Neprilysin, obesity and the metabolic syndrome

Abstract

ObjectiveNeprilysin (NEP), a zinc metallo-endopeptidase, has a role in blood pressure control and lipid metabolism. The present study tested the hypothesis that NEP is associated with insulin resistance and features of the metabolic syndrome (MetS) in a study of 318 healthy human subjects and in murine obesity and investigated NEP production by adipocytes in-vitro.Methods and ResultsIn 318 white European males, plasma NEP was elevated in the MetS and increased progressively with increasing MetS components. Plasma NEP activity correlated with insulin, homeostasis model assessment and body mass index in all subjects (p<0.01). Quantitative RT-PCR and Western blotting showed that in human pre-adipocytes NEP expression is upregulated 25-30 fold during differentiation into adipocytes. Microarray analysis of mRNA from differentiated human adipocytes confirmed high NEP expression comparable to adiponectin and plasminogen activator inhibitor-1. In a murine model of diet-induced insulin resistance, plasma NEP levels were significantly higher in high fat diet (HFD)-fed compared with normal chow diet (NCD)-fed animals (1642±529 and 820±487 pg/μl, respectively; p<0.01). Tissue NEP was increased in mesenteric fat in HFD compared with NCD-fed mice (p<0.05). NEP knock out mice did not display any changes in insulin resistance, glucose tolerance or body and epididymal fat pad weight compared to wild type mice.ConclusionsIn humans, NEP activity correlated with body mass index and measures of insulin resistance with increasing levels in subjects with multiple cardiovascular risk factors. NEP protein production in human adipocytes increased during cell differentiation and plasma and adipose tissue levels of NEP were increased in obese insulin resistant mice. Our results indicate that NEP associates with cardio-metabolic risk in the presence of insulin resistance and increases in obesity.

Improved glycaemia in high-fat-fed neprilysin-deficient mice is associated with reduced DPP-4 activity and increased active GLP-1 levels

“…Recombinant human DPP-4 (R&D Systems, Minneapolis, MN, USA) was then added at a final concentration of 0.01, 0.05 or 0.1 µmol/l, and incubated for 1 h at 37°C. When 1:1, 1:5 and 1:10 molar ratios of neprilysin to DPP-4 were tested, the 1:5 and 1:10 ratios approximated those documented in plasma from lean and obese humans [3, 16, 17]. Samples were assayed for neprilysin and DPP-4 activities as described above.…”

“…Neprilysin (encoded by Nep , also known as Mme ) is a widely expressed plasma membrane peptidase with increased levels in metabolically altered states [1–3]. We and others have demonstrated that reducing neprilysin activity may be beneficial via improving insulin secretion [4] and sensitivity [5–7].…”

Blood-Based Biomarkers for Metabolic Syndrome

“…NEP is expressed by adipocytes [43], plays a role in inhibiting peptide signalling events, and is involved in the metabolism of a number of regulatory proteins [44]. This study showed that the circulating levels of NEP mRNA in a mouse model of obesity were higher after 15 weeks on a high-fat diet, with a progressive increase from week 7 to week 15 [43]. This suggests a potential of adipose tissue-derived NEP mRNA in the plasma as a biomarker for MetS.…”

Does GLP-1 suppress its own basal secretion?

“…It should be noted that the basal levels of the total GLP-1 in the plasma of the lean group of subjects was approximately three-fold higher than that in the obese group. This difference may be due to a similar three-fold increase in plasma levels of neprilysin in obese compared to lean human subjects (17) Neprilysin has been shown to degrade GLP-1 (18) at several sites (19) and likely would reduce plasma levels of immunoreactive (total) GLP-1 (18) Recently, it has been demonstrated that there is considerable variability in specificity, sensitivity and precision of all measurable isoforms of GLP-1 levels as measured in different commercial assay Kits (20). These investigators report that the Linco (now Millipore) active ELISA GLP-1 kit detect only the active isoform and is capable of recognizing as little as 1 pmol/L differences in GLP-1 (7-36)amide levels.…”