Introduction - The dipeptide L-alanyl-L-glutamine (Ala-Glut) has been shown to improve glycaemic control in intensive care patients and rescue pancreatic β-cells from inflammatory challenge in vitro. Thus, Ala/Glut supplementation may constitute a promising therapeutic intervention in type 2 diabetes mellitus (T2DM). Chronic exposure of β-cells to saturated fats causes endoplasmic reticulum (ER) stress, impaired insulin secretion and cell death, contributing to β-cell dysfunction and loss in T2DM.
Objectives - To evaluate the potential of Ala-Glut to protect β-cells against lipotoxicity induced by the saturated fatty acid palmitate.
Methods - Rat islets and BRIN-BD11 β-cells were exposed to palmitate with or without Ala-Glut. Cell viability was monitored by FDA/PI and MTT assays. β-cell function was evaluated through glucose-stimulated insulin secretion assays. Expression levels of proteins involved with the ER stress response were determined by immunoblot analysis and cellular bioenergetics was monitored by extracellular flux analysis using the XFe96 seahorse analyser.
Results - Addition of Ala-Glut conferred a concentration-dependent protective effect against palmitate-induced loss of viability. Exposure to palmitate for 24h dramatically impaired chronic and acute insulin secretion. However, co-incubation in the presence of Ala-Glut enhanced insulin secretion by approximately 3-fold compared to palmitate alone. Importantly, this protection was abolished if glutamine metabolism was blocked using a specific glutaminase inhibitor. Palmitate also induced a robust ER stress response as revealed by a time-dependent induction of ATF4 and Chop. Ala-Glut prevented ATF4 and Chop accumulation, which resulted in decreased activation of Caspase-3 and partial attenuation of cell death. Finally, Ala-Glut also had a beneficial effect on cellular bioenergetics including glycolytic and mitochondrial metabolism.
Conclusions – While lipotoxicity plays an important role in the pathogenesis of T2DM, our results reveal that the dipeptide Ala-Glut can protect pancreatic β-cells against toxicity induced by palmitate, highlighting its therapeutic potential and warranting further investigation in clinical settings.