Dissolution of calcium pyrophosphate crystals by polyphosphates: an in vitro and ex vivo study

Objective-To determine the dissolving ability (DA) of linear pentasodium tr ipolyphosphate (PSTP), cyclic trisodium metaphosphate (TSMP), polymeric sod ium metaphosphate (SMP) on synthetic crystals of calcium pyrophosphate dihy drate (CPPD) and on crystalline aggregates of menisci from patients with ch ondrocalcinosis (CC). Methods-Synthetic CPPD crystals were mixed with phosphate buffered saline ( PBS), which contained the different polyphosphates, for one hour at 37 degr eesC. The calcified menisci were obtained from the knees of four female pat ients with CPPD disease who underwent total arthroscopic meniscectomy for d egenerative meniscal lesions. Meniscal cryosections and fragments were incu bated in SMP (15 mg/ml PBS) at 37 degreesC for one hour and 24 hours, respe ctively. Histological evaluation on meniscal samples after polyphosphate in cubation was carried out by ordinary transmitted light microscopy and polar ised light microscopy. The dissolution of CPPD crystals by polyphosphates w as assessed by atomic absorption spectroscopy, which determined the amount of calcium liberated from synthetic crystals and meniscal fragments. Cytoto xicity of SNIP was evaluated by tetrazolium salt assay and by an ultrastruc tural study on cultured chondrocytes. Results-SMP and PSTP showed higher DA on CPPD crystals than TSMP. Analysis of the DA values at increasing concentrations of SMP showed that a concentr ation of 15 mg/ml completely dissolved 2.0 mg CPPD crystals. The solution o f meniscal CPPD crystals showed a significant increase of calcium concentra tion after three hours and 24 hours of SMP incubation (p=0.0001; Kruskal-Wa llis analysis of variance) compared with fragments incubated in PBS control solution. Macroscopic and microscopic evaluation of meniscal specimens sho wed a notable reduction of CPPD deposits. A 50% inhibitory dose on cultured chondrocytes was reached at the maximum concentration of SMP used in this work (15 mg/ml); ultrastructural analysis did not show morphological altera tions in the treated cells. Conclusion-The results of this study indicate that linear polyphosphates ar e effective in dissolving both synthetic and ex vivo CPPD crystal aggregate s. This suggests a potential therapeutic use for these molecules in the tre atment of symptomatic CC.