Increase in type I and type IV collagenolytic activity in primary cultures of keratoconus cornea

The collagenolytic activities were assayed in fibroblast cultures established from ten keratoconus and six control corneal explants. The assays included those for both type I and type IV collagenase. The amount of free, directly assayable type I collagenase was highly increased in the media of keratoconus primary cell cultures. Also the activity of type IV collagenase was increased significantly in these cultures but was detectable only after proteolytic activation. The total hydroxyproline content of keratoconus corneas was decreased when compared to controls. However the activity of the prolyl-4-hydroxylase, reflecting the biosynthesis of collagen, was higher in the keratoconus corneal tissue, either expressed per DNA, soluble protein or hydroxyproline content of corneas. The enhancement in collagenolytic processes could explain the pathological tissue destruction in keratoconus corneas and this enhancement is maintained still in primary cultures of keratoconus corneal fibroblasts.