Neprilysin is a zinc-dependent enzyme embedded in cell membranes throughout the body, where it chops up small signaling peptides once they have done their job. It has over 50 known or suspected peptide targets, ranging from hormones that regulate blood pressure to the amyloid-beta fragments linked to Alzheimer’s disease.1PubMed. A Test in Context: Neprilysin: Function, Inhibition, and Biomarker That breadth of action is what makes neprilysin so medically interesting and so tricky to manipulate: blocking it to help the heart may, in theory, affect the brain, and vice versa.
How Neprilysin Works
Neprilysin belongs to a large family of metalloproteinases that rely on a zinc atom at their active site to slice peptide bonds. The zinc is held in place by specific amino acid residues, and when a peptide substrate enters the enzyme’s binding groove, the zinc activates a water molecule that breaks the peptide apart.2Scientific Reports. Structure of neprilysin in complex with the active metabolite of sacubitril The enzyme preferentially cuts next to hydrophobic amino acids, which is part of what gives it such a wide substrate range.3PubMed Central. Bioinformatic analysis of the neprilysin (M13) family of peptidases reveals complex evolutionary and functional relationships Rather than recognizing one specific peptide like a lock and key, neprilysin has a relatively open binding pocket that accommodates many different small peptides. It acts as an endopeptidase, meaning it cuts internal bonds within a peptide chain rather than trimming residues off the ends.
This promiscuity is both its defining feature and the reason drug designers have to think carefully about consequences. The same enzyme that degrades natriuretic peptides in the heart also breaks down enkephalins in the nervous system and amyloid-beta in the brain.4PubMed. A Test in Context: Neprilysin: Function, Inhibition, and Biomarker You cannot inhibit neprilysin in one organ and leave it alone everywhere else, at least not with current drugs.
Where It Shows Up in the Body
Neprilysin is an integral membrane protein, meaning it sits anchored in the outer surface of cells with its catalytic domain facing outward, ready to intercept peptides in the surrounding fluid. It plays roles in the kidney, cardiovascular system, immune response, and fetal development, among other systems.5PubMed Central. Neprilysin expression and functions in development, ageing and disease The highest concentrations are found in the kidney and lung, but substantial amounts also turn up in the brain, intestine, and immune cells.6PubMed. Tissue-specific expression of rat neutral endopeptidase (neprilysin) mRNAs
In the kidney, neprilysin is concentrated on the brush border of proximal tubule cells, the surface facing into the tubule lumen where it can intercept filtered peptides before they travel further down the nephron. Studies in kidney-derived cell lines show that the enzyme is delivered directly to this apical surface rather than first appearing elsewhere on the cell and being redirected, which underscores how tightly its placement is controlled. In the brain, different cell types express different versions of the enzyme’s messenger RNA. Neurons in the cortex express one transcript variant, while the insulating cells of white matter tracts express another, suggesting that the enzyme’s regulation is fine-tuned depending on the tissue and cell type.7PubMed. Tissue-specific expression of rat neutral endopeptidase (neprilysin) mRNAs
The Heart Failure Connection
The reason most people encounter the word “neprilysin” today is heart failure treatment. The heart produces natriuretic peptides in response to stretching and pressure overload. These peptides tell blood vessels to relax and instruct the kidneys to excrete more sodium and water, which lowers blood volume and eases the heart’s workload. Neprilysin is one of the key enzymes that breaks down natriuretic peptides, effectively putting a time limit on their protective effects.8PubMed Central. Roles of Natriuretic Peptides and the Significance of Neprilysin in Cardiovascular Diseases In heart failure, the body needs those natriuretic peptides to stick around longer. Block the enzyme, and the peptides accumulate, delivering a sustained blood-pressure-lowering, fluid-unloading effect.
This idea is the basis for sacubitril/valsartan, the drug combination sold under the brand name Entresto. Sacubitril is a prodrug: the body converts it into an active molecule called LBQ657, which binds tightly inside neprilysin’s active site and blocks it. Crystal structures show that LBQ657 coordinates with the catalytic zinc and fits snugly into multiple sub-pockets of the enzyme, producing a highly potent and reversible inhibition.9PubMed Central. Structure of neprilysin in complex with the active metabolite of sacubitril Valsartan, the other half of the pill, blocks the angiotensin II receptor, so the drug attacks heart failure from two directions: boosting protective natriuretic peptides while also blocking a hormone pathway that raises blood pressure and promotes fluid retention.
The landmark trial that proved the combination worked, called PARADIGM-HF, enrolled patients with heart failure and reduced pumping ability. Compared with enalapril, a standard treatment, sacubitril/valsartan cut the combined risk of cardiovascular death or hospitalization for heart failure by about 20%, with a consistent benefit regardless of what other medications patients were taking.10PubMed. Effects of Sacubitril/Valsartan in the PARADIGM-HF Trial According to Background Therapy Subsequent analyses pooling data across the full range of heart-pumping ability found a similar pattern: roughly a 16% reduction in cardiovascular death and a 16% reduction in heart failure hospitalization.11PubMed. Sacubitril/Valsartan Across the Spectrum of Ejection Fraction in Heart Failure When tested in patients hospitalized for acute decompensated heart failure, sacubitril/valsartan lowered NT-proBNP, a blood marker of cardiac stress, by roughly 47% compared with about 25% for enalapril, with the difference visible as early as one week into treatment.12PubMed. Angiotensin-Neprilysin Inhibition in Acute Decompensated Heart Failure
Neprilysin and Amyloid-Beta in the Brain
Before the heart failure drug era, neprilysin was already on researchers’ radar because of Alzheimer’s disease. Amyloid-beta, the small peptide that accumulates into plaques in Alzheimer’s brains, is one of neprilysin’s natural substrates. In the brain, neprilysin is transported along axons to presynaptic terminals, where it can degrade amyloid-beta right at the sites most vulnerable to plaque formation. Animal experiments using gene therapy to boost neprilysin levels in the hippocampus showed that the enzyme could abolish the rise in amyloid-beta seen in neprilysin-deficient mice and significantly slow plaque development in mice engineered to overproduce amyloid precursor protein.13Journal of Neuroscience. Presynaptic Localization of Neprilysin Contributes to Efficient Clearance of Amyloid-β Peptide in Mouse Brain
The problem is that neprilysin levels in the brain drop with age. Studies of human brain tissue have found that neprilysin protein levels decline in the temporal and frontal cortex as people get older, in both healthy individuals and those with Alzheimer’s. The decline correlates inversely with insoluble amyloid-beta levels, meaning lower neprilysin tracks with higher amyloid deposits.14PubMed. Age-dependent decline of neprilysin in Alzheimer’s disease and normal brain: inverse correlation with A beta levels In Alzheimer’s patients specifically, neprilysin is reduced compared to age-matched controls, and a greater proportion of the remaining enzyme shows signs of oxidative damage, which could impair its activity further.15PubMed. Oxidized neprilysin in aging and Alzheimer’s disease brains One experimental approach has been to attach neprilysin to a “brain shuttle” molecule that helps it cross the blood-brain barrier. In animal studies, this shuttle-delivered neprilysin reduced amyloid-beta levels in both brain tissue and cerebrospinal fluid in a dose-dependent manner.16PLOS ONE. Brain Shuttle Neprilysin reduces central Amyloid-β levels
Does Blocking Neprilysin for Heart Failure Hurt the Brain?
This is the question that has dogged sacubitril/valsartan since its approval. If neprilysin helps clear amyloid-beta in the brain, and the drug inhibits neprilysin systemically, could long-term use accelerate Alzheimer’s pathology? The concern is reasonable on paper, but the clinical evidence so far has been reassuring. A 2024 review of clinical trials, real-world studies, and pharmacovigilance databases found no signal of increased cognitive decline in patients treated with sacubitril/valsartan.17PubMed Central. Association between treatment with sacubitril/valsartan and the risk of Alzheimer’s disease: a clinical update
There is a nuance, though. Blood-based amyloid biomarkers do show perturbations in patients on the drug, meaning the levels of amyloid fragments detectable in blood tests shift in ways that could look like increased amyloid burden if you were screening for Alzheimer’s using those tests. But brain imaging studies have not shown a corresponding increase in actual amyloid load.18PubMed Central. Association between treatment with sacubitril/valsartan and the risk of Alzheimer’s disease: a clinical update The practical takeaway for clinicians is that blood-based amyloid biomarkers need to be interpreted with caution in anyone taking sacubitril/valsartan, because the drug itself can shift the numbers independent of any actual brain pathology. There is also the possibility that sacubitril/valsartan does not penetrate the blood-brain barrier well enough to substantially inhibit neprilysin in the brain, but this remains an area of active investigation.
Pain and Enkephalins
Neprilysin is one of two main enzymes that break down enkephalins, the body’s own opioid-like pain-relief molecules. The other is aminopeptidase N. Together, these two enzymes keep enkephalin levels low by degrading them rapidly after release. Blocking both enzymes simultaneously, using compounds called dual enkephalinase inhibitors, allows enkephalins to linger longer at opioid receptors and produce stronger natural pain relief.19PubMed. Inhibiting the breakdown of endogenous opioids and cannabinoids to alleviate pain
This approach is attractive because it works with the body’s own opioid system rather than flooding it with an external drug. The analgesic effects have been demonstrated in animal models of both inflammatory and neuropathic pain. Because the strategy amplifies only the enkephalins the body is already producing at the site of injury or inflammation, rather than activating every opioid receptor system-wide, the hope is that dual enkephalinase inhibitors could provide pain relief with fewer side effects than synthetic opioids such as morphine or fentanyl.20PubMed. Dual Enkephalinase Inhibitors and Their Role in Chronic Pain Management Some researchers have also proposed that these compounds could help manage opioid withdrawal by supporting endogenous opioid tone during the acute withdrawal period.21PubMed. The inhibition of enkephalin catabolism by dual enkephalinase inhibitor: A novel possible therapeutic approach for opioid use disorders Several dual enkephalinase inhibitors have entered early-stage clinical trials, though none has yet reached routine clinical use.
CD10 and Cancer Diagnosis
Neprilysin has a second identity in cancer biology: it is the same protein as the cell-surface marker CD10, originally discovered as the “common acute lymphoblastic leukemia antigen” (CALLA). Before anyone knew it was an enzyme, CD10 was identified as a molecule that appeared on the surface of leukemia cells, and it became a standard tool for classifying blood cancers.22PubMed Central. Role of B Cell Development Marker CD10 in Cancer Progression and Prognosis CD10 is present on blast cells in roughly 94% of B-lineage acute lymphoblastic leukemia cases and about 40% of T-cell cases.23PubMed. Clinical significance of CD10 expression in childhood acute lymphoblastic leukemia
Beyond blood cancers, CD10 expression has been studied in solid tumors. In skin pathology, researchers found that the connective tissue surrounding squamous cell carcinomas consistently expressed CD10, while benign skin lesions and precancerous patches did not. This stromal CD10 expression correlated with markers of cell proliferation and immune cell changes in the tumor environment, suggesting it may reflect the tumor’s invasive behavior rather than being a passive bystander.24PubMed. Stromal CD10 expression, as well as increased dermal macrophages and decreased Langerhans cells, are associated with malignant transformation of keratinocytes Whether neprilysin’s enzymatic activity contributes to tumor behavior or whether it is simply a useful surface marker for pathologists varies by cancer type and remains an active area of research.
Blood Sugar and Metabolic Effects
One of neprilysin’s less publicized substrates is GLP-1 (glucagon-like peptide-1), the gut hormone that helps regulate blood sugar after meals. GLP-1 stimulates insulin release and is already the target of blockbuster diabetes and weight-loss drugs. Neprilysin contributes to GLP-1 breakdown, and in animal studies, mice lacking the neprilysin gene showed improved blood sugar control when fed a high-fat diet, with higher active GLP-1 levels and better beta cell function in the pancreas.25PubMed Central. Improved glycaemia in high-fat-fed neprilysin-deficient mice is associated with reduced DPP-4 activity and increased active GLP-1 levels
Neprilysin also appears to increase the activity of DPP-4, the enzyme that existing diabetes drugs (the “gliptin” class) already target. This creates an intriguing overlap: neprilysin inhibition may boost GLP-1 both directly, by preventing neprilysin from degrading it, and indirectly, by reducing DPP-4 activity.26PubMed Central. Effects of neprilysin and neprilysin inhibitors on glucose homeostasis: Controversial points and a promising arena Some clinical observations in heart failure patients treated with sacubitril/valsartan have hinted at improved glycemic control, but the metabolic effects of neprilysin inhibition in humans are still being sorted out, and the evidence is not yet strong enough to position neprilysin inhibitors as diabetes treatments.
Measuring Neprilysin in the Blood
Soluble fragments of neprilysin circulate in the bloodstream, and there has been interest in using them as biomarkers for heart failure severity or drug response. This turns out to be more complicated than it sounds. Different immunoassays measure different parts of the neprilysin molecule, and they can give contradictory results. In one study comparing four neprilysin assays in heart failure patients, one assay showed that neprilysin levels were lower in heart failure compared to healthy controls, while three other assays showed that levels were higher.27Clinical Chemistry. Plasma Neprilysin in Heart Failure: Response Dynamics and Clinical Associations Are Immunoassay Dependent All four assays agreed that neprilysin levels did not differ between heart failure with reduced pumping and heart failure with preserved pumping. The disagreement between assays likely reflects the fact that neprilysin gets cleaved into multiple circulating fragments, and each assay recognizes a different fragment. Until the field standardizes which form of neprilysin to measure and how, plasma neprilysin is unlikely to become a routine clinical test.
Neprilysin Across Species
Neprilysin is not unique to humans. The enzyme family is remarkably well conserved across the animal kingdom, which is one reason model organisms have been so useful for studying it. The fruit fly genome contains 24 genes belonging to the same metalloprotease family, some of which are direct counterparts of human neprilysin. In flies, these enzymes turn out to be required for normal reproduction, paralleling findings in mammals where neprilysin has roles in reproductive biology.28PubMed Central. Neprilysins: an evolutionarily conserved family of metalloproteases that play important roles in reproduction in Drosophila The roundworm genome also carries a full complement of neprilysin-like genes, giving researchers two convenient model systems to probe the enzyme’s functions using genetic tools that are difficult to apply in mammals.29BioEssays. The neprilysin family of zinc metalloendopeptidases: Genomics and function
The deep evolutionary conservation suggests that neprilysin’s core function, degrading small signaling peptides to regulate their duration and intensity, was established early in animal evolution and proved too useful to discard. It also means that findings in model organisms, while not directly translatable to human medicine, can reveal fundamental aspects of how this enzyme interacts with its many substrates and how its loss or overactivity disrupts normal physiology.
Epigenetic Regulation and Tissue-Specific Silencing
Given how important neprilysin is, the question of what controls its levels in different tissues has practical implications. In certain diseases, neprilysin fails to increase its expression even when its substrates are accumulating. One example comes from chronic pancreatitis, where neprilysin should help break down substance P, an inflammatory peptide. In diseased pancreatic tissue, neprilysin expression did not increase to match the inflammatory load, and this failure was linked to overexpression of a small regulatory RNA molecule called miR-128a rather than to mutations in the neprilysin gene itself or chemical silencing of its promoter region.30European Surgical Research. Substance P and Neprilysin in Chronic Pancreatitis This finding hints that neprilysin levels may be controlled post-transcriptionally in ways that could, in principle, be therapeutically targeted: lower the regulatory brake and the enzyme might ramp itself up without any need for gene therapy or drug infusion. Whether this approach could work in the brain to slow amyloid-beta accumulation, or in the heart to modulate natriuretic peptide turnover, remains speculative but scientifically interesting.