Common defects of ABCG2, a high-capacity urate exporter, cause gout: a function-based genetic analysis in a Japanese population

GLUT2/SLC2A2 is a bi-directional urate transporter

Recent genetic studies showed an association between solute carrier 2A2 (SLC2A2), which encodes glucose transporter 2 (GLUT2), and serum urate concentrations; however, urate transport activity of GLUT2 has not been studied contrary to its function as a sugar transporter. Here, we hypothesized that GLUT2 acts also as a urate transporter, which led us to conduct cell-based functional analyses using HEK-derived 293A cells. We found that radiolabeled [8-14C]-urate was incorporated into GLUT2-expressing cells more compared to control cells and this elevated cellular activity was almost completely inhibited by GLUT2 inhibitors, demonstrating that GLUT2 is a urate transporter. Regarding the concentration dependence of GLUT2-mediated urate transport, no saturable properties were observed within an experimentally achievable range (0-500 μM), suggesting that GLUT2 mediates the robust transport of urate. Moreover, the GLUT2-mediated urate transport was not inhibited by 10 mM glucose; GLUT2-mediated sugar transport was hardly affected by 500 μM urate. As these concentrations of urate and glucose were relevant to their maximum levels in healthy humans, our results suggest that GLUT2 maintains its urate transport ability under physiological conditions, Furthermore, using a cell-based urate efflux assay system, we successfully demonstrated that urate secretion was accelerated in GLUT2-expressing cells than in control cells. Therefore, GLUT2 may also function as a urate exporter. The present study revealed that GLUT2 is a bi-directional urate transporter. Our findings contribute to a deeper understanding of urate-handling systems in the body. To elucidate the physiological role of GLUT2 as a urate transporter, further studies are required.

Genetic background of selected hyperuricemia causing gout with pediatric onset

Elevated serum uric acid levels are the essential pathophysiology of gout. Although gout rarely develops in childhood, chronic persistent hyperuricemia can induce precipitation and deposition of sodium urate crystals, leading to the development of gout. Hyperuricemia is caused by increased uric acid production and/or decreased uric acid excretion capacity of the kidneys and/or intestinal tract. Increased production of uric acid, the final metabolite of purine, is associated with an increase of phosphoribosyl pyrophosphate, the key compound in the purine synthesis pathways, as observed in hypoxanthine-guanine phosphoribosyltransferase deficiency. Another mechanism for increased uric acid production is increased adenosine triphosphate consumption that is found in glycogen storage disease type I. On the other hand, in uromodulin-associated kidney disease, the accumulation of abnormal uromodulin in the kidneys leads to tubulointerstitial damage and fibrosis, and the ability to excrete uric acid is compromised, with reduced secretion and increased reabsorption in the proximal tubules. Decreased uric acid excretion from the kidneys or intestinal tract is also mediated by decreased function of the ATP-binding cassette subfamily G member 2, a urate transporter that acts in the urate secretion. This review summarizes the selected pathophysiological mechanisms underlying the genetic basis of hyperuricemia and gout in children, both in terms of purine metabolism and uric acid excretion.

Identification of pathogenic variants in the ABCG2 gene in patients with severe familial hyperuricemia and gout

We report the identification of two pathogenic variants in the ABCG2 gene, encoding a urate exporter, in two probands (male and female) with severe familial gouty phenotypes and hyperuricemia. Clinico-genetic analyses identified p.I63YfsTer54 (rs565722112) and p.G74D (rs199976573) as potentially causal mutations; functional analyses demonstrated that these two variants are deficient in plasma membrane localization and functionally null. Our data show that dysfunctional variants in the ABCG2 gene are strong risk factors for hyperuricemia and gout in both males and females.

The Effects of Astaxanthin on Metabolic Syndrome: A Comprehensive Review

Metabolic syndrome (MS) represents a complex cluster of metabolic disorders primarily characterized by obesity, insulin resistance, hyperglycemia, dyslipidemia, hypertension, and hyperuricemia. Diet and functional ingredients play a pivotal role in seeking non-pharmacological strategies to prevent and ameliorate MS. Astaxanthin (AST), a carotenoid found in various marine organisms, exhibits exceptional antioxidant properties and holds great promise as a natural compound that improves MS. This article introduces the basic properties of AST, including its absorptance and metabolic pathways, along with various isomers. Most importantly, we comprehensively review the effects and mechanisms of AST on improving the primary components of MS. These mechanisms primarily involve regulating signal transduction, transport, or metabolic pathways within the body, as well as influencing intestinal microbiota and metabolites, thereby exerting positive effects on metabolism and inhibiting the occurrence of MS. This review emphasizes the potential efficacy of AST in managing MS. However, more studies are needed to confirm the clinical effect of AST on MS and reveal potential molecular mechanisms.

Gout: global epidemiology, risk factors, comorbidities and complications: a narrative review

BACKGROUND

Gout is one of the oldest known diseases and the most common form of inflammatory arthritis. The established risk factors for gout include hyperuricemia, chronic renal disease, genetic, alcohol consumption, dietary factors, diuretic use, hypertension, obesity, and metabolic syndrome. Patients with gout have an increased risk of all-cause mortality, particularly from cardiovascular disease, cancer, and infectious diseases. Gout is also associated with several complications, such as nephrolithiasis. This literature review describes the global epidemiology and trends associated with gout, before providing an overview of its risk factors and complications.

METHODS

This research used the narrative review method. Thorough searches were performed in PubMed and Google scholar, up to June 15, 2024, for articles that evaluated the risk factors, comorbidities or complications associated with gout. Moreover, we also included studies that reported the epidemiological characteristics or burden of gout at the global, regional, or national level.

RESULTS

Gout is more prevalent in developed countries, than in developing countries, although its prevalence is increasing globally. In addition, gout is much more prevalent among males than among females. Hyperuricemia has the largest role in the development of gout, although many risk factors contribute to the increasing prevalence of gout, including genes, several medications, and diet. Gout is associated with several comorbidities and complications, which need to be taken into consideration when managing gout. In recent years, gout has been found to be associated with several new comorbidities.

CONCLUSIONS

Our findings provide a comprehensive and informative overview that can be useful for the prevention, diagnosis, and management of gout.

The development of a novel high-throughput membrane potential assay and a solid-supported membrane (SSM)-based electrophysiological assay to study the pharmacological inhibition of GLUT9/SLC2A9 isoforms in a drug discovery program

GLUT9/SLC2A9 is a urate transporter and takes a fundamental role in the maintenance of normal serum urate levels. GLUT9 is the sole transporter of reabsorbed urate from renal epithelial cells to blood, thus making it an ideal pharmacological target for the development of urate-lowering drugs. None of the three currently available assays for studying GLUT9 pharmacological inhibition can support a high throughput drug discovery screening campaign. In this manuscript we present two novel assay technologies which can be used in a drug discovery screening cascade for GLUT9: a GLUT9 membrane potential assay for primary screening; and a solid-supported membrane (SSM)-based supported electrophysiological assay for secondary screening.

The relationship between serum uric acid and gastrointestinal bleeding in peritoneal dialysis patients: a propensity score analysis

PURPOSE

Gastrointestinal bleeding is an important gastrointestinal complication among peritoneal dialysis patients and correlated with a higher risk of mortality. Increased uric acid levels are a significant complication for peritoneal dialysis patients and have been associated with an increased risk of hemorrhagic stroke. The objective of the present study was to investigate the relationship between serum uric acid levels and gastrointestinal bleeding in peritoneal dialysis patients.

METHODS

A total of 2498 peritoneal dialysis patients were recruited. Based on the optimal uric acid cutoff value, two groups of patients were divided. We constructed a propensity-score-matched population of 1762 patients by matching sex, age, and body mass index. Survival outcomes between the two groups were compared using adjusted Kaplan-Meier curves. We constructed the restricted cubic splines regression to assess the correlation between levels of uric acid and gastrointestinal bleeding. A multivariate Cox proportional hazards regression was performed to test whether higher levels of uric acid are an independent risk factor for gastrointestinal bleeding. We performed a forest plot to show interaction effects in different subgroups.

RESULTS

According to restricted cubic splines regression, uric acid levels were positively correlated with the risk of gastrointestinal bleeding events. After adjusted different confounding factors, patients with high levels of uric acid were prone to experience gastrointestinal bleeding (HR 1.868, 95%CI 1.001-3.486). In subgroups, the interaction between higher levels of uric acid and utilizing proton pump inhibitors was significant (P for interaction = 0.034). Further research found that taking proton pump inhibitors could decrease the risk of gastrointestinal bleeding in peritoneal dialysis patients accompanied high levels of uric acid.

CONCLUSION

The baseline high levels of uric acid are an independent risk factor for gastrointestinal bleeding in patients undergoing peritoneal dialysis.

Gout-associated SNP at the IL1RN-IL1F10 region is associated with altered cytokine production in PBMCs of patients with gout and controls

OBJECTIVES

Gout is caused by the response of the innate immune system to monosodium urate (MSU) crystals. A recent gout GWAS identified a signal of genetic association at a locus encompassing IL1RN-IL1F10. Colocalisation analysis using Genotype Tissue Expression Database (GTEx) eQTL data showed that the signal overlaps with genetic control of IL1RN/IL1F10 gene expression. We assess the functional implications of IL1RN rs9973741, the lead gout-associated variant.

METHODS

We conducted functional validation of IL1RN rs9973741 in patients with gout and controls. The transcription level of IL1RN/IL1F10 was investigated in unstimulated or MSU-crystal co-stimulated PBMCs. Ex vivo functional assays were performed in PBMCs stimulated with C16 + MSU crystals or LPS for 24 h. Cytokine levels were assessed by ELISA.

RESULTS

In unstimulated PBMCs, no association of IL1RN rs9973741 (gout risk allele G) to IL1RN expression was observed while IL-1F10 was hindered by low expression at both transcriptional and protein levels. However, G allele carriers showed lower IL1RN expression in PBMCs stimulated with C16/MSU crystal and lower concentrations of circulating IL-1Ra in both controls and gout patients. PBMCs depicted less spontaneous IL-1Ra release in GG homozygous controls and lower IL-1Ra production in response to C16 + MSU crystal costimulation in patients with gout. The G allele was associated with elevated IL-1β cytokine production in response to C16 + MSU crystal stimulation in controls.

CONCLUSIONS

The gout risk allele G associates with lower circulating IL-1Ra, lower IL-1Ra production in PBMC assays and elevated IL-1β production in PBMCs challenged with C16 + MSU crystals but not in unchallenged cells. Our data indicate that the genetic signal that associates with gout at IL1RN-IL1F10 region functions to alter expression of IL-1Ra when stimulated by MSU crystals.

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.

Modulation of ABCG2 Transporter Activity by Ko143 Derivatives

ABCG2 is a multidrug transporter that protects tissues from xenobiotics, affects drug pharmacokinetics, and contributes to multidrug resistance of cancer cells. Here, we present tetracyclic fumitremorgin C analog Ko143 derivatives, evaluate their in vitro modulation of purified ABCG2, and report four high-resolution cryo-EM structures and computational analyses to elucidate their interactions with ABCG2. We found that Ko143 derivatives that are based on a ring-opened scaffold no longer inhibit ABCG2-mediated transport activity. In contrast, closed-ring, tetracyclic analogs were highly potent inhibitors. Strikingly, the least potent of these compounds, MZ82, bound deeper into the central ABCG2 cavity than the other inhibitors and it led to partial closure of the transmembrane domains and increased flexibility of the nucleotide-binding domains. Minor structural modifications can thus convert a potent inhibitor into a compound that induces conformational changes in ABCG2 similar to those observed during binding of a substrate. Molecular dynamics simulations and free energy binding calculations further supported the correlation between reduced potency and distinct binding pose of the compounds. We introduce the highly potent inhibitor AZ99 that may exhibit improved in vivo stability.

A genome-wide association analysis reveals new pathogenic pathways in gout

Gout is a chronic disease that is caused by an innate immune response to deposited monosodium urate crystals in the setting of hyperuricemia. Here, we provide insights into the molecular mechanism of the poorly understood inflammatory component of gout from a genome-wide association study (GWAS) of 2.6 million people, including 120,295 people with prevalent gout. We detected 377 loci and 410 genetically independent signals (149 previously unreported loci in urate and gout). An additional 65 loci with signals in urate (from a GWAS of 630,117 individuals) but not gout were identified. A prioritization scheme identified candidate genes in the inflammatory process of gout, including genes involved in epigenetic remodeling, cell osmolarity and regulation of NOD-like receptor protein 3 (NLRP3) inflammasome activity. Mendelian randomization analysis provided evidence for a causal role of clonal hematopoiesis of indeterminate potential in gout. Our study identifies candidate genes and molecular processes in the inflammatory pathogenesis of gout suitable for follow-up studies.

The impact of chrysanthemi indici flos-enriched flavonoid part on the model of hyperuricemia based on inhibiting synthesis and promoting excretion of uric acid

ETHNOPHARMACOLOGICAL RELEVANCE

In recent years, in addition to hypertension, hyperglycemia, and hyperlipidemia, the prevalence of hyperuricemia (HUA) has increased considerably. Being the fourth major health risk factor, HUA can affect the kidneys and cardiovascular system. Chrysanthemi Indici Flos is a flavonoid-containing traditional Chinese patent medicine that exhibits a uric acid (UA)-lowering effect. However, the mechanisms underlying Chrysanthemi Indici Flos-enriched flavonoid part (CYM.E) mediated alleviation of HUA remain unelucidated.

AIM OF THE STUDY

This study aimed to elucidate the efficacy of CYM.E in preventing and treating HUA and its specific effects on UA-related transport proteins, to explore possible mechanism.

METHODS

The buddleoside content in CYM.E was determined through high-performance liquid chromatography. HUA was induced in mice models using adenine and potassium oxonate. Subsequently, mice were administered 10 mg/kg allopurinol, and 30, 60, and 90 mg/kg CYM.E to evaluate the effects of CYM.E on the of HUA mice model. Herein, plasma uric acid (UA), creatinine (CR), blood urea nitrogen (BUN), total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-c), and low-density lipoprotein cholesterol (LDL-c) contents, along with serum alanine aminotransferase (ALT), and aspartate aminotransferase (AST) activities were measured. Additionally, xanthine oxidase (XOD) and adenosine deaminase (ADA) activities in the liver were determined. The histomorphologies of the liver and kidney tissues were examined through hematoxylin and eosin staining. The messenger RNA (mRNA) expression of facilitated glucose transporter 9 (GLUT9), organic anion transporter (OAT)1, OAT3, and adenosine triphosphate binding cassette subfamily G2 (ABCG2) in the kidney was assessed by real-time quantitative polymerase chain reaction. Furthermore, the expression of urate transporter 1 (URAT1), GLUT9, OAT1, and OAT3 in the kidney, OAT4, and ABCG2 proteins was determined by immunohistochemistry and western blotting.

RESULTS

The buddleoside content in CYM.E was approximately 32.77%. CYM.E improved body weight and autonomous activity in HUA mice. Additionally, it reduced plasma UA, BUN, and CR levels and serum ALT and AST activities, thus improving hepatic and renal functions, which further reduced the plasma UA content. CYM.E reduced histopathological damage to the kidneys. Furthermore, it lowered plasma TC, TG, and LDL-c levels, thereby improving lipid metabolism disorder. CYM.E administration inhibited hepatic XOD and ADA activities and reduced the mRNA expression of renal GLUT9. CYM.E inhibited the protein expression of renal URAT1, GLUT9, and OAT4, and increased the mRNA and protein expression of renal OAT1, OAT3, and ABCG2. Altogether, these results show that CYM.E could inhibit the production and promote reabsorption of UA and its excretion.

Whole-genome sequencing reveals rare variants associated with gout in Taiwanese males

To identify rare variants (RVs) of gout, we sequenced the whole genomes of 321 male gout patients and combined these with those of 64 male gout patients and 682 normal controls at Taiwan Biobank. We performed ACAT-O to identify 682 significant RVs (p < 3.8 × 10-8) clustered on chromosomes 1, 7, 10, 16, and 18. To prioritize causal variants effectively, we sifted them by Combined Annotation-Dependent Depletion score >10 or |effect size| ≥ 1.5 for those without CADD scores. In particular, to the best of our knowledge, we identified the rare variants rs559954634, rs186763678, and 13-85340782-G-A for the first time to be associated with gout in Taiwanese males. Importantly, the RV rs559954634 positively affects gout, and its neighboring gene NPHS2 is involved in serum urate and expressed in kidney tissues. The kidneys play a major role in regulating uric acid levels. This suggests that rs559954634 may be involved in gout. Furthermore, rs186763678 is in the intron of NFIA that interacts with SLC2A9, which has the most significant effect on serum urate. Note that gene-gene interaction NFIA-SLC2A9 is significantly associated with serum urate in the Italian MICROS population and a Croatian population. Moreover, 13-85340782-G-A significantly affects gout susceptibility (odds ratio 6.0; P = 0.038). The >1% carrier frequencies of these potentially pathogenic (protective) RVs in cases (controls) suggest the revealed associations may be true; these RVs deserve further studies for the mechanism. Finally, multivariate logistic regression analysis shows that the rare variants rs559954634 and 13-85340782-G-A jointly are significantly associated with gout susceptibility.

Lactiplantibacillus plantarum 06CC2 Enhanced the Expression of Intestinal Uric Acid Excretion Transporter in Mice

ATP-binding cassette transporter subfamily G member 2 (ABCG2) is responsible for the excretion of foreign substances, such as uric acid (UA) and indoxyl sulfate (IS), from the body. Given the importance of increased ABCG2 expression in UA excretion, we investigated the enhancement of intestinal ABCG2 expression using Lactiplantibacillus plantarum 06CC2 (LP06CC2). Mice were reared on a potassium oxonate-induced high-purine model at doses of 0.02% or 0.1% LP06CC2 for three weeks. Results showed that LP06CC2 feeding resulted in increased ABCG2 expression in the small intestine. The expression level of large intestinal ABCG2 also showed a tendency to increase, suggesting upregulation of the intestinal excretion transporter ABCG2 by LP06CC2. Overall, LP06CC2 treatment increased fecal UA excretion and showed a trend towards increased fecal excretion of IS, suggesting that LP06CC2 treatment enhanced the expression of intestinal ABCG2, thereby promoting the excretion of UA and other substances from the intestinal tract.

The pathogenesis of gout: molecular insights from genetic, epigenomic and transcriptomic studies

The pathogenesis of gout involves a series of steps beginning with hyperuricaemia, followed by the deposition of monosodium urate crystal in articular structures and culminating in an innate immune response, mediated by the NLRP3 inflammasome, to the deposited crystals. Large genome-wide association studies (GWAS) of serum urate levels initially identified the genetic variants with the strongest effects, mapping mainly to genes that encode urate transporters in the kidney and gut. Other GWAS highlighted the importance of uncommon genetic variants. More recently, genetic and epigenetic genome-wide studies have revealed new pathways in the inflammatory process of gout, including genetic associations with epigenomic modifiers. Epigenome-wide association studies are also implicating epigenomic remodelling in gout, which perhaps regulates the responsiveness of the innate immune system to monosodium urate crystals. Notably, genes implicated in gout GWAS do not include those encoding components of the NLRP3 inflammasome itself, but instead include genes encoding molecules involved in its regulation. Knowledge of the molecular mechanisms underlying gout has advanced through the translation of genetic associations into specific molecular mechanisms. Notable examples include ABCG2, HNF4A, PDZK1, MAF and IL37. Current genetic studies are dominated by participants of European ancestry; however, studies focusing on other population groups are discovering informative population-specific variants associated with gout.

Suppression of Ehrlich ascites tumor cell proliferation via G1 arrest induced by dietary nucleic acid-derived nucleosides

The nucleic acids found in food play a crucial role in maintaining various bodily functions. This study investigated the potential anticancer effects of dietary nucleic acids, an area that is still not fully understood. By utilizing an in vivo mouse model and an in vitro cell model, we discovered an anti-proliferative impact of RNA in both systems. DNA exhibited anti-proliferative effects in the mouse model, while this phenomenon wasn't observed in the in vitro cell model using Ehrlich ascites tumor (EAT) cells. Conversely, DNA hydrolysate demonstrated distinct anti-proliferative effects in EAT cells, suggesting that nucleotides or nucleosides generated during nucleic acid digestion act as active constituents. Furthermore, we examined various nucleosides and two sodium-independent equilibrative nucleoside transporter inhibitors (ENTs), identifying guanosine and 2'-deoxyguanosine as pivotal in the anti-proliferative effect. We also found that the anti-proliferation activity with both nucleosides was suppressed by the treatment of dipyridamole, a non-selective inhibitor for ENT1 and ENT2, but not nitrobenzylthioinosine, a low inhibitor for ENT2. The uptake of these compounds into cells is likely facilitated by ENT2. These nucleotides impeded the progression of cancer cells from the G1 phase to the S phase in the cell cycle. Another significant finding is the increased expression of CCAAT/enhancer-binding protein (C/EBPβ) induced by guanosine and 2'-deoxyguanosine. Furthermore, immunostaining revealed that C/EBPβ diffuses into the nucleus, indicating its presence. This suggests that guanosine or 2-deoxyguanosine induces G1 arrest in cancer cells via the activation of C/EBPβ. Encouraged by these promising results, guanosine and 2'-deoxyguanosine show potential applications in cancer prevention.

Hyperuricemia Subtypes Classified According to Renal Uric Acid Handling Manifesting Distinct Phenotypic and Genetic Profiles in People With Gout

OBJECTIVE

Hyperuricemia can be stratified into four subtypes according to renal uric acid handling. The aim of this study was to comprehensively describe the biologic characteristics (including genetic background) of clinically defined hyperuricemia subtypes in two large geographically independent gout cohorts.

METHODS

Hyperuricemia subtype was defined as renal uric acid overload (ROL), renal uric acid underexcretion (RUE), combined, or renal normal. Twenty single nucleotide polymorphisms (SNPs) previously identified as gout risk loci or associated with serum urate (SU) concentration in the East Asian population were genotyped. Weighted polygenic risk scores were calculated to assess the cumulative effect of genetic risks on the subtypes.

RESULTS

Of the 4,873 participants, 8.8% had an ROL subtype, 60.9% RUE subtype, 23.1% combined subtype, and 7.2% normal subtype. The ROL subtype was independently associated with older age at onset, lower SU, tophi, and diabetes mellitus; RUE was associated with lower body mass index (BMI) and non-diabetes mellitus; the combined subtype was associated with younger age at onset, higher BMI, SU, estimated glomerular filtration rate (eGFR), and smoking; and the normal subtype was independently associated with older age at onset, lower SU, and eGFR. Thirteen SNPs were associated with gout with 6 shared loci and subtype-dependent risk loci patterns. High polygenic risk scores were associated with ROL subtype (odds ratio [OR] = 9.63, 95% confidence interval [95% CI] 4.53-15.12), RUE subtype (OR = 2.18, 95% CI 1.57-3.03), and combined subtype (OR = 6.32, 95% CI 4.22-9.48) compared with low polygenic risk scores.

CONCLUSION

Hyperuricemia subtypes classified according to renal uric acid handling have subtype-specific clinical and genetic features, suggesting subtype-unique pathophysiologic mechanisms.

An ATP13A1-assisted topogenesis pathway for folding multi-spanning membrane proteins

Many multi-spanning membrane proteins contain poorly hydrophobic transmembrane domains (pTMDs) protected from phospholipid in mature structure. Nascent pTMDs are difficult for translocon to recognize and insert. How pTMDs are discerned and packed into mature, muti-spanning configuration remains unclear. Here, we report that pTMD elicits a post-translational topogenesis pathway for its recognition and integration. Using six-spanning protein adenosine triphosphate-binding cassette transporter G2 (ABCG2) and cultured human cells as models, we show that ABCG2's pTMD2 can pass through translocon into the endoplasmic reticulum (ER) lumen, yielding an intermediate with inserted yet mis-oriented downstream TMDs. After translation, the intermediate recruits P5A-ATPase ATP13A1, which facilitates TMD re-orientation, allowing further folding and the integration of the remaining lumen-exposed pTMD2. Depleting ATP13A1 or disrupting pTMD-characteristic residues arrests intermediates with mis-oriented and exposed TMDs. Our results explain how a "difficult" pTMD is co-translationally skipped for insertion and post-translationally buried into the final correct structure at the late folding stage to avoid excessive lipid exposure.

Signaling pathways in uric acid homeostasis and gout: From pathogenesis to therapeutic interventions

Uric acid is a product of purine degradation, and uric acid may have multiple physiologic roles, including the beneficial effects as an antioxidant and neuroprotector, maintenance of blood pressure during low salt ingestion, and modulation of immunity. However, overproduction of metabolic uric acid, and/or imbalance of renal uric acid secretion and reabsorption, and/or underexcretion of extrarenal uric acid, e.g. gut, will contribute to hyperuricemia, which is a common metabolic disease. Long-lasting hyperuricemia can induce the formation and deposition of monosodium urate (MSU) crystals within the joints and periarticular structures. MSU crystals further induce an acute, intensely painful, and sterile inflammation conditions named as gout by NLRP3 inflammasome-mediated cleavage of pro-IL-1β to bioactive IL-1β. Moreover, hyperuricemia and gout are associated with multiple cardiovascular and renal disorders, e.g., hypertension, myocardial infarction, stroke, obesity, hyperlipidemia, type 2 diabetes mellitus and chronic kidney disease. Although great efforts have been made by scientists of modern medicine, however, modern therapeutic strategies with a single target are difficult to exert long-term positive effects, and even some of these agents have severe adverse effects. The Chinese have used the ancient classic prescriptions of traditional Chinese medicine (TCM) to treat metabolic diseases, including gout, by multiple targets, for more than 2200 years. In this review, we discuss the current understanding of urate homeostasis, the pathogenesis of hyperuricemia and gout, and both modern medicine and TCM strategies for this commonly metabolic disorder. We hope these will provide the good references for treating hyperuricemia and gout.

Prediction and causal inference of hyperuricemia using gut microbiota

Hyperuricemia (HUA) is a symptom of high blood uric acid (UA) levels, which causes disorders such as gout and renal urinary calculus. Prolonged HUA is often associated with hypertension, atherosclerosis, diabetes mellitus, and chronic kidney disease. Studies have shown that gut microbiota (GM) affect these chronic diseases. This study aimed to determine the relationship between HUA and GM. The microbiome of 224 men and 254 women aged 40 years was analyzed through next-generation sequencing and machine learning. We obtained GM data through 16S rRNA-based sequencing of the fecal samples, finding that alpha-diversity by Shannon index was significantly low in the HUA group. Linear discriminant effect size analysis detected a high abundance of the genera Collinsella and Faecalibacterium in the HUA and non-HUA groups. Based on light gradient boosting machine learning, we propose that HUA can be predicted with high AUC using four clinical characteristics and the relative abundance of nine bacterial genera, including Collinsella and Dorea. In addition, analysis of causal relationships using a direct linear non-Gaussian acyclic model indicated a positive effect of the relative abundance of the genus Collinsella on blood UA levels. Our results suggest abundant Collinsella in the gut can increase blood UA levels.

Gut microbiota plays a significant role in gout

With the development of social economy, the incidence of gout is increasing, which is closely related to people's increasingly rich diet. Eating a diet high in purine, fat, sugar and low-fibre for a long time further aggravates gout by affecting uric acid metabolism. The renal metabolism mechanism of uric acid has been thoroughly studied. To find a new treatment method for gout, increasing studies have recently been conducted on the mechanism of intestinal excretion, metabolism and absorption of uric acid. The most important research is the relationship between intestinal microbiota and the risk of gout. Gut microbiota represent bacteria that reside in a host's gastrointestinal tract. The composition of the gut microbiota is associated with protection against pathogen colonization and disease occurrence. This review focuses on how gut microbiota affects gout through uric acid and discusses the types of bacteria that may be involved in the occurrence and progression of gout. We also describe potential therapy for gout by restoring gut microbiota homeostasis and reducing uric acid levels. We hold the perspective that changing intestinal microbiota may become a vital method for effectively preventing or treating gout.

A Possible Therapeutic Application of the Selective Inhibitor of Urate Transporter 1, Dotinurad, for Metabolic Syndrome, Chronic Kidney Disease, and Cardiovascular Disease

The reabsorption of uric acid (UA) is mainly mediated by urate transporter 1 (URAT1) and glucose transporter 9 (GLUT9) in the kidneys. Dotinurad inhibits URAT1 but does not inhibit other UA transporters, such as GLUT9, ATP-binding cassette transporter G2 (ABCG2), and organic anion transporter 1/3 (OAT1/3). We found that dotinurad ameliorated the metabolic parameters and renal function in hyperuricemic patients. We consider the significance of the highly selective inhibition of URAT1 by dotinurad for metabolic syndrome, chronic kidney disease (CKD), and cardiovascular disease (CVD). The selective inhibition of URAT1 by dotinurad increases urinary UA in the proximal tubules, and this un-reabsorbed UA may compete with urinary glucose for GLUT9, reducing glucose reabsorption. The inhibition by dotinurad of UA entry via URAT1 into the liver and adipose tissues increased energy expenditure and decreased lipid synthesis and inflammation in rats. Such effects may improve metabolic parameters. CKD patients accumulate uremic toxins, including indoxyl sulfate (IS), in the body. ABCG2 regulates the renal and intestinal excretion of IS, which strongly affects CKD. OAT1/3 inhibitors suppress IS uptake into the kidneys, thereby increasing plasma IS, which produces oxidative stress and induces vascular endothelial dysfunction in CKD patients. The highly selective inhibition of URAT1 by dotinurad may be beneficial for metabolic syndrome, CKD, and CVD.

Relationship Between Serum Uric Acid and Carotid Plaque in Patients With Coronary Artery Disease by Sex and Blood Pressure Status

The purpose of this study was to explore the sex difference and effects of blood pressure (BP) on the relationship between serum uric acid (SUA) and carotid plaque in patients with coronary heart disease (CHD). This large multicenter retrospective study included 12099 patients with CHD (aged 35-75 years) between January 1, 2014 and September 30, 2020. Patients were divided into three groups according to systolic BP (SBP) and diastolic BP (DBP), and the SUA levels in males and females were converted into three groups. Logistic regression was used to analyze the influence of sex and BP on the relationship between SUA levels and carotid plaque in patients with CHD. In the model of male BP subgroups, using the BP of group A (normal with SBP <120 mmHg and DBP <80 mmHg) as a reference, SUA levels were significantly correlated with the occurrence of carotid plaque under different BP states (P < .001). In contrast, in the model of female BP subgroups, most of these correlations were not statistically significant. Our study showed that SUA levels were significantly associated with carotid plaque occurrence in males with CHD, which remained significant across different BP states.

Plasma and Urinary Metabolomic Analysis of Gout and Asymptomatic Hyperuricemia and Profiling of Potential Biomarkers: A Pilot Study

Gout results from monosodium urate deposition caused by hyperuricemia, but most individuals with hyperuricemia remain asymptomatic. The pathogenesis of gout remains uncertain. To identify potential biomarkers distinguishing gout from asymptomatic hyperuricemia, we conducted a genetic analysis of urate transporters and metabolomic analysis as a proof-of-concept study, including 33 patients with gout and 9 individuals with asymptomatic hyperuricemia. The variant allele frequencies of rs72552713, rs2231142, and rs3733591, which are related to serum urate levels (SUA) and gout, did not differ between the gout and asymptomatic hyperuricemia groups. In metabolomic analysis, the levels of citrate cycle intermediates, especially 2-ketoglutarate, were higher in patients with gout than in those with asymptomatic hyperuricemia (fold difference = 1.415, p = 0.039). The impact on the TCA cycle was further emphasized in high-risk gout (SUA ≥ 9.0 mg/dL). Of note, urinary nicotinate was the most prominent biomarker differentiating high-risk gout from asymptomatic hyperuricemia (fold difference = 6.515, p = 0.020). Although urate transporters play critical roles in SUA elevation and promote hyperuricemia, this study suggests that the progression from asymptomatic hyperuricemia to gout might be closely related to other genetic and/or environmental factors affecting carbohydrate metabolism and urinary urate excretion.

Examining the Association of Rare Allelic Variants in Urate Transporters SLC22A11, SLC22A13, and SLC17A1 with Hyperuricemia and Gout

Genetic variations in urate transporters play a significant role in determining human urate levels and have been implicated in developing hyperuricemia or gout. Polymorphism in the key urate transporters, such as ABCG2, URAT1, or GLUT9 was well-documented in the literature. Therefore in this study, our objective was to determine the frequency and effect of rare nonsynonymous allelic variants of SLC22A11, SLC22A13, and SLC17A1 on urate transport. In a cohort of 150 Czech patients with primary hyperuricemia and gout, we examined all coding regions and exon-intron boundaries of SLC22A11, SLC22A13, and SLC17A1 using PCR amplification and Sanger sequencing. For comparison, we used a control group consisting of 115 normouricemic subjects. To examine the effects of the rare allelic nonsynonymous variants on the expression, intracellular processing, and urate transporter protein function, we performed a functional characterization using the HEK293A cell line, immunoblotting, fluorescent microscopy, and site directed mutagenesis for preparing variants in vitro. Variants p.V202M (rs201209258), p.R343L (rs75933978), and p.P519L (rs144573306) were identified in the SLC22A11 gene (OAT4 transporter); variants p.R16H (rs72542450), and p.R102H (rs113229654) in the SLC22A13 gene (OAT10 transporter); and the p.W75C variant in the SLC17A1 gene (NPT1 transporter). All variants minimally affected protein levels and cytoplasmic/plasma membrane localization. The functional in vitro assay revealed that contrary to the native proteins, variants p.P519L in OAT4 (p ≤ 0.05), p.R16H in OAT10 (p ≤ 0.05), and p.W75C in the NPT1 transporter (p ≤ 0.01) significantly limited urate transport activity. Our findings contribute to a better understanding of (1) the risk of urate transporter-related hyperuricemia/gout and (2) uric acid handling in the kidneys.

Intestine-Targeted Explosive Hydrogel Microsphere Promotes Uric Acid Excretion for Gout Therapy

Uric acid metabolism disorder triggers metabolic diseases, especially gout. However, increasing uric acid excretion remains a challenge. Here, an accelerative uric acid excretion pathway via an oral intestine-explosive hydrogel microsphere merely containing uricase and dopamine is reported. After oral administration, uricase is exposed and immobilized on intestinal mucosa along with an in situ dopamine polymerization via a cascade reaction triggered by the intestinal specific environment. By this means, trace amount of uricase is required to in situ up-regulate uric acid transporter proteins of intestinal epithelial cells, causing accelerated intestinal uric acid excretion. From in vitro data, the uric acid in fecal samples from gout patients could be significantly reduced by up to 37% by the mimic mucosa-immobilized uricase on the isolated porcine tissues. Both hyperuricemia and acute gouty arthritis in vivo mouse models confirm the uric acid excretion efficacy of intestine-explosive hydrogel microspheres. Fecal uric acid excretion is increased around 30% and blood uric acid is reduced more than 70%. In addition, 16S ribosomal RNA sequencing showed that the microspheres optimized intestinal flora composition as well. In conclusion, a unique pathway via the intestine in situ regulation to realize an efficient uric acid intestinal excretion for gout therapy is developed.

Eupatilin inhibits xanthine oxidase in vitro and attenuates hyperuricemia and renal injury in vivo

Uric acid (UA) is the final metabolite of purines in the liver that can cause hyperuricemia at high levels. The kidneys are the main excretory organs for UA. The excessive accumulation of UA in the kidneys causes the development of hyperuricemia that often leads to renal injury. Eupatilin (Eup) is a flavonoid natural product that possesses various pharmacological properties such as antioxidant, anti-cancer, and anti-inflammatory. We were interested in exploring the potential role of Eup in lowering UA and nephroprotective. We initially investigated the effects of Eup on xanthin oxidase (XOD) activity in vitro, followed by investigating its ability to lower UA levels, anti-inflammatory effects, nephroprotective effects, and the underlying mechanisms using hyperuricemia rats sustained at high UA level. The results showed that Eup had an inhibitory effect on XOD activity in vitro and significantly reduced serum UA, creatinine, BUN, IL-1β and IL-6 levels in hyperuricemic rats, ameliorating inflammation, renal oxidative stress and pathological injury. Furthermore, Eup inhibited ADA and XOD enzyme activities in the liver and serum and modulated GLUT9, URAT1 and ABCG2 protein expression in the kidneys and ileum. Our findings provide a scientific basis for suggesting Eup as an option for a potential treatment for hyperuricemia.

Intestinal uric acid excretion contributes to serum uric acid decrease during acute gout attack

OBJECTIVE

Spontaneous serum uric acid (SUA) decrease has been found in many patients during acute gout attacks, but its mechanism remains unclear.

METHODS

The spontaneous regulation of SUA during a gout attack and its possible causes were evaluated in patients with gout. The mechanism of the spontaneous SUA decrease was further studied in Caco2 cells and a monosodium urate (MSU)-induced gout model of wild-type mice and ABCG2-/- mice. The urate transport function of intestinal epithelial cells was detected by transwell culture of Caco2 cells. Expression of ATP-binding cassette super-family G member 2 (ABCG2), IL-1β and phosphoinositide 3-kinase (PI3K)/Akt was analysed using real-time PCR, western blotting, or immunofluorescence assays.

RESULTS

SUA decreased during acute gout attacks in both the gout patients and MSU-induced gouty mice. Increased serum CRP and IL-1β levels were correlated with the SUA decrease. Intestinal uric acid excretion and expression of ABCG2 were upregulated in the mice during acute gout attacks. In the ABCG2-/- mice, intestinal uric acid excretion significantly decreased during gout attacks. In an in vitro study of a transwell culture, ABCG2 and its upstream PI3K/Akt pathway were significantly upregulated in intestinal epithelial cells. However, ABCG2 expression and its associated intestinal uric acid transport were inhibited when PI3K/Akt was blocked by a PI3K inhibitor, LY294002.

CONCLUSIONS

Increased intestinal urate excretion resulted in spontaneous SUA downregulation during acute gout attacks. Inflammation-induced PI3K/Akt activation and ABCG2 expression in epithelial cells might contribute to the upregulation of intestinal uric acid excretion.

Dysuricemia

Gout results from elevated serum urate (SU) levels, or hyperuricemia, and is a globally widespread and increasingly burdensome disease. Recent studies have illuminated the pathophysiology of gout/hyperuricemia and its epidemiology, diagnosis, treatment, and complications. The genetic involvement of urate transporters and enzymes is also proven. URAT1, a molecular therapeutic target for gout/hyperuricemia, was initially derived from research into hereditary renal hypouricemia (RHUC). RHUC is often accompanied by complications such as exercise-induced acute kidney injury, which indicates the key physiological role of uric acid. Several studies have also revealed its physiological role as both an anti-oxidant and a pro-oxidant, acting as both a scavenger and a generator of reactive oxygen species (ROSs). These discoveries have prompted research interest in SU and xanthine oxidoreductase (XOR), an enzyme that produces both urate and ROSs, as status or progression biomarkers of chronic kidney disease and cardiovascular disease. The notion of "the lower, the better" is therefore incorrect; a better understanding of uric acid handling and metabolism/transport comes from an awareness that excessively high and low levels both cause problems. We summarize here the current body of evidence, demonstrate that uric acid is much more than a metabolic waste product, and finally propose the novel disease concept of "dysuricemia" on the path toward "normouricemia", or optimal SU level, to take advantage of the dual roles of uric acid. Our proposal should help to interpret the spectrum from hypouricemia to hyperuricemia/gout as a single disease category.

Overnight changes in uric acid, xanthine oxidoreductase and oxidative stress levels and their relationships with sleep-disordered breathing in patients with coronary artery disease

Serum uric acid (UA) level is associated with the high cumulative incidence or prevalence of coronary artery disease (CAD), and hyperuricemia is considered as an independent risk marker for CAD. Sleep-disordered breathing (SDB) is also associated with an increased risk of CAD. Several studies have shown that SDB is associated with hyperuricemia, but the mechanisms are unclear. We measured serum levels of UA and xanthine oxidoreductase (XOR) activity and urinary levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), all of which were assessed at 6 p.m. and the following 6 a.m. in males with CAD. In addition, nocturnal pulse oximetry was performed for the night. Overall 32 eligible patients with CAD were enrolled. Serum UA levels significantly increased overnight. (5.32 ± 0.98 mg/dl to 5.46 ± 1.02 mg/dl, p < 0.001) Moreover, XOR activity and urinary 8-OHdG levels significantly increased from 6 p.m. to 6 a.m. Furthermore, 3% Oxygen desaturation index (ODI) was correlated with the overnight changes in XOR activity (r = 0.36, P = 0.047) and urinary 8-OHdG levels (r = 0.41, P = 0.02). In addition, 3%ODI was independently correlated with the changes in XOR activity (correlation coefficient, 0.36; P = 0.047) and 8-OHdG (partial correlation coefficient, 0.63; P = 0.004) in multivariable analyses. SDB severity was associated with the overnight changes in XOR activity and urinary 8-OHdG, suggesting that SDB may be associated with oxidative stress via UA production. This trial is registered at University Hospital Medical Information Network (UMIN), number: UMIN000021624.

Inhibition of the uric acid efflux transporter ABCG2 enhances stimulating effect of soluble uric acid on IL-1β production in murine macrophage-like J774.1 cells

Soluble uric acid (UA) absorbed by cells through UA transporters (UATs) accumulates intracellularly, activates the NLRP3 inflammasome and thereby increases IL-1β secretion. ABCG2 transporter excludes intracellular UA. However, it remains unknown whether ABCG2 inhibition leads to intracellular accumulation of UA and increases IL-1β production. In this study, we examined whether genetic and pharmacological inhibition of ABCG2 could increase IL-1β production in mouse macrophage-like J774.1 cells especially under hyperuricemic conditions. We determined mRNA and protein levels of pro-IL-1β, mature IL-1β, caspase-1 and several UATs in culture supernatants and lysates of J774.1 cells with or without soluble UA pretreatment. Knockdown experiments using an shRNA against ABCG2 and pharmacological experiments with an ABCG2 inhibitor were conducted. Extracellularly applied soluble UA increased protein levels of pro-IL-1β, mature IL-1β and caspase-1 in the culture supernatant from lipopolysaccharide (LPS)-primed and monosodium urate crystal (MSU)-stimulated J774.1 cells. J774.1 cells expressed UATs of ABCG2, GLUT9 and MRP4, and shRNA knockdown of ABCG2 increased protein levels of pro-IL-1β and mature IL-1β in the culture supernatant. Soluble UA increased mRNA and protein levels of ABCG2 in J774.1 cells without either LPS or MSU treatment. An ABCG2 inhibitor, febuxostat, but not a urate reabsorption inhibitor, dotinurad, enhanced IL-1β production in cells pretreated with soluble UA. In conclusion, genetic and pharmacological inhibition of ABCG2 enhanced IL-1β production especially under hyperuricemic conditions by increasing intracellularly accumulated soluble UA that activates the NLRP3 inflammasome and pro-IL-1β transcription in macrophage-like J774.1 cells.

SVCT2/SLC23A2 is a sodium-dependent urate transporter: functional properties and practical application

Urate transporters play a pivotal role in urate handling in the human body, but the urate transporters identified to date do not account for all known molecular processes of urate handling, suggesting the presence of latent machineries. We recently showed that a urate transporter SLC2A12 is also a physiologically important exporter of ascorbate (the main form of vitamin C in the body) that would cooperate with an ascorbate importer, sodium-dependent vitamin C transporter 2 (SVCT2). Based on the dual functions of SLC2A12 and cooperativity between SLC2A12 and SVCT2, we hypothesized that SVCT2 might be able to transport urate. To test this proposal, we conducted cell-based analyses using SVCT2-expressing mammalian cells. The results demonstrated that SVCT2 is a novel urate transporter. Vitamin C inhibited SVCT2-mediated urate transport with a half-maximal inhibitory concentration of 36.59 μM, suggesting that the urate transport activity may be sensitive to physiological ascorbate levels in blood. Similar results were obtained for mouse Svct2. Further, using SVCT2 as a sodium-dependent urate importer, we established a cell-based urate efflux assay that will be useful for identification of other novel urate exporters as well as functional characterization of nonsynonymous variants of already-identified urate exporters including ATP-binding cassette transporter G2. While more studies will be needed to elucidate the physiological impact of SVCT2-mediated urate transport, our findings deepen understanding of urate transport machineries.

Asymptomatic hyperuricaemia in chronic kidney disease: mechanisms and clinical implications

Asymptomatic hyperuricaemia (HU) is considered a pathogenic factor in multiple disease contexts, but a causative role is only proven for the crystalline form of uric acid in gouty arthritis and urate nephropathy. Epidemiological studies document a robust association of HU with hypertension, cardiovascular disease (CVD) and CKD progression, but CKD-related impaired uric acid (UA) clearance and the use of diuretics that further impair UA clearance likely accounts for these associations. Interpreting the available trial evidence is further complicated by referring to xanthine oxidase inhibitors as urate-lowering treatment, although these drugs inhibit other substrates, so attributing their effects only to HU is problematic. In this review we provide new mechanistic insights into the biological effects of soluble and crystalline UA and discuss clinical evidence on the role of asymptomatic HU in CKD, CVD and sterile inflammation. We identify research areas with gaps in experimental and clinical evidence, specifically on infectious complications that represent the second common cause of death in CKD patients, referred to as secondary immunodeficiency related to kidney disease. In addition, we address potential therapeutic approaches on how and when to treat asymptomatic HU in patients with kidney disease and where further interventional studies are required.

Impact of Hyper- and Hypo-Uricemia on Kidney Function

Uric acid (UA) forms monosodium urate (MSU) crystals to exert proinflammatory actions, thus causing gout arthritis, urolithiasis, kidney disease, and cardiovascular disease. UA is also one of the most potent antioxidants that suppresses oxidative stress. Hyper andhypouricemia are caused by genetic mutations or polymorphism. Hyperuricemia increases urinary UA concentration and is frequently associated with urolithiasis, which is augmented by low urinary pH. Renal hypouricemia (RHU) is associated with renal stones by increased level of urinary UA, which correlates with the impaired tubular reabsorption of UA. Hyperuricemia causes gout nephropathy, characterized by renal interstitium and tubular damage because MSU precipitates in the tubules. RHU is also frequently associated with tubular damage with elevated urinary beta2-microglobulin due to increased urinary UA concentration, which is related to impaired tubular UA reabsorption through URAT1. Hyperuricemia could induce renal arteriopathy and reduce renal blood flow, while increasing urinary albumin excretion, which is correlated with plasma xanthine oxidoreductase (XOR) activity. RHU is associated with exercise-induced kidney injury, since low levels of SUA could induce the vasoconstriction of the kidney and the enhanced urinary UA excretion could form intratubular precipitation. A U-shaped association of SUA with organ damage is observed in patients with kidney diseases related to impaired endothelial function. Under hyperuricemia, intracellular UA, MSU crystals, and XOR could reduce NO and activate several proinflammatory signals, impairing endothelial functions. Under hypouricemia, the genetic and pharmacological depletion of UA could impair the NO-dependent and independent endothelial functions, suggesting that RHU and secondary hypouricemia might be a risk factor for the loss of kidney functions. In order to protect kidney functions in hyperuricemic patients, the use of urate lowering agents could be recommended to target SUA below 6 mg/dL. In order to protect the kidney functions in RHU patients, hydration and urinary alkalization may be recommended, and in some cases an XOR inhibitor might be recommended in order to reduce oxidative stress.

Cannabis Pharmacogenomics: A Path to Personalized Medicine

Cannabis and related compounds have created significant research interest as a promising therapy in many disorders. However, the individual therapeutic effects of cannabinoids and the incidence of side effects are still difficult to determine. Pharmacogenomics may provide the answers to many questions and concerns regarding the cannabis/cannabinoid treatment and help us to understand the variability in individual responses and associated risks. Pharmacogenomics research has made meaningful progress in identifying genetic variations that play a critical role in interpatient variability in response to cannabis. This review classifies the current knowledge of pharmacogenomics associated with medical marijuana and related compounds and can assist in improving the outcomes of cannabinoid therapy and to minimize the adverse effects of cannabis use. Specific examples of pharmacogenomics informing pharmacotherapy as a path to personalized medicine are discussed.

Vitamin C transporter SVCT1 serves a physiological role as a urate importer: functional analyses and in vivo investigations

Uric acid, the end product of purine metabolism in humans, is crucial because of its anti-oxidant activity and a causal relationship with hyperuricemia and gout. Several physiologically important urate transporters regulate this water-soluble metabolite in the human body; however, the existence of latent transporters has been suggested in the literature. We focused on the Escherichia coli urate transporter YgfU, a nucleobase-ascorbate transporter (NAT) family member, to address this issue. Only SLC23A proteins are members of the NAT family in humans. Based on the amino acid sequence similarity to YgfU, we hypothesized that SLC23A1, also known as sodium-dependent vitamin C transporter 1 (SVCT1), might be a urate transporter. First, we identified human SVCT1 and mouse Svct1 as sodium-dependent low-affinity/high-capacity urate transporters using mammalian cell-based transport assays. Next, using the CRISPR-Cas9 system followed by the crossing of mice, we generated Svct1 knockout mice lacking both urate transporter 1 and uricase. In the hyperuricemic mice model, serum urate levels were lower than controls, suggesting that Svct1 disruption could reduce serum urate. Given that Svct1 physiologically functions as a renal vitamin C re-absorber, it could also be involved in urate re-uptake from urine, though additional studies are required to obtain deeper insights into the underlying mechanisms. Our findings regarding the dual-substrate specificity of SVCT1 expand the understanding of urate handling systems and functional evolutionary changes in NAT family proteins.

The effect of dapagliflozin on uric acid excretion and serum uric acid level in advanced CKD

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) exhibit renoprotective effect in patients with chronic kidney disease (CKD) and reduce serum uric acid (UA) in patients with diabetes mellitus. However, it is not clarified whether SGLT2i reduce serum UA levels in patients with advanced CKD. This study aimed to investigate the impact of SGLT2i on change in serum UA levels in patients with advanced CKD. Data of 121 Japanese patients with CKD who were newly administered 10 mg dapagliflozin in our department between August 2021 and August 2022 were analyzed. Changes in UA and fractional excretion of UA (FEUA) were analyzed using multiple regression analysis. Of 75 patients, 21 (28.0%) patients, 24 (32.0%) patients, 29 (38.7%) patients, and 1 (1.3%) patient were categorized as having CKD stage 3a, 3b, 4, and 5, respectively. The median age was 67 years, and 72.0% were male. 23 (30.7%) of patients had diabetes mellitus. The median estimated glomerular filtration rate, serum UA, and FEUA were 35.7 mL/min/1.73 m², 6.4 mg/dL, and 6.76%, respectively, at the time of dapagliflozin administration. After administration, serum UA decreased to 5.6 mg/dL and FEUA increased to 9.22%. Dapagliflozin increases FEUA and reduces serum UA levels in patients with advanced CKD.

Rational design of a genome-based insulated system in Escherichia coli facilitates heterologous uricase expression for hyperuricemia treatment

Hyperuricemia is a prevalent disease worldwide that is characterized by elevated urate levels in the blood owing to purine metabolic disorders, which can result in gout and comorbidities. To facilitate the treatment of hyperuricemia through the uricolysis, we engineered a probiotic Escherichia coli Nissle 1917 (EcN) named EcN C6 by inserting an FtsP-uricase cassette into an "insulated site" located between the uspG and ahpF genes. Expression of FtsP-uricase in this insulated region did not influence the probiotic properties or global gene transcription of EcN but strongly increased the enzymatic activity for urate degeneration, suggesting that the genome-based insulated system is an ideal strategy for EcN modification. Oral administration of EcN C6 successfully alleviated hyperuricemia, related symptoms and gut microbiota in a purine-rich food-induced hyperuricemia rat model and a uox-knockout mouse model. Together, our study provides an insulated site for heterologous gene expression in EcN strain and a recombinant EcN C6 strain as a safe and effective therapeutic candidate for hyperuricemia treatment.

Urate Transporter 1 Can Be a Therapeutic Target Molecule for Chronic Kidney Disease and Diabetic Kidney Disease: A Retrospective Longitudinal Study

Chronic kidney disease (CKD) is a major global health problem for which there are no curative drug treatments. Hyperuricemia is one of risk factors for CKD. The evidence on effects of uric acid (UA)-lowering treatments on the progression of CKD was very limited and previous meta-analyses used only trials which primarily used xanthin oxidase (XO) inhibitors because the reports on fulminant hepatitis due to benzbromarone kept us from using uricosuric agents for hyperuricemia patients. Dotinurad, a novel selective urate reabsorption inhibitor for the treatment of hyperuricemia, reduces serum UA levels by selectively inhibiting urate transporter 1 (URAT1). We retrospectively picked up patients who had taken dotinurad from June 2018 to August 2021 and compared metabolic parameters at baseline with the data at 3 and 6 months after the start of dotinurad. We found 84 patients, and approximately 74% of patients were complicated with CKD. After the start of dotinurad, improvements in serum lipids, systolic blood pressure, body weight, and albuminuria, in addition to reduction in serum UA, were observed. Dotinurad increased urinary UA excretion, and was effective to reduce serum UA in patients with both UA underexcretion type and renal UA overload type. Furthermore, urinary UA excretion was significantly and negatively correlated with serum creatine levels at baseline and at 6 months after the start of dotinurad, and the change in urinary UA excretion after 3 months was significantly and negatively correlated with change in serum creatine levels. The property of dotinurad, which selectively inhibits URAT1, but not other UA transporters, such as ATP-binding cassette, subfamily G, and 2 (ABCG2), which ABCG2 is a UA and uremic toxin exporter, may be beneficially associated with pathology of CKD. URAT1 can be a therapeutic target molecule for CKD and DKD.

Urate Transporter ABCG2 Function and Asymptomatic Hyperuricemia: A Retrospective Cohort Study of CKD Progression

RATIONALE & OBJECTIVE

Treatment of asymptomatic hyperuricemia is not commonly implemented. However, it is unclear whether urate deposition that begins during asymptomatic hyperuricemia can induce nephropathy. Dysfunction of ATP-binding cassette subfamily G member 2 (ABCG2), a urate efflux transporter, leads to elevated serum uric acid concentration (SUA). We investigated the association between asymptomatic hyperuricemia and decreased estimated glomerular filtration rate (eGFR), and the impact of ABCG2 on this relationship.

STUDY DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

1,885 Japanese adults undergoing routine health care follow-up between 2007 and 2017 who had eGFR ≥60 mL/min/1.73 m², of which 311 had asymptomatic hyperuricemia (SUA >7.0 mg/dL). Study participants were classified into 3 categories of estimated ABCG2 function (full, 75%, and ≤50% function).

PREDICTORS

Baseline SUA and estimated ABCG2 function.

OUTCOME

Change in eGFR over time.

ANALYTICAL APPROACH

Linear mixed-effect models were used to analyze the relationship between asymptomatic hyperuricemia, ABCG2 function, and eGFR decline.

RESULTS

Asymptomatic hyperuricemia was negligibly associated with eGFR decline overall. However, among those with eGFR 60-89 mL/min/1.73 m² and ≤50% ABCG2 function, eGFR decline was associated with asymptomatic hyperuricemia (P = 0.03). ABCG2 was not associated with eGFR reductions when the SUA was <6.0 mg/dL. Among participants with SUA ≥6.0 mg/dL and eGFR 60-89 mL/min/1.73 m², ≤50% ABCG2 function was associated with approximately 1.2-fold faster eGFR decline compared with fully functional ABCG2 (P = 0.02). Among the participants with SUA ≥6.0 mg/dL and eGFR 60-89 mL/min/1.73 m², the adjusted eGFR slopes (given as mean ± standard error of the mean, in mL/min/1.73 m² per year) were -0.946 ± 0.049, -1.040 ± 0.046, and -1.148 ± 0.069 for full, 75%, and ≤50% ABCG2 function, respectively.

LIMITATIONS

Lack of measurement of urinary urate and uremic toxins that are known to be transported by ABCG2, and no independent validation cohort.

CONCLUSIONS

Asymptomatic hyperuricemia was not associated with eGFR decline, except when in the presence of ≤50% ABCG2 function.

PLAIN-LANGUAGE SUMMARY

The urate transporter ABCG2 is a protein that regulates serum urate concentrations; when dysfunctional, it can lead to elevated serum concentrations of this compound (ie, hyperuricemia). Although persistent hyperuricemia induces gout and kidney injury, the effects on organs during the asymptomatic phase have yet to be established. Therefore, to clarify the relationship between ABCG2, asymptomatic hyperuricemia, and kidney function, we conducted a retrospective cohort study of 1,885 healthy participants, including 311 participants with asymptomatic hyperuricemia. We found that the coexistence of asymptomatic hyperuricemia and severe ABCG2 dysfunction was associated with the age-dependent decline in kidney function. We concluded that asymptomatic hyperuricemia represents a risk factor for chronic kidney disease, at least in individuals with highly dysfunctional ABCG2. This new finding highlights the potential importance of ABCG2 in the pathogenesis of hyperuricemia-induced kidney injury.

Evaluation of ABCG2-mediated extra-renal urate excretion in hemodialysis patients

Two-thirds of urate is excreted via the renal pathway and the remaining one-third via the extra-renal pathway, the latter mainly via the intestine in healthy individuals. ABCG2, a urate exporter, is expressed in various tissues including the kidney and intestine, and its dysfunction leads to hyperuricemia and gout. ABCG2 is regarded as being responsible for most of the extra-renal urate excretion. However, the extra-renal urate excretion capacity via ABCG2 remains undefined in end-stage kidney diseases. Therefore, we evaluated the capacity of extra-renal ABCG2 using 123 anuric hemodialysis patients whose urate excretion depended on only the extra-renal pathway. ABCG2 function in each participant was estimated based on ABCG2 dysfunctional variants. We computed the uric acid pool (Pool_UA) from bodyweight and serum urate level (SUA) using previously reported radio-isotopic data, and we analyzed the association between ABCG2 function and the Pool_UA. SUA and Pool_UA increased significantly with ABCG2 dysfunction, and extra-renal ABCG2 could excrete up to approximately 60% of the daily uric acid turnover in hemodialysis patients. Our findings indicate that the extra-renal urate excretion capacity can expand with renal function decline and highlight that the extra-renal pathway is particularly important in the uric acid homeostasis for patients with renal dysfunction.

Association between Serum Uric Acid and Liver Enzymes in Adults Aged 20 Years and Older in the United States: NHANES 2005-2012

Although the relationship between serum uric acid (SUA) and nonalcoholic fatty liver disease has been widely reported, the relationship between SUA and liver enzymes has rarely been reported. The purpose of this study was to evaluate the association of SUA levels with alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in populations aged 20 years and older in the United States. We analyzed 7165 individuals aged 20 years and older from the National Health and Nutrition Examination Survey (NHANES) in the United States. Weighted multiple linear regression models were used to analyze the relationship between SUA and ALT and AST. A generalized additive model and a smooth curve fitting were used to observe the linear relationship. SUA was positively correlated with ALT and AST. In addition, the overall increasing trend of ALT and SUA was observed across the SUA quartile groups. In the stratified analysis by sex and race, the SUA levels in male, female, Mexican American, and Non-Hispanic White individuals, and those of another race, were positively correlated with ALT and AST. However, the SUA levels in Non-Hispanic Black individuals had a nonlinear relationship with ALT and AST. In individuals aged 20 years and older in the United States (excluding Non-Hispanic Black individuals), SUA levels were positively associated with ALT and AST. Therefore, with a rise in SUA levels, liver function should be monitored or intervened with in people aged 20 years and older in the United States.

The Mechanism of Sodium-Glucose Cotransporter-2 Inhibitors in Reducing Uric Acid in Type 2 Diabetes Mellitus

Hyperuricemia is a common comorbidity in patients with type 2 diabetes mellitus (T2DM), as insulin resistance (IR) or hyperinsulinemia is associated with higher serum uric acid (SUA) levels due to decreased uric acid (UA) secretion, and SUA vice versa is an important risk factor that promotes the occurrence and progression of T2DM and its complications. Growing evidence suggests that sodium-glucose cotransporter 2 inhibitors (SGLT-2i), a novel anti-diabetic drug initially developed to treat T2DM, may exert favorable effects in reducing SUA. Currently, one of the possible mechanisms is that SGLT2i increases urinary glucose excretion, probably inhibiting glucose transport 9 (GLUT9)-mediated uric acid reabsorption in the collecting duct, resulting in increased uric acid excretion in exchange for glucose reabsorption. Regardless of this possible mechanism, the underlying comprehensive mechanisms remain poorly elucidated. Therefore, in the present review, a variety of other potential mechanisms will be covered to identify the therapeutic role of SGLT-2i in hyperuricemia.

New insight into the management of renal excretion and hyperuricemia: Potential therapeutic strategies with natural bioactive compounds

Hyperuricemia is the result of increased production and/or underexcretion of uric acid. Hyperuricemia has been epidemiologically associated with multiple comorbidities, including metabolic syndrome, gout with long-term systemic inflammation, chronic kidney disease, urolithiasis, cardiovascular disease, hypertension, rheumatoid arthritis, dyslipidemia, diabetes/insulin resistance and increased oxidative stress. Dysregulation of xanthine oxidoreductase (XOD), the enzyme that catalyzes uric acid biosynthesis primarily in the liver, and urate transporters that reabsorb urate in the renal proximal tubules (URAT1, GLUT9, OAT4 and OAT10) and secrete urate (ABCG2, OAT1, OAT3, NPT1, and NPT4) in the renal tubules and intestine, is a major cause of hyperuricemia, along with variations in the genes encoding these proteins. The first-line therapeutic drugs used to lower serum uric acid levels include XOD inhibitors that limit uric acid biosynthesis and uricosurics that decrease urate reabsorption in the renal proximal tubules and increase urate excretion into the urine and intestine via urate transporters. However, long-term use of high doses of these drugs induces acute kidney disease, chronic kidney disease and liver toxicity. Therefore, there is an urgent need for new nephroprotective drugs with improved safety profiles and tolerance. The current systematic review summarizes the characteristics of major urate transporters, the mechanisms underlying the pathogenesis of hyperuricemia, and the regulation of uric acid biosynthesis and transport. Most importantly, this review highlights the potential mechanisms of action of some naturally occurring bioactive compounds with antihyperuricemic and nephroprotective potential isolated from various medicinal plants.

[Association of Abnormal Disulfide Bond Formation with Disease Development and Progression]

As intermolecular and intramolecular disulfide bridges in proteins play a vital role in the stability of the final protein structure, the disruption of disulfide bridges in proteins may lead to disease development and progression. Therefore, understanding the association of abnormal protein disulfide bond formation with disease development and progression can be useful for developing novel drugs for various diseases. Considering that disulfide-linked protein folding involves redox reactions in the endoplasmic reticulum, this process may be affected by oxidative stress. We hypothesized that oxidative stress-related diseases may be induced by abnormal protein disulfide bond formation. This review introduces the association of abnormal protein disulfide bond formation with disease development and progression.

Chronic Kidney Disease Stage G4 in a Diabetic Patient Improved by Multi-Disciplinary Treatments Based Upon Literature Search for Therapeutic Evidence

In the EMPA-REG OUTCOME trial, sodium-glucose cotransporter 2 (SGLT2) inhibitor, empagliflozin, reduced incident or worsening nephropathy. In the LEADER trial, a glucagon-like peptide 1 (GLP-1) receptor agonist, liraglutide, resulted in lower rates of the development and progression of diabetic kidney disease than placebo. Therefore, the American Diabetes Association and the European Association for the Study of Diabetes recommend the decision to treat high-risk individuals with a GLP-1 receptor agonist or SGLT2 inhibitor to reduce chronic kidney disease (CKD) progression should be considered. A 72-year-old male obese diabetic patient developed CKD stage G4 despite of use of both SGLT2 inhibitor and GLP-1 receptor agonist. We started using sodium bicarbonate because he showed metabolic acidosis due to uremia. We also started to use spherical carbonaceous adsorbent which adsorbs indole, the precursor of indoxyl sulfate, uremic toxin. We started the treatment with finerenone, a nonsteroidal, selective mineralocorticoid receptor antagonist, which has been recently shown to lower risks of CKD progression. Considering unfavorable effects of hyperuricemia on CKD, to treat his hyperuricemia, we started to use dotinurad, a novel selective urate reabsorption inhibitor, which reduces serum urate levels by selective inhibition of urate transporter 1. The improvement of CKD stage G4 in a diabetic patient was obtained by such multi-disciplinary treatments in addition to SGLT2 inhibitor and GLP-1 receptor agonist.