SLC2A9 is a newly identified urate transporter influencing serum urate concentration, urate excretion and gout

A mendelian randomization analysis: The causal association between serum uric acid and atrial fibrillation

BACKGROUND

Observational studies have shown that high levels of serum uric acid (UA) were associated with atrial fibrillation (AF). However, the causal effect of urate on the risk of AF is still unknown. To clarify the potential causal association between UA and AF, we performed a Mendelian randomization (MR) analysis using genetic instrumental variables (IVs).

MATERIALS AND METHODS

From the Korean GWAS dataset of 633 patients with AF (mean age 50.6 ± 7.8 years, 80.9% male, Yonsei AF Ablation cohort) who underwent radiofrequency catheter ablation and the data from 3533 controls (from the Korea Genome Epidemiology Study), we selected 9 SNPs, with a P value less than .05, associated with an increased UA serum level. Additionally, we calculated the weighted genetic risk score (wGRS) using the selected 9 SNPs, to use it as an instrumental variable. A Mendelian randomization analysis was calculated by a 2-stage estimator method.

RESULTS

The conventional association between the serum UA and AF was significant (P = .001) after adjusting for potential confounding factors. The SNP rs1165196 on SLC17A1 (F-statistics = 208.34, 0.18 mg/mL per allele change, P < .001) and wGRS (F-statistics = 222.26, 0.20 mg/mL per 1SD change, P < .001) were significantly associated with an increase in the UA level. The MR analysis was causally associated with rs1165196 (estimated odds ratio (OR), 0.21, 95% confidence interval (CI), 0.06-0.75, P = .017), but not wGRS (estimated OR, 1.07, 95% CI, 0.57-2.01, P = .832).

CONCLUSION

The serum UA level was independently associated with the AF risk.

Glucose, Fructose, and Urate Transporters in the Choroid Plexus Epithelium

The choroid plexus plays a central role in the regulation of the microenvironment of the central nervous system by secreting the majority of the cerebrospinal fluid and controlling its composition, despite that it only represents approximately 1% of the total brain weight. In addition to a variety of transporter and channel proteins for solutes and water, the choroid plexus epithelial cells are equipped with glucose, fructose, and urate transporters that are used as energy sources or antioxidative neuroprotective substrates. This review focuses on the recent advances in the understanding of the transporters of the SLC2A and SLC5A families (GLUT1, SGLT2, GLUT5, GLUT8, and GLUT9), as well as on the urate-transporting URAT1 and BCRP/ABCG2, which are expressed in choroid plexus epithelial cells. The glucose, fructose, and urate transporters repertoire in the choroid plexus epithelium share similar features with the renal proximal tubular epithelium, although some of these transporters exhibit inversely polarized submembrane localization. Since choroid plexus epithelial cells have high energy demands for proper functioning, a decline in the expression and function of these transporters can contribute to the process of age-associated brain impairment and pathophysiology of neurodegenerative diseases.

Mechanistic Insights of Soluble Uric Acid-related Kidney Disease

Hyperuricemia, defined as the presence of elevated serum uric acid (sUA), could lead to urate deposit in joints, tendons, kidney and other tissues. Hyperuricemia as an independent risk factor was common in patients during the causation and progression of kidney disease. Uric acid is a soluble final product of endogenous and dietary purine metabolism, which is freely filtered in kidney glomeruli where approximately 90% of filtered uric acid is reabsorbed. Considerable studies have demonstrated that soluble uric acid was involved in the pathophysiology of renal arteriolopathy, tubule injury, tubulointerstitial fibrosis, as well as glomerular hypertrophy and glomerulosclerosis. In the review, we summarized the mechanistic insights of soluble uric acid related renal diseases.

Characterizations of the Urate Transporter, GLUT9, and Its Potent Inhibitors by Patch-Clamp Technique

Glucose transporter 9 (GLUT9), which transports urate in an electrogenic and voltage-dependent manner, plays an important role in the maintenance of normal blood uric acid/urate levels. In the present study, we established a cell model based on the single-electrode patch-clamp technique for characterization of GLUT9 and explored the inhibitory effects of benzobromarone (BM) and probenecid (PB) on urate-induced currents in mouse GLUT9a (mGLUT9a)-expressing HEK-293T cells. The results showed that uric acid, rather than glucose perfusion, led to a rapid and large outward current by mGLUT9a in dose-, voltage-, and pH-dependent manners. BM prominently and irreversibly inhibited the uric acid-induced currents through mGLUT9a, and PB weakly and reversibly inhibited mGLUT9a. We found that depletion of K⁺ in the external solution significantly strengthened the blockade of BM on mGLUT9a. In addition, an enhanced inhibitory rate of BM was detected when the pH of the external solution was changed from 7.4 to 5.5, indicating that BM functions optimally in an acidic environment. In conclusion, the combination of the established cell model with patch-clamp techniques first revealed the function properties of GLUT9 inhibitors and may provide potential benefits to the study of GLUT9 inhibitors as antihyperuricemic or antigout agents.

Whole genome sequence analysis identifies a PAX2 mutation to establish a correct diagnosis for a syndromic form of hyperuricemia

Hereditary hyperuricemia may occur as part of a syndromic disorder or as an isolated nonsyndromic disease, and over 20 causative genes have been identified. Here, we report the use of whole genome sequencing (WGS) to establish a diagnosis in a family in which individuals were affected with gout, hyperuricemia associated with reduced fractional excretion of uric acid, chronic kidney disease (CKD), and secondary hyperparathyroidism, that are consistent with familial juvenile hyperuricemic nephropathy (FJHN). However, single gene testing had not detected mutations in the uromodulin (UMOD) or renin (REN) genes, which cause approximately 30-90% of FJHN. WGS was therefore undertaken, and this identified a heterozygous c.226G>C (p.Gly76Arg) missense variant in the paired box gene 2 (PAX2) gene, which co-segregated with renal tubulopathy in the family. PAX2 mutations are associated with renal coloboma syndrome (RCS), which is characterized by abnormalities in renal structure and function, and anomalies of the optic nerve. Ophthalmological examination in two adult brothers affected with hyperuricemia, gout, and CKD revealed the presence of optic disc pits, consistent with optic nerve coloboma, thereby revising the diagnosis from FJHN to RCS. Thus, our results demonstrate the utility of WGS analysis in establishing the correct diagnosis in disorders with multiple etiologies.

Genetic architecture of complex traits and disease risk predictors

Genomic prediction of complex human traits (e.g., height, cognitive ability, bone density) and disease risks (e.g., breast cancer, diabetes, heart disease, atrial fibrillation) has advanced considerably in recent years. Using data from the UK Biobank, predictors have been constructed using penalized algorithms that favor sparsity: i.e., which use as few genetic variants as possible. We analyze the specific genetic variants (SNPs) utilized in these predictors, which can vary from dozens to as many as thirty thousand. We find that the fraction of SNPs in or near genic regions varies widely by phenotype. For the majority of disease conditions studied, a large amount of the variance is accounted for by SNPs outside of coding regions. The state of these SNPs cannot be determined from exome-sequencing data. This suggests that exome data alone will miss much of the heritability for these traits-i.e., existing PRS cannot be computed from exome data alone. We also study the fraction of SNPs and of variance that is in common between pairs of predictors. The DNA regions used in disease risk predictors so far constructed seem to be largely disjoint (with a few interesting exceptions), suggesting that individual genetic disease risks are largely uncorrelated. It seems possible in theory for an individual to be a low-risk outlier in all conditions simultaneously.

Diagnostic Accuracy of Single Spot Urine for Detecting Renal Uric Acid Underexcretion in Men

Background

The uric acid (UA) clearance test to evaluate the hyperuricemia phenotype requires a great deal of time. However, the utility of single spot urine is scarce. The study aimed to determine the diagnostic accuracy of single spot urine for predicting renal UA underexcretion (the decreased UA excretion) in men.

Methods

A total of 73 male participants aged 20 - 74 years with a UA level of 6.0 - 7.9 mg/dL were enrolled in the study. Renal UA underexcretion was defined as < 7.3 mL/min using the 60-min method. Urinary UA to creatinine ratio (UACR), fractional clearance of urate (FCU), and the Simkin index were calculated. A receiver operating characteristic (ROC) analysis was performed to compare the diagnostic utility of these parameters for predicting UA underexcretion.

Results

In the ROC analysis, the area under the curve values of the UACR, FCU, and the Simkin index for predicting UA underexcretion were 0.903 (95% confidence interval (CI): 0.830 - 0.976), 0.841 (95% CI: 0.749 - 0.933), and 0.779 (95% CI: 0.673 - 0.885), respectively. An optimal UACR cutoff of 0.460 (sensitivity 89.2%, specificity 80.6%, overall diagnostic accuracy 84.9%, positive predictive value 82.5%, and negative predictive value 87.9%) was identified.

Conclusions

These results suggest that the UACR is a simple and efficient test with high sensitivity and specificity levels for predicting renal UA underexcretion in men.

Advances in our understanding of gout as an auto-inflammatory disease

Gout, the most common inflammatory arthritis, is the result of hyperuricemia and inflammation induced by monosodium urate (MSU) crystal deposition. However, most people with hyperuricemia will never develop gout, implying a molecular-genetic contribution to the development of gout. Recent genomic studies reveal links between certain genetic variations and gout. We highlight recent advances in our understanding of gout as an auto-inflammatory disease. We review the auto-inflammatory aspects of gout, including the inflammasome and thirteen gout-associated inflammatory-pathway genes and associated comorbidities. This information provides important insights into emerging immune-modulating targets in the management of gout, and future novel therapeutic targets in gout treatment. Cumulatively, this has important implications for treating gout as an auto-inflammatory disease, as opposed to a purely metabolic disease.

Glucose transporters in adipose tissue, liver, and skeletal muscle in metabolic health and disease

A family of facilitative glucose transporters (GLUTs) is involved in regulating tissue-specific glucose uptake and metabolism in the liver, skeletal muscle, and adipose tissue to ensure homeostatic control of blood glucose levels. Reduced glucose transport activity results in aberrant use of energy substrates and is associated with insulin resistance and type 2 diabetes. It is well established that GLUT2, the main regulator of hepatic hexose flux, and GLUT4, the workhorse in insulin- and contraction-stimulated glucose uptake in skeletal muscle, are critical contributors in the control of whole-body glycemia. However, the molecular mechanism how insulin controls glucose transport across membranes and its relation to impaired glycemic control in type 2 diabetes remains not sufficiently understood. An array of circulating metabolites and hormone-like molecules and potential supplementary glucose transporters play roles in fine-tuning glucose flux between the different organs in response to an altered energy demand.

Hyperuricemia and gout caused by missense mutation in d-lactate dehydrogenase

Gout is caused by deposition of monosodium urate crystals in joints when plasma uric acid levels are chronically elevated beyond the saturation threshold, mostly due to renal underexcretion of uric acid. Although molecular pathways of this underexcretion have been elucidated, its etiology remains mostly unknown. We demonstrate that gout can be caused by a mutation in LDHD within the putative catalytic site of the encoded d-lactate dehydrogenase, resulting in augmented blood levels of d-lactate, a stereoisomer of l-lactate, which is normally present in human blood in miniscule amounts. Consequent excessive renal secretion of d-lactate in exchange for uric acid reabsorption culminated in hyperuricemia and gout. We showed that LDHD expression is enriched in tissues with a high metabolic rate and abundant mitochondria and that d-lactate dehydrogenase resides in the mitochondria of cells overexpressing the human LDHD gene. Notably, the p.R370W mutation had no effect on protein localization. In line with the human phenotype, injection of d-lactate into naive mice resulted in hyperuricemia. Thus, hyperuricemia and gout can result from the accumulation of metabolites whose renal excretion is coupled to uric acid reabsorption.

Mathematical modeling analysis of hepatic uric acid disposition using human sandwich-cultured hepatocytes

Uric acid is biosynthesized from purine by xanthine oxidase (XO) mainly in the liver and is excreted into urine and feces. Although several transporters responsible for renal and intestinal handling of uric acid have been reported, information on hepatic transporters is limited. In the present study, we studied quantitative contribution of transporters for hepatic handling of uric acid by mathematical modeling analysis in human sandwich-cultured hepatocytes (hSCH). Stable isotope-labeled hypoxanthine, hypoxanthine-¹³C2,¹⁵N (HX), was incubated with hSCH and formed ¹³C2,¹⁵N-labeled xanthine (XA) and uric acid (UA) were measured by LC-MS/MS time dependently. Rate constants for metabolism and efflux and uptake transport across sinusoidal and bile canalicular membranes of HX, XA and UA were estimated in the presence of inhibitors of XO and uric acid transporters. An XO inhibitor allopurinol significantly decreased metabolisms of HX and XA. Efflux into bile canalicular lumen was negligible and sinusoidal efflux was considered main efflux pathway of formed UA. Transporter inhibition study highlighted that GLUT9 strongly and MRP4 intermediately contribute to the sinusoidal efflux of UA with minor contribution of NPT1/4. Modeling analysis developed in the present study should be useful for quantitative prediction of uric acid disposition in liver.

Soluble Uric Acid Is an Intrinsic Negative Regulator of Monocyte Activation in Monosodium Urate Crystal-Induced Tissue Inflammation

Although monosodium urate (MSU) crystals are known to trigger inflammation, published data on soluble uric acid (sUA) in this context are discrepant. We hypothesized that diverse sUA preparation methods account for this discrepancy and that an animal model with clinically relevant levels of asymptomatic hyperuricemia and gouty arthritis can ultimately clarify this issue. To test this, we cultured human monocytes with different sUA preparation solutions and found that solubilizing uric acid (UA) by prewarming created erroneous results because of UA microcrystal contaminants triggering IL-1β release. Solubilizing UA with NaOH avoided this artifact, and this microcrystal-free preparation suppressed LPS- or MSU crystal-induced monocyte activation, a process depending on the intracellular uptake of sUA via the urate transporter SLC2A9/GLUT9. CD14⁺ monocytes isolated from hyperuricemic patients were less responsive to inflammatory stimuli compared with monocytes from healthy individuals. Treatment with plasma from hyperuricemic patients impaired the inflammatory function of CD14⁺ monocytes, an effect fully reversible by removing sUA from hyperuricemic plasma. Moreover, Alb-creERT2;Glut9 ^lox/lox mice with hyperuricemia (serum UA of 9-11 mg/dl) showed a suppressed inflammatory response to MSU crystals compared with Glut9 ^lox/lox controls without hyperuricemia. Taken together, we unravel a technical explanation for discrepancies in the published literature on immune effects of sUA and identify hyperuricemia as an intrinsic suppressor of innate immunity, in which sUA modulates the capacity of monocytes to respond to danger signals. Thus, sUA is not only a substrate for the formation of MSU crystals but also an intrinsic inhibitor of MSU crystal-induced tissue inflammation.

Sex Differences in Urate Handling

Hyperuricemia, or elevated serum urate, causes urate kidney stones and gout and also increases the incidence of many other conditions including renal disease, cardiovascular disease, and metabolic syndrome. As we gain mechanistic insight into how urate contributes to human disease, a clear sex difference has emerged in the physiological regulation of urate homeostasis. This review summarizes our current understanding of urate as a disease risk factor and how being of the female sex appears protective. Further, we review the mechanisms of renal handling of urate and the significant contributions from powerful genome-wide association studies of serum urate. We also explore the role of sex in the regulation of specific renal urate transporters and the power of new animal models of hyperuricemia to inform on the role of sex and hyperuricemia in disease pathogenesis. Finally, we advocate the use of sex differences in urate handling as a potent tool in gaining a further understanding of physiological regulation of urate homeostasis and for presenting new avenues for treating the constellation of urate related pathologies.

Molecular and Histopathological Study on the Ameliorative Impacts of Petroselinum Crispum and Apium Graveolens against Experimental Hyperuricemia

Hyperuricemia is an abnormal metabolic condition characterized by an increase in uric acid levels in the blood. It is the cause of gout, manifested by inflammatory arthritis, pain and disability. This study examined the possible ameliorative impacts of parsley (PAR) and celery (CEL) as hypouricemic agents at biochemical, molecular and cellular levels. PAR and CEL alone or in combination were orally administered to hyperuricemic (HU) mice and control mice for 10 consecutive days. Serum levels of uric acid and blood urea nitrogen (BUN), xanthine oxidase activity, antioxidants, inflammatory (IL-1β and TNF-α) and anti-inflammatory cytokines (IL-10) were measured. mRNA expression of urate transporters and uric acid excretion genes in renal tissues were examined using qRT-PCR (quantitative real time PCR). Normal histology and immunoreactivity of transforming growth factor-beta 1 (TGF-β1) in kidneys was examined. Administration of PAR and CEL significantly reduced serum BUN and uric acids in HU mice, ameliorated changes in malondialdehyde, catalase, and reduced glutathione, glutathione peroxidase (GPX), IL-1β, TNF-α and IL-10 in hyperuricemic mice. Both effectively normalized the alterations in mURAT-1, mGLUT-9, mOAT-1 and mOAT-3 expression, as well as changes in TGF-β1 immunoreactivity. Interestingly, combined administration of PAR and CEL mitigated all examined measurements synergistically, and improved renal dysfunction in the hyperuricemic mice. The study concluded that PAR and CEL can potentially reduce damaging cellular, molecular and biochemical effects of hyperuricemia both individually and in combination.

Can Probiotics and Diet Promote Beneficial Immune Modulation and Purine Control in Coronavirus Infection?

Infection caused by the SARS-CoV-2 coronavirus worldwide has led the World Health Organization to declare a COVID-19 pandemic. Because there is no cure or treatment for this virus, it is emergingly urgent to find effective and validated methods to prevent and treat COVID-19 infection. In this context, alternatives related to nutritional therapy might help to control the infection. This narrative review proposes the importance and role of probiotics and diet as adjunct alternatives among the therapies available for the treatment of this new coronavirus. This review discusses the relationship between intestinal purine metabolism and the use of Lactobacillus gasseri and low-purine diets, particularly in individuals with hyperuricemia, as adjuvant nutritional therapies to improve the immune system and weaken viral replication, assisting in the treatment of COVID-19. These might be promising alternatives, in addition to many others that involve adequate intake of vitamins, minerals and bioactive compounds from food.

The ABCG2 Q141K hyperuricemia and gout associated variant illuminates the physiology of human urate excretion

The pathophysiological nature of the common ABCG2 gout and hyperuricemia associated variant Q141K (rs2231142) remains undefined. Here, we use a human interventional cohort study (ACTRN12615001302549) to understand the physiological role of ABCG2 and find that participants with the Q141K ABCG2 variant display elevated serum urate, unaltered FEUA, and significant evidence of reduced extra-renal urate excretion. We explore mechanisms by generating a mouse model of the orthologous Q140K Abcg2 variant and find male mice have significant hyperuricemia and metabolic alterations, but only subtle alterations of renal urate excretion and ABCG2 abundance. By contrast, these mice display a severe defect in ABCG2 abundance and function in the intestinal tract. These results suggest a tissue specific pathobiology of the Q141K variant, support an important role for ABCG2 in urate excretion in both the human kidney and intestinal tract, and provide insight into the importance of intestinal urate excretion for serum urate homeostasis.

The common ABCG2 variant Q141K contributes to hyperuricemia and gout risk. Here, using a human interventional study and a new orthologous mouse model, the authors report a tissue specific pathobiology of the Q141K variant, and support a significant role for ABCG2 in urate excretion in both the kidney and intestine.

Identification of blood cell transcriptome-based biomarkers in adulthood predictive of increased risk to develop metabolic disorders using early life intervention rat models

Calorie restriction during gestation in rats has long-lasting adverse effects in the offspring. It induces metabolic syndrome-related alterations, which are partially reversed by leptin supplementation during lactation. We employed these conditions to identify transcript-based nutrient sensitive biomarkers in peripheral blood mononuclear cells (PBMCs) predictive of later adverse metabolic health. The best candidate was validated in humans. Transcriptome analysis of PBMCs from adult male Wistar rats of three experimental groups was performed: offspring of control dams (CON), and offspring of 20% calorie-restricted dams during gestation without (CR) and with leptin supplementation throughout lactation (CR-LEP). The expression of 401 genes was affected by gestational calorie restriction and reversed by leptin. The changes preceded metabolic syndrome-related phenotypic alterations. Of these genes, Npc1 mRNA levels were lower in CR vs CON, and normalized to CON in CR-LEP. In humans, NPC1 mRNA levels in peripheral blood cells (PBCs) were decreased in subjects with mildly impaired metabolic health compared to healthy subjects. Therefore, a set of potential transcript-based biomarkers indicative of a predisposition to metabolic syndrome-related alterations were identified, including NPC1, which was validated in humans. Low NPC1 transcript levels in PBCs are a candidate biomarker of increased risk for impaired metabolic health in humans.

Omega-3 Polyunsaturated Fatty Acids Inhibit the Function of Human URAT1, a Renal Urate Re-Absorber

The beneficial effects of fatty acids (FAs) on human health have attracted widespread interest. However, little is known about the impact of FAs on the handling of urate, the end-product of human purine metabolism, in the body. Increased serum urate levels occur in hyperuricemia, a disease that can lead to gout. In humans, urate filtered by the glomerulus of the kidney is majorly re-absorbed from primary urine into the blood via the urate transporter 1 (URAT1)-mediated pathway. URAT1 inhibition, thus, contributes to decreasing serum urate concentration by increasing net renal urate excretion. Here, we investigated the URAT1-inhibitory effects of 25 FAs that are commonly contained in foods or produced in the body. For this purpose, we conducted an in vitro transport assay using cells transiently expressing URAT1. Our results showed that unsaturated FAs, especially long-chain unsaturated FAs, inhibited URAT1 more strongly than saturated FAs. Among the tested unsaturated FAs, eicosapentaenoic acid, α-linolenic acid, and docosahexaenoic acid exhibited substantial URAT1-inhibitory activities, with half maximal inhibitory concentration values of 6.0, 14.2, and 15.2 μM, respectively. Although further studies are required to investigate whether the ω-3 polyunsaturated FAs can be employed as uricosuric agents, our findings further confirm FAs as nutritionally important substances influencing human health.

Deciphering genetic signatures by whole exome sequencing in a case of co-prevalence of severe renal hypouricemia and diabetes with impaired insulin secretion

Background

Renal hypouricemia (RHUC) is a hereditary disorder where mutations in SLC22A12 gene and SLC2A9 gene cause RHUC type 1 (RHUC1) and RHUC type 2 (RHUC2), respectively. These genes regulate renal tubular reabsorption of urates while there exist other genes counterbalancing the net excretion of urates including ABCG2 and SLC17A1. Urate metabolism is tightly interconnected with glucose metabolism, and SLC2A9 gene may be involved in insulin secretion from pancreatic β-cells. On the other hand, a myriad of genes are responsible for the impaired insulin secretion independently of urate metabolism.

Case presentation

We describe a 67 year-old Japanese man who manifested severe hypouricemia (0.7 mg/dl (3.8–7.0 mg/dl), 41.6 μmol/l (226–416 μmol/l)) and diabetes with impaired insulin secretion. His high urinary fractional excretion of urate (65.5%) and low urinary C-peptide excretion (25.7 μg/day) were compatible with the diagnosis of RHUC and impaired insulin secretion, respectively. Considering the fact that metabolic pathways regulating urates and glucose are closely interconnected, we attempted to delineate the genetic basis of the hypouricemia and the insulin secretion defect observed in this patient using whole exome sequencing. Intriguingly, we found homozygous Trp258* mutations in SLC22A12 gene causing RHUC1 while concurrent mutations reported to be associated with hyperuricemia were also discovered including ABCG2 (Gln141Lys) and SLC17A1 (Thr269Ile). SLC2A9, that also facilitates glucose transport, has been implicated to enhance insulin secretion, however, the non-synonymous mutations found in SLC2A9 gene of this patient were not dysfunctional variants. Therefore, we embarked on a search for causal mutations for his impaired insulin secretion, resulting in identification of multiple mutations in HNF1A gene (MODY3) as well as other genes that play roles in pancreatic β-cells. Among them, the Leu80fs in the homeobox gene NKX6.1 was an unreported mutation.

Conclusion

We found a case of RHUC1 carrying mutations in SLC22A12 gene accompanied with compensatory mutations associated with hyperuricemia, representing the first report showing coexistence of the mutations with opposed potential to regulate urate concentrations. On the other hand, independent gene mutations may be responsible for his impaired insulin secretion, which contains novel mutations in key genes in the pancreatic β-cell functions that deserve further scrutiny.

Uricostatic and uricosuric effect of grapefruit juice in potassium oxonate-induced hyperuricemic mice

The aim of this study was to examine the preventive action of grapefruit juice (GFJ) against potassium oxonate-induced hyperuricemic mice. The results showed that GFJ significantly (p < .05) inhibit the serum and hepatic xanthine oxidase enzyme, lower uric acid level, serum creatinine, uromodulin, and blood urea nitrogen levels to normal and lower inflammation related genes IL-1β, caspase-1, NLRP3, and ASC. Furthermore, histopathology analysis revealed that GFJ markedly improve the renal and intestinal morphology. The mRNA expression of urate transporter 1, glucose transporter 9 were downregulated, whereas ATP-binding cassette transporter (ABCG2) was upregulated in the GFJ-treated group. The results of immunohistochemistry revealed that the ABCG2 protein expression in the small and large intestine was significantly upregulated after the GFJ administration. These results suggested that GFJ can be used as a urate lowering agent and future mechanistic studies should be conducted. PRACTICAL APPLICATIONS: The results of current study indicated that utilization of GFJ as an anti-hyperuricemic agent for the treatment of hyperuricemia. This article will be very valuable for all those peoples which are directly or indirectly linked with this disease.

Gene polymorphisms of uric acid are associated with pre-eclampsia in South Africans of African ancestry

Objectives: To investigate the association of uric acid gene polymorphisms and Pre-eclampsia.Methods: 637 women of African ancestry [280 controls, 357 pre-eclampsia (early-onset = 187, late-onset = 170]) retrospectively. The rs505802, rs1212986, and rs1014290 SNPs were genotyped from purified DNA using real-time PCR.Results: CT genotype (rs505802) was higher in pre-eclampsia [Adjusted p = 0.028*: OR (95% CI) = 1.73 (1.258-2.442)] and late-onset pre-eclampsia [Adjusted p = 0.027*: OR (95% CI) = 1.75 (1.165-2.2628)] than controls. CT genotype (rs1014290) was higher in early-onset pre-eclampsia [Adjusted p-value = 0.040*: OR (95% CI) = 1.60 (1.102-2.325)] than controls.Conclusion: The genotyped rs505802 and rs1014290 are significantly associated with pre-eclampsia.

Effects of uric acid dysregulation on the kidney

Recently, research has redirected its interests in uric acid (UA) from gout, an inflammatory disease in joints, to groups of closely interrelated pathologies associated with cardiovascular and kidney dysfunction. Many epidemiological, clinical, and experimental studies have shown that UA may play a role in the pathophysiology of the cardiorenal syndrome continuum; however, it is still unclear if it is a risk factor or a causal role. Hyperuricemia has been well studied in the past two decades, revealing mechanistic insights into UA homeostasis. Likewise, some epidemiological and experimental evidence suggests that hypouricemia can lead to cardiorenal pathologies. The goal of this review is to highlight why studying both hyperuricemia and hypouricemia is warranted as well as to summarize the relevance of UA to kidney function.

Serum Uric Acid is Associated with Renal Prognosis of Lupus Nephritis in Women but not in Men

Lupus nephritis (LN) is a major complication of systemic lupus erythematosus. Early intervention in lupus nephritis improves prognosis. There is an association between hyperuricemia and lupus nephritis; nevertheless, the sex-specific role of uric acid in lupus nephritis remains unclear. We retrospectively analyzed 578 patients diagnosed with LN by renal biopsy. We determine the relationship of serum uric acid to progression of LN using Kaplan–Meier survival analyses and Cox proportional hazards models. The primary end point was LN progression defined as the initiation of dialysis or kidney transplantation. Men had higher mean serum uric acid levels than did women. Every 1 mg/dL increase in baseline uric acid level increased the risk of LN progression by 15.1%. The serum uric acid level was an independent risk factor for LN progression in women (hazard ratio [HR], 1.158; confidence interval [CI], 1.018–1.317; p = 0.028) but not in men (HR, 1.499; CI, 0.964–2.331; p = 0.072). Sensitivity analysis involving serum uric acid terciles generated consistent and robust results. Serum uric acid level was an independent risk factor for LN progression in women but not in men.

Mouse models for human hyperuricaemia: a critical review

Hyperuricaemia (increased serum urate concentration) occurs mainly in higher primates, including in humans, because of inactivation of the gene encoding uricase during primate evolution. Individuals with hyperuricaemia might develop gout - a painful inflammatory arthritis caused by monosodium urate crystal deposition in articular structures. Hyperuricaemia is also associated with common chronic diseases, including hypertension, chronic kidney disease, type 2 diabetes and cardiovascular disease. Many mouse models have been developed to investigate the causal mechanisms for hyperuricaemia. These models are highly diverse and can be divided into two broad categories: mice with genetic modifications (genetically induced models) and mice exposed to certain environmental factors (environmentally induced models; for example, pharmaceutical or dietary induction). This Review provides an overview of the mouse models of hyperuricaemia and the relevance of these models to human hyperuricaemia, with an emphasis on those models generated through genetic modifications. The challenges in developing and comparing mouse models of hyperuricaemia and future research directions are also outlined.

Impact of modifiable risk factors on Alzheimer's disease: A two-sample Mendelian randomization study

With the steadily increasing prevalence of Alzheimer's disease (AD) and great difficulties encountered for AD drug development presently, much interest has been devoted to identifying modifiable risk factors to lower the risk of AD, while the causal associations between risk factors and AD remain inconclusive. The present study conducted a comprehensive evaluation of the causal associations between risk factors and AD development by taking the recent advancements of Mendelian randomization (MR). Inverse variance weighted (IVW), MR-Egger, weighted median, and weighted mode were used for complementary calculation. A total of 45 risk factors and corresponding studies were covered in the study. This two-sample MR (2SMR) analysis provided a suggestive association between genetically predicted higher years of schooling and reduced risks of AD, and each standard deviation (3.71 years) increased in years of schooling was associated with a 41% reduction in the risk of AD (IVW, OR: 0.59, 95% CI: 0.45-0.77). At the same time, it was genetically predicted that urate might be a risk factor in AD, and it was found that each standard deviation increase in urate levels (1.33 mg/dL) was associated with a 0.09-fold increase in the risk of AD (IVW, OR: 1.09, 95% CI: 1.01-1.18). To summarize, the 2SMR analysis indicated a suggestive association between genetically predicted higher years of schooling and reduced risks of AD, and between genetically predicted higher urate levels and increased risks of AD. The findings provide useful clues to help combat AD and warrants future studies.

Association of Serum Uric Acid with Metabolic Syndrome and Its Components: A Mendelian Randomization Analysis

Background

The role of uric acid on metabolic syndrome (MetS) has always been controversial. This study aims to explore associations between uric acid with MetS and its components in Chinese female health check-up population.

Methods

1381 subjects constituted the longitudinal health check-up cohort. Health examination and genotyping were performed. Unadjusted and adjusted observational analyses were implemented to evaluate observational associations between uric acid with MetS and its components. Mendelian randomization analysis was performed to estimate the causal effect using variation at rs11722228 (SLC2A9) as an instrument for uric acid.

Results

An increase of 65% in risk of MetS per standard deviation increase in uric acid was found using unadjusted observational analyses. This association attenuated on adjustment for potential confounders. Similar patterns were found in the association analyses of uric acid with hyperglycemia, hypertension, and dyslipidemia. Neither by performing unadjusted nor adjusted analysis did we see evidence for association of uric acid on overweight and obesity. Mendelian randomization analyses showed no evidence of causal association between uric acid and MetS and MetS components.

Conclusions

We found no causal evidence to support that increased serum uric acid is a causal risk factor for MetS or its components. Hence, there remains no strong evidence for the effeteness of undergoing urate-lowering therapy to prevent the onset of MetS or cardiovascular disease in health management.

Impact of Lesinurad and allopurinol on experimental Hyperuricemia in mice: biochemical, molecular and Immunohistochemical study

BACKGROUND

Hyperuricemia is an abnormal increase in uric acid levels in the blood. It is the cause of gout that manifested by inflammatory arthritis and painful disable. Therefore, current study evaluated the potential ameliorative impact of Lesinurad and Allopurinol on the kidneys of hyperuricemic mice at the biochemical, molecular and cellular levels.

METHODS

Lesinurad and allopurinol alone or in combination were orally administered to hyperuricemic and control mice for seven consecutive days. Levels of uric acid and blood urea nitrogen, along with antioxidants and inflammatory cytokines (IL-1β and TNF-α) were measured in the serum. The mRNA expression of mouse urate anion transporter-1, glucose transporter 9, organic anion transporters, in renal tissues were examined using quantitative real time PCR. Simultaneously, the immunoreactivity of transforming growth factor-beta 1 was examined immunohistochemically.

RESULTS

Lesinurad and allopurinol administration resulted in significant decrease in serum levels of uric acid, blood urea nitrogen, xanthine oxidase activity, catalase, glutathione peroxidase and inflammatory cytokines (IL-1β and TNF-α) reported in hyperuricemic mice. Both partially reversed oxonate-induced alterations in renal mURAT-1, mGLUT-9, mOAT-1 and mOAT-3 expressions, as well as alterations in the immunoreactivity of TGF- β1, resulting in the increase of renal uric acid secretion and excretion. The combined administration of lesinurad and ALP restored all altered parameters in a synergistic manner, improving renal function in the hyperuricemic mouse model employed.

CONCLUSION

This study confirmed synergistic ameliorative hypouricemic impact of both lesinurad and allopurinol in the treatment of hyperuricemia in mice at the biochemical, molecular and cellular levels.

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.

Refining genome-wide associated loci for serum uric acid in individuals with African ancestry

OBJECTIVE

Serum uric acid is the end-product of purine metabolism and at high levels is a risk factor for several human diseases including gout and cardiovascular disease. Heritability estimates range from 0.32 to 0.63. Genome-wide association studies (GWAS) provide an unbiased approach to identify loci influencing serum uric acid. Here, we performed the first GWAS for serum uric acid in continental Africans, with replication in African Americans.

METHODS

Africans (n = 4126) and African Americans (n = 5007) were genotyped on high-density GWAS arrays. Efficient mixed model association, a variance component approach, was used to perform association testing for a total of ~ 18 million autosomal genotyped and imputed variants. CAVIARBF was used to fine map significant regions.

RESULTS

We identified two genome-wide significant loci: 4p16.1 (SLC2A9) and 11q13.1 (SLC22A12). At SLC2A9, the most strongly associated SNP was rs7683856 (P = 1.60 × 10-44). Conditional analysis revealed a second signal indexed by rs6838021 (P = 5.75 × 10-17). Gene expression and regulatory motif data prioritized a single-candidate causal variant for each signal. At SLC22A12, the most strongly associated SNP was rs147647315 (P = 6.65 × 10-25). Conditional analysis and functional annotation prioritized the missense variant rs147647315 (R (Arg) > H (His)) as the sole causal variant. Functional annotation of these three signals implicated processes in skeletal muscle, subcutaneous adipose tissue and the kidneys, respectively.

CONCLUSIONS

This first GWAS of serum uric acid in continental Africans identified three associations at two loci, SLC2A9 and SLC22A12. The combination of weak linkage disequilibrium in Africans and functional annotation led to the identification of candidate causal SNPs for all three signals. Each candidate causal variant implicated a different cell type. Collectively, the three associations accounted for 4.3% of the variance of serum uric acid.

Glycosylation of immunoglobulin G is regulated by a large network of genes pleiotropic with inflammatory diseases

Effector functions of immunoglobulin G (IgG) are regulated by the composition of a glycan moiety, thus affecting activity of the immune system. Aberrant glycosylation of IgG has been observed in many diseases, but little is understood about the underlying mechanisms. We performed a genome-wide association study of IgG N-glycosylation (N = 8090) and, using a data-driven network approach, suggested how associated loci form a functional network. We confirmed in vitro that knockdown of IKZF1 decreases the expression of fucosyltransferase FUT8, resulting in increased levels of fucosylated glycans, and suggest that RUNX1 and RUNX3, together with SMARCB1, regulate expression of glycosyltransferase MGAT3. We also show that variants affecting the expression of genes involved in the regulation of glycoenzymes colocalize with variants affecting risk for inflammatory diseases. This study provides new evidence that variation in key transcription factors coupled with regulatory variation in glycogenes modifies IgG glycosylation and has influence on inflammatory diseases.

Contribution of Rare Variants of the SLC22A12 Gene to the Missing Heritability of Serum Urate Levels

Gout is a common arthritis caused by monosodium urate crystals. The heritability of serum urate levels is estimated to be 30-70%; however, common genetic variants account for only 7.9% of the variance in serum urate levels. This discrepancy is an example of "missing heritability." The "missing heritability" suggests that variants associated with uric acid levels are yet to be found. By using genomic sequences of the ToMMo cohort, we identified rare variants of the SLC22A12 gene that affect the urate transport activity of URAT1. URAT1 is a transporter protein encoded by the SLC22A12 gene. We grouped the participants with variants affecting urate uptake by URAT1 and analyzed the variance of serum urate levels. The results showed that the heritability explained by the SLC22A12 variants of men and women exceeds 10%, suggesting that rare variants underlie a substantial portion of the "missing heritability" of serum urate levels.

The Effects of Hyperuricemia on the Prognosis of IgA Nephropathy are More Potent in Females

Hyperuricemia is a potential risk factor for immunoglobulin A nephropathy (IgAN) progression but its sex-specific effects on IgAN progression remain unclear. This study aimed to determine the effect of serum uric acid on IgAN progression and whether its effect varied according to sex. A total of 4339 patients who diagnosed with IgAN by renal biopsy were retrospectively analyzed. We assessed the association of serum uric acid on IgAN progression using Kaplan–Meier survival analyses and Cox proportional hazards models. The study’s primary end point was IgAN progression that was defined as a 50% decline in the estimated glomerular filtration rate or the initiation of dialysis. On average, the serum uric acid levels were higher in the men than in the women. In the fully adjusted Cox proportional hazards model that considered all subjects, the risk of IgAN progression increased by about 25.6% for every 1 mg/dL increase in the baseline uric acid level. The serum uric acid level was an independent risk factor for IgAN progression in both sexes but its effect was more pronounced in the women (hazard ratio [HR], 1.383; confidence interval [CI],1.263 to 1.514; p < 0.001) than in the men (HR, 1.181; CI, 1.097 to 1.272; p < 0.001) (p_interaction < 0.001). A sensitivity analysis involving serum uric acid quartiles generated consistent and robust results. In conclusion, the serum uric acid level was an independent risk factor for IgAN progression and its effect was more pronounced among the women compared with that among the men.

Hyperuricemia and Hypertension: Links and Risks

Hyperuricemia has long been recognized to be associated with increased cardiovascular risk, including risk of developing hypertension. Epidemiological findings suggest that the link with hypertension is stronger in children and adolescents. Uric acid acts as a strong antioxidant compound in the extracellular environment but has pro-inflammatory effects within the intracellular setting. A chronic phase of microvascular injury is known to occur after prolonged periods of hyperuricemia. This is proposed to contribute to afferent arteriolopathy and elevation of blood pressure that may become unresponsive to uric acid-lowering therapies over time. Studies have struggled to infer direct causality of hyperuricemia due to a vast number of confounders including body mass index. The aim of this review is to present the available data and highlight the need for large scale prospective randomized controlled trials in this area. At present, there is limited evidence to support a role for uric acid-lowering therapies in helping mitigate the risk of hypertension.

Corneal Endothelial Morphology and Thickness Changes in Patients with Gout

Objectives:

To investigate corneal endothelial cell density (ECD), morphology, and central corneal thickness (CCT) in patients with gout compared with healthy subjects.

Materials and Methods:

Fifty eyes of 50 gout patients and 50 eyes of 50 healthy subjects without gout or any other systemic disease were included in this study. After detailed ophthalmologic examination, specular microscopy (Tomey EM-4000; Tomey Corp) measurement was performed for all participants. ECD, average cell area (ACA), coefficient of variation (CV), hexagonality ratio, and CCT values were recorded.

Results:

Mean ECD and hexagonality ratio were lower (p=0.004 and p=0.002) and CV, ACA, and CCT values were higher (p=0.001, p=0.007, and p=0.001) in patients with gout when compared to healthy subjects. There were significant correlations between gout disease duration and CD and hexagonality ratio (p=0.019 and p=0.043) and also between uric acid value and hexagonality ratio and CCT (p=0.044 and p=0.003).

Conclusion:

Altered corneal endothelial function was found in patients with gout when compared to healthy subjects and the alteration increased as gout duration and uric acid value increased.

Genetically Elevated Serum Uric Acid and Renal Function in an Apparently Healthy Population

BACKGROUND

The association between uric acid and kidney disease has been extensively investigated. Numerous studies have reported the association between circulating levels of uric acid and renal function.

OBJECTIVES

To test, by the Mendelian randomization method, whether there is a causal association between circulating levels of uric acid and renal function.

METHODS

In 989 participants, estimated glomerular filtration rate (eGFR) was calculated, the circulating level of uric acid was tested, and the uric acid polymorphism (rs11722228) was genotyped.

RESULTS

After adjusting for age, gender, smoking history, alcohol intake, antihypertensive medication, body mass index, waist-to-hip ratio, and levels of urea nitrogen and creatinine, a significant allelic difference was found in uric acid levels for each genotype (p < 0.0001). Furthermore, the circulating levels of uric acid were negatively associated with eGFR after adjusting for cardiovascular risk factors and other potential confounders (p < 0.0001). Meanwhile, eGFR was significantly associated with the genotypes of rs11722228 (β = -0.07; p = 0.02).

CONCLUSIONS

Evidence from the Mendelian randomization approach implied a causal relationship between uric acid and renal function in an apparently healthy population.

Idiopathic renal hypouricemia: A case report and literature review

Idiopathic renal hypouricemia is a rare hereditary condition. Type 2 renal hyperuricemia (RHUC2) is caused by a mutation in the SLC2A9 gene, which encodes a high‑capacity glucose and urate transporter, glucose transporter (GLUT)9. RHUC2 predisposes to exercise‑induced acute renal failure (EIARF) and nephrolithiasis, which is caused by a defect in renal tubular urate transport and is characterized by increased clearance of renal uric acid. In the present study a case of a 35‑year‑old Chinese man with EIARF is reported. The patient had isolated renal hypouricemia, with a serum uric acid level of 21 µmol/l and a fractional excretion of uric acid of 200%. The mutational analysis revealed a homozygous mutation (c.857G>A in exon 8) in the SLC2A9 gene. The patient's family members carried the same mutation, but were heterozygous and clinically asymptomatic. In conclusion, to the best of our knowledge, this is the first report of a RHUC2 patient with a GLUT9 mutation, p.W286X, which may be a pathogenic mutation of RHUC2. Further investigation into the functional role of GLUT9 in this novel SLC2A9 mutation is required.

Interaction Between ITM2B and GLUT9 Links Urate Transport to Neurodegenerative Disorders

Hyperuricemia plays a critical causative role in gout. In contrast, hyperuricemia has a protective effect in neurodegenerative disorders, including Alzheimer's Disease. Genetic variation in the SLC2A9 gene, encoding the urate transporter GLUT9, exerts the largest single-gene effect on serum uric acid (SUA). We report here the identification of two GLUT9-interacting proteins, integral membrane protein 2B (ITM2B) and transmembrane protein 85 (TMEM85), isolated from a human kidney cDNA library using the dual-membrane yeast two-hybrid system. ITM2B is a ubiquitously expressed, N-glycosylated transmembrane regulatory protein, involved in familial dementias and retinal dystrophy; the function of TMEM85 is less defined. Using coimmunoprecipitation, we confirmed the physical interaction between ITM2B or TMEM85 and N-terminal GLUT9 isoforms (GLUT9a and GLUT9b) in transfected HEK 293T cells and Xenopus oocytes, wherein ITM2B but not TMEM85 inhibited GLUT9-mediated urate uptake. Additionally, co-expression of ITM2B with GLUT9 in oocytes inhibited N-glycosylation of GLUT9a more than GLUT9b and stimulated urate efflux by both isoforms. However, urate uptake by N-glycosylation and N-terminal deletion GLUT9 mutants was efficiently inhibited by ITM2B, indicating that neither N-glycosylation nor the N terminus is necessary for functional interaction of GLUT9 with ITM2B. Notably, ITM2B variants linked to familial Danish dementia and retinal dystrophy significantly attenuated the inhibition of GLUT9-mediated urate influx. We propose ITM2B as a potential regulatory link between urate homeostasis and neurodegenerative disorders.

Phloretin ameliorates hyperuricemia-induced chronic renal dysfunction through inhibiting NLRP3 inflammasome and uric acid reabsorption

BACKGROUND

Hyperuricemia (HUA) is an important risk factor for renal diseases and contributes to renal fibrosis. It has been proved that phloretin has antioxidant and anti-inflammatory properties and could inhibit uric acid (UA) uptake in vitro. However, whether phloretin has a renal protective role in vivo remains unknown.

PURPOSE

This study aims to evaluate the therapeutic effect of phloretin on HUA-induced renal injury in mice and to reveal its underlying mechanism.

METHODS

Mice were induced hyperuricemic by oral gavage of adenine/potassium oxonate. The effects of phloretin on renal function, fibrosis, oxidative stress, inflammation, and UA metabolism in HUA mice were evaluated. The effect of phloretin on NLRP3 pathway was analyzed in human renal tubular cell lines (HK-2).

RESULTS

HUA mice showed renal dysfunction with increased renal fibrosis, inflammation and mitochondrial stress. By contrast, phloretin reduced the level of serum blood urea nitrogen (BUN), urinary albumin to creatinine ratio (UACR), tubular necrosis, extracellular matrix (ECM) deposition and interstitial fibroblasts in HUA mice. The renal infiltration of inflammatory cells, cytokines such as NOD-like receptor family pyrin domain containing 3 (NLRP3) and interleukin-1β (IL-1β) release, mitochondrial reactive oxygen species (ROS) and morphological lesions in HUA mice also decreased. Furthermore, phloretin partly inhibited renal glucose transporter 9 (GLUT9) and promoted urinary UA excretion in HUA mice. In vitro, phloretin suppressed the NLPR3 pathway under LPS or UA stimulation in HK-2 cells.

CONCLUSIONS

Phloretin could effectively attenuate UA-induced renal injury via co-inhibiting NLRP3 and UA reabsorption, and thus it might be a potential therapy to hyperuricemia-related renal diseases.

Genetically determined serum urate levels and cardiovascular and other diseases in UK Biobank cohort: A phenome-wide mendelian randomization study

BACKGROUND

The role of urate in cardiovascular diseases (CVDs) has been extensively investigated in observational studies; however, the extent of any causal effect remains unclear, making it difficult to evaluate its clinical relevance.

METHODS AND FINDINGS

A phenome-wide association study (PheWAS) together with a Bayesian analysis of tree-structured phenotypic model (TreeWAS) was performed to examine disease outcomes related to genetically determined serum urate levels in 339,256 unrelated White British individuals (54% female) in the UK Biobank who were aged 40-69 years (mean age, 56.87; SD, 7.99) when recruited from 2006 to 2010. Mendelian randomization (MR) analyses were performed to replicate significant findings using various genome-wide association study (GWAS) consortia data. Sensitivity analyses were conducted to examine possible pleiotropic effects on metabolic traits of the genetic variants used as instruments for urate. PheWAS analysis, examining the association with 1,431 disease outcomes, identified 13 distinct phecodes representing 4 disease groups (inflammatory polyarthropathies, hypertensive disease, circulatory disease, and metabolic disorders) and 9 disease outcomes (gout, gouty arthropathy, pyogenic arthritis, essential hypertension, coronary atherosclerosis, ischemic heart disease, chronic ischemic heart disease, myocardial infarction, and hypercholesterolemia) that were associated with genetically determined serum urate levels after multiple testing correction (p < 3.35 × 10-4). TreeWAS analysis, examining 10,750 ICD-10 diagnostic terms, identified more sub-phenotypes of cardiovascular and cerebrovascular diseases (e.g., angina pectoris, heart failure, cerebral infarction). MR analysis successfully replicated the association with gout, hypertension, heart diseases, and blood lipid levels but indicated the existence of genetic pleiotropy. Sensitivity analyses support an inference that pleiotropic effects of genetic variants on urate and metabolic traits contribute to the observational associations with CVDs. The main limitations of this study relate to possible bias from pleiotropic effects of the considered genetic variants and possible misclassification of cases for mild disease that did not require hospitalization.

CONCLUSION

In this study, high serum urate levels were found to be associated with increased risk of different types of cardiac events. The finding of genetic pleiotropy indicates the existence of common upstream pathological elements influencing both urate and metabolic traits, and this may suggest new opportunities and challenges for developing drugs targeting a common mediator that would be beneficial for both the treatment of gout and the prevention of cardiovascular comorbidities.

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.

Learning Physiology From Inherited Kidney Disorders

The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.

Taurine Inhibited Uric Acid Uptake in HK-2 Renal Tubular Epithelial Cells

It has been confirmed by our laboratory that taurine could decrease uric acid levels in hyperuricemic rats and regulate the expressions of some urate transporters. The present study aims to investigate the effects of taurine on uric acid uptake in human renal proximal tubular epithelial cells (HK-2). The cell growth inhibition rate was measured by MTS assay, which was up to 50% after treatment with 1.5 mmol/L uric acid. After administration of 15 mmol/L taurine, the inhibition rate and uric acid uptake were both significantly decreased. Then the HK-2 cells were grouped as follows: control group (C); model group (M), in which 1.5 mmol/L uric acid was added to the medium; taurine group (MT), in which 1.5 mmol/L uric acid and 15 mmol/L taurine were added to the medium; and taurine control group (T), in which 15 mmol/L taurine was added to the medium. The mRNA and protein expression levels of URAT1 and GLUT9 were measured by real-time PCR and western-blot. The results showed that URAT1 and GLUT9 mRNA/protein expression levels in group M were significantly increased compared with group C, and they were both down-regulated in MT group. In addition, the expression levels of these two transporters in group T were significantly lower than group C. The results indicated that taurine could inhibit uric acid uptake and down-regulate the expressions of URAT1 and GLUT9 in HK-2 cells.

Baseline urate level and renal function predict outcomes of urate-lowering therapy using low doses of febuxostat and benzbromarone: a prospective, randomized controlled study in a Chinese primary gout cohort

Background

Low doses of febuxostat or benzbromarone are widely used in Asian countries, but lacking studies to compare the efficacy and safety of the two urate-lowering drugs.

Methods

To compare the efficacy and safety of low-dose febuxostat with low-dose benzbromarone in patients with primary gout, a randomized controlled, open-label trial was performed among male patients with primary gout for urate-lowering therapy (ULT) in a dedicated gout clinic in China. Randomization was carried out by a third-party institution according to random number table. Patients were randomly assigned 1:1 to febuxostat group (Feb group) (20 mg daily) or benzbromarone group (Ben group) (25 mg daily) and treated for 12 weeks. General information and biochemical data were collected at baseline and at every visit monthly. Clinical characteristics before and after the ULT were analyzed in the two groups by SPSS and EmpowerStats software.

Results

Two hundred forty patients were enrolled and randomized in the two groups, with 214 patients completing 12 weeks’ ULT (105 in the Feb group and 109 in the Ben group). After 12 weeks, substantial percentages of patients in both Feb and Ben group achieved the target serum uric acid (sUA) (< 360 μmol/L) and serum urate levels were reduced significantly for both groups (Feb 39.5% and 156.83 μmol/L vs. Ben 35.7% and 163.99 μmol/L). Multivariate analysis suggests baseline sUA level and renal function were associated with the outcome of the rate of achieving target sUA (RAT). Sub-group analysis suggests low doses of febuxostat and benzbromarone rendered better RAT for patients with sUA < 540 μmol/L and creatinine clearance rate (Ccr) ≤ 110 mL min⁻¹ 1.73 m⁻² at baseline. The drugs were well tolerated, and the incidence of gout flares in Feb group was similar with that in Ben group (22.85% vs. 33.94%).

Conclusion

Overall, febuxostat 20 mg daily and benzbromarone 25 mg daily reduced sUA, and gout patients with sUA level < 540 μmol/L or Ccr ≤ 110 mL min⁻¹ 1.73 m⁻² at baseline had better chance to achieve target uric acid levels. The current study suggests sUA level and renal function are key factors to consider when recommending low doses of febuxostat and benzbromarone to gout patients.

Trial registration

Registered with ChiCTR, No. ChiCTR1800019352 (retrospectively registered).

Unraveling the functional role of the orphan solute carrier, SLC22A24 in the transport of steroid conjugates through metabolomic and genome-wide association studies

Variation in steroid hormone levels has wide implications for health and disease. The genes encoding the proteins involved in steroid disposition represent key determinants of interindividual variation in steroid levels and ultimately, their effects. Beginning with metabolomic data from genome-wide association studies (GWAS), we observed that genetic variants in the orphan transporter, SLC22A24 were significantly associated with levels of androsterone glucuronide and etiocholanolone glucuronide (sentinel SNPs p-value <1x10-30). In cells over-expressing human or various mammalian orthologs of SLC22A24, we showed that steroid conjugates and bile acids were substrates of the transporter. Phylogenetic, genomic, and transcriptomic analyses suggested that SLC22A24 has a specialized role in the kidney and appears to function in the reabsorption of organic anions, and in particular, anionic steroids. Phenome-wide analysis showed that functional variants of SLC22A24 are associated with human disease such as cardiovascular diseases and acne, which have been linked to dysregulated steroid metabolism. Collectively, these functional genomic studies reveal a previously uncharacterized protein involved in steroid homeostasis, opening up new possibilities for SLC22A24 as a pharmacological target for regulating steroid levels.

An update on the genetics of hyperuricaemia and gout

A central aspect of the pathogenesis of gout is elevated urate concentrations, which lead to the formation of monosodium urate crystals. The clinical features of gout result from an individual's immune response to these deposited crystals. Genome-wide association studies (GWAS) have confirmed the importance of urate excretion in the control of serum urate levels and the risk of gout and have identified the kidneys, the gut and the liver as sites of urate regulation. The genetic contribution to the progression from hyperuricaemia to gout remains relatively poorly understood, although genes encoding proteins that are involved in the NLRP3 (NOD-, LRR- and pyrin domain-containing 3) inflammasome pathway play a part. Genome-wide and targeted sequencing is beginning to identify uncommon population-specific variants that are associated with urate levels and gout. Mendelian randomization studies using urate-associated genetic variants as unconfounded surrogates for lifelong urate exposure have not supported claims that urate is causal for metabolic conditions that are comorbidities of hyperuricaemia and gout. Genetic studies have also identified genetic variants that predict responsiveness to therapies (for example, urate-lowering drugs) for treatment of hyperuricaemia. Future research should focus on large GWAS (that include asymptomatic hyperuricaemic individuals) and on increasing the use of whole-genome sequencing data to identify uncommon genetic variants with increased penetrance that might provide opportunities for clinical translation.

Nutritional Risk Factors, Microbiota and Parkinson's Disease: What Is the Current Evidence?

Parkinson’s disease (PD) is a frequent neurodegenerative disease among elderly people. Genetic and underlying environmental factors seem to be involved in the pathogenesis of PD related to degeneration of dopaminergic neurons in the striatum. In previous experimental researches oxidative stress, mitochondrial dysfunction, homocysteine, and neuroinflammation have been reported as potential mechanisms. Among environmental factors, nutrition is one of the most investigated areas as it is a potentially modifiable factor. The purpose of this review is to provide current knowledge regarding the relation between diet and PD risk. We performed a comprehensive review including the most relevant studies from the year 2000 onwards including prospective studies, nested case-control studies, and meta-analysis. Among dietary factors we focused on specific nutrients and food groups, alcoholic beverages, uric acid, and dietary patterns. Furthermore, we included studies on microbiota as recent findings have shown a possible impact on neurodegeneration. As a conclusion, there are still many controversies regarding the relationship between PD and diet which, beside methodological differences among studies, may be due to underlying genetic and gender-specific factors. However, some evidence exists regarding a potential protective effect of uric acid, poly-unsaturated fatty acids, coffee, and tea but mainly in men, whereas dairy products, particularly milk, might increase PD risk through contaminant mediated effect.

MiR-143-3p directly targets GLUT9 to reduce uric acid reabsorption and inflammatory response of renal tubular epithelial cells

GLUT9 is generally considered to be associated with the uric acid transport, which plays an important role in the regulation of serum uric acid level. In this study, the expression level of miR-143-3p was significantly decreased in hyperuricemia mice model group compared with the normal control by miRNA microarray, the same results were confirmed in the hyperuricemia patients and the healthy control group. It is predicted that GLUT9 may be the target gene of miR-143-3p by target scan and other net-software. GLUT9 as the downstream target gene of miR-143-3p was determinated by fluorescence enzyme activity assay. Western blotting and qRT-PCR indicated that the expression of GLUT9 in human renal tubular epithelial cells transfected with miR-143-3p mimics was significantly reduced. Meanwhile inflammatory factors IL-1β and MCP-1 significantly decreased. In conclusion, miR-143-3p can reduce uric acid reabsorption by inhibiting its downstream target gene GLUT9.

Genome-wide association study revealed novel loci which aggravate asymptomatic hyperuricaemia into gout

Objective

The first ever genome-wide association study (GWAS) of clinically defined gout cases and asymptomatic hyperuricaemia (AHUA) controls was performed to identify novel gout loci that aggravate AHUA into gout.

Methods

We carried out a GWAS of 945 clinically defined gout cases and 1003 AHUA controls followed by 2 replication studies. In total, 2860 gout cases and 3149 AHUA controls (all Japanese men) were analysed. We also compared the ORs for each locus in the present GWAS (gout vs AHUA) with those in the previous GWAS (gout vs normouricaemia).

Results

This new approach enabled us to identify two novel gout loci (rs7927466 of CNTN5 and rs9952962 of MIR302F) and one suggestive locus (rs12980365 of ZNF724) at the genome-wide significance level (p<5.0×10^–8). The present study also identified the loci of ABCG2, ALDH2 and SLC2A9. One of them, rs671 of ALDH2, was identified as a gout locus by GWAS for the first time. Comparing ORs for each locus in the present versus the previous GWAS revealed three ‘gout vs AHUA GWAS’-specific loci (CNTN5, MIR302F and ZNF724) to be clearly associated with mechanisms of gout development which distinctly differ from the known gout risk loci that basically elevate serum uric acid level.

Conclusions

This meta-analysis is the first to reveal the loci associated with crystal-induced inflammation, the last step in gout development that aggravates AHUA into gout. Our findings should help to elucidate the molecular mechanisms of gout development and assist the prevention of gout attacks in high-risk AHUA individuals.

Increased urinary glucose excretion is associated with a reduced risk of hyperuricaemia

AIM

To investigate the association of urinary glucose excretion with levels of serum uric acid in adults with newly diagnosed diabetes.

METHODS

A total of 597 people with newly diagnosed diabetes, confirmed in an oral glucose tolerance test, were included in the present study. The participants were divided into two groups: 142 participants with low urinary glucose excretion and 455 with high urinary glucose excretion. Demographic characteristics and clinical variables were evaluated. The association of urinary glucose excretion with uric acid was analysed using multivariable regression analysis.

RESULTS

The low urinary glucose excretion group had a significantly higher prevalence of hyperuricaemia than the high urinary glucose excretion group. Moreover, urinary glucose excretion was negatively associated with uric acid level. The correlation remained significant after adjusting for potential confounders, including gender, age, fasting plasma glucose, 2-h plasma glucose and BMI. The results also showed that participants with high urinary glucose excretion were at decreased risk of hyperuricaemia (odds ratio 0.47, 95% CI 0.27-0.80; P = 0.006).

CONCLUSION

Urinary glucose excretion was independently associated with uric acid level in participants with newly diagnosed diabetes. In addition to lowering blood glucose, promoting urinary glucose excretion may also be an effective approach to reducing serum uric acid levels, especially for people with diabetes complicated with hyperuricaemia.