Conjugated autoxidizable triene (CAT) assay: a novel spectrophotometric method for determination of antioxidant capacity using triacylglycerol as ultraviolet probe

Approaches of lipid oxidation mechanisms in oil matrices using association colloids and analysis methods for the lipid oxidation

Lipid oxidation is one of the key chemical reactions in foods containing fats and oils during production and storage. For several decades, many researchers have tried to understand the mechanisms of lipid oxidation and ways to control the rates of lipid oxidation. Theories of autoxidation or free radical chain reaction have been developed to successfully explain the phenomenon observed in oxidized lipids. Many studies have been conducted to explain the other factors that can affect the lipid oxidation such as food matrix, oxidation time and temperature, transition metal ions, pigments with sensitizing abilities, and surface-active compounds such as phospholipids, free fatty acids, monoacylglycerols, and diacylglycerols. Several strategies were developed to evaluate the degree of oxidation and oxidative stability. This review provides crucial information on the mechanism of lipid oxidation affected amphiphilic compounds and association colloids. This review article will extensively discuss about the methods for determining the oxidative stability.

Comparative study between apocynin and protocatechuic acid regarding antioxidant capacity and vascular effects

Reactive oxygen species (ROS) derived from NOX enzymes activity play an important role in the development of cardiovascular diseases. Compounds able to decrease oxidative stress damage are potential candidates as drugs and/or supplements for hypertension treatment. Here, we aimed to compare in vitro ROS scavenging potency, effective NOX inhibition and effects on vascular reactivity of apocynin to another phenolic compound, protocatechuic acid, in vascular cells from spontaneously hypertensive rat (SHR), where redox signaling is altered and contributes to the development and/or maintenance of hypertension. We evaluated the in vitro antioxidant capacity and free radical scavenging capacity of both phenolic compounds. Moreover, we investigated the effect of both compounds on lipid peroxidation, lucigenin chemiluminescence, nitric oxide (NO•) levels and ROS concentration in vascular cells of SHR or human umbilical vein endothelial cell (HUVEC). Apocynin and protocatechuic acid presented antioxidant capacity and ability as free radical scavengers, decreased thiobarbituric acid reactive substances (TBARS) in aortic cells from SHR, and increased NO• concentration in isolated HUVEC. Both compounds were able to reduce lucigenin chemiluminescence and increased the potency of acetylcholine in aorta of SHR. However, in SHR aortas, only apocynin diminished the contraction induced by phenylephrine. In conclusion, these results strongly reinforce the potential application of substances such as apocynin and protocatechuic acid that combine abilities as scavenging and/or prevention of ROS generation, establishment of NO bioactivity and modulation of vascular reactivity. Due to its phytochemical origin and low toxicity, its potential therapeutic use in vascular diseases should be considered.

A new colorimetric method for determining antioxidant levels using 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS)

We describe here a novel assay that determines the total a+ntioxidative activities of known antioxidants and antioxidants in beverages. The method employs the substrate 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) that yields the colored product 3,5,3’,5’-tetrabromoazobenzene sulfate sodium salt (azo-TBBS). The amounts of azo-TBBS are measured using HPLC and then used to calculate total antioxidative capacity (TAC) values. We first show that the TAC values measured using the new DBNBS system were significantly higher compared with the control. The assay was validated through further analysis of 56 compounds, including previously characterized antioxidants. The data are consistent with published values. Here we describe in detail the application of the DBNBS method to the measurement of the TAC values of eight beverages, including wines and fruit juices. The DBNBS assay employs a readily applicable protocol that sensitively determines the levels of antioxidants in foodstuffs.

- A new DBNBS-mediated antioxidant assay system is compared with standard DPPH and ORAC assays

- DBNBS traps hydrogen radicals to generate a readily measured colored reduction product that quantifies antioxidant levels

Lipid oxidation in emulsions and bulk oils: a review of the importance of micelles

Lipid oxidation is a major cause of quality deterioration in food products. In these foods, lipids are often present in a bulk or in emulsified forms. In both systems, the rate, extent and pathway of oxidation are highly dependent on the presence of colloidal structures and interfaces because these are the locations where oxidation normally occurs. In bulk oils, reverse micelles (association colloids) are present and are believed to play a crucial role on lipid oxidation. Conversely, in emulsions, surfactant micelles are present that also play a major role in lipid oxidation pathways. After a brief description of lipid oxidation and antioxidants mechanisms, this review discusses the current understanding of the influence of micellar structures on lipid oxidation. In particular, is discussed the major impact of the presence of micelles in emulsions, or reverse micelles (association colloids) in bulk oil on the oxidative stability of both systems. Indeed, both micelles in emulsions and associate colloids in bulk oils are discussed in this review as nanoscale structures that can serve as reservoirs of antioxidants and pro-oxidants and are involved in their transport within the concerned system. Their role as nanoreactors where lipid oxidation reactions occur is also commented.

Oleochemistry potential from Brazil northeastern exotic plants

Caatinga is a Brazilian semi-arid ecosystem that stands out for presenting unique environmental characteristics with a dry, spiny and deciduous shrub/forest vegetation with several species that can be renewable oil sources with potential applicability in oleochemical and nutrition. Caatinga oilseeds have a high content of unsaturated fatty acids, phytosterols and sterols, and this composition is related to its nutritional potential. The present review summarizes the knowledge on the oil contents and fatty acid profiles of seeds from six representatives caatinga species. It was observed that plants species like Caju (Anacardium occidentale L.), Favela (Cnidoscolus quercifolius Pohl), Licuri (Syagrus coronata (Mart.) Becc.), Pinhão-bravo (Jatropha mollissima Pohl Baill), Pequi (Caryocar brasiliense Camb) and Oiticica (Licania rígida Benth) contains approximately 33.1, 33.5, 49.2, 18.3, 70.16 and 57.0% w/w of oil, respectively, on a dry weight basis. Their fatty acid profiles are mostly saturated for Licuri oil, with a high content of lauric acid (up to 40%) and unsaturated for Favela, Pinhão-bravo, Cashew nut, Pequi and Oiticica oils. Oiticica oil shows a high concentration of unusual conjugated polyunsaturated fatty acids, like α-Eleostearic and Licanic acid with 16.90 and 43.20% w/w, respectively.

Synthesis and Evaluation of Antioxidant Activities of Novel Hydroxyalkyl Esters and Bis-Aryl Esters Based on Sinapic and Caffeic Acids

Novel hydroxyalkyl esters and bis-aryl esters were synthesized from sinapic and caffeic acids and aliphatic α,ω-diols of increasing chain lengths from 2 to 12 carbon atoms. Then, their antiradical reactivity (DPPH assay) and their antioxidant activity in a model oil-in-water emulsion (CAT assay) were evaluated. All the esters showed lower antiradical activities compared to their corresponding phenolic acid. This decrease was associated with the steric hindrance in hydroxyalkyl esters, and intramolecular interactions in bis-aryl esters. Regarding the two bis-aryl esters series in emulsion, the antioxidant capacity was improved with alkyl chain lengthening up to four carbons, after which it decreased for longer chains. This "cutoff" effect was not observed for both hydroxyalkyl esters series for which the alkyl chain lengthening results in a decrease of the antioxidant activity.

Investigation on the Double CutOff Phenomenon Observed in Protocatechuic Acid and Its Alkyl Esters under Various CAT-Based Assays

A strange cutoff phenomenon of a series of protocatechuic acid alkyl esters had been noticed using the conjugated autoxidizable triene (CAT) assay. Two parabolic shapes of antioxidant activities of protocatechuic acid alkyl esters described as ″the double cutoff effect″ have been speculated as a result of an oxidative driving force generated in the aqueous phase. The aim of this research was to investigate the double cutoff effect using various types of oxidation driving forces in different CAT-based assays. To further explain the phenomenon, the natural oxidation of conjugated autoxidizable triene (NatCAT) assay has been developed for the first time by relying solely on only the lipid autoxidation of tung oil-in-water (O/W) emulsions. In conclusion, NatCAT exhibited different antioxidant and oxidation patterns from both CAT and apolar radical-initiated CAT assays, and only one cutoff point was obtained. This discovery would lead to a greater understanding of the complexity of antioxidant/lipid oxidation dynamics in O/W emulsion systems.

Sinapine, but not sinapic acid, counteracts mitochondrial oxidative stress in cardiomyocytes

Introduction

When confronted to stress or pathological conditions, the mitochondria overproduce reactive species that participate in the cellular dysfunction. These organelles are however difficult to target with antioxidants. A feature of mitochondria that can be used for this is the negatively charged compartments they form. Most of mitochondrion-targeting antioxidants are therefore cationic synthetic molecules. Our hypothesis is that such mitochondriotropic traits might also exists in natural molecules.

Aim

We tested here whether sinapine, a natural phenolic antioxidant-bearing a permanent positive charge, can target mitochondria to modulate mitochondrial oxidative stress.

Methods

Experiments were performed in-vitro, in-cellulo, ex-vivo, and in-vivo, using cardiac tissue. The sinapic acid -lacking the positively-charged-choline-moiety present in sinapine-was used as a control. Sinapine entry into mitochondria was investigated in-vivo and in cardiomyocytes. We used fluorescent probes to detect cytosolic (H₂DCFDA) and mitochondrial (DHR₁₂₃) oxidative stress on cardiomyocytes induced with either hydrogen peroxide (H₂O₂) or antimycin A, respectively. Finally, ROS production was measured with DHE 10 min after ischemia-reperfusion (IR) on isolated heart, treated or not with sinapine, sinapic acid or with a known synthetic mitochondrion-targeted antioxidant (mitoTempo).

Results

We detected the presence of sinapine within mitochondria in-vitro, after incubation of isolated cardiomyocytes, and in-vivo, after oral treatment. The presence of sinapic acid was not detected in the mitochondria. Both the sinapine and the sinapic acid limited cytosolic oxidative stress in response to H₂O₂. Only sinapine was able to blunt oxidative stress resulting from antimycin A-induced mtROS. Both mitoTempo and sinapine improved cardiac functional recovery following IR. This was associated with lower ROS production within the cardiac tissue.

Conclusion

Sinapine, a natural cationic hydrophilic phenol, commonly and substantially found in rapeseed species, effectively (i) enters within the mitochondria, (ii) selectively decreases the level of mitochondrial oxidative stress and, (iii) efficiently limits ROS production during cardiac ischemia-reperfusion.

•

Sinapine, a choline ester of sinapic acid, enters within mitochondria, whereas sinapic acid does not.

•

Sinapine reduces mitochondrial oxidative stress, whereas sinapic acid does not.

•

Sinapine reduces cardiac reactive oxygen species production during ischemia-reperfusion, whereas sinapic does not.

Nanoliposomes and Tocosomes as Multifunctional Nanocarriers for the Encapsulation of Nutraceutical and Dietary Molecules

Nanoscale lipid bilayers, or nanoliposomes, are generally spherical vesicles formed by the dispersion of phospholipid molecules in a water-based medium by energy input. The other nanoscale object discussed in this entry, i.e., tocosome, is a recently introduced bioactive carrier made mainly from tocopheryl phosphates. Due to their bi-compartmental structure, which consists of lipidic and aqueous compartments, these nanocarriers are capable of carrying hydrophilic and hydrophobic material separately or simultaneously. Nanoliposomes and tocosomes are able to provide protection and release of sensitive food-grade bioactive materials in a sustained manner. They are being utilized for the encapsulation of different types of bioactive materials (such as drugs, vaccines, antimicrobials, antioxidants, minerals and preservatives), for the enrichment and fortification of different food and nutraceutical formulations and manufacturing of functional products. However, a number of issues unique to the nutraceutical and food industry must first be resolved before these applications can completely become a reality. Considering the potentials and promises of these colloidal carrier systems, the present article reviews various aspects of nanoliposomes, in comparison with tocosomes, including the ingredients used in their manufacture, formation mechanisms and issues pertaining to their application in the formulation of health promoting dietary supplements and functional food products.

Eleostearic phospholipids as probes to evaluate antioxidants efficiency against liposomes oxidation

Regardless of the applications: therapeutic vehicle or membrane model to mimic complex biological systems; it is of a great importance to develop simplified, reproducible and rapid model assays allowing for a relevant assessment of the liposomal membrane oxidation and therefore antioxidant activity of selected molecules. Here, we describe a new and high-throughput assay that we called "Vesicle Conjugated Autoxidizable Triene (VesiCAT)". It is based on specific UV absorbance spectral properties of a new phospholipid probe, synthesized with natural conjugated eleostearic acid extracted from Tung oil. The VesiCAT assay has been developed with two different radical generators (2,2'-azobis(2-amidinopropane) dihydrochloride; AAPH and 2,2'-azobis(2,4-dimethylvaleronitrile); AMVN), producing a constant flux of oxidant species, either in membrane or in aqueous phase. This method appears very efficient in assessing the effect of various pure antioxidant molecules in their ability to preserve liposomes from oxidative degradation. In addition, the AAPH- and AMVN-induced oxidations offer the possibility of extracting different but complementary information with respect to the antioxidants efficacy.

Octyl gallate, a food additive with potential beneficial properties to treat Helicobacter pylori infection

Helicobacter pylori infection is marked by intense production of reactive oxygen species (ROS) through the activation of neutrophils that are constantly attracted to the infected gastric mucosa. Here, gallic acid and its alkyl esters were evaluated as compounds able to act as antimicrobial agents and inhibitors of ROS released by H. pylori-activated neutrophils simultaneously. We found that the higher hydrophobicity caused by esterification of gallic acid led to a significant increase in its ability as a cytotoxic agent against H. pylori, a scavenger of ROS and an inhibitor of NADPH oxidase in neutrophils. Octyl gallate, a widely used food additive, showed the highest antimicrobial activity against H. pylori, with a minimum inhibitory concentration (MIC) value of 125 μg mL^-1, whereas gallic acid had a MIC value higher than 1000 μg mL^-1. The production of superoxide anion radicals was almost 100% abolished by the addition of 10 μM (2.82 μg mL^-1) octyl gallate, whereas gallic acid inhibited around 20%. A similar tendency was also found when measuring the production of hypochlorous acid. The protective effect of the esters was cytochemically confirmed. In conclusion, this study showed that hydrophobicity is a crucial factor to obtain a significant anti-ROS and anti-H. pylori activity. Finally, it highlights octyl gallate, a food additive widely used in the food industry, as a promising molecule in the treatment of H. pylori infection.

Comparison of Antioxidant Evaluation Assays for Investigating Antioxidative Activity of Gallic Acid and Its Alkyl Esters in Different Food Matrices

The addition of antioxidants is one of the strategies to inhibit lipid oxidation, a major cause of lipid deterioration in foods leading to rancidity development and nutritional losses. However, several studies have been reported that conventional antioxidant assays, e.g., TPC, ABTS, FRAP, and ORAC could not predict antioxidant performance in several foods. This study aimed to investigate the performance of two recently developed assays, e.g., the conjugated autoxidizable triene (CAT) and the apolar radical-initiated conjugated autoxidizable triene (ApoCAT) assays to predict the antioxidant effectiveness of gallic acid and its esters in selected food models in comparison with the conventional antioxidant assays. The results indicated that the polarities of the antioxidants have a strong impact on antioxidant activities. In addition, different oxidant locations demonstrated by the CAT and ApoCAT assays influenced the overall antioxidant performances of the antioxidants with different polarities. To validate the predictability of the assays, the antioxidative performance of gallic acid and its alkyl esters was investigated in oil-in-water (O/W) emulsions, bulk soybean oils, and roasted peanuts as the lipid food models. The results showed that only the ApoCAT assay could be able to predict the antioxidative performances in O/W emulsions regardless of the antioxidant polarities. This study demonstrated that the relevance of antioxidant assays to food models was strongly dependent on physical similarities between the tested assays and the food structure matrices.

Enhanced lipid and biomass production by a newly isolated and identified marine microalga

BACKGROUND

The increasing demand for microalgae lipids as an alternative to fish has encouraged researchers to explore oleaginous microalgae for food uses. In this context, optimization of growth and lipid production by the marine oleaginous V₂-strain-microalgae is of great interest as it contains large amounts of mono-unsaturated (MUFAs) and poly-unsaturated fatty acids (PUFAs).

METHODS

In this study, the isolated V₂ strain was identified based on 23S rRNA gene. Growth and lipid production conditions were optimized by using the response surface methodology in order to maximize its cell growth and lipid content that was quantified by both flow cytometry and the gravimetric method. The intracellular lipid bodies were detected after staining with Nile red by epifluorescence microscopy. The fatty acid profile of optimal culture conditions was determined by gas chromatography coupled to a flame ionization detector.

RESULTS

The phenotypic and phylogenetic analyses showed that the strain V₂ was affiliated to Tetraselmis genus. The marine microalga is known as an interesting oleaginous species according to its high lipid production and its fatty acid composition. The optimization process showed that maximum cell abundance was achieved under the following conditions: pH: 7, salinity: 30 and photosynthetic light intensity (PAR): 133 μmol photons.m^-2.s^-1. In addition, the highest lipid content (49 ± 2.1% dry weight) was obtained at pH: 7, salinity: 37.23 and photosynthetic light intensity (PAR): 188 μmol photons.m^-2.s^-1. The fatty acid profile revealed the presence of 39.2% and 16.1% of total fatty acids of mono-unsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs), respectively. Omega 3 (ω3), omega 6 (ω6) and omega 9 (ω9) represented 5.28%, 8.12% and 32.8% of total fatty acids, respectively.

CONCLUSIONS

This study showed the successful optimization of salinity, light intensity and pH for highest growth, lipid production and a good fatty acid composition, making strain V₂ highly suitable for food and nutraceutical applications.

What makes good antioxidants in lipid-based systems? The next theories beyond the polar paradox

The polar paradox states that polar antioxidants are more active in bulk lipids than their nonpolar counterparts, whereas nonpolar antioxidants are more effective in oil-in-water emulsion than their polar homologs. However, recent results, showing that not all antioxidants behave in a manner proposed by this hypothesis in oil and emulsion, lead us to revisit the polar paradox and to put forward new concepts, hypotheses, and theories. In bulk oil, new evidences have been brought to demonstrate that the crucial site of oxidation is not the air-oil interface, as postulated by the polar paradox, but association colloids formed with traces of water and surface active molecules such as phospholipids. The role of these association colloids on lipid oxidation and its inhibition by antioxidant is also addressed as well as the complex influence of the hydrophobicity on the ability of antioxidants to protect lipids from oxidation. In oil-in water emulsion, we have covered the recently discovered non linear (or cut-off) influence of the hydrophobicity on antioxidant capacity. For the first time, different mechanisms of action are formulated in details to try to account for this nonlinear effect. As suggested by the great amount of biological studies showing a cut-off effect, this phenomenon could be widespread in dispersed lipid systems including emulsions and liposomes as well as in living systems such as cultured cells. Works on the cut-off effect paves the way for the determination of the critical chain length which corresponds to the threshold beyond which antioxidant capacity suddenly collapses. The systematic search for this new physico-chemical parameter will allow designing novel phenolipids and other amphiphilic antioxidants in a rational fashion. Finally, in both bulk oils and emulsions, we feel that it is now time for a paradigm shift from the polar paradox to the next theories.

Redox-active biflavonoids from Garcinia brasiliensis as inhibitors of neutrophil oxidative burst and human erythrocyte membrane damage

ETHNOPHARMACOLOGICAL RELEVANCE

Garcinia brasiliensis, a plant native to the Brazilian Amazon Rainforest, is used in traditional medicine to treat inflammation of the urinary tract, peptic ulcers, arthritis and other conditions.

AIM OF THE STUDY

The purposes of this study were to analyze the chemical constituents of G. brasiliensis branches and leaves and to evaluate the potential of isolated compounds to act as inhibitors of both the oxidative burst of stimulated neutrophils and oxidative damage in human erythrocyte membranes to verify the antioxidant and anti-inflammatory effects of this plant.

MATERIALS AND METHODS

Neutrophils were isolated from the blood of healthy donors by Ficoll-Paque density gradient centrifugation. Superoxide anion and total reactive oxygen species (ROS) produced by stimulated neutrophils were measured by WST-1 reduction and luminol-enhanced chemiluminescence assays, respectively. Radical-induced lipoperoxidation and hemolysis were performed using erythrocytes from the blood of healthy donors. Compounds were isolated from G. brasiliensis branches and leaves by HPLC microfractionation, and structure elucidation of the isolated compounds was performed based on NMR and HR-MS analyses.

RESULTS

The biflavonoids procyanidin, fukugetin, amentoflavone and podocarpusflavone isolated from G. brasiliensis showed potent inhibitory effects on the oxidative burst of human neutrophils, inhibiting ROS production by 50% at 1 μmol L(-1). These biflavonoids also proved to be potent inhibitors of hemolysis (with 88 ± 7% inhibition at 50 µmol L(-1) for procyanidin) and lipid peroxidation in human erythrocytes, with a malondialdehyde level (a biomarker of oxidative stress) of 8.5 ± 0.3 nmol/mg Hb at 50 µmol L(-1) for procyanidin.

CONCLUSIONS

These findings indicate that the biflavonoids extracted from G. brasiliensis branches and leaves modulate oxidative stress via inhibition of NADPH oxidase and ROS production by stimulated human neutrophils. Furthermore, the biflavonoids exhibited potent inhibition of oxidant hemolysis and lipid peroxidation induced by AAPH in human erythrocytes. Therefore, these studies suggest the use of G. brasiliensis extract as an antioxidant and anti-inflammatory agent.

Synthesis of Lipophilic Antioxidants by a Lipase-B-Catalyzed Addition of Peracids to the Double Bond of 4-Vinyl-2-methoxyphenol

4-Vinyl guaiacol (2) was lipophilized through the electrophilic addition of peracids to its vinylic double bond. Those peracids were formed in situ, by the Candida antarctica lipase-B-assisted perhydrolysis of carboxylic acids ranging from C2 to C18, in hydrogen peroxide solution. The addition of peracids with 4-8 carbons in their alkyl chains led to the formation of two regioisomers, with the prevalence of hydroxyesters bearing a primary free hydroxyl (4c-4e). This prevalence became more pronounced when peracids with longer alkyl chains (C10-C18) were used. In this case, only isomers 4f-4h were formed. The antioxidant activity of the resulting hydroxyesters was assessed by means of the conjugated autoxidizable triene (CAT) assay, and it was found out that the 4-vinyl guaiacol antioxidant activity was significantly increased by grafting alkyl chains with 2-8 carbons.

Apolar Radical Initiated Conjugated Autoxidizable Triene (ApoCAT) Assay: Effects of Oxidant Locations on Antioxidant Capacities and Interactions

Development of an antioxidant assay explaining antioxidant behaviors in complex food systems has been a challenging topic for food scientists. This research aimed to investigate antioxidant capacities and interactions of selected synthetic antioxidants and commercial natural antioxidant extracts using the CAT assay and a newly developed ApoCAT assay, which used water- and lipid-soluble azo radical initiators, respectively. Results suggested that the higher the hydrophobicity of an antioxidant, the higher the antioxidant capacity of an antioxidant observed in the ApoCAT assay. The relationship between the two different assays was explained by the ratio between the ApoCAT and the CAT values. Interestingly, all lipophilic derivatives of the antioxidants exhibited higher ApoCAT/CAT ratios than their hydrophilic derivatives. In the case of the commercial food-grade antioxidants, green tea extract and mixed tocopherols showed a higher antioxidant capacity in the ApoCAT assay than in the CAT assay, while grape seed and rosemary extracts did not show significantly different changes in behaviors in both assays. The study on antioxidant interactions revealed that additive, synergistic, and antagonistic effects between hydrophilic antioxidants and natural extracts, and mixed tocopherols could be observed in both the CAT and the ApoCAT assays, depending on the combined ratios. In most cases, at a particular ratio, the synergistic effect reached the maximum level before suddenly dropping to additive and antagonistic effects in both assays.

Antioxidant activity of protocatechuates evaluated by DPPH, ORAC, and CAT methods

Hibiscus sabdariffa L. is a worldwide consumed plant, principally after infusion of its dried sepals and calyces, which are usually discarded. Nevertheless, they represent a potential source of natural bioactive compounds, e.g. polyphenols, which could add value to this under-exploited plant. Protocatechuic acid (PA) was chosen as a model of the phenolic acids that can be extracted from H. sabdariffa. In order to modify PA hydrophilic character, which limits its use in lipid-rich food products, PA was esterified to C1-C18 alcohols, and the impact of lipophilization on its antioxidant activity was evaluated in both, an homogeneous (DPPH and ORAC methods) and an heterogeneous (CAT method) system. Results herein obtained showed that, depending on the grafted alkyl chain length, lipophilization could positively affect the antioxidant activity of PA in heterogeneous media; therefore, support its use as an innovative way to synthesize molecules with an improved antioxidant capacity and potential to be used as multifunctional preservatives in food.

Hydrophobicity and antioxidant activity acting together for the beneficial health properties of nordihydroguaiaretic acid

Nordihydroguaiaretic acid (NDGA) and rosmarinic acid (RA), phenolic compounds found in various plants and functional foods, have known antioxidant and anti-inflammatory properties. In the present study, we comparatively investigated the importance of hydrophobicity and oxidisability of NDGA and RA, regarding their antioxidant and pharmacological activities. Using a panel of cell-free antioxidant protocols, including electrochemical measurements, we demonstrated that the anti-radical capacities of RA and NDGA were similar. However, the relative capacity of NDGA as an inhibitor of NADPH oxidase (ex vivo assays) was significantly higher compared to RA. The inhibitory effect on NADPH oxidase was not related to simple scavengers of superoxide anions, as confirmed by oxygen consumption by the activated neutrophils. The higher hydrophobicity of NDGA was also a determinant for the higher efficacy of NDGA regarding the inhibition of the release of hypochlorous acid by PMA-activated neutrophil and cytokine (TNF-α and IL-10) production by Staphylococcus aureus-stimulated peripheral blood mononuclear cells. In conclusion, although there have been extensive studies about the pharmacological properties of NDGA, our study showed, for the first time, the importance not only of its antioxidant activity, but also its hydrophobicity as a crucial factor for pharmacological action.

Antioxidant properties and efficacies of synthesized alkyl caffeates, ferulates, and coumarates

Caffeic, ferulic, and coumaric acids were lipophilized with saturated fatty alcohols (C1-C20). The antioxidant properties of these hydroxycinnamic acids and their alkyl esters were evaluated in various assays. Furthermore, the antioxidant efficiency of the compounds was evaluated in a simple o/w microemulsion using the conjugated autoxidizable triene (CAT) assay. All evaluated phenolipids had radical scavenging, reducing power, and metal chelating properties. Only caffeic acid and caffeates were able to form a complex with iron via their catechol group in the phenolic ring. In the o/w emulsion, the medium chain phenolipids of the three homologues series were most efficient. The antioxidant properties and efficacies were dependent upon functional groups substituted to the ring structure and were in the following order: caffeic acid and caffeates > ferulic acid and ferulates > coumaric acid and coumarates. Moreover, the results demonstrated that the test system has an impact on the antioxidative properties measured.

Caffeic Acid phenethyl ester: consequences of its hydrophobicity in the oxidative functions and cytokine release by leukocytes

Numerous anti-inflammatory properties have been attributed to caffeic acid phenethyl ester (CAPE), an active component of propolis. NADPH oxidases are multienzymatic complexes involved in many inflammatory diseases. Here, we studied the importance of the CAPE hydrophobicity on cell-free antioxidant capacity, inhibition of the NADPH oxidase and hypochlorous acid production, and release of TNF-α and IL-10 by activated leukocytes. The comparison was made with the related, but less hydrophobic, caffeic and chlorogenic acids. Cell-free studies such as superoxide anion scavenging assay, triene degradation, and anodic peak potential (E_pa) measurements showed that the alterations in the hydrophobicity did not provoke significant changes in the oxidation potential and antiradical potency of the tested compounds. However, only CAPE was able to inhibit the production of superoxide anion by activated leukocytes. The inhibition of the NADPH oxidase resulted in the blockage of production of hypochlorous acid. Similarly, CAPE was the more effective inhibitor of the release of TNF-α and IL-10 by Staphylococcus aureus stimulated cells. In conclusion, the presence of the catechol moiety and the higher hydrophobicity were essential for the biological effects. Considering the involvement of NADPH oxidases in the genesis and progression of inflammatory diseases, CAPE should be considered as a promising anti-inflammatory drug.

Voltammetric determination of TBHQ at a glassy carbon electrode surface activated by in situ chemical oxidation

Bare GCE surface is directly activated by in situ chemical method, and the modified GCE exhibits a rougher surface and a negative-charge characteristic.

Apocynin: chemical and biophysical properties of a NADPH oxidase inhibitor

Apocynin is the most employed inhibitor of NADPH oxidase (NOX), a multienzymatic complex capable of catalyzing the one-electron reduction of molecular oxygen to the superoxide anion. Despite controversies about its selectivity, apocynin has been used as one of the most promising drugs in experimental models of inflammatory and neurodegenerative diseases. Here, we aimed to study the chemical and biophysical properties of apocynin. The oxidation potential was determined by cyclic voltammetry (Epa = 0.76V), the hydrophobicity index was calculated (logP = 0.83) and the molar absorption coefficient was determined (e275nm = 1.1 × 104 M-1 cm-1). Apocynin was a weak free radical scavenger (as measured using the DPPH, peroxyl radical and nitric oxide assays) when compared to protocatechuic acid, used here as a reference antioxidant. On the other hand, apocynin was more effective than protocatechuic acid as scavenger of the non-radical species hypochlorous acid. Apocynin reacted promptly with the non-radical reactive species H2O2 only in the presence of peroxidase. This finding is relevant, since it represents a new pathway for depleting H2O2 in cellular experimental models, besides the direct inhibition of NADPH oxidase. This could be relevant for its application as an inhibitor of NOX4, since this isoform produces H2O2 and not superoxide anion. The binding parameters calculated by fluorescence quenching showed that apocynin binds to human serum albumin (HSA) with a binding affinity of 2.19 × 104 M-1. The association did not alter the secondary and tertiary structure of HSA, as verified by synchronous fluorescence and circular dichroism. The displacement of fluorescent probes suggested that apocynin binds to site I and site II of HSA. Considering the current biomedical applications of this phytochemical, the dissemination of these chemical and biophysical properties can be very helpful for scientists and physicians interested in the use of apocynin.

Antioxidants and physical integrity of lipid bilayers under oxidative stress

Giant unilamellar vesicles (GUVs of diameter 5-25 μm) of soy phosphatidylcholine (PC), resistant to intense light exposure (400-440 nm, ~15 mW·mm(-2)), underwent budding when containing chlorophyll a (Chla) in the lipid bilayer ([PC]:[Chla] = 1500:1). On the basis of image heterogeneity analysis using inverted microscopy, a dimensionless entropy parameter for the budding process was shown to increase linearly during an initial budding process. Lipophilic β-carotene (β-Car, [PC]:[β-Car] = 500:1) reduced the initial budding rate by a factor of 2.4, while the hydrophilic glycoside rutin ([PC]:[rutin] = 500:1) had no effect. Chla photosensitized oxidation of PC to form linoleoyl hydroperoxides, further leading to domains of higher polarity in the vesicles, is suggested to trigger budding. The average dipole moment (μ) of linoleic acid hydroperoxides was calculated using density functional theory (DFT) to have the value of 2.84 D, while unoxidized linoleic acid has μ = 1.86 D. β-Carotene as a lipophilic antioxidant and singlet-oxygen quencher seems to hamper oxidation in the lipid bilayers and delay budding in contrast to rutin located in the aqueous phase. The effect on budding of GUVs as a detrimental process for membranes is suggested for use in assays for evaluation of potential protectors of cellular integrity and functions under oxidative stress.

Determination of antimutagenic properties of apigenin-7-O-rutinoside, a flavonoid isolated from Mentha longifolia (L.) Huds. ssp. longifolia with yeast DEL assay

Lamiaceae is an important plant family that has been investigated for its medicinal properties due to its large amounts of phenolic acids and flavonoids. Flavonoids have been shown to have antioxidant and antimutagenic activities in different test systems, but their certain mechanisms are still unclear. This study was designed to evaluate the mutagenic and antimutagenic activities of apigenin 7-O-rutinoside, a flavonoid isolated from Mentha longifolia (L.) Huds. ssp. longifolia. The possible antimutagenic potential of apigenin 7-O-rutinoside (A7R) was examined against mutagens ethyl methanesulfonate (EMS) and acridine (AC) in a eukaryotic cell system Saccharomyces cerevisiae RS112. The results showed that A7R has different inhibition rates against EMS and AC-induced mutagenicity. Thus, the properties of A7R are of great pharmacological importance and might be beneficial for reducing the risk of reactive oxygen species-related diseases.

Antioxidant properties of chlorogenic acid and its alkyl esters in stripped corn oil in combination with phospholipids and/or water

In bulk oil, it is generally thought that hydrophilic antioxidants are more active than lipophilic antioxidants. To test this hypothesis, the antioxidant activity of phenolics with increasing hydrophobicity was evaluated in stripped corn oil using both conjugated diene and hexanal measurements. Chlorogenic acid and its butyl, dodecyl, and hexadecyl esters were used as model phenolic antioxidants with various hydrophobicities. Results showed that hydrophobicity did not correlate well with antioxidant capacity. The combination of chlorogenic acid derivatives with dioleoylphosphatidylcholine (DOPC) and/or water was also studied to determine if the physical structure in the oil affected antioxidant activity. DOPC alone made hexadecyl chlorogenate a less effective antioxidant, but it did not change the antioxidant capacity of chlorogenic acid. In contrast, the combination of DOPC and water (∼400 ppm) renders chlorogenic acid a less active antioxidant, whereas it does not change the activity of hexadecyl chlorogenate. These results show, in bulk oil, that intrinsic parameters such as the hydrophobicity of lipophilized phenolics do not exert a strong influence on antioxidant capacity, but they can be highly influential if potentialized by extrinsic factors such as physical structures in the oil.

Does hydrophobicity always enhance antioxidant drugs? A cut-off effect of the chain length of functionalized chlorogenate esters on ROS-overexpressing fibroblasts

OBJECTIVES

Phenolic antioxidants are currently attracting a growing interest as potential therapeutic agents to counteract diseases associated with oxidative stress. However, their high hydrophilicity results in a poor bioavailability hindering the development of efficient antioxidant strategies. A promising way to overcome this is to increase their hydrophobicity by lipophilic moiety grafting to form the newly coined 'phenolipids'. Although hydrophobicity is generally considered as advantageous regarding antioxidant properties, it is nevertheless worth investigating whether increasing hydrophobicity necessarily leads to a more efficient antioxidant drug.

METHODS

To answer this question, the antioxidant capacity of a homologous series of phenolics (chlorogenic acid and its methyl, butyl, octyl, dodecyl and hexadecyl esters) toward mitochondrial reactive oxygen species (ROS) generated in a ROS-overexpressing fibroblast cell line was investigated using 2',7'-dichlorodihydrofluorescein.

KEY FINDINGS

Overall, the long chain esters (dodecyl and hexadecyl esters) were more active than the short ones (methyl, butyl, and octyl esters), with an optimal activity for dodecyl chlorogenate. Moreover, dodecyl chlorogenate exerted a strong antioxidant capacity, for concentration and incubation time below the cytotoxicity threshold, making it a promising candidate for further in-vivo studies. More importantly, we found that the elongation of the chain length from 12 to 16 carbons led unexpectedly to a 45% decrease of antioxidant capacity.

CONCLUSION

The understanding of this sudden collapse of the antioxidant capacity through the cut-off theory will be discussed in this article, and may contribute towards development of a rational approach to design novel amphiphilic antioxidant drugs, especially phenolipids with medium fatty chain.

Methods for evaluating the potency and efficacy of antioxidants

PURPOSE OF REVIEW

The aim of this article is to present a brief panorama of the most widely used methods and of new analytical approaches for evaluating antioxidant capacity and to discuss them in terms of advantages and drawbacks.

RECENT FINDINGS

To date, many in-vitro tests are available from the chemical assay performed in a homogenous solution such as oxygen radical antioxidant capacity assay to more complex cell-based methods using exogenic probes to detect oxidation. In complement to these existing methods, novel approaches have recently been developed such as the conjugated autoxidizable triene assay implemented in emulsions and using tung oil as ultraviolet probe.

SUMMARY

The complexity and diverse range of research topics investigated have led to the development of a multitude of tests, but unfortunately none of them are universal. Thus, one of the major challenges is to know which method is best suited for a particular application.

Differentiation between phenol- and amino-substances in voltammetry determination of synthetic antioxidants in oils

The paper describes a method of voltammetric determination of antioxidants in lubricating oils developed with the use of Linear Sweep Voltammetry (LSV) and Fast Scan Differential Pulse Voltammetry (FSDPV). Experimental conditions have been found for simultaneous determination of phenol-based antioxidants and amino-antioxidants: the phenols can be electrochemically oxidized using the polarisation of gold disc electrode (AuDE) in the potential range of 0–1400 mV in 0.2 M H2SO4 in the presence of ethanol and acetonitrile at the ratio of 3:1. Secondary aromatic amines can be determined directly in this supporting electrolyte; the presence of phenolic antioxidants does not interfere with this analysis. On the other hand, secondary aromatic amines interfere with the determination of phenolic substances; therefore, the amines present have to be eliminated in a suitable way. A procedure for masking the aromatic amines using their reaction with nitrous acid has been suggested and optimised. The nitrosamines thus formed can be used for sensitive and selective determination of amino-antioxidants by means of cathodic reduction on the hanging mercury drop electrode (HMDE) using Fast Scan Differential Pulse Voltammetry. The method was applied in analysis of real samples of lubricating oils.

Relationship between hydrophobicity and antioxidant ability of "phenolipids" in emulsion: a parabolic effect of the chain length of rosmarinate esters

The polar paradox predicts that hydrophobic antioxidants are more active in emulsions than their hydrophilic homologues, thus assuming a linear dependency between hydrophobicity and antioxidant capacity. In contrast, we formulate in this paper an alternative hypothesis assuming a possible nonlinear dependency. To verify this so-called "nonlinear hypothesis", the antioxidant capacity of a homologous series of rosmarinic acid and its alkyl esters (methyl, butyl, octyl, dodecyl, hexadecyl, octadecyl, and eicosyl) was evaluated using a newly developed conjugated autoxidizable triene (CAT) assay. It appeared that the antioxidant capacity increases as the alkyl chain is lengthened, with a maximum for the octyl chain, after which further chain extension leads to a collapse in antioxidant capacity. This nonlinear effect was discussed in relation to the "cutoff effect" generally observed in studies using cultured cells. This new hypothesis may provide a better understanding of the antioxidant behavior of phenolics in emulsion which is a key to develop new antioxidant strategies to protect lipid substrates from oxidation. Moreover, the lipophilization with medium chain appeared as a promising way to enhance the antioxidant capacity of phenolics since octyl rosmarinate was three times more effective than rosmarinic acid which is already one of the most powerful known phenolic antioxidant. Finally, this work paves the way for systematic investigation of the chain length effect to design new "phenolipids" in a rational fashion.

Kinetic and stoichiometry of the reaction of chlorogenic acid and its alkyl esters against the DPPH radical

The lipophilization of polar antioxidants such as phenolics is an efficient way to enhance their solubility in apolar media. Thus, in emulsified systems, lipophilized antioxidants are supposed to locate at the lipid/aqueous phase interface and to lead to a better protection of unsaturated lipids. Herein, the antiradical activity of chlorogenic acid (5-CQA) and its corresponding esters with seven fatty alcohols (from methanol to eicosanol) have been achieved using the well-known 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Hydrophobation was shown to significantly improve the antiradical activity of 5-CQA esters which reached a maximum for butyl- and octyl-chlorogenate. In addition, for both 5-CQA and its esters, it was demonstrated that the global mechanism of DPPH* stabilization proceeded likely by electron transfer (ET), while it appeared that the pathways of DPPH* stabilization were different between 5-CQA and its esters, as confirmed by the LC-MS characterization of reaction products. Finally, strong differences were found between the tested molecules allowing the proposal of different DPPH* stabilization pathways by electron transfer for 5-CQA and its esters.