Ascorbic acid accumulates in cartilage in vivo.
BACKGROUND: Ascorbic acid plays an important role in collagen synthesis. Though ascorbic acid concentrations in many tissues and in plasma have been characterized, little is known about in vivo levels in cartilage. MATERIALS AND METHODS: To discern the role of ascorbic acid in cartilage, we conducted a dose-response study measuring ascorbic acid levels in various guinea pig tissues and fluids in response to this vitamin. To our knowledge, this is the first such study in cartilage. RESULTS: Ascorbic acid was higher in synovial fluid compared to paired plasma, and higher in cartilage than paired synovial fluid. Tissue levels were normalized to DNA to compare ascorbic acid concentrations relative to a measure of tissue cellularity. Normalized cartilage ascorbic acid concentrations were intermediate between liver (lowest) and adrenal (highest), two well-known concentrators of ascorbic acid. All tissues and fluids showed a saturation-effect characterized by large differences in ascorbic acid concentrations between low- and medium-dose groups and smaller concentration differences between medium- and high-dose groups. CONCLUSIONS: Cartilage, a tissue dependent on ascorbic acid for extracellular matrix production of collagen, concentrates ascorbic acid. This concentrating ability is consistent with the chondrocyte expression of SVCT2, a sodium-dependent ascorbic acid transporter.
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