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.

Free radicals and chemiluminescence as products of the spontaneous oxidation of sulfide in seawater, and their biological implications.

The discovery of symbioses between marine invertebrates and sulfide-oxidizing bacteria at deep-sea hydrothermal vents and in other high-sulfide marine environments has stimulated research into the adaptations of metazoans to potentially toxic concentrations of sulfide. Most of these studies have focused on a particular action of sulfide--its disruption of aerobic metabolism by the inhibition of mitochondrial respiration--and on the adaptations of sulfide-tolerant animals to avoid this toxic effect (1). We propose that sulfidic environments impose another, hitherto over-looked type of toxicity: exposure to free radicals of oxygen, which may be produced during the spontaneous oxidation of sulfide, thus imposing an oxidative stress. Here we present evidence that oxygen- and sulfur-centered free radicals are produced during the oxidation of sulfide in seawater, and we propose a reaction pathway for sulfide oxidation that is consistent with our observations. We also show that chemiluminescence at visible wavelengths occurs during sulfide oxidation, providing a possible mechanism for the unexplained light emission from hydrothermal vents (2, 3).

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.

Neurophysiological Correlates of the Behavioral Response to Light in the Sea Anemone Anthopleura elegantissima.

Neurophysiological responses to light in Anthopleura elegantissima do not involve the ectodermal slow system 1 (SS1). Activities in both the endodermal slow system 2 (SS2) and the through conducting nerve net (TCNN) change when the lighting changes, but the response is not consistent. Thus, photoreception in A. elegantissima probably occurs in the endoderm because SS2 and the TCNN are involved and SS1 is not. We hypothesize either that the photoreception occurs in sensory cells in a local nerve net, with the information then being transmitted to the muscles, or that the muscles themselves are light sensitive. In either case, the TCNN and SS2 become involved after the transduction, and as a consequence--rather than the cause--of muscular activation. The conducting systems of zooxanthellate specimens have a higher frequency of activity than those of apozooxanthellate individuals.

Heat flux, oxygen flux, and mitochondrial redox state as a function of oxygen availability and ciliary activity in excised gills of Mytilus edulis.

The ciliated gill of bivalve molluscs is situated at an interface between animal and environment. Cilia propel water past the gills to deliver oxygen and nutrition to the animal. Ciliary activity is driven by dynein ATPases and requires a continual supply of ATP at a rate sufficient to match the rate of ATP hydrolysis. Control of the balance between ATP supply and demand in the ciliated gill, and how this balance may be altered by environmental stresses, is unknown. In this pilot study, metabolic flux of excised gills from the marine mussel Mytilus edulis was examined in response to oxygen availability and to serotonin-stimulated ciliary activity. Heat flux and oxygen flux were measured simultaneously with calorespirometry. In parallel experiments, the redox state of mitochondrial cytochromes was determined with in vivo spectrophotometry. Above 4 kPa pO2, heat flux was supported by aerobic metabolism. Anoxic heat flux was less than 5% of aerobic heat flux. Heat and oxygen fluxes nearly doubled in gills in the presence of 10 microM serotonin; however, half-maximal pO2 for heat and oxygen fluxes and for reduction of mitochondrial cytochromes remained unchanged from control levels. In gills having inactive cilia in half-strength seawater, half-maximal pO2 for heat and oxygen fluxes and for cytochrome reduction nearly doubled compared with valves in full-strength seawater. These data indicate that limitation to oxygen delivery imposed by boundary layers may be reduced when ciliary beat frequency is elevated, leading to enhanced oxygen flux to intracellular mitochondrial which matches the increased energy demand by the cilia.

Diffusion Limitation and Hyperoxic Enhancement of Oxygen Consumption in Zooxanthellate Sea Anemones, Zoanthids, and Corals.

Depending on their size and morphology, anthozoan polyps and colonies may be diffusion-limited in their oxygen consumption, even under well-stirred, air-saturated conditions. This is indicated by an enhancement of oxygen consumption under steady-state hyperoxic conditions that simulate the levels of O2 produced photosynthetically by zooxanthellae in the hosts' tissues. Such hyperoxia in the tissues of zooxanthellate species negates the effect of the diffusive boundary layer, and increases the rate of oxygen consumption; thus, in many cases, the rate of respiration measured under normoxia in the dark may not be representative of the rate during the day when the zooxanthellae are photosynthesizing and when the supply of oxygen for respiration is in the tissues themselves, not from the environment. These results have implications in respirometric methodology and in calculating the rate of gross photosynthesis in energetic studies. The activity of cytochrome c oxidase is higher in aposymbiotic than in zooxanthellate specimens of the sea anemone Aiptasia pulchella, and this may indicate a compensation for the relative hypoxia in the tissues of the former, enhancing the delivery of oxygen to the mitochondria from the environment.

Oxygen detoxification in algal-invertebrate symbioses from the Great Barrier Reef.

Examination of 34 species of symbiotic invertebrates in four phyla has confirmed the generality of a direct relationship between chlorophyll concentration and the activities of superoxide dismutase and catalase, two enzymes involved in the detoxification of active oxygen. On a finer scale, activities of these enzymes also depend on the localization of the algal symbions (intracellular or extracellular) and hence on the extent to which photosynthetic O2 actually contacts animal cytoplasm, and on the solar irradiance experienced by the symbionts. Differences in SOD activity among organs of Tridacna crocea are not fully explained by local O2 levels but are further related to organ-specific retes of O2 consumption. This result is discussed in terms of known mechanisms of superoxide radical production in mitochondria and differences in O2 utilization concentrations among various organs in bivalve molluscs.