Nitric oxide inhibits prooxidant actions of uric acid during copper-mediated LDL oxidation

Association of serum uric acid and fasting plasma glucose with cognitive function: a cross-sectional study

BACKGROUND

The combined effect of serum uric acid (SUA) and blood glucose on cognition has not been explored. This study aimed to examine the separate and combined association of SUA and fasting plasma glucose (FPG) or diabetes mellitus (DM) with cognition in a sample of Chinese middle-aged and elderly population.

METHODS

A total of 6,509 participants aged 45 years or older who participated in the China Health and Retirement Longitudinal Study (CHARLS, 2011) were included. The three cognitive domains assessed were episodic memory, mental status, and global cognition (the sum of the first two terms). Higher scores indicated better cognition. SUA and FPG were measured. The participants were grouped based on SUA and FPG quartiles to evaluate their combined associations of cognition with SUA Q1-Q3 only (Low SUA), with FPG Q4 only (High FPG), without low SUA and high FPG levels (Non), and with low SUA and high FPG levels (Both), multivariate linear regression models were used to analyze their association.

RESULTS

Lower SUA quartiles were associated with poorer performance in global cognition and episodic memory compared with the highest quartile. Although no association was found between FPG or DM and cognition, high FPG or DM combined with low SUA levels in women (β_FPG = -0.983, 95% CI: -1.563--0.402; β_DM = -0.800, 95% CI: -1.369--0.232) had poorer cognition than those with low SUA level only (β_FPG = -0.469, 95% CI: -0.926--0.013; β_DM = -0.667, 95% CI: -1.060--0.275).

CONCLUSION

Maintaining an appropriate level of SUA may be important to prevent cognitive impairment in women with high FPG.

Role of Serum Uric Acid as a Protective Biomarker in Patients with Different Histopathological Grades of Oral Squamous Cell Carcinoma: a Case-Control Study

The antioxidant properties of uric acid may have a protective effect against the formation of oxygen radicals and subsequently against carcinogenicity. The present study aimed at evaluating the serum level of uric acid in patients with oral squamous cell carcinoma (OSCC) with different histopathological grades. In this descriptive-analytical, case-control study, patients with OSCC and healthy controls were selected and matched regarding age and gender. The serum samples were collected from patients (before radiotherapy and chemotherapy) and controls, and their serum uric acid levels were measured enzymatically. Data were analyzed using independent t-test and ANOVA at 0.05 level of significance. The mean serum uric acid level in OSCC patients (4.2 ± 1.5 mg/dL) and healthy controls (4.38 ± 1.22 mg/dL) was not significantly different (P = 0.377). No significant association was noted between the histopathological grade of OSCC and mean serum uric acid (P = 0.781). The serum uric acid level had a direct significant correlation with age in OSCC patients (P < 0.001). The results of this study did not support the role of uric acid as a protective biomarker in OSCC. Further prospective studies are recommended to better elucidate the role of uric acid in the etiology of OSCC.

Association between serum copper levels and prevalence of hyperuricemia: a cross-sectional study

Hyperuricemia has been recognized as a worldwide public health concern. This study was conducted to examine the association between serum copper (Cu) concentration and the prevalence of hyperuricemia in a middle-aged and elderly population. Serum Cu concentration was measured by Roche modular P800 using the PAESA method. Serum uric acid (UA) concentration was detected by a Beckman Coulter AU 5800. Presence of hyperuricemia was defined as serum UA ≥ 416 μmol/L for men and ≥360 μmol/L for women. The association between serum Cu concentration and the prevalence of hyperuricemia was evaluated by logistic regression. The prevalence of hyperuricemia was 17.6% (n = 6,212) in the present study. Relative to the lowest quintile, the age- and sex-adjusted odds ratios for hyperuricemia were 1.38 (95% CI: 1.12 to 1.70), 1.34 (95% CI: 1.07 to 1.66), and 1.53 (95% CI: 1.23 to 1.91) in the third, fourth, and fifth serum Cu concentration quintiles (P for trend < 0.001). Similar results were found both in men and women subgroups. None of the findings were materially altered after adjustment for additional potential confounders. In conclusion, in this population-based cross-sectional study, serum Cu concentration was positively associated with the prevalence of hyperuricemia.

The lipid peroxidation in patients with nephrolithiasis before and after extracorporeal shock wave lithotripsy

AIM

To evaluate the level of lipid peroxidation in patients with nephrolithiasis before and after extracorporeal shock wave lithotripsy (ESWL).

MATERIALS & METHODS

Isoprostane concentration (8-isoPGF_2α) was measured in urine, and thiobarbituric acid reactive substance production in serum and erythrocytes. In addition, the concentrations of selected compounds (uric acid, glucose and creatinine) were measured in serum.

RESULTS

The patients (before and after ESWL) demonstrated significantly higher levels of two different biomarkers of lipid peroxidation compared with the control group. A correlation was identified between increased amounts of uric acid and biomarkers of lipid peroxidation in patients with nephrolithiasis, both before and after ESWL.

CONCLUSION

Uric acid may be associated with lipid peroxidation in patients with nephrolithiasis.

Targeting urate to reduce oxidative stress in Parkinson disease

Oxidative stress has been implicated as a core contributor to the initiation and progression of multiple neurological diseases. Genetic and environmental factors can produce oxidative stress through mitochondrial dysfunction leading to the degeneration of dopaminergic and other neurons underlying Parkinson disease (PD). Although clinical trials of antioxidants have thus far failed to demonstrate slowed progression of PD, oxidative stress remains a compelling target. Rather than prompting abandonment of antioxidant strategies, these failures have raised the bar for justifying drug and dosing selections and for improving study designs to test for disease modification by antioxidants. Urate, the main antioxidant found in plasma as well as the end product of purine metabolism in humans, has emerged as a promising potential neuroprotectant with advantages that distinguish it from previously tested antioxidant agents. Uniquely, higher urate levels in plasma or cerebrospinal fluid (CSF) have been linked to both a lower risk of developing PD and to a slower rate of its subsequent progression in numerous large prospective epidemiological and clinical cohorts. Laboratory evidence that urate confers neuroprotection in cellular and animal models of PD, possibly via the Nrf2 antioxidant response pathway, further strengthened its candidacy for rapid clinical translation. An early phase trial of the urate precursor inosine demonstrated its capacity to safely produce well tolerated, long-term elevation of plasma and CSF urate in early PD, supporting a phase 3 trial now underway to determine whether oral inosine dosed to elevate urate to concentrations predictive of favorable prognosis in PD slows clinical decline in people with recently diagnosed, dopamine transporter-deficient PD.

Relationship of urinary isoprostanes to prostate cancer occurrence

To estimate the oxidative stress in patients with prostate cancer and in a control group, we used the biomarker of lipid peroxidation-isoprostanes (8-isoPGF(2)) and the level of selected antioxidants (glucose and uric acid [UA]). The level of urinary isoprostanes was determined in patients and controls using an immunoassay kit according to the manufacturer's instruction. The levels of UA and glucose were also determined in serum by the use of UA Assay Kit and Glucose Assay Kit. We observed a statistically increased the level of isoprostanes in urine of patients with prostate cancer in compared with a control group. The concentration of tested antioxidants in blood from patients with prostate cancer was also higher than in healthy subjects. Moreover, our experiments indicate that the correlation between the increased amount of UA and the lipid peroxidation exists in prostate cancer patients (in all tested groups). Prostate cancer risk by urinary isoprostanes level was analyzed, and a positive association was found (relative risk for highest vs. lowest quartile of urinary isoprostanes = 1.6; 95 % confidence interval 1.2-2.4; p for trend = 0.03). We suggest that reactive oxygen species induce peroxidation of unsaturated fatty acid in patients with prostate cancer, and the level of isoprostanes may be used as a non-invasive marker for determination of oxidative stress. We also propose that UA may enhance the oxidative stress in patients with prostate cancer.

Naturally high plasma glucose levels in mourning doves (Zenaida macroura) do not lead to high levels of reactive oxygen species in the vasculature

Plasma glucose (P(Glu)) concentrations in birds are 1.5-2 times higher than those of mammals of similar body mass. In mammals, sustained elevations of P(Glu) lead to oxidative stress and free radical-mediated scavenging of endogenous vasodilators (e.g., nitric oxide), contributing to elevated blood pressure. Despite the relatively high P(Glu) levels in birds, they appear resistant to the development of oxidative stress in tissues such as the heart, brain and kidneys. To our knowledge no information exists on oxidative stress susceptibility in the resistance vasculature of birds. Therefore, we compared endogenous antioxidant mechanisms in the resistance vasculature of mourning doves (MODO; Zenaida macroura) and rats (Rattus norvegicus). Reactive oxygen species (ROS) were assessed with the fluorescent indicator 7'-dichlorodihydrofluorescein diacetate, acetyl ester in mesenteric arteries from rats and wild-caught MODO. Despite having significantly higher P(Glu) than rats, there were no significant differences in ROS levels between mesenteric arteries from rats or doves. Although superoxide dismutase and catalase activities were lower in the plasma, total antioxidant capacity, uric acid, vitamin E (α-tocopherol), and carotenoids (lutein and zeaxanthin) were significantly higher in MODO than in rats. Thus, compared to rats, MODO have multiple circulating antioxidants that may prevent the development of oxidative stress in the vasculature.

Effect of single bout of maximal exercise on plasma antioxidant status and paraoxonase activity in young sportsmen

The purpose of this study was to elucidate the participation of plasma PON1 (paraoxonase activity [PON] and arylesterase activity [ARE]) in antioxidant defense in response to a single bout of maximal exercise. PON, ARE, lipid profile, lipid peroxidation (thiobarbituric acid reactive substances [TBARS]), total antioxidant status (ferric reducing ability of plasma [FRAP]), concentration of uric acid [UA], and total bilirubin (TBil) were determined in the plasma before, at the bout and 2 h after maximal exercise on a treadmill in young sportsmen. Chosen physiological parameters also were controlled during maximal exercise. Following maximal exercise, the unaltered level of TBARS and increased FRAP were registered. ARE increment was the highest (37.6%) of all measured variables but lasted for a short time. UA increment was lower than ARE but long-lasting and correlated with FRAP. PON activity increment was associated with the combined effect of body weight, lean, body mass index (BMI) and basal metabolic rate (BMR). We conclude that PON1 is a co-factor of the first line of antioxidant defense during maximal exercise. Its activity is associated with body composition and not the physical fitness of the subjects.

Reactions of peroxynitrite with uric acid: formation of reactive intermediates, alkylated products and triuret, and in vivo production of triuret under conditions of oxidative stress

Hyperuricemia is associated with hypertension, metabolic syndrome, preeclampsia, cardio-vascular disease and renal disease, all conditions associated with oxidative stress. We hypothesized that uric acid, a known antioxidant, might become prooxidative following its reaction with oxidants; and, thereby contribute to the pathogenesis of these diseases. Uric acid and 1,3-(15)N(2)-uric acid were reacted with peroxynitrite in different buffers and in the presence of alcohols, antioxidants and in human plasma. The reaction products were identified using liquid chromatography-mass spectrometry (LC-MS) analyses. The reactions generate reactive intermediates that yielded triuret as their final product. We also found that the antioxidant, ascorbate, could partially prevent this reaction. Whereas triuret was preferentially generated by the reactions in aqueous buffers, when uric acid or 1,3-(15)N(2)-uric acid was reacted with peroxynitrite in the presence of alcohols, it yielded alkylated alcohols as the final product. By extension, this reaction can alkylate other biomolecules containing OH groups and others containing labile hydrogens. Triuret was also found to be elevated in the urine of subjects with preeclampsia, a pregnancy-specific hypertensive syndrome that is associated with oxidative stress, whereas very little triuret is produced in normal healthy volunteers. We conclude that under conditions of oxidative stress, uric acid can form reactive intermediates, including potential alkylating species, by reacting with peroxynitrite. These reactive intermediates could possibly explain how uric acid contributes to the pathogenesis of diseases such as the metabolic syndrome and hypertension.

Inactivation of nitric oxide by uric acid

The 1980 identification of nitric oxide (NO) as an endothelial cell-derived relaxing factor resulted in an unprecedented biomedical research of NO and established NO as one of the most important cardiovascular, nervous and immune system regulatory molecule. A reduction in endothelial cell NO levels leading to "endothelial dysfunction" has been identified as a key pathogenic event preceding the development of hypertension, metabolic syndrome, and cardiovascular disease. The reduction in endothelial NO in cardiovascular disease has been attributed to the action of oxidants that either directly react with NO or uncouple its substrate enzyme. In this report, we demonstrate that uric acid (UA), the most abundant antioxidant in plasma, reacts directly with NO in a rapid irreversible reaction resulting in the formation of 6-aminouracil and depletion of NO. We further show that this reaction occurs preferentially with NO even in the presence of oxidants peroxynitrite and hydrogen peroxide and that the reaction is at least partially blocked by glutathione. This study shows a potential mechanism by which UA may deplete NO and cause endothelial dysfunction, particularly under conditions of oxidative stress in which UA is elevated and intracellular glutathione is depleted.

Design, synthesis, and biological characterization of potential antiatherogenic nitric oxide releasing tocopherol analogs

Synthesis and biological characterization of a series of alpha-tocopherol analogs with NO-releasing capacity are reported. The selected NO-donor moieties were nitrooxy and furoxan. All products were tested for their in vitro NO-releasing capacities, vasodilating properties, and antiplatelet activity. They were also capable of preventing LDL oxidation.

The High Atherosclerotic Risk Among Epileptics: the Atheroprotective Role of Multivitamins

Neurologists have little concern about the high atherosclerotic risk among epileptics. Recent evidences mount that chronic epilepsy and prolonged use of antiepileptic drugs (AEDs) are associated with multiple risk factors that are critically implicated in pathobiology and dysfunction of the vessel wall through complex molecular mechanisms that promote atherogenesis. This review is concerned with three metabolic alterations, which are attributed as major risk factors for atherosclerosis among epileptics: altered metabolism of a) homocysteine (Hcy), b) lipids and lipoproteins, and c) uric acid. Most conventional AEDs reduce folic acid levels, thereby raising Hcy levels. Hyperhomosysteinemia is recently believed to induce endothelial dysfunction and promote atherosclerosis through complex oxidative and excitatory neurotoxic molecular mechanisms. However, Hcy itself is a convulsing substance with increased seizure recurrence and intractability to antiepileptic medications. AEDs can disturb lipid metabolism with resultant hypercholestrolemia and dyslipidemia, common recognized risks for atherosclerosis. Altered uric acid metabolism is common among epileptics. Uric acid has been implicated in endothelial cell damage and decreased endothelial nitric oxide bioavailability. In the presence of atherosclerotic milieu, uric acid interacts with other substrate toxicities and increased reactive oxygen species, accelerating atherosclerosis. The above information forms the rationale for future routine screening and correction of such metabolic alterations in epileptics. A convincing argument now develops that routine polyvitamin supplementation (folic acid, vitamin B12, vitamin B6, vitamin C, vitamin E, and beta-carotene) becomes increasingly important for women and men receiving AEDs at all ages. The atheroprotective effect of multivitamins is through their antioxidant and anti-inflammatory effects together with their lipid and Hcy lowering effects.

Uric acid: A new look at an old risk marker for cardiovascular disease, metabolic syndrome, and type 2 diabetes mellitus: The urate redox shuttle

Background

The topical role of uric acid and its relation to cardiovascular disease, renal disease, and hypertension is rapidly evolving. Its important role both historically and currently in the clinical clustering phenomenon of the metabolic syndrome (MS), type 2 diabetes mellitus (T2DM), atheroscleropathy, and non-diabetic atherosclerosis is of great importance.

Results

Uric acid is a marker of risk and it remains controversial as to its importance as a risk factor (causative role). In this review we will attempt to justify its important role as one of the many risk factors in the development of accelerated atherosclerosis and discuss its importance of being one of the multiple injurious stimuli to the endothelium, the arterial vessel wall, and capillaries. The role of uric acid, oxidative – redox stress, reactive oxygen species, and decreased endothelial nitric oxide and endothelial dysfunction cannot be over emphasized.

In the atherosclerotic prooxidative environmental milieu the original antioxidant properties of uric acid paradoxically becomes prooxidant, thus contributing to the oxidation of lipoproteins within atherosclerotic plaques, regardless of their origins in the MS, T2DM, accelerated atherosclerosis (atheroscleropathy), or non-diabetic vulnerable atherosclerotic plaques. In this milieu there exists an antioxidant – prooxidant urate redox shuttle.

Conclusion

Elevations of uric acid > 4 mg/dl should be considered a "red flag" in those patients at risk for cardiovascular disease and should alert the clinician to strive to utilize a global risk reduction program in a team effort to reduce the complications of the atherogenic process resulting in the morbid – mortal outcomes of cardiovascular disease.