Emerging antimicrobial peptides in gastrointestinal disorders: Dual role in immunity and therapy

Table 1 Key antimicrobial peptides: Structural classes, mechanisms, molecular targets, and gastrointestinal relevance

AMP	Structural class	Primary mechanism(s)	Molecular target(s)	GI relevance	Ref.
HD-5, HD-6	α-Defensin	Membrane disruption; microbiome shaping via crypt gradients	Lipid II (HD-5); self-assembly nets (HD-6)	Paneth cell-derived; reduced in ileal Crohn’s disease	[4,14]
hBD-2	β-Defensin (inducible)	Membrane disruption; CCR6-mediated chemotaxis	Lipid II; CCR6	NF-κB-induced in IBD epithelium; inducible barrier	[4,5]
LL-37	Cathelicidin (α-helix)	Membrane disruption; DNA binding; receptor-mediated signalling	FPR2/ALX (approximately 200 nM), EGFR, TLR9 via DNA	Wound healing; context-dependent pro-/anti-tumour in CRC	[17,21]
Buforin II	α-Helix (proline hinge)	Non-lytic entry; DNA/RNA binding	dsDNA minor groove; rRNA	Model for resistance-refractory intracellular targeting	[5,9]
Nisin	Lantibiotic (cyclic)	Lipid II sequestration and pore formation	Lipid II pyrophosphate (approximately 1 nM)	Narrow-spectrum; resistance-resistant dual-mechanism paradigm	[2,20]
Microcin J25	Lasso peptide	RNA polymerase inhibition; membrane-independent	RNA polymerase β-subunit	Efficacious in DSS-induced colitis; selective microbiome modulator	[22]
CRAMP	Cathelicidin (α-helix)	Membrane disruption; FPR2/ALX immunomodulation	Microbial membranes; FPR2/ALX	Anti-inflammatory in murine colitis; restores diversity	[23]

AMP: Antimicrobial peptide; CCR6: C-C chemokine receptor type 6; CRAMP: Cathelicidin-related antimicrobial peptide; CRC: Colorectal cancer; DSS: Dextran sodium sulfate; dsDNA: Double-stranded DNA; EGFR: Epidermal growth factor receptor; FPR2/ALX: Formyl peptide receptor 2/Lipoxin A4 receptor; GI: Gastrointestinal; IBD: Inflammatory bowel disease; NF-κB: Nuclear factor kappa B; RNA: Ribonucleic acid; rRNA: Ribosomal RNA; TLR9: Toll-like receptor 9.

Table 2 Preclinical studies of antimicrobial peptide activity in gastrointestinal and related disease models

No.	Ref.	Peptide	Model / route	Dose	Key findings	Sig.
1	Moghaddam et al[49]	CM11; CM15 (cecropin-melittin hybrids)	In vitro: P. aeruginosa, S. aureus, V. cholerae, A. baumannii, E. coli (ATCC and clinical)	MIC 4 mg/L; MBC 16 mg/L	Complete kill at 30-40 minutes; CM11 MIC/MBC stable at 48 hours; CM15 MIC doubled at 48 hours	P < 0.05
2	Shang et al[22]	MccJ25 (lasso peptide, 21-aa)	DSS-induced UC; C57BL/6J/oral gavage	5 mg/kg and 10 mg/kg	↓ DAI, ↑ colon length; ↓ TNF-α, IFN-γ, IL-1β, IL-6; ↑ TJ proteins; ↑ Lactobacillus, ↓ Bacteroides and Akkermansia; co-housing confirmed microbiota as key mechanism	P < 0.05
3	Jiang et al[23]	CRAMP (cathelicidin-related; murine LL-37 homologue)	3% DSS-induced acute UC; C57BL/6J/IP	4 mg/kg/day	↑ body weight, ↑ colon length, ↓ DAI, ↓ MPO; ↑ TJ proteins; ↓ IL-6, TNF-α, MCP-1, CRP; ↑ GSH-PX, ↓ MDA; ↑ Verrucomicrobiota	P < 0.05-0.001
4	Liu et al[44]	Abaecin (proline-rich, bee-derived; non-lytic)	2.5% DSS-induced acute UC; C57BL/6J/rectal	5 mg/kg	↑ colon length and body weight, ↓ DAI; ↓ LPS, D-LA, DAO; ↓ IL-1β, IL-6, TNF-α, IFN-γ (IL-10 unchanged); ↑ ZO-1, occludin, claudin-1; ↓ NF-κB/MAPK; ↓ Bacteroides, Barnesiella, Escherichia, ↑ Lactobacillus	P < 0.05-0.01
5	Sun et al[45]	Chensinin-1b (from R. chensinensis)	RAW264.7 + LPS (in vitro) and 4% DSS-induced UC; BALB/c/IP	10-40 μmol/L; 1.5 and 3 mg/kg	↓ M1 markers (TNF-α, IL-6, NO, CD86), ↑ M2 markers (IL-10, TGF-β1, Arg-1, CD206); ↓ NF-κB/MAPK; ↑ body weight and colon length, ↓ DAI; high dose superior to cyclosporine A	P < 0.05-0.01
6	Zhao et al[43]	DP7 (12-aa; machine-learning designed)	4% DSS-induced UC (multi-arm: FMT, antibiotic, pseudo-germ-free); C57BL/6/IV	0.5 mg/kg q2d	↓ weight loss, ↓ DAI, ↑ colon length; ↑ ZO-1, claudin-1, occludin; ↓ IL-1β, IL-6, ↑ IL-10; ↑ Muribaculaceae; DP7-FMT > DSS-FMT, immune effects microbiota-dependent	P < 0.05-0.0001
7	Sun et al[46]	R7I (IRPI × 7; anti-proteolytic; trypsin/chymotrypsin/pepsin-resistant)	E. coli ATCC 25922 enteritis; C57BL/6/oral gavage	20 mg/kg, 30 mg/kg, 40 mg/kg	↓ intestinal and hepatic inflammation, restored barrier; modulated microbiota (↓ Clostridia, ↑ Odoribacteraceae); normalised gut metabolites	P < 0.05

Arg-1: Arginase-1; ATCC: American Type Culture Collection; CD206: Cluster of differentiation 206; CRAMP: Cathelicidin-related antimicrobial peptide; CRP: C-reactive protein; DAI: Disease activity index; DAO: Diamine oxidase; DP7: Designed peptide 7; DSS: Dextran sodium sulfate; FMT: Faecal microbiota transplantation; GSH-PX: Glutathione peroxidase; IFN-γ: Interferon gamma; IL: Interleukin; IP: Intraperitoneal; IRPI: Isoleucine-arginine-proline-isoleucine motif; IV: Intravenous; LPS: Lipopolysaccharide; MAPK: Mitogen-activated protein kinase; MBC: Minimum bactericidal concentration; MccJ25: Microcin J25; MCP-1: Monocyte chemoattractant protein-1; MDA: Malondialdehyde; MIC: Minimum inhibitory concentration; MPO: Myeloperoxidase; NF-κB: Nuclear factor kappa B; NO: Nitric oxide; q2d: Every 2 days; R7I: Arginine-isoleucine repeat peptide (IRPI × 7); RAW264.7: Murine macrophage cell line; TGF-β1: Transforming growth factor beta 1; TJ: Tight junction; UC: Ulcerative colitis; ZO-1: Zonula occludens-1.

Table 3 Clinical studies of antimicrobial peptide-based interventions

No.	AMP	Indication	Phase	Design /groups	Key findings	Safety	Ref.
1	Pexiganan (MSI-78)	Infected diabetic foot ulcers	3	2 double-blind RCTs; pexiganan 1% cream vs oral ofloxacin vs placebo (n = 835)	Cream equivalent to ofloxacin (85%-90% improvement; 42%-47% eradication); no pexiganan resistance (ofloxacin resistance emerged); study 304 + combined met equivalence, study 303 failed	Well tolerated; no systemic toxicity	[19]
2	Iseganan (IB-367; protegrin-1 analogue)	Oral mucositis (stomatotoxic chemotherapy)	3	Double-blind RCT; iseganan 9 mg oral rinse 6 ×/day vs placebo (n = 323; 163 vs 160)	Primary endpoint (UOM prevention by day 21) not met: 43% vs 33% UOM-free (P = 0.067); significant reductions in peak mouth pain (P = 0.041), peak throat pain (P = 0.048), and NCI CTC stomatitis (P = 0.013)	Well tolerated; no systemic absorption	[60]
3	Iseganan (IB-367)	Oral mucositis (radiotherapy, H&N cancer)	3	Double-blind 3-arm RCT; iseganan + SOC vs placebo + SOC vs SOC (n = 545)	OM prevention not met (9% vs 9% OM-free, P = 0.998); both intervention arms > SOC alone; benefit attributed to oral hygiene/vehicle, not AMP	Nausea higher with iseganan (51%); no systemic absorption	[59]
4	hLF1-11 (lactoferrin 1-11)	Infection prevention, autologous HSCT	1	Open-label single 5-mg IV dose in autologous HSCT recipients (n = 8; part of a 3-study first-in-human programme, total n = 56)	Well tolerated; no immunogenicity (no anti-hLF1-11 IgG/IgE); IL-6/TNF-α attenuation trend on LPS stimulation (NS); safety/PD only; PK not determinable (peptide unquantifiable in plasma), no efficacy data	No serious drug-related AEs; reversible transaminase rise	[54]
5	LTX-109 (Lytixar; peptidomimetic)	Nasal MRSA/MSSA carriage	1/2a	Dose-escalating vehicle-controlled; 1%, 2%, 5% nasal gel TID × 3 days	Significant decolonisation below detection limit at 2% and 5% doses from day 2 (P = 0.0008 and P = 0.0012 vs vehicle, respectively) and sustained through day 4 (P = 0.0180 and P = 0.0105); 1% dose showed reduction from day 1 but did not reach significance vs vehicle; effect not durable; recolonisation occurred in all but one subject by approximately 5 days post-treatment, with no significant difference vs vehicle from baseline to week 9 (P = 0.2754); low resistance propensity supported by preclinical/mechanistic data, not demonstrated in this trial; minimal systemic absorption (Cmax 3.72–11.7 ng/mL in the 5% group; undetectable by 1 week)	No systemic issues; minor reversible local lesions	[55]
6	Dusquetide (SGX942; IDR pentapeptide)	Severe oral mucositis (H&N CRT)	2 (Ph 3 failed)	Double-blind dose-escalating RCT; 0.5 mg/kg, 1.0 mg/kg, 1.5 mg/kg IV twice weekly vs placebo (n = 111)	In overall population: 50% ↓ severe OM duration, 18 to 9 days (67% ↓ in high-risk cisplatin subgroup, 30 → 10 days, P = 0.04); 39% ↓ AUC (WHO Grade-time score); 71% ↓ SOM rate at 1-month follow-up; ↓ infection rate; 7% relative ↓ in SOM incidence: 74% → 69%	No dose-limiting toxicity; AEs consistent with CRT	[64]
7	Omiganan (CLS001)	Atopic dermatitis (mild-moderate)	2	Double-blind vehicle-controlled; 1%, 1.75%, 2.5% gel BID × 28 days (n = 80)	93.5% S. aureus reduction at 2.5% (P = 0.02); dysbiosis recovered; clinical EASI/SCORAD not met; microbiome normalisation insufficient for symptom relief	No systemic AEs; good local tolerability	[56]
8	Omiganan (CLS001)	Facial seborrheic dermatitis	2	3-arm RCT; omiganan 1.75% vs ketoconazole 2% vs placebo BID × 4 weeks	Omiganan showed no improvement vs placebo (SDASI P = 0.143, IGA P = 0.097, %BSA P = 0.522) and did not significantly reduce Malassezia (-3.7%, P = 0.563), explaining the failure; staphylococcus declined in all arms including placebo with no omiganan-specific effect (not a primary driver); ketoconazole met all clinical endpoints (SDASI P = 0.025, IGA P = 0.005, %BSA P = 0.005) with reduced Malassezia and restored barrier function	Mild application-site reactions; no systemic AEs	[57]
9	Omiganan (CLS001)	HPV anogenital warts and vulvar HSIL	2	Two concurrent vehicle-controlled RCTs; 2.5% gel QD × 12 weeks (n = 36)	First demonstration of topical AMP antiviral activity in HPV-induced disease: Significant reduction in HPV viral load in AGW patients (-96.6%; 95%CI: -99.9 to -7.4%; P = 0.045), but no significant difference in lesion clearance or wart count/size vs placebo (near-significant trend in wart height reduction, -30.3%, P = 0.054). In the vulvar HSIL arm, no significant difference in viral load or lesion response vs placebo. Reduction in viral load did not translate into clinically meaningful lesion regression in either indication	No serious AEs; excellent local tolerability	[58]
10	Oral LL-37 (CAS001; via GMO L. lactis)	COVID-19 (SARS-CoV-2 Omicron BA.5.1.3)	2	Open-label, randomized, placebo-controlled, single-center; Oral LL-37 vs L. lactis placebo (n = 238; 129 vs 109); early (≤ 6 days) vs late (≥ 7 days) initiation	Significantly shortened nucleic-acid negative conversion time when started early (9.80 days vs 14.04 days, P = 0.0044; early vs placebo HR 2.427, P = 0.0097); early > late initiation; LL-37 acts via viral envelope disruption (and ACE2 blockade)	No serious AEs; no systemic toxicity	[63]

ACE2: Angiotensin-converting enzyme 2; AE: Adverse event; AGW: Anogenital warts; AMP: Antimicrobial peptide; BID: Twice daily; COVID-19: Coronavirus disease 2019; CRT: Chemoradiotherapy; EASI: Eczema Area and Severity Index; GMO: Genetically modified organism; H&N: Head and neck; hLF1-11: Human lactoferrin peptide 1-11; HR: Hazard ratio; HSCT: Haematopoietic stem cell transplantation; HSIL: High-grade squamous intraepithelial lesion; HPV: Human papillomavirus; IDR: Innate defence regulator; IGA: Investigator’s Global Assessment; LPS: Lipopolysaccharide; MRSA: Methicillin-resistant Staphylococcus aureus; MSSA: Methicillin-sensitive Staphylococcus aureus; NCI CTC: National Cancer Institute Common Toxicity Criteria; NS: Not significant; OM: Oral mucositis; Ph: Phase; PK: Pharmacokinetics; QD: Once daily; RCT: Randomized controlled trial; SARS-CoV-2: Severe acute respiratory syndrome coronavirus 2; SCORAD: Scoring Atopic Dermatitis; SDASI: Seborrheic Dermatitis Area and Severity Index; SOC: Standard of care; TID: Three times daily; UOM: Ulcerative oral mucositis.