Inhibitory effects of areca nut extracts on phagocytosis of Actinobacillus actinomycetemcomitans ATCC 33384 by neutrophils

Background: Areca quid chewers have a higher prevalence of periodontal disease than non-chewers. Little is known about the influence of areca quid on the immune system. This study was to determine the possible effects of the areca nut on phagocytic activity of human neutrophils. Methods: Aqueous extracts of ripe areca nut without husk (rANE), fresh and tender areca nut with husk (tANE), a major alkaloid (arecoline), and a phenolic component ([+]-catechin) of areca nut were examined for their effects on cellular viability using trypan blue exclusion assay. The possible effects on the phagocytic activity of neutrophils against a periodontal pathogen, Actinobacillus actinomycetemcomitans ATCC 33384, were determined using flow cytometry and confocal laser scanning microscopy. Results: At the concentrations tested, rANE, tANE, arecoline, and (+)-catechin did not significantly affect viability of neutrophils. However, rANE, tANE, arecoline, and (+)-catechin inhibited the phagocytic activity of neutrophils in a dose-dependent manner. Approximately 50% of the relative phagocytic activity of neutrophils was affected when 50 mu g/ml of rANE, 400 mu g/ml of tANE, 20,000 mu g/ml of arecoline, or 2,500 mu g/ml of (+)-catechin was used. Decreased levels of internalized fluorescent bacteria were also demonstrated. However, arecoline or (+)-catechin alone could not be used to explain the inhibitory effects observed for rANE and tANE. Conclusions: Components of areca nut reduced the uptake of A. actinomycetemcomitans ATCC 33384 by human neutrophils. The inhibition of areca nut on phagocytosis of neutrophils may be one possible mechanism by which the areca nut compromises the periodontal health of areca quid chewers.