Activity and Expression of Enkephalinase and Aminopeptidase N in Regions of the Mesocorticolimbic System are Selectively Modified by Acute Ethanol Administration

Abstract

Opioid peptides play a key role in ethanol reinforcement and alcohol drinking behavior. However, regulation of opioid levels by peptidase-degrading activities in ethanol's actions in brain is still unclear. The aim of this work was to study the acute effects of ethanol (2.5 g/kg) on enkephalinase (NEP) and aminopeptidase N (APN) activities and expression in regions of the mesocorticolimbic system, as well as on corticosterone levels in serum for up to 24 h after administration. Enzymatic activities were measured by fluorometric assays, mRNA's expression by reverse transcriptase polymerase chain reaction (RT-PCR) and corticosterone levels by radioimmunoassay. Acute ethanol administration modified peptidase activity and expression with different kinetics. Ethanol induced a transitory increase and decrease in NEP and APN activities in the frontal cortex (FC) and ventral tegmental area (VTA), whereas only increases in these activities were observed in the nucleus accumbens (NAcc). Ethanol induced an increase in NEP mRNA in the FC and decreases in APN mRNA in the FC and NAcc. In contrast, ethanol produced biphasic effects on both enzymes expression in the VTA. Corticosterone levels were not changed by ethanol. Our results suggest that NEP and APN could play a main role in ethanol reinforcement through regulation of opioid levels in mesolimbic areas.

Sialorphin Potentiates Effects of [Met5]Enkephalin without Toxicity by Action other than Peptidase Inhibition

“…Earlier studies have demonstrated rapid degradation of opioid peptides by any of 5 types of peptidase: 1) aminopeptidase N (EC 3.4.11.2), which cleaves the Tyr 1 -Gly 2 amide bond; 2) dipeptidyl peptidase III (EC 3.4.14.4), which hydrolyzes the Gly 2 -Gly 3 bond; 3) dipeptidyl carboxypeptidase (EC 3.4.15.1, also known as the angiotensin I-converting enzyme); 4) neutral endopeptidase (EC 3.4.24.11, also known as enkephalinase), which cleaves the Gly 3 -Phe 4 bond; and 5) carboxypeptidase A (EC 3.4.17.1) (Khaket et al, 2012;Morales-Mulia et al, 2012). The membrane-bound three enzymes, aminopeptidase N (APN), dipeptidyl carboxypeptidase, and neutral endopeptidase (NEP), play an essential role in the degradation of [Met 5 ]enkephalin (ME) in three different types of isolated preparation: guinea pig ileum (Aoki et al, 1984), mouse vas deferens (MVD) (Aoki et al, 1986) and rat vas deferens (Cui et al, 1986).…”