Use of preproenkephalin knockout mice and selective inhibitors of enkephalinases to investigate the role of enkephalins in various behaviours.
BACKGROUND
The most simple and efficient method to study the physiological role of enkephalins is to increase the lifetime of these endogenous opioid peptides by inhibiting their inactivating enzymes. Enkephalins are degraded by the concomitant action of two metallopeptidases: neutral endopeptidase (NEP, EC3.4.21.11) and aminopeptidase N (APN, EC3.4.11.2), both enzymes releasing inactive metabolites.


OBJECTIVE
Potent dual inhibitors have been developed, such as RB101. However, NEP and APN have a broad specificity and can cleave various peptides in vitro. Therefore, it was essential to investigate the specific involvement of enkephalins in the various pharmacological responses induced by dual inhibitors.


METHODS
We compared the pharmacological responses induced by RB101 in wild-type and preproenkephalin-deficient mice (Penk1-/-) using several behavioural assays.


RESULTS
In all the tests used (hot plate test, force swim test, castor-oil-induced diarrhoea), RB101 induced strong effects in wild-type animals, whereas slight effects were observed in Penk1-/- animals. These residual effects are blocked by pre-administration of the opioid antagonist naloxone, supporting the involvement of the opioid receptors in the responses observed.


CONCLUSIONS
The pharmacological effects induced by dual inhibitors acting on both NEP and APN are mainly due to the protection of the endogenous enkephalins at supraspinal and peripheral levels. It could be speculated that the residual effects observed in Penk1-/- mice after RB101 administration could be due to the direct action of other opioid peptides or through an indirect effect involving the protection of other peptide substrates of NEP or APN, as substance P or angiotensin.
Noble
Florence
F
Université Paris Descartes, Faculté de Pharmacie, Neuropsychopharmacologie des addictions et Université Paris 7, Paris 75010, France. florence.noble@univ-paris5.fr
Benturquia
Nadia
N
Bilkei-Gorzo
Andras
A
Zimmer
Andreas
A
Roques
Bernard P
BP
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D018826:CD13 Antigens / Q000037:antagonists & inhibitors / Q000378:metabolism; D004220:Disulfides / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004745:Enkephalins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D007275:Injections, Intravenous; D051379:Mice; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D015260:Neprilysin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010649:Phenylalanine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D011498:Protein Precursors / Q000172:deficiency / Q000235:genetics*; D013550:Swimming / Q000502:physiology / Q000523:psychology
D004220:Disulfides; D004745:Enkephalins; D004791:Enzyme Inhibitors; D009292:Narcotic Antagonists; D011498:Protein Precursors; C074024:RB 101; D009270:Naloxone; D010649:Phenylalanine; D009271:Naltrexone; D009020:Morphine; C033660:preproenkephalin; D018826:CD13 Antigens; D015260:Neprilysin; C055382:naltrindole