Association between serum level of uric acid in Japanese young patients with coronary spastic angina receiving coronary angiography

Endothelial dysfunction may trigger coronary spastic angina (CSA). However, the risk factors for CSA in young patients remain unclear. This study aimed to investigate the age-dependent role of serum uric acid levels in patients with CSA. We enrolled 423 patients who underwent an ergonovine tolerance test during coronary angiography for the CSA evaluation. We categorized the patients as (1) young (age ≤ 65 years) CSA-positive (n = 33), (2) young CSA-negative (n = 138), (3) elderly (age > 66 years) CSA-positive (n = 42), and (4) elderly CSA-negative (n = 210) groups. In the young groups, the smoker proportion (57.6 vs. 38.4%, p = 0.04) and serum uric acid levels (6.3 ± 1.4 vs. 5.4 ± 1.5 mg/dl, p = 0.006) were significantly higher in the CSA-positive compared with the CSA-negative group. Conversely, in the elderly group, the male proportion (66.6 vs. 47.1%, p = 0.02) and alcohol consumption level (40.5 vs. 21.0%, p = 0.01) were significantly higher in the CSA-positive compared with the CSA-negative group. The multivariate analysis in young groups revealed the independent association between the serum uric acid level (p = 0.02) and the presence of CSA. Our results indicate that elevated serum uric acid levels may affect CSA development in young patients.

Association of Mutations Identified in Xanthinuria with the Function and Inhibition Mechanism of Xanthine Oxidoreductase

Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the two-step reaction from hypoxanthine to xanthine and from xanthine to uric acid in purine metabolism. XOR generally carries dehydrogenase activity (XDH) but is converted into an oxidase (XO) under various pathophysiologic conditions. The complex structure and enzymatic function of XOR have been well investigated by mutagenesis studies of mammalian XOR and structural analysis of XOR-inhibitor interactions. Three XOR inhibitors are currently used as hyperuricemia and gout therapeutics but are also expected to have potential effects other than uric acid reduction, such as suppressing XO-generating reactive oxygen species. Isolated XOR deficiency, xanthinuria type I, is a good model of the metabolic effects of XOR inhibitors. It is characterized by hypouricemia, markedly decreased uric acid excretion, and increased serum and urinary xanthine concentrations, with no clinically significant symptoms. The pathogenesis and relationship between mutations and XOR activity in xanthinuria are useful for elucidating the biological role of XOR and the details of the XOR reaction process. In this review, we aim to contribute to the basic science and clinical aspects of XOR by linking the mutations in xanthinuria to structural studies, in order to understand the function and reaction mechanism of XOR in vivo.

Uric acid and hypertension: a focused review and practical recommendations

: Uric acid levels are higher in humans than in other mammals. Best known as an extracellular antioxidant, uric acid also increases salt sensitivity, fat storage, and lipogenesis. Xanthine oxidase-related oxidative stress may also induce endothelial dysfunction and renal vasoconstriction. Renal structure abnormalities contribute to salt-sensitive and uric acid-independent hypertension. Maternal hyperuricemia during pregnancy and hyperuricemia early in life are likewise independent risk factors for hypertension. Genetic polymorphism is potentially involved in the activity of xanthine oxidoreductase, but further studies are needed. Xanthine oxidase inhibition consistently decreases blood pressure in younger hypertensive patients, albeit modestly. Hyperuricemia affects one out of five adults as a result of the Western diet, insulin resistance, and renal dysfunction. This review advocates lifestyle changes to maintain uric acid levels within the normal range in young (pre)hypertensive individuals or normotensives with a family history of hypertension, metabolic disorders, or obesity; moreover, antihypertensive medications that increase uric acid levels should be avoided.

U-shaped association between serum uric acid concentration and mortality in hypertrophic cardiomyopathy patients

Background. No study has examined the effect of low serum uric acid (SUA) concentrations on mortality in hypertrophic cardiomyopathy (HCM) patients. The aim of the present study was to assess the relations between both low and high SUA concentrations and the risk of mortality across the full range of SUA concentrations in a retrospective cohort of HCM patients.Methods. A total of 454 HCM patients were enrolled in the study, and SUA concentrations were measured at baseline. The primary and secondary endpoints were all-cause mortality and HCM-related mortality, respectively. The associations between SUA concentrations and endpoints were analysed.Results. During a median follow-up of 3.8 years, there were 80 (17.6%) all-cause mortality events, and 52 of them (11.5%) were ascribed to HCM-related mortality. Patients with SUA concentrations of 250-350 µmol/L had the lowest all-cause mortality rate (11.8%) and HCM-related mortality rate (5.0%). Both low and high SUA concentrations were associated with increased all-cause and HCM-related mortality. Adjusted HRs were 2.52 (95% CI 1.13-5.61, p = 0.024) and 4.86 (95% CI 1.74-13.58, p = 0.003) for all-cause mortality and HCM-related mortality in the lowest SUA group (<250 µmol/L) when compared with the reference group (250-350 µmol/L), respectively. The corresponding HRs in the highest SUA group (≥450 µmol/L) were 2.73 (95% CI 1.42-5.23, p = 0.003) and 4.14 (95% CI 1.70-10.13, p = 0.002), respectively.Conclusions. Both low and high SUA concentrations were significantly associated with increased risk of all-cause mortality and HCM-related mortality, which supported a U-shaped association between SUA concentrations and mortality in HCM patients.

Hyperuricemia and Hypertension: Links and Risks

Hyperuricemia has long been recognized to be associated with increased cardiovascular risk, including risk of developing hypertension. Epidemiological findings suggest that the link with hypertension is stronger in children and adolescents. Uric acid acts as a strong antioxidant compound in the extracellular environment but has pro-inflammatory effects within the intracellular setting. A chronic phase of microvascular injury is known to occur after prolonged periods of hyperuricemia. This is proposed to contribute to afferent arteriolopathy and elevation of blood pressure that may become unresponsive to uric acid-lowering therapies over time. Studies have struggled to infer direct causality of hyperuricemia due to a vast number of confounders including body mass index. The aim of this review is to present the available data and highlight the need for large scale prospective randomized controlled trials in this area. At present, there is limited evidence to support a role for uric acid-lowering therapies in helping mitigate the risk of hypertension.

Severe Hypouricemia Impairs Endothelium-Dependent Vasodilatation and Reduces Blood Pressure in Healthy Young Men: A Randomized, Placebo-Controlled, and Crossover Study

Background

Uric acid (UA) is a plasmatic antioxidant that has possible effects on blood pressure. The effects of UA on endothelial function are unclear. We hypothesize that endothelial function is not impaired unless significant UA depletion is achieved through selective xanthine oxidase inhibition with febuxostat and recombinant uricase (rasburicase).

Methods and Results

Microvascular hyperemia, induced by iontophoresis of acetylcholine and sodium nitroprusside, and heating‐induced local hyperemia after iontophoresis of saline and a specific nitric oxide synthase inhibitor were assessed by laser Doppler imaging. Blood pressure and renin‐angiotensin system markers were measured, and arterial stiffness was assessed. CRP (C‐reactive protein), allantoin, chlorotyrosine/tyrosine ratio, homocitrulline/lysine ratio, myeloperoxidase activity, malondialdehyde, and interleukin‐8 were used to characterize inflammation and oxidative stress. Seventeen young healthy men were enrolled in a randomized, double‐blind, placebo‐controlled, 3‐way crossover study. The 3 compared conditions were placebo, febuxostat alone, and febuxostat together with rasburicase. The allantoin (μmol/L)/UA (μmol/L) ratio differed between sessions (P<0.0001). During the febuxostat‐rasburicase session, heating‐induced hyperemia became altered in the presence of nitric oxide synthase inhibition; and systolic blood pressure, angiotensin II, and myeloperoxidase activity decreased (P≤0.03 versus febuxostat). The aldosterone concentration decreased in the febuxostat‐rasburicase group (P=0.01). Malondialdehyde increased when UA concentration decreased (both P<0.01 for febuxostat and febuxostat‐rasburicase versus placebo). Other parameters remained unchanged.

Conclusions

A large and short‐term decrease in UA in humans alters heat‐induced endothelium‐dependent microvascular vasodilation, slightly reduces systolic blood pressure through renin‐angiotensin system activity reduction, and markedly reduces myeloperoxidase activity when compared with moderate UA reduction. A moderate or severe hypouricemia leads to an increase in lipid peroxidation through loss of antioxidant capacity of plasma.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT03395977.

Effect of Gender, Age, Diet and Smoking Status on the Circadian Rhythm of Serum Uric Acid of Healthy Indians of Different Age Groups

The circadian rhythm of uric acid concentration was studied under near-normal tropical conditions in 162 healthy volunteers (103 males and 59 females; 7 to 75 year). They were mostly medical students, staff members and members of their families. They were classified into 4 age groups: A (7-20 y; N = 42), B (21-40 y; N = 60), C (41-60 y; N = 35) and D (61-75 y; N = 25). They followed a diurnal activity from about 06:00 to about 22:00 and nocturnal rest. Blood samples were collected from each subject every 6 for 24 h (4 samples). Serum uric acid was measured spectrophotometrically. Data from each subject were analyzed by cosinor rhythmometry. Effects of gender, age, diet (vegetarian vs. omnivore), and smoking status on the rhythm-adjusted mean (MESOR) and circadian amplitude were examined by multiple-analysis of variance. A marked circadian variation was found in uric acid concentration in healthy Indians of all age groups. Furthermore, both the MESOR and circadian amplitude underwent changes with advancing age. In addition to effects of gender and age, diet and smoking were also found to affect the MESOR of circulating uric acid concentration in healthy Indians residing in northern India. The present observations confirmed a definite rhythm in uric acid concentrations with significant effect of gender, age, diet, and smoking status on uric acid concentration in clinical health. Mapping the circadian rhythm of serum uric acid is needed to explore their role in different pathophysiological conditions.

Uric Acid Level Has a U-shaped Association with Clinical Outcomes in Patients with Vasospastic Angina

No data are available on the association of serum uric acid and vasospastic angina (VSA) which has endothelial dysfunction as a possible pathophysiologic mechanism. Low uric acid level might cause adverse outcomes in VSA in connection with endothelial dysfunction. We enrolled 818 VSA patients whose uric acid level was measured at admission. Patients were categorized according to tertiles of uric acid level: group I, ≤ 4.8 mg/dL; group II, 4.9-5.9 mg/dL; and group III, ≥ 6.0 mg/dL. Primary outcome was major adverse cardiac events (MACEs), defined as a composite of cardiac death, acute myocardial infarction (MI), ischemic stroke, coronary revascularization, and rehospitalization for angina. Median follow-up duration was 49.2 months. Median uric acid values were 4.1 mg/dL for group I, 5.4 mg/dL for group II, and 6.7 mg/dL for group III. In the overall population, group II had a significantly lower incidence of MACE compared to group I (47 [17.1%] vs. 66 [24.6%]; hazard ratio [HR], 1.52; 95% confidence interval [CI], 1.02-2.26; P = 0.040) and a tendency of lower incidence of MACEs compared to Group III (47 [17.1%] vs. 62 [22.5%]; HR, 1.44; 95% CI, 0.98-2.13; P = 0.067). Among group I patients, those who received nitrates had a higher incidence of MACEs than those without nitrate therapy (P < 0.001). Low uric acid level was associated with adverse clinical outcomes, while high uric acid level had a trend toward an increase in it. Use of nitrate in patients with low uric acid level might have adverse effects on clinical outcomes of VSA.

Physiological functions and pathogenic potential of uric acid: A review

Uric acid is synthesized mainly in the liver, intestines and the vascular endothelium as the end product of an exogenous pool of purines, and endogenously from damaged, dying and dead cells, whereby nucleic acids, adenine and guanine, are degraded into uric acid. Mentioning uric acid generates dread because it is the established etiological agent of the severe, acute and chronic inflammatory arthritis, gout and is implicated in the initiation and progress of the metabolic syndrome. Yet, uric acid is the predominant anti-oxidant molecule in plasma and is necessary and sufficient for induction of type 2 immune responses. These properties may explain its protective potential in neurological and infectious diseases, mainly schistosomiasis. The pivotal protective potential of uric acid against blood-borne pathogens and neurological and autoimmune diseases is yet to be established.

Serum uric acid levels during leprosy reaction episodes

Background. Leprosy reactions are acute inflammatory episodes that occur mainly in the multibacillary forms of the disease. The reactions are classified as type 1 (reverse reaction) or type 2 (erythema nodosum leprosum). Leprosy-associated oxidative stress has been widely demonstrated. Several recent studies have shown uric acid (UA) to have antioxidative effects under pathologic conditions. The objective of this study was to assess serum levels of UA in patients with leprosy reactions, with the aim of monitoring their levels before and after treatment, compared with levels in leprosy patients without reactions.

Methods. The study included patients aged 18–69 years assisted at a leprosy treatment reference center in the Central Region of Brazil. Patients who were pregnant; were using immunosuppressant drugs or immunobiologicals; or had an autoimmune disease, human immunodeficiency virus infection, acquired immune deficiency syndrome, or tuberculosis were excluded. Upon recruitment, all individuals were clinically assessed for skin lesions and neural or systemic impairment. Some patients had already completed treatment for leprosy, while others were still undergoing treatment or had initiated treatment after being admitted. The treatment of the reactional episode was started only after the initial evaluation. Laboratory assessments were performed upon admission (baseline) and at approximately 30 and 60 days (time points 1 and 2, respectively).

Results. A total of 123 leprosy patients were recruited between June 2012 and June 2015; among them, 56, 42, and 25 presented with type 1, type 2, and no reactions, respectively. Serum UA levels were significantly reduced in patients with type 2 leprosy reactions compared with patients in the control group and remained lower in the two subsequent assessments, after initiation of anti-reaction treatments, with similar values to those recorded before the treatment.

Discussion. The decreased serum UA levels in patients with type 2 leprosy reactions might be due to the consumption of UA to neutralize the enhanced production of oxygen- and nitrogen-reactive species that occurs during type 2 reactions. The maintenance of the reduced levels in the follow-up assessments may indicate persistence of oxidative stress in the initial post-treatment stages, despite improved clinical conditions. The results of this study suggest that serum UA may play an antioxidative role during type 2 leprosy reactions.