Presence of a non-sulphated glucosaminoglycan in embryonic cornea

Native hyaluronan produces less hypersensitivity than cross-linked hyaluronan

Hyaluronan has been used in patients with osteoarthritis to relieve the painful symptoms associated with this condition. The native form of hyaluronan and artificially cross-linked forms of hyaluronan (such as Hylan G-F 20) are widely used brands that are approved by the Food and Drug Administration for use in patients with osteoarthritis. Clinical evidence suggests that some of these hyaluronan products may induce an antigenic reaction in some patients. Therefore, it was critical to do controlled studies on the potential antigenic reaction induced by these substances. The purpose of this study was to assess the immunologic reactions resulting from the native or cross-linked forms of hyaluronan products in guinea pigs after subcutaneous injection. Guinea pigs were sensitized to hyaluronan via three subcutaneous injections. Active cutaneous or delayed-type hypersensitivity to hyaluronan was studied. The elicitation of antihyaluronan antibodies also was studied by indirect competitive ELISAs. Our results showed that Synvisc induced delayed-type hypersensitivity in guinea pigs, however, no hypersensitivity to the native hyaluronan was observed. This delayed-type hypersensitivity reaction to the cross-linked form of hyaluronan was confirmed by our finding that sera from guinea pigs sensitized to the cross-linked form showed increased antihyaluronan-specific antibodies in competitive ELISAs. In a direct comparison, the native form of hyaluronan produced significantly less hypersensitivity than an artificially cross-linked form of high molecular weight hyaluronan. The hypersensitivity to the cross-linked form of hyaluronan can be explained in part by its elicitation of ant-hyaluronan immunoglobulins in sensitized animals.

Proteoglycan changes during restoration of transparency in corneal scars

Corneal scars generated in rabbits by penetrating wounds are initially opaque but become transparent within a year. Previous studies have shown that the corneal stroma consists of proteoglycans and collagen fibrils spaced at regular intervals and that the interfibrillar spaces, the presumed location of proteoglycans, are abnormally large in opaque scars. In the present study, the size and glycosaminoglycan composition of the corneal stromal proteoglycans were determined in corneal scars during the restoration of transparency. The results showed that initially opaque scars which contained the large interfibrillar spaces also contained unusually large chondroitin sulfate proteoglycans with glycosaminoglycan side chains of normal size. These opaque scars also lacked the keratan sulfate proteoglycan but did contain hyaluronic acid. In the 1-year-old scars there was a restoration of normal interfibrillar spacing, and a return to corneal stromal proteoglycans of normal size and composition. These correlations suggest that the corneal stromal proteoglycans may play a fundamental role in regulating corneal collagen fibril spacing.