Renal xanthine oxidoreductase activity during development of hypertension in spontaneously hypertensive rats

Oxidative Stress: A Putative Link Between Lower Urinary Tract Symptoms and Aging and Major Chronic Diseases

Aging and major chronic diseases are risk factors for lower urinary tract symptoms (LUTS). On the other hand, oxidative stress (OS) is one of the fundamental mechanisms of aging and the development of chronic diseases. Therefore, OS might be a candidate mechanism linking these two clinical entities. This article aims to summarize the studies on the prevalence of LUTS, the role of OS in aging and chronic diseases, and the potential mechanisms supporting the putative link. A comprehensive literature search was performed to identify recent reports investigating LUTS and OS in major chronic diseases. In addition, studies on the impact of OS on the lower urinary tract, including bladder, urethra, and prostate, were collected and summarized. Many studies showed LUTS are prevalent in aging and major chronic diseases, including obesity, metabolic syndrome, diabetes, cardiovascular disease, hypertension, obstructive sleep apnea, autoimmune diseases, Alzheimer’s disease, and Parkinson’s disease. At the same time, OS is a key component in the pathogenesis of those chronic diseases and conditions. Recent studies also provided evidence that exacerbated OS can cause functional and/or structural changes in the bladder, urethra, and prostate, leading to LUTS. The reviewed data support the concept that OS is involved in multiple risk factors-associated LUTS, although further studies are needed to confirm the causative relationship. The specific ROS/RNS and corresponding reactions/pathways involved in chronic diseases and associated LUTS should be identified in the future and could serve as therapeutic targets.

Febuxostat ameliorates high salt intake-induced hypertension and renal damage in Dahl salt-sensitive rats

OBJECTIVE

Several clinical studies have reported that xanthine oxidoreductase inhibitors have antihypertensive and renal protective effects but their mechanisms have not been fully determined. This study aims to clarify these mechanisms by examining the effects of febuxostat, which is a novel selective xanthine oxidoreductase inhibitor, in Dahl salt-sensitive rats.

METHODS

Eight-week-old male Dahl salt-sensitive rats were fed a normal salt (0.6% NaCl) or high salt (8% NaCl) diet for 8 weeks. A portion of the rats that were fed high salt diet were treated with febuxostat (3 mg/kg per day) simultaneously. Additionally, acute effects of febuxostat (3 mg/kg per day) were examined after high salt diet feeding for 4 or 8 weeks.

RESULTS

Treatment with febuxostat for 8 weeks attenuated high salt diet-induced hypertension, renal dysfunction, glomerular injury, and renal interstitial fibrosis. Febuxostat treatment reduced urinary excretion of H2O2 and malondialdehyde and renal thiobarbituric acid reactive substances content. High salt diet increased xanthine oxidoreductase activity and expression in the proximal tubules and medullary interstitium. Febuxostat completely inhibited xanthine oxidoreductase activity and attenuated the high salt diet-increased xanthine oxidoreductase expression. Febuxostat transiently increased urine volume and Na+ excretion without change in blood pressure or urinary creatinine excretion after high salt diet feeding for 4 or 8 weeks.

CONCLUSION

Febuxostat ameliorates high salt diet-induced hypertension and renal damage with a reduction of renal oxidative stress in Dahl salt-sensitive rats. The antihypertensive effect of febuxostat may be mediated in part by diuretic and natriuretic action.

Inorganic nitrate attenuates cardiac dysfunction: role for xanthine oxidoreductase and nitric oxide

Nitric oxide (NO) is a vasodilator and independent modulator of cardiac remodelling. Commonly, in cardiac disease (e.g. heart failure) endothelial dysfunction (synonymous with NO-deficiency) has been implicated in increased blood pressure (BP), cardiac hypertrophy and fibrosis. Currently no effective therapies replacing NO have succeeded in the clinic. Inorganic nitrate (NO₃ ^- ), through chemical reduction to nitrite and then NO, exerts potent BP-lowering but whether it might be useful in treating undesirable cardiac remodelling is unknown. In a nested age- and sex-matched case-control study of hypertensive patients +/- left ventricular hypertrophy (NCT03088514) we show that lower plasma nitrite concentration and vascular dysfunction accompany cardiac hypertrophy and fibrosis in patients. In mouse models of cardiac remodelling, we also show that restoration of circulating nitrite levels using dietary nitrate improves endothelial dysfunction through targeting of xanthine oxidoreductase (XOR)-driven H₂ O₂ and superoxide, and reduces cardiac fibrosis through NO-mediated block of SMAD-phosphorylation leading to improvements in cardiac structure and function. We show that via these mechanisms dietary nitrate offers easily translatable therapeutic options for treatment of cardiac dysfunction.

Redox control of vascular biology

Redox control is lost when the antioxidant defense system cannot remove abnormally high concentrations of signaling molecules, such as reactive oxygen species (ROS). Chronically elevated levels of ROS cause oxidative stress that may eventually lead to cancer and cardiovascular and neurodegenerative diseases. In this review, we focus on redox effects in the vascular system. We pay close attention to the subcompartments of the vascular system (endothelium, smooth muscle cell layer) and give an overview of how redox changes influence those different compartments. We also review the core aspects of redox biology, cardiovascular physiology, and pathophysiology. Moreover, the topic-specific knowledgebase DES-RedoxVasc was used to develop two case studies, one focused on endothelial cells and the other on the vascular smooth muscle cells, as a starting point to possibly extend our knowledge of redox control in vascular biology.

Effect of Long-Term Allopurinol Therapy on Left Ventricular Mass Index in Patients with Ischemic Heart Disease; A Cross-Sectional Study

Background

Left ventricular hypertrophy (LVH), as assessed by measurement of left ventricular mass (LVM), is one of the most important cardiovascular risk factors. It is commonly present in patients with ischemic heart disease (IHD), irrespective of the level of blood pressure; recently, oxidative stress has been shown to be an important factor in its development. The question then arises: can this risk factor be modified by antioxidant treatment (e.g., with allopurinol, a xanthine oxidase inhibitor)?

Methods

This is an observational study with a cross-sectional design which explored the association between long-term (>12 months) allopurinol therapy and LV mass index (LVMI) as well as geometry in patients generally receiving standard treatments for IHD. The primary endpoint was LVMI measurement (by 2D-echocardiography) and secondary endpoints included the association of allopurinol use with LV function (ejection fraction), blood pressure, glycemic control, and lipid profile.

Results

Ninety-six patients on standard anti-ischemic drug treatment (control group) and 96 patients who were additionally taking allopurinol (minimum dose 100 mg/day) were enrolled. Both groups were matched for age, sex, height, and co-morbidities, but poorer kidney function in the allopurinol group required further sub-group analysis based on renal function. Allopurinol treatment was associated with the lowest LVMI in the patients with normal serum creatinine (median LVMI; 70.5 g/m²): corresponding values were 76.0 and 87.0 in the control group with, respectively, normal and elevated serum creatinine, and 89.5 in the allopurinol group with elevated serum creatinine (P=0.027). In addition, allopurinol was associated with better glycemic control (HbA1c) with a difference of 0.8% (95% CI; 1.3, 0.2) (P=0.004) as compared with control patients.

Conclusion

In our population, treatment with allopurinol (presumably because of its anti-oxidant properties) has shown a tendency to be associated with smaller LVM in IHD patients with normal serum creatinine, along with better glycemic control.

Hyperuricemia, Acute and Chronic Kidney Disease, Hypertension, and Cardiovascular Disease: Report of a Scientific Workshop Organized by the National Kidney Foundation

Urate is a cause of gout, kidney stones, and acute kidney injury from tumor lysis syndrome, but its relationship to kidney disease, cardiovascular disease, and diabetes remains controversial. A scientific workshop organized by the National Kidney Foundation was held in September 2016 to review current evidence. Cell culture studies and animal models suggest that elevated serum urate concentrations can contribute to kidney disease, hypertension, and metabolic syndrome. Epidemiologic evidence also supports elevated serum urate concentrations as a risk factor for the development of kidney disease, hypertension, and diabetes, but differences in methodologies and inpacts on serum urate concentrations by even subtle changes in kidney function render conclusions uncertain. Mendelian randomization studies generally do not support a causal role of serum urate in kidney disease, hypertension, or diabetes, although interpretation is complicated by nonhomogeneous populations, a failure to consider environmental interactions, and a lack of understanding of how the genetic polymorphisms affect biological mechanisms related to urate. Although several small clinical trials suggest benefits of urate-lowering therapies on kidney function, blood pressure, and insulin resistance, others have been negative, with many trials having design limitations and insufficient power. Thus, whether uric acid has a causal role in kidney and cardiovascular diseases requires further study.

Evaluation of the Effectiveness of Xanthine Oxidoreductase Inhibitors on Haemodialysis Patients using a Marginal Structural Model

A lower serum uric acid (UA) level has been associated with a higher mortality rate in haemodialysis patients. We investigated the long-term confounding factors of UA and mortality, and fitted a marginal structural model (MSM) based on the causal effect of xanthine oxidoreductase inhibitors (XORi). In total, 2429 patients on regular dialysis from April 2013 to March 2016 were included, and divided into quintiles by serum UA with Kaplan Meier (KM) curves and log rank analysis. Baseline characteristics were evaluated for relationships with all-cause mortality and cardiovascular disease (CVD) using the Cox hazard model. The MSM was used to control for time-dependent confounders of the XORi treatment effect. KM curves indicated that patients in the highest UA quintile had better outcomes than those in the lowest UA quintile. UA was not correlated with all-cause mortality or CVD events in the Cox model; however, the hazard ratio (HR) for mortality was 0.96 for the baseline administration of XORi. The MSM analysis for the effect of XORi treatment on all-cause mortality revealed a HR of 0.24 (95% confidence interval: 0.15-0.38) in all cohorts. These results suggest that XORi improved all-cause mortality in end-stage renal disease, irrespective of the serum UA level.

The Future Challenge of Reactive Oxygen Species (ROS) in Hypertension: From Bench to Bed Side

Reactive oxygen species (ROS) act as signaling molecules that control physiological processes, including cell adaptation to stress. Redox signaling via ROS has quite recently become the focus of much attention in numerous pathological contexts, including neurodegenerative diseases, kidney and cardiovascular disease. Imbalance in ROS formation and degradation has also been implicated in essential hypertension. Essential hypertension is characterized by multiple genetic and environmental factors which do not completely explain its associated risk factors. Thereby, even if advances in therapy have led to a significant reduction in hypertension-associated complications, to interfere with the unbalance of redox signals might represent an additional therapeutic challenge. The decrease of nitric oxide (NO) levels, the antioxidant activity commonly found in preclinical models of hypertension and the ability of antioxidant approaches to reduce ROS levels have spurred clinicians to investigate the contribution of ROS in humans. Indeed, particular effort has recently been devoted to understanding how redox signaling may contribute to vascular pathobiology in human hypertension. However, although biomarkers of oxidative stress have been found to positively correlate with blood pressure in preclinical model of hypertension, human data are less convincing. We herein provide an overview of the most relevant mechanisms via which oxidative stress might contribute to the pathophysiology of essential hypertension. Moreover, alternative approaches, which are directed towards improving antioxidant machinery and/or interfering with ROS production, are also discussed.

Renal denervation attenuates hypertension and renal dysfunction in a model of cardiovascular and renal disease, which is associated with reduced NADPH and xanthine oxidase activity

Oxidative stress is considered a central pathophysiological event in cardiovascular disease, including hypertension. Early age reduction in renal mass is associated with hypertension and oxidative stress in later life, which is aggravated by increased salt intake. The aim of the present study was to examine if renal sympathetic denervation can exert blood pressure lowering effects in uninephrectomized (UNX) rats (3-week old) fed with high salt (HS, 4%; w/w) diet for 4 weeks. Moreover, we investigated if renal denervation is associated with changes in NADPH and xanthine oxidase-derived reactive oxygen species.

Rats with UNX + HS had reduced renal function, elevated systolic and diastolic arterial pressures, which was accompanied by increased heart weight, and cardiac superoxide production compared to sham operated Controls. UNX + HS was also associated with higher expression and activity of NADPH and xanthine oxidase in the kidney. Renal denervation in rats with UNX + HS attenuated the development of hypertension and cardiac hypertrophy, but also improved glomerular filtration rate and reduced proteinuria. Mechanistically, renal denervation was associated with lower expression and activity of both NADPH oxidase and xanthine oxidase in the kidney, but also reduced superoxide production in the heart.

In conclusion, our study shows for the first time that renal denervation has anti-hypertensive, cardio- and reno-protective effects in the UNX + HS model, which can be associated with decreased NADPH oxidase- and xanthine oxidase-derived reactive oxygen species (i.e., superoxide and hydrogen peroxide) in the kidney.

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Uninephrectomy + high salt intake (UNX + HS) is linked with hypertension and renal dysfunction.

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UNX + HS increases renal NADPH oxidase-mediated O₂^•− and H₂O₂ production.

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UNX + HS increases renal xanthine oxidase-mediated H₂O₂ production.

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Renal denervation attenuates development of hypertension and renal dysfunction.

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Renal denervation is associated with lower NADPH and xanthine oxidase activity.

Uric Acid and New Onset Left Ventricular Hypertrophy: Findings From the PAMELA Population

BACKGROUND

The association between serum uric acid (SUA) and left ventricular hypertrophy (LVH) is controversial and the ability of SUA in predicting incident LVH remains unsettled. Thus, we evaluated the relationship of SUA with new-onset echocardiographic LVH over a 10-year period in subjects of the general population enrolled in the Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) study.

METHODS

The study included 960 subjects with normal LV mass index (LVMI) at baseline echocardiographic evaluation and a readable echocardiogram at the end of follow-up. Cut-points for LVH were derived from reference values of the healthy fraction of the PAMELA population.

RESULTS

Over a 10-year period, 258 participants (26.9%) progressed to LVH. The incidence of new-onset LVH increased from the lowest (23%) to intermediate (25%) and the highest baseline SUA tertile (32%). After adjusting for confounders (not including body mass index (BMI)), each 1 mg/dl increase in SUA entailed a 26% higher risk of incident LVH. Adjusted odd ratio of LVH risk in the highest SUA tertile was 96% higher than in the lowest tertile (odds ratio (OR) = 1.966, 95% CI = 1.158-3.339, P = 0.0123). Correction for BMI reduced the magnitude and statistical significance of ORs.

CONCLUSIONS

The study shows that SUA is a predictor of long-term echocardiographic changes from normal LVMI to LVH in a community sample. Thus, life-style and pharmacologic measures aimed to reduce SUA levels may concur to preventing LVH development in the general population.

Febuxostat, a novel xanthine oxidoreductase inhibitor, improves hypertension and endothelial dysfunction in spontaneously hypertensive rats

Xanthine oxidase (XO) is an enzyme responsible for the production of uric acid. XO produces considerable amount of oxidative stress throughout the body. To date, however, its pathophysiologic role in hypertension and endothelial dysfunction still remains controversial. To explore the possible involvement of XO-derived oxidative stress in the pathophysiology of vascular dysfunction, by use of a selective XO inhibitor, febuxostat, we investigated the impact of pharmacological inhibition of XO on hypertension and vascular endothelial dysfunction in spontaneously hypertensive rats (SHRs). Sixteen-week-old SHR and normotensive Wistar-Kyoto (WKY) rats were treated with tap water (control) or water containing febuxostat (3 mg/kg/day) for 6 weeks. Systolic blood pressure (SBP) in febuxostat-treated SHR (220 ± 3 mmHg) was significantly (P < 0.05) decreased compared with the control SHR (236 ± 4 mmHg) while SBP in febuxostat-treated WKY was constant. Acetylcholine-induced endothelium-dependent relaxation in aortas from febuxostat-treated SHR was significantly (P < 0.05) improved compared with the control SHR, whereas relaxation in response to sodium nitroprusside was not changed. Vascular XO activity and tissue nitrotyrosine level, a representative indicator of local oxidative stress, were considerably elevated in the control SHR compared with the control WKY, and this increment was abolished by febuxostat. Our results suggest that exaggerated XO activity and resultant increase in oxidative stress in this experimental model contribute to the hypertension and endothelial dysfunction, thereby supporting a notion that pharmacological inhibition of XO is valuable not only for hyperuricemia but also for treating hypertension and related endothelial dysfunction in human clinics.

"Repurposing" of Xanthine Oxidoreductase as a Nitrite Reductase: A New Paradigm for Therapeutic Targeting in Hypertension

SIGNIFICANCE

In contrast to nitric oxide (NO), which has well-established, important effects in regulation of cardiovascular homeostasis, its oxidative metabolite nitrite has, until recently, been considered to be of minor functional significance.

RECENT ADVANCES

However, this view of nitrite has been radically revised over the past 10 years with evidence now supporting a critical role for this anion as a storage form of NO.

CRITICAL ISSUES

Importantly, while hypoxia and acidosis have been shown to play a pivotal role in the generation of nitrite to NO, a number of mammalian nitrite reductases have been identified that facilitate the reduction of nitrite. Critically, these nitrite reductases have been demonstrated to operate under physiological pH conditions and in normoxia, extending the functional remit of this anion from an ischemic mediator to an important regulator of physiology. One particular nitrite reductase that has been shown to operate under a wide range of environmental conditions is the enzyme xanthine oxidoreductase (XOR).

FUTURE DIRECTIONS

In this review, we discuss the evidence supporting a role for XOR as a nitrite reductase while focusing particularly on its function in hypertension. In addition, we discuss the potential merit in exploiting this activity of XOR in the therapeutics of hypertension.

Association between xanthine dehydrogenase tag single nucleotide polymorphisms and essential hypertension

The present study aimed to investigate the association between xanthine dehydrogenase (XDH) gene polymorphism and essential hypertension in the rural Han Chinese population of Fuxin, Liaoning. Han Chinese individuals, who had lived in rural areas of Fuxin, were selected as subjects for the present study. A total of 521 unrelated patients with hypertension were selected, along with a further 533 unrelated individuals with normal blood pressure, in order to serve as controls. Five tag single nucleotide polymorphisms (SNP) of the XDH gene were selected. An estimation of SNP allele frequency was determined using DNA pooling and pyrosequencing methods. Prior to Bonferroni correction, T allele frequency for rs206811 was significantly higher in patients with hypertension, as compared with the controls (64.1 vs. 59.4%; P=0.031); C allele frequency for rs1042039 was significantly higher in patients with hypertension, as compared with the controls (66.1 vs. 60.6%; P=0.011), C allele frequency for rs1054889 was significantly lower in patients with hypertension, as compared with the controls (38.8 vs. 44.8%; P=0.007); and A allele frequency for rs2073316 was significantly lower in patients with hypertension, as compared with the controls (29.2 vs. 34.4%; P=0.013). However, once a Bonferroni correction for multiple testing was applied, the XDH gene polymorphisms rs1042039, rs1054889, and rs2073316 were shown to be associated with hypertension (P=0.044, 0.035, and 0.039, respectively). These results suggest that the XDH gene polymorphisms rs1042039, rs1054889, and rs2073316 may be associated with hypertension in the rural Han Chinese population.

Essential hypertension and oxidative stress: New insights

Essential hypertension is a highly prevalent pathological condition that is considered as one of the most relevant cardiovascular risk factors and is an important cause of morbidity and mortality around the world. Despite the fact that mechanisms underlying hypertension are not yet fully elucidated, a large amount of evidence shows that oxidative stress plays a central role in its pathophysiology. Oxidative stress can be defined as an imbalance between oxidant agents, such as superoxide anion, and antioxidant molecules, and leads to a decrease in nitric oxide bioavailability, which is the main factor responsible for maintaining the vascular tone. Several vasoconstrictor peptides, such as angiotensin II, endothelin-1 and urotensin II, act through their receptors to stimulate the production of reactive oxygen species, by activating enzymes like NADPH oxidase and xanthine oxidase. The knowledge of the mechanism described above has allowed generating new therapeutic strategies against hypertension based on the use of antioxidants agents, including vitamin C and E, N-Acetylcysteine, polyphenols and selenium, among others. These substances have different therapeutic targets, but all represent antioxidant reinforcement. Several clinical trials using antioxidants have been made. The aim of the present review is to provide new insights about the key role of oxidative stress in the pathophysiology of essential hypertension and new clinical attempts to demonstrate the usefulness of antioxidant therapy in the treatment of hypertension.

New roles for old pathways? A circuitous relationship between reactive oxygen species and cyclo-oxygenase in hypertension

Elevated production of prostanoids from the constitutive (COX-1) or inducible (COX-2) cyclo-oxygenases has been involved in the alterations in vascular function, structure and mechanical properties observed in cardiovascular diseases, including hypertension. In addition, it is well known that production of ROS (reactive oxygen species) plays an important role in the impaired contractile and vasodilator responses, vascular remodelling and altered vascular mechanics of hypertension. Of particular interest is the cross-talk between NADPH oxidase and mitochondria, the main ROS sources in hypertension, which may represent a vicious feed-forward cycle of ROS production. In recent years, there is experimental evidence showing a relationship between ROS and COX-derived products. Thus ROS can activate COX and the COX/PG (prostaglandin) synthase pathways can induce ROS production through effects on different ROS generating enzymes. Additionally, recent evidence suggests that the COX-ROS axis might constitute a vicious circle of self-perpetuating vasoactive products that have a pathophysiological role in altered vascular contractile and dilator responses and hypertension development. The present review discusses the current knowledge on the role of oxidative stress and COX-derived prostanoids in the vascular alterations observed in hypertension, highlighting new findings indicating that these two pathways act in concert to induce vascular dysfunction.

High-dose allopurinol reduces left ventricular mass in patients with ischemic heart disease

OBJECTIVES

This study sought to ascertain if high-dose allopurinol regresses left ventricular mass (LVM) in patients with ischemic heart disease (IHD).

BACKGROUND

LV hypertrophy (LVH) is common in patients with IHD including normotensive patients. Allopurinol, a xanthine oxidase inhibitor, has been shown to reduce LV afterload in IHD and may therefore also regress LVH.

METHODS

A randomized, double-blind, placebo-controlled, parallel group study was conducted in 66 patients with IHD and LVH, comparing 600 mg/day allopurinol versus placebo therapy for 9 months. The primary outcome measure was change in LVM, assessed by cardiac magnetic resonance imaging (CMR). Secondary outcome measures were changes in LV volumes by CMR, changes in endothelial function by flow-mediated dilation (FMD), and arterial stiffness by applanation tonometry.

RESULTS

Compared to placebo, allopurinol significantly reduced LVM (allopurinol -5.2 ± 5.8 g vs. placebo -1.3 ± 4.48 g; p = 0.007) and LVM index (LVMI) (allopurinol -2.2 ± 2.78 g/m(2) vs. placebo -0.53 ± 2.5 g/m(2); p = 0.023). The absolute mean difference between groups for change in LVM and LVMI was -3.89 g (95% confidence interval: -1.1 to -6.7) and -1.67 g/m(2) (95% confidence interval: -0.23 to -3.1), respectively. Allopurinol also reduced LV end-systolic volume (allopurinol -2.81 ± 7.8 mls vs. placebo +1.3 ± 7.22 mls; p = 0.047), improved FMD (allopurinol +0.82 ± 1.8% vs. placebo -0.69 ± 2.8%; p = 0.017) and augmentation index (allopurinol -2.8 ± 5.1% vs. placebo +0.9 ± 7%; p = 0.02).

CONCLUSIONS

High-dose allopurinol regresses LVH, reduces LV end-systolic volume, and improves endothelial function in patients with IHD and LVH. This raises the possibility that allopurinol might reduce future cardiovascular events and mortality in these patients. (Does a Drug Allopurinol Reduce Heart Muscle Mass and Improve Blood Vessel Function in Patients With Normal Blood Pressure and Stable Angina?; ISRCTN73579730).

Long-term inhibition of xanthine oxidase by febuxostat does not decrease blood pressure in deoxycorticosterone acetate (DOCA)-salt hypertensive rats

Xanthine oxidase and its products, uric acid and ROS, have been implicated in the pathogenesis of cardiovascular disease, such as hypertension. We have previously reported that allopurinol inhibition of XO does not alter the progression of deoxycorticosterone acetate (DOCA)-salt hypertension in rats. However other researchers have observed a reduction in blood pressure after allopurinol treatment in the same model. To resolve this controversy, in this study we used the newer and more effective XO inhibitor febuxostat, and hypothesized that a more complete XO blockade might impair hypertension development and its end-organ consequences. We used DOCA-salt hypertensive rats and administered vehicle (salt water) or febuxostat (orally, 5 mg/kg/day in salt water) in a short-term "reversal" experiment (2 weeks of treatment 3 weeks after DOCA-salt beginning) and a long-term "prevention" experiment (treatment throughout 4 weeks of DOCA-salt). We confirmed XO inhibition by febuxostat by measuring circulating and tissue levels of XO metabolites. We found an overall increase in hypoxanthine (XO substrate) and decrease in uric acid (XO product) levels following febuxostat treatment. However, despite a trend for reduced blood pressure in the last week of long-term febuxostat treatment, no statistically significant difference in hemodynamic parameters was observed in either study. Additionally, no change was observed in relative heart and kidney weight. Aortic media/lumen ratio was minimally improved by long-term febuxostat treatment. Additionally, febuxostat incubation in vitro did not modify contraction of aorta or vena cava to norepinephrine, angiotensin II or endothelin-1. We conclude that XO inhibition is insufficient to attenuate hypertension in the rat DOCA-salt model, although beneficial vascular effects are possible.

Advanced kidney failure and hyperuricemia

Metabolic end products accumulate in kidney failure, including uric acid (UA), a terminal product of purine catabolism. Hyperuricemia (HUA) can cause gout and has been increasingly linked with cardiovascular (CV) morbidity and mortality, outcomes that are highly prevalent in patients with kidney disease. Serum UA levels rise as glomerular filtration declines, whereas the frequency of gouty attacks declines and the incidence of CV death rises precipitously. Herein, we review the kinetics of UA metabolism in CKD and dialysis and discuss the possible mechanisms of gout mitigation in kidney failure and the potential contribution of hyperuricemic milieu to CV outcomes in patients with kidney disease.

Allopurinol does not decrease blood pressure or prevent the development of hypertension in the deoxycorticosterone acetate-salt rat model

Reactive oxygen species play an important role in the pathogenesis of hypertension, disease in which reactive oxygen species levels and markers of oxidative stress are increased. Xanthine oxidase (XO) is a reactive oxygen species-producing enzyme the activity of which may increase during hypertension. Studies on XO inhibition effects on blood pressure have yielded controversial results. We hypothesized that XO inhibition would decrease blood pressure or attenuate the development of deoxycorticosterone acetate (DOCA)-salt hypertension. We administered the XO inhibitor, allopurinol (50 mg/kg per day, orally) or its vehicle to rats during the established or development stages of DOCA-salt hypertension. We validated XO inhibition by high-performance liquid chromatography measurements of XO metabolites in urine, serum, and tissues demonstrating a decrease in products, increase in substrates, and detection of the active metabolite of allopurinol, oxypurinol. We monitored blood pressure continuously through radiotelemetry and performed gross evaluations of target organs of hypertension. Allopurinol treatment did not impact the course of DOCA-salt hypertension regardless of the timing of administration. Aside from a significant decrease in pulse pressure in allopurinol-treated rats, no positive differences were observed between the allopurinol and the vehicle-treated rats. We conclude that XO does not play an important role in the development or maintenance of hypertension in the rat DOCA-salt hypertension model.

Allopurinol benefits left ventricular mass and endothelial dysfunction in chronic kidney disease

Allopurinol ameliorates endothelial dysfunction and arterial stiffness among patients without chronic kidney disease (CKD), but it is unknown if it has similar effects among patients with CKD. Furthermore, because arterial stiffness increases left ventricular afterload, any allopurinol-induced improvement in arterial compliance might also regress left ventricular hypertrophy (LVH). We conducted a randomized, double-blind, placebo-controlled, parallel-group study in patients with stage 3 CKD and LVH. We randomly assigned 67 subjects to allopurinol at 300 mg/d or placebo for 9 months; 53 patients completed the study. We measured left ventricular mass index (LVMI) with cardiac magnetic resonance imaging (MRI), assessed endothelial function by flow-mediated dilation (FMD) of the brachial artery, and evaluated central arterial stiffness by pulse-wave analysis. Allopurinol significantly reduced LVH (P=0.036), improved endothelial function (P=0.009), and improved the central augmentation index (P=0.015). This study demonstrates that allopurinol can regress left ventricular mass and improve endothelial function among patients with CKD. Because LVH and endothelial dysfunction associate with prognosis, these results call for further trials to examine whether allopurinol reduces cardiovascular events in patients with CKD and LVH.

Oxidative Stress and Vascular Damage in Hypertension: Role of Angiotensin II

Reactive oxygen species are oxygen derivates and play an active role in vascular biology. These compounds are generated within the vascular wall, at the level of endothelial and vascular smooth muscle cells, as well as by adventitial fibroblasts. In healthy conditions, ROS are produced in a controlled manner at low concentrations and function as signaling molecules regulating vascular contraction-relaxation and cell growth. Physiologically, the rate of ROS generation is counterbalanced by the rate of elimination. In hypertension, an enhanced ROS generation occurs, which is not counterbalanced by the endogenous antioxidant mechanisms, leading to a state of oxidative stress. In the present paper, major angiotensin II-induced vascular ROS generation within the vasculature, and relative sources, will be discussed. Recent development of signalling pathways whereby angiotensin II-driven vascular ROS induce and accelerate functional and structural vascular injury will be also considered.

Effect of allopurinol on blood pressure and aortic compliance in hypertensive patients

BACKGROUND

Arterial hypertension is commonly associated with hyperuricemia. Several studies have shown that allopurinol reduces arterial blood pressure in animal models and in adolescent patients with newly diagnosed hypertension. Moreover, allopurinol has shown beneficial effects on endothelial function and arterial wave reflection in contrast to uricosuric agents. Antihypertensive drugs produce different effects on serum uric acid levels.

OBJECTIVE

The aim of the study was to evaluate the influence of allopurinol on blood pressure and aortic compliance in patients with arterial hypertension depending on hypotensive therapy with angiotensin-converting enzyme inhibitor (ACE-I) or thiazide diuretic, hypotensive drugs with distinct effects on serum uric acid levels and conversely, a positive influence on pulse wave velocity (PWV) in the aorta.

MATERIAL AND METHODS

Sixty-six patients aged 25-70 (mean age 46.17 ± 10.89) with mild and moderate arterial hypertension diagnosed on the basis of office blood pressure, were studied. They were randomized to antihypertensive therapy on either perindopril (n = 35) or hydrochlorothiazide (n = 31). After 8 weeks of antihypertensive therapy, 150 mg of allopurinol daily was added for the next 8 weeks. Measurement of the serum uric acid level, PWV and 24-h ambulatory blood pressure monitoring (ABPM) were performed at baseline, after 8 weeks antihypertensive therapy and again after the final 8 weeks with the additional allopurinol.

RESULTS

No significant changes in systolic (SBP) and diastolic blood pressure (DBP) or ABPM were observed after allopurinol treatment in either of the subgroups receiving ACE-I or thiazide-based antihypertensive therapy. The mean PWV decreased from 10.7 ± 1.4 m/s to 10.0 ± 1.2 m/s (p = 0.00008) in the ACE-I-based therapy subgroup and from 11.5 ± 1.7 m/s to 10.4 ± 1.5 m/s (p = 0.00002) in the thiazide-based therapy subgroup after treatment with allopurinol. However, significant correlations were found between PWV changes and the basic PWV (r = -0.52; p < 0.001) or SBP changes (r = 0.29; p < 0.019) after allopurinol treatment.

CONCLUSIONS

Allopurinol does not produce additional antihypertensive effects in patients with treated arterial hypertension. Allopurinol increases aortic compliance independently of ACE-I or thiazide-based, antihypertensive therapy. However, this effect is significantly dependent on the initial PWV in the aorta and on SBP changes during allopurinol therapy.

The role of oxidative stress in the pathophysiology of hypertension

Hypertension is considered to be the most important risk factor in the development of cardiovascular disease. An increasing body of evidence suggests that oxidative stress, which results in an excessive generation of reactive oxygen species (ROS), has a key role in the pathogenesis of hypertension. The modulation of the vasomotor system involves ROS as mediators of vasoconstriction induced by angiotensin II, endothelin-1 and urotensin-II, among others. The bioavailability of nitric oxide (NO), which is a major vasodilator, is highly dependent on the redox status. Under physiological conditions, low concentrations of intracellular ROS have an important role in the normal redox signaling maintaining vascular function and integrity. However, under pathophysiological conditions, increased levels of ROS contribute to vascular dysfunction and remodeling through oxidative damage. In human hypertension, an increase in the production of superoxide anions and hydrogen peroxide, a decrease in NO synthesis and a reduction in antioxidant bioavailability have been observed. In turn, antioxidants are reducing agents that can neutralize these oxidative and otherwise damaging biomolecules. The use of antioxidant vitamins, such as vitamins C and E, has gained considerable interest as protecting agents against vascular endothelial damage. Available data support the role of these vitamins as effective antioxidants that can counteract ROS effects. This review discusses the mechanisms involved in ROS generation, the role of oxidative stress in the pathogenesis of vascular damage in hypertension, and the possible therapeutic strategies that could prevent or treat this disorder.

Cyclic stretch, reactive oxygen species, and vascular remodeling

Blood vessels respond to changes in mechanical load from circulating blood in the form of shear stress and mechanical strain as the result of heart propulsions by changes in intracellular signaling leading to changes in vascular tone, production of vasoactive molecules, and changes in vascular permeability, gene regulation, and vascular remodeling. In addition to hemodynamic forces, microvasculature in the lung is also exposed to stretch resulting from respiratory cycles during autonomous breathing or mechanical ventilation. Among various cell signaling pathways induced by mechanical forces and reported to date, a role of reactive oxygen species (ROS) produced by vascular cells receives increasing attention. ROS play an essential role in signal transduction and physiologic regulation of vascular function. However, in the settings of chronic hypertension, inflammation, or acute injury, ROS may trigger signaling events that further exacerbate smooth muscle hypercontractility and vascular remodeling associated with hypertension and endothelial barrier dysfunction associated with acute lung injury and pulmonary edema. These conditions are also characterized by altered patterns of mechanical stimulation experienced by vasculature. This review will discuss signaling pathways regulated by ROS and mechanical stretch in the pulmonary and systemic vasculature and will summarize functional interactions between cyclic stretch- and ROS-induced signaling in mechanochemical regulation of vascular structure and function.

Uric acid and left ventricular hypertrophy in Japanese men

BACKGROUND

Experimental studies have reported that allopurinol protects hypertensive rats from left ventricular hypertrophy (LVH) with negligible effects on blood pressure (BP). Uric acid (UA) was thought to induce cardiomyocyte growth and interstitial fibrosis of the heart, partly via activation of the renin-angiotensin system. In the present study, the relationship between serum UA levels and electrocardiographically-diagnosed LVH (ECG-LVH) was examined in Japanese men not taking medication for hypertension (HTN), which could confound the association.

METHODS AND RESULTS

A total of 3,305 male workers aged 35-66 years (mean age+/-SD, 48.0+/-7.1) were studied. LVH was defined as meeting the ECG criteria (ie, Sokolow-Lyon voltage and/or Cornell voltage QRS duration product). Subjects were divided into 3 groups by tertile of serum UA level. The highest tertile (UA range 0.39-0.65 mmol/L or 6.6-11.0 mg/dl) had a significantly increased prevalence of LVH compared with the lowest tertile independent of age, body mass index, serum creatinine level, HTN, diabetes and hyperlipidemia (odds ratio 1.58, 95% confidence interval 1.23-2.02, P<0.001). Similar results were obtained in both the normal and high BP subgroups.

CONCLUSIONS

UA concentration independently and positively associated with ECG-LVH in Japanese men.

Associations of hypertension and its complications with variations in the xanthine dehydrogenase gene

Hyperuricemia and oxidative stress participate in the pathophysiology of hypertension and its complications. Xanthine dehydrogenase (XDH) produces urate and, in its oxidase isoform, reactive oxygen species. Here we have studied whether or not the genetic variations in XDH could be implicated in hypertension and its complications. By sequencing the promoter region and all exons of XDH in 48 subjects, we identified three missense mutations (G172R, A932T, N1109T) in a heterozygous state in addition to 34 variations, including 15 common single nucleotide polymorphisms (SNPs). The three missense mutations and eight common SNPs (11488C>G, 37387A>G, 44408A>G, 46774G>A, 47686C>T, 49245A>T, 66292C>G, and 69901A>C) were genotyped in 953 hypertensive Japanese subjects and in 1,818 subjects from a general Japanese population. Four hypertensive patients with rare missense mutations (G172R or N1109T) in homozygous form had severe hypertension. Multivariate logistic regression analysis showed a significant association of three SNPs with hypertension in men: 47686C>T (exon 22, odds ratio [OR]: 1.52, p = 0.047) and 69901A>C (intron 31, OR: 3.14, p = 0.039) in the recessive model, and 67873A>C (N1109T) (exon 31, OR: 1.84, p = 0.018) in the dominant model. After full adjustment for all confounding factors, only one polymorphism (69901A>C) was found to be associated with carotid atherosclerosis in the dominant model (p = 0.028). Multiple logistic regression analysis showed that one SNP (66292C>G) was significantly associated with chronic kidney disease (CKD: estimated creatinine clearance < 60 ml/min) in the recessive model (p = 0.0006). Our results suggest that genetic variations in XDH contribute partly to hypertension and its complications, including atherosclerosis and CKD.

Role of oxidative stress in the renal abnormalities induced by experimental hyperuricemia

Endothelial dysfunction is a characteristic feature during the renal damage induced by mild hyperuricemia. The mechanism by which uric acid reduces the bioavailability of intrarenal nitric oxide is not known. We tested the hypothesis that oxidative stress might contribute to the endothelial dysfunction and glomerular hemodynamic changes that occur with hyperuricemia. Hyperuricemia was induced in Sprague-Dawley rats by administration of the uricase inhibitor, oxonic acid (750 mg/kg per day). The superoxide scavenger, tempol (15 mg/kg per day), or placebo was administered simultaneously with the oxonic acid. All groups were evaluated throughout a 5-wk period. Kidneys were fixed by perfusion and afferent arteriole morphology, and tubulointerstitial 3-nitrotyrosine, 4-hydroxynonenal, NOX-4 subunit of renal NADPH-oxidase, and angiotensin II were quantified. Hyperuricemia induced intrarenal oxidative stress, increased expression of NOX-4 and angiotensin II, and decreased nitric oxide bioavailability, systemic hypertension, renal vasoconstriction, and afferent arteriolopathy. Tempol treatment reversed the systemic and renal alterations induced by hyperuricemia despite equivalent hyperuricemia. Moreover, because tempol prevented the development of preglomerular damage and decreased blood pressure, glomerular pressure was maintained at normal values as well. Mild hyperuricemia induced by uricase inhibition causes intrarenal oxidative stress, which contributes to the development of the systemic hypertension and the renal abnormalities induced by increased uric acid. Scavenging of the superoxide anion in this setting attenuates the adverse effects induced by hyperuricemia.

A comparison of reactive oxygen species metabolism in the rat aorta and vena cava: focus on xanthine oxidase

Reactive oxygen species (ROS) are important mediators in vascular biology. Venous function, although relevant to cardiovascular disease, is still understudied. We compared aspects of ROS metabolism between a major artery (the aorta) and a major vein (the vena cava, VC) of the rat, with the hypothesis that venous ROS metabolism would be overall increased compared with its arterial counterpart. Superoxide and hydrogen peroxide (H2O2) release in basal conditions was higher in VC compared with aorta. The antioxidant capacity for H2O2 was also higher in VC than in aorta. Exogenous superoxide induced a higher contraction in VC compared with aorta. Protein expression of three major ROS metabolizing enzymes, xanthine oxidase (XO), CuZn-SOD, and catalase, was higher in VC compared with aorta. Because XO seemed a likely source of the higher VC ROS levels, we examined it further and found higher mRNA expression and activity of XO in VC compared with aorta. We also investigated the impact of XO inhibition by allopurinol on aorta and VC functional responses to norepinephrine, ANG II, ET-1, and ACh. Maximal ET-1-mediated contraction was decreased by allopurinol in VC but not in the aorta. Our results suggest that there are overall differences in ROS metabolism between aorta and VC, with the latter operating normally at a higher set point, releasing but also being able to handle, higher ROS levels. We propose XO to be an important source for these differences. The result of this particular comparison may be reflective of a general arteriovenous contrast.

The role of urate and xanthine oxidase inhibitors in cardiovascular disease

Many studies have shown a strong correlation between urate levels and cardiovascular disease. The formation of urate is complex as the same enzyme that produces urate, xanthine oxidase (XO) also catalyzes the formation of reactive oxygen species (ROS). There is some evidence that the urate molecule has free radical scavenging properties in vitro and acute infusions of urate improve endothelial function in at-risk populations. High levels of ROS are clearly linked to worse outcome in a variety of conditions. Allopurinol has been the archetypal XO inhibitor for over 40 years. Small studies have demonstrated its beneficial effects, mainly in heart failure but also in a variety of other cohorts of patients with cardiovascular risk. It is a safe agent, provided suitable patients are chosen and monitored carefully. Newer promising agents like oxypurinol have not shown the expected benefits in larger multicentered studies. This review looks at the biology of urate, its role in cardiovascular disease, the possible mechanisms by which XO inhibitors exert their beneficial effect on endothelial dysfunction, and examines the possible causes for the failure of newer agents to live up to expectations.

NADPH oxidases, reactive oxygen species, and hypertension: clinical implications and therapeutic possibilities

Reactive oxygen species (ROS) influence many physiological processes including host defense, hormone biosynthesis, fertilization, and cellular signaling. Increased ROS production (termed "oxidative stress") has been implicated in various pathologies, including hypertension, atherosclerosis, diabetes, and chronic kidney disease. A major source for vascular and renal ROS is a family of nonphagocytic NAD(P)H oxidases, including the prototypic Nox2 homolog-based NAD(P)H oxidase, as well as other NAD(P)H oxidases, such as Nox1 and Nox4. Other possible sources include mitochondrial electron transport enzymes, xanthine oxidase, cyclooxygenase, lipoxygenase, and uncoupled nitric oxide synthase. NAD(P)H oxidase-derived ROS plays a physiological role in the regulation of endothelial function and vascular tone and a pathophysiological role in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis, and rarefaction, important processes underlying cardiovascular and renal remodeling in hypertension and diabetes. These findings have evoked considerable interest because of the possibilities that therapies against nonphagocytic NAD(P)H oxidase to decrease ROS generation and/or strategies to increase nitric oxide (NO) availability and antioxidants may be useful in minimizing vascular injury and renal dysfunction and thereby prevent or regress target organ damage associated with hypertension and diabetes. Here we highlight current developments in the field of reactive oxygen species and cardiovascular disease, focusing specifically on the recently identified novel Nox family of NAD(P)H oxidases in hypertension. We also discuss the potential role of targeting ROS as a therapeutic possibility in the management of hypertension and cardiovascular disease.

Therapeutic effects of xanthine oxidase inhibitors: renaissance half a century after the discovery of allopurinol

The prototypical xanthine oxidase (XO) inhibitor allopurinol, has been the cornerstone of the clinical management of gout and conditions associated with hyperuricemia for several decades. More recent data indicate that XO also plays an important role in various forms of ischemic and other types of tissue and vascular injuries, inflammatory diseases, and chronic heart failure. Allopurinol and its active metabolite oxypurinol showed considerable promise in the treatment of these conditions both in experimental animals and in small-scale human clinical trials. Although some of the beneficial effects of these compounds may be unrelated to the inhibition of the XO, the encouraging findings rekindled significant interest in the development of additional, novel series of XO inhibitors for various therapeutic indications. Here we present a critical overview of the effects of XO inhibitors in various pathophysiological conditions and also review the various emerging therapeutic strategies offered by this approach.

Targeting reactive oxygen species in hypertension

PURPOSE OF REVIEW

Hypertension is a major risk factor for vascular diseases such as stroke, myocardial infarction, and renal microvascular disease. The mechanism by which vascular disease develops is complex, and growing evidence suggests that an increase in reactive oxygen species during hypertension is a major contributing factor. NADPH oxidase, the primary source of reactive oxygen species in the cardiovascular system, is a strong candidate for the development of therapeutic agents to ameliorate hypertension and end-organ damage.

RECENT FINDINGS

Various scavengers and inhibitors of reactive oxygen species have been proposed for use in animal as well as human studies. While many of these agents are effective at lowering tissue reactive oxygen species levels, their specificity is a serious concern. Our laboratory has developed cell-permeant peptidic inhibitors targeting key interactions among the different NAD(P)H oxidase homologues. One of these inhibitors targeting nox2 and p47-phox interaction has proven useful in attenuating target neoplasia and hypertrophy.

SUMMARY

Strategies aimed at specifically inhibiting NAD(P)H oxidase have proven effective in attenuating cardiovascular oxidative stress. The development of new inhibitors targeting novel oxidase homologues appears to hold significant promise for clarifying the physiologic role of these homologues as well as for the development of new antioxidant therapies.

Acute inhibition of the endogenous xanthine oxidase improves renal hemodynamics in hypercholesterolemic pigs

Hypercholesterolemia (HC), a major risk factor for onset and progression of renal disease, is associated with increased oxidative stress, potentially causing endothelial dysfunction. One of the sources of superoxide anion is xanthine oxidase (XO), but its contribution to renal endothelial function in HC remains unclear. We tested the hypothesis that XO modulates renal hemodynamics and endothelial function in HC pigs. Four groups (n = 23) of female domestic pigs were studied 12 wk after either normal (n = 11) or HC diet (n = 12). Oxidative stress was assessed by plasma isoprostanes and oxidized LDL, and the XO system by plasma uric acid, urinary xanthine, and renal XO expression (by immunoblotting and immunohistochemistry). Renal hemodynamics and function were studied with electron beam-computed tomography before and after endothelium-dependent (ACh) and -independent (sodium nitroprusside) challenge, during a concurrent intrarenal infusion of either oxypurinol or saline (n = 5-6 in each group). HC showed elevated oxidative stress, higher plasma uric acid (23.8 +/- 3.8 vs. 6.2 +/- 0.8 microM/mM creatinine, P = 0.001), lower urinary xanthine, and greater renal XO expression compared with normal. Inhibition of XO in HC significantly improved the blunted responses to ACh of cortical perfusion (13.5 +/- 12.1 and 37.2 +/- 10.6%, P = 0.01 and P = not significant vs. baseline, respectively), renal blood flow, and glomerular filtration rate; restored medullary perfusion; and improved the blunted cortical perfusion response to sodium nitroprusside. This study demonstrates that the endogenous XO system is activated in swine HC. Furthermore, it suggests an important role for XO in regulation of renal hemodynamics, function, and endothelial function in experimental HC.