title: Factors affecting antimicrobial activity of MUC7 12-mer, a human salivary mucin-derived peptide.
abstract: BACKGROUND
  MUC7 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.
  
  
  METHODS
  Minimal 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 microM. 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.
  
  
  RESULTS
  The MICs of MUC7 12-mer against organisms tested ranged from 6.25-50 microM. 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 microM) 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 degrees C did not affect the activity.
  
  
  CONCLUSIONS
  MUC7 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.
authors.affiliation: Department of Oral Biology, School of Dental Medicine, University at Buffalo, SUNY, 3435 Main Street, Buffalo, USA, NY 14214. gwei@buffalo.edu.
authors.forename: Guo-Xian
authors.initials: GX
authors.lastname: Wei
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Campagna
authors.forename: Libuse A
authors.initials: LA
authors.lastname: Bobek
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D002176:Candida albicans / Q000187:drug effects; D002412:Cations / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D003067:Coenzymes / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D009077:Mucins / Q000494:pharmacology*; D012471:Salivary Proteins and Peptides / Q000494:pharmacology*; D013295:Streptococcus mutans / Q000187:drug effects; D013696:Temperature
chemical_list: D000890:Anti-Infective Agents; D002412:Cations; D002614:Chelating Agents; D003067:Coenzymes; D004791:Enzyme Inhibitors; C083238:MUC7 protein, human; D008670:Metals; D009077:Mucins; D012471:Salivary Proteins and Peptides; D004492:Edetic Acid