(11g) Epigallocatechin Gallate Alters Leukotoxin Binding to Host and Bacterial Cell Membranes

Localized aggressive periodontitis (LAP) is a disease caused by Aggregatibacter actinomycetemcomitans. Not all strains of Aa are associated with disease however. Those that are most closely associated with disease produce more of a protein toxin, leukotoxin (LtxA) than nonpathogenic strains, demonstrating a close association between LtxA and pathogenicity. LtxA acts by killing immune cells, thus limiting the host’s immune response to infection. Thus, inhibition of LtxA function represents a possible therapeutic option that would eliminate this immunosuppressive function and enable clearance of the bacteria by normal immune mechanisms. Here, we have investigated the anti-LtxA properties of catechins, polyphenolic molecules isolated from various plant-based sources, including green tea. We observed that at very low concentrations, galloylated catechins significantly alter the structure of LtxA, and as a result, LtxA is unable to bind to cholesterol on the host cell membrane, an essential component of the toxin’s initial interactions with host cells. Interestingly, we observed that one of these galloylated catechins, epigallocatechin gallate (EGCg) prevents release of LtxA into the bacterial supernatant. We used a series of quantitative immunoblots and fluorescence spectroscopy to show that EGCg promotes binding of LtxA to the bacterial membrane. Together, these results demonstrate that a small molecule, EGCg, inhibits the affinity of LtxA for the host cell membrane while increasing the affinity of LtxA for the bacterial cell membrane. The implications of this phenomenon in immunosuppression are currently being investigated in a co-culture experiment.