Acute effects of microcystins on the transcription of antioxidant enzyme genes in crucian carp Carassius auratus

Microcystin-leucine-arginine Modulates the Expression Patterns of Proinflammatory Cytokines and an Apoptotic Gene in Chicken Liver

Microcystins (MCs) are included in drinking water and a family of cyclic heptapeptide hepatotoxins that have been implicated in the impairment of liver function in various animals. There is scarce information on the effect of MCs on cytokines and apoptotic gene expression and on whether MCs can induce inflammation and apoptosis in avian hepatic tissue. This study investigated the expression of genes related to proinflammatory interleukins, apoptosis, and antioxidant function in chicken liver tissues cultured in the presence of different doses of microcystin-leucine-arginine (MC-LR). Livers were collected from five hens and liver slices were placed in sterile tubes containing Dulbecco's medium supplemented with 0, 1, 10, or 100 ng/mL of MC-LR. After 6 h of cultivation, total RNA was extracted and quantitative PCR analysis was performed for interleukin genes (IL-1β, IL-6, and IL-8), TNF sf15, an apoptotic gene (caspase-3), and genes involved in antioxidant function ([catalase [CAT ], glutathione peroxidase [GSH-PX ], and superoxide dismutase [SOD]). Liver tissues in each group were fixed for histopathology. MC-LR downregulated the mRNA levels of IL-1β, IL-8, and TNF sf15 as compared to the control (0 ng/mL) in dose-dependent patterns; however, the differences were not significant. The expression of IL-6 in liver tissues exposed to 100 ng/mL of MC-LR was significantly (P<0.05) lower than that in tissues exposed to 1 ng/mL. In contrast, MC-LR upregulated the mRNA expression of caspase-3 and genes involved in antioxidant function in the liver tissues after 6 h, without the difference reaching statistical significance. Hepatocytes showed vacuolar degeneration and focal necrosis according to the dose of MC-LR. This study highlighted the risk of low doses of MC-LR in chicken liver. Moreover, MC-LR could modulate the transcriptional patterns of at least IL-6 in liver-tissue culture of chicken after 6 h of exposure.

Stress-responsive expression of a glutathione S-transferase (delta) gene in waterflea Daphnia magna challenged by microcystin-producing and microcystin-free Microcystis aeruginosa

Harmful cyanobacterial blooms resulting from eutrophication and global warming have emerged as a worldwide environmental concern. Some zooplankton populations, including Daphnia, have been shown to adapt locally to microcystin-producing Microcystis. Previous in vitro experiments indicate that glutathione-S-transferase (GST) may act as the first step of detoxification in Daphnia by conjugating microcystins (MCs) with glutathione. The GST family is categorized into many classes, and different classes present distinct responses to MC detoxification. To date, however, the molecular mechanism of single class GST participation in buffering the toxic effects of MCs in Daphnia remains poorly known. In this study, a full-length delta-GST cDNA of Daphnia magna (Dm-dGST) was isolated and characterized through bioinformatics. Differential gene expression studies revealed that short-term exposure to microcystin-producing (MP) Microcystis aeruginosa increased Dm-dGST transcript levels. By contrast, long-term exposure to MP or microcystin-free (MF) M. aeruginosa decreased Dm-dGST transcript levels. Together with changes in three other antioxidation biomarkers (catalase, CuZn- and Mn-superoxide dismutase), it is concluded that Dm-dGST can potentially biotransform MCs to reduce their toxicity. The present study highlights the importance of Dm-dGST in response to MC toxicity and may thus facilitate future research on the molecular mechanisms of MC tolerance in zooplankton under an increasing eutrophic world.

Organ-dependent response in antioxidants, myoglobin and neuroglobin in goldfish (Carassius auratus) exposed to MC-RR under varying oxygen level

Cyanobacterial bloom, a common phenomenon nowadays often results in the depletion of dissolved oxygen (hypoxia) and releases microcystin-RR (MC-RR) in the water. Information on the combined effects of MC-RR and hypoxia on the goldfish is lacking, therefore, this study is aimed at evaluating the effect of two doses of MC-RR on the antioxidants and globin mRNA of goldfish under normoxia, hypoxia and reoxygenation. The result showed that MC-RR at both doses (50 and 200 μg kg(-1) body weight) significantly (p<0.05) induced superoxide dismutase activities in the liver and kidney but catalase activities and total antioxidant capacity were low in these organs during hypoxia and reoxygenation compared to normoxia and control. Myoglobin and neuroglobin mRNAs in MC-RR group were significantly induced in the brain only and are believed to protect the brain from oxidative damage. However, other organs were unprotected and extensive damage was observed in the liver cells. Our results clearly demonstrated that MC-RR and hypoxia-reoxygenation transitions were synergistically harmful to the goldfish and could impair its adaptation to hypoxia, especially during reoxygenation.

In situ studies on growth, oxidative stress responses, and gene expression of juvenile bighead carp (Hypophthalmichthys nobilis) to eutrophic lake water dominated by cyanobacterial blooms

Cyanobacterial blooms have received increasing attention as a public biohazard for human and animal health. To assess the effect of cyanobacteria-dominant lake water on juvenile fish, we measured the responses of specific growth rate, condition factor, body weight and body length, oxidative stress, and related gene expression of juvenile bighead carp Hypophthalmichthys nobilis exposed to in situ eutrophic lake (Chl a was around 7.0μgL(-1)). Results showed in situ cyanobacteria-dominant lake water had no effect on the growth performance, but significantly elevated the contents of malondialdehyde, the expression of heat shock protein 70, and the activity of superoxide dismutase, indicating that oxidative stress occurred. Meanwhile in situ lake water significantly decreased the expression of catalase and glutathione S-transferase genes. We conclude that in situ cyanobacteria-dominated lake water was harmful to juvenile bighead carp based on the oxidative stress and changes in the related gene expression levels.

Toxic effect on tissues and differentially expressed genes in hepatopancreas identified by suppression subtractive hybridization of freshwater pearl mussel (Hyriopsis cumingii) following microcystin-LR challenge

Microcystins are a family of potent hepatotoxins produced by freshwater cyanobacteria and can cause animal intoxications and human diseases. In this study, the effect of microcystin-LR (MC-LR) on the tissues of freshwater pearl mussel (Hyriopsis cumingii) was evaluated and differentially expressed genes in the hepatopancreas of the mussel exposed to MC-LR were identified. HPLC analysis of cell extracts from various tissues of the mussel indicated that the hepatopancreas had the highest MC-LR levels (55.78 ± 6.73 μg g⁻¹ DW) after 15-day exposure. The MC-LR concentration in gill or muscle was an order of magnitude less than in hepatopancreas or gonad. Subtractive cDNA library was constructed by suppression subtractive hybridization (SSH), and ∼400 positive clones were sequenced, from which 98 high quality sequences were obtained by BLAST analysis. The screening identified numerous genes involved in apoptosis, signal transduction, cytoskeletal remodel, innate immunity, material and energy metabolism, translation and transcription which were extensively discussed. The results of this study add large amount of information to the mussel genome data, and for the first time present the basic data on toxicity effect of MC-LR on mussel.

Expression and activity of glutathione S-transferases and catalase in the shrimp Litopenaeus vannamei inoculated with a toxic Microcystis aeruginosa strain

Microcystin (MC) produced during cyanobacteria blooms is notably toxic to human and wildlife. Conjugation with reduced glutathione (GSH) by glutathione S-transferase (GST) and the antioxidant enzymes defenses (e.g. catalase, CAT) are important biochemical defense mechanisms against MCs toxicity. We investigated the enzymatic activity of CAT and GST and the gene expression levels of CAT and eight GST isoforms in the hepatopancreas of the globally farmed shrimp Litopenaeus vannamei 48-h after injection with a sub-lethal dose of 100 μg kg⁻¹ of a toxic Microcystis aeruginosa extract. MCs caused up-regulation for GSTΩ, μ and a MAPEG isoform, by 12-, 2.8- and 1.8-fold, respectively, and increases in the total GST enzyme activity and CAT enzyme activity. The study points to the importance of further characterization for the L. vannamei GST isoforms and GST/CAT post-translational regulation processes to better understand the key mechanisms involved in the shrimp's defense against MC exposure.

Toxicity assessment of simulated urban runoff containing polycyclic musks and cadmium in Carassius auratus using oxidative stress biomarkers

The objective of this study was to assess potential toxic effects of simulated urban runoff on Carassius auratus using oxidative stress biomarkers. The activity of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and the content of malondialdehyde (MDA) in the liver of C. auratus were analyzed after a 7-, 14- and 21-day exposure to simulated urban runoff containing galaxolide (HHCB) and cadmium (Cd). The results showed that the activity of antioxidant enzymes and the content of MDA increased significantly exposed to the simulated urban runoff containing HHCB alone or mixture of HHCB and Cd. The activity of the investigated enzymes and the content of MDA then returned to the blank level over a longer period of exposure. The oxidative stress could be obviously caused in the liver of C. auratus under the experimental conditions. This could provide useful information for toxic risk assessment of urban runoff.

Multilevel ecotoxicity assessment of polycyclic musk in the earthworm Eisenia fetida using traditional and molecular endpoints

The ecotoxicity assessment of galaxolide (HHCB) and tonalide (AHTN) was investigated in the earthworm Eisenia fetida using traditional and novel molecular endpoints. The median lethal concentration (LC(50)) for 7-day and 14-day exposures was 573.2 and 436.3 μg g(-1) for AHTN, and 489.0 and 392.4 μg g(-1) for HHCB, respectively. There was no observed significant effect on the growth rate of E. fetida after a 28-day exposure except that at the highest concentration (100 μg g(-1)) of AHTN and HHCB, whereas a significant decrease of cocoon production was found in earthworms exposed to 50 and 100 μg g(-1). To assess molecular-level effect, the expression of encoding antioxidant enzymes and stress protein genes were investigated upon sublethal exposures using the quantitative real time PCR assay. The expression level of SOD, CAT and calreticulin genes was up-regulated significantly, while the level of annetocin (ANN) and Hsp70 gene expression was down-regulated in E. fetida. Importantly, the level of ANN expression had a significant positive correlation with the reproduction rate of earthworms. Furthermore, the lowest observed effect concentration (LOECs) of ANN expression level was 3 μg g(-1) for AHTN and 10 μg g(-1) for HHCB, suggesting that ANN gene expression can serve as a more sensitive indicator of exposure to AHTN and HHCB than traditional endpoints such as cocoon production. The transcriptional responses of these genes may provide early warning molecular biomarkers for identifying contaminant exposure, and the data obtained from this study will contribute to better understand the toxicological effect of AHTN and HHCB.

Acute effects of pure cylindrospermopsin on the activity and transcription of antioxidant enzymes in tilapia (Oreochromis niloticus) exposed by gavage

The cyanobacterial toxin cylindrospermopsin (CYN) is a widely distributed contaminant of freshwater systems with the consequent risk for human and wildlife, particularly fish. However, CYN toxicity data on fish are still scarce. It is known that CYN inhibits glutathione synthesis and this could contribute to oxidative damage. In the present work tilapia (Oreochromis niloticus) were exposed by gavage to 200 and 400 μg/kg bw of pure CYN and sacrificed after 24 h. The activity and relative mRNA expression by real-time PCR of antioxidant enzymes glutathione peroxidase (GPx) and soluble glutathione-S-transferases (sGST) and the sGST protein abundance by Western blot analysis were evaluated in liver and kidney. Also the induction of lipid peroxidation (LPO) was assayed. Results show an increase of LPO products in both organs. Moreover, CYN altered the activity, gene expression and protein abundance of the enzymes, indicating the importance of GPx and sGST in CYN pathogenicity. This is the first time that CYN is reported to affect these enzymes in fish and they have shown to be responsive biomarkers of CYN toxicity.

Acute effects of microcystins exposure on the transcription of antioxidant enzyme genes in three organs (liver, kidney, and testis) of male Wistar rats

Microcystins (MCs) induce the production of reactive oxygen species (ROS) in various tissues in mammals, whereas the endogenous antioxidant enzymes are responsible to scavenge the ROS. ROS can modulate the antioxidant enzyme activities by regulating the mRNA levels. The present study was undertaken to find out the relationship between the transcriptional alterations of antioxidant enzymes and MCs stimulation in rats. The time-dependent changes of relative transcription abundance of catalase (CAT), Mn-superoxide dismutase (Mn-SOD), Cu,Zn-superoxide dismutase (Cu,Zn-SOD), glutathione reductase (GR), glutathione peroxidase (GPx), and gamma-glutamylcysteine synthetase (γ-GCS) were investigated in three organs (liver, kidney, and testis) of male Wistar rats injected intravenously (i.v.) with 80 μg MC-LR(equivalent)/kg body weight using the quantitative real-time PCR (qPCR) method. We found that MCs could affect the transcriptional activities of these antioxidant enzymes in liver, kidney, and testis of MCs-treated rats and we speculated the possible causation of the transcriptional change. The altered transcription of antioxidant enzymes may play an important role in counteracting the potential deleterious effects of elevated oxidative stress induced by MCs, and this will provide us new insights into the possible role of antioxidant enzymes in the toxicological mechanisms of MCs at molecular level.

Subchronic effects of cyanobacterial cells on the transcription of antioxidant enzyme genes in tilapia (Oreochromis niloticus)

The increasing occurrence of toxic cyanobacterial blooms in eutrophic water bodies is nowadays of worldwide concern due to their ability to produce toxins such as microcystins (MCs). These cyanobacterial toxins have been shown to affect aquatic organisms such as fish, resulting in oxidative stress. Among the antioxidant enzymes, glutathione peroxidase (GPx) and soluble glutathione-S-transferases (sGST) play an important role in the detoxification of MCs. In the present work tilapia (Oreochromis niloticus) were orally exposed to cyanobacterial cells containing MCs and non-containing MCs for 21 days. The activity and relative mRNA expression by real-time PCR of both enzymes and the GST protein abundance by Western blot analysis were evaluated in liver and kidney. Also the induction of lipid peroxidation (LPO) was assayed. MCs containing cyanobacterial cells induced an increase of LPO products in both organs, and MCs containing and MCs non-containing cyanobacterial cells altered the activity, gene expression and protein abundance of the enzymes, indicating the importance of GPx and sGST in MCs detoxification. Moreover, liver, the main organ involved in biodegradation and biotransformation, experienced an adaptative response to the toxic insult. These results show for the first time that the subchronic exposure to cyanobacterial cells causes changes in antioxidant and detoxification enzymes and that GPx and GST gene expression are good markers of these alterations in tilapia.

The profound effects of microcystin on cardiac antioxidant enzymes, mitochondrial function and cardiac toxicity in rat

Deaths from microcystin toxication have widely been attributed to hypovolemic shock due to hepatic interstitial hemorrhage, while some recent studies suggest that cardiogenic complication is also involved. So far, information on cardiotoxic effects of MC has been rare and the underlying mechanism is still puzzling. The present study examined toxic effects of microcystins on heart muscle of rats intravenously injected with extracted MC at two doses, 0.16LD(50) (14 microg MC-LReq kg(-1) body weight) and 1LD(50) (87 microg MC-LReq kg(-1) body weight). In the dead rats, both TTC staining and maximum elevations of troponin I levels confirmed myocardial infarction after MC exposure, besides a serious interstitial hemorrhage in liver. In the 1LD(50) dose group, the coincident falls in heart rate and blood pressure were related to mitochondria dysfunction in heart, while increases in creatine kinase and troponin I levels indicated cardiac cell injury. The corresponding pathological alterations were mainly characterized as loss of adherence between cardiac myocytes and swollen or ruptured mitochondria at the ultrastructural level. MC administration at a dose of 1LD(50) not only enhanced activities and up-regulated mRNA transcription levels of antioxidant enzymes, but also increased GSH content. At both doses, level of lipid peroxides increased obviously, suggesting serious oxidative stress in mitochondria. Simultaneously, complex I and III were significantly inhibited, indicating blocks in electron flow along the mitochondrial respiratory chain in heart. In conclusion, the findings of this study implicate a role for MC-induced cardiotoxicity as a potential factor that should be considered when evaluating the mechanisms of death associated with microcystin intoxication in Brazil.