Antioxidant properties and neuroprotective effects of Esc-1GN through the regulation of MAPK and AKT signaling

Antioxidants in anti-Alzheimer's disease drug discovery

Oxidative stress is widely recognized as a key contributor to the pathogenesis of Alzheimer's disease (AD). While not the sole factor, it is closely linked to critical pathological features, such as the formation of senile plaques and neurofibrillary tangles. The development of agents with antioxidant properties has become an area of growing interest in AD research. Between 2015 and 2024, several antioxidant-targeted drugs for AD progressed to clinical trials, with increasing attention to the evaluation of antioxidant properties during their development. Oxidative stress plays a pivotal role in linking various AD hypotheses, underscoring its importance in understanding the disease mechanisms. Despite this, comprehensive reviews addressing advancements in AD drug development from the perspective of antioxidant capacity remain limited, hindering the design of novel compounds. This review aims to explore the mechanistic relationship between oxidative stress and AD, summarize methods for assessing antioxidant capacity, and provide an overview of antioxidant compounds with anti-AD properties reported over the past decade. The goal is to offer strategies for identifying effective antioxidant-based therapies for AD and to deepen our understanding of the role of oxidative stress in AD pathology.

Cath-DM-NT, a peptide derived from the skin of Duttaphrynus melanostictus, shows dual lectin-like and antioxidant activity

Chansu, a mixture extracted from Duttaphrynus melanostictus or Bufo gargarizans Cantor, is a traditional Chinese medicine with a broad range of medical applications. However, the peptides/proteins in it have not received adequate attention. Herein, a Cathelicidin-DM-derived peptide named Cath-DM-NT was identified from the skin of D. melanostictus. Previous studies have shown that Cathelicidin-DM has significant antibacterial activity, while Cath-DM-NT has no antibacterial activity. In this study, Cath-DM-NT is found to have lectin-like activity which can agglutinate erythrocytes and bacteria, and bind to lipopolysaccharide (LPS). In addition, Cath-DM-NT has antioxidant activity, which can scavenge 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and nitric oxide (NO) radicals and reduce Fe3+. Consistently, Cath-DM-NT can protect PC12 cells from H2O2-induced oxidative damage and carrageenan-induced paw edema, reduce malondialdehyde (MDA) and reactive oxygen species (ROS) accumulation, and restore superoxide dismutase (SOD) and glutathione (GSH) levels. Our study suggests that Cath-DM-NT can serve as a lead compound for the development of drugs with dual lectin and antioxidant effects.

Hylin-a1: A Pan-Inhibitor against Emerging and Re-Emerging Respiratory Viruses

Pandemic and epidemic outbreaks of respiratory viruses are a challenge for public health and social care system worldwide, leading to high mortality and morbidity among the human populations. In light of the limited efficacy of current vaccines and antiviral drugs against respiratory viral infections and the emergence and re-emergence of new viruses, novel broad-spectrum antiviral drugs are needed for the prevention and treatment of these infections. Antimicrobial peptides with an antiviral effect, also known as AVPs, have already been reported as potent inhibitors of viral infections by affecting different stages of the virus lifecycle. In the present study, we analyzed the activity of the AVP Hylin-a1, secreted by the frog Hypsiboas albopunctatus, against a wide range of respiratory viruses, including the coronaviruses HCoV-229E and SARS-CoV-2, measles virus, human parainfluenza virus type 3, and influenza virus H1N1. We report a significant inhibitory effect on infectivity in all the enveloped viruses, whereas there was a lack of activity against the naked coxsackievirus B3. Considering the enormous therapeutic potential of Hylin-a1, further experiments are required to elucidate its mechanism of action and to increase its stability by modifying the native sequence.

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.

Anurans against SARS-CoV-2: A review of the potential antiviral action of anurans cutaneous peptides

At the end of 2019, in China, clinical signs and symptoms of unknown etiology have been reported in several patients whose sample sequencing revealed pneumonia caused by the SARS-CoV-2 virus. COVID-19 is a disease triggered by this virus, and in 2020, the World Health Organization declared it a pandemic. Since then, efforts have been made to find effective therapeutic agents against this disease. Identifying novel natural antiviral drugs can be an alternative to treatment. For this reason, antimicrobial peptides secreted by anurans' skin have gained attention for showing a promissory antiviral effect. Hence, this review aimed to elucidate how and which peptides secreted by anurans' skin can be considered therapeutic agents to treat or prevent human viral infectious diseases. Through a literature review, we attempted to identify potential antiviral frogs' peptides to combat COVID-19. As a result, the Magainin-1 and -2 peptides, from the Magainin family, the Dermaseptin-S9, from the Dermaseptin family, and Caerin 1.6 and 1.10, from the Caerin family, are molecules that already showed antiviral effects against SARS-CoV-2 in silico. In addition to these peptides, this review suggests that future studies should use other families that already have antiviral action against other viruses, such as Brevinins, Maculatins, Esculentins, Temporins, and Urumins. To apply these peptides as therapeutic agents, experimental studies with peptides already tested in silico and new studies with other families not tested yet should be considered.

Antitumor Effects of Scorpion Peptide Smp43 through Mitochondrial Dysfunction and Membrane Disruption on Hepatocellular Carcinoma

Smp43, a cationic antimicrobial peptide identified from the venom gland of the Egyptian scorpion Scorpio maurus palmatus, shows cytotoxicity toward hepatoma cell line HepG2 by membrane disruption. However, its underlying detailed mechanisms still remain to be further clarified. In the present study, we evaluated the cellular internalization of Smp43 and explored its effects on cell viability, cell cycle, apoptosis, autophagy, necrosis, and factor expression related to these cellular processes in human HepG2. Smp43 was found to suppress the growth of HepG2, Huh7, and human primary hepatocellular carcinoma cells while showing low toxicity to normal LO2 cells. Furthermore, Smp43 could interact with the cell membrane and be internalized into HepG2 cells via endocytosis and pore formation, which caused a ROS production increase, mitochondrial membrane potential decline, cytoskeleton disorganization, dysregulation of cyclin expression, mitochondrial apoptotic pathway activation, and alteration of MAPK as well as PI3K/Akt/mTOR signaling pathways. Finally, Smp43 showed effective antitumor protection in the HepG2 xenograft mice model. Overall, these findings indicate that Smp43 significantly exerts antitumor effects via induction of apoptosis, autophagy, necrosis, and cell cycle arrest due to its induction of mitochondrial dysfunction and membrane disruption. This discovery will extend the antitumor mechanisms of antimicrobial peptides and contribute to the development of antitumor agents against hepatocellular carcinoma.

Brevinin-2GHk, a Peptide Derived from the Skin of Fejervarya limnocharis, Inhibits Zika Virus Infection by Disrupting Viral Integrity

Several years have passed since the Zika virus (ZIKV) pandemic reoccurred in 2015–2016. However, there is still a lack of proved protective vaccines or effective drugs against ZIKV. The peptide brevinin-2GHk (BR2GK), pertaining to the brevinin-2 family of antimicrobial peptides, has been reported to exhibit only weak antibacterial activity, and its antiviral effects have not been investigated. Thus, we analyzed the effect of BR2GK on ZIKV infection. BR2GK showed significant inhibitory activity in the early and middle stages of ZIKV infection, with negligible cytotoxicity. Furthermore, BR2GK was suggested to bind with ZIKV E protein and disrupt the integrity of the envelope, thus directly inactivating ZIKV. In addition, BR2GK can also penetrate the cell membrane, which may contribute to inhibition of the middle stage of ZIKV infection. BR2GK blocked ZIKV E protein expression with an IC₅₀ of 3.408 ± 0.738 μΜ. In summary, BR2GK was found to be a multi-functional candidate and a potential lead compound for further development of anti-ZIKV drugs.

Antiviral activity and mechanism of ESC-1GN from skin secretion of hylarana guentheri against influenza a virus

Development of new and effective anti-influenza drugs is critical for prophylaxis and treatment of influenza A virus infection. A wide range of amphibian skin secretions have been identified to show antiviral activity. Our previously reported ESC-1GN, a peptide from the skin secretion of Hylarana guentheri, displayed good antimicrobial and anti-inflammatory effects. Here, we found that ESC-1GN possessed significant antiviral effects against influenza A viruses. Moreover, ESC-1GN could inhibit the entry of divergent H5N1 and H1N1 virus strains with the IC50 values from 1.29 to 4.59 μM. Mechanism studies demonstrated that ESC-1GN disrupted membrane fusion activity of influenza A viruses by interaction with HA2 subunit. The results of site-directed mutant assay and molecular docking revealed that E105, N50 and the residues around them on HA2 subunit could form hydrogen bonds with amino acid on ESC-1GN, which were critical for ESC-1GN binding to HA2 and inhibiting the entry of influenza A viruses. Altogether, these not only suggest that ESC-1GN maybe represent a new type of excellent template designing drugs against influenza A viruses, but also it may shed light on the immune mechanism and survival strategy of H. guentheri against viral pathogens.

Esc-1GN shows therapeutic potentials for acne vulgaris and inflammatory pain

The inflammatory response plays important roles in acne vulgaris and pain pathogenesis. In previous study, Esc-1GN with anti-inflammatory, antimicrobial, and lipopolysacchride (LPS) binding activity was identified from the skin of the frog Hylarana guentheri. Here, we report its therapeutic potentials for acne vulgaris and inflammatory pain. Esc-1GN destroyed the cell membrane of Propionibacteria acnes in the membrane permeability assays. In addition, bacterial agglutination test suggested that Esc-1GN triggered the agglutination of P. acnes, which was affected by LPS and Ca²⁺ . Meanwhile, in vivo anti-P. acnes and anti-inflammatory effects of Esc-1GN were confirmed by reducing the counts of P. acnes in mice ear, relieving P. acnes-induced mice ear swelling, decreasing mRNA expression and the production of pro-inflammatory cytokines, and attenuating the infiltration of inflammatory cells. Moreover, Esc-1GN also displayed antinociceptive effect in mice induced by acetic acid and formalin. Therefore, Esc-1GN is a promising candidate drug for treatment of acne vulgaris and inflammatory pain.