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Whether early life acetaminophen (APAP) exposures injure the developing lung is controversial. We sought to correlate murine pulmonary developmental expression profiles of Cyp2e1 to susceptibility to APAP exposure. P14 C57BL/6 mice were exposed to APAP (140 mg/kg x 1, IP) and assessed for evidence of a histologic, metabolic, functional, and/or transcriptional pulmonary response. Similar experiments were performed in P14 IL6 -/- mice given the controversial role of IL6 in APAP-induced tissue injury. No evidence of hepatic injury was noted in APAP exposed P14 mice. In contrast, within 6 hours of exposure pulmonary tissue demonstrated histologic and functional evidence of injury and increased mitochondrial load by fluorescent lifetime imaging microscopy (FLIM). The pulmonary transcriptional response was marked by increased expression of Cyp2e1 , Nrf2 targets, and pro-inflammatory genes. Specifically, APAP exposure increased pulmonary IL6 mRNA, protein and associated STAT3 signaling. In contrast, IL6 -/- demonstrated attenuated STAT3 signaling and injury at 6 hours of exposure. At P28, functional and stereologic assessment of both WT and IL6 -/- mice exposed to a single dose of APAP at P14 revealed persistent abnormalities consistent with lung enlargement and alveolar simplification. Developmentally regulated surges in pulmonary Cyp2e1 expression correlate with sensitivity to APAP exposures that do not cause recognizable hepatic injury. A single exposure during this developmental window is enough to cause persistent functional and stereological abnormalities. These results highlight the need to further study the relationship between developmentally-regulated pulmonary Cyp2e1 expression, APAP exposures and long-term pulmonary dysfunction.

Acetaminophen (N-acetyl-p-aminophenol [APAP]) toxicity is a common cause of acute liver failure. Innate immune signaling and specifically NFκB activation play a complex role in mediating the hepatic response to toxic APAP exposures. While inflammatory innate immune responses contribute to APAP-induced injury, these same pathways play a role in regeneration and repair. Previous studies have shown that attenuating IκBβ/NFκB signaling downstream of TLR4 activation can limit injury, but whether this pathway contributes to APAP-induced hepatic injury is unknown. We hypothesized that the absence of IκBβ/NFκB signaling in the setting of toxic APAP exposure would attenuate APAP-induced hepatic injury. To test this, we exposed adult male WT and IκBβ -/- mice to APAP (280 mg/kg, IP) and evaluated liver histology at early (2-24 hr) and late (48-72 hr) time points. Furthermore, we interrogated the hepatic expression of NFκB inflammatory (Cxcl1, Tnf, Il1b, Il6, Ptgs2, and Ccl2), anti-inflammatory (Il10, Tnfaip3, and Nfkbia), and Nrf2/antioxidant (Gclc, Hmox, and Nqo1) target genes previously demonstrated to play a role in APAP-induced injury. Conflicting with our hypothesis, we found that hepatic injury was similar in WT and IκBβ -/- mice. Acutely, the induced expression of some target genes was similar in WT and IκBβ -/- mice (Tnfaip3, Nfkbia, and Gclc), while others were either not induced (Cxcl1, Tnf, Ptgs2, and Il10) or significantly attenuated (Ccl2) in IκBβ -/- mice. At later time points, APAP-induced hepatic expression of Il1b, Il6, and Gclc was significantly attenuated in IκBβ -/- mice. Based on these findings, the therapeutic potential of targeting IκBβ/NFκB signaling to treat toxic APAP-induced hepatic injury is likely limited., (© 2022 American Association for Anatomy.)