Degradation of endomorphin-2 at the supraspinal level in mice is initiated by dipeptidyl peptidase IV: an in vitro and in vivo study

• Published in: Biochemical pharmacology 2003-08, Vol.66 (4), p.653-661
• Main Authors: Sakurada, Chikai, Sakurada, Shinobu, Hayashi, Takafumi, Katsuyama, Sou, Tan-No, Koichi, Sakurada, Tsukasa
• Format: Article
• Language: English
• Subjects: Aminopeptidases - physiology; Analgesics, Opioid - metabolism; Animals; Antinociception; Biological and medical sciences; Brain - metabolism; Dipeptidyl Peptidase 4 - physiology; Dipeptidyl peptidase IV; Endomorphin-2; Male; Medical sciences; Metabolic pathway; Mice; Mouse brain; Oligopeptides - metabolism; Oligopeptides - pharmacology; Pharmacology. Drug treatments; Spinal Cord - physiology; Synaptic membranes; Synaptic Membranes - metabolism
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(03)00391-5

Endomorphin-2 (Tyr–Pro–Phe–PheNH2) was discovered as an endogenous ligand for the μ-opioid receptor. The physiological function of endomorphin-2 as a neurotransmitter or neuromodulator may cease through the rapid enzymatic process in the synapse of brain, as for other neuropeptides. The present study was conducted to examine the metabolism of endomorphin-2 by synaptic membranes prepared from mouse brain. Major metabolites were free tyrosine, free phenylalanine, Tyr–Pro and PheNH2. Both the degradation of endomorphin-2 and the accumulation of major metabolites were inhibited by specific inhibitors of dipeptidyl peptidase IV, such as diprotin A and B. On the other hand, the accumulation of Phe–PheNH2 and Pro–Phe–PheNH2 was increased in the presence of bestatin, an aminopeptidase inhibitor, whereas that of free phenylalanine and PheNH2 was decreased. Furthermore, purified dipeptidyl peptidase IV hydrolyzed endomorphin-2 at the cleavage site, Pro2–Phe3 bond. Thus, degradation of endomorphin-2 by brain synaptic membranes seems to take place mainly through the cleavage of Pro2–Phe3 bond by dipeptidyl peptidase IV, followed by release of free phenylalanine and PheNH2 from the liberated fragment, Phe–PheNH2 by aminopeptidase. We have also examined that the effect of diprotin A on the antinociception induced by intracerebroventricularly administered endomorphin-2 in the mouse paw withdrawal test. Diprotin A simultaneously injected with endomorphin-2 enhanced endomorphin-2-induced antinociception. These results indicate that dipeptidyl peptidase IV may be an important peptidase responsible for terminating endomorphin-2-induced antinociception at the supraspinal level in mice.