Metabolism of beta-endorphin in plasma studied by liquid chromatography-electrospray ionization mass spectrometry

[Octarphin--Nonopioid Peptide of the Opioid Origin]

The data on the properties and mechanism of action of the peptide octarphin (TPLVTLFK, the fragment 12-19 of β-endorphin)--a selective agonist of nonopioid (insensitive to the action of the opioid antagonist naloxone) β-endorphin receptor found on n immune cells (peritoneal macrophages, T and B lymphocytes of spleen and blood), endocrine (adrenal cortex, hypothalamus), cardiovascular (cardiomyocytes) systems are analyzed and systematized. Binding to the receptor octarphin increases increases the mitogen-induced pro- liferation of human and mouse T and B lymphocytes in vitro, activates murine peritoneal macrophages in vitro and in vivo, stimulates growth of human T-lymphoblast cell lines Jurkat and MT-4, inhibits adenylate cyclase activity of rat adrenal cortex membranes and suppresses the secretion of glucocorticoids from the adrenal gland into the blood. It was shown that in a concentration range of 1-1000 nM the peptide increases the activity of inducible NO-synthase (iNOS), and the content of NO and cGMP in lipopolysaccharide-activated murine peritoneal macrophages. Taking into account that NO acts as a primary activator of soluble guanylate cyclase (sGC), it can be assumed that the activating effect of octarphin on macrophages is realized in the following way: increase in th iNOS expression --> increase in the NO production --> increase in the sGC activity --> increase in intracellular levels of cGMP.

Beta-endorphin 1-31 biotransformation and cAMP modulation in inflammation

A large body of evidence now exists for the immune cell expression, production, and the release of beta-endorphin (BE 1–31) within inflamed tissue. The inflammatory milieu is characterised by increased acidity, temperature and metabolic activity. Within these harsh conditions BE 1–31 is even more susceptible to increased enzymatic degradation over that of plasma or other non-injured tissue. To elucidate the biotransformation pathways of BE 1–31 and provide an insight to the impact of inflamed tissue environments, BE 1–31 and three of its major N-terminal fragments (BE 1–11, BE 1–13 and BE 1–17) were incubated in inflamed tissue homogenates at pH 5.5 for 2 hrs. In addition, the potency of BE 1–31 and five main N – terminal fragments (BE 1–9, BE 1–11, BE 1–13, BE 1–17, BE 1–20) was assessed at mu-opioid receptors (MOR), delta-opioid receptors (DOR), and kappa-opioid receptors (KOR). Opioid receptor potency was investigated by examining the modulation of forskolin induced cAMP accumulation. The majority of the N-terminal fragment of BE 1–31 had similar efficacy to BE 1–31 at MOR. The shortest of the major N-terminal fragments (BE 1–9), had partial agonist activity at MOR but possessed the highest potency of all tested peptides at DOR. There was limited effect for BE 1–31 and the biotransformed peptides at KOR. Major N-terminal fragments produced within inflamed tissue have increased presence within inflamed tissue over that of the parent molecule BE 1–31 and may therefore contribute to BE 1–31 efficacy within disease states that involve inflammation.

Targeting dynorphin/kappa opioid receptor systems to treat alcohol abuse and dependence

This review represents the focus of a symposium that was presented at the "Alcoholism and Stress: A Framework for Future Treatment Strategies" conference in Volterra, Italy on May 3-6, 2011 and organized/chaired by Dr. Brendan M. Walker. The primary goal of the symposium was to evaluate and disseminate contemporary findings regarding the emerging role of kappa-opioid receptors (KORs) and their endogenous ligands dynorphins (DYNs) in the regulation of escalated alcohol consumption, negative affect and cognitive dysfunction associated with alcohol dependence, as well as DYN/KOR mediation of the effects of chronic stress on alcohol reward and seeking behaviors. Dr. Glenn Valdez described a role for KORs in the anxiogenic effects of alcohol withdrawal. Dr. Jay McLaughlin focused on the role of KORs in repeated stress-induced potentiation of alcohol reward and increased alcohol consumption. Dr. Brendan Walker presented data characterizing the effects of KOR antagonism within the extended amygdala on withdrawal-induced escalation of alcohol self-administration in dependent animals. Dr. Georgy Bakalkin concluded with data indicative of altered DYNs and KORs in the prefrontal cortex of alcohol dependent humans that could underlie diminished cognitive performance. Collectively, the data presented within this symposium identified the multifaceted contribution of KORs to the characteristics of acute and chronic alcohol-induced behavioral dysregulation and provided a foundation for the development of pharmacotherapeutic strategies to treat certain aspects of alcohol use disorders.

Study of beta endorphin metabolism in inflamed tissue, serum and trypsin solution by liquid chromatography-tandem mass spectrometric analysis

Beta endorphin (β-END) is recognised as one of the most significant endogenous neuropeptides, responsible for a wide range of biological activities in the body. However, within the body β-END is exposed to hydrolysis by a variety of enzymes. In this study, we investigated the metabolism and fragmentation pattern of β-END in rat inflamed tissue, in rat serum and in trypsin solution. β-END (1-31)-rat was incubated at 37 °C in each matrix for different incubation times. The resultant fragments were separated using a C4 column and detected by mass spectrometry using total ion current mode. Structural information for the fragments was elucidated using tandem mass spectrometry. Incubation of β-END (1-31)-rat in trypsin solution and in rat serum resulted in 8 and 13 fragments, respectively. Incubation in inflamed rat paw tissue resulted in 22 fragments at pH 7.4 and 26 fragments at pH 5.5. Some of these fragments were common to both pH values. The degradation of β-END (1-31)-rat in inflamed tissue at pH 5.5 was faster than that at pH 7.4. Secondary fragmentation of some larger primary fragments was also observed in this study.

Limited effects of beta-endorphin compared to loperamide or fentanyl in a neuroendocrine biomarker assay in non-human primates

The in vivo pharmacodynamics of the opioid neuropeptide beta-endorphin (a major endogenous agonist at the mu-opioid receptor) is difficult to determine in non-human primate models with translational value, or in humans. The present studies therefore employed a neuroendocrine biomarker assay, prolactin release, to systematically compare the in vivo profile of i.v. beta-endorphin (0.01-0.32 mg/kg; i.v.) in gonadally intact male rhesus monkeys (n=4) to that of the peripherally selective mu-agonist loperamide (0.01-0.32 mg/kg; i.v.) and the centrally penetrating mu-agonist fentanyl (0.0056-0.018 mg/kg; i.v.). Studies utilized a standardized time course design (measuring prolactin levels 5-120 min after agonist administration). Beta-endorphin displayed only limited effectiveness in causing prolactin release when tested over this 30-fold dose range, compared to loperamide or fentanyl. Furthermore, two of the four subjects were only minimally responsive to beta-endorphin. This differential responsiveness was not due to the presence of a previously described single nucleotide polymorphism at the OPRM1 gene (C77G), known to affect beta-endorphin pharmacodynamics in vitro. In vivo biotransformation studies with MALDI-mass spectrometry determined that full-length beta-endorphin was detectable in all subjects up to at least 5 min after i.v. administration. Thus, the relative ineffectiveness of i.v. beta-endorphin in this assay does not appear to be principally due to rapid generation of non-opioid fragments of this neuropeptide.

Monitoring the neuropeptide metabolites by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The developments of bio-analytical methods for analyzing bioactive peptides are of paramount importance. Neuropeptides and their bioactive fragments play a vital role in the regulation of many biological processes and diseases. This paper presents the use of matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) method for monitoring neuropeptides along with their degradation products in plasma samples from cancer patients. The neuropeptides focused in this study were beta-endrophin, substance P, and bradykinin. The method involves the enzyme digestion of the neuroactive peptides followed by MALDI-MS sample preparation and subsequent acquisition of the MS spectral data. The mass spectral profile identifies most of the C-terminal and N-terminal peptides, and the mass accuracy was in the range of -1.68 to 1.46 Da with the mass spectrometer utilised. Analysis of the neuropeptide degradation patterns from the cancer patients were compared with the controls showed similar results. The study reveals that this approach can be used to identify the enzymatic digestion products of protein.