Black rice anthocyanins alleviate hyperuricemia in mice: Possible inhibitory effects on xanthine oxidase activity by cyanidin 3-O-glucoside

Ilex cornuta leaves extracts ameliorate hyperuricemia by modulating uric acid transporters

ETHNOPHARMACOLOGICAL RELEVANCE

Ilex cornuta is a valuable species of the Holly genus (Aquifoliaceae), and mainly distributed in eastern China. It is not only made into tea, namely Kudingcha, but also used as traditional medicine to relieve cough, headache, gout, and nourish liver and kidney.

AIM OF THE STUDY

The purpose of this study was to explore the exact efficacy of different extracts from Ilex cornuta in the treatment of hyperuricemia in vitro and in vivo, and to explore its pharmacological mechanism, so as to bring new ideas for the development of new drugs for reducing uric acid (UA) and anti-gout.

MATERIALS AND METHODS

Five crude extracts from Ilex cornuta leaves were extracted by different methods. Then, the xanthine oxidase inhibitory activity and antioxidant capacity of 5 extracts in vitro were compared to screen the extract with the most UA regulating potential. In vivo experiment, hyperuricemia model of mice was established by intragastric administration of potassium oxonate and feeding high yeast diet. Biochemical indexes such as serum UA level, xanthine oxidase activity, liver and kidney index of mice in each group were detected. The pathological sections of kidney and liver tissues were also observed and compared. The mechanism of Ilex cornuta leaves (western blotting, and RT-qPCR) in the treatment of hyperuricemia was further explored by targeting UA transporters ABCG2, GLUT9, and URAT1.

RESULTS

The in vitro results of inhibitory activity of xanthine oxidase showed that the crude saponin extract was the best, followed by crude flavonoids extract. Then, the in vivo results reflected that both crude saponins and crude flavonoids extracts could significantly reduce the serum UA level, inhibit the activity of xanthine oxidase in serum and liver, and maintain serum urea nitrogen and creatinine at normal level. Meanwhile, there was no liver and kidney injury in mice. Through the comparison of the mechanism results, it was found that both extracts could up-regulate the expression of ABCG2 protein and mRNA related to UA excretion, and down-regulate the expression of GLUT9 and URAT1 protein and mRNA.

CONCLUSION

The crude flavonoids and saponins of Ilex cornuta leaves not only inhibited XOD activity in vitro, but also significantly controlled XOD activity and reduced UA level in hyperuricemia mice in vivo. One of the potential mechanisms was to regulate UA level in vivo by regulating ABCG2, GLUT9, and URAT1 transporters directly related to UA transport, thus achieving the effect of intervening hyperuricemia. This study provided a preliminary experimental basis for the development of new drugs of Ilex cornuta leaves for treating hyperuricemia.

Inhibition of Xanthine Oxidase by 4-nitrocinnamic Acid: In Vitro and In Vivo Investigations and Docking Simulations

Background: Cinnamic acid and its derivatives have gained significant attention in recent medicinal research due to their broad spectrum of pharmacological properties. However, the effects of these compounds on xanthine oxidase (XO) have not been systematically investigated, and the inhibitory mechanism remains unclear.

Objectives: The objective of this study was to screen 18 compounds and identify the XO inhibitor with the strongest inhibitory effect. Furthermore, we aimed to study the inhibitory mechanism of the identified compound.

Methods: The effects of the inhibitors on XO were evaluated using kinetic analysis, docking simulations, and in vivo study. Among the compounds tested, 4-NA was discovered as the first XO inhibitor and exhibited the most potent inhibitory effects, with an IC50 value of 23.02 ± 0.12 μmol/L. The presence of the nitro group in 4-NA was found to be essential for enhancing XO inhibition. The kinetic study revealed that 4-NA inhibited XO in a reversible and noncompetitive manner. Moreover, fluorescence spectra analysis demonstrated that 4-NA could spontaneously form complexes with XO, referred to as 4-NA-XO complexes, with the negative values of △H and ΔS.

Results: This suggests that hydrogen bonds and van der Waals forces play crucial roles in the binding process. Molecular docking studies further supported the kinetic analysis and provided insight into the optimal binding conformation, indicating that 4-NA is located at the bottom outside the catalytic center through the formation of three hydrogen bonds. Furthermore, animal studies confirmed that the inhibitory effects of 4-NA on XO resulted in a significant reduction of serum uric acid level in hyperuricemia mice.

Conclusion: This work elucidates the mechanism of 4-NA inhibiting XO, paving the way for the development of new XO inhibitors.

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Anthocyanins-natural pigment of colored rice bran: Composition and biological activities

Rice by-products are a potential source of various bioactive substances with great processing potential, which are receiving increasing attention. Among them, rice bran is a by-product of rice milling, with high nutritional value and health benefits. Colored rice bran contains a large amount of anthocyanins responsible for color and bioactivities. And anthocyanins are often added to foods as a natural pigment, serving to enhance both the visual appeal and nutritional value. Recent advances in the composition and bioactivities of four common colored rice bran anthocyanins (black, purple, red, and purple red rice) are reviewed in this paper. Rice bran anthocyanins have been confirmed to exhibit biological potential for human health, with their main biological activities being antioxidant, anti-atherosclerosis, anti-cancer, neuroprotective, retinoprotective, immunomodulatory, anti-aging and anti-obesity effects. The structure of anthocyanins determines their biological activities. The anthocyanins composition of rice bran with different colors varied greatly, while that of rice bran with the same color is also slightly different, which is attributed to the rice varieties, growing environment and cropping conditions. However, it remains necessary to conduct further clinical studies to support the health activities of anthocyanins. The present review provides information value for the further development and comprehensive utilization of rice bran anthocyanins.

Physicochemical and Digestible Properties of Parboiled Black Rice With Different Amylose Contents

The varieties of black rice with different amylose contents (waxy; medium-amylose: 16.03%; high-amylose: 27.14%) were parboiled and then evaluated for physicochemical and digestible properties. The color, crystalline structure, and swelling property of parboiled rice were analyzed, and the water molecular mobility, texture, and starch digestibility of cooked parboiled rice were determined. The color of black rice was only slightly changed after the parboiling treatment. The crystalline structures of waxy and medium-amylose rice were severely damaged by the parboiling treatment, while the highly crystalline structure was retained in parboiled high-amylose rice. During heating in water, parboiled high-amylose rice had a lower water absorption ratio (WAR) and volume expansion ratio (VER) than the other two varieties. After cooking, parboiled high-amylose rice had higher water molecular mobility and harder texture compared with the other two varieties. Cooked parboiled high-amylose rice contained higher content of resistant starch than cooked parboiled waxy and medium-amylose rice.