Dietary red palm oil olein attenuates myocardial ischaemia/reperfusion injury: Effects on glutathione peroxidase transcription and extracellular signal-regulated kinases 1/2
Dietary red palm oil (RPO) supplementation offers protection against ischaemia/reperfusion injury. Several pathways have been suggested to convey this protection. Recently it has been shown that RPO supplementation increases glutathione peroxidase (GPX) activity in the myocardium, but the mechanism behind this increase in GPX activity remains unknown. Antioxidant activity is known to play a role in pro-survival kinase signaling. The involvement of extracellular signal regulated kinases (ERK) early in reperfusion gave different results in previous studies, depending upon the diet to which RPO was supplemented. The aims of this study were to investigate the effects of dietary RPO supplementation on ERK 1/2 phosphorylation and GPX1, GPX3 and GPX4 transcription. Male Wistar rats were randomly divided into two groups. 1) SRC control group fed a standard rat chow diet (SRC) for 6 weeks and 2) RPO experimental group fed a standard rat chow diet supplemented with 2 ml of RPO olein per day. After the feeding period, rats were sacrificed and hearts perfused on a working heart perfusion apparatus. Cardiac function was measured before and after ischaemia in order to determine aortic output recovery. Hearts were also freeze clamped at 20 min perfusion, 10 min reperfusion and 25 min reperfusion, in order to determine the level of ERK and phosphorylated ERK by Western blotting. Regulation of glutathione peroxidase mRNA was determined before ischaemia using real-time polymerase chain reaction (RT-PCR). RPO supplementation did not produce significant changes in GPX1 or GPX3 mRNA expression when compared to the SRC control group. The mRNA expression of GPX4 was significantly higher in the RPO supplemented group when compared to controls. ERK44 phosphorylation was significantly higher in the RPO supplemented group when compared to the control group at 20 min perfusion. Our results confirmed improved aortic output recovery in the RPO group, as reported in previous studies after ischaemia/ reperfusion injury. The minor changes found in ERK phosphorylation in this study may suggest that RPO has little effect on this pathway. However, the increase at baseline should be investigated further. Our findings also suggest that RPO may increase glutathione peroxidase activity, through up- regulation of the mRNA levels of GPX4.