Uric acid induces oxidative stress via an activation of the renin-angiotensin system in 3T3-L1 adipocytes

Relationship between serum uric acid and mortality among hemodialysis patients: Retrospective analysis of Korean end-stage renal disease registry data

Background

It is thought that hyperuricemia might lower the risk of mortality among hemodialysis patients, unlike in the general population, but the evidence is controversial. The aim of the current study was to evaluate the impact of serum uric acid level on the long-term clinical outcomes of hemodialysis patients in Korea.

Methods

Retrospective analysis was performed on data from the End-Stage Renal Disease Registry of the Korean Society of Nephrology. This included data for 7,333 patients (mean age, 61 ± 14 years; 61% male) who received hemodialysis from January 2001 through April 2015. Initial laboratory data were used in the analysis.

Results

The mean serum uric acid level in this study was 7.1 ± 1.7 mg/dL. Body mass index, normalized protein catabolic rate, albumin, and cholesterol were positively correlated with serum uric acid level after controlling for age and sex. After controlling for demographic data, comorbidities, and residual renal function, a higher uric acid level was independently associated with a significantly lower all-cause mortality (hazard ratio [HR], 0.90 per 1 mg/dL increase in uric acid level; 95% confidence interval [CI], 0.83-0.97; P = 0.008), but not cardiovascular mortality (HR, 0.90; 95% CI, 0.80-1.01; P = 0.078). Comparing uric acid levels in the highest and lowest quintiles, the HR for all-cause mortality was 0.65 (95% CI, 0.42-0.99; P = 0.046).

Conclusion

Hyperuricemia was strongly associated with a lower risk of all-cause mortality, but there seems to be no significant association between serum uric acid level and cardiovascular mortality among Korean hemodialysis patients with end-stage renal disease.

Associations of plasma uric acid and purine metabolites with blood pressure in children: the KOALA Birth Cohort Study

OBJECTIVE

Elevated serum uric acid concentration has been associated with high blood pressure (BP) and hypertension. A putative underlying mechanism is the accumulation of reactive oxygen species when uric acid is generated by an increased enzyme activity of xanthine oxidase (XO). The aims of the present study were to investigate the associations between plasma uric acid concentration, purine metabolite ratios, as proxies for increased XO activity, and SBP and DBP in school-age children.

METHODS

Cross-sectional analyses were performed in 246 children (46% boys; mean age 7.1 years) from the Dutch KOALA Birth Cohort Study. Purine metabolites were determined with ultra-performance liquid chromatography-tandem mass spectrometry. During a home visit, a nurse collected a blood sample and measured BP three times; in addition, parents measured their child's BP on three consecutive days, in the morning and evening. Generalized estimating equations were used for analyses while controlling for variables such as sex, age, BMI, physical activity, and dietary intake.

RESULTS

In multivariable analysis, uric acid (per SD of 38 μmol/l) was associated with DBP z-scores [sβ 0.07; confidence interval (CI), 0.01-1.14], but not with SBP z-scores. Higher ratios of uric acid/xanthine (per SD of 138) (sβ 0.09; CI, 0.01-0.17) and xanthine/hypoxanthine (per SD of 321) (sβ 0.08; CI, 0.02-0.17) were associated with higher DBP z-scores, but not with SBP z-scores.

CONCLUSION

In school-age children, uric acid and the ratios of uric acid/xanthine and xanthine/hypoxanthine were significantly associated with DBP z-scores. Suggesting that, both uric acid concentration and increased XO activity are associated with BP.

Hyperuricaemia and risk of nonalcoholic fatty liver disease: A meta-analysis

BACKGROUND

The association between hyperuricaemia and nonalcoholic fatty liver disease (NAFLD), one of the leading causes of cirrhosis worldwide, has been demonstrated in recent epidemiological studies. This meta-analysis was conducted to summarize all available data and to estimate the risk of NAFLD among subjects with hyperuricaemia.

METHODS

Comprehensive literature review was conducted using MEDLINE and EMBASE database through August 2016 to identify studies that compared the risk of NAFLD among subjects with hyperuricaemia vs those with normal uric acid level. Effect estimates from individual study were extracted and combined together using random-effect, generic inverse variance method of DerSimonian and Laird.

RESULTS

Twenty-five studies met the eligibility criteria and were included in the meta-analysis. The risk of NAFLD in subjects with hyperuricaemia was significantly higher than subjects with normal uric acid level with the pooled odds ratio (OR) of 1.97 (95% confidence interval (CI), 1.69-2.29). The heterogeneity between studies of the overall analysis was high with an I² of 87%. Subgroup analysis based on 11 studies that provided data on males subgroup and nine studies that provided data on females subgroup showed that the risk was significantly increased for both sexes with pooled OR of 1.64 (95% CI, 1.40-1.93) among males and pooled OR of 2.21 (95% CI, 1.85-2.64) among females.

CONCLUSIONS

A significantly increased risk of NAFLD among patients with hyperuricaemia was demonstrated in this meta-analysis. Further studies are required to establish the role of uric acid in the pathogenesis of NAFLD.

Close linkage between serum uric acid and cardiac dysfunction in patients with ischemic heart disease according to covariance structure analysis

High serum uric acid (UA) level has been assumed to be a risk factor for left ventricular (LV) dysfunction; however, the precise relationship between these conditions has not been fully examined because many confounding factors are associated with UA level. We herein examined the precise relationship by proposing structural equation models. The study population consisted of 1432 cases with ischemic heart disease who underwent cardiac catheterization. Multiple regression analyses and covariance structure analyses were performed to elucidate the cause-and-effect relationship between UA level and LV ejection fraction (LVEF). A path model exploring the factors contributing to LVEF showed that high UA was a significant cause of reduced LVEF (P = 0.004), independent of other significant factors. The degree of atherosclerosis, as estimated by the number of diseased coronary vessels, was significantly affected by high UA (P = 0.005); and the number of diseased coronary vessels subsequently led to reduced LVEF (P < 0.001). Another path model exploring the factors contributing to UA level showed that LVEF was a significant cause of high UA (P = 0.001), while other risk factors were also independent contributing factors. This study clearly demonstrated that there was a close link between high UA and LV dysfunction, which was represented by possible cause-and-effect relationship.

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.

Gypenosides Inhibits Xanthine Oxidoreductase and Ameliorates Urate Excretion in Hyperuricemic Rats Induced by High Cholesterol and High Fat Food (Lipid Emulsion)

BACKGROUND The aim of this study was to study the effects of gypenosides (GPS) on lowering uric acid (UA) levels in hyperuricemic rats induced by lipid emulsion (LE) and the related mechanisms. GPS are natural saponins extracted from Gynostemma pentaphyllum. MATERIAL AND METHODS Forty-eight male SD rats were randomly divided into six groups: normal, model, two positive controls, and two GPS treated groups (two different doses of GPS). The normal group rats were fed a basic diet, and the other rats were orally pretreated with LE. Urine and blood were collected at regular intervals. Full automatic biochemical analyzer was used to detect the concentration levels of serum UA (SUA), serum creatinine (SCr), BUN, and urine UA (UUA), and urine creatinine (UCr) and fractional excretion of UA (FEUA). ELISA kits were used to detect enzymes activities: xanthine oxidase (XOD), adenosime deaminase (ADA), guanine deaminase (GDA), and xanthine dehydrogenase (XDH). Immunohistochemistry was used to observe kidney changes and protein (URAT1, GLUT9, and OAT1) expression levels. RT-PCR was used to detect the relevant mRNA expression levels. RESULTS Treatment with GPS significantly reduced the SUA, prevented abnormal weight loss caused by LE, and improved kidney pathomorphology. Treatment with GPS also decreased the levels of XOD, ADA, and XDH expression, increased the kidney index and FEUA, downregulated URAT1 and GLUT9 expression and upregulated OAT1 expression in the kidney. CONCLUSIONS GPS may be an effective treatment for hyperuricemia via a decrease in xanthine oxidoreductase through the XOD/XDH system; and via an increase in urate excretion through regulating URAT1, GLUT9, and OAT1 transporters.

Role of γ-glutamyl transferase levels in prediction of high cardiovascular risk among patients with non-alcoholic fatty liver disease

BACKGROUND & OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) is an important cause of elevated liver functions. There is evidence showing an association between NAFLD and subclinical atherosclerosis independent of traditional risk factors. We undertook this retrospective study to determine the association of Framingham cardiovascular risk scoring system with liver function tests and inflammatory markers and to find the role of liver function tests in determination of CVD risk among non-obese and non-diabetic subjects with non-alcoholic fatty liver disease.

METHODS

A total of 2058 patients were included in the study. Framingham cardiovascular risk scoring was done of all patients according to the age, gender, systolic blood pressure, serum total cholesterol and HDL cholesterol levels, smoking and antihypertensive medication history. Liver function test, lipid profile, insulin, uric acid, ferritin levels, etc. were determined.

RESULTS

According to the ultrasonography findings, patients were grouped as without any fatty infiltration of the liver (control group) (n=982), mild (n= 473), moderate (n=363) and severe fatty liver disease (n= 240) groups. In severe fatty liver disease group, the mean Framingham cardiovascular risk score was significantly higher than that of other groups. t0 here was a positive correlation between GGT, uric acid and ferritin levels with Framingham cardiovascular score. In multivariate analysis, high GGT levels were positively associated with high-risk disease presence (OR: 3.02, 95% CI: 2.62-3.42) compared to low GGT levels independent of the age and sex.

INTERPRETATION & CONCLUSIONS

Cardiovascular disease risk increases with the presence and stage of fatty liver disease. Our findings showed a positive correlation between elevated GGT levels and Framingham cardiovascular risk scoring system among non-diabetic, non-obese adults which could be important in clinical practice. Though in normal limits, elevated GGT levels among patients with fatty liver disease should be regarded as a sign of increased cardiovascular disease risk. Larger studies are warranted to elucidate the role of GGT in prediction of cardiovascular risk.

Baseline and Change in Uric Acid Concentration Over Time Are Associated With Incident Hypertension in Large Korean Cohort

BACKGROUND

It is uncertain whether high-baseline uric acid (UA) or change in UA concentration over time is related to development of incident hypertension. To investigate relationships between: (i) baseline serum UA concentration and (ii) change in UA concentration and incident hypertension.

METHODS

About 96,606 Korean individuals (with follow-up UA data available for 56,085 people) participating in a health check program was undertaken. Cox regression models were used to estimate adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) for incident hypertension according to UA quartiles regarding the lowest UA quartile as the reference, and also according to change in UA concentration comparing individuals with an increase in UA to those with a decrease in UA concentration over time.

RESULTS

Total follow up time was 8 years (median follow-up 3.3 years; interquartile range, 1.9-5.1). About 10,405 cases of incident hypertension occurred. In the fully adjusted regression models, the HRs (95% CI) for incident hypertension comparing the highest vs. the lowest quartiles of UA were 1.29 (1.19-1.38) in men and 1.24 (1.09-1.42) in women, with statistically significant P for trend for both gender. Additionally, stable or increasing UA concentration over time was associated with increased risk of incident hypertension, particularly in participants with baseline UA concentration ≥median (aHRs 1.14; 95% CI (1.03-1.26) and 1.18; 95% CI (0.98-1.40) in men and women, respectively).

CONCLUSIONS

High initial UA concentration and increases in UA concentration over time should be considered independent risk factors for hypertension.

Activation of Renal (Pro)Renin Receptor Contributes to High Fructose-Induced Salt Sensitivity

A high-fructose diet is shown to induce salt-sensitive hypertension, but the underlying mechanism largely remains unknown. The major goal of the present study was to test the role of renal (pro)renin receptor (PRR) in this model. In Sprague-Dawley rats, high-fructose intake increased renal expression of full-length PRR, which were attenuated by allopurinol. High-fructose intake also upregulated renal mRNA and protein expression of sodium/hydrogen exchanger 3 and Na/K/2Cl cotransporter, as well as in vivo Na/K/2Cl cotransporter activity, all of which were nearly completely blocked by a PRR decoy inhibitor PRO20 or allopurinol treatment. Parallel changes were observed for indices of intrarenal renin-angiotensin-system including renal and urinary renin and angiotensin II levels. Radiotelemetry demonstrated that high-fructose or a high-salt diet alone did not affect mean arterial pressure, but the combination of the 2 maneuvers induced a ≈10-mm Hg increase of mean arterial pressure, which was blunted by PRO20 or allopurinol treatment. In cultured human kidney 2 cells, both fructose and uric acid increased protein expression of soluble PRR in a time- and dose-dependent manner; fructose-induced PRR upregulation was inhibited by allopurinol. Taken together, our data suggest that fructose via uric acid stimulates renal expression of PRR/soluble PRR that stimulate sodium/hydrogen exchanger 3 and Na/K/2Cl cotransporter expression and intrarenal renin-angiotensin system to induce salt-sensitive hypertension.

Association between Serum Uric Acid and Elevated Alanine Aminotransferase in the General Population

Background: Both the serum uric acid (SUA) level and elevated alanine aminotransferase (ALT) are related to metabolic syndrome. However, the association between SUA and elevated ALT has not been elucidated in the general population. The objective of this study was to investigate the association between SUA and elevated ALT in the general population of China; Methods: A total of 11,572 adults (≥35 years of age) participated in this survey. Elevated ALT was defined as >40 U/L. SUA ≥ 7.0 mg/dL in males or ≥6.0 mg/dL in females was defined as hyperuricemia. SUA within the reference range was divided into quartiles, and its associations with elevated ALT were evaluated by logistic regressions; Results: A total of 7.4% participants had elevated ALT. The prevalence of hyperuricemia was 14.9% in males and 7.3% in females. There was a significantly positive dose-response association between SUA levels and the prevalence of elevated ALT. After adjusting for potential confounders, a positive relationship for elevated ALT was observed in subjects with hyperuricemia (odds ratio [OR]: 2.032, 95% confidence interval [CI]: 1.443–2.861 for men; OR: 2.045, 95% CI: 1.221–3.425 for women, both p < 0.05). Within the reference range, the association between SUA and elevated ALT persisted in the fourth quartile (OR: 1.467, 95% CI: 1.063–2.025 for men; OR: 1.721, 95% CI: 1.146–2.585 for women, both p < 0.05); Conclusions: Our results indicated that an increased SUA level, even within the reference range, was independently associated with elevated ALT in Chinese adults.

The predictive value of mean serum uric acid levels for developing prediabetes

AIMS

We aimed to assess the predictive value of mean serum uric acid (SUA) levels for incident prediabetes.

METHODS

Normoglycemic adults (n=39,353) were followed for a median of 3.0years. Prediabetes is defined as impaired fasting glucose (IFG), impaired glucose tolerance (IGT), or impaired HbA1c (IA1c), based on the American Diabetes Association criteria. Serum SUA levels were measured annually. Four diagnostic strategies were used to detect prediabetes in four separate analyses (Analysis 1: IFG. Analysis 2: IFG+IGT. Analysis 3: IFG+IA1c. Analysis 4: IFG+IGT+IA1c). Cox proportional hazards regression models were used to assess the relationship between SUA quintiles and prediabetes. C-statistic was additionally used in the final analysis to assess the accuracy of predictions based upon baseline SUA and mean SUA, respectively.

RESULTS

After adjustment for potential confounders, the hazard ratios (95% confidence interval) of prediabetes for the highest versus lowest quintile of mean SUA were 1.22 (1.10, 1.36) in analysis 1; 1.59 (1.23, 2.05) in analysis 2; 1.62 (1.34, 1.95) in analysis 3 and 1.67 (1.31, 2.13) in analysis 4. In contrast, for baseline SUA, significance was only reached in analyses 3 and 4. Moreover, compared with baseline SUA, mean SUA value was associated with a significant increase in the C-statistic (P<0.001).

CONCLUSIONS

Mean SUA value was strongly and positively related to prediabetes risk, and showed better predictive ability for prediabetes than baseline SUA.

Albuminuria enhances NHE3 and NCC via stimulation of mitochondrial oxidative stress/angiotensin II axis

Imbalance of salt and water is a frequent and challenging complication of kidney disease, whose pathogenic mechanisms remain elusive. Employing an albumin overload mouse model, we discovered that albuminuria enhanced the expression of NHE3 and NCC but not other transporters in murine kidney in line with the stimulation of angiotensinogen (AGT)/angiotensin converting enzyme (ACE)/angiotensin (Ang) II cascade. In primary cultures of renal tubular cells, albumin directly stimulated AGT/ACE/Ang II and upregulated NHE3 and NCC expression. Blocking Ang II production with an ACE inhibitor normalized the upregulation of NHE3 and NCC in cells. Interestingly, albumin overload significantly reduced mitochondrial superoxide dismutase (SOD2), and administration of a SOD2 mimic (MnTBAP) normalized the expression of NHE3, NCC, and the components of AGT/ACE pathway affected by albuminuria, indicating a key role of mitochondria-derived oxidative stress in modulating renin-angiotensin system (RAS) and renal sodium transporters. In addition, the functional data showing the reduced urinary excretion of Na and Cl and enhanced response to specific NCC inhibitor further supported the regulatory results of sodium transporters following albumin overload. More importantly, the upregulation of NHE3 and NCC and activation of ACE/Ang II signaling pathway were also observed in albuminuric patient kidneys, suggesting that our animal model accurately replicates the human condition. Taken together, these novel findings demonstrated that albuminuria is of importance in resetting renal salt handling via mitochondrial oxidative stress-initiated stimulation of ACE/Ang II cascade. This may also offer novel, effective therapeutic targets for dealing with salt and water imbalance in proteinuric renal diseases.

Regulation of uric acid metabolism and excretion

Purines perform many important functions in the cell, being the formation of the monomeric precursors of nucleic acids DNA and RNA the most relevant one. Purines which also contribute to modulate energy metabolism and signal transduction, are structural components of some coenzymes and have been shown to play important roles in the physiology of platelets, muscles and neurotransmission. All cells require a balanced quantity of purines for growth, proliferation and survival. Under physiological conditions the enzymes involved in the purine metabolism maintain in the cell a balanced ratio between their synthesis and degradation. In humans the final compound of purines catabolism is uric acid. All other mammals possess the enzyme uricase that converts uric acid to allantoin that is easily eliminated through urine. Overproduction of uric acid, generated from the metabolism of purines, has been proven to play emerging roles in human disease. In fact the increase of serum uric acid is inversely associated with disease severity and especially with cardiovascular disease states. This review describes the enzymatic pathways involved in the degradation of purines, getting into their structure and biochemistry until the uric acid formation.

Overweight modifies the longitudinal association between uric acid and some components of the metabolic syndrome: The Tromsø Study

BACKGROUND

Elevated uric acid (UA) is associated with the presence of the metabolic syndrome (MetS). In a prospective cohort study, we assessed whether baseline and longitudinal change in UA were risk factors for development of MetS and its individual components.

METHODS

We included 3087 women and 2996 men who had UA measured in the population based Tromsø Study 1994-95. The participants were stratified according to body mass index (BMI). Endpoints were MetS and each component of the syndrome after 7 years, according to the revised National Cholesterol Education Program's Adult Treatment Panel III (NCEP-ATP III) definition.

RESULTS

Multiple logistic regression analyses showed that higher baseline UA was associated with higher odds of developing elevated blood pressure in overweight subjects (BMI ≥ 25 kg/m(2), odds ratio [OR] per 59 μmol/L UA increase 1.44, 95 % confidence interval [CI] = 1.17-1.77, P = 0.001), but not in normal-weight subjects (BMI < 25 kg/m(2), P for interaction = 0.04). Overweight also modified the association between baseline UA and the development of elevated fasting glucose (P for interaction = 0.01). UA was a predictor of MetS in all subjects (OR per 59 μmol/L UA increase 1.29, 95 % CI 1.18-1.41, P < 0.001). Furthermore, longitudinal UA change was independently associated with the development of MetS in all subjects (OR per 59 μmol/L UA increase over 7 years 1.28, 95 % CI 1.16-1.42, P < 0.001).

CONCLUSION

Increased levels of baseline UA independently predicted development of elevated blood pressure and higher fasting glycemia in the overweight, but not the normal-weight subjects. Baseline UA and longitudinal increase in UA over 7 years was associated with the development of MetS in all subjects. Whether increased UA should be treated differently in normal-weight and overweight persons needs further study.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

Nox4 has a crucial role in uric acid‑induced oxidative stress and apoptosis in renal tubular cells

The purpose of the present study was to evaluate the effects of uric acid in promoting tubular cell apoptosis and verify the role of nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4)‑induced oxidative stress in this process. HK‑2 cells were used as a human proximal tubular cell model and co‑cultured with various concentrations of uric acid with or without pre‑treatment with the Nox4 inhibitor diphenylene iodonium (DPI). The apoptotic rate and the amount of reactive oxygen species (ROS) were examined by flow cytometry. Furthermore, levels of Nox4, phosphorylated (p)‑P38, p‑extracellular signal‑regulated kinase (ERK), B‑cell lymphoma 2 (Bcl‑2) and Bcl‑2‑extra large (Bax) were detected by western blot analysis. The results showed that treatment with uric acid decreased HK‑2 cell viability and promoted apoptosis in a dose‑dependent manner. This was paralleled with an upregulation of Nox4 as well as ROS overproduction, which activated the phosphorylation of P38/ERK and caused an imbalance of Bax/Bcl‑2 in HK‑2 cells. Of note, inhibition of Nox4 with DPI prevented uric acid‑induced cell injury by suppressing ROS generation and P38/ERK activation. In conclusion, it was demonstrated that elevated uric acid promoted ROS‑induced tubular cell apoptosis by upregulating Nox4 expression. The present study therefore provided possible mechanisms and a potential therapeutic target of uric acid‑induced chronic kidney disease.

Prevalence of hyperuricemia among Beijing post-menopausal women in 10 years

OBJECTIVES

The objective of this study was to explore the trend and risk factors of the prevalence of hyperuricemia among post-menopausal women in Beijing over a ten years period.

METHOD

This research was based on two cross-sectional surveys in post-menopausal women in Beijing. A total of 1881 post-menopausal women were included. Subjects answered a questionnaire and underwent a physical examination and blood test. Serum uric acid >357 μmol/L was diagnosed as hyperuricemia, and another diagnosis criterion (serum uric acid >416 μmol/L) was applied in these women.

RESULTS

Serum uric acid levels and hyperuricemia prevalence increased remarkably in the 10-year period. The prevalence of hyperuricemia increased more than 2-fold after being adjusted by age. Multivariate logistic regression models revealed hyperuricemia associated with age, education level, urban residents, alcohol consumption, hypertension, obesity, and dyslipidemia. With the increasing number of traditional cardiovascular risk factors (including hypertension, obesity, diabetes, and dyslipidemia), the risk of hyperuricemia increased significantly, and the accumulative effect of the factors on the risk of hyperuricemia was determined.

CONCLUSION

The prevalence of hyperuricemia was high and exhibited a remarkable, increasing trend in Beijing community-based, post-menopausal women. Better management of relative factors could help to prevent further increases in the burden of hyperuricemia in post-menopausal women in this region.

Hyperuricaemia in patients with type 2 diabetes in a tertiary healthcare centre in sub-Saharan Africa: prevalence and determinants

Hyperuricaemia in type 2 diabetes mellitus (T2DM) has been less well investigated in sub-Saharan Africans. Our study of 438 patients found that alcohol intake, body mass index ≥25 kg/m², hydrochlorothiazide use, statin use, diabetic retinopathy and glomerular filtration rate <60 mL/min/1.73m² were independently positively associated with hyperuricaemia; whereas smoking reduced this risk. Hyperuricaemia is strongly associated with some modifiable factors, diabetic complications and certain drugs. Our results suggest that further studies should evaluate the potential cost-benefit of screening for hyperuricaemia in type 2 diabetes.

High Uric Acid Induces Insulin Resistance in Cardiomyocytes In Vitro and In Vivo

Clinical studies have shown hyperuricemia strongly associated with insulin resistance as well as cardiovascular disease. Direct evidence of how high uric acid (HUA) affects insulin resistance in cardiomyocytes, but the pathological mechanism of HUA associated with cardiovascular disease remains to be clarified. We aimed to examine the effect of HUA on insulin sensitivity in cardiomyocytes and on insulin resistance in hyperuricemic mouse model. We exposed primary cardiomyocytes and a rat cardiomyocyte cell line, H9c2 cardiomyocytes, to HUA, then quantified glucose uptake with a fluorescent glucose analog, 2-NBDG, after insulin challenge and detected reactive oxygen species (ROS) production. Western blot analysis was used to examine the levels of insulin receptor (IR), phosphorylated insulin receptor substrate 1 (IRS1, Ser307) and phospho-Akt (Ser473). We monitored the impact of HUA on insulin resistance, insulin signaling and IR, phospho-IRS1 (Ser307) and phospho-Akt levels in myocardial tissue of an acute hyperuricemia mouse model established by potassium oxonate treatment. HUA inhibited insulin-induced glucose uptake in H9c2 and primary cardiomyocytes. It increased ROS production; pretreatment with N-acetyl-L-cysteine (NAC), a ROS scavenger, reversed HUA-inhibited glucose uptake induced by insulin. HUA exposure directly increased the phospho-IRS1 (Ser307) response to insulin and inhibited that of phospho-Akt in H9C2 cardiomyocytes, which was blocked by NAC. Furthermore, the acute hyperuricemic mice model showed impaired glucose tolerance and insulin tolerance accompanied by increased phospho-IRS1 (Ser307) and inhibited phospho-Akt response to insulin in myocardial tissues. HUA inhibited insulin signaling and induced insulin resistance in cardiomyocytes in vitro and in vivo, which is a novel potential mechanism of hyperuricemic-related cardiovascular disease.

Association of AGTR1 Promoter Methylation Levels with Essential Hypertension Risk: A Matched Case-Control Study

The purpose of the present study was to investigate whether methylation of the angiotensin II type 1 receptor (AGTR1) promoter contributed to the risk of essential hypertension (EH). A total of 96 EH cases and 96 gender- and age-matched healthy controls were recruited. Methylation of 8 CpG dinucleotides (CpG1-8) in the AGTR1 promoter was examined using the bisulphite pyrosequencing technology. Three CpG dinucleotides (CpG6-8) could not be well sequenced, therefore only the remaining 5 CpG sites were analysed. A significantly lower CpG1 methylation level was identified in EH cases than in controls (cases vs. controls: 6.74 ± 4.32% vs. 9.66 ± 5.45%, p = 0.007), and no significant association was observed in the remaining analyses. In addition, significantly lower CpG1 (p = 0.028) and higher CpG2 (p = 0.032) methylation levels were observed in males than in females. In the breakdown association test by gender, a higher CpG1 methylation level was also identified in EH in both males (p = 0.034) and females (p = 0.020). Receiver operating characteristic curves showed that CpG1 methylation was a significant predictor of EH. Furthermore, CpG1 methylation was inversely correlated with uric acid levels in controls. The present study suggests that CpG1 hypomethylation in the AGTR1 promoter is likely associated with the risk of EH in the population assessed.

The association between the serum levels of uric acid and alanine aminotransferase in a population-based cohort

BACKGROUND & AIMS

Elevated serum uric acid levels reflect and also cause both oxidative stress and insulin resistance and are frequently observed in patients with the metabolic syndrome. A strong association exists between the metabolic syndrome and non-alcoholic fatty liver disease (NAFLD). Therefore, we aimed to test the association between uric acid and elevated alanine aminotransferase (ALT), as a surrogate for NAFLD, using real-world data.

METHODS

Data used for the cross-sectional study were obtained from Maccabi Healthcare System, a 2-million member health maintenance organization in Israel. The population consisted of individuals aged 20-60 years who underwent blood tests for ALT and uric acid between 1997 and 2012. Individuals with secondary liver disease, celiac, and inflammatory bowel-disease were excluded. Subgroup analysis was performed in subjects who were given the diagnosis of fatty liver in their medical records (n = 2628).

RESULTS

The study population included 82,608 people (32.5% men, mean age 43.91 ± 10.15 years). There was a significant positive dose-response association between serum uric acid levels and the rate of elevated serum ALT (P for trend <0.001). In multivariable model, controlling for potential confounders, the association between uric acid and elevated ALT persisted (OR = 2.10, 95% CI 1.93-2.29, for the fourth quartile vs. the first). This association was maintained in all categories of gender and BMI. Similar results were observed among patients diagnosed with fatty liver (OR = 1.77, 1.22-2.57).

CONCLUSIONS

Serum uric acid is independently associated with elevated ALT, as a surrogate for NAFLD, and thus may serve as a serum marker for liver damage and should be further investigated as a risk factor for NAFLD.

Uric acid as a modulator of glucose and lipid metabolism

In humans, uric acid is the final oxidation product of purine catabolism. The serum uric acid level is based on the balance between the absorption, production and excretion of purine. Uric acid is similarly produced in the liver, adipose tissue and muscle and is primarily excreted through the urinary tract. Several factors, including a high-fructose diet and the use of xenobiotics and alcohol, contribute to hyperuricaemia. Hyperuricaemia belongs to a cluster of metabolic and haemodynamic abnormalities, called metabolic syndrome, characterised by abdominal obesity, glucose intolerance, insulin resistance, dyslipidaemia and hypertension. Hyperuricaemia reduction in the Pound mouse or fructose-fed rats, as well as hyperuricaemia induction by uricase inhibition in rodents and studies using cell culture have suggested that uric acid plays an important role in the development of metabolic syndrome. These studies have shown that high uric acid levels regulate the oxidative stress, inflammation and enzymes associated with glucose and lipid metabolism, suggesting a mechanism for the impairment of metabolic homeostasis. Humans lacking uricase, the enzyme responsible for uric acid degradation, are susceptible to these effects. In this review, we summarise the current knowledge of the effects of uric acid on the regulation of metabolism, primarily focusing on liver, adipose tissue and skeletal muscle.

Dispelling dogma and misconceptions regarding the most pharmacologically targetable source of reactive species in inflammatory disease, xanthine oxidoreductase

Xanthine oxidoreductase (XOR), the molybdoflavin enzyme responsible for the terminal steps of purine degradation in humans, is also recognized as a significant source of reactive species contributory to inflammatory disease. In animal models and clinical studies, inhibition of XOR has resulted in diminution of symptoms and enhancement of function in a number of pathologies including heart failure, diabetes, sickle cell anemia, hypertension and ischemia-reperfusion injury. For decades, XOR involvement in pathologic processes has been established by salutary outcomes attained from treatment with the XOR inhibitor allopurinol. This has served to frame a working dogma that elevation of XOR-specific activity is associated with enhanced rates of reactive species generation that mediate negative outcomes. While adherence to this narrowly focused practice of designating elevated XOR activity to be "bad" has produced some benefit, it has also led to significant underdevelopment of the processes mediating XOR regulation, identification of alternative reactants and products as well as micro-environmental factors that alter enzymatic activity. This is exemplified by recent reports: (1) identifying XOR as a nitrite reductase and thus a source of beneficial nitric oxide ((•)NO) under in vivo conditions similar to those where XOR inhibition has been assumed an optimal treatment choice, (2) describing XOR-derived uric acid (UA) as a critical pro-inflammatory mediator in vascular and metabolic disease and (3) ascribing an antioxidant/protective role for XOR-derived UA. When taken together, these proposed and countervailing functions of XOR affirm the need for a more comprehensive evaluation of product formation as well as the factors that govern product identity. As such, this review will critically evaluate XOR-catalyzed oxidant, (•)NO and UA formation as well as identify factors that mediate their production, inhibition and the resultant impact on inflammatory disease.

Resveratrol inhibits the intracellular calcium increase and angiotensin/endothelin system activation induced by soluble uric acid in mesangial cells

Resveratrol (Resv) is natural polyphenol found in grapes. This study evaluated the protective effect of Resv against the effects of uric acid (UA) in immortalized human mesangial cells (ihMCs). ihMCs were preincubated with Resv (12.5 µM) for 1 h and treated with UA (10 mg/dL) for 6 or 12 h. The intracellular calcium concentration [Ca²⁺]i was quantified by fluorescence using flow cytometry. Angiotensinogen (AGT) and pre-pro endothelin-1 (ppET-1) mRNA were assayed by quantitative real-time RT-PCR. Angiotensin II (AII) and endothelin-1 (ET-1) were assayed by ELISA. UA significantly increased [Ca²⁺]i. Pre-incubation with Resv significantly reduced the change in [Ca²⁺]i induced by UA. Incubation with UA for 6 or 12 h also increased AGT mRNA expression and AII protein synthesis. Resv blunted these increases in AGT mRNA expression and AII protein. Incubation with UA in the ihMCs increased ppET-1 expression and ET-1 protein synthesis at 6 and 12 h. When ihMCs were pre-incubated with Resv, UA had a significantly diminished effect on ppET-1 mRNA expression and ET-1 protein synthesis at 6 and 12 h, respectively. Our results suggested that UA triggers reactions including AII and ET-1 production in mesangial cells. The renin-angiotensin system may contribute to the pathogenesis of renal function and chronic kidney disease. Resv can minimize the impact of UA on AII, ET-1 and the increase of [Ca²⁺]i in mesangial cells, suggesting that, at least in part, Resv can prevent the effects of soluble UA in mesangial cells.

Uric Acid Puzzle: Dual Role as Anti-oxidantand Pro-oxidant

Hyperuricemia is known to be associated with the presence of cardiovascular and metabolic syndrome and with the development of incipient kidney disease and an accelerated renal progression. However, an elevated uric acid level was not generally regarded as a true etiology or mediator, but an indicator of these diseases. Uric acid has recently regained the clinical interest and popularity based on emerging data suggesting the causative role of hyperuricemia in cardiovascular and renal disease. Experimental data demonstrates oxidative stress is one of the earliest phenomena observed in vascular, renal, liver cells and adipocytes exposed to uric acid. Since uric acid is one of the major antioxidants of plasma acting as a free radical scavenger and a chelator of transitional metal ion, uric acid-induced oxidative stress seems paradoxical. Data regarding the clinical implication of hyperuricemia is even more confusing, which defines hyperuricemia as a useless parameter to be eliminated from routine follow-up or a major risk factor to be therapeutic target. With a review of experimental and epidemiologic data, the presence of molecular switch to regulate the role of uric acid as anti- or pro-oxidant in different compartment of our body is suggested, which may shed light on understanding the paradoxical role of uric acid and solving the "uric acid debate".