Browsing by Author "Lorincz, Caeley Rae"

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    Functional adaptation of bone: interactive effects of diet and mechanical loading environment
    (2009) Lorincz, Caeley Rae; Zernicke, Ronald F.; Reimer, Raylene
    Nutritional status and physical loading remain two of the most influential modifiable risk factors in the development of osteopenia and osteoporosis. Creating optimal dietary and mechanical loading environments during the susceptible period surrounding development should encourage establishment of peak bone mass and may attenuate bone-related fragility fractures later in life. These studies were designed to investigate the interrelations between a diet previously denoted as deleterious for skeletal integrity (i.e., high saturated fat and sucrose (HFS)) and exogenous loading regimes previously deemed osteogenic. A cantilever loading device was used to apply non­invasive loads 5d/wk for 3wk to the tibiae of skeletally immature female C57BL/6 mice consuming either low-fat complex carbohydrate (LFCC) or HFS diets. Upon completion of the intervention, half the tibiae from each diet cohort were scanned using micro­computed tomography and tested for structural integrity by three-point bending. Expression of RANKL, OPG, COX-2, PPAR-y, and Cathepsin-K mRNA were measured in the other half of tibiae. Serum markers of bone formation ( osteocalcin) and markers of bone resorption (i.e., tartrate resistant acid phosphatase) were measured in cardiac blood. Mice fed an HFS diet were significantly heavier and fatter than LFCC mice. After normalizing for differences in body mass, HFS mice had compromised tibial structural and geometrical parameters, as well as elevated serum markers of bone resorption. RANKL mRNA was significantly elevated, and COX-2 mRNA tended to be elevated in this cohort, suggesting bone loss associated with the chronic inflammatory state of diet­induced obesity. High-magnitude, low-frequency loading did not benefit mice fed a LFCC diet, but did improve structural and geometrical properties in mice fed the HFS diet. When brief rest-periods ( ?? 1 s) were interspersed with the high-frequency loading regime (30 Hz), however, both groups showed positive skeletal adaptation. Adaptation observed in the LFCC cohort was primarily structural, while changes in the HFS cohort were principally geometrical. The reasons for this difference have yet to be elucidated. These data emphasize the complex interrelations between diet and external loading environments on bone health during periods of growth, and highlight the potential for osteogenic loading regimes for individuals with varied nutritional status.