João Sarkis Yunes

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Determination of total antioxidant capacity, instead of the measurements of limited number of antioxidants, is very important for the understanding of how antioxidants interact with reactive oxygen species (ROS). Several techniques already exist with this propose, although some of them are extremely time-consuming. A new methodology is proposed, based on(More)
[D-Leu1]Microcystin-LR was identified as the most abundant microcystin from a laboratory strain of the cyanobacterium Microcystis sp. isolated from a hepatotoxic Microcystis bloom from brackish waters in the Patos Lagoon estuary, southern Brazil. Toxicity of [D-Leu1]microcystin-LR, according to bioassay and protein phosphatase inhibition assay, was similar(More)
Harmful Trichodesmium blooms have been reported on the continental slope of the southwestern South Atlantic Ocean; we sampled six such blooms. The highest saxitoxin concentration was observed where the number of colonies was proportionally greater relative to the total density of trichomes. Trichodesmium blooms are harmful to shrimp larvae and may lead to(More)
Microcystins produced by cyanobacteria are potent inhibitors of some protein phosphatases, but recent evidence also indicates its potential to generate oxidative stress. In the present study, the effects of microcystin raw extracts (Mic; 0.01 and 20microg/L) and purified okadaic acid (OA; 0.01 and 10microg/L) on short- and long-term memory alteration and(More)
Antioxidant responses and oxidative stress were evaluated in the hepatopancreas of the estuarine crab Chasmagnathus granulatus (Decapoda, Brachyura) after oral microcystin administration. Responses were evaluated through antioxidant enzyme activities (catalase-(CAT), superoxide dismutase, glutathione-S-transferase- (GST)). Nonproteic sulfhydril (NP-SH)(More)
Multidrug resistance (MDR) is an obstacle in cancer treatment. An understanding of how tumoral cells react to oxidants can help us elucidate the cellular mechanism involved in resistance. Microcystins are cyanobacteria hepatotoxins known to generate oxidative stress. The aim of this study was to compare the sensitivity to microcystins of human tumoral cell(More)
Microcystins are hepatotoxins suspected to generate oxidative stress. This mechanism was evaluated in gills of the estuarine crab Chasmagnathus granulatus (Decapoda, Brachyura). Adult male crabs were fed ground beef with or without vitamin E (600 mg/kg). Microcystin (1.21 microg/kg) was daily administered through forced ingestion, for 7 days. After(More)
Microcystins are usually the predominant cyanotoxins present in both drinking and recreational waters after cyanobacterial blooms. Their classic toxic effect is hepatotoxicity through inhibition of serine/threonine phosphatases. However, recent studies also reported oxidative stress generation and disruption of ion regulation in aquatic organisms after(More)
The effects of aqueous extracts from a cyanobacteria species, Anabaena spiroides, on fish (Odontesthes argentinensis), crab (Callinectes sapidus), and purified eel acetylcholinesterase (AChE) activity were studied. In vitro concentrations of A. spiroides aqueous extract that inhibited 50% of enzyme activity (IC50) were 23.0, 17.2, and 45.0 mg/L of(More)
We evaluated the effects of aqueous extracts of the cyanobacterium-producing microcystin (MC), Microcystis aeruginosa (strain RST9501), on detoxification capacity and glutathione (GSH) synthesis in liver, brain, gill, and muscle-as well as apoptotic protease (calpain) activity in liver and brain-in the common carp Cyprinus carpio (Teleostei: Cyprinidae).(More)