Relationship Between Genetic Polymorphisms Of Drug Metabolizing Enzymes And The Susceptibility To Antituberculosis Drug-induced Liver Injury

【Background】Tuberculosis (TB) is still one of serious infectious diseases of respiratory tractin the world. It is estimated that there are about1.3million new patients every year inour country, and China belongs to the world’s22TB high-burden countries, thenumber of TB stand second place in the world.Isoniazid, rifampicin, and pyrazinamide are traditionally used as first-linetherapy for TB, however, liver injury frequently develops in patients receiving thesedrugs. Toxicity increases when these drugs are used in combination. The incidence ofantituberculosis drug-induced liver injury (ATDLI) ranges from2.5to34.9%indifferent regimens. Several risk factors have been associated with the development ofATDLI, such as female, older age, HIV infection, lower level of serum albumin, highalcohol intake, hepatitis B or C virus infection, and so on. But the pathogenic mechanisms of ATDLI are poorly understood, the prevailing theory for ATDLI is thatmultiple steps were involved in the development of this phenotype, including thedrugs reach to the liver, formation of reactive metabolites, and acts as an immunogento bind to a protein, lead to the occurrence of ATDLI. In the above processes,drug-metabolizing enzymes had critical effects by both the synthesis anddetoxification of reactive metabolites. Studies showed that metabolic enzymes activityhad differences in individual, and the genetic polymorphism of drug metabolizingenzymes had great impact on their metabolism capacity, so the genotyping of drugmetabolizing enzymes may be a useful predictive tool for predicting ATDLI.There are many methods to detect the genetic polymorphisms, such asrestriction fragment length polymorphism, direct sequencing, gene-chip technology,however, these methods have low sensitivity and accuracy, or expensive, unsuitablefor automatic handling and difficult to detect large quantities of samples with highthroughput. But MassARRAY technique is a flexible, accurate and efficient geneticanalysis technology, and a suitable way for genotyping research with high throughput.It overcomes the methods mentioned above, and was gradually used and discussed bymore and more scholars.【Objective】To find various genotypes of drug metabolizing enzymes closely related toATDLI, as to establish the early warning system for ATDLI. We try to forecast therisk of liver injury by screening the genotypes, and provide the scientific direction forindividual administration.【Method】The randomly compared research method was used to analyze the1637caseswith tuberculosis (TB) who had been hospitalized from May2010to March2011,228TB patients with ATDLI and300TB patients without ATDLI were selected as case and control according to the inclusion criteria (we added72TB patients with ATDLIcollected in2009in the second part).1. Determine the incidence of ATDLI according to the medical records andinclusion criteria of liver injury.2. The genes encoding GSTM1and GSTT1were amplified using multiple PCRmethod, the relation between GSTM1, GSTT1null genotypes and ATDLIwas analyzed.3. Genetic polymorphisms of NAT2and CYP2E1were analyzed in TB patientswith or without hepatotoxicity after antituberculosis chemotherapy usingMassARRAY method.【Result】1. Two hundred and thirty-one (14.1%) patients had ATDLI in1637TBpatients.2. The frequencies of GSTM1null genotype were58.3%in the ATDLI patientsand50.7%in controls (OR=1.363,95%CI=0.963~1.929), which thedifference was not significant (P>0.05). The GSTM1null genotype (OR:1.64, P>0.05) had higher risk of ATDLI than GSTM1non-null genotype.3. In the promoter area of NAT2, the genotypes containing T allele ofrs4646243and A allele of rs4646246were revealed with significantlyprotective effects against ATDLI (0.569vs0.488，p=0.0126and0.567vs0.490，p=0.0177, respectively). In addition, the homozygote genotypescontaining minor allele of rs1115784, rs1041983and rs1799930showed asignificant association with the development of ATDLI. Especially, thehomozygote mutated genotypes of rs1041983and rs1799930were revealedhighly ATDLI risk (0.491vs0.373， p<0.0001and0.336vs0.217，p<0.0001,respectively).4. We identified two blocks in10tagging SNPs, and found significantassociation of haplotype ‘TGAA’ in block1and ‘TAG’ in block2with ATDLI. Additionally, two protective haplotypes associated with ATDLIwere observed:‘CGGG’ in block1and ‘CGG’ in block2.5. Our study failed to show any significant association between CYP2E1susceptibility to ATDLI.【Conclution】1. GSTM1and GSTT1genotypes might not have association with risk of theATDLI in Chinese Han population.2. NAT2genotypes might have significant association with the risk of ATDLIin Chinese Han population. We can detect NAT2to select high risk patientsfor ATDLI before initiation of the chemotherapy of TB.3. CYP2E1gene polymorphisms might have no association with risk of theATDLI in Chinese Han population.4. MassARRAY technique is a flexible, accurate and efficient genetic analysistechnology. It’s a suitable way for genotyping research of high throughputdetection of mass samples.