Treating Hyperuricemia: The Last Word Hasn't Been Said Yet

The Results of the URRAH (Uric Acid Right for Heart Health) Project: A Focus on Hyperuricemia in Relation to Cardiovascular and Kidney Disease and its Role in Metabolic Dysregulation

The relationship between Serum Uric Acid (UA) and Cardiovascular (CV) diseases has already been extensively evaluated, and it was found to be an independent predictor of all-cause and cardiovascular mortality but also acute coronary syndrome, stroke and heart failure. Similarly, also many papers have been published on the association between UA and kidney function, while less is known on the role of UA in metabolic derangement and, particularly, in metabolic syndrome. Despite the substantial number of publications on the topic, there are still some elements of doubt: (1) the better cut-off to be used to refine CV risk (also called CV cut-off); (2) the needing for a correction of UA values for kidney function; and (3) the better definition of its role in metabolic syndrome: is UA simply a marker, a bystander or a key pathological element of metabolic dysregulation?. The Uric acid Right for heArt Health (URRAH) project was designed by the Working Group on uric acid and CV risk of the Italian Society of Hypertension to answer the first question. After the first papers that individuates specific cut-off for different CV disease, subsequent articles have been published responding to the other relevant questions. This review will summarise most of the results obtained so far from the URRAH research project.

Non-Haemodynamic Mechanisms Underlying Hypertension-Associated Damage in Target Kidney Components

Arterial hypertension (AH) is a global challenge that greatly impacts cardiovascular morbidity and mortality worldwide. AH is a major risk factor for the development and progression of kidney disease. Several antihypertensive treatment options are already available to counteract the progression of kidney disease. Despite the implementation of the clinical use of renin-angiotensin aldosterone system (RAAS) inhibitors, gliflozins, endothelin receptor antagonists, and their combination, the kidney damage associated with AH is far from being resolved. Fortunately, recent studies on the molecular mechanisms of AH-induced kidney damage have identified novel potential therapeutic targets. Several pathophysiologic pathways have been shown to play a key role in AH-induced kidney damage, including inappropriate tissue activation of the RAAS and immunity system, leading to oxidative stress and inflammation. Moreover, the intracellular effects of increased uric acid and cell phenotype transition showed their link with changes in kidney structure in the early phase of AH. Emerging therapies targeting novel disease mechanisms could provide powerful approaches for hypertensive nephropathy management in the future. In this review, we would like to focus on the interactions of pathways linking the molecular consequences of AH to kidney damage, suggesting how old and new therapies could aim to protect the kidney.

Role of Uric Acid in Vascular Remodeling: Cytoskeleton Changes and Migration in VSMCs

The mechanisms by which hyperuricemia induces vascular dysfunction and contributes to cardiovascular disease are still debated. Phenotypic transition is a property of vascular smooth muscle cells (VSMCs) involved in organ damage. The aim of this study was to investigate the effects of uric acid (UA) on changes in the VSMC cytoskeleton, cell migration and the signals involved in these processes. MOVAS, a mouse VSMC line, was incubated with 6, 9 and 12 mg/dL of UA, angiotensin receptor blockers (ARBs), proteasome and MEK-inhibitors. Migration property was assessed in a micro-chemotaxis chamber and by phalloidin staining. Changes in cytoskeleton proteins (Smoothelin B (SMTB), alpha-Smooth Muscle Actin (αSMA), Smooth Muscle 22 Alpha (SM22α)), Atrogin-1 and MAPK activation were determined by Western blot, immunostaining and quantitative reverse transcription PCR. UA exposition modified SMT, αSMA and SM22α levels (p < 0.05) and significantly upregulated Atrogin-1 and MAPK activation. UA-treated VSMCs showed an increased migratory rate as compared to control cells (p < 0.001) and a re-arrangement of F-actin. Probenecid, proteasome inhibition and ARBs prevented the development of dysfunctional VSMC. This study shows, for the first time, that UA-induced cytoskeleton changes determine an increase in VSMC migratory rate, suggesting UA as a key player in vascular remodeling.

Association between serum uric acid levels and simple renal cyst risk in a nondiabetic population: A nested case-control study

BACKGROUND

Previous studies have found a relationship between hypertension or cardiovascular disease and simple renal cysts (SRCs) in health check-up population, but SRCs incidence is still controversially associated with serum uric acid (SUA) concentration in the nondiabetic participants. In this single-centre nest case-control study, serum uric acid levels were examined in relation to the incidence of SRCs in nondiabetic individuals.

METHOD

Participants who underwent at least two renal ultrasound examinations with an interval of more than 12 months were enrolled. The results of clinical examinations, laboratory tests and abdominal ultrasound tests were recorded for each participant and analysed in this retrospective observation study.

RESULT

A total of 144 control and 144 SRC patients were ultimately confirmed and included in further analysis. Hyperuricaemia (OR 2.846, 95% CI 1.519-5.332, p = 0.001) was significantly correlated with SRC formation according to multivariable analysis. In both the male and female groups, SRC patients had significantly higher serum uric acid levels compared with control subjects. In 54 SRC patients with cyst puncture, the serum uric acid concentration was positively correlated with the uric acid concentration in cyst fluid (r = 0.6144, p < 0.0001). The serum uric acid concentration was positively correlated with the maximum cyst diameter in the SRC patients (r = 0.4531, p < 0.0001).

CONCLUSION

In a nondiabetic population, hyperuricaemia was significantly independently associated with a higher SRCs incidence. In SRC participants with cyst puncture, the SUA level had a significantly positive correlation with the uric acid level in cyst fluid. In SRC patients, the SUA level had a significantly positive correlation with cyst maximum diameter.

Prevalence of Hyperuricemia and Its Association with Cardiovascular Risk Factors and Subclinical Target Organ Damage

The role of uric acid levels in the cardiovascular continuum is not clear. Our objective is to analyze the prevalence of hyperuricemia (HU) and its association with cardiovascular risk factors (CVRF), subclinical target organ damage (sTOD), and cardiovascular diseases (CVD). We evaluated the prevalence of HU in 6.927 patients included in the baseline visit of the IBERICAN study. HU was defined as uric acid levels above 6 mg/dL in women, and 7 mg/dL in men. Using adjusted logistic regression models, the odds ratios were estimated according to CVRF, sTOD, and CVD. The prevalence of HU was 16.3%. The risk of HU was higher in patients with pathological glomerular filtration rate (aOR: 2.92), heart failure (HF) (aOR: 1.91), abdominal obesity (aOR: 1.80), hypertension (HTN) (aOR: 1.65), use of thiazides (aOR: 1.54), left ventricular hypertrophy (LVH) (aOR: 1.36), atrial fibrillation (AFIB) (aOR: 1.29), and albuminuria (aOR: 1.27). On the other hand, being female (aOR: 0.82) showed a reduced risk. The prevalence of HU was higher in men, in patients presenting CVRF such as HTN and abdominal obesity, and with co-existence of LVH, atrial fibrillation (AFIB), HF, and any form of kidney injury. These associations raise the possibility that HU forms part of the early stages of the cardiovascular continuum. This may influence its management in Primary Healthcare because the presence of HU could mean an increased CV risk in the patients.

Chronic kidney disease: Which role for xanthine oxidoreductase activity and products?

The present review explores the role of xanthine oxidoreductase (XOR) in the development and progression of chronic kidney disease (CKD). Human XOR is a multi-level regulated enzyme, which has many physiological functions, but that is also implicated in several pathological processes. The main XOR activities are the purine catabolism, which generates uric acid, and the regulation of cell redox state and cell signaling, through the production of reactive oxygen species. XOR dysregulation may lead to hyperuricemia and oxidative stress, which could have a pathogenic role in the initial phases of CKD, by promoting cell injury, hypertension, chronic inflammation and metabolic derangements. Hypertension is common in CKD patients and many mechanisms inducing it (upregulation of renin-angiotensin-aldosterone system, endothelial dysfunction and atherosclerosis) may be influenced by XOR products. High XOR activity and hyperuricemia are also risk factors for obesity, insulin resistance, type 2 diabetes and metabolic syndrome that are frequent CKD causes. Moreover, CKD is common in patients with gout, which is characterized by hyperuricemia, and in patients with cardiovascular diseases, which are associated with hypertension, endothelial dysfunction and atherosclerosis. Although hyperuricemia is undoubtedly related to CKD, controversial findings have been hitherto reported in patients treated with urate-lowering therapies.

Uric acid and arterial stiffness in children and adolescents: Role of insulin resistance and blood pressure

Several studies describe the association between serum uric acid (SUA) and arterial stiffness in adults. Uric acid contributes through several mechanisms to the increase in blood pressure (BP) and adversely affects the insulin signaling pathway. Moreover, SUA predict the development of hypertension and insulin resistance up to type 2 diabetes. Early arterial stiffening, estimated by carotid-femoral pulse wave velocity (PWV), may already be present in pediatric age. Aim of our study was to investigate the relationship between SUA and PWV in a pediatric population and its interaction with insulin resistance and BP. In 322 children and adolescents (56.2% male, mean age 11.3 [SD 2.8] years), we measured weight, height, waist circumference, BP and PWV. We also assayed SUA and estimated glomerular filtration rate (eGFR) and calculated HOMA-index as a marker of insulin resistance. Simple and multiple regression analyses were performed to assess variables associated with PWV. Mediation models were applied to identify the direct and indirect effects of individual variables on PWV. On univariate analysis, age (p < 0.001), waist circumference-to-height ratio (p = 0.036), systolic and diastolic BP (SBP and DBP) z-score (p < 0.001), heart rate (p = 0.028), SUA (p = 0.002), HOMA-index (p < 0.001), and eGFR (p = 0.014) were significantly associated with PWV. The multiple regression model showed that only age (p = 0.028), SBP z-score (p = 0.006), and heart rate (p = 0.001) were significantly associated with PWV. The results were superimposable when the DBP z-score replaced the SBP z-score in the model. Mediation models showed that the effect of eGFR on PWV was fully mediated by SUA (p = 0.015) and that the effect of SUA on PWV was totally mediated by HOMA-index (p < 0.001). Both SUA (p < 0.01) and HOMA-index (p < 0.01) had a significant association with higher SBP (DBP) z-scores. The double mediation model including both BP and HOMA-index showed that the SUA effect on PWV was totally mediated by both variables (p = 0.005, for HOMA-index, p = 0.004, for SBP z-score and p = 0.007, for combined effect). The results were superimposable when the DBP z-score replaced the SBP z-score in the model. In conclusion, insulin resistance and BP are both important mediators of the association between SUA and vascular stiffness in pediatric age.

SGLT2 Inhibition and Uric Acid Excretion in Patients with Type 2 Diabetes and Normal Kidney Function

Background and objectives: Sodium glucose transporter 2 (SGLT2)-inhibitor-induced uric acid lowering may contribute to kidney protective effects of the drug-class in people with type 2 diabetes. This study investigates mechanisms of plasma uric acid lowering by SGLT2-inhibitors in people with type 2 diabetes with a focus on urate transporter (URAT)1. Methods: We conducted an analysis of two randomized, clinical trials. First, in the Renoprotective Effects of Dapagliflozin in Type 2 Diabetes (RED) study, 44 people with type 2 diabetes were randomized to dapagliflozin or gliclazide for 12 weeks. Plasma uric acid, fractional uric acid excretion and hemodynamic kidney function were measured in the fasted state and during clamped eu- or hyperglycemia. Second, in the Uric Acid Excretion study (UREX) study, 10 people with type 2 diabetes received 1-week empagliflozin, benzbromarone and their combination in a cross-over design and effects on plasma uric acid, fractional uric acid excretion and 24-hr uric acid excretion were measured. Results: In the RED study, compared to the fasted state (5.3±1.1mg/dL), acute hyperinsulinemia and hyperglycemia significantly reduced plasma uric acid by 0.2±0.3 and 0.4±0.3 mg/dL (both p<0.001), while increasing fractional uric acid excretion (by 3.2±3.1% and 8.9±4.5% respectively (both p<0.001). Dapagliflozin reduced plasma uric acid by 0.8±0.8mg/dL, 1.0±1.0mg/dL and by 0.8±0.7mg/dL during fasting, hyperinsulinemic-euglycemic and hyperglycemic conditions (p<0.001), whereas fractional uric acid excretion in 24-hr urine increased by 3.0±2.1% (p<0.001) and 2.6±4.5% during hyperinsulinemic-euglycemic conditions (p=0.003). Fractional uric acid excretion strongly correlated to fractional glucose excretion (r= 0.35, p=0.02). In the UREX study, empagliflozin and benzbromarone both significantly reduced plasma uric acid and increased fractional uric acid excretion. Effects of combination therapy did not differ from benzbromarone monotherapy. Conclusion: In conclusion, SGLT2-inhibitors induce uric acid excretion, which is strongly linked to urinary glucose excretion and which is attenuated during concomitant pharmacological blockade of URAT1.

Uric acid lowering for slowing CKD progression after the CKD-FIX trial: a solved question or still a dilemma?

Hyperuricemia has been associated with several cardiovascular risk factors and is a well-known predictor of kidney disease. In vitro studies as well as animal models highlighted a role for uric acid in the development and progression of haemodynamic and tissue damage at the renal level leading to glomerular and tubulointerstitial abnormalities. Urate-lowering treatment, especially by xanthine oxidase inhibitors, has been proposed in order to improve kidney outcomes. However, recent randomized controlled trials failed to demonstrate a beneficial effect of allopurinol or febuxostat on renal disease, casting doubts on the role of this therapeutical approach to improve nephroprotection. We provide a critical overview of current literature on this topic and offer a possible interpretation of results from recent intervention trials with urate-lowering treatment on renal outcomes.

Serum Uric Acid and Kidney Disease Measures Independently Predict Cardiovascular and Total Mortality: The Uric Acid Right for Heart Health (URRAH) Project

Background: Serum uric acid predicts the onset and progression of kidney disease, and the occurrence of cardiovascular and all-cause mortality. Nevertheless, it is unclear which is the appropriate definition of hyperuricemia in presence of chronic kidney disease (CKD). Our goal was to study the independent impact of uric acid and CKD on mortality. Methods: We retrospectively investigated 21,963 patients from the URRAH study database. Hyperuricemia was defined on the basis of outcome specific cut-offs separately identified by ROC curves according to eGFR strata. The primary endpoints were cardiovascular and all-cause mortality. Results: After a mean follow-up of 9.8 year, there were 1,582 (7.20%) cardiovascular events and 3,130 (14.25%) deaths for all causes. The incidence of cardiovascular and all-cause mortality increased in parallel with reduction of eGFR strata and with progressively higher uric acid quartiles. During 215,618 person-years of follow-up, the incidence rate for cardiovascular mortality, stratified based on eGFR (>90, between 60 and 90 and <60 ml/min) was significantly higher in patients with hyperuricemia and albuminuria (3.8, 22.1 and 19.1, respectively) as compared to those with only one risk factor or none (0.4, 2.8 and 3.1, respectively). Serum uric acid and eGFR significantly interact in determining cardiovascular and all-cause mortality. For each SUA increase of 1 mg/dl the risk for mortality increased by 10% even after adjustment for potential confounding factors included eGFR and the presence of albuminuria. Conclusions: hyperuricemia is a risk factor for cardiovascular and all-cause mortality additively to eGFR strata and albuminuria, in patients at cardiovascular risk.

Rationale, design, demographics, and baseline characteristics of the randomised, controlled, phase 2b SAPPHIRE study of verinurad plus allopurinol in patients with chronic kidney disease and hyperuricaemia

BACKGROUND

Verinurad is a human uric acid transporter (URAT1) inhibitor known to decrease serum uric acid (sUA) levels and may reduce albuminuria. In a Phase 2a study (NCT03118739), treatment with verinurad + febuxostat lowered urine albumin-to-creatinine ratio (UACR) at 12 weeks by 39% (90% confidence interval: 4%, 62%) among patients with type 2 diabetes mellitus, hyperuricaemia and albuminuria. The Phase 2 b, randomised, placebo-controlled Study of verinurAd and alloPurinol in Patients with cHronic kIdney disease and hyperuRicaEmia (SAPPHIRE; NCT03990363) will examine the effect of verinurad + allopurinol on albuminuria and estimated glomerular filtration rate (eGFR) slope among patients with chronic kidney disease (CKD) and hyperuricaemia.

METHODS

Adults (≥18 years of age) with CKD, eGFR ≥25 mL/min/1.73 m2, UACR 30-5000 mg/g and sUA ≥6.0 mg/dL will be enrolled. Approximately 725 patients will be randomised 1:1:1:1:1 to 12, 7.5 or 3 mg verinurad + allopurinol, allopurinol or placebo. An 8-week dose-titration period will precede a 12-month treatment period; verinurad dose will be increased to 24 mg at month 9 in a subset of patients in the 3 mg verinurad + allopurinol arm. The primary efficacy endpoint is change from baseline in UACR at 6 months. Secondary efficacy endpoints include changes in UACR, eGFR and sUA from baseline at 6 and 12 months.

CONCLUSIONS

This study will assess the combined clinical effect of verinurad + allopurinol on kidney function in patients with CKD, hyperuricaemia and albuminuria, and whether this combination confers renoprotection beyond standard-of-care.