Bisphosphonates are effective agents for the management of osteoporosis. Their low bioavailability and low potency necessitate frequent administration on an empty stomach, which may reduce compliance. Gastrointestinal intolerance limits maximal dosing. Although intermittent intravenous treatments have been used, the optimal doses and dosing interval have not been systematically explored. We studied the effects of five regimens of zoledronic acid, the most potent bisphosphonate, on bone turnover and density in 351 postmenopausal women with low bone mineral density in a one-year, randomized, double-blind, placebo-controlled trial. Women received placebo or intravenous zoledronic acid in doses of 0.25 mg, 0.5 mg, or 1 mg at three-month intervals. In addition, one group received a total annual dose of 4 mg as a single dose, and another received two doses of 2 mg each, six months apart. Lumbar-spine bone mineral density was the primary end point. There were similar increases in bone mineral density in all the zoledronic acid groups to values for the spine that were 4.3 to 5.1 percent higher than those in the placebo group (P<0.001) and values for the femoral neck that were 3.1 to 3.5 percent higher than those in the placebo group (P<0.001). Biochemical markers of bone resorption were significantly suppressed throughout the study in all zoledronic acid groups. Myalgia and pyrexia occurred more commonly in the zoledronic acid groups, but treatment-related dropout rates were similar to that in the placebo group. Zoledronic acid infusions given at intervals of up to one year produce effects on bone turnover and bone density as great as those achieved with daily oral dosing with bisphosphonates with proven efficacy against fractures, suggesting that an annual infusion of zoledronic acid might be an effective treatment for postmenopausal osteoporosis.

Bone remodeling replaces old and damaged bone with new bone through a sequence of cellular events occurring on the same surface without any change in bone shape. It was initially thought that the basic multicellular unit (BMU) responsible for bone remodeling consists of osteoclasts and osteoblasts functioning through a hierarchical sequence of events organized into distinct stages. However, recent discoveries have indicated that all bone cells participate in BMU formation by interacting both simultaneously and at different differentiation stages with their progenitors, other cells, and bone matrix constituents. Therefore, bone remodeling is currently considered a physiological outcome of continuous cellular operational processes optimized to confer a survival advantage. Bone remodeling defines the primary activities that BMUs need to perform to renew successfully bone structural units. Hence, this review summarizes the current understanding of bone remodeling and future research directions with the aim of providing a clinically relevant biological background with which to identify targets for therapeutic strategies in osteoporosis.

Type I mucopolysaccharidosis (MPS I) is a lysosomal storage disorder caused by the deficiency of α-L-iduronidase, which results in glycosaminoglycan accumulation in tissues. Clinical manifestations include skeletal dysplasia, joint stiffness, visual and auditory defects, cardiac insufficiency, hepatosplenomegaly, and mental retardation (the last being present exclusively in the severe Hurler variant). The available treatments, enzyme-replacement therapy and hematopoietic stem cell (HSC) transplantation, can ameliorate most disease manifestations, but their outcome on skeletal and brain disease could be further improved. We demonstrate here that HSC gene therapy, based on lentiviral vectors, completely corrects disease manifestations in the mouse model. Of note, the therapeutic benefit provided by gene therapy on critical MPS I manifestations, such as neurologic and skeletal disease, greatly exceeds that exerted by HSC transplantation, the standard of care treatment for Hurler patients. Interestingly, therapeutic efficacy of HSC gene therapy is strictly dependent on the achievement of supranormal enzyme activity in the hematopoietic system of transplanted mice, which allows enzyme delivery to the brain and skeleton for disease correction. Overall, our data provide evidence of an efficacious treatment for MPS I Hurler patients, warranting future development toward clinical testing.