Mathematical Model of Metabolism and Electrophysiology of Amino Acid and Glucose Stimulated Insulin Secretion: In Vitro Validation Using a β-Cell Line

Abstract

We integrated biological experimental data with mathematical modelling to gain insights into the role played by L-alanine in amino acid-stimulated insulin secretion (AASIS) and in D-glucose-stimulated insulin secretion (GSIS), details important to the understanding of complex β-cell metabolic coupling relationships. We present an ordinary differential equations (ODEs) based simplified kinetic model of core metabolic processes leading to ATP production (glycolysis, TCA cycle, L-alanine-specific reactions, respiratory chain, ATPase and proton leak) and Ca2+ handling (essential channels and pumps in the plasma membrane) in pancreatic β-cells and relate these to insulin secretion. Experimental work was performed using a clonal rat insulin-secreting cell line (BRIN-BD11) to measure the consumption or production of a range of important biochemical parameters (D-glucose, L-alanine, ATP, insulin secretion) and Ca2+ levels. These measurements were then used to validate the theoretical model and fine-tune the parameters. Mathematical modelling was used to predict L-lactate and L-glutamate concentrations following D-glucose and/or L-alanine challenge and Ca2+ levels upon stimulation with a non metabolizable L-alanine analogue. Experimental data and mathematical model simulations combined suggest that L-alanine produces a potent insulinotropic effect via both a stimulatory impact on β-cell metabolism and as a direct result of the membrane depolarization due to Ca2+ influx triggered by L-alanine/Na+ co-transport. Our simulations indicate that both high intracellular ATP and Ca2+ concentrations are required in order to develop full insulin secretory responses. The model confirmed that K+ ATP channel independent mechanisms of stimulation of intracellular Ca2+ levels, via generation of mitochondrial coupling messengers, are essential for promotion of the full and sustained insulin secretion response in β-cells.

Nutrient regulation of insulin secretion and action

“…We have consistently shown that alanine is consumed by b-cell lines and islet cells and increases insulin secretion (Dixon et al 2003, Newsholme et al 2010, Salvucci et al 2013, findings that are supported by observations from other b-cell lines including murine and human (Dunne et al 1990, McCluskey et al 2011, Kasabri et al 2012). More recently, we have created an integrated mathematical model which predicted that increased intracellular ATP and Ca 2C levels were critical for glucose plus amino acid-stimulated insulin secretion in BRIN-BD11 cells (Salvucci et al 2013). Furthermore, additional analyses demonstrated that alanine-mediated Na C co-transport acted synergistically with membrane depolarisation and led to K C ATP -independent Ca 2C influx (McClenaghan et al 1998, Salvucci et al 2013.…”

“…Furthermore, additional analyses demonstrated that alanine-mediated Na C co-transport acted synergistically with membrane depolarisation and led to K C ATP -independent Ca 2C influx (McClenaghan et al 1998, Salvucci et al 2013. However, the mechanism of action of alanine-induced insulin secretion is multifactorial and includes conversion to pyruvate (Salvucci et al 2013), glutamate, aspartate and lactate ( Fig. 1; Newsholme et al 2010).…”

“…More recently, we have created an integrated mathematical model which predicted that increased intracellular ATP and Ca 2C levels were critical for glucose plus amino acid-stimulated insulin secretion in BRIN-BD11 cells (Salvucci et al 2013). Furthermore, additional analyses demonstrated that alanine-mediated Na C co-transport acted synergistically with membrane depolarisation and led to K C ATP -independent Ca 2C influx (McClenaghan et al 1998, Salvucci et al 2013. However, the mechanism of action of alanine-induced insulin secretion is multifactorial and includes conversion to pyruvate (Salvucci et al 2013), glutamate, aspartate and lactate ( Fig.…”

Regulatory principles in metabolism–then and now

“…Trinh et al [24] developed and applied the elementary mode analysis as a tool for metabolic pathway analysis in the study of cell physiology and as a basis of metabolic engineering. Salvucci et al [26] integrated biological experimental data with mathematical modelling for the study of regulation of insulin secretion by amino acids and glucose in pancreatic β-cells. In a different approach, other researchers applied mathematical models to gain insights into regulation of metabolic pathways.…”

Hard-to-cook bean ( Phaseolus vulgaris L.) proteins hydrolyzed by alcalase and bromelain produced bioactive peptide fractions that inhibit targets of type-2 diabetes and oxidative stress

“…Glucose homeostasis requires of insulin secretion, which is mainly regulated by blood glucose. Other compounds such as amino acids may also regulate insulin secretion (Salvucci, Neufeld, & Newsholme, 2013). The stimulating action of amino acids can be attributed to the generation of ATP, direct membrane depolarization (L-arginine and L-lysine) and membrane depolarization through co-transport of Na+ (Liu, Jeppesen, Gregersen, Chen, & Hermansen, 2008).…”