Isolation and structural elucidation of an ichthyocrinotoxin from the smooth trunkfish (Lactophrys triqueter Linnaeus)

Stonefish (Synanceia spp.) Ichthyocrinotoxins: An ecological review and prospectus for future research and biodiscovery

Marine organisms possess a diverse array of unique substances, many with wide ranging potential for applications in medicine, industry, and other sectors. Stonefish (Synanceia spp.), a bottom-dwelling fish that inhabit shallow and intertidal waters throughout the Indo-Pacific, harbour two distinct substances, a venom, and an ichthyocrinotoxin. Stonefish are well-known for the potent venom associated with their dorsal spines as it poses a significant risk to public health. Consequently, much of the research on stonefish focusses on the venom, with the aim of improving outcomes in cases of envenomation. However, there has been a notable lack of research on stonefish ichthyocrinotoxins, a class of toxin that is synthesised within specialised epithelial cells (i.e., tubercles) and exuded onto the skin. This has resulted in a substantial knowledge gap in our understanding of these animals. This review aims to bridge this gap by consolidating literature on the ecological functions and biochemical attributes of ichthyocrinotoxins present in various fish species and juxtaposing it with the current state of knowledge of stonefish ecology. We highlight the roles of ichthyocrinotoxins in predator defence, bolstering innate immunity, and mitigating integumentary interactions with parasites and detrimental fouling organisms. The objective of this review is to identify promising research avenues that could shed light on the ecological functions of stonefish ichthyocrinotoxins and their potential practical applications as therapeutics and/or industrial products.

Further isolation and characterization of grammistins from the skin secretion of the soapfish Grammistes sexlineatus

Soapfishes contain peptide toxins (grammistins) in the skin secretion. Two grammistins (Gs 1 and Gs 2) and six grammistins (Pp 1, Pp 2a, Pp 2b, Pp 3, Pp 4a and Pp 4b) have already been isolated from Grammistes sexlineatus and Pogonoperca punctata, respectively. In this study, five grammistins (Gs A-E), together with grammistins Gs 1 and Gs 2, were further isolated from G. sexlineatus by gel filtration and reverse-phase HPLC. Sequence analyses revealed that grammistins Gs A (28 residues) and Gs C (26 residues) are analogous to grammistin Pp 3 and grammistin Gs B (12 residues) to grammistin Pp 1, while grammistins Gs D (13 residues) and Gs E (13 residues) are identical with grammistins Pp 1 and Pp 2b, respectively. Grammistins Gs A-C exhibited antibacterial activity with a broad spectrum against nine species of bacteria in common with the other grammistins but had no hemolytic activity differing from the other grammistins. Grammistins Gs A-E, Gs 1 and Gs 2 could release carboxyfluorescein entrapped within liposomes made of either phosphatidylcholine or phosphatidylglycerol/phosphatidylcholine (3:1), demonstrating their membrane-lytic activity. However, no clear relationship between the membrane-lytic activity and the biological activity of grammistins was recognized.

Isolation and structures of grammistins, peptide toxins from the skin secretion of the soapfish Grammistes sexlineatus

Two peptide toxins (named grammistins Gs 1 and Gs 2) with hemolytic and ichthyotoxic activities were isolated from the skin secretion of the soapfish Grammistes sexlineatus. Grammistin Gs 2 showed 6-11 x higher hemolytic activity and 10x higher ichthyotoxicity than grammistin Gs 1. The complete amino acid sequences of Gs 1 comprising 25 residues and Gs 2 comprising 24 residues were determined. Although a search by the database failed to find any homologous toxins from other sources, the grammistins were similar in secondary structures as well as biological activities to the two classes of peptide toxins, melittin from the bee venom and pardaxins from the skin secretion of two species of soles. CD experiments and helical wheel projections showed that the grammistins were randomly coiled in distilled water but formed amphiphilic alpha-helices in the presence of SDS micelles. In addition, they were found to be surface seeking peptides by the Eisenberg plot and assumed to exist as aggregates of 3-4 molecules. Interestingly, grammistin Gs 2 is much more abundant in amphiphilic alpha-helices and much higher in biological activities than melittin and pardaxins as well as grammistin Cs 1.

Occurrence of toxins, other than paralysing type, in the skin of Tetraodontiformes fish

Puffer fish (Tetraodontidae and Diodontidae) possess paralysing toxins (tetrodotoxin and analogues) that are secreted upon stimulation. In a previous work it was demonstrated that mucous secretion from the puffer fish Sphoeroides spengleri, when mixed in sea water passing through the orobranchial cavity of groupers, induced cardiorespiratory alterations. In the present study, skin secretions from Ciclichthys spinosus, S. spengleri and Diodon hystrix were tested on crustacean nerves, sea urchin eggs and mouse erythrocyte suspensions to verify neurotoxic and cytotoxic activities. Ciclichthys spinosus and D. hystrix secretions induced transient depolarizations with 0.16 mg and blocked crustacean nerve conduction after prolonged exposure. Both secretions had cytotoxic effects; when applied to sea urchin eggs they caused cleavage inhibition and anomalies in a dose-dependent manner (ED50 +/- S. E. M. = 2.59 +/- 0.08 mg/ml for C. spinosus and 1.23 +/- 0.07 mg/ml for D. hystrix); moreover, hemolysis occurred with an ED50 = 0.76 mg/ml of 0.5% mouse erythrocyte suspensions to C. spinosus and 0.59 mg/ml to D. hystrix. These secretions were not lethal in acute toxicity tests, even at 335 mg/ml. The neurotoxic components were thermolabile while the hemolytic activity was resistant to boiling. Tests with the secretion from S. spengleri did not show cytotoxic effects but promptly blocked action potentials of crustacean nerves and were lethal for mice in acute toxicity rests. When applied to groupers, the C. spinosus secretion caused cardiorespiratory alterations. These results suggest the presence of neurotoxins (other than tetrodotoxin) and cytotoxins in skin of diodontid puffer fish.

Distribution and chemical composition of the toxic skin secretions from trunkfish (family Ostraciidae)

The components of the mucus skin secretions from eight species of trunkfish found in the coastal waters of Australia were analyzed by combined chemical ionization-gas chromatography mass spectrometry. The species investigated were Anoplacapros lenticularis, Aracana aurita, Aracana ornata, Lactoria fornasini, Ostracion cubicus, Rhinesomas reipublicae, Strophiurichthys inermis and Strophiurichthys robustus. The beta-substituted choline chloride esters (mainly acetoxy, but with some species having butyryloxy, valeryloxy and one species with caproyloxy) of palmitic acid were the predominant components in almost all cases. High concentrations of monounsaturated palmitic acid were present in S. inermis and S. robustus. Trace quantities of C14, C17 and C18 choline chloride esters were also detected as were compounds where the choline moiety was modified by addition of one extra carbon.

[Venomous animals and their venoms]

Animal venoms have aroused great interest during the past decades. During recent years, especially substances from marine animals have been investigated, not only in regard to their chemical structures but also to their biological relevance. Neurotoxic peptides from scorpions opened new aspects of action mechanisms on cell membranes; from snake venoms also ingredients have been obtained which serve as valuable pharmaceutical drugs.

A non-proteinaceous toxin from the venomous spines of the lionfish Pterois volitans (Linnaeus)

The venomous spines of P. volitans contain a non-proteinaceous ichthyotoxin of low molecular weight. This toxin could be isolated only from spines excised from the living fish; the toxin is apparently destroyed following death, as the extracts of the spines of the dead fish were non-toxic.