INHIBITION OF CORNEAL METABOLISM OF DESLORELIN BY EDTA AND ZNCL2

It was the aim of this study to determine whether deslorelin is degrad ed by the rabbit corneal tissue and to further delineate the mechanism s. Deslorelin was incubated with intact cornea either alone or in the presence of 0.1 mM ouabain, 0.1% 2,4-dinitrophenol, 0.1 mM phosphorami don, 0.1 mM N-tosyl-L-phenylalanine chloromethylketone (TPCK), 0.1-2% EDTA, 0.1-1% ZnCl2, 0.1% dithiothreitol (DTT), or 0.1% N-ethylmaleimid e (NEM) at 37 degrees C. In addition, deslorelin alone was incubated w ith cornea at 4 degrees C. Following a 90-min incubation, the supernat ants were analyzed using a reversed-phase HPLC. Metabolite peaks obser ved in controls at 37 degrees C were not detected in the low-temperatu re study, suggesting inhibition of metabolism at low temperature. Inta ct drug remaining in the supernatant was not altered by ouabain and di nitrophenol, suggesting that energy-dependent corneal uptake is not li kely for deslorelin. Phosphoramidon and TPCK failed to alter desloreli n levels, indicating that phosphoramidon and TPCK-sensitive endopeptid ases did not contribute to the observed metabolism. DTT and NEM also f ailed to affect deslorelin levels. However, 2% EDTA and 1% ZnCl2 signi ficantly elevated the intact deslorelin levels by 44 and 60%, respecti vely, and the metabolite peaks almost completely disappeared. These ob servations are consistent with the corneal metabolism of deslorelin by either metallo-peptidases or metal-dependent peptidases.