Catechin-mediated restructuring of a bacterial toxin inhibits activity

Abstract

Background: Catechins, polyphenols derived from tea leaves, have been shown to have antibacterial properties, through direct killing of bacteria as well as through inhibition of bacterial toxin activity. In particular, certain catechins have been shown to have bactericidal effects on the oral bacterium, Aggregatibacter actinomycetemcomitans, as well as the ability to inhibit a key virulence factor of this organism, leukotoxin (LtxA). The mechanism of catechin-mediated inhibition of LtxA has not been shown. Methods: In this work, we studied the ability of six catechins to inhibit LtxA-mediated cytotoxicity in human white blood cells, using Trypan blue staining, and investigated the mechanism of action using a combination of techniques, including fluorescence and circular dichroism spectroscopy, confocal microscopy, and surface plasmon resonance. Results: We found that all the catechins except (−)-catechin inhibited the activity of this protein, with the galloylated catechins having the strongest effect. Pre-incubation of the toxin with the catechins increased the inhibitory action, indicating that the catechins act on the protein, rather than the cell. The secondary structure of LtxA was dramatically altered in the presence of catechin, which resulted in an inhibition of toxin binding to cholesterol, an important initial step in the cytotoxic mechanism of the toxin. Conclusions: These results demonstrate that the catechins inhibit LtxA activity by altering its structure to prevent interaction with specific molecules present on the host cell surface. General Significance: Galloylated catechins modify protein toxin structure, inhibiting the toxin from binding to the requisite molecules on the host cell surface.

Epigallocatechin gallate inhibits leukotoxin release by Aggregatibacter actinomycetemcomitans by promoting association with the bacterial membrane

“…Each curve was normalized by dividing by the corresponding 1‐hr time point of each growth curve to facilitate comparison between the curves. For a negative control, the same concentrations of C, a nongalloylated catechin was used; nongalloylated catechins, such as C, have been shown to have limited antibacterial properties (Ikigai, Nakae, Hara, Nakae, Hara, & Shimamura, ), and we have previously shown that C has limited anti‐toxin activity, in contrast to the galloylated catechins (Chang et al, ). Figure a shows that micromolar concentrations of EGCg inhibit the growth of A. actinomycetemcomitans .…”

“…Grape extract was shown to inhibit the activity of the cholera toxin (CT) produced by Vibrio cholerae (Reddy et al, ); when the authors investigated the inhibitory activity of the specific polyphenolic compounds comprising the extract, they observed that EGCg was the most active component (Cherubin et al, ). Similarly, we have shown that EGCg deactivates the toxic activity of the leukotoxin (LtxA) produced by A. actinomycetemcomitans by altering the secondary structure of LtxA and inhibiting the toxin's binding to cholesterol on the host cell membrane (Chang et al, ). Our finding closely reflects a previous study, in which it was shown that Psidium guajava (guava) extracts, particularly those from the leaves and twigs, neutralized the activity of LtxA by binding directly to the secreted LtxA rather than interacting with the host cell (Kwamin et al, ); guava leaves and bark have been reported to contain significant amounts of polyphenolic compounds, including catechins (Barbalho et al, ).…”

“…Over 4,000 naturally occurring polyphenols have been reported to have biological activity (Daglia, ), including catechins, which are extracts found in the green tea leaf, as well as in grape seeds, kiwi, strawberries, red wine, cacao, and other plant sources (Zanwar, Badole, Shende, Badole, & Shende, ). Among the catechin derivatives, epigallocatechin gallate (EGCg) has been frequently noted for its therapeutic effects (Ahn, Kawamura, Kim, Kawamura, & Kim, ; Chakrawarti, Agrawal, Dang, Agrawal, Dang, Gupta, & Gabrani, ; Chang, Huang, Lin, Huang, Lin, & Brown, ; Friedman, Henika, Levin, Mandrell, & Kozukue, ; Osterburg, Gardner, Hyon, Gardner, Hyon, Neely, & Babcock, ). Studies have shown that EGCg effectively lysed Acinetobacter baumannii clinical isolates that are highly antibiotic‐resistant (Osterburg et al, ) and inhibited the growth of Clostridium perfringens , a gram‐positive bacteria (Ahn et al, ).…”

Aggregatibacter actinomycetemcomitans leukotoxin: From mechanism to targeted anti‐toxin therapeutics

“…Catechins are polyphenols commonly found in foods like green tea, cocoa, red wine, along with a variety of fruits and vegetables, and are attributed to numerous health benefits due to their antioxidant and antimicrobial properties (Taylor, Hamilton‐Miller, & Stapleton, 2005; Yamagata, Tagami, & Yamori, 2015). Inspired by a report of inhibition of LtxA activity by catechins (Kawashima, 2011), as well as inhibition of A. actinomycetemcomitans OMVs (Saito, Tsuzukibashi, & Takada, 2012), we conducted a study to understand the mechanism of this inhibition (Chang, Huang, Lin, & Brown, 2019). This study investigated the inhibitory effects of six catechins.…”

Antibacterial effect of green tea and pomegranate peel extracts on Streptococcus mutans of orthodontic treated patients

“…Catechins are the most frequent and abundant polyphenolic compounds. The major green tea catechins include epigallocatechin-3-gallate (EGCG) and epicatechin −3-gallate (ECG), which constitute about 50 to 65% of total catechins and have a broad spectrum of antimicrobial activity against both of grampositive and gram-negative bacteria (Chang, Huang, Lin, & Brown, 2019).…”