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
This is the annual report for the new OSQR-approved Project 5450-51000-046-00D that replaces Project 5450-51000-039-00D. (See separate annual report terminating that project.) To determine obesity on osteoclast activity and bone resorption, six-wk-old male C57BL/6mice (n=21) were assigned to two groups and fed either a control (10 kcal% energy as fat) or high-fat diet (HFD, 45 kcal% energy as fat) for 14 weeks. Bone marrow stromal/osteoblastic cells were cultured. Osteoprogenitor activity (alkaline phosphatase positive colonies) and mineralization (calcium nodule formation) were determined. Gene expression was measured using quantitative real-time PCR. Bone structure of proximal and mid-shaft tibia was evaluated by micro-computed tomography. We found that obesity induced by a high-fat diet increases bone resorption and decreases cancellous bone mass but has no effect on cortical bone mass in the tibia in mice. HFD may blunt any positive effects of increased body weight on bone. To determine whether obesity induced by a high-fat diet exacerbates the increase in inflammatory cytokine production and bone loss caused by estrogen deficiency (ovariectomy), mice with either OVX or sham-operated were be randomly assigned to two groups: one fed a normal-fat control diet, the other a high-fat diet for 3 mos. Changes in bone structure and other serum markers related to bone metabolism were measured. To determine the effect of marginal Mg deficiency on inflammatory stress of obesity, an experiment was started in March 2010 using male rats; analysis of tissues and fluids from rats fed 50%, 100%, and 150% of the magnesium requirement and either normal or high fat diet for 12 weeks are being analyzed. Rats under similar conditions for 24 weeks will be terminated to obtain tissues and fluids for analysis in October 2010. Only finding to date is that rats fed the high fat diet and 150% the magnesium requirement are the most obese.
1. High-fat diet decreases cancellous bone mass and increases bone resporption in mice: Whether body mass derived from an obesity condition or excessive fat accumulation is beneficial or detrimental to bone has not been established; neither have the mechanisms by which obesity affects bone metabolism. ARS scientists at Grand Forks, ND, demonstrated that mice on a high-fat diet had higher serum tartrate-resistant acid phosphatase and leptin but lower osteocalcin concentrations than those fed the normal-fat diet. The high-fat diet increased multinucleated tartrate-resistant acid phosphatase -positive osteoclasts in bone marrow compared to the control diet. Despite being much heavier, mice fed the high-fat diet had lower trabecular bone mass than mice on the control diet. These findings suggest that obesity induced by a high-fat diet increases bone resorption that may blunt any positive effects of increased body weight on bone.