Gut microbiota variation between climatic zones and due to migration strategy in passerine birds.

Introduction: Decreasing biotic diversity with increasing latitude is an almost universal macroecological pattern documented for a broad range of taxa, however, there have been few studies focused on changes in gut microbiota (GM) across climatic zones. Methods: Using 16S rRNA amplicon profiling, we analyzed GM variation between temperate (Czechia) and tropical (Cameroon) populations of 99 passerine bird species and assessed GM similarity of temperate species migrating to tropical regions with that of residents/short-distance migrants and tropical residents. Our study also considered the possible influence of diet on GM. Results: We observed no consistent GM diversity differences between tropical and temperate species. In the tropics, GM composition varied substantially between dry and rainy seasons and only a few taxa exhibited consistent differential abundance between tropical and temperate zones, irrespective of migration behavior and seasonal GM changes. During the breeding season, trans-Saharan migrant GM diverged little from species not overwintering in the tropics and did not show higher similarity to tropical passerines than temperate residents/short-distance migrants. Interestingly, GM of two temperate-breeding trans-Saharan migrants sampled in the tropical zone matched that of tropical residents and converged with other temperate species during the breeding season. Diet had a slight effect on GM composition of tropical species, but no effect on GM of temperate hosts. Discussion: Consequently, our results demonstrate extensive passerine GM plasticity, the dominant role of environmental factors in its composition and limited effect of diet.

Urinary Metabolome Analysis Reveals Potential Microbiota Alteration and Electrophilic Burden Induced by High Red Meat Diet: Results from the French NutriNet-Santé Cohort and an In Vivo Intervention Study in Rats.

SCOPE: High red and processed meat consumption is associated with several adverse outcomes such as colorectal cancer and overall global mortality. However, the underlying mechanisms remain debated and need to be elucidated. METHODS AND RESULTS: Urinary untargeted Liquid Chromatography-Mass Spectrometry (LC-MS) metabolomics data from 240 subjects from the French cohort NutriNet-Santé are analyzed. Individuals are matched and divided into three groups according to their consumption of red and processed meat: high red and processed meat consumers, non-red and processed meat consumers, and at random group. Results are supported by a preclinical experiment where rats are fed either a high red meat or a control diet. Microbiota derived metabolites, in particular indoxyl sulfate and cinnamoylglycine, are found impacted by the high red meat diet in both studies, suggesting a modification of microbiota by the high red/processed meat diet. Rat microbiota sequencing analysis strengthens this observation. Although not evidenced in the human study, rat mercapturic acid profile concomitantly reveals an increased lipid peroxidation induced by high red meat diet. CONCLUSION: Novel microbiota metabolites are identified as red meat consumption potential biomarkers, suggesting a deleterious effect, which could partly explain the adverse effects associated with high red and processed meat consumption.

Divergent gut microbiota in two closely related house mouse subspecies under common garden conditions.

The gastrointestinal microbiota (GM) is considered an important component of the vertebrate holobiont. GM-host interactions influence the fitness of holobionts and are, therefore, an integral part of evolution. The house mouse is a prominent model for GM-host interactions, and evidence suggests a role for GM in mouse speciation. However, previous studies based on short 16S rRNA GM profiles of wild house mouse subspecies failed to detect GM divergence, which is a prerequisite for the inclusion of GM in Dobzhansky-Muller incompatibilities. Here, we used standard 16S rRNA GM profiling in two mouse subspecies, Mus musculus musculus and M. m. domesticus, including the intestinal mucosa and content of three gut sections (ileum, caecum, and colon). We reduced environmental variability by sampling GM in the offspring of wild mice bred under seminatural conditions. Although the breeding conditions allowed a contact between the subspecies, we found a clear differentiation of GM between them, in all three gut sections. Differentiation was mainly driven by several Helicobacters and two H. ganmani variants showed a signal of codivergence with their hosts. Helicobacters represent promising candidates for studying GM-host coadaptations and the fitness effects of their interactions.

Discovery and quantification of lipoamino acids in bacteria.

Improving knowledge about metabolites produced by the microbiota is a key point to understand its role in human health and disease. Among them, lipoamino acid (LpAA) containing asparagine and their derivatives are bacterial metabolites which could have an impact on the host. In this study, our aim was to extend the characterization of this family. We developed a semi-targeted workflow to identify and quantify new candidates. First, the sample preparation and analytical conditions using liquid chromatography (LC) coupled to high resolution mass spectrometry (HRMS) were optimized. Using a theoretical homemade database, HRMS raw data were manually queried. This strategy allowed us to find 25 new LpAA conjugated to Asn, Gln, Asp, Glu, His, Leu, Ile, Lys, Phe, Trp and Val amino acids. These metabolites were then fully characterized by MS2, and compared to the pure synthesized standards to validate annotation. Finally, a quantitative method was developed by LC coupled to a triple quadrupole instrument, and linearity and limit of quantification were determined. 14 new LpAA were quantified in gram positive bacteria, Lactobacilus animalis, and 12 LpAA in Escherichia coli strain Nissle 1917.

Towards Aldehydomics: Untargeted Trapping and Analysis of Reactive Diet-Related Carbonyl Compounds Formed in the Intestinal Lumen.

Lipid peroxidation and subsequent formation of toxic aldehydes, such as 4-hydroxynonenal, is known to be involved in numerous pathophysiological processes, possibly including the development of colorectal cancer. This work aimed at the development of an untargeted approach using high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) for tracking aldehydes in both suspect screening and untargeted methods in fecal water, representing the aqueous environment of colon epithelial cells. This original approach is based on the introduction of a characteristic isotopic labeling by selective derivatization of the carbonyl function using a brominated reagent. Following a metabolomics workflow, the developed methodology was applied to the characterization of aldehyde compounds formed by lipid peroxidation in rats fed two different diets differentially prone to lipoperoxidation. Derivatized aldehydes were first selectively detected on the basis of their isotopic pattern, then annotated and finally identified by tandem mass spectrometry. This original approach allowed us to evidence the occurrence of expected aldehydes according to their fatty acid precursors in the diet, and to characterize other aldehydes differentiating the different diets.

Safety assessment of cosmetics by read across applied to metabolomics data of in vitro skin and liver models.

As a result of the cosmetics testing ban, safety evaluations of cosmetics ingredients must now be conducted using animal-free methods. A common approach is read across, which is mainly based on structural similarities but can also be conducted using biological endpoints. Here, metabolomics was used to assess biological effects to enable a read across between a candidate cosmetic ingredient, DIV665, only studied using in vitro assays, and a structurally similar reference compound, PA102, previously investigated using traditional in vivo toxicity methods. The (1) cutaneous distribution after topical application, (2) skin metabolism, (3) liver metabolism and (4) effect on the intracellular metabolomic profiles of in vitro skin and hepatic models, SkinEthic®RHE model and HepaRG® cells were investigated. The compounds exhibited similar skin penetration and skin and liver metabolism, with small differences attributed to their physicochemical properties. The effects of both compounds on the metabolome of RHE and HepaRG® cells were similarly small, both in terms of the metabolites modulated and the magnitude of changes. The patterns of metabolome changes did not fit with any known signature relating to a mode of action known to be linked to liver toxicity e.g. modification of the Krebs cycle, urea synthesis and lipid metabolism, were more reflective of transient adaptive responses. Overall, these studies indicate that PA102 is biologically similar to DIV665, allowing read across of safety endpoints, such as in vivo sub-chronic (but not reproduction toxicity) studies, for the former to be applied to DIV665. Based on this, in the absence of animal data (which is prohibited for new chemicals), it could be concluded that DIV665 applied according to the consumer topical use scenario, is similar to PA102, and is predicted to exhibit low local skin and systemic toxicity.

Untargeted Lipidomic Profiling of Dry Blood Spots Using SFC-HRMS.

Lipids are essential cellular constituents that have many critical roles in physiological functions. They are notably involved in energy storage and cell signaling as second messengers, and they are major constituents of cell membranes, including lipid rafts. As a consequence, they are implicated in a large number of heterogeneous diseases, such as cancer, diabetes, neurological disorders, and inherited metabolic diseases. Due to the high structural diversity and complexity of lipid species, the presence of isomeric and isobaric lipid species, and their occurrence at a large concentration scale, a complete lipidomic profiling of biological matrices remains challenging, especially in clinical contexts. Using supercritical fluid chromatography coupled with high-resolution mass spectrometry, we have developed and validated an untargeted lipidomic approach to the profiling of plasma and blood. Moreover, we have tested the technique using the Dry Blood Spot (DBS) method and found that it allows for the easy collection of blood for analysis. To develop the method, we performed the optimization of the separation and detection of lipid species on pure standards, reference human plasma (SRM1950), whole blood, and DBS. These analyses allowed an in-house lipid data bank to be built. Using the MS-Dial software, we developed an automatic process for the relative quantification of around 500 lipids species belonging to the 6 main classes of lipids (including phospholipids, sphingolipids, free fatty acids, sterols, and fatty acyl-carnitines). Then, we compared the method using the published data for SRM 1950 and a mouse blood sample, along with another sample of the same blood collected using the DBS method. In this study, we provided a method for blood lipidomic profiling that can be used for the easy sampling of dry blood spots.

Multiplatform metabolomics for an integrative exploration of metabolic syndrome in older men.

BACKGROUND: Metabolic syndrome (MetS), a cluster of factors associated with risks of developing cardiovascular diseases, is a public health concern because of its growing prevalence. Considering the combination of concomitant components, their development and severity, MetS phenotypes are largely heterogeneous, inducing disparity in diagnosis. METHODS: A case/control study was designed within the NuAge longitudinal cohort on aging. From a 3-year follow-up of 123 stable individuals, we present a deep phenotyping approach based on a multiplatform metabolomics and lipidomics untargeted strategy to better characterize metabolic perturbations in MetS and define a comprehensive MetS signature stable over time in older men. FINDINGS: We characterize significant changes associated with MetS, involving modulations of 476 metabolites and lipids, and representing 16% of the detected serum metabolome/lipidome. These results revealed a systemic alteration of metabolism, involving various metabolic pathways (urea cycle, amino-acid, sphingo- and glycerophospholipid, and sugar metabolisms…) not only intrinsically interrelated, but also reflecting environmental factors (nutrition, microbiota, physical activity…). INTERPRETATION: These findings allowed identifying a comprehensive MetS signature, reduced to 26 metabolites for future translation into clinical applications for better diagnosing MetS. FUNDING: The NuAge Study was supported by a research grant from the Canadian Institutes of Health Research (CIHR; MOP-62842). The actual NuAge Database and Biobank, containing data and biologic samples of 1,753 NuAge participants (from the initial 1,793 participants), are supported by the Fonds de recherche du Québec (FRQ; 2020-VICO-279753), the Quebec Network for Research on Aging, a thematic network funded by the Fonds de Recherche du Québec - Santé (FRQS) and by the Merck-Frost Chair funded by La Fondation de l'Université de Sherbrooke. All metabolomics and lipidomics analyses were funded and performed within the metaboHUB French infrastructure (ANR-INBS-0010). All authors had full access to the full data in the study and accept responsibility to submit for publication.

Does the Phytochemical Diversity of Wild Plants Like the Erythrophleum genus Correlate with Geographical Origin?

Secondary metabolites are essential for plant survival and reproduction. Wild undomesticated and tropical plants are expected to harbor highly diverse metabolomes. We investigated the metabolomic diversity of two morphologically similar trees of tropical Africa, Erythrophleum suaveolens and E. ivorense, known for particular secondary metabolites named the cassaine-type diterpenoids. To assess how the metabolome varies between and within species, we sampled leaves from individuals of different geographic origins but grown from seeds in a common garden in Cameroon. Metabolites were analyzed using reversed phase LC-HRMS(/MS). Data were interpreted by untargeted metabolomics and molecular networks based on MS/MS data. Multivariate analyses enabled us to cluster samples based on species but also on geographic origins. We identified the structures of 28 cassaine-type diterpenoids among which 19 were new, 10 were largely specific to E. ivorense and five to E. suaveolens. Our results showed that the metabolome allows an unequivocal distinction of morphologically-close species, suggesting the potential of metabolite fingerprinting for these species. Plant geographic origin had a significant influence on relative concentrations of metabolites with variations up to eight (suaveolens) and 30 times (ivorense) between origins of the same species. This shows that the metabolome is strongly influenced by the geographical origin of plants (i.e., genetic factors).

Early Detection of the Root-Knot Nematode Meloidogyne hapla Through Developing a Robust Quantitative PCR Approach Compliant with the Minimum Information for Publication of Quantitative Real-Time PCR Experiments Guidelines.

Root-knot nematodes (RKNs) are major threats to crops through attacking the roots, which induces an abnormal development of the plant. Meloidogyne hapla is of particular concern, as it is currently expanding its distribution area and displays a wide host range. Effective plant protection against this RKN requires early detection, as even a single individual can cause severe economic losses on susceptible crops. Molecular tools are of particular value for this purpose, and among them, quantitative PCR (qPCR) presents many advantages (i.e., sensitivity, specificity, and rapidity of diagnosis at a reduced cost). Although a few studies have already been proposed for detecting M. hapla through this technique, they lack experimental details and performance testing, suffer from low taxonomic resolution, and/or require expensive hydrolysis probes. Here, we propose a qPCR detection method that uses SYBR Green with developed primers amplifying a fragment of the cytochrome oxidase I mitochondrial region. The method was developed and evaluated following the minimum information for publication of quantitative real-time PCR experiments (MIQE) guidelines to ensure its quality (i.e., sensitivity, specificity, repeatability, reproducibility, and robustness). The results demonstrate that the newly developed method fulfills its goals, as it proved specific to M. hapla and allowed for a reproductible detection level as low as 1.25 equivalent of a juvenile individual. All criteria associated with the MIQE guidelines were also met, so the method is of general use for the reliable early detection of M. hapla.

Osmolality-based normalization enhances statistical discrimination of untargeted metabolomic urine analysis: results from a comparative study.

INTRODUCTION: Because of its ease of collection, urine is one of the most commonly used matrices for metabolomics studies. However, unlike other biofluids, urine exhibits tremendous variability that can introduce confounding inconsistency during result interpretation. Despite many existing techniques to normalize urine samples, there is still no consensus on either which method is most appropriate or how to evaluate these methods. OBJECTIVES: To investigate the impact of several methods and combinations of methods conventionally used in urine metabolomics on the statistical discrimination of two groups in a simple metabolomics study. METHODS: We applied 14 different strategies of normalization to forty urine samples analysed by liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS). To evaluate the impact of these different strategies, we relied on the ability of each method to reduce confounding variability while retaining variability of interest, as well as the predictability of statistical models. RESULTS: Among all tested normalization methods, osmolality-based normalization gave the best results. Moreover, we demonstrated that normalization using a specific dilution prior to the analysis outperformed post-acquisition normalization. We also demonstrated that the combination of various normalization methods does not necessarily improve statistical discrimination. CONCLUSIONS: This study re-emphasized the importance of normalizing urine samples for metabolomics studies. In addition, it appeared that the choice of method had a significant impact on result quality. Consequently, we suggest osmolality-based normalization as the best method for normalizing urine samples. TRIAL REGISTRATION NUMBER: NCT03335644.

Oral and vaginal microbiota in selected field mice of the genus Apodemus: a wild population study.

Animal-associated microbiota is expected to impose crucial effects on the host's fitness-related performance, including reproduction. Most research to date has focused on interactions between the host with its gut microbiota; however, there remain considerable gaps in knowledge regarding microbial consortia in other organs, including interspecific divergence, temporal stability, variation drivers, and their effects on the host. To fill these gaps, we examined oral and vaginal microbiota composition in four free-living mouse species of the genus Apodemus, each varying in the degree of female promiscuity. To assess temporal stability and microbiota resistance to environmental change, we exposed one of the species, Apodemus uralensis, to standardized captive conditions and analyzed longitudinal changes in its microbiota structure. Our results revealed the existence of a "core" oral microbiota that was not only shared among all four species but also persisted almost unchanged in captivity. On the other hand, vaginal microbiota appears to be more plastic in captive conditions and less species-specific in comparison with oral microbiota. This study is amongst the first to describe oral microbiota dynamics. Furthermore, the vaginal microbiota results are especially surprising in light of the well-known role of stable vaginal microbiota as a defense against pathogens. The results indicate the existence of diverse mechanisms that shape each microbiota. On the other hand, our data provides somewhat ambiguous support for the systematic effect of phylogeny and social system on both oral and vaginal microbiota structures.

How being synanthropic affects the gut bacteriome and mycobiome: comparison of two mouse species with contrasting ecologies.

BACKGROUND: The vertebrate gastrointestinal tract is colonised by microbiota that have a major effect on the host's health, physiology and phenotype. Once introduced into captivity, however, the gut microbial composition of free-living individuals can change dramatically. At present, little is known about gut microbial changes associated with adaptation to a synanthropic lifestyle in commensal species, compared with their non-commensal counterparts. Here, we compare the taxonomic composition and diversity of bacterial and fungal communities across three gut sections in synanthropic house mouse (Mus musculus) and a closely related non-synanthropic mound-building mouse (Mus spicilegus). RESULTS: Using Illumina sequencing of bacterial 16S rRNA amplicons, we found higher bacterial diversity in M. spicilegus and detected 11 bacterial operational taxonomic units with significantly different proportions. Notably, abundance of Oscillospira, which is typically higher in lean or outdoor pasturing animals, was more abundant in non-commensal M. spicilegus. ITS2-based barcoding revealed low diversity and high uniformity of gut fungi in both species, with the genus Kazachstania clearly dominant. CONCLUSIONS: Though differences in gut bacteria observed in the two species can be associated with their close association with humans, changes due to a move from commensalism to captivity would appear to have caused larger shifts in microbiota.

Gut microbiota in a host-brood parasite system: insights from common cuckoos raised by two warbler species.

An animal's gut microbiota (GM) is shaped by a range of environmental factors affecting the bacterial sources invading the host. At the same time, animal hosts are equipped with intrinsic mechanisms enabling regulation of GM. However, there is limited knowledge on the relative importance of these forces. To assess the significance of host-intrinsic vs environmental factors, we studied GM in nestlings of an obligate brood parasite, the common cuckoo (Cuculus canorus), raised by two foster species, great reed warblers (Acrocephalus arundinaceus) and Eurasian reed warblers (A. scirpaceus), and compared these with GM of the fosterers' own nestlings. We show that fecal GM varied between cuckoo and warbler nestlings when accounting for the effect of foster/parent species, highlighting the importance of host-intrinsic regulatory mechanisms. In addition to feces, cuckoos also expel a deterrent secretion, which provides protection against olfactory predators. We observed an increased abundance of bacterial genera capable of producing repulsive volatile molecules in the deterrent secretion. Consequently, our results support the hypothesis that microbiota play a role in this antipredator mechanism. Interestingly, fosterer/parent identity affected only cuckoo deterrent secretion and warbler feces microbiota, but not that of cuckoo feces, suggesting a strong selection of bacterial strains in the GM by cuckoo nestlings.

Characterizing ecological interaction networks to support risk assessment in classical biological control of weeds.

A key element in weed biological control is the selection of a biological control agent that minimizes the risks of non-target attack and indirect effects on the recipient community. Network ecology is a promising approach that could help decipher tritrophic interactions in both the native and the invaded ranges, to complement quarantine-based host-specificity tests and gain insights on potential interactions of biological control agents. This review highlights practical questions addressed by networks, including 1) biological control agent selection, based on specialization indices, 2) risk assessment of biological control agent release into a novel environment, via particular patterns of association such as apparent competition between agent(s) and native herbivore(s), 3) network comparisons through structural metrics, 4) potential of network modelling and 5) limits of network construction methods.

Global Profiling of Toxicologically Relevant Metabolites in Urine: Case Study of Reactive Aldehydes.

Among the numerous unknown metabolites representative of our exposure, focusing on toxic compounds should provide more relevant data to link exposure and health. For that purpose, we developed and applied a global method using data independent acquisition (DIA) in mass spectrometry to profile specifically electrophilic compounds originating metabolites. These compounds are most of the time toxic, due to their chemical reactivity toward nucleophilic sites present in biomacromolecules. The main line of cellular defense against these electrophilic molecules is conjugation to glutathione, then metabolization into mercapturic acid conjugates (MACs). Interestingly, MACs display a characteristic neutral loss in MS/MS experiments that makes it possible to detect all the metabolites displaying this characteristic loss, thanks to the DIA mode, and therefore to highlight the corresponding reactive metabolites. As a proof of concept, our workflow was applied to the toxicological issue of the oxidation of dietary polyunsaturated fatty acids, leading in particular to the formation of toxic alkenals, which lead to MACs upon glutathione conjugation and metabolization. By this way, dozens of MACs were detected and identified. Interestingly, multivariate statistical analyses carried out only on extracted HRMS signals of MACs yield a better characterization of the studied groups compared to results obtained from a classic untargeted metabolomics approach.

Lactose and Fructo-oligosaccharides Increase Visceral Sensitivity in Mice via Glycation Processes, Increasing Mast Cell Density in Colonic Mucosa.

BACKGROUND & AIMS: Irritable bowel syndrome (IBS) is characterized by abdominal pain, bloating, and erratic bowel habits. A diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) can reduce symptoms of IBS, possibly by reducing microbial fermentation products. We investigated whether ingestion of FODMAPs can induce IBS-like visceral hypersensitivity mediated by fermentation products of intestinal microbes in mice. METHODS: C57Bl/6 mice were gavaged with lactose, with or without the antiglycation agent pyridoxamine, or saline (controls) daily for 3 weeks. A separate group of mice were fed a diet containing fructo-oligosaccharides, with or without pyridoxamine in drinking water, or a normal chow diet (controls) for 6 weeks. Feces were collected and analyzed by 16S ribosomal RNA gene sequencing and bacterial community analyses. Abdominal sensitivity was measured by electromyography and mechanical von Frey filament assays. Colon tissues were collected from some mice and analyzed by histology and immunofluorescence to quantify mast cells and expression of advanced glycosylation end-product specific receptor (AGER). RESULTS: Mice gavaged with lactose or fed fructo-oligosaccharides had increased abdominal sensitivity compared with controls, associated with increased numbers of mast cells in colon and expression of the receptor for AGER in proximal colon epithelium. These effects were prevented by administration of pyridoxamine. Lactose and/or pyridoxamine did not induce significant alterations in the composition of the fecal microbiota. Mass spectrometric analysis of carbonyl compounds in fecal samples identified signatures associated with mice given lactose or fructo-oligosaccharides vs controls. CONCLUSIONS: We found that oral administration of lactose or fructo-oligosaccharides to mice increases abdominal sensitivity, associated with increased numbers of mast cells in colon and expression of AGER; these can be prevented with an antiglycation agent. Lactose and/or pyridoxamine did not produce alterations in fecal microbiota of mice. Our findings indicate that preventing glycation reactions might reduce abdominal pain in patients with IBS with sensitivity to FODMAPs.

Long-fragment targeted capture for long-read sequencing of plastomes.

PREMISE: Third-generation sequencing methods generate significantly longer reads than those produced using alternative sequencing methods. This provides increased possibilities for the study of biodiversity, phylogeography, and population genetics. We developed a protocol for in-solution enrichment hybridization capture of long DNA fragments applicable to complete plastid genomes. METHODS AND RESULTS: The protocol uses cost-effective in-house probes developed via long-range PCR and was used in six non-model monocot species (Poaceae: African rice, pearl millet, fonio; and three palm species). DNA was extracted from fresh and silica gel-dried leaves. Our protocol successfully captured long-read plastome fragments (3151 bp median on average), with an enrichment rate ranging from 15% to 98%. DNA extracted from silica gel-dried leaves led to low-quality plastome assemblies when compared to DNA extracted from fresh tissue. CONCLUSIONS: Our protocol could also be generalized to capture long sequences from specific nuclear fragments.

Fecal microbiota associated with phytohaemagglutinin-induced immune response in nestlings of a passerine bird.

The vertebrate gastrointestinal tract is inhabited by a diverse community of bacteria, the so-called gut microbiota (GM). Research on captive mammalian models has revealed tight mutual interactions between immune functions and GM. However, our knowledge of GM versus immune system interactions in wild populations and nonmammalian species remains poor. Here, we focus on the association between GM community structure and immune response measured via the phytohaemagglutinin (PHA) skin swelling test in 12-day-old nestlings of a passerine bird, the barn swallow (Hirundo rustica). The PHA test, a widely used method in field ecoimmunology, assesses cell-mediated immunity. GM structure was inferred based on high-throughput 16S rRNA sequencing of microbial communities in fecal samples. We did not find any association between PHA response and GM diversity; however, our data revealed that the intensity of PHA response was correlated with differences in GM composition at the whole-community level. Ten bacterial operational taxonomic units corresponding to both putative commensal and pathogens were identified as drivers of the compositional variation. In conclusion, our study suggests existence of GM versus immune system interactions in a free-living nonmammalian species, which corresponds with previous research on captive vertebrates.

Metabolic Effects of a Chronic Dietary Exposure to a Low-Dose Pesticide Cocktail in Mice: Sexual Dimorphism and Role of the Constitutive Androstane Receptor.

BACKGROUND: Epidemiological evidence suggests a link between pesticide exposure and the development of metabolic diseases. However, most experimental studies have evaluated the metabolic effects of pesticides using individual molecules, often at nonrelevant doses or in combination with other risk factors such as high-fat diets. OBJECTIVES: We aimed to evaluate, in mice, the metabolic consequences of chronic dietary exposure to a pesticide mixture at nontoxic doses, relevant to consumers' risk assessment. METHODS: A mixture of six pesticides commonly used in France, i.e., boscalid, captan, chlorpyrifos, thiofanate, thiacloprid, and ziram, was incorporated in a standard chow at doses exposing mice to the tolerable daily intake (TDI) of each pesticide. Wild-type (WT) and constitutive androstane receptor-deficient (CAR-/-) male and female mice were exposed for 52 wk. We assessed metabolic parameters [body weight (BW), food and water consumption, glucose tolerance, urinary metabolome] throughout the experiment. At the end of the experiment, we evaluated liver metabolism (histology, transcriptomics, metabolomics, lipidomics) and pesticide detoxification using liquid chromatography-mass spectrometry (LC-MS). RESULTS: Compared to those fed control chow, WT male mice fed pesticide chow had greater BW gain and more adiposity. Moreover, these WT males fed pesticide chow exhibited characteristics of hepatic steatosis and glucose intolerance, which were not observed in those fed control chow. WT exposed female mice exhibited fasting hyperglycemia, higher reduced glutathione (GSH):oxidized glutathione (GSSG) liver ratio and perturbations of gut microbiota-related urinary metabolites compared to WT mice fed control chow. When we performed these experiments on CAR-/- mice, pesticide-exposed CAR-/- males did not exhibit BW gain or changes in glucose metabolism compared to the CAR-/- males fed control chow. Moreover, CAR-/- females fed pesticide chow exhibited pesticide toxicity with higher BWs and mortality rate compared to the CAR-/- females fed control chow. CONCLUSIONS: To our knowledge, we are the first to demonstrate a sexually dimorphic obesogenic and diabetogenic effect of chronic dietary exposure to a common mixture of pesticides at TDI levels, and to provide evidence for a partial role for CAR in an in vivo mouse model. This raises questions about the relevance of TDI for individual pesticides when present in a mixture. https://doi.org/10.1289/EHP2877.