Flavanols in somatic cell division and male meiosis of tea (Camellia sinensis) anthers

Young anthers excised from closed tea flower buds ( Camellia sinensis L.) were stained as fresh tissues with p-dimethylaminocinnamaldehyde reagent to localize flavanols associated with nuclei and chromosomes, apart from those flavanols stored in vacuoles. This staining reagent yields a blue colour for flavanols. In the nonsporogenic somatic cells of developing anthers, flavanols were found to be attached to chromosomes at all mitotic stages. Male meiosis started at a bud size of about 3.5 mm in diameter in pollen mother cells which displayed generally more or less pronounced blue nuclei and cytoplasm. The meiotic divisions from prophase I to telophase II were characterized by blue stained nuclei and chromosomes, but within the cytoplasm there was, if any, a random and very poor reaction for flavanols. Metaphase and telophase of meiotic divisions showed maximally condensed chromosomes staining dark blue. Early in telophase II, the cytoplasm was again stained blue; this faded at late tetrad stage. Flavanols of young mitotic and older non-mitotic anthers were determined using high pressure liquid chromatography--chemical reaction detection (HPLC-CRD). Catechin, epicatechin, B2, and epigallocatechin were minor compounds, whereas epicatechin gallate and epigallocatechin gallate were found in higher amounts. The major flavanol compound of the anthers, epicatechin gallate, exhibited a significant affinity to histone sulphate, as shown by UV-VIS spectroscopic titration.     

Interactions between cocoa flavanols and inorganic nitrate: Additive effects on endothelial function at achievable dietary amounts

Dietary intervention studies have shown that flavanols and inorganic nitrate can improve vascular function, suggesting that these two bioactives may be responsible for beneficial health effects of diets rich in fruits and vegetables. We aimed to study interactions between cocoa flavanols (CF) and nitrate, focusing on absorption, bioavailability, excretion, and efficacy to increase endothelial function. In a double-blind randomized, dose–response crossover study, flow-mediated dilation (FMD) was measured in 15 healthy subjects before and at 1, 2, 3, and 4 h after consumption of CF (1.4–10.9 mg/kg bw) or nitrate (0.1–10 mg/kg bw). To study flavanol–nitrate interactions, an additional intervention trial was performed with nitrate and CF taken in sequence at low and high amounts. FMD was measured before (0 h) and at 1 h after ingestion of nitrate (3 or 8.5 mg/kg bw) or water. Then subjects received a CF drink (2.7 or 10.9 mg/kg bw) or a micro- and macronutrient-matched CF-free drink. FMD was measured at 1, 2, and 4 h thereafter. Blood and urine samples were collected and assessed for CF and nitric oxide (NO) metabolites with HPLC and gas-phase reductive chemiluminescence. Finally, intragastric formation of NO after CF and nitrate consumption was investigated. Both CF and nitrate induced similar intake-dependent increases in FMD. Maximal values were achieved at 1 h postingestion and gradually decreased to reach baseline values at 4 h. These effects were additive at low intake levels, whereas CF did not further increase FMD after high nitrate intake. Nitrate did not affect flavanol absorption, bioavailability, or excretion, but CF enhanced nitrate-related gastric NO formation and attenuated the increase in plasma nitrite after nitrate intake. Both flavanols and inorganic nitrate can improve endothelial function in healthy subjects at intake amounts that are achievable with a normal diet. Even low dietary intake of these bioactives may exert relevant effects on endothelial function when ingested together.     

Tea flavanols inhibit cell growth and DNA topoisomerase II activity and induce endoreduplication in cultured Chinese hamster cells

Tea polyphenols are promising chemopreventive anticancer agents, the properties of which have been studied both in vitro and in vivo, providing evidence that – within this group of compounds – the tea flavanols are able to inhibit carcinogenesis, an effect that in some cases could be correlated with increased cell apoptosis and decreased cell proliferation. Of four main tea flavanols, namely (−)-epigallocatechin-3-gallate (EGCG), (−)-epigallocatechin (EGC), (+)-catechin (CA) and (−)-epicatechin (EC), it was found that EGCG was the most potent to inhibit dose dependently the topoisomerase II (TOPO II) catalytic activity isolated from hamster ovary AA8 cells. In the range of concentrations that caused TOPO II inhibition, a high level of endoreduplication, a rare phenomenon that consists in two successive rounds of DNA replication without intervening mitosis, was observed, while neither micronuclei nor DNA strand breaks (Comet assay) were detected at the same doses. We propose that the anticarcinogenic effect of tea flavanols can be partly explained by their potency and effectiveness to induce endoreduplication. Concerning such an induction, maximum effect seems to require a pyrogallol structure at the B-ring. Additional substitution with a galloylic residue at the C3 hydroxyl group leads to further augmentation of the effect. Thus, we suggest that the chemopreventive properties of tea flavanols can be at least partly due to their ability to interfere with the cell cycle and block cell proliferation at early stages of mitosis.     

Cocoa flavanols and cardiovascular health

Fruits and vegetables have historically been considered rich sources of essential dietary micronutrients, soluble fiber, and antioxidants. More recently they are have been recognized as important sources for a wide array of phytochemicals that individually, or in combination, may benefit vascular health. Flavonoids are the largest, and most widely distributed class of phytochemicals, and can be further subdivided into several different sub-classes. Several epidemiology studies have observed an inverse association between flavonoid intake and risk of cardiovascular mortality. One sub-class of flavonoids, the flavanols, is found in foods such as grapes, red wine, tea, cocoa and chocolate; however, it is important to note that common food processing practices can significantly reduce the levels of these compounds found in finished food products. Recent studies have examined the potential of flavanol-rich cocoa and chocolates to influence vascular health. In this review, we discuss evidence for the hypothesis that the consumption of flavanol-rich cocoa can reduce the risk for cardiovascular disease through a multiplicity of mechanisms, including changes in oxidant defense mechanisms, vascular reactivity, cytokine production, and platelet function. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth-promoting nitrogen nutrition affects flavonoid biosynthesis in young apple (Malus domestica Borkh.) leaves

Enhanced shoot growth and a decrease in flavonoid concentration in apple trees grown under high nitrogen (N) supply was observed in previous studies, along with increasing scab susceptibility of cultivar "Golden Delicious" after high N nutrition. Several hypotheses have suggested that there is a trade-off between primary and secondary metabolism because of competition for common substrates, but nothing is known about regulation at the enzyme level. In this study, a set of experiments was performed to elucidate the effect of N nutrition on the activities of key enzymes involved in flavonoid biosynthesis (phenylalanine ammonia-lyase [PAL], chalcone synthase/chalcone isomerase [CHS/CHI}, flavanone 3-hydroxylase [FHT], flavonol synthase [FLS], dihydroflavonol 4-reductase [DFR]) and the accumulation of different groups of phenylpropanoids. The inhibition of flavonoid accumulation by high N nutrition could be confirmed, but the influence of N supply on the flavonoid enzymes CHS/CHI, FHT, DFR, and FLS was not evident. However, PAL activity seems to be downregulated, thus forming a bottleneck resulting in a generally decreased flavonoid accumulation. Furthermore, the response of the scab-resistant cultivar "Rewena" to high N nutrition was not as strong as that of the susceptible cultivar "Golden Delicious".     

Nuclei of tea flowers as targets for flavanols

The tea plant (Camellia sinensis L.) is famous for its flavanol-based constituents being valuable for human health. These flavanols associate with the nuclei of tea flowers, which is demonstrated histochemically by blue colouration using the selective staining reagent p-dimethylaminocinnamaldehyde (DMACA). Sepals, petals, stamens, pollen tubes, ovaries and ovules were studied. All these organs were shown to contain flavanols in vacuolar compartments, in nuclei and, exceptionally, also in the cytoplasm of pollen tubes. In all cells, even in those lacking vacuoles, the nuclei stained blue for flavanols. The extremely divergent development, shape and function of the diverse flower organs did not basically influence the nuclear flavanol association. Nevertheless, within the limits of this study, a few tissue-dependent differences in staining intensity were obvious. Interactions between epicatechin and nuclear histone proteins (histone sulphate) were studied by UV-VIS spectroscopic titration and by means of Mauser diagrams. The results show that the observed association equilibria are strongly dependent on pH (8.0 and 7.4) and on the buffer used (Tris, phosphate).