Quantitative mass spectrometric analysis and post-extraction stability assessment of the euglenoid toxin euglenophycin

Euglenophycin is a recently discovered toxin produced by at least one species of euglenoid algae. The toxin has been responsible for several fish mortality events. To facilitate the identification and monitoring of euglenophycin in freshwater ponds, we have developed a specific mass spectrometric method for the identification and quantitation of euglenophycin. The post-extraction stability of the toxin was assessed under various conditions. Euglenophycin was most stable at room temperature. At 8 °C there was a small, but statistically significant, loss in toxin after one day. These methods and knowledge of the toxin's stability will facilitate identification of the toxin as a causative agent in fish kills and determination of the toxin's distribution in the organs of exposed fish.

Identification of euglenophycin--a toxin found in certain euglenoids

Currently cyanoprokaryotic algae, diatoms, haptophytes, dinoflagellates, euglenoids, and rhaphidophytes are known to produce algal toxins. A previous study by the authors reported euglenoid algae producing toxin(s) in aquaculture ponds, with confirmation based on positive fish bioassays following exposure to the isolated clonal algal cultures. Toxicity was observed in euglenoid culture isolates obtained from the pond as well as a clonal, culture collection taxon. Here we provide conclusive evidence for euglenoid toxin production, including HPLC/MS, MS/MS, and NMR analyses of a clonal (non-axenic) isolate of Euglena sanguinea grown in batch culture. Following wet chemical serial fractionation, toxic activity was identified in both the methanol and hexane extracts. These extracts were then purified using HPLC. Bioassay-guided HPLC fractionation of these two extracts demonstrated that a single class of toxic compounds, identical in mass and similar in molecular structure, was produced by this organism. The toxic compounds exhibited a maximal UV absorbance at 238nm and gave diagnostic mass peaks at 306 (MH(+)) and 288 (MH(+)-H(2)O). Unambiguous molecular structural determination was carried out by high field NMR analysis operating in 1- and 2-dimensions. Though a predominant isomer represented the bulk of the toxin, several stereo- and structural isomers were evidenced by NMR, and HPLC/MS. This compound is an alkaloid similar in structure to fire ant venom. The compound exhibits ichthyotoxic, herbicidal and anticancer activity at low ppm to ppb dosages.

Isolation, purification, and full NMR assignments of cyclopamine from Veratrum californicum

BACKGROUND

The Hedgehog signaling pathway is essential for embryogenesis and for tissue homeostasis in the adult. However, it may induce malignancies in a number of tissues when constitutively activated, and it may also have a role in other forms of normal and maladaptive growth. Cyclopamine, a naturally occurring steroidal alkaloid, specifically inhibits the Hedgehog pathway by binding directly to Smoothened, an important Hedgehog response element. To use cyclopamine as a tool to explore and/or inhibit the Hedgehog pathway in vivo, a substantial quantity is required, and as a practical matter cyclopamine has been effectively unavailable for usage in animals larger than mice.

RESULTS

In this paper, we report a rapid and efficient isolation and purification of large quantities of cyclopamine from the roots and rhizomes of Veratrum californicum Dur. (the Corn Lily or Western false hellebore). We also provide unambiguous assignments of the carbon and proton resonances by using the multinuclear spectra and the spin coupling networks.

CONCLUSION

This method could meet a very real need within diverse scientific communities by allowing cyclopamine to become more readily available.

Antimicrobial activity in the common seawhip, Leptogorgia virgulata (Cnidaria: Gorgonaceae)

Antimicrobial activity was examined in the gorgonian Leptogorgia virgulata (common seawhip) from South Carolina waters. Extraction and assay protocols were developed to identify antimicrobial activity in crude extracts of L. virgulata. Detection was determined by liquid growth inhibition assays using Escherichia coli BL21, Vibrio harveyii, Micrococcus luteus, and a Bacillus sp. isolate. This represents the first report of antimicrobial activity in L. virgulata, a temperate/sub-tropical coral of the western Atlantic Ocean. Results from growth inhibition assays guided a fractionation scheme to identify active compounds. Reverse-phase HPLC, HPLC-mass spectrometry, and 1H and 13C NMR spectroscopy were used to isolate, purify, and characterize metabolites in antimicrobial fractions of L. virgulata. Corroborative HPLC-MS/NMR evidence validated the presence of homarine and a homarine analog, well-known emetic metabolites previously isolated from L. virgulata, in coral extracts. In subsequent assays, partially-purified L. virgulata fractions collected from HPLC-MS fractionation were shown to contain antimicrobial activity using M. luteus and V. harveyii. This study provides evidence that homarine is an active constituent of the innate immune system in L. virgulata. We speculate it may act synergistically with cofactors and/or congeners in this octocoral to mount a response to microbial invasion and disease.

Demonstration of toxicity to fish and to mammalian cells by Pfiesteria species: comparison of assay methods and strains

Toxicity and its detection in the dinoflagellate fish predators Pfiesteria piscicida and Pfiesteria shumwayae depend on the strain and the use of reliable assays. Two assays, standardized fish bioassays (SFBs) with juvenile fish and fish microassays (FMAs) with larval fish, were compared for their utility to detect toxic Pfiesteria. The comparison included strains with confirmed toxicity, negative controls (noninducible Pfiesteria strains and a related nontoxic cryptoperidiniopsoid dinoflagellate), and P. shumwayae strain CCMP2089, which previously had been reported as nontoxic. SFBs, standardized by using toxic Pfiesteria (coupled with tests confirming Pfiesteria toxin) and conditions conducive to toxicity expression, reliably detected actively toxic Pfiesteria, but FMAs did not. Pfiesteria toxin was found in fish- and algae-fed clonal Pfiesteria cultures, including CCMP2089, but not in controls. In contrast, noninducible Pfiesteria and cryptoperidiniopsoids caused no juvenile fish mortality in SFBs even at high densities, and low larval fish mortality by physical attack in FMAs. Filtrate from toxic strains of Pfiesteria spp. in bacteria-free media was cytotoxic. Toxicity was enhanced by bacteria and other prey, especially live fish. Purified Pfiesteria toxin extract adversely affected mammalian cells as well as fish, and it caused fish death at environmentally relevant cell densities. These data show the importance of testing multiple strains when assessing the potential for toxicity at the genus or species level, using appropriate culturing techniques and assays.

Microfluorimetric analysis of a purinergic receptor (P2X7) in GH4C1 rat pituitary cells: effects of a bioactive substance produced by Pfiesteria piscicida

Pfiesteria piscicida Steidinger & Burkholder is a toxic dinoflagellate that leads to fish and human toxicity. It produces a bioactive substance that leads to cytotoxicity of GH4C1 rat pituitary cells. Extracellular adenosine 5'-triphosphate (ATP) acting on P2X7 purinergic receptors induces the formation of a nonselective cation channel, causing elevation of the cytosolic free calcium followed by a characteristic permeabilization of the cell to progressively larger ions and subsequent cell lysis. We investigated whether GH4C1 rat pituitary cells express functional P2X7 receptors, and if so, are they activated by a bioactive substance isolated from toxic P. piscicida cultures. We tested the selective agonist 2'-3'-O-(benzoyl-4-benzoyl)-ATP (BzATP) and antagonists piridoxalphosphate-6-azophenyl-2'-4'-disulfonic acid (PPADS) and oxidized-ATP (oxATP) using elevated cytosolic free calcium in Fura-2 loaded cells, and induced permeability of these cells to the fluorescent dye YO-PRO-1 as end points. We demonstrated that in GH4C1 cells, BzATP induces both the elevation of cytosolic free calcium and the permeabilization of the cell membrane. ATP-induced membrane permeabilization was inhibited by PPADS reversibly and by oxATP irreversibly. The putative Pfiesteria toxin (pPfTx) also elevated cytosolic free calcium in Fura-2 in GH4C1 cells and increased the permeability to YO-PRO-1 in a manner inhibited fully by oxATP. This study indicates that GH4C1 cells express a purinoceptor with characteristics consistent with the P2X7 subtype, and that pPfTx mimics the kinetics of cell permeabilization by ATP.

Current progress in isolation and characterization of toxins isolated from Pfiesteria piscicida

The isolation and partial purification of toxic substances derived from Pfiesteria piscicida Steidinger & Burkholder extracts is described. Four distinct bioassay systems were used to monitor bioactivity of the P. piscicida extracts, including a high throughput cell cytotoxicity assay and a reporter gene assay as well as assays using brine shrimp and fish. Using these bioassays to guide fractionation, we have isolated two distinct, active fractions from Pfiesteria culture medium and cell mass extracts on the basis of their solubility characteristics. We have identified and characterized a bioactive lipophilic substance from Pfiesteria-derived extracts as di(2-ethylhexyl)phthalate, a commonly used plasticizer. The source of this typically man-made substance has been identified as originating from Instant Ocean (Aquarium Systems, Mentor, OH, USA), a commercially available seawater salt mixture used to prepare our mass culture growth medium. We have developed chromatographic methodology to isolate a bioactive polar compound isolated from extracts of Pfiesteria culture and presently report the characterization of the activity of this substance. The molecular structural analysis of the polar active component(s) using mass spectrometry and nuclear magnetic resonance spectroscopy is currently under way.

Biomonitoring brevetoxin exposure in mammals using blood collection cards

A method has been tested in laboratory mice to monitor for the presence of brevetoxins in blood after exposure. The use of blood collection cards is an adaptation of a method employed for routine diagnostic and genetic testing of newborns. Blood is collected and applied to a 0.5-inch diameter circle on a specially prepared blood collection card and allowed to dry. The blood spots are then extracted and the presence of toxin activity is first screened using a high throughput receptor binding assay. Positive samples are then examined for specific brevetoxin congeners by liquid chromatography-tandem mass spectrometry. Preliminary experiments tested the efficiency and linearity of toxin extraction from blood spiked with brevetoxin-3 (PbTx-3). Blood from treated mice was tested for the presence of brevetoxin at different times following exposure to a sublethal dose (180 microg/kg PbTx-3). Brevetoxin activity determined by receptor assay increased to 25 +/- 7.4 nM PbTx-3 equivalents within 4 hr after exposure and was still detectable in three of four animals 24 hr after exposure. Tandem mass spectrometry provided confirmation of PbTx-3, which also increased for the time points between 0.5 and 4.0 hr exposure. However, PbTx-3 was not detected at 24 hr, which suggested the formation of a biologically active metabolite. We anticipate that this approach will provide a method to biomonitor brevetoxins in living marine resources (e.g., finfish), protected species, and humans.

Identification of a P2X7 receptor in GH(4)C(1) rat pituitary cells: a potential target for a bioactive substance produced by Pfiesteria piscicida

We examined the pharmacologic activity of a putative toxin (pPfTx) produced by Pfiesteria piscicida by characterizing the signaling pathways that induce the c-fos luciferase construct in GH(4)C(1) rat pituitary cells. Adenosine-5'-triphosphate (ATP) was determined to increase and, at higher concentrations, decrease luciferase activity in GH(4)C(1) rat pituitary cells that stably express c-fos luciferase. The inhibition of luciferase results from cytotoxicity, characteristic of the putative P. piscicida toxin (pPfTx). The actions of both pPfTx and ATP to induce c-fos luciferase were inhibited by the purinogenic receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS). Further characterization of a P2X receptor on the GH(4)C(1) cell was determined by the analog selectivity of P2X agonists. The P2X1/P2X3 agonist alpha,beta-methylene ATP (alpha,beta-MeATP) failed to increase or decrease c-fos luciferase. However, the P2X7 agonist 2',3'-(4-benzoyl)benzoyl ATP (BzATP), which had a predominant cytotoxic effect, was more potent than ATP. Immunoblot analysis of GH(4)C(1) cell membranes confirmed the presence of a 70-kDa protein that was immunoreactive to an antibody directed against the carboxy-terminal domain unique to the P2X7 receptor. The P2X7 irreversible antagonist oxidized-ATP (oxATP) inhibited the action of ATP, BzATP, and pPfTx. These findings indicate that GH(4)C(1) cells express purinogenic receptors with selectivity consistent with the P2X7 subtype and that this receptor pathway mediates the induction of the c-fos luciferase reporter gene by ATP and the putative Pfiesteria toxin

Detection of domoic acid in northern anchovies and California sea lions associated with an unusual mortality event

The occurrence of an unusual mortality event involving California sea lions (Zalophus californianus) along the central California coast in May 1998 was recently reported. The potent neurotoxin domoic acid (DA), produced naturally by the diatom Pseudo-nitzschia australis and transmitted to the sea lions via planktivorous northern anchovies (Engraulis mordax), was identified as the probable causative agent. Details of DA analyses for anchovy tissues and sea lion feces are described. Domoic acid levels were estimated in anchovy samples by HPLC-UV, and in sea lion feces using the same method as well as a microplate receptor binding assay, with absolute confirmation by tandem mass spectrometry. The highest DA concentrations in anchovies occurred in the viscera (223 +/- 5 microg DA g(-1)), exceeding values in the body tissues by seven-fold and suggesting minimal bioaccumulation of DA in anchovy tissue. HPLC values for DA in sea lion fecal material (ranging from 152 to 136.5 microg DA g(-1)) required correction for interference from an unidentified compound. Inter-laboratory comparisons of HPLC data showed close quantitative agreement. Fecal DA activity determined using the receptor binding assay corresponded with HPLC values to within a factor of two. Finally, our detection of P. australis frustules, via scanning electron microscopy, in both anchovy viscera and fecal material from sea lions exhibiting seizures provides corroborating evidence that this toxic algal species was involved in this unusual sea lion mortality event.

Mortality of sea lions along the central California coast linked to a toxic diatom bloom

Over 400 California sea lions (Zalophus californianus) died and many others displayed signs of neurological dysfunction along the central California coast during May and June 1998. A bloom of Pseudo-nitzschia australis (diatom) was observed in the Monterey Bay region during the same period. This bloom was associated with production of domoic acid (DA), a neurotoxin that was also detected in planktivorous fish, including the northern anchovy (Engraulis mordax), and in sea lion body fluids. These and other concurrent observations demonstrate the trophic transfer of DA resulting in marine mammal mortality. In contrast to fish, blue mussels (Mytilus edulus) collected during the DA outbreak contained no DA or only trace amounts. Such findings reveal that monitoring of mussel toxicity alone does not necessarily provide adequate warning of DA entering the food web at levels sufficient to harm marine wildlife and perhaps humans.

Okadaic acid production from the marine dinoflagellate Prorocentrum belizeanum Faust isolated from the Belizean coral reef ecosystem

A species of epiphytic Prorocentrum (Dinophyta, Prorocentrales, collected from the macroalga Dictyota dichotoma, was brought into culture. Based on morphological characteristics, this isolate was identified as Prorocentrum belizeanum. Analysis of the culture extract using high-performance liquid chromatography and liquid chromatography-mass spectrometry indicated the production of okadaic acid, a toxic polyether linked with the human diseases, diarrhetic shellfish poisoning and ciguatera fish poisoning.

Neuroexcitatory actions of ciguatoxin on brain regions associated with thermoregulation

We have investigated the action of ciguatoxin (CTX) in the mouse following i.p. administration. CTX (0.5 mouse units) induced a rapid (10-20 min) decrease in body temperature that persisted for several hours. This corresponded closely with a neuroexcitatory action of ciguatoxin on c-fos mRNA in the brain. We identified the neuronal pathways activated by CTX action in the mouse brain by immunostaining of c-fos translational product, a biomarker for neuroexcitability. c-fos-like immunoreactivity was prominent in the hypothalamus, including the medial preoptic and supraoptic nuclei. Immunostaining was also evident in certain regions of the brain stem, including the locus coeruleus, dorsolateral parabranchial nucleus, area postrema and the nucleus of the solitary tract. These studies indicate that CTX has neuroexcitatory actions on brain stem regions receiving vagal afferents and ascending pathways associated with visceral and thermoregulatory responses.

Development of rapid and sensitive high throughput pharmacologic assays for marine phycotoxins

The lack of rapid, high throughput assays is a major obstacle to many aspects of research on marine phycotoxins. Here we describe the application of microplate scintillation technology to develop high throughput assays for several classes of marine phycotoxin based on their differential pharmacologic actions. High throughput "drug discovery" format microplate receptor binding assays developed for brevetoxins/ciguatoxins and for domoic acid are described. Analysis for brevetoxins/ciguatoxins is carried out by binding competition with [3H] PbTx-3 for site 5 on the voltage dependent sodium channel in rat brain synaptosomes. Analysis of domoic acid is based on binding competition with [3H] kainic acid for the kainate/quisqualate glutamate receptor using frog brain synaptosomes. In addition, a high throughput microplate 45Ca flux assay for determination of maitotoxins is described. These microplate assays can be completed within 3 hours, have sensitivities of less than 1 ng, and can analyze dozens of samples simultaneously. The assays have been demonstrated to be useful for assessing algal toxicity and for assay-guided purification of toxins, and are applicable to the detection of biotoxins in seafood.