Mechanisms involved in the inhibition of osteoclast generation by the benzothiophene SERM LY117018.

Selective estrogen receptor modulators are compounds that act via estrogen receptors in different tissues to mediate either estrogenic or estrogen antagonistic effects in osteoporosis patients. The aim of this study was to assess the effect of the selective estrogen receptor modulator LY117018, a raloxifene analogue, on osteoclastogenesis in vitro. In primary murine bone marrow cultures osteoclasts, defined as TRAP-positive multinucleated cells, were induced by 10(-8) M 1,25-dihydroxyvitamin D(3). LY117018 at concentrations between 10(-12) M and 10(-9) M significantly reduced the number of osteoclasts. At higher concentrations no effect of LY117018 on osteoclast generation was observed. LY117018 enhanced alkaline phosphatase activity of mouse calvaria osteoblasts at a concentration of 10(-14) to 10(-7) M, but had no influence on the proliferation and transcription of RANKL and osteoprotegerin. In order to study the effect of the compound on the production of cytokines that can stimulate bone resorption, spleen cells were incubated with LY117018. Data from four-color flow cytometric analysis indicate a significantly decreased frequency of tumor necrosis factor-α positive CD8(+) cells after treatment with LY117018. These findings suggest that LY117018 can significantly inhibit the generation of osteoclasts and stimulate osteogenic differentiation in vitro. Suppression of tumor necrosis factor-α production by LY117018 may contribute to its anti-osteoclastogenic effect.

Reversible cytotoxic oedema in the splenium of the corpus callosum related to tetracycline therapy.

We report a symptomatic girl with reversible circumscribed cytotoxic oedema in the splenium of the corpus callosum (CC) that occurred, to our knowledge, for the first time in relation to tetracycline treatment. After stopping tetracycline therapy the girl recovered completely and the CC lesion, clearly visible on diffusion-weighted MR imaging (DWI), disappeared. Reversible circumscribed cytotoxic oedema (CCO) of the splenium of the CC is a well-defined entity that is found to be associated with administration of antiepileptic drugs, alterations in therapy using arginin-vasopressin and metronidazole or infections with influenza and rotavirus. CCO of splenium of the CC is clearly visible on DWI, shows no enhancement after administration of contrast medium and is completely reversible in most cases.

Bone morphogenetic proteins 5 and 6 stimulate osteoclast generation.

Bone regeneration is required for fracture-healing, and different procedures have been used to promote osteogenesis. Recently, BMP-2 has been shown to induce bone formation in vivo and has been tested in clinical trials. A recent in vitro study evaluated the osteogenic activity of 14 BMPs on osteoblastic progenitor cells with an osteogenic hierarchical model in which BMP-2 and BMP-6 may play an important role in inducing osteoblast differentiation. Although the relative osteoinductive activity of each BMP is important, bone regeneration is a process consisting of bone formation and bone resorption. Therefore, it remains unclear which effects BMP-5 and -6 have on the generation of osteoclasts and by which mechanism osteoclastogenesis is stimulated. To compare osteoclastic potency of each BMP, primary murine bone marrow cells were treated with human recombinant BMP-2, BMP-5, or BMP-6 and 1,25-(OH)2 vitamin D3 and stained for the TRAP enzyme. Osteogenic activity of BMP-5 was determined by measuring induction of ALP-activity and proliferation after incubation with primary murine osteoblasts. For elucidating the molecular mechanism, primary bone marrow cells with various concentrations of OPG were added to the TRAP assay and mRNA levels of RANKL and OPG were measured after stimulation with BMP-5. The presented data show that BMP-5 and BMP-6, unlike BMP-2, enhanced the formation of murine TRAP+/MNCs in a biphasic curve. BMP-5 and -6 were less potent in stimulating osteoclastogenesis compared to BMP-2. Concerning the effects of BMP-5 on osteoblasts, there was a dose-dependent increase of ALP activity and proliferation up to a maximum dose of 300 ng/mL. At the mRNA level, BMP-5 increased the RANKL/OPG ratio. In conclusion, this study demonstrates that in contrast to BMP-2, BMP-5 and -6 influences the generation of osteoclasts in a biphasic mode. Both proteins might be very important regulators of bone homeostasis, and therefore, potent candidates for future treatment strategies of bone regeneration.