高糖環境下維生素

高糖環境下維生素 E 對低密度脂蛋白糖化與氧化之影響

The Effect of Vitamin E on Glycation and Oxidation ofLow Density

Lipoprotein in High Glucose Concentration

中文摘要 糖尿病患長期處於高血糖環境下，葡萄糖自動氧化及蛋白質糖化作用過程會引發 自由基的產生，增加糖尿病患體內之氧化壓力。研究顯示自由基攻擊血液低密度 脂蛋白及糖化作用的修飾可能是引發糖尿病患產生血管性併發症之主因。研究亦 證實維生素 E 可降低氧化壓力，降低低密度脂蛋白 (LDL) 對氧化的感受性，有 利於延緩併發症的發生。本研究以分別以體外試驗及動物實驗模式探討，體外試 驗將低密度脂蛋白 (LDL) 以不同濃度葡萄糖溶液 (0、5、25 & 50 mM glucose) 、在有無添加脂質過氧化物 MDA 及有無富含維生素 E 處理下，於不同 時間點 (第 0、1、3 & 7 天) 進行糖化程度、TBARs 測定、離體銅離子誘導後氧 化延遲時間試驗、維生素 E 含量、洋菜膠電泳試驗，以探討維生素 E 對脂蛋白 糖化及氧化之影響。另以動物實驗進行不同劑量維生素 E 投與對糖尿病鼠 LDL 糖化及氧化的影響。結果顯示：native LDL 在高糖環境 (25、50 mM) 及伴隨 MDA 處理處理下，會增加 LDL 糖化程度、LDL 縮短氧化延遲時間、增加 TBARs 值及降低 LDL 維生素 E 含量，且隨著實驗天數增加有更顯著差異。維生素 E 添 加後，LDL 維生素 E 含量較添加前高，添加維生素 E 之 LDL，顯著延長氧化延 遲時間、降低 TBARs 值及增加 LDL 維生素 E 含量。此外，1.1%洋菜膠電泳試 驗結果顯示，無添加維生素 E 之 LDL 隨著實驗天數增加，葡萄糖濃度，伴隨 MDA 的添加，其在電泳膠片上有較大的移動度。添加維生素 E 後，各組間則無 顯著差異。動物實驗模式中以 STZ 誘發老鼠產生糖尿病，投予不同維生素 E 含 量 (1x、5x、10x 及 20x) 飼料，結果顯示，糖尿病誘發經餵食實驗飲食四週後， 糖尿病組禁食血糖值及糖化血色素均較誘發前及空白組高。血脂質部分，E 10x 組有較低總膽固醇濃度、高及低密度脂蛋白膽固醇濃度。E 5x 組與 E 10x 組 LDL 氧化延遲時間均顯著較 E 1x 組延長。E 10x 組有顯著較低 TBARs 值。E 5x 組及 E 20x 組有顯著較低 LDL 維生素 E 含量。本研究得知 LDL 處於高葡萄糖濃度下， 會增加糖化作用並引發自由基作用，增加對氧化的感受性；而維生素 E 的添加， 可藉著降低 LDL 之氧化壓力，降低對氧化的感受性，降低 LDL 被氧化所修飾之 機會。

英文摘要

Reactive oxygen species, which can be generated during glucose autoxidation and during protein glycation, may be response for increased oxidative stress in diabetes patients with high blood glucose concentration. It may be the major reason that reactive oxygen species-modified and glycated of protein, especially in collagen and

low density lipoprotein (LDL) has been implicated in mediating diabetic

complications (for example: hyperliperemia). Numerous studies have documented that a-tocopherol could decrease the susceptibility of LDL to oxidation both in vivo and in vitro. The present study was undertaken to investigate the effect of

a-tocopherol on LDL glycation and oxidation, we test the effect of a-tocopherol on LDL oxidative susceptibility and glycation, after enrichment of plasma with α -tocopherol in vitro and also different doses of a-tocopherol supplementation in streptozotocin (STZ)-induced diabetic rat. In vitro study, we incubated LDL in different concentration of glucose (0、5、25 & 50 mM) with and without

malondialdehyde (MDA), and with and without a-tocopherol enriched, sampling in different time points (Day 0、1、3 & 7). We measured the glycation degree of LDL, LDL TBARs test, LDL oxidized lag time, the concentration of a-tocopherol on LDL and 1.1% agarose gel electrophoresis of LDL. The animal study, we test the effect with different doses of a-tocopherol after in vivo supplement in STZ-induced diabetic rat. The in vitro result showed that native LDL with high glucose treatment and with MDA treatment had higher glycation degree of LDL, MDA production of LDL, and shorter LDL oxidized lag time, the lower concentration of a-tocopherol of LDL. After a-tocopherol enriched, LDL had more content of a-tocopherol. The a-tocopherol enriched LDL with high glucose showed a lower glycation degree of LDL, MDA production and longer LDL oxidized lag time. In 1.1% agarose gel electrophoresis of native LDL showed increasing electrophoretic mobility under high glucose

concertration and with MDA. After a-tocopherol enriched, it showed no difference between all treatments. In animal study, after STZ-induced and 4-week

supplementation, the diabetic rat had higher fasting blood glucose and hemoglobin A1C (HbA1C) than control group. E 10x group had lower total cholesterol

concentration, HDL-cholesterol and LDL-cholesterol compared with E 1x group. In E 10x group, a-tocopherol supplement clearly decreased the oxidative susceptibility of LDL as evidenced by prolongation of the lag phase of LDL oxidation and a lower MDA production. In conclusion, LDL readily increased oxidative stress under high glucose concentration and elevated the oxidative susceptibility of LDL. a-Tocopherol supplementations decreases individual oxidative stress, declines the oxidative