Ferreri Carla, Samadi Abdelouahid, Sassatelli Fabio, Landi Laura, Chatgilialoglu Chryssostomos
I.S.O.F., Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy.
J Am Chem Soc. 2004 Feb 4;126(4):1063-72. doi: 10.1021/ja038072o.
Trans unsaturated fatty acids in humans may be originated by two different contributions. The exogenous track is due to dietary supplementation of trans fats and the endogenous path deals with free-radical-catalyzed cis-trans isomerization of fatty acids. Arachidonic acid residue (5c,8c,11c,14c-20:4), which has only two out of the four double bonds deriving from the diet, was used to differentiate the two paths and to assess the importance of a radical reaction. A detailed study on the formation of trans phospholipids catalyzed by the HOCH2CH2S* radical was carried out on L-alpha-phosphatidylcholine from egg lecithin and 1-stearoyl-2-arachidonoyl-L-alpha-phosphatidylcholine (SAPC) in homogeneous solution or in large unilamellar vesicles (LUVET). Thiyl radicals were generated from the corresponding thiol by either gamma-irradiation or UV photolysis, and the reaction course was followed by GC, Ag/TLC, and 13C NMR analyses. The isomerization was found to be independent of cis double bond location (random process) in i-PrOH solution. In the case of vesicles, the supramolecular organization of lipids produced a dramatic change of the isomerization outcome: (i) in egg lecithin, the reactivity of arachidonate moieties is higher than that of oleate and linoleate residues, (ii) in the linoleate residues of egg lecithin, the 9t,12c-18:2 isomer prevailed on the 9c,12t-18:2 isomer (3:1 ratio), and (iii) a regioselective isomerization of SAPC arachidonate residues occurred in the 5 and 8 positions. This effect of "positional preference" indicates that thiyl radicals entering the hydrophobic region of the membrane bilayer start to isomerize polyunsaturated fatty acid residues having the double bonds nearest to the membrane surfaces. We propose that arachidonic acid and its trans isomers can function as biomarkers in membranes for distinguishing the two trans fatty acid-forming pathways.
人体内的反式不饱和脂肪酸可能源于两种不同的来源。外源途径是由于膳食中反式脂肪的补充，而内源途径则涉及脂肪酸的自由基催化顺反异构化。花生四烯酸残基（5c,8c,11c,14c-20:4），其四个双键中只有两个来自饮食，被用于区分这两种途径并评估自由基反应的重要性。在均相溶液或大单层囊泡（LUVET）中，对来自卵磷脂的L-α-磷脂酰胆碱和1-硬脂酰-2-花生四烯酰-L-α-磷脂酰胆碱（SAPC）上由HOCH2CH2S*自由基催化的反式磷脂形成进行了详细研究。通过γ射线辐照或紫外光解从相应的硫醇产生硫自由基，并通过气相色谱、银薄层层析和13C核磁共振分析跟踪反应过程。发现在异丙醇溶液中异构化与顺式双键位置无关（随机过程）。在囊泡的情况下，脂质的超分子组织使异构化结果发生了显著变化：（i）在卵磷脂中，花生四烯酸部分的反应性高于油酸和亚油酸残基；（ii）在卵磷脂中亚油酸残基中，9t,12c-十八碳二烯酸异构体比9c,12t-十八碳二烯酸异构体占优势（3:1比例）；（iii）SAPC花生四烯酸残基在5和8位发生区域选择性异构化。这种“位置偏好”效应表明，进入膜双层疏水区域的硫自由基开始使双键最靠近膜表面的多不饱和脂肪酸残基异构化。我们提出花生四烯酸及其反式异构体可以作为膜中的生物标志物，用于区分两种反式脂肪酸形成途径。
