Long-term alcohol consumption in the rat affects femur cross-sectional geometry and bone tissue material properties

Background: Alcohol consumption previously has been demonstrated to reduce the density and strength of cortical bone of young, actively growing rats. Osteoblast activity and trabecular bone volume were also significantly lower. A germane question arising from these studies is whether the detrimental effects would persist into adulthood. To address this issue, a long-term study was undertaken with animals that consumed alcohol throughout their life and into old age. Methods: One-month-old female Sprague-Dawley rats were divided into three diet groups: alcohol-fed, pair-fed, and chow-fed. The alcohol-fed animals received a modified Lieber-DeCarli diet that contained 35% ethanol-derived calories. The pair-fed group served as a caloric-equivalent control, and the chow-fed animals served as a completely untreated control. Animals were euthanized after five time periods on the diets that represented three stages of the life span: young (3 months), adult (6, 9, 12 months), and aged (18 months). The left femur was isolated and mechanically tested in 3-point bending for mechanical properties. Results: In the young animals, alcohol consumption produced dramatic reductions in both extrinsic (whole bone) and intrinsic (tissue material) properties, which is consistent with results from previous studies on growing rats. For the adult animals, however, the alcohol groups were only slightly lower and the differences were not statistically significant. The aged animals showed diminished properties due to alcohol, but only for the intrinsic material properties. The extrinsic properties remained similar to controls as a result of greater radial expansion in the femur diaphysis. Despite the cross-sectional areas being the same, this expansion gave rise to higher cross-sectional moment of inertia values in the alcohol animals. The thickness of the cortical wall was lowest in the alcohol group at all time points. Conclusions: Long-term alcohol consumption produced two major effects in the oldest animals studied: the quality of the cortical bone tissue was diminished, as evidenced by reduced elastic modulus and ultimate strength values, and the bone seemed to compensate for this by expanding the cross-section to produce larger cross-sectional moment of inertia values. The reduced bone tissue quality is consistent with the lower ash percent values in the alcohol animals, but other factors such as the quality of the collagen and mineral crystal may also be important contributors.