Beta-endorphin. Biological activity of synthetic analogs with analgesia inhibiting property in rat vas deferens and guinea pig ileum assays

Three synthetic analogs of human beta-endorphin (beta h-EP) (I, [Gln8, Gly31]-beta h-EP-Gly-Gly-NH2; II, [Arg9,12,24,28,29]-beta h-EP and III, [Cys11,26, Phe27, Gly31]-beta h-EP), which have been shown to possess potent inhibiting activity to beta h-EP-induced analgesia, were assayed in rat vas deferens and guinea pig ileum bioassay systems. In the rat vas deferens assay, relative potencies of these analogs were beta h-EP, 100; I, 30; II, 40; III, 1, whereas in the guinea pig ileum assay: beta h-EP, 100; I, 184; II, 81; III, 163. From previous studies on their analgesia potency in mice and opiate receptor-binding activity in rat brain membranes, their activity in rat vas deferens correlates well with the analgesic potency and the activity from guinea pig ileum assay shows good correlations with that from the opiate receptor-binding assay.

Effect of human beta-endorphin on plasma aldosterone concentrations in normal human subjects

beta-Endorphin recently was proposed as a possible physiological stimulus of aldosterone secretion based on studies in animals. Since human beta-endorphin (beta h-endorphin) does not contain the ACTH-(4-10) homology common to other ACTH-related neuropeptides that stimulate aldosterone, its mechanism of stimulation might differ from that of the other peptides. In the present study, we infused beta h-endorphin into six normal subjects under carefully controlled conditions at dosage levels several orders of magnitude higher than endogenous levels. No increase in plasma aldosterone was found in these subjects ingesting a normal sodium intake despite the fact that other biological actions of beta h-endorphin were manifest. By contrast, an equimolar infusion of ACTH-(1-24) caused a significant increase in plasma aldosterone. These studies do not support a significant role for beta h-endorphin in control of aldosterone secretion in man and are consistent with the concept that the ACTH-(4-10) amino acid sequence, common to ACTH, beta-lipotropin, gamma-lipotropin, beta MSH, and alpha MSH, is a major determinant of their aldosterone-stimulating capacity.

Characterization of immunoreactive beta-endorphin secreted from cultured human corticotropin-secreting adenomas

Seven human corticotropin-secreting adenomas causing Cushing's disease or Nelson's syndrome were maintained in long-term culture. Pooled media from the individual adenomas were analyzed for the composition of their secretory products. From a radioimmunoassay (RIA) with 100% cross-reactivity for human beta-endorphin (beta h-EP) and beta-lipotropin (beta h-LPH), immunoreactive beta h-EP (IR X beta h-EP) was found to be the predominant secretory product after Sephadex G-50 analysis in 4 cases (40-80% of total IR), immunoreactive beta h-LPH (IR X beta h-LPH) predominated in 1 case, and both were equipresent in 2-cases. IR X beta h-EP was further purified by high-performance liquid chromatography (HPLC) and analyzed in 4 cases with ion-exchange chromatography on SP-Sephadex C-25 and a RIA which completely cross-reacts with beta h-EP, [N alpha-Ac]-beta h-EP, beta h-EP-(1-27) and [N alpha-Ac]-beta h-EP-(1-27). In all cases, the IR X beta h-EP was the main component (40-70%); the remaining IR material was attributable partially to [N alpha-Ac]-beta h-EP or other, less defined immunoreactive material. In 3 cases, enough IR X beta h-EP material was available for HPLC and to perform a radioreceptor assay using tritiated beta h-EP as primary ligand. The displacing potency of these preparations relative to synthetic beta h-EP was related to the content of the immunoreactive component eluting in the position of synthetic beta h-EP.

Preparation and properties of tritiated human [Tyr18, Trp27]-beta-endorphin

Tritiated [Tyr18, Trp27]-beta h-EP was prepared from the corresponding diiodotyrosine derivative by catalytic reduction in the presence of carrier free tritium gas. A photoaffinity probe for beta-endorphin (beta-EP) receptors was prepared by selective modification of [Tyr18, Trp27]-beta h-endorphin with 2-nitro-4-azidophenylsulfenyl chloride (2,4-NAPS-C1) under acidic conditions to yield [Trp18-2,4-NAPS-Trp27]-beta h-endorphin (NAPS-beta-EP). NAPS-beta-EP was purified by high performance liquid chromatography and characterized by ultraviolet absorption spectroscopy and peptide mapping. Tritiated NAPS-beta-EP was prepared from tritiated [Tyr18, Trp27]-beta h-endorphin with 2,4-NAPS-C1. The ability of NAPS-beta-EP to form covalent bonds to macromolecules due to photolysis was established using bovine serum albumin. The efficiency of photolytic cross-linking was 15% and the equilibrium dissociation constant was 1.3 X 10(-5) M.

Protease inhibition increases the analgesic potency of peptide E

Peptide E (PE), an opioid peptide from adrenal medulla, is known to possess very low analgesic potency when injected intracerebroventricularly in mice. The present study showed that PE analgesia was increased by co-injection with protease inhibitors (bacitracin and bestatin).

Evidence for the existence of [Gln9]-beta-lipotropin in human pituitary glands

The isolation of two peptides similar in amino acid composition to that of human beta-lipotropin is presented. Peptide patterns after enzymatic digestions of these two peptides by Staphylococcus aureus protease and by trypsin were nearly identical. Paper electrophoresis and amino acid analyses of acidic peptides generated from the enzymatic digestions of these two peptides indicate that there is an amide difference between the two peptides. It is proposed that this amide difference is in amino acid residue number nine, and that one is the human beta-lipotropin and the other its [Gln9] analog.

Binding characteristics of dermorphin, and [dermorphin1-7]-beta c-endorphin in rat brain membranes

Dermorphin and a camel beta-endorphin (beta c-EP) analog in which residues 1-7 correspond to the dermorphin sequence ([Dermorphin1-7]-beta c-EP) have been investigated with respect to their receptor binding characteristics using human and camel beta-EP as reference peptides. Tritiated dihydromorphine, [D-Ala2, D-Leu5]-enkephalin, ethylketocyclazocine and human beta-endorphin were used as primary ligands in the rat brain membrane preparation for radioreceptor assay. Camel beta-endorphin was the most potent peptide in all experiments. [Dermorphin1-7]-beta c-EP is significantly less potent towards 3H-ethylketocyclazocine and 3H-[D-Ala2, D-Leu5]-enkephalin but is as potent towards 3H-dihydromorphine and 3H-human beta-endorphin. Dermorphin itself weakly displaces tritiated dihydromorphine, [D-Ala2, D-Leu5]-enkephalin and ethylketocyclazocine (potency relative to camel beta-EP, 1-4%) but it is more potent (9%) in competition with tritiated human beta-endorphin. Dermorphin and the [Dermorphin-1-7]-beta c-EP appear to interact preferentially with mu opiate receptors.

Beta-endorphin. Binding activity of synthetic analogs with various chain lengths in neuroblastoma x glioma NG108-15 cell membranes

Inhibition of binding of beta h-endorphin or Leu-enkephalin by beta h-endorphin analogs of various chain lengths in memmbrane preparations of the neuroblastoma x glioma NG108-15 cells has been investigated. The removal of even a single residue from the C-terminus results in the inability of the resulting peptide to completely displace beta h-endorphin. In addition, the proportion of nondisplaceable binding increases with decreasing chain length.

Insulin-like growth factor I/somatomedin C (IGF-I/Sm C): comparison of natural, solid phase synthetic and recombinant DNA analog peptides in two radioligand assays

Investigation of the biologic activity of Insulin-like Growth Factor I/Somatomedin C (IGF-I/Sm C) has been hampered by the scarcity of purified material. The synthesis of this molecule by the solid phase procedure and an analog of IGF-I/Sm C by recombinant DNA technology offers promise that studies of the biologic activity of IGF-I/Sm C will soon be possible. We have found that natural IGF-I/Sm C and the two synthetic peptides behave similarly in two radioligand systems, providing evidence that these molecules possess the requisite structural integrity for use in such biological studies.

Human beta-endorphin. Synthesis and biological activity of analogs with modifications in residue positions 3, 4 or 5

Three analogs of human beta-endorphin (beta h-EP) have been synthesized by the solid-phase method: [Phe2, Gly4]-beta h-EP(I), [Tyr5]-beta h-EP (II), and [Trp5[-beta h-ET (III). Analogs I and II are related to the highly potent hybrid analog [dermorphin1-7]-beta c-EP (beta c-EP). Radio-receptor-binding and analgesic assays gave relative potencies as follows, respectively: beta h-FP, 100, 100; I, 51, 43; II, 64, 30; III, 15, 4. The high potency of [dermorphin 1-7]-beta c-EP is not due to any one of the following structural elements: D-Ala2, Phe3-Gly4, Tyr5, and Pro6. Increasing hydrophobicity in position 5 (Met in beta-EP) leads to decreasing biological activity.

Human beta-endorphin. Synthesis and biological activity of analogs with modification in residue positions 8, 27, and 9 or 11

Three analogs of human beta-endorphin (beta h-ER) were synthesized by the solid-phase method: [Gln8,Trp27]-beta h-EP (I), [Gln8,Arg9,Trp27]-beta h-EP (II), and [Gln9,Arg11,Trp27]-beta h-EP (III). Radioreceptor binding assay with use of tritiated beta h-EP as primary ligand gave relative potencies as follows: beta h-EP, 100;I, 778;II, 467;III, 449. Relative potencies in an analgesic assay were: beta h-EP, 100;I, 114;II, 165;III, 83. The 8-11 segment of beta h-EP can tolerate a net increase in charge of +2 without diminishing analgesic potency. The substitution of Glu8 may be one of the more dependable means of designing beta-endorphin antagonists.

Synthesis of human pancreatic growth hormone-releasing factor and two omission analogs by segment-coupling method in aqueous solution

The human growth hormone-releasing factor (GRF) peptides [GlyS15]-GRF-(1-15) (IV), trifluoroacetyl-GRF-(20-44) (VI), trifluoroacetyl-GRF-(18-44) (VIII), and trifluoroacetyl-GRF-(16-44) (X) were synthesized by the solid-phase method. Each of the peptides was reacted with citraconic anhydride and the trifluoroacetyl group was removed by reaction with 10% hydrazine in water. The citraconylated GRF-(1-15) peptide was coupled to the (20-44), (18-44) or (16-44) peptides by reaction with silver nitrate/N-hydroxysuccinimide to give GRF-(1-15)-(20-44) (XII), GRF-(1-15)-(18-44) (XIII), or GRF-(1-44), respectively. GRF-(1-44) was shown to stimulate the release of rat growth hormone from rat pituitary cells with an ED50 = 8.8 X 10(-11)M. Peptides XII and XIII were inactive, either as agonists or as antagonists of the action of GRF-(1-44).

Synthesis and biological activity of human inhibin-like peptide-(1-31)

A peptide containing 31 amino acids with inhibin-like activity has been synthesized by the solid-phase method. The synthetic product was shown to be homogeneous in high-performance liquid chromatography and paper electrophoresis. In the mouse pituitary incubation system, the follitropin-suppressing activity of the synthetic peptide was comparable to that of the natural product. It was also active in suppressing lutropin-releasing hormone-induced follitropin release in vivo in immature male rats.

Conformational comparison of human pituitary growth hormone and human chorionic somatomammotropin (human placental lactogen) by second-order absorption spectroscopy

Second-order absorption spectra strongly suggest the presence of a hydrogen bond between the single Trp of human pituitary growth hormone (hGH) and a carboxylate ion. This hydrogen-bonded complex is buried within the hydrophobic interior of the hGH molecule. Although the homologous Trp in human chorionic somatomammotropin [human placental lactogen, HCS(hPL)] is also buried within the hydrophobic interior of the molecule, there is no evidence that it is hydrogen bonded in the native protein. However, during the early stages of thermolysin digestion of HCS(hPL), both difference and second-order absorption spectra do indicate the transient presence of a similar hydrogen-bonded Trp-carboxylate complex. The molar extinction coefficients of hGH and HCS(hPL) have been refined.

beta-Endorphin: evidence for the existence of opioid and non-opioid binding components for the tritiated human hormone in NG108-15 cells

Human beta-endorphin (beta h-EP) binding on neuroblastoma X glioma hybrid NG108-15 cells using tritiated human beta endorphin (3H-beta h-EP) as a primary ligand was found to have a component which was not displacable with [D-Ser2 )-Leu-enkephalin-Thr6 (DSLET). The beta h-EP binding on these cells after saturation of the delta opiate sites with 200 nM DSLET was further characterized with synthetic beta h-EP analogs. The nonopioid binding site appears to recognize beta h-EP-(6-31), beta h-EP-(21-31) and beta h-EP-(28-31). Under these conditions, these COOH-terminal segments fully displace the tritiated beta h-EP. However, beta h-EP-(1-27) does not further displace 3H-beta h-EP in the presence of DSLET. The fact that a combination of DSLET and beta h-EP-(6-31) results in a full displacement of 3H-beta h-EP provides direct evidence for the existence of two binding sites for beta h-EP in NG108-15 cells, one recognizing the NH2-terminal enkephalin sequence and the other the non-opioid COOH-terminal segment.

Structural requirements and species specificity of the inhibition by beta-endorphin of heavy acetylcholinesterase from vertebrate skeletal muscle

The molecular forms of acetylcholinesterase in extracts of gastrocnemius muscle from four vertebrate species and in electric eel (Electrophorus) electric organ were separated and identified by low-salt precipitation and velocity sedimentation. The activity of the heavy insoluble (A12) form of human muscle acetylcholinesterase was inhibited by synthetic human beta-endorphin (500 mM). The homologous form in rat muscle extracts was poorly inhibited by human beta-endorphin at the same concentration, but was more effectively inhibited by camel beta-endorphin. The activities of heavy forms of pseudocholinesterase, present in small amounts in both species, were not reduced by beta-endorphin. Selective inhibition of homologous heavy forms of acetylcholinesterase activity by camel and human beta-endorphin was also seen in skeletal muscle extracts from frog and pigeon, but with decreased effectiveness. No inhibition was detectable in the heavy acetylcholinesterase form from extracts of electric organ tissue of the electric eel. The inhibition of heavy acetylcholinesterase activity in human muscle by human beta-endorphin was dependent on the presence of its NH2-terminal pentapeptide sequence. Maximal inhibitory potency depended on the presence of the entire amino acid sequence, since potency was considerably reduced in synthetic peptide analogues lacking either middle or COOH-terminal segments of beta-endorphin. The relative potency of beta-endorphin from various species as inhibitors of rat heavy acetylcholinesterase activity was also investigated. beta-Endorphin sequences most closely resembling that of the rat peptide (camel, equine) were most potent, whereas those with sequence differences of more than one amino-acid were less potent (turkey, human) or had no inhibitory activity (ostrich). The selective inhibition of heavy acetylcholinesterase by beta-endorphin thus exhibits species specificity, even among mammals, in which homologues of this molecular form of the enzyme are otherwise indistinguishable.

Beta-endorphin: demonstration of binding sites in three human neuroblastoma cell lines specific for the COOH-terminal segment of the human hormone

This communication reports for the first time specific binding sites in human neuroblastoma cells for human beta-endorphin (beta h-EP). Three cell lines (IMR-32, NMB and Kelly) were investigated and found to bind tritiated beta h-EP with an apparent dissociation constant of 2.2-4.2 nM. Further characterization with camel beta-EP and synthetic analogs indicated that the binding is most likely mediated by the COOH-terminal segments. beta h-EP-(6-31) had significant potency (15-75%) and beta h-EP-(1-27) was without displacing activity. The camel beta-EP has below 1% of the human beta-EP activity.

beta-Endorphin-induced analgesia is inhibited by synthetic analogs of beta-endorphin

Competitive antagonism of human beta-endorphin (beta h-EP)-induced analgesia by synthetic beta h-EP analogs with high in vitro opiate receptor binding to in vivo analgesic potency ratio has been demonstrated. A parallel shift of the dose-response curve for analgesia to the right was observed when either beta h-EP or [ Trp27 ] -beta h-EP was coinjected with various doses of [Gln8, Gly31 ]-beta h-EP-Gly-Gly-NH2, [Arg9,19,24,28,29]-beta h-EP, or [ Cys11 ,26, Phe27 , Gly31 ]-beta h-EP. It was estimated that the most potent antagonist, [Gln8, Gly31 ]-beta h-EP-Gly-NH2, is at least 200 times more potent than naloxone.

beta-Endorphin: characterization of binding sites specific for the human hormone in human glioblastoma SF126 cells

The established human glioblastoma cell line SF126 was found to bind tritiated human beta-endorphin (beta h-EP) in a saturable fashion. From displacement studies, the ED50 was estimated to be about 2.5 nM. The Kd was estimated as 1.9 X 10(-9) M and Scatchard analysis showed a biphasic pattern with a predominant low-affinity component. Binding reached a maximum at about 90 min at 22 degrees C and was instantaneously reversible. Tritiated [D-Ala2,D-Leu5]enkephalin and tritiated dihydromorphine did not bind to the cells. Sodium at a concentration of 150 mM decreased the specific binding by 80%. The interaction with the cellular binding site appeared to be mediated by the COOH-terminal segment of beta h-EP, as beta h-EP-(6-31) retained a high potency for displacing tritiated beta h-EP, and beta h-EP-(1-27) has no activity. Camel beta-EP was only about 1% as active as the human hormone.

Effects of beta-endorphin fragment 6-31 on morphine- and beta-endorphin-induced growth hormone and prolactin release

A fragment of human beta-endorphin (beta h-EP-(6-31] has been proposed as an endogenous inhibitor of beta-endorphin. We have evaluated the effects of the fragment on beta-endorphin- and morphine-induced prolactin and growth hormone release. It inhibited both morphine- and beta-endorphin-induced prolactin release, while it was ineffective on the release of growth hormone.

Development and characterization of a homologous radioimmunoassay for equine prolactin

A specific and sensitive homologous radioimmunoassay has been developed for equine prolactin, suitable for measuring prolactin concentrations in serum of horses. The sensitivity of the assay ranged from 0.4 to 0.6 ng/ml and the intra- and inter-assay coefficients of variation averaged 6.9 and 15.4%, respectively, for five doses of hormone. Cross-reactivity with other mammalian and nonmammalian prolactins and growth hormones was less than 20 and 0.3%, respectively. Cross-reactivity with equine growth hormone was less than 0.07%. Equine serum and pituitary extracts showed parallel dilution-response curves with equine prolactin. The percentage recovery of exogenous equine prolactin in serum was 89%. Preliminary analysis of several physiological samples (stallions, pregnant, and nonpregnant mares) yielded values from 0.6 to 12.0 ng/ml.

Isolation, structure, and synthesis of a human seminal plasma peptide with inhibin-like activity

A basic peptide isolated from pooled human seminal plasma exhibited inhibin-like activity by suppressing pituitary follicle-stimulating hormone secretion in vitro and in vivo. The peptide has been characterized and sequenced, and a 31-amino-acid synthetic replicate showed full biological activity in vitro.

beta-endorphin-(1-27) is an antagonist of beta-endorphin analgesia

beta h-Endorphin-(1-27), a naturally occurring fragment of human beta-endorphin (beta h-endorphin), diminishes the analgesic effect of beta h-endorphin when coinjected intra-cerebroventricularly into mice. A parallel shift in the dose-response curve of beta h-endorphin in the presence of beta h-endorphin-(1-27) suggests competition at the same site. The potency of beta h-endorphin-(1-27) in antagonizing analgesia is greater than 4 times greater than that of the opiate antagonist naloxone.