The seasonality and role of the neurotoxin tetramine in the salivary glands of the red whelk Neptunea antiqua (L.)

Particle binding capacity of snail saliva

Gastropods forage with their radula, a thin chitinous membrane with embedded teeth, which scratch across the substrate to lose food particles. During this interaction, the risk of loosening particles is obvious without having a specialized mechanism holding them on the tooth surface. As mucus secretions are essential in molluscan life cycles and the locomotion and attachment gels are known to have an instant high adhesion, we have hypothesized that the saliva could support particle retention during feeding. As adhesion of snail saliva was not studied before, we present here an experimental setup to test its particle-binding capacity using a large land snail (Lissachatina fulica, Stylommatophora, Heterobranchia). This experiment was also applied to the gels produced by the snail foot for comparison and can be potentially applied to various fluids present at a small volume in the future. We found, that the saliva has high particle retention capacity that is comparable to the foot glue of the snail. To gain some insight into the properties of the saliva, we additionally studied it in the scanning electron microscope, estimated its viscosity in a de-wetting experiment, and investigated its elemental composition using energy dispersive X-ray spectroscopy reveling higher contents of Ca, Zn and other potential cross-linkers similar to those found in the glue.

[Tetramine Contents in the Salivary Glands from 16 Species of Marine Carnivorous Gastropods Collected along Japanese Coasts]

Tetramine (tetramethyl ammonium ion), a neurotoxin, is present at high levels in the salivary glands of buccinid gastropods and is responsible for human intoxication due to consumption of the gastropods. We used LC-MS/MS to examine the tetramine contents of salivary glands from 16 species of carnivorous gastropods collected along Japanese coasts. Tetramine was detected in all specimens except for Babylonia japonica. High levels of tetramine were detected in whelks, Neptunea lamellosa (1,380-9,410 μg/g of salivary gland) and N. purpurea (1,190-7,400 μg/g of salivary gland). Although consumption of N. lamellosa is well-known cause of foodborne tetramine poisoning, it was newly discovered that N. purpurea has tetramine. In addition, we found 7 other species of gastropods containing tetramine: Siphonalia cassidariaeformis (117-135 μg/g), S. fusoides (204 μg/g), Buccinum inclytum (2.94-3.40 μg/g), and B. aniwanum (0.700 μg/g) of the family Buccinidae, and Fusinus perplexus (397 μg/g), F. ferrugineus (105 μg/g), and F. forceps salisburyi (67.5 μg/g) of the family Fasciolariidae. The present study, together with previous studies, shows that gastropods with salivary glands containing more than 1,000 μg tetramine/g of salivary gland, including the genus Neptunea as well as Fusitriton oregonesis and Hemifusus tuba, carry a high risk of tetramine poisoning, and their salivary glands should be removed before consumption to prevent food poisoning.

Tetramine in the Salivary Glands of Marine Carnivorous Snails: Analysis, Distribution, and Toxicological Aspects

Focusing on tetramine, tetramethylammonium ion, contained in the salivary glands of marine carnivorous snails, this paper gives an overview of analytical methods, distribution in marine snails, and toxicological aspects. Some Neptunea snails have often caused food poisoning in North Atlantic and Northeast Asia regions, especially in Japan. The toxin of both N. arthritica and N. antiqua was first proven to be tetramine in 1960. Subsequent research on marine snail tetramine has progressed with the development of analytical methods. Of the various methods developed, the LC/ESI-MS method is most recommended for tetramine analysis in terms of sensitivity, specificity, and versatility. Accumulated data show that tetramine is ubiquitously contained at high concentrations (usually several mg/g) in the salivary glands of Neptunea snails. Tetramine is also found in the muscle and viscera of Neptunea snails and even in the salivary gland of marine snails other than Neptunea species, although mostly at low levels (below 0.1 mg/g). Interestingly, the major toxin in the salivary glands of Fusitriton oregonensis and Hemifusus tuba is distinguishable from tetramine. In tetramine poisoning, diverse symptoms attributable to the ganglion-blocking action of tetramine, such as visual disturbance, headache, dizziness, abdominal pain, and nausea, develop within 30 min after ingestion of snails because of rapid absorption of tetramine from the gastrointestinal tract. The symptoms are generally mild and subside in a short time (within 24 at most) because of rapid excretion through the kidney. However, it should be kept in mind that tetramine poisoning can be severe in patients with kidney dysfunction, as shown by two recent case reports. Finally, given the diffusion of tetramine from the salivary gland to the muscle during boiling and thawing of snails, removal of salivary glands from live snails is essential to avoid tetramine poisoning.

Critical Tetramine Poisoning after Sea Snail Ingestion in a Patient on Peritoneal Dialysis: A Case Report

Tetramine in gastropods can cause poisoning symptoms with various side effects. Most of these symptoms are mild and spontaneously resolved due to the rapid excretion of tetramine through the kidneys; however, patients with kidney dysfunction can present severe symptoms. A 48-year-old woman with end-stage kidney disease due to diabetic nephropathy and undergoing peritoneal dialysis (PD) visited our emergency department (ED) with complaints of general weakness, vomiting, and shortness of breath after ingesting some sea snails. On ED arrival, she was in a respiratory failure state; therefore, invasive mechanical ventilation was immediately initiated. Chest radiography showed diffuse severe pulmonary edema and her vital signs fluctuated; thus, continuous renal replacement therapy (CRRT) was initiated at the intensive care unit to treat tetramine intoxication and control volume status. Her condition gradually improved, and she was successfully weaned from mechanical ventilation on the 5th day of admission and moved to the general ward on the 10th day. CRRT was switched to PD. She fully recovered and was discharged on the 15th day of admission. Therefore, clinicians should explain the risk associated with gastropod ingestion to patients with kidney dysfunction and recognize that the clinical course of tetramine toxicity can be critical.

A review of food poisoning caused by local food in Japan

Increasingly popular worldwide, Japanese cuisine includes several raw preparations such as sashimi and sushi; however, limited information on food poisoning from Japanese local food is available in English literature. Without appropriate knowledge, physicians may underdiagnose traveler's diarrhea among people returning from Japan. To provide accurate information to primary care physicians worldwide, we conducted a narrative review on food poisoning research published in Japanese and English over the past four years, considering the frequency and clinical importance of various presentations.

Salivary Glands in Predatory Mollusks: Evolutionary Considerations

Many marine mollusks attain or increase their predatory efficiency using complex chemical secretions, which are often produced and delivered through specialized anatomical structures of the foregut. The secretions produced in venom glands of Conus snails and allies have been extensively studied, revealing an amazing chemical diversity of small, highly constrained neuropeptides, whose characterization led to significant pharmacological developments. Conversely, salivary glands, the other main secretory structures of molluscan foregut, have been neglected despite their shared occurrence in the two lineages including predatory members: Gastropoda and Cephalopoda. Over the last few years, the interest for the chemistry of salivary mixtures increased based on their potential biomedical applications. Recent investigation with -omics technologies are complementing the classical biochemical descriptions, that date back to the 1950s, highlighting the high level of diversification of salivary secretions in predatory mollusks, and suggesting they can be regarded as a pharmaceutical cornucopia. As with other animal venoms, some of the salivary toxins are reported to target, for example, sodium and/or potassium ion channels or receptors and transporters for neurotransmitters such as, glutamate, serotonin, neurotensin, and noradrenaline, thus manipulating the neuromuscular system of the preys. Other bioactive components possess anticoagulant, anesthetic and hypotensive activities. Here, we overview available knowledge on the salivary glands of key predatory molluscan taxa, gastropods, and cephalopods, summarizing their anatomical, physiological and biochemical complexity in order to facilitate future comparative studies on main evolutionary trends and functional convergence in the acquisition of successful predatory strategies.

Anticancer properties of lamellarins

In 1985 the first lamellarins were isolated from a small oceanic sea snail. Today, more than 50 lamellarins have been inventoried and numerous derivatives synthesized and tested as antiviral or anticancer agents. The lead compound in the family is lamellarin D, characterized as a potent inhibitor of both nuclear and mitochondrial topoisomerase I but also capable of directly interfering with mitochondria to trigger cancer cell death. The pharmacology and chemistry of lamellarins are discussed here and the mechanistic portrait of lamellarin D is detailed. Lamellarins frequently serve as a starting point in the design of anticancer compounds. Extensive efforts have been devoted to create novel structures as well as to improve synthetic methods, leading to lamellarins and related pyrrole-derived marine alkaloids.

Naturally occurring food toxins

Although many foods contain toxins as a naturally-occurring constituent or, are formed as the result of handling or processing, the incidence of adverse reactions to food is relatively low. The low incidence of adverse effects is the result of some pragmatic solutions by the US Food and Drug Administration (FDA) and other regulatory agencies through the creative use of specifications, action levels, tolerances, warning labels and prohibitions. Manufacturers have also played a role by setting limits on certain substances and developing mitigation procedures for process-induced toxins. Regardless of measures taken by regulators and food producers to protect consumers from natural food toxins, consumption of small levels of these materials is unavoidable. Although the risk for toxicity due to consumption of food toxins is fairly low, there is always the possibility of toxicity due to contamination, overconsumption, allergy or an unpredictable idiosyncratic response. The purpose of this review is to provide a toxicological and regulatory overview of some of the toxins present in some commonly consumed foods, and where possible, discuss the steps that have been taken to reduce consumer exposure, many of which are possible because of the unique process of food regulation in the United States.

Dramatic intraspecimen variations within the injected venom of Conus consors: an unsuspected contribution to venom diversity

With the advent of highly sensitive mass spectrometry techniques, the minute amount of various secretions produced by living animals can be studied to a level of details never attained before. In this study, we used LC-ESI-MS to analyse the injected venom of an indo-pacific piscivorous cone snail, Conus consors. While long-term follow up of several captive specimens have revealed a typical "venom fingerprint" for this species, dramatic variations were also observed. In the most extreme case, a single cone snail unexpectedly produced two very distinct venom profiles containing completely different sets of peptides with no overlap of detected masses. Surprisingly, there was no correlation between the peptides produced in the venom duct and those obtained after milking live cone snails, implying yet unknown mechanisms of selection and regulation. Our study defines the notion of intraspecimen variation and demonstrates how this phenomenon contributes to the overall venom diversity.

Lectins associated with the feeding organs of the oyster Crassostrea virginica can mediate particle selection

Despite advances in the study of particle selection in suspension-feeding bivalves, the mechanisms upon which bivalves rely to discriminate among particles have not been elucidated. We hypothesized that particle sorting in suspension-feeding bivalves could be based, in part, on a biochemical recognition mechanism mediated by lectins within the mucus that covers the feeding organs. Using Crassostrea virginica, the Eastern oyster, our investigations demonstrated that lectins from oyster mucus can specifically bind several microalgal species as well as different types of red blood cells (RBC), triggering their agglutination. Agglutination of microalgal species and RBC varied with the source of mucus (gills vs. labial palps). Hemagglutination and hemagglutination inhibition assays emphasized that mucus contains several lectins. In feeding experiments, Nitzschia closterium and Tetraselmis maculata were separately incubated with mucus before being fed to oysters. Results showed that pre-treating these microalgae with mucus significantly alters the ability of oysters to sort particles. In another experiment, oysters were fed a mixture of microspheres coated with either bovine serum albumin (BSA) or glucosamide-BSA. Results show that oysters preferentially ingest microspheres with bound carbohydrates, highlighting probable interactions between lectins and carbohydrates in the mechanisms of microalgae recognition. This study confirms the presence of lectins in mucus that covers the feeding organs of oysters and suggests a new concept with regard to particle processing by suspension-feeding bivalves: specific interactions between carbohydrates on the surface of particles and lectins within the mucus mediate the selection and rejection processes.

Identification of tetramine, a toxin in whelks, as the cause of a poisoning incident in Korea and the distribution of tetramine in fresh and boiled whelk (Neptunea intersculpta)

An investigation was conducted into the clinical symptoms and causative agent associated with a whelk poisoning incident that occurred in March 2005 in Korea. The whelk consumed in the poisoning incident was identified as Neptunea intersculpta. All of the 17 patients suffered from eyeball pain, headache, dizziness, abdominal pain, and nausea but no diarrhea. The causative agent was identified as tetramine, based on results from liquid chromatography-tandem mass spectrometry. Based on the tetramine concentration in the leftover whelk meat and the amount of meat consumed, the amount of tetramine ingested by the patients was estimated to be > or = 10 mg. This is the first report of the identification of tetramine as the causative agent in whelk poisoning in Korea. The anatomical distribution of tetramine in fresh and boiled N. intersculpta was examined. The toxin concentration in the meat was higher in specimens boiled in the shell than in fresh specimens collected on the same date. In meat boiled separately after removing the shell, the salivary gland, and the midgut gland, the tetramine concentration was much lower than that in fresh specimens or those boiled in the shell. This result suggests that boiling the meat after removing the salivary gland is a suitable way to prevent tetramine poisoning.

Tetramethylenedisulfotetramine: old agent and new terror

Tetramethylenedisulfotetramine has accounted for numerous intentional and unintentional poisonings in China. In May 2002, the first known case of human illness in the United States caused by tetramethylenedisulfotetramine, a banned neurotoxic rodenticide from China, occurred in New York City. The clinical presentation after tetramethylenedisulfotetramine exposure is dose dependent, and the most recognized complication is status epilepticus. Poisonings may be fatal within hours. No known antidote exists, and treatment is mainly supportive. Anecdotal reports, case reports, and 2 animal studies suggest possible success with certain pharmacologic interventions, including pyridoxine and chelation therapy. Pesticide and rodenticide poisonings, whether intentional or unintentional, pose a serious threat to populations, and the availability of a banned rodenticide such as tetramethylenedisulfotetramine, with its associated morbidity and lethality, is a serious public health concern. Given the recent case report that confirms the presence of tetramethylenedisulfotetramine in the United States, the toxicity of the compound, its unique physical properties, the absence of an antidote, and the history of its use as an agent of intentional mass poisoning, public health entities have undertaken educational efforts to inform the public, health care providers, and emergency personnel of this potentially lethal rodenticide.

Status epilepticus from an illegally imported Chinese rodenticide: "tetramine"

INTRODUCTION

The following case report demonstrates the severe consequences of refractory convulsive status epilepticus from an unfamiliar imported toxin, tetramethylenedisulfotetramine (TETS), and the difficulties of identifying the offending agent.

CASE REPORT

A previously healthy 15-month-old girl was found by her parents playing with a white rodenticide powder brought from China. Fifteen minutes later, the child developed generalized seizures and was brought to an Emergency Department (ED). Her initial fingerstick blood glucose was 108 mg/dL. In the ED, the child was intubated for status epilepticus. Despite aggressive therapy with lorazepam, phenobarbital, and pyridoxine, she had 4 h of intermittent generalized seizure activity. She was extubated on the third hospital day, but appeared to have absence seizures and cortical blindness. Continuous electroencephalogram monitoring, performed weeks later, revealed severe diffuse cerebral dysfunction with multiple epileptogenic foci. The child remains developmentally delayed and is on valproic acid therapy for seizure control. Translation of the Chinese package labeling did not clarify its contents. Tetramethylenedisulfotetramine was finally confirmed by gas chromatography-mass spectrometry (GC-MS) in this rodenticide product and then quantified against a TETS standard that was synthesized in our laboratory.

CONCLUSION

Tetramethylenedisulfotetramine is grouped with other "cage convulsants," such as picrotoxin, since they have a similar intercalating cyclical molecular structure and cause seizures through non-competitive gamma-aminobutyric acid (GABA) antagonism. The oral lethal dose 50% (LD50) in humans is estimated to be as low as 100 microg/kg. Our patient has severe diffuse cerebral dysfunction likely secondary to prolonged seizure activity after exposure to TETS.

[Toxicity and tetramine contents of salivary glands from carnivorous gastropods]

Salivary glands from 29 species of marine carnivorous gastropods in nine families were examined for lethal activity against mice and tetramine content. Mouse lethality was assayed by intravenous injection of buffer extracts into mice, and was detected in 14 species. Heat-stability tests confirmed that toxins in four species were thermolabile, while those in eight species were thermostable. Based on the tetramine contents determined by the colorimetric method using methanolic extracts, the thermostable toxins in seven species (Neptunea eulimatalamellosa, N. vinosa, N. arthritica, N. bulbacea, N. intersculpta f. pribiloffensis, N. intersculpta f. frater pilsbry and Hemifusus tuba) were considered to be tetramine contained at high levels (more than 900 micrograms/g salivary gland), but that in one species (Buccinum opisthoplectum) appeared to be a low-molecular-weight compound differing from tetramine. It is interesting that one (Hemifusus tuba) of the seven species containing high amounts of tetramine belongs to the family Melongenidae, although the other six Neptunea species are members of the family Buccinidae, as expected from previous studies.