The ultrastructure and calcification of matrix vesicles in osteoarthritic articular cartilage

Abstract

Osteoarthritis progresses through the abrasion of articular cartilage and associated changes, such as those in calcification. In this study, initial cartilage calcification was examined by electron microscopy with microwave fixation to preserve the matrix vesicles. We developed a procedure for the separation of functionally active matrix vesicles from the osteoarthritic cartilage. Isolated matrix vesicles bound with unit membranes possessed osmiophilic properties and were filled with much protein content. Calcium content in matrix vesicle fractions was extremely high compared to that of phosphate content. Elution profiles of the matrix vesicles showed rich calcium content, moderate activity of alkaline phosphatase, and lactate dehydrogenase in a high molecular weight area. The matrix vesicles in osteoarthritis accumulated large amounts of calcium and moderate amounts of phosphate prior to the appearance of crystals.