Serum Dickkopf-1 Is Increased and Correlates with Bone Mineral Density in Patients with Thalassemia-Induced Osteoporosis. Reduction Post Zoledronic Acid Administration

Osteoporosis represents an important cause of morbidity in adult patients with thalassemia. Its pathogenesis is multifactorial, and includes mainly bone marrow expansion, endocrine dysfunction and iron overload. Bone metabolism is altered in thalassemia. Osteoclast function is elevated, while osteoblast activity seems to be reduced and thus the balance of bone remodeling is in favor of bone loss. The exact mechanisms of osteoblast dysfunction have not been fully clarified to-date. Wingless-type ( Wnt ) signaling is an important pathway for osteoblast differentiation. Dickkopf-1 (Dkk-1) protein is an inhibitor of Wnt pathway and is implicated in the pathogenesis of several bone disorders. Collagen type-I is the main structural protein of the bone. The collagen type-I alpha (COLIA)-1 specific protein (Sp)-1 polymorphism has been related to osteoporosis in thalassemia. The aim of this study was to evaluate the serum levels of Dkk-1 in patients with thalassemia-induced osteoporosis who receive therapy with zoledronic acid (ZOL) and evaluate possible correlations with clinical and laboratory data, including the COLIA-1 Sp1 polymorphism. Sixty-six patients (21M/45F; median age 35.5 years) with thalassemia and osteoporosis were studied. Patients were blindly randomized to receive ZOL at a dose of 4 mg, iv, in 15 min infusion, every 6 months (group A, n=23) or every 3 months (group B, n=21), or to receive placebo every 3 months (group C, n=22) for a period of one year. All patients received oral calcium (500 mg) during the treatment period. Dkk-1 was measured at baseline and after 12 months of therapy using ELISA methodology (Biomedica Medizinprodukte, Wien, Austria) along with a series of serum bone remodeling indices: bone resorption markers [C-telopeptide of type-I collagen (CTX), tartrate-resistant acid phosphatase isoform-5b (TRACP-5b)], bone formation markers [bone-specific alkaline phosphatase (bALP), osteocalcin, and C-terminal propeptide of collagen type-I (CICP)], and osteoclast regulators [receptor activator of nuclear factor-kappa B ligand (RANKL), osteoprotegerin (OPG), and osteopontin]. The above bone markers were also evaluated in 30, age- and gender-matched, healthy controls. The G-->T mutation at base 1 of intron 1 at the binding site of the Sp1 transcription factor of the COLIA-1 gene was detected by polymerase chain reaction using mutagenesis primers followed by restriction enzyme analysis in all patients. BMD of the lumbar spine (L1-L4), femoral neck (FN) and wrist (W) was determined using DEXA, before and 12 months after treatment. At baseline, all patients had increased serum levels of Dkk-1 (mean±SD: 39±17.1 pmol/L) compared to controls (27.4±9.7 pmol/L; p