Kinetic study on the inhibition of xanthine oxidase by acylated derivatives of flavonoids synthesised enzymatically

Enhanced Enzymatic Synthesis of Puerarin Palmitate with Different Acyl Donors for Lipid Solubility Improvement

Puerarin is a flavonoid known as a natural antioxidant found in the root of Pueraria robata. Its antioxidant, anticancer, and anti-inflammatory effects have attracted attention as a potential functional ingredient in various bioindustries. However, puerarin has limited bioavailability owing to its low lipid solubility and stability. Acylation is proposed as a synthesis method to overcome this limitation. In this study, lipase-catalyzed acylation of puerarin and various acyl donors was performed, and the enzymatic synthetic condition was optimized. Under the condition (20 g/L of Novozym 435, palmitic anhydride, 1:15, 40 °C, tetrahydrofuran (THF)), the synthesis of puerarin ester achieved a significantly high conversion (98.97%) within a short time (3 h). The molecule of the synthesized puerarin palmitate was identified by various analyses such as liquid chromatography-mass spectrometry (LC-MS), Fourier-transform infrared spectroscopy (FT-IR), and carbon-13 nuclear magnetic resonance (13C NMR). The lipid solubility and the radical scavenging activity were also evaluated. Puerarin palmitate showed a slight decrease in antioxidant activity, but lipid solubility was significantly improved, improving bioavailability. The high conversion achieved for puerarin esters in this study will provide the foundation for industrial applications.

Improved antioxidant activity of rutin via lipase-mediated esterification with oleic acid

BACKGROUND

Oxidation is a major problem for oils and fats, which can be mitigated by antioxidants. Rutin has excellent antioxidant activity, but its poor lipid solubility greatly limits its practical application. In this study, an efficient enzymatic synthesis route of lipophilic rutin ester was established using oleic acid as an acyl donor, and the antioxidant potential of rutin oleate was evaluated for the first time by proton (¹ H) nuclear magnetic resonance (NMR) spectroscopy.

RESULTS

The synthesized product was finally identified as rutin oleate by Fourier transform infrared, high-performance liquid chromatography-mass spectrometry, and ¹ H, carbon-13, and DEPT-135 NMR analyses, and the acylation site was the 4‴-OH of the rhamnose group in the rutin molecule. The maximum conversion was over 93% after 48 h of reaction using Novozym 435 as catalyst under the best conditions among these tests. The conversion of rutin ester decreased with the increase of carbon chain length and the number of carbon-carbon double bonds of the fatty acid molecule. Most importantly, rutin oleate exhibited antioxidant capacity comparable to butylated hydroxytoluene and its counterparts (rutin and oleic acid) at low temperatures (60° C), but had a significant advantage at high temperatures (120° C).

CONCLUSION

The antioxidant activity of rutin was significantly enhanced by lipase-mediated esterification with oleic acid. Therefore, rutin oleate could be further developed as a novel antioxidant for use in oil- and fat-based foods. © 2023 Society of Chemical Industry.

An efficient method based on an inhibitor-enzyme complex to screen an active compound against lipase from Toona sinensis

As a popular vegetable, Toona sinensis has a wide range of bioactivities including lipase inhibitory activity. In the present study, an efficient and rapid method using a ligand-enzyme complex was established for screening of an active compound against lipase from Toona sinensis. The ethyl acetate extract of Toona sinensis showed good lipase inhibitory activity. After incubation with lipase, one of the compounds in the extract decreased significantly while comparing the HPLC chromatograms before and after incubation, which indicated that it may be the active compound bound to lipase. Then, the compound was isolated using a Sephadex LH-20 column and identified as 1,2,3,4,6-penta-O-galloyl-β-D-glucose. The in vitro activity test showed that the compound had good inhibitory activity against lipase, and its IC₅₀ value was 118.8 ± 1.53 μg mL^-1. The kinetic experiments indicated that 1,2,3,4,6-penta-O-galloyl-β-D-glucose inhibited lipase through mixed competitive and non-competitive inhibitions. Further docking results showed that the target compound could bind to the active site of lipase stably through seven hydrogen bonds, resulting in a docking energy of -8.31 kcal mol^-1. The proposed method can not only screen the lipase inhibitors from Toona sinensis quickly and effectively, but also provide an effective way for the rapid screening of active substances in natural food and plants.

The xanthine oxidase and its associated activities in the ovine milk and liver: distinctive in impact of in vivo molybdenum

Xanthine oxidase is molybdenum and iron-containing flavoprotein, catalyzing the final oxidation stage of purines and oxidative transformation of pterins and some aliphatic and aromatic aldehydes. Despite the importance of this enzyme, the distribution of xanthine oxidase in traditional household animal’s milk and tissues is unknown. Formerly, we have found most of the xanthine oxidase molecules in animal milk are inactive because of a lack of molybdenum. Ovine milk was processed by inserting in vivo molybdenum (tungsten) into drinking water. We gave opposite dates in the presence of tungsten too. Heating the milk of animals at 80 °C for 5 minutes in the presence of molybdenum and cysteine led to a sharp increase of xanthine oxidase and its associated – nitrate reductase and nitrite reductase activities. The change of xanthine oxidase and its associated activities were examined by spectrophotometry after treatment. It was established that metal ions added in drinking water for animals have an impact on enzyme activities. The activity is formed in the ovine liver even in the absence of exogenous molybdenum in drinking water. The associated activities of liver enzymes in the presence of molybdenum in drinking water had slightly increased. Tungsten-containing water led to the loss of all activities of liver xanthine oxidase. It is proposed that the liver contains a special protein involving in the incorporation of molybdenum (or tungsten) into xanthine oxidase molecule, however, the milk or mammary gland compounds lack this protein.

Anti-inflammatory drugs as new inhibitors to xanthine oxidase: In vitro and in silico approach

The two important targets to treat gout disease are (1) control the hyperuricemia by the inhibition of Xanthine Oxidase (XO) and (2) treatment of acute attacks of gout by the use of anti-inflammatory drugs. It is important to distinguish between therapy to manage hyperuricemia and to reduce acute inflammation. While reducing hyperuricemia is resolved very slowly with available drugs, gout symptoms like pain and inflammation may become persistent. The objective of this study is to find a relevant treatment with a beneficial double effect. (1) As an anti-inflammatory, analgesic, and antipyretic effect and (2) as XO inhibitory effect, which is the main objective of this study. We investigated the effect of five non-steroidal anti-inflammatory drugs (NSAIDs) against human and bovine milk xanthine oxidases (HXO and BXO) using the double enzyme detection method (DED) and molecular docking with the Autodock vina program. in vitro results show that the NSAIDs give an important inhibition to HXO and BXO with an IC₅₀ of 2.04 ± 0.13 μg/ml, 2.75 ± 0.23 μg/ml, 1.45 ± 0.19 μg/ml, 0.31 ± 0.13 μg/ml and 1.27 ± 0.11 μg/ml, for HXO, and 2.96 ± 0.27 μg/ml, 9.46 ± 0.13 μg/ml, 6.21 ± 1.17 μg/ml, 0.83 ± 0.11 μg/ml, and 3.48 ± 0.13 μg/ml, for BXO, for respectively, Naproxen, Ibuprofen, Diclofenac, Indomethacin, and Celecoxib. Testing the inhibitory activity of these drugs on both XOs shows an important inhibition, especially from Indomethacin, which could be a promising lead compound for reducing acute inflammation and at the same time controlling hyperuricemia.

Design, synthesis and biological evaluation of N-(3-(1H-tetrazol-1-yl)phenyl)isonicotinamide derivatives as novel xanthine oxidase inhibitors

In our previous study, we reported a series of N-phenylisonicotinamide derivatives as novel xanthine oxidase (XO) inhibitors and identified N-(3-cyano-4-((2-cyanobenzyl)oxy)phenyl)isonicotinamide (compound 1) as the most potent one with an IC₅₀ value of 0.312 μM. To further optimize the structure and improve the potency, a structure-based drug design (SBDD) strategy was performed to construct the missing H-bond between the small molecule and the Asn768 residue of XO. We introduced a tetrazole moiety at the 3'-position of the phenyl to serve as an H-bond acceptor and obtained a series of N-(3-(1H-tetrazol-1-yl)phenyl)isonicotinamide derivatives (2a-t and 6-8). Besides, to investigate the influence of the amide-reversal, some N-(pyridin-4-yl)-3-(1H-tetrazol-1-yl)benzamide derivatives (3c, 3e, 3i, 3k and 3u) were also synthesized and evaluated. Biological evaluation and structure-activity relationship analysis demonstrated that the 3'-(1H-tetrazol-1-yl) moiety was an excellent fragment for the N-phenylisonicotinamide scaffold; a substituted benzyloxy, especially, an m-cyanobenzyloxy (e.g., 2s), linking at the 4'-position was welcome for the potency; and the amide-reversal could damage the potency, so maintenance of the N-phenylisonicotinamide scaffold was essential. In summary, starting from compound 1, the SBDD effort successfully identified a promising XO inhibitor 2s (IC₅₀ = 0.031 μM), with a 10-fold gain in potency. Its potency was very close to the positive control topiroxostat (IC₅₀ = 0.021 μM). A Lineweaver-Burk plot indicated that compound 2s acted as a mixed-type XO inhibitor. Molecular docking and molecular dynamics simulations revealed that the tetrazole moiety could occupy the Asn768-sub-pocket with N-4 atom accepting an H-bond from the Asn768 residue, as expected.

Determination of Urinary Caffeine Metabolites as Biomarkers for Drug Metabolic Enzyme Activities

Caffeine is commonly taken via the daily dietary consumption of caffeine-containing foods. The absorbed caffeine is metabolized to yield various metabolites by drug-metabolizing enzymes, and measuring the levels of each caffeine metabolite can provide useful information for evaluating the phenotypes of those enzymes. In this study, the urinary concentrations of caffeine and its 13 metabolites were determined, and the phenotypes of drug metabolic enzymes were investigated based on the caffeine metabolite ratios. Human urine samples were pretreated using solid phase extraction, and caffeine and its metabolites were analyzed using liquid chromatography-tandem mass spectrometry. Based on the urinary caffeine metabolite concentrations, the caffeine metabolite ratios were calculated for six human subjects at specified time points after caffeine intake. Variations in urinary metabolite levels among individuals and time points were reported. In addition, the resultant enzyme activities showed different patterns, depending on the metabolite ratio equations applied. However, some data presented a constant metabolite ratio range, irrespective of time points, even at pre-dose. This suggests the possibility of urinary caffeine metabolite analysis for routine clinical examination. These findings show that urinary caffeine and the metabolite analysis would be useful in evaluating metabolic phenotypes for personalized medicine.

Screening and Evaluation of Xanthine Oxidase Inhibitors from Gnetum parvifolium in China

As a traditional natural medicine for treating many kinds of diseases, Gnetum parvifolium showed apparent inhibition on xanthine oxidase (XO). In this study, ultrafiltration combined with liquid chromatography-mass spectrometry (LC-MS) is used for the screening of XO inhibitors from Gnetum parvifolium. Their antioxidation, XO inhibition, and enzymic kinetic parameters are also determined. Finally, piceatannol (1), rhaponiticin (2), resveratrol (3), and isorhapontigenin (4) are screened out and identified as XO inhibitors from the extract of Gnetum parvifolium. Four inhibitors show better inhibition than allopurinol and good radical scavenging abilities. However, the antioxidant activities are weaker than ascorbic acid. The kinetic parameters illustrate the inhibition mode of XO by piceatannol is competitive type, while the inhibition modes for rhaponiticin, resveratrol and isorhapontigenin are uncompetitive types. In order to evaluate the difference among samples obtained in China, the amounts of four inhibitors and related activities in 20 samples are assessed and analyzed by partial least squares analysis. The results indicate piceatannol contribute the highest coefficients in three kinds of activities. Based on these findings, more comprehensive research on pharmaceutical and biochemical activities of these four XO inhibitors could be conducted in future.

Analysis of Fluorescence Spectra of Citrus Polymethoxylated Flavones and Their Incorporation into Mammalian Cells

Citrus polymethoxylated flavones (PMFs) influence biochemical cascades in human diseases, yet little is known about how these compounds interact with cells and how these associations influence the actions of these compounds. An innate attribute of PMFs is their ultraviolet-light-induced fluorescence, and the fluorescence spectra of 14 PMFs and 7 PMF metabolites were measured in methanol. These spectra were shown to be strongly influenced by the compounds' hydroxy and methoxy substituents. For a subset of these compounds, the fluorescence spectra were measured when bound to human carcinoma Huh7.5 cells. Emission-wavelength maxima of PMF metabolites with free hydroxyl substituents exhibited 70-80 nm red shifts when bound to the Huh7.5 cells. Notable solvent effects of water were observed for nearly all these compounds, and these influences likely reflect the effects of localized microenvironments on the resonance structures of these compounds when bound to human cells.