Neprilysin inhibition in mouse islets enhances insulin secretion in a GLP-1 receptor dependent manner

Abstract

Neprilysin, a widely expressed peptidase upregulated in type 2 diabetes, is capable of cleaving and inactivating the insulinotropic glucagon-like peptide-1 (GLP-1). Like dipeptidyl peptidase-4 (DPP-4), inhibition of neprilysin activity under diabetic conditions is associated with increased active GLP-1 levels and improved glycemic control. While neprilysin expression has been demonstrated in islets, its local contribution to GLP-1-mediated insulin secretion remains unknown. We investigated in vitro whether islet neprilysin inhibition enhances insulin secretion in response to glucose and/or exogenous GLP-1, and whether these effects are mediated by GLP-1 receptor (GLP-1R). Further, we compared the effect of neprilysin versus DPP-4 inhibition on insulin secretion. Isolated islets from wild-type (Glp1r) and GLP-1 receptor knockout (Glp1r) mice were incubated with or without the neprilysin inhibitor thiorphan and/or the DPP-4 inhibitor sitagliptin for 2.5 hours. During the last hour, insulin secretion was assessed in response to 2.8 mmol/l or 20 mmol/l glucose alone or plus exogenous active GLP-1. In Glp1r islets, neprilysin inhibition enhanced 2.8 mmol/l and 20 mmol/l glucose- and GLP-1-mediated insulin secretion to the same extent as DPP-4 inhibition. These effects were blunted in Glp1r islets. In conclusion, inhibition of islet neprilysin in vitro increases glucose-mediated insulin secretion in a GLP-1R-dependent manner and enhances the insulinotropic effect of exogenous active GLP-1. Thus, neprilysin inhibitors may have therapeutic potential in type 2 diabetes by preserving islet-derived and circulating active GLP-1 levels.

Neprilysin inhibition: a new therapeutic option for type 2 diabetes?

“…This is supported by recent studies in humans treated with ARNi [17,22], and by observations in animals [12,23]. We have shown that inhibition of islet neprilysin in vitro enhances both glucose-and GLP-1-mediated insulin secretion in a GLP-1 receptor-dependent manner, raising the possibility that islet neprilysin inhibition improves beta cell function by preserving islet-and/or gut-derived active GLP-1 [23]. Moreover, we demonstrated in vivo in high-fat fed, neprilysin-deficient mice that elevated active GLP-1 levels in plasma were associated with improved glucose tolerance as a result of enhanced beta cell function and insulin sensitivity [12].…”

“…One potential mechanism by which neprilysin inhibition improves glucose homeostasis may be by increasing levels, and thereby the insulinotropic effects, of GLP-1 [2,3]. This is supported by recent studies in humans treated with ARNi [17,22], and by observations in animals [12,23]. We have shown that inhibition of islet neprilysin in vitro enhances both glucose-and GLP-1-mediated insulin secretion in a GLP-1 receptor-dependent manner, raising the possibility that islet neprilysin inhibition improves beta cell function by preserving islet-and/or gut-derived active GLP-1 [23].…”

“…Positive impact of neprilysin deficiency or inhibition on glucose homeostasis In isolated pancreatic islets from C57BL/6 mice, pharmacological inhibition of neprilysin increased glucose-stimulated insulin secretion (GSIS) [23]. Also, islets from neprilysin-deficient mice were protected against palmitate-induced insulin secretory dysfunction in vitro [24].…”

Maternal Overweight Downregulates MME (Neprilysin) in Feto-Placental Endothelial Cells and in Cord Blood

“…Moreover, recent literature suggests that elevated MME participates in the development of insulin resistance. On one hand, MME cleaves peptides stimulating insulin secretion, i.e., glucagon [40] and GLP1 (glucagon-like peptide 1) [41], and thus MME may reduce systemic insulin secretion [42]. On the other hand, membrane-associated MME modulates internalization and cellular localization of the insulin receptor, as shown by MME knockdown and overexpression in insulin target cells [43].…”

Plasma levels of glucagon but not GLP-1 are elevated in response to inflammation in humans

“…Increased concentrations of glucagon and GLP-1 were recently reported in sepsis (11,12) and critically ill patients (13), in mice following LPS injection (23), and in humans with burn lesions(24). Estimation of plasma GLP-1 in mice is troublesome due to the rapid degradation by neprilysin (25,26), and the assays employed in the current human study and in other previously published studies also cross-react with GLP-1 1-36NH 2 that is cosecreted with glucagon (17). Therefore, one may speculate that the reported increases in GLP-1 actually reflect increased glucagon secretion from pancreatic alpha cells, as captured in the study presented here.…”