Biochimie et Toxicologie des Substances Bioactives

Ants (Formicidae) represent a taxonomically diverse group of hymenopterans with over 13,000 extant species, the majority of which inject or spray secretions from a venom gland. The evolutionary success of ants is mostly due to their unique eusociality that has permitted them to develop complex collaborative strategies, partly involving their venom secretions, to defend their nest against predators, microbial pathogens, ant competitors, and to hunt prey. Activities of ant venom include paralytic, cytolytic, haemolytic, allergenic, pro-inflammatory, insecticidal, antimicrobial, and pain-producing pharmacologic activities, while non-toxic functions include roles in chemical communication involving trail and sex pheromones, deterrents, and aggregators. While these diverse activities in ant venoms have until now been largely understudied due to the small venom yield from ants, modern analytical and venomic techniques are beginning to reveal the diversity of toxin structure and function. As such, ant venoms are distinct from other venomous animals, not only rich in linear, dimeric and disulfide-bonded peptides and bioactive proteins, but also other volatile and non-volatile compounds such as alkaloids and hydrocarbons. The present review details the unique structures and pharmacologies of known ant venom proteinaceous and alkaloidal toxins and their potential as a source of novel bioinsecticides and therapeutic agents.

Trikafta, currently the leading therapeutic in cystic fibrosis (CF), has demonstrated a real clinical benefit. This treatment is the triple combination therapy of two folding correctors elexacaftor/tezacaftor (VX445/VX661) plus the gating potentiator ivacaftor (VX770). In this study, our aim was to compare the properties of F508del-CFTR in cells treated with either lumacaftor (VX809), tezacaftor, elexacaftor, elexacaftor/tezacaftor with or without ivacaftor. We studied F508del-CFTR function, maturation and membrane localisation by Ussing chamber and whole-cell patch-clamp recordings, Western blot and immunolocalisation experiments. With human primary airway epithelial cells and the cell lines CFBE and BHK expressing F508del, we found that, whereas the combination elexacaftor/tezacaftor/ivacaftor was efficient in rescuing F508del-CFTR abnormal maturation, apical membrane location and function, the presence of ivacaftor limits these effects. The basal F508del-CFTR short-circuit current was significantly increased by elexacaftor/tezacaftor/ivacaftor and elexacaftor/tezacaftor compared to other correctors and nontreated cells, an effect dependent on ivacaftor and cAMP. These results suggest that the level of the basal F508del-CFTR current might be a marker for correction efficacy in CF cells. When cells were treated with ivacaftor combined to any correctors, the F508del-CFTR current was unresponsive to the subsequently acute addition of ivacaftor, unlike the CFTR (cystic fibrosis transmembrane conductance regulator) potentiators genistein and Cact-A1 which increased elexacaftor/tezacaftor/ivacaftor and elexacaftor/tezacaftor-corrected F508del-CFTR currents. These findings show that ivacaftor reduces the correction efficacy of Trikafta. Thus, combining elexacaftor/tezacaftor with a different potentiator might improve the therapeutic efficacy for treating CF patients.

Using an integrated transcriptomic and proteomic approach, we characterized the venom peptidome of the European red ant, Manica rubida . We identified 13 “myrmicitoxins” that share sequence similarities with previously identified ant venom peptides, one of them being identified as an EGF-like toxin likely resulting from a threonine residue modified by O- fucosylation. Furthermore, we conducted insecticidal assays of reversed-phase HPLC venom fractions on the blowfly Lucilia caesar, permitting us to identify six myrmicitoxins (i.e., U 3 -, U 10 -, U 13 -, U 20 -MYRTX-Mri1a, U 10 -MYRTX-Mri1b, and U 10 -MYRTX-Mri1c) with an insecticidal activity. Chemically synthesized U 10 -MYRTX-Mri1a, -Mri1b, -Mri1c, and U 20 -MYRTX-Mri1a irreversibly paralyzed blowflies at the highest doses tested (30–125 nmol·g –1 ). U 13 -MYRTX-Mri1a, the most potent neurotoxic peptide at 1 h, had reversible effects after 24 h (150 nmol·g –1 ). Finally, U 3 -MYRTX-Mri1a has no insecticidal activity, even at up to 55 nmol·g –1 . Thus, M. rubida employs a paralytic venom rich in linear insecticidal peptides, which likely act by disrupting cell membranes.

The venom peptide bicarinalin, previously isolated from the ant Tetramorium bicarinatum, is an antimicrobial agent with a broad spectrum of activity. In this study, we investigate the potential of bicarinalin as a novel agent against Helicobacter pylori, which causes several gastric diseases. First, the effects of synthetic bicarinalin have been tested against Helicobacter pylori: one ATCC strain, and forty-four isolated from stomach ulcer biopsies of Peruvian patients. Then the cytoxicity of bicarinalin on human gastric cells and murine peritoneal macrophages was measured using XTT and MTT assays, respectively. Finally, the preventive effect of bicarinalin was evaluated by scanning electron microscopy using an adherence assay of H. pylori on human gastric cells treated with bicarinalin. This peptide has a potent antibacterial activity at the same magnitude as four antibiotics currently used in therapies against H. pylori. Bicarinalin also inhibited adherence of H. pylori to gastric cells with an IC50 of 0.12 μg·mL−1 and had low toxicity for human cells. Scanning electron microscopy confirmed that bicarinalin can significantly decrease the density of H. pylori on gastric cells. We conclude that Bicarinalin is a promising compound for the development of a novel and effective anti-H. pylori agent for both curative and preventive use.

BACKGROUND: P17, a peptide isolated from Tetramorium bicarinatum ant venom, is known to induce an alternative phenotype of human monocyte-derived macrophages via activation of an unknown G protein-coupled receptor (GPCR). OBJECTIVE: We sought to investigate the mechanism of action and the immunomodulatory effects of P17 mediated through MRGPRX2 (Mas-related G protein-coupled receptor X2). METHODS: To identify the GPCR for P17, we screened 314 GPCRs. Upon identification of MRGPRX2, a battery of in silico, in vitro, ex vivo, and in vivo assays along with the receptor mutation studies were performed. In particular, to investigate the immunomodulatory actions, we used β-hexosaminidase release assay, cytokine releases, quantification of mRNA expression, cell migration and differentiation assays, immunohistochemical labeling, hematoxylin and eosin, and immunofluorescence staining. RESULTS: ]P17 lost its activity partially. P17 activated LAD2 cells to recruit THP-1 and human monocytes in Transwell migration assay, whereas MRGPRX2-impaired LAD2 cells cannot. In addition, P17-treated LAD2 cells stimulated differentiation of THP-1 and human monocytes, as indicated by the enhanced expression of macrophage markers cluster of differentiation 11b and TNF-α by quantitative RT-PCR. Immunohistochemical and immunofluorescent staining suggested monocyte recruitment in mice ears injected with P17. CONCLUSIONS: Our data provide novel structural information regarding the interaction of P17 with MRGPRX2 and intracellular pathways for its immunomodulatory action.

Stakeholders are critical environmental managers in human-dominated landscapes. In some contexts, stakeholders can be forced to personally act following their own observations and risk perception instead of science recommendation. In particular, biological invasions need rapid control actions to reduce potential socio-ecological impacts, while science-based risk assessments are rather complex and time-delayed. Although they can lead to important detrimental effects on biodiversity, potential time-delayed disconnections between stakeholders' action and science recommendations are rarely studied. Using the case study of western European beekeepers controlling the invasive Asian hornet Vespa velutina nigrithorax for its suspected impact on honey bee colonies , we analysed mechanisms underlying personal actions of stakeholders and how they evolved in science disconnection. Personal actions of stakeholders were causal-effect linked with their risk observation but disconnected to time-delayed science predictions and recommendations. Unfortunately, these science-disconnected actions also led to dramatic impacts on numerous species of the local entomofauna. These results highlight the need to improve mutual risk communication between science and action in the early-stages of management plans to improve the sustainably of stakeholders’ practices. • Current global changes can lead to time lags between science and action. • We analyse stakeholder actions and how they evolved in science disconnection. • Stakeholder actions are disconnected to time-delayed science recommendations. • Science-disconnected actions impact local biodiversity. • Improving risk communication to biological invasion is urgently required.

Hymenopterans represent one of the most abundant groups of venomous organisms but remain little explored due to the difficult access to their venom. The development of proteo-transcriptomic allowed us to explore diversity of their toxins offering interesting perspectives to identify new biological active peptides. This study focuses on U 9 function, a linear, amphiphilic and polycationic peptide isolated from ant Tetramorium bicarinatum venom. It shares physicochemical properties with M-Tb1a, exhibiting cytotoxic effects through membrane permeabilization. In the present study, we conducted a comparative functional investigation of U 9 and M-Tb1a and explored the mechanisms underlying their cytotoxicity against insect cells. After showing that both peptides induced the formation of pores in cell membrane, we demonstrated that U 9 induced mitochondrial damage and, at high concentrations, localized into cells and induced caspase activation. This functional investigation highlighted an original mechanism of U 9 questioning on potential valorization and endogen activity in T . bicarinatum venom.

Ants are among the most abundant terrestrial invertebrate predators on Earth. To overwhelm their prey, they employ several remarkable behavioral, physiological, and biochemical innovations, including an effective paralytic venom. Ant venoms are thus cocktails of toxins finely tuned to disrupt the physiological systems of insect prey. They have received little attention yet hold great promise for the discovery of novel insecticidal molecules. To identify insect-neurotoxins from ant venoms, we screened the paralytic activity on blowflies of nine synthetic peptides previously characterized in the venom of Tetramorium bicarinatum. We selected peptide U11, a 34-amino acid peptide, for further insecticidal, structural, and pharmacological experiments. Insecticidal assays revealed that U11 is one of the most paralytic peptides ever reported from ant venoms against blowflies and is also capable of paralyzing honeybees. An NMR spectroscopy of U11 uncovered a unique scaffold, featuring a compact triangular ring helix structure stabilized by a single disulfide bond. Pharmacological assays using Drosophila S2 cells demonstrated that U11 is not cytotoxic, but suggest that it may modulate potassium conductance, which structural data seem to corroborate and will be confirmed in a future extended pharmacological investigation. The results described in this paper demonstrate that ant venom is a promising reservoir for the discovery of neuroactive insecticidal peptides.

Modern home‐range estimation typically relies on data derived from expensive radio‐ or GPS‐tracking. Although trapping represents a low‐cost alternative to telemetry, evaluation of the performance of home‐range estimators on trap‐derived data is lacking. Using simulated data, we evaluated three variables reflecting the key trade‐offs ecologists face when designing a trapping study: 1) the number of observations obtained per individual, 2) the trap density and 3) the proportion of the home range falling inside the trapping area. We compared the performance of five home‐range estimators (MCP: Minimum Convex Polygon, LoCoH: Local Convex Hull, KDE: Kernel Density Estimation, AKDE: Autocorrelated Kernel Density Estimation, BicubIt: Bicubic Interpolation). We further explored the potential benefits of combining these estimators with asymptotic models, which leverage the saturating behavior of changes in the estimated home‐range area as the number of observations increases to improve accuracy, as well as different data‐ordering procedures. We then quantified the bias in home‐range size under the different scenarios investigated. The number of observations and the proportion of the home range within the trapping grid were the most important predictors of the accuracy and the precision of home‐range estimates. The use of asymptotic models helped to obtain accurate estimates at smaller sample sizes, while distance ordering improved the precision and asymptotic consistency of estimates. While AKDE was the best performing estimator under most conditions evaluated, bicubic interpolation was a viable alternative under common real‐world conditions of low trap density and area covered. A case study using empirical data from white‐tailed deer in Florida and another from jaguars in Belize demonstrated support for the findings of our simulation results. Although researchers with trap data often overlook home‐range estimation, our results indicate that these data have the capacity to yield accurate estimates of home‐range size. Trapping data can, therefore, lower the economic costs of home‐range analysis, potentially enlarging the span of species, researchers and questions studied in ecology and conservation.

The oil sands area of northern Alberta has river sediments that contain natural bitumen. Eggs and fish in these rivers may be exposed to bitumen-related chemicals early in life. This paper assesses a short embryo-larval fish exposure to oil sands sediment and follows the fish behaviour as they mature in clean water and examines their breeding success as adults (5 months afterwards). The three different oil sands river sediments tested were: a sediment collected outside of the bitumen deposit (tested at 3 g/L, Reference sediment from upstream Steepbank River site), and two sediments collected within the deposit (each tested at low (1 g/L) and high (3 g/L) concentrations). The sediments within the bitumen deposit were from the Ells and Steepbank (Stp) Rivers, and both contained significant total PAHs (>170 ng/g wet weight sediment) and alkylated PAHs (>4480 ng/g). Fish were exposed to these sediments for 21 days (as eggs and larval fish), and then transferred permanently to clean water to mature and breed. There was a significant decrease in the number of egg clutches produced by fish exposed early in life to Stp downstream high sediment (compared to Reference sediment). There was also a decrease in overall cumulative egg production, with fish from Stp downstream high sediment producing just over 1000 eggs in total while fish exposed to Ref sediment produced nearly 6900 eggs. The fish with reduced egg production were also less social than expected as they matured, and they had a lower % of early vitellogenic eggs in their ovaries. Overall, the exposure shows that a single, brief exposure during early life stages to natural bitumen can affect fish in adulthood. Naturally occurring bitumen-derived PAHs can reduce fish reproductive output by complex mechanisms, measurable as lower ovary maturity and changes in social behaviour.

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If you decide to make a list of the stinging insects to most carefully avoid on Earth, The Sting of the Wild is the perfect guide. This book is an entertaining tale of Justin Schmidt's life long research that will incontestably spark the interest of all entomologists. The book provides interesting ecological and behavioral information on a broad array of stinging insects (that is, wasps, hornets, bees, and ants) examined in an evolutionary context. Why do some hymenoptera venoms hurt and some others do not? Why is the bullet ant considered to have the most painful sting among insects? And why is the venom of the Maricopa harvester ant the most toxic for vertebrates? Through the author's own experience, the book discusses the relationship between hymenoptera and vertebrates, particularly humans. Schmidt explains how the evolution of a sting as well as pain-inducing venom has been critical to the rise of sociality among hymenoptera.

Venom production is an evolutionary innovation that has emerged in numerous phyla across the animal kingdom, such as in Chordates (fish, amphibians, reptiles, and mammals), Cnidarians (jellyfish and sea anemones), Arthropods (insects, myriapods, and arachnids), Mollusks (such as octopuses and cone snails), Annelids, and Echinoderms (sea urchins and starfish). These venoms are complex cocktails of bioactive molecules selected over millions of years of evolution to fulfill specific functions, primarily for defense or predation. While the study of venoms was initially driven by the search for remedies in cases of envenomation, venoms are now seen as natural sources of molecules with high therapeutic potential. For many years, the most studied venoms were those of snakes, scorpions, spiders, and cone snails. However, the implementation of the venomics approach, which combines genomic, transcriptomic, and proteomic techniques, has overcome limitations such as the quantity of raw venom required and has greatly accelerated research in this field. Among the first beneficiaries of these advances are ants, whose venom has long been neglected. In this context, the BTSB team previously deciphered the venom of the ant Tetramorium bicarinatum and discovered that it contained 37 peptides. Subsequent work by the team and their collaborators characterized the biological effects of some of these peptides. Two cytotoxic peptides named MYRTX-Tb9a and MYRTX-Tb0a were discovered, each inducing cell death via different mechanisms. Other studies highlighted the peptide MYRTX-Tb1a, a modulator of G protein-coupled receptors (GPCRs) involved in the immune response. The discovery of these biological activities encouraged the laboratory to investigate new properties within the T. bicarinatum peptide library. This project thus aimed to screen this peptide library for various physiological effects on human cancer or neuronal cells. The screening focused on anticancer properties (proliferation, migration), as well as ion flux modulations mediated by GPCRs or ion channels. Two peptides showed promising activities during the screening phase. One peptide, MYRTX-Tb8a, demonstrated the ability to induce strong calcium mobilization from intracellular stores in a GPCR-dependent manner across multiple cell lines, although the target receptor has not yet been identified. The second peptide, MYRTX-Tb11a, was initially shown to modulate membrane depolarization induced by KCl, and later inhibited currents mediated by Kv1.3 and KCa1.1 channels during patch-clamp analysis. Interestingly, similar effects were observed for its analogue MYRTX-Ta11a, derived from the ant Tetramorium africanum. These doctoral studies have highlighted new biological effects of ant venom peptides, but further studies will be necessary, particularly to determine the target receptor of MYRTX-Tb8a and to evaluate the specificity of MYRTX-Tb11a by testing it on other ion channels, especially potassium channels. These results confirm the relevance of continuing the investigation of ant venom peptides, particularly those from T. bicarinatum.

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Animal venoms are natural libraries of bioactive compounds, called toxins, which have been finetuned through the course of evolution. However, numerous venomous organisms are still neglected, especially venomous insects. Several studies of ant venoms revealed that they were peptide-rich. Furthermore, the characterization of the ant Tetramorium bicarinatum venom peptidome revealed that, despite the diversity of mature peptides, they belonged to 3 superfamilies of precursors, some of which have already been described in other aculeate hymenoptera. This study also observed that genes encoding some of them were expressed outside the venom apparatus. These results raise questions about the mechanisms involved in the diversification of peptide toxins from ant venoms, as well as their role apart from the venomous function. To address these issues, the first part of this thesis work consisted in the characterization via proteotranscriptomics approaches of 7 venoms from ants belonging to the different phylogenetic tribes of the Myrmicinae subfamily, and of the venom of one species. belonging to a close subfamily, the Pseudomyrmecinae. A total of 100 peptide toxins with various structures were thus identified and classified into 8 precursor superfamilies. The second part explored the link between peptide toxins of T. bicarinatum venom and its innate immunity via molecular and cellular biology methods. The presence of transcripts encoding certain peptides have been verified in organs which are involved in innate immunity of insects (i.e. fat bodies, digestive tracts). The expression of the genes encoding them has also been evaluated following a bacterial infection. It has thus been shown that the transcripts encoding the selected venom peptides are present in the organs tested, and that some are produced in fat bodies in response to a bacterial infection. These results confirm the existence of a link between the venom peptides and the innate immunity of the ant T. bicarinatum, although further studies are needed

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