Koichi Aizawa

Tomato paste fraction inhibiting the formation of advanced glycation end-products.

A water-soluble and low-molecular-weight fraction (SB) was obtained from tomato paste. The effects of SB on the formation of advanced glycation end-products (AGE) in protein glycation were studied by the methods of specific fluorescence, ELISA and a Western blot analysis, using the anti-AGE antibody after incubating protein with sugar. The results suggest that SB had strong inhibitory activity, in comparison with aminoguanidine as a positive control, and that the inhibitory mechanism of SB differed from that of aminoguanidine to involve trapping of reactive dicarbonyl intermediates in the early stage of glycation. SB contained an antioxidant, rutin, which showed potent inhibitory activity. The results also suggest that rutin chiefly contributed to inhibiting the formation of AGE, and that other compounds in SB may also have been related to the activity.

Scabronines B, C, D, E and F, novel diterpenoids showing stimulating activity of nerve growth factor-synthesis, from the mushroom Sarcodon scabrosus

Abstract Novel cyathane-type diterpenoids, scabronines B – F (1 – 5) were isolated from the mushroom Sarcodon scabrosus . Their structures were determined by interpretation of their spectral data and chemical transformation. The absolute stereochemistry of scabronine C (2) was confirmed by the exciton chirality method, and the chemical transformation of scabronines B, C and D (1, 2 and 3) clarified their absolute structures. The absolute stereochemistries of scabronines E and F (4 and 5) were determined by comparison of their CD spectra with that of erinacine A (7). Among these compounds, scabronines B, C and E (1, 2 and 4) exhibit stimulating activity of the synthesis of a nerve growth factor.

Kinetic Study of the Quenching Reaction of Singlet Oxygen by Carotenoids and Food Extracts in Solution. Development of a Singlet Oxygen Absorption Capacity (SOAC) Assay Method

A kinetic study of the quenching reaction of singlet oxygen (1O2) with eight kinds of carotenoids and α-tocopherol was performed in ethanol/chloroform/D2O (50:50:1, v/v/v) solution at 35 °C. The overall rate constants, kQ (=kq+kr, physical quenching+chemical reaction), for the reaction of carotenoids with 1O2 were measured, using the competition reaction method, where endoperoxide was used as a singlet oxygen generator, 2,5-diphenyl-3,4-benzofuran (DPBF) as an UV-vis absorption prove, and α-tocopherol as a standard compound. The rate constants, kQ (S) and kQ (t1/2), were determined by analyzing the first-order rate constant (S) and the half-life (t1/2) of the decay curve of DPBF with carotenoids, respectively, showing good accordance with each other. Similar measurements were performed for tomato and carrot extracts. From the results, a new assay method that can quantify the singlet oxygen absorption capacity (SOAC) of antioxidants, including carotenoids, α-tocopherol, and vegetable extracts, has been proposed.

Inhibitory effect of a bitter melon extract on the P‐glycoprotein activity in intestinal Caco‐2 cells

Extracts of bitter melon, soybean, dokudami and welsh onion by 40% methanol increased the accumulation of rhodamine‐123 by Caco‐2 cells, suggesting that these extracts inhibited P‐glycoprotein (P‐gp). The extract of bitter melon was separated in a tC18 cartridge column and the eluate from 80% acetonitrile most markedly increased the [3H]‐daunomycin accumulation by Caco‐2 cells. The inhibitory compounds in the bitter melon fraction were isolated by HPLC with Pegasil C4 and Pegasil ODS columns. The HPLC fraction having the highest activity was analyzed by 1H‐NMR and FAB‐MS, and the active compound was identified as 1‐monopalmitin. The inhibitory activities of 1‐monopalmitin and its related compounds suggested that the inhibition of P‐gp activity was not dependent on the degree of unsaturation of fatty acid in the monoglyceride, but on the chain length. It was also suggested that the monoglyceride structure played an important role in the inhibition of P‐gp activity. Monoglycerides could therefore alter the pharmacokinetics of drugs by inhibiting the P‐gp‐mediated efflux.

Alleviative Effects of Quercetin and Onion on Male Reproductive Toxicity Induced by Diesel Exhaust Particles

Diesel exhaust particles (DEPs) are particulate matter from diesel exhaust that contain many toxic compounds, such as polyaromatic hydrocarbons (PAHs). Some toxicities of PAH are thought to be expressed via aryl hydrocarbon receptors (AhRs). The male reproductive toxicity of DEPs might depend on AhR activation induced by PAHs. We hypothesized that AhR antagonists protect against the male reproductive toxicity of DEPs. Quercetin is a flavonoid and a well-known AhR antagonist, while onion contains many flavonoids, including quercetin. Hence, we examined whether quercetin and onion have alleviative effects against the male reproductive toxicity induced by DEPs. BALB/c male mice were fed quercetin- or onion-containing diets and received 10 injections of DEP suspension or vehicle into the dorsal subcutaneous layer over 5 weeks. The mice were euthanized at 2 weeks, after the last treatment, and their organs were collected. Daily sperm production and total incidence of sperm abnormalities were significantly affected in the DEP groups as compared with the vehicle group, but the total incidence of sperm abnormalities in the quercetin + DEP-treated mice was significantly reduced as compared with the DEP-treated mice. The numbers of Sertoli cells were significantly decreased in DEP-treated mice as compared with the vehicle-treated mice, but, the numbers of Sertoli cells were significantly increased in the quercetin and the onion + DEP-treated mice as compared with the DEP-treated mice. These results clearly indicate alleviative effects of quercetin and onion against the male reproductive toxicity induced by DEP.

Dietary capsanthin, the main carotenoid in paprika (Capsicum annuum), alters plasma high-density lipoprotein-cholesterol levels and hepatic gene expression in rats.

The effects of dietary capsanthin, the main carotenoid in paprika (Capsicum annuum), on lipid metabolism were examined. Young male Wistar rats were fed diets containing paprika powder, paprika organic solvent extract, residue of paprika extract, and purified capsanthin. Administration of purified capsanthin for 2 weeks resulted in a significant increase in plasma HDL-cholesterol (P < 0.05) without detectable differences in plasma total cholesterol and TAG concentrations. A statistically significant correlation (r 0.567; P < 0.001) was found between dietary capsanthin concentrations and plasma HDL-cholesterol concentrations. Animals receiving diets containing two different capsanthin concentrations exhibited dose-dependent increases in plasma HDL-cholesterol (r 0.597; P < 0.005). While capsanthin was absent in the liver of animals fed the basal diet, it increased markedly in capsanthin-fed animals (P < 0.001). Quantitative analyses of hepatic mRNA levels revealed that capsanthin administration resulted in up-regulation of mRNA for apoA5 and lecithin cholesterol acyltransferase (LCAT), without significant differences in other mRNA levels related to HDL-cholesterol metabolism. These results suggest that capsanthin had an HDL-cholesterol-raising effect on plasma, and the potential to increase cholesterol efflux to HDL particles by increasing apoA5 levels and/or enhancement of LCAT activity.

Structural features of arabinogalactan-proteins from the fruit of Lycium chinense Mill.

In addition to the other arabinogalactan-proteins (AGPs) (Cp-1-C and -D) already reported, two kinds of AGP (Cp-2-B and Hp-2-C) were obtained from the fruit of Lycium chinense Mill. The ratio of arabinose to galactose was approximately 1:1 in both samples, and the carbohydrate was linked O-glycosidically to serine in Cp-2-B, and to both serine and threonine residues of the protein in Hp-2-C. The weight-average molecular weight was 71,000 for Cp-2-B and 120,000 for Hp-2-C. Both samples also contained non-reducing terminal 3-O- and 4-O-substituted galacturonic acids. The ratio of 6-O-substituted galactose (linear part) and 3,6-di-O-substituted galactose (branching point) was almost unity in both samples, being obviously different from the case of Cp-1-C (predominant in the branching domain) and Cp-1-D (predominant in the linear domain). These results offer fresh insight into the grouping of the AGPs, based on the ratio of 6-O- and 3,6-di-O-substituted galactosyl residues.

Development of Singlet Oxygen Absorption Capacity (SOAC) Assay Method. 2. Measurements of the SOAC Values for Carotenoids and Food Extracts

Recently a new assay method that can quantify the singlet oxygen absorption capacity (SOAC) of antioxidants was proposed. In the present work, kinetic study of the reaction of singlet oxygen ((1)O(2)) with carotenoids and vegetable extracts has been performed in ethanol/chloroform/D(2)O (50:50:1, v/v/v) solution at 35 °C. Measurements of the second-order rate constants (k(Q)(S)) and the SOAC values were performed for eight kinds of carotenoids and three kinds of vegetable extracts (red paprika, carrot, and tomato). Furthermore, measurements of the concentrations of the carotenoids included in vegetable extracts were performed, using a HPLC technique. From the results, it has been clarified that the total (1)O(2)-quenching activity (that is, the SOAC value) for vegetable extracts may be explained as the sum of the product {Σ k(Q)(Car-i)(S) [Car-i](i)} of the rate constant (k(Q)(Car-i)(S)) and the concentration ([Car (i)]) of carotenoids included in vegetable extracts.

Development of Singlet Oxygen Absorption Capacity (SOAC) Assay Method. 3. Measurements of the SOAC Values for Phenolic Antioxidants

Measurements of the singlet oxygen ((1)O(2)) quenching rates (k(Q) (S)) and the relative singlet oxygen absortpion capacity (SOAC) values were performed for 16 phenolic antioxidants (tocopherol derivatives, ubiquinol-10, caffeic acids, and catechins) and vitamin C in ethanol/chloroform/D(2)O (50:50:1, v/v/v) solution at 35 °C. It has been clarified that the SOAC method is useful to evaluate the (1)O(2)-quenching activity of lipophilic and hydrophilic antioxidants having 5 orders of magnitude different rate constants from 1.38 × 10(10) M(-1) s(-1) for lycopene to 2.71 × 10(5) for ferulic acid. The logarithms of the k(Q) (S) and the SOAC values for phenolic antioxidants were found to correlate well with their peak oxidation potentials (E(p)); the antioxidants that have smaller E(p) values show higher reactivities. In previous works, measurements of the k(Q) (S) values for many phenolic antioxidants were performed in ethanol. Consequently, measurements of the k(Q) (S) and relative SOAC values were performed for eight carotenoids in ethanol to investigate the effect of solvent on the (1)O(2)-quenching rate. The k(Q) (S) values for phenolic antioxidants and carotenoids in ethanol were found to correlate linearly with the k(Q) (S) values in ethanol/chloroform/D(2)O solution with a gradient of 1.79, except for two catechins. As the relative rate constants (k(Q)(AO) (S)/k(Q)(α-Toc) (S)) of antioxidants (AO) are equal to the relative SOAC values, the SOAC values do not depend on the kinds of solvent used, if α-tocopherol is used as a standard compound. In fact, the SOAC values obtained for carotenoids in mixed solvent agreed well with the corresponding ones in ethanol.

Toll-like Receptors as a Target of Food-derived Anti-inflammatory Compounds

Background: Vegetable-rich diets are associated with the reduced risk of inflammatory diseases. Results: Iberin, an isothiocyanate compound from cabbage, targeted TLRs, disrupted TLR dimerization, and inhibited the inflammatory responses. Conclusion: The TLR dimerization step is a target of food-derived anti-inflammatory compounds. Significance: These findings extend our understanding of how isothiocyanates show their medical benefits as anti-inflammatory food components. Toll-like receptors (TLRs) play a key role in linking pathogen recognition with the induction of innate immunity. They have been implicated in the pathogenesis of chronic inflammatory diseases, representing potential targets for prevention/treatment. Vegetable-rich diets are associated with the reduced risk of several inflammatory disorders. In the present study, based on an extensive screening of vegetable extracts for TLR-inhibiting activity in HEK293 cells co-expressing TLR with the NF-κB reporter gene, we found cabbage and onion extracts to be the richest sources of a TLR signaling inhibitor. To identify the active substances, we performed activity-guiding separation of the principal inhibitors and identified 3-methylsulfinylpropyl isothiocyanate (iberin) from the cabbage and quercetin and quercetin 4′-O-β-glucoside from the onion, among which iberin showed the most potent inhibitory effect. It was revealed that iberin specifically acted on the dimerization step of TLRs in the TLR signaling pathway. To gain insight into the inhibitory mechanism of TLR dimerization, we developed a novel probe combining an isothiocyanate-reactive group and an alkyne functionality for click chemistry and detected the probe bound to the TLRs in living cells, suggesting that iberin disrupts dimerization of the TLRs via covalent binding. Furthermore, we designed a variety of iberin analogues and found that the inhibition potency was influenced by the oxidation state of the sulfur. Modeling studies of the iberin analogues showed that the oxidation state of sulfur might influence the global shape of the isothiocyanates. These findings establish the TLR dimerization step as a target of food-derived anti-inflammatory compounds.