NAD+-Boosting Ameliorates Heme Protein–Mediated Acute Kidney Injury

Key Points. Understanding how heme proteins/heme induce AKI and whether NAD+-boosting ameliorates heme protein–mediated AKI is clinically relevant. Heme proteins/heme directly decrease kidney NAD+ content and NAD+-boosting is markedly protective in heme protein–mediated AKI. These findings provide new insights in heme protein–mediated AKI and support interest in NAD+-boosting as a therapeutic strategy in AKI. Background. Understanding how heme proteins and heme induce AKI is clinically relevant from numerous perspectives, and, in this regard, a widely used model of heme protein–mediated AKI (HP-AKI) involves the glycerol model in mice. Using this model, we have previously demonstrated that NAD+ content is decreased in HP-AKI. Because there is significant current interest in NAD+-boosting as a strategy in clinical AKI, we examined the effect of NAD+-boosting in this model. Methods. NAD+-boosting was achieved by the administration of nicotinamide mononucleotide (NMN) in the glycerol model of HP-AKI. The effect of NMN, compared with vehicle, was examined in mice with HP-AKI and with sham AKI at day 1 after HP-AKI was induced. Results. The administration of NMN preserved kidney NAD+ content in HP-AKI, and compared with the administration of vehicle in HP-AKI, NMN improved glomerular filtration markers; reduced histologic injury as assessed by tubular necrosis, dilation, and cast formation and by assessment of dystrophic calcification; reduced expression of kidney injury marker 1, a sensitive marker of AKI; preserved mitochondrial ultrastructure and increased expression of proteins that promote mitochondrial integrity; reduced apoptosis as assessed by terminal deoxynucleotidyl transferase–mediated digoxigenin-deoxyuridine nick-end labeling staining and genes and protein expression that contribute to apoptosis, while increasing expression of an anti-apoptotic gene; reduced expression of several renal injury-related genes; and mitigated the severity of the senescence phenotype, as assessed by multiple markers. Finally, the administration of myoglobin or heme in vivo diminished kidney NAD+ content in mice with intact kidneys. Conclusions. These findings demonstrate the remarkable protective effects of NAD+-boosting by NMN in HP-AKI as revealed by a multitude of markers relevant to AKI. The reduction in NAD+ content in the kidney in HP-AKI may reflect the direct effects of heme proteins and/or heme. We suggest that these findings support current interest in NAD+-boosting as a therapeutic strategy in clinical AKI.