Analysis of the structure and electrophysiological actions of halitoxins: 1,3 alkyl-pyridinium salts from Callyspongia ridleyi

Mechanisms of action of ionic liquids on living cells: the state of the art

Ionic liquids (ILs) are a relatively new class of organic electrolytes composed of an organic cation and either an organic or inorganic anion, whose melting temperature falls around room-temperature. In the last 20 years, the toxicity of ILs towards cells and micro-organisms has been heavily investigated with the main aim to assess the risks associated with their potential use in (industrial) applications, and to develop strategies to design greener ILs. Toxicity, however, is synonym with affinity, and this has stimulated, in turn, a series of biophysical and chemical-physical investigations as well as few biochemical studies focused on the mechanisms of action (MoAs) of ILs, key step in the development of applications in bio-nanomedicine and bio-nanotechnology. This review has the intent to present an overview of the state of the art of the MoAs of ILs, which have been the focus of a limited number of studies but still sufficient enough to provide a first glimpse on the subject. The overall picture that emerges is quite intriguing and shows that ILs interact with cells in a variety of different mechanisms, including alteration of lipid distribution and cell membrane viscoelasticity, disruption of cell and nuclear membranes, mitochondrial permeabilization and dysfunction, generation of reactive oxygen species, chloroplast damage (in plants), alteration of transmembrane and cytoplasmatic proteins/enzyme functions, alteration of signaling pathways, and DNA fragmentation. Together with our earlier review work on the biophysics and chemical-physics of IL-cell membrane interactions (Biophys. Rev. 9:309, 2017), we hope that the present review, focused instead on the biochemical aspects, will stimulate a series of new investigations and discoveries in the still new and interdisciplinary field of "ILs, biomolecules, and cells."

Identification of a 3-Alkylpyridinium Compound from the Red Sea Sponge Amphimedon chloros with In Vitro Inhibitory Activity against the West Nile Virus NS3 Protease

Viruses are underrepresented as targets in pharmacological screening efforts, given the difficulties of devising suitable cell-based and biochemical assays. In this study we found that a pre-fractionated organic extract of the Red Sea sponge Amphimedon chloros was able to inhibit the West Nile Virus NS3 protease (WNV NS3). Using liquid chromatography⁻mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy, the identity of the bioactive compound was determined as a 3-alkylpyridinium with m/z = 190.16. Diffusion Ordered Spectroscopy (DOSY) NMR and NMR relaxation rate analysis suggest that the bioactive compound forms oligomers of up to 35 kDa. We observed that at 9.4 μg/mL there was up to 40⁻70% inhibitory activity on WNV NS3 protease in orthogonal biochemical assays for solid phase extracts (SPE) of A. chloros. However, the LC-MS purified fragment was effective at inhibiting the protease up to 95% at an approximate amount of 2 µg/mL with negligible cytotoxicity to HeLa cells based on a High-Content Screening (HCS) cytological profiling strategy. To date, 3-alkylpyridinium type natural products have not been reported to show antiviral activity since the first characterization of halitoxin, or 3-alkylpyridinium, in 1978. This study provides the first account of a 3-alkylpyridinium complex that exhibits a proposed antiviral activity by inhibiting the NS3 protease. We suggest that the here-described compound can be further modified to increase its stability and tested in a cell-based assay to explore its full potential as a potential novel antiviral capable of inhibiting WNV replication.

Polymeric alkylpyridinium salts permit intracellular delivery of human Tau in rat hippocampal neurons: requirement of Tau phosphorylation for functional deficits

Patients suffering from tauopathies including frontotemporal dementia (FTD) and Alzheimer's disease (AD) present with intra-neuronal aggregation of microtubule-associated protein Tau. During the disease process, Tau undergoes excessive phosphorylation, dissociates from microtubules and aggregates into insoluble neurofibrillary tangles (NFTs), accumulating in the soma. While many aspects of the disease pathology have been replicated in transgenic mouse models, a region-specific non-transgenic expression model is missing. Complementing existing models, we here report a novel region-specific approach to modelling Tau pathology. Local co-administration of the pore-former polymeric 1,3-alkylpyridinium salts (Poly-APS) extracted from marine sponges, and synthetic full-length 4R recombinant human Tau (hTau) was performed in vitro and in vivo. At low doses, Poly-APS was non-toxic and cultured cells exposed to Poly-APS (0.5 µg/ml) and hTau (1 µg/ml; ~22 µM) had normal input resistance, resting-state membrane potentials and Ca(2+) transients induced either by glutamate or KCl, as did cells exposed to a low concentration of the phosphatase inhibitor Okadaic acid (OA; 1 nM, 24 h). Combined hTau loading and phosphatase inhibition resulted in a collapse of the membrane potential, suppressed excitation and diminished glutamate and KCl-stimulated Ca(2+) transients. Stereotaxic infusions of Poly-APS (0.005 µg/ml) and hTau (1 µg/ml) bilaterally into the dorsal hippocampus at multiple sites resulted in hTau loading of neurons in rats. A separate cohort received an additional 7-day minipump infusion of OA (1.2 nM) intrahippocampally. When tested 2 weeks after surgery, rats treated with Poly-APS+hTau+OA presented with subtle learning deficits, but were also impaired in cognitive flexibility and recall. Hippocampal plasticity recorded from slices ex vivo was diminished in Poly-APS+hTau+OA subjects, but not in other treatment groups. Histological sections confirmed the intracellular accumulation of hTau in CA1 pyramidal cells and along their processes; phosphorylated Tau was present only within somata. This study demonstrates that cognitive, physiological and pathological symptoms reminiscent of tauopathies can be induced following non-mutant hTau delivery into CA1 in rats, but functional consequences hinge on increased Tau phosphorylation. Collectively, these data validate a novel model of locally infused recombinant hTau protein as an inducer of Tau pathology in the hippocampus of normal rats; future studies will provide insights into the pathological spread and maturation of Tau pathology.

Analysis of the toxicity and histopathology induced by the oral administration of Pseudanabaena galeata and Geitlerinema splendidum (cyanobacteria) extracts to mice

Cyanobacteria are common members of the freshwater microbiota in lakes and drinking water reservoirs, and are responsible for several cases of human intoxications in Brazil. Pseudanabaena galeata and Geitlerinema splendidum are examples of the toxic species that are very frequently found in reservoirs in Sao Paulo, which is the most densely populated area in Brazil. In the search for toxic strains collected from water reservoirs and maintained in the Cyanobacterial Culture Collection (CCIBt) of the Institute of Botany of Brazil, the acetic acid extracts (AE) of P. galeata CCIBt 3082 and G. splendidum CCIBt 3223 were analyzed by planar chromatography, which indicated the absence of cyanotoxins. Animal tests were then carried out, and both extracts were found to induce toxic effects in mice when administered intraperitoneally. The present study aimed to investigate whether the oral ingestion of the above mentioned cyanobacteria extracts would also induce toxic effects in mice. Necropsy and histopathological studies were conducted using tissue samples from the animals, which were euthanized one week after the administration of the extracts. The AE of P. galeata did not cause death but did induce transient symptoms, including eyebrow ptosis, straub tail, and pain. The euthanized animals presented hemorrhage in the liver, whereas the histological analysis showed disorganization of the hepatic parenchyma, necrosis, hyperemia, and proximity of the centrilobular vein in the liver. In addition, alterations in the convoluted tubules of the kidneys were observed, and the lungs were unaffected. The AE of G. splendidum caused only one death, and induced transient symptoms, such as dyspnea, paralysis, and pain, in the other mice. The necropsy of the euthanized mice showed hemorrhage in the lungs and liver. The lungs presented hemorrhagic focuses, alveolar collapse, and granulomatous foci. The liver presented hemorrhagic and enlarged sinusoids, hyperemia, proximity of the centrilobular vein, and disorganization of the hepatic parenchyma. Some areas also exhibited an inflammatory infiltrate and calcified tissue inside blood vessels. Necrosis and rupture of the convoluted tubule cells were observed in the kidneys. Further analysis of the both extracts indicated the lack of hemolytic activity, and the presence of two unknown anti-AChE substances in the AE of G. splendidum. Thus, P. galeata and G. splendidum are producers of novel toxins that affect mammals when administered orally.

Evaluation of the antifouling properties of 3-alyklpyridine compounds

One of the most promising alternative technologies to antifouling (AF) biocides based on toxic heavy metals lies in the development of natural eco-friendly biocides. The present study evaluates the AF potential of structurally different compounds containing a 3-alkylpyridine moiety. The products, namely poly 3-alkylpyridinium salts, saraine, and haminols, were either extracted or derived from natural sources (the sponges Haliclona sp. and Reniera sarai and the mollusc Haminoea fusari), or obtained by chemical synthesis. All the molecules tested showed generally good anti-settlement activity against larvae of the barnacle Amphibalanus (=Balanus) amphitrite (EC(50) values between 0.19 and 3.61 μg ml(-1) and low toxicity (LC(50) values ranging from 2.04 to over 100 μg ml(-1)) with non-target organisms. For the first time, the AF potential of a synthetic monomeric 3-alkylpyridine was demonstrated, suggesting that chemical synthesis is as a realistic way to produce large amounts of these compounds for future research and development of environmentally-friendly AF biocides.

Chemical synthesis and biological activities of 3-alkyl pyridinium polymeric analogues of marine toxins

Two new large poly-1,3-dodecylpyridinium salts, APS12 and APS12-2 of 12.5- and 14.7-kDa size, respectively, were synthesised and tested for their pore-forming and transfection capabilities in HEK 293 and undifferentiated mouse ES cells using patch-clamp recording, Ca(2+) imaging and flow cytometry. Polymerisation reactions were enhanced by microwaves, and the product sizes were controlled by altering the irradiation time. This method can also be applied to obtain polymers with variable linking chains as shown by the preparation of poly-(1,3-octylpyridinium) salt of 11.9-kDa size. Molecular weights of the final products were determined using ESIMS analysis, which also indicated the products to be amongst the largest macro-cycles ever recorded, up to a 900-membered ring. Anti-bacterial, haemolytic and anti-acetylcholinesterase activities were also reported for the two dodecyl pyridinium polymers. These biological activities are characteristic to the structurally related marine toxin, poly-APS.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12154-010-0036-4) contains supplementary material, which is available to authorized users.

Chemical warfare in the sea: The search for antibiotics from Red Sea corals and sponges

Marine sponges and corals are widely recognized as rich sources of novel bioactive natural products. These organisms are frequently colonized by bacteria. Some of these bacteria can be pathogenic or serve as beneficial symbionts. Therefore, these organisms need to regulate the bacteria they encounter and resist microbial pathogens. One method is by chemical defense. Antimicrobial assays performed with extracts of 23 Red Sea corals and sponges against bacteria isolated from their natural environment revealed considerable variability in antimicrobial activity. Soft corals exhibited appreciable activity; sponges showed variability, and stony corals had little or no activity. Among the soft corals, Xenia macrospiculata exhibited the highest activity. Bioassay-directed fractionation of the extract indicated that the activity was due to a range of compounds, one of which was isolated and identified as the diterpene desoxyhavannahine. Among the sponges, Amphimedon chloros exhibited strong activity. Bioassay-directed fractionation resulted in the isolation of the pyridinium alkaloid antibiotics, the halitoxins and amphitoxins. These compounds showed selective activity against specific bacteria, rather than being broad-spectrum. They were highly active against seawater bacteria, whereas bacteria associated with the sponge were resistant. This selective toxicity may be important in enabling certain bacteria to live in close association with their sponge host while it maintains a chemical defense against microbial pathogenesis. The halitoxin-resistant bacteria were identified by 16S rRNA gene analysis as Alphaproteobacteria, closely related to other Alphaproteobacteria isolated from various marine sponges. The study of microbial communities associated with sponges and corals has important implications for the production of symbiont-derived bioactive compounds and for the use of corals and sponges as source material for microbial diversity in screening programs for natural products.

Structural and formulation factors influencing pyridinium lipid-based gene transfer

A series of pyridinium lipids containing a heterocyclic ring and a nitrogen atom were synthesized to determine the structure-activity relationship for gene delivery. Pyrylium chloroaluminate was synthesized by monoacylation of mesityl oxide and converted into pyrylium hexafluorophosphate, which was used as the key intermediate for reaction with different primary amines, to yield hydroxyethylpyridinium hexafluorophosphate and aminoethylpyridinium hexafluorophosphate. Acylation of these pyridinium salts with different types of fatty acid chlorides afforded the final pyridinium lipids, which were mixed with a co-lipid, such as L-alpha-dioleoylphosphatidylethanolamine (DOPE) and cholesterol (Chol) to prepare cationic liposomes by sonication. These liposomes were mixed with plasmid DNA encoding enhanced green fluorescent protein (pCMS-EGFP) or luciferase (pcDNA3-Luc) and transfected into Chinese hamster ovary (CHO) cells. Several factors including hydrophobic anchor chain length, anchor chain type, configuration of double bond, linker type, co-lipid type, cationic lipid/co-lipid molar ratio, charge ratio (N/P), and cell type had significant influence on transfection efficiency and cytotoxicity. Pyridinium lipids with amide linker showed significantly higher transfection efficiency compared to their ester counterparts. Liposomes prepared at a 1:1 molar ratio of pyridinium lipid and co-lipid showed higher transfection efficiency when either DOPE or cholesterol was used as a co-lipid to prepare cationic liposomes for complex formation with plasmid DNA at 3:1(+/-) charge ratio. Pyridinium liposomes based on a hydrophobic anchor chain length of 16 showed higher transfection efficiency and lower cytotoxicity. The pyridinium lipid with a trans-configuration of the double bond in the fatty acid chain showed higher transfection efficiency than its counterpart with cis-configuration at the same fatty acid chain length. In the presence of serum, C16:0 and Lipofectamine significantly decreased their transfection efficiencies, which were completely lost at a serum concentration of 30% and higher, while C16:1 trans-isomer still had high transfection efficiency under these conditions. In conclusion, pyridinium lipids showed high transfection efficiency and have the potential to be used as transfection reagents in vitro and in vivo.

A comparative study of the actions of alkylpyridinium salts from a marine sponge and related synthetic compounds in rat cultured hippocampal neurones

Background

Polymeric alkylpyridinium salts (poly-APS), are chemical defences produced by marine sponges including Reniera sarai. Poly-APS have previously been shown to effectively deliver macromolecules into cells. The efficiency of this closely follows the ability of poly-APS to form transient pores in membranes, providing strong support for a pore-based delivery mechanism. Recently, water soluble compounds have been synthesised that are structurally related to the natural polymers but bear a different number of pyridinium units. These compounds may share a number of bio-activities with poly-APS. Using electrophysiology, calcium imaging and 1,6-diphenyl-1,3,5-hexatriene imaging, the pore forming properties of poly-APS and four related synthetic oligomers have been tested on primary cultured rat hippocampal neurones.

Results

Acute application of poly-APS (0.5 μg/ml), reduced membrane potential, input resistance and suppressed action potential firing. Poly-APS evoked inward cation currents with linear current-voltage relationships similar to actions of pore formers on other cell types. Poly-APS (0.005–5 μg/ml) also produced Ca²⁺ transients in ~41% of neurones. The dose-dependence of poly-APS actions were complex, such that at 0.05 μg/ml and 5 μg/ml poly-APS produced varying magnitudes of membrane permeability depending on the order of application. Data from surface plasmon resonance analysis suggested accumulation of poly-APS in membranes and subsequent enhanced poly-APS binding. Even at 10–100 fold higher concentrations, none of the synthetic compounds produced changes in electrophysiological characteristics of the same magnitude as poly-APS. Of the synthetic oligomers tested compounds 1 (monomeric) and tetrameric 4 (5–50 μg/ml) induced small transient currents and 3 (trimeric) and 4 (tetrameric) produced significant Ca²⁺ transients in hippocampal neurones.

Conclusion

Poly-APS induced pore formation in hippocampal neurones and such pores were transient, with neurones recovering from exposure to these polymers. Synthetic structurally related oligomers were not potent pore formers when compared to poly-APS and affected a smaller percentage of the hippocampal neurone population. Poly-APS may have potential as agents for macromolecular delivery into CNS neurones however; the smaller synthetic oligomers tested in this study show little potential for such use. This comparative analysis indicated that the level of polymerisation giving rise to the supermolecular structure in the natural compounds, is likely to be responsible for the activity here reported.

A pyridinium derivative from Red Sea soft corals inhibited voltage-activated potassium conductances and increased excitability of rat cultured sensory neurones

BACKGROUND

Whole cell patch clamp recording and intracellular Ca2+ imaging were carried out on rat cultured dorsal root ganglion (DRG) neurones to characterize the actions of crude extracts and purified samples from Red Sea soft corals. The aim of the project was to identify compounds that would alter the excitability of DRG neurones.

RESULTS

Crude extracts of Sarcophyton glaucum and Lobophyton crassum attenuated spike frequency adaptation causing DRG neurones to switch from firing single action potentials to multiple firing. The increase in excitability was associated with enhanced KCl-evoked Ca2+ influx. The mechanism of action of the natural products in the samples from the soft corals involved inhibition of voltage-activated K+ currents. An active component of the crude marine samples was identified as 3-carboxy-1-methyl pyridinium (trigonelline). Application of synthetic 3-carboxy-1-methyl pyridinium at high concentration (0.1 mM) also induced multiple firing and reduced voltage-activated K+ current. The changes in excitability of DRG neurones induced by 3-carboxy-1-methyl pyridinium suggest that this compound contributes to the bioactivity produced by the crude extracts from two soft corals.

CONCLUSION

Sarcophyton glaucum and Lobophyton crassum contain natural products including 3-carboxy-1-methyl pyridinium that increase the excitability of DRG neurones. We speculate that in addition to developmental control and osmoregulation these compounds may contribute to chemical defenses.

Pore forming polyalkylpyridinium salts from marine sponges versus synthetic lipofection systems: distinct tools for intracellular delivery of cDNA and siRNA

Background

Haplosclerid marine sponges produce pore forming polyalkylpyridinium salts (poly-APS), which can be used to deliver macromolecules into cells. The aim of this study was to investigate the delivery of DNA, siRNA and lucifer yellow into cells mediated by poly-APS and its potential mechanisms as compared with other lipofection systems (lipofectamine and N⁴,N⁹-dioleoylspermine (LipoGen)). DNA condensation was evaluated and HEK 293 and HtTA HeLa cells were used to investigate pore formation and intracellular delivery of cDNA, siRNA and lucifer yellow.

Results

Poly-APS and LipoGen were both found to be highly efficient DNA condensing agents. Fura-2 calcium imaging was used to measure calcium transients indicative of cell membrane pore forming activity. Calcium transients were evoked by poly-APS but not LipoGen and lipofectamine. The increases in intracellular calcium produced by poly-APS showed temperature sensitivity with greater responses being observed at 12°C compared to 21°C. Similarly, delivery of lucifer yellow into cells with poly-APS was enhanced at lower temperatures. Transfection with cDNA encoding for the expression enhanced green fluorescent protein was also evaluated at 12°C with poly-APS, lipofectamine and LipoGen. Intracellular delivery of siRNA was achieved with knockdown in beta-actin expression when lipofectamine and LipoGen were used as transfection reagents. However, intracellular delivery of siRNA was not achieved with poly-APS.

Conclusion

Poly-APS mediated pore formation is critical to its activity as a transfection reagent, but lipofection systems utilise distinct mechanisms to enable delivery of DNA and siRNA into cells.

Irreversible and reversible pore formation by polymeric alkylpyridinium salts (poly-APS) from the sponge Reniera sarai

1. In this study, we investigated the electrophysiological actions of a high molecular weight fraction, predominantly containing two polymeric 1,3-alkylpyridinium salts (poly-APS) of 5.5 and approximately 19 kDa isolated from the marine sponge Reniera sarai. The biological properties of poly-APS are of particular interest because this preparation may be used to deliver macromolecules into the intracellular environment without producing long-term damage to cells. Poly-APS (50-0.05 micro g ml(-1)) was applied to cultured dorsal root ganglion neurones or HEK 293 cells and changes in cell membrane properties were measured using whole-cell patch-clamp recording and fura-2 Ca(2+) imaging. 2. Poly-APS (50 micro g ml(-1)) evoked irreversible depolarisations in membrane potential and reductions in input resistance. However, doses of 5 micro g ml(-1) and less produced reversible effects on these cell membrane characteristics and on Ca(2+) permeability. 3. At 0.05 micro g ml(-1), poly-APS could robust transient increases in Ca(2+) permeability without damaging the neurones or subsequently attenuating Ca(2+) entry through voltage-activated channels. 4. Bathing cells in NaCl-based extracellular medium containing 1.5 mM zinc attenuated the irreversible and reversible effects of poly-APS on membrane properties (membrane potential, input resistance and whole-cell currents). In both DRG neurones and HEK 293 cells, zinc attenuated Ca(2+) entry evoked by poly-APS. These effects of zinc were only observed if zinc was continually present during poly-APS application. However, zinc failed to attenuate the actions of poly-APS if it was applied after the sponge toxin preparation had evoked changes in membrane properties. 5. In conclusion, the pore-forming preparation poly-APS can have dose-dependent interactions with cell membranes and at low doses these can be reversible. Additionally, the interactions between poly-APS and cell membranes could be attenuated by zinc.

Toxic effects of head-to-tail 3-alkylpyridinium polymers isolated from the marine sponge Reniera sarai in rat

Toxic water soluble polymeric 3-alkylpyridinium salts (poly APS; MW 18900 and 5520Da) were isolated from the marine sponge Raniera sarai. In vitro they strongly inhibited acetylcholinesterase. In order to evaluate the role of acetylcholinesterase inhibition in toxin lethality, and to assess other possible lethal effects, in vivo experiments were performed on male Wistar rats, and ECG, blood pressure and breathing pattern were monitored. The results showed that none of the animals died due to the acetylcholinesterase inhibitory action of poly-APS. Doses lower than 1mg/kg caused only transient bradycardia and transient prolongation of expirium. At doses above 2.7mg/kg of poly-APS all treated animals died, but signs were not typical of acetylcholinesterase inhibition. Arterial blood pressure fell to mid-circulatory pressure, and breathing stopped after a few breaths with an increase of the residual volume. Autopsy of the experimental animals that died due to the effects of the toxin revealed that mid-size and small sized blood vessels in the heart and lungs were filled with granular brownish material with inclusions of red blood cells and platelets. Data obtained on blood samples from animals treated with poly-APS also revealed numerous thrombocyte aggregates. In vitro poly-APS induced thrombocyte aggregation in a dose dependent manner. The acetylcholinesterase-inhibitory effects were most pronounced only at lower doses of poly-APS. With higher doses those effects were masked or covered by other, more pronounced and faster developing lethal effects of the toxin such as platelet aggregation. Therefore it is reasonable to assume that acetylcholinesterase inhibitory effects are not responsible for the lethal activity of the toxin.