ABCG2 dysfunction causes hyperuricemia due to both renal urate underexcretion and renal urate overload

Isorhamnetin ameliorates hyperuricemia by regulating uric acid metabolism and alleviates renal inflammation through the PI3K/AKT/NF-κB signaling pathway

Hyperuricemia is a chronic metabolic disease with high incidence, and it has become a severe health risk in modern times. Isorhamnetin is a natural flavonoid found in a variety of plants, especially fruits such as buckthorn. The in vivo hyperuricemia ameliorating effect of isorhamnetin and the specific molecular mechanism were profoundly investigated using a hyperuricemia mouse model in this study. Results indicated that isorhamnetin showed a significant uric acid-lowering effect in mice. Isorhamnetin was able to reduce uric acid production by inhibiting XOD activity. Furthermore, it reduced the expression of GLUT9 to inhibit uric acid reabsorption and enhanced the expression of ABCG2, OAT1, and OAT3 to promote uric acid excretion. Metabolomics analysis revealed that gavage administration of isorhamnetin restored purine metabolism and riboflavin metabolism disorders and thus significantly alleviated hyperuricemia in mice. Furthermore, the alleviating effect of isorhamnetin on hyperuricemia-induced renal inflammation and its specific mechanism were explored through network pharmacology and molecular validation experiments. Network pharmacology predicted that seven targets were enriched in the PI3K/AKT pathway (CDK6, SYK, KDR, RELA, PIK3CG, IGF1R, and MCL1) and four targets were enriched in the NF-κB pathway (SYK, PARP1, PTGS2, and RELA). Western blot analysis validated that isorhamnetin inhibited the phosphorylation of PI3K and AKT and down-regulated the expression of NF-κB p65. It indicated that isorhamnetin could inhibit the PI3K/AKT/NF-κB signaling pathway to reduce the levels of renal inflammatory factors (TNF-α, IL-β and IL-6) and ultimately ameliorate hyperuricemia-induced renal inflammation in mice. This study provides a comprehensive and strong theoretical basis for the application of isorhamnetin in the field of functional foods or dietary supplements to improve hyperuricemia.

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.

Allopurinol, Febuxostat, and Nonuse of Xanthine Oxidoreductase Inhibitor Treatment in Patients Receiving Hemodialysis: A Longitudinal Analysis

Rationale & Objective

Allopurinol and febuxostat, which are xanthine oxidoreductase inhibitors, have been widely used as uric acid-lowering medications. However, evidence regarding their cardiovascular effects in hemodialysis is insufficient. This study compared the effects of allopurinol and febuxostat on mortality and cardiovascular outcomes in patients receiving hemodialysis.

Study Design

A retrospective observational cohort study.

Setting & Participants

Data of 6,791 patients who had no history of topiroxostat usage and underwent maintenance hemodialysis between March 2016 and March 2019 at Yokohama Daiichi Hospital, Zenjinkai, and its affiliated dialysis clinics in Japan's Kanagawa and Tokyo metropolitan areas were collected.

Exposure

Allopurinol, febuxostat, and nontreatment.

Outcomes

All-cause mortality, cardiovascular disease (CVD) events, heart failure (HF), acute myocardial infarction (AMI), and stroke.

Analytical Approach

For the main analyses, marginal structural Cox proportional hazards models were used to estimate HRs adjusted for time-varying confounding and selection bias because of censoring.

Results

Allopurinol and febuxostat showed significantly better survival than nontreatment for all-cause mortality (HR, 0.40; 95% CI, 0.30-0.54 and HR, 0.49; 95% CI, 0.38-0.63, respectively), without significant difference between allopurinol and febuxostat. Allopurinol showed significantly better survival than nontreatment, whereas febuxostat did not for CVD events (HR, 0.89; 95% CI, 0.84-0.95 and HR, 1.01; 95% CI, 0.96-1.07, respectively), HF (HR, 0.71; 95% CI, 0.56-0.90 and HR, 1.03; 95% CI, 0.87-1.21, respectively), and AMI (HR, 0.48; 95% CI, 0.25-0.91 and HR, 0.76; 95% CI, 0.49-1.19, respectively). No comparisons showed significant results for stroke.

Limitations

The ratio of renal or intestinal excretion of uric acid and uremic toxins could not be elucidated, and we could not investigate gene polymorphism because of the large number of cases.

Conclusions

Allopurinol and febuxostat improved survival for all-cause mortality. Allopurinol and not febuxostat reduced the risk of CVD events, HF, and AMI.

Discovery and prioritization of genetic determinants of kidney function in 297,355 individuals from Taiwan and Japan

Current genome-wide association studies (GWAS) for kidney function lack ancestral diversity, limiting the applicability to broader populations. The East-Asian population is especially under-represented, despite having the highest global burden of end-stage kidney disease. We conducted a meta-analysis of multiple GWASs (n = 244,952) on estimated glomerular filtration rate and a replication dataset (n = 27,058) from Taiwan and Japan. This study identified 111 lead SNPs in 97 genomic risk loci. Functional enrichment analyses revealed that variants associated with F12 gene and a missense mutation in ABCG2 may contribute to chronic kidney disease (CKD) through influencing inflammation, coagulation, and urate metabolism pathways. In independent cohorts from Taiwan (n = 25,345) and the United Kingdom (n = 260,245), polygenic risk scores (PRSs) for CKD significantly stratified the risk of CKD (p < 0.0001). Further research is required to evaluate the clinical effectiveness of PRSCKD in the early prevention of kidney disease.

Insight into selenium biofortification and the selenite metabolic mechanism of Monascus ruber M7

Monascus species are functional fermentation fungi with great potential for selenium (Se) supplementation. This study investigated the effects of Se bio-fortification on the growth, morphology, and biosynthesis of Monascus ruber M7. The results demonstrated a significant increase in the yield of orange and red Monascus pigments (MPs) in red yeast rice (RYR) by 38.52% and 36.57%, respectively, under 20 μg/mL of selenite pressure. Meanwhile, the production of citrinin (CIT), a mycotoxin, decreased from 244.47 μg/g to 175.01 μg/g. Transcriptome analysis revealed significant upregulation of twelve genes involved in MPs biosynthesis, specifically MpigE, MpigF, and MpigN, and downregulation of four genes (mrr3, mrr4, mrr7, and mrr8) associated with CIT biosynthesis. Additionally, three genes encoding cysteine synthase cysK (Log2FC = 1.6), methionine synthase metH (Log2FC = 2.2), and methionyl-tRNA synthetase metG (Log2FC = 1.8) in selenocompound metabolism showed significantly upregulated. These findings provide insights into Se biotransformation and metabolism in filamentous fungi.

Integrative multi-target analysis of Urtica dioica for gout arthritis treatment: a network pharmacology and clustering approach

Urtica dioica (stinging nettle) has been traditionally used in Chinese medicine for the treatment of joint pain and rheumatoid arthritis. This study aims to elucidate the active compounds and mechanisms by which it acts against gout arthritis (GA). Gout-related genes were identified from the DisGeNet, GeneCards, and OMIM databases. These genes may play a role in inhibiting corresponding proteins targeted by the active compounds identified from the literature, which have an oral bioavailability of ≥ 30% and a drug-likeness score of ≥ 0.18. A human protein-protein interaction network was constructed, resulting in sixteen clusters containing plant-targeted genes, including ABCG2, SLC22A12, MAP2K7, ADCY10, RELA, and TP53. The key bioactive compounds, apigenin-7-O-glucoside and kaempferol, demonstrated significant binding to SLC22A12 and ABCG2, suggesting their potential to reduce uric acid levels and inflammation. Pathway enrichment analysis further identified key metabolic pathways involved, highlighting a dual mechanism of anti-inflammatory and urate-lowering effects. These findings underscore the potential of U. dioica in targeting multiple pathways involved in GA, combining traditional medicine with modern pharmacology. This integrated approach provides a foundation for future research and the development of multi-target therapeutic strategies for managing gout arthritis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-024-00254-9.

WWC1 upregulation accelerates hyperuricemia by reduction in renal uric acid excretion through Hippo signaling pathway

Hyperuricemia (HUA) is a metabolic disorder characterized by elevated serum uric acid (UA), primarily attributed to the hepatic overproduction and renal underexcretion of UA. Despite the elucidation of molecular pathways associated with this underexcretion, the etiology of HUA remains largely unknown. In our study, using by Uox knockout rats, HUA mouse, and cell line models, we discovered that the increased WWC1 levels were associated with decreased renal UA excretion. Additionally, using knockdown and overexpression approaches, we found that WWC1 inhibited UA excretion in renal tubular epithelial cells. Mechanistically, WWC1 activated the Hippo pathway, leading to phosphorylation and subsequent degradation of the downstream transcription factor YAP1, thereby impairing the ABCG2 and OAT3 expression through transcriptional regulation. Consequently, this reduction led to a decrease in UA excretion in renal tubular epithelial cells. In conclusion, our study has elucidated the role of upregulated WWC1 in renal tubular epithelial cells inhibiting the excretion of UA in the kidneys and causing HUA.

Effects of Smilax China L. extracts on Hyperuricemia chicken model via inhibiting xanthine oxidase activity

Hyperuricemia (HUA) is a metabolic disorder caused by excessive production of uric acid (UA) or impaired uric acid metabolism. Smilax China L. has a wide range of pharmacological activities such as immunomodulatory, anti-inflammatory, and antioxidant. Its roots and rhizomes have been widely used for the treatment of HUA. However, its mechanisms for treating HUA and reducing renal impairment have not been fully elucidated. In the present study, we evaluated the effect of Smilax China L. extract (SC) on UA metabolism and further explored its mechanism of action by feeding a high-calcium and high-protein diet to chickens to induce a model of HUA in chickens. SC significantly reduced serum UA levels and improved renal function in hyperuricemic chickens. Meanwhile, SC was able to inhibit the activity of xanthine oxidase (XOD) in vivo and in vitro, reducing the production of uric acid. In addition, SC was able to increase the expression of Breast Cancer Resistance Protein (BCRP) in the kidney and ileum and increase uric acid excretion. Therefore, our results suggest that SC may be a candidate for anti-hyperuricemia.

Changes in alcohol intake and serum urate changes: longitudinal analyses of annual medical examination database

INTRODUCTION

Despite the established cross-sectional association between alcohol intake and serum urate (SU), its longitudinal association remains unknown. This study aimed to determine whether changes in alcohol intake have a clinically relevant association with SU change.

METHOD

We conducted retrospective analyses using systematically collected annual medical examination data from October 2012 to October 2022 in a Japanese preventive medicine centre. The exposure was changes in alcohol intake between two consecutive visits. The association of SU changes with alcohol intake changes was estimated by mixed-effect linear regression with adjustment for relevant covariates.

RESULTS

We analysed 63 486 participants (median age, 47.0 years; 55% women; 58.6% regular alcohol drinkers with a median of 1.4 drinks/day) with 370 572 visits. The median SU level was 5.3 mg/dL, and 506 (0.8%) participants had diagnoses of gout or hyperuricemia without medication use during the study period. Decreasing one daily alcohol intake had a clinically small association with SU changes (-0.019 (95% CI: -0.021 to -0.017) mg/dL). Beer had the largest association with SU (-0.036 (95% CI: -0.039 to -0.032) mg/dL for one beer decrease). Complete discontinuation of any alcohol from a mean of 0.8 drinks/day was associated with -0.056 mg/dL (95% CI: -0.068 to -0.043) decrease in SU; the association became larger in hyperuricemic participants (-0.110 mg/dL (95% CI: -0.154 to -0.066) for alcohol discontinuation from a mean of 1.0 drinks/day).

CONCLUSIONS

This study revealed changes in alcohol intake had small associations with SU change at the general Japanese population level. Complete discontinuation of alcohol in hyperuricemic participants had only modest improvement in SU.

Effects of stocking density on the homeostasis of uric acid and related liver and kidney functions in ducks

OBJECTIVE

Stocking density (SD) is an important issue in the poultry industry, which is related to the production performance, intestinal health and immune status. In the present study, the effects of SD on the metabolism and homeostasis of uric acid as well as the related functions of the liver and kidney in ducks were examined.

METHODS

A total of 360 healthy 56-day-old Shan-ma ducks were randomly divided into the low stocking density (n = 60, density = 5 birds/m2), medium stocking density (n = 120, density = 10 birds/m2) and high stocking density groups (HSD; n = 180, density = 15 birds/m2). Samples were collected in the 3rd, 6th, and 9th weeks of the experiment for analysis.

RESULTS

The serum levels of uric acid, lipopolysaccharide and inflammatory cytokines (interleukin-1β [IL-1β], IL-8, and tumor necrosis factor-α [TNF-α]) were increased significantly in the HSD group. Serious histopathological lesions could be seen in both the livers and kidneys in the HSD group in the 9th week. The mRNA expression levels of inflammatory cytokines (IL-8 and TNF-α) and related pathway components (toll-like receptor 4, myeloid differentiation primary response gene 88, and nuclear factor-κB) were increased significantly in both the livers and kidneys in the HSD group. The mRNA expression levels of enzymes (adenosine deaminase, xanthine oxidase, phosphoribosyl pyrophosphate amidotransferase, and phosphoribosyl pyrophosphate synthetase 1) related to the synthesis of uric acid increased significantly in the livers in the HSD group. However, the mRNA expression level of solute carrier family 2 member 9, which plays an important role in the excretion of uric acid by the kidney, was decreased significantly in the kidneys in the HSD group.

CONCLUSION

These results indicated that a higher SD could cause tissue inflammatory lesions in the liver and kidney and subsequently affect the metabolism and homeostasis of uric acid, and is helpful for guiding decisions related to the breeding and production of ducks.

Proline-derived quinoline formamide compounds as human urate transporter 1 inhibitors with potent uric acid-lowering activities

We report the design and synthesis of a series of proline-derived quinoline formamide compounds as human urate transporter 1 (URAT1) inhibitors via a ligand-based pharmacophore approach. Structure-activity relationship studies reveal that the replacement of the carboxyl group on the polar fragment with trifluoromethanesulfonamide and substituent modification at the 6-position of the quinoline ring greatly improve URAT1 inhibitory activity compared with lesinurad. Compounds 21c, 21e, 24b, 24c, and 23a exhibit potent activities against URAT1 with IC50 values ranging from 0.052 to 0.56 μM. Furthermore, compound 23a displays improved selectivity towards organic anion transporter 1 (OAT1), good microsomal stability, low potential for genotoxicity and no inhibition of the hERG K+ channel. Compounds 21c and 23a, which have superior pharmacokinetic properties, also demonstrate significant uric acid-lowering activities in a mouse model of hyperuricemia. Notably, 21c also exhibits moderate anti-inflammatory activity related to the gout inflammatory pathway. Compounds 21c and 23a with superior druggability are potential candidates for the treatment of hyperuricemia and gout.

Chinese Sumac (Rhus chinensis Mill.) Fruits Prevent Hyperuricemia and Uric Acid Nephropathy in Mice Fed a High-Purine Yeast Diet

Hyperuricemia (HUA) is a prevalent chronic disease, characterized by excessive blood uric acid levels, that poses a significant health risk. In this study, the preventive effects and potential mechanisms of ethanol extracts from Chinese sumac (Rhus chinensis Mill.) fruits on HUA and uric acid nephropathy were comprehensively investigated. The results demonstrated a significant reduction in uric acid levels in hyperuricemia mice after treatment with Chinese sumac fruit extract, especially in the high-dose group, where the blood uric acid level decreased by 39.56%. Visual diagrams of the kidneys and hematoxylin and eosin (H&E)-stained sections showed the extract's effectiveness in protecting against kidney damage caused by excessive uric acid. Further investigation into its mechanism revealed that the extract prevents and treats hyperuricemia by decreasing uric acid production, enhancing uric acid excretion, and mitigating the oxidative stress and inflammatory reactions induced by excessive uric acid in the kidneys. Specifically, the extract markedly decreased xanthine oxidase (XOD) levels and expression in the liver, elevated the expression of uric acid transporters ABCG2, and lowered the expression of uric acid reabsorption proteins URAT1 and SLC2A9. Simultaneously, it significantly elevated the levels of endogenous antioxidant enzymes (SOD and GSH) while reducing the level of malondialdehyde (MDA). Furthermore, the expression of uric-acid-related proteins NLRP3, ACS, and Caspase-3 and the levels of IL-1β and IL-6 were significantly reduced. The experimental results confirm that Chinese sumac fruit extract can improve HUA and uric acid nephropathy in mice fed a high-purine yeast diet. This finding establishes a theoretical foundation for developing Chinese sumac fruit as a functional food or medicine for preventing and treating HUA.

Understanding Hyperuricemia: Pathogenesis, Potential Therapeutic Role of Bioactive Peptides, and Assessing Bioactive Peptide Advantages and Challenges

Hyperuricemia is a medical condition characterized by an elevated level of serum uric acid, closely associated with other metabolic disorders, and its global incidence rate is increasing. Increased synthesis or decreased excretion of uric acid can lead to hyperuricemia. Protein peptides from various food sources have demonstrated potential in treating hyperuricemia, including marine organisms, ovalbumin, milk, nuts, rice, legumes, mushrooms, and protein-rich processing by-products. Through in vitro experiments and the establishment of cell or animal models, it has been proven that these peptides exhibit anti-hyperuricemia biological activities by inhibiting xanthine oxidase activity, downregulating key enzymes in purine metabolism, regulating the expression level of uric acid transporters, and restoring the composition of the intestinal flora. Protein peptides derived from food offer advantages such as a wide range of sources, significant therapeutic benefits, and minimal adverse effects. However, they also face challenges in terms of commercialization. The findings of this review contribute to a better understanding of hyperuricemia and peptides with hyperuricemia-alleviating activity. Furthermore, they provide a theoretical reference for developing new functional foods suitable for individuals with hyperuricemia.

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.

GLUT9 as a potential drug target for chronic kidney disease: Drug target validation by a Mendelian randomization study

Although chronic kidney disease (CKD) is recognized as a major public health concern, effective treatment strategies have yet to be developed. Identification and validation of drug targets are key issues in the development of therapeutic agents for CKD. Uric acid (UA), a major risk factor for gout, has also been suggested to be a risk factor for CKD, but the efficacy of existing urate-lowering therapies for CKD is controversial. We focused on five uric acid transporters (ABCG2, SLC17A1, SLC22A11, SLC22A12, SLC2A9) as potential drug targets and evaluated the causal association between serum UA levels and estimated glomerular filtration rate (eGFR) using single-SNP Mendelian Randomization. The results showed a causal association between genetically predicted changes in serum UA levels and eGFR when genetic variants were selected from the SLC2A9 locus. Estimation based on a loss-of-function mutation (rs16890979) showed that the changes in eGFR per unit increase in serum UA level was -0.0082 ml/min/1.73 m2 (95% CI -0.014 to -0.0025, P = 0.0051). These results indicate that SLC2A9 may be a novel drug target for CKD that preserves renal function through its urate-lowering effect.

Increased prevalence of gout in patients with inflammatory bowel disease: A population-based study

Background and Aim

Arthritis is a recognized extra-intestinal manifestation of inflammatory bowel disease (IBD). Studies show altered uric acid metabolism in IBD. This study aims to investigate the association between IBD and gout.

Methods

We used a multi-center database (Explorys Inc.) consisting of data from several US healthcare systems. We identified adults diagnosed with Crohn's disease (CD) and ulcerative colitis (UC) between 1999 and 2022. In this cohort, we identified patients diagnosed with gout. We collected demographic data and identified patients diagnosed with IBD-associated arthritis and those who had intestinal resection. Risk factors associated with gout were collected. Multivariate analysis was used.

Results

Out of the 69 260 780 patients in the database, we identified 209 020 patients with UC (0.30%) of whom 9130 had gout (4.3%). Additionally, 249 480 had CD (0.36%) of whom 14 000 had gout (5.61%). Males were more prevalent in the UC and gout group than in the CD and gout group (58% vs 51%). After adjustment, CD was significantly associated with gout (odds ratio [OR] 1.68, confidence interval [CI]: 1.60-1.75). UC was also significantly associated with gout (OR 1.38, CI: 1.31-1.44). In subgroup analysis with intestinal resection, CD patients who had intestinal resection had higher association with gout versus those without surgery (OR 2.34, CI: 2.25-2.43). Similar increase was observed in the UC group with intestinal resection (OR 1.53, CI: 1.49-1.56).

Conclusion

IBD is strongly associated with gout, with higher correlation observed with CD. Intestinal resection is associated with an increase in the risk of gout. Patients with IBD who present with new-onset arthritis should be investigated for gout.

Laboratory Findings of Benign Convulsions With Mild Gastroenteritis: A Meta-Analysis

Investigating factors associated with benign convulsions with mild gastroenteritis (CwG) is important for early detection and treatment. In previous studies, uric acid (UA) has been reported to be associated with CwG. However, the association between CwG and abnormal laboratory values remains inconclusive. We performed a meta-analysis of recent reports to determine the association between CwG and laboratory findings, including UA, in patients with acute gastroenteritis without convulsions. We conducted electronic searches of three databases (PubMed, EMBASE, and Cochrane Library) and one scholarly search engine (Google Scholar (Google, Inc., Mountain View, CA, USA)) up to February 2023 for studies on CwG. Eligible studies were observational studies that assessed patients with CwG, reported laboratory data, and stated the presence or absence of convulsions during illness episodes. Patients were children with mild gastroenteritis, with the exposure group developing convulsions and the control group not. The outcome was a comparison of laboratory data between the two groups. The effect size was calculated using the standardized mean difference (SMD), and random-effects models were used for the analysis because of high heterogeneity. In total, 148 articles were included in this study. After the screening, nine studies, including 8,367 patients, were selected for the meta-analysis. The most prevalent laboratory finding was an increased serum UA level, with an SMD of 1.42 (N = 6,411; 95% confidence interval (CI): (1.12, 1.72); Z = 9.242, p< 0.001; I ² = 81.68%, p= 0.002). The optimal serum UA cutoff value was 7.21 mg/dL, with an area under the receiver operating characteristic (ROC) curve (AUC) of 0.827 (95% CI: (0.807, 0.846)). This meta-analysis suggests that CwG is strongly associated with increased serum UA levels. These results demonstrate that more attention should be paid when interpreting laboratory findings in pediatric patients with acute gastroenteritis.

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.

Global status and trends in gout research from 2012 to 2021: a bibliometric and visual analysis

BACKGROUND

Gout is the most common inflammatory arthritis with an increasing prevalence and incidence across the globe. We aimed to provide a comprehensive and systematic knowledge map of gout research to determine its current status and trends over the past decade.

METHODS

Publications on gout research were obtained from the Web of Science Core Collection (WOSCC) database. Bibliometric R, VOSviewer, and Citespace were employed to analyze the eligible literature.

RESULTS

A total of 5535 publications concerning gout research between 2012 and 2021 were included. Most publications and citations both numerically came from China. The strongest international cooperation belonged to the USA. The University of Auckland was the most productive institution with a leading place in research collaboration. The prime funding agency was the National Natural Science Foundation of China. Most papers were published in Clinical Rheumatology. Annals of the Rheumatic Diseases achieved the highest number of citations, H-index and IF, which showed the most excellent comprehensive strength. The individual author with the most paper authorship was Dalbeth Nicola with 241 publications and 46 H-index. Keywords and co-citation analysis discovered that pathological mechanism remains the future hotspot in gout research. It may involve gout connection with gut microbiota, NLRP3 inflammasome, xanthine oxidase, and urate-transporter ABCG2. In addition, besides metabolic diseases, the relationship between gout and heart failure may need more attention.

CONCLUSION

This study clarified the current status and research frontier in gout over the past decade, which would provide valuable research references for later researchers. Key Points •We disclosed the current status and frontier directions of gout over the past 10 years worldwide. •We identified future hotspots of gout research, including gout connection with gut microbiota, NLRP3 inflammasome, xanthine oxidase, and urate-transporter ABCG2. •We discovered that the relationship between gout and heart status would be the research frontier.

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.

NRBP1 modulates uric acid transporter ABCG2 expression by activating the Wnt/β-catenin pathway in HK-2 cells

BACKGROUND

Nuclear receptor binding protein 1 (NRBP1) and ATP-binding cassette subfamily G member 2 (ABCG2) was the gout risk gene and high-capacity urate exporter respectively. However, the relationship between NRBP1 and ABCG2 and the underlying molecular mechanism contributing to these associations are unknown.

METHODS

Firstly, the efficiency of the overexpression and knockdown of NRBP1 was confirmed by western blot. Next, the effect of NRBP1 overexpression and knockdown on the expression of ABCG2, organic anion transporter 1 (OAT1), glucose transporter 9 (GLUT9) and urate transporter 1 (URAT1) was detected by qRT-PCR and western blot. At the same time, the cellular location of ABCG2 and its expression after NRBP1 overexpression and knockdown was tested by immunofluorescence (IF) staining. Then, the mechanism of NRBP1 modulates ABCG2 expression was evaluated by western blot with or without the β-catenin inhibitor (21H7).

RESULTS

The lentivirus system was used to generate stable NRBP1 overexpression, while the plasmids carrying a NRBP1 siRNA was generated to knockdown NRBP1 expression in HK-2 cells. Meanwhile, the overexpression of NRBP1 significantly decreased the mRNAs and proteins expression of GLUT9 and URAT1, while the knockdown of NRBP1 increased the mRNAs and proteins expression of ABCG2 significantly. In addition, the NRBP1 modulates the expression of ABCG2 was by ctivating the Wnt/β-catenin pathway in HK-2 cells according to the IF and western blot results.

CONCLUSION

Taken together, our study demonstrated that NRBP1 inhibition played an essential role in attenuating hyperuricemia and gout by upregulation of ABCG2 via Wnt/β-catenin signaling pathway in HK-2 cells.

Review of Urate-Lowering Therapeutics: From the Past to the Future

We reviewed all currently available ULT, as well as any medications in development using following databases: United States Food and Drug Administration (FDA), European Medicines Agency (EMA), Japanese Pharmaceutical and Medical Devices Agency (PMDA), and ClinicalTrials.gov. We identified a total of 36 drugs, including 10 approved drugs, 17 in clinical testing phases, and 9 in preclinical developmental phases. The 26 drugs currently undergoing testing and development include 5 xanthine oxidase inhibitors, 14 uricosurics, 6 recombinant uricases, and one with multiple urate-lowering mechanisms of action. Herein, we reviewed the benefit and risk of each drug summarizing currently available drugs. New trials of uricosuric agents are underway to develop the new indication. New drugs are going on to improve the potency of recombinant uricase and to develop the new route administration of such as oral formulation. This review will provide valuable information on the properties, indications, and limitations of ULTs.

Genetic polymorphisms and decreased protein expression of ABCG2 urate transporters are associated with susceptibility to gout, disease severity and renal-overload hyperuricemia

Gout is a common crystal induced disease of high personal and social burden, characterised by severe arthritis and comorbidity if untreated. Impaired function of ABCG2 transporter is causative in gout and may be responsible for renal-overload type hyperuricemia. Despite its importance, there is limited information on how clinical parameters correlate with protein expression and that with genetic changes. Urate and clinical parameters of 78 gouty patients and healthy controls were measured among standardised circumstances from a Hungarian population. ABCG2 membrane expression of red blood cells was determined by flow cytometry-based method and SNPs of this protein were analysed by TaqMan-based qPCR. The prevalence of ABCG2 functional polymorphisms in gouty and control patients were 32.1 and 13.7%, respectively. Most common SNP was Q141K while one sample with R236X, R383C and the lately described M71V were found in the gouty population. These polymorphisms showed strong linkage with decreased protein expression while the latter was also associated with higher fractional urate excretion (FUE) and urinary urate excretion (UUE). This study firstly evaluated ABCG2 protein expression in a clinically defined gouty population while also proving its associations between ABCG2 genetic changes and renal-overload hyperuricemia. The paper also highlighted relations between ABCG2 SNPs, gout susceptibility and disease severity characterised by an early onset disease with frequent flares and tophi formation.

Folic acid and zinc improve hyperuricemia by altering the gut microbiota of rats with high-purine diet-induced hyperuricemia

A high-purine diet can cause hyperuricemia and destroy the microbial composition of the gut microbiota. Both folic acid and zinc significantly reduce uric acid levels and alleviate hyperuricemia. However, whether the underlying mechanisms are associated with the regulation of the gut microbiota remain unknown. To explore alterations of the gut microbiota related to folic acid and zinc treatment in rats with hyperuricemia in our study. A hyperuricemic rat model was established with a high-purine diet. The effects of folic acid and zinc on uric acid levels were evaluated. Alterations of the gut microbiota related to hyperuricemia and the treatments were evaluated by sequencing using the Illumina MiSeq system. The results demonstrated that uric acid levels dropped observably, and the activities of adenosine deaminase (ADA) and xanthine oxidase (XOD) were downregulated after folic acid or zinc intervention. 16S rRNA gene sequencing-based gut microbiota analysis revealed that folic acid and zinc enhanced the abundance of probiotic bacteria and reduced that of pathogenic bacteria, thus improving intestinal barrier function. PICRUST analysis indicated that folic acid and zinc restored gut microbiota metabolism. These findings indicate that folic acid and zinc ameliorate hyperuricemia by inhibiting uric acid biosynthesis and stimulating uric acid excretion by modulating the gut microbiota. Thus, folic acid and zinc may be new and safe therapeutic agents to improve hyperuricemia.

Genome-wide meta-analysis between renal overload type and renal underexcretion type of clinically defined gout in Japanese populations

Despite progress in understanding of the genetic basis of gout, the precise factors affecting differences in gout susceptibility among different gout subtypes remain unclear. Using clinically diagnosed gout patients, we conducted a genome-wide meta-analysis of two distinct gout subtypes: the renal overload type and the renal underexcretion type. We provide genetic evidence at a genome-wide level of significance that supports a positive association between ABCG2 dysfunction and acquisition of the renal overload type.

Relationship between bisphenol A, bisphenol S, and bisphenol F and serum uric acid concentrations among school-aged children

Background

Hyperuricemia has a suspected relationship with hypertension, metabolic syndrome, kidney disease, and cardiovascular disease. Endocrine disruptors may affect uric acid metabolism; however, few epidemiologic studies have been performed in children regarding newly developed bisphenol A (BPA) substitutes. We evaluated the associations between BPA, bisphenol S (BPS), and bisphenol F (BPF) exposure and serum uric acid concentrations in 6-year-old Korean children.

Methods

From the Environment and Development of Children cohort study, six-year-old children (N = 489; 251 boys) who underwent an examination during 2015–2017 were included. Anthropometry, questionnaires, and biological samples were evaluated. BPA, BPS, and BPF levels were measured from spot urine samples, and log-transformed or categorized into groups for analysis. We constructed linear regression models adjusting for age, sex, urinary creatinine levels, body mass index z-scores, and estimated glomerular filtration rates.

Results

Mean serum uric level was 4.2 mg dL^-1 (0.8 SD) without sex-differences. Among the three bisphenols, higher BPS exposure was associated with increased serum uric acid concentrations (P-value for trend = 0.002). When BPS levels were categorized into three groups (non-detection < 0.02 μg L^-1 vs. medium BPS; 0.02–0.05 μg L^-1 vs. high BPS ≥ 0.05 μg L^-1), the high BPS group showed higher serum uric acid concentrations (by 0.26 mg dL^-1, P = 0.003) than the non-detection group after adjusting for covariates, which was significant in boys but not girls.

Discussions

Urinary BPS levels was positively associated with serum uric acid concentrations in 6-year-old children, and the association was more pronounced in boys. Considering the increasing use of BPS and concerning effect of hyperuricemia on health outcomes, their positive relationship should be investigated further.

The chemistry, processing, and preclinical anti-hyperuricemia potential of tea: a comprehensive review

Hyperuricemia is an abnormal purine metabolic disease that occurs when there is an excess of uric acid in the blood, associated with cardiovascular diseases, hypertension, gout, and renal disease. Dietary intervention is one of the most promising strategies for preventing hyperuricemia and controlling uric acid concentrations. Tea (Camellia sinensis) is known as one of the most common beverages and the source of dietary polyphenols. However, the effect of tea on hyperuricemia is unclear. Recent evidence shows that a lower risk of hyperuricemia is associated with tea intake. To better understand the anti-hyperuricemia effect of tea, this review first briefly describes the pathogenesis of hyperuricemia and the processing techniques of different types of tea. Next, the epidemiological and experimental studies of tea and its bioactive compounds on hyperuricemia in recent years were reviewed. Particular attention was paid to the anti-hyperuricemia mechanisms targeting the hepatic uric acid synthase, renal uric acid transporters, and intestinal microbiota. Additionally, the desirable intake of tea for preventing hyperuricemia is provided. Understanding the anti-hyperuricemia effect and mechanisms of tea can better utilize it as a preventive dietary strategy.HighlightsHigh purine diet, excessive alcohol/fructose consumption, and less exercise/sleep are the induction factors of hyperuricemia.Tea and tea compounds showed alleviated effects for hyperuricemia, especially polyphenols.Tea (containing caffeine or not) is not associated with a higher risk of hyperuricemia.Xanthine oxidase inhibition (reduce uric acid production), Nrf2 activation, and urate transporters regulation (increase uric acid excretion) are the potential molecular targets of anti-hyperuricemic effect of tea.About 5 g tea intake per day may be beneficial for hyperuricemia prevention.

Cardiometabolic genomics and pharmacogenomics investigations in Filipino Americans: Steps towards precision health and reducing health disparities

Background

Filipino Americans (FAs) are the third-largest Asian American subgroup in the United States (US). Some studies showed that FAs experience more cardiometabolic diseases (CMDs) than other Asian subgroups and non-Hispanic Whites. The increased prevalence of CMD observed in FAs could be due to genetics and social/dietary lifestyles. While FAs are ascribed as an Asian group, they have higher burdens of CMD, and adverse social determinants of health compared to other Asian subgroups. Therefore, studies to elucidate how FAs might develop CMD and respond to medications used to manage CMD are warranted. The ultimate goals of this study are to identify potential mechanisms for reducing CMD burden in FAs and to optimize therapeutic drug selection. Collectively, these investigations could reduce the cardiovascular health disparities among FAs.

Rationale and design

This is a cross-sectional epidemiological design to enroll 300 self-identified Filipino age 18 yrs. or older without a history of cancer and/or organ transplant from Virginia, Washington DC, and Maryland. Once consented, a health questionnaire and disease checklist are administered to participants, and anthropometric data and other vital signs are collected. When accessible, we collect blood samples to measure basic blood biochemistry, lipids, kidney, and liver functions. We also extract DNA from the blood or saliva for genetic and pharmacogenetic analyses. CMD prevalence in FAs will be compared to the US population. Finally, we will conduct multivariate analyses to ascertain the role of genetic and non-genetic factors in developing CMD in FAs. Virginia Commonwealth University IRB approved all study materials (Protocol HM20018500).

Summary

This is the first community-based study to involve FAs in genomics research. The study is actively recruiting participants. Participant enrollment is ongoing. At the time of this publication, the study has enrolled 97 participants. This ongoing study is expected to inform future research to reduce cardiovascular health disparities among FAs.

Discovery of novel verinurad analogs as dual inhibitors of URAT1 and GLUT9 with improved Druggability for the treatment of hyperuricemia

Verinurad (RDEA3170) is a selective URAT1 inhibitor under investigation for the treatment of gout and hyperuricemia. In an effort to further improve the pharmacodynamics/pharmacokinetics of verinurad and to increase the structural diversity, we designed novel verinurad analogs by introducing a linker (e.g. aminomethyl, amino or oxygen) between the naphthalene and the pyridine ring to increase the flexibility. These compounds were synthesized and tested for their in vitro URAT1-inhibitory activity. Most compounds exhibited potent inhibitory activities against URAT1 with IC₅₀ values ranging from 0.24 μM to 16.35 μM. Among them, compound KPH2f exhibited the highest URAT1-inhibitory activity with IC₅₀ of 0.24 μM, comparable to that of verinurad (IC₅₀ = 0.17 μM). KPH2f also inhibited GLUT9 with an IC₅₀ value of 9.37 ± 7.10 μM, indicating the dual URAT1/GLUT9 targeting capability. In addition, KPH2f showed little effects on OAT1 and ABCG2, and thus was unlikely to cause OAT1/ABCG2-mediated drug-drug interactions and/or to neutralize the uricosuric effects of URAT1/GLUT9 inhibitors. Importantly, KPH2f (10 mg/kg) was equally effective in reducing serum uric acid levels and exhibited higher uricosuric effects in a mice hyperuricemia model, as compared to verinurad (10 mg/kg). Furthermore, KPH2f demonstrated favorable pharmacokinetic properties with an oral bioavailability of 30.13%, clearly better than that of verinurad (21.47%). Moreover, KPH2f presented benign safety profiles without causing hERG toxicity, cytotoxicity in vitro (lower than verinurad), and renal damage in vivo. Collectively, these results suggest that KPH2f represents a novel, safe and effective dual URAT1/GLUT9 inhibitor with improved druggabilities and is worthy of further investigation as an anti-hyperuricemic drug candidate.

Hypouricaemic and nephroprotective effects of Poria cocos in hyperuricemic mice by up-regulating ATP-binding cassette super-family G member 2

CONTEXT

Poria coco F.A.Wolf (Polyporaceae) dispels dampness and promotes diuresis implying hypouricaemic action.

OBJECTIVE

To examine hypouricaemic action of Poria coco.

MATERIALS AND METHODS

Ethanol extract (PCE) was prepared by extracting the sclerotium of P. cocos with ethanol, and the water extract (PCW) was produced by bathing the remains with water. PCE and PCW (50, 100 and 200 mg/kg, respectively) were orally administered to hyperuricemic Kunming mice (n = 8) to examine its hypouricaemic effect. Also, molecular docking was performed.

RESULTS

P. cocos showed excellent hypouricaemic action, decreasing the serum uric acid of hyperuricaemia (HUA) control (526 ± 112 μmol/L) to 178 ± 53, 153 ± 57 and 151 ± 62 μmol/L (p < 0.01) by PCE and 69 ± 23, 63 ± 15 and 62 ± 20 μmol/L (p < 0.01) by PCW, respectively. According to SCrs, BUNs and H&E staining, PCE and PCW partially attenuated renal dysfunction caused by HUA. They presented no negative effects on ALT, AST and ALP activities. They elevated ABCG2 (ATP-binding cassette super-family G member 2) mRNA and protein expression in comparison to HUA control. In molecular docking, compound 267, 277, 13824, 15730 and 5759 were predicted as the top bioactives of P. cocos against HUA, which even presented better scores than the positive compound, oestrone 3-sulfate.

DISCUSSION AND CONCLUSIONS

This paper demonstrated the hypouricaemic and nephroprotective effects of P. cocos in hyperuricemic mice by up-regulating ABCG2. These results may be useful for the development of a hypouricaemic agent.

Saengmaeksan, a traditional herbal formulation consisting of Panax ginseng, ameliorates hyperuricemia by inhibiting xanthine oxidase activity and enhancing urate excretion in rats

Background

Saengmaeksan (SMS) is a traditional Korean medicine composed of three herbs, Panax ginseng, Schisandra chinensis, and Liriope platyphylla. SMS is used to treat respiratory and cardiovascular disorders. However, whether SMS exerts antihyperuricemic effects is unknown.

Methods

Effects of the SMS extract in water (SMS-W) and 30% ethanol (SMS-E) were studied in a rat model of potassium oxonate-induced hyperuricemia. Uric acid concentrations and xanthine oxidase (XO) activities were evaluated in the serum, urine, and hepatic tissue. Using renal histopathology to assess kidney function and uric acid excretion, we investigated serum creatinine and blood urea nitrogen concentrations, as well as protein levels of renal urate transporter 1 (URAT1), glucose transporter 9 (GLUT9), and organic anion transporter 1 (OAT1). The effects of SMS on in vitro XO activity and uric acid uptake were also evaluated. The components of SMS were identified using Ultra Performance Liquid Chromatography (UPLC).

Results

SMS-E reduced serum uric acid and creatinine concentrations, and elevated urine uric acid excretion. SMS-E lowered XO activities in both the serum and liver, and downregulated the expression of renal URAT1 and GLUT9 proteins. SMS-E reduced renal inflammation and IL-1β levels in both the serum and kidneys. SMS-E inhibited both in vitro XO activity and urate uptake in URAT1-expressing oocytes. Using UPLC, 25 ginsenosides were identified, all of which were present in higher levels in SMS-E than in SMS-W.

Conclusion

SMS-E exhibited antihyperuricemic effects by regulating XO activity and renal urate transporters, providing the first evidence of its applicability in the treatment of hyperuricemia and gout.

Multidrug efflux transporter ABCG2: expression and regulation

The adenosine triphosphate (ATP)-binding cassette efflux transporter G2 (ABCG2) was originally discovered in a multidrug-resistant breast cancer cell line. Studies in the past have expanded the understanding of its role in physiology, disease pathology and drug resistance. With a widely distributed expression across different cell types, ABCG2 plays a central role in ATP-dependent efflux of a vast range of endogenous and exogenous molecules, thereby maintaining cellular homeostasis and providing tissue protection against xenobiotic insults. However, ABCG2 expression is subjected to alterations under various pathophysiological conditions such as inflammation, infection, tissue injury, disease pathology and in response to xenobiotics and endobiotics. These changes may interfere with the bioavailability of therapeutic substrate drugs conferring drug resistance and in certain cases worsen the pathophysiological state aggravating its severity. Considering the crucial role of ABCG2 in normal physiology, therapeutic interventions directly targeting the transporter function may produce serious side effects. Therefore, modulation of transporter regulation instead of inhibiting the transporter itself will allow subtle changes in ABCG2 activity. This requires a thorough comprehension of diverse factors and complex signaling pathways (Kinases, Wnt/β-catenin, Sonic hedgehog) operating at multiple regulatory levels dictating ABCG2 expression and activity. This review features a background on the physiological role of transporter, factors that modulate ABCG2 levels and highlights various signaling pathways, molecular mechanisms and genetic polymorphisms in ABCG2 regulation. This understanding will aid in identifying potential molecular targets for therapeutic interventions to overcome ABCG2-mediated multidrug resistance (MDR) and to manage ABCG2-related pathophysiology.

Increase of serum uric acid levels associated with APOE ε2 haplotype: a clinico-genetic investigation and in vivo approach

Elevated serum uric acid (SUA)-hyperuricemia-is caused by overproduction of urate or by its decreased renal and/or intestinal excretion. This disease, which is increasing in prevalence worldwide, is associated with both gout and metabolic diseases. Several studies have reported relationships between apolipoprotein E (APOE) haplotypes and SUA levels in humans; however, their results remain inconsistent. This prompted us to investigate the relationship between APOE polymorphisms and SUA levels. Our subjects were 5,272 Japanese men, premenopausal women, and postmenopausal women. Multiple linear regression analyses revealed the ε2 haplotype of APOE to be independently associated with higher SUA in men (N = 1,726) and postmenopausal women (N = 1,753), but not in premenopausal women (N = 1,793). In contrast, the ε4 haplotype was little related to SUA levels in each group. Moreover, to examine the effect of Apoe deficiency on SUA levels, we conducted animal experiments using Apoe knockout mice, which mimics ε2/ε2 carriers. We found that SUA levels in Apoe knockout mice were significantly higher than those in wild-type mice, which is consistent with the SUA-raising effect of the ε2 haplotype observed in our clinico-genetic analyses. Further analyses suggested that renal rather than intestinal underexcretion of urate could be involved in Apoe deficiency-related SUA increase. In conclusion, we successfully demonstrated that the ε2 haplotype, but not the ε4 haplotype, increases SUA levels. These findings will improve our understanding of genetic factors affecting SUA levels.

Dietary Acid Load Is Positively Associated with the Incidence of Hyperuricemia in Middle-Aged and Older Korean Adults: Findings from the Korean Genome and Epidemiology Study

Hyperuricemia has been associated with a number of chronic diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Dietary acid load plays a key role in regulating uric acid levels. We hypothesized that potential renal acid load (PRAL) and net endogenous acid production (NEAP) score would be positively associated with the incidence of hyperuricemia. Data from the Health Examinees study, a part of the Korean Genome and Epidemiology Study were used. The PRAL and NEAP scores were calculated to evaluate the dietary acid load. Hyperuricemia was defined as follows: >7.0 mg/dL and >6.0 mg/dL of serum uric acid levels in men and women, respectively. Multivariable Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the incidence of hyperuricemia. We identified 2500 new cases of hyperuricemia during a mean follow-up of 5.0 years (223,552 person years). The participants in the highest quartiles of the PRAL and NEAP score had 21% (HR: 1.21, 95% CI: 1.07–1.35, p for trend <0.0001) and 17% (HR: 1.17, 95% CI: 1.04–1.31, p for trend <0.0001) higher risks for hyperuricemia, respectively, than those in the lowest quartiles, after adjusting for covariates. In this prospective cohort study, a higher dietary acid load was positively associated with a higher incidence of hyperuricemia in Korean adults. This suggests that an alkaline diet may be an effective strategy to reduce the future risk of elevated uric acid levels.

Eggshell Membrane Ameliorates Hyperuricemia by Increasing Urate Excretion in Potassium Oxonate-Injected Rats

Hyperuricemia is the primary cause of gouty arthritis and other metabolic disorders. Eggshell membrane (EM) is an effective and safe supplement for curing pain and stiffness connected with osteoarthritis. However, the effect of EM on hyperuricemia is unclear. This study determines the effects of EM on potassium oxonate-injected hyperuricemia. Uric acid, creatinine, blood urea nitrogen concentrations in the serum, and xanthine oxidase activity in the liver are measured. Protein levels of renal urate transporter 1 (URAT1), organic anion transporters 1 (OAT1), glucose transporter 9 (GLUT9), and ATP-binding cassette transporter G2 (ABCG2) in the kidney are determined with renal histopathology. The results demonstrate that EM reduces serum uric acid levels and increases urine uric acid levels in hyperuricemic rats. Moreover, EM downregulates renal URAT1 protein expression, upregulates OAT1 and ABCG2, but does not change GLUT9 expression. Additionally, EM does not change xanthine oxidase activity in the liver or the serum. EM also decreases uric acid uptake into oocytes expressing hURAT1. Finally, EM markedly reduces renal inflammation and serum interleukin-1β levels. These findings suggest that EM exhibits antihyperuricemic effects by promoting renal urate excretion and regulating renal urate transporters. Therefore, EM may be useful in the prevention and treatment of gout and hyperuricemia.

The gut microbiota mediates the protective effects of anserine supplementation on hyperuricaemia and associated renal inflammation

Hyperuricaemia is a disease associated with elevated serum uric acid content, which has emerged rapidly in recent decades. The drugs used to treat clinical hyperuricaemia have side effects, and their safety is poor. However, anserine is a natural carnosine derivative that shows an anti-hyperuricaemic effect. A previous study demonstrated that anserine inhibits uric acid synthesis and promotes uric acid excretion, but there is no evidence regarding the effect of anserine from the perspective of the gut microbiota. In this study, the anti-hyperuricaemic and anti-inflammatory effects of anserine were explored in a diet-induced hyperuricaemic mouse model. Anserine alleviated hyperuricaemia and renal inflammation phenotypes, inhibited uric acid biosynthesis, promoted uric acid excretion, and inhibited NLRP3 inflammasome and TLR4/MyD88/NF-κB signalling pathway activation. The results showed that the anti-hyperuricaemic effect of anserine was dependent on the gut microbiota in the germ-free mice experiment. Furthermore, anserine treatment reversed gut microbiota dysbiosis, repaired the intestinal epithelial barrier and increased short-chain fatty acid production. Moreover, the anti-hyperuricaemic effect of anserine was transmissible by transplanting the faecal microbiota from anserine-treated mice, indicating that the protective effects were at least partially mediated by the gut microbiota. Thus, we identified a new and safe prebiotic material to alleviate hyperuricaemia and provided ideas for the development of oligopeptides.

Ameliorative effect and mechanism of Yi-Suan-Cha against hyperuricemia in rats

BACKGROUND

This study aimed to evaluate the urate-lowering effects of Yi-Suan-Cha and explore its underlying mechanisms in experimental hyperuricemia induced in rats.

METHODS

Forty-eight male SD rats were randomly allocated into normal control, model, allopurinol, benzbromarone, low-dose Yi-Suan-Cha (0.2 g/ml), and high-dose Yi-Suan-Cha (0.4 g/ml) groups (n = 8 rats per group). Rat models of hyperuricemia were established through intragastric administration of adenine 25 mg/kg + potassium oxalate 300 mg/kg for 3 weeks. After the last administration, serum uric acid, creatinine, and urea nitrogen levels were measured. Renal histopathology was observed by hematoxylin-eosin staining. Xanthine oxidase level in serum and liver homogenates was measured by ELISA. The protein and mRNA expression of URAT1, ABCG2, OAT1, and GLUT9 in the kidney was detected by Western blotting and RT-PCR, respectively.

RESULTS

The serum uric acid levels were significantly lowered in all medication groups than in the model group. The benzbromarone and both Yi-Suan-Cha groups showed clear kidney structures with no obvious abnormalities. Compared with the normal control group, the model group showed increased URAT1/GLUT9 protein expression and decreased ABCG2/OAT1 protein expression. Compared with the model group, both Yi-Suan-Cha groups showed decreased URAT1/GLUT9 protein expression and increased ABCG2/OAT1 protein expression. Compared with that in the normal control group, URAT1/GLUT9 mRNA expression increased in the model group. Compared with the model group, the low-dose and high-dose Yi-Suan-Cha groups showed decreased URAT1/GLUT9 mRNA expression and increased ABCG2/OAT1 mRNA expression.

CONCLUSION

Yi-Suan-Cha may lower uric acid level by downregulating URAT1/GLUT9 expression and upregulating ABCG2/OAT1 expression.

The biology of urate

Urate is the end-product of the purine metabolism in humans. The dominant source of urate is endogenous purines and the remainder comes through diet. Approximately two thirds of urate is eliminated via the kidney with the rest excreted in the feces. While the transporter BCRP, encoded by ABCG2, has been found to play a role in both the gut and kidney, SLC22A12 and SLC2A9 encoding URAT1 and GLUT9, respectively, are the two transporters best characterized. Only 8-12% of the filtered urate is excreted by the kidney. Renal elimination of urate depends substantially on specific transporters, including URAT1, GLUT9 and BCRP. Studies that have assessed the biologic effects of urate have produced highly variable results. Although there is a suggestion that urate may have anti-oxidant properties in some circumstances, the majority of evidence indicates that urate is pro-inflammatory. Hyperuricemia can result in the formation of monosodium urate (MSU) crystals that may be recognized as danger signals by the immune system. This immune response results in the activation of the NLRP3 inflammasome and ultimately in the production and release of interleukin-1β, and IL-18, that mediate both inflammation, pyroptotic cell death, and necroinflammation. It has also been demonstrated that soluble urate mediates effects on the kidney to induce hypertension and can induce long term epigenetic reprogramming in myeloid cells to induce "trained immunity." Together, these sequelae of urate are thought to mediate most of the physiological effects of hyperuricemia and gout, illustrating this biologically active molecule is more than just an "end-product" of purine metabolism.

The Role of ABCG2 in the Pathogenesis of Primary Hyperuricemia and Gout-An Update

Urate homeostasis in humans is a complex and highly heritable process that involves i.e., metabolic urate biosynthesis, renal urate reabsorption, as well as renal and extrarenal urate excretion. Importantly, disturbances in urate excretion are a common cause of hyperuricemia and gout. The majority of urate is eliminated by glomerular filtration in the kidney followed by an, as yet, not fully elucidated interplay of multiple transporters involved in the reabsorption or excretion of urate in the succeeding segments of the nephron. In this context, genome-wide association studies and subsequent functional analyses have identified the ATP-binding cassette (ABC) transporter ABCG2 as an important urate transporter and have highlighted the role of single nucleotide polymorphisms (SNPs) in the pathogenesis of reduced cellular urate efflux, hyperuricemia, and early-onset gout. Recent publications also suggest that ABCG2 is particularly involved in intestinal urate elimination and thus may represent an interesting new target for pharmacotherapeutic intervention in hyperuricemia and gout. In this review, we specifically address the involvement of ABCG2 in renal and extrarenal urate elimination. In addition, we will shed light on newly identified polymorphisms in ABCG2 associated with early-onset gout.

Porphyrin accumulation in humans with common dysfunctional variants of ABCG2, a porphyrin transporter: potential association with acquired photosensitivity

Photosensitivity is a skin reaction disorder mediated by phototoxic and/or photoallergic mechanisms. The accumulation of porphyrins is generally considered to induce phototoxicity. ATP-binding cassette subfamily G member 2 (ABCG2) has been identified as a transporter of porphyrins and its common variants—p.Gln126Ter (rs72552713) and p.Gln141Lys (rs2231142)—reportedly decrease the function of porphyrin transport in vitro; however, the physiological importance of ABCG2 as a porphyrin transporter remains to be fully elucidated. We herein investigated whether ABCG2 dysfunction could lead to porphyrin accumulation and photosensitivity in Japanese subjects, and found it to be significantly correlated with erythrocyte protoporphyrin levels (P = 0.012). This appears to be the first clinical finding of ABCG2 dysfunction-associated protoporphyrin accumulation in humans. We divided the patients into a chronic actinic dermatosis (CAD) group and a non-CAD group. CAD was diagnosed based on the criteria of reduced minimal erythema doses to ultraviolet B (UVB) and/or ultraviolet A (UVA). The non-CAD group was composed of patients who exhibited normal reactions to UVB and UVA on phototesting, but had histories of recurrent erythema/papules on sun-exposed areas. Estimated ABCG2 function according to ABCG2 genotypes in the non-CAD group was significantly lower than in the general Japanese population (P = 0.045). In contrast, no difference was found in ABCG2 function between the CAD group and the general population, suggesting that ABCG2 dysfunction might be a genetic factor in non-CAD patients with clinical photosensitivity. In this context, genetic dysfunction of ABCG2 might be an overlooked pathological etiology of “photosensitivity of unknown cause.”

Aboriginal Bacterial Flora in the Uricase-Deficient Rat Gut is Not the Main Factor Affecting Serum Uric Acid

The relationship between intestinal bacteria and hyperuricemia is a hot research topic. To better understand this relationship, uricase-deficient Sprague–Dawley rats (Kunming-DY rats) were used. The wild-type rats and Kunming-DY rats were used as controls. Kunming-DY rats were treated with ampicillin (90 mg/kg) and ciprofloxacin (150 mg/kg) for 5 days. Bacterial 16S rDNA in the fresh stool was sequenced, and the abundance was calculated. The rats' serum uric acid (SUA) level was assayed, and the rats' intake and output in 24 h were recorded. The bacterial diversity in three groups' fresh stool was analyzed. The gut bacterial diversity and abundance changed in the Kunming-DY rats. More than 99% of bacteria were inhibited or killed by the combination of antibiotics. In contrast to each of the antibiotics alone, the combination of antibiotics lowered the Kunming-DY rats' SUA level; it also caused mild diarrhea, which increased uric acid excretion through stool. These results suggested that the aboriginal gut bacteria in uricase-deficient rats play a minor role in determining the SUA levels. It is too early to conclude that aboriginal gut bacteria are a tempting target for lowering SUA levels.

Sex-Specific Association of Uric Acid and Kidney Function Decline in Taiwan

An elevated serum urate concentration is associated with kidney damage. Men’s uric acid levels are usually higher than women’s. However, postmenopausal women have a higher risk of gout than men, and comorbidities are also higher than in men. This study examined the sex differences in the relationship between hyperuricemia and renal progression in early chronic kidney disease (CKD) and non-CKD, and further examined the incidence of CKD in non-CKD populations among patients over 50 years of age. We analyzed 1856 women and 1852 men participating in the epidemiology and risk factors surveillance of the CKD database. Women showed a significantly higher risk of renal progression and CKD than men within the hyperuricemia group. After adjusting covariates, women, but not men resulted in an hazard ratio (HR) for developing renal progression (HR = 1.12; 95% CI 1.01–1.24 in women and HR = 1.03; 95% CI 0.93–1.13 in men) and CKD (HR = 1.11; 95% CI 1.01–1.22 in women and HR = 0.95; 95% CI 0.85–1.05 in men) for each 1 mg/dL increase in serum urate levels. The association between serum urate levels and renal progression was stronger in women. Given the prevalence and impact of kidney disease, factors that impede optimal renal function management in women and men must be identified to provide tailored treatment recommendations.

From purines to purinergic signalling: molecular functions and human diseases

Purines and their derivatives, most notably adenosine and ATP, are the key molecules controlling intracellular energy homoeostasis and nucleotide synthesis. Besides, these purines support, as chemical messengers, purinergic transmission throughout tissues and species. Purines act as endogenous ligands that bind to and activate plasmalemmal purinoceptors, which mediate extracellular communication referred to as "purinergic signalling". Purinergic signalling is cross-linked with other transmitter networks to coordinate numerous aspects of cell behaviour such as proliferation, differentiation, migration, apoptosis and other physiological processes critical for the proper function of organisms. Pathological deregulation of purinergic signalling contributes to various diseases including neurodegeneration, rheumatic immune diseases, inflammation, and cancer. Particularly, gout is one of the most prevalent purine-related disease caused by purine metabolism disorder and consequent hyperuricemia. Compelling evidence indicates that purinoceptors are potential therapeutic targets, with specific purinergic agonists and antagonists demonstrating prominent therapeutic potential. Furthermore, dietary and herbal interventions help to restore and balance purine metabolism, thus addressing the importance of a healthy lifestyle in the prevention and relief of human disorders. Profound understanding of molecular mechanisms of purinergic signalling provides new and exciting insights into the treatment of human diseases.

Anti-hyperuricemic potential of stevia (Stevia rebaudiana Bertoni) residue extract in hyperuricemic mice

Hyperuricemia (HUA) is considered a potent risk factor for the development of gout, renal failure, and cardiovascular disease. The current project was designed to use stevia (Stevia rebaudiana Bertoni) byproduct, named stevia residue extract (STVRE), for the treatment of HUA. Male Kunming mice were divided into six groups: normal control, model control, positive control (allopurinol, 5 mg per kg body weight [bw]), STVRE-1 (75 mg per kg bw), STVRE-2 (150 mg per kg bw), and STVRE-3 (300 mg per kg bw). HUA was induced by the administration of potassium oxonate (100 mg per kg bw), fructose (10% w/v), and yeast extract (100 mg per kg bw) for 8 weeks. STVRE significantly (p < 0.05) decreased uric acid (UA) production and ameliorated UA excretion by interacting with urate transporters. The STVRE remarkably attenuated oxidative stress mediated by UA and downregulated inflammatory-related response markers such as COX-2, NF-κB, PGE2, IL-1β, and TNF-α. Furthermore, STVRE also reversed HUA-induced abnormalities in kidneys compared with the MC group. The results of our study suggest that STVRE has potential to attenuate hyperuricemia and renal protective effects, and may be used as a natural supplement for the possible treatment of UA-related disorders.

The Epidemiology and Genetics of Hyperuricemia and Gout across Major Racial Groups: A Literature Review and Population Genetics Secondary Database Analysis

Gout is an inflammatory condition caused by elevated serum urate (SU), a condition known as hyperuricemia (HU). Genetic variations, including single nucleotide polymorphisms (SNPs), can alter the function of urate transporters, leading to differential HU and gout prevalence across different populations. In the United States (U.S.), gout prevalence differentially affects certain racial groups. The objective of this proposed analysis is to compare the frequency of urate-related genetic risk alleles between Europeans (EUR) and the following major racial groups: Africans in Southwest U.S. (ASW), Han-Chinese (CHS), Japanese (JPT), and Mexican (MXL) from the 1000 Genomes Project. The Ensembl genome browser of the 1000 Genomes Project was used to conduct cross-population allele frequency comparisons of 11 SNPs across 11 genes, physiologically involved and significantly associated with SU levels and gout risk. Gene/SNP pairs included: ABCG2 (rs2231142), SLC2A9 (rs734553), SLC17A1 (rs1183201), SLC16A9 (rs1171614), GCKR (rs1260326), SLC22A11 (rs2078267), SLC22A12 (rs505802), INHBC (rs3741414), RREB1 (rs675209), PDZK1 (rs12129861), and NRXN2 (rs478607). Allele frequencies were compared to EUR using Chi-Square or Fisher’s Exact test, when appropriate. Bonferroni correction for multiple comparisons was used, with p < 0.0045 for statistical significance. Risk alleles were defined as the allele that is associated with baseline or higher HU and gout risks. The cumulative HU or gout risk allele index of the 11 SNPs was estimated for each population. The prevalence of HU and gout in U.S. and non-US populations was evaluated using published epidemiological data and literature review. Compared with EUR, the SNP frequencies of 7/11 in ASW, 9/11 in MXL, 9/11 JPT, and 11/11 CHS were significantly different. HU or gout risk allele indices were 5, 6, 9, and 11 in ASW, MXL, CHS, and JPT, respectively. Out of the 11 SNPs, the percentage of risk alleles in CHS and JPT was 100%. Compared to non-US populations, the prevalence of HU and gout appear to be higher in western world countries. Compared with EUR, CHS and JPT populations had the highest HU or gout risk allele frequencies, followed by MXL and ASW. These results suggest that individuals of Asian descent are at higher HU and gout risk, which may partly explain the nearly three-fold higher gout prevalence among Asians versus Caucasians in ambulatory care settings. Furthermore, gout remains a disease of developed countries with a marked global rising.

Chlorogenic acid supplementation ameliorates hyperuricemia, relieves renal inflammation, and modulates intestinal homeostasis

Hyperuricemia (HUA) is induced by abnormal purine metabolism and elevated serum uric acid (UA) concentrations, and it is often accompanied by inflammatory responses and intestinal disorders. This study aims to assess the protective effects of chlorogenic acid (CGA) on HUA in mice. CGA or allopurinol was given to mice with HUA induced by hypoxanthine and potassium oxonate. CGA lowered the levels of UA, blood urea nitrogen (BUN), creatinine (CR), AST, and ALT; inhibited xanthine oxidase (XOD) activity; and downregulated the mRNA expression of UA secretory proteins in HUA mice. Moreover, CGA significantly reduced serum lipopolysaccharides (LPS) levels and the mRNA expression of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, NOD-like receptor superfamily pyrin domain containing 3 (NLRP3), and caspase-1, and it inhibited the activation of the toll-like receptor 4/myeloid differentiation factor 88/nuclear factor kappa B (TLR4/MyD88/NF-κB) signaling pathway in the kidney, resulting in inflammation relief in HUA mice. In addition, CGA treatment increased the production of fecal short-chain fatty acids (SCFAs) in HUA mice. Additional investigations showed that CGA significantly lowered the mRNA expression of ileal IL-1β and IL-6, and it increased the mRNA expression of intestinal tight junction proteins (zonula occludens-1 (ZO-1) and occludin). Also, CGA increased the relative abundance of SCFA-producing bacteria, including Bacteroides, Prevotellaceae UGC-001, and Butyricimonas, and it reversed the purine metabolism and glutamate metabolism functions of gut microbiota. In conclusion, CGA may be a potential candidate for relieving the symptoms of HUA and regulating its associated inflammatory responses and intestinal homeostasis.

Molecular Pathophysiology of Uric Acid Homeostasis

Uric acid, the end product of purine metabolism, plays a key role in the pathogenesis of gout and other disease processes. The circulating serum uric acid concentration is governed by the relative balance of hepatic production, intestinal secretion, and renal tubular reabsorption and secretion. An elegant synergy between genome-wide association studies and transport physiology has led to the identification and characterization of the major transporters involved with urate reabsorption and secretion, in both kidney and intestine. This development, combined with continued analysis of population-level genetic data, has yielded an increasingly refined mechanistic understanding of uric acid homeostasis as well as greater understanding of the genetic and acquired influences on serum uric acid concentration. The continued delineation of novel and established regulatory pathways that regulate uric acid homeostasis promises to lead to a more complete understanding of uric acid-associated diseases and to identify new targets for treatment.

The prevalence of the gout-associated polymorphism rs2231142 G>T in ABCG2 in a pregnant female Filipino cohort

Gout is a metabolic disorder and one of the most common arthritic conditions. Hyperuricemia is the hallmark of developing gout and mostly caused by uric acid underexcretion. Gout disproportionately affects people of specific races and ethnicities. Filipinos are the second-largest Asian population in the USA and reported to have a higher prevalence of gout and hyperuricemia than non-Filipino counterparts and Filipinos residing in the Philippines. The genetic polymorphism rs2231142 G>T in the ABCG2 has been strongly associated with hyperuricemia and gout across multiple populations. However, the prevalence of this variant in Filipinos is unknown. Therefore, assessing the prevalence of this variant may provide insights on the high prevalence of hyperuricemia and gout in Filipinos. A total of 190 DNA samples from pregnant females who self-identified as a Filipino from the Hawaii Biorepository Bank were genotyped for rs2231142 G>T in the ABCG2. The prevalence of the gout risk allele (T) (46%) was significantly higher in Filipinos than in samples of Caucasians (12%, p < 0.001), Han Chinese (29%, p = 0.014), and African Americans (3%, p < 0.001). Similarly, the prevalence of the gout-risk genotype (TT) (21%) was significantly higher in Filipinos than in samples of Caucasians (1%, p < 0.001), Han Chinese (9%, p = 0.002), and African Americans (0.1%, p < 0.001). Though there were no gout cases in this cohort, these findings are suggestive of a genetic basis to the high prevalence of hyperuricemia and gout in Filipinos. This might also explain the reported reduced urinary uric acid excretion in Filipinos compared with Caucasians. Key Points • The Filipinos have the highest prevalence of the gout-associated risk allele (T) of the rs2231142 G>T in ABCG2. • The high prevalence of the risk allele (T) of the rs2231142 G>T in ABCG2 may partly explain the reduced urinary urate excretion and early-onset gout in Filipinos. • The high prevalence of the risk allele (T) of the rs2231142 G > T in ABCG2 may predispose Filipinos to hyperuricemia and gout when acculturated to high-purine diet.