Analysis of the pH-Dependent Fe(III) Ion Chelating Activity of Anthocyanin Extracted from Black Soybean [Glycine max (L.) Merr.] Coats

Foliar application of iron impacts flavonoid glycosylation and promotes flavonoid metabolism in coloured rice

Coloured rice is known as a healthcare food owing its rich flavonoid content. To better understand the effects of iron on the flavonoid metabolism of coloured rice grains, different concentrations of FeSO4 were foliar sprayed on to red rice Yuhongdao 5815 (RR) and black rice Nanheinuo (BR). The results revealed the association of iron with the increased accumulation of anthocyanins in BR and proanthocyanins in RR along with enhancements in their antioxidant capacities and total flavonoid contents. Metabolomic analysis revealed that the differential metabolites between the iron treated coloured rice and the control primarily occurred because of the O-linked glycosylation of aglycones, which are involved in the flavonoid pathway. RR exhibited a significantly higher number of differential metabolites compared with BR. Thus, foliar FeSO4 application affects the O-linked glycosylation and positively regulates flavonoid metabolism.

Anthocyanins and reactive oxygen species: a team of rivals regulating plant development?

Anthocyanins are a family of water-soluble vacuolar pigments present in almost all flowering plants. The chemistry, biosynthesis and functions of these flavonoids have been intensively studied, in part due to their benefit for human health. Given that they are efficient antioxidants, intense research has been devoted to studying their possible roles against damage caused by reactive oxygen species (ROS). However, the redox homeostasis established between antioxidants and ROS is important for plant growth and development. On the one hand, high levels of ROS can damage DNA, proteins, and lipids, on the other, they are also required for cell signaling, plant development and stress responses. Thus, a balance is needed in which antioxidants can remove excessive ROS, while not precluding ROS from triggering important cellular signaling cascades. In this article, we discuss how anthocyanins and ROS interact and how a deeper understanding of the balance between them could help improve plant productivity, nutritional value, and resistance to stress, while simultaneously maintaining proper cellular function and plant growth.

Cyanidin-3-glucoside inhibits ferroptosis in renal tubular cells after ischemia/reperfusion injury via the AMPK pathway

BACKGROUND

Ferroptosis, which is characterized by lipid peroxidation and iron accumulation, is closely associated with the pathogenesis of acute renal injury (AKI). Cyanidin-3-glucoside (C3G), a typical flavonoid that has anti-inflammatory and antioxidant effects on ischemia‒reperfusion (I/R) injury, can induce AMP-activated protein kinase (AMPK) activation. This study aimed to show that C3G exerts nephroprotective effects against I/R-AKI related ferroptosis by regulating the AMPK pathway.

METHODS

Hypoxia/reoxygenation (H/R)-induced HK-2 cells and I/R-AKI mice were treated with C3G with or without inhibiting AMPK. The level of intracellular free iron, the expression of the ferroptosis-related proteins acyl-CoA synthetase long chain family member 4 (ACSL4) and glutathione peroxidase 4 (GPX4), and the levels of the lipid peroxidation markers 4-hydroxynonenal (4-HNE), lipid reactive oxygen species (ROS) and malondialdehyde (MDA) were examined.

RESULTS

We observed the inhibitory effect of C3G on ferroptosis in vitro and in vivo, which was characterized by the reversion of excessive intracellular free iron accumulation, a decrease in 4-HNE, lipid ROS, MDA levels and ACSL4 expression, and an increase in GPX4 expression and glutathione (GSH) levels. Notably, the inhibition of AMPK by CC significantly abrogated the nephroprotective effect of C3G on I/R-AKI models in vivo and in vitro.

CONCLUSION

Our results provide new insight into the nephroprotective effect of C3G on acute I/R-AKI by inhibiting ferroptosis by activating the AMPK pathway.

Microscale thermophoresis as a powerful growing analytical technique for the investigation of biomolecular interaction and the determination of binding parameters

The in vitro panel of technologies to address biomolecular interactions are in play, however microscale thermophoresis is continuously increasing in use to represent a key player in this arena. This review highlights the usefulness of microscale thermophoresis in the determination of molecular and biomolecular affinity interactions. This work reviews the literature from January 2016 to January 2022 about microscale thermophoresis. It gives a summarized overview about both the state-of the art and the development in the field of microscale thermophoresis. The principle of microscale thermophoresis is also described supported with self-created illustrations. Moreover, some recent advances are mentioned that showing application of the technique in investigating biomolecular interactions in different fields. Finally, advantages as well as drawbacks of the technique in comparison with other competing techniques are summarized.

Antagonism of Cyanamide-3-O-glucoside and protocatechuic acid on Aflatoxin B1-induced toxicity in zebrafish larva (Danio rerio)

The zebrafish model was used to evaluate the antioxidant properties of cyanidin-3-O-glucoside (C₃G) and its metabolite protocatechuic acid (PCA) against aflatoxin B₁ (AFB₁)-induced hepatotoxicity and oxidative stress. In this study, zebrafish larvae were cultured for 3 days post fertilization (dpf) and then induced with AFB₁. After induced 4 h, 8 h, 12 h, and 24 h, 5 μg/mL C₃G/PCA was added and then co-cultured to 5 dpf, respectively. The experiments showed that C₃G/PCA suppressed AFB₁-induced zebrafish liver atrophy and delayed the absorption of the yolk sac. In addition, reactive oxygen species (ROS) and cell death were also significantly decreased by 5 μg/mL C₃G/PCA (P ˂ 0.05). C₃G/PCA significantly reduced hepatic biomarkers in the serum contents (P ˂ 0.05). Besides, glutathione (GSH) contents were significantly upregulated, and the activities of superoxide dismutase (SOD) and catalase (CAT) were significantly elevated in zebrafish (P ˂ 0.05). The addition of 5 μg/mL C₃G/PCA was capable of reducing the apoptotic levels of caspase-9 and caspase-3 after 100 ng/mL AFB₁ intoxication. In conclusion, these results suggested that C₃G and its metabolite PCA might antagonize the hepatotoxicity of AFB₁, reduce oxidative damage and inhibit cell death.

Incorporation of gelatin and Fe2+ increases the pH-sensitivity of zein-anthocyanin complex films used for milk spoilage detection

In this study, blueberry anthocyanins, gelatin and Fe²⁺ were incorporated into zein matrix via electrospinning method to prepare colorimetric indicator films for monitoring milk freshness. Gelatin and Fe²⁺ were incorporated into the film to improve visual discrimination of indicator films' color changes in milk with different freshness degrees and in solution with pH 3-7. Results of SEM, FT-IR and XRD showed that there were intermolecular hydrogen bonds among components, which associated with the larger color difference of indicator films. UV-vis spectral analysis showed that blueberry anthocyanin solutions containing both gelatin and Fe²⁺ displayed the highest intensity absorption peaks. The optimal ability to distinguish the pH (3-7) of solutions was presented by the indicator film incorporating gelatin (1% (w/v)) and Fe²⁺ (0.07 mg/mL). Gelatin and Fe²⁺ increased the color-responsive sensitivity of the indicator film to pH. The film could be successfully used to detect the freshness of milk, whose color changes were visually perceivable: from purple black (fresh milk) to royal purple (spoiling milk) and then to violet red (spoiled milk). The color parameters (L*, a*, R, G and B) of the film revealed a high correlation with the pH/acidity of the milk during storage. The successful application of the indicator film embedding gelatin and Fe²⁺ for monitoring milk quality changes indicated that the addition of special substances could provide great potential for monitoring freshness and preparing intelligent packaging of food.

Experimental and theoretical research on the effect of coupling heat and pH on the structure and antioxidant activity of cyanidin-3-O-glucoside from black soybean coat

BACKGROUND

Since anthocyanin has good coloration and antioxidant properties, many studies have focused on exploring the stability and antioxidant activity of anthocyanin. The objective of this work was to study effects of pH and temperature on the bioactivity of cyanidin-3-O-glucoside (C3G) and ultra-performance liquid chromatography-photodiode array-electrospray ionization-quadrupole-time-of-flight mass spectrometry (UPLC-PDA-ESI-Q-TOF-MS) and density functional theory (DFT) were used to explain the mechanism of structural transformation of C3G affecting their bioactivity at the molecular level.

RESULTS

During the heating process at pH 2.2 to 7.0，the flavylium cation content of C3G decreased from 92.71% to 51.64% and the chalcone content increased from 7.29% to 30.61%. The quinoidal base and first discovery of the degradation product of the C3G, 1-(3,4-dihydroxy-phenyl)-2-(3, 4,5-trihydroxy-6-hydroxymethyl-tetrahydro-pyran-2-yloxy)-ethanone, were only detected in heated samples at pH 7.0. DFT revealed the antioxidant mechanism was mediated by sequential proton loss electron transfer and the antioxidant activity of C3G in pH 5.0 and 7.0 environments was higher than that in the pH 2.2 environment.

CONCLUSIONS

The results revealed the thermal degradation products of C3G included catechin, 3,4-dihydroxybenzoic acid, 2,4,6-trihydroxy-benzaldehyde and 1-(3,4-Dihydroxy-phenyl)-2-(3,4,5-trihydroxy-6-hydroxymethyl-tetrahydro-pyran-2-yloxy)-ethanone. C3G had higher antioxidant activity in weakly acidic to near-neutral environments and the reactive sites were most likely at the 4'-OH and 5-OH sites. © 2021 Society of Chemical Industry.

Cu2+-Induced self-assembly and amyloid formation of a cyclic D,L-α-peptide: structure and function

In a wide spectrum of neurodegenerative diseases, self-assembly of pathogenic proteins to cytotoxic intermediates is accelerated by the presence of metal ions such as Cu²⁺. Only low concentrations of these early transient oligomeric intermediates are present in a mixture of species during fibril formation, and hence information on the extent of structuring of these oligomers is still largely unknown. Here, we investigate dimers as the first intermediates in the Cu²⁺-driven aggregation of a cyclic D,L-α-peptide architecture. The unique structural and functional properties of this model system recapitulate the self-assembling properties of amyloidogenic proteins including β-sheet conformation and cross-interaction with pathogenic amyloids. We show that a histidine-rich cyclic D,L-α-octapeptide binds Cu²⁺ with high affinity and selectivity to generate amyloid-like cross-β-sheet structures. By taking advantage of backbone amide methylation to arrest the self-assembly at the dimeric stage, we obtain structural information and characterize the degree of local order for the dimer. We found that, while catalytic amounts of Cu²⁺ promote aggregation of the peptide to fibrillar structures, higher concentrations dose-dependently reduce fibrillization and lead to formation of spherical particles, showing self-assembly to different polymorphs. For the initial self-assembly step to the dimers, we found that Cu²⁺ is coordinated on average by two histidines, similar to self-assembled peptides, indicating that a similar binding interface is perpetuated during Cu²⁺-driven oligomerization. The dimer itself is found in heterogeneous conformations that undergo dynamic exchange, leading to the formation of different polymorphs at the initial stage of the aggregation process.

Interference of anthocyanin extracted from black soybean coats on aflatoxin B1-human serum albumin in the binding process

The effect of the anthocyanin cyanidin-3-O-glucoside (C3G) and its main gastrointestinal metabolites (PCA and PGA) on the binding of AFB1 and HSA were studied via spectrometry. C3G is relatively stable in the gastric environment, and the intestinal environment promotes its metabolism into PCA and PGA. Binary fluorescence experiments showed that both AFB1 and C3G, including PCA and PGA, can react with HSA. AFB1, C3G and PCA can bind at site I and site II of HSA; PGA binds at site II. The presence of C3G/PCA/PGA inhibits the degree of quenching. C3G/PCA does not change the quenching mechanism; it is still static quenching; however, dynamic quenching occurs in the (AFB1-HSA)-PGA system. In addition, the apparent binding constant and number of binding sites of AFB1-HSA also diminish to different degrees. C3G and its metabolites (PCA and PGA) interfere with the interaction between AFB1 and HSA, and can reduce AFB1 transport at pH 7.4 in vitro.Abbreviations: C3G: cyanidin-3-O-glucoside; M: metabolite; PCA: protocatechuic acid; PGA: phloroglucinol aldehyde; AFB1: aflatoxin B1; HSA: human serum albumin.

Effect of organic acid on cyanidin-3-O-glucoside oxidation mediated by iron in model Chinese bayberry wine

Cyanidin-3-O-glucoside (C3G) is principal anthocyanin in Chinese bayberry wine and its degradation is main problem with respect to wine color. Effect of five organic acids existing in bayberry wine on C3G oxidation mediated by iron was investigated in model wine. Fe(II) oxidation was found to follow a decreasing order in oxalate > citrate > tartrate > malate model wine whereas it hardly occurred in succinate model wine. The C3G oxidation mediated by iron followed an increasing order in citrate > oxalate > succinate > malate > tartrate model wine. More degradation products were observed in succinate, malate and tartrate model wine than in citrate and oxalate model wine. C3G degradation mediated by Fe(III) was faster than that mediated by Fe(II) in oxalate, succinate, malate, and tartrate model wine, but not in citrate model wine. C3G oxidation mediated by iron is probably not main mechanism of anthocyanin degradation in bayberry wine.

Interaction of Protein Isolate with Anthocyanin Extracted from Black Soybean and Its Effect on the Anthocyanin Stability

The interactions between black soybean protein isolate (B-SPI) and cyanidin 3-O-glucoside (C3G), anthocyanin extracted from black soybean coat was investigated under neutral conditions. The fluorescence spectra showed that C3G had fluorescence quenching effects on B-SPI. Thermodynamic parameters showed that ∆G < 0, which demonstrated that the binding was a spontaneous reaction. Since ΔH > 0 and ΔS > 0, the interactions between C3G and B-SPI was mainly hydrophobic interactions. Fourier infrared spectroscopy results suggested that the contents of α-helix and β-sheet structure showed an increasing trend, whereas the β-angle content displayed a decreasing trend. The degradation of C3G followed first-order kinetics at 85 °C and 100 °C. After the interactions with B-SPI, the degradation rate constant was decreased and the half-life of C3G was prolonged from 70.25 ± 0.90 min to 175.64 ± 38.04 min at 85 °C, from 62.68 ± 1.1 min to 72.51 ± 2.5 min at 100 °C (p < 0.05). The results indicated that the interactions of B-SPI and C3G improved the thermal stability of C3G under heating conditions.

The Anti-inflammatory Effects of Dietary Anthocyanins against Ulcerative Colitis

Ulcerative colitis (UC), which is a major form of inflammatory bowel disease (IBD), is a chronic relapsing disorder of the gastrointestinal tract affecting millions of people worldwide. Alternative natural therapies, including dietary changes, are being investigated to manage or treat UC since current treatment options have serious negative side effects. There is growing evidence from animal studies and human clinical trials that diets rich in anthocyanins, which are pigments in fruits and vegetables, protect against inflammation and increased gut permeability as well as improve colon health through their ability to alter bacterial metabolism and the microbial milieu within the intestines. In this review, the structure and bioactivity of anthocyanins, the role of inflammation and gut bacterial dysbiosis in UC pathogenesis, and their regulation by the dietary anthocyanins are discussed, which suggests the feasibility of dietary strategies for UC mitigation.

Purification and Characterization of a Cadmium-Binding Protein from Lentinula edodes

Many organisms possess the ability to produce metal-binding proteins to absorb cadmium. Metallothioneins, an important family of cysteine-rich metal-binding proteins, have been isolated and well characterized. However, Lentinula edodes may have a different type of cadmium-binding protein that contains fewer cysteine residues. In the present study, we purified a cadmium-binding protein from L. edodes (LECBP) by gel filtration and anion exchange chromatography and then identified LECBP by LC-MS/MS. We found LECBP to be a novel cadmium-binding protein, which contained 220 amino acid residues but no cysteine residue. LECBP had a high binding affinity for Cd(II) with a K_d value of 97.3 μM. The percentages of α-helix, β-sheet, β-turn, and random coil in LECBP were 15.7%, 39.4%, 8.0%, and 37.1%, respectively. In addition, high temperatures and an acidic environment influenced the conformation of LECBP. Our results will thus provide a new perspective to understand the mechanism of cadmium accumulation in L. edodes.