NAD+ depletion drives age-related monocyte hyperinflammation after stroke and is reversed by nicotinamide riboside.

BACKGROUND: Aging exacerbates post-stroke inflammation, contributing to worse neurological outcomes. However, the mechanisms underlying this age-dependent immune dysregulation remain unclear. Because immune cell metabolism critically shapes inflammatory responses, we investigated whether the metabolic state of circulating monocytes, key immune cells that traffic to the ischemic brain, is altered by age after stroke. We further examined whether enhancing cellular NAD+ availability with nicotinamide riboside (NR) could mitigate age-associated neuroinflammatory responses and improve stroke outcome. METHODS: Ischemic stroke was induced in young and aged mice using the distal middle cerebral artery occlusion model. We assessed monocyte metabolic profiles via untargeted metabolomics, mitochondrial function assays, multi-analyte cytokine/chemokine profiling, and flow cytometry. Given the contribution of monocyte-derived intestinal macrophages to gut barrier disruption after stroke, we evaluated gut barrier integrity, immune cell composition, and systemic inflammation. Stroke outcomes were also determined by infarct size, motor function, and brain inflammatory status. RESULTS: Our findings show that the availability of the essential energy co-factor, NAD+, is a key age-dependent factor that regulates monocyte and intestinal macrophage immune responses after stroke. Aged monocytes showed decreased NAD+ levels and increased inflammatory responses compared to young monocytes. Pretreatment with NR elevated cellular NAD+ levels in aged monocytes, normalized intestinal macrophage numbers and activation states, preserved gut barrier integrity, reduced systemic and brain inflammation, and improved stroke outcomes in aged mice. CONCLUSION: These findings highlight the importance of NAD+ in mitigating the post-stroke response in aging and the potential of NAD+ supplementation as a preventive strategy for patients at risk for cerebrovascular disease.