NAD+ Boosting Is Protective in the Murine Model of Heme Protein-Mediated AKI (HP-AKI)

Background: Our prior study showed that renal NAD+ content is reduced following heme-mediated acute kidney injury (HP-AKI) [Kidney360. 15;3(10):1672-1682, 2022]. As NAD+ deficiency has been shown to have a pathogenetic role in other AKI models, we now investigate whether NAD+ boosting is protective in this model. Methods: HP-AKI was induced in mice by intramuscular injection of hypertonic glycerol. The NAD+ precursor nicotinamide mononucleotide (NMN) was administered daily from 2 days prior to, until 1 day after HP-AKI induction. Renal function was assessed by serum creatinine and BUN, and renal injury was assessed by histologic examination. NAD+ levels and gene/protein expression were also evaluated. Results: One dayafter HP-AKI induction, mice treated with NMN had a significantly lower serum creatinine and BUN compared with vehicle-treated mice (2.6±0.1 vs 0.8±0.2 mg/dL, P<0.0001 and 139±7 vs 69±15 mg/dL, P=0.0014, respectively). At this time point after HP-AKI, semiquantitative scoring of histologic injury showed that NMN-treated mice displayed significantly less renal injury compared with vehicle-treated mice as assessed by 5 established indices (range: 58% to 77% reduction). Our studies confirmed that renal NAD+ levels are reduced (61%) in the HP-AKI model at 1 day, and that NMN treatment significantly boosted NAD+ levels in this model compared with vehicle-treated mice (93.2±5.7 vs 39.0±4.4 nmol/mg kidney, P<0.001). Analysis of renal gene and protein expression revealed that at one day after HP-AKI, mice treated with NMN had significantly lower expression of markers of inflammation (PAI1, IL6) and apoptosis (BAX/BCL2, cleaved caspase3), and significantly preserved mitochondrial viability/integrity markers (NRF-1, p-AMPK) compared with vehicle-treated mice. Conclusion: As in our prior study, we confirm that NAD+ levels are significantly reduced in the HP-AKI model, and we now demonstrate that NMN administration preserves NAD+ levels, with a concomitant protection against acute kidney injury. We also show that NMN treatment protects mitochondria and reduces inflammation and apoptosis. The present data indicate that the NAD+ boosting effect of NMN reduces inflammation and apoptosis in this model, likely through preservation of mitochondrial integrity. Collectively, these findings uncover the protective effects of this treatment in HP-AKI. Funding: NIDDK Support