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The contribution of glycation to cataract formation in diabetes
1National Vision Research Institute of Australia, Carlton, Australia.
Background:
Despite extensive research, the mechanisms responsible for Type II diabetic cataract formation are still unknown. Recent data have favored non-enzymatic glycation. However, the pathways by which hyperglycemia leads to cataract are still unknown. Two possible routes were explored; modification of the lens proteins leading to Advanced Glycation Endproduct (AGE) formation and modification of the ATPase pumps leading to osmotic stress.
Methods:
The extent of AGE formation was monitored in fetal bovine eyes using non-tryptophan fluorescence. The amount of carbohydrate bound the proteins was measured after reduction with radiolabelled sodium borohydride. Secondary structure estimations were performed by analysis of data obtained using circular dichroism. The effect of glycation on the Na, K-ATPase ion pumps was investigated by comparing the uptake of radioactive 86Rb in the presence of high concentrations of glucose and fructose.
Results:
These studies were aimed at determining which of these mechanisms is the more likely route for cataract formation. The first mechanism was examined using two approaches. Firstly, by investigating the effects of increased glucose on the secondary and tertiary structure of lens proteins. Detailed analysis of the structures of the lens proteins in the presence of 200 mM glucose revealed that only alpha-crystallin was slightly affected. More important, however, this change did not lead to any significant aggregation. The second approach involved comparing the mechanism of action and possible benefits of anti-glycating agents.
Conclusion:
It is concluded that Type II diabetes cataracts are unlikely to arise as a result of AGE formation, but rather they form because of disruption of the cells, as a result of osmotic stress, brought about by glycation of the ion pumps.
Insights
Type II diabetic cataracts likely form due to osmotic stress from glycation of ion pumps, not Advanced Glycation Endproduct (AGE) formation. This research clarifies diabetic cataract mechanisms.
Area of Science:
- Ophthalmology
- Endocrinology
- Biochemistry
Background:
- Mechanisms of Type II diabetic cataract formation remain unclear.
- Non-enzymatic glycation is a suspected contributor to diabetic cataracts.
- Hyperglycemia's specific pathways to cataractogenesis are under investigation.
Purpose of the Study:
- To investigate the roles of Advanced Glycation Endproduct (AGE) formation and ATPase pump modification in diabetic cataractogenesis.
- To determine the primary mechanism leading to cataract formation in Type II diabetes.
Main Methods:
- Assessed AGE formation using non-tryptophan fluorescence in bovine eyes.
- Measured protein-bound carbohydrates via radiolabeled sodium borohydride reduction.
- Analyzed protein secondary structure using circular dichroism.
- Investigated glycation effects on Na, K-ATPase activity using 86Rb uptake.
Main Results:
- Increased glucose (200 mM) minimally affected lens protein secondary/tertiary structure, with no significant aggregation.
- Alpha-crystallin showed slight structural changes but no aggregation under high glucose conditions.
- The study explored anti-glycating agents as a secondary approach.
Conclusions:
- Diabetic cataracts are unlikely to result from Advanced Glycation Endproduct (AGE) formation.
- Cataract formation is more likely due to osmotic stress caused by glycation of ion pumps, disrupting lens cells.
- Glycation of ATPase pumps is identified as the probable cause of diabetic cataracts.