Effect of agents which modify reticuloendothelial system function on acute phalloidin-induced lethality and hepatotoxicity in mice.

The relationship between reticuloendothelial system (RES) function and acute phalloidin intoxication was studied in mice. Pretreatment with compounds that stimulate (zymosan) or depress (methyl palmitate and praseodymium nitrate, Pr(NO3)3) the RES resulted in protection against phalloidin-induced lethality and hepatotoxicity, as assessed by morphological analysis. However, triolein (which stimulates the RES) was ineffective against phalloidin. The timing of pretreatment with the effective compounds showed a correlation between modified in vivo RES function (phagocytosis) and protection against the toxin. The effects of pretreatment with zymosan and Pr(NO3)3 were further characterized. Hepatic damage induced by phalloidin was significantly decreased by these agents, as judged by morphological analysis as well as by serum aspartate aminotransferase and alanine aminotransferase release. This study also showed that there was no correlation between the capacity of Kupffer cells to produce nitrite and prophylaxis against phalloidin. However, liver cell proliferation was increased by zymosan and Pr(NO3)3 in parallel with protection against the toxin. Furthermore, freshly isolated hepatocytes from zymosan- or Pr(NO3)3-treated mice were less sensitive to phalloidin in vitro. These results indicate that the protective effect of these agents against phalloidin-induced hepatotoxicity may be mediated by their mitogenic properties.

Protection by indomethacin against the lethality and hepatotoxicity of phalloidin in mice.

The present study examined the possible involvement of endogenous cyclooxygenase-derived factors in the lethality and hepatic hemorrhagic necrosis induced by phalloidin. Mice were pretreated with indomethacin, aspirin or ibuprofen (all inhibitors of cyclooxygenase) and injected with phalloidin (2 mg/kg). The toxin induced 75% lethality and caused severe hemorrhagic necrosis of the liver associated with increased serum levels of AST and ALT. Indomethacin completely prevented the mortality and hepatic damage elicited by phalloidin as judged by morphologic analysis and serum AST and ALT release. The in vitro addition of indomethacin to suspensions of freshly-isolated hepatocytes decreased plasma membrane bleb formation induced by phalloidin. In contrast to indomethacin, aspirin and ibuprofen did not influence phalloidin toxicity in vivo. These results suggest that inhibition of prostanoids per se may not be the sole mechanism of protection by indomethacin.

New substrates of the multispecific bile acid transporter in liver cells: interference of some linear renin inhibiting peptides with transport protein(s) for bile acids.

Interactions between some stable linear peptides with renin inhibitory activity and a multispecific transport system in the basolateral plasma membrane of liver cells was studied on cell suspensions. The peptides used in our experiments were taken up by liver cells and subsequently eliminated without any biotransformation (e.g., proteolysis). No degradation products could be detected in the extracellular medium by thin-layer chromatography. All peptides tested inhibited the uptake of physiological and of some foreign substrates of the multispecific bile acid transporter (MT). The phalloidin response of liver cells was also inhibited to a similar degree in a concentration-dependent manner. The potency of inhibition did not correlate with the lipophilic properties of the peptides. On the other hand a tight correlation could be documented between the inhibition of cholate transport and that of the phalloidin response. Transport inhibition of typical substrates of the MT by the above renin inhibitors was competitive. In contrast, the transport of a typical substrate of the bilirubin carrier (rifampicin), of amino acids (alpha-aminoisobutyric acid), long chain fatty acids (oleic acid) and cationic compounds (thiamin hydrochloride) was not inhibited by the same renin inhibitors. These results indicate that linear renin inhibiting peptides are taken up into liver cells by carrier proteins related to the MT.

Effect of diltiazem on acetaminophen and phalloidine hepatotoxicity.

The protective effect of diltiazem on acetaminophen and phalloidine hepatotoxicity has been studied in male CD-1 mice. Groups of 8 mice each received 0.9% NaCl or 6, 12, 18 and 24 mg/kg of diltiazem 20 minutes after 750 mg/kg of acetaminophen and were sacrificed 24 hours later to assess liver toxicity. Dosages of at least 12 mg/kg were required to prevent the increase in alanine transaminase (ALT) and only the 24 mg/kg hindered the appearance of histological lesions. ALT remained close to control values 48 hours after the administration of the 24 mg/kg dose of diltiazem. Diltiazem was less effective in preventing hepatotoxicity when administered 3 hours after acetaminophen. Diltiazem (24 mg/kg) reduced the increase in ALT induced by 1.1 mg/kg of phalloidine by 58% (4460 +/- 317 U/mL v.s. 1852 +/- 339 U/mL; p less than 0.05). It is concluded that high doses of diltiazem, administered early after the toxicant, prevent hepatic toxicity of acetaminophen but produce only a modest effect on phalloidine hepatotoxicity.

Wedelolactone and coumestan derivatives as new antihepatotoxic and antiphlogistic principles.

For the study of structure-activity relationships, the antihepatotoxic wedelolactone (7-methoxy-5,11,12-trihydroxy-coumestan) and 6 coumestan derivatives were synthesized by the application of a modified method of Wanzlich. An evaluation of the biological characteristics of the synthetic compounds and acuminatin from Musa acuminata showed that most of the wedelolactone derivatives significantly protected primary cultured liver cells from the toxicity of CCl4, galactosamine (Galc), and phalloidin, and strongly inhibited the activity of 5-lipoxygenase in porcine leukocytes. The hepatocyte protective activity was dependent on the C-7 substitution with pharmacological efficacy decreasing in the following order: EtO greater than MeO greater than OH greater than CH3(CH2)9. In addition, a free OH at C-5 of the wedelolactone molecule was shown to be important in protecting hepatocytes from CCl4 and Galc damage. Similar observation regarding the effect of C-7 substitution in wedelolactone was obtained in the 5-lipoxygenase test. In general, an increase in the lipophilicity in ring A increased the inhibition of 5-lipoxygenase activity. The synthetic wedelolactone was also found to have stimulatory effect on the RNA synthesis in isolated nuclei from hepatocytes.

Antamanide antagonizes the phalloidin-induced negative inotropic effect and blocks voltage dependently the fast outward K+ current in voltage-clamped frog muscle fibres.

The effects of antamanide (10(-14)-10(-5) M) and N-acetyl-secophalloidin (10(-7)-5 X 10(-3) M) a neutral non-toxic derivative of phalloidin, were tested on voltage-clamped single frog muscle fibres. Antamanide protected muscle fibres against the negative inotropic effect of phalloidin but blocked the fast potassium permeability in the same concentration range and the same voltage-dependent manner as did phalloidin. N-Acetyl-secophalloidin exhibited a strongly attenuated blocking effect on K+ permeability in a 1,000-fold higher concentration range than phalloidin. Neither antamanide nor N-acetyl-secophalloidin affected the contractile properties. These results suggest the existence in the frog muscle membrane of a receptor with two sites for phalloidin and antamanide which acts on potassium conductance.

Prevention of phalloidin-induced lesions on isolated rat hepatocytes by novel synthetic analogues of somatostatin.

Exposure of freshly isolated hepatocytes to phalloidin produced blebs on their surfaces: this phenomenon was time- and dose-dependent and irreversible. When hepatocytes were pretreated with somatostatin or with some of its synthetic analogues, formation of blebs was dramatically reduced. This cytoprotective effect was dose-dependent: the dose-response profiles enabled the determination of the CD50 values, i.e., the concentrations of analogues that yielded 50% cytoprotection. The analogues with sequences of amino acids in the retro form, compared to those in somatostatin-14, exhibited higher cytoprotection; the retro hexapeptide, cyclo(-Phe-Thr-Lys-D-Trp-Phe-D-Pro-), was 27 times more active than somatostatin-14. Specificity of cytoprotection was examined by pretreating hepatocytes with biologically active peptide hormones prior to exposure to phalloidin. On a molar basis, prolactin and thyroid-stimulating hormone possessed activity comparable to that of somatostatin-14, whereas glucagon was twice as active. Insulin, vitamin A and propranolol exercised less than 10% protection. The synthetic analogues of somatostatin are potent protective agents against cell lesions induced by phalloidin. Formation of blebs on hepatocytes by toxins and their prevention by agents of interest may serve as a suitable morphological assay for screening of cytotoxicity and cytoprotection.

Molecular aspects of cytoprotection by modified somatostatins.

Somatostatin and cyclic modifications of this molecule inhibit the development of protrusions on the surface of isolated hepatocytes in presence of phalloidin. This prevention of phalloidin injury is caused by competitive inhibition of the phallotoxin uptake. Transport inhibition is not a hormonal effect of somatostatin. The concentrations needed are in the micromolar range. The most protective somatostatin modifications lack hormonal activity (GH release). Somatostatin and its analogs are substrates of a hepatocellular transporter which also translocates other cyclopeptides, among them phalloidin, antamanide, and several organic anions, such as iodipamide and fusidic acid. Physiological substrates of this multispecific transport system are bile acids. The protection of phallotoxin injury by somatostatin is a specific mechanism only representative for liver cells. No other cell contains the above multispecific transporter.

Lithium perhydroantamanide complex (2:1): exposure of the peptide backbone in the analog of antamanide with antitoxic impotency.

The synthetic analog of antamanide in which all four phenylalanyl residues are hydrogenated to cyclohexylalanyl (Cha) residues, cyclic(Val-Pro-Pro-Ala-Cha-Cha-Pro-Pro-Cha-Cha), has a complete loss of antitoxic potency despite its ability to form ion complexes in the same manner as antamanide. The conformation of Li+.perhydroantamanide has been established in the present paper by x-ray diffraction analysis of a single crystal. The backbone encapsulates a Li+ ion in an almost identical manner as in Li+ antamanide. However, in Li+ antamanide the four phenyl groups are folded against the globular backbone, thus providing a hydrophobic surface for the complex, whereas in Li+ X perhydroantamanide the four cyclohexyl moieties are extended away from the folded backbone, resulting in the exposure of large portions of the polar backbone to the environment. As a consequence, four NH groups form hydrogen bonds with Br- ions, three C--O groups form hydrogen bonds with water molecules, and one C--O group makes a ligand to an additional external Li+ ion. The internal Li+ ion is pentacoordinated, whereas the external Li+ ion is tetracoordinated. The large change of the hydrophobicity around the midsection of the perhydroantamanide complex may be related to the biological inactivity. The content per asymmetric unit of the crystal is C64H102N10O10 X 2Li+ X 4H2O X 2CH3CN.2Br- in space group P2(1)2(1)2(1) with a = 21.740(7), b = 21.566(4), and c = 17.361(4) A. The agreement factor is 8.2% for 5135 data.

Antihepatoxic constituents of Garcinia kola seeds.

Kolaviron, a fraction of defatted methanolic extract and biflavanones of Garcinia kola seeds significantly antagonized the lethal poisoning of mice with phalloidin. Garcinia biflavanones GB1, GB2 and kolaflavanone were isolated as the active constituents.

Effect of silybin on phalloidin-actin interactions in vitro.

The possible antagonism between silybin and phalloidin an F-actin has been examined in vitro. Phalloidin protects F-actin against denaturation by potassium iodine, cytochalasin B, DNase and pronase. Silybin does not counteract the effect of phalloidin on F-actin. However, silybin alone slowed the rate of polymerization of actin, but this effect was moderate and obtained with very high concentrations. These results indicate that the site of action in vitro of silybin is not actin.

Phalloidin hepatotoxicity in rats in vivo. Effect of a sympatholytic agent: propranolol.

Phalloidin, one of the main toxins of Amanita phalloides, induced hepatotoxicity in female Wistar rats at 0.9 mg/kg dose i.p. Biliary secretion was selectively inhibited after 3h, but was restored after 24 h. Phalloidin also induced a cytolytic lesion, but not a fatty liver, as in alpha-amanitin intoxication. Propranolol pretreatment (30 min prior to phalloidin injection) did not afford protection against hepatotoxicity, but increased alkaline phosphatase, 5'-nucleotidase and aminotransferase activities.

Decreased phalloidin response, phallotoxin uptake and bile acid transport in hepatocytes prepared from wistar rats treated chronically with diethylnitrosamine.

Isolated hepatocytes prepared from rats pretreated with diethylnitrosamine (0.5 mg/kg DENA/DAY P.O.) are less sensitive to phalloidin poisoning. They take up lower amounts of both phallotoxins and bile acids than controls. The degree of inhibition depends on the period of pretreatment.

[The effects of flavonoids on rat liver during chronic palloidin intoxication/Morphological and biochemical studies (author's transl)]. / Zur Wirkung von Flavonoiden an der Rattenleber bei chronischer Phalloidin-Vergiftung. Morphologische und klinisch-chemische Untersuchungen.

Continuous intraperitoneal administration of phalloidin (0.5 mg/kg body weight/day) leads to an alteration of intracellular contractile acto-myosinfilaments in rat liver. The hepatocytes show an accumulation of fibrillar material with some loss of contractile function of the pericanalicular web. Biochemically an increase of serum transaminases and alkaline phosphatase occurs. Histochemically the liver exhibitis changes in the distribution of some hepatocellular enzymes. The influence of the flavonoid (+)-cyanidanol-3 on these phalloidin-induced lesions was studied by histochemical, immunofluorescence and biochemical methods. The results imply, that (+)-cyanidanol-3 is probably protecting the plasma membrane of hepatocytes and therefore reduces the entrance of phalloidin into the cytoplasm. In addition an increased activity of the reticuloendothelial system was observed, perhaps resulting from the flavonoid administration. Both effects could be discussed as mechanisms of flavonoid action in the liver.

Inhibitory effects of 4,4'-diisothiocyano stilbene-2,2'-disulfonic acid (DIDS) in the response of isolated hepatocytes to phalloidin.

4,4'-Diisothiocyano stilbene-2,2'-disulfonic acid (DIDS) inhibits the typical development of protrusions, regularly seen after treatment of isolated hepatocytes with phalloidin. The degree of inhibition depends on the time of preincubation and on the concentration of DIDS, but not on the concentration of phalloidin. DIDS is more effective than H2DIDS. The inhibition by both compounds is irreversible. The binding capacity of hepatocytes for H2DIDS is much higher than that of the phalloidin-insensitive hepatoma cells. Gel electrophoresis of lysates from cells, pretreated with 3H2DIDS demonstrates that actin binds very little of the inhibitor. Our results suggest that a protein structure on the surface of hepatocytes, needed for the response to phalloidin, is influenced by DIDS or H2DIDS.

Anti-phalloidine and anti-alpha-amanitine action of silybin in comparison with compounds similar to structural parts of silybin.

Silybin significantly antagonises the lethal poisoning of mice with alpha-amanitine or phalloidine. In the same test, taxifolin, coniferyl alcohol, fisetin and (+)-catechin were not effective.

The role of bile acids in phalloidin poisoning.

Glycocholate and other bile acids inhibit the response of isolated hepatocytes to phalloidin in a concentration dependent manner. It is suggested that the inhibition is due to a block of phalloidin uptake. This interaction might explain the high specificity of phalloidin for liver tissue.