Subcutaneous and Orbital Adipose Tissues: Intrinsic Differences in Carotenoid Contents and Lipidomic Compositions

The color difference in human subcutaneous fat (SF) and orbital fat (OF) is apparent, but the reasons have been rarely elaborated. We speculate that differences in carotenoid and lipid contents may account for the discrepancy in color. In this study, the intrinsic differences in SF and OF were analyzed using ultrahigh-performance liquid chromatography coupled with Q-Exactive liquid chromatography mass spectrometry/mass spectrometry (UPLC-QE Plus LC-MS/MS). Lipid profiling was performed in an independent batch. The morphology between orbital septum and SF differed statistically in the size of adipocytes and the distribution area of adipocytes. We compared carotenoid contents between two groups (seven samples) and found that lutein was more abundant in SF than that in OF with a p-value of 0.0409, suggesting that lutein could be mainly responsible for the yellow color of adipose tissue. Lipidomic results proved that SF and OF were well differentiated. Totally, 402 lipid features were detected, with 349 features in the positive ion mode and 53 features in the negative ion mode. Features (99.9%) in the positive ion mode and features (98.7%) in the negative ion mode well described various separation patterns in principal component analysis. Thirty-two features selected by variable importance in projection might account for the diversity of compounds in SF and OF. In conclusion, SF and OF differed from each other in carotenoids and lipidome. It is helpful to study the metabolism process of lipid droplets in adipocytes.