Ultrastructure abnormalities in proteoglycans, collagen fibrils, and elastic fibers in normal and myxomatous mitral valve chordae tendineae

Normal and myxomatous chordae tendineae were studied using light and electr on microscopy. to assess the alterations in the appearance and mutual arran gement of proteoglycans, collagen fibrils, and elastic fibers. Specific sta ining with ruthenium red and cuprolinic blue in a critical electrolyte conc entration mode were used to localize proteoglycans. Fresh tissues were fixe d in glutaraldehyde containing the cationic dyes and embedded into Spurr re sin. Semithin sections of LR White (London Resin Co., Basingstoke, U.K.)-em bedded tissue were used for histochemistry. In normal chordae tendineae, th e fibrosa comprised close-packed collagen fibrils intermixed with elastic f ibers. These were surrounded by a thin layer of elastic fibers and collagen fibrils, both of which were closely associated with proteoglycans. In myxo matous chordae tendineae, alterations were observed in the connective tissu e. Proteoglycans were more abundant and were distributed throughout the tis sue. The outermost layer was transformed into an undifferentiated electron- dense mass surrounding the central fibrosa, which contained degraded elasti c fibers and collagen fibrils. Collagen fibrils had faint banding or lacked a banding pattern altogether. Spaces between collagen fibrils were occupie d by abnormal proteoglycans or proteoglycan aggregates. Elastic fibers show ed varying degrees of degeneration and were occasionally replaced by electr on-lucent spaces containing microfibrils. Accumulation of abnormal proteogl ycan was also observed around degenerated elastic fibres and collagen fibri ls. (C) 1999 by Elsevier Science Inc.