| Summary: | For thousands of years, habitats of amphibians have changed dramatically from the initial marine to current freshwater aquatic types. This transition provided diverse resources but presented significant challenges from the environment and from predators. As a consequence, amphibians adapted to secrete abundant noxious substances from their skins in order to survive. These substances attracted the attention of many researchers in recent times who believe that there is a great potential in these secretions to discover new pharmaceuticals from natural products. In recent years, the biochemical/pharmaceutical components including peptides, proteins and nucleic acids, derived from amphibians, have been subjected to intensive studies. Original research work on these bioactive substances such as bradykinin-related peptides and antimicrobial peptides, indicates that they have some clear clinical therapeutic implications including uses as anti-inflammatories, anti-bacterials and even anticancer agents. This project mainly focused on the isolation and activity evaluation of three novel peptides derived from three different frog species belonging to different families. In the genomic aspect of the study, three novel peptides were identified by molecular cloning and named according to their molecular masses. Two bradykinin-related peptides, named R-13-R (QUB1379) and RVA-(V1,T6)-BK (QUB1344), were identified from the skin secretions of the Chinese brown frog, Rana chensinensis and the Bamboo leaf frog, Odorrana versabilis, respectively. A novel dermaseptin peptide, named dermaseptin-Ph (QUB2536), was isolated from skin secretions of the Northern orange-legged leaf frog, Phyllomedusa hypochondrialis. The cDNAs were cloned by molecular cloning and the primary structures of their respective encoded peptide biosynthetic precursors were deduced by translation. Reverse phase high performance liquid chromatography (RP-HPLC) and tandem mass spectrometry (MS/MS) techniques were applied to confirm their structures. The peptides were then synthesised by a solid phase peptide synthesis (SPPS) technique and their degrees of putity were identified by matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometer analysis. The determination of the bioactivities of the three novel peptides was carried out by employment of a series of bioassays. QUB1379 was found to be a bradykinin-receptor antagonist which inhibited the function of bradykinin inducing vasodilation on rat tail artery tissues and contraction on rat ileum tissues. However, the other novel bradykinin-related peptide, QUB 1344, exhibited a BK-receptor agonist-like function which induced the contraction of rat bladder and uterus tissues. The novel dermaseptin peptide, QUB2536, had a broad-spectrum of anticancer activities against PC-3 cells (ATCC-CRL-1435), U251MG cells (ECACC-09063001), H157 cells (ATCC-CRL-5802), MCF-7 cells (ATCC-HTB-22) and MDA-MB-435S cells (ATCC-HTB-129) and effective growth inhibitory activity against Gram-negative bacteria Escherichia coli (NCTC 10418) and Pseudomonas aeruginosa (ATCC 27853); Gram-positive bacteria Staphylococcus aureus (NCTC 10788) and Enterococcus faecalis (NCTC 12697); and pathogenic yeast Candida albicans (NCYC 1467). In recent years, both agonists and antagonists have significant clinical therapeutics based on the literature published. Kinin receptors are involved in pain and other neurological reactions. Various modifications of kinin receptor antagonists agents rely on the natural BRPs discovered from the natural world. What’s more, due to the rapid development of multi-drug resistant bacteria, discovering and producing of new types of antibiotics is in urge of investigation. Hence, this project can provide new insight for the research and development of new agents. Besides, great efforts need to be made to identify and assess new substances discovered from natural source.
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