Mechanism of Lysine Oxidation in Human Lens Crystallins during Aging and in Diabetes
Mechanism of Lysine Oxidation in Human Lens Crystallins during Aging and in Diabetes
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DOI：
10.1074/jbc.m109.032094
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发表时间：
2009-12-11
影响因子：
4.8
通讯作者：
Monnier, Vincent M.
中科院分区：
文献类型：
--
作者：
Fan, Xingjun;Zhang, Jianye;Monnier, Vincent M.
晶状体核硬化过程中的氧化机制了解甚少，尤其是金属催化氧化。赖氨酰氧化产物己二酸半醛（丙烯醛赖氨酸，ALL）及其氧化终产物2 - 氨基己二酸（2 - AAA）作为年龄和糖尿病存在与否的函数进行了测定。令人惊讶的是，虽然ALL和2 - AAA都随年龄增长而增加，且与白内障等级和350nm处的蛋白质吸光度密切相关，但糖尿病仅增加ALL的形成，而不增加2 - AAA。为了阐明氧化机制，兔晶状体用高压氧（HBO）处理48小时，并用气相和液相色谱 - 质谱法分析蛋白质中的ALL、2 - AAA以及多种糖基化产物。暴露于HBO后，兔晶状体肿胀，晶状体核发黄。与对照组相比，核蛋白组分中与蛋白质结合的ALL增加了8倍。甲基乙二醛氢咪唑酮和羧乙基 - 赖氨酸大幅增加，但2 - AAA没有增加，这表明将ALL氧化为2 - AAA需要更苛刻的条件。实际上，后者只有在谷胱甘肽耗尽时才会形成，且由H₂O₂催化。羧甲基 - 赖氨酸和乙二醛氢咪唑酮（糖基/脂质氧化的两种标志物）以及晶状体血糖标志物（果糖 - 赖氨酸、葡萄糖间距蛋白）都没有因HBO而升高，排除了显著的脂质过氧化和葡萄糖参与的可能性。这些发现强烈表明二羰基/金属催化赖氨酸氧化为丙烯醛赖氨酸，其中低水平的谷胱甘肽结合抗坏血酸衍生的H₂O₂可能有助于2 - AAA的形成，因为在有甲基乙二醛而非抗坏血酸存在的情况下，几乎没有2 - AAA形成。一个重要的转化结论是螯合剂可能有助于延缓核硬化。
Oxidative mechanisms during nuclear sclerosis of the lens are poorly understood, in particular metal-catalyzed oxidation. The lysyl oxidation product adipic semialdehyde (allysine, ALL) and its oxidized end-product 2-aminoadipic acid (2-AAA) were determined as a function of age and presence of diabetes. Surprisingly, whereas both ALL and 2-AAA increased with age and strongly correlated with cataract grade and protein absorbance at 350 nm, only ALL formation but not 2-AAA was increased by diabetes. To clarify the mechanism of oxidation, rabbit lenses were treated with hyperbaric oxygen (HBO) for 48 h, and proteins were analyzed by gas and liquid chromatography mass spectrometry for ALL, 2-AAA, and multiple glycation products. Upon exposure to HBO, rabbit lenses were swollen, and nuclei were yellow. Protein-bound ALL increased 8-fold in the nuclear protein fractions versus controls. A dramatic increase in methylglyoxal hydroimidazolone and carboxyethyl-lysine but no increase of 2-AAA occurred, suggesting more drastic conditions are needed to oxidize ALL into 2-AAA. Indeed the latter formed only upon depletion of glutathione and was catalyzed by H2O2. Neither carboxymethyl-lysine nor glyoxal hydroimidazolone, two markers of glyco-/lipoxidation, nor markers of lenticular glycemia (fructose-lysine, glucospane) were elevated by HBO, excluding significant lipid peroxidation and glucose involvement. The findings strongly implicate dicarbonyl/metal catalyzed oxidation of lysine to allysine, whereby low GSH combined with ascorbate-derived H2O2 likely contributes toward 2-AAA formation, since virtually no 2-AAA formed in the presence of methylglyoxal instead of ascorbate. An important translational conclusion is that chelating agents might help delay nuclear sclerosis.