Isoniazid metabolism and hepatotoxicity

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.

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

Tuberculosis is still a major problem in some developed and developing countries. The poor compliance to the treatment of tuberculosis patients due to the adverse events was supposed to be an important factor contributing to the high prevalence. This review aims to clarify the role and the pharmacological mechanism of the genes involved in the isoniazid-induced hepatotoxicity. We selected English articles of studies in human from PubMed up to May 2014 with the keywords pharmacogenetic, isoniazid and hepatotoxicity, N-acetyl transferase 2 (NAT2), CYP2E1 and glutathione S transferase (GST). Polymorphisms of NAT2, CYP2E1 and GST1 could increase patients' susceptibility to isoniazid-induced hepatotoxicity. The rapid acetylators of NAT2 and rapid metabolizers of CYP2E1 showed increased concentrations of hepatotoxic metabolites. However, the rapid metabolizers of GST1 could decrease the concentration of hepatotoxic metabolites. Some studies of human leukocyte antigen (HLA), Uridine 5'-dipphospho (UDP) glucuronosyltransferase (UGT), nitric oxide synthase (NOS), Broad complex, Tramtrack, Bric-a-brac (BTB) and cap'n'collar type of basic region leucine zipper factor family (CNC) homolog (BACH) and Maf basic leucine zipper protein (MAFK) polymorphisms showed their roles in isoniazid-induced hepatotoxicity by modifying the expression of antioxidant enzymes. A better insight into the role of polymorphisms of HLA, UGT, NOS, BACH and MAFK in addition to NAT2, CYP2E1 and GST1 in the hepatotoxicity of isoniazid may support physicians in monitoring patients hepatotoxicity symptoms and laboratory data and optimizing pharmacotherapy. Future studies about the role of such polymorphisms in different ethnicities are suggested.

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Pharmacogenetics of isoniazid-induced hepatotoxicity

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.

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

Background Isoniazid [isonicotinic acid (INA) hydrazide, INH; PubChem ID 3767] [1] is a first-line antimycobacterial agent used to treat active or latent tuberculosis (TB) infections generated by Mycobacterium tuberculosis [2–4]. INH has been in clinical use for over 60 years [1] and standard regimens for active TB infections include 2 months of treatment with INH, rifampicin, pyrazinamide, and ethambutol or streptomycin, followed by an additional 4 months of INH and rifampicin treatment [2,4,5]. Management of latent TB infections typically involves administration of INH alone (for 6 or 9 months) or in combination with rifapentine (for 3 months) to individuals at high risk of developing active TB [6,7]. Although effective, current therapeutic regimens are very lengthy and difficult to implement [8], and TB remains a major global health problem, with more than 9 million new cases and 1.5 million deaths reported in 2013 [9].

PharmGKB summary: isoniazid pathway, pharmacokinetics.

BACKGROUND AND OBJECTIVE Of three first-line anti-tuberculosis (anti-TB) drugs, isoniazid is most commonly associated with hepatotoxicity. Differences in INH-induced toxicity have been attributed to genetic variability at several loci, NAT2, CYP2E1, GSTM1and GSTT1, that code for drug-metabolizing enzymes. This study evaluated whether the polymorphisms in these enzymes were associated with an increased risk of anti-TB drug-induced hepatitis in patients and could potentially be used to identify patients at risk of liver injury. 

METHODS AND DESIGN In a cross-sectional study, 2244 tuberculosis patients were assessed two months after the start of treatment. Anti-TB drug-induced liver injury (ATLI) was defined as an ALT, AST or bilirubin value more than twice the upper limit of normal. NAT2, CYP2E1, GSTM1 and GSTT1 genotypes were determined using the PCR/ligase detection reaction assays. 

RESULTS 2244 patients were evaluated, there were 89 cases of ATLI, a prevalence of 4% 9 patients (0.4%) had ALT levels more than 5 times the upper limit of normal. The prevalence of ATLI was greater among men than women, and there was a weak association with NAT2*5 genotypes, with ATLI more common among patients with the NAT2*5*CT genotype. The sensitivity of the CT genotype for identifying patients with ATLI was 42% and the positive predictive value 5.9%. CT ATLI was more common among slow acetylators (prevalence ratio 2.0 (95% CI 0.95,4.20) )compared to rapid acetylators. There was no evidence that ATLI was associated with CYP2E1 RsaIc1/c1genotype, CYP2E1 RsaIc1/c2 or c2/c2 genotypes, or GSTM1/GSTT1 null genotypes. 

CONCLUSIONS In Xinjiang Uyghur TB patients, liver injury was associated with the genetic variant NAT2*5, however the genetic markers studied are unlikely to be useful for screening patients due to the low sensitivity and low positive predictive values for identifying persons at risk of liver injury.

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The incidence of liver injury in Uyghur patients treated for TB in Xinjiang Uyghur autonomous region, China, and its association with hepatic enzyme polymorphisms nat2, cyp2e1, gstm1 and gstt1.

Jinfeng Ma

Papers

The incidence of liver injury in Uyghur patients treated for TB in Xinjiang Uyghur autonomous region, China, and its association with hepatic enzyme polymorphisms nat2, cyp2e1, gstm1 and gstt1.