Evaluation of the Impact of Diabetes on Retinal Metabolites by NMR Spectroscopy

Abstract

Purpose/Aim of the study: Diabetic retinopathy (DR) is a leading cause of blindness in working age adults in developed countries. Changes in metabolites and in metabolic pathways of the retina caused by hyperglycemia may compromise the physiology of the retina. Using nuclear magnetic resonance (NMR) spectroscopy, we aimed to investigate the effect of diabetes on the levels of intermediate metabolites in rat retinas and the metabolic pathways that could be affected.

Materials and Methods: Diabetes was induced in male Wistar rats with a single injection of streptozotocin (65 mg/Kg, i.p.). Metabolic alterations were analyzed in streptozotocin-induced diabetic rat retinas by ¹H NMR spectroscopy. Glucose uptake was measured with 2-deoxy-d-[1-³H]glucose. Lactate production was evaluated by ¹H NMR spectroscopy using [U-¹³C]glucose.

Results: Tissue levels of several metabolic intermediates were quantified, but no significant changes in the levels of most metabolites were detected, with the exceptions of glucose, significantly increased, and lactate, significantly reduced in diabetic rat retinas, as compared to age-matched controls. The cytosolic redox ratio, indirectly evaluated by lactate-to-pyruvate ratio, was significantly reduced in diabetic rat retinas, as well as glucose uptake. Parallel studies demonstrated that lactate production rates were significantly diminished, suggesting a reduction in the glycolytic flux.

Conclusions: These results suggest that diabetes may significantly decrease glycolysis in the retina since higher intracellular glucose levels do not translate into higher intracellular lactate levels or into higher rates of lactate production. These changes may alter the normal functioning of the retina during diabetes and may contribute for vision loss in DR.

KEYWORDS::

• Diabetes
• Diabetic retinopathy
• Glucose uptake
• Glycolysis
• Lactate
• Nuclear magnetic resonance
• Streptozotocin

ACKNOWLEDGMENTS

This work was supported by the Foundation for Science and Technology, Portugal (POCTI/CBO/38545/01 and POCTI/CBO/38611/01) and FEDER.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.