Investigation of the Inhibition Mechanism of Xanthine Oxidoreductase by Oxipurinol: A Computational Study

Xanthine oxidoreductase (XOR) is an enzyme found in various organisms. It converts hypoxanthine to xanthine and urate, which are crucial steps in purine elimination in humans. Elevated uric acid levels can lead to conditions like gout and hyperuricemia. Therefore, there is significant interest in developing drugs that target XOR for treating these conditions and other diseases. Oxipurinol, an analogue of xanthine, is a well-known inhibitor of XOR. Crystallographic studies have revealed that oxipurinol directly binds to the molybdenum cofactor (MoCo) in XOR. However, the precise details of the inhibition mechanism are still unclear, which would be valuable for designing more effective drugs with similar inhibitory functions. In this study, molecular dynamics and quantum mechanics/molecular mechanics calculations are employed to investigate the inhibition mechanism of XOR by oxipurinol. The study examines the structural and dynamic effects of oxipurinol on the pre-catalytic structure of the metabolite-bound system. Our results provide insights on the reaction mechanism catalyzed by the MoCo center in the active site, which aligns well with experimental findings. Furthermore, the results provide insights into the residues surrounding the active site and propose an alternative mechanism for developing alternative covalent inhibitors.

Computational Characterization of the Inhibition Mechanism of Xanthine Oxidoreductase by Topiroxostat

Xanthine oxidase (XO) is a member of the molybdopterin-containing enzyme family. It interconverts xanthine to uric acid as the last step of purine catabolism in the human body. The high uric acid concentration in the blood directly leads to human diseases like gout and hyperuricemia. Therefore, drugs that inhibit the biosynthesis of uric acid by human XO have been clinically used for many years to decrease the concentration of uric acid in the blood. In this study, the inhibition mechanism of XO and a new promising drug, topiroxostat (code: FYX-051), is investigated by employing molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) calculations. This drug has been reported to act as both a noncovalent and covalent inhibitor and undergoes a stepwise inhibition by all its hydroxylated metabolites, which include 2-hydroxy-FYX-051, dihydroxy-FYX-051, and trihydroxy-FYX-051. However, the detailed mechanism of inhibition of each metabolite remains elusive and can be useful for designing more effective drugs with similar inhibition functions. Hence, herein we present the computational investigation of the structural and dynamical effects of FYX-051 and the calculated reaction mechanism for all of the oxidation steps catalyzed by the molybdopterin center in the active site. Calculated results for the proposed reaction mechanisms for each metabolite's inhibition reaction in the enzyme's active site, binding affinities, and the noncovalent interactions with the surrounding amino acid residues are consistent with previously reported experimental findings. Analysis of the noncovalent interactions via energy decomposition analysis (EDA) and noncovalent interaction (NCI) techniques suggests that residues L648, K771, E802, R839, L873, R880, R912, F914, F1009, L1014, and A1079 can be used as key interacting residues for further hybrid-type inhibitor development.

Development of a new method based on gold nanoparticles for determination of uric acid in urine samples

In the current work, we have reported a fast and easy method based on gold nanoparticles for the determination of uric acid in urine samples. In the first stage, gold nanoparticles were synthesized using the chemical reduction method and then applied as a sensor to measure uric acid concentration based on its strong reducing property. The main parameters affecting response signals such as pH, reagent concentration, and time are optimized using the multivariate method. Under the optimum conditions, the calibration graphs were linear in the range of 0.5 - 10.0 mg.L^-1 with limits of detection of 0.2 mg.L^-1 and RSD% of 1.2% These results show that this nano-based method is a very sensitive and simple method for the determination of uric acid in urine samples.

Managing Cardiovascular Risk in Patients with Rheumatic Disease

Individuals with rheumatoid arthritis, systemic lupus erythematosus, or gout have increased risk of cardiovascular disease (CVD) compared with the general population. This risk relates to a combination of traditional cardiovascular risk factors and disease-specific factors. Screening for CVD is important because CVD contributes to significant morbidity and mortality. Management includes tight control of disease activity to reduce inflammation, but with care to minimize use of nonsteroidal anti-inflammatory drugs and prolonged courses of high-dose corticosteroids. Traditional cardiovascular risk factors should be managed with a combination of lifestyle interventions and pharmacotherapy. The decision to start antihypertensive and lipid-lowering therapy should be based on individual CVD risk.

The Reactive Species Interactome in the Brain

Significance: Redox pioneer Helmut Sies attempted to explain reactive species' challenges faced by organelles, cells, tissues, and organs via three complementary definitions: (i) oxidative stress, that is, the disturbance in the prooxidant-antioxidant defense balance in favor of the prooxidants; (ii) oxidative eustress, the low physiological exposure to prooxidants; and (iii) oxidative distress, the supraphysiological exposure to prooxidants. Recent Advances: Identification, concentration, and interactions are the most important elements to improve our understanding of reactive species in physiology and pathology. In this context, the reactive species interactome (RSI) is a new multilevel redox regulatory system that identifies reactive species families, reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species, and it integrates their interactions with their downstream biological targets. Critical Issues: We propose a united view to fully combine reactive species identification, oxidative eustress and distress, and the RSI system. In this view, we also propose including the forgotten reactive carbonyl species, an increasingly rediscovered reactive species family related to the other reactive families, and key enzymes within the RSI. We focus on brain physiology and pathology to demonstrate why this united view should be considered. Future Directions: More studies are needed for an improved understanding of the contributions of reactive species through their identification, concentration, and interactions, including in the brain. Appreciating the RSI in its entirety should unveil new molecular players and mechanisms in physiology and pathology in the brain and elsewhere.

Carotid Plaques From Symptomatic Patients Are Characterized by Local Increase in Xanthine Oxidase Expression

[Figure: see text].

Managing Cardiovascular Risk in Patients with Rheumatic Disease

Individuals with rheumatoid arthritis, systemic lupus erythematosus, or gout have increased risk of cardiovascular disease (CVD) compared with the general population. This risk relates to a combination of traditional cardiovascular risk factors and disease-specific factors. Screening for CVD is important because CVD contributes to significant morbidity and mortality. Management includes tight control of disease activity to reduce inflammation, but with care to minimize use of nonsteroidal anti-inflammatory drugs and prolonged courses of high-dose corticosteroids. Traditional cardiovascular risk factors should be managed with a combination of lifestyle interventions and pharmacotherapy. The decision to start antihypertensive and lipid-lowering therapy should be based on individual CVD risk.

Propolis relieves the cardiotoxicity of chlorpyrifos in diabetic rats via alleviations of paraoxonase-1 and xanthine oxidase genes expression

Pesticides cardiotoxicity in case of diabetic-induced cardiac complications is unidentified. The probable amelioration role of propolis is gauged against the cardiotoxic effects of chlorpyrifos in the diabetic rats through paraoxonase-1 (PON1) and xanthine oxidase (XO) genes dysregulation. Fifty-six male rats were distributed (n = 7) into eight groups. The first one saved as control whereas the 2nd, 3rd, and 4th were kept for propolis aqueous extract (100 mg/kg), diabetes (60 mg/kg streptozotocin) and chlorpyrifos (2.5 mg/kg), respectively. The 5th was diabetes/chlorpyrifos combination, while 6th, 7th, and 8th were intubated with propolis for four weeks after diabetic induction, chlorpyrifos intoxication, and their combination, respectively. The plasma glucose, lipid profiles, cardiac enzymes and interleukin-6 (IL-6) significantly elevated, while insulin decreased in the diabetic and combination groups. Although the cardiac acetylcholinesterase, total thiols, and PON1 significantly reduced after diabetic and/or chlorpyrifos gavage, the protein carbonyl, superoxide dismutase, catalase, and XO significantly elevated. The mRNA genes expression of PON1 and XO have also confirmed the enzymatic activities. Interestingly, propolis significantly restored the hyperglycemia, hypoinsulinemia, hyperlipidemia, IL-6 elevations, and antioxidant defense system disorder. These records revealed that the immunomodulatory, anti-diabetic and antioxidant tasks are fine pointers for the cardiovascular defender of propolis especially during diabetes and/or pesticides exposure.

Inhibitors of Xanthine Oxidase: Scaffold Diversity and Structure-Based Drug Design

Xanthine oxidase (XO) is the enzyme responsible for the catabolism of purines and their conversion into uric acid. XO is thus the target for the treatment of hyperuricemia and gout. For more than 50 years the only XO inhibitor drug available on the market was the purine analogue allopurinol. In the last decade there has been a resurgence in the search for new inhibitors of XO, as the activity of XO and hyperuricemia have also been associated with a variety of conditions such as diabetes, hypertension, and other cardiovascular diseases. In recent years the non-purine inhibitor febuxostat was approved in Europe and the USA for the treatment of hyperuricemia. This drug was followed by another XO inhibitor called topiroxostat. This review discusses the molecular structures and activities of the multiple classes of inhibitors that have been developed since the discovery of allopurinol, with a brief review of the molecular interactions between inhibitors and XO active site residues for the most important molecules. The challenges ahead for the discovery of new inhibitors of XO with novel chemical structures are discussed.

First Report on Association of Hyperuricemia with Type 2 Diabetes in a Vietnamese Population

BACKGROUND

Uric acid is a powerful free-radical scavenger in humans, but hyperuricemia may induce insulin resistance and beta-cell dysfunction. The study aimed to evaluate the association between hyperuricemia and hyperglycemia, considering the confounding factors in a Vietnamese population.

METHODS

A population-based cross-sectional study recruited 1542 adults aged 50 to 70 years to collect data on socioeconomic status, lifestyle factors, and clinical patterns. Associations between hyperuricemia and hyperglycemia (isolated impaired fasting glucose (IFG), isolated impaired glucose tolerance (IGT), combined IFG-IGT, and type 2 diabetes (T2D)) were evaluated by multinomial logistic regression analysis in several models, adjusting for the confounding factors including socioeconomic status, lifestyle factors, and clinical measures.

RESULTS

Uric acid values were much higher in IFG, IFG-IGT, and T2D groups compared to those in the normal glucose tolerance (NGT) group. The significant association of hyperuricemia with IFG, IFG-IGT, and T2D was found in the model unadjusted and remained consistently in several models adjusted for socioeconomic status, lifestyle factors, and clinical patterns. In the final model, the consistent hyperglycemia risk was found in total sample (OR = 2.23 for IFG, OR = 2.29 for IFG-IGT, and 1.75 for T2D, P ≤ 0.006) and in women (OR = 2.90 for IFG, OR = 3.96 for IFG-IGT, and OR = 2.49 for T2D, P < 0.001) but not in men.

CONCLUSIONS

It is the first report in Vietnamese population suggesting the significant association of hyperuricemia with IFG, IFG-IGT, and T2D; and the predominant association was found in women than in men, taken into account the confounding factors.

Xanthine oxidase inhibitors from an endophytic fungus Lasiodiplodia pseudotheobromae

Two new compounds, lasdiplactone (1) and lasdiploic acid (2) and one known compound 3 were isolated from the chloroform extract of cell free filtrate of the endophytic fungus Lasiosdiplodia pseudotheobromae. The structures of new compounds were determined by interplay of spectral techniques (IR, mass, ¹H NMR, ¹³C NMR, DEPT, and 2D NMR). The absolute configuration at C-4 position of 1 was established as S using a process similar to modified Mosher's method. The absolute configuration of 2 was established by comparing its ECD spectrum with the calculated ECD spectra of all possible isomers. In the in vitro XO inhibition assay, the highest inhibition was exhibited by 3 with an IC₅₀ of 0.38 ± 0.13 μg/ml, followed by 2 with an IC₅₀ of 0.41 ± 0.1 μg/ml and the least in 1. The oxidized form of 1 also showed high XO inhibition with IC₅₀ of 0.35 ± 0.13 μg/ml.

Lower serum uric acid level strongly predict short-term poor functional outcome in acute stroke with normoglycaemia: a cohort study in China

BACKGROUND

Conflicting results on the correlation between hyperuricemia and the prognosis of stroke had been reported and the close association between serum uric acid (SUA) and abnormal glycomatabolism might further complicate the assessment of the correlation. We aimed to investigate SUA in predicting the prognosis of acute stroke in different glycometabolism status.

METHODS

A total of 2907 patients aged from 18 to 85 (1220 diabetes mellitus (DM), 777 prediabetes and 910 normoglycemia) were selected from the Abnormal Glucose Regulation in Patients with Acute Stroke across China (ACROSS-China) study. The patients were divided into groups according to the SUA quartile as well as decile. The correlations between SUA and the poor outcome (mRS > 2) at discharge were assessed stratified by glucose metabolism status. Multivariate logistic regression was used to analyze the potential risk factors of poor in-hospital outcome of stroke and the risk-adjustment of the correlation between SUA and the prognosis of stroke. P < 0.05 was considered statistically significant.

RESULTS

SUA were divided first as Quartile1 to 4 (Quartile1 < 221 μmol L-1; Quartile2 (221-286) μmol L-1; Quartile3 (286-352) μmol L-1 and Quartile4 > 352 μmol L-1), then as decile1 to 10. In normoglycaemia, SUA quartiles, deciles and continuous SUA concentration were independently significantly associated with poor outcome. Q1 was independently associated with the higher possibility of poor functional outcome (compared to Q4, odds ratios (ORs) with 95% confidential interval (CI) was 3.79 (1.23-8.67) in Q1); Lower level of SUA in DM was also associated with poor functional outcome at discharge compared to the highest level of SUA(Q4)(OR with 95% CI, 2.07 (1.05-4.08)), however, lower SUA level was also related to severer stroke at admission in DM as well as in prediabetes (P < 0.001 in DM and 0.023 in prediabetes) and severer stroke resulted in worse functional outcome at discharge (OR with 95% CI, 12.15 (8.08-18.21) in DM and 11.58 (7.50-23.25) in prediabetes). But in normoglycamic stroke, SUA levels did not differ in stroke severity at admission (P = 0.066).

CONCLUSIONS

Low SUA level (<221 μmol L-1) independently and strongly predicts the short-term poor functional outcome in acute stroke with normoglycaemia other than diabetes or prediabetes.

Xanthine Oxidase: Isolation, Assays of Activity, and Inhibition

Xanthine oxidase (XO) is an important enzyme catalyzing the hydroxylation of hypoxanthine to xanthine and xanthine to uric acid which is excreted by kidneys. Excessive production and/or inadequate excretion of uric acid results in hyperuricemia. This paper presents a detailed review of methods of isolation, determination of xanthine oxidase activity, and the effect of plant extracts and their constituents on it. Determining the content and activities of XO can be used for diagnostic purposes. Testing inhibition of XO is important for detection of potentially effective compounds or extracts that can be used to treat diseases that are caused by increased activity of XO.In vitrobioassays are used to examine test material for XO inhibition, as inhibitors of XO may be potentially useful for the treatment of gout or other XO induced diseases. Several authors reported on the XO inhibitory potential of traditionally used medicinal plants.

Serum uric acid and outcome after acute ischemic stroke: PREMIER study

BACKGROUND

Current evidence shows that uric acid is a potent antioxidant whose serum concentration increases rapidly after acute ischemic stroke (AIS). Nevertheless, the relationship between serum uric acid (SUA) levels and AIS outcome remains debatable. We aimed to describe the prognostic significance of SUA in AIS.

METHODS

We studied 463 patients (52% men, mean age 68 years, 13% with glomerular filtration rate <60 ml/min at hospital arrival) with AIS pertaining to the multicenter registry PREMIER, who had SUA measurements at hospital presentation. Multivariate models were constructed to analyze the association of SUA with functional outcome as assessed by the modified Rankin scale (mRS) at 30-day, 3-, 6- and 12-month follow-up. A mRS 0-1 was regarded as a very good outcome.

RESULTS

Mean SUA concentration at hospital arrival was 6.1 ± 3.7 mg/dl (362.8 ± 220.0 μmol/l). Compared with cases with higher SUA levels at hospital admission, patients with ≤4.5 mg/dl (≤267.7 μmol/l; the lowest tertile of the sample) had more cases of a very good 30-day outcome (30.5 vs. 18.9%, respectively; p = 0.004). SUA was not associated with mortality or functional dependence (mRS >2) at 30 days, or with any outcome measure at 3, 6 or 12 months poststroke. After adjustment for age, gender, stroke type and severity (NIHSS <9), time since event onset, serum creatinine, hypertension, diabetes and smoking, a SUA ≤4.5 mg/dl (≤267.7 μmol/l) was positively associated with a very good short-term outcome (odds ratio: 1.76, 95% confidence interval: 1.05-2.95; negative predictive value: 81.1%), but not at 3, 6 or 12 months of follow-up. When NIHSS was entered in the multivariate model as a continuous variable, the independent association of SUA with outcome was lost. Compared with cases with higher levels, patients with SUA ≤4.5 mg/dl (≤267.7 μmol/l) were more frequently younger than 55 years, women, with mild strokes, with normal serum creatinine and fewer had hypertension. The time since event onset to hospital arrival was not significantly associated with AIS severity or SUA levels; nevertheless, a nonsignificant tendency was observed for patients with severe strokes and high SUA levels arriving in <24 h.

CONCLUSIONS

A low SUA concentration is modestly associated with a very good short-term outcome. Our findings support the hypothesis that SUA is more a marker of the magnitude of the cerebral infarction than an independent predictor of stroke outcome.

Xanthine oxidase inhibitory activity of constituents of Cinnamomum cassia twigs

A methanol extract of the twigs of Cinnamomum cassia was found to inhibit xanthine oxidase. Purification of the methanol extract afforded three new phenolic glycosides, cinnacasolide A-C (11-13), together with 10 known compounds (1-10). The structures of the three new compounds were determined by interpretation of spectroscopic data. Cinnamaldehyde derivatives 1-5 and 7 were significant inhibitors of xanthine oxidase, with IC(50) values ranging from 7.8 to 36.3 μg/mL. The results indicate that the acyl group of these cinnamaldehyde derivatives plays an important role in the inhibition of xanthine oxidase.

Aldehyde and xanthine oxidase activities in tissues of streptozotocin-induced diabetic rats: effects of vitamin E and selenium supplementation

Effects of vitamin E and selenium supplementation on aldehyde oxidase (AO) and xanthine oxidase (XO) activities and antioxidant status in liver, kidney, and heart of streptozotocin (STZ)-induced diabetic rats were examined. AO and XO activities increased significantly after induction of diabetes in rats. Following oral vitamin E (300 mg/kg) and sodium selenite (0.5 mg/kg) intake once a day for 4 weeks, XO activity decreased significantly. AO activity decreased significantly in liver, but remained unchanged in kidney and heart of vitamin E- and selenium-treated rats compared to the diabetic rats. Total antioxidants status, paraoxonase-1 (PON1) and erythrocyte superoxide dismutase activities significantly decreased in the diabetic rats compared to the controls, while a higher fasting plasma glucose level was observed in the diabetic animals. The glutathione peroxidase activity remained statistically unchanged. Malondialdehyde and oxidized low-density lipoprotein levels were higher in the diabetic animals; however, these values were significantly reduced following vitamin E and selenium supplementation. In summary, both AO and XO activities increase in STZ-induced diabetic rats, and vitamin E and selenium supplementation can reduce these activities. The results also indicate that administration of vitamin E and selenium has hypolipidemic, hypoglycemic, and antioxidative effects. It decreases tissue damages in diabetic rats, too.

Uric acid as one of the important factors in multifactorial disorders--facts and controversies

With considering serum concentration of the uric acid in humans we are observing hyperuricemia and possible gout development. Many epidemiological studies have shown the relationship between the uric acid and different disorders such are obesity, metabolic syndrome, hypertension and coronary artery disease. Clinicians and investigators recognized serum uric acid concentration as very important diagnostic and prognostic factor of many multifactorial disorders. This review presented few clinical conditions which are not directly related to uric acid, but the concentrations of uric acid might have a great impact in observing, monitoring, prognosis and therapy of such disorders. Uric acid is recognized as a marker of oxidative stress. Production of the uric acid includes enzyme xanthine oxidase which is involved in producing of radical-oxigen species (ROS). As by-products ROS have a significant role in the increased vascular oxidative stress and might be involved in atherogenesis. Uric acid may inhibit endothelial function by inhibition of nitric oxide-function under conditions of oxidative stress. Down regulation of nitric oxide and induction of endothelial dysfunction might also be involved in pathogenesis of hypertension. The most important and well evidenced is possible predictive role of uric acid in predicting short-term outcome (mortality) in acute myocardial infarction (AMI) patients and stroke. Nephrolithiasis of uric acid origin is significantly more common among patients with the metabolic syndrome and obesity. On contrary to this, uric acid also acts is an “antioxidant”, a free radical scavenger and a chelator of transitional metal ions which are converted to poorly reactive forms.