Objectives: Porphyromonas gingivalis,a Gram negative bacterium associated with active lesions of chronic periodontitis, produces several proteinases which are presumably involved in host colonization, perturbation of immune system and tissue destruction. The aims of this study were to investigate the degradation of human transferrin by P. gingivalisand to demonstrate the production of toxic hydroxyl radicals catalyzed by the iron-containing transferrin fragments generated. Methods: Transferrin and transferrin fragments were detected by polyacrylamide gel electrophoresis followed by Western immunoblotting or autoradiography. Hydroxyl radical formation was determined by a hypoxanthine/xanthine oxidase system and spin trapping/electron paramagnetic resonance spectrometry. Results: P. gingivalisas well as purified gingipains were found to cleave transferrin into fragments of various sizes. Interestingly, gingival crevicular fluid samples from diseased but not from healthy periodontal sites contained low molecular mass fragments of transferrin. Using 55Fe-transferrin, it was found that degradation by P. gingivalisresulted in the production of free iron as well as iron-bound to low molecular mass peptide fragments. Subsequently, bacterial cells assimilated intracellularly the radiolabelled iron. Lastly, the degradation products of transferrin were capable of catalyzing the formation of hydroxyl radicals. Conclusion: Our study indicates that P. gingivalisgingipains degrade transferrin providing an assimilable source of iron. The iron bound to transferrin fragments can contribute to tissue destruction by catalyzing the formation of toxic hydroxyl radicals. This work was supported by the Canadian Institutes of Health Research.

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