Natural toxins最新文献

Bioassay-guided fractionation of the hexane:ethyl acetate (1:1) extract of the leaves of Leucophyllum frutescens (Berl.) I.M.Johnst (Scrophulariaceae) led to the isolation of its phytotoxic constituents diayangambin (1), epiyangambin (2), diasesartemin (3) and epiashantin (4). Phytotoxicity was demonstrated as inhibition of seed germination of Agrostis stolonifera cv. penncross (Poaceae) and inhibition of development of Lactuca sativa L. (Asteraceae) seedlings in a microassay using 24-well plates. Compound 1 was the most phytotoxic to L. sativa, showing strong inhibitory activity at 110 microM. Compound 1 was more active than 2 and 3 in inhibiting the growth of A. stolonifera with I(50) values of 160, 670 and 930 microM, respectively. At a concentration of 500 microM, these compounds inhibited all phases of onion root cell division. This is the first demonstration of antimitotic activity of these furofuran lignans, and the first report of their isolation from this species.

Maitotoxin (MTX), a putative Ca(2+) channel activator produced by the dinoflagellate Gambierdiscus toxicus showed extremely potent hemolytic and ichthyotoxic activities. Hemolysis of 1% mouse blood cell suspension in saline occurred at 15 nM of MTX. The activity was enhanced six-fold in the presence of 10 microM of Ca(2+) and completely blocked by EDTA2Na, indicating its dependency on external Ca(2+). The MTX-induced hemolysis was little affected by L-type Ca(2+) channel blockers (diltiazem, nifedipine, verapamil) but was strongly inhibited by calmodulin blockers (prenylamine and chlorpromazine) or a phospholipase A2 inhibitor (quinacrine). MTX was mimicked by a calcium ionophore, calcimycin. Based on these results, a series of cellular events triggered by MTX were presumed to occur in the following sequence: increased Ca(2+) entry in cells, activation of calmodulin, promotion of phospholipase A2 activity, and finally destruction of cell membrane resulting from hydrolysis of membrane lipids. The sensitivity of blood cells to MTX varied significantly, dependent on the animal sources. Nucleated blood cells of carps and chickens were 100 times more resistant than those of mammals. LC(50) of MTX to freshwater fish Tanichthys albonubes in Ca(2+) free media (pH 8) was 5 nM but was markedly lowered to 3 pM by raising pH to 8 and increasing Ca(2+) concentration to 2 mM. In a marine environment MTX was 2000 times more toxic to fish than 42-di-hydrobrevetoxin-B (PbTx-3), one of the best known ichthyotoxins of red-tide origins.

A new brevetoxin B analog, brevetoxin B4 (BTXB4), was isolated as the major toxin in greenshell mussels, Perna canaliculus, collected in New Zealand at the time of the neurotoxic shellfish poisoning incident. The new analog accounted for nearly two-thirds of the mouse lethality of the shellfish and was determined to be a mixture of N-myristoyl-BTXB2 and N-palmitoyl-BTXB2.

Two samples of Narthecium asiaticum Maxim leaves collected in Japan were found to contain 103 microg(-1) and 160 microg g(-1) dry matter of 3-methoxy-2(5H)-furanone respectively. 3-Methoxy-2(5h)-furanone was suggested to be the toxic principle of N. asiaticum causing nephrotoxicity in cattle in Japan. Two other furanones, which are thought to be non-toxic, were also isolated from the two samples. These were 4-methoxy-2(5H)-furanone and 5-hydroxy-4-methoxy-2(5H)-furanone.

The kinetics of the production of fusaproliferin by Fusarium subglutinans ITEM 2404 in maize and rice cultures was investigated at various incubation temperatures. The growth rate of F. subglutinans was highest at 20 degrees C and 25 degrees C in maize cultures and at 15 degrees C in rice cultures. Although the growth rate was higher in rice than in maize, the maximal production of fusaproliferin was obtained in maize cultures, with a maximum yield (4309 microg g(-1)) at 20 degrees C for 6 weeks. In rice cultures the optimal incubation regimen was at 15 degrees C for 6 weeks, with a fusaproliferin level of 1557 microg g(-1). The production of fusaproliferin at 25 degrees C and 30 degrees C in both substrates was very low, with maximal yield at 25 degrees C of 979 microg g(-1) after 2 weeks and 143 microg g(-1) after 3 weeks in maize and rice cultures, respectively.

Alterations in regional brain concentration of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their metabolites were investigated in male BALB/c mice injected intraperitoneally with bacterial lipopolysaccharide (LPS, 2 mg kg(-1)) or recombinant murine tumor necrosis factor alpha (TNFalpha, 0.1 mg kg(-1)) at 2, 6, 12 and 24 h after the injection. At 2 h post-injection the LPS administration resulted in hypothermia, which was not apparent at later time points. No consistent effects were observed by either LPS or TNFalpha on peripheral leukocyte counts or plasma transaminase levels. Both LPS and TNFalpha slightly elevated NE metabolism in the striatum at 2-12 h. Concentrations of DA and its metabolites were significantly elevated only in the hypothalamus following TNFalpha at 24 h. Tumor necrosis factor alpha exerted pronounced effects on 5-HT metabolism in most brain regions at 2 h. Results suggest that the effect of LPS is more complex compared with TNFalpha because of the endogenous production of other cytokines including the TNFalpha.

The occurrence of an unusual mortality event involving California sea lions (Zalophus californianus) along the central California coast in May 1998 was recently reported. The potent neurotoxin domoic acid (DA), produced naturally by the diatom Pseudo-nitzschia australis and transmitted to the sea lions via planktivorous northern anchovies (Engraulis mordax), was identified as the probable causative agent. Details of DA analyses for anchovy tissues and sea lion feces are described. Domoic acid levels were estimated in anchovy samples by HPLC-UV, and in sea lion feces using the same method as well as a microplate receptor binding assay, with absolute confirmation by tandem mass spectrometry. The highest DA concentrations in anchovies occurred in the viscera (223 +/- 5 microg DA g(-1)), exceeding values in the body tissues by seven-fold and suggesting minimal bioaccumulation of DA in anchovy tissue. HPLC values for DA in sea lion fecal material (ranging from 152 to 136.5 microg DA g(-1)) required correction for interference from an unidentified compound. Inter-laboratory comparisons of HPLC data showed close quantitative agreement. Fecal DA activity determined using the receptor binding assay corresponded with HPLC values to within a factor of two. Finally, our detection of P. australis frustules, via scanning electron microscopy, in both anchovy viscera and fecal material from sea lions exhibiting seizures provides corroborating evidence that this toxic algal species was involved in this unusual sea lion mortality event.

Sterigmatocystin-O-methyltransferase (ST-OMTase), an enzyme catalyzing O-methylation of sterigmatocystin with S-adenosylmethionine (SAM), was purified to electrophoretic homogeneity by immunoaffinity chromatography. A novel spectrofluorometric method was established to quantitatively determine the enzymatic activity of ST-OMTase. The purified protein, with a molecular weight of 40 kDa by SDS-PAGE, was sensitive to thiol reagents and low concentrations of heavy metal ions. Using a nutritional shift assay, the expression patterns for ST-OMTase and the transcripts of its corresponding gene, omtA, correlated well with that for aflatoxin B(1) formation. Neither methyltransferase activity nor omtA, mRNA was detected in the fungal cultures of nonaflatoxigenic isolates, including A. flavus, A. sojae, A. nidulans and A. versicolor under optimal growing conditions for aflatoxin B(1) production.

The principal substance in Narthecium ossifragum (L.) Huds, responsible for the nephrotoxic effects on cattle, moose, goats and other ruminants has been isolated and identified by X-ray crystallography as 3-methoxy-2(5H)-furanone. The Fourier-transform infra-red, 1H and 13C nuclear magnetic resonance, and mass spectra are also given. The concentration in four different batches of plant material varied from 113 to 344 microg g(-1) (wet weight). Extracts of N. ossifragum and fractions derived from them, including purified 3-methoxy-2(5H)-furanone, were each dosed intraruminally, to young goats. 3-Methoxy-2(5H)-furanone of 99.9% purity (15 mg kg(-1) live weight) caused increased concentration of creatinine in serum within 2-3 days, typical of kidney damage caused by N. ossifragum, while toxic effect was obtained down to 4 mg kg(-1) live weight with less purified material (> or = 95%). Toxic effect was also obtained with synthesized 3-methoxy-2(5H)-furanone (30 mg kg(-1) live weight). The isomer 4-methoxy-2(5H)-furanone, detected in some of the batches of the plant material, was not toxic when dosed at 60 mg kg(-1) live weight.

In October of 1996, a Gymnodinium breve bloom occurred in shellfish harvesting waters of Alabama, Mississippi and Louisiana, Gulf of Mexico, USA. Bloom densities reached 5.6x10(5) cells liter(-1) and bloom residence at shellfish sampling stations ranged from 3 to 28 days. Brevetoxin-2 dominated G. breve toxin profiles in bloom seawater extracts. Shellfish toxicity, assessed by mouse bioassay, exceeded the guidance level for up to 75 days after the bloom had dissipated. Cytotoxicity assays and mouse bioassays showed similar temporal patterns of shellfish toxicity, but the two methods differed in estimations of brevetoxin-3 equivalent toxicity by a factor of 93 to 1. LC-ESI-MS showed the temporal patterns in shellfish toxicity reflected metabolism of G. breve toxins. The molecular ions m/z 1004, 1017 and 1033 dominated LC-ESI-MS spectra of toxic chromatographic fractions from the extracts and were identified as brevetoxin metabolites on the basis of LC-APCI-MS-MS. The discrepancy between cytotoxicity and mouse bioassay estimates of brevetoxin-3 equivalent toxicity resulted from the difference in extraction efficiency of solvents used in the respective methods and the relative sensitivity of the assays to toxin metabolite mixtures present in the extracts. The normalized cytotoxicity assay showed 75% agreement with mouse bioassay positive test samples and 64% agreement with mouse bioassay negative test samples. Published in 1999 by John Wiley & Sons, Ltd.