Green Tea Catechins Quench the Fluorescence of Bacteria-Conjugated Alexa Fluor Dyes

Abstract

Accumulating evidence suggests that Green tea polyphenolic catechins, especially the (-)-epigallocatechin gallate (EGCG), can be cross-linked to many proteins, and confer a wide range of anti-bacterial activities possibly by damaging microbial cytoplasmic lipids and proteins. At the doses that conferred protection against lethal polymicrobial infection (induced by cecal ligation and puncture), EGCG significantly reduced bacterial loads particularly in the liver and lung. To elucidate its bactericidal mechanisms, we determined whether EGCG affected the fluorescence intensities of bacteria-conjugated Alexa Fluor 488 or 594 dyes. When mixed with unconjugated Alexa Fluor 488 or 594 dyes, EGCG or analogs did not affect the fluorescence intensity of these dyes. In a sharp contrast, EGCG and some analogs (e.g., Catechin Gallate, CG), markedly reduced the fluorescence intensity of Gram-positive Staphylococcus aureus-conjugated Alexa 594 and Gram-negative Escherichia coli-conjugated Alexa 488. Interestingly, co-treatment with ethanol impaired the EGCG-mediated fluorescence quenching of the G+ S. aureus, but not of the G- E. coli-conjugated Alexa Flour dyes. In light of the notion that Alexa Fluor dyes can be quenched by aromatic amino acids, it is plausible that EGCG exerts anti-microbial activities possibly by altering microbial protein conformations and functions. This possibility can now be explored by screening other fluorescence-quenching agents for possible antimicrobial activities.

Molecular mechanism and therapeutic modulation of high mobility group box 1 release and action: an updated review

“…Even when given orally, EGCG still rescued mice from lethal sepsis, significantly increasing animal survival rates from 16% to 44% [141]. Intriguingly, we found that EGCG facilitated bacterial elimination in selective organs (e.g., the liver and lung) in an animal model of sepsis [147]. It is not yet known whether these antibacterial properties are attributable to the possibilities that EGCG directly kill microbes by altering microbial protein conformations and functions, or indirectly by modulating macrophage-associated innate immune responses.…”

EGCG induces G-CSF expression and neutrophilia in experimental sepsis

“…5). In light of the findings that EGCG dramatically reduced bacterial loads in the liver [35], it is possible that elevation of peritoneal neutrophils may facilitate elimination of invading pathogens in the peritoneal cavity.…”

“…Remarkably, the elevation of peritoneal G-CSF levels was associated with a specific increase in neutrophil counts in the peritoneal fluid. It remains to be determined whether the elevated G-CSF might have facilitated the proliferation of neutrophil, which may contribute to an effective bacterial elimination during a late stage of sepsis [35]. Indeed, G-CSF has been shown to stimulate the proliferation of neutrophils [36;37], and widely used to accelerate recovery from neutropenia (an abnormal neutrophil deficiency) in cancer patients undergoing chemotherapy [38], preventing cancer patients from subsequent infections and sepsis.…”

“…After all, EGCG also exhibits a wide spectrum of anti-bacterial [35;51;52], anti-viral [53;54], anti-fungal [55], and anti-inflammatory [20;21;23] properties, which may collectively account for its protective effects in animal models of lethal sepsis. Given the essential roles of the innate immune cells (such as macrophages, monocytes and neutrophils) in eliminating invading pathogens and initiating inflammatory responses [19], it may be important to develop anti-inflammatory agents capable of facilitating microbial elimination for the treatment of lethal inflammatory diseases.…”

Inhibition by Epigallocatechin Gallate of IL-1–Induced Urokinase-Type Plasminogen Activator Expression and Collagen Degradation by Corneal Fibroblasts

“…13 (-)-Epigallocatechin-3-gallate (EGCG), the principal polyphenol in extracts of green tea, has been shown to possess various beneficial effects on cancer, [14][15][16] allergy, 17 hypertension, 18 atherosclerosis, 19 diabetes, 20 as well as bacterial and viral infection. 21,22 EGCG has thus been found to suppress tumor growth and angiogenesis by inhibiting MMP2 and -9 expression in tumor cells. 23,24 Topical administration of EGCG was also shown to inhibit corneal neovascularization in rabbits through suppression of the expression of VEGF and cyclooxygenase-2, 25 to attenuate inflammatory responses of the ocular surface in a mouse model of dry eye, 26 and to limit the development of corneal opacity caused by alkali-burn injury to the cornea in mice.…”