Diversity in the chemical nature and mechanism of response to tumor promoters.
Explore the source record for details and available documents.
Acrylamides↗
SEARCH · Search PubMed
Results for “Polyether Toxins”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Sodium as a mediator of non-phorbol tumor promoter action. Down-modulation of the epidermal growth factor receptor by palytoxin.
Previous studies have shown that palytoxin, a non-(12-O-tetradecanoylphorbol-13-acetate)-type tumor promoter, is able to down-modulate the epidermal growth factor (EGF) receptor through a sodium-dependent pathway in Swiss 3T3 cells. A role for sodium is supported by the observation that the sodium proton exchanger monensin and the sodium-conducting ionophore gramicidin mimic palytoxin action by causing a decrease in both high and low affinity EGF binding. However, in addition to causing sodium influx, these agents can induce other cellular effects including changes in membrane polarization, intracellular pH, and macromolecular synthesis. To determine whether any of these factors might be responsible for palytoxin action in our system, we examined the role of each of them in palytoxin-induced inhibition of EGF binding. Although palytoxin depolarizes the membrane, the observation that potassium-induced depolarization of the membrane does not cause a decrease in EGF binding, in conjunction with the fact that monensin hyperpolarizes the membrane, indicates that depolarization of the membrane is not responsible for palytoxin-induced changes in the EGF receptor. An investigation of intra-cellular pH suggests that the palytoxin effects are not mediated by proton flux. In addition, nigericin-mediated changes in intracellular pH do not cause an inhibition of EGF binding. Finally, studies conducted in the presence of cycloheximide indicate that protein synthesis is not required for palytoxin action and that inhibition of EGF receptor biosynthesis does not account for palytoxin-induced loss of EGF-binding sites. These results suggest that sodium may act as a second messenger in the signal transduction mechanism by which palytoxin modulates the EGF receptor.
Acrylamides↗
Dual effect of ouabain on the palytoxin-induced contraction and norepinephrine release in the guinea-pig vas deferens.
Palytoxin (PTX), C129H223N3O54, isolated from marine coelenterates of Palythoa tuberculosa, caused a first rapid contraction followed by the slow phasic contraction of guinea-pig vas deferens. In the presence of ouabain (10(-5) M), PTX (10(-8) M) failed to cause the first contraction; however, the second contraction was potentiated. In the presence of phentolamine (10(-6) M), the second contraction was inhibited selectively. When ouabain was applied to the muscle in the presence of phentolamine, both first and second contractile responses to PTX were abolished. When the muscle was exposed to the potassium-depleted solution, the first contractile response to PTX was rather potentiated. PTX caused the release of norepinephrine from the muscle. Exposure of the muscle to ouabain (10(-5) M) markedly increased the PTX-induced release. It is indicated that the first and second contractile responses to PTX have entirely different properties. The second response is due to a release of norepinephrine from nerves and was potentiated by ouabain through the increase in the norepinephrine release, whereas the first response was not due to the norepinephrine release but presumably to a direct action on smooth muscle cell and was inhibited by ouabain. The mechanism of the action of PTX was discussed in the relation with Na,K-ATPase.
Acrylamides↗
Inhibitory effect of ouabain on the palytoxin-induced contraction of human umbilical artery.
Palytoxin (PTX), C129H223O3N54, isolated from marine coelenterates of Palythoa tuberculosa, caused contraction of the human umbilical artery in a dose-dependent manner (10(-11)-10(-8) M). Pretreatment with ouabain (10(-5) M) abolished the PTX (10(-8) M)-induced contraction but had no effect on the serotonin- (10(-6) M) and potassium- (40 mM) induced contractions. When the muscle was exposed to a potassium-free medium, application of PTX was able to cause a contraction similar to the contraction in normal medium. In the presence of verapamil (3 X 10(-6) M) or in the calcium-free medium. PTX-induced contraction was inhibited. In the depolarized muscle with 126 mM potassium, PTX did not induce a contraction whereas serotonin did. Our results suggest that PTX causes calcium influx through the plasma membrane of the umbilical artery, causing contraction. The site of action of PTX is presumably related to the Na,K-ATPase on the plasma membrane, although the precise relation between the site of action and increase in calcium influx is not known now.
Acrylamides↗
Heterologous regulation of the epidermal growth factor receptor by palytoxin, a non-12-O-tetradecanoylphorbol-13-acetate-type tumor promoter.
Previous results have established that 12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoters can alter the properties of the epidermal growth factor (EGF) receptor through activation of protein kinase C. In order to determine whether other, non-TPA-type tumor promoters might similarly influence growth-mediating receptors, we investigated the effect of palytoxin on EGF binding in Swiss 3T3 fibroblasts and human epidermal carcinoma (A431) cells. In both cell types, pretreatment with a low dose of palytoxin (1-11 pM) at 37 degrees C causes a decrease in EGF binding. In Swiss 3T3 cells the inhibitory effect is temperature dependent and does not occur at 4 degrees C, indicating that palytoxin is not directly competing with EGF for binding. As assessed by effects on DNA synthesis, palytoxin is not toxic at these concentrations and does not appear to be mitogenic for these cells. Although palytoxin, like phorbol esters, alters EGF binding, its action in Swiss 3T3 cells differs from that of TPA-type tumor promoters in at least 4 respects: (a) the kinetics and dose dependence differ significantly from that of phorbol dibutyrate; (b) the effect is not readily reversible; (c) there is loss of low-affinity as well as high-affinity binding sites; (d) the effect is independent of cellular protein kinase C levels. These results indicate that palytoxin is capable of heterologous regulation of the EGF receptor through a novel mechanism and suggest that certain non-TPA-type tumor promoters as well as TPA-type tumor promoters may act in part through modulation of growth regulatory pathways.
Acrylamides↗
Interaction between palytoxin and purified Na, K-ATPase.
Explore the source record for details and available documents.
Acrylamides↗
Two-sided functional Na,K-ATPase-liposomes for characterizing the permeability and side of action of pump inhibitors.
Explore the source record for details and available documents.
Acrylamides↗
Compounds from the sea with actions on the cardiovascular and central nervous systems.
Recent efforts at probing into the oceans have produced evidence that marine invertebrates such as gorgonians and sponges offer a rich reserve of pharmacologically interesting molecules. Our investigations indicate that it is possible to obtain novel compounds both structurally and pharmacologically. For example, autonomium from a sponge is a dual adrenergic combined with cholinergic molecule, with a structure that may be considered a hybrid between a catecholamine and choline. Various terpenoids and indole derivatives from marine organisms have been found to possess activities on the central nervous system. Several peptides from sea anemones are cardiotonic and have initiated a new concept of chemical structure believed to be associated with cardiac activity. A number of closely related halogenated cyclic ethers are good inhibitors of drug metabolism. Thus, there seems little doubt that the sea warrants an extensive chemical and pharmacological examination.
Acrylamides↗
Cardiovascular toxicity of palytoxin in anesthetized dogs.
Cardiovascular toxicity of palytoxin (PTX), isolated from Palythoa tuberculosa, was examined in pentobarbital-anesthetized dogs. In intact dogs, PTX at doses below 0.05 microgram/kg i.v. caused a sustained rise in arterial pressure. PTX at doses above 0.06 microgram/kg i.v. caused a transient rise in arterial pressure followed by rapid hypotension and resulting in death within 5 min. In open-chest dogs, a sublethal dose of PTX caused constriction of coronary, femoral and renal arteries. Renal blood flow was interrupted by a sublethal dose of PTX. PTX at a dose of 0.04 microgram/kg, which was lethal for this preparation, caused a rapid interruption of renal and coronary blood flows. Total peripheral resistance increased and cardiac output fell abruptly at this dose. It is suggested that PTX exerts its toxic action through intense vasoconstriction in the whole body, particularly in the coronary and renal vascular beds, and through depression of the cardiac function.
Acrylamides↗
Palytoxin isolated from marine coelenterates. The inhibitory action on (Na,K)-ATPase.
Palytoxin (PTX), C129H223N3O54, a highly toxic substance isolated from zoanthids of Palythoa tuberculosa, inhibited (Na,K)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) prepared from guinea pig heart and hog cerebral cortex in a dose-dependent manner at concentrations greater than 10(-8) M. In the presence of Na (100 mM) and K (20 mM), PTX showed potency nearly equal to that of ouabain. When the ATPase was activated by the various Na concentrations at a constant K concentration, both PTX and ouabain inhibited the ATPase activity noncompetitively. On the other hand, when K concentration was changed at a constant Na concentration, PTX caused a competitive inhibition in all ranges of K concentrations employed, whereas ouabain caused a competitive inhibition at low concentrations and a noncompetitive inhibition at high concentrations.
Acrylamides↗
Involvement of the sugar moiety in the inhibitory action of the cardiac glycosides on the palytoxin-induced responses in vascular smooth muscles.
The effects of ouabain and other cardiotonic steroids were examined to investigate whether changes in Na,K-adenosine triphosphatase (ATPase) activity modified the actions of palytoxin (PTX) in rabbit aortic vascular smooth muscle. The effects of these agents on rabbit aorta were compared with those on rat aorta, as it is known that the concentration of cardiac glycosides required to inhibit Na,K-ATPase of rat aorta is markedly higher than that of other species. PTX induced contraction in rabbit and rat aortas in a similar concentration range (10(-11) to 10(-8) M). PTX rapidly decreased tissue K content of these preparations. Ouabain (2 X 10(-5) M) inhibited both the contraction and the loss of tissue K in rabbit aorta but not in rat aorta. In rabbit aorta, convallatoxin (2 X 10(-5) M), which has one rhamnose as a sugar moiety like ouabain, and cymarin (2 X 10(-5) M), which has one cymarose, inhibited the PTX-induced contraction and the loss of tissue K, although ouabagenin, convallatoxigenin and cymarigenin (strophanthidin) (2 X 10(-5) M) did not. Other cardiotonic steroids, digoxin and digitoxin, which have 3 U of digitoxose as a sugar component, or the corresponding aglycones failed to inhibit the PTX-responses. On the other hand, all the cardiotonic steroids at concentration of 2 X 10(-5) M equally inhibited the reuptake of K and relaxation of norepinephrine-induced contractions induced by the readdition of K. Inhibition of Na-K pump by K-free solution potentiated rather than inhibited the PTX-induced contraction. These results suggest that the specific sugar moiety of cardiac glycosides is important for the inhibitory effect exerted by these compounds on the PTX-induced responses and that the inhibition is not related to the activity of the Na,K-ATPase.
Acrylamides↗
Activation of stress-activator protein kinase/c-Jun N-terminal kinase by the non-TPA-type tumor promoter palytoxin.
Previous studies have shown that structurally diverse tumor promoters can modulate protein kinases involved in signal transduction. In this study, we show that palytoxin, a potent non-12-O-tetradecanoylphorbol-13-acetate (TPA)-type skin tumor promoter, induces a signaling pathway leading to the activation of the stress-activated protein kinases/c-Jun N-terminal kinases (JNK) in Swiss 3T3 fibroblasts. Treatment of cells with doses as low as 0.1 mN palytoxin results in significant activation of JNK. In contrast to epidermal growth factor, which induces a transient activation of JNK in Swiss 3T3 cells, palytoxin causes prolonged enzyme activation. Since stimulation of ion flux appears to play an important role in the mechanism of action of palytoxin in other systems, we investigated the role of sodium and calcium in the activation of JNK: (a) our results show that incubation of Swiss 3T3 cells in a sodium-free medium dramatically reduced the magnitude of JNK activation by palytoxin; and (b) we found that the sodium ionophore gramicidin activates JNK. Together, these results suggest that sodium influx, which is a hallmark of palytoxin action, may play a key role in the activation of JNK by palytoxin. Our results indicate that calcium influx is not necessary or sufficient for palytoxin-induced activation of JNK. In contrast to palytoxin, the TPA-type tumor promoter phorbol 12,13-dibutyrate and the non-TPA-type tumor promoters thapsigargin and okadaic acid do not appear to activate JNK in this system. In contrast to phorbol 12,13-dibutyrate, palytoxin does not activate the p42/p44 mitogen-activated protein kinases. Our results demonstrate that Swiss 3T3 fibroblasts, palytoxin can activate a protein kinase signaling pathway that is distinct from that activated by the prototypical phorbol ester tumor promoters and other potent skin tumor promoters.
3T3 Cells↗
Palytoxin-induced Na+ influx into yeast cells expressing the mammalian sodium pump is due to the formation of a channel within the enzyme.
Palytoxin forms ionic channels in animal cell membranes but does not have similar effects on bacteria or yeast cells. These channels appear to be associated with the sodium pump. Using a heterologous expression system for the mammalian sodium pump in the yeast Saccharomyces cerevisiae, we recently demonstrated palytoxin-induced K+ efflux from yeast cells. Using the same system, we now show that the palytoxin-induced Na+ influx measured by others in animal cells is also directly associated with the sodium pump. Under the influence of palytoxin, yeast cells that express the mammalian sodium pump exchange extracellular Na+ ions for intracellular K+ ions with a stoichiometry of approximately 1:1. Both fluxes can be inhibited by ouabain. K+ efflux can also be observed when extracellular Na+ is replaced by Li+, Cs+, or NH4+. These data suggest that all palytoxin-induced ion fluxes measured so far in various cell systems are directly associated with the sodium pump. Palytoxin-induced Na+ influx or K+ efflux does not occur with yeast cells that express a truncated form of the sodium pump that is missing 44 of the carboxyl-terminal amino acids of the alpha 1 subunit. Scatchard analysis reveals only a slightly lower affinity of the truncated form for [3H]ouabain compared with the affinity of the native enzyme. Yeast cells expressing the truncated enzyme can bind [3H]ouabain, which can be displaced by palytoxin. Therefore, the inability of the truncated form to conduct ions under the influence of palytoxin is not due to the removal of the palytoxin binding site but rather to the removal of a part of the enzyme that participates in a direct or indirect way in the formation of the palytoxin-induced channel. Based on these findings, we conclude that palytoxin opens a channel within and not merely in the vicinity of the sodium pump. This might be the same channel that under normal conditions actively transports Na+ and K+ ions.
Acrylamides↗
Possible mechanism of palytoxin-induced Ca++ mobilization in porcine coronary artery.
We investigated the mechanisms involved in palytoxin (PTX)-induced cytosolic Ca++ ([Ca++]i) mobilization and contraction in porcine coronary arteries using a fluorescent Ca++ indicator fura-PE3. PTX (1 pM-10 nM) induced concentration-dependent and sustained increases in [Ca++]i and tension, both of which were partially inhibited by 10 microM verapamil or 1 microM nicardipine. In Ca++-free solution containing 1 mM EGTA, PTX did not increase [Ca++]i. In nominally Ca++-free solution (no EGTA), however, PTX increased [Ca++]i, which was presumed to be due to release of Ca++ from intracellular stores. PTX-induced rise in [Ca++]i was dependent on external Na+ because it did not increase [Ca++]i in Na+-free solutions containing verapamil. An increase in [Ca++]i in response to 65.4 mM KCl also involved a verapamil-resistant but external Na+-dependent component. After blockage of voltage-dependent Ca++ channels with verapamil, elevation of external K+ to 65.4 mM enhanced the responses of [Ca++]i and tension to PTX. PTX at 10 and 100 pM depolarized the membrane by 4.5 +/- 0.8 and 18.6 +/- 1.7 mV, respectively. Because PTX is known to increase membrane Na+ permeability, our results suggest that an increase in cytosolic Na+ and the depolarization were primary events required for the PTX-induced Ca++ mobilization and that Ca++ influxes through voltage-dependent Ca++ channels and Na+-Ca++ exchange and Ca++ release from Ca++ stores, which was triggered by increased Ca++ entry, were responsible for the PTX-induced increase in [Ca++]i.
Acrylamides↗
Brevetoxins, unique activators of voltage-sensitive sodium channels, bind to specific sites in rat brain synaptosomes.
The polyether lipid-soluble toxins isolated from the marine dinoflagellate Ptychodiscus brevis (formerly Gymnodinium breve) have been determined to bind to a unique site associated with rat brain synaptosomes. Using [3H]brevetoxin PbTx-3 as a specific probe, binding was determined at 4 degrees in rat brain synaptosomes using a rapid centrifugation technique. Rosenthal analysis yields a KD of 2.9 nM and a Bmax of 6.8 pmol of toxin/mg of protein. Labeled probe can be displaced by unlabeled PbTx-3, PbTx-2, or synthetic PbTx-3 (reduced PbTx-2) but not by a nontoxic, synthetic oxidized derivative of PbTx-2. Competition experiments using natural toxin probes specific for sites 1-4 of the voltage-dependent sodium channel have illustrated that PbTx-3 does not bind to any of the previously described sites associated with the channel. A fifth site is proposed. In addition, because of the varied nomenclature associated with the brevetoxins, a new classification system is proposed.
Aconitine↗
Recent methods for detection of seafood toxins: recent immunological methods for ciguatoxin and related polyethers.
A brief summation of the methods for detection of each of the marine toxins is presented in this report. The toxins are brevetoxin (PbTx), palytoxin (PTX), okadaic acid (OA), paralytic shellfish toxins (PSP) and ciguatoxin (CTX). The immunological and biotechnical procedures developed for each of these toxins are reviewed. Details of the recent methodology (solid-phase immunobead assay) for detection of ciguatoxin and related polyethers with monoclonal antibodies and receptors are presented. The capabilities of immunological technology for assessment of toxins in seafood products are promising and will probably be widely used in the future for seafood monitoring.
Animals↗
An improved method for the microscale preparation and characterization of hapten-protein conjugates: the use of cholesterol as a model for nonchromophore hydroxylated haptens.
A minute amount (0.446 micromol) of cholesterol (Chol) was converted into an hemisuccinate derivative (Chol HS) using an excess of succinic anhydride. The optimal conditions for synthesis of Chol HS were explored by checkerboard experiments in which various succinic anhydride/Chol molar ratios ranging from 5:1 to 30:1 were assayed over a wide temperature range (50-85 degrees C) and for various incubation times (3-8 h). Total conversion was obtained at the higher reagent ratios, temperatures, and incubation times. Subsequently, this carboxylic derivative was first covalently linked to bovine serum albumin (BSA) then to various proteins (casein, ovalbumin, and hemocyanins) or to a synthetic homopolymer (poly-DL-Lysine) via a modified version of the mixed anhydride method of Erlanger, performed in a reversed micellar medium. The assessment of the number of haptenic groups per mole of BSA (epitope density) was achieved chromatographically by two methods according to a Chol standard curve established at 207 nm with linearity in the range 0-50 microg. These procedures involving an alkaline hydrolysis of a sample of either the conjugate (direct method) or the unreacted Chol HS (indirect method) yielded an acceptable level of agreement and concordant results in all cases. The influence of the activated hapten/BSA molar ratio on the coupling efficiency was investigated by the direct method within the range 10:1 to 250:1. Using the optimal conditions determined for Chol HS synthesis (a molar reagent ratio of 30:1 with incubation at 65 degrees C for 6 h) and for BSA haptenation (a 100-fold molar excess of activated hapten, with a carrier stock concentration of 5 mg/mL), epitope density of the conjugates lied between 23 and 27. By reacting the same amount of activated hapten ( approximately 216 microg) with identical amounts of various carriers (300 microg), conjugation efficiency was found similar on a microgram of Chol bound per milligram of carrier basis. This simple and reproducible conjugation and analysis procedures should provide a general method applicable to poorly available and weakly immunogenic haptens bearing hydroxyl groups such as polyether-type marine toxins.
Animals↗
Preliminary results towards ciguatoxin immunodetection.
Due to the lack of purified ciguatoxin (CTX), monensin was used as a model for developing an enzyme immunoassay to detect CTX. Specific antibodies directed against monensin have been produced in rabbits and mice using a monensin-protein immunogen obtained in bulk quantities. Rabbit polyclonal and mouse monoclonal (MAb) antibodies of high specificity and affinity have been produced. Using MAb 2H8, in a competitive micro-ELISA performed in Terasaki plates, the detection limit for free monensin was 75 pg. No cross-reactivity was detected against CTX but a procedure requiring only 100 micrograms of hapten is under current investigation with a brevetoxin (PbTx-3), another marine toxin with a polyether backbone structure similar to CTX and recently commercially available.
Animals↗