LL-37: The Antimicrobial Peptide
By Jay Campbell
August 19th, 2021
One of the biggest challenges facing the healthcare industry today is when once-effective drugs suddenly stop working against pathogens.
So much so that the World Health Organization has deemed it to be a global crisis:
“Antimicrobial Resistance (AMR) occurs when bacteria, viruses, fungi and parasites change over time and no longer respond to medicines [i.e. become resistant] making infections harder to treat and increasing the risk of disease spread, severe illness and death… antimicrobial medicines become ineffective and infections become increasingly difficult or impossible to treat.”
In the United States alone, we have over 2.8 million antibiotic-resistant infections annually and 35,000 people die as a result, costing our healthcare system over $4.6 billion each year.
Fortunately, there’s a little-known therapeutic peptide called LL-37 that is proving to be effective as an antimicrobial treatment.
Fungal infections, bacterial infections, viral infections — there has yet to be a pathogen that LL-37 can’t handle!
Keep reading and you’ll see why LL-37 might be one of the biggest Golden Age breakthroughs for modern medicine.
What Is LL-37?
LL-37 is a 37-amino-acid peptide that is directly derived from the C-terminal of a larger protein in your body known as a cathelicidin, which simply refers to an antimicrobial peptide that kills foreign micro-organisms via membrane disruption.
(The amino acid sequence starts with two leucines, hence the “double L” at the start of the name)
This cathelicidin, known as hCAP18, is the ONLY naturally-produced human cathelicidin in existence and it can be found in multiple parts of your body:
“Peptide LL-37 is produced by mucosal epithelial cells, neutrophils, monocytes, macrophages, mast cells, NK cells, T and B lymphocytes, adipocytes, and keratinocytes. Its expression is regulated by various endogenous factors, including proinflammatory cytokines, growth factors, as well as an active form of vitamin D” (Source)
“LL-37 is expressed in many types of tissue cells such as keratinocytes, differentiated epithelial cells in the colon, airway, ocular surface, genitals, in eccrine glands, Brunner glands in the duodenum, myelocytes, mesenchymal stromal cells (MSCs), and cells of testes.” (Source)
Its history dates all the way back to 1995, and it gets a bit complex:
“hCAP18 [human 18 kDa cathelicidin antimicrobial protein] is the only human cathelicidin. The [host defence peptide] it releases, LL-37, has been extensively studied since its discovery in 1995, and is a paradigm for the multiple roles of cathelicidin peptides in host defence”
“Three different groups independently reported the human cathelicidin, hCAP18, in 1995. One used PCR probes based on porcine PR-39, and identified the pro-form of a peptide they called FALL-39. The second went looking for the human equivalent of LPS-binding CAP18, using oligonucleotide probes based on the rabbit sequence, while the third directly isolated a 19 kDa protein from the specific granules of human neutrophils and then isolated its cDNA from a chronic myeloid leukaemia library”
“The human cathelicidin HDP, LL-37, an amphipathic α-helical peptide, had a quite medium-sensitive antimicrobial activity and, unusually, the capacity to adopt this structure also in aqueous solutions at physiological salt concentrations”
The transition from hCAP18 to LL-37 happens via “extracellular cleavage of the C-terminal end of the 18 kDa hCAP18 protein by serine proteases of the kallikrein family in keratinocytes and proteinase 3 (PR3) in neutrophils” (Source)
And in case you’re wondering what all the fuss around antimicrobial peptides (AMPs) is about:
“…much attention and effort have been paid to AMPs as new antimicrobials to treat microbial infections, especially those caused by antibiotic-resistant pathogens, because these biomolecules provide several advantages over conventionally used antibiotics such as:
(a) lower levels of resistance; (b) broad-spectrum activity with the least toxicity to the host; (c) synergistic effects on the antimicrobial activity of antibiotics; and (d) rapid killing.
These properties have led AMPs to be considered the best candidate to overcome antibiotic resistance.”
Hence why this peptide is being studied so rigorously.
LL-37’s Mechanism of Action
LL-37’s primary mode of action involves a direct attack on the cell membrane of the pathogen it is targeting:
“The amphipathic nature of antimicrobial peptides contributes to their ability to interact with bacterial membranes. Most antimicrobial peptides have a net positive charge and are thus called cationic antimicrobial peptides.
Electrostatic interactions between the cationic antimicrobial peptides and anionic bacterial membranes stabilize the binding of these antimicrobial peptides to the membranes. Subsequently, the bacterial membrane is disrupted, leading to insertion of antimicrobial peptides into the membranes and, often, the formation of pores.
In summary, antimicrobial peptide binding leads to a breakdown of membrane potential, an alteration in membrane permeability, and metabolite leakage, ultimately causing bacterial cell death.”
The second part of LL-37 exerting its effects on an organism involves the immune system:
“LL-37 has a chemotactic effect, acting upon and inducing migration of human peripheral blood monocytes, neutrophils and T cells. It was shown to modulate expression of hundreds of genes in monocytes and other cells, including those for chemokines and chemokine receptors.
Human neutrophils exposed to LL-37 increase the production of reactive oxygen species and exhibit delayed apoptosis.
Thus, during infection, LL-37 released by degranulation of neutrophils or secreted from other cells would be expected to modulate the innate immune response through a variety of way”
Finally, there are the simultaneously pro-inflammatory and anti-inflammatory pathways that can both be triggered by LL-37:
“Exposure to LL-37 results in recruitment of inflammatory cells, induction of M1 macrophages and stimulation of inflammatory responses such as inflammasome activation and type I IFN production. Type I IFN production is promoted via LL-37 protection of both RNA and DNA, allowing for activation of endosomal TLR7 and TLR9 respectively. LL-37, expressed on the surface of neutrophils is recognized by anti-LL-37 autoantibodies, which promotes NETosis, generating a source of additional LL-37 DNA complexes.
However, LL-37 has strong anti-inflammatory effects such as neutralization of TLR4 activation by LPS, downmodulation of inflammatory cytokine responses and preventing invasion and inflammatory responses to pathogenic bacteria.”
(FYI – inflammation needs to be regulated properly, otherwise you have systemic and chronic inflammation that leads to a whole host of age-related diseases)
In summation, we have a lot of things happening at the same time when LL-37 is involved in killing a foreign agent within the body.
Let’s see how this applies towards fully optimizing our health!
Top 7 Health Benefits of LL-37
If you take a quick look on PubMed, there are around 1,776 research papers on LL-37 published between 1996 and the time of this writing.
So surely there must be an extraordinary amount of evidence supporting the use of this peptide in clinics and hospitals.
As with almost every single peptide I cover on this website, the answer is a resounding YES!
LL-37 Is A Potent Antibiotic
Despite this being LL-37’s claim to fame, there has yet to be a study done in humans where LL-37 is directly used as an antibacterial treatment.
Yet it’s been studied in vivo and in vitro across several types of bacteria:
- Staphylococcus aureus: Rapid elimination of bacteria with LL-37 when compared to antibiotics and silver nanoparticles
- Staphylococcus epidermidis: LL-37 may be able to prevent bacterial colonization
- Escherichia coli: LL-37 was able to reduce biofilm formation for a multidrug-resistant variant of the bacteria, which is essential for bacteria to develop resistance against antibiotics
- Pseudomonas aeruginosa: LL-37 also inhibited biofilm formation successfully
Even with this limited data set, we can already see that LL-37 is effectively a broad spectrum antibiotic.
LL-37 Could Exert Antifungal Effects
LL-37 has been primarily tested against two types of fungal infections to date.
The first one is Aspergillus fumigatus, whereby LL-37 was able to inhibit infection in a mouse study via multiple paths of action:
“LL37-treated mice showed lower amounts of fungi load, moderate pathological damage, and reduced proinflammatory cytokines. Further, LL37 transgenic mice (LL37+/+) were examined to investigate the effects of endogenous LL37 in an A. fumigatus infection model and showed lower susceptibility to A. fumigatus infection in comparison with wild-type mice.
In addition, LL37 also played a protective role in an immunosuppressed mouse model of A. fumigatus infection. Thus, LL37 inhibits A. fumigatus infection via directly binding to mycelia and reducing excessive inflammation”
The second one is Candida albicans, which has been studied more extensively.
In this case, the primary path of action seems to involve binding to the cell wall of the fungal pathogen:
“Using transmission electron microscopy, carbohydrate analyses, and staining for β-1,3-glucan, changing of C. albicans cell wall integrity was detected upon LL-37 treatment. In addition, LL-37 also affected cell wall architecture of the pathogen.
Finally, DNA microarray analysis and quantitative PCR demonstrated that sub-lethal concentrations of LL-37 modulated the expression of genes with a variety of functions, including transporters, regulators for biological processes, response to stress or chemical stimulus, and pathogenesis”
It will be interesting to see if LL-37 can maintain this track record across other types of fungal infections.
LL-37 Has Antiviral Properties
Although LL-37 is not primarily being investigated for some purpose, experiments have been done to see if the peptide has a broader spectrum of therapeutic use.
It’s only been tested against a few viruses in cell culture studies, but the reported observations are nevertheless worth looking at
- Reducing the infectiousness of HIV
- Exert both a protective effect and direct activity against RSV (respiratory syncytial virus)
- Inhibits infection by EBOV (2014-2016 West Africa Ebola virus)
- Inhibits influenza A viruses through disrupting viral membranes
How, you may ask?
One partially completed mechanism of action observed in influenza A provides further insight, although it’s not clear if the same can be said for LL-37’s anti-viral activity against all viruses:
“LL-37 does not block hemagglutination activity, cause viral aggregation, or reduce viral uptake by epithelial cells, rather it inhibits viral replication at a post-entry step prior to viral RNA or protein synthesis in the cell. Likely sources of LL-37 in the [Influenza A]-infected respiratory tract include infiltrating neutrophils, macrophages and respiratory epithelial cells”
To make a short story even shorter, we’ll have to see if this efficacy holds up in animals and humans.
LL-37 May Fix Problems With Gut Health
The only study I could find demonstrating therapeutic use of LL-37 for this purpose involved using rats, and the end result was a positive influence on the regulation of gut microbiota:
“CAMP treatment promoted insulin and glucagon secretion from isolated rat islets. Thus, CAMP is a promoter of islet paracrine signaling that enhances islet function and glucoregulation.
Finally, daily treatment with the CAMP/LL-37 peptide in vivo in BBdp rats resulted in enhanced β-cell neogenesis and upregulation of potentially beneficial gut microbes. In particular, CAMP/LL-37 treatment shifted the abundance of specific bacterial populations, mitigating the gut dysbiosis observed in the BBdp rat.
Taken together, these findings indicate a novel functional role for CAMP/LL-37 in islet biology and modification of gut microbiota.”
Dr. William Seeds, one of the world’s most renowned peptide physicians, can personally attest to this.
Here’s how he explains what’s happening in your gut:
“When you consume fiber and carbohydrates, you’re giving microbes what they need to create short-chain fatty acids such as butyric acid. Butyric acid is produced when “good” bacteria in your gut break down the fiber. It provides 80% of the energy provided to your intestinal cells comes from it, which in turn makes the cell healthy and allows it to function probably.
When those cells are healthy and the butyric acid is working, the cells make their own antimicrobial, i.e. LL-37, and it sits in the colon and helps attack the “bad” bacteria.
Let’s say you eat the wrong diet or you get an infection. The cells in your colon are up-regulating LL-37 to deal with the parasite butthe “good” bacteria can’t produce as much butyric acid, so LL-37 production goes down. Hence, you’re in a great position to use LL-37 to help fight the infection”
One testimonial from a user on a popular Internet forum for Chronic Fatigue Syndrome (CFS) patients notes how LL-37 helped fixed their leaky gut issues:
“I have had 10 years recurring athletes foot that produced painful cracks skin on my pinky toe fold/crease (where it meets the rest of the foot). So I bought it specifically for the athletes foot issues (tried everything and it never went away). Surprisingly it fixed my IBS, leaky gut issues, and also my stomach was super sensitive and wrecked from 4 years of pain killers from CFS/Fibro nerve pain.
3 months later, all my stomach issues are gone and athletes foot entirely gone. BPC-157 and LL-37 have been absolutely miraculous for me, I’m now working part time after 10 years bed bound and on good days I hover around 80-90% healthy. Now I just need something to bring my energy levels back to normal.”
Even Carl Lanore from SuperHuman Radio health has used LL-37 to treat his own gut health problems, which he discusses in great detail in the YouTube video below:
LL-37 Shows Promise In Healing Wounds
One interesting study I found on LL-37 involved examining its stability in a stimulated non-healing wound environment using fluid samples from the wounds of nine patients suffering from venous leg ulcers (more on that later).
The results were interesting, to say the least:
“Incubation of LL-37 (10 µg/ml) at 37°C for 6 h resulted in complete degradation by the serine proteinase trypsin (≥10 ng/ml), while no degradation was observed with matrix metalloproteinase-9. LL-37 susceptibility to trypsin was diminished considerably in the presence of wound fluid, and there was no apparent cleavage of exogenous LL-37 incubated in wound fluid for up to 24 h at 37°C even when using fluids from ulcers with resident P. aeruginosa (n=2).
In conclusion, LL-37 was degraded by trypsin, but not by matrix metalloproteinase-9, and was fairly resistant to proteolytic cleavage ex vivo by incubation with wound fluid from non-healing venous leg ulcers. Thus, the proteolytic environment of chronic wounds does not seem to prevent the therapeutic use of topical LL-37″
And when mice were treated with LL-37 following a deep tissue injury that induced pressure ulcers, there was a noticeable amount of healing:
“At 5 μg/ml, LL-37/CS inhibited the growth of Staphylococcus aureus. The area of the pressure ulcers was significantly lower in mice receiving LL-37/CS hydrogel in comparison to all other 3 groups on days 11 (84.24% ± 0.25%), 13 (56.22% ± 3.91%) and 15 (48.12% ± 0.28%).
Histological examination on days 15 and 21 showed increased epithelial thickness and density of newly-formed capillary with naked LL-37 and more so with LL-37/CS.
The expression of key macromolecules in the process of angiogenesis (i.e., hypoxia inducible factor-1α (HIF-1α) and vascular endothelial growth factor-A (VEGF-A)) in wound tissue was increased at both the mRNA and protein levels.”
Similar observations have been noted against multi-drug resistant bacteria as well, which makes you wonder what’s really going on.
One possible mechanism to explain these findings involves LL-37’s ability to break down the biofilm formed by bacteria (i.e. communities of microorganisms):
“The resistance of chronic wounds to heal has been shown to be associated with the presence of multispecies pathogenic biofilms. As previously stated, once biofilm is broken down, the underlying bacterial colonies can be targeted by the immune system as well as by antibiotics, potentially allowing recovery of the otherwise non-healing wound. LL-37 is capable of performing all of these functions (anti-biofilm, antimicrobial, immune-modulating), and when administered topically, can potentially avoid the many hurdles of systemic peptide delivery”
Yet there are many more actions simultaneously taking place, two of which involve angiogenesis and regulating inflammation:
“The peptide attracts inflammatory cells, including monocytes and granulocytes. LL-37 modulates the inflammatory phase of wound healing through release of proteins and peptides that govern the inflammatory process. Keratinocytes (skin epithelial cells) are activated by LL-37, which in turn results in activation of growth factors in outer skin layer with a consequent cell migration. This is assumed to result in re-epithelization and closure of the wound.
Additionally, the production of vascular growth factors such as VEGF and the activation of endothelial cells in blood vessels are also important for the formation of new blood vessels that is observed after treatment with [LL-37]”
Stay tuned — you’re about to see just how well this applies towards humans…
LL-37 Demonstrates Clinical Safety And Efficacy For Addressing Venous Leg Ulcers
You may have never heard of this type of sore, but they’re far more common than you think:
“Venous leg ulcers are the most common type of leg ulcer, accounting for 80% to 85% of all cases and mainly affecting older adults. Women are about twice as likely as men to have them — roughly 42% to 18%, respectively. Experts say a venous leg ulcer is more likely to occur in women between ages 40 and 49 and in men between ages 70 and 79.
While most heal within three months, some ulcers can take up to two years or more to finally get better. And a small number — approximately 15% — never fully go away.”
Left untreated, they can lead to more serious complications and even the possible amputation of the affected leg.
A Phase 1/2a clinical trial conducted in 2014 revealed LL-37 to be safe and effective for treating chronic leg ulcers at the right dose:
“The healing rate constants for 0.5 and 1.6 mg/mL of LL-37 were approximately six- and threefold higher than for placebo (p = 0.003 for 0.5 mg/mL and p = 0.088 for 1.6 mg/mL). Square-root transformed wound area data showed improved healing for the 0.5 and 1.6 mg/mL dose groups compared with pretreatment values (p < 0.001 and p = 0.011, respectively).
Consistently, treatment with the two lower doses markedly decreased the mean ulcer area (68% for 0.5 mg/mL and 50% for 1.6 mg/mL groups). No difference in healing was observed between the groups receiving 3.2 mg/mL of LL-37 and placebo.”
Notably, this was a synthetic form of LL-37 known as Ropocamptide (same amino acid sequence, though) that was applied to the wounds locally via a topical solution.
It is manufactured by Swedish pharmaceutical company Promore Pharma and the early clinical trial results are already showing much promise.
Since this trial did not show any significant adverse events related to the drug itself, the Phase 2b study (HEAL LL-37) was randomized and double-blinded to include a total of 144 patients.
The final results are expected to be published later in 2021, but here is what is being reported so far:
“…larger wounds (≥10cm2) healed significantly faster among patients treated with ropocamptide as compared with placebo. Patients treated with the most effective dose of ropocamptide, which is 0.5 mg/ml, demonstrated a more than three-fold higher frequency of completely healed wounds”
“In patients with larger wounds that were treated with 0.5 mg/ml ropocamptide, 28.1% achieved complete wound healing, in the group treated with 1.6 mg/ml ropocamptide 19.6%, whereas only 8.1% of patients in the placebo group showed complete healing. This difference is statistically significant (p <0.05) for the most effective dose group”
“The mean reduction in wound size after discontinuation of treatment was 33.7% for patients treated with placebo, and 56.3% for patients treated with the most effective dose of ropocamptide (0.5 mg / ml)”
“…there are an estimated 13-18 million patients with VLUs and these wounds constitutes the largest category of all chronic, or hard-to-heal, ulcers. VLU represent significant challenges to patients and healthcare systems since they are frequent, costly to manage, recurring, and may persist for months or years.
Standard treatment consists of compression bandaging and there are no approved prescription pharmaceuticals for VLUs on the traditional pharmaceutical markets. The cost for treating one VLU episode exceeds 10,000 USD”
This is one of the closest therapeutic peptides to full FDA approval I’ve covered so far, so keep your eyes open!
Miscellaneous Applications Of LL-37
LL-37’s complex and multi-faceted mechanism of action means it could be useful for other ailments as well.
Some of them include:
- Being used as a possible vaginal contraceptive, and maybe as a preventative tool against sexually transmitted infections
- A biomarker for diseases such as urinary tract infections, chronic inflammatory lung disease and acute heart failure
- The management of melanoma via an improved immune-related response
- Treating tuberculosis in combination with vitamin D and 4-phenylbutyrate
- Improving lung function, according to one Reddit user
- Addressing the survival rate of sepsis
Not a lot to go off of, but these things are worth further study and investigation.
The BEST Dose of LL-37 for Treating Microbial Infections
The dosage recommendations for LL-37 seem to differ depending on who you ask, but they all fit within a tight range.
Carl Lanore of SuperHuman Radio recommends 125 mcg per day injected subcutaneously for 50 days, followed by a 2-4 week break before doing a second round if necessary.
He even provides more specific instructions on how to prepare the solution if you have a 5mg bottle of LL-37:
“Take one 5 milligram vial (5,000 mg) of LL37 add 4 milliliters of bacteriostatic water to this. This will fill up the vial all the way to the stopper (video below is for BPc157 but can be used to illustrate the reconstitution process for LL37 however the dosing is different). Allow it to sit overnight in the refrigerator and the next morning begin dosing at 10 units per injection. This will be 125 micrograms of LL37 which will last you 50 doses or 50 days”
Dr. William Seeds recommends 100mcg of LL-37 injected subcutaneously twice a day (once in morning and once at night) for 4-6 weeks.
Outside of those two authoritative sources, there really isn’t much else out there to say on this topic.
Like I always say, you are 100% responsible for how you use this peptide and how you react to it.
Start with the minimum effective dose possible, monitor your body’s reactions, and use common sense.
LL-37’s Side Effects and Safety Profile
So what can we reasonably expect from LL-37 in terms of side effects, given insufficient data in humans?
Even though the venous leg ulcer trials showed a favorable safety profile with a low occurrence of side effects, it’s important to remember the peptide was administered locally to the site of infection as a topical solution… thus we don’t know what would happen when the peptide is injected subcutaneously.
However, there are other potential side effects of LL-37 you should know about:
- Possibly ineffective (i.e. nothing happens)
- Elevated levels of LL-37 are seen in patients with psoriasis and contact dermatitis, along with rosacea
- Bacteria may eventually develop resistance to LL-37 after prolonged use
One scientific review expands on the possibility of bacterial resistance, noting that LL-37 is not the be-all and end-all of treating such infections:
“Previous findings suggest that the likelihood of AMP resistance is low in comparison to antibiotic resistance, yet a review by Maria-Neto et al. described the development of AMP resistance as inevitable. Several studies have examined the ability of bacteria to acquire resistance following serial passages of sub-lethal concentrations of LL-37.
The use of sub-minimal inhibitory concentration (MIC) values of LL-37 led Staphylococcus aureus to develop resistance after three passages, and was found to develop stable resistance within 168 generations of increasingly large concentrations of LL-37.
Multiple more studies have reported the induction of AMP-resistant phenotypes following prolonged exposure to LL-37, including in Salmonella typhimurium and Clostridioides difficile“
And on the subject of cancer, the consensus on whether it promotes or suppresses tumor growth is uncertain:
“Accumulating evidence indicates that LL-37 also plays a significant role in human cancer. LL-37 induces tumorigenic effects in cancers of the ovary, lung, breast, prostate, pancreas, as well as in malignant melanoma and skin squamous cell carcinoma. In contrast, LL-37 displays an anti-cancer effect in colon cancer, gastric cancer, hematologic malignancy and oral squamous cell carcinoma.
Mechanistically, LL-37-induced activation of membrane receptors and subsequent signaling pathways lead to alteration of cellular functions. Different membrane receptors on various cancer cells appear to be responsible for the tissue-specific effects of LL-37″
Moreover, scientists are currently working to develop new ways of using LL-37 that keep all the redeeming qualities while fixing the issues that could make it unfit on its own as a therapeutic tool.
Issues such as “costly to synthesize” (due to its length), “vulnerable to proteases” (i.e. metabolic degradation), and “toxicity and hemolysis against eukaryotic cells” (Source).
These new methods include different delivery systems, modifying the LL-37 structure, and combining it with other medical treatments for a better effect.
Two final points to close off this section…
Additionally, LL-37 is dependent on Vitamin D for proper expression, so make sure you are supplementing appropriately and getting 20-30 minutes of sunlight every day.
The #1 Place To Buy Pharmaceutical-Grade LL-37 Online
Given the experimental status of LL-37, I have to be extremely careful in who I recommend as a vendor for this peptide.
The good news is that Limitless Life Nootropics currently offers LL-37 in their inventory and they have
Use code JAY15 to get 15% off your order!
As with every other product, this company guarantees you are receiving the highest purity and quality of any peptide product you purchase from them.
The only other way to get a peptide like this is through a compounding pharmacy, many of which are being suppressed through unreasonable regulatory force.
So stock up while you can before supplies run out!
Additional Reading Resources for LL-37
LL-37 is still undergoing extensive testing before it can be used in humans for its primary purpose of stopping bacterial, viral, and fungal functions.
So until we get to the point where it will be a go-to in medical care, here are some helpful resources to learn more about this therapeutic peptide…
The International Peptide Society has a comprehensive webinar covering what we know to date about LL-37.
And as always…
Raise Your Vibration To Optimize Your Love Creation!
PS – When you’re ready to learn how to use peptides at a much deeper level, you have two options.
- You can set up a private One on One Call with me.
- Joining The Fully Optimized Health Mastermind with two Monthly 60 Minute Group Coaching Calls with Me and Daniel Kelly Discussing Fully Optimized Living including Peptides, Hormones, Gray Market Agents, Performance Enhancement and Raising Your Vibration.