Influence of Carbon Chain Length on Formation and Composition of Triglycerides in Free Fatty Acid- induced Steatosis

Background: Fatty liver, also called hepatic steatosis, is characterized by an imbalance between uptake, metabolism and excretion of free fatty acids (FFA). The resulting FFA-overload leads to the formation of triglyceride (TG)-filled lipid droplets in the cytoplasm of hepatocytes [1,2]. Our aim was to study the impact of FFA with different carbon chain length on the formation of TGs in hepatic steatosis. Further, we investigated how FFA-uptake and TG-metabolism is regulated by insulin and leptin in primary mouse hepatocytes.

Methods: Hepatocytes were isolated from the C57BL/6N mice. For inducing steatosis we incubated freshly isolated mouse hepatocytes with oleic acid (OA), palmitic acid (PA), stearic acid (SA), capric acid (CA), lauric acid (LA) and myristic acid (MA) at different concentrations for 24h. The intracellular lipid droplets were quantified by neutral fat staining with Sudan 7B. The quantitative profiling of the lipid composition was accomplished by AG Shevchenkob on a Q Exactive mass spectrometer and the FFA composition was accomplished by AG Schillerc using UV-VIS-spectroscopy in combination with MALDI MS and NMR spectroscopy.

Results: We demonstrated that OA and PA significantly increased the intracellular lipid contents in cultured hepatocytes in a concentration-dependent manner. In particular, palmitic, oleic and stearic acid resulted in an increased accumulation of intracellular TG, each with a different spectrum of individual TG species indicating intensive metabolism such as chain elongation and desaturation. Thus, PA mainly increased [48:x]-triglycerides, whereas OA and SA preferably induced [54:x]-triglycerides. Though insulin principally increased OA-induced steatosis, its potential was rather limited. In contrast, leptin elicited a remarkable ability to decrease OA-induced steatosis.

Conclusions: Palmitic acid [16:0] and oleic acid [18:1] are able to induce steatosis in primary mouse hepatocytes, whereas fatty acids with shorter carbon chains were almost ineffective in the analysed concentration range. Each FFA with steatotic effects induced a specific spectrum of intracellular TGs. reflecting a rich interconvertion to longer and less saturated species. Amount and pattern of the TG accumulation is modulated by insulin and leptin enhancing and lowering steatosis, respectively.

References:

[1] Anderson N, Borlak J. Pharmacol Rev. 2008 Sep;60(3):311 – 57.

[2] Niklas J, Bonin A. et al. BMB Rep. 2012 Jul;45(7):396 – 401.