EFFECTS OF PROTEOLYTIC-ENZYME INHIBITORS ON NASAL ABSORPTION OF SALMON-CALCITONIN IN RATS

Proteolytic enzyme inhibitors were examined as absorption enhancers for the nasal absorption of salmon calcitonin (SCT) in rats. Bestatin, diprotinin, leupeptin, aprotinin, soybean trypsin inhibitor and camostat mesilate were used as enzyme inhibitors. The nasal absorption of SCT was evaluated by measuring its hypocalcemic effects. The peptidase activities of rat nasal mucosal tissue were high and found to be in the following order: leucine aminopeptidase (2.72 nmol/min per mg protein) > dipeptidyl aminopeptidase (1.84 nmol/min per mg protein) > cathepsin (650 pmol/min per mg protein)> trypsin.(4.61 pmol/min per mg protein). Nasal administration of SCT (10 IU/kg, pH 7.0) showed low pharmacological availability (3.2%). Coadministration with bestatin (aminopeptidase inhibitor, 0.01-1 mM) or diprotinin A (dipeptidyl peptidase inhibitor, 0.1-1 mM) did not change the hypocalcemic effects. Coadministration with aprotinin (trypsin inhibitor, 10(3)-10(4) KIU/ml), camostat mesilate (aminopeptidase and trypsin inhibitor, 0.1-10 mM) or leupeptin (trypsin and cathepsin B inhibitor, 0.1-1 mM) enhanced the hypocalcemic effects and, thus, the nasal absorption of SCT. The hypocalcemic effects of SCT at various pH values (pH 4.0, 7.0 and 8.0) with or without aprotinin were the highest at pH 4.0. The pharmacological availabilities after nasal administration of SCT (10 IU/kg) at pH 4.0 and 7.0 were increased from 5.4 to 7.5% and from 3.2 to 6.9% by aprotinin (10(4) KIU/ml), respectively. Therefore, inhibitors which have a trypsin inhibitory activity are useful for enhancing nasal absorption of SCT.