Denosumab Versus Zoledronic Acid in Thalassemia-Induced Osteoporosis

Despite the significant improvements in the therapeutic management of beta thalassemia major (BTM) over the past few decades, osteoporosis is still a common finding, even in optimally treated patients. The relationships between bone mineral densities (BMD) and several clinical characteristics or hematological markers have been described. Chronic anemia, bone marrow expansion due to ineffective erythropoiesis, iron toxicity, calcium and zinc deficiencies, low vitamin D levels and endocrine complications have been suggested to contribute to the etiology of bone diseases in BTM. Nevertheless, the complex etiological mechanisms of this heterogeneous osteopathy remain incompletely clarified. A complex mechanism controls bone remodeling in human. This mechanism includes the receptor activator of nuclear factor kappa B ligand (RANKL), its natural receptor (RANK) and osteoprotegerin (OPG). The RANK/RANKL pathway is an essential to promote osteoclast formation and activation and prolongs osteoclast survival. OPG acts as a decoy receptor for RANKL and prevents its interaction with RANK thereby inhibiting osteoclast formation, function, and survival. Alteration of the RANK/RANKL/OPG system for increased osteoclastic activity and enhanced osteoblastic dysfunction is proposed as an important mechanism in the etiology of osteoporosis in BTM. Hypogonadism, a common finding in BTM, is associated with enhanced RANKL activity. The sex steroid hormones, androgen, and estrogens, via their respective nuclear receptors, regulate BMD in humans and mice. Testosterone is likely to have direct and indirect inhibitory effects on human osteoclast formation and bone resorption. Animal model and cell culture studies suggest a direct inhibitory effect of androgens on the OPG/RANKL cytokines system. In human osteoblastic cells, testosterone and 5-dihydrotestosterone mediate an androgen receptor-induced specific inhibition of OPG messenger ribonucleic acid (mRNA) expression. Androgens have also been shown to block RANKL-induced osteoclastic formation while RANKL expression was found to be up-regulated in osteoblastic cells from androgen receptor-deficient mice. The effect of oestradiol (E2) on osteoclast precursors and osteoclasts seems to be mediated by osteoblastic cells. Inhibitory effect of E2 is associated with the stimulated secretion of OPG by osteoblasts. Previous studies have focused on the characteristics of thalassemic patients with osteoporosis and their response to therapy with bisphosphonate. Because RANK-RANKL and OPG play a significant role in bone resorption and seem to be the principal implicated mechanism for the development of osteoporosis in BTM, we will conduct this prospective study to evaluate the anti-RANKL denosumab versus zoledronic acid on TM-induced osteoporosis.