High-pressure liquid chromatography and radioimmunoassay for the specific and quantitative determination of endorphins and related peptides

Condition-dependent presence of beta-lipotropin-like peptide in human keratinocytes

This study aimed to characterize the beta-endorphin-immunoreactive material (betaE-IR) detectable in normal human keratinocytes (NHK). The effects of different culturing conditions and UV-irradiation on production of betaE-IR by NHK were assessed by radioimmunoassay and HPLC. All culture systems contained low levels of betaE-IR that was increased in conditioned media after UV-irradiation under certain conditions. NHK grown in nutrient-poor medium contained highest levels of betaE-IR that exhibited beta-lipotropin-like properties after HPLC analysis. The other culturing conditions displayed no authentic betaE-related peptides. Our results indicate that under certain culturing conditions NHK can produce POMC peptides like beta-lipotropin, which can be induced by UV-radiation.

Developmental and regional alteration of methionine enkephalin-like immunoreactivity in seizure-susceptible E1 mouse brain

Methionine enkephalin-like immunoreactivity (ME-LI) in the brain of El mice (seizure-susceptible strain) was measured by radioimmunoassay (RIA) to elucidate the relation between seizures and the opioid system. The lyophilized supernatants of tissue extracts were subjected to ME RIA. The concentration of ME-LI in 25-day-old El mice that had no seizures was significantly decreased in the hippocampus. At the age of 50 days when El mice displayed abortive seizures, the levels of ME-LI in both El(+) and nonstimulated El(o) mice were also significantly reduced in the hippocampus and septal area. It was further shown that the ME-LI concentrations in both 150-day-old adult El(+) during interictal periods and El(o) mice were markedly decreased in the cerebral cortex, septal area, and striatum, as compared with the corresponding regions in ddY mice (seizure-nonsusceptible strain; the mother strain of El). The decrease of ME-LI in the El mouse brain was generally compatible with our previous findings concerning the up-regulation of opioid delta receptors in this species. These results suggest that the reduction of ME-LI in the El mouse brain is not due to convulsions, but could be associated with the pathogenesis of seizure diathesis and seizure manifestations in the El mouse.

Simultaneous analysis of methionine- and leucine-enkephalin from rat brain: quantification by liquid chromatography-electrochemistry

This study focuses on the application of liquid chromatography with electrochemical detection (LC-ED) for the analysis of methionine-enkephalin (ME) and leucine-enkephalin (LE) extracted from rat brain regions. The high applied potentials necessary for enkephalin detection required the development of an efficient sample processing protocol. Brain extracts were processed using chromatographic mode sequencing (CMS). The decrease in electroactive interfering substances by CMS improved the chromatographic resolution of ME and LE and the electrode performance. Other qualitative and analytical methods were used to evaluate the enkephalin data obtained by LC-ED for rat brain regions. This study demonstrates that LC-ED provides both the sensitivity and specificity necessary for the analysis of enkephalins from rat brain regions.

Increased concentration of alpha- and gamma-endorphin in post mortem hypothalamic tissue of schizophrenic patients

The concentrations of alpha-, beta- and gamma-endorphin were determined by radioimmunoassay in HPLC fractionated extracts of post mortem hypothalamic tissue obtained from schizophrenic patients and controls. The hypothalamic concentration of alpha- and gamma-endorphin was significantly higher in patients than in controls (+72.9% and +50.5% respectively). No difference was found in the concentration of beta-endorphin, the putative precursor of alpha- and gamma-endorphins. These results suggest a deviant metabolism of beta-endorphin in the brain of schizophrenic patients. Whether this phenomenon is related to the psychopathology, or is a consequence of ante mortem farmacotherapy, remains to be established.

Modified forms of vasopressin and oxytocin in a bovine pineal preparation

A bovine pineal acid extract displays a vasotocin-like bioactivity in several bioassays, and is recognized by antibodies against the Pro-Arg-Gly-amide ending common to vasopressin and vasotocin. By using molecular sieve filtration and reversed-phase HPLC, a vasopressin- and oxytocin-like peptide was isolated from this pineal preparation, while no evidence for a vasotocin-like peptide was obtained. The isolated neuropeptides contain a modified amino acid at position 2. This structural difference with authentic pituitary vasopressin and oxytocin may alter their biological and immunological properties, which have been interpreted as vasotocin-like, and thus underlies the controversy concerning the existence of vasotocin in the mammalian pineal gland.

Determination of β-Endorphin and Fragments Thereof in Human Plasma Using High-Performance Liquid Chromatography and a Multiple Radioimmunoassay System

A method for the determination of β-endorphin and β-endorphin fragments in human plasma was developed. β-Endorphin-related peptides were extracted from plasma using octadecasilyl-silica cartridges. Extracts were subjected to re versed-phase high-performance liquid chromatography (HPLC). Extracts as well as HPLC column eluates were assayed using a multiple radioimmunoassay system; several antibodies directed against various distinct regions of the β-endorphin molecule were employed. Using this method, evidence for the presence of multiple β-endorphin fragments in the plasma of healthy young volunteers (under normal conditions) was obtained.

Determination of beta-endorphin and substance P in small volumes of human cerebrospinal fluid

A reversed-phase high-performance liquid chromatography procedure combined with radioimmunoassay (rp-HPLC-RIA) is presented. It makes possible the quantitative determination of the neuropeptides, beta h-endorphin and substance P, in small volumes of cerebrospinal fluid (CSF). The concentration-dependence of the recovery of the method is demonstrated and the effect of free silanol groups of the stationary phase on the recovery is discussed. CSF was shown to contain 9.6 +/- 1.1 fmol beta h-endorphin and 12.0 +/- 0.9 fmol substance P per ml.

Separation and detection of closely related endorphins by liquid chromatography-electrochemistry

The specific aim of this study was to investigate the selectivity of liquid chromatography--electrochemistry for minor variations in the structure of small endorphins. Using isocratic mobile phases, chromatographic conditions were established for the separation of a series of closely related endorphins. Hydrodynamic voltammetry showed that each peptide exhibited a characteristic oxidative behavior that was also reflected in peak current ratios. Changes in a small moiety altered both the chromatographic behavior and electroactivity of these neuropeptides.

Antisera to synthetic peptide recognize high molecular weight enkephalin-containing proteins

Antisera to a synthetic peptide corresponding to the 95-117 sequence of proenkephalin were used to develop a sensitive radioimmunoassay. Gel-filtration of acid extracts of bovine adrenal medulla and purified chromaffin granules revealed that the antisera recognized high molecular weight material (Mr approximately 5,000-30,000). The material in peak I ( Mr 20 ,000-30,000) and peak II (Mr 10,000-20,000) was further purified by immunoaffinity chromatography. Sequential digestion of each of these fractions with trypsin and carboxypeptidase B generated immunoreactive Met-enkephalin. This study demonstrates that antisera against a synthetic peptide cross-react with high molecular weight enkephalin-containing precursors, validating the use of these antisera in studies of enkephalin biosynthesis.

Isolation and characterization of alpha-endorphin and gamma-endorphin from single human pituitary glands

alpha-Endorphin and gamma-endorphin, two closely related peptides of the pro-opiomelanocortin family with characteristic biological activities, were purified to homogeneity from single human pituitary glands and chemically identified. Isolation of the peptides was based on size fractionation by Sephadex G-75 chromatography followed by two HPLC steps using reverse-phase and paired-ion reverse-phase systems and was monitored by radioimmunoassay. During the isolation procedure alpha- and gamma-endorphin-sized material behaved chromatographically and immunologically indistinguishably from synthetic alpha- and gamma-endorphin. The amino acid composition and NH2-terminus of isolated peptides demonstrated their identity as authentic alpha-endorphin and gamma-endorphin. Acetylated forms were absent. In addition, evidence is provided that large forms with alpha- and gamma-endorphin immunoreactivity detected during gel filtration are human lipotropin-(1-74) and -(1-75), respectively. The data substantiate that alpha-endorphin and gamma-endorphin exist as endogenous peptides in the human pituitary gland.

Naltrexone-sensitive behavioral actions of the ACTH 4-9 analog (Org 2766)

The effects of the ACTH 4-9 analog (Org 2766) and the COOH-terminal tripeptide of Org 2766 (Phe-D-Lys-Phe; PDLP) on retrieval of one-trial learning passive avoidance behavior were compared with those of beta-endorphin, [Met5]-enkephalin, [D-Ala2,Met5]-enkephalin, des-Tyr1-[Met5]-enkephalin and des-enkephalin-gamma-endorphin (DE gamma E). Amounts of intracerebroventricularly administered Org 2766, PDLP, [Met5]-enkephalin, [D-Ala2,Met5]-enkephalin and DE gamma E, which induced a comparable attenuation of passive avoidance behavior were determined. Pretreatment with the opiate antagonist naltrexone prevented the attenuating effect of these peptides on passive avoidance behavior except that of DE gamma E. The attenuating effect of Org 2766 and of [Met5]-enkephalin was reversed to facilitation of passive avoidance behavior in the presence of naltrexone. Subcutaneous treatment with Org 2766 and [D-Phe7]-ACTH 4-10 decreased electrical self-stimulation behavior elicited from the medial septal area. Naltrexone prevented the inhibitory effect of Org 2766 on this behavior, but not that of [D-Phe7]-ACTH 4-10. Although the attenuating effect of PDLP on passive avoidance behavior was not reduced by pretreatment with [Met5]-enkephalin- or beta-endorphin-antiserum, and PDLP induced neither analgesia nor excessive grooming, the data suggest that the inhibitory effect of Org 2766 and PDLP on passive avoidance behavior and electrical self-stimulation are mediated by endorphin systems in the brain.

beta-Endorphin immunoreactive materials in human plasma determined by a multiple radioimmunoassay system

Extracts of plasma obtained from adult humans before and immediately after physical stress were subjected to high pressure liquid chromatography (HPLC); extracts or HPLC fractions, resp., were analysed for the presence of human beta-endorphin (beta H-endorphin) or fragments thereof by several radioimmunoassays using antibodies directed against the C-terminus and two "middle" regions of beta H-endorphin. Using an antibody ("Don Antonio") apparently directed against a beta H-endorphin fragment including positions 17 to 22 or somewhat adjacent regions, concentrations of beta H-endorphin immunoreactivity were found to be in the well-known range under normal conditions and to increase after physical stress. However, only a minor portion of this material proved to be identical with beta H-endorphin, whereas the major portion behaved like a smaller fragment thereof. In addition, high amounts of an immunoreactive material obviously containing a C-terminal sequence of beta H-endorphin were found, indicating the presence of an immunologically relevant beta H-endorphin fragment in the plasma.