Abstract
Bone is the living composite biomaterial having unique structural property. Presently, there is a considerable gap in our understanding of bone structure and composition in the native state, particularly with respect to the trabecular bone, which is metabolically more active than cortical bones, and is readily lost in post-menopausal osteoporosis. We used solid-state nuclear magnetic resonance (NMR) to compare trabecular bone structure and composition in the native state between normal, bone loss and bone restoration conditions in rat. Trabecular osteopenia was induced by lactation as well as prolonged estrogen deficiency (bilateral ovariectomy, Ovx). Ovx rats with established osteopenia were administered with PTH (parathyroid hormone, trabecular restoration group), and restoration was allowed to become comparable to sham Ovx (control) group using bone mineral density (BMD) and µCT determinants. We used a technique combining 1H NMR spectroscopy with 31P and 13C to measure various NMR parameters described below. Our results revealed that trabecular bones had diminished total water content, inorganic phosphorus NMR relaxation time (T1) and space between the collagen and inorganic phosphorus in the osteopenic groups compared to control, and these changes were significantly reversed in the bone restoration group. Remarkably, bound water was decreased in both osteopenic and bone restoration groups compared to control. Total water and T1 correlated strongly with trabecular bone density, volume, thickness, connectivity, spacing and resistance to compression. Bound water did not correlate with any of the microarchitectural and compression parameters. We conclude that total water, T1 and atomic space between the crystal and organic surface are altered in the trabecular bones of osteopenic rats, and PTH reverses these parameters. Furthermore, from these data, it appears that total water and T1 could serve as trabecular surrogates of micro-architecture and compression strength.
Highlights
Skeleton maintains its unique biomaterial composition and strength by the dynamic process of remodeling involving bone resorption by osteoclasts and bone formation by osteoblasts
Assessment of trabecular bone quality by established parameters Induction of trabecular osteopenia in adult rats by bilateral Ovx serves as the WHO-recommended preclinical model for postmenopausal osteoporosis
bone mineral density (BMD), trabecular bone volume (BV/total volume (TV)), Tb.Th, Tb.N and Conn.D were significantly reduced in Ovx and lactation groups compared to sham (Fig 1a– g)
Summary
Skeleton maintains its unique biomaterial composition and strength by the dynamic process of remodeling involving bone resorption by osteoclasts and bone formation by osteoblasts. Cortical bones, accounting for 80% of the weight of a skeleton primarily afford bone biomechanical strength. Trabecular bones, accounting for the remaining 20% of the weight of the skeleton serve to maintain mechanical strength and more importantly, control mineral (calcium and phosphorus) metabolism and are metabolically more active than the cortical bones[1,2]. Loss of trabecular bones may occur as a result of increased remodeling rate and/or a negative remodeling balance and is a hallmark of postmenopausal osteopenia[3]. Pregnancy and lactation are two physiologic states, when mobilization of calcium from bone to blood and milk necessitate bone loss to occur, mostly at the trabecular sites[4]. Bone restoration or new bone formation is only achieved by administering parathyroid hormone to postmenopausal women suffering from osteoporosis [7]
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