Oxidative effects and toxin bioaccumulation after dietary microcystin intoxication in the hepatopancreas of the crab Neohelice (Chasmagnathus) granulata

Acute toxic effects of microcystin-LR on crayfish (Procambarus clarkii): Insights from antioxidant system, histopathology and intestinal flora

To study the toxic effects of microcystin-LR (MC-LR) on crayfish, adult male Procambarus clarkii were exposed to different concentrations of MC-LR for 96 h. In the meantime, the accumulation characteristics of MC-LR and the alternations of antioxidant system, histopathology and intestinal flora of P. clarkii were investigated. The results demonstrated that the hepatopancreas, gills and intestines of P. clarkii could effectively accumulate MC-LR. Antioxidant-related genes such as Mn-sod, cat, gst, gpx, mt and hsp70 showed different expression trends in different organs to respond to MC-LR-induced oxidative stress. MC-LR led to histological changes in the hepatopancreas, gills and intestines, thus affecting their corresponding physiological functions. Additionally, the abundances of bacterial phyla including Firmicutes and Planctomycetes and genera including Dysgonomonas, Brevundimonas and Anaerorhabdus in the intestine were significantly changed after MC-LR exposure, and the disruption of intestinal flora might further cause abnormal intestinal microbial metabolism and genetics in P. clarkii. This study provides novel mechanistic insights into the toxic impacts of microcystins on aquatic crustaceans. HIGHLIGHTS: • MC-LR was significantly accumulated in the hepatopancreas, gills and intestines of P. clarkii. • MC-LR induced the differential expression of antioxidant-related genes of P. clarkii. • MC-LR caused histological alterations in the hepatopancreas, gills and intestines of P. clarkii. • MC-LR affected the intestinal microbial composition and function of P. clarkii.

Integrated analysis of mRNA and microRNA expression profiles in hepatopancreas of Litopenaeus vannamei under acute exposure to MC-LR

Intensive shrimp farming is often threatened by microcystins Hepatopancreas is the primary target organ of MCs in shrimp. To investigate the response of hepatopancreas to acute MC-LR exposure, the expression profiles of RNA-seq and miRNA-seq in the hepatopancreas of L. vannamei were determined, and data integration analysis was performed at 72 h after MC-LR injection. The expression of 5 DEGs and three DEMs were detected by Quantitative PCR (qPCR). The results showed that the cumulative mortality rate of shrimp in MC-LR treatment group was 41.1%. A total of 1229 differentially expressed genes (844 up- and 385 down-regulated) and 86 differentially expressed miRNAs (40 up- and 46 down-regulated) were identified after MC-LR exposure. Functional analysis indicated that DEGs is mainly involved in the oxidative activity process in molecular functional categories, and proteasome was the most enriched KEGG pathway for mRNAs profile. According to the functional annotation of target genes of DEMs, protein binding was the most important term in the GO category, and protein processing in endoplasmic reticulum (ER) was the most enriched KEGG pathway. The regulatory network of miRNAs and DEGs involved in the pathway related to protein degradation in endoplasmic reticulum was constructed, and miR-181-5p regulated many genes in this pathway. The results of qPCR showed that there were significant differences in the expression of five DEGs and three DEMs, which might play an important role in the toxicity and hepatopancreas detoxification of MC-LR in shrimp. The results revealed that MC-LR exposure affected the degradation pathway of misfolded protein in ER of L. vannamei hepatopancreas, and miR-181-5p might play an important role in the effect of MC-LR on the degradation pathway of misfolded protein.

Mercury Induced Tissue Damage, Redox Metabolism, Ion Transport, Apoptosis, and Intestinal Microbiota Change in Red Swamp Crayfish (Procambarus clarkii): Application of Multi-Omics Analysis in Risk Assessment of Hg

As one of the most toxic elements, mercury (Hg) is a widespread toxicant in aquatic environments. Crayfish are considered suitable for indicating the impact of heavy metals on aquatic crustaceans. Nevertheless, Hg toxicity on Procambarus clarkii is largely unknown. In this research, the acute Hg-induced alterations of biochemical responses, histopathology, hepatopancreatic transcriptome, and intestinal microbiome of Procambarus clarkii were studied. Firstly, Hg induced significant changes in reactive oxygen species (ROS) and malonaldehyde (MDA) content as well as antioxidant enzyme activity. Secondly, Hg exposure caused structural damage to the hepatopancreas (e.g., vacuolization of the epithelium and dilatation of the lumen) as well as to the intestines (e.g., dysregulation of lamina epithelialises and extension of lamina proprias). Thirdly, after treatment with three different concentrations of Hg, RNA-seq assays of the hepatopancreas revealed a large number of differentially expressed genes (DEGs) linked to a specific function. Among the DEGs, a lot of redox metabolism- (e.g., ACOX3, SMOX, GPX3, GLO1, and P4HA1), ion transport- (e.g., MICU3, MCTP, PYX, STEAP3, and SLC30A2), drug metabolism- (e.g., HSP70, HSP90A, CYP2L1, and CYP9E2), immune response- (e.g., SMAD4, HDAC1, and DUOX), and apoptosis-related genes (e.g., CTSL, CASP7, and BIRC2) were identified, which suggests that Hg exposure may perturb the redox equilibrium, disrupt the ion homeostasis, weaken immune response and ability, and cause apoptosis. Fourthly, bacterial 16S rRNA gene sequencing showed that Hg exposure decreased bacterial diversity and dysregulated intestinal microbiome composition. At the phylum level, there was a marked decrease in Proteobacteria and an increase in Firmicutes after exposure to high levels of Hg. With regards to genus, abundances of Bacteroides, Dysgonomonas, and Arcobacter were markedly dysregulated after Hg exposures. Our findings elucidate the mechanisms involved in Hg-mediated toxicity in aquatic crustaceans at the tissue, cellular, molecular as well as microbial levels.

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.

Challenges of using blooms of Microcystis spp. in animal feeds: A comprehensive review of nutritional, toxicological and microbial health evaluation

Microcystis spp., are Gram-negative, oxygenic, photosynthetic prokaryotes which use solar energy to convert carbon dioxide (CO₂) and minerals into organic compounds and biomass. Eutrophication, rising CO₂ concentrations and global warming are increasing Microcystis blooms globally. Due to its high availability and protein content, Microcystis biomass has been suggested as a protein source for animal feeds. This would reduce dependency on soybean and other agricultural crops and could make use of "waste" biomass when Microcystis scums and blooms are harvested. Besides proteins, Microcystis contain further nutrients including lipids, carbohydrates, vitamins and minerals. However, Microcystis produce cyanobacterial toxins, including microcystins (MCs) and other bioactive metabolites, which present health hazards. In this review, challenges of using Microcystis blooms in feeds are identified. First, nutritional and toxicological (nutri-toxicogical) data, including toxicity of Microcystis to mollusks, crustaceans, fish, amphibians, mammals and birds, is reviewed. Inclusion of Microcystis in diets caused greater mortality, lesser growth, cachexia, histopathological changes and oxidative stress in liver, kidney, gill, intestine and spleen of several fish species. Estimated daily intake (EDI) of MCs in muscle of fish fed Microcystis might exceed the provisional tolerable daily intake (TDI) for humans, 0.04 μg/kg body mass (bm)/day, as established by the World Health Organization (WHO), and is thus not safe. Muscle of fish fed M. aeruginosa is of low nutritional value and exhibits poor palatability/taste. Microcystis also causes hepatotoxicity, reproductive toxicity, cardiotoxicity, neurotoxicity and immunotoxicity to mollusks, crustaceans, amphibians, mammals and birds. Microbial pathogens can also occur in blooms of Microcystis. Thus, cyanotoxins/xenobiotics/pathogens in Microcystis biomass should be removed/degraded/inactivated sufficiently to assure safety for use of the biomass as a primary/main/supplemental ingredient in animal feed. As an ameliorative measure, antidotes/detoxicants can be used to avoid/reduce the toxic effects. Before using Microcystis in feed ingredients/supplements, further screening for health protection and cost control is required.

Effect of maduramicin on crayfish (Procambius clarkii): Hematological parameters, oxidative stress, histopathological changes and stress response

Maduramicin, an extensively used anticoccidial drug, has been introduced into environment due to poorly absorbed in the intestine of broiler chicken. To understand the potential ecological toxicity of maduramicin on aquatic organisms, acute and subacute toxicity, hemolymph biochemistry, histopathology and the expressions of drug metabolism and stress response genes of crayfish (Procambius clarkii) were investigated in this study. For the first time, the 96 h median lethal concentration (LC₅₀) of maduramicin on crayfish was 67.03 mgL^-1 with a 95% confidence interval (54.06-81.32 mgL^-1). Then, the crayfish were exposed to 0.7 mgL^-1 (1/100 LC₅₀), 3.5 mgL^-1 (1/20 LC₅₀) and 7.0 mgL^-1 (1/10 LC₅₀) maduramicin for 28 days. Maduramicin significantly altered biochemical parameters including AST, ALT, CK, LDH and ALP of hemolymph in crayfish at several time points. The activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) of crayfish gills, hepatopancreas and abdominal muscle were significantly decreased or elevated by different concentrations of maduramicin treatment at varying time points. Furthermore, histopathological damage of crayfish gills, hepatopancreas and abdominal muscle were observed in a concentration-dependent manner. The expressions of metabolic and stress response genes (CYP450, GST, COX1, COX2, HSP70 and MT) in hepatopancreas of crayfish were significantly up-regulated by maduramicin (7.0 mgL^-1) treatment for 8 h to 7 d, and returned to normal levels after the removal of maduramicin for 3-7 days. In conclusion, our findings demonstrated that environmental exposure of maduramicin threaten to the health of crayfish living in the areas nearby livestock farms or pharmaceutical factory. Crayfish exhibited resistance to the stress of maduramicin via activating drug metabolite and detoxification pathways.

Microcystin-LR-induced changes of hepatopancreatic transcriptome, intestinal microbiota, and histopathology of freshwater crayfish (Procambarus clarkii)

As a hepatotoxin, microcystin-LR (MC-LR) poses a great threat to aquatic organisms. In this research, the hepatopancreatic transcriptome, intestinal microbiota, and histopathology of Procambarus clarkii (P. clarkii) in response to acute MC-LR exposure were studied. RNA-seq analysis of hepatopancreas identified 372 and 781 differentially expressed genes (DEGs) after treatment with 10 and 40 μg/L MC-LR, respectively. Among the DEGs, 23 genes were immune-related and 21 genes were redox-related. GO functional enrichment analysis revealed that MC-LR could impact nuclear-transcribed mRNA catabolic process, cobalamin- and heme-related processes, and sirohydrochlorin cobaltochelatase activity of P. clarkii. In addition, the only significantly enriched KEGG pathway induced by MC-LR was galactose metabolism pathway. Meanwhile, sequencing of the bacterial 16S rRNA gene demonstrated that MC-LR decreased bacterial richness and diversity, and altered the intestinal microbiota composition. At the phylum level, after 96 h, the abundance of Verrucomicrobia decreased after treatment with 10 and 40 μg/L MC-LR, while Firmicutes increased in the 40 μg/L MC-LR-treated group. At the genus level, the abundances of 15 genera were significantly altered after exposure to MC-LR. Our research demonstrated that MC-LR exposure caused histological alterations such as structural damage of hepatopancreas and intestines. This research provides an insight into the mechanisms associated with MC-LR toxicity in aquatic crustaceans.

Effects of MCLR exposure on sex hormone synthesis and reproduction-related genes expression of testis in male Rana nigromaculata

Microcystin-leucine-arginine (MCLR) is the most popular and toxic variant among microcystins, which can cause severe reproductive toxicity to animals. However, the mechanisms of reproductive toxicity induced by MCLR in amphibians are still not entirely clear. In the current study, toxicity mechanisms of MCLR on the reproductive system of male Rana nigromaculata followed by low concentration (0, 0.1, 1, and 10 μg/L) and short-term (0, 7, and 14 days) MCLR exposure were shown. It was observed that MCLR could be bioaccumulated in the testes of male frogs, and the theoretical bioaccumulation factor values were 0.24 and 0.19 exposed to 1 μg/L and 10 μg/L MCLR for 14 days, respectively. MCLR exposure significantly decreased testosterone (T) concentrations and increased estradiol (E2) concentrations exposed to 1 and 10 μg/L MCLR for 14 days. The mRNA levels of HSD17B3 were downregulated, and HSD17B1 and CYP19A1 mRNA expression levels were upregulated, respectively. Only 10 μg/L MCLR group showed significant induction of follicle-stimulating hormone (FSH) levels and cyclic adenosine monophosphate (cAMP) content. Moreover, AR and ESR1 mRNA expression levels were significantly upregulated exposed to 1 and 10 μg/L MCLR for 14 days, respectively. Our results suggested that low-concentration MCLR induced transcription changes of CYP19A1, HSD17B3, and HSD17B1 led to endocrine disorders, and caused interference of spermatogenesis by the decrease of T and abnormal gene expressions of AR and ESR1 in the testes of R. nigromaculata.

Age-dependent antioxidant responses to the bioconcentration of microcystin-LR in the mysid crustacean, Neomysis awatschensis

Microcystins (MCs) are naturally occurring algal toxins in the aquatic environment and pose a serious threat to the ecosystem. In general, aquatic populations are structured by organisms of different ages, with varying degrees of biochemical and physiological responses. In this study, juvenile and adult marine mysids (Neomysis awatschensis) were exposed to MC-Leucine Arginine (MC-LR) (0.1, 1, and 10 μg L^-1) for 7 days, and the bioconcentration dynamics and responses of antioxidant defense system were measured during the exposure and additional depuration periods (7 days). MC-LR bioconcentrated in a dose-dependent manner, from a threshold concentration of 1 μg L^-1 in both stages, and the levels reduced gradually during the depuration phase. Bioconcentration patterns of MC-LR were highly age-specific, as juvenile mysids showed peaks during the exposure period, whereas adults exhibited a peak on the first day of depuration. After exposure to 10 μg L^-1 concentration, elevated levels of malondialdehyde (MDA) and glutathione (GSH) were observed during the late (days 5 and 7) exposure and early (days 1 and 3) depuration periods in juvenile mysids, while adult mysids showed a peak on day 7 of the exposure period. Age-specific responses were also observed in the enzymatic activities of glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR). Juvenile mysids showed a significant elevation in all enzymatic activities during the exposure and/or depuration phase upon exposure to 10 μg L^-1 MC-LR, but only CAT and SOD enzymes showed significant changes during the exposure and/or depuration periods in adults. Overall, our results indicate the bioconcentration potential of MC-LR and its threshold in the marine mysid, in addition to age-specific MC-LR dynamics and subsequent biochemical responses.

Effect of pure microcystin-LR on activity and transcript level of immune-related enzymes in the white shrimp (Litopenaeus vannamei)

Microcystins (MCs) in freshwater and marine waters released by toxin-producing cyanobacteria have negative impacts to the aquatic environment. This study aimed to investigate the effect of pure microcystin-LR on activity and transcript level of immune-related enzymes in the white shrimp Litopenaeus vannamei. After exposed to varying concentrations of pure microcystin-LR (MC-LR) for 30 days, the activity of superoxide dismutase (SOD), lysozyme (LZM), glutathione peroxidase (GPx), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP) and transcript level of cMn-sod, lzm, gpx were investigated in the hepatopancreas of white shrimp (L. vannamei). Immune-related enzyme activities responded differently to MC-LR exposure. SOD, GPx, and POD activity in the hepatopancreas were activated in a concentration-dependent manner while LZM activity was significantly inhibited in the treatment groups. ACP and AKP activity showed an increase, followed by a decrease. The transcript levels of cMn-sod, lzm, and gpx were consistent with changes in their encoding enzyme activity. These results demonstrated that sub-chronical exposure to MC-LR induced the alteration of immune-related enzymes and corresponding genes in the hepatopancreas, which may help explain the presence of detoxification mechanisms in crustaceans and how they were protected from MC-LR stress for a long period of time.

Microcystin-LR bioconcentration induces antioxidant responses in the digestive gland of two marine bivalves Crassostrea gigas and Mytilus edulis

Microcystins (MCs) are a major group of potent cyanobacterial toxins found in freshwater and even brackish waterbodies. To understand the putative correlation between bioconcentration of MCs and antioxidant responses of the digestive gland of bivalves, Pacific oyster Crassostrea gigas and blue mussel Mytilus edulis were exposed to different concentrations (0.1, 1, 10 and 20μgL^-1) of MC-Leucine-Arginine (LR) for seven days. MC-LR bioconcentrated in the digestive glands of both bivalves during exposure period. The levels were slightly reduced when the bivalves were exposed to seawater during depuration (7days), while approximately 0.1μgL^-1 of MC-LR was observed in the 10 and 20μgL^-1 exposed bivalves at the end of depuration. Intracellular malondialdehyde (MDA) and glutathione (GSH) levels were significantly elevated in the 10 and 20μgL^-1 exposed bivalves at 7day, and the levels were maintained during depuration in both bivalves. Overall, significant higher levels of enzymatic activities of antioxidant defense systems such as glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) were observed in the 10 and 20μgL^-1 exposed bivalves. Interestingly, most of higher levels of Pacific oyster were detected at exposure period, while blue mussel showed higher levels at depuration phase, suggesting a species-specific sensitivity upon MC-LR. These patterns were correlated with the bioconcentration patterns of MC-LR as Pacific oyster was highly accumulated by MC-LR during exposure period, but blue mussel showed prolonged high levels of MC-LR for depuration phase. Our results will be useful to understand species-specific bioconcentration of MC-LR in bivalves and their effects on intracellular oxidative status via accumulation.

Accumulation and detoxification dynamics of microcystin-LR and antioxidant responses in male red swamp crayfish Procambarus clarkii

MC-LR is one of major microcystin isoforms with potent hepatotoxicity. In the present study, we aim to: 1) explore the dynamics of MC-LR accumulation and elimination in different tissues of male red swamp crayfish Procambarus clarkii; 2) reveal the mechanisms underlying hepatic antioxidation and detoxification. In the semi-static toxicity tests under the water temperature of 25±2°C, P. clarkii were exposed to 0.1, 1, 10 and 100μg/L MC-LR for 7days for accumulation and subsequently relocated to freshwater for another 7days to depurate MC-LR. MC-LR was measured in the hepatopancreas, intestine, abdominal muscle and gill by HPLC. The enzyme activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST), content of glutathione (GSH), and transcripts of Mn-sod, cat, gpx1, Mu-gst, heat shock protein90 (hsp90), hsp70 and hsp60 in hepatopancreas were detected. The results showed that P. clarkii accumulated more MC-LR in intestine, and less in abdominal muscle and gill during accumulation period and eliminated the toxin more quickly in gill and abdominal muscle, and comparatively slowly in intestine during depuration period. The fast increase of SOD and CAT activities at early stage, subsequent decrease at later stage of accumulation period and then fast increase during depuration period were partially consistent with the transcriptional changes of their respective genes. GPx was activated by longer MC-LR exposure and gpx1 mRNA expression showed uncoordinated regulation pattern compared with its enzyme. Hsp genes were up-regulated when P. clarkii was exposed to MC-LR.

Activity and Transcriptional Responses of Hepatopancreatic Biotransformation and Antioxidant Enzymes in the Oriental River Prawn Macrobrachium nipponense Exposed to Microcystin-LR

Microcystins (MCs) are a major group of cyanotoxins with side effects in many organisms; thus, compounds in this group are recognized as potent stressors and health hazards in aquatic ecosystems. In order to assess the toxicity of MCs and detoxification mechanism of freshwater shrimp Macrobrachium nipponense, the full-length cDNAs of the glutathione S-transferase (gst) and catalase (cat) genes were isolated from the hepatopancreas. The transcription level and activity changes in the biotransformation enzyme (glutathione S-transferase (GST)) and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)) in the hepatopancreas of M. nipponense exposed to MC-LR (0.2, 1, 5, and 25 μg/L) for 12, 24, 72 and 96 h were analyzed. The results showed that the isolated full-length cDNAs of cat and gst genes from M. nipponense displayed a high similarity to other crustaceans, and their mRNAs were mainly expressed in the hepatopancreas. MC-LR caused significant increase of GST activity following 48-96 h (p < 0.05) and an increase in SOD activity especially in 24- and 48-h exposures. CAT activity was activated when exposed to MC-LR in 12-, 24- and 48-h exposures and then it was inhibited at 96-h exposure. There was no significant effect on GPx activity after the 12- and 24-h exposures, whereas it was significantly stimulated after the 72- and 96-h exposures (p < 0.05). The transcription was altered similarly to enzyme activity, but the transcriptional response was generally more immediate and had greater amplitude than enzymatic response, particularly for GST. All of the results suggested that MC-LR can induce antioxidative modulation variations in M. nipponense hepatopancreas in order to eliminate oxidative damage.