Introduction: We recently showed that patients with primary Sjögren Syndrome (pSS) have significantly higher bone mineral density (BMD) in the lumbar spine and femoral neck compared with healthy controls. The majority of those patients (69%) were using hydroxychloroquine (HCQ), which may have favourable effects on BMD.
Aim: To evaluate whether HCQ modulates human bone cells in vitro.
Methods: Osteoblasts were differentiated from human mesenchymal stromal cells. We measured alkaline phosphatase (ALP) for osteoblastic differentiation and calcium incorporation as a measure for mineralization at day 7 and 18, respectively. Osteoclasts were cultured from peripheral blood mononuclear cells. At day 14 of culture, the osteoclasts were counted using tartrate-resistant acid phosphatase staining and osteoclast activity was measured using von Kossa staining of hydroxyapatite-coated surfaces. All cultures were treated with different HCQ doses (control, 0.2, 1 and 5 μg/ml). Additionally, polymerase chain reaction (PCR) technique was used for osteoblast gene expression.
Results: We observed that osteoblast differentiation decreased dose-dependently by HCQ with a 3.1-fold decrease between the highest dose and controls as assessed by ALP measurements. Also, mineralization of these cultures diminished by increased HCQ doses. Using the highest HCQ dose almost no mineralization was observed. PCR analysis showed a dose-dependent decrease of osteopontin and osteocalcin expression.
Osteoclast numbers were also decreased (1.9-fold) following 5 μg/ml HCQ treatment. This was reflected by strongly reduced bone resorption as assessed by resorption pit number (3.5-fold) and resorption surface (9.0-fold).
Conclusion: We demonstrate that HCQ is suppressing both bone formation and resorption. Based on the clinical data we assume that HCQ is favouring bone formation, but additional work is required to evaluate the contribution of bone resorption and formation to the observed phenotype. Therefore, the use of HCQ as an explanation for the higher BMD in pSS patients may be the consequence of reduced bone turnover.
14 May 2016 - 17 May 2016