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Gallic Acid, chemically 3,4,5-trihydroxybenzoic acid, C6H2(OH)3COOH, is a clear crystalline compound found in many plants and can be prepared commercially by the hydrolysis of tannic acid with sulfuric acid. Gallic acid has two fuctional groups in the same molecule, hydroxyl groups and a carboxylic acid group. They can yield various kinds of esters and salts. Gallic acid forms pyrogallol, or 1,2,3-trihydroxybenzene, C6H3(OH)3, which are widely used in the manufacturing azo dyes and photographic developers and to treat certain skin diseases. Gallic acid and its derivatives are used in making dyes and inks, photographic developers and used as astringents in medically. Some gallates are used as antioxidants in foods. Tannins (tannic acid or gallotannic acid) are esters of digallic acid. They are widely used in tanning leather , dyeing fabrics, manufacturing inks, and in various medical applications (as astringents and to treat some skin diseases).
Curr Drug Metab. 2003 Jun;4(3):241-8. Related Articles, Links
Gallic acid and gallic acid derivatives: effects on drug metabolizing enzymes.
Ow YY, Stupans I.
Center for Pharmaceutical Research, School of Pharmaceutical, Molecular and Biomedical Sciences, University of South Australia, SA, 5000, Australia.
Gallic acid and its structurally related compounds are found widely distributed in fruits and plants. Gallic acid, and its catechin derivatives are also present as one of the main phenolic components of both black and green tea. Esters of gallic acid have a diverse range of industrial uses, as antioxidants in food, in cosmetics and in the pharmaceutical industry. In addition, gallic acid is employed as a source material for inks, paints and colour developers. Studies utilising these compounds have found them to possess many potential therapeutic properties including anti-cancer and antimicrobial properties. In this review, studies of the effects of gallic acid, its esters, and gallic acid catechin derivatives on Phase I and Phase II enzymes are examined. Many published reports of the effects of the in vitro effects of gallic acid and its derivatives on drug metabolising enzymes concern effects directly on substrate (generally drug or mutagen) metabolism or indirectly through observed effects in Ames tests. In the case of the Ames test an antimutagenic effect may be observed through inhibition of CYP activation of indirectly acting mutagens and/or by scavenging of metabolically generated mutagenic electrophiles. There has been considerable interest in the in vivo effects of the gallate esters because of their incorporation into foodstuffs as antioxidants and in the catechin gallates with their potential role as chemoprotective agents. Principally an induction of Phase II enzymes has been observed however more recent studies using HepG2 cells and primary cultures of human hepatocytes provide evidence for the overall complexity of actions of individual components versus complex mixtures, such as those in food. Further systematic studies of mechanisms of induction and inhibition of drug metabolising enzymes by this group of compounds are warranted in the light of their distribution and consequent ingestion, current uses and suggested therapeutic potential. However, it must be noted that numerous constituents of foodstuffs have been found to be potent modulators of xenobiotic metabolism and the net human health effects may depend on concentrations of individual components and individual genetic makeup.
Nutr Cancer. 2004;49(2):191-9. Related Articles, Links
Cytotoxicity and antiproliferative activities of several phenolic compounds against three melanocytes cell lines: relationship between structure and activity.
Yanez J, Vicente V, Alcaraz M, Castillo J, Benavente-Garcia O, Canteras M, Teruel JA.
Department of Pathology, Faculty of Medicine, University of Murcia, Spain.
Polyphenolic compounds are widely distributed in the vegetable kingdom and are therefore consumed regularly in the human diet. Epidemiological studies suggest that foods rich in polyphenolic compounds contribute to reducing the risk of cancer. The purpose of our work is to: 1) study the possible cytotoxicity and antiproliferative effects of 13 polyphenolic compounds on 3 cell lines of melanocytes, 2 of melanoma (B16F10 and SK-MEL-1), and 1 of nontransformed melanocytes (Melan-a); and 2) identify the possible relationship between the chemical structure of the tested compounds and their effect on cellular viability. The said polyphenolic compounds corresponded to 8 flavonoids with varying hydroxyl and methoxyl substituents, related structurally through the oxidation state of their flavonoid skeleton, a catechin polymer and 4 phenolic acids. The cytotoxic activity of all the studied compounds was modest or not apparent. The flavonoids luteolin, tangeretin, baicalein, quercetin, and myricetin, and gallic acid showed antiproliferative effects on the tested lines. Our results suggest that a correlation exists between the structural oxidation state and the position, number, and nature of substituents of the polyphenolic compounds studied and their antiproliferative effects.
Free Radic Biol Med. 2004 Aug 1;37(3):287-303. Related Articles, Links
Potential toxicity of flavonoids and other dietary phenolics: significance for their chemopreventive and anticancer properties.
Galati G, O'Brien PJ.
Department of Pharmacology and Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada M5S 2S2.
Flavonoids, including isoflavones, are natural components in our diet and, with the burgeoning interest in alternative medicine, are increasingly being ingested by the general population. Plant phenolics, which form moieties on flavonoid rings, such as gallic acid, are also widely consumed. Several beneficial properties have been attributed to these dietary compounds, including antioxidant, anti-inflammatory, and anticarcinogenic effects. Flavonoid preparations are marketed as herbal medicines or dietary supplements for a variety of alleged nontoxic therapeutic effects. However, they have yet to pass controlled clinical trials for efficacy, and their potential for toxicity is an understudied field of research. This review summarizes the current knowledge regarding potential dietary flavonoid/phenolic-induced toxicity concerns, including their pro-oxidant activity, mitochondrial toxicity (potential apoptosis-inducing properties), and interactions with drug-metabolizing enzymes. Their chemopreventive activity in animal in vivo experiments may result from their ability to inhibit phase I and induce phase II carcinogen metabolizing enzymes that initiate carcinogenesis. They also inhibit the promotion stage of carcinogenesis by inhibiting oxygen radical-forming enzymes or enzymes that contribute to DNA synthesis or act as ATP mimics and inhibit protein kinases that contribute to proliferative signal transduction. Finally, they may prevent tumor development by inducing tumor cell apoptosis by inhibiting DNA topoisomerase II and p53 downregulation or by causing mitochondrial toxicity, which initiates mitochondrial apoptosis. While most flavonoids/phenolics are considered safe, flavonoid/phenolic therapy or chemopreventive use needs to be assessed as there have been reports of toxic flavonoid-drug interactions, liver failure, contact dermatitis, hemolytic anemia, and estrogenic-related concerns such as male reproductive health and breast cancer associated with dietary flavonoid/phenolic consumption or exposures.
J Ethnopharmacol. 2002 Jun;81(1):135-7. Related Articles, Links
Cancer chemopreventive effects of a Brazilian folk medicine, Juca, on in vivo two-stage skin carcinogenesis.
Nakamura ES, Kurosaki F, Arisawa M, Mukainaka T, Takayasu J, Okuda M, Tokuda H, Nishino H, Pastore F.
Toyama Medical and Pharmaceutical University, Sugitani 2630, Toyama 930-0194, Japan.
Gallic acid (1) and methyl gallate (2) were isolated from Juca, a Brazilian folk medicine, fruits of Caesalpinia ferrea MART (Leguminosae), decreased significantly the average number of papillomas per mouse in the experiment of the promoting effects of 12-O-tetra- decanoylphorbol-13-acetate (TPA) on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene (DMBA).
Int J Food Sci Nutr. 2004;55(5):351-362. Related Articles, Links
Protection capacity against low-density lipoprotein oxidation and antioxidant potential of some organic and non-organic wines.
Kalkan Yildirim H, Delen Akc Ay Y, Guvenc U, Yildirim Sozmen E.
Department of Food Engineering Ege University 35100 Bornova Izmir.
Current research suggests that phenolics from wine may play a positive role against oxidation of low-density lipoprotein (LDL), which is a key step in the development of atherosclerosis. Considering the effects of different wine-making techniques on phenols and the wine consumption preference influencing the benefical effects of the product, organically and non-organically produced wines were obtained from the grapes of Vitis vinifera origin var: Carignan, Cabernet Sauvignon, Merlot, Grenache, Columbard and Semillon. Levels of total phenols [mg/l gallic acid equivalents (GAE)], antioxidant activity (%) and inhibition of LDL oxidation [%, inhibition of diene and malondialdehyde (MDA) formation] were determined. Some phenolic acids (gallic acid, p-hydroxybenzoic acid, syringic acid, 2,3-dihydroxybenzoic acid, ferulic acid, p-coumaric acid and vanillic acid) were quantified by high-performance liquid chromatography equipped with an electrochemical detection carried at +0.65 V (versus Ag/AgCl, 0.5 muA full scale). The highest concentrations of gallic, syringic and ferulic acids were found in organic Cabernet Sauvignon; 2,3-dihydroxybenzoic acid in organic Carignan and p-coumaric and vanillic acids in non-organic Merlot wine. High levels of antioxidant activity (AOA), inhibition of LDL oxidation and total phenol levels were found in non-organic Merlot (101.950% AOA; 88.570% LDL-diene; 41.000% LDL-MDA; 4700.000 mg/l GAE total phenol) and non-organic Cabernet Sauvignon (92.420% AOA; 91.430% LDL-diene; 67.000% LDL-MDA; 3500.000 mg/l GAE total phenol) grape varieties. Concentrations of some individual phenolic constituents (ferulic, p-coumaric, vanillic) are correlated with high antioxidant activity and inhibition of LDL oxidation.The best r value for all examined characteristics was determined for gallic acid, followed by 2,3-dihydroxybenzoic, syringic, ferulic and p-coumaric acids. Negative correlation of vanillic with MDA and p-hydroxybenzoic acid with LDL were confirmed by principal component analysis (PCA) analyses. Red wines display a higher antioxidant activity (81.110% AOA) than white ones (19.512% AOA). The avarage level of LDL inhibition capacity in red wine was determined as 87.072% and for the white as 54.867%.
Biochem Biophys Res Commun. 2004 Dec 17;325(3):807-11. Related Articles, Links
Green tea polyphenols as inhibitors of ribonuclease A.
Ghosh KS, Maiti TK, Dasgupta S.
Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India.
Ribonucleases (RNases), which are essential for cleavage of RNA, may be cytotoxic due to undesired cleavage of RNA in the cell. The quest for small molecule inhibitors of members of the ribonuclease superfamily has become indispensable with a growing number exhibiting unusual biological properties. Thus, inhibitors of RNases may serve as potential drug candidates. Green tea catechins (GTC), particularly its major constituent (-)-epigallocatechin-3-gallate (EGCG), have reported potential against cell proliferation and angiogenesis induced by several growth factors including angiogenin, a member of the RNase superfamily. This study reports the inhibition of bovine pancreatic ribonuclease A (RNase A) by EGCG and GTC. This has been checked qualitatively by an agarose gel based assay. Enzyme kinetic studies with cytidine 2',3' cyclic monophosphate as the substrate have also been conducted. Results indicate substantial inhibitory activity of a noncompetitive nature with an inhibition constant of approximately 80muM for EGCG and approximately 100muM for GTC measured in gallic acid equivalents.
FEBS Lett. 2004 Nov 5;577(1-2):239-44. Related Articles, Links
Potential anti-atherogenic cell action of the naturally occurring 4-O-methyl derivative of gallic acid on Ang II-treated macrophages.
Oliveira MV, Badia E, Carbonneau MA, Grimaldi P, Fouret G, Lauret C, Leger CL.
Laboratoire de Nutrition Humaine et Atherogenese, EA 2993, Institut de Biologie, Universite Montpellier I, Montpellier, France.
We have recently established that the blood concentrations of gallic acid (GA), a polyphenolic component naturally found in food, and its O-methyl derivatives are very low (practically 1 muM) in physiological (postprandial) condition. Using acellular oxidant systems and macrophage-differentiated promonocytes (MDPs) THP-1, we show here that the direct and indirect (through depressing effect on the superoxide cell production) antioxidant properties of these components were not effective at these concentrations. In contrast, 4-O-methyl GA was the most efficient component to depress AT1R and CD36 mRNA expression in Ang II-treated MDPs, suggesting a strong inhibition of Ang II-triggered pro-atherogenic mechanisms of foam cell formation.