Inhibition of morphine tolerance development by a substance P-opioid peptide chimera.

The neuropeptide substance P (SP), apart from its traditional role in spinal nociceptive processing, is an important regulatory effector of opioid-dependent analgesic processes. The present study stems from our original findings indicating that 1) pharmacologically administered SP mediates a strong inhibitory activity on the development of morphine tolerance in rats, and that 2) a novel SP-opioid peptide chimera YPFFGLM-NH(2), designated ESP7, produces opioid-dependent analgesia without tolerance development. To further examine the effects of simultaneous activation of two distinct opposing spinal systems on opioid tolerance and the mechanisms underlying chimeric peptide function, a second SP-opioid chimera was synthesized. This chimera, designated ESP6 (YPFFPLM-NH(2)), contains overlapping domains of endomorphin-2 and SP, respectively. ESP6 is distinguished from ESP7 by a glycine to proline substitution at position 5. Intrathecal administration of morphine sulfate (MS) with ESP6 leads to a prolongation of MS analgesia over a 5-day period. The analgesia produced by ESP6 and MS is opioid receptor-dependent, due to the ability of naltrexone to block the analgesic response. Furthermore, when ESP6 and MS are administered with concurrent NK-1 receptor blockade, a decay in analgesic potency similar to that seen with MS alone results. The presence of a proline in ESP6 appears to reduce its conformational flexibility, limit its potency at the micro-opioid receptor, and hinder its analgesic effectiveness alone. However, ESP6 represents a novel adjuvant for the maintenance of opioid analgesia over time and provides a means to predict the pharmacological properties of a chimera from its structure.

A substance P-opioid chimeric peptide as a unique nontolerance-forming analgesic.

To elucidate mechanisms of acute and chronic pain, it is important to understand how spinal excitatory systems influence opioid analgesia. The tachykinin substance P (SP) represents the prototypic spinal excitatory peptide neurotransmitter/neuromodulator, acting in concert with endogenous opioid systems to regulate analgesic responses to nociceptive stimuli. We have synthesized and pharmacologically characterized a chimeric peptide containing overlapping NH(2)- and COOH-terminal functional domains of the endogenous opioid endomorphin-2 (EM-2) and the tachykinin SP, respectively. Repeated administration of the chimeric molecule YPFFGLM-NH(2), designated ESP7, into the rat spinal cord produces opioid-dependent analgesia without loss of potency over 5 days. In contrast, repeated administration of ESP7 with concurrent SP receptor (SPR) blockade results in a progressive loss of analgesic potency, consistent with the development of tolerance. Furthermore, tolerant animals completely regain opioid sensitivity after post hoc administration of ESP7 alone, suggesting that coactivation of SPRs is essential to maintaining opioid responsiveness. Radioligand binding and signaling assays, using recombinant receptors, confirm that ESP7 can coactivate mu-opioid receptors (MOR) and SPRs in vitro. We hypothesize that coincidental activation of the MOR- and SPR-expressing systems in the spinal cord mimics an ongoing state of reciprocal excitation and inhibition, which is normally encountered in nociceptive processing. Due to the ability of ESP7 to interact with both MOR and SPRs, it represents a unique prototypic, anti-tolerance-forming analgesic with future therapeutic potential.

Photodeposition of micrometer-scale polymer patterns on optical imaging fibers.

Microstructures were fabricated on optical imaging fibers with a photopolymerization technique. Monodisperse polymeric microarrays were produced containing spots of 2.5 micrometers in diameter spaced 4.5 micrometers apart. Polymer microarrays were also deposited on other substrates by using imaging fibers for light delivery. The technique allows micrometer-scale photopatterning with masks larger than the desired dimensions.