Neprilysin Deficiency Protects Against Fat-Induced Insulin Secretory Dysfunction by Maintaining Calcium Influx

Neprilysin contributes to free fatty acid (FFA)-induced cellular dysfunction in nonislet tissues in type 2 diabetes. Here, we show for the first time that with prolonged FFA exposure, islet neprilysin is upregulated and this is associated with reduced insulin pre-mRNA and ATP levels, oxidative/nitrative stress, impaired potassium and calcium channel activities, and decreased glucose-stimulated insulin secretion (GSIS). Genetic ablation of neprilysin specifically protects against FFA-induced impairment of calcium influx and GSIS in vitro and in vivo but does not ameliorate other FFA-induced defects. Importantly, adenoviral overexpression of neprilysin in islets cultured without FFA reproduces the defects in both calcium influx and GSIS, suggesting that upregulation of neprilysin per se mediates insulin secretory dysfunction and that the mechanism for protection conferred by neprilysin deletion involves prevention of reduced calcium influx. Our findings highlight the critical nature of calcium signaling for normal insulin secretion and suggest that interventions to inhibit neprilysin may improve β-cell function in obese humans with type 2 diabetes

Neprilysin Inhibitors and Angiotensin(1-7) in COVID-19.

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

peer reviewedNeprilysin is a widely expressed peptidase with broad substrate specificity that preferentially hydrolyses oligopeptide substrates, many of which regulate the cardiovascular, nervous and immune systems. Emerging evidence suggests that neprilysin also hydrolyses peptides that play an important role in glucose metabolism. In recent studies in humans, a dual angiotensin receptor-neprilysin inhibitor (ARNi) improved glycaemic control and insulin sensitivity in individuals with type 2 diabetes and/or obesity. Moreover, preclinical studies have also reported that neprilysin inhibition, alone or in combination with renin-angiotensin system blockers, elicits beneficial effects on glucose homeostasis. Since neprilysin inhibitors have been approved for the treatment of heart failure, their repurposing for treating type 2 diabetes would provide a novel therapeutic strategy. In this review, we evaluate existing evidence from preclinical and clinical studies in which neprilysin is deleted/inhibited, we highlight potential mechanisms underlying the beneficial glycaemic effects of neprilysin inhibition, and discuss possible deleterious effects that may limit the efficacy and safety of neprilysin inhibitors in the clinic. We also review the favourable impact neprilysin inhibition can have on diabetic complications, in addition to glucose control. Finally, we conclude that neprilysin inhibitors may be a useful therapeutic option for treating type 2 diabetes; however, their combination with angiotensin II receptor blockers is needed to circumvent deleterious consequences of neprilysin inhibition alone

Acute Inhibition of Intestinal Neprilysin Enhances Insulin Secretion via GLP-1 Receptor Signaling in Male Mice.

peer reviewedThe peptidase neprilysin modulates glucose homeostasis by cleaving and inactivating insulinotropic peptides, including some produced in the intestine such as glucagon-like peptide-1 (GLP-1). Under diabetic conditions, systemic or islet-selective inhibition of neprilysin enhances beta-cell function through GLP-1 receptor (GLP-1R) signaling. While neprilysin is expressed in intestine, its local contribution to modulation of beta-cell function remains unknown. We sought to determine whether acute selective pharmacological inhibition of intestinal neprilysin enhanced glucose-stimulated insulin secretion under physiological conditions, and whether this effect was mediated through GLP-1R. Lean chow-fed Glp1r+/+ and Glp1r-/- mice received a single oral low dose of the neprilysin inhibitor thiorphan or vehicle. To confirm selective intestinal neprilysin inhibition, neprilysin activity in plasma and intestine (ileum and colon) was assessed 40 minutes after thiorphan or vehicle administration. In a separate cohort of mice, an oral glucose tolerance test was performed 30 minutes after thiorphan or vehicle administration to assess glucose-stimulated insulin secretion. Systemic active GLP-1 levels were measured in plasma collected 10 minutes after glucose administration. In both Glp1r+/+ and Glp1r-/- mice, thiorphan inhibited neprilysin activity in ileum and colon without altering plasma neprilysin activity or active GLP-1 levels. Further, thiorphan significantly increased insulin secretion in Glp1r+/+ mice, whereas it did not change insulin secretion in Glp1r-/- mice. In conclusion, under physiological conditions, acute pharmacological inhibition of intestinal neprilysin increases glucose-stimulated insulin secretion in a GLP-1R-dependent manner. Since intestinal neprilysin modulates beta-cell function, strategies to inhibit its activity specifically in the intestine may improve beta-cell dysfunction in type 2 diabetes

L’invalidation sélective de la néprilysine dans les entérocytes augmente la sécrétion d’insuline chez les souris sous régime riche en graisses

peer reviewedIntroduction : La néprilysine est une peptidase ubiquitaire qui peut moduler l'homéostasie glucidique en clivant des peptides insulinotropes. Les souris invalidées pour la néprilysine (NEP-/-) sont protégées contre le dysfonctionnement des cellules beta induit par un régime riche en graisses (HFD). Les peptides insulinotropes étant produits dans l’intestin, nous avons déterminé si l’invalidation sélective de la néprilysine dans les entérocytes augmentait la sécrétion d'insuline en réponse au glucose, comme observé chez des souris NEP-/- soumises à un HFD. Méthodes : Nous avons généré des souris présentant une invalidation conditionnelle de néprilysine dans les entérocytes (NEPgut-/-) en croisant des souris Vil1-cre et des souris NEPflox/flox. Pour valider le modèle génétique, nous avons mesuré l’activité de la néprilysine dans les intestins, d’autres tissus (pancréas et rein) et dans le plasma d’une première cohorte de souris. L’homéostasie glucidique et la sécrétion d’insuline ont été déterminées par test d’hyperglycémie provoquée par voie orale (HGPO) dans une deuxième cohorte de souris soumises à un HFD pendant 14 semaines. Résultats : L'activité de la néprilysine était presque abolie dans tout l'intestin des souris NEPgut-/- versus souris témoins (Vil1-cre et NEPflox/flox), et était similaire dans le plasma, le pancréas et les reins de toutes les souris. Après 14 semaines sous HFD, les souris NEPgut-/- présentaient une glycémie à jeun abaissée, une amélioration de la tolérance au glucose et une augmentation de la sécrétion d’insuline en réponse au glucose en comparaison aux souris Vil1-cre et NEPflox/flox, et ce malgré un poids similaire. Conclusion : L’invalidation spécifique de la néprilysine dans les entérocytes améliore la tolérance au glucose et la sécrétion d’insuline en réponse au glucose chez des souris soumises à un HFD. Dès lors, des stratégies thérapeutiques visant à inhiber spécifiquement la néprilysine dans l’intestin pourraient protéger contre le dysfonctionnement des cellules bêta induit par les lipides

A Mouse Model of Beta-Cell Dysfunction as Seen in Human Type 2 Diabetes

Loss of first-phase insulin release is an early pathogenic feature of type 2 diabetes (T2D). Various mouse models exist to study T2D; however, few recapitulate the early β-cell defects seen in humans. We sought to develop a nongenetic mouse model of T2D that exhibits reduced first-phase insulin secretion without a significant deficit in pancreatic insulin content. C57BL/6J mice were fed 10% or 60% fat diet for three weeks, followed by three consecutive, once-daily intraperitoneal injections of the β-cell toxin streptozotocin (STZ; 30, 50, or 75 mg/kg) or vehicle. Four weeks after injections, the first-phase insulin response to glucose was reduced in mice when high-fat diet was combined with 30, 50, or 75 mg/kg STZ. This was accompanied by diminished second-phase insulin release and elevated fed glucose levels. Further, body weight gain, pancreatic insulin content, and β-cell area were decreased in high fat-fed mice treated with 50 and 75 mg/kg STZ, but not 30 mg/kg STZ. Low fat-fed mice were relatively resistant to STZ, with the exception of reduced pancreatic insulin content and β-cell area. Together, these data demonstrate that in high fat-fed mice, three once-daily injections of 30 mg/kg STZ produces a model of β-cell failure without insulin deficiency that may be useful in studies investigating the etiology and progression of human T2D

Acute inhibition of intestinal neprilysin enhances glucose-stimulated insulin secretion in mice

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

peer reviewedNeprilysin, 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