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Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan and * Department of Food Science and Human Nutrition, Faculty of Human Life Science, Fuji Women’s University, Ishikari 061-3204, Japan
2To whom correspondence should be addressed. E-mail: hara{at}chem.agr.hokudai.ac.jp.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • calcium absorption • difructose anhydride III • rats • ovariectomy
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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,2
). Because Ca is a major component of bone, it is necessary to have an adequate Ca intake. However, the Ca intake in Japan is lower than the dietary reference intake of Ca (3
,4
). The recommended dietary allowance for Ca of Japanese adults is 600 mg/d (5
), and the Ca requirement for Japanese elderly women was estimated by balance study as 788 mg/d (3
). Mean intake of Ca in Japan (547 mg/d) has not reached the recommended dietary allowance (6
). Moreover, women with postmenopausal osteoporosis are particularly susceptible to impaired Ca absorption. Previous studies have shown that ovarian hormone deficiency impairs intestinal Ca absorption in postmenopausal or oophorectomized women (7
,8
). Ovariectomized (OVX)3
rats are a popular model for postmenopausal osteoporosis (9
–11
); however, some studies have reported that Ca absorption was also decreased in OVX rats (12
–14
).
Several reports have indicated that ingestion of fermentable dietary fibers (15
–17
), sugar alcohols (18
) and oligosaccharides (19
,20
) increases Ca absorption in rats. Difructose anhydride III (DFAIII) is an indigestible saccharide with a unique structure shown in Figure 1
; it is prepared from inulin with Arthrobacter sp. H65–7 inulin fructotransferase (Inulinase II; EC 2.4.1.93) (21
). Recently, a procedure was established for the mass production of DFAIII using a bacterial enzyme (22
). In previous studies, we reported that DFAIII promoted Ca absorption in in vivo and in vitro experiments (23
,24
). However, it is not clear whether DFAIII promotes Ca absorption in OVX rats.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Female Sprague-Dawley rats (6 wk old; Japan Clea, Tokyo, Japan) weighing 
150 g were housed in individual stainless steel cages with wire-mesh bottoms. The cages were placed in a room with controlled temperature (22–24°C), relative humidity (40–60%) and lighting (lights on 0800–2000h). The rats had free access to water and the semipurified stock diets shown in Table 1
for an acclimation period of 7 d. This study was approved by the Hokkaido University Animal Committee, and the rats were maintained in accordance with the Hokkaido University guidelines for the care and use of laboratory animals.
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In Experiment 1, the acclimatized rats were divided into two groups; one group of rats underwent bilateral ovariectomy (OVX) and the other group underwent bilateral laparotomy (sham). All rats had free access to deionized water and the stock diet for 5 d to recover from surgical damage. The rats in each group were divided into four subgroups of 8–10, and were fed diets containing four levels of Ca (1.0, 2.0, 3.0 and 4.0 g Ca/kg diet) for 3 wk. To create graded levels of Ca in the diet, CaCO3 was replaced with sucrose. Feces were collected during the last 3 d of the test period.
In Experiment 2, OVX and sham rats were each divided into two diet subgroups of 10, i.e., sham + control diet, sham + DFAIII (30 g/kg diet) diet, OVX + control diet, and OVX + DFAIII (30 g/kg diet) diet. Feces were collected during the last 3 d of the test period. At the end of experiment, the rats were anesthetized (Nembutal: sodium pentobarbital, 50 mg/kg body weight, Abbott Laboratories, North Chicago, IL) and killed.
The duodenum and colon were removed and were used in an everted sac study as follows: 3-cm segments of the lower part of duodenum and the proximal colon were everted and ligated with surgical silk at one end. Artificial serosal fluid (30 mmol/L Tris-HCl, pH 7.4, containing 125 mmol/L NaCl, 4 mmol/L KCl, 10 mmol/L glucose and 1.25 mmol/L CaCl2 · 2H2O, treated with 100% O2 and warmed to 37°C) was instilled into each sac from the other end, which was then ligated. The sacs were transferred to individual flasks containing 30 mL of gassed and warmed artificial mucosal fluid (30 mmol/L Tris-HCl, pH 7.4, containing 125 mmol/L NaCl, 4 mmol/L KCl, 10 mmol/L glucose and 10 mmol/L CaCl2 · 2H2O). Sacs were incubated for 30 min at 37°C while being shaken at 110 oscillations/min. Then the serosal fluid was collected and sacs were weighed. Ca concentration in the serosal fluid stands for transport of Ca into the serosal side. Ca concentration in the serosal fluid was assayed to determine the Ca absorption rate of the sacs (23
). The Ca absorption was expressed as µmol Ca transferred/(g sac · h).
In Experiment 3, two groups of OVX rats underwent cecocolonectomy or a sham operation. Briefly, the cecum and colon were removed after ligation of blood vessels, and end-to-end anastomosis was carried out between the cut edge of the ileum and the rectum (cecocolonectomy) (25
). Rats of the other group underwent transsection of the terminal ileum and reanastomosis (sham). All rats were deprived of food and water for 24 h after the surgery. After a 5-d recovery period with a stock diet, both groups of rats were divided into four diet subgroups, i.e., control, polyethylene glycol (PEG), DFAIII (15 g/kg diet, 1.5%) and DFAIII (30 g/kg diet, 3%) diet. Each subgroup was then fed one of the four test diets for 4 wk. Because DFAIII is an unabsorbable compound with a low molecular weight (MW 324), ingestion of DFAIII should raise the osmotic pressure of the chyme in the small intestine. To examine the effect of the osmotic pressure of the lumen on Ca absorption, we set up another control group fed a diet containing PEG 400 (37 g/kg diet) to adjust the osmotic pressure to that of the 3% DFAIII diet. Osmotic pressure of the luminal chyme may influence the transit time of the gastrointestinal tract (26
,27
). We measured gastrointestinal transit time of cecocolonectomized rats 21 d after feeding the test diets. Briefly, rats were deprived of food for 15 h, and fed 1 g of test diet containing 0.3% carmine. After the feed had been consumed, the usual test diets were given. The time to the first excretion of colored feces after consumption of the carmine diet was taken as the gastrointestinal transit time (28
). Feces were collected during the last 3 d of the test period. On the last day of the test period, rats were killed under pentobarbital anesthesia, and both femurs in all rats were removed and carefully cleaned of adherent tissue. The left femurs were measured for bone strength. The right femurs were freeze-dried for measurement of mineral contents. The small intestine and the cecum were removed with their contents. The contents were collected and stored at -40°C until subsequent analyses. In all experiments, body weight and food intake were measured every day. After killing, the uterus of each rat was removed and weighed to confirm the success of the ovariectomy.
Analytical methods.
Freeze-dried feces were milled, and the powdered feces were wet-ashed with an acid mixture (16 mol/L HNO3/9 mol/L HClO4 = 3:1) without drying. The amounts of Ca and magnesium (Mg) in the right femurs were measured after the samples had been wet-ashed in the same way as the feces. Ca and Mg concentrations in those solutions were measured by atomic absorption spectrophotometry (AA-6400F; Shimadzu Corporation, Kyoto, Japan) after appropriate dilution with 0.1 mol/L HCl. Phosphate (P) was determined in the femoral solutions by the molybdovanadate method (29
). Ca concentration of the artificial serosal fluid in the everted sacs was assayed with a commercial kit (Calcium-C test; Waco Pure Chemical Industries, Osaka, Japan).
The maximum breaking force of the left femoral diaphysis (the center of the femur) was measured as the bone strength. A three-point bending test (30
) was performed with a rheometer (RE-3305 Rheoner, Yamaden, Tokyo, Japan) under the following conditions: sample space, 1.0 cm; pranger speed, 30 mm/min; and load range, 20 kg.
The intestinal contents were homogenized with nine volumes of deionized water. The pH values of the homogenized samples were measured with a semiconducting electrode (ISFET pH sensor 0010–15C, Horiba, Kyoto, Japan). The organic acids in the intestinal contents were measured by HPLC (Organic Acid Analysis System, Shimadzu, Kyoto, Japan) as previously described (31
).
Calculations and statistical analyses.
Ca absorption was calculated using the following equations: 1) net Ca absorption (mmol) = total Ca intake - Ca excretion in feces; and 2) Ca absorption rate (%) = 100 x (total Ca intake - Ca excretion in feces)/total Ca intake.
Values shown represent the means ± SEM. Statistical analyses were performed by two-way ANOVA (treatment x diet) in Experiments 1–3 except for the results for cecal parameters (Table 4)
and transit time (Fig. 4)
, which were analyzed by one-way ANOVA. The significance of intergroup differences was evaluated by Duncan’s multiple-range test (32
) (P < 0.05). If the variance was unequal, log transformations of the data were performed before ANOVA. All statistical analyses were done using SPSS for Windows, Version 10.0 J (SPSS, Chicago, IL).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Body weight gain was higher in OVX rats than in sham rats; the mean final body weight of OVX rats (271 g) was higher than that of sham rats (248 g) (P < 0.001). However, there were no differences in food intake between groups. This result agrees with the previous report (33
). The uterine weight was much lower in the OVX rats (0.034 g/100 g body) than in the sham rats (0.212 g/100 g body), indicating the success of the surgical procedure in all rats in the OVX group. Ca intake did not differ during the test period between sham and OVX rats fed the same level of Ca diet (Table 2
). Fecal Ca excretion was higher in OVX rats than in sham rats. Net Ca absorption in OVX rats was lower than that in sham rats. In particular, in OVX rats fed 3.0 and 4.0 g Ca/kg diets, Ca absorption was lower than in sham rats fed the same levels of Ca diets. Ca absorption rate was also lower in OVX rats than in sham rats. The reduction in Ca absorption rate was seen in OVX rats fed 2.0 g and 3.0 g Ca/kg diet groups compared with sham rats.
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Body weight gain was higher in OVX rats than in sham rats fed the control and DFAIII diets. The mean final body weight of OVX rats (298 g) was higher than the sham-operated rats (273 g) (P < 0.001). Food intake did not differ between groups. The uterine weight was much lower in the OVX rats (0.035 g/100 g body) than in the sham (0.185 g/100 g body). Ca absorption rate in OVX rats was lower than that in sham rats in both the control and DFAIII groups (Fig. 2
). The Ca absorption rate in the DFAIII group was higher than that in the control group in both OVX and sham rats. Moreover, the Ca absorption rate in OVX rats fed the DFAIII diet did not differ from that in the sham control group. Ca absorptive activity [µmol/(g sac · h)] in the everted sacs of the duodenum from OVX rats fed the control diet was lower than that from the sham control. The absorptive capacity of the duodenal sacs in OVX rats fed the DFAIII diet did not differ from that of the sham rats. In the everted colonic sacs of the sham rats, the absorptive capacity was higher in the sacs of rats fed the DFAIII diet than in the sacs of rats fed the control diet. Absorptive capacity of the colonic sacs of OVX rats fed the DFAIII diet was also higher than that of those fed the control diet, although the difference was not significant.
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There were no differences in body weight gain or food intake among groups. The Ca absorption rate in sham rats fed both 1.5 and 3% DFAIII diets were higher than that in sham rats fed control and PEG diets, and feeding low levels of DFAIII promoted greater Ca absorption (Fig. 3
). There were no observed differences in Ca absorption rate in sham and cecocolonectomized rats fed the control diet. However, Ca absorption in cecocolonectomized rats was lower than that in sham rats in the PEG, 1.5% DFAIII and 3% DFAIII diet groups. In the case of cecocolonectomized rats, Ca absorption rate in the PEG group was lower than that in the control group. There were no differences in absorption between the DFAIII and control groups; however, Ca absorption in rats fed both the 1.5 and 3% DFAIII diets was higher compared with the PEG group (another control group). Transit times of the chyme in cecocolonectomized OVX rats shown in Figure 4
were shorter in the PEG and 3% DFAIII groups than in the control group. Transit time of the rats fed the 3% DFAIII diet did not differ from that of rats fed the PEG diet.
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). The femoral Ca content was higher in sham rats fed 1.5% DFAIII diet than that in sham rats fed the control diet. The femoral Mg content did not differ among the groups. The maximum breaking force of the femur did not differ between sham and cecocolonectomized rats. However, the maximum breaking force of the femur was higher in cecocolonectomized rats fed 1.5% DFAIII diet than in rats fed the control diet (Fig. 5
).
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). Cecal pH values in rats fed DFAIII diets were lower than those in rats fed the control diet. There were no differences in cecum parameters between rats fed the control diet and those fed the PEG diet. |
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Holzherr et al. (7
) and Kalu (9
) also reported similar observations in humans and animals. In this study, we showed that the decrease in Ca balance by ovariectomy depends on dietary Ca levels, i.e., net Ca absorption and the Ca absorption rate fell in rats fed 2.0, 3.0 and 4.0 g Ca/kg diets but not in those fed 1.0 g Ca/kg diet (Table 2)
. The reduction in Ca absorption in rats fed 1.0 g Ca/kg diet was small and without significant difference. In this very low Ca level, the major part of Ca absorption may depend on active transport in the duodenum (35
). It may be a reason for the lack of significant difference between sham and OVX rats in Ca absorption in the 1.0 g Ca/kg diet group. In the present study, we revealed a decrease in Ca absorptive capacity by ovariectomy in the duodenum in an in vitro experiment using everted sacs (Fig. 2)
, in which Ca concentration of mucosal fluids was much higher than Km value of active transport system (10 vs. 1.25 mmol/L). This finding suggests that OVX impaired passive transport system for Ca, and this reduction shown by in vitro observation is involved in the lower Ca absorption observed in the in vivo balance study in OVX rats. However, the precise mechanism for the reduction of duodenal Ca absorptive capacity remains unknown.
In the present study, we estimated that a 3.0 g Ca/kg diet level is the minimum requirement of Ca carbonate in rats because there was no change in net Ca absorption between the 3.0 and 4.0 g Ca/kg diets (36
). Also, the reduction of net Ca absorption was the greatest in rats fed the 3.0 g Ca/kg diet. From these results, we chose to use 3.0 g Ca/kg diet in subsequent experiments.
In Experiments 2 and 3, we showed that the reduction of Ca absorption by ovariectomy was restored by feeding DFAIII (Figs. 2
, 3)
. The presence of fermentation products in the large intestine is one of the promotive factors of Ca absorption in the large intestine (8
,15
–17
,37
,38
). Some studies have suggested that microbial fermentation products produced from indigestible saccharides are responsible for the enhancement of Ca absorption in the large intestine (8
,37
,38
). In the present study, we showed a decrease in cecal pH and an increase in SCFA contents in rats fed DFAIII (Table 4)
. In Experiment 3, we found that the ingestion of DFAIII increased Ca absorption in sham rats. However, the increase was abolished by cecocolonectomy (Fig. 3)
. These results show that DFAIII enhanced Ca absorption in the large intestine and this increase may be associated with cecal fermentation of DFAIII. Moreover, the rate of Ca absorption in the everted colonic sacs of the DFAIII group was higher than that in the control group, indicating that Ca absorptive capacity in the colon is increased by DFAIII feeding. This finding indicates that the adaptive increase in the absorptive system contributes to the enhancement of absorption by the large bowel induced by DFAIII feeding.
Canceling of promotive effects of DFAIII by removal of the large intestine (Fig. 3)
showed that the small intestine does not contribute to the action of DFAIII. However, we previously demonstrated that DFAIII dramatically promoted Ca transport of the stripped jejunal mucosa in an in vitro study (24
). In in vivo experiments, we must consider the effects of transit time on Ca absorption rate in the small intestine. Gastrointestinal transit time of the chyme in cecocolonectomized OVX rats was shortened by ingestion of DFAIII (Fig. 4)
. DFAIII is an indigestible disaccharide, which generally act as an osmotic laxative and accelerates intestinal transit speed in a manner similar to lactulose (26
,27
). Intestinal transit time is thought to be a determining factor in the rate of mineral absorption (39
,40
). In the case of cecocolonectomized rats, shortening the transit time in the small intestine decreases Ca absorption in this segment and may directly reduce Ca balance. In this study, we evaluated the effect of the transit time of the small intestine on Ca absorption by using a PEG diet with the same osmotic pressure as the 3% DFAIII diet. The transit time in the PEG-fed rat was shortened and very similar to that in rats fed the 3% DFAIII diet (Fig. 4)
. We showed that Ca absorption was reduced by feeding PEG, but not by feeding DFAIII in cecocolonectomized rats. PEG had no direct effects on Ca transport in a previous in vitro study (37
), and PEG did not affect fermentation in the large intestine (Table 4)
. Shortening the small intestinal transit time by feeding PEG and also DFAIII may be a factor in decreasing Ca absorption; however, direct promotive effects of DFAIII on the small intestinal cells may overcome the negative effect of shortening transit time.
Ca absorption rate in the cecocolonectomized rats was higher in the 3% DFAIII group than in the PEG group even though the transit time of rats fed the 3% DFAIII diet was the same as that of rats fed the PEG diet (Fig. 4)
. This in vivo finding supports the in vitro study described above in which it was shown that DFAIII itself has the ability to promote Ca transport by stimulating the small intestinal mucosa because we could not detect any SCFA in the small intestinal chyme of cecocolonectomized rats (Experiment 3, data not shown). Mechanisms for increasing Ca absorption in the small intestine by DFAIII remain unclear; however, Mineo et al. (24
) suggested that this action is involved in the paracellular pathway of the mucosal epithelia and that DFAIII directly affects epithelial tissue to promote this pathway. Another study also showed that a sugar alcohol, maltitol, enhanced Ca absorption in the lower part of the small intestine in rats by modulating the nonsaturable component of Ca transfer (18
).
In the present study, increases in bone-breaking force and femoral Ca content were observed in rats fed the DFAIII diets (Table 3
and Fig. 5
). An enhancement of Ca absorption due to feeding of DFAIII may cause an increase in femoral Ca content and bone strength. This finding is in agreement with the findings of other studies that reported that increasing Ca absorption affected bone characteristics in rats (12
,18
,30
). However, it is not clear whether increases in femoral Ca content and bone strength depend completely on the promotion in Ca absorption by DFAIII. Fini et al. (41
) reported that some essential amino acids and carbohydrate lactose, which induce growth hormone and insulin-like growth factor I responses, could be useful for bone formation, due to their combined action of increasing Ca absorption. Factors other than Ca absorption are also necessary to promote bone formation. Further studies are required to examine the effects of DFAIII on bone characteristics in rats.
In conclusion, ovarian hormone deficiency impaired Ca absorption, and feeding DFAIII at a low level restored the ovariectomy-induced reduction in Ca absorption. The large intestine is involved in the beneficial effects of DFAIII, and supplemental feeding of DFAIII increased bone Ca content and strength.
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FOOTNOTES |
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3 Abbreviations used: DFAIII, difructose anhydride III; OVX, ovariectomy; PEG, polyethylene glycol; SCFA, short-chain fatty acids.
Manuscript received 12 May 2002. Initial review completed 19 June 2002. Revision accepted 31 July 2002.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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  S. Ishizuka, S. Tanaka, H. Xu, and H. Hara Fermentable Dietary Fiber Potentiates the Localization of Immune Cells in the Rat Large Intestinal Crypts Experimental Biology and Medicine, October 1, 2004; 229(9): 876 - 884. [Abstract] [Full Text] [PDF]
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 T. Suzuki and H. Hara Various Nondigestible Saccharides Open a Paracellular Calcium Transport Pathway with the Induction of Intracellular Calcium Signaling in Human Intestinal Caco-2 Cells J. Nutr., August 1, 2004; 134(8): 1935 - 1941. [Abstract] [Full Text] [PDF]
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K. Shiga, H. Hara, G. Okano, M. Ito, A. Minami, and F. Tomita Ingestion of Difructose Anhydride III and Voluntary Running Exercise Independently Increase Femoral and Tibial Bone Mineral Density and Bone Strength with Increasing Calcium Absorption in Rats J. Nutr., December 1, 2003; 133(12): 4207 - 4211. [Abstract] [Full Text] [PDF]
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K. Afsana, K. Shiga, S. Ishizuka, and H. Hara Ingestion of an Indigestible Saccharide, Difructose Anhydride III, Partially Prevents the Tannic Acid-Induced Suppression of Iron Absorption in Rats J. Nutr., November 1, 2003; 133(11): 3553 - 3560. [Abstract] [Full Text] [PDF]
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