Dynorphin B 1-13

Endogenous opioid peptides, found in the central and peripheral nervous systems, perform neuromodulatory roles, and display a wide range of functional and pharmacological properties in vitro and in vivo. In this study, we investigated the effects of prodynorphin gene products on intracellular signaling events and cell survival in rat pheochromocytoma PC12 cells. Leumorphin, but not other prodynorphin gene products including dynorphin A, beta-neoendorphin and rimorphin (dynorphin B), increased cell viability in PC12 cells. The cytoprotective effect of leumorphin was dependent on the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways, but was insensitive to both naloxone, a general antagonist of the opioid receptor, and nor-binaltorphimine, a specific antagonist of the kappa opioid receptor. Moreover, a competition-binding assay clearly revealed that leumorphin had another binding site(s) in addition to that for the kappa opioid receptor. Interestingly, leumorphin induced activation of the epidermal growth factor receptor via a Src-dependent mechanism, which was proved to be responsible for the increased survival response. Flow cytometric and microscopic analysis showed that leumorphin rescued cells from serum deprivation-induced apoptosis.

Enzymatic degradation is a major concern in peptide analysis. Postmortem metabolism in biological samples entails considerable risk for measurements misrepresentative of true in vivo concentrations. It is therefore vital to find reliable, reproducible, and easy-to-use procedures to inhibit enzymatic activity in fresh tissues before subjecting them to qualitative and quantitative analyses. The aim of this study was to test a benchtop thermal stabilization method to optimize measurement of endogenous opioids in brain tissue. Endogenous opioid peptides are generated from precursor proteins through multiple enzymatic steps that include conversion of one bioactive peptide to another, often with a different function. Ex vivo metabolism may, therefore, lead to erroneous functional interpretations. The efficacy of heat stabilization was systematically evaluated in a number of postmortem handling procedures. Dynorphin B (DYNB), Leu-enkephalin-Arg(6) (LARG), and Met-enkephalin-Arg(6)-Phe(7) (MEAP) were measured by radioimmunoassay in rat hypothalamus, striatum (STR), and cingulate cortex (CCX). Also, simplified extraction protocols for stabilized tissue were tested. Stabilization affected all peptide levels to varying degrees compared to those prepared by standard dissection and tissue handling procedures.

Dynorphin A-(1-17) acts through non-opioid mechanisms to produce dose-related neurological deficits following injection into the lumbar spinal subarachnoid space in rats. Hindlimb motor function was examined following subarachnoid injection of dynorphin A fragments and other opioid peptides derived from prodynorphin to establish: (1) which portion(s) of the dynorphin A molecule cause hindlimb motor dysfunction, and (2) whether these paralytic actions are shared by other opioids (dynorphin B, alpha-neo-endorphin, and beta-neo-endorphin) derived from the same promolecule. To minimize the influence of enzymatic inactivation on relative bioactivities, peptides were coinjected with a combination of peptidase inhibitors previously shown to enhance the actions of dynorphin A fragments in vitro. Dynorphin A-(1-17) and -(2-17) produced dose-related neurological deficits with equal potencies and durations. Although without effect when injected alone, dynorphin A-(1-8), -(1-7) and -(3-8) caused transient motor dysfunction when co-injected with peptidase inhibitors. In contrast, dynorphin A-(1-6), -(1-5) and -(6-17) did not disrupt hindlimb motor function with or without peptidase inhibition. Dynorphin B, alpha-neo-endorphin and beta-neo-endorphin also caused hindlimb dysfunction which was potentiated by peptidase inhibition.