No abstract

Most peptides have not proved useful as neuroactive drugs because they are blocked by the blood-brain barrier and do not reach their receptors within the brain.Intraperitoneally administered L-serinyl JD-glucosde aalgues of [Metslenkephaln (glycopeptides) have been shown to be transported across the blood-brain barrier to bind with targeted p and &oplod receptors in the mouse brain. The opioid nature of the bing has been demonstrated with intracerebroventricularly a ered naloxone. Paradoxically, glucosylation decreases the ipophlt of the peptides while promoting transport across the phc endothe layer. It is suggested that glucose transporter GLUT-1 is responsible for the transport of the peptide message. Profound and long-lasting anesla has been observed in mice (tail-ck and hot-plate assays) with two of the glycopeptide a ues when administered intraperitoneally.

In order to provide new insight into the determining factors of membrane-bound peptide conformation which might play an important role in peptide-receptor docking and further biological behaviors, the dodecylphosphocholine (DPC) micelle-bound conformations of bifunctional peptide derivatives of δ-preferring opioid agonists and NK1 antagonists (1: Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-O-3,5-Bzl(CF3)2; 2: Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-NH-3,5-Bzl(CF3)2; 3: Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-NH-Bzl) were determined based on 2D NMR studies. Although the differences in the primary sequence were limited to the C-terminus, the obtained NMR conformations were unexpectedly different for each compound. Moreover, their biological activities showed different trends in direct relation to the compound-specific conformations in DPC micelles. The important result is that not only were the NK1 antagonist activities different (the pharmacophore located at the C-terminus), but the opioid agonist activities (this pharmacophore was at the structurally preserved N-terminus) also were shifted, suggesting that a general conformational change in the bioactive state was induced due to relatively small and limited structural modifications.

Osteoarthritis (OA) is a chronic condition characterized by pain during joint movement. Additionally, patients with advanced disease experience pain at rest (i.e., ongoing pain)that is generally resistant to non-steroidal anti-inflammatory drugs (NSAIDs). Injection of monosodium iodoacetate (MIA) into the intra-articular space of the rodent knee is a well-established model of OA that elicits weight-bearing asymmetry and referred tactile and thermal hypersensitivity. Whether ongoing pain is present in this model is unknown. Additionally, the possible relationship of ongoing pain to MIA dose is not known. MIA produced weight asymmetry, joint osteolysis, and cartilage erosion across a range of doses (1, 3, and 4.8 mg). However, only rats treated with the highest dose of MIA showed conditioned place preference to a context paired with intra-articular lidocaine, indicating relief from ongoing pain. Diclofenac blocked the MIA-induced weight asymmetry but failed to block MIA-induced ongoing pain. Systemic AMG9810, a TRPV1 antagonist, effectively blocked thermal hypersensitivity, but failed to block high dose MIA-induced weight asymmetry or ongoing pain. Additionally, systemic or intra-articular HC030031, a TRPA1 antagonist, failed to block high dose MIA-induced weight asymmetry or ongoing pain. Our studies suggest that a high dose of intra-articular MIA induces ongoing pain originating from the site of injury that is dependent on afferent fiber activity but apparently independent of TRPV1 or TRPA1 activation. Identification of mechanisms driving ongoing pain may enable development of improved treatments for patients with severe OA pain and diminish the need for joint replacement surgery.

A series of bifunctional peptides that act as agonists for δ and μ opioid receptors with δ selectivity and as antagonist for neurokinin-1 (NK1) receptors were designed and synthesized for potential application as analgesics in various pain states. The peptides were characterized using radioligand binding assays and functional assays using cell membrane and animal tissue. Optimization was performed on the fifth residue which serves as an address moiety for both receptor recognitions. It had critical effects on both activities at δ/μ opioid receptors and NK1 receptors. Among the synthesized peptides, H-Tyr-D-Ala-Gly-Phe-Met-Pro-Leu-Trp-O-3,5-Bzl(CF 3 ) 2 (5) and H-Tyr-DAla-Gly-Phe-Nle-Pro-Leu-Trp-O-3,5-Bzl(CF 3 ) 2 (7) had excellent agonist activity for both δ opioid and μ opioid receptors and excellent antagonist activity for NK1 receptors. These results indicate that the rational design of multifunctional ligands with opioid agonist and neurokinin-1 antagonist activities can be accomplished and may provide a new tool for treatment of chronic and several pain states.