Nicotinamide-rich diet protects the heart against ischaemia-reperfusion in mice: a crucial role for cardiac SUR2A

Abstract

It is a consensus view that a strategy to increase heart resistance to ischaemia-reperfusion is a warranted. Here, based on our previous study, we have hypothesized that a nicotinamide-rich diet could increase myocardial resistance to ischaemia-reperfusion. Therefore, the purpose of this study was to determine whether nicotinamide-rich diet would increase heart resistance to ischaemia-reperfusion and what is the underlying mechanism. Experiments have been done on mice on control and nicotinamide-rich diet (mice were a week on nicotinamide-rich diet) as well as on transgenic mice overexpressing SUR2A (SUR2A mice), a regulatory subunit of cardioprotective ATP-sensitive K(+) (K(ATP)) channels and their littermate controls (WT). The levels of mRNA in heart tissue were measured by real-time RT-PCR, whole heart and single cell resistance to ischaemia-reperfusion and severe hypoxia was measured by TTC staining and laser confocal microscopy, respectively. Nicotinamide-rich diet significantly decreased the size of myocardial infarction induced by ischaemia-reperfusion (from 42.5+/-4.6% of the area at risk zone in mice on control diet to 26.8+/-1.8% in mice on nicotinamide-rich diet, n=6-12, P=0.031). The cardioprotective effect of nicotinamide-rich diet was associated with 11.46+/-1.22 times (n=6) increased mRNA levels of SUR2A in the heart. HMR1098, a selective inhibitor of the sarcolemmal K(ATP) channels opening, abolished cardioprotection afforded by nicotinamide-rich diet. Transgenic mice with a sole increase in SUR2A expression had also increased cardiac resistance to ischaemia-reperfusion. We conclude that nicotinamide-rich diet up-regulate SUR2A and increases heart resistance to ischaemia-reperfusion.

Graphical abstract

Fig. 1

Expression of SUR2A in hearts of mice on control and nicotinamide-rich diet. Representative progress curves for the real-time PCR amplification of SUR2A (A and C) and GAPDH (B and D) cDNA from mice on control or nicotinamide-rich diet (as labelled on the figure) and a corresponding bar graphs (E and F). Each bar represents mean ± standard error of the mean (n = 6 for each). *P < 0.05.

Fig. 2

Resistance of hearts to ischaemia–reperfusion from mice on control and nicotinamide-rich diet. (A) Typical photographs of myocardial slices from mice exposed to ischaemia–reperfusion under depicted conditions. Infarcted areas are pale/grey while viable myocardium is dark/red. (B) Bar graphs depict myocardial infarct size expressed as a percentage of area at risk zone (n = 6–12). *P < 0.05.

Fig. 3

A sole increase in expression mimics the cardioprotective effect of nicotinamide-rich diet. (A) Real-time RT-PCR of K_ATP channel subunits in the heart. Bar graphs represent cycling thresholds of the real-time RT-PCR progress curves of K_ATP channel-forming subunits. Each bar represents mean ± SEM (n = 6 for each), *P < 0.05. (B) Bar graphs depict myocardial infarct size expressed as a percentage of area at risk zone (n = 5–9), *P < 0.05. (C) Laser confocal images of cardiac cells from wild type (WT) and transgenic (SUR2A) mice exposed to hypoxia (magnification was 40×). Bar graph depicts percentage of cells that died/survived 30 min-long hypoxia, n = 14–28, *P < 0.01.

Fig. 4

HMR1098, a selective antagonist of sarcolemmal K_ATP channels, abolishes cardioprotection afforded by nicotinamide-rich diet. (A) Bar graph depicting percentage of cells from mice on nicotinamide-rich diet in the absence (nicotinamide) or presence of 30 μM HMR 1098 (nicotinamide/HMR1098) that died following 30 min-long hypoxia, n = 1698–1863, *P < 0.01. (B) Bar graphs depicting myocardial infarct size in mice on nicotinamide-rich diet in the absence (nicotinamide) or presence of 30 μM HMR 1098 (nicotinamide/HMR1098; n = 5–6), *P < 0.01.