title: Effect of guanidino modification and proline substitution on the in vitro stability and blood-brain barrier permeability of endomorphin II.
abstract: Endomorphin II (ENDII), an endogenous ligand for the mu-opioid receptor, was investigated as a possible analgesic with fewer side effects than morphine. To improve CNS entry of END II, structural modification was also examined to determine whether Pro(4) substitution and cationization affected physico-chemical characteristics, blood-brain barrier (BBB) transport, and analgesic profile. END II and its Pro(4)-substituted analog, Morphiceptin (MOR), were cationized by guanidino (GU)-addition. MOR was seven times less lipophilic than END II, whereas GU-addition decreased lipophilicity of both peptides. MOR did not affect in vitro BBB permeability; however, GU-addition increased permeability of MOR by 31%. MOR decreased protein binding by 23% compared to END II, whereas GU-addition increased protein binding of both peptides by 71 and 113%, respectively. MOR increased brain t(1/2) compared to END II. GU-addition significantly increased t(1/2) of MOR and END II in both brain (sixfold and 10-fold, respectively) and serum (over 10-fold). Pro(4)-substitution and GU-addition enhanced the in vivo analgesia profiles of i.v. administered END II and MOR, but decreased i.c.v. analgesia profiles. This study demonstrates Pro(4)-substitution decreases protein binding and enhances brain stability while cationization enhances both brain and serum stability with variable effects on BBB permeability. The analgesic profiles show that both Pro(4)-substitution and cationization enhance i.v. analgesia and thus, are promising structural modifications for the development of successful opioid drugs.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Arizona, 1501 North Campbell Avenue, Tucson, Arizona 85724, USA.
authors.forename: Vincent S
authors.initials: VS
authors.lastname: Hau
authors.forename: Jason D
authors.initials: JD
authors.lastname: Huber
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Campos
authors.forename: Andrzej W
authors.initials: AW
authors.lastname: Lipkowski
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Misicka
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Davis
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001798:Blood Proteins / Q000737:chemistry; D001812:Blood-Brain Barrier; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D004723:Endorphins / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology; D006146:Guanidines / Q000737:chemistry*; D006207:Half-Life; D007202:Indicators and Reagents; D007276:Injections, Intraventricular; D008055:Lipids / Q000737:chemistry; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009842:Oligopeptides / Q000737:chemistry / Q000493:pharmacokinetics*; D010147:Pain Measurement / Q000187:drug effects; D010539:Permeability; D011392:Proline / Q000737:chemistry*; D011485:Protein Binding; D012995:Solubility
chemical_list: D001798:Blood Proteins; D004723:Endorphins; D006146:Guanidines; D007202:Indicators and Reagents; D008055:Lipids; D009842:Oligopeptides; C105294:endomorphin 2; C028889:morphiceptin; D011392:Proline