A Test in Context: Neprilysin

Finding a reliable assay for soluble neprilysin

BACKGROUND

Lack of validation and standardization of research-use-only (RUO) immunoassays brings with it inherent threats to authenticity and functional quality. Poor correlation between different commercial neprilysin RUO immunoassays is concerning and discordant findings need to be resolved. We seek to identify and validate reliable neprilysin immunoassays to strengthen the scientific rigor and reproducibility of neprilysin-related investigation and of biomarker research in general.

METHODS

Soluble neprilysin (sNEP) concentrations were determined in cohorts (n = 532) from Spain (Cohort 1), New Zealand (NZ, Cohort 2) and Singapore (Cohort 3), using commercial kits from six vendors. Apparent sNEP concentrations were correlated between different assays and with plasma neprilysin activity. Assay reliability was further validated by performance verification, MS analysis and cross-reactivity tests.

RESULTS

sNEP in Cohorts 1 and 2 measured concurrently in Spain and NZ showed significant inter-laboratory correlation only for the Aviscera Bioscience sNEP ELISA SK00724-01. Neprilysin concentrations obtained with the R&D systems and SK00724-01 ELISAs correlated with each other but not with neprilysin activity. In Cohort 3, sNEP concentrations from the Perkin Elmer AlphaLISA and Biotechne ELLA assays agreed (r = 0.89) and both correlated with neprilysin activity (r = 0.87, 0.77 respectively). MS analysis detected authentic neprilysin in the AlphaLISA kit calibrator and in antibody pull-down material from human plasma. The AlphaLISA assay performed within acceptable limits (spike and recovery, dilutional linearity, inter- and intra-assay CV) and showed no cross-reactivity against neprilysin substrates and closely-related analogues.

CONCLUSION

AlphaLISA and ELLA assays provide reliable measures of sNEP concentrations. Reliability of other commercial neprilysin assays remains in question.

Drug Treatment of Heart Failure in Children: Gaps and Opportunities

Medical therapy for pediatric heart failure is based on a detailed mechanistic understanding of the underlying causes, which are diverse and unlike those encountered in most adult patients. Diuresis and improved perfusion are the immediate goals of care in the child with acute decompensated heart failure. Conversion to maintenance oral therapy for heart failure is based on the results of landmark studies in adults, as well as recent pediatric clinical trials and heart failure guidelines. There will continue to be an important role for newer drugs, some of which are in active trials in adults, and some of which are already approved for use in children. The need to plan for clinical trials in children during drug development for heart failure is emphasized.

Early B-Type Natriuretic Peptide Change in HFrEF Patients Treated With Sacubitril/Valsartan: A Pooled Analysis of EVALUATE-HF and PROVE-HF

OBJECTIVES

This study assessed changes in B-type natriuretic peptide (BNP) among patients with heart failure with reduced ejection fraction (HFrEF) treated with sacubitril/valsartan (Sac/Val) according to standard prescribing information.

BACKGROUND

Through inhibition of neprilysin, Sac/Val may increase BNP concentrations.

METHODS

In an individual patient analysis from the EVALUATE-HF (Study of Effects of Sacubitril/Valsartan vs. Enalapril on Aortic Stiffness in Patients With Mild to Moderate HF With Reduced Ejection Fraction) (n = 221) and the PROVE-HF (Effects of Sacubitril/Valsartan Therapy on Biomarkers, Myocardial Remodeling and Outcomes) (n = 146) studies, we examined changes in BNP, N-terminal pro-BNP (NT-proBNP), and urinary cyclic guanosine monophosphate (ucGMP) from baseline to week 4 and week 12.

RESULTS

Median (IQRs) concentration of BNP at baseline, week 4, and week 12 were 145 [IQR: 55-329], 136 [IQR: 50-338], and 135 [IQR: 51-299] ng/L, respectively. There was no significant change from baseline to week 4 (0% [-30% to +41%]; P = 0.36) or week 12 (+1% [-36% to +50%]; P = 0.97). By week 12, one-half of the study participants had a BNP decline. There was no association between Sac/Val dose and BNP changes. Change in BNP was directly associated with change in NT-proBNP (rho: = 0.81; P < 0.001), which decreased by -30% (-50% to -8%) and -32% (-54% to -1%) to weeks 4 and 12 (P < 0.001 for both). In contrast, change in BNP was only weakly associated with change in ucGMP (rho: = 0.19; P < 0.001). Increases in ucGMP were observed regardless of whether BNP was decreased (+11% [-34% to +115%]), unchanged (+34% [-15% to +205%]), or increased (+57% [-12% to +14%]).

CONCLUSIONS

In this pooled analysis of patients with HFrEF with standard indications for Sac/Val treatment, there was no significant overall increase in BNP concentrations, and patients demonstrated increase in ucGMP regardless of the trajectory of BNP change. (Study of Effects of Sacubitril/Valsartan vs. Enalapril on Aortic Stiffness in Patients With Mild to Moderate HF With Reduced Ejection Fraction [EVALUATE-HF]; NCT02874794) (Effects of Sacubitril/Valsartan Therapy on Biomarkers, Myocardial Remodeling and Outcomes [PROVE-HF]; NCT02887183).

Dynamic Changes in Pentraxin-3 and Neprilysin in ST Segment Elevation Myocardial Infarction

Pentraxin-3 (PTX3) and neprilysin have been associated with increased morbidity and mortality in chronic inflammatory disease and heart failure, but these biomarkers have been studied less in patients with ST segment elevation myocardial infarction (STEMI). We investigated the dynamic changes in these biomarkers, as well as the well-known C-reactive protein (CRP), in STEMI patients. PTX3, neprilysin and CRP were measured in samples from 165 STEMI patients, collected at the acute stage, 1–3 days after and 3 months after percutaneous coronary intervention (PCI), and from 40 healthy donors. Patient survival was followed for approximately 8 years after the PCI. As compared with samples from healthy donors, plasma levels of CRP and PTX3 were significantly increased in the acute samples and 1–3 days after PCI, but not at 3 months. CRP levels peaked at 1–3 days, while PTX3 was similarly high in both acute and 1–3 days samples. For neprilysin, no significant differences were observed at the group level. We found no significant differences when comparing patients with patent versus occluded culprit vessels or between patients having a thrombus aspiration or not. However, we found a significant reduction in survival for individuals with PTX3 above the median, both for samples collected at the acute stage and 1–3 days after PCI (p = 0.0001 and p = 0.0008, respectively). For CRP, no significant differences were observed using this approach, but patients above the reference range for healthy donors in the acute samples showed significantly lower survival (p = 0.0476). Conclusions: Survival analysis suggests that PTX3 might be a promising marker to predict mortality in this patient population.

Differential and targeted vesiculation: pathologic cellular responses to elevated arterial pressure

Extracellular vesicles are small membrane-enclosed particles released during cell activation or injury. They have been investigated for several decades and found to be secreted in various diseases. Their pathogenic role is further supported by the presence of several important molecules among their cargo, including proteins, lipids, and nucleic acids. Many studies have reported enhanced and targeted extracellular vesicle biogenesis in diseases that involve chronic or transient elevation of arterial pressure resulting in endothelial dysfunction, within either the general circulatory system or specific local vascular beds. In addition, several associated pathologic processes have been studied and reported. However, the role of elevated pressure as a common pathogenic trigger across vascular domains and disease chronicity has not been previously described. This review will therefore summarize our current knowledge of the differential and targeted biogenesis of extracellular vesicles in major diseases that are characterized by elevated arterial pressure leading to endothelial dysfunction and propose a unified theory of pressure-induced extracellular vesicle-mediated pathogenesis.

Reduction of Pulmonary Hypertension After Transition to Sacubitril/Valsartan in Patients With Heart Failure With Preserved Ejection Fraction

Objectives: Although the PARAGON-HF trial failed to reach its primary endpoint, subgroups of patients with heart failure with preserved ejection fraction (HFpEF) still appear to benefit from Sacubitril/Valsartan therapy. As HFpEF patients with pulmonary hypertension display a specifically high mortality and morbidity, we evaluated the effect of Sacubitril/Valsartan in this subgroup of HFpEF patients.

Methods: In this retrospective case-series of 18 patients with HFpEF and pulmonary hypertension, right heart catheterisation (RHC) for determination of invasive pulmonary pressure were performed at baseline (pre-Sacubitril/Valsartan) and 99 (71–156) days after transition from angiotensin-converting enzyme inhibitors and angiotensin receptor blockers to Sacubitril/Valsartan (post-Sacubitril/Valsartan). Results are given as median and interquartile range.

Results: After conversion to Sacubitril/Valsartan, RHC showed significantly reduced pulmonary artery pressure (PAP) and mean pulmonary capillary wedge pressure (PCWP) compared to pre-Sacubitril/Valsartan [PAP systolic/diastolic/mean 44 (38–55)/15 (11–20)/27 (23–33) mm Hg vs. 51 (41–82)/22 (13–29)/33 (28–52) mm Hg, p < 0.05 and p < 0.01, respectively; PCWP 16 (12–20) mm Hg vs. 22 (15–27) mm Hg, p < 0.05]. Median Sacubitril/Valsartan dosage was 24/26 mg BID (24/26 BID−49/51 mg BID). Clinically, New York Heart Association functional class improved in 12 of the 18 patients (p < 0.01) after conversion to Sacubitril/Valsartan. Echocardiographic parameters of left ventricular function and cardiovascular co-medication did not differ markedly between pre- and post-Sacubitril/Valsartan.

Conclusion: Sacubitril/Valsartan therapy is associated with an improvement of pulmonary hypertension in HFpEF patients.

Aβ31-35 Decreases Neprilysin-Mediated Alzheimer's Amyloid-β Peptide Degradation

Alzheimer's disease is associated with the deposition of extracellular senile plaques, made primarily of amyloid-β (Aβ), particularly peptides Aβ_1-42 and Aβ_1-40. Neprilysin, or neutral endopeptidase (NEP), catalyzes proteolysis of the amyloid peptides (Aβ) and is recognized as one of the major regulators of the levels of these peptides in the brain, preventing Aβ accumulation and plaque formation. Here, we used a combination of techniques to elucidate the mechanism of Aβ binding and cleavage by NEP. Our findings indicate that the Aβ_31-X cleavage products remain bound to the neprilysin active site, reducing proteolytic activity. Interestingly, it was already shown that this Aβ_31-35 sequence is also critical for recognition of Aβ peptides by other targets, such as the serpin-enzyme complex receptor in neuronal cells.

Sacubitril/valsartan in chronic kidney disease: From pharmacological mechanism to clinical application

Chronic kidney disease (CKD) is an irreversible, progressive disease characterized by persistent kidney damage, and significantly increased risks of cardiovascular event. However, therapeutic strategies to prevent or slow the progression of CKD remain limited. Sacubitril/valsartan (LCZ696), the representative of the first novel angiotensin receptor-neprilysin inhibitor, has been incorporated into clinical practice guidelines for improving outcomes as a milestone in patients with heart failure. Considering the complex and close relationship between CKD and heart failure, LCZ696 may be beneficial in the treatment of CKD. This review summarizes the pharmacological mechanism and clinical application of LCZ696 in patients with CKD, including its effect on cardiovascular risk and renal outcome, together with potential adverse events. Additionally, due to the influence of serum creatinine and estimated glomerular filtration rate on LCZ696 in patients with heart failure, we also discussed the effects of LCZ696 in patients with advanced CKD and end-stage renal disease. It should be noted that, current clinical studies on LCZ696 are mostly carried out in patients with heart failure, and renal indicators are selected as secondary outcomes. Therefore, more researches should be conducted in patients with CKD alone in the future, to determine the efficacy and safety of LCZ696 in patients with CKD.

Optimization of Enzymolysis Clearance Strategy To Enhance Renal Clearance of Radioligands

The kidney is the main dose-limiting organ in radioligand therapy (RLT), and there is an urgent need for reducing renal radioactivity accumulation. According to the enzymolysis clearance strategy, the first objective of this study is to test whether enzymolysis efficiency can be improved by introducing a hydrophobic amino acid with a bulkier side chain to the second position of the cleavable sequence, and the second objective is to screen an optimal sequence to minimize the renal uptake. Four exendin 4 (Ex4) peptide analogues with different cleavable sequences were synthesized and labeled with 68Ga. Both in vitro and in vivo metabolism studies were performed using either the model compounds or the complete probes. The in vitro stabilities of the tracers were evaluated in PBS and mouse serum. The microPET images were acquired in the INS-1 tumor model at different time points, and the radioactivity uptakes of the probes in tumors and kidneys were determined and compared. All the probes were stable in both PBS and mouse serum for at least 1 h. The in vitro cleavage study for both model compounds and intact probes showed enzymolysis efficiency in the following order: MWK > MFK > MVK > MGK. The in vivo metabolism study confirmed that a fragment of 68Ga-NOTA-Met-OH appeared in both kidney and urine samples for all analogues with MVK, MFK, and MWK sequences. The microPET images showed that the tumor uptakes of all the modified probes were comparable to those of the control, while the kidney uptakes were significantly reduced by inserting the MWK, MFK, or MVK linker. The tumor-to-kidney ratios at 0.5, 1, and 2 h time points showed the following order: 68Ga-NOTA-MWK-Ex4 > 68Ga-NOTA-MFK-Ex4 > 68Ga-NOTA-MVK-Ex4. In this study, based on the enzymolysis clearance strategy and the preference of the enzyme, different sequences were designed and compared both in vitro and in vivo. The results indicated that the larger the steric hindrance of the second hydrophobic amino acid side chain, the more effective the enzymatic hydrolysis, with enzymolysis efficiency in the following order: MWK > MFK > MVK > MGK. MWK appears to be the most effective sequence in reducing renal radioactivity accumulation of exendin 4 peptide derivatives.

Serum neprilysin levels are elevated in preeclampsia

OBJECTIVE

To evaluate the possible associations between serum Neprilysin (NEP) levels and preeclampsia and mild and severe preeclampsia subgroups.

MATERIALS AND METHODS

Fifty-five consecutive women with mild preeclampsia and fifty-five consecutive women with severe preeclampsia were compared with 110 approximately gestational age-matched (±1 week) women with an uncomplicated pregnancy.

RESULTS

Mean serum NEP was significantly higher in women with preeclampsia compared to that of the gestational age-matched-controls (231.62 ± 65.30 pg/mL vs. 187.75 ± 84.38 pg/mL, p < 0.001). Mean serum NEP was significantly higher in the mild preeclampsia group compared to its gestational age-matched control group (228.84 ± 67.26 pg/mL vs. 186.14 ± 85.09 pg/mL, p = 0.008); and in the severe preeclampsia group compared to its gestational age-matched control group (234.45 ± 63.85 pg/mL vs. 189.29 ± 84.59 pg/mL, p = 0.004). Serum NEP was positively correlated with systolic and diastolic blood pressure, BUN, uric acid, and creatinine.

CONCLUSION

Mean serum NEP was significantly higher in women with preeclampsia than women with an uncomplicated pregnancy. Further studies are needed to elucidate the possible therapeutic role of NEP inhibitors to treat preeclampsia.

Sacubitril/Valsartan as a Therapeutic Tool Across the Range of Heart Failure Phenotypes and Ejection Fraction Spectrum

Heart failure (HF) is a complex syndrome caused by a variety of structural or functional cardiac abnormalities as a consequence of several involved pathophysiological pathways. In the last decades, left ventricular ejection fraction (LVEF) has represented the principal criterion used to stratify HF, to interpret ventricular function and to identify therapeutic strategies. However, this chimeric parameter oversimplifies the multiple pathways and mechanisms underlying the progression of HF. Indeed, HF should be more appropriately considered as the final stage of multiple disease states, characterized by distinct phenotypes on the basis of key clinical and molecular variables, such as underlying etiologies and conditions, demographic and structural features and specific biomarkers. Accordingly, HF should be viewed as a continuous spectrum in which the specific phenotypes need to be accurately identified with the aim to improve the disease management with a more tailored approach. In such a complex and heterogeneous scenario, the clinical benefits of an angiotensin receptor neprilysin inhibition strategy, namely in the single pill sacubitril/valsartan (S/V), have been shown across the entire HF continuum, representing a fundamental therapeutic strategy, although with different magnitudes depending on the severity and the stage of the clinical syndrome. In this viewpoint paper we have reconsidered the role of S/V in the light of different HF phenotypes and on the basis of HF considered as a whole spectrum.

Circulating heart failure biomarkers beyond natriuretic peptides: review from the Biomarker Study Group of the Heart Failure Association (HFA), European Society of Cardiology (ESC)

New biomarkers are being evaluated for their ability to advance the management of patients with heart failure. Despite a large pool of interesting candidate biomarkers, besides natriuretic peptides virtually none have succeeded in being applied into the clinical setting. In this review, we examine the most promising emerging candidates for clinical assessment and management of patients with heart failure. We discuss high-sensitivity cardiac troponins (Tn), procalcitonin, novel kidney markers, soluble suppression of tumorigenicity 2 (sST2), galectin-3, growth differentiation factor-15 (GDF-15), cluster of differentiation 146 (CD146), neprilysin, adrenomedullin (ADM), and also discuss proteomics and genetic-based risk scores. We focused on guidance and assistance with daily clinical care decision-making. For each biomarker, analytical considerations are discussed, as well as performance regarding diagnosis and prognosis. Furthermore, we discuss potential implementation in clinical algorithms and in ongoing clinical trials.

Angiotensin Receptor Blocker and Neprilysin Inhibitor Suppresses Cardiac Dysfunction by Accelerating Myocardial Angiogenesis in Apolipoprotein E-Knockout Mice Fed a High-Fat Diet

Materials and Methods

Male apolipoprotein E-knockout mice fed a high-fat diet were divided into control (CTL), valsartan (30 mg/kg) (VAL), sacubitril (30 mg/kg) (SAC), and valsartan plus sacubitril (30 mg/kg each) (VAL/SAC) groups after 4 weeks of prefeeding and were subsequently treated for 12 weeks.

Results

The VAL/SAC group exhibited significantly higher serum brain natriuretic peptide levels; more subtle changes in left ventricular systolic diameter, fractional shortening, and ejection fraction, and significantly higher expression levels of natriuretic peptide precursor B and markers of angiogenesis, including clusters of differentiation 34, vascular endothelial growth factor A, and monocyte chemotactic protein 1, than the CTL group.

Conclusions

Valsartan plus sacubitril preserved left ventricular systolic function in apolipoprotein E-knockout mice fed a high-fat diet. This result suggests that myocardial angiogenic factors induced by ARNI might provide cardioprotective effects.

Redox-Active Metal Ions and Amyloid-Degrading Enzymes in Alzheimer's Disease

Redox-active metal ions, Cu(I/II) and Fe(II/III), are essential biological molecules for the normal functioning of the brain, including oxidative metabolism, synaptic plasticity, myelination, and generation of neurotransmitters. Dyshomeostasis of these redox-active metal ions in the brain could cause Alzheimer’s disease (AD). Thus, regulating the levels of Cu(I/II) and Fe(II/III) is necessary for normal brain function. To control the amounts of metal ions in the brain and understand the involvement of Cu(I/II) and Fe(II/III) in the pathogenesis of AD, many chemical agents have been developed. In addition, since toxic aggregates of amyloid-β (Aβ) have been proposed as one of the major causes of the disease, the mechanism of clearing Aβ is also required to be investigated to reveal the etiology of AD clearly. Multiple metalloenzymes (e.g., neprilysin, insulin-degrading enzyme, and ADAM10) have been reported to have an important role in the degradation of Aβ in the brain. These amyloid degrading enzymes (ADE) could interact with redox-active metal ions and affect the pathogenesis of AD. In this review, we introduce and summarize the roles, distributions, and transportations of Cu(I/II) and Fe(II/III), along with previously invented chelators, and the structures and functions of ADE in the brain, as well as their interrelationships.

Proteo-Trancriptomic Analyses Reveal a Large Expansion of Metalloprotease-Like Proteins in Atypical Venom Vesicles of the Wasp Meteorus pulchricornis (Braconidae)

Meteorus pulchricornis (Ichneumonoidea, Braconidae) is an endoparasitoid wasp of lepidopteran caterpillars. Its parasitic success relies on vesicles (named M. pulchricornis Virus-Like Particles or MpVLPs) that are synthesized in the venom gland and injected into the parasitoid host along with the venom during oviposition. In order to define the content and understand the biogenesis of these atypical vesicles, we performed a transcriptome analysis of the venom gland and a proteomic analysis of the venom and purified MpVLPs. About half of the MpVLPs and soluble venom proteins identified were unknown and no similarity with any known viral sequence was found. However, MpVLPs contained a large number of proteins labelled as metalloproteinases while the most abundant protein family in the soluble venom was that of proteins containing the Domain of Unknown Function DUF-4803. The high number of these proteins identified suggests that a large expansion of these two protein families occurred in M. pulchricornis. Therefore, although the exact mechanism of MpVLPs formation remains to be elucidated, these vesicles appear to be “metalloproteinase bombs” that may have several physiological roles in the host including modifying the functions of its immune cells. The role of DUF4803 proteins, also present in the venom of other braconids, remains to be clarified.

Current and emerging drug targets in heart failure treatment

After initial strategies targeting inotropism and congestion, the neurohormonal interpretative model of heart failure (HF) pathophysiology has set the basis for current pharmacological management of HF, as most of guideline recommended drug classes, including beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and mineralocorticoid receptor antagonists, blunt the activation of detrimental neurohormonal axes, namely sympathetic and renin–angiotensin–aldosterone (RAAS) systems. More recently, sacubitril/valsartan, a first-in-class angiotensin receptor neprilysin inhibitor, combining inhibition of RAAS and potentiation of the counter-regulatory natriuretic peptide system, has been consistently demonstrated to reduce mortality and HF-related hospitalization. A number of novel pharmacological approaches have been tested during the latest years, leading to mixed results. Among them, drugs acting directly at a second messenger level, such as the soluble guanylate cyclase stimulator vericiguat, or other addressing myocardial energetics and mitochondrial function, such as elamipretide or omecamtiv-mecarbil, will likely change the therapeutic management of patients with HF. Sodium glucose cotransporter 2 inhibitors, initially designed for the management of type 2 diabetes mellitus, have been recently demonstrated to improve outcome in HF, although mechanisms of their action on cardiovascular system are yet to be elucidated. Most of these emerging approaches have shifted the therapeutic target from neurohormonal systems to the heart, by improving cardiac contractility, metabolism, fibrosis, inflammation, and remodeling. In the present paper, we review from a pathophysiological perspective current and novel therapeutic strategies in chronic HF.

A Contemporary View of Natriuretic Peptides in the SARS-CoV-2 Era

The heart releases natriuretic peptides (NPs) which represent an important hormonal axis with cardiorenal protective effects. In view of their properties, NPs have pathophysiologic, diagnostic and prognostic implications in several cardiovascular diseases (CVDs). Severe pulmonary inflammation, as induced by the SARS-COV2, may increase pulmonary pressure with potential influence on NPs release, whereby normal cardiovascular integrity becomes impaired. Moreover, pre-existing CVDs are strong negative prognostic factors since they exacerbate the effects of the viral infection and lead to worse outcomes. In this context, it may be expected that NPs exert a key protective role toward the virus infection whereas an impairment of NPs release contributes to the virus deleterious effects. In this review article we explore the potential involvement of NPs in the COVID-19 disease. To this aim, we will first focus on the interactions between NPs and the Ang II/ATIR arm of the renin-angiotensin-aldosterone system (RAAS) as well as with the protective ACE2/Ang (1-7) arm of the RAAS. Subsequently, we will review evidence that strongly supports the role of increased NT-proBNP level as a marker of cardiac damage and of worse prognosis in the COVID-19 affected patients. Finally, we will discuss the potential therapeutic benefits of these protective hormones toward the viral infection through their endothelial protective function, anti-inflammatory and anti-thrombotic effects. In conclusion, the potential implications of NPs in the SARS-CoV-2 infection, as discussed in our article, represent an important issue that deserves to be fully investigated.

Wide-Ranging Effects on the Brain Proteome in a Transgenic Mouse Model of Alzheimer's Disease Following Treatment with a Brain-Targeting Somatostatin Peptide

Alzheimer’s disease is the most common neurodegenerative disorder characterized by the pathological aggregation of amyloid-β (Aβ) peptide. A potential therapeutic intervention in Alzheimer’s disease is to enhance Aβ degradation by increasing the activity of Aβ-degrading enzymes, including neprilysin. The somatostatin (SST) peptide has been identified as an activator of neprilysin. Recently, we demonstrated the ability of a brain-penetrating SST peptide (SST-scFv8D3) to increase neprilysin activity and membrane-bound Aβ42 degradation in the hippocampus of mice overexpressing the Aβ-precursor protein with the Swedish mutation (APPswe). Using LC–MS, we further evaluated the anti-Alzheimer’s disease effects of SST-scFv8D3. Following a triple intravenous injection of SST-scFv8D3, the LC–MS analysis of the brain proteome revealed that the majority of downregulated proteins consisted of mitochondrial proteins regulating fatty acid oxidation, which are otherwise upregulated in APPswe mice compared to wild-type mice. Moreover, treatment with SST-scFv8D3 significantly increased hippocampal levels of synaptic proteins regulating cell membrane trafficking and neuronal development. Finally, hippocampal concentrations of growth-regulated α (KC/GRO) chemokine and degradation of neuropeptide-Y were elevated after SST-scFv8D3 treatment. In summary, our results demonstrate a multifaceted effect profile in regulating mitochondrial function and neurogenesis following treatment with SST-scFv8D3, further suggesting the development of Alzheimer’s disease therapies based on SST peptides.

Broadening COVID-19 Interventions to Drug Innovation: Neprilysin Pathway as a Friend, Foe, or Promising Molecular Target?

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus is anticipated to transition to an endemic state as vaccines are providing relief in some, but not all, countries. Drug discovery for COVID-19 can offer another tool in the fight against the pandemic. Additionally, COVID-19 impacts multiple organs that call for a systems medicine approach to planetary health and therapeutics innovation. In this context, innovation for drugs that prevent and treat COVID-19 is timely and much needed. As the virus variants emerge under different ecological conditions and contexts in the long haul, a broad array of vaccine and drug options will be necessary. This expert review article argues for a need to expand the COVID-19 interventions, including and beyond vaccines, to stimulate discovery and development of novel medicines against SARS-CoV-2 infection. The Renin-Angiotensin-Aldosterone System (RAAS) is known to play a major role in SARS-CoV-2 infection. Neprilysin (NEP) and angiotensin-converting enzyme (ACE) have emerged as the pharmaceutical targets of interest in the search for therapeutic interventions against COVID-19. While the NEP/ACE inhibitors offer promise for repurposing against COVID-19, they may display a multitude of effects in different organ systems, some beneficial, and others adverse, in modulating the inflammation responses in the course of COVID-19. This expert review offers an analysis and discussion to deepen our present understanding of the pathophysiological function of neprilysin in multiple organs, and the possible effects of NEP inhibitor-induced inflammatory responses in COVID-19-infected patients.

Circulating Neprilysin Level Predicts the Risk of Cardiovascular Events in Hemodialysis Patients

Background: Neprilysin inhibition has demonstrated impressive benefits in heart failure treatment, and is the current focus of interest in cardiovascular (CV) and kidney diseases. However, the role of circulating neprilysin as a biomarker for CV events is unclear in hemodialysis (HD) patients.

Methods: A total of 439 HD patients from the K-cohort were enrolled from June 2016 to April 2019. The plasma neprilysin level and echocardiographic findings at baseline were examined. The patients were prospectively followed up to assess the primary endpoint (composite of CV events and cardiac events).

Results: Plasma neprilysin level was positively correlated with left ventricular (LV) mass index, LV end-systolic volume, and LV end-diastolic volume. Multivariate linear regression analysis revealed that neprilysin level was negatively correlated with LV ejection fraction (β = −2.14; p = 0.013). The cumulative event rate of the composite of CV events was significantly greater in neprilysin tertile 3 (p = 0.049). Neprilysin tertile 3 was also associated with an increased cumulative event rate of cardiac events (p = 0.016). In Cox regression analysis, neprilysin tertile 3 was associated with a 2.61-fold risk for the composite of CV events [95% confidence interval (CI), 1.37–4.97] and a 2.72-fold risk for cardiac events (95% CI, 1.33–5.56) after adjustment for multiple variables.

Conclusions: Higher circulating neprilysin levels independently predicted the composite of CV events and cardiac events in HD patients. The results of this study suggest the importance of future studies on the effect of neprilysin inhibition in reducing CV events.

Therapeutic Assessment of Combination Therapy with a Neprilysin Inhibitor and Angiotensin Type 1 Receptor Antagonist on Angiotensin II-Induced Atherosclerosis, Abdominal Aortic Aneurysms, and Hypertension

Combined neprilysin (NEP) inhibition (sacubitril) and angiotensin type 1 receptor (AT1R) antagonism (valsartan) is used in the treatment of congestive heart failure and is gaining interest for other angiotensin II (AngII)-related cardiovascular diseases. In addition to heart failure, AngII promotes hypertension, atherosclerosis, and abdominal aortic aneurysms (AAAs). Similarly, NEP substrates or products have broad effects on the cardiovascular system. In this study, we examined NEP inhibition (with sacubitril) and AT1R antagonism (with valsartan) alone or in combination on AngII-induced hypertension, atherosclerosis, or AAAs in male low-density lipoprotein receptor-deficient mice. Preliminary studies assessed drug delivery via osmotic minipumps for simultaneous release of sacubitril and/or valsartan with AngII over 28 days. Mice were infused with AngII (1000 ng/kg per minute) in the absence (vehicle) or presence of sacubitril (1, 6, or 9 mg/kg per day), valsartan (0.3, 0.5, 1, 6, or 20 mg/kg per day), or the combination thereof (1 and 0.3, or 9 or 0.5 mg/kg per day of sacubitril and valsartan, respectively). Plasma AngII and renin concentrations increased 4-fold at higher valsartan doses, indicative of removal of AngII negative feedback on renin. Sacubitril doubled plasma AngII concentrations at lower doses (1 mg/kg per day). Valsartan dose-dependently decreased systolic blood pressure, aortic atherosclerosis, and AAAs of AngII-infused mice, whereas sacubitril had no effect on atherosclerosis or AAAs but reduced blood pressure of AngII-infused mice. Combination therapy with sacubitril and valsartan did not provide additive benefits. These results suggest limited effects of combination therapy with NEP inhibition and AT1R antagonism against AngII-induced hypertension, atherosclerosis, or AAAs. SIGNIFICANCE STATEMENT: The combination of valsartan (angiotensin type 1 receptor antagonist) and sacubitril (neprilysin inhibitor) did not provide benefit above valsartan alone on AngII-induced hypertension, atherosclerosis, or abdominal aortic aneurysms in low-density lipoprotein receptor-deficient male mice. These results do not support this drug combination in therapy of these AngII-induced cardiovascular diseases.

Neprilysin Inhibition Increases Glucagon Levels in Humans and Mice With Potential Effects on Amino Acid Metabolism

Context

Inhibitors of the protease neprilysin (NEP) are used for treating heart failure, but are also linked to improvements in metabolism. NEP may cleave proglucagon-derived peptides, including the glucose and amino acid (AA)-regulating hormone glucagon. Studies investigating NEP inhibition on glucagon metabolism are warranted.

Objective

This work aims to investigate whether NEP inhibition increases glucagon levels.

Methods

Plasma concentrations of glucagon and AAs were measured in eight healthy men during a mixed meal with and without a single dose of the NEP inhibitor/angiotensin II type 1 receptor antagonist, sacubitril/valsartan (194 mg/206 mg). Long-term effects of sacubitril/valsartan (8 weeks) were investigated in individuals with obesity (n = 7). Mass spectrometry was used to investigate NEP-induced glucagon degradation, and the derived glucagon fragments were tested pharmacologically in cells transfected with the glucagon receptor (GCGR). Genetic deletion or pharmacological inhibition of NEP with or without concomitant GCGR antagonism was tested in mice to evaluate effects on AA metabolism.

Results

In healthy men, a single dose of sacubitril/valsartan significantly increased postprandial concentrations of glucagon by 228%, concomitantly lowering concentrations of AAs including glucagonotropic AAs. Eight-week sacubitril/valsartan treatment increased fasting glucagon concentrations in individuals with obesity. NEP cleaved glucagon into 5 inactive fragments (in vitro). Pharmacological NEP inhibition protected both exogenous and endogenous glucagon in mice after an AA challenge, while NEP-deficient mice showed elevated fasting and AA-stimulated plasma concentrations of glucagon and urea compared to controls.

Conclusion

NEP cleaves glucagon, and inhibitors of NEP result in hyperglucagonemia and may increase postprandial AA catabolism without affecting glycemia.

Pregnancy-specific Reference Intervals for BNP and NT-pro BNP-Changes in Natriuretic Peptides Related to Pregnancy

Context

Cardiac disease is the leading cause of maternal mortality in the UK, so accurate cardiovascular diagnoses in pregnancy are essential. BNP (B-type natriuretic peptide) and NT-pro BNP (N-terminal-pro BNP) are useful clinical tools for investigating suspected peripartum cardiomyopathy but, as the pregnancy-specific reference intervals are undefined, it is uncertain how they should be interpreted in pregnant women.

Objectives

To define trimester-specific 95% reference intervals for BNP and NT-pro BNP in pregnancy.

Methods

Longitudinal study of 260 healthy pregnant women, with sampling in each trimester.

Results

The upper reference limit for NT-pro BNP was 200 pg/mL in the first and second trimesters, and 150 pg/mL in the third. Levels were significantly reduced in overweight women in the third trimester (P = .0001), which supports the partitioning of reference intervals by body mass index (BMI). The upper limit for BNP was 50 pg/mL, with no detectable trimester-related differences. Although other biomarkers (hemoglobin and platelets) fell throughout pregnancy, both natriuretic peptides were initially elevated before falling by the third trimester, suggesting that the observed changes in natriuretic peptides are driven by dynamic interplay between cardiac strain and progressive hemodilution. NT-pro BNP in the first trimester was inversely associated with neonatal birthweight at term (P = .011).

Conclusion

Cardiac biomarkers have an important role for investigating suspected disease in high-risk pregnant women, but a robust assessment of the levels expected in healthy pregnant women is an essential prerequisite to their application in clinical practice. This study has defined trimester- and BMI-specific reference intervals for NT-pro BNP and BNP, which may improve how women with suspected cardiovascular disease are investigated in pregnancy.

Circulating neprilysin hypothesis: A new opportunity for sacubitril/valsartan in patients with heart failure and preserved ejection fraction?

BACKGROUND

Circulating Neprilysin (sNEP) has emerged as a potential prognostic biomarker in heart failure (HF). In PARAGON-HF benefit of sacubitril/valsartan was only observed in patients with left ventricular ejection fraction (LVEF) ≤57%. We aimed to assess the prognostic value of sNEP in outpatients with HF and LVEF >57%, in comparison with patients with LVEF ≤57%.

METHODS

Consecutive HF outpatients were included from May-2006 to February-2016. The primary endpoint was the composite of all-cause death or HF hospitalization and the main secondary endpoint was the composite of cardiovascular death or HF hospitalization. For the later competing risk methods were used.

RESULTS

sNEP was measured in 1428 patients (age 67.7±12.7, 70.3% men, LVEF 35.8% ±14), 144 of which had a LVEF >57%. sNEP levels did not significantly differ between LVEF groups (p = 0.31). During a mean follow-up of 6±3.9 years, the primary endpoint occurred in 979 patients and the secondary composite endpoint in 714 (in 111 and 84 of the 144 patients with LVEF >57%, respectively). sNEP was significantly associated with both composite endpoints. Age- and sex- adjusted Cox regression analyses showed higher hazard ratios for sNEP in patients with LVEF >57%, both for the primary (HR 1.37 [1.16-1.61] vs. 1.04 [0.97-1.11]) and the secondary (HR 1.38 [1.21-1.55] vs. 1.11 [1.04-1.18]) composite endpoints.

CONCLUSIONS

sNEP prognostic value in patients with HF and LVEF >57% outperforms that observed in patients with lower LVEF. Precision medicine using sNEP may identify HF patients with preserved LVEF that may benefit from treatment with sacubitril/valsartan.

Effect of Neprilysin Inhibition on Left Ventricular Remodeling in Patients With Asymptomatic Left Ventricular Systolic Dysfunction Late After Myocardial Infarction

BACKGROUND

Patients with left ventricular (LV) systolic dysfunction after myocardial infarction are at a high risk of developing heart failure. The addition of neprilysin inhibition to renin angiotensin system inhibition may result in greater attenuation of adverse LV remodeling as a result of increased levels of substrates for neprilysin with vasodilatory, antihypertrophic, antifibrotic, and sympatholytic effects.

METHODS

We performed a prospective, multicenter, randomized, double-blind, active-comparator trial comparing sacubitril/valsartan 97/103 mg twice daily with valsartan 160 mg twice daily in patients ≥3 months after myocardial infarction with a LV ejection fraction ≤40% who were taking a renin angiotensin system inhibitor (equivalent dose of ramipril ≥2.5 mg twice daily) and a β-blocker unless contraindicated or intolerant. Patients in New York Heart Association class ≥II or with signs and symptoms of heart failure were excluded. The primary outcome was change from baseline to 52 weeks in LV end-systolic volume index measured using cardiac magnetic resonance imaging. Secondary outcomes included other magnetic resonance imaging measurements of LV remodeling, change in NT-proBNP (N-terminal pro-B-type natriuretic peptide) and high-sensitivity cardiac troponin I, and a patient global assessment of change questionnaire.

RESULTS

From July 2018 to June 2019, we randomized 93 patients with the following characteristics: mean age, 60.7±10.4 years; median time from myocardial infarction, 3.6 years (interquartile range, 1.2-7.2); mean LV ejection fraction, 36.8%±7.1%; and median NT-proBNP, 230 pg/mL (interquartile range, 124-404). Sacubitril/valsartan, compared with valsartan, did not significantly reduce LV end-systolic volume index; adjusted between-group difference, -1.9 mL/m² (95% CI, -4.9 to 1.0); P=0.19. There were no significant between-group differences in NT-proBNP, high-sensitivity cardiac troponin I, LV end-diastolic volume index, left atrial volume index, LV ejection fraction, LV mass index, or patient global assessment of change.

CONCLUSIONS

In patients with asymptomatic LV systolic dysfunction late after myocardial infarction, treatment with sacubitril/valsartan did not have a significant reverse remodeling effect compared with valsartan. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03552575.

Urinary neprilysin for early detection of acute kidney injury after cardiac surgery: A prospective observational study

BACKGROUND

Acute kidney injury (AKI) predicts adverse outcomes after cardiac surgery. The accuracy of using changes in serum creatinine for diagnosis and grading of AKI is limited in the peri-operative cardiac surgical setting and AKI may be underdiagnosed due to haemodilution from cardiopulmonary bypass priming and the need for intra-operative and postoperative volume resuscitation.

OBJECTIVES

To determine whether the urinary biomarker neprilysin can be used as a marker for the early detection of AKI after cardiac surgery.

DESIGN

Prospective, observational cohort study.

SETTING

Austrian tertiary referral centre.

PATIENTS

96 Patients undergoing elective cardiac surgery with cardiopulmonary bypass.

MAIN OUTCOME MEASURES

Differences and discriminatory power of neprilysin levels early after cardiac surgery and on postoperative day 1 between patients with or without AKI, as defined by the Kidney Disease Improving Global Outcomes Group.

RESULTS

AKI was found in 27% (n=26). The median neprilysin levels on postoperative day 1 were significantly higher in the AKI than in the non-AKI group, 4.0 [interquartile range (IQR): 2 to 6.25] vs. 2.0 ng ml [IQR: 1.0 to 4.5], P = 0.0246, respectively. In addition, the median neprilysin levels at the end of surgery were significantly different between both groups, 5.0 [IQR: 2.0 to 9.0] vs. 2.0 ng ml [IQR: 1.0 to 4.0], P = 0.0055, respectively. The discriminatory power of neprilysin for detecting early AKI corresponded to an area under the curve of 0.77 (95% confidence interval, 0.65 to 0.90).

CONCLUSION

Urinary neprilysin has potential as a biomarker for the early detection of AKI after cardiac surgery and has comparable discriminatory power to recently studied AKI biomarkers.

TRIAL REGISTRATION

The trial was registered at ClinicalTrials.gov (NCT03854825, https://clinicaltrials.gov/ct2/show/NCT03854825).

A Low-Sodium Diet Boosts Ang (1-7) Production and NO-cGMP Bioavailability to Reduce Edema and Enhance Survival in Experimental Heart Failure

Sodium restriction is often recommended in heart failure (HF) to block symptomatic edema, despite limited evidence for benefit. However, a low-sodium diet (LSD) activates the classical renin-angiotensin-aldosterone system (RAAS), which may adversely affect HF progression and mortality in patients with dilated cardiomyopathy (DCM). We performed a randomized, blinded pre-clinical trial to compare the effects of a normal (human-equivalent) sodium diet and a LSD on HF progression in a normotensive model of DCM in mice that has translational relevance to human HF. The LSD reduced HF progression by suppressing the development of pleural effusions (p < 0.01), blocking pathological increases in systemic extracellular water (p < 0.001) and prolonging median survival (15%, p < 0.01). The LSD activated the classical RAAS by increasing plasma renin activity, angiotensin II and aldosterone levels. However, the LSD also significantly up-elevated the counter-regulatory RAAS by boosting plasma angiotensin converting enzyme 2 (ACE2) and angiotensin (1-7) levels, promoting nitric oxide bioavailability and stimulating 3'-5'-cyclic guanosine monophosphate (cGMP) production. Plasma HF biomarkers associated with poor outcomes, such as B-type natriuretic peptide and neprilysin were decreased by a LSD. Cardiac systolic function, blood pressure and renal function were not affected. Although a LSD activates the classical RAAS system, we conclude that the LSD delayed HF progression and mortality in experimental DCM, in part through protective stimulation of the counter-regulatory RAAS to increase plasma ACE2 and angiotensin (1-7) levels, nitric oxide bioavailability and cGMP production.

Local Action of Neprilysin Exacerbates Pressure Overload Induced Cardiac Remodeling

[Figure: see text].

Angiotensin Receptor-Neprilysin Inhibitors and the Natriuretic Peptide Axis

PURPOSE OF THE REVIEW

The purpose of this review is to describe the effects of angiotensin receptor neprilysin inhibitor (ARNI) therapy on the natriuretic peptide axis (NPA), with a particular focus on B-type natriuretic peptide (BNP), atrial natriuretic peptide (ANP), and C-type natriuretic peptide (CNP) to better understand the biology behind the improved outcomes in patients with heart failure with reduced ejection fraction (HFrEF).

RECENT FINDINGS

BNP, ANP, and CNP are the three main natriuretic peptides (NP); they share a common structure and ultimately mediate their actions by activating cyclic guanosine monophosphate (cGMP). ARNI therapy results in a decrease of N-terminal pro-BNP (NT-proBNP) and increase of BNP levels respectively. It is been questioned whether these changes may result from unique laboratory assays characteristics rather than actual biological implications. It appears to be that the prognostic accuracy of BNP for cardiovascular outcomes remains independent and comparable to that of NT-proBNP while on ARNI therapy. ANP levels also increase with ARNI therapy, but no consistent change has been described for CNP levels. There is evidence that the changes in BNP and NT-proBNP correlate with improvement in echocardiographic parameters of volume and function. The dual effect of neprilysin inhibition and angiotensin receptor blockade has substantial implications on the natriuretic peptide axis (NPA). The changes seen in BNP and NT-proBNP specifically have shown to correlate with improvement in echocardiographic parameters. Further results exploring the biologic effects of ARNI therapy on other NPs are still pending and likely will provide further insights in the mechanisms behind the improvement in cardiac function and clinical outcomes.

Neprilysin inhibition does not alter dynamic of proenkephalin-A 119-159 and pro-substance P in heart failure

AIMS

As NEP degrades many substrates, the specific therapeutic mechanism of NEP inhibition with angiotensin receptor neprilysin inhibitor (ARNi) in heart failure with reduced ejection fraction (HFrEF) is not entirely evident. The aim of this study was to investigate the response of two substrates of NEP-the tachykinin and enkephalin systems-to the initiation of ARNi therapy in HFrEF.

METHODS AND RESULTS

Between 2016 and 2018, 141 consecutive patients with stable HFrEF [74 with initiation of ARNi and 67 controls on continuous angiotensin converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) therapy] were prospectively enrolled. Plasma proenkephalin-A 119-159 (PENK) and pro-substance P (pro-SP) were serially determined. Proenkephalin-A 119-159 and pro-SP correlated strongly with each other (r_s  = 0.67, P < 0.001) and kidney function (r_s  = -0.66, P < 0.001 and r_s  = -0.54, P < 0.001) and modestly with NT-proBNP (r_s  = 0.32, P < 0.001 and r_s  = 0.24, P = 0.006, respectively). Concentrations of circulating PENK were slightly elevated after 1 and 2 year follow-up compared with baseline (BL) [BL median: 67.4 pmol/L (IQR: 57.3-89.8), 1 year: 83.5 pmol/L (IQR: 62.4-111.6), 2 years: 92.3 pmol/L (IQR: 63.1-101.9); BL vs. 1 year: P = 0.017 and BL vs. 2 years: P = 0.019] in the overall analysis, but lost significance at 2 year follow-up when assessed in paired subanalysis (P = 0.116). Plasma pro-SP levels remained comparable during the entire follow-up [BL median: 78.3 pmol/L (IQR: 67.9-90.6), 1 year: 75.9 pmol/L (IQR: 58.6-96.3), 2 years: 79.7 pmol/L (IQR: 59.9-105.3); P = ns for both timepoints]. Biomarker patterns of ARNi patients were independent from baseline therapy, that is, ACEi or ARB (P > 0.05 between groups).

CONCLUSIONS

Although enkephalins and SP are known substrates of NEP, NEP inhibition by ARNi does not clearly affect the circulating precursors PENK and pro-SP in HFrEF.

The influence of sex and body mass index on the association between soluble neprilysin and risk of heart failure hospitalizations

A higher neprilysin activity has been suggested in women. In this retrospective analysis, we evaluated the association of sex and body mass index (BMI) with soluble neprilysin (sNEP) and recurrent admissions among 1021 consecutive HF outpatients. The primary and secondary endpoints were the number of HF hospitalizations and all-cause mortality, respectively. The association between sNEP with either endpoint was evaluated across sex and BMI categories (≥ 25 kg/m² vs. < 25 kg/m²). Bivariate count regression (Poisson) was used, and risk estimates were expressed as incidence rates ratio (IRR). During a median follow-up of 6.65 years (percentile 25%-percentile 75%:2.83–10.25), 702 (68.76%) patients died, and 406 (40%) had at least 1 HF hospitalization. Median values of sNEP and BMI were 0.64 ng/mL (0.39–1.22), and 26.9 kg/m² (24.3–30.4), respectively. Left ventricle ejection fraction was < 40% in 78.9% of patients, and 28% were women. In multivariable analysis, sNEP (main effect) was positively associated with HF hospitalizations (p = 0.001) but not with mortality (p = 0.241). The predictive value of sNEP for HF hospitalizations varied non-linearly across sex and BMI categories (p-value for interaction = 0.003), with significant and positive effect only on women with BMI ≥ 25 kg/m² (p = 0.039). For instance, compared to men, women with sNEP of 1.22 ng/mL (percentile 75%) showed a significantly increased risk (IRRs: 1.26; 95% CI: 1.05–1.53). The interaction analysis for mortality did not support a differential prognostic effect for sNEP (p = 0.072). In conclusion, higher sNEP levels in overweight women better predicted an increased risk of HF hospitalization.

RAAS Blockade and COVID-19: Mechanistic Modeling of Mas and AT1 Receptor Occupancy as Indicators of Pro-Inflammatory and Anti-Inflammatory Balance

ACE inhibitors (ACEis) and angiotensin receptor blockers (ARBs) are standard-of-care treatments for hypertension and diabetes, common comorbidities among hospitalized patients with coronavirus disease 2019 (COVID-19). Their use in the setting of COVID-19 has been heavily debated due to potential interactions with ACE2, an enzyme that links the pro-inflammatory and anti-inflammatory arms of the renin angiotensin system, but also the entryway by which severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) invades cells. ACE2 expression is altered by age, hypertension, diabetes, and the virus itself. This study integrated available information about the renin angiotensin aldosterone system (RAAS) and effects of SARS-CoV-2 and its comorbidities on ACE2 into a mechanistic mathematical model and aimed to quantitatively predict effects of ACEi/ARBs on the RAAS pro-inflammatory/anti-inflammatory balance. RAAS blockade prior to SARS-CoV-2 infection is predicted to increase the mas-AT1 receptor occupancy ratio up to 20-fold, indicating that in patients already taking an ACEi/ARB before infection, the anti-inflammatory arm is already elevated while the pro-inflammatory arm is suppressed. Predicted pro-inflammatory shifts in the mas-AT1 ratio due to ACE2 downregulation by SARS-CoV-2 were small relative to anti-inflammatory shifts induced by ACEi/ARB. Predicted effects of changes in ACE2 expression with comorbidities of diabetes, hypertension, or aging on mas-AT1 occupancy ratio were also relatively small. Last, predicted changes in the angiotensin (Ang(1-7)) production rate with ACEi/ARB therapy, comorbidities, or infection were all small relative to exogenous Ang(1-7) infusion rates shown experimentally to protect against acute lung injury, suggesting that any changes in the ACE2-Ang(1-7)-mas arm may not be large enough to play a major role in COVID-19 pathophysiology.

The Association between Neprilysin gene polymorphisms and Alzheimer's disease in Tibetan population

OBJECTIVES

Alzheimer's disease (AD) is a well-known neurodegenerative disease, of which the hallmark is the disposition of β-amyloid (Aβ) in the form of plaque in the brain. Neprilysin (NEP) is the major enzyme to degrade Aβ and prevent accumulation of Aβ. The present study was undertaken to elucidate the correlation between the NEP gene polymorphisms and AD in Chinese Tibetan population.

METHODS

Ninety-nine sporadic AD Tibetan patients and 113 healthy Tibetan controls were enrolled in this study. The genotype frequencies and allele frequencies of multiple NEP gene loci were analyzed using the case-control association analysis.

RESULTS

No significant correlation was found between polymorphisms of NEP gene loci (rs9829757, rs1816558, rs6776185, rs3736187, rs701109, rs989692) and the occurrence of AD in Tibetan population. However, allele C of NEP gene locus (rs701109) and allele T of gene locus (rs3736187) were possible risk factors of male AD patients in Tibetan population.

CONCLUSIONS

NEP gene loci (rs701109, rs989692, rs9829757, rs3736187, rs1816558, rs6776185) were polymorphic in Tibetan population. No difference was found between these loci but for that male gender combined with allele C of NEP gene locus (rs701109) and T of gene locus (rs3736187) might be risk factors for AD in Tibet.

The Drosophila melanogaster Neprilysin Nepl15 is involved in lipid and carbohydrate storage

The prototypical M13 peptidase, human Neprilysin, functions as a transmembrane "ectoenzyme" that cleaves neuropeptides that regulate e.g. glucose metabolism, and has been linked to type 2 diabetes. The M13 family has undergone a remarkable, and conserved, expansion in the Drosophila genus. Here, we describe the function of Drosophila melanogaster Neprilysin-like 15 (Nepl15). Nepl15 is likely to be a secreted protein, rather than a transmembrane protein. Nepl15 has changes in critical catalytic residues that are conserved across the Drosophila genus and likely renders the Nepl15 protein catalytically inactive. Nevertheless, a knockout of the Nepl15 gene reveals a reduction in triglyceride and glycogen storage, with the effects likely occurring during the larval feeding period. Conversely, flies overexpressing Nepl15 store more triglycerides and glycogen. Protein modeling suggests that Nepl15 is able to bind and sequester peptide targets of catalytically active Drosophila M13 family members, peptides that are conserved in humans and Drosophila, potentially providing a novel mechanism for regulating the activity of neuropeptides in the context of lipid and carbohydrate homeostasis.

CD10 (neprilysin) expression: a potential adjunct in the distinction of hibernoma from morphologic mimics

Although the morphologic diagnosis of hibernoma is usually straightforward, some hibernomas have atypical morphologic features, mimicking atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLs). In addition, the multivacuolated brown fat cells may be mistaken for lipoblasts by pathologists, especially those without significant soft tissue tumor exposure. Thus, we continue to receive in consultation cases of hibernoma sent for MDM2 fluorescence in situ hybridization testing to exclude ALT/WDL. Testing hibernomas for MDM2 amplification, however, adds cost and delays the final diagnosis. Recently, we have noted expression of neprilysin (CD10, CALLA), a zinc-dependent metalloproteinase involved in the inactivation of various peptide hormones, in brown fat cells, and wished to explore the potential utility of this widely available, inexpensive ancillary test in the differential diagnosis of hibernoma. Formalin-fixed, paraffin-embedded tissue sections from well-characterized cases of hibernoma (n = 48), brown fat (n = 21), ALTs/WDLs (n = 17), pleomorphic liposarcomas (PLPSs) (n = 6), lipomas (n = 5), and fat necrosis (n = 5) were immunostained for CD10, using a commercially available antibody and routine laboratory protocols. CD10 expression was evaluated in both adipocytes and in surrounding stromal cells. The hibernomas occurred in 28 men and 20 women, ranging from 11 to 76 years of age and involved the extremities (n = 25), pelvis (n = 7), abdomen/pelvis/retroperitoneum (n = 7), head and neck region (n = 6), back (n = 2), and chest (n = 1). All showed diffuse, strong CD10 expression in multivacuolated brown fat cells and in the majority of adjacent univacuolated fat cells. Brown adipose tissue from various anatomic structures showed an identical pattern of immunoreactivity. In contrast, CD10 expression was present in the adipocytes of only 3 of 17 (18%) ALTs/WDLs and was absent in lipomas and fat necrosis. Lipoblasts expressed CD10 in 3 PLPSs. Expression of CD10 by surrounding fibroblastic stromal cells was more widespread, present in 13 hibernomas, 10 ALTs/WDLs, 1 instance of fat necrosis, 6 PLPSs, and 4 examples of brown fat. We conclude that immunohistochemistry for CD10 may represent a useful, rapid and inexpensive ancillary test in the differential diagnosis of hibernoma from potential morphologic mimics, especially when morphologic features favor hibernoma. CD10 expression in adipocytes, however, should be rigorously distinguished from fibroblastic stromal cell CD10 expression, a nonspecific finding.

Structural analysis of Mycobacterium tuberculosis M13 metalloprotease Zmp1 open states

Zinc metalloprotease 1 (Zmp1), a Mycobacterium tuberculosis 75 kDa secreted enzyme, mediates key stages of tuberculosis disease progression. The biological activity of Zmp1 presumably stems from its ability to degrade bacterium- and/or host-derived peptides. The crystal structures of Zmp1 and related M13 metalloproteases, such as neprilysin and endothelin-converting enzyme-1 were determined only in the closed conformation, which cannot capture substrates or release proteolytic products. Thus, the mechanisms of substrate binding and selectivity remain elusive. Here we report two open-state cryo-EM structures of Zmp1, revealed by our SAXS analysis to be the dominant states in solution. Our structural analyses reveal how ligand binding induces a conformational switch in four linker regions to drive the rigid body motion of the D1 and D2 domains, which form the sizable catalytic chamber. Furthermore, they offer insights into the catalytic cycle and mechanism of substrate recognition of M13 metalloproteases for future therapeutic innovations.

Sacubitril/valsartan for the management of heart failure: A perspective viewpoint on current evidence

Current international guidelines recommend switching angiotensin converting enzyme inhibitors (ACE-i) or angiotensin receptor blockers (ARBs) to sacubitril/valsartan (S/V) in stable outpatients affected by heart failure with reduced ejection fraction (HFrEF) who remain symptomatic despite being on optimal medical therapy. Since these guidelines were published, new data may support further clinical applications and benefits of S/V beyond ambulatory HFrEF patients. The efficacy of S/V seems to be consistent across a wider array of subgroups including age, sex, etiology of HF, comorbidities, EF and estimated cardiovascular risk, with safety and tolerability profiles similar to ACE-I and ARBs. Additional clinical trial data are required to confirm the potential benefits of S/V in patients with mid-range or preserved EF, as suggested by analysis of PARAGON-HF, or in combination with sodium-glucose co-transporter 2 inhibitors or in post-myocardial infarction HF. In this article we summarize the new evidence on the effects and safety profile of S/V in HF and discuss current perspectives and persisting gaps. Currently, available evidence may support S/V as a first-line therapy in outpatient or in-hospital HFrEF patients, and possibly also in HFmrEF patients.

Neprilysin expression and functions in development, ageing and disease

Neprilysin (NEP) is an integral membrane-bound metallopeptidase with a wide spectrum of substrates and physiological functions. It plays an important role in proteolytic processes in the kidney, cardiovascular regulation, immune response, cell proliferation, foetal development etc. It is an important neuropeptidase and amyloid-degrading enzyme which makes NEP a therapeutic target in Alzheimer's disease (AD). Moreover, it plays a preventive role in development of cancer, obesity and type-2 diabetes. Recently a role of NEP in COVID-19 pathogenesis has also been suggested. Despite intensive research into NEP structure and functions in different organisms, changes in its expression and regulation during brain development and ageing, especially in age-related pathologies, is still not fully understood. This prevents development of pharmacological treatments from various diseases in which NEP is implicated although recently a dual-acting drug sacubitril-valsartan (LCZ696) combining a NEP inhibitor and angiotensin receptor blocker has been approved for treatment of heart failure. Also, various natural compounds capable of upregulating NEP expression, including green tea (EGCG), have been proposed as a preventive medicine in prostate cancer and AD. This review summarizes the existing literature and our own research on the expression and activity of NEP in normal brain development, ageing and under pathological conditions.

Tumour suppression through modulation of neprilysin signaling: A comprehensive review

Peptidases are emerging as promising drug targets in tumour suppression. Neprilysin, also known as neutral endopeptidase, is a cell surface peptidase that degrades various peptides such as angiotensin II, endothelin I, Substance P, etc., and reduces their local concentration. Neprilysin is expressed in various tissues such as kidney, prostate, lung, breast, brain, intestine, adrenal gland, etc. The tumour-suppressor mechanisms of neprilysin include its peptidase activity that degrades mitogenic growth factors such as fibroblast growth factor-2 and insulin-like growth factors, and the protein-protein interaction of neprilysin with phosphatase and tensin homolog, focal adhesion kinase, ezrin/radixin/moesin, and phosphoinositide 3-kinase. Studies have shown that the levels of neprilysin play an important role in malignancies. NEP is downregulated in prostate, renal, lung, breast, urothelial, cervical, hepatic cancers, etc. Histone deacetylation and hypermethylation of the neprilysin promoter region are the common mechanisms involved in the downregulation of neprilysin. Downregulation of the peptidase promotes angiogenesis, cell survival and cell migration. This review presents an overview of the role of neprilysin in malignancy, the tumour suppression mechanisms of neprilysin, the epigenetic mechanisms responsible for downregulation of neprilysin, and the potential pharmacological approaches to upregulate neprilysin levels and its activity.

Renal Denervation to Treat Heart Failure

Heart failure (HF) is a global pandemic with a poor prognosis after hospitalization. Despite HF syndrome complexities, evidence of significant sympathetic overactivity in the manifestation and progression of HF is universally accepted. Confirmation of this dogma is observed in guideline-directed use of neurohormonal pharmacotherapies as a standard of care in HF. Despite reductions in morbidity and mortality, a growing patient population is resistant to these medications, while off-target side effects lead to dismal patient adherence to lifelong drug regimens. Novel therapeutic strategies, devoid of these limitations, are necessary to attenuate the progression of HF pathophysiology while continuing to reduce morbidity and mortality. Renal denervation is an endovascular procedure, whereby the ablation of renal nerves results in reduced renal afferent and efferent sympathetic nerve activity in the kidney and globally. In this review, we discuss the current state of preclinical and clinical research related to renal sympathetic denervation to treat HF.

Neprilysin as a Biomarker: Challenges and Opportunities

Neprilysin (NEP) inhibition is a successful novel therapeutic approach in heart failure with reduced ejection fraction. Assessing individual NEP status might be important for gathering insights into mechanisms of disease and optimising individualised patient care. NEP is a zinc-dependent multisubstrate-metabolising oligoendopeptidase localised in the plasma membrane with the catalytic site facing the extracellular space. Although NEP activity in vivo is predominantly tissue-based, NEP can be released into the circulation via ectodomain shedding and exosomes. Attempts to determine circulating NEP concentrations and activity have not yet resulted in convincingly coherent results relating NEP biomarkers to heart failure disease severity or outcomes. NEP is naturally expressed on neutrophils, opening up the possibility of measuring a membrane-associated form with integrity. Small studies have linked NEP expression on neutrophils with inflammatory state and initial data might indicate its role in heart failure with reduced ejection fraction. Future studies need to assess the regulation of systemic NEP activity, which is assumed to be tissue-based, and the relationship of NEP activation with disease state. The relationship between tissue NEP activity and easily accessible circulating NEP biomarkers and the impact of the latter remains to be established.

BNP and NT-proBNP Interpretation in the Neprilysin Inhibitor Era

PURPOSE OF REVIEW

Describe the mechanisms that may influence change in measured natriuretic peptide levels when using the neprilysin inhibitor sacubitril to treat a patient with heart failure.

RECENT FINDINGS

Prior to the introduction of the neprilysin inhibitor sacubitril as part of a chemical combination with the angiotensin receptor blocker valsartan shown to reduce mortality and heart failure hospitalizations in patients with heart failure with reduced ejection fraction, the natriuretic peptide assays for B-type natriuretic peptide (BNP) and the amino-terminal proBNP (NT-proBNP) assays were shown to have similar diagnostic accuracy to differentiate heart failure from other etiologies of shortness of breath. Sacubitril/valsartan use has been shown to result in a modest and chronic elevation of BNP while reducing levels of NT-prBNP. This review explores the potential impact of these findings on interpreting natriuretic peptide results for diagnosis and prognosis, as well as explore the challenges associated with the heterogeneity of this finding, highlighting the impact of inhibiting neprilysin, a non-specific endopeptidase with multiple target sites within BNP and other proteins. With increased uptake of sacubitril/valsartan expected in patients with heart failure, interpretation of natriuretic peptide assays becomes somewhat more complex, particularly for BNP. However, knowing a baseline steady-state concentration and using the same assay can assist with BNP interpretation for diagnosis and prognosis.

Repurposing of existing FDA approved drugs for Neprilysin inhibition: An in-silico study

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Drug repurposing of FDA approved drugs from ZINC 12 database was done using the crystal structure of extracellular domain of human NEP (PDB ID: 5JMY)

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The interactions with catalytic triad of HIS583, HIS587 and GLU646 are important for NEP inhibition.

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Based on XP molecular docking, binding energy, IFD-SP and MD simulation top 4 NEP inhibitors were identified.

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ZINC000000601283 and ZINC000003831594 were found to be stable during MD simulation and may act as NEP inhibitors.

Neprilysin (NEP) is a neutral endopeptidase with diverse physiological roles in the body. NEP's role in degradation of diverse classes of peptides such as amyloid beta, natriuretic peptide, substance P, angiotensin, endothelins, etc., is associated with pathologies of alzheimer's, kidney and heart diseases, obesity, diabetes and certain malignancies. Hence, the functional inhibition of NEP in the above systems can be a good therapeutic target. In the present study, in-silico drug repurposing approach was used to identify NEP inhibitors. Molecular docking was carried out using GLIDE tool. 2934 drugs from the ZINC12 database were screened using high throughput virtual screening (HTVS) followed by standard precision (SP) and extra precision (XP) docking. Based on the XP docking score and ligand interaction, the top 8 hits were subjected to free ligand binding energy calculation, to filter out 4 hits (ZINC000000001427, ZINC000001533877, ZINC000000601283, and ZINC000003831594). Further, induced fit docking-standard precision (IFD-SP) and molecular dynamics (MD) studies were performed. The results obtained from MD studies suggest that ZINC000000601283-NEP and ZINC000003831594-NEP complexes were most stable for 20ns simulation period as compared to ZINC000001533877-NEP and ZINC000000001427-NEP complexes. Interestingly, ZINC000000601283 and ZINC000003831594 showed similarity in binding with the reported NEP inhibitor sacubitrilat. Findings from this study suggest that ZINC000000601283 and ZINC000003831594 may act as NEP inhibitors. In future studies, the role of ZINC000000601283 and ZINC000003831594 in NEP inhibition should be tested in biological systems to evaluate therapeutic effect in NEP associated pathological conditions.

Soluble neprilysin and long-term clinical outcomes in patients with coronary artery disease undergoing percutaneous coronary intervention: a retrospective cohort study

Background

Neprilysin has an essential role in regulating fluid balance and vascular resistance, and neprilysin inhibitors have shown beneficial effects in patients with heart failure. However, the potential predictive value of neprilysin levels as a biomarker for cardiovascular risk remains unclear. The aim of this study was to assess the prognostic value of soluble neprilysin (sNEP) levels in patients with ischemic heart disease.

Methods

Neprilysin levels were measured in 694 consecutive patients with coronary artery disease (CAD) undergoing percutaneous coronary intervention (PCI). These patients were classified into two groups according to their serum levels of neprilysin and categorized into the lower neprilysin group (n = 348) and the higher neprilysin group (n = 346). The primary clinical endpoint was all-cause mortality, and the secondary endpoint was a composite of major adverse cardiac events (MACE).

Results

The median sNEP level was 76.0 pg/ml. The median sNEP levels were higher in patients with left ventricular ejection fraction (LVEF) ≥40% (77.6 pg/ml, interquartile range 46.6–141.3) than in those with LVEF < 40% (70.0 pg/ml, interquartile range 47.1–100.6; P = 0.032). Among all patients, each clinical outcome and MACE did not differ significantly according to the groups divided into median, tertile, or quartile of sNEP levels during a median follow-up of 28.4 months. We did not find a significant relationship between sNEP levels and clinical outcomes in multivariate Cox regression analysis. Among patients with LVEF < 40%, an increased sNEP level was associated with a higher rate of all-cause death (adjusted hazard ratio 2.630, 95% confidence interval 1.049–6.595, P = 0.039).

Conclusion

Serum sNEP levels are not associated with long-term mortality or cardiovascular outcomes after PCI in patients with CAD. In the LVEF < 40% group, increased sNEP levels may be associated with a higher risk of all-cause death.

Cardiovascular Outcomes with Sacubitril-Valsartan in Heart Failure: Emerging Clinical Data

One of the defining features of heart failure (HF) is neurohormonal activation. The renin-angiotensin-aldosterone-system (RAAS) and sympathetic nervous system (SNS) cause vasoconstriction and fluid retention and, in response, the secretion of natriuretic peptides (NPs) from volume and pressure-overloaded myocardium promotes vasodilation and diuresis. Inhibition of the RAAS with either angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blockers (ARB) has been the cornerstone of medical treatment for HF with a reduced ejection fraction (HFrEF) but, until recently, it was unclear how the beneficial effects of NPs may be augmented in patients with HF. Neprilysin, a metalloproteinase widely distributed throughout the body, plays a role in degrading the gross excess of circulating NPs in patients with HF. Early studies of neprilysin inhibition suggested possible physiological benefits. In 2014, the PARADIGM-HF trial found that sacubitril-valsartan, a combination of the ARB valsartan, and the neprilysin inhibitor sacubitril, was superior to enalapril in patients with HFrEF, reducing the relative risk of cardiovascular (CV) death or first hospitalisation with HF by 20%. Almost half of the patients with HF symptoms have a “preserved” ejection fraction (HFpEF); however, the PARAGON-HF study found that sacubitril-valsartan in patients with LVEF ≥45% had no effect on CV death or first and recurrent hospitalisations with HF compared to valsartan. Guidelines across the world have changed to include sacubitril-valsartan for patients with HFrEF yet, nearly 6 years after PARADIGM-HF, there is still uncertainty as to when and in whom sacubitril-valsartan should be started. Furthermore, there may yet be subsets of patients with HFpEF who might benefit from treatment with sacubitril-valsartan. This review will describe the mechanisms behind the outcome benefit of sacubitril-valsartan in patients with HFrEF and to consider its future role in the management of patients with HF.

Heart Failure With Reduced Ejection Fraction Is Characterized by Systemic NEP Downregulation

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The kidneys might play a crucial role in regulating systemic NEP actions based on 20 to 100 higher NEP content and activity of the kidneys compared with any other organ.

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Tissue NEP expression seems to be downregulated and translates into reduced tissue protein concentrations and activity in HF.

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Neither plasma or liquor NEP concentrations and activities reflect tissue NEP regulation; therefore, using NEP as a circulating biomarker seems to be questionable.

Based on the investigation of neprilysin (NEP) regulation in a translational porcine model of chronic heart failure (HF), this study concluded: 1) that kidneys might play a crucial part in systemic NEP regulation based on 20 to 100 higher NEP content and/or activity compared with any other organ; 2) NEP seems to be downregulated under HF conditions; and 3) that the value of plasma NEP concentrations and activity as biomarkers is questionable. For the first time, these data provide basic knowledge on HF-related pathophysiological alterations of the NEP system and contribute to understanding the mechanism of action of angiotensin-receptor neprilysin-inhibitors, which remains elusive despite broad clinical applications.

Increased concentrations of bioactive adrenomedullin subsequently to angiotensin-receptor/neprilysin-inhibitor treatment in chronic systolic heart failure

AIMS

The clinically investigated rationale for neprilysin (NEP)-inhibition by angiotensinreceptor-NEPinhibitor (ARNi) therapy is to induce elevations in endogenous natriuretic peptides. NEP, however, cleaves a broad spectrum of substrates, which partially hold significant implications in heart failure with reduced ejection fraction (HFrEF). The effect of NEP inhibition on these peptides has not been investigated thoroughly. This study explored the response of adrenomedullin (ADM) regulation to the initiation of ARNi.

METHODS

Seventy-four patients with stable HFrEF and initiation of ARNi were prospectively enrolled, 67 patients on continuous angiotensin-converting-enzyme inhibitor(ACEi)/angiotensin-receptor blocker (ARB) therapy served as control. Plasma bioactive-ADM (bio-ADM), mid-regional-pro-ADM (MR-proADM), B-typenatriuretic peptide (BNP) and N-terminal-pro-BNP (NT-proBNP) were determined at baseline, short-term, 1-year and 2-year follow up.

RESULTS

Following ARNi initiation both bio-ADM and MR-proADM concentrations were significantly increased at early and long-term follow up (bio-ADM [pg/mL]: 26.0 [interquartile range {IQR}: 17.7-37.5] vs. 50.8 [IQR: 36.5-78.1] vs. 54.6 [IQR: 42.0-97.1] vs. 57.4 [IQR: 48.5-161.6]; MR-proADM [nmol/L]: 0.87 [IQR: 0.64-1.12] vs. 1.25 [IQR: 0.93-1.79] vs. 1.42 [IQR: 0.95-1.90] vs. 1.60 [IQR: 1.12-2.46], P < .0001 for all). The ratios bio-ADM/MR-proADM and BNP/NT-proBNP increased during ARNi-therapy proving improved availability of bioactive peptides. The proportional increase of bio-ADM markedly exceeded BNP increase. Patients converted to ARNi showed similar biomarker patterns irrespective of baseline renin-angiotensin system blocker therapy, i.e. ACEi or ARB (P > .05 for all), indicating that activation of the ADM-axis arises particularly from NEPinhibition.

CONCLUSION

The significant increase of MR-proADM and bio-ADM together with an elevated bioADM/MR-proADM ratio suggest both enhanced formation and reduced breakdown of bioactive ADM following the initiation of ARNi. Activation of the ADM-axis represents a so far unrecognized effect of ARNi.