G. Repetto

Neutral red uptake assay for the estimation of cell viability/cytotoxicity

The neutral red uptake assay provides a quantitative estimation of the number of viable cells in a culture. It is one of the most used cytotoxicity tests with many biomedical and environmental applications. It is based on the ability of viable cells to incorporate and bind the supravital dye neutral red in the lysosomes. Most primary cells and cell lines from diverse origin may be successfully used. Cells are seeded in 96-well tissue culture plates and are treated for the appropriate period. The plates are then incubated for 2 h with a medium containing neutral red. The cells are subsequently washed, the dye is extracted in each well and the absorbance is read using a spectrophotometer. The procedure is cheaper and more sensitive than other cytotoxicity tests (tetrazolium salts, enzyme leakage or protein content). Once the cells have been treated, the assay can be completed in <3 h.

A test battery for the ecotoxicological evaluation of pentachlorophenol

Experimental bioassays are currently used in ecotoxicology and environmental toxicology to provide information for risk assessment evaluation of new chemicals and to investigate their effects and mechanisms of action; in addition, ecotoxicological models are used for the detection, control and monitoring of the presence of pollutants in the environment. As a single bioassay will never provide a full picture of the quality of the environment, a representative, cost-effective and quantitative test battery should be developed. The effects of pentachlorophenol were studied using a battery of ecotoxicological model systems, including immobilization of Daphnia magna, bioluminiscence inhibition in the bacterium Vibrio fischeri, growth inhibition of the alga Chlorella vulgaris, and micronuclei induction in the plant Allium cepa. The inhibition of cell proliferation and MTT reduction were investigated in Vero cells. Neutral red uptake, cell growth, MTT reduction, lactate dehydrogenase leakage and activity were studied in the salmonid fish cell line RTG-2, derived from the gonad of rainbow trout. Pentachlorophenol was very toxic for all biota and cells. The system most sensitive to pentachlorophenol, was micronuclei induction in A. cepa, followed by D. magna immobilization, bioluminescence inhibition in V. fischeri bacteria at 60 min and cell proliferation inhibition of RTG-2 cells at 72 h. Inhibition of cell proliferation and MTT reduction on Vero monkey cells showed intermediate sensitivity.

Ecotoxicological evaluation of carbamazepine using six different model systems with eighteen endpoints

The occurrence of pharmaceutically active compounds in the aquatic environment has been recognized as one of the emerging issues in environmental chemistry. However, the ecotoxicological effects of pharmaceuticals have still not been researched adequately. Carbamazepine, an anticonvulsant commonly present in surface and groundwater, was studied, using six ecotoxicological model systems with eighteen endpoints evaluated at different exposure time periods. The battery included the immobilization of Daphnia magna, bioluminescence inhibition in the bacterium Vibrio fischeri, growth inhibition of the alga Chlorella vulgaris, and micronuclei induction and root growth inhibition in the plant Allium cepa. Cell morphology, neutral red uptake, total protein content, MTS metabolization, lactate dehydrogenase leakage and activity and glucose-6-phosphate dehydrogenase activity were studied in the salmonid fish cell line RTG-2. The total protein content, LDH activity, neutral red uptake and MTT metabolization in Vero monkey kidney cells were also investigated. The most sensitive system to carbamazepine was the Vero cell line, followed by Chlorella vulgaris, Vibrio fischeri, Daphnia magna, Allium cepa, and RTG-2 cells. EC50 values from 19 microM in Vero cells at 72 h to more than 1200 microM in other systems, were obtained. Comparing the concentrations in water and the toxicity quantified in our assay systems, carbamazepine is not expected to produce acute toxic effects in the aquatic biota under these circumstances, but chronic and synergistic effects with other chemicals cannot be excluded.

Influence of microcystin-LR on the activity of membrane enzymes in rat intestinal mucosa.

The objective of the present study was to evaluate the effects of microcystin-LR (MCLR) on the activity of membrane enzymes from intestinal mucosa. In addition, serum chemistry and peroxidative status of both serum and intestinal homogenate were evaluated after treatment with MCLR. Wistar rats were treated with intraperitoneal injection of either 100 μg pure MCLR/Kg body weight or saline solution. A significant increase in liver weight and altered serum enzyme activities were found in MCLR-treated rats, indicating damage to the liver in these rats, as previously suggested. A higher specific activity of sucrase (1.5-fold) was observed after the administration of MCLR, whereas other intestinal apical membrane enzymes, such as lactase, maltase and alkaline phosphatase were not modified by the treatment. The specific activities of acid phosphatase and succinate dehydrogenase, markers for lysosomal and mitochondrial membranes, respectively, were also increased (32% and 60%, respectively) in treated rats. The analysis of lipid peroxidation showed that the peroxidative status was increased in both serum and intestinal mucosa from MCLR-treated rats, reflecting an excess production of oxygen free radicals induced by this cyanobacterial toxin. In conclusion, this study shows that acute exposure to MCLR affects the intestinal physiology by modifying the intestinal peroxidation status as well as the activity of membrane enzymes.ResumenEn este trabajo se analiza la acción de la toxina microcistina-LR (MCLR) sobre la actividad de diversas enzimas de membrana en la mucosa intestinal. Para ello, se utilizan ratas Wistar a las que se inyecta por vía intraperitoneal 100 μg MCLR/Kg peso corporal o bien solución salina (grupo control). Asimismo, se realiza un estudio bioquímico en suero, y se determina el grado de peroxidación lipídica en la mucosa intestinal y suero de estos animales tras el tratamiento con MCLR. La toxina induce daño hepático severo en las ratas tratadas, como lo demuestra el aumento del peso del hígado y diversas alteraciones de las enzimas hepáticas en suero. Por lo que respecta a las enzimas de membrana, las ratas tratadas con MCLR presentan un aumento en la actividad de la enzima sacarasa en la mucosa intestinal, no alterándose otras enzimas apicales como la lactasa, maltasa o fosatasa alcalina. MCLR también produce un aumento en la actividad de la fosfatasa ácida y succinato deshidrogenasa, marcadores respectivos de membranas lisosomales y mitocondriales. Además, los niveles de peroxidación lipídica en suero y mucosa intestinal aparecen anormalmente elevados tras el tratamiento, como consecuencia de la producción excesiva de radicales libres de oxígeno inducida por la toxina. Por consiguiente, la intoxicación aguda con MCLR afecta a la fisiología intestinal provocando una modificación del estado peroxidativo y alterando la actividad de las enzimas de membrana intestinales.

Comparative in vitro effects of sodium arsenite and sodium arsenate on neuroblastoma cells

The toxic effects of arsenic at different cellular levels were assessed using two inorganic chemical species: sodium arsenite and sodium arsenate, representing the trivalent and pentavalent states of arsenic, respectively. Mouse neuroblastoma cell cultures (Neuro-2a) were exposed for 24 h, and cytotoxic effects evaluated were: cell proliferation by quantification of total protein content; cytoplasmic membrane integrity to cytosolic lactate dehydrogenase leakage; lysosomal hexosaminidase release; lactate dehydrogenase activity; mitochondrial succinate dehydrogenase activity; relative neutral red uptake by lysosomes; lysosomal hexosaminidase sphingolipid degradation activity; and acetylcholinesterase activity. As(III) was found to be five times more toxic than As(V) to neuroblastoma cell proliferation, but the relative extent of other alterations differed. Special sensitivity was detected for lactate dehydrogenase inhibition. Hexosaminidase activity was also very susceptible, being inhibited at low concentrations and stimulated at high concentrations. Less sensitive were the inhibition of cell proliferation, relative neutral red uptake, and acetylcholinesterase activity. As(III) was lysosomotropic, with secretion of hexosaminidase, but the release was decreased by As(V). Mitochondrial succinate dehydrogenase was inhibited by As(III) and stimulated by As(V). Minor sensitivity to cytoplasmic lactate dehydrogenase leakage for both compounds also shows that functional metabolic alterations produced by arsenic are more important than structural damage.

Tribromophenol induces the differentiation of SH-SY5Y human neuroblastoma cells in vitro

Tribromophenol is a pesticide with fungicide activity, presently used as a replacement of pentachlorophenol as a wood preservative, and as a flame retardant in electronic and electrotechnical devices. Retinoic acid differentiated and non-differentiated SH-SY5Y human neuroblastoma cell cultures were exposed to a range of concentrations of tribromophenol for 24, 48 and 72 h and the effects evaluated at morphological, basal cytotoxicity and biochemical levels. Neuroblastoma cell number, evaluated by quantification of total protein content, was increasingly inhibited in accordance with the concentration of tribromophenol and the exposure time period. According to the mean effective concentrations, differentiated cultures were nearly three times more sensitive than naive cells. Lysosomal function evaluated by the neutral red uptake was stimulated, particularly in non-differentiated cells. MTS metabolization was stimulated by all the treatments, with more potency at 24 h for differentiated cells. Acetylcholinesterase activity increased with the time of exposure in non-differentiated cells, while in differentiated cells the activity was doubled at 24 h. Morphological alterations were evident from 12.5 microM, showing hydropic degeneration and reduction in cell number, and from that concentration, piknosis and apoptotic bodies were observed. In conclusion, the main effects detected for tribromophenol were the induction of neuroblastoma cell differentiation, as expressed by the inhibition of cell growth and the increase in acetylcholinesterase activity with a critical cell concentration of 0.1 microM. Apoptosis was observed at high concentrations. The induction of cell differentiation and the special sensitivity of differentiated cells can explain some mechanisms involved in the embryotoxic and foetotoxic potential of tribromophenol.

In vitro effects of mercuric chloride and methylmercury chloride on neuroblastoma cells

An in vitro model system has been developed to establish dose-response relationships of mercuric chloride (HgCl(2)) and methylmercuric chloride (HgCH(3)Cl). Mouse neuroblastoma cell cultures (Neuro-2a) were exposed for 24 hr and cytotoxic effects evaluated with eight different endpoints. Toxic indicators assessed in the in vitro test system were as follows: cell proliferation by quantification of total protein content; cytoplasmic membrane integrity by cytosolic lactate dehydrogenase leakage; lysosomal membrane stability by hexosaminidase release; lactate dehydrogenase activity; mitochondrial succinate dehydrogenase activity; relative neutral red uptake by lysosomes; lysosomal hexosaminidase sphingolipid degradation activity; acetylcholinesterase activity. The toxicity of the two chemical species of mercury on neuroblastoma cells differed. HgCl(2) inhibited LDH activity specifically and very potently. Gross disruption of cytoplasmic membrane was accompanied by stimulation of hexosaminidase. HgCH(3)Cl was 50 times more toxic than HgCl(2) to cell proliferation and also caused important alterations in both membrane stability and metabolic activities over a narrow range of doses. The data suggest that HgCl(2) acts mainly on cell membranes and LDH, whereas, although HgCH(3)Cl is more cytotoxic, it does not affect any of the above-mentioned endpoints as specifically.

Cyanobacteria and microcystins occurrence in the Guadiana River (SW Spain)

This work reports on the survey carried out to determine the presence of microcystins (MCs) by using ELISA tests and HPLC-UV for such determination in different sample sites along the Spanish course of the Guadiana River. The most important cyanobacteria species identified were, Microcystis aeruginosa and Oscillatoria spp. The highest total microcystin content recorded was 6.40 µg L−1 in 2002. The main toxins found were microcystins RR and LR, with microcystin YR present at trace levels. Improvements in sample clean up were carried out by using Immunoaffinity solid phase extraction (SPE) and its advantages regarding to conventional SPE were clearly demonstrated. The confirmation of MCs presence in the evaluated water reservoirs, underlines the necessity of monitoring programs as well as the improvement of analytical methodologies to efficiently prevent the human health risks as a consequence of MCs contamination.

In vitro effects of lithium and nickel at different levels on Neuro-2a mouse Neuroblastoma cells

Lithium and nickel present low toxicity, but are able to cause alterations in different tissues. The toxic effects of lithium and nickel at different cellular levels were assessed using two inorganic chemical species: lithium chloride and nickel(II) chloride. Mouse neuroblastoma cell cultures (Neuro-2a) were exposed to both compounds for 24 h. The cytotoxic effects evaluated were cell proliferation by quantification of total protein content, cytoplasmic membrane integrity to cytosolic lactate dehydrogenase leakage, and lysosomal hexosaminidase release. Metabolic markers were lactate dehydrogenase activity and mitochondrial succinate dehydrogenase activity. Lysosomal markers were relative neutral red uptake by lysosomes, and lysosomal hexosaminidase sphingolipid degradation activity. Acetylcholinesterase activity on intact cells was also quantified. Nickel was found to be 36 times more toxic than lithium to neuroblastoma cell proliferation (EC(50)= 0.29 and 10.5 mM, respectively), but the relative extent of other alterations differed. Lithium stimulated nearly all the indicators studied, particularly lactate dehydrogenase, mitochondrial succinate dehydrogenase and acetylcholinesterase activities, as well as hexosaminidase release. In contrast, nickel mainly stimulated hexosaminidase release and inhibited lactate dehydrogenase activity. The stabilization of the cytoplasmic membrane to lactate dehydrogenase leakage simultaneously with the secretion of lysosomal hexosaminidase for both compounds also shows that functional metabolic alterations produced by lithium and nickel are more important than cytoplasmic damage.

Changes in antioxidative activities induced by Fe (II) and Fe(III) in cultured Vero cells

The toxicity of iron (II) and iron (III) chlorides was studied at different biochemical and cellular levels, including antioxidative and metabolic enzymes and two general indicators of cytotoxicity in Vero monkey kidney cells after 24-h exposure. Iron (II) was fourfold more toxic than Fe (III) in cell proliferation, with EC50 of 5.5 and 22 mM, respectively. Metabolic markers were far more sensitive than cytotoxicity assays at these concentrations. At the highest concentrations of toxicant tested [10 mM Fe(II) and 50 mM Fe (III)], both species produced nearly total inhibition of the relative uptake of neutral red (RNRU) and phosphofructokinase activity (PFK), and stimulated intracellular specific lactate dehydrogenase activity (LDH). Succinate dehydrogenase (SDH) and hexosaminidase (HEX) activities were reduced in a dose-dependent manner, as was the antioxidative enzyme glucose-6-phosphate dehydrogenase (G-6-PDH) with both forms of iron. Glutathione reductase (GOR) and glutathione-S-transferase (GST) activities were stimulated by Fe (II) but were inhibited by the higher Fe (III) concentrations. In conclusion, the experimental model may be useful for the study of different metabolic effects induced by the two oxidation states of iron.