The effect of insulin infusion on the metabolites in cerebral tissues assessed with proton magnetic resonance spectroscopy in young healthy subjects with high and low insulin sensitivity

Abstract

OBJECTIVE-Insulin may play important roles in brain metabolism. Proton magnetic resonance spectroscopy (1H-MRS) of the central nervous system gives information on neuronal viability, cellular energy, and membrane status. To elucidate the specific role of insulin action in the brain, we estimated neurometabolites with 1H-MRS and assessed their regulation by insulin infusion and their relationship with insulin sensitivity. RESEARCH DESIGN AND METHODS-We studied 16 healthy young men. 1H-MRS was performed at baseline and after 240 min of euglycemic-hyperinsulinemic clamp. Voxels were positioned in the left frontal lobe, left temporal lobe, and left thalamus. The ratios of N-acetylaspartate (NAA), choline-containing compounds (Cho), myo-inositol, and glutamate/ glutamine/γ-aminobutyric acid complex (Glx) to creatine (Cr) and nonsuppressed water signal were determined. The participants were divided into subgroups of high (high IS) and low (low IS) insulin sensitivity. RESULTS-Baseline neurometabolic substrates were not different between the groups. Insulin infusion resulted in an increase in frontal NAA/Cr and NAA/H2O and frontal and temporal Glx/ Cr and Glx/H2O and a decrease in frontal Cho/Cr and temporal Cho/H 2O and myo-inositol/H2O (all P < 0.05, except temporal Glx/H2O, P = 0.054, NS) in the high-IS, but not in the low-IS, group. Insulin sensitivity correlated positively with frontal NAA/Cr and NAA/H 2O and temporal Glx/H2O and negatively with temporal myo-inositol/Cr and myo-inositol/H2O assessed during the second 1H-MRS (all P < 0.05). CONCLUSIONS-Insulin might influence cerebral metabolites, and this action is impaired in subjects with low whole-body insulin sensitivity. Thus, our results provide a potential link between insulin resistance and altered metabolism of the central nervous system. © 2013 by the American Diabetes Association.