LL-37

LL-37 stands alone as the single antimicrobial peptide that the body produces internally, part of a peptide family called cathelicidins, natural germ-fighting molecules. Built from 37 amino acids and carrying a strong positive charge, it is cut out of a bigger precursor protein. Its research reach goes beyond direct microbe killing: scientists have also studied how it helps skin cells migrate into a wound and how it encourages new blood vessel growth, with one placebo-controlled trial testing it on people with long-lasting leg wounds.

What it is

LL-37 is cut from a larger precursor protein called hCAP18 and carries a strong positive electrical charge, a property researchers link to how it interacts with and disrupts microbial cell membranes. Laboratory tests show it working against many kinds of bacteria, viruses and fungi.

Beyond killing microbes directly, LL-37 is studied for helping skin cells called keratinocytes move into a wound and for encouraging new blood vessel growth, both steps that matter in healing damaged tissue. This dual interest, in microbes and in wound repair, is why the compound appears in both infection and tissue healing research.

How it is studied

Laboratory work has tested LL-37 against bacteria grown as sticky surface colonies called biofilms and, in an older landmark study, against a panel of disease causing microbes using standard dilution assays. One placebo controlled human trial applied it as a topical gel to chronic leg wounds that were not healing on their own.

What studies report

A laboratory biofilm study using a standard Centers for Disease Control reactor reported that LL-37 reduced a resistant Staphylococcus aureus biofilm more than antibiotics and silver nanoparticles tested under the same conditions, with more than a four-log (ten-thousand-fold) reduction in surviving bacteria. [1]
A laboratory panel study reported that LL-37 was active against a range of bacteria, including Pseudomonas aeruginosa, E. coli and vancomycin-resistant enterococci, though it was less potent than a comparison peptide and lost activity against some strains, including one resistant form of Staphylococcus aureus, in high-salt conditions. [2]
The first published human trial, a placebo controlled study in 34 people with long standing venous leg ulcers, reported meaningfully faster healing over four weeks, with the best performing concentration reducing ulcer area by 68 percent. [3]

What is not known

The venous leg ulcer trial is the only human trial identified for this entry, so it is not known whether the wound healing result holds up in a larger or more varied group of patients, or in other wound types that appear elsewhere in this compound's research summary only as a stated interest rather than a completed study. The antimicrobial and biofilm findings come entirely from laboratory dishes and standardized lab strains, and have not been separately confirmed against infections in living human skin.

Reported adverse findings

The human trial reported no local or systemic safety concerns with topical LL-37 at any of the three concentrations tested, though the highest concentration showed no healing advantage over placebo. [3]

Regulatory status

The United States Food and Drug Administration has not approved LL-37 for any use. Its most advanced published human evidence is a single placebo controlled trial in chronic leg ulcers, short of what regulators typically require for approval.