Novel pro-oxidant activity assay for polyphenols, vitamins C and E using a modified CUPRAC method

Evaluation of the Antioxidant and Anti-Inflammatory Activities and Acute Toxicity of Caco Seed (Chrysobalanus icaco L.) in Murine Models

Chysobalanus icaco L. (C. icaco) is a plant that is native to tropical America and Africa. It is also found in the southeast region of Mexico, where it is used as food and to treat certain diseases. This study aimed to carry out a phytochemical analysis of an aqueous extract of C. icaco seed (AECS), including its total phenol content (TPC), total flavonoid content (TFC), and condensed tannins (CT). It also aimed to examine the antioxidant and metal-ion-reducing potential of the AECS in vitro, as well as its toxicity and anti-inflammatory effect in mice. Antioxidant and metal-ion-reducing potential was examined by inhibiting DPPH, ABTS, and FRAP. The acute toxicity test involved a single administration of different doses of the AECS (0.5, 1, and 2 g/kg body weight). Finally, a single administration at doses of 150, 300, and 600 mg/kg of the AECS was used in the carrageenan-induced model of subplantar acute edema. The results showed that the AECS contained 124.14 ± 0.32 mg GAE, 1.65 ± 0.02 mg EQ, and 0.910 ± 0.01 mg of catechin equivalents/g dried extract (mg EC/g de extract) for TPC, TFC and CT, respectively. In the antioxidant potential assays, the values of the median inhibition concentration (IC50) of the AECS were determined with DPPH (0.050 mg/mL), ABTS (0.074 mg/mL), and FRAP (0.49 mg/mL). Acute toxicity testing of the AECS revealed no lethality, with a median lethal dose (LD50) value of >2 g/kg by the intragastric route. Finally, for inhibition of acute edema, the AECS decreased inflammation by 55%, similar to indomethacin (59%, p > 0.05). These results demonstrated that C. icaco seed could be considered a source of bioactive molecules for therapeutic purposes due to its antioxidant potential and anti-inflammatory activity derived from TPC, with no lethal effect from a single intragastric administration in mice.

The mechanistic insights into the role of pH and solvent on antiradical and prooxidant properties of polyphenols - Nine compounds case study

Polyphenols are the most widely intake exogenous antioxidants. Their properties prevent the accumulation of radicals in the body and the development of oxidative stress, a recognized trigger for some diseases and a manifestation of others. Nonetheless, apart from their beneficial effects, polyphenols might also exhibit prooxidant potential, often observed as the oxidation of transition state metals, resulting in amplified radical production. DFT studies at the B3LYP/6-311++G(d,p) level of theory were conducted on nine common polyphenolic compounds to assess both activities in physiologically relevant media. It has been found that there is a fine line between antioxidant and prooxidant character, and increasing pH values promote the occurrence of the latter. Anthocyanidins proved to be the most potent radical scavengers, particularly under slightly alkaline conditions, followed by flavonoids and phenolic acids last. Antiradical activity is better in a polar solvent than in apolar one, due to the possibility of dissociation.

Antiphotoaging and Skin-Protective Activities of Ardisia silvestris Ethanol Extract in Human Keratinocytes

Ardisia silvestris is a traditional medicinal herb used in Vietnam and several other countries. However, the skin-protective properties of A. silvestris ethanol extract (As-EE) have not been evaluated. Human keratinocytes form the outermost barrier of the skin and are the main target of ultraviolet (UV) radiation. UV exposure causes skin photoaging via the production of reactive oxygen species. Protection from photoaging is thus a key component of dermatological and cosmetic products. In this research, we found that As-EE can prevent UV-induced skin aging and cell death as well as enhance the barrier effect of the skin. First, the radical-scavenging ability of As-EE was checked using DPPH, ABTS, TPC, CUPRAC, and FRAP assays, and a 3-(4-5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide assay was used to examine cytotoxicity. Reporter gene assays were used to determine the doses that affect skin-barrier-related genes. A luciferase assay was used to identify possible transcription factors. The anti-photoaging mechanism of As-EE was investigated by determining correlated signaling pathways using immunoblotting analyses. As-EE had no harmful effects on HaCaT cells, according to our findings, and As-EE revealed moderate radical-scavenging ability. With high-performance liquid chromatography (HPLC) analysis, rutin was found to be one of the major components. In addition, As-EE enhanced the expression levels of hyaluronic acid synthase-1 and occludin in HaCaT cells. Moreover, As-EE dose-dependently up-regulated the production of occludin and transglutaminase-1 after suppression caused by UVB blocking the activator protein-1 signaling pathway, in particular, the extracellular response kinase and c-Jun N-terminal kinase. Our findings suggest that As-EE may have anti-photoaging effects by regulating mitogen-activated protein kinase, which is good news for the cosmetics and dermatology sectors.

Chemical Stability of Ascorbic Acid Integrated into Commercial Products: A Review on Bioactivity and Delivery Technology

The L-enantiomer of ascorbic acid is commonly known as vitamin C. It is an indispensable nutrient and plays a key role in retaining the physiological process of humans and animals. L-gulonolactone oxidase, the key enzyme for the de novo synthesis of ascorbic acid, is lacking in some mammals including humans. The functionality of ascorbic acid has prompted the development of foods fortified with this vitamin. As a natural antioxidant, it is expected to protect the sensory and nutritional characteristics of the food. It is thus important to know the degradation of ascorbic acid in the food matrix and its interaction with coexisting components. The biggest challenge in the utilization of ascorbic acid is maintaining its stability and improving its delivery to the active site. The review also includes the current strategies for stabilizing ascorbic acid and the commercial applications of ascorbic acid.

One‒pot green synthesized protein‒based silver nanocluster as prooxidant biosensor

In this study, silver nanoclusters as prooxidant biosensor were eco‒friendly synthesized using chicken egg white protein without any chemical reducing agents for measuring copper(II)-induced prooxidant activities of catechin, epicatechin, epigallocatechin gallate, resveratrol, gallic acid, chlorogenic acid, and rutin. The prooxidant activities were evaluated via measuring the absorption at 450 nm wavelength of the Cu(I)‒neocuproine chelate formed by extraction of protein-bound Cu(I) with neocuproine reagent. Accuracy was determined by evaluating recovery values of wine, grape and apple samples and the obtained values were between 97.2%‒98.9%. Intra-day precision and inter-day reproducibility experiments were studied with three different experiments in a day and three different days respectively. The obtained relative standard deviation values were 0.96% and 1.91%. The detection limit of the biosensor was found as 0.2 µM. The total prooxidant activities of fresh apple and grape fruits, apple and grape juices, and red wine were determined and the results obtained were compared with the findings of the carbonyl assay. In this study, a cheap, easily applicable, sensitive, and reproducible biosensor was developed. It was seen that it could be used in the measurement of the prooxidant activity of different food samples and give an idea about diet, healthy life, and nutrition.

Rapeseed oil fortified with micronutrients improves cognitive alterations associated with metabolic syndrome

Metabolic syndrome represents a major risk factor for severe comorbidities such as cardiovascular diseases or diabetes. It is also associated with an increased prevalence of emotional and cognitive alterations that in turn aggravate the disease and related outcomes. Identifying therapeutic strategies able to improve those alterations is therefore a major socioeconomical and public health challenge. We previously reported that both hippocampal inflammatory processes and neuronal plasticity contribute to the development of emotional and cognitive alterations in db/db mice, an experimental model of metabolic syndrome that displays most of the classical features of the syndrome. In that context, nutritional interventions with known impact on those neurobiological processes appear as a promising alternative to limit the development of neurobiological comorbidities of metabolic syndrome. We therefore tested here whether n-3 polyunsaturated fatty acids (n-3 PUFAs) associated with a cocktail of antioxidants can protect against the development of behavioral alterations that accompany the metabolic syndrome. Thus, this study aimed: 1) to evaluate if a diet supplemented with the plant-derived n-3 PUFA α-linolenic acid (ALA) and antioxidants (provided by n-3 PUFAs-rich rapeseed oil fortified with a mix of naturally constituting antioxidant micronutrients, including coenzyme Q10, tocopherol, and the phenolic compound canolol) improved behavioral alterations in db/db mice, and 2) to decipher the biological mechanisms underlying this behavioral effect. Although the supplemented diet did not improve anxiety-like behavior and inflammatory abnormalities, it reversed hippocampus-dependent spatial memory deficits displayed by db/db mice in a water maze task. It concomitantly changed subunit composition of glutamatergic AMPA and NMDA receptors in the hippocampus that has been shown to modulate synaptic function related to spatial memory. These data suggest that changes in local neuronal plasticity may underlie cognitive improvements in db/db mice fed the supplemented diet. The current findings might therefore provide valuable data for introducing new nutritional strategies for the treatment of behavioral complications associated with MetS.

Baicalein, as a Prooxidant, Triggers Mitochondrial Apoptosis in MCF-7 Human Breast Cancer Cells Through Mobilization of Intracellular Copper and Reactive Oxygen Species Generation

Background

Baicalein, a natural flavonoid derived from traditional Chinese herb Scutellaria baicalensis Georg (known as Huang Qin in Chinese), has been reported to exhibit notable antitumor activity in various cancer cells, including breast cancer. However, the detailed mechanisms underlying its induced apoptosis as a prooxidant in breast cancer cells are still unknown.

Materials and methods

In this study, we investigated the effect of endogenous copper on cytotoxic activity of baicalin against human breast cancer MCF-7 cells in vitro.

Results

Baicalein could remarkably reduce the cell viability in both dose- and time-dependent manners in MCF-7 cells but with lower cytotoxic effects on normal breast epithelial cells, MCF-10A. Such cell death could be prevented by pretreatment with Cu (I)-specific chelator neocuproine (Neo) and reactive oxygen species (ROS) scavengers. Meanwhile, baicalein could induce MCF-7 cell morphological changes, promote apoptotic cell death and increase the apoptotic cell number. Moreover, DCHF-DA staining, flow cytometry and Western blotting analyses proved that baicalein triggered the mitochondrial-dependent apoptotic pathway, as indicated by enhancement the level of intracellular ROS, disruption of mitochondrial membrane potential (ΔΨm), downregulation of anti-apoptotic protein Bcl-2, upregulation of pro-apoptotic protein Bax, release of cytochrome C and activation of caspase-9 and caspase-3 in MCF-7 cells. The pretreatment with Neo remarkably weakened these effects of baicalein. Furthermore, we confirmed that the prooxidant action of baicalein involved the direct production of hydroxyl radicals through redox recycling of copper ions.

Conclusion

These findings suggested that baicalein, acting as a prooxidant, could trigger apoptosis in MCF-7 cells occurs via the ROS-mediated intrinsic mitochondria-dependent pathway.

A novel gold nanocluster-based fluorometric biosensor for measuring prooxidant activity with a large Stokes shift

A chicken egg white protein-protected gold nanocluster (CEW-AuNC) based fluorogenic biosensor, where protein was used as both reducing and protecting agent, was developed to determine the Cu(II)-induced prooxidant activity of natural antioxidants abundant in food and biological samples. Gold nanoclusters, prepared using egg white proteins, exhibited strong fluorescence. The prooxidant activity of the tested antioxidants was indirectly measured by their reducing action on Cu(II) to Cu(I), and the reduced cuprous ion was bound to the thiol groups in the CEW-AuNC structure, causing a decrease in fluorescence intensity. Epicatechin, catechin, epigallocatechin gallate, morin, rutin, quercetin, gallic, chlorogenic, and rosmarinic acids, glutathione, cysteine, N-acetyl cysteine, bilirubin, resveratrol, and α-tocopherol were studied as natural antioxidants. A fluorometric method showing a large Stokes shift with excitation/emission maxima at 360∕640 nm was developed to sensitively measure the decrease in the fluorescence of CEW-AuNC associated with the binding of copper(I) to the protein structure. Total prooxidant activities of the binary, ternary, and quaternary synthetic mixtures and of some food and synthetic serum samples were determined. The biosensor response was statistically compared to that of its spectrophotometric counterpart. This method can be used for the control of the oxidative stability of foods with a prolonged shelf life.

A paper-based device for simultaneous determination of antioxidant activity and total phenolic content in food samples

We report the first use of a paper-based device as a simple, low-cost and rapid detection platform for simultaneous determination of antioxidant activity and total phenolic content in food samples. Two antioxidant activity assays including 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonate) radical cation (ABTS) assay and cupric reducing antioxidant capacity (CUPRAC) assay and one total phenolic content assay, Folin Ciocaltue reagent (FC) assay were simultaneously employed as a proof-of-concept. The device composed of a central sample zone connected to four pretreatment zones and consecutive detection zones to accommodate all three assays and a sample blank measurement. The analysis was achieved by dropping the samples onto the sample zone to flow to the pretreatment and detection zones containing the stored reagents for each antioxidant assay making the color change that was measured using imageJ software. Assay optimization including key reagent concentrations, reaction time, and surface modification were carried out to obtain sensitive and wide linear rage analyses. Various antioxidant standards were then evaluated to determine the analytical features of the method. The paper-based assays were successfully applied to detect antioxidant activity and total phenolic content in 10 beverage samples with similar gallic acid equivalent (GAE) values to those obtained from traditional assays at a 95% confidence interval. Moreover, the GAE values of the samples obtained from three assay analyses were well correlated to each other with relatively high Pearson's correlation coefficients. These results indicated that the assays gave accurate results and are suitable for simultaneous analysis of antioxidant activity and total phenolic content in real samples.

Protein-Protected Gold Nanocluster-Based Biosensor for Determining the Prooxidant Activity of Natural Antioxidant Compounds

In this work, chicken egg white protein (CEW)-protected gold nanoclusters (CEW-AuNCs) were prepared from CEW and HAuCl4 to measure the Cu(II)-induced prooxidant activity of antioxidant compounds such as epicatechin, epigallocatechin gallate, catechin, rosmarinic acid, resveratrol, ascorbic acid, and glutathione. These compounds reduced Cu(II) to Cu(I), and the latter was mainly bound to thiol groups in the CEW-AuNC structure. As the protein-bound Cu(I) may act as a catalytic center for generating reactive oxygen species, the Cu(II) reducing ability of antioxidants is an indirect measure of their prooxidant potency. The bound Cu(I) may be released with the cuprous-selective ligand neocuproine (Nc), forming the basis of a spectrophotometric method measuring absorbance at 450 nm wavelength of the Cu(I)-Nc chelate. The developed method involved a one-pot synthesis and determination without preseparation and was applied to binary synthetic mixtures of studied antioxidant compounds and to certain herbal plant (green tea, linden, echinacea, and artichoke leaf) extracts to determine the total prooxidant activities. The obtained results were statistically compared with those of the literature Cu(II)-Nc assay using a calcium proteinate-based solid biosensor. The developed biosensor was durable, reliable, easily applicable, and of low cost and wide linear range and could determine the prooxidant activities of natural antioxidant samples with high reproducibility.

Comparative Evaluation of the Antioxidant Capacities, Organic Acids, and Volatiles of Papaya Juices Fermented by Lactobacillus acidophilus and Lactobacillus plantarum

Fermentation of foods by lactic acid bacteria is a useful way to improve the nutritional value of foods. In this study, the health-promoting effects of fermented papaya juices by two species, Lactobacillus acidophilus and Lactobacillus plantarum, were determined. Changes in pH, reducing sugar, organic acids, and volatile compounds were determined, and the vitamin C, total phenolic content, and flavonoid and antioxidant capacities during the fermentation process were investigated. Juices fermented by Lactobacillus acidophilus and Lactobacillus plantarum had similar changes in pH and reducing sugar content during the 48 h fermentation period. Large amounts of aroma-associated compounds and organic acids were produced, especially lactic acid, which increased significantly (p<0.05) (543.18 mg/100 mL and 571.29 mg/100 mL, resp.), improving the quality of the beverage. In contrast, the production of four antioxidant capacities in the fermented papaya juices showed different trends after 48 hours’ fermentation by two bacteria. Lactobacillus plantarum generated better antioxidant activities compared to Lactobacillus acidophilus after 48 h of fermentation. These results indicate that fermentation of papaya juice can improve its utilization and nutritional effect.

Selective Targeting of Cancer Cells by Oxidative Vulnerabilities with Novel Curcumin Analogs

Recently, research has focused on targeting the oxidative and metabolic vulnerabilities in cancer cells. Natural compounds like curcumin that target such susceptibilities have failed further clinical advancements due to the poor stability and bioavailability as well as the need of high effective doses. We have synthesized and evaluated the anti-cancer activity of several monocarbonyl analogs of curcumin. Interestingly, two novel analogs (Compound A and I) in comparison to curcumin, have increased chemical stability and have greater anti-cancer activity in a variety of human cancer cells, including triple-negative, inflammatory breast cancer cells. In particular, the generation of reactive oxygen species was selective to cancer cells and occurred upstream of mitochondrial collapse and execution of apoptosis. Furthermore, Compound A in combination with another cancer-selective/pro-oxidant, piperlongumine, caused an enhanced anti-cancer effect. Most importantly, Compound A was well tolerated by mice and was effective in inhibiting the growth of human triple-negative breast cancer and leukemia xenografts in vivo when administered intraperitoneally. Thus, exploiting oxidative vulnerabilities in cancer cells could be a selective and efficacious means to eradicate malignant cells as demonstrated by the curcumin analogs presented in this report with high therapeutic potential.

Pro-apoptotic and cytotoxic effects of enriched fraction of Elytranthe parasitica (L.) Danser against HepG2 Hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC), the most common type of liver cancer accounts for more than one million deaths worldwide. Current treatment modality for HCC is marginally effective. Plants belonging to Mistletoe family (Loranthaceae) have been used in chemotherapy for many years. The present study was aimed at exploring the anti-proliferative, pro-oxidant and pro-apoptotic potential of stem of Elytranthe parasitica (L.) Danser (EP), a parasitic shrub belonging to Loranthaceae.

Methods

Elytranthe parasitica (L.) Danser, a climbing parasitic shrub was investigated for its cytotoxic activity against HepG2, a hepatocellular carcinoma cell line by Sulforhodamine B (SRB) assay. Further, pro-oxidant activity of EP extract/fractions was studied using copper phenanthroline assay. To understand the mechanism of cell death, the pro-apoptotic effects of Hep-G2 cells treated with EP extract/fractions were visualized by dual staining using acridine orange and ethidium bromide, a morphological marker of apoptosis. Phytochemical profiling of EP was explored by estimating the phenol, flavonoid and tannin content in its various fractions and extract. The occurrence of gallic acid, a principal polyphenol in EP extract and fractions was detected and further quantified using HPTLC (High Performance Thin Layer Chromatography) fingerprinting.

Result

Active fraction of Elytranthe parasitica, EP.DEE exhibited potent cytotoxic activity in a dose dependent manner against HepG2 hepatocellular carcinoma cell line with an IC50 of 56.7 ± 7.8 μg/mL. Dual staining with acridine orange and ethidium bromide revealed that HepG2 cells treated with EP active fractions underwent cell death chiefly by apoptosis. Highest phenol, flavonoid and tannin content were observed in active fractions, EP.EA (Ethyl acetate fraction) and EP.DEE (Diethyl ether fraction). Gallic acid was identified and quantified in EP extract and active fractions, EP.DEE and EP.EA.

Conclusion

Our findings indicate EP active fraction could be a promising contender in the treatment of hepatocellular carcinoma.

Vitamin E supplementation fails to impact measures of oxidative stress or the anaemia of feline chronic kidney disease: a randomised, double-blinded placebo control study

This study was designed to test the hypothesis that supplementation with vitamin E, an antioxidant, in cats with chronic kidney disease (CKD), would reduce oxidative stress and its impact on RBC membrane fragility, resulting in these cats maintaining a greater packed cell volume (PCV) compared with CKD cats not receiving supplementation.

Thirty‐six cats with CKD were randomly assigned to receive either daily vitamin E or a placebo for 3 months in a double‐blinded study design.

History and physical examination, blood pressure, complete blood count (CBC), PCV, biochemical profile and urinalysis (UA) were determined. Parameters of oxidative stress and osmotic fragility were measured. Cats were administered vitamin E or placebo once daily for 3 months. Cats were then reassessed and the diagnostics were repeated.

Twenty‐four cats completed the study, 11 in the vitamin E group and 13 in the placebo group. There were no significant differences between the two groups at the start, or upon completion of the study with regard to biochemical parameters, oxidative stress, erythrocyte osmotic fragility or PCV. None of these parameters changed significantly in either group over the treatment period.

Daily supplementation with 30 IU of vitamin E did not affect the measures of oxidative stress or the anaemia seen in cats with CKD.

Insights on antioxidant assays for biological samples based on the reduction of copper complexes-the importance of analytical conditions

Total antioxidant capacity assays are recognized as instrumental to establish antioxidant status of biological samples, however the varying experimental conditions result in conclusions that may not be transposable to other settings. After selection of the complexing agent, reagent addition order, buffer type and concentration, copper reducing assays were adapted to a high-throughput scheme and validated using model biological antioxidant compounds of ascorbic acid, Trolox (a soluble analogue of vitamin E), uric acid and glutathione. A critical comparison was made based on real samples including NIST-909c human serum certified sample, and five study samples. The validated method provided linear range up to 100 µM Trolox, (limit of detection 2.3 µM; limit of quantification 7.7 µM) with recovery results above 85% and precision <5%. The validated developed method with an increased sensitivity is a sound choice for assessment of TAC in serum samples.