmaceutical medication, be they receptors, transporters or enzymes. These proteins are under the control of genes. The study of these genes and the interplay between multiple genes is pharmacogenomics, with individual genes being termed pharmacogenes. The greatest understanding of pharmacogenetics is of the drug metabolising enzymes, the cytochrome P450s. Almost the entire UK population is likely to have at least one genetic variant that controls these P450s and thus the phenotype for metabolic competence. This means two patients receiving the same medication and dose may have very different responses, from adverse reaction to being ineffective. An individual military person's response to medications can be predicted from their pharmacogenetics, as an example; the response to the commonly prescribed 'pain killers', codeine, tramadol, hydrocodone or oxycodone. These opioids are metabolised into their active forms by the cytochrome 2D6. Four phenotypes classify an individual's metabolic competency: ultra-rapid, extensive, intermediate or poor. A poor metaboliser is at risk of ineffective pain relief from one of the opioids listed, whereas an ultra-rapid metaboliser is at risk of overexposure and subsequent dependency or abuse. In white European populations, the prevalence of the phenotypes is well known and may be used to guide prescribing; however, in other populations such as Nepalese or Pacific Islander the distribution of these phenotypes is unknown. Genotyping provides a framework for the precise treatment of patients and cost-effective use of medication for the UK Armed Forces, as well as potentially providing equity for minority groups.
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Affiliation(s)
| | - K King
- Academic Department of Military General Practice, Defence Medical Services, Birmingham, UK
| | - G Steventon
- Defence Science and Technology Laboratory, Salisbury, UK
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Stocco MR, Tyndale RF. Cytochrome P450 enzymes and metabolism of drugs and neurotoxins within the mammalian brain. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2022; 95:73-106. [PMID: 35953164 DOI: 10.1016/bs.apha.2022.04.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Cytochrome P450 enzymes (CYPs) that metabolize xenobiotics are expressed and active in the brain. These CYPs contribute to the metabolism of many centrally acting compounds, including clinically used drugs, drugs of abuse, and neurotoxins. Although CYP levels are lower in the brain than in the liver, they may influence central substrate and metabolite concentrations, which could alter resulting centrally-mediated responses to these compounds. Additionally, xenobiotic metabolizing CYPs are highly variable due to genetic polymorphisms and regulation by endogenous and xenobiotic molecules. In the brain, these CYPs are sensitive to xenobiotic induction. As a result, CYPs in the brain vary widely, including among humans, and this CYP variation may influence central metabolism and resulting response to centrally acting compounds. It has been demonstrated, using experimental manipulation of CYP activity in vivo selectively within the brain, that CYP metabolism in the brain alters central substrate and metabolite concentrations, as well as drug response and neurotoxic effects. This suggests that variability in xenobiotic metabolizing CYPs in the human brain may meaningfully contribute to individual differences in response to, and effects of, centrally acting drugs and neurotoxins. This chapter will provide an overview of CYP expression in the brain, endogenous- and xenobiotic-mediated CYP regulation, and the functional impact of CYP-mediated metabolism of drugs and neurotoxins in the brain, with a focus on experimental approaches in mice, rats, and non-human primates, and a discussion regarding the potential role of xenobiotic metabolizing CYPs in the human brain.
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Affiliation(s)
- Marlaina R Stocco
- Department of Psychological and Brain Sciences, University of California, Santa Barbara, Santa Barbara, CA, United States
| | - Rachel F Tyndale
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON, Canada; Campbell Family Mental Health Research Institute, CAMH, Toronto, ON, Canada; Department of Psychiatry, University of Toronto, Toronto, ON, Canada.
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Evidence for Gender Differences in the Amphetamine/Methamphetamine Ratio in the Hair of Subjects undergoing Fitness-to-Drive Testing. Clin Chim Acta 2022; 530:87-93. [PMID: 35276222 DOI: 10.1016/j.cca.2022.03.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 02/11/2022] [Accepted: 03/07/2022] [Indexed: 11/20/2022]
Abstract
BACKGROUND AND AIMS Retrospective analysis of hair testing data provides insights in drugs abuse patterns and improves results interpretation. Cases from subjects undergoing driving fitness assessment (2010-2020) were examined to evidence patterns in methamphetamine (MA) abuse. MATERIALS AND METHODS All cases with positive MA (≥0.025 ng/mg) were included (n=585). Data available were gender, age, MA and A (amphetamine) in hair (h), hair color/treatment, length of proximal hair. Cases with Ah/MAh≤0.35 (n=469) were arbitrarily selected to remove as many combined A, MA users. ANOVA was performed to detect Ah/MAh predictors. RESULTS No predictors affected Ah/MAh. A bimodal frequency distribution was observed. We clustered cases in two groups (1, Ah/MAh 0.025-0.070; 2, Ah/MAh 0.071-0.120) and performed logistic regression. Only gender exhibited significant difference across groups (p=0.0080). Odds ratio for females falling into group 2 was 2.86 times higher (CI97.5 1.34-6.44). CONCLUSION Literature data support the hypothesis that the two Ah/MAh groups represent different phenotypes of the CYP2D6-mediated MA N-demethylation. Whether gender plays a role in such difference could not be confirmed. However, these results provide further suggestion of an association of gender and pharmacogenomics with MA disposition, requiring these factors to be considered in future research.
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Stocco MR, El-Sherbeni AA, Zhao B, Novalen M, Tyndale RF. The role of CYP2D in rat brain in methamphetamine-induced striatal dopamine and serotonin release and behavioral sensitization. Psychopharmacology (Berl) 2021; 238:1791-1804. [PMID: 33649968 PMCID: PMC8233297 DOI: 10.1007/s00213-021-05808-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 02/22/2021] [Indexed: 11/28/2022]
Abstract
RATIONALE Cytochrome P450 2D (CYP2D) enzymes metabolize many addictive drugs, including methamphetamine. Variable CYP2D metabolism in the brain may alter CNS drug/metabolite concentrations, consequently affecting addiction liability and neuropsychiatric outcomes; components of these can be modeled by behavioral sensitization in rats. METHODS To investigate the role of CYP2D in the brain in methamphetamine-induced behavioral sensitization, rats were pretreated centrally with a CYP2D irreversible inhibitor (or vehicle) 20 h prior to each of 7 daily methamphetamine (0.5 mg/kg subcutaneous) injections. In vivo brain microdialysis was used to assess brain drug and metabolite concentrations, and neurotransmitter release. RESULTS CYP2D inhibitor (versus vehicle) pretreatment enhanced methamphetamine-induced stereotypy response sensitization. CYP2D inhibitor pretreatment increased brain methamphetamine concentrations and decreased the brain p-hydroxylation metabolic ratio. With microdialysis conducted on days 1 and 7, CYP2D inhibitor pretreatment exacerbated stereotypy sensitization and enhanced dopamine and serotonin release in the dorsal striatum. Day 1 brain methamphetamine and amphetamine concentrations correlated with dopamine and serotonin release, which in turn correlated with the stereotypy response slope across sessions (i.e., day 1 through day 7), used as a measure of sensitization. CONCLUSIONS CYP2D-mediated methamphetamine metabolism in the brain is sufficient to alter behavioral sensitization, brain drug concentrations, and striatal dopamine and serotonin release. Moreover, day 1 methamphetamine-induced neurotransmitter release may be an important predictor of subsequent behavioral sensitization. This suggests the novel contribution of CYP2D in the brain to methamphetamine-induced behavioral sensitization and suggests that the wide variation in human brain CYP2D6 may contribute to differential methamphetamine responses and chronic effects.
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Affiliation(s)
- Marlaina R. Stocco
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario Canada ,Campbell Family Mental Health Research Institute, CAMH, Toronto, Ontario Canada
| | - Ahmed A. El-Sherbeni
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario Canada ,Department of Clinical Pharmacy, Tanta University, Tanta, Egypt
| | - Bin Zhao
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario Canada ,Campbell Family Mental Health Research Institute, CAMH, Toronto, Ontario Canada
| | - Maria Novalen
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario Canada ,Campbell Family Mental Health Research Institute, CAMH, Toronto, Ontario Canada
| | - Rachel F. Tyndale
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario Canada ,Campbell Family Mental Health Research Institute, CAMH, Toronto, Ontario Canada ,Department of Psychiatry, University of Toronto, Toronto, Ontario Canada
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Lennox RD, Cecchini-Sternquist M. Safety and tolerability of sauna detoxification for the protracted withdrawal symptoms of substance abuse. J Int Med Res 2018; 46:4480-4499. [PMID: 30209965 PMCID: PMC6259397 DOI: 10.1177/0300060518779314] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Objective Protracted drug withdrawal symptoms can last months or years after drug cessation, often precipitating a return to substance misuse. We evaluated the safety and preliminary health benefits of a unique chemical exposure regimen based on exercise, sauna and therapeutic nutrients. Methods This was a prospective evaluation of 109 individuals sequentially enrolled into a sauna detoxification component of a multi-modal, long-term residential substance abuse treatment centre. Results Data from medical charts, client self-reports and Short Form Health Survey (SF-36) responses indicated that the Hubbard sauna detoxification method was well tolerated, with a 99% completion rate, including one human immunodeficiency virus and nine hepatitis C positive clients. There were no cases of dehydration, overhydration or heat illness. Statistically significant improvements were seen in both mental and physical SF-36 scores at regimen completion, as well as in Addiction Severity Index and Global Appraisal of Individual Needs Short Screener change scores at rehabilitation program discharge, compared with enrolment. Conclusions The regimen lacked serious adverse events, had a very low discontinuation rate and high client-reported satisfaction. The SF-36 data indicated improved physical and emotional symptoms. Therefore, broader investigation of this sauna-based treatment regimen is warranted.
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Affiliation(s)
- Richard D Lennox
- Chestnut Global Partners, Chestnut Health Systems, Martin Luther King Drive, Bloomington, Illinois, USA
| | - Marie Cecchini-Sternquist
- Chestnut Global Partners, Chestnut Health Systems, Martin Luther King Drive, Bloomington, Illinois, USA
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Fattore L, Diana M. Drug addiction: An affective-cognitive disorder in need of a cure. Neurosci Biobehav Rev 2016; 65:341-61. [DOI: 10.1016/j.neubiorev.2016.04.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 03/24/2016] [Accepted: 04/11/2016] [Indexed: 12/22/2022]
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de la Torre R, Yubero-Lahoz S, Pardo-Lozano R, Farré M. MDMA, methamphetamine, and CYP2D6 pharmacogenetics: what is clinically relevant? Front Genet 2012; 3:235. [PMID: 23162568 PMCID: PMC3495276 DOI: 10.3389/fgene.2012.00235] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Accepted: 10/16/2012] [Indexed: 11/17/2022] Open
Abstract
In vitro human studies show that the metabolism of most amphetamine-like psychostimulants is regulated by the polymorphic cytochrome P450 isozyme CYP2D6. Two compounds, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA), were selected as archetypes to discuss the translation and clinical significance of in vitro to in vivo findings. Both compounds were chosen based on their differential interaction with CYP2D6 and their high abuse prevalence in society. Methamphetamine behaves as both a weak substrate and competitive inhibitor of CYP2D6, while MDMA acts as a high affinity substrate and potent mechanism-based inhibitor (MBI) of the enzyme. The MBI behavior of MDMA on CYP2D6 implies that subjects, irrespective of their genotype/phenotype, are phenocopied to the poor metabolizer (PM) phenotype. The fraction of metabolic clearance regulated by CYP2D6 for both drugs is substantially lower than expected from in vitro studies. Other isoenzymes of cytochrome P450 and a relevant contribution of renal excretion play a part in their clearance. These facts tune down the potential contribution of CYP2D6 polymorphism in the clinical outcomes of both substances. Globally, the clinical relevance of CYP2D6 polymorphism is lower than that predicted by in vitro studies.
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Affiliation(s)
- Rafael de la Torre
- Human Pharmacology and Clinical Neurosciences Research Group, Neurosciences Research Program, IMIM-Hospital del Mar Medical Research Institute Barcelona, Spain ; Department of Experimental and Health Sciences, Universitat Pompeu Fabra Barcelona, Spain
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Wu C, Jiang XL, Shen HW, Yu AM. Effects of CYP2D6 status on harmaline metabolism, pharmacokinetics and pharmacodynamics, and a pharmacogenetics-based pharmacokinetic model. Biochem Pharmacol 2009; 78:617-24. [PMID: 19445902 DOI: 10.1016/j.bcp.2009.05.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Revised: 05/06/2009] [Accepted: 05/07/2009] [Indexed: 12/31/2022]
Abstract
Harmaline is a beta-carboline alkaloid showing neuroprotective and neurotoxic properties. Our recent studies have revealed an important role for cytochrome P450 2D6 (CYP2D6) in harmaline O-demethylation. This study, therefore, aimed to delineate the effects of CYP2D6 phenotype/genotype on harmaline metabolism, pharmacokinetics (PK) and pharmacodynamics (PD), and to develop a pharmacogenetics mechanism-based compartmental PK model. In vitro kinetic studies on metabolite formation in human CYP2D6 extensive metabolizer (EM) and poor metabolizer (PM) hepatocytes indicated that harmaline O-demethylase activity (V(max)/K(m)) was about 9-fold higher in EM hepatocytes. Substrate depletion showed mono-exponential decay trait, and estimated in vitro harmaline clearance (CL(int), microL/min/10(6)cells) was significantly lower in PM hepatocytes (28.5) than EM hepatocytes (71.1). In vivo studies in CYP2D6-humanized and wild-type mouse models showed that wild-type mice were subjected to higher and longer exposure to harmaline (5 and 15mg/kg; i.v. and i.p.), and more severe hypothermic responses. The PK/PD data were nicely described by our pharmacogenetics-based PK model involving the clearance of drug by CYP2D6 (CL(CYP2D6)) and other mechanisms (CL(other)), and an indirect response PD model, respectively. Wild-type mice were also more sensitive to harmaline in marble-burying tests, as manifested by significantly lower ED(50) and steeper Hill slope. These findings suggest that distinct CYP2D6 status may cause considerable variations in harmaline metabolism, PK and PD. In addition, the pharmacogenetics-based PK model may be extended to define PK difference caused by other polymorphic drug-metabolizing enzyme in different populations.
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Affiliation(s)
- Chao Wu
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, The State University of New York, Buffalo, NY 14260-1200, USA
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Ray R, Tyndale RF, Lerman C. Nicotine dependence pharmacogenetics: role of genetic variation in nicotine-metabolizing enzymes. J Neurogenet 2009; 23:252-61. [PMID: 19169923 PMCID: PMC3772540 DOI: 10.1080/01677060802572887] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Nicotine-dependence pharmacogenetics research is an emerging field, and a number of studies have begun to characterize the clinical relevance and predictive power of genetic variation in drug-metabolizing enzymes and drug target genes for response to medication. The present paper focuses on evidence for the role of nicotine-metabolizing enzymes in smoking behavior and response to treatment. Nicotine metabolism is mediated primarily by cytochrome P450 2A6 (CYP2A6). Genetic variation in the CYP2A6 gene has been linked with several smoking behavior phenotypes. Individuals who carry null or reduced activity alleles for CYP2A6 smoke fewer cigarettes per day, are less dependent on nicotine, and may have an easier time quitting smoking. A phenotypic measure of CYP2A6 enzyme activity, defined as the ratio of the nicotine metabolites 3'hydroxycotinine/cotinine, also predicts successful quitting with the transdermal nicotine patch, and counseling alone. Faster metabolizers of nicotine respond more poorly to these treatments; however, they may be excellent candidates for non-nicotine therapies, such as bupropion. Inherited variation in the CYP2B6 enzyme is also associated with response to bupropion treatment and counseling alone for smoking cessation. Inhibition of the CYP2A6 enzyme to slow nicotine metabolism is a promising approach to increase nicotine availability and potentially reduce harm from tobacco smoking.
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Affiliation(s)
- Riju Ray
- Abramson Cancer Center and Department of Psychiatry, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Rachel F. Tyndale
- Centre for Addiction and Mental Health and Department of Pharmacology, Toronto, Ontario, Canada
| | - Caryn Lerman
- Abramson Cancer Center and Department of Psychiatry, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Raunio H, Pokela N, Puhakainen K, Rahnasto M, Mauriala T, Auriola S, Juvonen RO. Nicotine metabolism and urinary elimination in mouse: in vitro and in vivo. Xenobiotica 2008; 38:34-47. [PMID: 18098062 DOI: 10.1080/00498250701708539] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
This study aimed at elucidating the in vivo metabolism of nicotine both with and without inhibitors of nicotine metabolism. Second, the role of mouse CYP2A5 in nicotine oxidation in vitro was studied as such information is needed to assess whether the mouse is a suitable model for studying chemical inhibitors of the human CYP2A6. The oxidation of nicotine to cotinine was measured and the ability of various inhibitors to modify this reaction was determined. Nicotine and various inhibitors were co-administered to CD2F1 mice, and nicotine and urinary levels of nicotine and four metabolites were determined. In mouse liver microsomes anti-CYP2A5 antibody and known chemical inhibitors of the CYP2A5 enzyme blocked cotinine formation by 85-100%, depending on the pre-treatment of the mice. The amount of trans-3-hydroxycotine was five times higher than cotinine N-oxide, and ten times higher than nicotine N-1-oxide and cotinine. Methoxsalen, an irreversible inhibitor of CYP2A5, significantly reduced the metabolic elimination of nicotine in vivo, but the reversible inhibitors had no effect. It is concluded that the metabolism of nicotine in mouse is very similar to that in man and, therefore, that the mouse is a suitable model for testing novel chemical inhibitors of human CYP2A6.
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Affiliation(s)
- H Raunio
- Department of Pharmacology and Toxicology, University of Kuopio, Kuopio, Finland
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Lee AS, Gutiérrez-Arcelus M, Perry GH, Vallender EJ, Johnson WE, Miller GM, Korbel JO, Lee C. Analysis of copy number variation in the rhesus macaque genome identifies candidate loci for evolutionary and human disease studies. Hum Mol Genet 2008; 17:1127-36. [PMID: 18180252 DOI: 10.1093/hmg/ddn002] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Copy number variants (CNVs) are heritable gains and losses of genomic DNA in normal individuals. While copy number variation is widely studied in humans, our knowledge of CNVs in other mammalian species is more limited. We have designed a custom array-based comparative genomic hybridization (aCGH) platform with 385 000 oligonucleotide probes based on the reference genome sequence of the rhesus macaque (Macaca mulatta), the most widely studied non-human primate in biomedical research. We used this platform to identify 123 CNVs among 10 unrelated macaque individuals, with 24% of the CNVs observed in multiple individuals. We found that segmental duplications were significantly enriched at macaque CNV loci. We also observed significant overlap between rhesus macaque and human CNVs, suggesting that certain genomic regions are prone to recurrent CNV formation and instability, even across a total of approximately 50 million years of primate evolution ( approximately 25 million years in each lineage). Furthermore, for eight of the CNVs that were observed in both humans and macaques, previous human studies have reported a relationship between copy number and gene expression or disease susceptibility. Therefore, the rhesus macaque offers an intriguing, non-human primate outbred model organism with which hypotheses concerning the specific functions of phenotypically relevant human CNVs can be tested.
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Affiliation(s)
- Arthur S Lee
- Department of Pathology, Brigham and Women's Hospital, 221 Longwood Ave., Boston, MA 02115, USA
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Abstract
Accumulating data support the role of genetic factors in smoking initiation, progression to tobacco dependence, and smoking persistence. This review summarizes current research on the heritability of tobacco use phenotypes and genetic association studies of smoking-related behaviors. Although progress has been made in genetics research on smoking behavior, many studies have methodological limitations, including insufficient samples for detecting gene-gene and gene-environment interactions and use of less refined phenotypes. Pharmacogenetic investigations also are identifying variants in drug-metabolizing enzymes, receptors, and transporters that modify therapeutic response to smoking cessation medications; however, the field is relatively new, and most findings in this area have yet to be replicated. As this research advances, it will be important to study and address practical, economic, ethical, and social barriers to the translation of genetics research on tobacco use to clinical practice.
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Affiliation(s)
- Robert A Schnoll
- Department of Psychiatry, University of Pennsylvania, 3535 Market Street, Philadelphia, PA 19104, USA.
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Alonso-Navarro H, Martínez C, García-Martín E, Benito-León J, García-Ferrer I, Vázquez-Torres P, Puertas I, López-Alburquerque T, Agúndez JAG, Jiménez-Jiménez FJ. CYP2C19 polymorphism and risk for essential tremor. Eur Neurol 2006; 56:119-23. [PMID: 16960452 DOI: 10.1159/000095702] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2006] [Accepted: 07/12/2006] [Indexed: 11/19/2022]
Abstract
Many patients with essential tremor (ET) develop acute adverse effects to primidone. We investigated the association between CYP2C19 polymorphism (possibly related to primidone metabolism) and the risk for developing essential ET and acute adverse effects to primidone. Leukocytary DNA from 200 ET patients and 300 healthy controls was studied for the genotype CYP2C19 and the occurrence of CYP2C19 allelic variants by using allele-specific PCR amplification and Sma I and BamH I RFLP analyses. The frequencies of the genotype CYP2C19*1/CYP2C19*2 and of the allelic variant CYP2C19*2 were significantly higher in ET patients than in controls. The mean age at onset of ET did not differ significantly between patients with genotypes CYP2C19*1/CYP2C19*2andCYP2C19*1/CYP2C19*1. The frequencies of the genotype CYP2C19*1/CYP2C19*2 and the allelic variant CYP2C19*2 were similar in ET patients who developed acute adverse effects to primidone, in those who tolerated primidone and in controls; the frequencies were also similar in patients with head, voice, tongue and chin tremor compared with controls. These results suggest that heterozygosis CYP2C19*1/CYP2C19*2 is associated with the risk for ET, but not with the age at onset of ET, the presentation of acute side effects of primidone, or the existence of head, voice, tongue or chin tremor.
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Affiliation(s)
- Hortensia Alonso-Navarro
- Department of Medicine-Neurology, Hospital Príncipe de Asturias, Universidad de Alcalá, Alcalá de Henares, Spain
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Alonso-Navarro H, Jiménez-Jiménez FJ, García-Agúndez JA. Papel del polimorfismo genético CYP2C19 en los efectos adversos a fármacos y en el riesgo para diversas enfermedades. Med Clin (Barc) 2006; 126:697-706. [PMID: 16759580 DOI: 10.1157/13088772] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
There are a great number of polymorphic genes in the human genome. Many of them codify enzymes that metabolizes drugs and xenobiotic agents, including carcinogens. Among the better known of them, there are a number of isozymes of the microsomal oxidative system (CYP3A4, CYP2C9, CYP2C19 y CYP2D6). This article reviews the following issues: a) frequency of presentation of the "poor metabolizer" genotype and/or phenotype for substrates of CYP2C19; b) role of CYP2C19 polymorphism on the metabolism of some drugs (mephenytoine and other antiepileptic drugs, proton pump inhibitors, several antidepressants and anxyolitics, the antimalaria aggent proguanyl, and propranolol, among others, use this metabolic pathway), and c) possible role of CYP2C19 polymorphism in the risk for development of neoplasia and other diseases (systemic lupus erythematosus, psoriasis, hip osteonecrosis, Alzheimer's disease, amyotrophic lateral sclerosis, essential tremor).
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Abstract
Smoking is a complex behavior influenced by environ-mental and genetic factors. A number of twin studies demonstrate genetic influences on multiple aspects of smoking including initiation, dependence, continuation, amount consumed, and cessation. It is likely that this genetic risk involves a complex interaction between multiple genes in different biologic pathways. These may include genes involved in the general aspect of dependence (eg, genes within the dopaminergic system) and those more specific to nicotine dependence (eg, genes encoding nicotinic acetylcholine receptors and nicotine-metabolizing enzymes). Genome-wide linkage analyses and gene association studies provide approaches for identifying these genes. This review provides a brief highlight of data from some of the candidate gene association studies and discusses some of the discrepancies found in the literature. In addition, the authors have reviewed some recent studies examining how genetic variations in drug-metabolizing enzymes and drug targets can influence the response to treatment with drugs such as bupropion and nicotine.These latter studies provide the potential for maximizing treatment efficacy by individualizing the type, dosage, and duration of the treatment based on an individual's genotype/phenotype. Significant advances have been made in understanding the genetic contribution to smoking behaviors. These and future studies will provide potential directions for novel prevention and treatment strategies.
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Affiliation(s)
- Nael Al Koudsi
- Department of Pharmacology, Centre for Addiction and Mental Health, University of Toronto, Canada
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Haberl M, Anwald B, Klein K, Weil R, Fuss C, Gepdiremen A, Zanger UM, Meyer UA, Wojnowski L. Three haplotypes associated with CYP2A6 phenotypes in Caucasians. Pharmacogenet Genomics 2005; 15:609-24. [PMID: 16041240 DOI: 10.1097/01.fpc.0000171517.22258.f1] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The human cytochrome P450 2A6 (CYP2A6) enzyme metabolizes several xenobiotic compounds of clinical or toxicological importance. We aimed to identify genetic variants and major CYP2A6 haplotypes associated with CYP2A6 phenotypic variation. CYP2A6 mRNA level, protein level, activity and haplotypes were determined in Caucasian liver samples via real-time polymerase chain reaction, Western blot, coumarin 7-hydroxylation, DNA sequencing and genotyping, respectively. Phenotypes were then analyzed for associations with haplotypes. CYP2A6 transcript, protein and activity levels were correlated among each other. In 45 African-American, 156 Caucasian, 47 Chinese, 50 Japanese and 47 Korean DNA samples, we detected 95 different polymorphisms in the CYP2A6 gene, 49 of which had not been described previously. Caucasian variants formed 33 haplotypes which built four clades. Allele *9B and the CYP2A7/2A6 partial deletion allele CYP2A6*12B were both associated with decreased expression. The latter haplotype extends at least over 147 kb up into the CYP2B6 gene. A haplotype almost identical to allele *1A was associated with decreased expression and activity of CYP2A6 compared to all other haplotypes. In summary A CYP2A6*1A-like allele, *9B and *12B are major genetic determinants of CYP2A6 phenotype variation in Caucasians.
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Tomfohr J, Lu J, Kepler TB. Pathway level analysis of gene expression using singular value decomposition. BMC Bioinformatics 2005; 6:225. [PMID: 16156896 PMCID: PMC1261155 DOI: 10.1186/1471-2105-6-225] [Citation(s) in RCA: 253] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2005] [Accepted: 09/12/2005] [Indexed: 11/11/2022] Open
Abstract
Background A promising direction in the analysis of gene expression focuses on the changes in expression of specific predefined sets of genes that are known in advance to be related (e.g., genes coding for proteins involved in cellular pathways or complexes). Such an analysis can reveal features that are not easily visible from the variations in the individual genes and can lead to a picture of expression that is more biologically transparent and accessible to interpretation. In this article, we present a new method of this kind that operates by quantifying the level of 'activity' of each pathway in different samples. The activity levels, which are derived from singular value decompositions, form the basis for statistical comparisons and other applications. Results We demonstrate our approach using expression data from a study of type 2 diabetes and another of the influence of cigarette smoke on gene expression in airway epithelia. A number of interesting pathways are identified in comparisons between smokers and non-smokers including ones related to nicotine metabolism, mucus production, and glutathione metabolism. A comparison with results from the related approach, 'gene-set enrichment analysis', is also provided. Conclusion Our method offers a flexible basis for identifying differentially expressed pathways from gene expression data. The results of a pathway-based analysis can be complementary to those obtained from one more focused on individual genes. A web program PLAGE (Pathway Level Analysis of Gene Expression) for performing the kinds of analyses described here is accessible at .
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Affiliation(s)
- John Tomfohr
- Department of Biostatistics and Bioinformatics and Center for Bioinformatics and Computational Biology, Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina 27708, USA
| | - Jun Lu
- Department of Biostatistics and Bioinformatics and Center for Bioinformatics and Computational Biology, Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina 27708, USA
| | - Thomas B Kepler
- Department of Biostatistics and Bioinformatics and Center for Bioinformatics and Computational Biology, Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina 27708, USA
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Ozdemir V, Lerer B. Pharmacogenomics and the Promise of Personalized Medicine. DRUGS AND THE PHARMACEUTICAL SCIENCES 2005. [DOI: 10.1201/9780849359507.ch2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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Caron L, Karkazis K, Raffin TA, Swan G, Koenig BA. Nicotine addiction through a neurogenomic prism: ethics, public health, and smoking. Nicotine Tob Res 2005; 7:181-97. [PMID: 16036275 PMCID: PMC2613832 DOI: 10.1080/14622200500055251] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Studies are under way to examine the neurogenetic factors contributing to smoking behaviors. The combined approaches of genomics, molecular biology, neuroscience, and pharmacology are expected to fuel developments in pharmacogenetics, to create new genetic tests, and ultimately to provide the basis for innovative strategies for smoking cessation and prevention. The emergence of a neurogenomic understanding of nicotine addiction is likely to induce fundamental changes in popular, clinical, and public health views of smoking, which could significantly shape existing practices and policies to reduce tobacco use. Still a nascent area of research, nicotine addiction provides an excellent case study through which to anticipate key ethical and policy issues in both behavioral genetics and the neurogenomics of addictive behaviors.
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Affiliation(s)
- Lorraine Caron
- Agence d'évaluation des technologies et des modes d'intervention en santé, Montreal, Canada
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21
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Malaiyandi V, Sellers EM, Tyndale RF. Implications of CYP2A6 genetic variation for smoking behaviors and nicotine dependence. Clin Pharmacol Ther 2005; 77:145-58. [PMID: 15735609 DOI: 10.1016/j.clpt.2004.10.011] [Citation(s) in RCA: 169] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Nicotine is the primary addictive compound in tobacco smoke. In this review we summarize nicotine dependence and the genetics of smoking in brief before focusing on cytochrome P450 (CYP) 2A6. In humans nicotine is mainly inactivated to cotinine and CYP2A6 mediates approximately 90% of this conversion. Some, but not all, studies suggest that genetic variation in CYP2A6 may play a role in smoking. We review some of the recent findings on the influence of CYP2A6 genetic polymorphisms on nicotine kinetics, smoking behaviors, and how the gene appears to exert differential effects during various stages of smoking (eg, initiation, conversion to dependence, amount smoked during dependence, and quitting). These new findings will be put in the context of the discrepancies found in the literature. Implications of these recent findings on current and novel treatment approaches for smoking cessation and tobacco-related lung cancer will also be discussed.
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Affiliation(s)
- Viba Malaiyandi
- Department of Pharmacology and Medicine, 1 King's College Circle, University of Toronto, Canada M5S 1A8
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22
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Yamada H, Ishii Y, Oguri K. Metabolism of Drugs of Abuse: Its Contribution to the Toxicity and the Inter-Individual Differences in Drug Sensitivity. ACTA ACUST UNITED AC 2005. [DOI: 10.1248/jhs.51.1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Hideyuki Yamada
- Graduate School of Pharmaceutical Sciences, Kyushu University
| | - Yuji Ishii
- Graduate School of Pharmaceutical Sciences, Kyushu University
| | - Kazuta Oguri
- School of Pharmaceutical Sciences, Kyusyu University of Health and Welfare
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23
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Yu AM, Idle JR, Gonzalez FJ. Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates. Drug Metab Rev 2004; 36:243-77. [PMID: 15237854 DOI: 10.1081/dmr-120034000] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Cytochrome P450 2D6 (CYP2D6) is the first well-characterized polymorphic phase I drug-metabolizing enzyme, and more than 80 allelic variants have been identified for the CYP2D6 gene, located on human chromosome 22q13.1. Human debrisoquine and sparteine metabolism is subdivided into two principal phenotypes--extensive metabolizer and poor metabolizer--that arise from variant CYP2D6 genotypes. It has been estimated that CYP2D6 is involved in the metabolism and disposition of more than 20% of prescribed drugs, and most of them act in the central nervous system or on the heart. These drug substrates are characterized as organic bases containing one nitrogen atom with a distance about 5, 7, or 10 A from the oxidation site. Aspartic acid 301 and glutamic acid 216 were determined as the key acidic residues for substrate-enzyme binding through electrostatic interactions. CYP2D6 transgenic mice, generated using a lambda phage clone containing the complete wild-type CYP2D6 gene, exhibits enhanced metabolism and disposition of debrisoquine. This transgenic mouse line and its wild-type control are models for human extensive metabolizers and poor metabolizers, respectively, and would have broad application in the study of CYP2D6 polymorphism in drug discovery and development, and in clinical practice toward individualized drug therapy. Endogenous 5-methoxyindole- thylamines derived from 5-hydroxytryptamine were identified as high-affinity substrates of CYP2D6 that catalyzes their O-demethylations with high enzymatic capacity and specificity. Thus, polymorphic CYP2D6 may play an important role in the interconversions of these psychoactive tryptamines, including a crucial step in a serotonin-melatonin cycle.
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Affiliation(s)
- Ai-Ming Yu
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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24
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Metz CN, Gregersen PK, Malhotra AK. Metabolism and biochemical effects of nicotine for primary care providers. Med Clin North Am 2004; 88:1399-413, ix. [PMID: 15464104 DOI: 10.1016/j.mcna.2004.06.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Nicotine is a colorless and volatile liquid alkaloid naturally occurring in the leaves and stems of Nicotiana tabacum and Nicotiana rustica. Nicotine, the primary component of tobacco, is responsible for both tobacco product addiction (with chronic exposure) and the odor associated with tobacco. In addition to cigarettes, nicotine is found in chewing gum, transdermal patches, nasal spray, and sublingual tablets. Following its inhalation and absorption, nicotine and its metabolic products exert diverse physiologic and pharmacologic effects. This article covers the absorption and metabolism of nicotine, nicotine toxicity, pharmacologic effects of nicotine, nicotine-drug interactions, and the use of nicotine for the treatment of disease.
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Affiliation(s)
- Christine N Metz
- Laboratory of Medicinal Biochemistry, Center for Patient-Oriented Research, North Shore Long Island Jewish Research Institute, 350 Community Drive, Manhasset, NY 11030, USA.
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25
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Morrison A, Levy R. Toward individualized pharmaceutical care of East Asians: the value of genetic testing for polymorphisms in drug-metabolizing genes. Pharmacogenomics 2004; 5:673-89. [PMID: 15335288 DOI: 10.1517/14622416.5.6.673] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Research into the relationship between genetics and drug response has focused on polymorphisms in genes that encode drug-metabolizing enzymes, particularly the genes of cytochrome P450 superfamily 2, which affect the clearance of the anticoagulant warfarin, proton pump inhibitors, tricyclic antidepressants, and many other clinically relevant drugs. Much of this work has targeted East Asians, a genetically distinguishable and populous group. Researchers have identified polymorphisms that inactivate gene function, compared polymorphism frequencies in East-Asian and Caucasian populations, and determined the effects on the pharmacokinetic parameters of drugs. Detection in an individual of polymorphisms known to inactivate a drug-metabolizing enzyme is predictive of poor metabolism of drugs processed by that pathway, which itself may be predictive of an atypical drug response. Genetic tests can be used to screen for individuals with poor metabolizer phenotypes, with the ultimate goal of predicting the clinical effects of drugs.
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26
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Schoedel KA, Hoffmann EB, Rao Y, Sellers EM, Tyndale RF. Ethnic variation in CYP2A6 and association of genetically slow nicotine metabolism and smoking in adult Caucasians. PHARMACOGENETICS 2004; 14:615-26. [PMID: 15475735 DOI: 10.1097/00008571-200409000-00006] [Citation(s) in RCA: 209] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Genetically variable CYP2A6 is the primary enzyme that inactivates nicotine to cotinine. Our objective was to investigate allele frequencies among five ethnic groups and to investigate the relationship between genetically slow nicotine metabolic inactivation and smoking status, cigarette consumption, age of first smoking and duration of smoking. Chinese, Japanese, Canadian Native Indian, African-North American and Caucasian DNA samples were assessed for CYP2A6 allelic frequencies (CYP2A6*1B-*12,*1x2). Adult Caucasian non-smokers (n = 224) (1-99 cigarettes/lifetime) and smokers (n = 375) (> or = 100 cigarettes/lifetime) were assessed for demographics, tobacco/drug use history and DSM-IV dependence and genotyped for CYP2A6 alleles associated with decreased nicotine metabolism (CYP2A6*2, CYP2A6*4, CYP2A6*9, CYP2A6*12). CYP2A6 allele frequencies varied substantially among the ethnic groups. The proportion of Caucasian slow nicotine inactivators was significantly lower in current, DSM-IV dependent smokers compared to non-smokers [7.0% and 12.5%, respectively, P = 0.03, odds ratio (OR) = 0.52; 95% confidence interval (CI) 0.29-0.95]; non-dependent smokers showed similar results. Daily cigarette consumption (cigarettes/day) was significantly (P = 0.003) lower for slow (21.3; 95% CI 17.4-25.2) compared to normal inactivators (28.2; 95% CI 26.4-29.9); this was observed only in DSM-IV dependent smokers. Slow inactivators had a significantly (P = 0.03) lower age of first smoking compared to normal inactivators (13.0 years of age; 95% CI 12.1-14.0 versus 14.2; 95% CI 13.8-14.6), and a trend towards smoking for a shorter duration. This study demonstrates that slow nicotine inactivators are less likely to be adult smokers (dependent or non-dependent). Slow inactivators also smoked fewer cigarettes per day and had an earlier age of first smoking (only dependent smokers).
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Affiliation(s)
- Kerri A Schoedel
- Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada
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27
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Abdel-Rahman SM, Kauffman RE. THEINTEGRATION OFPHARMACOKINETICS ANDPHARMACODYNAMICS: Understanding Dose-Response. Annu Rev Pharmacol Toxicol 2004; 44:111-36. [PMID: 14744241 DOI: 10.1146/annurev.pharmtox.44.101802.121347] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Pharmacokinetic (PK) and pharmacodynamic (PD) studies have proven to be powerful and instructive tools, particularly in elucidating important aspects of human pharmacology. Nevertheless, they remain imperfect tools in that they only allow researchers to indirectly extrapolate, through computational modeling, the dynamic processes of drug action. Furthermore, neither tool alone provides a complete nor necessarily relevant picture of drug action. This review explores the utility and applications of PK and PD in the study of drugs, provides examples of lessons learned from their application to studies of human pharmacology, points out some of their limitations, and advances the thesis that these tools ideally should be employed together in an integrated approach. As we continue to apply these tools across the continuum of age and disease, they provide a powerful means to enhance our understanding of drug action, drug interactions, and intrinsic host factors that influence pharmacologic response.
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Affiliation(s)
- Susan M Abdel-Rahman
- Division of Pediatric Clinical Pharmacology and Medical Toxicology, The Children's Mercy Hospital and Clinics, Department of Pediatrics, University of Missouri-Kansas City, Kansas City, Missouri 64108, USA.
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28
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Domino EF, Kadoya C, Matsuoka S, Ni L, Fedewa KS. Comparative American and Japanese tobacco smoke uptake parameters after overnight tobacco deprivation. Prog Neuropsychopharmacol Biol Psychiatry 2003; 27:973-84. [PMID: 14499314 DOI: 10.1016/s0278-5846(03)00157-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
American and Japanese overnight deprived tobacco smokers were compared with respect to expired CO, plasma nicotine and cotinine, and red cell carboxyhemoglobin. The participants were 51 of 59 American and 55 of 86 Japanese cigarette smokers of mixed gender who met similar strict criteria. Female and male American tobacco smokers were similar in mean age, number of cigarettes smoked per day, machine-rated nicotine and tar yield per cigarette and per 24 h plasma cotinine, calculated previous 24 h nicotine dose, and exhaled CO. Only mean plasma nicotine levels were significantly higher in American females. American and Japanese female smokers had similar tobacco uptake parameters. American and Japanese male smokers differed; the latter had higher plasma nicotine and lower cotinine levels as well as calculated 24 h dose of nicotine and lower exhaled CO. Japanese females and males were similar in all tobacco smoke uptake parameters. When the two racial groups were compared, irrespective of gender, the only statistically significant differences were lower mean exhaled CO levels and percent COHb in the Japanese. It is concluded that Japanese males inhale cigarettes in moderation compared to Americans. The results are discussed in relation to known ethnic, social, and genetic differences in CYP2A6 gene polymorphism.
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Affiliation(s)
- Edward F Domino
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109-0632, USA.
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29
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Domino EF, Ni L. Clinical phenotyping strategies in selection of tobacco smokers for future genotyping studies. Prog Neuropsychopharmacol Biol Psychiatry 2002; 26:1071-8. [PMID: 12452528 DOI: 10.1016/s0278-5846(02)00224-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Various behavioral and chemical measures were studied as potential simplified phenotyping techniques in overnight abstinent tobacco smokers. Irrespective of the machine-rated nicotine delivery (yield) of the cigarette used, there was a statistically significant correlation between the number of cigarettes consumed per day and overnight abstinence plasma cotinine concentration (r=.88) and its calculated nicotine dose per day (r=.88). Exhaled carbon monoxide (CO) levels correlated well with the number of cigarettes smoked (r=.83) and the Fagerström dependence scores (r=.85). The greater the Fagerström scores, the greater the daily cigarette consumption and plasma cotinine concentrations. After overnight abstinence, the baseline mean+/-S.D. heart rate was 62.9+/-10.0/min, the systolic blood pressure was 115.6+/-13.3 mm Hg and the diastolic blood pressure was 67.1+/-10.9 mm Hg. There were no statistically significant gender differences. Persons who were outliers on any measure are potential candidates for future genotyping studies. Preliminary guidelines of what is needed are described.
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Affiliation(s)
- Edward F Domino
- Department of Pharmacology, University of Michigan. Ann Arbor, MI 48109-0632, USA.
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30
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Howard LA, Sellers EM, Tyndale RF. The role of pharmacogenetically-variable cytochrome P450 enzymes in drug abuse and dependence. Pharmacogenomics 2002; 3:185-99. [PMID: 11972441 DOI: 10.1517/14622416.3.2.185] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
The risk of drug dependence is determined by the interaction of drug, individual and environment. 'Pharmacogenetics' is the study of the influence of heredity on the response to drugs and their fate in the body; these studies aim to improve the understanding of inter-individual variability in drug response. The authors have applied this research approach to the study of drug metabolism and dependence. Specifically the interaction of genetically variable hepatic cytochrome P450 (CYP) enzymes and their effect on self-administration of drugs has been examined. Many drugs of abuse are substrates (e.g., amphetamines, codeine, nicotine) or inhibitors (e.g., (-)-cocaine) of polymorphic CYPs. Drug metabolism by genetically polymorphic enzymes can have significant clinical implications relating to drug toxicity, therapeutic failure, drug-drug interactions, disease susceptibility and abuse liability. There is good evidence that drug metabolism by genetically variable CYPs can influence the risk of drug dependence, the amount of drug consumed by dependent individuals and some of the toxicities associated with drug-taking behavior. It is anticipated that pharmacogenetics will be used to identify individuals at a greater risk for specific drug dependencies, provide information that can lead to novel treatment and prevention approaches as well as provide guidance for individualization of treatment choice.
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Affiliation(s)
- Lisa A Howard
- Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
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31
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Tyndale RF, Sellers EM. Genetic variation in CYP2A6-mediated nicotine metabolism alters smoking behavior. Ther Drug Monit 2002; 24:163-71. [PMID: 11805739 DOI: 10.1097/00007691-200202000-00026] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Approximately 50% of the initiation of tobacco dependence is genetically influenced, whereas maintenance of dependent smoking behavior and amount smoked have approximately 70% genetic contribution (1-5). Determining the variation in nicotine's inactivation is important because of nicotine's role in producing tobacco dependence and regulating smoking patterns (6-11). The genetically polymorphic CYP2A6 enzyme is responsible for the majority of the metabolic inactivation of nicotine to cotinine (12-14). Both in vitro and in vivo studies have demonstrated considerable interindividual variation in CYP2A6 activity (15-17). CYP2A6 is genetically polymorphic, individuals carrying inactive CYP2A6 alleles have decreased nicotine metabolism, are less likely to become smokers and if they do, they smoke fewer cigarettes per day (13,18,19). The decrease in smoking behavior was confirmed by measuring carbon monoxide (CO, a measure of smoke inhalation) levels, plasma and urine nicotine and cotinine levels, and cigarette counts (13,18,19). A duplication variant in the CYP2A6 gene locus has been identified which increases nicotine inactivation and increases smoking (19). CYP2A6 can also activate tobacco smoke procarcinogens (e.g. NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone); current studies are investigating the role of CYP2A6 in risk for lung cancer. Based on these epidemiologic data it was postulated that inhibition of CYP2A6 activity might be useful in a therapeutic context. Kinetic studies in humans indicated that selective CYP2A6 inhibitors decrease the metabolic removal of nicotine. It was also shown that inhibiting CYP2A6 in vivo (phenocopying, or mimicking the genetic defect) in smokers results in decreased smoking, making nicotine orally bioavailable, and the rerouting of procarcinogens to detoxifying pathways (20-22).
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Xu C, Rao YS, Xu B, Hoffmann E, Jones J, Sellers EM, Tyndale RF. An in vivo pilot study characterizing the new CYP2A6*7, *8, and *10 alleles. Biochem Biophys Res Commun 2002; 290:318-24. [PMID: 11779172 DOI: 10.1006/bbrc.2001.6209] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We developed genotyping assays for CYP2A6*7 (Ile471Thr) and CYP2A6*8 (Arg485Leu). We found higher allelic frequencies in Japanese and Chinese versus Caucasians and identified an allele in which both substitutions occur together (CYP2A6*10). We created a homology model for predicting the impact of allelic variants on enzymatic activity and subsequently tested this in vivo in a pilot kinetic study. Consistent with our homology model predictions, we found (i) that CYP2A6*7 produces an enzyme that has decreased (not inactive) activity for metabolizing nicotine and coumarin; (ii) that CYP2A6*8 is unlikely to affect catalytic activity in vivo; and (iii) that having both substitutions together on an allele (CYP2A6*10) dramatically reduces function and may be fully inactive for some substrates. In conclusion, this study identifies, at relatively high frequency in Asians, an allele with decreased activity (may be substrate selective), a fully functional allele, and an allele containing both substitutions in which function is dramatically reduced.
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Affiliation(s)
- C Xu
- Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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33
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Chew M, White JM, Somogyi AA, Bochner F, Irvine RJ. Precipitated withdrawal following codeine administration is dependent on CYP genotype. Eur J Pharmacol 2001; 425:159-64. [PMID: 11513833 DOI: 10.1016/s0014-2999(01)01185-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The role of metabolic polymorphism in the development of physical dependence to codeine was assessed in cytochrome P450 2D2 (CYP2D2) deficient Dark Agouti and CYP2D2 intact Sprague-Dawley rats by assessment of the severity of naloxone precipitated withdrawal after codeine and morphine administration. Plasma morphine concentrations after codeine were significantly higher (P<0.01) in Sprague-Dawley than in Dark Agouti rats with metabolic ratios of 0.71 +/- 0.27 and 0.07 +/- 0.04, respectively. Withdrawal after codeine resulted in significantly greater hypothermia (3.5-4 degrees C, P<0.0001) in Sprague-Dawley animals compared to the other groups. Body weight loss was similar for all groups ranging from 6.2 +/- 0.4 to 8.2 +/- 0.6 g. When strain and treatment data were combined, a relationship between body temperature and plasma morphine concentration could be described by the inverse Hill equation (r(2)=0.76, EC(50)=556 +/- 121 ng/ml, n=2.9 +/- 1.5). These data indicate that dependence and withdrawal after codeine administration are dependent on its bioconversion to morphine.
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Affiliation(s)
- M Chew
- Department of Clinical and Experimental Pharmacology, Adelaide University, 5005, Adelaide, Australia
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