Mauro Eugênio Medina Nunes

Is the lobster cockroach Nauphoeta cinerea a valuable model for evaluating mercury induced oxidative stress

Organic and inorganic forms of mercury are highly neurotoxic environmental contaminants. The exact mechanisms involved in mercury neurotoxicity are still unclear. Oxidative stress appears to play central role in this process. In this study, we aimed to validate an insect-based model for the investigation of oxidative stress during mercury poisoning of lobster cockroach Nauphoeta cinerea. The advantages of using insects in basic toxicological studies include the easier handling, rapid proliferation/growing and absence of ethical issues, comparing to rodent-based models. Insects received solutions of HgCl2 (10, 20 and 40mgL(-1) in drinking water) for 7d. 24h after mercury exposure, animals were euthanized and head tissue samples were prepared for oxidative stress related biochemical determinations. Mercury exposure caused a concentration dependent decrease in survival rate. Cholinesterase activity was unchanged. Catalase activity was substantially impaired after mercury treatment 40mgL(-1). Likewise, GST had a significant decrease, comparing to control. Peroxidase and thioredoxin reductase activity was inhibited at concentrations of 20mgL(-1) and 40mgL(-1) comparing to control. These results were accompanied by decreased GSH levels and increased hydroperoxide and TBARS formation. In conclusion, our results show that mercuric compounds are able to induce oxidative stress signs in insect by modulating survival rate as well as inducing impairments on important antioxidant systems. In addition, our data demonstrates for the first time that Nauphoeta cinerea represents an interesting animal model to investigate mercury toxicity and indicates that the GSH and thioredoxin antioxidant systems plays central role in Hg induced toxicity in insects.

Eugenia uniflora leaves essential oil induces toxicity in Drosophila melanogaster: involvement of oxidative stress mechanisms

Eugenia uniflora L. (Myrtaceae family), also known as “pitanga”, is a tree species widely used in popular medicine. Despite the well documented beneficial effects of the extracts and essential oils from this plant, little is known about its toxicity. We performed a phytochemical fingerprinting and evaluated the toxicity induced by the Eugenia uniflora leaves essential oil in a Drosophila melanogaster model. In order to understand the biochemical mechanisms involved in E. uniflora essential oil toxicity, changes in the Nrf2 signaling as well as the hallmarks of oxidative stress were measured. The exposure of adult flies to the essential oil via a fumigant method resulted in increased mortality and locomotor deficits. In parallel, an oxidative stress response signaling, evidenced by changes in ROS production, lipid peroxidation, alterations in the activity of antioxidant enzymes and expression of Nrf2 protein targets occurred. In the light of our findings, attention is drawn to the indiscriminate use of this plant for medicinal purposes. In addition, a potential bio-insecticidal activity of Eugenia uniflora volatile compounds is suggested, a fact that needs to be further explored.

Oxidative stress markers in fish (Astyanax sp. and Danio rerio) exposed to urban and agricultural effluents in the Brazilian Pampa biome.

Aquatic ecosystems are under constant risk due to industrial, agricultural, and urban activities, compromising water quality and preservation of aquatic biota. The assessment of toxicological impacts caused by pollutants to aquatic environment using biomarker measurements in fish can provide reliable data to estimate sublethal effects posed by chemicals in contaminated areas. In this study, fish (Astyanax sp. and Danio rerio) exposed to agricultural and urban effluents at the Vacacaí River, Brazil, were tested for potential signs of aquatic contamination. This river comprehends one of the main watercourses of the Brazilian Pampa, a biome with a large biodiversity that has been neglected in terms of environmental and social-economic development. Sites S1 and S2 were chosen by their proximity to crops and wastewater discharge points, while reference site was located upstream of S1 and S2, in an apparently non-degraded area. Fish muscle and brain tissues were processed for determination of acetylcholinesterase as well as oxidative stress-related biomarkers. The results showed signs of environmental contamination, hallmarked by significant changes in cholinesterase activity, expression of metallothionein, antioxidant enzymes, glutathione levels, and activation of antioxidant/cell stress response signaling pathways in fish exposed to contaminated sites when compared to reference. Based on these results, it is evidenced that urban and agricultural activities are posing risk to the environmental quality of water resources at the studied area. It is also demonstrated that cell stress biomarkers may serve as important tools for biomonitoring and development of risk assessment protocols in the Pampa biome.

Fumigant activity of the Psidium guajava var. pomifera (Myrtaceae) essential oil in Drosophila melanogaster by means of oxidative stress.

The guava fruit, Psidium guajava var. pomifera (Myrtaceae family), is a native plant from South America. Its leaves and fruits are widely used in popular medicine in tropical and subtropical countries. Drosophila melanogaster has been used as one of the main model organisms in genetic studies since the 1900s. The extensive knowledge about this species makes it one of the most suitable organisms to study many aspects of toxic compound effects. Due to the lack of studies on the effects of the bioactive compounds present in the P. guajava var. pomifera essential oil, we performed a phytochemical characterization by CG-MS and evaluated the toxicity induced by the essential oil in the D. melanogaster insect model. In order to understand the biochemical mechanisms of toxicity, changes on the Nrf2 signaling as well as hallmarks of oxidative stress response were followed in the exposed flies. Our results showed that exposure of insects to the P. guajava oil increased mortality and locomotor deficits in parallel with an oxidative stress response signaling. Therefore, it suggested a bioinsecticidal activity for P. guajava volatile compounds by means of oxidative stress. Further studies are ongoing to identify which oil compounds are responsible for such effect.

Assessment of Water Pollution Signs in the Brazilian Pampa Biome Using Stress Biomarkers in Fish (Astyanax sp.)

Located in southern Brazil, the Pampa biome has been under constant threat due to improper management of human effluents and use of pesticides. These contaminants accumulate mainly in water resources resulting in chronic poisoning of aquatic biota. Up to date, no studies on the assessment of environmental quality in the Brazilian portion of Pampa biome have been undertaken. Thereby, our main goal in this study was to investigate the ecotoxicological risks caused by human activity in the Santa Maria River, a major water course in the Brazilian Pampa biome. Brain and muscle tissues were used for determining oxidative stress and cholinesterase biomarkers in fish (Astyanax sp.) exposed to urban and agricultural effluents. A substantial decrease in fish muscle acetylcholinesterase activity was observed in exposed animals, compared to controls (kept under laboratory conditions). In parallel, increased lipid peroxidation and significant changes in stress-responsive antioxidant enzymes (GST, CAT, GPx, and TrxR) were detected. In the fish brain, a significant increase in GST activity is reported. In conclusion, our results showed significant changes in biomarkers of water contamination in Astyanax captured in Santa Maria River, pointing to important levels of water pollution in the region and validating the use of Astyanax in biomonitoring programs within the Pampa biome borders.

N -acetylcysteine inhibits Mancozeb-induced impairments to the normal development of zebrafish embryos

Mancozeb (MZ), a manganese/zinc-containing ethylene-bis-dithiocarbamate (EBCD) fungicide has been claimed to present low acute toxicity and short environmental persistence, however, its effects on embryogenesis in non-target organisms is unclear. Here, we used zebrafish embryos (5 hpf) to assess the potential embryotoxic effects induced by MZ (up to 72 hpf) as well as the role of reactive oxygen species (ROS) in this process by pre-treatment with a classical antioxidant (N-acetylcysteine, NAC). Markers of reactive oxygen species production (ROS), glutathione (GSH) levels and glutathione S-transferase (GST) activity were measured along with genotoxicity (comet assay), cell death (Acridine Orange) and behavioral parameters (spontaneous movement, touch stimulation and swimming response), in order to determine potential mechanisms of embryotoxicity. According to results, MZ was able to induce morphological abnormalities such as body axis distortion, DNA damage, cell death, increased ROS generation and changes in behavioral endpoints during zebrafish development. All these toxic effects were inhibited by the pre-treatment with NAC indicating a key role of redox unbalance during MZ-induced embryotoxicity. At least in our knowledge, this is the first report on the deleterious effect of MZ to the normal embryogenesis of zebrafish. In addition, the importance of ROS generation during this pathophysiological condition was highlighted.