Acetylation phenotype and genotype in aboriginal leprosy patients from the north-west region of Western Australia

Efficacy, safety, and pharmacokinetics of isoniazid affected by NAT2 polymorphisms in patients with tuberculosis: A systematic review

N-acetyltransferase 2 (NAT2) genetic polymorphisms might alter isoniazid metabolism leading to toxicity. We reviewed the impact of NAT2 genotype status on the pharmacokinetics, efficacy, and safety of isoniazid, a treatment for tuberculosis (TB). A systematic search for research articles published in Scopus, PubMed, and Embase until August 31, 2023, was conducted without filters or limits on the following search terms and Boolean operators: "isoniazid" AND "NAT2." Studies were selected if NAT2 phenotypes with pharmacokinetics or efficacy or safety of isoniazid in patients with TB were reported. Patient characteristics, NAT2 status, isoniazid pharmacokinetic parameters, early treatment failure, and the prevalence of drug-induced liver injury were extracted. If the data were given as a median, these values were standardized to the mean. Forty-one pharmacokinetics and 53 safety studies were included, but only one efficacy study was identified. The average maximum concentrations of isoniazid were expressed as supratherapeutic concentrations in adults (7.16 ± 4.85 μg/mL) and children (6.43 ± 3.87 μg/mL) in slow acetylators. The mean prevalence of drug-induced liver injury was 36.23 ± 19.84 in slow acetylators, which was significantly different from the intermediate (19.49 ± 18.20) and rapid (20.47 ± 20.68) acetylators. Subgroup analysis by continent showed that the highest mean drug-induced liver injury prevalence was in Asian slow acetylators (42.83 ± 27.61). The incidence of early treatment failure was decreased by genotype-guided isoniazid dosing in one study. Traditional weight-based dosing of isoniazid in most children and adults yielded therapeutic isoniazid levels (except for slow acetylators). Drug-induced liver injury was more commonly observed in slow acetylators. Genotype-guided dosing may prevent early treatment failure.

Conference report: pharmacogenomics in special populations at WCP2018

The 18th World Congress of Basic and Clinical Pharmacology (WCP2018), coordinated by IUPHAR and hosted by the Japanese Pharmacological Society and the Japanese Society of Clinical Pharmacology and Therapeutics, was held in July 2018 at the Kyoto International Conference Center, in Kyoto, Japan. Having as its main theme 'Pharmacology for the Future: Science, Drug Development and Therapeutics', WCP2018 was attended by over 4500 delegates, representing 78 countries. The present report is an overview of a symposium at WCP2018, entitled Pharmacogenomics in Special Populations, organized by IUPHAR´s Pharmacogenetics/Genomics (PGx) section. The PGx section congregates distinguished scientists from different continents, covering expertise from basic research, to clinical implementation and ethical aspects of PGx, and one of its major activities is the coordination of symposia and workshops to foster exchange of PGx knowledge (https://iuphar.org/sections-subcoms/pharmacogenetics-genomics/). The symposium attracted a large audience to listen to presentations covering various areas of research and clinical adoption of PGx in Oceania, Africa, Latin America and Asia.

E. coli nitroreductase/CB1954 gene-directed enzyme prodrug therapy: role of arylamine N-acetlytransferase 2

Gene-directed enzyme prodrug therapy is a promising approach to the local management of cancer and a number of gene prodrug combinations have entered clinical trials. The antitumor activity of Escherichia coli nitroreductase (NTR) in combination with the prodrug CB1954 relies on the reduction of the nitro groups to reactive N-hydroxylamine intermediates that are toxic in proliferating and nonproliferating cells. We examined whether secondary metabolic activation of the N-hydroxylamines by sulfotransferases or acetyltransferases altered cell responsiveness to the drug. We evaluated the coexpression of NTR with the human cytosolic sulfotransferases SULT1A1, 1A2, 1A3, 1E1 and 2A1, or the human arylamine N-acetyltransferases NAT1 and NAT2 on SKOV3 cell survival. Only NAT2 significantly altered the toxicity of CB1954, decreasing the IC(50) 16-fold from 0.61 to 0.04 microM. These results suggest that one or more of the N-hydroxyl metabolites are a substrate for O-acetylation by NAT2. We also examined the bystander effect of SKOV3 cells expressing NTR or NTR plus NAT2. Addition of the acetyltransferase resulted in a significant decreased bystander effect (P>0.01), possibly due to a lower concentration of reactive metabolites in the culture medium. These results suggest that a combination of bacterial NTR and NAT2 may provide a greater clinical response at therapeutic concentrations of CB1954 provided the reduction in bystander effect is not clinically significant. Moreover, endogenous NAT2, which is localized predominantly in the liver and gut, may be involved in the dose-limiting hepatic toxicity and gastrointestinal side effects seen in patients treated with the higher doses of CB1954.

Global pharmacogenetics: giving the genome to the masses

With pharmacogenetics comes the promise of individualized therapy selection for many common diseases where multiple treatment options are available. Recent advances including the Human Genome Project, the International HapMap project, advances in throughput and reduction in cost of genetic testing, and the inclusion of genotype-related dosing recommendations into package inserts all point to the integration of pharmacogenetics into clinical practice. However, many countries will not have access to pharmacogenetics resources in the near future. Generation of global genotype profiles will provide a useful, but not perfect resource for incorporating pharmacogenetics into national drug formularies in the form of prioritization or surveillance where individual genotype data would not be attainable. The PharmacoGenetics for Every Nation Initiative is a first step to making pharmacogenetics applicable on a global level.

Deciphering the ancient and complex evolutionary history of human arylamine N-acetyltransferase genes

The human N-acetyltransferase genes NAT1 and NAT2 encode two phase-II enzymes that metabolize various drugs and carcinogens. Functional variability at these genes has been associated with adverse drug reactions and cancer susceptibility. Mutations in NAT2 leading to the so-called slow-acetylation phenotype reach high frequencies worldwide, which questions the significance of altered acetylation in human adaptation. To investigate the role of population history and natural selection in shaping NATs variation, we characterized genetic diversity through the resequencing and genotyping of NAT1, NAT2, and the pseudogene NATP in a collection of 13 different populations with distinct ethnic backgrounds and demographic pasts. This combined study design allowed us to define a detailed map of linkage disequilibrium of the NATs region as well as to perform a number of sequence-based neutrality tests and the long-range haplotype (LRH) test. Our data revealed distinctive patterns of variability for the two genes: the reduced diversity observed at NAT1 is consistent with the action of purifying selection, whereas NAT2 functional variation contributes to high levels of diversity. In addition, the LRH test identified a particular NAT2 haplotype (NAT2*5B) under recent positive selection in western/central Eurasians. This haplotype harbors the mutation 341T-->C and encodes the "slowest-acetylator" NAT2 enzyme, suggesting a general selective advantage for the slow-acetylator phenotype. Interestingly, the NAT2*5B haplotype, which seems to have conferred a selective advantage during the past approximately 6,500 years, exhibits today the strongest association with susceptibility to bladder cancer and adverse drug reactions. On the whole, the patterns observed for NAT2 well illustrate how geographically and temporally fluctuating xenobiotic environments may have influenced not only our genome variability but also our present-day susceptibility to disease.

Arylamine N-acetyltransferase-2 genotypes in the Thai population

AIMS

To determine the frequencies of the major arylamine- N-acetyltransferase-2 (NAT2) alleles in the Thai population.

METHODS

DNA samples from 235 Thai individuals were analysed by polymerase chain reaction with restriction fragment length polymorphism assays.

RESULTS

The frequency distribution of major NAT2 alleles, including NAT2*4, NAT2*5, NAT2*6 and NAT2*7 were 0.381 (95% CI 0.337, 0.426), 0.038 (0.023, 0.060), 0.326 (0.283, 0.370) and 0.204 (0.169, 0.244), respectively. When converted to phenotypes, the study population comprised 63.8% rapid acetylators and 36.2% slow acetylators.

CONCLUSIONS

The pattern of NAT2 alleles of Thais is similar to those of many Asian populations, although the frequency of NAT2*4 is significantly lower and NAT2*7 is higher than that of Oriental populations.

Slow acetylator phenotype and genotype in HIV-positive patients with sulphamethoxazole hypersensitivity

AIMS

To test the role of acetylator status, and to investigate the reported discrepancy between acetylator phenotype and genotype in HIV-positive patients with sulphamethoxazole (SMX) hypersensitivity.

METHODS

Forty HIV-positive patients (32 of whom were SMX-hypersensitive), and 26 healthy volunteers, were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, and phenotyped using dapsone (50 mg) as a probe, for acetylator status. Sequencing of the NAT2 exon was performed where discrepancy between phenotyping and genotyping was detected. Our results were also pooled with published studies addressing slow acetylator status in HIV-positive SMX-hypersensitive patients.

RESULTS

Slow acetylator genotype and phenotype frequencies did not differ between HIV-positive SMX-hypersensitive and nonhypersensitive patients, and healthy controls, which was further confirmed in a meta-analysis of published studies (pooled odds ratio 2.25, 95% confidence interval 0.45, 11.17). Discordance between phenotype and genotype was resolved in four of the subjects by sequencing of the whole NAT2 exon, which revealed rare mutations, leaving three (9%) HIV-positive SMX-hypersensitive patients and one (4%) healthy volunteer who continued to demonstrate the discordance.

CONCLUSIONS

Slow acetylator phenotype or genotype is unlikely to predispose to SMX hypersensitivity in HIV-positive patients, although a minor role cannot be excluded. Phenotype-genotype discrepancies are partly due to nondetection of all rare alleles by PCR methodology, and can be circumvented by sequencing of the gene in patients showing a discrepancy.

Allele and genotype frequencies of polymorphic cytochromes P4502D6, 2C19 and 2E1 in aborigines from western Australia

The polymorphisms of the important xenobiotic metabolizing enzymes CYP2D6, CYP2C19 and CYP2E1 have been studied extensively in a large number of populations and show significant heterogeneity in the frequency of different alleles/genotypes and in the prevalence of the extensive and poor metabolizer phenotypes. Understanding of inter-ethnic differences in genotypes is important in prediction of either beneficial or adverse effects from therapeutic agents and other xenobiotics. Since no data were available for Australian Aborigines, we investigated the frequencies of alleles and genotypes for CYP2D6, CYP2C19 and CYP2E1 in a population living in the far north of Western Australia. Because of its geographical isolation, this population can serve as a model to study the impact of evolutionary forces on the distribution of different alleles for xenobiotic metabolizing enzymes. Twelve CYP2D6 alleles were analysed. The wild-type allele *1 was the most frequent (85.81%) and the non-functional alleles (*4, * 5, * 16) had an overall frequency of less than 10%. Only one subject (0.4%) was a poor metabolizer for CYP2D6 because of the genotype *5/*5. For CYP2C19, the frequencies of the *1 (wild-type) and the non-functional (*2 and *3) alleles were 50.2%, 35.5% and 14.3%, respectively. The combined CYP2C19 genotypes (*2/*2, *2/*3 or *3/*3) correspond to a predicted frequency of 25.6% for the CYP2C19 poor metabolizer phenotype. For CYP2EI, only one subject had the rare c2 allele giving an overall allele frequency of 0.2%. For CYP2D6 and CYP2C19, allele frequencies and predicted phenotypes differed significantly from those for Caucasians but were similar to those for Orientals indicating a close relationship to East Asian populations. Differences between Aborigines and Orientals in allele frequencies for CYP2D6* 10 and CYP2E1 c2 may have arisen through natural selection, or genetic drift, respectively.

Genotyping of the polymorphic N-acetyltransferase (NAT2) and loss of heterozygosity in bladder cancer patients

Acetylation is one of the major routes in metabolism and detoxification of a large number of drugs, chemicals and carcinogens. Slow acetylators are said to be more susceptible to developing bladder cancer and because of investigations about tumor risk based on phenotyping procedures, it was our aim to study the distribution of allelic constellations of the N-acetyltransferase (NAT2) by genotyping patients with bladder cancer. We analysed NAT2 gene of blood and tumor DNA from 60 patients with primary bladder cancer and DNA of blood samples from 154 healthy individuals. Using ASO-PCR/RFLP techniques we identified 70% of patients with bladder cancer (n = 42) to be slow acetylators while genotyping of controls resulted in 61% with slow acetylators (n = 94). In addition, dividing bladder cancer patients in males and females the genotype NAT2*5B/NAT2*6A occured with much higher frequencies in males (OR = 4, 95%); CI = 1.8-8.9). Furthermore, investigating bladder cancer tissues we could detect loss of heterozygosity (LOH) in slow and rapid acetylator genotypes. In eleven out of 60 tumor samples (18.3%) we observed allelic loss at the NAT2 locus while in control DNA of blood from the same patients both alleles were still detectable.

Molecular mechanisms of genetic polymorphisms of drug metabolism

One of the major causes of interindividual variation of drug effects is genetic variation of drug metabolism. Genetic polymorphisms of drug-metabolizing enzymes give rise to distinct subgroups in the population that differ in their ability to perform certain drug biotransformation reactions. Polymorphisms are generated by mutations in the genes for these enzymes, which cause decreased, increased, or absent enzyme expression or activity by multiple molecular mechanisms. Moreover, the variant alleles exist in the population at relatively high frequency. Genetic polymorphisms have been described for most drug metabolizing enzymes. The molecular mechanisms of three polymorphisms are reviewed here. The acetylation polymorphism concerns the metabolism of a variety of arylamine and hydrazine drugs, as well as carcinogens by the cytosolic N-acetyltransferase NAT2. Seven mutations of the NAT2 gene that occur singly or in combination define numerous alleles associated with decreased function. The debrisoquine-sparteine polymorphism of drug oxidation affects the metabolism of more than 40 drugs. The poor metabolizer phenotype is caused by several "loss of function" alleles of the cytochrome P450 CYP2D6 gene. On the other hand, "ultrarapid" metabolizers are caused by duplication or amplification of an active CYP2D6 gene. Intermediate metabolizers are often heterozygotes or carry alleles with mutations that decrease enzyme activity only moderately. The mephenytoin polymorphism affects the metabolism of mephenytoin and several other drugs. Two mutant alleles of CYP2C19 have so far been identified to cause this polymorphism. These polymorphisms show recessive transmission of the poor or slow metabolizer phenotype, i.e. two mutant alleles define the genotype in these individuals. Simple DNA tests based on the primary mutations have been developed to predict the phenotype. Analysis of allele frequencies in different populations revealed major differences, thereby tracing the molecular history and evolution of these polymorphisms.

Enzyme kinetic properties of human recombinant arylamine N-acetyltransferase 2 allotypic variants expressed in Escherichia coli

Arylamine N-acetyltransferase (NAT2) catalyses the N-acetylation of primary arylamine and hydrazine drugs and chemicals. N-Acetylation is subject to polymorphism, and humans can be categorized as either fast or slow acetylators according to their ability to N-acetylate certain arylamine substrates in vivo. Genetic variants at the polymorphic NAT2 locus have been described. We expressed five of the most common NAT2 variants (NAT2 4, NAT2 5A, NAT2 5B, NAT2 6A and NAT2 7B) in Escherichia coli as a convenient source of the human variants. The apparent Km values (at 100 microM acetyl CoA as co-substrate) of the different NAT2 variants for sulphamethazine, dapsone, p-anisidine, 2-aminofluorene, procainamide and isoniazid were determined. Data show that the apparent Km of the slow variant NAT2 7B for the arylamine sulphamethazine was 10-fold lower than all the other allotypes. The apparent Km for the structurally related sulphone antibiotic dapsone was 5-fold lower for the slow variant NAT2 7B when compared with the wild-type NAT2 4. These results indicate that the NAT2 7B specific amino acid substitution, Gly286-Glu, is important in promoting the binding of sulphamethazine and dapsone to the active site.