The mechanical information transmitted into the cytoplasm also triggers a biological cascade, starting with NO and PGE(2) and followed by Wnt/beta catenin signaling. This information is transmitted to the bone surface through the canalicular network, particularly to the lining cells, and is able to trigger bone remodeling by directing the osteoblast activity and the osteoclastic resorption. Furthermore, the osteocyte death seems to play also an important role. The outcome of micro-cracks in the vicinity of osteocytes may interrupt the canalicular network and trigger cell apoptosis in the immediate surrounding environment. This apoptosis appears to transmit a message to the bone surface and activate remodeling. The osteocyte network also plays a recognized endocrine role, particularly concerning phosphate regulation and vitamin D metabolism. Both the suppression of estrogen following menopause and chronic use of systemic glucocorticoids induce osteocyte apoptosis. On the other hand, physical activity has a positive impact in the reduction of apoptosis. In addition, some osteocyte molecular elements like sclerostin, connexin 43, E11/gp38, and DKK1 are emerging as promising targets for the treatment of various osteo-articular pathologies.

Physical activity is known to have an anabolic effect on bone tissue. It has been shown to increase the bone mineral density (BMD) in young adults, as well as in teenagers. But there is little information about the effect of intensive physical activity in childhood, particularly at the prepubertal stage. To examine the influence of an early intensive physical training on BMD, we have studied a group of elite prepubertal girls, at the starting phase of their peak bone mass acquisition. Subjects were engaged either in sport requiring significant impact loading on the skeleton, or in sport without impact loading. Forty-one healthy prepubertal girls took part in this study. The sport group consisted of 10 swimmers (10.5 +/- 1.4 years old) and 18 gymnasts (10.4 +/- 1.3 years old), who had performed 3 years of high-level sport training (8-12 h per week for swimmers, 10-15 h per week for gymnasts). Thirteen girls (10.7 +/- 1 years old) doing less than 3 h per week of physical activity served as a control group. BMD measurements were done using dual-energy X-ray absorptiometry. There was no statistical significant difference between groups as regards age, body height and weight, and body composition. There was no statistical significant difference between swimmers and controls for all the BMD measurements. Mean BMD in gymnasts was statistically higher than in the control group for mid-radius (+15.5%, p < 0.001), distal radius (+33%, p < 0.001), L2-4 vertebrae (+11%, p < 0.05), femoral neck (+15%, p < 0.001) and Ward's triangle (+15%, p < 0.01). Moreover, in gymnasts, BMD at radius, trochanter and femoral neck was above normative values. We conclude that physical activity in childhood could be an important factor in bone mineral acquisition in prepubertal girls, but only if the sport can induce bone strains during a long-term program: gymnastics has such characteristics, unlike swimming. Such acquisition could provide protection against risks of osteoporosis in later life, but this remains debatable.

The aim of the study was to determine the influence of obesity on bone status in prepubertal children. This study included 20 obese prepubertal children (10.7 +/- 1.2 years old) and 23 maturation-matched controls (10.9 +/- 1.1 years old). Bone mineral area, bone mineral content (BMC), bone mineral density (BMD), and calculation of bone mineral apparent density (BMAD) at the whole body and lumbar spine (L1-L4) and body composition (lean mass and fat mass) were assessed by DXA. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the calcaneus were measured with a BUA imaging device. Expressed as crude values, DXA measurements of BMD at all bone sites and BUA (69.30 versus 59.63 dB/MHz, P < 0.01) were higher in obese children. After adjustment for body weight and lean mass, obese children displayed lower values of whole-body BMD (0.88 versus 0.96 g/cm2, P < 0.05) and BMC (1190.98 versus 1510.24 g, P < 0.01) in comparison to controls. When results were adjusted for fat mass, there was no statistical difference between obese and control children for DXA and ultrasound results. Moreover, whole-body BMAD was lower (0.086 versus 0.099 g/cm3, P < 0.0001), whereas lumbar spine BMAD was greater (0.117 versus 0.100 g/cm3, P < 0.001) in obese children. Thus, it was observed that, in obese children, cortical and trabecular bone displayed different adaptation patterns to their higher body weight. Cortical bone seems to enhance both size and BMC and trabecular bone to enhance BMC. Finally, considering total body weight and lean mass of obese children, these skeletal responses were not sufficient to compensate for the excess load on the whole body.

In postmenopausal women previously treated with a bisphosphonate and low BMD, denosumab treatment resulted in greater BMD increases than ibandronate at all measured sites. No new safety risks with denosumab treatment were identified.

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Denosumab reduces the risk of new vertebral and nonvertebral fractures. Previous trials suggest that the efficacy of antiresorptives on fractures might differ by patients' characteristics, such as age, bone mineral density (BMD), and fracture history. In the FREEDOM study, 7808 women aged 60 to 90 years with osteoporosis were randomly assigned to receive subcutaneous injections of denosumab (60 mg) or placebo every 6 months for 3 years. New vertebral and nonvertebral fractures were radiologically confirmed. Subgroup analyses described in this article were prospectively planned before study unblinding to evaluate the effect of denosumab on new vertebral and nonvertebral fractures across various subgroups. Compared with placebo, denosumab decreased the risk of new vertebral fractures in the overall study population over 3 years. This effect did not significantly differ for any of the nine subgroups analyzed ( p > 0.09 for all potential interactions). Denosumab also reduced all nonvertebral fractures by 20% in the full study cohort over 3 years. This risk reduction was statistically significant in women with a baseline femoral neck BMD T-score À2.5 but not in those with a T-score > À2.5; in those with a body mass index (BMI) < 25 kg/m 2 but not ! 25 kg/m 2 ; and in those without but not with a prevalent vertebral fracture. These differential treatment effects were not explained by differences in BMD responses to denosumab. Denosumab 60 mg administered every 6 months for 3 years in women with osteoporosis reduced the risk of new vertebral fractures to a similar degree in all subgroups. The effect of denosumab on nonvertebral fracture risk differed by femoral neck BMD, BMI, and prevalent vertebral fracture at baseline. ß