Only the NAD precursor nicotinamide riboside maintains cardioprotection under clinically relevant conditions, possibly through activation of glycolysis

Abstract Purpose Cardioprotective strategies against ischaemia-reperfusion injury (IRI) that remain effective in the clinical arena need to be developed. Here, we examined the efficacy of the cardioprotective compounds fingolimod (Fingo), empagliflozin (Empa), melatonin (Mela) and nicotinamide riboside (NR) in the presence of drugs routinely used clinically in IRI conditions such as cardiac by-pass surgery and PCI procedures (opiates, benzodiazepines, P2Y12 antagonist, propofol). Furthermore, we examine the mechanism of protection of effective compound(s). Methods Following pilot dose-response curves of each compound, cardioprotective efficacy of Fingo, Empa, Mela and NR in an in vivo rat model employing a clinically relevant anaesthetic background therapy (fentanyl-midazolam) were examined alone or in combination. Drugs were administered 30 min before 25 min left ascending coronary (LAD) ischaemia. Infarct size (IS) was determined following 2 h of reperfusion. Effective treatments were then tested in the presence of a P2Y12 antagonist (cangrelor) or propofol anaesthesia. Finally, the underlying metabolic mechanism of the efficient compound(s) was explored in an ex vivo Langendorff-perfused mouse heart model of cardiac IRI. Results We found that among these four compounds, only singular NR was able to reduce IS (30±14% vs 60±16%, P=0.009 vs control, Fig.1A) in vivo in the presence of clinically relevant background anaesthesia. NR still reduced IS in the presence of cangrelor (51±18% vs 71±4%, P=0.016 vs control, Fig.1B), but lost protection in the presence of propofol anaesthesia (62±16% vs 60±14%, P=0.839 vs control, Fig.1C). Furthermore, NR showed protection in the ex vivo model of IRI, where isolated hearts were perfused with glucose (G) and free fatty acid (FFA) palmitate (G+FFA): (IS%: 40±14% vs 64±12%, P=0.003 vs control; LDH release: 28.3±7.2 U/min/GWW vs 37.8±3.7 U/min/GWW, P=0.005 vs control; Rate-Pressure-Product (RPP) recovery (43±12% vs 31±8%, P=0.031 vs control, Fig.2A-C). However, NR's protection was lost when 1) glycolysis was by-passed, by replacing glucose in the perfusate with lactate (L) and pyruvate (P) (LP+FFA) or 2) glycolysis was overly activated by adding insulin to the perfusate (G+FFA+insulin) (Fig.2). Conclusion Our data suggests that NR is a promising cardioprotective agent to target cardiac ischaemia-reperfusion injury in clinical conditions employing opioid agonists, benzodiazepines and platelet P2Y12 inhibitors. This protecti