Extracellular NAD response to post-hepatectomy liver failure: bridging preclinical and clinical findings.

Liver fibrosis progressing to cirrhosis is a major risk factor for liver cancer, impacting surgical treatment and survival. Our study focuses on the role of extracellular nicotinamide adenine dinucleotide (eNAD) in liver fibrosis, analyzing liver disease patients undergoing surgery. Additionally, we explore NAD's therapeutic potential in a mouse model of extended liver resection and in vitro using 3D hepatocyte spheroids. eNAD correlated with aspartate transaminase (AST) and bilirubin after liver resection (AST: r = 0.2828, p = 0.0087; Bilirubin: r = 0.2584, p = 0.0176). Concordantly, post-hepatectomy liver failure (PHLF) was associated with higher eNAD peaks (n = 10; p = 0.0063). Post-operative eNAD levels decreased significantly (p < 0.05), but in advanced stages of liver fibrosis or cirrhosis, this decline not only diminished but actually showed a trend towards an increase. The expression of NAD biosynthesis rate-limiting enzymes, nicotinamide phosphoribosyltransferase (NAMPT) and nicotinamide mononucleotide adenylyltransferase 3 (NMNAT3), were upregulated significantly in the liver tissue of patients with higher liver fibrosis stages (p < 0.0001). Finally, the administration of NAD in a 3D hepatocyte spheroid model rescued hepatocytes from TNFalpha-induced cell death and improved viability (p < 0.0001). In a mouse model of extended liver resection, NAD treatment significantly improved survival (p = 0.0158) and liver regeneration (p = 0.0186). Our findings reveal that eNAD was upregulated in PHLF, and rate-limiting enzymes of NAD biosynthesis demonstrated higher expressions under liver fibrosis. Further, eNAD administration improved survival after extended liver resection in mice and enhanced hepatocyte viability in vitro. These insights may offer a potential target for future therapies.