Host/microbiota interactions-derived tryptophan metabolites modulate oxidative stress and inflammation via aryl hydrocarbon receptor signaling

Wogonin improves colitis by activating the AhR pathway to regulate the plasticity of ILC3/ILC1

BACKGROUND

Intestinal barrier dysfunction caused by the disrupted balance of group 3 innate lymphoid cells (ILC3)/group 1 innate lymphoid cells (ILC1) is a significant feature in the pathogenesis of inflammatory bowel disease (IBD). Activation of aryl hydrocarbon receptor (AhR) signaling contributes to the maintenance of ILC3/ILC1 balance. Wogonin, a natural flavonoid from Scutellaria baicalensis Georgi, can repair intestinal mucosal damage of IBD. However, it remains unclear if wogonin can exert a therapeutic effect by activating the AhR pathway to regulate the plasticity of ILC3/ILC1.

PURPOSE

In this study, we investigated the immunomodulatory effects of wogonin on IBD and its potential mechanisms in vitro and in vivo.

STUDY DESIGN AND METHODS

Chronic colitis was induced by four cycles of 2 % DSS treatment in mice. 20 mg kg-1/day wogonin was administrated by oral gavage and mice were treated intraperitoneally with 10 mg kg-1/2 days CH223191 to block the AhR pathway. Colon tissues were processed for histopathological examination and evaluation of the epithelial barrier function by immunohistochemistry. The activation of the AhR pathway and the plasticity of ILC3/ILC1 were determined by western blot and flow cytometry. Then, we also detected the intestinal microflora and their metabolites by 16 s sequencing and non-targeted Metabolomics analysis. Furthermore, an in vitro culture system consisting of MNK3 cells and NCM460 cells, and a CETSA assay were performed to confirm the molecular mechanism.

RESULTS

Wogonin ameliorated histological severity of the colon, decreased the secretion of inflammatory factors, and increased tight junction proteins in colitis mice. These effects are associated with the tendency of conversion from ILC3 to ILC1 prevented by wogonin, which was offset by AhR antagonist CH223191. In addition, wogonin exerted the curative effect by altering gut microbiota to produce metabolites such as Kynurenic acid, and 1H-Indole-3-carboxaldehyde as AhR endogenous ligands. In vitro data further verified that wogonin as an exogenous ligand directly binds to the structural domain of AhR by CETSA. Also, the supernatant of MNK-3 cells stimulated with wogonin enhanced expression of Occludin and Claudin1 in NCM460 cells induced by LPS.

CONCLUSION

Cumulatively, our study illustrated that wogonin improved the outcomes of DSS-induced chronic colitis via regulating the plasticity of ILC3/ILC1. Its specific mechanism is to binding to AhR directly, and to activate the AhR pathway indirectly by altering the tryptophan metabolisms of gut microbiota.

Redox organization of living systems

Redox organization governs an underlying simplicity in living systems. Critically, redox reactions enable the essential characteristics of life: extraction of energy from the environment, use of energy to support metabolic and structural organization, use of dynamic redox responses to defend against environmental threats, and use of redox mechanisms to direct differentiation of cells and organ systems essential for reproduction. These processes are sustained through a redox context in which electron donor/acceptor couples are poised at substantially different steady-state redox potentials, some with relatively reducing steady states and others with relatively oxidizing steady states. Redox-sensitive thiols of the redox proteome, as well as low molecular weight redox-active molecules, are maintained individually by the kinetics of oxidation-reduction within this redox system. Recent research has revealed opposing network interactions of the metallome, redox proteome, metabolome and transcriptome, which appear to be an evolved redox response structure to maintain stability of an organism in the presence of variable oxidative environments. Considerable opportunity exists to improve human health through detailed understanding of these redox networks so that targeted interventions can be developed to support new avenues for redox medicine.

Metabolomics perspectives into the co-exposure effect of polycyclic aromatic hydrocarbons and metals on renal function: A meet-in-the-middle approach

Studies on the dose effects of kidney impairment and metabolomes in co-exposure to polycyclic aromatic hydrocarbons (PAHs) and metals are limited. We aimed to identify overall associations and metabolic perturbations in 130 participants (53 petrochemical workers and 77 controls) exposed to a PAHs-metals mixture in Southern China. The urinary 7 hydroxylated PAHs and 15 metal(loid)s were determined, and serum creatinine, beta-2 microglobulin, and estimated glomerular filtration rate were health outcomes. The liquid chromatography-mass spectrometry-based method was applied to serum metabolomics. Generalized weighted quantile sum (gWQS) regressions were used to estimate the overall dose-response relationships, and pathway analysis, "meet-in-the-middle" approach, and mediation effect analyses were conducted to identify potential metabolites and biological mechanisms linking exposure with nephrotoxic effects. Our results indicated that renal function reduction was associated with a PAHs-metals mixture in a dose-dependent manner, and 1-hydroxynaphthalene and copper were the most predominant contributors among the two families of pollutants. Furthermore, the metabolic disruptions associated with the early onset of kidney impairment induced by the combination of PAHs and metals encompassed pathways such as phenylalanine-tyrosine-tryptophan biosynthesis, phenylalanine metabolism, and alpha-linolenic acid metabolism. In addition, the specifically identified metabolites demonstrated excellent potential as bridging biomarkers connecting the reduction in renal function with the mixture of PAHs and metals. These findings shed light on understanding the overall associations and metabolic mechanism of nephrotoxic effects of co-exposure to PAHs and metals.

Positive modulation of a new reconstructed human gut microbiota by Maitake extract helpfully boosts the intestinal environment in vitro

The human gut is a complex environment where the microbiota and its metabolites play a crucial role in the maintenance of a healthy state. The aim of the present work is the reconstruction of a new in vitro minimal human gut microbiota resembling the microbe-microbe networking comprising the principal phyla (Bacillota, Bacteroidota, Pseudomonadota, and Actinomycetota), to comprehend the intestinal ecosystem complexity. In the reductionist model, we mimicked the administration of Maitake extract as prebiotic and a probiotic formulation (three strains belonging to Lactobacillus and Bifidobacterium genera), evaluating the modulation of strain levels, the release of beneficial metabolites, and their health-promoting effects on human cell lines of the intestinal environment. The administration of Maitake and the selected probiotic strains generated a positive modulation of the in vitro bacterial community by qPCR analyses, evidencing the prominence of beneficial strains (Lactiplantibacillus plantarum and Bifidobacterium animalis subsp. lactis) after 48 hours. The bacterial community growths were associated with the production of metabolites over time through GC-MSD analyses such as lactate, butyrate, and propionate. Their effects on the host were evaluated on cell lines of the intestinal epithelium and the immune system, evidencing positive antioxidant (upregulation of SOD1 and NQO1 genes in HT-29 cell line) and anti-inflammatory effects (production of IL-10 from all the PBMCs). Therefore, the results highlighted a positive modulation induced by the synergic activities of probiotics and Maitake, inducing a tolerogenic microenvironment.

Intestinal Mucosal Immune Barrier: A Powerful Firewall Against Severe Acute Pancreatitis-Associated Acute Lung Injury via the Gut-Lung Axis

The pathogenesis of severe acute pancreatitis-associated acute lung injury (SAP-ALI), which is the leading cause of mortality among hospitalized patients in the intensive care unit, remains incompletely elucidated. The intestinal mucosal immune barrier is a crucial component of the intestinal epithelial barrier, and its aberrant activation contributes to the induction of sustained pro-inflammatory immune responses, paradoxical intercellular communication, and bacterial translocation. In this review, we firstly provide a comprehensive overview of the composition of the intestinal mucosal immune barrier and its pivotal roles in the pathogenesis of SAP-ALI. Secondly, the mechanisms of its crosstalk with gut microbiota, which is called gut-lung axis, and its effect on SAP-ALI were summarized. Finally, a number of drugs that could enhance the intestinal mucosal immune barrier and exhibit potential anti-SAP-ALI activities were presented, including probiotics, glutamine, enteral nutrition, and traditional Chinese medicine (TCM). The aim is to offer a theoretical framework based on the perspective of the intestinal mucosal immune barrier to protect against SAP-ALI.

Current updates on metabolites and its interlinked pathways as biomarkers for diabetic kidney disease: A systematic review

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes mellitus (DM) that poses a serious risk as it can lead to end-stage renal disease (ESRD). DKD is linked to changes in the diversity, composition, and functionality of the microbiota present in the gastrointestinal tract. The interplay between the gut microbiota and the host organism is primarily facilitated by metabolites generated by microbial metabolic processes from both dietary substrates and endogenous host compounds. The production of numerous metabolites by the gut microbiota is a crucial factor in the pathogenesis of DKD. However, a comprehensive understanding of the precise mechanisms by which gut microbiota and its metabolites contribute to the onset and progression of DKD remains incomplete. This review will provide a summary of the current scenario of metabolites in DKD and the impact of these metabolites on DKD progression. We will discuss in detail the primary and gut-derived metabolites in DKD, and the mechanisms of the metabolites involved in DKD progression. Further, we will address the importance of metabolomics in helping identify potential DKD markers. Furthermore, the possible therapeutic interventions and research gaps will be highlighted.

The role of aryl hydrocarbon receptor in vitiligo: a review

Vitiligo is an acquired autoimmune dermatosis characterized by patchy skin depigmentation, causing significant psychological distress to the patients. Genetic susceptibility, environmental triggers, oxidative stress, and autoimmunity contribute to melanocyte destruction in vitiligo. Due to the diversity and complexity of pathogenesis, the combination of inhibiting melanocyte destruction and stimulating melanogenesis gives the best results in treating vitiligo. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that can regulate the expression of various downstream genes and play roles in cell differentiation, immune response, and physiological homeostasis maintenance. Recent studies suggested that AhR signaling pathway was downregulated in vitiligo. Activation of AhR pathway helps to activate antioxidant pathways, inhibit abnormal immunity response, and upregulate the melanogenesis gene, thereby protecting melanocytes from oxidative stress damage, controlling disease progression, and promoting lesion repigmentation. Here, we review the relevant literature and summarize the possible roles of the AhR signaling pathway in vitiligo pathogenesis and treatment, to further understand the links between the AhR and vitiligo, and provide new potential therapeutic strategies.

The nuclear factor kappa B signaling pathway is a master regulator of renal fibrosis

Renal fibrosis is increasingly recognized as a global public health problem. Acute kidney injury (AKI) and chronic kidney disease (CKD) both result in renal fibrosis. Oxidative stress and inflammation play central roles in progressive renal fibrosis. Oxidative stress and inflammation are closely linked and form a vicious cycle in which oxidative stress induces inflammation through various molecular mechanisms. Ample evidence has indicated that a hyperactive nuclear factor kappa B (NF-ƙB) signaling pathway plays a pivotal role in renal fibrosis. Hyperactive NF-ƙB causes the activation and recruitment of immune cells. Inflammation, in turn, triggers oxidative stress through the production of reactive oxygen species and nitrogen species by activating leukocytes and resident cells. These events mediate organ injury through apoptosis, necrosis, and fibrosis. Therefore, developing a strategy to target the NF-ƙB signaling pathway is important for the effective treatment of renal fibrosis. This Review summarizes the effect of the NF-ƙB signaling pathway on renal fibrosis in the context of AKI and CKD (immunoglobulin A nephropathy, membranous nephropathy, diabetic nephropathy, hypertensive nephropathy, and kidney transplantation). Therapies targeting the NF-ƙB signaling pathway, including natural products, are also discussed. In addition, NF-ƙB-dependent non-coding RNAs are involved in renal inflammation and fibrosis and are crucial targets in the development of effective treatments for kidney disease. This Review provides a clear pathophysiological rationale and specific concept-driven therapeutic strategy for the treatment of renal fibrosis by targeting the NF-ƙB signaling pathway.

The Role of Tryptophan Metabolism in the Occurrence and Progression of Acute and Chronic Kidney Diseases

Acute kidney injury (AKI) and chronic kidney disease (CKD) are common kidney diseases in clinics with high morbidity and mortality, but their pathogenesis is intricate. Tryptophan (Trp) is a fundamental amino acid for humans, and its metabolism produces various bioactive substances involved in the pathophysiology of AKI and CKD. Metabolomic studies manifest that Trp metabolites like kynurenine (KYN), 5-hydroxyindoleacetic acid (5-HIAA), and indoxyl sulfate (IS) increase in AKI or CKD and act as biomarkers that facilitate the early identification of diseases. Meanwhile, KYN and IS act as ligands to exacerbate kidney damage by activating aryl hydrocarbon receptor (AhR) signal transduction. The reduction of renal function can cause the accumulation of Trp metabolites which in turn accelerate the progression of AKI or CKD. Besides, gut dysbiosis induces the expansion of Enterobacteriaceae family to produce excessive IS, which cannot be excreted due to the deterioration of renal function. The application of Trp metabolism as a target in AKI and CKD will also be elaborated. Thus, this study aims to elucidate Trp metabolism in the development of AKI and CKD, and explores the relative treatment strategies by targeting Trp from the perspective of metabolomics to provide a reference for their diagnosis and prevention.

Melatonin and Its Metabolites Can Serve as Agonists on the Aryl Hydrocarbon Receptor and Peroxisome Proliferator-Activated Receptor Gamma

Melatonin is widely present in Nature. It has pleiotropic activities, in part mediated by interactions with high-affinity G-protein-coupled melatonin type 1 and 2 (MT1 and MT2) receptors or under extreme conditions, e.g., ischemia/reperfusion. In pharmacological concentrations, it is given to counteract the massive damage caused by MT1- and MT2-independent mechanisms. The aryl hydrocarbon receptor (AhR) is a perfect candidate for mediating the latter effects because melatonin has structural similarity to its natural ligands, including tryptophan metabolites and indolic compounds. Using a cell-based Human AhR Reporter Assay System, we demonstrated that melatonin and its indolic and kynuric metabolites act as agonists on the AhR with EC50's between 10-4 and 10-6 M. This was further validated via the stimulation of the transcriptional activation of the CYP1A1 promoter. Furthermore, melatonin and its metabolites stimulated AhR translocation from the cytoplasm to the nucleus in human keratinocytes, as demonstrated by ImageStream II cytometry and Western blot (WB) analyses of cytoplasmic and nuclear fractions of human keratinocytes. These functional analyses are supported by in silico analyses. We also investigated the peroxisome proliferator-activated receptor (PPAR)γ as a potential target for melatonin and metabolites bioregulation. The binding studies using a TR-TFRET kit to assay the interaction of the ligand with the ligand-binding domain (LBD) of the PPARγ showed agonistic activities of melatonin, 6-hydroxymelatonin and N-acetyl-N-formyl-5-methoxykynuramine with EC50's in the 10-4 M range showing significantly lower affinities that those of rosiglitazone, e.g., a 10-8 M range. These interactions were substantiated by stimulation of the luciferase activity of the construct containing PPARE by melatonin and its metabolites at 10-4 M. As confirmed by the functional assays, binding mode predictions using a homology model of the AhR and a crystal structure of the PPARγ suggest that melatonin and its metabolites, including 6-hydroxymelatonin, 5-methoxytryptamine and N-acetyl-N-formyl-5-methoxykynuramine, are excellent candidates to act on the AhR and PPARγ with docking scores comparable to their corresponding natural ligands. Melatonin and its metabolites were modeled into the same ligand-binding pockets (LBDs) as their natural ligands. Thus, functional assays supported by molecular modeling have shown that melatonin and its indolic and kynuric metabolites can act as agonists on the AhR and they can interact with the PPARγ at high concentrations. This provides a mechanistic explanation for previously reported cytoprotective actions of melatonin and its metabolites that require high local concentrations of the ligands to reduce cellular damage under elevated oxidative stress conditions. It also identifies these compounds as therapeutic agents to be used at pharmacological doses in the prevention or therapy of skin diseases.

Oxidative stress and inflammation are mediated via aryl hydrocarbon receptor signalling in idiopathic membranous nephropathy

Membranous nephropathy (MN) patients are diagnosed by the presence of phospholipase A2 receptor (PLA2R) before they progress to renal failure. However, the subepithelium-like immunocomplex deposit-mediated downstream molecular pathways are poorly understood. The aryl hydrocarbon receptor (AHR), NF-ƙB and Nrf2 pathways play central roles in the pathogenesis and progression of chronic kidney disease. However, their mutual effects on MN require further examination. Thus, we investigated the effect of AHR signalling on the NF-ƙB and Nrf2 pathways in IMN patients, cationic bovine serum albumin (CBSA)-injected rats and zymosan activation serum (ZAS)-treated podocytes. IMN patients show significantly decreased serum total protein and albumin levels, increased urine protein levels and intrarenal IgG4 and PLA2R protein expression in glomeruli compared with controls. IMN patients exhibited increased mRNA expression of intrarenal AHR and its target genes, including CYP1A1, CYP1A2, CYP1B1 and COX-2. This increase was accompanied by significantly upregulated protein expression of CD3, NF-ƙB p65 and COX-2 and significantly downregulated Nrf2 and HO-1 expression. Similarly, CBSA-induced rats showed severe proteinuria and activated intrarenal AHR signalling. This was accompanied by significantly upregulated protein expression of intrarenal p-IκBα, NF-κB p65 and its gene products, including COX-2, MCP-1, iNOS, 12-LOX, p47phox and p67phox, and significantly downregulated protein expression of Nrf2 and its gene products, including HO-1, catalase, GCLC, GCLM, MnSOD and NQO1. These results were further verified in ZAS-induced podocytes. Treatment with the AHR antagonist CH223191 and AHRsiRNA significantly preserved podocyte-specific protein expression and improved the NF-ƙB and Nrf2 pathways in ZAS-induced podocytes. In contrast, similar results were obtained in ZAS-induced podocytes treated with the NF-ƙB inhibitor BAY 11-7082 and NF-κBp65 siRNA. However, neither method had a significant effect on AHR signalling. Collectively, these results indicate that the NF-ƙB pathway is a downstream target of AHR signalling. Our findings suggest that blocking AHR signalling inhibits oxidative stress and inflammation, thereby improving proteinuria and renal injury.

Fuzhuan brick tea ameliorates hepatic steatosis and steatohepatitis through gut microbiota-derived aryl hydrocarbon receptor ligands in high-fat diet-induced obese mice

High-fat diet (HFD) induced obesity and its associated conditions, such as hepatic steatosis and steatohepatitis, are major health concerns worldwide. Previous studies have reported the excellent efficiency of Fuzhuan brick tea (FBT) in attenuating HFD-induced obesity and metabolic disorders. In this study, we investigated the effects of FBT on hepatic steatosis and simple steatohepatitis in HFD-induced obese mice, as well as the metabolic function of the gut microbiome using metagenomics and metabolomics. The results showed that FBT ameliorated dyslipidemia, hepatic steatosis and steatohepatitis in HFD-induced obese mice by normalizing the gut microbiota structure and tryptophan metabolism. FBT increased the cecal abundance of aryl hydrocarbon receptor (AhR)-ligand producing bacteria such as Lactobacillus_reuteri and Lactobacillus_johnsonii, at the expense of AhR-ligand consuming bacteria, such as Faecalibaculum_rodentium and Escherichia_coli, and elevated the cecal contents of AhR-ligands such as IAA, IPA, and KYNA. Furthermore, FBT regulated the expressions of AhR and its targeted lipometabolic genes such as Pemt, Fasn, and SREBP-1c, as well as other inflammatory genes including TNF-α, IL-6, and IL-1β in the liver of mice. Overall, these findings highlight the beneficial effects of FBT on obesity-related hepatic steatosis and steatohepatitis via microbiota-derived AhR signaling.

The roles of gut microbiota and its metabolites in diabetic nephropathy

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes, which increases the risk of renal failure and causes a high global disease burden. Due to the lack of sustainable treatment, DN has become the primary cause of end-stage renal disease worldwide. Gut microbiota and its metabolites exert critical regulatory functions in maintaining host health and are associated with many pathogenesis of aging-related chronic diseases. Currently, the theory gut-kidney axis has opened a novel angle to understand the relationship between gut microbiota and multiple kidney diseases. In recent years, accumulating evidence has revealed that the gut microbiota and their metabolites play an essential role in the pathophysiologic processes of DN through the gut-kidney axis. In this review, we summarize the current investigations of gut microbiota and microbial metabolites involvement in the progression of DN, and further discuss the potential gut microbiota-targeted therapeutic approaches for DN.

Environmental Air Pollutants Affecting Skin Functions with Systemic Implications

The increase in air pollution worldwide represents an environmental risk factor that has global implications for the health of humans worldwide. The skin of billions of people is exposed to a mixture of harmful air pollutants, which can affect its physiology and are responsible for cutaneous damage. Some polycyclic aromatic hydrocarbons are photoreactive and could be activated by ultraviolet radiation (UVR). Therefore, such UVR exposure would enhance their deleterious effects on the skin. Air pollution also affects vitamin D synthesis by reducing UVB radiation, which is essential for the production of vitamin D3, tachysterol, and lumisterol derivatives. Ambient air pollutants, photopollution, blue-light pollution, and cigarette smoke compromise cutaneous structural integrity, can interact with human skin microbiota, and trigger or exacerbate a range of skin diseases through various mechanisms. Generally, air pollution elicits an oxidative stress response on the skin that can activate the inflammatory responses. The aryl hydrocarbon receptor (AhR) can act as a sensor for small molecules such as air pollutants and plays a crucial role in responses to (photo)pollution. On the other hand, targeting AhR/Nrf2 is emerging as a novel treatment option for air pollutants that induce or exacerbate inflammatory skin diseases. Therefore, AhR with downstream regulatory pathways would represent a crucial signaling system regulating the skin phenotype in a Yin and Yang fashion defined by the chemical nature of the activating factor and the cellular and tissue context.

Laminaria Japonica Polysaccharide Improved the Productivities and Systemic Health of Ducks by Mediating the Gut Microbiota and Metabolome

This study investigated the beneficial effects of a Laminaria japonica polysaccharide (LJPS) on the systemic health of ducks by modulating the gut microbiome and metabolome. Our findings demonstrated that the LJPS supplementation enhanced the overall growth performance and physiological immune and antioxidant index of ducks. In addition, the LJPS-fed group significantly increased abundances of intestinal Bacteroides and Prevotellaceae with decreased α-diversity than that in the control group. Among the total of 1840 intestinal metabolites, 186 metabolites were identified to be differentially regulated by LJPS feeding (upregulated 143 metabolites and downregulated 43 metabolites), which is closely associated with some of the growth-related metabolic pathways. Lastly, the correlation analysis recapitulates that the beneficial effects of LJPS underlie the alterations in intestinal microbiota and metabolites. Taken together, LJPS supplementation improved the physiological parameters and richness of some beneficial microbes and upregulated certain metabolic pathways, which facilitated better productivities and systemic health of ducks.

Modulating AHR function offers exciting therapeutic potential in gut immunity and inflammation

Aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a classical exogenous synthetic ligand of AHR that has significant immunotoxic effects. Activation of AHR has beneficial effects on intestinal immune responses, but inactivation or overactivation of AHR can lead to intestinal immune dysregulation and even intestinal diseases. Sustained potent activation of AHR by TCDD results in impairment of the intestinal epithelial barrier. However, currently, AHR research has been more focused on elucidating physiologic AHR function than on dioxin toxicity. The appropriate level of AHR activation plays a role in maintaining gut health and protecting against intestinal inflammation. Therefore, AHR offers a crucial target to modulate intestinal immunity and inflammation. Herein, we summarize our current understanding of the relationship between AHR and intestinal immunity, the ways in which AHR affects intestinal immunity and inflammation, the effects of AHR activity on intestinal immunity and inflammation, and the effect of dietary habits on intestinal health through AHR. Finally, we discuss the therapeutic role of AHR in maintaining gut homeostasis and relieving inflammation.

Cryo-EM structure of the cytosolic AhR complex

Aryl hydrocarbon receptor (AhR) is an important ligand-activated transcription factor involved in the regulation of various important physiological functions. Here, we report the cryo-EM structures of the Hsp90-AhR-p23 complex with or without bound XAP2, where the structure of the mouse AhR PAS-B domain is resolved. A highly conserved bridge motif of AhR is responsible for the interaction with the Hsp90 dimeric lumen. The ligand-free AhR PAS-B domain is attached to the Hsp90 dimer and is stabilized in the complex with bound XAP2. In addition, the DE-loop and a group of conserved pocket inner residues in the AhR PAS-B domain are found to be important for ligand binding. These results reveal the structural basis of the biological functions of AhR. Moreover, the protein purification method presented here allows the isolation of stable mouse AhR protein, which could be used to develop high-sensitivity biosensors for environmental pollutant detection.

Aryl hydrocarbon receptor dependent anti-inflammation and neuroprotective effects of tryptophan metabolites on retinal ischemia/reperfusion injury

Glaucoma is the major cause of irreversible blindness in the world characterized by progressive retinal neurodegeneration, in which local inflammation in retina is involved in persistent loss of retinal ganglion cells (RGCs). In order to explore whether aryl hydrocarbon receptor (AhR) and its agonists tryptophan metabolites are involved in the development of glaucoma, we collected serum and retinas from non-glaucoma controls and patients with glaucoma. Results showed altered serum tryptophan metabolism and reduced retinal AhR expression in glaucoma patients. We also showed intraperitoneally injection of tryptophan metabolite 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) down-regulated retinal local inflammation and protected RGC apoptosis from retinal ischemia/reperfusion (IR) injury via AhR activation. We further revealed that ITE could inhibit inflammation in BV2 microglia and alleviate the neurotoxicity of microglial conditioned medium to RGCs under IR. Finally, we illustrated the possible mechanism that ITE limited ERK and NFκB dependent microglial inflammation. In summary, these findings suggest the critical role of tryptophan metabolism and retinal AhR signaling in modulating local inflammation mediated by microglia in glaucoma, and provide a novel avenue to targeting the intrinsically altered AhR signaling resulted from disturbed tryptophan metabolism for glaucoma treatment.

Indole-3-propionic acid alleviates chondrocytes inflammation and osteoarthritis via the AhR/NF-κB axis

BACKGROUND

Osteoarthritis (OA) is a common chronic disease characterized by chronic inflammation and extracellular matrix degradation. Indole-3-propionic acid (IPA) is a tryptophan metabolite secreted by intestinal flora, which can exert anti-inflammatory effects in a variety of diseases. In this study, we further investigated the potential therapeutic role of IPA in OA and the underlying mechanism.

METHODS

IL-1β was utilized to induce chondrocyte inflammation. Then, the cytotoxicity of IPA on rat chondrocytes was assessed. Meanwhile, RT-qPCR, Griess reaction, ELISA, Western blot and immunofluorescence were performed to evaluate the expression of inflammatory factors and stromal proteins, and the NF-κB pathway in chondrocytes treated with IL-1β alone, with IPA or with aryl hydrocarbon receptor (AhR) knockdown. An OA rat model was established by anterior cruciate ligament transection, and hematoxylin-eosin staining, Safranin-O/Fast Green staining and immunochemistry were applied to estimate OA severity.

RESULTS

IPA did not affect cellular viability at concentrations up to 80 µM. IPA significantly inhibited the IL-1β-induced expression of inflammatory factors (Nitric oxide, PGE2, TNF-α, IL-6, iNOS and COX-2) and matrix-degrading enzymes (MMP-3, MMP-13 and ADAMTS-5), upregulated the expression of anabolic markers (aggrecan and collagen-II) and inactivated the NF-κB pathway. However, AhR knockdown could abolish the above protection capabilities and the suppression of the NF-κB pathway induced by IPA. Furthermore, IPA significantly reduced serum inflammatory cytokines expression, cartilage destruction and synovitis in vivo, demonstrating its protective role in OA progression.

CONCLUSION

IPA improved IL-1β-induced chondrocyte inflammation and extracellular matrix degradation through the AhR/NF-κB axis, which provides an innovative therapeutic strategy for OA.

Gut microbiota and its metabolites - molecular mechanisms and management strategies in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the major microvascular complications of diabetes mellitus and is also one of the serious risk factors in cardiovascular events, end-stage renal disease, and mortality. DKD is associated with the diversified, compositional, and functional alterations of gut microbiota. The interaction between gut microbiota and host is mainly achieved through metabolites, which are small molecules produced by microbial metabolism from exogenous dietary substrates and endogenous host compounds. The gut microbiota plays a critical role in the pathogenesis of DKD by producing multitudinous metabolites. Nevertheless, detailed mechanisms of gut microbiota and its metabolites involved in the occurrence and development of DKD have not been completely elucidated. This review summarizes the specific classes of gut microbiota-derived metabolites, aims to explore the molecular mechanisms of gut microbiota in DKD pathophysiology and progression, recognizes biomarkers for the screening, diagnosis, and prognosis of DKD, as well as provides novel therapeutic strategies for DKD.

Homeostatic regulation of the aryl hydrocarbon receptor-cytochrome P450 1a axis by Scutellaria baicalensis-Coptis chinensis herb pair and its main constituents

ETHNOPHARMACOLOGICAL RELEVANCE

Scutellaria baicalensis (SB) and Coptis chinensis (CC) are widely used traditional Chinese medicine (TCM) for "heat-clearing and damp-drying" and "purging fire and detoxifying". SB-CC are commonly used as a herbal pair for synergistic treatment of various diseases such as bacteria-related infections, metabolic syndromes, and some inflammatory disorders. This herbal pair is commonly used in many famous TCM formula, like Huang-Lian-Jie-Du, Gegen-Qinlian, Banxia Xiexin decoction. Aryl hydrocarbon receptor (AHR) plays an essential role in the disposition of both xenobiotics and endogenous substances through the induction of cytochrome P450 1A (CYP1A) enzymes. Regulation of the AHR-CYP1A axis is increasingly implicated in drug-drug and drug-herb interactions. Research on SB-CC for regulatory effect on the AHR-CYP1A axis is only limited to few compounds.

AIM OF THE STUDY

This study aimed to systematically investigate the regulatory effect of SB-CC and its main constitutes on the AHR-CYP1A axis in vitro and in vivo.

MATERIALS AND METHODS

The livers of mice treated with SB-CC extract were subjected to RNA-sequencing (RNA-seq). The key target genes related to drug metabolism were screened, and the differential expression genes (DEGs) were validated by qRT-PCR, Western blot, and enzyme activity assay. Luciferase reporter gene, qRT-PCR, and Western blot assays were used to determine whether SB-CC and their main constituents could activate AHR and regulate CYP1A expression in HepG2 cells. The effect of SB-CC on the pharmacokinetics of phenacetin, a CYP1A substrate, were further observed in mice to test the net effect of SB-CC on CYP1A functions. The potential CYP1A inhibitors in SB-CC were screened and their inhibitory mechanisms were also studied using human liver microsomes.

RESULTS

AHR and drug metabolism system, especially CYP1A1 and CYP1A2, were strongly affected in the liver of SB-CC-treated mice. These results were further validated by the findings that SB-CC increased CYP1A's mRNA, protein expression and activity in mouse liver. In HepG2 cells, SB, CC, baicalin, baicalein, chrysin, oroxylin A, berberine, coptisine and epiberberine increased CYP1A1 mRNA expression in an AHR-dependent way. Interestingly, SB-CC treatment for 14 days only slightly increased the systemic exposure of paracetamol in mice. In the CYP1A inhibition assay, SB, CC, baicalin, baicalein, wogonoside, wogonin, chrysin, oroxylin A, scutellarein, columbamine, coptisine, palmatine, epiberberine, and berberrubine inhibited CYP1A activity in different degree.

CONCLUSIONS

These results suggested that SB-CC exerted dual regulatory effect on the AHR-CYP1A axis by increasing CYP1A expression but simultaneously inhibiting CYP1A activity, which may contribute to a tight modulation of AHR signaling for homeostatic control.

Role of Micronutrients and Gut Microbiota-Derived Metabolites in COVID-19 Recovery

A balanced and varied diet provides diverse beneficial effects on health, such as adequate micronutrient availability and a gut microbiome in homeostasis. Besides their participation in biochemical processes as cofactors and coenzymes, vitamins and minerals have an immunoregulatory function; meanwhile, gut microbiota and its metabolites coordinate directly and indirectly the cell response through the interaction with the host receptors. Malnourishment is a crucial risk factor for several pathologies, and its involvement during the Coronavirus Disease 2019 pandemic has been reported. This pandemic has caused a significant decline in the worldwide population, especially those with chronic diseases, reduced physical activity, and elder age. Diet and gut microbiota composition are probable causes for this susceptibility, and its supplementation can play a role in reestablishing microbial homeostasis and improving immunity response against Coronavirus Disease 2019 infection and recovery. This study reviews the role of micronutrients and microbiomes in the risk of infection, the severity of disease, and the Coronavirus Disease 2019 sequelae.

Aryl hydrocarbon receptor: From pathogenesis to therapeutic targets in aging-related tissue fibrosis

Aging promotes chronic inflammation, which contributes to fibrosis and decreases organ function. Fibrosis, the excessive synthesis and deposition of extracellular matrix components, is the main cause of most chronic diseases including aging-related organ failure. Organ fibrosis in the heart, liver, and kidneys is the final manifestation of many chronic diseases. The aryl hydrocarbon receptor (AHR) is a cytoplasmic receptor and highly conserved transcription factor that is activated by a variety of small-molecule ligands to affect a wide array of tissue homeostasis functions. In recent years, mounting evidence has revealed that AHR plays an important role in multi-organ fibrosis initiation, progression, and therapy. In this review, we summarise the relationship between AHR and the pathogenesis of aging-related tissue fibrosis, and further discuss how AHR modulates tissue fibrosis by regulating transforming growth factor-β signalling, immune response, and mitochondrial function, which may offer novel targets for the prevention and treatment of this condition.