LL-37 is the only human cathelicidin antimicrobial peptide — a 37-amino-acid cationic host-defense peptide derived from hCAP18. Its plasma half-life is on the order of minutes due to rapid serine protease cleavage. All mechanistic and PK data are from in-vitro and animal studies.
Yes — naturally produced in neutrophils, epithelial cells, NK cells
Endogenous
FDA Approval
Not Approved
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WADA / Anti-Doping Status
Not prohibited; detection difficult (endogenous baseline)
WADA 2026 list
Data Quality
In-vitro and animal studies only — no published human PK; endogenous baseline complicates exogenous detection
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Important: LL-37 is an endogenous human peptide. Baseline plasma and tissue levels vary considerably between individuals and are influenced by infection, inflammation, vitamin D status, and site of measurement. Any assessment of "exogenous" LL-37 must account for this natural variability.
Mechanism of Action
LL-37 exerts effects through at least two distinct, concentration-dependent mechanisms.
Antimicrobial Membrane Disruption
At its C-terminus, LL-37 adopts an amphipathic alpha-helical conformation that electrostatically targets the anionic phospholipids (phosphatidylglycerol, lipopolysaccharide) of bacterial membranes. This causes membrane permeabilization and bacteriolysis. At concentrations above approximately 10 µg/mL in vitro, the same mechanism disrupts host cell membranes, causing cytotoxicity — a key limitation for therapeutic development.
Immunomodulation via Pattern Recognition Receptors
At sub-antimicrobial concentrations, LL-37 acts as a pleiotropic immunomodulator. It binds TLR4 and can antagonize LPS-induced signaling, reducing pro-inflammatory cytokine output (TNF-α, IL-6). Via FPRL1 (formyl peptide receptor-like 1), it induces neutrophil and monocyte chemotaxis. Via P2X7, it can trigger IL-1β release. It also activates the EGFR pathway, promoting epithelial migration and wound closure.
Anti-Biofilm Activity
LL-37 disrupts established bacterial biofilms at concentrations well below its minimum inhibitory concentration (MIC) for planktonic bacteria. This is attributed to interference with the c-di-GMP signaling cascade that maintains biofilm architecture. This property is particularly studied in the context of chronic wound and lung infections (Pseudomonas aeruginosa in cystic fibrosis).
PK/PD Dissociation: Like all short peptides, LL-37's plasma half-life (minutes) does not predict its biological effect duration. Local concentrations at epithelial surfaces, inflammatory exudate, or injection sites may be sustained longer than plasma measurements suggest. However, no human data quantify this effect duration.
Clearance Timeline (Illustrative — No Human Data)
Data Limitation: The following table is illustrative only. No formal human pharmacokinetic study for exogenous LL-37 has been published. Plasma half-life is extrapolated from in-vitro proteolysis data. Individual variation due to protease activity levels, inflammation state, and endogenous baseline is unknown.
Time After Administration
Estimated Remaining (%)
Notes
T = 0
100%
Dose administered
T = 1 half-life (~mins)
~50%
Rapid proteolytic cleavage begins immediately
T = 2 half-lives (~mins)
~25%
Cleavage by cathepsin G, elastase, proteinase 3
T = 5 half-lives (~mins)
~3%
Plasma level effectively undetectable
T = 30–60 min
Unknown — endogenous baseline
Signal indistinguishable from endogenous LL-37 at this point
Route of Administration
Route
Bioavailability
Notes
Topical (skin/wound)
Local activity, no systemic absorption documented
Most studied route; wound-healing applications
Intranasal
Local mucosal activity; limited systemic PK data
Explored for respiratory tract infections (preclinical)
Intravenous (IV)
No published data
Rapid systemic proteolysis expected; cytotoxicity risk at effective concentrations
Subcutaneous (SC)
No published data
Local depot possible but no human PK characterized
Oral
Not viable
Degraded by gastric and intestinal proteases; no GI transporter (unlike KPV)
Inhalation
Local airway activity documented (preclinical)
Cystic fibrosis / P. aeruginosa biofilm research context
Detection Window
Detecting exogenous LL-37 administration presents unique analytical challenges not encountered with synthetic research peptides:
Matrix
Detection Window
Challenge
Plasma
Minutes (if detectable above baseline)
Endogenous LL-37 baseline: ~0.2–5 µg/mL in healthy adults; exogenous signal rapidly lost to proteolysis
Urine
No data
Rapid degradation fragments are not specific to exogenous administration
Tissue / local site
Unknown
Local concentration may differ from plasma; no validated assay for exogenous vs endogenous
Anti-Doping Note: No sports anti-doping organization has established a validated test for exogenous LL-37 administration as of May 2026. The endogenous nature of the peptide, its rapid clearance, and the lack of a synthetic-specific biomarker make detection methodologically unresolved.
LL-37's plasma half-life is on the order of minutes due to rapid proteolytic cleavage by serine proteases — including cathepsin G, neutrophil elastase, and proteinase 3 — present in plasma and at inflammatory sites. No formal human pharmacokinetic study has been published as of May 2026. This means the exact half-life in humans remains uncharacterized.
Plasma clearance is very rapid (minutes). However, LL-37 may exert local effects at sites of administration — particularly topical wound beds or mucosal surfaces — for longer than plasma data would suggest, because local protease inhibitors (like SLPI) partially protect it from degradation. The biological activity duration in humans is not systematically quantified.
Yes — LL-37 is the only cathelicidin produced in humans, naturally expressed in neutrophils, monocytes, NK cells, mast cells, and epithelial cells. Healthy adults have baseline plasma LL-37 levels of approximately 0.2–5 µg/mL, with levels rising sharply during infection or inflammation. This endogenous baseline complicates both detection of exogenous administration and interpretation of any clinical signal, since it is difficult to attribute observed changes to exogenous peptide vs. natural fluctuation.
No. LL-37 is not FDA approved for any indication. It is a research-stage compound studied in in-vitro models and animal systems. As of May 2026, no Phase 3 clinical trials have been completed and no NDA or BLA has been filed. It should not be confused with approved antimicrobial therapies.
In preclinical models: (1) broad-spectrum antimicrobial activity against bacteria, fungi, and enveloped viruses via membrane disruption; (2) immunomodulation — reduces LPS-driven inflammation via TLR4 antagonism at low concentrations; (3) chemotaxis — recruits neutrophils and monocytes via FPRL1; (4) wound healing — promotes epithelial migration and angiogenesis via EGFR; (5) anti-biofilm — disrupts Pseudomonas biofilm architecture. All evidence is from in-vitro and animal models.
No validated anti-doping test for exogenous LL-37 exists as of May 2026. The combination of factors makes detection technically challenging: (1) rapid plasma half-life means the intact peptide is gone within minutes; (2) proteolytic fragments are not distinguishable from endogenous degradation products; (3) naturally variable baseline levels mean no "abnormal" threshold is established; (4) WADA has not included LL-37 on the prohibited list. This does not mean it is safe or approved — only that testing is unresolved.
At high concentrations — typically above ~10 µg/mL in in-vitro assays — LL-37's membrane-disrupting mechanism is non-selective and damages host cell membranes as well as pathogen membranes. This manifests as hemolysis of red blood cells and cytotoxicity to epithelial cells. The therapeutic window between antimicrobially effective concentrations and host-toxic concentrations is narrow, and this narrow window is a primary obstacle to systemic therapeutic development. This threshold has not been determined in humans.
Several key distinctions: (1) Origin — LL-37 is endogenous to humans; BPC-157 and TB-500 are synthetic analogs of non-human or partial sequences; (2) Primary activity — LL-37's primary characterized role is antimicrobial/immunomodulatory; BPC-157 and TB-500 are primarily studied for tissue repair; (3) Detection — LL-37 baseline variability makes exogenous detection harder; (4) Evidence base — all three lack approved human data, but LL-37 has the most extensive in-vitro mechanistic literature given its endogenous biology.
Primary References
Vandamme D, Landuyt B, Luyten W, Schoofs L. "A comprehensive summary of LL-37, the factotum human cathelicidin peptide." Cell Immunol. 2012;280(1):22–35. PMID: 22677462
Mookherjee N, Anderson MA, Haagsman HP, Davidson DJ. "Antimicrobial host defence peptides: functions and clinical potential." Nat Rev Drug Discov. 2020;19(5):311–332. PMID: 32107480
Pfalzgraff A, Brandenburg K, Weindl G. "Antimicrobial peptides and their therapeutic potential for bacterial skin infections and wounds." Front Pharmacol. 2018;9:281. PMID: 29643807
Dean SN, Bishop BM, van Hoek ML. "Susceptibility of Pseudomonas aeruginosa biofilm to alpha-helical peptides: D-enantiomer of LL-37." Front Microbiol. 2011;2:128. PMID: 21747787
Halflife Labs Editorial Team
Reviewed by researchers with backgrounds in pharmacology and peptide biochemistry. All claims are citation-backed; no sponsored content. Last reviewed: 2026-05-19 · View methodology
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