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Journal of the American College of Nutrition, Vol. 23, No. 6, 712S-714S (2004)
Published by the American College of Nutrition

A Study on Spontaneously Obese Rat (Minko Rat) with Abnormal Lipid Metabolism, Strength and Mineral Concentrations in Bone

Ryuji Takeda, MD, Takashi Nakamura, MD, PhD, Masayo Imanishi, Madoka Ishida, Fumiko Yano, Takahisa Takeda, MD, PhD and Mieko Kimura, PhD

Graduate School of Medicine, Kyoto University (R.T., T.N.), JAPAN
Takeda Research Institute of Life Science (R.T., M.I., M.I., T.T., M.K.), JAPAN
Kyoto School of Biology-Oriented Science and Technology, Kinki University, Wakayama (F.Y.), JAPAN

Address reprint requests to: Ryuji Takeda, MD, Takeda Research Institute of Life Science, Kyoto Research Park, 134 Tyudoji Minamimachi Shimogyoku Kyoto 600-8813, JAPAN. E-mail: tls{at}takedahp.or.jp


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Objectives: In view of the prevalence of osteoporosis in Japan, which surveys have shown has almost doubled over the last ten years, contributory factors, additional to the mineral status, that affect bone stiffness have been explored in spontaneously obese (Minko) rats.

Methods: Bone stiffness and strength as well as content of Mg, Ca, P, Na, K, and trace minerals in femurs were compared in male and female Minko rats, which have abnormal lipid metabolism.

Results: Mechanical study of femurs indicated that bone stiffness of male rats was significantly higher than that of female rats, but that Mg, Ca, P, Na, Zn, Sr and Fe concentrations in male rats were significantly lower than that of female rats, while S and K concentrations in male rats were significantly higher than that of female rats.

Conclusions: These results suggest that bone strength isn’t determined only by mineral concentrations such as Mg, Ca and P. We reported that the bone strength of "Minko Rats" was significantly higher than bone strength of control rats, but there was no significant difference of Ca and P concentrations between the two groups of rats.

Key words: bone strength, Ca, Mg P, lipid metabolism, obese rat


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Osteoporosis is a major public health problem in Japan. Nationwide surveys on hip fracture were conducted in 1987, 1992, and 1997. The annual number of hip fracture was 53,000 in the 1987 report, which increased to 76,600 after 5 years in 1992, and further increased to 92,400 in the 1997 survey, showing an increase of 1.7-fold within 10 years [1].

Although bone densitometry is often used as an indicator to evaluate bone fragility, bone mineral density isn’t always an index of bone strength. There are many well known factors affecting bone strength [2]. The cholesterol synthetic pathway may be important also in bone metabolism [3]. At this time, the relationship between strength and mineral concentration in bone of spontaneously obese male and female rats, named "Minko Rat", with abnormal lipid metabolism was studied.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Male and female Minko rats with abnormal lipid metabolism (3 weeks old) were given a commercial diet and tap water ad libitum until 39 weeks of age. They were fasted overnight and blood was collected from the abdominal aorta under anesthesia with sodium pentobarbital, and the femurs and tibias were removed and weighed. The right femur was tested by the three-point bending method using a mechanical testing machine (Model TK-252C, Muromachi Kikai Co., Ltd., Tokyo, Japan), and magnesium (Mg), calcium (Ca), phosphorus (P), sodium (Na), sulphur (S), potassium (K), zinc (Zn), strontium (Sr) and iron (Fe) concentrations in the tibia were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES: Perking-Elmer Co. Ltd., USA).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSION
 REFERENCES
 
Male rats were significantly heavier than female rats at 6 weeks after birth (Fig. 1). Femoral length and weight in male rats were significantly higher than that of female rats, and mechanical study of bone indicated that bone stiffness of male rats was significantly greater than that of female rats (Table 1).



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  		Fig. 1. Growth curve of female and male Minko rats. Data are Mean. Body weight showed significantly higher levels in male Minko rats than in female Minko rats at 6 weeks after birth.

 

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  		Table 1. Bone Parameters of Female and Male Minko Rats

 
Mg and other mineral concentrations in rat tibia are shown in Table 2 and Fig. 2. Mg, Ca, P, Na, Zn, Sr and Fe concentrations in the tibia of male rats were significantly lower than that of female rats, but S and K concentrations in the tibia of male rats were significantly higher than that of female rats. There was a significant correlation between Ca and P (p < 0.001), Ca and Mg (p < 0.001), Ca and Na (p < 0.001), P and Mg (p < 0.001), P and Na (p = 0.003), Mg and Na (p < 0.001), S and K (p = 0.045) in female rats (Table 3). There was a significant correlation between Ca and P (p = 0.025), Ca and Mg (p < 0.001), Ca and Na (p = 0.001), P and Mg (p = 0.012), P and S (p = 0.007), P and Sr (p = 0.004), Mg and Na (p = 0.002) in male rats (Table 4). There was a significant positive correlation between bone stiffness and Zn (p = 0.038) only in female rats, but there was no significant correlation between bone stiffness and other minerals including Ca.


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  		Table 2. Mineral Concentrations in Tibia of Female and Male Minko Rats

 


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  		Fig. 2. Comparison of mineral concentrations in tibia between Female and Male Minko rats. Results represent mean values (expressed as the percent of mineral concentrations in male rats per those in female rats). *p < 0.05; **p < 0.01 vs. female Minko rats.

 

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  		Table 3. Correlation Coefficients between Bone Parameters and Mineral Concentrations in Tibia of Female Minko Rats

 

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  		Table 4. Correlation Coefficients between Bone Parameters and Mineral Concentrations in Tibia of Male Minko Rats

 
Although many epidemiological studies have been conducted to examine the relationship between Ca intake and bone mass, the results are not necessarily concordant [4]. Some studies have shown that in a population where the dietary Ca intake was high, there was little association between Ca intake and bone mineral density (BMD) or risk of hip fracture [5,6]. Excessive Ca intake leads to decreasing Mg concentration in rat tibia, and impaired bone quality [7].

Basle et al. [8] reported that in bone, there was no significant age-dependent variation in the concentration of Ca, P, Na, K, Mg, Cu, Zn, Fe, Sr, Al, B and Si in control or in osteoporotic subjects, moreover, the concentration of elements in bone tissue did not differ between the two groups. However, Yoshinaga et al. reported sex- and age-related variations in contemporary Japanese ribs, and the organic matter content of the bone, represented by C or N concentration, was a factor, which contributed to the elemental variation of the bone [9]. On the other hand, we reported that bone strength of "Minko Rats" was significantly high compared with control rats, but there was no significant difference of Ca and P concentrations between the two group’s rats [10].


   CONCLUSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
REFERENCES
 
Variation in elemental concentrations of rat bone that was found in the Minko rat, that has abnormal fat metabolism, and the greater bone strength of the Minko rat as compared with controls, suggest that bone strength is not determined only by mineral concentrations. Sex difference and organic content of the bone play roles.

Received August 5, 2004.
   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 

  1. Orimo H, Hashimoto T, Sakata K, et al: Trend of the incidence of hip fracture in Japan, 1987–1997. The third nation-wide survey. J Bone Miner Metab18 :126 –131,2000 .
  2. Frost HM: Emerging views about "osteoporosis", bone health, strength, fragility, and their determinants. J Bone Miner Metab20 :319 –325,2002[Medline]
  3. Mundy G, Garrett R, Harris S, et al: Stimulation of bone formation in vitro and in rodents by statins. Science286 :1946 –1949,1999 .[Abstract/Free Full Text]
  4. Cumming RG: Calcium intake and bone mass a quantitative review of the evidence. Calcify Tissue Into47 :194 –201,1990 .
  5. Cooper C, Barker DJP, Wickham C: Physical activity, muscle strength, and calcium intake in fracture of the proximal femur in Britain. Brit Med J297 :1443 –1446,1988 .
  6. Wickham CAC, Walsh K, Cooper C, et al: Dietary calcium, physical activity, and risk of hip fracture: a prospective study. Brit Med J299 :889 –892,1989 .
  7. Kimura M, Takeda T, Matsumura K, et al: Effects of trace elements status by over intake of calcium. Boomed Rees Trace Elements9 :201 –220,1998 .
  8. Basle MF, Mauras Y, Audran M, Clochon P, Rebel A, Allain P: Concentration of bone elements in osteoporosis. J Bone Miner Res5 :41 –47,1990 .[Medline]
  9. Yoshinaga J, Suzuki T, Morita M: Sex- and age-related variation in elemental concentrations of contemporary Japanese ribs. Sci Total Environ79 :209 –221,1989 .[Medline]
  10. Takeda R, Nakamura T, Ishida M, et al: Mineral concentration in tibia: genealogy in bone strength. Osteoporosis Japan11 :51 ,2003 .




This Article
Right arrow Abstract Freely available
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Right arrow Articles by Takeda, R.
Right arrow Articles by Kimura, M.

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