Kavita R Hegde and Shambhu D Varma
Objective: We have previously demonstrated that pyruvate protects the lens against oxidative stress in vitro as well as prevents cataract formation in vivo induced by oxidative stress. The effects have been attributed to its property of scavenging various reactive oxygen species (ROS). Additionally we hypothesize that the preventive effect is also due to its effect of stimulating glycolysis.
Methods: This has been tested as follows: freshly isolated mice lenses were incubated for 4 hours in Tyrode medium containing 5-3H-glucose as a tracer in the presence and absence of 2 mM sodium pyruvate and determining generation of 3H2O and 3H-lactate separated by column chromatography in succession through homemade anion exchange column followed by the phenylboronate and formate mini-columns.
Results: the concentration of 3H2O in the medium at the end of incubation was 95 μM in the controls incubated without pyruvate. In the presence of pyruvate (2 mM) added to the medium, the concentration of 3H2O attained in the medium was 152 μM. The corresponding value expressed on the basis of lens weight was 46 nanomoles/lens in the control group vs. 88 nanomoles/lens with 2 mM pyruvate.
Conclusion: As hypothesized, pyruvate was found to stimulate glycolysis in the lens as indicated by the enhanced generation of both 3H2O and 3H-lactate in lenses incubated in its presence as compared to controls. The observed metabolic stimulation is attributed to recycling of NAD generated during the reduction of pyruvate to lactate, NAD being the required cofactor in the oxidation of glyceraldehyde-3-phosphate to 1,3-diphosphoglycerate. That such stimulation is involved in its protective effect is also apparent by our previous reports showing higher ATP levels in the lenses cultured in medium generating ROS in the presence of pyruvate than in its absence, the primary source of ATP in lens being glycolysis.
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