Elafin

Elafin is the mature 57-residue product of the trappin-2 precursor, expressed at epithelial surfaces in skin, lung and gut. Its primary function is to restrain neutrophil elastase and proteinase 3, serine proteases that neutrophils release to kill pathogens but which also digest elastin, collagen and endothelial barriers in the process. Beyond protease inhibition it has direct anti-inflammatory activity through NF-kB inhibition and modest antimicrobial activity. As a drug candidate, under the name tiprelestat, it has been given intravenously to reduce inflammatory complications after cardiac and oesophageal surgery and in hospitalised COVID-19, and it is being explored in pulmonary arterial hypertension. This is a hospital-setting biologic, not a peptide anyone is running at home.

Targets: Neutrophil elastase, Proteinase 3, NF-kB signalling, Epithelial and endothelial barrier integrity

• · A randomised placebo-controlled trial in coronary artery bypass surgery used a single 200 mg intravenous dose of elafin. Hospital setting only.
• · The COMCOVID randomised trial gave 100 mg tiprelestat intravenously twice daily for seven days in hospitalised COVID-19 patients.

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• uncommonInfusion-related reaction
• uncommonTransient blood pressure change during infusion
• uncommonImmunogenicity / anti-drug antibodies— An inherent consideration with any recombinant protein given repeatedly.

• Not applicable outside a supervised clinical setting - this compound is not available to or appropriate for self-administration.

• redundantNeutrophil elastase inhibitors such as alvelestat or sivelestat — Same enzymatic target by a different route.

• · Trials tracked neutrophil elastase activity, IL-6, IL-8 and organ-specific endpoints; all of this is done in hospital.

Investigational; not approved in any jurisdiction and not sold on the research-peptide market.

• COMCOVID randomised double-blind placebo-controlled trial of tiprelestat in hospitalised COVID-19, Advances in Therapy 2025 (trial)
• Randomised placebo-controlled trial of intravenous elafin 200 mg in coronary artery bypass graft surgery (trial)
• Sallenave, secretory leukocyte protease inhibitor and elafin in host defence (review) (review)

Neutrophils kill pathogens partly by releasing serine proteases - elastase and proteinase 3 - into the extracellular space. Those enzymes do not discriminate. They digest elastin, collagen, surfactant proteins and endothelial junction proteins alongside whatever they were aimed at, and that collateral digestion is a substantial part of the tissue damage in acute inflammation, ischaemia-reperfusion injury and ARDS. Elafin is the body's local brake on that process, expressed at epithelial surfaces in skin, lung and gut. It inhibits neutrophil elastase and proteinase 3 in an essentially irreversible fashion through a canonical inhibitor mechanism, presenting a reactive site loop that the protease attacks and cannot release. There is a second, non-enzymatic arm: elafin inhibits NF-kB signalling directly, reducing pro-inflammatory transcription independently of protease inhibition. It also has modest broad-spectrum antimicrobial activity, consistent with its position as an epithelial defence molecule. The structural detail that matters for delivery is the transglutaminase anchoring. The full-length trappin-2 precursor carries a cementoin domain that gets cross-linked into extracellular matrix, which localises the inhibitor to the tissue that needs it. Recombinant mature elafin given intravenously does not do that, which is part of why systemic dosing has produced clean biomarker effects and murky clinical ones. And that is exactly the trial pattern. In the coronary bypass study, elafin reached high plasma concentrations and reduced elastase activity as designed, and the troponin release curve did not significantly change. In COMCOVID the biology behaved and the trial was too small to say anything about outcomes. This is a drug that reliably does what its mechanism says and has not yet demonstrated that doing so changes what happens to patients.

The honest answer is that what goes wrong with elafin is a development story rather than a user story. Nobody is running this at home. What went wrong clinically is instructive though. In the cardiac surgery trial the drug did exactly what it was designed to do - reached high plasma concentrations, reduced elastase activity - and the patients' troponin release was not significantly different. That gap between pharmacodynamic success and clinical failure is the most common way a mechanistically elegant drug dies, and it is worth internalising when reading about any compound in this class whose case rests on mechanism. In COMCOVID the failure was operational. A trial powered for 296 patients enrolled 17 because the pandemic receded. The results are reported honestly and mean very little about efficacy. The compound-specific risks that would matter if it ever reached the market are the standard biologic ones: infusion reactions, transient blood pressure change during infusion, and immunogenicity with repeated dosing. And one theoretical concern worth stating: neutrophil elastase exists because it kills pathogens. Inhibiting it during an active infection is a trade-off, not a free win, and the COVID-19 setting was precisely where that trade-off was being tested.

• Neutrophil elastase (ELANE) — Tight-binding, essentially irreversible canonical serine protease inhibition; association constants in the high-affinity range

  Blocks degradation of elastin, collagen, surfactant protein and endothelial junction proteins - the collateral damage arm of neutrophil activation.

• Proteinase 3 (PRTN3) — Comparable tight-binding inhibition

  The second major neutrophil serine protease, and notably also the autoantigen in granulomatosis with polyangiitis.

• NF-kB signalling — Not a protease interaction; direct inhibition of the pathway

  Reduced pro-inflammatory cytokine transcription independent of protease inhibition. Explains part of the IL-6 and IL-8 effects seen in trials.

• Epithelial and endothelial barrier integrity — Downstream consequence of protease inhibition

  Preservation of junctional proteins that elastase would otherwise digest - the mechanistic basis for the gut, lung and vascular protection claims.

• Bacterial membranes — Modest broad-spectrum antimicrobial activity

  A minor arm compared with the protease inhibition, but consistent with its role as an epithelial host-defence molecule.

• Perioperative elafin for ischaemia-reperfusion injury during coronary artery bypass graft surgery Randomised, double-blind, placebo-controlled · n=87 · 1 weeks · 2015

  87 patients randomised 1:1 to a single 200 mg intravenous dose of elafin or placebo after induction of anaesthesia. Elafin achieved high plasma concentrations and reduced elastase activity but did not significantly reduce the primary endpoint of cardiac troponin I release over 48 hours (ratio 0.74, p=0.18). No effect on MRI-detected infarction or inflammatory markers overall; a post-hoc signal of lower troponin at 6 hours. The authors concluded there was no strong evidence of benefit.

• COMCOVID: tiprelestat for treatment of hospitalised COVID-19 Randomised, double-blind, placebo-controlled · n=17 · 4 weeks · 2025

  Multicentre trial across seven German sites giving 100 mg tiprelestat or placebo intravenously twice daily for up to seven days, with follow-up to day 29. Only 17 patients were enrolled (9 active, 8 placebo) against a planned 296, because recruitment collapsed as the pandemic waned. No severe COVID-19 progression in the treatment group and less oxygen support (2.4 versus 4.0 days), but the sample size makes efficacy conclusions impossible. Safety and tolerability were the meaningful outputs.

Hours: biomarker effects appear within hours of infusion - reduced elastase activity, reduced IL-6. This is a fast-acting drug at the pharmacodynamic level. Days: the clinical windows the trials assessed - 48 hours for troponin in cardiac surgery, seven days of dosing with follow-up to day 29 in COMCOVID. There is no cycling and no long-term protocol. Elafin is used as a defined short course timed to an acute inflammatory insult, which is a completely different usage model from everything else in this class.

There is no consumer stacking conversation to have, because elafin is not available outside clinical trials and is not sold on the research-peptide market in any meaningful way. The only pharmacologically relevant combination is with other neutrophil elastase inhibitors - alvelestat, sivelestat - which hit the same enzyme by a small-molecule route. That is redundancy rather than synergy. Worth knowing conceptually: alpha-1 antitrypsin is the body's main systemic elastase inhibitor and is available as an approved augmentation therapy for alpha-1 antitrypsin deficiency. If you are thinking about elastase inhibition as a therapeutic idea, that is the approved version of it.

Against everything else in this class: elafin is what a peptide looks like when it is developed properly. Randomised, double-blind, placebo-controlled trials with prespecified primary endpoints, published including the negative result. That is the standard the rest of this shelf is being measured against, and almost none of it comes close. Against alpha-1 antitrypsin augmentation: alpha-1 antitrypsin is the approved elastase inhibitor, used for a genetic deficiency. Elafin's proposition was a targeted epithelial inhibitor for acute settings rather than chronic replacement. Against small-molecule elastase inhibitors such as sivelestat, approved in Japan for ARDS, and alvelestat in development: same enzyme, different modality, and none of them have produced a decisive clinical result either. That pattern suggests the problem may be the hypothesis rather than the molecule. Against KPV or any other NF-kB modulator here: elafin also inhibits NF-kB, but it does so as a secondary mechanism alongside a highly specific enzymatic action, and it has been tested in randomised trials. KPV has mouse models.

Not applicable. Elafin is an investigational recombinant protein administered in hospital settings and is not commercially available or sold on the research-peptide market.

• ?No published human pharmacokinetic parameters - no volume of distribution, clearance figure, protein binding or subcutaneous bioavailability.
• ?The molecular weight is not stated in the Core record and was not independently confirmed in this session; the mature chain is 57 residues.
• ?A phase 1 subcutaneous safety study is referenced in the development literature but its details were not resolved in this session.
• ?COMCOVID enrolled 17 of a planned 296 patients, so its apparent benefits on oxygen support duration are not interpretable.
• ?The pulmonary arterial hypertension development work was not verified in this session.
• ?Whether inhibiting neutrophil elastase during active infection carries a net risk has not been resolved by any trial.

• Perioperative elafin for ischaemia-reperfusion injury during coronary artery bypass graft surgery: a randomised controlled trial Alam SR et al., Heart, 2015 · PMID 26310261

  The cleanest test of elafin's clinical hypothesis. Target engagement confirmed, clinical endpoint unchanged - a useful reminder that a working mechanism is not a working drug.

• Tiprelestat for treatment of hospitalized COVID-19: results of the double-blind randomized placebo-controlled COMCOVID trial Bergs I et al., Advances in Therapy, 2025 · PMID 40956387

  The most recent clinical data, and an honest example of a trial that recruited 17 of a planned 296 patients and reported anyway.