Nature’s blueprint for wound recovery

Despite a broad toolkit of modern wound-care methods—including debridement, antibiotics, autologous grafts, negative pressure wound therapy, and bioprinting—achieving complete healing in severe acute and chronic wounds remains a complex task [1]. Patients with burns and diabetic ulcers are particularly vulnerable; these wounds often exhibit impaired vascularization, dysregulated immune responses, and delayed re-epithelialization, while microbial biofilms further compromise standard treatments.

Consequently, researchers are seeking topical agents that can simultaneously target multiple stages of the healing process. Hints for such a search are found in nature: some animals have evolved skin defense mechanisms that merge antimicrobial action with inflammatory regulation and tissue repair.

One of the most promising avenues is the study of amphibian skin. Unlike many terrestrial vertebrates, amphibians possess skin that lacks scales or other dense protective structures, leaving them in constant contact with water, microorganisms, and environmental stressors. In response, they have developed a sophisticated system of skin secretions rich in bioactive peptides. These molecules not only restrain the growth of bacteria, fungi, and viruses but also modulate inflammation, support skin cell migration and proliferation, stimulate the formation of new blood vessels, and assist in extracellular matrix remodeling [1, 2].

This combination of protective and restorative properties makes amphibian-derived peptides a compelling platform for developing new therapeutics capable of controlling infection while actively supporting the healing process [3, 4].

Studied species and evolutionary rationale

To date, 8,919 amphibian species are known to science, with the vast majority of wound-healing peptides described in the order Anura (frogs and toads), which includes 7,864 species. This is logically grounded: tailless amphibians possess the most developed secretory granular glands. These glands serve as "reservoirs" for complex mixtures of bioactive compounds. Under stress or injury, they discharge peptides onto the skin surface that not only deter predators and inhibit microbial growth but also regulate regeneration.

Research has focused heavily on the genera Odorrana, Rana, Pelophylax, Xenopus, Phyllomedusa, Bufo, and Duttaphrynus. Well-characterized peptide families were first identified in these amphibians: dermaseptins in South American frogs of the genus Phyllomedusa, magainins in the African clawed frog Xenopus laevis, and temporins, brevinins, and cathelicidins in other genera [1, 2].

The case of Nanorana parkeri, a frog from the Qinghai-Tibet Plateau, is particularly illustrative. Adaptation to extreme UV radiation and low microbial diversity led to the emergence of the peptide SC17-2. Interestingly, it lacks antibacterial activity but possesses potent angiogenic and wound-healing properties [1]. This demonstrates that the ecological features of the habitat directly shape the functional profile of skin peptides.

In contrast, skin secretions from the order Urodela (salamanders and newts) and the order Gymnophiona (caecilians) remain far less explored. At the time of the review’s publication, not a single wound-healing peptide had been described from the Gymnophiona order, highlighting a vast, untapped chemical reservoir.

From peptidomics to in vivo testing

The discovery of amphibian peptides typically follows a standardized workflow:

1. Secretory Collection: Secretions are stimulated via mild electrostimulation, massage, or UVB exposure.
2. Initial Processing: Samples are immediately transferred to acidic or protease-inhibitor solutions to preserve peptide structure, followed by centrifugation, desalination, and lyophilization.
3. Peptidomic and Proteomic Analysis: The complex mixture is separated using Reverse-Phase High-Performance Liquid Chromatography (RP-HPLC) and analyzed via tandem mass spectrometry to determine molecular weights and fragmentation patterns.
4. Sequence Identification: De novo sequencing combined with transcriptomic analysis of the skin glands ensures accurate identification and helps uncover new peptide families [1].
5. Functional Screening: Identified candidates undergo in vitro testing, including cell migration (scratch assays) on HaCaT keratinocytes and HSF fibroblasts, proliferation assays, and tube formation in HUVEC endothelial cultures.
6. Safety and Selectivity: Counter-screening for hemolysis and cytotoxicity is mandatory to filter out candidates with unacceptable therapeutic indices [1].
7. In Vivo Validation: Promising peptides move into animal models, including full-thickness excision wounds, burn models, and diabetic models (chemical, genetic, or dietary), as well as infected wounds using pathogens like Staphylococcus aureus and Pseudomonas aeruginosa.
8. Standardization Efforts: Cross-study comparison remains difficult due to variations in experimental design, such as animal species, wound size, and dosing regimens. Establishing standardized protocols is a top priority for the field.

Peptides and their targets: functional classification

Amphibian peptides are multifunctional, often influencing several regenerative processes simultaneously.

• Antimicrobial and anti-inflammatory peptides

MSI-1 (derived from magainin-2) and Pse-T2 (a truncated pseudin-2 analog) disrupt bacterial membranes while suppressing pro-inflammatory cytokines such as TNF-α, IL-6, and IL-1β. In infected burn models, MSI-1 has been shown to reduce sub-eschar bacterial colonization and improve survival rates [1].

• Pro-regenerative and immunomodulatory peptides

Andersonin-W1 (AW1) from Odorrana andersonii targets the TLR4 protein, balancing the initial inflammatory response before preventing excessive chronic inflammation. It also promotes skin cell migration and angiogenesis.

Similarly, the peptide FZ1 acts as an integrin αvβ3 agonist, facilitating tissue repair and vascularization.

• Antioxidant peptides

Antioxidin-RL from Odorrana livida inhibits the formation of reactive oxygen species (ROS), protecting cells from oxidative damage while supporting collagen type I synthesis.

TAT-conjugated UIFSPs from Pelophylax nigromaculatus have shown success in protecting the skin from UVB-induced damage by modulating stress-response pathways [1].

• Radioprotective peptides

RIFSP-2 protects cells from ionizing radiation by targeting the SCD1 enzyme, which in turn suppresses the STING protein—a key driver of radiation-induced inflammation. This mechanism helps tissues recover faster after exposure [1].

• Scar-reducing peptides

OA-GL21 from Odorrana andersonii has demonstrated the ability to accelerate healing without significant scar formation in preliminary studies, though further rigorous validation is required [1].

Structural and physicochemical hallmarks

Most of the studied molecules carry a net positive charge and possess amphipathic properties, meaning they contain both hydrophilic (water-attracting) and hydrophobic (fat-attracting) regions. This allows them to interact effectively with both microbial membranes and human skin cells. Notably, some peptides feature a specific cyclic structure known as the "Rana box". This structural motif significantly enhances the molecule's stability by protecting it against proteolytic degradation by enzymes typically present in the wound bed.

The road to the clinic: barriers and strategies

Despite impressive laboratory results, the gap between bench and bedside remains wide. Of the 188 patents involving anuran antimicrobial peptides, only six explicitly claimed wound-healing activity, and four of those have already expired [1]. Currently, only one amphibian-derived candidate—the PD-DP-008 (JIJ02) gel for acne treatment—has reached Phase I clinical trials.

The primary obstacles include peptide instability in the wound environment, where they are prone to enzymatic degradation and sensitive to pH or temperature fluctuations. Furthermore, some peptides may be cytotoxic to human cells. To overcome these barriers, researchers are employing structural modifications, such as cyclization (e.g., the "Rana box" motif), D-amino acid substitution, and PEGylation. The cyclic analog CyRL-QN15, for instance, shows significantly higher proteolytic stability than its linear counterpart [1, 5].

Advanced delivery systems, such as integration into hydrogels, nanofibers, and nanoparticles, are also being developed to protect the peptides and ensure sustained release. Coupled with AI-assisted sequence design and high-throughput virtual screening, these strategies aim to transform amphibian peptides into a new generation of reliable, multifunctional wound-healing therapeutics.

References

1. Deng C.-J., Wang Y., Yang X.-W. Amphibian-derived peptides as novel therapeutics for skin wound healing: mechanisms, applications, and challenges. Zool Res 2026; 47(3): 727–747.
2. Xu X., Lai R. The chemistry and biological activities of peptides from amphibian skin secretions. Chem Rev 2015; 115(4): 1760–1846.
3. Mangoni M.L., McDermott A.M., Zasloff M. Antimicrobial peptides and wound healing: biological and therapeutic considerations. Exp Dermatol 2016; 25(3): 167–173.
4. Fan X.Y., Ye J.H., Zhong W.L. et al. The promoting effect of animal bioactive proteins and peptide components on wound healing: a review. Int J Mol Sci 2024; 25(23): 12561.
5. Muttenthaler M., King G.F., Adams D.J. et al. Trends in peptide drug discovery. Nat Rev Drug Discov 2021;  20(4): 309–325.