The role of ROS in microcystin-LR-induced hepatocyte apoptosis and liver injury in mice

Regulation of TGF-β1, PI3K/PIP3/Akt, Nrf-2/Keap-1 and NF-κB signaling pathways to avert bifenthrin induced hepatic injury: A palliative role of daidzein

Bifenthrin (BFN) is a noxious insecticide which is reported to damage various body organs. Daidzein (DZN) is a natural flavone with excellent pharmacological properties. This research was conducted to evaluate the alleviative strength of DZN to counteract BFN prompted liver toxicity in male albino rats. Thirty-two rats were divided into 4 groups i.e., the control, BFN (7 mg /kg), BFN (7 mg/kg) + DZN (20 mg/kg) and DZN (20 mg/kg) alone group. The biochemical assessment was performed by using qRT PCR as well as standard ELISA protocols. The findings are validated by applying pharmacodynamic techniques including molecular simulation. It was observed that BFN reduced the gene expressions of phosphoinositide 3-kinase (PI3K), phosphatidylinositol-3, 4, 5-triphosphate (PIP3), Protein kinase B (Akt), nuclear factor erythroid 2-related factor 2 (Nrf-2) while promoting the gene expressions of Kelch-like ECH-associated protein 1 (Keap-1). Moreover, BFN notably reduced the activities of glutathione reductase (GSR), heme-oxygenase-1 (HO-1), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) while elevating the levels of reactive oxygen species (ROS) and malondialdehyde (MDA). BFN promoted the levels of matrix metallopeptidase 2 (MMP-2), Procollagen III N-terminal Pro-peptide (PIIINP), alkaline phosphatase (ALP), transforming growth factor-beta-1 (TGF-β1), aspartate aminotransferase (AST), tissue inhibitor of matrix metalloproteinases 1 (TIMP1), and alanine aminotransferase (ALT). The levels of nuclear factor- kappa B (NF-κB), interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2) were increased following the BFN intoxication. BFN enhanced the expressions of cysteine-aspartic acid protease-3 (Caspase-3) and Bcl-2-associated X protein (Bax) while suppressing the gene expression of B-cell lymphoma-2 (Bcl-2). Moreover, BFN disrupted the normal histology of liver tissues. Nonetheless, DZN treatment remarkably alleviated hepatic damages owing to its antioxidative, anti-apoptotic as well as anti-inflammatory abilities. However, DZN supplementation remarkably safeguarded which is further confirmed by in-silico assessment.

Derivatization of Microcystins Can Increase Target Inhibition while Reducing Cellular Uptake

Microcystins, a large family of nonribosomal cyclic heptapeptides known for their hepatotoxicity, are among the best-studied cyanobacterial toxins. Recently, they have been discussed as leads for the development of anticancer drug substances. Their main mode-of-action is inhibition of the eukaryotic serine/threonine protein phosphatases 1 and 2A. Unlike many cytotoxins that can cross cell membranes by passive diffusion, microcystins depend on active uptake via organic anion transporting polypeptides 1B1 or 1B3. Both phosphatase inhibition and transportability strongly depend on the structure of the individual microcystin. Here, we present how chemical modification of positions 2 and 4 of the microcystin core structure can alter these two properties. Aiming to reduce transportability and increase phosphatase inhibition, we used pharmacophore modeling to investigate the phosphatase inhibition potential of microcystins derivatized with small molecules containing a variety of functional groups. The respective derivatives were synthesized using click chemistry. We discovered that some derivatized microcystins can address a yet undescribed subpocket of the protein phosphatase 1. The derivatized microcystins were tested for phosphatase 1 inhibition and cytotoxicity on transporter-expressing cell lines, revealing that target inhibition and transportability of microcystins can independently be influenced by the physicochemical properties, especially of the residue located in position 2 of the microcystin. Derivatization with small acids or amino acids resulted in microcystins with a favorable ratio of inhibition to transportability, making these derivatives potentially suitable for drug development.

Classification machine learning to detect de facto reuse and cyanobacteria at a drinking water intake

Harmful algal blooms (HABs) or higher levels of de facto water reuse (DFR) can increase the levels of certain contaminants at drinking water intakes. Therefore, the goal of this study was to use multi-class supervised machine learning (SML) classification with data collected from six online instruments measuring fourteen total water quality parameters to detect cyanobacteria (corresponding to approximately 950 cells/mL, 2900 cells/mL, and 8600 cells/mL) or DFR (0.5, 1 and 2 % of wastewater effluent) events in the raw water entering an intake. Among 56 screened models from the caret package in R, four (mda, LogitBoost, bagFDAGCV, and xgbTree) were selected for optimization. mda had the greatest testing set accuracy, 98.09 %, after optimization with 7 false alerts. Some of the most important water parameters for the different models were phycocyanin-like fluorescence, UVA254, and pH. SML could detect algae blending events (estimated <9000 cells/mL) due in part to the phycocyanin-like fluorescence sensor. UVA254 helped identify higher concentrations of DFR. These results show that multi-class SML classification could be used at drinking water intakes in conjunction with online instrumentation to detect and differentiate HABs and DFR events. This could be used to create alert systems for the water utilities at the intake, rather than the finished water, so any adjustment to the treatment process could be implemented.

Alleviation of microcystin-leucine arginine -induced hepatotoxicity: An updated overview

OBJECTIVES

Contamination of surface waters is a major health threat for all living creatures. Some types of blue-green algae that naturally occur in fresh water, are able to produce various toxins, like Microcystins (MCs). Microcystin-leucine arginine (MC-LR) produced by Microcystis aeruginosa is the most toxic and abundant isoforms of MCs, and it causes hepatotoxicity. The present article reviews preclinical experiments examined different treatments, including herbal derivatives, dietary supplements and drugs against MC-LR hepatotoxicity.

METHODS

We searched scientific databases Web of Science, Embase, Medline (PubMed), Scopus, and Google Scholar using relevant keywords to find suitable studies until November 2023.

RESULTS

MC-LR through Organic anion transporting polypeptide superfamily transporters (OATPs) penetrates and accumulates in hepatocytes, and it inhibits protein phosphatases (PP1 and PP2A). Consequently, MC-LR disturbs many signaling pathways and induces oxidative stress thus damages cellular macromolecules. Some protective agents, especially plants rich in flavonoids, and natural supplements, as well as chemoprotectants were shown to diminish MC-LR hepatotoxicity.

CONCLUSION

The reviewed agents through blocking the OATP transporters (nontoxic nostocyclopeptide-M1, captopril, and naringin), then inhibition of MC-LR uptake (naringin, rifampin, cyclosporin-A, silymarin and captopril), and finally at restoration of PPAse activity (silybin, quercetin, morin, naringin, rifampin, captopril, azo dyes) exert hepatoprotective effect against MC-LR.

α-LA attenuates microcystin-LR-induced hepatocellular oxidative stress in mice through Nrf2-mediated antioxidant and detoxifying enzymes

Microcystins constitute a class of toxins synthesized by cyanobacteria and are known to inflict significant damage on the antioxidant defense system of living organisms, primarily targeting the liver. α-Lipoic acid (α-LA) is universally recognized as a potent antioxidant in biological systems. It exerts its beneficial effects through multiple mechanisms-directly neutralizing reactive oxygen species (ROS) and free radicals, and indirectly enhancing antioxidant defenses by facilitating the regeneration of glutathione (GSH). However, the precise modus operandi of α-LA's protective effect against Microcystin-LR-induced hepatotoxicity remains incompletely elucidated. The present study, therefore, employed α-LA to explore its protective role against Microcystin-LR exposure in mice. A model of Microcystin-LR-induced hepatic injury was established by administering Microcystin-LR into the peritoneal cavity of BALB/c mice daily over a two-week period. Thereafter, BALB/c mice were pre-treated with varying concentrations of α-LA via oral gavage for a duration of 7 days, followed by a 7-day exposure to Microcystin-LR. Our findings reveal that α-LA pre-treatment significantly mitigated hepatic pathologies in Microcystin-LR-exposed mice. Furthermore, α-LA administration led to a notable elevation in the activities and expression levels of nuclear factor erythroid 2-related factor 2, superoxide dismutase, glutathione peroxidase, glutathione S-transferase, and glutathione-indicative of its antioxidative capacity. Concurrently, a significant decrease was observed in the activities and expression levels of malondialdehyde and cytochrome P450 2E1. Consequently, α-LA emerges as a promising therapeutic candidate for the amelioration of liver oxidative damage subsequent to Microcystin-LR exposure.

Hawthorn fruit extract protect against MC-LR-induced hepatotoxicity by attenuating oxidative stress and apoptosis

Microcystins (MCs) is a class of cyclic heptapeptide compounds with biological activity. There is no effective treatment for liver injury caused by MCs. Hawthorn is a medicinal and edible plant traditional Chinese medicine with hypolipidemic, reducing inflammation and oxidative stress in the liver. This study discussed the protective effect of hawthorn fruit extract (HFE) on liver damage caused by MC-LR and the underlying molecular mechanism. After MC-LR exposure, pathological changes were observed and hepatic activity of ALT, AST and ALP were increased obviously, but they were remarkably restored with HFE administration. In addition, MC-LR could significantly reduce SOD activity and increase MDA content. Importantly, MC-LR treatment resulted in mitochondrial membrane potential decreased, and Cytochrome C release, eventually leading to cell apoptosis rate increase. HFE pretreatment could significantly alleviate the above abnormal phenomena. To examine the mechanism of protection, the expression of critical molecules in the mitochondrial apoptosis pathway was examined. The levels of Bcl-2 was inhibited, and the levels of Bax, Caspase-9, Cleaved Caspase-9, and Cleaved caspase-3 were upregulated after MC-LR treatment. HFE reduced MC-LR-induced apoptosis via reversing the expression of key proteins and genes in the mitochondrial apoptotic pathway. Hence, HFE could alleviate MC-LR induced hepatotoxicity by reducing oxidative stress and apoptosis.

Dietary Thymoquinone Alone or Combined with Swimming Exercise Protect against Microcystin-LR-Induced Oxidative Injury in Mice

Microcystin-leucine-arginine (MCLR) is the most abundant cyanotoxin produced by cyanobacteria. It induces potent cytotoxicity through oxidative stress and DNA damage. Thymoquinone (TQ) is a natural nutraceutical antioxidant derived from black cumin (Nigella sativa). Physical exercise (EX) improves whole-body metabolic homeostasis. Therefore, this study examined the protective role of swimming exercise and TQ against MC-induced toxicity in mice. Fifty-six healthy adult male albino mice (25-30 g) were randomized into seven groups; group (I) was the negative control and received oral physiological saline for 21 days; group (II) received water EX for 30 min daily; group (III) was intraperitoneally injected with TQ (5 mg/kg daily, for 21 days); group (IV) was intraperitoneally administered MC (10 μg/kg daily, for 14 days) and acted as the positive toxic control; group (V) was treated with MC and water EX; group (VI) was injected with MC and TQ; finally, group (VII) was treated with MC with TQ and water EX. In comparison with the control group, the results showed hepatic, renal, and cardiac toxicity in the MCLR-treated group, indicated by a significant increase (p < 0.05) in serum levels of alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine transferase (ALT), cholesterol, lactate dehydrogenase (LDH), creatine kinase (CK), creatine kinase-myocardial band (CK-MB), urea, creatinine, interleukin-6, interleukin -1β, and tumor necrosis factor-α levels. In addition, there were significant elevations (p < 0.05) in malondialdehyde (MDA) and nitric oxide (NO) levels and a significant decrease in reduced glutathione (GSH), glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD) in hepatic, cardiac, and renal tissues. Treatment with either TQ or water EX significantly improved (p < 0.05) the MC-induced toxicity with superiority of the TQ group in the restoration of normal ranges; however, cotreatment with both TQ and swimming EX showed the most improvement and restoration to normal ranges as a result of increasing EX clinical efficacy by TQ.

The Abnormal Proliferation of Hepatocytes is Associated with MC-LR and C-Terminal Truncated HBX Synergistic Disturbance of the Redox Balance

Background

Microcystin-LR (MC-LR) and hepatitis B virus (HBV) are associated with hepatocellular carcinoma (HCC). However, the concentrations of MC-LR in drinking water and the synergistic effect of MC-LR and HBV on hepatocellular carcinogenesis through their disturbance of redox balance have not been fully elucidated.

Methods

We measured the MC-LR concentrations in 168 drinking water samples of areas with a high incidence of HCC. The relationships between MC-LR and both redox status and liver diseases in 177 local residents were analyzed. The hepatoma cell line HepG2 transfected with C-terminal truncated hepatitis B virus X gene (Ct-HBX) were treated with MC-LR. Reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) were measured. Cell proliferation, migration, invasion, and apoptosis were assessed with cell activity assays, scratch and transwell assays, and flow cytometry, respectively. The mRNA and protein expression-related redox status genes were analyzed with qPCR and Western blotting.

Results

The average concentration of MC-LR in well water, river water and reservoir water were 57.55 ng/L, 76.74 ng/L and 132.86 ng/L respectively, and the differences were statistically significant (P < 0.05). The MC-LR levels in drinking water were correlated with liver health status, including hepatitis, clonorchiasis, glutamic pyruvic transaminase abnormalities and hepatitis B surface antigen carriage (all P values < 0.05). The serum MDA increased in subjects who drank reservoir water and were infected with HBV (P < 0.05). In the cell experiment, ROS increased when Ct-HBX-transfected HepG2 cells were treated with MC-LR, followed by a decrease in SOD and GSH and an increase in MDA. MC-LR combined with Ct-HBX promoted the proliferation, migration and invasion of HepG2 cells, upregulated the mRNA and protein expression of MAOA gene, and downregulated UCP2 and GPX1 genes.

Conclusion

MC-LR and HBV may synergistically affect redox status and play an important role in hepatocarcinoma genesis.

The presence of polystyrene nanoplastics enhances the MCLR uptake in zebrafish leading to the exacerbation of oxidative liver damage

The accumulation of diminutive plastic waste in the environment, including microplastics and nanoplastics, has threatened the health of multiple species. Nanoplastics can adsorb the pollutants from the immediate environment, and may be used as carriers for pollutants to enter organisms and bring serious ecological risk. To evaluate the toxic effects of microcystin-LR (MCLR) on the liver of adult zebrafish (Danio rerio) in the presence of 70 nm polystyrene nanoplastics (PSNPs), zebrafish were exposed to MCLR alone (0, 0.9, 4.5 and 22.5 μg/L) and a mixture of MCLR + PSNPs (100 μg/L) for three months. The results indicated that groups with combined exposure to MCLR and PSNPs further enhanced the accumulation of MCLR in the liver when compared to groups only exposed to MCLR. Cellular swelling, fat vacuolation, and cytoarchitectonic damage were observed in zebrafish livers after exposure to MCLR, and the presence of PSNPs exacerbated these adverse effects. The results of biochemical tests showed the combined effect of MCLR + PSNPs enhanced MCLR-induced hepatotoxicity, which could be attributed to the altered levels of reactive oxygen species, malondialdehyde and glutathione, and activities of catalase. The expression of genes related to antioxidant responses (p38a, p38b, ERK2, ERK3, Nrf2, HO-1, cat1, sod1, gax, JINK1, and gstr1) was further performed to study the mechanisms of MCLR combined with PSNPs aggravated oxidative stress of zebrafish. The results showed that PSNPs could improve the bioavailability of MCLR in the zebrafish liver by acting as a carrier and accelerate MCLR-induced oxidative stress by regulating the levels of corresponding enzymes and genes.

Identification of Novel Molecular Targets of Four Microcystin Variants by High-Throughput Virtual Screening

Highly toxic microcystins (MCs) perform complex interactions with many proteins that induce cellular dysregulation, leading to the development of several diseases including cancer. There is significant diversity and chemical complexity among MC congeners, which makes it difficult to identify structure-dependent toxicity outcomes and their long-term effects. The aim of this study was to exploratory identify likely molecular targets of the main MC variants (MC-LA, MC-LR, MC-RR, and MC-LY) by conducting a computational binding affinity analysis using AutoDock Vina to evaluate the interaction of the toxins with 1000 proteins related to different biological functions. All four variants showed strong in silico interactions with proteins that regulate metabolism/immune system, CD38 (top scoring hit, −11.5 kcal/mol); inflammation, TLR4 (−11.4 kcal/mol) and TLR8 (−11.5 kcal/mol); neuronal conduction, BChE; renin–angiotensin signaling, (ACE); thyroid hormone homeostasis (TTR); and cancer-promoting processes, among other biochemical activities. The results show MCs have the potential to bind onto distinct molecular targets which could generate biochemical alterations through a number of signal transduction pathways. In short, this study broadens our knowledge about the mechanisms of action of different variants of microcystins and provides information for future direct experimentation.

Protective Effect of Vitamin E on Cadmium-Induced Renal Oxidative Damage and Apoptosis in Rats

Cadmium (Cd), a widely distributed heavy metal, is extremely toxic to the kidney. Vitamin E (VE) is an important antioxidant in the body. It is known that VE exerts a protective effect on renal oxidative damage caused by Cd, but the effect and mechanism of VE on apoptosis are not fully understood. Thus, we conducted this study to explore the protective effect of VE on Cd-induced renal apoptosis and to elucidate its potential mechanism. Thirty-two 9-week-old male Sprague-Dawley rats were randomly divided into four groups, namely control, VE (100 mg/kg VE), Cd (5 mg/kg CdCl₂), and VE + Cd (100 mg/kg VE + 5 mg/kg CdCl₂), and received intragastric administration of Cd and/or VE for 4 weeks. The results showed that Cd exposure significantly reduced the weight of the body and kidney, elevated the accumulation of Cd in the kidney as well as the levels of BUN and Scr in serum, caused renal histological alterations, decreased the GSH and T-AOC contents and antioxidant enzyme (SOD, CAT, GSH-PX) activities, and increased renal MDA content. And the increased number of TUNEL-positive cells by Cd was accompanied by upregulated mRNA and protein expressions of apoptotic regulatory molecules (Bax, Caspase-3, GRP94, GRP78, Caspase-8) and downregulated Bcl-2 expressions. However, the combined treatment of Cd and VE could restore the above parameters to be close to those in the control rats. In conclusion, VE supplement could alleviate Cd-induced rat renal damage and oxidative stress through enhancing the antioxidant defense system and inhibiting apoptosis of renal cells.

Edaravone prevents high glucose-induced injury in retinal Müller cells through thioredoxin1 and the PGC-1α/NRF1/TFAM pathway

CONTEXT

Oxidative injury in a high-glucose (HG) environment may be a mechanism of diabetic retinopathy (DR) and edaravone can protect retinal ganglion cells by scavenging ROS.

OBJECTIVE

To explore the effect of edaravone on HG-induced injury.

MATERIALS AND METHODS

First, Müller cells were cultured by different concentrations of glucose for different durations to obtain a suitable culture concentrations and duration. Müller cells were then divided into Control, HG + Vehicle, HG + Eda-5 μM, HG + Eda-10 μM, HG + Eda-20 μM, and HG + Eda-40 μM groups. Cells were cultured by 20 mM glucose and different concentrations of edaravone for 72 h.

RESULTS

The IC₅₀ of glucose at 12-72 h is 489.3, 103.5, 27.92 and 20.71 mM, respectively. When Müller cells were cultured in 20 mM glucose for 72 h, the cell viability was 52.3%. Edaravone significantly increased cell viability compared to Vehicle (68.4% vs 53.3%; 78.6% vs 53.3%). The EC₅₀ of edaravone is 34.38 μM. HG induced high apoptosis rate (25.5%), while edaravone (20 and 40 μM) reduced it to 12.5% and 6.89%. HG increased the DCF fluorescence signal (189% of Control) and decreased the mitochondrial membrane potential by 57%. Edaravone significantly decreased the DCF fluorescence signal (144% and 132% of Control) and recovered the mitochondrial membrane potential to 68% and 89% of Control. Furthermore, HG decreased the expression of TRX1, PGC-1α, NRF1 and TFAM, which were restored by edaravone.

DISCUSSION AND CONCLUSION

These findings provide a new potential approach for the treatment of DR and indicated new molecular targets in the prevention of DR.

Microcystin-Induced Immunotoxicity in Fishes: A Scoping Review

Cyanobacteria (blue-green algae) have been present on Earth for over 2 billion years, and can produce a variety of bioactive molecules, such as cyanotoxins. Microcystins (MCs), the most frequently detected cyanotoxins, pose a threat to the aquatic environment and to human health. The classic toxic mechanism of MCs is the inhibition of the protein phosphatases 1 and 2A (PP1 and PP2A). Immunity is known as one of the most important physiological functions in the neuroendocrine-immune network to prevent infections and maintain internal homoeostasis in fish. The present review aimed to summarize existing papers, elaborate on the MC-induced immunotoxicity in fish, and put forward some suggestions for future research. The immunomodulatory effects of MCs in fish depend on the exposure concentrations, doses, time, and routes of exposure. Previous field and laboratory studies provided strong evidence of the associations between MC-induced immunotoxicity and fish death. In our review, we summarized that the immunotoxicity of MCs is primarily characterized by the inhibition of PP1 and PP2A, oxidative stress, immune cell damage, and inflammation, as well as apoptosis. The advances in fish immunoreaction upon encountering MCs will benefit the monitoring and prediction of fish health, helping to achieve an ecotoxicological goal and to ensure the sustainability of species. Future studies concerning MC-induced immunotoxicity should focus on adaptive immunity, the hormesis phenomenon and the synergistic effects of aquatic microbial pathogens.

Microcystin-LR inhibits testosterone synthesis via reactive oxygen species-mediated GCN2/eIF2α pathway in mouse testes

Previous studies demonstrated that microcystin-leucine-arginine (MC-LR) disrupted testosterone (T) synthesis, but the underlying mechanisms are not entirely elucidated. This study aims to explore the role of reactive oxygen species (ROS)-mediated GCN2/eIF2α activation on MC-LR-induced disruption of testicular T synthesis. Male mice were intraperitoneally injected with MC-LR (0 or 20 μg/kg) daily for 5 weeks. Serum T was decreased in MC-LR-exposed mice (0.626 ± 0.122 vs 24.565 ± 8.486 ng/ml, P < 0.01), so did testicular T (0.667 ± 0.15 vs 8.317 ± 1.387 ng/mg protein, P < 0.01). Steroidogenic proteins including StAR, CYP11A1 and CYP17A1 were downregulated in MC-LR-exposed mouse testes and TM3 cells. Mechanistically, p-GCN2 and p-eIF2α were elevated in MC-LR-exposed TM3 cells. GCN2iB attenuated MC-LR-induced GCN2 and eIF2α phosphorylation in TM3 cells. Moreover, GCN2iB attenuated MC-LR-induced downregulation of steroidogenic proteins in TM3 cells. Further analysis found that cellular ROS were elevated and HO-1 was upregulated in MC-LR-exposed TM3 cells. PBN rescued MC-LR-induced activation of GCN2/eIF2α signaling in TM3 cells. Additionally, pretreatment with PBN attenuated MC-LR induced downregulation of steroidogenic proteins and synthases in TM3 cells. These results suggest that ROS-mediated GCN2/eIF2α activation contributes partially to MC-LR-caused downregulation of steroidogenic proteins and synthases. The present study provides a new clue for understanding the mechanism of MC-LR-induced endocrine disruption.

A Brief Review of the Structure, Cytotoxicity, Synthesis, and Biodegradation of Microcystins

Harmful cyanobacterial blooms pose an environmental health hazard due to the release of water-soluble cyanotoxins. One of the most prevalent cyanotoxins in nature is microcystins (MCs), a class of cyclic heptapeptide hepatotoxins, and they are produced by several common cyanobacteria in aquatic environments. Once released from cyanobacterial cells, MCs are subjected to physical chemical and biological transformations in natural environments. MCs can also be taken up and accumulated in aquatic organisms and their grazers/predators and induce toxic effects in several organisms, including humans. This brief review aimed to summarize our current understanding on the chemical structure, exposure pathway, cytotoxicity, biosynthesis, and environmental transformation of microcystins.

Microcystin Toxicokinetics, Molecular Toxicology, and Pathophysiology in Preclinical Rodent Models and Humans

Microcystins are ubiquitous toxins produced by photoautotrophic cyanobacteria. Human exposures to microcystins occur through the consumption of contaminated drinking water, fish and shellfish, vegetables, and algal dietary supplements and through recreational activities. Microcystin-leucine-arginine (MCLR) is the prototypical microcystin because it is reported to be the most common and toxic variant and is the only microcystin with an established tolerable daily intake of 0.04 µg/kg. Microcystin toxicokinetics is characterized by low intestinal absorption, rapid and specific distribution to the liver, moderate metabolism to glutathione and cysteinyl conjugates, and low urinary and fecal excretion. Molecular toxicology involves covalent binding to and inhibition of protein phosphatases, oxidative stress, cell death (autophagy, apoptosis, necrosis), and cytoskeleton disruption. These molecular and cellular effects are interconnected and are commonly observed together. The main target organs for microcystin toxicity are the intestine, liver, and kidney. Preclinical data indicate microcystins may also have nervous, pulmonary, cardiac, and reproductive system toxicities. Recent evidence suggests that exposure to other hepatotoxic insults could potentiate microcystin toxicity and increase the risk for chronic diseases. This review summarizes the current knowledge for microcystin toxicokinetics, molecular toxicology, and pathophysiology in preclinical rodent models and humans. More research is needed to better understand human toxicokinetics and how multifactorial exposures contribute to disease pathogenesis and progression.

Acute exposure to microcystin-LR induces hepatopancreas toxicity in the Chinese mitten crab (Eriocheir sinensis)

The Chinese mitten crab is an important economic species in the Chinese aquaculture industry due to its rich nutritional value and distinct flavor. The hepatopancreas is a popular edible part of the Chinese mitten crab, and therefore, hepatopancreatic health directly determines its quality. However, a large-scale outbreak of hepatopancreatic necrosis syndrome ("Shuibiezi" disease in Chinese), which is caused by abiotic agents correlated with cyanobacteria bloom outbreaks, adversely affects the Chinese mitten crab breeding industry. Cyanobacterial blooms that occur in high-density farming ponds can produce microcystin-LR (MC-LR), which is hepatotoxic in fish and mammals. Hepatopancreas toxicity of MC-LR (0, 25, 50 and 75 μg/kg) was investigated after 48 h of exposure. The MC-LR can cause hepatopancreatic injury by inducing hepatopancreatic structural damage, subcellular structural changes, and cell apoptosis, followed by enhanced lipid peroxidase, reactive oxygen species, and apoptosis-related enzyme (Caspase 3, 8, and 9) activities. These in turn promote gene and protein expression of apoptosis-associated proteases (Caspase 3, 7, and 8, Bcl-2, and Bax), and alter antioxidant system responses (superoxide dismutase, glutathione S-transferase, glutathione peroxidase, glutathione reductase activities, and glutathione content). The present study is the first report on MC-LR hepatotoxicity in the Chinese mitten crab and confirms hepatopancreas toxicity, providing a theoretical basis for enhancing MCs resistance and developing preventive and curative measures against hepatopancreatic disease in the Chinese mitten crab breeding industry.

Effect of Oversulfation on the Composition, Structure, and In Vitro Anti-Lung Cancer Activity of Fucoidans Extracted from Sargassum aquifolium

Intensive efforts have been undertaken in the fields of prevention, diagnosis, and therapy of lung cancer. Fucoidans exhibit a wide range of biological activities, which are dependent on the degree of sulfation, sulfation pattern, glycosidic branches, and molecular weight of fucoidan. The determination of oversulfation of fucoidan and its effect on anti-lung cancer activity and related signaling cascades is challenging. In this investigation, we used a previously developed fucoidan (SCA), which served as a native fucoidan, to generate two oversulfated fucoidan derivatives (SCA-S1 and SCA-S2). SCA, SCA-S1, and SCA-S2 showed differences in compositions and had the characteristic structural features of fucoidan by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) analyses. The anticancer properties of SCA, SCA-S1, and SCA-S2 against human lung carcinoma A-549 cells were analyzed in terms of cytotoxicity, cell cycle, Bcl-2 expression, mitochondrial membrane potential (MMP), expression of caspase-3, cytochrome c release, Annexin V/propidium iodide (PI) staining, DNA fragmentation, and the underlying signaling cascades. Our findings indicate that the oversulfation of fucoidan promotes apoptosis of lung cancer cells and the mechanism may involve the Akt/mTOR/S6 pathway. Further in vivo research is needed to establish the precise mechanism whereby oversulfated fucoidan mitigates the progression of lung cancer.

Protective effect of argan oil on DNA damage in vivo and in vitro

Background: Iron-overload is a well-known cause for the development of chronic liver diseases and known to induce DNA damage.Material and methods: The protective effect of argan oil (AO) from the Argania spinosa fruit and olive oil (OO) (6% AO or OO for 28 days) was evaluated on a mouse model of iron overload (3.5mg Fe²⁺/liter) and in human fibroblasts where DNA damage was induced via culture under hyperoxia (40% oxygen).Results: Iron treatment induced DNA damage in liver tissue while both oils were able to decrease it. We confirmed this effect in vitro in MRC-5 fibroblasts under hyperoxia. A cell-free ABTS assay suggested that improvement of liver toxicity by both oils might depend on a high content in tocopherol, phytosterol and polyphenol compounds known for their antioxidant potential. The antioxidant effect of AO was confirmed in fibroblasts by reduced intracellular peroxide levels after hyperoxia. However, we could not find a significant decrease of genes encoding pro-inflammatory cytokines (TNFα, IL-6, IL-1β, COX-2) or senescence markers (p16 and p21) for the oils in mouse liver.Conclusion: We found a striking effect of AO by ameliorating DNA damage after iron overload in a mouse liver model and in human fibroblasts by hyperoxia adding compelling evidence to the protective mechanisms of AO and OO.

Dose-Response Study of Microcystin Congeners MCLA, MCLR, MCLY, MCRR, and MCYR Administered Orally to Mice

Microcystins are common freshwater cyanobacterial toxins that affect liver function. The toxicities of five microcystin congeners (microcystin-LA (MCLA), MCLR, MCLY, MCRR, and MCYR) commonly observed in harmful algal blooms (HABs) were evaluated in BALB/c mice after a single oral administration of doses ranging from those that were no observed adverse effect levels (NOAELs) to lowest observed adverse effect levels (LOAELs). Animals were monitored for changes in behavior and appearance, and euthanized 24 h after dosing. Test endpoints included clinical changes, necropsy observations, and serum indicators of hepatic toxicity and general homeostasis. Doses were 0.5-7 mg/kg MCLA, 0.5-11 mg/kg MCLR, 1-7 mg/kg MCLY, 7-22 mg/kg MCRR, and 3-11 mg/kg MCYR. MCLA at 3 mg/kg elevated liver/body weight ratio and liver score, ALT, AST, and GLDH, indicating hepatic toxicity, reduced serum glucose and highly elevated total serum bilirubin. MCLR and MCLY induced similar effects with LOAELs of 5 mg/kg, although a greater extent and severity of effects were observed in MCLR animals. MCRR exposure at 22 mg/kg was associated with reduced serum glucose. MCYR induced scattered liver effects at 7 mg/kg and reduced serum glucose levels at 5 mg/kg. The results indicate significant differences in congener-induced toxicity after microcystin exposure.

De Novo Profiling of Long Non-Coding RNAs Involved in MC-LR-Induced Liver Injury in Whitefish: Discovery and Perspectives

Microcystin-LR (MC-LR) is a potent hepatotoxin for which a substantial gap in knowledge persists regarding the underlying molecular mechanisms of liver toxicity and injury. Although long non-coding RNAs (lncRNAs) have been extensively studied in model organisms, our knowledge concerning the role of lncRNAs in liver injury is limited. Given that lncRNAs show low levels of sequence conservation, their role becomes even more unclear in non-model organisms without an annotated genome, like whitefish (Coregonus lavaretus). The objective of this study was to discover and profile aberrantly expressed polyadenylated lncRNAs that are involved in MC-LR-induced liver injury in whitefish. Using RNA sequencing (RNA-Seq) data, we de novo assembled a high-quality whitefish liver transcriptome. This enabled us to find 94 differentially expressed (DE) putative evolutionary conserved lncRNAs, such as MALAT1, HOTTIP, HOTAIR or HULC, and 4429 DE putative novel whitefish lncRNAs, which differed from annotated protein-coding transcripts (PCTs) in terms of minimum free energy, guanine-cytosine (GC) base-pair content and length. Additionally, we identified DE non-coding transcripts that might be 3′ autonomous untranslated regions (3′UTRs) of mRNAs. We found both evolutionary conserved lncRNAs as well as novel whitefish lncRNAs that could serve as biomarkers of liver injury.

Microcystin-leucine arginine induced the apoptosis of GnRH neurons by activating the endoplasmic reticulum stress resulting in a decrease of serum testosterone level in mice

Microcystin-leucine arginine (MC-LR) is a kind of toxin produced by cyanobacterial, resulting in decrease of testosterone levels in serum and leading to impaired spermatogenesis. Gonadotropin-releasing hormone (GnRH) neurons play crucial roles in the regulation of testosterone release. Meanwhile, it has been demonstrated that MC-LR is capable of entering the GnRH neurons and inducing apoptosis. Nevertheless, the molecular mechanism of MC-LR induced apoptosis of GnRH neurons remains elusive. In present study, we found that MC-LR inhibited the cell viability of GT1-7 cells. In addition, we discovered apoptosis of GnRH neurons and GT1-7 cells treated with MC-LR. And increased intracellular ROS production and the release of intracellular Ca²⁺ were all observed following exposure to MC-LR. Furthermore, we also found the endoplasmic reticulum stress (ERs) and autophagy were activated by MC-LR. Additionally, pretreatment of the ERs inhibitor (4-Phenyl butyric acid) reduced the apoptotic rate of GT1-7 cells comparing with MC-LR exposure alone. Comparing with MC-LR treatment alone, apoptotic cell death was increased by pretreatment of GT1-7 cells with an autophagy inhibitor (3-methyladenine). Together, our data implicated that the treatment of MC-LR induced the apoptosis of GnRH neurons by activating the ERs resulting in a decrease of serum testosterone level in mice. Autophagy is a protective cellular process which was activated by ER stress and thus protected cells from apoptosis upon MC-LR exposure.

An identified PfHMGB1 promotes microcystin-LR-induced liver injury of yellow catfish (Pelteobagrus fulvidraco)

Microcystin-LR (MC-LR) is a potent hepatotoxin that can cause liver inflammation and injury. However, the mode of action of related inflammatory factors is not fully understood. PfHMGB1 is an inflammatory factor induced at the mRNA level in the liver of juvenile yellow catfish (Pelteobagrus fulvidraco) that were intraperitoneally injected with 50 μg/kg MC-LR. The PfHMGB1 mRNA level was highest in the liver and muscle among 11 tissues examined. The full-length cDNA sequence of PfHMGB1 was cloned and overexpressed in E. coli, and the purified protein rPfHMGB1 demonstrated DNA binding affinity. Endotoxin-free rPfHMGB1 (6-150 μg/mL) also showed dose-dependent hepatotoxicity and induced inflammatory gene expression of primary hepatocytes. PfHMGB1 antibody (anti-PfHMGB1) in vitro reduced MC-LR (30 and 50 μmol/L)-induced hepatotoxicity, suggesting PfHMGB1 is important in the toxic effects of MC-LR. In vivo study showed that MC-LR upregulated PfHMGB1 protein in the liver. The anti-PfHMGB1 blocked its counterpart and reduced ALT/AST activities after MC-LR exposure. Anti-PfHMGB1 partly neutralized MC-LR-induced hepatocyte disorganization, nucleus shrinkage, mitochondria, and rough endoplasmic reticula destruction. These findings suggest that PfHMGB1 promotes MC-LR-induced liver damage in the yellow catfish. HMGB1 may help protect catfish against widespread microcystin pollution.

Global transcriptomic profiling of microcystin-LR or -RR treated hepatocytes (HepaRG)

The canonical mode of action (MOA) of microcystins (MC) is the inhibition of protein phosphatases, but complete characterization of toxicity pathways is lacking. The existence of over 200 MC congeners complicates risk estimates worldwide. This work employed RNA-seq to provide an unbiased and comprehensive characterization of cellular targets and impacted cellular processes of hepatocytes exposed to either MC-LR or MC-RR congeners. The human hepatocyte cell line, HepaRG, was treated with three concentrations of MC-LR or -RR for 2 h. Significant reduction in cell survival was observed in LR1000 and LR100 treatments whereas no acute toxicity was observed in any MR-RR treatment. RNA-seq was performed on all treatments of MC-LR and -RR. Differentially expressed genes and pathways associated with oxidative and endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) were highly enriched by both congeners as were inflammatory pathways. Genes associated with both apoptotic and inflammatory pathways were enriched in LR1000. We present a model of MC toxicity that immediately causes oxidative stress and leads to ER stress and the activation of the UPR. Differential activation of the three arms of the UPR and the kinetics of JNK activation ultimately determine whether cell survival or apoptosis is favored. Extracellular exosomes were enrichment of by both congeners, suggesting a previously unidentified mechanism for MC-dependent extracellular signaling. The complement system was enriched only in MC-RR treatments, suggesting congener-specific differences in cellular effects. This study provided an unbiased snapshot of the early systemic hepatocyte response to MC-LR and MC-RR congeners and may explain differences in toxicity among MC congeners.

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Microcystin-LR and microcystin-RR have similar transcriptional responses.

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Genes associated with oxidative stress and the unfolded protein response were enriched by congeners.

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Genes associated with extracellular exosomes were enriched, suggesting a potential new mechanism for cell signaling.

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Complement associated genes were strongly enriched only by microcystin-RR.

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Identified a potential molecular mechanism underlying the cellular fate of hepatocyte.

Taxifolin ameliorates iron overload-induced hepatocellular injury: Modulating PI3K/AKT and p38 MAPK signaling, inflammatory response, and hepatocellular regeneration

Although physiological levels of iron are essential for numerous biological processes, excess iron causes critical tissue injury. Under iron overload conditions, non-chelated iron generates reactive oxygen species that mediate iron-induced tissue injury with subsequent induction of apoptosis, necrosis, and inflammatory responses. Because liver is a central player in iron metabolism and storage, it is vulnerable to iron-induced tissue injury. Taxifolin is naturally occurring compound that has shown potent antioxidant and potential iron chelation competency. The aim of the current study was to investigate the potential protective effects of taxifolin against iron-induced hepatocellular injury and to elucidate the underlining mechanisms using rats as a mammalian model. The results of the current work indicated that taxifolin inhibited iron-induced apoptosis and enhanced hepatocellular survival as demonstrated by decreased activity of caspase-3 and activation of the pro-survival signaling PI3K/AKT, respectively. Western blotting analysis revealed that taxifolin enhanced liver regeneration as indicated by increased PCNA protein abundance. Taxifolin mitigated the iron-induced histopathological aberration and reduced serum activity of liver enzymes (ALT and AST), highlighting enhanced liver cell integrity. Mechanistically, taxifolin modulated the redox-sensitive MAPK signaling (p38/c-Fos) and improved redox status of the liver tissues as indicated by decreased lipid peroxidation and protein oxidation along with enhanced total antioxidant capacity. Interestingly, it decreased liver iron content and down-regulated the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β. Collectively, these data highlight, for the first time, the ameliorating effects of taxifolin against iron overload-induced hepatocellular injury that is potentially mediated through anti-inflammatory, antioxidant, and potential iron chelation activities.

Effect of microcystin on the expression of Nrf2 and its downstream antioxidant genes from Cristaria plicata

Microcystin (MC) is a cyclic heptapeptide toxin. Nuclear factor erythocyte 2-related factor 2 (Nrf2) can enhance cellular survival by mediating phase 2 detoxification and antioxidant genes. In this study, CpNrf2 cDNA sequences were cloned from freshwater bivalve Cristaria plicata. The full-length CpNrf2 cDNA sequence was 4259 bp, and its homology was the highest with Mizuhopecten yessoensis, reaching 46%. CpNrf2 transcription levels were examined in all tested tissues, and the highest level was in hepatopancreas from C. plicata. The recombinant protein pET32-CpNrf2 was purified with the content of 1.375 mg/mL. The expression levels of CpNrf2 mRNA were raised in hepatopancreas after MC stimulation. After CpNrf2 knockdown, CpNrf2 mRNA levels were significantly down-regulated after 24 h. Compared with control group, the expression levels of ARE-driven enzymes (CpMnSOD, CpCuZnSOD, CpTRX, CpPrx, CpSe-GPx and Cpsigma-GST) were significantly increased, and those enzyme activities were also significantly up-regulated in MC-stimulated group. However, in CpNrf2-iRNA group, they were significantly down-regulated. The results revealed that Nrf2/ARE pathway is very crucial to protect molluscs from MC.

Luciferase reporter assay for small-molecule inhibitors of MIR92b-3p function: Screening cyanopeptolins produced by Nostoc from the Baltic Sea

We developed a cell sensor that detects the liver cancer-specific microRNA MIR92b-3p, involved in hepatocellular carcinoma development and hepatitis C virus infection. To validate our small-molecule screen that employs a Huh7 human hepatoma cell line stably transfected with a pmirGLO vector containing dual luciferase reporters, we used i) a MIR92b-3p antisense or a MIR92b-3p mimicking agent (concentrations from 0.1 pM to 100 nM), ii) expression of XIST, a long non-coding RNA that is a cellular target of MIR92b, and iii) ectopic expression of Luc2 luciferase. This reporter system was used to test four cyanopeptolins from a de novo library of peptides that were isolated from the Baltic Sea cyanobacteria Nostoc edaphicum strain CCNP1411. Exposure of the Huh7-pmirGLO-MIR92b-3p cells to increasing concentrations (from 10 nM to 100 μM) of the cyanopeptolins and microcystin-LR (MC-LR; a treatment control) did not lead to a dose-dependent restoration of the luciferase signal. Instead, when the reporter cells were treated with MC-LR, the luciferase signal decreased markedly, most likely due to non-target, toxic effects of MC-LR on the cells. Although the first use of this reporter system to screen selected Nostoc peptides did not identify inhibitors of MIR92b, this method provides a means to identify functional miRNA regulators and could be readily extended to other compounds.

Hydrogen Sulfide Signaling Protects Chlamydomonas reinhardtii Against Allelopathic Damage From Cyanobacterial Toxin Microcystin-LR

Cyanobacterial blooms have become more frequent and serious in recent years. Not only do massive blooms cause environmental pollution and nutrient eutrophication, but they also produce microcystins (MCs), a group of toxic cycloheptapeptides, which threaten aquatic ecosystem and human health. As such, clarifying the allelopathic interactions between cyanobacteria and other algae is critical to better understand the driving factors of blooms. To date, however, such studies remain largely insufficient. Here, we treated model alga Chlamydomonas reinhardtii with microcystin-LR (MC-LR) to determine its allelopathic effects. Results showed that MC-LR markedly suppressed C. reinhardtii cell viability. Comparative proteomic and physiological analyses revealed that MC-LR significantly up-regulated protein abundance of antioxidants ascorbate peroxidase (APX) and catalase (CAT) at the beginning stage of exposure. This was accompanied by an over-accumulation of hydrogen peroxide (H₂O₂), suggesting that MC-LR suppresses cell viability via oxidative damage. Furthermore, we found that MCs induced desulfhydrase (DES) activity for hydrogen sulfide (H₂S) generation at the beginning stage. Additional H₂S donors reactivated antioxidant enzyme activity, which reduced H₂O₂ accumulation and ultimately enhanced C. reinhardtii tolerance to MC-LR damage. This effect could be reserved by inhibiting H₂S biosynthesis. Simultaneously, we found that H₂S also suppressed MC-LR-induced cell autophagy, and thus attenuated the toxic effects of MC-LR. Our findings suggest that oxidative bursts may be the main reason for the allelopathic effects of MC-LR on C. reinhardtii viability and that H₂S signaling may enhance C. reinhardtii tolerance to MC-LR through the activation of antioxidant enzyme activity and suppression of cell autophagy.

α-Lipoic acid protects against microcystin-LR induced hepatotoxicity through regeneration of glutathione via activation of Nrf2

Microcystins (MCs), as the most dominant bloom-forming strains in eutrophic surface water, can induce hepatotoxicity by oxidative stress. Alpha-lipoic acid (α-LA) is a super antioxidant that can induce the synthesis of antioxidants, such as glutathione (GSH), by nuclear factor erythroid 2-related factor 2 (Nrf2). However, the potential molecular mechanism of α-LA regeneration of GSH remains unclear. The present study aimed to investigate whether α-LA could reduce the toxicity of MCs induced in human hepatoma (HepG2), Bel7420 cells, and BALB/c mice by activating Nrf2 to regenerate GSH. Results showed that exposure to 10 μM microcystin-leucine arginine (MC-LR) reduced viability of HepG2 and Bel7402 cells and promoted the formation of reactive oxygen species (ROS) compared with untreated cells. Moreover, the protection of α-LA included reducing the level of ROS, increasing superoxide dismutase activity, and decreasing malondialdehyde. Levels of reduced glutathione (rGSH) and rGSH/oxidized glutathione were significantly increased in cells cotreated with α-LA and MC-LR compared to those treated with MC-LR alone, indicating an ability of α-LA to attenuate oxidative stress and MC-LR-induced cytotoxicity by increasing the amount of rGSH. α-LA can mediate GSH regeneration through the Nrf2 pathway under the action of glutathione reductase in MC-LR cell lines. Furthermore, the data also showed that α-LA-induced cytoprotection against MC-LR is associated with Nrf2 mediate pathway in vivo. These findings demonstrated the potential of α-LA to resist MC-LR-induced oxidative damage of liver.

The Comparative Toxicity of 10 Microcystin Congeners Administered Orally to Mice: Clinical Effects and Organ Toxicity

Microcystins (MCs) are common cyanobacterial toxins that occur in freshwaters worldwide. Only two of the >200 MC variants have been tested for potential toxicity after oral exposure. This paper reports on the toxicity of 10 different MC congeners identified in algal blooms, microcystin-LR (MCLR), MCLA, MCLF, MCLW, MCLY, MCRR, [Asp3]MCRR, [Asp3,Dhb7]MCRR, MCWR, and MCYR after single administrations to BALB/c mice. In a preliminary MCLR dose–response study of 3 to 9 mg/kg doses, ≥5 mg/kg induced clinical changes, increased serum levels of ALT, AST, and GLDH, liver congestion, increased liver/body weight ratios, and reduced serum glucose and total protein. Based on the extent of these effects, the 10 congeners were administered as single 7 mg/kg oral doses and toxicity evaluated. The greatest toxicity was observed with MCLA and MCLR including a high percentage of moribundity. In addition to eliciting effects similar to those listed above for MCLR, MCLA also induced serum alterations indicative of jaundice. MCLY, and MCYR induced changes like those noted with MCLR, but to lesser extents. MCLW and MCLF exhibited some serum and morphological changes associated with hepatic toxicity, while there were few indications of toxicity after exposures to MCRR, [Asp³]MCRR, [Asp³,Dhb⁷]MCRR, or MCWR. These data illustrate a wide spectrum of hepatic effects and different potencies of these MC congeners.

Cylindrospermopsin-Microcystin-LR Combinations May Induce Genotoxic and Histopathological Damage in Rats

Cylindrospermopsin (CYN) and microcystins (MC) are cyanotoxins that can occur simultaneously in contaminated water and food. CYN/MC-LR mixtures previously investigated in vitro showed an induction of micronucleus (MN) formation only in the presence of the metabolic fraction S9. When this is the case, the European Food Safety Authority recommends a follow up to in vivo testing. Thus, rats were orally exposed to 7.5 + 75, 23.7 + 237, and 75 + 750 μg CYN/MC-LR/kg body weight (b.w.). The MN test in bone marrow was performed, and the standard and modified comet assays were carried out to measure DNA strand breaks or oxidative DNA damage in stomach, liver, and blood cells. The results revealed an increase in MN formation in bone marrow, at all the assayed doses. However, no DNA strand breaks nor oxidative DNA damage were induced, as shown in the comet assays. The histopathological study indicated alterations only in the highest dose group. Liver was the target organ showing fatty degeneration and necrotic hepatocytes in centrilobular areas, as well as a light mononuclear inflammatory periportal infiltrate. Additionally, the stomach had flaking epithelium and mild necrosis of epithelial cells. Therefore, the combined exposure to cyanotoxins may induce genotoxic and histopathological damage in vivo.

Epigenetic modification of H3K4 and oxidative stress are involved in MC-LR-induced apoptosis in testicular cells of SD rats

Microcystin-leucine arginine (MC-LR) is a cyclic heptapeptide, produced by aquatic cyanobacteria such as microcystis, with strong reproductive toxicity which poses greater threat to the reproductive abilities of humans and animals. By exploring the role of trimethylation of histone H3 at lysine 4 (H3K4me3) and the role of oxidative stress in MC-LR-induced apoptosis in testicular Sertoli cells in Sprague-Dawley (SD) rats, this study indicated that MC-LR increased the expression levels of apoptosis-related genes by raising the levels of H3K4me3. 5'-Deoxy-5'-methylthioadenosine (MTA), the inhibitor of H3K4me3, reduced apoptosis, indicating for the first time that epigenetic modification is closely related to the testicular reproductive toxicity induced by MC-LR. MC-LR also induced oxidative stress by stimulating the generation of reactive oxygen species (ROS), and subsequently triggering mitochondria-mediated apoptotic pathway by decreasing mitochondrial membrane potential and increasing the levels of Bax, Bcl-2, Caspase-3, and so on. MC-LR-induced apoptosis of testicular cells could be decreased after pretreatment with oxidative stress inhibitor N-acetyl-cysteine (NAC). Furthermore, the pathological damage to mitochondria and testes were observed in SD rats. These results show that MC-LR can induce apoptosis by raising the levels of H3K4me3, and pretreatment with MTA can ameliorate the MC-LR-induced apoptosis of cocultured cells by lowering the levels of H3K4me3. Furthermore, NAC has a protective effect on MC-LR-induced apoptosis of testicular cells in SD rats by inhibiting the oxidative stress.

Microcystin-LR exposure decreased the fetal weight of mice by disturbance of placental development and ROS-mediated endoplasmic reticulum stress in the placenta

The placenta is essential for sustaining the growth of the fetus. The aim of this study was to investigate the role of the placenta in MCLR-induced significant reduction in fetal weight, especially the changes in placental structure and function. Pregnant mice were intraperitoneally injected with MCLR (5 or 20 μg/kg) from gestational day (GD) 13 to GD17. The results showed MCLR reduced fetal weight and placenta weight. The histological specimens of the placentas were taken for light and electron microscopy studies. The internal space of blood vessels decreased obviously in the placental labyrinth layer of mice treated with MCLR. After the ultrastructural examination, the edema and intracytoplasmic vacuolization, dilation of the endoplasmic reticulum and corrugation of the nucleus were observed. In addition, maternal MCLR exposure caused a reduction of 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2) expression in placentae, a critical regulator of fetal development. Several genes of placental growth factors, such as Vegfα and Pgf and several genes of nutrient transport pumps, such as Glut1 and Pcft were depressed in placentas of MCLR-treated mice, however nutrient transporters Fatp1 and Snat4 were promoted. Moreover, significant increases in malondialdehyde (MDA) revealed the occurrence of oxidative stress caused by MCLR, which was also verified by remarkable decrease in the glutathione levels, total antioxidant capacity (T-AOC) as well as the activity of antioxidant enzymes. Real-time PCR and western blot analysis revealed that GRP78, CHOP, XBP-1, peIF2α and pIRE1 were remarkable increased in placentas of MCLR-treated mice, indicating that endoplasmic reticulum (ER) stress pathway was activated by MCLR. Furthermore, oxidative stress and ER stress consequently triggered apoptosis which contributed to the impairment of placental development. Collectively, these results suggest maternal MCLR exposure results in reduced fetal body weight, which might be associated with ROS-mediated endoplasmic reticulum stress and impairment in placental structure and function.

Co-exposure with titanium dioxide nanoparticles exacerbates MCLR-induced brain injury in zebrafish

Owing to the eutrophication in freshwater and industrial emissions, the detected concentrations of MCLR and nano-TiO₂ in nature water increase year by year. The purpose of this study was to evaluate the joint effect of microcystin-LR (MCLR) and titanium dioxide nanoparticles (nano-TiO₂) on the zebrafish brain and to investigate the underlying mechanisms. In this study, four-month old zebrafish were exposed to 0, 0.5, 4, and 32 μg/L MCLR and MCLR-co-nano-TiO₂ (100 μg/L) for 45 days. Obvious brain injury characterized by formation of glial scars and ventriculomegaly was observed in both MCLR groups and MCLR-co-nano-TiO₂ groups. In addition, our results showed the existence of nano-TiO₂ aggravated MCLR-induced abnormity of swimming behavior and social behavior of zebrafish. To clarify the mechanisms of nano-TiO₂ aggravated MCLR-induced brain injury, we firstly examined the reactive oxygen species (ROS) generation in the zebrafish brain. The results showed that co-exposure with nano-TiO₂ could further increase ROS content compared with MCLR only groups. We also detected a significant change of lipid peroxidation products (MDA, malondialdehyde) content, antioxidant enzyme (SOD, superoxide dismutase) activity, and non-enzymatic antioxidant (GSH, glutathione) content in MCLR-co-nano-TiO₂ groups. Transcriptional analysis indicated the expression of genes related to the antioxidant system was significantly altered in the zebrafish brain. Collectively, the observations in this study showed that the existence of nano-TiO₂ could exacerbate the damage of the zebrafish brain through the aggravation of MCLR-induced oxidative stress, ultimately leading to the abnormity of swimming behavior and social behavior.

Characterization of microcystin-induced apoptosis in HepG2 hepatoma cells

Microcystins (MCs) are a class of hepatotoxins that are commonly produced by freshwater cyanobacteria. MCs harm liver cells through inhibiting protein phosphatases 1 and 2A (PP1 and PP2A) and can produce dualistic effects, i.e., cell death and uncontrolled cellular proliferation. The induction of programmed cell death, i.e., apoptosis, in MC treated hepatic cells has been described previously; however, its exact pathway remains unclear. To address this, HepG2 human hepatoma cells were exposed to MC-LR, the most prevalent isomer of MCs, and morphological and physiological responses were examined. Microscopy and Alamar Blue assay showed that HepG2 cells responded to MC-LR treatment with apoptosis characteristics, such as clumping and shrinking of cells and detachment from the monolayer culture surface. A fluorescent caspase activation assay further revealed activation of all tested apoptosis-dependent caspases (i.e., caspase-3/7, 8 and 9) after 24 h of MC-LR treatment. Furthermore, caspase-8 was found being activated 4 h after MC-LR treatment, earlier than observed activation of caspase-9 (8 h after MC-LR treatment). These data demonstrated that MC-LR can induce apoptosis of HepG2 cells through both extrinsic and intrinsic pathways and that the extrinsic pathway may be activated before the intrinsic pathway. This indicates that extrinsic pathway is more sensitive than intrinsic pathway in MC induced apoptosis. This knowledge contributes to a better understanding of MC hepatotoxicity and can be further used for developing treatments for MC exposed hepatic cells.

The role of ERK-RSK signaling in the proliferation of intrahepatic biliary epithelial cells exposed to microcystin-leucine arginine

Microcystin-leucine arginine (MC-LR) is a potent specific hepatotoxin produced by cyanobacteria in diverse water systems, and it has been documented to induce liver injury and hepatocarcinogenesis. However, its toxic effects on intrahepatic biliary epithelial cells have not been invested in detail. In this study, we aimed to investigate the effects of MC-LR exposure on the intrahepatic biliary epithelial cells in the liver. MC-LR was orally administered to mice at 1 μg/L, 7.5 μg/L, 15 μg/L, or 30 μg/L for 180 consecutive days for histopathological and immunoblot analysis. We observed that MC-LR can enter intrahepatic bile duct tissue and induce hyperplasia of mice. Human primary intrahepatic biliary epithelial cells (HiBECs) were cultured with various concentrations of MC-LR for 24 h, meanwhile the cell viability and proteins level were detected. Western blotting analysis revealed that MC-LR increased RSK phosphorylation via ERK signaling. RSK participated in cell proliferation and cell cycle progression. Taken together, after chronic exposure, MC-LR-treated mice exhibited abnormal bile duct hyperplasia and thickened bile duct morphology through activating the ERK-RSK signaling. These data support the potential toxic effects of MC-LR on bile duct tissue of the liver.

A Review of Cardiovascular Toxicity of Microcystins

The mortality rate of cardiovascular diseases (CVD) in China is on the rise. The increasing burden of CVD in China has become a major public health problem. Cyanobacterial blooms have been recently considered a global environmental concern. Microcystins (MCs) are the secondary products of cyanobacteria metabolism and the most harmful cyanotoxin found in water bodies. Recent studies provide strong evidence of positive associations between MC exposure and cardiotoxicity, representing a threat to human cardiovascular health. This review focuses on the effects of MCs on the cardiovascular system and provides some evidence that CVD could be induced by MCs. We summarized the current knowledge of the cardiovascular toxicity of MCs, with regard to direct cardiovascular toxicity and indirect cardiovascular toxicity. Toxicity of MCs is mainly governed by the increasing level of reactive oxygen species (ROS), oxidative stress in mitochondria and endoplasmic reticulum, the inhibition activities of serine/threonine protein phosphatase 1 (PP1) and 2A (PP2A) and the destruction of cytoskeletons, which finally induce the occurrence of CVD. To protect human health from the threat of MCs, this paper also puts forward some directions for further research.

Crude extract of cyanobacterium Radiocystis fernandoi strain R28 induces anemia and oxidative stress in fish erythrocytes

The cyanobacterium Radiocystis fernandoi has been frequently identified in cyanobacterial blooms in Brazil. Recently, R. fernandoi strain R28, which produces microcystin (MC)-RR and MC-YR, was isolated from the Furnas reservoir, Minas Gerais, Brazil. The present study evaluated the hematological variables and erythrocyte antioxidant responses, lipid peroxidation (LPO), and genotoxicity in a neotropical fish (Hoplias malabaricus) after acute and subchronic exposure to a crude extract (CE) of R. fernandoi strain R28. Acute exposure (12 or 96 h) consisted of a single intraperitoneal (i.p.) CE injection, and subchronic exposure consisted of one i.p. CE injection every 72 h for 30 days. After acute exposure, fish exhibited macrocytic anemia (12 h post-injection) followed by normocytic anemia (96 h post-injection). The increased activity of superoxide dismutase, glutathione peroxidase, glutathione-S-transferase, and the glutathione level in the erythrocytes did not prevent oxidative stress, manifested as lipid peroxidation and elevated DNA damage after acute exposure. After subchronic exposure, the hematological variables recovered, and the absence of erythrocyte oxidative stress suggests possible modulation by other biological factors, including a possible decrease in MC uptake by the cells and/or increasing detoxification efficiency that precludes erythrocyte damage.

D-ribose is elevated in T1DM patients and can be involved in the onset of encephalopathy

Although many mechanisms have been proposed for diabetic encephalopathy in type 2 diabetes mellitus (T2DM), the risk factors for cognitive impairment in type 1 diabetes mellitus (T1DM) are less clear. Here, we show that streptozotocin (STZ)-induced T1DM rats showed cognitive impairment in both Y maze and Morris water maze assays, accompanied with D-ribose was significantly increased in blood and urine, in addition to D-glucose. Furthermore, advanced glycation end products (AGE), Tau hyperphosphorylation and neuronal death in the hippocampal CA4/DG region were detected in T1DM rats. The expression and activity of transketolase (TKT), an important enzyme in the pentose shunt, were decreased in the brain, indicating that TKT may be involved in D-ribose metabolism in T1DM. Support for these change was demonstrated by the activation of TKT with benfotiamine (BTMP) treatment. Decreased D-ribose levels but not D-glucose levels; markedly reduced AGE accumulation, Tau hyperphosphorylation, and neuronal death; and improved cognitive ability in T1DM rats were shown after BTMP administration. In clinical investigation, T1DM patients had high D-ribose levels in both urine and serum. Our work suggests that D-ribose is involved in the cognitive impairment in T1DM and may provide a potentially novel target for treating diabetic encephalopathy.

Inhaled Methane Protects Rats Against Neurological Dysfunction Induced by Cerebral Ischemia and Reperfusion Injury: PI3K/Akt/HO-1 Pathway Involved

BACKGROUND AND AIMS

Cerebral ischemia and reperfusion (I/R) could produce excess reactive oxygen species (ROS), which in turn induce neurological dysfunction and inflammation in cerebral tissues. This study was designed to study the effect of methane on cerebral I/R injury.

METHODS

Fifty Sprague-Dawley (SD) rats were used to induce an animal model of cerebral I/R injury. Methane was mixed with air to achieve a final concentration of 2.2%. Rats started to inhale methane-air mixture after ischemia and continued it during the reperfusion. The neurological deficits, malondialdehyde (MDA) and tumor necrosis factor-α (TNF-α) in the brain tissue were examined. The protein kinase B (Akt) phosphorylation and heme oxygenase-1 (HO-1) expression was measured by Western Blot. The neurological deficits were re-measured after rats were treated with the HO-1 inhibitor Zinc protoporphyrin IX (ZnPP-IX), phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and Akt inhibitor triciribine.

RESULTS

Cerebral I/R induced neurological deficit, which was significantly decreased by methane. MDA and TNF-α levels were significantly enhanced by cerebral I/R, while methane caused significant reduction of MDA and TNF-α levels. Methane significantly increased Akt phosphorylation and HO-1 expression. The HO-1 inhibitor ZnPP-IX, PI3K inhibitor LY294002 and Akt inhibitor triciribine all significantly abolished the effect of methane on neurological deficit.

CONCLUSIONS

This finding suggests the possible application of methane for cerebral I/R injury and PI3K/Akt/HO-1 dependent antioxidant pathway may be involved.

Low-dose PCB126 compromises circadian rhythms associated with disordered glucose and lipid metabolism in mice

It has been documented that 3, 3', 4, 4', 5-pentachlorobiphenyl (PCB126) elicits diverse detrimental effects on human health including metabolic syndrome and non-alcoholic fatty-liver disease (NAFLD), through a wide array of non-carcinogenic mechanisms, which require further detailed investigations. The circadian clock system consists of central clock machinery (located in the suprachiasmatic nucleus in the hypothalamus) and the peripheral clocks (located in nearly all peripheral tissues). Peripheral clocks in the liver play fundamental roles in maintaining liver homeostasis, including the regulation of energy metabolism and the expression of enzymes that fine-tune the absorption and metabolism of xenobiotics. However, the molecular basis of whether PCB126 disrupts liver homeostasis (e.g., glucose and lipid metabolism) by dysregulating the circadian clock system is still unknown. Thus, we performed a set of comprehensive analyses of glucose and lipid metabolism in the liver tissues from low-dose PCB126-treated mice. Our results demonstrated that PCB126 diminished glucose and cholesterol levels in serum and elevated glucose and cholesterol levels in the liver. Moreover, PCB126 compromised PGC1α and PDHE1α, which are the driving force for mitochondrial biogenesis and entry of pyruvate into the tricarboxylic acid (TCA) cycle, respectively, and resulted in the accumulation of glucose, glycogen and pyruvate in the liver after PCB126 exposure. Additionally, PCB126 blocked hepatic cholesterol metabolism and export pathways, leading to an elevated localization of hepatic cholesterol. Mechanistic investigations illustrated that PCB126 greatly altered the expression profile of core clock genes and their target rhythm genes involved in orchestrating glucose and cholesterol metabolism. Together, our results demonstrated that a close correlation between PCB126-disturbed glucose and lipid metabolism and disordered physiological oscillation of circadian genes.

Neurotoxicity induced by microcystins and cylindrospermopsin: A review

Microcystins (MCs) and cylindrospermopsin (CYN) are among the most frequent toxins produced by cyanobacteria. These toxic secondary metabolites are classified as hepatotoxins and cytotoxin, respectively. Furthermore, both may present the ability to induce damage to the nervous system. In this sense, there are many studies manifesting the potential of MCs to cause neurotoxicity both in vitro and in vivo, due to their probable capacity to cross the blood-brain-barrier through organic anion transporting polypeptides. Moreover, the presence of MCs has been detected in brain of several experimental models. Among the neurological effects, histopathological brain changes, deregulation of biochemical parameters in brain (production of oxidative stress and inhibition of protein phosphatases) and behavioral alterations have been described. It is noteworthy that minority variants such as MC-LF and -LW have demonstrated to exert higher neurotoxic effects compared to the most studied congener, MC-LR. By contrast, the available studies concerning CYN-neurotoxic effects are very scarce, mostly showing inflammation and apoptosis in neural murine cell lines, oxidative stress, and alteration of the acetylcholinesterase activity in vivo. However, more studies are required in order to clarify the neurotoxic potential of both toxins, as well as their possible contribution to neurodegenerative diseases.

Effects of microcystin-LR on the immune dysfunction and ultrastructure of hepatopancreas in giant freshwater prawn Macrobrachium rosenbergii

Microcystins (MCs), produced by cyanobacteria, can strongly inhibit the activity of protein phosphatase, and exhibit strong hepatotoxicity. Macrobrachium rosenbergii is an important aquaculture economic species. Cyanobacterial blooms occur frequently during the culture of M. rosenbergii. However, the effects of MCs on the M. rosenbergii immune function have not been studied. In the present study, M. rosenbergii were exposed to environment-related concentrations of MC-LR type (0.5 and 5 μg/L) for 3 weeks. Hepatopancreatic histology was investigated, and antioxidant enzymes activity, acid phosphatase, alkaline phosphatase and lysozyme activity in hepatopancreas were also analyzed. Results showed that MC-LR could damage M. rosenbergii hepatopancreas, induce hepatopancreatic apoptosis and antioxidant dysfunctions. The expression profiles of major immune-related genes after MC-LR exposure were also detected. Some genes with antibacterial functions were suppressed, and the expression of apoptosis-related genes were up-regulated. After MC-LR exposure, the cumulative mortality of M. rosenbergii infected with Vibrio vulnificus and Aeromonas hydrophila were much higher than the control in a time-dose dependent manner. These results indicated the potential negative influence of MC-LR on the immune function of M. rosenbergii.

Microcystin-LR disturbs testicular development of giant freshwater prawn Macrobrachium rosenbergii

Microcystins (MCs) are produced by cyanobacterial blooms and known for their hepatotoxicity. They could cause serious damage to the reproduction of higher vertebrate mice and fish. However, few studies have focused on the reproductive toxicity of MCs to invertebrates. Giant freshwater prawn Macrobrachium rosenbergii are highly cultivated in China. During their breeding process, M. rosenbergii are often infested by cyanobacteria blooms. In the present study, to investigate the toxic effect of MCs on the testicular development of M. rosenbergii. Male M. rosenbergii were exposed to environmental relevant concentration of MC-LR for 1, 2 and 3 weeks. Results showed that MC-LR entered M. rosenbergii testis, down-regulated hemolymph testosterone (T) levels, and damaged testicular germ cells, mitochondria and cell junctions, and inhibited testicular development. Moreover, MC-LR could significantly induce the expression of gonadal development related genes in testis and eyestalk). The present results indicate that MC-LR can disrupt the testicular development of M. rosenbergii by affecting T levels and gonadal development related genes in the testis and eyestalk.

Glutathione peroxidase-1 overexpressing transgenic mice are protected from neurotoxicity induced by microcystin-leucine-arginine

Although it has been well-recognized that microcystin-leucine-arginine (MCLR), the most common form of microcystins, induces neurotoxicity, little is currently known about the underlying mechanism for this neurotoxicity. Here, we found that MCLR (10 ng/μL/mouse, i.c.v.) induces significant neuronal loss in the hippocampus of mice. MCLR-induced neurotoxicity was accompanied by oxidative stress, as shown by a significant increase in the level of 4-hydroxynonenal, protein carbonyl, and reactive oxygen species (ROS). Superoxide dismutase-1 (SOD-1) activity was significantly increased, but glutathione peroxidase (GPx) level was significantly decreased following MCLR insult. In addition, MCLR significantly inhibited GSH/GSSG ratio, and significantly induced NFκB DNA binding activity. Because reduced activity of GPx appeared to be critical for the imbalance between activities of SODs and GPx, we utilized GPx-1 overexpressing transgenic mice to ascertain the role of GPx-1 in this neurotoxicity. Genetic overexpression of GPx-1 or NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly attenuated MCLR-induced hippocampal neuronal loss in mice. However, PDTC did not exert any additive effect on neuroprotection mediated by GPx-1 overexpression, indicating that NFκB is a neurotoxic target of MCLR. Combined, these results suggest that MCLR-induced neurotoxicity requires oxidative stress associated with failure in compensatory induction of GPx, possibly through activation of the transcription factor NFκB.

Total C-21 steroidal glycosides, isolated from the root tuber of Cynanchum auriculatum Royle ex Wight, attenuate hydrogen peroxide-induced oxidative injury and inflammation in L02 cells

Oxidative stress plays an important role in the pathology of liver disorders. Total C-21 steroidal glycosides (TCSGs), isolated from the root tuber of Cynanchum auriculatum Royle ex Wight, have been reported to exert numerous effects, including liver protective and antioxidant effects. In order to investigate the potential mechanisms underlying the protective effects of TCSGs on liver function, the present study used the human normal liver cell line, L02, to evaluate the effects of TCSGs on hydrogen peroxide (H₂O₂)-induced oxidative injury and inflammatory responses. The L02 cells were pretreated with various concentrations of TCSGs, followed by exposure to 1.5 mM H₂O₂. Cell viability was determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-di-phenyltetrazolium bromide (MTT) assay. The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and nitric oxide (NO) were measured using colorimetric assays. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and the production of malondialdehyde (MDA) were also determined. Intracellular reactive oxygen species (ROS) levels were detected using a fluorescent probe. H₂O₂-induced oxidative toxicity was attenuated following treatment with TCSGs, as indicated by the increase in cell viability, the decreased levels of ALT, AST, LDH, NO, MDA and ROS, and the increased activities of SOD, CAT and GSH-Px. To further explore the possible mechanisms of action of TCSGs, the nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF)-κB pathways were examined. The results revealed that treatment with TCSGs markedly induced Nrf2 nuclear translocation and upregulated the expression of heme oxygenase-1 (HO-1) in the L02 cells damaged by H₂O₂. In addition, pretreatment with TCSGs inhibited the NF-κB signaling pathway by blocking the degradation of the inhibitor of nuclear factor κBα (IκBα), thereby reducing the expression and nuclear translocation of NF-κB, as well as reducing the expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2). On the whole, the findings of this study demonstrate that TCSGs can protect L02 cells against H₂O₂-induced oxidative toxicity and inflammatory injury by increasing the expression of Nrf2 and HO-1, mediated by the NF-κB signaling pathway.

The differential effects of microcystin-LR on mitochondrial DNA in the hippocampus and cerebral cortex

Microcystin-LR (MC-LR) is the most abundant toxicant among microcystin variants produced by cyanobacteria. MC-induced toxicity is broadly reported to pose a threat to aquatic animals and humans and has been associated with the dysfunction of some organs such as liver and kidney. However, MC-induced neurotoxicity has not been well characterized after long-term exposure. This study was designed to investigate the neurotoxic effects after chronic oral administration of MC-LR. In our trial, C57/BL6 mice received MC-LR at 0, 1, 5, 10, 20 and 40 μg/L in drinking water for twelve months. Our data demonstrated that mitochondrial DNA (mtDNA) damage was evident in the damaged neurons as a result of chronic exposure. Histopathological abnormalities and mtDNA damage were observed in the hippocampus and cerebral cortex. Furthermore, MC-LR exerted distinct effects on these two brain regions. The hippocampus was more susceptible to the treatment of MC-LR compared with the cerebral cortex. However, no strong relationships were observed between the genotoxic effects and exposure doses. In conclusion, this study has provided a mtDNA-related mechanism for underlying chronic neurotoxicity of MC-LR and suggested the presence of differential toxicant effects on the hippocampus and cerebral cortex.

Highly efficient production of functional recombinant human fibroblast growth factor 22 in E. coli and its protective effects on H2O2-lesioned L02 cells

In the 22 member mammalian FGF family, FGF22 belongs to FGF7 subfamily, and its effects are largely confined to the brain and skin. To explore the functions of FGF22 on other tissues and develop a large-scale production of recombinant human FGF22 (rhFGF22) without a fusion tag, a plasmid encoding human FGF22 (pET3a-rhFGF22) was used to express rhFGF22 in E. coli BL21 (DE3) pLysS. A large amount of rhFGF22 inclusion body protein was obtained. A two-step denaturing method successfully solubilized rhFGF22, and it was refolded and then purified in one step via heparin affinity chromatography. A yield of 105 mg rhFGF22 with a purity of up to 95% was obtained from 100 g wet bacteria. It was found that the rhFGF22 had biological activity, since it effectively attenuated H₂O₂-induced human hepatic L02 cell death. Analysis by qRT-PCR and Western blot demonstrated that rhFGF22 protects L02 cells from H₂O₂-induced oxidative damage via suppression of mitochondrial apoptosis pathways. In conclusion, the strategy described in this paper may provide a novel means to solve the production of insoluble rhFGF22 and shine new light on its translational potential.