Influence of genetic variants on toxicity to anti-tubercular agents: a systematic review and meta-analysis (protocol)

Population Pharmacokinetic Modeling of Bedaquiline among Multidrug-Resistant Pulmonary Tuberculosis Patients from China

Bedaquiline has been widely used as a part of combination dosage regimens for the treatment of multidrug-resistant tuberculosis (MDR-TB) patients with limited options. Although the effectiveness and safety of bedaquiline have been demonstrated in clinical trials, limited studies have investigated the significant pharmacokinetics and the impact of genotype on bedaquiline disposition. Here, we developed a population pharmacokinetic model of bedaquiline to describe the concentration-time data from Chinese adult patients diagnosed with MDR-TB. A total of 246 observations were collected from 99 subjects receiving the standard recommended dosage. Bedaquiline disposition was well described by a one-compartment model with first-order absorption. Covariate modeling identified that gamma-glutamyl transferase (GGT) and the single-nucleotide polymorphism (SNP) rs319952 in the AGBL4 gene were significantly associated with the apparent clearance of bedaquiline. The clearance (CL/F) was found to be 1.4 L/h lower for subjects with allele GG in SNP rs319952 than for subjects with alleles AG and AA and to decrease by 30% with a doubling in GGT. The model-based simulations were designed to assess the impact of GGT/SNP rs319952 on bedaquiline exposure and showed that patients with genotype GG in SNP rs319952 and GGT ranging from 10 to 50 U/L achieved the targeted maximum serum concentration at steady state (C_max,ss). However, when GGT was increased to 100 U/L, C_max,ss was 1.68-fold higher than the highest concentration pursued. The model developed provides the consideration of genetic polymorphism and hepatic function for bedaquiline dosage in MDR-TB adult patients.

Genetic Variants and Drug Efficacy in Tuberculosis: A Step toward Personalized Therapy

Tuberculosis (TB) continues to be a major infectious disease affecting individuals worldwide. Current TB treatment strategy recommends the standard short-course chemotherapy regimen containing first-line drug, i.e., isoniazid, rifampicin, pyrazinamide, and ethambutol to treat patients suffering from drug-susceptible TB. Although Mycobacterium tuberculosis, the causing agent, is susceptible to drugs, some patients do not respond to the treatment or treatment may result in serious adverse reactions. Many studies revealed that anti-TB drug-related toxicity is associated with genetic variations, and these variations may also influence attaining maximum drug concentration. Thus, inter-individual diversities play a characteristic role by influencing the genes involved in drug metabolism pathways. The development of pharmacogenomics could bring a revolution in the field of treatment, and the understanding of germline variants may give rise to optimized targeted treatments and refine the response to standard therapy. In this review, we briefly introduced the field of pharmacogenomics with the evolution in genetics and discussed the pharmacogenetic impact of genetic variations on genes involved in the activities, such as anti-TB drug transportation, metabolism, and gene regulation.

Absence of significant association between UGT2B4 genetic variants and the susceptibility to anti-tuberculosis drug-induced liver injury in a Western Chinese population

WHAT IS KNOWN AND OBJECTIVE

Combination regimens of six-month duration may increase the incidence of anti-tuberculosis drug-induced liver injury (ATLI), which is clinically characterized by mild cholestasis and hepatocanalicular lesions. UGT2B4 is a predominant UDP-glucuronosyltransferase enzyme in the human liver that plays an important role in the detoxification of bile acids, which yields water-soluble inactive compounds that can easily be excreted in the bile or urine. This study aimed to investigate the potential association between UGT2B4 variants and the susceptibility to ATLI.

METHODS

Genomic DNA was extracted from whole blood sample of each patient, and all SNPs were genotyped using an improved multiplex ligation detection reaction method. Clinical symptoms and laboratory results were recorded regularly. Five genetic variants at UGT2B4(rs1131878, rs1966151, rs28361541, rs4557343 and rs79407331) were identified in a prospective study of 118 ATLI cases and 628 non-ATLI controls. All participants were treated by first-line anti-TB drugs in Western China Hospital. The potential association between SNPs, ATLI risk and clinical phenotypes were determined based on the distribution of allelic frequencies and different genetic models.

RESULTS AND DISCUSSION

Statistical comparisons of cases and controls after correction for multiple testing did not yield any significant association between genetic variants at UGT2B4 and risk of ATLI via the analyses of single locus and subgroup differences.

WHAT IS NEW AND CONCLUSION

This is the first study aimed to investigate the association of UGT2B4 polymorphisms with ATLI risk. Our results revealed that UGT2B4 genetic variants are unlikely to confer susceptibility to ATLI in the Western Chinese Han population.

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.

Additional compounds and the therapeutic potential of Cnidoscolus chayamansa (McVaugh) against hepatotoxicity induced by antitubercular drugs

Previously non-isolated compounds (scopoletin and β-D-Glucopyranoside, (1R)-O-isopropyl 6-O-(2,3,4-tri-O-acetyl-β-D-xylopyranosyl)-2,3,4-triacetate) were isolated from an organic extract of the Cnidoscolus chayamansa stem. Also, lupeol acetate (main compound, 49.7 mg/g of dry extract) and scopoletin (0.19 mg/g of dry extract) were quantified by HPLC analysis from this organic extract. The protective activity of the C. chayamansa organic extract against hepatotoxicity induced by antitubercular drugs [Rifampicin (50 mg/kg), Isoniazid (50 mg/kg), and Pyrazinamide (100 mg/kg)] are reported. The extract was tested at 200 and 400 mg/kg in Balb/C mice during 85 days, using silymarin (2.5 mg/kg) as positive control. Liver damage was determined using biochemical parameters (AST, ALT, ALP, CHOL, HDL TG, Urea, and CREA), histological analysis, and evaluation of oxidative stress (SOD, CAT, Gpx, Lpx and POx). The extract at both doses favored body weight gain with respect to the anti-TB group; the dose of 200 mg/kg was better. Also, the extract at both doses decreased the values of transaminases (AST, ALT) enzymes (p < 0.05) vs. anti-TB group. In oxidative stress parameters, the SOD value was decreased, as were the levels of peroxidation of lipids and oxidative protein in the group with C. chayamansa extract at 200 and 400 mg/kg vs. the anti-TB group. Histological analyses from liver showed the absence of steatosis in the extract group at 400 mg/kg, and moderate steatosis in the silymarin and extract (at 200 mg/kg) groups with respect to anti-TB group, which demonstrated a steatosis. It should be noted that during the study period, none of the treated mice died. In conclusion, the CHCl₃: MeOH extract of C. chayamansa has a hepatoprotective effect against hepatotoxicity induced by anti-TB drugs.

Association of PXR and CAR Polymorphisms and Antituberculosis Drug-Induced Hepatotoxicity

A combination therapy of multiple drugs including isoniazid, rifampicin, ethambutol and pyrazinamide has been proven to be an effective option for the vast majority of tuberculosis (TB) patients. However, various adverse drug reactions (ADRs) limit its merit, with anti-TB drug-induced hepatotoxicity (ATDH) being a common and sometimes severe ADR. This study aimed to investigate the association between polymorphisms in two nuclear receptor genes, pregnane X receptor (PXR) and constitutive androstane receptor (CAR), and the risk of ATDH in a Chinese population. Subjects with or without hepatotoxicity during anti-TB treatment were recruited. DNA was extracted from peripheral blood and genotypes of the selected single nucleotide polymorphisms (SNPs) were determined by using the improved multiplex ligation detection reaction technique. Three genetic models (additive, dominant, and recessive) as well as haplotype, SNP-SNP interaction analyses were used to evaluate the genetic risk of ATDH. A total of 502 subjects (203 ATDH and 299 non-ATDH) were enrolled. The results showed that the minor allele of rs7643645 and the H0010001 haplotype in PXR were associated with decreased risk of ATDH, suggesting that drug-metabolizing enzymes regulated by PXR are involved in the pathogenesis of ATDH. More studies are required to verify this result.

CYP genetic variants and toxicity related to anti-tubercular agents: a systematic review and meta-analysis

BACKGROUND

Treatment with anti-tuberculosis drugs may cause patients to experience serious adverse effects. Genetic factors, such as polymorphisms of CYP genes, may increase the likelihood of a patient experiencing such adverse drug reactions. In this systematic review and meta-analysis, we synthesised evidence for associations between CYP genetic variants and anti-tuberculosis drug-related toxicity outcomes.

METHODS

We searched MEDLINE, PubMed, EMBASE, BIOSIS and Web of Science to identify relevant studies. We performed meta-analyses to obtain an effect estimate for each genetic variant on each outcome, and stratified all analyses by country. We qualitatively assessed the methodological quality of the included studies.

RESULTS

We included data from 28 distinct cohorts of patients in the review. We identified many areas of concern with regard to the quality of included studies. Patients with homozygous mutant-type or heterozygous genotype at the CYP2E1 RsaI polymorphism were significantly less likely to experience hepatotoxicity than patients with homozygous wild-type genotype (odds ratio [OR] = 0.75, 95% confidence interval [CI] 0.56-1.00; p = 0.047, I2 = 58.2%). No significant differences were observed for the CYP2E1 DraI and PstI polymorphisms. For the 96-bp deletion-insertion single-nucleotide polymorphism (SNP) of the CYP2E1 gene, homozygous mutant-type significantly increased hepatotoxicity risk compared with homozygous wild-type (OR = 8.20, 95% CI 1.38-48.68, I2 = 0%); no significant difference was observed for heterozygous genotype compared with homozygous wild-type (OR = 0.77, 95% CI 0.19-3.21, I2 = 0%).

CONCLUSIONS

Generally, we identified that coverage of the association between SNPs of CYP genes and anti-tuberculosis drug-related toxicity outcomes is incomplete. We observed significant associations between the RsaI and 96-bp deletion-insertion SNPs of the CYP2E1 gene and anti-tuberculosis drug-related hepatotoxicity. We were unable to comment on the impact of ethnicity on the investigated associations, as information on participants' ethnicity was sparsely reported in the included studies.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number: CRD42017068448.

Oxidative Stress and First-Line Antituberculosis Drug-Induced Hepatotoxicity

Hepatotoxicity induced by antituberculosis drugs is a serious adverse reaction with significant morbidity and even, rarely, mortality. This form of toxicity potentially impacts the treatment outcome of tuberculosis in some patients. Covering only first-line antituberculosis drugs, this review addresses whether and how oxidative stress and, more broadly, disturbance in redox homeostasis alongside mitochondrial dysfunction may contribute to the hepatotoxicity induced by them. Risk factors for such toxicity that have been identified, in addition to genetic factors, principally include old age, malnutrition, alcoholism, chronic hepatitis C and chronic hepatitis B infection, HIV infection, and preexisting liver disease. Importantly, these comorbid conditions are associated with oxidative stress. Thus, the shared pathogenetic mechanism(s) for liver injury might be in operation due to disease-drug interaction. Our current ability to predict, prevent, or treat hepatotoxicity (other than removing potentially hepatotoxic drugs) remains limited. More translational research to unravel the pathogenesis, inclusive of the underlying molecular basis, regarding antituberculosis drug-induced hepatotoxicity is needed, and so is clinical research pertaining to the advances in therapy with antioxidants and drugs related to antioxidants, especially those for management of mitochondrial dysfunction. The role of pharmacogenetics in the clinical management of drug-induced hepatotoxicity also likely merits further evaluation.