Studies on the interaction mechanism between xanthine oxidase and osmundacetone: Molecular docking, multi-spectroscopy and dynamical simulation

Xanthine oxidase (XO) is a key enzyme in uric acid production, and its molybdopterin (Mo-Pt) domain is an important catalytic center when xanthine and hypoxanthine are oxidated. It is found that the extract of Inonotus obliquus has an inhibitory effect on XO. In this study, five key chemical compounds were initially identified using liquid chromatography-mass spectrometry (LC-MS), and two compounds, osmundacetone ((3E)-4-(3,4-dihydroxyphenyl)-3-buten-2-one) and protocatechuic aldehyde (3,4-dihydroxybenzaldehyde), were screened as the XO inhibitors by ultrafiltration technology. Osmundacetone bound XO strongly and competitively inhibited XO with a half-maximal inhibitory concentration of 129.08 ± 1.71 μM, and its inhibition mechanism, was investigated. Osmundacetone and XO via static quenching and spontaneously bound with XO with high affinity, primarily via hydrophobic interactions and hydrogen bonds. Molecular docking studies showed that osmundacetone was inserted into the Mo-Pt center and interacted with hydrophobic residues of Phe911, Gly913, Phe914, Ser1008, Phe1009, Thr1010, Val1011, and Ala1079 of XO. In summary, these findings suggest that provide theoretical basis for the research and development of XO inhibitors from Inonotus obliquus.

Anti-gout activity and the interaction mechanisms between Sanghuangporus vaninii active components and xanthine oxidase

Xanthine oxidase (XO) plays a critical role in the progression of gout. We showed in a previous study that Sanghuangporus vaninii (S. vaninii), a perennial, medicinal, and edible fungus traditionally used to treat various symptoms, contains XO inhibitors. In the current study, we isolated an active component of S. vaninii using high performance countercurrent chromatography and identified it as davallialactone using mass spectrometry with 97.726 % purity. A microplate reader showed that davallialactone had mixed inhibition of XO activity with a half-inhibitory concentration value of 90.07 ± 2.12 μM. In addition, the collision between davallialactone and XO led to fluorescence quenching and conformational changes in XO, which were mainly driven by hydrophobicity and hydrogen bonding. Molecular simulations further showed that davallialactone was located at the center of the molybdopterin (Mo-Pt) of XO and interacted with amino acid residues Phe798, Arg912, Met1038, Ala1078, Ala1079, Gln1194, and Gly1260, suggesting that entering the enzyme-catalyzed reaction was unfavorable for the substrate. We also observed face-to-face π-π interactions between the aryl ring of davallialactone and Phe914. Cell biology experiments indicated that davallialactone reduced the expression of the inflammatory factors, tumor necrosis factor alpha and interleukin-1 beta (P < 0.05), can effectively alleviate cellular oxidative stress. This study showed that davallialactone significantly inhibits XO and has the potential to be developed into a novel medicine to prevent hyperuricemia and treat gout.

Screening and Inhibition Mechanism of Xanthine Oxidase Inhibitors in Ethanolic Extracts of Chimonanthus salicifolius Hu Leaves

This study aimed to evaluate the inhibition of the ethanol elutions of Chimonanthus salicifolius Hu leaves (CsHL) against xanthine oxidase (XO). The results of XO inhibition assay and enzymatic superoxide free radical scavenging assay in vitro showed that 70 % ethanol eluate (EE) had the best inhibitory effect and followed by 40 % EE. High performance liquid chromatograph analysis showed that quercetin and kaempferol were the potential active components of XO inhibition. The inhibition mechanism of quercetin and kaempferol on XO was investigated by kinetic analysis and fluorescence quenching titration assay. The molecular simulation further revealed that quercetin and kaempferol bind to XO mainly by hydrogen bonding and van der Waals, blocking the entry of substrates and leading to the inhibition of XO. In conclusion, the CsHL have inhibitory effects on XO activity, which provides a theoretical basis for relieving or preventing hyperuricemia and gout as a natural food or medicinal plant in the future.

Unveiling the inhibitory mechanism of aureusidin targeting xanthine oxidase by multi-spectroscopic methods and molecular simulations

Xanthine oxidase (XO) is a key target for gout treatment. Great efforts have been made towards the discovery and development of new XO inhibitors. Aureusidin (AUR), a natural compound, emerges as the second reported XO inhibitor with an aurone skeleton with an IC₅₀ value of 7.617 ± 0.401 μM in vitro. The inhibitory mechanism of AUR against XO was explored through enzyme kinetic studies, multi-spectroscopic methods, computer simulation techniques, and ADME prediction. The results showed that AUR acts as a rapid reversible and mixed-type XO inhibitor and its binding to XO was driven by hydrogen bonding and hydrophobic interaction. Moreover, AUR presented a strong fluorescence quenching effect through a static quenching process and induced a conformation change of XO. Its binding pattern with XO was revealed through molecular docking, and its affinity toward XO was enhanced through interactions with key amino acid residues in the active pocket of XO. Further, AUR demonstrated good stability and pharmacokinetic behavior properties in molecular dynamics simulation and ADME prediction. In short, the current work clarified in depth the inhibitory mechanism of AUR on XO firstly and then provided fresh insights into its further development as a natural potent XO inhibitor with aurone skeleton.

The inhibitory kinetics of vitamins B9, C, E, and D3 on bovine xanthine oxidase: Gout treatment

BACKGROUND

Over-consumption of foods high in purines like seafood, red meat, and alcoholic beverages leads to hyperuricemia causing gout attacks. Xanthine oxidase was reported responsible for the overproduction of uric acid.

MATERIAL AND METHODS

We intend to test in silico and in vitro, the inhibition effect of four vitamins against bovine milk xanthine oxidase (BXO). We performed Molecular docking with GOLD v4.0, and the biological activity prediction with the PASS server. The best-selected vitamins were chosen based on their best PLPchem score. The BXO constant K_m and V_max were determined in vitro, and then the vitamins were tested for their inhibition effect to BXO. Furthermore, the inhibition constant Ki of each inhibitor were determined using Dixon method, the vitamins chosen were vitamin E, vitamin B9, vitamin D3, and vitamin C.

RESULTS

The in silico results show that the tested vitamins were the best inhibitors model with PLPchem scores up to 70 comparing to the control. The in vitro results show that BXO have a K_m value of 163.55 μM with V_max of 37 U, vitamins B9, E, C, and D3 were potent inhibitors to BXO with an IC50 of 34.10 ± 0.21, 36.68 ± 1.50, 39.01 ± 0.02, and 100.28 ± 0.33 μM, respectively comparing to the control (32.03 ± 0.73 μM). The kinetic study shows that all tested vitamins were Non-competitive inhibitors, the Ki values were 15 ± 1.76 μM, 29 ± 1.06 μM, 12 ± 1.41 μM, and 20 ± 0.71 μM, for respectively vitamins B9, E, C, and D3.

CONCLUSION

The obtained results promise an excellent strategy using vitamins to enhance immunity, treat hyperuricemia, and minimize the usual drug side effects.

Inhibition of porphyra polysaccharide on xanthine oxidase activity and its inhibition mechanism

Xanthine oxidase (XO) is a purine catabolic enzyme related to hyperuricemia and gout. Porphyra polysaccharide (PP) is a kind of sulfated polysaccharide with potent biological activity. Herein, the interaction mechanism between PP and XO was studied by enzyme kinetics and multi-spectroscopy methods for the first time. Inhibition kinetics assay showed that PP reversibly inhibited XO activity in a mixed competitive manner with an IC₅₀ of 10.53 ± 0.69 mg/ml. Fluorescence titration studies and thermodynamic parameter calculations revealed that PP could spontaneously bind to XO through hydrophobic interactions, with a class of binding site. Circular dichroism analysis demonstrated that PP induced secondary structure rearrangement and conformational change of XO. Molecular docking further revealed that PP inserted into the hydrophobic cavity of XO, occupying the catalytic center, leading to the inhibition of XO activity. This study may provide new insights into the inhibitory mechanism of PP as a promising XO inhibitor.