Osteoporosis is a disease of aging that leads to ~2 million fractures and ~$17 billion in healthcare costs annually. Although several drugs are FDA-approved for the treatment of osteoporosis, the potential for serious side effects (e.g., osteonecrosis of the jaw, atypical femur fractures) has led most physicians to use these drugs only for the treatment, but not the prevention, of osteoporosis. This has led to the current situation where most postmenopausal women must wait until they develop frank osteoporosis (i.e., fractures, or sufficiently high fracture risk) to begin drug therapy. As such, there is a compelling need for novel, relatively low-risk and low-cost pharmacological approaches to prevent osteoporosis. The current proposal aims to translate evidence from rodent studies showing that the sympathetic nervous system (SNS) is an important regulator of bone metabolism to a simple, cost-effective, and safe approach for osteoporosis prevention. In key Preliminary Data, we obtained multiple lines of evidence to establish clearly the role of the SNS in regulating human bone metabolism. A critical component of these data was a ?proof-of- concept? interventional study demonstrating that ?1-selective blockers (atenolol, nebivolol), but not a non- selective ?-AR blocker (propranolol), have favorable effects on bone turnover and bone mineral density (BMD) in postmenopausal women. Based on these data, we will perform a randomized, double-blind, placebo- controlled 2 year clinical trial addressing the following Specific Aims: (1) Test the hypothesis that treatment with a widely used, inexpensive, and relatively ?1-selective blocker (atenolol) will prevent bone loss at the lumbar spine and femur neck as assessed by dual-energy X-ray absorptiometry in 420 postmenopausal women without pre-existing osteoporosis (Aim 1a); and evaluate the tolerability and safety of atenolol when used for the prevention of bone loss (Aim 1b). (2) Evaluate the effects of atenolol on trabecular and cortical bone microarchitecture using high resolution-peripheral quantitative computed tomography (Aim 2a), on bone turnover markers (Aim 2b), and test whether baseline measures of bone turnover or of sympathetic activity (resting heart rate, plasma catecholamine levels) are predictive of the BMD response to atenolol over 2 years (Aim 2c). (3) In a subset of patients, explore the underlying molecular and cellular mechanisms for the effects of ?1-selective blockade on bone in humans using analyses of osteoblast populations isolated from bone biopsies as well as tissue-level bone formation rates on quadruple-labelled bone biopsies (Aim 3). The proposed studies will rigorously test whether atenolol is efficacious and safe for the prevention of osteoporosis in postmenopausal women and also further define the mechanisms of SNS effects on bone in humans. If our proposed clinical trial demonstrates protection from bone loss in postmenopausal women by atenolol, this would fill a crucial clinical need, as these women currently have virtually no pharmacological options for osteoporosis prevention.
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