Natural Amphibian-Derived Host Defense Peptides: Peptide Immunomodulators with Potential Therapeutic Value.

Due to the rapid evolution of bacterial drug resistance, anti-infective treatment has become a global problem. Therefore, there is an urgent need to develop alternative treatment strategies. Host defense peptides (HDPs) are important components of the natural immune system and are widely distributed in the animal and plant kingdoms. Amphibians, especially their skin, provide a rich source of natural HDPs encoded by genes. These HDPs exhibit not only broad-spectrum antimicrobial activity but also a wide range of immunoregulatory characteristics, including modulation of antiinflammatory and proinflammatory reactions, regulation of specific cellular functions, enhancement of immune chemotaxis, regulation of adaptive immunity, and promotion of wound healing. They also show potent therapeutic effects on infectious and inflammatory diseases caused by pathogenic microorganisms. Thus, in the current review, we summarize the extensive immunomodulatory functions of natural amphibian HDPs, as well as the challenges of clinical development and potential solutions, which have important implications for the development of new anti-infective drugs.

Cathelicidin-NV from Nanorana ventripunctata effectively protects HaCaT cells, ameliorating ultraviolet B-induced skin photoaging.

Cathelicidins are diverse effector molecules in the vertebrate immune system and are related to immune regulation, inflammatory response, wound healing, and blood vessel formation. However, little is known about their free radical scavenging ability, especially in vivo. In this study, a cathelicidin molecule (cathelicidin-NV, ARGKKECKDDRCRLLMKRGSFSYV) previously identified from the spot-bellied plateau frog (Nanorana ventripunctata) (Anura, Dicroglossidae, Dicroglossinae) by us was shown to alleviate ultraviolet B (UVB)-induced skin photoaging in mice. Cathelicidin-NV effectively suppressed cytotoxicity, DNA fragmentation, apoptosis and reduced the protein expression levels of JNK, c-Jun, and MMP-1, which are involved in the regulation of collagen degradation in HaCaT cells induced by UVB irradiation. Furthermore, cathelicidin-NV also scavenged UVB-induced intracellular reactive oxygen species (ROS). Taken together, cathelicidin-NV directly scavenged excessive intracellular ROS to protect HaCaT cells, and subsequently alleviated UVB-induced skin photoaging. This study extends reports on the antioxidant function of the cathelicidin family. In addition, the properties of cathelicidin-NV make it an excellent candidate for the prevention and treatment of UV-induced skin photoaging.

Discovery of Antioxidant Peptides from Amphibians: A Review.

In recent years, bioactive peptide drugs have attracted growing attention due to the increasing difficulty in developing new drugs with novel chemical structures. In addition, many diseases are linked to excessive oxidation in the human body. Therefore, the role of peptides with antioxidant activity in counteracting diseases related to oxidative stress is worth exploring. Amphibians are a major repository for bioactive peptides that protect the skin from biotic and abiotic stresses, such as microbial infection and radiation injury. We characterized the first amphibian- derived gene-encoded antioxidant peptides in 2008. Since then, a variety of antioxidant peptides have been detected in different amphibian species. In this work, the physicochemical properties of antioxidant peptides identified from amphibians are reviewed for the first time, particularly acquisition methods, amino acid characteristics, antioxidant mechanisms, and application prospects. This review should provide a reference for advancing the identification, structural analysis, and potential therapeutic value of natural antioxidant peptides.

A Frog Peptide Ameliorates Skin Photoaging Through Scavenging Reactive Oxygen Species.

Although many bioactive peptides have been identified from the frog skins, their protective effects and the molecular mechanisms against skin photodamage are still poorly understood. In this study, a novel 20-residue peptide (antioxidin-NV, GWANTLKNVAGGLCKMTGAA) was characterized from the skin of plateau frog Nanorana ventripunctata. Antioxidin-NV obviously decreased skin erythema, thickness and wrinkle formation induced by Ultraviolet (UV) B exposure in hairless mice. In UVB-irradiated keratinocytes (HaCaT cells) and hairless mice, it effectively inhibited DNA damage through reducing p-Histone H2A.X (γH2AX) expression, alleviated cell apoptosis by decreasing the expression of apoptosis-specific protein (cleaved caspase 3), and reduced interleukin-6 (IL-6) production via blocking UVB-activated Toll-like receptor 4 (TLR4)/p38/JNK/NF-κB signaling. In UVB-irradiated human skin fibroblasts (HSF cells) and hairless mice, it effectively restored HSF cells survival rate, and rescued α-SMA accumulation and collagen (especially type I collagen) production by restoring transforming growth factor-ß1 (TGF-ß1)/Smad2 signaling. We found that antioxidin-NV directly and rapidly scavenged intracellular and mitochondrial ROS in HaCaT cells upon UVB irradiation, and quickly eliminated the artificial free radicals, 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+). Taken together, antioxidin-NV directly and rapidly scavenged excessive ROS upon UVB irradiation, subsequently alleviated UVB-induced DNA damage, cell apoptosis, and inflammatory response, thus protecting against UVB-induced skin photoaging. These properties makes antioxidin-NV an excellent candidate for the development of novel anti-photoaging agent.

Alpinia oxyphylla Miq. Extract Prevents Diabetes in Mice by Modulating Gut Microbiota.

Recently, the role of gut microbiota in the development of obesity and type 2 diabetes mellitus (T2DM) has been highlighted. We performed an 8-week administration protocol on T2DM (C57BL/6J db-/db-) mice and fecal samples were collected. Comparisons of fecal bacterial communities were performed between db-/db- mice and normal mice (DB/DB) and between the db-/db mice treated and untreated with AOE using next-generation sequencing technology. Our results showed that the db-/db-AOE group had improved glycemic control and renal function compared with the db-/db-H2O group. Compared with the db-/db-H2O group, AOE administration resulted in significantly increased ratio of Bacteroidetes-to-Firmicutes in db-/db- mice. In addition, the abundance of Akkermansia was significantly increased, while Helicobacter was significantly suppressed in the db-/db-AOE group compared with the db-/db-H2O group. Our data suggest that AOE treatment decreased blood glucose levels and significantly reduced damage of renal pathology in the T2DM mice by modulating gut microbiota composition.