Abstract
BackgroundMUC7 12-mer (RKSYKCLHKRCR), a cationic antimicrobial peptide derived from the human low-molecular-weight salivary mucin MUC7, possesses potent antimicrobial activity in vitro. In order to evaluate the potential therapeutic application of the MUC7 12-mer, we examined the effects of mono- and divalent cations, EDTA, pH, and temperature on its antimicrobial activity.MethodsMinimal Inhibitory Concentrations (MICs) were determined using a liquid growth inhibition assay in 96-well microtiter plates. MUC7 12-mer was added at concentrations of 1.56–50 μM. MICs were determined at three endpoints: MIC-0, MIC-1, and MIC-2 (the lowest drug concentration showing 10%, 25% and 50% of growth, respectively). To examine the effect of salts or EDTA, a checkerboard microdilution technique was used. Fractional inhibitory concentration index (FICi) was calculated on the basis of MIC-0. The viability of microbial cells treated with MUC7 12-mer in the presence of sodium or potassium was also determined by killing assay or flow cytometry.ResultsThe MICs of MUC7 12-mer against organisms tested ranged from 6.25–50 μM. For C. albicans, antagonism (FICi 4.5) was observed for the combination of MUC7 12-mer and calcium; however, there was synergism (FICi 0.22) between MUC7 12-mer and EDTA, and the synergism was retained in the presence of calcium at its physiological concentration (1–2 mM). No antagonism but additivity or indifference (FICi 0.55–2.5) was observed for the combination of MUC7 12-mer and each K+, Na+, Mg2+, or Zn2+. MUC7 12-mer peptide (at 25 μM) also exerted killing activity in the presence of NaCl, (up to 25 mM for C. albicans and up to 150 mM for E. coli, a physiological concentration of sodium in the oral cavity and serum, respectively) and retained candidacidal activity in the presence of KCl (up to 40 mM). The peptide exhibited higher inhibitory activity against C. albicans at pH 7, 8, and 9 than at pH 5 and 6, and temperature up to 60°C did not affect the activity.ConclusionMUC7 12-mer peptide is effective anticandidal agent at physiological concentrations of variety of ions in the oral cavity. These results suggest that, especially in combination with EDTA, it could potentially be applied as an alternative therapeutic agent for the treatment of human oral candidiasis.
Highlights
MUC7 12-mer (RKSYKCLHKRCR), a cationic antimicrobial peptide derived from the human low-molecular-weight salivary mucin MUC7, possesses potent antimicrobial activity in vitro
The Minimal Inhibitory Concentrations (MICs) of MUC7 12-mer decreased 8 fold when combined with EDTA; Fractional inhibitory concentration index (FICi) of 0.22 was obtained in this case, indicating a synergism between MUC7 12-mer and EDTA
Our previous study showed that that EDTA enhanced the antifungal activity of MUC7 peptides in human saliva mainly by chelating the divalent cations [8]. In support of this discovery, the results of this study indicated that EDTA has a synergistic effect on the antimicrobial activity of MUC7 12-mer (Table 1), and abrogates the activity that was inhibited by Ca2+ (Table 2)
Summary
MUC7 12-mer (RKSYKCLHKRCR), a cationic antimicrobial peptide derived from the human low-molecular-weight salivary mucin MUC7, possesses potent antimicrobial activity in vitro. Cationic antimicrobial peptides (CAMPs) are one of the body's host defenses against invading microorganisms These peptides have broad-spectrum antimicrobial activity, including antibacterial, antiviral, and antifungal activity. The representative MUC7 peptide, MUC7 12-mer (RKSYKCLHKRCR), a cationic peptide spanning residues 40–51 of the MUC7, possesses potent antimicrobial activity in low-ionic-strength buffers and in low salt RPMI 1640 medium. This peptide exhibits synergistic antifungal effects with histatin 5 12-mer (Hsn5 12-mer) and with miconazole [7]
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