Rationale and Objective: Loss of bone mass and strength are important consequences of spinal cord injury (SCI). Almost every SCI patient shows bone loss, which approaches 50% in the long-bones below the level of lesion in those with complete paralysis, and is associated with spontaneous fractures, morbidity, and increased cost of care (Comarr et al., 1962; Nottage, 1981; Bauman et al., 1999; Chantraine, 1978; Jiang et al., 2006). Bisphosphonates, which are a mainstay in preventing osteoporosis in the elderly, at best slow modestly SCI-related bone loss, and in some clinical trials have had no effect (Bauman et al., 2005; Gilchrist et al., 2007). There are approximately 50,000 veterans with SCI in the United States. Thus, there is a great need for safe, effective, and affordable therapies to prevent bone loss after SCI.

This application explores the potential use of nandrolone, a synthetic androgen (e.g., an anabolic steroid), to block bone loss after SCI. In a preliminary study, we modeled SCI by mid-thoracic spinal cord transection in male rats. We found that SCI significantly reduced bone mineral density (BMD), an index of bone loss, for the major bones of the thigh and calf. Nandrolone significantly reduced loss of bone due to SCI. In another animal model of bone loss due to paralysis, in this case caused by severing the sciatic nerve (e.g., cutting a major nerve in the leg), nandrolone prevented 60% to 80% of bone loss in male rats (Cardozo et al., in press). These are, to our knowledge, the first observations that demonstrate the potent beneficial effect of nandrolone on bone loss due to paralysis, particularly to SCI. Next, we explored the potential mechanism by which this agent protects against SCI bone loss. Interestingly, effects of nandrolone on bone after denervation were inhibited by cyclosporine A, an inhibitor of calcineurin (Klee et al., 1998;). Calcineurin is a protein found in cells, which is known to be involved in bone metabolism. Whether nandrolone blocks bone loss after SCI over the long term is not known. The details of the specific molecular mechanisms by which nandrolone regulates calcineurin signaling to slow bone loss in paralysis are also unknown. Finally, the spinal cord transection model used in our initial studies is not suitable for long-term studies in male rats, which presents an issue because 80% of those with SCI are men, and both male and female hormones affect bone, though in distinct ways.

We propose the following objectives to address the need for more practical animal models and the need to understand in more detail the benefits and molecular mechanisms of nandrolone on bone after paralysis.

Objective 1: The complete transection model used in our preliminary studies is limited by the great difficulties posed by expression of urine from the bladder and thus a heavy burden of animal care, and poor long-term survival. Development of more practical models is needed. Studies in this application will establish a novel model of SCI-related bone loss in male rats in which SCI is produced by a partial transection of the spinal cord. We will then use this model to evaluate long-term efficacy of nandrolone in preventing bone loss after SCI.

Objective 2: We will also test the effect of nandrolone on differentiation and activity of bone cells and one potential mechanism for nandrolone action to protect against bone loss in paralysis that was suggested by our preliminary data: Activation by nandrolone of calcineurin.

The types of patients helped by the research will include persons with SCI and potentially those with other forms of paralysis including nerve injury and stroke.

With respect to applicability of research, results of the research may be applied to slow or prevent bone loss after SCI. It is uncertain as yet whether this benefit will be to delay the onset of severe bone loss or, instead, whether bone loss can be blocked completely. In either case, one can envision the use of nandrolone to at least spare bone until neuroreparative treatments become available or functional electrical stimulation devices become more advanced and practical for widespread use. It remains possible that nandrolone will be useful in rebuilding bone in SCI as well, although additional testing will be needed to test this possibility. Knowledge regarding molecular mechanisms will be applicable in a more fundamental way, by providing insights into basic mechanisms of nandrolone action. The animal model to be developed and characterized will provide a basis for numerous subsequent long-term studies of changes in muscle and bone and of effects of interventions on the physiological deficits that ensue from chronic SCI. Additionally, the model will allow further studies of molecular mechanisms of chronic changes in muscle and bone and on interventions to prevent bone loss and muscle atrophy. Finally, findings may be applicable by providing insight for future related basic science studies, or directing the development of future pharmaceuticals.

The projected time to achieve a patient-related outcome is as follows: (1) preclinical testing will be complete in 2 years after initiation of funding and (2) testing in human subjects will be completed in 5 years.