Applied nutritional investigationIncrease in bone mineral density through oral administration of shark gelatin to ovariectomized rats
Introduction
Bone is an important organ in which to regulate mineral homeostasis. Menopause causes physiologic changes that lead to an imbalance between bone formation and bone absorption, resulting in a net bone loss and osteoporosis mainly due to estrogen deficiency. Such unbalance is likely to be accelerated by aging. Milk protein [1], soy isoflavone [2], collagen hydrolysate [3], [4], and xylitol [5] have become potentially known as food factors for improving bone mineral density (BMD). Many collagen products (gelatin or collagen hydrolysate) are marketed as health supplements with claims to improve bone density and strength. However, research studies on the physiologic effect of an oral collagen intake have been limited to studies by Moskowitz [3] claiming the effectiveness of a collagen hydrolysate for managing bone joint diseases and osteoporosis and by Koyama et al. [4] claiming effectiveness for increasing bone density.
The incidence of bovine spongiform encephalopathy has resulted in marine collagen hydrolysates from fish scale, skin, and bone being sold as supplements and cosmetics in Japan. The demand for collagen hydrolysates of marine origin has increased rapidly. Shark fin is commonly used in Chinese cuisine, but dermal collagen is not yet utilized despite being a promising source of collagen. Shark skin collagen has been reported as an important source of marine collagen [6].
The present study was carried out by orally administering gelatin to ovariectomized rats as an osteoporotic animal model to investigate its influence on bone density and the composition of bone matrix proteins.
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Materials
Four-week-old female Wistar rats were purchased from SLC Japan. Type I collagen was prepared from fresh great blue shark (Prionace glauca) skin according to the method described in our previous study [7] and orally administered after heat denaturation. Albumin from chicken egg white was purchased from Sigma. The concentration of calcium in the plasma of the rats was measured with a calcium C test kit (Wako). Hyaluronic acid and dermatan sulfate from pig skin and chondroitin sulfate from shark
Effect of shark gelatin on the basic parameters and BMD
The experimental data from the rats are listed in Table 3. Although the final body weight of all experimental rats fed on the low-protein diet was relatively low, there was no significant difference between experimental groups in final body weight, food intake, femoral bone weight, and bone length.
Figure 1 shows the BMD of slice numbers 4 and 17 from the experimental rat femur. There were no differences among the sham rats, but the BMD of the sham albumin-fed rats was higher than that of the
Discussion
Osteoporosis is a typical type of osteosis with advancing age that results from an imbalance between bone formation and bone resorption. The experimental animal models for menopausal osteoporosis and/or senile osteoporosis result from ovariectomy and a low-protein diet, respectively. These models are commonly used to elucidate the effect on BMD. The effects of milk protein [11], soybean isoflavones [2], clodronate [12], etidronate [13], and estradiol [8] on BMD, for example, have been
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This work was supported by the New Energy and Industrial Technology Development Organization as a grant-aided project (ID 01A42004) and by grants for scientific research (14560222 and 16580220) from the Ministry of Education, Science, and Culture of Japan.