Yoritaka Aoyama

6-Hydroxyflavonoids as α-Glucosidase Inhibitors from Marjoram (Origanum majorana) Leaves

A methanol extract of marjoram leaves strongly inhibited rat intestinal α-glucosidase. Five 6-hydroxyflavonoids, 6-hydroxyapigenin (scutellarein; IC50 for sucrose hydrolysis by rat intestinal α-glucosidase, 12 μM), 6-hydroxyapigenin-7-O-β-D-glucopyranoside (>500 μM), 6-hydroxyluteolin-7-O-β-D-glucopyranoside (300 μM), 6-hydroxyapigenin-7-O-(6-O-feruloyl)-β-D-glucopyranoside (>500 μM), and 6-hydroxyluteolin-7-O-(6-O-feruloyl)-β-D-glucopyranoside (>500 μM), were isolated as active principles and related compounds. The two feruloylglucosides are novel compounds.

Ingestion of insoluble dietary fibre increased zinc and iron absorption and restored growth rate and zinc absorption suppressed by dietary phytate in rats

We examined the effects of ingestion of five types of insoluble fibre on growth and Zn absorption in rats fed a marginally Zn-deficient diet (6.75 mg (0.103 mmol) Zn/kg diet) with or without added sodium phytate (12.6 mmol/kg diet). The types of insoluble fibre tested were corn husks, watermelon skin, yam-bean root (Pachyrhizus erosus) and pineapple core, and cellulose was used as a control (100 g/kg diet). Body-weight gain in the cellulose groups was suppressed by 57 % by feeding phytate. Body-weight gain in phytate-fed rats was 80 % greater in the watermelon skin fibre and yam-bean root fibre group than that in the cellulose group. Zn absorption ratio in the cellulose groups was lowered by 46 and 70 % in the first (days 7-10) and second (days 16-19) measurement periods with feeding phytate. In the rats fed the phytate-containing diets, Zn absorption ratio in the watermelon skin, yam-bean root and pineapple core fibre groups was 140, 80 and 54 % higher respectively than that in the cellulose group, in the second period. Fe absorption was not suppressed by phytate, however, feeding of these three types of fibre promoted Fe absorption in rats fed phytate-free diets. The concentration of soluble Zn in the caecal contents in the watermelon skin fibre or yam-bean root fibre groups was identical to that in the control group in spite of a higher short-chain fatty acid concentration and lower pH in the caecum. These findings indicate that ingestion of these types of insoluble fibre recovered the growth and Zn absorption suppressed by feeding a high level of phytate, and factors other than caecal fermentation may also be involved in this effect of insoluble fibre.

Ingestion of water-soluble soybean fiber improves gastrectomy-induced calcium malabsorption and osteopenia in rats

OBJECTIVEnTotal gastrectomy produces calcium malabsorption and osteopenia. We examined the effects of feeding water-soluble soybean fiber (WSSF), a highly fermentable dietary fiber with low viscosity, on calcium absorption and bone characteristics in totally gastrectomized rats.nnnMETHODSnMale Sprague-Dawley rats were assigned to two groups: sham operation and gastrectomy. After the postoperative recovery period, rats of each group were fed diets with or without WSSF (50 g/kg diet) for 4 wk.nnnRESULTSnNet calcium absorption and femoral dry weight and calcium content and maximum breaking force were lower in the gastrectomy groups than in the sham groups. In the gastrectomy groups, calcium absorption and these femoral parameters were higher in rats fed the WSSF diet than in rats fed the WSSF-free diet. Feeding WSSF increased the concentrations of short-chain fatty acids and soluble calcium and decreased the pH in cecal contents. Net calcium absorption in gastrectomized rats correlated positively with the concentration of total short-chain fatty acids (the sum of acetic, propionic, and butyric acids) in cecal contents (r = 0.545, P < 0.05) and negatively with cecal pH (r = -0.628, P < 0.05).nnnCONCLUSIONSnThese findings indicate that ingestion of WSSF partly prevents the diminished calcium absorption after total gastrectomy in rats, resulting in the improvement of postgastrectomy osteopenia. The increase of calcium absorption may be associated with cecal fermentation of WSSF.

Ingestion of the soluble dietary fibre, polydextrose, increases calcium absorption and bone mineralization in normal and total-gastrectomized rats

We previously demonstrated that feeding a highly fermentable and water-soluble dietary fibre, guar-gum hydrolysate (GGH) increased intestinal absorption of insoluble Ca salts in total-gastrectomized rats. In the present study, we examined the effects of feeding a less fermentable and water-soluble fibre, polydextrose (PD), on Ca absorption and bone mineralization in the normal and total-gastrectomized rats in comparison with the effects of GGH. Apparent Ca absorption was severely lowered by gastrectomy, and PD feeding (50 g/kg diet) partially restored the reduction of Ca absorption similarly to GGH feeding (50 g/kg diet). PD feeding also increased the Ca absorption in normal rats, but not GGH feeding. Femur Ca concentration was reduced with gastrectomy. Feeding PD for 21 d increased the bone Ca concentration in both normal and gastrectomized rats, but GGH feeding did not. In rats fed PD, pH of the caecal contents was lower than in rats fed fibre-free and GGH diets; however, soluble Ca concentration in the caecal contents was not different between the diet groups. Short-chain fatty acid concentrations were much lower in the PD groups than in the GGH groups. We also examined in vitro Ca absorption by using everted sacs of the small intestine. Addition of PD to the serosal medium of the ileal sacs increased Ca absorption, but addition of GGH did not. These results suggest that the small intestine rather than the large intestine is responsible for the increase in Ca absorption in rats fed PD, and suggests that the mechanism for the increase by PD may be different from that by GGH.

Enteral administration of soyabean lecithin enhanced lymphatic absorption of triacylglycerol in rats

As the physiological roles of dietary lecithin have not yet been clearly defined, we examined the effects of lecithin on lipid absorption in male Wistar rats with a mesenteric lymph cannula. Lymphatic absorption was observed after the infusion of 1 ml emulsion containing 100 mg test oil emulsified with sodium taurocholate (10 g/l) in three separate experiments. Test oils (100 mg) were: soyabean oil (triacylglycerol (TG) source, SO) and soyabean oil+lecithin (75 mg soyabean oil+25 mg lecithin, LE) in Expt 1; SO, LE or soyabean oil+lysolecithin (75 mg soyabean oil plus 25 mg lysolecithin, LY) in Expt 2; hydrolysed soyabean oil (HSO) or HSO+lysolecithin (75 mg HSO+25 mg lysolecithin, HLY) in Expt 3. After LE and LY infusions, lymph flow and the lymphatic output of TG was higher than after SO infusion at 0-30 min and 0-90 min respectively (Expts 1 and 2). Lecithin-induced increases in lymph TG output remained constant when HSO was infused (Expt 3). There were no differences in the TG:phospholipid ratio in the lymph after infusion among the groups; nevertheless, the lymphatic output of TG was much higher after infusion with LE than with SO. Fatty acid was released more efficiently from SO than from LE and LY by in vitro digestion with rat bile-pancreatic juice. These present results demonstrate that a TG emulsion containing soyabean lecithin or its hydrolysates promote lymphatic TG output and suggest that the increases in TG absorption do not depend on TG digestion.

Effects of Adding Some Dietary Fibers to a Cystine Diet on the Activities of Liver Antioxidant Enzymes and Serum Enzymes in Rats

This study investigates whether some dietary fibers can the toxicity due to cystine added to the diet. Wistar rats were investigated for the effects of adding pectin, sugar beet fiber or konjac mannan to a cystine diet on the growth rate and on the activities of liver antioxidant enzymes and serum enzymes. The addition of pectin, sugar beet fiber or konjac mannan to the cystine diet resulted in a significant increase in both the food intake and body weight gain. Feeding the cystine diet caused lower activities of total and Cu, Zn-superoxide dismutase, and of catalase in the liver. The addition of pectin to the cystine diet counteracted the activities of the total and Cu,Zn-superoxide dismutase, and of catalase in liver. Of the dietary fibers tested, konjac mannan prevented the elevation of the two enzyme activities in the serum induced by feeding the cystine diet, indicating that this fiber might have the ability to alleviate hepatic damage due to dietary cystine.

Massive large bowel resection decreases bone strength and magnesium content but not calcium content of the femur in rats

We examined the effects of massive large bowel resection (cecocolonectomy) on calcium and magnesium absorption and bone characteristics in rats. Male Sprague-Dawley rats were divided into two groups: sham-operated and cecocolonectomized rats. The rats were fed a sucrose-based diet containing casein at 250 g/kg diet for 10 d after a 9- to 10-d postoperative recovery period. Apparent magnesium absorption but not calcium absorption was lower in the resection group than in the sham group. There was a tendency of lower serum magnesium concentration (P = 0.070) but not calcium concentration (P = 0.418) in the resection group compared with the sham group. The maximum breaking force and magnesium content but not the calcium content of the femur were lower in the resection group than in the sham group. These results suggest that massive large bowel resection influences magnesium kinetics and decreases bone strength through reduction of the magnesium content of the femur in rats. Femoral breaking force was positively correlated (r = 0.617, P = 0.011) with only the magnesium content. We conclude that the changes in magnesium kinetics caused by cecocolonectomy could contribute to the fragility of bone.

Casein binds to the cell membrane and induces intracellular calcium signals in the enteroendocrine cell: a brief communication.

Dietary protein but not amino acids stimulates cholecystokinin (CCK) secretion in rat mucosal cells. However, the dietary protein sensory mechanisms and the intracellular signal pathway in the enteroendocrine cells have not yet been clarified. The relationship between dietary protein binding to cell membrane and intracellular calcium responses were examined in the CCK-producing enteroendocrine cell line STC-1. The binding of solubilized STC-1 cell membrane to proteins was analyzed using a surface plasmon resonance sensor. Intracellular calcium concentrations of STC-1 cell suspensions loaded with Fura-2 AM were measured using a spectrafluorophotometer system with continuous stirring. Intracellular calcium concentrations in STC-1 cells were increased by exposure to α-casein or casein sodium, but not to bovine serum albumin. Solubilized STC-1 membranes bound to α-casein and casein sodium but did not bind to bovine serum albumin. α-Casein demonstrated higher membrane binding and intracellular calcium stimulating activities than casein sodium. Thus, protein binding to the STC-1 cell membrane and intracellular calcium responses were correlated. Intracellular calcium responses to α-casein were suppressed by an L-type calcium channel blocker. These results suggest that casein, a dietary protein, binds to a putative receptor on the CCK-producing enteroendocrine cell membrane and elicits the subsequent intracellular calcium response via an L-type calcium channel.

Dietary iron-deficiency up-regulates hephaestin mRNA level in small intestine of rats

Hephaestin is a protein, recently found from the study of sla (sex-linked anemia) mouse. Hephaestin is suggested to transport iron from intestinal enterocytes into the circulation. Iron is essential for living and for humans to maintain a constant total iron concentration in whole body. In this study, it was found that dietary iron-deficiency up-regulated hephaestin mRNA level in the proximal small intestine of rats. Therefore, it is suggested that in dietary iron-deficiency, hephaestin gene expression in proximal small intestine is up-regulated to absorb more iron from diet.

Ingestion of sugar beet fiber enhances irradiation-induced aberrant crypt foci in the rat colon under an apoptosis-suppressed condition

The induction of aberrant crypt foci (ACF) by irradiation of γ-rays (60Co), and the effect of dietary sugar beet fiber (SBF) on irradiation-induced ACF were examined. We found that abdominal irradiation of γ-rays could induce ACF in the rat colon. The irradiation was performed once a week at a dose rate of 2 or 3 Gy per irradiation. Irradiation-induced ACF were observed in the colon at 10 weeks after the first irradiation at dose of 2 Gy for six times or 3 Gy for four times. Dietary SBF had no effect on the number of ACF, aberrant crypts (AC) or AC/focus induced by abdominal γ-irradiation. However, an ingestion of SBF resulted in an increase in the number of these parameters in apoptosis-suppressed rats by cycloheximide (CHX). An injection of CHX suppressed irradiation-induced apoptosis of the colonic epithelial cells for at least 6 h after the irradiation. In CHX-injected rats, an ingestion of SBF significantly increased the number of ACF, AC and AC/focus compared with fiber-free fed rats at 9 weeks after the first irradiation. On the other hand, in saline-injected rats, no significant difference was found between SBF and fiber-free diets in the number of ACF, AC and AC/focus through the experimental period. These results suggest that dietary SBF may be involved in the elimination of abnormal cells from an irradiated colon through the apoptosis of colonic epithelial cells. In this study, we have shown a new method for inducing ACF by using γ-rays which were not influenced by luminal contents such as bacterial enzyme, at least in the initiation stage.