Hiroe Kikuzaki’s research while affiliated with Nara University and other places

We found that a water-soluble extract of coriander (Coriandrum sativum L.) (leaves, petioles and stems) inhibits antigen-induced degranulation of RBL-2H3 cells, a rat basophil leukemia cell line. The aim of this study was to elucidate the anti-degranulation active components in the extract. The methanol-eluate fraction obtained by fractionation of the water-soluble extract using MCI gel column chromatography had strong activity, and eight components were isolated and identified. Two of them were identified as new compounds, (3S)-3-methyl-6-hydroxyisocoumarin 8-O-β-D-glucopyranoside (compound 1) and (7S,8R)-7,8-dihydro-8-β-D-glucopyranosyloxy-4-methoxy-7-methyl-5H-fro[2,3-g][2]benzopyran-5-one (compound 2). As a result of evaluation of anti-degranulation activity of eight components, seven of them, such as tryptophan, phenylalanine, dihydroxycoumarin glucoside, quercetin glycoside, rutin, compound 1, and compound 2, had the activity. These results indicated that the water-soluble extract of coriander contains several anti-degranulation substances.

Oxidative stress causes the progression of diabetes and its complications; thus, maintaining the balance between reactive oxygen species produced by hyperglycemia and the antioxidant defense system is important. We herein examined the antioxidant potential of non-extractable fractions of dried persimmon (NEP) against oxidative stress in diabetic rats. Rats with streptozotocin-induced type 1 diabetes (50 mg/kg body weight) were administered NEP for 9 weeks. Antioxidant enzyme activities and concentration of antioxidants in liver tissues were analyzed with a microplate reader. Extensor digitorum longus (EDL) and soleus muscle fibers were stained with succinate dehydrogenase and muscle fiber sizes were measured. The administration of NEP increased the body weight of diabetes rats. Regarding antioxidant activities, the oxygen radical absorbance capacity and superoxide dismutase activity in liver tissues significantly increased. In addition, increases in glutathione peroxidase activity in liver tissues and reductions in the cross-sectional area of EDL muscle fibers were significantly suppressed. In these results, NEP improved the antioxidant defense system in the liver tissues of diabetic rats, in addition to attenuating of muscle fibers atrophy against oxidative damage induced by hyperglycemia.

Cuminum cyminum L. (cumin) is an annual plant of the Umbelliferae family native to Egypt. We previously showed that the aqueous extract of cumin seeds suppresses degranulation by downregulating the activation of antigen-induced intracellular signaling molecules in rat basophilic leukemia RBL-2H3 cells. However, the active substances in the extract have not yet been identified. Accordingly, herein, we aimed to ascertain the water-soluble substances present in cumin seeds that inhibit degranulation, which led to the identification of umbelliferose, a characteristic trisaccharide present in plants of the Umbelliferae family. Our study is the first to reveal the degranulation-suppressing activity of umbelliferose, and quantification studies suggest that cumin seed powder contains 1.6% umbelliferose. Raffinose, an isomer of umbelliferose, was also found to significantly suppress antigen-induced degranulation, but less so than umbelliferose. Both umbelliferose and raffinose contain sucrose subunits in their structures, with galactose moieties bound at different sites. These differences in structure suggest that the binding of galactose to the sucrose subunit at the α1-2 bond contributes to its strong degranulation-inhibiting properties.

Histamine, known as bioactive amine, is synthesized through histidine decarboxylase (HDC). HDC is the sole enzyme that catalyzes histamine production in the human body and thus HDC inhibitor is expected to control histamine-mediating biological activity by controlling histamine production. In the present study, active compound that inhibits HDC activity was sought from strawberry cultivar 'Tokun' that was the most effective cultivar among 11 different cultivar of strawberries. From active fraction of ethyl acetate soluble part, tiliroside, a flavonoid glucoside, was isolated as an HDC inhibitor with IC50 = 40.3 μM. Casuarictin, an ellagitannin, was detected from some active fractions and showed potent inhibition with IC50 = 3.3 μM. Judging from potency of inhibition and content of 'Tokun' extract, casuarictin rather than tiliroside contributed to HDC inhibition of 'Tokun' extract more effectively. Tiliroside, on the other hand, was thought to be a possible marker to predict effective strawberry cultivar for HDC inhibition.

Vegetables are rich sources of nutrients such as fiber, minerals, vitamins, and antioxidants. Vegetables also contain various free-form amino acids, which improves their nutritional and palatable value. Cooking alters the content of free amino acids in vegetables, which affects their nutritional values. In this study, free amino acid levels were evaluated after cooking vegetables by different methods, boiling, roasting in an oven, and using a microwave. Results showed that many vegetables analyzed contain aspartate and glutamine abundantly. On the other hand, hydroxyproline, cysteine, ornithine and citrulline are the free amino acids existing at low or undetectable levels in all vegetables tested. The total free amino acid content in vegetables tended to decrease after boiling, and almost the same amount of free amino acids was obtained in the cooking liquid. Roasting of vegetables in an oven resulted in an increase in the content of specific amino acids, including γ-aminobutyric acid (GABA). Thus, it is important to choose the right cooking methods to prevent the loss of free amino acids. The results of the present study emphasize the changes in the contents of free amino acids during cooking with methods that are typically used on a daily basis. Our study on the dynamics of free amino acids caused by various cooking methods provides ample information for future nutritional studies.

Rugosin G, an ellagitannin trimer, was isolated from the water-soluble fraction of red rose petals, and its inhibitory activity against recombinant human histidine decarboxylase was investigated. Rugosin G showed potent inhibition compared to ellagitannin monomers and a dimer with macrocyclic structure (oenothein B), suggesting the potent inhibition of rugosin G was attributed to its linear oligomeric conformation. Abbreviations: HDC, histidine decarboxylase; Me2CO, acetone; EtOAc, ethyl acetate

Sugarcane extract (Saccharum officinarum extract: SOE), a byproduct containing polyphenols obtained through the process of making raw sugar from sugarcane, exhibited an effect on the discoloration of salmon that suggests SOE inhibits lipid oxidation, which inhibits discoloration of carotenoid as a result. Therefore, we considered an in vitro evaluation method for inhibiting discoloration of carotenoid, and used this method to measure SOE's inhibitive effect on carotenoid discoloration. The results showed that the methylene chloride soluble portion (low-polarity fraction) had the strongest inhibitive effect. We then refined and isolated the components of the methylene chloride-soluble portion to obtain 13 known components and one new compound. Structural analysis revealed that the new compound is 3-[2-(β-D-glucopyranosyloxy)-4,6-dimethoxyphenyl]-1-(4-methoxyphenyl)-1-propanone, which is a glycoside of retrodihydrochalcone. The results suggest that, combined with the content and antioxidant effect of the isolated compounds, simulanol, a lignan, contributes most to inhibiting carotenoid discoloration through the methylene chloride-soluble portion in SOE.

Objective Secretory sphingomyelinase (sSMase) is one of the key enzymes involved in oxidative stress-related diseases [Biol. Pharm. Bull, 2013]. The elevation of its activity resulted in an increase of ceramide that is the bioactive lipid inducing cellular apoptosis, proliferation, and differentiation. In this study, we searched for novel sSMase inhibitors during some antioxidants which are expected to ameliorate oxidative stress-related diseases. Methods Each of several antioxidants was incubated with and sSMase derived from rats in the assay mixture (pH 5.0) and analyzed their inhibitory activity by using HPLC. Results Epicatechin 3-O-gallate (ECg) significantly inhibited sSMase activity as compared with non-gallate type catechins. In addition, Anti-Oxidant Biofactor (AOB) extract that is the mixture of fermented grain foods and catechins, markedly inhibited sSMase activity. Conclusion ECg and some gallate type catechins had a strong inhibitory effect on sSMase in a physiological plasma concentration (IC50=1.7–25.7 µM). This inhibition may be due to their specific structures such as galloyl residue, and it depends on the reducing activity. Moreover, antioxidant mixture such as AOB might inhibit synergistically sSMase. It will be further discussed.

Strawberry fruit contains many constituents, some of which have the potential to inhibit histidine decarboxylase (HDC) activity. HDC converts l-histidine to histamine, which is associated with allergic and other biological reactions in the human body. The HDC inhibition levels were different and the component ratios varied by genotype in strawberry. Among the 11 cultivars collected locally in Japan, ‘Tokun’ had an approximately ten times higher inhibition ratio than the lowest cultivar. The reproducibility was confirmed using five cultivars under the same conditions in a glass greenhouse, suggesting that genotypic variation is a major factor of HDC inhibition. The potential inhibitors of HDC might be polyphenols because they showed moderate correlations with HDC inhibition rates. Among the polyphenols, the anthocyanin content possessed a moderate negative correlation. Ascorbic acid, which contributes to the overestimation of total polyphenol, did not independently inhibit HDC activity. These findings will support the identification of potential HDC inhibitors in strawberry and indicated that genotypic differences would make useful probes for inhibitor identification. © 2017, Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.