Which is more important, xanthine oxidase activity or uric acid itself, in the risk for cardiovascular disease?

Intestinal FXR deficiency induces dysregulation of xanthine oxidase and accounts for sex difference in hyperuricemia

Overproduction of uric acid caused by increased expression and/or enhanced activity of xanthine oxidase (XO) is one of the major etiologies of hyperuricemia, which had a significant sex differences. As an important enzyme involved in production of reactive oxygen species and uric acid, activity of XO is highly correlated with hyperuricemia and its complications. However, the mechanisms underlying XO dysregulation remain unclear, and sex difference in the prevalence of hyperuricemia has been well known. To explore the potential role of intestinal farnesoid X receptor (FXR) on XO regulation and production, and the mechanisms of sex differences in this pathological process. Two hundred and sixty-one dyslipidemia participants and intestine-specific FXR-knockout mice were used to study the relationship between the intestinal FXR and the serum uric acid level. Western blotting, quantitative real-time PCR, and dual-luciferase reporter assay, were applied to clarify the regulatory role of FXR deficiency on XO. Special inhibitors, agonists, siRNA, sex hormones were used to investigate the mechanism of sex difference in FXR deficiency induced hyperuricemia in cell and animal model. Serum fibroblast growth factor 19 (FGF19) levels were lower in hyperuricemia patients in a sex difference manner. Increased local TNFα level driven by intestinal FXR deficiency/inhibition induced overexpression and hyperactivity of intestinal XO, leading to elevated intestinal uric acid synthesis, and subsequently resulting in hyperuricemia. We found that estrogens inhibited XO expression and activity, whereas androgens enhanced XO activity, leading to the sex difference in FXR deficiency induced hyperuricemia. Infliximab treatment eliminated the sex difference in uric acid levels in intestinal FXR-knockout mice. This study demonstrated the role of intestinal FXR in the pathogenesis of hyperuricemia, and partially elucidated the mechanisms underlying the sex differences of hyperuricemia.

Exercise and hyperuricemia: an opinion article

Hyperuricaemia (HUA) is an abnormally high concentration of serum urate caused by either an excess of uric acid production or decreased excretion capacity in the body. Serum urate concentration forms sodium salts that deposit in the soft tissues of the joints, ultimately leading to gout. Additionally, HUA is strongly associated with several acute and chronic illnesses. In various clinical guidelines and practices, xanthine oxidase inhibitors, such as allopurinol and febuxostat, are commonly used as the initial medication for treating HUA. However, extended usage of urate-lowering drugs may have risks, including cardiovascular thrombotic events and hepatic impairment. Implementing a scientifically informed fitness diet in conjunction with appropriate exercise may decrease HUA. Unfortunately, there is currently a shortfall in exercise intervention trials for individuals suffering from HUA. Most of the previous evidence suggesting that exercise improves serum urate levels comes from intervention trials in other populations, and serum urate is only one of the outcomes observed. This opinion article analyses the causes of HUA, offers dietary and exercise guidance with the aim of furnishing a point of reference for individuals with HUA or fitness enthusiasts.

Interaction of Tri-Cyclic Nucleobase Analogs with Enzymes of Purine Metabolism: Xanthine Oxidase and Purine Nucleoside Phosphorylase

Fluorescent markers play important roles in spectroscopic and microscopic research techniques and are broadly used in basic and applied sciences. We have obtained markers with fluorescent properties, two etheno derivatives of 2-aminopurine, as follows: 1,N2-etheno-2-aminopurine (1,N2-ε2APu, I) and N2,3-etheno-2-aminopurine (N2,3-ε2APu, II). In the present paper, we investigate their interaction with two key enzymes of purine metabolism, purine nucleoside phosphorylase (PNP), and xanthine oxidase (XO), using diffraction of X-rays on protein crystals, isothermal titration calorimetry, and fluorescence spectroscopy. Crystals were obtained and structures were solved for WT PNP and D204N-PNP mutant in a complex with N2,3-ε2APu (II). In the case of WT PNP-1,N2-ε2APu (I) complex, the electron density corresponding to the ligand could not be identified in the active site. Small electron density bobbles may indicate that the ligand binds to the active site of a small number of molecules. On the basis of spectroscopic studies in solution, we found that, in contrast to PNP, 1,N2-ε2APu (I) is the ligand with better affinity to XO. Enzymatic oxidation of (I) leads to a marked increase in fluorescence near 400 nm. Hence, we have developed a new method to determine XO activity in biological material, particularly suitable for milk analysis.

Is cardiac function associated with the clinical course of disease in patients with gout? A prospective study

OBJECTIVE

To analyze the function of the left heart in patients with different courses of gout, the independent influencing factors for left heart functional changes, and interactions between left atrial and left ventricular functions.

METHODS

Patients with gout (n = 171) were selected; 87 patients with a disease course <10 years were included in Group I, and 84 patients with a disease course ≥10 years were included in Group II. Ninety-four healthy volunteers comprised the control group.

RESULTS

The intergroup differences in cardiac strain parameters were statistically significant (p < .05). Moreover, the differences gradually declined with disease progression. Multivariate logistic regression analysis showed that uric acid was an independent predictor of decreased left ventricular global longitudinal strain (LVGLS). Moreover, LVGLS had a positive effect on the left atrial systolic rate (LASr) and the left atrial systolic contraction time (LASct) but no interaction with the left atrial systolic contraction duration (LAScd).

CONCLUSION

The course of the disease significantly affected the function of the left heart in gout patients, and uric acid was observed to be an independent predictor of decreased LVGLS in gout patients.

Anti-Hyperuricemia Activity and Potential Mechanisms of Medicinal Mushroom Activity: A Review of Preclinical Studies

Hyperuricemia (HUA) is characterized by abnormally elevated levels of serum uric acid, the product of purine metabolism. The primary symptom of HUA is gout; however, asymptomatic HUA is associated with complications such as hypertension, kidney disease, cardiovascular disease, and metabolic syndrome. The activation of xanthine oxidase (XO), a pivotal enzyme in uric acid biosynthesis, is coupled with extensive reactive oxygen species generation, leading to inflammatory responses, and triggers the development of HUA and its complications. In clinical practice, XO inhibitors are primarily used to treat HUA; however, their prolonged use is accompanied by serious adverse effects. Mushrooms and their bioactive constituents have shown promising anti-HUA activities in both in vitro and in vivo studies, including inhibition of urate production, modulation of renal urate transporters, enhancement of intestinal uric acid excretion, and antioxidant, anti-inflammatory, and antimetabolic syndrome properties. Clinical trials are necessary to validate the beneficial effects and safety of mushrooms in preventing or alleviating HUA and attenuating the associated complications. This review presents contemporary insights into the pathogenesis of HUA, the bioactive components of mushrooms, their therapeutic potential, and the underlying mechanisms involved in ameliorating HUA.

Update in uric acid, hypertension, and cardiovascular diseases

A direct relationship between serum uric acid levels and hypertension, cardiovascular, renal and metabolic diseases has been reported in many basic and epidemiological studies. Among these, high blood pression is one of the most common features associated with hyperuricemia. In this regard, several small-scale interventional studies have demonstrated a significant reduction in blood pressure in hypertensive or prehypertensive patients on uric acid-lowering drugs. These observation or intervention studies have led to affirm that there is a causal relationship between uric acid and hypertension. While the clinical association between uric acid and high blood pressure is notable, no clear conclusion has yet been reached as to whether lowering uric acid is beneficial to prevent cardiovascular and renal metabolic diseases. Recently, several prospective randomized controlled intervention trials using allopurinol and other uric acid-lowering drugs have been reported, and the results from these trials were almost negative, suggesting that the correlation between hyperuricemia and cardiovascular disease has no causality. However, it is important to note that in some of these recent studies there were high dropout rates and an important fraction of participants were not hyperuricemic. Therefore, we should carry caution in interpreting the results of these studies. This review article presents the results of recent clinical trials using uric acid-lowering drugs, focusing on hypertension and cardiovascular and renal metabolic diseases, and discusses the future of uric acid therapy.

Urinary isoxanthopterin as a novel predictor following catheter ablation for atrial fibrillation

Background

Oxidative stress is associated with atrial fibrillation recurrence following catheter ablation. Urinary isoxanthopterin (U-IXP) is one of the noninvasive markers which reflect the reactive oxygen species; however, its ability to predict atrial tachyarrhythmias (ATAs) occurrence following catheter ablation remains uncertain.

Methods

Among the patients who received scheduled catheter ablation for atrial fibrillation, baseline U-IXP levels were measured just before the procedure. The prognostic impact of baseline U-IXP upon postprocedural ATAs occurrence was investigated.

Results

Among 107 patients (71 years old, 68% men), baseline U-IXP level was 0.33 nmol/gCr on the median. During a mean of 603 days of follow-up, 32 patients had ATAs. Baseline higher U-IXP was independently associated with the occurrence of ATAs following catheter ablation with a hazard ratio of 4.69 (95% confidence interval: 1.82-12.37, p  = .001) adjusted for the left atrial diameter, a persistent type, and hypertension which were potential confounders, with a cutoff of 0.46 nmol/gCr, which stratified cumulative incidence of ATAs occurrence ( p  < .001).

Conclusion

U-IXP can be used as the noninvasive predictive biomarker for ATAs following catheter ablation for atrial fibrillation.

Differential effect of a xanthine oxidase inhibitor on arterial stiffness and carotid atherosclerosis: a subanalysis of the PRIZE study

Atherosclerosis and arterial stiffness are phenotypes of atherosclerotic vascular damage. Atherosclerosis originates from endothelial vascular damage and forms focal morphological lesions; arterial stiffness originates from diffuse medial-layer damage in the arterial tree. Thus, the two phenomena reflect different facets of atherosclerotic vascular damage, and they both gradually progress. We conducted a subanalysis to compare the long-term effects of febuxostat on atherosclerosis and arterial stiffness in the PRIZE study (a multicenter, prospective, randomized, open-label, blinded-endpoint clinical trial to examine the effect of febuxostat on carotid atherosclerosis). Among 514 study participants, arterial stiffness parameters (brachial-ankle pulse wave velocity or cardio-ankle vascular index) were obtained at baseline, 12 months, and 24 months in 100 subjects. Among them, 48 subjects were allocated to the control group (i.e., nonpharmacological lifestyle modification for hyperuricemia), and 52 subjects were allocated to the febuxostat treatment group. While the decrease in serum uric acid was greater in the febuxostat group than in the control group, the adjusted percentage decrease in arterial stiffness parameters at month 24 was greater in the febuxostat group than in the control group, with a mean between-group difference (febuxostat - control) of -5.099% (95% confidence interval (CI) -10.009% to -0.188%, p = 0.042). Thus, long-term treatment with febuxostat may exert beneficial effects on arterial stiffness without improving carotid atherosclerosis. A long-term study to examine the effect of febuxostat on cardiovascular outcomes related to increased arterial stiffness is warranted.

Antioxidant enzymes and vascular diseases

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play a fundamental role in regulating endothelial function and vascular tone in the physiological conditions of a vascular system. However, oxidative stress has detrimental effects on human health, and numerous studies confirmed that high ROS/RNS production contributes to the initiation and progression of cardiovascular diseases. The antioxidant defense has an essential role in the homeostatic functioning of the vascular endothelial system. Endogenous antioxidative defense includes various molecules and enzymes such as superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidase. Together all these antioxidative enzymes are essential for defense against harmful ROS features. ROS are mainly generated from redox-active compounds involved in the mitochondrial respiratory chain. Thus, targeting antioxidative enzymes and mitochondria oxidative balance may be a promising approach for vascular diseases occurrence and treatment. This review summarized the most recent research on the regulation of antioxidative enzymes in vascular diseases.