Measurement of cerebral oxidative glucose consumption in patients with type 1 diabetes mellitus and hypoglycemia unawareness using ¹³C nuclear magnetic resonance spectroscopy

The aim of the present study was to use ¹³C nuclear magnetic resonance (NMR) to measure the cerebral oxidative metabolic rate of glucose (CMRglc[ox]) in patients with diabetes and to compare these measurements with those collected from matched controls. We elected to study a group with type 1 diabetes mellitus and hypoglycemia unawareness because we had previously found such patients to have higher brain glucose concentrations than healthy volunteers under steady-state conditions. We sought to determine if this difference in steady-state brain concentrations could be explained by a difference in CMRglc(ox). Time courses of ¹³C label incorporation in brain amino acids were measured in occipital cortex during infusion of [1-¹³C]glucose. These time courses were fitted using a 1-compartment metabolic model to determine CMRglc(ox). Our results show that the tricarboxylic acid cycle (TCA) cycle rate (V_TCA, which is twice CMRglc[ox]) in subjects with type 1 diabetes mellitus was not significantly different from that of healthy controls (0.84 ± 0.03 vs 0.79 ± 0.03 μmol/[g min], n = 5 in each group, mean ± SEM). We conclude that the changes in steady-state brain glucose concentrations that we observed in patients with type 1 diabetes mellitus in a previous study (J Neurosci Res. 2005;79:42-47) cannot be explained by changes in oxidative glucose consumption.