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Miura,Takehito 三 浦 健 人 |
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北海道 |
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博士（農学） |
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甲 第１０７号 |
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平成１０年９月３０日 |
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学位規則第４条第１項該当 |
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生物環境科学専攻 | ||
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Bioavability of Unutilized Natural Calcium and lts Effects on Bone Metabolism in Rats （未利用天然カルシウムのラツトにおける生体利用性および骨代謝に与える影響） | ||
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Osteoporosis is a multifactolial desease characterized by decreased bone mass and an increased risk of fracture and associated with estrogen deficiency following menopause. Inadequate calcium intake is one of the risk factors of osteoporosis. It is difficult to obtain an adequate amount of calcium from a normal diet. Increasing public consciousness of the importance of adequate dietary calcium has led to a great deal of demand for calcium supplements and fortifiications. We have previously paid attention upon the several unutilized natural resources. Bovine bone is the unutilized natural resource containing significant amount of calcium and phosphorus and has been reported to be effective for bone metabolism as a dietaly calcium source. The total bone extract (TBE) is a new mineral preparation made from bovine bone rendered soluble by lactic acid and citric acid with decompxssion. It is suspected to contain not only bone minerals, but also some bone matrix proteins. Fossil shellfish (FPS) is the natural resource that had not been utilized and naturally contains various minerals, i.e., calcium, phosphorus, magnesium, iron and other trace elements. Ezo giant scallop shell powder (SHL) is generally used as dietary calcium source. The purpose of this study was to utilize efficiently these unutilized natural resources as the dietary mineral source and to clalify the mineral bioavailability of these natural resources and their effects of bone metabolism. In the chapter I, the author examined whether the apparent mineral absorption, serum biochemical indices and tissue minerals were dififerent in the male growing nits fed on TBE and FPS as dietary calcium source in cornparison with calcium carbonate and bovine bone powder (BBP) commonly used calcium supplements. The rats were fed on the diet containing calcium cafbonate, TBE, FPS or BBP as a calcium source (calcium = 0.5%) for 28 days. Serum ALP and TRACP concentrations wers variant among the groups. They were the highest in the rats fed on calcium carbonate and the lowest in the rats fed on TBE among the groups. The apparent calcium and phosphorus absorptions in the FPS group was significantly higher than those in the other groups. The calcium absorption ratios in the FPS group and TBE group were signifilcantly higher than that in the BBP group and similar to the control group. There were no signifilcant differences in the femur dry weight, ash contents and mineral contents among the groups. The dry weight, ash contents, calcium and phosphorus contents in kidney were significantly increased in the rats fed FPS. It was indicated in the present study that TBE, solubilized bovine bone with lactic acid and citric acid under decompression, and FPS, the unutilzed natural resource, were useful as the dietary calcium source with respect to apparent mineral absorption and bone mineral content. The supplementation of calcium with the calcium-enriched foods and calcium preparations is necessary for the daily diet to ensure an adequate intake of calcium and to build a healthy bone. To evaluate the bioavailability and the effect on the bone metabolism of mineral supplements made from unutilized natural resources as the dietary mineral, we investigated whether oral administration of TBE,FPS, SHL, extracts of FPS and SHL with lactate and citrate (FSX and SHX, respectively) as the dietary calcium source would influence the intestinal mineral absorption, the serum markers of bone metabolism and calcium metabolism and bone mineral density in the ovariectomized (OVX) rat model of osteoporosis at marginal dietary calcium level. Calcium absorption ratios in OVX ruts weir depressed relative to sham-operated rats. Calcium from the TBE, FSX and SHX were more highly absorbed than from calcium carbonate in OVX rats. Moreover, the apparent calcium absorption ratio in the rats fed FSX and SHX was higher than in the rats fed FPS and SHL, respectively. The calcium in TBE, FSX and SHX was deduced to exist in the form of calcium lactate salts by X-ray diffraction study and had high solubility in the water. It was considered that the higher absorbability of calcium in TBE, FSX and SHX might be due to their high solubility. TBE contained some proteins such as collagen and other bone matrix proteins and these proteins were suggested to be effective to produce bone rnatrix proteins in OVX rats. Bone mineralization process consists of cellular production of an appropriate rnatlix that is prior to the accumulation of minerals. It was considered that the deposition of minerals to the rnatlix was expected to observe in more longer feeding period. Moreover, an positive effect of TBE, FSX and SHX on bone metabolism was suggested from the results indicating higher values for BMD of femur in the OVX-rats fed TBE, FSX and SHX. The differences in BMD of proximal and distal sites of the femur, which were rich in trabecular bone, weir significant but in BMD of the epiphysis, which is mainly cortical bone, they were not. Because trabecular bone represents only about 20% of the total skeleton, it was considered that only trabecular bone was increased in the OVX-rats fed FSX and SHX. These results suggested that an acceleration of bone loss in the trabecular bone due to OVX was suppressed by feeding with TBE, FSX and SHX. rnle serum CT and PTH levels in the OVX-TBE group were considered to have a tendency to indicate improving bone metabolism. TBE, FSX and SHX, calcium sources solubilized with lactate and citrate under decompression, were effective for bone metabolism and good source of dietary calcium with respect to the apparent calcium absorption and bone mineral density. In the present study, the apparent absorption ratio of calcium from TBE was higher than that of BBP at adequate calcium level in growing rats and than that of calcium carbonate at marginal calcium level in OVX rats. The apparent absorption ratio of calcium from FPS was higher than that of calcium carbonate at adequate calcium level in growing rats, but not at marginal calcium level in OVX rats. Bioavailability of calcium from FPS and SHL was increased by solubilizing with lactate and citrate under deconpression in OVX rats. TBE, FSX and SHX, calcium sources solubilized with lactate and citrate under decompressing, were effective for bone metabolism and good source of dietary calcium with respect to the apparent calcium absorption, bone mineral content and bone mineral density. |
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