Insulinotropic Effects of Neprilysin and/or Angiotensin Receptor Inhibition in Mice

RNA-Seq transcriptomic landscape profiling of spontaneously hypertensive rats in youth treated with a ARNI versus ARB

Angiotensin receptor-neprilysin inhibitor (ARNI) and angiotensin II receptor blockers (ARB) are antihypertension medications that improve cardiac remodeling and protect the heart. However, at the early stage of hypertension, it is still unclear how these two drugs affect the transcriptomic profile of multiple organs in hypertensive rats and the transcriptomic differences between them. We performed RNA sequencing to define the RNA expressing profiles of the eight tissues (atrium, ventricle, aorta, kidney, brain, lung, white fat, and brown fat) in spontaneously hypertensive rats (SHRs) and SHRs treated with ARNI or ARB. Acquired data was processed and analyzed by computational analyses (i.e., clustering, DEG, functional association, WGCNA, and protein-protein interaction (PPI) network analysis). We discovered that various tissues produced significant transcriptomic changes at the early stage of hypertension. The transcriptomic differences are notably in brown fat, kidney, lung, and brain tissues between ARNI and ARB treatment. Meanwhile, ARNI or ARB treatment can reverse the dysregulated expression genes related to the metabolism process, especially in brown fat, lung, and kidney tissues under hypertension. The current study has presented a comprehensive rat RNA-Seq transcriptomic landscape in SHRs and compared the transcriptome differences between ARNI and ARB treatment as a biomedical research resource for further study.

LCZ696, an Angiotensin Receptor-Neprilysin Inhibitor, Ameliorates Endothelial Dysfunction in Diabetic C57BL/6 Mice

AIMS

LCZ696 (sacubitril/valsartan) exerts cardioprotective effects. Recent studies have suggested that it improves the endothelial function; however, the underlying mechanisms have not been thoroughly investigated. We investigated whether LCZ696 ameliorates diabetes-induced endothelial dysfunction.

METHODS

Diabetes was induced using streptozotocin in 8-week-old male C57BL/6 mice. Diabetic mice were randomly assigned to receive LCZ696 (100 mg/kg/day), valsartan (50 mg/kg/day), or a vehicle for three weeks. The endothelium-dependent and endothelium-independent vascular responses of the aortic segments were determined based on the response to acetylcholine and sodium nitroprusside, respectively. Human umbilical vein endothelial cells (HUVEC) and aortic segments obtained from C57BL/6 mice were used to perform in vitro and ex vivo experiments, respectively.

RESULTS

LCZ696 and valsartan reduced the blood pressure in diabetic mice (P＜0.05). The administration of LCZ696 (P＜0.001) and valsartan (P＜0.01) ameliorated endothelium-dependent vascular relaxation, but not endothelium-independent vascular relaxation, under diabetic conditions. LCZ696, but not valsartan, increased eNOSSer1177 (P=0.06) and Akt (P＜0.05) phosphorylation in the aorta. In HUVEC, methylglyoxal (MGO), a major precursor of advanced glycation end products, decreased eNOSSer1177 phosphorylation (P＜0.05) and increased eNOSThr495 phosphorylation (P＜0.001). However, atrial natriuretic peptide (ANP) reversed these effects. ANP also ameliorated the MGO-induced impairment of endothelium-dependent vascular relaxation in the aortic segments (P＜0.05), although L-NAME completely blocked this effect (P＜0.001).

CONCLUSION

LCZ696 ameliorated diabetes-induced endothelial dysfunction by increasing the bioavailability of ANP. Our findings suggest that LCZ696 has a vascular protective effect in a diabetic model and highlight that it may be more effective than valsartan.

Gut-specific Neprilysin Deletion Protects Against Fat-induced Insulin Secretory Dysfunction in Male Mice

Neprilysin is a ubiquitous peptidase that can modulate glucose homeostasis by cleaving insulinotropic peptides. While global deletion of neprilysin protects mice against high-fat diet (HFD)-induced insulin secretory dysfunction, strategies to ablate neprilysin in a tissue-specific manner are favored to limit off-target effects. Since insulinotropic peptides are produced in the gut, we sought to determine whether gut-specific neprilysin deletion confers beneficial effects on insulin secretion similar to that of global neprilysin deletion in mice fed a HFD. Mice with conditional deletion of neprilysin in enterocytes (NEPGut-/-) were generated by crossing Vil-Cre and floxed neprilysin mice. Neprilysin activity was almost abolished throughout the gut in NEPGut-/- mice, and was similar in plasma, pancreas, and kidney in NEPGut-/- vs control mice. An oral glucose tolerance test was performed at baseline and following 14 weeks of HFD feeding, during which glucose tolerance and glucose-stimulated insulin secretion (GSIS) were assessed. Despite similar body weight gain at 14 weeks, NEPGut-/- displayed lower fasting plasma glucose levels, improved glucose tolerance, and increased GSIS compared to control mice. In conclusion, gut-specific neprilysin deletion recapitulates the enhanced GSIS seen with global neprilysin deletion in HFD-fed mice. Thus, strategies to inhibit neprilysin specifically in the gut may protect against fat-induced glucose intolerance and beta-cell dysfunction.

Neprilysin deficiency reduces hepatic gluconeogenesis in high fat-fed mice

Neprilysin is a peptidase that cleaves glucoregulatory peptides, including glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK). Some studies suggest that its inhibition in diabetes and/or obesity improves glycemia, and that this is associated with enhanced insulin secretion, glucose tolerance and insulin sensitivity. Whether reduced neprilysin activity also improves hepatic glucose metabolism has not been explored. We sought to determine whether genetic deletion of neprilysin suppresses hepatic glucose production (HGP) in high fat-fed mice. Nep+/+ and Nep-/- mice were fed high fat diet for 16 weeks, and then underwent a pyruvate tolerance test (PTT) to assess hepatic gluconeogenesis. Since glycogen breakdown in liver can also yield glucose, we assessed liver glycogen content in fasted and fed mice. In Nep-/- mice, glucose excursion during the PTT was reduced when compared to Nep+/+ mice. Further, liver glycogen levels were significantly greater in fasted but not fed Nep-/- versus Nep+/+ mice. Since gut-derived factors modulate HGP, we tested whether gut-selective inhibition of neprilysin could recapitulate the suppression of hepatic gluconeogenesis observed with whole-body inhibition, and this was indeed the case. Finally, the gut-derived neprilysin substrates, GLP-1 and CCK, are well-known to suppress HGP. Having previously demonstrated elevated plasma GLP-1 levels in Nep-/- mice, we now measured plasma CCK bioactivity and reveal an increase in Nep-/- versus Nep+/+ mice, suggesting GLP-1 and/or CCK may play a role in reducing HGP under conditions of neprilysin deficiency. In sum, neprilysin modulates hepatic gluconeogenesis and strategies to inhibit its activity may reduce HGP in type 2 diabetes and obesity.

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

The 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.