Uric acid concentrations and the mechanisms of cardiovascular disease

IL-12B Polymorphisms Are Associated with the Presence of Premature Coronary Artery Disease and with Cardiovascular Risk Factors: The Genetics of Atherosclerotic Disease Mexican Study

The aim of this study was to evaluate the association of the IL-12B polymorphisms with the presence of premature coronary artery disease (pCAD) and with cardiovascular risk factors. The study included 2163 individuals (1133 patients with pCAD and 1030 healthy controls). Seven IL-12B polymorphisms (rs1363670, rs3212220, rs3212227, rs6887695, rs1433048, rs2853694, and rs1368439) were determined by TaqMan assays. The associations were evaluated by logistic regression using inheritance models adjusted for confounding variables. The rs1363670 was associated with a low risk of pCAD (odds ratio [OR] 0.718, p_dominant = 0.034; OR 0.701, p_heterozygote = 0.024; OR 0.702, p_codominant1 = 0.025). The association of the polymorphisms with cardiovascular risk factors was evaluated independently in each group. In controls, the rs3212227, rs3212220, and rs6887695 polymorphisms were associated with subcutaneous abdominal fat > p75, whereas the rs6887695 was associated with a high risk of central obesity. In pCAD patients, the rs2853694 was associated with a low risk of insulin resistance; and association of rs3212227 and rs3212220 with a low risk of metabolic syndrome was found, and the rs6887695 polymorphism was nominally associated with a high risk of hyperuricemia. In conclusion, the IL-12B rs1363670 polymorphism was associated with a low risk of pCAD, and in both pCAD patients and healthy controls, some IL-12B polymorphisms were associated with cardiovascular risk factors.

Association of gout with CAD and effect of antigout therapy on CVD risk among gout patients

Hyperuricemia has been identified as an independent risk factor for coronary artery disease (CAD), with a dose-response association. In this study, we explored the causal association between gout and antigout medication and the risk of incidental CAD. We sampled data from the National Health Insurance Research Database and recruited 37,091 patients as the gout cohort, and 37,091 controls. Our primary endpoint was the diagnosis of CAD during follow-up. The overall study population was followed up until CAD diagnosis, withdrawal from the National Health Insurance program, or the end of the study. Cox proportional hazards regression models were used to examine the effect of gout on the risk of CAD, represented by the HR with the 95% CI. Patients with gout were at greater risk of CAD, compared with those without gout: HR=1.49 after adjusting for potential confounders. Non-steroidal anti-inflammatory drugs and prednisolone use was associated with a reduced risk of CAD: HR=0.63 and 0.50, respectively. Patients with gout, treated with antigout medication, exhibited a reduced risk of CAD compared with non-gout patients. Among patients with gout, those on antigout therapy had 32% lower risk compared with those not on antigout therapy: adjusted HR=0.68, 95% CI 0.63 to 0.73. Gout increases the risk of CAD, and the use of antigout medication reduces CAD risk. These results indicate that gout or hyperuricemia is a modifiable risk factor for CAD.

Dietary Antioxidant Supplements and Uric Acid in Chronic Kidney Disease: A Review

Increased serum levels of uric acid have been associated with the onset and development of chronic kidney disease (CKD), cardiovascular disease, and mortality, through several molecular pathogenetic mechanisms, such as inflammation and oxidative stress. Oxidative stress is present even in the early stages of CKD, progresses parallelly with the deterioration of kidney function, and is even more exacerbated in end-stage renal disease patients undergoing maintenance hemodialysis. Although acting in the plasma as an antioxidant, once uric acid enters the intracellular environment; it behaves as a powerful pro-oxidant. Exogenous intake of antioxidants has been repeatedly shown to prevent inflammation, atherosclerosis and oxidative stress in CKD patients. Moreover, certain antioxidants have been proposed to exert uric acid-lowering properties. This review aims to present the available data regarding the effects of antioxidant supplements on both oxidative stress and uric acid serum levels, in a population particularly susceptible to oxidative damage such as CKD patients.

Associations of serum uric acid with total and cause-specific mortality: Findings from individuals and pooling prospective studies

BACKGROUND AND AIMS

There is considerable controversy regarding the link between serum uric acid (SUA) and mortality. We prospectively evaluated the association between SUA and risk of total and cause specific (coronary heart disease [CHD], cerebrovascular and cancer) mortality by using the National Health and Nutrition Examination Surveys (NHANES, 1999-2010). Furthermore, a systematic review and meta-analysis of cohort studies was performed to investigate pooled associations of SUA with all-cause and cause-specific mortality.

METHODS

Vital status through December 31, 2011 was ascertained. PubMed-Medline, SCOPUS, Web of Science and Google Scholar databases were searched (up to April 2018). Adjusted Cox proportional hazard regression models were used to determine the association between SUA and mortality. The DerSimonian-Laird method and generic inverse variance methods were used for quantitative data synthesis.

RESULTS

Overall, 21,025 individuals were included (mean age = 47.6 years, 48.7% men) and 3520 deaths occurred during the 144 months of follow-up. In adjusted models, individuals in the highest quartile of SUA had 10 and 8% greater risk of CHD and stroke mortality, whereas there was no link between SUA, all-cause and cancer mortality. The associations of CHD and stroke mortality with SUA were more pronounced in women and, among women, in those aged >50 years. Furthermore, all-cause mortality was positively and significantly related to SUA concentrations only in women. In the meta-analysis, SUA was shown to predict the risk of total (21%), CHD (24%) and stroke (29%) mortality. Furthermore, participants with a higher level of central adiposity had a greater risk of mortality from CHD and stroke for the same level of SUA.

CONCLUSIONS

Our results highlight the adverse impact of SUA on mortality, particularity in older (>50 years) women. The clinical implications of these findings remain to be established in future trials.

Sex-Specific Relationship Between Serum Uric Acid and Risk of Stroke: A Dose-Response Meta-Analysis of Prospective Studies

Background

Conflicting findings of the association between serum uric acid (UA) and stroke have been reported in both men and women, and it is unclear whether this association was different between men and women. We preformed this meta‐analysis to assess the sex‐specific effect of serum UA on the risk of stroke and its subtypes.

Methods and Results

Prospective studies that reported sex‐specific association of UA levels with stroke or reported in a certain sex were included. Dose‐response relationships were assessed by the generalized least squares trend estimation, and summary effect estimates were evaluated with random‐effect models. Subgroup and sensitivity analyses were performed to assess the potential sources of heterogeneity and the robustness of the pooled estimation. Altogether, 13 prospective studies were identified in this study. The summary of relative risks (95% CIs) of stroke for a 1‐mg/dL increase in serum UA levels were 1.10 (1.05–1.14) for men and 1.11 (1.09–1.13) for women. There is no significant difference in the effect of UA on future stroke risk between men and women (P_interaction=0.736). Subgroup analyses showed that the significant associations persisted in most stratifications, and sensitivity analyses according to various inclusion criteria yielded similar results. A nonlinear relationship was observed in men (P_{non‐linearity}<0.001), with risk increasing significantly from a UA of 6 mg/dL and more steeply at higher UA levels.

Conclusions

Elevated serum UA levels were significantly associated with modestly increased risk of stroke in both men and women and have similar adverse effects on development of stroke in both sexes.

Hyperuricemia and the risk for coronary heart disease morbidity and mortality a systematic review and dose-response meta-analysis

Considerable controversy exists regarding the association between hyperuricemia and coronary heart disease (CHD). Therefore, we performed a systematic review and dose-response meta-analysis of prospective studies to examine the controversy. Prospective cohort studies with relative risks (RRs) and 95% confidence intervals (CIs) for CHD according to serum uric acid levels in adults were eligible. A random-effects model was used to compute the pooled risk estimate. The search yielded 29 prospective cohort studies (n = 958410 participants). Hyperuricemia was associated with increased risk of CHD morbidity (adjusted RR 1.13; 95% CI 1.05 to 1.21) and mortality (adjusted RR 1.27; 95% CI 1.16 to 1.39). For each increase of 1 mg/dl in uric acid level, the pooled multivariate RR of CHD mortality was 1.13 (95% CI 1.06 to 1.20). Dose-response analysis indicated that the combined RR of CHD mortality for an increase of 1 mg uric acid level per dl was 1.02 (95% CI 0.84 to 1.24) without heterogeneity among males (P = 0.879, I² = 0%) and 2.44 (95% CI 1.69 to 3.54) without heterogeneity among females (P = 0.526, I² = 0%). The increased risk of CHD associated with hyperuricemia was consistent across most subgroups. Hyperuricemia may increase the risk of CHD events, particularly CHD mortality in females.

Higher serum uric acid and lipoprotein(a) are correlated with coronary spasm

It has been reported that a major cause of coronary vasospastic angina (VSA) is endothelial dysfunction of the coronary artery. On the other hand, some studies showed that serum uric acid and lipoprotein(a) are correlated with endothelial dysfunction. Thus, we examined whether uric acid and lipoprotein(a), are correlated with VSA. Four hundred forty-one patients with suspected VSA who underwent a coronary angiogram with acetylcholine provocation (ACh test) during an 8-year period were enrolled. We divided them into a VSA group, who showed coronary spasm by the ACh test, and an atypical chest pain (ACP) group, who showed negative ACh test. We compared serum markers between the two groups, including low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, high-sensitivity C-reactive protein (hs-CRP), lipoprotein(a), fibrinogen, total plasminogen activator inhibitor-1, and uric acid. Uric acid, hs-CRP, and lipoprotein(a) were significantly higher in the VSA group than in the ACP group (all P < 0.05) while there were no significant differences in the other parameters. Multivariate analyses identified uric acid and lipoprotein(a) as significant independent markers for VSA. Uric acid and lipoprotein(a) are correlated with VSA, and medical intervention to decrease uric acid and lipoprotein(a) might be effective in controlling VSA.

Lowering serum urate does not improve endothelial function in patients with type 2 diabetes

AIMS/HYPOTHESIS

Endothelial dysfunction contributes to excess cardiovascular risk in patients with type 2 diabetes. There is strong evidence of an association between high serum uric acid concentrations and endothelial dysfunction, and uric acid has been proposed as an independent cardiovascular risk factor in type 2 diabetes. We hypothesised that lowering of uric acid concentrations might allow restoration of endothelial function in this high-risk group.

METHODS

Intravenous urate oxidase (1.5 mg) was administered to ten patients with type 2 diabetes and ten healthy participants in a two-way, randomised, placebo-controlled, crossover study. Forearm blood flow responses to intra-brachial acetylcholine, sodium nitroprusside and N(G)-monomethyl-L-arginine (L-NMMA) were measured using venous occlusion plethysmography. The augmentation index (AIx) was determined by pulse wave analysis as a measure of large arterial stiffness.

RESULTS

Acetylcholine and L-NMMA evoked lesser responses in patients with type 2 diabetes than in healthy participants. Baseline AIx was higher in patients with type 2 diabetes (mean +/- SD: 13.1 +/- 6.9%) than in healthy participants (2.0 +/- 5.1%; p = 0.006). Urate oxidase lowered serum uric acid concentrations by 64 +/- 11% (p < 0.001), but this had no effect on forearm blood flow responses or AIx in either group.

CONCLUSIONS/INTERPRETATION

Substantial short-term lowering of uric acid did not have a direct vascular effect, suggesting that, on its own, this might not be an effective strategy for restoring endothelial function in patients with type 2 diabetes.

Measuring circulating antioxidants in wild birds

Antioxidants protect against free radical damage, which is associated with various age-related pathologies. Antioxidants are also an important buffer against the respiratory burst of the immune system. This protection presumably has costs and therefore might underlie important life-history trade-offs. Studying such trade-offs in a comparative context requires field-applicable methods for assessing antioxidant capacity in wild animals. Here, we present modifications to a simple spectrophotometric assay (the TEAC or TAS assay) that can be applied to miniscule amounts of blood plasma to determine circulating antioxidant capacity. Additionally, uric acid, the most abundant circulating antioxidant, should be measured independently. Uric acid in birds is derived from amino acid catabolism, perhaps incidentally to its antioxidant function. The assay was validated in experimental studies on chickens showing effects of diet on antioxidant capacity, and in field measurements on 92 species of birds, which demonstrate substantial species differences in constitutive antioxidant capacity. Furthermore, most wild birds demonstrate a dramatic change in antioxidant capacity due to stress. These results show that this technique detects variation appropriate for both interspecific and intraspecific studies, and that antioxidants and uric acid change in response to conditions of interest to field ecologists, such as diet and stress.

Interactions of peroxynitrite with uric acid in the presence of ascorbate and thiols: implications for uncoupling endothelial nitric oxide synthase

It has been suggested that uric acid acts as a peroxynitrite scavenger although it may also stimulate lipid peroxidation. To gain insight into how uric acid may act as an antioxidant, we used electron spin resonance to study the reaction of uric acid and plasma antioxidants with ONOO-. Peroxynitrite reacted with typical plasma concentrations of urate 16-fold faster than with ascorbate and 3-fold faster than cysteine. Xanthine but not other purine-analogs also reacted with peroxynitrite. The reaction between ONOO- and urate produced a carbon-centered free radical, which was inhibited by either ascorbate or cysteine. Moreover, scavenging of ONOO- by urate was significantly increased in the presence of ascorbate and cysteine. An important effect of ONOO- is oxidation of tetrahydrobiopterin, leading to uncoupling of nitric oxide synthase. The protection of eNOS function by urate, ascorbate and thiols in ONOO(-)-treated bovine aortic endothelial cells (BAECs) was, therefore, investigated by measuring superoxide and NO using the spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine (CMH) and the NO-spin trap Fe[DETC]2. Peroxynitrite increased superoxide and decreased NO production by eNOS indicating eNOS uncoupling. Urate partially prevented this effect of ONOO- while treatment of BAECs with the combination of either urate with ascorbate or urate with cysteine completely prevented eNOS uncoupling caused by ONOO-. We conclude that the reducing and acidic properties of urate are important in effective scavenging of peroxynitrite and that cysteine and ascorbate markedly augment urate's antioxidant effect by reducing urate-derived radicals.