Effects of ergotamine on the central nervous system using untargeted metabolomics analysis in a mouse model.

The ergot alkaloid ergotamine is produced by Claviceps purpurea, a parasitic fungus that commonly infects crops and pastures of high agricultural and economic importance. In humans and livestock, symptoms of ergotism include necrosis and gangrene, high blood pressure, heart rate, thermoregulatory dysfunction and hallucinations. However, ergotamine is also used in pharmaceutical applications to treat migraines and stop post-partum hemorrhage. To define its effects, metabolomic profiling of the brain was undertaken to determine pathways perturbed by ergotamine treatment. Metabolomic profiling identified the brainstem and cerebral cortex as regions with greatest variation. In the brainstem, dysregulation of the neurotransmitter epinephrine, and the psychoactive compound 2-arachidonylglycerol was identified. In the cerebral cortex, energy related metabolites isobutyryl-L-carnitine and S-3-oxodecanoyl cysteamine were affected and concentrations of adenylosuccinate, a metabolite associated with mental retardation, were higher. This study demonstrates, for the first time, key metabolomic pathways involved in the behavioural and physiological dysfunction of ergot alkaloid intoxicated animals.

The discovery of a new antibody for BRIL-fused GPCR structure determination.

G-protein-coupled receptors (GPCRs)-the largest family of cell-surface membrane proteins-mediate the intracellular signal transduction of many external ligands. Thus, GPCRs have become important drug targets. X-ray crystal structures of GPCRs are very useful for structure-based drug design (SBDD). Herein, we produced a new antibody (SRP2070) targeting the thermostabilised apocytochrome b562 from Escherichia coli M7W/H102I/R106L (BRIL). We found that a fragment of this antibody (SRP2070Fab) facilitated the crystallisation of the BRIL-tagged, ligand bound GPCRs, 5HT1B and AT2R. Furthermore, the electron densities of the ligands were resolved, suggesting that SPR2070Fab is versatile and adaptable for GPCR SBDD. We anticipate that this new tool will significantly accelerate structure determination of other GPCRs and the design of small molecular drugs targeting them.

Biased Ligands Differentially Shape the Conformation of the Extracellular Loop Region in 5-HT2B Receptors.

G protein-coupled receptors are linked to various intracellular transducers, each pathway associated with different physiological effects. Biased ligands, capable of activating one pathway over another, are gaining attention for their therapeutic potential, as they could selectively activate beneficial pathways whilst avoiding those responsible for adverse effects. We performed molecular dynamics simulations with known ß-arrestin-biased ligands like lysergic acid diethylamide and ergotamine in complex with the 5-HT2B receptor and discovered that the extent of ligand bias is directly connected with the degree of closure of the extracellular loop region. Given a loose allosteric coupling of extracellular and intracellular receptor regions, we delineate a concept for biased signaling at serotonin receptors, by which conformational interference with binding pocket closure restricts the signaling repertoire of the receptor. Molecular docking studies of biased ligands gathered from the BiasDB demonstrate that larger ligands only show plausible docking poses in the ergotamine-bound structure, highlighting the conformational constraints associated with bias. This emphasizes the importance of selecting the appropriate receptor conformation on which to base virtual screening workflows in structure-based drug design of biased ligands. As this mechanism of ligand bias has also been observed for muscarinic receptors, our studies provide a general mechanism of signaling bias transferable between aminergic receptors.

Coalescing beneficial host and deleterious antiparasitic actions as an antischistosomal strategy.

Conventional approaches for antiparasitic drug discovery center upon discovering selective agents that adversely impact parasites with minimal host side effects. Here, we show that agents with a broad polypharmacology, often considered 'dirtier' drugs, can have unique efficacy if they combine deleterious effects on the parasite with beneficial actions in the host. This principle is evidenced through a screen for drugs to treat schistosomiasis, a parasitic flatworm disease that impacts over 230 million people. A target-based screen of a Schistosoma serotoninergic G protein coupled receptor yielded the potent agonist, ergotamine, which disrupted worm movement. In vivo, ergotamine decreased mortality, parasite load and intestinal egg counts but also uniquely reduced organ pathology through engagement of host GPCRs that repressed hepatic stellate cell activation, inflammatory damage and fibrosis. The unique ability of ergotamine to engage both host and parasite GPCRs evidences a future strategy for anthelmintic drug design that coalesces deleterious antiparasitic activity with beneficial host effects.

Contractile Response of Bovine Lateral Saphenous Vein to Ergotamine Tartrate Exposed to Different Concentrations of Molecularly Imprinted Polymer.

Ergot alkaloids, in their active isomeric form, affect animal health and performance, and adsorbents are used to mitigate toxicities by reducing bioavailability. Adsorbents with high specificity (molecularly imprinted polymers: MIP) adsorb ergot alkaloids in vitro, but require evaluation for biological implications. Using ex vivo myography, synthetic polymers were evaluated for effects on the bioactivity of ergotamine tartrate (ETA). Polymers were first evaluated using isotherms. Lateral saphenous veins were collected from 17 steers for four independent studies: dose response of ETA, adsorbent dose response, validation of pre-myograph incubation conditions and MIP/ non-molecularly imprinted polymer (NIP) comparison. Norepinephrine normalized percent contractile response to increasing ETA exhibited a sigmoidal dose response (max: 88.47 and log of the effective molar concentration (EC50) (-log [ETA]) of 6.66 ± 0.17 M). Although sample preparation time affected contractile response (p < 0.001), pre-myograph incubation temperature (39 vs. 21 °C, 1 h) had no effect (p > 0.05). Isothermal adsorption showed a maximum adsorption of 3.27E-008 moles·mg-1 and affinity between 0.51 and 0.57 mg (R²: 0.83-0.92) for both polymers, with no significant difference between polymers (p > 0.05). No significant differences in maximum inhibitory (p = 0.96) and IC50 responses (p = 0.163) between MIP and NIP were noticed. Normalized percent contraction could be predicted from the in vitro adsorption data (R² = 0.87, p < 0.01), for both polymers. These studies indicate that synthetic polymers are potentially effective adsorbents to mitigate ergot toxicity caused by ergot alkaloids, with little evidence of significant differences between MIP and NIP in aqueous media.

5-HT2C Receptor Structures Reveal the Structural Basis of GPCR Polypharmacology.

Drugs frequently require interactions with multiple targets-via a process known as polypharmacology-to achieve their therapeutic actions. Currently, drugs targeting several serotonin receptors, including the 5-HT2C receptor, are useful for treating obesity, drug abuse, and schizophrenia. The competing challenges of developing selective 5-HT2C receptor ligands or creating drugs with a defined polypharmacological profile, especially aimed at G protein-coupled receptors (GPCRs), remain extremely difficult. Here, we solved two structures of the 5-HT2C receptor in complex with the highly promiscuous agonist ergotamine and the 5-HT2A-C receptor-selective inverse agonist ritanserin at resolutions of 3.0 Å and 2.7 Å, respectively. We analyzed their respective binding poses to provide mechanistic insights into their receptor recognition and opposing pharmacological actions. This study investigates the structural basis of polypharmacology at canonical GPCRs and illustrates how understanding characteristic patterns of ligand-receptor interaction and activation may ultimately facilitate drug design at multiple GPCRs.

Assessment of the transmembrane domain structures in GPCR Dock 2013 models.

The community-wide blind prediction of G-protein coupled receptor (GPCR) structures and ligand docking has been conducted three times and the quality of the models was primarily assessed by the accuracy of ligand binding modes. The seven transmembrane (TM) helices of the receptors were taken as a whole; thus the model quality within the 7TM domains has not been evaluated. Here we evaluate the 7TM domain structures in the models submitted for the last round of prediction - GPCR Dock 2013. Applying the 7 × 7 RMSD matrix analysis described in our prior work, we show that the models vary widely in prediction accuracy of the 7TM structures, exhibiting diverse structural differences from the targets. For the prediction of the 5-hydroxytryptamine receptors, the top 7TM models are rather close to the targets, which however are not ranked top by ligand-docking. On the other hand, notable deviations of the TMs are found in in the previously identified top docking models that closely resemble other receptors. We further reveal reasons of success and failure in ligand docking for the models. This current assessment not only complements the previous assessment, but also provides important insights into the current status of GPCR modeling and ligand docking.

Structural insights into the extracellular recognition of the human serotonin 2B receptor by an antibody.

Monoclonal antibodies provide an attractive alternative to small-molecule therapies for a wide range of diseases. Given the importance of G protein-coupled receptors (GPCRs) as pharmaceutical targets, there has been an immense interest in developing therapeutic monoclonal antibodies that act on GPCRs. Here we present the 3.0-Å resolution structure of a complex between the human 5-hydroxytryptamine 2B (5-HT2B) receptor and an antibody Fab fragment bound to the extracellular side of the receptor, determined by serial femtosecond crystallography with an X-ray free-electron laser. The antibody binds to a 3D epitope of the receptor that includes all three extracellular loops. The 5-HT2B receptor is captured in a well-defined active-like state, most likely stabilized by the crystal lattice. The structure of the complex sheds light on the mechanism of selectivity in extracellular recognition of GPCRs by monoclonal antibodies.

A dynamic view of molecular switch behavior at serotonin receptors: implications for functional selectivity.

Functional selectivity is a property of G protein-coupled receptors that allows them to preferentially couple to particular signaling partners upon binding of biased agonists. Publication of the X-ray crystal structure of serotonergic 5-HT1B and 5-HT2B receptors in complex with ergotamine, a drug capable of activating G protein coupling and ß-arrestin signaling at the 5-HT1B receptor but clearly favoring ß-arrestin over G protein coupling at the 5-HT2B subtype, has recently provided structural insight into this phenomenon. In particular, these structures highlight the importance of specific residues, also called micro-switches, for differential receptor activation. In our work, we apply classical molecular dynamics simulations and enhanced sampling approaches to analyze the behavior of these micro-switches and their impact on the stabilization of particular receptor conformational states. Our analysis shows that differences in the conformational freedom of helix 6 between both receptors could explain their different G protein-coupling capacity. In particular, as compared to the 5-HT1B receptor, helix 6 movement in the 5-HT2B receptor can be constrained by two different mechanisms. On the one hand, an anchoring effect of ergotamine, which shows an increased capacity to interact with the extracellular part of helices 5 and 6 and stabilize them, hinders activation of a hydrophobic connector region at the center of the receptor. On the other hand, this connector region in an inactive conformation is further stabilized by unconserved contacts extending to the intracellular part of the 5-HT2B receptor, which hamper opening of the G protein binding site. This work highlights the importance of considering receptor capacity to adopt different conformational states from a dynamic perspective in order to underpin the structural basis of functional selectivity.

Cyclolization of D-lysergic acid alkaloid peptides.

The tripeptide chains of the ergopeptines, a class of pharmacologically important D-lysergic acid alkaloid peptides, are arranged in a unique bicyclic cyclol based on an amino-terminal α-hydroxyamino acid and a terminal orthostructure. D-lysergyl-tripeptides are assembled by the nonribosomal peptide synthetases LPS1 and LPS2 of the ergot fungus Claviceps purpurea and released as N-(D-lysergyl-aminoacyl)-lactams. We show total enzymatic synthesis of ergopeptines catalyzed by a Fe²âº/2-ketoglutarate-dependent dioxygenase (EasH) in conjunction with LPS1/LPS2. Analysis of the reaction indicated that EasH introduces a hydroxyl group into N-(D-lysergyl-aminoacyl)-lactam at α-C of the aminoacyl residue followed by spontaneous condensation with the terminal lactam carbonyl group. Sequence analysis revealed that EasH belongs to the wide and diverse family of the phytanoyl coenzyme A hydroxylases. We provide a high-resolution crystal structure of EasH that is most similar to that of phytanoyl coenzyme A hydroxylase, PhyH, from human.

Structural basis for molecular recognition at serotonin receptors.

Serotonin or 5-hydroxytryptamine (5-HT) regulates a wide spectrum of human physiology through the 5-HT receptor family. We report the crystal structures of the human 5-HT1B G protein-coupled receptor bound to the agonist antimigraine medications ergotamine and dihydroergotamine. The structures reveal similar binding modes for these ligands, which occupy the orthosteric pocket and an extended binding pocket close to the extracellular loops. The orthosteric pocket is formed by residues conserved in the 5-HT receptor family, clarifying the family-wide agonist activity of 5-HT. Compared with the structure of the 5-HT2B receptor, the 5-HT1B receptor displays a 3 angstrom outward shift at the extracellular end of helix V, resulting in a more open extended pocket that explains subtype selectivity. Together with docking and mutagenesis studies, these structures provide a comprehensive structural basis for understanding receptor-ligand interactions and designing subtype-selective serotonergic drugs.

Structural features for functional selectivity at serotonin receptors.

Drugs active at G protein-coupled receptors (GPCRs) can differentially modulate either canonical or noncanonical signaling pathways via a phenomenon known as functional selectivity or biased signaling. We report biochemical studies showing that the hallucinogen lysergic acid diethylamide, its precursor ergotamine (ERG), and related ergolines display strong functional selectivity for ß-arrestin signaling at the 5-HT2B 5-hydroxytryptamine (5-HT) receptor, whereas they are relatively unbiased at the 5-HT1B receptor. To investigate the structural basis for biased signaling, we determined the crystal structure of the human 5-HT2B receptor bound to ERG and compared it with the 5-HT1B/ERG structure. Given the relatively poor understanding of GPCR structure and function to date, insight into different GPCR signaling pathways is important to better understand both adverse and favorable therapeutic activities.

Capillary electrophoretic determination of antimigraine formulations containing caffeine, ergotamine, paracetamol and domperidone or metoclopramide.

A novel, fast, sensitive and specific technique using capillary electrophoresis coupled to a diode array detector has been developed for the separation and simultaneous determination of two antimigraine mixtures in tablet formulation. The two combinations are ergotamine tartrate (ERG), caffeine (CAF) and paracetamol (PAR) with either domperidone (DOM), combination (I) or metoclopramide (MET), combination (II). The proposed method utilized a fused silica capillary (55 cm × 75 µm i.d.) and background electrolyte composed of phosphate buffer (25 mM, pH 9.8). The separation was achieved at 20 KV applied voltage and at 25°C. The described method was linear over the range of 1-80 and 2-100 µg/mL for CAF and MET, respectively, and 1-80 µg/mL for DOM, ERG and PAR. Intra-day and inter-day relative standard deviation (n = 5) was ≤1.10%. The limits of detection of CAF and PAR were 0.20 and 0.10 µg/mL, respectively, and 0.50 µg/mL for MET, DOM and ERG. Other aspects of analytical validation were also evaluated. The proposed method was successfully applied to the analysis of the two combinations in their tablets. Therefore, the proposed method is suitable for the routine control of these ingredients in multicomponent dosage forms.

Degradation and epimerization of ergot alkaloids after baking and in vitro digestion.

The degradation and epimerization of ergot alkaloids (EAs) in rye flour were investigated after baking cookies and subsequently subjecting them to an in vitro digestion model. Different steps of digestion were analyzed using salivary, gastric, and duodenal juices. The degradation and bidirectional conversion of the toxicologically relevant (R)-epimers and the biologically inactive (S)-epimers for seven pairs of EAs were determined by a HPLC method coupled with fluorescence detection. Baking cookies resulted in degradation of EAs (2-30 %) and a shift in the epimeric ratio toward the (S)-epimer for all EAs. The applied digestion model led to a selective toxification of ergotamine and ergosine, two ergotamine-type EAs. The initial percentage of the toxic (R)-epimer in relation to the total toxin content was considerably increased after digestion of cookies. Ergotamine and ergosine increased from 32 to 51 % and 35 to 55 %, respectively. In contrast, EAs of the ergotoxine type (ergocornine, α- and ß-ergocryptine, and ergocristine) showed an epimeric shift toward their biologically inactive (S)-epimers. Further experiments indicated that the selective epimerization of ergotamine EAs occurs in the duodenal juice only. These results demonstrate that toxification of EAs in the intestinal tract should be taken into consideration.

Dihydroergotamine, ergotamine, methysergide and sumatriptan - basic science in relation to migraine treatment.

The 5-hydroxytryptamine (5-HT) receptor family mediates the effects of several drugs highly effective in migraine primarily by activating 5-HT(1B) , 5-HT(1D) , and 5-HT(1F) receptors. Ergotamine, dihydroergotamine, and methysergide, as well as the "triptan" sumatriptan, are all agonists for these receptors. The receptor profile and degree of selectivity of these four drugs differ, which is reflected by their side effects that limit their use in the acute and prophylactic treatment of migraine. The acute antimigraine efficacy of these remedies is very much dependent on the formulation used where, in general, parenteral formulations are more effective in reliving the symptoms of a migraine attack.

Fragmentation patterns of selected ergot alkaloids by electrospray ionization tandem quadrupole mass spectrometry.

Tall fescue toxicosis and other maladies in livestock result from the ingestion of vasoconstrictive ergot alkaloids produced by fungal endophytes associated symbiotically with the grass. In order to facilitate future analyses of grass extracts considered responsible for outbreak of related livestock diseases, we examined the electrospray ionization mass spectra of specific ergot alkaloids under conditions that permit protonation. Our purposes were both to record the spectra with interpretation of mechanisms of fragmentation and to derive commonalities that would allow the prediction of mass spectra of related compounds for which standards were not readily available. With [M + H](+) values in parentheses, water-insoluble lysergic acid peptide ergot derivatives ergovaline (m/z 534), ergotamine (m/z 582), ergocornine (m/z 562), ergocryptine (m/z 576) and ergocrystine (m/z 610) exhibited a consistent loss of water (-18 u) from the C-12' alpha-hydroxy functionality. Of this group, ergovaline and ergotamine generated an m/z 320 fragment deriving from cleavage of ring E amide and ether functions with retention of the peptide ring system methyl group. Ergocornine, ergocryptine and ergocrystine similarly formed an m/z 348 fragment with retention of isopropyl. These assignments were supported by the lack of similar fragments from the water-soluble ergot ergonovine, which lacks a peptide ring system. Clavine-type ergot alkaloids lysergic acid and lysergol lack any substituents beyond simple ones directly on the C-8 position and, similarly to ergonovine, lack significant fragments at m/z 268, 251 and 225 shared by the peptide ergot alkaloids.

Antagonistic effects of simultaneous exposure of ergot alkaloids on kidney adenosine triphosphatase system.

Much of the research on fescue toxicosis has concentrated on evaluating animal response to grazing endophyte-infected (E+) versus endophyte-free tall fescue or the effects of single toxins such as ergonovine (EN), ergovaline (EV), or ergotamine (ET) on animal performance. Such approaches have eliminated the opportunity to test the possible additive, synergistic, or antagonistic interactions of one or more ergot alkaloids with the other ergot alkaloids found in E+ tall fescue. This study was conducted to determine the effects of simultaneous exposure of pairs of EN, EV, and ET on the kidney adenosine triphosphatase (ATPase) system in vitro. Tests were performed using three separate rat kidney homogenates and were repeated four times at concentrations of 0, 75, and 200 microM. Individually, EN, EV, and ET induced dose-dependent inhibitions of kidney Na(+)/K(+) ATPase, with EN being most potent, followed by purified EV, and then by ET. The ergot alkaloids inhibited Mg(2+) ATPase to a lesser degree than Na(+)/K(+) ATPase, with EN again being the most potent toxin. Simultaneous exposure to any combination of the ergot alkaloid pairs tested (EV + ET, EV + EN, and ET + EN) resulted in significant interactions (P < 0.05), indicating antagonistic effects on the inhibition of Na(+)/K(+) ATPase and Mg(2+) ATPase for most concentration combinations. These interactions suggest that in studies of the effects of any ergot alkaloid on animal performance, effects of other ergot alkaloids may also be present. Effects may not be additive, as was the case in this study, and the presence of one toxin may enhance or hinder the effectiveness of others.

The pharmacology of ergotamine and dihydroergotamine.

The ergot alkaloids are a family of chemical entities that have many pharmacologic effects. Their diversity results from their interaction with multiple receptors, their variable receptor affinity and intrinsic activity, and their variable organ-specific receptor access. Ergotamine tartrate (ET) was one of the first ergot alkaloids to be isolated. Dihydroergotamine (DHE) is synthesized by reducing an unsaturated bond in ergotamine (E); this modification results in a changed pharmacologic profile. Dihydroergotamine exhibits greater alpha-adrenergic antagonist activity and much less potent arterial vasoconstriction and emetic potential. Both E and DHE are 5-HT1A, 5-HT1B, 5-HT1D, and 5-HT1F receptor agonists. The vasoconstrictor activities of these ergot compounds have long been believed to be the basis of their clinical effects, but recent evidence suggests that their antimigraine action may result in part from their inhibitory effects on neurogenic inflammation and neuronal transmission and not from vasoconstriction. Improvements in assay methodology have provided more accurate determination of the pharmacokinetics of E and DHE. The long duration of action appears to result from active metabolites and tight tissue binding. Intranasal (IN) administration of DHE delivers adequate plasma concentrations of the drug without the need for parenteral administration and should further expand its role in migraine pharmacotherapy.

Mass spectrometry as an aid to the identification of ergots and dihydroergots: comparison of hard and soft ionization techniques.

An analysis of the 70 eV electron impact (EI) and fast atom bombardment (FAB) mass spectral features of a variety of ergoline and dihydroergoline derivatives of therapeutic importance is presented with emphasis upon analytical utility. Derivatives which carry non-peptide based C-8 substituents are fully characterized by EI-MS through provision of molecular wieght evidence and fragment ions diagnostic of both the ergoline skeleton and the C-8 substituent. Peptidic ergolines and dihydroergolines are poorly characterized by EI-MS, but their FAB-MS clearly reveal [M + 1]+ (high intensity) and [M - 1]- (high to low intensity) ions in positive and negative ion spectra, respectively. Negative FAB spectra of salts also display diagnostic anion-base conjugate ions.