Sachie Okubo

Inhibition of the infectivity of influenza virus by tea polyphenols

(-)Epigallocatechin gallate (EGCg) and theaflavin digallate (TF3) (1-10 microM) inhibited the infectivity of both influenza A virus and influenza B virus in Madin-Darby canine kidney (MDCK) cells in vitro. Study by electron microscope revealed that EGCg and TF3 (1 mM) agglutinated influenza viruses as well as did antibody, and that they prevented the viruses from adsorbing to MDCK cells. EGCg and TF3 more weakly inhibited adsorption of the viruses to MDCK cells. EGCg and TF3 (1-16 microM) also inhibited haemagglutination by influenza viruses. These findings suggest that tea polyphenols bind to the haemagglutinin of influenza virus, inhibit its adsorption to MDCK cells, and thus block its infectivity.

Mechanism of Synergy between Epigallocatechin Gallate and β-Lactams against Methicillin-Resistant Staphylococcus aureus

ABSTRACT Compared to MICs (more than 800 μg/ml) of (−)-epigallocatechin gallate (EGCg) against Escherchia coli, MICs of EGCg against methicillin-susceptible and methicillin-resistantStaphylococcus aureus (MSSA and MRSA) were 100 μg/ml or less. Furthermore, less than 25 μg EGCg per ml obviously reversed the high level resistance of MRSA to all types of tested β-lactams, including benzylpenicillin, oxacillin, methicillin, ampicillin, and cephalexin. EGCg also induced a supersusceptibility to β-lactams in MSSA which does not express mecA, encoding penicillin-binding protein 2′ (PBP2′). The fractional inhibitory concentration (FIC) indices of the tested β-lactams against 25 isolates of MRSA were from 0.126 to 0.625 in combination with 6.25, 12.5 or 25 μg of EGCg per ml. However, no synergism was observed between EGCg and ampicillin against E. coli. EGCg largely reduced the tolerance of MRSA and MSSA to high ionic strength and low osmotic pressure in their external atmosphere, indicating damage of the cell wall. Unlike dextran and lipopolysaccharide, peptidoglycan fromS. aureus blocked both the antibacterial activity of EGCg and the synergism between EGCg and oxacillin, suggesting a direct binding of EGCg with peptidoglycan on the cell wall. EGCg showed a synergistic effect with dl-cycloserine (an inhibitor of cell wall synthesis unrelated to PBP2′) but additive or indifferent effect with inhibitors of protein and nuclear acid synthesis. EGCg did not suppress either PBP2′ mRNA expression or PBP2′ production, as confirmed by reverse transcription-PCR and a semiquantitative PBP2′ latex agglutination assay, indicating an irrelevance between the synergy and PBP2′ production. In summary, both EGCg and β-lactams directly or indirectly attack the same site, peptidoglycan on the cell wall. EGCg synergizes the activity of β-lactams against MRSA owing to interference with the integrity of the cell wall through direct binding to peptidoglycan.

The bactericidal activity of tea and coffee

Extracts of black tea, green tea, pu‐erh tea or coffee inhibited the growth of various bacteria known to cause diarrhoeal diseases. Tea or coffee also showed bactericidal activity against Staphylococcus aureus and Vibrio parahaemolyticus.

The Protective Activity of Tea Catechins against Experimental Infection by Vibrio cholerae O1

Tea catechins inhibited the fluid accumulation induced by cholera toxin in sealed adult mice. The catechins also reduced fluid accumulation by Vibrio cholerae O1 in ligated intestinal loops of rabbits. These findings suggest that tea catechins may possess protective activity against V. cholerae O1.

Inhibition of influenza virus infection by tea.

Extracts of black tea inhibited the infectivity of influenza virus A and influenza virus B for Madin‐Darby Canine Kidney cells. Tea extract inhibited virus adsorption to the cells but did not inhibit virus replication in the cells.

Mitogenic activity of (−)epigallocatechin gallate on B-cells and investigation of its structure-function relationship

(-)Epigallocatechin gallate (EGCg), the main constituent of green tea, strongly enhanced the direct plaque-forming cell (PFC) response to sheep red blood cells (SRBC) in vitro and showed strong mitogenic activity for mouse splenic B-cells but not for splenic T-cells and thymocytes. The enhancement of B-cell proliferation was not mediated by macrophages since their removal did not eliminate the activity. Among the derivatives of catechin examined, (+)catechin (C); (-)epicatechin (EC); (-)-epigallocatechin (EGC); (-)epicatechin gallate (ECg); (-)epigallocatechin gallate (EGCg); and theaflavin digallate (TF3), only the derivatives with the galloyl group (ECg, EGCg, and TF3) displayed significant enhancement of the spontaneous proliferation of B-cells. Structural analogs of the catechin and galloyl groups were also examined in the system. Gallic acid and tannic acid induced some enhancement, but rutin, pyrogallol and caffeine did not. The results indicate that the galloyl group on EGCg was responsible for enhancement. However, the basic conformations of the catechins are also important, because ECg, EGCg, TF3, gallic acid, and tannic acid had quite different potencies to induce B-cell proliferation.

The anti‐haemolysin activity of tea and coffee

Extracts of tea and coffee inhibited the haemolytic activities of Staphylococcus aureusα‐toxin and Vibrio parahaemolyticus thermostable direct haemolysin (Vp‐TDH). Black tea had the strongest anti‐haemolysin activity. Green tea was more active than pu‐erh tea. Coffee had anti‐Vp‐TDH activity but not anti‐α‐toxin activity.

Nitazoxanide, a Nitrothiazolide Antiparasitic Drug, Is an Anti-Helicobacter pylori Agent with Anti-Vacuolating Toxin Activity

Nitazoxanide (NTZ), a synthesized drug of the nitrothiazolide class, was initially developed as an antiparasitic compound. This compound has recently been shown to have antibacterial activities against some bacterial pathogens. In the present study, NTZ and its main metabolite tizoxanide (TIZ) were found to have strong minimum inhibitory concentrations (MICs) against both metronidazole (MTZ)-resistant strains and sensitive clinical isolates of Helicobacter pylori. The MIC90 of both NTZ and TIZ against 37 clinical isolates was 8 μg/ml. Vacuolating toxin activity of H. pylori assayed by HeLa cell vacuole formation was inhibited by NTZ at a sub-MIC. In contrast, urease production by H. pylori was not specifically affected by the sub-MIC of NTZ. An acidic pH (pH 5.0) medium reduced the antimicrobial activity of the drug in terms of growth inhibition due to the low growth rate of the bacteria, but killing activity of NTZ against the bacteria was still observed. Thus, it was apparent that both NTZ and TIZ are highly effective against H. pylori, even when the bacteria are resistant to MTZ.

Erythrocyte-dependent mitogenic activity of epigallocatechin gallate on mouse splenic B cells.

We previously reported that epigallocatechin gallate (EGCg), the main constituent of tea catechins, displays mitogenic effect on mouse splenic B cells. During research into the mechanism(s), it was found that the mitogenic activity of EGCg was dependent on the presence of red blood cells (RBC). When RBC in T cell-depleted spleen cells were removed, EGCg did not enhance the proliferation of B cells and even showed toxic effect at 25-50 micrograms/ml. When mouse, rabbit or sheep RBC as well as RBC-ghosts were added into the cultures, EGCg showed the mitogenic activity at a range of 1-50 micrograms/ml. Thereafter, we preincubated RBC with EGCg at 4 degrees C for various times and then washed the RBC to remove free EGCg in the suspensions. The EGCg-preincubated RBC also enhanced B cell proliferation. As short as ten minutes was sufficient for EGCg to bind to RBC membrane. These results indicate that EGCg first attached to the membrane of RBC and then stimulated B cell proliferation. The above results suggest an important immunoregulatory function of RBC.

A cytotoxic serine proteinase isolated from mouse submandibular gland

We have isolated a novel cytotoxic factor from the submandibular glands of male BALB/c mice by Sephadex G-50 gel filtration chromatography and reverse-phase HPLC. The cytotoxic factor is a serine proteinase, which belongs to the mouse glandular kallikrein (mGK) family, with an Mr of approximately 27,000. The purified serine proteinase showed cytotoxic activity against mouse thymocytes in a dose-dependent manner, and a serine proteinase inhibitor, diisopropyl fluorophosphate, blocked its cytotoxic activity.