LL-37 Reconstitution Calculator

No. LL-37 is the only human cathelicidin, an endogenous host-defense peptide; it has no FDA or EMA approval for any indication. Clinical translation remains stalled by proteolytic degradation, concentration-dependent cytotoxicity, rapid clearance, and high production cost. All therapeutic efficacy data are preclinical (in-vitro and animal). Use in humans is off-label or research-grade; legal status and compounding requirements vary by jurisdiction.

No human therapeutic dose is established. Community protocols commonly use body-weight-based SC 150–500 µg/day, with systemic immune research using 250–500 µg once daily in 4–8-week cycles (community protocol). Quantitative anchors from research: bactericidal MICs run from 1.5 µg/mL against A. baumannii in vitro, with survival benefit in systemically infected mice (animal), to 256 µg/mL against carbapenem-resistant P. aeruginosa (in-vitro). Host-cell cytotoxicity appears at 1–10 µM (~4.5–45 µg/mL; LL-37 MW ≈ 4.5 kDa), so systemic dosing has a narrow window, which is why localized and encapsulated formats dominate preclinical development.

Subcutaneous is the practical systemic route: SC injection produces two-phase absorption, predominantly renal clearance, and visible uptake into immune-rich tissues (lymph nodes, spleen); IV is cleared rapidly, largely by the liver (animal). Topical application directly to wounds is well validated in mouse models, improving re-epithelialization, granulation, and bacterial clearance (animal). Oral delivery is effectively non-viable without engineered carriers due to gut proteolysis and rapid mucosal/salivary clearance. For wound-related goals, local/topical formats are preferable; for systemic immune modulation, SC injection is the standard research approach (community protocol).

LL-37 is cytotoxic to many human cell types at 1–10 µM in vitro, and endogenous levels reach ~300 µM in psoriatic lesions (observational/in-vitro). It has dual pro- and anti-inflammatory actions, including NLRP3 inflammasome activation in rosacea-like skin. Cancer effects are context-dependent: it suppresses growth in gastric, colon, and hematologic models but promotes ovarian, lung, breast, prostate, and melanoma progression; pancreatic cancer is promoted via FPRL1, P2X7, and CXCR4 stabilization (in-vitro/animal). No human cancer-safety data exist; individuals with a history of any LL-37-sensitive malignancy should avoid use (practitioner consensus).

LL-37 clears rapidly: IV bolus is removed from blood within hours (mainly hepatic), and SC dosing follows two-phase kinetics (animal). Tissue proteases degrade the peptide, and stability in wound environments is poor without carrier materials. Community protocols run 4–8-week cycles with off-periods of at least equal length; no data support continuous long-term use (community protocol). Lyophilized peptide stores stably frozen; reconstituted solution is typically refrigerated and used within a month (practitioner consensus).

The strongest preclinical support is for (1) antimicrobial therapy: all 43 tested clinical bacterial isolates were susceptible to recombinant LL-37 (in-vitro); it improved survival in mouse sepsis via macrophage pyroptosis suppression and neutrophil extracellular trap induction (animal); (2) wound healing: accelerated diabetic wound closure via TFEB-dependent autophagy and improved MRSA-infected wound healing (animal); (3) antivirals: direct activity against both enveloped viruses and non-enveloped viruses such as rhinovirus and enteroviruses, though citrullination by host PAD enzymes during infection attenuates this (in-vitro). In humans, the best-established data are biomarker-level (periodontal disease, infections), not treatment outcomes (observational).

Note: LL-37 does not uniformly protect against fungi. In cystic fibrosis-relevant models, LL-37 and its fragment RK-31 paradoxically stimulated growth and gliotoxin production of the pulmonary fungus Aspergillus fumigatus, so antifungal expectations should be tempered (in-vitro/animal).

Derivatives are engineered to fix LL-37's weaknesses and generally outperform it. RP557 showed MIC 32 µg/mL versus 256 µg/mL for LL-37 against carbapenem-resistant P. aeruginosa, removed ~50% of mature biofilm at 64 µg/mL, and potentiated carbapenems 4–16× (in-vitro). LL-37-derived peptides achieved lower MICs and faster killing against ESKAPE pathogens with low mammalian cytotoxicity (in-vitro). Truncation, retro-inversion, and nanocarrier strategies address instability and toxicity. Full-length LL-37 remains the biological reference; engineered analogs are the more clinically translatable molecules.

Yes: host-directed induction is an established alternative strategy. Butyrate and vitamin D3 are potent endogenous inducers of LL-37, proposed as anti-infective therapy that bypasses delivery and stability problems entirely. In tuberculosis trials, vitamin D adjunctive therapy showed modest benefit primarily in vitamin D-deficient subgroups; however, the only human-intervention evidence connected to LL-37 is a probiotic RCT. Optimizing vitamin D status (and possibly short-chain fatty acid intake) is the best-supported way to raise systemic LL-37 without administering the peptide itself. Conversely, smoking suppresses endogenous LL-37 levels (e.g., reduced gingival crevicular fluid LL-37 in smokers with periodontitis), so tobacco cessation is advisable for anyone seeking to raise LL-37 naturally.