Mechanism of Ethanol-Induced Insulin Secretion from INS-1 and INS-1E Tumor Cell Lines

Abstract

Alcohol causes reactive hypoglycemia by attenuating the release of counter regulatory hormones, redistribution of pancreatic blood flow and direct stimulation of insulin secretion. Objective of this study was characterization of ethanol-induced insulin secretion. Signaling of ethanol- and glucose-induced insulin release from INS-1 and INS-1E cells was compared. Both cell lines responded similarly to all experimental interventions. In contrast to glucose, ethanol-induced insulin secretion was not hindered in calcium depleted medium or by addition of 10 μM BAPTA/AM (intracellular chelator). Inhibitor of protein kinase C Bisindolylmaleimide (3 μM) abolished glucose- but not ethanol-induced insulin secretion. Tetanus toxin (20 nM), inhibitor of SNARE proteins complex formation, blocked ethanol-induced insulin secretion. Both 5 mM N-ethylamaleimide and 10 μM ZnCl₂ (inhibitor of protein tyrosine phosphatases), which block disassembly of SNARE complexes and their further participation in exocytosis, increased basal insulin secretion. In contrast to glucose, already high insulin secretion was further increased after ethanol stimulation in either treatment. Conclusion: Signaling of ethanol-induced insulin secretion from INS-1 and INS-1E cell lines bypasses calcium and PKC involving steps, is sensitive to tetanus toxin but resistant to N-ethymaleimide and ZnCl₂. An extra pool of secretory vesicles not available for glucose is exploited for exocytosis after ethanol stimulation.

Ethanol induced impairment of glucose metabolism involves alterations of GABAergic signaling in pancreatic β-cells

“…Our result is in agreement with previous studies performed in humans (Boden et al, 1993) and rat islets (Singh et al, 1980). However, enhancement of insulin concentration by ethanol was also observed in rat serum (Huang and Sjoholm, 2008) and in the culture media of INS-1 cells (Hafko et al, 2009). These controversial data may be due to various research conditions.…”

Cell Swelling-induced Peptide Hormone Secretion

“…ZnCl 2 was shown to be effective inhibitor of dephosphorylation of phosphotyrosyl residues [84] and affecting exocytosis by similar mechanism as NEM. Essentially the same results received with ZnCl 2 as with NEM [83] strengthen our hypothesis that an extra pool of secretory vesicles is available for exocytosis in this type of stimulation.…”

“…This response to stimulation suggests the presence of a separate pool of secretory granules available for swelling-induced but not glucose-induced exocytosis after treatment. Interestingly, high insulin secretion from NEM treated cells further increased also after ethanol stimulation [83] suggesting similar pathway for permeant effect. ZnCl 2 was shown to be effective inhibitor of dephosphorylation of phosphotyrosyl residues [84] and affecting exocytosis by similar mechanism as NEM.…”

“…Surprisingly, stimulating effect of ethanol was completely suppressed by noradrenalin in both tumor cell lines [95]. In contrast to hypotonicity, ethanol stimulated insulin secretion also from INS-1E tumor cells either in presence or absence of Ca 2+ in the medium [83]. This short survey documents how signaling and response of tumor-derived cells to cell swelling varies markedly between different cell lines.…”

Cell Swelling-induced Insulin Secretion from INS-1E Cells is Inhibited by Extracellular Ca²⁺ and is Tetanus Toxin Resistant

“…Recently Madsen et al [22] found that calcineurin and calcium/calmodulin suppress exocytosis of renin from juxtaglomerular cells independent of PKA. It is of interest that ethanol effect which in many aspects shares common mechanisms and properties with hypotonic stimulation [18,23,24] on insulin secretion from INS-1E cell line is not hindered by the presence of calcium [25]. It is likely that swelling and secretion-inducing effect of various permeants utilizes different pathways.…”