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  1. #1
    Senior Member FunkOdyssey's Avatar
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    I found this interesting.

    <div class='quotetop'>QUOTE </div><div class='quotemain'>Cancer Res. 2005 Mar 15;65(6):2059-64.
    The antifolate activity of tea catechins.

    Navarro-Perán E, Cabezas-Herrera J, García-Cánovas F, Durrant MC, Thorneley RN, Rodríguez-López JN.

    Grupo de Investigación de Enzimología, Departamento de Bioquímica y Biología Molecular A, Facultad de Biología, Universidad de Murcia, Spain.

    Abstract

    A naturally occurring gallated polyphenol isolated from green tea leaves, (-)-epigallocatechin gallate (EGCG), has been shown to be an inhibitor of dihydrofolate reductase (DHFR) activity in vitro at concentrations found in the serum and tissues of green tea drinkers (0.1-1.0 micromol/L). These data provide the first evidence that the prophylactic effect of green tea drinking on certain forms of cancer, suggested by epidemiologic studies, is due to the inhibition of DHFR by EGCG and could also explain why tea extracts have been traditionally used in "alternative medicine" as anticarcinogenic/antibiotic agents or in the treatment of conditions such as psoriasis. EGCG exhibited kinetics characteristic of a slow, tight-binding inhibitor of 7,8-dihydrofolate reduction with bovine liver DHFR (K(I) = 0.109 micromol/L), but of a classic, reversible, competitive inhibitor with chicken liver DHFR (K(I) = 10.3 micromol/L). Structural modeling showed that EGCG can bind to human DHFR at the same site and in a similar orientation to that observed for some structurally characterized DHFR inhibitor complexes. The responses of lymphoma cells to EGCG and known antifolates were similar, that is, a dose-dependent inhibition of cell growth (IC50 = 20 micromol/L for EGCG), G0-G1 phase arrest of the cell cycle, and induction of apoptosis. Folate depletion increased the sensitivity of these cell lines to antifolates and EGCG. These effects were attenuated by growing the cells in a medium containing hypoxanthine-thymidine, consistent with DHFR being the site of action for EGCG.

    PMID: 15781612</div>
    <div class='quotetop'>QUOTE </div><div class='quotemain'>J Antimicrob Chemother. 2006 Jun;57(6):1083-92. Epub 2006 Apr 3.
    Tea polyphenol epigallocatechin-3-gallate inhibits ergosterol synthesis by disturbing folic acid metabolism in Candida albicans.

    Navarro-Martínez MD, García-Cánovas F, Rodríguez-López JN.

    Grupo de Investigación de Enzimología, Departamento de Bioquímica y Biología Molecular A, Facultad de Biología, Universidad de Murcia, E-30100 Espinardo, Murcia, Spain.
    Abstract

    OBJECTIVES: Elucidation of the mechanism of action of epigallocatechin-3-gallate (EGCG) against Candida albicans and demonstration of the connection between its antifolate activity and other metabolic pathways involved in C. albicans survival are the major objectives of this study. METHODS: C. albicans ATCC 10231 and 12 clinical isolates were used. MICs of EGCG against C. albicans were determined according to NCCLS. C. albicans dihydrofolate reductase (DHFR) was purified using methotrexate-affinity chromatography and its inhibition by EGCG studied by spectroscopic techniques. Synergy experiments were performed by chequerboard tests by combining eight doubling concentrations of EGCG with another eight dilutions of azole compounds or terbinafine. Reversion experiments with leucovorin or S-adenosylmethionine were carried out, and the content of ergosterol was determined by a spectrophotometric method. RESULTS: EGCG is an efficient inhibitor of C. albicans DHFR (K(i) = 0.7 microM). As with other antifolates, the effects of EGCG on C. albicans can be highly attenuated by growing the cells in the presence of leucovorin. EGCG showed synergy with inhibitors of the ergosterol biosynthesis pathway in C. albicans such as azole antifungals and terbinafine. We demonstrate that by disturbing the folate metabolism, EGCG can inhibit ergosterol production. The molecular connection between the pathways is discussed. CONCLUSIONS: EGCG acts as an antifolate compound on C. albicans, disturbing its folic acid metabolism. This effect could explain the molecular mechanism for the synergy between EGCG and azole antifungals, and could represent a starting point for therapies involving antifolates and azoles used as an alternative for the treatment of C. albicans infections.

    PMID: 1658513</div>
    <div class='quotetop'>QUOTE </div><div class='quotemain'>Proteins. 2008 Jul;72(1):240-51.
    Mechanism of inhibition of wt-dihydrofolate reductase from E. coli by tea epigallocatechin-gallate.

    Spina M, Cuccioloni M, Mozzicafreddo M, Montecchia F, Pucciarelli S, Eleuteri AM, Fioretti E, Angeletti M.

    Department of Molecular, Cellular and Animal Biology, University of Camerino, Via Gentile III da Varano, 62032, Camerino (MC), Italy. michele.spina@unicam.it
    Abstract

    Dihydrofolate reductase (DHFR) is a ubiquitous enzyme involved in major biological process, including DNA synthesis and cancer inhibition, and its modulation is the object of extensive structural, kinetic, and pharmacological studies. In particular, earlier studies showed that green tea catechins are powerful inhibitors of bovine liver and chicken liver DHFR. In this article, we report the results of inhibition kinetics for the enzyme from another source (DHFR from E. coli) exerted by (-)-epigallocatechingallate (EGCG). Using different analytical techniques, we reported that EGCG acts as a bisubstrate inhibitor on the bacterial DHFR. Moreover, the combined approach of biosensor, kinetic, and molecular modelling analysis disclosed the ability of EGCG to bind to the enzyme both on substrate (DHF) and cofactor (NADPH) site. Collectively, our data have confirmed the selectivity of antifolate compounds with respect to the different source of enzyme (bacterial or mammalian DHFR) and the possible role of tea catechins as chemopreventive agents. 2008 Wiley-Liss, Inc.

    PMID: 1821496</div>
    <div class='quotetop'>QUOTE </div><div class='quotemain'>Int J Mol Sci. 2009 Dec 18;10(12):5398-410.
    Binding of natural and synthetic polyphenols to human dihydrofolate reductase.

    Sánchez-Del-Campo L, Sáez-Ayala M, Chazarra S, Cabezas-Herrera J, Rodríguez-López JN.

    Departamento de Bioquímica y Biología Molecular A, Facultad de Biología, Universidad de Murcia, E-30100 Espinardo, Murcia, Spain.
    Abstract

    Dihydrofolate reductase (DHFR) is the subject of intensive investigation since it appears to be the primary target enzyme for antifolate drugs. Fluorescence quenching experiments show that the ester bond-containing tea polyphenols (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) are potent inhibitors of DHFR with dissociation constants (K(D))of 0.9 and 1.8 muM, respectively, while polyphenols lacking the ester bound gallate moiety [e.g., (-)-epigallocatechin (EGC) and (-)-epicatechin (EC)] did not bind to this enzyme. To avoid stability and bioavailability problems associated with tea catechins we synthesized a methylated derivative of ECG (3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin; TMECG), which effectively binds to DHFR (K(D) = 2.1 muM). In alkaline solution, TMECG generates a stable quinone methide product that strongly binds to the enzyme with a K(D) of 8.2 nM. Quercetin glucuronides also bind to DHFR but its effective binding was highly dependent of the sugar residue, with quercetin-3-xyloside being the stronger inhibitor of the enzyme with a K(D) of 0.6 muM. The finding that natural polyphenols are good inhibitors of human DHFR could explain the epidemiological data on their prophylactic effects for certain forms of cancer and open a possibility for the use of natural and synthetic polyphenols in cancer chemotherapy.

    PMID: 20054477</div>
    "Also, can I rig some sort of enema out of household items?" -Tussman

    "I don't have the stamina for a 3-some, and I am a one-pump chump" -Ubiyca

  2. #2
    Senior Member FunkOdyssey's Avatar
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    On the other hand, this may not actually affect humans in practice:

    <div class='quotetop'>QUOTE </div><div class='quotemain'>J Physiol Pharmacol. 2009 Sep;60(3):103-8.
    Greeen tea extracts lower serum folates in rats at very high dietary concentrations only and do not affect plasma folates in a human pilot study.

    Augustin K, Frank J, Augustin S, Langguth P, Ohrvik V, Witthoft CM, Rimbach G, Wolffram S.

    Institute of Human Nutrition and Food Science, Christian Albrechts University, Kiel, Germany.
    Abstract

    Green tea catechins (GTC) have been shown to inhibit the activities of enzymes involved in folate uptake. Hence, regular green tea drinkers may be at risk of impaired folate status. The present experiments aimed at studying the impact of dietary GTC on folate concentrations and metabolism. In a human pilot study (parallel design) healthy men consumed for 3 weeks 6 capsules (approximately 670 mg GTC) per day (2 capsules with each principal meal) containing aqueous extracts of the leaves of Camellia sinensis (n=17) or placebo (n=16). No differences in plasma folate concentrations were observed between treatments. We further fed groups of 10 male rats diets fortified with 0, 0.05, 0.5, 1, or 5 g GTC/kg for 6 weeks. Only at the highest intake, GTC significantly decreased serum 5-methyl-tetrahydrofolate concentrations in rats, while mRNA concentrations of reduced folate carrier, proton-coupled folate transporter/heme carrier protein 1, and dihydrofolate reductase (DHFR) remained unchanged in intestinal mucosa. Using an in vitro enzyme activity assay, we observed a time- and dose-dependent inhibition of DHFR activity by epigallocatechin gallate and a green tea extract. Our data suggest that regular green tea consumption is unlikely to impair folate status in healthy males, despite the DHFR inhibitory activity of GTC.

    PMID: 19826188</div>
    "Also, can I rig some sort of enema out of household items?" -Tussman

    "I don't have the stamina for a 3-some, and I am a one-pump chump" -Ubiyca

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