Amphibian skin secretions contain biologically-active compounds, such as anti-microbial peptides and trypsin inhibitors, which are used by biomedical researchers as a source of potential novel drug leads or pharmacological agents. Here, we report the application of a recently developed technique within our laboratory to "shotgun" clone the cDNAs encoding two novel but structurally-related peptides from the lyophilised skin secretions of one species of European frog, Rana esculenta and one species of Chinese frog, Odorrana schmackeri. Bioanalysis of the peptides established the structure of a 17-mer with an N-terminal Ala (A) residue and a C-terminal Cys (C) residue with a single disulphide bridge between Cys 12 and 17, which is a canonical Kunitz-type protease inhibitor motif (-CKAAFC-). Due to the presence of this structural attribute, these peptides were named kunitzin-RE (AAKIILNPKFRCKAAFC) and kunitzin-OS (AVNIPFKVHLRCKAAFC). Synthetic replicates of these two novel peptides were found to display a potent inhibitory activity against Escherichia coli but were ineffective at inhibiting the growth of Staphylococcus aureus and Candida albicans at concentrations up to 160 μM, and both showed little haemolytic activity at concentrations up to 120 μM. Subsequently, kunitzin-RE and kunitzin-OS were found to be a potent inhibitor of trypsin with a Ki of 5.56 μM and 7.56 μM that represent prototypes of a novel class of highly-attenuated amphibian skin protease inhibitor. Substitution of Lys-13, the predicted residue occupying the P1 position within the inhibitory loop, with Phe (F) resulted in decrease in trypsin inhibitor effectiveness and antimicrobial activity against Esherichia coli, but exhibits a potential inhibition activity against chymotrypsin.

The amphibian temporins, amongst the smallest antimicrobial peptides (AMPs), are α-helical, amphipathic, hydrophobic and cationic and are active mainly against Gram-positive bacteria but inactive or weakly active against Gram-negative bacteria. Here, we report two novel members of the temporin family, named temporin-1Ee (FLPVIAGVLSKLFamide) and temporin-1Re (FLPGLLAGLLamide), whose biosynthetic precursor structures were deduced from clones obtained from skin secretion-derived cDNA libraries of the European edible frog, Pelophylax kl. esculentus, by 'shotgun' cloning. Deduction of the molecular masses of each mature processed peptide from respective cloned cDNAs was used to locate respective molecules in reverse-phase HPLC fractions of secretion. Temporin-1Ee (MIC = 10 μM) and temporin-1Re (MIC = 60 μM) were both found to be active against Gram-positive Staphylococcus aureus, but retaining a weak haemolytic activity. To our knowledge, Single-site substitutions can dramatically change the spectrum of activity of a given temporin. Compared with temporine-1Ec, just one chemically-conservative substitution (Val8 instead of Leu8), temporin-1Ee bearing a net charge of +2 displays broad-spectrum activity with particularly high potency on the clinically relevant Gram-negative strains, Escherichia coli (MIC = 40 μM). These factors bode well for translating temporins to be potential drug candidates for the design of new and valuable anti-infective agents.

The currently used anti-cytokine therapeutic antibodies cannot selectively neutralize pathogenic cytokine signaling that cause collateral damage to protective signaling cascades carrying the potential for unwanted side effects. The variable domains of heavy-chain only antibodies (HCAbs) discovered in Camelidae are stable and display to be fully functional in antigen-binding against variable targets, which seem to be attractive candidates for the next-generation biologic drug study. The purpose of our study was to establish a simple prokaryotic expression system for large-scale expression, purification, and refolding of the recombinant anti-tumor necrosis factor α (TNF-α) fusion protein (FVH1-1) from inclusion bodies. Over 95% purity of the recombinant anti-TNF-α fusion proteins was obtained by just one purification step in our developed prokaryotic expression system, while the results of surface plasmon resonance (SPR) established the high-efficiency potent binding ability of FVH1-1 to human TNF-α. The counteraction of TNF-α cytotoxic effect experiment on the mouse fibroblast fibrosarcoma cell line (L929) confirmed that the expressed FVH1-1 were able to selectively and highly combine with human recombinant TNF-α (hTNF-α) in vitro. Western blot results showed that FVH1-1 can inhibit the activation of caspase-9 and PARP, which are the apoptotic signaling pathway proteins activated by hTNF-α. Meanwhile, lysosome autophagy signaling pathways stimulated by hTNF-α were inhibited by FVH1-1, which down-regulated the expression of LC3II/LC3I and up-regulated the expression of P62, indicating that the autophagy linked with TNF-α-induced apoptosis in response to rheumatoid arthritis. The results of the AIA rat model experiment presented that FVH1-1 can reduce the degree of joint swelling and inflammatory factors to a certain extent in vivo.