Intralipid/Heparin Infusion Alters Brain Metabolites Assessed With 1H-MRS Spectroscopy in Young Healthy Men.

Context: We previously demonstrated that insulin infusion altered metabolite concentrations in cerebral tissues assessed with proton magnetic resonance spectroscopy (1H-MRS) in young subjects with high insulin sensitivity, but not in those with low insulin sensitivity. Fat overload is an important factor leading to insulin resistance.

Objective: The purpose of the current study was to examine the effect of elevated circulating free fatty acid (FFA) levels on metabolites in cerebral tissues assessed with 1H-MRS.

Design: The study group comprised 10 young, healthy male subjects. 1H-MRS was performed at baseline and after 4-hour Intralipid (Fresenius Kabi)/heparin or saline infusions administered in random order. Voxels were positioned in the left frontal lobe, left temporal lobe, and hippocampus. The ratios of N-acetylaspartate (NAA), choline (Cho)-containing compounds, myo-inositol (mI), and glutamate/glutamine/γ-aminobutyric acid complex (Glx) to creatine (Cr) and nonsuppressed water signal were determined.

Results: Intralipid/heparin infusion resulted in a significant increase in circulating FFAs (P < 0.0001). Significant changes in brain neurometabolite concentrations in response to Intralipid/heparin infusion were increases in frontal mI/Cr (P = 0.041) and mI/H2O (P = 0.037), decreases in frontal and hippocampal Glx/Cr (P = 0.018 and P = 0.015, respectively) and Glx/H2O (P = 0.03 and P = 0.067, respectively), and a decrease in hippocampal NAA/Cr (P = 0.007) and NAA/H2O (P = 0.019). No changes in neurometabolites were observed during the saline infusion.

Conclusions: Acute circulating FFA elevation influenced cerebral metabolites in healthy humans and lipid-induced insulin resistance could be partly responsible for these effects.