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Biomedical subjects

B N Timmermann

Publications and source records attributed to B N Timmermann.

31 records · Page 2Linked to original sources
PubMed1999

Antioxidant chemistry of green tea catechins. Identification of products of the reaction of (-)-epigallocatechin gallate with peroxyl radicals.

(-)-Epigallocatechin gallate (EGCG), isolated from green tea, displays antioxidant properties and is thought to act as an antioxidant in biological systems. However, the specific mechanisms of its antioxidant actions remain unclear. In this study, we have isolated and identified for the first time two reaction products of EGCG derived from its reaction with peroxyl radicals generated by thermolysis of the initiator 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). The products include a seven-membered B-ring anhydride and a novel dimer. The identification of these products provides the first unambiguous proof that the principal site of antioxidant reactions on the EGCG molecule is the trihydroxyphenyl B ring, rather than the 3-galloyl moiety. In contrast to phenoxyl radicals from simple phenolic antioxidants, an initially formed EGCG phenoxyl radical apparently does not form stable addition products with AMVN-derived peroxyl radicals. Characteristic reaction products may provide novel markers for EGCG antioxidant reactions in living systems.

Antioxidants↗
PubMed1999

Flavonoids and terpenoids from Luma gayana (Barn.) Burret.

The flavonoids 5-hydroxy-7-methoxyflavanone, 6,8-dimethyl-5,7-dihydroxyflavanone and 2',4'-dihydroxy-6'-methoxy-3',5'-dimethylchalcone, a mixture of alkyl esters of p-coumaric acid, the triterpenoids oleanolic acid and maslinic acid, the monoterpenoid 1 alpha,2 beta,4 beta-trihydroxy-p-menthane, the sesquiterpenoid clovandiol and beta-sitosterol were isolated from the aerial parts of Luma gayana (Barn.) Burret. This is the first report on the chemistry of this species.

Chile↗
PubMed1998

Lignans from Chilean propolis.

Three new (1, 3, 4) and two known lignans (2 and 5) were isolated from Chilean propolis. Compound 1 was identified as a trimeric coniferyl alcohol acetate and 3 as the diastereomer of the dimeric coniferyl alcohol acetate 2. Compound 4 was identified as a dihydrobenzofuran lignan aldehyde, which was isolated together with the related known acetate 5.

Chile↗
PubMed1998

Maxillary palps can mediate taste rejection of plant allelochemicals by caterpillars.

All caterpillars possess a pair of maxillary palps that "drum" the surface of foods during feeding. These chemosensory organs contain over 65% of a caterpillar's taste receptor cells, but their functional significance remains largely unknown. We examined their role in rejection of plant allelochemicals, using the tobacco hornworm (Manduca sexta) as a model insect and an extract from a plant species (Grindelia glutinosa) as a model stimulus. We selected this system because hornworms reject foods containing Grindelia extract, and because preliminary studies indicated that their maxillary palps respond to this extract. We hypothesized that Grindelia extract elicits rejection through stimulating: (1) olfactory receptor cells, (2) taste receptor cells, (3) oral mechanoreceptors, and/or (4) a postingestive response mechanism. Our results were consistent only with hypothesis 2: caterpillars approached Grindelia-treated diets without apparent hesitation, but rejected it within 6 s of initiating biting; Grindelia-treated solutions stimulated taste receptor cells in the maxillary palp, but not the other gustatory chemosensilla; and ablating the maxillary palps eliminated rejection of Grindelia-treated diets. Our results demonstrate that taste receptor cells in the maxillary palps mediate rejection of Grindelia extract, and provide the first direct evidence for the role of maxillary palps in rejection of plant allelochemicals.

Action Potentials↗
PubMed1998

Mass spectrometry of selected components of biological interest in green tea extracts.

Mass spectrometric methods including EIMS, FABMS, and LC/ESIMS have been surveyed as tools for the detection of catechins in extracts of green tea (Camellia sinensis). EIMS provide both molecular weight and structure information, including epimer differentiation, on compounds 1, 2, and 4 and some structural information with compounds 5 and 6. FABMS gives both molecular weight and structure information, by an retro-Diels-Alder mechanism, on all compounds. LC/ESIMS provides unambiguous molecular weight information on all compounds and some additional structural data are evident in the mass spectra of 5 and 6. LC/ESIMS is, thus, shown to be an appropriate method for the direct analysis of crude extracts of green tea. The information obtained in this work will be of importance in future studies involving identification of the components of green tea and for characterization of synthetic analogues.

Catechin↗
PubMed1998

A new antitubercular mulinane diterpenoid from Azorella madreporica Clos.

Bioactivity-guided fractionation of the petroleum ether extract of Azorella madreporica Clos has led to the isolation of the novel, antitubercular mulinane diterpenoid 1. The structure has been elucidated on the basis of its 1D and 2D NMR spectra and by comparison with mulinolic acid 2 and a dehydration product 3 obtained from 1. The MIC of 1 for growth inhibition of the H37Rv strain of Mycobacterium tuberculosis was determined as 20 microg/mL. LC-MS and NMR have suggested the presence of this new compound in four other species of Azorella.

Antitubercular Agents↗
PubMed1998

(-)-Epigallocatechin-3-gallate inhibition of ultraviolet B-induced AP-1 activity.

Green tea polyphenols have been shown to inhibit cancer in a variety of tumor models, including ultraviolet B (UVB)-induced non-melanoma skin cancer. In green tea extracts, the major dry mass constituent is the family of catechins, of which (-)-epigallocatechin-(3)-gallate (EGCG) is considered to be important for the chemopreventive activity. EGCG has been shown to have antioxidant properties, but there has been little progress toward identifying the specific targets and mechanisms of its action. Using cultured human keratinocytes, we show that UVB-induced AP-1 activity is inhibited by EGCG in a dose range of 5.45 nM to 54.5 microM. EGCG is effective at inhibiting AP-1 activity when applied before, after or both before and after UVB irradiation. EGCG also inhibits AP-1 activity in the epidermis of a transgenic mouse model. This work begins to define a mechanism by which EGCG could be acting to inhibit UVB-induced tumor formation.

Animals↗
PubMed1996

Prevention of photocarcinogenesis by topical administration of pure epigallocatechin gallate isolated from green tea.

Topical application of purified (-)-epigallocatechin-3-gallate (EGCG), a polyphenolic antioxidant isolated from green tea, inhibited photocarcinogenesis in BALB/cAnNHsd mice with no visible toxicity. Mice were treated with 0, 10, or 50 mg of EGCG in 200 microliters of acetone three times weekly for three weeks before ultraviolet (UV) treatments began and throughout the experiment. UV radiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps for 25 weeks. In the photocarcinogenesis study, mice received a total dose of approximately 2.1 x 10(6) J/m2. Skin cancer incidence in UV-irradiated mice was 96% at 28 weeks after the first UV treatment; EGCG at 10 or 50 mg reduced this incidence to 62% and 29%, respectively. UV-induced immunosuppression, assessed by the inability of UVB-irradiated mice to reject a syngeneic antigenic tumor, was not influenced by topical EGCG. Oral administration of 0, 100, or 500 mg of pure EGCG per liter of drinking water (approximately 0, 0.56, or 2.8 mg/day, respectively) did not decrease UV-induced skin tumor incidence, rate of primary tumor growth, or inability to reject antigenic tumors. Thus induction of skin tumors by UV radiation was significantly reduced by topical, but not by oral, administration of purified EGCG through a mechanism distinct from inhibition of photoimmunosuppression.

Administration, Topical↗
PubMed1996

Inhibitory effect of six green tea catechins and caffeine on the growth of four selected human tumor cell lines.

Green tea is an aqueous infusion of dried unfermented leaves of Camellia sinensis (family Theaceae) from which numerous biological activities have been reported including antimutagenic, antibacterial, hypocholesterolemic, antioxidant, antitumor and cancer preventive activities. From the aqueous-alcoholic extract of green tea leaves, six compounds (+)-gallocatechin (GC), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and caffeine, were isolated and purified. Together with (+)-catechin, these compounds were tested against each of four human tumor cells lines (MCF-7 breast carcinoma, HT-29 colon carcinoma, A-427 lung carcinoma and UACC-375 melanoma). The three most potent green tea components against all four tumor cell lines were EGCG, GC and EGC. EGCG was the most potent of the seven green tea components against three out of the four cell lines (i.e. MCF-7 breast cancer, HT-29 colon cancer and UACC-375 melanoma). On the basis of these extensive in vitro studies, it would be of considerable interest to evaluate all three of these components in comparative preclinical in vivo animal tumor model systems before final decisions are made concerning which of these potential chemopreventive drugs should be taken into broad clinical trials.

Caffeine↗
PubMedDate not supplied

Triterpenoids from Acaena pinnatifida R. et P.

Eight urs-12-ene triterpenoids, beta-sitosterol, (+)-catechin, and apigenin 7-O-glucoside were isolated from the leaves of Acaena pinnatifida R. et P. The triterpenoids were characterized as pomolic acid, pomolic acid-3-acetate, tormentic acid, 2-epi-tormentic acid, euscaphic acid, tormentic acid glucoside, niga-ichigoside F1, and niga-ichigoside F2.

Chile↗
PubMedDate not supplied

Phytochemical, morphological, and biological investigations of propolis from Central Chile.

Propolis from central Chile was investigated for its plant origin by microscopical analysis of pollen grains and leaf fragments found in the sample. The pollen grains that appear with significant higher frequency in the sample corresponded to four native and two introduced species, whereas leaf fragments corresponded to four native species. Seventeen phenolic compounds that belong to the phenylpropane, benzaldehyde, dihydrobenzofuran, or benzopyran classes, were isolated from an organic extract that was found to have a moderate growth inhibitory activity against Mycobacterium avium, M. tuberculosis, and two strains of Staphylococcus aureus. The components responsible for activity were determined.

Animals↗
PubMedDate not supplied

Propolis from Chilean matorral hives.

Viscidone (0.5%), vanillin, 3',4'-(methylendioxy)acetophenone, 3-ethoxy-4-methoxybenzaldehyde, cinnamic acid, 3-methoxy-4-hydroxymethyl ester were isolated from propolis of hives from Cuncumen. This is the first report on propolis composition of an arid and a Mediterranean type climate area.

Animals↗