Epithelial Defensin hBD-3 Activity against Periodontal Pathogens

Defensins are cationic peptides with broad-spectrum antibiotic activity. Human neutrophils contain four alpha-defensins known as Human Neutrophil Peptide (HNP) 1-4. Epithelial cells produce four beta-defensins known as human Beta Defensin (hBD) 1-4. Gram-negative anaerobic bacteria associated with periodontal disease are resistant to human neutrophil alpha-defensins, but are killed by beta-defensins. Compared with alpha-defensins, beta-defensins have additional hydrophobic amino acid residues near the N-terminus and cationic residues at the C-terminus. Objectives: Determine whether the N- or C-terminal region of hBD-3 accounts for activity against periodontal pathogens A.a. (Aggregatibacter actinomycetemcomitans; Y4; ATCC43718) and P.g. (Porphyromonas gingivalis; ATCC33277). Methods: Bacteria were incubated under anaerobic conditions with HNP-1 purified from neutrophils, recombinant hBD-3, or synthetic peptides CHRG07 and CHRG01, which have sequences derived from the N- and C-terminus of hBD-3 (Hoover et al. Antimicrob Agents Chemother 47:2804, 2003).  Viability was determined by diluting, plating, and counting colonies. Results: A.a. was resistant to HNP-1, but 5µM hBD-3 or CHRG07 killed 90 to 99% of the bacteria within 4 h. CHRG01 was much less active. In contrast, P.g. 33277 was resistant to 60µM hBD-3, and 100µM CHRG07 caused only 43±5% loss of viability. CHRG01 had no effect. Conclusions: The hBD-3 N-terminus, which contains a mixture of hydrophobic and cationic residues, is more important than the cationic C-terminus for activity against A.a.  Further studies are needed to determine whether arginine- and lysine-specific gingipain proteases produced by P.g. destroy the peptides and account for low activity against P.g. 33277.  

Supported by the UTHSC Dental Alumni Endowment Fund.