Pancreatic Islets from Type 2 Diabetic Patients Have Functional Defects and Increased Apoptosis That Are Ameliorated by Metformin

Abstract

Several properties of pancreatic beta-cells in type 2 diabetes (T2D) were studied by using islets isolated from T2D subjects. Moreover, because metformin has protective effects on nondiabetic beta-cells exposed to high glucose or free fatty acid levels, we investigated its direct action on T2D islet cells. Diabetic islets were characterized by reduced insulin content, decreased amount of mature insulin granules, impaired glucose-induced insulin secretion, reduced insulin mRNA expression, and increased apoptosis with enhanced caspase-3 and -8 activity. These alterations were associated with increased oxidative stress, as shown by higher nitrotyrosine concentrations, increased expression of protein kinase C-beta2 and nicotinamide adenine dinucleotide phosphate reduced-oxidase, and changes in mRNA expression of manganese- superoxide dismutase, Cu/Zn-superoxide dismutase, catalase, and glutathione peroxidase. Twenty-four-hour incubation of T2D islets with metformin was associated with increased insulin content, increased number and density of mature insulin granules, improved glucose-induced insulin release, and increased insulin mRNA expression. Moreover, apoptosis was reduced, with concomitant decrease of caspase-3 and -8 activity. These changes were accompanied by reduction or normalization of several markers of oxidative stress. Thus, T2D islets have several functional and survival defects, which can be ameliorated by metformin; the beneficial effects of the drug are mediated, at least in part, by a reduction of oxidative stress.

The endoplasmic reticulum in pancreatic beta cells of type 2 diabetes patients

“…Pancreas procurement and islet isolation Pancreases were obtained with the approval of the local Ethics Committee and processed as described [27][28][29]. Thirty-one glands were used.…”

“…For morphological and morphometric studies, as well as for LCM experiments, pancreatic samples were obtained immediately before islet preparation. Islet isolation was performed by enzymatic digestion and density gradient purification [27][28][29]. Handpicked islets were kept at 37°C in a CO 2 incubator for 3-6 days before the experiments were performed, with no difference between non-diabetic and diabetic islets in terms of length of incubation.…”

“…Culture medium consisted of M199 medium, containing 5.5 mmol/l glucose, 10% (vol./vol.) bovine serum and antibiotics [27][28][29]. In a separate series of experiments, islets were cultured for an additional 24 h in the presence of 11.1 mmol/l glucose to assess the impact of increasing glucose concentration on some of the studied parameters.…”

“…Insulin secretion studies Insulin secretion studies were performed by batch incubation [27][28][29] in 22 control and nine type 2 diabetic preparations. Islet samples were kept at 37°C for 45 min in Krebs-Ringer bicarbonate (KRB), 0.5% (vol./vol.)…”

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

“…At the final stage of T2D, hyperglycemia is no longer just a consequence of peripheral insulin resistance, but also a result of b-cell failure and 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).…”