Uric acid biorhythm, a feature of long-term variation in a clinical laboratory database

Background: The biorhythm of serum uric acid was evaluated in a large sample of a clinical laboratory database by spectral analysis and the influence of the gender and age on uric acid variability. Methods: Serum uric acid values were extracted from a large database of a clinical laboratory from May 2000 to August 2006. Outlier values were excluded from the analysis and the remaining data (n = 73,925) were grouped by gender and age ranges. Rhythm components were obtained by the Lomb Scargle method and Cosinor analysis. Results: Serum uric acid was higher in men than in women older than 13 years (p<0.05). Compared with 0-12 year group, uric acid increased in men but not in women older than 13 years (p<0.05). Circannual (12 months) and transyear (17 months) rhythm components were detected, but they were significant only in adult individuals (>26 years, p<0.05). Cosinor analysis showed that midline estimating statistic of rhythm (MESOR) values were higher in men (range: 353-368 mu mol/L) than in women (range: 240-278 mu mol/L; p<0.05), independent of the age and rhythm component. The extent of predictable change within a cycle, approximated by the double amplitude, represented up to 20% of the corresponding MESOR. Conclusions: Serum uric acid biorhythm is dependent on gender and age and it may have relevant influence on preanalytical variability of clinical laboratory results.

The relationship between training status, blood pressure and uric acid in adults and elderly

Abstract Background Hypertension can be generated by a great number of mechanisms including elevated uric acid (UA) that contribute to the anion superoxide production. However, physical exercise is recommended to prevent and/or control high blood pressure (BP). The purpose of this study was to investigate the relationship between BP and UA and whether this relationship may be mediated by the functional fitness index. Methods All participants (n = 123) performed the following tests: indirect maximal oxygen uptake (VO2max), AAHPERD Functional Fitness Battery Test to determine the general fitness functional index (GFFI), systolic and diastolic blood pressure (SBP and DBP), body mass index (BMI) and blood sample collection to evaluate the total-cholesterol (CHOL), LDL-cholesterol (LDL-c), HDL-cholesterol (HDL-c), triglycerides (TG), uric acid (UA), nitrite (NO2) and thiobarbituric acid reactive substances (T-BARS). After the physical, hemodynamic and metabolic evaluations, all participants were allocated into three groups according to their GFFI: G1 (regular), G2 (good) and G3 (very good). Results Baseline blood pressure was higher in G1 when compared to G3 (+12% and +11%, for SBP and DBP, respectively, p<0.05) and the subjects who had higher values of BP also presented higher values of UA. Although UA was not different among GFFI groups, it presented a significant correlation with GFFI and VO2max. Also, nitrite concentration was elevated in G3 compared to G1 (140±29 μM vs 111± 29 μM, for G3 and G1, respectively, p<0.0001). As far as the lipid profile, participants in G3 presented better values of CHOL and TG when compared to those in G1. Conclusions Taking together the findings that subjects with higher BP had elevated values of UA and lower values of nitrite, it can be suggested that the relationship between blood pressure and the oxidative stress produced by acid uric may be mediated by training status.

Expression, purification, and structural insights for the human uric acid transporter, GLUT9, using the Xenopus laevis oocytes system.

The urate transporter, GLUT9, is responsible for the basolateral transport of urate in the proximal tubule of human kidneys and in the placenta, playing a central role in uric acid homeostasis. GLUT9 shares the least homology with other members of the glucose transporter family, especially with the glucose transporting members GLUT1-4 and is the only member of the GLUT family to transport urate. The recently published high-resolution structure of XylE, a bacterial D-xylose transporting homologue, yields new insights into the structural foundation of this GLUT family of proteins. While this represents a huge milestone, it is unclear if human GLUT9 can benefit from this advancement through subsequent structural based targeting and mutagenesis. Little progress has been made toward understanding the mechanism of GLUT9 since its discovery in 2000. Before work can begin on resolving the mechanisms of urate transport we must determine methods to express, purify and analyze hGLUT9 using a model system adept in expressing human membrane proteins. Here, we describe the surface expression, purification and isolation of monomeric protein, and functional analysis of recombinant hGLUT9 using the Xenopus laevis oocyte system. In addition, we generated a new homology-based high-resolution model of hGLUT9 from the XylE crystal structure and utilized our purified protein to generate a low-resolution single particle reconstruction. Interestingly, we demonstrate that the functional protein extracted from the Xenopus system fits well with the homology-based model allowing us to generate the predicted urate-binding pocket and pave a path for subsequent mutagenesis and structure-function studies.

PLACENTAL URIC ACID TRANSPORTER GLUT9 IS MODULATED BY FREE IODINE

PLACENTAL URIC ACID TRANSPORTER GLUT9 IS MODULATED BY FREE IODINE Objectives: Materno-fetal transplacental transport is crucial for the fetal well-being. The altered expression of placental transport proteins under specific pathophysiological conditions may affect the intrauterine environment. Pre-eclampsia is often associated with high maternal uric acid serum levels. The regulation of the placental uric transport system and its transporter glucose transporter (GLUT)-9 are not fully understood yet. The aim of this study was to investigate the placental urate transport and to characterize its transporter GLUT9. Methods: In this study we used a transepithelial transport (Transwell®) model to assess uric acid transport activity. Electrophysiological techniques and radioactive ligand up-take assays were used to measure transport activity of GLUT9 expressed in Xenopus oocytes. Results: In the Transwell/model uric acid is transported across the BeWo choriocarcinoma cell monolayer with 530 pmol/min at the linear stage. We could successfully over-express GLUT9 using the Xenopus laevis oocytes expression system. Chloride modulates the urate transport system: interestingly replacing chloride with iodine resulted in a complete loss of urate transport activity.We determined the IC50 of iodine at 30uM concentration. In radioactive up-take experiments iodinehad noeffect on uric acid transport. Conclusions: In vitro the “materno-fetal” transport of uric acid is slow. This indicates that in vivo the child is protected from short-term fluctuations of maternal uric acid serum concentrations. The different results regarding iodine-mediated regulation of GLUT9 transport activity between electrophysiological and radioactive ligand uptake experiments may suggest that iodine does not directly inhibit uric acid transport, but changes the mode of up-take from an electrogenic to an electroneutral transport. GLUT9 is not an uric acid uniporter, there are more ions involved in the transport. This may allow regulating uric acid transport by the change from an active to a passive transport.

Placental Uric Acid Transport System: Glucose Transporter 9 (SLC2A9)

Placental Uric Acid Transport System: Glucose Transporter 9 (SLC2A9). INTRODUCTION: Pre-eclampsia, a pregnancy-specific disease, contributes substantially to perinatal morbidity and mortality of both the mother and her child. Pre-eclampsia is often associated with high maternal urate serum levels, which in turn has been shown to play a role in the pathogenesis of this disease. The aim of this study was to investigate the glucose transporter GLUT9-mediated placental uric acid transport system. METHODS: In this study western blot, immunofluorescence techniques as well as a transepithelial transport (Transwell) model were used to assess GLUT9 protein expression and, respectively, uric acid transport activity. Electrophysiological techniques and transmission electron microscopy (TEM) were used to characterize the properties and the structure of GLUT9. RESULTS: Uric acid is transported across a BeWo choriocarcinoma cell monolayer with 530 pmol/min. We could successfully overexpress and for the first time purify the GLUT9b isoform using the Xenopus laevis oocytes expression system. Chloride seems to modulate the urate transport system. TEM revealed that GLUT9b isoform is present as monomer and dimmer in the Xenopus laevis overexpression model. A class average of all the particles allowed us to develop a first model of human GLUT9b structure, which was derived from the published crystal structure of the bacterial homologue of GLUT1-4. CONCLUSIONS: In vitro the “materno-fetal” transport of uric acid is slow indicating that in vivo the fetus might be protected from short-term fluctuations of maternal urate serum levels. The low-resolution structure obtained from TEM validates the proposed homology model regarding the structure of human GLUT9b. In ongoing studies this model is used to perform virtual screening to identify novel modulators of the urate transport system enabling the development of novel therapies in pregnancy complications.

Uric Acid and Cardiovascular Events: A Mendelian Randomization Study

Obesity and diets rich in uric acid-raising components appear to account for the increased prevalence of hyperuricemia in Westernized populations. Prevalence rates of hypertension, diabetes mellitus, CKD, and cardiovascular disease are also increasing. We used Mendelian randomization to examine whether uric acid is an independent and causal cardiovascular risk factor. Serum uric acid was measured in 3315 patients of the Ludwigshafen Risk and Cardiovascular Health Study. We calculated a weighted genetic risk score (GRS) for uric acid concentration based on eight uric acid-regulating single nucleotide polymorphisms. Causal odds ratios and causal hazard ratios (HRs) were calculated using a two-stage regression estimate with the GRS as the instrumental variable to examine associations with cardiometabolic phenotypes (cross-sectional) and mortality (prospectively) by logistic regression and Cox regression, respectively. Our GRS was not consistently associated with any biochemical marker except for uric acid, arguing against pleiotropy. Uric acid was associated with a range of prevalent diseases, including coronary artery disease. Uric acid and the GRS were both associated with cardiovascular death and sudden cardiac death. In a multivariate model adjusted for factors including medication, causal HRs corresponding to each 1-mg/dl increase in genetically predicted uric acid concentration were significant for cardiovascular death (HR, 1.77; 95% confidence interval, 1.12 to 2.81) and sudden cardiac death (HR, 2.41; 95% confidence interval, 1.16 to 5.00). These results suggest that high uric acid is causally related to adverse cardiovascular outcomes, especially sudden cardiac death.

Health through diet; a practical guide to the uric-acid-free diet, founded on eighteen years' personal experience

Mode of access: Internet.

The influence of bird droppings and uric acid on the radial growth of five species of saxicolous lichens

Bird droppings were applied over 1 year as a thick paste and as a suspension in deionized water to five species of lichens with different distributions on and off bird perching stones. The paste and suspension increased the radial growth of Parmelia conspersa while the paste increased the growth of Xanthoria parietina and reduced the growth and caused loss of colour in Parmelia glabratula ssp. fuliginosa. There were no statistically significant effects of paste or suspension on the growth of Physcia grisea or Parmelia saxatilis. In P. conspersa and X. parietina the growth responses were similar through the year but in P. glabratula the inhibitory effect of the paste was significant after 8 months growth. Application of a suspension of uric acid over 1 year had no statistically significant effects on the growth of P. conspersa, P. glabratula or X. parietina and was unlikely to be responsible for the effects of bird droppings on growth. The growth responses of the five species agreed well with their distributions in the field.

The impact of serum uric acid on the diagnostic of metabolic syndrome in apparently healthy Brazilian middle-aged men

Background: Hyperuricemia is related to Metabolic Syndrome (MetS) and cardiovascular diseases, but the use of serum uric acid (UA) to diagnose MetS is currently ignored in clinical practices. Objectives: To examine the impact of serum UA on the diagnostic of MetS and the relationship of serum UA with cardiometabolic risk factors in apparently healthy Brazilian middle-aged men residents in a city of Minas Gerais. Methods: In a cross-sectional analysis, 289 apparently healthy middle-aged men underwent anthropometric, clinical, sociodemographic and blood serum biochemical evaluation. By using receive operating curve the internal cutoff of serum UA was determined (5.25 mg/dL). Results: Subjects with two or more components of MetS exhibited higher serum UA as compared to those with one or none component. The inclusion of serum UA ≥ 5.25mg/dL as an additional component of MetS increased the occurrence of this syndrome by 13%. Subjects with UA ≥ 5.25mg/dL showed high prevalence for MetS and association with its components (central obesity, hypertriglyceridemia, dyslipidemia and hypertension) as well as atherogenic risk. Conclusions: Serum UA has an important impact on the diagnostic of MetS and is related to cardiometabolic risk factors in apparently healthy Brazilian middle-aged men. Its use in clinical practices could aggregate accuracy to diagnose MetS.

Electrocatalytic oxidation of ascorbic acid using a single layer of gold nanoparticles immobilized on 1,6-hexanedithiol modified gold electrode

This paper describes the electrocatalytic oxidation of ascorbic acid (AA) in phosphate buffer solution by the immobilized citrate capped gold nanoparticles (AuNPs) on 1,6-hexanedithiol (HDT) modified Au electrode. X-ray photoelectron spectrum (XPS) of HDT suggests that it forms a monolayer on Au surface through one of the two single bondSH groups and the other single bondSH group is pointing away from the electrode surface. The free single bondSH groups of HDT were used to covalently attach colloidal AuNPs. The covalent attachment of AuNPs on HDT monolayer was confirmed from the observed characteristic carboxylate ion stretching modes of citrate attached with AuNPs in the infra-red reflection absorption spectrum (IRRAS) in addition to a higher reductive desorption charges obtained for AuNPs immobilized on HDT modified Au (Au/HDT/AuNPs) electrode in 0.1 M KOH when compared to HDT modified Au (Au/HDT) electrode. The electron transfer reaction of [Fe(CN)6]4−/3− was markedly hindered at the HDT modified Au (Au/HDT) electrode while it was restored with a peak separation of 74 mV after the immobilization of AuNPs on Au/HDT (Au/HDT/AuNPs) electrode indicating a good electronic communication between the immobilized AuNPs and the underlying bulk Au electrode through a HDT monolayer. The Cottrell slope obtained from the potential-step chronoamperometric measurements for the reduction of ferricyanide at Au/HDT/AuNPs was higher than that of bare Au electrode indicating the increased effective surface area of AuNPs modified electrode. The Au/HDT/AuNPs electrode exhibits excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA) by enhancing the oxidation peak current to more than two times with a 210 mV negative shift in the oxidation potential when compared to a bare Au electrode. The standard heterogeneous electron transfer rate constant (ks) calculated for AA oxidation at Au/HDT/AuNPs electrode was 5.4 × 10−3 cm s−1. The oxidation peak of AA at Au/HDT/AuNPs electrode was highly stable upon repeated potential cycling. Linear calibration plot was obtained for AA over the concentration range of 1–110 μM with a correlation coefficient of 0.9950. The detection limit of AA was found to be 1 μM. The common physiological interferents such as glucose, oxalate ions and urea do not show any interference within the detection limit of AA. The selectivity of the AuNPs modified electrode was illustrated by the determination of AA in the presence of uric acid.

Electrocatalytic oxidation of ascorbic acid by ferrocene in lipid film cast on a glassy carbon electrode

A ferrocene-dimyristoyl phosphatidylcholine (DMPC) film electrode was prepared by casting the solution of ferrocene and DMPC in chloroform onto a glassy carbon electrode surface. Ferrocene retained in the biological membrane gave a couple of irreversible peaks of cyclic voltammogram. The electrode exhibited good electrocatalytic activity for the oxidation of ascorbic acid (H(2)A) in phosphate buffer (pH 6.64) with an anodic peak potential of +340 mV (vs. Ag/AgCl). The anodic current was directly proportional to the square root of the scan rate below 150 mV s(-1). The influence of the pH value was investigated and it was observed that pH 6.64 was the suitable value to the anodic peak potential and current. The thickness of the film and the interference of uric acid were also studied. The electrode can be used to determine H(2)A in the presence of equimolar uric acid. The catalytic peak current increased linearly with the concentration of H(2)A in the range of 1 X 10(-4)-5 X 10(-3) mol L-1.

Electrocatalytic oxidation of ascorbic acid by norepinephrine embedded in lipid cast film at glassy carbon electrode

A stable lipid cast film was made by casting a lipid in chloroform onto a glassy carbon electrode. We imbedded a new mediator norepinephrine into this lipid cast film, which was considered as a biological membrane model. Through electro catalytic oxidation of ascorbic acid by this system, the anodic overpotential was reduced by about 250 mV compared with that obtained at a bare glassy carbon electrode. The electrochemical behavior of norepinephrine in the cast film was controlled by diffusion. The obtained diffusion coefficient of ascorbic acid was 1.87 x 10(-5) cm 2 s(-1). The catalytic current increased linearly with the concentration of ascorbic acid in the range from 0.5 to 10 mM. Using cyclic voltammetry, we obtained two peaks for ascorbic acid and uric acid in the same solution. The separation between the two peaks is about 147 mV. (C) 2001 Elsevier Science Ltd. All rights reserved.

FIA determination of ascorbic acid at low potential using a ruthenium oxide hexacyanoferrate modified carbon electrode

The anodic oxidation of ascorbic acid on a ruthenium oxide hexacyanoferrate modified electrode was characterized by cyclic voltammetry. On this modified surface, the electrocatalytic process allows the determination of ascorbic acid to be performed at 0.0 V and pH 6.9 with a limit of detection of 2.2 mu M in a flow injection configuration. Under this experimental condition, no interference from glucose, nitrite and uric acid was noticed. Lower detection limit values were obtained by measuring flow injection analysis (FIA) responses at 0.4 V (0.14 mu M), but a concurrent loss of selectivity is expected at this more positive potential. Under optimal FIA operating conditions, the linear response of the method was extended up to 1 mM ascorbic acid. The repeatability of the method for injections of a 1.0 mM ascorbic acid solution was 2.0% (n=10). The usefulness of the method was demonstrated by an addition-recovery experiment with urine samples and the recovered values were in the 98-104% range. (c) 2007 Elsevier B.V. All rights reserved.

Electrocatalytic behavior of glassy carbon electrodes modified with multiwalled carbon nanotubes and cobalt phthalocyanine for selective analysis of dopamine in presence of ascorbic acid

This work describes the development, electrochemical characterization and utilization of a cobalt phthalocyanine modified carbon nanotube electrode for the quantitative determination of dopamine in 0.2 mol L-1 phosphate buffer contaminated with high concentration of ascorbic acid. The electrode surface was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy which showed a modified surface presenting a charge transfer resistance of 500 Omega, against the 16.46 k Omega value found for the bare glassy carbon surface. A pseudo rate constant value of 5.4 x 10(-4) cm s(-1) for dopamine oxidation was calculated. Voltammetric experiments showed a shift of the peak potential of DA oxidation to less positive value at 390 mV as compared with that of a bare GC electrode at 570 mV. The electrochemical determination of dopamine, in presence of ascorbic acid in concentrations up to 0.1 mol L-1 by differential pulse voltarnmetry, yielded a detection limit as low as 2.56 x 10(-7) mol L-1.