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

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

Automated summary

The color difference between subcutaneous fat (SF) and orbital fat (OF) in humans is likely due to differences in carotenoid and lipid contents. Using UPLC-QE Plus LC-MS/MS analysis, it was found that SF and OF differed in morphology, with lutein being more abundant in SF and potentially responsible for the yellow color of adipose tissue. Lipidomic analysis confirmed the differentiation between SF and OF, providing insights into the metabolism process of lipid droplets in adipocytes.