Natural toxins最新文献

A bloom of the pennate diatom Pseudo-nitzschia, several species of which are associated with the production of the potent excitotoxin domoic acid, was observed in a Puget Sound, Washington embayment in July and August of 1997. Penn Cove, which receives nutrients from the nearby Skagit River and abundant sunshine during summer months due to its location in the rain shadow of the Olympic Mountains, is the home of a commercial mussel farm which supplies shellfish to many coastal areas of the USA. Levels of domoic acid in mussels increased to 3 ppm on 6 and 10 July, corresponding to the observation of a brown algal bloom in Penn Cove. Four species of Pseudo-nitzschia (P. pungens, P. multiseries, P. australis, and P. pseudodelicatissima) were present in our samples from the cove, corresponding to levels of domoic acid in seawater ranging from 0.1-0.8 mirog l(-1) as measured by a receptor binding assay. The highest Pseudo-nitzschia concentration during the time of our sampling was 13 million cells per liter on 28 July. The bloom of Pseudo-nitzschia occurred after a period of strong discharge from the Skagit River and rain accompanied by elevated south and southeasterly winds. Stratification of the cove, providing optimal bloom conditions, was facilitated by weak winds, sunshine, and a freshwater lens at the mouth of the cove. The position of the Pseudo-nitzschia bloom was influenced by buoyancy fronts caused by exchange of water within the cove with that of Saratoga Passage. The decay of this bloom in Penn Cove was accompanied by decreasing nitrate levels at all measured depths. These and future observations aid in the development of a model for prediction of toxic bloom events in the shallow embayments of Puget Sound.

The natural occurrence of ochratoxin A in grain samples of 23 rice cultivars was in the range 0.01-1.0 ng g(-1) rice. Samples from the same cultivars were surface sterilized with NaClO, dried to 19% water content and equilibrated at water activity (a(w)) 0.75 and 20 degrees C for 8 days. Varietal differences in equilibrium w/w water content (p < 0.0001) were found, reflected by differences in amylose and protein contents. Samples were then inoculated with an isolate of Penicillium verrucosum with 1 ml spore suspension to each 50 g rice sample; and incubated at a(w) 0.75 and 20 degrees C for 23 weeks. During incubation, ochratoxin A was accumulated in all cultivars. Significant varietal differences in ochratoxin A accumulation were observed (p < 0.0001). Grain samples with less than 19.5% equilibrium water content accumulated less ochratoxin A (p < 0.005). In a multiple regression analysis accumulated ochratoxin A content was expressed as a function of natural occurrence of ochratoxin A (p < 0.05), equilibrium water content at time of inoculation (p < 0.005), 1000-grain weight (p < 0.1), and chalkiness of endosperm (p < 0.05), with p < 0.0001 for the full function. Naturally occurring ochratoxin A was the strongest independent variable with p < 0.0005 for the slope coefficient in single regression. Rice cultivars IR8, IR24, IR620030-18-2-2 and R91-1081-1 had exceptionally low accumulation of ochratoxin A.

A comparative study of the metabolism of 1,2,3 (14)C-ODAP and 4,5 (14)C-ODAP in mice, rats and chicks has been carried out. Following oral administration of 1,2,3 (14)C-ODAP to either black or white mice, nearly 16% of the radioactivity appeared in the expired CO2 within 8 h, while in the rat only 3% of it appeared and in chicks it was less than 2%. No 14CO2 appeared in the expired air in mice given 4,5 (14)C-ODAP. Electrophoregrams of the spot urine samples from the animals given 1,2,3 (14)C-ODAP showed the presence of one radioactive metabolite (metabolite-1) in addition to ODAP. While the urine from rats and mice given 4,5 (14)C-ODAP indicated the presence of metabolite-1 as well as 14C-oxalate, in chicks, however, no 14C-oxalate was present and only metabolite-1 could be detected. The results indicate that ODAP can to some extent undergo oxidation in vivo in mice (and to a lesser extent in rats) leading to the formation of CO2 and oxalate and a similar pathway might be more prominent in humans leading to a near complete oxidation of ODAP.

The skin secretion of the caecilian Siphonops paulensis (SpSS) induces a time-and dose-dependent hemolytic response on red blood cells (RBC). When RBC from various animals species were subjected to the action of SpSS, a range of sensitivities was evident, sheep erythrocytes being the most susceptible, human, mouse and rabbit having moderate susceptibility, cow, snake and toad erythrocytes being more resistant, while S. paulensis RBC were entirely resistant. The hemolytic activity of SpSS was inhibited at temperatures higher than 60 degrees C. Both trypsin- and chymotrypsin-treated SpSS were ineffective in inducing RBC lysis. The treatment of SpSS with sheep RBC ghosts reduced its activity. There is no phospholipase activity in the SpSS.

A new analog of yessotoxin, 1-desulfoyessotoxin, was isolated from the digestive glands of mussels growing in the Sognefjord, Norway. Its structure was determined by NMR and negative ion CID MS/MS experiments. 1-Desulfoyessotoxin can be detected by the fluorometric HPLC method analogous with other yessotoxins.

The neurotoxins kainic acid and domoic acid are potent agonists at the kainate and alphaamino-5-methyl-3-hydroxyisoxazolone-4-propionate (AMPA) subclasses of ionotropic glutamate receptors. Although it is well established that AMPA receptors mediate fast excitatory synaptic transmission at most excitatory synapses in the central nervous system, the role of the high affinity kainate receptors in synaptic transmission and neurotoxicity is not entirely clear. Kainate and domoate differ from the natural transmitter, L-glutamate, in their mode of activation of glutamate receptors; glutamate elicits rapidly desensitizing responses while the two neurotoxins elicit non-desensitizing or slowly desensitizing responses at AMPA receptors and some kainate receptors. The inability to produce desensitizing currents and the high affinity for AMPA and kainate receptors are undoubtedly important factors in kainate and domoate-mediated neurotoxicity. Mutagenesis studies on cloned glutamate receptors have provided insight into the molecular mechanisms responsible for these unique properties of kainate and domoate.

Conformational behaviour of kainic acid in aqueous solution was elucidated by molecular mechanics and dynamics. The pucker of the five-membered ring in kainic acid was examined and compared with that of model compounds. In cyclopentane there is no barrier to pseudorotation, so that all puckered states coexist. In pyrrolidinium, the presence of a hetero-atom in the ring introduces a small barrier (about 0.6 kcal mol(-1)) to pseudorotation, separating two stable regions, A and B, which are equivalent by symmetry. In proline, the presence of the carboxylate group on C2 removes the symmetry but two stable conformational minima, A and B, remain. In kainic acid, the presence of side-chains on C3 and C4 introduces complications resulting in additional sub-minima in both regions, A and B. In solution, kainic acid is a complex mixture of conformers with comparable energies, because of the combination of several stable states of the pyrrolidinium ring with the torsional degrees of freedom arising from the two side-chains. The individual geometries, energies, and estimates of relative populations of these conformers were obtained from molecular dynamics simulations. The calculations were validated by a comparison of predicted inter-proton distances and vicinal proton coupling constants with the experimental quantities derived from NMR spectra.

The placental and lactational transfer of ochratoxin A (OA) was investigated in a cross-fostering study in rats. Dams were given 50 microg OA(-1) kg body weight by gastric intubations 5 times a week for 2 weeks before mating, during gestation and then 7 days a week during lactation. Neonates from OA-treated dams were cross-fostered at birth to control dams treated with only vehicle. In the same way, neonates from control dams were cross-fostered to OA-treated dams. Treatment with OA did not result in any effects on birth weight or growth development of the pups during the first 21 days of life. There were no effects on milk quality as measured by milk lipids, protein or lactose concentrations, or on milk production, assessed by the mammary gland content of RNA and DNA. A mean milk:blood ratio of approximately 0.6 was found. The dose of OA from milk to the suckling pup at 14 days of age can be calculated to about 50 microg kg(-1) body weight(-1) day, which is similar to the dose given to the dams. Pups exposed to OA only via milk had blood and kidney levels of OA approximately 3 times higher than their dams, indicating a high absorption and/or a low excretion of OA in the sucklings. At 14 days of age the highest blood and kidney levels of OA were found in offspring exposed both via placenta and milk, with the highest contribution from milk. Offspring exposed only via milk had about 4-5 times higher levels of OA in blood and kidney compared to offspring exposed only via placenta. As milk could be a significant source of OA exposure in newborns, adverse health effects resulting from postnatal exposure should be studied and evaluated in the risk assessment of OA.

Domoic acid (DA) was first detected in shellfish in New Zealand after the implementation of a comprehensive biotoxin monitoring programme for amnesic, paralytic, diarrhetic and neurotoxic shellfish toxins, following a suspected neurotoxic shellfish poisoning (NSP) event in early 1993. Both phytoplankton monitoring and shellfish flesh testing programmes have led to an extensive database which has helped link species of Pseudo-nitzschia to specific DA outbreaks. In 1994, P. pungens and P. turgidula were associated with DA contamination of shellfish, and cultured isolates of these species proved to be toxin producers. During 1996 the use of species-specific ribosomal RNA (rRNA)-targeted oligonucleotide probes and DA immunoassays led to the discovery of toxin production by P. fraudulenta, and showed the nontoxic P. heimii to be a major bloom former. Pseudo-nitzschia delicatissima, P. pseudodelicatissima and P. multiseries, also identified using rRNA-targeted probes, have been linked to DA contamination of New Zealand shellfish; P. australis is the main cause of DA in scallops. The relative amnesic shellfish poisoning (ASP) risk associated with different species, largely determined by DA immunoassays of cultured isolates, is now used by some regulators to refine risk assessments. Species identification is therefore vital so that shellfish growers, and health and industry officials, can make safe and economically sound harvesting decisions. The development and field trialling of DNA probes is proving invaluable in this context.