Establishment of mouse as an animal model for study of diabetic cataracts: biochemical studies.

AIM: The primary aim of this study was to understand the pathogenesis of diabetic cataracts at biochemical level in an animal model where lens aldose reductase (AR) activity is low, similar to that in the human lens. METHODS: Mouse, which is known to have low lens AR, was selected for these studies. Diabetes was induced by intraperitoneal administration of streptozotocin. Biochemical changes in the lens were monitored in freshly isolated lenses with standard chromatographic, enzymatic and culture experiments described in the section on methods. RESULTS: The present studies provide evidence of significant biochemical changes associated with such cataract formation despite very low levels of aldose reductase. The level of glycated proteins increased to 9 mg/100 mg of total water-soluble lens protein in the diabetic lenses, as compared with the normal lenses where it was only about 1.3 mg/100 mg of total protein. Glutathione (GSH), the major antioxidant in the lens, decreased from 2.35 micro mol/g in the normal lenses to about 1.17 micro mol/g in the diabetic lenses. Malonadehyde, a product of lipid peroxidation, increased from 50 micro mol/100 g in the normal to 70 micro mol/100 g in the diabetic lens. The level of adenosine triphosphate (ATP), an indicator of the overall metabolic status of the tissue, also decreased from 962 +/- 154 nmol/g in the normal to 487 +/- 130 nmol/g in the diabetic lenses. The function of the Na+-K+ ATPase was also adversely affected in diabetes, as indicated by the ability of the lens to accumulate (86)rubidium ions against its concentration gradient. The transport activity, expressed as CL/CM, was 24 in the normal lens, whereas it was only 12 in the diabetic lens. The level of sorbitol in the diabetic lens was only in the micromolar region. Hence, it was considered osmotically insignificant. CONCLUSION: Overall, the results suggest that induction of cataracts in diabetes can be related to multiple biochemical effects such as oxidative stress and glycation. Sorbitol accumulation in low aldose reductase situations, being minor, could, however, act synergistically with other factors.

Establishment of the mouse as a model animal for the study of diabetic cataracts.

The purpose of the present study was to investigate the suitability of using the mouse, a species known to have a low lens aldose reductase activity, as a model animal for studying the pathogenesis of diabetic cataract. Earlier studies with diabetic rats whose cataract development is much faster can only partially explain the etiology of cataracts in humans where lens aldose reductase is substantially low. CD-1 mice were injected intraperitoneally with streptozotocin according to Rossini's method. Blood glucose levels were estimated after 7 days, and animals having blood glucose between 300 and 400 mg/dl were selected for further experiments. Development of lenticular opacity was followed by examining the animals every 3-4 weeks by direct ophthalmoscopy, slitlamp examination and Scheimpflug photography. Additionally, the animals were sacrificed at appropriate intervals, eyes enucleated and subjected to morphological studies. The presence of refractive changes and early cataract in the diabetic mice was initially ascertained by the distorted appearance of the grid pattern when seen through the isolated lenses. Early cataracts were visible on slitlamp examination and by ophthalmoscopy as early as 3-4 weeks after the establishment of diabetes. Advanced opacity was clearly documentable by photography after 5-6 months. Similar to that in other species, a single layer of anterior epithelial cells abutting the anterior capsule was seen in the histological sections of normal mouse lenses. On the contrary, the epithelium in the diabetic lens was multilayered, and numerous nucleated cells were visible in the superficial anterior cortex. These studies therefore suggest that further studies with mice may throw additional light on the contribution of diabetes in the pathogenesis of cataracts in low lens aldose reductase models.