Evidence for the involvement of GPR40 and NADPH oxidase in palmitic acid-induced superoxide production and insulin secretion

Abstract

G protein coupled receptor 40 (GPR40) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex have been shown to be involved in the fatty acid amplification of glucose-stimulated insulin secretion (GSIS). The effect of palmitic acid on superoxide production and insulin secretion by INS-1E cells and the possible involvement of GPR40 and NADPH oxidase in these processes were examined in this study. Cells were incubated during 1 h with palmitic acid in low and high glucose concentrations, a GPR40 agonist (GW9508) and inhibitors of NADPH oxidase (diphenyleneiodonium, DPI) and PKC (calphostin C). GW9508 induced superoxide production at 2.8 and 5.6 mM glucose concentrations and stimulated insulin secretion at 16.7 mM glucose concentration involving both PKC and NADPH oxidase activation. Palmitic acid induced superoxide production through NADPH oxidase and GPR40-dependent pathways and the stimulation of insulin secretion in the presence of a high glucose concentration was reduced by knockdown of GPR40 using siRNA. Our results suggest that palmitic acid induces superoxide production and potentiates GSIS through NADPH oxidase and GPR40 pathways in pancreatic ? cells.

The novel NADPH oxidase 4 inhibitor GLX351322 counteracts glucose intolerance in high-fat diet-treated C57BL/6 mice

“…7B). Sodium palmitate is thought to stimulate insulin release by interaction with the FFA receptor FFAR1/GPR40 and via increased long-chain Acyl-CoA esters, and longterm palmitate effects are known to be deleterious for beta-cells [22,32,33]. We observed that palmitate-stimulated insulin release was decreased by GLX351322 at a concentration of 2 µM (Fig.…”

“…Thus, it may be that insulin release is stimulated in the 4 short term by increased ROS production, whereas a long-term NOX-activation leads to loss of beta-cell function. Not only glucose in vitro or hyperglycemia in vivo promotes beta-cell activation of NOX, but also sodium palmitate, a free fatty acid which is increased in Type 2 diabetes, and which stimulates the release of insulin in short-term experiments, but inhibits beta-cell function after a prolonged exposure period [20][21][22].…”

Melatonin modifies basal and stimulated insulin secretion via NADPH oxidase

“…Melatonin can affect many systems in the cell, such as the mitochondrial metabolism (Ramis et al 2015); hence, it is plausible that the absence of melatonin may induce ROS production not only through NOX but also through other oxidant sources, such as the mitochondria. However, it is important to consider that DHE is a specific probe for the detection of cytosolic ROS content (Zhao et al 2003, Dikalov 2011, and previous publications have already shown that most of the ROS products generated after glucose stimulation are superoxide, which was confirmed using SOD linked to polyethylene glycol (PEG-SOD) (Graciano et al 2013).…”

“…Recent evidence shows that insulin secretion is inversely related to ROS concentration (Rebelato et al 2011, Graciano et al 2013. Under low glucose, high ROS content limits insulin secretion to basal levels (Munhoz et al 2016).…”

“…Data from our group demonstrate that ROS production through NADPH oxidase (NOX) complex (Rebelato et al 2012, Graciano et al 2013) has a significant role in the process of insulin secretion, negatively regulating GSIS in pancreatic islets and modulating glucose metabolism (Morgan et al 2009, Rebelato et al 2011. Briefly, NOX consists of two membrane-bound subunits, gp91 phox and p22 phox , which form the flavocytochrome b 558 enzymatic core.…”