LL-37

LL-37's neurological relevance starts with how the compound reaches the central nervous system. Amphipathic α-helical peptide cleaved from hCAP-18 by proteinase 3. Disrupts microbial membranes electrostatically. Neutralises LPS. Modulates immune cell signalling via FPR2 and P2X7 receptors. Active against gram-positive, gram-negative, mycobacterial, and biofilm phenotypes. Direct blood-brain barrier transport is rarely the dominant route for peptide compounds; vagal-afferent gut-brain signalling and effects on cerebral vasculature where the barrier is locally compromised typically produce the CNS phenotype. The detail follows.

Central nervous system access

LL-37 reaches the central nervous system through one or more of three documented routes: direct blood-brain barrier transport, vagal-afferent signalling via the gut-brain axis, and direct action on cerebral vasculature in regions where the barrier is locally compromised. The compound's subq/topical/nebulised route(s) and Variable; tissue-localised half-life set the timeline for CNS exposure. Amphipathic α-helical peptide cleaved from hCAP-18 by proteinase 3. The CNS-relevant phenotype that emerges from this mechanism is the substrate of the cognitive effects described below.

Inflammation and neurological recovery

One of the most replicated effects across compounds in LL-37's class (Cathelicidin antimicrobial peptide) is reduction of inflammatory cytokines (TNF-α, IL-1β, IL-6) in tissues including the central nervous system. For users whose cognitive complaints track with chronic low-grade neuroinflammation — long-COVID, post-viral cognitive fog, post-concussion lingering symptoms, chronic stress — this anti-inflammatory layer is often the most operationally relevant mechanism. LL-37's contribution operates on the same axis at 100-500 mcg per dose.

Receptor pharmacology and selectivity profile

LL-37's receptor-level pharmacology determines its selectivity profile and its overlap with companion peptides. Amphipathic α-helical peptide cleaved from hCAP-18 by proteinase 3. Disrupts microbial membranes electrostatically. Neutralises LPS. Modulates immune cell signalling via FPR2 and P2X7 receptors. Active against gram-positive, gram-negative, mycobacterial, and biofilm phenotypes. The selectivity (or lack thereof) for the principal target relative to off-target receptors is the basis for both the clinical phenotype and the side-effect profile. In stack design this matters: pairing LL-37 with peptides engaging the same primary receptor produces competition rather than synergy.

Dose timing for LL-37 is less time-sensitive given the longer half-life. Consistency through the cycle is more important than the precise clock time of individual doses.

LL-37 stacks well with compounds on complementary pathways. The pairings below are the conventional combinations from the cognitive neuroscience community.

• LL-37 + Semax: Elevates BDNF and NGF in hippocampus and cortex. Pairs naturally with LL-37's mechanism in cognitive / neurological protocols.
• LL-37 + Selank: Modulates GABA-A receptor systems indirectly. Pairs naturally with LL-37's mechanism in cognitive / neurological protocols.
• LL-37 + Semax + Selank Blend: Semax raises BDNF and modulates dopamine systems; Selank stabilises GABAergic and serotonergic tone. Pairs naturally with LL-37's mechanism in cognitive / neurological protocols.
• LL-37 + DSIP: Mechanism remains incompletely characterised. Pairs naturally with LL-37's mechanism in cognitive / neurological protocols.

Lens-specific safety considerations for cognitive / neurological use of LL-37: Site reactions common (peptide is cationic). Histamine-like flush possible. Caution in mast-cell-activation conditions. Additional cognitive / neurological monitoring at baseline and 6–8 week follow-up is appropriate.