A polymorphism in the major gene regulating serum uric acid associates with clinic SBP and the white-coat effect in a family-based study

Association of serum uric acid levels with blood pressure and the incidence of hypertension in the middle-aged and elderly populations

OBJECTIVE

This study aimed to investigate the relationship between serum uric acid (SUA) levels and hypertension in the middle-aged and elderly populations.

METHODS

The cross-sectional analysis included 13 349 middle-aged and elderly general health checkup examinees without cardiovascular disease. The retrospective cohort analysis included 6659 normotensive participants (mean age: 64.6 years). Participants were divided into three groups based on their SBP/DBP levels: normal (<120/<80 mmHg), high normal (120-129/<80 mmHg), and elevated (130-139/80-89 mmHg), and were classified into three groups based on the results of 75 g oral glucose tolerance test: normoglycemia, prediabetes, and diabetes.

RESULTS

SUA levels were significantly associated with SBP and DBP in this cross-sectional study. Over a mean 6.5-year follow-up period, 2038 participants developed hypertension. According to the SUA quartiles, the incidence of hypertension increased [26.1% in quartile (Q1) (≤4.1 mg/dl), 28.6% in Q2 (4.2-4.9 mg/dl), 32.6% in Q3 (5.0-5.8 mg/dl), 34.9% in Q4 (≥5.9 mg/dl); P for trend <0.001]. In multivariable analyses, SUA levels were positively associated with hypertension incidence only in the normal BP group [Q4 vs. Q1 odds ratio (OR): 1.64, 95% confidence intervals (CIs): 1.11-2.44; Q3 vs. Q1 OR: 1.69, 95% CI: 1.19-2.42] and in the normoglycemic group (Q4 vs. Q1 OR: 1.34, 95% CI: 1.02-1.76; Q3 vs. Q1 OR: 1.36, 95% CI: 1.07-1.74).

CONCLUSION

In the middle-aged and elderly populations, normotensive or normoglycemic individuals with SUA levels at least 5 mg/dl may be potential targets for SUA management to prevent hypertension.

Uric Acid and Hypertension: a Review of Evidence and Future Perspectives for the Management of Cardiovascular Risk

Uric acid is the final product of purine metabolism, and its increased serum levels have been directly involved in the pathogenesis and natural history of hypertension. The relationship between elevated uric acid and hypertension has been proven in both animals and humans, and its relevance is already evident in childhood and adolescent population. The mechanism responsible for blood pressure increase in hyperuricemic subjects is implicating both oxidative stress and intracellular urate activity with a primary involvement of XOR (xanthine-oxidoreductase activity). An increase in the relative risk of hypertension has been confirmed by genetic data and by large meta-analyses of epidemiological data. The effects of urate-lowering treatment on blood pressure control in patients with elevated serum uric acid has been investigated in a small number of reliable studies with a large heterogeneity of patient populations and study designs. However, 2 large meta-analyses suggest a significant effect of urate-lowering treatment on blood pressure, thus confirming the significant relationship between high serum urate and blood pressure. The future research should be focused on a more appropriate identification of patients with cardiovascular hyperuricemia by considering the correct cardiovascular threshold of serum urate, the time-course of uricemia fluctuations, and the identification of reliable markers of urate overproduction that could significantly clarify the clinical and therapeutic implications of the interaction between serum uric acid and hypertension.

Uric Acid and Oxidative Stress-Relationship with Cardiovascular, Metabolic, and Renal Impairment

Background: The connection between uric acid (UA) and renal impairment is well known due to the urate capacity to precipitate within the tubules or extra-renal system. Emerging studies allege a new hypothesis concerning UA and renal impairment involving a pro-inflammatory status, endothelial dysfunction, and excessive activation of renin–angiotensin–aldosterone system (RAAS). Additionally, hyperuricemia associated with oxidative stress is incriminated in DNA damage, oxidations, inflammatory cytokine production, and even cell apoptosis. There is also increasing evidence regarding the association of hyperuricemia with chronic kidney disease (CKD), cardiovascular disease, and metabolic syndrome or diabetes mellitus. Conclusions: Important aspects need to be clarified regarding hyperuricemia predisposition to oxidative stress and its effects in order to initiate the proper treatment to determine the optimal maintenance of UA level, improving patients’ long-term prognosis and their quality of life.

Excess comorbidities in gout: the causal paradigm and pleiotropic approaches to care

Gout is a common hyperuricaemic metabolic condition that leads to painful inflammatory arthritis and a high comorbidity burden, especially cardiometabolic-renal (CMR) conditions, including hypertension, myocardial infarction, stroke, obesity, hyperlipidaemia, type 2 diabetes mellitus and chronic kidney disease. Substantial advances have been made in our understanding of the excess CMR burden in gout, ranging from pathogenesis underlying excess CMR comorbidities, inferring causal relationships from Mendelian randomization studies, and potentially discovering urate crystals in coronary arteries using advanced imaging, to clinical trials and observational studies. Despite many studies finding an independent association between blood urate levels and risk of incident CMR events, Mendelian randomization studies have largely found that serum urate is not causal for CMR end points or intermediate risk factors or outcomes (such as kidney function, adiposity, metabolic syndrome, glycaemic traits or blood lipid concentrations). Although limited, randomized controlled trials to date in adults without gout support this conclusion. If imaging studies suggesting that monosodium urate crystals are deposited in coronary plaques in patients with gout are confirmed, it is possible that these crystals might have a role in the inflammatory pathogenesis of increased cardiovascular risk in patients with gout; removing monosodium urate crystals or blocking the inflammatory pathway could reduce this excess risk. Accordingly, data for CMR outcomes with these urate-lowering or anti-inflammatory therapies in patients with gout are needed. In the meantime, highly pleiotropic CMR and urate-lowering benefits of sodium-glucose cotransporter 2 (SGLT2) inhibitors and key lifestyle measures could play an important role in comorbidity care, in conjunction with effective gout care based on target serum urate concentrations according to the latest guidelines.

Uric Acid Is Not Associated With Blood Pressure Phenotypes and Target Organ Damage According to Blood Pressure Phenotypes

BACKGROUND

Hypertensive patients with increased serum uric acid (SUA) are at increased cardiovascular (CV) risks. Both the European and American hypertension guidelines endorse the utilization of 24 h-ambulatory blood pressure monitoring (24 h-ABPM) for hypertensive patients with increased CV risk. While there is difference in identifying uric acid as a CV risk factor between the European and American guidelines. Therefore, it is unknown whether 24 h-ABPM should be used routinely in hypertensive patients with increased SUA.

METHODS

To address this knowledge gap, we investigated (i) the correlation between SUA and 24 h-ABP; (ii) the association between SUA and blood pressure (BP) phenotypes (controlled hypertension [CH], white-coat uncontrolled hypertension [WCUH], masked uncontrolled hypertension [MUCH], and sustained uncontrolled hypertension [SUCH]); (iii) the association between SUA and target organ damage (TOD: microalbuminuria, left ventricular hypertrophy [LVH], and arterial stiffness) according to BP phenotypes.

RESULTS

In 1,336 treated hypertensive patients (mean age 61.2 and female 55.4%), we found (i) there was no correlation between SUA and 24 h, daytime, and nighttime systolic blood pressure/diastolic blood pressure, respectively; (ii) in reference to CH, SUA increase was not associated WCUH (odds ratio [OR] 0.968, P = 0.609), MUCH (OR 1.026, P = 0.545), and SUCH (OR 1.003, P = 0.943); (iii) the overall prevalence of microalbuminuria, LVH, and arterial stiffness was 2.3%, 16.7%, and 23.2%, respectively. After adjustment for covariates, including age, sex, smoking, body mass index, diabetes mellitus, and estimated glomerular filtration rate, there was no association between SUA and TOD in all BP phenotypes.

CONCLUSIONS

These preliminary findings did not support routine use of 24 h-ABPM in treated hypertensive patients with increased SUA.

Uric Acid and Hypertension: An Update With Recommendations

The association between increased serum urate and hypertension has been a subject of intense controversy. Extracellular uric acid drives uric acid deposition in gout, kidney stones, and possibly vascular calcification. Mendelian randomization studies, however, indicate that serum urate is likely not the causal factor in hypertension although it does increase the risk for sudden cardiac death and diabetic vascular disease. Nevertheless, experimental evidence strongly suggests that an increase in intracellular urate is a key factor in the pathogenesis of primary hypertension. Pilot clinical trials show beneficial effect of lowering serum urate in hyperuricemic individuals who are young, hypertensive, and have preserved kidney function. Some evidence suggest that activation of the renin-angiotensin system (RAS) occurs in hyperuricemia and blocking the RAS may mimic the effects of xanthine oxidase inhibitors. A reduction in intracellular urate may be achieved by lowering serum urate concentration or by suppressing intracellular urate production with dietary measures that include reducing sugar, fructose, and salt intake. We suggest that these elements in the western diet may play a major role in the pathogenesis of primary hypertension. Studies are necessary to better define the interrelation between uric acid concentrations inside and outside the cell. In addition, large-scale clinical trials are needed to determine if extracellular and intracellular urate reduction can provide benefit hypertension and cardiometabolic disease.

Uric acid and cardiometabolic diseases

Hyperuricemia, which has been considered as a cause of gout and nephrolithiasis has recently been suggested to be associated with hypertension, coronary heart disease, heart failure, atrial fibrillation, insulin resistance, and nonalcoholic fatty liver disease. Several clinical and experimental studies have supported uric acid (UA) as an independent risk factor for predicting disease development along with the traditional risk factors. The mechanism by which UA causes cardiometabolic disease has not been fully elucidated to date; however, it has been explained by several hypotheses such as oxidative stress, reduced nitric oxide bioavailability, inflammation, endothelial dysfunction, and so on. Although evidence of the preventive and therapeutic effects of UA lowering therapy on cardiometabolic diseases is still insufficient, it is expected to be considered as a new treatment strategy for such diseases through additional, carefully designed, large-scale clinical studies.

Purine Metabolite Signatures and Type 2 Diabetes: Innocent Bystanders or Actionable Items?

PURPOSE OF REVIEW

This article reviews evidence linking cardiometabolic conditions with changes in purine metabolites, including increased serum uric acid (sUA), and discusses intervention studies that investigated the therapeutic relevance of these associations.

RECENT FINDINGS

Metabolic and epidemiological findings support a correlation between sUA and circulating levels of other purines with insulin resistance (IR) and risk factors for cardiovascular disease (CVD). In addition, increased activity of xanthine oxidoreductase (XOR), the rate-limiting enzyme for UA production, has been detected in tissues targeted by obesity. Yet, inhibition of XOR in pre-clinical and clinical studies generally failed to support a causal role for excess sUA in IR and CVD. The lack of efficacy of XOR inhibitors strongly suggests that UA is a marker of, rather than a direct contributory factor for, cardiometabolic diseases. Validation of the function of other purines will require a paradigm shift, from a "UA-centric" view to a more granular assessment of the entire purine network and its interaction with other pathways.

Association of plasma xanthine oxidoreductase activity with blood pressure affected by oxidative stress level: MedCity21 health examination registry

Xanthine oxidoreductase (XOR) inhibitor administration reduces uric acid and reactive oxygen species (ROS) production, and also lowers blood pressure (BP). However, the associations of plasma XOR activity, uric acid level, and oxidative stress levels with BP remain unclear. This cross-sectional study included 156 subjects (68 males, 88 females) registered in the MedCity21 health examination registry without anti-hypertensive or anti-hyperuricemic agent administration. Plasma XOR activity was measured using our highly sensitive novel assay, which is unaffected by uric acid in the sample. BP was also determined, and serum uric acid and derivative of reactive oxygen metabolites (d-ROMs) levels were simultaneously measured. Median plasma XOR activity, serum uric acid, d-ROMs, and mean arterial pressure (MAP) values were 25.7 pmol/h/mL, 5.4 mg/dL, 305 Carr U, and 89.0 mmHg, respectively. Multiple regression analysis showed that plasma XOR activity (β = 0.211, p = 0.019), but not serum uric acid (β = 0.072, p = 0.502), was significantly associated with MAP. In subjects with lower but not higher d-ROMs level, an independent association of plasma XOR activity with MAP was observed (β = 0.428, p = 0.001 and β = 0.019, p = 0.891, respectively; p for interaction = 0.046). XOR may contribute to the pathophysiology of higher BP through ROS but not uric acid production, especially in patients with lower oxidative stress.

[Hyperuricemia, gout and high cardiovascular risk - how to manage them in clinical practice]

In recent years, the relationship of hyperuricemia and gout with a high risk of cardiovascular disease has been widely discussed. Therefore, it is important to systematically examine patients in order to diagnose comorbidities, among which cardiovascular disease and its complications occupy a leading place and consider mandatory treatment of patients with hyperuricemia and gout with high cardiovascular risk with lowering drugs, which fully reflects the provisions of the latest European recommendations for the management and treatment of patients with gout.

Potential Dangers of Serum Urate-Lowering Therapy

In observational studies, high serum urate levels are associated with adverse outcomes, including mortality. However, the hypothesis that urate-lowering may improve nongout outcomes has not been confirmed by placebo-controlled clinical trials. On the contrary, 7 recent placebo-controlled trials of urate-lowering drugs with different mechanisms of action (uricosuric: lesinurad; xanthine oxidase inhibition: febuxostat; uricase: pegloticase) have observed higher mortality or trends to higher mortality in gout patients, with the largest decreases in serum urate. Because all urate-lowering mechanisms were implicated, this raises safety concerns about urate-lowering itself. Far from unexpected, the higher mortality associated with more intense urate-lowering is in line with the U-shaped association of urate with mortality in some observational studies. Urate accounts for most of the antioxidant capacity of plasma, and strategies to increase urate are undergoing clinical trials in neurological disease. Post hoc analysis of recent trials should explore whether the magnitude of urate-lowering is associated with adverse outcomes, and safety trials are needed before guidelines recommend lowering serum urate below certain thresholds.

Hyperuricemia, Acute and Chronic Kidney Disease, Hypertension, and Cardiovascular Disease: Report of a Scientific Workshop Organized by the National Kidney Foundation

Urate is a cause of gout, kidney stones, and acute kidney injury from tumor lysis syndrome, but its relationship to kidney disease, cardiovascular disease, and diabetes remains controversial. A scientific workshop organized by the National Kidney Foundation was held in September 2016 to review current evidence. Cell culture studies and animal models suggest that elevated serum urate concentrations can contribute to kidney disease, hypertension, and metabolic syndrome. Epidemiologic evidence also supports elevated serum urate concentrations as a risk factor for the development of kidney disease, hypertension, and diabetes, but differences in methodologies and inpacts on serum urate concentrations by even subtle changes in kidney function render conclusions uncertain. Mendelian randomization studies generally do not support a causal role of serum urate in kidney disease, hypertension, or diabetes, although interpretation is complicated by nonhomogeneous populations, a failure to consider environmental interactions, and a lack of understanding of how the genetic polymorphisms affect biological mechanisms related to urate. Although several small clinical trials suggest benefits of urate-lowering therapies on kidney function, blood pressure, and insulin resistance, others have been negative, with many trials having design limitations and insufficient power. Thus, whether uric acid has a causal role in kidney and cardiovascular diseases requires further study.

Uric acid and cardiovascular risk: What genes can say

BACKGROUND

Although the relationship of elevated serum uric acid levels and cardiovascular disease has been established in a great number of studies, the causal relevance of this finding remains ambiguous. An approach to evaluate the causal relevance of biomarkers is to exploit the natural randomised allocation of allelic variation in genes affecting their level, also known as Mendelian randomisation.

AIM

The aim of this paper is to review the current literature regarding serum uric acid levels and cardiovascular and renal disease risk in Mendelian randomisation studies.

METHODS

PubMed and Scopus databases were searched to retrieve Mendelian studies regarding uric acid, hyperuricaemia and cardiovascular risk.

CONCLUSIONS

Genetic evidence based on conventional and novel Mendelian randomisation approaches suggest a modest, if any, causal effect of serum uric acid concentration on the development of cardiovascular disease, suggesting that further study of uric acid genes is needed in order to elucidate the relationship of serum uric acid levels and cardiovascular disease.

Dietary Sodium Modifies Serum Uric Acid Concentrations in Humans

BACKGROUND

Subjects with hypertension are frequently obese or insulin resistant, both conditions in which hyperuricemia is common. Obese and insulin-resistant subjects are also known to have blood pressure that is more sensitive to changes in dietary sodium intake. Whether hyperuricemia is a resulting consequence, moderating or contributing factor to the development of hypertension has not been fully evaluated and very few studies have reported interactions between sodium intake and serum uric acid.

METHODS

We performed further analysis of our randomized controlled clinical trials (Australian New Zealand Clinical Trials Registry #12609000161224 and #12609000292279) designed to assess the effects of modifying sodium intake on concentrations of serum markers, including uric acid. Uric acid and other variables (including blood pressure, renin, and aldosterone) were measured at baseline and 4 weeks following the commencement of low (60 mmol/day), moderate (150 mmol/day), and high (200-250 mmol/day) dietary sodium intake.

RESULTS

The median aldosterone-to-renin ratio was 1.90 [pg/ml]/[pg/ml] (range 0.10-11.04). Serum uric acid fell significantly in both the moderate and high interventions compared to the low sodium intervention. This pattern of response occurred when all subjects were analyzed, and when normotensive or hypertensive subjects were analyzed alone.

CONCLUSIONS

Although previously reported in hypertensive subjects, these data provide evidence in normotensive subjects of an interaction between dietary sodium intake and serum uric acid. As this interaction is present in the absence of hypertension, it is possible it could play a role in hypertension development, and will need to be considered in future trials of dietary sodium intake.

CLINICAL TRIALS REGISTRATION

The trials were registered with the Australian and New Zealand Clinical Trials Registry as ACTRN12609000161224 and ACTRN1260.

Genome-wide association study for white coat effect in Japanese middle-aged to elderly people: The HOMED-BP study

BACKGROUND

White coat effect (WCE), the blood pressure (BP) difference between clinical and non-clinical settings, can lead to clinical problems such as misdiagnosis of hypertension. Etiology of WCE has been still unclear, especially from genetic aspects. The present article investigated association between genome-wide single nucleotide polymorphisms (SNPs) and WCE in patients with essential hypertension.

METHODS

The present cross-sectional analyses were based on 295 Japanese essential hypertensive outpatients aged ≧40 years enrolled in randomized control study, Hypertension Objective Treatment Based on Measurement by Electrical Devices of Blood Pressure (HOMED-BP) study, who were not taking antihypertensive medications before the randomization. Home and clinic BP were measured. WCE was defined by subtracting home BP from clinic BP. Genotyping was conducted with 500K DNA microarray chips. Association between genome-wide SNPs and WCE were analyzed. For replication (p < 10^-4), we analyzed participants from Ohasama study who took no antihypertension medications and whose SNPs were collected.

RESULTS

Genome-wide SNPs were not significantly associated with WCE of systolic and diastolic BP after corrections of multiple comparisons (p < 2 × 10^-7). We found suggestive SNPs associated with WCE of systolic and diastolic BP (p < 10^-4). However, the consistent results were not obtained in the replication study.

CONCLUSION

The present article showed no significant association between genome-wide SNPs and WCE. Since there were several suggestive SNPs associated with WCE, the present study warrants a further study with bigger sample size for investigating the genetic influence on WCE.

Uric acid in the pathogenesis of metabolic, renal, and cardiovascular diseases: A review

The association between uric acid (UA) on one side and systemic hypertension (Htn), dyslipidemia, glucose intolerance, overweight, fatty liver, renal disease and cardiovascular disease (CVD) on the other side is well recognized. However, the causal relationship between UA and these different clinical problems is still debatable. The recent years have witnessed hundreds of experimental and clinical trials that favored the opinion that UA is a probable player in the pathogenesis of these disease entities. These studies disclosed the strong association between hyperuricemia and metabolic syndrome (MS), obesity, Htn, type 2 diabetes mellitus (DM), non-alcoholic fatty liver disease, hypertriglyceridemia, acute kidney injury, chronic kidney disease (CKD), coronary heart disease (CHD), heart failure and increased mortality among cardiac and CKD patients. The association between UA and nephrolithiasis or preeclampsia is a non-debatable association. Recent experimental trials have disclosed different changes in enzyme activities induced by UA. Nitric oxide (NO) synthase, adenosine monophosphate kinase (AMPK), adenosine monophosphate dehydrogenase (AMPD), and nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase are affected by UA. These changes in enzymatic activities can lead to the observed biochemical and pathological changes associated with UA. The recent experimental, clinical, interventional, and epidemiologic trials favor the concept of a causative role of UA in the pathogenesis of MS, renal, and CVDs.

Impact of comorbidities on gout and hyperuricaemia: an update on prevalence and treatment options

Gout, the most prevalent inflammatory arthritis worldwide, is associated with cardiovascular and renal diseases, and is an independent predictor of premature death. The frequencies of obesity, chronic kidney disease (CKD), hypertension, type 2 diabetes, dyslipidaemias, cardiac diseases (including coronary heart disease, heart failure and atrial fibrillation), stroke and peripheral arterial disease have been repeatedly shown to be increased in gout. Therefore, the screening and care of these comorbidities as well as of cardiovascular risk factors are of outmost importance in patients with gout. Comorbidities, especially CKD, and drugs prescribed for their treatment, also impact gout management. Numerous epidemiological studies have shown the association of asymptomatic hyperuricaemia with the above-mentioned diseases and cardiovascular risk factors. Animal studies have also produced a mechanistic approach to the vascular toxicity of soluble urate. However, causality remains uncertain because confounders, reverse causality or common etiological factors might explain the epidemiological results. Additionally, these uncertainties remain unsolved despite recent studies using Mendelian randomisation or therapeutic approaches. Thus, large randomised placebo-controlled trials are still needed to assess the benefits of treating asymptomatic hyperuricaemia.

Serum uric acid levels and multiple health outcomes: umbrella review of evidence from observational studies, randomised controlled trials, and Mendelian randomisation studies

Objective To map the diverse health outcomes associated with serum uric acid (SUA) levels.Design Umbrella review.Data sources Medline, Embase, Cochrane Database of Systematic Reviews, and screening of citations and references.Eligibility criteria Systematic reviews and meta-analyses of observational studies that examined associations between SUA level and health outcomes, meta-analyses of randomised controlled trials that investigated health outcomes related to SUA lowering treatment, and Mendelian randomisation studies that explored the causal associations of SUA level with health outcomes.Results 57 articles reporting 15 systematic reviews and144 meta-analyses of observational studies (76 unique outcomes), 8 articles reporting 31 meta-analyses of randomised controlled trials (20 unique outcomes), and 36 articles reporting 107 Mendelian randomisation studies (56 unique outcomes) met the eligibility criteria. Across all three study types, 136 unique health outcomes were reported. 16 unique outcomes in meta-analyses of observational studies had P<10-6, 8 unique outcomes in meta-analyses of randomised controlled trials had P<0.001, and 4 unique outcomes in Mendelian randomisation studies had P<0.01. Large between study heterogeneity was common (80% and 45% in meta-analyses of observational studies and of randomised controlled trials, respectively). 42 (55%) meta-analyses of observational studies and 7 (35%) meta-analyses of randomised controlled trials showed evidence of small study effects or excess significance bias. No associations from meta-analyses of observational studies were classified as convincing; five associations were classified as highly suggestive (increased risk of heart failure, hypertension, impaired fasting glucose or diabetes, chronic kidney disease, coronary heart disease mortality with high SUA levels). Only one outcome from randomised controlled trials (decreased risk of nephrolithiasis recurrence with SUA lowering treatment) had P<0.001, a 95% prediction interval excluding the null, and no large heterogeneity or bias. Only one outcome from Mendelian randomisation studies (increased risk of gout with high SUA levels) presented convincing evidence. Hypertension and chronic kidney disease showed concordant evidence in meta-analyses of observational studies, and in some (but not all) meta-analyses of randomised controlled trials with respective intermediate or surrogate outcomes, but they were not statistically significant in Mendelian randomisation studies.Conclusion Despite a few hundred systematic reviews, meta-analyses, and Mendelian randomisation studies exploring 136 unique health outcomes, convincing evidence of a clear role of SUA level only exists for gout and nephrolithiasis.

Effect of Uric Acid Lowering on Renin-Angiotensin-System Activation and Ambulatory BP: A Randomized Controlled Trial

BACKGROUND AND OBJECTIVES

Higher serum uric acid levels, even within the reference range, are strongly associated with increased activity of the renin-angiotensin system (RAS) and risk of incident hypertension. However, the effect of lowering serum uric acid on RAS activity in humans is unknown, although the data that lowering serum uric acid can reduce BP are conflicting.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a double-blind placebo-controlled trial conducted from 2011 to 2015, we randomly assigned 149 overweight or obese adults with serum uric acid ≥5.0 mg/dl to uric acid lowering with either probenecid or allopurinol, or to placebo. The primary endpoints were kidney-specific and systemic RAS activity. Secondary endpoints included mean 24-hour systolic BP, mean awake and asleep BP, and nocturnal dipping.

RESULTS

Allopurinol and probenecid markedly lowered serum uric acid after 4 and 8 weeks compared with placebo (mean serum uric acid in allopurinol, probenecid, and placebo at 8 weeks was 2.9, 3.5, and 5.6 mg/dl, respectively). The change in kidney-specific RAS activity, measured as change in the median (interquartile range) renal plasma flow response to captopril (in ml/min per 1.73 m2) from baseline to 8 weeks, was -4 (-25 to 32) in the probenecid group (P=0.83), -4 (-16 to 9) in the allopurinol group (P=0.32), and 1 (-21 to 17) in the placebo group (P=0.96), with no significant treatment effect (P=0.77). Similarly, plasma renin activity and plasma angiotensin II levels did not significantly change with treatment. The change in mean (±SD) 24-hour systolic BPs from baseline to 8 weeks was -1.6±10.1 with probenecid (P=0.43), -0.4±6.1 with allopurinol (P=0.76), and 0.5±6.0 with placebo (P=0.65); there was no significant treatment effect (P=0.58). Adverse events occurred in 9%, 12%, and 2% of those given probenecid, allopurinol, or placebo, respectively.

CONCLUSIONS

In contrast to animal experiments and observational studies, this randomized, placebo-controlled trial found that uric acid lowering had no effect on kidney-specific or systemic RAS activity after 8 weeks or on mean systolic BP. These data do not support the hypothesis that higher levels of uric acid are a reversible risk factor for increased BP.

Opposing effects of sodium intake on uric acid and blood pressure and their causal implication

Reducing uric acid is hypothesized to lower blood pressure, although evidence is inconsistent. In this ancillary of the DASH-Sodium trial, we examined whether sodium-induced changes in serum uric acid (SUA) were associated with changes in blood pressure. One hundred and three adults with prestage or stage 1 hypertension were randomly assigned to receive either the DASH diet or a control diet (typical of the average American diet) and were fed each of the three sodium levels (low, medium, and high) for 30 days in random order. Body weight was kept constant. SUA was measured at baseline and following each feeding period. Participants were 55% women and 75% black. Mean age was 52 (SD, 10) years, and mean SUA at baseline was 5.0 (SD, 1.3) mg/dL. Increasing sodium intake from low to high reduced SUA (-0.4 mg/dL; P < .001) but increased systolic (4.3 mm Hg; P < .001) and diastolic blood pressure (2.3 mm Hg; P < .001). Furthermore, changes in SUA were independent of changes in systolic (P = .15) and diastolic (P = .63) blood pressure, regardless of baseline blood pressure, baseline SUA, and randomized diet, as well as sodium sensitivity. Although both SUA and blood pressure were influenced by sodium, a common environmental factor, their effects were in opposite directions and were unrelated to each other. These findings do not support a consistent causal relationship between SUA and BP.

Serum uric acid and acute kidney injury: A mini review

Acute kidney injury causes great morbidity and mortality in both the community and hospital settings. Understanding the etiological factors and the pathophysiological principles resulting in acute kidney injury is essential in prompting appropriate therapies. Recently hyperuricemia has been recognized as a potentially modifiable risk factor for acute kidney injury, including that associated with cardiovascular surgery, radiocontrast administration, rhabdomyolysis, and associated with heat stress. This review discussed the evidence that repeated episodes of acute kidney injury from heat stress and dehydration may also underlie the pathogenesis of the chronic kidney disease epidemic that is occurring in Central America (Mesoamerican nephropathy). Potential mechanisms for how uric acid might contribute to acute kidney injury are also discussed, including systemic effects on renal microvasculature and hemodynamics, and local crystalline and noncrystalline effects on the renal tubules. Pilot clinical trials also show potential benefits of lowering uric acid on acute kidney injury associated with a variety of insults. In summary, there is mounting evidence that hyperuricemia may have a significant role in the development of acute kidney injury. Prospective, placebo controlled, randomized trials are needed to determine the potential benefit of uric acid lowering therapy on kidney and cardio-metabolic diseases.

Functional Regression Models for Epistasis Analysis of Multiple Quantitative Traits

To date, most genetic analyses of phenotypes have focused on analyzing single traits or analyzing each phenotype independently. However, joint epistasis analysis of multiple complementary traits will increase statistical power and improve our understanding of the complicated genetic structure of the complex diseases. Despite their importance in uncovering the genetic structure of complex traits, the statistical methods for identifying epistasis in multiple phenotypes remains fundamentally unexplored. To fill this gap, we formulate a test for interaction between two genes in multiple quantitative trait analysis as a multiple functional regression (MFRG) in which the genotype functions (genetic variant profiles) are defined as a function of the genomic position of the genetic variants. We use large-scale simulations to calculate Type I error rates for testing interaction between two genes with multiple phenotypes and to compare the power with multivariate pairwise interaction analysis and single trait interaction analysis by a single variate functional regression model. To further evaluate performance, the MFRG for epistasis analysis is applied to five phenotypes of exome sequence data from the NHLBI’s Exome Sequencing Project (ESP) to detect pleiotropic epistasis. A total of 267 pairs of genes that formed a genetic interaction network showed significant evidence of epistasis influencing five traits. The results demonstrate that the joint interaction analysis of multiple phenotypes has a much higher power to detect interaction than the interaction analysis of a single trait and may open a new direction to fully uncovering the genetic structure of multiple phenotypes.

The widely used statistical methods test interaction for single phenotype. However, we often observe pleotropic genetic interaction effects. The simultaneous gene-gene (GxG) interaction analysis of multiple complementary traits will increase statistical power to detect GxG interactions. Although GxG interactions play an important role in uncovering the genetic structure of complex traits, the statistical methods for detecting GxG interactions in multiple phenotypes remains less developed owing to its potential complexity. Therefore, we extend functional regression model from single variate to multivariate for simultaneous GxG interaction analysis of multiple correlated phenotypes. Large-scale simulations are conducted to evaluate Type I error rates for testing interaction between two genes with multiple phenotypes and to compare power with traditional multivariate pair-wise interaction analysis and single trait interaction analysis by a single variate functional regression model. To further evaluate performance, the MFRG for interaction analysis is applied to five phenotypes of exome sequence data from the NHLBI’s Exome Sequencing Project (ESP) to detect pleiotropic GxG interactions. 267 pairs of genes that formed a genetic interaction network showed significant evidence of interactions influencing five traits.

Serum uric acid and the risk of cardiovascular and renal disease

Substantial evidence suggests that chronic hyperuricemia is an independent risk factor for hypertension, metabolic syndrome, chronic kidney disease (CKD) and cardiovascular diseases. This highlights the need for greater attention to serum uric acid levels when profiling patients, and suggests that the threshold above which uricemia is considered abnormal is 6  mg/dl, in light of the available evidence. Another important question is whether lowering serum uric acid can improve cardiovascular and renal outcomes, and what therapeutic mechanism of action could provide more clinical benefits to patients; the available literature shows a trend toward improvement associated with administration of urate-lowering drugs, in particular for the xanthine oxidase inhibitors. The demonstrated efficacy of urate-lowering therapy on outcomes other than gout flares leads to the consideration that treatment may be beneficial even in the absence of overt gout when hyperuricemia accompanies other clinical conditions, such as urate deposition, advanced CKD or cardiovascular risk factors.

Uric acid in metabolic syndrome: From an innocent bystander to a central player

Uric acid, once viewed as an inert metabolic end-product of purine metabolism, has been recently incriminated in a number of chronic disease states, including hypertension, metabolic syndrome, diabetes, non-alcoholic fatty liver disease, and chronic kidney disease. Several experimental and clinical studies support a role for uric acid as a contributory causal factor in these conditions. Here we discuss some of the major mechanisms linking uric acid to metabolic and cardiovascular diseases. At this time the key to understanding the importance of uric acid in these diseases will be the conduct of large clinical trials in which the effect of lowering uric acid on hard clinical outcomes is assessed. Elevated uric acid may turn out to be one of the more important remediable risk factors for metabolic and cardiovascular diseases.

A genetic marker of hyperuricemia predicts cardiovascular events in a meta-analysis of three cohort studies in high risk patients

INTRODUCTION

The strongest genetic marker of uric acid levels, the rs734553 SNP in the GLUT9 urate transporter gene, predicts progression to kidney failure in CKD patients and associates with systolic BP and carotid intima media thickness in family-based studies.

METHODS

Since genes are transmitted randomly (Mendelian randomization) we used this gene polymorphism as an unconfounded research instrument to further explore the link between uric acid and cardiovascular disease (cardiovascular death, and non-fatal myocardial infarction and stroke) in a meta-analysis of three cohort studies formed by high risk patients (MAURO: 755 CKD patients; GHS: 353 type 2 diabetics and coronary artery disease and the TVAS: 119 patients with myocardial infarction).

RESULTS

In separate analyses of the three cohorts, the incidence rate of CV events was higher in patients with the rs734553 risk (T) allele (TT/GT) than in those without (GG patients) and the HR in TT/GT patients in the three cohorts (range 1.72-2.14) coherently signaled an excessive cardiovascular risk with no heterogeneity (I2 = 0.01). The meta-analytical estimate (total number of patients, n = 1227; total CV events, n = 222) of the HR for the combined end-point in TT/GT patients was twice higher (pooled HR: 2.04, 95% CI: 1.11-3.75, P = 0.02) than in GG homozygotes.

CONCLUSIONS

The T allele of the rs734553 polymorphism in the GLUT9 gene predicts a doubling in the risk for incident cardiovascular events in patients at high cardiovascular risk. Findings in this study are compatible with the hypothesis of a causal role of hyperuricemia in cardiovascular disease in high risk conditions.

A Mendelian Randomization Study of Circulating Uric Acid and Type 2 Diabetes

We aimed to investigate the causal effect of circulating uric acid concentrations on type 2 diabetes risk. A Mendelian randomization study was performed using a genetic score with 24 uric acid-associated loci. We used data of the European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct case-cohort study, comprising 24,265 individuals of European ancestry from eight European countries. During a mean (SD) follow-up of 10 (4) years, 10,576 verified incident case subjects with type 2 diabetes were ascertained. Higher uric acid was associated with a higher diabetes risk after adjustment for confounders, with a hazard ratio (HR) of 1.20 (95% CI 1.11, 1.30) per 59.48 µmol/L (1 mg/dL) uric acid. The genetic score raised uric acid by 17 µmol/L (95% CI 15, 18) per SD increase and explained 4% of uric acid variation. By using the genetic score to estimate the unconfounded effect, we found that a 59.48 µmol/L higher uric acid concentration did not have a causal effect on diabetes (HR 1.01 [95% CI 0.87, 1.16]). Including data from the Diabetes Genetics Replication And Meta-analysis (DIAGRAM) consortium, increasing our dataset to 41,508 case subjects with diabetes, the summary odds ratio estimate was 0.99 (95% CI 0.92, 1.06). In conclusion, our study does not support a causal effect of circulating uric acid on diabetes risk. Uric acid-lowering therapies may therefore not be beneficial in reducing diabetes risk.

The discovery of hypertension: evolving views on the role of the kidneys, and current hot topics

Primary hypertension is increasingly common and is associated with significant morbidity. Here, we review the history of its discovery and rise during the last century with an emphasis on studies trying to identify its cause. Early studies identified a defect in sodium excretion by the kidney as being central to the pathogenesis. Recent studies have focused on a variety of genetic, congenital (fetal programming), and acquired mechanisms for causing the defect in natriuresis. Certain risk factors are apparent, including genetic polymorphisms that regulate sodium excretion, a congenital reduction in nephron number, obesity and hyperleptinemia, an elevated sympathetic nervous system, diet (salt and fructose), and metabolic (hyperuricemia) mechanisms. The kidney shows evidence for renal arteriolar vasoconstriction, an intrarenal inflammatory response, local oxidative stress, and intrarenal activation of the renin-angiotensin system. Recent studies suggest that intrarenal T cells have an important role in causing hypertension to be persistent, likely due to the induction of a local autoimmune response to neoantigens such as heat shock protein 70 and protein aggregates formed by isoketals resulting from lipid peroxidation. Salt retention due to impairment in pressure-diuresis leads to the release of cardiotonic steroids and central nervous system effects that cause systemic vasoconstriction and a rise in blood pressure. Some recent studies suggest that salt may increase blood pressure not simply by effects on extracellular volume but rather as a consequence of hyperosmolarity. These new insights could lead to new approaches for the prevention and treatment of this important disease.

Association of Uric Acid Genetic Risk Score With Blood Pressure

High levels of serum uric acid are associated with hypertension in observational studies. The aim of this study was to investigate the association of uric acid gene variants with blood pressure. We studied 5791 participants aged ≥55 years from the Rotterdam Study. Thirty gene variants identified for serum uric acid level were used to compile genetic risk score (GRS). We used linear regression models to investigate the association of the uric acid GRS with systolic and diastolic blood pressure in the whole study population and separately in participants with and without comorbidities and medication use. In the age- and sex-adjusted model, each SD increase in uric acid GRS was associated with 0.75 mm Hg lower systolic blood pressure (95% confidence interval, −1.31 to −0.19) and 0.42 mm Hg lower diastolic blood pressure (95% confidence interval, −0.72 to −0.13). The association did not attenuate after further adjustment for antihypertensive medication use and conventional cardiovascular risk factors. In subgroup analysis, the association of uric acid GRS with systolic blood pressure was significantly stronger in participants (n=885) on diuretic treatment ( P for interaction, 0.007). In conclusion, we found that higher uric acid GRS is associated with lower systolic and diastolic blood pressure. Diuretics treatment may modify the association of uric acid genetic risk score and systolic blood pressure. Our study suggests that genome wide association study’s findings can be associated with an intermediate factor or have a pleiotropic role and, therefore, should be applied for Mendelian Randomization with caution.