Quartz Crystal Microbalance Assay of Clinical Calcinosis Samples and Their Synthetic Models Differentiates the Efficacy of Chelation-Based Treatments

Citric acid is more effective than sodium thiosulfate in chelating calcium in a dissolution model of calcinosis

Calcinosis cutis affects 20-40% of patients with systemic sclerosis. This study tests the hypothesis that calcium-chelating polycarboxylic acids can induce calcium dissolution without skin toxicity or irritancy. We compared citric acid (CA) and ethylenediaminetetraacetic acid (EDTA) to sodium thiosulfate (STS) for their ability to chelate calcium in vitro using a pharmaceutical dissolution model of calcinosis (hydroxyapatite (HAp) tablet), prior to evaluation of toxicity and irritancy in 2D in vitro skin models. Resultant data was used to predict therapeutic concentrations for application in a validated 3D skin irritation model (SkinEthic™; EpiSkin SA) and to assay maximal percutaneous absorption. Dissolution performance was further assessed via ability to dissolve a calcified matrix laid down in vitro. Pharmacological dissolution studies identified that polycarboxylic acids were superior to STS in dissolving HAp tablets. In vitro, compounds had little effect on cell numbers at concentrations of < 10 mM. When applied topically to 3D models as near-saturated solutions, chelators were not irritant nor did they impact model structure histologically. CA was the most efficient chelator of calcium salts. This study highlights polycarboxylic acids, particularly CA, as potential therapies to target calcinosis cutis: these should now be investigated in human studies.

Diagnosis and management of systemic sclerosis-related calcinosis

INTRODUCTION

Calcinosis is common in patients with systemic sclerosis (SSc) and refers to the sub-epidermal deposition of calcium salts in the skin. SSc-related calcinosis is associated with significant morbidity, including through cutaneous ulceration and predisposition to become infected.

AREAS COVERED

After briefly addressing aetiopathogenesis, we describe the clinical burden of SSc-associated calcinosis and provide a structured and practical clinical approach to diagnosis and assessment, including discussion of the role of different imaging modalities. The multi-faceted treatment of SSc-associated calcinosis is presented under three broad headings of 'general measures,' and 'medical treatment' and 'surgical treatment.' We adopted a narrative approach to identify relevant manuscripts to inform our review.

EXPERT OPINION

SSc-related calcinosis is an area of major unmet clinical need and for too long has been a neglected area of research. Safe and effective treatments are badly needed to improve patient quality of life and outcomes. To facilitate future clinical trials, we require increased understanding of pathogenesis (to inform selection of potential targeted therapies) and reliable outcome measures, including those which will measure the impact and severity of calcinosis from the patient perspective. International collaborative research is ongoing to develop outcome measures and treatments for this potentially devastating complication of SSc.