Polymorphism of the N-acetyltransferase 2 gene as a susceptibility risk factor for antituberculosis drug-induced hepatotoxicity in Tunisian patients with tuberculosis

Pharmacogenomic heterogeneity of N-acetyltransferase 2: a comprehensive analysis of real world data in Indian tuberculosis patients and from literature and database review

BACKGROUND

Isoniazid is primarily metabolized by the arylamine N-acetyltransferase 2 (NAT2) enzyme. Single nucleotide polymorphisms (SNPs) in the NAT2 gene could classify an individual into three distinct phenotypes: rapid, intermediate and slow acetylators. NAT2 SNPs and the slow acetylator phenotype have been implicated as risk factors for the development of antitubercular drug-induced liver injury (AT-DILI) in several tuberculosis (TB) populations.

PATIENTS AND METHODS

We conducted a prospective observational study to characterize and compare the NAT2 SNPs, genotypes and phenotypes among patients with TB and AT-DILI from the Southern and Western regions of India. The NAT2 pharmacogenomic profile of patients from these regions was compared with the reports from several geographically diverse TB populations and participants of different genetic ancestries extracted from literature reviews and the 'All of Us' Research Program database, respectively.

RESULTS

The TB patients of Southern and Western regions of India and several other geographically closer regions exhibited near similar NAT2 MAF characteristics. However significant heterogeneity in NAT2 SNPs was observed within and between countries among AT-DILI populations and the participants of different genetic ancestry from the 'All of Us' Research Program database. The MAF of the NAT2 SNPs rs1041983, rs1801280, rs1799929, rs1799930 and rs1208 of the TB patients from Southern and Western Indian Sites were in near range to that of the South Asian genetic ancestry of 'All of Us' Research Program database. About one-third of the total TB patients from the Southern and Western regions of India were NAT2 slow acetylators, among whom a relatively higher proportion experienced AT-DILI.

CONCLUSION

Further studies exploring the risk of NAT2 SNPs in different AT-DILI patients with larger sample sizes and a population-specific approach are required to establish a policy for NAT2 genotyping as a pre-emptive biomarker for AT-DILI monitoring for personalized isoniazid therapy in clinics.

NAT2 Slow Acetylator Phenotype as a Significant Risk Factor for Hepatotoxicity Caused by Antituberculosis Drugs: Results From a Multiethnic Nested Case-Control Study

BACKGROUND

Under standard therapies, the incidence of drug-induced liver injury (DILI) in patients with tuberculosis ranges from 2% to 28%. Numerous studies have identified the risk factors for antituberculosis DILI; however, none have been conducted in a multiethnic real-world setting. The primary outcome of the current study was to identify the risk factors that could be used as the best predictors of DILI in a multiethnic cohort.

METHODS

A nested case-control study was conducted in patients at the tuberculosis clinic of Luigi Sacco Hospital in Milan.

RESULTS

The study included 102 patients (mean age [SD], 45.6 [15.6] years). For each patient with hepatotoxicity, 2 controls were matched for sex, age, body mass index, tuberculosis/tuberculosis infection diagnosis, and index date. We found that N-acetyltransferase 2 gene (NAT2) slow acetylator status was the best independent predictor of DILI (odds ratio, 5.97 [95% confidence interval, 1.38-25.76]; P = .02].

CONCLUSIONS

NAT2 genotype-guided dosing may help optimize antituberculosis drug treatment and prevent treatment failure.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov NCT06539455.

Pharmacogenomic insights into tuberculosis treatment shows the NAT2 genetic variants linked to hepatotoxicity risk: a systematic review and meta-analysis

BACKGROUND

Tuberculosis (TB) patients undergoing anti-tuberculosis treatment often face serious adverse drug reactions, such as hepatotoxicity. Genetic variants of the N-acetyltransferase 2 (NAT2) gene have been linked to an increased risk of these toxic events.

OBJECTIVE

This study aims to provide a comprehensive evaluation of the evidence linking NAT2 genetic variants to anti-tuberculosis drug-related hepatotoxicity (ATDH).

METHOD

A comprehensive review and meta-analysis was performed by accessing databases such as PubMed, Scopus, and Web of Science. A total of 24 articles were incorporated into the dataset. Meta-analyses were conducted to gather estimates of the association between the slow acetlylators (SA) genotype and ATDH. The studies were stratified by ethnicity, regimen, genotyping methods, criteria for liver toxicity, and dosage. Also, meta-analysis for the specific SA type that was most likely responsible for the ATDH was also conducted.

RESULTS

The included studies showed individuals with a slow NAT2 acetylator had a significantly greater risk of experiencing hepatotoxicity ATDH (odds ratio [OR] 2.52 (95% CI: 1.95-3.27; p value < 0.001) compared to individuals with other types of acetylator (i.e., rapid and immediate). Among individuals with slow acetylator NAT2*5/7, NAT2*5/6, and NAT2*6/6 genotypes, there is a greater likelihood of association compared to other variations.

CONCLUSION

Our meta-analysis confirms a significant association between slow NAT2 acetylator and increased hepatotoxicity risk. The findings from the present underscore the potential of pharmacogenomic testing to improve TB treatment outcomes. By identifying patients with the slow acetylator NAT2 genotype, healthcare providers can predict an increased risk of anti-tuberculosis drug-induced hepatotoxicity. This allows for personalized treatment strategies, such as adjusting drug dosages or selecting alternative therapies, to minimize adverse effects and optimize efficacy.

Isoniazid-historical development, metabolism associated toxicity and a perspective on its pharmacological improvement

Despite the extraordinary anti-tubercular activity of isoniazid (INH), the drug-induced hepatotoxicity and peripheral neuropathy pose a significant challenge to its wider clinical use. The primary cause of INH-induced hepatotoxicity is in vivo metabolism involving biotransformation on its terminal -NH2 group owing to its high nucleophilic nature. The human N-acetyltransferase-2 enzyme (NAT-2) exploits the reactivity of INH's terminal -NH2 functional group and inactivates it by transferring the acetyl group, which subsequently converts to toxic metabolites. This -NH2 group also tends to react with vital endogenous molecules such as pyridoxine, leading to their deficiency, a major cause of peripheral neuropathy. The elevation of liver functional markers is observed in 10%-20% of subjects on INH treatment. INH-induced risk of fatal hepatitis is about 0.05%-1%. The incidence of peripheral neuropathy is 2%-6.5%. In this review, we discuss the genesis and historical development of INH, and different reported mechanisms of action of INH. This is followed by a brief review of various clinical trials in chronological order, highlighting treatment-associated adverse events and their occurrence rates, including details such as geographical location, number of subjects, dosing concentration, and regimen used in these clinical studies. Further, we elaborated on various known metabolic transformations highlighting the involvement of the terminal -NH2 group of INH and corresponding host enzymes, the structure of different metabolites/conjugates, and their association with hepatotoxicity or neuritis. Post this deliberation, we propose a hydrolysable chemical derivatives-based approach as a way forward to restrict this metabolism.

Protein Haptenation and Its Role in Allergy

Humans are exposed to numerous electrophilic chemicals either as medicines, in the workplace, in nature, or through use of many common cosmetic and household products. Covalent modification of human proteins by such chemicals, or protein haptenation, is a common occurrence in cells and may result in generation of antigenic species, leading to development of hypersensitivity reactions. Ranging in severity of symptoms from local cutaneous reactions and rhinitis to potentially life-threatening anaphylaxis and severe hypersensitivity reactions such as Stephen-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), all these reactions have the same Molecular Initiating Event (MIE), i.e. haptenation. However, not all individuals who are exposed to electrophilic chemicals develop symptoms of hypersensitivity. In the present review, we examine common chemistry behind the haptenation reactions leading to formation of neoantigens. We explore simple reactions involving single molecule additions to a nucleophilic side chain of proteins and complex reactions involving multiple electrophilic centers on a single molecule or involving more than one electrophilic molecule as well as the generation of reactive molecules from the interaction with cellular detoxification mechanisms. Besides generation of antigenic species and enabling activation of the immune system, we explore additional events which result directly from the presence of electrophilic chemicals in cells, including activation of key defense mechanisms and immediate consequences of those reactions, and explore their potential effects. We discuss the factors that work in concert with haptenation leading to the development of hypersensitivity reactions and those that may act to prevent it from developing. We also review the potential harnessing of the specificity of haptenation in the design of potent covalent therapeutic inhibitors.

Influence of N-acetyltransferase 2 polymorphisms and clinical variables on liver function profile of tuberculosis patients

BACKGROUND

Single nucleotide polymorphisms (SNPs) in the N-acetyltransferase 2 (NAT2) gene as well as several other clinical factors can contribute to the elevation of liver function test values in tuberculosis (TB) patients receiving antitubercular therapy (ATT).

RESEARCH DESIGN AND METHODS

A prospective study involving dynamic monitoring of the liver function tests among 130 TB patients from baseline to 98 days post ATT initiation was undertaken to assess the influence of pharmacogenomic and clinical variables on the elevation of liver function test values. Genomic DNA was extracted from serum samples for the assessment of NAT2 SNPs. Further, within this study population, we conducted a case control study to identify the odds of developing ATT-induced drug-induced liver injury (DILI) based on NAT2 SNPs, genotype and phenotype, and clinical variables.

RESULTS

NAT2 slow acetylators had higher mean [90%CI] liver function test values for 8-28 days post ATT and higher odds of developing DILI (OR: 2.73, 90%CI: 1.05-7.09) than intermediate acetylators/rapid acetylators.

CONCLUSION

The current study findings provide evidence for closer monitoring among TB patients with specific NAT2 SNPs, genotype and phenotype, and clinical variables, particularly between the period of more than a week to one-month post ATT initiation for better treatment outcomes.

Correlation of N-acetyltransferase 2 genotype and acetylation status with plasma isoniazid concentration and its metabolic ratio in ethiopian tuberculosis patients

Unfavorable treatment outcomes for tuberculosis (TB) treatment might result from altered plasma exposure to antitubercular drugs in TB patients. The present study investigated the distribution of the N-Acetyltransferase 2 (NAT2) genotype, isoniazid acetylation status, genotype-phenotype concordance of NAT2, and isoniazid plasma exposure among Ethiopian tuberculosis patients. Blood samples were collected from newly diagnosed TB patients receiving a fixed dose combination of first-line antitubercular drugs daily. Genotyping of NAT2 was done using TaqMan drug metabolism assay. Isoniazid and its metabolite concentration were determined using validated liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 120 patients (63 male and 57 female) were enrolled in this study. The mean daily dose of isoniazid was 4.71 mg/kg. The frequency of slow, intermediate, and fast NAT2 acetylators genotypes were 74.2%, 22.4%, and 3.3% respectively. The overall median isoniazid maximum plasma concentration (Cmax) was 4.77 µg/mL and the AUC0-7 h was 11.21 µg.h/mL. The median Cmax in slow, intermediate, and fast acetylators were 5.65, 3.44, and 2.47 μg/mL, respectively. The median AUC0-7 h hour in slow, intermediate, and fast acetylators were 13.1, 6.086, and 3.73 mg•h/L, respectively. The majority (87.5%) of the study participants achieved isoniazid Cmax of above 3 µg/mL, which is considered a lower limit for a favorable treatment outcome. There is 85% concordance between the NAT2 genotype and acetylation phenotypes. NAT2 genotype, female sex, and dose were independent predictors of Cmax and AUC0-7 h (p < 0.001). Our finding revealed that there is a high frequency of slow NAT2 genotypes. The plasma Cmax of isoniazid was higher in the female and slow acetylators genotype group. The overall target plasma isoniazid concentrations in Ethiopian tuberculosis patients were achieved in the majority of the patients. Therefore, it is important to monitor adverse drug reactions and the use of a higher dose of isoniazid should be closely monitored.

NAT2 Gene rs1041983 is Associated with Anti-Tuberculosis Drug Induced Hepatotoxicity Among Pediatric Tuberculosis in Bandung, Indonesia

Background

As pediatric tuberculosis (TB) globally is still reported challenging in diagnosis, to date, a lot of efforts have been established to eliminate the disease including proper treatment regimen using anti-TB drugs. However, antituberculosis drug-induced hepatotoxicity (ADIH) is known to interfere the success of the prescribed therapy. ADIH was found to be correlated with polymorphisms of NAT2 gene, that is responsible to transcript the NAT2 enzyme, a metabolizer of isoniazid (INH). The most common NAT2 gene polymorphisms in Asian population associated with ADIH are rs1041983, rs1799929, rs1799930 and rs1799931. The study aimed to investigate the 4 single nucleotide polymorphisms (SNPs) in pediatric TB that experienced ADIH.

Methods

We conducted a case-control study comparing 31 each of pediatric TB experience with and without ADIH. All pediatric TB was selected from 451 pediatric TB Registry of Respirology Division, Department of Child Health Faculty of Medicine Universitas Padjadjaran/Dr Hasan Sadikin Hospital during January 2016 to July 2018. Genomic DNA PCR and sequencing to identify polymorphisms of rs1041983, rs1799929, rs1799930 and rs1799931 were performed in both groups. Data analysis was performed using the Epi info Ver. 7 software.

Results

Thirty-one pediatric TB experiences with and without ADIH were enrolled in this study. SNP rs1041983 significantly affected the occurrence of ADIH (OR 2.39, CI 95% (1.15-4.96), p=0.019). The rs1799929, rs1799930 and rs1799931 did not significantly affect the occurrence of ADIH (p=0.133, p=0.150 and p=0.659, respectively).

Conclusion

Polymorphism SNP rs1041983 had association with the occurrence of ADIH.

Hepatotoxicity during TB treatment in people with HIV/AIDS related to NAT2 polymorphisms in Pernambuco, Northeast Brazil

INTRODUCTION AND OBJECTIVE

Hepatotoxicity during tuberculosis (TB) treatment is frequent and may be related to the Arylamine N-Acetyltransferase (NAT2) acetylator profile, in which allele frequencies differ according to the population. The aim of this study was to investigate functional polymorphisms in NAT2 associated with the development of hepatotoxicity after initiating treatment for TB in people living with HIV/AIDS (PLWHA) in Pernambuco, Northeast Brazil.

MATERIAL AND METHODS

This was a prospective cohort study that investigated seven single nucleotide polymorphisms located in the NAT2 coding region in 173 PLWHA undergoing TB treatment. Hepatotoxicity was defined as elevated aminotransferase levels and identified as being three times higher than it was before initiating TB treatment, with associated symptoms of hepatitis. A further 80 healthy subjects, without HIV infection or TB were used as a control group. All individuals were genotyped by direct sequencing.

RESULTS

The NAT2*13A and NAT2*6B variant alleles were significantly associated with the development of hepatotoxicity during TB treatment in PLWHA (p<0.05). Individual comparisons between the wild type and each variant genotype revealed that PLWHA with signatures NAT2*13A/NAT2*13A (OR 4.4; CI95% 1.1-18.8; p 0.037) and NAT2*13A/NAT2*6B (OR 4.4; CI95% 1.5-12.7; p 0.005) significantly increased the risk of hepatotoxicity.

CONCLUSION

This study suggests that NAT2*13A and NAT2*6B variant alleles are risk factors for developing hepatotoxicity, and PLWHA with genotypes NAT2*13A/NAT2*13A and NAT2*13A/NAT2*6B should be targeted for specific care to reduce the risk of hepatotoxicity during treatment for tuberculosis.

Development of a limited sampling strategy for the estimation of isoniazid exposure considering N-acetyltransferase 2 genotypes in Korean patients with tuberculosis

A limited sampling strategy (LSS) to estimate the exposure to isoniazid was developed considering N-acetyltransferase 2 (NAT2) genotypes in Korean patients with tuberculosis. The influence of the genotypes on the pharmacokinetics of isoniazid was also evaluated. A total of 33 participants participated in the study and received isoniazid 300 mg once daily. Evaluable participants consist of ten slow (SA), fourteen intermediate (IA) and six rapid acetylators (RA). As expected, isoniazid exposure was higher (mean AUC, 28.4 versus 7.6 mg*h/L) and systemic clearance lower (mean apparent clearance, 14.8 versus 50.6 L/h) in SAs than RAs. The formulas to estimate isoniazid exposure were constructed using one or more concentration-time points that correlate with the area under the concentration-time curve (AUC). The LSS using a formula of single concentration-time point at 4 h post dose (C₄) is applicable for all acetylators to the therapeutic drug monitoring (TDM) of isoniazid in patients with tuberculosis when evaluated using the Deming regression and Bland-Altman plot (AUC = 1.53 + 10.03*C₄, adjusted r² = 0.95, p < 0.001). Considering that SAs are more prone to adverse effects, pre-dose NAT2 genotyping would be valuable for optimal isoniazid dosing in conjunction with TDM.

Pharmacogenetic considerations in the treatment of co-infections with HIV/AIDS, tuberculosis and malaria in Congolese populations of Central Africa

BACKGROUND

HIV-infection, tuberculosis and malaria are the big three communicable diseases that plague sub-Saharan Africa. If these diseases occur as co-morbidities they require polypharmacy, which may lead to severe drug-drug-gene interactions and variation in adverse drug reactions, but also in treatment outcomes. Polymorphisms in genes encoding drug-metabolizing enzymes are the major cause of these variations, but such polymorphisms may support the prediction of drug efficacy and toxicity. There is little information on allele frequencies of pharmacogenetic variants of enzymes involved in the metabolism of drugs used to treat HIV-infection, TB and malaria in the Republic of Congo (ROC). The aim of this study was therefore to investigate the occurrence and allele frequencies of 32 pharmacogenetic variants localized in absorption distribution, metabolism and excretion (ADME) and non-ADME genes and to compare the frequencies with population data of Africans and non-Africans derived from the 1000 Genomes Project.

RESULTS

We found significant differences in the allele frequencies of many of the variants when comparing the findings from ROC with those of non-African populations. On the other hand, only a few variants showed significant differences in their allele frequencies when comparing ROC with other African populations. In addition, considerable differences in the allele frequencies of the pharmacogenetic variants among the African populations were observed.

CONCLUSIONS

The findings contribute to the understanding of pharmacogenetic variants involved in the metabolism of drugs used to treat HIV-infection, TB and malaria in ROC and their diversity in different populations. Such knowledge helps to predict drug efficacy, toxicity and ADRs and to inform individual and population-based decisions.

The role of NAT2 polymorphism and methylation in anti-tuberculosis drug-induced liver injury in Mongolian tuberculosis patients

WHAT IS KNOWN AND OBJECTIVE

Anti-tuberculosis drug-induced liver injury (ATLI) is one of the most significant adverse reactions for this line of therapy. N-acetyltransferase 2 (NAT2) is an important metabolic enzyme involved in drug metabolism and detoxification. Genetic polymorphism and DNA methylation have been proven to be key factors that affect the expression of NAT2. Therefore, the objective of the study was to investigate the relationship between NAT2 gene polymorphism and DNA methylation in the promoter region with ATLI risk in Mongolian tuberculosis patients.

METHODS

Our study is a case-control design. Chi-square test, Mann-Whitney U non-parametric test and Pearson test were all used to analyse existing relationships. The association between NAT2 gene acetylation phenotype and the total methylation of the NAT2 promoter region was analysed by means of binary logistic regression analysis. The general situation of the patients was evaluated by questionnaire, and the NAT2 genotyping of the three major polymorphism loci of gene coding was carried out by a gene sequencing technique. The methylation status of the NAT2 gene promoter region was detected by bisulphite sequencing and mass spectrometry.

RESULT AND DISCUSSION

Our study found that the detection rate of ATLI in Mongolian tuberculosis patients was 27.6%. There were no significant differences in demographic characteristics and living habits amongst the two groups, while significant differences were observed in the polymorphism of the NAT2 genes 481 (rs1799929) and 590 (rs1799930) and the acetylation phenotype. Moreover, the composition and distribution of the NAT2*4/4 and NAT2*4/5 genotypes were found in the two groups. The risk of ATLI in the slow acetylation type was 3.56 times higher than that of the fast acetylation type. Compared with the control group, the CpG5, CpG10, CpG11.12 and total methylation of the NAT2 promoter region in the ATLI group showed a hypermethylated pattern (P < .05). However, on performing binary logistic regression, neither the slow acetylation, intermediate acetylation nor rapid acetylation were found to be associated with ATLI (P > .05). It was found that the total methylation of NAT2 gene promoter region was an independent influencing factor of ATLI in Mongolian tuberculosis patients. With the increase of the total methylation level of NAT2 gene promoter region, the risk of ATLI increased gradually. (OR = 8.371, 95% CI: 2.391 ~ 29.315). CpG1, CpG4, CpG9, CpG10 and CpG11.12 were positively correlated with a total methylation level in the ATLI group.

WHAT IS NEW AND CONCLUSION

The detection rate of ATLI in Mongolian tuberculosis patients was 27.6%, and there were differences in the NAT2 genotypes and acetylated phenotypes. The slow acetylated type was the risk factor for ATLI. Methylation in the promoter region of the NAT2 gene has an effect on the risk of ATLI. After adjusting for the interference of three acetylation types, it was found that the total methylation of the promoter region of NAT2 gene in Mongolian tuberculosis patients is an independent influencing factor of ATLI. Furthermore, there is a moderate to high correlation between some sites and the overall level of methylation.

N-Acetyl Cysteine as an Adjunct in the Treatment of Tuberculosis

Oxidative stress is a common feature of tuberculosis (TB), and persons with reduced antioxidants are at more risk of TB. TB patients with relatively severe oxidative stress had also more advanced disease as measured by the Karnofsky performance index. Since adverse effects from anti-TB drugs are also mediated by free radicals, TB patients are prone to side effects, such as hearing loss. In previous articles, researchers appealed for clinical trials aiming at evaluating N-acetyl cysteine (NAC) in attenuating the dreaded hearing loss during multidrug-resistant TB (MDR-TB) treatment. However, before embarking on such trials, considerations of NAC's overall impact on TB treatment are crucial. Unfortunately, such a comprehensive report on NAC is missing in the literature and this manuscript reviews the broader effect of NAC on TB treatment. This paper discusses NAC's effect on mycobacterial clearance, hearing loss, drug-induced liver injury, and its interaction with anti-TB drugs. Based on the evidence accrued to date, NAC appears to have various beneficial effects on TB treatment. However, despite the favorable interaction between NAC and first-line anti-TB drugs, the interaction between the antioxidant and some of the second-line anti-TB drugs needs further investigations.

The Identification of Admixture Patterns Could Refine Pharmacogenetic Counseling: Analysis of a Population-Based Sample in Mexico

Pharmacogenetic analysis has generated translational data that could be applied to guide treatments according to individual genetic variations. However, pharmacogenetic counseling in some mestizo (admixed) populations may require tailoring to different patterns of admixture. The identification and clustering of individuals with related admixture patterns in such populations could help to refine the practice of pharmacogenetic counseling. This study identifies related groups in a highly admixed population-based sample from Mexico, and analyzes the differential distribution of actionable pharmacogenetic variants. A subsample of 1728 individuals from the Mexican Genomic Database for Addiction Research (MxGDAR/Encodat) was analyzed. Genotyping was performed with the commercial PsychArray BeadChip, genome-wide ancestry was estimated using EIGENSOFT, and model-based clustering was applied to defined admixture groups. Actionable pharmacogenetic variants were identified with a query to the Pharmacogenomics Knowledge Base (PharmGKB) database, and functional prediction using the Variant Effect Predictor (VEP). Allele frequencies were compared with chi-square tests and differentiation was estimated by F_ST. Seven admixture groups were identified in Mexico. Some, like Group 1, Group 4, and Group 5, were found exclusively in certain geographic areas. More than 90% of the individuals, in some groups (Group 1, Group 4 and Group 5) were found in the Central-East and Southeast region of the country. MTRR p.I49M, ABCG2 p.Q141K, CHRNA5 p.D398N, SLCO2B1 rs2851069 show a low degree of differentiation between admixture groups. ANKK1 p.G318R and p.H90R, had the lowest allele frequency of Group 1. The reduction in these alleles reduces the risk of toxicity from anticancer and antihypercholesterolemic drugs. Our analysis identified different admixture patterns and described how they could be used to refine the practice of pharmacogenetic counseling for this admixed population.

A review of clinical pharmacogenetics Studies in African populations

Effective interventions and treatments for complex diseases have been implemented globally, however, coverage in Africa has been comparatively lower due to lack of capacity, clinical applicability and knowledge on the genetic contribution to disease and treatment. Currently, there is a scarcity of genetic data on African populations, which have enormous genetic diversity. Pharmacogenomics studies have the potential to revolutionise treatment of diseases, therefore, African populations are likely to benefit from these approaches to identify likely responders, reduce adverse side effects and optimise drug dosing. This review discusses clinical pharmacogenetics studies conducted in African populations, focusing on studies that examined drug response in complex diseases relevant to healthcare. Several pharmacogenetics associations have emerged from African studies, as have gaps in knowledge.

Isoniazid acetylation phenotypes in the Sudanese population; findings and implications

Background

Isoniazid (INH) is the mainstay antimicrobial in the treatment of tuberculosis (TB). It is acetlylated in the liver to acetyl-INH. However, there is variation in rate of acetylation of INH among TB patients (i.e. fast, intermediate or slow acetylators) which impacts on the treatment outcomes.

Aim

The isoniazid acetylation phenotypes in the expatriate Sudanese population were determined to provide future guidance since TB is prevalent in Sudan.

Methods

A community-based trial among Sudanese expatriates in Saudi Arabia was undertaken to identify INH-acetylation phenotypes. After overnight fasting, a single dose of 200 mg of INH was given to the volunteers. Three hours later, 5 ml of blood were drawn from each volunteer and prepared for High-Performance Liquid Chromatography (HPLC) analysis. The main outcomes were INH and Acetyl-INH concentrations in plasma and the subsequent Acetyl-INH/INH metabolic ratio (MR).

Results

The findings suggest that slow acetylation is highly prevalent among the study participants (n = 43; 84.31%). Moreover, there was no statistically significant correlation between age and the MR (r = −0.18, P = 0.20). Further, there was no significant association between gender and the MR (P = 0.124). Similarly, no significant association was found between smoking habits and MR (P = 0.24).

Conclusion

Isoniazid phenotyping suggests predominantly slow acetylation among the Sudanese in this sample. The study found no statistically significant associations between the MR and age or gender or smoking.

Targeted ultra-deep sequencing of a South African Bantu-speaking cohort to comprehensively map and characterize common and novel variants in 65 pharmacologically-related genes

BACKGROUND

African populations are characterised by high genetic diversity, which provides opportunities for discovering and elucidating novel variants of clinical importance, especially those affecting therapeutic outcome. Significantly more knowledge is however needed before such populations can take full advantage of the advances in precision medicine. Coupled with the need to concisely map and better understand the pharmacological implications of genetic diversity in populations of sub-Sharan African ancestry, the aim of this study was to identify and characterize known and novel variants present within 65 important absorption, distribution, metabolism and excretion genes.

PATIENTS AND METHODS

Targeted ultra-deep next-generation sequencing was used to screen a cohort of 40 South African individuals of Bantu ancestry.

RESULTS

We identified a total of 1662 variants of which 129 are novel. Moreover, out of the 1662 variants 22 represent potential loss-of-function variants. A high level of allele frequency differentiation was observed for variants identified in this study when compared with other populations. Notably, on the basis of prior studies, many appear to be pharmacologically important in the pharmacokinetics of a broad range of drugs, including antiretrovirals, chemotherapeutic drugs, antiepileptics, antidepressants, and anticoagulants. An in-depth analysis was undertaken to interrogate the pharmacogenetic implications of this genetic diversity.

CONCLUSION

Despite the new insights gained from this study, the work illustrates that a more comprehensive understanding of population-specific differences is needed to facilitate the development of pharmacogenetic-based interventions for optimal drug therapy in patients of African ancestry.

Association of genetic polymorphisms of CYP2E1, NAT2, GST and SLCO1B1 with the risk of anti-tuberculosis drug-induced liver injury: a systematic review and meta-analysis

OBJECTIVES

The objective of this study was to investigate the association between genetic polymorphisms of N-acetyltransferase 2 (NAT2), cytochrome P450 2E1 (CYP2E1), glutathione S-transferase (GST) and solute carrier organic anion transporter family member 1B1 (SLCO1B1) and the risk of anti-tuberculosis drug-induced liver injury (ATDILI).

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

PubMed, Embase, Web of Science and Cochrane Reviews databases were searched through April 2019.

ELIGIBILITY CRITERIA

We included case-control or cohort studies investigating an association between NAT2, CYP2E1, GST or SLCO1B1 polymorphisms and the ATDILI risk in patients with tuberculosis.

DATA EXTRACTION AND SYNTHESIS

Three authors screened articles, extracted data and assessed study quality. The strength of association was evaluated for each gene using the pooled OR with a 95% CI based on the fixed-effects or random-effects model. Sensitivity analysis was performed to confirm the reliability and robustness of the results.

RESULTS

Fifty-four studies were included in this analysis (n=26 for CYP2E1, n=35 for NAT2, n=19 for GST, n=4 for SLCO1B1). The risk of ATDILI was significantly increased with the following genotypes: CYP2E1 RsaI/PstI c1/c1 (OR=1.39, 95% CI 1.06 to 1.83), NAT2 slow acetylator (OR=3.30, 95% CI 2.65 to 4.11) and GSTM1 null (OR=1.30, 95% CI 1.12 to 1.52). No significant association with ATDILI was found for the genetic polymorphisms of CYP2E1 DraI, GSTT1, GSTM1/GSTT1, SLCO1B1 388A>G and SLCO1B1 521T>C (p>0.05).

CONCLUSIONS

ATDILI is more likely to occur in patients with NAT2 slow acetylator genotype, CYP2E1 RsaI/PstI c1/c1 genotype and GSTM1 null genotype. Close monitoring may be warranted for patients with these genotypes.

NAT2 variants and toxicity related to anti-tuberculosis agents: a systematic review and meta-analysis

BACKGROUND

Tuberculosis (TB) patients receiving anti-tuberculosis treatment may experience serious adverse drug reactions (ADRs) such as hepatotoxicity. Variants of the N-acetyltransferase 2 (NAT2) gene may increase the risk of experiencing such toxicity events.

OBJECTIVE

To provide a comprehensive evaluation of the evidence base for associations between NAT2 variants and anti-tuberculosis drug-related toxicity.

METHOD

This was a systematic review and meta-analysis. We searched for studies in Medline, PubMed, EMBASE, BIOSIS and Web of Science. We included data from 41 articles (39 distinct cohorts of patients). We pooled effect estimates for each genotype on each outcome using meta-analyses stratified by country.

RESULTS

We assessed the quality of the included studies, which was variable, with many areas of concern. Slow/intermediate NAT2 acetylators were statistically significantly more likely to experience hepatotoxicity than rapid acetylators (OR 1.59, 95%CI 1.26-2.01). Heterogeneity was not detected in the overall pooled analysis (I² = 0%). NAT2 acetylator status was significantly associated with the likelihood of experiencing anti-tuberculosis drug-related hepatotoxicity.

CONCLUSION

We encountered several challenges in performing robust syntheses of data from pharmacogenetic studies, and we outline recommendations for the future reporting of pharmacogenetic studies to enable high-quality systematic reviews and meta-analyses to be performed.

Pharmacogenetic association between NAT2 gene polymorphisms and isoniazid induced hepatotoxicity: trial sequence meta-analysis as evidence

Hepatotoxicity is a severe problem generally faced by tuberculosis (TB) patients. It is a well-known adverse reaction due to anti-TB drugs in TB patients undergoing long-term treatment. The studies published previously have explored the connection of N-acetyltransferase 2 (NAT2) gene polymorphisms with isoniazid-induced hepatotoxicity, but the results obtained were inconsistent and inconclusive. A comprehensive trial sequence meta-analysis was conducted employing 12 studies comprising 3613 controls and 933 confirmed TB cases using the databases namely, EMBASE, PubMed (Medline) and Google Scholar till December 2017. A significant association was observed with individuals carrying variant allele at position 481C>T (T vs. C: P = 0.001; OR = 1.278, 95% CI = 1.1100–1.484), at position 590G>A (A vs. G: P = 0.002; OR = 1.421, 95% CI = 1.137–1.776) and at position 857G>A (A vs. G: P = 0.0022; OR = 1.411, 95% CI = 1.052–1.894) to higher risk of hepatotoxicity vis-à-vis wild-type allele. Likewise, the other genetic models of NAT2 gene polymorphisms have also shown increased risk of hepatotoxicity. No evidence of publication bias was observed. These results suggest that genetic variants of NAT2 gene have significant role in isoniazid induced hepatotoxicity. Thus, NAT2 genotyping has the potential to improve the understanding of the drug–enzyme metabolic capacity and help in early predisposition of isoniazid-induced hepatotoxicity.

The association between the NAT2 genetic polymorphisms and risk of DILI during anti-TB treatment: a systematic review and meta-analysis

AIMS

The aim of this study is to evaluate the potential association between N-acetyltransferase type 2 (NAT2) polymorphisms and drug-induced liver injury during anti-TB treatment (AT-DILI).

METHODS

We conducted a systematic review and performed a meta-analysis to clarify the role of NAT2 polymorphism in AT-DILI. PubMed, Medline and EMBASE databases were searched for studies published in English to December 31, 2017, on the association between the NAT2 polymorphism and AT-DILI risk. Outcomes were pooled with random-effects meta-analysis. Details were registered in the PROSPERO register (number: CRD42016051722).

RESULTS

Thirty-seven studies involving 1527 cases and 7184 controls were included in this meta-analysis. The overall odds ratio (OR) of AT-DILI associated with NAT2 slow acetylator phenotype was 3.15 (95% CI 2.58-3.84, I²  = 51.3%, P = 0.000). The OR varied between different ethnic populations, ranging from 6.42 (95% CI 2.41-17.10, I²  = 2.3%) for the West Asian population to 2.32 (95% CI 0.58-9.24, I²  = 80.3%) for the European population. Within the slow NAT2 genotype, variation was also observed; NAT2*6/*7 was associated with the highest risk of AT-DILI (OR = 1.68, 95% CI 1.09-2.59) compared to the other slow NAT2 acetylators combined.

CONCLUSIONS

NAT2 slow acetylation was observed to increase the risk of AT-DILI in tuberculosis patients. Our results support the hypothesis that the slow NAT2 genotype is a risk factor for AT-DILI.

Association and clinical utility of NAT2 in the prediction of isoniazid-induced liver injury in Singaporean patients

BACKGROUND AND AIMS

Isoniazid (INH) is part of the first-line-therapy for tuberculosis (TB) but can cause drug-induced liver injury (DILI). Several candidate single nucleotide polymorphisms (SNPs) have been previously identified but the clinical utility of these SNPs in the prediction of INH-DILI remains uncertain. The aim of this study was to assess the association between selected candidate SNPs and the risk of INH-DILI and to assess the clinical validity of associated variants in a Singaporean population.

METHODS

This was a case-control study where 24 INH-DILI cases and 79 controls were recruited from the TB control unit in a tertiary hospital. Logistic regression was used to test for the association between candidate SNPs and INH-DILI. NAT2 acetylator status was inferred from genotypes and tested for association with INH-DILI. Finally, clinical validity measures were estimated for significant variants.

RESULTS

Two SNPs in NAT2 (rs1041983 and rs1495741) and NAT2 slow acetylators (SA) were significantly associated with INH-DILI (OR (95% CI) = 13.86 (4.30-44.70), 0.10 (0.03-0.33) and 9.98 (3.32-33.80), respectively). Based on an INH-DILI prevalence of 10%, the sensitivity, specificity, positive and negative predictive values of NAT2 SA were 75%, 78%, 28% and 97%, respectively. The population attributable fraction (PAF) and number needed to test (NNT) for NAT2 SA were estimated to be 0.67 and 4.08, respectively. A model with clinical and NAT2 acetylator status provided significantly better prediction for INH-DILI than a clinical model alone (area under receiver operating characteristic curve = 0.863 vs. 0.766, respectively, p = 0.027).

CONCLUSIONS

We show the association between NAT2 SA and INH-DILI in a Singaporean population and demonstrated its clinical utility in the prediction of INH-DILI.

Adverse Drug Reactions: Type A (Intrinsic) or Type B (Idiosyncratic)

Hepatotoxic adverse drug reactions are associated with significant morbidity and mortality and are the leading cause of postmarketing regulatory action in the United States. They are classified as Type A (intrinsic) or Type B (idiosyncratic). Type A are predictable, dose-related toxicities, often identified in preclinical or clinical trials, and usually occur in overdose settings or with pre-existing hepatic impairment. Type B are not clearly related to increasing dose and are associated with drug-specific and patient-specific characteristics and environmental risks. Rare Type B reactions are often identified postmarketing. Identification and management, including electronic resources, has evolved.

Tuberculosis of the Liver, Biliary Tract, and Pancreas

Tuberculosis of the liver, biliary tract, and pancreas is discussed. In addition, tuberculosis in the setting of HIV-AIDS and liver transplantation is explored. Drug-induced liver injury secondary to antituberculosis medication and monitoring and prophylactic treatment for such injury is also considered.

[Personalized drug therapy based on genetics. Possibilities and examples from clinical practice]

BACKGROUND

Pharmacogenetics are an important component in the individualization of treatment; however, pharmacogenetic diagnostics have so far not been used to any great extent in clinical practice. A consistent consideration of individual patient factors, such as pharmacogenetics may help to improve drug therapy and increase individual safety and efficacy aspects.

OBJECTIVE

A brief summary of structures and effects of genetic variations on drug efficacy is presented. Some frequently prescribed pharmaceuticals are specified. Furthermore, the feasibility of pharmacogenetic diagnostics and dose recommendations in the clinical practice are described.

CURRENT DATA

The European Medicines Agency (EMA) as the European approval authority has already extended the drug labels of more than 70 pharmaceuticals by information on pharmacogenetic biomarkers and the U.S. Food and Drug Administration (FDA) more than 150. This is a crucial step towards targeted medicine. Guidelines on dose and therapy adjustments are provided by the Clinical Pharmacogenetics Implementation Consortium of the Pharmacogenomics Research Network.

CONCLUSION

It is fundamental to consider individual patient factors for successful drug therapy. Dose and therapy recommendations based on pharmacogenetic diagnostics are highly important for individualization as well as improvement of safety and efficiency of drug therapy.

Prevention of isoniazid toxicity by NAT2 genotyping in Senegalese tuberculosis patients

Isoniazid (INH), recommended by WHO (World Health Organization) in the treatment of tuberculosis (TB), is metabolized primarily by the genetically polymorphic N-acetyltransferase 2 (NAT2) enzyme. The human population is divided into three different phenotypic groups according to acetylation rate: slow, intermediate, and fast acetylators. The objective of this study was to explore the relationship between NAT2 genotypes and the serum concentrations of INH. Blood samples from 96 patients with TB were taken for the analysis. NAT2 polymorphisms on coding region were examined by polymerase chain reaction (PCR) direct sequencing; the acetylation status was obtained by measuring isoniazid (INH) and its metabolite, acetylisoniazid (AcINH) in plasma was obtained by using the liquid chromatography coupled to mass spectrometry. TB patients were distributed into two groups of fast and slow acetylators according to the acetylation index calculated based on the plasma concentration of INH in the 3rd hour (T3) after an oral dose. Our PCR analysis identified several alleles, where NAT2*4, NAT2*5A, NAT2*6A, and NAT2*13A were the most important. The concentrations of INH varied between 1.10 mg/L and 13.10 mg/L at the 3rd hour and between 0.1 and 9.5 mg/L at the 6th hour. The use of the acetylating index I₃ allowed the classification of tested patients into two phenotypic groups: slow acetylators (44.3% of TB patients), and rapid acetylators (55.7%). Patient’s acetylation profile provides valuable information on their therapeutic, pharmacological, and toxicological responses.

Optimizing treatment outcome of first-line anti-tuberculosis drugs: the role of therapeutic drug monitoring

INTRODUCTION

Tuberculosis (TB) remains one of the world's deadliest communicable diseases. Although cure rates of the standard four-drug (rifampicin, isoniazid, pyrazinamide, ethambutol) treatment schedule can be as high as 95-98 % under clinical trial conditions, success rates may be much lower in less well resourced countries. Unsuccessful treatment with these first-line anti-TB drugs may lead to the development of multidrug resistant and extensively drug resistant TB. The intrinsic interindividual variability in the pharmacokinetics (PK) of the first-line anti-TB drugs is further exacerbated by co-morbidities such as HIV infection and diabetes.

METHODS

Therapeutic drug monitoring has been proposed in an attempt to optimize treatment outcome and reduce the development of drug resistance. Several studies have shown that maximum plasma concentrations (C max), especially of rifampicin and isoniazid, are well below the proposed target C max concentrations in a substantial fraction of patients being treated with the standard four-drug treatment schedule, even though treatment's success rate in these studies was typically at least 85 %.

DISCUSSION

The proposed target C max concentrations are based on the concentrations of these agents achieved in healthy volunteers and patients receiving the standard doses. Estimation of C max based on one or two sampling times may not have the necessary accuracy since absorption rate, especially for rifampicin, may be highly variable. In addition, minimum inhibitory concentration (MIC) variability should be taken into account to set clinically meaningful susceptibility breakpoints. Clearly, there is a need to better define the key target PK and pharmacodynamic (PD) parameters for therapeutic drug monitoring (TDM) of the first-line anti-TB drugs to be efficacious, C max (or area under the curve (AUC)) and C max/MIC (or AUC/MIC).

CONCLUSION

Although TDM of first-line anti-TB drugs has been successfully used in a limited number of specialized centers to improve treatment outcome in slow responders, a better characterization of the target PK and/or PK/PD parameters is in our opinion necessary to make it cost-effective.

Susceptibility of N-acetyltransferase 2 slow acetylators to antituberculosis drug-induced liver injury: a meta-analysis

AIM

This study aimed to evaluate the association between N-acetyltransferase 2 (NAT2) gene polymorphisms and the risk of antituberculosis drug-induced liver injury (ATLI).

MATERIALS & METHODS

A meta-analysis was performed including 27 studies with 1289 cases and 5462 controls. Odds ratio with 95% CI was used to evaluate the strength of association.

RESULTS

Our meta-analysis found that NAT2 slow acetylators were associated with increased risk of ATLI compared with fast and intermediate acetylators when standard dose of isoniazid was administrated (odds ratio: 3.08; 95% CI: 2.29-4.15).

CONCLUSION

Individuals with NAT2 slow acetylators may have increased risk of ATLI when standard dose of isoniazid was used. Detection of NAT2 genotype may benefit to the prevention of ATLI.

Polymorphism of PXR gene associated with the increased risk of drug-induced liver injury in Indonesian pulmonary tuberculosis patients

WHAT IS KNOWN AND OBJECTIVE

Tuberculosis is still a major infectious disease in Indonesia. Patients are treated mostly using fixed-dose combination treatment in primary public health facilities. The incidence of antituberculosis drug-induced liver injury (AT-DILI) is approximately 10% among Indonesian tuberculosis patients who used standard fixed combination regimens during the intensive phase of treatment. However, information regarding genetic polymorphism associated with the increase risk of drug-induced liver injury is still limited. The aim of this study was to investigate pregnane X receptor (PXR) gene polymorphisms as one of the risk factors of AT-DILI.

METHODS

In this prospective cohort study, we recruited 106 adult patients diagnosed with pulmonary tuberculosis and treated with category I FDC (fixed-dose combination). The identification of SNP -25385C>T (rs3814055) was conducted by ARMS (amplification refractory mutation system). Hepatotoxicity was defined as ALT and/or AST levels above the normal threshold on the second, fourth and sixth months of monitoring during tuberculosis treatment.

RESULTS AND DISCUSSION

The logistic regression analysis showed that patients with the TT genotype of PXR gene (rs3814055) significantly had a greater risk of AT-DILI (OR 8·89; 95% CI 1·36-57·93, P < 0·05), compared with those of wild-type CC genotype.

WHAT IS NEW AND CONCLUSION

The result suggests that in Indonesian patients with tuberculosis, the risk of having AT-DILI was associated with TT genotype of the PXR gene.

Pharmacogenomics Implications of Using Herbal Medicinal Plants on African Populations in Health Transition

The most accessible points of call for most African populations with respect to primary health care are traditional health systems that include spiritual, religious, and herbal medicine. This review focusses only on the use of herbal medicines. Most African people accept herbal medicines as generally safe with no serious adverse effects. However, the overlap between conventional medicine and herbal medicine is a reality among countries in health systems transition. Patients often simultaneously seek treatment from both conventional and traditional health systems for the same condition. Commonly encountered conditions/diseases include malaria, HIV/AIDS, hypertension, tuberculosis, and bleeding disorders. It is therefore imperative to understand the modes of interaction between different drugs from conventional and traditional health care systems when used in treatment combinations. Both conventional and traditional drug entities are metabolized by the same enzyme systems in the human body, resulting in both pharmacokinetics and pharmacodynamics interactions, whose properties remain unknown/unquantified. Thus, it is important that profiles of interaction between different herbal and conventional medicines be evaluated. This review evaluates herbal and conventional drugs in a few African countries and their potential interaction at the pharmacogenomics level.

A 30-years review on pharmacokinetics of antibiotics: is the right time for pharmacogenetics?

Drug bioavailability may vary greatly amongst individuals, affecting both efficacy and toxicity: in humans, genetic variations account for a relevant proportion of such variability. In the last decade the use of pharmacogenetics in clinical practice, as a tool to individualize treatment, has shown a different degree of diffusion in various clinical fields.

In the field of infectious diseases, several studies identified a great number of associations between host genetic polymor-phisms and responses to antiretroviral therapy. For example, in patients treated with abacavir the screening for HLA-B*5701 before starting treatment is routine clinical practice and standard of care for all patients; efavirenz plasma levels are influenced by single nucleotide polymorphism (SNP) CYP2B6-516G> T (rs3745274). Regarding antibiotics, many studies investigated drug transporters involved in antibiotic bioavailability, especially for fluoroquinolones, cephalosporins, and antituberculars. To date, few data are available about pharmacogenetics of recently developed antibiotics such as tigecycline, daptomycin or linezolid. Considering the effect of SNPs in gene coding for proteins involved in antibiotics bioavailability, few data have been published.

Increasing knowledge in the field of antibiotic pharmacogenetics could be useful to explain the high drug inter-patients variability and to individualize therapy. In this paper we reported an overview of pharmacokinetics, pharmacodynamics, and pharmacogenetics of antibiotics to underline the importance of an integrated approach in choosing the right dosage in clinical practice.

Genetic variation in aryl N-acetyltransferase results in significant differences in the pharmacokinetic and safety profiles of amifampridine (3,4-diaminopyridine) phosphate

The clinical use of amifampridine phosphate for neuromuscular junction disorders is increasing. The metabolism of amifampridine occurs via polymorphic aryl N-acetyltransferase (NAT), yet its pharmacokinetic (PK) and safety profiles, as influenced by this enzyme system, have not been investigated. The objective of this study was to assess the effect of NAT phenotype and genotype on the PK and safety profiles of amifampridine in healthy volunteers (N = 26). A caffeine challenge test and NAT2 genotyping were used to delineate subjects into slow and fast acetylators for PK and tolerability assessment of single, escalating doses of amifampridine (up to 30 mg) and in multiple daily doses (20 mg QID) of amifampridine. The results showed that fast acetylator phenotypes displayed significantly lower C max, AUC, and shorter t 1/2 for amifampridine than slow acetylators. Plasma concentrations of the N-acetyl metabolite were approximately twofold higher in fast acetylators. Gender differences were not observed. Single doses of amifampridine demonstrated dose linear PKs. Amifampridine achieved steady state plasma levels within 1 day of dosing four times daily. No accumulation or time-dependent changes in amifampridine PK parameters occurred. Overall, slow acetylators reported 73 drug-related treatment-emergent adverse events versus 6 in fast acetylators. Variations in polymorphic NAT corresponding with fast and slow acetylator phenotypes significantly affects the PK and safety profiles of amifampridine.

[Tuberculosis: relevance of isoniazid dosage in prevention of liver side effects]

OBJECTIVE

Several recent studies have established a correlation between NAT2 polymorphism and hepatotoxicity induced by isoniazid. The objective of this work was to assess the place of isoniazid dosage, marker of acetylation phenotype, in clinical practice in the department of Haute-Garonne.

METHODS

Data from reportable disease of tuberculosis and the results of isoniazid dosage performed at the pharmacokinetics and clinical toxicology laboratory were used during the period 2009-2012.

RESULTS

The current practice of dosage is far from being systematical: only 3.9% of patients who developed tuberculosis have benefited from isoniazid dosage. The isoniazid initial posology was adapted to the acetylation capacity for only 33.3% of patients.

CONCLUSION

A decision tree was realized and used to identify populations (low metabolism) liable to benefit from isoniazid dosage.

Clinical and pharmacogenomic implications of genetic variation in a Southern Ethiopian population

Africa is home to genetically diverse human populations. We compared the genetic structure of the Wolaita ethnic population from southern Ethiopia (WETH, n=120) with HapMap populations using genome-wide variants. We investigated allele frequencies of 443 clinically and pharmacogenomically relevant genetic variants in WETH compared to HapMap populations. We found that WETH were genetically most similar to the Kenya Maasai and least similar to the Japanese in HapMap. Variant alleles associated with increased risk of adverse reactions to drugs used for treating tuberculosis (rs1799929 and rs1495741 in NAT2), thromboembolism (rs7294, rs9923231 and rs9934438 in VKORC1), and HIV/AIDS and solid tumors (rs2242046 in SLC28A1) had significantly higher frequencies in WETH compared to African ancestry HapMap populations. Our results illustrate that clinically relevant pharmacogenomic loci display allele frequency differences among African populations. We conclude that drug dosage guidelines for important global health diseases should be validated in genetically diverse African populations.

N-acetyltransferase 2 (NAT2) genotype as a risk factor for development of drug-induced liver injury relating to antituberculosis drug treatment in a mixed-ethnicity patient group

PURPOSE

This study aims to assess whether NAT2 genotype affects susceptibility to moderate to severe liver injury in patients undergoing drug treatment for tuberculosis with isoniazid-containing regimens.

METHODS

Twenty-six patients of European or South Asian ethnicity, who had suffered liver injury during treatment with isoniazid-containing drug regimens and 101 ethnically matched controls were genotyped for the NAT2*5, NAT2*6, and NAT2*7 alleles. Genotyping for additional polymorphisms in the NAT gene region was also performed on 20 of the 26 cases. NAT2 genotype frequency between cases and controls was compared.

RESULTS

NAT2 genotypes predicting a slow acetylator phenotype were found to be associated with an increased risk of isoniazid-related liver injury (odds ratio (OR) = 4.25 (95% confidence interval (CI), 1.36-13.22); p = 0.012) with 85% of the cases being slow acetylators compared with 56% of the controls. There was no evidence for an increased risk for the slow acetylator genotype in patients with the most severe cases of liver injury, who underwent liver transplantation.

CONCLUSIONS

The NAT2 slow acetylator genotype appears to be a significant risk factor for moderate and severe drug- induced liver injury. However, the overall effect size is modest and generally in line with effects described previously for this genotype in milder drug-induced liver injury. Additional genetic risk factors may also contribute.

Polymorphisms in CYP2E1, GSTM1 and GSTT1 and anti-tuberculosis drug-induced hepatotoxicity

Anti-tuberculosis drug-induced hepatitis (ATD- induced hepatitis) has been linked to polymorphisms in genes encoding drug metabolizing enzymes. N-acetyltransferase 2 (NAT2), cytochrome P450 2E1 (CYP2E1) and glutathione S-transferase (loci GSTM1 and GSTT1) are involved in the metabolism of isoniazid, the most toxic drug for the treatment of tuberculosis (TB). This study was designed to determine the frequency and to evaluate whether polymorphisms at CYP2E1, GSTM1 and GSTT1 genes are associated with drug response, as well as to identify clinical risk factors for ATD-induced hepatitis. A total of 245 Brazilian patients undergoing treatment for TB were genotyped using polymerase chain reaction and restriction fragment length polymorphism and sequencing methods. The frequencies of the CYP2E1 polymorphic alleles RsaI, PstI and DraI are 8%, 8.5% and 12%, respectively. GSTM1 and GSTT1 genes are deleted in 42.9% and 12.4% of the population, respectively. Fifteen patients (6.1%) developed hepatotoxicity. Clinical (HIV, female sex and extrapulmonary TB) and genetic characteristics (CYP2E1 without any mutations, having NAT2 slow acetylator profile) are at higher risk of developing ATD-induced hepatitis in this population. Genotyping for GSTM1 and GSTT1 showed no influence on drug response.

Association of N-acetyltransferase 2 and cytochrome P450 2E1 gene polymorphisms with antituberculosis drug-induced hepatotoxicity in Western India

BACKGROUND AND AIM

Tuberculosis (TB) is a major public health problem in India. Despite the treatment availability and monitoring, drug-induced hepatotoxicity (DIH) is a serious concern and can lead to discontinuation of treatment. Anti-TB DIH is well known and can aggravate because of pharmacokinetic and pharmacodynamic interactions. Genetic polymorphism in the drug-metabolizing enzyme genes is an important factor that predisposes certain fraction of the population to drug-induced toxicity. The purpose of this study was to assess the association of N-acetyltransferase 2 (NAT2) and cytochrome P450 2E1 (CYP2E1) gene polymorphism with anti-TB DIH in Western Indian population.

METHODS

A prospective cohort study of 215 patients taking treatment against TB was performed. The NAT2 and CYP2E1 genotypes were determined using polymerase chain reaction and restriction fragment length polymorphism methods. Logistic regression model was used to calculate odds ratio at 95% confidence interval and their respective P values.

RESULTS

The risk of anti-TB DIH was significantly higher in slow acetylator (SA) than in intermediate and rapid acetylator of NAT2 genotypes (odds ratio: 2.3, P = 0.01). We also observed the homozygous point mutation at position 481, associated with higher risk of hepatotoxicity (P < 0.01). The major haplotype NAT2*4 seems to provide protection in DIH compared with non-DIH TB patients (P = 0.04). However, we did not find a significant association between CYP2E1 genotypes and anti-TB DIH.

CONCLUSION

Increased susceptibility to isoniazid (INH)-induced hepatotoxicity due to presence of NAT2 SA polymorphism was demonstrated in Western Indian population. NAT2 genotyping can therefore serve as an important tool for identifying patients predisposed to anti-TB DIH.

Pharmacogenomics of adverse drug reactions

Considerable progress has been made in identifying genetic risk factors for idiosyncratic adverse drug reactions in the past 30 years. These reactions can affect various tissues and organs, including liver, skin, muscle and heart, in a drug-dependent manner. Using both candidate gene and genome-wide association studies, various genes that make contributions of varying extents to each of these forms of reactions have been identified. Many of the associations identified for reactions affecting the liver and skin involve human leukocyte antigen (HLA) genes and for reactions relating to the drugs abacavir and carbamazepine, HLA genotyping is now in routine use prior to drug prescription. Other HLA associations are not sufficiently specific for translation but are still of interest in relation to underlying mechanisms for the reactions. Progress on non-HLA genes affecting adverse drug reactions has been less, but some important associations, such as those of SLCO1B1 and statin myopathy, KCNE1 and drug-induced QT prolongation and NAT2 and isoniazid-induced liver injury, are considered. Future prospects for identification of additional genetic risk factors for the various adverse drug reactions are discussed.

Pharmacogenomics and Personalized Medicine for Infectious Diseases

Humans have been plagued by the scourge of invasion by pathogens leading to infectious diseases from the time in memoriam and are still the cause of morbidity and mortality among millions of individuals. Trying to understand the disease mechanisms and finding the remedial measures have been the quest of humankind. The susceptibility to disease of an individual in a given population is determined by ones genetic buildup. Response to treatment and the disease prognosis also depends upon individual’s genetic predisposition. The environmental stress induces mutations and is leading to the emergence of ever-increasing more dreaded infectious pathogens, and now we are in the era of increasing antibiotic resistance that has thrown up a challenge to find new treatment regimes. Discoveries in the science of high-throughput sequencing and array technologies have shown new hope and are bringing a revolution in human health. The information gained from sequencing of both human and pathogen genomes is a way forward in deciphering host-pathogen interactions. Deciphering the pathogen virulence factors, host susceptibility genes, and the molecular programs involved in the pathogenesis of disease has paved the way for discovery of new molecular targets for drugs, diagnostic markers, and vaccines. The genomic diversity in the human population leads to differences in host responses to drugs and vaccines and is the cause of poor response to treatment as well as adverse reactions. The study of pharmacogenomics of infectious diseases is still at an early stage of development, and many intricacies of the host-pathogen interaction are yet to be understood in full measure. However, progress has been made over the decades of research in some of the important infectious diseases revealing how the host genetic polymorphisms of drug-metabolizing enzymes and transporters affect the bioavailability of the drugs which further determine the efficacy and toxicology of the drugs used for treatment. Further, the field of structural biology and chemistry has intertwined to give rise to medical structural genomics leading the way to the discovery of new drug targets against infectious diseases. This chapter explores how the advent of “omics” technologies is making a beginning in bringing about a change in the prevention, diagnosis, and treatments of the infectious diseases and hence paving way for personalized medicine.

Slow N-acetyltransferase 2 genotype contributes to anti-tuberculosis drug-induced hepatotoxicity: a meta-analysis

Pathogenesis and genetic factors influencing predisposition to antituberculosis drug-induced hepatotoxicity (ATDH) are not clear. Polymorphism at the genetic locus of a drug and xenobiotic compound metabolizing enzyme, N-acetyltransferase type 2 (NAT2), is reported to be associated with the excess generation of toxic reactive metabolites. To date, many case-control studies have been carried out to investigate the relationship between the NAT2 polymorphisms and ATDH, but the results have been inconsistent. To investigate this inconsistency, a meta-analysis was performed. Databases including PubMed, Web of Science, EMBASE and CNKI were searched to find relevant studies. A total of 26 case-control studies, involving 1,198 cases and 2,921 controls were included. Overall, we found significant association between slow acetylator genotype of NAT2 and ATDH (OR = 3.10, 95% CI: 2.47-3.88, P < 10(-5)). Significant results were also found in East Asians, South Asians, Brazilians and Middle Eastern when stratified by ethnicity. However, no significant associations were found for Caucasians. This meta-analysis demonstrated that the slow acetylator genotype of NAT2 is a risk factor associated with increased ATDH susceptibility, but these associations vary in different ethnic populations.

Pharmacogenetic study of drug-metabolising enzyme polymorphisms on the risk of anti-tuberculosis drug-induced liver injury: a meta-analysis

Background

Three first-line antituberculosis drugs, isoniazid, rifampicin and pyrazinamide, may induce liver injury, especially isoniazid. This antituberculosis drug-induced liver injury (ATLI) ranges from a mild to severe form, and the associated mortality cases are not rare. In the past decade, many investigations have focused the association between drug-metabolising enzyme (DME) gene polymorphisms and risk for ATLI; however, these studies have yielded contradictory results.

Methods

PubMed, EMBASE, ISI web of science and the Chinese National Knowledge Infrastructure databases were systematically searched to identify relevant studies. A meta-analysis was performed to examine the association between polymorphisms from 4 DME genes (NAT2, CYP2E1, GSTM1 and GSTT1) and susceptibility to ATLI. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Heterogeneity among articles and their publication bias were also tested.

Results

38 studies involving 2,225 patients and 4,906 controls were included. Overall, significantly increased ATLI risk was associated with slow NAT2 genotype and GSTM1 null genotype when all studies were pooled into the meta-analysis. Significantly increased risk was also found for CYP2E1*1A in East Asians when stratified by ethnicity. However, no significant results were observed for GSTT1.

Conclusions

Our results demonstrated that slow NAT2 genotype, CYP2E1*1A and GSTM1 null have a modest effect on genetic susceptibility to ATLI.

Role of pharmacogenomics in the treatment of tuberculosis: a review

BACKGROUND

Tuberculosis is one of the major public health problems worldwide. Modern antituberculous treatment can cure most patients; cure rates > 95% are achieved with standard short-course chemotherapy regimens containing isoniazid, rifampicin, pyrazinamide, and ethambutol among patients with drug-susceptible strains of tuberculosis; however, a small proportion do not respond to treatment or develop serious adverse events. Pharmacogenomic studies of drugs used in the treatment of tuberculosis could help us understand intersubject variations in treatment response. In this review, we compiled pharmacogenomic data on antituberculous drugs that were available from different settings that would give a better insight into the role of pharmacogenomics in the treatment of tuberculosis, thereby enhancing the efficacy and limiting the toxicity of existing antituberculosis medications.

METHODS

The PubMed database was searched from 1960 to the present using the keywords "tuberculosis", "antituberculosis treatment", "isoniazid", "rifampicin", "pyrazinamide", "ethambutol", "pharmacogenomics", and "polymorphism". Abstracts from meetings and review articles were included.

CONCLUSION

Studies conducted in different settings suggest that pharmacogenomics plays a significant role in isoniazid metabolism, and impacts both treatment efficacy and frequency of adverse reactions. Single nucleotide polymorphisms influencing plasma rifampicin concentrations are also reported. No data are available regarding other first-line drugs, ie, ethambutol and pyrazinamide. There is a need to incorporate pharmacogenomics into clinical trials of tuberculosis in order to understand the factors impacting therapeutic success and occurrence of adverse drug effects.