Mechanism of Chain Termination in Lipid Peroxidation by Carotenes: A Theoretical Study

Daily Dietary Antioxidant Interactions Are Due to Not Only the Quantity but Also the Ratios of Hydrophilic and Lipophilic Phytochemicals

The hydrophilic extracts of mulberry (HEM) and blueberry (HEB) and lipophilic extracts of mango (LEM) and watermelon (LEW) were mixed in different ratios to assess the antioxidant interactions by chemical-based (DPPH and ABTS assays) and H9c2 cell-based models. There were both synergistic and antagonistic antioxidant interactions among these fruits. Some groups with combinational extracts showed stronger synergistic antioxidant effects than the individual groups, and others (HEM-LEW F1/10, LEW-LEM F5/10, and HEB-LEM F3/10) showed stronger antagonistic effects than the individual groups based on the indicators [the values of DPPH, ABTS, and MTT; the expression of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and malondialdehyde (MDA); the release of lactate dehydrogenase (LDH); and the quantification of cellular antioxidant activity]. The principal component analysis (PCA) showed that samples could be defined by two principal components: PC1, the main phenolic acids and anthocyanins, and PC2, carotenoids. From our results, primarily, carotenoids were in the majority in antagonistic groups, and phenolics and anthocyanins were in the majority in synergistic groups. However, the combinational groups containing only hydrophilic compounds did not always show synergistic effects. Therefore, the compatibility of diets indicates balancing the ratios of hydrophilic and lipophlic compounds in our daily food. In addition, the expression of enzymes (SOD, GSH-Px, and CAT) may not be sensitive to the changes of antioxidant activity caused by the combinations with different ratios of hydrophilic and lipophilc compounds. The different structures of lipophilic compounds (β-carotene and lycopene) could influence the antagonistic effects.

Peroxyl radical reactions with carotenoids in microemulsions: Influence of microemulsion composition and the nature of peroxyl radical precursor

The reactions of acetylperoxyl radicals with different carotenoids (7,7'-dihydro-β-carotene and ζ-carotene) in SDS and CTAC microemulsions of different compositions were investigated using laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy. The primary objective of this study was to explore the influence of microemulsion composition and the type of surfactant used on the yields and kinetics of various transients formed from the reaction of acetylperoxyl radicals with carotenoids. Also, the influence of the site (hydrocarbon phases or aqueous phase) of generation of the peroxyl radical precursor was examined by using 4-acetyl-4-phenylpiperidine hydrochloride (APPHCl) and 1,1-diphenylacetone (11DPA) as water-soluble and lipid-soluble peroxyl radical precursors, respectively. LFP of peroxyl radical precursors with 7,7'-dihydro-β-carotene (77DH) in different microemulsions gives rise to the formation of three distinct transients namely addition radical (λmax=460 nm), near infrared transient1 (NIR, λmax=700 nm) and 7,7'-dihydro-β-carotene radical cation (77DH(•+), λmax=770 nm). In addition, for ζ-carotene (ZETA) two transients (near infrared transient1 (NIR1, λmax=660 nm) and ζ-carotene radical cation (ZETA(•+), λmax=730-740 nm)) are generated following LFP of peroxyl radical precursors in the presence of ζ-carotene (ZETA) in different microemulsions. The results show that the composition of the microemulsion strongly influences the observed yield and kinetics of the transients formed from the reactions of peroxyl radicals (acetylperoxyl radicals) with carotenoids (77DH and ZETA). Also, the type of surfactant used in the microemulsions influences the yield of the transients formed. The dependence of the transient yields and kinetics on microemulsion composition (or the type of surfactant used in the microemulsion) can be attributed to the change of the polarity of the microenvironment of the carotenoid. Furthermore, the nature of the peroxyl radical precursor used (water-soluble or lipid-soluble peroxyl radical precursors) has little influence on the yields and kinetics of the transients formed from the reaction of peroxyl radicals with carotenoids. In the context of the interest in carotenoids as radical scavenging antioxidants, the fates of the addition radicals (formed from the reaction of carotenoid with peroxyl radicals) and carotenoid radical cations are discussed.

Radical-induced Cis-Trans isomerization of fatty acids: a theoretical study

Trans fatty acids (TFAs) create deleterious effects; thus their existence in humans is a great health concern. TFAs can be obtained through diet, or they can be formed endogenously by radical-induced cis to trans isomerization. The mechanism of isomerization of fatty acid catalyzed by radicals including nitrogen dioxide (NO2(•)), thiyl (RS(•)), and peroxide (ROO(•)) radicals were investigated using density functional theory. With linoleic acid, a fatty acid consisting of two homoconjugated C═C bonds, we found that the radical addition mechanism is more favorable than the hydrogen abstraction mechanism. For all investigated radicals, the isomerization catalyzed by RS(•) radical involves the smallest reaction barrier. We found that NO2(•) reactions through the N-terminus are more favorable than reactions through the O-terminus. The reaction barriers for NO2(•) catalyzed isomerizations were found to be lowered to a larger extent in polar solvent. β-carotene and lycopene were shown to protect fatty acids from isomerization by intercepting the isomerization-causing radicals.

Effect of computed tomography scanning parameters on gold nanoparticle and iodine contrast

PURPOSE

Gold nanoparticles (gold-NPs) have lately been proposed as alternative contrast agents to iodine-based contrast agents (iodine-CA) for computed tomography (CT) angiography. The aims of this study were to confirm an appropriate environment in which to evaluate such novel contrast agents, to investigate the comparative contrast of iodine-CA versus gold-NP, and to determine optimal scanning parameters for gold-NP.

MATERIALS AND METHODS

Three different clinical scanners were used to acquire CT images. A range of concentrations (10 mM to 1.5 M) of gold-NP and iodine-CA were scanned with varying x-ray tube voltages and currents, reconstruction kernels, protocols, and scanner models. The different environments investigated were air, water, and water with a bone simulant (Ca3(PO4)2). Regression coefficients were derived from the attenuation values plotted against concentration and compared for statistical significance using t values.

RESULTS

As expected, contrast was linearly related to concentrations up to 500 to 1000 mM, depending on the conditions used, whereupon a plateau of 3000 Hounsfield units was reached. Attenuation was significantly different depending on the environment used (air, water, or water and bone simulant). Contrast is dependent on the x-ray tube voltage used, with the contrast produced from iodine-CA sharply declining with increasing voltage, whereas the contrast of gold-NP varied less with tube voltage but was maximal at 120 kV in water with bone simulant. Current, reconstruction kernels, protocols, and scanner model had less effect on contrast.

CONCLUSION

Water with a bone simulant is a preferable environment for evaluating novel cardiac CT contrast agents. Relative iodine-CA versus gold-NP contrast is dependent on the scanning conditions used. Optimal scanning conditions for gold-NP will likely use an x-ray tube voltage of 120 kV.

Novel phytonutrient contributors to antioxidant protection against cardiovascular disease

The associations linking endothelial inflammation, endothelial oxidative stress, and atherogenesis and the potential for dietary phytonutrients to decrease the impact of these associations were assessed. A detailed literature review was conducted and summarized. A large body of scientific evidence describes the interactions among endothelial inflammation, endothelial oxidative stress, and atherogenesis. A growing body of research indicates that several dietary phytonutrients (astaxanthin, lycopene, lutein, and glabridin) can decrease the risk for atherosclerosis by decreasing endothelial inflammation and oxidative stress. The consumption of foods or dietary supplements that provide astaxanthin, lycopene, lutein, and glabridin can ameliorate endothelial inflammation and oxidative stress, retard atherogenesis, and decrease the risk for atherogenic cardiovascular disease.

β-carotene radical cation addition to green tea polyphenols. Mechanism of antioxidant antagonism in peroxidizing liposomes

Green tea polyphenols, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG), all showed antioxidative effect in liposomes for lipid oxidation initiated in the lipid phase (antioxidant efficiency EC > EGCG > ECG > EGC) or in the aqueous phase (EC ≫ EGC > EGCG > ECG) as monitored by the formation of conjugated dienes. For initiation in the lipid phase, β-carotene, itself active as an antioxidant, showed antagonism with the polyphenols (EC > ECG > EGCG > EGC). The Trolox equivalent antioxidant capacity (TEAC EGC > EGCG > ECG > EC) correlates with the lowest phenol O-H bond dissociation enthalpy (BDE) as calculated by density functional theory (DFT). Surface-enhanced Raman spectroscopy (SERS) was used to assess the reducing power of the phenolic hydroxyls in corroboration with DFT calculations. For homogeneous (1:9 v/v methanol/chloroform) solution, the β-carotene radical cation reacted readily with each of the polyphenol monoanions (but not with the neutral polyphenols) with a rate approaching the diffusion limit for EC as studied by laser flash photolysis at 25 °C monitoring the radical cation at 950 nm. The rate constant did not correlate with polyphenol HOMO/LUMO energy gap (DFT calculations), and β-carotene was not regenerated by an electron transfer reaction (monitored at 500 nm). It is suggested that the β-carotene radical cation is rather reacting with the tea polyphenols through addition, as further evidenced by steady-state absorption spectroscopy and liquid chromatography-mass spectroscopy (LC-MS), in effect preventing regeneration of β-carotene as an active lipid phase antioxidant and leading to the observed antagonism.