Tsuneo Namba

Bio: Tsuneo Namba is an academic researcher from University of Toyama. The author has contributed to research in topics: Glycyrrhizin & Liver injury. The author has an hindex of 51, co-authored 224 publications receiving 7527 citations. Previous affiliations of Tsuneo Namba include Cairo University & National Research Institute of Police Science.

Mechanism of antihepatotoxic activity of glycyrrhizin. I: Effect on free radical generation and lipid peroxidation.

Abstract: The mechanism of antihepatotoxic action of atractylon, a main sesquiterpenic constituent of ATRACTYLODES rhizomes, was studied. Atractylon inhibited carbon tetrachloride (CCl 4 )-induced cytotoxicity in primary cultured rat hepatocytes and CCl 4 -induced lipid peroxidation by rat liver microsomes. However, atractylon increased the free radical generation by CCl 4 with rat liver microsomes in the presence of a radical trapping agent, phenyl T-butyl nitrone (PBN). In addition, atractylon generated free radical PER SE. Experiments using 13 CCl 4 instead of CCl 4 indicated that the increased free radicals consisted of those from 13 CCl 4 and from atractylon. Accumulated data support that although both CCl 4 and atractylon generate free radicals respectively by rat liver microsomes, free radical from CCl 4 conducts lipid peroxidation and produces liver lesion, while atractylon forms free radical which scavenges CCl 3 radical in the absence of PBN, inhibits lipid peroxidation by CCl 4 and suppresses CCl 4 -induced liver lesion.

Four Di-O-caffeoyl Quinic Acid Derivatives from Propolis. Potent Hepatoprotective Activity in Experimental Liver Injury Models

Abstract: The water extract of propolis (PWE) showed a strong hepatoprotective activity against CCl4-toxicity in rats and D-galactosamine (GalN)/lipopolysaccharide (LPS)-induced liver injury in mice. The PWE also showed a significant hepatoprotective activity against CCl4-induced liver cell injury in cultured rat hepatocytes. The in vitro hepatoprotective activity guided fractionation and chemical analysis led to the isolation of four dicaffeoyl quinic acid derivatives from the PWE. The structure of these isolates was determined to be methyl 3,4-di-O-caffeoyl quinate (1), 3,4-di-O-caffeoyl quinic acid (2), methyl 4,5-di-O-caffeoyl quinate (3), and 3,5-di-O-caffeoyl quinic acid (4) by spectroscopic methods. These compounds were more potent hepatoprotective agents than glycyrrhizin at a concentration of 10 micrograms/ml and 1 was the most potent among the four compounds in the cultured hepatocytes. Quinic acid (5) alone did not show hepatoprotective effects in cultured rat hepatocytes against CCl4-toxicity. On the other hand, chlorogenic acid (6) or caffeic acid alone was found to be less potent than the dicaffeoyl quinic acid derivatives.

Screening of various plant extracts used in ayurvedic medicine for inhibitory effects on human immunodeficiency virus type 1 (HIV-1) protease

Abstract: To identify substances with anti-human immunodeficiency virus (HIV) activity in traditional medicines, water and methanol extracts of crude drugs used in Indian traditional medicine (Ayurveda) were subjected to screening for their inhibitory effects on HIV type 1 protease (PR) The enzyme activity was determined by HPLC and of the 39 crude drugs tested, the extracts of the seeds of Areca catechu, the bark of Eugenia jambolana, the bark of Saraca indica and the stem bark of Terminalia arjuna inhibited the HIV-1 PR activity by more than 70% at a concentration of 02 mg/mL The most potent inhibition was shown by the A catechu extract, from which some procyanidins were isolated One of them, arecatannin B1 showed significant HIV-1-PR inhibitory activity

Inhibitory effects of Egyptian folk medicines on human immunodeficiency virus (HIV) reverse transcriptase

Abstract: Extracts of 41 medicinal plants used in Egyptian folk medicine were screened for their inhibitory effects on human immunodeficiency virus-1 reverse transcriptase. The extracts of fruits of Phyllanthus emblica, Quercus pedunculata, Rumex cyprius, Terminalia bellerica, Terminalia chebula and Terminalia horrida showed significant inhibitory activity with IC50 < or = 50 micrograms/ml. Through a bioassay guided-fractionation of the methanol extract of the fruit of P. emblica, putranjivain A (1) was isolated as a potent inhibitory substance with IC50 = 3.9 microM, together with 1,6-di-O-galloyl-beta-D-glucose (2), 1-O-galloyl-beta-D-glucose (3), kaempferol-3-O-beta-D-glucoside (4), quercetin-3-O-beta-D-glucoside (5) and digallic acid (6). The inhibitory mode of action by 1, 2 and 6 was non-competitive with respect to the substrate but competitive with respect to a template-primer. Furthermore, the stereochemistry of 1 was established in this paper by nuclear magnetic resonance spectroscopy.

Effect of tea polyphenols on glucan synthesis by glucosyltransferase from Streptococcus mutans

Abstract: In the course of our studies on the development of anti-plaque agents for prevention of dental caries, we investigated effects of some of tea preparations and their individual components on the glucan synthesis catalyzed by glucosyltransferase (GTF) from Streptococcus mutans. Extracts of green tea and black tea, and polyphenol mixtures showed appreciable inhibition in the synthesis of insoluble glucan. Among the components isolated from tea infusions, theaflavin and its mono- and digallates had potent inhibitory activities at concentrations of 1-10 mM against GTF. (+)-Catechin, (-)-epicatechin and their enantiomers had moderate inhibitory activities at these concentrations, while galloyl esters of (-)-epicatechin, (-)-epigallocatechin and (-)-gallocatechin had increased inhibitory activities.

Plant Products as Antimicrobial Agents

Abstract: The use of and search for drugs and dietary supplements derived from plants have accelerated in recent years. Ethnopharmacologists, botanists, microbiologists, and natural-products chemists are combing the Earth for phytochemicals and “leads” which could be developed for treatment of infectious diseases. While 25 to 50% of current pharmaceuticals are derived from plants, none are used as antimicrobials. Traditional healers have long used plants to prevent or cure infectious conditions; Western medicine is trying to duplicate their successes. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found in vitro to have antimicrobial properties. This review attempts to summarize the current status of botanical screening efforts, as well as in vivo studies of their effectiveness and toxicity. The structure and antimicrobial properties of phytochemicals are also addressed. Since many of these compounds are currently available as unregulated botanical preparations and their use by the public is increasing rapidly, clinicians need to consider the consequences of patients self-medicating with these preparations.

Tannins and Human Health: A Review

Abstract: Tannins (commonly referred to as tannic acid) are water-soluble polyphenols that are present in many plant foods. They have been reported to be responsible for decreases in feed intake, growth rate, feed efficiency, net metabolizable energy, and protein digestibility in experimental animals. Therefore, foods rich in tannins are considered to be of low nutritional value. However, recent findings indicate that the major effect of tannins was not due to their inhibition on food consumption or digestion but rather the decreased efficiency in converting the absorbed nutrients to new body substances. Incidences of certain cancers, such as esophageal cancer, have been reported to be related to consumption of tannins-rich foods such as betel nuts and herbal teas, suggesting that tannins might be carcinogenic. However, other reports indicated that the carcinogenic activity of tannins might be related to components associated with tannins rather than tannins themselves. Interestingly, many reports indicated negative association between tea consumption and incidences of cancers. Tea polyphenols and many tannin components were suggested to be anticarcinogenic. Many tannin molecules have also been shown to reduce the mutagenic activity of a number of mutagens. Many carcinogens and/or mutagens produce oxygen-free radicals for interaction with cellular macromolecules. The anticarcinogenic and antimutagenic potentials of tannins may be related to their antioxidative property, which is important in protecting cellular oxidative damage, including lipid peroxidation. The generation of superoxide radicals was reported to be inhibited by tannins and related compounds. The antimicrobial activities of tannins are well documented. The growth of many fungi, yeasts, bacteria, and viruses was inhibited by tannins. We have also found that tannic acid and propyl gallate, but not gallic acid, were inhibitory to foodborne bacteria, aquatic bacteria, and off-flavor-producing microorganisms. Their antimicrobial properties seemed to be associated with the hydrolysis of ester linkage between gallic acid and polyols hydrolyzed after ripening of many edible fruits. Tannins in these fruits thus serve as a natural defense mechanism against microbial infections. The antimicrobial property of tannic acid can also be used in food processing to increase the shelf-life of certain foods, such as catfish fillets. Tannins have also been reported to exert other physiological effects, such as to accelerate blood clotting, reduce blood pressure, decrease the serum lipid level, produce liver necrosis, and modulate immunoresponses. The dosage and kind of tannins are critical to these effects. The aim of this review is to summarize and analyze the vast and sometimes conflicting literature on tannins and to provide as accurately as possible the needed information for assessment of the overall effects of tannins on human health.