Nonprotein neurotoxins

Toxins from harmful algae in fish from Scottish coastal waters

Harmful algal bloom events are increasing in a number of water bodies around the world with significant economic impacts on the aquaculture, fishing and tourism industries. As well as their potential impacts on human health, toxin exposure from harmful algal blooms (HABs) has resulted in widespread morbidity and mortality in marine life, including top marine predators. There is therefore a need for an improved understanding of the trophic transfer, and persistence of toxins in marine food webs. For the first time, the concentrations of two toxin groups of commercial and environmental importance, domoic acid (DA) and saxitoxin (including Paralytic Shellfish Toxin (PST) analogues), were measured in the viscera of 40 different fish species caught in Scotland between February and November, 2012 to 2019. Overall, fish had higher concentrations of DA compared to PSTs, with a peak in the summer / autumn months. Whole fish concentrations were highest in pelagic species including Atlantic mackerel and herring, key forage fish for marine predators including seals, cetaceans and seabirds. The highest DA concentrations were measured along the east coast of Scotland and in Orkney. PSTs showed highest concentrations in early summer, consistent with phytoplankton bloom timings. The detection of multiple toxins in such a range of demersal, pelagic and benthic fish prey species suggests that both the fish, and by extension, piscivorous marine predators, experience multiple routes of toxin exposure. Risk assessment models to understand the impacts of exposure to HAB toxins on marine predators therefore need to consider how chronic, low-dose exposure to multiple toxins, as well as acute exposure during a bloom, could lead to potential long-term health effects ultimately contributing to mortalities. The potential synergistic, neurotoxic and physiological effects of long-term exposure to multiple toxins require investigation in order to appropriately assess the risks of HAB toxins to fish as well as their predators.

Marine invertebrate interactions with Harmful Algal Blooms - Implications for One Health

Harmful Algal Blooms (HAB) are natural atypical proliferations of micro or macro algae in either marine or freshwater environments which have significant impacts on human, animal and ecosystem health. The causative HAB organisms are primarily dinoflagellates and diatoms in marine and cyanobacteria within freshwater ecosystems. Several hundred species of HABs, most commonly marine dinoflagellates affect animal and ecosystem health either directly through physical, chemical or biological impacts on surrounding organisms or indirectly through production of algal toxins which transfer through lower-level trophic organisms to higher level predators. Traditionally, a major focus of HABs has concerned their natural production of toxins which bioaccumulate in filter-feeding invertebrates, which with subsequent trophic transfer and biomagnification cause issues throughout the food web, including the human health of seafood consumers. Whilst in many regions of the world, regulations, monitoring and risk management strategies help mitigate against the impacts from HAB/invertebrate toxins upon human health, there is ever-expanding evidence describing enormous impacts upon invertebrate health, as well as the health of higher trophic level organisms and marine ecosystems. This paper provides an overview of HABs and their relationships with aquatic invertebrates, together with a review of their combined impacts on animal, human and ecosystem health. With HAB/invertebrate outbreaks expected in some regions at higher frequency and intensity in the coming decades, we discuss the needs for new science, multi-disciplinary assessment and communication which will be essential for ensuring a continued increasing supply of aquaculture foodstuffs for further generations.

Rapid and Sensitive ELISA Screening Assay for Several Paralytic Shellfish Toxins in Human Urine

Paralytic shellfish poisoning is caused by a group of paralytic shellfish toxins that are produced by dinoflagellates. Toxins in this group include saxitoxin, neosaxitoxin and gonyautoxins. A rapid diagnostic test to identify poisoning by these toxins can be helpful in guiding the appropriate treatment of victims. Additionally, quick receipt of diagnostic results can provide timely proof that shellfish harvesting should be stopped in a given area, thereby preventing additional exposures. We have developed and validated a rapid urinary enzyme-linked immunosorbent assay-based screening test to diagnose exposure to several major paralytic shellfish toxins. The lower limit of detection (LLOD) for multiple paralytic shellfish toxins was characterized as 0.02, 0.10, 0.10, 1.0, 1.0 and 15 ng/mL for saxitoxin, gonyautoxin 2,3, decarbamoyl gonyautoxin 2,3, decarbamoyl saxitoxin, neosaxitoxin and gonyautoxin 1,4, respectively. No interferences were identified in unspiked pooled urine or in specimens collected from unexposed individuals indicating that this method is specific for the paralytic shellfish toxins tested. The accuracy of this test was demonstrated in 10 individual urine specimens with osmolalities ranging from 217 to 1,063 mOsmol/kg and pHs ranging between 5.06 and 7.45. These specimens were spiked with toxins at their LLODs and the presence of toxins at these concentrations was accurately identified in all cases. These results indicate that this diagnostic test can be used to rapidly and accurately screen urine for paralytic shellfish toxins.

Biotechnological and Pharmacological Applications of Biotoxins and Other Bioactive Molecules from Dinoflagellates

The long-lasting interest in bioactive molecules (namely toxins) produced by (microalga) dinoflagellates has risen in recent years. Exhibiting wide diversity and complexity, said compounds are well-recognized for their biological features, with great potential for use as pharmaceutical therapies and biological research probes. Unfortunately, provision of those compounds is still far from sufficient, especially in view of an increasing demand for preclinical testing. Despite the difficulties to establish dinoflagellate cultures and obtain reasonable productivities of such compounds, intensive research has permitted a number of advances in the field. This paper accordingly reviews the characteristics of some of the most important biotoxins (and other bioactive substances) produced by dinoflagellates. It also presents and discusses (to some length) the main advances pertaining to dinoflagellate production, from bench to large scale-with an emphasis on material published since the latest review available on the subject. Such advances encompass improvements in nutrient formulation and light supply as major operational conditions; they have permitted adaptation of classical designs, and aided the development of novel configurations for dinoflagellate growth-even though shearing-related issues remain a major challenge.

Experimental study of tetrodotoxin, a long-acting topical anesthetic

PURPOSE

To determine the effectiveness and toxicity of tetrodotoxin for use as a long-acting topical anesthetic.

METHODS

Four groups of six rabbits each received a 40-microl aliquot of either tetrodotoxin in one of three concentrations (10 mM, 1 mM, or 0.1 mM) or proparacaine 0.5% into the inferior conjunctival cul-de-sac of one eye, with the fellow eye of each rabbit receiving 40 microl of a 60-mM, pH 4.3 sodium citrate vehicle as a control. Corneal sensation was tested for up to 8 hours after administration of drugs, and response was noted by no blink, partial blink without full eyelid closure, and full blink. Slit-lamp examination at 12 and 24 hours after administration and pachymetry before and 24 hours after administration were performed to detect corneal toxicity.

RESULTS

Rabbits receiving all three concentrations of tetrodotoxin did not demonstrate any ocular irritation, corneal thickening, or signs of systemic toxicity. At a dose of 10 mM, tetrodotoxin produced an anesthetic effect lasting up to 8 hours. At 1 mM, tetrodotoxin was an effective but shorter-acting anesthetic. At 0.1 mM, tetrodotoxin had no significant anesthetic effect. Proparacaine-treated rabbits initially were anesthetic, but this effect was largely gone by 1 hour and completely gone by 3 hours.

CONCLUSIONS

Tetrodotoxin is a long-acting topical anesthetic in the rabbit cornea. Although additional toxicity studies are required, tetrodotoxin may provide an effective, long-lasting topical anesthetic for use in pain control after corneal procedures such as photorefractive keratectomy.

Urinary elimination of saxitoxin after intravenous injection

Paralytic shellfish poisoning is a serious public health concern throughout the world. An analytical method with diagnostic potential was used to isolate and measure saxitoxin, the most potent and studied paralytic shellfish poisoning toxin, in the urine of rats injected i.v. with sublethal doses (2 micrograms/kg) of saxitoxin. Urine was collected at intervals between 4 and 144 hr after injection. Saxitoxin was isolated from urine with an ion-exchange procedure, identified, and measured with a precolumn-oxidation-HPLC procedure coupled with fluorescence detection. The identity of oxidized saxitoxin was confirmed with electrospray ionization mass spectrometry. Four hours after injection, approximately 19% of the injected saxitoxin dose was excreted. By 24 hr, approximately 58% of the administered dose was excreted. Average total urinary excretion of administered saxitoxin was approximately 68% for the full study period. These results demonstrate that small quantities of unmetabolized saxitoxin can be detected in rat urine up to 144 hr after i.v. administration, and that the analytical method may have diagnostic potential for saxitoxin intoxication and paralytic shellfish poisoning.

Prophylaxis and treatment with a monoclonal antibody of tetrodotoxin poisoning in mice

The ability of a tetrodotoxin (TTX)-specific monoclonal antibody to confer passive protection against lethal TTX challenge was investigated. The monoclonal antibody, T20G10, has an estimated affinity for TTX of approximately 10(-9) M and is about 50-fold less reactive with anhydrotetrodotoxin and unreactive with tetrodonic acid by competitive immunoassay. T20G10 specifically inhibited TTX binding in an in vitro radioligand receptor binding assay, but had no effect on the binding of saxitoxin to the sodium channel on rat brain membranes. In prophylaxis studies, mice were administered T20G10 via the tail vein 30 min prior to i.p. TTX challenge (10 micrograms/kg). Under these conditions, 100 micrograms T20G10 protected 6/6 mice, whereas 3/6 mice were protected with 50 micrograms T20G10. Non-specific control monoclonal antibody did not protect against lethality. Therapy studies simulating oral intoxication were performed with mice given a lethal dose of TTX by gavage in a suspension of non-fat dry milk in phosphate-buffered saline. Death occurred within 25-35 min in 6/6 mice not treated with T20G10. However, 500 micrograms T20G10 administered via the tail vein 10-15 min after oral TTX exposure prevented death in 6/6 mice. Lower doses of mAb conferred less protection.

Development of a monoclonal-based enzyme-linked immunoassay for saxitoxin-induced protein

A monoclonal antibody was generated against saxitoxin-induced protein (SIP) from the small shore crab Hemigrapsus oregenesis. SIP was induced by saxitoxin injection and could be detected in the crude crab extracts with both polyclonal and monoclonal antibody preparations. On Western blots, the polyclonal serum reacted against several bands which were induced by saxitoxin in the crude extracts. These bands represented proteins related to SIP. The monoclonal (4G5), however, was specific for the 79,000 mol. wt subunit of SIP. A triple antibody sandwich ELISA was developed in which polyclonal anti-SIP IgG was used as a trapping layer and monoclonal 4G5 was used as the detection layer. This assay was shown to be more specific and more accurate than a direct bind assay which employed the polyclonal antiserum alone. Although the polyclonal serum was more sensitive than the monoclonal on Western blots, the triple antibody sandwich and direct bind ELISAs were of comparable sensitivity.

Polyclonal anti-idiotypes induce specific anti-saxitoxin antibody responses

Polyclonal BALB/C mouse and New Zealand White rabbit anti-idiotypic antibodies were raised by immunization with a protein G-purified burro anti-saxitoxin IgG antibody preparation. Following absorption of non-anti-idiotype reactivity, murine and rabbit IgG were purified by protein A chromatography and used to immunize BALB/C mice for the induction of anti-saxitoxin antibody responses. Unconjugated BALB/C anti-idiotypes did not induce significant anti-saxitoxin reactivity in BALB/C mice, even after repeated immunizations. However, BALB/C mice immunized with purified BALB/C anti-idiotypes conjugated to keyhole limpet hemocyanin, or with purified, unconjugated rabbit anti-idiotypes, as aluminum hydroxide precipitates, induced significant and specific anti-saxitoxin immune responses. Saxitoxin, a sodium channel blocker, can protect cells treated with veratridine and ouabain, whose respective actions are to open sodium channels and to block the activity of Na/K-ATPase. The anti-idiotype-induced anti-saxitoxin antibodies inhibited saxitoxin from protecting against cell death induced by veratridine and ouabain treatment. These and other published experimental results strengthen the concept of anti-idiotype-based vaccines in eliciting protective immunity against a variety of low molecular weight, nonproteinaceous biological and chemical toxins, whose extreme toxicity does not allow their use as safe immunogens.

Central and peripheral cardio-respiratory effects of saxitoxin (STX) in urethane-anesthetized guinea-pigs

Effects of saxitoxin (STX; 10 micrograms/kg; i.p.) on cardio-respiratory activities were evaluated in urethane-anesthetized guinea-pigs. Concurrent recordings were made of electrocorticogram (ECoG), bulbar respiratory-related unit activities, diaphragmatic electromyogram (DEMG), electrocardiogram (Lead II ECG), blood pressure, heart rate, end-tidal CO2, arterial O2/CO2 tensions, and arterial pH. The average time to STX-induced respiratory failure was about 10 min. The most striking effect prior to apnea was a state of progressive bradypnea which emerged 5-7 min after the toxin administration. Other noteworthy responses included (i) a time-dependent decrease in ECoG amplitudes which typically began before the development of a bradypneic profile; (ii) an increasing degree of diaphragm neuromuscular blockade; (iii) a state of combined hypercapnia and uncompensated acidemia; (iv) a declining blood pressure; (v) an incrementally dysfunctional myocardial performance; and (vi) an increasingly degenerative central respiratory activity profile which ultimately culminated in a complete loss of central respiratory drive. The therapeutic effect of intratracheally administered oxygen was equivocal in that the cardio-respiratory activities, be they of central of peripheral nature, remained conspicuously dysfunctional and precarious despite 100% oxygen ventilation. What can be inferred from this study is two-fold. First, STX-induced ventilatory insufficiency can be attributed to a loss of functional integrity of both central and peripheral respiratory system components. That is, although diaphragm blockade contributes significantly to STX-induced respiratory failure, analyses of single respiratory unit activity data revealed that the central respiratory rhythmogenic mechanism also appeared to play a pivotal role in the development of a bradypneic profile which promotes, and directly causes, a complete loss of respiratory drive. Second, a state of unabating depression of central respiratory activities, which seemed to be refractory to the effect of O2, suggests STX has a direct and persistent action on medullary rhythmogenic mechanisms. In conclusion, these findings indicate that both central and peripheral cardio-respiratory components are critically involved in STX-induced apnea, dysfunctional cardiovascular performance, and lethality.

Anti-idiotype vaccines in toxicology

The majority of naturally occurring biological and chemical toxins are highly lethal, nonproteinaceous, low molecular weight substances which exert their toxicity through a variety of mechanisms. Their relative small size and extreme in vivo toxicity have hampered the development of protective vaccines. We have investigated the feasibility of anti-idiotype-based vaccines which utilize antibodies for inducing a systemic and protective immunity against the in vivo toxicity of some of these toxic substances. A murine IgG1 monoclonal anti-T-2 mycotoxin antibody protective against mycotoxin toxicity was generated. This antibody was used to produce a second generation monoclonal anti-idiotype antibody which was capable of serologically mimicking the tertiary conformation of the nominal antigen, i.e., T-2 mycotoxin. Administration of the monoclonal anti-idiotype antibody to mice induced a circulating and protective antibody response against the in vitro and in vivo toxicity of T-2 mycotoxin. Antibody-based vaccines may represent the only safe and effective strategy for the design of protective vaccines against small nonproteinaceous toxic compounds whose extreme toxicity prevents their use as safe immunogens. The potential of antibody-based vaccines for producing protective immunity against low molecular weight chemical and biological toxins is discussed.

A monoclonal antibody-based immunoassay for detecting tetrodotoxin in biological samples

Spleen cells from mice hyperimmunized with a keyhole limpet hemocyanin-tetrodotoxin-formaldehyde conjugate were fused with murine P3X63Ag8.653 myeloma cells. A single hybridoma clone was identified that secretes an IgG1,k monoclonal antibody (MAb), designated T20G10, against tetrodotoxin (TTX), with an estimated affinity of 1.2 x 10(8) L/M. Competitive inhibition enzyme immunoassays (CIEIAs) for detecting TTX were developed using this MAb. A direct CIEIA using alkaline phosphatase-labeled MAb detected TTX with sensitivities at IC50 and IC20 of 6-7 ng/ml and 2-3 ng/ml, respectively. The accuracy of the direct CIEIA was comparable with the high-performance liquid chromatography (HPLC) and the mouse bioassay systems, but the direct CIEIA exhibited greater sensitivity. The direct CIEIA was also more cost effective, as it required less sample preparation, a shorter assay time, and reduced investment in equipment than either of the other assay systems.

Anti-idiotype-based vaccines against biological toxins

Biological toxins produced by living organisms represent one of the major sources of contamination of stored grain and agricultural products, and other food sources. The majority of these biological toxins are highly lethal, nonproteinaceous low-molecular-weight chemical compounds which exert their potent toxicity through a variety of mechanisms. Because of their small size, they generally do not induce a significantly high affinity protective antibody response upon toxin exposure, even when conjugated to large protein carriers which enhance their immunogenicity. Moreover, the very toxic nature of biological toxins precludes their use as immunogens in the induction of protective immunity. To circumvent this difficulty, an attempt was made to develop antibody (anti-idiotype)-based vaccines against a protein synthesis inhibitor, the trichothecene mycotoxin T-2, and the sodium channel blockers tetrodotoxin and saxitoxin. Protective monoclonal antitoxin antibodies were first generated and then used to induce specific monoclonal anti-idiotype antibodies. Specific anti-idiotype antibodies were assessed for their ability to induce in vivo protective immunity against toxicity.

Protection against tetrodotoxin and saxitoxin intoxication by a cross-protective rabbit anti-tetrodotoxin antiserum

A tetrodotoxin-formaldehyde-keyhole limpet hemocyanin conjugate was used to immunize a rabbit for the production of anti-toxin antiserum. The antiserum cross-reacted against both tetrodotoxin (TTX) and saxitoxin (STX), and in a quantitative in vitro assay was able to protect cells in a dose-dependent manner from the effects of either TTX or STX. The antiserum was also able to passively protect mice challenged in vivo with either toxin. Hybridomas producing monoclonal antibodies against toxin were obtained from the spleens of mice immunized with the same conjugate.

Respiratory and cardiovascular effects of tetrodotoxin in urethane-anesthetized guinea pigs

Cardiorespiratory effects of tetrodotoxin (TTX) (15 micrograms/kg, i.p.) were investigated in urethane-anesthetized guinea pigs acutely instrumented for the recording of medullary respiratory-related units (RRUs), diaphragm electromyogram (DEMG), electrocorticogram (ECoG), electrocardiogram (ECG), blood pressure (BP), endtidal CO2, and arterial O2 and CO2. Respiratory system responses showed a hyperventilatory profile during the initial stage of intoxication. This was followed by an abrupt onset of a progressive decrease in the respiratory frequency, and a respiratory rate depression-related respiratory failure. The average time to TTX-induced respiratory arrest and death was 10.3 +/- 4.2 min. Concurrently recorded inspiratory and expiratory RRU activities indicated that respiration invariably failed in an end-expiratory position as manifested by a sustained period of expiratory RRU discharge. The progressive rate depression prior to respiratory arrest was temporally correlated only to a concomitantly augmenting expiratory RRU discharge duration. Inspiratory RRU discharge duration, on the other hand, did not display any significant change throughout the course of intoxication. The asymmetry in RRU response patterns indicates either an expiratory network component's particular sensitivity to perturbation by TTX or a dissociative trend in some bulbar respiratory rhythmogenic mechanisms. Peripheral cardiorespiratory changes were also quite profound. These included a gradual and steadfast decline in BP, a steadily decreasing amplitude in DEMG oscillations, and a state of progressive hypercapnia and hypoxemia. Changes in heart rate and ECG waveform attributes prior to respiratory arrest were not appreciable. In conclusion, in addition to a variety of TTX-induced peripheral cardiorespiratory effects, findings from this study have revealed a central respiratory system component that appears to show an unusual sensitivity to perturbation by TTX. The significance of this unique phenomenon as it relates to the nature and extent of TTX-induced central respiratory depression is discussed.

In vitro and in situ inhibition of the sodium channel blocker saxitoxin by monoclonal antibodies

The sodium channel blocker saxitoxin (STX) was conjugated to keyhole limpet hemocyanin (KLH) and used to immunize BALB/c mice. Anti-STX antibodies were detected in serum by an enzyme-linked immunosorbent assay (ELISA) within a week or two after the first immunization. Spleens from immunized mice were fused with NS-1 myeloma cells and approximately 7000 resultant hybrids were screened by ELISA for reactivity to STX. Two stable hybrids were isolated, subcloned, and characterized. These hybrids, termed S1A5 and S3E.2, secreted specific anti-STX antibodies that did not recognize the closely related toxin tetrodotoxin (TDT), as determined by competition ELISA. The S1A5 monoclonal antibody (mAb) was of the IgMk class and S3E.2 of the IgG1k subclass with affinity constants (Ka values) of approximately 10(6) M-1. The protective ability of these antibodies was tested by a competitive displacement assay for [3H]STX binding on rat brain membranes. Purified S3E.2 strongly displaced [3H]STX binding, whereas S1A5 weakly inhibited [3H]STX binding to membranes. One nanomole of S3E.2 or S1A5 was able to bind 0.03 nmol or 0.005 nmol, respectively, of STX. The S3E.2 mAb offered partial protection against STX-induced reduction of peripheral nerve action potential in rat tibial nerve when administered in situ at concentrations 10- to 30-fold greater than STX. The S1A5 mAb, despite its ability to inhibit STX binding in vitro, was completely ineffectual in situ. These antibodies, particularly S3E.2, thus represent potentially useful reagents for neurobiologic research, detection of toxin contamination, and diagnosis of poisoning, and may provide protection against the toxicity of STX in vivo.

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.

Mosquito inoculation: an alternative bioassay for toxins

Mosquitoes were evaluated as a bioassay host for several classes of biological toxins. Mosquitoes were sensitive to snake toxic or neurotoxic phospholipase A2 enzymes (but not to nontoxic phospholipase A2 enzymes), cobrotoxin, saxitoxin, microcystin and the scorpion insect sodium channel toxin. Mosquitoes were not sensitive to ricin, diphtheria toxin, anthrax toxin, botulinum toxin, tetanus toxin, conotoxin G or a scorpion sodium channel toxin toxic to mammals. Specific antisera neutralization tests with mosquitoes gave comparable results to those of a mouse assay. The mosquito is a suitable bioassay animal for many, but not all biological toxins, and offers a safer, more efficient and economical assay than mice.

Respiratory failure and lethal hypotension due to blue-ringed octopus and tetrodotoxin envenomation observed and counteracted in animal models

The effects of crude blue-ringed octopus venom gland extract and tetrodotoxin (TTX) on anaesthetised rats and rabbits were studied. Paralysis of the respiratory musculature causing anoxia and cyanosis was overcome with positive, artificial respiration. The second lethal mechanism of the toxins: rapid and severe hypotension, had to be counteracted peripherally, since neural transmission had been drastically reduced by the toxins. Noradrenaline, d-amphetamine, phenylephrine and methoxamine, agonists acting on vascular adrenergic a-receptors, were tested.

Acute toxic effects in mice of an extract from the marine algae Gonyaulax monilata

Unialgal cultures of Gonyaulax monilata were cultured and harvested. A modified Westphall procedure was used to prepare an extract which did not contain saxitoxin, the gonyautoxins and structurally related toxins. The extract was administered i.p. to young adult, male CD-1 mice and produced: sedation, abdominal constriction, fecal clumping in the perianal area, ataxia, tremors, cyanosis, loss of reflexes, convulsions and death (LD50 = 2.28 mg/kg). Gross and microscopic pathology in the treated mice included: acute active hyperemia of the viscera, multifocal areas of necrosis of the musculature of the intestinal wall and diaphragm and the presence of cytoplasmic vacuoles in the peripheral margins of the acinar portion of the pancreas. Clinical pathology of the mice which survived 24 hr included significant elevation in the levels of serum lactic dehydrogenase, glutamic pyruvic and glutamic oxaloacetic transaminases. Some of these mice also had significantly decreased white blood cell counts. The extract administered orally produced similar signs without the abdominal constriction and convulsions (median lethal oral dose = 6.73 mg/kg). Gross pathology findings included extensive and severe congestion of the abdominal visceral organs. Vehicle control mice were normal. In conclusion, G. monilata, previously reported as nontoxic in homeotherms, yields an extract which contains a water soluble glycosidic substance(s) which is lethal to mice.

Neutralization of saxitoxin by anti-saxitoxin rabbit serum

This study examined the ability of anti-saxitoxin rabbit serum to neutralize saxitoxin, both in vitro and in vivo. In vitro, two rabbit antisera decreased [3H]-saxitoxin binding to specific sites in rat brain membranes. The more potent of these sera, antiserum A, when combined with saxitoxin in vitro, decreased saxitoxin's lethal potency based on mouse bioassay. Antiserum A also neutralized saxitoxin in vivo, as illustrated by the fact that mice injected i.p. with antiserum A (1:4) survived a s.c. injection 1 hr later of 16.7 micrograms saxitoxin/kg (1 LD99). Finally, antiserum A prevented death when injected i.v. immediately after s.c. injection of 16.7 micrograms saxitoxin/kg, however, antiserum injected by the i.p. and i.m. routes caused no significant increase in survival. This study indicates that antiserum can neutralize saxitoxin both in vitro and in vivo.

A competitive displacement assay to detect saxitoxin and tetrodotoxin

An assay is described which detects saxitoxin (STX) and tetrodotoxin (TTX) by their competitive displacement of [3H]saxitoxin from its receptor in rat brain membranes. The assay has a sensitivity of 0.15 ng STX/ml and 0.8 ng TTX/ml for buffer samples. The assay was also applied to detection of these toxins in unextracted human plasma and found to have a sensitivity of 0.5 ng STX/ml and 0.6 ng TTX/ml. The competitive displacement assay appears to be the most sensitive procedure yet for detection of STX and TTX.