Biochemical and molecular aspects of spectral diagnosis in calcinosis cutis

Dystrophic calcinosis: structural and morphological composition, and evaluation of ethylenediaminetetraacetic acid ('EDTA') for potential local treatment

BACKGROUND

To perform a detailed morphological analysis of the inorganic portion of two different clinical presentations of calcium-based deposits retrieved from subjects with SSc and identify a chemical dissolution of these deposits suitable for clinical use.

METHODS

Chemical analysis using Fourier Transform IR spectroscopy ('FTIR'), Raman microscopy, Powder X-Ray Diffraction ('PXRD'), and Transmission Electron Microscopy ('TEM') was undertaken of two distinct types of calcinosis deposits: paste and stone. Calcinosis sample titration with ethylenediaminetetraacetic acid ('EDTA') assessed the concentration at which the EDTA dissolved the calcinosis deposits in vitro.

RESULTS

FTIR spectra of the samples displayed peaks characteristic of hydroxyapatite, where signals attributable to the phosphate and carbonate ions were all identified. Polymorph characterization using Raman spectra were identical to a hydroxyapatite reference while the PXRD and electron diffraction patterns conclusively identified the mineral present as hydroxyapatite. TEM analysis showed differences of morphology between the samples. Rounded particles from stone samples were up to a few micron in size, while needle-like crystals from paste samples reached up to 0.5 µm in length. Calcium phosphate deposits were effectively dissolved with 3% aqueous solutions of EDTA, in vitro. Complete dissolution of both types of deposit was achieved in approximately 30 min using a molar ratio of EDTA/HAp of ≈ 300.

CONCLUSIONS

Stone and paste calcium-based deposits both comprise hydroxyapatite, but the constituent crystals vary in size and morphology. Hydroxyapatite is the only crystalline polymorph present in the SSc-related calcinosis deposits. Hydroxyapatite can be dissolved in vitro using a dosage of EDTA considered safe for clinical application. Further research is required to establish the optimal medium to develop the medical product, determine the protocol for clinical application, and to assess the effectiveness of EDTA for local treatment of dystrophic calcinosis.

Calciphylaxis and its co-occurrence with connective tissue diseases

Calciphylaxis, also known as calcific uremic arteriopathy, is a rare calcification syndrome that presents as ischemic skin necrosis and severe pain. It has a high mortality rate and is characterised by calcification of the small and medium arteries and micro-thrombosis. Calciphylaxis mainly occurs in patients with end-stage renal disease. In recent years, there have been an increasing number of cases of calciphylaxis associated with connective tissue diseases. Given the absence of clear diagnostic criteria for calciphylaxis thus far, an early diagnosis is crucial for designing an effective multidisciplinary treatment plan. In this article, we review the research progress on calciphylaxis and describe its characteristics in the context of connective tissue diseases.

Management of calcinosis cutis in rheumatic diseases

Calcinosis (hydroxyapatite and calcium phosphate crystal deposition) within the extracellular matrix of the dermis and subcutaneous tissue is a frequent manifestation of adult and pediatric systemic autoimmune rheumatic diseases, specifically systemic sclerosis, dermatomyositis, mixed connective tissue disease and systemic lupus erythematosus. In this article, we review classification of calcinosis, highlight mechanisms that may contribute to the pathogenesis of calcinosis and summarize the evidence evaluating non-pharmacologic and pharmacologic interventions for the treatment of calcinosis.

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

This paper sets out in vitro protocols for studying the relative effectiveness of chelators used in the dissolution-based treatment of hard calcinosis. Pulverized hard calcinosis samples from human donors or synthetic hydroxyapatite nanoparticles were deposited by electrophoretic deposition on the surface of a quartz crystal microbalance sensor. Over 150 deposits of <20 μg were dissolved over the course of 1 h by aliquots of buffered, aqueous solutions of two calcium chelators, EDTA and citrate, with the surface-limited dissolution kinetics monitored with <1 s time resolution. There was no statistically significant difference in dissolution rate between the four synthetic hydroxyapatite materials in EDTA, but the dissolution rates in citrate were lower for hydroxyapatite produced by acetate or nitrate metathesis. Hard calcinosis and synthetic hydroxyapatites showed statistically identical dissolution behavior, meaning that readily available synthetic mimics can replace the rarer samples of biological origin in the development of calcinosis treatments. EDTA dissolved the hydroxyapatite deposits more than twice as fast as citrate at pH 7.4 and 37 °C, based on a first-order kinetic analysis of the initial frequency response. EDTA chelated 6.5 times more calcium than an equivalent number of moles of citrate. Negative controls using nonchelating N,N,N',N'-tetraethylethylenediamine (TEEDA) showed no dissolution effect. Pharmaceutical dissolution testing of synthetic hydroxyapatite tablets over 6 h showed that EDTA dissolved the tablets four to nine times more quickly than citrate.

Systemic sclerosis-related calcinosis

Purpose

To provide an update on the clinical burden of calcinosis (subcutaneous or intracutaneous deposition of calcium salts) in patients with systemic sclerosis (SSc), and discuss advances in our understanding of pathogenesis, associates, and measurement techniques, as well as an overview of the current approach to management.

Methods

Four case scenarios are presented, to illustrate the clinical spectrum of calcinosis. Epidemiology (including associates), pathogenesis, imaging and measurement, and treatment are reviewed.

Results

Calcinosis represents a major clinical problem in patients with SSc. Up to 40% of patients are affected, the proportion depending in part on how carefully calcinosis is looked for. Associates of calcinosis include longer disease duration, anticentromere antibody, and digital ulceration. When severe, calcinosis causes pain, disability, and disfigurement. Pathogenesis is unknown, but tissue ischaemia, microtrauma, and loss of balance between calcification stimulants and inhibitors are likely contributors. Calcinosis deposits are mainly composed of hydroxyapatite. They are very visible on plain radiographs, and radiographic scoring systems are being developed, and other imaging modalities (including computed tomography and ultrasound) are being explored. Despite a number of proposed treatments, currently there is no effective ‘disease-modifying’ therapy for calcinosis and the main aspects of management are antibiotics, analgesics, multidisciplinary team input, and surgical debulking.

Conclusions

Up until recently, SSc-related calcinosis has received very little attention in terms of research into pathogenesis, measurement, and treatment. This imbalance is now being redressed and although we still do not have an effective treatment, progress is being made.

Raman spectroscopy for label-free identification of calciphylaxis

Calciphylaxis is a painful, debilitating, and premorbid condition, which presents as calcified vasculature and soft tissues. Traditional diagnosis of calciphylaxis lesions requires an invasive biopsy, which is destructive, time consuming, and often leads to exacerbation of the condition and infection. Furthermore, it is difficult to find small calcifications within a large wound bed. To address this need, a noninvasive diagnostic tool may help clinicians identify ectopic calcified mineral and determine the disease margin. We propose Raman spectroscopy as a rapid, point-of-care, noninvasive, and label-free technology to detect calciphylaxis mineral. Debrided calciphylactic tissue was collected from six patients and assessed by microcomputed tomography (micro-CT). Micro-CT confirmed extensive deposits in three specimens, which were subsequently examined with Raman spectroscopy. Raman spectra confirmed that deposits were consistent with carbonated apatite, consistent with the literature. Raman spectroscopy shows potential as a noninvasive technique to detect calciphylaxis in a clinical environment.