Inhibition of NAD kinase conferring detrimental effect elevates hepatic NAD+ level against acetaminophen-induced acute liver injury in mice

Acetaminophen (APAP) overdose induces acute liver injury (ALI), even acute liver failure (ALF). There is a significant unmet need to furtherly elucidate the mechanisms and find new therapeutic target. Recently, emerging evidence indicates that nicotinamide adenine dinucleotide (NAD + ) plays a crucial role in APAP-induced ALI. Herein, we firstly investigated the protein expression of NAD kinase (NADK), as the rate-limiting enzyme converting NAD + to nicotinamide adenine dinucleotide phosphate (NADP + ), and found it was positively correlated with APAP-induced ALI in a dose- and time-dependent manner. Additionally, supplementation of N-acetylcysteine (NAC), known as an antidote of APAP, mitigated the ALI and downregulated the expression of NADK which was also in a dose-dependent manner. Moreover, pretreatment with methotrexate (MTX), the inhibitor of NADK, attenuated the levels of transaminases, alleviated morphological abnormalities, and improved oxidative stress triggered by APAP overdose, which was attributed to elevated hepatic NAD + pool. Subsequently, the increased NAD + upregulated the expression of Sirt1, SOD2 and attenuated DNA damage. Collectively, elevated expression of NADK is related to APAP-induced ALI, and inhibition of NADK alleviates the ALI through elevating liver NAD + level and improving antioxidant capacity. • The expression of NADK was positively correlated with APAP-induced ALI. • Inhibition of NADK alleviated APAP-induced ALI. • Inhibition of NADK increased the level of NAD + and activated Sirt1/SOD2.