Hsiao G, Ko F N, Lin C N, Teng C M
Pharmacological Institute, College of Medicine, National Taiwan University, Taipei, Taiwan.
Biochim Biophys Acta. 1996 Nov 14;1298(1):119-30. doi: 10.1016/s0167-4838(96)00123-9.
Isotorachrysone inhibited iron-induced lipid peroxidation with an IC50 value of 1.64 +/- 0.08 microM in rat brain homogenates, and was comparable in potency to butylated hydroxytoluene and was more potent than alpha-tocopherol or desferrioxamine. The mechanism of antioxidant properties were then examined. Isotorachrysone could scavenge the stable free radical diphenyl-p-picrylhydrazyl. And it was an efficient direct scavenger of water-soluble peroxyl radicals with stoichiometry factor of 0.53 +/- 0.05 in the aqueous phase and also toward lipid-soluble peroxyl radicals in tissue homogenates. The oxygen consumption during peroxidation induced by radicals on human erythrocyte ghosts was suppressed by isotorachrysone. Furthermore, it was reactive towards superoxide anion with a second-order rate constant of 5.06 +/- 0.65 x 10(5) M-1 S-1. But it did not react with hydrogen peroxide detected within the sensitivity limit of our assay. Using ascorbate/iron ion/H2O2 as a hydroxyl radical generating system and deoxyribose as a probe, isotorachrysone was effective with hydroxyl radicals with a second-order rate constant of 3.88 +/- 0.54 x 10(11) M-1 S-1 under stimulation by iron-EDTA. On the other hand, isotorachrysone retarded the peroxidation of human low density lipoprotein (LDL) initiated by both aqueous and lipophilic peroxyl radicals. And it also suppressed copper-catalyzed human LDL oxidation, as measured by fluorescence intensity, electrophoretic mobility, and thiobarbituric acid-reactive substances formation in a concentration-dependent manner. Our results show that isotorachrysone is potentially an effective and versatile antioxidant, and can help protecting LDL against oxidation.
异荭草素在大鼠脑匀浆中抑制铁诱导的脂质过氧化，IC50值为1.64±0.08微摩尔，其效力与丁基化羟基甲苯相当，比α-生育酚或去铁胺更有效。随后研究了其抗氧化特性的机制。异荭草素能够清除稳定的自由基二苯基-对-苦味酰基肼。在水相中，它是水溶性过氧自由基的高效直接清除剂，化学计量系数为0.53±0.05，对组织匀浆中的脂溶性过氧自由基也有清除作用。异荭草素抑制了自由基诱导的人红细胞膜过氧化过程中的氧气消耗。此外，它与超氧阴离子反应，二级速率常数为5.06±0.65×10⁵ M⁻¹ S⁻¹。但在我们检测的灵敏度范围内，它不与过氧化氢反应。以抗坏血酸/铁离子/H₂O₂作为羟基自由基产生系统，以脱氧核糖作为探针，在铁-乙二胺四乙酸刺激下，异荭草素对羟基自由基有效，二级速率常数为3.88±0.54×10¹¹ M⁻¹ S⁻¹。另一方面，异荭草素延缓了由水溶性和亲脂性过氧自由基引发的人低密度脂蛋白（LDL）的过氧化。并且它还以浓度依赖的方式抑制铜催化的人LDL氧化，通过荧光强度、电泳迁移率和硫代巴比妥酸反应性物质的形成来衡量。我们的结果表明，异荭草素可能是一种有效且通用的抗氧化剂，有助于保护LDL免受氧化。
