N-acetyltransferase 2, cytochrome P4502E1 and glutathione S-transferase genotypes in antitubercular treatment-induced hepatotoxicity in North Indians

WHAT IS KNOWN AND OBJECTIVE

Tuberculosis (TB) is a major cause of illness and death in developing countries. Hepatotoxicity is a serious side effect of antituberculosis treatment (ATT). NAT2, CYP2E1 and glutathione S-transferase (GST) gene polymorphisms may play an important role in ATT-induced hepatotoxicity. So, elucidating the genetics involved in anti-TB drug-induced hepatotoxicity in patients would be of utmost clinical significance. Therefore, the objective of the study was to elucidate the role of NAT2, CYP2E1 and GST gene polymorphisms in ATT-induced hepatotoxicity in North Indian patients.

METHODS

Three hundred patients with pulmonary and extra-pulmonary TB were enrolled. Total genomic DNA was isolated from each patient's peripheral lymphocytes using phenol-chloroform method, and genetic polymorphic analysis for N-acetyltransferase 2 (NAT2), cytochrome P4502E1 (CYP2E1) and GST was performed by polymerase chain reaction (PCR) with restriction fragment length polymorphism (RFLP).

RESULTS AND DISCUSSION

Of the 300 patients, 185 were males and 115 females. Among them, 33 males and 22 females developed ATT-induced hepatotoxicity. There were significant increases in alanine aminotransferase, aspartate aminotransferase and bilirubin levels in patients with ATT-induced hepatotoxicity at 1 month of treatment. NAT2 5/7 and 6/7 were significantly higher in hepatotoxicity patients as compared to the non-hepatotoxicity group. c1/c1 allele of CYP2E1 gene was lower (50·9%) in ATT-induced hepatotoxicity patients as compared to non-hepatotoxicity patients (61·2%), whereas c1/c2 and c2/c2 alleles were higher, but not statistically significant. GSTM1 was significantly higher in hepatotoxicity patients as compared to non-hepatotoxicity patients, whereas GSTT1 and GSTT1/M1 were lower, but not statistically significant.

WHAT IS NEW AND CONCLUSION

This study indicates that patients with slow-acetylator genotypes (NAT2 5/7, 6/7) and GSTM1 allele of GST enzyme were at higher risk of ATT-induced hepatotoxicity.

Comparison between acetylator phenotype and genotype polymorphism of n-acetyltransferase-2 in tuberculosis patients

BACKGROUND

Isoniazid (INH) is one of the most important drugs of antitubercular treatment regime, and in some cases it causes hepatotoxicity. It is metabolized by hepatic N-acetyltransferase-2 (NAT2).

AIM

To compare whether both methods, i.e., genotype NAT2 and phenotype test of measuring serum INH levels, are useful to identify acetylator status of patients on antitubercular treatment (ATT).

METHODS

A total of 251 tuberculosis (TB) patients on standard treatment were followed up to 6 months for this study. NAT2 genotype was assessed by PCR with restriction fragment length polymorphism (RFLP) whereas serum INH levels were measured by fluorometry.

RESULTS

Of the 251 patients, 50 (19.9%) developed ATT-induced hepatotoxicity. By phenotypic estimation, in the hepatotoxicity group, 17/50 (34%) were slow acetylators whereas 33/50 (66%) were fast acetylators. Genotypically, 19/50 (38%) were slow acetylators and 31/50 (62%) fast acetylators. By phenotypic analysis, in non-hepatotoxicity group, 46/201 (22.9%) were slow acetylators and 155/201 (77.1%) fast acetylators. By genotypic analysis, 30/201 (14.9%) were slow acetylators and 171/201 (85%) fast acetylators. Overall, slow acetylators (25.1%) measured phenotypically were not significantly different from slow acetylators (19.5%) measured genotypically.

CONCLUSION

This study suggests that the acetylator status of TB patients can be detected by phenotypic method as efficaciously as by genotypic method. Therefore, phenotypic method can replace genotypic method to determine acetylating status as phenotypic method is simple and inexpensive.