An unusual vitamin E constituent (alpha-tocomonoenol) provides enhanced antioxidant protection in marine organisms adapted to cold-water environments.

A new vitamin E constituent having an unusual methylene unsaturation at the isoprenoid-chain terminus of alpha-tocopherol (alpha-Toc) was isolated from chum salmon eggs and was found to have identical antioxidant activity as does alpha-Toc in methanol or liposomal suspension at 37 degrees C. Here we report that this marine-derived tocopherol (MDT) is broadly distributed with alpha-Toc in the tissue of marine fish, and that the MDT composition of total vitamin E is greater in the flesh of cold-water salmon (12-20%) than in that of tropical fish (< or =2.5%). Vitamin E analysis of cultured masu salmon maintained on a MDT-deplete diet showed substantially less MDT content than native masu salmon, suggesting a trophic origin of MDT. This contention is supported by the finding of MDT in marine plankton from the cold waters of Hokkaido. We found that MDT inhibited peroxidation of cholesterol-containing phosphatidylcholine liposomes to a greater extent than did alpha-Toc at 0 degrees C. Furthermore, the ratios of the rate constants for MDT and alpha-Toc to scavenge peroxyl radicals increased with decreasing rates of radical flux in liposomes and fish oil at 0 degrees C, indicating that the enhanced activity of MDT at low temperature is attributed to its greater rate of diffusion in viscous lipids. These results suggest that MDT production, or its trophic accumulation, may reduce lipid peroxidation in marine organisms functionally adapted to cold-water environments.

Ultraviolet irradiation of titanium dioxide in aqueous dispersion generates singlet oxygen.

We previously reported that irradiation of titanium dioxide (TiO2) in ethanol generates both singlet oxygen (1O2) and superoxide anion (O2*-) as measured by EPR spectroscopy. The present study describes the production of reactive oxygen species upon irradiation of TiO2 in aqueous suspension as determined by EPR spectroscopy using 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TMP) and 5,5-dimethyl-pyrroline-N-oxide (DMPO). Photoproduction of 1O2 by suspended TiO2, detected as 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (4-oxo-TEMPO), was measured in water and deuterium oxide (D2O) in the presence or absence of sodium azide (NaN3) and under air or argon atmospheres. Production of a DMPO-OH adduct was examined in 4-oxo-TMP containing medium in the presence or absence of dimethyl sulfoxide (DMSO). The signal for the DMPO spin adduct of superoxide anion was not observed in aqueous conditions. Kinetic analysis revealed that 1O2 was produced at the surface of irradiated TiO2 in aqueous suspension as was observed in ethanol. Kinetic analysis revealed that the formation of DMPO-OH adduct reflects oxidation of DMPO by 1O2 rather than the trapping of the hydroxyl radical produced by the reaction of photo-exited TiO2 and water. The production of large amounts of 1O2 by TiO2 in aqueous suspension as compared to those in ethanol and possible formation of hydroxyl radical in aqueous suspension but not in alcohol, suggest that irradiation of TiO2 in aqueous environments is biologically more important than that in non-aqueous media.

Irradiation of titanium dioxide generates both singlet oxygen and superoxide anion.

Although photoexcited TiO2 has been known to initiate various chemical reactions, such as the generation of reactive oxygen species, precise mechanism and chemical nature of the generated species remain to be elucidated. The present work demonstrates the generation of singlet oxygen by irradiated TiO2 in ethanol as measured by ESR spectroscopy using 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TMP) as a 1O2-sensitive trapping agent. Under identical conditions, the superoxide ion was also detected by spin trapping agent 5,5-dimethyl-pyrroline-N-oxide (DMPO). Kinetic analysis in the presence of both 4-oxo-TMP and DMPO revealed that singlet oxygen is produced directly at the irradiated TiO2 surface but not by a successive reaction involving superoxide anion. The basis for this view is the fact that DMPO added in the mixture increased the signals responsible for 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy (4-oxo-TEMPO), a reaction product of 4-oxo-TMP and 1O2. The detailed mechanism for the generation of 1O2 and superoxide ion by irradiated TiO2 and reactions between these species and DMPO are discussed.

Sunscreens, oxidative stress and antioxidant functions in marine organisms of the Great Barrier Reef.

An overview of the biochemical photophysiology of tropical, reef-building corals is presented with a discussion on the biosynthetic relationship between natural UV-absorbing sunscreens and certain antioxidant functions in marine organisms. Our studies reveal that marine organisms, including 'UV-extremophilic' bacteria, are a rich source of novel antioxidants having potential for the development of commercial and biomedical applications. Novel sunscreening agents derived from tropical marine organisms of the Great Barrier Reef are in development. New marine-derived antioxidants are being isolated for testing as chemopreventatives in a variety of oxidatively degenerative diseases.

A new vitamin E (alpha-tocomonoenol) from eggs of the Pacific salmon Oncorhynchus keta.

A novel alpha-tocomonoenol 3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyl-12-tridecenyl )-2H-1- benzopyran-6-ol[ having an unusual methylene unsaturation at the isoprenoid-chain terminus of alpha-tocopherol was isolated from the lipophilic fraction of chum salmon eggs. The structure of this marine-derived tocopherol (MDT) was established by spectral analyses. The peroxyl radical-trapping activities of MDT and alpha-tocopherol were compared in aqueous phosphatidylcholine liposomal suspension and in methanolic solution at 37 degrees C. The antioxidant activity of MDT was found to be identical to that of alpha-tocopherol under the experimental conditions of measurement.

Ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs) are acquired from their diet by medaka fish (Oryzias latipes) but not by SKH-1 hairless mice.

To assess whether vertebrates can acquire, from their diet, ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs), medaka fish and hairless mice were maintained for 150 and 130 days, respectively, on diets either including Mastocarpus stellatus (rich in MAAs) or the same diets without this red alga. In medaka, the MAAs palythine and asterina-330, present in trace quantities in the diet with added M. stellatus, were present in significantly greater quantities in the eyes of fish fed this diet than in the eyes of control fish. Only traces of MAAs were present in the skin of medaka fed the diet containing MAAs. Shinorine, the principal MAA in M. stellatus, was not found in any tissues of medaka, which raises questions about the specificity of transport of MAAs. In hairless mice, no dietary MAAs were found in the tissues of the eyes, skin, or liver after maintenance on the experimental diet. Low concentrations of shinorine were present only in the tissues of the small and large intestines. These results indicate that MAAs are acquired from their diet and translocated to superficial tissues by teleost fish, but that mammals may be incapable of such. Thus, dietary supplementation with MAAs may be useful in aquacultured species of fish, but MAAs as 'dietary sunscreens' may not be an option for mammals, including humans. Nevertheless, our demonstration of the uptake of shinorine by human skin cancer cells in culture raises evolutionary questions regarding the organ specificity of the capacity for the cellular transport of MAAs.

Uric acid photo-oxidation assay: in vitro comparison of sunscreening agents.

We present a new method to evaluate the photo-oxidative activity of sunscreening agents based on the photodynamic oxidation of uric acid. Uric acid was selected as the oxidant probe for its high reactivity to singlet oxygen and oxygen radicals, high sensitivity of detection using electrochemical (EC) techniques, low light absorptivity and high photochemical stability in the UVA/B region of interest, and stability to autoxidation. The method is demonstrated by the photodynamic oxidation of uric acid on co-irradiation with Rose Bengal, a highly efficient photosensitizing dye for the production of singlet oxygen (1O2). Using this assay we found that the relative photodynamic oxidation rates of UVB-absorbing sunscreens in 80% methanol on irradiation with >290 nm light decreased in the order 2-ethylhexyl 4-dimethylaminobenzoate (DMABA-2EH) >> 2-ethylhexyl 4-methoxycinnamate (MCA-2EH) and the experimental sunscreens, 1-(1,1-dimethylethyl)-3-octanoyl-4,4-dimethyl- 1,4,5,6,-tetrahydropyridine (ICI-319) and 1-(2-methylpropyl)-3-propionyl-4,4-dimethyl-1,4,5,6-tetrahydropyridine (ICI-855). The relative photodynamic oxidation rates of UVA-absorbing sunscreens decreased in the order 4-tert-butyl-4'-methoxydibenzoylmethane (BMDBM) and 4-(2-propyl)benzophenone (PB) > 2-hydroxy-4'-methoxy-benzophenone (HMB) and 2,2'-dihydroxy-4-methoxybenzophenone (DHMB). We have confirmed the photodynamic activity of DMABA-2EH for the production of singlet oxygen (1O2) using electron paramagnetic resonance (EPR) spectroscopy and the reagent 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TEMP). We failed to detect the photodynamic production of the oxyradicals, superoxide (O2.-) and hydroxyl radical (HO.) using N-tert-butyl-a-phenylnitrone (PBN) and 5,5-dimethyl-1-pyrrolidine-1-oxide (DMPO) as a result of photochemical interference caused by these spin-trapping reagents. The uric acid photo-oxidation assay was also used to compare the photodynamic reactivity of light-reflective, microfine oxides TiO2, ZnO and ZrO2 suspended in aqueous 80% methanol. All of the microfine oxides (uncoated) showed greater photodynamic reactivity in equimolar dispersion than did any of the organic UVA- and UVB-absorbing sunscreens in homogeneous solution. In this assay the photodynamic oxidation rates for the microfine oxides decreased in the order ZnO >> TiO2 (anatase) > ZrO2 > TiO2 (rutile).

Nature's sunscreen from the Great Barrier Reef, Australia.

All shallow-water marine organisms have natural features and behaviours that can reduce exposure to UV radiation and limit the amount of photodamage to functional biomolecules and organelles. Protection from UV radiation often includes the production of UV-absorbing compounds which, in marine organisms, are usually mycosporine-like amino acids (MAAs) having a range of absorption maxima between 310 and 360 nm. Shallow-water corals produce large quantities of MAAs and their apparent ability to withstand long-term environmental UV exposure suggests utilization of their UV-absorbing chromophore for sunscreen applications. We present an overview of the biochemical photophysiology of tropical reef-building corals, and of the development of a new class of synthetic sunscreen, 1-alkyl-3-alkanoyl-1,4,5,6-tetrahydropyridines, based on their natural UV protection. Several sunscreen candidates have been examined for sunscreen suitability and a limited selection is being tested for potential use in human skin-care and cosmetic products.