Prolonged Exposure to Free Fatty Acids Has Cytostatic and Pro-Apoptotic Effects on Human Pancreatic Islets

TLDR

The study evaluated the impact of 48‑hour preculture of isolated human islets with 1.0 or 2.0 mmol l⁻¹ free fatty acids (2:1 oleate:palmitate) to better understand lipotoxicity in β‑cells. The authors used this FFA exposure to assess functional, metabolic, and apoptotic pathways in the islets, examining changes in insulin secretion, glucose metabolism, and cell death mechanisms. FFA treatment increased triglyceride accumulation, reduced insulin content and glucose‑stimulated insulin release, impaired glucose utilization and oxidation, and triggered caspase‑dependent apoptosis in β‑cells, effects partially alleviated by ceramide or serine protease inhibition and linked to decreased Bcl‑2 expression.

Abstract

In an effort to better understand the phenomenon of lipotoxicity in human β-cells, we evaluated the effects of 48-h preculture with 1.0 or 2.0 mmol/l free fatty acid (FFA) (2:1 oleate to palmitate) on the function and survival of isolated human islets and investigated some of the possible mechanisms. Compared with control islets, triglyceride content was significantly increased and insulin content and glucose-stimulated insulin release were significantly reduced in islets precultured with increased FFA concentrations. These changes were accompanied by a significant reduction of glucose utilization and oxidation. By cell death detection techniques, it was observed that exposure to FFAs induced a significant increase of the amount of dead cells. Electron microscopy showed the involvement of β-cells, with morphological appearance compatible with the presence of apoptotic phenomena. FFA-induced islet cell death was blocked by inhibition of upstream caspases and partially prevented by inhibiton of ceramide synthesis or serine protease activity, whereas inhibition of nitric oxide synthesis had no effect. RT-PCR studies revealed no major change of iNOS and Bax mRNA expression and a marked decrease of Bcl-2 mRNA expression in the islets cultured with FFA. Thus, prolonged exposure to FFAs has cytostatic and pro-apoptotic effects on human pancreatic β-cells. The cytostatic action is likely to be due to the FFA-induced reduction of intraislet glucose metabolism, and the proapoptotic effects are mostly caspase mediated, partially dependent on ceramide pathway, and possibly Bcl-2 regulated.