Defensin alpha 4

Also known as: Corticostatin HP-4, HNP-4, Neutrophil defensin 4, DEFA4, P12838

**Mechanism of Action** Defensin alpha 4 (HNP-4) is a cationic host-defense peptide stored in neutrophil azurophilic granules. Its mechanism involves electrostatic interaction with negatively charged microbial membranes, leading to membrane permeabilization and disruption. It also exhibits immunomodulatory properties, including chemotactic activity for immune cells and modulation of cytokine release. HNP-4 displays preferential activity against Gram-negative bacteria, with weaker effects against Gram-positive bacteria and fungi, likely due to differences in membrane composition and charge distribution. **Key Research Findings** Preclinical studies demonstrate HNP-4’s broad-spectrum antimicrobial activity, with minimal inhibitory concentrations (MICs) in the low micromolar range against pathogens such as *Escherichia coli* and *Pseudomonas aeruginosa*. Compared to other human neutrophil defensins (e.g., HNP-1–3), HNP-4 shows distinct potency and target selectivity, possibly due to its unique disulfide bonding pattern and reduced net positive charge. Research also highlights its role in innate immunity, including synergy with other antimicrobial peptides and modulation of inflammatory responses. However, its therapeutic development remains experimental, with limited *in vivo* efficacy data. **Clinical Relevance** HNP-4 is under investigation as a potential antimicrobial agent, particularly against antibiotic-resistant Gram-negative infections. Its dual antimicrobial and immunomodulatory functions may offer advantages over conventional antibiotics, though challenges include cytotoxicity at high concentrations and susceptibility to proteolytic degradation. Current research focuses on structural optimization and delivery systems to enhance stability and selectivity. No clinical trials have been reported to date. For research purposes only — not medical advice.

Key data

Mechanism of action

Host-defense peptide that has antimicrobial activity against Gram-negative bacteria, and to a lesser extent also against Gram-positive bacteria and fungi (PubMed:15317502, PubMed:15616305, PubMed:2500436, PubMed:2501794, PubMed:30658057). Exhibits antimicrobial activity against Gram-negative E.coli and E.aerogenes and Gram-positive S.faecalis, S.aureus and B.cereus and the yeast C.albicans (in vitro) (PubMed:15317502, PubMed:15616305, PubMed:17088326, PubMed:2500436, PubMed:2501794, PubMed:30658057). Interacts with pathogenic surface proteins and toxins, such as HIV-1 surface protein gp120 and B.anthracis anthrax lethal factor lef (PubMed:15620707, PubMed:30658057). Protects blood cells against infection with HIV-1 (in vitro) (PubMed:15620707). Inhibits enzymatic activity of B.anthracis lef/anthrax lethal factor (in vitro) (PubMed:30658057). Inhibits corticotropin (ACTH)-stimulated corticosterone production (in vitro) (PubMed:2843187)

Research & studies

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