Ushio Sankawa’s research while affiliated with The University of Tokyo and other places

Two new isoflavone dimers, kudzuisoflavone A and B have been isolated from yeast extracttreated cell suspension cultures of Pueraria lobata (Leguminosae). Their structures were characterized by spectral data, and they were considered to be formed by phenol oxidative coupling of two isoflavone moieties through C -C ortho-ortho and ortho-para couplings, respectively.

Hydrogenperoxide exogenously administerd to the suspension-cultured cells of Pueraria lobata stimulated a rapid disappearance of the constitutive isoflavonoids (malonylglucosides of daidzein and genistein) from the methanol soluble fraction of the cells, in a similar manner as observed in the cells treated with yeast extract or glycoprotein preparation of Phyto­phthora megasperma f. sp. glycinea. Rapid generation of H 2 O 2 was detected within 10 min after elicitation at the cell surface, presumably preceded by the activation of plasma membrane NAD(P)H-oxidases. Pretreatment of some representative NAD(P)H-oxidase inhibitors such as SHAM, DEDTC and KCN (1 mᴍ each) to the cells 1 h before elicitation resulted in almost complete inhibition of the elicitor-stimulated metabolism of isoflavonoids for 4 h, whereas treatment of the inhibitors at 1 h after elicitation showed no significant effect on the rapid isoflavonoid metabolism. These findings suggest that this type of response to elicitation could be regarded as a plausible initial defense strategy prior to the appearance of de novo synthesized defensive barriers such as phytoalexins and lignin in plant-pathogen interaction.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Chalcone synthase (CHS), a key enzyme in flavonoid biosynthesis, catalyses sequential decarboxylative condensations of p-coumaroyl-CoA with three malonyl-CoA molecules and cyclizes the resulting tetraketide intermediate to produce chalcone. Phenylglyoxal, an Arg selective reagent, was found to inactivate the enzyme, although no Arg is found at the active site. Conserved, non-active site Arg residues of CHS were individually mutated and the results were discussed in the context of the 3D structure of CHS. Arg199 and Arg350 were shown to provide important interactions to maintain the structural integrity and foldability of the enzyme. Arg68, Arg172 and Arg328 interact with highly conserved Gln33/Phe215, Glu380 and Asp311/Glu314, respectively, thus helping position the catalytic Cys-His-Asn triad and the (372)GFGPG loop in correct topology at the active site. In particular, a mutation of Arg172 resulted in selective impairment in the cyclization activities of CHS and stilbene synthase, a related enzyme that catalyses a different cyclization of the same tetraketide intermediate. These Arg residues and their interactions are well conserved in other enzymes of the CHS superfamily, suggesting that they may serve similar functions in other enzymes. Mutations of Arg68 and Arg328 had been found in mutant plants that showed impaired CHS activity.

Glucose and lipid metabolic parameters play crucial roles in metabolic syndrome and its major feature of insulin resistance. This study was designed to investigate whether dietary astaxanthin oil (ASX-O) has potential effects on metabolic syndrome features in an SHR/NDmcr-cp (cp/cp) rat model. Oral administration of ASX (50 mg/kg/day) for 22 weeks induced a significant reduction in arterial blood pressure in SHRcp. It also significantly reduced the fasting blood glucose level, homeostasis index of insulin resistance (HOMA-IR), and improved insulin sensitivity. The results also showed an improved adiponectin level, a significant increase in high-density lipoprotein cholesterol, a significant decrease in plasma levels of triglycerides, and non-esterified fatty acids. Additionally, ASX showed significant effects on the white adipose tissue by decreasing the size of the fat cells. These results suggest that ASX ameliorates insulin resistance by mechanisms involving the increase of glucose uptake, and by modulating the level of circulating lipid metabolites and adiponectin.

When anthocyanin synthesis was induced in cell suspension cultures of carrot (Daucus carota L. cv. Kurodagosun) by transfer to medium lacking 2,4-dichlorophenoxyacetic acid (2,4-D), phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), chalcone synthase (CHS, EC 6.-.-.-), and chalcone-flavanone isomerase (CHFI, EC 5.5.1.6) activities appeared, reaching maxima 6–7 days after transfer. The maximum specific activity of CHS was much lower than that of PAL or CHFI. In a medium containing 2,4-D, no anthocyanin was synthesized, PAL and CHFI activities were suppressed and CHS activity could not be detected at all. The activities of PAL and CHS in cells cultured without 2,4-D for 6 days began to decrease within 3–6 h of 2,4-D addition. CHS activity was completely repressed 24–36 h after the addition, but CHFI activity was almost unchanged at this time. After culture without 2,4-D for 6 days, cell suspensions were transferred to fresh media either lacking or containing 2,4-D. After transfer, PAL increased in both media within 3 h, whereas CHS activity and anthocyanin accumulation were coordinated and both were completely regulated by 2,4-D. Changes in CHS activity rather than PAL activity correlate with changes in anthocyanin accumulation under various culture conditions.

We investigated the effects of a dietary astaxanthin (ASX-O) on oxidative parameters in spontaneously hypertensive rats (SHR), by determination of the level of nitric oxide (NO) end products nitrite/nitrate (NO2-/NO3-) and lipid peroxidation in ASX-O-treated SHR. Oral administration of the ASX-O significantly reduced the plasma level of NO2-/NO3- compared to the control vehicle (p<0.05). The lipid peroxidation level, however, was reduced in both ASX-O- and olive oil-treated groups. We also analyzed the post-treatment effects of ASX-O on the vascular tissues by examining the changes in the aorta and coronary arteries and arterioles. The dietary ASX-O showed significant reduction in the elastin bands in the rat aorta (p<0.05). It also significantly decreased the [wall : lumen] aerial ratio of the coronary arteries. These results suggest that ASX-O can modulate the oxidative condition and may improve vascular elastin and arterial wall thickness in hypertension.

Astaxanthin (1), a red-orange carotenoid pigment, is a powerful biological antioxidant that occurs naturally in a wide variety of living organisms. The potent antioxidant property of 1 has been implicated in its various biological activities demonstrated in both experimental animals and clinical studies. Compound 1 has considerable potential and promising applications in human health and nutrition. In this review, the recent scientific literature (from 2002 to 2005) is covered on the most significant activities of 1, including its antioxidative and anti-inflammatory properties, its effects on cancer, diabetes, the immune system, and ocular health, and other related aspects. We also discuss the green microalga Haematococcus pluvialis, the richest source of natural 1, and its utilization in the promotion of human health, including the antihypertensive and neuroprotective potentials of 1, emphasizing our experimental data on the effects of dietary astaxanthin on blood pressure, stroke, and vascular dementia in animal models, is described.

Introduction. Stilbene synthase [STS; Enzyme Commission (EC) 2.3.1.95] and chalcone synthase (CHS; EC 2.3.1.74) are members of the type III polyketide synthases (PKSs) and plant-specific enzymes. 1 CHS is widely found in higher plants and plays a key role in the flavonoid biosynthesis by supplying chalcone to downstream enzymes. In contrast, a limited number of plants have STS essential for the synthesis of resveratrol utilized in the stilbenoid biosynthesis. 2 The members of CHS superfamily, including STS, produce linear polyketide intermediates by a common catalytic mechanism where coenzyme A (CoA)-linked starter molecules are iteratively condensed by acetyl units from malonyl-CoA. 3 STS and CHS share around 70% sequence identity without significant deletions and insertions; therefore, the enzymatic mechanism of STS has been considered to be very close to that of CHS. STS and CHS catalyze condensation reactions of pcoumaroyl-CoA and 3 acetyl units from malonyl-CoA, and produce a common linear tetraketide intermediate. In the following cyclization reaction, however, STS and CHS catalyze aldol and Claisen condensation of the tetraketide, resulting in 2 different final products, resveratrol and chalcone, respectively. The crystal structure and molecular mechanism of CHS from Medicago sativa (alfalfa) have recently been reported, 4 but the primary determinant of the cyclization reactions catalyzed by STS and CHS was not clear. More recently, the crystal structure of STS from Pinus silvestris (pine) was reported and provided a framework for understanding the specificity in the cyclization reaction. 5 This report describes the crystal structures of STS from Arachis hypogaea (peanut) in the absence and presence of its final product resveratrol at 2.4 A and 2.9 A, respectively. Detailed structural comparisons of STS from A. hypogaea (peanut STS) with STS from P. silvestris (pine STS) and CHS (alfalfa CHS) evidently revealed common differences between STS and CHS in the local conformation around the active site pocket.