Cancer chemoprevention with green tea catechins by targeting receptor tyrosine kinases

Recent studies indicate that receptor tyrosine kinases (RTKs), which play important roles in cell proliferation, are one of the possible targets of green tea catechins (GTCs) in cancer cell growth inhibition. (-)-Epigallocatechin-3-gallate (EGCG), the major catechin in green tea, inhibits cell proliferation and induces apoptosis in various types of cancer cells, including colorectal cancer and hepatocellular carcinoma cells, by blocking the activation of the epidermal growth factor receptor (EGFR) family of RTKs. EGCG inhibits the activation of insulin-like growth factor-1 receptor (IGF-1R) and VEGFR2, the other members of the RTK family, and this effect is also associated with the anticancer and chemopreventive properties of this agent. EGCG suppresses the activation of EGFR in part by altering membrane lipid organization and causing the subsequent inhibition of the dimerization and activation of this receptor. Preliminary trials have shown that GTCs successfully prevent the development and progression of precancerous lesions, such as colorectal adenomas, without causing severe adverse effects. The present report reviews evidence indicating that GTCs exert anticancer and chemopreventive effects by inhibiting the activation of specific RTKs, especially EGFR, IGF-1R, and VEGFR2, and concludes that targeting RTKs and their related signaling pathways by using tea catechins could be a promising strategy for the prevention of human cancers.     

The viscoelastic properties of soybean curd (tofu) as affected by soymilk concentration and type of coagulant

The viscoelastic properties of different types of tofu were investigated. Soymilk concentrations were 5, 6, 7, 8 and 9%. Coagulants used were 30 mm CaSO₄ or 30 mm glucono‐delta‐lactone (GDL). As the concentration of soymilk was increased viscosity and handling difficulties increased. A high concentration of soymilk in tofu gave a high break stress and produced hard tofu. The four‐element Burgers model fitted the creep behaviour and both viscous and elastic parameters could be acquired from model analysis, reflecting changes in elasticity and viscosity of tofu. The constant viscous parameter in the model increased with increasing soymilk concentration. The viscous parameters of viscoelastic materials like tofu gel, obtained from small deformation tests, seemed to correlate, to some extent, with the break stress obtained from large deformation tests. For hard tofu production increasing the soymilk concentration within a certain range and the partial replacement of calcium sulphate coagulant by GDL could be effective options.     

Effects of dissolved organic matter surrogates on the partitioning of 17beta-estradiol and p-nonylphenol between synthetic membrane vesicles and water

Partition coefficients of two estrogenic compounds, 17beta-estradiol (E2) and p-nonylphenol (NP), between synthetic membrane vesicles (K'lipw values) and water were determined using equilibrium dialysis to evaluate the potential biological uptake of these compounds with and without the presence of dissolved natural organic matter (DOM) surrogates, Suwannee River fulvic acid, dialyzed Aldrich humic acid, and polyphenolic tannic acid. Overall, K'lipw values for E2 and NP reduced by 20-30% with the increase of DOM concentration from 0 to approximately 4 mg of C/L, a typical DOM concentration in the aquatic environment. This trend for E2 and NP is similar to that obtained by other researchers for moderately hydrophobic compounds including polycyclic aromatic hydrocarbons with three or four rings. A three-phase compartment model with three independent interactions, the sorption of E2 or NP by DOM surrogate (Koc), the sorption of DOM surrogates by membrane vesicles (KlipDOM), and the partition of E2 or NP by membrane vesicles (Klipw), was proposed, and K'lipw values for E2 or NP in the presence of DOM were calculated. The model predicted the decrease in Klipw values with the increase of DOM concentration, and the predictions using the three linear interactions agreed satisfactorily with the experimental results at relatively lower concentration of DOM.     

Multifunctional Initiator with Platinum-Acetylide Dendritic Core for Living Polymerization of Isocyanides

A novel multifunctional initiator has been developed by peripheral modification of a Pt-acetylide dendrimer. Pd–Pt μ-ethynediyl units were introduced to the first-generation dendrimer by a divergent method. The dendritic initiator was applicable to the living polymerization of aryl isocyanides, producing high molecular weight polymers with a narrow polydispersity index in quantitative yields. The ³¹P NMR spectrum of the resulting polymer suggested that all Pd–Pt μ-ethynediyl units in the dendritic molecule actually functioned as an initiator.     

A Method for Systematic Assessment of Intrinsically Disordered Protein Regions by NMR

Intrinsically disordered proteins (IDPs) that lack stable conformations and are highly flexible have attracted the attention of biologists. Therefore, the development of a systematic method to identify polypeptide regions that are unstructured in solution is important. We have designed an “indirect/reflected” detection system for evaluating the physicochemical properties of IDPs using nuclear magnetic resonance (NMR). This approach employs a “chimeric membrane protein”-based method using the thermostable membrane protein PH0471. This protein contains two domains, a transmembrane helical region and a C-terminal OB (oligonucleotide/oligosaccharide binding)-fold domain (named NfeDC domain), connected by a flexible linker. NMR signals of the OB-fold domain of detergent-solubilized PH0471 are observed because of the flexibility of the linker region. In this study, the linker region was substituted with target IDPs. Fifty-three candidates were selected using the prediction tool POODLE and 35 expression vectors were constructed. Subsequently, we obtained ¹⁵N-labeled chimeric PH0471 proteins with 25 IDPs as linkers. The NMR spectra allowed us to classify IDPs into three categories: flexible, moderately flexible, and inflexible. The inflexible IDPs contain membrane-associating or aggregation-prone sequences. This is the first attempt to use an indirect/reflected NMR method to evaluate IDPs and can verify the predictions derived from our computational tools.     

Effect of modifying metabolic network on poly-3-hydroxybutyrate biosynthesis in recombinant Escherichia coli

The regulatory mechanism for poly-3-hydroxybutyrate (PHB) biosynthesis in recombinant Escherichia coli is markedly different from that of Ralstonia eutropha (formerly, Alcaligenes eutrophus) since the former efficiently synthesizes PHB during growth without any nutrient limitation. To analyze how the central metabolic pathways should be balanced with pathways necessary for cell growth and PHB formation, a stoichiometric model was developed to predict the theoretical maximum PHB production capacity for different metabolic variants. Flux analysis results illustrated the importance of the availability of acetyl-CoA and NADPH for achieving the maximum yield of PHB. In order to examine whether the increased availability of the above substances can enhance PHB synthesis in recombinant E. coli, both genetic and environmental perturbations were attempted. Several E. coli K12 derivatives, namely, HMS174, TA3516 (pta-/ack-), and DF11 (pgi-), were transformed with a plasmid which contains the native phb operon. The fermentation characteristics of these recombinant strains were studied and compared. In this study we examined the effects of intracellular acetyl-CoA accumulation, which may promote PHB synthesis in vivo, by perturbations induced from attenuation of acetate kinase and phosphotransacetylase (TA3516, blocked in the acetate pathway) and by cultivation of E. coli HMS174 on gluconate; it can convert gluconate to acetyl-CoA at a higher rate. The effects of intracellular accumulation of NADPH were investigated by introducing a perturbation induced from attenuation of phosphoglucose isomerase, which redirects the carbon flow to the pentose-phosphate (PP) pathway. Results from the analyses of these perturbations indicate that intracellular buildup of acetyl-CoA may not be able to promote PHB synthesis in vivo. On the other hand, since the biosynthesis of PHB in the pgi- mutant strain can utilize the NADPH overproduced through the PP pathway, the growth of the pgi- mutant on glucose was recovered, indicating that the overproduction of NADPH might be able to enhance PHB synthesis.     

Enhanced production of hydroxymethylfurfural from fructose with solid acid catalysts by simple water removal methods

This paper demonstrates two simple ways to increase 5-hydroxymethylfurfural (HMF) yield (selectivity) in fructose dehydration with various solid acid catalysts. One is a water removal from the reaction mixture by a mild evacuation at 0.97 × 10⁵ Pa; it increases HMF yield for various catalysts (heteropoly acid, zeolite, and acidic resin). The removal of water suppresses two undesired reactions: the hydrolysis of HMF to levulinic acid and the reaction of partially dehydrated intermediates to condensation products. The other method is a decrease in the particle (bead) size of the resin (Amberlyst-15). The crushed and sieved Amberlyst-15 powder in a size of 0.15–0.053 mm shows 100% HMF yield at high fructose concentration (50 wt.% in DMSO), which is to our knowledge the highest yield to date. Near-infrared spectroscopic characterization of adsorbed water suggests that the enhanced yield can be caused by an improved removal of adsorbed water in a small-size resin particle.     

Regiospecific analysis by ethanolysis of oil with immobilized <Emphasis Type="Italic">Candida antarctica</Emphasis> lipase

A mixture of oil/ethanol (1∶3, w/w) was shaken at 30°C with 4% immobilized Candida antarctica lipase by weight of the reaction mixture. The reaction regiospecifically converted FA at the 1- and 3-positions to FA ethyl esters, and the lipase acted on C₁₄−C₂₄ FA to a similar degree. The content of 2-MAG reached a maximum after 4 h; the content was 28–29 mol% based on the total amount of FA in the reaction mixture at 59–69% ethanolysis. Only 2-MAG were present in the reaction mixture during the first 4 h, and 1(3)-MAG were detected after 7 h. After removal of ethanol from the 4-h reaction mixture by evaporation, 2-MAG were fractionated by silica gel column chromatography. The contents of FA in the 2-MAG obtained by ethanolysis of several oils coincided well with FA compositions at the 2-position, which was analyzed by Grignard degradation. It was shown that ethanolysis of oil with C. antarctica lipase can be applied to analysis of FA composition at the 2-position in TAG.