A new approach to measuring vitamin D in human adipose tissue using time-of-flight secondary ion mass spectrometry: a pilot study.

Circulating concentrations of vitamin D, 25(OH)D, and 1,25(OH)2D are lower in obese than lean individuals, but little is known about the adipose tissue content of these molecules. The aim of this study was to explore the possibility to use time-of-flight secondary ion mass spectrometry (TOF-SIMS) to measure vitamin D and its metabolites in fat tissue in obese and lean subjects. Abdominal subcutaneous adipose tissue (SAT) biopsies were obtained from three lean and three obese women, and paired biopsies SAT and visceral adipose tissue (VAT) were obtained from three obese subjects during gastric bypass surgery. TOF-SIMS was used to measure vitamin D3, 25(OH)D3, and 1,25(OH)2D3 in adipose tissue. We found that vitamin D3, 25(OH)D3, and 1,25(OH)2D3 in adipose tissue can be measured with TOF-SIMS. In adipose tissue, vitamin D3 and its metabolites were located in adipocyte lipid droplets. The content of vitamin D3 (P=0.006) and 25(OH)D3 (P=0.018) were lower in SAT in obese compared with lean women. TOF-SIMS has the potential to semi-quantitatively measure vitamin D metabolites in adipose tissue, and offers a possibility to compare vitamin D levels in different depots and groups of individuals. It also gives the opportunity to explore the localization of vitamin D metabolites at a cellular level.