Michiyo Furugori

Intestinal absorption of luteolin and luteolin 7-O-β-glucoside in rats and humans

In this study, we investigated the intestinal absorption of luteolin and luteolin 7‐O‐β‐glucoside in rats by HPLC. The absorption analysis using rat everted small intestine demonstrated that luteolin was converted to glucuronides during passing through the intestinal mucosa and that luteolin 7‐O‐β‐glucoside was absorbed after hydrolysis to luteolin. Free luteolin, its conjugates and methylated conjugates were present in rat plasma after dosing. This suggests that some luteolin can escape the intestinal conjugation and the hepatic sulfation/methylation. LC/MS analysis showed that the main conjugate which circulates in the blood was a monoglucuronide of the unchanged aglycone. Luteolin in propyleneglycol was absorbed more rapidly than that in 0.5% carboxymethyl cellulose. The plasma concentration of luteolin and its conjugates reached the highest level 15 min and 30 min after dosing with luteolin in propyleneglycol, respectively. HPLC analysis also allowed us to demonstrate the presence of free luteolin and its monoglucuronide in human serum after ingestion of luteolin.

Radioprotective effects of antioxidative plant flavonoids in mice

Radioprotective effects of tea infusions and plant flavonoids were investigated by using the micronucleus test for anticlastogenic activity and the thiobarbituric acid assay for antioxidative activity. A single gastric intubation of rooibos tea (Aspalathus linearis) infusion at 1 ml per mouse 2 h prior to gama-ray irradiation (1.5 Gy) reduced the frequency of micronucleated reticulocytes (MNRETs). After the fractionation of rooibos tea infusion, the flavonoid fraction was found to be most anticlastogenic and antioxidative. From this fraction, luteolin was isolated as an effective component. Then, anticlastogenic effects of 12 flavonoids containing luteolin and their antioxidative activities against lipid peroxidation by Fentons reagent were examined. A good correlation (r=0.717) was observed between both activities. Luteolin showed the most effective potency. A gastric intubation of luteolin (10 micromoles/kg) 2 h prior to gamma-ray irradiation (6 Gy) suppressed lipid peroxidation in mouse bone marrow and spleen and a trend of protective effect of luteolin against the decrease of endogenous ascorbic acid in mouse bone marrow after gamma-ray irradiation (3 Gy) was observed. These results suggest that plant flavonoids, which show antioxidative potency in vitro, work as antioxidants in vivo and their radioprotective effects may be attributed to their scavenging potency towards free radicals such as hydroxyl radicals. Therefore, the flavonoids contained in tea, vegetables and fruits seem to be important as antioxidants in the human diet.

Protection by αG-Rutin, a Water-soluble Antioxidant Flavonoid, against Renal Damage in Mice Treated with Ferric Nitrilotriacetate

The protective effect of aG‐Rutin against ferric nitrilotriacetate (Fe‐NTA)‐induced renal damage was studied in male ICR mice. Fe‐NTA induces renal lipid peroxidation, leading to a high incidence of renal cell carcinoma in rodents. Administration of αG‐Rutin (50 μmol as rut in/leg) by gastric intubation 30 min after i.p. injection of Fe‐NTA (7 mg Fe/kg) most effectively suppressed renal lipid peroxidation. Repeated i.p. injection of Fe‐NTA (2 mg FeAg/day for the first 3 days and 3 mg Fe/ kg/day for 12 days, 5 days a week) causes subacute nephrotoxicity as revealed by induction of karyomegalic cells in renal proximal tubules. A protective effect was observed in mice given αG‐Rutin 30 min after each Fe‐NTA treatment. To elucidate the mechanism of protection by αG‐Rutin, the pharmacokinetics and hydroxyl radical‐scavenging effect of αG‐Rutin were investigated by HPLC analysis and by electron spin resonance (ESR) spin trapping with 5,5‐dimethyl‐l‐pyrroline‐N‐oxide (DMPO), respectively. When mice were given αG‐Rutin (50 μmol as rutin Ag) by gastric intubation, rapid absorption into the circulation was observed. The plasma concentration of äG‐Rutin reached the highest level 30 min after oral administration and then decreased to the control level within 60 min. äG‐Rutin inhibited the formation of DMPO‐OH in a concentration‐dependent manner. Further, chelating activity of äG‐Rutin to ferric ions was shown by spectrophotometric analysis. These results suggest that absorbed äG‐Rutin works as an antioxidant in vivo either by scavenging reactive oxygen species or by chelating ferric ions and this serves to prevent oxidative renal damage in mice treated with Fe‐NTA.

Identification of 6-methylsulfinylhexyl isothiocyanate as an apoptosis-inducing component in wasabi

The ethanol extract from Japanese horseradish wasabi was found to inhibit cell proliferation in human monoblastic leukemia U937 cells by inducing apoptotic cell death. Separation by methods including silica gel chromatography and preparative HPLC gave an active compound, which was identified as 6-methylsulfinylhexyl isothiocyanate (6-HITC). Several lines of evidence indicated that 6-HITC induced apoptosis in U937 cells and human stomach cancer MKN45 cells. Thus, 6-HITC is potentially useful as a natural anti-cancer agent.

Formation of mutagenic and carcinogenic heterocyclic amines in the model systems without heating

Abstract Cooked food-borne heterocyclic amines (HCAs) show strong mutagenic activity toward Salmonella typhimurium TA98 strain in the presence of metabolic activation system. They also induce several kinds of tumors in mice and rats. Among them, 2-amino-3, 4-dimethylaminoimidazo [4,5-f] quinoxaline (MeIQ x ) and 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) are also isolated from a reaction mixture consisting of d -glucose, amino acid and creatinine by heating at 128 °C for 2 h. There is no report on the formation of HCAs under mild conditions. In the present study, a mixture of d -glucose, glycine and creatinine was dissolved in 0.2 M phosphate buffer solution (pH7.4) and kept at 37 °C for 84 days. Aliquots of the reaction solution were treated with blue cotton and the adsorbates were extracted with NH 4 OH–MeOH mixture. By applying the extract to HPLC and LC-MS analysis, MeIQ x was isolated and identified. When phenylalanine was used instead of glycine in the above model system, PhIP was formed. These results show that heating process is not essential for the formation of HCAs. Therefore, HCAs may be formed in our body tissues and in the long storage of manufactured foods.

Inhibitory Effect of Tea Extracts on the Formation of Heterocyclic Amines During Cooking of Hamburger

Tea extracts from green tea, black tea, polei tea, and rooibos tea showed an inhibitory effect on the formation of mutagenic and carcinogenic heterocyclic amines, such as 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-arnino-l-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), during cooking of hamburger. In the case of green tea samples, the catechin fraction and powder reduced the MelQx content to 54% and 26% of the control, respectively. PhIP content was also suppressed to 7.0%-19.8% of the control by the addition of crude extract or a catechin fraction or powder. Catechins con-taining (-)epigallocatechin gallate and flavonoids were useful components in these tea samples, and they may act mainly as antioxidants and radical-scavenging agents.