Abstract 409: Size-dependent Acute Cellular Responses of Unbound Free Fatty Acids

Abstract

Introduction The level of free fatty acids (FFAs) in serum determines the pathophysiological condition. Most FFAs are carried in albumin-bound forms, but very small portion is remained unbound. Due to the methodological limitations, there is little known about the effect of unbound form. Objectives: This study aimed to understand the effect of local increase of unbound FFAs. Methods and Results: We synthesized the nano- and micro-particles of linoleate (LNP and LMP respectively) in unbound forms. The sizes of linoleate particles in distilled water, in serum-free, and in serum-added culture media were measured by dynamic light scattering. We confirmed that the size of LNPs in serum-added media were ~ 200 nm in diameter without aggregation. By the treatments of LNPs and LMPs in macrophage cell line (RAW 264.7), we studied size-dependent cellular responses including viability, lipid storage, and intracellular translocation. Increased lipid droplets in LNPs-treated cells were analyzed based on label-free coherent anti-Stokes Raman scattering imaging. We also found that LNPs (250 μM), not LMPs, activated the translocation toward nucleus of fatty acid binding protein 4 (FABP4), a carrier of intracellular FFA, by western blotting and immunocytochemistry. It was noteworthy that the nano-sized unbound FFA could induce post-transcriptional gene expression unlikely micro-sized FFAs. In the cells whose FABP4 function was inhibited by the chemical inhibitor, the cell death was significantly increased through apoptosis in short exposed time. This cell death response was mediated by endoplasmic reticulum stress suggesting the protective role of FABP4 on the imbalanced FFA metabolisms. Conclusions: We showed the size-dependent cellular responses by nano- and micro-sized unbound FFAs and the protective role of FABP4 on the FFA metabolisms. These findings provide the insights into acute cellular responses of unbound FFA.