Epidemiological, clinical and experimental studies have established a positive correlation between green tea consumption and cardiovascular health. Catechins, the major polyphenolic compounds in green tea, exert vascular protective effects through multiple mechanisms, including antioxidative, anti-hypertensive, anti-inflammatory, anti-proliferative, anti-thrombogenic, and lipid lowering effects. (1) Tea catechins present antioxidant activity by scavenging free radicals, chelating redox active transition-metal ions, inhibiting redox active transcription factors, inhibiting pro-oxidant enzymes and inducing antioxidant enzymes. (2) Tea catechins inhibit the key enzymes involved in lipid biosynthesis and reduce intestinal lipid absorption, thereby improving blood lipid profile. (3) Catechins regulate vascular tone by activating endothelial nitric oxide. (4) Catechins prevent vascular inflammation that plays a critical role in the progression of atherosclerotic lesions. The anti-inflammatory activities of catechins may be due to their suppression of leukocyte adhesion to endothelium and subsequent transmigration through inhibition of transcriptional factor NF-kB-mediated production of cytokines and adhesion molecules both in endothelial cells and inflammatory cells. (5) Catechins inhibit proliferation of vascular smooth muscle cells by interfering with vascular cell growth factors involved in atherogenesis. (6) Catechins suppress platelet adhesion, thereby inhibiting thrombogenesis. Taken together, catechins may be novel plant-derived small molecules for the prevention and treatment of cardiovascular diseases. This review highlights current developments in green tea extracts and vascular health, focusing specifically on the role of tea catechins in the prevention of various vascular diseases and the underlying mechanisms for these actions. In addition, the possible structure-activity relationship of catechins is discussed.

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Green Tea Catechins and Cardiovascular Health : An Update

Studies of interaction between colchicine and bovine serum albumin by fluorescence quenching method

Interaction of β-Lactoglobulin with Resveratrol and its Biological Implications

In 1970, three laboratories independently made a discovery that, for aromatic fluorophores embedded into different rigid and highly viscous media, the spectroscopic properties do not conform to classical rules. The fluorescence spectra can depend on excitation wavelength, and the excited-state energy transfer, if present, fails at the "red" excitation edge. These red-edge effects were related to the existence of excited-state distribution of fluorophores on their interaction energy with the environment and the slow rate of dielectric relaxation of this environment. In these conditions the site-selection can be provided by variation of the energy of illuminating light quanta, and the behaviour of selected species can be followed as a function of time and other variables. These observations found extensive application in different areas of research: colloid and polymer science, molecular biophysics, photochemistry and photobiology. In particular, they led to the development of very productive methods of studying the dynamics of dielectric relaxations in protein and membranes, using the tryptophan emission and the emission of a variety of probes. These studies were extended to the time domain with the observation of new site-selective effects in emission intensity and anisotropy decays. They stimulated the emergence and development of cryogenic energy-selective and single-molecular techniques that became valuable tools in their own right in chemistry and biophysics research. Site-selection effects were discovered for electron-transfer and proton-transfer reactions if they depended on the dynamics of the environment. This review is focused on the progress in the field of red-edge effects, their applications and prospects.

The red‐edge effects: 30 years of exploration

Animal and epidemiological studies suggest that green tea catechins may reduce the risk of cardiovascular diseases [e.g., coronary heart disease (CHD)]. The health benefit of green tea has been attributed to its antioxidant and anti-inflammatory properties; however, considerable evidence suggests that green tea and its catechins may reduce the risk of CHD by lowering the plasma levels of cholesterol and triglyceride. Although the mechanism underlying such effect of green tea is yet to be determined, it is evident from in vitro and in vivo studies that green tea or catechins inhibit the intestinal absorption of dietary lipids. Studies in vitro indicate that green tea catechins, particularly (-)-epigallocatechin gallate, interfere with the emulsification, digestion, and micellar solubilization of lipids, critical steps involved in the intestinal absorption of dietary fat, cholesterol, and other lipids. Based on the observations, it is likely that green tea or its catechins lower the absorption and tissue accumulation of other lipophilic organic compounds. The available information strongly suggests that green tea or its catechins may be used as safe and effective lipid-lowering therapeutic agents.

Green tea as inhibitor of the intestinal absorption of lipids : potential mechanism for its lipid-lowering effect

Recent studies have shown that various synthetic as well as therapeutically active naturally occurring flavonols possess novel luminescence properties that can potentially serve as highly sensitive monitors of their microenvironments in biologically relevant systems. We report a study on the interactions of bovine serum albumin (BSA) with the model flavonol 3-hydroxyflavone (3HF), using the excited-state proton-transfer (ESPT) luminescence of 3HF as a probe. Upon addition of BSA to the flavonoid solutions, we observe remarkable changes in the absorption, ESPT fluorescence emission and excitation profiles as well as anisotropy (r) values. Complexation of 3HF with protein results in a pronounced shift (20 nm) of the ESPT emission maximum of the probe (from lambda(max)(em) = 513 nm to lambda(max)(em) = 533 nm) accompanied by a significant increase in fluorescence intensity. The spectral data also suggest that, in addition to ESPT, the protein environment induces proton abstraction from 3HF leading to formation of anionic species in the ground state. Fairly high values of anisotropy are observed in the presence of BSA for the tautomer (r = 0.25) as well as anion (r = 0.35) species of 3HF, implying that both the species are located in motion-restricted environments of BSA molecules. Analysis of relevant spectroscopic data leads to the conclusions that two binding sites are involved in BSA-3HF interaction, and the interaction is slightly positively cooperative in nature with a similar binding constant of 1.1 - 1.3 x 10(5) M(-1) for both these sites. Proteins 2001;43:75-81.

Jayanti Guharay

Papers

Protein-flavonol interaction: fluorescence spectroscopic study.

Excited-state intramolecular proton transfer (ESIPT) and charge transfer (CT) fluorescence probe for model membranes

Influence of different environments on the excited-state proton transfer and dual fluorescence of fisetin

Excited state proton transfer fluorescence of 3-hydroxyflavone in model membranes

Characterization of the fluorescence emission properties of prodan in different reverse micellar environments.