Protective role of blood PAF-acetylhydrolases against oxidation of lipids

血浆PAF-乙酰水解酶（PAF-AH）优先水解sn-2位具有ω-羧基和ω-羧基短脂肪酰链的磷脂酰胆碱。由于这些磷脂是由非酶自由基介导的氧化产生的，因此假设这种LDL相关酶在清除LDL颗粒氧化产生的促炎磷脂中起保护作用。另一方面，在4%的日本人群中发现了功能丧失突变（Val 279 Phe），流行病学研究表明，该突变是与氧化应激相关的动脉粥样硬化疾病的危险因素。在这项研究中，我们通过ESI-MS/MS分析检查了Val 279 Phe突变受试者中是否引起氧化磷脂酰胆碱蓄积。当LDL用5μM Cu^<2+>处理3 h时，16：0-18：2（+O）、18：0-18：2（+P）、16：0-18：2（+2O）和18：0-18：2（+2O）在来自该突变受试者的LDL中积累。在无Cu^2+的条件下孵育16 h，可检测到16：0- 18：2（+O）、18：0 - 18：2（+O）和16：0-18：2（+2 O）。相反，当用Cu^ +处理血浆PAF-AH活性正常的受试者的LDL时，这些氧化磷脂没有被检测到<2>。此外，当用DFP处理来自具有正常PAF-AH酶活性的受试者的LDL时，这些在来自PAF-AH缺乏的受试者的LDL中积累的氧化磷脂酰胆碱的量显著增加。这些结果表明，具有羟基和过氧化氢长脂肪酰基链的磷脂酰胆碱是该酶的生理底物之一，并且该酶可能在这些氧化磷脂的降解中起作用。

Plasma PAF-acetylhydrolase (PAF-AH) preferentially hydrolyzes phosphatidylcholines with ω-carboxyl and ω-aldehydic short fatty acyl chains at the sn-2 position. Since these phospholipids are generated by non-enzymatic radical mediated oxidation, this LDL-associated enzyme is hypothesized to play a protective role in removal of pro-inflammatory phospholipids generated by oxidation of LDL particles. On the other hand, a loss-of-function mutation (Val279Phe) is found in 4% of Japanese populations and epidemiological studies suggest that this mutation is a risk factor for atherosclerotic diseases related to oxidative stress. In this study, we examined if accumulation of oxidized phosphatidylcholines is caused in the subjects with Val279Phe mutation by ESI-MS/MS analysis. When the LDL was treated with 5μM of Cu^<2+> for 3 h, 16:0-18:2 (+O), 18:0-18:2 (+P), 16:0-18:2 (+2O) and 18:0-18:2 (+2O) were accumulated in the LDL from the subject with this mutation. In addition, 16:0-18:2 (+O), 18:0-18:2 (+O) and 16:0-18:2 (+2O) were detected by incubating the LDL without Cu^<2+> for 16 h. By contrast, these oxidized phospholipids were not detected, when the LDL from the subjects with normal plasma PAF-AH activity was treated with Cu^<2>+. Furthermore, when the LDL from the subjects with normal PAF-AH enzyme activity was treated with DFP, the amounts of these oxidized phosphatidylcholines, which were accumulated in the LDL from the subjects with PAF-AH deficiency, were significantly increased. These results suggest that phosphatidylcholines with hydroxyl and hydroperoxyl long fatty acyl chains are one of the physiological substrates for this enzyme and this enzyme might play a role in degradation of these oxidized phospholipids.