Vasorelaxin: a novel arterial smooth muscle-relaxing eicosapeptide from the skin secretion of the Chinese piebald odorous frog (Odorrana schmackeri)

Pharmacological Effects of a Novel Bradykinin-Related Peptide (RR-18) from the Skin Secretion of the Hejiang Frog (Ordorrana hejiangensis) on Smooth Muscle

Bradykinin (BK) and bradykinin-related peptides (BRPs), which were identified from a diversity of amphibian skin secretions, exerted contractile and relaxing effects on non-vascular and vascular smooth muscle, respectively. Here, we report a novel bradykinin-related peptide with a molecular mass of 1890.2 Da, RVAGPDKPARISGLSPLR, which was isolated and identified from Ordorrana hejiangensis skin secretions, followed by a C-terminal extension sequence VAPQIV. The biosynthetic precursor-encoding cDNA was cloned by the “shotgun” cloning method, and the novel RR-18 was identified and structurally confirmed by high-performance liquid chromatography (HPLC) and tandem mass spectrometry (MS/MS). Subsequently, the myotropic activity of the synthetic replicate of RR-18 was investigated on the rat bladder, uterus, tail artery and ileum smooth muscle. The peptide was named RR-18 in accordance (R = N-terminal arginine, R = C-terminal arginine, 18 = number of residues). In this study, the synthetic replicates of RR-18 showed no agonist/antagonism of BK-induced rat bladder and uterus smooth muscle contraction. However, it displayed an antagonism of bradykinin-induced rat ileum contraction and arterial smooth muscle relaxation. The EC₅₀ values of BK for ileum and artery, were 214.7 nM and 18.3 nM, respectively. When the tissue was pretreated with the novel peptide, RR-18, at the maximally effective concentration of bradykinin (1 × 10⁻⁶ M), bradykinin-induced contraction of the ileum and relaxation of the arterial smooth muscle was reduced by 50–60% and 30–40%, respectively. In conclusion, RR-18 represents novel bradykinin antagonising peptide from amphibian skin secretions. It may provide new insight into possible treatment options for chronic pain and chronic inflammation.

Discovery of Novel Caeridins from the Skin Secretion of the Australian White's Tree Frog, Litoria caerulea

Abundant biologically active peptides have been discovered from frog skin secretions, a rich natural source of bioactive compounds with great potential in drug discovery. In this study, three Caeridin peptides, namely, Caeridin-1, S5-Caeridin-1, and Caeridin-a1, were discovered from the skin secretion of the Australian White's tree frog, Litoria caerulea, for the first time, by means of combining transcriptomic and peptidomic analyses. It also represents the first report on bioactive Caeridins since this family of peptides was initially studied 20 years ago. Chemically synthetic versions of each natural Caeridin demonstrated promising bioactivities either on rat smooth muscles or against microbial growth. Specifically, Caeridin-1 produced contraction of rat bladder smooth muscle, while S5-Caeridin-1 induced relaxation of rat ileum smooth muscle, both at nanomolar concentrations. Moreover, Caeridin-a1 was shown to potently inhibit the growth of the planktonic Gram-positive bacteria Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), and Enterococcus faecalis (E. faecalis), the Gram-negative bacterium, Escherichia coli (E. coli), and the yeast, Candida albicans (C. albicans). The discovery of these Caeridins may induce further intensive and systematic studies of frog skin peptides to promote the discovery of natural templates as lead compounds for drug discovery and therapeutic application.

Assessment of antimicrobial and wound healing effects of Brevinin-2Ta against the bacterium Klebsiella pneumoniae in dermally-wounded rats

Antimicrobial peptides (AMPs) are regarded as promising alternatives for antibiotics due to their inherent capacity to prevent microbial drug resistance. Amphibians are rich source of bioactive molecules, which provide numerous AMPs with various structures as drug candidates. Here, we isolated and identified a novel AMP Brevinin-2Ta (B-2Ta) from the skin secretion of the European frog, Pelophylax kl. esculentus. In vitro studies revealed that it showed broad antimicrobial activities against S. aureus, E. coli and C. albicans with low cytotoxicity to erythrocytes. Furthermore, we examined the anti-inflammation effect in vivo by using Klebsiella pneumoniae-infected Sprague-Dawley (SD) rats. The wound closure outcomes revealed that B-2Ta effectively restrained the bacterial infection at a dose of 10 times minimal inhibitory concentration (MIC) during the 14 days of the wound healing process. Ultra-structure analyses showed that B-2Ta caused structural damage to the microorganism, and bacterial culture found that the number of microbes was significantly reduced by the end of treatment. Immunohistochemistry for the inflammatory marker IL-10 and the endothelial cell marker CD31 suggested positive effects on inflammatory status and epithelial migration and angiogenesis following treatment of the infected granulation tissues with B-2Ta. These results exhibited the continuous phase of inflammation reduction and wound healing acceleration in the B-2Ta-modulated re-epithelialisation of K. pneumoniae infected rats. Taken together, these data demonstrated that B-2Ta has great potential to be developed as antibacterial agents in clinic.

Cationicity-enhanced analogues of the antimicrobial peptides, AcrAP1 and AcrAP2, from the venom of the scorpion, Androctonus crassicauda, display potent growth modulation effects on human cancer cell lines

The non disulphide-bridged peptides (NDBPs) of scorpion venoms are attracting increased interest due to their structural heterogeneity and broad spectrum of biological activities. Here, two novel peptides, named AcrAP1 and AcrAP2, have been identified in the lyophilised venom of the Arabian scorpion, Androctonus crassicauda, through “shotgun” molecular cloning of their biosynthetic precursor-encoding cDNAs. The respective mature peptides, predicted from these cloned cDNAs, were subsequently isolated from the same venom sample using reverse phase HPLC and their identities were confirmed by use of mass spectrometric techniques. Both were found to belong to a family of highly-conserved scorpion venom antimicrobial peptides - a finding confirmed through the biological investigation of synthetic replicates. Analogues of both peptides designed for enhanced cationicity, displayed enhanced potency and spectra of antimicrobial activity but, unlike the native peptides, these also displayed potent growth modulation effects on a range of human cancer cell lines. Thus natural peptide templates from venom peptidomes can provide the basis for rational analogue design to improve both biological potency and spectrum of action. The diversity of such templates from such natural sources undoubtedly provides the pharmaceutical industry with unique lead compounds for drug discovery.