Modulating pancreatic cancer microenvironment: The efficacy of Huachansu in mouse models via TGF-β/Smad pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Huachansu (HCS) is a traditional Chinese medicine obtained from the dried skin glands of Bufo gargarizans and clinical uses of HCS have been approved in China to treat malignant tumors. The traditional Chinese medicine theory states that HCS relieves patients with cancer by promoting blood circulation to remove blood stasis. Clinical observation found that local injection of HCS given to pancreatic cancer patients can significantly inhibit tumor progression and assist in enhancing the efficacy of chemotherapy. However, the material basis and underlying mechanism have not yet been elucidated.

AIM OF THE STUDY

To investigate the therapeutic potential of HCS for the treatment of pancreatic cancer in in situ transplanted tumor nude mouse model. Furthermore, this study sought to elucidate the molecular mechanisms underlying its efficacy and assess the impact of HCS on the microenvironment of pancreatic cancer. To identify the antitumor effect of HCS in in situ transplanted tumor nude mouse model and determine the Chemopreventive mechanism of HCS on tumor microenvironment (TME).

METHODS

Using the orthotopic transplantation nude mouse model with fluorescently labeled pancreatic cancer cell lines SW1990 and pancreatic stellate cells (PSCs), we examined the effect of HCS on the pancreatic ductal adenocarcinoma (PDAC) microenvironment based on the transforming growth factor β (TGF-β)/Smad pathway. The expression of TGF-β, smad2, smad3, smad4, collagen type-1 genes and proteins in nude mouse model were detected by qRT-PCR and Western blot.

RESULTS

HCS significantly reduced tumor growth rate, increased the survival rate, and ameliorated the histopathological changes in the pancreas. It was found that HCS concentration-dependently reduced the expression of TGF-β1 and collagen type-1 genes and proteins, decreased the expression of Smad2 and Smad3 genes, and downregulated the phosphorylation level of Smad2/3. Additionally, the gene and protein expression of Smad4 were promoted by HCS. Further, the promoting effect gradually enhanced with the rise of HCS concentration.

CONCLUSIONS

The results demonstrated HCS could regulate the activity of the TGF-β/Smad pathway in PDAC, improved the microenvironment of PDAC and delayed tumor progression. This study not only indicated that the protective mechanism of HCS on PDAC might be attributed partly to the inhibition of cytokine production and the TGF-β/Smad pathway, but also provided evidence for HCS as a potential medicine for PDAC treatment.

Divergent Nine-Step Syntheses of Perhydrohistrionicotoxin Analogs and Their Inhibition Activity Toward Chicken α4β2-Neuronal Nicotinic Acetylcholine Receptors

Histrionicotoxin (HTX) alkaloids, which are isolated from Colombian poison dart frogs, are analgesic neurotoxins that modulate nicotinic acetylcholine receptors (nAChRs) as antagonists. Perhydrohistrionicotoxin (pHTX) is the potent synthetic analogue of HTX and possesses a 1-azaspiro[5.5]undecane skeleton common to the HTX family. Here, we show for the first time the divergent nine-step synthesis of pHTX and its three stereoisomers from the known aldehyde through a one-step construction of the 1-azaspiro[5.5]undecane framework from a linear amino ynone substrate. Surprisingly, some pHTX diastereomers exhibited antagonistic activities on the chicken α4β2-neuronal nAChRs that were more potent than pHTX.

Efficacy and Safety of Huachansu as an Adjuvant Therapy for Non-Small Cell Lung Cancer: An Overview of Systematic Reviews and Meta-Analyses

OBJECTIVE

The purpose of this overview is to assess systematic reviews (SRs)/ meta-analyses (MAs) of Huachansu (HCS) combination chemotherapy for treating non-small cell lung cancer (NSCLC) and provide summarized evidence for clinical decision making.

METHODS

From the creation of the database to JUNE 2023, 8 databases in English and Chinese were searched. SRs/MAs that met the inclusion and exclusion criteria were included. Two reviewers independently screened research, extracted data and assessed methodological quality, risk of bias, report quality and evidence quality by using relevant criteria from AMSTAR-2, ROBIS scale, PRISMA, and GRADE system.

RESULTS

The short-term effect, long-term effect, quality of life improvement, safety and pain relief effect in 8 included SRs/MAs were assessed in this overview according to quantitative synthesis. Results assessed by AMSTAR-2, PRISMA, and ROBIS were generally unsatisfactory, with the results of the AMSTAR-2 assessment showing that all of them were of low or critically low quality; the number of items in the included research that were fully reported (compliance was 100%) by the PRISMA checklist was only 50%, while there were 38.10% of the research reporting less than 60% completeness; the ROBIS assessment showed a small number of systems to be low risk of bias. In addition, 26 items were rated as moderate quality, while 50.94% of items were rated as low or critically low quality by GRADE.

CONCLUSION

HCS may be a promising adjuvant therapy for NSCLC. However, high-quality SRs/MAs and randomized control trials (RCTs) should be conducted to provide sufficient evidence so as to draw a definitive conclusion.

Compound-composed Chinese medicine of Huachansu triggers apoptosis of gastric cancer cells through increase of reactive oxygen species levels and suppression of proteasome activities

BACKGROUND

Huachansu (HCS), a known Chinese patent drug extracted from the Chinese toad skin, is frequently used for the treatment of various advanced cancers, especially gastric cancer, due to the good therapeutic effect. However, it is rather difficult to clarify the active substances and molecular mechanisms involved owing to the lack of appropriate research strategies. We recently proposed the concept and research ideas of compound-composed Chinese medicine formula.

PURPOSE

To discover compound-composed Chinese medicine from Huachansu and to explore its mechanism of action in inducing apoptosis of gastric cancer cells.

METHOD

Network pharmacology combined with serum pharmacochemistry was utilized to screen the predominant active constituents from HCS against gastric cancer. Then, the compound-composed Chinese medicine of HCS (CCMH) was prepared according to their relative contents in serum. The pharmacological effects and potential mechanisms for CCMH were investigated by assays for cell viability, cell cycle, apoptosis, mitochondrial membrane potential (MMP), proteomics, reactive oxygen species (ROS), N-Acetylcysteine (NAC) antagonism, proteasome activity, and western blot.

RESULTS

CCMH was comprised of arenobufagin (11.14%), bufalin (18.67%), bufotalin (7.33%), cinobufagin (16.67%), cinobufotalin (16.74%), gamabufotalin (8.45%), resibufogenin (12.03%), and telocinobufagin (8.97%). CCMH evidently induced proliferation inhibition, cell cycle arrest, apoptosis, and MMP collapse in gastric cancer cells, possessing the better activities than HCS. Proteomic analysis showed that CCMH influenced ROS pathway, ubiquitin proteasome system, and PI3K/Akt and MAPK signaling pathways. CCMH markedly enhanced intracellular ROS levels in gastric cancer cells, which was reversed by NAC. Accordingly, NAC antagonized the apoptosis-inducing effect of CCMH. Significantly decreased proteasome 20S activity by CCMH was observed in gastric cancer cells. CCMH also regulated the expression of key proteins in PI3K/Akt and MAPK signaling pathways.

CONCLUSION

CCMH possesses more significant apoptotic induction effects on gastric cancer cells than HCS, which is achieved primarily through suppression of proteasome activities and increase of ROS levels, followed by regulating PI3K/Akt and MAPK signaling pathways. Network pharmacology combined with serum pharmacochemistry is an effective strategy for discovering compound-composed Chinese medicine from traditional Chinese medicine, which can help clarify the pharmacological substances and mechanisms of action for traditional Chinese medicine.

Efficacy and safety of Huachansu combined with adjuvant chemotherapy in resected colorectal cancer patients: a prospective, open-label, randomized phase II study

Although some studies in China have suggested Huachansu (HCS) combined with chemotherapy is effective in the treatment of various cancers, there are few studies on colorectal cancer (CRC), especially in postoperative adjuvant chemotherapy. The aim of this study was to test the hypothesis that HCS combined with adjuvant chemotherapy would improve survival probability in resected CRC patients. This was a prospective, open-label, randomized phase II study. Patients with stage III or high-risk stage II resected CRC were randomly assigned to the chemotherapy and HCS + chemotherapy groups. The Chemotherapy group was treated with the FOLFOX regimen for ≥ 6 cycles or the CAPEOX regimen for ≥ 4 cycles. The HCS + chemotherapy group was treated with HCS on the basis of the chemotherapy group. The primary endpoint was 3-year disease-free survival (DFS), and the secondary endpoints were 3-year overall survival (OS) and toxicity. A total of 250 patients were included in this study (126 chemotherapy, 124 HCS + chemotherapy). There were significant differences in 3-year DFS between the two groups (median 28.7 vs. 31.6 months, respectively; P = 0.027), but no significant differences in 3-year OS between the two groups (median 32.7 vs. 34 months, respectively; P = 0.146). No patients experienced grade four adverse events, and the rates of leukopenia, neutropenia, and diarrhea in the HCS + chemotherapy group were lower than that those in the chemotherapy group. HCS combined with adjuvant chemotherapy after radical resection for patients with stage III or high-risk stage II CRC was demonstrated to be an effective and feasible treatment.

Cinobufagin inhibits tumor progression and reduces doxorubicin resistance by enhancing FOXO1-mediated transcription of FCGBP in osteosarcoma

ETHNOPHARMACOLOGICAL RELEVANCE

Cinobufagin (Huachansu), an aqueous extract from the dried skin of the toad Bufo bufo gargarizans Cantor (frog skin), is a biologically active ingredient of a traditional Chinese medicine cinobufacini that can treat multiple bone pathological conditions such as bone pain, bone tumors, and osteosarcoma.

AIM OF THE STUDY

The study aimed to explore the roles and molecular mechanisms of cinobufagin underlying osteosarcoma development and doxorubicin (ADR) resistance.

MATERIALS AND METHODS

Cell viability, migration, and invasion were examined by CCK-8, wound healing, and Transwell invasion assays, respectively. RNA sequencing analysis was performed in MNNG/HOS cells treated with or without cinobufagin. The relationships of cinobufagin, forkhead box O1 (FOXO1), and Fc fragment of IgG binding protein (FCGBP) were examined by luciferase reporter, immunofluorescence (IF), RT-qPCR, and chromatin immunoprecipitation (ChIP) assays together with weighted gene co-expression network analysis (WGCNA) analysis. Epithelial-mesenchymal transition (EMT) marker levels were examined through the Western blot assay. The function and molecular basis of cinobufagin in osteosarcoma were further investigated by mouse xenograft experiments.

RESULTS

Cinobufagin reduced cell viability, weakened ADR resistance, and inhibited cell migration/invasion/EMT in osteosarcoma cells. Cinobufagin enhanced FOXO1-mediated transcription of downstream genes including FCGBP. FCGBP knockdown partly abrogated the effect of cinobufagin on osteosarcoma cell development. Cinobufagin inhibited the growth of mouse osteosarcoma xenografts in vivo. Cinobufagin reduced the expression of Ki-67 and MMP9 and facilitated caspase-3 expression in osteosarcoma xenografts.

CONCLUSION

Cinobufagin suppressed tumor progression and reduced ADR resistance by potentiating FOXO1-mediated transcription of FCGBP in osteosarcoma.

Screening of Bufadienolides from Toad Venom Identifies Gammabufotalin as a Potential Anti-inflammatory Agent

Toad venom (Chansu) is used in the treatment of infectious and inflammatory diseases in China and East/Southeast Asian countries. However, the anti-inflammatory components of toad venom have not yet been systematically evaluated and clearly defined. To investigate the anti-inflammatory effects of toad venom and identify new anti-inflammatory ingredients, we used zebrafish, an alternative drug screening model, to evaluate the anti-inflammatory effects of 14 bufadienolides previously isolated from toad venom. Most of the bufadienolides were found to exert significant anti-inflammatory effects on lipopolysaccharide-, CuSO₄-, or tail transection-induced zebrafish inflammatory models. Moreover, gammabufotalin ( 6: ) inhibits lipopolysaccharide-induced inflammation by suppressing the myeloid differentiation primary response 88/nuclear factor-kappa B and STAT3 signal pathways. This study confirms the potential of zebrafish in drug screening, clarifies the anti-inflammatory effects of bufadienolides from toad venom, and indicates that gammabufotalin may be developed as a novel therapeutic agent for inflammatory diseases in the future.

A comparative study of synthetic approaches towards total synthesis of histrionicotoxin: a selective inhibitor of nicotinic acetylcholine receptors

The aim of this review is to provide a critical and comparative account of the total synthetic approaches toward histrionicotoxins, alkaloids isolated from skin extracts of Colombian poison arrow frog Dendrobates histrionicus. We have summarized the maneuvers in each paper by graphically detailing the synthesis and associated reaction niceties of only the key intermediates by different researchers. Fascinating structural feature of histrionicotoxins is "8-hydroxy-l-azaspiro[5.5]undecane core" with two side chains at C-2 and C-7 which differ in their length and nature of unsaturation. All synthetic approaches to histrionicotoxins aim at the construction of key intermediate "azaspiro[5.5]undecane ring" and installation of side chains at C-2 and C-7.

Discovery of 3-peptide substituted arenobufagin derivatives as potent antitumor agents with low cardiotoxicity

Active natural productscan be valuable lead compounds and numerous drugs derived from natural products have successfully entered the clinic. Arenobufagin, one of the important active components of toad venom, indicates significant antitumor activities with limited preclinical development for its strong cardiotoxicity. Ten 3-monopeptide substituted arenobufagin derivatives have been designed and synthesized. Antitumor activity and cardiotoxicity assays lead to the discovery of compound ZM226 as a potent antitumor agent with low cardiotoxicity. These findings suggest optimization of arenobufagin on position 3 maybe an efficacious strategy for the development of antitumor drug candidates derived from arenobufagin.

Chemical profile of the parotoid gland secretion of the Amazonian toad (Rhinella margaritifera)

The secreted poisonin bufonids (Anura: Bufonidae) include proteins, biogenic amines, toxic bufadienolides and alkaloids. The chemical composition of the methanolic extract of parotoid gland secretions by the Amazonian toad Rhinella margaritifera was evaluated in a UFLC-DAD-micrOTOF system. Of the twenty three compounds found in the methanolic extract, eighteen were identified by the mass/charge ratio as: five arginine diacids, six bufagenins (telocinobufagin, marinobufagin, bufotalin, cinobufotalin, bufalin and cinobufagin), six bufotoxins, and an alkaloid (dehydrobufotenin).

Predation of treefrogs (Anura: Hylidae) with toxic skin secretions by the black lion tamarin (Leontopithecus chrysopygus, Callitrichinae)

We report on the predation of a veined treefrog (Trachycephalus venulosus) and an ocellated treefrog (Itapotihyla langsdorffii), both species with noxious skin secretions, by black lion tamarins (Leontopithecus chrysopygus). The two predation events took place in Morro do Diabo State Park, an Atlantic Forest reserve in southeastern Brazil. The veined treefrog was removed from a tree hollow by an adult male, whereas the ocellated treefrog was caught on the ground after it jumped from the tree attempting to escape capture. The frogs were completely ingested and no food sharing occurred in either of the events. We did not observe any signs of irritation during the event or when the group was followed in the next day in either of the cases. These are the first reports of lion tamarins ingesting anurans with noxious secretions on the skin.

Adapting to an invasive species: toxic cane toads induce morphological change in Australian snakes

The arrival of invasive species can devastate natural ecosystems, but the long-term effects of invasion are less clear. If native organisms can adapt to the presence of the invader, the severity of impact will decline with time. In Australia, invasive cane toads (Bufo marinus) are highly toxic to most snakes that attempt to eat them. Because snakes are gape-limited predators with strong negative allometry for head size, maximum relative prey mass (and thus, the probability of eating a toad large enough to be fatal) decreases with an increase in snake body size. Thus, the arrival of toads should exert selection on snake morphology, favoring an increase in mean body size and a decrease in relative head size. We tested these predictions with data from specimens of four species of Australian snakes, collected over >80 years. Geographic information system layers provided data on the duration of toad exposure for each snake population, as well as environmental variables (latitude, precipitation, and temperature). As predicted, two toad-vulnerable species (Pseudechis porphyriacus and Dendrelaphis punctulatus) showed a steady reduction in gape size and a steady increase in body length with time since exposure to toads. In contrast, two species at low risk from toads (Hemiaspis signata and Tropidonophis mairii) showed no consistent change in these morphological traits as a function of the duration of toad exposure. These results provide strong evidence of adaptive changes in native predators as a result of the invasion of toxic prey.

Study on mechanism of action of Chinese medicine Chan Su: dose-dependent biphasic production of nitric oxide in trophoblastic BeWo cells

BACKGROUND

Chan Su, a traditional Chinese medicine, is used for treating the heart diseases and other systemic illnesses. Our studies with animal model have revealed its role in increasing intracellular calcium concentration in cardiomyocytes. Nitric oxide (NO), a second messenger molecule, and its metabolites have been demonstrated to maintain and modulate multiple physiologic functions including the cardiovascular and reproductive systems. In order to explore the mechanism of action of Chan Su, we studied the ability of Chan Su to stimulate NO production in cultured trophoblastic BeWo cells.

MATERIALS AND METHODS

BeWo cell is a cloned established cell line purified from human choriocarcinoma. These cells have some similarities in biological behavior with endothelial cells. Therefore, BeWo cell line may act as a model system for production of nitric oxide by Chan Su both in placenta and in cardiovascular tissue, and the results can easily be extrapolated to cardiomyocytes. Very small amount of ethanol extract of Chan Su was added to the cultured cells in KBM buffer and a chemiluminescence system was used for the measurement of nitric oxide. The amounts of Chan Su extract added to cultured cells were comparable to expected level of Chan Su in human serum after ingestion. We also repeated these experiments with bufalin, the active component of Chan Su.

RESULTS

The ethanol extract of Chan Su (5 and 10 microg/ml) significantly increased NO production up to 110% of basal control value, but higher concentrations (40 and 80 microg/ml) of Chan Su (as expected in an overdose) resulted in decreased NO production below the control level. This biphasic effect on nitric oxide production was also observed with bufalin, the active component of Chan Su responsible for its digoxin-like immunoreactivity. The presence of bufalin in Chan Su preparation was confirmed by thin layer chromatography (TLC) analysis.

CONCLUSIONS

Chan Su as well as bufalin is able to modulate the production of NO in BeWo cell line.

The synthesis of (+)-allopumiliotoxin 323B'

This paper describes the synthesis of (+)-allopumiliotoxin 323B' (1) using the intramolecular [3 + 2]-cycloaddition reaction of the (Z)-N-alkenylnitrone 4. This synthesis began with (R)-tert-butyl-3-hydroxy-pent-4-enoate [(R)-13] which was obtained by enzymatic resolution with Amano PS lipase. A series of manipulations gave intermediate 17 and in situ coupling with 4-benzoyloxybutanal lead to the (Z)-N-alkenylnitrone 4 which underwent an intramolecular [3 + 2]-cycloaddition reaction to give the isoxazolidine 3 as the major cycloadduct. Isoxazolidine 3 provided the piperidinone 24 which upon diastereofacial selective addition of MeMgBr gave the required tertiary alcohol 25. Formation of the indolizidine core 2 was achieved by an intramolecular S(N)2 reaction. The side chain was assembled from a Wittig reaction between the phosphorane 8 and the enantiomerically pure aldehyde 9. Further modifications afforded the aldehyde 7 which underwent an aldol condensation with the potassium enolate of the indolizidone core 2. Dehydration gave the enone 37 which was converted into the anti-diol 38 by intramolecular hydride reduction. Finally, deprotection of the BOM protecting group gave (+)-allopumiliotoxin 323B' (1).

Electrophysiological effects of a neurotoxin extracted from the skin of the Australian frog Pseudophryne coriacea

1. The electrophysiological effects of a pumiliotoxin-B-like alkaloid extracted from the skin of the Australian frog Pseudophryne coriacea (PsC) have been studied in rat superior cervical ganglia at 37 degrees C. 2. PsC (50 mg/ml) elicits a broadening of the evoked compound action potential and, at rest, the appearance of spontaneous spike discharge at 10-20 Hz. Action potentials presumably originate far away from the soma, which is invaded in a typical IS-SD sequence. 3. The toxin effect is not related to any direct action on the preganglionic fibers of the sympathetic trunk, and does not involve synaptic mechanisms. 4. Two-electrode voltage-clamp experiments showed that the main properties of the major voltage-dependent ionic currents are apparently unaffected by the toxin, while the cell input resistance is considerably reduced. 5. The data are consistent with the hypothesis that PsC elicits a cationic permeability increase generating a pacemaker current in a region close to the cell soma.

Morphology of the large granular alveoli of the parotid glands in toad (Bufo ictericus) before and after compression

The parotid glands of toads are constituted by an accumulation of venom-producing granular alveoli. Parotid glands of Bufo ictericus were manually compressed and immediately excised. Normal glands (not submitted to compression) were also excised and processed for histological and ultrastructural observations. The glandular body of large granular alveoli in parotid glands is formed by a myoepithelial layer, internally covered by a syncytial secretory layer. In the normal parotid gland this layer is very electron dense, thus preventing clear visualization of organelles. Large secretion granules are located in the main secretion mass, near the syncytium. In the compressed parotid gland, the myoepithelium shows a number of alterations, including presence of myelin figures and foci of degradation in the cytoplasm. The organelles of the syncytial cytoplasm are easily observed. The mitochondria are swollen; the cristae are shortened or absent. Syncytial secretion granules and lengthened structures linked to the syncytial matrix are to be seen. A large amount of smooth endoplasmic reticulum is present, while the rough endoplasmic reticulum is reduced. This large quantity of smooth endoplasmic reticulum suggests enhanced synthesis of the cardiotoxic steroids of the venom. Alterations in the mitochondria and the presence of myelin figures and degenerative foci in the cytoplasm may probably be regarded as consequences of the cellular injury provoked by compression.

Pharmacological actions of "kyushin," a drug containing toad venom: cardiotonic and arrhythmogenic effects, and excitatory effect on respiration

The cardiotonic and arrhythmogenic effects, and the excitatory effect on respiration of "Kyushin," a drug containing toad venom, were studied in comparison with those of digoxin. In anesthetized rabbits, the maximum rate of rise of left ventricular systolic pressure (max dP/dt) was measured as an index of cardiotonic effect, and the respiratory flow was measured as an index of respiratory function. Intraduodenal (i.d.) administration of 80 mg/kg "Kyushin" produced a cardiotonic effect and an excitatory effect on respiration, but i.d. administration of 16 mg/kg digoxin produced only a cardiotonic effect, and conversely inhibited respiration. In anesthetized open-chest guinea pigs, myocardial contractile force was measured as an index of cardiotonic effect and the arrhythmogenic effect was evaluated from the appearance of arrhythmic myocardial contraction. By i.d. administration of a 20% ethanol suspension or solution, "Kyushin" and digoxin showed a cardiotonic activity with doses higher than 40 mg/kg and 0.25 mg/kg, respectively. The arrhythmogenic doses of "Kyushin" and digoxin by i.d. administration were 2560 mg/kg and 2 mg/kg, respectively, suggesting that the safety margin of "Kyushin" is broader than that of digoxin.

Interaction of narcotic antagonist naltrexone with nicotinic acetylcholine receptor

The interactions of naltrexone with the nicotinic acetylcholine receptor were studied electrophysiologically using the frog sciatic nerve-sartorius muscle and biochemically using membranes from the electric organ of Torpedo ocellata. At nanomolar concentrations naltrexone increased the peak amplitude of endplate currents with little change in the decay time constant. At micromolar concentrations there was a concentration-dependent depression of endplate current and miniature endplate current amplitudes and decay time constants. Decay time constant depression was enhanced with hyperpolarization. Only marginal curvature was induced in peak endplate current amplitude versus membrane voltage plots by naltrexone. Naltrexone had no effect on single channel conductance but decreased open channel lifetime, according to fluctuation analysis. Naltrexone alone (less than or equal to 3 microM) did not impair binding of [125I]alpha-bungarotoxin to the receptor in a fast pre-equilibration assay, but increased the ability of acetylcholine to displace [125I]alpha-bungarotoxin. The drug displaced the agonist-stimulated binding of [3H]perhydrohistrionicotoxin to the channel site. Biphasic functional changes in neuromuscular transmission can be attributed to an allosteric mechanism with increased agonist binding to the nicotinic receptor at nanomolar concentrations and caused a non-competitive blockade of the ionic channel at micromolar concentrations.

Actions of Gila monster venom on dispersed acini from guinea pig pancreas

Venom from Gila monster (family Helodermatidae) contains a pancreatic secretagogue. In dispersed acini from guinea pig pancreas, the venom increased enzyme secretion to the same extent as did vasoactive intestinal peptide, secretin, or PHI. The abilities of vasoactive intestinal peptide and Gila monster venom to stimulate enzyme secretion were not altered by boiling but were abolished by incubation with trypsin or chymotrypsin. Like vasoactive intestinal peptide, secretin, and PHI, the venom caused a 50- to 60-fold increase in cellular cAMP and inhibited binding of 125I-vasoactive intestinal peptide to its membrane receptors on pancreatic acini. The action of venom on enzyme secretion was inhibited by [Gln9]secretin-(5-27), a vasoactive intestinal peptide receptor antagonist, but was not altered by atropine, a cholinergic receptor antagonist, or by dibutyryl cGMP, a cholecystokinin receptor antagonist. Gila monster venom contained no immunoreactive vasoactive intestinal peptide by radioimmunoassay. These results indicate that venom from Gila monster contains a peptide that can stimulate pancreatic enzyme secretion by interacting with vasoactive intestinal peptide receptors on pancreatic acinar cells and thereby activating adenylate cyclase and increasing cellular cAMP.

Perhydrohistrionicotoxin: a potential ligand for the ion conductance modulator of the acetylcholine receptor

Histrionicotoxin from the Colombian frog Dendrobates histrionicus and its perhydro derivative reversibly block the acetylcholine-sensitive ion conductance system in frog neuromuscular preparations. The perhydro derivative and [3H]perhydrohistrionicotoxin, like histrionicotoxin, caused a significant decrease in the peak amplitude of the end-plate current and shortened its rise time and half-decay time. In membrane preparations from Torpedo electroplax, [3H]perhydrohistrionicotoxin bound reversibly to a limited number of high-affinity sites [dissociation constant, (KD) = 0.4 micronM]. The ratio of perhydrohistrionicotoxin to acetylcholine binding sites in these membrane preparations approached 2. Histrionicotoxins, local anesthetics, and certain cholinergic agonists inhibited binding of perhydrohistrionicotoxin. Binding of perhydrohistrionicotoxin to membranes was decreased by heat or treatment with proteases. Treatment of membranes with Triton X-100 solubilized acetylcholine binding proteins and apparently also perhydrohistrionicotoxin-binding proteins. However, the detergent Triton X-100 also bound [3H]perhydrohistrionicotoxin. This nonspecific binding was not saturable and complicated studies on the antagonism by drugs of binding of [3H]perhydrohistrionicotoxin. In solubilized preparations the binding protein for acetylcholine could be removed by affinity chromatography or immunoprecipitation without affecting binding of perhydrohistrionicotoxin. Sephadex chromatography also separated acetylcholine- from perhydrohistrionicotoxin-binding proteins. Perhydrohistrionicotoxin did not bind significantly to purified acetylcholine-receptor protein but presumably bound to an ion conductance modulator protein that was associated with the acetylcholine-receptor in intact membrane and readily separable from the receptor protein after solubilization.

Acetylcholine receptor and ion conductance modulator sites at the murine neuromuscular junction: evidence from specific toxin reactions

The perhydro derivative of histrionicotoxin reversibly blocks the excitatory ionic transduction system in the synaptic and sarcolemmal membranes of mammalian skeletal muscle cells. The efficacy of perhydrohistrionicotoxin as an antagonist at the post-synaptic membrane is increased by the transient presence of acetylcholine in the endplate of innervated muscles and at extrajunctional receptors in denervated muscles. alpha-Bungarotoxin and [(3)H]monoacetyl-alpha-bungarotoxin block the endplate acetylcholine receptors, each binding to the same extent. The effect of bungarotoxin is partially reversible. These electrophysiological results, together with the effects of perhydrohistrionicotoxin and/or d-tubocurarine on the binding of [(3)H]monoacetyl-alpha-bungarotoxin at endplates of murine diaphragm muscle and on the bungarotoxin-elicited irreversible blockade of neuromuscular transmission, suggest that at least two types of sites participate in the synaptic excitation by acetylcholine. One site, competitively blocked by bungarotoxin and by curare, is presumably the acetylcholine receptor. Binding of bungarotoxin at this site is responsible for an irreversible blockade of neuromuscular transmission. The second site, competitively blocked by bungarotoxin and perhydrohistrionicotoxin, is proposed to be part of the cholinergic ion conductance modulator. Binding of bungarotoxin to this site does not result in an irreversible blockade.