Tissue distribution and pharmacokinetics of isoxanthohumol from hops in rodents


Lowering effect of combined sweet potato and onion intake on plasma quercetin concentration and underlying mechanism involving intestinal β-glucosidase activity.

A combined intake of cooked sweet potato and fried onion in humans was found to suppress the increase of plasma quercetin metabolite concentration. Experiments using rat β-glucosidase indicated that excess carbohydrate digestion products, especially glucose-containing saccharides, interfere with the deglycosylation of quercetin glucosides during intestinal epithelial uptake. Combined meals of sweet potato and onion may lower the bioavailability of onion quercetin glucosides.

Bioscience, Biotechnology, and Biochemistry


8-Prenylnaringenin tissue distribution and pharmacokinetics in mice and its binding to human serum albumin and cellular uptake in human embryonic kidney cells.

8-Prenylnaringenin (8-PN), a hop flavonoid, is a promising food substance with health benefits. Compared with nonprenylated naringenin, 8-PN exhibits stronger estrogenic activity and prevents muscle atrophy. Moreover, 8-PN prevents hot flushes and bone loss. Considering that prenylation reportedly improves the bioavailability of flavonoids, we compared the parameters related to the bioavailability [pharmacokinetics and tissue distribution in C57/BL6 mice, binding affinity to human serum albumin (HSA), and cellular uptake in HEK293 cells] of 8-PN and its mother (non-prenylated) compound naringenin. C57/BL6 mice were fed an 8-PN or naringenin mixed diet for 22 days. The amount of 8-PN (nmol/g tissue) in the kidneys (16.8 ± 9.20), liver (14.8 ± 2.58), muscles (3.33 ± 0.60), lungs (2.07 ± 0.68), pancreas (1.80 ± 0.38), heart (1.71 ± 0.27), spleen (1.36 ± 0.29), and brain (0.31 ± 0.09) was higher than that of naringenin. A pharmacokinetic study in mice demonstrated that the of 8-PN (50 mg/kg body weight) was lower than that of naringenin; however, the plasma concentration of 8-PN 8 h after ingestion was higher than that of naringenin. The binding affinity of 8-PN to HSA and cellular uptake in HEK293 cells were higher than those of naringenin. 8-PN bioavailability features assessed in mouse or human model experiments were obviously different from those of naringenin.


Eriocitrin Contained in Lemon Peel Ameliorates Disuse Muscle Atrophy by Suppressing the Expression of Atrogin-1 and MuRF-1 in Denervated Mice.

Unloading stress enhances oxidative stress, which in turn induces disuse muscle atrophy. This study evaluated the suppressive effect of lemon peel extract containing eriocitrin on muscle atrophy. Both lemon peel extract and eriocitrin suppressed weight loss in the gastrocnemius muscle under denervation in C57BL/6 mice. The mRNA level of ubiquitin ligases and their transcription factor were downregulated by eriocitrin. Eriocitrin inhibited the increase in lipid peroxidation and the ratio of glutathione disulfide/glutathione. These data suggest that eriocitrin ameliorated disuse muscle atrophy by suppressing the expression of ubiquitin ligase genes by its antioxidative effect.


Suppressive effects of quercetin on hydrogen peroxide-induced caveolin-1 phosphorylation in endothelial cells

Caveolin-1 is a major protein of the caveolae structure in vascular endothelial cell membrane. Phosphorylation of caveolin-1 is one of the initial events leading to exacerbation of vascular permeability caused by oxidative stress. Although quercetin is known to be an anti-atherosclerosis factor that acts as a dietary antioxidant, little is known about its role in the regulation of caveolin-1 phosphorylation. In this study, we investigated the inhibitory effect of quercetin on hydrogen peroxide-induced caveolin-1 phosphorylation in human umbilical vein endothelial cells. Quercetin inhibited caveolin-1 phosphorylation in cells pretreated with quercetin for 24 h and then exposed to hydrogen peroxide. However, quercetin 3--β-glucuronide, a conjugated metabolite of quercetin, did not exert this inhibitory effect. Exposure to hydrogen peroxide increased vascular permeability and reduced mRNA expression of the intercellular adhesion protein, vascular endothelial cadherin (VE-cadherin). By contrast, pretreatment with quercetin suppressed the increase in vascular permeability and decreased VE-cadherin expression. These results indicate that deconjugated quercetin can play a role in the prevention of altered vascular permeability under oxidative stress by suppressing caveolin-1 phosphorylation. Thus, dietary quercetin may be beneficial for the maintenance of endothelial cell function.

Journal of Clinical Biochemistry and Nutrition


Chocolate as a food matrix reduces the bioavailability of galloylated catechins from green tea in healthy women.

In this study, we evaluated the food matrix effects of chocolate on the absorption of green tea catechins (GTCs), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), and (-)-epigallocatechin gallate (EGCg), in five healthy 22-year-old women. In the single-intake experiment, the plasma concentrations of ECg (P < 0.05, at 1.5 h) and EGCg (P < 0.05, at 6 h) but not those of EC and EGC were reduced by the chocolate matrix. Regardless of the chocolate matrix, ECg and EGCg were mainly present as their aglycones in the plasma, whereas EGC and EC were found mostly as conjugated metabolites. After daily intake of GTCs mixed with chocolate for 14 days followed by overnight fasting, ECg but not EGCg was detected in the plasma. To compare the plasma profiles of ECg and EGCg, a mixture containing approximately equal amounts of ECg and EGCg was administered to nine rats for 14 days. Following treatment and overnight food deprivation, the plasma content of ECg was higher than that of EGCg. After a single injection of the same mixture in seven rats, ECg levels were higher than those of EGCg, and a greater amount of conjugated metabolites of ECg than those of EGCg was detected in the plasma 10 h after administration. In conclusion, the chocolate matrix affects the plasma profiles of GTCs, particularly ECg. ECg appears to persist in the plasma for a longer period, regardless of the chocolate matrix.


Inhibitory effect of catecholic colonic metabolites of rutin on fatty acid hydroperoxide and hemoglobin dependent lipid peroxidation in Caco-2 cells.

To determine the preventive effect of dietary rutin on oxidative damages occurring in the digestive tract, 13-hydroperoxyoctadecadienoic acid and hemoglobin were exposed to Caco-2 intestinal cells after the pretreatment with colonic rutin metabolites. Among four catechol-type metabolites, quercetin and 3,4-dihydroxytoluene exerted significant protection on 13-hydroperoxyoctadecadienoic and hemoglobin-dependent lipid peroxidation of this epithelial cell. Compared with quercetin, a much lower concentration allowed 3,4-dihydroxytoluene to maximize the protective effect, though it needed a longer pre-incubation period. Neither quercetin nor 3,4-dihydroxytoluene affected the expression of peroxiredoxin-6 protein, which comprises the cellular antioxidant defense system. It is concluded that 3,4-dihydroxytoluene is a plausible rutin colonic metabolite that can suppress oxidative damages of intestinal epithelial cells by directly inhibiting lipid peroxidation. This result may illuminate the preventive role of dietary rutin against colorectal cancer incidence in relation to the consumption of red and processed meat.


8-Prenylnaringenin promotes recovery from immobilization-induced disuse muscle atrophy through activation of the Akt phosphorylation pathway in mice.

8-Prenylnaringenin (8-PN) is a prenylflavonoid that originates from hop extracts and is thought to help prevent disuse muscle atrophy. We hypothesized that 8-PN affects muscle plasticity by promoting muscle recovery under disuse muscle atrophy. To test the promoting effect of 8-PN on muscle recovery, we administered an 8-PN mixed diet to mice that had been immobilized with a cast to one leg for 14 days. Intake of the 8-PN mixed diet accelerated recovery from muscle atrophy, and prevented reductions in Akt phosphorylation. Studies on cell cultures of mouse myotubes in vitro demonstrated that 8-PN activated the PI3K/Akt/P70S6K1 pathway at physiological concentrations. A cell-culture study using an inhibitor of estrogen receptors and an in vivo experiment with ovariectomized mice suggested that the estrogenic activity of 8-PN contributed to recovery from disuse muscle atrophy through activation of an Akt phosphorylation pathway. These data strongly suggest that 8-PN is a naturally occurring compound that could be used as a nutritional supplement to aid recovery from disuse muscle atrophy.

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology


Effect of quercetin and its metabolite on caveolin-1 expression induced by oxidized LDL and lysophosphatidylcholine in endothelial cells.

Oxidized low-density lipoprotein contributes to atherosclerotic plaque formation, and quercetin is expected to exert anti-atherosclerotic effects. We previously reported accumulation of conjugated quercetin metabolites in the aorta of rabbits fed high-cholesterol diets with quercetin glucosides, resulting in attenuation of lipid peroxidation and inhibition of lipid accumulation. Caveolin-1, a major structural protein of caveolae in vascular endothelial cells, plays a role in atherosclerosis development. Here we investigated effects of oxidized low-density lipoprotein, quercetin and its metabolite, quercetin 3-O--glucuronide, on caveolin-1 expression. Oxidized low-density lipoprotein significantly upregulated caveolin-1 mRNA expression. An oxidized low-density lipoprotein component, lysophosphatidylcholine, also induced expression of both caveolin-1 mRNA and protein. However, lysophosphatidylcholine did not affect the location of caveolin-1 proteins within caveolae structures. Co-treatment with quercetin or quercetin 3-O--glucuronide inhibited lysophosphatidylcholine-induced caveolin-1 expression. Quercetin and quercetin 3-O--glucuronide also suppressed expression of adhesion molecules induced by oxidized low-density lipoprotein and lysophosphatidylcholine. These results strongly suggest lysophosphatidylcholine derived from oxidized low-density lipoprotein contributes to atherosclerotic events by upregulating caveolin-1 expression, resulting in induction of adhesion molecules. Quercetin metabolites are likely to exert an anti-atherosclerotic effect by attenuating caveolin-1 expression in endothelial cells.


Anti-inflammatory effects and molecular mechanisms of 8-prenyl quercetin.

PQ as a potential inhibitor revealed anti-inflammatory effect in both cell and animal models at least by targeting SEK1-JNK1/2 and MEK1-ERK1/2.


Preventive effect of dietary quercetin on disuse muscle atrophy by targeting mitochondria in denervated mice.

Quercetin is a major dietary flavonoid in fruits and vegetables. We aimed to clarify the preventive effect of dietary quercetin on disuse muscle atrophy and the underlying mechanisms. We established a mouse denervation model by cutting the sciatic nerve in the right leg (SNX surgery) to lack of mobilization in hind-limb. Preintake of a quercetin-mixed diet for 14days before SNX surgery prevented loss of muscle mass and atrophy of muscle fibers in the gastrocnemius muscle (GM). Phosphorylation of Akt, a key phosphorylation pathway of suppression of protein degradation, was activated in the quercetin-mixed diet group with and without SNX surgery. Intake of a quercetin-mixed diet suppressed the generation of hydrogen peroxide originating from mitochondria and elevated mitochondrial peroxisome proliferator-activated receptor- coactivator 1 mRNA expression as well as NADH dehydrogenase 4 expression in the GM with SNX surgery. Quercetin and its conjugated metabolites reduced hydrogen peroxide production in the mitochondrial fraction obtained from atrophied muscle. In C2C12 myotubes, quercetin reached the mitochondrial fraction. These findings suggest that dietary quercetin can prevent disuse muscle atrophy by targeting mitochondria in skeletal muscle tissue through protecting mitochondria from decreased biogenesis and reducing mitochondrial hydrogen peroxide release, which can be related to decreased hydrogen peroxide production and/or improvements on antioxidant capacity of mitochondria.


Effect of Processed Onions on the Plasma Concentration of Quercetin in Rats and Humans.

Onion is a popular source of antioxidative flavonoid quercetin and its vascular function attracts considerable attention in relation to anti-atherosclerotic effect. The present study estimated the effect of food processing on the bioavailability of onion quercetin aglycone and its glucosides provided through the consumption of onion products. The intake of a peel powder-containing meal showed a significantly higher bioavailability than the peel extract, bulb powder, bulb extract, and bulb sauté containing meals. Hence, food processing of onion peel may enhance the health impact of onion quercetin by elevating its bioavailability.


3-O-Acyl-epicatechins Increase Glucose Uptake Activity and GLUT4 Translocation through Activation of PI3K Signaling in Skeletal Muscle Cells.

Tea catechins promote glucose uptake in skeletal muscle cells. In this study, we investigated whether the addition of an acyl group to the C-3 position of catechins to generate 3-O-acyl-catechins promoted glucose uptake in L6 myotubes. 3-O-Myristoyl-(-)-epicatechin (EC-C14) and 3-O-palmitoyl-(-)-epicatechin (EC-C16) promoted glucose uptake and translocation of glucose transporter (GLUT) 4 in the cells. The effect of 3-O-acyl-(-)-epicatechins was stronger than that of (-)-epicatechin (EC), whereas neither 3-O-myristoyl-(+)-catechin (C-C14) nor 3-O-palmitoyl-(+)catechin (C-C16) promoted glucose uptake or GLUT4 translocation as well as (+)-catechin (C). We further investigated an affinity of catechins and 3-O-acyl-catechins to the lipid bilayer membrane by using surface plasma resonance analysis. Maximum binding amounts of EC-C16 and C-C16 to the lipid bilayer clearly increased compared with that of (-)-EC and (+)-C, respectively. We also examined the mechanism of GLUT4 translocation and found EC-C14 and EC-C16 induced the phosphorylation of PI3K, but did not affect phosphorylation of Akt or IR. In conclusion, the addition of an acyl group to the C-3 position of (-)-EC increases its affinity for the lipid bilayer membrane and promotes GLUT4 translocation through PI3K-dependent pathways in L6 myotubes.

International Journal of Molecular Sciences


Biological impacts of resveratrol, quercetin, and N-acetylcysteine on oxidative stress in human gingival fibroblasts.

In periodontitis, production of reactive oxygen species (ROS) by neutrophils induces oxidative stress and deteriorates surrounding tissues. Antioxidants reduce damage caused by ROS and are used to treat diseases involving oxidative stress. This study summarizes the different effects of resveratrol, quercetin, and N-acetylcysteine (NAC) on human gingival fibroblasts (HGFs) under oxidative stress induced by hydrogen peroxide. Real-time cytotoxicity analyses reveals that resveratrol and quercetin enhanced cell proliferation even under oxidative stress. Of the antioxidants tested, resveratrol is the most effective at inhibiting ROS production. HGFs incubated with resveratrol and quercetin up-regulate the transcription of type I collagen gene after 3 h, but only resveratrol sustained this up-regulation for 24 h. A measurement of the oxygen consumption rate (OCR, mitochondrial respiration) shows that resveratrol generates the highest maximal respiratory capacity, followed by quercetin and NAC. Simultaneous measurement of OCR and the extracellular acidification rate (non-mitochondrial respiration) reveals that resveratrol and quercetin induce an increase in mitochondrial respiration when compared with untreated cells. NAC treatment consumes less oxygen and enhances more non-mitochondrial respiration. In conclusion, resveratrol is the most effective antioxidant in terms of real-time cytotoxicity analysis, reduction of ROS production, and enhancement of type I collagen synthesis and mitochondrial respiration in HGFs.

Journal of Clinical Biochemistry and Nutrition


N-myristoylated ubiquitin ligase Cbl-b inhibitor prevents on glucocorticoid-induced atrophy in mouse skeletal muscle.

A DGpYMP peptide mimetic of tyrosine(608)-phosphorylated insulin receptor substrate-1 (IRS-1), named Cblin, was previously shown to significantly inhibit Cbl-b-mediated IRS-1 ubiquitination. In the present study, we developed N-myristoylated Cblin and investigated whether it was effective in preventing glucocorticoid-induced muscle atrophy. Using HEK293 cells overexpressing Cbl-b, IRS-1 and ubiquitin, we showed that the 50% inhibitory concentrations of Cbl-b-mediated IRS-1 ubiquitination by N-myristoylated Cblin and Cblin were 30 and 120M, respectively. Regarding the DEX-induced atrophy of C2C12 myotubes, N-myristoylated Cblin was more effective than Cblin for inhibiting the DEX-induced decreases in C2C12 myotube diameter and IRS-1 degradation. The inhibitory efficacy of N-myristoylated Cblin on IRS-1 ubiquitination in C2C12 myotubes was approximately fourfold larger than that of Cblin. Furthermore, N-myristoylation increased the incorporation of Cblin into HEK293 cells approximately 10-folds. Finally, we demonstrated that N-myristoylated Cblin prevented the wet weight loss, IRS-1 degradation, and MAFbx/atrogin-1 and MuRF-1 expression in gastrocnemius muscle of DEX-treated mice approximately fourfold more effectively than Cblin. Taken together, these results suggest that N-myristoylated Cblin prevents DEX-induced skeletal muscle atrophy in vitro and in vivo, and that N-myristoylated Cblin more effectively prevents muscle atrophy than unmodified Cblin.


Catechins in tea suppress the activity of cytochrome P450 1A1 through the aryl hydrocarbon receptor activation pathway in rat livers.

Polycyclic aromatic hydrocarbons (PAHs) and halogenated aromatic hydrocarbons (HAHs) develop various adverse effects through activation of an aryl hydrocarbon receptor (AhR). The suppressive effects of brewed green tea and black tea on 3-methylcholanthrene (MC)-induced AhR activation and its downstream events were examined in the liver of rats. Ad-libitum drinking of green tea and black tea suppressed MC-induced AhR activation and elevation of ethoxyresorufin O-deethylase activity in the liver, whereas the teas themselves did not induce them. Tea showed a suppressive fashion on the expression of cytochrome P450 1A1 (CYP1A1). Tea suppressed the AhR activation induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) ex vivo. A part of catechins and theaflavins was present in plasma and liver as conjugated and intact forms. The results of this study suggested that active component(s) of tea are incorporated in the liver and suppress the activity of CYP1As through the AhR activation pathway.

International Journal of Food Sciences and Nutrition


Effects of dietary soy protein on skeletal muscle volume and strength in humans with various physical activities

Background: In recent years, the number of bedridden people is rapidly increasing due to aging or lack of exercise in Japan. This problem is becoming more serious, since there is no countermeasure against it. In the present study, we designed to investigate whether dietary proteins, especially soy, had beneficial effects on skeletal muscle in 59 volunteers with various physical activities. Methods: We subjected 59 volunteers with various physical activities to meal intervention examination. Persons with low and high physical activities were divided into two dietary groups, the casein diet group and the soy diet group. They ate daily meals supplemented with 7.8 g of powdered casein or soy protein isolate every day for 30 days. Bedridden patients in hospitals were further divided into three dietary groups: the no supplementation diet group, the casein diet group and the soy diet group. They were also subjected to a blood test, a urinalysis, magnetic resonance imaging analysis and muscle strength test of the knee before and after the meal intervention study. Results: Thirty-day soy protein supplementation significantly increased skeletal muscle volume in participants with low physical activity, compared with 30-day casein protein supplementation. Both casein and soy protein supplementation increased the volume of quadriceps femoris muscle in bedridden patients. Consistently, soy protein significantly increased their extension power of the knee, compared with casein protein. Although casein protein increased skeletal muscle volume more than soy protein in bedridden patients, their muscle strength changes by soy protein supplementation were bigger than those by casein protein supplementation. Conclusions: The supplementation of soy protein would be one of the effective foods which prevent the skeletal muscle atrophy caused by immobilization or unloading. J. Med. Invest. 62: 177-183, August, 2015

The Journal of Medical Investigation : JMI


Comparison of Isoflavone Absorption by Soybean Products in Humans

大豆の加工形態によるイソフラボン生体吸収量の比較

We investigated the bioavailability of soy isoflavones from processed soybean products. Five healthy male volunteers ingested soy milk, soy curd (tofu) , boiled soybeans (nimame) , or fermented soybeans (natto) in a single dose, and blood was collected 90 min later for measurement of the plasma isoflavone concentration. Each subject ingested test meals containing an isoflavone equivalent of 50 mg aglycone. The total amount of each isoflavone was determined by HPLC analysis after deconjugation of conjugated metabolites using sulfatase H-1. The concentration of glycitein was below the detection limit before and after intake of the soybean products. The concentrations of daidzein and genistein were elevated in all subjects after ingestion of all the test meals, and the concentration of genistein was higher than that of daidzein except after ingestion of fermented soybeans. Ingestion of boiled soybeans appeared to result in a higher concentration of total isoflavones (daizein and genistein) than ingestion of soy curd. These results suggest that the bioavailability of isoflavones from soybeans varies according to the type of processing.

本試験は, 大豆イソフラボンの吸収性を大豆の加工形態の違いから比較した．5名の健常人男性が豆乳, 豆腐, 大豆煮豆, 納豆をそれぞれ単回摂取し, 摂取90分後の血中イソフラボン濃度の上昇値を吸収量とした．試験食中に含まれるダイゼイン, ゲニステイン, グリシテインとこれらの配糖体であるダイジン, ゲニスチン, グリシチンの合計をアグリコン換算で50 mg含むように摂取量を調整した．摂取前後の血中イソフラボンはアグリコンとして定量した．ダイゼイン, ゲニステインは試験食摂取後すべての被験者で上昇し, 摂取量に対する上昇値は納豆を除いてゲニステインがダイゼインより高い値であった．アグリコン換算した血漿中の総イソフラボン濃度の上昇は煮豆が豆腐に比べて大きい傾向を示した．以上の結果は大豆の加工形態がイソフラボンの生体吸収性に影響することを示唆するものである．

Journal of Japanese Society of Nutrition and Food Science


Cellular uptake of quercetin and luteolin and their effects on monoamine oxidase-A in human neuroblastoma SH-SY5Y cells


Specific localization of quercetin-3-O-glucuronide in human brain.

In recent years, many papers have suggested that dietary flavonoids may exert beneficial effects in the brain tissue for the protection of neurons against oxidative stress and inflammation. However, the bioavailability of flavonoids across the blood-brain barrier and the localization in the brain remain controversial. Thus, we examined the localization of quercetin-3-O-glucuronide (Q3GA), a major phase-II metabolite of quercetin, in the human brain tissues with or without cerebral infarction by immunohistochemical staining using anti-Q3GA antibody. A significant immunoreactivity was observed in the epithelial cells of the choroid plexus, which constitute the structural basis of the blood-cerebrospinal fluid (CSF) barrier, and in the foamy macrophages of recent infarcts. The cellular accumulation of Q3GA was also reproduced in vitro in macrophage-like RAW264, microglial MG6, and brain capillary endothelial RBEC1. It is of interest that a common feature of these cell lines is the deconjugation of Q3GA, resulting in the cellular accumulation of non-conjugated quercetin and the methylated forms. We then examined the anti-inflammatory activity of Q3GA and the deconjugated forms in the lipopolysaccharide-stimulated macrophage cells and revealed that the deconjugated forms (quercetin and a methylated form isorhamnetin), but not Q3GA itself, exhibited inhibitory effects on the inflammatory responses through attenuation of the c-Jun N-terminal kinase pathway. These results suggested that a quercetin glucuronide can pass through the blood-brain barrier, perhaps the CSF barrier, accumulate in specific types of cells, such as macrophages, and act as anti-inflammatory agents in the brain through deconjugation into the bioactive non-conjugated forms.


Molecular mechanisms of cadmium-induced fibroblast growth factor 23 upregulation in osteoblast-like cells.

Itai-itai disease is thought to be the result of chronic cadmium (Cd) intoxication. Renal proximal tubules are a major target of Cd toxicity. The whole mechanism of the adverse effects of Cd remains unresolved, especially how renal damage is related to the development of bone lesions. Fibroblast growth factor 23 (FGF23) is a bone-derived phosphaturic factor that regulates vitamin D and inorganic phosphate metabolism in the kidney. To clarify the role of FGF23 on Cd toxicity, we investigated the mechanisms of Cd-induced FGF23 production in the bone. Cd injection into mice significantly increased plasma FGF23 concentrations, but did not change FGF23 mRNA expression in bone. GalNAc-T3 is involved in secreting intact FGF23. To determine potential roles of GalNAc-T3 in Cd-induced FGF23 production, we examined the effect of Cd on GalNAc-T3 mRNA expression in vivo and in vitro. GalNAc-T3 gene expression was significantly increased in the bones of Cd-injected mice. Cd also enhanced the expression of GalNAc-T3 in cultured osteosarcoma UMR106 cells and primary osteocytes. Cd activated aryl hydrocarbon receptors (AhR) and AhR were required for GalNAc-T3 gene expression induced by Cd. In addition, Cd-dependent FGF23 production was completely inhibited by an AhR antagonist. AhR siRNA markedly suppressed the stimulation of transcriptional activity by Cd. Furthermore, Cd induced AhR activation via phosphorylation of Ser-68 by p38 kinase in the nuclear export signal of AhR. Thus, Cd stimulated GalNAc-T3 gene transcription via enhanced AhR binding to the GalNAc-T3 promoter. These findings suggest that the Cd-induced increase in GalNAc-T3 suppresses proteolytic processing of FGF23 and increases serum FGF23 concentrations.


The First Synthesis of Uralenol, 5'-Prenylated Quercetin via Palladium-catalyzed O-dimethylallylation Reaction with Concurrent Acetyl Migration


Mitochondrial dysfunction leads to deconjugation of quercetin glucuronides in inflammatory macrophages.

Dietary flavonoids, such as quercetin, have long been recognized to protect blood vessels from atherogenic inflammation by yet unknown mechanisms. We have previously discovered the specific localization of quercetin-3-O-glucuronide (Q3GA), a phase II metabolite of quercetin, in macrophage cells in the human atherosclerotic lesions, but the biological significance is poorly understood. We have now demonstrated the molecular basis of the interaction between quercetin glucuronides and macrophages, leading to deconjugation of the glucuronides into the active aglycone. In vitro experiments showed that Q3GA was bound to the cell surface proteins of macrophages through anion binding and was readily deconjugated into the aglycone. It is of interest that the macrophage-mediated deconjugation of Q3GA was significantly enhanced upon inflammatory activation by lipopolysaccharide (LPS). Zymography and immunoblotting analysis revealed that -glucuronidase is the major enzyme responsible for the deglucuronidation, whereas the secretion rate was not affected after LPS treatment. We found that extracellular acidification, which is required for the activity of -glucuronidase, was significantly induced upon LPS treatment and was due to the increased lactate secretion associated with mitochondrial dysfunction. In addition, the -glucuronidase secretion, which is triggered by intracellular calcium ions, was also induced by mitochondria dysfunction characterized using antimycin-A (a mitochondrial inhibitor) and siRNA-knockdown of Atg7 (an essential gene for autophagy). The deconjugated aglycone, quercetin, acts as an anti-inflammatory agent in the stimulated macrophages by inhibiting the c-Jun N-terminal kinase activation, whereas Q3GA acts only in the presence of extracellular -glucuronidase activity. Finally, we demonstrated the deconjugation of quercetin glucuronides including the sulfoglucuronides in vivo in the spleen of mice challenged with LPS. These results showed that mitochondrial dysfunction plays a crucial role in the deconjugation of quercetin glucuronides in macrophages. Collectively, this study contributes to clarifying the mechanism responsible for the anti-inflammatory activity of dietary flavonoids within the inflammation sites.


Prenylation enhances quercetin uptake and reduces efflux in Caco-2 cells and enhances tissue accumulation in mice fed long-term.

Prenyl flavonoids are widely distributed in plant foods and have attracted appreciable attention in relation to their potential benefits for human health. Prenylation may enhance the biological functions of flavonoids by introducing hydrophobic properties in their basic structures. Previously, we found that 8-prenyl naringenin exerted a greater preventive effect on muscle atrophy than nonprenylated naringenin in a mouse model. Here, we aimed to estimate the effect of prenylation on the bioavailability of dietary quercetin (Q). The cellular uptake of 8-prenyl quercetin (PQ) and Q in Caco-2 cells and C2C12 myotube cells was examined. Prenylation significantly enhanced the cellular uptake by increasing the lipophilicity in both cell types. In Caco-2 cells, efflux of PQ to the basolateral side was <15% of that of Q, suggesting that prenylation attenuates transport from the intestine to the circulation. After intragastric administration of PQ or Q to mice or rats, the area under the concentration-time curve for PQ in plasma and lymph was 52.5% and 37.5% lower than that of Q, respectively. PQ and its O-methylated form (MePQ) accumulated at much higher amounts than Q and O-methylated Q in the liver (Q: 3400%; MePQ: 7570%) and kidney (Q: 385%; MePQ: 736%) of mice after 18 d of feeding. These data suggest that prenylation enhances the accumulation of Q in tissues during long-term feeding, even though prenylation per se lowers its intestinal absorption from the diet.


Soy Glycinin Contains a Functional Inhibitory Sequence against Muscle-Atrophy-Associated Ubiquitin Ligase Cbl-b.

Background. Unloading stress induces skeletal muscle atrophy. We have reported that Cbl-b ubiquitin ligase is a master regulator of unloading-associated muscle atrophy. The present study was designed to elucidate whether dietary soy glycinin protein prevents denervation-mediated muscle atrophy, based on the presence of inhibitory peptides against Cbl-b ubiquitin ligase in soy glycinin protein. Methods. Mice were fed either 20% casein diet, 20% soy protein isolate diet, 10% glycinin diet containing 10% casein, or 20% glycinin diet. One week later, the right sciatic nerve was cut. The wet weight, cross sectional area (CSA), IGF-1 signaling, and atrogene expression in hindlimb muscles were examined at 1, 3, 3.5, or 4 days after denervation. Results. 20% soy glycinin diet significantly prevented denervation-induced decreases in muscle wet weight and myofiber CSA. Furthermore, dietary soy protein inhibited denervation-induced ubiquitination and degradation of IRS-1 in tibialis anterior muscle. Dietary soy glycinin partially suppressed the denervation-mediated expression of atrogenes, such as MAFbx/atrogin-1 and MuRF-1, through the protection of IGF-1 signaling estimated by phosphorylation of Akt-1. Conclusions. Soy glycinin contains a functional inhibitory sequence against muscle-atrophy-associated ubiquitin ligase Cbl-b. Dietary soy glycinin protein significantly prevented muscle atrophy after denervation in mice.


Isoflavones derived from soy beans prevent MuRF1-mediated muscle atrophy in C2C12 myotubes through SIRT1 activation.

Proinflammatory cytokines are factors that induce ubiquitin-proteasome-dependent proteolysis in skeletal muscle, causing muscle atrophy. Although isoflavones, as potent antioxidative nutrients, have been known to reduce muscle damage during the catabolic state, the non-antioxidant effects of isoflavones against muscle atrophy are not well known. Here we report on the inhibitory effects of isoflavones such as genistein and daidzein on muscle atrophy caused by tumor necrosis factor (TNF)- treatment. In C2C12 myotubes, TNF- treatment markedly elevated the expression of the muscle-specific ubiquitin ligase MuRF1, but not of atrogin-1, leading to myotube atrophy. We found that MuRF1 promoter activity was mediated by acetylation of p65, a subunit of NFB, a downstream target of the TNF- signaling pathway; increased MuRF1 promoter activity was abolished by SIRT1, which is associated with deacetylation of p65. Of interest, isoflavones induced expression of SIRT1 mRNA and phosphorylation of AMP kinase, which is well known to stimulate SIRT1 expression, although there was no direct effect on SIRT1 activation. Moreover, isoflavones significantly suppressed MuRF1 promoter activity and myotube atrophy induced by TNF- in C2C12 myotubes. These results suggest that isoflavones suppress myotube atrophy in skeletal muscle cells through activation of SIRT1 signaling. Thus, the efficacy of isoflavones could provide a novel therapeutic approach against inflammation-related muscle atrophy.

Journal of Nutritional Science and Vitaminology


Evaluation of the inhibitory effects of quercetin-related flavonoids and tea catechins on the monoamine oxidase-A reaction in mouse brain mitochondria.

Quercetin, a typical dietary flavonoid, is thought to exert antidepressant effects by inhibiting the monoamine oxidase-A (MAO-A) reaction, which is responsible for regulation of the metabolism of the neurotransmitter 5-hydroxytryptamine (5-HT) in the brain. This study compared the MAO-A inhibitory activity of quercetin with those of O-methylated quercetin (isorhamnetin, tamarixetin), luteolin, and green tea catechins ((-)-epicatechin, (-)-epicatechin gallate, (-)-epigallocatechin, and (-)-epigallocatechin gallate) by measuring the formation of the oxidative deamination product of 5-HT, 5-hydroxyindole aldehyde (5-HIAL), in mouse brain mitochondria. Quercetin was inferior to luteolin in the inhibition of MAO-A activity, whereas isorhamnetin, tamarixetin, and tea catechins scarcely exerted inhibitory activity. Quercetin did not affect MAO-A activity in mouse intestinal mitochondria, indicating that it does not evoke side effects on the metabolism of dietary monoamines in the gut. These data suggest that quercetin is a weak (but safe) MAO-A inhibitor in the modulation of 5-HT levels in the brain.

Journal of Agricultural and Food Chemistry


Prevention of disuse muscle atrophy by dietary ingestion of 8-prenylnaringenin in denervated mice

Flavonoids have attracted considerable attention in relation to their effects upon health. 8-Prenylnaringenin (8-PN) is found in the common hop (Humulus lupulus) and assumed to be responsible for the health impact of beer consumption. We wanted to clarify the effects of prenylation on the physiological functions of dietary flavonoids by comparing the effects of 8-PN with that of intact naringenin in the prevention of disuse muscle atrophy using a model of denervation in mice. Consumption of 8-PN (but not naringenin) prevented loss of weight in the gastrocnemius muscle further supported by the lack of induction of the protein content of a key ubiquitin ligase involved in muscle atrophy, atrogin-1, and by the activation of Akt phosphorylation. 8-PN content in the gastrocnemius muscle was tenfold higher than that of naringenin. These results suggested that, compared with naringenin, 8-PN was effectively concentrated into skeletal muscle to exert its preventive effects upon disuse muscle atrophy. It is likely that prenylation generates novel functions for 8-PN by enhancing its accumulation into muscle tissue through dietary intake.


Suppression of lipopolysaccharide and galactosamine-induced hepatic inflammation by red grape pomace.

Grape pomace is generated in the production process of wine and grape juices and is an industrial waste. This study investigated whether an intake of grape pomace was able to suppress chronic inflammation induced by lipopolysaccharide (LPS) and galactosamine (GalN) in vivo. When Sprague-Dawley rats were orally given methanolic extracts from red and white grape pomace, the extracts inhibited the LPS/GalN-evoked activation of nuclear factor-κB (NF-κB) dose-dependently, and red grape pomace exerted a stronger effect than white grape one. Next, rats were fed an AIN93 M-based diet containing 5% red grape pomace for 7 days, followed by the intraperitoneal injection of LPS and GalN. The intake of the red grape pomace-supplemented diet was found to suppress the LPS/GalN-induced activation of NF-κB and expression of inducible nitric oxide synthase and cyclooxygenase-2 proteins. These results suggest that red grape pomace may contain an abundance of effective compound(s) for anti-inflammatory action.


An Efficient Method for C8-Prenylation of Flavonols and Flavanones


Antagonistic effect of the Ainu-selected traditional beneficial plants on the transformation of an aryl hydrocarbon receptor.

Transformation of an aryl hydrocarbon receptor (AhR) is the initial step to express the multiple toxicity of halogenated and polycyclic aromatic hydrocarbons (HAHs and PAHs) including dioxins. Therefore, it has been suggested that suppression of the transformation induced by HAHs and PAHs leads to reduce their toxicological effects. In this study, the antagonistic effect of 110 indigenous plants (192 plant parts) used as medicine and/or food by the Ainu on the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced AhR transformation was investigated. Of these, a stalk of Aralia elata (Miq.) Seemann and a bark of Fraxinus mandshurica Rupr. var. japonica Maxim. exhibited the strong antagonistic effect in a dose-dependent manner. An antioxidative activity and polyphenol content were also measured, and the strong correlation (r= 0.96) between these two parameters could be confirmed. However, correlation coefficients of the antagonistic effect of 192 extracts compared to their antioxidative activity and polyphenol content were 0.17 and 0.20, respectively. These results suggest that the Ainu-selected traditional beneficial plants are useful source for findings of novel AhR antagonists, and the antagonistic activity of these plants may be independent on their antioxidative activity and polyphenol content. PRACTICAL APPLICATION: Our findings lead to discovery of the valuable plants used by the Ainu and the novel active compounds useful for human's life, and furthermore, may contribute to the development of new medicines and functional foods.


Bioavailability of orally administered water-dispersible hesperetin and its effect on peripheral vasodilatation in human subjects: implication of endothelial functions of plasma conjugated metabolites.

Hesperetin is an aglycone of citrus flavonoids and is expected to exert a vasodilatation effect in vivo. We developed water-dispersible hesperetin by the process of micronization to enhance the bioavailability of hesperetin. This study aimed to assess the effect of this process on the bioavailability of hesperetin and to estimate its efficiency on vasodilatation-related functions using endothelial cells in vitro and a human volunteer study at a single dose in vivo. We found that water-dispersible hesperetin was absorbed rapidly, with its maximum plasma concentration (C(max)) being 10.2 ± 1.2 μM, and that the time to reach C(max), which is within 1 h if 150 mg of this preparation was orally administered in humans. LC-MS analyses of the plasma at C(max) demonstrated that hesperetin accumulated in the plasma as hesperetin 7-O-β-D-glucuronide (Hp7GA), hesperetin 3'-O-β-D-glucuronide (Hp3'GA) and hesperetin sulfate exclusively. Similar to hesperetin, Hp7GA enhanced nitric oxide (NO) release by inhibiting nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase) activity in a human umbilical vein endothelial cell culture system, indicating that plasma hesperetin metabolites can improve vasodilatation in the vascular system. A volunteer study using women with cold sensitivity showed that a single dose of water-dispersible hesperetin was effective on peripheral vasodilatation.These results strongly suggest that rapid accumulation with higher plasma concentration enables hesperetin to exert a potential vasodilatation effect by the endothelial action of its plasma metabolites. Water-dispersible hesperetin may be useful to improve the health effect of dietary hesperetin.


Rantes secreted from macrophages disturbs skeletal muscle regeneration after cardiotoxin injection in Cbl-b-deficient mice

Deficiency of the Cbl-b ubiquitin ligase gene activates macrophages in mice. This study aimed to elucidate the pathophysiological roles of macrophages in muscle degeneration/regeneration in Cbl-b-deficient mice. We examined immune cell infiltration and cytokine expression in cardiotoxin-injected tibialis anterior muscle of Cbl-b-deficient mice. Ablation of the Cbl-b gene expression delayed regeneration of cardiotoxin-induced skeletal muscle damage compared with wild-type mice. CD8-positive T cells were still present in the damaged muscle on day 14 after cardiotoxin injection in Cbl-b-deficient mice, but there was dispersal of the same cells over that time-frame in wild-type mice. Infiltrating macrophages in Cbl-b-deficient mice showed strong expression of RANTES (regulated-on-activation, normal T cell expressed and secreted), a chemokine for CD8-positive T cells. In turn, a neutralizing antibody against RANTES significantly suppressed the infiltration of CD8-positive T cells into the muscle, resulting in restoration of the disturbed muscle regeneration. Cbl-b is an important regulatory factor for cytotoxic T-cell infiltration via RANTES production in macrophages.


Quercetin Prevents Unloading-Derived Disused Muscle Atrophy by Attenuating the Induction of Ubiquitin Ligases in Tail-Suspension Mice.

The effects of quercetin (1) were investigated on disused muscle atrophy using mice that underwent tail suspension. Periodic injection of 1 into the gastrocnemius muscle suppressed muscle weight loss and ubiquitin ligase expression. Compound 1 reduced the enhancement of lipid peroxidation in the muscle. Injection of N-acetyl-l-cysteine, but not flavone (2), also prevented muscle weight loss and enhancement of lipid peroxidation. These findings demonstrate that 1 can prevent disused muscle atrophy by attenuating the expression of ubiquitin ligases and that such prevention originates from its antioxidant activity.


D-pinitol and myo-inositol stimulate translocation of glucose transporter 4 in skeletal muscle of C57BL/6 mice.

Diabetes mellitus is a complex disease that is characterized by the defection of insulin sensitivity in such peripheral tissues as skeletal muscle, adipose tissue and liver. We have previously demonstrated that certain inositol derivatives stimulated glucose uptake accompanied by the translocation of glucose transporter 4 (GLUT4) to the plasma membrane in L6 myotubes. We investigated in this present study whether an oral intake of D-pinitol (PI) and myo-inositol (MI) would affect GLUT4 translocation in the skeletal muscle of mice. PI or MI at 1 g/kg BW administered orally to mice 30 min before a post-oral injection of glucose at 2 g/kg BW resulted in both PI and MI increasing GLUT4 translocation in the skeletal muscle and lowering the plasma glucose and insulin levels. PI and MI, therefore, have the potential to prevent diabetes mellitus by reducing the postprandial blood glucose level and stimulating GLUT4 translocation in the skeletal muscle.

Bioscience, Biotechnology, and Biochemistry


Suppression mechanisms of flavonoids on aryl hydrocarbon receptor-mediated signal transduction.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates biological and toxicological effects by binding to its agonists such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Previously we demonstrated that flavonoids suppressed the TCDD-induced DNA-binding activity of the AhR in a structure-dependent manner. In this study, we investigated the mechanisms by which flavonoids suppressed the AhR-mediated signal transduction in mouse hepatoma Hepa-1c1c7 cells. Flavones and flavonols suppressed the TCDD-induced nuclear translocation of the AhR and dissociation of its partner proteins, heat shock protein 90 and X-associated protein 2, whereas flavanones and catechins did not. Flavonoids of all these four subclasses suppressed the phosphorylation of both AhR and Arnt and the formation of a heterodimer consisting of these proteins. Since certain flavonoids are known to inhibit mitogen-activated protein kinases (MAPKs), we confirmed the contribution of MAPK/ERK kinase (MEK) to the AhR-mediated signal transduction by using U0126, an inhibitor of MEK1/2. U0126 suppressed TCDD-induced phosphorylation of the AhR and Arnt followed by the DNA-binding activity of the AhR. Flavanones and catechins suppressed the TCDD-induced phosphorylation of ERK1/2. The inhibition of MEK/ERK phosphorylation is one of the mechanisms by which flavanones and catechins suppress the AhR-mediated signal transduction in Hepa-1c1c7 cells.


Inhibition of P-glycoprotein enhances the suppressive effect of kaempferol on transformation of the aryl hydrocarbon receptor.

Dioxins enter the body mainly through the diet, bind to the aryl hydrocarbon receptor (AhR), and cause various toxicological effects. In this study, we found that oral administration of kaempferol or ginkgo biloba extract (EGb) containing 24% flavonol at 100 mg/kg body weight suppressed AhR transformation induced by 3-methylcholanthrene at 10 mg/kg body weight in the liver of mice. The suppressive effect of kaempferol was enhanced by verapamil, an inhibitor of P-glycoprotein (P-gp), in ex vivo experiments using a hepatic cytosolic fraction and 2,3,7,8-tetrachlorodibenzo-p-dioxin. Enhancement of the suppressive effect by verapamil was also observed in mouse hepatoma Hepa-1c1c7 cells, accompanied by an increase in the uptake of kaempferol into the cells. In conclusion, inhibition of P-gp enhanced the suppressive effect of kaempferol on AhR transformation through an increase in the intracellular kaempferol concentration.


Subcellular localization of flavonol aglycone in hepatocytes visualized by confocal laser scanning fluorescence microscope.

Flavonoids are widely distributed in the plant kingdom and show various biological activities. The bioavailability of flavonoids in biological samples has conventionally been quantified by high-performance liquid chromatography and mass spectrometry, but with these analytical techniques it is difficult to estimate the subcellular localization of flavonoids in intact cells. In this study, we attempted to examine the localization of flavonoids in cultured cells using a confocal laser scanning fluorescence microscope and mouse hepatoma Hepa-1c1c7 cells. Five flavonol aglycones showed autofluorescence in the cells under the conditions (Ex. 488 nm to Em. 515-535 nm), whereas three flavonol glycosides and eight compounds belonging to other flavonoid subclasses, i.e., flavones, flavanones, and catechins, did not. The autofluorescence of galangin and kaempferol appeared stronger in the nucleus than cytoplasm, suggesting that they are incorporated into the cells and accumulated in the nucleus. The proposed method provided evidence that flavonol aglycones are incorporated into, and accumulated in the nucleus of, hepatocytes.


Cacao polyphenol extract suppresses transformation of an aryl hydrocarbon receptor in C57BL/6 mice.

Dioxins enter the body through the diet and cause various toxicological effects through transformation of an aryl hydrocarbon receptor (AhR). Plant extracts and phytochemicals including flavonoids are reported to suppress this transformation. This paper investigates the suppression by a cacao polyphenol extract (CPE) of AhR transformation in vivo. The CPE was administered orally to C57BL/6 mice at 100 mg/kg of body weight, followed 1 h later by 3-methylcholanthrene (MC), an AhR agonist, injected intraperitoneally at 10 mg/kg of body weight. CPE suppressed the MC-induced transformation to the control level by inhibiting the formation of a heterodimer between AhR and an aryl hydrocarbon receptor nuclear translocator in the liver at 3 h postadministration. It also suppressed MC-induced cytochrome P4501A1 expression and NAD(P)H:quinone-oxidoreductase activity, whereas it increased glutathione S-transferase activity at 25 h. CPE constituents and their metabolites might contribute, at least in part, to the suppression of AhR transformation. The results indicate that the intake of CPE suppressed the toxicological effects of dioxins in the body.

Journal of Agricultural and Food Chemistry


Interaction between the aryl hydrocarbon receptor and its antagonists, flavonoids.

Flavonoids have been reported to be dietary antagonists of an aryl hydrocarbon receptor (AhR). However, little is known about the molecular mechanism on their antagonistic effects. In this study, the inhibitory effect of flavonoids on ligand binding to the AhR and interaction between flavonoids and the AhR complex (AhRc) were investigated in each flavonoid subclass. Flavone, flavonol, and flavanone but not catechin inhibited the specific binding between the AhR and 3-methylcholanthrene dose-dependently, indicating that the former three subclasses possibly act as competitive antagonists of the AhR. However, catechin in addition to the former three subclasses directly interacted with the AhRc by surface plasmon resonance analysis. The dissociation constant values showed an inverse correlation with the suppressive effect on the DNA binding activity. These results suggest that flavone, flavonol, and flavanone act as competitive antagonists of the AhR, while catechin associates with the AhRc and indirectly exhibits its antagonistic effects.

Biochemical and Biophysical Research Communications


Identification of a functional 2-keto-myo-inositol dehydratase gene of Sinorhizobium fredii USDA191 required for myo-inositol utilization.

Sinorhizobium fredii USDA191 is a Gram-negative bacterium capable of forming nitrogen-fixing nodules on soybean roots. The USDA191 idhA gene encoding myo-inositol dehydrogenase, an enzyme necessary for myo-inositol utilization, is known to be involved in competitive nodulation and nitrogen fixation. In Bacillus subtilis, myo-inositol dehydrogenase catalyzes the first step of the myo-inositol catabolic pathway. Recently iolE was identified as the gene encoding 2-keto-myo-inositol dehydratase, which catalyzes the second step in the pathway. Here we report the presence of 2-keto-myo-inositol dehydratase activity in free-living USDA191 cells cultured in a medium containing myo-inositol. An iolE ortholog was cloned from USDA191. USDA191 iolE was expressed in Escherichia coli as a His(6)-tag fusion and purified to exhibit 2-keto-myo-inositol dehydratase activity. Inactivation of USDA191 iolE led to defective myo-inositol utilization. USDA191 iolE partially complemented a B. subtilis iolE deficient mutant. These results suggest that S. fredii USDA191 utilizes a myo-inositol catabolic pathway, analogous to that of B. subtilis, involving at least idhA and iolE.


Screening of indigenous plants from Japan for modulating effects on transformation of the aryl hydrocarbon receptor.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor with which halogenated and polycyclic aromatic hydrocarbons such as dioxins and benzo[a]pyrene interact as ligands. Since such compounds cause various toxicological effects, including cancer, through the transformation of AhR, it is important to determine influence of modulating factors. It has been reported that certain plant components such as flavonoids and indoles can affect AhR transformation. In this study, to obtain clues to novel ligands of AhR, 191 species of indigenous plants were collected in Japan, and their 50% methanolic extracts (total 368 plant parts) were tested for modulating effects on AhR transformation in a cell-free system using a rat hepatic cytosolic fraction. Among tested extracts at a concentration of 1 mg dry weight of plant/mL, 174 of 368 extracts suppressed 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced AhR transformation to 50% or less, while 9 extracts per se induced AhR transformation equivalent to more than 20% of that induced by 1 nM TCDD. Mallotus japonicus (Thunb.) Muell. (leaf) and Trichosanthes rostrata Kitamura (fruit and fruit skin) strongly suppressed 1 nM TCDD-induced AhR transformation, while Phellodendron amurense Ruprecht (seed) per se strongly induced AhR transformation. These results suggest that a large variety of plants in Japan contain various compounds modulating, mainly suppressing, AhR transformation.

Asian Pacific Journal of Cancer Prevention : APJCP


Molokhia (Corchorus olitorius L.) extract suppresses transformation of the aryl hydrocarbon receptor induced by dioxins.

Dioxins enter the body mainly through diet and cause the various toxicological effects by binding to the cytosolic aryl hydrocarbon receptor (AhR) followed by its transformation. In recent reports, it has been shown that certain natural compounds suppress AhR transformation in vitro. In this study, we demonstrated that ethanolic extract from molokhia, known as Egyptian spinach, showed the strongest suppressive effect on AhR transformation induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in cell-free system using rat hepatic cytosol among 41 kinds of extracts from vegetables and fruits. The molokhia extract also suppressed TCDD-induced AhR transformation in mouse hepatoma Hepa-1c1c7 cells and in intestinal permeability system constructed with human colon adenocarcinoma Caco-2 cells and human hepatoma HepG2 cells. Moreover, oral administration of the molokhia extract (100mg/kg body weight) decreased 3-methylcholanthrene-induced AhR transformation to the control level by inhibiting translocation of the AhR from cytosol into the nucleus in the liver of rats. The molokhia extract-administered rat liver showed a tolerance to TCDD-induced AhR transformation by ex vivo experiment. These results indicate that molokhia is an attractive food for isolation and identification of a natural antagonist for the AhR.


Anthocyans fail to suppress transformation of aryl hydrocarbon receptor induced by dioxin.

Dioxins induce adverse effects through transformation of the cytosolic aryl hydrocarbon receptor (AhR). Our previous study found that flavones and flavonols at dietary levels suppress AhR transformation. In the present study, we investigated whether 20 anthocyans dissolved in trifluoroacetic acid (TFA)-MeOH suppressed AhR transformation in a cell-free system and in Hepa-1c1c7 cells. Although four compounds at 50 muM suppressed 0.1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced AhR transformation and their effects were dose-dependent in the cell-free system, they were ineffective at 0.5 muM, which is close to physiological concentration. Moreover, no anthocyan at 50 muM tested here suppressed 0.1 nM TCDD-induced AhR transformation in Hepa-1c1c7 cells. We also confirmed that protocatechuic acid and related compounds, which are possible metabolites of anthocyans, did not affect the transformation in the cell-free system. It is concluded that anthocyans are not suitable candidates for protection from dioxin toxicity.

Bioscience, Biotechnology, and Biochemistry


A new southwestern chemistry-based ELISA for detection of aryl hydrocarbon receptor transformation: application to the screening of its receptor agonists and antagonists.

Halogenated aromatic hydrocarbons (HAHs), such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), produce a wide variety of biological and toxic effects mainly through the aryl hydrocarbon receptor (AhR)-dependent mechanism. After the binding of HAHs, the AhR subsequently transforms its form in order to interact with a specific DNA sequence, the dioxin responsive element (DRE). Thus, detection of the transformed AhR is a target for estimation of the biological and toxic potency of ligands. In this study, we have developed a simple method for quantitative assessment of the transformation state of AhR based on an enzyme-linked immunosorbent assay (ELISA) combined with southwestern chemistry technique (SW-ELISA) that detects the complex of transformed AhR:fluorescein isothiocyanate (FITC)-labeled DRE probe. SW-ELISA has shown the response to HAHs including TCDD and other known agonists in a dose-dependent manner. In the case of TCDD, SW-ELISA has revealed a minimum detection limit (MDL) of 2 pM (0.026 pg/assay), a median effective concentration (EC(50)) value of 0.125 nM (1.6 pg/assay), and a maximum response at 10 nM (129 pg/assay). Furthermore, SW-ELISA provides the confirmation that flavonoids, the potent antagonists for AhR as reported previously, show the inhibitory effects on TCDD-induced AhR transformation. These results indicate that SW-ELISA is a new and straightforward method for the detection of AhR transformation and will be useful in screening of agonists or antagonists for AhR.


Anthocyan does not suppress transformation of aryl hydrocarbon receptor induced by dioxin.

Dioxins cause a variety of toxic effects through transformation of a cytosolic aryl hydrocarbon receptor (AhR). We have previously demonstrated that certain natural flavones and flavonols at the dietary levels suppress AhR transformation. In this study, we investigated whether 5 anthocyanidins, 15 anthocyanins, and protocatechuic acid suppress AhR transformation in mouse hepatoma Hepa-1c1c7 cells. All the compounds tested here at 5 microM unexpectedly failed to suppress the transformation induced by 0.1 nM TCDD, indicating that anthocyan does not have a potential to prevent dioxin toxicity.