Bortezomib Effects Proliferation And Apoptosis On Osteoblast In Myeloma Bone Disease

[Background] Multiple myeloma is the disease with the highest incidence of bone involvement among the malignant diseases. It has a severe impact on patients' quality of life. Complex interactions between myeloma cells and bone marrow promote osteoclastic bone resorption and suppress osteoblast activity, there is uncoupled or severely imbalanced bone remodeling with increased bone resorption and decreased or absent bone formation. Bisphosphonates are specific inhibitors of osteoclast activity and are the current mainstay of therapy for myeloma bone disease. They reduce skeletal damage but do not restore bone formation. Thus, new approaches of prevent inhibition of bone formation is important to prevent the development of myeloma bone disease. Clinical data indicate that Bortezomib has potential to regulate bone turnover. But lytic lesions have not been reported to heal in patients receiving Bortezomib. Mechanism of increasing markers related to osteoblast by Bortezomib is uncleard. Effecting on osteoblast was investigate on Bortezomib in vitro to explore the clinical significance in myeloma bone disease.[Objectives] The effect of proliferation,apoptosis or markers related to osteoblast were observed by proteasome inhibitor bortezomib .Evaluate the clinical significance on Bortezomib in myeloma bone disease.[Methods] Bortezomib effect proliferation and apoptosis on osteoblast were observed in different culture condition in vitro. Cell growth index were evaluated by MTT assay. Analysis number of mineralized nodules after alizarin red staining. Annexin V/PI staining was performed to detect apoptosisi rate. RT-PCR and Wstern blot were used to detect mRNA and protein of osteoblast markers Runx2/cbfa1, osteocalcin(OCN) and osterix(OSX).[Rusults] Bortezomib had toxicity and inhibited proliferation of MC-3T3E1 cells in a dose-dependent manner, and the 48h IC50 was 38.1nM. Bortezomib in low concentration(5nM) didn't have effect on osteoblast cell proliferation(P>0.10). But at this concentration the decrease of early opoptosis rates was 49.6% and 61.7% for MC-3T3E1 at myeloma cell cocultured and conditioned medium. After the treatment of low does Bortezomib, the mRNA and protein level of osteoblast marker OCN and OSX but not Runx2/cbfa1 were increased, while no significant change was observed in activity of Alkaline phosphatase. In addition, induction culture can not increase the formation with Bortezomib alone.[Conclusion] Proteasome inhibitor bortezomib in low concentration promote the activity of osteoblast internal mechanisms prevents the apoptosis of osteoblast which were induced by myeloma cells, and it can up-regulat transcription and secretion of osteoblast markers which were related Runx2/cbfa1 path way. It may protect function of osteoblasts in myeloma bone disease.