In addition, this is the first study showing a direct effect of Ris on osteocytes through the upregulation of COX-2 gene expression.
All these findings suggest an effect of Ris on osteoblastic lineage and support the hypothesis of a neoformative activity of bisphosphonates.
The inhibition of remodelling along with the increase of wall thickness supported the hypothesis of a direct effect of Ris on osteoblastic lineage.
Nevertheless, when we inhibited the COX-2 pathway using NS-398, the effect of Ris on cell viability was significantly reduced, at least at the highest concentrations.
Even if the result confirms a positive effect of Ris on cell lifespan, this effect can not completely explain our histomorphometric data that showed an increased wall thickness, the end product of osteoblastic activity, also with respect to controls.
Our histomorphometric data show that the main effect of Ris on remodeling in glucocorticoid-induced osteoporosis is the prolonged lifespan of osteocytes, characterized by reduced Bone Formation Rate, activation frequency and prolonged active Formation Period associated with increased wall thickness, according to our previous results [ 16].
To confirm this hypothesis, we evaluated the effect of Ris at different concentrations on COX-2 as well as on b-ALP gene expression in vitro.
The effects of RIS were more pronounced in lumbar vertebrae than contralateral tibias, because BPs tend to bind with the bone which has the highest turnover rate [ 25].
To verify this hypothesis, we studied the effect of Ris by evaluating histomorphometric parameters in rat tibiae and apoptosis and COX-2 expression in femur specimens in the presence or absence of a negative effect on osteoblastic/osteocytic lineage induced by glucocorticoids.
We evaluated, using bone marrow stromal cells and MLO-y4 osteocytes, the effect of Ris at concentrations of 0, 0.1 to 10 μM with or without COX-2 inhibitor NS-398 (0.1 μM) after three days of culture.
