Prolyl Endopeptidase: Inhibition In Vivo by N‐Benzyloxycarbonyl‐Prolyl‐Prolinal

Abstract: The activity of prolyl endopeptidase in homogenates of mouse tissues was determined 30 min after intraperitoneal injection of N‐benzyloxycarbonyl‐prolylprolinal (1.25 mg/kg), a potent transition state analog inhibitor (K₁= 14 nM) of prolyl endopeptidase (EC 3.4.21.26). A more than 85% decrease of enzyme activity was obtained in all tissues. The in vivo degradation of potential prolyl endopeptidase substrates was studied by following the release of sulfamethoxazole from N‐benzyloxycarbonylglycyl‐prolyl‐sulfamethoxazole, a model synthetic substrate of the enzyme. When this substrate was given intraperitoneally, its enzymatic degradation was blocked after administration of the inhibitor in a dose‐ and time‐dependent manner, indicating inhibition of the enzyme in vivo. Of interest is the long duration of the inhibition. After a relatively low inhibitor dose (5 mg/kg) significant inhibition was seen in most tissues even after 6 h. The brain was particularly sensitive to the effect of the inhibitor. Since prolyl endopeptidase readily degrades many proline‐containing neuropeptides, the inhibitor should be of value in studies on the role of the enzyme in neuropeptide metabolism.