Deficiency of N -acetyltransferase increases the interactions of isoniazid with endobiotics in mouse liver

Abstract

Acetylation is the major metabolic pathway of isoniazid (INH) mediated by N-acetyltransferases (NATs). Previous reports suggest that slow acetylators have higher risks of INH hepatotoxicity than rapid acetylators, but the detailed mechanisms remain elusive. The current study used Nat1/2(−/−) mice to mimic NAT slow metabolizers and to investigate INH metabolism in the liver. We found that INH acetylation is abolished in the liver of Nat1/2(−/−) mice, suggesting that INH acetylation is fully dependent on NAT1/2. In addition to the acetylation pathway, INH can be hydrolyzed to form hydrazine (Hz) and isonicotinic acid (INA). We found that INA level was not altered in the liver of Nat1/2(−/−) mice, indicating that deficiency of NAT1/2 has no effect on INH hydrolysis. Because INH acetylation was abolished and INH hydrolysis was not altered in Nat1/2(−/−) mice, we expected an extremely high level of INH in the liver. However, we only observed a modest accumulation of INH in the liver of Nat1/2(−/−) mice, suggesting that there are alternative pathways in INH metabolism in NAT1/2 deficient condition. Our further studies revealed that the conjugated metabolites of INH with endobiotics, including fatty acids and vitamin B6, were significantly increased in the liver of Nat1/2(−/−) mice. In summary, this study illustrated that deficiency of NAT1/2 decreases INH acetylation, but increases the interactions of INH with endobiotics in the liver. These findings can be used to guide future studies on the mechanisms of INH hepatotoxicity in NAT slow metabolizers.

Cell Type–Specific Roles of CD38 in the Interactions of Isoniazid with NAD+in the Liver

“…3B), which is because deficiency of NAT slows down INH acetylation, leading to INH accumulation in the liver and therefore increasing the interactions between INH and NAD + . The increase of INH-NAD in the liver of Nat1/2(-/-) mice is consistent with our previous finding that NAT deficiency increases the interactions of INH with endobiotics in the liver (Wang et al, 2017).…”

“…After INH administration, both INH-NAD and AcINH-NAD were quickly formed in the liver, and reached the highest levels at 15 min, and then decreased to undetectable levels after 4 hr ( Fig. 2C and D), which is consistent with the pharmacokinetics of hepatic INH and AcINH (Wang et al, 2017 than INH-NAD by comparing their peak areas ( Fig. 2C and D), although the differences of their ionization efficiencies cannot be ruled out.…”

The Effect of Bergenin on Isonicotinic Acid Hydrazide and Rifampicin-Induced Liver Injury Revealed by RNA Sequencing

“…INH is metabolized by N-acetyltransferases (Nat1, Nat2) to acetyl hydrazine and finally hydrolyzed to non-toxic diacetyl hydrazine for excretion. The in-duction of INH+RIF leads to the down-regulation of Nat1 and Nat2 expression, which leads to reduced acetylation of INH and production of toxic hydrazine [21,22], which was also observed in this study and reversed by the BER intervention (Figures 3A,B and 7A). Furthermore, due to the overlapping substrate specificity and the unresolved functional significance of the Nat1 and Nat2 allelic variants, caution must be exercised in interpreting the tissue localization of them based on metabolic activity.…”

Genetic Variations Associated with Anti-Tuberculosis Drug-Induced Liver Injury

“…Using a high-dose treatment of isoniazid in an animal model, an overdose of isoniazid resulted in the accumulation of oleoyl-I-carnitine and linoleoyl-I-carnitine in the liver, which further led to mitochondrial dysfunction [54]. A recent study used Nat1/2 −/− mice as a genetic model for NAT slow metabolizers revealed increases in interactions of isoniazid with certain endobiotics, including fatty acids and vitamin B6, which may provide novel insights into the mechanisms of isoniazid-induced liver injury [55]. However, more experiments are required to illustrate the role of NAT2 variants in a higher risk of AT-DILI.…”