Nicotinamide Offers Multiple Protective Mechanisms in Stroke as a Precursor for NAD<sup>+</sup>, as a PARP Inhibitor and by Partial Restoration of Mitochondrial Function

The purpose of the current study was to investigate aspects of improved bioenergetic function using nicotinamide during stroke. Using a global ischemia-reperfusion mouse model, ATP was depleted by 50% in the brain. The use of nicotinamide to provide a large reserve of brain NAD⁺ restored ATP levels to 61% of control levels. Alternatively, using nicotinamide as a PARP inhibitor restored ATP levels up to 72%. However, using a large reserve of NAD⁺ in the brain together with PARP inhibition proved to be additive, restoring ATP to 85% of control levels during the first critical 5 min of reperfusion. NAD⁺ and ATP levels correlated almost exactly. Brain mitochondrial function was also examined after cerebral ischemia-reperfusion. State 3 respiration of complex I was found to be abolished. However, this was a non-permanent inhibition of activity in vitro, since (NADH ubiquinone oxideroductase) complex I activity in these mitochondria was restored upon the addition of NADH. In vivo, the use of increased brain NAD⁺ and PARP inhibition was able to partially restore mitochondrial respiration. Taken together, the results show that nicotinamide offers a substantial protective role in terms of preservation of cellular ATP and mitochondrial NAD-linked respiration.