Structure and function of a novel antioxidant peptide from the skin of tropical frogs

Enhancing Antimicrobial Peptides from Frog Skin: A Rational Approach

Antimicrobial resistance is a global health threat, which has been worsened by the slow development of new antibiotics. The rational design of natural-derived antimicrobial peptides (AMPs) offers a promising alternative for enhancing the efficacy of AMPs and accelerating drug discovery. This paper describes the rational design of improved peptide derivatives starting from hylin-Pul3, a peptide previously isolated from the frog Boana pulchella, by optimizing its hydrophobicity, cationicity, and amphipathicity. In silico screening identified six promising candidates: dHP3-31, dHP3-50, dHP3-50.137, dHP3-50.190, dHP3-84, and dHP3-84.39. These derivatives exhibited enhanced activity against Gram-negative bacteria, emphasizing the role of cationicity and the strategic arginine incorporation. Hemolytic assays revealed the derivatives' improved selectivity, particularly for the derivatives with "imperfect amphipathicity". In fibroblast assays, dHP3-84 was well-tolerated, while dHP3-84.39 promoted cell proliferation. Antioxidant assays (ABTS assays) highlighted the Trp-containing derivatives' (dHP3-50.137, dHP3-31) significant activity. The lipid membrane interaction studies showed that hylin-Pul3 disrupts membranes directly, while dHP3-84.39, dHP3-50, and dHP3-50.137 promote vesicle aggregation. Conversely, dHP3-84 did not induce membrane disruption or aggregation, suggesting an intracellular mode of action. Machine learning models were effective in predicting bioactivity, as these predicted AMPs showed enhanced selectivity and potency. Among them, dHP3-84 demonstrated broad-spectrum potential. These findings highlight the value of rational design, in silico screening, and structure-activity studies in optimizing AMPs for therapeutic applications.

The combination of RL-QN15 and OH-CATH30 promotes the repair of acne via the TLR2/NF-κB pathway

Acne is a prevalent and chronic inflammatory skin disease, and its treatment remains a huge clinical challenge. In the present study, we evaluated the therapeutic potential of combining the peptides RL-QN15 and OH-CATH30 for the treatment of acne in mice. Results indicated that the topical application of RL-QN15 and OH-CATH30 significantly inhibited the proliferation of Propionibacterium acnes (P. acnes) and alleviated acne-induced edema. Furthermore, the combined treatment suppressed the overexpression of proinflammatory cytokines induced by P. acnes, including interleukin -1 beta (IL-1β), interleukin -6 (IL-6), interleukin -8 (IL-8), tumor necrosis factor-alpha (TNF-α) induced by P. acnes and facilitated collagen deposition, thereby effectively mitigating skin damage associated with acne. Mechanistically, the combination of RL-QN15 and OH-CATH30 inhibited the expression of toll-like receptor 2 (TLR2) and activation nuclear factor kappa-B (NF-κB) signaling pathway (phosphorylation of P65 and IκB) in both mice and RAW 264.7 cells. These results suggested that this combination may inhibit the excretion of inflammatory factors and facilitate the collagen deposition by TLR2/NF-κB signaling. Overall, our study demonstrates the potent therapeutic effects of the combined application of RL-QN15 and OH-CATH30, highlights the TLR2/NF-κB pathway as a key target in acne treatment, and provides a novel strategy for developing innovative acne therapeutics.

Novel tryptophyllin peptides from Physalaemus centralis inhibit oxidative stress-induced endothelial dysfunction in rat aorta preparation

Amphibian skin is a rich source of molecules with biotechnological potential, including the tryptophyllin family of peptides. Here, we report the identification and characterization of two tryptophyllin peptides, FPPEWISR and FPWLLS-NH2, from the skin of the Central Dwarf Frog, Physalaemus centralis. These peptides were identified through cDNA cloning and sequence comparison. FPWLLS-NH2 shares its primary structure with a previously identified peptide from the skin of Pelophylax perezi, named PpT-2. Another peptide, FPPEWISR, is novel and was named PcT-1. After solid-phase peptide synthesis, both peptides exhibited significant antioxidant activity, with PcT-1 and PpT-2 demonstrating ABTS radical scavenging capacities of 0.305 and 0.269 mg Trolox equivalents/mg peptide, respectively, and ORAC values of 0.319 and 0.248 mg Trolox equivalents/mg peptide. Additionally, PcT-1 and PpT-2 inhibited AAPH-induced hemolysis in human red blood cells, achieving a protection level comparable to Trolox at 0.2 mg/mL. In rat aorta preparations, both peptides partially restored acetylcholine-induced vasorelaxation following pyrogallol-induced oxidative stress, with a greater protective effect of PpT-2. Hemolytic activity assay indicated no cytotoxicity in human red blood cells, and tests on Galleria mellonella larvae confirmed their low toxicity in vivo. These findings highlight the biotechnological potential of PcT-1 and PpT-2 as antioxidant agents, paving the way for new therapeutic applications in combating oxidative stress-related diseases.

Reactivity of amino acids and short peptide sequences: identifying bioactive compounds via DFT calculations

Bioactive peptides are short amino acid sequences that play important roles in various physiological processes, including antioxidant and protective effects. These compounds can be obtained through protein hydrolysis and have a wide range of potential applications in a variety of areas. However, despite the potential of these compounds, more in-depth knowledge is still necessary to better understand details regarding their chemical reactivity and electronic properties. In this study, we used molecular modeling techniques to investigate the electronic structure of isolated amino acids (AA) and short peptide sequences. Details on the relative alignments between the frontier electronic levels, local chemical reactivity and donor-acceptor properties of the 20 primary amino acids and some di- and tripeptides were evaluated in the framework of the density functional theory (DFT). Our results suggest that the electronic properties of isolated amino acids can be used to interpret the reactivity of short sequences. We found that aromatic and charged amino acids, as well as Methionine, play a key role in determining the local reactivity of peptides, in agreement with experimental data. Our analyses also allowed us to identify the influence of the relative position of AA and terminations on the local reactivity of the sequences, which can guide experimental studies and help to propose/evaluate possible mechanisms of action. In summary, our data indicate that the position of active sites of polypeptides can be predicted from short sequences, providing a promising strategy for the synthesis and bioprospection of new optimized compounds.

Exploration of antioxidant peptides from crocodile (Crocodylus siamensis) meat using modern information technology: Virtual-screening and antioxidant mechanisms

To develop a safe, stable and easily absorbed new antioxidant peptide. The myofibrillar protein hydrolysates of Siamese crocodile meat were prepared and purified, their free radical scavenging and Fe2+ chelating ability were determined. The results showed that isolated component 3 of neutral protease hydrolysate (N3) had the highest antioxidant activity. Subsequently, liquid chromatography-mass spectrometry was applied to appraise the amino acid sequences within the N3 component, and 8 novel antioxidant peptides were screened by bioinformatics analysis, the antioxidant test proved that all 8 synthetic peptides had certain antioxidant activity. Among them, there was no significant difference in the DPPH radical scavenging capacity of GWDK, LWDK, ERWP, LGWK and LWAK (P > 0.05), which were higher than that of DFRDY and WYRDD (P < 0.05), the ABTS radical scavenging ability of DFRDY was similar to WYRDD (P > 0.05), but remarkably stronger than that of the other 6 peptides (P < 0.05). Finally, the binding mechanism of 8 novel peptides to Keap1 protein was explored through molecular docking, and it was found that hydrogen bonding and hydrophobic interaction were the primary forces that bind antioxidant peptides to Keap1 protein.

The Role of Amphibian AMPs Against Oxidative Stress and Related Diseases

Amphibians use their skin as an effective defense mechanism against predators and microorganisms. Specialized glands produce antimicrobial peptides (AMPs) that possess antioxidant properties, effectively reducing reactive oxygen species (ROS) levels. These peptides are promising candidates for treating diseases associated with oxidative stress (OS) and redox imbalance, including neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS), as well as age-related conditions, like cardiovascular diseases and cancer. This review highlights the multifaceted roles of AMPs and antioxidant peptides (AOPs) in amphibians, emphasizing their protective capabilities against oxidative damage. They scavenge ROS, activate antioxidant enzyme systems, and inhibit cellular damage. AOPs often share structural characteristics with AMPs, suggesting a potential evolutionary connection and similar biosynthetic pathways. Peptides such as brevinin-1FL and Cath-KP demonstrate neuroprotective effects, indicating their therapeutic potential in managing oxidative stress-related diseases. The antioxidant properties of amphibian-derived peptides pave the way for novel therapeutic developments. However, a deeper understanding of the molecular mechanisms underlying these peptides and their interactions with oxidative stress is essential to addressing ROS-related diseases and advancing therapeutic strategies in clinical practice.

Skin secretions of Leptodactylidae (Anura) and their potential applications

The skin of anuran species is a protective barrier against predators and pathogens, showing also chemical defense by substances that represent a potential source for bioactive substances. This review describes the current chemical and biological knowledge from the skin secretions of Leptodactylidae species, one of the most diverse neotropical frog families. These skin secretions reveal a variety of substances such as amines (12), neuropeptides (16), and antimicrobial peptides (72). The amines include histamine and its methylated derivatives, tryptamine derivatives and quaternary amines. The peptides of Leptodactylidae species show molecular weight up to 3364 Da and ocellatins are the most reported. The peptides exhibit commonly glycine (G) or glycine-valine (GV) as C-terminal amino acids, and the most common N-terminal amino acids are glutamic acid (E), lysine (K), and valine (V). The substances from Leptodactylidae species have been evaluated against pathogenic microorganisms, particularly Escherichia coli and Staphylococcus aureus, and the most active peptides showed MIC of 1-15 µM. Furthermore, some compounds showed also pharmacological properties such as immunomodulation, treatment of degenerative diseases, anticancer, and antioxidant. Currently, only 9% of the species in this family have been properly studied, highlighting a large number of unstudied species such as an entire subfamily (Paratelmatobiinae). The ecological context, functions, and evolution of peptides and amines in this family are poorly understood and represent a large field for further exploration.

Antioxidant peptides, the guardian of life from oxidative stress

Reactive oxygen species (ROS) are produced during oxidative metabolism in aerobic organisms. Under normal conditions, ROS production and elimination are in a relatively balanced state. However, under internal or external environmental stress, such as high glucose levels or UV radiation, ROS production can increase significantly, leading to oxidative stress. Excess ROS production not only damages biomolecules but is also closely associated with the pathogenesis of many diseases, such as skin photoaging, diabetes, and cancer. Antioxidant peptides (AOPs) are naturally occurring or artificially designed peptides that can reduce the levels of ROS and other pro-oxidants, thus showing great potential in the treatment of oxidative stress-related diseases. In this review, we discussed ROS production and its role in inducing oxidative stress-related diseases in humans. Additionally, we discussed the sources, mechanism of action, and evaluation methods of AOPs and provided directions for future studies on AOPs.

Food-derived Peptides as Promising Neuroprotective Agents: Mechanism and Therapeutic Potential

Many food-derived peptides have the potential to improve brain health and slow down neurodegeneration. Peptides are produced by the enzymatic hydrolysis of proteins from different food sources. These peptides have been shown to be involved in antioxidant and anti-inflammatory activity, neuro-transmission modulation, and gene expression regulation. Although few peptides directly affect chromatin remodeling and histone alterations, others indirectly affect the neuroprotection process by interfering with epigenetic changes. Fish-derived peptides have shown neuroprotective properties that reduce oxidative stress and improve motor dysfunction in Parkinson's disease models. Peptides from milk and eggs have been found to have anti-inflammatory properties that reduce inflammation and improve cognitive function in Alzheimer's disease models. These peptides are potential therapeutics for neurodegenerative diseases, but more study is required to assess their efficacy and the underlying neuroprotective benefits. Consequently, this review concentrated on each mechanism of action used by food-derived peptides that have neuroprotective advantages and applications in treating neurodegenerative diseases. This article highlights various pathways, such as inflammatory pathways, major oxidant pathways, apoptotic pathways, neurotransmitter modulation, and gene regulation through which food-derived peptides interact at the cellular level.

Effect of sublethal concentrations of glyphosate-based herbicides (Roundup Active®) on skin of the tropical frog (Dendropsophus molitor)

In Colombia, glyphosate (GP) is used to control weeds, with Roundup Active® being the most widely used. This use has affected aquatic ecosystems, causing malformations in amphibians. The Savannah frog (D. molitor) is a tropical frog inhabiting the mountain of Colombia. In the present study, we determined the effect of sublethal concentrations of GP (Roundup Active®) on the skin of D. molitor. Twenty-four tadpoles were exposed to concentrations of GP (T1: 0, T2: 1.4, T3: 3.6, and T4: 5.6 a.e mg/L) during 31 days. In 10 individuals per treatment, two skin regions were evaluated: dorsal cranial and caudal ventral to determine histopathological alterations. Morphometric analysis of the layers of the skin was performed: epidermis, dermis, and hypodermis-muscular. T1 did not present histopathological alterations. Since T2 was identified, glandular cell hyperplasia and hypertrophy increased melanophores and melanin accumulations in the highest concentrations of GP. The ultrastructure revealed an increase in excretory glands in the dermis. In the other layers, an increase of melanophores and melanocyte clusters was observed accompanied by vacuolization of basal cells. The morphometry showed an increase in the thickness of the dermis in the dorso-cranial region in T2 compared to the other treatments, while the ventral caudal region exhibited a variation in the thickness of the dermis from T2 and a decrease in T4. Despite evaluating sublethal concentrations, the skin of D. molitor tadpoles presents histopathological, ultrastructural, and morphometric alterations that could affect the survival of the species in the natural environment.

Potential of omega-3 and conjugated fatty acids to control microglia inflammatory imbalance elicited by obesogenic nutrients

High-fat diet-induced obesity detrimentally affects brain function by inducing chronic low-grade inflammation. This neuroinflammation is, at least in part, likely to be mediated by microglia, which are the main immune cell population in the brain. Microglia express a wide range of lipid-sensitive receptors and their activity can be modulated by fatty acids that cross the blood-brain barrier. Here, by combining live cell imaging and FRET technology we assessed how different fatty acids modulate microglia activity. We demonstrate that the combined action of fructose and palmitic acid induce Ikβα degradation and nuclear translocation of the p65 subunit nuclear factor kB (NF-κB) in HCM3 human microglia. Such obesogenic nutrients also lead to reactive oxygen species production and LynSrc activation (critical regulators of microglia inflammation). Importantly, short-time exposure to omega-3 (EPA and DHA), CLA and CLNA are sufficient to abolish NF-κB pathway activation, suggesting a potential neuroprotective role. Omega-3 and CLA also show an antioxidant potential by inhibiting reactive oxygen species production, and the activation of LynSrc in microglia. Furthermore, using chemical agonists (TUG-891) and antagonists (AH7614) of GPR120/FFA4, we demonstrated that omega-3, CLA and CLNA inhibition of the NF-κB pathway is mediated by this receptor, while omega-3 and CLA antioxidant potential occurs through different signaling mechanisms.

3D high-precision melt electro written polycaprolactone modified with yeast derived peptides for wound healing

In this study melt electro written (MEW) scaffolds of poly(ε-caprolactone) PCL are decorated with anti-inflammatory yeast-derived peptide for skin wound healing. Initially, 13 different yeast-derived peptides were screened and analyzed using both in vitro and in vivo assays. The MEW scaffolds are functionalized with the selected peptide VLSTSFPPW (VW-9) with the highest activity in reducing pro-inflammatory cytokines and stimulating fibroblast proliferation, migration, and collagen production. The peptide was conjugated to the MEW scaffolds using carbodiimide (CDI) and thiol chemistry, with and without plasma treatment, as well as by directly mixing the peptide with the polymer before printing. The MEW scaffolds modified using CDI and thiol chemistry with plasma treatment showed improved fibroblast and macrophage penetration and adhesion, as well as increased cell proliferation and superior anti-inflammatory properties, compared to the other groups. When applied to full-thickness excisional wounds in rats, the peptide-modified MEW scaffold significantly enhanced the healing process compared to controls (p < 0.05). This study provides proof of concept for using yeast-derived peptides to functionalize biomaterials for skin wound healing.

Commentary: On the merit of an early contributor of the "Preparation for Oxidative Stress" (POS) theory

This commentary acknowledges the contributions of the Ukrainian biologist, Dr. Volodymyr Lushchak, to the understanding of the physiological adaptive strategy called "Preparation for Oxidative Stress" (POS). In the 1990s, various studies revealed that activities of antioxidant enzymes rose in animals under hypometabolic conditions. These timely observations allowed scientists to propose that this increase could prepare animals for reoxygenation events following the release of oxygen restriction, but in doing so, would trigger oxidative damage, hence the use of the term "preparation". Over next 25 years, the phenomenon was described in detail in more than one hundred studies of animals under conditions of aestivation, hypoxia/anoxia, freezing, severe dehydration, ultraviolet exposure, air exposure of water-breathing animals, salinity stress, and others. The POS phenomenon remained without a mechanistic explanation until 2013, when it was proposed that a small increase in oxyradical formation during hypoxia exposure (in hypoxia-tolerant animals) could activate redox-sensitive transcription factors that, in turn, would initiate transcription and translation of antioxidant enzymes. Dr. Lushchak, who studied goldfish under severe hypoxia in the 1990s, had actually proposed the increased production of oxyradicals under this condition and concluded that it would lead to an upregulation of antioxidant enzymes, the hallmark of the POS strategy. However, his research partner at the time, Dr. Hermes-Lima, thought the idea did not have sufficient evidence to support it and recommended the removal of this explanation. In those days, the main line of thinking was that increased oxyradical formation under hypoxia was "impossible". So, as it turns out, the ideas of Dr. Lushchak were well ahead of his time. It then took >10 years before the biochemical and molecular mechanisms responsible for triggering the POS response were clarified. In the present article, this fascinating history is described to highlight Dr. Lushchak's contributions and insights about the POS theory.

Comparative in silico and in vitro study of the stability and biological activity of an octapeptide from microalgae Isochrysis zhanjiangensis and its truncated short peptide

In this study, the structural characteristics and active sites of the octapeptide (IIAVEAGC), the pentapeptide (IIAVE) and tripeptide (AGC) were studied in silica and in vitro.

Antioxidant and Neuroprotective Effects of the First Tryptophyllin Found in Snake Venom (Bothrops moojeni)

In this study, we report the isolation, characterization, and synthesis of the peptide BmT-2 belonging to the tryptophyllins family, isolated from the venom of the snake Bothrops moojeni. This is the first time a tryptophyllin is identified in snake venom. We tested whether BmT-2 had cytotoxic effects and antioxidant activity in a set of experiments that included both in vitro and cell-based assays. BmT-2 presented a radical scavenging activity toward ABTS^• and AAPH-derived radicals. BmT-2 protected fluorescein, DNA molecules, and human red blood cells (RBCs) from free radicals generated by the thermal decomposition of AAPH. The novel tryptophyllin was not toxic in cell viability tests, where it (up to 0.4 mg/mL) did not cause hemolysis of human RBCs and did not cause significant loss of cell viability, showing a CC₅₀ > 1.5 mM for cytotoxic effects against SK-N-BE(2) neuroblastoma cells. BmT-2 prevented the arsenite-induced upregulation of Nrf2 in Neuro-2a neuroblasts and the phorbol myristate acetate-induced overgeneration of reactive oxygen species and reactive nitrogen species in SK-N-BE(2) neuroblastoma cells. Electronic structure calculations and full atomistic reactive molecular dynamics simulations revealed the relevant contribution of aromatic residues in BmT-2 to its antioxidant properties. Our study presents a novel peptide classified into the family of the tryptophyllins, which has been reported exclusively in amphibians. Despite the promising results on its antioxidant activity and low cytotoxicity, the mechanisms of action of BmT-2 still need to be further elucidated.

Pervaporation Membranes for Seawater Desalination Based on Geo-rGO-TiO2 Nanocomposites: Part 2-Membranes Performances

This is part 2 of the research on pervaporation membranes for seawater desalination based on Geo-rGO-TiO₂ nanocomposite. The quality of the Geo-rGO-TiO₂ pervaporation membranes (PV), as well as the suitability of the built pervaporation system, is thoroughly discussed. The four membranes described in detail in the first article were tested for their capabilities using the parameters turbidity, salinity, total suspended solids (TSS), and electrical conductivity (EC). The membranes' flux permeate was measured as a function of temperature, and salt rejection was calculated using the electrical conductivity values of the feed and permeate. Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) techniques were used to investigate changes in the chemical composition and internal structure of the membranes after use in pervaporation systems. The morphology of the membrane's surfaces was examined by means of scanning electron microscopy (SEM), and the elemental distribution was observed by using X-ray mapping and energy dispersive spectroscopy (EDS). The results showed that the pervaporation membrane of Geo-rGO-TiO₂ (1, 3) achieved a permeate flux as high as 2.29 kg/m²·h with a salt rejection of around 91%. The results of the FTIR and XRD measurements did not show any changes in the functional group and chemical compositions of the membrane after the pervaporation process took place. Long-term pressure and temperature feed cause significant cracking in geopolymer and Geo-TiO₂ (3) membranes. SEM results revealed that the surface of all membranes is leached out, and elemental distribution based on X-ray mapping and EDS observations revealed the addition of Na+ ions on the membrane surface. The study's findings pave the way for more research and development of geopolymers as the basic material for inorganic membranes, particularly with the addition of rGO-TiO₂ nanocomposites.

Multiple Mechanistic Action of Brevinin-1FL Peptide against Oxidative Stress Effects in an Acute Inflammatory Model of Carrageenan-Induced Damage

Amphibian skin is acknowledged to contain an antioxidant system composed of various gene-encoded antioxidant peptides, which exert significant effects on host defense. Nevertheless, recognition of such peptides is in its infancy so far. Here, we reported the antioxidant properties and underlying mechanism of a new antioxidant peptide, brevinin-1FL, identified from Fejervarya limnocharis frog skin. The cDNA sequence encoding brevinin-1FL was successfully cloned from the total cDNA of F. limnocharis and showed to contain 222 bp. The deduced mature peptide sequence of brevinin-1FL was FWERCSRWLLN. Functional analysis revealed that brevinin-1FL could concentration-dependently scavenge ABTS⁺, DPPH, NO, and hydroxyl radicals and alleviate iron oxidation. Besides, brevinin-1FL was found to show neuroprotective activity by reducing contents of MDA and ROS plus mitochondrial membrane potential, increasing endogenous antioxidant enzyme activity, and suppressing H₂O₂-induced death, apoptosis, and cycle arrest in PC12 cells which were associated with its regulation of AKT/MAPK/NF-κB signal pathways. Moreover, brevinin-1FL relieved paw edema, decreased the levels of TNF-α, IL-1β, IL-6, MPO, and malondialdehyde (MDA), and restored catalase (CAT) and superoxide dismutase (SOD) activity plus glutathione (GSH) contents in the mouse injected by carrageenan. Together, these findings indicate that brevinin-1FL as an antioxidant has potent therapeutic potential for the diseases induced by oxidative damage. Meanwhile, this study will help us further comprehend the biological functions of amphibian skin and the mechanism by which antioxidants protect cells from oxidative stress.

Isolation and identification of antioxidative peptides from crocodile meat hydrolysates using silica gel chromatography

Crocodiles are cultured in large numbers in Asia and other places in order to protect wild resources and meet the needs of human life. In this study, crocodile (Crocodylus siamensis) meat proteins were extracted and hydrolyzed into peptides, their antioxidant peptides were isolated and purified by silica gel chromatography and identified by LC/MS. Crocodile meat proteins were optimally extracted with water and hydrolyzed by papain based on the degree of hydrolysis and antioxidant activity. The hydrolysates were fractionated by ultrafiltration into 3 kDa, 3–30 kDa, and ≥ 30 kDa fractions. The 3 kDa fraction showed most antioxidant activity of the hydrolysates. Its active peptides were separated by silica gel column chromatography and purified by silica gel TLC, based on TLC bio-autographic assays of the activity. Four highly active peptides were identified by LC/MS as SSLTIQFVEGQFVDSYDPTIENTFTK, VPPHIY, VAPEEHPVLLTEAPLNPK, and RNGLPGPIGPAG. The identified peptides were synthesized and showed 50% free radical scavenging activities at 1.0 mg/mL, equal or higher to ascorbic acid at 0.5 mg/mL, in both DPPH and ABTS assays. The results indicated that the 3 kDa hydrolyzed peptides of crocodile meat had high antioxidant activity and the active peptides can be effectively separated and purified by silica gel column chromatography and TLC.

A new peptide originated from amphibian skin alleviates the ultraviolet B-induced skin photodamage

Although amphibian-derived bioactive peptides have attracted increasing attention for their potential use in the treatment of photodamage, research is still in its infancy. In this study, we obtained a new antioxidant peptide, named OA-GI13 (GIWAPWPPRAGLC), from the skin of the odorous frog Odorrana andersonii and determined its effects on ultraviolet B (UVB)-induced skin photodamage as well as its possible molecular mechanisms. Results showed that OA-GI13 directly scavenged free radicals, maintained the viability of hydrogen peroxide-challenged keratinocytes, promoted the release of superoxide dismutase, catalase, and glutathione, and reduced the level of lactate dehydrogenase. Furthermore, topical application of OA-GI13 in mice alleviated dorsal skin erythema and edema and protected the skin against UVB irradiation by increasing antioxidant levels and decreasing peroxide, malondialdehyde, and 8-hydroxydeoxyguanosine levels. OA-GI13 also alleviated oxidative stress injury in vivo and in vitro, possibly by inhibiting p38 protein phosphorylation. Our study confirmed the anti-photodamage effects of this novel amphibian-derived peptide, thus providing a new molecule for the development of drugs and topical agents for the treatment of skin photodamage.

Neuroprotective effects on microglia and insights into the structure-activity relationship of an antioxidant peptide isolated from Pelophylax perezi

Tryptophyllins constitute a heterogeneous group of peptides that are one of the first classes of peptides identified from amphibian’s skin secretions. Here, we report the structural characterization and antioxidant properties of a novel tryptophyllin‐like peptide, named PpT‐2, isolated from the Iberian green frog Pelophylax perezi. The skin secretion of P. perezi was obtained by electrical stimulation and fractionated using RP‐HPLC. De novo peptide sequencing was conducted using MALDI MS/MS. The primary structure of PpT‐2 (FPWLLS‐NH₂) was confirmed by Edman degradation and subsequently investigated using in silico tools. PpT‐2 shared physicochemical properties with other well‐known antioxidants. To test PpT‐2 for antioxidant activity in vitro, the peptide was synthesized by solid phase and assessed in the chemical‐based ABTS and DPPH scavenging assays. Then, a flow cytometry experiment was conducted to assess PpT‐2 antioxidant activity in oxidatively challenged murine microglial cells. As predicted by the in silico analyses, PpT‐2 scavenged free radicals in vitro and suppressed the generation of reactive species in PMA‐stimulated BV‐2 microglia cells. We further explored possible bioactivities of PpT‐2 against prostate cancer cells and bacteria, against which the peptide exerted a moderate antiproliferative effect and negligible antimicrobial activity. The biocompatibility of PpT‐2 was evaluated in cytotoxicity assays and in vivo toxicity with Galleria mellonella. No toxicity was detected in cells treated with up to 512 µg/ml and in G. mellonella treated with up to 40 mg/kg PpT‐2. This novel peptide, PpT‐2, stands as a promising peptide with potential therapeutic and biotechnological applications, mainly for the treatment/prevention of neurodegenerative disorders.

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-β1 (TGF-β1)/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.

Acetylated cashew gum and fucan for incorporation of lycopene rich extract from red guava (Psidium guajava L.) in nanostructured systems: Antioxidant and antitumor capacity

Industrial application of lycopene is limited due to its chemical instability and low bioavailability. This study proposes the development of fucan-coated acetylated cashew gum nanoparticles (NFGa) and acetylated cashew gum nanoparticles (NGa) for incorporation of the lycopene-rich extract from red guava (LEG). Size, polydispersity, zeta potential, nanoparticles concentration, encapsulation efficiency, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to characterize nanoparticles. The antioxidant activity was determinated and cell viability was evaluated in the human breast cancer cells (MCF-7) and human keratinocytes (HaCaT) by MTT assay. The toxic effect was evaluated by hemolysis test and by Galleria mellonella model. NFGa showed higher stability than NGa, having a size of 162.10 ± 3.21 nm, polydispersity of 0.348 ± 0.019, zeta potential -30.70 ± 0.53 mV, concentration of 6.4 × 10⁹ nanoparticles/mL and 60% LEG encapsulation. Microscopic analysis revealed a spherical and smooth shape of NFGa. NFGa showed antioxidant capacity by ABTS method and ORAC assay. The NFGa presented significant cytotoxicity against MCF-7 from the lowest concentration tested (6.25-200 μg/mL) and did not affect the cell viability of the HaCaT. NFGa showed non-toxic effect in the in vitro and in vivo models. Therefore, NFGa may have a promising application in LEG stabilization for antioxidant and antitumor purposes.

The peptide secreted at the water to land transition in a model amphibian has antioxidant effects

In addition to the morphophysiological changes experienced by amphibians during metamorphosis, they must also deal with a different set of environmental constraints when they shift from the water to the land. We found that Pithecopus azureus secretes a single peptide ([M + H]+ = 658.38 Da) at the developmental stage that precedes the onset of terrestrial behaviour. De novo peptide and cDNA sequencing revealed that the peptide, named PaT-2, is expressed in tandem and is a member of the tryptophyllins family. In silico studies allowed us to identify the position of reactive sites and infer possible antioxidant mechanisms of the compounds. Cell-based assays confirmed the predicted antioxidant activity in mammalian microglia and neuroblast cells. The potential neuroprotective effect of PaT-2 was further corroborated in FRET-based live cell imaging assays, where the peptide prevented lipopolysaccharide-induced ROS production and glutamate release in human microglia. In summary, PaT-2 is the first peptide expressed during the ontogeny of P. azureus, right before the metamorphosing froglet leaves the aquatic environment to occupy terrestrial habitats. The antioxidant activity of PaT-2, predicted by in silico analyses and confirmed by cell-based assays, might be relevant for the protection of the skin of P. azureus adults against increased O₂ levels and UV exposure on land compared with aquatic environments.

Study on the structure-activity relationship of watermelon seed antioxidant peptides by using molecular simulations

Our previous studies had shown that watermelon seed antioxidant peptides (WSAPs: P1-P5) possessed good activities. However, the structure-activity relationship of P1 is still unclear. Quantum chemistry and molecular docking were used to investigate the antioxidant mechanism of P1. The active site of P1 is located at C₆H₁₄ on Arg. P1 can bind to DPPH/ABTS through hydrogen bond and hydrophobic interaction. Compared with P2-P4, P1 has the strongest antioxidant capacity. The molecular simulation showed that P1 could enhance the stability of Keap1 by interacting with Asn382, Arg380 and Tyr 334 in the active sites. Compared with the model group, the expression of Keap1 was down-regulated (p < 0.05), while the expression of Nrf2 and HO-1 was up-regulated (p < 0.05) after P1 treatment. P1 has the potential ability to activate the signaling pathway Keap1-Nrf2 and improve the antioxidant defense system. This study provides a new perspective for the rational design and mechanism of antioxidant peptides.

A Review of Bioactive Peptides: Chemical Modification, Structural Characterization and Therapeutic Applications

In recent years, the development and applications of protein drugs have attracted extensive attention from researchers. However, the shortcomings of protein drugs also limit their further development. Therefore, bioactive peptides isolated or simulated from protein polymers have broad application prospects in food, medicine, biotechnology, and other industries. Such peptides have a molecular weight distribution between 180 and 1000 Da. As a small molecule substance, bioactive peptide is usually degraded by various enzymes in the organism and have a short half-life. At the same time, such substances have poor stability and are difficult to produce and store. Therefore, these active peptides may be modified through phosphorylation, glycosylation, and acylation. Compared with other protein drugs, the modified active peptides are more easily absorbed by the body, have longer half-life, stronger targeting, and fewer side effects in addition to higher bioavailability. In the light of their functions, bioactive peptide can be divided into antimicrobial, anti-tumour, anti-angiogenic, antioxidant, anti-fatigue, and anti-hypertensive peptides. This article mainly focuses on the introduction of several promising biologically active peptides functioning as antimicrobial, anti-tumour, antiangiogenic, and antioxidant peptides from the three aspects modification, structural characteristics and mechanism of action.

Antioxidant activities of major tryptophyllin L peptides: A joint investigation of Gaussian-based 3D-QSAR and radical scavenging experiments

The red tree frog Litoria rubella from Australia has been studied for several decades showing that their dorsal skin glands secrete a number of small peptides containing a Pro-Trp sequence, known as tryptophyllin L peptides. Although peptides from many genera of Australian frogs have been reported to possess a variety of biological activities, the bioactivities of this peptide family have remained to be discovered. In this study, we investigated the antioxidant potency of a number of tryptophyllin L peptides for the first time using a joint statistical and experimental approach in which predictions based on Gaussian three-dimensional quantitative structure-activity relationship (3D-QSAR) models were employed to guide an in vitro experimental investigation. Two tryptophyllin tripeptides P-W-L (OH) and P-W-L (NH₂ ) were predicted to have the Trolox equivalent antioxidant capacity (TEAC) values of 0.80 and 0.87 μM Trolox/μM peptide, respectively. With those promising results, antioxidant capabilities of five tryptophyllin L peptides with the common core Pro-Trp-Leu were synthesized and subjected to 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing ability of plasma (FRAP) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS˙⁺ ) radical scavenging assays. The tests indicated that all the tested tryptophyllin L peptides, noticeably S-P-W-L (OH) and F-P-W-L (NH₂ ), are strong ABTS˙⁺ radical scavengers and moderate scavengers in the other two assays. The results, thus, suggested that the tryptophyllin L peptides are likely to be a part of the skin antioxidant system helping the frog to cope with drastic change in oxygen exposure and humidity, as they inhabit over a large area of Australia with a wide climate variation.

Cardiovascular Active Peptides of Marine Origin with ACE Inhibitory Activities: Potential Role as Anti-Hypertensive Drugs and in Prevention of SARS-CoV-2 Infection

Growing interest in hypertension-one of the main factors characterizing the cardiometabolic syndrome (CMS)-and anti-hypertensive drugs raised from the emergence of a new coronavirus, SARS-CoV-2, responsible for the COVID19 pandemic. The virus SARS-CoV-2 employs the Angiotensin-converting enzyme 2 (ACE2), a component of the RAAS (Renin-Angiotensin-Aldosterone System) system, as a receptor for entry into the cells. Several classes of synthetic drugs are available for hypertension, rarely associated with severe or mild adverse effects. New natural compounds, such as peptides, might be useful to treat some hypertensive patients. The main feature of ACE inhibitory peptides is the location of the hydrophobic residue, usually Proline, at the C-terminus. Some already known bioactive peptides derived from marine resources have potential ACE inhibitory activity and can be considered therapeutic agents to treat hypertension. Peptides isolated from marine vertebrates, invertebrates, seaweeds, or sea microorganisms displayed important biological activities to treat hypertensive patients. Here, we reviewed the anti-hypertensive activities of bioactive molecules isolated/extracted from marine organisms and discussed the associated molecular mechanisms involved. We also examined ACE2 modulation in sight of SARS2-Cov infection prevention.

Isolation and Sequencing of Cu-, Fe-, and Zn-Binding Whey Peptides for Potential Neuroprotective Applications as Multitargeted Compounds

This study aims to isolate metal-binding peptides and synthesize promising amino acid sequences to potentially act as neuroprotective compounds in the future, targeting different mechanisms. Fractions of whey metal-binding peptides (Cu, Fe, and Zn) isolated by immobilized metal affinity chromatography showed different amino acid profiles according to the metal. The Cu-binding peptides presented roughly twofold increase in the in vitro antioxidant, as assessed by oxygen radical absorbance capacity and anticholinesterase activities over the hydrolysate. This is probably because of the higher concentration of aromatic and basic residues, the latter being crucial for binding to the anionic sites of acetylcholinesterase. Six peptide sequences were synthesized based on the metal-binding sites, molecular mass, hydrophobicity, and bioactivity probability. Among the synthetic peptides, the VF dipeptide stood out both for its in vitro antioxidant and anticholinesterase activities. This peptide, as well as the fraction of Cu-binding peptides, should be further studied because it may act through different mechanisms related to neurodegenerative diseases, in addition to the chelation of the excess of metals in the central nervous system.

Antimicrobial Property and Mode of Action of the Skin Peptides of the Sado Wrinkled Frog, Glandirana susurra, against Animal and Plant Pathogens

The Sado wrinkled frog Glandirana susurra has recently been classified as a new frog species endemic to Sado Island, Japan. In this study, we cloned 12 cDNAs encoding the biosynthetic precursors for brevinin-2SSa–2SSd, esculentin-2SSa, ranatuerin-2SSa, brevinin-1SSa–1SSd, granuliberin-SSa, and bradykinin-SSa from the skin of G. susurra. Among these antimicrobial peptides, we focused on brevinin-2SSb, ranatuerin-2SSa, and granuliberin-SSa, using their synthetic replicates to examine their activities against different reference strains of pathogenic microorganisms that infect animals and plants. In broth microdilution assays, brevinin-2SSb displayed antimicrobial activities against animal pathogens Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa, and Candida albicans and plant pathogens Xanthomonas oryzae pv. oryzae, Clavibacter michiganensis subsp. michiganensis, and Pyricularia oryzae. Ranatuerin-2SSa and granuliberin-SSa were active against C. albicans and C. michiganensis subsp. michiganensis, and granuliberin-SSa also was active against the other plant pathogenic microbes. Scanning electron microscopic observations demonstrated that brevinin-2SSb, ranatuerin-2SSa, and granuliberin-SSa induced morphological abnormalities on the cell surface in a wide range of the reference pathogens. To assess the bacterial-endotoxin-binding ability of the peptides, we developed an enzyme-linked endotoxin-binding assay system and demonstrated that brevinin-2SSb and ranatuerin-2SSa both exhibited high affinity to lipopolysaccharide and moderate affinity to lipoteichoic acid.

Somuncurins: Bioactive Peptides from the Skin of the Endangered Endemic Patagonian Frog Pleurodema somuncurense

The skin glands of amphibian species hold a major component of their innate immunity, namely a unique set of antimicrobial peptides (AMPs). Although most of them have common characteristics, differences in AMP sequences allow a huge repertoire of biological activity with varying degrees of efficacy. We present the first study of the AMPs from Pleurodema somuncurence (Anura: Leptodactylidae: Leiuperinae). Among the 11 identified mature peptides, three presented antimicrobial activity. Somuncurin-1 (FIIWPLRYRK), somuncurin-2 (FILKRSYPQYY), and thaulin-3 (NLVGSLLGGILKK) inhibited Escherichia coli growth. Somuncurin-1 also showed antimicrobial activity against Staphylococcus aureus. Biophysical membrane model studies revealed that this peptide had a greater permeation effect in prokaryotic-like membranes and capacity to restructure liposomes, suggesting fusogenic activity, which could lead to cell aggregation and disruption of cell morphology. This study contributes to the characterization of peptides with new sequences to enrich the databases for the design of therapeutic agents. Furthermore, it highlights the importance of investing in nature conservation and the power of genetic description as a strategy to identify new compounds.

The Antioxidant Peptide Salamandrin-I: First Bioactive Peptide Identified from Skin Secretion of Salamandra Genus (Salamandra salamandra)

Amphibian skin is a multifunctional organ that plays key roles in defense, breathing, and water balance. In this study, skin secretion samples of the fire salamander (Salamandra salamandra) were separated using RP-HPLC and de novo sequenced using MALDI-TOF MS/MS. Next, we used an in silico platform to screen antioxidant molecules in the framework of density functional theory. One of the identified peptides, salamandrin-I, [M + H]⁺ = 1406.6 Da, was selected for solid-phase synthesis; it showed free radical scavenging activity against DPPH and ABTS radicals. Salamandrin-I did not show antimicrobial activity against Gram-positive and -negative bacteria. In vitro assays using human microglia and red blood cells showed that salamandrin-I has no cytotoxicity up to the concentration of 100 µM. In addition, in vivo toxicity tests on Galleria mellonella larvae resulted in no mortality at 20 and 40 mg/kg. Antioxidant peptides derived from natural sources are increasingly attracting interest. Among several applications, these peptides, such as salamandrin-I, can be used as templates in the design of novel antioxidant molecules that may contribute to devising strategies for more effective control of neurological disease.

Neuroprotection by Walnut-Derived Peptides through Autophagy Promotion via Akt/mTOR Signaling Pathway against Oxidative Stress in PC12 Cells

Natural-derived peptides are effective substances in attenuating oxidative stress. However, their specific mechanisms have not been fully elucidated, especially in peptide-mediated autophagy. In the present study, TWLPLPR, YVLLPSPK, and KVPPLLY, novel peptides from Juglans mandshurica Maxim, prevented reactive oxygen species (ROS) production, elevated glutathione peroxidase (GSH-Px) activity and adenosine 5'-triphosphate (ATP) levels, and ameliorated apoptosis in Aβ_25-35 (at a concentration of 50 μM for 24 h)-induced PC12 cells (P < 0.01). Both western blot and immunofluorescence analysis illustrated that the peptides regulated Akt/mTOR signaling through p-Akt (Ser473) and p-mTOR (S2481) and promoted autophagy by increasing the levels of LC3-II/LC3-I and Beclin-1 while lowering p62 expression (P < 0.01). The autophagy inhibitor (3-methyladenine, 3-MA) and inducer (rapamycin, RAPA) were combined used to confirm the contribution of peptide-regulated autophagy in antioxidative effects. Moreover, the peptides increased the levels of LAMP1, LAMP2, and Cathepsin D (P < 0.05) and promoted the fusion with lysosomes to form autolysosomes, accelerating ROS removal. These data suggested that walnut-derived peptides regulated oxidative stress by promoting autophagy in the Aβ_25-35-induced PC12 cells.

Novel Ocellatin Peptides Mitigate LPS-induced ROS Formation and NF-kB Activation in Microglia and Hippocampal Neurons

Cutaneous secretions of amphibians have bioactive compounds, such as peptides, with potential for biotechnological applications. Therefore, this study aimed to determine the primary structure and investigate peptides obtained from the cutaneous secretions of the amphibian, Leptodactylus vastus, as a source of bioactive molecules. The peptides obtained possessed the amino acid sequences, GVVDILKGAAKDLAGH and GVVDILKGAAKDLAGHLASKV, with monoisotopic masses of [M + H]^± = 1563.8 Da and [M + H]^± = 2062.4 Da, respectively. The molecules were characterized as peptides of the class of ocellatins and were named as Ocellatin-K1(1-16) and Ocellatin-K1(1-21). Functional analysis revealed that Ocellatin-K1(1-16) and Ocellatin-K1(1-21) showed weak antibacterial activity. However, treatment of mice with these ocellatins reduced the nitrite and malondialdehyde content. Moreover, superoxide dismutase enzymatic activity and glutathione concentration were increased in the hippocampus of mice. In addition, Ocellatin-K1(1-16) and Ocellatin-K1(1-21) were effective in impairing lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) formation and NF-kB activation in living microglia. We incubated hippocampal neurons with microglial conditioned media treated with LPS and LPS in the presence of Ocellatin-K1(1-16) and Ocellatin-K1(1-21) and observed that both peptides reduced the oxidative stress in hippocampal neurons. Furthermore, these ocellatins demonstrated low cytotoxicity towards erythrocytes. These functional properties suggest possible to neuromodulatory therapeutic applications.

Identification and characterization of novel antioxidant peptides from crucian carp (Carassius auratus) cooking juice released in simulated gastrointestinal digestion by UPLC-MS/MS and in silico analysis

The objective of this work was to separate, identify and assess antioxidant peptides from the simulated gastrointestinal (GI) digestion of crucian carp (Carassius auratus) cooking juice (CCCJ), which has been previously found with this activity. The CCCJ after simulated GI digestion treatment was separated gradually by ultrafiltration and RP-HPLC. Five novel antioxidant peptides with 10-13 amino acid residues were identified by UPLC-MS/MS. Their in silico assessments showed amphiphilic nature, good sensory quality and different target sites in the human body. Meanwhile, their three-dimensional structure predictions exhibited at least one β-turn, β-sheet and/or α-helix with partial hydrophobic and/or net-charged residues exposed to the external medium, which was good evidence for high antioxidant activity. Ultimately, four novel peptides with high antioxidant activity were found, among which IREADIDGDGQVN (1401 Da), PEILPDGDHD (1107 Da) and ASDEQDSVRL (1119 Da) exerted the highest DPPH radical scavenging activity with IC₅₀ of 1.78, 1.18 and 1.45 mM, respectively, while APLEEPSSPH (1063 Da) showed the highest Fe²⁺ chelating ability with IC₅₀ of 0.09 mM. This work could help understand the mechanism of CCCJ on human health promotion and improve the economic value of the crucian carp processing industry.

In Vitro and In Silico Antioxidant Activity of Novel Peptides Prepared from Paeonia Ostii 'Feng Dan' Hydrolysate

Antioxidant peptides derived from natural products have superior performance and broader application prospects. In this study, five novel antioxidant peptides were prepared from Paeonia ostii (P. ostii) seed meal, moreover the bioactive and the relationship between structure and properties of antioxidant peptides were elucidated by quantum chemical calculations. The free radical-scavenging activities were used as indexes to purify and concentrate the antioxidant peptides through five proteases and separation techniques. FSAP (Phe-Ser-Ala-Pro), PVETVR (Pro-Val-Glu-Thr-Val-Arg), QEPLLR (Gln-Glu-Pro-Leu-Leu-Arg), EAAY (Glu-Ala-Ala-Tyr) and VLRPPLS (Val-Leu-Arg-Pro-Pro-Leu-Ser) were identified by nano liquid chromatography–tandem mass spectrometry (LC-MS/MS). In vitro antioxidant activity test, EAAY exhibited the highest 2, 2’-azino-bis (ABTS) and hydroxyl radical-scavenging activity of 98.5% ± 1.1% and 61.9% ± 1.3%, respectively (p < 0.01), at 0.5 mg/mL. In silico calculations were carried out using the density functional theory (DFT) with the B3LYP/6-31G* basis set. According to natural bond orbital (NBO) analysis, the bioactivity of free-radical scavenging of the peptides was presumed. Moreover, the antioxidant peptides demonstrated no obvious cytotoxicity to L929 fibroblast cells. Therefore, the peptides from P. ostii seed by-products might potentially have excellent uses in functional foods, nutraceuticals and pharmacological products.

Organization of the Skin Immune System and Compartmentalized Immune Responses in Infectious Diseases

The skin is an organ harboring several types of immune cells that participate in innate and adaptive immune responses. The immune system of the skin comprises both skin cells and professional immune cells that together constitute what is designated skin-associated lymphoid tissue (SALT). In this review, I extensively discuss the organization of SALT and the mechanisms involved in its responses to infectious diseases of the skin and mucosa. The nature of these SALT responses, and the cellular mediators involved, often determines the clinical course of such infections. I list and describe the components of innate immunity, such as the roles of the keratinocyte barrier and of inflammatory and natural killer cells. I also examine the mechanisms involved in adaptive immune responses, with emphasis on new cytokine profiles, and the role of cell death phenomena in host-pathogen interactions and control of the immune responses to infectious agents. Finally, I highlight the importance of studying SALT in order to better understand host-pathogen relationships involving the skin and detail future directions in the immunological investigation of this organ, especially in light of recent findings regarding the skin immune system.

In Silico Analysis of Bioactive Peptides in Invasive Sea Grass Halophila stipulacea

Halophila stipulacea is a well-known invasive marine sea grass in the Mediterranean Sea. Having been introduced into the Mediterranean Sea via the Suez Channel, it is considered a Lessepsian migrant. Although, unlike other invasive marine seaweeds, it has not demonstrated serious negative impacts on indigenous species, it does have remarkable invasive properties. The present in-silico study reveals the biotechnological features of H. stipulacea by showing bioactive peptides from its rubisc/o protein. These are features such as antioxidant and hypolipideamic activities, dipeptidyl peptidase-IV and angiotensin converting enzyme inhibitions. The reported data open up new applications for such bioactive peptides in the field of pharmacy, medicine and also the food industry.

Identification and Characterization of a Novel Gene-encoded Antioxidant Peptide from Odorous Frog Skin

Background:

Amphibian skin plays an essential role in protecting organisms from harmful external factors such as UV radiation. How amphibians protect themselves from reactive oxygen species following long-term sun exposure is an important and interesting question. Amphibian skins possess a novel antioxidant system composed of various Antioxidant Peptides (AOPs), which maintain redox homeostasis. However, only a few AOPs have been identified so far.

Methods:

Using combinational methods of peptidomics and genomics, we characterized a novel gene-encoded antioxidant peptide (herein named OA-VI12) from Odorrana andersonii skin secretions, which was produced by the post-translational processing of a 59-residue prepropeptide. The amino acid sequence of the OA-V112 was 'VIPFLACRPLGL', with a molecular mass of 1298.6 Da and no observed post-transcriptional modifications. Functional analysis demonstrated that OA-VI12 was capable of scavenging ABTS+, DPPH, NO and decreasing the Fe3+ production.

Results:

We determined that the C7 amino acid was responsible for ABTS+ and Fe3+ scavenging, activities, the F4, C7, and P9 amino acids were crucial for DPPH scavenging activity, and the P9 amino acid was responsible for NO scavenging activity. Unlike several other amphibian peptides, OA-VI12 did not accelerate wound healing in a full-thickness skin-wound mouse model and did not demonstrate direct microbial killing. Here, we identified and named a novel gene-encoded antioxidant peptide from the skin secretions of an odorous frog species, which may assist in the development of potential antioxidant candidates.

Conclusion:

This study may help improve our understanding of the molecular basis of amphibians’ adaptation to environments experiencing long-term UV radiation.

Identification and characterization of a novel gene-encoded antioxidant peptide obtained from amphibian skin secretions

Amphibian skin is known to secrete gene-encoded antioxidant peptides of small molecular weight, which play important roles in host defense. However, recognition of such peptides is still in its infancy. Here, we discovered a novel gene-encoded antioxidant peptide (named OM-GF17) from skin secretions of amphibian species, Odorrana margaretae. Produced by the post-translational processing of a 61-residue prepropeptide, the amino acid sequence of OM-GF17 was 'GFFKWHPRCGEEHSMWT', with a molecular mass of 2135.7 Da. Functional analysis revealed that OM-GF17 scavenged ABTS⁺, DPPH, NO and decreased iron oxidation. Our results also implied that five amino acid residues, including Cys, Pro, Met, Trp, and Phe, be related to the antioxidant activity of OM-GF17. Furthermore, OM-GF17 did not exhibit direct microbe-killing activity. This novel gene-encoded antioxidant peptide could help in the development of new antioxidant agents and increase our understanding of the biological functions of amphibian skin. [Formula: see text].

Redox tuning of Ca2+ signaling in microglia drives glutamate release during hypoxia

Hypoxia causes oxidative stress and excitotoxicity, culminating in neuronal damage during brain ischemia. Hypoxia also activates microglia, the myeloid resident cells of the brain parenchyma. Upon activation, microglia release high amounts of the neurotransmitter glutamate, contributing for neuronal excitotoxicity during brain insults. Here, we reveal a signaling pathway controlling glutamate release from human microglia during hypoxia. We show that hypoxia-mediated redox imbalance promotes the activation of endoplasmic reticulum inositol 1,4,5-trisphosphate (InsP₃) receptors leading to Ca²⁺ mobilization into the cytosol. Increasing cytosolic Ca²⁺ signaling in microglia activates the non-receptor protein tyrosine kinase Src at the plasma membrane. Src activation enhances the permeability of microglial gap junctions promoting the release of glutamate during hypoxia. Preventing the hypoxia-triggered redox imbalance, using the dietary antioxidants neochlorogenic acid or vitamin C, inhibits InsP₃-dependent Ca²⁺ signaling and abrogates the release of glutamate. Overall, modulating microglial Ca²⁺ signaling in response to changes in the redox microenvironment might be critical for controlling glutamate excitotoxicity during hypoxia.