Hyaluronan concentration in non-inflamed and rheumatoid synovium

The concentration of hyaluronan was measured by a novel application of an ELISA technique, using biotinylated hyaluronan binding-region (HABr) derived from cartilage proteoglycan core-protein, to digested frozen sections of synovium. The relative extractability of hyaluronan, from sections of synovium by short-term washes in buffer, was assessed by the same method. The distribution of hyaluronan in adjacent sections was assessed histochemically using the biotinylated HABr and alkaline phosphatase-conjugated streptavidin. Hyaluronan concentrations were lower in rheumatoid synovium (0.71 +/- 0.10 mg/cm3; mean +/- S.E.M.) than in non-inflamed synovium (1.07 +/- 0.16 mg/cm3). However, the ratio of extractable or 'free' hyaluronan to non-extractable or 'bound' hyaluronan, was greatly increased in rheumatoid synovium, being 4.53 +/- 0.40 (mean +/- S.E.M.) compared with 1.87 +/- 0.42 in non-inflamed synovium. Histochemical staining showed hyaluronan to be concentrated in the lining layer of non-inflamed samples, whereas in rheumatoid synovium the stain was more uniformly distributed throughout the tissue. Although the total concentration of hyaluronan was not increased in rheumatoid synovium, the increased proportion of 'free', and therefore presumably mobile, hyaluronan molecules together with increased synovial bulk may contribute to the known increases in serum levels of hyaluronan in patients with RA.