Capture of Electrophilic Quinones in the Extracellular Space: Evidence for a Phase Zero Reaction.

Electrophilic quinones are produced during the combustion of gasoline in the atmosphere. Although these reactive species covalently bind to protein-based nucleophiles in cells, resulting in the formation of protein adducts involved in the modulation of redox signaling pathways and cytotoxicity, the extracellular regulation of quinones is not understood. In this study, incubation of 1,2-naphthoquinone (1,2-NQ) with the low-molecular-weight fraction of mouse plasma resulted in the consumption of cysteine (CysSH) in the plasma in a concentration-dependent manner. Covalent modification of albumin was markedly repressed by the addition of either the low-molecular-weight fraction of mouse plasma or CysSH, suggesting that CysSH protects by forming a conjugate with 1,2-NQ. Similar phenomena also occurred for other atmospheric quinones 1,4-NQ and 1,4-benzoquinone (1,4-BQ). The addition of cystine to a culture medium without amino acids enhanced the release of CysSH from A431 cells and blocked 1,2-NQ-mediated arylation of intracellular proteins, suggesting that 1,2-NQ interacts with extracellular CysSH. Liquid chromatography-tandem mass spectrometry analysis revealed that 1,2-NQ and 1,4-BQ undergoes nucleophilic attack by CysSH, yielding a 1,2-NQH2-SCys adduct and 1,4-BQH2-SCys adduct, respectively. Unlike 1,2-NQ and 1,4-BQ, the authentic 1,2-NQH2-SCys adduct and 1,4-BQH2-SCys adduct had little effect on the covalent modification of cellular proteins and viability of A431 cells. These results suggest that electrophilic quinones are readily trapped by CysSH released from A431 cells, forming less-toxic CysSH adducts and thereby repressing covalent modification of cellular proteins. These findings provide evidence for the existence of a "phase zero" reaction of electrophiles prior to their uptake by cells.

Potential Association between Methylmercury Neurotoxicity and Inflammation.

Methylmercury (MeHg) is the causal substrate of Minamata disease and a major environmental toxicant. MeHg is widely distributed, mainly in the ocean, meaning its bioaccumulation in seafood is a considerable problem for human health. MeHg has been intensively investigated and is known to induce inflammatory responses and neurodegeneration. However, the relationship between MeHg-induced inflammatory responses and neurodegeneration is not understood. In the present review, we first describe recent findings showing an association between inflammatory responses and certain MeHg-unrelated neurological diseases caused by neurodegeneration. In addition, cell-specific MeHg-induced inflammatory responses are summarized for the central nervous system including those of microglia, astrocytes, and neurons. We also describe MeHg-induced inflammatory responses in peripheral cells and tissue, such as macrophages and blood. These findings provide a concept of the relationship between MeHg-induced inflammatory responses and neurodegeneration, as well as direction for future research of MeHg-induced neurotoxicity.

Cysteine Trisulfide Protects E. coli from Electrophile-Induced Death through the Generation of Cysteine Hydropersulfide.

Hydropersulfide and polysulfide species have recently been shown to elicit a wide variety of biological and physiological responses. In this study, we examine the effects of cysteine trisulfide (Cys-SSS-Cys; also known as thiocystine) treatment on E. coli. Previous studies in mammalian cells have shown that Cys-SSS-Cys treatment results in protection from the electrophiles. Here, we show that the protective effect of Cys-SSS-Cys treatment against electrophile-induced cell death is conserved in E. coli. This protection correlates with the rapid generation of cysteine hydropersulfide (Cys-SSH) in the culture media. We go on to demonstrate that an exogenous phosphatase expressed in E. coli, containing only a single catalytic cysteine, is protected from electrophile-induced inactivation in the presence of hydropersulfides. These data together demonstrate that E. coli can utilize Cys-SSS-Cys to generate Cys-SSH and that the Cys-SSH can protect cellular thiols from reactivity with the electrophiles.

Nrf2 Activation and Its Coordination with the Protective Defense Systems in Response to Electrophilic Stress.

Molecular responses mediated by sensor proteins are important for biological defense against electrophilic stresses, such as xenobiotic electrophile exposure. NF-E2-related factor 2 (Nrf2) has an essential function as a master regulator of such cytoprotective molecular responses along with sensor protein Kelch-like ECH-associated protein 1. This review focuses on Nrf2 activation and its involvement with the protective defense systems under electrophilic stresses integrated with our recent findings that reactive sulfur species (RSS) mediate detoxification of electrophiles. The Nrf2 pathway does not function redundantly with the RSS-generating cystathionine γ-lyase pathway, and vice versa.

The Uptake and Release of Polysulfur Cysteine Species by Cells: Physiological and Toxicological Implications.

Hydropersulfides and related polysulfides have recently become topics of significant interest due to their physiological prevalence and proposed biological functions. Currently, examination of the effects of hydropersulfide treatment on cells is difficult due to their lack of inherent stability with respect to disproportionation. Herein, it is reported that the treatment of a variety of cell types with cysteine trisulfide (also known as thiocystine; Cys-SSS-Cys), results in an increase in intracellular hydropersulfide levels (e.g., cysteine hydropersulfide; Cys-SSH, and glutathione hydropersulfide; GSSH). Thus, Cys-SSS-Cys represents a possible pharmacological agent for examining the effects of hydropersulfides on cell function/viability. It has also been found that cells with increased intracellular hydropersulfide levels can export Cys-SSH into the extracellular media. Interestingly, the Cys-SSH is the major hydropersulfide exported by cells, although GSSH is the predominant intracellular species. The possible implications of cellular export are discussed.

Replication fork progression is paused in two large chromosomal zones flanking the DNA replication origin in Escherichia coli.

Although the speed of nascent DNA synthesis at individual replication forks is relatively uniform in bacterial cells, the dynamics of replication fork progression on the chromosome are hampered by a variety of natural impediments. Genome replication dynamics can be directly measured from an exponentially growing cell population by sequencing newly synthesized DNA strands that were specifically pulse-labeled with the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU). However, a short pulse labeling with BrdU is impracticable for bacteria because of poor incorporation of BrdU into the cells, and thus, the genomewide dynamics of bacterial DNA replication remain undetermined. Using a new thymidine-requiring Escherichia coli strain, eCOMB, and high-throughput sequencing, we succeeded in determining the genomewide replication profile in bacterial cells. We also found that fork progression is paused in two ~200-kb chromosomal zones that flank the replication origin in the growing cells. This origin-proximal obstruction to fork progression was overcome by an increased thymidine concentration in the culture medium and enhanced by inhibition of transcription. These indicate that DNA replication near the origin is sensitive to the impediments to fork progression, namely a scarcity of the DNA precursor deoxythymidine triphosphate and probable conflicts between replication and transcription machineries.

The Capture of Cadmium by Reactive Polysulfides Attenuates Cadmium-Induced Adaptive Responses and Hepatotoxicity.

Cadmium (Cd) is an environmental electrophile that modifies protein nucleophiles, thereby modulating cellular signaling and toxicity. While reactive persulfides/polysulfides exhibit relatively high nucleophilic properties, their roles in the altered gene expression and toxicity caused by Cd remain unclear. Exposing primary mouse hepatocytes to Cd caused heat shock protein 70 (HSP70) and metallothionein (MT)-I/II to be upregulated and cytotoxicity to occur. These effects were blocked in the presence of polysulfide sodium tetrasulfide (Na2S4). Electrospray ionization mass spectrometry analysis indicated that cadmium sulfide (CdS) and cadmium thiosulfate (CdS2O3) were produced when Cd reacted with Na2S4. Authentic CdS did not cause cellular signaling responses to be activated or hepatotoxic effects, while CdS2O3 had effects similar to those of Cd. HSP70 and MT-I/II upregulation and hepatotoxicity caused by exposure to Cd were significantly enhanced by the deletion of cystathionine γ-lyase (CSE), which catalyzes the formation of reactive persulfides/polysulfides. Deleting CSE also exacerbated Cd-mediated liver injury, whereas little hepatic damage was found when CdS or Na2S4 along with Cd was administered. Overall, the results suggest that the persulfide/polysulfide-mediated formation of sulfur adducts of Cd such as CdS rather than CdS2O3 is, at least in part, involved in decreasing the level of Cd-mediated activation of cellular signaling and toxicity.

Recombinase and translesion DNA polymerase decrease the speed of replication fork progression during the DNA damage response in Escherichia coli cells.

The SOS response is a DNA damage response pathway that serves as a general safeguard of genome integrity in bacteria. Extensive studies of the SOS response in Escherichia coli have contributed to establishing the key concepts of cellular responses to DNA damage. However, how the SOS response impacts on the dynamics of DNA replication fork movement remains unknown. We found that inducing the SOS response decreases the mean speed of individual replication forks by 30-50% in E. coli cells, leading to a 20-30% reduction in overall DNA synthesis. dinB and recA belong to a group of genes that are upregulated during the SOS response, and encode the highly conserved proteins DinB (also known as DNA polymerase IV) and RecA, which, respectively, specializes in translesion DNA synthesis and functions as the central recombination protein. Both genes were independently responsible for the SOS-dependent slowdown of replication fork progression. Furthermore, fork speed was reduced when each gene was ectopically expressed in SOS-uninduced cells to the levels at which they are expressed in SOS-induced cells. These results clearly indicate that the increased expression of dinB and recA performs a novel role in restraining the progression of an unperturbed replication fork during the SOS response.

DNA polymerase IV mediates efficient and quick recovery of replication forks stalled at N2-dG adducts.

Escherichia coli DNA polymerase IV (Pol IV, also known as DinB) is a Y-family DNA polymerase capable of catalyzing translesion DNA synthesis (TLS) on certain DNA lesions, and accumulating data suggest that Pol IV may play an important role in copying various kinds of spontaneous DNA damage including N(2)-dG adducts and alkylated bases. Pol IV has a unique ability to coexist with Pol III on the same ß clamp and to positively dissociate Pol III from ß clamp in a concentration-dependent manner. Reconstituting the entire process of TLS in vitro using E. coli replication machinery and Pol IV, we observed that a replication fork stalled at (-)-trans-anti-benzo[a]pyrene-N(2)-dG lesion on the leading strand was efficiently and quickly recovered via two sequential switches from Pol III to Pol IV and back to Pol III. Our results suggest that TLS by Pol IV smoothes the way for the replication fork with minimal interruption.

A single-molecule approach to DNA replication in Escherichia coli cells demonstrated that DNA polymerase III is a major determinant of fork speed.

The replisome catalyses DNA synthesis at a DNA replication fork. The molecular behaviour of the individual replisomes, and therefore the dynamics of replication fork movements, in growing Escherichia coli cells remains unknown. DNA combing enables a single-molecule approach to measuring the speed of replication fork progression in cells pulse-labelled with thymidine analogues. We constructed a new thymidine-requiring strain, eCOMB (E. coli for combing), that rapidly and sufficiently incorporates the analogues into newly synthesized DNA chains for the DNA-combing method. In combing experiments with eCOMB, we found the speed of most replication forks in the cells to be within the narrow range of 550-750 nt s(-1) and the average speed to be 653 ± 9 nt s(-1) (± SEM). We also found the average speed of the replication fork to be only 264 ± 9 nt s(-1) in a dnaE173-eCOMB strain producing a mutant-type of the replicative DNA polymerase III (Pol III) with a chain elongation rate (300 nt s(-1) ) much lower than that of the wild-type Pol III (900 nt s(-1) ). This indicates that the speed of chain elongation by Pol III is a major determinant of replication fork speed in E. coli cells.

Interaction between Escherichia coli DNA polymerase IV and single-stranded DNA-binding protein is required for DNA synthesis on SSB-coated DNA.

DNA polymerase IV (Pol IV) is one of three translesion polymerases in Escherichia coli. A mass spectrometry study revealed that single-stranded DNA-binding protein (SSB) in lysates prepared from exponentially-growing cells has a strong affinity for column-immobilized Pol IV. We found that purified SSB binds directly to Pol IV in a pull-down assay, whereas SSBΔC8, a mutant protein lacking the C-terminal tail, failed to interact with Pol IV. These results show that the interaction between Pol IV and SSB is mediated by the C-terminal tail of SSB. When polymerase activity was tested on an SSBΔC8-coated template, we observed a strong inhibition of Pol IV activity. Competition experiments using a synthetic peptide containing the amino acid sequence of SSB tail revealed that the chain-elongating capacity of Pol IV was greatly impaired when the interaction between Pol IV and SSB tail was inhibited. These results demonstrate that Pol IV requires the interaction with the C-terminal tail of SSB to replicate DNA efficiently when the template ssDNA is covered with SSB. We speculate that at the primer/template junction, Pol IV interacts with the tail of the nearest SSB tetramer on the template, and that this interaction allows the polymerase to travel along the template while disassembling SSB.

Clinical utility of anti-Ro52 antibody confirmation in anti-MDA5 antibody-positive dermatomyositis: A case report.

This case report highlights dermatomyositis (DM) characterised by the concurrent presence of anti-melanoma differentiation-associated protein 5 (anti-MDA5) and anti-Ro52 antibodies. A 64-year-old woman initially presented with erythema on the palms, which later spread to the dorsum of the hands, followed by involvement of the face, forehead, and upper eyelids. The patient reported joint pain, fatigue, and dyspnea. Physical examination revealed characteristic cutaneous manifestations, including heliotrope rash and Gottron's sign, accompanied by skin ulceration and muscle weakness. Blood tests showed elevated levels of creatine phosphokinase and C-reactive protein. A high-resolution computed tomography (HRCT) scan revealed interstitial lung disease (ILD) with an organising pneumonia (OP) pattern. Magnetic resonance imaging (MRI) confirmed the presence of myositis. Autoantibody analysis revealed concurrent positivity for both anti-MDA5 and anti-Ro52 antibodies. At the time of diagnosis, she had no respiratory impairment, but had an elevated C-reactive protein and high levels of anti-MDA5 antibody. She was started on triple combination therapy with glucocorticoids, cyclophosphamide, and tacrolimus. She had worsening oxygenation and elevated ferritin during the first weeks of treatment, but then her symptoms improved. Early detection of a co-positive anti-Ro52 antibody led to early initiation of triple combination therapy and a good prognosis.

[Supersulfides to Regulate Electrophilic Stress].

Environmental electrophiles modify thiol groups of proteins in organs, disrupting cellular functions carried out by the modified proteins and increasing the risk of various diseases. The transcription factor NF-E2-related factor 2 (Nrf2) plays a crucial role in detoxifying electrophiles by forming glutathione adducts and subsequently excreting them into extracellular spaces. Supersulfides such as cysteine persulfides (CysSSH) produced by cystathionine γ-lyase (CSE) capture environmental electrophiles through sulfur adduct formation. However, the Nrf2 and CSE contributions to blocking environmental electrophile-mediated toxicity have yet to be evaluated. Therefore, we assessed the individual and combined roles of Nrf2 and CSE in suppressing toxicity induced by environmental electrophiles using Nrf2 knockout (KO), CSE KO, and Nrf2/CSE double KO (DKO) mice. Our findings indicate that CSE/Nrf2 DKO mice are more sensitive to environmental electrophiles compared to their single KO counterparts, highlighting the distinct mechanisms through which both pathways mitigate the toxic effects of reactive electrophiles. Moreover, diverse metabolites produced by symbiotic gut bacteria in the human body are known to exert various effects on host organ functions beyond the intestinal tract. We observed reduced blood supersulfide levels in mice lacking gut microflora compared to normal mice. Furthermore, we identified intestinal bacteria belonging to the families Ruminococcaceae and Lachnospiraceae as high CysSSH-producing bacteria. This suggests that the gut microbiota serves as a source of in vivo supersulfide molecules. These findings suggest that supersulfide derived from gut bacteria may act protectively against environmental electrophilic exposure in the host.

Multi-defense Pathways against Electrophiles through Adduct Formation by Low Molecular Weight Substances with Sulfur Atoms.

There is a variety of electrophiles in the environment. In addition, there are precursor chemicals that undergo metabolic activation by enzymes and conversion to electrophiles in the body. Although electrophiles covalently bind to protein nucleophiles, they also form adducts associated with adaptive or toxic responses. Low molecular weight compounds containing sulfur are capable of blocking such adduct formation by capturing the electrophiles. In this review, we present out findings on the capture and inactivation of electrophiles by 1) intracellular glutathione, 2) reactive sulfur species and 3) extracellular cysteine (formed during the production of sulfur adducts). These actions not only substantially suppress electrophilic activity but also regulate protein adduct formation.

Extracellularly secreted cysteine derived from cystine regulates oxidative and electrophilic stress in HepG2 cells.

While cysteine (CysSH) is known to be exported into the extracellular space, its biological significance is not well understood. The present study examined the movement of extracellular CysSH using stable isotope-labeled cystine (CysSSCys), which is transported into cells and reduced to CysSH. Exposure of HepG2 cells to 100 µM stable isotope-labeled CysSSCys resulted in 70 µM labeled CysSH in cell medium 1 h after CysSSCys exposure. When the cell medium was collected and incubated with either hydrogen peroxide (H2O2) or atmospheric electrophiles, such as 1,2-naphthoquinone, 1,4-naphthoquinone and 1,4-benzoquinone, CysSH in the cell medium was almost completely consumed. In contrast, extracellular levels of CysSH were unaltered during exposure of HepG2 cells to H2O2 for up to 2 h, suggesting redox cycling of CysSSCys/CysSH in the cell system. Experiments with and without changing cell medium containing CysSH from HepG2 cells revealed that oxidative and electrophilic modifications of cellular proteins, caused by exposure to H2O2 and 1,2-naphthoquinone, were significantly repressed by CysSH in the medium. We also examined participation of enzymes and/or antioxidants in intracellular reduction of CysSSCys to CysSH. These results provide new findings that extracellular CysSH derived from CysSSCys plays a role in the regulation of oxidative and electrophilic stress.

Hydrogen gas and the gut microbiota are potential biomarkers for the development of experimental colitis in mice.

Inflammatory bowel disease (IBD) is a chronic disease characterised by repeated relapses and remissions and a high recurrence rate even after symptom resolution. The primary method for IBD diagnosis is endoscopy; however, this method is expensive, invasive, and cumbersome to use serially. Therefore, more convenient and non-invasive methods for IBD diagnosis are needed. In this study, we aimed to identify biological gas markers for the development of gut inflammation. Using dextran sulphate sodium (DSS)-induced colitis mouse models, five biological gases were analysed to identify predictive markers for the development of gut inflammation. Additionally, the correlation between the changes in gas composition, gut microbiota, and inflammatory markers was assessed. The hydrogen (H2) level was found to be negatively correlated with the level of lipocalin-2 (LCN2), a gut inflammation biomarker, and weight loss due to DSS-induced colitis. Furthermore, gut microbes belonging to the Rikenellaceae and Akkermansiaceae families were positively correlated with LCN2 levels and weight loss, whereas Tannerellaceae abundance was negatively correlated with LCN2 level and weight loss and positively correlated with H2 levels. This study provides new insights for IBD diagnosis; the H2 levels in biological gases are a potential biomarker for intestinal inflammation, and specific gut microbes are associated with H2 level changes.

SCIATIC DENERVATION-INDUCED SKELETAL MUSCLE ATROPHY IS ASSOCIATED WITH PERSISTENT INFLAMMATION AND INCREASED MORTALITY DURING SEPSIS.

ABSTRACT: Background: Patients with underlying skeletal muscle atrophy are likely to develop aggravated sepsis. However, no study has experimentally verified the association between the prognosis of sepsis and muscle atrophy, and the mechanism of aggravation of sepsis under muscle atrophy remains unclear. In this study, we investigated the effect of skeletal muscle atrophy induced by sciatic denervation (DN), an experimental muscle atrophy model, on sepsis prognosis. Methods: Skeletal muscle atrophy was induced by DN of the sciatic nerve in C57BL/6J male mice. Cecal ligation and puncture (CLP) was performed to induce sepsis. Results: The survival rates of the sham and DN groups 7 days after CLP were 63% and 35%, respectively, wherein an approximately 30% reduction was observed in the DN group ( P < 0.05, vs. sham-CLP). The DN group had a higher bacterial count in the blood 48 h after CLP ( P < 0.05, vs. sham-CLP). Notably, NOx (a metabolite of nitric oxide) concentrations in DN mice were higher than those in sham mice after CLP ( P < 0.05, vs. sham-CLP), whereas serum platelet levels were lower 48 h after CLP ( P < 0.05, vs. sham-CLP). In organ damage analysis, DN mice presented increased protein expression of the kidney injury molecule (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL), a kidney injury marker, after CLP (NGAL 48 h after CLP, P < 0.05, vs. sham-CLP; KIM-1 24 h after CLP, P < 0.01, vs. sham-CLP). Furthermore, nitro tyrosine levels in the kidneys of DN mice were higher 48 h after CLP compared with those in sham-CLP mice, indicating the accumulation of nitrative stress ( P < 0.05, vs. sham-CLP). Serum cytokine levels were increased in both groups after CLP, but decreased in the sham group 48 h after CLP and remained consistently higher in the DN group (tumor necrosis factor [TNF]-α: P < 0.05, sham-CLP vs. DN-CLP; interleukin (IL)-1ß: P < 0.01, sham-CLP vs. DN-CLP; IL-6: P < 0.05, DN vs. DN-CLP; IL-10: P < 0.05, sham-CLP vs. DN-CLP). Conclusions: We verified that skeletal muscle atrophy induced by DN is associated with poor prognosis after CLP-induced sepsis. Importantly, mice with skeletal muscle atrophy presented worsening sepsis prognosis at late onset, including prolonged infection, persistent inflammation, and kidney damage accumulation, resulting in delayed recovery.

Spatio-temporal distribution of reactive sulfur species during methylmercury exposure in the rat brain.

Brain susceptibility to methylmercury (MeHg) is developmentally and regionally specific in both humans and rodents, but the mechanism is not well clarified. Reactive sulfur species (RSS) with high nucleophilicity can react with MeHg, leading to the formation of a less toxic metabolite bismethylmercury sulfide, thus exerting cytoprotection. In this study, we assessed the variation of RSS content in the rat brain and evaluated its relevance in sensitivity to MeHg. Analyses of fetal/juvenile rat brains showed low RSS levels in early developmental stages. Site-specific analysis of adult rat brains revealed that cerebellar RSS levels were lower than those of the hippocampus. Microscopically, RSS levels of the granular cell layer were lower than those of the molecular layer in the cerebellum. Thus, low RSS levels corresponded with age and site of the brain that is vulnerable to MeHg. Taken together with the finding that brain RSS were consumed during MeHg exposure, these results indicate that RSS is a factor that defines the specificity of MeHg vulnerability in the brain.

Potentiation of methylmercury toxicity by combined metal exposure: In vitro and in vivo models of a restricted metal exposome.

Methylmercury (MeHg) is a prevalent toxic metal that readily modifies protein thiols. Reactive persulfides that play a role in redox homeostasis are able to inactivate this metal through sulfur adduct formation. Although humans are exposed to other metals that could consume reactive persulfides on a daily basis, the health effects of combined exposure to MeHg and other metals remain unexplored. This study aimed to examine potential MeHg toxicity during exposure to MeHg with other metals capable of consuming reactive persulfides. We designed a simple system to assess the risk of combined exposure to metals based on reactivity to reactive persulfides and mercury accumulation. Among the metals examined in a cell-free system, copper, cadmium, nickel, and MeHg consumed Na2S2, used as a model of reactive persulfides, whereas zinc, iron, lithium, strontium, tin, and aluminum did not. In HepG2 cells, binary exposure to MeHg and copper, but not aluminum, increased the consumption of extracellular reactive persulfides. Binary exposure exacerbated MeHg-induced cytotoxicity by promoting the modification of intracellular proteins by MeHg. In a mouse model, binary exposure to MeHg and copper resulted in elevated mercury accumulation in the fetuses and placenta of pregnant mice, as well as the brain and liver of non-pregnant mice. Our study suggests that MeHg sensitivity can be increased by combined exposure with other electrophilic metals. In particular, binary exposure to MeHg and copper during pregnancy exacerbated mercury accumulation in offspring.

Gut microbiota reinforce host antioxidant capacity via the generation of reactive sulfur species.

Gut microbiota act beyond the gastrointestinal tract to regulate the physiology of the host. However, their contribution to the antioxidant capacity of the host remains largely understudied. In this study, we observe that gut bacteria increase the steady-state plasma levels of high-antioxidant molecules, reactive sulfur species (RSS), such as hydrogen sulfide and cysteine persulfide (CysSSH), in the host. Moreover, gut bacteria utilize cystine as a substrate to enzymatically produce CysSSH. Administration of cystine to mice increases their plasma levels of RSS and suppresses the concanavalin-A-induced oxidative stress and liver damage in a gut-microbiota-dependent manner. We find that gut bacteria belonging to the Lachnospiraceae and Ruminococcaceae families have a high capacity to produce RSS, requiring pyridoxal 5'-phosphate for their enzymatic reactions. Collectively, our data demonstrate that gut microbiota enhance the antioxidant capacity of the host through the generation of RSS.