1a. Objectives (from AD-416)
To determine how nutritional, hormonal, and physiological factors affect bone loss/gain in obesity through modifying obesity-induced inflammatory stress. Specifically, we will determine the extent to which obesity is associated with elevated levels of pro-inflammatory cytokines known to promote bone resorption, determine how obesity affects functions of bone cells and bone metabolism, determine the extent to which existing chronic inflammatory stress (induced experimentally by lipopolysaccharide implantation), estrogen deficiency (affected by ovariectomy), and subclinical magnesium intake impair bone health in obese animal models and in obese human subjects, and determine how moderate physical activity preserves bone structure as compared to caloric restriction during weight reduction in an obese animal model.
1b. Approach (from AD-416)
Studies will utilize cell culture, animal models and human subjects. We will use diet-induced obese mice or rats to determine the mechanisms by which adiposity interacts with other dietary, hormonal and physiological factors, such as estrogen deficiency, chronic inflammation, magnesium intake, and moderate exercise, and affects bone structure and functions of osteoblasts and osteoclasts. Human studies will use the in-house Community Studies Unit and the Metabolic Research Unit to conduct supplementation and controlled feeding experiments, respectively. We will determine whether 300 mg/d Mg supplementation to obese postmenopausal women with suspected marginal magnesium deficiency, ameliorates pro-inflammatory cytokine production and improves biomarkers of bone resorption and formation balance.
3. Progress Report
An experiment was conducted to determine the effect of obesity on osteoclast activity and bone microstructure. Six-wk-old male C57BL/6mice were fed either a normal fat diet (10 kcal% energy as fat) or a high-fat diet (45 kcal% energy as fat) for 14 weeks. Serum levels of osteocalcin and tartrate-resistant acid phosphatase (TRAP) were analyzed. Bone marrow cells were cultured for osteoclast formation. Expression of osteoblast and osteoclast specific genes was measured by using quantitative real-time PCR. Bone structure of proximal and mid-shaft femur was evaluated by micro-computed tomography. An experiment was conducted to determine whether estrogen deficiency exacerbates the detrimental effect of a high-fat diet on bone structure in a mouse model. Forty-eight female C57BL/6J ovariectomized or sham operated mice (24 each) at 4-mo-old were used. Then, ovariectomized and sham-operated mice were randomly assigned to either a normal-fat diet or a high-fat diet for 3 mos. Changes in bone structure and other serum markers related to bone metabolism were measured. Data will be analyzed. An animal study is in progress to determine whether obesity exacerbates the bone loss induced by chronic inflammation. Forty-eight female C57BL/6J mice aged 6-wks were randomly assigned to four groups in a 2 x 2 factorial design (control or 1.5 µg/d LPS) and fed either a normal-fat control diet or a high-fat diet. Animals were implanted with a slow release LPS or a placebo pellet subcutaneously in the dorsal region of the neck. The experiment will last for 3 months and will be finished by the end of this year. An experiment was completed in which male rats were fed 50%, 100%, or 150% of the magnesium requirement and either normal or high-fat (butter oil) diet for 12 and 24 weeks. The objective of the experiment was to determine whether marginal magnesium deficiency exacerbates inflammatory stress associated with obesity. Some results have been published in abstract form for a presentation at the Experimental Biology 2011 meeting held in Washington, DC, and a manuscript is in progress. An experiment was started in June 2011 to determine whether magnesium deficiency enhances or magnesium supplementation alleviates chronic inflammation and bone loss in obese and estrogen-deficient female rats. Female rats aged 65-75 days have been assigned to dietary treatments of 50%, 100%, or 150% of the magnesium requirement and 10% or 45% dietary fat for 24 weeks; one-half of the rats have been ovariectomized. Increased fat is being supplied by high-oleic sunflower oil. No reportable findings have been obtained to date. A protocol has been written for a human study with the objective to determine whether magnesium supplementation decreases chronic inflammation and bone loss in obese postmenopausal women.
Yan, C., Cao, J.J., Wu, M., Jiang, T., Yoshimura, A., Gao, H., Zhang, W. 2010. Suppressor of cytokine signaling 3 inhibits LPS-induced IL-6 expression in osteoblasts by suppressing CCAAT/enhancer-binding protein ß activity. Journal of Biological Chemistry. 285(48):37227-37239.