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K.R. Hegde, S.D. Varma; Apoptosis in the Diabetic Mouse Lens Inhibition by Pyruvate . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3861.
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Purpose: We have recently established a mouse model for a study of the pathogenesis of diabetic cataracts independent of aldose reductase activity. Electron microscopic studies demonstrated pronounced nuclear changes reminiscent of apoptosis such as chromatin compaction and margination. The present studies were conducted to determine if these are reflective of DNA degradation and if such degradation could be prevented by pyruvate treatment. Methods: Diabetes was induced in CD–1 mice by streptozotocin. A subgroup of the diabetic animals was maintained on a diet containing 2% sodium pyruvate. The animals were sacrificed after nine weeks, lenses isolated and fixed in 4% buffered formalin and embedded in paraffin for section cutting and staining with TUNEL reagent containing TdT and fluorescein labeled dUTP, and with Hoechst dye. TUNEL reactivity was detected at 450–500/515–565 nm excitation and emission wave lengths. Hoechst staining was detected at 346/460 nm excitation/emission wavelengths. Results: The number of TUNEL positive cells, indicative of DNA nicks, was significantly greater in the diabetic lenses than in the normal lenses, in anterior as well as the equatorial regions of the tissue containing the cells differentiating into the fiber cells. In addition, there was an aberrant posterior migration of the differentiating cells, similar to than in human diabetic cataracts. Interestingly, the number of the TUNEL positive cells remained minimal, if any, in the lenses of pyruvate treated diabetic group. The posterior migration of the epithelial cells also was inhibited. The overall nuclear morphology, as evident by Hoechst staining also remained closer to the normal controls. Conclusions: The results suggest that diabetes, in addition to causing membrane and cytosolic changes in the tissue lipids and proteins, also adversely affects cell repair. This is evident by the presence of DNA nicks, detected histochemically by TUNEL and by nuclear changes noted by electron microscopy. The protective effects of pyruvate against these apoptotic changes are attributable to its oxyradical scavenging properties as well as to its property of inhibiting glycation of the amino groups of the proteins and nucleic acids. The former would prevent free radical induced DNA base modifications as well as cleavage of its phosphodiester bonds.
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