Antifungal Activity of Human Salivary Mucin-Derived Peptide, MUC7-12-mer-D Isomer

Objectives: MUC7-12-mer (RKSYKCLHKRCR, aa 40-51 of the parent human salivary mucin, MUC7) exhibits potent in vitro antifungal activity in low-ionic-strength buffers. It is, however, less potent in buffers with increased ionic-strength and in human saliva. In this study we investigated antifungal activity and toxicity of MUC7-12-mer, D amino acid isomer, and compared them to those of MUC7-12-mer, natural L form. Methods: Fungicidal activity on C. albicans (DIS and ATCC 96112) was tested in 10 mM Na phosphate buffer (pH 7.4) containing increasing concentration of NaCl (12.5 to 100 mM), and in clarified saliva. Toxicity was evaluated by hemolysis assay in PBS (phosphate-buffered saline), IGP (isotonic glucose-phosphate buffer; 1 mM phosphate buffer supplemented with 287 mM glucose), and LYMG (modified RPMI 1640 medium, supplemented with 287 mM glucose), using human erythrocytes. Results: The candidacidal activities of tested peptides were dose dependent. At concentration of 25 µM, 12-mer-D achieved 85% killing in the presence of 100 mM NaCl, while 12-mer-L showed less than 20% killing. In saliva, at 100 µM concentration, 12-mer-D exhibited 92% killing, while 12-mer-L only 56%. Both peptides showed relatively low hemolysis comparing to magainin-II and amphotericin B, even at 100 µM concentration. The values for 12-mer-D were: 3.5, 36, and 20% in PBS, IGP and LYMG, respectively; and for 12-mer-L: 4.3, 56, and 36%, in PBS, IGP and LYMG, respectively. Magainin-II showed 0, 92 and 66% hemolysis, respectively in PBS, IGP and LYM; amphotericin B showed 100% hemolysis in all three buffers at 25, 50 and 100 µM concentrations. Conclusions: Comparing to MUC7-12-mer-L, MUC7-12-mer-D isomer exhibited higher candidacidal activities in high ionic strength buffer and in saliva, yet a lower toxicity toward human red blood cells. MUC7-12-D thus appears to be an excellent candidate for investigation of its antifungal activity in vivo. Supported by NIH/NIDCR grant DE09820.