Long-term effects of neutral proteases on collagen degradation in the rabbit cornea
Oswald, Jeffrey P.
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I have investigated the effects of neutral proteases on the collagen in the rabbit cornea. Knowing that matrix metalloproteinanse I (MMP I - collagenase) is the primary source of interstial collagen degradation, we asked what the long term affects were of other neutral proteases on collagen degradation. By exposing 3mm rabbit eye corneal punches to various concentrations of endo and exopeptidases, I have shown that leucine aminopeptidase, carboxypeptidase B, carboxypeptidase A, alpha chymotrypsin (bovine), L-tosylamido-2-phenyl ethyl chlorolmethyl ketone- trypsin, plasmin (human), cathepsin G (human), and elastase (human), all have some degradative effect on interstitial collagen ranging from 0.5% to 13% of the total collagen present in corneal punches in 4 days. These findings suggest that these proteases may have very significant effects on overal all collagen metabolism over extended time periods. By heat denaturing the collagen in corneal punches, I have also shown that 63% to 73% of the total collagen in young corneal punches will solubilize out in neutral buffer, while only 22% to 33% of the total collagen in mature corneal punches is liberated. This finding suggest that collagen crosslinking by x j nondisulfide bonds is somewhat effected by aging. Finally, by exposing sections of a 2mm peripheral ring of an 8mm central W corneal punch to neutral buffer, I have shown that 1% to 6.6% of the native interstitial collagen will solubilize out of the medial and lateral sections of the ring, but not in the superior and inferior zones. These findings suggest a regional physiological difference on the surface of the eye, possibly in the area where the eyelids meet during blinking.