Oxidative Stress Biomarker Responses Research Articles

Calcium reduces the effects of cadmium on the responses of biomarkers in freshwater fish (Oreochromis niloticus)

ABSTRACT The hardness of freshwaters varies depending on geographical locations and calcium is the most important element determining water hardness. Thus, the present study focused on responses of oxidative stress biomarkers in the liver and ATPase activities in the gill of freshwater fish (Oreochromis niloticus) after acute and chronic cadmium exposures in differing calcium levels (30, 60 and 120 mg Ca/L). Fish were exposed to Cd for acute (25 µM, 3 days) and chronic (5 µM, 30 days) durations. There were significant (p < 0.05) alterations in the oxidative stress parameters after cadmium exposures. In the liver, activities of catalase and superoxide dismutase increased in both durations, though activities of glutathione peroxidase, glutathione reductase and glutathione S-transferase decreased. Likewise, levels of glutathione and malondialdehyde increased significantly in both durations. In the gill, there were significant decreases in Na,K-ATPase activity and increases in Mg-ATPase activity. However, calcium alone did not cause any alteration (p > 0.05) in the responses of biomarkers. Data also showed that alterations in biomarkers were highest at the lowest calcium levels. Present data emphasised that calcium protected the fish against the toxic effects of cadmium and suggested that metal toxicity varies depending on the chemical quality of waters from different geographical areas.

Responses of oxidative stress biomarkers of freshwater fish (Oreochromis niloticus) exposed to Cr6+, Hg2+, Ni2+ and Zn2+ in differing calcium levels

Freshwaters from different geographical locations show different hardness, affecting metal uptake and toxicity in fish. The most important ion that determines water hardness is calcium. In this study, acute and chronic effects of metals on the oxidative stress biomarkers in the liver of freshwater fish (Oreochromis niloticus) were investigated in differing Ca2+ (30, 60 and 120 mg Ca2+/L) levels. Fish were exposed to Cr6+, Ni2+ and Zn2+ (30 μM) and Hg2+ (0.3 μM) for 3 days in acute experiments, while they were exposed to Cr6+, Ni2+ and Zn+2 (10 μM) and Hg2+ 0.03 μM) for 30 days in chronic experiments. Data showed that the oxidative stress biomarkers significantly (p < 0.05) altered after metal exposures at all calcium levels, though there was no significant change (p > 0.05) among calcium controls. In both acute and chronic exposures, catalase CAT) and superoxide dismutase (SOD) activities increased significantly, while glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione S-transferase (GST) activities decreased. There were significant decreases in total glutathione (GSH) levels in acute exposures, though GSH levels increased in chronic exposures. Malondialdehyde (MDA) levels significantly increased in both durations. The highest significant alterations in the biomarkers occurred at the lowest Ca2+ levels. GPX and GST were found to be the most sensitive enzymes in all exposures and the least alterations in biomarker response occurred in fish exposed to Ni2+. This study demonstrated that calcium levels (hardness) were important factors in the evaluation of metal toxicity for freshwater fish.

Trophic Transfer of Single-Walled Carbon Nanotubes at the Base of the Food Chain and Toxicological Response.

The potential for trophic transfer of single-walled carbon nanotubes (SWCNTs) was assessed using the green algae Tetraselmis suecica and the blue mussel Mytilus edulis in a series of laboratory experiments. Swanee River Natural Organic Matter (SRNOM)-dispersed SWCNTs were introduced into growing algal cultures. Light microscopical observations, confirmed by scanning electronic microscopy (SEM) and Raman spectroscopy, showed that SWCNT agglomerates adhered to the external algal cell walls and transmission electronic microscopy (TEM) results suggested internalization. A direct effect of SWCNT exposure on the algae was a significant decrease in growth, expressed as chlorophyll a concentration and cell viability. Mussels, fed with algae in the presence of SWCNTs, led to significantly increased pseudofaeces production, indicating selective feeding. Nevertheless, histological sections of the mussel digestive gland following exposure showed evidence of SWCNT-containing algae. Furthermore, DNA damage and oxidative stress biomarker responses in the mussel haemocytes and gill tissue were significantly altered from baseline values and were consistent with previously observed responses to SWCNT exposure. In conclusion, the observed SWCNT-algal interaction demonstrated the potential for SWCNT entrance at the base of the food chain, which may facilitate their trophic transfer with potential consequences for human exposure and health.

Accumulation and Elimination of Cadmium by the Nile Tilapia (Oreochromis niloticus) in differing Temperatures and Responses of Oxidative Stress Biomarkers.

The aims of this study were to investigate the accumulation (15 days) and elimination (15 and 30 days) of cadmium (Cd) in the liver, gill, kidney and muscle of Oreochromis niloticus following exposures to different concentrations (1 and 2mg/L) of Cd at different water temperatures (20, 25, 30 oC). Additionally, responses of oxidative stress biomarkers (superoxide dismutase, SOD; catalase CAT; glutathione peroxidase, GPx and malondialdehyde, MDA) of the liver were determined following Cd exposures. In accumulation period, Cd levels increased significantly in all the tissues at all temperatures and tissue accumulation order was kidney > liver > gill. All tissues, except the muscle, accumulated Cd in relation to exposure concentrations and water temperatures. There was no measurable level of Cd accumulation in the muscle, except in fish exposed to 2mg Cd/L at 30 oC. Likewise, elimination of Cd from the tissues also increased in depends on periods and water temperatures. The order of Cd elimination from the tissues was gill > liver > kidney. The oxidative stress biomarkers also responded to both Cd exposure and temperature increases. The activities of antioxidant enzymes such as SOD, CAT, GPx and MDA levels in the liver increased in relation to increases in Cd concentrations and water temperatures.

Biomarker responses of cardiac oxidative stress to high intensity interval training in rats

Abstract Aim: The present study aimed to verify the cardiac oxidative stress biomarker responses to high-intensity interval training (HIIT) in rats. Methods: Sixteen male Wistar rats weighing 250 to 300 g were equally divided into two groups (8 animals/group): sedentary control (SC) and trained group (HIIT). The exercise protocol consisted of high-intensity swimming (14% of body weight, 20 s of activity with 10 s of pause performed 14 times) which was performed for 12 consecutive days. Results: The cardiac tissue concentrations of malondialdehyde and carbonylated proteins showed no significant changes; on the other hand, hydroperoxide levels were higher in the HIIT group than in the SC group. The activities of superoxide dismutase, catalase, and glutathione peroxidase enzymes and the levels of reduced glutathione and sulfhydryl remained unchanged. Conclusion: It is possible to conclude that short-term high-intensity interval training induces changes in the cardiac oxidative stress biomarker but with no effect on the antioxidant enzymes.

Haloadaptative Responses of Aspergillus sydowii to Extreme Water Deprivation: Morphology, Compatible Solutes, and Oxidative Stress at NaCl Saturation.

Water activity (aw) is critical for microbial growth, as it is severely restricted at aw < 0.90. Saturating NaCl concentrations (~5.0 M) induce extreme water deprivation (aw ≅ 0.75) and cellular stress responses. Halophilic fungi have cellular adaptations that enable osmotic balance and ionic/oxidative stress prevention to grow at high salinity. Here we studied the morphology, osmolyte synthesis, and oxidative stress defenses of the halophile Aspergillus sydowii EXF-12860 at 1.0 M and 5.13 M NaCl. Colony growth, pigmentation, exudate, and spore production were inhibited at NaCl-saturated media. Additionally, hyphae showed unpolarized growth, lower diameter, and increased septation, multicellularity and branching compared to optimal NaCl concentration. Trehalose, mannitol, arabitol, erythritol, and glycerol were produced in the presence of both 1.0 M and 5.13 M NaCl. Exposing A. sydowii cells to 5.13 M NaCl resulted in oxidative stress evidenced by an increase in antioxidant enzymes and lipid peroxidation biomarkers. Also, genes involved in cellular antioxidant defense systems were upregulated. This is the most comprehensive study that investigates the micromorphology and the adaptative cellular response of different non-enzymatic and enzymatic oxidative stress biomarkers in halophilic filamentous fungi.

Banded tetra (Astyanax aeneus) as bioindicator of trace metals in aquatic ecosystems of the Yucatan Peninsula, Mexico: Experimental biomarkers validation and wild populations biomonitoring.

Bioindicator organisms are important tools in environmental monitoring studies. Understanding this, the overall goal of the present study was to evaluate the sensitivity and viability of the native fish species Banded tetra, (Astyanax aeneus; Günther, 1860), widely spread in the aquatic ecosystems of the Yucatan Peninsula in Mexico, as a bioindicator organism. In order to do this, we performed a bioassay at sublethal concentrations using copper (CuSO4) to experimentally evaluate and validate the relationship between the trace metals and oxidative stress biomarkers response [(catalase (CAT), lipoperoxidation content (LPO)], detoxification [(glutathione S-transferase (GST), metallothionein content (MT)] and neurotoxicity (AChE) in muscle of A. aeneus. Results showed changes in biomarkers after 96h: Catalase activity (CAT) was significantly higher above 1.5 and 2mg/L (154.35 and 172.50% increase, respectively); lipid peroxidation contents (TBARS), GST activity, and MT content were very similar to CAT activity at 1.5 and 2mg/L of Cu. In terms of neurotoxicity, AChE activity was significantly inhibited at 0.1mg/L (64%; p<0.001) and 0.5mg/L (44%; p<0.001) of Cu. Based on the bioassay results, we performed a trace metal monitoring campaign in muscle of A. aeneus caught in 15 sites with different anthropogenic activities, during the summer of 2017, to establish a baseline of trace metals pollution in the state of Campeche. A. aeneus showed the highest trace metal accumulation in the following order: Al>Fe>Mn>Zn>Cu>Hg>Cr>Pb>Cd>V>As, while sites were arrange as follows: Xnoha lagoon>Palizada River>Candelaria River>Ululmal>Maravillas>López Mateos. PCA showed a cluster between biomarkers (GST, CAT, TBARS, and MT) and concentration of metals (Cd, Cu, Fe, Zn, Hg and Cr). Conversely, AChE inhibition was not related to a specific metal, but highest inhibitions (>50%) were present in those sites with intensive agricultural practices. These results determined that, based on its physiological response and trace metal bioaccumulation, Astyanax aeneus can be considered a good bioindicator for evaluating the presence of trace metals in tropical aquatic systems of the Yucatan Peninsula.

Nutrients and salinity influence Prymnesium parvum (UTEX LB 2797) elicited sublethal toxicity in Pimephales promelas and Danio rerio

The magnitude, frequency, and duration of harmful algal blooms (HABs) are increasing worldwide, primarily due to climate change and anthropogenic activities. Prymnesium parvum is a euryhaline and eurythermal HAB forming species that has expanded throughout North America, resulting in massive fish kills. Previous aquatic ecology and toxicology efforts supported an understanding of conditions resulting in P. parvum HABs and fish kills; however, the primary endpoint selected for these studies was acute mortality. Whether adverse sublethal responses to P. parvum occur in fish are largely unknown. To begin to address this question, molecular and biochemical oxidative stress (OS) biomarker responses and photomotor behavioral alterations were investigated in two common fish models, the fathead minnow (Pimephales promelas) and zebrafish (Danio rerio). Varying nutrient and salinity conditions influenced P. parvum related OS biomarkers and fish behavioral responses in zebrafish and fathead minnows, which were heightened by nonoptimal conditions for P. parvum growth. Such sublethal observations present important considerations for future aquatic assessments and management of P. parvum HABs.

Fish biomarker responses to perturbation by drought in streams

ABSTRACT Drought can be viewd as a perturbation in running waters and fish are often trapped in isolated pools, where deterioration of water quality may be stressful. We investigated how this extreme condition influences response of oxidative stress biomarkers. The response of the characid Astyanax elachylepis was assessed during the dry and rainy seasons in intermittent and perennial (control) sites in streams from Brazilian savannah (Cerrado). We predicted that the biomarkers would be enhanced in the dry season in intermittent streams only due the environmentally harsh conditions in the few isolated pools that remain filled with water. As predicted, fish from the intermittent stream in the dry season presented higher gill MDA values, indicating greater stress. In the liver, MDA values were higher in the dry season for both intermittent and perennial streams, suggesting a generalized seasonal response. As expected, some antioxidant response enzymes changed in the intermittent sites during the dry season. Therefore, oxidative stress biomarkers vary seasonally, with greater increase in intermittent sites. These evidences contribute for the understanding of the spatio-temporal variation of the fish responses and fish resistance to perturbations by drought in tropical environments.

Assessing a polluted river environment by oxidative stress biomarker responses in caddisfly larvae

The effluents of wastewater treatment plants (WWTPs) contain various anthropogenic pollutants that produce negative effects in river ecosystems. Although the oxidative stress responses in aquatic organisms are useful tools for assessing such effects, the responses of aquatic insects to WWTP effluents are poorly understood. This work investigated the responses of antioxidants (superoxide dismutase, catalase, and oxy-radical absorbance capacity), oxidative damage (lipid peroxidation), and energy reserves in caddisfly (Stenopsyche marmorata) larvae caused by the WWTP effluent in two parts of the Chikumagawa River during different seasons. It was found that effluent strongly influenced the antioxidants and oxidative damage and depleted the energy reserves. Hence, both the oxidative stress biomarkers and energy reserves in aquatic insects can be used for assessing the impacts of wastewater effluents. Lipid peroxidation proceeded more intensely at some reference sites than at the effluent-impacted sites, indicating that the use of a single biomarker could lead to a misunderstanding of the effect of pollutant mixtures in field studies. To mitigate this issue, a new reference-impacted approach based on the integrated biomarker response (IBRRI) method has been developed to assess anthropogenic impacts while considering spatiotemporal fluctuations due to the natural variations in a river system. This approach produced larger IBRRI values at higher concentrations of anthropogenic pollutants, which correlated with higher ammonium and nitrate concentrations. Therefore, IBRRI is a potentially useful tool for assessing the impact of WWTP effluents under variable spatiotemporal conditions.

Assessing biochar impact on earthworms: Implications for soil quality promotion.

Potential harmful effects of spent coffee grounds (SCGs)-derived biochar on earthworms (Lumbricus terrestris) were investigated through two complementary experiments, which assessed the avoidance response of earthworms to biochar-amended soils (experiment 1), and the response of oxidative stress biomarkers and digestive enzymes (experiment 2). The main results were: 1) the highest dose of biochar (5% w/w) caused a significant avoidance response of earthworms (75% individuals avoided these treated soils after 48 h); 2) signs of oxidative stress were early detected in earthworms exposed to biochar (1 and 5% w/w) as indicated by the integrated biological response index; 3) earthworms exposed to biochar-amended soils for 30 d experienced a significant increase of digestive enzyme activities measured in both the gastrointestinal tissue and the luminal content; 4) interaction between earthworms and biochar led to a higher soil extracellular enzyme activities in the 1% biochar treatment than that of control and 5% biochar treatments. These findings suggest that the joint application of SCG-biochar and L. terrestris is a workable approach for improving soil quality in terms of soil biochemical promotion, although earthworms may develop some physiological mechanisms of biochar tolerance (antioxidant defenses).

Xenobiotic biotransformation, oxidative stress and obesogenic molecular biomarker responses in Tilapia guineensis from Eleyele Lake, Nigeria

Despite the important ecosystem and hydrological roles of coastal and inland waters, there are no established biomonitoring protocols for evaluating environmental, wildlife and human health for these coastlines in Nigeria. In the present study, contaminants tissue burden and effects at molecular and physiological levels, were investigated in Tilapia guineensis from a man-made lake (Eleyele Lake) that is used for municipal domestic water supply and compared to a reference site (Igboho Lake). Gene expression of phase I and II biotransformation systems, oxidative stress and obesogen responses were analyzed using real-time PCR, and these results were related to general health index (condition factor: CF) and muscle burden of trace metals, aliphatic and polycyclic aromatic hydrocarbons (PAHs). We observed a significant increase in phase I and II biotransformation systems, oxidative stress and obesogen responses in male and female fish from Eleyele lake compared with the reference site. Overall, our data showed significant relationships between biological responses and tissue concentrations of metals and PAHs for the Eleyele lake compared with the reference site. Given that a positive influence on genes and pathways associated with metabolic status has been previously associated with peroxisome proliferator activated receptors (PPARs), xenobiotic compounds that activate PPARs may produce changes in energy and metabolic processes, leading to obesity. The high CF (>1 = good health condition) observed, coupled with the high muscle burden of inorganic and organic contaminants in fish from Eleyele lake, suggest a potential obesogenic effect in these fishes. These findings represent co-relational evidence that the Eleyele lake is contaminated and consequently affecting biological and physiological integrity of organisms inhabiting the lake. These findings also suggest potential health risks for humans, since the lake is extensively used for domestic water supply and fisheries.

Uptake and elimination of emerging polyfluoroalkyl substance F-53B in zebrafish larvae: Response of oxidative stress biomarkers

6:2 chlorinated polyfluorinated ether sulfonate (F-53B) has been widely applied as a mist suppressant to replace perfluorooctane sulfonate (PFOS) in the metal plating industry in China for decades. Recently, F-53B has been frequently identified in the aquatic environment and wild-caught fish. However, studies on the uptake and elimination kinetics, and the toxicological effects of F-53B were very scarce. In this study, zebrafish larvae (72 h post fertilization, hpf) were exposed to F-53B (10, 100 μg/L) for 48 h, followed by a 24 h of depuration to examine both the dynamics of accumulation and elimination of F-53B and responses of antoxidant defense system in fish. The results showed that F-53B rapidly accumulated in zebrafish larvae in a concentration and time-dependent manner with BCF values of 3612–3615, but was eliminated slowly (half-life ranged from 241.5 to 258.6 h). F-53B exposure induced oxidative stress in zebrafish larvae, as reflected by the reduction in the GSH and MDA contents, CAT, SOD, CuZn-SOD, and GSH-ST activities, and the increase in GSH-Px activity as well as CAT and SOD protein levels. However, these oxidative stress markers were restored to control levels except for a decrease in protein level of SOD after depuration. Collectively, the results of this work indicate that F-53B behaves like PFOS and is bioaccumulative and persistent in zebrafish larvae, and further induced oxidative stress responses.

Systemic Inflammation and Oxidative Stress Biomarkers Response to Life Style Modification among Obese Patients with Non-Alcoholic Steatohepatitis

Background: Oxidative status may be an influential factor for increasing the progress and decreasing the effectiveness of nonalcoholic steatohepatitis treatment.

Hematological indices and oxidative stress biomarkers response to the starvation of Clarias gariepinus

Starvation effects for five weeks on energy reserves, oxidative stress and hematological indices in Nile catfish Clarias gariepinus was studied. The low protein level in starved fish may result from the lowering effect of prolonged starvation on protein synthesis rather than due to its degenerating protein. Moreover, the elevated level of serum amino acids may promote gluconeogenesis in liver. In addition, the lipid depletion in starved fish may be related to the preferential uses of lipids as an energy to starve fish. Also, unchanged glycemic level may introduce a potent evidence for the presence of active gluconeogenesis, depending on both amino and fatty acids precursors. Also, kidney and liver showed disturbances in metabolites associated with oxidative damage such as elevations in total peroxide, carbonyl protein and DNA fragmentation; these may cause dysfunction to these organs after five weeks of starvation. Total peroxide, carbonyl protein and DNA fragmentation were significantly increased in gills, liver and kidney by 29.9, 30.9 and 30.5; 83.6, 84.6 and 53.7; 82.4, 43.3 and 75.7%, respectively. Starvation induced severe anemia and loss of body weight in the fish. However, white muscle did not show any oxidative damage after five weeks of starvation.

Effects of Oxygen Availability on Oxidative Stress Biomarkers in the Mediterranean Mussel Mytilus galloprovincialis.

In aquatic environments, hypoxia and oxygen-deficient areas are increasing worldwide. Transitions in oxygen levels can influence the production of reactive oxygen species (ROS), eventually leading to oxidative stress. The transcriptional response of oxidative stress biomarkers was evaluated by qPCR in gill tissue from Mytilus galloprovincialis experimentally subjected to 48-h air exposure followed by 48-h re-oxygenation, as compared to normoxic control mussels. Superoxide dismutases (CuZnsod and Mnsod), catalase (cat), and glutathione S-transferase (gst) were over-expressed early after 8-h air exposure and returned to normoxic levels during re-oxygenation. Moreover, the mRNAs and protein expression patterns of heat shock proteins (HSP70 and HSP90) and metallothioneins (MT-10 and MT-20) were modulated by oxygen availability with increased levels during re-oxygenation suggesting the participation of these cytoprotective mechanisms in the physiological oxidative stress response when oxygen concentration was restored. Overall, the observed modulation of the oxidative stress-related and general stress genes indicates that M. galloprovincialis responds to changes in oxygen availability enhancing the antioxidant potential under low oxygen conditions for dealing with the oxidative burst during future re-oxygenation. The present investigation brings further insights in understanding how intertidal molluscs cope with short-term oxygen variations and gives useful biomarkers for environmental monitoring of hypoxic areas that are predicted to occur in the next future.

Co-exposure of Freshwater Microalgae to Tetrabromobisphenol A and Sulfadiazine: Oxidative Stress Biomarker Responses and Joint Toxicity Prediction.

Combined toxicity and oxidative stress biomarker responses were determined for tetrabromobisphenol A (TBBPA) and sulfadiazine (SDZ) to the unicellular green alga Scenedesmus obliquus. Concentration-response analyses were performed for single toxicants and for mixtures containing TBBPA and SDZ with two different mixture ratios. The effect concentrations and the observed effects of the mixtures were compared to the predictions of the joint toxicity by the concentration addition (CA) model and independent action (IA) model. Results showed that the observed joint toxicity was within the scope of the highest (TBBPA) and lowest (SDZ) toxicity observed for the individual components. Furthermore, co-exposure of S. obliquus to TBBPA and SDZ provided preliminary evidence that the mixtures induced oxidative stress leading to cell damage. The CA and IA models proved to be valid for the prediction of the joint toxicity of TBBPA and SDZ. This study highlights a combined environmental risk assessment for two emerging pollutants.

Oxidative stress and antioxidant biomarker responses after a moderate-intensity soccer training session

ABSTRACTThe present study investigated the effects of a moderate-intensity soccer training session on the production of reactive oxygen species (ROS) and the antioxidant capacity in athletes along with the biomarkers creatine kinase and transaminases for lesions in muscle and liver cells. Twenty-two male soccer players participated in this study. Blood samples were collected 5 min before and after a moderate-intensity game simulation. The results showed a decrease in the concentration of reduced glutathione (GSH) from an elevation in the production of ROS that maintained the redox homeostasis. Although the session promoted an elevated energy demand, observed by an increase in lactate and glucose levels, damage to muscle and/or liver cells was only suggested by a significant elevation in the levels of alanine transaminase (ALT). Of the two biomarkers analysed, the results suggest that measurements of the ALT levels could be adopted as a method to monitor recovery in athletes.

DNA damage and repair, oxidative stress and metabolism biomarker responses in lungs of rats exposed to ambient atmospheric 1-nitropyrene

1-Nitropyrene (1-NP) is a mutagenic and carcinogenic pollutant very widespread in the environment. However, the relative investigations on genotoxicity, oxidative stress and metabolic enzymes in lungs of mammalian caused by 1-NP have not been fully established. In this study, the 1-NP solutions at 3 dosages (1.0×10−5, 4.0×10−5 and 1.6×10−4mg/kg body weight) were respectively given to rats by the intratracheal instillation. The responses of 1-NP on DNA damage and repair, oxidative stress and metabolism biomarkers in rat lungs after exposure to 1-NP were measured. The results showed 1-NP at three dosages induced obvious DNA strand breaks, 8-OH-dG formation and DNA-protein cross-link in rat lungs compared with the control. Higher dosage 1-NP (4.0×10−5 and 1.6×10−4mg/kg body weight) greatly activated DNA repair gene OGG1 and inhibited MTH1 and XRCC1 expressions, and they significantly elevated the levels of GADD153, heme oxygenase-1 and malondialdehyde and decreased SOD activity, accompanied by the increases of CYP450, CYP1A1, CYP1A2 and GST levels. These results suggested the genotoxicity of 1-NP might rely on 1-NP-caused DNA damage and its combined effects on the suppression of DNA repair and the enhancement of oxidative stress and metabolic enzyme activity.

Cylindrospermopsin effects on cell viability and redox milieu of Neotropical fish Hoplias malabaricus hepatocytes.

Cylindrospermopsin (CYN) is a cyanotoxin that is cytotoxic to a wide variety of cells, particularly to the hepatocytes. In this study, the toxic effects of purified CYN were investigated in primary cultured hepatocytes of Neotropical fish Hoplias malabaricus. After isolation, attachment, and recovery for 72h, the cells were exposed for 72h to 0, 0.1, 1.0, 10, and 100μgl-1 of CYN. Then, cell viability and a set of oxidative stress biomarker responses were determined. Catalase, superoxide dismutase, glucose-6-phosphate dehydrogenase, and glutathione S-transferase activities were not affected by exposure to CYN. Concentration-dependent decrease of glutathione reductase activity occurred for most CYN-exposed groups, whereas non-protein thiol content increased only for the highest CYN concentration. Lipid peroxidation, protein carbonylation, and DNA damage levels were not altered, but reactive oxygen species levels increased in the cells exposed to the highest concentration of CYN. Cell viability decreased in all the groups exposed to CYN. Thus, CYN may cause a slight change in redox balance, but it is not the main cause of cell death in H. malabaricus hepatocytes.