Relative sarcolipin (SLN) and sarcoplasmic reticulum Ca2+ ATPase (SERCA1) transcripts levels in closely related endothermic and ectothermic scombrid fishes: Implications for molecular basis of futile calcium cycle non-shivering thermogenesis (NST).

Regional endothermy is the ability of an animal to elevate the temperature of specific regions of the body above that of the surrounding environment and has evolved independently among several fish lineages. Sarcolipin (SLN) is a small transmembrane protein that uncouples the sarcoplasmic reticulum calcium ATPase pump (SERCA1b) resulting in futile Ca2+ cycling and is thought to play a role in non-shivering thermogenesis (NST) in cold-challenged mammals and possibly some fishes. This study investigated the relative expression of sln and serca1 transcripts in three regionally-endothermic fishes (the skipjack, Katsuwonus pelamis, and yellowfin tuna, Thunnus albacares, both of which elevate the temperatures of their slow-twitch red skeletal muscle (RM) and extraocular muscles (EM), as well as the cranial endothermic swordfish, Xiphias gladius), and closely related ectothermic scombrids (the Eastern Pacific bonito, Sarda chiliensis, and Pacific chub mackerel, Scomber japonicus). Using Reverse Transcription quantitative PCR (RT-qPCR) and species-specific primers, relative sln expression trended higher in both the RM and EM for all four scombrid species compared to white muscle. In addition, relative serca1 expression was found to be higher in RM of skipjack and yellowfin tuna in comparison to white muscle. However, neither sln nor serca1 transcripts were higher in swordfish RM, EM or cranial heater tissue in comparison to white muscle. A key phosphorylation site in sarcolipin, threonine 5, is conserved in the swordfish, but is mutated to alanine or valine in tunas and the endothermic smalleye Pacific opah, Lampris incognitus, which should result in increased uncoupling of the SERCA pump. Our results support the role of potential SLN-NST in endothermic tunas and the lack thereof for swordfish.

Organ-specific mercury stable isotopes, speciation and particle measurements reveal methylmercury detoxification processes in Atlantic Bluefin Tuna.

Identifying metabolism and detoxification mechanisms of Hg in biota has important implications for biomonitoring, ecotoxicology, and food safety. Compared to marine mammals and waterbirds, detoxification of MeHg in fish is understudied. Here, we investigated Hg detoxification in Atlantic bluefin tuna Thunnus thynnus using organ-specific Hg and Se speciation data, stable Hg isotope signatures, and Hg and Se particle measurements in multiple tissues. Our results provide evidence for in vivo demethylation and biomineralization of HgSe particles, particularly in spleen and kidney. We observed a maximum range of 1.83‰ for δ202Hg between spleen and lean muscle, whereas Δ199Hg values were similar across all tissues. Mean percent methylmercury ranged from 8% in spleen to 90% in lean muscle. The particulate masses of Hg and Se were higher in spleen and kidney (Hg: 61% and 59%, Se: 12% and 6%, respectively) compared to muscle (Hg: 2%, Se: 0.05%). Our data supports the hypothesis of an organ-specific, two-step detoxification of methylmercury in wild marine fish, consisting of demethylation and biomineralization, like reported for waterbirds. While mass dependent fractionation signatures were highly organ specific, stable mass independent fractionation signatures across all tissues make them potential candidates for source apportionment studies of Hg using ABFT.

First record of mercury concentrations and stable isotopes (13C & 15N) in albacore (Thunnus alalunga) from the Western Equatorial Atlantic Ocean.

This paper reports the first record of total mercury (THg) concentrations in albacore (Thunnus alalunga), one of the main tuna species caught from the Western Equatorial Atlantic Ocean and presents a preliminary comparison with other regions and tuna species. Mean, standard deviation and range of concentrations in T. alalunga (515 ± 145 ng g-1 ww; 294-930 ng g-1 ww) with 92 % being of methyl-Hg, are higher than in albacore from other Atlantic Ocean subregions despite their smaller body size. These concentrations are similar to those from the Pacific and Indian oceans, but lower than in the Mediterranean. Compared to other sympatric tuna species, concentrations are higher than those in T. albacares and similar to T. obesus. These results are discussed considering the potential differences in stable isotope values (13C and 15N) of T. alalunga populations from multiple oceanic areas and compared to other tuna species worldwide.

Differentiation of three commercial tuna species through GC-Q-TOF and UPLC-Q/Orbitrap mass spectrometry-based metabolomics and chemometrics.

Food fraud is common in the tuna industry because of the economic benefits involved. Ensuring the authenticity of tuna species is crucial for protecting both consumers and tuna stocks. In this study, GC-Q-TOF and UPLC-Q/Orbitrap mass spectrometry-based metabolomics were used to investigate the metabolite profiles of three commercial tuna species (skipjack tuna, bigeye tuna and yellowfin tuna). A total of 22 and 77 metabolites were identified with high confidence using GC-Q-TOF and UPLC-Q/Orbitrap mass spectrometry, respectively. Further screening via chemometrics revealed that 38 metabolites could potentially serve as potential biomarkers. Hierarchical cluster analysis showed that the screened metabolite biomarkers successfully distinguished the three tested tuna species. Furthermore, a total of 27 metabolic pathways were identified through enrichment analysis based on the Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways.

Effects of dietary hydrolysate supplementation on growth, body composition, hematological responses, and liver histology of juvenile giant trevally (Caranx ignobilis Forsskal, 1775).

A feeding study was conducted to investigate how fish protein hydrolysate (FPH) supplementation affected the growth, feed utilization, body composition, and hematology of juvenile giant trevally (Caranx ignobilis Forsskal, 1775). Seven isonitrogenous (52% protein) and isocaloric diets (10% lipid) were formulated, wherein shrimp hydrolysate (SH) and tuna hydrolysate (TH) were used to replace fishmeal at inclusion levels of 0 (control), 30, 60, and 90 g/kg and labeled as control, SH30, SH60, SH90, TH30, TH60, and TH90, respectively. Each diet was fed to triplicate groups of juvenile giant trevally for 8 weeks. The results showed higher final body weight and specific growth rate in fish fed SH30, SH60, TH30, and TH60 than fed control diet. No difference was observed in feed intake, but reduced feed conversion ratio (FCR) was found in fish fed SH30, SH60, TH30, and TH60, demonstrating these diets improved feed utilization. TH90 caused deposition of lipid droplet in the hepatocyte, a sign of liver damage. Total monounsaturated fatty acids, polyunsaturated fatty acids (PUFA), and highly unsaturated fatty acids in fish were not affected by FPH supplementation. Fish fed TH30 showed lower ∑n - 3 PUFA than the fish fed remaining dietary treatments. The elevated serum protein was seen in fish fed control, SH30, SH60, and TH30, demonstrating that these diets were beneficial for the innate immune response in giant trevally. The results indicate that TH and SH could be incorporated into diets of giant trevally at 30-60 g/kg, replacing 7%-13% fishmeal with enhanced growth and health benefits.

Interspecific, ontogenetic and temporal variations in stable isotopes of small tuna species in the northeast Atlantic Ocean.

In order to study the trophic level of small tuna species and their contribution to the carbon flow in pelagic food webs, an analysis of carbon and nitrogen stable isotopes was carried out. The investigation was focused on four small tuna species (Auxis rochei, Auxis thazard, Euthynnus alletteratus and Sarda sarda) commonly harvested in the northeast Atlantic Ocean. The isotope analysis showed how the results for S. sarda are different from the rest of the species analysed, with a higher trophic level, similar to other major tuna species. The greatest niche overlap in δ13C and δ15N occurs among A. rochei, A. thazard and E. alletteratus. Auxis rochei and E. alletteratus showed a size-dependent variability in δ15N, and in δ13C for S. sarda. The small tuna S. sarda exhibits the highest migration rates among various geographical areas in comparison to other small pelagic tunas, and the seasonal variability of isotope values in the area studied can be attributed to the incorporation of larger individuals with a higher lipid content. The results of this work provide new information on the ecological role played by small tuna in food webs, which is more complex and varied than currently thought. This knowledge is essential for a more effective management of fisheries.

Preparation, identification, activity prediction, and protective effects on IR-HepG2 cells of five novel DPP-IV inhibitory peptides from protein hydrolysate of skipjack tuna dark muscles.

To produce peptides with high dipeptidyl peptidase IV (DPP-IV) inhibitory activity, neutrase was selected from five proteases (trypsin, neutrase, pepsin, alcalase and flavor protease) with the highest degree of hydrolysis (DH) (18.23 ± 1.08%) and DPP-IV inhibitory rate (53.35 ± 4.02%) to produce protein hydrolysate (NPH) from the dark muscles of skipjack tuna (Katsuwonus pelamis). Then, NPH-1 was isolated from NPH by gel permeation chromatography and found to possess the highest DPP-IV inhibitory rate (65.12 ± 7.94% at 0.5 mg ml-1) in the separated components (including NPH-1, NPH-2, NPH-3 and NPH-4). Subsequently, the available prediction models of tripeptides and tetrapeptides with the DPP-IV inhibitory rate were established using an artificial neural network (ANN). The RMSE (0.56 and 0.33 for the model established through collected tripeptides and tetrapeptides, respectively) and R2 (0.95 and 0.99 for the model established through collected tripeptides and tetrapeptides, respectively) of the ANN model's parameters were within acceptable limits, indicating that this model is available. Next, the ANN model was applied to predict tripeptides and tetrapeptides from the hydrolysate of skipjack tuna dark muscles, and five peptides (Ala-Pro-Pro (APP), Pro-Pro-Pro (PPP), Asp-Pro-Leu-Leu (DPLL), Glu-Ala-Val-Pro (EAVP) and Glu-Ala-Iie-Pro (EAIP)) possessing a noticeable DPP-IV inhibitory rate (with DPP-IV IC50 values of 42.46 ± 5.02, 37.71 ± 9.17, 58.85 ± 14.42, 49.94 ± 6.69 and 57.15 ± 6.13 µM, respectively) were screened from the protein hydrolysate. The above five peptides were proved to effectively promote glucose consumption in the insulin resistant-HepG2 (IR-HepG2) cell model considering that the glucose consumption rates of APP, PPP, DPLL, EAVP and EAIP treatment groups are all more than twice that of the dexamethasone group. Accordingly, mechanistic studies showed that these peptides interacted with PI3K/AKT and AMPK signaling pathways and promoted the phosphorylation of PI3K p110, AKT and AMPK (the protein expressions of PI3K p110, p-AKT and p-AMPK in APP, PPP, DPLL, EAVP and EAIP treatment groups are 1.64-2.22 fold compared with that in the dexamethasone group), thereby enhancing glucose uptake and further alleviating insulin resistance. These findings demonstrated that skipjack tuna dark muscle is a potential DPP-IV inhibitory peptide source, and five DPP-IV inhibitory peptides from its hydrolysate may exert potent anti-diabetic activity. In comparison, PPP may be the most potential active ingredient for healthy food against type 2 diabetes mellitus in the five screened peptides considering synthetically the DPP-IV inhibitory rate, bioavailability and synthesis cost.

Omega-3 meat enrichment and L-FABP, PPARA, and LPL genes expression are modified by the level and period of tuna oil supplementation in slow-growing chickens.

This study proposes a strategy to manipulate the fatty acid (FA) content in slow-growing Korat chicken (KRC) meat using tuna oil (TO). To determine the optimal level and feeding period of TO supplementation, we conducted a study investigating the effects of dietary TO levels and feeding periods on meat quality, omega-3 polyunsaturated fatty acid (n-3 PUFA) composition, and gene expression related to FA metabolism in KRC breast meat. At 3 wk of age, 700 mixed-sex KRC were assigned to seven augmented factorial treatments with a completely randomized design, each consisting of four replicate pens containing 25 chickens per pen. The control group received a corn-soybean-based diet with 4.5% rice bran oil (RBO), while varying amounts of TO (1.5%, 3.0%, or 4.5%) replaced a portion of the RBO content in the experimental diets. The chickens were fed these diets for 3 and 6 wk, respectively, before being slaughtered at 9 wk. Our results indicated no significant interactions between TO levels and feeding periods on the growth performance or meat quality of KRC (P > 0.05). However, the liver fatty acid-binding protein gene (L-FABP, also known as FABP1), responsible for FA transport and accumulation, showed significantly higher expression in the chickens supplemented with 4.5% TO (P < 0.05). The chickens supplemented with 4.5% TO for a longer period (3 to 9 wk of age) exhibited the lowest levels of n-6 PUFA and n-6 to n-3 ratio, along with the highest levels of eicosapentaenoic acid, docosahexaenoic acid, and n-3 PUFA in the breast meat (P < 0.05). However, even a short period of supplementation with 4.5% TO (6 to 9 wk of age) was adequate to enrich slow-growing chicken meat with high levels of n-3 PUFA, as recommended previously. Our findings indicated that even a short period of tuna oil supplementation could lead to desirable levels of omega-3 enrichment in slow-growing chicken meat. This finding has practical implications for the poultry industry, providing insights into optimal supplementation strategies for achieving desired FA profiles without adversely affecting growth performance or meat quality.

This study investigated the effect of different levels and feeding periods of tuna oil (TO), a source of omega-3 polyunsaturated fatty acids (n-3 PUFA), was used to modify the fatty acid (FA) profile in slow-growing Korat chicken (KRC) meat. The interaction between TO supplementation levels and feeding periods did not influence growth performance or meat quality in KRC. However, higher level of TO supplementation led to increased expression of the liver fatty acid-binding protein gene, which is involved in FA transport and accumulation. The highest levels of eicosapentaenoic acid, docosahexaenoic acid, and n-3 PUFA were detected in the chickens that were fed 4.5% TO supplementation for a long period (3 to 9 wk of age). These chickens also had the lowest amounts of omega-6 polyunsaturated fatty acids (n-6 PUFA) and n-6 to n-3 ratio. Interestingly, even a short period of 4.5% TO supplementation (6 to 9 wk of age) in slow-growing chickens was sufficient to enrich the KRC meat with n-3 PUFA. These findings highlight the potential for improving the nutritional profile of chicken meat by regulating TO supplementation in the diet.

Cardiovascular complications are resolved by tuna protein hydrolysate supplementation in rats fed with a high-fat diet.

This study is aimed to investigate whether tuna protein hydrolysate (TPH) supplementation could alleviate cardiovascular complications induced by a high-fat diet (HFD) in rats. Rats were fed a HFD for 16 weeks and given TPH (100 mg/kg, 300 mg/kg, or 500 mg/kg) or metformin (100 mg/kg) (n = 8) for the last four weeks. TPH had the following effects: resolved their impaired glucose tolerance, hyperglycemia, dyslipidemia, obesity, and hypertension (p < 0.05); alleviated left ventricular dysfunction and hypertrophy (p < 0.05), and vascular dysfunction and hypertrophy (p < 0.05); adipocyte hypertrophy; increases in circulating leptin and tumor necrosis factor (TNF-α) were mitigated (p < 0.05); increased renin-angiotensin system (RAS), oxidative stress, and decreased nitric oxide metabolites were modulated (p < 0.05). TPH restored the expression of angiotensin II receptor type 1 (AT1R)/NADPH oxidase 2 (NOX2), endothelial nitric oxide synthase (eNOS), nuclear factor erythroid 2-related factor (Nrf2)/heme oxygenase-1 (HO-1), and peroxisome proliferator-activated receptor γ (PPARγ)/the nuclear factor kappa B (NF-κB) protein in cardiovascular tissue (p < 0.05). In metabolic syndrome (MS) rats, metformin and TPH had comparable effects. In conclusion, TPH alleviated cardiovascular complications related to MS. It suppressed RAS, oxidative stress, and inflammation that were associated with modulation of AT1R/NOX2, eNOS, Nrf2/HO-1, and PPARγ/NF-κB expression.

Detection, Identification, and Inactivation of Histamine-forming Bacteria in Seafood: A Mini-review.

Seafood is one of the essential sources of nutrients for the human diet. However, they can be subject to contamination and can cause foodborne illnesses, including scombroid fish poisoning caused by histamine. Many microorganisms can produce enzymes that eventually decompose endogenous histidine to histamine in postmortem fish muscles and tissues. One of these is histamine-forming bacteria (HFB), primarily found in the gills, gut, and skin of fishes. Previous studies linked a plethora of Gram-negative HFB including Morganella spp. and Photobacterium spp. to scombroid fish poisoning from many types of seafood, especially the Scombridae family. These bacteria possess the hdc gene to produce histidine decarboxylase enzyme. It was reported that Gram-negative HFB produced 6345 ppm in tuna and 1223 ppm in Spanish mackerel. Interestingly, Gram-positive HFB have been isolated in the seafood samples with lower histamine levels. It suggests that Gram-negative HFB are the major contributor to the accumulation of histamine in seafood. Several analytical methods are available to detect and identify HFB and their histamine metabolites from seafood substrates. Rapid test kits can be used in food production settings for early detection of histamine to avoid food intoxication. Furthermore, high hydrostatic pressure and irradiation treatment could prevent the proliferation of HFB and inactivate the existing histidine decarboxylase (HDC) activity. As demonstrated in different seafood model systems, the HDC activity was deactivated at a maximum high hydrostatic pressure level of 400 MPa. The complete inactivation of HFB was achieved by gamma irradiation at a dose of 4.0 kGy. Other postharvest treatments, like enzymatic degradation and electrolyzed oxidizing water, were studied as sustainable methods for bacterial growth prevention and enzyme inactivation. However, other HFB react differently to these treatment conditions, and further studies are recommended.

Effects of elevated CO2 on metabolic rate and nitrogenous waste handling in the early life stages of yellowfin tuna (Thunnus albacares).

Ocean acidification is predicted to have a wide range of impacts on fish, but there has been little focus on broad-ranging pelagic fish species. Early life stages of fish are thought to be particularly susceptible to CO2 exposure, since acid-base regulatory faculties may not be fully developed. We obtained yellowfin tuna (Thunnus albacares) from a captive spawning broodstock population and exposed them to control or 1900 µatm CO2 through the first three days of development as embryos transitioned into yolk sac larvae. Metabolic rate, yolk sac depletion, and oil globule depletion were measured to assess overall energy usage. To determine if CO2 altered protein catabolism, tissue nitrogen content and nitrogenous waste excretion were quantified. CO2 exposure did not significantly impact embryonic metabolic rate, yolk sac depletion, or oil globule depletion, however, there was a significant decrease in metabolic rate at the latest measured yolk sac larval stage (36 h post fertilization). CO2-exposure led to a significant increase in nitrogenous waste excretion in larvae, but there were no differences in nitrogen tissue accumulation. Nitrogenous waste accumulated in embryos as they developed but decreased after hatch, coinciding with a large increase in nitrogenous waste excretion and increased metabolic rate in newly hatched larvae. Our results provide insight into how yellowfin tuna are impacted by increases in CO2 in early development, but more research with higher levels of replication is needed to better understand long-term impacts and acid-base regulatory mechanisms in this important pelagic fish.

Bioactive Peptides from Skipjack Tuna Cardiac Arterial Bulbs (II): Protective Function on UVB-Irradiated HaCaT Cells through Antioxidant and Anti-Apoptotic Mechanisms.

The aim of this study was to investigate the protective function and mechanism of TCP3 (PKK), TCP6 (YEGGD) and TCP9 (GPGLM) from skipjack tuna cardiac arterial bulbs on skin photoaging using UVB-irradiated HaCaT cell model. The present results indicated that TCP3 (PKK), TCP6 (YEGGD) and TCP9 (GPGLM) had significant cytoprotective effect on UVB-irradiated HaCaT cells (p < 0.001). Hoechst 33342 staining showed that apoptosis of UV-irradiated HaCaT cells could be significantly reduced by the treatment of TCP3 (PKK), TCP6 (YEGGD) and TCP9 (GPGLM); JC-1 staining showed that TCP3 (PKK), TCP6 (YEGGD) and TCP9 (GPGLM) could protect HaCaT cells from apoptosis by restoring mitochondrial membrane potential (MMP); Furthermore, TCP3 (PKK), TCP6 (YEGGD) and TCP9 (GPGLM) could significantly down-regulate the ratio of Bax/Bcl-2 and reduce the expression level of the apoptosis-executing protein Caspase-3 by decreasing the expression of protein Caspase-8 and Caspase-9 (p < 0.05). The action mechanism indicated that TCP3 (PKK), TCP6 (YEGGD) and TCP9 (GPGLM) could up-regulate the expression levels of Nrf2, NQO1 and HO-1 (p < 0.05), which further increased the activity of downstream proteases (SOD, CAT and GSH-Px), and scavenged reactive oxygen species (ROS) and decreased the intracellular levels of malondialdehyde (MDA). In addition, molecular docking indicated that TCP3 (PKK) and TCP6 (YEGGD) could competitively inhibit the Nrf2 binding site because they can occupy the connection site of Nrf2 by binding to the Kelch domain of Keap1 protein. TCP9 (GPGLM) was inferred to be non-competitive inhibition because it could not bind to the active site of the Kelch domain of Keap1 protein. In summary, the antioxidant peptides TCP3 (PKK), TCP6 (YEGGD) and TCP9 (GPGLM) from cardiac arterial bulbs of skipjack tuna can effectively protect HaCaT cells from UVB-irradiated damage and can be used in the development of healthy and cosmetic products to treat diseases caused by UV radiation.

The response surface methodology for optimization of Halomonas sp. C2SS100 lipase immobilization onto CaCO3 for treatment of tuna wash processing wastewater.

An immobilized enzyme could exhibit selectively modified physicochemical properties, and it might offer a better environment for the enzyme activity. In this study, the immobilization yield of crude Halomonas sp. lipase was optimized to improve its stability. Thanks to its high adsorption capacity, CaCO3 has been chosen as support for the immobilization process. Furthermore, response surface methodology (RSM) was used to determine optimal conditions for the immobilization of the bacterial lipase. Five tested factors (enzyme solution, support amount, time, temperature, and acetone volume) were optimized applying a central composite design of RSM. The maximum yield of lipase immobilization was improved to 96%. Furthermore, a biochemical characterization proved a significant improvement of the immobilized lipase stability. The immobilized enzyme is more stable at extreme pH values and high temperatures than the free one. We also tested the reusability of the immobilized lipase by evaluating the recovery of the support using simple filtration. Thanks to its high stability, the immobilized lipase was invested in an effective treatment of tuna wash processing wastewater. The oil biodegradation efficiency was established at 81.5% and was confirmed by Fourier transformation infrared spectrometry. Likewise, the biological oxygen demand values were reduced which makes a possible reduction of the wastewater pollution degree.

Trace metal accumulation in Atlantic bluefin tuna and correlations with protein-lipid composition.

This study determines the biochemical composition and metal concentrations (Hg, Fe, Zn, Cu) in muscle tissue of reared Atlantic bluefin tuna and investigates whether protein-lipid composition affects metal accumulation. A significant positive relationship was found between Hg concentrations and protein content, whereas a strong negative relationship between Hg concentrations and lipid content was revealed. Opposite results were obtained, correlating Zn concentrations with biochemical components. No correlations between the concentrations of the other two metals and the protein or lipid components were observed. Evidently, biochemical components may influence the accumulation of certain metals, but not in the same way. Although the analyzed tuna samples represent a rich source of essential metals, Hg may pose a risk to consumers. Our results suggest that a lower level of Hg can be associated with greater lipid and lower protein content. Consumers could reduce the health risk from Hg by choosing constantly high-fat bluefin tuna.

Bioactive Peptides from Skipjack Tuna Cardiac Arterial Bulbs: Preparation, Identification, Antioxidant Activity, and Stability against Thermal, pH, and Simulated Gastrointestinal Digestion Treatments.

Cardiac arterial bulbs of Skipjack tuna (Katsuwonus pelamis) are rich in elastin, and its hydrolysates are high quality raw materials for daily cosmetics. In order to effectively utilizing Skipjack tuna processing byproducts-cardiac arterial bulbs and to prepare peptides with high antioxidant activity, pepsin was selected from six proteases for hydrolyzing proteins, and the best hydrolysis conditions of pepsin were optimized. Using ultrafiltration and chromatographic methods, eleven antioxidant peptides were purified from protein hydrolysate of tuna cardiac arterial bulbs. Four tripeptides (QGD, PKK, GPQ and GLN) were identified as well as seven pentapeptides (GEQSN, GEEGD, YEGGD, GEGER, GEGQR, GPGLM and GDRGD). Three out of them, namely the tripeptide PKK and the pentapeptides YEGGD and GPGLM exhibited the highest radical scavenging activities on 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and superoxide anion assays. They also showed to protect plasmid DNA and HepG2 cells against H2O2-induced oxidative stress. Furthermore, they exhibited high stability under temperature ranged from 20-100 °C, pH values ranged from 3-11, and they simulated gastrointestinal digestion for 240 min. These results suggest that the prepared eleven antioxidant peptides from cardiac arterial bulbs, especially the three peptides PKK, YEGGD, and GPGLM, could serve as promising candidates in health-promoting products due to their high antioxidant activity and their stability.

Purification and Identification of Novel Myeloperoxidase Inhibitory Antioxidant Peptides from Tuna (Thunnas albacares) Protein Hydrolysates.

Antioxidative peptides that inhibit myeloperoxidase (MPO) enzyme activity can effectively defend against oxidative stress damage. The antioxidant peptides from tuna protein were produced using alcalase hydrolysis and purified by ultrafiltration and Sephadex G-15, and the fractions with the highest free radicals scavenging ability and oxygen radical absorbance capacity (ORAC) values were sequenced using HPLC-MS/MS. Fifty-five peptide sequences were identified, 53 of which were successfully docked into MPO. The representative peptide ACGSDGK had better antioxidant activity and inhibition of MPO chlorination and peroxidation than the reference peptide hLF1-11. The docking model further showed intense molecular interactions between ACGSDGK and MPO, including hydrogen bonds, charge, and salt bridge interactions, which occluded the active site and blocked the catalytic activity of MPO. These results suggested that the antioxidant peptide ACGSDGK has the potential to inhibit oxidative stress and alleviate inflammation in vivo because of its inhibitory effect on the MPO enzyme.

Valorization of Side Stream Products from Sea Cage Fattened Bluefin Tuna (Thunnus thynnus): Production and In Vitro Bioactivity Evaluation of Enriched ω-3 Polyunsaturated Fatty Acids.

The valorization of side streams from fishery and aquaculture value-chains is a valuable solution to address one of the challenges of the circular economy: turning wastes into profit. Side streams produced after filleting of sea cage fattened bluefin tuna (Thunnus thynnus) were analyzed for proximate composition and fatty acid profile to evaluate the possibility of producing tuna oil (TO) as a valuable source of ω-3 polyunsaturated fatty acids (PUFA) and testing its bioactivity in vitro. Ethyl esters of total fatty acids (TFA), obtained from TO, were pre-enriched by urea complexation (PUFA-Ue) and then enriched by short path distillation (SPD) up to almost 85% of the PUFA fraction (PUFA-SPe). The bioactivity of TFA, PUFA-SPe, and ethyl esters of depleted PUFA (PUFA-SPd) were tested in vitro, through analysis of lipid metabolism genes, in gilthead sea bream (Sparus aurata) fibroblast cell line (SAF-1) exposed to oils. TFA and PUFA-SPd upregulated transcription factors (pparß and pparγ) and lipid metabolism-related genes (D6D, fas, fabp, fatp1, and cd36), indicating the promotion of adipogenesis. PUFA-SPe treated cells were similar to control. PUFA-SPe extracted from farmed bluefin tuna side streams could be utilized in fish feed formulations to prevent excessive fat deposition, contributing to improving both the sustainability of aquaculture and the quality of its products.

Dose effect of high-docosahexaenoic acid tuna oil on dysbiosis in high-fat diet mice.

BACKGROUND: The health benefits of tuna oil, which is different from the fish oil commonly studied, and its higher docosahexaenoic acid (DHA) content, have attracted much scientific attention in recent years. In this study, prepared tuna oil with higher DHA (HDTO) content was employed. It was the first to integrate microbiome and metabolome from a dose-effect perspective to investigate the influence of HDTO on gut dysbiosis and metabolic disorders in diet-induced obese mice. RESULTS: Higher DHA tuna oil was effective in reversing high-fat-diet-induced metabolic disorders and altering the composition and function of gut microbiota, but these effects were not uniformly dose dependent. The flora and metabolites that were targeted to be regulated by HDTO supplementation were Prevotella, Bifidobacterium, Olsenella, glycine, l-aspartate, l-serine, l-valine, l-isoleucine, l-threonine, l-tyrosine, glyceric acid, glycerol, butanedioic acid, and citrate, respectively. Functional pathway analysis revealed that alterations in these metabolic biomarkers were associated with six main metabolic pathways: glycine, serine, and threonine metabolism; glycerolipid metabolism; glyoxylate and dicarboxylate metabolism; alanine, aspartate, and glutamate metabolism; aminoacyl-tRNA biosynthesis, and the citrate cycle (TCA cycle). CONCLUSION: Various doses of HDTO could attenuate endogenous disorders to varying degrees by regulating multiple perturbed pathways to the normal state. This explicit dose research for novel fish oil with high-DHA will provide a valuable reference for those seeking to exploit its clinical therapeutic potential. © 2022 Society of Chemical Industry.

LC/MS analysis of storage-induced plasmalogen loss in ready-to-eat fish.

Plasmalogens are functional and oxidation-sensitive phospholipids abundant in fish. Chilling and freezing are common storage methods for maintaining the quality of fish, but their effect on plasmalogen preservation has not been studied. Therefore, plasmalogen loss in ready-to-eat tuna meat during storage under different conditions was investigated. LC/MS was used to analyze the time- and temperature-dependent changes of plasmalogens, which was the most evident for the species with an ethanolamine headgroup and polyunsaturated fatty acyl chains. Moreover, a series of oxidized plasmalogen molecules were identified, and their storage-induced accumulation was observed. Plasmalogen loss was strongly correlated with total lipid oxidation and phospholipid degradation. Repeated freeze-thaw cycles were found to accelerate the loss of plasmalogens, whereas the different thawing methods did not. The present study provides a deeper understanding of changes in lipid nutrients from fish meat during storage and demonstrates the importance of using advanced strategies to maintain food quality.

Onset of nutrient consumption during early life stage digestive system development of two tuna species (Thunnus orientalis and Thunnus albacares).

To specify the timing of exogenous nutrient consumption in the larvae of two commercially important tuna species, the Pacific bluefin tuna (PBF) Thunnus orientalis and the yellowfin tuna (YFT) Thunnus albacares, the gene expressions of peptide transporter 1 (PEPT1) were examined. The mRNA expressions of PEPT1 first occurred at 2 days post hatching (dph) in PBF larvae and 3 dph for the YFT, and PEPT1 was found to only be expressed in the intestinal tract. The histological changes of the digestive tract of the YFT larvae were observed and compared to PBF larvae from a previous study. The intestines were developed at the hatching day for both species. It was found that the developmental timing of internal organs differed between the species, with the YFT showing an approximately one-day delay. The major organs such as liver, pancreas and gall bladder that excrete digestive enzymes appeared at 1 dph for PBF and 2 dph for YFT. The development of external morphological features was similar to organ development timings, with mouth-opening and first feeding starting at 2 dph for PBF, and 3 dph for YFT. Growth during the first month is rapid and variable for both species, ranging from 1.06 to 1.56 mm/d. Our findings provide new information about the early onset of feeding and larval development for the two species which would contribute to future aquaculture.