Nagaraj R H, Prabhakaram M, Ortwerth B J, Monnier V M
Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106.
Diabetes. 1994 Apr;43(4):580-6. doi: 10.2337/diab.43.4.580.
Recent work from our laboratory revealed a correlation between the degree of protein pigmentation in human cataractous lens and the advanced Maillard reaction as reflected by pentosidine formation. Although the data suggested a role for ascorbate in pentosidine formation in senile cataractous lenses, elevated pentosidine levels in diabetic cataracts suggested that glucosylation may be involved directly in pentosidine biosynthesis. To clarify this issue, we quantified pentosidine in lenses from rats with experimental galactosemia with and without aldose reductase inhibitor treatment. At 12 months, pentosidine-like fluorescence (335/385 nm) was three to six times higher (P < 0.0001) in water soluble and insoluble crystallins of galactosemic compared with nongalactosemic rats. Actual pentosidine levels increased shortly after onset of galactosemia. Contents in water-insoluble crystallins were 6.32 +/- 2.2 and 1.40 +/- 0.66 pmol/mg protein in galactosemic and control lenses, respectively (P < 0.001). Fluorescence and pentosidine were suppressed to almost control levels upon treatment with sorbinil. Incubation experiments showed that pentosidine could form slowly from galactose, but much more rapidly from ascorbate and its oxidation products. Its formation could be inhibited partly by both reduced and oxidized glutathione or epsilon-aminocaproic acid. The requirement of oxygen for pentosidine formation suggests that oxidative stress associated with glutathione depletion and ascorbate oxidation are plausible mechanisms for rapid pentosidine formation upon onset of galactosemia. In contrast, Maillard reaction by glycoxidation products may account for the sustained increase in pentosidine. Both these events may be linked to the newly recognized pseudohypoxic state of cells exposed to high sugar concentrations.
我们实验室最近的研究表明，人类白内障晶状体中蛋白质色素沉着程度与晚期美拉德反应（以戊糖苷的形成为标志）之间存在相关性。虽然数据表明抗坏血酸在老年性白内障晶状体中戊糖苷形成过程中发挥作用，但糖尿病性白内障中戊糖苷水平升高表明糖基化可能直接参与戊糖苷的生物合成。为阐明这一问题，我们对实验性半乳糖血症大鼠晶状体中的戊糖苷进行了定量分析，这些大鼠有的接受了醛糖还原酶抑制剂治疗，有的未接受该治疗。12个月时，与非半乳糖血症大鼠相比，半乳糖血症大鼠水溶性和不溶性晶状体蛋白中戊糖苷样荧光（335/385纳米）高出三至六倍（P < 0.0001）。半乳糖血症发作后不久，实际戊糖苷水平就开始升高。半乳糖血症大鼠和对照大鼠晶状体中不溶性晶状体蛋白的含量分别为6.32±2.2和1.40±0.66皮摩尔/毫克蛋白（P < 0.001）。用索比尼尔治疗后，荧光和戊糖苷被抑制到几乎与对照水平相当。孵育实验表明，戊糖苷可由半乳糖缓慢形成，但由抗坏血酸及其氧化产物形成的速度要快得多。其形成可被还原型和氧化型谷胱甘肽或ε-氨基己酸部分抑制。戊糖苷形成需要氧气，这表明与谷胱甘肽耗竭和抗坏血酸氧化相关的氧化应激是半乳糖血症发作后戊糖苷快速形成的合理机制。相比之下，糖氧化产物引发的美拉德反应可能是戊糖苷持续增加的原因。这两个事件可能都与新认识到的暴露于高糖浓度下细胞的假性缺氧状态有关。
