Toxin and toxicity identification of mangrove horseshoe crab Carcinoscorpius rotundicauda collected from South China

Saving the overlooked mangrove horseshoe crabs-A perspective from enhancing mangrove ecosystem conservation

Despite being widely distributed in Asia, Carcinoscorpius rotundicauda is often overlooked and, its population status remains unclear. Moreover, it is threatened by illegal harvesting and degradation of mangrove ecosystems. Protecting its habitat is essential for population and biodiversity conservation, as mangroves provide nursery grounds and food supply for C. rotundicauda. This review discusses the biological characteristics of C. rotundicauda, including ecology, nutrition, life history, toxicology, and immunology. It also presents information about its distribution and population status. The review emphasizes the challenges faced by C. rotundicauda and proposes a conservation framework that involves the participation of local residents to facilitate conservation efforts. Collaboration between local residents and communities is proposed to protect and monitor the mangrove ecosystem. Additionally, this framework can support field research, protect C. rotundicauda juveniles and other species, and ensure the livelihood of local residents through participation in carbon trading markets and eco-industries such as eco-farming and eco-tourism.

Tetrodotoxins in Larval Development of Ribbon Worm Cephalothrix cf. simula (Palaeonemertea, Nemertea)

The toxic ribbon worm, Cephalothrix cf. simula (Palaeonemertea, Nemertea), possesses extremely high concentrations of tetrodotoxin (TTX). Although TTX has been found in the eggs of this species, the fate of the toxin in the ontogeny of the animal has not been explored. Here, using high performance liquid chromatography with tandem mass spectrometry and immunohistochemistry with anti-TTX antibodies, we examined levels, profile, and localization of TTX and its analogues (TTXs) in larvae of C. cf. simula throughout 41 days post-fertilization. A detailed investigation of cells in sites of TTX-accumulation was performed with light and electron microscopy. Newly hatched larvae possessed weak TTX-like immunoreactivity in all cells. With subsequent development, intensity of TTX-labeling in the ectodermal structures, mesodermal cells and apical cylinder of the apical gland increased. In the ectodermal structures, an intense TTX-labeling was observed in the multiciliated, type II granular, type I mucoid, and basal cells of the epidermis, and in the type III granular cells of the mouth gland. In the mesoderm, TTX was localized in the muscle and unigranular parenchyma-like cells. Eggs and larvae of C. cf. simula contained five TTXs, with two major toxins - TTX and 5,6,11-trideoxyTTX. Level and relative proportion of TTXs did not differ significantly among developmental stages, confirming that larvae obtained toxins from maternal eggs and were able to retain it. The results of this study provide insights into the formation of TTX-bearing apparatus of C. cf. simula through the larval development.

Simultaneous analysis of paralytic shellfish toxins and tetrodotoxins in human serum by liquid chromatography coupled to Q-Exactive high-resolution mass spectrometry

Paralytic shellfish toxins (PSTs) and tetrodotoxins (TTXs) are powerful neurotoxins. Previous research reported that PSTs and TTXs are found together in seafoods and may pose a serious hazard to public health. In this study, a new analytical method combining modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) with high-performance liquid chromatography coupled to Q-Exactive Orbitrap high-resolution mass spectrometry was developed and validated for the quantification of 10 PSTs and 2 TTXs in human serum. Chromatographic separation was achieved using the HILIC TSK-Gel Amide-80 column. The mass spectrometer was operated in full scan/dd-MS²(data-dependent MS²) mode, and for quantification analysis. The dd-MS² resolution was set to 17,500 fullwidthat halfmaximum （FWHM）. Results showed that methanol with 1 % (v/v) acetic acid extraction combined with 50 mg graphitized carbon black (GCB) and 50 mg octadecyl bonded silica gel (C18) was most suitable for purification. The mean recovery for all toxins ranged from 85.3 % to 118.2 % (RSD < 12 %). The limits of detection and quantification for human serum were in the ranges of 0.67-2.61 and 2.23-8.69 ng mL^-1, respectively. The method was applied to analyze toxins in serum samples obtained from three poisoned patients in a case of poisoning caused by consumption of toxin-contaminated gastropoda (Bullacta exerata). The study has important application for rapid and accurate diagnosis of PSTs and TTXs toxin poisoning patients in clinic.

Tetrodotoxin in Asian horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus across different life stages from northern Beibu Gulf, China

Horseshoe crabs (HSCs) are a group of ancient chelicerates with great ecological and biomedical importance. Food poisonings caused by the consumption of Asian HSCs have significant impacts on public health and safety. This study measured tetrodotoxin (TTX) concentrations in two HSC species across various life stages in May 2020 from the northern Beibu Gulf, their most important spawning and nursery habitats in China. The average TTX contents in both Carcinoscorpius rotundicauda and Tachypleus tridentatus ranged 6.2-8.0 μg/kg and 3.8-8.4 μg/kg, respectively. While sampling location, growth and molt stages have little influence on TTX distribution in both species, significantly higher levels of TTX were detected in hemolymph, but lower in pooled tissues of early-instar juvenile T. tridentatus. These results provide a regional view of TTX occurrence and distribution in HSCs during their spawning season, which are critical for future studies to enhance understanding of TTX dynamics and formation in HSCs.

An Overview of the Anatomical Distribution of Tetrodotoxin in Animals

Tetrodotoxin (TTX), a potent paralytic sodium channel blocker, is an intriguing marine toxin. Widely distributed in nature, TTX has attracted attention in various scientific fields, from biomedical studies to environmental safety concerns. Despite a long history of studies, many issues concerning the biosynthesis, origin, and spread of TTX in animals and ecosystems remain. This review aims to summarize the current knowledge on TTX circulation inside TTX-bearing animal bodies. We focus on the advances in TTX detection at the cellular and subcellular levels, providing an expanded picture of intra-organismal TTX migration mechanisms. We believe that this review will help address the gaps in the understanding of the biological function of TTX and facilitate the development of further studies involving TTX-bearing animals.

Simultaneous Determination of Tetrodotoxin in the Fresh and Heat-Processed Aquatic Products by High-Performance Liquid Chromatography-Tandem Mass Spectrometry

Tetrodotoxin (TTX) was simultaneously detected in the fresh and heat-processed aquatic products by high-performance liquid chromatography-tandem mass spectrometry method. The detection conditions were investigated, including the chromatography column and mobile phase. Based on the optimized parameters, a sensitive determination method of TTX was established. The proposed method featured the merits of a good linear relationship between signal and TTX concentration (R2 = 0.9998), a wide detection matrix-based range of 0.2-100 ng/g, and a low detection limit of 0.2 ng/g, etc. The spiked assays evidenced its accuracy and reliability with recoveries of 90.5-107.2%. Finally, the developed method was simultaneously successfully applied in the determination of TTX in various fresh and heat-processed aquatic products.

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 440 papers for 2019), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Methods used to study marine fungi and their chemical diversity have also been discussed.

Tetrodotoxin in marine bivalves and edible gastropods: A mini-review

Tetrodotoxin (TTX) is a potent neurotoxin responsible for countless human intoxications and deaths around the world. The distribution of TTX and its analogues is diverse and the toxin has been detected in organisms from both marine and terrestrial environments. Increasing detections seafood species, such as bivalves and gastropods, has drawn attention to the toxin, reinvigorating scientific interest and regulatory concerns. There have been reports of TTX in 21 species of bivalves and edible gastropods from ten countries since the 1980's. While TTX is structurally dissimilar to saxitoxin (STX), another neurotoxin detected in seafood, it has similar sodium channel blocking action and potency and both neurotoxins have been shown to have additive toxicities. The global regulatory level for the STX group toxins applied to shellfish is 800 μg/kg. The presence of TTX in shellfish is only regulated in one country; The Netherlands, with a regulatory level of 44 μg/kg. Due to the recent interest surrounding TTX in bivalves, the European Food Safety Authority established a panel to assess the risk and regulation of TTX in bivalves, and their final opinion was that a concentration below 44 μg of TTX per kg of shellfish would not result in adverse human effects. In this article, we review current knowledge on worldwide TTX levels in edible gastropods and bivalves over the last four decades, the different methods of detection used, and the current regulatory status. We suggest research needs that will assist with knowledge gaps and ultimately allow development of robust monitoring and management protocols.