Carotenoids as antioxidants: spin trapping EPR and optical study.

The role of several natural and synthetic carotenoids as scavengers of free radicals was studied in homogeneous solutions. A set of free radicals: *OH, *OOH, and *CH(3) were generated by using the Fenton reaction in dimethyl sulfoxide. It was shown that the spin trapping technique is more informative than optical methods for the experimental conditions under study. 5,5-Dimethyl-pyrroline-N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN) were used as spin traps for the EPR studies. The results show that the scavenging ability of the carotenoids towards radical *OOH correlates with their redox properties.     

Carotenoids as scavengers of free radicals in a Fenton reaction: antioxidants or pro-oxidants?

The spin trapping EPR technique was used to study the influence of carotenoids (beta-carotene, 8'-apo-beta-caroten-8'-al, canthaxanthin, and ethyl 8'-apo-beta-caroten-8'-oate) on the yield of free radicals in the Fenton reaction (Fe(2+) + H(2)O(2) --> Fe(3+) + .OH + -OH) in the organic solvents, DMSO, and methanol. DMPO and PBN were used as spin trapping agents. It was demonstrated that carotenoids could increase or decrease the total yield of free radicals depending on the oxidation potential of the carotenoids and the nature of the radicals. A reaction mechanism is suggested which includes the reduction of Fe(3+) to Fe(2+) by carotenoids. The effectiveness of this carotenoid-driven Fenton reaction increases with a decrease of the scavenging rates for free radicals and with decreasing oxidation potentials of carotenoids.     

Carotenoids as a Raman-active probes of erythrocyte membrane structure.

1. Erythrocyte ghosts exhibit resonance-enhanced Raman bands at 1530 cm(-1) and 1165 cm(-1) attributable to v(-C=C-) and v(=C-C=), respectively, of the conjugated polyene chains in carotenoids. In lipid extract of ghosts, these resonance-enhanced bands lie at 1527 and 1158 cm(-1). The spectra indicate the presence of membrane-bound beta-carotene. 2. The resonance-enhanced Raman spectrum of beta-carotene in lecithin liposomes is identical to that obtained with hexane or chloroform solutions. 3. Increasing proportions of cholesterol in cholesterol-lecithin liposomes up to a cholesterol: phospholipid molar ratio of 0.8-0.9 drastically decreases the intensity of both resonance-enhanced bands. 4. In ghosts the carotenoid bands respond to membrane perturbations. Trypsinization, lysolecithin treatment and reduction of pH increase the intensities of the 1530 and 1165 cm(-1) bands. In contrast, a decrease in the intensity of both bands follows equilibration of ghosts for 15 min at approx. 50 degrees C or addition of (0.1%) sodium dodecyl sulfate. 5. We suggest that perturbants known to change lipid-protein interactions in erythrocyte membranes modify the microenvironment and/or configuration of the membrane-bound carotenoid.     

Role of physiological antioxidants in chromium(VI)-induced cellular injury.

Chromium(VI) compounds are well known to be potent toxic and carcinogenic agents. Because chromium(VI) is easily taken up by cells and is subsequently reduced to the trivalent form, the formation of chromium(III) or other intermediate oxidation states such as chromium(V) and (IV) is believed to play a role in the adverse biological effects of chromium(VI) compounds. Recent in vitro studies have shown that this reduction process generates free radical species such as active oxygen radicals. Furthermore, physiological antioxidants are reported to modify the genotoxic and toxic effects of chromate. This article reviewed the recent in vitro and in vivo studies of the effects of antioxidants including active oxygen scavengers; glutathione; vitamins B2, E, and C, on chromate-induced injury such as DNA lesions; lipid peroxidation; enzyme inhibition; cytotoxicity; mutation; and so on. In addition, the mechanism of action of these antioxidants was discussed with respect to the formation of active oxygen radicals and paramagnetic chromium such as chromium(V) and (III). Such studies may help elucidate the mechanism of chromium(VI) toxicity as well as the mechanism of protection.     

Imidazolopyrazinones as potential antioxidants

A series of imidazolopyrazinones 3, substituted at C-2, and C-2/C-6, has been prepared. The compounds behaved as quenchers of superoxide anion. The more active compounds are structurally related to coelenterazine, a natural substrate of marine bioluminescence. Theoretical parameters based on Hartree-Fock instabilities have been examined.     

Carotenoids and UV protection.

Photooxidative processes play a role in the pathobiochemistry of various disorders of light-exposed tissue. After irradiation of skin with UV light, erythema (sunburn) is an initial effect suitable for monitoring the direct biological response. Carotenoids are efficient in photoprotection, scavenging singlet oxygen and peroxyl radicals. Intervention studies with supplements or a carotenoid-rich diet documented efficiency in systemic photoprotection, measuring a decreased sensitivity against UV-induced erythema. For successful intervention, treatment with carotenoids is needed for a period of at least ten weeks. An increased consumption of carotenoids may contribute to life-long protection against UV-induced damage.     

Action of quinolinic and indolinonic aminoxyls as radical-scavenging antioxidants.

The kinetic studies on the actions of quinolinic and indolinonic aminoxyls in the oxidation of lipid peroxidation induced by free radicals were carried out to evaluate their antioxidant activity. These aminoxyls showed a similar reactivity toward peroxyl radical with alpha-tocopherol. The antioxidant efficacies of aminoxyls against oxidation of methyl linoleate in homogeneous solution were smaller than that of alpha-tocopherol. Hydroxylamine, a reduced form of aminoxyl, possessed a comparative antioxidant efficacy with alpha-tocopherol and was capable of suppressing the consumption of alpha-tocopherol. Aminoxyls showed more potent antioxidant activity than alpha-tocopherol against the oxidation of methyl linoleate micelles induced by peroxyl radical or by a combination of copper ion and hydrogen peroxide. These results suggest that quinolinic and indolinonic aminoxyls may act as potent antioxidants against lipid peroxidation, especially in the presence of a good reductant which reduces aminoxyl radicals to hydroxylamines.     

Imidazole derivatives as antioxidants and selective inhibitors of nNOS.

The reperfusion of ischemic tissue often delays its physiological and functional recovery; this paradoxical effect is ascribed to increased release of free radicals including O(2)(-) and NO. For these reasons, scavenging reactive oxygen species or inhibition the NO synthesis has been shown to result in an enhanced neuronal survival after cerebral ischemia. Many authors believe that therapy for stroke patients would be a cocktail of drugs with various mechanisms of action. Combination therapy is a difficult and complicated avenue for drug development because of the possibility of drug-drug interactions. An alternative approach would be to combine multiple activities within the same compound. In consideration of the free-radical scavenging and inhibitory effect on NOS of various natural and synthetic compounds, the aim of this study was to analyze the antioxidant properties of some imidazole derivatives previously synthesized in our laboratory. Results obtained in the present study provide evidence that tested compounds exhibit interesting antioxidant properties, expressed either by their capacity to scavenge free radicals or their ability to reduce lipid peroxidation. In particular, compounds A and B represent chemical structures which can be easily modified to improve the observed antioxidant properties and to provide new therapeutic strategies focused on multiple downstream events.     

Carotenoids in fish. XIX. Carotenoids in the eggs of Oncorhynchus keta (Walbaum)

The author investigated the presence of various carotenoids in the eggs of Oncorhynchus keta by means of columnar and thin-layer chromatography. The investigations revealed the presence of the following carotenoids: canthaxanthin, lutein-epoxide, 4-hydroxy-4-keto-ß-carotene, tunaxanthin, astaxanthin ester and asterin acid. Astaxanthin ester comprised the greatest part, 67.8% of, all carotenoids.     

Carotenoids in fish. XX. Carotenoids in Salmo gairdneri rich. And Salmo trutta morpha fario L.

The author investigated the presence of various carotenoids in Salmo gairdneri Rich. and Salmo trutta morpha fario L. from the trout fish farm (artificial food) and from the river as the natural conditions (natural food).The findings of these investigations indicate that the trout bred in natural conditions are richer in carotenoids, provitamins of vitamin A, than are trout from the trout fish farm. In all probability the variety of food available in natural conditions provides better facilities for the accumulation of carotenoids in the body of trout in their natural habitat.     

Sphingomyelin and derivatives as cellular signals.

This comprehensive review was necessitated by recent observations suggesting that sphingomyelin and derivatives may serve second messenger functions. It has attempted to remain true to the theme of cellular signalling. Hence, it has focussed on the lipids involved primarily with respect to their metabolism and properties in mammalian systems. The enzymology involved has been emphasized. An attempt was made to define directions in which signals may be flowing. However, the evidence presented to date is insufficient to conclusively designate the mechanisms of stimulated lipid metabolism. Hence, the proposed pathways must be viewed as preliminary. Further, the biologic functions of these lipids is for the most part uncertain. Thus, it is difficult to presently integrate this sphingomyelin pathway into the greater realm of cell biology. Nevertheless, the present evidence appears to suggest that a sphingomyelin pathway is likely to possess important bioregulatory functions. Hopefully, interest in this novel pathway will grow and allow a more complete understanding of the roles of these sphingolipids in physiology and pathology.