Chronic leucine exposure results in reduced but reversible glucose-stimulated insulin secretion in INS-1 cells

Abstract

Previous studies have demonstrated that sustained high leucine exposure decreases glucose-stimulated insulin secretion (GSIS). However, whether this effect is recoverable following the removal of leucine is unclear. Pancreatic/duodenal homeobox-1 (PDX-1) and its downstream target, glucose transporter 2 (GLUT2), are reported to be positively associated with insulin secretion. However, it also remains unclear whether the effect of leucine on GSIS is accompanied by alterations in PDX-1 and GLUT2. In the present study, insulin secretion, insulin content, PDX-1 and GLUT2 protein expression in INS-1 (rat insulinoma cell line) cells were assessed following a 24-h incubation in 40 mmol/l leucine. Half of the cells were incubated in leucine-free media for a further 24 h to observe the abovementioned effects. In contrast to the control, 40 mmol/l leucine for 24 or 48 h diminished GSIS at high glucose concentrations by 11% (P=0.026) or 22% (P=0.003), insulin content by 14% (P=0.008) or 20% (P=0.002), as well as decreasing PDX-1 and GLUT2 expression. When leucine was removed from the media for a further 24-h incubation, in comparison with those cells that were maintained in leucine treatment for 24 and 48 h, the high GSIS increased by 13% (P=0.032) and 27% (P=0.002), insulin content was augmented by 10% (P=0.014) and 20% (P=0.003), and the protein expression of PDX-1 and GLUT2 also increased. The present study demonstrates that sustained high concentrations of leucine induce a reversible impairment of GSIS and alter insulin content, which is mediated by PDX-1 and GLUT2, in INS-1 cells.

Alpha-Mangostin Improves Insulin Secretion and Protects INS-1 Cells from Streptozotocin-Induced Damage

“…In addition, oxidative stress can lead to pancreatic β-cell loss through apoptosis or necrosis. STZ also affects many cellular processes such as proliferation, differentiation, response to inflammation, and autophagy [ 3 , 37 , 38 , 39 , 40 , 41 ].…”

“…Diabetes is a chronic metabolic disorder whose prevalence is increasing annually. It represents a major social issue associated with modern lifestyle worldwide [ 1 , 2 , 3 ]. Thus, the identification of compounds capable of preventing or treating diabetes is of great importance.…”

“…Thus, the identification of compounds capable of preventing or treating diabetes is of great importance. Type 1 diabetes is an autoimmune disorder caused by pancreatic β-cells loss, while type 2 diabetes is a heterogeneous disease which is caused by pancreatic β-cells dysfunction and insufficient insulin release in response to glucose in peripheral tissues such as skeletal muscle (glucose disposal), liver (glucose production), and adipose tissue (lipolysis) [ 3 , 4 , 5 , 6 , 7 ]. The combination of failed metabolic response in skeletal muscle and pancreatic β-cells dysfunction causes an increase of glucose production by the liver [ 8 ].…”

Momordica balsamina Fruit Extracts Enhances Selected Aspects of the Insulin Synthesis/Secretion Pathway

“…The RIN-m5F cells were stimulated by treatment with varying doses of MB fruit extracts for the insulin synthesis and secretions assays following method detailed by (Zhang et al, 2014), with modifications. Subsequently, the sum of intracellular and extracellular insulin quantities was summed to calculate the overall quantity of synthesized insulin.…”

Effect of Cinnamomum cassia Stem-Bark Extracts on the Synthesis and Secretion of Insulin in RIN-m5F Cells

“…Insulin content was determined from cells lysed with RIPA lysis buffer and the released insulin was measured from the aliquots of the medium. Analysis of the glucose stimulated insulin synthesis was carried out following the modified method described by Zhang et al (2014) by ELISA (Sigma-Aldrich, SA), subsequent to the manufactures protocol. Concentrations of both the insulin content and secreted insulin were standardized to overall protein content which was determined by means of Lowry protein assay kit (Thermo Fisher Scientific, SA).…”