Raised serum hyaluronate levels in scleroderma: an effect of growth factor induced activation of connective tissue cells?

The circulating levels of hyaluronate were determined in 36 patients with scleroderma and in 36 control subjects matched for age and sex. The mean serum hyaluronate concentration in patients with progressive systemic sclerosis (n = 25) was 131 +/- 67 (SD) microgram/l and significantly greater (p less than 0.001) than that of the controls (mean level 49 +/- 21 (SD) microgram/l). Hyaluronate levels in patients with localised scleroderma (n = 4) were 141 +/- 47 (SEM) microgram/l and in patients with scleroderma-associated overlap syndromes (n = 7) 202 +/- 54 (SEM) microgram/l. The increase in serum hyaluronate probably reflected an enhanced synthesis or outflow of hyaluronate from the connective tissue, or both; it could not be explained by affection of the liver, which is the catabolic site of hyaluronate. The hyaluronate values were not related to certain serological indicators of inflammatory activity or to the extent of the skin lesions or the severity of internal organ manifestations. A positive correlation was noted between circulating platelet counts and hyaluronate levels (p less than 0.001). Plasma beta-thromboglobulin was measured in 15 of the patients with systemic sclerosis and found to correlate positively with platelet counts. Raised levels of beta-thromboglobulin were associated with the highest hyaluronate values. Platelet-derived growth factor, which stimulates connective tissue cells and is stored in the alpha-granules of platelets together with beta-thromboglobulin, was shown to enhance hyaluronate synthesis in fibroblast cultures. The results suggest an involvement in scleroderma of connective tissue activating substances released from platelets.