title: Degradation of endomorphin-2 at the supraspinal level in mice is initiated by dipeptidyl peptidase IV: an in vitro and in vivo study.
abstract: Endomorphin-2 (Tyr-Pro-Phe-PheNH(2)) was discovered as an endogenous ligand for the mu-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 PheNH(2). 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-PheNH(2) and Pro-Phe-PheNH(2) was increased in the presence of bestatin, an aminopeptidase inhibitor, whereas that of free phenylalanine and PheNH(2) was decreased. Furthermore, purified dipeptidyl peptidase IV hydrolyzed endomorphin-2 at the cleavage site, Pro(2)-Phe(3) bond. Thus, degradation of endomorphin-2 by brain synaptic membranes seems to take place mainly through the cleavage of Pro(2)-Phe(3) bond by dipeptidyl peptidase IV, followed by release of free phenylalanine and PheNH(2) from the liberated fragment, Phe-PheNH(2) 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.
authors.affiliation: Department of Biochemistry, Daiichi College of Pharmaceutical Sciences, 22-1 Tamagawa-cho, Minami-ku, Fukuoka 815-8511, Japan.
authors.forename: Chikai
authors.initials: C
authors.lastname: Sakurada
authors.forename: Shinobu
authors.initials: S
authors.lastname: Sakurada
authors.forename: Takafumi
authors.initials: T
authors.lastname: Hayashi
authors.forename: Sou
authors.initials: S
authors.lastname: Katsuyama
authors.forename: Koichi
authors.initials: K
authors.lastname: Tan-No
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Sakurada
mesh_terms: D000626:Aminopeptidases / Q000502:physiology; D000701:Analgesics, Opioid / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D018819:Dipeptidyl Peptidase 4 / Q000502:physiology*; D008297:Male; D051379:Mice; D009842:Oligopeptides / Q000378:metabolism* / Q000494:pharmacology; D013116:Spinal Cord / Q000502:physiology; D013570:Synaptic Membranes / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D009842:Oligopeptides; C105294:endomorphin 2; C041445:diprotin A; D000626:Aminopeptidases; D018819:Dipeptidyl Peptidase 4