Background and Aim: Hepatic phase I drug-metabolizing enzymes CYP2E1, CYP1A2
and CYP3A4 catalyze the biotransformation of Acetaminophen (APAP) and are important in the
mediation of toxicity. The potential role of other hepatic and non-hepatic Phase I enzymes in APAP
toxicity has not been established.
Methods: PCR array containing 84 genes involved in phase I drug metabolism was examined in subgroups
of hospitalized children for APAP overdose, categorized as no toxicity (ALT ≤ 45 IU/L, n=5)
and moderate toxicity (ALT ≥ 500 IU/L, n=5).
Results: Significant downregulation was observed for ALDH6A1, CYP4F12 and GZMB in the no
toxicity subgroup and ALDH1A1, CYP27A1 and GZMB in the moderate toxicity subgroup. qRTPCR
confirmed significant downregulation for ALDH1A1, CYP4F12, and GZMB. In-silico analysis
identified GZMB 3’UTR to be a target of miR-378a-5p. Overexpression of miR-378a-5p reduced the
luciferase activity of GZMB 3’UTR reporter plasmid reportedly by 50%. NK-92 cells transfected
with the miR-378a-5p mimic extended the effect of APAP on GZMB protein expression compared to
mimic controls. In addition, miR-378a-5p was significantly upregulated in blood samples of children
with APAP overdose undergoing NAC treatment.
Conclusion: Overall, our study suggests the presence of a novel signaling pathway, whereby miR-
378a-5p inhibits GZMB expression in children with APAP overdose.