Separation of tetrodotoxin and paralytic shellfish poisons by high-performance liquid chromatography with a fluorometric detection using o-phthalaldehyde

Simultaneous determination of ten paralytic shellfish toxins and tetrodotoxin in scallop and short-necked clam by ion-pair solid-phase extraction and hydrophilic interaction chromatography with tandem mass spectrometry

Paralytic shellfish toxins and tetrodotoxin (puffer-fish toxin), the latter of which was recently found in bivalves from Europe, Japan, and New Zealand, are potent neurotoxins. A simple and effective clean-up procedure was developed for the simultaneous determination of ten paralytic shellfish toxins (gonyautoxins 1-6, decarbamoylgonyautoxins 2 and 3, and N-sulfocarbamoylgonyautoxins 2 and 3) and tetrodotoxin in the scallop, Mizuhopecten (Patinopecten) yessoensis, and the short-necked clam, Ruditapes philippinarum. To reduce matrix effects, 1% aqueous acetic acid extracts of the bivalves were cleaned up by ion-pair solid-phase extraction using a graphite carbon cartridge with tridecafluoroheptanoic acid as the volatile ion-pair reagent, followed by fourfold dilution. The ten paralytic shellfish toxins and tetrodotoxin were then separated on a hydrophilic interaction chromatography column and quantified by tandem mass spectrometry. The limits of detection and the limits of quantification for the ten PSTs ranged from 0.09 to 13.0 µg saxitoxin equivalents/kg and from 0.26 to 39.4 µg saxitoxin equivalents/kg, respectively. The limit of detection and the limit of quantification for tetrodotoxin ranged from 27.4 to 27.9 µg/kg and from 83.1 to 84.4 µg/kg, respectively. The proposed method yielded minimal matrix effects for the 11 analytes, thus allowing their quantification by simple external calibration. The proposed method also gave good mean recoveries of the 11 analytes ranging from 75.7 to 96.2% with relative standard deviations less than 16% at three fortification levels for the ten paralytic shellfish toxins (total concentrations of 277, 554, and 1107 µg saxitoxin equivalents/kg) and tetrodotoxin (100, 200, and 400 µg/kg) in the two bivalve samples. Finally, the proposed method was applied for the determination of the ten paralytic shellfish toxins and tetrodotoxin in scallop and short-necked clam samples.

Endogenous signaling pathways and chemical communication between sperm and egg

Red abalone (Haliotis rufescens) sperm detect a waterborne chemical cue released by conspecific eggs, and change their swimming behavior to increase the likelihood of fertilization success. Previously, we isolated the natural sperm attractant by bioassay-guided fractionation and high-performance liquid chromatography, and chemically identified it as the free-amino acid l-tryptophan (l-Trp). In the present study, levels of this ecologically meaningful compound were quantified in various abalone tissues, and in freshly spawned eggs. Tryptophan was the least abundant of 19 dissolved free amino acids (DFAAs) in ovary, testis, foot muscle, gill, stomach and hemolymph. As a proportion of the DFAA pool, however, Trp concentrations were significantly elevated in eggs (three- to seven-times higher) relative to all other sampled tissues. Natural rates of Trp release from eggs also were measured and correlated with fertility. Fertilization success peaked during an initial 30 min period (post-spawn), but decreased to nil over the next 50 min. Closely paralleling these events, Trp accumulated in seawater around freshly spawned eggs for the first 45 min (post-spawn) before decaying rapidly from solution. Older eggs stopped releasing Trp approximately when they became infertile, revealing a critical link between gamete physiology and chemical signaling. This apparent negative feedback loop did not arise from tryptophan oxidation, uptake by bacteria in seawater, or a degrading enzyme released by eggs. As a metabolic precursor critical to development of the larval nervous system, Trp could be an honest indicator of egg fitness for prospective sperm suitors. Our results suggest that endogenous signaling pathways have been co-opted for external communication between gametes, as an adaptation to increase reproductive success by promoting sperm navigation towards fertile eggs.

Pharmacological discrimination between effects of carbamazepine on hippocampal basal, Ca(2+)- and K(+)-evoked serotonin release

To elucidate mechanisms of hippocampal serotonin release and possible mechanisms of clinical action of carbamazepine (CBZ), we determined interaction between antagonists of N-type (omega-conotoxin GVIA:GVIA), P-type (omega-agatoxin IVA:IVA) Ca(2+) channels, Na(+) channel (tetrodotoxin: TTX) and CBZ on hippocampal basal, Ca(2+)- and K(+)-evoked serotonin releases, using microdialysis in freely moving rats. Basal release was reduced by TTX, GVIA and IVA (GVIA>IVA). Ca(2+)-evoked release was reduced by GVIA but unaffected by TTX and IVA. K(+)-evoked release was reduced by TTX, GVIA and IVA (GVIA<IVA). TTX inhibited actions of IVA and GVIA on respective basal and K(+)-evoked releases, without affecting Ca(2+)-evoked release. Perfusion with 100 microM CBZ (estimated-concentration in hippocampal tissue: 19+/-2 microM) enhanced basal and Ca(2+)-evoked releases, but reduced K(+)-evoked release, whereas 1000 microM CBZ (estimated-concentration in hippocampal tissue: 188+/-16 microM) reduced three types of releases. Under condition of pretreatment with 100 and 1000 microM CBZ, TTX unaffected basal and K(+)-evoked releases. Under condition of pretreatment with 100 microM CBZ, IVA and GVIA unaffected basal and K(+)-evoked releases, respectively, but GVIA reduced basal, Ca(2+)-evoked releases and IVA also reduced K(+)-evoked release. Under condition of pretreatment with 1000 microM CBZ, GVIA unaffected three types of releases, and IVA unaffected basal release but reduced K(+)-evoked release. These findings contribute towards the possible mechanisms of concentration-dependent antiepileptic action of CBZ, which possibly inhibits Na(+) channel related neurotransmitter release mechanisms during K(+)-evoked stage, and simultaneously enhances N-type Ca(2+) channel related basal serotonin release at the resting stage.

Separation of paralytic shellfish poisoning toxins on Chromarods-SIII by thin-layer chromatography with the Iatroscan (mark 5) and flame thermionic detection

Thin-layer chromatography (TLC) on Chromarods-SIII with the Iatroscan (Mark-5) and a flame thermionic detector (FTID) was used to develop a rapid method for the detection of paralytic shellfish poisoning (PSP) toxins. The effect of variation in hydrogen (H2) flow, air flow, scan time and detector current on the FTID peak response for both phosphatidylcholine (PC) and PSP were studied in order to define optimum detection conditions. A combination of hydrogen and air flow-rates of 50 ml/min and 1.5-2.0 l/min respectively, along with a scan time of 40 s/rod and detector current of 3.0 A (ampere) or above were found to yield the best results for the detection of PSP compounds. Increasing the detector current level to as high as 3.3 A gave about 130 times more FTID response than did flame ionization detection (FID), for PSP components. Quantities of standards as small as 1 ng neosaxitoxin (NEO), 5 ng saxitoxin (STX), 5 ng B1-toxins (B1), 2 ng gonyautoxin (GTX) 2/3, 6 ng GTX 1/4 and 6 ng C-toxins (C1/C2) could be detected with the FTID. The method detection limits for toxic shellfish tissues using the FTID were 0.4, 2.1, 0.8 and 2.5 micrograms per g tissue for GTX 2/3, STX, NEO and C toxins, respectively. The FTID response increased with increasing detector current and with increasing the scan time. Increasing hydrogen and air flow-rates resulted in decreasing sensitivity within defined limits. Numerous solvent systems were tested, and, solvent consisting of chloroform: methanol-water-acetic acid (30:50:8:2) could separate C toxins from GTX, which eluted ahead of NEO and STX. Accordingly, TLC/FTID with the Iatroscan (Mark-5) seems to be a promising, relatively inexpensive and rapid method of screening plant and animal tissues for PSP toxins.

Fluorometric detection of paralytic shellfish poisoning toxins

A rapid qualitative screening method was developed for the fractionation of paralytic shellfish poisoning toxins. Periodic acid, t-butyl hydroperoxide, and hydrogen peroxide were tested as oxidants for the fluorometric detection of paralytic shellfish toxins. Hydrogen peroxide was found to be the most convenient and efficient oxidant since the fluorescence can be detected after the incubation of toxins at 100 degrees C for 3-5 min. In addition to the structure of the compound, the incubation temperature and time, the amount of acid, and the peroxide concentration affect the fluorescence reaction. This method was more efficient than the previously published peroxidation methods which involved lengthy incubation periods or time-consuming pH adjustment. Also, far greater sensitivity was achieved with the new method with levels of 0.027, 0.054, 0.023, 0.003, 0.0002, and 0.0006 pmol being easily detected for saxitoxin, neosaxitoxin, gonyautoxin 1 and 4, gonyautoxin 2 and 3, C toxins, and B toxins, respectively. The method is particularly valuable for the screening of fractions separated by column chromatography.

Use of a channel biosensor for the assay of paralytic shellfish toxins

Gonyautoxin (GTX), saxitoxin (STX) and tetrodotoxin (TTX), also known as paralytic shellfish poisons (PSP), block Na+ channels, including those in the frog bladder membrane. A tissue biosensor has been developed, consisting of a Na+ electrode covered with a frog bladder membrane integrated within a flow cell. The direction of Na+ transfer, investigated in the absence of Na+ channel blockers, established that active transport of Na+ occurs across the frogs bladder membrane from the internal to the external face. Transfer was shown to be TTX sensitive. The tissue sensor response to each of the different PSP was recorded and the results compared with toxicities determined by the standard mouse bio-assay. Using high concentrations of TTX from the puffer fish Takifugu niphobles, a linear correlation was found between the results from the two assay systems. However, the tissue biosensor system was also able to detect very low concentrations of TTX in samples from two species of puffer fish (Takifugu niphobles and Takifugu pardalis) at concentrations below the detection limit of the mouse bio-assay.

Development of an ultra high sensitive tissue biosensor for determination of swellfish poisoning, tetrodotoxin

A simple tissue biosensor for measuring Na+ channel blockers such as tetrodotoxin (TTX) and saxitoxin (STX) has been developed. The membrane of frog bladder has Na+ channels which control the passage of Na+. It is well known that TTX blocks Na+ channels. The tissue biosensor consists of a Na+ electrode integrated within a flow cell. The tip of the electrode was covered with frog bladder membrane sandwiched between two sheets of cellulose acetate membrane, and the electrode was set in a flow cell. A solution of 8% NaCl was carried in the cell and the output of the electrode allowed to stabilize. TTX was injected into the sensor system and measured from the inhibition ratio of the sensor peak output. One assay took approximately 5 min. The lower limit of detection was 86 fg. The continuous determination of TTX was feasible for 250 h in the presence of 0.003% NaN3. A Linear correlation was obtained between TTX activities of F-niphobles and F-parudale determined by the methods of TTX sensor and mouse assay.

Protection against nerve toxicity by monoclonal antibodies to the sodium channel blocker tetrodotoxin

The sodium channel blocker, tetrodotoxin (TDT), was conjugated to keyhole limpet hemocyanin (KLH) and used to immunize BALB/c mice. Anti-TDT antibodies were detected in serum by ELISA and reached stable levels 4-5 wk after the first immunization. Spleens from immunized mice were fused with NS-1 mouse myeloma cells and approximately 9,329 resultant hybrids were screened by ELISA for reactivity to TDT. Two stable hybrids were isolated, subcloned, and characterized. These hybrids, termed TD13a1 and TD2C5, secreted specific anti-TDT antibodies that recognized TDT but not the related sodium channel blocker, saxitoxin (STX), as determined by competition ELISA. Both antibodies were of the IgG1k subclass with Ka's approaching 10(7) M-1. The inhibitory ability of these antibodies was tested by a competitive displacement assay for [3H]STX on rat brain membranes. Both antibodies strongly inhibited TDT binding to membranes. A nanomole of TD2C5 was able to bind approximately 1.8 nmol of TDT, whereas a comparable amount of TD13a1 bound half as much. Furthermore, TD2C5 was able to protect against TDT-induced reduction of peripheral nerve action potentials in rat tibial nerve when administered in situ. These antibodies thus represent potentially useful reagents for neurobiologic research, detection of toxin contamination and diagnosis of poisoning, and may provide protection against the toxicity of TDT in vivo.

Monoclonal antibody raised against tetrodonic acid, a derivative of tetrodotoxin

Tetrodonic acid, a relatively non-toxic derivative of tetrodotoxin, was conjugated with bovine serum albumin and injected i.p. to BALB/c mice. After several injections, spleen cells were isolated, fused with myeloma cells X63-Ag8-6.5.3. and cloned by the limiting dilution method. The monoclonal antibody produced in ascites fluid in the mouse by the cloned cell showed an increasing reactivity with tetrodotoxin at concentrations ranging from 0.03 to 100 micrograms per well.