Adipocyte-derived kynurenine promotes obesity and insulin resistance by activating the AhR/STAT3/IL-6 signaling

Dysregulation of miR-21-5p in children with obesity and its predictive value for metabolic syndrome

BACKGROUND

microRNAs (miRNAs) could mediate the glucose and lipid metabolism progress in metabolic syndrome (MetS).

OBJECTIVES

To analyze the value of miRNA (miR)-21-5p for MetS diagnosis in children with obesity. Function of miR-21-5p has been explored by the prediction of target genes and functional and pathway enrichment analysis.

METHODS

Relative miR-21-5p level was examined by qRT-PCR. Predictive value of miR-21-5p for MetS was assessed by ROC curve. miRBase, TargetScan, and miRWalk databases were used to screen the target genes of miR-21-5p. GO and KEGG were operated to analyze the function of candidate genes of miR-21-5p.

RESULTS

Overexpressed miR-21-5p was discovered in MetS children (P < 0.001). High miR-21-5p level could predict MetS patients from children with obesity. Serum miR-21-5p level was closely related to BMI (r = 0.631, P < 0.001), FBG (r = 0.341, P < 0.001), Fasting Insulin (r = 0.438, P < 0.001), TG (r = 0.662, P < 0.001), SBP (r = 0.432, P < 0.001), DBP (r = 0.524, P < 0.001), and HDL-C (r = -0.201, P < 0.001). High miR-21-5p level could predict MetS patients from children with obesity (AUC= 0.827, sensitivity= 0.750, specificity=0.806, cutoff value= 1.0293, P < 0.001). Venn diagram found 83 intersection genes among 3 databases. GO and KEGG analyses indicated that candidate genes of miR-21-5p were mainly correlated with Axon guidance, FoxO signaling pathway, cytokine-cytokine receptor interaction, and insulin resistance pathways.

CONCLUSION

Blood miR-21-5p was elevated in MetS children, and could predict MetS subjects from children with obesity. miR-21-5p could regulate the MetS development via FoxO signaling pathway and insulin resistance pathways.

Exploring tryptophan metabolism in cardiometabolic diseases

Tryptophan (Trp) metabolism is linked to health and disease, with indoleamine 2,3-dioxygenase 1 (IDO) being a key enzyme in its breakdown outside the liver. This process produces metabolites that influence metabolic and inflammatory responses. A distinctive feature of the gut is its involvement in three major Trp catabolic pathways: the IDO-driven kynurenine pathway, bacteria-produced indoles, and serotonin. Dysregulation of these pathways is associated with gastrointestinal and chronic inflammatory diseases. Understanding these mechanisms could reveal how gut function affects overall systemic health and disease susceptibility. Here, we review current insights into Trp metabolism, its impact on host physiology and cardiometabolic diseases, and its role in the gut-periphery connection, highlighting its relevance for therapeutic innovation.

AhR-Induced Anti-Inflammatory Effects on a Caco-2/THP-1 Co-Culture Model of Intestinal Inflammation Are Mediated by PPARγ

The aryl hydrocarbon receptor (AhR) and the peroxisome proliferator-activated receptor γ (PPARγ) are ligand-activated transcription factors that have in recent years been investigated for their anti-inflammatory properties for treatment of inflammatory bowel diseases (IBDs). These are globally prevalent chronic maladies of the gut that lack cost-efficient therapeutical options capable of inducing long-term remission. In the present study, we used an in vitro Transwell® co-culture model composed of Caco-2 epithelial cells in the apical compartment and lipopolysaccharide-treated (LPS) THP-1 macrophages in the basolateral compartment. Secretion of cytokines, disruption of epithelial integrity, and expression of surface markers and junctional proteins were assessed in order to investigate interactions between AhR and PPARγ on the ligand-elicited effects on the control of inflammation. The results revealed that the potent AhR ligand 6-formylindolo[3,2-b]carbazole (FICZ) attenuated LPS-induced IL-6 release by macrophages, which then stabilized Caco-2 monolayer permeability by decreasing claudin-2 expression. These effects were disrupted by GW9662 and to some extent by CH223191, inhibitors of PPARγ and AhR, respectively. Our main findings evidence PPARγ might be a downstream regulator of AhR activation essential for its ligand-based anti-inflammatory effects, suggesting it might be employed as either an auxiliary target or as a biomarker of therapeutical efficacy on AhR-based IBD pharmacotherapy.

The dichotomic role of cytokines in aging

The chronic inflammation present in aged individuals is generally depicted as a detrimental player for longevity. Here, it is discussed several beneficial effects associated with the cytokines that are chronically elevated in inflammaging. These cytokines, such as IL-1β, type I interferons, IL-6 and TNF positively regulate macroautophagy, mitochondrial function, anti-tumor immune responses and skeletal muscle biogenesis, possibly contributing to longevity. On the other side, the detrimental and antagonistic role of these cytokines including the induction of sarcopenia, tissue damage and promotion of tumorigenesis are also discussed, underscoring the dichotomy associated with inflammaging and its players. In addition, it is discussed the role of the anti-inflammatory cytokine IL-10 and other cytokines that affect aging in a more linear way, such as IL-11, which promotes senescence, and IL-4 and IL-15, which promotes longevity. It is also discussed more specific regulators of aging that are downstream cytokines-mediated signaling.

Exploring tryptophan metabolism: The transition from disturbed balance to diagnostic and therapeutic potential in metabolic diseases

The rapidly rising prevalence of metabolic diseases has turned them into an escalating global health concern. By producing or altering metabolic products, the gut microbiota plays a pivotal role in maintaining human health and influencing disease development. These metabolites originate from the host itself or the external environment. In the system of interactions between microbes and the host, tryptophan (Trp) plays a central role in metabolic processes. As the amino acid in the human body that must be obtained through dietary intake, it is crucial for various physiological functions. Trp can be metabolized in the gut into three main products: The gut microbiota regulates the transformation of 5-hydroxytryptamine (5-HT, serotonin), kynurenine (Kyn), and various indole derivatives. It has been revealed that a substantial correlation exists between alterations in Trp metabolism and the initiation and progression of metabolic disorders, including obesity, diabetes, non-alcoholic fatty liver disease, and atherosclerosis, but Trp metabolites have not been comprehensively reviewed in metabolic diseases. As such, this review summarizes and analyzes the latest research, emphasizing the importance of further studying Trp metabolism within the gut microbiota to understand and treat metabolic diseases. This carries potential significance for improving human health and may introduce new therapeutic strategies.

The Impact of SGLT1 Inhibition on Frailty and Sarcopenia: A Mediation Mendelian Randomization Study

BACKGROUND

Although pharmacological effects of SGLT2 inhibitors on the development of frailty and sarcopenia were known, the role of SGLT1 remained less clear. The present study investigated the possible effect of SGLT1 inhibition on these conditions and explored potential mediators.

METHODS

A two-sample Mendelian randomization (MR) analysis was performed to assess the effect of SGLT1 inhibition on frailty index (FI) and low grip strength in individuals aged 60 years and older using both the FNIH and EWGSOP criteria. Subsequently, a two-step MR analysis was conducted to investigate the mediating role of insulin resistance phenotype and identify potential mediators of the effect of SGLT1 inhibition on the FI and low grip strength from 1558 plasma proteins and 1352 metabolites.

RESULTS

Genetically predicted SGLT1 inhibition was associated with decreased FI (β: -0.290 [95% CI: -0.399, -0.181]) and reduced risk of low grip strength in individuals aged 60 years and older under both FNIH (β: -0.796 [95% CI: -1.216, -0.376]) and EWGSOP criteria (β: -0.287 [95% CI: -0.532, -0.041]). The two-step MR analysis demonstrated the role of insulin resistance phenotype in mediating SGTL1 inhibition on alleviating frailty (mediation proportion = 19.56% [95% CI: 8.42%, 30.70%]). After screening, 24 proteins and 16 metabolites were identified as mediators of the impact of SGLT1 inhibition on FI. Additionally, 13 proteins and 16 metabolites were found to mediate the effect of SGLT1 inhibition on low grip strength according to FNIH criteria while 22 proteins and 6 metabolites were shown to mediate the impact of SGLT1 inhibition on low grip strength under EWGSOP criteria.

CONCLUSIONS

SGLT1 inhibition potentially mitigated frailty and sarcopenia through several biological mediators, shedding new light for therapeutic intervention.

Kynurenine-AhR reduces T-cell infiltration and induces a delayed T-cell immune response by suppressing the STAT1-CXCL9/CXCL10 axis in tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is a critical global health issue that is complicated by the ability of the pathogen to delay the host's T-cell immune response. This delay in T-cell recruitment to the site of infection is a pivotal survival strategy for Mtb, allowing it to establish a persistent chronic infection. To investigate the underlying mechanisms, this study focused on Mtb's exploitation of host tryptophan metabolism. Mtb upregulates indoleamine 2,3-dioxygenase 1 (IDO1) in inflammatory macrophages, thereby increasing kynurenine (Kyn) production. Kyn then activates the aryl hydrocarbon receptor (AhR), leading to the upregulation of suppressor of cytokine signaling 3 and subsequent inhibition of the JAK-STAT1 signaling pathway. This results in reduced secretion of the chemokines CXCL9 and CXCL10, which are crucial for T-cell recruitment to the lungs. Supported by in vivo mouse models, our findings reveal that disrupting this pathway through AhR knockout significantly enhances T-cell infiltration and activity, thereby undermining Mtb-induced immunosuppression. In contrast, additional Kyn injection obviously inhibited T-cell infiltration and activity. These results highlight potential therapeutic targets of AhR and IDO1, offering new avenues for enhancing the host immune response against tuberculosis and guiding future vaccine development efforts.

Research progress on the association of insulin resistance with type 2 diabetes mellitus and Alzheimer's disease

Type 2 diabetes mellitus (T2DM) is a metabolic disorder that is characterized by insulin resistance and hyperglycemia. It is also known to be a risk factor for Alzheimer's disease (AD). Insulin plays a crucial role in regulating the body's metabolism and is responsible for activating the Phosphoinotide-3-Kinase (PI3K)/Protein Kinase B (Akt) signaling pathway. This pathway is activated when insulin binds to the insulin receptor on nerve cells, and it helps regulate the metabolism of glucose and lipids. Dysfunction in the insulin signaling pathway can lead to a decrease in brain insulin levels and insulin sensitivity, thereby inducing disruptions in insulin signal transduction and leading to disorders in brain energy metabolism. Moreover, these dysfunctions also contribute to the accumulation of β-amyloid (Aβ) deposition and the hyperphosphorylation of Tau protein, both of which are characteristic features of AD. Therefore, this article focuses on insulin resistance to reveal the complex mechanism between brain insulin resistance and AD occurrence in T2DM. On this basis, this article further summarizes the biological effects and mechanisms of antidiabetic drugs on the two diseases, aiming to provide new ideas for the discovery of drugs for the treatment of T2DM combined with AD.

Lactobacillus murinus alleviates insulin resistance via promoting L-citrulline synthesis

AIMS

The role of Lactobacillus murinus as a potential probiotic is being explored. Our objectives were to explore the effects of Lactobacillus murinus on insulin resistance and the underlying mechanism.

METHODS

Insulin resistance animal models were applied to study the effect of L. murinus and the underlying mechanism by six weeks of treatment. Metformin was administered in vitro to analyze the growth and metabolites of L. murinus. Serum metabolites were further analyzed after L. murinus administration. The effect of L-citrulline and the underlying mechanism in alleviating insulin resistance were evaluated.

RESULTS

L. murinus not only reduced body weight gain and postprandial blood glucose (PBG) but improved impaired glucose tolerance (IGT) and insulin resistance. Moreover, L. murinus inhibited the secretion of pro-inflammatory factors (IL-1β, IL-6 and TNF-α) while promoted the secretion of anti-inflammatory factor (IL-10). Further, L. murinus promoted the expression of carnitine palmitoyl transferase 1 (CPT1) while inhibited phosphoenolpyruvate carboxykinase (PCK) and glucose-6-phosphatase (G6Pase). A total of 147 metabolites of L. murinus were identified, in which the content of L-citrulline increased to 7.94 times after metformin regulation. Further, the serum concentration of L-citrulline significantly increased after L. murinus administration. Similarly, L-citrulline reduced body weight gain and PBG, improved IGT and insulin resistance. Additionally, L-citrulline improved inflammation, promoted CPT1 while inhibited PCK and G6Pase.

CONCLUSIONS

L. murinus mediated by L-citrulline alleviated insulin resistance via promoting fatty acid oxidation and inhibiting gluconeogenesis, suggesting that supplementation of L. murinus could be a potential therapeutic approach for type 2 diabetes related to insulin resistance.

Tissue adaptation to metabolic stress: insights from SUMOylation

Post-translational modification (PTM) plays a crucial role in adaptation of mammals to environmental changes, enabling them to survive in stressful situations. One such PTM is SUMO modification, which is evolutionarily conserved. It involves the covalent and reversible attachment of a small ubiquitin-like modifier (SUMO) to lysine (Lys) residues in the target protein. SUMOylation regulates various functions, including cell proliferation, differentiation, apoptosis, senescence, and maintenance of specific cellular activities. It achieves this by influencing protein-protein interactions, subcellular localization, protein stability, and DNA binding activity. Mounting evidence suggests that SUMOylation is implicated in the pathogenesis of metabolic disorders such as obesity, insulin resistance, and fatty liver. This review aims to provide an overview of the role of SUMOylation in regulating tissue adaptation to metabolic stress. Recent advancements in spectroscopic techniques have shed light on potential targets of SUMOylation and the underlying regulatory mechanisms have been elucidated, laying the theoretical foundation for the development of targeted SUMOylation interventions for metabolic syndrome while minimizing side effects.

Metabolic profiling of tryptophan pathways: Implications for obesity and metabolic dysfunction-associated steatotic liver disease

BACKGROUND AND AIMS

The rise in obesity highlights the need for improved therapeutic strategies, particularly in addressing metabolic dysfunction-associated steatotic liver disease (MASLD). We aim to assess the role of tryptophan metabolic pathways in the pathogenesis of obesity and in the different histological stages of MASLD.

MATERIALS AND METHODS

We used ultra-high performance liquid chromatography to quantify circulating levels of 15 tryptophan-related metabolites from the kynurenine, indole and serotonin pathways. A cohort of 76 subjects was analysed, comprising 18 subjects with normal weight and 58 with morbid obesity, these last being subclassified into normal liver (NL), simple steatosis (SS) and metabolic dysfunction-associated steatohepatitis (MASH). Then, we conducted gene expression analysis of hepatic IDO-1 and kynyrenine-3-monooxygenase (KMO).

RESULTS

Key findings in obesity revealed a distinct metabolic signature characterized by a higher concentration of different kynurenine-related metabolites, a decrease in indole-3-acetic acid and indole-3-propionic acid, and an alteration in the serotonin pathway. Elevated tryptophan levels were associated with MASLD presence (37.659 (32.577-39.823) μM of tryptophan in NL subjects; 41.522 (38.803-45.276) μM in patients with MASLD). Overall, pathway fluxes demonstrated an induction of tryptophan catabolism via the serotonin pathway in SS subjects and into the kynurenine pathway in MASH. We found decreased IDO-1 and KMO hepatic expression in NL compared to SS.

CONCLUSIONS

We identified a distinctive metabolic signature in obesity marked by changes in tryptophan catabolic pathways, discernible through altered metabolite profiles. We observed stage-specific alterations in tryptophan catabolism fluxes in MASLD, highlighting the potential utility of targeting these pathways in therapeutic interventions.

Macrophages and T cells in metabolic disorder-associated cancers

Cancer and metabolic disorders have emerged as major global health challenges, reaching epidemic levels in recent decades. Often viewed as separate issues, metabolic disorders are shown by mounting evidence to heighten cancer risk and incidence. The intricacies underlying this connection are still being unraveled and encompass a complex interplay between metabolites, cancer cells and immune cells within the tumour microenvironment (TME). Here, we outline the interplay between metabolic and immune cell dysfunction in the context of three highly prevalent metabolic disorders, namely obesity; two associated liver diseases, metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH); and type 2 diabetes. We focus primarily on macrophages and T cells, the critical roles of which in dictating inflammatory response and immune surveillance in metabolic disorder-associated cancers are widely reported. Moreover, considering the ever-increasing number of patients prescribed with metabolism disorder-altering drugs and diets in recent years, we discuss how these therapies modulate systemic and local immune phenotypes, consequently impacting cancer malignancy. Collectively, unraveling the determinants of metabolic disorder-associated immune landscape and their role in fuelling cancer malignancy will provide a framework essential to therapeutically address these highly prevalent diseases.

Ten metabolites-based algorithm predicts the future development of type 2 diabetes in Chinese

INTRODUCTION

Type 2 diabetes (T2D) is a heterogeneous metabolic disease with large variations in the relative contributions of insulin resistance and β-cell dysfunction across different glucose tolerance subgroups and ethnicities. A more precise yet feasible approach to categorize risk preceding T2D onset is urgently needed. This study aimed to identify potential metabolic biomarkers that could contribute to the development of T2D and investigate whether their impact on T2D is mediated through insulin resistance and β-cell dysfunction.

METHODS

A non-targeted metabolomic analysis was performed in plasma samples of 196 incident T2D cases and 196 age- and sex-matched non-T2D controls recruited from a long-term prospective Chinese community-based cohort with a follow-up period of ∼ 16 years.

RESULTS

Metabolic profiles revealed profound perturbation of metabolomes before T2D onset. Overall metabolic shifts were strongly associated with insulin resistance rather than β-cell dysfunction. In addition, 188 out of the 578 annotated metabolites were associated with insulin resistance. Bi-directional mediation analysis revealed putative causal relationships among the metabolites, insulin resistance and T2D risk. We built a machine-learning based prediction model, integrating the conventional clinical risk factors (age, BMI, TyG index and 2hG) and 10 metabolites (acetyl-tryptophan, kynurenine, γ-glutamyl-phenylalanine, DG(18:2/22:6), DG(38:7), LPI(18:2), LPC(P-16:0), LPC(P-18:1), LPC(P-20:0) and LPE(P-20:0)) (AUROC = 0.894, 5.6% improvement comparing to the conventional clinical risk model), that successfully predicts the development of T2D.

CONCLUSIONS

Our findings support the notion that the metabolic changes resulting from insulin resistance, rather than β-cell dysfunction, are the primary drivers of T2D in Chinese adults. Metabolomes as a valuable phenotype hold potential clinical utility in the prediction of T2D.

Role of the intestinal microbiota in contributing to weight disorders and associated comorbidities

SUMMARYThe gut microbiota is a major factor contributing to the regulation of energy homeostasis and has been linked to both excessive body weight and accumulation of fat mass (i.e., overweight, obesity) or body weight loss, weakness, muscle atrophy, and fat depletion (i.e., cachexia). These syndromes are characterized by multiple metabolic dysfunctions including abnormal regulation of food reward and intake, energy storage, and low-grade inflammation. Given the increasing worldwide prevalence of obesity, cachexia, and associated metabolic disorders, novel therapeutic strategies are needed. Among the different mechanisms explaining how the gut microbiota is capable of influencing host metabolism and energy balance, numerous studies have investigated the complex interactions existing between nutrition, gut microbes, and their metabolites. In this review, we discuss how gut microbes and different microbiota-derived metabolites regulate host metabolism. We describe the role of the gut barrier function in the onset of inflammation in this context. We explore the importance of the gut-to-brain axis in the regulation of energy homeostasis and glucose metabolism but also the key role played by the liver. Finally, we present specific key examples of how using targeted approaches such as prebiotics and probiotics might affect specific metabolites, their signaling pathways, and their interactions with the host and reflect on the challenges to move from bench to bedside.

The kynurenine pathway regulated by intestinal innate lymphoid cells mediates postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is a prevalent neurological complication that can impair learning and memory for days, months, or even years after anesthesia/surgery. POCD is strongly associated with an altered composition of the gut microbiota (dysbiosis), but the accompanying metabolic changes and their role in gut-brain communication and POCD pathogenesis remain unclear. Here, the present study reports that anesthesia/surgery in aged mice induces elevated intestinal indoleamine 2,3-dioxygenase (IDO) expression and activity, which shifts intestinal tryptophan (TRP) metabolism toward more IDO-catalyzed kynurenine (KYN) and less gut bacteria-catabolized indoleacetic acid (IAA). Both anesthesia/surgery and intraperitoneal KYN administration induce increased KYN levels that correlate with impaired spatial learning and memory, whereas dietary IAA supplementation attenuates the anesthesia/surgery-induced cognitive impairment. Mechanistically, anesthesia/surgery increases interferon-γ (IFN-γ)-producing group 1 innate lymphoid cells (ILC1) in the small intestine lamina propria and elevates intestinal IDO expression and activity, as indicated by the higher ratio of KYN to TRP. The IDO inhibitor 1-MT and antibodies targeting IFN-γ or ILCs mitigate anesthesia/surgery-induced cognitive dysfunction, suggesting that intestinal ILC1 expansion and the ensuing IFN-γ-induced IDO upregulation may be the primary pathway mediating the shift to the KYN pathway in POCD. The ILC1-KYN pathway in the intestine could be a promising therapeutic target for POCD.

Multi-omics analyses reveal aberrant differentiation trajectory with WNT1 loss-of-function in type XV osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a group of severe genetic bone disorders characterized by congenital low bone mass, deformity, and frequent fractures. Type XV OI is a moderate to severe form of skeletal dysplasia caused by WNT1 variants. In this cohort study from southern China, we summarized the clinical phenotypes of patients with WNT1 variants and found that the proportion of type XV patients was around 10.3% (25 out of 243) with a diverse spectrum of phenotypes. Functional assays indicated that variants of WNT1 significantly impaired its secretion and effective activity, leading to moderate to severe clinical manifestations, porous bone structure, and enhanced osteoclastic activities. Analysis of proteomic data from human skeleton indicated that the expression of SOST (sclerostin) was dramatically reduced in type XV patients compared to patients with COL1A1 quantitative variants. Single-cell transcriptome data generated from human tibia samples of patients diagnosed with type XV OI and leg-length discrepancy, respectively, revealed aberrant differentiation trajectories of skeletal progenitors and impaired maturation of osteocytes with loss of WNT1, resulting in excessive CXCL12+ progenitors, fewer mature osteocytes, and the existence of abnormal cell populations with adipogenic characteristics. The integration of multi-omics data from human skeleton delineates how WNT1 regulates the differentiation and maturation of skeletal progenitors, which will provide a new direction for the treatment strategy of type XV OI and relative low bone mass diseases such as early onset osteoporosis.

Long-Term Exposure to Polystyrene Microspheres and High-Fat Diet-Induced Obesity in Mice: Evaluating a Role for Microbiota Dysbiosis

BACKGROUND

Microplastics (MPs) have become a global environmental problem, emerging as contaminants with potentially alarming consequences. However, long-term exposure to polystyrene microspheres (PS-MS) and its effects on diet-induced obesity are not yet fully understood.

OBJECTIVES

We aimed to investigate the effect of PS-MS exposure on high-fat diet (HFD)-induced obesity and underlying mechanisms.

METHODS

In the present study, C57BL/6J mice were fed a normal diet (ND) or a HFD in the absence or presence of PS-MS via oral administration for 8 wk. Antibiotic depletion of the microbiota and fecal microbiota transplantation (FMT) were performed to assess the influence of PS-MS on intestinal microbial ecology. We performed 16S rRNA sequencing to dissect microbial discrepancies and investigated the dysbiosis-associated intestinal integrity and inflammation in serum.

RESULTS

Compared with HFD mice, mice fed the HFD with PS-MS exhibited higher body weight, liver weight, metabolic dysfunction-associated steatotic liver disease (MASLD) activity scores, and mass of white adipose tissue, as well as higher blood glucose and serum lipid concentrations. Furthermore, 16S rRNA sequencing of the fecal microbiota revealed that mice fed the HFD with PS-MS had greater α -diversity and greater relative abundances of Lachnospiraceae, Oscillospiraceae, Bacteroidaceae, Akkermansiaceae, Marinifilaceae, Deferribacteres, and Desulfovibrio, but lower relative abundances of Atopobiaceae, Bifidobacterium, and Parabacteroides. Mice fed the HFD with PS-MS exhibited lower expression of MUC2 mucin and higher levels of lipopolysaccharide and inflammatory cytokines [tumor necrosis factor-α (TNF-α ), interleukin-6 (IL-6), IL-1β , and IL-17A] in serum. Correlation analyses revealed that differences in the microbial flora of mice exposed to PS-MS were associated with obesity. Interestingly, microbiota-depleted mice did not show the same PS-MS-associated differences in Muc2 and Tjp1 expression in the distal colon, expression of inflammatory cytokines in serum, or obesity outcomes between HFD and HFD + PS-MS. Importantly, transplantation of feces from HFD + PS-MS mice to microbiota-depleted HFD-fed mice resulted in a lower expression of mucus proteins, higher expression of inflammatory cytokines, and obesity outcomes, similar to the findings in HFD + PS-MS mice.

CONCLUSIONS

Our findings provide a new gut microbiota-driven mechanism for PS-MS-induced obesity in HFD-fed mice, suggesting the need to reevaluate the adverse health effects of MPs commonly found in daily life, particularly in susceptible populations. https://doi.org/10.1289/EHP13913.

Therapeutic modulation of the kynurenine pathway in severe mental illness and comorbidities: A potential role for serotonergic psychedelics

Mounting evidence points towards a crucial role of the kynurenine pathway (KP) in the altered gut-brain axis (GBA) balance in severe mental illness (SMI, namely depression, bipolar disorder, and schizophrenia) and cardiometabolic comorbidities. Preliminary evidence shows that serotonergic psychedelics and their analogues may hold therapeutic potential in addressing the altered KP in the dysregulated GBA in SMI and comorbidities. In fact, aside from their effects on mood, psychedelics elicit therapeutic improvement in preclinical models of obesity, metabolic syndrome, and vascular inflammation, which are highly comorbid with SMI. Here, we review the literature on the therapeutic modulation of the KP in the dysregulated GBA in SMI and comorbidities, and the potential application of psychedelics to address the altered KP in the brain and systemic dysfunction underlying SMI and comorbidities. Psychedelics might therapeutically modulate the KP in the altered GBA in SMI and comorbidities either directly, via altering the metabolic pathway by influencing the rate-limiting enzymes of the KP and affecting the levels of available tryptophan, or indirectly, by affecting the gut microbiome, gut metabolome, metabolism, and the immune system. Despite promising preliminary evidence, the mechanisms and outcomes of the KP modulation with psychedelics in SMI and systemic comorbidities remain largely unknown and require further investigation. Several concerns are discussed surrounding the potential side effects of this approach in specific cohorts of individuals with SMI and systemic comorbidities.

Metabolic Assessment in Non-Dialysis Patients with Chronic Kidney Disease

Purpose

The aim of this study was to investigate the changes of different metabolites in the body fluids of non-dialysis patients with chronic kidney disease (CKD) using a metabolomics approach. The goal was to identify early biomarkers of CKD progression through metabolic pathway analysis.

Patients and Methods

Plasma samples from 47 patients with stages 1-4 CKD not requiring dialysis and 30 healthy controls were analyzed by liquid chromatography-mass spectrometry (LC-MS). Using multivariate data analysis, specifically a partially orthogonal least squares discriminant analysis model (OPLS-DA), we investigated metabolic differences between different stages of CKD. The sensitivity and specificity of the analysis were evaluated using the Area Under Curve (AUC) method. Furthermore, the metabolic pathways were analyzed using the Met PA database.

Results

Plasma samples from CKD patients and controls were successfully differentiated using an OPLS-DA model. Initially, twenty-five compounds were identified as potential plasma metabolic markers for distinguishing CKD patients from healthy controls. Among these, six compounds (ADMA, D-Ornithine, Kynurenine, Kynurenic acid, 5-Hydroxyindoleacetic acid, and Gluconic acid) were found to be associated with CKD progression It has been found to be associated with the progression of CKD. Changes in metabolic pathways associated with CKD progression include arginine and ornithine metabolism, tryptophan metabolism, and the pentose phosphate pathway.

Conclusion

By analyzing the metabolic pathways of different metabolites, we have identified the significant impact of CKD progression. The main metabolic pathways involved are Arginine and Ornithine metabolism, Tryptophan metabolism, and Pentose phosphate pathway. ADMA, D-Ornithine, L-Kynurenine, Kynurenic acid, 5-Hydroxyindoleacetic acid, and Gluconic acid could serve as potential early biomarkers for CKD progression. These findings have important implications for the early intervention and treatment of CKD, as well as for further research into the underlying mechanisms of its pathogenesis.

Confronting the global obesity epidemic: investigating the role and underlying mechanisms of vitamin D in metabolic syndrome management

The escalating prevalence of MetS, driven by global obesity trends, underscores the urgent need for innovative therapeutic strategies. To gain a deeper understanding of the therapeutic potential of vitamin D in addressing MetS, we embarked on a targeted literature review that thoroughly examines the scientific underpinnings and pivotal discoveries derived from pertinent studies, aiming to unravel the intricate mechanisms through which vitamin D exerts its effects on MetS and its components. This article explores the multifunctional role of vitamin D in the management of MetS, focusing on its regulatory effects on insulin sensitivity, lipid metabolism, inflammation, and immune response. Through an extensive review of current research, we unveil the complex mechanisms by which vitamin D influences MetS components, highlighting its potential as a therapeutic agent. Our analysis reveals that vitamin D's efficacy extends beyond bone health to include significant impacts on cellular and molecular pathways critical to MetS. We advocate for further research to optimize vitamin D supplementation as a component of precision medicine for MetS, considering the safety concerns related to dosage and long-term use.

Kynurenine pathway in type 2 diabetes: Role of metformin

The Kynurenine pathway (KP) which is involved in the synthesis of nicotinamide adenine dinucleotide (NAD) from tryptophan (Trp) is intricate in the development of insulin resistance (IR) and type 2 diabetes (T2D). Inflammatory reactions in response to cardiometabolic disorders can induce the development of IR through the augmentation of KP. However, kynurenine (KYN), a precursor of kynurenic acid (KA) is increased following physical exercise and involved in the reduction of IR. Consequently, KP metabolites KA and KYN have anti-diabetogenic effects while other metabolites have diabetogenic effects. KP modulators, either inhibitors or activators, affect glucose homeostasis and insulin sensitivity in T2D in a bidirectional way, either protective or detrimental, that is not related to the KP effect. However, metformin through inhibition of inflammatory signaling pathways can reduce the activation of KP in T2D. These findings indicated a strong controversy regarding the role of KP in T2D. Therefore, the objectives of this mini review were to clarify how KP induces the development of IR and T2D. In addition, this review aimed to find the mechanistic role of antidiabetic drug metformin on the KP, and how KP modulators affect the pathogenesis of T2D.

Identification and Validation of CXCL2 as a Key Gene for Childhood Obesity

This study aims to identify the key genes and their regulatory networks by bioinformatics, increasing understanding of childhood obesity. The data comes from the GEO and Immport database. The immune microenvironment was explored in GSE104815. Key genes were identified by intersection of DEGs with the immune gene set. Enrichment analysis revealed gene-related functions and correlation analysis explored the relationship. Regulatory networks were constructed based on miRcode, TarBase and TargetScan databases. GSE29718 was used to validate our findings. Intercellular communication and cell differentiation trends were further explored using single-cell data from GSE153643. Based on our research, the immune microenvironment in the obese group showed higher immune infiltration. We found 962 DEGs and CXCL2 was identified as the key gene. The co-regulatory network of lncRNA-miRNA-mRNA suggested that obtaining TM4SF19-AS1, GUSBP11, AC105020.1, LINC00189, COL4A2-AS2, VIPR1-AS1 and LINC00242 may regulate CXCL2 (r > 0.9 and P < 0.01). Differential expression of CXCL2 was validated in GSE29718 (P < 0.05) and CXCL2 was identified as a biomarker for childhood obesity (AUC = 0.885). GSVA enrichment analysis revealed many pathways of high group obtaining the TNF-α signaling via NF-κB pathway and interferon γ response pathway. In GSE153643, 11 cell types were identified and CXCL2 was highly expressed in monocyte, macrophage, endothelial cell and pericyte. In CXCL2 high expressing macrophages, there was a tendency for cells to polarize toward M1 macrophages (P < 0.05). In summary, we identified CXCL2 as a potential biomarker of childhood obesity. The development of childhood obesity may be associated with the activation of immune infiltration of macrophage M1 polarization by CXCL2 expression.

Anti-adipogenesis effect of indole-3-acrylic acid on human preadipocytes and HFD-induced zebrafish

BACKGROUND

Obesity, defined as excessive or abnormal body fat accumulation, which could significantly increase the risk of cardiovascular disease, type 2 diabetes mellitus (T2DM) diseases and seriously affect people's quality of life. More than 2 billion people are overweight, and the incidence of obesity is increasing rapidly worldwide, it has become a widely concerned public health issue in the world. Diverse evidence show that active metabolites are involved in the pathophysiological processes of obesity.

AIMS

However, whether the downstream catabolite of tryptophan, 3-indole acrylic acid (IA), is involved in obesity remains unclear.

METHODS

We collected the samples of serum from peripheral blood of obesity and health controls, and liquid chromatography-mass spectrometry (LC-MS) was performed to identify the plasma levels of IA. Additionally, we verified the potential benefits of IA on human preadipocytes and HFD- induced zebrafish by cell viability assay, flow cytometry assay, Oil red O staining, total cholesterol (T-CHO), triglyceride (TG) and nonesterified free fatty acids (NEFA) measurements and Nile Red staining. RNA-Seq, functional analysis and western blot revealed the mechanisms underlying the function of IA.

RESULTS

We found that the content of IA in peripheral blood serum of overweight people was significantly lower than that of normal people. In addition, supplementation with IA in zebrafish larvae induced by a high fat diet (HFD) dramatically reduced HFD induced lipid accumulation. IA had no effect on proliferation and apoptosis of preadipocytes, but significantly inhibited adipogenesis of preadipocytes by down-regulate CEBPα and PPARγ. RNA-Seq and functional analysis revealed that IA regulated the adipogenesis of preadipocytes through stimulate the phosphorylation of STAT1.

CONCLUSIONS

Taken together, IA has been identified as a potent metabolite for the prevention or treatment of obesity.

Risk of Fat Mass- and Obesity-Associated Gene-Dependent Obesogenic Programming by Formula Feeding Compared to Breastfeeding

It is the purpose of this review to compare differences in postnatal epigenetic programming at the level of DNA and RNA methylation and later obesity risk between infants receiving artificial formula feeding (FF) in contrast to natural breastfeeding (BF). FF bears the risk of aberrant epigenetic programming at the level of DNA methylation and enhances the expression of the RNA demethylase fat mass- and obesity-associated gene (FTO), pointing to further deviations in the RNA methylome. Based on a literature search through Web of Science, Google Scholar, and PubMed databases concerning the dietary and epigenetic factors influencing FTO gene and FTO protein expression and FTO activity, FTO's impact on postnatal adipogenic programming was investigated. Accumulated translational evidence underscores that total protein intake as well as tryptophan, kynurenine, branched-chain amino acids, milk exosomal miRNAs, NADP, and NADPH are crucial regulators modifying FTO gene expression and FTO activity. Increased FTO-mTORC1-S6K1 signaling may epigenetically suppress the WNT/β-catenin pathway, enhancing adipocyte precursor cell proliferation and adipogenesis. Formula-induced FTO-dependent alterations of the N6-methyladenosine (m6A) RNA methylome may represent novel unfavorable molecular events in the postnatal development of adipogenesis and obesity, necessitating further investigations. BF provides physiological epigenetic DNA and RNA regulation, a compelling reason to rely on BF.

Kynurenines as a Novel Target for the Treatment of Inflammatory Disorders

This review discusses the potential of targeting the kynurenine pathway (KP) in the treatment of inflammatory diseases. The KP, responsible for the catabolism of the amino acid tryptophan (TRP), produces metabolites that regulate various physiological processes, including inflammation, cell cycle, and neurotransmission. These metabolites, although necessary to maintain immune balance, may accumulate excessively during inflammation, leading to systemic disorders. Key KP enzymes such as indoleamine 2,3-dioxygenase 1 (IDO1), indoleamine 2,3-dioxygenase 2 (IDO2), tryptophan 2,3-dioxygenase (TDO), and kynurenine 3-monooxygenase (KMO) have been considered promising therapeutic targets. It was highlighted that both inhibition and activation of these enzymes may be beneficial, depending on the specific inflammatory disorder. Several inflammatory conditions, including autoimmune diseases, for which modulation of KP activity holds therapeutic promise, have been described in detail. Preclinical studies suggest that this modulation may be an effective treatment strategy for diseases for which treatment options are currently limited. Taken together, this review highlights the importance of further research on the clinical application of KP enzyme modulation in the development of new therapeutic strategies for inflammatory diseases.

Increased Tryptophan Catabolism Provides Predictive Value to Chronic Heart Failure Patients with Low-Grade Inflammation

Kynurenine to tryptophan ratio (KTR), which serves as an indicator for evaluating indoleamine-2,3-dioxygenase activity and inflammation, has been reported to be linked with cardiovascular incidences. However, its correlation with cardiovascular outcomes in patients suffering from heart failure (HF) remains to be explored. The objective of this study was to investigate the prognostic value of KTR in HF. The concentration of tryptophan and kynurenine were quantified by liquid chromatography-tandem mass spectrometry, and the KTR value was calculated in a population of 3150 HF patients. The correlation between plasma KTR levels and the occurrence of adverse cardiovascular events was evaluated for its prognostic value. We also assessed the role of KTR in addition to the classic inflammatory biomarker hypersensitive C-reactive protein (hs-CRP) in different subtypes of HF. We found that increased KTR levels were associated with an elevated risk and severity of the primary endpoints in different subtypes of HF. The simultaneous evaluation of KTR and hs-CRP levels enhanced risk categorization among HF patients. Furthermore, the KTR index presented complementary prognostic value for those HF patients with low-grade inflammation (hs-CRP ≤ 6 mg/L). Our results indicated plasma KTR is an independent risk factor for cardiovascular events. Plasma KTR levels in patients with HF can provide both concurrent and complementary prognostic value to hs-CRP.

Sinomenine ameliorates bleomycin-induced pulmonary fibrosis by inhibiting the differentiation of fibroblast into myofibroblast

Idiopathic pulmonary fibrosis (IPF) represents a severe interstitial lung disease characterized by limited therapeutic interventions. Recent study has suggested that sinomenine (SIN), an alkaloid derived from the roots of Sinomenium acutum, demonstrates efficacy in interrupting aerobic glycolysis, a predominant metabolic pathway in myofibroblasts. However, its pharmacological potential in the context of pulmonary fibrosis remains inadequately explored. In the present study, we established a bleomycin (BLM)-induced pulmonary fibrosis mouse model and subjected the mice to a one-week regimen of SIN treatment to assess its efficacy. Additionally, a TGF-β1-induced primary lung fibroblast model was employed to investigate the molecular mechanism underlying the effects of SIN. Our observations revealed robust anti-pulmonary fibrosis properties associated with SIN treatment, as evidenced by reduced extracellular matrix deposition, diminished hydroxyproline contents, improved Ashcroft scores, and enhanced lung function parameters. Furthermore, SIN administration significantly impeded TGF-β1-induced fibroblast-to-myofibroblast differentiation. Mechanistically, SIN exerted its beneficial effects by mitigating aerobic glycolysis, achieved through the inhibition of the expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (Pfkfb3). Notably, the protective effects of SIN on fibroblasts were reversed upon ectopic overexpression of Pfkfb3. In conclusion, our data underscore the potential of SIN to attenuate fibroblast-to-myofibroblast differentiation by modulating Pfkfb3-associated aerobic glycolysis and SIN emerges as a promising anti-fibrotic agent for pulmonary fibrosis in clinical practice.

Kynurenine acts as a signaling molecule to attenuate pulmonary fibrosis by enhancing the AHR-PTEN axis

INTRODUCTION

Pulmonary fibrosis (PF) is a fatal fibrotic lung disease without any options to halt disease progression. Feasible evidence suggests that aberrant metabolism of amino acids may play a role in the pathoetiology of PF. However, the exact impact of kynurenine (Kyn), a metabolite derived from tryptophan (Trp) on PF is yet to be addressed.

OBJECTIVES

This study aims to elucidate the role of kynurenine in both the onset and advancement of PF.

METHODS

Liquid chromatography-tandem mass spectrometry was employed to assess Kyn levels in patients with idiopathic PF and PF associated with Sjögren's syndrome. Additionally, a mouse model of PF induced by bleomycin was utilized to study the impact of Kyn administration. Furthermore, cell models treated with TGF-β1 were used to explore the mechanism by which Kyn inhibits fibroblast functions.

RESULTS

We demonstrated that high levels of Kyn are a clinical feature in both idiopathic PF patients and primary Sjögren syndrome associated PF patients. Further studies illustrated that Kyn served as a braking molecule to suppress fibroblast functionality, thereby protecting mice from bleomycin-induced lung fibrosis. The protective effects depend on AHR, in which Kyn induces AHR nuclear translocation, where it upregulates PTEN expression to blunt TGF-β mediated AKT/mTOR signaling in fibroblasts. However, in fibrotic microenviroment, the expression of AHR is repressed by methyl-CpG-binding domain 2 (MBD2), a reader interpreting the effect of DNA methylation, which results in a significantly reduced sensitivity of Kyn to fibroblasts. Therefore, exogenous administration of Kyn substantially reversed established PF.

CONCLUSION

Our studies not only highlighted a critical role of Trp metabolism in PF pathogenesis, but also provided compelling evidence suggesting that Kyn could serve as a promising metabolite against PF.

Pulmonary Hypertension and Hyperglycemia-Not a Sweet Combination

Hyperglycemia and pulmonary hypertension (PH) share common pathological pathways that lead to vascular dysfunction and resultant cardiovascular complications. These shared pathologic pathways involve endothelial dysfunction, inflammation, oxidative stress, and hormonal imbalances. Individuals with hyperglycemia or pulmonary hypertension also possess shared clinical factors that contribute to increased morbidity from both diseases. This review aims to explore the relationship between PH and hyperglycemia, highlighting the mechanisms underlying their association and discussing the clinical implications. Understanding these common pathologic and clinical factors will enable early detection for those at-risk for complications from both diseases, paving the way for improved research and targeted therapeutics.

Metabolic liability for weight gain in early adulthood

While weight gain is associated with a host of chronic illnesses, efforts in obesity have relied on single "snapshots" of body mass index (BMI) to guide genetic and molecular discovery. Here, we study >2,000 young adults with metabolomics and proteomics to identify a metabolic liability to weight gain in early adulthood. Using longitudinal regression and penalized regression, we identify a metabolic signature for weight liability, associated with a 2.6% (2.0%-3.2%, p = 7.5 × 10-19) gain in BMI over ≈20 years per SD higher score, after comprehensive adjustment. Identified molecules specified mechanisms of weight gain, including hunger and appetite regulation, energy expenditure, gut microbial metabolism, and host interaction with external exposure. Integration of longitudinal and concurrent measures in regression with Mendelian randomization highlights the complexity of metabolic regulation of weight gain, suggesting caution in interpretation of epidemiologic or genetic effect estimates traditionally used in metabolic research.

A new framework for exploratory network mediator analysis in omics data

Omics methods are widely used in basic biology and translational medicine research. More and more omics data are collected to explain the impact of certain risk factors on clinical outcomes. To explain the mechanism of the risk factors, a core question is how to find the genes/proteins/metabolites that mediate their effects on the clinical outcome. Mediation analysis is a modeling framework to study the relationship between risk factors and pathological outcomes, via mediator variables. However, high-dimensional omics data are far more challenging than traditional data: (1) From tens of thousands of genes, can we overcome the curse of dimensionality to reliably select a set of mediators? (2) How do we ensure that the selected mediators are functionally consistent? (3) Many biological mechanisms contain nonlinear effects. How do we include nonlinear effects in the high-dimensional mediation analysis? (4) How do we consider multiple risk factors at the same time? To meet these challenges, we propose a new exploratory mediation analysis framework, medNet, which focuses on finding mediators through predictive modeling. We propose new definitions for predictive exposure, predictive mediator, and predictive network mediator, using a statistical hypothesis testing framework to identify predictive exposures and mediators. Additionally, two heuristic search algorithms are proposed to identify network mediators, essentially subnetworks in the genome-scale biological network that mediate the effects of single or multiple exposures. We applied medNet on a breast cancer data set and a metabolomics data set combined with food intake questionnaire data. It identified functionally consistent network mediators for the exposures' impact on the outcome, facilitating data interpretation.

IDO1 Inhibition Promotes Activation of Tumor-intrinsic STAT3 Pathway and Induces Adverse Tumor-protective Effects

Pharmacological inhibition of IDO1 exhibits great promise as a strategy in cancer therapy. However, the failure of phase III clinical trials has raised the pressing need to understand the underlying reasons for this outcome. To gain comprehensive insights into the reasons behind the clinical failure of IDO1 inhibitors, it is essential to investigate the entire tumor microenvironment rather than focusing solely on individual cells or relying on knockout techniques. In this study, we conducted single-cell RNA sequencing to determine the overall response to apo-IDO1 inhibitor administration. Interestingly, although apo-IDO1 inhibitors were found to significantly activate intratumoral immune cells (mouse colon cancer cell CT26 transplanted in BALB/C mice), such as T cells, macrophages, and NK cells, they also stimulated the infiltration of M2 macrophages. Moreover, these inhibitors prompted monocytes and macrophages to secrete elevated levels of IL-6, which in turn activated the JAK2/STAT3 signaling pathway in tumor cells. Consequently, this activation enables tumor cells to survive even in the face of heightened immune activity. These findings underscore the unforeseen adverse effects of apo-IDO1 inhibitors on tumor cells and highlight the potential of combining IL-6/JAK2/STAT3 inhibitors with apo-IDO1 inhibitors to improve their clinical efficacy.

Diabetes Mellitus, Energy Metabolism, and COVID-19

Obesity, diabetes mellitus (mostly type 2), and COVID-19 show mutual interactions because they are not only risk factors for both acute and chronic COVID-19 manifestations, but also because COVID-19 alters energy metabolism. Such metabolic alterations can lead to dysglycemia and long-lasting effects. Thus, the COVID-19 pandemic has the potential for a further rise of the diabetes pandemic. This review outlines how preexisting metabolic alterations spanning from excess visceral adipose tissue to hyperglycemia and overt diabetes may exacerbate COVID-19 severity. We also summarize the different effects of SARS-CoV-2 infection on the key organs and tissues orchestrating energy metabolism, including adipose tissue, liver, skeletal muscle, and pancreas. Last, we provide an integrative view of the metabolic derangements that occur during COVID-19. Altogether, this review allows for better understanding of the metabolic derangements occurring when a fire starts from a small flame, and thereby help reducing the impact of the COVID-19 pandemic.

Gut microbiota in overweight and obesity: crosstalk with adipose tissue

Overweight and obesity are characterized by excessive fat mass accumulation produced when energy intake exceeds energy expenditure. One plausible way to control energy expenditure is to modulate thermogenic pathways in white adipose tissue (WAT) and/or brown adipose tissue (BAT). Among the different environmental factors capable of influencing host metabolism and energy balance, the gut microbiota is now considered a key player. Following pioneering studies showing that mice lacking gut microbes (that is, germ-free mice) or depleted of their gut microbiota (that is, using antibiotics) developed less adipose tissue, numerous studies have investigated the complex interactions existing between gut bacteria, some of their membrane components (that is, lipopolysaccharides), and their metabolites (that is, short-chain fatty acids, endocannabinoids, bile acids, aryl hydrocarbon receptor ligands and tryptophan derivatives) as well as their contribution to the browning and/or beiging of WAT and changes in BAT activity. In this Review, we discuss the general physiology of both WAT and BAT. Subsequently, we introduce how gut bacteria and different microbiota-derived metabolites, their receptors and signalling pathways can regulate the development of adipose tissue and its metabolic capacities. Finally, we describe the key challenges in moving from bench to bedside by presenting specific key examples.

Nutritional Approaches Targeting Gut Microbiota in Oxidative-Stress-Associated Metabolic Syndrome: Focus on Early Life Programming

Metabolic syndrome (MetS) denotes a constellation of risk factors associated with the development of cardiovascular disease, with its roots potentially traced back to early life. Given the pivotal role of oxidative stress and dysbiotic gut microbiota in MetS pathogenesis, comprehending their influence on MetS programming is crucial. Targeting these mechanisms during the early stages of life presents a promising avenue for preventing MetS later in life. This article begins by examining detrimental insults during early life that impact fetal programming, ultimately contributing to MetS in adulthood. Following that, we explore the role of oxidative stress and the dysregulation of gut microbiota in the initiation of MetS programming. The review also consolidates existing evidence on how gut-microbiota-targeted interventions can thwart oxidative-stress-associated MetS programming, encompassing approaches such as probiotics, prebiotics, postbiotics, and the modulation of bacterial metabolites. While animal studies demonstrate the favorable effects of gut-microbiota-targeted therapy in mitigating MetS programming, further clinical investigations are imperative to enhance our understanding of manipulating gut microbiota and oxidative stress for the prevention of MetS.

The potential of aryl hydrocarbon receptor as receptors for metabolic changes in tumors

Cancer cells can alter their metabolism to meet energy and molecular requirements due to unfavorable environments with oxygen and nutritional deficiencies. Therefore, metabolic reprogramming is common in a tumor microenvironment (TME). Aryl hydrocarbon receptor (AhR) is a ligand-activated nuclear transcription factor, which can be activated by many exogenous and endogenous ligands. Multiple AhR ligands can be produced by both TME and tumor cells. By attaching to various ligands, AhR regulates cancer metabolic reprogramming by dysregulating various metabolic pathways, including glycolysis, lipid metabolism, and nucleotide metabolism. These regulated pathways greatly contribute to cancer cell growth, metastasis, and evading cancer therapies; however, the underlying mechanisms remain unclear. Herein, we review the relationship between TME and metabolism and describe the important role of AhR in cancer regulation. We also focus on recent findings to discuss the idea that AhR acts as a receptor for metabolic changes in tumors, which may provide new perspectives on the direction of AhR research in tumor metabolic reprogramming and future therapeutic interventions.

Functionally conserved PPARG exonic circRNAs enhance intramuscular fat deposition by regulating PPARG and HSL

Circular RNAs (circRNA) are a kind of endogenous biological macromolecules that play significant roles in many biological processes, including adipogenesis, a precisely orchestrated process that is mediated by a large number of factors. Among them, peroxisome proliferator-activated receptor gamma (PPARG), is undoubtedly the most important regulator of adipocyte development in all types of adipose tissue. The formation of intramuscular fat (IMF), is a key factor that influences the meat quality in livestock animals. PPARG has been demonstrated to show a positive correlation with IMF deposition although the regulatory mechanism involved is not known. This study demonstrates that PPARG mediates IMF deposition by producing multiple exonic circRNAs (circPPARGs). Three circPPARGs promote adipogenic differentiation and inhibit the proliferation of intramuscular preadipocytes and these effects are conserved across several species including buffaloes, cattle and mice. Notably, circPPARG1 interacts with PPARG protein to inhibit the transcription of hormone sensitive lipase (HSL) involved in lipolysis. In addition, the positive effects of circPPARG1 on IMF deposition were identified in mice in vivo. Thus, PPARG drives IMF deposition, not only through the common transcription factor pathway, but also by producing circRNAs. This study provides new insights into our understanding of the regulatory mechanisms of PPARG in IMF deposition.

Hallmarks of the metabolic secretome

The identification of novel secreted factors is advancing at an unprecedented pace. However, there is a critical need to consolidate and integrate this knowledge to provide a framework of their diverse mechanisms, functional significance, and inter-relationships. Complicating this effort are challenges related to nonstandardized methods, discrepancies in sample handling, and inconsistencies in the annotation of unknown molecules. This Review aims to synthesize the rapidly expanding field of the metabolic secretome, encompassing the five major types of secreted factors: proteins, peptides, metabolites, lipids, and extracellular vesicles. By systematically defining the functions and detection of the components within the metabolic secretome, this Review provides a primer into the advances of the field, and how integration of the techniques discussed can provide a deeper understanding of the mechanisms underlying metabolic homeostasis and its disorders.

Effect of metformin on Wnt5a in individuals new-onset type 2 diabetes with different body mass indexes: The evidences from the real word research

Aim

Metformin is a first-line therapy for the treatment of Type 2 diabetes mellitus (T2DM), due to its inhibition of hepatic gluconeogenesis. Wingless family member 5a (Wnt5a) was significantly decreased in newly diagnosed T2DM patients and regulates secretion of β cells through the Wnt/calcium signalling cascades. This study aims to investigate how metformin works on glucose-lowering effects in diabetes and whether the mechanism underlying it is associated with Wnt5a.

Methods

A total of 144 participants were enrolled in this study. Serum Wnt5a levels were measured by an enzyme-linked immunosorbent assay (ELISA). The demographic and clinical parameters were evaluated in normal weight, overweight and obese new-onset T2DM subjects grouped.

Results

Wnt5a was increased in overweight T2DM patients and obese T2DM patients compared with the levels in normal Body Mass Index (BMI) T2DM. The level of Wnt5a gradually increased after 3 and 6 months of metformin treatment. Among the three groups, the most significant improvement in blood glucose was observed in the obese type 2 diabetic patients, and the improvement showed a significant correlation with Wnt5a protein after patients received metformin treatment. Pearson correlation showed that there was a significant relationship between △2hOGTT and Wnt5a. After further adjusting for sex and age, a significant association existed only between Wnt5a and 2-h oral glucose tolerance test(2hOGTT), and this association was negative.

Conclusion

Our results indicate that Wnt5a may play a role in the mechanism by which metformin improves blood glucose in patients with type 2 diabetes.

Elevated indoleamine 2,3-dioxygenase activity is associated with endothelial dysfunction in people living with HIV and ROS production in human aortic endothelial cells in vitro

The precise role of indoleamine 2,3-dioxygenase (IDO) in cardiovascular diseases (CVD) among people living with HIV (PLWH) is still under debate, despite recognized links. This study aimed to investigate the impact of elevated IDO activity on endothelial dysfunction in PLWH. A total of 38 PLWH, who had not previously received anti-retroviral therapy (ART), were enrolled in the study. These participants were monitored for 36 months following the initiation of ART. Measurements including plasma levels of IDO activity, markers of endothelial dysfunction, inflammatory factors, and lipids. In vitro, human aortic endothelial cells (HAEC) were exposed to interferon-γ, an IDO inhibitor, a kynurenine 3-hydroxylase (KMO) inhibitor, as well as different concentrations of kynurenine. Pre-ART, PLWH demonstrated notably elevated plasma concentrations of soluble intercellular adhesion molecule 1 (sICAM-1), soluble vascular cell adhesion molecule 1(sVCAM-1), and IDO activity in comparison to healthy controls. Post-ART, both IDO activity and sICAM-1 levels experienced a significant decrease, with IDO activity reaching levels comparable to those observed in healthy controls. Furthermore, a positive correlation was observed between IDO activity and sICAM-1 (p = 0.0002), as well as sVCAM-1 (p < 0.0001) before ART. In vitro, the augmentation of kynurenine concentration in the medium and the induction of IDO expression in HAEC resulted in increased production of reactive oxygen species (ROS), with minimal impact on endothelial dysfunction. From these findings, it can be concluded that long-term ART has the potential to restore the heightened IDO activity observed in PLWH. The overexpression of IDO primarily influences the expression of ROS in HAEC.

Ubc9 regulates the expression of MHC II in dendritic cells to enhance DSS-induced colitis by mediating RBPJ SUMOylation

SUMOylation is an evolutionary conserved regulatory mechanism, in which Ubc9 is the only E2 conjugating enzyme. Previous studies demonstrated that SUMOylation is involved in multiple biological processes, but its role in dendritic cells (DCs) remains to be fully addressed. Herein in this report, we found that DCs deficient in Ubc9 protected mice from dextran sulfate sodium (DSS)-induced colitis, as evidenced by the ameliorated weight loss, colon length, and disrupted colon structure. Mechanistically, Ubc9 mediated SUMOylation of RBPJ, by which it stabilized RBPJ from ubiquitin-mediated degradation to enhance its transcriptional activity, while Ciita, a critical transcription factor, is a direct target downstream of RBPJ, which forms an enhanceosome complex to transcribe the expression of MHC II genes. Therefore, loss of Ubc9 abolished RBPJ SUMOylation, which was coupled with reduced Ciita transcription, thereby attenuating the expression of MHC class II genes. As a consequence of defective MHC II expression, Ubc9-/- DCs were featured by the impaired capability to process antigen and to prime effector CD4+ T cells, thereby protecting mice from DSS-induced colitis. Together, our results shed novel insight into the understanding of SUMOylation in the regulation of DC functions in pathological conditions.

Non-Toxicological Role of Aryl Hydrocarbon Receptor in Obesity-Associated Multiple Myeloma Cell Growth and Survival

Obesity is not only a risk factor for multiple myeloma (MM) incidence, but it is also associated with an increased risk of progression from myeloma precursors-monoclonal gammopathy of undetermined significance-and smoldering myeloma. Adipocytes in the bone marrow (BMAs) microenvironment have been shown to facilitate MM cell growth via secreted factors, but the nature of these secreted factors and their mechanism of action have not been fully elucidated. The elevated expression of aryl hydrocarbon receptor (AhR) is associated with a variety of different cancers, including MM; however, the role of AhR activity in obesity-associated MM cell growth and survival has not been explored. Indeed, this is of particular interest as it has been recently shown that bone marrow adipocytes are a source of endogenous AhR ligands. Using multiple in vitro models of tumor-adipocyte crosstalk to mimic the bone microenvironment, we identified a novel, non-toxicological role of the adipocyte-secreted factors in the suppression of AhR activity in MM cells. A panel of six MM cell lines were cultured in the presence of bone marrow adipocytes in (1) a direct co-culture, (2) a transwell co-culture, or (3) an adipocyte-conditioned media to interrogate the effects of the secreted factors on MM cell AhR activity. Nuclear localization and the transcriptional activity of the AhR, as measured by CYP1A1 and CYP1B1 gene induction, were suppressed by exposure to BMA-derived factors. Additionally, decreased AhR target gene expression was associated with worse clinical outcomes. The knockdown of AhR resulted in reduced CYP1B1 expression and increased cellular growth. This tumor-suppressing role of CYP1A1 and CYP1B1 was supported by patient data which demonstrated an association between reduced target gene expression and worse overall survival. These data demonstrated a novel mechanism by which bone marrow adipocytes promote MM progression.

Crosstalk between Exercise-Derived Endocannabinoidome and Kynurenines: Potential Target Therapies for Obesity and Depression Symptoms

The kynurenine pathway (KP) and the endocannabinoid system (ECS) are known to be deregulated in depression and obesity; however, it has been recognized that acute physical exercise has an important modulating role inducing changes in the mobilization of their respective metabolites-endocannabinoids (eCBs) and kynurenines (KYNs)-which overlap at some points, acting as important antidepressant, anti-nociceptive, anti-inflammatory, and antioxidant biomarkers. Therefore, the aim of this review is to analyze and discuss some recently performed studies to investigate the potential interactions between both systems, particularly those related to exercise-derived endocannabinoidome and kynurenine mechanisms, and to elucidate how prescription of physical exercise could represent a new approach for the clinical management of these two conditions.

Nitric Oxide as a Determinant of Human Longevity and Health Span

The master molecular regulators and mechanisms determining longevity and health span include nitric oxide (NO) and superoxide anion radicals (SOR). L-arginine, the NO synthase (NOS) substrate, can restore a healthy ratio between the dangerous SOR and the protective NO radical to promote healthy aging. Antioxidant supplementation orchestrates protection against oxidative stress and damage-L-arginine and antioxidants such as vitamin C increase NO production and bioavailability. Uncoupling of NO generation with the appearance of SOR can be induced by asymmetric dimethylarginine (ADMA). L-arginine can displace ADMA from the site of NO formation if sufficient amounts of the amino acid are available. Antioxidants such as ascorbic acids can scavenge SOR and increase the bioavailability of NO. The topics of this review are the complex interactions of antioxidant agents with L-arginine, which determine NO bioactivity and protection against age-related degeneration.

Aryl hydrocarbon receptor utilises cellular zinc signals to maintain the gut epithelial barrier

Zinc and plant-derived ligands of the aryl hydrocarbon receptor (AHR) are dietary components affecting intestinal epithelial barrier function. Here, we explore whether zinc and the AHR pathway are linked. We show that dietary supplementation with an AHR pre-ligand offers protection against inflammatory bowel disease in a mouse model while protection fails in mice lacking AHR in the intestinal epithelium. AHR agonist treatment is also ineffective in mice fed zinc depleted diet. In human ileum organoids and Caco-2 cells, AHR activation increases total cellular zinc and cytosolic free Zn2+ concentrations through transcription of genes for zinc importers. Tight junction proteins are upregulated through zinc inhibition of nuclear factor kappa-light-chain-enhancer and calpain activity. Our data show that AHR activation by plant-derived dietary ligands improves gut barrier function at least partly via zinc-dependent cellular pathways, suggesting that combined dietary supplementation with AHR ligands and zinc might be effective in preventing inflammatory gut disorders.

High-fat diet-disturbed gut microbiota-colonocyte interactions contribute to dysregulating peripheral tryptophan-kynurenine metabolism

BACKGROUND

Aberrant tryptophan (Trp)-kynurenine (Kyn) metabolism has been implicated in the pathogenesis of human disease. In particular, populations with long-term western-style diets are characterized by an excess of Kyn in the plasma. Host-gut microbiota interactions are dominated by diet and are essential for maintaining host metabolic homeostasis. However, the role of western diet-disturbed gut microbiota-colonocyte interactions in Trp metabolism remains to be elucidated.

RESULTS

Here, 4-week-old mice were fed with a high-fat diet (HFD), representing a typical western diet, for 4 weeks, and multi-omics approaches were adopted to determine the mechanism by which HFD disrupted gut microbiota-colonocyte interplay causing serum Trp-Kyn metabolism dysfunction. Our results showed that colonocyte-microbiota interactions dominated the peripheral Kyn pathway in HFD mice. Mechanistically, persistent HFD-impaired mitochondrial bioenergetics increased colonic epithelial oxygenation and caused metabolic reprogramming in colonites to support the expansion of Proteobacteria in the colon lumen. Phylum Proteobacteria-derived lipopolysaccharide (LPS) stimulated colonic immune responses to upregulate the indoleamine 2,3-dioxygenase 1 (IDO1)-mediated Kyn pathway, leading to Trp depletion and Kyn accumulation in the circulation, which was further confirmed by transplantation of Escherichia coli (E.coli) indicator strains and colonic IDO1 depletion. Butyrate supplementation promoted mitochondrial functions in colonocytes to remodel the gut microbiota in HFD mice, consequently ameliorating serum Kyn accumulation.

CONCLUSIONS

Our results highlighted that HFD disrupted the peripheral Kyn pathway in a gut microbiota-dependent manner and that the continuous homeostasis of gut bacteria-colonocytes interplay played a central role in the regulation of host peripheral Trp metabolism. Meanwhile, this study provided new insights into therapies against western diet-related metabolic disorders. Video Abstract.

Deficiency of Adipose Aryl Hydrocarbon Receptor Protects against Diet-Induced Metabolic Dysfunction through Sexually Dimorphic Mechanisms

The molecular mechanisms underlying diet-induced obesity are complex and remain unclear. The activation of the aryl hydrocarbon receptor (AhR), a xenobiotic sensor, by obesogens may contribute to diet-induced obesity through influences on lipid metabolism and insulin resistance acting at various sites, including adipose tissue. Thus, our hypothesis was that conditional AhR depletion, specifically from mature adipose tissue (CadKO), would improve high-fat diet (HFD)-induced metabolic dysfunction. CadKO protects mice from HFD-induced weight gain. CadKO females eat fewer calories, leading to increased energy expenditure (EE) and improved glucose tolerance on HFD. Our exploration of adipose tissue biology suggests that the depletion of AhR from adipocytes provides female mice with an increased capacity for adipogenesis and lipolysis, allowing for the maintenance of a healthy adipocyte phenotype. The HFD-induced leptin rise was reduced in CadKO females, but the hypothalamic leptin receptor (LepR) was increased in the energy regulatory regions of the hypothalamus, suggesting an increased sensitivity to leptin. The estrogen receptor α (ERα) was higher in CadKO female adipose tissue and the hypothalamus. CadKO males displayed a delayed progression of obesity and insulin resistance. In males, CadKO ameliorated proinflammatory adipocytokine secretion (such as TNFα, IL1β, IL6) and displayed reduced inflammatory macrophage infiltration into adipose depots. Overall, CadKO improves weight control and systemic glucose homeostasis under HFD challenge but to a more profound extent in females. CadKO facilitates a lean phenotype in females and mediates healthy adipose-hypothalamic crosstalk. In males, adipose-specific AhR depletion delays the development of obesity and insulin resistance through the maintenance of healthy crosstalk between adipocytes and immune cells.

Synergistic effect of endurance training and nettle leaf extract on the IDO1-KYN-AHR pathway homeostasis and inhibiting of liver toxicity in rats with STZ-induced diabetes

Introduction

Diabetes adversely affects a number of hepatic molecular pathways, including the kynurenine (KYN) pathway. KYN is produced by indoleamine 2,3-dioxygenase (IDO) and activates the aryl hydrocarbon receptor (AHR). This study evaluated the effect of endurance training (EndTr) and nettle leaf extract (NLE) on the IDO1-KYN-AHR pathway in the livers of rats with streptozotocin-induced diabetes.

Methods

We divided 48 rats into six groups: controls (Ct), treated with EndTr (EndTr), diabetes-induced (D), D treated with NLE (D + NLE), D treated with EndTr (D + EnTr), and D treated with EndTr and NLE (D + EndTr + NLE). EndTr, D + EnTr, and D + EndTr + NLE groups were subjected to training with running on treadmill for 8 weeks, 5 days per week, 25 min in first session to 59 min at last session with intensity of 55% to 65% VO2max. Using real-time PCR gene (Ahr, Cyp1a1, and Ido1) expressions and ELISA, malondialdehyde (MDA) and protein (IDO1, AHR, and CYP1A1) levels were determined in the liver samples.

Results

A significant three-way interaction of exercise, nettle, and diabetes was observed on the all variables (P< 0.001). In particular, significant increases in blood glucose level (BGL), in gene and protein expression, and in MDA and KYN levels were observed in the liver samples of the D group versus the Ct group (P< 0.05). BGL and liver MDA levels were significantly lower in the D + EndTr and D + NLE groups than that in the D group. However, the D + EndTr + NLE group showed a more significant decrease in these factors (P< 0.05). In addition, liver KYN levels were significantly lower in the EndTr group compared with that in the Ct group as well as in the D + EndTr + NLE and D + EndTr groups compared with that in the D groups (P< 0.05). Whereas both the EndTr and D + NLE groups showed lower Ahr expression and AHR level compared with the Ct and D groups, respectively (P< 0.05), the D + EndTr + NLE group showed a higher significant reduction in the AHR level than the D group (P< 0.05). The Cyp1a1 expression and IDO1 level significantly decreased only in the D + EndTr + NLE group compared to that in the D group (P< 0.05).

Conclusion

Overall, this study showed that the combination of EndTr and NLE may synergistically restore the imbalanced IDO1-KYN-AHR pathway in diabetic liver.

The Kynurenine Pathway in Healthy Subjects and Subjects with Obesity, Depression and Chronic Obstructive Pulmonary Disease

Background: Changes in tryptophan metabolism through the kynurenine pathway (KP) are observed in several disorders and coupled with pathophysiological deviations. Methods: This study retrospectively compared the KP in serum in healthy subjects (108) with subjects with obesity (141), depression (49), and chronic obstructive pulmonary disease (COPD) (22) participating in four clinical studies and explored predictors of the changes in the KP metabolites. Results: Compared with the healthy group, the KP was upregulated in the disease groups with high kynurenine, quinolinic acid (QA), kynurenine/tryptophan-ratio and QA/xanthurenic acid-ratio and low kynurenic acid/QA-ratio. Tryptophan and xanthurenic acid were upregulated in the depressed group compared with the groups with obesity and COPD. The covariates BMI, smoking, diabetes, and C-reactive protein explained the significant differences between the healthy group and the group with obesity but not between the healthy group and the groups with depression and COPD, indicating that different pathophysiological conditions result in the same changes in the KP. Conclusions: The KP was significantly upregulated in the disease groups compared with the healthy group, and there were significant differences between the disease groups. Different pathophysiological abnormalities seemed to result in the same deviations in the KP.

Deficiency of interleukin-6 receptor ameliorates PM2.5 exposure-induced pulmonary dysfunction and inflammation but not abnormalities in glucose homeostasis

BACKGROUND

Ambient fine particulate matter (PM_2.5) exposure increases local and systemic interleukin-6 (IL-6). However, the pathogenic role of IL-6 signalling following PM_2.5 exposure, particularly in the development of pulmonary dysfunction and abnormal glucose homeostasis, has hardly been investigated.

RESULTS

In the study, IL-6 receptor (IL-6R)-deficient (IL-6R^-/-) and wildtype littermate (IL-6R^+/+) mice were exposed to concentrated ambient PM_2.5 (CAP) or filtered air (FA), and their pulmonary and metabolic responses to these exposures were analyzed. Our results demonstrated that IL-6R deficiency markedly alleviated PM_2.5 exposure-induced increases in lung inflammatory markers including the inflammation score of histological analysis, the number of macrophages in bronchoalveolar lavage fluid (BALF), and mRNA expressions of TNFα, IL-1β and IL-6 and abnormalities in lung function test. However, IL-6R deficiency did not reduce the hepatic insulin resistance nor systemic glucose intolerance and insulin resistance induced by PM_2.5 exposure.

CONCLUSION

Our findings support the crucial role of IL-6 signalling in the development of pulmonary inflammation and dysfunction due to PM_2.5 exposure but question the putative central role of pulmonary inflammation for the extra-pulmonary dysfunctions following PM_2.5 exposure, providing a deep mechanistic insight into the pathogenesis caused by PM_2.5 exposure.