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Marine Bioactive Peptides—Structure, Function, and Application

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A special issue of Marine Drugs (ISSN 1660-3397).

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 19927

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Prof. Dr. Chang-Feng Chi

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National and Provincial Joint Laboratory of Exploration and Utilization of Marine Aquatic Genetic Resources, National Engineering Research Center of Marine Facilities Aquaculture, School of Marine Science and Technology, Zhejiang Ocean University, Zhoushan 316022, China
Interests: marine peptides; structure identification; structure–function relationship; antioxidant activity; cytoprotection; Nrf2 pathway; non-alcoholic fatty liver disease (NAFLD); angiotensin-I-converting enzyme (ACE)-inhibitory; hypolipidemic activities; hypotensive activity; neuropeptides; cephalopods; neuroendocrine immune regulation; reproductive regulation
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Prof. Dr. Bin Wang

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Zhejiang Provincial Engineering Technology Research Center of Marine Biomedical Products, School of Food and Pharmacy, Zhejiang Ocean University, Zhoushan 316022, China
Interests: marine peptides; structure identification; structure–function relationship; antioxidant activity; cytoprotection; Nrf2 pathway; non-alcoholic fatty liver disease (NAFLD); angiotensin-I-converting enzyme (ACE)-inhibitory; hypolipidemic activities; hypotensive activity
Special Issues, Collections and Topics in MDPI journals

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Dear Colleagues,

In recent years, peptides generated from various marine organisms have attracted wide attention due to their diverse chemical structures and bioactivities, including antioxidant, immune-modulating, angiotensin-I-converting enzyme (ACE)-inhibitory, hypotensive, hypolipidemic, antiviral, cytotoxic, neurotoxic, anticoagulant, antifreeze, etc. Moreover, bioactive peptides can serve as additional functional components used in health foods, nutraceuticals, bio-preservatives, cosmetics, and pharmaceuticals.

The Special Issue on “Marine Bioactive Peptides—Structure, Function, and Application” aims to collect papers on up-to-date information regarding the preparation, structural identification, activity and functional evaluation, and application of marine bioactive peptides.

We look forward to receiving your contributions.

Prof. Dr. Chang-Feng Chi
Prof. Dr. Bin Wang
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Marine Drugs is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

marine peptides
protein hydrolysate
biotechnological production
structure identification
structural modification
bioactivity and function
structure–function relationship
bioavailability
nutritional value
functional foods
application

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Related Special Issue

Marine Bioactive Peptides—Structure, Function, and Application 2.0 in Marine Drugs (9 articles)

Published Papers (11 papers)

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Editorial

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6 pages, 233 KiB

Open AccessEditorial

Marine Bioactive Peptides—Structure, Function and Application

by Chang-Feng Chi and Bin Wang

Mar. Drugs 2023, 21(5), 275; https://doi.org/10.3390/md21050275 - 28 Apr 2023

Cited by 6 | Viewed by 2151

Abstract

Marine organisms live in harsh marine habitats, causing them to have significantly different and more diverse proteins than those of terrestrial organisms [...] Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

Research

Jump to: Editorial

24 pages, 4475 KiB

Open AccessArticle

Eighteen Novel Bioactive Peptides from Monkfish (Lophius litulon) Swim Bladders: Production, Identification, Antioxidant Activity, and Stability

by Yan Sheng, Wan-Yi Wang, Ming-Feng Wu, Yu-Mei Wang, Wang-Yu Zhu, Chang-Feng Chi and Bin Wang

Mar. Drugs 2023, 21(3), 169; https://doi.org/10.3390/md21030169 - 7 Mar 2023

Cited by 69 | Viewed by 3178

Abstract

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

O_{2}^{-} \cdot

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. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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20 pages, 7586 KiB

Open AccessArticle

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

by Jing Kong, Xiao-Meng Hu, Wei-Wei Cai, Yu-Mei Wang, Chang-Feng Chi and Bin Wang

Mar. Drugs 2023, 21(2), 105; https://doi.org/10.3390/md21020105 - 1 Feb 2023

Cited by 61 | Viewed by 3260

Abstract

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. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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12 pages, 901 KiB

Open AccessArticle

Identification of Bioactive Peptides from a Laminaria digitata Protein Hydrolysate Using In Silico and In Vitro Methods to Identify Angiotensin-1-Converting Enzyme (ACE-1) Inhibitory Peptides

by Diane Purcell, Michael A. Packer and Maria Hayes

Mar. Drugs 2023, 21(2), 90; https://doi.org/10.3390/md21020090 - 27 Jan 2023

Cited by 11 | Viewed by 3511

Abstract

Bioactive peptides range in size from 2–30 amino acids and may be derived from any protein-containing biomass using hydrolysis, fermentation or high-pressure processing. Pro-peptides or cryptides result in shorter peptide sequences following digestion and may have enhanced bioactivity. Previously, we identified a protein hydrolysate generated from Laminaria digitata that inhibited ACE-1 in vitro and had an ACE-1 IC₅₀ value of 590 µg/mL compared to an ACE-1 IC₅₀ value of 500 µg/mL (~2.3 µM) observed for the anti-hypertensive drug Captopril©. A number of peptide sequences (130 in total) were identified using mass spectrometry from a 3 kDa permeate of this hydrolysate. Predicted bioactivities for these peptides were determined using an in silico strategy previously published by this group utilizing available databases including Expasy peptide cutter, BIOPEP and Peptide Ranker. Peptide sequences YIGNNPAKGGLF and IGNNPAKGGLF had Peptide Ranker scores of 0.81 and 0.80, respectively, and were chemically synthesized. Synthesized peptides were evaluated for ACE-1 inhibitory activity in vitro and were found to inhibit ACE-1 by 80 ± 8% and 91 ± 16%, respectively. The observed ACE-1 IC₅₀ values for IGNNPAKGGLF and YIGNNPAKGGLF were determined as 174.4 µg/mL and 133.1 µg/mL. Both peptides produced sequences following simulated digestion with the potential to inhibit Dipeptidyl peptidase IV (DPP-IV). Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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15 pages, 3060 KiB

Open AccessArticle

Characterisation of Bioactive Peptides from Red Alga Gracilariopsis chorda

by Martin Alain Mune Mune, Yoshikatsu Miyabe, Takeshi Shimizu, Wataru Matsui, Yuya Kumagai and Hideki Kishimura

Mar. Drugs 2023, 21(1), 49; https://doi.org/10.3390/md21010049 - 11 Jan 2023

Cited by 13 | Viewed by 2653

Abstract

In this study, we studied the bioactive peptides produced by thermolysin hydrolysis of a water-soluble protein (WSP) from the red alga Gracilariopsis chorda, whose major components are phycobiliproteins and Ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCo). The results showed that WSP hydrolysate exhibited significantly higher ACE inhibitory activity (92% inhibition) compared to DPP-IV inhibitory activity and DPPH scavenging activity. The phycobiliproteins and RuBisCo of G. chorda contain a high proportion of hydrophobic (31.0–46.5%) and aromatic (5.1–46.5%) amino acid residues, which was considered suitable for the formation of peptides with strong ACE inhibitory activity. Therefore, we searched for peptides with strong ACE inhibitory activity and identified two novel peptides (IDHY and LVVER). Then, their interaction with human ACE was evaluated by molecular docking, and IDHY was found to be a promising inhibitor. In silico analysis was then performed on the structural factors affecting ACE inhibitory peptide release, using the predicted 3D structures of phycobiliproteins and RuBisCo. The results showed that most of the ACE inhibitory peptides are located in the highly solvent accessible α-helix. Therefore, it was suggested that G. chorda is a good source of bioactive peptides, especially ACE-inhibitory peptides. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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14 pages, 5699 KiB

Open AccessArticle

Immunoenhancing Effects of Cyclina sinensis Pentadecapeptide through Modulation of Signaling Pathways in Mice with Cyclophosphamide-Induced Immunosuppression

by Rui Zhao, Xiao-Xia Jiang, Qiao-Ling Zhao, Han-Wei Ye, Yi Lin, Ju Huang and Yun-Ping Tang

Mar. Drugs 2022, 20(9), 560; https://doi.org/10.3390/md20090560 - 31 Aug 2022

Cited by 4 | Viewed by 2379

Abstract

Our study aimed to investigate the immune-enhancing mechanism of the pentadecapeptide (RVAPEEHPVEGRYLV) from Cyclina sinensis (SCSP) in a cyclophosphamide (CTX)-induced murine model of immunosuppression. Our results showed that SCSP treatment significantly increased mouse body weight, immune organ indices, and the production of serum IL-6, IL-1β, and tumor necrosis factor (TNF)-α in CTX-treated mice. In addition, SCSP treatment enhanced the proliferation of splenic lymphocytes and peritoneal macrophages, as well as phagocytosis of the latter in a dose-dependent manner. Moreover, SCSP elevated the phosphorylation levels of p38, ERK, JNK, PI3K and Akt, and up-regulated IKKα, IKKβ, p50 NF-κB and p65 NF-κB protein levels, while down-regulating IκBα protein levels. Our results indicate that SCSP has immune-enhancing activities, and that it can activate the MAPK/NF-κB and PI3K/Akt pathways to enhance immunity in CTX-induced immunosuppressed mice. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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16 pages, 3637 KiB

Open AccessArticle

Investigation of the In Vivo, In Vitro, and In Silico Wound Healing Potential of Pinctada martensii Purified Peptides

by Ting Zhang, Faming Yang, Xiaoming Qin, Xianmei Yang, Chaohua Zhang, Zhaoyi Wan and Haisheng Lin

Mar. Drugs 2022, 20(7), 417; https://doi.org/10.3390/md20070417 - 26 Jun 2022

Cited by 9 | Viewed by 2433

Abstract

Previous studies found that both oral and topical administration of enzymatic digestion products < 3 K Da ultrafiltration fractions of Pinctada martensii mantle (PMPs) had pro-healing effects. Thus, we further purified them by Sephadex-G25 and screened them by cellular assays to obtain Pinctada martensii purified peptides (PMPPs). In this study, we explored the mechanism of PMPPs on wound healing by in vivo, in vitro, and in silico experiments. LC-MS/MS results showed that PMPPs consisted of 33 peptides with molecular weights ranging from 758.43 to 2014.04 Da, and the characteristic peptide was Leu-Asp. The results of cellular assays showed that PMPPs promoted the proliferation of human skin fibroblasts (HSF) (135%) and human immortalized keratinocyte (HaCaT) cells (125%) very significantly at 12.5 μg/mL. The in vivo results showed that PMPPs could achieve scarless healing by inhibiting the inflammatory response, accelerating the epithelialization process, and regulating collagen I/III ratio. The optimal peptide sequence FAFQAEIAQLMS of PMPPs was screened for key protein receptors in wound healing (EGFR1, FGFR1, and MMP-1) with the help of molecular docking technique, which also showed to be the key pro-healing active peptide sequence. Therefore, it may provide a therapeutic strategy with great potential for wound healing. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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16 pages, 4389 KiB

Open AccessArticle

Antioxidative Effect of Chlorella Pyrenoidosa Protein Hydrolysates and Their Application in Krill Oil-in-Water Emulsions

by Yujia Liu, Yuli Qi, Qi Wang, Fawen Yin, Honglei Zhan, Han Wang, Bingnan Liu, Yoshimasa Nakamura and Jihui Wang

Mar. Drugs 2022, 20(6), 345; https://doi.org/10.3390/md20060345 - 25 May 2022

Cited by 9 | Viewed by 2701

Abstract

Chlorella pyrenoidosa is an excellent source of protein, and in this research, we assessed the antioxidant and emulsifying effects of Chlorella protein hydrolysate (CPH) using neutral proteases and alkaline proteases, as well as the properties of CPH-derived krill oil-in-water (O/W) emulsions. The CPHs exhibited the ability to scavenge several kinds of free radicals, including 1,1-diphenyl-2-picrylhydrazyl (DPPH), O₂⁻, hydroxyl, and ABTS. Additionally, the CPHs (5 mg/mL) scavenged approximately 100% of the DPPH and ABTS. The CPHs showed similar emulsifying activities to Tween 20 and excellent foaming activities (max FS 74%), which helped to stabilize the krill oil-in-water emulsion. Less than 10 mg/mL CPHs was able to form fresh krill oil-in-water emulsions; moreover, the CPHs (5 mg/mL) in a krill O/W emulsion were homogenous, opaque, and stable for at least 30 days. Based on their inhibitory effects on the peroxide value (POV) and thiobarbituric acid reactive substances (TRABS), the CPHs were found to be able to inhibit lipid oxidation in both emulsifying systems and krill O/W emulsions. Thus, the CPHs could improve superoxide dismutase (SOD) activities by 5- or 10-fold and decrease the high reactive oxygen species (ROS) level caused by the addition of H₂O₂ in vitro. In conclusion, health-promoting CPHs could be applied in krill oil-in-water emulsions as both emulsifiers and antioxidants, which could help to improve the oxidative and physical stability of emulsions. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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20 pages, 5284 KiB

Open AccessArticle

Novel Antioxidant Collagen Peptides of Siberian Sturgeon (Acipenserbaerii) Cartilages: The Preparation, Characterization, and Cytoprotection of H₂O₂-Damaged Human Umbilical Vein Endothelial Cells (HUVECs)

by Yan Sheng, Yi-Ting Qiu, Yu-Mei Wang, Chang-Feng Chi and Bin Wang

Mar. Drugs 2022, 20(5), 325; https://doi.org/10.3390/md20050325 - 14 May 2022

Cited by 74 | Viewed by 4892

Abstract

For making full use of aquatic by-products to produce high value-added products, Siberian sturgeon (Acipenser baerii) cartilages were degreased, mineralized, and separately hydrolyzed by five kinds of proteases. The collagen hydrolysate (SCH) generated by Alcalase showed the strongest 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·) and hydroxide radical (HO·) scavenging activity. Subsequently, thirteen antioxidant peptides (SCP1-SCP3) were isolated from SCH, and they were identified as GPTGED, GEPGEQ, GPEGPAG, VPPQD, GLEDHA, GDRGAEG, PRGFRGPV, GEYGFE, GFIGFNG, PSVSLT, IELFPGLP, LRGEAGL, and RGEPGL with molecular weights of 574.55, 615.60, 583.60, 554.60, 640.64, 660.64, 885.04, 700.70, 710.79, 602.67, 942.12, 714.82, and 627.70 Da, respectively. GEYGFE, PSVSLT, and IELFPGLP showed the highest scavenging activity on DPPH· (EC₅₀: 1.27, 1.05, and 1.38 mg/mL, respectively) and HO· (EC₅₀: 1.16, 0.97, and 1.63 mg/mL, respectively), inhibiting capability of lipid peroxidation, and protective functions on H₂O₂-damaged plasmid DNA. More importantly, GEYGFE, PSVSLT, and IELFPGLP displayed significant cytoprotection on HUVECs against H₂O₂ injury by regulating the endogenous antioxidant enzymes of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) to decrease the contents of reactive oxygen species (ROS) and malondialdehyde (MDA). Therefore, the research provided better technical assistance for a higher-value utilization of Siberian sturgeon cartilages and the thirteen isolated peptides—especially GEYGFE, PSVSLT, and IELFPGLP—which may serve as antioxidant additives for generating health-prone products to treat chronic diseases caused by oxidative stress. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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17 pages, 6281 KiB

Open AccessArticle

Monkfish Peptides Mitigate High Fat Diet-Induced Hepatic Steatosis in Mice

by Jiena Ye, Xiaoxiao Tian, Qiongfen Wang, Jiawen Zheng, Yanzhuo Yang, Baogui Xu, Shuai Zhang, Falei Yuan and Zuisu Yang

Mar. Drugs 2022, 20(5), 312; https://doi.org/10.3390/md20050312 - 5 May 2022

Cited by 16 | Viewed by 3453

Abstract

Non-alcoholic fatty liver disease (NAFLD) is a hepatic metabolic syndrome usually accompanied by fatty degeneration and functional impairment. The aim of the study was to determine whether monkfish peptides (LPs) could ameliorate high-fat diet (HFD)-induced NAFLD and its underlying mechanisms. NAFLD was induced in mice by giving them an HFD for eight weeks, after which LPs were administered in various dosages. In comparison to the HFD control group: body weight in the LP-treated groups decreased by 23–28%; triacylglycerol levels in the blood decreased by 16–35%; and low-density lipoproteins levels in the blood decreased by 23–51%. Additionally, we found that LPs elevated the activity of hepatic antioxidant enzymes and reduced the inflammatory reactions within fatty liver tissue. Investigating the effect on metabolic pathways, we found that in LP-treated mice: the levels of phospho-AMP-activated protein kinase (p-AMPK), and phospho-acetyl CoA carboxylase (p-ACC) in the AMP-activated protein kinase (AMPK) pathway were up-regulated and the levels of downstream sterol regulatory element-binding transcription factor 1 (SREBP-1) were down-regulated; lipid oxidation increased and free fatty acid (FFA) accumulation decreased (revealed by the increased carnitine palmitoyltransferase-1 (CPT-1) and the decreased fatty acid synthase (FASN) expression, respectively); the nuclear factor erythroid-2-related factor 2 (Nrf2) antioxidant pathway was activated; and the levels of heme oxygenase-1 (HO-1) and nicotinamide quinone oxidoreductase 1 (NQO1) were increased. Overall, all these findings demonstrated that LPs can improve the antioxidant capacity of liver to alleviate NAFLD progression mainly through modulating the AMPK and Nrf2 pathways, and thus it could be considered as an effective candidate in the treatment of human NAFLD. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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13 pages, 2649 KiB

Open AccessArticle

Extraction and Identification of Three New Urechis unicinctus Visceral Peptides and Their Antioxidant Activity

by Jingjing Li, Jiajun Lu, Charles Asakiya, Kunlun Huang, Xiuzhi Zhou, Qingliang Liu and Xiaoyun He

Mar. Drugs 2022, 20(5), 293; https://doi.org/10.3390/md20050293 - 27 Apr 2022

Cited by 11 | Viewed by 2852

Abstract

The viscera of Urechis unicinctus with polypeptides, fatty acids, and amino acids are usually discarded during processing to food. In order to improve the utilization value of the viscera of Urechis unicinctus and avoid resource waste, antioxidant polypeptides were isolated from the viscera of Urechis unicinctus. First, a protein hydrolysate of Urechis unicinctus (UUPH) was prepared by ultrasonic-assisted enzymatic hydrolysis, and the degree of hydrolysis was as high as 79.32%. Subsequently, three new antioxidant peptides (P1, P2, and P3) were purified from UUPH using ultrafiltration and chromatography, and their amino acid sequences were identified as VTSALVGPR, IGLGDEGLRR, TKIRNEISDLNER, respectively. Then, the antioxidant activity of the polypeptide was predicted by the structure–activity relationship and finally verified by experiments on eukaryotic cells. The P1 peptide exhibited the strongest antioxidant activity among these three antioxidant peptides. Furthermore, P1, P2, and P3 have no toxic effect on RAW264.7 cells at the concentration of 0.01~2 mg/mL and can protect RAW264.7 cells from H₂O₂-induced oxidative damage in a concentration-dependent manner. These results suggested that these three new antioxidant peptides were isolated from the viscera of Urechis unicinctus, especially the P1 peptide, which might serve as potential antioxidants applied in health-derived food or beverages. This study further developed a new use of the by-product of Urechis unicinctus, which improved the comprehensive utilization of marine biological resources. Full article

(This article belongs to the Special Issue Marine Bioactive Peptides—Structure, Function, and Application)

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