Quinolinic acid, a tryptophan metabolite of the skin microbiota, negatively regulates the NLRP3 inflammasome through the aryl hydrocarbon receptor in psoriasis

Atopic Dermatitis and Psoriasis: Similarities and Differences in Metabolism and Microbiome

Atopic dermatitis and psoriasis are common chronic inflammatory diseases of high incidence that share some clinical features, including symptoms of pruritus and pain, scaly lesions, and histologically, acanthosis and hyperkeratosis. Meanwhile, they are both commonly comorbid with metabolic disorders such as obesity and diabetes, indicating that both diseases may exist with significant metabolic disturbances. Metabolomics reveals that both atopic dermatitis and psoriasis have abnormalities in a variety of metabolites, including lipids, amino acids, and glucose. Meanwhile, recent studies have highlighted the importance of the microbiome and its metabolites in the pathogenesis of atopic dermatitis and psoriasis. Metabolic alterations and microbiome dysbiosis can also affect the immune, inflammatory, and epidermal barrier, thereby influencing the development of atopic dermatitis and psoriasis. Focusing on the metabolic and microbiome levels, this review is devoted to elaborating the similarities and differences between atopic dermatitis and psoriasis, thus providing insights into the intricate relationship between both conditions.

The role of adipokines in the pathogenesis of psoriasis - a focus on resistin, omentin-1 and vaspin

BACKGROUND

Psoriasis is a chronic immune-mediated skin condition with several types of manifestation, including psoriatic arthritis. In recent years, studies have demonstrated multiple molecules and mechanisms that play important roles in the pathophysiology of psoriasis. Studies have been conducted to determine the role of adipokines, bioactive peptides secreted by the adipose tissue, in the pathogenesis of inflammatory diseases. These studies have shown that adipokines are dysregulated in psoriasis and their abnormal expression profile could contribute to the inflammatory mechanisms observed in psoriasis.

AREAS COVERED

In this review, we discuss the immunomodulatory features of resistin, omentin-1, and vaspin, and discuss their potential involvement in the pathogenesis of psoriasis.

EXPERT OPINION

The adipokines resistin, omentin, and vaspin appear to be promising therapeutic targets in psoriasis. It is important to seek to block the action of resistin, either by blocking its receptors or by blocking its systemic effects with antibodies. In the case of omentin and vaspin, substances that are receptor mimetics of these adipokines should be sought and studies conducted of their analogues for the treatment of psoriasis. To introduce these therapies into clinical practice, multicentre clinical trials are required to confirm their efficacy and safety after initial studies in animal models.

Microbial metabolites affect tumor progression, immunity and therapy prediction by reshaping the tumor microenvironment (Review)

Several studies have indicated that the gut microbiome and tumor microbiota may affect tumors. Emerging metabolomics research illustrates the need to examine the variations in microbial metabolite composition between patients with cancer and healthy individuals. Microbial metabolites can impact the progression of tumors and the immune response by influencing a number of mechanisms, including modulation of the immune system, cancer or immune‑related signaling pathways, epigenetic modification of proteins and DNA damage. Microbial metabolites can also alleviate side effects and drug resistance during chemotherapy and immunotherapy, while effectively activating the immune system to exert tumor immunotherapy. Nevertheless, the impact of microbial metabolites on tumor immunity can be both beneficial and harmful, potentially influenced by the concentration of the metabolites or the specific cancer type. The present review summarizes the roles of various microbial metabolites in different solid tumors, alongside their influence on tumor immunity and treatment. Additionally, clinical trials evaluating the therapeutic effects of microbial metabolites or related microbes on patients with cancer have been listed. In summary, studying microbial metabolites, which play a crucial role in the interaction between the microbiota and tumors, could lead to the identification of new supplementary treatments for cancer. This has the potential to improve the effectiveness of cancer treatment and enhance patient prognosis.

Dysregulated tryptophan metabolism and AhR pathway contributed to CXCL10 upregulation in stable non-segmental vitiligo

BACKGROUND

Tryptophan metabolism dysregulation has been observed in vitiligo. However, drawing a mechanistic linkage between this metabolic disturbance and vitiligo pathogenesis remains challenging.

OBJECTIVE

Aim to reveal the characterization of tryptophan metabolism in vitiligo and investigate the role of tryptophan metabolites in vitiligo pathophysiology.

METHODS

LC-MS/MS, dual-luciferase reporter assay, ELISA, qRT-PCR, small interfering RNA, western blotting, and immunohistochemistry were employed.

RESULTS

Kynurenine pathway activation and KYAT enzyme-associated deviation to kynurenic acid (KYNA) in the plasma of stable non-segmental vitiligo were determined. Using a public microarray dataset, we next validated the activation of kynurenine pathway was related with inflammatory-related genes expression in skin of vitiligo patients. Furthermore, we found that KYNA induced CXCL10 upregulation in keratinocytes via AhR activation. Moreover, the total activity of AhR agonist was increased while the AhR concentration per se was decreased in the plasma of vitiligo patients. Finally, higher KYAT, CXCL10, CYP1A1 and lower AhR expression in vitiligo lesional skin were observed by immunohistochemistry staining.

CONCLUSION

This study depicts the metabolic and genetic characterizations of tryptophan metabolism in vitiligo and proposes that KYNA, a tryptophan-derived AhR ligand, can enhance CXCL10 expression in keratinocytes.

Targeting the NLRP3 inflammasome in psoriasis

The NLRP3 inflammasome, a complex consisting of the nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing protein 3, has emerged as a critical mediator of pathological inflammation and a significant therapeutic target for various inflammatory diseases. Psoriasis, a chronic inflammatory skin condition without a definitive cure, has shown promising results in animal models through the inhibition of the NLRP3 inflammasome. This review aims to explore the development of the NLRP3 inflammasome in psoriasis and the molecular mechanisms responsible for its inhibition by natural products and small molecules currently being developed for psoriasis treatment. Furthermore, we are examining clinical trials using agents that block the NLRP3 pathway for the treatment of psoriasis. This study is timely to provide a new perspective on managing psoriasis.

Forsythiaside A attenuates lipopolysaccharide-induced mouse mastitis by activating autophagy and regulating gut microbiota and metabolism

Mastitis is an inflammatory disease of the mammary gland with a high incidence in lactating animals, significantly impacting their health and breastfeeding. Moreover, mastitis adversely affects milk quality and yield, resulting in substantial economic losses for the dairy farming industry. Forsythiaside A (FTA), a phenylethanol glycoside analog extracted from Forsythia, exhibits notable anti-inflammatory and antioxidant properties. However, its protective effects and specific mechanisms against mastitis remain unclear. In this study, a lipopolysaccharide (LPS)-induced mouse mastitis model was used to investigate the protective effect of FTA on LPS-induced mastitis and its potential mechanism using histological assays, Western blot, qRT-PCR, FITC-albumin permeability test, 16s rRNA gene sequencing analysis and non-targeted metabolomics assays to investigate the protective effect of FTA on LPS-induced mastitis model and its potential mechanism. The results demonstrated that FTA significantly mitigated LPS-induced mouse mastitis by reducing inflammation and apoptosis levels, modulating the PI3K/AKT/mTOR signaling pathways, inducing autophagy, and enhancing antioxidant capacity and the expression of tight junction proteins. Furthermore, FTA increased the abundance of beneficial microbiota while decreasing the levels of harmful microbiota in mice, thus counteracting the gut microbiota disruption induced by LPS stimulation. Intestinal metabolomics analysis revealed that FTA primarily regulated LPS-induced metabolite alterations through key metabolic pathways, such as tryptophan metabolism. This study confirms the anti-inflammatory and antioxidant effects of FTA on mouse mastitis, which are associated with key metabolic pathways, including the restoration of gut microbiota balance and the regulation of tryptophan metabolism. These findings provide a novel foundation for the treatment and prevention of mammalian mastitis using FTA.

The role of the kynurenine pathway in cardiovascular disease

The kynurenine pathway (KP) serves as the primary route for tryptophan metabolism in most mammalian organisms, with its downstream metabolites actively involved in various physiological and pathological processes. Indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) serve as the initial and pivotal enzymes of the KP, with IDO playing important and intricate roles in cardiovascular diseases. Multiple metabolites of KP have been observed to exhibit elevated concentrations in plasma across various cardiovascular diseases, such as atherosclerosis, hypertension, and acute myocardial infarction. Multiple studies have indicated that kynurenine (KYN) may serve as a potential biomarker for several adverse cardiovascular events. Furthermore, Kynurenine and its downstream metabolites have complex roles in inflammation, exhibiting both inhibitory and stimulatory effects on inflammatory responses under different conditions. In atherosclerosis, upregulation of IDO stimulates KYN production, mediating aromatic hydrocarbon receptor (AhR)-induced exacerbation of vascular inflammation and promotion of foam cell formation. Conversely, in arterial calcification, this mediation alleviates osteogenic differentiation of vascular smooth muscle cells. Additionally, in cardiac remodeling, KYN-mediated AhR activation exacerbates pathological left ventricular hypertrophy and fibrosis. Interventions targeting components of the KP, such as IDO inhibitors, 3-hydroxyanthranilic acid, and anthranilic acid, demonstrate cardiovascular protective effects. This review outlines the mechanistic roles of KP in coronary atherosclerosis, arterial calcification, and myocardial diseases, highlighting the potential diagnostic, prognostic, and therapeutic value of KP in cardiovascular diseases, thus providing novel insights for the development and application of related drugs in future research.

Dietary tryptophan alleviates intestinal inflammation caused by long photoperiod via gut microbiota derived tryptophan metabolites-NLRP3 pathway in broiler chickens

Light pollution is a potential risk factor for intestinal health. Tryptophan plays an important role in the inhibition of intestinal inflammation. However, the mechanism of tryptophan in alleviating intestinal inflammation caused by long photoperiod is still unclear. This study investigated the anti-inflammatory effect of dietary tryptophan on intestinal inflammatory damage induced by long photoperiod and its potential mechanism in broiler chickens. We found that dietary tryptophan mitigated long photoperiod-induced intestinal tissue inflammatory damage and inhibited the activation of Nucleotide-Binding Oligomerization Domain, Leucine-Rich Repeat and Pyrin Domain-Containing 3 inflammasome. Moreover, dietary tryptophan significantly increased the relative abundance of Faecalibacterium, Enterococcus, and Lachnospiraceae_NC2004_group were significantly decreased the relative abundance of Ruminococcus_torques_group and norank_f_UCG-010 under the condition of long photoperiod (P < 0.05). The results of tryptophan targeted metabolomics show that tryptophan significantly increased indole-3-acetic acid (IAA) and indole-3 lactic acid (ILA), and significantly decreased xanthurenic acid (XA) under long photoperiod (P < 0.05). In conclusion, the results indicated that dietary tryptophan alleviates intestinal inflammatory damage caused by long photoperiod via the inhibition of Nucleotide-Binding Oligomerization Domain, Leucine-Rich Repeat and Pyrin Domain-Containing 3 inflammasome activation, which was mediated by tryptophan metabolites. Therefore, tryptophan supplementation could be a promising way to protect the intestine health under the condition of long photoperiod.

Pathological and Therapeutical Implications of Pyroptosis in Psoriasis and Hidradenitis Suppurativa: A Narrative Review

This manuscript explores the role of pyroptosis, an inflammatory programmed cell death, in the pathogenesis of two chronic dermatoses, psoriasis and hidradenitis suppurativa (HS). The diseases, though clinically diverse, share common pathogenetic pathways involving the unbalanced interaction between the adaptive and innate immune systems. This review focuses on the molecular changes in psoriatic and HS skin, emphasizing the activation of dendritic cells, secretion of interleukins (IL-17, IL-22, and TNF-α), and the involvement of inflammasomes, particularly NLRP3. This manuscript discusses the role of caspases, especially caspase-1, in driving pyroptosis and highlights the family of gasdermins (GSDMs) as key players in the formation of pores leading to cell rupture and the release of proinflammatory signals. This study delves into the potential therapeutic implications of targeting pyroptosis in psoriasis and HS, examining existing medications like biologics and Janus kinase inhibitors. It also reviews the current limitations and challenges in developing therapies that selectively target pyroptosis. Additionally, the manuscript explores the role of pyroptosis in various inflammatory disorders associated with psoriasis and HS, such as inflammatory bowel disease, diabetes mellitus, and cardiovascular disorders. The review concludes by emphasizing the need for further research to fully elucidate the pathomechanisms of these dermatoses and develop effective, targeted therapies.

A bibliometrics study on the status quo and hot topics of pathogenesis of psoriasis based on Web of Science

BACKGROUND

Psoriasis is an immune-mediated chronic inflammatory skin disease. Great progress has been made in the pathogenesis of psoriasis in recent years, but there is no bibliometric study on the pathogenesis of psoriasis. The purpose of this study was to use bibliometrics method to analyze the research overview and hot spots of pathogenesis of psoriasis in recent 10 years, so as to further understand the development trend and frontier of this field.

METHODS

The core literatures on the pathogenesis of psoriasis were searched in the Web of Science database, and analyzed by VOSviewer, CiteSpace, and Bibliometrix in terms of the annual publication volume, country, institution, author, journal, keywords, and so on.

RESULTS

A total of 3570 literatures were included. China and the United States were the main research countries in this field, and Rockefeller University was the main research institution. Krueger JG, the author, had the highest number of publications and the greatest influence, and Boehncke (2015) was the most cited local literature. J INVEST DERMATOL takes the top spot in terms of the number of Dermatol articles and citation frequency. The main research hotspots in the pathogenesis of psoriasis are as follows: (1) The interaction between innate and adaptive immunity and the related inflammatory loop dominated by Th17 cells and IL-23/IL-17 axis are still the key mechanisms of psoriasis; (2) molecular genetic studies represented by Long Non-Coding RNA (LncRNA); (3) integrated research of multi-omics techniques represented by gut microbiota; and (4) Exploring the comorbidity mechanism of psoriasis represented by Metabolic Syndrome (MetS).

CONCLUSION

This study is a summary of the current research status and hot trend of the pathogenesis of psoriasis, which will provide some reference for the scholars studying the pathogenesis of psoriasis.

Genistein upregulates AHR to protect against environmental toxin-induced NASH by inhibiting NLRP3 inflammasome activation and reconstructing antioxidant defense mechanisms

We have previously proven that the environmental toxin could accelerate the development and progression of nonalcoholic steatohepatitis (NASH). However, the underlying mechanism associated with such excessive inflammation hasn't been fully illustrated. Although Genistein has been well accepted for its capability in anti-inflammation and anti-oxidation, its effect in ameliorating contaminants-induced NASH still needs to be identified. In this study, using chickens and primary chicken hepatocytes as models, we found that NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome were over-activated in bromoacetic acid (BAA, one of the typical environmental toxins)-induced NASH, characterized by the infiltration of inflammatory cell, and the increase of NLRP3, Caspase-1 p20, and cytokines (IL-1β, IL-18) expressions. Interestingly, genistein treatment could recover these changes, with the signs of restored activities of anti-oxidases, decreased expressions of NLRP3 inflammasome components, and increased levels of elements in phase I metabolic system. The detailed mechanism was that, via up-regulating aryl hydrocarbon receptor (AHR), genistein lifted mRNA levels of Cyp1-related genes to reconstruct cytochrome P450 (CYP450) systems, and the raised AHR negatively regulated NLRP3 inflammasome activity to relieve inflammation. More important, the interaction and co-localization between AHR and NLRP3 was first proved, and genistein could promote the levels of AHR that interacted with NLRP3, which thereafter blocked the activation of NLRP3 inflammasome. Conclusively, in this research, we confirmed the AHR-dependent protective role of genistein in environmental toxin-linked NASH, which shed light on the potential precautions for contaminants-induced NASH.

Activation of the aryl hydrocarbon receptor in inflammatory bowel disease: insights from gut microbiota

Inflammatory bowel disease (IBD) is a chronic inflammatory intestinal disease that affects more than 3.5 million people, with rising prevalence. It deeply affects patients' daily life, increasing the burden on patients, families, and society. Presently, the etiology of IBD remains incompletely clarified, while emerging evidence has demonstrated that altered gut microbiota and decreased aryl hydrocarbon receptor (AHR) activity are closely associated with IBD. Furthermore, microbial metabolites are capable of AHR activation as AHR ligands, while the AHR, in turn, affects the microbiota through various pathways. In light of the complex connection among gut microbiota, the AHR, and IBD, it is urgent to review the latest research progress in this field. In this review, we describe the role of gut microbiota and AHR activation in IBD and discussed the crosstalk between gut microbiota and the AHR in the context of IBD. Taken as a whole, we propose new therapeutic strategies targeting the AHR-microbiota axis for IBD, even for other related diseases caused by AHR-microbiota dysbiosis.

Impact of Gut Bacterial Metabolites on Psoriasis and Psoriatic Arthritis: Current Status and Future Perspectives

There is growing evidence that supports a role of gut dysbiosis in the pathogenesis of psoriasis (Pso). Thus, probiotic supplementation and fecal microbiota transplantation may serve as promising preventive and therapeutic strategies for patients with Pso. One of the basic mechanisms through which the gut microbiota interacts with the host is through bacteria-derived metabolites, usually intermediate or end products produced by microbial metabolism. In this study, we provide an up-to-date review of the most recent literature on microbial-derived metabolites and highlight their roles in the immune system, with a special focus on Pso and one of its most common comorbidities, psoriatic arthritis.

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.

Tapinarof for psoriasis and atopic dermatitis: 15 years of clinical research

Tapinarof is a topical, aryl-hydrocarbon receptor agonist that has recently received FDA-approval for the treatment of psoriasis. This novel therapeutic has also been shown to be effective for atopic dermatitis and is currently in phase 3 for this indication. Beyond good efficacy and fast onset of action in patients with psoriasis, the clinical response to tapinarof is notable for durable remission or near remission, maintained for an average of 130 days beyond treatment discontinuation in patients with psoriasis in phase 3 studies. Tapinarof is usually well tolerated but can induce a follicular inflammatory reaction and dermatitis in some patients. This narrative review covers the historical development of this molecule, safety and efficacy data from clinical trials conducted with various topical formulations, and practical considerations derived from our 15 years of clinical trial experience with the drug.