Alanyl-glutamine improves pancreatic β-cell function following ex vivo inflammatory challenge

Abstract

Obesity-associated diabetes and concomitant inflammation may compromise pancreatic b-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 b-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 b-cells were exposed to IMMs and then cultured with or without Ala-Gln for 24 h. Chronic insulin secretion, the L-glutamineglutathione (GSH) axis, and the level of insulin receptor b (IR-b), 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 1b (IL1b), IL6, IL10 and tumour necrosis factor alpha (TNFa) in the IMMs, were higher following exposure to LPS. Subsequently, when b-cells were exposed to IMMs, chronic insulin secretion, and IR-b 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 b-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.

An in vitro model to consider the effect of 2 mM glutamine and KNK437 on endotoxin-stimulated release of heat shock protein 70 and inflammatory mediators

“…Before these experiments, a range of glutamine doses (2 to 6.8 mM) were evaluated in a whole blood endotoxin model from healthy volunteers (n ¼ 3). Our previous results suggested that 2 mM glutamine was the most effective dose, in addition to which it has previously been acknowledged as representing physiological concentrations of glutamine in the serum [25,26].…”

Early initiation of low-level parenteral dextrose induces an accelerated diabetic phenotype in septic C57BL/6J mice

“…IL-1β activation plays a role in the development of insulin resistance in peripheral glucose disposing tissue by direct inhibition of insulin receptor substrate-1 signaling and indirectly through the production of pro-inflammatory cytokines and generation of reactive oxygen species (Strowig et al 2012). In the pancreas, the combination of low-dose IL-1β and TNF-α also suppresses insulin production by pancreatic islets (Mehta et al 1994), and lipopolysaccharide-induced IL-1β has been shown to suppress pancreatic beta cell function in vitro (Cruzat et al 2015). Thus, in sepsis, inflammasome activation may act to disrupt normal disposal of glucose in peripheral metabolic tissue and impair insulin secretion.…”

Prospective evaluation of glutamine and phospholipids levels in first degree relatives of patients with Type 1 Diabetes from a multiethnic population

“…The altered levels of glutamine, phospholipids, and other metabolites in children at high risk for T1D, before the seroconversion of pancreatic autoantibodies have been repported [2, 3]. This dysregulation in the metabolism of lipids may be an early marker of autoimmunity, but it still remains unclear if these individuals with low phospholipids levels will have a higher risk of developing T1D [4–6]. …”

“…Besides, phospholipids may also be a key modulator of insulin release. Therefore, it would be of general importance to identify metabolic patterns that would predict the risk for T1D later in life [4–6]. …”