Cc-CATH3

A series of amino-terminal truncated analogues of quail antimicrobial peptide Cc-CATH3(1-29) were created and examined antibacterial activity against Gram-positive bacteria, cytotoxicity against mouse fibroblast cell line, and membrane perturbation activity against various membrane models. Parent peptide Cc-CATH3(1-29) and the first four-residue truncated peptide Cc-CATH3(5-29) were active in all tested experiments. In contrast, the eight- and twelve-residue truncated variants Cc-CATH3(9-29) and Cc-CATH3(13-29) appeared to have lost activities. Cc-CATH3(1-29) and Cc-CATH3(5-29) possessed antibacterial activity with minimum inhibitory concentrations of 2-4 and 1-2 µM, respectively. For cytotoxicity, Cc-CATH3(1-29) and Cc-CATH3(5-29) displayed cytotoxicity with the IC50 values of 9.33 and 4.93 μM, respectively. Cc-CATH3(5-29) induced greater liposome membranes disruption than Cc-CATH3(1-29) regardless of lipid type and composition. The leakage results of Cc-CATH3(1-29) share a similar trend with that in Cc-CATH3(5-29); they exhibit no preferential binding to anionic phospholipids. In conclusion, the results suggested that the first four residues at the N-terminus "RVRR" is not essential for presenting all test activities. In contrast, residues five to eight of "FWPL" are necessary as the exclusion of this short motif in Cc-CATH3(9-29) and Cc-CATH3(13-29) leads to a loss of activities. This study will be beneficial for further design and development of Cc-CATH3 to be novel antibiotic.

As the most common fungal pathogen of humans, severe drug resistance has emerged in the clinically isolated Candida albicans, which lead to the urgency to develop novel antifungal agents. Here, four our previously characterized cathelicidins (cathelicidin-BF, Pc-CATH1, Cc-CATH2, Cc-CATH3) were selected and their antifungal activities against C. albicans were evaluated in vitro and in vivo using amphotericin B and LL-37 as control. Results showed that all four cathelicidins could eradicate standard and clinically isolated C. albicans strains with most MIC values ranging from 1 to 16 μg/ml, in less than 0.5 h revealed by time-kill kinetic assay. Four peptides only exhibited slight hemolytic activity with most HC50 > 200 μg/ml, and retained potent anti-C. albicans activity at salt concentrations below and beyond physiological level. In animal experiment, 50 mg/kg administration of the four cathelicidins could significantly reduce the fungal counts in a murine oral candidiasis model induced by clinically isolated C. albicans. The antibiofilm activity of cathelicidin-BF, the most potent among the five peptides was evaluated, and result showed that cathelicidin-BF strongly inhibited C. albicans biofilm formation at 20 μg/ml. Furthermore, cathelicidin-BF also exhibited potent anti-C. albicans activity in established biofilms as measured by metabolic and fluorescent viability assays. Structure-function analyses suggest that they mainly adopt an α-helical conformations, which enable them to act as a membrane-active molecule. Altogether, the four cathelicidins display great potential for antifungal agent development against candidiasis.