房水抗坏血酸对紫外线B诱导的晶状体上皮细胞DNA损伤的影响。

The effect of aqueous humor ascorbate on ultraviolet-B-induced DNA damage in lens epithelium.

作者信息

Reddy V N, Giblin F J, Lin L R, Chakrapani B

机构信息

Eye Research Institute, Oakland University, Rochester, Michigan 48309-4401, USA.

出版信息

Invest Ophthalmol Vis Sci. 1998 Feb;39(2):344-50.

PMID:9477992

Abstract

PURPOSE

High levels of ascorbic acid are known to be present in the aqueous humor of many diurnal species, whereas nocturnal animals have low concentrations of the compound. The purpose of this study was to test the hypothesis that the high concentration of aqueous ascorbate in diurnal animals protects the lens against ultraviolet (UV)-induced damage to the eye. This study compares the effect of UV-B-induced DNA strand breaks on the lens epithelia of guinea pigs and rats after depletion or elevation of aqueous humor ascorbate, respectively.

METHODS

Eyes of guinea pigs and rats were exposed to UV-B radiation (0.25-0.75 J/cm2 on the cornea) for 10 minutes, and DNA strand breaks in lens epithelium were measured by single-cell gel electrophoresis. Ascorbic acid concentration in the aqueous humor, lens, and lens-capsule epithelium were assayed by spectrophotometric and electrochemical methods. For depletion of aqueous humor and lens ascorbate in guinea pigs, the animals were maintained on an ascorbate-deficient diet. Aqueous ascorbic acid was elevated in the rat by intraperitoneal injections of sodium ascorbate (1 g/kg).

RESULTS

The ascorbate concentration in the aqueous humor of the normal rat was approximately 3% that of the guinea pig, whereas the concentration of the compound in the lens of the normal rat was 10% that of the guinea pig. Guinea pigs fed an ascorbate-deficient diet showed a dramatic drop of more than 80% in aqueous humor ascorbate in the first week, whereas lens ascorbate decreased by approximately 25% during this time period. After a single intraperitoneal injection of sodium ascorbate in the rat, aqueous humor ascorbic acid increased nearly 30 times that in the control, whereas lens ascorbate increased by approximately 30%. The extent of DNA damage in the lens epithelium of a normal rat exposed to UV-B was significantly greater than that occurring in lenses of normal guinea pigs after exposure to the same dose of radiation. Lenses from ascorbate-deficient guinea pigs showed 50% more DNA damage than those from normal guinea pigs after UV exposure, whereas the lenses in ascorbate-injected rats exhibited significant protection against UV-induced DNA strand breaks.

CONCLUSIONS

High levels of ascorbic acid in the aqueous humor had a protective effect against UV-induced DNA damage to lens epithelium. The results were consistent with the hypothesis that high ascorbic acid in diurnal animals protects the lens against the cataractogenic effect of UV radiation in sunlight.

摘要

目的

已知许多昼行性物种的房水中存在高水平的抗坏血酸，而夜行性动物体内该化合物的浓度较低。本研究的目的是检验以下假设：昼行性动物房水中高浓度的抗坏血酸盐可保护晶状体免受紫外线（UV）诱导的眼部损伤。本研究分别比较了房水抗坏血酸耗竭或升高后，UV-B诱导的DNA链断裂对豚鼠和大鼠晶状体上皮的影响。

方法

将豚鼠和大鼠的眼睛暴露于UV-B辐射（角膜上为0.25 - 0.75 J/cm²）10分钟，通过单细胞凝胶电泳测量晶状体上皮中的DNA链断裂情况。采用分光光度法和电化学方法测定房水、晶状体及晶状体囊上皮中的抗坏血酸浓度。为使豚鼠房水和晶状体中的抗坏血酸耗竭，让动物维持抗坏血酸缺乏饮食。通过腹腔注射抗坏血酸钠（1 g/kg）使大鼠房水中的抗坏血酸升高。

结果

正常大鼠房水中抗坏血酸盐浓度约为豚鼠的3%，而正常大鼠晶状体中该化合物的浓度为豚鼠的10%。喂食抗坏血酸缺乏饮食的豚鼠在第一周房水抗坏血酸急剧下降超过80%，而在此期间晶状体抗坏血酸下降约25%。大鼠腹腔注射一次抗坏血酸钠后，房水抗坏血酸增加至对照的近30倍，而晶状体抗坏血酸增加约30%。暴露于UV-B的正常大鼠晶状体上皮中的DNA损伤程度显著大于暴露于相同剂量辐射后的正常豚鼠晶状体。UV暴露后，抗坏血酸缺乏的豚鼠晶状体的DNA损伤比正常豚鼠多50%，而注射抗坏血酸的大鼠晶状体对UV诱导的DNA链断裂表现出显著的保护作用。