Intracellular production and extracellular release of oxygen radicals by PMNs and oxidative stress on PMNs during phagocytosis of periodontopathic bacteria

Abstract

In this study we investigated intracellular and extracellular oxygen radical production by polymorphonuclear leukocytes (PMNs) during the phagocytosis of periodontopathic bacteria. In in vitro assays, bacteria of the species Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Fusobacterium nucleatum were phagocytosed at 37°C for 4 h by purified peripheral human PMNs from healthy subjects (n = 6). Superoxide production during phagocytosis was determined by flow cytometry and with a fluorescence/luminescence microplate reader. After phagocytosis, oxidative stress was determined by flow cytometry. Both the intracellular and extracellular oxygen radical production by PMNs phagocytosing F. nucleatum was significantly greater than that of PMNs phagocytosing P. gingivalis and A. actinomycetemcomitans (P ≪ 0.01 by the Mann-Whitney test). Moreover, after 4 h of incubation, the oxidative stress of PMNs phagocytosing F. nucleatum was significantly greater than that of PMNs phagocytosing P. gingivalis and A. actinomycetemcomitans. We conclude that a high level of superoxide production by PMNs may damage not only periodontopathic bacteria but also PMNs themselves, and may be correlated with the destruction of periodontal tissue.