Vitamin D and/or calcium deficient diets may differentially affect muscle fiber neuromuscular junction innervation.

INTRODUCTION: There is evidence that supports a role for Vitamin D (Vit. D) in muscle. The exact mechanism by which Vit. D deficiency impairs muscle strength and function is not clear. METHODS: Three-week-old mice were fed diets with varied combinations of Vit. D and Ca2+ deficiency. Behavioral testing, genomic and protein analysis, and muscle histology were performed with a focus on neuromuscular junction (NMJ) -related genes. RESULTS: Vit. D and Ca2+ deficient mice performed more poorly on given behavioral tasks than animals with Vit. D deficiency alone. Genomic and protein analysis of the soleus and tibialis anterior muscles revealed changes in several Vit. D metabolic, NMJ-related, and protein chaperoning and refolding genes. CONCLUSIONS: These data suggest that detrimental effects of a Vit. D deficient or a Vit. D and Ca2+ deficient diet may be a result of differential alterations in the structure and function of the NMJ and a lack of a sustained stress response in muscles. Muscle Nerve 54: 1120-1132, 2016.

Raloxifene and teriparatide (hPTH 1-34) have complementary effects on the osteopenic skeleton of ovariectomized rats.

The skeletal efficacy of raloxifene (Ral) plus weekly teriparatide [recombinant human parathyroid hormone (1-34), TPTD] combinations relative to each treatment alone or sequentially were evaluated in osteopenic, ovariectomized rats. In the first study, 6-month-old Sprague-Dawley rats were ovariectomized (Ovx) and permitted to lose bone for 1 month before treatment for the following 3 months. Raloxifene (Ral, 1 mg/kg/day orally) was evaluated alone and in combination with TPTD (10 or 30 microg/kg/week) administered weekly by subcutaneous injection. QCT, biomechanical testing, and histomorphometry were used to quantitate skeletal effects. Weekly TPTD alone at either dose had no skeletal effect relative to Ovx. Daily Ral prevented further loss of vertebral bone mineral density (BMD), resulting in BMD that was significantly greater than Ovx, but significantly less than age-matched, sham-Ovx, vehicle controls (sham). The raloxifene plus 30 microg/kg/week TPTD group had vertebral BMD that was significantly greater than Ovx, Ral alone, and both TPTD dose-alone groups. Therefore, the Ral plus TPTD group completely restored bone mass to sham levels. Compression testing of lumbar vertebra L5 confirmed increased strength for both Ral plus TPTD combinations relative to Ovx, with strength not different from sham. Histomorphometry of the proximal tibial metaphysis showed that Ovx significantly increased eroded surface and bone formation compared to sham. Raloxifene treatment restored eroded surface and bone formation rate back to sham levels. Raloxifene plus TPTD at 30 microg/kg/week resulted in a significantly higher mineral appositional rate compared to Ral and sham, which was not different from Ovx and TPTD alone. Raloxifene plus TPTD at both doses had eroded surfaces that were significantly less than Ovx but not different from sham or Ral alone. In a sequential study, 6-month-old Ovx rats were permitted to develop osteopenia for 2 months before a daily TPTD 80 microg/kg/day subcutaneous injection was initiated. Following 2 months of TPTD treatment, animals were either (1) continued on TPTD, (2) discontinued from TPTD, (3) switched to Ral 3 mg/kg/day, oral, or 17 alpha-ethynyl estradiol (EE2) 0.1 mg/kg/day, oral, for another 2 months. Raloxifene and EE2 maintained most of TPTD-induced new bone in Ovx rats by preventing the increase in bone turnover rate after withdrawal of TPTD. Raloxifene also restored the elevated bone formation activity induced by TPTD to the level of sham. These data suggest that Ral and TPTD have complementary interactions in osteopenic, Ovx rats. Raloxifene inhibited bone resorption, and reduced high bone turnover without significantly retarding TPTD stimulation of bone formation activity.

Novel and selective small molecule stimulators of osteoprotegerin expression inhibit bone resorption.

Osteoprotegerin (OPG), a secreted member of the tumor necrosis factor receptor superfamily, is a potent inhibitor of osteoclast formation and bone resorption. Because OPG functions physiologically as a locally generated (paracrine) factor, we used high-throughput screening to identify small molecules that enhance the activity of the promoter of the human OPG gene. We found three structurally unrelated compounds that selectively increased OPG gene transcription, OPG mRNA levels, and OPG protein production and release by osteoblastic cells. Structural analysis of one compound, a benzamide derivative, led to the identification of four related molecules, which are also OPG inducers. The most potent of these compounds, Cmpd 5 inhibited osteoclast formation and parathyroid hormone-induced calvarial bone resorption. In vivo, Cmpd 5 completely blocked resorptive activity (serum calcium, osteoclast number) in parathyroid hormone-treated rats. Furthermore, Cmpd 5 reduced the ability of a rat breast cancer to metastasize to bone. Finally, the compound also prevented bone loss in a rat adjuvant arthritis model. These results provide proof of the concept that low molecular weight compounds can enhance OPG production in ways that can result in effective therapies.