The effect of dietary Red Palm Oil on the functional recovery and the PKB/Akt pathway in the ischaemic/reperfused isolated rat heart

[摘要] ENGLISH ABSTRACT: IntroductionCardiovascular disease is one of the leading causes of death in the world.Formation of harmful reactive oxygen species (ROS) is associated withseveral pathological conditions, and contributes to ischaemia/reperfusioninjury. Antioxidants can be added to the diet in an attempt to decrease theprevalence of cardiovascular disease by decreasing the harmful effects ofischaemia/reperfusion injury.Red Palm Oil (RPO) consists of saturated, monounsaturated andpolyunsaturated fatty acids and is rich in antioxidants such as -carotene,tocopherols and tocotrienols.It has previously been shown that RPO-supplementation improvedreperfusion mechanical function. In these studies it was found that RPOmight exert its beneficial effects during reperfusion through increased PKB/Aktpathway activity, which may lead to inhibition of apoptosis and improvedmechanical function.AimsThe aims of this study were: 1) to determine whether RPO-supplementationprotected against ischaemia/reperfusion injury in the isolated perfused ratheart, 2) to confirm RPO-supplementation's effect on the PKB/Akt pathwayactivity and, 3) to elucidate the regulators in the PKB/Akt pathway that RPOsupplementationinfluenced.MethodsMale Wistar rats were divided into 4 groups, 2 control groups and 2experimental groups. The 2 control groups were fed a standard rat chow(SRC) for 4 weeks. The two experimental groups received SRC and RPOsupplementationfor 4 weeks. Hearts were excised and transferred to aLangendorff perfusion apparatus and perfused with Krebs-Henseleit buffer. Mechanical functional recovery was measured after 25 min of total global noflowischaemia. The following parameters were also measured during varioustime points in the protocol: left ventricular develop pressure, heart rate,coronary flow, rate pressure product. Hearts were also freeze-clamped forbiochemical analysis at 10 min during reperfusion. The biochemical analysiswas aimed at determining PKB/Akt involvement.In a second protocol, hearts were subjected to the same perfusion protocol,but wortmannin was also added to the perfusion fluid, in order to inhibit PI3-kinase.ResultsHearts from the RPO-supplemented rats showed an improved RPP recovery(92.26 ± 5.89 % vs 63.86 ± 7.74 %) after 10 min of reperfusion. This findingcorroborated the findings of previous studies. Hearts of the RPOsupplementedrats perfused with wortmannin, showed increased RPPrecoveries at several time points.Biochemical results showed that wortmannin did indeed inhibit PI3-Kphosphorylation in the RPO-supplemented group, as was expected. TheRPO-supplemented group that was perfused with wortmannin had anincreased PKB/Akt (Ser473) phosphoyrylation, when compared to thewortmannin control group. It was also found that the combination of RPO andwortmannin had prosurvival effects.DiscussionThis study showed that RPO-supplementation offered protection againstischaemia/reperfusion injury in the Langendorff-perfusion apparatus at 10 mininto reperfusion. Thereafter the significance of the protection was lost. Thisprotection has been confirmed in several previous studies and severalmechanisms have been proposed for this protection.Since no conclusive evidence exists on the precise mechanism of protection,our investigation focused on the regulators of the pro-survival PKB/Aktpathway. An improved functional recovery was also seen in the RPO-supplementedgroup that was perfused with wortmannin. This was an unexpected finding,because Wortmannin is a known PI3-kinase inhibitor (as was confirmed byour biochemical data). PI3-kinase phosphorylation leads to PKB/Aktphosphorylation and therefore, activation of a pro-survival pathway. It wouldbe expected that wortmannin would inhibit PKB/Akt and thus decrease thesurvival of the cells. The RPO-supplementation thus reversed wortmannin'sdetrimental effect to such an extent that the functional recovery was far betterthan RPO-supplementation alone.In the RPO + wortmannin group, PKB/Akt (Ser473) phosphorylation wasincreased, contrary to previous findings. This is an indication that RPO mayhave the ability to override wortmannin's inhibitory effect on PI3-kinase, orthat PKB/Akt (Ser473) may be phosphorylated independently of PI3-kinase.

[发布机构] Stellenbosch University