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

Abstract

In an effort to better understand the phenomenon of lipotoxicity in human ␤-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 ␤-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 proapoptotic effects on human pancreatic ␤-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.

Glucagon-like peptide-1 prevents beta cell glucolipotoxicity

“…The addition of GLP-1 completely prevented lipotoxicity. The relatively high basal level of apoptosis is similar to that reported by previous studies of isolated intact human islets (9%) [14] or of islets after dispersion (22%) [10]. This might be due in part to: (i) the presence of a low concentration of serum in the incu- bation medium; (ii) the stress imposed by the dissociation process; and (iii) central necrosis of islets after their isolation.…”

“…However, chronic hyperglycaemia causes beta cell dysfunction characterised by reduced insulin biosynthesis [6] and increased levels of apoptosis (glucotoxicity) [7,8,9,10,11]. Similarly, acute exposure to NEFA potentiates glucose-induced insulin secretion by beta cells [12], whereas prolonged exposure to high concentrations of NEFA triggers beta cell apoptosis (lipotoxicity) [13,14,15,16,17]. A recent study showed that protein kinase B (PKB) activation can rescue MIN6 cells from oleate cytotoxicity [18].…”

Human triglyceride-rich lipoproteins impair glucose metabolism and insulin signalling in L6 skeletal muscle cells independently of non-esterified fatty acid levels

“…Taking together the results of all these studies, elevated NEFA levels have been convincingly shown to play a causal role in the pathogenesis of insulin resistance. In addition, several studies have demonstrated that NEFAs are also capable of inducing beta cell dysfunction [14][15][16][17], the other major metabolic abnormality of type 2 diabetes.…”

Macrophage migration inhibitory factor deficiency protects pancreatic islets from palmitic acid‐induced apoptosis

“…[1][2][3] Namely, long-term exposure to high levels of free fatty acids and/or glucose causes multiple functional changes in b-cells, including impaired insulin expression, synthesis and secretion, dysfunction in glucose metabolism, stress of the endoplasmic reticulum, mitochondrial dysfunction, upregulated cytokine production and eventually apoptosis. [4][5][6] One of the free fatty acids that is present at very high concentration in the serum of obese C57BL/6 mice (around 150 mM) 7 and induces pancreatic islet death in vitro through induction of mitochondria-and ceramide-dependent pathways is palmitic acid (PA). 4,8 The role of pro-inflammatory mediators in b-cell failure during obesity-associated T2D has been discovered in the previous century, but just recently emphasized.…”

“…[4][5][6] One of the free fatty acids that is present at very high concentration in the serum of obese C57BL/6 mice (around 150 mM) 7 and induces pancreatic islet death in vitro through induction of mitochondria-and ceramide-dependent pathways is palmitic acid (PA). 4,8 The role of pro-inflammatory mediators in b-cell failure during obesity-associated T2D has been discovered in the previous century, but just recently emphasized. The mediators such as leptin and adiponectin or cytokines (IL-6, TNF-a, IL-1b, MCP-1, IL-17, IL-18) produced by adipocytes are involved in development of insulin resistance in both obese and T2D subjects.…”