A comparison between the enzymes in the cornea of the vitamin-A deficient rat and those of rat leucocytes

Abstract

The rat was used to investigate the hypothesis that leucocyte enzymes are responsible for corneal liquefaction (keratomalacia) as seen in severe vitamin-A deficiency. Extracts of rat leucocytes and rat corneas were examined for collagenolytic activity. A distinction was made, in the corneas from vitamin-A deficient rats, between those heavily infiltrated with leucocytes and those only slightly infiltrated. The substrates used were acid-soluble collagen, [ 3 H]elastin, [ 14 C]acetyl-casein and azocasein. Inhibitor studies were used to characterize the enzymes found. Rat leucocytes were shown to contain collagenase, elastase and probably Cathepsin G. Rat leucocyte collagenase, like the human neutrophil enzyme, can be distinguished from tissue collagenases by the fact that it is readily extractable without the need for tissue culture. It digests soluble collagen to produce the typical 3/4, 1/4 split products, is inhibited by metal chelators and is unaffected by inhibitors of serine proteinases. We have been able to extract collagenase (mainly in a latent form) from the infiltrated corneas of vitamin-A deficient rats but not from non-infiltrated corneas or from corneas of normal rats. The extractable rat corneal collagenase can be activated by mercurials and has similar properties to rat leucocyte collagenase. We suggest that since rat leucocytes, containing an extractable collagenase, are present in large numbers in ulcerating corneas of vitamin-A deficient rats and since ulcerating rat corneas contain an extractable collagenase, it is reasonable to consider that leucocyte collagenase plays an important part in the final stages of the corneal destruction seen in vitamin-A deficiency.