Determinants of species susceptibility to oxidative stress: A comparison of channel catfish and brown bullhead

Xenobiotic-mediated productions of reactive oxygen species, via enzymemediated redox cycling, have been implicated in a variety of toxicological phenomena including lipid peroxidation, enzyme inactivation and oxidative DNA damage leading to cancer. A comparison was undertaken of two benthic freshwater fish species that appear to differ markedly in their susceptibility to chemical carcinogenesis—the channel catfish (Ictalurus punctatus) and the more cancer-prone brown bullhead (Ameriurus nebulosus)-in terms of basic biochemical characteristics related to oxidative stress. This has included analysis of microsomal redox cycling of model xenobiotics (e.g. menadione) as well as antioxidant and other detoxifying enzymes in hepatic tissue of the two species. In addition, endpoints of oxidative stress, such as altered glutathione status and oxidative DNA damage, were examined. These studies have revealed numerous qualitative and quantitative differences between the two species both in terms of basal enzyme activities and in species response to model prooxidants. For example, bullhead appear to possess a greater capacity for microsomal redox cycling of xenobiotics, but have glutathione-dependent defense systems less able to withstand oxidative challenge. These and other interspecific differences have allowed for an improved understanding of the basic mechanisms which may underly species susceptibility to oxidative stress and critical manifestations such as cancer.     

Short-time induction of oxidative stress in hepatocytes of the European flounder (Platichthys flesus).

Oxidative stress induced by xenobiotic compounds has been studied using primary hepatocytes of juvenile European flounder (Platichthys flesus L.) caught in a low polluted area of the German Bight, Tiefe Rinne (Landwüst et al., 1996.). Cells were exposed to known oxidative stressors such as hydrogen peroxide and benzo[a]pyrene (B[a]p) in various concentrations (50 and 100 microM) up to 6 days. Cell mortality was determined using fluorescent ethidium homodimer-1 and calcein AM. Oxidative stress response was measured by image analysis using dihydrorhodamine 123, which is converted to fluorescent rhodamine 123 in the presence of intracellular ROS. Oxyradical formation was initiated already after 2 h of exposure to low concentrations of B[a]p and hydrogen peroxide. Probably due to a membrane stabilising effect of the serum factors the addition of fetal bovine serum to the culture medium had a protecting influence on the hepatocytes and resulted in (1) an increased cell viability and (2) reduced formation of intracellular ROS during exposure. In conclusion, the assay is a sensitive tool for testing the potential of various xenobiotics to induce oxidative stress in living hepatocytes.     

Nrf2参与水生动物氧化应激调控的研究进展

环境变化会诱导机体活性氧(reactive oxygen species, ROS)水平升高,从而产生氧化应激。氧化应激对所有生物的生存、生长、发育和进化都具有深远的影响。核因子E2相关因子2 (nuclear factor erythroid 2 related factor 2, Nrf2)被公认为细胞氧化应激调控的主导者,与伴侣蛋白Kelch样环氧氯丙烷相关蛋白1 (kelch-like ECH-associated protein 1, Keap1)一起控制数百个解毒酶和抗氧化蛋白编码基因的表达。近年来, Nrf2在水生动物中逐渐获得重视,并在一些模式鱼类如斑马鱼、鲤鱼及其他一些鱼类和水生无脊椎动物中得到研究。介绍了Nrf2的结构以及调控机制,回顾了近年来水生动物Nrf2通路参与氧化应激调控所取得的进展。研究表明, Nrf2在水生动物中广泛存在,在非生物(金属、有机污染物、无机盐、药物及微塑料等)、生物(细菌、病毒、有毒藻类)以及生境变化(冰融、盐胁迫)诱导的氧化应激调控中发挥重要作用。Nrf2一经激活入核,在小Maf蛋白的协助下与抗氧化反应元件(antioxidant-responseelement,ARE)结合,启动一系列ARE驱动基因的表达,并和孕烷X受体(pregnane X receptor, Pxr)、丝裂原活化蛋白激酶(mitogen-activated protein kinase, MAPK)以及芳烃受体(arylhydrocarbonreceptor,AhR)等细胞通路协同作用参与一系列生理过程。Nrf2在水生动物响应环境变化过程中发挥重要的细胞保护机制,有望发展成为抗逆育种潜在的基因靶点。     

Oxidative damage in rainbow trout caged in a polluted river

Sewage treatment works (STWs) are a common source of chemicals entering into the aquatic environment. In order to assess effects of these effluents on oxidative stress parameters in aquatic organisms, we caged rainbow trout at five sites: upstream, near an STW effluent, and three sites downstream in the river Viskan in western Sweden for 14 days during autumn, 2006. We then measured protein carbonyls in plasma as well as 20S proteosome activity and lipid peroxidation products, i.e. MDA and 4-HNE, in liver samples. Levels of both lipid and protein oxidative damage products were elevated in fish caged near the STW effluent while 20S activity showed no differences. This argues that complex mixtures of chemicals entering into the aquatic environment do have deleterious effects on fish. Additionally, oxidative stress parameters can serve as a biomarker in aquatic organisms.     

北极细菌Pseudoalteromonas sp.A2对H2O2胁迫的转录组分析

海水中的高溶解氧浓度、低温和UV辐射导致了氧胁迫是北极海洋细菌面临的主要胁迫因素之一。本文对北极细菌Pseudoalteromonas sp.A2对H₂O₂导致的氧胁迫的应答特征进行了转录组测序和基因差异表达的比较分析,以期发现与氧胁迫相关的关键功能基因。研究表明,与对照组相比,1 mmol/L的H₂O₂可导致菌株A2转录组的很大变化,包括109个基因的显著上调与174个基因的显著下调。COG分析表明,在功能已知的基因中,与转录后修饰、蛋白质转换和分子伴侣相关的基因大部分显著上调,而与氨基酸运输和代谢等相关基因则大部分显著下调。值得指出的是,有18个与鞭毛相关的基因和4个与热激蛋白相关的基因显著上调;同时,有9个与细胞色素和细胞色素氧化酶相关的基因和5个与TonB依赖受体相关的基因显著下调。在GO分析表明具有抗氧化活性的18个基因中,只有1个基因的表达显著上调,而有2个显著下调。简言之,RNA-Seq表明,除了传统的抗氧化基因和应激蛋白外,鞭毛相关基因和功能未知基因在菌株Pseudoalteromonas sp.A2的氧胁迫适应性中起着重要作用。该转录组分析和氧胁迫相关基因的发现有助于了解北极细菌的氧胁迫适应机制。     

Antioxidant response of the seagrass Posidonia oceanica when epiphytized by the invasive macroalgae Lophocladia lallemandii

The aim was to evaluate the antioxidant defences and the occurrence of oxidative damage in Posidonia oceanica under a stress situation due to the epiphytism of the invasive macroalgae Lophocladia lallemandii. P. oceanica leaves were collected in the absence (control station) and in the presence of the epiphytic algae L. lallemandii and the antioxidant enzyme activities, markers of oxidative damage, and hydrogen peroxide production were determined. Antioxidant enzyme - catalase, glutathione peroxidase and superoxide dismutase - activities were significantly higher in Posidonia epiphytized by L. lallemandii. Malondialdehyde, protein carbonyl derivates, and glutathione levels were also higher in L. lallemandii epiphytized P. oceanica leaves compared to control samples. The production of hydrogen peroxide was also significantly increased when Posidonia was epiphytized by L. lallemandii. The invasion of P. oceanica meadows by L. lallemandii appeared to induce oxidative stress in the seagrass as evidenced by increased levels of oxidative stress markers and antioxidant defences.     

Effect of seasonality on oxidative stress responses and metal accumulation in soft tissues of Aulacomya atra,a mussel from the South Atlantic Patagonian coast

This study investigated the effects of pollution and its interaction with temperature on the oxidative status of the ribbed mussel Aulacomya atra in the southern Atlantic Patagonian coast. Animals were collected from four sites with different degree and type of human activity impact, during the summer and winter of 2011. Seawater chromium, copper, manganese, nickel and zinc concentrations were measured, as well as metal accumulation, lipid peroxidation, protein oxidation, reduced glutathione levels, and enzymatic activities of superoxide dismutase and glutathione-S-transferase in gills and digestive glands.Metal bioaccumulation and oxidative stress responses in both tissues were generally higher in mussels from harbor areas. Water temperature had a remarkable effect on gill SOD activity and protein oxidation during winter in mussels from all locations.Methodologically, we conclude that measuring both metal bioaccumulation and oxidative stress responses allowed for a more accurate assessment of the biological effects of metal present in seawater.     

An in vitro procedure for evaluation of early stage oxidative stress in an established fish cell line applied to investigation of PHAH and pesticide toxicity

Oxidative stress by increased production of reactive oxygen species such as superoxide has been implicated in the toxicity of PCB's and non-target toxicity of many pesticides. We report the development of a microplate-based method for determination of early stage oxidative stress using an established cell line (EPC) from a skin tumour of carp Cyprinus carpio L. and 2',7'-dichlorodihydrofluorescein diacetate (H(2)-DCFDA) as a fluorescent probe for detection of reactive oxygen species (ROS) formation. Sublethal concentrations of the herbicide Paraquat, an established redox cycling agent and a crude PCB mixture, Arochlor 1254 elicited a linear increase in ROS formation over 2 h exposure which was some 45- and 10-fold higher, respectively, than attributable to basal respiration, confirming the suitability and response of the test system. Whilst in vivo studies in mammals have implicated early stage oxidative stress in the toxicity of pesticides, we did not observe an increase in ROS production after exposure of EPC cells to sublethal concentrations of Carbaryl, 2,4-DDT, Lindane or Malathion implying that this is not the causative mechanism of acute toxicity in this fish cell line. The apparent involvement of oxidative stress in their mammalian toxicity may therefore be an indirect effect or dependent upon compound metabolism.     

Gold nanoparticles and oxidative stress in Mytilus edulis

Little is known about potential environmental impact of nanoparticles. Gold nanoparticles can cause unexpected biological responses. Here, Mytilus edulis were exposed (24h) to gold-citrate nanoparticles (GNP), menadione and both compounds simultaneously (GNP/menadione). Protein ubiquitination and carbonylation were determined in gill, mantle and digestive gland, along with traditional oxidative stress biomarkers; catalase activity and neutral red retention time assay (haemolymph). 2DE gels were performed on gill proteins (menadione; GNP/menadione). Our results reveal that GNP may induce oxidative stress.     

Oxygen radical formation in anoxic transgression and anoxia-reoxygenation: Foe or phantom? Experiments with a hypoxia tolerant bivalve

Intertidal blue mussels, Mytilus edulis, experience hypoxia reoxygenation during tidal emersion and resubmersion cycles, and this is often suggested to represent a major stress for the animals, especially for their respiratory tissues, the gills. We exposed mussels to experimental short and prolonged anoxia and subsequent reoxygenation and analyzed the respiratory response in excised gill tissue and the effects of treatment on reactive oxygen species (mainly ROS: superoxide anion, O₂^·− and hydrogen peroxide, H₂O₂), formation using live imaging techniques and confocal microscopy. Our aim was to understand if this “natural stress” would indeed produce oxidative damage and whether antioxidant defenses are induced under anoxia, to prevent oxidative damage during reoxygenation. Exposure to declining pO₂ in the respiration chamber caused an increase of gill metabolic rate between 21 and 10 kPa, a pO₂ range in which whole animal respiration is reported to be oxyregulating. Exposure of the animals to severe anoxia caused an onset of anaerobiosis (succinate accumulation) and shifted high and low critical p_c values (p_c1: onset of oxyregulation in gills, p_c2: switch from oxyregulation to oxyconformity) to higher pO₂. Concentrations of both ROS decreased strongly during anoxic exposure of the mussels and increased upon reoxygenation. This ROS burst induced lipid peroxidation in the mantle, but neither were protein carbonyl levels increased (oxidative damage in the protein fraction), nor did the tissue glutathione concentration change in the gills. Further, analysis of apoptosis markers indicated no induction of cell death in the gills. To our knowledge, this is the first paper that directly measures ROS formation during anoxia reoxygenation in mussels. We conclude that hypoxia tolerant intertidal mussels do not suffer major oxidative stress in gill and mantle tissues under these experimental conditions.     

菲律宾蛤仔(Venerupis philippinarum)Rho型GST和微粒体型GST的序列分析及表达特征研究

谷胱甘肽硫转移酶是一类在细胞解毒和抗氧化过程中发挥重要作用的超家族酶系。采用cDNA末端快速扩增技术,从菲律宾蛤仔中克隆获得Rho型GST和微粒体型GST基因的全长序列(分别命名为VpGSTR和VpGSTMi)。序列分析显示,VpGSTR和VpGSTMi的cDNA全长分别为942bp和661bp,编码234和149个氨基酸。系统分析结果表明,菲律宾蛤仔GSTR与GSTMi在进化树上的位置与其分类所处的位置一致。荧光定量PCR结果发现,VpGSTR和VpGSTMi广泛分布于所检测组织中,且在肝胰腺组织中表达量最高。在鳗弧菌侵染后,VpGSTR和VpGSTMi基因表达量在24h内均表现出明显的上升趋势。上述结果表明,VpGSTR和VpGSTMi可能在菲律宾蛤仔抵御细菌侵染导致的氧化应激中发挥重要功能。     

不同粒径TiO_2颗粒对海洋微藻的毒性效应

本实验以新月菱形藻为受试生物,研究了低浓度不同粒径TiO2颗粒(21nm、60nm和400nm)对海洋微藻生长、抗氧化酶活性(超氧化物歧化酶SOD、过氧化氢酶CAT和过氧化物酶POD)、脂质过氧化产物(MDA)含量的影响,并测定了相应的活性氧自由基(ROS)的含量,初步探讨了TiO2颗粒对海洋微藻的作用机制。结果表明,1mg/L TiO2颗粒对新月菱形藻生长的抑制作用随着粒径的减小而逐渐增强,第48h、72h、96h呈现出显著的纳米效应。TiO2颗粒可以诱导藻细胞内ROS的含量增加,对藻细胞产生氧化胁迫,新月菱形藻的抗氧化酶活性发生应激响应,以清除过量的ROS,但剩余的ROS对藻细胞产生氧化损伤,导致MDA含量升高,并且纳米级TiO2颗粒对新月菱形藻的氧化损伤大于微米级颗粒。在不同粒径TiO2颗粒的胁迫下,藻细胞SOD和CAT活性的响应也存在差异。本研究将为开展人工纳米材料对海洋生态系统影响的潜在风险评估提供科学依据。     

Effects of nanoparticles in Mytilus edulis gills and hepatopancreas - a new threat to marine life?

Every day new extraordinary properties of nanoparticles (a billionth of a meter) are discovered and worldwide millions are invested into nanotechnology and nanomaterials. Risks to marine organisms are still not fully understood and biomarkers to detect health effects are not implemented, yet. We used the filter feeding blue mussel as a model to analyse uptake and effects of nanoparticles from glass wool, a new absorbent material suggested for use in floating oil spill barriers. In both, gills and hepatopancreas we analysed uptake of nanomaterials by transmission electronmicroscopy (TEM) in unstained ultrathin sections over a period of up to 16 days. Lysosomal stability and lipofuscin content as general indicators of cellular pathology and oxidative stress were also measured. As portals of uptake, diffusion and endocytosis were identified resulting in nanoparticle accumulation in endocytotic vesicles, lysosomes, mitochondria and nuclei. Dramatic decrease of lysosomal membrane stability occurred after 12h of exposure. Lysosomal damage was followed by excessive lipofuscin accumulation indicative of severe oxidative stress. Increased phagocytosis by granulocytes, autophagy and finally apoptosis of epithelial cells of gills and primary and secondary digestive tubules epithelial cells indicated progressive cell death. These pathological responses are regarded as general indices of toxic cell injury and oxidative stress. By the combinational use of biomakers with the ultrastructural localisation of nanoparticle deposition, final evidence of cause-effect relationships is delivered.     

Tissue-specific changes in OGG1 and SOD mRNA expression caused by NaOCl exposure in black seabream (<Emphasis Type="Italic">Acanthopagrus schlegelii</Emphasis>)

The DNA-damage defense mechanism was studied in black seabreams after oxidative stress caused by exposure to sodium hypochlorite (NaOCl). Liver, muscle, and brain tissues were obtained after different NaOCl-exposure times (0, 24, 48, 72, and 96 h) and concentrations (0.5, 1, 1.5, 2, and 3 mg/L), after which oxoguanine glycosylase (OGG1) and superoxide dismutase (SOD) mRNA-expression levels were analyzed. At all NaOCl concentrations tested, liver OGG1 expression increased to a maximum in a time-dependent manner after NaOCl exposure and then decreased. In muscles, OGG1 expression increased over time following exposure to a low concentration of NaOCl (0.5, 1, and 1.5 mg/L), whereas it showed a mixed pattern (both increases and decreases observed) in the high-concentration groups (2 and 3 mg/L). SOD mRNA expression increased over time, both in the liver and muscles. In the brain, both OGG1 and SOD mRNA expression levels were highest after exposure to the lowest NaOCl concentration (0.5 mg/L), whereas basal levels were maintained over time at higher concentrations. These results indicate that OGG1 and SOD provide resistance to oxidative stress in black seabreams. In addition, continuous exposure to oxidative stress can suppress enzyme expression, suggesting a risk for long-term exposure to NaOCl.     

军曹鱼（Rachycentron canadum）幼鱼对环境低氧胁迫氧化应激与能量利用指标的响应

本文探究环境低氧对军曹鱼(Rachycentron canadum)氧化应激和能量利用指标的影响，为军曹鱼的健康养殖提供参考依据。通过设置低氧胁迫–恢复实验，将军曹鱼幼鱼(平均体质量(220.67±20.73)g)在低氧((2.64±0.25)mg/L)胁迫3 h及复氧((6.34±0.15)mg/L)8 h、24 h和48 h后，测定其肝脏和肌肉组织的氧化应激与能量利用指标。结果显示，低氧胁迫后，肝脏中丙二醛（Malondialdehyde，MDA)、过氧化氢酶(Catalase，CAT)和谷胱甘肽还原酶(Glutathione Reductase，GR)活力均显著低于对照组(p<0.05)，乳酸脱氢酶(Lactate Dehydrogenase，LDH)活性显著高于对照组(p <0.05)；肌肉中MDA和脂质过氧化物(Lipid Peroxidase，LPO)活性均显著低于对照组(p<0.05)，超氧化物歧化酶(Superoxide Dismutase，SOD)和LDH活性均显著高于对照组(p<0.05)；肌糖原和肝糖原含量极显著低于对照组(p<0.01)。复氧过程中，肝脏和肌肉中MDA、LPO、SOD、CAT、谷胱甘肽过氧化物酶(Glutathione Peroxidase，GPx)和GR含量均出现不同程度的升高；肝糖原在复氧24 h后显著高于对照组(p<0.05)，复氧48 h后显著低于对照组(p<0.05)；肌糖原在复氧8 h、24 h和48 h后均显著低于对照组(p<0.05)。研究表明，低氧胁迫能够对军曹鱼幼鱼机体造成一定的氧化损伤，肝脏和肌肉组织的酶活力和能量供应发生变化；低氧胁迫后的再复氧环境，对机体造成更为强烈的氧化损伤，可通过自身生理调节逐渐恢复到正常水平。     

Seasonal variation of oxidative biomarkers in gills and digestive gland of green-lipped mussel Perna viridis from Arabian Sea

Investigations on seasonal variation in oxidative stress biomarkers were carried out on the natural population of green-lipped mussel Perna viridis collected from Bambolim beach area of Goa. Oxidative stress indices such as lipid peroxidation (LPX), hydrogen peroxide (H₂O₂), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione transferase (GST), glutathione reductase (GR), reduced glutathione (GSH) and ascorbic acid (ASA) were measured in gills and digestive gland of P. viridis during February, May, August and November. The present study reveals two important aspects regarding the antioxidant defence status of tissues of P. viridis. Firstly, antioxidant capacity of tissues of P. viridis exhibits seasonal variation. Secondly, various components of antioxidant capacity such as oxidative stress markers, levels of antioxidant enzymes and small antioxidant molecules vary differently in tissues with respect to different seasons. Although the oxidative stress status of gills and digestive gland of P. viridis expressed in terms of LPX and H₂O₂ was the lowest in February, its level was maximal in gills and digestive gland during May and November, respectively. While activities of SOD and GPX of tissues of P. viridis were found to be low in August, activities of CAT and GR were recorded to be low in February. GST activity in gills although remained high in February, in digestive gland elevated values were recorded in August and November. A seasonal variation in the levels of small antioxidant molecules was also noticed. Among non enzymatic antioxidants ASA content of tissues was maximal in May and August in comparison to February and November, but GSH remained high in November. It therefore appears that environmental factors may play a crucial role in regulating the oxidative stress capacity of tissues of P. viridis.     

不同长牡蛎群体对海水酸化的生理响应差异分析

海水酸化暴露可对海洋生物产生多层面的影响。本研究以潮间带野生与潮下带养殖长牡蛎(不同生境背景)的不同组织(鳃、外套膜及消化腺)为研究对象,分析在室内调控p CO2模拟海水酸化暴露条件下,其基础代谢活动、能量代谢以及氧化应激相关指标的变化情况。结果显示:海水酸化暴露后,两种长牡蛎(Crassostrea gigas)的基础代谢过程均受到了一定抑制作用且受影响程度差异明显。潮间带野生与潮下带养殖长牡蛎的关键生理过程(能量代谢及氧化应激)对海水酸化暴露存在不同的响应变化,表明两种长牡蛎应对海水酸化的调节机制可能存在差异。依据PLS-DA分析结果显示,在所有生理指标中,对样本的差异贡献较高(VIP值1)的指标为:SDH、AST、ATPase、ATP含量、糖原含量、CAT、GST及SOD,表明海水酸化暴露后,在两种长牡蛎的3种组织中上述指标的响应变化程度更大。综合评价分析多个生理指标的整体变化揭示:在海水酸化暴露条件下,潮间带野生长牡蛎比潮下带养殖长牡蛎对海水酸化的生理响应更为剧烈;相比于鳃及消化腺组织,长牡蛎外套膜组织可能受影响更大。     

The effect of long-term depuration on levels of oxidative stress biomarkers in mullets (Mugil cephalus) chronically exposed to contaminants

The present study aimed to obtain additional data on the effect of long-term depuration on the levels of oxidative stress biomarkers, and to clarify the role of mullets for monitoring pollution in River Douro estuary. Mullets chronically exposed to a mixture of contaminants in Douro estuary were captured in Spring of 2001, 2002 and 2003. The activities of antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX); and oxidative damages in lipids (lipid peroxidation) and in proteins (protein carbonyl content) were assessed at capture day and after transfer to unpolluted seawater for 1, 4 and 8 months. An overall decrease in the activities of the antioxidant enzymes was detected, except for the GPX after 4 months depuration. CAT activity exhibited the more significant decrease at the end of the long-term depuration. The decrease in SOD activity after 1 month of depuration was then maintained during the remaining depuration period. Regarding oxidative damages, a decrease in lipid peroxidation as well as the content of oxidised proteins was observed during depuration. Indeed, at capture the activities of antioxidant defences were higher as a result of the formation of reactive oxygen species (ROS) from the metabolism of pollutants. The oxidative damaged molecules were repaired or degraded during the depuration period, supporting the use of such damages as indicators of exposure to pro-oxidant pollutants.     

Protein carbonyls and antioxidant defenses in corkwing wrasse (Symphodus melops) from a heavy metal polluted and a PAH polluted site

The use of fish in environmental monitoring has become increasingly important in recent years as anthropogenic substances, many of which function as prooxidants, are accumulating in aquatic environments. We have measured a battery of antioxidant defenses as a measure of oxidative status, as well as protein carbonylation as a measure of oxidative damage, in corkwing wrasse (Symphodus melops) captured near a disused copper mine, where water and sediment are contaminated with heavy metals, and an aluminum smelter, a site contaminated with PAHs. Results were compared to two different reference sites. Fish at the heavy metal site had lower glucose-6-phosphate dehydrogenase activity and elevated protein carbonyls (1.8 times) compared to fish from the reference site. At the PAH site, EROD was increased 2-fold, while total glutathione and methemoglobin reductase concentration, were decreased. No differences were seen in protein carbonyl levels at the PAH site. Measures of both antioxidant defenses and oxidative damage should be used when assessing effects of xenobiotics on oxidative stress in fish species.     

Microcystin-induced oxidative stress in Laeonereis acuta (Polychaeta, Nereididae)

Oxidative stress induced by microcystins was evaluated in an estuarine worm, Laeonereis acuta (Nereididae). Ten organisms were exposed to lyophilized cells of a toxic Microcystisaeruginosa strain RST9501 ( approximately 2 microg/mL microcystins, MC); 10 were exposed to lyophilized cells of a nontoxic Aphanotece sp. strain RSMan92 and 10 were maintained without cyanobacterial cells. Exposure time was 48 h. The enzymatic antioxidant defenses, as well as the oxidative damage, were analyzed. Toxic and nontoxic cyanobacteria lowered catalase activity with no changes in glutathione reductase and glutathione-S-transferase activities. This may have led to toxin intracellular accumulation, which should favor oxidative stress generation, observed by the high lipid peroxide and DNA-protein crosslink levels in the group exposed to MC.