Neuzil J, Upston J M, Witting P K, Scott K F, Stocker R
Biochemistry Group, The Heart Research Institute, Sydney, Australia.
Biochemistry. 1998 Jun 23;37(25):9203-10. doi: 10.1021/bi9730745.
The oxidation of low-density lipoprotein (LDL) is thought to contribute to atherogenesis. 15-Lipoxygenase (15LO) induces LDL oxidation, and phospholipase A2 enhances this process [Sparrow, C. P. , Parthasarathy, S., and Steinberg, D. (1988) J. LipidRes. 29, 745-753]. As the underlying mechanism of the enhancing effect has not been investigated previously, we here show that in the presence of soybean 15LO (SLO) or human 15LO (rhLO), the addition of lipoprotein lipase, porcine pancreatic, or human type IIa secretory phospholipase A2 (sPLA2) greatly enhanced the accumulation of hydro(pero)xides of all major classes of LDL's lipids. Hydroperoxides of free fatty acids accumulated exclusively as enzymic products with kinetics reflecting both the formation of free fatty acids and the initial 'build-up' of alpha-tocopheroxyl radical. In contrast, hydroperoxides of cholesteryl esters and phosphatidylcholine accumulated linearly over comparatively longer periods of time and, in the case of rhLO, well beyond inactivation of the oxygenase. With SLO, formation of oxidized esterified lipids occurred nonenzymically, independent of the presence of lipase and despite the oxygenase remaining active until the end of the incubation. Enhancement of rhLO-induced LDL lipid peroxidation by sPLA2 was eliminated by a neutralizing anti-sPLA2 antibody, indicating that lipolytic activity was required for this effect. LDL depleted of alpha-tocopherol was resistant to oxidation by 15LO alone, whereas lipase overcame this resistance, demonstrating that lipases enhance 15LO-induced enzymic and nonenzymic peroxidation of LDL lipids. This is likely due to provision of free fatty acid substrate, resulting in an enhanced rate of free radical formation which itself causes nonenzymic peroxidation of esterified lipids. As lipases and 15LO are present in atherosclerotic lesions, our findings could be of pathophysiological significance.
低密度脂蛋白（LDL）的氧化被认为与动脉粥样硬化的发生有关。15-脂氧合酶（15LO）可诱导LDL氧化，而磷脂酶A2可增强这一过程[Sparrow, C. P., Parthasarathy, S., and Steinberg, D. (1988) J. Lipid Res. 29, 745 - 753]。由于此前尚未对这种增强作用的潜在机制进行研究，我们在此表明，在存在大豆15LO（SLO）或人15LO（rhLO）的情况下，添加脂蛋白脂肪酶、猪胰脂肪酶或人IIa型分泌性磷脂酶A2（sPLA2）可极大地增强LDL所有主要脂质类别的氢（过）氧化物的积累。游离脂肪酸的氢过氧化物仅作为酶促产物积累，其动力学反映了游离脂肪酸的形成以及α-生育酚自由基的初始“积累”。相比之下，胆固醇酯和磷脂酰胆碱的氢过氧化物在相对较长的时间内呈线性积累，就rhLO而言，甚至在加氧酶失活后仍持续积累。对于SLO，氧化酯化脂质的形成是非酶促的，与脂肪酶的存在无关，尽管加氧酶在孵育结束前仍保持活性。sPLA2对rhLO诱导的LDL脂质过氧化的增强作用可被中和性抗sPLA2抗体消除，表明这种作用需要脂解活性。缺乏α-生育酚的LDL单独对15LO氧化具有抗性，而脂肪酶可克服这种抗性，这表明脂肪酶可增强15LO诱导的LDL脂质的酶促和非酶促过氧化。这可能是由于提供了游离脂肪酸底物，导致自由基形成速率加快，而自由基本身会引起酯化脂质的非酶促过氧化。由于脂肪酶和15LO存在于动脉粥样硬化病变中，我们的发现可能具有病理生理学意义。
