Distribution of xanthine dehydrogenase and oxidase activities in human and rabbit tissues

Reactive oxygen species promote endurance exercise-induced adaptations in skeletal muscles

The discovery that contracting skeletal muscle generates reactive oxygen species (ROS) was first reported over 40 years ago. The prevailing view in the 1980s was that exercise-induced ROS production promotes oxidation of proteins and lipids resulting in muscle damage. However, a paradigm shift occurred in the 1990s as growing research revealed that ROS are signaling molecules, capable of activating transcriptional activators/coactivators and promoting exercise-induced muscle adaptation. Growing evidence supports the notion that reduction-oxidation (redox) signaling pathways play an important role in the muscle remodeling that occurs in response to endurance exercise training. This review examines the specific role that redox signaling plays in this endurance exercise-induced skeletal muscle adaptation. We begin with a discussion of the primary sites of ROS production in contracting muscle fibers followed by a summary of the antioxidant enzymes involved in the regulation of ROS levels in the cell. We then discuss which redox-sensitive signaling pathways promote endurance exercise-induced muscle adaptation and debate the strength of the evidence supporting the notion that redox signaling plays an essential role in muscle adaptation to endurance exercise training. In hopes of stimulating future research, we highlight several important unanswered questions in this field.

Serum uric acid and left ventricular hypertrophy in hypertensive patients in Ado-Ekiti

Introduction

systemic hypertension is a foremost risk factor for cardiovascular morbidity and mortality. Its actions are manifested on organs like the brain, heart and kidneys. High serum uric acid (SUA) escalates cardiovascular vulnerability in patients with systemic hypertension.

Methods

a cross-sectional study was performed in 271 (178 females, 93 males) patients with systemic hypertension. Two hundred and seventy one healthy age and sex matched non-hypertensive persons obliged as controls. Left ventricular hypertrophy (LVH) was estimated by echocardiography. Blood samples were collected for measuring uric acid levels.

Results

mean SUA was significantly higher among the hypertensive patients (371±125μmol/L) than in the controls (269 ± 101.4μmol/L; p < 0.001), and the prevalence of hyperuricemia was 46.9% among the hypertensives and 11.1% among the controls (P < 0.001). Independent predictors of SUA were class of systemic hypertension, left ventricular mass index (LVMI), body mass index (BMI) and age. However, class of hypertension was the best independent predictor of SUA levels in the multivariate regression model (β = 0.597). Linear regression revealed SUA levels ≥ 430μmols/l as a predictor of stage 2 hypertension (F = 26.620, p = < 0.001). Among the hypertensive patients, LVH was present in 39.3% of those with hyperuricemia and in 28.0% of those with normal SUA levels (p = 0.003).

Conclusion

results indicate serum uric acid is positively correlated with hypertension and a reliable indicator of LVH in study population.

Excess Iron Enhances Purine Catabolism Through Activation of Xanthine Oxidase and Impairs Myelination in the Hippocampus of Nursing Piglets

BACKGROUND

Few studies have addressed the risk of nutritional iron overexposure in infancy. We previously found that excess dietary iron in nursing piglets resulted in iron overload in the liver and hippocampus and diminished socialization with novel conspecifics in a test for social novelty preference.

OBJECTIVES

This experiment aimed to identify metabolites and metabolic pathways affected by iron overload in the liver and hippocampus of nursing piglets.

METHODS

Liver and hippocampal tissues collected from 22-d-old piglets (Hampshire × Yorkshire crossbreed; 5.28 ± 0.53 kg body weight; 50% male) that received orally 0 (NI group) or 50 mg iron/(d · kg body weight) (HI group) from postnatal day (PD) 2 to PD21 were analyzed for mRNA and protein expression and enzyme activity of xanthine oxidase (XO). Untargeted metabolomics was performed using GC-MS. Expression of myelin basic protein (MBP) in the hippocampus was determined using western blot.

RESULTS

There were 108 and 126 metabolites identified in the hippocampus and liver, respectively. Compared with NI, HI altered 15 metabolites (P < 0.05, q < 0.2) in the hippocampus, including a reduction in myo-inositol (0.86-fold) and N-acetylaspartic acid (0.84-fold), 2 metabolites important for neuronal function and myelination. Seven metabolites involved in purine and pyrimidine metabolism (e.g., hypoxanthine, xanthine, and β-alanine) were coordinately changed in the hippocampus (P < 0.05, q < 0.2), suggesting that iron excess enhanced purine catabolism. The mRNA expression (2.3-fold) (P < 0.05) and activity of XO, a rate-limiting enzyme in purine degradation, was increased. Excess iron increased hippocampal lipid peroxidation by 74% (P < 0.05) and decreased MBP by 44% (P = 0.053). The hepatic metabolome was unaffected.

CONCLUSIONS

In nursing piglets, excess iron enhances hippocampal purine degradation through activation of XO, which may induce oxidative stress and alter energy metabolism in the developing brain.

Activity of xanthine oxidase in plasma correlates with indices of insulin resistance and liver dysfunction in patients with type 2 diabetes mellitus and metabolic syndrome: A pilot exploratory study

Aims/Introduction

There is controversy as to whether hyperuricemia is an independent risk factor for cardiometabolic diseases. The serum level of uric acid is affected by a wide variety of factors involved in its production and excretion. In contrast, evidence has accumulated that locally‐ and systemically‐activated xanthine oxidase (XO), a rate‐limiting enzyme for production of uric acid, is linked to metabolic derangement in humans and rodents. We therefore explored the clinical implication of plasma XO activity in patients with type 2 diabetes mellitus and metabolic syndrome (MetS).

Materials and Methods

We enrolled 60 patients with type 2 diabetes mellitus and MetS. MetS was defined according to the 2005 International Diabetes Federation guidelines. Plasma XO activity was measured by highly‐sensitive fluorometric assay measuring the conversion of pterin to isoxanthopterin, and explored associations between the value of plasma XO activity and metabolic parameters.

Results

The value of plasma XO activity was correlated with indices of insulin resistance and the level of circulating liver transaminases. In contrast, the level of serum uric acid was not correlated with indices of insulin resistance. The value of plasma XO activity was not correlated with the serum uric acid level.

Conclusions

Plasma XO activity correlates with indices of insulin resistance and liver dysfunction in Japanese patients with type 2 diabetes mellitus and MetS. Through assessing the plasma XO activity, patients showing normal levels of serum uric acid with higher activity of XO can be screened, thereby possibly providing a clue to uncovering metabolic risks in type 2 diabetes mellitus and MetS patients.

In vivo evidence of free radical generation in the mouse lung after exposure to Pseudomonas aeruginosa bacterium: an ESR spin-trapping investigation

In the Pseudomonas aeruginosa-induced rodent pneumonia model, it is thought that free radicals are significantly associated with the disease pathogenesis. However, until now there has been no direct evidence of free radical generation in vivo. Here we used electron spin resonance (ESR) and in vivo spin trapping with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone to investigate free radical production in a murine model. We detected and identified generation of lipid-derived free radicals in vivo (a(N) =14.86 ± 0.03 G and a(H)(β) =2.48 ± 0.09 G). To further investigate the mechanism of lipid radical production, we used modulating agents and knockout mice. We found that with GdCl(3) (phagocytic toxicant), NADPH-oxidase knockout mice (Nox2(-)/(-)), allopurinol (xanthine-oxidase inhibitor) and Desferal (metal chelator), generation of lipid radicals was decreased; histopathological and biological markers of acute lung injury were noticeably improved. Our study demonstrates that lipid-derived free radical formation is mediated by NADPH-oxidase and xanthine-oxidase activation and that metal-catalysed hydroxyl radical-like species play important roles in lung injury caused by Pseudomonas aeruginosa.

Training-induced adaptation in purine metabolism in high-level sprinters vs. triathletes

The aim of this study was to assess the effect of training loads on metabolic response of purine derivatives in highly trained sprinters (10 men, age range 20-29 yr) in a 1-yr cycle, compared with endurance-training mode in triathletes (10 men, age range 21-28 yr). A four-time measurement of respiratory parameters, plasma hypoxanthine (Hx) concentration, and erythrocyte hypoxanthine-guanine phosphoribosyl transferase (HGPRT) activity was administered in four characteristic training phases (general, specific, competition, and transition). A considerably lower postexercise plasma concentration of Hx in sprinters (8.1-18.0 μmol/l) than in triathletes (14.1-24.9 μmol/l) was demonstrated in all training phases. In both groups, a significant decrease in plasma Hx concentration in the competition phase and a considerable increase in the transition phase were observed. It was found that the resting erythrocyte HGPRT activity increased in the competition period and declined in the transition phase. Sprinters showed higher HGPRT activity (58.5-71.8 nmol IMP·mg Hb(-1)·h(-1)) than triathletes (55.8-66.6 nmol IMP·mg Hb(-1)·h(-1)) in all examinations. The results suggest a more effective use of anaerobic metabolic energy sources induced by sprint training characterized by higher amount of exercise in the anaerobic lactacid and the nonlactacid zone. The changes in plasma Hx concentration and erythrocyte HGPRT activity might serve as sensitive metabolic indicators in the training control, especially in sprint-trained athletes. These parameters may provide information about the energetic status of the muscles in highly trained athletes in which no significant adaptation changes are detected by means of commonly acknowledged biochemical and physiological parameters.

The cellular and molecular origin of reactive oxygen species generation during myocardial ischemia and reperfusion

Myocardial ischemia-reperfusion injury is an important cause of impaired heart function in the early postoperative period subsequent to cardiac surgery. Reactive oxygen species (ROS) generation increases during both ischemia and reperfusion and it plays a central role in the pathophysiology of intraoperative myocardial injury. Unfortunately, the cellular source of these ROS during ischemia and reperfusion is often poorly defined. Similarly, individual ROS members tend to be grouped together as free radicals with a uniform reactivity towards biomolecules and with deleterious effects collectively ascribed under the vague umbrella of oxidative stress. This review aims to clarify the identity, origin, and progression of ROS during myocardial ischemia and reperfusion. Additionally, this review aims to describe the biochemical reactions and cellular processes that are initiated by specific ROS that work in concert to ultimately yield the clinical manifestations of myocardial ischemia-reperfusion. Lastly, this review provides an overview of several key cardioprotective strategies that target myocardial ischemia-reperfusion injury from the perspective of ROS generation. This overview is illustrated with example clinical studies that have attempted to translate these strategies to reduce the severity of ischemia-reperfusion injury during coronary artery bypass grafting surgery.

The Significance of the Measurement of Serum Xanthine Oxidase and Oxidation Markers in Patients with Acute Organophosphorus Pesticide Poisoning

This study investigated whether xanthine oxidase (XO) plays an important role in the mechanism of toxicity of acute organophosphorus pesticide poisoning (AOPP). The serum activities of XO, superoxide dismutase (SOD), paraoxonase-1 (PON1), butyrylcholinesterase (BChE) and malondialdehyde (MDA) were compared in 49 patients with AOPP and 50 age- and gender-matched healthy controls. Serum XO and MDA activities were higher and the serum SOD, PON1 and BChE activities were lower in the AOPP patients compared with the controls. Pearson correlation analysis demonstrated a significant negative correlation between XO activity and the SOD, PON1 and BChE activities, but a significant positive correlation between XO activity and MDA. These results suggest that increased activity of XO and decreased antioxidant enzyme activity contribute to the development of oxidative injury in AOPP patients. Thus, effective antioxidant therapy may be a therapeutic option following AOPP.

Identification of proteins binding to E-Box/Ku86 sites and function of the tumor suppressor SAFB1 in transcriptional regulation of the human xanthine oxidoreductase gene

The xanthine oxidoreductase gene (XOR) encodes an important source of reactive oxygen species and uric acid, and its expression is associated with various human diseases including several forms of cancer. We previously reported that basal human XOR (hXOR) expression is restricted or repressed by E-box and TATA-like elements and a cluster of transcriptional proteins, including AREB6-like proteins and DNA-dependent protein kinase (DNA-PK). We now demonstrate that the cluster contains the tumor suppressors SAFB1, BRG1, and SAF-A. We further demonstrate that SAFB1 silencing increases hXOR expression and that SAFB1 directly binds to the E-box. Multiple studies in vitro and in vivo including pulldown, immunoprecipitation and chromatin immunoprecipitation analyses indicate that SAFB1, Ku86, and BRG1 associate with each other. The results suggest that the SAFB1 complex binds to the hXOR promoter in a chromatin environment and plays a critical role in restricting hXOR expression via its direct interaction with the E-box, DNA-PK, and tumor suppressors. Moreover, we demonstrate that the cytokine, oncostatin M (OSM), induces the phosphorylation of SAFB1 and that the OSM-induced hXOR mRNA expression is significantly inhibited by silencing the DNA-PK catalytic subunit or SAFB1 expression. The present studies for the first time demonstrate that hXOR is a tumor suppressor-targeted gene and that the phosphorylation of SAFB1 is regulated by OSM, providing a molecular basis for understanding the role of SAFB1-regulated hXOR transcription in cytokine stimulation and tumorigenesis.

Xanthine oxidoreductase and neurological sequelae of carbon monoxide poisoning

Neurological sequelae (NS) is a common complication of carbon monoxide (CO) poisoning and structural alterations of myelin basic protein have been proven to initiate immunological reactions leading to NS. To determine whether xanthine oxidoreductase (XOR) participates in the pathophysiology of CO-mediated NS, we examined myelin basic protein in CO poisoned XOR-depleted rats and performed radial maze studies to evaluate the alteration of cognitive function. Carbon monoxide poisoned XOR-depleted rats did not exhibit myelin basic protein alterations or impaired cognitive function, both found in CO poisoned control rats. These results indicate that XOR is essential to the pathological cascade of CO-mediated NS.

Serum level of uric acid, partly secreted from the failing heart, is a prognostic marker in patients with congestive heart failure

BACKGROUND

A recent study suggested that xanthine oxidase is activated in congestive heart failure (CHF). However, whether uric acid (UA) is secreted from the failing heart remains unknown, so it is currently unclear whether serum UA can provide prognostic information independent of brain natriuretic peptide (BNP).

METHODS AND RESULTS

Serum UA was measured in the aortic root (AO) and the coronary sinus (CS) of 74 patients with CHF. The serum UA level was significantly higher in the CS than in the AO. The transcardiac gradient of UA (CS-AO) increased with the severity of CHF, inversely correlated with left ventricular ejection fraction (LVEF) and positively correlated with left ventricular end-diastolic volume index. The plasma levels of norepinephrine, BNP, UA, and LVEF were monitored prospectively in 150 CHF patients for a mean follow-up of 3 years. High plasma levels of UA (p<0.001) and BNP (p<0.001) were shown by multivariate stepwise analysis to be independent predictors of mortality.

CONCLUSIONS

High plasma UA level, partly secreted from the failing heart, is a prognostic predictor independent of BNP in patients with CHF. Monitoring a combination of BNP and UA may be useful for the management of patients with CHF.

Uric acid, left ventricular mass index, and risk of cardiovascular disease in essential hypertension

Elevated serum uric acid (UA) is frequently encountered in individuals with hypertension, but whether the relationship between UA and cardiovascular events is circumstantial or causal remains to be answered. We examined the association between serum UA and left ventricular mass index (LVMI) and investigated prospectively whether the combination of UA and LVMI can predict the incidence of cardiovascular disease (CVD) in asymptomatic subjects with essential hypertension. A total of 619 subjects (mean age, 61 years; 52% female) free of prior CVD were included in this study. A significant association between UA and LVMI was also confirmed in multiple regression analysis (male: F=4.29, P<0.04; female: F=4.24, P<0.05). During follow-up (mean, 34 months), 28 subjects (14 female) developed CVD including myocardial infarction, angina pectoris, congestive heart failure, cerebral infarction, and transient cerebral ischemia. Sex-specific median values were used to separate the higher group from the lower group of UA and LVMI. Kaplan-Meier curves showed a significantly poorer survival rate in the group with higher UA and LVMI (LVMI, male: >126.9, female: >112.0 g/m2; UA, male: >374.7, female: >303.3 micromol/L; log-rank chi2=13.18; P<0.01). Multivariate Cox regression analysis showed that the combination of higher UA and LVMI was an independent predictor for CVD events (hazard ratio, 2.38; P<0.03). Our findings demonstrate that UA is independently associated with LVMI and suggest that the combination of hyperuricemia combined with left ventricular hypertrophy is an independent and powerful predictor for CVD. The association between UA and CVD events may be introduced in part because of a direct association of UA with LVMI.

Chronic xanthine oxidase inhibition prevents myofibrillar protein oxidation and preserves cardiac function in a transgenic mouse model of cardiomyopathy

Heart failure is a clinical syndrome associated with elevated levels of oxygen-derived free radicals. Xanthine oxidase activity is believed to be one source of reactive oxygen species in the failing heart. Interventions designed to reduce oxidative stress are believed to have significant therapeutic potential in heart failure. This study tested the hypothesis that xanthine oxidase activity would be elevated in a mouse model of dilated cardiomyopathy and evaluated the effect of chronic oral allopurinol, an inhibitor of xanthine oxidase, on contractility and progressive ventricular dilation in these mice. Nontransgenic and transgenic mice containing a troponin I truncation were treated with oral allopurinol from 2–4 mo of age. Myocardial xanthine oxidase activity was threefold higher in untreated transgenic mice compared with nontransgenic mice. Analyses of myofilament proteins for modification of carbonyl groups demonstrated myofibrillar protein damage in untreated transgenic mice. Treatment with allopurinol for 2 mo suppressed xanthine oxidase activity and myofibrillar protein oxidation. Allopurinol treatment also alleviated ventricular dilation and preserved shortening fraction in the transgenic animals. In addition, cardiac muscle twitch tension was preserved to 70% of nontransgenic levels in allopurinol-treated transgenic mice, a significant improvement over untreated transgenic mice. These findings indicate that chronic inhibition of xanthine oxidase can alter the progression of heart failure in dilated cardiomyopathy.

Oxidative stress in the placenta

Pregnancy is a state of oxidative stress arising from increased placental mitochondrial activity and production of reactive oxygen species (ROS), mainly superoxide anion. The placenta also produces other ROS including nitric oxide, carbon monoxide, and peroxynitrite which have pronounced effects on placental function including trophoblast proliferation and differentiation and vascular reactivity. Excessive production of ROS may occur at certain windows in placental development and in pathologic pregnancies, such as those complicated by preeclampsia and/or IUGR, overpowering antioxidant defenses with deleterious outcome. In the first trimester, establishment of blood flow into the intervillous space is associated with a burst of oxidative stress. The inability to mount an effective antioxidant defense against this results in early pregnancy loss. In late gestation increased oxidative stress is seen in pregnancies complicated by diabetes, IUGR, and preeclampsia in association with increased trophoblast apoptosis and deportation and altered placental vascular reactivity. Evidence for this oxidative stress includes increased lipid peroxides and isoprostanes and decreased expression and activity of antioxidants. The interaction of nitric oxide and superoxide produces peroxynitrite, a powerful prooxidant with diverse deleterious effects including nitration of tyrosine residues on proteins thus altering function. Nitrative stress, subsequent to oxidative stress is seen in the placenta in preeclampsia and diabetes in association with altered placental function.

Characterization of Proteins Binding to E-box/Ku86 Sites and Function of Ku86 in Transcriptional Regulation of the Human Xanthine Oxidoreductase Gene

We reported previously that E-box and TATA-like elements repress human xanthine oxidoreductase gene (hXOR) expression. In the present investigation, we determined the means by which the E-box site functions in this basal repression. DNA affinity purification demonstrated that at least five proteins are involved in the nuclear protein complex binding to the E-box and adjacent Ku86-binding sites. Amino acid sequence analysis demonstrated that three proteins, DNA-PK catalytic subunit, Ku86, and Ku70 are components of DNA-dependent protein kinase (DNA-PK). By electrophoretic mobility shift assays, gel-shift, and site-directed mutagenesis, we confirmed Ku86 binding to the Ku86 site. Studies indicated that the other two proteins of the complex are AREB6-like proteins binding to the E-box. Pull-down and immunoprecipitation analyses demonstrated the binding of Ku86 to AREB6-like proteins. The functional loss of Ku86 increases hXOR promoter activity and transcript expression. Based on the findings, we propose that DNA-PK/AREB6-like proteins play a central role in repression of basal hXOR activity. AREB6-like proteins specifically bind to the E-box, whereas Ku86 binds an adjacent site and recruits DNA-PK catalytic subunit and Ku70 proteins. A working model is presented to account for the role of DNA-PK and AREB6-like proteins in regulating hXOR activity.

Mammalian molybdo-flavoenzymes, an expanding family of proteins: structure, genetics, regulation, function and pathophysiology

The molybdo-flavoenzymes are structurally related proteins that require a molybdopterin cofactor and FAD for their catalytic activity. In mammals, four enzymes are known: xanthine oxidoreductase, aldehyde oxidase and two recently described mouse proteins known as aldehyde oxidase homologue 1 and aldehyde oxidase homologue 2. The present review article summarizes current knowledge on the structure, enzymology, genetics, regulation and pathophysiology of mammalian molybdo-flavoenzymes. Molybdo-flavoenzymes are structurally complex oxidoreductases with an equally complex mechanism of catalysis. Our knowledge has greatly increased due to the recent crystallization of two xanthine oxidoreductases and the determination of the amino acid sequences of many members of the family. The evolution of molybdo-flavoenzymes can now be traced, given the availability of the structures of the corresponding genes in many organisms. The genes coding for molybdo-flavoenzymes are expressed in a cell-specific fashion and are controlled by endogenous and exogenous stimuli. The recent cloning of the genes involved in the biosynthesis of the molybdenum cofactor has increased our knowledge on the assembly of the apo-forms of molybdo-flavoproteins into the corresponding holo-forms. Xanthine oxidoreductase is the key enzyme in the catabolism of purines, although recent data suggest that the physiological function of this enzyme is more complex than previously assumed. The enzyme has been implicated in such diverse pathological situations as organ ischaemia, inflammation and infection. At present, very little is known about the pathophysiological relevance of aldehyde oxidase, aldehyde oxidase homologue 1 and aldehyde oxidase homologue 2, which do not as yet have an accepted endogenous substrate.

Uric acid and survival in chronic heart failure: validation and application in metabolic, functional, and hemodynamic staging

BACKGROUND

Serum uric acid (UA) could be a valid prognostic marker and useful for metabolic, hemodynamic, and functional (MFH) staging in chronic heart failure (CHF).

METHODS AND RESULTS

For the derivation study, 112 patients with CHF (age 59+/-12 years, peak oxygen consumption [Vo2] 17+/-7 mL/kg per minute) were recruited. In separate studies, we validated the prognostic value of UA (n=182) and investigated the relationship between MFH score and the decision to list patients for heart transplantation (n=120). In the derivation study, the best mortality predicting UA cutoff (at 12 months) was 565 micromol/L (9.50 mg/dL) (independently of age, peak Vo2, left ventricular ejection fraction, diuretic dose, sodium, creatinine, and urea; P<0.0001). In the validation study, UA >or=565 micromol/L predicted mortality (hazard ratio, 7.14; P<0.0001). In 16 patients (from both studies) with UA >or=565 micromol/L, left ventricular ejection fraction <or=25% and peak Vo2 <or=14 mL/kg per min (MFH score 3), 12-month survival was lowest (31%) compared with patients with 2 (64%), 1 (77%), or no (98%, P<0.0001) risk factor. In an independent study, 51% of patients with MFH score 2 and 81% of patients with MFH score 3 were listed for transplantation. The positive predictive value of not being listed for heart transplantation with an MFH score of 0 or 1 was 100%.

CONCLUSIONS

High serum UA levels are a strong, independent marker of impaired prognosis in patients with moderate to severe CHF. The relationship between serum UA and survival in CHF is graded. MFH staging of patients with CHF is feasible.

Elevated serum uric acid levels are associated with diastolic dysfunction in patients with dilated cardiomyopathy

OBJECTIVE

To assess whether serum uric acid, which is a marker of impaired oxidative metabolism, might correlate with left ventricular systolic and diastolic dysfunction in patients with chronic heart failure (CHF).

BACKGROUND

Uric acid levels, which are frequently elevated in patients with CHF, correlate with leg vascular resistance. The effects of elevated levels of uric acid on cardiac function in patients with CHF have never been evaluated.

METHODS

We studied 150 outpatients with CHF who came to our heart failure clinic. Patients underwent a complete echo-Doppler examination, with measurement of mitral E wave and mitral A wave velocities, E/A ratio, E wave deceleration time (DtE), left ventricular volumes, ejection fraction, and stroke volume. A restrictive mitral filling pattern (RMFP) was defined as either E/A ratio >2 or E/A >1 and DtE <140 milliseconds.

RESULTS

Mean age was 62.2 +/- 7.8 years (86% male); 24 patients (16%) had an RMFP. Patients with an RMFP had significantly higher uric acid levels compared with patients without RMFP (0.48 +/- 0.14 mmol/L vs 0.38 +/- 0.08 mmol/L, respectively, P <.001). Uric acid levels correlated significantly with mitral E wave velocity (r =.22, P <.01), E/A ratio (r =.21, P <.05), DtE (r =.26, P <.01), and RMFP (P =.0001). There was no correlation between uric acid and left ventricular volumes, ejection fraction, or stroke volume. In a multivariate model, uric acid predicted DtE independently of renal function, diuretic dose, and left ventricular volumes.

CONCLUSION

Elevated uric acid levels are associated with diastolic dysfunction in CHF. Xanthine oxydase inhibition in patients with CHF might theoretically result in an improvement of diastolic function.

[Formation and removal of reactive oxygen species, lipid peroxides and free radicals, and their biological effects]

It is well known that biomembranes and subcellular organelles are susceptible to lipid peroxidation. There is a steadily increasing body of evidence indicating that lipid peroxidation is involved in basic deteriorative mechanisms, e.g., membrane damage, enzyme damage, and nucleic acid mutagenicity. The formation of lipid peroxides can be induced by enzymatic or nonenzymatic peroxidation in the presence of oxygen. The mechanisms of formation and removal of reactive oxygen species, lipid peroxides, and free radicals in biological systems are briefly reviewed. In recent years, there has been renewed interest in the role played by lipid peroxidation in many disease states. Xanthine oxidase has been shown to generate reactive oxygen species, superoxide (O2-.), and hydrogen peroxide (H2O2) that are involved in the peroxidative damage to cells that occurs in ischemia-reperfusion injury. During ischemia, this enzyme is induced from xanthine dehydrogenase. We have shown that peroxynitrite (a reactive nitrogen species) has the potential to convert xanthine dehydrogenase to oxidase. The following biological effects of lipid peroxidation were found: a) the lipid peroxidation induced by ascorbic acid and Fe2+ affects the membrane transport in the kidney cortex and the cyclooxygenase activity in the kidney medulla, and b) the hydroperoxy adducts of linoleic acid and eicosapentaenoic acid inhibit the cyclooxygenase activity in platelets. The balance between the formation and removal of lipid peroxides determines the peroxide level in cells. This balance can be disturbed if cellular defenses are decreased or if there is a significant increase in peroxidative reactions. Once lipid peroxidation is initiated, the reactive intermediate formed induces cell damage.

Cellular distribution, metabolism and regulation of the xanthine oxidoreductase enzyme system

Xanthine oxidase (EC 1.1.3.22) and xanthine dehydrogenase (EC 1.1.1. 204) are both members of the molybdenum hydroxylase flavoprotein family and represent different forms of the same gene product. The two enzyme forms and their reactions are often referred to as xanthine oxidoreductase (XOR) activity. Physiologically, XOR is known as the rate-limiting enzyme in purine catabolism but has also been shown to be able to metabolize a number of other physiological compounds. Recent studies have also demonstrated its ability to metabolize xenobiotics, including a number of anticancer compounds, to their active metabolites. During the past 10 years, evidence has mounted to support a role for XOR in the pathophysiology of inflammatory diseases and atherosclerosis as well as its previously determined role in ischemia-reperfusion injury. While significant progress has recently been made in our understanding of the physiological and biochemical nature of this enzyme system, considerable work still needs to be done. This paper will review some of the more recent work characterizing the interactions and the factors that influence the interactions of XOR with various physiological and xenobiotic compounds.

Molecular mechanisms of ischemic neuronal injury

Brain ischemia triggers a complex cascade of molecular events that unfolds over hours to days. Identified mechanisms of postischemic neuronal injury include altered Ca(2+) homeostasis, free radical formation, mitochondrial dysfunction, protease activation, altered gene expression, and inflammation. Although many of these events are well characterized, our understanding of how they are integrated into the causal pathways of postischemic neuronal death remains incomplete. The primary goal of this review is to provide an overview of molecular injury mechanisms currently believed to be involved in postischemic neuronal death specifically highlighting their time course and potential interactions.

Repressed expression of the human xanthine oxidoreductase gene. E-box and TATA-like elements restrict ground state transcriptional activity

Studies were initiated to address the basis for the low xanthine oxidoreductase (XOR) activity in humans relative to nonprimate mammalian species. The expression of the XOR in humans is strikingly lower than in mice, and both transcription rates and core promoter activity of the gene are repressed. Analysis of human XOR promoter activity in hepatocytes and vascular endothelial cells showed that the region from -258 to -1 contains both repressor and activator binding regions regulating core promoter activity. The region between -138 and -1 is necessary and sufficient for initiating, and the region between -258 and -228 is critical for restricting core promoter activity. Within the latter region, site-directed mutations identified a consensus sequence "acacaggtgtgg" (-242 to -230) that contains an E-box that binds a repressor. In addition, the TATA-like element is also required to restrict promoter activity and TFIID binds to this site. The results demonstrate that both an E-box and TATA-like element are required to restrict gene activity. A model is proposed to account for human XOR regulation.

Increased metabolism of infused 1-methylxanthine by working muscle

Exogenous substrates for capillary endothelial enzymes have potential as markers for changes in capillary recruitment (albeit nutritive flow). The metabolism of infused 1-methylxanthine (1-MX) to 1-methylurate (1-MU) by capillary endothelial xanthine oxidase of the constant-flow perfused rat hindlimb was shown previously to decrease with oxygen uptake (VO2) when nutritive flow was decreased. In the present study, the metabolism of 1-MX was investigated under conditions when VO2 and nutritive flow are known to increase during muscle contraction. The constant-flow red blood cell-perfused rat hindlimb at 37 degrees C was used with sciatic nerve stimulation, and perfusate samples from whole hindlimb and working muscles taken for analysis of oxygen, lactate, 1-MX and 1-MU. Flow to muscle was assessed separately using fluorescent microspheres and was found to increase 2.3-fold to the working muscles while flow to the non-working leg muscles decreased to compensate. The activity of xanthine oxidase of whole muscle extracts was not altered by contraction. Samples from the vein draining the working muscles, and microsphere measurements of flow, indicated increased VO2 (5.5-fold to 249.2 +/- 43.1 micromol h-1 g-1, P < 0.001), and 1-MX conversion (2.5-fold to 1.87 +/- 0.25 micromol h-1 g-1, P < 0.01) (SEM are shown). It is concluded that as 1-MX metabolism parallels VO2, this substrate may be a useful indicator of changes in capillary (nutritive) surface area in muscle.

The glycolytic pathway to coronary heart disease: a hypothesis

Coronary heart disease (CHD) is pathogenetically linked to numerous metabolic disturbances. These are inextricably interrelated, constituting identifiable clusters or syndromes of cardiovascular risk. Prominent among these is the insulin resistance syndrome, whose components, including hyperuricemia, have all been linked to CHD pathogenesis. Many mechanisms have been put forward to account for the emergence of this syndrome, but none offer a satisfactory explanation for the involvement of hyperuricemia. Possible explanations relate to the observation of glycolytic disturbances in insulin-resistant and hyperuricemic states. This might be expected from the fact that uric acid production is linked to glycolysis and that glycolysis is controlled by insulin. Phosphoribosylpyrophosphate (PPRP) is an important metabolite in this respect. Its availability depends on ribose-5-phosphate (R-5-P), the production of which is governed by glycolytic flux. Diversion of glycolytic intermediates toward R-5-P, PPRP, and uric acid will follow if there is diminished activity of glyceraldehyde-3-phosphate dehydrogenase (GA3PDH), which is regulated by insulin. Serum triglyceride concentrations may also increase, as might be expected from accumulation of glycerol-3-phosphate. Thus, intrinsic defects in GA3PDH and a loss of its responsiveness to insulin, by causing accumulation of glycolytic intermediates, may explain the association between insulin resistance, hyperuricemia, and hypertriglyceridemia. This scenario raises the possibility that disturbances of a single glycolytic enzyme may be pivotal in the modulation of metabolic risk factors for CHD.

Xanthine dehydrogenase/xanthine oxidase and oxidative stress

Xanthine dehydrogenase (XDH) and xanthine oxidase (XOD) are single-gene products that exist in separate but interconvertible forms. XOD utilizes hypoxanthine or xanthine as a substrate and O2 as a cofactor to produce superoxide (·O2 (-)) and uric acid. XDH acts on these same substrates but utilizes NAD as a cofactor to produce NADH instead of ·O2 (-) and uric acid. XOD has been proposed as a source of oxygen radicals in polymorphonuclear, endothelial, epithelial, and connective tissue cells. However, several questions remain about the physiological significance and functions of XOD on aging and oxidative stress. XOD is reported to play an important role in cellular oxidative status, detoxification of aldehydes, oxidative injury in ischemia-reperfusion, and neutrophil mediation. For example, XOD may serve as a messenger or mediator in the activation of neutrophil, T cell, cytokines, or transcription in defense mechanisms rather than as a free radical generator of tissue damage. Emerging evidence on the synergistic interactions of ·O2 (-), a toxic product of XOD and nitric oxide, may be another illustration of XOD involvement in tissue injury and cytotoxicity in an emergent condition such as ischemia or inflammation.

Elimination of theophylline metabolites in healthy adults

The metabolism of theophylline (TP) (540 mg per os) was determined by measuring plasma and saliva concentrations of TP and its metabolites, 0-24 h after loading, and urinary excretion 0-48 h after loading. TP and its five metabolites were separated and quantified by combining high-performance liquid chromatography and capillary electrophoresis. In addition to TP, 1,3-U, 3-X and 1-U were consistently found in plasma and saliva. The area under the plasma concentration-time curve (AUC) showed that TP accounted for 91 +/- 4% (mean +/- SD) of the total AUC in plasma with 1,3-U accounting for 3.1 +/- 1.4%, 3-X for 3.4 +/- 1.8% and 1-U for 2.5 +/- 1.5%. The urine analyses showed that unchanged TP accounted for 19 +/- 5% of total excretion, the remainder being 1, 3-dimethyluric acid (1,3-U, 41 +/- 6%), 1-methylxanthine (1-X, 2 +/- 0.8%), 1-methyluric acid (1-U, 26 +/- 6%), 3-methylxanthine (3-X, 11 +/- 3%) and 3-methyluric acid (3-U, 1 +/- 0.3%). Highest excretion rates were observed for 1,3-U (70 +/- 29 mumol/h), 1-U (40 +/- 26 mumol/h) and 3-X (20 +/- 15 mumol/h) 6-9 h after TP ingestion suggesting the high excretion of 1,3-U, 1-U and 3-X by the kidneys. The highest excretion rate of TP (50 +/- 8 mumol/h) occurring at 0-6 h after the load and rapidly declining thereafter, indicated the lower excretion of TP compared with its metabolites. N3-demethylation of TP accounted for 34 +/- 6% of the urinary metabolites, N1-demethylation of TP for 15 +/- 3% and C8-oxidation of TP for 51 +/- 9%. C8-oxidation of 1-X and 3-X was 93 +/- 4%, and 9 +/- 4%, respectively, of the excreted amount of monomethylxanthine plus formed monomethylurate. Since the extent of all metabolic reactions remained constant during the load, it is suggested that TP is metabolized by hepatic reactions that occurred simultaneously and not sequentially.

Reperfusion injury as the mechanism of brain damage after perinatal asphyxia

Upon reperfusion of ischemic tissues, reactive oxygen metabolites are generated and are responsible for much of the organ damage. Experimental studies have revealed two main sources of these metabolites: 1) the oxidation of hypoxanthine to xanthine and on to uric acid by the oxidase form of xanthine oxidoreductase and 2) neutrophils accumulating in ischemic and reperfused tissue. Blocking either source will reduce reperfusion damage in a number of experimental situations. Although xanthine oxidoreductase activity may be unmeasurably low in organs other than liver and intestine, it may be involved in reperfusion injury elsewhere because of its localization in capillary endothelial cells. Time course considerations suggest that substrate accumulation and NADH inhibition of dehydrogenase activity may be more important in the pathogenesis than conversion of xanthine dehydrogenase into the oxidase form. Neutrophil accumulation may be partly due to oxidants in the first place, suggesting a link between the two sources of reactive oxygen metabolites. In the clinical context, many of the sequelae of perinatal asphyxia may be accounted for by reperfusion damage to organs such as brain, kidney, heart, liver, and lungs. During asphyxia, substrates of xanthine oxidase accumulate, upon resuscitation the cosubstrate oxygen is introduced, and evidence for oxidant production and effects has been obtained. In the pathogenesis of brain damage after asphyxia, both microvascular injury and parenchymal cell damage are important. Oxygen metabolites are involved in the former, but in the latter process their role is less clear because ischemia-reperfusion triggers not only oxidant production but many other phenomena, including gene activation, ATP depletion, glutamate accumulation, and increase of intracellular calcium. A severe insult results in cell necrosis, but more moderate asphyxia may cause delayed neuronal death through apoptosis. The time course of the changes in high energy phosphates as well as of selective neuronal death suggest that in the first hours of life there is a "therapeutic window," with future possibilities for prevention of permanent damage.

Catecholamines oxidation by xanthine oxidase

Dopamine and structurally related catecholamines in the presence of hydrogen peroxide are oxidized in vitro by xanthine oxidase producing the corresponding melanin pigments. The kinetic parameters of the reaction, measured as aminochrome formation, have been calculated. The rate of peroxidation depends on enzyme and hydrogen peroxide concentration. The optimum pH for the peroxidative activity of the enzyme is around 8.5. Activation of the peroxidative reaction is also elicited by catechol compounds through a redox cycle mechanism. Implications about the possible biochemical relevance of xanthine oxidase activity on catecholamines oxidation are discussed.

Allopurinol reduces bacterial translocation, intestinal mucosal lipid peroxidation, and neutrophil-derived myeloperoxidase activity in chronic portal hypertensive and common bile duct-ligated growing rats

Bacterial translocation (BT) from the gastrointestinal tract has been thought to play a role in the pathogenesis of septic complications in patients with chronic portal hypertension (PH) and obstructive jaundice. The purpose of this study was to investigate the incidence of BT and to assess the role of intestinal mucosal malondialdehyde (MDA) levels as an indicator of lipid peroxidation and polymorphonuclear neutrophil-derived myeloperoxidase (MPO) in chronic portal hypertensive and common bile duct-ligated rats. Twenty male rats were subjected to sham laparotomy (SL), 20 rats to calibrated portal vein constriction (PH), 20 rats to common bile duct ligation (CBDL), and 10 rats served as a nonoperated control group (NOP). After 4 wk, 10 animals of each operated group received 50 mg/kg allopurinol intraperitoneally, at 24 h, and again 2 h prior to estimation of BT, intestinal mucosal MDA, and MPO activities. In the NOP and SL groups, BT to the mesenteric lymph nodes (MLN) and spleen was present. In PH and in CBDL rats, BT to liver, portal vein, peritoneum, and caval vein occurred. Allopurinol treatment attenuated the frequence of BT in PH and decreased BT in CBDL rats significantly (p < 0.05). Ileal mucosal MDA levels (nanomoles/g) in untreated rats increased from 45.1 +/- 7.9 in SL to 98.2 +/- 9.1 in PH and to 102.2 +/- 11 in CBDL rats (p < 0.01). In the allopurinol groups the increase of MDA to 49.1 +/- 1.3 in PH, and 66.2 +/- 2.2 in CBDL was significantly lower (p < 0.01). MPO activity (units/g) in the ileal mucosa increased in untreated rats from 319 +/- 129 after SL to 866 +/- 104 after PH and to 1016 +/- 104 after CBDL (p < 0.01). Allopurinol significantly attenuated MPO activity to 369 +/- 44 in PH, and to 372 +/- 60 in CBDL animals (p < 0.01). In PH and CBDL rats significant BT, intestinal mucosal lipid peroxidation, and polymorphonuclear neutrophil-derived MPO activity occurred. Allopurinol reduced BT and improved intestinal mucosal MDA and MPO activities, suggesting that there might be an association between BT and intestinal mucosal lipid peroxidation.

Neutrophils obtained from obliterative atherosclerotic patients exhibit enhanced resting respiratory burst and increased degranulation in response to various stimuli

Tissue destruction in atherosclerosis is partly due to uncontrolled protease and oxygen radical release. In this study we investigated the release of elastase and myeloperoxidase, as well as the production of reactive oxygen species by polymorphonuclear leukocytes (PMNLs) obtained from patients with obliterative atherosclerotic of the lower legs. In addition we measured the plasma concentration of xanthine oxidase. PMNLs of atherosclerotic patients have a greater ability to increase elastase and myeloperoxidase release after their stimulation with formyl-methionin-leucyl-phenylalanin (fMLP) and calcium ionophore, A23187, independently of their age, than PMNLs of healthy middle-aged subjects. Similarly to healthy elderly subjects there was an increased superoxide anion (O2-) production under basal condition in both atherosclerotic patient age-groups. The activation of PMNLs with fMLP and A23187 enhanced O2- formation both in healthy subjects and in patients with atherosclerotic disease of the lower legs, however the increase was significantly less in the latter group. No biochemical parameters showed significant correlation with patient's risk factors, however myeloperoxidase production was significantly higher in less severe stage of the disease (P < 0.05). We found that patients with atherosclerotic disease of the lower legs have higher plasma xanthine oxidase level than control subjects. This study indicates an other piece of evidence suggesting the activation and involvement of neutrophils in the pathogenesis of atherosclerosis of the lower legs. The similar tendencies in the reactivity of neutrophils during aging and in atherosclerosis suggest that atherosclerosis may be an early aging process.

Xanthine oxidase/dehydrogenase is present in human placenta

Xanthine dehydrogenase/oxidase (XDH, EC 1.1.1.204, XO, EC 1.2.3.2) produces uric acid, and in the oxidase form also generates the free radical superoxide. Previous reports failed to demonstrate XDH/XO activity in human placenta. Our objective was to determine evidence of XDH/XO in human placenta. We developed a cDNA probe for human XDH/XO and used it to detect mRNA by Northern hybridization. Immunohistochemical localization of the enzyme in placental tissue was performed using a specific antibody for XDH/XO and ABC-peroxidase. Enzyme activity assay was determined by the conversion of [14C] xanthine to [14C] uric acid. mRNA was detected in all placental samples (n = 4). Villous and non-villous trophoblast cells expressed immunohistochemical staining for XOD (n = 4). Enzyme activity was detected in all placentae (n = 6). Despite previous reports, we found mRNA, XDH/XO protein and enzyme activity in human placenta localized to trophoblast cells. Enzyme activity was much lower than in liver. Several conditions in the maternal-fetal unit could potentially increase XDH/XO activity and conversion of the enzyme to its oxidase form.

Elimination of theobromine metabolites in healthy adults

The metabolism of theobromine (TB) (500 mg per os) was determined by measuring plasma and saliva concentrations of TB and its metabolites 0-24 h after the load, and urinary excretion 0-48 h after the load. TB and its six metabolites were separated and quantified by combining high performance liquid chromatography and capillary electrophoresis. The urine analyses showed that unchanged TB accounted for 21 +/- 4% (mean +/- SD) of total excretion, the remainder being 7-methylxanthine (7-X, 36 +/- 5%), 3-methylxanthine (3-X, 21 +/- 4%), 6-amino-5[N-methylformylamino]-1-methyluracil (6-AMMU, 11 +/- 4%), 7-methyluric acid (7-U, 10 +/- 2%), 3,7-dimethyluric acid (3,7-U, 1.3 +/- 0.6%) and 3-methyluric acid (3-U, 0.5 +/- 0.4%). In addition to TB, 7-X and 3-X were consistently found in plasma and saliva; 6-AMMU and 7-U were found in plasma and saliva at concentrations < or = 2 mumol l-1 and 0.2 mumol l-1, respectively. TB concentrations in plasma and saliva were similar, whereas the saliva concentrations for 7-X and 3-X were found to be 63 +/- 17% of the plasma concentrations for 7-X and 74 +/- 13% for 3-X, respectively. The high urinary-to-plasma concentration ratio of 7-U (200-300) suggests high excretion of 7-U by the kidneys. Excretion of 7-X, 3-X and 6-AMMU was also high (urinary-to-plasma concentration ratio 45-150), whereas the excretion of TB was significantly lower than its metabolites (urinary-to-plasma concentration ratio 4-6). N3-demethylation of TB accounted for 58 +/- 7% of the urinary metabolites, N7-demethylation for 27 +/- 6%, C8-oxidation of 7-X for 22 +/- 4%, C8-oxidation of 3-X for 2 +/- 2% and formation of 6-AMMU for 13 +/- 4%. The ratio of N3- to N7-demethylation of TB remained constant during the load, but the large interindividual variation observed in ratio makes it unsuitable as a function test for evaluation of liver disease.

Hyperuricemia and xanthine oxidase in preeclampsia, revisited

Hyperuricemia is associated with the severity of preeclampsia and with fetal outcome. Traditionally the high uric acid concentration in preeclampsia has been attributed soley to renal dysfunction. Preeclampsia is also characterized by increased free radical formation and elevated oxidative stress. Xanthine dehydrogenase/oxidase produces uric acid. Xanthine dehydrogenase/oxidase is present as two isoforms in vivo. Uric acid production is coupled with formation of reactive oxygen species when the enzyme is in the oxidase form. Several factors can increase the holoenzyme activity and the conversion of xanthine dehydrogenase/oxidase to its oxidase form. These factors include hypoxia-reperfusion, cytokines, and increased substrate availability (xanthine and hypoxanthine). Preeclampsia is characterized by hyperuricemia and signs of increased formation of reactive oxygen species and decreased levels of antioxidants. Preeclampsia is also characterized by shallow implantation, producing a relatively hypoxic maternal-fetal interface, and increased turnover of trophoblast tissue, which can result in higher xanthine and hypoxanthine concentrations and higher levels of circulating cytokines. These mechanisms can lead to increased production of uric acid and free radicals and contribute to the hyperuricemia and increased oxidative stress present in preeclampsia.

The pharmacokinetics or oral and intravenous allopurinol and intravenous oxypurinol in the horse

The pharmacokinetics of oral and intravenous allopurinol was studied in five horses and compared with intravenous oxypurinol. The plasma concentration vs. time curves, following intravenous administration of 5 mg/kg, were best described by the biexponential equations Cp = 106.58e(-25.14t) + 159.93e(-10.96t) for allopurinol and Cp = 321.09e(-9.72t) + 82.39e(-0.44t) for oxypurinol, with an elimination half-life (t1/2 beta) of 0.09 h and an area under the curve (AUC) of 19.8 mumol.h/L after intravenous administration, while the t1/2 beta and AUC of oxypurinol were 1.09 h and 231 mumol.h/L, respectively. The bioavailability of allopurinol was low (14.3%), although no allopurinol was detected in the plasma of two horses after oral administration of allopurinol was equivalent to that of intravenously injected oxypurinol. The results suggest that allopurinol is rapidly metabolised in vivo and that the majority of the pharmacological activity of allopurinol in the horse may result from the action of the active metabolite, oxypurinol.

A re-evaluation of the tissue distribution and physiology of xanthine oxidoreductase

Xanthine oxidoreductase is an enzyme which has the unusual property that it can exist in a dehydrogenase form which uses NAD+ and an oxidase form which uses oxygen as electron acceptor. Both forms have a high affinity for hypoxanthine and xanthine as substrates. In addition, conversion of one form to the other may occur under different conditions. The exact function of the enzyme is still unknown but it seems to play a role in purine catabolism, detoxification of xenobiotics and antioxidant capacity by producing urate. The oxidase form produces reactive oxygen species and, therefore, the enzyme is thought to be involved in various pathological processes such as tissue injury due to ischaemia followed by reperfusion, but its role is still a matter of debate. The present review summarizes information that has become available about the enzyme. Interpretations of contradictory findings are presented in order to reduce confusion that still exists with respect to the role of this enzyme in physiology and pathology.

The effect of amflutizole, a xanthine oxidase inhibitor, on ischemia-evoked purine release and free radical formation in the rat cerebral cortex

The efflux of hypoxanthine, xanthine and uric acid into cortical superfusates was studied with the cortical cup technique in the rat. Twenty minutes of four vessel occlusion followed by reperfusion results in a massive increase in the efflux of these purine metabolites. Amflutizole, 10 microM administered topically into the cortical cups, enhanced the ischemia-evoked release of hypoxanthine while it suppressed xanthine formation. Uric acid levels were not affected. Amflutizole also eliminated the ischemia/reperfusion-evoked generation of free radical adducts of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) detected by electron spin resonance. These results are consistent with a block of xanthine oxidase by amflutizole and support the involvement of xanthine oxidase in free radical mediated tissue damage following ischemia/reperfusion.

The total peroxyl radical-trapping ability of plasma and cerebrospinal fluid in normal and preeclamptic parturients

Plasma and cerebrospinal fluid total peroxyl radical-trapping antioxidative parameter (TRAP) and the main antioxidant components of TRAP (vitamin E, ascorbic acid, uric acid, protein sulfhydryl groups, and the unidentified antioxidant proportion) were analyzed in 11 preeclamptic parturients, 9 healthy parturients with an uncomplicated pregnancy, and 10 healthy nonpregnant women. In addition, the possible effects of ongoing labor were studied in 10 healthy parturients. The samples of plasma and cerebrospinal fluid (CSF) were collected at cesarean section (pregnant women) or minor surgical procedure (nonpregnant women). Normal pregnancy or ongoing labor induced no significant changes in total TRAP, as compared with nonpregnant women, but significant changes in the percentage contributions of individual antioxidants were noted in plasma and CSF. In preeclampsia, a significant increase in TRAP was noted in both plasma and CSF. This increase was mainly due to an increased proportion of uric acid and unidentified antioxidants in plasma samples, and an increased proportion of unidentified antioxidants in CSF. The concentration of CSF ascorbic acid was decreased in preeclampsia, and a negative correlation between CSF ascorbic acid and blood pressure was observed.

Modulation of the xanthine oxidase/xanthine dehydrogenase ratio by reaction of malondialdehyde with NH2-groups

The potential of xanthine oxidoreductase to generate oxygen radicals depends on the ratio of xanthine dehydrogenase and xanthine oxidase. Previous studies showed that the lipid peroxidation products, malondialdehyde and 4-hydroxynonenal have different effects on xanthine oxidoreductase activity. These results suggest that the activity of xanthine oxidase, but not xanthine dehydrogenase, is influenced by NH2-group modulation. We therefore investigated the influence of malondialdehyde on xanthine oxidoreductase. Malondialdehyde reacted with NH2-groups to form Schiff bases, and this reaction was associated with inhibition of xanthine oxidase; SH-groups were not affected. Malondialdehyde had no influence on the xanthine dehydrogenase activity. The inhibited xanthine oxidase was converted to an active xanthine dehydrogenase by dithiothreitol treatment. These experiments indicate the importance of NH2-groups for xanthine oxidase but not for xanthine dehydrogenase activity. Beside the well known regulation of the xanthine dehydrogenase/xanthine oxidase ratio by the redox status of SH-groups, substances reacting with NH2-groups of the xanthine oxidoreductase are also able to change the xanthine dehydrogenase/xanthine oxidase activity ratio, thereby influencing the potential to generate oxygen radicals by xanthine oxidoreductase.

Immunohistochemical localization of xanthine oxidase in human cardiac and skeletal muscle

The generation of a monoclonal antibody specific to xanthine oxidase and its use in the distribution of the enzyme in human tissue is described. Xanthine oxidase was purified from human and bovine milk by a rapid method, allowing for minimal proteolytic degradation, and the purified enzyme preparations were used for the immunization of BALB/c mice as well as for the subsequent selection of hybridomas. The hybridoma clone X1-7, IgG (2a, kappa-light chain) was selected for further analysis and demonstrated to precipitate xanthine oxidase from human liver and skeletal muscle extracts. As determined by SDS-polyacrylamide gel electrophoresis of eluates from affinity chromatography, the X1-7 antibody bound to a main protein of 155 kDa, from human milk and skeletal muscle, and to proteins of 155, 143 and 95 kDa from human liver. Immunohistochemical studies, using two of the monoclonal antibodies with differing epitope specificity, revealed xanthine oxidase to be localized mainly in the vascular smooth muscle cells but also in a proportion of endothelial cells of capillaries and smaller vessels in both human cardiac and skeletal muscle. Immunoreactivity was additionally observed in human macrophages and mast cells. The results of the present study confirm previous reports of the presence of xanthine oxidase in capillary endothelial cells, but also demonstrates additional localization of the enzyme in vascular smooth muscle cells, macrophages and mast cells. The current findings verify that the distribution of xanthine oxidase in human tissue includes cardiac and skeletal muscle.