Neurotoxicity induced by microcystins and cylindrospermopsin: A review.

Microcystins (MCs) and cylindrospermopsin (CYN) are among the most frequent toxins produced by cyanobacteria. These toxic secondary metabolites are classified as hepatotoxins and cytotoxin, respectively. Furthermore, both may present the ability to induce damage to the nervous system. In this sense, there are many studies manifesting the potential of MCs to cause neurotoxicity both in vitro and in vivo, due to their probable capacity to cross the blood-brain-barrier through organic anion transporting polypeptides. Moreover, the presence of MCs has been detected in brain of several experimental models. Among the neurological effects, histopathological brain changes, deregulation of biochemical parameters in brain (production of oxidative stress and inhibition of protein phosphatases) and behavioral alterations have been described. It is noteworthy that minority variants such as MC-LF and -LW have demonstrated to exert higher neurotoxic effects compared to the most studied congener, MC-LR. By contrast, the available studies concerning CYN-neurotoxic effects are very scarce, mostly showing inflammation and apoptosis in neural murine cell lines, oxidative stress, and alteration of the acetylcholinesterase activity in vivo. However, more studies are required in order to clarify the neurotoxic potential of both toxins, as well as their possible contribution to neurodegenerative diseases.

Effects of depuration on oxidative biomarkers in tilapia (Oreochromis niloticus) after subchronic exposure to cyanobacterium producing cylindrospermopsin.

Cylindrospermopsin (CYN) is a cytotoxic polyketide-derived alkaloid produced by several freshwater cyanobacterial species. It is now considered the second most studied cyanotoxin worldwide. Among the toxic mechanisms suggested for CYN pathogenicity are inhibition of protein and glutathione synthesis, genotoxicity by DNA fragmentation, and oxidative stress. The study of depuration of cyanobacterial toxins by aquatic organisms, particularly by fish, is important for fish economy and public health, but in the case of CYN is practically nonexistent. In this work, we investigated the efficiency of two distinct depuration periods, 3 or 7d, in a clean environment, as a mean of restoring the levels of several oxidative stress biomarkers in tilapia (Oreochromis niloticus) subchronically exposed to CYN by immersion in an Aphanizomenon ovalisporum culture (by adding 10 µg CYN/L every two days during 14 d). Lipid peroxidation (LPO) and DNA oxidation returned to normal values after 7d of depuration, whereas the time needed for restoring of the oxidatively damaged proteins was longer. Superoxide dismutase (SOD) and gamma-glutamyl-cysteine-synthetase (γ-GCS) activities recovered after just 3d of depuration, while catalase (CAT) activity needed up to 7d to return to control values. Ratio of reduced glutathione to oxidized glutathione (GSH/GSSG) returned to control levels after 7d of depuration in both organs. These results validate the depuration process as a very effective practice for detoxification in fish contaminated with these toxins.

Alteración de biomarcadores de estrés oxidativo en Tilapia (Oreochromis niloticus) expuesta a dosis repetidas de Cilindrospermopsina por diferentes vías de exposición / Alteration of oxidative stress biomarkers in Tilapia (Oreochromis niloticus) exposed to repeated doses of Cylindrospermopsin by different exposure routes

Las cianobacterias tienen capacidad de sintetizar una gran variedad de metabolitos secundarios, identificándose entre ellos la Cilindrospermopsina (CYN), toxina principalmente citotóxica. En general, la exposición a esta molécula se caracteriza por una toxicidad tardía sobre múltiples órganos, principalmente hígado y riñón. Se han sugerido varios mecanismos de acción tóxica: inhibición de la síntesis de proteínas y de glutatión y más recientemente el estrés oxidativo. El objetivo del presente estudio fue investigar la influencia del tiempo y de la vía de exposición sobre la inducción de estrés oxidativo como mecanismo de acción tóxica asociado a la patogenicidad de CYN, en pescados de consumo público, Tilapias (Oreochromis niloticus), expuestos a dosis repetidas de la toxina mediante inmersión en biomasa de Aphanizomenon ovalisporum o por vía oral con células liofilizadas de A. ovalisporum durante tres períodos de 7, 14 y 21 días. Los biomarcadores ensayados en hígado y riñón de los peces fueron: peroxidación lipídica, oxidación de proteínas, oxidación del ADN, las actividades glutatión-Stransferasa, glutatión peroxidasa, superóxido dismutasa, catalasa γ- glutamilcisteín sintetasa, y la relación glutatión reducido y oxidado (GSH/GSSG). Se observó una inducción de estrés oxidativo en hígado y riñón de las tilapias expuestas a dosis repetidas de CYN, manifestado por una alteración en los niveles de peroxidación lipídica, oxidación de proteínas y de ADN, así como en las actividades de las enzimas antioxidantes estudiadas y en los niveles de glutation a lo largo de los tres períodos de exposición. En general, las alteraciones más significativas se observaron en tilapias expuestas a CYN por inmersión en biomasa de A. ovalisporum durante un periodo de 21 días, demostrándose así que estos efectos se ven influenciados por la vía y el tiempo de exposición (AU)

Cyanobacteria are able to synthesize a large variety of secondary metabolites, including Cylindrospermopsin (CYN), a mainly cytotoxic toxin. In general, exposure to this molecule is characterized by late toxicity on multiple organs, mainly liver and kidney. Several mechanisms of action have been suggested; as inhibition of protein and glutathione synthesis and more recently oxidative stress. The aim of this study was to investigate the influence of time and route of exposure on the induction of oxidative stress as a mechanism of toxic action associated with CYN pathogenicity in public-consumed fish exposed to repeated doses of CYN by immersion, containing a culture of A. ovalisporum or orally with lyophilized cells of Aphanizomenon ovalisporum for three periods of exposure: 7, 14 and 21 days. Fish biomarkers tested in liver and kidney were: lipid peroxidation, protein oxidation, DNA oxidation, activities glutathione-Stransferase, glutathione peroxidase, superoxide dismutase, catalase, γ-glutamylcysteine synthetase, and glutathione reduced/glutathione oxidized ratio. An induction of oxidative stress was observed in liver and kidney of tilapia fishes exposed to repeated doses of CYN. Alterations in lipid peroxidation levels, protein and DNA oxidation process, as well as in the activity of the studied antioxidant enzymes and glutathione levels for all three periods of exposure tested, were observed. In general, the most significant changes were observed in tilapias exposed to CYN by immersion in a CYN-containing culture of A. ovalisporum over 21 days, thus demonstrates that these effects are influenced by the route and time of exposure (AU)

The protective role of l-carnitine against cylindrospermopsin-induced oxidative stress in tilapia (Oreochromis niloticus).

Cylindrospermopsin (CYN) is one of the most important cyanotoxins in terms of both human health and environmental quality and is produced by several different species of cyanobacteria, including Aphanizomenon ovalisporum. The principal mechanisms of action of CYN involve inhibition of protein and glutathione synthesis. In addition, CYN-mediated genotoxicity results from DNA fragmentation. The results of both in vivo and in vitro studies suggest that oxidative stress also plays a significant role in CYN pathogenesis in fish. We investigated the protective effects of l-carnitine (LC) pre-treatment on A. ovalisporum-induced oxidative stress in cells containing CYN and deoxy-CYN, or pure standard CYN, in tilapia (Oreochromis niloticus) that had been acutely exposed via oral administration. Various oxidative stress markers, including lipid peroxidation (LPO), protein oxidation, DNA oxidation, and the ratio of reduced glutathione to oxidised glutathione (GSH/GSSG), and the activities of NADPH oxidase, superoxide dismutase (SOD), catalase (CAT), and gamma-glutamyl-cysteine synthetase (γ-GCS), were evaluated in the livers and kidneys of fish in the absence and presence of 400 or 880mgLC/kgfish/day during a 21 day period prior to CYN-intoxication. The results of our study demonstrated for the first time the beneficial antioxidant effects of LC dietary supplementation on oxidative stress status in fish. No pro-oxidant effects were detected at any of the LC doses assayed, suggesting that LC is a chemoprotectant that reduces hepatic and renal oxidative stress and may be effective when used for the prophylaxis and treatment of CYN-related intoxication in fish.

Cyanobacterium producing cylindrospermopsin cause oxidative stress at environmentally relevant concentrations in sub-chronically exposed tilapia (Oreochromis niloticus).

Cylindrospermopsin (CYN) is a potent cyanobacterial cytotoxin produced by certain freshwater cyanobacteria. Structurally, it is an alkaloid with a tricyclic guanidine moiety combined with hydroxymethyluracil. It has proved to be a potent inhibitor of protein synthesis, and to deplete hepatic glutathione. Recently, some studies have shown that CYN produces changes in some oxidative stress biomarkers in fish acutely exposed to pure CYN by oral and intraperitoneal (i.p.) routes. In the present study tilapia (Oreochromis niloticus) were exposed by immersion to lyophilized Aphanizomenon ovalisporum cells added to the aquaria using two concentration levels, 10 or 100 µg CYN L(-1), during two different exposure times: 7 and 14 d. Fish were sacrificed and liver and kidney were extracted. The oxidative status of fish was evaluated by analyzing in both organs the following biomarkers: lipid peroxidation (LPO), protein oxidation, DNA oxidation, reduced-oxidized glutathione ratio (GSH/GSSG), and changes in the activity of Glutathione-S-transferase (GST), Glutathione Peroxidase (GPx), Superoxide dismutase (SOD), Catalase (CAT), and γ-Glutamyl-cysteine synthetase (GCS). In general, major changes were observed in tilapia treated with 100 µg CYN L(-1) after 14 d of exposure. However, some endpoints were altered at the lowest concentration assayed only after 7d of exposure, such as DNA oxidation and γ-GCS in kidney, and CAT and GSH/GSSG decrease in the liver and kidney. The kidney was the most affected organ. These findings confirm that the oxidative stress play a role in the pathogenicity induced by CYN in this fish species, and the results obtained could be useful for future ecotoxicological risks assessment studies, for the protection of fish and aquatic ecosystems. To our knowledge this is the first study dealing with the oxidative stress changes induced by cyanobacterial cells containing CYN and its derivative deoxy-CYN on fish exposed sub-chronically under laboratory conditions.