Articular Cartilage Vesicles Generate Calcium Pyrophosphate Dihydrate‐Like Crystals in Vitro

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Abstract
Objective. To identify the morphology of a mineral‐forming fraction of adult porcine hyaline articular cartilage digest and characterize the mineral it forms.Methods. Electron microscopy, Fourier transform infrared (FTIR) spectroscopy, x‐ray microanalysis, compensated polarized light microscopy, and biochemical studies including 14C‐labeled UDPG pyrophosphohydrolase radiometric assay.Results. This fraction of articular cartilage digest contained membrane‐limited vesicles resembling growth plate cartilage matrix vesicles and formed mineral after only 24 hours in physiologic salt solution containing 1 mM ATP. The mineral contained inorganic pyrophosphate, 95% of which derived from ATP, and phosphate, 93% of which derived from inorganic phosphate in the medium. The FTIR spectrum of this mineral closely resembled the spectrum of standard calcium pyrophosphate dihydrate (CPPD) crystals. Compensated polarized light microscopy showed positively birefringent, rod‐shaped crystals morphologically identical to CPPD. Ca:P ratios, defined by energy‐dispersive microanalysis, were also consistent with CPPD.Conclusion. The articular cartilage vesicle fraction of porcine hyaline cartilage is capable of generating mineral that strongly resembles CPPD.

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