Trimethylamine oxide accumulation in marine animals: relationship to acylglycerol storagej

Mechanistic Insights into Choline Degradation Catalyzed by the Choline Trimethylamine-Lyase CutC

Choline trimethylamine-lyase (CutC) is a prominent glycyl radical enzyme that catalyzes the degradation of choline into nitrogenous metabolites trimethylamine (TMA) and acetaldehyde. Choline and TMA are crucial nitrogen-containing compounds and play essential roles in various biological pathways, including neurotransmission and global metabolic functions. Although many experimental studies have been dedicated to elucidating the function of CutC, its exact catalytic mechanism remains elusive. Herein, we employed molecular dynamics (MD) simulations and quantum mechanics/molecular mechanics (QM/MM) methodologies to investigate the reaction mechanism of CutC in detail. Our calculation results reveal that the enzymatic reaction is initiated by a two-step hydrogen atom transfer (HAT) mechanism, a typical process mediated by a cysteine radical in glycyl radical enzymes (GREs). Significantly, in our suggested reaction mechanism, unlike the previously proposed 1,2-elimination pathway, a more favorable stepwise 1,2-migration of the TMA group occurs after the formation of a substrate radical. This migration of the TMA group leads to the formation of a hemiaminal intermediate, which is likely to be eliminated outside of CutC. Furthermore, our mechanistic investigations indicate that the residue Glu440, adjacent to the choline substrate, plays a pivotal role in helping substrate binding through a hydrogen bond rather than serving as a general base for proton abstraction. These findings provide deeper insights into the catalytic strategy that CutC employs for C-N bond cleavage in choline metabolism and broaden the mechanistic repertoire documented for glycyl radical enzymes in mediating elimination reactions.

Spiny dogfish, Squalus suckleyi, shows a good tolerance for hypoxia but need long recovery times

Pacific spiny dogfish, Squalus suckleyi, move to shallow coastal waters during critical reproductive life stages and are thus at risk of encountering hypoxic events which occur more frequently in these areas. For effective conservation management, we need to fully understand the consequences of hypoxia on marine key species such as elasmobranchs. Because of their benthic life style, we hypothesized that S. suckleyi are hypoxia tolerant and able to efficiently regulate oxygen consumption, and that anaerobic metabolism is supported by a broad range of metabolites including ketones, fatty acids and amino acids. Therefore, we studied oxygen consumption rates, ventilation frequency and amplitude, blood gasses, acid-base regulation, and changes in plasma and tissue metabolites during progressive hypoxia. Our results show that critical oxygen levels (P crit) where oxyregulation is lost were indeed low (18.1% air saturation or 28.5 Torr at 13°C). However, many dogfish behaved as oxyconformers rather than oxyregulators. Arterial blood PO2 levels mostly decreased linearly with decreasing environmental PO2. Blood gases and acid-base status were dependent on open versus closed respirometry but in both set-ups ventilation frequency increased. Hypoxia below Pcrit resulted in an up-regulation of anaerobic glycolysis, as evidenced by increased lactate levels in all tissues except brain. Elasmobranchs typically rely on ketone bodies as oxidative substrates, and decreased concentrations of acetoacetate and β-hydroxybutyrate were observed in white muscle of hypoxic and/or recovering fish. Furthermore, reductions in isoleucine, glutamate, glutamine and other amino acids were observed. After 6 hours of normoxic recovery, changes persisted and only lactate returned to normal in most tissues. This emphasizes the importance of using suitable bioindicators adjusted to preferred metabolic pathways of the target species in conservation physiology. We conclude that Pacific spiny dogfish can tolerate severe transient hypoxic events, but recovery is slow and negative impacts can be expected when hypoxia persists.

Feed Components and Timing to Improve the Feed Conversion Ratio for Sustainable Aquaculture Using Starch

Aquaculture contributes to the sustainable development of food security, marine resource conservation, and economy. Shifting aquaculture feed from fish meal and oil to terrestrial plant derivatives may result in cost savings. However, many carnivorous fish cannot be sustained on plant-derived materials, necessitating the need for the identification of important factors for farmed fish growth and the identification of whether components derived from terrestrial plants can be used in feed. Herein, we focused on the carnivorous fish leopard coral grouper (P. leopardus) to identify the essential growth factors and clarify their intake timing from feeds. Furthermore, we evaluated the functionality of starch, which are easily produced by terrestrial plants. Results reveal that carbohydrates, which are not considered essential for carnivorous fish, can be introduced as a major part of an artificial diet. The development of artificial feed using starch offers the possibility of increasing the growth of carnivorous fish in aquaculture.

Dietary betaine and/or TMAO affect hepatic lipid accumulation and glycometabolism of Megalobrama amblycephala exposed to a high-carbohydrate diet

A 12-week experiment was conducted to explore the effects of betaine and/or TMAO on growth, hepatic health, gut microbiota, and serum metabolites in Megalobrama amblycephala fed with high-carbohydrate diets. The diets were as follows: CD group (control diet, 28.5% carbohydrate), HCD group (high-carbohydrate diet, 38.2% carbohydrate), HBD group (betaine-added diet, 38.3% carbohydrate + 1.2% betaine), HTD group (TMAO-added diet, 38.2% carbohydrate + 0.2% TMAO), and HBT group (diet added with both betaine and TMAO, 38.2% carbohydrate + 1.2% betaine + 0.2% TMAO). The results showed that the hepatosomatic index (HSI); whole-body crude fat; hepatic lipid accumulation; messenger RNA expression levels of gk, fpbase, g6pase, ahas, and bcat; serum branched-chain amino acids (BCAAs); ratio of Firmicutes-to-Bacteroidetes; and abundance of the genus Aeromonas were all significantly increased, while the abundance levels of the genus Lactobacillus and phyla Tenericutes and Bacteroidetes were drastically decreased in the HCD group. Compared with the HCD group, the HSI; whole-body crude fat; hepatic lipid accumulation; expression levels of fbpase, g6pase, pepck, ahas, and bcat; circulating BCAA; ratio of Firmicutes-to-Bacteroidetes; and abundance levels of the genus Aeromonas and phyla Tenericutes and Bacteroidetes were significantly downregulated in the HBD, HTD, and HBT groups. Meanwhile, the expression levels of pk were drastically upregulated in the HBD, HTD, and HBT groups as well as the abundance of Lactobacillus in the HBT group. These results indicated that the supplementation of betaine and/or TMAO in high-carbohydrate diets could affect the hepatic lipid accumulation and glycometabolism of M. amblycephala by promoting glycolysis, inhibiting gluconeogenesis and biosynthesis of BCAA, and mitigating the negative alteration of gut microbiota. Among them, the combination of betaine and TMAO had the best effect.

The characteristics of trimethylamine N-oxide content in different classes of marine animals over the coastal and offshore areas of China

Trimethylamine N-oxide (TMAO) is widely present in marine animals. However, the characteristics of TMAO content in different classes of marine animals are insufficiently understood. In this study, the TMAO content in 79 marine animals (48 species, 7 classes) collected in the coastal and offshore areas of China during year 2019-2022 was analysed. The results showed that the TMAO content of the total samples varied from 0 to 139.19 mmol kg-1. The TMAO content in the classes Bivalvia, Gastropoda, Polychaeta and Holothuroidea varied from 0.06 ± 0.09 to 0.38 ± 0.63 mmol kg-1, but it varied from 30.20 ± 24.20 to 75.90 ± 38.59 mmol kg-1 in the classes Crustacea, Cephalopoda, and Osteichthyes. The TMAO content in the latter 3 classes was 2-3 orders of magnitude higher than that of the former 4 classes. It was inferred that the significant difference was related to the food sources or physiological metabolic mechanisms of different classes.

Oxidative stress and cryoresistance of sturgeon sperm: A review

Currently, the majority of sturgeons are relict fishes of high economic value yet endangered with extinction. Cryopreservation of sperm has great potential in fish farming and conservation, but the problem of low cryoresistance of sturgeon sperm has not yet been solved. The goal of this work was to review current literature data on the causes of low tolerance of sturgeon sperm to cryodamage. The influence of cryopreservation on the parameters of physiology and metabolism of sturgeon sperm (morphology and fine ultrastructure, mobility and fertilization ability, integrity of the plasma membrane, protein, lipid and metabolite profiles, antioxidant status, DNA damage), as well as on biomarkers of oxidative stress (lipids peroxidation levels and carbonyl derivatives of proteins) is discussed. Since the development of oxidative stress is an important mechanism of sperm cryodamage induction, the review presents the literature on the role of oxygen-derived species in damage of sturgeon reproductive cells caused by cryopreservation. Particular attention is paid to the system of antioxidant protection of sturgeon seminal plasma and spermatozoa, represented by antioxidant enzymes and low molecular weight antioxidants capable of utilizing various reactive forms of oxygen and nitrogen. The review discusses the results of lipidomic and proteomic studies of sturgeon sperm, which made it possible to obtain new data on the lipid composition of cell membranes, to detect proteins involved in the protection of sturgeon spermatozoa from oxidative damage during cryopreservation. This review presents the use of «omics» technology to elucidate the mechanism of cryodamage in sturgeon sperm. Additionally, the review summarizes information on the unique anatomical, morphological, biochemical, and physiological features of sturgeon sperm, which may be associated with low cryoresistance of sturgeon, in order to establish prospects for further research on improving the methods of the conservation of sperm of these threatened species.

Identifying the key factors affecting the trimethylamine N-oxide content of teleost fishes collected from the marginal seas of China and the epipelagic zone of the northwest Pacific Ocean

To identify the key factors influencing the trimethylamine N-oxide (TMAO) content of teleost fishes living in shallow seas and the epipelagic zone of the deep ocean, the muscle TMAO content was measured in 152 teleost fishes (21 species) collected from the marginal seas of China and the epipelagic zone of the northwest Pacific Ocean (NWPO) during May-July 2021. The results showed that the TMAO content in all fishes varied from 4.99 to 82.97 mmol kg-1, and it varied notably among different species, e.g., the highest average content (72.71 ± 8.22 mmol kg-1 in Argyrosomus argentatus) was 1 order of magnitude higher than the lowest one (Scomber japonicus), but the ratios of the highest content to the lowest content in each species varied from 1.29 to 3.28, suggesting that the interspecific variations in TMAO content were obviously greater than the intraspecific variations. Moreover, no correlation was observed between the TMAO content of the 152 fishes and the corresponding environmental factors of seawater depth, salinity and temperature, indicating that species played a more important role than environmental factors in driving TMAO accumulation. To exclude the influence of species, intraspecies correlations between TMAO content and environmental factors were analyzed. In the marginal seas of China, only ∼8 % of the TMAO content of teleost fishes (1 species) showed a positive correlation with salinity and depth, but ∼50 % of the TMAO content (5 species) was negatively correlated with temperature. Moreover, the TMAO content of the fish increased by 4.66 ± 1.38 % compared with their corresponding intraspecific average values for every 1 °C of temperature decrease. A similar phenomenon was also found in the TMAO content of pelagic teleost fishes in the NWPO, suggesting that temperature was a key environmental factor affecting the TMAO content of teleost fishes in shallow seas and the epipelagic zone of the deep ocean.

1H-NMR-Based Metabolic Profiling in Muscle and Liver Tissue of Juvenile Turbot (Scophthalmus maximus) Fed with Plant and Animal Protein Sources

Circular economy driven feed ingredients and emerging protein sources, such as insects and microbial meals, has the potential to partially replace fishmeal in diets of high-trophic fish. Even though growth and feed performance are often unaffected at low inclusion levels, the metabolic effects are unknown. This study examined the metabolic response of juvenile turbot (Scophthalmus maximus) to diets with graded fishmeal replacement with plant, animal, and emerging protein sources (PLANT, PAP, and MIX) in comparison to a commercial-like diet (CTRL). A ¹H-nuclear magnetic resonance (NMR) spectroscopy was used to assess the metabolic profiles of muscle and liver tissue after feeding the fish the experimental diets for 16 weeks. The comparative approach revealed a decrease in metabolites that are associated with energy deficiency in both tissues of fish fed with fishmeal-reduced diets compared to the commercial-like diet (CTRL). Since growth and feeding performance were unaffected, the observed metabolic response suggests that the balanced feed formulations, especially at lower fishmeal replacement levels, have the potential for industry application.

The role of gut-dependent molecule trimethylamine N-oxide as a novel target for the treatment of chronic kidney disease

Trimethylamine N-oxide (TMAO) is an intestinal uremic toxin molecule mainly excreted by the kidney. Therefore, the plasma TMAO concentration is significantly increased in chronic kidney disease (CKD) patients, and plasma TMAO can be cleared by dialysis. Furthermore, TMAO damage the kidney mainly through three mechanisms: oxidative stress, inflammation and endoplasmic reticulum stress. Clinical experiments have indicated that higher TMAO levels are strongly related to the elevated incidence and mortality of cardiovascular (CV) events in CKD patients. Moreover, experimental data have shown that high levels of TMAO directly aggravate atherosclerosis, thrombosis and enhance myocardial contractility, resulting in myocardial ischemia and stroke. Specially, there are currently four potential ways to reduce blood TMAO concentration or block the effect of TMAO, including reducing the intake of trimethylamine (TMA) precursors in the diet, regulating the intestinal flora to reduce TMA production, interrupting the role of flavin-dependent monooxygenase isoforms (FMOs) to reduce the generation of TMAO, and blocking the TMAO receptor protein kinase R-like endoplasmic reticulum kinase (PERK). We hope that more clinical studies and clinicians will focus on clinical treatment to reduce the concentration of TMAO and alleviate renal damage.

Metabolism response mechanism in the gill of Oreochromis mossambicus under salinity, alkalinity and saline-alkalinity stresses

Saline-alkalinity is one of the important ecological parameter that has an impact function on the physiological metabolism, osmoregulation, survival, growth, development and distribution of teleost fish. Oreochromis mossambicus, a species of euryhaline that can withstand a wide variety of salinities, may be used as a research model animal in environmental studies. In order to detect the metabolism responses and mechanisms of different osmotic stresses tolerance in the gills of O. mossambicus, in present study, the metabolic responses of O. mossambicus subjected to salinity (25 g/L, S_S), alkalinity (4 g/L, A_S) and saline-alkalinity stress (salinity: 25 g/L, alkalinity: 4 g/L; SA_S) with the control environment (freshwater, C_S) were investigated by LC-MS/MS-based metabolomics. The metabolism results indicated that numerous metabolites were identified between the stress groups and the control group. In addition, under three osmotic stresses, the amino acid and carbohydrate metabolism, levels of amino acids, osmolytes and energy substances, such as L-lysine, arachidonic acid, docosahexaenoic acids, creatine and taurine, were significantly affected and changed in the metabolism of the gills of O. mossambicus. The metabolism data indicated that signal transduction and regulation pathways, including FoxO signaling pathway, mTOR signaling pathway and prolactin signaling pathway, were enriched in the gill during adaptation to high salinity, alkalinity and saline-alkalinity stress. The results of this study provide more comprehensive and reliable data for the osmotic pressure regulation mechanism and biological response of euryhaline teleost, and provide reliable scientific basis for the breeding and research of high salinity tolerance population, and further promote the development and utilization of saline-alkalinity water resources.

Gut microbiome and metabolites, the future direction of diagnosis and treatment of atherosclerosis?

Over the past few decades, the treatment of atherosclerotic cardiovascular disease has mainly been through an LDL lowering strategy and treatments targeting other traditional risk factors for atherosclerosis, which has significantly reduced cardiovascular mortality. However, the overall benefit of targeting these risk factors has stagnated, and the discovery of new therapeutic targets for atherosclerosis remains a challenge. Accumulating evidence from clinical and animal experiments has revealed that the gut microbiome play a significant role in human health and disease, including cardiovascular diseases. The gut microbiome contribute to host health and disease through microbial composition and function. The gut microbiome function like an endocrine organ by generating bioactive metabolites that can impact atherosclerosis. In this review, we describe two gut microbial metabolites/pathways by which the gut affects atherosclerotic cardiovascular disease. On the one hand, we discuss the effects of trimethylamine oxide (TMAO), bile acids and aromatic amino acid metabolites on the development of atherosclerosis, and the protective effects of beneficial metabolites short chain amino acids and polyamines on atherosclerosis. On the other hand, we discuss novel therapeutic strategies for directly targeting gut microbial metabolites to improve cardiovascular outcomes. Reducing gut-derived TMAO levels and interfering with the bile acid receptor farnesoid X receptor (FXR) are new therapeutic strategies for atherosclerotic disease. Enzymes and receptors in gut microbiota metabolic pathways are potential new drug targets. We need solid insight into these underlying mechanisms to pave the way for therapeutic strategies targeting gut microbial metabolites/pathways for atherosclerotic cardiovascular disease.

Panax notoginseng saponins alleviate damage to the intestinal barrier and regulate levels of intestinal microbes in a rat model of chronic kidney disease

OBJECTIVES

Chronic kidney disease (CKD) is a long-term condition characterized by poor prognosis and a high mortality rate. Panax notoginseng saponins (PNS) are the main active ingredient of the traditional Chinese herb Panaxnotoginseng(Burk.)F.H.Chen, which has been widely reported to have various pharmacological effects. Here, we examined the effect of PNS on renal function and the modulation of intestinal flora and intestinal barrier in a rat model of adenine-induced CKD.

METHODS

Adenine was used to establish a rat model of CKD, biochemical testing, histopathologic examination, ELISA, immunohistochemical assay, western blot assay, and fecal microbiota 16s rRNA analysis was used to test the effect of PNS on CKD rats.

RESULTS

Adenine induced a significant decrease in glomerular filtration rate, an increase in urinary protein excretion rate, and pathological damage to renal tissue in CKD rats. TNF-α, MCP-1, IL-1β, IL-18, TMAO, and endotoxin levels were increased in the blood of the model rats. Application of PNS countered the effects of adenine, restoring the above parameters to the level observed in healthy rats. In addition, activation of the inflammatory proteins NF-κB (p65) and NLRP3 and the fibrosis-associated proteins α-SMA and smad3 were inhibited in the kidneys of CKD rats. Furthermore, PNS promoted the expression of the tight junction proteins Occludin and ZO-1, increased SIgA levels, strengthened intestinal immunity, reduced mechanical damage to the intestine, was reduced levels of DAO and D-LA. Our data suggest PNS may delay CKD by restoring gut microbiota, and through the subsequent generation of a microbial barrier and modulation of microbiota metabolites.

CONCLUSIONS

In conclusion, PNS may inhibit the development of inflammation and fibrosis in the kidney tissue through regulation of intestinal microorganisms and inhibition of the activation of pro-inflammatory and pro-fibrotic proteins in the kidney.

Innate immunity and protective effects of orally administered betaine against viral and bacterial diseases in the olive flounder Paralichthys olivaceus (Temminck & Schlegel)

Sustainable methods that increase farmed fish yield while controlling infections are required to prevent economic losses in aquaculture farms. In this study, we evaluated the effects of betaine-supplemented (0%, 0.1%, 0.5%, and 1.0%) feed on the growth and immunity of the olive flounder Paralichthys olivaceus. Feed conversion ratios, post-infection cumulative mortality rates and innate immune responses were monitored. Weight gain was significantly higher with 0.5% and 1.0% than with 0% and 0.1% betaine-supplemented feed. Lysozyme activity was highest with 1.0% betaine. Respiratory burst activity was highest with 0.5% and 1.0% betaine. Serum bactericidal activity against Edwardsiella tarda was highest with 1.0% betaine (40% increase in survival rates compared with those in the control). Furthermore, serum virucidal activity against the viral haemorrhagic septicaemia virus (VHSV) was higher with 1.0% betaine than with other concentrations. With 0.5% and 1.0% betaine, the survival rates against VHSV were higher than those in the control until day 11, after which they declined. Our study suggests that betaine is a promising agent for promoting the growth of and enhancing immunity against E. tarda in olive flounders. Our findings may further contribute to developing necessary alternatives to conventional antibiotics in fish farming.

Implications of trimethylamine N-oxide (TMAO) and Betaine in Human Health: Beyond Being Osmoprotective Compounds

Osmolytes are naturally occurring small molecular weight organic molecules, which are accumulated in large amounts in all life forms to maintain the stability of cellular proteins and hence preserve their functions during adverse environmental conditions. Trimethylamine N-oxide (TMAO) and N,N,N-trimethylglycine (betaine) are methylamine osmolytes that have been extensively studied for their diverse roles in humans and have demonstrated opposing relations with human health. These osmolytes are obtained from food and synthesized endogenously using dietary constituents like choline and carnitine. Especially, gut microbiota plays a vital role in TMAO synthesis and contributes significantly to plasma TMAO levels. The elevated plasma TMAO has been reported to be correlated with the pathogenesis of numerous human diseases, including cardiovascular disease, heart failure, kidney diseases, metabolic syndrome, etc.; Hence, TMAO has been recognized as a novel biomarker for the detection/prediction of several human diseases. In contrast, betaine acts as a methyl donor in one-carbon metabolism, maintains cellular S-adenosylmethionine levels, and protects the cells from the harmful effects of increased plasma homocysteine. Betaine also demonstrates antioxidant and anti-inflammatory activities and has a promising therapeutic value in several human diseases, including homocystinuria and fatty liver disease. The present review examines the multifarious functions of TMAO and betaine with possible molecular mechanisms towards a better understanding of their emerging and diverging functions with probable implications in the prevention, diagnosis, and treatment of human diseases.

Cephalopods as Challenging and Promising Blue Foods: Structure, Taste, and Culinary Highlights and Applications

Foods are complex systems due to their biological origin. Biological materials are soft matter hierarchically structured on all scales from molecules to tissues. The structure reflects the biological constraints of the organism and the function of the tissue. The structural properties influence the texture and hence the mouthfeel of foods prepared from the tissue, and the presence of flavour compounds is similarly determined by biological function. Cephalopods, such as squid, cuttlefish, and octopuses, are notoriously known for having challenging texture due to their muscles being muscular hydrostats with highly cross-linked collagen. Similar with other marine animals such as fish and crustaceans, cephalopods are rich in certain compounds such as free amino acids and free 5′-ribonucleotides that together elicit umami taste. Scientific investigations of culinary applications of cephalopods as foods must therefore involve mechanical studies (texture analysis), physicochemical measurements of thermodynamic properties (protein denaturation), as well as chemical analysis (taste and aroma compounds). The combination of such basic science investigations of food as a soft material along with an exploration of the gastronomic potential has been termed gastrophysics. In this review paper, we reviewed available gastrophysical studies of cephalopod structure, texture, and taste both as raw, soft material and in certain preparations.

Trimethylamine N-Oxide Reduces the Susceptibility of Escherichia coli to Multiple Antibiotics

Trimethylamine N-oxide (TMAO), an important intestinal flora-derived metabolite, plays a role in the development of cardiovascular disease and tumor immunity. Here, we determined the minimum inhibitory concentration (MIC) of antibiotics against Escherichia coli under gradient concentrations of TMAO and performed a bacterial killing analysis. Overall, TMAO (in the range of 10 ~ 100 mM) increased the MIC of quinolones, aminoglycosides, and β-lactams in a concentration-dependent manner, and increased the lethal dose of antibiotics against E. coli. It implies that TMAO is a potential risk for failure of anti-infective therapy, and presents a case for the relationship between intestinal flora-derived metabolites and antibiotic resistance. Further data demonstrated that the inhibition of antibiotic efficacy by TMAO is independent of the downstream metabolic processes of TMAO and the typical bacterial resistance mechanisms (mar motif and efflux pump). Interestingly, TMAO protects E. coli from high-protein denaturant (urea) stress and improves the viability of bacteria following treatment with two disinfectants (ethanol and hydrogen peroxide) that mediate protein denaturation by chemical action or oxidation. Since antibiotics can induce protein inactivation directly or indirectly, our work suggests that disruption of protein homeostasis may be a common pathway for different stress-mediated bacterial growth inhibition/cell death. In addition, we further discuss this possibility, which provides a different perspective to address the global public health problem of antibiotic resistance.

Identifying a Correlation among Qualitative Non-Numeric Parameters in Natural Fish Microbe Dataset Using Machine Learning

Recent technical innovations and developments in computer-based technology have enabled bioscience researchers to acquire comprehensive datasets and identify unique parameters within experimental datasets. However, field researchers may face the challenge that datasets exhibit few associations among any measurement results (e.g., from analytical instruments, phenotype observations as well as field environmental data), and may contain non-numerical, qualitative parameters, which make statistical analyses difficult. Here, we propose an advanced analysis scheme that combines two machine learning steps to mine association rules between non-numerical parameters. The aim of this analysis is to identify relationships between variables and enable the visualization of association rules from data of samples collected in the field, which have less correlations between genetic, physical, and non-numerical qualitative parameters. The analysis scheme presented here may increase the potential to identify important characteristics of big datasets.

Taurine Alleviates Trimethylamine N-Oxide-Induced Atherosclerosis by Regulating Bile Acid Metabolism in ApoE-/- Mice

Trimethylamine N-oxide (TMAO) widely exists in seafood and is associated with the atherosclerosis progress, but dietary seafood reduced the cardiovascular risk. This intimates that there may be some ingredients in seafood to offset the cardiovascular risk caused by TMAO. Taurine is a marker ingredient in seafood. Thus, this study determined the influences of taurine on TMAO-induced atherosclerosis in apolipoprotein-E-deficient mice. The results showed that dietary taurine significantly reduced the TMAO-induced atherosclerotic lesion area. Further studies found that taurine increased the hepatic- and serum-conjugated bile acid/unconjugated bile acid ratio via increasing hepatic gene expression of conjugated bile acid synthesis. Meanwhile, taurine changed TMAO-induced abnormal bile acid profiles in the gallbladder. Moreover, taurine increased bile acid deconjugation by enhancing the genera Ruminiclostridium level and increased excretion of fecal neutral sterols. Additionally, taurine attenuated inflammation in the serum and artery. These results indicate that taurine alleviated TMAO-induced atherosclerosis via regulating bile acid metabolism.

Interplay between diet and gut microbiome, and circulating concentrations of trimethylamine N-oxide: findings from a longitudinal cohort of US men

OBJECTIVES

Gut-produced trimethylamine N-oxide (TMAO) is postulated as a possible link between red meat intake and poor cardiometabolic health. We investigated whether gut microbiome could modify associations of dietary precursors with TMAO concentrations and cardiometabolic risk markers among free-living individuals.

DESIGN

We collected up to two pairs of faecal samples (n=925) and two blood samples (n=473), 6 months apart, from 307 healthy men in the Men's Lifestyle Validation Study. Diet was assessed repeatedly using food-frequency questionnaires and diet records. We profiled faecal metagenome and metatranscriptome using shotgun sequencing and identified microbial taxonomic and functional features.

RESULTS

TMAO concentrations were associated with the overall microbial compositions (permutational analysis of variance (PERMANOVA) test p=0.001). Multivariable taxa-wide association analysis identified 10 bacterial species whose abundance was significantly associated with plasma TMAO concentrations (false discovery rate <0.05). Higher habitual intake of red meat and choline was significantly associated with higher TMAO concentrations among participants who were microbial TMAO-producers (p<0.05), as characterised based on four abundant TMAO-predicting species, but not among other participants (for red meat, P-interaction=0.003; for choline, P-interaction=0.03). Among abundant TMAO-predicting species, Alistipes shahii significantly strengthened the positive association between red meat intake and HbA1c levels (P-interaction=0.01). Secondary analyses revealed that some functional features, including choline trimethylamine-lyase activating enzymes, were associated with TMAO concentrations.

CONCLUSION

We identified microbial taxa that were associated with TMAO concentrations and modified the associations of red meat intake with TMAO concentrations and cardiometabolic risk markers. Our data underscore the interplay between diet and gut microbiome in producing potentially bioactive metabolites that may modulate cardiometabolic health.

Characterization of short-chain fatty acids in patients with ulcerative colitis: a meta-analysis

BACKGROUND

Studies investigating the changes in short-chain fatty acids (SCFAs) in patients with ulcerative colitis (UC) have yielded inconsistent results. We performed a meta-analysis of studies that investigated the alterations in different SCFAs among UC patients to assess their role in the development of UC.

METHODS

Three databases were searched for relevant studies published as of April 2021. Results are presented as standardized mean difference (SMD) with 95% confidence interval (95% CI).

RESULTS

Eleven studies were included in the meta-analysis. Compared to healthy subjects, UC patients had significantly lower concentrations of total SCFAs (SMD = - 0.88, 95%CI - 1.44, - 0.33; P < 0.001), acetate (SMD = - 0.54, 95% CI - 0.91, - 0.17; P = 0.004), propionate, (SMD = - 0.37, 95% CI - 0.66, - 0.07; P = 0.016), and valerate (SMD = - 0.91, 95% CI - 1.45, - 0.38; P < 0.001). On subgroup analysis based on disease status, patients with active UC had reduced concentrations of acetate (SMD = - 1.83, 95% CI - 3.32, - 0.35; P = 0.015), propionate (SMD = - 2.51, 95% CI - 4.41, - 0.61; P = 0.009), and valerate (SMD = - 0.91, 95% CI - 1.45, - 0.38; P < 0.001), while UC patients in remission had similar concentrations with healthy subjects. Patients with active UC had lower butyrate level (SMD = - 2.09, 95% CI - 3.56, - 0.62; P = 0.005) while UC patients in remission had higher butyrate level (SMD = 0.71, 95% CI 0.33, 1.10; P < 0.001) compared with healthy subjects.

CONCLUSION

UC patients had significantly decreased concentrations of total SCFAs, acetate, propionate, and valerate compared with healthy subjects. In addition, inconsistent changes of certain special SCFAs were observed in UC patients with different disease status.

Characterization of the Trimethylamine N-Oxide Transporter From Pelagibacter Strain HTCC1062 Reveals Its Oligotrophic Niche Adaption

Trimethylamine N-oxide (TMAO), which was detected at nanomolar concentrations in surface seawaters, is an important carbon, nitrogen and/or energy source for marine bacteria. It can be metabolized by marine bacteria into volatile methylated amines, the second largest source of nitrogen after N2 gas in the oceans. The SAR11 bacteria are the most abundant oligotrophic plankton in the oceans, which represents approximately 30% of the bacterial cells in marine surface waters. Genomic analysis suggested that most SAR11 bacteria possess an ATP-binding cassette transporter TmoXWV that may be responsible for importing TMAO. However, it was still unclear whether SAR11 bacteria can utilize TMAO as the sole nitrogen source and how they import TMAO. Here, our results showed that Pelagibacter strain HTCC1062, a SAR11 bacterium, can grow with TMAO as the sole nitrogen source. TmoXWV from strain HTCC1062 (TmoXWV1062) was verified to be a functional TMAO importer. Furthermore, TmoX1062, the periplasmic substrate binding protein of TmoXWV1062, was shown to have high binding affinities toward TMAO at 4°C (Kd = 920 nM), 10°C (Kd = 500 nM) and 25°C (Kd = 520 nM). The high TMAO binding affinity and strong temperature adaptability of TmoX1062 reveal a possible oligotrophic niche adaptation strategy of strain HTCC1062, which may help it gain a competitive advantage over other bacteria. Structure comparison and mutational analysis indicated that the TMAO binding mechanism of TmoX1062 may have differences from the previously reported mechanism of TmoX of Ruegeria pomeroyi DSS-3. This study provides new insight into TMAO utilization by the widespread SAR11 bacteria.

Transcriptional response to prolonged perchlorate exposure in the methanogen Methanosarcina barkeri and implications for Martian habitability

Observations of trace methane (CH4) in the Martian atmosphere are significant to the astrobiology community given the overwhelming contribution of biological methanogenesis to atmospheric CH4 on Earth. Previous studies have shown that methanogenic Archaea can generate CH4 when incubated with perchlorates, highly oxidizing chaotropic salts which have been found across the Martian surface. However, the regulatory mechanisms behind this remain completely unexplored. In this study we performed comparative transcriptomics on the methanogen Methanosarcina barkeri, which was incubated at 30˚C and 0˚C with 10-20 mM calcium-, magnesium-, or sodium perchlorate. Consistent with prior studies, we observed decreased CH4 production and apparent perchlorate reduction, with the latter process proceeding by heretofore essentially unknown mechanisms. Transcriptomic responses of M. barkeri to perchlorates include up-regulation of osmoprotectant transporters and selection against redox-sensitive amino acids. Increased expression of methylamine methanogenesis genes suggest competition for H2 with perchlorate reduction, which we propose is catalyzed by up-regulated molybdenum-containing enzymes and maintained by siphoning diffused H2 from energy-conserving hydrogenases. Methanogenesis regulatory patterns suggest Mars' freezing temperatures alone pose greater constraints to CH4 production than perchlorates. These findings increase our understanding of methanogen survival in extreme environments and confers continued consideration of a potential biological contribution to Martian CH4.

Scope of Archaea in Fish Feed: a New Chapter in Aquafeed Probiotics?

The outbreak of diseases leading to substantial loss is a major bottleneck in aquaculture. Over the last decades, the concept of using feed probiotics was more in focus to address the growth and health of cultivable aquatic organisms. The objective of this review is to provide an overview of the distinct functionality of archaea from conventional probiotics in nutrient utilization, specific caloric contribution, evading immune response and processing thermal resistance. The prime limitation of conventional probiotics is the viability of desired microbes under harsh feed processing conditions. To overcome the constraints of commercial probiotics pertaining to incompatibility towards industrial processing procedure, a super microbe, archaea, appears to be a potential alternative approach in aquaculture. The peculiarity of the archaeal cell wall provides them with heat stability and rigidity under industrial processing conditions. Besides, archaea being one of the gut microbial communities participates in various health-oriented biological functions in animals. Thus, the current review devoted that administration of archaea in aquafeed could be a promising strategy in aquaculture. Archaea may be used as a potential probiotic with the possible modes of functions and advantages over conventional probiotics in aquafeed preparation. The present review also provides the challenges associated with the use of archaea for aquaculture and a brief outline of the patents on archaea to highlight the various use of archaea in different sectors.

Metabolism response of grazing yak to dietary concentrate supplementation in warm season

Supplementary feeding has a significant effect on the growth performance of grazing yaks. However, as far as is known, little information is available concerning how energy or protein feed supplementation affects the serum metabolome of grazing yaks during the warm season. We investigated the effects of supplementation with two different concentrates on the serum metabolome in grazing yaks using nuclear magnetic resonance spectroscopy in conjunction with multivariate data analysis. Twenty-four 2-year-old female yaks (133.04 ± 6.52 kg BW) were randomly divided into three groups and fed three different regimes (n = 8 per group): (1) grazing plus hull-less barley (HLB) supplementation, (2) grazing plus rapeseed meal (RSM) supplementation, and (3) grazing without supplementation. Both HLB and RSM supplementation significantly increased the average daily gain (ADG), and ADG under HLB supplementation was 11.9% higher (P < 0.05) than that of the RSM group. Supplementation markedly altered glucose, lipid, and protein metabolism, with the difference manifested as increased levels of some amino acids, acetyl-glycoproteins, low-density lipoproteins, and very low-density lipoproteins . Furthermore, the levels of 3-hydroxybutyrate, acetoacetate, and lactate metabolism were decreased. Serum metabolite changes in yaks in the HLB supplementation treatment differed from those in the RSM supplementation treatment; the difference was primarily manifested in lipid- and protein-related metabolites. We conclude that both the energy supplementation (HLB) and the protein supplementation (RSM) could remarkably promote the growth of yak heifers during the warm season, and the effect of energy supplementation was superior. Supplementary feeding changed the serum metabolite levels of yak heifers, indicating that such feeding could improve glucose's energy-supply efficiency and increase the metabolic intensity of lipids and proteins. Supplementation of yaks with HLB was more efficient in the promotion of yak glucose and protein anabolism compared to supplementation with RSM, while having a lesser effect on lipid metabolism.

Effect of TMAO on the Structure and Phase Transition of Lipid Membranes: Potential Role of TMAO in Stabilizing Cell Membranes under Osmotic Stress

Extremophiles adopt strategies to deal with different environmental stresses, some of which are severely damaging to their cell membrane. To combat high osmotic stress, deep-sea organisms synthesize osmolytes, small polar organic molecules, like trimethylamine-N-oxide (TMAO), and incorporate them in the cell. TMAO is known to protect cells from high osmotic or hydrostatic pressure. Several experimental and simulation studies have revealed the roles of such osmolytes on stabilizing proteins. In contrast, the effect of osmolytes on the lipid membrane is poorly understood and broadly debated. A recent experiment has found strong evidence of the possible role of TMAO in stabilizing lipid membranes. Using the molecular dynamics (MD) simulation technique, we have demonstrated the effect of TMAO on two saturated fully hydrated lipid membranes in their fluid and gel phases. We have captured the impact of TMAO's concentration on the membrane's structural properties along with the fluid/gel phase transition temperatures. On increasing the concentration of TMAO, we see a substantial increase in the packing density of the membrane (estimated by area, thickness, and volume) and enhancement in the orientational order of lipid molecules. Having repulsive interaction with the lipid head group, the TMAO molecules are expelled away from the membrane surface, which induces dehydration of the lipid head groups, increasing the packing density. The addition of TMAO also increases the fluid/gel phase transition temperature of the membrane. All of these results are in close agreement with the experimental observations. This study, therefore, provides a molecular-level understanding of how TMAO can influence the cell membrane of deep-sea organisms and help in combating the osmotic stress condition.

1H NMR-based metabolomic analysis of cuttlefish, Sepia pharaonis (Ehrenberg, 1831) exposed to hypoxia stresses and post-anoxia recovery

Oxygen deficiency (hypoxia and anoxia) is an emerging concern in estuarine and coastal ecosystems worldwide. Previous studies on Mollusca Cephalopoda have focused on the effects of hypoxia stress on physiological performance and survival, but there are few reports on the molecular mechanism, and the application of metabolomics in cephalopods remains unknown. In this study, a ¹H nuclear magnetic resonance (NMR) based metabolomics approach was applied to investigate the metabolites profiles of Sepia pharaonis (Ehrenberg, 1831) during hypoxia and post-anoxia recovery. The results revealed that obvious tissue-specific metabolic responses were induced by hypoxia stresses. Hypoxia exposure influenced the levels of many metabolites (e.g. BCAAs, lactate, and betaine strongly accumulated in the hepatic tissue while arginine and ATP significantly reduced; lactate and adenosine significantly increased in gills whereas arginine and choline significantly decreased; GABA, taurine and adenosine levels increased in brain but a significant depletion of N-Acetylaspartate and glycogen was found), disturbed energy and amino acid metabolism, and broke the balance of neurotransmitters and osmoregulators. Notably, almost all metabolites returned to pre-exposure levels after acute hypoxia recovery. However, we noted a pronounced depletion of the amino acid pool (arginine, glutamine, and alanine) in hepatic and gills after recovery, as well as organic osmolytes fluctuations (choline, betaine, and taurine). This work highlights the potential of metabolomics methods to elucidate the response of cuttlefish to hypoxia stress, as well as to provide knowledge on metabolic changes in cephalopods under the influences of environmental stress.

Thermal Range and Physiological Tolerance Mechanisms in Two Shark Species from the Northwest Atlantic

Spiny dogfish (Squalus acanthias) and smoothhound (Mustelus canis) sharks in the northwest Atlantic undergo seasonal migrations driven by changes in water temperature. However, the recognized thermal habitats of these regional populations are poorly described. Here, we report the thermal range, catch frequency with bottom temperature, and catch frequency with time of year for both shark species in Narragansett Bay, Rhode Island. Additionally, we describe levels of two thermal stress response indicators, heat-shock protein 70 and trimethylamine N-oxide, with an experimental increase in water temperature from 15 °C to 21 °C. Our results show that S. acanthias can be found in this region year-round and co-occurs with M. canis from June to November. Further, adult S. acanthias routinely inhabits colder waters than M. canis (highest catch frequencies at bottom temperatures of 10 °C and 21 °C, respectively), but both exhibit similar upper thermal ranges in this region (bottom temperatures of 22-23 °C). Additionally, acute exposure to a 6 °C increase in water temperature for 72 hours leads to a nearly threefold increase in heat-shock protein 70 levels in S. acanthias but not M. canis. Therefore, these species display differences in their thermal tolerance and stress response with experimental exposure to 21 °C, a common summer temperature in Narragansett Bay. Further, in temperature-stressed S. acanthias there is no accumulation of trimethylamine N-oxide. At the whole-organism level, elasmobranchs' trimethylamine N-oxide regulatory capacity may be limited by other factors. Alternatively, elasmobranchs may not rely on trimethylamine N-oxide as a primary thermal protective mechanism under the conditions tested. Findings from this study are in contrast with previous research conducted with elasmobranch cells in vitro that showed accumulation of trimethylamine N-oxide after thermal stress and subsequent suppression of the heat-shock protein 70 response.

Dietary metabolism, the gut microbiome, and heart failure

Advances in our understanding of how the gut microbiota contributes to human health and diseases have expanded our insight into how microbial composition and function affect the human host. Heart failure is associated with splanchnic circulation congestion, leading to bowel wall oedema and impaired intestinal barrier function. This situation is thought to heighten the overall inflammatory state via increased bacterial translocation and the presence of bacterial products in the systemic blood circulation. Several metabolites produced by gut microorganisms from dietary metabolism have been linked to pathologies such as atherosclerosis, hypertension, heart failure, chronic kidney disease, obesity, and type 2 diabetes mellitus. These findings suggest that the gut microbiome functions like an endocrine organ by generating bioactive metabolites that can directly or indirectly affect host physiology. In this Review, we discuss several newly discovered gut microbial metabolic pathways, including the production of trimethylamine and trimethylamine N-oxide, short-chain fatty acids, and secondary bile acids, that seem to participate in the development and progression of cardiovascular diseases, including heart failure. We also discuss the gut microbiome as a novel therapeutic target for the treatment of cardiovascular disease, and potential strategies for targeting intestinal microbial processes.

A Multi-omic Association Study of Trimethylamine N-Oxide

Trimethylamine N-oxide (TMAO) is a circulating metabolite that has been implicated in the development of atherosclerosis and cardiovascular disease (CVD). In this paper, we identify blood markers, metabolites, proteins, gut microbiota patterns, and diets that are significantly associated with levels of plasma TMAO. We find that kidney markers are strongly associated with TMAO and identify CVD-related proteins that are positively correlated with TMAO. We show that metabolites derived by the gut microbiota are strongly correlated with TMAO and that the magnitude of this correlation varies with kidney function. Moreover, we identify diet-associated patterns in the microbiome that are correlated with TMAO. These findings suggest that both the process of TMAO accumulation and the mechanism by which TMAO promotes atherosclerosis are a complex interplay between diet and the microbiome on one hand and other system-level factors such as circulating proteins, metabolites, and kidney function.

Mechanoregulation of titanium dioxide nanoparticles in cancer therapy

Titanium dioxide (TiO₂) nanoparticles (NPs), first developed in the 1990s, have been applied in numerous biomedical fields such as tissue engineering and therapeutic drug development. In recent years, TiO₂-based drug delivery systems have demonstrated the ability to decrease the risk of tumorigenesis and improve cancer therapy. There is increasing research on the origin and effects of pristine and doped TiO₂-based nanotherapeutic drugs. However, the detailed molecular mechanisms by which drug delivery to cancer cells alters sensing of gene mutations, protein degradation, and metabolite changes as well as its associated cumulative effects that determine the microenvironmental mechanosensitive metabolism have not yet been clearly elucidated. This review focuses on the microenvironmental influence of TiO₂-NPs induced various mechanical stimuli on tumor cells. The differential expression of genome, proteome, and metabolome after treatment with TiO₂-NPs is summarized and discussed. In the tumor microenvironment, mechanosensitive DNA mutations, gene delivery, protein degradation, inflammatory responses, and cell viability affected by the mechanical stimuli of TiO₂-NPs are also examined.

Metabolic adaptation to feed restriction on the green sturgeon (Acipenser medirostris) fingerlings

Food restriction may cause severe biological effects on wildlife and lead to population decline and extinction. The objective of the current study was to examine the metabolic effects on green sturgeon in response to feed restriction. Green sturgeon fingerlings were fed for two weeks at 12.5, 25, 50 and 100% of the optimum feeding rate (OFR), which corresponded to 0.25, 0.50, 1.00, and 2.00% body weight per day. We characterized the changes in hydrophilic and hydrophobic metabolites from extracts of muscle, liver, and kidney using nuclear magnetic resonance spectroscopy followed by multivariate statistical analysis. The results of principal component analysis (PCA) score plots from the analyses of hydrophilic metabolites showed that they exhibited a greater response to feed restriction than hydrophobic metabolites. In general, the hydrophilic metabolites in tissues from fish fed ≦25% of the OFR were separated from those fed 100% of the OFR in the PCA score plots. Among the three types of tissues examined, the overall metabolite changes showed a greater response to feed restriction in kidney tissue than in liver or muscle tissues. Numerous glucogenic amino acids in muscle and most amino acids in the kidney were decreased under feed restriction conditions. A significant decrease in ketone bodies (3-hydroxyisobutyrate) was observed in the muscle. Most fatty acids except for glycerol, phospholipid and cholesterol in the liver and kidney tissues were decreased under feed restriction conditions. Creatine phosphate, taurine and glycine were also significantly increased in tissues under feed restriction conditions. In conclusion, this study suggests that the manipulation of feed restriction under the current conditions perturbed metabolites related to energy metabolism, osmolality regulation, and antioxidation capacity in the sturgeon.

Metabolomic profiles differ among unique genotypes of a threatened Caribbean coral

Global threats to reefs require urgent efforts to resolve coral attributes that affect survival in a changing environment. Genetically different individuals of the same coral species are known to exhibit different responses to the same environmental conditions. New information on coral physiology, particularly as it relates to genotype, could aid in unraveling mechanisms that facilitate coral survival in the face of stressors. Metabolomic profiling detects a large subset of metabolites in an organism, and, when linked to metabolic pathways, can provide a snapshot of an organism’s physiological state. Identifying metabolites associated with desirable, genotype-specific traits could improve coral selection for restoration and other interventions. A key step toward this goal is determining whether intraspecific variation in coral metabolite profiles can be detected for species of interest, however little information exists to illustrate such differences. To address this gap, we applied untargeted ¹H-NMR and LC-MS metabolomic profiling to three genotypes of the threatened coral Acropora cervicornis. Both methods revealed distinct metabolite “fingerprints” for each genotype examined. A number of metabolites driving separation among genotypes were identified or putatively annotated. Pathway analysis suggested differences in protein synthesis among genotypes. For the first time, these data illustrate intraspecific variation in metabolomic profiles for corals in a common garden. Our results contribute to the growing body of work on coral metabolomics and suggest future work could identify specific links between phenotype and metabolite profile in corals.

Unveiling hákarl: A study of the microbiota of the traditional Icelandic fermented fish

Hákarl is produced by curing of the Greenland shark (Somniosus microcephalus) flesh, which before fermentation is toxic due to the high content of trimethylamine (TMA) or trimethylamine N-oxide (TMAO). Despite its long history of consumption, little knowledge is available on the microbial consortia involved in the fermentation of this fish. In the present study, a polyphasic approach based on both culturing and DNA-based techniques was adopted to gain insight into the microbial species present in ready-to-eat hákarl. To this aim, samples of ready-to-eat hákarl were subjected to viable counting on different selective growth media. The DNA directly extracted from the samples was further subjected to Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) and 16S amplicon-based sequencing. Moreover, the presence of Shiga toxin-producing Escherichia coli (STEC) and Pseudomonas aeruginosa was assessed via qualitative real-time PCR assays. pH values measured in the analyzed samples ranged from between 8.07 ± 0.06 and 8.76 ± 0.00. Viable counts revealed the presence of total mesophilic aerobes, lactic acid bacteria and Pseudomonadaceae. Regarding bacteria, PCR-DGGE analysis highlighted the dominance of close relatives of Tissierella creatinophila. For amplicon sequencing, the main operational taxonomic units (OTUs) shared among the data set were Tissierella, Pseudomonas, Oceanobacillus, Abyssivirga and Lactococcus. The presence of Pseudomonas in the analyzed samples supports the hypothesis of a possible role of this microorganism on the detoxification of shark meat from TMAO or TMA during fermentation. Several minor OTUs (<1%) were also detected, including Alkalibacterium, Staphylococcus, Proteiniclasticum, Acinetobacter, Erysipelothrix, Anaerobacillus, Ochrobactrum, Listeria and Photobacterium. Analysis of the yeast and filamentous fungi community composition by PCR-DGGE revealed the presence of close relatives of Candida tropicalis, Candida glabrata, Candida parapsilosis, Candida zeylanoides, Saccharomyces cerevisiae, Debaryomyces, Torulaspora, Yamadazyma, Sporobolomyces, Alternaria, Cladosporium tenuissimum, Moristroma quercinum and Phoma/Epicoccum, and some of these species probably play key roles in the development of the sensory qualities of the end product. Finally, qualitative real-time PCR assays revealed the absence of STEC and Pseudomonas aeruginosa in all of the analyzed samples.

Metabolic responses in the gills of tongue sole (Cynoglossus semilaevis) exposed to salinity stress using NMR-based metabolomics

Salinity is an important environmental factor affecting fish physiology. Tongue sole (Cynoglossus semilaevis) is a euryhaline species that can survive in a wide range of salinity, and might be used as a promising model animal for environmental science. In this study, by using the nuclear magnetic resonance (¹H NMR)-based metabolomics, amino acids analysis and real-time quantitative PCR assay, we investigated the metabolic responses in the gills and plasma of tongue sole subjected to hypo- (0 ppt, S0) and hyper-osmotic stress (50 ppt, S50) from isosmotic environment (30 ppt, S30). The results showed that the metabolic profiles of S50 were significantly different from those of S0 and S30 groups, and a clear overlap was found between the latter two groups. Ten metabolites were significantly different between the salt stress groups and the isosmotic group. Taurine and creatine elevated in both S0 and S50 groups. Choline decreased in S50 group while increased in S0 group. Amino acids and energy compounds were higher in the gills of S50 group. The metabolic network showed that ten metabolic pathways were all found in S50 group, while seven pathways were observed in S0 group. Meanwhile, the transcript levels of the Tau-T and ATP synthase in the gills increased with increasing salinity. Aspartate and methionine exhibited significant differences in the plasma among the groups, but did not show differences in the gills. Comparatively, glutamate exhibited significant differences both in the plasma and the gills. Overall, these findings provide a preliminary profile of osmotic regulation in euryhaline fish.

STC1 and PTHrP Modify Carbohydrate and Lipid Metabolism in Liver of a Teleost Fish

Stanniocalcin 1 (STC1) and parathyroid hormone-related protein (PTHrP) are calciotropic hormones in vertebrates. Here, a recently hypothesized metabolic role for these hormones is tested on European sea bass treated with: (i) teleost PTHrP(1-34), (ii) PTHrP(1-34) and anti-STC1 serum (pro-PTHrP groups), (iii) a PTHrP antagonist PTHrP(7-34) or (iv) PTHrP(7-34) and STC1 (pro-STC1 groups). Livers were analysed using untargeted metabolic profiling based on proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Concentrations of branched-chain amino acid (BCAA), alanine, glutamine and glutamate increased in pro-STC1 groups suggesting their mobilization from the muscle to the liver for degradation and gluconeogenesis from alanine and glutamine. In addition, only STC1 treatment decreased the concentrations of succinate, fumarate and acetate, indicating slowing of the citric acid cycle. In the pro-PTHrP groups the concentrations of glucose, erythritol and lactate decreased, indicative of gluconeogenesis from lactate. Taurine, trimethylamine, trimethylamine N-oxide and carnitine changed in opposite directions in the pro-STC1 versus the pro-PTHrP groups, suggesting opposite effects, with STC1 stimulating lipogenesis and PTHrP activating lipolysis/β-oxidation of fatty acids. These findings suggest a role for STC1 and PTHrP related to strategic energy mechanisms that involve the production of glucose and safeguard of liver glycogen reserves for stressful situations.

Microbial trimethylamine metabolism in marine environments

Trimethylamine (TMA) is common in marine environments. Although the presence of this compound in the oceans has been known for a long time, unlike the mammalian gastrointestinal tract, where TMA metabolism by microorganisms has been studied intensely, many questions remain unanswered about the microbial metabolism of marine TMA. This minireview summarizes what is currently known about the sources and fate of TMA in marine environments and the different pathways and enzymes involved in TMA metabolism in marine bacteria. This review also raises several questions about microbial TMA metabolism in the marine environments and proposes potential directions for future studies.

High Hydrostatic Pressure Inducible Trimethylamine N-Oxide Reductase Improves the Pressure Tolerance of Piezosensitive Bacteria Vibrio fluvialis

High hydrostatic pressure (HHP) exerts severe effects on cellular processes including impaired cell division, abolished motility and affected enzymatic activities. Transcriptomic and proteomic analyses showed that bacteria switch the expression of genes involved in multiple energy metabolism pathways to cope with HHP. We sought evidence of a changing bacterial metabolism by supplying appropriate substrates that might have beneficial effects on the bacterial lifestyle at elevated pressure. We isolated a piezosensitive marine bacterium Vibrio fluvialis strain QY27 from the South China Sea. When trimethylamine N-oxide (TMAO) was used as an electron acceptor for energy metabolism, QY27 exhibited a piezophilic-like phenotype with an optimal growth at 30 MPa. Raman spectrometry and biochemistry analyses revealed that both the efficiency of the TMAO metabolism and the activity of the TMAO reductase increased under high pressure conditions. Among the two genes coding for TMAO reductase catalytic subunits, the expression level and enzymatic activity of TorA was up-regulated by elevated pressure. Furthermore, a genetic interference assay with the CRISPR-dCas9 system demonstrated that TorA is essential for underpinning the improved pressure tolerance of QY27. We extended the study to Vibrio fluvialis type strain ATCC33809 and observed the same phenotype of TMAO-metabolism improved the pressure tolerance. These results provide compelling evidence for the determinant role of metabolism in the adaption of bacteria to the deep-sea ecosystems with HHP.

Untargeted metabolic profiling reveals distinct patterns of thermal sensitivity in two related notothenioids

Antarctic marine ectothermal animals may be affected more than temperate species by rising temperatures due to ongoing climate change. Their specialisation on stable cold temperatures makes them vulnerable to even small degrees of warming. Thus, addressing the impacts of warming on Antarctic organisms and identifying their potentially limited capacities to respond is of interest. The objective of the study was to determine changes in metabolite profiles related to temperature acclimation. In a long-term experiment adult fish of two Antarctic sister species Notothenia rossii and Notothenia coriiceps were acclimated to 0°C and 5°C for three months. Impacts and indicators of acclimation at the cellular level were determined from metabolite profiles quantified in gill tissue extracts using nuclear magnetic resonance (NMR) spectroscopy. Furthermore, the metabolite profiles of the two con-generic species were compared. NMR spectroscopy identified 37 metabolites that were present in each sample, but varied in their absolute concentration between species and between treatments. A decrease in amino acid levels indicated an increased amino acid catabolism after incubation to 5°C. In addition, long term warming initiated shifts in organic osmolyte concentrations and modified membrane structure observed by altered levels of phospholipid compounds. Differences in the metabolite profile between the two notothenioid species can be related to their divergent lifestyles, especially their different rates of motor activity. Increased levels of the Krebs cycle intermediate succinate and a higher reduction of amino acid concentrations in warm-acclimated N. rossii showed that N. rossii is more affected by warming than N. coriiceps.

Synthetic capacity does not predict elasmobranchs' ability to maintain trimethylamine oxide without a dietary contribution

Trimethylamine oxide (TMAO) is an organic osmolyte and universal protein stabilizer. Its role as a cytoprotectant is particularly important in ureosmotic elasmobranchs that accumulate high levels of urea, a macromolecular perturbant. Feeding is a key component in the turnover and maintenance of these nitrogenous compounds. However, previous studies examining TMAO regulation have been largely completed using starved individuals, when nitrogen balance is altered. Here, under fed conditions, we test the importance of dietary TMAO on long-term maintenance in three elasmobranch species with differing endogenous synthetic capacities. Smoothhounds (Mustelus canis), spiny dogfish (Squalus acanthias), and little skates (Leucoraja erinacea) exhibited species- and tissue-specific differences in their ability to conserve TMAO when fed a low TMAO diet for 56days. Smoothhounds, a species with the capacity for endogenous production, exhibited a decrease in muscle TMAO. Spiny dogfish and little skates, species with no reported ability for synthesis, exhibited decreases in plasma and liver TMAO, respectively. Our findings are contrary to previous starvation studies demonstrating constant levels of TMAO for up to 56days in elasmobranchs. Further, the previously reported synthetic capacity of these species did not correlate with their ability to conserve TMAO and cannot be used to predict a species reliance on dietary contributions for prolonged maintenance. It is possible that all species rely to a degree on absorption of TMAO from the diet or that alternate synthetic or regulatory pathways play a larger role than previously thought.

1H-NMR metabolomic study of whole blood from hatchling loggerhead sea turtles (Caretta caretta) exposed to crude oil and/or Corexit

We used proton nuclear magnetic resonance spectroscopy (1H-NMR) to evaluate metabolic impacts of environmentally relevant crude oil and Corexit exposures on the physiology of hatchling loggerhead sea turtles (Caretta caretta). Sample extraction and data acquisition methods for very small volume whole blood samples and sources of variation between individual hatchlings were assessed. Sixteen unclotted, whole blood samples were obtained from 7-day-old hatchlings after a 4-day cutaneous exposure to either control seawater, crude oil, Corexit 9500A or a combination of crude oil and Corexit 9500A. After extraction, one- and two-dimensional 1H-NMR spectra of the samples were obtained, and 17 metabolites were identified and confirmed in the whole blood spectra. Variation among samples due to the concentrations of metabolites 3-hydroxybutyrate, lactate, trimethylamine oxide and propylene glycol did not statistically correlate with treatment group. However, the characterization of the hatchling loggerhead whole blood metabolome provides a foundation for future metabolomic research with sea turtles and a basis for the study of tissues from exposed hatchling sea turtles.