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LL-37 is a human cathelicidin antimicrobial peptide, a defence molecule of the innate immune system. It is naturally present in saliva, where it plays an important role in host defence against bacterial and fungal pathogens. It is also known as CAP18. A review describes antimicrobial peptides such as cathelicidins as produced by intestinal epithelial and immune cells, where they help tune the balance between pro-inflammatory and anti-inflammatory signalling.
LL-37 is a human cathelicidin antimicrobial peptide naturally present in saliva, described as playing an important role in host defence against bacterial and fungal pathogens. A review describes LL-37 as an antimicrobial peptide involved in antimicrobial defence, inflammatory regulation, tissue repair, and bone regeneration in the oral cavity. More generally, cathelicidin-derived antimicrobial peptides such as LL-37 are described as part of the first line of defense of the innate immune system.
LL-37 is described in a human review as an antimicrobial peptide involved in antimicrobial defence, inflammatory regulation, tissue repair, and bone regeneration in the oral cavity. In a human review, salivary and gingival crevicular fluid LL-37 levels were associated with disease activity and treatment responses. In a human observational study, the authors concluded that salivary LL-37 is a reliable, non-invasive biomarker for early detection and monitoring of oral carcinogenesis.
The facts describe LL-37 as the antimicrobial peptide cathelicidin, also known as CAP18 or in its hCAP18 precursor form.
In laboratory studies with cultured bacteria, LL-37 appears to kill bacteria by disrupting their membranes, with cytoplasmic membrane permeabilization identified as a key mechanism. In in vitro work, LL37 showed strong outer membrane-permeabilizing activity against E. coli. In in vitro work, this membrane disruption by LL37 correlated with surface charge neutralization of the bacteria, as shown by zeta potential measurements.
In cell-culture (in vitro) studies, LL-37 inactivated the nuclear factor-κB (NF-κB) pathway. The inactivation was evidenced by reduced p65 phosphorylation, impaired nuclear translocation, and decreased binding to the IL-6 promoter. In gastric cancer cells, the NF-κB inhibitor BAY 11-7082 mimicked the suppressive effects of LL-37.
In a human observational study, salivary cathelicidin LL-37 levels increased progressively from healthy controls to OSCC cases (p < 0.001). The study measured salivary LL-37 by ELISA in 80 participants divided into four groups: OSCC, tobacco-associated oral potentially malignant disorders (OPMDs), non-tobacco-associated OPMDs, and healthy controls. The authors concluded that salivary LL-37 may serve as a non-invasive biomarker for early detection and monitoring of oral carcinogenesis.
In this observational study in people, plasma LL 37 levels were evaluated in 58 individuals with obstructive sleep apnea and 20 healthy controls. Plasma LL 37 levels were significantly reduced in individuals with severe OSA compared with healthy controls. Mean plasma LL 37 was higher in the AHI < 15 group (75.3 ± 29.3 ng/L) than in the AHI ≥ 15 group (47.1 ± 18.3 ng/L).
In a human observational study, plasma LL-37 levels showed significant negative correlations with the percentage of Stage N1 sleep, the arousal index, the apnea-hypopnea index, and the oxygen desaturation index. In the same human observational study, plasma LL-37 levels showed significant positive correlations with the percentage of Stage N3 sleep, the percentage of REM sleep, the mean percentage of peripheral oxygen saturation, and the minimum percentage of peripheral oxygen saturation. Multiple regression analysis in this human observational study identified the percentage of Stage N1 sleep as an independent factor associated with plasma LL-37 levels.
A review lists cytotoxicity at higher concentrations as one factor affecting the clinical use of LL-37. In a cell study using human dermal fibroblasts, LL37 and its fragments were reported to be non-toxic in cytotoxicity assays. Together, these sources describe LL-37 as non-toxic to cultured human fibroblasts while noting cytotoxicity at higher concentrations.
A review states that clinical use of LL-37 is affected by proteolytic degradation, cytotoxicity at higher concentrations, microbial tolerance, biofilm protection, rapid salivary clearance, and high production costs. Another paper notes that issues such as potency and stability limit the potential of host defense peptides, a group that includes LL-37, to serve as new antibiotics. A third review describes proteolytic instability, narrow therapeutic windows, and manufacturing cost as persistent barriers to antimicrobial peptide therapeutics, including LL-37-based approaches.
In in vitro studies, copper(II) and zinc(II) both bind LL-37 at physiological pH through the N-terminal amino group and a carboxylate donor. In in vitro studies, copper(II) progressively recruits backbone amide nitrogen donors with LL-37, ultimately forming highly stable 4N complexes. In the same in vitro studies, zinc(II) forms hydroxo-containing species, consistent with its preferred tetrahedral coordination geometry; the pH at which this and the copper amide binding occur is not specified.
FOR RESEARCH USE ONLY — Products are sold exclusively for in vitro and preclinical laboratory research. Not for human consumption or administration. Not intended for diagnostic or therapeutic use. These statements have not been evaluated by the FDA.