Brown adipose tissue triglyceride content is associated with decreased insulin sensitivity, independently of age and obesity

The aim of the present study was to determine whether single-voxel proton magnetic resonance spectroscopy (H-1-MRS) can non-invasively assess triglyceride content in both supraclavicular fat depots and subcutaneous white adipose tissue (WAT) to determine whether these measurements correlate to metabolic variables. A total of 25 healthy volunteers were studied using F-18-fluorodeoxyglucose positron emission tomography (PET) and O-15-H2O PET perfusion during cold exposure, and H-1-MRS at ambient temperature. Image-guided biopsies were collected from nine volunteers. The supraclavicular triglyceride content determined by H-1-MRS varied between 60 and 91% [mean +/- standard deviation (s.d.) 77 +/- 10%]. It correlated positively with body mass index, waist circumference, subcutaneous and visceral fat masses and 8-year diabetes risk based on the Framingham risk score and inversely with HDL cholesterol and insulin sensitivity (M-value; euglycaemic-hyperinsulinaemic clamp). Subcutaneous WAT had a significantly higher triglyceride content, 76-95% (mean +/- s.d. 87 +/- 5%; p = 0.0002). In conclusion, the triglyceride content in supraclavicular fat deposits measured by H-1-MRS may be an independent marker of whole-body insulin sensitivity, independent of brown adipose tissue metabolic activation.