Abstract
Obesity-associated diabetes and concomitant inflammation may compromise pancreatic β-cell integrity and function. l-glutamine and l-alanine are potent insulin secretagogues, with antioxidant and cytoprotective properties. Herein, we studied whether the dipeptide l-alanyl-l-glutamine (Ala-Gln) could exert protective effects via sirtuin 1/HUR (SIRT1/HUR) signalling in β-cells, against detrimental responses following ex vivo stimulation with inflammatory mediators derived from macrophages (IMMs). The macrophages were derived from blood obtained from obese subjects. Macrophages were exposed (or not) to lipopolysaccharide (LPS) to generate a pro-inflammatory cytokine cocktail. The cytokine profile was determined following analysis by flow cytometry. Insulin-secreting BRIN-BD11 β-cells were exposed to IMMs and then cultured with or without Ala-Gln for 24 h. Chronic insulin secretion, the l-glutamine-glutathione (GSH) axis, and the level of insulin receptor β (IR-β), heat shock protein 70 (HSP70), SIRT1/HUR, CCAAT-enhancer-binding protein homologous protein (CHOP) and cytochrome c oxidase IV (COX IV) were evaluated. Concentrations of cytokines, including interleukin 1β (IL1β), IL6, IL10 and tumour necrosis factor alpha (TNFα) in the IMMs, were higher following exposure to LPS. Subsequently, when β-cells were exposed to IMMs, chronic insulin secretion, and IR-β and COX IV levels were decreased, but these effects were partially or fully attenuated by the addition of Ala-Gln. The glutamine-GSH axis and HSP70 levels, which were compromised by IMMs, were also restored by Ala-Gln, possibly due to protection of SIRT1/HUR levels, and a reduction of CHOP expression. Using an ex vivo inflammatory approach, we have demonstrated Ala-Gln-dependent β-cell protection mediated by coordinated effects on the glutamine-GSH axis, and the HSP pathway, maintenance of mitochondrial metabolism and stimulus-secretion coupling essential for insulin release.
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