[Structure and mode of action of the amatoxins]

Mushroom Toxins: Chemistry and Toxicology

Mushroom consumption is a global tradition that is still gaining popularity. However, foraging for wild mushrooms and accidental ingestion of toxic mushrooms can result in serious illness and even death. The early diagnosis and treatment of mushroom poisoning are quite difficult, as the symptoms are similar to those caused by common diseases. Chemically, mushroom poisoning is related to very powerful toxins, suggesting that the isolation and identification of toxins have great research value, especially in determining the lethal components of toxic mushrooms. In contrast, most of these toxins have remarkable physiological properties that could promote advances in chemistry, biochemistry, physiology, and pharmacology. Although more than 100 toxins have been elucidated, there are a number of lethal mushrooms that have not been fully investigated. This review provides information on the chemistry (including chemical structures, total synthesis, and biosynthesis) and the toxicology of these toxins, hoping to inspire further research in this area.

Enzymatic preparation of silybin phase II metabolites: sulfation using aryl sulfotransferase from rat liver

Aryl sulfotransferase IV (AstIV) from rat liver was overexpressed in Escherichia coli and purified to homogeneity. Using the produced mammalian liver enzyme, sulfation-the Phase II conjugation reaction-of optically pure silybin diastereoisomers (silybin A and B) was tested. As a result, silybin B was sulfated yielding 20-O-silybin B sulfate, whereas silybin A was completely resistant to the sulfation reaction. Milligram-scale sulfation of silybin B was optimized employing resting E. coli cells producing AstIV, thus avoiding the use of expensive 3'-phosphoadenosine-5'-phosphate cofactor and laborious enzyme purification. Using this approach, we were able to reach 48 % conversion of silybin B into its 20-sulfate within 24 h. The sulfated product was isolated by solid phase extraction and its structure was characterized by HRMS and NMR. Sulfation reaction of silybin appeared strictly stereoselective; only silybin B was sulfated by AstIV.

Sensitivity of alpha-amanitin to oxidation by a lactoperoxidase-hydrogen peroxide system

Oxidation of alpha-amanitin - a potent hepatotoxin found in the mushroom Amanita phalloides - by a lactoperoxidase-hydrogen peroxide system was investigated by different techniques. (i). UV spectroscopy of the mixture after 24 h incubation reveals a significant decrease in the absorbance range characteristic of the putative reactive moiety of the toxin, the tryptathionine group. (ii). Formation of a new product was detected by Thin Layer Chromatography. (iii). In vivo experiments with non-inbred male albino mice showed a lowered toxicity of the modified toxin in comparison with that of the native one. Taking into account the latter results concerning the sensitivity of the toxin towards an oxidising system, the formation and reactivity of an alpha-amanitin derivative is discussed in the course of A. phalloides poisoning (inhibition of RNA polymerase type II and development of damaging radical species).

Time-dependent RNA synthesis in different skin layers after wounding. Experimental investigations in vital and postmortem biopsies

Incision wounds were made on the outer ear of rats and two biopsies were taken for examination after different survival times. In each case a biopsy was made of vital tissue and a second of postmortem tissue after refrigeration for 24 h. The biopsies were exposed to a solution containing the RNA precursor 3H-cytidine for 1 h, washed and fixed in formalin. Sections 5 microns thick were then autoradiographically prepared and automatically evaluated using Quantimet 920. The intravital specimens showed a significant increase in 3H-cytidine incorporation in the basal cell layer after survival times of 10-24 h. No increase was seen in the stratum corneum, corium or cartilage tissue. The investigated distance from the wound margin did not have any significant bearing on the results. The 3H-cytidine incorporation rate in postmortem tissue was practically identical with that of vital tissue, but no increase was observed in the rate of RNA synthesis in the basal cells as a function of the age of the wound. It may therefore be assumed that this method provides no additional information as to the age of wounds in postmortem examination.

Concentration of particular high molecular mass phosphoproteins in rat liver nuclei and nuclear matrix decreases following inhibition of RNA synthesis by alpha-amanitin

Purified liver nuclei were isolated from rats treated with non-lethal doses of alpha-amanitin, actinomycin D, galactosamine or cycloheximide. The nuclei were incubated in the presence of adenosine 5'-[gamma-32P]triphosphate, and digested with DNAase or DNAase plus high salt concentrations to prepare nuclear residual structures. Using SDS-polyacrylamide gel electrophoresis followed by autoradiography, samples from untreated rats were shown to contain major phosphoproteins in the range 76-260 kDa, with a prominent triplet of bands with 110, 117 and 128 kDa. Treatment of animals with alpha-amanitin or high doses of actinomycin D and galactosamine caused a significant decrease in the concentration of a few phosphorylated species, including the 110 kDa protein in whole nuclei, and their disappearance from the nuclear matrix or residual ribonucleoprotein structures after 1-3 h. The changes were reversible, complete recovery being observed after 5 h in the case of alpha-amanitin. No similar results were obtained with nuclei from rats treated with the translation inhibitor cycloheximide. The data are discussed in view of a possible effect of certain high molecular mass phosphoproteins on reactions of the heterogeneous nuclear RNA/mRNA pathway in the cell.

The toxic peptides from Amanita mushrooms

The results of 50 years of effort in the chemistry of Amanita toxins are reviewed. The phallotoxins, fast acting components, but not responsible for fatal intoxications after ingestion, are bicyclic heptapeptides. They combine with F-actin, stabilizing this protein against several destabilizing influences. The virotoxins likewise fast acting are monocyclic heptapeptides. The amatoxins which are the real toxins lead to death within several days by inhibiting the enzymatic synthesis of m-RNA. They are bicyclic octapeptides. The structures of all of these compounds are described, as well as conformations, chemical reactions and modification, syntheses and correlations between structures and biological activities.

Isolation of a lethal toxin from Cortinarius orellanus Fr

The fungal toxin 'orellanine', isolated by Grzymala (10) from Cortinarius orellanus, seems to be a heterogeneous mixture of several toxic and nontoxic substances. We succeeded in isolating a lethal toxin which is sensitive to light and which is striking because of its long latency period. We consider this the main toxin of C. orellanus. Even in extremely high doses of ten times LD 100 mice do not die earlier than 48 hours after application. The paper gives details about the isolation and several properties of this slow acting toxin.

Composition of hnRNA-associated proteins in rat liver is specifically altered after cycloheximide treatment

Rats were treated with non-lethal doses of alpha-amanitin or cycloheximide. Nuclei were prepared and the particles carrying heterogeneous nuclear RNA (30--40 S-particles) isolated by density gradient centrifugation. In the case of alpha-amanitin the yield of particles was reduced to about 45%. Cycloheximide affected the composition of proteins associated with the nuclear RNA. In particular, the concentration of a 110 000 molecular weight protein as determined by sodium dodecylsulfate gel electrophoresis was reduced to 20--30% after 2 h and then increased to 150--180% of the control before it approached the normal level after 30 h. Possible mechanisms underlying these changes are discussed.

On the nephrotoxicity of alpha-amanitin and the antagonistic effects of silymarin in rats

In human beings, poisoning by the deathcup mushroom causes renal lesions in addition to extremely severe liver damage. It is known from animal experiments that silymarin, a polyhydroxyphenylchromanone, is capable of counteracting this alpha-amanitin-induced liver damage. The purpose of the present work was to ascertain whether renal damage could be induced in rats by giving alpha-amanitin, and whether silymarin would have any effect on such renal damage. The fact that alpha-amanitin produces pathological changes in the kidneys and that these lesions can be almost completely prevented by pretreating rats with silymarin has now been amply demonstrated by biochemical and histological techniques alike.

Amatoxins, phallotoxins, phallolysin, and antamanide: the biologically active components of poisonous Amanita mushrooms

This review gives a comprehensive account of the molecular toxicology of the bicyclic peptides obtained from the poisonous mushrooms of the genus Amanita. The discussion of the biochemical events will be preceded by a consideration of the chemistry of the toxic peptides. The structural features essential for biological activities of both the amatoxins and the phallotoxins will be discussed, also including the most important analytical data. Similar consideration will be given to antamanide, a cyclic peptide, which counteracts phalloidin. In addition, the phallolysins, three cytolytic proteins from Amanita phalloides will be discussed. The report on the biological activity of the amatoxins will deal with the sensitivity of the different RNA-polymerases towards the toxins and with their action on various cell types. Consideration will also be given to systems in which alpha-amanitin was used and can be used as a molecular tool; in the past, many investigators used the inhibitor in molecular biology, genetics, and even in physiological research. As for the phallotoxins, discussion of the affinity of these toxins for actin is provied. Further discussion attempts to understand the course of intoxication by filling in the gap between the first molecular event, formation of microfilaments, and the various lesions in hepatocytes during the intoxication.

Modification of actins by phallotoxins

Phallotoxins bind to filamentous actin (F-actin) from liver or rabbit muscle with Kdiss approximately 10(-8) M. By this combination the structure of F-actin is stabilized to such an extent that it will be resistant to the depolymerizing action of 0.6 M KI and of deoxyribonuclease I, to denaturation by heat (70 degrees C), and to local ruptures caused by ultrasonication or by cytochalasin B. The structural features of phallotoxins essential for affinity to F-actin are specific.

[Effect of silymarin on the total dry mass of hepatocytes inacute poisoning by phalloidin and alpha-amanitine (author's transl)]

The effects of silymarin on the total dry mass and class pattern of rat hepatocytes have been studied during acute poisoning by phalloidin and alpha-amanitine. Phalloidin (2/5 of the LD50) after 3 h causes a marked change in the hepatocyte class pattern due to a displacement of a high percentage of cells in the intervals among classes, while the cell dry mass increases slightly. alpha-Amanitine (1/4 or 1/2 of the LD50) after 3 h causes a decrease in the number of classes of hepatocytes due to a disappearance of the heavier ones, a displacement of cells in the intervals among classes, an appearance of very light cells, and a decrease by about 25% in the mean dry mass of the hepatocytes. Silymarin, administered 30 min before poisoning, prevents all the changes due to 2/5 of the LD50 of phalloidin and to 1/4 of the LD50 of alpha-amanitine, and strongly reduces the effects of 1/2 of the LD50 of alpha-amanitine. The effects of alpha-amanitine and phalloidin and the protective action of silymarin on the dry mass and class pattern of hepatocytes are discussed.

[Localisation of the α-amanitin-sensitive RNA-polymerase in nuclei of Acetabularia]

An isolation medium for nuclei of Acetabularia mediterranea is described. The medium offers the possibility to keep nuclei alive (verified by reimplantation) for at least 10 min and to obtain nuclei with radioactively labelled RNA.The influence of α-amanitin on nucleolar and nucleoplasmatic RNA-synthesis is investigated autoradiographically. Amanitin inhibits the incorporation of uridine into the nucleoplasmatic RNA, whereas incorporation into the RNA of nucleoli is hardly or not at all influenced.We conclude that, in agreement with findings on animal cells, α-amanitin inhibits at least one of the RNA-polymerases localized in the nucleoplasm but does not markedly influence the RNA-polymerase of the nucleoli.