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

Preparation, characterization and analysis of anthocyanin arbutin co-amorphous complexes and evaluation of the inhibition of tyrosinase

Natural phenolic compounds, such as anthocyanins and arbutin, have demonstrated significant potential as tyrosinase (TYR) inhibitors. However, the application of anthocyanins in biological systems is hindered by their instability under alkaline conditions, elevated temperatures, and light exposure. In contrast, arbutin exhibits superior stability while also functioning as a TYR inhibitor. To overcome these limitations, this study developed an Anthocyanin-α-Arbutin Co-amorphous (AAC) system aimed at enhancing both the stability of anthocyanins and their TYR inhibitory properties. Kinetic studies revealed that anthocyanins, arbutin, and AAC act as reversible mixed-type TYR inhibitors, with competitive inhibition as the predominant mechanism. Each compound exhibited distinct inhibition sites. Fluorescence analysis demonstrated that anthocyanins induce a fluorescence burst in TYR, likely attributed to Tyr residues, whereas α-arbutin and AAC enhance the fluorescence intensity of TYR. Moreover, α-arbutin and AAC were found to decrease the microenvironmental hydrophobicity surrounding tyrosine (Tyr) residues while increasing it around tryptophan (Trp) residues, suggesting potential conformational changes in tyrosinase. Molecular docking analysis indicated that hydrogen bonding and π-π stacking interactions occurred between anthocyanins and arbutin in the AAC system. Specifically, anthocyanins primarily interacted with TYR through π-π and π-alkyl interactions, while α-arbutin predominantly bound to TYR via hydrogen bonding. Consistent with the interaction study, α-arbutin was found to associate with tyrosinase mainly through hydrogen bonding and van der Waals forces. These findings provide novel insights into the interactions between anthocyanins and α-arbutin in the context of food science and lay a foundation for the development of innovative TYR inhibitors.

Investigation of resveratrol as a xanthine oxidase inhibitor: Mechanistic insights and therapeutic implications for gout and hyperuricemia

Gout predominantly stems from hyperuricemia, precipitating the accumulation of urate crystals and consequent joint inflammation, swelling, and pain, thereby compromising the quality of life and presenting a formidable medical dilemma. Although conventional treatments like allopurinol and febuxostat target uric acid reduction via xanthine oxidase (XO) inhibition, they often entail adverse effects, prompting the exploration of safer alternatives. Resveratrol, a polyphenolic compound abundant in fruits and vegetables, has emerged as a potential XO inhibitor. However, its precise inhibitory mechanisms remain poorly understood. This study aims to comprehensively investigate resveratrol's XO inhibition through mechanistic insights, molecular docking simulations, animal model experiments, and biochemical analysis, contributing valuable insights to the development of novel therapeutics for hyperuricemia and gout.

Changes in blood glucose and metabolism in hyperuricemia mice

The aim of this study is to explore the changes in blood uric acid level, blood glucose, and metabolism in hyperuricemia (HUA) mice. The urate oxidase gene of C57BL/6J mouse is knocked out by targeted gene modification technology, and a spontaneous HUA mouse model is established. In the experiment, 20 urate oxidase gene knockout homozygous and wild type C57BL/6J mice are selected to construct the experimental group (EG) and the control group (CG), and the mice in both groups receive multiple intraperitoneal injections of low dose streptozotocin (STZ) solution. The changes in metabolic related indicators such as blood glucose, pancreatic β cell function, water intake, urination, food intake, and body weight are observed and compared between the EG and CG mice. Baseline indicators other than body weight between the two groups of mice before the experiment have no significant difference, P > 0.05. After the injection of STZ solution, body weight between the two groups has significant difference, P < 0.05. Before the experiment and less than 19 days after the start of the experiment, daily water intake and urine output between the two groups of mice have no significant difference, P > 0.05. After the experiment reaches 19 days, two groups' water intake and urine output have significant difference, P < 0.05. Daily food intake between the two groups of mice has no significant difference, P > 0.05. Before the injection of STZ solution, fasting blood glucose levels between the two groups of mice has no significant difference, P > 0.05. The plasma insulin level of the EG mice was higher than that of the CG mice, with significant difference (P < 0.05). At the same time, the Homeostasis Model Assessment of Insulin Resistance index and fasting blood uric acid level of the EG mice were overall higher than those of the CG mice, with significant difference (P < 0.05). From the seventh day after the injection of STZ solution, the random blood glucose level, fasting blood glucose level, fasting insulin level, and blood uric acid level of the EG mice were higher than those of the CG mice, with significant difference (P < 0.05). For spontaneous HUA mice, the continuous increase in blood uric acid level caused by the disease may cause the increase in blood sugar content, thus promoting the occurrence of diabetes. Second, the content of uric acid in spontaneous HUA mice is maintained at a high level, which will bring or aggravate the damage of pancreatic islet β cells.

Protective Effects of Black Rice Anthocyanins on D-Galactose-Induced Renal Injury in Mice: The Role of Nrf2 and NF-κB Signaling and Gut Microbiota Modulation

BACKGROUND/OBJECTIVES

This study aimed to evaluate the renal protective effects of black rice anthocyanins (BRAs) against renal injury in mice induced by D-galactose (D-gal).

METHODS

The renal aging mouse model was established by thirteen consecutive weeks of subcutaneous injections of D-gal. The serum levels of urea nitrogen (BUN), creatinine (CRE), uric acid (UA), antioxidant enzymes (e.g., GSH-Px and SOD), and total antioxidant capacity (T-AOC), as well as the contents of inflammatory factors (IL-1β, IL-6, and TNF-α) in kidney tissues were evaluated. Additionally, the relative expression of the NQO1, HO-1, IKKβ, NF-kBp65, and TLR4 proteins was examined.

RESULTS

BRA treatment significantly reduced serum levels of BUN, and CRE increased the concentrations of antioxidant enzymes and total antioxidant capacity in renal tissues, and reduced the levels of inflammatory factors. Furthermore, BRAs restored the relative expression of the NQO1, HO-1, IKKβ, NF-kBp65, and TLR4 proteins to normal levels and promoted the recovery of the renal tissue architecture.

CONCLUSIONS

It was demonstrated that BRAs could potentially prevent and protect against kidney injury by modulating the Nrf2 and NF-κB signaling pathways, attenuating oxidative stress and inflammatory responses, and modulating the gut microflora. These findings provide a scientific basis for the application of BRAs as a natural bioactive substance in the field of nephroprotection, especially against the renal degeneration that accompanies the aging process.

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.

Microneedle Electrode Patch Modified with Graphene Oxide and Carbon Nanotubes for Continuous Uric Acid Monitoring and Diet Management in Hyperuricemia

Hyperuricemia is a common disorder induced by purine metabolic abnormality, which will further cause chronic kidney disease, cardiovascular disease, and gout. Its main pathological characteristic is the high uric acid (UA) level in the blood, so that the detection of UA is highly important for hyperuricemia diagnosis and therapy. Herein, we report a biocompatible and minimally invasive microneedle electrode patch (MEP) for continuous UA monitoring and diet management in hyperuricemia. The composite of graphene oxide and carboxylated multiwalled carbon nanotubes was modified on the microneedle electrode surface to enhance its sensitivity, selectivity, and stability, thus realizing the continuous detection of UA in the interstitial fluid to accurately predict the UA level in the blood. This further allowed us to study the hypouricemic effect of anthocyanins on the hyperuricemia model mouse. It was found that anthocyanins extracted from blueberry can effectively inhibit the activity of xanthine oxidase to reduce the production of UA. The UA level of hyperuricemia model mice fed with anthocyanins is ∼1.7 fold lower than that of the control group. We believe that this MEP offers enormous promise for continuous UA monitoring and diet management in hyperuricemia.

Breeding Rice to Increase Anthocyanin Yield Per Area through Small, Black Grain Size and Three Grains per Spikelet

Rice varieties with high anthocyanin content are often recognized for their vibrant colors and health benefits. The demand for rice with high anthocyanin is increasing domestically and internationally due to consumers becoming more health-conscious. However, the current increase in yield might not raise the anthocyanin content due to its location in the grain pericarp and seed coat, which are relative to the grain surface area. This study aims to develop rice lines to increase anthocyanin yield per production area by improving rice varieties with small, black, and three grains per spikelet. Accordingly, six rice recombinant inbred lines (RILs) were bred by crossing Niaw Dam Chaw Mai Pai 49 (NDCMP49) with Khao Nok (LLR059). The grain color, size, and number of grains per spikelet were selected from the F1 to the F4 population through the pedigree selection method. Six RILs and their parents were assigned in a randomized complete block design (RCBD) with three replications under field conditions during the rainy season of 2021 and 2022 in four locations. The results showed statistically significant differences in environmental conditions, affecting productivity and the yield components of rice lines. Consequently, the rice lines adapted to a specific environment, and there were significant differences in genotype. This study identified three RILs with higher yield performance (13-1 (3842 kg/ha), 374-1 (3699 kg/ha), and 903-3 (3550 kg/ha)) compared with the parent NDCMP49 (1996 kg/ha). However, the grain yields were unstable in the three top-yielding RILs due to varying environmental conditions, indicating that selective breeding requires a specific, narrow environment. Based on grain yield and grain size, the RILs performed better in the grain surface area than in the parent NDCMP49. Moreover, only two RILs (374-1 and 903-3) produced the highest anthocyanin content and yield, although this was lower than in the parent NDCMP49. However, the 374-1 and 903-3 RILs produced more grains, black grains, and three grains per spikelet with high yield and moderate anthocyanin content. They can, therefore, be backcrossed to the parent NDCMP49 to increase the accumulated anthocyanin content with a stable, high yield. This work provides a resource of small grains, black grains, and three grains per spikelet in the rice breeding line for breeding programs in the future.

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.