Gelatinase concentration in tears of corneal-grafted patients

Gelatinolytic enzymes, which degrade type IV basement membrane collagen, have been shown to be expressed by corneal cells, either constitutively (gelatinase A or MMP-2) or after induction (gelatinase B or MMP-9). Our aim was to determine whether an enhanced MMP-9 and eventually MMP-2 concentration in tears could be evidenced in the case of corneal-graft failure.

The amount of MMP-2 and MMP-9 gelatinolytic enzymes was measured by quantitative zymography in tears of twenty-one controls (84 samplings) and in tears of twenty-three corneal-grafted patients in a one-year post-graft follow-up study.

The mean MMP-2 values in controls were of 8.4 (+/-7.3) pg/10 micrograms protein and the mean MMP-9 values in controls were of 73 (+/-76) pg/10 micrograms protein. No active gelatinase form was detected in any of controls, but in all cases of corneal graft failure, the active forms of both enzymes were present, and enzyme concentrations were higher than control values. All patients had significantly higher MMP-9 values than controls at each sampling time (p < 0.0001). The "corneal-graft failure" patient group had statistically significant higher MMP-9 concentrations in tears than the "successful-graft" patient group at one month (p = 0.0312), four months (p = 0.0158) and one year (p < 0.01) after the graft. The presence of active MMP-9 was highly significant of graft failure four months and one year after the graft (p < 0.0001). In contrast, MMP-2 increase was delayed, with significantly higher MMP-2 values than controls in all patients at four months (p = 0.0231) and one year (p = 0.0001) after the graft, but MMP-2 values could not discriminate between patient groups.

In our study, all cases of graft failure showed abnormally high levels of the active forms of metalloproteinase enzymes, and these values far exceeded the maximum control concentration. MMP-9 measurements in tears made between one and four months after corneal transplantation, and while local corticotherapy is steadily established, should help in predicting corneal graft rejection.