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Effects of dietary Garcinia kola supplementation and oxidative stress in isolated perfused rat hearts
Background: Oxidative stress and chronic inflammation contributes significantly to the pathogenesis of several ischaemic heart diseases, including atherosclerotic plaque rupture and myocardial infarction. It is widely demonstrated that ischaemia, followed by reperfusion, results in alterations of the mitochondrial and endothelial function through uncontrolled cascades of events characterized by free radical release and inflammation. Recent experimental evidence shows that modulation of inflammatory and antioxidant signaling mediators may determine the host outcome following myocardial ischaemia-reperfusion injury. Investigations from the past decade indicate that food supplements may play an important role in the prevention and management of chronic inflammatory diseases. Garcinia kola seeds are flavonoid rich nut from a tropical flowering, non-timber plant of the Guttiferae family. This plant is highly valued in several African cultures for its use in herbal medicine. Recently, the majority of experimental research has linked phytochemicals found in Garcinia kola nut, to its proposed beneficial effects in treatment and management of oxidative stress related-chronic diseases. Research performed in our laboratory demonstrated that kolaviron, a prominent Garcinia kola flavonoid extract, reduces myocardial apoptosis during ischaemia-reperfusion injury. Therefore, the aim of our current study was to determine the effects of Garcinia kola supplementation on cardiac inflammatory and antioxidant signaling pathways during ischaemia-reperfusion using a Wistar rat heart model. Materials and Methods: Male wistar rats were randomly divided into two groups: a control group receiving 2ml/kg corn oil and the experimental group receiving 100mg/kg Garcinia kola dissolved in corn oil, daily for 4 weeks. After the feeding period, blood samples were collected and lymphocytic DNA damage was analyzed using the alkaline comet assay. Furthermore, rat hearts were isolated and perfused with Krebs-Henseleit buffer on a working heart perfusion apparatus to measure myocardial functional parameters. Myocardial functional recovery was measured after 15 minutes global ischaemia followed by 25 minutes reperfusion. Hearts were freeze clamped at three different time points for myocardial cytokine concentration determinations using multiplex electrochemilunescent immunoassay. Nuclear factor kappa beta (NF- kβ), p38 mitogen activated protein kinases (p38 MAPK), protein kinase B/Akt (PKB/Akt), nitro-tyrosine, inducible nitric oxide (iNOS), cyclooxygenase-2 (COX-2), poly (adenosine-di-phosphate) ribose polymerase-1 (PARP-1) and caspase-3 expression and their phosphorylated forms (where applicable) were analyzed using the Western blot technique. Results: Dietary Garcinia kola supplementation significantly improved functional recovery when compared to the control group as reflected by the improved aortic output recovery (68.47 ± 6.16% versus 44.96 ± 7.00%; p<0.05). Our biochemical results supports the hypothesis that, dietary Garcinia kola supplementation modulates different cardiac proteins in terms of expression and activation at different time points when compared to the control group. We show that, before induction of ischaemia, Garcinia kola supplementation attenuates expression of inflammatory mediators and pro-apoptotic proteins when compared to the control group. The improved functional recovery was associated with a prompt inflammatory response, activation of PKB/Akt and attenuation of protein nitrosylation after 10 minutes of reperfusion. Modulation of NF-kβ and the p38 MAPK family proteins expression could have also played a significant role in myocardial functional recovery. Conclusion: We have shown that a 4 week period of dietary Garcinia kola supplementation at 100mg/kg daily improves cardiac functional recovery following ischaemia-reperfusion injury. We propose that dietary Garcinia kola supplementation protects cardiac myocytes from ischaemia-reperfusion induced oxidative stress through the induction of a prompt inflammatory response and controlled expression and/or activation of the, NF-kβ, PKB/Akt and p38 MAPK protein signaling pathways PARP-1 and caspase. Finally, we demonstrated that dietary Garcinia kola supplementation did not induce rat lymphocytic DNA damage when compared to the control group.