A new sensitive and quantitative chemiluminescent assay to monitor intracellular xanthine oxidase activity for rapid screening of inhibitors in living endothelial cells

Screening and analysis of xanthine oxidase inhibitors in jute leaves and their protective effects against hydrogen peroxide-induced oxidative stress in cells

Jute (Corchorus capsularis L.) is an annual herb of the bast fiber plant and has great potentials in food and medicinal usages because of its various bioactivities. In this study, ultrafiltration coupled with high-performance liquid chromatography-mass spectrometry was established for screening xanthine oxidase inhibitors from the jute leaves extract. Under the optimum screening conditions, three inhibitors were successfully screened and identified as chlorogenic acid, echinacoside, and isorhamnetin-rutinoside with UV and MS data. The fluorescent quenching analysis showed that three inhibitors quenched the fluorescence intensities of enzyme with different binding capacities. For further exploring the bioactivity of three inhibitors, the protective effects on hydrogen peroxide-induced oxidative stress was investigated using human normal liver cell (LO2), human gastric mucosal epithelial cell (GES-1), and human umbilical vein endothelial cell (HUVEC). As a result, they exhibited protective effects on three injured cells in dose-dependent manners without cytotoxicity. To evaluate the difference among different jute species obtained in our laboratories, the amounts of three compounds in ten samples were assessed and analyzed. The results showed that it could be divided into three groups. The jute leaves showed nutrient and medical potentials and deserved further research on pharmaceutical and biochemical utilization in future.

Peptides from Cauliflower By-Products, Obtained by an Efficient, Ecosustainable, and Semi-Industrial Method, Exert Protective Effects on Endothelial Function

The large amount of cauliflower industry waste represents an unexplored source of bioactive compounds. In this work, peptide hydrolysates from cauliflower leaves were characterized by combined bioanalytical approaches. Twelve peptide fractions were studied to evaluate unexplored biological activities by effect-based cellular bioassays. A potent inhibition of intracellular xanthine oxidase activity was observed in human vascular endothelial cells treated with one fraction, with an IC50 = 8.3 ± 0.6 μg/ml. A different fraction significantly induced the antioxidant enzyme superoxide dismutase 1 and decreased the tumor necrosis factor α-induced VCAM-1 expression, thus leading to a significant improvement in the viability of human vascular endothelial cells. Shotgun peptidomics and bioinformatics were used to retrieve the most probable bioactive peptide sequences. Our study shows that peptides from cauliflower waste should be recycled for producing valuable products useful for the prevention of endothelial dysfunction linked to atherogenesis progression.

MOF based fluorescent assay of xanthine oxidase for rapid inhibitor screening with real-time kinetics monitoring

The activity assay of xanthine oxidase (XO) is of great application value in clinical diagnosis because the abnormal level of this enzyme is related to a series of pathological states. In this work, a Zr based metal-organic framework (BTB-MOF) with stable photoluminescence in pure water and buffer solution was synthesized. The examination about the fluorescent responses of this material to xanthine and its oxidation product, uric acid, showed that, although both of them affected the emission of BTB-MOF in quenching form, the efficiencies presented much difference. Taking advantage of this feature, a fluorescent method was developed for the activity assay of XO, that is, BTB-MOF was added to the enzymatic oxidation system as a sensor to transduce the proceeding of the reaction real-timely to the signal of fluorescent intensity change. Our method can work under the interference of normal biologically related species, and precisely reflect XO activity in the range of 0.2-40 U L^-1 (detection limit = 0.004 U L^-1). With consecutive fluorescence intensity scan, this assay could be applied as a high speed screening method of XO inhibitors with the testing time of 1 min. This work shows the wide potential application of MOFs in enzyme analysis.

Effect of apple polyphenols on vascular oxidative stress and endothelium function: a translational study

SCOPE

We aimed examining apple polyphenols' effect on uricemia and endothelial function in a sample of overweight subjects.

METHODS AND RESULTS

This was a two-phased study. In vitro experiment aimed to evaluate apple polyphenols' ability to lower uric acid in comparison with allopurinol. In vivo study consisted in a randomized, double-blind, parallel placebo-controlled clinical trial involving 62 overweight volunteers with suboptimal values of fasting plasma glucose (100 mg/dL≤FPG≤125 mg/dL), randomized to 300 mg apple polyphenols or placebo for 8 weeks. Apple polyphenols extract inhibited xanthine oxidase activity, with an IC50 = 130 ± 30 ng/mL; reducing uric acid production with an IC50 = 154 ± 28 ng/mL. During the trial, after the first 4 weeks of treatment, FPG decreased in the active treated group (-6.1%, p < 0.05), while no significant changes were observed regarding the other hematochemistry parameters. After 4 more weeks of treatment, active-treated patients had an improvement in FPG compared to baseline (-10.3%, p < 0,001) and the placebo group (p < 0,001). Uric acid (-14.0%, p < 0.05 versus baseline; p < 0.05 versus placebo) and endothelial reactivity (0.24±0.09, p = 0.009 versus baseline; p < 0.05 versus placebo) significantly improved too.

CONCLUSION

In vivo, apple polyphenols extract has a positive effect on vascular oxidative stress and endothelium function and reduce FPG and uric acid by inhibiting xanthine oxidase, as our In vitro experiment attests.

Caveolin-1: An Oxidative Stress-Related Target for Cancer Prevention

Aberrant oxidative metabolism is one of the hallmarks of cancer. Reactive species overproduction could promote carcinogenesis via inducing genetic mutations and activating oncogenic pathways, and thus, antioxidant therapy was considered as an important strategy for cancer prevention and treatment. Caveolin-1 (Cav-1), a constituent protein of caveolae, has been shown to mediate tumorigenesis and progression through oxidative stress modulation recently. Reactive species could modulate the expression, degradation, posttranslational modifications, and membrane trafficking of Cav-1, while Cav-1-targeted treatments could scavenge the reactive species. More importantly, emerging evidences have indicated that multiple antioxidants could exert antitumor activities in cancer cells and protective activities in normal cells by modulating the Cav-1 pathway. Altogether, these findings indicate that Cav-1 may be a promising oxidative stress-related target for cancer antioxidant prevention. Elucidating the underlying interaction mechanisms between oxidative stress and Cav-1 is helpful for enhancing the preventive effects of antioxidants on cancer, for improving clinical outcomes of antioxidant-related therapeutics in cancer patients, and for developing Cav-1 targeted drugs. Herein, we summarize the available evidence of the roles of Cav-1 and oxidative stress in tumorigenesis and development and shed novel light on designing strategies for cancer prevention or treatment by utilizing the interaction mode between Cav-1 and oxidative stress.

Fructose Intake, Serum Uric Acid, and Cardiometabolic Disorders: A Critical Review

There is a direct relationship between fructose intake and serum levels of uric acid (UA), which is the final product of purine metabolism. Recent preclinical and clinical evidence suggests that chronic hyperuricemia is an independent risk factor for hypertension, metabolic syndrome, and cardiovascular disease. It is probably also an independent risk factor for chronic kidney disease, Type 2 diabetes, and cognitive decline. These relationships have been observed for high serum UA levels (>5.5 mg/dL in women and >6 mg/dL in men), but also for normal to high serum UA levels (5-6 mg/dL). In this regard, blood UA levels are much higher in industrialized countries than in the rest of the world. Xanthine-oxidase inhibitors can reduce UA and seem to minimize its negative effects on vascular health. Other dietary and pathophysiological factors are also related to UA production. However, the role of fructose-derived UA in the pathogenesis of cardiometabolic disorders has not yet been fully clarified. Here, we critically review recent research on the biochemistry of UA production, the relationship between fructose intake and UA production, and how this relationship is linked to cardiometabolic disorders.