Bioactive alkaloids from the venom of Dendrobatoidea Cope, 1865: a scoping review.

Bioactive compounds derived from secondary metabolism in animals have refined selectivity and potency for certain biological targets. The superfamily Dendrobatoidea is adapted to the dietary sequestration and secretion of toxic alkaloids, which play a role in several biological activities, and thus serve as a potential source for pharmacological and biotechnological applications. This article constitutes a scoping review to understand the trends in experimental research involving bioactive alkaloids derived from Dendrobatoidea based upon scientometric approaches. Forty-eight (48) publications were found in 30 journals in the period of 60 years, between 1962 and 2022. More than 23 structural classes of alkaloids were cited, with 27.63% for batrachotoxins, 13.64% for pyridinics, with an emphasis on epibatidine, 16.36% for pumiliotoxins, and 11.82% for histrionicotoxins. These tests included in vivo (54.9%), in vitro (39.4%), and in silico simulations (5.6%). Most compounds (54.8%) were isolated from skin extracts, whereas the remainder were obtained through molecular synthesis. Thirteen main biological activities were identified, including acetylcholinesterase inhibitors (27.59%), sodium channel inhibitors (12.07%), cardiac (12.07%), analgesic (8.62%), and neuromuscular effects (8.62%). The substances were cited as being of natural origin in the "Dendrobatidae" family, genus "Phyllobates," "Dendrobates," and seven species: Epipedobates tricolor, Phyllobates aurotaenia, Oophaga histrionica, Oophaga pumilio, Phyllobates terribilis, Epipedobates anthonyi, and Ameerega flavopicta. To date, only a few biological activities have been experimentally tested; hence, further studies on the bioprospecting of animal compounds and ecological approaches are needed.

Poor alkaloid sequestration by arrow poison frogs of the genus Phyllobates from Costa Rica.

Frogs of the genus Phyllobates from Colombia are known to contain the highly toxic alkaloid batrachotoxin, but species from Central America exhibit only very low levels or are entirely free of this toxin. In the present study alcohol extracts from 101 specimens of Phyllobates lugubris and Phyllobates vittatus and 21 of three sympatric species (Dendrobates pumilio, Dendrobates auratus, Dendrobates granuliferus) from Costa Rica were analyzed by gas chromatography-mass spectrometry. Whereas the extracts of the Dendrobates species exhibited typical profiles of toxic alkaloids, those of the two Phyllobates species contained low levels of few alkaloids only, batrachotoxin was not detected. Although the feeding pattern of the Dendrobates and Phyllobates species are similar as revealed by examination of their stomach content (mainly ants and mites), the Phyllobates species are poorly sequestering alkaloids from their food source in contrast to the Dendrobates frogs.

Relaxation of rabbit corpus cavernosum by selective activators of voltage-gated sodium channels: role of nitric oxide-cyclic guanosine monophosphate pathway.

OBJECTIVES: To investigate the capacity of voltage-gated Na(+) channel activators such as batrachotoxin, aconitine, veratridine, Ts1 (formerly Tityus gamma-toxin), and brevetoxin-3 to induce relaxation of rabbit isolated corpus cavernosum (RbCC) and the pharmacologic mechanisms underlying this phenomenon. The voltage-gated Na(+) channels of the corpus cavernosum are essential for erectile function. A number of biologic toxins exert their effects by modifying the properties of these channels. METHODS: Male New Zealand white rabbits were anesthetized with pentobarbital sodium. Strips of RbCC were transferred to 10-mL organ baths containing oxygenated and warmed Krebs solution. The RbCC strips were connected to force-displacement transducers, and changes in isometric force were recorded using a PowerLab 400 data acquisition system. Corporeal smooth muscle was precontracted submaximally with phenylephrine (10 micromol/L). RESULTS: The binding site-2 (batrachotoxin, aconitine, and veratridine) and binding site-5 (brevetoxin-3) voltage-gated Na(+) channel activators caused slow-onset RbCC relaxations, and the binding site-4 activator Ts1 produced transitory relaxations followed by a return to baseline. The Na(+)channel blockers tetrodotoxin and saxitoxin (0.1 micromol/L each) abolished the relaxations induced by these agonists. Similarly, the nitric oxide synthase inhibitor N(omega)-nitro-l-arginine methyl ester (100 micromol/L) markedly reduced the relaxations and l-arginine (1 mmol/L) restored the relaxations. The soluble guanylyl cyclase inhibitor 1H-[1,2,4] oxidiazolo[4,3-alpha] quinoxalin-1-one (10 micromol/L) reduced the relaxations, and the phosphodiesterase type 5 inhibitor sildenafil (100 nmol/L) significantly potentiated the relaxations by all activators. CONCLUSIONS: Our results indicate that the relaxations evoked by selective activators of voltage-gated Na(+) channels are mediated by the release of nitric oxide from nitrergic nerves and the activation of the nitric oxide-cyclic guanosine monophosphate pathway in the smooth muscle cells of erectile tissue.

The permeation and activation properties of brain sodium channels change during development.

BTX-modified sodium channels from 15-day embryonic (E15) rat forebrains were studied in planar lipid bilayers. Compared to postnatal sodium channels, E15 channels had a lower maximal single channel conductance, whereas their permeation pathway sensed a comparable surface charge density and had a similar apparent binding affinity for sodium ions. The steady-state activation curve of E15 channels was significantly more hyperpolarized and had a shallower slope than postnatal channels. The apparent BTX binding affinity was significantly lower for E15 channels than for postnatal channels. Finally, E15 channel alpha-subunits displayed a lower apparent molecular weight, and a lower sialylation level than postnatal sodium channel alpha-subunits. Together with previous studies, our data suggested that the observed functional differences between E15 and postnatal voltage-dependent sodium channels cannot be explained solely by the observed differences in channel sialylation, and hence they also appeared to reflect the presence of other channel structural differences.

Alkaloids from frog skins: selective probes for ion channels and nicotinic receptors.

Amphibian skin has provided a wide range of biologically active alkaloids, many of which have unique profiles of pharmacological activity and therapeutic potential. Over three hundred alkaloids have been identified and structures of over a dozen different classes of alkaloids have been elucidated. These include the batrachotoxins, which were shown to be potent and selective activators and ligands for sodium channels, the histrionicotoxins, which were shown to be potent non-competitive blockers and ligands for nicotine receptor channel complexes, the pumiliotoxins and related allo- and homo-pumiliotoxins, which were shown to have myotonic and cardiotonic activity due to effects on sodium channels, and epibatidine, which was shown to have potent antinociceptive activity due to selective agonist activity at nicotinic receptors. These alkaloids are known in nature only in amphibian skin, except for homobatrachotoxin, which was recently identified in feathers and skin of a bird. Further classes of alkaloids from amphibian skin include monocyclic pyrrolidines and piperidines, bicyclic decahydroquinolines, pyrrolizidines, indolizidines, and quinolizidines and tricyclic gephyrotoxins, pyrrolizidine oximes, pseudophrynamines, and coccinellines. These alkaloids also have activity in ion channels. It appears likely that all of the frog skin alkaloids are taken up and sequestered into the skin from the diet, which for such amphibians consists mainly of small arthropods. The pyrrolidines, piperidines, 3,5-disubstituted pyrrolizidines and 3,5-disubstituted indolizidines appear likely to be derived from ants, the coccinellines and related tricyclics from beetles and the pyrrolizidine oximes from millipedes. The origins of the batrachotoxins, histrionicotoxins, pumiliotoxins and epibatidine are of particular interest in view of their remarkable biological activities.

Alkaloids from frog skins: selective probes for ion channels and nicotinic receptors

Amphibian skin has provided a wide range of biologically active alkaloids, many of wich have unique profiles of pharmacological activity and therapeutic potential. Over three hundred alkaloids have been identified and structures of over a dozen different classes of alkaloids have been elucidated. These iclude the batrachotoxins, wich were shown to be potent and selective activators and ligands for sodium channels, the histrionicotoxins, wich were shoen to be potent non-competitive blockers and ligands for nicotine receptor channel complexes, the pumiliotoxins and related allo-and homo-pumiliotoxins, wich were shown to have myotonic and cardiotonic activity due to effects on sodium channels, and epibatidine, wich was shown to have potent antinociceptive activity due to selective agonist activity at nicotinic receptors. These alkaloids are known in nature only in amphibian skin, except for homobatrachotoxin, wich was recently identified in feathers and skin of a bird. Further classes of alkaloids from amphibian skin include monocyclic pyrrolidines and piperidines, bicyclic decahydroquinolines, pyrrolizidines, and quinolozidines and tricyclic gephyrotoxins, pyrrolizidine oximes, etc..

Expression of sodium channels with different saxitoxin affinity during rat forebrain development.

This work characterizes the development of the saxitoxin (STX)-sensitive Na+ channels from rat whole forebrain between embryonic day 15 (E15) and postnatal day 90 (P90), both with binding studies and with single channel studies. The Na+ channel total mRNA and the individual mRNAs encoding Na+ channels I, II and III were also determined. The total STX binding rose about 40-fold from E15 to reach a plateau at P30 and its temporal course correlated with the expression of Na+ channel total mRNA. Low affinity and high-affinity STX binding sites, predominant in embryonic and postnatal forebrains, respectively, were found. The single channel studies of batrachotoxin-modified channels also revealed two main populations. In E15 only low-affinity channels (KD = 32.7 nM; 200 mM NaCl) and in P30 only high affinity ones (KD = 1.6 nM) were present. At P0 channels with intermediate affinity (KD range 3-34 nM) were observed. The increase in affinity was due to a gradual increase in the STX association rate.

Batrachotoxin-modified sodium channels from squid optic nerve in planar bilayers. Ion conduction and gating properties.

Squid optic nerve sodium channels were characterized in planar bilayers in the presence of batrachotoxin (BTX). The channel exhibits a conductance of 20 pS in symmetrical 200 mM NaCl and behaves as a sodium electrode. The single-channel conductance saturates with increasing the concentration of sodium and the channel conductance vs. sodium concentration relation is well described by a simple rectangular hyperbola. The apparent dissociation constant of the channel for sodium is 11 mM and the maximal conductance is 23 pS. The selectivity determined from reversal potentials obtained in mixed ionic conditions is Na+ approximately Li+ greater than K+ greater than Rb+ greater than Cs+. Calcium blocks the channel in a voltage-dependent manner. Analysis of single-channel membranes showed that the probability of being open (Po) vs. voltage relation is sigmoidal with a value of 0.5 between -90 and -100 mV. The fitting of Po requires at least two closed and one open state. The apparent gating charge required to move through the whole transmembrane voltage during the closed-open transition is four to five electronic charges per channel. Distribution of open and closed times are well described by single exponentials in most of the voltage range tested and mean open and mean closed times are voltage dependent. The number of charges associated with channel closing is 1.6 electronic charges per channel. Tetrodotoxin blocked the BTX-modified channel being the blockade favored by negative voltages. The apparent dissociation constant at zero potential is 16 nM. We concluded that sodium channels from the squid optic nerve are similar to other BTX-modified channels reconstituted in bilayers and to the BTX-modified sodium channel detected in the squid giant axon.