Isolation and Structural Elucidation of Novel Mycosporine-Like Amino Acids as Alarm Cues in the Defensive Ink Secretion of the Sea Hare Aplysia californica

Isolation and Structure Elucidation of Novel Mycosporine-like Amino Acids from the Two Intertidal Red Macroalgae Bostrychia scorpioides and Catenella caespitosa

This study presents a phytochemical survey of two common intertidal red algal species, Bostrychia scorpioides and Catenella caespitosa, regarding their MAA (mycosporine-like amino acid) composition, which are known as biogenic sunscreen compounds. Six novel MAAs from Bostrychia scorpioides named bostrychines and two novel MAAs from Catenella caespitosa named catenellines were isolated using a protocol which included silica gel column chromatography, flash chromatography on reversed phase material and semipreparative HPLC (High-Performance Liquid Chromatography). The structure of the novel MAAs was elucidated using NMR (Nuclear Magnetic Resonance) and HR-MS (High-Resolution Mass Spectrometry), and their absolute configuration was confirmed by ECD (Electronic Circular Dichroism). All isolated MAAs possess a cyclohexenimine scaffold, and the metabolites from B. scorpioides are related to the known MAAs bostrychines A-F, which contain glutamine, glutamic acid and/or threonine in their side chains. The new MAAs from C. caespitosa contain taurine, an amino sulfonic acid that is also present in another MAA isolated from this species, namely, catenelline. Previous and new data confirm that intertidal red algae are chemically rich in MAAs, which explains their high tolerance against biologically harmful ultraviolet radiation.

A Plastic Biosynthetic Pathway for the Production of Structurally Distinct Microbial Sunscreens

Mycosporine-like amino acids (MAAs) are small, colorless, and water-soluble secondary metabolites. They have high molar extinction coefficients and a unique UV radiation absorption mechanism that make them effective sunscreens. Here we report the discovery of two structurally distinct MAAs from the lichen symbiont strain Nostoc sp. UHCC 0926. We identified these MAAs as aplysiapalythine E (C23H38N2O15) and tricore B (C34H53N4O15) using a combination of high-resolution liquid chromatography-mass spectrometry (HR-LCMS) analysis and nuclear magnetic resonance (NMR) spectroscopy. We obtained a 8.3 Mb complete genome sequence of Nostoc sp. UHCC 0926 to gain insights into the genetic basis for the biosynthesis of these two structural distinct MAAs. We identified MAA biosynthetic genes encoded in three separate locations of the genome. The organization of biosynthetic enzymes in Nostoc sp. UHCC 0926 necessitates a branched biosynthetic pathway to produce two structurally distinct MAAs. We detected the presence of such discontiguous MAA biosynthetic gene clusters in 12% of the publicly available complete cyanobacterial genomes. Bioinformatic analysis of public MAA biosynthetic gene clusters suggests that they are subject to rapid evolutionary processes resulting in highly plastic biosynthetic pathways that are responsible for the chemical diversity in this family of microbial sunscreens.

Low temporal dynamics of mycosporine-like amino acids in benthic cyanobacteria from an alpine lake

Cyanobacteria are one of the oldest organisms on Earth and they originated at a time when damaging ultraviolet (UV) C radiation still reached the surface. Their long evolution led to several adaptations to avoid deleterious effects caused by exposure to solar UV radiation. Synthesis of sunscreen substances, such as mycosporine-like amino acids (MAAs), allows them to photosynthesise with reduced risk of cell damage. The interplay of solar UV radiation and MAAs is well documented for cyanobacteria in the plankton realm, but little is known for those in the benthic realm, particularly of clear alpine lakes.Here, we assessed the temporal dynamics of MAAs in the benthic algal community of one clear alpine lake dominated by cyanobacteria during the ice-free season and along a depth gradient using state-of-the-art analytical methods (high-performance liquid chromatography, nuclear magnetic resonance, liquid chromatography-mass spectrometry). We differentiated between the epilithic cyanobacterial community and the overlying loosely attached filamentous cyanobacteria, as we expected they will have an important shielding/shading effect on the former. We hypothesised that in contrast to the case of phytoplankton, benthic cyanobacteria will show less pronounced temporal changes in MAAs concentration in response to changes in solar UV exposure.Three UV-absorbing substances were present in both types of communities, whereby all were unknown. The chemical structure of the dominant unknown substance (maximum absorption at 334 nm) resulted in the identification of a novel MAA that we named aplysiapalythine-D for its similarity to the previously described aplysiapalythine-C.Chlorophyll-a-specific MAA concentrations for epilithic and filamentous cyanobacteria showed a significant decrease with depth, although only traces were found in the former community. The temporal dynamics in MAA concentrations of filamentous cyanobacteria showed no significant variations during the ice-free season.Our result on the low temporal MAA dynamics agrees with the reduced growth rates of benthic cyanobacteria reported for cold ecosystems. The permanent presence of this community, which is adapted to the high UV levels characteristic of clear alpine lakes, probably represents the most important primary producers of these ecosystems.

Bioactive Compounds from Marine Heterobranchs

The natural products of heterobranch molluscs display a huge variability both in structure and in their bioactivity. Despite the considerable lack of information, it can be observed from the recent literature that this group of animals possesses an astonishing arsenal of molecules from different origins that provide the molluscs with potent chemicals that are ecologically and pharmacologically relevant. In this review, we analyze the bioactivity of more than 450 compounds from ca. 400 species of heterobranch molluscs that are useful for the snails to protect themselves in different ways and/or that may be useful to us because of their pharmacological activities. Their ecological activities include predator avoidance, toxicity, antimicrobials, antifouling, trail-following and alarm pheromones, sunscreens and UV protection, tissue regeneration, and others. The most studied ecological activity is predation avoidance, followed by toxicity. Their pharmacological activities consist of cytotoxicity and antitumoral activity; antibiotic, antiparasitic, antiviral, and anti-inflammatory activity; and activity against neurodegenerative diseases and others. The most studied pharmacological activities are cytotoxicity and anticancer activities, followed by antibiotic activity. Overall, it can be observed that heterobranch molluscs are extremely interesting in regard to the study of marine natural products in terms of both chemical ecology and biotechnology studies, providing many leads for further detailed research in these fields in the near future.

High-value compounds from the molluscs of marine and estuarine ecosystems as prospective functional food ingredients: An overview

Extensive biodiversity and availability of marine and estuarine molluscs, along with their their wide-range of utilities as food and nutraceutical resources developed keen attention of the food technologists and dieticians, particularly during the recent years. The current review comprehensively summarized the nutritional qualities, functional food attributes, and bioactive properties of these organisms. Among the phylum mollusca, Cephalopoda, Bivalvia, and Gastropoda were mostly reported for their nutraceutical applications and bioactive properties. The online search tools, like Scifinder/Science Direct/PubMed/Google Scholar/MarinLit database and marine natural product reports (1984-2019) were used to comprehend the information about the molluscs. More than 1334 secondary metabolites were reported from marine molluscs between the periods from 1984 to 2019. Among various classes of specialized metabolites, terpenes were occupied by 55% in gastropods, whereas sterols occupied 41% in bivalves. The marketed nutraceuticals, such as CadalminTM green mussel extract (Perna viridis) and Lyprinol® (Perna canaliculus) were endowed with potential anti-inflammatory activities, and were used against arthritis. Molluscan-derived therapeutics, for example, ziconotide was used as an analgesic, and elisidepsin was used in the treatment of cancer. Greater numbers of granted patents (30%) during 2016-2019 recognized the increasing importance of bioactive compounds from molluscs. Consumption of molluscs as daily diets could be helpful in the enhancement of immunity, and reduce the risk of several ailments. The present review comprehended the high value compounds and functional food ingredients from marine and estuarine molluscs.

Identification and distribution of mycosporine-like amino acids in Brazilian cyanobacteria using ultrahigh-performance liquid chromatography with diode array detection coupled to quadrupole time-of-flight mass spectrometry

RATIONALE

Mycosporine-like amino acids (MAAs) are UV-absorbing compounds produced by fungi, algae, lichens, and cyanobacteria when exposed to UV radiation. These compounds have photoprotective and antioxidant functions and have been widely studied for possible use in sunscreens and anti-aging products. This study aims to identify MAA-producing cyanobacteria with potential application in cosmetics.

METHODS

A method for the identification of MAAs was developed using ultrahigh-performance liquid chromatography with diode array detection coupled to quadrupole time-of-flight mass spectrometry (UHPLC-DAD/QTOFMS). Chromatographic separation was carried out using a Synergi 4 μ Hydro-RP 80A column (150 × 2,0 mm) at 30°C with 0.1% formic acid aqueous solution + 2 mM ammonium formate and acetonitrile/water (8:2) + 0.1% formic acid as a mobile phase.

RESULTS

Out of the 69 cyanobacteria studied, 26 strains (37%) synthesized MAAs. Nine different MAAs were identified using UHPLC-DAD/QTOFMS. Iminomycosporines were the major group detected (7 in 9 MAAs). In terms of abundance, the most representative genera for MAA production were heterocyte-forming groups. Oscilatoria sp. CMMA 1600, of homocyte type, produced the greatest diversity of MAAs.

CONCLUSIONS

The UHPLC-DAD/QTOFMS method is a powerful tool for identification and screening of MAAs in cyanobacterial strains as well as in other organisms such as dinoflagellates, macroalgae, and microalgae. The different cyanobacterial genera isolated from diverse Brazilian biomes and environments are prolific sources of MAAs.

Seasonal Variation of Mycosporine-Like Amino Acids in Three Subantarctic Red Seaweeds

UV-absorbing compounds, such as mycosporine-like amino acids (MAAs), are a group of secondary metabolites present in many marine species, including red seaweeds. In these organisms, the content and proportion of the composition of MAAs vary, depending on the species and several environmental factors. Its high cosmetic interest calls for research on the content and composition of MAAs, as well as the dynamics of MAAs accumulation in seaweeds from different latitudes. Therefore, this study aimed to survey the content of UV-absorbing MAAs in three Subantarctic red seaweeds during a seasonal cycle. Using spectrophotometric and HPLC techniques, the content and composition of MAAs of intertidal Iridaea tuberculosa, Nothogenia fastigiate, and Corallina officinalis were assessed. Some samples were also analyzed using high-resolution mass spectrometry coupled with HPLC-ESI-MS in order to identify more precisely the MAA composition. I. tuberculosa exhibited the highest MAA values (above 1 mg g-1 of dried mass weight), while C. officinalis showed values not exceeding 0.4 mg g-1. Porphyra-334 was the main component in N. fastigiata, whereas I. tuberculosa and C. officinalis exhibited a high content of palythine. Both content and composition of MAAs varied seasonally, with high concentration recorded in different seasons, depending on the species, i.e., winter (I. tuberculosa), spring (N. fastigiata), and summer (C. officinalis). HPLC-ESI-MS allowed us to identify seven different MAAs. Two were recorded for the first time in seaweeds from Subantarctic areas (mycosporine-glutamic acid and palythine-serine), and we also recorded an eighth UV-absorbing compound which remains unidentified.

Absolute Configuration of Mycosporine-Like Amino Acids, Their Wound Healing Properties and In Vitro Anti-Aging Effects

Mycosporine-like amino acids (MAAs) are water-soluble metabolites, reported to exhibit strong UV-absorbing properties. They have been found in a wide range of marine organisms, especially those that are exposed to extreme levels of sunlight, to protect them against solar radiation. In the present study, the absolute configuration of 14 mycosporine-like-amino acids was determined by combining the results of electronic circular dichroism (ECD) experiments and that of advanced Marfey's method using LC-MS. The crystal structure of a shinorine hydrate was determined from single crystal X-ray diffraction data and its absolute configuration was established from anomalous-dispersion effects. Furthermore, the anti-aging and wound-healing properties of these metabolites were evaluated in three different assays namely the inhibition of collagenase, inhibition of advanced glycation end products (AGEs) and wound healing assay (scratch assay).

Bostrychines A-F, Six Novel Mycosporine-Like Amino-Acids and a Novel Betaine from the Red Alga Bostrychia scorpioides

Various red algae have repeatedly been reported to produce a variety of UV-absorbing mycosporine-like amino acids (MAAs), compounds that are well-known as natural sun-screens, as well as a plethora of betaines, metabolites which contribute to the osmotic balance under salt stress. Among other Rhodophyta, Bostrychia scorpioides, which is thriving as epiphyte on salt marsh plants in Europe and hence experiences extreme environmental conditions such as desiccation, UV-stress and osmotic stress, has barely been investigated for its secondary metabolites. In the present study, seven mycosporine like-amino acids and two betaines were isolated from Bostrychia scorpioides using various chromatographic techniques. Their structures were confirmed by Nuclear Magnetic Resonance (NMR) spectroscopy and High Resolution Mass Spectrometry (HRMS). Six MAAs and one betaine were chemically characterized as new natural products.

Chemical profiling of mycosporine-like amino acids in twenty-three red algal species

Rhodophyta produce a variety of chemically different mycosporine-like amino acids (MAAs), compounds that are known as some of the strongest ultraviolet (UV) absorbing molecules in nature. Accordingly, they primarily act as photoprotectants against harmful levels of solar ultraviolet radiation in the UV-A and UV-B range. In order to get a deeper understanding of the chemical diversity of MAAs in red algae, pure standards of eleven mycosporine-like amino acids were isolated from three different species (Agarophyton chilense, Pyropia plicata and Champia novae-zelandiae) using various chromatographic methods. Their structures were confirmed by nuclear magnetic resonance and mass spectrometry. Four out of the eleven MAAs are reported for the first time in algae. In addition, a new high-performance liquid chromatography method was developed for the separation of all isolated MAAs and successfully applied for the analysis of twenty-three red algal species of marine origin. All of them contained MAAs, the most abundant compounds were shinorine, palythine, asterina-330 and porphyra-334. For some samples, the direct assignment of MAAs based on their UV spectra was not possible; therefore, the target analytes were enriched by a simple concentration step, followed by liquid chromatography-mass spectrometry analysis of the extracts. This approach enabled a deeper insight into the MAA pattern of red algae, indicating that not only the four dominant ones are synthesized but also many others, which were often described as unknown compounds in previous studies.

Finding food: how marine invertebrates use chemical cues to track and select food

This review covers recent research on how marine invertebrates use chemical cues to find and select food.

Chemical mediation as a structuring element in marine gastropod predator-prey interactions

Some diterpenoid compounds protect the sacoglossansElysiasp. andCyerce nigricansfrom their carnivorous predator the dorid nudibranch,Gymnodorissp., unlike chemically unprotected gastropods that are consumed by this voracious nudibranch (photo Philippe Bourseiller).

Are embryonic developing modes determinant in the acquisition and levels of photoprotective compounds in slipper limpets of the Crepipatella genus?

The type of embryonic development (mixed and direct) and its influence on the accumulation and translocation of photoprotective compounds from the mother to the encapsulated embryo was studied in the intertidal gastropods Crepipatella peruviana and Crepipatella dilatata during their reproductive peak. HPLC/MS was used to determine type and levels of sunscreen compounds (total carotenoids; TC/and mycosporine-like amino acid; MAA) in brooding females, capsule walls and early and pre-hatching embryos of both species. Photoprotective compounds were only quantified in nurse eggs of C. dilatata. Our results indicate that females of both species can accumulate TC and MAA at different levels, and they are able to transfer them selectively to capsule walls, embryos and nurse eggs. Palythine-serine (MW=244Da; λmax=320nm) and MAA-330 (MW=234Da; λmax=330nm) constitute total MAA pool in brooding females, whereas brooded embryos incorporate palythine (MW=244Da; λmax=320nm) to the MAA pool. Although TC was transferred from the mother to the embryo through the yolk in both species, MAA trespass showed differences. Females of C. peruviana transfer MAA to their embryos through the embryonic yolk; C. dilatata can transfer MAA only through their nurse eggs, which are consumed by embryos during the terminal stages of intracapsular development. Differences between mixed and direct embryonic development, as well as environmental UV-R levels, which the recently hatched larvae and juveniles of C. peruviana and C. dilatata are exposed to, would determine levels of sunscreen compounds in each species. Higher TC and MAA levels in pre-hatching larvae of C. peruviana compared to C. dilatata, indicate a necessity of C. peruviana for protection against UV-R radiation during approximately 15days when their veliger larvae remain in the water column before metamorphosis is complete. Conversely, low photoprotective levels in pre-hatching juveniles of C. dilatata could be related to low UV-R exposure levels due to the direct incorporation to the benthos and the presence of a protective shell.

Chemical Diversity and Biological Properties of Secondary Metabolites from Sea Hares of Aplysia Genus

The marine environment is an important source of structurally-diverse and biologically-active secondary metabolites. During the last two decades, thousands of compounds were discovered in marine organisms, several of them having inspired the development of new classes of therapeutic agents. Marine mollusks constitute a successful phyla in the discovery of new marine natural products (MNPs). Over a 50-year period from 1963, 116 genera of mollusks contributed innumerous compounds, Aplysia being the most studied genus by MNP chemists. This genus includes 36 valid species and should be distinguished from all mollusks as it yielded numerous new natural products. Aplysia sea hares are herbivorous mollusks, which have been proven to be a rich source of secondary metabolites, mostly of dietary origin. The majority of secondary metabolites isolated from sea hares of the genus Aplysia are halogenated terpenes; however, these animals are also a source of compounds from other chemical classes, such as macrolides, sterols and alkaloids, often exhibiting cytotoxic, antibacterial, antifungal, antiviral and/or antifeedant activities. This review focuses on the diverse structural classes of secondary metabolites found in Aplysia spp., including several compounds with pronounced biological properties.

Mycosporine-Like Amino Acids and Their Derivatives as Natural Antioxidants

Mycosporine-like amino acids (MAAs) are water-soluble molecules that absorb UV-A and UV-B radiation and disperse the energy as heat. MAAs show great diversity in their molecular structures, which exhibit a range of molecular weights spanning 188 to 1050 Daltons. MAAs are utilized in a wide variety of organisms including prokaryotes and eukaryotic micro-organisms that inhabit aquatic, terrestrial, and marine environments. These features suggest that MAAs are stable and fundamental molecules that allow these organisms to live under UV irradiation. MAAs are thought to have been greatly important to ancient forms of life on Earth, functioning as a primary sunscreen to reduce short-wavelength light. Structurally different MAAs might have been developed in MAA-producing organisms during their environmental adaptation. Harmful irradiation directly damages biomolecules, including lipids, proteins and DNA, and induces oxidative stress through radical-propagating processes. Thus, MAAs are expected to play an additional role in the antioxidant system. This review focuses on MAAs with radical scavenging activities. To cover all the reported MAAs known thus far, we surveyed the CAS database and have summarized the structures and the chemical and physical properties of these MAAs, including their antioxidant activities.

The relationship between UV-irradiance, photoprotective compounds and DNA damage in two intertidal invertebrates with contrasting mobility characteristics

The photoprotective role of mycosporine-like amino acids (MAA) against the generation of DNA cyclobutane pyrimidine dimers (CPD) was studied in the sessile intertidal anemone Actinia tenebrosa and the mobile intertidal gastropod Diloma aethiops through 27months at a mid-latitude New Zealand location. MAA were sequestered by A. tenebrosa and D. aethiops from their diet, although maximum total MAA levels in both species were not correlated with seasonal variation in maximum ambient UV-B levels recorded at the collection site. Temporal changes in total MAA in A. tenebrosa showed a six months lag-time in their concentration regarding to the environmental UV-B levels. This lag period corresponded to an observed increase in CPD production from spring to summer; suggesting that MAA do not completely protect the anemone from UV-B during summer. For D. aethiops, total MAA concentrations did not change significantly during the study, although qualitative changes in MAA were apparent. A month lag-time in MAA concentration in D. aethiops and possibly the physical barrier that the shell confers to the animal, can explain reduced CPD levels in comparative terms with A. tenebrosa. Although MAA are used by invertebrates for photoprotection, contrasting mobility characteristics and the presence of physical adaptations can confer them important protection levels during temporal changes of UV-B at mid-latitude places of the Southern Hemisphere.

Marine natural products

This review covers the literature published in 2011 for marine natural products, with 870 citations (558 for the period January to December 2011) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1152 for 2011), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Mycosporine-like amino acids are multifunctional molecules in sea hares and their marine community

Molecules of keystone significance are relatively rare, yet mediate a variety of interactions between organisms. They influence the distribution and abundance of species, the transfer of energy across multiple trophic levels, and thus they play significant roles in structuring ecosystems. Despite their potential importance in facilitating our understanding of ecological systems, only three molecules thus far have been proposed as molecules of keystone significance: saxitoxin and dimethyl sulfide in marine communities and tetrodotoxin in riparian communities. In the course of studying the neuroecology of chemical defenses, we identified three mycosporine-like amino acids (MAAs)--N-ethanol palythine (= asterina-330), N-isopropanol palythine (= aplysiapalythine A), and N-ethyl palythine (= aplysiapalythine B)--as intraspecific alarm cues for sea hares (Aplysia californica). These alarm cues are released in the ink secretion of sea hares and cause avoidance behaviors in neighboring conspecifics. Further, we show that these three bioactive MAAs, two [aplysiapalythine A (APA) and -B (APB)] being previously unknown molecules, are present in the algal diet of sea hares and are concentrated in their defensive secretion as well as in their skin. MAAs are known to be produced by algae, fungi, and cyanobacteria and are acquired by many aquatic animals through trophic interactions. MAAs are widely used as sunscreens, among other uses, but sea hares modify their function to serve a previously undocumented role, as intraspecific chemical cues. Our findings highlight the multifunctionality of MAAs and their role in ecological connectivity, suggesting that they may function as molecules of keystone significance in marine ecosystems.