Genetics of hyperuricemia and gout: implications for the present and future

Identification of Hyperuricemia Alleviating Peptides from Yellow Tuna Thunnus albacares

The development of food-derived antihyperuricemic substances is important for alleviating hyperuricemia (HUA) and associated inflammation. Here, novel peptides fromThunnus albacares (TAP) with strong antihyperuricemic activity were prepared. TAP was prepared by alkaline protease (molecular weight <1000 Da), with an IC50 value of xanthine oxidase inhibitory activity of 2.498 mg/mL, and 5 mg/mL TAP could reduce uric acid (UA) by 33.62% in human kidney-2 (HK-2) cells (P < 0.01). Mice were fed a high-purine diet and injected with potassium oxonate to induce HUA. Oral administration of TAP (600 mg/kg/d) reduced serum UA significantly by 42.22% and increased urine UA by 79.02% (P < 0.01) via regulating urate transporters GLUT9, organic anion transporter 1, and ATP-binding cassette subfamily G2. Meantime, TAP exhibited hepatoprotective and nephroprotective effects, according to histological analysis. Besides, HUA mice treated with TAP showed anti-inflammatory activity by decreasing the levels of toll-like receptor 4, nuclear factors-κB p65, NLRP3, ASC, and Caspase-1 in the kidneys (P < 0.01). According to serum non-targeted metabolomics, 91 differential metabolites between the MC and TAP groups were identified, and purine metabolism was considered to be the main pathway for TAP alleviating HUA. In a word, TAP exhibited strong antihyperuricemic activity both in vitro and in vivo.

Association and interaction between dietary patterns and gene polymorphisms in Liangshan residents with hyperuricemia

Hyperuricemia (HUA) is associated with dietary and genetic factors. However, studies on dietary patterns and their interaction effect with genes on the risk of HUA are limited. We aimed to explore the association between dietary patterns and HUA, and dietary patterns—gene interactions on the risk of HUA. A population-based cross-sectional study was conducted in adults aged 18 and older in Liangshan Yi Autonomous Prefecture of China. Dietary consumption was collected using a standard Food Frequency Questionnaire. Vein blood samples were collected after overnight fasting, and DNA was extracted from peripheral blood leukocytes. Dietary patterns were derived using principal component and factor analysis. Of the 2646 participants, the prevalence of HUA was 26.8%. Three dietary patterns were classified. Of them, a dietary pattern with higher meat consumption (defined as meat-based) had the strongest association with HUA than a dietary pattern with plant-based or local special diet-based. A higher frequency of T allele at ABCG2 rs2231142 and SLC2A9 rs11722228 loci was observed in participants with HUA than those without HUA. An additive interaction of meat-based dietary pattern with rs2231142 locus was significantly associated with an increased risk of HUA. The relative excess risks of interaction, attributable proportion of interaction, and synergy index (S) were 0.482 (95% CI: 0.012–0.976), 0.203 (95% CI: 0.033–0.374), and 1.544 (95% CI: 1.012–2.355), respectively. In conclusion, a dietary pattern with meat-based was significantly associated with an increased risk of HUA. There was an additive interaction between a meat-based dietary pattern and the ABCG2 rs2231142 locus. Individuals with rs2231142 T allele were at higher risk of HUA than those with rs2231142 GG allele.

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.

Serum uric acid is positively associated with the prevalence of nonalcoholic fatty liver in non-obese type 2 diabetes patients in a Chinese population

AIMS

To investigate whether SUA is independently associated with NAFLD in non-obese type 2 diabetic patients in a Chinese population.

METHODS

A cross-sectional study was carried out among 400 non-obese type 2 diabetic inpatients. Patients were stratified according to SUA levels and presence/absence of NAFLD. The clinical and laboratory features were collected retrospectively. Multivariate logistic regression analysis was conducted to estimate odds ratios of SUA for NAFLD.

RESULTS

The levels of SUA were significantly higher in patients with NAFLD than those without NAFLD. SUA was positively associated with the risk factors of NAFLD such as BMI, serum insulin and lipids. The odds of NAFLD were increasingly higher from the second to the fourth quartile of SUA as compared to the lowest quartile. After adjustment for age, gender, BMI and other metabolic components, the odds of NAFLD remained significantly increased for quartile 4.

CONCLUSIONS

SUA levels are strongly and independently associated with the prevalence of NAFLD. SUA may be used as a useful predictor to stratify the higher risks for NAFLD of non-obese type 2 diabetes patients.

The Different Relationship between Homocysteine and Uric Acid Levels with Respect to the MTHFR C677T Polymorphism According to Gender in Patients with Cognitive Impairment

In an elderly population with cognitive impairment, we investigated the association between serum uric acid (sUA) and serum homocysteine (sHcy), known risk factors for cerebrovascular disease. We also investigated the potential effect of the C677T polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR) to the sUA level in different dementia types. Participants underwent a battery of tests including measurements of sUA, sHcy, folic acid, and vitamin B12 as well as genotyping of the MTHFR locus. Data from 861 subjects (597 females to 264 males) were retrospectively analyzed. Subjects with hyperhomocysteinemia had lower serum folic acid and vitamin B12 and higher sUA than those with normal sHcy. sUA was significantly associated with serum creatinine, HbA1c, and sHcy regardless of gender. The TT genotype was found to be associated with hyperhomocysteinemia in both genders (p = 0.001). The levels of hyperlipidemia, sHcy, and sUA differed according to dementia subtypes. High sUA were associated with hyperhomocystenemia in TT genotype only in dementia with vascular lesion. This study reveals that sUA is positively associated with sHcy. We speculate that the two markers synergistically increase cerebrovascular burden and suggested that dietary intervention for sUA and sHcy would be helpful for cognitive decline with vascular lesion.

Mangiferin Ameliorates Hyperuricemic Nephropathy Which Is Associated With Downregulation of AQP2 and Increased Urinary Uric Acid Excretion

Hyperuricemia is characterized by abnormally high level of circulating uric acid in the blood and is associated with increased risk of kidney injury. The pathophysiological mechanisms leading to hyperuricemic nephropathy (HN) involve oxidative stress, endothelial dysfunction, inflammation, and fibrosis. Mangiferin is a bioactive C-glucoside xanthone, which has been exerting anti-inflammatory, anti-fibrotic, and antioxidative effects in many diseases. This study aimed to evaluate the effect of mangiferin treatment in HN. In a mouse model of HN, we observed lower circulating urate levels and ameliorated renal dysfunction with mangiferin treatment, which was associated with reduced renal inflammation and fibrosis. We next investigated the mechanism of urate lowering effect of mangiferin. Metabolic cage experiment showed that mangiferin-administrated mice excreted significantly more urinary uric acid due to elevated urine output, but no marked change in urine uric acid concentration. Expressions of water channels and urate transporters were further assessed by western blot. Renal AQP2 expression was decreased, yet urate transporters URAT1, GLUT9, and OAT1 expressions were not affected by mangiferin in HN mice. Moreover, mangiferin treatment also normalized xanthine oxidase and SOD activity in HN mice, which would decrease uric acid synthesis and improve oxidative stress, respectively. Therefore, our results reveal a novel mechanism whereby mangiferin can reduce serum uric acid levels by promoting AQP2-related urinary uric acid excretion. This study suggested that mangiferin could be a multi-target therapeutic candidate to prevent HN via mechanisms that involve increased excretion and decreased production of uric acid and modulation of inflammatory, fibrotic, and oxidative pathways.

Target genes, variants, tissues and transcriptional pathways influencing human serum urate levels

Elevated serum urate levels cause gout and correlate with cardiometabolic diseases via poorly understood mechanisms. We performed a trans-ancestry genome-wide association study of serum urate in 457,690 individuals, identifying 183 loci (147 previously unknown) that improve the prediction of gout in an independent cohort of 334,880 individuals. Serum urate showed significant genetic correlations with many cardiometabolic traits, with genetic causality analyses supporting a substantial role for pleiotropy. Enrichment analysis, fine-mapping of urate-associated loci and colocalization with gene expression in 47 tissues implicated the kidney and liver as the main target organs and prioritized potentially causal genes and variants, including the transcriptional master regulators in the liver and kidney, HNF1A and HNF4A. Experimental validation showed that HNF4A transactivated the promoter of ABCG2, encoding a major urate transporter, in kidney cells, and that HNF4A p.Thr139Ile is a functional variant. Transcriptional coregulation within and across organs may be a general mechanism underlying the observed pleiotropy between urate and cardiometabolic traits.

Prescribing patterns of allopurinol and febuxostat according to directives on the reimbursement criteria and clinical guidelines: analysis of a primary care database

OBJECTIVE

According to American clinical guidelines, allopurinol and febuxostat may be prescribed as first-line therapy to treat hyperuricemia. However, the Italian Medicines Agency directive, called Nota 91, allows the reimbursement of second-line febuxostat in the case of failure and/or intolerance of a previous allopurinol therapy, so partially embracing European League Against Rheumatism recommendations and the British Society for Rheumatology Guideline. Such inconsistency might lead to heterogeneity among General Practitioners (GPs) in treatment of hyperuricemia. This study, therefore, aimed to evaluate the prescribing behavior of GPs in terms of compliance with Nota 91 and/or official guidelines.

METHODS

Using the Health Search Database, a retrospective cohort study was conducted to evaluate the patterns of use of allopurinol and febuxostat between 2011 and 2016.

RESULTS

In total, 44,257 and 5837 patients were prescribed with allopurinol and febuxostat, respectively. Among febuxostat users, 4321 (74%) had a previous allopurinol treatment; 92% of switches to febuxostat were related to hyperuricemia, whereas 9% of switchers presented intolerance to allopurinol; 26% of patients were prescribed with febuxostat as first-line therapy. The presence of diabetes and/or moderate/severe renal disease were statistically significant determinants of febuxostat use as first-line therapy.

CONCLUSION

Prescriptions of febuxostat were highly compliant to Nota 91. Only a sub-group of frontline prescriptions of febuxostat were mainly driven by the presence of renal dysfunction, which is able to increase the risk of allopurinol intolerance and/or inefficacy. These findings indicate that GPs' prescribing behavior for hyperuricemia is highly compliant with both regulatory directives and clinical guidelines.

Dietary factors are associated with serum uric acid trajectory differentially by race among urban adults

Serum uric acid (SUA), a causative agent for gout, is linked to dietary factors, perhaps differentially by race. Cross-sectional (SUAbase, i.e. baseline SUA) and longitudinal (SUArate; i.e. annual rate of change in SUA) associations of SUA with diet were evaluated across race and sex-race groups, in a large prospective cohort study of urban adults. Of 3720 African American (AA) and White urban adults participating in the Healthy Aging in Neighborhoods of Diversity across the Life Span study, longitudinal data (2004-2013, k=1·7 repeats, follow-up, 4·64 (sd 0·93) years) on n 2138 participants were used. The main outcome consisted of up to two repeated measures on SUA. Exposures included the dietary factors such as 'added sugar', 'alcoholic beverages', 'red meat', 'total fish', 'legumes', 'total dairy product', 'caffeine', 'vitamin C' and a composite measure termed 'dietary urate index'. Mixed-effects linear regression models were conducted, stratifying by race and by race×sex. A positive association between legume intake and SUArate was restricted to AA, whereas alcohol intake was positively associated with SUAbase overall without racial differences. Added sugars were directly related to SUAbase among White men (P<0·05 for race×sex interaction), whereas dairy product intake was linked with slower SUArate among AA women, unlike among White women. Nevertheless, dairy product intake was associated with a lower SUAbase among Whites. Finally, the dietary urate index was positively associated with both SUAbase and SUArate, particularly among AA. In sum, race and sex interactions with dietary intakes of added sugars, dairy products and legumes were detected in determining SUA. Similar studies are needed to replicate these findings.

Ligand Screening Systems for Human Glucose Transporters as Tools in Drug Discovery

Hexoses are the major source of energy and carbon skeletons for biosynthetic processes in all kingdoms of life. Their cellular uptake is mediated by specialized transporters, including glucose transporters (GLUT, SLC2 gene family). Malfunction or altered expression pattern of GLUTs in humans is associated with several widespread diseases including cancer, diabetes and severe metabolic disorders. Their high relevance in the medical area makes these transporters valuable drug targets and potential biomarkers. Nevertheless, the lack of a suitable high-throughput screening system has impeded the determination of compounds that would enable specific manipulation of GLUTs so far. Availability of structural data on several GLUTs enabled in silico ligand screening, though limited by the fact that only two major conformations of the transporters can be tested. Recently, convenient high-throughput microbial and cell-free screening systems have been developed. These remarkable achievements set the foundation for further and detailed elucidation of the molecular mechanisms of glucose transport and will also lead to great progress in the discovery of GLUT effectors as therapeutic agents. In this mini-review, we focus on recent efforts to identify potential GLUT-targeting drugs, based on a combination of structural biology and different assay systems.

Lumbar spinal stenosis attributable to tophaceous gout: case report and review of the literature

Objectives

Tophaceous gout seldom affects the axial skeleton. Symptoms vary according to the differential localization of urate deposits and the diagnosis is often delayed. Here, we report an unusual case of lumbar spinal stenosis caused by extradural tophaceous deposits.

Methods

We retrospectively reviewed a case of a patient with tophaceous gout of the lumbar spine and reviewed the relevant literature.

Results

A 62-year-old man with a 2-year history of lower back pain and a 3-month history of lower limb radiation pain and intermittent claudication was admitted. After laboratory and imaging investigations he underwent surgical decompression and stabilization. Histological analysis of the extracted specimen confirmed that it was gouty tophus. The patient’s symptoms improved progressively after the operation. He recovered very well with no complications.

Conclusion

The mechanism associated with axial gout is not yet clear. Obesity, inactivity, and previous degenerative disc disease may be the risk factors for spinal tophus. The clinical symptoms are diverse according to the differential localization of urate deposits. It is not easy to diagnose this disease radiographically by routine radiological examination. Analysis of a biopsy specimen is definitely the only way to confirm diagnosis. Surgical treatment should be considered in patients with spinal gout who are experiencing neurological deterioration.

Genetic risk scores, sex and dietary factors interact to alter serum uric acid trajectory among African-American urban adults

Serum uric acid (SUA), a causative agent for gout among others, is affected by both genetic and dietary factors, perhaps differentially by sex. We evaluated cross-sectional (SUAbase) and longitudinal (SUArate) associations of SUA with a genetic risk score (GRS), diet and sex. We then tested the interactive effect of GRS, diet and sex on SUA. Longitudinal data on 766 African-American urban adults participating in the Healthy Aging in Neighborhood of Diversity across the Lifespan study were used. In all, three GRS for SUA were created from known SUA-associated SNP (GRSbase (n 12 SNP), GRSrate (n 3 SNP) and GRStotal (n 15 SNP)). Dietary factors included added sugar, total alcohol, red meat, total fish, legumes, dairy products, caffeine and vitamin C. Mixed-effects linear regression models were conducted. SUAbase was higher among men compared with that among women, and increased with GRStotal tertiles. SUArate was positively associated with legume intake in women (γ=+0·14; 95 % CI +0·06, +0·22, P=0·001) and inversely related to dairy product intake in both sexes combined (γ=-0·042; 95 % CI -0·075, -0·009), P=0·010). SUAbase was directly linked to alcohol consumption among women (γ=+0·154; 95 % CI +0·046, +0·262, P=0·005). GRSrate was linearly related to SUArate only among men. Legume consumption was also positively associated with SUArate within the GRStotal's lowest tertile. Among women, a synergistic interaction was observed between GRSrate and red meat intake in association with SUArate. Among men, a synergistic interaction between low vitamin C and genetic risk was found. In sum, sex-diet, sex-gene and gene-diet interactions were detected in determining SUA. Further similar studies are needed to replicate our findings.

Assessment of genetic polymorphisms associated with hyperuricemia or gout in the Hmong

AIM

Hyperuricemia commonly causes gout. Minnesota Hmong exhibit a two- to fivefold higher prevalence of gout versus non-Hmong. To elucidate a possible genomic contribution to this disparity, prevalence of risk alleles for hyperuricemia in Hmong was compared with European (CEU) and Han-Chinese (CHB).

METHODS

In total, 235 Hmong were genotyped for eight SNPs representing five candidate genes (SLC22A12, SLC2A9, ABCG2, SLC17A1 and PDZK1).

RESULTS

The frequency of seven out of eight risk alleles in the Hmong was significantly different than CEU; six higher and one with lower prevalence. The frequency of three out of eight risk alleles in the Hmong was significantly different than CHB; two higher and one with lower prevalence.

CONCLUSION

Hyperuricemia risk alleles are more prevalent in the Hmong than CEU and HB.

Associations between interleukin and interleukin receptor gene polymorphisms and risk of gout

Gout is a self-limiting, auto-inflammatory arthritis induced by the deposition of monosodium urate crystals in the synovial fluid and periarticular tissues. The aim of this study was to investigate the associations between genetic variants in the interleukin (IL) and interleukin receptor (ILR) genes IL-33, IL-1RL1, IL-23R, and signal transducer and activator of transcription 4 (STAT4) and susceptibility to gout in Chinese Han male individuals. The genetic distributions of rs3939286 in IL-33, rs13015714 in IL-1RL1, rs10889677 in IL-23R, and rs7574865 in STAT4 were detected in 1100 men with gout and 1227 ethnically matched controls, using Taqman allelic discrimination real-time polymerase chain reaction (PCR). Differences in these polymorphisms between the groups were investigated using χ(2) tests. The genotype-phenotype relationship among gout patients was tested by analysis of variance. There was a significant difference in genotypic frequencies of IL-23R rs10889677 between gout patients and controls (χ(2) = 81.386, P < 0.001). However, there were no significant differences in distributions of the other polymorphisms between the groups. Our results revealed that the rs10889677 variant in IL-23R may be involved in the development of gout in Chinese Han male individuals. However, further studies in other ethnic groups are needed to confirm these results.

Transcriptome-based reconstructions from the murine knockout suggest involvement of the urate transporter, URAT1 (slc22a12), in novel metabolic pathways

URAT1 (slc22a12) was identified as the transporter responsible for renal reabsorption of the medically important compound, uric acid. However, subsequent studies have indicated that other transporters make contributions to this process, and that URAT1 transports other organic anions besides urate (including several in common with the closely related multi-specific renal organic anion transporters, OAT1 (slc22a6) and OAT3 (slc22a8)). These findings raise the possibility that urate transport is not the sole physiological function of URAT1. We previously characterized mice null for the murine ortholog of URAT1 (mURAT1; previously cloned as RST), finding a relatively modest decrement in urate reabsorptive capacity. Nevertheless, there were shifts in the plasma and urinary concentrations of multiple small molecules, suggesting significant metabolic changes in the knockouts. Although these molecules remain unidentified, here we have computationally delineated the biochemical networks consistent with transcriptomic data from the null mice. These analyses suggest alterations in the handling of not only urate but also other putative URAT1 substrates comprising intermediates in nucleotide, carbohydrate, and steroid metabolism. Moreover, the analyses indicate changes in multiple other pathways, including those relating to the metabolism of glycosaminoglycans, methionine, and coenzyme A, possibly reflecting downstream effects of URAT1 loss. Taken together with the available substrate and metabolomic data for the other OATs, our findings suggest that the transport and biochemical functions of URAT1 overlap those of OAT1 and OAT3, and could contribute to our understanding of the relationship between uric acid and the various metabolic disorders to which it has been linked.

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URAT1 handles multiple substrates suggesting functions beyond urate transport

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We determined metabolic constraints of gene expression changes in URAT1 null mice

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These suggest URAT1 involvement in multiple bioenergtic and biosynthetic pathways

SLC transporters as therapeutic targets: emerging opportunities

Solute carrier (SLC) transporters - a family of more than 300 membrane-bound proteins that facilitate the transport of a wide array of substrates across biological membranes - have important roles in physiological processes ranging from the cellular uptake of nutrients to the absorption of drugs and other xenobiotics. Several classes of marketed drugs target well-known SLC transporters, such as neurotransmitter transporters, and human genetic studies have provided powerful insight into the roles of more-recently characterized SLC transporters in both rare and common diseases, indicating a wealth of new therapeutic opportunities. This Review summarizes knowledge on the roles of SLC transporters in human disease, describes strategies to target such transporters, and highlights current and investigational drugs that modulate SLC transporters, as well as promising drug targets.

Uricosuric drugs: the once and future therapy for hyperuricemia?

PURPOSE OF REVIEW

Although uricosuric agents provide the most time-honoured approach to the control of hyperuricemia, their place in the armamentarium has been eclipsed by that of xanthine oxidase inhibitors. This review considers the potential for uricosuric agents from the perspective of recent progress in the understanding of urate transport systems.

RECENT FINDINGS

No new agents have yet become available, but promising new drugs are under development. Better understanding of the transporters URAT1 and ABCG2 in particular would appear to provide opportunities for more selective, better tolerated agents to increase the renal clearance of uric acid and thereby control hyperuricemia.

SUMMARY

Conceptually, modest inhibition of renal tubular reabsorption should provide effective relief for the millions of individuals who are now hyperuricemic and who suffer from its principal consequence, gout.

Functional polymorphisms of the ABCG2 gene are associated with gout disease in the Chinese Han male population

Background

Gout is a common type of arthritis that is characterized by hyperuricemia, tophi and joint inflammation. Genetic variations in the ABCG2 gene have been reported to influence serum uric acid levels and to participate in the pathogenesis of gout, but no further data have been reported in the Han Chinese population.

Methods

Peripheral blood DNA was isolated from 352 male patients with gout and 350 gout-free normal male controls. High-resolution melting analysis and Sanger sequencing were performed to identify the genetic polymorphisms V12M, Q141K and Q126X in the ABCG2 gene. Genotype and haplotype analyses were utilized to determine the disease odds ratios (ORs). A prediction model for gout risk using ABCG2 protein function was established based on the genotype combination of Q126X and Q141K.

Results

For Q141K, the A allele frequency was 49.6% in the gout patients and 30.9% in the controls (OR 2.20, 95% confidence interval (CI): 1.77–2.74, p = 8.99 × 10⁻¹³). Regarding Q126X, the T allele frequency was 4.7% in the gout patients and 1.7% in the controls (OR 2.91, 95% CI: 1.49–5.68, p = 1.57 × 10⁻³). The A allele frequency for V12M was lower (18.3%) in the gout patients than in the controls (29%) (OR 0.55, 95% CI 0.43–0.71, p = 2.55 × 10⁻⁶). In the order of V12M, Q126X and Q141K, the GCA and GTC haplotypes indicated increased disease risk (OR = 2.30 and 2.71, respectively). Patients with mild to severe ABCG2 dysfunction accounted for 78.4% of gout cases.

Conclusion

The ABCG2 126X and 141K alleles are associated with an increased risk of gout, whereas 12M has a protective effect on gout susceptibility in the Han Chinese population. ABCG2 dysfunction can be used to evaluate gout risk.