Ovothiol A is the Main Antioxidant in Fish Lens

Cemtirestat dimerization in liposomes and erythrocytes exposed to peroxyl radicals was reverted by thiol-disulfide exchange with GSH

In the model system of DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) liposomes exposed to peroxyl radicals generated by the azoinitiator AAPH, cemtirestat (CMTI-SH) inhibited lipid peroxidation more efficiently than the natural antioxidant glutathione. In the concentrations 100 to 500 µM, both CMTI-SH and GSH induced distinct lag phases in the initial stages of lipid peroxidation yet GSH produced consistently shorter induction periods (about twice) than equimolar CMTI-SH. Moreover, concentration dependence of lipid peroxidation inhibition measured at the 80th minute, revealed about three times higher IC50 value for GSH compared to CMTI-SH. When the incubations prolonged till 180 min no further absorbance changes at 270 and 302 nm, respectively, occurred. After addition of the reducing agent tris(2-carboxyethyl)phosphine, the absorbance peak at 270 nm shifted back to 302 nm. These findings pointed to the presence of reducible CMTI-SH disulfide whose definite structure was confirmed by proving identity of TLC retention and spectral data with those of the synthesized CMTI disulfide. When CMTI-SH and GSH were present simultaneously in the liposomal incubations, the mixing effect on the induction period was synergistic rather than additive. This was explained by ability of GSH to reduce CMTI disulfide which was proved in separate experiments with an authentic CMTI disulfide prepared synthetically. This finding was also demonstrated by experiment with CMTI-disulfide to protect the erythrocytes against oxidative damage induced by peroxyl radicals. To conclude, CMTI-SH scavenges reactive oxygen species yielding CMTI disulfide while GSH maintains CMTI-SH in the reduced state. This finding was also demonstrated by experiment with CMTI-disulfide to protect the erythrocytes against oxidative damage induced by peroxyl radicals. CMTI-SH would thus represent the first line of the cellular defense against peroxyl radical mediated oxidative stress.

Bis(1-methylimidazol-2-yl) diselenide and its evaluation as a chemical radio-protector: role of kinetic rate constants for ROS scavenging and glutathione peroxidase like activity

Bis(1-methylimidazol-2-yl) diselenide (MeImSe), a derivative of selenoneine, has been examined for bimolecular rate constants for scavenging of various radiolytically and non-radiolytically generated reactive oxygen species (ROS). Further, its potential to show glutathione peroxidase (GPx)-like activity and to protect in vitro models of DNA and lipid against radiation induced strand breakage and lipid peroxidation, respectively were studied. The results confirmed that MeImSe scavenged all major short-lived (hydroxyl radical) and long-lived (peroxyl radical, carbonate radical, nitrogen dioxide radical, hypochlorite and hydrogen peroxide) oxidants involved in the radiation toxicity either directly or through GPx-like catalytic mechanism. The rate constants of MeImSe for these oxidants were found to be comparable to analogous sulfur and selenium-based compounds. The enzyme kinetics study established that MeImSe took part in the GPx cycle through the reductive pathway. Further, MeImSe inhibited the radiation induced DNA strand cleavage and lipid peroxidation with half maximal inhibitory concentration (IC50) of ∼ 60 μM and ∼100 μM, respectively. Interestingly, MeImSe treatment in the above concentration range (>100 μM) did not show any significant toxicity in normal human lung fibroblast (WI26) cells. The balance between efficacy and toxicity of MeImSe as a chemical radioprotector was attributed to the formation of less reactive intermediates during its oxidation/reduction reactions as evidenced from NMR studies.HighlightsMeImSe, a derivative of selenoneine protects DNA and lipid from radiation damageMeImSe scavenges all major short- and long-lived oxidants involved in radiation toxicityRate constants of MeImSe for ROS scavenging determined by pulse radiolysis techniqueFirst organoselenium compound reported to scavenge nitrogen dioxide radicalMeImSe exhibits GPx-like activity through reductive pathway.

Insights on the UV-Screening Potential of Marine-Inspired Thiol Compounds

One of the major threats to skin aging and the risk of developing skin cancer is excessive exposure to the sun's ultraviolet radiation (UVR). The use of sunscreens containing different synthetic, organic, and inorganic UVR filters is one of the most widespread defensive measures. However, increasing evidence suggests that some of these compounds are potentially eco-toxic, causing subtle damage to the environment and to marine ecosystems. Resorting to natural products produced in a wide range of marine species to counteract UVR-mediated damage could be an alternative strategy. The present work investigates marine-inspired thiol compounds, derivatives of ovothiol A, isolated from marine invertebrates and known to exhibit unique antioxidant properties. However, their potential use as photoprotective molecules for biocompatible sunscreens and anti-photo aging formulations has not yet been investigated. Here, we report on the UVR absorption properties, photostability, and in vitro UVA shielding activities of two synthetic ovothiol derivatives, 5-thiohistidine and iso-ovothiol A, by spectrophotometric and fluorimetric analysis. We found that the UVA properties of these compounds increase upon exposure to UVA and that their absorption activity is able to screen UVA rays, thus reducing the oxidative damage induced to proteins and lipids. The results of this work demonstrate that these novel marine-inspired compounds could represent an alternative eco-friendly approach for UVR skin protection.

Animal Metabolite Database: Metabolite Concentrations in Animal Tissues and Convenient Comparison of Quantitative Metabolomic Data

The Animal Metabolite Database (AMDB, https://amdb.online) is a freely accessible database with built-in statistical analysis tools, allowing one to browse and compare quantitative metabolomics data and raw NMR and MS data, as well as sample metadata, with a focus on the metabolite concentrations rather than on the raw data itself. AMDB also functions as a platform for the metabolomics community, providing convenient deposition and exchange of quantitative metabolomic data. To date, the majority of the data in AMDB relate to the metabolite content of the eye lens and blood of vertebrates, primarily wild species from Siberia, Russia and laboratory rodents. However, data on other tissues (muscle, heart, liver, brain, and more) are also present, and the list of species and tissues is constantly growing. Typically, every sample in AMDB contains concentrations of 60-90 of the most abundant metabolites, provided in nanomoles per gram of wet tissue weight (nmol/g). We believe that AMDB will become a widely used tool in the community, as typical metabolite baseline concentrations in tissues of animal models will aid in a wide variety of fundamental and applied scientific fields, including, but not limited to, animal modeling of human diseases, assessment of medical formulations, and evolutionary and environmental studies.

The Application of Quantitative Metabolomics for the Taxonomic Differentiation of Birds

In the current pilot study, we propose the use of quantitative metabolomics to reconstruct the phylogeny of vertebrates, namely birds. We determined the concentrations of the 67 most abundant metabolites in the eye lenses of the following 14 species from 6 orders of the class Aves (Birds): the Black kite (Milvus migrans), Eurasian magpie (Pica pica), Northern raven (Corvus corax), Eurasian coot (Fulica atra), Godlewski's bunting (Emberiza godlewskii), Great crested grebe (Podiceps cristatus), Great tit (Parus major), Hawfinch (Coccothraustes coccothraustes), Hooded crow (Corvus cornix), House sparrow (Passer domesticus), Rock dove (Columba livia), Rook (Corvus frugilegus), Short-eared owl (Asio flammeus) and Ural owl (Strix uralensis). Further analysis shows that the statistical approaches generally used in metabolomics can be applied for differentiation between species, and the most fruitful results were obtained with hierarchical clustering analysis (HCA). We observed the grouping of conspecific samples independently of the sampling place and date. The HCA tree structure supports the key role of genomics in the formation of the lens metabolome, but it also indicates the influence of the species lifestyle. A combination of genomics-based and metabolomics-based phylogeny could potentially resolve arising issues and yield a more reliable tree of life.

Metabolomic Analysis Reveals That the Moor Frog Rana arvalis Uses Both Glucose and Glycerol as Cryoprotectants

Simple Summary

The moor frog Rana arvalis can tolerate freezing to low temperatures, up to −16 °C. We performed metabolomic analysis of the liver and hindlimb muscles of frozen and control R. arvalis. We found that the moor frog synthesizes glucose and glycerol in similar concentrations as low molecular weight cryoprotectants. This is the first such case reported for the genus Rana, which was believed to use glucose only. We found that freezing upregulates glycolysis, with the accumulation of several end products: lactate, alanine, ethanol, and, possibly, 2,3-butanediol. To our knowledge, this is also the first report of ethanol as an end product of glycolysis in terrestrial vertebrates. We observed highly increased concentrations of nucleotide degradation products, implying high level of stress. We found almost no signs of adaptations to reoxygenation stress, with overall low levels of antioxidants. We also performed metabolomics analysis of subcutaneous ice that was found to contain glucose, glycerol, and several other substances.

Abstract

The moor frog Rana arvalis is one of a few amphibians that can tolerate freezing to low temperatures, up to −16 °C. In this study, we performed metabolomic analysis of the liver and hindlimb muscles of frozen and control R. arvalis. We found that the moor frog synthesizes glucose and glycerol in similar concentrations as low molecular weight cryoprotectants. This is the first such case reported for the genus Rana, which was believed to use glucose only. We found that freezing upregulates glycolysis, with the accumulation of several end products: lactate, alanine, ethanol, and, possibly, 2,3-butanediol. To our knowledge, this is also the first report of ethanol as an end product of glycolysis in terrestrial vertebrates. We observed highly increased concentrations of nucleotide degradation products, implying high level of stress. The Krebs cycle arrest resulted in high concentrations of succinate, which is common for animals. However, we found almost no signs of adaptations to reoxygenation stress, with overall low levels of antioxidants. We also performed metabolomics analysis of subcutaneous ice that was found to contain glucose, glycerol, and several other substances.

Ergothioneine, Ovothiol A, and Selenoneine-Histidine-Derived, Biologically Significant, Trace Global Alkaloids

The history, chemistry, biology, and biosynthesis of the globally occurring histidine-derived alkaloids ergothioneine (10), ovothiol A (11), and selenoneine (12) are reviewed comparatively and their significance to human well-being is discussed.

A Survey on the Distribution of Ovothiol and ovoA Gene Expression in Different Tissues and Cells: A Comparative Analysis in Sea Urchins and Mussels

Ovothiols are histidine-derived thiols produced by a variety of marine invertebrates, protists and bacteria. These compounds, which are among the strongest natural antioxidants, are involved in controlling the cellular redox balance due to their redox exchange with glutathione. Although ovothiols were initially reported as protective agents against environmental stressors, new evidence suggests that they can also act as pheromones and participate in fundamental biological processes such as embryogenesis. To get further insight into the biological roles of ovothiols, we compared ovothiol biosynthesis in the sea urchin Paracentrotus lividus and in the mussel Mytilus galloprovincialis, the two species that represent the richest sources of these compounds among marine invertebrates. Ovothiol content was measured in different tissues and in the immune cells from both species and the expression levels of ovoA, the gene responsible for ovothiol biosynthesis, was inferred from publicly available transcriptomes. A comparative analysis of ovothiol biosynthesis in the two species allowed the identification of the tissues and cells synthesizing the metabolite and highlighted analogies and differences between sea urchins and mussels. By improving our knowledge on the biological roles of ovothiols and pointing out the existence of sustainable natural sources for their isolation, this study provides the basis for future biotechnological investigations on these valuable compounds.

Ovothiol ensures the correct developmental programme of the sea urchin Paracentrotus lividus embryo

Ovothiols are π-methyl-5-thiohistidines produced in great amounts in sea urchin eggs, where they can act as protective agents against the oxidative burst at fertilization and environmental stressors during development. Here we examined the biological relevance of ovothiol during the embryogenesis of the sea urchin Paracentrotus lividus by assessing the localization of the key biosynthetic enzyme OvoA, both at transcript and protein level, and perturbing its protein translation by morpholino antisense oligonucleotide-mediated knockdown experiments. In addition, we explored the possible involvement of ovothiol in the inflammatory response by assessing ovoA gene expression and protein localization following exposure to bacterial lipopolysaccharide. The results of the present study suggest that ovothiol may be a key regulator of cell proliferation in early developing embryos. Moreover, the localization of OvoA in key larval cells and tissues, in control and inflammatory conditions, suggests that ovothiol may ensure larval skeleton formation and mediate inflammatory processes triggered by bacterial infection. This work significantly contributes to the understanding of the biological function of ovothiols in marine organisms, and may provide new inspiration for the identification of the biological activities of ovothiols in humans, considering the pharmacological potential of these molecules.

First Report of OvoA Gene in Marine Arthropods: A New Candidate Stress Biomarker in Copepods

Ovothiol is one of the most powerful antioxidants acting in marine organisms as a defense against oxidative stress during development and in response to environmental cues. The gene involved in the ovothiol biosynthesis, OvoA, is found in almost all metazoans, but open questions existed on its presence among arthropods. Here, using an in silico workflow, we report a single OvoA gene in marine arthropods including copepods, decapods, and amphipods. Phylogenetic analyses indicated that OvoA from marine arthropods separated from the other marine phyla (e.g., Porifera, Mollusca) and divided into two separate branches, suggesting a possible divergence through evolution. In the copepod Calanus finmarchicus, we suggest that OvoA has a defense role in oxidative stress as shown by its high expression in response to a toxic diet and during the copepodite stage, a developmental stage that includes significant morphological changes. Overall, the results of our study open possibilities for the use of OvoA as a biomarker of stress in copepods and possibly also for other marine holozooplankters. The finding of OvoA in copepods is also promising for the drug discovery field, suggesting the possibility of using copepods as a new source of bioactive compounds to be tested in the marine biotechnological sector.

Biochemical Response to Freezing in the Siberian Salamander Salamandrella keyserlingii

Simple Summary

The Siberian salamander is a unique amphibian that is capable to survive long-term freezing at −55 °C. We used ¹H-NMR analysis to study quantitative changes of multiple metabolites in liver and hindlimb muscle of the Siberian salamander in response to freezing. For the majority of molecules we observed significant changes in concentrations. Glycerol content in frozen organs was as high as 2% w/w, which confirms its role as a cryoprotectant. No other putative cryoprotectants were detected. Freezing resulted in increased concentrations of glycolysis products: lactate and alanine. Unexpectedly, we detected no increase in concentrations of succinate, which accumulates under ischemia in various tetrapods. Freezing proved to be a dramatic stress with high levels of nucleotide degradation products. There was also significant increase in the concentrations of choline and glycerophosphocholine, which may be interpreted as the degradation of biomembranes. Thus, we found that freezing results not only in macroscopical damage due to ice formation, but also to degradation of DNA and biomembranes.

Abstract

The Siberian salamander Salamandrella keyserlingii Dybowski, 1870 is a unique amphibian that is capable to survive long-term freezing at −55 °C. Nothing is known on the biochemical basis of this remarkable freezing tolerance, except for the fact that it uses glycerol as a low molecular weight cryoprotectant. We used ¹H-NMR analysis to study quantitative changes of multiple metabolites in liver and hindlimb muscle of S. keyserlingii in response to freezing. For the majority of molecules we observed significant changes in concentrations. Glycerol content in frozen organs was as high as 2% w/w, which confirms its role as a cryoprotectant. No other putative cryoprotectants were detected. Freezing resulted in ischemia manifested as increased concentrations of glycolysis products: lactate and alanine. Unexpectedly, we detected no increase in concentrations of succinate, which accumulates under ischemia in various tetrapods. Freezing proved to be a dramatic stress with reduced adenosine phosphate pool and high levels of nucleotide degradation products (hypoxanthine, β-alanine, and β-aminoisobutyrate). There was also significant increase in the concentrations of choline and glycerophosphocholine, which may be interpreted as the degradation of biomembranes. Thus, we found that freezing results not only in macroscopical damage due to ice formation, but also to degradation of DNA and biomembranes.

Kinetic Studies of Antioxidant Properties of Ovothiol A

Ovothiol A (OSH) is one of the strongest natural antioxidants. So far, its presence was found in tissues of marine invertebrates, algae and fish. Due to very low pKa value of the SH group, under physiological conditions, this compound is almost entirely present in chemically active thiolate form and reacts with ROS and radicals significantly faster than other natural thiols. In biological systems, OSH acts in tandem with glutathione GSH, with OSH neutralizing oxidants and GSH maintaining ovothiol in the reduced state. In the present work, we report the rate constants of OSH oxidation by H₂O₂ and of reduction of oxidized ovothiol OSSO by GSH and we estimate the Arrhenius parameters for these rate constants. The absorption spectra of reaction intermediates, adduct OSSG and sulfenic acid OSOH, were obtained. We also found that OSH effectively quenches the triplet state of kynurenic acid with an almost diffusion-controlled rate constant. This finding indicates that OSH may serve as a good photoprotector to inhibit the deleterious effect of solar UV irradiation; this assumption explains the high concentrations of OSH in the fish lens. The unique antioxidant and photoprotecting properties of OSH open promising perspectives for its use in the treatment of human diseases.

Metabolic adaptations to marine environments: molecular diversity and evolution of ovothiol biosynthesis in Bacteria

Ovothiols are sulfur-containing amino acids synthesized by marine invertebrates, protozoans, and bacteria. They act as pleiotropic molecules in signaling and protection against oxidative stress. The discovery of ovothiol biosynthetic enzymes, sulfoxide synthase OvoA and β-lyase OvoB, paves the way for a systematic investigation of ovothiol distribution and molecular diversification in nature. In this work, we conducted genomic and metagenomics data mining to investigate the distribution and diversification of ovothiol biosynthetic enzymes in Bacteria. We identified the bacteria endowed with this secondary metabolic pathway, described their taxonomy, habitat and biotic interactions in order to provide insight into their adaptation to specific environments. We report that OvoA and OvoB are mostly encountered in marine aerobic Proteobacteria, some of them establishing symbiotic or parasitic relationships with other organisms. We identified a horizontal gene transfer event of OvoB from Bacteroidetes living in symbiosis with Hydrozoa. Our search within the Ocean Gene Atlas revealed the occurrence of ovothiol biosynthetic genes in Proteobacteria living in a wide range of pelagic and highly oxygenated environments. Finally, we tracked the evolutionary history of ovothiol biosynthesis from marine bacteria to unicellular eukaryotes and metazoans. Our analysis provides new conceptual elements to unravel the evolutionary and ecological significance of ovothiol biosynthesis.

Most abundant metabolites in tissues of freshwater fish pike-perch (Sander lucioperca)

Quantitative metabolomic analysis was performed for eleven tissues of freshwater fish pike-perch (Sander lucioperca), including gill, heart, liver, kidney, spleen, muscle, brain, milt, lens, aqueous (AH) and vitreous (VH) humors with the use of NMR spectroscopy. The absolute values of concentrations were determined for more than 65 most abundant metabolites in every tissue. It was found that from the metabolomic viewpoint, kidney and gill are the most similar tissues, while the metabolomic compositions of ocular tissues—lens, AH, and VH significantly differ from that of other tissues. The combinations of intracellular osmolytes and antioxidants are specific for every tissue. In particular, the concentration of antioxidant ovothiol A in the lens is much higher than in any other tissue, while the brain enjoys the elevated level of ascorbate. The most abundant osmolyte in the fish spleen, muscle, and heart is taurine, and in the brain, gill, and lens—myo-inositol. Other important osmolytes specific for particular tissues are N-acetyl-histidine, N-acetyl-aspartate, betaine, threonine-phosphoethanolamine, and serine-phosphoethanolamine. The quantitative data obtained in the present work can be used as the baseline metabolite concentrations in the fish tissues to evaluate the influence of seasonal, ecological and other factors on the fish metabolism.

Insights into the Light Response of Skeletonema marinoi: Involvement of Ovothiol

Diatoms are one of the most widespread groups of microalgae on Earth. They possess extraordinary metabolic capabilities, including a great ability to adapt to different light conditions. Recently, we have discovered that the diatom Skeletonema marinoi produces the natural antioxidant ovothiol B, until then identified only in clams. In this study, we investigated the light-dependent modulation of ovothiol biosynthesis in S. marinoi. Diatoms were exposed to different light conditions, ranging from prolonged darkness to low or high light, also differing in the velocity of intensity increase (sinusoidal versus square-wave distribution). The expression of the gene encoding the key ovothiol biosynthetic enzyme, ovoA, was upregulated by high sinusoidal light mimicking natural conditions. Under this situation higher levels of reactive oxygen species and nitric oxide as well as ovothiol and glutathione increase were detected. No ovoA modulation was observed under prolonged darkness nor low sinusoidal light. Unnatural conditions such as continuous square-wave light induced a very high oxidative stress leading to a drop in cell growth, without enhancing ovoA gene expression. Only one of the inducible forms of nitric oxide synthase, nos2, was upregulated by light with consequent production of NO under sinusoidal light and darkness conditions. Our data suggest that ovothiol biosynthesis is triggered by a combined light stress caused by natural distribution and increased photon flux density, with no influence from the daily light dose. These results open new perspectives for the biotechnological production of ovothiols, which are receiving a great interest for their biological activities in human model systems.

Metabolic response of the Siberian wood frog Rana amurensis to extreme hypoxia

The Siberian wood frog Rana amurensis is a recently discovered example of extreme hypoxia tolerance that is able to survive several months without oxygen. We studied metabolomic profiles of heart and liver of R. amurensis exposed to 17 days of extreme hypoxia. Without oxygen, the studied tissues experience considerable stress with a drastic decrease of ATP, phosphocreatine, and NAD+ concentrations, and concomitant increase of AMP, creatine, and NADH. Heart and liver switch to different pathways of glycolysis with differential accumulation of lactate, alanine, succinate, as well as 2,3-butanediol (previously not reported for vertebrates as an end product of glycolysis) and depletion of aspartate. We also observed statistically significant changes in concentrations of certain osmolytes and choline-related compounds. Low succinate/fumarate ratio and high glutathione levels indicate adaptations to reoxygenation stress. Our data suggest that maintenance of the ATP/ADP pool is not required for survival of R. amurensis, in contrast to anoxia-tolerant turtles.

First evidence of ovothiol biosynthesis in marine diatoms

Ovothiols are histidine-derived thiols that are receiving a great interest for their biological activities in human model systems. Thanks to the position of the thiol group on the imidazole ring of histidine, these compounds exhibit unusual antioxidant properties. They have been revealing a very promising pharmacological potential due to their anti-proliferative and anti-inflammatory properties, as well as anti-fibrotic activities not always related to their antioxidant power. Ovothiols occur in three differentially methylated forms (A, B and C), isolated from ovary, eggs and biological fluids of many marine invertebrates, mollusks, microalgae, and pathogenic protozoa. These molecules are synthesized by two enzymes: the sulfoxide synthase OvoA and the sulfoxide lyase OvoB. OvoA catalyzes the insertion of the sulfur atom of cysteine on the imidazole ring of histidine, leading to the formation of a sulfoxide intermediate. This is then cleaved by OvoB, giving 5-thiohistidine, finally methylated on the imidazole ring thanks to the methyltransferase domain of OvoA. Recent studies have shown that OvoA homologs are encoded in a wide variety of genomes suggesting that ovothiol biosynthesis is much more widespread in nature than initially thought. Here we have investigated the OvoA occurrence in diatoms, one of the most abundant group of microalgae, dominating marine and freshwater environments. They are considered a very good model system for both biology/photophysiology studies and for biotechnological applications. We have performed comparative sequence and phylogenetic analyses of OvoA from diatoms, highlighting a high degree of conservation of the canonical domain architecture in the analyzed species, as well as a clear clustering of OvoA in the two different morphological groups, i.e. centric and pennate diatoms. The in silico analyses have also revealed that OvoA gene expression is modulated by growth conditions. More importantly, we have characterized the thiol fraction from cultures of the coastal centric diatom Skeletonema marinoi, providing the first evidence of ovothiol B biosynthesis in diatoms.

Gametogenesis-Related Fluctuations in Ovothiol Levels in the Mantle of Mussels from Different Estuaries: Fighting Oxidative Stress for Spawning in Polluted Waters

Reactive oxygen species present a challenge for marine organisms releasing gametes into the water. Thiol-containing molecules protect cells against oxidative stress, and ovothiol (OSH), an antioxidant-reducing mercaptohistidine, has been described as especially relevant in the oocytes of marine invertebrates. Ovothiol synthase (ovoA), in charge of the first step in OSH synthesis, was sequenced in mussels, Mytilus galloprovincialis. Transcription levels of ovoA in mantle did not significantly change along the reproductive cycle. No alterations of ovoA transcription were observed after a laboratory copper (10 µg/L) exposure or in mussels captured in a highly polluted site. Conversely, the metabolomic analysis of the hydrophilic metabolite content in mantle clearly classified mussels according to their site of origin, especially at the most advanced stages of oogenesis. Quantification of OSH-A and -B and glutathione (GSH), revealed stable levels in mantle at early gametogenesis in the unpolluted sampling site, but a strong increase in female mantle previous to spawning in the polluted site. These increased concentrations under pollution suggest that OSH-A accumulates along oogenesis, independent of gene transcription regulation. The concerted accumulation of OSH-A and GSH suggests the building of a balanced cellular redox-system to scavenge ROS produced in the oocyte before and during fertilization.

Seasonal Variations and Interspecific Differences in Metabolomes of Freshwater Fish Tissues: Quantitative Metabolomic Profiles of Lenses and Gills

This work represents the first comprehensive report on quantitative metabolomic composition of tissues of pike-perch (Sander lucioperca) and Siberian roach (Rutilus rutilus lacustris). The total of 68 most abundant metabolites are identified and quantified in the fish lenses and gills by the combination of LC-MS and NMR. It is shown that the concentrations of some compounds in the lens are much higher than that in the gills; that indicates the importance of these metabolites for the adaptation to the specific living conditions and maintaining the homeostasis of the fish lens. The lens metabolome undergoes significant seasonal changes due to the variations of dissolved oxygen level and fish feeding activity. The most season-affected metabolites are osmolytes and antioxidants, and the most affected metabolic pathway is the histidine pathway. In late autumn, the major lens osmolytes are N-acetyl-histidine and threonine phosphoethanolamine (Thr-PETA), while in winter the highest concentrations were observed for serine phosphoethanolamine (Ser-PETA) and myo-inositol. The presence of Thr-PETA and Ser-PETA in fish tissues and their role in cell osmotic protection are reported for the first time. The obtained concentrations can be used as baseline levels for studying the influence of environmental factors on fish health.