Exploring the Efficacy of Hydroxybenzoic Acid Derivatives in Mitigating Jellyfish Toxin-Induced Skin Damage: Insights into Protective and Reparative Mechanisms.

The escalation of jellyfish stings has drawn attention to severe skin reactions, underscoring the necessity for novel treatments. This investigation assesses the potential of hydroxybenzoic acid derivatives, specifically protocatechuic acid (PCA) and gentisic acid (DHB), for alleviating Nemopilema nomurai Nematocyst Venom (NnNV)-induced injuries. By employing an in vivo mouse model, the study delves into the therapeutic efficacy of these compounds. Through a combination of ELISA and Western blot analyses, histological examinations, and molecular assays, the study scrutinizes the inflammatory response, assesses skin damage and repair mechanisms, and investigates the compounds' ability to counteract venom effects. Our findings indicate that PCA and DHB significantly mitigate inflammation by modulating critical cytokines and pathways, altering collagen ratios through topical application, and enhancing VEGF and bFGF levels. Furthermore, both compounds demonstrate potential in neutralizing NnNV toxicity by inhibiting metalloproteinases and phospholipase-A2, showcasing the viability of small-molecule compounds in managing toxin-induced injuries.

Comparative analysis of PacBio and ONT RNA sequencing methods for Nemopilema Nomurai venom identification.

Recent studies on marine organisms have made use of third-generation sequencing technologies such as Pacific Biosciences (PacBio) and Oxford Nanopore Technologies (ONT). While these specialized bioinformatics tools have different algorithmic designs and performance capabilities, they offer scalability and can be applied to various datasets. We investigated the effectiveness of PacBio and ONT RNA sequencing methods in identifying the venom of the jellyfish species Nemopilema nomurai. We conducted a detailed analysis of the sequencing data from both methods, focusing on key characteristics such as CD, alternative splicing, long-chain noncoding RNA, simple sequence repeat, transcription factor, and functional transcript annotation. Our findings indicate that ONT generally produced higher raw data quality in the transcriptome analysis, while PacBio generated longer read lengths. PacBio was found to be superior in identifying CDs and long-chain noncoding RNA, whereas ONT was more cost-effective for predicting alternative splicing events, simple sequence repeats, and transcription factors. Based on these results, we conclude that PacBio is the most specific and sensitive method for identifying venom components, while ONT is the most cost-effective method for studying venogenesis, cnidocyst (venom gland) development, and transcription of virulence genes in jellyfish. Our study has implications for future sequencing technologies in marine jellyfish, and highlights the power of full-length transcriptome analysis in discovering potential therapeutic targets for jellyfish dermatitis.

Therapeutic potential of enzymatically extracted eumelanin from squid ink in type 2 diabetes mellitus ICR mice: Multifaceted intervention against hyperglycemia, oxidative stress and depression.

BACKGROUND: Type 2 diabetes mellitus (T2DM) is a prevalent metabolic disease that poses significant health risks due to its numerous complications. However, the effects of eumelanin on oxidative stress, hyperglycemia and depression in diabetic mice have not been extensively studied. RESULTS: Our study employed an enzymatic approach to extract eumelanin from squid ink and characterized it using spectroscopic techniques. Remarkably, eumelanin extracted with alkaline-neutral-flavor protease (ANF) displayed superior inhibitory activity against α-glucosidase and α-amylase, while enhancing glucose utilization and hepatic glycogen synthesis in human hepatocellular carcinoma cell line (HepG2) insulin resistance model. Further evaluation of ANF in a T2DM ICR mouse model demonstrated its significant potential in alleviating hyperglycemia, reducing glycosylated serum protein levels, improving glucose tolerance and modulating total cholesterol and low-density lipoprotein levels, as well as antioxidant indices at a dosage of 0.04 g kg-1 . Additionally, ANF exhibited positive effects on energy levels and reduced immobility time in antidepressant behavioral experiments. Moreover, ANF positively influenced the density and infiltration state of renal cells, while mitigating inflammatory enlargement and deformation of liver cells, without inducing any adverse effects in mice. CONCLUSION: Overall, these findings underscore the significant therapeutic potential of ANF in the treatment of T2DM and its associated complications. By augmenting lipid and glucose metabolism, mitigating oxidative stress and alleviating depression, ANF emerges as a promising candidate for multifaceted intervention. © 2023 Society of Chemical Industry.

Hepatoprotective Effect of Oyster Peptide on Alcohol-Induced Liver Disease in Mice.

Alcohol-induced liver disease (ALD) has become one of the major global health problems, and the aim of this study was to investigate the characterization of the structure as well as the hepatoprotective effect and mechanism of oyster peptide (OP, MW < 3500 Da) on ALD in a mouse model. The results demonstrate that ethanol administration could increase the activities of aspartate aminotransferase (AST), alanine transaminase (ALT), γ-Glutamyl transferase (GGT), reactive oxygen species (ROS), malondialdehyde (MDA), and triglycerides (TG), as well as increase the interleukin-1ß (IL-1ß), interleukin-6 (IL-6), and tumor necrosis factor (TNF-α) levels (p < 0.01), and reduce the activity of superoxide dismutase (SOD) and the concentration of glutathione (GSH). Those changes were significantly reversed by the application of different doses of OP. Furthermore, the mRNA expressions of nuclear factor elythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and quinone oxidoreductase1 (NQO1) were significantly up-regulated in OP groups, and the mRNA expressions of nuclear factor kappa-light chain enhancer of B cells (NF-κB), TNF-α, and IL-6 were markedly reduced in OP groups compared to that of the model group. Thus, OP had a significant protective effect on ALD through the enhancement of the in vivo antioxidant ability and the inhibition of the inflammatory response as possible mechanisms of action, which therefore suggests that OP might be useful as a natural source to protect the liver from alcohol damage.

Fluoroalkenyl-Grafted Chitosan Oligosaccharide Derivative: An Exploration for Control Nematode Meloidogyne Incognita.

The exploration of novel, environmentally friendly, and efficient nematicides is essential, and modifying natural biomacromolecules is one feasible approach. In this study, 6-O-(trifluorobutenyl-oxadiazol)-chitosan oligosaccharide derivative was synthesized and characterized by FTIR, NMR, and TG/DTG. Its bioactivity and action mode against root-knot nematode M. incognita were estimated. The results show that the derivative shows high nematicidal activity against J2s, and egg hatching inhibitory activity at 1 mg/mL. The derivative may affect nematode ROS metabolism and further damage intestinal tissue to kill nematode. Meanwhile, by synergism with improving crop resistance, the derivative performed a high control effect on the nematode with low phytotoxicity. These findings suggested that chitosan oligosaccharide derivatives bearing fluoroalkenyl groups are promising green nematicides.

The Effect of N-Acetylation on the Anti-Inflammatory Activity of Chitooligosaccharides and Its Potential for Relieving Endotoxemia.

Endotoxemia is mainly caused by a massive burst of inflammatory cytokines as a result of lipopolysaccharide (LPS) invasion. Chitooligosaccharides (COS) is expected to be a potential drug for relieving endotoxemia due to its anti-inflammatory properties. However, the structural parameters of COS are often ambiguous, and the effect of degree of acetylation (DA) of COS on its anti-inflammatory remains unknown. In this study, four COSs with different DAs (0%, 12%, 50% and 85%) and the same oligomers distribution were successfully obtained. Their structures were confirmed by 1H NMR and MS analysis. Then, the effect of DA on the anti-inflammatory activity and relieving endotoxemia potential of COS was researched. The results revealed that COS with a DA of 12% had better anti-inflammatory activity than COSs with other DAs, mainly in inhibiting LPS-induced inflammatory cytokines burst, down-regulating its mRNA expression and reducing phosphorylation of IκBα. Furthermore, this COS showed an obviously protective effect on endotoxemia mice, such as inhibiting the increase in inflammatory cytokines and transaminases, alleviating the injury of liver and intestinal tissue. This study explored the effect of DA on the anti-inflammatory activity of COS for the first time and lays the foundation for the development of COS as an anti-inflammatory drug against endotoxemia.

Loading Effect of Chitosan Derivative Nanoparticles on Different Antigens and Their Immunomodulatory Activity on Dendritic Cells.

Drug carrier nanoparticles (NPs) were prepared by the polyelectrolyte method, with chitosan sulfate, with different substituents and quaternary ammonium chitosan, including C236-HACC NPs, C36-HACC NPs, and C6-HACC NPs. To evaluate whether the NPs are suitable for loading different antigens, we chose bovine serum albumin (BSA), ovalbumin (OVA), and myoglobin (Mb) as model antigens to investigate the encapsulation effect of the NPs. The characteristics (size, potential, and encapsulation efficiency) of the NPs were measured. Moreover, the NPs with higher encapsulation efficiency were selected for the immunological activity research. The results showed that chitosan derivative NPs with different substitution sites had different loading effects on the three antigens, and the encapsulation rate of BSA and OVA was significantly better than that of Mb. Moreover, the NPs encapsulated with different antigens have different immune stimulating abilities to DCS cells, the immune effect of OVA-coated NPs was significantly better than that of BSA-coated NPs and blank NPs, especially C236-HACC-OVA NPs. Furthermore, we found that C236-HACC-OVA NPs could increase the phosphorylation level of intracellular proteins to activate cell pathways. Therefore, C236-HACC NPs are more suitable for the loading of antigens similar to the OVA structure.

Preparation and Antioxidant Activity of Chitosan Dimers with Different Sequences.

As a popular marine saccharide, chitooligosaccharides (COS) has been proven to have good antioxidant activity. Its antioxidant effect is closely related to its degree of polymerization, degree of acetylation and sequence. However, the specific structure-activity relationship remains unclear. In this study, three chitosan dimers with different sequences were obtained by the separation and enzymatic method, and the antioxidant activity of all four chitosan dimers were studied. The effect of COS sequence on its antioxidant activity was revealed for the first time. The amino group at the reducing end plays a vital role in scavenging superoxide radicals and in the reducing power of the chitosan dimer. At the same time, we found that the fully deacetylated chitosan dimer DD showed the strongest DPPH scavenging activity. When the amino groups of the chitosan dimer were acetylated, it showed better activity in scavenging hydroxyl radicals. Research on COS sequences opens up a new path for the study of COS, and is more conducive to the investigation of its mechanism.

The improved antiviral activities of amino-modified chitosan derivatives on Newcastle virus.

Chitosan is widely used as a medical material because of its excellent biological activities. However, the low solubility of natural chitosan limited its medicinal activity to some extent. The solubility can be improved by introducing more active groups and lowering molecular weight. Therefore, 6-amine chitosan derivatives were synthesized in this paper since more active groups were introduced to increase the medicinal activity. Those derivatives were characterized by elemental analysis, HPLC, and FT-IR and the antiviral activity was tested by hemagglutination tests. Finally, 6-amine chitosan derivatives improved the antiviral activity, especially after the introduction of bromine ion. When 6-deoxy-6-bromo-N-phthaloyl chitosan was 1 g/L, they reduced the hemagglutination titer of virus to zero. The RT-PCR result showed that the expression level of TNF-α and IFN-ß increased significantly, which indicated that the antiviral activity of amino-modified chitosan worked through the stimulation of immune response.

Refinement and Neutralization Evaluation of the F(ab')2 Type of Antivenom against the Deadly Jellyfish Nemopilema nomurai Toxins.

Jellyfish stings threaten people's health and even life in coastal areas worldwide. Nemopilema nomurai is one of the most dangerous jellyfish in the East Asian Marginal Seas, which not only stings hundreds of thousands of people every year but also is assumed to be responsible for most deaths by jellyfish stings in China. However, there is no effective first-aid drug, such as antivenoms, for the treatment of severe stings by N. nomurai to date. In this study, we prepared a N. nomurai antiserum from rabbits using inactivated N. nomurai toxins (NnTXs) and isolated the IgG type of antivenom (IgG-AntiNnTXs) from the antiserum. Subsequently, IgG-AntiNnTXs were refined with multiple optimizations to remove Fc fragments. Finally, the F(ab')2 type of antivenom (F(ab')2-AntiNnTXs) was purified using Superdex 200 and protein A columns. The neutralization efficacy of both types of antivenom was analyzed in vitro and in vivo, and the results showed that both IgG and F(ab')2 types of antivenom have some neutralization effect on the metalloproteinase activity of NnTXs in vitro and could also decrease the mortality of mice in the first 4 h after injection. This study provides some useful information for the development of an effective antivenom for N. nomurai stings in the future.

Preparation of New Sargassum fusiforme Polysaccharide Long-Chain Alkyl Group Nanomicelles and Their Antiviral Properties against ALV-J.

Avian leukosis virus subgroup J (ALV-J) is an immunosuppressive virus which has caused heavy losses to the poultry breeding industry. Currently, there is no effective medicine to treat this virus. In our previous experiments, the low-molecular-weight Sargassum fusiforme polysaccharide (SFP) was proven to possess antiviral activity against ALV-J, but its function was limited to the virus adsorption stage. In order to improve the antiviral activity of the SFP, in this study, three new SFP long-chain alkyl group nanomicelles (SFP-C12M, SFP-C14M and SFP-C16M) were prepared. The nanomicelles were characterized according to their physical and chemical properties. The nanomicelles were characterized by particle size, zeta potential, polydispersity index, critical micelle concentration and morphology. The results showed the particle sizes of the three nanomicelles were all approximately 200 nm and SFP-C14M and SFP-C16M were more stable than SFP-C12M. The newly prepared nanomicelles exhibited a better anti-ALV-J activity than the SFP, with SFP-C16M exhibiting the best antiviral effects in both the virus adsorption stage and the replication stage. The results of the giant unilamellar vesicle exposure experiment demonstrated that the new virucidal effect of the nanomicelles might be caused by damage to the phospholipid membrane of ALV-J. This study provides a potential idea for ALV-J prevention and development of other antiviral drugs.

Characterization of Different Salt Forms of Chitooligosaccharides and Their Effects on Nitric Oxide Secretion by Macrophages.

In this paper, chitooligosaccharides in different salt forms, such as chitooligosaccharide lactate, citrate, adipate, etc., were prepared by the microwave method. They were characterized by SEM, FTIR, NMR, etc., and the nitric oxide (NO) expression was determined in RAW 264.7 cells. The results showed that pure chitooligosaccharide was an irregular spherical shape with rough surface, and its different salt type products are amorphous solid with different honeycomb sizes. In addition to the characteristic absorption peaks of chitooligosaccharides, in FTIR, the characteristic absorption of carboxyl group, methylene group, and aromatic group in corresponding acid appeared. The characteristic absorption peaks of carbon in carboxyl group, hydrogen and carbon in methyl, methylene group, and aromatic group in corresponding acid also appeared in NMR. Therefore, the sugar ring structure and linking mode of chitooligosaccharides did not change after salt formation of chitooligosaccharides. Different salt chitooligosaccharides are completely different in promoting NO secretion by macrophages, and pure chitooligosaccharides are the best.

Comprehensive Proteome Reveals the Key Lethal Toxins in the Venom of Jellyfish Nemopilema nomurai.

Jellyfish stings are a major threat to human beings in coastal areas of the world. Each year, hundreds of thousands of victims are stung by venomous jellyfish. Nemopilema nomurai is a dangerous species with a large number of victims including many deaths. N. nomurai venom is a complex cocktail that is rich in proteins and peptides, and it is secreted by nematocysts for prey or defense. Previous studies have identified hundreds of toxins in the venom of N. nomurai; however, it is unclear which toxin(s) is responsible for lethality. Herein, we isolated the lethal fraction (NnLF) from N. nomurai venom with multiple chromatography. NnLF showed strong lethality to mice, and the toxicology results were consistent with the clinical symptoms of dead patients after N. nomurai sting, which indicated that NnLF contained the key lethal toxins in the venom. Subsequently, proteomic analysis was performed to identify the toxins in NnLF, and a total of 13 toxin homologues were identified, including phospholipase, potassium channel inhibitor, hemolysin, thrombin, etc. Moreover, in vitro toxicity assays further verified the phospholipase A2 and hemolytic activity of NnLF. These results revealed that cell membrane-targeted toxins, including channel-forming toxins, potassium channel inhibitors, and especially phospholipases, played very important roles in the lethality of N. nomurai sting. Moreover, blood toxins such as thrombin-like toxin and hemolysins might be synergistically involved in lethality. These findings advance the understanding of lethality caused by N. nomurai sting and will be significant for the development of drugs to treat this jellyfish sting in the future.

Chitosan Oligosaccharide Fluorinated Derivative Control Root-Knot Nematode (Meloidogyne incognita) Disease Based on the Multi-Efficacy Strategy.

Plant root-knot nematode disease is a great agricultural problem and commercially available nematicides have the disadvantages of high toxicity and limited usage; thus, it is urgent to develop new nematicides derived from nature substances. In this study, a novel fluorinated derivative was synthesized by modifying chitosan oligosaccharide (COS) using the strategy of multiple functions. The derivatives were characterized by FTIR, NMR, elemental analysis, and TG/DTG. The activity assays show that the derivatives can effectively kill the second instar larvae of Meloidogyne incognita in vitro, among them, chitosan-thiadiazole-trifluorobutene (COSSZFB) perform high eggs hatching inhibitory activity. The derivatives can regulate plant growth (photosynthetic pigment), improve immunity (chitinase and ß-1,3-glucanase), and show low cytotoxicity and phytotoxicity. According to the multi-functional activity, the derivatives exhibit a good control effect on plant root-knot nematode disease in vivo. The results demonstrate that the COS derivatives (especially fluorinated derivative) perform multiple activities and show the potential to be further evaluated as nematicides.

Optimization of Oyster (Crassostrea talienwhanensis) Protein Hydrolysates Using Response Surface Methodology.

Oyster (Crassostrea talienwhanensis) protein was hydrolyzed by trypsin to produce peptides with different response values, and response surface methodology (RSM) was applied to optimize the hydrolysis conditions. The highest degree of hydrolysis (DH) of the oyster peptide (OP) was obtained at an enzyme concentration of 1593.2 U/g, a pH of 8.2, a hydrolysis temperature of 40.1 °C, a hydrolysis time of 6.0 h, and a water/material ratio of 8.2. The greatest hydroxyl-radical-scavenging activity of OP was obtained at an enzyme concentration of 1546.3 U/g, a pH of 9.0, a hydrolysis temperature of 50.2 °C, a hydrolysis time of 5.1 h, and a water/material ratio of 5.6. The largest branched-chain amino acid (BCAA) content of OP was obtained at an enzyme concentration of 1323.8 U/g, a pH of 8.3, a hydrolysis temperature of 41.7 °C, a hydrolysis time of 6.7 h, and a water/material ratio of 4.8. The three experimental values were significantly in agreement with the predicted values within the 95% confidence interval. Furthermore, ultrafiltration and chromatographic methods were used to purify the OP, and 13 peptides that were rich in Lys, Arg, His, and Thr were identified by LC-MS/MS. The results of this study offer different optimum hydrolysis conditions to produce target peptides from oyster protein by using RSM, and this study provide a theoretical basis for the high-value utilization of oyster protein.

Immunostimulatory Effects of Chitooligosaccharides on RAW 264.7 Mouse Macrophages via Regulation of the MAPK and PI3K/Akt Signaling Pathways.

Chitooligosaccharides (COS), the hydrolyzed products of chitin and chitosan, can be obtained by various methods. In this study, water-soluble COS were prepared from α- and ß-chitosan by microwave-assisted degradation and their immunostimulatory effects were investigated in RAW 264.7 macrophages. The results indicated that α-COS were more active than ß-COS in promoting the production of nitric oxide (NO) and cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6). Quantitative real-time reverse transcription polymerase chain reaction and Western blotting indicated that COS also enhanced the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and TNF-α. Further analyses demonstrated that COS induced the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38, p85 and Akt, and the nuclear translocation of p65, indicating that they are able to activate the mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinases (PI3K)/Akt signaling pathways dependent on nuclear factor (NF)-κB activation. In conclusion, COS activate RAW 264.7 cells via the MAPK and PI3K/Akt signaling pathways and are potential novel immune potentiators.

Preparation and Identification of Antioxidative Peptides from Pacific Herring (Clupea pallasii) Protein.

The aim of this study was to isolate and purify antioxidative peptides from Pacific herring (Clupea pallasii) protein. Five enzymes (pepsin, trypsin, papain, flavourzyme, and neutrase) were used for protein hydrolysis, and Pacific herring protein hydrolysates (PHPH) were separated by ultrafiltration. The fraction with the molecular weight below 3500 Da exhibited the highest in vitro antioxidant activities and cellular antioxidant activity. The PHPH was isolated and purified by consecutive chromatographic methods including gel filtration chromatography and reverse high-performance liquid chromatography (RP-HPLC). The purified antioxidant peptides were identified as Leu-His-Asp-Glu-Leu-Thr (MW = 726.35 Da) and Lys-Glu-Glu-Lys-Phe-Glu (MW = 808.40 Da), and the IC50 values of cellular antioxidant activity were 1.19 ± 0.05 mg/mL and 1.04 ± 0.06 mg/mL. The results demonstrate that is possible to produce natural antioxidative peptides from Pacific herring protein via enzymatic hydrolysis and purification.

Partial Characterization, the Immune Modulation and Anticancer Activities of Sulfated Polysaccharides from Filamentous Microalgae Tribonema sp.

Recently, Tribonema sp., a kind of filamentous microalgae, has been studied for biofuel production due to its accumulation of triacylglycerols. However, the polysaccharides of Tribonema sp. and their biological activities have rarely been reported. In this paper, we extracted sulfated polysaccharides from Tribonema sp. (TSP), characterized their chemical composition and structure, and determined their immunostimulation and anticancer activities on RAW264.7 macrophage cells and HepG2 cells. The results showed that TSP is a sulfated polysaccharide with a Mw of 197 kDa. TSP is a heteropolysaccharide that is composed mainly of galactose. It showed significant immune-modulatory activity by stimulating macrophage cells, such as upregulating interleukin 6 (IL-6), interleukin 10 (IL-10), and tumor necrosis factor α (TNF-α). In addition, TSP also showed significant dose-dependent anticancer activity (with an inhibition rate of up to 66.8% at 250 µg/mL) on HepG2 cells as determined by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cycle analysis indicated that the anticancer activity of TSP is mainly the result of induced cell apoptosis rather than affecting the cell cycle and mitosis of HepG2 cells. These findings suggest that TSP might have potential as an anticancer resource, but further research is needed, especially in vivo experiments, to explore the anticancer mechanism of TSP.

Analysis of the protective effects of γ-aminobutyric acid during fluoride-induced hypothyroidism in male Kunming mice.

CONTEXT: Compounds to treat hypothyroidism in the absence of cardiac side effects are urgently required. In this regard, γ-aminobutyric acid (GABA) has gained interest due to its anti-anxiolytic, antihypertensive and antioxidant properties, and reported benefits to the thyroid system. OBJECTIVE: We investigated the ability of GABA to ameliorate fluoride-induced thyroid injury in mice, and investigated the mechanism(s) associated with GABA-induced protection. MATERIALS AND METHODS: Adult male Kumning mice (N = 90) were exposed to NaF (50 mg/kg) for 30 days as a model of hypothyroidism. To evaluate the effects of GABA administration, fluoride-exposed mice received either thyroid tablets, or low (25 mg/kg), medium (50 mg/kg) or high (75 mg/kg) concentrations of pure GABA orally for 14 days groups (N = 10 each). The effects of low (50 mg/kg); medium (75 mg/kg) and high (100 mg/kg) concentrations of laboratory-separated GABA were assessed for comparison. Effects on thyroid hormone production, oxidative stress, thyroid function-associated genes, and side-effects during therapy were measured. RESULTS: GABA supplementation in fluoride-exposed mice significantly increased the expression of thyroid TG, TPO, and NIS (P < 0.05), significantly improved the thyroid redox state (P < 0.05), modulated the expression of thyroid function-associated genes, conferred liver metabolic protection, and prevented changes to myocardial morphology, thus reducing side effects. Both pure and laboratory-separated GABA displayed comparative protective effects. DISCUSSION AND CONCLUSION: Our findings support the assertion that GABA exerts therapeutic potential in hypothyroidism. The design and use of human GABA trials to improve therapeutic outcomes in hypothyroidism are now warranted.

Combined Proteome and Toxicology Approach Reveals the Lethality of Venom Toxins from Jellyfish Cyanea nozakii.

Jellyfish are a type of poisonous cnidarian invertebrate that secrete lethal venom for predation or defense. Human beings often become victims of jellyfish stings accidentally while swimming or fishing and suffer severe pain, itching, swelling, inflammation, shock, and even death. Jellyfish venom is composed of various toxins, and the lethal toxin is the most toxic and hazardous component of the venom, which is responsible for deaths caused by jellyfish stings and envenomation. Our previous study revealed many toxins in jellyfish venom, including phospholipase A2, metalloproteinase, and protease inhibitors. However, it is still unknown which type of toxin is lethal and how it works. Herein a combined toxicology analysis, proteome strategy, and purification approach was employed to investigate the lethality of the venom of the jellyfish Cyanea nozakii. Toxicity analysis revealed that cardiotoxicity including acute myocardial infarction and a significant decrease in both heart rate and blood pressure is the primary cause of death. Purified lethal toxin containing a fraction of jellyfish venom was subsequently subjected to proteome analysis and bioinformation analysis. A total of 316 and 374 homologous proteins were identified, including phospholipase A2-like toxins and metalloprotease-like toxins. Furthermore, we confirmed that the lethality of the jellyfish venom is related to metalloproteinase activity but without any phospholipase A2 activity or hemolytic activity. Altogether, this study not only provides a comprehensive understanding of the lethal mechanism of jellyfish venom but also provides very useful information for the therapeutic or rescue strategy for severe jellyfish stings.