Allantoin as an independent marker associated with carotid intima-media thickness in subclinical atherosclerosis

Novel Oxidative Stress Biomarkers with Risk Prognosis Values in Heart Failure

Oxidative stress (OS) is mediated by reactive oxygen species (ROS), which in cardiovascular and other disease states, damage DNA, lipids, proteins, other cellular and extra-cellular components. OS is both initiated by, and triggers inflammation, cardiomyocyte apoptosis, matrix remodeling, myocardial fibrosis, and neurohumoral activation. These have been linked to the development of heart failure (HF). Circulating biomarkers generated by OS offer potential utility in patient management and therapeutic targeting. Novel OS-related biomarkers such as NADPH oxidases (sNox2-dp, Nrf2), advanced glycation end-products (AGE), and myeloperoxidase (MPO), are signaling molecules reflecting pathobiological changes in HF. This review aims to evaluate current OS-related biomarkers and their associations with clinical outcomes and to highlight those with greatest promise in diagnosis, risk stratification and therapeutic targeting in HF.

Serum Uric Acid Levels and Subclinical Atherosclerosis: Results From the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

High serum uric acid (sUA) has been associated with coronary artery calcium (CAC) and increased carotid intima-media thickness (cIMT) in people at high cardiovascular risk. However, association is unclear in apparently healthy individuals. Our study aims to evaluate association between sUA and subclinical atherosclerosis measures: CAC and increased cIMT, in apparently healthy adults enrolled in ELSA-Brasil. A total of 4096 participants without previous coronary artery disease, stroke, and use of urate-lowering drugs, underwent CAC and cIMT assessment. All analyses were stratified by sex. Serum uric acid categorized by quintiles was the exposure variable. Thorough cardiovascular risk factor evaluation was performed, and association between sUA quintiles and CAC and cIMT was analyzed by linear regression using ln(CAC + 1) and cIMT, both as continuous variables. Median age of the sample was 49.0 (44.0-56.0) years (women: 55.1%; 59.1% were white). Mean values of sUA were 6.5 ± 1.4 mg/dL for men, and 4.9 ± 1.2 mg/dL for women. The highest quintile (Q5) of sUA was independently associated with cIMT in women (beta-coefficient: 0.022; 95% CI: 0.007-0.036; P = 0.003) and men (beta-coefficient: 0.020; 95% CI: 0.002-0.038; P = 0.032). Regarding CAC, no association was found: men's Q5 (beta-coefficient: -0.142; 95% CI: -0.436 to 0.153; P = 0.347) and women's Q5 (beta-coefficient: 0.046; 95% CI: -0.152 to 0.245; P = 0.647). In this cohort, the highest sUA quintiles were independently associated with cIMT in both women and men. No association was found between sUA and the presence of CAC.

Salivary metabolic signatures of carotid atherosclerosis in patients with type 2 diabetes hospitalized for treatment

Atherosclerosis is a life-threatening disease associated with morbidity and mortality in patients with type 2 diabetes (T2D). This study aimed to characterize a salivary signature of atherosclerosis based on evaluation of carotid intima-media thickness (IMT) to develop a non-invasive predictive tool for diagnosis and disease follow-up. Metabolites in saliva and plasma samples collected at admission and after treatment from 25 T2D patients hospitalized for 2 weeks to undergo medical treatment for diabetes were comprehensively profiled using metabolomic profiling with gas chromatography-mass spectrometry. Orthogonal partial least squares analysis, used to explore the relationships of IMT with clinical markers and plasma and salivary metabolites, showed that the top predictors for IMT included salivary allantoin and 1,5-anhydroglucitol (1,5-AG) at both the baseline examination at admission and after treatment. Furthermore, though treatment induced alterations in salivary levels of allantoin and 1,5-AG, it did not modify the association between IMT and these metabolites (p _interaction > 0.05), and models with these metabolites combined yielded satisfactory diagnostic accuracy for the high IMT group even after treatment (area under curve = 0.819). Collectively, this salivary metabolite combination may be useful for non-invasive identification of T2D patients with a higher atherosclerotic burden in clinical settings.

Effect of Qishen granules on isoproterenol-induced chronic heart failure in rats evaluated by comprehensive metabolomics

Qishen granules (QSG), a Chinese herbal formula, has been widely used in the treatment of myocardial ischemic chronic heart failure (CHF) for many years, but its mechanism of action is still unclear. In this study, comprehensive metabolomics was used to investigate the underlying protective mechanisms of QSG in an isoproterenol-induced CHF rat model. A total of 14 biomarkers were identified in serum and 34 biomarkers in urine, which were mainly related to fatty acid metabolism, bile acid metabolism, amino acid metabolism, purine metabolism, vitamin metabolism, and inflammation. Finally, 22 markers were selected for quantitative analysis of serum, urine, and fecal samples to verify the reliability of the results of untargeted metabolomics, and the results were similar to those of untargeted metabolomics. The correlation analysis showed that the targeted quantitative endogenous metabolites and CHF-related indexes were closely related. QSG might alleviate myocardial inflammatory response, oxidative stress, and amino acid metabolism disorder in CHF by regulating the level of endogenous metabolites. This study revealed QSG could regulate potential biomarkers and correlated metabolic pathway, which provided support for the further application of QSG.

Uric Acid Reacts with Peroxidasin, Decreases Collagen IV Crosslink, Impairs Human Endothelial Cell Migration and Adhesion

Uric acid is considered the main substrate for peroxidases in plasma. The oxidation of uric acid by human peroxidases generates urate free radical and urate hydroperoxide, which might affect endothelial function and explain, at least in part, the harmful effects of uric acid on the vascular system. Peroxidasin (PXDN), the most recent heme-peroxidase described in humans, catalyzes the formation of hypobromous acid, which mediates collagen IV crosslinks in the extracellular matrix. This enzyme has gained increasing scientific interest since it is associated with cardiovascular disease, cancer, and renal fibrosis. The main objective here was to investigate whether uric acid would react with PXDN and compromise the function of the enzyme in human endothelial cells. Urate decreased Amplex Red oxidation and brominating activity in the extracellular matrix (ECM) from HEK293/PXDN overexpressing cells and in the secretome of HUVECs. Parallelly, urate was oxidized to 5-hydroxyisourate. It also decreased collagen IV crosslink in isolated ECM from PFHR9 cells. Urate, the PXDN inhibitor phloroglucinol, and the PXDN knockdown impaired migration and adhesion of HUVECs. These results demonstrated that uric acid can affect extracellular matrix formation by competing for PXDN. The oxidation of uric acid by PXDN is likely a relevant mechanism in the endothelial dysfunction related to this metabolite.

Peroxiredoxin AhpC1 protects Pseudomonas aeruginosa against the inflammatory oxidative burst and confers virulence

Pseudomonas aeruginosa is an opportunistic bacterium in patients with cystic fibrosis and hospital acquired infections. It presents a plethora of virulence factors and antioxidant enzymes that help to subvert the immune system. In this study, we identified the 2-Cys peroxiredoxin, alkyl-hydroperoxide reductase C1 (AhpC1), as a relevant scavenger of oxidants generated during inflammatory oxidative burst and a mechanism of P. aeruginosa (PA14) escaping from killing. Deletion of AhpC1 led to a higher sensitivity to hypochlorous acid (HOCl, IC₅₀ 3.2 ± 0.3 versus 19.1 ± 0.2 μM), hydrogen peroxide (IC₅₀ 91.2 ± 0.3 versus 496.5 ± 6.4 μM) and the organic peroxide urate hydroperoxide. ΔahpC1 strain was more sensitive to the killing by isolated neutrophils and less virulent in a mice model of infection. All mice intranasally instilled with ΔahpC1 survived as long as they were monitored (15 days), whereas 100% wild-type and ΔahpC1 complemented with ahpC1 gene (ΔahpC1 attB:ahpC1) died within 3 days. A significantly lower number of colonies was detected in the lung and spleen of ΔahpC1-infected mice. Total leucocytes, neutrophils, myeloperoxidase activity, pro-inflammatory cytokines, nitrite production and lipid peroxidation were much lower in lungs or bronchoalveolar liquid of mice infected with ΔahpC1. Purified AhpC neutralized the inflammatory organic peroxide, urate hydroperoxide, at a rate constant of 2.3 ± 0.1 × 10⁶ M^-1s^-1, and only the ΔahpC1 strain was sensitive to this oxidant. Incubation of neutrophils with uric acid, the urate hydroperoxide precursor, impaired neutrophil killing of wild-type but improved the killing of ΔahpC1. Hyperuricemic mice presented higher levels of serum cytokines and succumbed much faster to PA14 infection when compared to normouricemic mice. In summary, ΔahpC1 PA14 presented a lower virulence, which was attributed to a poorer ability to neutralize the oxidants generated by inflammatory oxidative burst, leading to a more efficient killing by the host. The enzyme is particularly relevant in detoxifying the newly reported inflammatory organic peroxide, urate hydroperoxide.

Urate hydroperoxide oxidizes endothelial cell surface protein disulfide isomerase-A1 and impairs adherence

BACKGROUND

Extracellular surface protein disulfide isomerase-A1 (PDI) is involved in platelet aggregation, thrombus formation and vascular remodeling. PDI performs redox exchange with client proteins and, hence, its oxidation by extracellular molecules might alter protein function and cell response. In this study, we investigated PDI oxidation by urate hydroperoxide, a newly-described oxidant that is generated through uric acid oxidation by peroxidases, with a putative role in vascular inflammation.

METHODS

Amino acids specificity and kinetics of PDI oxidation by urate hydroperoxide was evaluated by LC-MS/MS and by stopped-flow. Oxidation of cell surface PDI and other thiol-proteins from HUVECs was identified using impermeable alkylating reagents. Oxidation of intracellular GSH and GSSG was evaluated with specific LC-MS/MS techniques. Cell adherence, detachment and viability were assessed using crystal violet staining, cellular microscopy and LDH activity, respectively.

RESULTS

Urate hydroperoxide specifically oxidized cysteine residues from catalytic sites of recombinant PDI with a rate constant of 6 × 10³ M^-1 s^-1. Incubation of HUVECs with urate hydroperoxide led to oxidation of cell surface PDI and other unidentified cell surface thiol-proteins. Cell adherence to fibronectin coated plates was impaired by urate hydroperoxide, as well as by other oxidants, thiol alkylating agents and PDI inhibitors. Urate hydroperoxide did not affect cell viability but significantly decreased GSH/GSSG ratio.

CONCLUSIONS

Our results demonstrated that urate hydroperoxide affects thiol-oxidation of PDI and other cell surface proteins, impairing cellular adherence.

GENERAL SIGNIFICANCE

These findings could contribute to a better understanding of the mechanism by which uric acid affects endothelial cell function and vascular homeostasis.

Identification of urate hydroperoxide in neutrophils: A novel pro-oxidant generated in inflammatory conditions

Uric acid is the final product of purine metabolism in humans and is considered to be quantitatively the main antioxidant in plasma. In vitro studies showed that the oxidation of uric acid by peroxidases, in presence of superoxide, generates urate free radical and urate hydroperoxide. Urate hydroperoxide is a strong oxidant and might be a relevant intermediate in inflammatory conditions. However, the identification of urate hydroperoxide in cells and biological samples has been a challenge due to its high reactivity. By using mass spectrometry, we undoubtedly demonstrated the formation of urate hydroperoxide and its corresponding alcohol, hydroxyisourate during the respiratory burst in peripheral blood neutrophils and in human leukemic cells differentiated in neutrophils (dHL-60). The respiratory burst was induced by phorbol myristate acetate (PMA) and greatly increased oxygen consumption and superoxide production. Both oxygen consumption and superoxide production were further augmented by incubation with uric acid. Conversely, uric acid significantly decreased the levels of HOCl, probably because of the competition with chloride by the catalysis of myeloperoxidase. In spite of the decrease in HOCl, the overall oxidative status, measured by GSH/GSSG ratio, was augmented in the presence of uric acid. In summary, the present results support the formation of urate hydroperoxide, a novel oxidant in neutrophils oxidative burst. Urate hydroperoxide is a strong oxidant and alters the redox balance toward a pro-oxidative environment. The production of urate hydroperoxide in inflammatory conditions could explain, at least in part, the harmful effect associated to uric acid.