The genetic basis of urate control and gout: Insights into molecular pathogenesis from follow-up study of genome-wide association study loci

Hyperuricemia and Gout Reduction by SGLT2 Inhibitors in Diabetes and Heart Failure: JACC Review Topic of the Week

Gout is characterized by increased production of purines (through the pentose phosphate pathway), which is coupled with reduced renal or intestinal excretion of urate. Concurrent upregulation of nutrient surplus signaling (mammalian target of rapamycin and hypoxia-inducible factor-1a) and downregulation of nutrient deprivation signaling (sirtuin-1 and adenosine monophosphate-activated protein kinase) redirects glucose toward anabolic pathways (rather than adenosine triphosphate production), thus promoting heightened oxidative stress and cardiomyocyte and proximal tubular dysfunction, leading to cardiomyopathy and kidney disease. Hyperuricemia is a marker (rather than a driver) of these cellular stresses. By inducing a state of starvation mimicry in a state of nutrient surplus, sodium-glucose cotransporter-2 inhibitors decrease flux through the pentose phosphate pathway (thereby attenuating purine and urate synthesis) while promoting renal urate excretion. These convergent actions exert a meaningful effect to lower serum uric acid by ≈0.6 to 1.5 mg/dL and to reduce the risk of gout by 30% to 50% in large-scale clinical trials.

Molecular characteristic analysis of single-nucleotide polymorphisms in SLC16A9/hMCT9

AIMS

Human monocarboxylate transporter 9 (hMCT9), encoded by SLC16A9, is a transporter that mediates creatine transport across the transmembrane. Previously, we reported that hMCT9 is an extracellular pH- and Na+-sensitive creatine transporter with two kinetic components. Recently, some variants of hMCT9 have been found to be associated with serum uric acid levels, hyperuricemia, and gout. Among these, two single-nucleotide polymorphisms (SNPs) have also been reported: rs550527563 (L93M) and rs2242206 (T258K). However, the effect of these SNPs on hMCT9 transport activity remains unclear. This study aimed to determine the influence of hMCT9 L93M and T258K on transport characteristics.

MAIN METHODS

hMCT9 L93M and T258K were constructed by site-directed mutagenesis and expressed in Xenopus laevis oocyte. Transport activity of uric acid and creatine via hMCT9 were measured by using a Xenopus laevis oocyte heterologous expression system.

KEY FINDINGS

We assessed the transport activity of uric acid and creatine, and observed that hMCT9-expressing oocytes transported uric acid approximately 3- to 4-fold more than water-injected oocytes. hMCT9 L93M slightly reduced the transport activity of creatine, whereas hMCT9 T258K did not affect the transport activity. Interestingly, hMCT9 T258K abolished Na+ sensitivity and altered the substrate affinity from two components to one.

SIGNIFICANCE

In conclusion, hMCT9 SNPs affect transport activity and characteristics. hMCT9 L93M and T258K may induce dysfunction and contribute to pathologies such as hyperuricemia and gout. This is a first study to evaluate molecular characteristics of hMCT9 SNPs.

Emerging Urate-Lowering Drugs and Pharmacologic Treatment Strategies for Gout: A Narrative Review

Hyperuricemia with consequent monosodium urate crystal deposition leads to gout, characterized by painful, incapacitating inflammatory arthritis flares that are also associated with increased cardiovascular event and related mortality risk. This narrative review focuses on emerging pharmacologic urate-lowering treatment (ULT) and management strategies in gout. Undertreated, gout can progress to palpable tophi and joint damage. In oral ULT clinical trials, target serum urate of < 6.0 mg/dL can be achieved in ~ 80-90% of subjects, with flare burden reduction by 1-2 years. However, real-world ULT results are far less successful, due to both singular patient nonadherence and prescriber undertreatment, particularly in primary care, where most patients are managed. Multiple dose titrations commonly needed to optimize first-line allopurinol ULT monotherapy, and substantial potential toxicities and other limitations of approved, marketed oral monotherapy ULT drugs, promote hyperuricemia undertreatment. Common gout comorbidities with associated increased mortality (e.g., moderate-severe chronic kidney disease [CKD], type 2 diabetes, hypertension, atherosclerosis, heart failure) heighten ULT treatment complexity and emphasize unmet needs for better and more rapid clinically significant outcomes, including attenuated gout flare burden. The gout drug armamentarium will be expanded by integrating sodium-glucose cotransporter-2 (SGLT2) inhibitors with uricosuric and anti-inflammatory properties as well as clinically indicated antidiabetic, nephroprotective, and/or cardioprotective effects. The broad ULT developmental pipeline is loaded with multiple uricosurics that selectively target uric acid transporter 1 (URAT1). Evolving ULT approaches include administering selected gut anaerobic purine degrading bacteria (PDB), modulating intestinal urate transport, and employing liver-targeted xanthine oxidoreductase mRNA knockdown. Last, emerging measures to decrease the immunogenicity of systemically administered recombinant uricases should simplify treatment regimens and further improve outcomes in managing the most severe gout phenotypes.

Familial Risk of Gout and Interaction With Obesity and Alcohol Consumption: A Population-Based Cohort Study in Korea

OBJECTIVE

Population-based studies of the familial aggregation of gout are scarce, and gene/environment interactions are not well studied. This study was undertaken to evaluate the familial aggregation of gout as well as assess interactions between family history and obesity or alcohol consumption on the development of gout.

METHODS

Using the Korean National Health Insurance database, which includes information regarding familial relationships and risk factor data, we identified 5,524,403 individuals from 2002 to 2018. Familial risk was calculated using hazard ratios (HRs) with 95% confidence intervals (95% CIs) to compare the risk in individuals with and those without affected first-degree relatives. Interactions between family history and obesity/alcohol consumption were assessed on an additive scale using the relative excess risk due to interaction (RERI).

RESULTS

Individuals with a gout-affected first-degree relative had a 2.42-fold (95% CI 2.39, 2.46) increased risk of disease compared to those with unaffected first-degree relatives. Having both a family history of gout and being either overweight or having moderate alcohol consumption was associated with a markedly increased risk of disease, with HRs of 4.39 (95% CI 4.29, 4.49) and 2.28 (95% CI 2.22, 2.35), respectively, which exceeded the sum of their individual risks but was only statistically significant in overweight individuals (RERI 0.96 [95% CI 0.85, 1.06]). Obese individuals (RERI 1.88 [95% CI 1.61, 2.16]) and heavy drinkers (RERI 0.36 [95% CI 0.20, 0.52]) had a more prominent interaction compared to overweight individuals and moderate drinkers, suggesting a dose-response interaction pattern.

CONCLUSION

Our findings indicate the possibility of an interaction between gout-associated genetic factors and obesity/alcohol consumption.

Susceptibility genes of hyperuricemia and gout

Gout is a chronic metabolic disease that seriously affects human health. It is also a major challenge facing the world, which has brought a heavy burden to patients and society. Hyperuricemia (HUA) is the most important risk factor for gout. In recent years, with the improvement of living standards and the change of dietary habits, the incidence of gout in the world has increased dramatically, and gradually tends to be younger. An increasing number of studies have shown that gene mutations may play an important role in the development of HUA and gout. Therefore, we reviewed the existing literature and summarized the susceptibility genes and research status of HUA and gout, in order to provide reference for the early diagnosis, individualized treatment and the development of new targeted drugs of HUA and gout.

Trends in the Contribution of Genetic Susceptibility Loci to Hyperuricemia and Gout and Associated Novel Mechanisms

Hyperuricemia and gout are complex diseases mediated by genetic, epigenetic, and environmental exposure interactions. The incidence and medical burden of gout, an inflammatory arthritis caused by hyperuricemia, increase every year, significantly increasing the disease burden. Genetic factors play an essential role in the development of hyperuricemia and gout. Currently, the search on disease-associated genetic variants through large-scale genome-wide scans has primarily improved our understanding of this disease. However, most genome-wide association studies (GWASs) still focus on the basic level, whereas the biological mechanisms underlying the association between genetic variants and the disease are still far from well understood. Therefore, we summarized the latest hyperuricemia- and gout-associated genetic loci identified in the Global Biobank Meta-analysis Initiative (GBMI) and elucidated the comprehensive potential molecular mechanisms underlying the effects of these gene variants in hyperuricemia and gout based on genetic perspectives, in terms of mechanisms affecting uric acid excretion and reabsorption, lipid metabolism, glucose metabolism, and nod-like receptor pyrin domain 3 (NLRP3) inflammasome and inflammatory pathways. Finally, we summarized the potential effect of genetic variants on disease prognosis and drug efficacy. In conclusion, we expect that this summary will increase our understanding of the pathogenesis of hyperuricemia and gout, provide a theoretical basis for the innovative development of new clinical treatment options, and enhance the capabilities of precision medicine for hyperuricemia and gout treatment.

A machine learning-assisted model for renal urate underexcretion with genetic and clinical variables among Chinese men with gout

OBJECTIVES

The objective of this study was to develop and validate a prediction model for renal urate underexcretion (RUE) in male gout patients.

METHODS

Men with gout enrolled from multicenter cohorts in China were analyzed as the development and validation data sets. The RUE phenotype was defined as fractional excretion of uric acid (FE_UA) <5.5%. Candidate genetic and clinical features were screened by the least absolute shrinkage and selection operator (LASSO) with 10-fold cross-validation. Machine learning algorithms (stochastic gradient descent (SGD), logistic regression, support vector machine) were performed to construct a predictive classifier of RUE. Models were assessed by the area under the receiver operating characteristic curve (AUC) and the precision-recall curve (PRC).

RESULTS

One thousand two hundred thirty-eight and two thousand twenty-three patients were enrolled as the development and validation cohorts, with 1220 and 754 randomly chosen patients genotyped, respectively. Rs3775948.GG of SLC2A9/GLUT9, rs504915.AA of NRXN2/URAT1, and 7 clinical features (age, hypertension, nephrolithiasis, blood glucose, serum urate, urea nitrogen, and creatinine) were generated by LASSO. Two additional SNP variants (rs2231142.GG of ABCG2 and rs11231463.GG of SLC22A9/OAT7) were selected based on their contributions to gout in the development cohort and their reported effects on renal urate handling. The optimized classifiers yielded AUCs of ~0.914 and PRCs of ~0.980 using these 11 variables. The SGD model was conducted in the validation cohort with an AUC of 0.899 and the PRC of 0.957.

CONCLUSIONS

A prediction model for RUE composed of four SNPs and readily accessible clinical features was established with acceptable accuracy for men with gout.