Neuropeptide enzyme hydrolysis in allergic human saliva

The activity of neuropeptide-degrading enzymes, and possible variations in this activity under allergic conditions, was examined in human saliva obtained from allergic volunteers and from an age- and sex-matching group of healthy controls, using leucine enkephalin as model substrate. The results obtained indicate that, under experimental conditions, the substrate was partially hydrolyzed by all three classes of enzymes known to degrade it in human saliva: aminopeptidases, dipeptidylaminopeptidases and dipeptidylcarboxypeptidases. In the presence of saliva obtained from allergic donors, a large increase in the activity of aminopeptidases, and a more limited increase in the activity of dipeptidylaminopeptidases, induced an increase of substrate hydrolysis with respect to that measured in the controls. The activity of all substrate-active enzymes, the allergy-associated variations in this activity, and the amount of substrate hydrolyzed, were found to be different in male and female saliva. Specifically, in the controls the gender-related differences in substrate hydrolysis were mainly caused by the higher activity of aminopeptidases observed in male as compared to female saliva. In contrast, in allergic saliva, a greater increase in the activity of aminopeptidases in female saliva reduced the gender-related differences in the pattern of hydrolysis, which was also different from that observed in the controls.