HANDLING OF PALMITIC ACID AND OLEIC ACID IN HUMAN SKELETAL MUSCLE CELLS

Obesity seems to be associated with type of dietary fat, and a positive association with saturated fatty acids (SFA) and a negative association with monounsaturated fatty acids (MUFA) have been found. In human skeletal muscle cells, SFA is reported to preferentially accumulate as diacylglycerol (DAG) and ceramides, while MUFA is reported to preferentially accumulate as triacylglyserol (TAG). In accordance to this, we have previously shown that the number of lipid droplets (LDs) is two-fold higher after pretreatment with oleic acid (OA) than palmitic acid (PA). PA has also been found to be more oxidized than OA. We wanted to study the handling of OA and PA in human myotubes, regarding uptake, oxidation and storage. Satellite cells were isolated from biopsy samples from M. obliquus internus abdominis and differentiated into multinucleated myotubes. Myotubes were pretreated for 24 h with 100 μM OA/PA, and the metabolism of [14C] OA/PA was studied. For imaging with fluorescence microscope, myotubes were stained with Bodipy and Hoescht, and LDs and nuclei were counted. Our results show that in human myotubes more OA than PA was stored, while PA was oxidized to a higher degree than OA. OA was stored mostly as TAG, while more PA than OA was stored in phospholipids. When long fatty acyl CoA synthetase was inhibited by Triacsin C, the storage of OA in TAG and DAG was reduced, but storage of PA remained unchanged. More OA than PA was subject to lipolysis; however the lipolysis seemed to parallel the storage in LDs. Thus, lipolysis might not be dependent on saturation of fatty acids stored but on the amount of lipids stored. In conclusion, our results indicate that PA has a higher turnover and is more available for oxidation than OA. This might be of importance in further studies of the link between intracellular lipids and the development of insulin resistance.