Xanthine Oxidase Inhibitor Allopurinol Research Articles

Use of a xanthine oxidase inhibitor in autoimmune hepatitis

A 62-year-old woman with type 1 autoimmune hepatitis (AIH) failed to sustain remission when steroids were withdrawn from a regimen of steroids and azathioprine (AZA). Thiopurine metabolites revealed elevated 6-MMP (6-methyl mercaptopurine) and low 6-TGN (6-thioguanine nucleotide) consistent with AZA-induced hepatotoxicity. Introducing the xanthine oxidase inhibitor allopurinol led to rapid normalization of alanine aminotransferase (ALT) and discontinuation of steroids.

The effect of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes: Results from a prospective pharmacological study

IntroductionThiopurine therapy is often discontinued in inflammatory bowel disease (IBD) patients. The xanthine oxidase (XO) inhibitor allopurinol has previously shown to enhance thiopurine efficacy and to prevent adverse reactions, the mechanism of this beneficial interaction is not completely clarified. The aim of this study is to observe possible effects of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes. MethodsA prospective study of IBD patients failing thiopurine therapy due to a skewed thiopurine metabolism was performed. Patients were treated with allopurinol and azathioprine or mercaptopurine. Xanthine oxidase, hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and thiopurine S-methyl transferase (TPMT) activities, and thiopurine metabolites concentrations were measured during thiopurine monotherapy, and after 4 and 12weeks of combination therapy. ResultsOf fifteen IBD patients, XO activity decreased from 0.18 (IQR 0.08–0.3) during thiopurine monotherapy to 0.14 (IQR 0.06–0.2) and 0.11 (IQR 0.06–0.2; p=0.008) mU/hour/ml at 4 and 12weeks, respectively. HGPRT activity increased from 150 (IQR 114–176) to 180 (IQR 135–213) and 204nmol/(h×mg protein) (IQR 173–213; p=0.013). TPMT activity seemed not to be affected. 6-Thioguanine nucleotide concentrations increased from 138 (IQR 119–188) to 235 (223–304) and to 265pmol/8×10^8 (IQR 188–344), whereas 6-methyl mercaptopurine ribonucleotides concentrations decreased from 13230 (IQR 7130–17420) to 690 (IQR 378–1325) and 540 (IQR 240–790) pmol/8×10^8 at 4 and 12weeks of combination therapy (both p<0.001). ConclusionAllopurinol and thiopurine combination-therapy seems to increase HGPRT and decrease XO activity in IBD patients, which at least in part may explain the observed changes in thiopurine metabolite concentrations.

Alkalizer Administration Improves Renal Function in Hyperuricemia Associated with Obesity

We evaluated the combination effect of the alkalizer citrate with the xanthine oxidase inhibitor allopurinol on renal function and uric acid in patients with hyperuricemia associated with obesity and/or metabolic syndrome (MetS), who were extracted from among the subjects enrolled in a prospective randomized controlled study aimed at assessing the efficacy of such a combination for improving renal function. We also conducted a post hoc analysis to examine influences on lipid profiles.Patients who consented to participate in the study were randomly allocated to receive either allopurinol alone (monotherapy) or in combination with a citrate preparation (combination therapy). The analysis population consisted of 31 obese patients with a body mass index greater than 25 kg/m2 (monotherapy, 15 patients; combination therapy, 16 patients). The creatinine clearance rate (Ccr), serum uric acid levels, and lipid profiles were measured before and at 12 weeks after the start of treatment.In the combination therapy group, Ccr increased significantly and serum uric acid levels decreased significantly in obese patients, while Ccr tended to increase and serum uric acid levels decreased, though not significantly, in patients with MetS-related clinical parameters. Overall, blood triglyceride levels tended to improve in the combination therapy group as compared with the monotherapy group.

Quiz Page December 2012: Bilateral Kidney Enlargement and Acute Kidney Injury in a Patient With HIV Infection

Quiz Page December 2012: Bilateral Kidney Enlargement and Acute Kidney Injury in a Patient With HIV Infection

Allopurinol attenuates left ventricular dysfunction in rats with early stages of streptozotocin‐induced diabetes

Xanthine oxidase-derived superoxide production and oxidative stress contribute to the development of diabetic complications including diabetic cardiomyopathy. We hypothesized that xanthine oxidase-inhibitor allopurinol (ALP) may decrease hyperglycemia-induced oxidative stress, ameliorate cardiomyocyte hypertrophy and fibrosis, and attenuate the development of left ventricle (LV) diastolic dysfunction in rats with streptozotocin (STZ)-induced diabetes. Control Sprague Dawley (C) or streptozotocin-induced diabetic (D) rats were either untreated or treated with allopurinol (100 mg/kg/day) for 4 weeks starting at 1 week after streptozotocin injection. Free 15-F2t-isoprostane, a specific indicator of oxidative stress was measured by enzymatic immunoassay. The cardiomyocyte cross-sectional area was assessed by hematoxylin and eosin-stained paraffin-embedded sections of LVs. Myocardial collagens I and III were assessed by immunol histochemistry and Western blotting. Echocardiography was performed to characterize cardiac structure and function. In diabetic rats, both plasma and cardiac tissue levels of free 15-F2t-isoprostane were increased (p < 0.05 vs. control), accompanied with significant increase (p < 0.05 vs. control) in cross-section area and myocardial collagen deposition of LV cardiomyocyte. Echocardiography in diabetic rats showed that LV weight/body weight ratio was significantly higher than in control rats, whereas the levels of LV end-diastolic volume and stroke volume were decreased (all p < 0.05 diabetic vs. control). All these changes were either attenuated or prevented by allopurinol. In addition, LV ejection fraction in diabetic rats treated with allopurinol was higher than that in untreated diabetic rats (p < 0.05). Allopurinol can attenuate hyperglycemia-induced oxidative stress, ameliorate cardiomyocyte hypertrophy and fibrosis and subsequently prevent left ventricular dysfunction in early diabetes.

PKC activation impairs endothelium‐dependent NO‐mediated dilation of coronary arterioles via enhanced superoxide production from xanthine oxidase

We examined the role of PKC‐mediated pathway in eliciting endothelial dysfunction using isolated and pressurized porcine coronary arterioles. Diameter changes were recorded using videomicroscopic techniques. Superoxide production was detected with dihydroethidium (DHE) staining. Incubation of coronary arterioles with the PKC activator phorbol 12, 13‐dibutyrate (PDBu) (1 nM, 60 minutes) attenuated arteriolar dilation to the endothelium‐dependent, NO‐mediated agonists adenosine and serotonin, but not the NO donor sodium nitroprusside. In the presence of superoxide scavenger TEMPOL (1 mM), xanthine oxidase inhibitor allopurinol (10 μM), c‐Jun N‐terminal kinase (JNK) inhibitor SP600125 (5 μM) or Rho‐kinase inhibitor Y‐27632 (0.1 μM), the adverse effects of PDBu on adenosine‐ and serotonin‐induced dilations were prevented. Nevertheless, the inhibitory effects of PDBu were insensitive to H2O2 scavenger PEG‐catalase (500 units/ml), NAD(P)H oxidase inhibitor apocynin (100 μM) or p38 kinase inhibitor SB203580 (0.1 μM). DHE staining revealed that PDBu generated TEMPOL‐sensitive superoxide production in the coronary arteriolar smooth muscle. In conclusion, activation of vascular PKC with PDBu inhibits endothelium‐dependent, NO‐mediated dilation in coronary arterioles by producing superoxide from xanthine oxidase, which appears to be linked with JNK and RhoA/Rho kinase activation.

A role for xanthine oxidase in the control of fetal cardiovascular function in late gestation sheep

Virtually nothing is known about the effects on fetal physiology of xanthine oxidase inhibition. This is despite maternal treatment with the xanthine oxidase inhibitor allopurinol being considered in human complicated pregnancy to protect the infant’s brain from excessive generation of ROS.We investigated the in vivo effects of maternal treatment with allopurinol on fetal cardiovascular function in ovine pregnancy in late gestation. Under anaesthesia, pregnant ewes and their singleton fetus were instrumented with vascular catheters and flow probes around an umbilical and a fetal femoral artery at 118±1 dGA (days of gestational age; termca. 145 days). Five days later, mothers were infused I.V. with either vehicle (n =11) or allopurinol (n =10). Fetal cardiovascular function was stimulated with increasing bolus doses of phenylephrine (PE) following maternal vehicle or allopurinol. The effects of maternal allopurinol on maternal and fetal cardiovascular function were also investigated following fetal NO blockade (n =6) or fetal β1-adrenergic antagonism (n =7). Maternal allopurinol led to significant increases in fetal heart rate, umbilical blood flow and umbilical vascular conductance, effects abolished by fetal β1-adrenergic antagonism but not by fetal NO blockade. Maternal allopurinol impaired fetal α1-adrenergic pressor and femoral vasopressor responses and enhanced the gain of the fetal cardiac baroreflex. These effects of maternal allopurinol were restored to control levels during fetal NO blockade. Maternal treatment with allopurinol induced maternal hypotension, tachycardia and acid–base disturbance. We conclude that maternal treatment with allopurinol alters in vivo maternal, umbilical and fetal vascular function via mechanisms involving NO and β1-adrenergic stimulation. The evidence suggests that the use of allopurinol in clinical practice should be approached with caution.

Allopurinol Acutely Increases Adenosine Triphospate Energy Delivery in Failing Human Hearts

This study tested the hypothesis that acute administration of the xanthine oxidase (XO) inhibitor allopurinol improves cardiac high-energy phosphate concentrations in human heart failure (HF) and increases the rate of adenosine triphosphate (ATP) synthesis through creatine kinase (CK), the primary myocardial energy reserve. Studies of patients and animal models implicate impaired myocardial high-energy phosphate availability in HF. The XO reaction is a critical terminal step in ATP and purine degradation and an important source of reactive oxygen species. Thus, XO inhibition is a potentially attractive means to improve energy metabolism in the failing human heart. We randomized 16 patients with nonischemic cardiomyopathy in a double-blind fashion to allopurinol (300 mg intravenously) or placebo infusion, 4-to-1, the latter for purposes of blinding only. The myocardial concentrations of ATP and creatine phosphate (PCr) and the rate of ATP synthesis through CK (CK flux) were determined by (31)P magnetic resonance spectroscopy. Allopurinol infusion increased mean cardiac PCr/ATP and PCr concentration by ∼11% (p < 0.02), and mean CK flux by 39% (2.07 ± 1.27 μmol/g/s to 2.87 ± 1.82 μmol/g/s, p < 0.007). Calculated cytosolic adenosine diphosphate concentration decreased, whereas the free energy of ATP hydrolysis (ΔG(∼ATP)) increased with allopurinol. The increased CK flux was disproportionate to substrate changes, indicating increased CK enzyme activity. Intravenous administration of the XO inhibitor allopurinol acutely improves the relative and absolute concentrations of myocardial high-energy phosphates and ATP flux through CK in the failing human heart, offering direct evidence that myofibrillar CK energy delivery can be pharmaceutically augmented in the failing human heart. (Intravenous Allopurinol in Heart Failure; NCT00181155).

Reactive Oxygen Species in Myocardial Reperfusion Injury: From Physiopathology to Therapeutic Approaches

Myocardial ischemia is a major cause of morbidity and mortality in the world. Although restoration of blood flow after prolonged ischemia is essential for cardiomyocytes salvation and to limit myocardial damage and cardiac dysfunction, reperfusion itself exacerbates myocardial injury. Considerable evidence attributes reactive oxygen species (ROS), produced either by the myocardium itself or by infiltrating inflammatory cells, as an early event in this process. Once produced, ROS can lead to cellular damage through a number of pathways including direct damage to membranes and proteins or indirect damage through the activation of pro-apoptotic pathways. While using antioxidants to scavenge free radicals or targeting the sources of ROS, such as xanthine oxidase, may be potential attractive approaches to reduce myocardial reperfusion injury, clinical trials using antioxidant therapies have been largely disappointing. Neither oxidant scavengers like N-acetylcysteine and vitamins E and C, nor xanthine oxidase inhibitor allopurinol have provided indisputable evidence of a clinical benefit despite numerous favourable studies in animal models. Evidence to support a role of ROS in myocardial injury reperfusion is strong, but the clinical approach used has so far been inadequate. Absence of optimal pharmacology, variation in end-points used and low specificity of the compounds used have often been pointed out. In addition, the efficacy of antioxidants is often evaluated based on indirect biomarkers, which are prone to variation. Thus, clinical trials could be improved by the standardisation of the methods to measure oxidative stress and their impact on prognosis outcome.

Abstract 9790: Endothelin-1 Inhibits Endothelium-Dependent NO-Mediated Dilation of Coronary Arterioles via p38 Kinase Linked Superoxide Production From NAD(P)H Oxidase

Elevated levels of endothelin (ET)-1, a potent constrictor peptide, are associated with higher risk of cardiovascular diseases by promoting vasoconstriction and oxidative stress. However, it remains unknown whether ET-1, at subvasomotor concentrations, exerts adverse effects on coronary vasomotor function. To address this issue without confounding influences from systemic and local factors, porcine coronary arterioles (50-100 μm) were isolated, cannulated and pressurized without flow for in vitro study. Diameter changes were recorded using a videomicrometer. Dihydroethidium (DHE) staining was used to detect superoxide production. Arterioles developed basal tone (60±3 µm) and dilated dose-dependently to the endothelium-dependent NO-mediated vasodilators serotonin (1 nM to 0.1 µM) and adenosine (1 nM to 10 µM). Extraluminal incubation with a clinically relevant subvasomotor concentration of ET-1 (10 pM, 60 minutes) significantly attenuated arteriolar dilation to adenosine and serotonin but not to endothelium-independent vasodilator sodium nitroprusside. The adverse effects of ET-1 on serotonin- and adenosine-induced dilations were prevented by pretreating the vessels with the ETA receptor antagonist BQ123 (1 μM), the superoxide scavenger TEMPOL (1 mM), the NAD(P)H oxidase inhibitor apocynin (100 μM) or the p38 kinase inhibitor SB203580 (0.1 μM). However, the adverse effects of ET-1 were not prevented by pretreating the vessels with ETB receptor antagonist BQ788 (0.1 μM), H2O2 scavenger catalase (1000 units/ml), xanthine oxidase inhibitor allopurinol (10 μM) or c-Jun N-terminal kinase inhibitor SP600125 (5 μM). DHE immunohistochemical staining showed that ET-1 generated TEMPOL- and SB203580-sensitive superoxide production in the arteriolar endothelium. Collectively, our data indicate that exposure of coronary arterioles to a pathophysiological concentration of ET-1 inhibits endothelium-dependent NO-mediated dilation in coronary arterioles by activation of ETA receptors leading to the production of superoxide from NAD(P)H oxidase, which appears to be linked with p38 kinase activation.

2011 Recommendations for the Diagnosis and Management of Gout and Hyperuricemia

Gout is a major health problem in the United States; it affects 8.3 million people, which is approximately 4% of the adult population. Gout is most often diagnosed and managed in primary care practices; thus, primary care physicians have a significant opportunity to improve patient outcomes. Following publication of the 2006 European League Against Rheumatism (EULAR) gout guidelines, significant new evidence has accumulated, and new treatments for patients with gout have become available. It is the objective of these 2011 recommendations to update the 2006 EULAR guidelines, paying special attention to the needs of primary care physicians. The revised 2011 recommendations are based on the Grading of Recommendations Assessment, Development, and Evaluation approach as an evidence-based strategy for rating quality of evidence and grading the strength of recommendation formulated for use in clinical practice. A total of 26 key recommendations, 10 for diagnosis and 16 for management, of patients with gout were evaluated, resulting in important updates for patient care. The presence of monosodium urate crystals and/or tophus and response to colchicine have the highest clinical diagnostic value. The key aspect of effective management of an acute gout attack is initiation of treatment within hours of symptom onset. Low-dose colchicine is better tolerated and is as effective as a high dose. When urate-lowering therapy (ULT) is indicated, the xanthine oxidase inhibitors allopurinol and febuxostat are the options of choice. Febuxostat can be prescribed at unchanged doses for patients with mild-to-moderate renal or hepatic impairment. The target of ULT should be a serum uric acid level that is ≤ 6 mg/dL. For patients with refractory and tophaceous gout, intravenous pegloticase is a new treatment option. This article is a summary of the 2011 clinical guidelines published in Postgraduate Medicine. This article provides a streamlined, accessible overview intended for quick review by primary care physicians, with the full guidelines being a resource for those seeking additional background information and expanded discussion.

Mechanistic Insights Into the Therapeutic Use of High-Dose Allopurinol in Angina Pectoris

The aim of this study was to evaluate the effect of high-dose allopurinol on vascular oxidative stress (OS) and endothelial function in subjects with stable coronary artery disease (CAD). Allopurinol, a xanthine oxidase inhibitor, prolongs the time to chest pain during exercise in angina. We sought to ascertain whether allopurinol also improves endothelial dysfunction in optimally treated CAD patients, because such an effect might be of value to reduce future cardiovascular mortality. The mechanism of the anti-ischemic effect of allopurinol could be related to its reducing xanthine oxidase-induced OS, and our second aim was to see whether allopurinol really does reduce vascular tissue OS in CAD patients. A randomized, double-blind, placebo-controlled, crossover study was conducted in 80 patients with CAD, comparing allopurinol (600 mg/day) with placebo. Endothelial function was assessed by forearm venous occlusion plethysmography, flow-mediated dilation, and pulse wave analysis. Vascular OS was assessed by intra-arterial co-infusion of vitamin C and acetylcholine. Compared with placebo, allopurinol significantly improved endothelium-dependent vasodilation, by both forearm venous occlusion plethysmography (93 ± 67% vs. 145 ± 106%, p = 0.006) and flow-mediated dilation (4.2 ± 1.8% vs. 5.4 ± 1.7%, p < 0.001). Vascular oxidative stress was completely abolished by allopurinol. Central augmentation index improved significantly with allopurinol (2.6 ± 7.0%, p < 0.001) but not with placebo. Our study demonstrates that, in optimally treated CAD patients, high-dose allopurinol profoundly reduces vascular tissue OS and improves 3 different measures of vascular/endothelial dysfunction. The former effect on OS might underpin the anti-ischemic effect of allopurinol in CAD. Both effects (on OS and endothelial dysfunction) increase the likelihood that high-dose allopurinol might reduce future cardiovascular mortality in CAD, over and above existing optimum therapy. (Exploring the therapeutic potential of xanthine oxidase inhibitor allopurinol in angina; ISRCTN15253766).

The ethanolic extract of Kaempferia parviflora reduces ischaemic injury in rat isolated hearts

The ethanolic extract of Kaempferia parviflora (KPE) has been reported to contain a range of flavonoids and to enhance endothelial synthesis of NO. We investigated the vascular relaxant, antioxidant and cardioprotective activities of KPE. Vascular function was assessed in rat aortic rings and superoxide generation determined using lucigenin enhanced chemiluminescence. Ischaemia and reperfusion were induced in rat isolated, perfused hearts. KPE caused vasorelaxation (R(max) 102 ± 2%), which was partly inhibited by removal of the endothelium (R(max) 91 ± 1%) or by N(G)-nitro-l-arginine (L-NNA, R(max) 83 ± 3%) or 1H-[1,2,4] oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, R(max) 80 ± 2%). In addition KPE caused concentration-dependent inhibition of the contractile response to exogenous Ca(2+). KPE (10(-3)M) also significantly inhibited superoxide radical generation induced by of xanthine/xanthine oxidase (2.3 ± 0.4% of control) to a similar extent to the xanthine oxidase inhibitor allopurinol (10(-4)M, 1.6 ± 0.5%) or by rat isolated aorta in the presence of NADPH (30.0 ± 6.3% of control) similarly to the NADPH oxidase inhibitor diphenyliodonium (5 × 10(-6)M, 23.1 ± 5.6%). In the presence of oxidant stress generated by pyrogallol endothelium-dependent relaxation of rat aortic rings was impaired (ACh R(max) control 99 ± 1%; pyrogallol 44 ± 5%), an effect that was significantly reduced by KPE (10(-4)M, ACh R(max) 82 ± 4%). In addition, KPE was found to attenuate the ventricular dysfunction caused by 20 min global ischaemia and 30 min reperfusion (I/R) in rat isolated hearts (dP/dt IR 1016 ± 242, IR+KPE 2238±233 mm Hg/s). KPE is an effective vasodilator and antioxidant that is able to prevent myocardial ischaemia-reperfusion injury. We suggest that KPE may be useful as an adjunct to thrombolytic therapy in the management of reperfusion injury.

Allopurinol Attenuates Left Ventricular Dysfunction In The Early Stage of Streptozotocin‐Induced Diabetes In Rats

Xanthine oxidase‐derived superoxide production and oxidative stress plays an important role in the development of diabetic complications (Diabetes 2002;51(4):1118–24) including diabetic cardiomyopathy. We hypothesized that treatment with the xanthine oxidase inhibitor allopurinol (ALP) may attenuate or prevent the development of left ventricle (LV) diastolic dysfunction, an early sign of diabetic cardiomyopathy (Cardiology 2002;98:33–9), in rats with streptozotocin (STZ)‐induced diabetes. Control Sprague‐Dawley (C) or STZ‐induced diabetic (D) rats (220±20g) were either untreated or treated with ALP (100 mg/kg/day) for four weeks starting at one week after STZ injection. In D rats, both plasma and cardiac tissue levels of 15‐F2t‐isoprostane, a specific index of oxidative damage, were increased (P&lt;0.05 vs. C) at the 5th week, accompanied with significant increase in left ventricle (LV) weight/body weight ratio and decreases in LV end‐diastolic volume and stroke volume (all P&lt;0.05 D vs. C). All these changes were either significantly attenuated or prevented by treatment with ALP. In addition, LV ejection fraction in D rats treated with ALP was higher than that in untreated D rats (P&lt;0.05). It is concluded that ALP can attenuate hyperglycemia‐induced oxidative stress and subsequently present left ventricular dysfunction in early diabetes.

Case report of extensive metabolism by aldehyde oxidase in humans: Pharmacokinetics and metabolite profile of FK3453 in rats, dogs, and humans

We describe the preclinical and clinical pharmacokinetic profiles of FK3453 [6-(2-amino-4-phenylpyrimidin-5-yl)-2-isopropylpyridazin-3(2H)-one] and the mechanism responsible for poor oral exposure of FK3453 in humans.FK3453 showed favourable profiles in preclinical pharmacokinetic studies, including satisfactory absolute bioavailability and total body clearance in animals (30.5%–41.4%, 54.7%–68.2%, and 71.3%–93.4% and 10.8–17.6, 1.9–17.1, and 5.0 mL/min/kg in male rats, female rats, and dogs, respectively), and good metabolic stability in liver microsomes (42.3, 14.5, and 1.1 mL/min/kg in male rats, dogs, and humans, respectively).However, despite these promising preclinical findings, plasma concentrations of FK3453 in humans were extremely low, with the oxidative metabolite of the aminopyrimidine moiety (M4) identified as a major metabolite. Given that aldehyde oxidase (AO) and xanthine oxidase (XO) were presumed to be the enzymes responsible for M4 formation, we investigated the mechanism of M4 formation using human liver subcellular fractions.M4 was detected in the incubation mixture with S9 and cytosol but not with microsomes, and M4 formation was inhibited by AO inhibitors (menadione, isovanillin) but not by cytochrome P-450 inhibitor (1-aminobenzotiazole) or XO inhibitor (allopurinol). These results suggest M4 formation is catalyzed by AO, and therefore, its poor exposure in humans was attributed to extensive AO metabolism.

Metabolomic profiling of the effects of allopurinol on Drosophila melanogaster

Metabolomic profiling using hydrophilic interaction chromatography in combination with Fourier transform mass spectrometry was used to study the effects of the xanthine oxidase inhibitor allopurinol on wild type Drosophila melanogaster. Allopurinol treatment phenocopied the rosy mutation causing an elevation in the levels of xanthine and hypoxanthine and a fall in the levels of uric acid and allantoin. However, in addition there were some unexpected metabolic changes after treatment. Ascorbic acid levels were undetectable, glutathione levels fell and glutathione disulphide levels rose, methionine S-oxide levels rose and riboflavin levels fell. The origin of this oxidative stress was not immediately apparent; however, there was a strong suggestion that it might be related to a fall in NADPH levels linked to a reduction in glucose-6-phosphate dehydrogenase activity, resulting in reduced levels of some metabolites in the pentose phosphate pathway. In addition to producing oxidative stress there were marked effects on tryptophan metabolism with most of the metabolites in the kynurenine pathway being lowered by allopurinol treatment. The effects on the kynurenine pathway could be related to the established use of allopurinol in treating schizophrenia.

The Xanthine Oxidase Inhibitor Allopurinol Results In A Loss Of Cytoprotection Conferred by Pharmacologic Pre-conditioning With Hydrogen Sulfide

Introduction: A growing body of literature has shown that pharmacologic pre-conditioning with hydrogen sulfide (HS) mitigates damage caused by ischemia-reperfusion injury (IRI). However, its protective mechanism remains unclear. As a reversible inhibitor of cytochrome c oxidase, HS reduces ATP synthesis by diminishing oxidative phosphorylation, resulting in increased xanthine oxidase (XO) activity and the generation of reactive oxygen species (ROS). It is hypothesized that this non-lethal level of free radicals is sufficient to upregulate cellular antioxidant enzymes and reduce IRI. Our laboratory has shown that a 10μM dose of the XO inhibitor allopurinol abrogates the protective effects of HS on skeletal muscle in the setting of IRI. However, other studies suggest that allopurinol protects from IRI by directly scavenging free radicals and decreasing ROS production. We hypothesize that higher concentrations of allopurinol are required to restore and complement the protective effects of pharmacologic preconditioning with HS in an in vitro model of IRI. Methods: Murine myoblasts were differentiated into myotubes and then treated with either 10μM HS, 100μM allopurinol, both 10μM HS and 100μM allopurinol, or vehicle alone (non-treated control). The experiment was replicated with a higher concentration of allopurinol (1mM). Cells were exposed to 3h of anoxia followed by 3h of normoxia (21% O2). Parallel control groups were exposed to normoxia for 6 hours. A TUNEL assay was performed to determine the apoptotic index (AI; number of TUNEL-positive cells divided by the total number of cells) for each group. Results: The AI of myotubes treated with 100μM allopurinol alone was unchanged from that of non-treated controls (9.1%±1.1% v. 10.2%±1.4%, p=0.194). For cells treated with 1mM allopurinol alone, the AI was similarly unchanged (9.5%±1.2%, p=0.317). Ten μM HS alone resulted in a significant decrease in AI when compared to non-treated controls (4.0%±0.4%, p<0.001). However, treatment with both 100μM allopurinol and HS resulted in an AI of 11.3%±0.8%, significantly greater than that of myotubes treated with HS alone (p<0.001) and unchanged from non-treated controls (p=0.974). Likewise, treatment with both 1mM allopurinol and HS resulted in an AI of 10.5%±0.9%, significantly greater than that of HS alone (p<0.001) and not significantly different from that of the untreated controls (p=0.448). Conclusions: Even in the presence of increased concentrations of allopurinol, the protective effects of HS in the setting of IRI are lost. Furthermore, in contrast to others' reports, allopurinol alone was found not to have a cytoprotective effect. These data suggest that the protective mechanism of HS is due at least in part to a xanthine oxidase-mediated pathway and the generation of low levels of ROS. These findings importantly expand our understanding of the pathophysiology of IRI and may help to delineate the clinical utility of HS.

Oxidative stress induces protein and DNA radical formation in follicular dendritic cells of the germinal center and modulates its cell death patterns in late sepsis

Profound depletion of follicular dendritic cells (FDCs) is a hallmark of sepsis-like syndrome, but the exact causes of the ensuing cell death are unknown. The cell death-driven depletion contributes to immunoparalysis and is responsible for most of the morbidity and mortality in sepsis. Here we have utilized immuno-spin trapping, a method for detection of free radical formation, to detect oxidative stress-induced protein and DNA radical adducts in FDCs isolated from the spleens of septic mice and from human tonsil-derived HK cells, a subtype of germinal center FDCs, to study their role in FDC depletion. At 24 h post-lipopolysaccharide administration, protein radical formation and oxidation were significantly elevated in vivo and in HK cells as shown by ELISA and confocal microscopy. The xanthine oxidase inhibitor allopurinol and the iron chelator desferrioxamine significantly decreased the formation of protein radicals, suggesting the role of xanthine oxidase and Fenton-like chemistry in radical formation. Protein and DNA radical formation correlated mostly with apoptotic features at 24 h and necrotic morphology of all the cell types studied at 48 h with concomitant inhibition of caspase-3. The cytotoxicity of FDCs resulted in decreased CD45R/CD138-positive plasma cell numbers, indicating a possible defect in B cell differentiation. In one such mechanism, radical formation initiated by xanthine oxidase formed protein and DNA radicals, which may lead to cell death of germinal center FDCs.

Olea europaea leaf (Ph.Eur.) extract as well as several of its isolated phenolics inhibit the gout-related enzyme xanthine oxidase

In Mediterranean folk medicine Olea europaea L. leaf (Ph.Eur.) preparations are used as a common remedy for gout. In this in vitro study kinetic measurements were performed on both an 80% ethanolic (v/v) Olea europaea leaf dry extract (OLE) as well as on nine of its typical phenolic constituents in order to investigate its possible inhibitory effects on xanthine oxidase (XO), an enzyme well known to contribute significantly to this pathological process. Dixon and Lineweaver-Burk plot analysis were used to determine K(i) values and the inhibition mode for the isolated phenolics, which were analysed by RP-HPLC for standardisation of OLE. The standardised OLE as well as some of the tested phenolics significantly inhibited the activity of XO. Among these, the flavone aglycone apigenin exhibited by far the strongest effect on XO with a K(i) value of 0.52 μM. In comparison, the known synthetic XO inhibitor allopurinol, used as a reference standard, showed a K(i) of 7.3 μM. Although the phenolic secoiridoid oleuropein, the main ingredient of the extract (24.8%), had a considerable higher K(i) value of 53.0 μM, it still displayed a significant inhibition of XO. Furthermore, caffeic acid (K(i) of 11.5 μM; 1.89% of the extract), luteolin-7-O-β-D-glucoside (K(i) of 15.0 μM; 0.86%) and luteolin (K(i) of 2.9 μM; 0.086%) also contributed significantly to the XO inhibiting effect of OLE. For oleuropein, a competitive mode of inhibition was found, while all other active substances displayed a mixed mode of inhibition. Tyrosol, hydroxytyrosol, verbascoside, and apigenin-7-O-β-D-glucoside, which makes up for 0.3% of the extract, were inactive in all tested concentrations. Regarding the pharmacological in vitro effect of apigenin-7-O-β-D-glucoside, it has to be considered that it is transformed into the active apigenin aglycone in the mammalian body, thus also contributing substantially to the anti-gout activity of olive leaves. For the first time, this study provides a rational basis for the traditional use of olive leaves against gout in Mediterranean folk medicine.

The Alkalizer Citrate Reduces Serum Uric Acid Levels and Improves Renal Function in Hyperuricemic Patients Treated with the Xanthine Oxidase Inhibitor Allopurinol

Objective. Hyperuricemia, an integral component of metabolic syndrome, is a major health problem causing gout and renal damage. Urine alkalizers such as citrate preparations facilitate renal excretion of the uric acid, but its supportive effect on xanthine oxidase inhibitors has not been tested yet. We performed a randomized, prospective study of the effect of a combination of allopurinol and a citrate preparation on renal function in patients with hyperuricemia, employing 70 patients who had hyperuricemia with serum uric acid levels ≥7.0 mg/dL, or those diagnosed as having hyperuricemia in the past. Methods. They were randomly enrolled into two study groups: the allopurinol monotherapy (MT) group or combination treatment (CT) group with allopurinol and a citrate preparation. Allopurinol (100–200 mg/day) in the absence or presence of a citrate preparation (3 g/day) was administered for 12 weeks and levels of serum uric acid, its urinary clearance (Cua), and the renal glomerular filtration rates assessed with the creatinine clearance (Ccr) were evaluated before and after the treatment. Results. Serum levels of uric acid decreased significantly in both groups, whereas the change observed was much greater in CT group. Cua was significantly increased in CT group but not in MT group. Ccr was not altered in both groups in general, whereas it was significantly increased in a fraction of CT group with decreased renal function. Conclusions. These results indicate that an additional use of citrate preparations with xanthine oxidase inhibitors is beneficial for patients with hyperuricemia, reducing circulating uric acid and improving their glomerular filtration rates.