Investigating Nicotinamide Adenine Dinucleotide Production and Consumption Imbalances in AKI

Background: Acute Kidney Injury(AKI) is a rapidly escalating global health crisis,affecting over 850 million people.Despite its high prevalence impacting about 1 in 5 people globally,there are currently no effective treatments,only limited supportive care.Central to the metabolic disturbances in AKI is Nicotinamide Adenine Dinucleotide(NAD+),a crucial co-factor for over 500 enzymatic reactions,including cellular respiration,DNA repair,and mitochondrial function.NAD+ also serves as a co-substrate for key regulatory enzymes such as sirtuins,polyADPribose polymerases(PARPs), and CD38,making it indispensable for maintaining metabolic homeostasis.Notably,AKI in humans directly correlate with disrupted NAD+ homeostasis,yet the underlying cause of this dysregulation remains unclear.Hence,my research question is if NAD+ depletion in AKI is driven by impaired production or excessive consumption,leading to imbalances in flux and homeostasis. Methods: We use a cisplatin-induced AKI mouse model to examine systemic NAD+ and metabolite flux changes.Using stable isotope tracing with labeled nicotinamide(NAM) and tryptophan(Trp),coupled with liquid chromatography-mass spectrometry(LCMS), we measure both steady-state metabolite levels and whole-body NAD+ metabolic turnover and flux. Results: Our data reveal that AKI disrupts NAD+ metabolism across tissues,creating an imbalance in NAM homeostasis due to the accumulation of toxic catabolites,N-Me-6PY and N-Me-4PY,and impaired NAD+ biosynthesis under AKI conditions.Isotope tracing with NAM indicates that NAD+ production via the Salvage pathway is dysregulated,particularly in the spleen and duodenum.Preliminary data from tryptophan tracing demonstrates higher concentration of NAM [M+6] and NAD+ [M+6] in the liver of AKI mice.This could be indicative of increased NAD+ synthesis and release of NAM into the circulation to compensate for disrupted Salvage synthesis across tissues.Additionally, the accumulation of Quinolinate [M+7] a key intermediate in the de novo pathway, in the spleen suggests a deficiency in quinolinate phosphoribosyl transferase (QPRT),the rate-limiting enzyme in this pathway. Conclusion: Collectively, our findings highlight the critical role of impaired NAD+ synthesis in disrupting NAD+ homeostasis during AKI and support exploring the protective potential of NAD+ precursor supplementation as a therapeutic strategy.