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Lipo-Endomorphin-1 Derivatives with Systemic Activity against Neuropathic Pain without Producing Constipation
Published: Friday, August 17, 2012
Author: Pegah Varamini et al.

by Pegah Varamini, Friederike M. Mansfeld, Joanne T. Blanchfield, Bruce D. Wyse, Maree T. Smith, Istvan Toth

To enhance the drug-like properties of the endogenous opioid peptide endomorphin-1 (1?=?Tyr-Pro-Trp-Phe-NH2), the N-terminus of the peptide was modified with 2-aminodecanoic acid, resulting in compound 3. Tyr in compound 1 was replaced with 2,6-dimethyltyrosine yielding compound 2. Derivative 2 was also substituted with 2-aminodecanoic acid producing compound, 4. Lipoamino acid-modified derivatives showed improved metabolic stability and membrane permeability while maintaining high µ-opioid (MOP) receptor binding affinity and acting as a potent agonist. In vivo studies showed dose-dependent antinociceptive activity following intravenous (i.v.) administration of compounds 3 and 4 in a chronic constriction injury (CCI)-rat model of neuropathic pain with ED50 values of 1.22 (±0.93) and 0.99 (±0.89) µmol/kg, respectively. Pre-treatment of animals with naloxone hydrochloride significantly attenuated the anti-neuropathic effects of compound 3, confirming the key role of opioid receptors in mediating antinociception. In contrast to morphine, no significant constipation was produced following i.v. administration of compound 3 at 16 µmol/kg. Furthermore, following chronic administration of equi-potent doses of compound 3 and morphine to rats, there was less antinociceptive tolerance for compound 3 compared with morphine.
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