Studies on Antioxidative effects of Pu-Erh-Tou Tea in the Inhibition of Low Density Lipoprotein Oxidation

• Main Authors: Liuchang, Huei-Chiuan, 劉張惠泉
• Other Authors: Lucy Sun Hwang
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/53249071149012778442

碩士 === 國立臺灣大學 === 食品科技研究所 === 85 === Oxidative modification of low density lipoprotein (LDL) plays a key role in the pathogenesis of atherosclerosis. Antioxidants, which can effectively inhibit LDL oxidation, may reduce early atherogenesis and slow down the progression to advanced stage. Oxidized LDL (oxLDL), which is no longer recognized by LDL receptor, is formed in the intimal area and taken up by the scavenger receptors of monocyte-derived macrophages, a process resulting in the formation of foam cells. Previous studies have reported that tea has a beneficial effect in lowering plasma cholesterol and preventing coronary heart disease. As potent antioxidants, catechins are suspected to exhibit the preventive effect in tea. This thesis intends to elucidate the potential of Pu-Erh-Tou tea, a fermented tea, to prevent LDL from oxidative modification in vitro and ex vivo. DPPH radical scavenging and inhibition of Cu2+-induced human LDL oxidation were chosen as the two in vitro assay systems. Male Sprague Dawley rats fed with a 1.0% cholesterol diet were used as the animal model. Results showed that the aqueous extracts of Pu-Erh-Tou (PET), green, pao-chung, oolong teas (IC50 values were 8.3, 7.5, 8.0 and 8.2 mg/mL, respectively) scavenged DPPH free radical better than that of black tea (14.3 mg/mL). The antioxidant potentials (IC50 values) to inhibit Cu2+- induced LDL oxidation were PET (1.4 mg/mL), green tea (1.8 mg/ mL), pao-chung tea (2.1 mg/mL), oolong tea (2.5 mg/mL), and black tea (3.3 mg/mL). Evidently, PET contained strong antioxidants that were capable of inhibiting human LDL oxidation in vitro. Male Sprague Dawley rats (body weight 216+20 g) were randomly assigned into four groups. Animals in each group were fed with one of the following experimental diets for 28 days: a high cholesterol diet (normal diet containing 1.0% cholesterol and 5.0% lard, w/w) (control group, n=7), a 1.0% probucol diet (HC plus 1.0% probucol) (PB group, n=7), a 1.0%-PET diet (HC diet plus 1.0% PET) (n=9), and a 2.0%-PET (HC diet plus 2.0% PET) (n=8). There was no significant difference in body weight at the end of this feeding experiment. The lag phases (Tlag, hr) in Cu2+-induced oxidation of LDL from these groups were control (2.5+0.8), 1.0% PET (10.6+3.7), 2.0% PET (14.4+4.0), and PB (35.8+8.3), respectively. Treatment with 1.0% PET, 2.0% PET, and 1.0% probucol led to 4.2 , 5.8, and 14.3 fold increases in lag phase. The content of a-tocopherol in LDL from 2.0% PET group (7.6+2.2 molecules/LDL) was significantly higher than those from control (5.0+0.9 molecules/LDL), 1.0% PET group (5.5+1.5 molecules/LDL), and 1.0% probucol group (5.3+1.3 molecules/LDL) (p<0.05). The content of polyunsaturated fatty acids (PUFA) in LDL from 2.0% PET group (1012+153 molecules/LDL) was significantly low than those from control (1321+349 molecules/LDL) (p<0.05) and 1.0% probucol (1498+189 molecules/LDL) (p<0.001) groups. Results from this animal study firmly demonstrated that feeding with aqueous extract of Pu-Erh-Tou tea reduced oxidative susceptibility of LDL from experimental animals. This study concludes that Pu-Erh-Tou tea contains strong antioxidants that can scavenge DPPH radical and inhibit LDL oxidation in vitro and in vivo. It suggests that uptake of Pu-Erh-Tou tea may have preventive effect in atherosclerosis and coronary heart disease.