Journal of natural toxins最新文献

The Stx family contains two types called Stx1 (verotoxin 1: VT1 or Shiga-like toxin: SLT1) and Stx2 (VT2, SLT2); both toxins are encoded by bacteriophages. Stx1 is identical to Shiga toxin produced by Shigella dysenteriae type I. Stx2 is heterogeneous and immunologically different from Stx1. Although many variations are found in Stx family, all Stx has an A-B structure: the A subunit has N-glycosidase activity and the B subunit binds to a membrane glycolipid, globotriaosylceramide (Gb3). The A subunit cleaves a single adenine residue from the 28S rRNA component of eukaryotic ribosomes, resulting in inhibition of protein synthesis. Stx-producing Escherichia coli (STEC) is known to cause hemorrhagic enterocolitis and hemolytic-uremic syndrome (HUS). Stx plays a role in the occurrence of blood in the feces and in the HUS by their action on the endothelial cells of blood vessels in the intestinal submucosa and in the renal glomeruli. Epidemiologically, Stx2 seems to be more important than Stx1 in development of HUS. The action of Stx is not limited to inhibition of protein synthesis. Stx induces macrophages to express tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and interleukin-6 (IL-6) in vitro. These cytokines and lipopolysaccharide (LPS) are reported to increase the susceptibility of cells to Stx. A variety of cells such as tubular epithelial cells, may be targets for Stx-mediated apoptosis. Apoptosis is considered to contribute to the pathogenesis of HUS caused by STEC. In this review, recent progress in Stx-related research is summarized.

An edema factor was isolated from the venom of Trimeresurus elegans using HW-55, CM-Cellulose, and Mono S column chromatographies. Homogeneity was demonstrated by the formation of a single band in polyacrylamide gel electrophoresis (pH 8.3). The edema factor has a molecular weight of 25,500, an isoelectric point of 7.5, and express edema, proteolytic and capillary permeability-increasing activities. Edema, proteolytic and capillary permeability-increasing activities are inhibited by ethylenediaminetetraacetic acid (EDTA), o-phenanthroline, and N-bromosuccinimide. Additionally, this factor exhibits kinin-releasing activity. The edema factor possesses proteolytic activity as shown by hydrolyzing the Val(3)-Asn(4), His(5)-Leu(6), Ser(9)-His(10), Ala(14)-Leu(15), Leu(15)-Tyr(16), Tyr(16)-Leu(17), and Glu(21)-Arg(22) bonds of oxidized insulin B chain. The A alpha, B beta, and gamma chains of human fibrinogen were also hydrolyzed. The edema factor was found to contain 1 mol of zinc and 2 mols of calcium per mol of protein and the amino-terminal sequence was determined.

Corn samples suspected of causing refusal-to-eat syndrome in dairy cattle were examined mycologically. Fusarium moniliforme (14 isolates) and F. proliferatum (12 isolates) were the predominant fungi present. These isolates were tested for mycotoxin production on rice at 25 degrees C. Each strain of F. moniliforme produced fumonisin B1 (FB1: 378-15,600 ppm) and fumonisin B2 (FB2: 2-1050 ppm). Each strain of F. proliferatum produced moniliformin (45-16,000 ppm), FB1 (27-6140 ppm), and FB2 (5-1550 ppm). In addition, a new Fusarium metabolite of molecular composition C21H38N2O6 was produced by 10 of the F. moniliforme isolates and 7 of the F. proliferatum isolates. The metabolite's 1H- and 13C-NMR, HRFAB/MS and IR spectra indicate an alpha amino acid. It is toxic to Lemna minor L. duckweed (LD50 100 micrograms/mL).

We used a polymerase chain reaction (PCR) based cloning strategy to isolate cinnamomin genes from Phytophthora cinnamomi 8601, a pathogen responsible for cranberry root rot. Complete DNA sequence analysis of nine recombinant clones revealed two different classes of genes, each class consisting of genes with identical DNA sequences. Both classes of genes (Cin-1 and Cin-2) contained an open reading frame encoding a protein of 122 amino acid residues. The encoded proteins, named cinnamomin-1 and cinnamomin-2 (Cin-1 and Cin-2), were highly homologous to other proteins of the elicitin family and contained a 19 amino acid residue long signal peptide sequence. Both Cin-1 and Cin-2 proteins showed higher degree of sequence homology to the alpha-elicitins than beta-elicitins; moreover, a Val residue was found at position 13 of the putative mature Cin-1 and Cin-2 proteins. Because alpha-elicitins and beta-elicitins are known to contain a Val and a Lys residue, respectively, at this position, we concluded that both Cin-1 and Cin-2 genes from P. cinnamomi 8601 encode for alpha cinnamomins, Cin-1 and Cin-2.

The psoralens are secondary plant metabolites found in many fruits and vegetables. Synthetic forms of 5-methoxypsoralen (bergapten) and 8-methoxypsoralen (xanthotoxin) have been used in combination with UV radiation in skin photochemotherapy for decades. However, handling or ingestion of psoralen-containing plants as well as medicinal use of these compounds have been shown to cause human health hazards. We evaluated the subacute toxicity of bergapten and xanthotoxin in a mammalian model by mixing individual chemicals into mouse diet at 0, 250, and 1000 ppm, and in combination at 500 ppm each. Feeding on individual dietary treatments at 1000 ppm significantly reduced total liver cytochrome P450 (CYP) levels in female mice compared with the control diet, but not in males. However, combining the two chemicals resulted in a significant induction of total CYP450 in both males and females. Both the combined diet and bergapten at 250 ppm caused a weak induction of CYP1A1. Weight gain was significantly less in males fed either the combined or 1000 ppm diets, while only the combined diet induced a significant weight reduction in females compared with the control diet. The psoralens also caused hypertrophy of centrolobular hepatocytes in livers of treated animals in a manner consistent with morphological alterations seen in rodent livers exposed to liver CYP-inducing agents. Neither bergapten nor xanthotoxin, however, induced a significant dose-dependent toxicity in either male or female mice, suggesting that mice may not represent a good laboratory animal model for evaluating the toxicological effects of psoralens.

The effects of intramuscular (i.m.) injection of a sub-lethal dose of cobra venom (0.015 microgram/gm body weight) on the histological and histochemical patterns of the kidney of rabbit were examined after 3, 6, and 12 hr. of envenomation. The histological observations after 3 hr. of envenomation showed glomerular congestion together with slight swelling of the cortical tubular epithelia. However, no changes were recorded in the medullar tubules. Serious alterations were recorded after 6 hr. of envenomation. It included thickening of the Bowman's capsules, signs of mesangiolysis, and glomerular collapse. The cortical tubular epithelia were swollen and revealed cytoplasmic granulation, coagulation, or depletion. Nuclear pyknosis and cellular damage were recorded in some areas. The medullar tubules showed cytoplasmic degeneration with no nuclear changes. By 12 hr. of envenomation a higher degree of severity was recorded. The glomerular tufts were hypertrophied or suffered from partial damage. Mesangiolysis and glomerulolysis were common and some glomerular tufts were completely transformed to clumps of hyaline casts. The cortical tubules showed hyaline coagulation, together with severe tubular damage in which the boundaries of the individual tubule cannot be identified. Numerous inflammatory cells were observed invading the damaged epithelial cells and the intertubular spaces. The medullar tubules showed swollen epithelia with cytoplasmic changes and nuclear pyknosis or karyolysis. Histochemically, the polysaccharide inclusion was increased in the glomerular tufts, the Bowman's capsules, and the basement membranes and brush borders of the renal tubules after 3 and 6 hr. of envenomation. By 12 hr. of envenomation, decreased PAS reactivity was recorded in all renal components except the glomerular tufts which exhibited intensive reactivity. Time-dependent depletion of lipid, protein, and RNA components was recorded in the renal tissues of the three envenomed groups. However, no changes in DNA reactivity were detected in renal tissues of the 3 hr. envenomed group. The nuclei of certain renal tubules revealed weak DNA reactivity after 6 hr. of envenomation, while most of the nuclei lost their contents by 12 hr. of envenomation. The results indicated serious histological and histochemical alterations induced in the renal tissues by 6 hr. of envenomation. Such alterations could indicate a disturbance in the functional activity of the kidney during envenomation. Therefore, nephrotoxicity should be considered as one of the serious consequences of such venom.

One virulence determinant of Staphylococcus aureus is Beta-toxin, a 37 Kd magnesium-dependent sphingomyelinase C. This toxin lyses erythrocytes (RBCs) containing sphingomyelin in the outer lipid layer of their plasma membrane. Although membranes of both human polymorphonuclear leukocytes (PMNs) and lymphocytes (MNLs) contain small amounts of sphingomyelin, the effect of Beta-toxin on these cells remains controversial. The purpose of this study was to investigate the hemolytic activity of this toxin on RBCs of various species and determine the leukotoxic nature on several types of human leukocytes. One nanogram of Beta-toxin lysed 115,000 sheep erythrocytes (sRBCs) and 82,000 human erythrocytes (hRBCs) in a 'hot-cold' assay and caused cytotoxicity to 325 PMNs and MNLs. Both hemolytic and leukotoxic activity were found to be magnesium-dependent. RBC susceptibility to Beta-toxin correlated with the reported sphingomyelin content of each species. Scanning electron microscopy (SEM) demonstrated that 'hot-cold' incubation with Beta-toxin in the presence of magnesium caused significant morphological changes in the surface structure of both RBCs and PMNs. The changes included the formation of pits and membrane invaginations in the RBCs. The PMNs lost their ruffled membrane appearance and showed overall membrane disintegration. This study demonstrated that the viability of sphingomyelin-containing PMNs and MNLs was significantly decreased by the addition of Beta-toxin, indicating that this toxin does, in fact, have a leukotoxic nature. Leukocytes did not have significant membrane invaginations unlike toxin-treated RBCs; therefore, it is possible that leukotoxicity does not result from membrane lysis.

The occurrence of palytoxin or its congener in fish extracts has been presented in this study. The presences of hemolytic factors in fish extracts of Hawaiian reef fish and their implication in ciguatera poisoning have been shown by the sheep erythrocyte assay. By use of the anti-palytoxin inhibition assay with fish extracts and sheep red blood cell (RBC), it was shown that palytoxin was one of the major factors in the lysis of sheep erythrocytes. Ouabain, an antagonist of palytoxin for the Na+/K+ ATPase receptor on RBC, also showed inhibition of sheep RBC lysis by fish extracts. From these results, it was concluded that, in part, palytoxin and other palytoxin-related, hemolysin-like factors in fish extracts were responsible for sheep cell hemolysis.

Pyrrolic metabolites from pyrrolizidine alkaloids (PAs) were detected in liver and dried blood samples using a gas chromatography/tandem mass spectrometry (GC/MS/MS) selected product-ion-monitoring method. A calibration curve was constructed using a protein-metabolite conjugate spiked into dried bovine blood. These spiked samples served as a model for tissues from animals poisoned by the toxic metabolite of PAs. Tissue samples from pigs fed various amounts of the PA alkaloid riddelliine (from Senecio riddellii) were analyzed for pyrrolic metabolites, and the results were applied to the calibration curve to provide a measure of the degree of PA poisoning. Pyrrolic metabolites were detected in liver and blood samples of all poisoned animals at levels between 2 and 64 ppm. Although differences in metabolite levels could be discerned under the reported experimental conditions, the amount detected did not correlate with the dose of riddelliine given; and livers fixed with formalin gave greatly reduced recovery than those same livers either frozen or freeze dried.

Pearce (1973) reported the absence of NGF in the venoms of bees, scorpions, spiders, and toads. Contrary to the negative findings in the past, results of this research prove the presence of NGF in bee and scorpion venoms. Venoms from various species of snake, bee, scorpion, and toad were screened by two methods: immunological test ELISA using antibodies versus mouse NGF and venom NGF and the biological test of neurite outgrowth, the characteristic of NGF on PC cells. The presence of NGF was detected in snake, bee, and scorpion venoms, but not in toad venom by these tests. NGF was isolated from bee venom by HPLC fractionation using ion exchange chromatography. The molecular weight of bee NGF was found to be 14.0 kDa resolving into a single band by PAGE. The biological activity of bee NGF on PC12 cells was found to be 1/10 of the venom NGF.