Microbial enzymes induce colitis by reactivating triclosan in the mouse gastrointestinal tract

Deciphering the triclosan degradation mechanism in Sphingomonas sp. strain YL-JM2C: Implications for wastewater treatment and marine resources

Triclosan (TCS), an antimicrobial agent extensively incorporated into pharmaceuticals and personal care products, poses significant environmental risks because of its persistence and ecotoxicity. So far, a few microorganisms were suggested to degrade TCS, but the microbial degradation mechanism remains elusive. Here, a two-component angular dioxygenase (TcsAaAb) responsible for the initial TCS degradation was characterized in Sphingomonas sp. strain YL-JM2C. Whole-cell biotransformation and crude enzyme assays demonstrated that TcsAaAb catalyzed the conversion of TCS to 4-chlorocatechol and 3,5-dichlorocatechol rather than the commonly suggested product 2,4-dichlorophenol. Then two intermediates were catabolized by tcsCDEF cluster via an ortho-cleavage pathway. Critical residues (N262, F279, and F391) for substrate binding were identified via molecular docking and mutagenesis. Further, TcsAaAb showed activity toward methyl triclosan and nitrofen, suggesting its versatile potential for bioremediation. In addition, TCS-degrading genes were also present in diverse bacterial genomes in wastewater, ocean and soil, and a relatively high gene abundance was observed in marine metagenomes, revealing the transformation fate of TCS in environments and the microbial potential in pollutant removal. These findings extend the understanding of the microbe-mediated TCS degradation and contribute to the mining of TCS-degrading strains and enzymes, as well as their application in the bioremediation of contaminated environments.

Characterizing the effects of triclosan and triclocarban on the intestinal epithelial homeostasis using small intestinal organoids

Intestinal epithelium has the largest surface of human body, contributes dramatically to defense of toxicant-associated intestinal injury. Triclosan (TCS) and triclocarban (TCC), extensively employed as antibacterial agents in personal care products (PCPs) and healthcare facilities, caused serious damage to human intestine. However, the role of the intestinal epithelium in TCS/TCC-induced intestinal toxicity and its underlying toxic mechanisms remain incompletely understood. In this study, a novel 3D intestinal organoid model was utilized to investigate that exposure to TCS/TCC led to a compromised self-renewal and differentiation of intestinal stem cells (ISCs). Consequently, this disrupted intestinal epithelial homeostasis ultimately caused a reduction in nutrient absorption and deficient of epithelial defense to exogenous and endogenous pathogens stimulation. The inhibition of the Wnt signaling pathway in intestinal stem cell was contributed to the intestinal toxicity of TCS/TCC. These results were further confirmed in vivo with mice exposed to TCS/TCC. The findings of this study provide evidence that TCS/TCC possess the capacity to disturb the homeostasis of the intestinal epithelium, and emphasize the credibility of organoids as a valuable model for toxicological studies, as they could faithfully recapitulate in vivo phenomena.

Advanced piperazine-containing inhibitors target microbial β-glucuronidases linked to gut toxicity

The gut microbiome plays critical roles in human homeostasis, disease progression, and pharmacological efficacy through diverse metabolic pathways. Gut bacterial β-glucuronidase (GUS) enzymes reverse host phase 2 metabolism, in turn releasing active hormones and drugs that can be reabsorbed into systemic circulation to affect homeostasis and promote toxic side effects. The FMN-binding and loop 1 gut microbial GUS proteins have been shown to drive drug and toxin reactivation. Here we report the structure-activity relationships of two selective piperazine-containing bacterial GUS inhibitors. We explore the potency and mechanism of action of novel compounds using purified GUS enzymes and co-crystal structures. Our results establish the importance of the piperazine nitrogen placement and nucleophilicity as well as the presence of a cyclohexyl moiety appended to the aromatic core. Using these insights, we synthesized an improved microbial GUS inhibitor, UNC10206581, that potently inhibits both the FMN-binding and loop 1 GUS enzymes in the human gut microbiome, does not inhibit bovine GUS, and is non-toxic within a relevant dosing range. Kinetic analyses demonstrate that UNC10206581 undergoes a slow-binding and substrate-dependent mechanism of inhibition similar to that of the parent scaffolds. Finally, we show that UNC10206581 displays potent activity within the physiologically relevant systems of microbial cultures and human fecal protein lysates examined by metagenomic and metaproteomic methods. Together, these results highlight the discovery of more effective bacterial GUS inhibitors for the alleviation of microbe-mediated homeostatic dysregulation and drug toxicities and potential therapeutic development.

Triclosan Dioxygenase: A Novel Two-component Rieske Nonheme Iron Ring-hydroxylating Dioxygenase Initiates Triclosan Degradation

The emerging contaminant triclosan (TCS) is widely distributed both in surface water and in wastewater and poses a threat to aquatic organisms and human health due to its resistance to degradation. The dioxygenase enzyme TcsAB has been speculated to perform the initial degradation of TCS, but its precise catalytic mechanism remains unclear. In this study, the function of TcsAB was elucidated using multiple biochemical and molecular biology methods. Escherichia coli BL21(DE3) heterologously expressing tcsAB from Sphingomonas sp. RD1 converted TCS to 2,4-dichlorophenol. TcsAB belongs to the group IA family of two-component Rieske nonheme iron ring-hydroxylating dioxygenases. The highest amino acid identity of TcsA and the large subunits of other dioxygenases in the same family was only 35.50%, indicating that TcsAB is a novel dioxygenase. Mutagenesis of residues near the substrate binding pocket decreased the TCS-degrading activity and narrowed the substrate spectrum, except for the TcsAF343A mutant. A meta-analysis of 1492 samples from wastewater treatment systems worldwide revealed that tcsA genes are widely distributed. This study is the first to report that the TCS-specific dioxygenase TcsAB is responsible for the initial degradation of TCS. Studying the microbial degradation mechanism of TCS is crucial for removing this pollutant from the environment.

Pulsed electric field enhanced Bacillus sp. DL4 biodegradation of triclosan: focusing on operational performance and metabolomic analysis

Electrochemical-assisted microbial degradation technology was considered a crucial strategy to reduce micropollutants, but the mechanism of the pulsed electric field (PEF) in affecting biodegradation had not been systematically studied. This study aimed to construct a bio-electrochemical system (BES) using PEF to investigate its effect on the degradation of triclosan (TCS) by the aerobic bacterium Bacillus sp. DL4. The operating optimal parameters for the BES (i.e. 0.01 A of the pulsed current, 1000 Hz of the pulse frequency, Fe (+)-C (-) of the plate materials, 4 cm of the plate spacing) were obtained by batch experiments. The maximum biomass (OD600 = 1.0 ± 0.05) was achieved and the removal efficiency of TCS reached above 95% in 24 h under the obtained operating conditions. Meanwhile, a thorough and methodical investigation of the metabolites in strain DL4 stimulated by PEF using untargeted Liquid Chromatography - Mass Spectrometry (LC-MS). In multivariate analysis, the experimental groups showed a notable separation in Principal Components Analysis (PCA) and Orthogonal Partial Least Squares Analysis discriminant analysis (OPLS-DA) score plots. A total of 3181 differential metabolites were obtained, and the up-regulated metabolites were mainly related to 'Aminoacyl-tRNA biosynthesis', 'Arginine and proline metabolism', 'Lysine degradation', 'ABC transporters', and 'TCA cycle', implying that PEF enhanced the degradation efficiency of TCS by enriching functional genes with transport ability and ion migration ability in cells. This study illuminated how PEF can affect TCS biodegradation and gives insights into the application prospect of electrochemical-assisted biodegradation technology in water environment treatment.

Toxicity evolution of triclosan during environmental transformation and human metabolism: Misgivings in the post-pandemic era

In the context of pandemic viruses and pathogenic bacteria, triclosan (TCS), as a typical antibacterial agent, is widely used around the world. However, the health risks from TCS increase with exposure, and it is widespread in environmental and human samples. Notably, environmental transformation and human metabolism could induce potentially undesirable risks to humans, rather than simple decontamination or detoxification. This review summarizes the environmental and human exposure to TCS covering from 2004 to 2023. Particularly, health impacts from the environmental and metabolic transformation of TCS are emphasized. Environmental transformations aimed at decontamination are recognized to form carcinogenic products such as dioxins, and ultraviolet light and excessive active chlorine can promote the formation of these dioxin congeners, potentially threatening environmental and human health. Although TCS can be rapidly metabolized for detoxification, these processes can induce the formation of lipophilic ether metabolic analogs via cytochrome P450 catalysis, causing possible adverse cross-talk reactions in human metabolic disorders. Accordingly, TCS may be more harmful in environmental transformation and human metabolism. In particular, TCS can stimulate the transmission of antibiotic resistance even at trace levels, threatening public health. Considering these accruing epidemiological and toxicological studies indicating the multiple adverse health outcomes of TCS, we call on environmental toxicologists to pay more attention to the toxicity evolution of TCS during environmental transformation and human metabolism.

Analysis of key circRNA events in the AOP framework of TCS acting on zebrafish based on the data-driven

Triclosan (TCS) is a broad-spectrum antibiotic widely used in various personal care products. Research has found that exposure to TCS can cause toxic effects on organisms including neurotoxicity, cardiotoxicity, disorders of lipid metabolism, and abnormal vascular development, and the corresponding toxic mechanisms are gradually delving into the level of abnormal expression of miRNA regulating gene expression. Although the downstream mechanism of TCS targeting miRNA abnormal expression to induce toxicity is gradually improving, its upstream mechanism is still in a fog. Starting from the abnormal expression data of circRNA in zebrafish larvae induced by TCS, this study conducted a hierarchical analysis of the expression levels of all circRNAs, differential circRNAs, and trend circRNAs, and identified 29 key circRNA events regulating miRNA abnormal expression. In combination with GO and KEGG, the effects of TCS exposure were analyzed from the function and signaling pathway of the corresponding circRNA host gene. Furthermore, based on existing literature evidence about the biological toxicity induced by TCS targeting miRNA as data support, a competing endogenous RNAs (ceRNA) network characterizing the regulatory relationship between circRNA and miRNA was constructed and optimized. Finally, a comprehensive Adverse Outcome Pathway (AOP) framework of multiple levels of events including circRNA, miRNA, mRNA, pathway, and toxicity endpoints was established to systematically elucidate the toxic mechanism of TCS. Moreover, the rationality of the AOP framework was verified from the expression level of miRNA and adverse outcomes such as neurotoxicity, cardiotoxicity, oxidative stress, and inflammatory response by knockdown of circRNA48. This paper not only provides the key circRNA events for exploring the upstream mechanism of miRNA regulating gene expression but also provides an AOP framework for comprehensively demonstrating the toxicity mechanism of TCS on zebrafish, which is a theoretical basis for subsequent hazard assessment and prevention and control of TCS.

Bioengineered human gut-on-a-chip for advancing non-clinical pharmaco-toxicology

INTRODUCTION

There is a growing need for alternative models to advance current non-clinical experimental models because they often fail to accurately predict drug responses in human clinical trials. Human organ-on-a-chip models have emerged as promising approaches for advancing the predictability of drug behaviors and responses.

AREAS COVERED

We summarize up-to-date human gut-on-a-chip models designed to demonstrate intricate interactions involving the host, microbiome, and pharmaceutical compounds since these models have been reported a decade ago. This overview covers recent advances in gut-on-a-chip models as a bridge technology between non-clinical and clinical assessments of drug toxicity and metabolism. We highlight the promising potential of gut-on-a-chip platforms, offering a reliable and valid framework for investigating reciprocal crosstalk between the host, gut microbiome, and drug compounds.

EXPERT OPINION

Gut-on-a-chip platforms can attract multiple end users as predictive, human-relevant, and non-clinical model. Notably, gut-on-a-chip platforms provide a unique opportunity to recreate a human intestinal microenvironment, including dynamic bowel movement, luminal flow, oxygen gradient, host-microbiome interactions, and disease-specific manipulations restricted in animal and in vitro cell culture models. Additionally, given the profound impact of the gut microbiome on pharmacological bioprocess, it is critical to leverage breakthroughs of gut-on-a-chip technology to address knowledge gaps and drive innovations in predictive drug toxicology and metabolism.

Gut microbial β-glucuronidases influence endobiotic homeostasis and are modulated by diverse therapeutics

Hormones and neurotransmitters are essential to homeostasis, and their disruptions are connected to diseases ranging from cancer to anxiety. The differential reactivation of endobiotic glucuronides by gut microbial β-glucuronidase (GUS) enzymes may influence interindividual differences in the onset and treatment of disease. Using multi-omic, in vitro, and in vivo approaches, we show that germ-free mice have reduced levels of active endobiotics and that distinct gut microbial Loop 1 and FMN GUS enzymes drive hormone and neurotransmitter reactivation. We demonstrate that a range of FDA-approved drugs prevent this reactivation by intercepting the catalytic cycle of the enzymes in a conserved fashion. Finally, we find that inhibiting GUS in conventional mice reduces free serotonin and increases its inactive glucuronide in the serum and intestines. Our results illuminate the indispensability of gut microbial enzymes in sustaining endobiotic homeostasis and indicate that therapeutic disruptions of this metabolism promote interindividual response variabilities.

Triclosan administration to humanized UDP-glucuronosyltransferase 1 neonatal mice induces UGT1A1 through a dependence on PPARα and ATF4

Triclosan (TCS) is an antimicrobial toxicant found in a myriad of consumer products and has been detected in human tissues, including breastmilk. We have evaluated the impact of lactational TCS on UDP-glucuronosyltransferase 1A1 (UGT1A1) expression and bilirubin metabolism in humanized UGT1 (hUGT1) neonatal mice. In hUGT1 mice, expression of the hepatic UGT1A1 gene is developmentally delayed resulting in elevated total serum bilirubin (TSB) levels. We found that newborn hUGT1 mice breastfed or orally treated with TCS presented lower TSB levels along with induction of hepatic UGT1A1. Lactational and oral treatment by gavage with TCS leads to the activation of hepatic nuclear receptors constitutive androstane receptor (CAR), peroxisome proliferator-activated receptor alpha (PPARα), and stress sensor, activating transcription factor 4 (ATF4). When CAR-deficient hUGT1 mice (hUGT1/Car-/-) were treated with TCS, TSB levels were reduced with a robust induction of hepatic UGT1A1, leaving us to conclude that CAR is not tied to UGT1A1 induction. Alternatively, when PPARα-deficient hUGT1 mice (hUGT1/Pparα-/-) were treated with TCS, hepatic UGT1A1 was not induced. Additionally, we had previously demonstrated that TCS is a potent inducer of ATF4, a transcriptional factor linked to the integrated stress response. When ATF4 was deleted in liver of hUGT1 mice (hUGT1/Atf4ΔHep) and these mice treated with TCS, we observed superinduction of hepatic UGT1A1. Oxidative stress genes in livers of hUGT1/Atf4ΔHep treated with TCS were increased, suggesting that ATF4 protects liver from excessive oxidative stress. The increase oxidative stress may be associated with superinduction of UGT1A1. The expression of ATF4 in neonatal hUGT1 hepatic tissue may play a role in the developmental repression of UGT1A1.

Discovery of a botanical compound as a broad-spectrum inhibitor against gut microbial β-glucuronidases from the Tibetan medicine Rhodiola crenulata

Gut microbial β-glucuronidases (gmβ-GUS) played crucial roles in regulating a variety of endogenous substances and xenobiotics on the circulating level, thus had been recognized as key modulators of drug toxicity and human diseases. Inhibition or inactivation of gmβ-GUS enzymes has become a promising therapeutic strategy to alleviate drug-induced intestinal toxicity. Herein, the Rhodiola crenulata extract (RCE) was found with potent and broad-spectrum inhibition on multiple gmβ-GUS enzymes. Subsequently, the anti-gmβ-GUS activities of the major constituents in RCE were tested and the results showed that 1,2,3,4,6-penta-O-galloyl-β-d-glucopyranose (PGG) acted as a strong and broad-spectrum inhibitor on multiple gmβ-GUS (including EcGUS, CpGUS, SaGUS, and EeGUS). Inhibition kinetic assays demonstrated that PGG effectively inhibited four gmβ-GUS in a non-competitive manner, with the Ki values ranging from 0.12 μM to 1.29 μM. Docking simulations showed that PGG could tightly bound to the non-catalytic sites of various gmβ-GUS, mainly via hydrogen bonding and aromatic interactions. It was also found that PGG could strongly inhibit the total gmβ-GUS activity in mice feces, with the IC50 value of 1.24 μM. Collectively, our findings revealed that RCE and its constituent PGG could strongly inhibit multiple gmβ-GUS enzymes, suggesting that RCE and PGG could be used for alleviating gmβ-GUS associated enterotoxicity.

Evolution of triclosan resistance modulates bacterial permissiveness to multidrug resistance plasmids and phages

The horizontal transfer of plasmids has been recognized as one of the key drivers for the worldwide spread of antimicrobial resistance (AMR) across bacterial pathogens. However, knowledge remain limited about the contribution made by environmental stress on the evolution of bacterial AMR by modulating horizontal acquisition of AMR plasmids and other mobile genetic elements. Here we combined experimental evolution, whole genome sequencing, reverse genetic engineering, and transcriptomics to examine if the evolution of chromosomal AMR to triclosan (TCS) disinfectant has correlated effects on modulating bacterial pathogen (Klebsiella pneumoniae) permissiveness to AMR plasmids and phage susceptibility. Herein, we show that TCS exposure increases the evolvability of K. pneumoniae to evolve TCS-resistant mutants (TRMs) by acquiring mutations and altered expression of several genes previously associated with TCS and antibiotic resistance. Notably, nsrR deletion increases conjugation permissiveness of K. pneumoniae to four AMR plasmids, and enhances susceptibility to various Klebsiella-specific phages through the downregulation of several bacterial defense systems and changes in membrane potential with altered reactive oxygen species response. Our findings suggest that unrestricted use of TCS disinfectant imposes a dual impact on bacterial antibiotic resistance by augmenting both chromosomally and horizontally acquired AMR mechanisms.

Human Airway Organoids and Multimodal Imaging-Based Toxicity Evaluation of 1-Nitropyrene

Despite significant advances in understanding the general health impacts of air pollution, the toxic effects of air pollution on cells in the human respiratory tract are still elusive. A robust, biologically relevant in vitro model for recapitulating the physiological response of the human airway is needed to obtain a thorough understanding of the molecular mechanisms of air pollutants. In this study, by using 1-nitropyrene (1-NP) as a proof-of-concept, we demonstrate the effectiveness and reliability of evaluating environmental pollutants in physiologically active human airway organoids. Multimodal imaging tools, including live cell imaging, fluorescence microscopy, and MALDI-mass spectrometry imaging (MSI), were implemented to evaluate the cytotoxicity of 1-NP for airway organoids. In addition, lipidomic alterations upon 1-NP treatment were quantitatively analyzed by nontargeted lipidomics. 1-NP exposure was found to be associated with the overproduction of reactive oxygen species (ROS), and dysregulation of lipid pathways, including the SM-Cer conversion, as well as cardiolipin in our organoids. Compared with that of cell lines, a higher tolerance of 1-NP toxicity was observed in the human airway organoids, which might reflect a more physiologically relevant response in the native airway epithelium. Collectively, we have established a novel system for evaluating and investigating molecular mechanisms of environmental pollutants in the human airways via the combinatory use of human airway organoids, multimodal imaging analysis, and MS-based analyses.

Toxic effects of triclosan on hepatic and intestinal lipid accumulation in zebrafish via regulation of m6A-RNA methylation

Triclosan (TCS), recognized as an endocrine disruptor, has raised significant concerns due to its widespread use and potential health risks. To explore the impact of TCS on lipid metabolism, both larval and adult zebrafish were subjected to acute and chronic exposure to TCS. Through analyzes of biochemical and physiological markers, as well as Oil Red O (ORO) and hematoxylin and eosin (H&E) staining, our investigation revealed that TCS exposure induced hepatic and intestinal lipid accumulation in larval and adult zebrafish, leading to structural damage and inflammatory responses in these tissues. The strong affinity of TCS with PPARγ and subsequent pathway activation indicate that PPARγ pathway plays a crucial role in TCS-induced lipid buildup. Furthermore, we observed a decrease in m6A-RNA methylation levels in the TCS-treated group, which attributed to the increased activity of the demethylase FTO and concurrent suppression of the methyltransferase METTL3 gene expression by TCS. The alteration in methylation dynamics is identified as a potential underlying mechanism behind TCS-induced lipid accumulation. To address this concern, we explored the impact of folic acid-a methyl donor for m6A-RNA methylation-on lipid accumulation in zebrafish. Remarkably, folic acid administration partially alleviated lipid accumulation by restoring m6A-RNA methylation. This restoration, in turn, contributed to a reduction in inflammatory damage observed in both the liver and intestines. Additionally, folic acid partially mitigates the up-regulation of PPARγ and related genes induced by TCS. These findings carry substantial implications for understanding the adverse effects of environmental pollutants such as TCS. They also emphasize the promising potential of folic acid as a therapeutic intervention to alleviate disturbances in lipid metabolism induced by environmental pollutants.

Conceptualizing the Role of the Microbiome as a Mediator and Modifier in Environmental Health Studies: A Scoping Review of Studies of Triclosan and the Microbiome

PURPOSE OF REVIEW

Triclosan is an endocrine-disrupting antimicrobial additive that is suspected of contributing to antibiotic resistance and altering the microbiome. In this scoping review, we summarize what is known about the association between triclosan exposure and the microbiome using evidence from in vivo and epidemiologic studies.

RECENT FINDINGS

Our review includes 11 rodent studies, seven fish studies, and five human studies. Evidence from animal studies suggests that triclosan decreases the diversity of the microbiome, although only one epidemiologic study agreed. Most studies suggest that triclosan alters the microbial community beta diversity, but disagree on which taxa contributed to compositional differences. Taxa in the Bacteroidetes, Firmicutes, and Proteobacteria may be more influenced by triclosan than those in other phyla. Studies on triclosan and the microbiome were scarce and were inconclusive as to the effects of triclosan on the microbiome. Additional research is needed to clarify windows of heightened susceptibility of the microbiome to triclosan. We recommend guidelines for future microbiome research in environmental health to increase comparability across studies.

Dietary flavonoids-microbiota crosstalk in intestinal inflammation and carcinogenesis

Colorectal cancer (CRC) is currently the third leading cancer and commonly develops from chronic intestinal inflammation. A strong association was found between gut microbiota and intestinal inflammation and carcinogenic risk. Flavonoids, which are abundant in vegetables and fruits, can inhibit inflammation, regulate gut microbiota, protect gut barrier integrity, and modulate immune cell function, thereby attenuating colitis and preventing carcinogenesis. Upon digestion, about 90% of flavonoids are transported to the colon without being absorbed in the small intestine. This phenomenon increases the abundance of beneficial bacteria and enhances the production of short-chain fatty acids. The gut microbe further metabolizes these flavonoids. Interestingly, some metabolites of flavonoids play crucial roles in anti-inflammation and anti-tumor effects. This review summarizes the modulatory effect of flavonoids on gut microbiota and their metabolism by intestinal microbe under disease conditions, including inflammatory bowel disease, colitis-associated cancer (CAC), and CRC. We focus on dietary flavonoids and microbial interactions in intestinal mucosal barriers as well as intestinal immune cells. Results provide novel insights to better understand the crosstalk between dietary flavonoids and gut microbiota and support the standpoint that dietary flavonoids prevent intestinal inflammation and carcinogenesis.

Multi-omics analysis of attenuated variant reveals potential evaluation marker of host damaging for SARS-CoV-2 variants

SARS-CoV-2 continues to threaten human society by generating novel variants via mutation and recombination. The high number of mutations that appeared in emerging variants not only enhanced their immune-escaping ability but also made it difficult to predict the pathogenicity and virulence based on viral nucleotide sequences. Molecular markers for evaluating the pathogenicity of new variants are therefore needed. By comparing host responses to wild-type and variants with attenuated pathogenicity at proteome and metabolome levels, six key molecules on the polyamine biosynthesis pathway including putrescine, SAM, dc-SAM, ODC1, SAMS, and SAMDC were found to be differentially upregulated and associated with pathogenicity of variants. To validate our discovery, human airway organoids were subsequently used which recapitulates SARS-CoV-2 replication in the airway epithelial cells of COVID-19 patients. Using ODC1 as a proof-of-concept, differential activation of polyamine biosynthesis was found to be modulated by the renin-angiotensin system (RAS) and positively associated with ACE2 activity. Further experiments demonstrated that ODC1 expression could be differentially activated upon a panel of SARS-CoV-2 variants of concern (VOCs) and was found to be correlated with each VOCs' pathogenic properties. Particularly, the presented study revealed the discriminative ability of key molecules on polyamine biosynthesis as a predictive marker for virulence evaluation and assessment of SARS-CoV-2 variants in cell or organoid models. Our work, therefore, presented a practical strategy that could be potentially applied as an evaluation tool for the pathogenicity of current and emerging SARS-CoV-2 variants.

Effects of triclosan exposure on stem cells from human exfoliated deciduous teeth (SHED) fate

Triclosan (TCS), a widely used broad-spectrum antibacterial agent and preservative, is commonly found in products and environments. Widespread human exposure to TCS has drawn increasing attention from researchers concerning its toxicological effect. However, minimal studies have focused on the impact of TCS exposure on human stem cells. Therefore, the aim of the present study was to evaluate the effects of TCS exposure on stem cells from human exfoliated deciduous teeth (SHED) and its molecular mechanisms. A series of experimental methods were conducted to assess cell viability, morphology, proliferation, differentiation, senescence, apoptosis, mitochondrial function, and oxidative stress after SHED exposure to TCS. Furthermore, transcriptome analysis was applied to investigate the response of SHED to different concentrations of TCS exposure and to explore the molecular mechanisms. We demonstrated that TCS has a dose-dependent proliferation and differentiation inhibition of SHED, while promoting cellular senescence, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and oxidative stress, as well as significantly induces apoptosis and autophagy flux inhibition at high concentrations. Interestingly, no significant morphological changes in SHED were observed after TCS exposure. Transcriptome analysis of normal and TCS-induced SHED suggested that SHED may use different strategies to counteract stress from different concentrations of TCS and showed significant differences. We discovered that TCS mediates cellular injury of SHED by enhancing the expression of PTEN, thereby inhibiting the phosphorylation levels of PI3K and AKT as well as mTOR expression. Collectively, our findings provide a new understanding of the toxic effects of TCS on human stem cell fate, which is important for determining the risk posed by TCS to human health.

Adverse effect of oxidized cholesterol exposure on colitis is mediated by modulation of gut microbiota

Both cholesterol and oxidized cholesterol (OXC) are present in human diets. The incidence of inflammatory bowel diseases (IBDs) is increasing in the world. The present study was to investigate the mechanism by which OXC promotes colitis using C57BL/6 mice as a model. Results shown that more severe colitis was developed in OXC-treated mice with the administration of dextran sulfate sodium (DSS) in water. Direct effects of short-term OXC exposure on gut barrier or inflammation were not observed in healthy mice. However, OXC exposure could cause gut microbiota dysbiosis with a decrease in the relative abundance of short-train fatty acids (SCFAs)-producing bacteria (Lachnospiraceae_NK4A136_group and Blautia) and an increase in the abundance of some potential harmful bacteria (Bacteroides). OXC-induced symptoms of colitis were eliminated when mice were administered with antibiotic cocktails, indicating the promoting effect of OXC on DSS-induced colitis was mediated by its effect on gut microbiota. Moreover, bacteria-depleted mice colonized with gut microbiome from OXC-DSS-exposed mice exhibited a severe colitis, further proving the gut dysbiosis caused by OXC exposure was the culprit in exacerbating the colitis. It was concluded that dietary OXC exposure increased the susceptibility of colitis in mice by causing gut microbiota dysbiosis.

Activity-based protein profiling in microbes and the gut microbiome

Activity-based protein profiling (ABPP) is a powerful chemical approach for probing protein function and enzymatic activity in complex biological systems. This strategy typically utilizes activity-based probes that are designed to bind a specific protein, amino acid residue, or protein family and form a covalent bond through a reactivity-based warhead. Subsequent analysis by mass spectrometry-based proteomic platforms that involve either click chemistry or affinity-based labeling to enrich for the tagged proteins enables identification of protein function and enzymatic activity. ABPP has facilitated elucidation of biological processes in bacteria, discovery of new antibiotics, and characterization of host-microbe interactions within physiological contexts. This review will focus on recent advances and applications of ABPP in bacteria and complex microbial communities.

CYP eicosanoid pathway mediates colon cancer-promoting effects of dietary linoleic acid

Human and animal studies support that consuming a high level of linoleic acid (LA, 18:2ω-6), an essential fatty acid and key component of the human diet, increases the risk of colon cancer. However, results from human studies have been inconsistent, making it challenging to establish dietary recommendations for optimal LA intake. Given the importance of LA in the human diet, it is crucial to better understand the molecular mechanisms underlying its potential colon cancer-promoting effects. Using LC-MS/MS-based targeted lipidomics, we find that the cytochrome P450 (CYP) monooxygenase pathway is a major pathway for LA metabolism in vivo. Furthermore, CYP monooxygenase is required for the colon cancer-promoting effects of LA, since the LA-rich diet fails to exacerbate colon cancer in CYP monooxygenase-deficient mice. Finally, CYP monooxygenase mediates the pro-cancer effects of LA by converting LA to epoxy octadecenoic acids (EpOMEs), which have potent effects on promoting colon tumorigenesis via gut microbiota-dependent mechanisms. Overall, these results support that CYP monooxygenase-mediated conversion of LA to EpOMEs plays a crucial role in the health effects of LA, establishing a unique mechanistic link between dietary fatty acid intake and cancer risk. These results could help in developing more effective dietary guidelines for optimal LA intake and identifying subpopulations that may be especially vulnerable to LA's negative effects.

Adverse effects of triclosan exposure on health and potential molecular mechanisms

With the COVID-19 pandemic, the use of disinfectants has grown significantly around the world. Triclosan (TCS), namely 5-chloro-2-(2,4-dichlorophenoxy) phenol or 2,4,4'-trichloro-2'-hydroxydiphenyl ether, is a broad-spectrum, lipophilic, antibacterial agent that is extensively used in multifarious consumer products. Due to the widespread use and bioaccumulation, TCS is frequently detected in the environment and human biological samples. Accumulating evidence suggests that TCS is considered as a novel endocrine disruptor and may have potential unfavorable effects on human health, but studies on the toxic effect mediated by TCS exposure as well as its underlying mechanisms of action are relatively sparse. Therefore, in this review, we attempted to summarize the potential detrimental effects of TCS exposure on human reproductive health, liver function, intestinal homeostasis, kidney function, thyroid endocrine, and other tissue health, and further explore its mechanisms of action, thereby contributing to the better understanding of TCS characteristics and safety. Moreover, our work suggested the need to further investigate the biological effects of TCS exposure at the metabolic level in vivo.

A holistic review on triclosan and triclocarban exposure: Epidemiological outcomes, antibiotic resistance, and health risk assessment

Triclosan (TCS) and triclocarban (TCC) are antimicrobials that are widely applied in personal care products, textiles, and plastics. TCS and TCC exposure at low doses may disturb hormone levels and even facilitate bacterial resistance to antibiotics. In the post-coronavirus disease pandemic era, chronic health effects and the spread of antibiotic resistance genes associated with TCS and TCC exposure represent an increasing concern. This study sought to screen and review the exposure levels and sources and changes after the onset of the coronavirus disease (COVID-19) pandemic, potential health outcomes, bacterial resistance and cross-resistance, and health risk assessment tools associated with TCS and TCC exposure. Daily use of antimicrobial products accounts for most observed associations between internal exposure and diseases, while secondary exposure at trace levels mainly lead to the spread of antibiotic resistance genes. The roles of altered gut microbiota in multi-system toxicities warrant further attention. Sublethal dose of TCC selects ARGs without obviously increasing tolerance to TCC. But TCS induce persistent TCS resistance and reversibly select antibiotic resistance, which highlights the benefits of minimizing its use. To derive reference doses (RfDs) for humans, more sensitive endpoints observed in populational studies need to be confirmed using toxicological tests. Additionally, the human equivalent dose is recommended to be incorporated into the health risk assessment to reduce uncertainty of extrapolation.

Microbial β-glucuronidases drive human periodontal disease etiology

Periodontitis is a chronic inflammatory disease associated with persistent oral microbial dysbiosis. The human β-glucuronidase (GUS) degrades constituents of the periodontium and is used as a biomarker for periodontitis severity. However, the human microbiome also encodes GUS enzymes, and the role of these factors in periodontal disease is poorly understood. Here, we define the 53 unique GUSs in the human oral microbiome and examine diverse GUS orthologs from periodontitis-associated pathogens. Oral bacterial GUS enzymes are more efficient polysaccharide degraders and processers of biomarker substrates than the human enzyme, particularly at pHs associated with disease progression. Using a microbial GUS-selective inhibitor, we show that GUS activity is reduced in clinical samples obtained from individuals with untreated periodontitis and that the degree of inhibition correlates with disease severity. Together, these results establish oral GUS activity as a biomarker that captures both host and microbial contributions to periodontitis, facilitating more efficient clinical monitoring and treatment paradigms for this common inflammatory disease.

Decipher enzymes from human microbiota for drug discovery and development

The human microbiota plays an important role in human health and contributes to the metabolism of therapeutic drugs affecting their potency. However, the current knowledge on human gut bacterial metabolism is limited and lacks an understanding of the underlying mechanisms of observed drug biotransformations. Despite the complexity of the gut microbial community, genomic and metagenomic sequencing provides insights into the diversity of chemical reactions that can be carried out by the microbiota and poses new challenges to functionally annotate thousands of bacterial enzymes. Here, we outline methods to systematically address the structural and functional space of the human microbiome, highlighting a combination of in silico and in vitro approaches. Systematic knowledge about microbial enzymes could eventually be applied for personalized therapy, the development of prodrugs and modulators of unwanted bacterial activity, and the further discovery of new antibiotics.

A New Fluorescent Probe Tool: ERNathG

β-d-Glucuronidase (GUS) plays a pivotal role in both clinical treatment assessment and environmental monitoring. Existing tools for GUS detection suffer from (1) poor continuity due to a gap between the optimal pH of the probes and the enzyme and (2) diffusion from the detection site due to lack of an anchoring structure. Here we report a novel GUS pH-matching and endoplasmic reticulum-anchoring strategy for GUS recognition. The new fluorescent probe tool was termed ERNathG, which was designed and synthesized with β-d-glucuronic acid as the GUS-specific recognition site and 4-hydroxy-1,8-naphthalimide as a fluorescence reporting group, with a p-toluene sulfonyl as an anchoring group. This probe enabled the continuous and anchored detection of GUS without pH-adjustment for the related assessment of common cancer cell lines and gut bacteria. The probe's properties are far superior to those of commonly used commercial molecules.

Microbiota-mediated reactivation of triclosan oxidative metabolites in colon tissues

Triclosan (TCS) is a widespread antimicrobial agent that is associated with many adverse health outcomes. Its gut toxicity has been attributed to the molecular modifications mediated by commensal microbes, but microbial transformations of TCS derivatives in the gut lumen are still largely unknown. Aromatic hydroxylation is the predominant oxidative metabolism of TCS that linked to its toxicological effects in host tissues. Here, we aimed to reveal the biological fates of hydroxyl-TCS (OH-TCS) in the colon, where intestinal microbes mainly reside. Unlike the profiles generated via host metabolism, OH-TCS species remain unconjugated in human stools from a cohort study. Through tracking molecular compositions in mouse intestinal tract, elevated abundance of free-form OH-TCS while reduced abundance of conjugated forms was observed in the colon digesta and mucosa. Using antibiotic-treated and germ-free mice, as well as in vitro approaches, we demonstrate that gut microbiota-encoded enzymes efficiently convert glucuronide/sulfate-conjugated OH-TCS, which are generated from host metabolism, back to their bioactive free-forms in colon tissues. Thus, host-gut microbiota metabolic interactions of TCS derivatives were proposed. These results shed light on the crucial roles of microbial metabolism in TCS toxicity, and highlight the importance of incorporating gut microbial transformations in health risk assessment of environmental chemicals.

Effects of in vitro simulated digestion and fecal fermentation of polysaccharides from straw mushroom (Volvariella volvacea) on its physicochemical properties and human gut microbiota

Herein, the fermentation and digestion behavior of Volvariella volvacea polysaccharide (VVP) were examined through the in vitro simulation experiment. The results revealed that succeeding the simulated salivary gastrointestinal digestion, the molecular weight of VVP was reduced by only 8.9 %. In addition, the reducing sugar, uronic acid, monosaccharide composition and Fourier transform infrared spectroscopy characteristics of VVP did not change significantly, which indicate that saliva-gastrointestinal could not digest VVP. However, 48 h of fecal fermentation of VVP dramatically reduced its molecular weight by 40.4 %. Furthermore, the molar ratios of the monosaccharide composition altered considerably due to the degradation of VVP by microorganisms and the metabolysis into different short-chain fatty acids (SCFAs). Meanwhile, the VVP also raised the proportion of Bacteroidetes to Firmicutes and promoted the proliferation of some beneficial bacteria including Bacteroides and Phascolarctobacterium, whereas it inhibited the growth of unfavorable bacteria such as Escherichia-shigella. Therefore, VVP has the potential to have a positive influence on health and hinder diseases by improving the intestinal microbial environment. These findings provide a theoretical foundation to further develop Volvariella volvacea as a healthy functional food.

Chemoproteomic Approaches for Unraveling Prokaryotic Biology

Bacteria are ubiquitous lifeforms with important roles in the environment, biotechnology, and human health. Many of the functions that bacteria perform are mediated by proteins and enzymes, which catalyze metabolic transformations of small molecules and modifications of proteins. To better understand these biological processes, chemical proteomic approaches, including activity-based protein profiling, have been developed to interrogate protein function and enzymatic activity in physiologically relevant contexts. Here, chemoproteomic strategies and technological advances for studying bacterial physiology, pathogenesis, and metabolism are discussed. The development of chemoproteomic approaches for characterizing protein function and enzymatic activity within bacteria remains an active area of research, and continued innovations are expected to provide breakthroughs in understanding bacterial biology.

Infant exposure to parabens, triclosan, and triclocarban via breastfeeding and formula supplementing in southern China

Parabens, triclosan (TCS), and triclocarban (TCC) are antimicrobial additives that are widely used in personal care products (PCPs) and may dysregulate infant gut microbiota and induce a series of chronic diseases. Dietary intake may be an underestimated exposure route of such antimicrobial additives in infants, but relevant data remain scarce. Therefore, this study determined five common preservatives, including methyl- (MeP), ethyl- (EtP), propyl- (PrP), butyl- (BuP), and benzyl-paraben (BeP), and two antimicrobials TCS and TCC, in major infant food sources (breastmilk, milk-based infant formula [MIF], and cereal-based complementary food [CCF]) in southern China. The health risks associated with dietary exposure among infants across different months of age were also evaluated. The results demonstrated a high incidence of MeP, EtP, PrP, and BeP in processed infant food products, while TCS and TCC were mainly detected in maternal breastmilk. Notably, MeP and EtP were found in all of the MIFs tested, while MeP, EtP, and BeP were detected in 85.6 %-100 % of the CCFs. By incorporating the human equivalent dose and an additional 10-fold margin of safety for infants into the health risk assessment, the 95th percentile hazard quotient of PrP via the ingestion of breastmilk among neonates exceeded 1. For the first time, the results showed that exposure to PrP via breastmilk intake may pose a considerable health risk to urban neonates in southern China. The health risks caused by antimicrobial exposure via ingesting MIF and CCF among infants were negligible. Thus, we recommend breastfeeding women reduce their consumption of PCPs and processed food, especially during the first month after delivery.

Multi-omic analysis of host-microbial interactions central to the gut-brain axis

The gut microbiota impact numerous aspects of human physiology, including the central nervous system (CNS). Emerging work is now focusing on the microbial factors underlying the bi-directional communication network linking host and microbial systems within the gastrointestinal tract to the CNS, the "gut-brain axis". Neurotransmitters are key coordinators of this network, and their dysregulation has been linked to numerous neurological disease states. As the bioavailability of neurotransmitters is modified by gut microbes, it is critical to unravel the influence of the microbiota on neurotransmitters in the context of the gut-brain axis. Here we review foundational studies that defined molecular relationships between the microbiota, neurotransmitters, and the gut-brain axis. We examine links between the gut microbiome, behavior, and neurological diseases, as well as microbial influences on neurotransmitter bioavailability and physiology. Finally, we review multi-omics technologies uniquely applicable to this area, including high-throughput genetics, modern metabolomics, structure-guided metagenomics, targeted proteomics, and chemogenetics. Interdisciplinary studies will continue to drive the discovery of molecular mechanisms linking the gut microbiota to clinical manifestations of neurobiology.

Tannic acid attenuates intestinal oxidative damage by improving antioxidant capacity and intestinal barrier in weaned piglets and IPEC-J2 cells

Tannic acid (TA) has received widespread attention for its beneficial biological function with antioxidant capacity. This study investigated the protective role of TA on the intestinal antioxidant capacity and intestinal barrier in weaned piglets and porcine intestinal epithelial cells (IPEC-J2). A total of 18 weaned piglets were randomly allocated into two groups (n = 9) and fed with a basal diet (control, CON) and a basal diet containing 1,000 mg/kg TA for two weeks. The in vivo results showed that treatment with TA increased both glutathione peroxidase (GSH-PX) activity and the protein expression of ZO-1 in the jejunum of weaned piglets, and reduced the level of malondialdehyde (MDA) in the serum and the mRNA and protein expression of Keap1 in the jejunum of weaned piglets. Furthermore, in vitro results indicated that TA treatment effectively alleviated tert-butyl hydroperoxide (TBH)-induced oxidative stress in IPEC-J2 cells, improved the antioxidant capacity by elevating the cell redox state and activating the Nrf2 pathway, and improved the intestinal barrier by upregulating the mRNA and protein expression of intestinal tight junction proteins and increasing the transepithelial electrical resistance (TEER) value. In conclusion, these results confirmed that TA relieves oxidative injury and improves intestinal barrier function and intestinal antioxidant capacity by activating the Nrf2 signaling pathway. These findings suggest that TA has the potential application in alleviating oxidative stress in the intestine of weaned piglets.

Characterizing the metabolic effects of the selective inhibition of gut microbial β-glucuronidases in mice

The hydrolysis of xenobiotic glucuronides by gut bacterial glucuronidases reactivates previously detoxified compounds resulting in severe gut toxicity for the host. Selective bacterial β-glucuronidase inhibitors can mitigate this toxicity but their impact on wider host metabolic processes has not been studied. To investigate this the inhibitor 4-(8-(piperazin-1-yl)-1,2,3,4-tetrahydro-[1,2,3]triazino[4',5':4,5]thieno[2,3-c]isoquinolin-5-yl)morpholine (UNC10201652, Inh 9) was administered to mice to selectively inhibit a narrow range of bacterial β-glucuronidases in the gut. The metabolomic profiles of the intestinal contents, biofluids, and several tissues involved in the enterohepatic circulation were measured and compared to control animals. No biochemical perturbations were observed in the plasma, liver or gall bladder. In contrast, the metabolite profiles of urine, colon contents, feces and gut wall were altered compared to the controls. Changes were largely restricted to compounds derived from gut microbial metabolism. This work establishes that inhibitors targeted towards bacterial β-glucuronidases modulate the functionality of the intestinal microbiota without adversely impacting the host metabolic system.

Sanghuangporus vaninii fruit body polysaccharide alleviates hyperglycemia and hyperlipidemia via modulating intestinal microflora in type 2 diabetic mice

The disease of type 2 diabetes mellitus (T2DM) is principally induced by insufficient insulin secretion and insulin resistance. In the current study, Sanghuangporus vaninii fruit body polysaccharide (SVP) was prepared and structurally characterized. It was shown that the yield of SVP was 1.91%, and SVP mainly contains small molecular weight polysaccharides. Afterward, the hypoglycemic and hypolipidemic effects and the potential mechanism of SVP in T2DM mice were investigated. The results exhibited oral SVP could reverse the body weight loss, high levels of blood glucose, insulin resistance, hyperlipidemia, and inflammation in T2DM mice. Oral SVP increased fecal short-chain fatty acids (SCFAs) concentrations of T2DM mice. Additionally, 16S rRNA sequencing analysis illustrated that SVP can modulate the structure and function of intestinal microflora in T2DM mice, indicating as decreasing the levels of Firmicutes/Bacteroidetes, Flavonifractor, Odoribacter, and increasing the levels of Weissella, Alloprevotella, and Dubosiella. Additionally, the levels of predicted metabolic functions of Citrate cycle, GABAergic synapse, Insulin signaling pathway were increased, and those of Purine metabolism, Taurine and hypotaurine metabolism, and Starch and sucrose metabolism were decreased in intestinal microflora after SVP treatment. These findings demonstrate that SVP could potentially play hypoglycemic and hypolipidemic effects by regulating gut microflora and be a promising nutraceutical for ameliorating T2DM.

Triclosan and triclocarban as potential risk factors of colitis and colon cancer: Roles of gut microbiota involved

In recent decades there has been a dramatic increase in the incidence and prevalence of inflammatory bowel disease (IBD), a chronic inflammatory disease of the intestinal tissues and a major risk factor of developing colon cancer. While accumulating evidence supports that the rapid increase of IBD is mainly caused by exposure to environmental risk factors, the identities of the risk factors, as well as the mechanisms connecting environmental exposure with IBD, remain largely unknown. Triclosan (TCS) and triclocarban (TCC) are high-volume chemicals that are used as antimicrobial ingredients in consumer and industrial products. They are ubiquitous contaminants in the environment and are frequently detected in human populations. Recent studies showed that exposure to TCS/TCC, at human exposure-relevant doses, increases the severity of colitis and exacerbates colon tumorigenesis in mice, suggesting that they could be risk factors of IBD and associated diseases. The gut toxicities of these compounds require the presence of gut microbiota, since they fail to induce colonic inflammation in mice lacking the microbiota. Regarding the functional roles of the microbiota involved, gut commensal microbes and specific microbial β-glucuronidase (GUS) enzymes mediate colonic metabolism of TCS, leading to metabolic reactivation of TCS in the colon and contributing to its subsequent gut toxicity. Overall, these results support that these commonly used compounds could be environmental risk factors of IBD and associated diseases through gut microbiota-dependent mechanisms.

The role of gut microbial β-glucuronidase in drug disposition and development

Gut microbial β-glucuronidase (gmGUS) is involved in the disposition of many endogenous and exogenous compounds. Preclinical studies have shown that inhibiting gmGUS activity affects drug disposition, resulting in reduced toxicity in the gastrointestinal tract (GIT) and enhanced systemic efficacy. Additionally, manipulating gmGUS activity is expected to be effective in preventing/treating local or systemic diseases. Although results from animal studies are promising, challenges remain in developing drugs by targeting gmGUS. Here, we review the role of gmGUS in host health under physiological and pathological conditions, the impact of gmGUS on the disposition of phenolic compounds, models used to study gmGUS activity, and the perspectives and challenges in developing drugs by targeting gmGUS.

Degradation of Triclosan in the Water Environment by Microorganisms: A Review

Triclosan (TCS), a kind of pharmaceuticals and personal care products (PPCPs), is widely used and has had a large production over years. It is an emerging pollutant in the water environment that has attracted global attention due to its toxic effects on organisms and aquatic ecosystems, and its concentrations in the water environment are expected to increase since the COVID-19 pandemic outbreak. Some researchers found that microbial degradation of TCS is an environmentally sustainable technique that results in the mineralization of large amounts of organic pollutants without toxic by-products. In this review, we focus on the fate of TCS in the water environment, the diversity of TCS-degrading microorganisms, biodegradation pathways and molecular mechanisms, in order to provide a reference for the efficient degradation of TCS and other PPCPs by microorganisms.

Lactational delivery of Triclosan promotes non-alcoholic fatty liver disease in newborn mice

Here we show that Triclosan (TCS), a high-volume antimicrobial additive that has been detected in human breastmilk, can be efficiently transferred by lactation to newborn mice, causing significant fatty liver (FL) during the suckling period. These findings are relevant since pediatric non-alcoholic fatty liver disease (NAFLD) is escalating in the United States, with a limited mechanistic understanding. Lactational delivery stimulated hepatosteatosis, triglyceride accumulation, endoplasmic reticulum (ER) stress, signs of inflammation, and liver fibrosis. De novo lipogenesis (DNL) induced by lactational TCS exposure is shown to be mediated in a PERK-eIF2α-ATF4-PPARα cascade. The administration of obeticholic acid (OCA), a potent FXR agonist, as well as activation of intestinal mucosal-regenerative gp130 signaling, led to reduced liver ATF4 expression, PPARα signaling, and DNL when neonates were exposed to TCS. It is yet to be investigated but mother to child transmission of TCS or similar toxicants may underlie the recent increases in pediatric NAFLD.

Alternaria alternata Mycotoxins Activate the Aryl Hydrocarbon Receptor and Nrf2-ARE Pathway to Alter the Structure and Immune Response of Colon Epithelial Cells

After ingestion of food commodities, the gastrointestinal tract (GIT) poses the first barrier against xenobiotics and pathogens. Therefore, it is regularly confronted with external stressors potentially affecting the inflammatory response and the epithelial barrier. Alternaria mycotoxins such as alternariol (AOH) and altertoxin II (ATX-II) are frequently occurring food and feed contaminants that are described for their immunomodulatory capacities. Hence, this study aimed at exploring the effect of AOH and ATX-II as single compounds or binary mixtures on the immune response and epithelial homeostasis in noncancerous colon epithelial cells HCEC-1CT. Both toxins suppressed mRNA levels of proinflammatory mediators interleukin-8 (IL-8), tumor necrosis factor α (TNF-α), and secretion of IL-8, as well as mRNA levels of the matrix metallopeptidase 2 (MMP-2). Binary combinations of AOH and ATX-II reduced the response of the single toxins. Additionally, AOH and ATX-II modified immunolocalization of transmembrane proteins such as integrin β1, zona occludens 1 (ZO-1), claudin 4 (Cldn 4), and occludin (Ocln), which support colonic tissue homeostasis and intestinal barrier function. Moreover, the cellular distribution of ZO-1 was affected by ATX-II. Mechanistically, these effects could be traced back to the involvement of several transcription factors. AOH activated the nuclear translocation of the aryl hydrocarbon receptor (AhR) and the nuclear factor erythroid 2-related factor 2 (Nrf2), governing cell metabolic competence and structural integrity. This was accompanied by altered distribution of the NF-κB p65 protein, an important regulator of inflammatory response. ATX-II also induced AhR and Nrf2 translocation, albeit failing to substantiate the effect of AOH on the colonic epithelium. Hence, both toxins coherently repress the intestinal immune response on the cytokine transcriptional and protein levels. Furthermore, both mycotoxins affected the colonic epithelial integrity by altering the cell architecture.

Metagenomics combined with activity-based proteomics point to gut bacterial enzymes that reactivate mycophenolate

Mycophenolate mofetil (MMF) is an important immunosuppressant prodrug prescribed to prevent organ transplant rejection and to treat autoimmune diseases. MMF usage, however, is limited by severe gastrointestinal toxicity that is observed in approximately 45% of MMF recipients. The active form of the drug, mycophenolic acid (MPA), undergoes extensive enterohepatic recirculation by bacterial β-glucuronidase (GUS) enzymes, which reactivate MPA from mycophenolate glucuronide (MPAG) within the gastrointestinal tract. GUS enzymes demonstrate distinct substrate preferences based on their structural features, and gut microbial GUS enzymes that reactivate MPA have not been identified. Here, we compare the fecal microbiomes of transplant recipients receiving MMF to healthy individuals using shotgun metagenomic sequencing. We find that neither microbial composition nor the presence of specific structural classes of GUS genes are sufficient to explain the differences in MPA reactivation measured between fecal samples from the two cohorts. We next employed a GUS-specific activity-based chemical probe and targeted metaproteomics to identify and quantify the GUS proteins present in the human fecal samples. The identification of specific GUS enzymes was improved by using the metagenomics data collected from the fecal samples. We found that the presence of GUS enzymes that bind the flavin mononucleotide (FMN) is significantly correlated with efficient MPA reactivation. Furthermore, structural analysis identified motifs unique to these FMN-binding GUS enzymes that provide molecular support for their ability to process this drug glucuronide. These results indicate that FMN-binding GUS enzymes may be responsible for reactivation of MPA and could be a driving force behind MPA-induced GI toxicity.