The Potency of Dioscorea (Dioscorea alata) Tuber Flour to Inhibit Atherosclerosis in Laboratory Rabbits

Abstract

Recently, cardiovascular disease is one of the main causes of adult mortality in the world including in Indonesia. One of major risk factors of cardiovascular disease is hyperlipidemia. Prolonged hyperlipidemia accompanied by LDL oxidation is the first step of the development of atherosclerosis. Selection of food consumed is one way to reduce the risk of the development of atherosclerosis. Dioscorea alata (DA) tuber has potency to reduce the risk of atherosclerosis because it contains several functional compounds; anthocyanins, dietary fiber, and diosgenin. This contents lower the risk by antioxidation, antihyperlipidemia, and antiaggregation mechanisms. The objective of this research was to study the effect of administration of DA flour to inhibit atherosclerosis in laboratory rabbits. There were five specific objectives of the research ; (1) to determine the citric acid concentration and the duration of steam blanching which produce DA flour with the higest bioactive compounds, (2) to determine antioxidation and anti platelet aggregation effects of DA flour by in vitro test, (3) to examine the effects of DA flour administration on the activity of antioxidant enzymes in serum and kidney by in vivo test, 4) to examine the effect of DA flour administration on blood lipid profiles of the rabbits; and (5) to analyze the development of atherosclerosis plaques in aorta, and examine the morphologic change in rabbits kidney tissues. The results showed that 1% citric acid soaking and 10 minutes blanching produced DA flour with the highest anthocyanins and polyphenolic retention as high as 44.51% or 104.36 mg/100 g flour and 62.58% or 198.52 mg equivalent gallic acid/100 g flour, respectively. The flour had antioxidant capacity equal to 1300 mg trolox/100 g. Five or ten minutes steam blanching could reduce the activity of polyphenol oxidase enzyme, therefore retarded the oxidation process that degraded polyphenolic compound. These treatments were applied to produce DA flour which later formulated into rabbits ration. DA water extracts and flours were co-administrated with high cholesterol ration to 30 male New Zealand White rabbits for 60 days with the following ration groups; 1) basal ration as negative control (K0); 2) basal ration with 0.5% cholesterol as positive control (K1); 3) basal ration with 0.5% cholesterol and 1.8 g/100 g of freeze dried DA extract (KE1); 4) basal ration with 0.5% cholesterol and 3.6 g/100 g of freeze dried DA extract (KE2); 5) 15% DA flour in basal ration with 0.5% cholesterol (KT1); and 6) 30% DA flour in basal ration with 0.5% cholesterol (KT2). Experiment on antioxidatif stress effect of DA flour in rabbits showed that the level of SOD serum in rabbit co-administrated with DA flour to high cholesterol ration was significantly higher compared to those fed with cholesterol ration. 30% DA flour substitution into the ration, significantly maintained the level of SOD serum equal to that of administrated with basal ration. The other stress oxidative parameters; malondialdehyde (MDA) and glutathione peroxidase (GSHPx) activities showed no differences between treatments. The administration of high cholesterol ration increased total cholesterol 16 fold as compared to those administrated with basal ration, and increased cholesterol LDL, and triacylglycerol level significantly. Co-administration of 15% and 30% DA flour to the high cholesterol ration could improve lipid profile towards normal condition. However, co-administration of water extract could not maintain a normal lipid profile. In aorta of rabbits fed with cholesterol co-administrated with water extract, there were moderate and severe atherosclerotic plaque formation. However, in aorta of rabbits fed with cholesterol co-administrated with 15% and 30% DA flour, no plaques development was found. The area of atherosclerotic plaques in cholesterol group occupied 24,4% of total aortic transversal section, whereas, in group fed with cholesterol co-administrated with extract DA KE1 and KE2 the areas were 23,93% and 22,24% respectively. The retention of bioactive compounds of DA could be done using citric acid at 1% concentration combined with a simple steam blanching process for 10 minutes. These treatments produced flour with high content of antocyanins and polyphenolic compound. In vitro experiment showed that the flour had antioxidant capacity equal to 1300 mg trolox, and also exhibited antiaggregation effect in concentration of 400 ppm. Co-administration of 30% DA flour to the high cholesterol ration could maintain the level of SOD serum and Cu,Zn SOD in kidney tissues of the rabbits. DA flour had also antihyperlipidemic effect by normalizing the blood lipid profil. Prolonged suplementation of the flour, could inhibit the formation of atherosclerosis plaques in rabbits aorta and improved the morphology of kidney tissues of the rabbits. Therefore, with this potency, the flour of DA tuber could be developed as a promising functional food to prevent the development of atherosclerotic plaques.