Interaction of ergovaline with serotonin receptor 5-HT2A in bovine ruminal and mesenteric vasculature

The C-8-S-isomers of ergot alkaloids - a review of biological and analytical aspects

Ergot alkaloids are secondary metabolites that are produced by fungi and contaminate cereal crops and grasses. The ergot alkaloids produced by Claviceps purpurea are the most abundant worldwide. The metabolites exist in two configurations, the C-8-R-isomer (R-epimer) and the C-8-S-isomer (S-epimer). These two configurations can interconvert to one another. Ergot alkaloids cause toxic effects after consumption of ergot-contaminated food and feed at various concentrations. For bioactivity reasons, the C-8-R-isomers have been studied to a greater extent than the C-8-S-isomer since the C-8-S-isomers were considered biologically inactive. However, recent studies suggest the contrary. Analytical assessment of ergot alkaloids now includes the C-8-S-isomers and high concentrations of specific C-8-S-isomers have been identified. The inclusion of the C-8-S-isomer in regulatory standards is reviewed. This review has identified that further research into the C-8-S-isomers of ergot alkaloids is warranted. In addition, the inclusion of the C-8-S-isomers into regulatory recommendations worldwide for food and feed should be implemented. The objectives of this review are to provide an overview of historic and current studies that have assessed the C-8-S-isomers. Specifically, this review will compare the C-8-R-isomers to the C-8-S-isomers with an emphasis on the biological activity and analytical assessment.

Ergot alkaloid consumption alters serotonin receptor-induced vasoactivity in ovine umbilical vasculature

Consumption of ergot alkaloids during the second half of gestation has been shown to decrease umbilical artery vasoactivity resulting in decreased birth weights. Negative vascular effects of ergot alkaloids are mediated predominantly through serotonergic and adrenergic receptors in other tissues. Vasoactivity of serotonin (5-HT) receptors 5-HT2A and 5-HT1B/1D in umbilical artery and vein from ewes receiving endophyte-infected seed (E + 1.77 mg ergovaline/hd/d) or a control total mixed ration (CON; 0 mg ergovaline/hd/d) tall fescue seed at d-110 and d-133 of gestation was evaluated. Gravid reproduction tracts were collected from ewes. Two-mm sections of umbilical artery and vein were exposed to increasing concentrations of a 5-HT1B/1D agonist and 5-HT2A agonist. The 5-HT1B/1D agonist did not stimulate a contractile response in artery or vein or either gestation time point. 5-HT2A agonist caused large responses in artery with greatest occurring at d-110 and decreasing in magnitude as days of gestation increased (p < 0.05). On d-110 and 133 of gestation, arteries from CON ewes had greater contractile response than arteries collected from E+ ewes (p < 0.05). Veins responded to increasing concentrations of the 5-HT2A agonist. Maximal d-110 vein response was greater than d-133 when exposed to 5-HT2A agonist (p < 0.05). Unlike the artery, veins from E+ ewes had greater d-133 contractile response than CON (p < 0.05). Vascular contractions of umbilical artery and vein are induced by 5-HT2A receptor activity and not 5-HT1B/1D. Umbilical artery 5-HT2A receptor activity was more sensitive to seed treatment and could be responsible for ergot alkaloid-induced intra-uterine growth restriction.

Duration of ergovaline exposure influences serotonin-mediated vasoactivity of bovine mesenteric vasculature

Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine peripheral and visceral vasculature. Ergovaline acts as both an agonist and an antagonist in bovine gut blood vessels through serotonin (5-HT) receptors and it appears that the type of action could be influenced by the extent of ERV exposure. Because it was unclear how the duration of ERV exposure influences 5-HT-mediated vasoactivity, experiments were designed to evaluate how simultaneous or prior ERV exposure influenced 5-HT-mediated vasoactivity of mesenteric artery (MA) and vein (MV) segments from Holstein steers (N = 10). Vessels were incubated in Krebs-Henseleit buffer containing 0, 0.01, or 0.1 μM ERV for 24 h prior to the 5-HT dose-response or exposed to fixed concentrations of 0, 0.01, or 0.1 μM ERV simultaneously during the 5-HT dose-response. Vessels were suspended in chambers of a multimyograph containing Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were exposed to increasing concentrations of 5-HT (5 × 10-8 M to 1 × 10-4 M) every 15 min and contractile responses were normalized as a percentage of the maximum contractile response induced by 120 mM KCl reference addition. Two-way analysis of variance was used to separately analyze data for each vessel type and duration of exposure using the MIXED procedure of SAS. When 5-HT concentration increased from 5 × 10-8 to 1 × 10-6 M, simultaneous addition of 0.1 μM ERV increased (P < 0.01) the contractile response of MV compared with additions of 0 and 0.01 μM ERV. At 1 × 10-4 M 5-HT, the simultaneous presence of 0.01 and 0.1 μM ERV decreased (P < 0.01) the contractile response of both MA and MV compared with 0 μM ERV addition. As 5-HT concentrations increased, the contractile response increased (P < 0.01) in both MA and MV with no previous ERV exposure, but decreased in MA and MV with 24 h prior exposure to 0.01 and 0.1 μM ERV. These data demonstrate that the duration of ERV exposure influences 5-HT-mediated vasoconstriction and likely vasorelaxation in bovine mesenteric vasculature. If ERV and 5-HT exposure occur simultaneously, ERV can act as a partial agonist of 5-HT-mediated vasoconstriction. If 5-HT exposure occurs after blood vessels have had prior ERV exposure, it appears that 5-HT may induce vasorelaxation of blood vessels. More research is needed to identify cellular and molecular mechanisms involved with 5-HT-mediated vasoactivity.

Influence of Prolonged Serotonin and Ergovaline Pre-Exposure on Vasoconstriction Ex Vivo

Ergot alkaloid mycotoxins interfere in many functions associated with serotonergic neurotransmitters. Therefore, the objective was to evaluate whether the association of serotonin (5-hydroxytryptamine, 5-HT) and ergot alkaloids during a 24 h pre-incubation could affect the vascular contractile response to ergot alkaloids. To evaluate the effects of 24 h exposure to 5-HT and ergot alkaloids (ergovaline, ERV), two assays were conducted. The first assay determined the half-maximal inhibitory concentration (IC₅₀) following the 24 h pre-exposure period, while the second assay evaluated the effect of IC₅₀ concentrations of 5-HT and ERV either individually or in combination. There was an interaction between previous exposure to 5-HT and ERV. Previous exposure to 5-HT at the IC₅₀ concentration of 7.57 × 10⁻⁷ M reduced the contractile response by more than 50% of control, while the exposure to ERV at IC₅₀ dose of 1.57 × 10⁻¹⁰ M tended to decrease (p = 0.081) vessel contractility with a response higher than 50% of control. The 24 h previous exposure to both 5-HT and ERV did not potentiate the inhibitory response of blood vessels in comparison with incubation with each compound alone. These results suggest receptor competition between 5-HT and ERV. More studies are necessary to determine the potential of 5-HT to treat toxicosis caused by ergot alkaloids.

Interaction between Grasses and Epichloë Endophytes and Its Significance to Biotic and Abiotic Stress Tolerance and the Rhizosphere

Cool-season grasses are the most common forage types in livestock operations and amenities. Several of the cool-season grasses establish mutualistic associations with an endophytic fungus of the Epichloë genus. The grasses and endophytic fungi have evolved over a long period of time to form host-fungus specific relationships that confer protection for the grass against various stressors in exchange for housing and nutrients to the fungus. This review provides an overview of the mechanisms by which Epichloë endophytes and grasses interact, including molecular pathways for secondary metabolite production. It also outlines specific mechanisms by which the endophyte helps protect the plant from various abiotic and biotic stressors. Finally, the review provides information on how Epichloë infection of grass and stressors affect the rhizosphere environment of the plant.

Ergot alkaloids reduce circulating serotonin in the bovine

Ergot alkaloids can interact with several serotonin (5-hydroxytryptamine [5-HT]) receptors provoking many physiological responses. However, it is unknown whether ergot alkaloid consumption influences 5-HT or its metabolites. Thus, two experiments were performed to evaluate the effect of ergot alkaloid feeding on 5-HT metabolism. In exp. 1, 12 Holstein steers (260 ± 3 kg body weight [BW]) were used in a completely randomized design. The treatments were the dietary concentration of ergovaline: 0, 0.862, and 1.282 mg/kg of diet. The steers were fed ad libitum, kept in light and temperature cycles mimicking the summer, and had blood sampled before and 15 d after receiving the treatments. The consumption of ergot alkaloids provoked a linear decrease (P = 0.004) in serum 5-HT. However, serum 5-hydroxytryptophan and 5-hydroxyindoleacetic acid did not change (P > 0.05) between treatments. In exp. 2, four ruminally cannulated Holstein steers (318 ± 3 kg BW) were used in a 4 × 4 Latin square design to examine the difference between seed sources on 5-HT metabolism. Treatments were: control-tall fescue seeds free of ergovaline, KY 32 seeds (L42-16-2K32); 5Way-endophyte-infected seeds, 5 way (L152-11-1739); KY31-endophyte-infected seeds, KY 31 (M164-16-SOS); and Millennium-endophyte-infected seeds, 3rd Millennium (L108-11-76). The endophyte-infected seed treatments were all adjusted to provide an ergovaline dosage of 15 μg/kg BW. The basal diet provided 1.5-fold the net energy requirement for maintenance. The seed treatments were dosed directly into the rumen before feeding. The experiment lasted 84 d and was divided into four periods. In each period, the steers received seeds for 7 d followed by a 14-d washout. Blood samples were collected on day 0 (baseline) and day 7 for evaluating the treatment response in each period. A 24 h urine collection was performed on day 7. Similar to exp. 1, serum 5-HT decreased (P = 0.008) with the consumption of all endophyte-infected seed treatments. However, there was no difference (P > 0.05) between the infected seeds. The urinary excretion of 5-hydroxyindoleacetic acid in the urine was not affected (P > 0.05) by the presence of ergot alkaloids. In conclusion, the consumption of ergot alkaloids decreases serum 5-HT with no difference between the source of endophyte-infected seeds in the bovine.

Use of Integrative Interactomics for Improvement of Farm Animal Health and Welfare: An Example with Fescue Toxicosis

Rapid scientific advances are increasing our understanding of the way complex biological interactions integrate to maintain homeostatic balance and how seemingly small, localized perturbations can lead to systemic effects. The ‘omics movement, alongside increased throughput resulting from statistical and computational advances, has transformed our understanding of disease mechanisms and the multi-dimensional interaction between environmental stressors and host physiology through data integration into multi-dimensional analyses, i.e., integrative interactomics. This review focuses on the use of high-throughput technologies in farm animal research, including health- and toxicology-related papers. Although limited, we highlight recent animal agriculture-centered reports from the integrative multi-‘omics movement. We provide an example with fescue toxicosis, an economically costly disease affecting grazing livestock, and describe how integrative interactomics can be applied to a disease with a complex pathophysiology in the pursuit of novel treatment and management approaches. We outline how ‘omics techniques have been used thus far to understand fescue toxicosis pathophysiology, lay out a framework for the fescue toxicosis integrome, identify some challenges we foresee, and offer possible means for addressing these challenges. Finally, we briefly discuss how the example with fescue toxicosis could be used for other agriculturally important animal health and welfare problems.

Molecular mechanisms in grass-Epichloë interactions: towards endophyte driven farming to improve plant fitness and immunity

All plants harbor many microbial species including bacteria and fungi in their tissues. The interactions between the plant and these microbes could be symbiotic, mutualistic, parasitic or commensalistic. Mutualistic microorganisms are endophytic in nature and are known to play a role in plant growth, development and fitness. Endophytes display complex diversity depending upon the agro-climatic conditions and this diversity could be exploited for crop improvement and sustainable agriculture. Plant-endophyte partnerships are highly specific, several genetic and molecular cascades play a key role in colonization of endophytes in host plants leading to rapid changes in host and endophyte metabolism. This results in the accumulation of secondary metabolites, which play an important role in plant defense against biotic and abiotic stress conditions. Alkaloids are one of the important class of metabolites produced by Epichloë genus and other related classes of endophytes and confer protection against insect and mammalian herbivory. In this context, this review discusses the evolutionary aspects of the Epichloë genus along with key molecular mechanisms determining the lifestyle of Epichloë endophytes in host system. Novel hypothesis is proposed to outline the initial cellular signaling events during colonization of Epichloë in cool season grasses. Complex clustering of alkaloid biosynthetic genes and molecular mechanisms involved in the production of alkaloids have been elaborated in detail. The natural defense and advantages of the endophyte derived metabolites have also been extensively discussed. Finally, this review highlights the importance of endophyte-arbitrated plant immunity to develop novel approaches for eco-friendly agriculture.

Ergot alkaloid mycotoxins: physiological effects, metabolism and distribution of the residual toxin in mice

The complex ergot alkaloids, ergovaline and ergotamine, cause dysregulation of physiological functions, characterised by vasoconstriction as well as thermoregulatory and cardiovascular effects in grazing livestock. To assess the effect of the mycotoxins, blood pressure and heart rate of male mice were measured, and metabolite profiling undertaken to determine relative abundances of both ergotamine and its metabolic products in body and brain tissue. Ergotamine showed similar cardiovascular effects to ergovaline, causing elevations in blood pressure and reduced heart rate. Bradycardia was preserved at low-levels of ergovaline despite no changes in blood pressure. Ergotamine was identified in kidney, liver and brainstem but not in other regions of the brain, which indicates region-specific effects of the toxin. The structural configuration of two biotransformation products of ergotamine were determined and identified in the liver and kidney, but not the brain. Thus, the dysregulation in respiratory, thermoregulatory, cardiac and vasomotor function, evoked by ergot alkaloids in animals observed in various studies, could be partially explained by dysfunction in the autonomic nervous system, located in the brainstem.

Ergot alkaloid exposure during gestation alters: II. Uterine and umbilical artery vasoactivity1

Previous research has shown that livestock exposed to ergot alkaloids results in decreased vasoactivity of gastrointestinal and peripheral vasculature. Little is known regarding the effect ergot alkaloid exposure during gestation may have on vasculature supporting the fetus. The objective of this study was to evaluate contractile responses of uterine and umbilical arteries collected from ewes consuming ergot alkaloids during gestation. On day 35 of gestation, 36 Suffolk ewes (78.24 ± 9.5 kg) were assigned to endophyte-infected (E+) or endophyte-free (E-) tall fescue seed treatments that were fed either throughout or switched on day 86 of gestation, creating four seed treatments E+E+, E+E-, E-E+, and E-E-. Ewes were fed E+ tall fescue seed to provide 1.77 mg of total ergovaline ⋅ hd-1 ⋅ d-1 with E- ewes receiving the same quantity of E- seed. Gestation was terminated on day 133, and sections of uterine artery and umbilical cord were surgically collected. Only collections from 28 ewes (n = 7/treatment) were of sufficient viability to proceed with the contractility experiments. Arteries were cleaned, sliced into 2-mm cross sections, and suspended in multi-myograph chambers containing 5 mL of continuously oxygenated Krebs-Henseleit buffer. Vessels were exposed to increasing concentrations (5 × 10-8 to 1 × 10-4 M) of norepinephrine, serotonin, ergotamine, and ergovaline (5 × 10-9 to 1 × 10-5M; extract of tall fescue seed) in 15-min intervals. Increasing concentrations of norepinephrine generated a contractile response by the uterine artery (P < 0.05), but no response in the umbilical artery. Increasing concentrations of serotonin resulted in negligible responses in uterine preparations, whereas umbilical artery preparations were responsive (P < 0.05) to serotonin. Ewes receiving E+E+ and E-E+ treatments had decreased vasoactivity in umbilical arteries to serotonin with a dextral shift in concentrations where the response curve initiated (P < 0.05). Interestingly, uterine arteries were not responsive to exposure to ergotamine or ergovaline, whereas umbilical arteries were responsive (P < 0.05). Umbilical arteries collected from ewes receiving E-E- and E+E- were more vasoactive to ergot alkaloids (P < 0.05) than other treatments. These findings indicate that maternal blood supply to the placenta appears protected from negative effects of ergot alkaloids; however, umbilical vasculature is not, and this could adversely influence fetal growth.