Wavelength dependence of mycosporine-like amino acid synthesis in Gyrodinium dorsum

Robust natural ultraviolet filters from marine ecosystems for the formulation of environmental friendlier bio-sunscreens

Ultraviolet radiation (UVR) has detrimental effects on human health. It induces oxidative stress, deregulates signaling mechanisms, and produces DNA mutations, factors that ultimately can lead to the development of skin cancer. Therefore, reducing exposure to UVR is of major importance. Among available measures to diminish exposure is the use of sunscreens. However, recent studies indicate that several of the currently used filters have adverse effects on marine ecosystems and human health. This situation leads to the search for new photoprotective compounds that, apart from offering protection, are environmentally friendly. The answer may lie in the same marine ecosystems since molecules such as mycosporine-like amino acids (MAAs) and scytonemin can serve as the defense system of some marine organisms against UVR. This review will discuss the harmful effects of UVR and the mechanisms that microalgae have developed to cope with it. Then it will focus on the biological distribution, characteristics, extraction, and purification methods of MAAs and scytonemin molecules to finally assess its potential as new filters for sunscreen formulation.

Mycosporine-Like Amino Acids: Potential Health and Beauty Ingredients

Human skin is constantly exposed to damaging ultraviolet radiation (UVR), which induces a number of acute and chronic disorders. To reduce the risk of UV-induced skin injury, people apply an additional external protection in the form of cosmetic products containing sunscreens. Nowadays, because of the use of some chemical filters raises a lot of controversies, research focuses on exploring novel, fully safe and highly efficient natural UV-absorbing compounds that could be used as active ingredients in sun care products. A promising alternative is the application of multifunctional mycosporine-like amino acids (MAAs), which can effectively compete with commercially available filters. Here, we outline a complete characterization of these compounds and discuss their enormous biotechnological potential with special emphasis on their use as sunscreens, activators of cells proliferation, anti-cancer agents, anti-photoaging molecules, stimulators of skin renewal, and functional ingredients of UV-protective biomaterials.

Seasonal Changes in Mycosporine-Like Amino Acid Production Rate with Respect to Natural Phytoplankton Species Composition

After in situ incubation at the site for a year, phytoplanktons in surface water were exposed to natural light in temperate lakes (every month); thereafter, the net production rate of photoprotective compounds (mycosporine-like amino acids, MAAs) was calculated using (13)C labeled tracer. This is the first report describing seasonal variation in the net production rate of individual MAAs in temperate lakes using a compound-specific stable isotope method. In the mid-latitude region of the Korean Peninsula, UV radiation (UVR) usually peaks from July to August. In Lake Paldang and Lake Cheongpyeong, diatoms dominated among the phytoplankton throughout the year. The relative abundance of Cyanophyceae (Anabaena spiroides) reached over 80% during July in Lake Cheongpyeong. Changes in phytoplankton abundance indicate that the phytoplankton community structure is influenced by seasonal changes in the net production rate and concentration of MAAs. Notably, particulate organic matter (POM) showed a remarkable change based on the UV intensity occurring during that period; this was because of the fact that cyanobacteria that are highly sensitive to UV irradiance dominated the community. POM cultured in Lake Paldang had the greatest shinorine (SH) production rate during October, i.e., 83.83 ± 10.47 fgC·L(-1)·h(-1). The dominance of diatoms indicated that they had a long-term response to UVR. Evaluation of POM cultured in Lake Cheongpyeong revealed that there was an increase in the net MAA production in July (when UVR reached the maximum); a substantial amount of SH, i.e., 17.62 ± 18.34 fgC·L(-1)·h(-1), was recorded during this period. Our results demonstrate that both the net production rate as well as the concentration of MAAs related to photoinduction depended on the phytoplankton community structure. In addition, seasonal changes in UVR also influenced the quantity and production of MAAs in phytoplanktons (especially Cyanophyceae).

The micosporine-like amino acids-rich aqueous methanol extract of laver (Porphyra yezoensis) inhibits adipogenesis and induces apoptosis in 3T3-L1 adipocytes

BACKGROUND/OBJECTIVES

Increased mass of adipose tissue in obese persons is caused by excessive adipogenesis, which is elaborately controlled by an array of transcription factors. Inhibition of adipogenesis by diverse plant-derived substances has been explored. The aim of the current study was to examine the effects of the aqueous methanol extract of laver (Porphyra yezoensis) on adipogenesis and apoptosis in 3T3-L1 adipocytes and to investigate the mechanism underlying the effect of the laver extract.

MATERIALS/METHODS

3T3-L1 cells were treated with various concentrations of laver extract in differentiation medium. Lipid accumulation, expression of adipogenic proteins, including CCAAT enhancer-binding protein α, peroxisome proliferator-activated receptor γ, fatty acid binding protein 4, and fatty acid synthase, cell viability, apoptosis, and the total content and the ratio of reduced to oxidized forms of glutathione (GSH/GSSG) were analyzed.

RESULTS

Treatment with laver extract resulted in a significant decrease in lipid accumulation in 3T3-L1 adipocytes, which showed correlation with a reduction in expression of adipogenic proteins. Treatment with laver extract also resulted in a decrease in the viability of preadipocytes and an increase in the apoptosis of mature adipocytes. Treatment with laver extract led to exacerbated depletion of cellular glutathione and abolished the transient increase in GSH/GSSG ratio during adipogenesis in 3T3-L1 adipocytes.

CONCLUSION

Results of our study demonstrated that treatment with the laver extract caused inhibition of adipogenesis, a decrease in proliferation of preadipocytes, and an increase in the apoptosis of mature adipocytes. It appears that these effects were caused by increasing oxidative stress, as demonstrated by the depletion and oxidation of the cellular glutathione pool in the extract-treated adipocytes. Our results suggest that a prooxidant role of laver extract is associated with its antiadipogenic and proapoptotic effects.

Modulation of viability and apoptosis of UVB-exposed human keratinocyte HaCaT cells by aqueous methanol extract of laver (Porphyra yezoensis)

We investigated the effect of 80% methanol extract of laver (Porphyra yezoensis) on the UVB-exposed HaCaT cells, human keratinocytes. The laver extract showed absorbance spectrum characteristic of porphyra-334 or shinorine, major mycosporine-like amino acids (MAAs) in red algae, and contained phenolic compounds. UVB exposure decreased cell viability and increased apoptotic cell fractions, and it also decreased the ratio of reduced (GSH) to oxidized glutathione (GSSG) and the total glutathione content. Post-treatment with the laver extract significantly increased the net viability and also the apoptotic cell fractions of UVB-exposed cells. The extract caused increase in GSH/GSSG ratio, yet it exacerbated the decrease in glutathione content in the UVB-exposed cells. These effects of the laver extract were also manifested in the sham-exposed cells, suggesting that those effects might be general phenomena caused by the laver extract. The extract treatment enhanced the UVB-induced phosphorylation of JNK and ERK, affecting more the latter. Our results suggest that the post-treatment with laver extract may protect UVB-exposed skin cells not only by increasing overall cell proliferation but also by enhancing apoptosis of damaged cells, via activating JNK and ERK signaling pathways, in which modulation of the content and redox status of glutathione may take significant parts.

Effect of ultraviolet radiation on photosynthesis, biomass, and fatty acid content and profile of a Scenedesmus rubescens-like microalga

The effects of ultraviolet radiation (UVR) and nitrogen (NaNO(3)) concentration on photosynthesis, biomass, and fatty acid content and profile of a Scenedesmus rubescens-like microalga were measured in an outdoor 8-day culture study. UV-induced photoinhibition decreased from 42.6% to 3.5%, in the presence of 75 mg/L NaNO(3) (HN) and from 52.9% to 22.6% in the presence of 7.5mg/L NaNO(3) (LN) nitrogen concentration, respectively. The concentrations of UV-absorbing compounds increased 4.3 and 4.9 times under HN and LN, respectively. Biomass accumulation was suppressed (10.7%) by UVR under HN, but not under LN conditions. Carotenoid content decreased from 1.05 ± 0.06 to 0.96 ± 0.15 (with UV radiation) and to 0.91 ± 0.07 (without UV radiation), respectively, under HN, while it decreased to 0.05 ± 0.04 (with UV radiation) and to 0.11 ± 0.08 (without UV radiation), respectively, under LN. The content of C18:1n9 fatty acids increased by about 430%, whereas that of C18:3n3 decreased by about 65% in both radiation treatments during nitrogen starvation. The results showed that the absence of UVR screening does not change the fatty acid content and profile of S. rubescens-like algae cultivated outdoors under HN and LN conditions.

ADAPTATION OF A PSYCHROPHILIC FRESHWATER DINOFLAGELLATE TO ULTRAVIOLET RADIATION(1)

Little is known about the UV photobiology of psychrophilic dinoflagellates, particularly in freshwater systems. We addressed the life strategies of Borghiella dodgei Moestrup, Gert. Hansen et Daugbjerg to cope with ambient levels of ultraviolet radiation (UVR) under cold conditions. Several physiological parameters related to growth, metabolism, and UVR protection were determined for 4 d in UVR-exposed and control cells by applying stable isotope analysis, spectrophotometry, and liquid chromatography-mass spectrometry (LC/MS). In UVR-exposed cells, assimilation of (15) N and (13) C and content of chl a and carotenoids, specifically diatoxanthin with respect to dinoxanthin and diadinoxanthin, were increased; furthermore, catalase activity showed a cyclic pattern with a strong increase after UVR exposure but a rapid return to preexposure levels. Both in UVR-exposed and control cells, no lipid peroxidation of galactolipids was observed. However, in UVR-exposed cells, content of galactolipids was higher and linked to an increase in monogalactosyldiacylglycerols (MGDGs). We concluded that Borghiella's adaptation to UVR depended on a general metabolic enhancement and efficient scavenging of oxygen radicals to mitigate and counteract damage. While Borghiella seemed to be well adapted to ambient UVR, the interactive effects of higher temperature and UVR on psychrophilic species in front of climate change merit further investigation.

Mycosporine-like amino acids: relevant secondary metabolites. Chemical and ecological aspects

Taxonomically diverse marine, freshwater and terrestrial organisms have evolved the capacity to synthesize, accumulate and metabolize a variety of UV-absorbing substances called mycosporine-like amino acids (MAAs) as part of an overall strategy to diminish the direct and indirect damaging effects of environmental ultraviolet radiation (UVR). Whereas the enzymatic machinery to synthesize MAAs was probably inherited from cyanobacteria ancestors via the endosymbionts hypothesis, metazoans lack this biochemical pathway, but can acquire and metabolize these compounds by trophic transference, symbiotic or bacterial association. In this review we describe the structure and physicochemical properties of MAAs, including the recently discovered compounds and the modern methods used for their isolation and identification, updating previous reviews. On this basis, we review the metabolism and distribution of this unique class of metabolites among marine organism.

UVB photoprotective role of mycosporines in yeast: photostability and antioxidant activity of mycosporine-glutaminol-glucoside

Several yeast species are able to synthesize and accumulate UV-radiation-absorbing mycosporine metabolites that are of unclear physiological function. In this work we analyzed the relationship between mycosporine-glutaminol glucoside (MGG) production, cell survival after UVB irradiation, and formation of cyclobutane pyrimidine dimers (CPDs). We also assessed the photostability and singlet oxygen quenching activity of MGG. A set of nine isolates of the basidiomycetous yeast Cryptococcus steppossus cultured in both dark and light conditions was used for the studies. Survival of the UVB-irradiated isolates and MGG concentration had a linear relationship when the concentration was over 2.5 mg g(-1). CPD accumulation and MGG accumulation were inversely related. MGG in aqueous solution was photostable with a photodecomposition quantum yield of 1.16 × 10(-5). MGG quenching of singlet oxygen was also observed, and the rate constant for the process in D(2)O was 5.9 × 10(7) M(-1) s(-1). Our results support the idea that MGG plays an important role as a UVB photoprotective metabolite in yeasts by protecting against direct damage on DNA and probably against indirect damage by singlet oxygen quenching.

Photoprotective compounds from marine organisms

The substantial loss in the stratospheric ozone layer and consequent increase in solar ultraviolet radiation on the earth's surface have augmented the interest in searching for natural photoprotective compounds in organisms of marine as well as freshwater ecosystems. A number of photoprotective compounds such as mycosporine-like amino acids (MAAs), scytonemin, carotenoids and several other UV-absorbing substances of unknown chemical structure have been identified from different organisms. MAAs form the most common class of UV-absorbing compounds known to occur widely in various marine organisms; however, several compounds having UV-screening properties still need to be identified. The synthesis of scytonemin, a predominant UV-A-photoprotective pigment, is exclusively reported in cyanobacteria. Carotenoids are important components of the photosynthetic apparatus that serve both light-harvesting and photoprotective functions, either by direct quenching of the singlet oxygen or other toxic reactive oxygen species or by dissipating the excess energy in the photosynthetic apparatus. The production of photoprotective compounds is affected by several environmental factors such as different wavelengths of UVR, desiccation, nutrients, salt concentration, light as well as dark period, and still there is controversy about the biosynthesis of various photoprotective compounds. Recent studies have focused on marine organisms as a source of natural bioactive molecules having a photoprotective role, their biosynthesis and commercial application. However, there is a need for extensive work to explore the photoprotective role of various UV-absorbing compounds from marine habitats so that a range of biotechnological and pharmaceutical applications can be found.

Mycosporine-like amino acids and marine toxins--the common and the different

Marine microorganisms harbor a multitude of secondary metabolites. Among these are toxins of different chemical classes as well as the UV-protective mycosporine-like amino acids (MAAs). The latter form a group of water-soluble, low molecular-weight (generally < 400) compounds composed of either an aminocyclohexenone or an aminocyclohexenimine ring, carrying amino acid or amino alcohol substituents. So far there has been no report of toxicity in MAAs but nevertheless there are some features they have in common with marine toxins. Among the organisms producing MAAs are cyanobacteria, dinoflagellates and diatoms that also synthesize toxins. As in cyclic peptide toxins found in cyanobacteria, amino acids are the main building blocks of MAAs. Both, MAAs and some marine toxins are transferred to other organisms e.g. via the food chains, and chemical modifications can take place in secondary consumers. In contrast to algal toxins, the physiological role of MAAs is clearly the protection from harmful UV radiation by physical screening. However, other roles, e.g. as osmolytes and antioxidants, are also considered. In this paper the common characteristics of MAAs and marine toxins are discussed as well as the differences.

Effects of solar ultraviolet radiation on photosynthesis of the marine red tide alga Heterosigma akashiwo (Raphidophyceae)

In order to assess the short- and long-term impacts of UV radiation (UVR, 280-400nm) on the red tide alga, Heterosigma akashiwo, we exposed the cells to three different solar radiation treatments (PAB: 280-700nm, PA: 320-700nm, P: 400-700nm) under both solar and artificial radiation. A significant decrease in the effective quantum yield (Y) during high irradiance periods (i.e., local noon) was observed, but the cells partially recovered during the evening hours. Exposure to high irradiances for 15, 30, and 60min under a solar simulator followed by the recovery (8h) under dark, 9 and 100micromolphotonsm(-2)s(-1) of PAR, highlighted the importance of the irradiance level during the recovery period. Regardless the radiation treatments, the highest recovery (both in rate and total Y) was found at a PAR irradiance of 9micromolphotonsm(-2)s(-1), while the lowest was observed at 100micromolphotonsm(-2)s(-1). In all experiments, PAR was responsible for most of the observed inhibition; nevertheless, the cells exposed only to PAR had the highest recovery in any condition, as compared to the other radiation treatments. In long-term experiments (10 days) using semi-continuous cultures, there was a significant increase of UV-absorbing compounds (UV(abc)) per cell from 1.2 to >4x10(-6)microgUV(abc)cell(-1) during the first 3-5 days of exposure to solar radiation. The highest concentration of UV(abc) was found in samples exposed in the PAB as compared to PA and P treatments. Growth rates (mu) mimic the behavior of UV-absorbing compounds, and during the first 5 days mu increased from <0.2 to ca. 0.8, and stayed relatively constant at this value during the rest of the experiment. The inhibition of the Y decreased with increasing acclimation of cells. All our data indicates that H. akashiwo is a sensitive species, but was able acclimate relatively fast (3-5 days) synthesizing UV-absorbing compounds and thus reducing any impact either on photosystem II or on growth.

UV-B-induced synthesis of mycosporine-like amino acids in three strains of Nodularia (cyanobacteria)

Three filamentous and heterocystous cyanobacterial strains of Nodularia, Nodularia baltica, Nodularia harveyana and Nodularia spumigena, have been tested for the presence and induction of ultraviolet-absorbing/screening mycosporine-like amino acids (MAAs) by simulated solar radiation in combination with 395 (receiving photosynthetically active radiation (PAR) only), 320 (receiving PAR + UV-A) and 295 (receiving PAR + UV-A + UV-B) nm cut-off filters. Absorption spectroscopic analyses of the methanolic extracts of samples revealed a typical MAA peak at 334 nm in all three cyanobacteria. Specific contents of MAAs had a pronounced induction in the samples covered with 295 nm cut-off filters after 72 h of irradiation. In comparison, there was little induction of MAAs in the samples covered by 395 and 320 nm cut-off filters. High performance liquid chromatographic (HPLC) studies revealed the presence of two types of MAAs in all three cyanobacteria, which were identified as shinorine and porphyra-334, both absorbing maximally at 334 nm. The occurrence of porphyra-334 is rare in cyanobacteria. Specific content of both shinorine and porphyra-334 were induced remarkably only in the samples covered with 295 nm cut-off filters. The results indicate that in comparison to UV-A and PAR, UV-B is more effective in eliciting MAAs induction in the studied cyanobacteria.

Wavelength-dependent induction of a mycosporine-like amino acid in a rice-field cyanobacterium, Nostoc commune: role of inhibitors and salt stress

Wavelength-dependent induction of a mycosporine-like amino acid (MAA) was studied in a nitrogen-fixing rice-field cyanobacterium, Nostoc commune. HPLC studies showed the presence of shinorine, a bisubstituted MAA containing both glycine and serine groups and having an absorption maximum at 334 nm. Exposure of cultures to simulated solar radiation in combination with various cut-off filters (WG 280, 295, 305, 320, 335, 345, GG 400, 420, 455, 475, OG 515, 530, 570, RG 645, 665; all Schott filter series) clearly indicated that MAAs were induced by UV-B radiation, while UV-A and PAR had very little effect on MAA induction in this organism. The ratio of the absorption at 334 nm (shinorine) to 665 nm (chlorophyll a) and the derived action spectrum also revealed the induction of MAAs to be UV-B dependent with a prominent peak at 290 nm and a second small peak at 310 nm. Various concentrations (50-300 mM) of NaCl were used to test whether another common stress factor, such as osmotic stress, also induces MAAs, as has been reported for other cyanobacterial species. The results indicate that cells grown at high concentration of NaCl but without UV-B did not show any MAA induction. In order to elucidate the possible photoreceptors, the effects of various inhibitors/quenchers on the induction of MAAs were studied. There was a marked reduction in the amount of MAA when the cells were irradiated with UV-B in the presence of inhibitors of the shikimate pathway (glyphosate, 1 mM), photosynthesis [3-(3,4-dichlorophenyl)-1,1-dimethylurea, 20 microM], protein synthesis (chloramphenicol, 25 microg ml(-1)), pterin synthesis (N-acetylserotonin, 5 mM, and 2,4-diamino-6-hydroxypyrimidine, 5 mM) and a quencher of the excited state of flavins and pterins (phenylacetic acid, 1 mM).

Linking marine biology and biotechnology

Studies of biological systems in which there is a direct link between the challenges faced by marine organisms and biotechnologies enable us to rationally search for active natural compounds and other novel biotechnologies. This approach is proving successful in developing new methods for the prevention of marine biofouling and for the identification of new lead compounds for the development of ultraviolet sunscreens.

Polychromatic action spectrum for the induction of a mycosporine-like amino acid in a rice-field cyanobacterium, Anabaena sp

A polychromatic action spectrum for the induction of an ultraviolet-absorbing/screening mycosporine-like amino acid (MAA) has been determined in a filamentous and heterocystous nitrogen-fixing rice-field cyanobacterium, Anabaena sp. High-performance liquid chromatographic (HPLC) studies revealed the presence of only one type of MAA, which was identified as shinorine, a bisubstituted MAA containing both glycine and serine groups having a retention time at 2.8 min and an absorption maximum at 334 nm. Exposure of cultures to simulated solar radiation in combination with various cut-off filters (WG 280, 295, 305, 320, 335, 345, GG 400, 420, 455, 475, OG 515, 530, 570, RG 645, 665 and a broad-band filter, UG 11) clearly revealed that the induction of the MAA takes place only in the UV range. Photosynthetic active radiation (PAR) had no significant impact on MAA induction. The ratio of the absorption at 334 nm (shinorine) to 665 nm (chlorophyll a) and the action spectrum also showed the induction of MAA to be UV dependent peaking in the UV-B range at around 290 nm. The results indicate that the studied cyanobacterium, Anabaena sp. may protect itself from deleterious short wavelength solar radiation by its ability to synthesize a mycosporine-like amino acid in response to UV-B radiation and thereby screen the negative effects of UV-B.

Induction of the synthesis of an UV-absorbing substance in the green alga Prasiola stipitata

The chlorophyte Prasiola stipitata produces a UV-absorbing substance with an absorption maximum at 324 nm. The wavelength-dependent induction of the synthesis of this substance was investigated using simulated solar radiation in combination with 15 cut-off and one broad-band filter. The algae were exposed from three different distances (89, 100 and 119 cm) to the solar simulator producing a maximum of 203.58, 1.24 and 46.86 W/m(2) and a minimum of 107.94, 0.64 and 24.44 W/m(2) irradiances for PAR, UV-B and UV-A, respectively. A polychromatic action spectrum was calculated from the pooled results showing a clear maximum at 300 nm in the long-wavelength UV-B range, but there is still some induction caused by UV-A and PAR. The ratio of the effectiveness from PAR to UV-A to UV-B amounts to 1:2:22.