Poster Sessions BP01: Energy Metabolism. NMR investigation of metabolic alterations in the brain of thiamine‐deficient rats

Abstract

Thiamine deficiency (TD) results in region‐selective impairment of brain metabolism. Since thiamine is a cofactor for enzymes involved in glucose metabolism, 1H and 13C‐NMR was used to investigate metabolic fluxes through the major pathways of glucose metabolism in vulnerable (medial thalamus, MT; inferior colliculus, IC) and nonvulnerable brain structures of rats made thiamine deficient following treatment with the central thiamine antagonist pyrithiamine vs. pair‐fed controls. Symptomatic stages of TD resulted in decreased glutamate and GABA in MT an IC confirming previous biochemical studies. 13C‐isotopomer analysis revealed decreased de novo synthesis of [4–13C]glutamate (30%p < 0.02) and [2–13C]GABA (60%p < 0.01) in MT and IC consistent with decreased activities of pyruvate‐ and α‐ketoglutarate dehydrogenases. These changes were accompanied by decreased consumption of glucose and increased synthesis of lactate from [1–13C]glucose confirming decreased mitochondrial metabolism. Accumulation of glyceraldehyde‐3‐phosphate suggested inhibition of glucose flux through the thiamine‐deficient enzyme transketolase. Onset of symptoms of TD and significant cell death was accompanied by decreased neuronal marker molecules NAA and NAAG in MT. Focal lactate accumulation resulting from decreased activities of mitochondrial thiamine‐dependent enzymes appears to play a key role in the pathogenesis of selective neuronal cell death in TD. [funded by CIHR Canada].