Effect of Catechins on Aggregatibacter actinomycetemcomitans Vesicles with THP-1 Cells

Objectives: A.a is implicated in the etiology of localized aggressive periodontitis and produces several potential virulence factors including leukotoxin and cytolethal distending toxin. It is reported that vesicles contained a large amount of leukotoxin have the function that binds to membrane of the target cell. It is known that green tea catechins have antibacterial and antitoxicial effect. The purpose of this study was to determine the inhibition effect of tea catechins against cytotoxic activity of A.a vesicles.

Methods: A.a vesicle was mixed with THP-1 cells derived from acute monocytic leukemia cells and incubated at 37°C for appropriate period. The number of THP-1 cells was counted to assess viability. To investigate the effect of individual catechin components (C, GC, Cg, EGCg) on cytotoxic activity by A.a vesicles, addition of catechins to reaction mixture contained THP-1 cells and vesicles were tested. To clarify the action for inhibitory activity of the catechins on the interaction of the THP-1 cells and vesicles, after catechins was added and incubated for 30 min to SP-DiOC18 stained vesicles, THP-1 cells were added. Then, incorporation of SP-DiOC18 was observed by fluorescence microscope.

Results: When individual component of catechins were added to the reaction mixture containing vesicles and THP-1 cells, each catechin had some effect on cytotoxic activity. In addition, pretreatment of vesicles with individual catechin components resulted in the reduction of cytotoxic activity. Furthermore, vesicles did not bind to THP-1 cells by fluorescence microscope. All catechin components inhibited the ability of vesicles binding to cell membrane.

Conclusions: Taken together, it is possible to postulate that the inhibitory mechanisms of catechin on leukotoxin activity could be a result of binding of individual catechin component to vesicle, which may lead to the aggregation of the enzyme and the blockage of enzymatic activity.