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In the study, papain was chosen from five proteases to hydrolyze proteins of monkfish swim bladders for effectively utilizing monkfish (Lophius litulon) processing byproducts, and the hydrolysis conditions of papain were optimized as hydrolysis temperature of 65 °C, pH 7.5, enzyme dose 2.5% and time 5 h using single-factor and orthogonal experiments. Eighteen peptides were purified from the swim bladder hydrolysate of monkfish by ultrafiltration and gel permeation chromatography methods and identified as YDYD, QDYD, AGPAS, GPGPHGPSGP, GPK, HRE, GRW, ARW, GPTE, DDGGK, IGPAS, AKPAT, YPAGP, DPT, FPGPT, GPGPT, GPT and DPAGP, respectively. Among eighteen peptides, GRW and ARW showed significant DPPH· scavenging activities with EC50 values of 1.053 ± 0.003 and 0.773 ± 0.003 mg/mL, respectively; YDYD, QDYD, GRW, ARW and YPAGP revealed significantly HO· scavenging activities with EC50 values of 0.150 ± 0.060, 0.177 ± 0.035, 0.201 ± 0.013, 0.183 ± 0.0016 and 0.190 ± 0.010 mg/mL, respectively; YDYD, QDYD, ARW, DDGGK and YPAGP have significantly O2−· scavenging capability with EC50 values of 0.126 ± 0.0005, 0.112 ± 0.0028, 0.127 ± 0.0002, 0.128 ± 0.0018 and 0.107 ± 0.0002 mg/mL, respectively; and YDYD, QDYD and YPAGP showed strong ABTS+· scavenging ability with EC50 values of 3.197 ± 0.036, 2.337 ± 0.016 and 3.839 ± 0.102 mg/mL, respectively. YDYD, ARW and DDGGK displayed the remarkable ability of lipid peroxidation inhibition and Ferric-reducing antioxidant properties. Moreover, YDYD and ARW can protect Plasmid DNA and HepG2 cells against H2O2-induced oxidative stress. Furthermore, eighteen isolated peptides had high stability under temperatures ranging from 25–100 °C; YDYD, QDYD, GRW and ARW were more sensitive to alkali treatment, but DDGGK and YPAGP were more sensitive to acid treatment; and YDYD showed strong stability treated with simulated GI digestion. Therefore, the prepared antioxidant peptides, especially YDYD, QDYD, GRW, ARW, DDGGK and YPAGP from monkfish swim bladders could serve as functional components applied in health-promoting products because of their high-antioxidant functions.

In this study, we investigate the ameliorating functions of QDYD (MSP2), ARW (MSP8), DDGGK (MSP10), YPAGP (MSP13) and DPAGP (MSP18) from monkfish swim bladders on an FFA-induced NAFLD model of HepG2 cells. The lipid-lowering mechanisms revealed that these five oligopeptides can up-regulate the expression of phospho-AMP-activated protein kinase ( -AMPK) proteins to inhibit the expression of the sterol regulatory element binding protein-1c (SREBP-1c) proteins on increasing lipid synthesis and up-regulating the expression of the PPAP-α and CPT-1 proteins on promoting the β-oxidation of fatty acids. Moreover, QDYD (MSP2), ARW (MSP8), DDGGK (MSP10), YPAGP (MSP13) and DPAGP (MSP18) can significantly inhibit reactive oxygen species' (ROS) production, promote the activities of intracellular antioxidases (superoxide dismutase, SOD; glutathione peroxidase, GSH-PX; and catalase, CAT) and bring down the content of malondialdehyde (MDA) derived from lipid peroxidation. Further investigations revealed that the regulation of these five oligopeptides on oxidative stress was achieved through activating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway to raise the expression levels of the heme oxygenase 1 (HO-1) protein and downstream antioxidant proteases. Therefore, QDYD (MSP2), ARW (MSP8), DDGGK (MSP10), YPAGP (MSP13) and DPAGP (MSP18) could serve as candidate ingredients to develop functional products for treating NAFLD.

Collagen is one of the most useful biomaterials and widely applied in functional food and cosmetics. However, some consumers have paid close attention to the safety of mammalian collagens because of the outbreaks of bovine spongiform encephalopathy (BSE), foot-and-mouth disease (FMD), and other prion diseases. Therefore, there is a strong demand for developing alternative sources of collagen, with one promising source being from the process by-products of commercial fisheries. In this report, acid-soluble collagen (ASC-SB) and pepsin-soluble collagen (PSC-SB) from swim bladders of miiuy croaker (Miichthys miiuy) were isolated with yields of 1.33 ± 0.11% and 8.37 ± 0.24% of dry swim bladder weight. Glycine was the major amino acid present, with a content of 320.5 (ASC-SB) and 333.6 residues/1000 residues (PSC-SB). ASC-SB and PSC-SB had much lower denaturation temperatures compared to mammalian collagen, a consequence of low imino acid contents (196.7 and 199.5 residues/1000 residues for ASC-SB and PSC-SB, respectively). The data of amino acid composition, SDS-PAGE pattern, UV and FTIR spectra confirmed that ASC-SB and PSC-SB were mainly composed of type I collagen. FTIR spectra data indicated there were more hydrogen bonding and intermolecular crosslinks in ASC-SB. These collagens showed high solubility in the acidic pH ranges and low NaCl concentrations (less than 2%). The Zeta potential values of ASC-SB and PSC-SB were 6.74 and 6.85, respectively. ASC-SB and PSC-SB presented irregular, dense, sheet-like films linked by random-coiled filaments under scanning electron microscopy. In addition, ASC-SB and PSC-SB could scavenge DPPH radical, hydroxyl radical, superoxide anion radical, and ABTS radical in a dose-dependent manner. Overall, the results indicate that collagens from the swim bladders of miiuy croaker are a viable substitute for mammalian collagen, with potential functional food and cosmeceutical applications.

A 30 years long data series on the infection dynamics of European eel (Anguilla anguilla L.) with the non-native invasive nematode Anguillicola crassus Kuwahara, Niimi & Hagaki, 1974 is presented. Parasite burden was evaluated for 30 years in inland and coastal waters in Mecklenburg-Western Pomerania from 1991 to 2020. The total prevalence, mean intensity and damage status of the swim bladders were very high during the first decade (1991–2000), and significantly decreased in both marine and freshwater eel populations in the following decades (2001–2010, 2011–2020). The parasite intensity of eels in coastal waters was significantly lower compared with the freshwater systems (61.3% vs 79.5% in the first decade), indicating the vulnerability of the parasites to brackish water conditions and the fact that the life cycle of A. crassus cannot be completed under high saline conditions. Eel caught in the western part of the Baltic Sea (west of Darss sill) had the lowest mean infection (51.8% in first decade) compared to the eastern part with 63.8%. Thus, besides different infection patterns caused by the environmental conditions, a temporal trend towards a reduced parasite intensity and a more balanced parasite–host relationship developed in the 30 years of interaction after the first invasion. Possible reasons and mechanisms for the observed trends in parasite–host interactions are discussed.

In this work, the hypolipidemic and antioxidative capacity of FSGLR (S7) and GIEWA (S10) from miiuy croaker swim bladders was explored systematically in an oleic acid (OA)-induced nonalcoholic fatty liver disease (NAFLD) model of HepG2 cells. Moreover, the hypolipidemic activity of S7 and S10 and their antioxidative abilities were preliminarily investigated in combination with molecular docking technology. The results indicated that S7 and S10 could decrease the amount of lipid accumulation and the content of triglycerides (TG) and total cholesterol (TC) in the OA-induced NAFLD cell model in a dose-dependent manner. In addition, S7 and S10 exhibited better bile salt binding, pancreatic lipase (PL) inhibition, and cholesterol esterase (CE) inhibition capacities. The hypolipidemic mechanisms of S7 and S10 were connected with the downregulation of the mRNA expression levels of adipogenic factors, including sterol-regulatory element-binding protein-1c (SREBP-1c), acetyl-CoA carboxylase (ACC), sterol-regulatory element-binding protein (SREBP)-2, hydroxymethylglutaryl-CoA reductase (HMGR), and fatty acid synthase (FAS) (p < 0.01), and the upregulation of the mRNA expression of β-oxidation-related factors, including carnitine palmitoyltransferase 1 (CPT-1), acyl-CoA oxidase 1 (ACOX-1), and peroxisome proliferator-activated receptor α (PPARα). Moreover, FSGLR (S7) and GIEWA (S10) could significantly protect HepG2 cells against OA-induced oxidative damage, and their antioxidant mechanisms were related to the increased activity of intracellular antioxidant proteases (superoxide dismutase, SOD; glutathione peroxidase, GSH-PX; catalase, CAT) to remove excess reactive oxygen species (ROS) and decrease the production of malondialdehyde (MDA). The presented findings indicate that the hypolipidemic and antioxidant functions and mechanisms of S7 and S10 could make them potential hypolipidemic and antioxidant candidates for the treatment of NAFLD.

Animal-derived biomaterials have been extensively employed in clinical practice owing to their compositional and structural similarities with those of human tissues and organs, exhibiting good mechanical properties and biocompatibility, and extensive sources. However, there is an associated risk of infection with pathogenic microorganisms after the implantation of tissues from pigs, cattle, and other mammals in humans. Therefore, researchers have begun to explore the development of non-mammalian regenerative biomaterials. Among these is the swim bladder, a fish-derived biomaterial that is rapidly used in various fields of biomedicine because of its high collagen, elastin, and polysaccharide content. However, relevant reviews on the biomedical applications of swim bladders as effective biomaterials are lacking. Therefore, based on our previous research and in-depth understanding of this field, this review describes the structures and compositions, properties, and modifications of the swim bladder, with their direct (including soft tissue repair, dural repair, cardiovascular repair, and edible and pharmaceutical fish maw) and indirect applications (including extracted collagen peptides with smaller molecular weights, and collagen or gelatin with higher molecular weights used for hydrogels, and biological adhesives or glues) in the field of biomedicine in recent years. This review provides insights into the use of swim bladders as source of biomaterial; hence, it can aid biomedicine scholars by providing directions for advancements in this field.

In the present research, the enzyme-facilitated collagen from sea eel (Muraenesox cinereus) swim bladder was isolated, and the collagen characteristics were analyzed. Then, the collagen sponge was prepared and its potential mechanism in promoting skin wound healing in mice was further investigated. Collagen was obtained from the swim bladder of sea eels employing the pepsin extraction technique. Single-factor experiments served as the basis for the response surface method (RSM) to optimize pepsin concentration, solid-liquid ratio, and hydrolysis period. With a pepsin concentration of 2067 U/g, a solid-liquid ratio of 1:83 g/mL, and a hydrolysis period of 10 h, collagen extraction achieved a yield of 93.76%. The physicochemical analysis revealed that the extracted collagen belonged to type I collagen, and the collagen sponge displayed a fibrous structure under electron microscopy. Furthermore, in comparison to the control group, mice treated with collagen sponge dressing exhibited elevated activities of superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (T-AOC), and glutathione peroxidase (GSH-Px), and decreased levels of malondialdehyde (MDA), interleukin (IL)-1β, interleukin (IL)-6, and tumor necrosis factor (TNF)-α. The collagen sponge dressing effectively alleviated inflammation in the wound area, facilitating efficient repair and rapid healing of the skin tissue. During the initial phase of wound healing, the group treated with collagen sponge dressing exhibited an enhancement in the expressions of cluster of differentiation (CD)31, epidermal growth factor (EGF), transforming growth factor (TGF)-β1, and type I collagen, leading to an accelerated rate of wound healing. In addition, this collagen sponge dressing could also downregulate the expressions of CD31, EGF, and type I collagen to prevent scar formation in the later stage. Moreover, this collagen treatment minimized oxidative damage and inflammation during skin wound healing and facilitated blood vessel formation in the wound. Consequently, it exhibits significant potential as an ideal material for the development of a skin wound dressing.

There is a growing demand for the identification of alternative sources of collagen not derived from land-dwelling animals. The present study explored the use of pepsin- and acid-based extraction protocols to isolate collagen from the swim bladders of Megalonibea fusca. After extraction, these acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) samples respectively were subjected to spectral analyses and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) characterization, revealing both to be comprised of type I collagen with a triple-helical structure. The imino acid content of these ASC and PSC samples was 195 and 199 residues per 1000 residues, respectively. Scanning electron microscopy demonstrated that samples of freeze-dried collagen exhibited a compact lamellar structure, while transmission electron microscopy and atomic force microscopy confirmed the ability of these collagens to undergo self-assembly into fibers. ASC samples exhibited a larger fiber diameter than the PSC samples. The solubility of both ASC and PSC was highest under acidic pH conditions. Neither ASC nor PSC caused any cytotoxicity when tested in vitro, which met one of the requirements for the biological evaluation of medical devices. Thus, collagen isolated from the swim bladders of Megalonibea fusca holds great promise as a potential alternative to mammalian collagen.

The impact of rohu swim bladder gelatin hydrolysate (SBGH) at different levels on textural, sensory, oxidative, and microbial properties of polyunsaturated fatty acids enriched rohu fish cooked sausages (PUFA-RFS) were investigated in the current study. SBGH addition enhanced the lightness values of PUFA-RFS compared to both control sausages (without SBGH and with butylated hydroxyanisole (BHA) (P > 0.05). PUFA-RFS added with 3% SBGH exhibited higher hardness, cohesiveness, and gumminess throughout the storage duration at both 4 °C and −20 °C temperatures when compared to other sausages counterparts. PUFA-RFS added with SBGH displayed lower PV, TBARS, and total microbial counts than the control sausages. Furthermore, PV, TBARS, and total microbial count values of sausage decreased with an increase in SBGH level, indicating retardation in lipid oxidation and microbial growth by SBGH in a dose-depended manner. Nevertheless, sausage added with 3% SBGH had higher overall acceptability than other sausage counterparts. Therefore, SBGH could retard lipid oxidation and improves textural properties of PUFA-enriched fish sausage.

Fishes are hosts to a range of taxonomically diverse parasites. This survey was intended to provide insight into the occurrence, distribution, prevalence, and intensity of parasites infesting the fingerlings of the tilapia, in Tigray. A total of 384 Oreochromis niloticus specimens were collected from Midmar consisting of 227 males and 157 females. External and internal organs were examined for parasite infection. Squash preparation of fish eyes was also examined to reveal the organisms through microscopic examination. The major groups of parasites were trematode, nematodes, protozoa and hirudinea. A total of 3762 genus Diplostomum were recorded affecting the health of 93% of fishes. Contracaecum species was the second most prevalent distributed majorly in the intestine (77.8%), pericardial cavity (19.1%), swim bladder (2.4%), gill (0.2%) and mouth (0.8%). The prevalence and mean intensity of Diplostomum spp., Contracaecum, Myxosporea, Clinostomum spp., Eustrongylides and Leeches was 93%(10.5), 62.2%(5.3), 39.3%(8.3), 2.1%(8.8),1.8%(5.7) and 1.6% (2.5), respectively. The mean temperature, dissolved oxygen, conductivity, and pH of the dam were 24.4°C, 7.55 mg/l, 849.5µs/cm, and 7.5, respectively. Therefore, responsible bodies in fisheries should perform a pre-stock assessment and provide fish farming extension services for optimum production and marketing of fish products with management and production enhancement methods.