Effects of kale (Brassica oleracea L. var. acephala DC) leaves extracts on the susceptibility of very low and low density lipoproteins to oxidation.

Of Brassicaceous plants, kale (Brassica oleraceae L. var. acephala DC) contains polyphenols, flavonoids, isoflavones and glucosinolates and so has antioxidant and anticarcinogenic properties. Antioxidants inhibit negative effects of free radicals and may, therefore, protect tissues against oxidative damage. Oxidation of lipoproteins is a key event in the development of atherosclerosis. In the current study, the levels of total phenolic and flavonoid contents and total antioxidant capacity of methanolic and aqueous extracts of kale leaves were determined. In addition, the susceptibility of isolated lipoproteins — very low density lipoprotein (VLDL) and low density lipoprotein (LDL) to the Cu2+-induced oxidation with various concentrations of metanolic and aqueous extracts was evaluated as t-lag values. Although aqueous extract had higher total antioxidant capacity, methanolic extract had higher total phenolic and flavonoid content (P<0.05). On the other hand, both extracts inhibited lipid peroxidation in both isolated VLDL and LDL. Inhibitory effect of extracts or increasing t-lag values, mainly in methanolic extract was found to be related to increasing the concentration of extracts. It was concluded that because of high antioxidant capacity and phenolic content, kale showed a protective effect on the oxidation of lipoproteins. Therefore, it may be speculated that kale consumption may play an important protective role in the cardiovascular and other related diseases resulting from imbalance of oxidant and antioxidant status.

EFFECT OF LOW LEVEL SOYBEAN ISOFLAVONES ON THE OXIDATIVE MODIFICATION OF LIPOPROTEINS IN HUMAN SERUM / 营养学报

Objective: To investigate the action of low level soybean isoflavones (genistin, genistein and daidzein) on the oxidative modification of lipoproteins in serum. Methods: After a system of lipoprotein oxidation mediated by Cu 2+ was established in a dilute serum, the effects of soybean isoflavones on the course and the end of lipoprotein oxidation could be reflected by monitoring the production of conjugated dienes and thiobarbituric acid-reactive substances (TBARS) respectively when isoflavones were added. Results: After 0.5-10 ?mol/L genistein, daidzein, genistin or ?-tocopherol was added into the lipoprotein system respectively before the oxidation initiated by Cu 2+ , the production of conjugated dienes or TBARS in the system was significantly reduced with a dose-dependent relationship. When the lipoprotein oxidation was initiated by Cu 2+ at 37 ℃ for 1 h or 1.5 h, soybean isoflavones also revealed strong inhibition on the oxidation in a weakening way. In comparison with soy isoflavones, ?-tocopherol had smaller inhibition on the production of conjugated dienes, but had promotion on the increase of TBARS. Conclusion: Lipoprotein oxidative modification in serum was weakened by low level soybean isoflavones, and its action after the oxidation initiated was more effective than that of ?-tocopherol.