How to Store LL-37: Stability and Handling, Per the Research

LL-37 is one of the most heavily studied human antimicrobial peptides, but very little of that literature is dedicated stability testing. That distinction matters for anyone reading about storage. Most of what circulates as "LL-37 storage guidance" is general lyophilized-peptide chemistry that applies to short synthetic peptides as a class. This page describes what LL-37 studies actually reported, and separately labels the parts that are general peptide-handling science. This page is for educational purposes only and is not medical advice; consult a licensed physician about any health decision.

What LL-37 is, according to the published literature

LL-37 is the 37-residue cathelicidin-derived human host defence peptide. A 2025 study in Frontiers in Cellular and Infection Microbiology described it as a vitamin D-inducible antimicrobial peptide and reported that it bound the SARS-CoV-2 spike protein and the accessory proteins ORF7a and ORF8 (PMID 41064641). A 2025 review in ACS Biomaterials Science & Engineering surveyed LL-37 derivatives, covering recent developments and the challenges facing the class as antimicrobial candidates (PMID 40423576). Because LL-37 is cationic and amphipathic, its measured behaviour in experiments depends heavily on the buffer, surface and temperature conditions used — which is why handling is a recurring methodological theme even in papers that are not about storage.

Compound-specific stability data versus general peptide science

This is the central honesty point of the page, so it comes first rather than last.

What LL-37 papers do describe

• Formulation into a protective carrier. A 2024 Antiviral Research study constructed exosome-loaded LL-37 and reported protection against Zika virus infection in its test systems (PMID 38460762). Carrier work of this kind is formulation science, not shelf-life testing, but it reflects the broader interest in presenting LL-37 in a form that survives a biological environment.
• Immobilisation onto a solid surface. Researchers modified polyetherketoneketone with LL-37 and reported enhanced antibacterial ability and bioactivity for the modified material in a 2022 Langmuir study (PMID 35380840).
• Behaviour in defined lipid systems. A 2024 Molecules paper presented a thermodynamic study of biomimetic Legionella gormanii bacterial membranes, characterising peptide interactions with model membrane films under controlled physical conditions (PMID 39339363).
• Production and characterisation workflows. A 2018 Molecules paper reported the expression, purification and characterisation of a novel hybrid peptide with potent antibacterial activity (PMID 29925795), illustrating that purity and characterisation are established upstream of any use of a peptide preparation.
• Design of more robust mimetics. A 2017 European Journal of Medicinal Chemistry study described pyrazole-derived ultra-short antimicrobial peptidomimetics with potent anti-biofilm activity (PMID 27718471), part of a wider medicinal-chemistry effort to replace long natural peptide sequences with smaller, more tractable molecules.

What the LL-37 literature in this citation set does not describe

None of the papers cited here reported a shelf-life study for LL-37: there is no accelerated-degradation dataset, no stated number of months at a given temperature, and no freeze–thaw cycle count in the verified literature used on this page. Anything stating a precise expiry figure for LL-37 is therefore drawing on supplier documentation or on general peptide chemistry, not on a published LL-37 stability trial. The sections below are labelled accordingly.

Refrigeration: lyophilized powder versus reconstituted solution

General peptide-handling science — not an LL-37-specific study finding. Peptide chemistry draws a sharp line between a freeze-dried (lyophilized) solid and a peptide dissolved in liquid. In the solid state, water activity is low, so the hydrolysis, oxidation and aggregation pathways that degrade peptides proceed far more slowly. Once a peptide is in solution, those pathways accelerate, and additional routes open up: adsorption of peptide onto container walls, pH drift, microbial growth in unpreserved water, and — for cationic, membrane-active peptides — association with any lipid or surfactant present.

Documentation supplied with research-use-only peptide materials commonly distinguishes a colder long-term condition for sealed lyophilized powder from a short-term refrigerated condition for solutions in use. Those conventions are laboratory practice and supplier labelling rather than findings from the LL-37 papers cited on this page.

Shelf life and expiry dating

General peptide-handling science. For research chemicals, an "expiry" or "retest" date on a label is typically a manufacturer's assignment based on its own internal testing or on class-level assumptions, not a regulatory stability filing of the kind required for an approved drug product. LL-37 itself is not an approved drug product; the studies gathered here are laboratory and clinical-science investigations, such as the 2020 study that measured salivary and serum cathelicidin LL-37 levels in subjects with rheumatoid arthritis and chronic periodontitis (PMID 32743970). Biological measurement of an endogenous peptide in human samples is a different activity from stability-testing a manufactured preparation, and the two literatures should not be merged.

In practice, analytical purity data (such as HPLC and mass-spectrometry characterisation of the kind reported alongside peptide production work in PMID 29925795) tell a laboratory more about a specific lot than a printed date does, because purity is measured on the material in hand.

Room temperature and travel

General peptide-handling science. The physical logic of transport is straightforward: degradation chemistry is temperature-dependent, so warm excursions consume stability budget, and repeated or prolonged excursions consume more of it. Sealed lyophilized powders are generally regarded in peptide chemistry as more tolerant of brief ambient exposure than aqueous solutions, which is why freeze-dried formats are the shipping form of choice for most synthetic peptides. Humidity is the second variable: a hygroscopic freeze-dried cake that absorbs moisture is no longer a dry solid, and the protective effect of low water activity is lost.

The LL-37 literature does not provide travel-specific stability data. What it does show is that experimental outcomes are condition-sensitive — the thermodynamic membrane study cited above worked at controlled temperature and surface pressure precisely because peptide–lipid behaviour changes with those variables (PMID 39339363).

Freezing and freeze–thaw cycles

General peptide-handling science. Freezing is used to slow molecular motion and suppress degradation chemistry, but the transition itself is a stress. Ice formation concentrates solutes in the remaining liquid phase, can shift local pH as buffer components crystallise at different rates, and creates ice–water interfaces at which peptides can unfold or aggregate. That is why repeated freeze–thaw cycling is generally treated in laboratory practice as more damaging than a single freeze, and why aliquoting is a standard laboratory convention: it converts many cycles on one vial into one cycle on many vials.

No freeze–thaw cycle count for LL-37 appears in the verified papers used here. Readers encountering a specific number should ask which dataset it came from.

Signs of degradation

General peptide-handling science. Visual and physical observations described across lyophilized-product handling include:

• Cake collapse, shrinkage, melting or a powder that has turned gummy or sticky — consistent with moisture ingress or a temperature excursion.
• Discolouration of a normally white-to-off-white solid.
• Cloudiness, haze, visible particulates, fibres or a precipitate in a solution that was previously clear — often associated with aggregation.
• Solid that will not fully dissolve, or a solution that gels.
• Loss of vacuum in a stoppered vial, or a compromised seal.

These are appearance-level observations, not assays. Analytical methods — chromatographic purity, mass confirmation and functional testing — are what the literature actually uses to establish that a preparation is what it claims to be, as in the characterisation work reported in PMID 29925795.

Surfaces, carriers and adsorption

Cationic peptides interact with the surfaces they touch, which is a handling issue as well as a biology issue. Researchers exploited exactly that property when they modified polyetherketoneketone with LL-37 and reported enhanced antibacterial ability and bioactivity for the resulting material (PMID 35380840). Deliberate immobilisation and unintended adsorption to a container wall are the same underlying chemistry pointed in different directions. Carrier strategies address a related problem: the 2024 exosome-loading study reported that LL-37 delivered in exosomes protected against Zika virus infection in its models (PMID 38460762), and the 2025 derivative review discussed how design changes have been pursued to address the practical limitations of the native sequence (PMID 40423576).

LL-37 Activity in Laboratory Systems: What Studies Report

Storage exists to preserve activity, so it is worth noting what activity the literature attributes to this peptide — and that LL-37 is not inert. A 2022 Biomedicines study reported that the host defence peptides LL-37 and lactoferrin triggered extracellular trap release from blood-derived circulating monocytes (PMID 35203676). A 2022 Journal of Immunology study reported that human cathelicidin peptide LL-37 induced cell death in autophagy-dysfunctional endothelial cells (PMID 35387840). A 2025 Communications Biology study reported that LAPTM5 exacerbated STING-mediated inflammation induced by LL-37 in a rosacea model by stabilising STING (PMID 41087666). Human-sample work also appears in this space: a 2024 Blood Advances study examined neutrophil functions in patients with neutropenia due to glycogen storage disease type 1b treated with empagliflozin (PMID 38531056). These are laboratory and clinical observations reported by researchers, not statements about any human use of a stored preparation.

How to read storage claims critically

1. Ask whether a number is compound-specific. A temperature or month figure quoted for LL-37 without a citation is almost certainly class-level peptide convention or supplier labelling.
2. Separate formulation studies from stability studies. Exosome loading (PMID 38460762) answers a delivery question, not a shelf-life question.
3. Treat appearance as a screen, not a test. Degradation can occur without any visible change.
4. Note the research-use context. LL-37 preparations sold for laboratory research are not approved drug products, and their labelling is not equivalent to pharmaceutical stability documentation.

Related reading

• LL-37: what the research covers
• How peptides are stored: general stability science

References

• Exploring the Antimicrobial Potential of LL-37 Derivatives: Recent Developments and Challenges (ACS Biomaterials Science & Engineering, 2025)
• LAPTM5 exacerbates STING-mediated inflammation induced by LL-37 through stabilizing STING in rosacea (Communications Biology, 2025)
• Vitamin D-inducible antimicrobial peptide LL-37 binds SARS-CoV-2 Spike and accessory proteins ORF7a and ORF8 (Frontiers in Cellular and Infection Microbiology, 2025)
• Construction of exosome-loaded LL-37 and its protection against zika virus infection (Antiviral Research, 2024)
• Thermodynamic Study on Biomimetic Legionella gormanii Bacterial Membranes (Molecules, 2024)
• Neutrophil functions in patients with neutropenia due to glycogen storage disease type 1b treated with empagliflozin (Blood Advances, 2024)
• Host Defense Peptides LL-37 and Lactoferrin Trigger ET Release from Blood-Derived Circulating Monocytes (Biomedicines, 2022)
• Human Cathelicidin Peptide LL-37 Induces Cell Death in Autophagy-Dysfunctional Endothelial Cells (Journal of Immunology, 2022)
• Enhanced Antibacterial Ability and Bioactivity of Polyetherketoneketone Modified with LL-37 (Langmuir, 2022)
• Salivary and serum cathelicidin LL-37 levels in subjects with rheumatoid arthritis and chronic periodontitis (International Journal of Rheumatic Diseases, 2020)
• Expression, Purification, and Characterization of a Novel Hybrid Peptide with Potent Antibacterial Activity (Molecules, 2018)
• Pyrazole derived ultra-short antimicrobial peptidomimetics with potent anti-biofilm activity (European Journal of Medicinal Chemistry, 2017)