Kinetics of the inflammatory response induced by free fatty acid accumulation in hepatocytes

BACKGROUND. The information available on time and dose effects of the exposure of hepatocytes to free fatty acids (FFA) in vitro is controversial, and very few studies have assessed the hepatocyte inflammatory response in an in vitro model. AIM. To analyze the effect of treatment with FFA on cell viability and on the kinetics of cytokine expression using hepatic cell lines. MATERIAL AND METHODS. Hepatic cell lines, IHH and HuH7, were cultured for 3 h, 6 h, 12 h and 24 h in an enriched medium with palmitic and oleic acids. The cytotoxicity of the FFA was assessed by the MTT test and the intracellular fat content determined cytofluorimetrically and by fluorescence microscopy using Nile Red staining. The expression of mRNA for interleukin (IL)-6, IL-8 and tumor necrosis factor (TNF)-α was assessed by real time reverse transcription-polymerase chain reaction (RT-PCR). RESULTS. Treatment with 600 μM FFA did not affect the viability of either cell line despite a significant increase in the intracellular content of lipid droplets already evident after 3 h of treatment. A time- and dose-dependent upregulation of the expression of IL-6 and IL-8 mRNA was observed during the treatment at 3 and 24 h. In contrast, TNF-α mRNA expression was highly upregulated at 3 h after FFA exposure but returned to control values at 24 h. In conclusion, hepatocytes exposed in vitro for a short time to low FFA concentrations showed a significant upregulation of IL-6 and IL-8 to,and a rapid but transitory elevation of TNF-α.