Protein phosphatase 2A regulates xanthine oxidase-derived ROS production in macrophages and influx of inflammatory monocytes in a murine gout model

Proteoglycan 4 (Lubricin) and regulation of xanthine oxidase in synovial macrophage as a mechanism of controlling synovitis

BACKGROUND

Synovial macrophages (SMs) are important effectors of joint health and disease. A novel Cx3CR1 + TREM2 + SM population expressing the tight junction protein claudin-5, was recently discovered in synovial lining. Ablation of these SMs was associated with onset of arthritis. Proteoglycan 4 (PRG4) is a mucinous glycoprotein that fulfills lubricating and homeostatic roles in the joint. The aim of this work is to study the role of PRG4 in modulating synovitis in the context of SM homeostasis and assess the contribution of xanthine oxidase (XO)-hypoxia inducible factor alpha (HIF-1a) axis to this regulation.

METHODS

We used Prg4FrtloxP/FrtloxP;R26FlpoER/+, a novel transgenic mouse, where the Prg4Frt allele normally expresses the PRG4 protein and was designed to flank the first two exons of Prg4 with a flippase recognition target and "LOXP" sites. Inducing flippase activity with tamoxifen (TAM) inactivates the Frt allele and thus creates a conditional knockout state. We studied anti-inflammatory SMs and XO by quantitative immunohistochemistry, isolated RNA and studied immune pathway activations by multiplexed assays and isolated SMs and studied PRG4 signaling dysfunction in relation to glycolytic switching due to pro-inflammatory activation. Prg4 inactivated mice were treated with oral febuxostat, a specific XO inhibitor, and quantification of Cx3CR1 + TREM2 + SMs, XO immunostaining and synovitis assessment were conducted.

RESULTS

Prg4 inactivation induced Cx3CR1 + TREM2 + SM loss (p < 0.001) and upregulated glycolysis and innate immune pathways in the synovium. In isolated SMs, Xdh (p < 0.01) and Hif1a (p < 0.05) were upregulated. Pro-inflammatory activation of SMs was evident by enhanced glycolytic flux and XO-generated reactive oxygen species (ROS). Febuxostat reduced glycolytic flux (p < 0.001) and HIF-1a levels (p < 0.0001) in SMs. Febuxostat also reduced systemic inflammation (p < 0.001), synovial hyperplasia (p < 0.001) and preserved Cx3CR1 + TREM2 + SMs (p < 0.0001) in synovia of Prg4 inactivated mice.

CONCLUSIONS

PRG4 is a biologically significant modulator of synovial homeostasis via inhibition of XO expression and downstream HIF-1a activation. PRG4 signaling is anti-inflammatory and promotes synovial homeostasis in chronic synovitis, where direct XO inhibition is potentially therapeutic in chronic synovitis.

Identification of key genes in gout and atherosclerosis and construction of molecular regulatory networks

Background

Gout is a type of chronic inflammatory disease linked to the accumulation of monosodium urate crystals, leading to arthritis. Studies have shown that patients with gout are more likely to develop atherosclerosis, but the specific mechanisms involved remain unknown. The purpose of the research was to explore the key molecules and potential mechanisms between gout and atherosclerosis.

Methods

Gene expression profiles for gout as well as atherosclerosis were obtained from the Gene Expression Omnibus (GEO) database, then differential analysis was utilized to identify common differentially expressed genes (DEGs) between the two diseases. The analysis of functional enrichment was conducted to investigate the biological processes that the DEGs might be involved in. The Cytoscape software was utilized to develop a protein-protein interaction (PPI) network as well as identify hub genes, while LASSO analysis was employed to select key genes. The TRRUST database was utilized to forecast transcription factors (TFs), and the miRTarBase database was utilized to forecast miRNAs.

Results

Four key genes, CCL3, TNF, CCR2, and CCR5, were identified. The receiver operating characteristic (ROC) curves showed that the areas under ROC curve (AUC) for these four key genes in both gout and atherosclerosis were greater than 0.9. The analysis of functional enrichment revealed that the DEGs were primarily involved in "regulation of T-cell activation", "chemokine signaling pathway", and other biological processes. The TRRUST prediction results indicated that RELA and NFKB1 are common regulatory transcription factors for CCR2, CCR5, CCL3, and TNF. The miRTarBase prediction results showed that hsa-miR-203a-3p is a common regulatory miRNA for TNF and CCR5.

Conclusion

This study preliminarily explored the potential key molecules and mechanisms between gout and atherosclerosis. These findings provide new insights for further research into identifying potential biomarkers and clinical treatment strategies for these two diseases.

Kaempferol attenuates hyperuricemia combined with gouty arthritis via urate transporters and NLRP3/NF-κB pathway modulation

Hyperuricemia (HUA), caused by purine disorders, can lead to gouty arthritis (GA). Kaempferol (KPF), a natural flavonoid, has anti-inflammatory properties, though its mechanism in treating HUA combined with GA remains unclear. This study used a mouse model of HUA combined with GA and in vitro models with HK-2 and THP-1 cells to explore KPF's effects. Cells were treated with KPF or inhibitors of ABCG2, ROS, NLRP3 inflammasome, and nuclear factor κB (NF-κB) pathway. Quantitative assays measured uric acid (UA), creatinine, oxidative stress biomarkers, and pro-inflammatory cytokines. Histopathological analyses showed KPF improved renal and joint inflammation caused by HUA and GA. KPF alleviated oxidative stress, reduced pro-inflammatory cytokines, and regulated UA levels through the modulation of urate transporters, NLRP3 inflammasome, and NF-κB pathway. KPF's actions, partly mediated by ROS reduction, suggest it is a promising candidate for treating HUA combined with GA.

Proteoglycan 4 (Lubricin) and Regulation of Xanthine Oxidase in Synovial Macrophage as A Mechanism of Controlling Synovitis

Background

Synovial macrophages (SMs) are important effectors of joint health and disease. A novel Cx3CR1 + TREM2 + SM population expressing the tight junction protein claudin-5, was recently discovered in synovial lining. Ablation of these SMs was associated with onset of arthritis. Proteoglycan 4 (PRG4) is a mucinous glycoprotein that fulfills lubricating and homeostatic roles in the joint. The aim of this work is to study the role of PRG4 in modulating synovitis in the context of SM homeostasis and assess the contribution of xanthine oxidase (XO)-hypoxia inducible factor alpha (HIF-1α) axis to this regulation.

Methods

We used Prg4 FrlioxP/FrtloxP ;R26 FlPoER/+ , a novel transgenic mouse, where the Prg4 Frt allele normally expresses the PRG4 protein and was designed to flank the first two exons of Prg4 with a flippase recognition target and "LOXP" sites. Inducing flippase activity with tamoxifen (TAM) inactivates the Frt allele and thus creates a conditional knockout state. We studied anti-inflammatory SMs and XO by quantitative immunohistochemistry, isolated RNA and studied immune pathway activations by multiplexed assays and isolated SMs and studied PRG4 signaling dysfunction in relation to glycolytic switching due to pro-inflammatory activation. Prg4 inactivated mice were treated with oral febuxostat, a specific XO inhibitor, and quantification of Cx3CR1 + TREM2 + SMs, XO immunostaining and synovitis assessment were conducted.

Results

Prg4 inactivation induced Cx3CR1 + TREM2 + SM loss (p < 0.001) and upregulated glycolysis and innate immune pathways in the synovium. In isolated SMs, Xdh (p < 0.01) and Hif1a (p < 0.05) were upregulated. Pro-inflammatory activation of SMs was evident by enhanced glycolytic flux and XO-generated reactive oxygen species (ROS). Febuxostat reduced glycolytic flux (p < 0.001) and HIF-1α levels (p < 0.0001) in SMs. Febuxostat also reduced systemic inflammation (p < 0.001), synovial hyperplasia (p < 0.001) and preserved Cx3CR1 + TREM2 + SMs (p < 0.0001) in synovia of Prg4 inactivated mice.

Conclusions

PRG4 is a biologically significant modulator of synovial homeostasis via inhibition of XO expression and downstream HIF-1a activation. PRG4 signaling is anti-inflammatory and promotes synovial homeostasis in chronic synovitis, where direct XO inhibition is potentially therapeutic in chronic synovitis.

Mechanism of Reactive Oxygen Species-Guided Immune Responses in Gouty Arthritis and Potential Therapeutic Targets

Gouty arthritis (GA) is an inflammatory disease caused by monosodium urate (MSU) crystals deposited in the joint tissues causing severe pain. The disease can recur frequently and tends to form tophus in the joints. Current therapeutic drugs for the acute phase of GA have many side effects and limitations, are unable to prevent recurrent GA attacks and tophus formation, and overall efficacy is unsatisfactory. Therefore, we need to advance research on the microscopic mechanism of GA and seek safer and more effective drugs through relevant targets to block the GA disease process. Current research shows that the pathogenesis of GA is closely related to NLRP3 inflammation, oxidative stress, MAPK, NET, autophagy, and Ferroptosis. However, after synthesizing and sorting out the above mechanisms, it is found that the presence of ROS is throughout almost the entire spectrum of micro-mechanisms of the gout disease process, which combines multiple immune responses to form a large network diagram of complex and tight connections involved in the GA disease process. Current studies have shown that inflammation, oxidative stress, cell necrosis, and pathological signs of GA in GA joint tissues can be effectively suppressed by modulating ROS network-related targets. In this article, on the one hand, we investigated the generative mechanism of ROS network generation and its association with GA. On the other hand, we explored the potential of related targets for the treatment of gout and the prevention of tophus formation, which can provide effective reference ideas for the development of highly effective drugs for the treatment of GA.

Targeting Liver Xor by GalNAc-siRNA Is an Effective Strategy for Hyperuricemia Therapy

Hyperuricemia, i.e., increased plasma uric acid concentration, is a common problem in clinical practice, leading to gout or nephrolithiasis, and is associated with other disorders, such as metabolic syndrome, cardiovascular disease, and chronic renal disease. Xanthine oxidoreductase (XOR) is a critical rate-limiting enzyme involved in uric acid synthesis and a promising target for hyperuricemia therapy. However, XOR inhibitors currently face clinical problems such as a short half-life and side effects. Here, we found that specifically targeting liver Xor with GalNAc-siRNAs had a good therapeutic effect on hyperuricemia. First, siRNAs were designed to target various sites in the homologous region between Homo sapiens and Mus musculus Xor mRNA and were screened in primary mouse hepatocytes. Then, the siRNAs were modified to increase their stability in vivo and conjugated with GalNAc for liver-specific delivery. The effects of GalNAc-siRNAs were evaluated in three hyperuricemia mouse models, including potassium oxonate and hypoxanthine administration in WT and humanized XDH mice and Uox knockout mice. Febuxostat, a specific XOR inhibitor used for hyperuricemia treatment, was used as a positive control. Targeting liver Xor with GalNAc-siRNAs by subcutaneous administration reduced plasma uric acid levels, uric acid accumulation in the kidney, renal inflammation, and fibrosis, thereby alleviating kidney damage in hyperuricemia mouse models without hepatoxicity. The results demonstrated that targeting liver Xor with GalNAc-siRNAs was a promising strategy for hyperuricemia therapy.

Gout therapeutics and drug delivery

Gout is a common inflammatory arthritis caused by persistently elevated uric acid levels. With the improvement of people's living standards, the consumption of processed food and the widespread use of drugs that induce elevated uric acid, gout rates are increasing, seriously affecting the human quality of life, and becoming a burden to health systems worldwide. Since the pathological mechanism of gout has been elucidated, there are relatively effective drug treatments in clinical practice. However, due to (bio)pharmaceutical shortcomings of these drugs, such as poor chemical stability and limited ability to target the pathophysiological pathways, traditional drug treatment strategies show low efficacy and safety. In this scenario, drug delivery systems (DDS) design that overcome these drawbacks is urgently called for. In this review, we initially describe the pathological features, the therapeutic targets, and the drugs currently in clinical use and under investigation to treat gout. We also comprehensively summarize recent research efforts utilizing lipid, polymeric and inorganic carriers to develop advanced DDS for improved gout management and therapy.

Effect of Alcohol Consumption Habits on Early Arterial Aging in Subjects with Metabolic Syndrome and Elevated Serum Uric Acid

BACKGROUND

Hyperuricemia is perceived as one of the risk factors for developing and progressing cardiovascular disease and metabolic syndrome through various pathological mechanisms. Endogenous synthesis and exogenous factors such as diet and beverages consumed play a major role in determining serum uric acid (sUA) levels. The aim of this study was to evaluate the effect of alcohol consumption on early arterial aging in middle-aged patients with metabolic syndrome (MetS) and hyperuricemia.

MATERIALS AND METHODS

This study included 661 middle-aged subjects (241 men and 420 women) from the Lithuanian High Cardiovascular Risk (LitHiR) primary prevention program. Characteristics of subjects such as blood pressure, laboratory testing, and the specialized nutrition profile questionnaire were evaluated. As an early marker of arterial stiffness, carotid-femoral pulse wave velocity (cfPWV) was assessed using a non-invasive applanation tonometry technique.

RESULTS

Hyperuricemia was present in 29% of men and 34% of women. Hyperuricemic men reported 1.6 times higher rates of alcohol drinking compared to men with normal sUA levels. After analyzing the correlation between alcohol consumption and cfPWV, no statistically significant relationships were found at a significance level of α = 0.05 but lowering the significance level to 0.06 revealed significant associations in men with normal sUA (ε2ordinal = 0.05, p = 0.06) and in women with increased sUA levels (ε2ordinal = 0.05, p = 0.08). Regression analysis showed that hyperuricemic men, consuming more than one unit of alcohol per week, had a significant impact on increasing cfPWV, while men with normal sUA levels, abstaining from alcohol entirely, resulted in a statistically significant decrease in cfPWV. Our results showed statistically significant relationships only among a group of men, although the women in the hyperuricemic group had a statistically higher cfPWV than women with normal sUA levels.

CONCLUSIONS

Drinking alcohol is associated with increased arterial stiffness among hyperuricemic middle-aged men with MetS.

Targeting reactive oxygen species and fat acid oxidation for the modulation of tumor-associated macrophages: a narrative review

Tumor-associated macrophages (TAMs) are significant immunocytes infiltrating the tumor microenvironment(TME). Recent research has shown that TAMs exhibit diversity in terms of their phenotype, function, time, and spatial distribution, which allows for further classification of TAM subtypes. The metabolic efficiency of fatty acid oxidation (FAO) varies among TAM subtypes. FAO is closely linked to the production of reactive oxygen species (ROS), which play a role in processes such as oxidative stress. Current evidence demonstrates that FAO and ROS can influence TAMs' recruitment, polarization, and phagocytosis ability either individually or in combination, thereby impacting tumor progression. But the specific mechanisms associated with these relationships still require further investigation. We will review the current status of research on the relationship between TAMs and tumor development from three aspects: ROS and TAMs, FAO and TAMs, and the interconnectedness of FAO, ROS, and TAMs.

New drug targets for the treatment of gout arthritis: what's new?

INTRODUCTION

Gout arthritis (GA) is an intermittent inflammatory disease affecting approximately 10% of the worldwide population. Symptomatic phases (acute flares) are timely spaced by asymptomatic periods. During an acute attack, redness, joint swelling, limited movement, and excruciating pain are common symptoms. However, the current available therapies are not fully effective in reducing symptoms and offer numerous side effects. Therefore, unveiling new drug targets and effector molecules are required in developing novel GA therapeutics.

AREAS COVERED

This review discusses the pathophysiological mechanisms of GA and explores potential pharmacological targets to ameliorate disease outcome. In addition, we listed promising pre-clinical studies demonstrating effector molecules with therapeutical potential. Among those, we emphasized the importance of natural products, including traditional Chinese medicine formulas and their multitarget mechanisms of action.

EXPERT OPINION

In our search, we observed that there is a massive gap between pre-clinical and clinical knowledge. Only a minority (4.4%) of clinical trials aimed to intervene by applying natural products or current hot targets described herein. In this sense, we envisage four possibilities for GA therapeutics, which include the repurposing of existing therapies, ALX/FPR2 agonism for improvement in disease outcome, the use of multitarget drugs (e.g. natural products), and targeting the neuroinflammatory component of GA.

The potential relationship of coronary artery disease and hyperuricemia: A cardiometabolic risk factor

Coronary arterial disease (CAD) is the leading cause of mortality in the world. Hyperuricemia has recently emerged as a novel independent risk factor of CAD, in addition to the traditional risk factors such as hyperlipidemia, smoking, and obesity. Several clinical studies have shown that hyperuricemia is strongly associated with the risk, progression and poor prognosis of CAD, as well as verifying an association with traditional CAD risk factors. Uric acid or enzymes in the uric acid production pathway are associated with inflammation, oxidative stress, regulation of multiple signaling pathways and the renin-angiotensin-aldosterone system (RAAS), and these pathophysiological alterations are currently the main mechanisms of coronary atherosclerosis formation. The risk of death from CAD can be effectively reduced by the uric acid-lowering therapy, but the interventional treatment of uric acid levels in patients with CAD remains controversial due to the diversity of co-morbidities and the complexity of causative factors. In this review, we analyze the association between hyperuricemia and CAD, elucidate the possible mechanisms by which uric acid induces or exacerbates CAD, and discuss the benefits and drawbacks of uric acid-lowering therapy. This review could provide theoretical references for the prevention and management of hyperuricemia-associated CAD.