Interethnic variation of drug metabolism

Pharmacokinetics of aspirin: evaluating shortcomings in the literature

INTRODUCTION

Aspirin is known for its therapeutic benefits in preventing strokes and relieving pain. However, it is toxic to some individuals, and the biological mechanisms causing toxicity are unknown. Limited literature is available on the role of glycine conjugation as the principal pathway in aspirin detoxification. Previous studies have quantified this two-step enzyme reaction as a singular enzymatic process. Consequently, the individual contributions of these enzymes to the kinetics remain unclear.

AREAS COVERED

This review summarized the available information on the pharmacokinetics and detoxification of aspirin by the glycine conjugation pathway. Literature searches were conducted using Google Scholar and the academic journal databases accessible through the North-West University Library. Furthermore, the factors affecting interindividual variation in aspirin metabolism and what is known regarding aspirin toxicity were discussed.

EXPERT OPINION

The greatest drawback in understanding the pharmacokinetics of aspirin is the limited information available on the substrate preference of the xenobiotic ligase (ACSM) responsible for activating salicylate to salicyl-CoA. Furthermore, previous pharmacokinetic studies did not consider the contribution of other substrates from the diet or genetic variants, to the detoxification rate of glycine conjugation. Impaired glycine conjugation might contribute to adverse health effects seen in Reye's syndrome and cancer.

Impact of cytochrome P450 2D6 polymorphisms on decision-making and clinical outcomes in adjuvant hormonal therapy for breast cancer

BACKGROUND

There are concerns that tamoxifen is less effective in Asian women because of the high prevalence of impaired function cytochrome P450 2D6 (CYP2D6) polymor-phisms.

AIM

To evaluate how knowledge of CYP2D6 genotype impacted the choice of hormonal agent and how CYP2D6 genotype and agent were associated with clinical outcomes.

METHODS

Eighty-two women were recruited. Seventy-eight completed CYP2D6 genotyping and were categorized into poor, intermediate (IM) and extensive or ultra metabolizer phenotypes. Women with poor metabolizer and IM phenotypes were recommended aromatase inhibitors as the preferred agent.

RESULTS

More than 70% of the women had an IM phenotype, 32% an extensive or ultra metabolizer phenotype, and 0% had a poor metabolizer phenotype. Regardless of genotype, more women opted for aromatase inhibitors. Overall, 80% of women completed 5 years of hormonal therapy. Five women developed recurrence, 3 contralateral breast cancer, 5 died, and 1 was diagnosed with a second primary cancer. Five-year recurrence-free and overall survival were slightly better in women with the extensive or ultra metabolizer phenotype compared to those with the IM phenotype, though not statistically significant [P = 0.743, hazard ratio (HR): 1.441, 95% confidence interval (CI): 0.191 to 10.17 and P = 0.798, HR: 1.327, 95%CI: 0.172 to 9.915, respectively]. Women receiving aromatase inhibitors also appeared to have a better, but also nonsignificant, 5-year recurrence-free and overall survival (P = 0.253, HR: 0.368, 95%CI: 0.031 to 0.258 and P = 0.292, HR: 0.252, 95%CI: 0.005 to 4.951, respectively).

CONCLUSION

The IM phenotype was highly prevalent but was not associated with clinical outcome.

Pazopanib in advanced soft tissue sarcomas

Pazopanib is the first and only tyrosine kinase inhibitor currently approved for the treatment of multiple histological subtypes of soft tissue sarcoma (STS). Initially developed as a small molecule inhibitor of vascular endothelial growth factor receptors, preclinical work indicates that pazopanib exerts an anticancer effect through the inhibition of both angiogenic and oncogenic signaling pathways. Following the establishment of optimal dosing and safety profiles in early phase studies and approval for the treatment of advanced renal cell carcinoma, pazopanib was investigated in STS. A landmark phase III randomized study demonstrated improved progression-free survival with pazopanib compared to that with placebo in pretreated patients with STS of various subtypes. The efficacy of pazopanib in specific STS subtypes has been further described in real-world-based case series in both mixed and subtype-specific STS cohorts. At present, there are no clinically validated predictive biomarkers for use in selecting patients with advanced STS for pazopanib therapy, limiting the clinical effectiveness and cost-effectiveness of the drug. In this review, we summarize the preclinical and clinical data for pazopanib, outline the evidence base for its effect in STS and explore reported studies that have investigated putative biomarkers.

Analyses of the genetic diversity and protein expression variation of the acyl: CoA medium-chain ligases, ACSM2A and ACSM2B

Benzoate (found in milk and widely used as preservative), salicylate (present in fruits and the active component of aspirin), dietary polyphenols produced by gut microbiota, metabolites from organic acidemias, and medium-chain fatty acids (MCFAs) are all metabolised/detoxified by the glycine conjugation pathway. Xenobiotics are first activated to an acyl-CoA by the mitochondrial xenobiotic/medium-chain fatty acid: CoA ligases (ACSMs) and subsequently conjugated to glycine by glycine N-acyltransferase (GLYAT). The MCFAs are activated to acyl-CoA by the ACSMs before entering mitochondrial β-oxidation. This two-step enzymatic pathway has, however, not been thoroughly investigated and the biggest gap in the literature remains the fact that studies continuously characterise the pathway as a one-step reaction. There are no studies available on the interaction/competition of the various substrates involved in the pathway, whilst very little research has been done on the ACSM ligases. To identify variants/haplotypes that should be characterised in future detoxification association studies, this study assessed the naturally observed sequence diversity and protein expression variation of ACSM2A and ACSM2B. The allelic variation, haplotype diversity, Tajima's D values, and phylogenetic analyses indicated that ACSM2A and ACSM2B are highly conserved. This confirmed an earlier hypothesis that the glycine conjugation pathway is highly conserved and essential for life as it maintains the CoA and glycine homeostasis in the liver mitochondria. The protein expression analyses showed that ACSM2A is the predominant transcript in liver. Future studies should investigate the effect of the variants identified in this study on the substrate specificity of these proteins.

Xenobiotic/medium chain fatty acid: CoA ligase - a critical review on its role in fatty acid metabolism and the detoxification of benzoic acid and aspirin

INTRODUCTION

Activation of fatty acids by the acyl-CoA synthetases (ACSs) is the vital first step in fatty acid metabolism. The enzymatic and physiological characterization of the human xenobiotic/medium chain fatty acid: CoA ligases (ACSMs) has been severely neglected even though xenobiotics, such as benzoate and salicylate, are detoxified through this pathway.

AREAS COVERED

This review will focus on the nomenclature and substrate specificity of the human ACSM ligases; the biochemical and enzymatic characterization of ACSM1 and ACSM2B; the high sequence homology of the ACSM2 genes (ACSM2A and ACSM2B) as well as what is currently known regarding disease association studies.

EXPERT OPINION

Several discrepancies exist in the current literature that should be taken note of. For example, the single nucleotide polymorphisms (SNPs) reported to be associated with aspirin metabolism and multiple risk factors of metabolic syndrome are incorrect. Kinetic data on the substrate specificity of the human ACSM ligases are non-existent and currently no data exist on the influence of SNPs on the enzyme activity of these ligases. One of the biggest obstacles currently in the field is that glycine conjugation is continuously studied as a one-step process, which means that key regulatory factors of the two individual steps remain unknown.

Pharmacogenetics: Its Place in Medicine and Biology

A young science serves its purpose if it leads not only to new knowledge, but to new insights and concepts. This article opens with examples to illustrate some former thinking that the introduction of pharmacogenetic has overcome. Pharmacogenetic case histories from discovery to the present illustrate the interlocking of observations, technical advances, and changing concepts. There are striking biological similarities between pharmacogenetics and those inborn factors that cause resistance to infectious disease: Both represent person-to-person variations that may help the survival of populations, one when facing massive toxic exposures, the other when facing plagues and epidemics. Thus pharmacogenetics represents a biologically necessary variability of the defenses against chemical intruders, and this includes drugs. While this variability is desirable, drug toxicity occurring on the basis of this variability must be avoided. The most successful defendants against toxicity due to polymorphic (ie, high incidence) variants should be the designers of new drugs. The only defender concerned with rare variants can be the attentive clinician.

Pharmacogenetics of Agents Acting on the Central Nervous System

This article will review the various agents affecting the central nervous system (CNS) such as the analgesics, antidepressants, anticonvulsants, antipsychotics, and benzodiazepines. Most of the research in pharmacogenetics with the CNS agents have been conducted in the antidepressants. The cytochrome 450 IID6 isozyme system has been shown to influence the disposition of the antidepressants and antipsychotics. Amitriptyline metabolism to nortriptyline and nortriptyline conversion to its 10-OH metabolite were shown to be influenced by the IID6 isozyme. Interestingly, imipramine metabolism to desipramine is only partially related to the IID6 isozyme. Biotransformation of imipramine to its 2-OH metabolite was shown to be affected by the IID6 isozyme, but its metabolism to the 10-OH remains to be investigated. Of the antipsychotic drugs, haloperidol and thioridazine are two agents most studied. Haloperidol is converted to a reduced metabolite via a ketone reductase enzyme. The reduced metabolite is oxidized back to Haloperidol. This oxidation pathway was reported to be affected by the IID6 isozyme. Thioridazine metabolism to mesoridazine and conversion of codeine to morphine appear to be also influenced by CP-450 IID6. Other 450 isozymes are reported to be involved with other CNS agents.

A review of the Institute of Medicine's analysis of using chimpanzees in biomedical research

We argue that the recommendations made by the Institute of Medicine's 2011 report, Chimpanzees in Biomedical and Behavioral Research: Assessing the Necessity, are methodologically and ethically confused. We argue that a proper understanding of evolution and complexity theory in terms of the science and ethics of using chimpanzees in biomedical research would have had led the committee to recommend not merely limiting but eliminating the use of chimpanzees in biomedical research. Specifically, we argue that a proper understanding of the difference between the gross level of examination of species and examinations on finer levels can shed light on important methodological and ethical inconsistencies leading to ignorance of potentially unethical practices and policies regarding the use of animals in scientific research.

The impact of genetic factors on response to anaesthetics

In recent years, exceptional progress has been observed in pharmacogenetics, i.e. investigations of inherited conditioning of the organism's response to drugs or xenobiotics. On the other hand, modern molecular biology techniques have been implemented, making it possible to perform studies determining the involvement of genetic factors in differing responses to agents employed in general anaesthesia. Unexpected and incorrect response of the organism to the administration of specific anaesthetics is most commonly associated with a genetic defect of the metabolic pathway of a given agent or its receptor. The majority of agents used in anaesthesia are metabolised in the liver by the cytochrome P450 superfamily enzymes (CYPs) and phase II drug-metabolising enzymes: glutathione S-transferases (GSTs), sulphotransferases (SULTs), UDP-glucuronosyltransferases (UGTs) and NAD(P)H:quinone oxidoreductase (NQO1). Propofol is presently widely used for gastrointestinal (GI) and several other procedures. Among genes associated with metabolism of the most commonly applied anaesthetics such as propofol and sevoflurane, the following ones can be mentioned: CYP2E1, CYP2B6, CYP2C9, GSTP1, UGT1A9, SULT1A1 and NQO1. Moreover, the basic mechanism of propofol action involves its interaction with an ionotropic receptor GABAA inhibiting transfer of nerve impulses. Molecular studies have shown that polymorphic changes in GABRG2 receptor gene turn out to be important in the propofol anaesthesia. Planning of optimal anaesthesia can be considerably assisted by the determination of genetic factors of prognostic value taking advantage of genotyping and making it possible to select anaesthetics and reduce risk of side effects as well as undesirable actions.

Considering CYP1A2 phenotype and genotype for optimizing the dose of olanzapine in the management of schizophrenia

INTRODUCTION

Schizophrenia, a mental disorder, is a debilitating condition which typically strikes young people in their early 20's. Antipsychotic medications are widely prescribed for the treatment of schizophrenia however a balancing act is necessary to provide the correct dose to each patient. It is suggested that a large number of patients discontinue antipsychotic pharmacotherapy because the treatments provided do not always reduce the positive symptoms of the disease, while many have adverse effects on the patients. This implies that neither the incorrect drug nor the optimal dosage for that patient is achieved.

AREAS COVERED

The current review investigates variability in response to olanzapine with a specific focus on the common intrinsic and extrinsic factors that influence both olanzapine and CYP1A2 activity. Furthermore, the authors discuss the utilization of phenotyping and genotyping of CYP1A2 and their potential utility in clinical practice for olanzapine dosing regimens. The authors also consider the potential of pharmacometrics compared to pharmacogenomics as a tool to personalize medicine.

EXPERT OPINION

Careful consideration must be given to the impact of a genetic variant on the disposition of a drug prior to implementing genetic 'tests' to determine response. CYP1A2 phenotypic assessment can yield important information regarding the disposition of olanzapine; however, it relies on the accuracy of the metric and the minimal impact of other metabolic pathways. The application of pharmacometrics provides an effective method to establish covariates that significantly influence olanzapine disposition which can incorporate phenotype and/or genotype.

Management of chronic kidney disease and dialysis in homeless persons

End-stage renal disease and dialysis are complicated illnesses to manage in homeless persons, who often suffer medical comorbidities, psychiatric disease, cognitive impairment and addictions; descriptions of this population and management strategies are lacking. A retrospective review of dialysis patients who were homeless or unstably housed was undertaken at an urban academic Canadian center from 2001 to 2011. Electronic hospital records were analyzed for demographic, housing, medical, and psychiatric history, dialysis history, adherence to treatment, and outcomes. Two detailed cases of homeless patients with chronic kidney disease are presented. Eleven homeless dialysis patients with a mean age of 52.7±12.3 years, mostly men and mostly from minority groups were dialyzed for 41.1±29.2 months. Most resided permanently in shelters, eventually obtained fistula access, and were adherent to dialysis schedules. Patients were often nonadherent to pre-dialysis management, resulting in emergency starts. Many barriers to care for homeless persons with end-stage kidney disease and on dialysis are identified, and management strategies are highlighted. Adherence is optimized with shelter-based health care and intensive team-oriented case management.

Genetic variability of drug-metabolizing enzymes: the dual impact on psychiatric therapy and regulation of brain function

Polymorphic drug-metabolizing enzymes (DMEs) are responsible for the metabolism of the majority of psychotropic drugs. By explaining a large portion of variability in individual drug metabolism, pharmacogenetics offers a diagnostic tool in the burgeoning era of personalized medicine. This review updates existing evidence on the influence of pharmacogenetic variants on drug exposure and discusses the rationale for genetic testing in the clinical context. Dose adjustments based on pharmacogenetic knowledge are the first step to translate pharmacogenetics into clinical practice. However, also clinical factors, such as the consequences on toxicity and therapeutic failure, must be considered to provide clinical recommendations and assess the cost-effectiveness of pharmacogenetic treatment strategies. DME polymorphisms are relevant not only for clinical pharmacology and practice but also for research in psychiatry and neuroscience. Several DMEs, above all the cytochrome P (CYP) enzymes, are expressed in the brain, where they may contribute to the local biochemical homeostasis. Of particular interest is the possibility of DMEs playing a physiological role through their action on endogenous substrates, which may underlie the reported associations between genetic polymorphisms and cognitive function, personality and vulnerability to mental disorders. Neuroimaging studies have recently presented evidence of an effect of the CYP2D6 polymorphism on basic brain function. This review summarizes evidence on the effect of DME polymorphisms on brain function that adds to the well-known effects of DME polymorphisms on pharmacokinetics in explaining the range of phenotypes that are relevant to psychiatric practice.

Systematic reviews of animal models: methodology versus epistemology

Systematic reviews are currently favored methods of evaluating research in order to reach conclusions regarding medical practice. The need for such reviews is necessitated by the fact that no research is perfect and experts are prone to bias. By combining many studies that fulfill specific criteria, one hopes that the strengths can be multiplied and thus reliable conclusions attained. Potential flaws in this process include the assumptions that underlie the research under examination. If the assumptions, or axioms, upon which the research studies are based, are untenable either scientifically or logically, then the results must be highly suspect regardless of the otherwise high quality of the studies or the systematic reviews. We outline recent criticisms of animal-based research, namely that animal models are failing to predict human responses. It is this failure that is purportedly being corrected via systematic reviews. We then examine the assumption that animal models can predict human outcomes to perturbations such as disease or drugs, even under the best of circumstances. We examine the use of animal models in light of empirical evidence comparing human outcomes to those from animal models, complexity theory, and evolutionary biology. We conclude that even if legitimate criticisms of animal models were addressed, through standardization of protocols and systematic reviews, the animal model would still fail as a predictive modality for human response to drugs and disease. Therefore, systematic reviews and meta-analyses of animal-based research are poor tools for attempting to reach conclusions regarding human interventions.

Animal models and conserved processes

BACKGROUND

The concept of conserved processes presents unique opportunities for using nonhuman animal models in biomedical research. However, the concept must be examined in the context that humans and nonhuman animals are evolved, complex, adaptive systems. Given that nonhuman animals are examples of living systems that are differently complex from humans, what does the existence of a conserved gene or process imply for inter-species extrapolation?

METHODS

We surveyed the literature including philosophy of science, biological complexity, conserved processes, evolutionary biology, comparative medicine, anti-neoplastic agents, inhalational anesthetics, and drug development journals in order to determine the value of nonhuman animal models when studying conserved processes.

RESULTS

Evolution through natural selection has employed components and processes both to produce the same outcomes among species but also to generate different functions and traits. Many genes and processes are conserved, but new combinations of these processes or different regulation of the genes involved in these processes have resulted in unique organisms. Further, there is a hierarchy of organization in complex living systems. At some levels, the components are simple systems that can be analyzed by mathematics or the physical sciences, while at other levels the system cannot be fully analyzed by reducing it to a physical system. The study of complex living systems must alternate between focusing on the parts and examining the intact whole organism while taking into account the connections between the two. Systems biology aims for this holism. We examined the actions of inhalational anesthetic agents and anti-neoplastic agents in order to address what the characteristics of complex living systems imply for inter-species extrapolation of traits and responses related to conserved processes.

CONCLUSION

We conclude that even the presence of conserved processes is insufficient for inter-species extrapolation when the trait or response being studied is located at higher levels of organization, is in a different module, or is influenced by other modules. However, when the examination of the conserved process occurs at the same level of organization or in the same module, and hence is subject to study solely by reductionism, then extrapolation is possible.

Ethnopsychopharmacology considerations for Asians and Asian Americans

Asians comprise more than 60% of the world's population and are the fastest growing minority group in the United States. Today's psychiatrist must learn to recognize and appreciate the unique factors that influence mental health outcomes in this group. Asian Americans are affected by psychiatric disorders at similar rates as non-Asians, but are significantly underrepresented in psychiatric clinics. When Asians and Asian Americans do present for psychiatric treatment, they often do so with higher severity of illness, and variable levels of compliance. Studies over the past three decades have suggested that pharmacokinetic and pharmacodynamic profiles of various psychotropic medications may be different in Asians, leading to differences in dosage requirements and side-effect profiles. These variations appear to be largely determined by genetic predisposition, but are also influenced by other factors such as environment, social support, cultural perceptions, and physicians' prescribing habits. In this paper, we provide an overview of biological and socio-cultural issues as they relate to psychopharmacology in Asians and Asian Americans, with the hope that a better understanding of these issues will lead to improved mental health care delivery to this population both in the United States, as well as in Asian countries.

Developmental pharmacology

Understanding the pharmacokinetics and pharmacodynamics of drugs used in psychopharmacology across the pediatric age spectrum from infants to adolescents represents a major challenge for clinicians. In pediatrics, treatment protocols use either standard dose reductions for these drugs for children below a certain age or use less conventional parameters such as weight for allometric dosing. The rationale behind this, however, is often lacking. In this review current available data on the developmental changes in absorption, distribution, metabolism, and elimination of drugs are presented with a specific focus on metabolic pathways, indicating significant differences in the development of enzymes involved in the biotransformation of drugs used in psychopharmacology. Major emphasis will be given to the genetic variation in CYP2D6 activity, the most important enzyme for the metabolism of many psychotropic medications. Finally, this review will summarize the role of the developmental pharmacologist in ensuring rational use of drugs in children with developmental disabilities and in translating pharmacological concepts from the bench to the clinic.

CYP2D6 genotype in relation to perphenazine concentration and pituitary pharmacodynamic tissue sensitivity in Asians: CYP2D6–serotonin–dopamine crosstalk revisited

OBJECTIVES

Hyperprolactinemia is a common side effect of first-generation antipsychotics mediated by antagonism of dopaminergic neurotransmission in the pituitary. Most first-generation antipsychotics are metabolized by CYP2D6 in the liver. Further, CYP2D6 is expressed in the human brain as a 5-methoxyindolethylamine O-demethylase potentially contributing to regeneration of serotonin from 5-methoxytryptamine. As dopaminergic neurotransmission is subject to regulation by serotonin, CYP2D6 may exert a nuanced (serotonergic) influence on dopaminergic tone in the pituitary. CYP2D6*10 is an allele associated with reduced enzyme function and occurs in high frequency (about 50%) in Asians. We prospectively evaluated significance of CYP2D6 genetic variation for prolactin response to perphenazine (a model first-generation antipsychotic) in Asians.

METHODS

A single oral dose of perphenazine (0.1 mg/kg) or placebo was administered to 22 medication-free nonsmoker healthy male Chinese-Canadian volunteers, following a double-blind within-subject randomized design. Blood samples were drawn at baseline and 2, 3, 4, 5 and 6 h after drug administration.

RESULTS

In volunteers with CYP2D6*10/CYP2D6*10 genotype, the mean area under curve (AUC0-6) for perphenazine concentration was 2.9-fold higher than those who carry the CYP2D6*1 allele (P<0.01). Notably, volunteers homozygous for CYP2D6*10 exhibited a significant reduction (66%) in mean pharmacodynamic tissue sensitivity as measured by the (prolactin-AUC0-6/perphenazine-AUC0-6) ratio (P=0.02).

CONCLUSIONS

CYP2D6 genotype is a significant contributor to perphenazine concentration in Chinese-Canadians. Importantly, prolactin response, when normalized per unit perphenazine concentration, appears to be blunted in volunteers homozygous for CYP2D6*10. We suggest that CYP2D6 genetic variation may potentially influence pharmacodynamic tissue sensitivity in the pituitary, presumably through disposition of an endogenous substrate (e.g. 5-methoxytryptamine).

Estimating the genetic component (RGC) in pharmacokinetic variability of the antiretroviral didanosine among healthy Brazilians

BACKGROUND

We estimate the variance between between- and within-subjects, using mixed effect models, as a way to assess the genetic component in explaining the observed heterogeneity of ddl kinetics among healthy individuals. Our work expands on a previous reported method known as RGC.

METHODS

Repeated measurements of ddl concentration in the serum were obtained from 48 healthy adult volunteers enrolled in two bioequivalence study. We use the NONMEM program (Non-linear Mixed Effect Model) to estimate the between- and within-subject variability and the corresponding pharmacokinetic parameters. We assess the genetic contribution to the variability of each pharmacokinetic parameter through the RGC method.

RESULTS

Pharmacokinetic parameters, expressed as functions of covariates gender and creatinine clearance (CLCR), were: Oral clearance (CL = 55.1 + 240 * CLCR + 16.6 l/h for male and CL = 55.1 + 240 * CLCR for female), central volume (V2 = 9.82), inter-compartmental clearance (Q = 40.90/h), peripheral volume (V3 = 62.7 + 22.90 for male and V3 = 62.70 for female), absorption rate constant (Ka = 1.51 h(-1)) and duration of the dose administration (D = 0.44 h). The RGC of CL, Q, V3, Ka and D were 0.58, 0.97, 0.60, 0.53 and 0.88, respectively.

CONCLUSION

We estimated parameter-specific RGC indices and rank them according to the potential genetic contribution as an explanation for the observed variance. Our study design improved precision by decreasing background noise and, thus, improved the chances that indices such as the RGC are in fact describing genetic variability.

Differences in drug pharmacokinetics between East Asians and Caucasians and the role of genetic polymorphisms

Interethnic variability in pharmacokinetics can cause unexpected outcomes such as therapeutic failure, adverse effects, and toxicity in subjects of different ethnic origin undergoing medical treatment. It is important to realize that both genetic and environmental factors can lead to these differences among ethnic groups. The International Conference on Harmonization (ICH) published a guidance to facilitate the registration of drugs among ICH regions (European Union, Japan, the United States) by recommending a framework for evaluating the impact of ethnic factors on a drug's effect, as well as its efficacy and safety at a particular dosage and dosage regimen. This review focuses on the pharmacokinetic differences between East Asians and Caucasians. Differences in metabolism between East Asians and Caucasians are common, especially in the activity of several phase I enzymes such as CYP2D6 and the CYP2C subfamily. Before drug therapy, identification of either the genotype and/or the phenotype for these enzymes may be of therapeutic value, particularly for drugs with a narrow therapeutic index. Furthermore, these differences are relevant for international drug approval when regulatory agencies must decide if they accept results from clinical trials performed in other parts of the world.

Pharmacogenomics and drug response in cardiovascular disorders

There are a total of 17 families of drugs that are used for treating the heterogeneous group of cardiovascular diseases. We propose a comprehensive pharmacogenomic approach in the field of cardiovascular therapy that considers the five following sources of variability: the genetics of pharmacokinetics, the genetics of pharmacodynamics (drug targets), genetics linked to a defined pathology and its corresponding drug therapies, the genetics of physiologic regulation, and environmental–genetic interactions. Examples of the genetics of pharmacokinetics are presented for phase I (cytochromes P450) and phase II (conjugating enzymes) drug-metabolizing enzymes and for phase III drug transporters. The example used to explain the genetics of pharmacodynamics is glycoprotein IIIa and the response to antiplatelet effects of aspirin. Genetics linked to a defined pathology and its corresponding drug therapies is exemplified by ADRB1, ACE, CETP and APOE and drug response in metabolic syndrome. The examples of cytochrome P450s, APOE and ADRB2 in relation to ethnicity, age and gender are presented to describe genetics of physiologic regulation. Finally, environmental–genetic interactions are exemplified by CYP7A1 and the effects of diet on plasma lipid levels, and by APOE and the effects of smoking in cardiovascular disease. We illustrate this five-tiered approach using examples of cardiovascular drugs in relation to genetic polymorphism.

Relationship between Type A and B personality and debrisoquine hydroxylation capacity

AIM

A person with Type A personality is an 'aggressor' compared with the rarely harried Type B. Although debrisoquine hydroxylase (CYP2D6) capacity has been associated with personality, no study has specifically investigated its association with personality Type A and B. Therefore the aim of this research was to study the impact of CYP2D6 on Type A and B personality.

METHODS

Type A and B personality questionnaires were administered to 48 healthy patients undergoing elective orthopaedic surgery. After obtaining informed consent, patients were genotyped for the various CYP2D6 alleles by allele-specific polymerase chain reaction. Based on the genotypes, patients were grouped as extensive metabolizer (EM)1 (normal) (CYP2D6*1/*1), EM2 (intermediate) (CYP2D6*1/*4, CYP2D6*1/*5, CYP2D6*1/*9 and CYP2D6*1/*10) and EM3 (slow) (CYP2D6*4/*10, CYP2D6*5/*10, CYP2D6*10/*10 and CYP2D6*10/*17). Chi(2) was used to determine the relationship between the groups and personality types.

RESULTS

The percentages of patients who were of the EM1, EM2 and EM3 groups were 20.8%, 52.1% and 27.1%, respectively. There was a significant difference (P = 0.032) between the three groups in terms of personality type, in which EM1 showed a tendency to be of personality Type A while EM2 and EM3 tended to be of personality Type B.

CONCLUSION

The study suggests that there is a relationship between CYP2D6 activity and Type A and B personality.

Pharmacogenomics of human UDP-glucuronosyltransferase enzymes

UDP-glucuronosyltransferase (UGT) enzymes comprise a superfamily of key proteins that catalyze the glucuronidation reaction on a wide range of structurally diverse endogenous and exogenous chemicals. Glucuronidation is one of the major phase II drug-metabolizing reactions that contributes to drug biotransformation. This biochemical process is also involved in the protection against environmental toxicants, carcinogens, dietary toxins and participates in the homeostasis of numerous endogenous molecules, including bilirubin, steroid hormones and biliary acids. Over the years, significant progress was made in the field of glucuronidation, especially with regard to the identification of human UGTs, study of their tissue distribution and substrate specificities. More recently, the degree of allelic diversity has also been revealed for several human UGT genes. Some polymorphic UGTs have demonstrated a significant pharmacological impact in addition to being relevant to drug-induced adverse reactions and cancer susceptibility. This review focuses on human UGTs, the description of the nature of polymorphic variations and their functional impact. The pharmacogenomic implication of polymorphic UGTs is presented, more specifically the role of UGT polymorphisms in modifying cancer risk and their impact on individual risk to drug-induced toxicities.

Psychopharmacological research ethics: special issues affecting US ethnic minorities

RATIONALE

This article is intended to explore how minority status and cultural factors affect the participation of subjects in clinical psychopharmacology research.

OBJECTIVES AND METHODS

A literature review was performed using key words "clinical psychopharmacology trials", "psychiatric ethics" and "minority groups". Major goals of this review were to examine current knowledge base and identify existing gaps in this fairly new area of psychiatric research.

RESULTS

We found extremely few papers addressing the issue directly. Most references to minority groups were made peripherally, and many of these were extrapolated to psychiatric patients from work done on medical populations. We found no empirical studies done in psychiatric populations.

CONCLUSIONS

Systematic, well-designed research studies are needed to elucidate how culture, race and ethnicity impact on such issues as accrual, retention, informed consent and safeguards against the potential exploitation of minority research subjects. On the basis of the literature review and our personal experience doing clinical research with minority patients, we provide several recommendations and specific suggestions to clinical researchers who include minority patients in their clinical trials.

Inhibition kinetics of monoclonal antibodies against cytochromes P450

Monoclonal antibodies (MAbs) inhibitory to individual cytochromes P450 (P450s) are of tremendous utility in identification of P450s responsible for the metabolism of a given drug or drug candidate in pharmaceuticals. In the present study, two inhibitory MAbs against CYP2D6 (MAb(2D6-50,) IgG(2b) and MAb(2D6-184), IgG(2a)) were developed by hybridoma technology to exhibit their high specificity and potency. The MAbs were further employed to assess the quantitative role (47-93%) of CYP2D6 to the metabolism of bufuralol in human liver microsomes from seven donors. Together with the MAb inhibitory to CYP3A4 as previously reported (Mei et al., 1999), the MAbs were used to study the inhibition kinetics of dextromethorphan O-demethylation (CYP2D6), testosterone 6beta-hydroxylation (CYP3A4) and aflatoxin B1 3-hydroxylation (CYP3A4), respectively, with an adequate size of sample measurement. A kinetic model was proposed to fit the experimental observations with three-dimensional nonlinear regression, thereby resulting in a solution of kinetic parameters, i.e., K(I), K(S), V(max), alpha, and beta (changes in K(I) or K(S) and V(max) in the presence of the MAb). As a result, dissociation constants (K(I)) of the MAbs for the enzymes and the maximal inhibition (beta) values for the P450-catalyzed reactions were predicted to have 0.04 to 0.25 microM and > or =94%, respectively. The results have demonstrated that the model can accurately predict the kinetic parameters and provide some insights into the understanding of the mechanism of MAb interaction with P450 enzyme in nature and the applications of the MAbs in qualitative and quantitative identification of P450s involved in drug metabolism.

Pharmacogenetics of bipolar disorder

To review the pharmacogenetics of bipolar disorders, the authors searched databases for genetic association and linkage studies involving response to long-term prophylactic lithium treatment, as well as treatment with antidepressants or clozapine. Significant ethnic variations in the metabolism and efficacy of antidepressants, as well as clozapine, have been reported by several groups. Systematic studies suggest that that genetic factors affect the response to prophylactic lithium treatment. Numerous associations between the three traits of interest and candidate gene polymorphisms have been proposed. Among these, an association between the serotonin transporter gene and response to serotonin reuptake inhibitors appears robust. Considerable interest has also focused on serotonergic gene polymorphisms and response to clozapine. Response to pharmacotherapy in bipolar disorders may be mediated by genetic factors, but the role played by heritability is unknown.

CYP2D6 allele frequency in European Caucasians, Asians, Africans and their descendants

Over 40 cytochrome P450 (CYP) 2D6 allelic variants have been discovered thus far. The alleles may be classified on the basis of the level of activity for which they encode CYP2D6 enzymes, into functional, non-functional and reduced function groups. CYP2D6 allele frequency is known to vary amongst racial/ethnic groups. Generally, for European Caucasians and their descendants, the functional group of alleles are predominant, with a frequency of 71%. Non-functional alleles represent 26% of the variability, mainly CYP2D6*4. In Asians and their close descendants, functional alleles represent only ~ 50% of the frequency of CYP2D6 alleles. Asians and Pacific Islanders have a high frequency (median = 41%) of a reduced function allele, CYP2D6*10, contributing to the population shift to the right of metabolic rates indicating slower metabolism. Information concerning Amerindians from North (Canada), Central and South America indicate comparatively low frequencies of CYP2D6*10, perhaps a "founders" effect. The frequency of functional alleles in Africans and African Americans is also about 50%. Both Africans and African Americans have reduced function alleles representing 35% of allele variation, mainly CYP2D6*17. African Americans, however, have more than twice the median frequency of nonfunctional alleles compared with Africans (14.5% vs 6.3%). Non-functional and reduced function alleles represent about 50% of allele frequency in Black populations but a much greater variety than carried in Asians. Since alleles which encode for no or reduced functioning clearly affect metabolic activity of drugs mediated by CYP2D6, studies are needed in populations in which these alleles play a major role in order to assure optimal dosing recommendations are based on empirical pharmacogenetics.

Genetic Polymorphism of Human Cytochrome P450 Involved in Drug Metabolism

Recent advances in human gene analysis promoted by the human genome project have brought us a massive amount of information. These data can be seen and analyzed by personal computer through individual Web sites. As a result, the best use of bioinformatic is essential for recent molecular biology research. Genetic polymorphism of drug-metabolizing enzymes influences individual drug efficacy and safety through the alteration of pharmacokinetics and disposition of drugs. Considerable amounts of data have now accumulated as allelic differences of various drug metabolizing enzymes. Current understanding of genotype information on cytochrome P450 is hereby summarized, based on the Web site for their use in individual optimization of drug therapy.

Molecular basis of ethnic differences in drug disposition and response

Ethnicity is an important demographic variable contributing to interindividual variability in drug metabolism and response. In this rapidly expanding research area many genetic factors that account for the effects of ethnicity on pharmacokinetics, pharmacodynamics, and drug safety have been identified. This review focuses on recent developments that have improved understanding of the molecular mechanisms responsible for such interethnic differences. Genetic variations that may provide a molecular basis for ethnic differences in drug metabolizing enzymes (CYP 2C9, 2C19, 2D6, and 3A4), drug transporter (P-glycoprotein), drug receptors (adrenoceptors), and other functionally important proteins (eNOS and G proteins) are discussed. A better understanding of the molecular basis underlying ethnic differences in drug metabolism, transport, and response will contribute to improved individualization of drug therapy.

Relationship of phenol sulfotransferase activity (SULT1A1) genotype to sulfotransferase phenotype in platelet cytosol

Sulfation catalysed by human cytosolic sulfotransferases is generally considered to be a detoxification mechanism. Recently, it has been demonstrated that sulfation of heterocyclic aromatic amines by human phenol sulfotransferase (SULT1A1) can result in a DNA binding species. Therefore, sulfation capacity has the potential to influence chemical carcinogenesis in humans. To date, one genetic polymorphism (Arg213His) has been identified that is associated with reduced platelet sulfotransferase activity. In this study, data on age, race, gender, SULT1A1 genotype and platelet SULT1A1 activity were available for 279 individuals. A simple colorimetric phenotyping assay, in conjunction with genotyping, was employed to demonstrate a significant correlation (r = 0.23, P < 0.01) of SULT1A1 genotype and platelet sulfotransferase activity towards 2-naphthol, a marker substrate for this enzyme. There was also a difference in mean sulfotransferase activity based on gender (1.28 nmol/min/mg, females; 0.94 nmol/min/mg, males, P = 0.001). DNA binding studies using recombinant SULT1A1*1 and SULT1A1*2 revealed that SULT1A1*1 catalysed N-hydroxy-aminobiphenyl (N-OH-ABP) DNA adduct formation with substantially greater efficiency (5.4 versus 0.4 pmol bound/mg DNA/20 min) than the SULT1A1*2 variant. A similar pattern was observed with 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5b]pyridine (N-OH-PhIP) (4.6 versus 1.8 pmol bound/mg DNA/20 min).

Mimicking gene defects to treat drug dependence

The genetic basis for drug dependence has focused on genes that encode receptors involved in the reinforcing properties of drugs of abuse or that determine drug-taking behavior (e.g. impulsivity, etc.). Pharmacogenetic variations in the patterns of metabolism among individuals can also importantly modulate the risk of drug dependence. Cytochrome P450 drug metabolizing enzymes (CYPs), can activate (e.g. codeine to morphine) or deactivate (e.g. nicotine to cotinine) drugs of abuse. Some CYPs are polymorphic, that is, there are gene mutations which result in individuals with no (null mutations) or decreased enzyme activity (e.g. CYP2D6*10). Individuals with two null mutations appear in the population as phenotypic poor metabolizers. Using in vitro studies, we have identified drugs of abuse that are substrates of the polymorphic enzymes CYP2D6 (codeine, amphetamines, dextromethorphan), CYP2A6 (nicotine) and CYP2C19 (flunitrazepam). In human experimental studies, we have shown that CYP phenotype and genotype affect abuse liability of CYP2D6 metabolized drugs of abuse. In addition, we inhibited CYP2D6 and decreased individuals' risk of dependence experimentally (codeine, dextromethorphan) and treated codeine dependence. In epidemiologic studies CYP2D6 and CYP2A6 null mutations protect individuals from becoming codeine and tobacco dependent, respectively. With respect to CYP2A6, individuals with mutations, smoke fewer cigarettes and can quit more easily. Inhibiting CYP2A6 (e.g. tranylcypromine, methoxsalen) decreases smoking and the activation of procarcinogens. By mimicking these gene defects the risk of dependence can be decreased in individuals and new treatments developed.

A functional polymorphism of the cytochrome P450 1A2 (CYP1A2) gene: association with tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a common and potentially irreversible side effect associated with long-term treatment with typical antipsychotics. Approximately, 80% or more of patients with schizophrenia are smokers. Smoking is a potent inducer of the CYP1A2 enzyme, and is known to cause a significant decrease in plasma concentrations of some antipsychotics. Therefore, person-to-person differences in the extent of CYP1A2 induction by smoking may contribute to risk for the development of TD. Recently, a (C-->A) genetic polymorphism in the first intron of the CYP1A2 gene was found to be associated with variation in CYP1A2 inducibility in healthy volunteer smokers. The aim of this study was to test the clinical importance of the (C-->A) polymorphism in CYP1A2 in relation to TD severity. A total of 85 patients with schizophrenia were assessed for TD severity using the Abnormal Involuntary Movement Scale (AIMS), and were subsequently genotyped for the (C-->A) polymorphism in CYP1A2. The mean AIMS score in patients with the (C/C) genotype (associated with reduced CYP1A2 inducibility) was 2.7- and 3.4-fold greater than in those with the (A/C) or (A/A) genotype, respectively (F[2,82] = 7.4, P = 0.0007). Further, a subanalysis in the 44 known smokers in our sample, revealed a more pronounced effect. The means AIMS score in smokers was 5.4- and 4. 7-fold greater in (C/C) homozygotes when compared to heterozygotes and (A/A) homozygotes, respectively (F[2,41] = 3.7, P = 0.008). These data suggest that the (C-->A) genetic polymorphism in the CYP1A2 gene may serve as a genetic risk factor for the development of TD in patients with schizophrenia. Further studies in independent samples are warranted to evaluate the applicability of our findings to the general patient population receiving antipsychotic medications.

Psychopharmacology research in the English-speaking Caribbean

Ethnic differences in patients' responses to drugs used to treat psychiatric disorders have been increasingly reported. Differences can be found in the English-speaking Caribbean population due to its multi-ethnic composition. With the goal of identifying studies on psychopharmacology and ethnicity, we searched for all abstracts and full papers on clinical psychopharmacology emerging from research in the English-speaking Caribbean published in the West Indies Medical Journal, the Caribbean Medical Journal and Medline. We found no studies focusing on this topic, although there were some which may indirectly imply the existence of such differences. High blood levels of imipramine have been found in Barbadian patients, and the majority of cases of neuroleptic malignant syndrome have been reported in Africans, as well as high levels of CPK. However, the numbers of patients studied have not been large enough to be representative. A significantly higher incidence of alcoholism has also been reported in males of East Indian origin. We concluded there is an urgent need in the region for undertaking this type of research to ensure a more favorable treatment outcome of patients treated with such drugs.

Pharmacogenetics and psychopharmacotherapy

Response to drugs can vary between individuals and between different ethnic populations. The biological (age, gender, disease and genetics), cultural and environmental factors which contribute to these variations are considered in this review. The most important aspect is the genetic variability between individuals in their ability to metabolize drugs due to expression of 'polymorphic' enzymes. Polymorphism enables division of individuals within a given population into at least two groups, poor metabolisers (PMs) and extensive metabolisers (EMs) of certain drugs. The two most extensively studied genetic polymorphisms are those involving cytochrome P450 2D6 (CYP2D6) and CYP2C19. CYP2D6 metabolizes a number of antidepressants, antipsychotics, beta-adrenoceptor blockers, and antiarrhythmic drugs. About 7% of Caucasians and 1% of Asians are PMs of CYP2D6 substrates. CYP2C19 enzyme participates in the metabolism of omeprazole, propranolol and psychotropic drugs such as hexobarbital, diazepam, citalopram, imipramine, clomipramine and amitriptyline. The incidence of PMs of CYP2C19 substrates is much higher in Asians (15-30%) than in Caucasians (3-6%). Variations in metabolism of psychotropic drugs result in variations in their pharmacokinetic parameters. This may lead to clinically significant intra- and inter-ethnic differences in pharmacological responses. Such variations are discussed in this review. Differential receptor-mediated response may play a role in ethnic differences in responses to antipsychotics and tricyclic antidepressants, but such pharmacodynamic factors remain to be systematically investigated. The results of studies of ethnic differences in response to psychopharmacotherapy appear to be discrepant, most probably due to limitations of study design, small sample size, inadequately defined study sample, and lack of control of confounding factors. The clinical value of understanding pharmacogenetics is in its use to optimize therapeutic efficacy, to prevent toxicity of those drugs whose metabolism is catalysed by polymorphic isoenzymes, and to contribute to the rational design of new drugs. Finally, applications and impact of pharmacogenetics in the field of psychopharmacotherapy are discussed.

Ethnicity, culture, and neuropsychiatry

The purpose of this paper is to review the research on the relationships among ethnicity, culture, neuropsychiatric diagnosis, and treatment. Psychiatric nurses provide care to an ethnically and culturally diverse group of clients. Knowledge of ethnic and cultural differences are essential to diagnosis and treatment. Ethnic diversity affects psychiatric diagnosis. Cross-ethnic differences in genetics, diet, environmental exposure, and fetal, childhood, and adolescent development may result in varied experiences of psychiatric illness among ethnic groups. Ethnic diversity also affects psychiatric treatment. There are dramatic ethnic differences in the metabolism of psychotropic medications and the effects of drugs on target organs. These differences are again due to genetic variation, exposure to different diets and environments, and other medications in use. Cultural diversity influences both diagnosis and treatment. Cultural forces shape symptom formation and the expression of distress, creating many sources for misdiagnosis based on DSM-IV criteria. The culture-bound syndromes represent unique illness forms with a natural history distinct from DSM classification. Culture also influences treatment expectations, therapeutic compliance, family involvement, and the interpretation of side effects, all of which help determine whether or not treatment will be effective. Neuropsychiatric nurses can contribute to research by studying cross-ethnic differences and similarities in biological markers of mental illness. A second significant area for research is that of ethnicity and psychotropic drug metabolism and pharmacodynamics.

Addressing human variability in risk assessment--the robustness of the intraspecies uncertainty factor

Addressing human variability and sensitive subpopulations is one of the challenges of risk assessment and is an important aspect of the Food Quality Protection Act, the law passed in 1996 that regulates food use pesticides in the United States. The intraspecies uncertainty factor is intended to address differences in susceptibility within the human population. This paper examines the history and scientific basis for the intraspecies uncertainty factor. Our best source of knowledge about human variability in the response to chemicals comes from clinical trials of pharmaceuticals. This large body of data allows both qualitative and quantitative characterization of variability in pharmacokinetic and pharmacodynamic parameters in the general population and in subgroups such as children. The preponderance of evidence in the areas of pharmacodynamics and pharmacokinetics supports the routine use of an intraspecies uncertainty factor in the range of 1-10 as being protective of greater than 99% of the human population. The intraspecies uncertainty factor is highly protective of various subpopulations, including infants and children.

Frequency of cytochrome P450 CYP2C9 variants in a Turkish population and functional relevance for phenytoin

AIMS

The genetically polymorphic cytochrome P450 enzyme CYP2C9 metabolizes many important drugs. We studied the frequency of the amino acid variants cysteine144 (CYP2C9*2 ) and leucine359 (CYP2C9*3 ) in a Turkish population and the correlation between genotype and phenotype using phenytoin as probe drug.

METHODS

CYP2C9 alleles *2 and *3 were measured in 499 unrelated Turkish subjects by PCR and restriction fragment length pattern analysis. Phenotyping was performed in a subgroup of 101 volunteers with a single oral dose of 300 mg phenytoin and concentration analysis in serum drawn 12 h after dosage.

RESULTS

CYP2C9 allele frequencies in 499 unrelated Turkish subjects were 0.794 for CYP2C9*1, 0.106 for CYP2C9*2 and 0. 100 for CYP2C9*3. Mean phenytoin serum concentrations at 12 h after dosage were 4.16 mg l-1 (95% CI 3.86-4.46) in carriers of the genotype CYP2C9*1/1, 5.52 mg l-1 (4.66-6.39) in CYP2C9*1/2, and 5.65 mg l-1 (4.86-6.43) in CYP2C9*1/3. These differences were significant and accounted for 31% of total variability in phenytoin trough levels. Mean 12 h concentration ratios of 5-(para-hydroxyphenyl)-5-phenylhydantoin/phenytoin (p-HPPH/P) were 0. 43 (0.39-0.47) for CYP2C9*1/1 compared with 0.26 (0.21-0.31) for CYP2C9*1/2, 0.14 (0.13-0.14) for CYP2C9*2/2, 0.21 (0.18-0.24) for CYP2C9*1/3, and 0.02 for CYP2C9*3/3; all mutant genotypes were significantly different compared with CYP2C9*1/1.

CONCLUSIONS

Frequency of the two CYP2C9 variants in Turkish subjects was in a similar range as in other Caucasian populations. A significant proportion of the interindividual variability in phenytoin trough levels is explained by the genotypes. The 12 h serum concentrations after a single phenytoin dose may be used for routine phenotyping of CYP2C9 mediated metabolic clearance and the p-HPPH/P ratios may be even more sensitive indicators of CYP2C9 activity.

Phenotypes and genotypes for CYP2D6 and CYP2C19 in a black Tanzanian population

AIMS

CYP2D6 and CYP2C19 are polymorphically expressed enzymes that show marked interindividual and interethnic variation. The aim of this study was to determine the frequency of the defective alleles in CYP2D6 and CYP2C19 in Africans and to test whether the genotype for CYP2C19 is better correlated with the proguanil/cylcoguanil ratio than the mephenytoin S/R ratio.

METHODS

Two hundred and sixteen black Tanzanians were phenotyped for CYP2D6 with the use of sparteine, and for CYP2C19 with the use of mephenytoin and proguanil. Of these 196 subjects were also genotyped for CYP2D6 (including the CYP2D6*1, CYP2D6*3 and CYP2D6*4 alleles) and 195 were genotyped for CYP2C19 (including the CYP2C19*1, CYP2C19*2 and the CYP2C19*3 alleles). Furthermore 100 subjects were examined for the allele duplication in CYP2D6, leading to ultrarapid metabolism, with long PCR.

RESULTS

The sparteine metabolic ratio (MR) was statistically significantly higher in the Tanzanian group of homozygous, extensive metabolizers compared to a historical control group of white Danish extensive metabolizers. Only one poor metabolizer for CYP2D6 (MR=124 and genotype CYP2D6*1/CYP2D6*4 ) was found. The gene frequencies were 0.96 for the CYP2D6*1 allele and 0.04 for the CYP2D6*4 allele. No CYP2D6*3 alleles were found. Nine subjects had an allele duplication in CYP2D6 (9%). For CYP2C19 there were seven subjects (3. 6%) who were phenotyped as poor metabolizers, but only three subjects (1.5%) had a genotype (CYP2C19*2/CYP2C19*2 ) indicative of poor metabolism. The gene frequencies were 0.90 for the CYP2C19*1 allele and 0.10 for the CYP2C19*2 allele. No CYP2C19*3 alleles were found. The mephenytoin S/R ratios were not bimodally distributed.

CONCLUSIONS

Both the genotyping and phenotyping results show that there is a substantial difference between an African black population and a Caucasian population in the capacity to metabolize drugs via CYP2D6 and CYP2C19.

Phenol sulphotransferase SULT1A1 polymorphism: molecular diagnosis and allele frequencies in Caucasian and African populations

Sulphation, catalysed by members of the sulphotransferase (SULT) enzyme family, is an important component of the body's chemical defence mechanism, but also acts to bioactivate mutagens such as hydroxylated aryl and heterocyclic amines. A major human sulphotransferase, SULT1A1 (P-PST), metabolizes and/or bioactivates many drugs, iodothyronines and hydroxylated aromatic amines. The enzyme activity varies widely within the population and is under genetic control. We have developed an assay detecting a G-->A transition in SULT1A1 that causes an Arg213-->His substitution associated with low SULT activity and altered enzyme properties, and have used it to assess the SULT1A1 genotype in Caucasian (n=293) and African (Nigerian, n=52) populations. We show that the mutant SULT1A1*2 allele is present at frequencies of 0.321 and 0.269 in the Caucasian and African populations respectively. We also demonstrate a significant age-related difference in SULT1A1 genotype within our Caucasian population, with increasing incidence of SULT1A1*1 homozygosity and decreasing incidence of SULT1A1*2 homozygosity with increasing age, indicating a potential association of SULT1A1*1 allozyme(s) with protection against cell and/or tissue damage during aging.

Optimizing drug therapy based on genetic differences: implications for the clinical setting

Differences in drug responses due to gene alterations are rapidly being identified. Gene alterations may inhibit the function of an enzyme so that an active drug accumulates, causing adverse reactions with normal doses. Alternatively, gene alterations may accelerate enzymatic function so that an active drug is rapidly eliminated, causing subtherapeutic responses to normal doses. Mutations and polymorphisms have been identified that affect a person's response to many currently prescribed medications including cardiovascular, anti-infective, chemotherapeutic, psychiatric, and analgesic drugs. The potential exists for drug therapy to be optimized by selecting medication and doses based on a person's genotype rather than by trial and error. In the near future, advanced practice nurses in the acute care setting may be expected to order, provide patient education about, and explain results of genetic tests before initiating a specific drug therapy. Advanced practice nurses must be knowledgeable about what genetic tests are analyzing and their benefits, limitations, and risks.

Common genomic variation in the APOC3 promoter associated with variation in plasma lipoproteins

We hypothesized that common genomic variation that affected the expression and/or function of the products of the APOC3, APOE, FABP2, and PON1 genes would be associated with variation in biochemical phenotypes in a previously unstudied human sample. We determined genotypes of functional genomic variants of APOC3, APOE, FABP2, and PON1 in 509 adult aboriginal Canadians from an isolated community in Northern Ontario. We tested for genotype associations with plasma lipoprotein traits. We found that (1) common variation at nucleotide -455 of the APOC3 promoter was associated with variation in plasma triglycerides (P = .006) and (2) common variation of APOE determining plasma isoforms of apo E was associated with variation in plasma apo B (P = .009). Analysis of subjects classed by APOC3 markers showed that homozygosity for presence of a C at nucleotide -455 and a T at nucleotide -482 was associated with significantly increased plasma triglycerides in both men and women. Furthermore, this allele was approximately twice as frequent in subjects within the highest quartile of plasma triglycerides as in subjects within the lowest quartile. Since the DNA variation detected by the APOC3 markers affects in vitro expression of the gene product, it is possible that the marker itself caused the associations. However, the associations could also have resulted from linkage disequilibrium with other functional variants in APOC3 or the closely linked APOA1 and/or APOA4 genes.

Clinical pharmacokinetic considerations in the elderly. An update

There are a number of areas in which advances have been made over the last few years in the area of pharmacokinetics in the elderly. There is increasing understanding of the diversity of cytochrome P450s (CYP) and the variability of the age-related decline in CYP activity. This has helped to explain some of the interindividual variability in drug metabolism with age. The importance of ethnic differences has emerged, but specific work is needed in this area in the elderly. Differences in the handling of chiral compounds has been reported but as yet no clinically important findings that may lead to a change in clinical practice have emerged. The emerging importance of extrahepatic drug metabolism, especially in the intestine, has added a new complexity to our understanding of pharmacokinetics. The issue of frailty is also discussed in this article. Whether it will be of value at the bedside has yet to emerge. Nonetheless, as a concept, recent data has supported its potential use to define those more at risk of clinically meaningful pharmacokinetic alterations. Other advances have included the appreciation that selectivity in induction and inhibition in the elderly are due to the existence of multiple CYP forms. Similarly, the role of these various enzymes in disease is also improving our clinical understanding, as exemplified in Parkinson's disease.

Bioavailability of oral cyclosporine in healthy Mexican volunteers: evidence for interethnic variability

The existence of population variations in cyclosporine pharmacokinetics could be expected, as this drug, similar to nifedipine, is biotransformed by cytochrome P-450 subfamily 3A4, and the existence of interethnic variability in nifedipine disposition has been demonstrated previously. The bioavailability of oral cyclosporine was studied in 23 healthy Mexican volunteers receiving 7.5-mg/kg doses of cyclosporine. Blood samples were drawn over 24 hours, and concentration of cyclosporine in whole blood was determined by a radioimmunoassay using monoclonal antibodies specific for the unchanged drug. The bioavailability of cyclosporine exhibited wide interindividual variability. Maximum concentration (Cmax) ranged from 528 ng/mL to 2,689 ng/mL, area under the concentration-time curve (AUC) ranged from 6,550 ng.hr/mL to 18,562 ng.hr/mL, and time to reach Cmax (tmax) ranged from 1 to 8 hours. Half-life (t1/2) exhibited less important variations, ranging from 4.4 to 9.1 hours. The bioavailability of oral cyclosporine in Mexicans was higher than that reported for white populations under similar conditions. The present results suggest the existence of interethnic variability in the pharmacokinetics of cyclosporine, as is the case with nifedipine.

Common genomic variants associated with variation in plasma lipoproteins in young aboriginal Canadians

We hypothesized that common genomic variants would be associated with variation in lipoprotein phenotypes in young subjects. We determined genotypes of FABP2, PON, APOC3, and APOE in 188 aboriginal Canadians, aged 9 to 17 years. We found that 13 of 32 possible genotype-phenotype associations were significant: (1) the FABP2 codon 54 genotype was associated with variation in plasma triglycerides (P = .045); (2) the PON codon 192 genotype was associated with variation in plasma total and LDL cholesterol and apoB (P = .0099, P = .0088, and P = .016, respectively); (3) the APOC3 insulin-response-element genotype was associated with variation in plasma triglycerides, HDL cholesterol, apoA-I, the total cholesterol to HDL cholesterol ratio, and the apoB to apoA-I ratio (P = .0014, P = .0069, P = .045, P = .0021, and P = .0081, respectively); and (4) the APOE restriction isotype was associated with variation in plasma LDL cholesterol, apoB, the total cholesterol to HDL cholesterol ratio, and the apoB to apoA-I ratio (P = .025, P = .034, P = .045, and P = .047, respectively). The average young age and relative absence of age-dependent secondary environmental factors could have eased the identification of small genetic effects on lipoprotein phenotypes in this study sample.

Pharmacogenetics of antidepressants: clinical aspects

Plasma concentrations and response to antidepressants vary considerably between patients treated with similar dosages. Most antidepressants and also antipsychotics are metabolized by the polymorphic debrisoquine/sparteine hydroxylase, i.e., cytochrome P450 (CYP)2D6. About 7% of Caucasians are poor metabolizers (PM), and such patients might develop adverse drug reactions when treated with recommended doses of, for example, tricyclic antidepressants. In contrast, ultrarapid metabolizers with multiple CYP2D6 genes might require high doses of such drugs for optimal therapy. The mean CYP2D6 activity is lower in Oriental than in Caucasian populations, because of a frequent mutation causing decreased enzyme activity. Drugs metabolized by the same enzyme may interact with each other. For example, the potent CYP2D6 inhibitor fluoxetine increases the plasma concentrations of tricyclic antidepressants. Another enzyme catalyzing the metabolism of antidepressants is the polymorphic S-mephenytoin hydroxylase. CYP2C19, which catalyses the metabolism of, for example, citalopram, clomipramine and moclobemide. Various probe drugs may be used for phenotyping CYP2D6 (debrisoquine, dextromethorphan and sparteine) and CYP2C19 (mephenytoin and omeprazole). Allele-specific polymerase chain reaction (PCR)-based methods are now available for genotyping using leukocyte DNA. A major advantage of genotyping compared with phenotyping is that the former may be performed in blood samples from patients irrespective of treatment.