Clinical evidence for the influence of uric acid on hypertension, cardiovascular disease, and kidney disease: A statistical modeling perspective

Antihyperuricemic effects of thiadiazolopyrimidin-5-one analogues in oxonate treated rats

Hyperuricemia is a risk factor for not only gout, but also to a variety of disorders that affect the vital organ systems of the human body. The xanthine oxidase (XO) is the key enzyme in the production of uric acid and its inhibition can inhibit hyperuricemia. Although, XO inhibitor allopurinol is widely prescribed antigout agent but its use is not without any side effects. Previously, we described the synthesis of four novel thiadiazolopyrimidin-5-one analogues as effective XO inhibitors and molecular docking studies also confirmed this. When these analogues were tested in potassium oxonate treated rats, their serum uric acid and creatinine levels were dropped significantly from 4.85±0.03 mg/dl to 1.21±0.01 mg/dl and 0.92±0.02 mg/dl to 0.40±0.02 mg/dl respectively. Among the pyrimidine analogues tested, 6a was most potent. Histological examinations of both liver and kidney tissues exhibited severe necrosis in oxonate treated rats and pyrimidine analogues could significantly attenuate this with a correlative inhibitory profile of hepatic XO from the same rats. Our results demonstrate antihyperuricemic effect of novel thiadiazolopyrimidin-5-one analogues in oxonate treated rats, which can be further explored not only as antigout therapeutics but also in other systems where hyperuricemia is the driving cause of the disease.

Total saponins from Discorea nipponica makino ameliorate urate excretion in hyperuricemic rats

Objective:

The objective was to study the mechanism of reducing level of the uric acid by rhizoma dioscoreae nipponese.

Materials and Methods:

A total of 40 rats were divided into four groups: A normal group, hyperuricemia group, benzbromarone group (9 mg/kg) and total saponins from rhizoma dioscoreae nipponese (TDN) group (40 mg/kg). Adenine (100 mg/kg) and ethambutol (250 mg/kg) were used to induce hyperuricemic rats. Immunohistochemical and Western blotting methods were used to detect the mRNA and proteins expressions of rat organic anion transporter1 (rOAT1), rat organic anion transporter3 (rOAT3) and rat urate transporter1 (rURAT1) in the kidneys of different groups.

Results:

It was found that the reduced concentration of blood uric acid was due to the enhancement of renal uric acid excretion. It was realized by up-regulating proteins expressions of rOAT1 and rOAT3 and down-regulating of rURAT1.

Conclusion:

The findings suggested that there were uricosuric effects of TDN by regulating renal organic ion transporters in hyperuricemic animals. Altogether, TDN may be a good Chinese herb in treating hyperuricemia, even a potential drug for gouty arthritis.

Local cAMP signaling in disease at a glance

The second messenger cyclic AMP (cAMP) operates in discrete subcellular regions within which proteins that synthesize, break down or respond to the second messenger are precisely organized. A burgeoning knowledge of compartmentalized cAMP signaling is revealing how the local control of signaling enzyme activity impacts upon disease. The aim of this Cell Science at a Glance article and the accompanying poster is to highlight how misregulation of local cyclic AMP signaling can have pathophysiological consequences. We first introduce the core molecular machinery for cAMP signaling, which includes the cAMP-dependent protein kinase (PKA), and then consider the role of A-kinase anchoring proteins (AKAPs) in coordinating different cAMP-responsive proteins. The latter sections illustrate the emerging role of local cAMP signaling in four disease areas: cataracts, cancer, diabetes and cardiovascular diseases.

Dietary sugar and artificial sweetener intake and chronic kidney disease: a review

Sugar consumption, especially in the form of fructose, has been hypothesized to cause kidney disease. This review provides an overview of the epidemiologic evidence that sugar consumption increases CKD risk. Research supports a causal role of sugar in several kidney disease risk factors, including increasing serum uric acid levels, diabetes, and obesity. Sugar may also harm the kidney via other mechanisms. There is no evidence that sucrose is any safer for the kidney than high fructose corn syrup (HFCS) because both are similar in composition. To date, 5 epidemiologic studies have directly evaluated the relationship between sugar consumption (in the form of sugar-sweetened beverages) and CKD. Although most studies suggest that the risk of CKD is elevated among consumers of sugar-sweetened beverages, only 2 studies report statistically significant associations. Three studies have also examined diet soda consumption, with two reporting positive and significant associations. Confounding by unmeasured lifestyle factors may play a role in the positive results whereas poor measurement of sugar and artificial sweetener intake could explain null results. Nevertheless, the hypothesis that sugar causes kidney disease remains plausible, and alternative research designs may be needed.

Impact of genetic polymorphisms of SLC2A2, SLC2A5, and KHK on metabolic phenotypes in hypertensive individuals

Objective

In the past few decades, consumption of added sugars has increased dramatically. Studies have linked high sugar intake with increased risk for a number of diseases. Importantly, fructose, a component of sugar, has been linked with the development of features of metabolic syndrome. This study determined if single nucleotide polymorphisms in genes involved in fructose transport (solute carrier family 2 facilitated glucose transporter, member 2 (SLC2A2) and solute carrier family 2 facilitated glucose/fructose transporter, member 5 (SLC2A5)) and metabolism (ketohexokinase (KHK)) affect inter-individual variability in metabolic phenotypes, such as increased serum uric acid levels.

Materials/Methods

The influence of SLC2A2, SLC2A5, and KHK SNPs on metabolic phenotypes was tested in 237 European Americans and 167 African Americans from the Pharmacogenomic Evaluation and Antihypertensive Responses (PEAR) study. Using baseline untreated fasting data, associations were considered significant if p≤0.005. These SNPs were then evaluated for potential replication (p≤0.05) using data from the Genetic Epidemiology of Responses to Antihypertensives (GERA) studies.

Results

SLC2A5 rs5438 was associated with an increase in serum uric acid in European American males. However, we were unable to replicate the association in GERA. The minor allele of SLC2A2 rs8192675 showed an association with lower high-density lipoproteins in European Americans (A/A: 51.0 mg/dL, A/G: 47.0 mg/dL, G/G: 41.5 mg/dL, p = 0.0034) in PEAR. The association between rs8192675 and lower high-density lipoproteins was replicated in the combined European American GERA study samples (A/A: 47.6 mg/dL, A/G: 48.6 mg/dL, G/G: 41.9 mg/dL, p = 0.0315).

Conclusions

The association between SLC2A2 rs8192675 and high-density lipoproteins suggests the polymorphism may play a role in influencing high-density lipoproteins and thus metabolic risk of cardiovascular disease.

Polydatin ameliorates renal injury by attenuating oxidative stress-related inflammatory responses in fructose-induced urate nephropathic mice

A series of studies have recently demonstrated that the oxidative stress, nuclear factor-kappa B (NF-κB) activation and the subsequent coordinated inflammatory responses played an important role in the pathogenesis of urate nephropathy (UN). Polydatin has been suggested to have the properties of anti-oxidative, anti-inflammatory and nephroprotective effects. However, the possible protective and beneficial effects of polydatin on UN are not fully elucidated. Therefore, we investigated the potential beneficial effects and possible mechanisms of polydatin on UN. In this study, polydatin showed inhibitory activities on xanthine oxidase to repress the level of serum uric acid in vivo and in vitro. Further investigations revealed that polydatin displayed little toxic effects and significantly ameliorated the renal function in fructose-induced UN mice. The nephroprotective activities of polydatin was not only due to the effects on remarkably attenuating the oxidative stress induced by uric acid, but also on markedly suppressing the oxidative stress-related inflammatory cascade, including decreasing the expressions of NF-κB p65, COX-2 and iNOS proteins and inhibiting the productions of TNF-α, PGE(2) and IL-1β. These findings elucidated that polydatin exhibited prominent nephroprotective activities and low toxic effects.

Association between SLC2A9 transporter gene variants and uric acid phenotypes in African American and white families

OBJECTIVES

SLC2A9 gene variants associate with serum uric acid in white populations, but little is known about African American populations. Since SLC2A9 is a transporter, gene variants may be expected to associate more closely with the fractional excretion of urate, a measure of renal tubular transport, than with serum uric acid, which is influenced by production and extrarenal clearance.

METHODS

Genotypes of single nucleotide polymorphisms (SNPs) distributed across the SLC2A9 gene were obtained in the Genetic Epidemiology Network of Arteriopathy cohorts. The associations of SNPs with serum uric acid, fractional excretion of urate and urine urate-to-creatinine ratio were assessed with adjustments for age, sex, diuretic use, BMI, homocysteine and triglycerides.

RESULTS

We identified SLC2A9 gene variants that were associated with serum uric acid in 1155 African American subjects (53 SNPs) and 1132 white subjects (63 SNPs). The most statistically significant SNPs in African American subjects (rs13113918) and white subjects (rs11723439) were in the latter half of the gene and explained 2.7 and 2.8% of the variation in serum uric acid, respectively. After adjustment for this SNP in African Americans, 0.9% of the variation in serum uric acid was explained by an SNP (rs1568318) in the first half of the gene. Unexpectedly, SLC2A9 gene variants had stronger associations with serum uric acid than with fractional excretion of urate.

CONCLUSIONS

These findings support two different loci by which SLC2A9 variants affect uric acid levels in African Americans and suggest SLC2A9 variants affect serum uric acid level via renal and extrarenal clearance.

The dual actions of Sanmiao wan as a hypouricemic agent: down-regulation of hepatic XOD and renal mURAT1 in hyperuricemic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Sanmiao wan (SMW) is widely used for the treatment of gout and hyperuricemia in traditional Chinese medicine.

AIM OF THE STUDY

The aim of the present study was to investigate the hypouricemic effects of SMW and its possible mechanism in potassium oxonate-induced hyperuricemic mice.

MATERIALS AND METHODS

SMW at 489, 978 and 1956 mg/kg was orally administered to hyperuricemic and normal mice, and standard drug allopurinol (2.5mg/kg) was served as a positive control. The effects of SMW on serum, urine and liver levels of uric acid, serum levels of creatinine, and activity of hepatic xanthine oxidase (XOD) were measured in mice. Moreover, the effects of SMW on the mRNA and protein levels of hepatic XOD and renal urate transporter 1 (mURAT1) in mice were analyzed by semi-quantitative RT-PCR and Western blotting methods, respectively.

RESULTS

SMW significantly reduced uric acid levels in serum and liver, inhibited hepatic XOD activity, mRNA and protein levels in hyperuricemic mice. Furthermore, SMW could effectively down-regulate renal mURAT1 mRNA and protein levels of hyperuricemic mice. And it reversed oxonate-induced elevation in serum creatinine levels of mice. However, SMW did not show any effects in normal mice.

CONCLUSION

These findings suggested that SMW produced dual hypouricemic actions by suppressing hepatic XOD to reduce uric acid production and down-regulating renal mURAT1 to decrease urate reabsorption and enhance urate excretion in hyperuricemic mice.

Genome-wide linkage analysis for uric acid in families enriched for hypertension

BACKGROUND

Uric acid is heritable and associated with hypertension and insulin resistance. We sought to identify genomic regions influencing serum uric acid in families in which two or more siblings had hypertension.

METHODS

Uric acid levels and microsatellite markers were assayed in the Genetic Epidemiology Network of Arteriopathy (GENOA) cohort (1075 whites and 1333 blacks) and the Hypertension Genetic Epidemiology Network (HyperGEN) cohort (1542 whites and 1627 blacks). Genome-wide linkage analyses of uric acid and bivariate linkage analyses of uric acid with an additional surrogate of insulin resistance were completed. Pathway analysis explored gene sets enriched at loci influencing uric acid.

RESULTS

In the GENOA white cohort, loci influencing uric acid were identified on chromosome 8 at 135 cM [multipoint logarithm of odds score (MLS) = 2.4], on chromosome 9 at 113 cM (MLS = 3.7) and on chromosome 16 at 93 cM (MLS = 2.3), but did not replicate in HyperGEN. At these loci, there was evidence of pleiotropy with other surrogates of insulin resistance and genes in the fructose and mannose metabolism pathway were enriched. In the HyperGEN-black cohort, there was some evidence of a locus for uric acid on chromosome 4 at 135 cM (MLS = 2.4) that had modest replication in GENOA (MLS = 1.2).

CONCLUSIONS

Several novel loci linked to uric acid were identified but none showed clear replication. Widespread diuretic use, a medication that raises uric acid levels, was an important study limitation. Bivariate linkage analyses and pathway analysis were consistent with genes regulating insulin resistance and fructose metabolism contributing to the heritability of uric acid.

Does uric acid provide information about maternal condition and fetal outcome in pregnant women with hypertension?

OBJECTIVE

To evaluate associations between maternal serum uric acid (UA) levels, maternal status, and fetal outcome.

METHODS

Maternal UA, urinary protein-creatinine ratio (P/C), blood pressure (BP), gestational age at delivery, and birth weight were evaluated in hypertensive pregnant women (n = 58). These were divided into two groups: high UA (> or =357 micromol/L) or normal UA (<357 micromol/L).

RESULTS

Maternal diastolic BP and P/C ratio were higher in pregnant women with elevated UA levels. Systolic BP, gestational age and birth weight were not significantly different.

CONCLUSION

UA equal or above 357 micromol/L in pregnant hypertensive women was associated with proteinuria and diastolic BP, but not with fetal outcome.

Uric acid: bystander or culprit in hypertension and progressive renal disease?

In humans, uric acid is the main urinary metabolite of purines. Serum levels are higher compared with other mammalians. Uric acid is an antioxidant and perhaps helps to control blood pressure during a low Na+ diet through stimulation of the renin-angiotensin system. Serum uric acid is also considered a marker of tubular reabsorption and 'effective' circulating blood volume. Moreover, hyperuricemia seems to be a cofactor in Na+ -sensitive hypertension, a marker and possibly itself responsible for microvascular damage through stimulation of the renin-angiotensin system, inhibition of endothelial nitric oxide, and proliferative effects on vascular smooth muscle. As fructose-rich diets increase uric acid levels, hyperuricemia may also play a role in the metabolic syndrome, triggering insulin resistance and hypertension.A number of studies on rats rendered hyperuricemic by administration of uricase inhibitors have recently confirmed induction of arterial hypertension and microvascular injury, particularly in the remnant kidney or in cyclosporine-induced renal fibrosis.

Mutations in the SLC2A9 gene cause hyperuricosuria and hyperuricemia in the dog

Allantoin is the end product of purine catabolism in all mammals except humans, great apes, and one breed of dog, the Dalmatian. Humans and Dalmatian dogs produce uric acid during purine degradation, which leads to elevated levels of uric acid in blood and urine and can result in significant diseases in both species. The defect in Dalmatians results from inefficient transport of uric acid in both the liver and renal proximal tubules. Hyperuricosuria and hyperuricemia (huu) is a simple autosomal recessive trait for which all Dalmatian dogs are homozygous. Therefore, in order to map the locus, an interbreed backcross was used. Linkage mapping localized the huu trait to CFA03, which excluded the obvious urate transporter 1 gene, SLC22A12. Positional cloning placed the locus in a minimal interval of 2.5 Mb with a LOD score of 17.45. A critical interval of 333 kb containing only four genes was homozygous in all Dalmatians. Sequence and expression analyses of the SLC2A9 gene indicated three possible mutations, a missense mutation (G616T;C188F) and two promoter mutations that together appear to reduce the expression levels of one of the isoforms. The missense mutation is associated with hyperuricosuria in the Dalmatian, while the promoter SNPs occur in other unaffected breeds of dog. Verification of the causative nature of these changes was obtained when hyperuricosuric dogs from several other breeds were found to possess the same combination of mutations as found in the Dalmatian. The Dalmatian dog model of hyperuricosuria and hyperuricemia underscores the importance of SLC2A9 for uric acid transport in mammals.

Development of High-specificity Antibodies against Renal Urate Transporters Using Genetic Immunization

Recently three proteins, playing central roles in the bidirectional transport of urate in renal proximal tubules, were identified: two members of the organic anion transporter (OAT) family, OAT1 and OAT3, and a protein that designated renal urate-anion exchanger (URAT1). Antibodies against these transporters are very important for investigating their expressions and functions. With the cytokine gene as a molecular adjuvant, genetic immunization-based antibody production offers several advantages including high specificity and high recognition to the native protein compared with current methods. We fused high antigenicity fragments of the three transporters to the plasmids pBQAP-TT containing T-cell epitopes and flanking regions from tetanus toxin, respectively. Gene gun immunization with these recombinant plasmids and two other adjuvant plasmids, which express granulocyte/ macrophage colony-stimulating factor and FMS-like tyrosine kinase 3 ligand, induced high level immunoglobulin G antibodies, respectively. The native corresponding proteins of URAT1, OAT1 and OAT3, in human kidney can be recognized by their specific antibodies, respectively, with Western blot analysis and immunohistochemistry. Besides, URAT1 expression in Xenopus oocytes can also be recognized by its corresponding antibody with immuno-fluorescence. The successful production of the antibodies has provided an important tool for the study of UA transporters.

Uric acid and the development of hypertension: the normative aging study

Experimental evidence supports a causative role for uric acid in the pathogenesis of hypertension. Prospective studies have variably adjusted for relevant confounders and have been of relatively limited duration. We prospectively examined the relationship between uric acid level and the development of hypertension in the Normative Aging Study, a longitudinal cohort of healthy adult men. Of the 2280 initial men in the Normative Aging Study, 2062 had available information for inclusion in the analysis. Cox proportional hazards model was used to examine the relationship between baseline serum uric acid level and the development of hypertension adjusting for age, body mass index, abdominal circumference, smoking, alcohol, plasma triglycerides, total cholesterol, and plasma glucose. A total of 892 men developed hypertension over a mean of 21.5 years of follow-up. Serum uric acid level independently predicted the development of hypertension in age-adjusted (relative risk [RR]: 1.10; 95% CI: 1.06 to 1.15: P<0.001) and multivariable (RR: 1.05; 95% CI: 1.01 to 1.10; P=0.02) models. Among 1277 men at risk for the development of hypertension at the time of their first serum creatinine measurement, 508 (39.8%) developed hypertension over a mean of 10.3+/-5.5 years of follow-up. Additionally adjusting for calculated glomerular filtration rate in this subset, serum uric acid remained associated with the development of hypertension (RR: 1.06; 95% CI: 1.01 to 1.12; P=0.03). The baseline serum uric acid level is a durable marker of risk for the development of hypertension. The association is independent of elements of the metabolic syndrome, alcohol intake, and renal function.

Alterations of uromodulin biology: a common denominator of the genetically heterogeneous FJHN/MCKD syndrome

Autosomal dominant hyperuricemia, gout, renal cysts, and progressive renal insufficiency are hallmarks of a disease complex comprising familial juvenile hyperuricemic nephropathy and medullary cystic kidney diseases type 1 and type 2. In some families the disease is associated with mutations of the gene coding for uromodulin, but the link between the genetic heterogeneity and mechanism(s) leading to the common phenotype symptoms is not clear. In 19 families, we investigated relevant biochemical parameters, performed linkage analysis to known disease loci, sequenced uromodulin gene, expressed and characterized mutant uromodulin proteins, and performed immunohistochemical and electronoptical investigation in kidney tissues. We proved genetic heterogeneity of the disease. Uromodulin mutations were identified in six families. Expressed, mutant proteins showed distinct glycosylation patterns, impaired intracellular trafficking, and decreased ability to be exposed on the plasma membrane, which corresponded with the observations in the patient's kidney tissue. We found a reduction in urinary uromodulin excretion as a common feature shared by almost all of the families. This was associated with case-specific differences in the uromodulin immunohistochemical staining patterns in kidney. Our results suggest that various genetic defects interfere with uromodulin biology, which could lead to the development of the common disease phenotype. 'Uromodulin-associated kidney diseases' may be thus a more appropriate term for this syndrome.

Uric acid, microalbuminuria and cardiovascular events in high-risk patients

BACKGROUND

Elevated levels of serum uric acid and albuminuria are associated with cardiovascular disease, but the relationships have not consistently been demonstrated to be independent of hypertension, other risk factors, or each other. The purpose of this study was to evaluate people at high risk for cardiovascular disease for the influence of uric acid and microalbuminuria on cardiovascular events.

METHODS

Consecutive consenting patients undergoing elective angiography (n = 316) had coronary artery disease, risk factors, renal function and diuretic use assessed at baseline. Cardiovascular mortality and major clinical events (myocardial infarction, stroke, amputation, and kidney failure) were ascertained over 5 years.

RESULTS

Cardiovascular events occurred in 10% of the patients. Significant correlates (p < 0.05) of cardiovascular events with baseline measures included uric acid > or =5.2 mg/dl, total cholesterol > or =200 mg/dl, severe angiographic coronary artery disease, loop diuretic therapy, and diagnosis of hypertension. A stepwise Cox modeling procedure identified uric acid (p = 0.040), the interaction of hypertension and uric acid (p = 0.029), the interaction of total cholesterol and severe coronary artery disease (p = 0.001) and loop diuretic therapy (p = 0.009) as significant independent predictors of events. Although microalbuminuria was not retained in the final multivariate model, it was associated with poorer cardiovascular disease outcomes. The mean event-free survival for albumin-to-creatinine >30 mg/g was 51 months and for albumin-to-creatinine <30 mg/g the mean was 57 months (p = 0.021).

CONCLUSIONS

Uric acid > or =5.2 mg/dl independently imparted a 3.5-fold increased risk (OR 3.5, 95% CI 1.0-11.9) for cardiovascular death and major clinical events over a 5-year period. Uric acid may be a contributing factor to the progression of atherosclerosis and its complications.

Does asymptomatic hyperuricaemia contribute to the development of renal and cardiovascular disease? An old controversy renewed

Recent studies in both humans and experimental animals have led to renewed interest in uric acid and its association with hypertension, cardiovascular events and renal disease progression. This has also refuelled a longstanding debate regarding the precise role of this ubiquitous breakdown product of purine metabolism in these disease processes. Various lines of evidence suggest that uric acid may have a direct role in the pathogenesis of hypertension and vascular disease. Regardless of this possibility, it is apparent that serum uric acid levels serve as a powerful 'biomarker' or independent predictor of prognosis and outcome in certain renal, cardiovascular and cerebrovascular diseases. Whether these outcomes can be improved by specifically treating asymptomatic hyperuricaemia remains inadequately resolved at this stage. Data from various animal studies suggests that lowering uric acid levels may be of benefit, but the crucial human studies are still lacking. This review will examine some of the recent evidence supporting a causal and contributory role for uric acid in cardiovascular and renal disease. How clarification of the role of uric acid may guide future treatment strategies will also be discussed.