Inhibitory effect of ebselen on lactate dehydrogenase activity from mammals: a comparative study with diphenyl diselenide and diphenyl ditelluride.

Ebselen is a seleno compound whose antioxidant properties have been attributed to its thiol-peroxidase and thioredoxin-like activity. However, the excessive oxidation of thiols can be potentially toxic. Thus, this work investigated whether lactate dehydrogenase (LDH) can be a possible in vitro target to the toxicity of ebselen, in comparison with diphenyl diselenide [(PhSe)(2)] and diphenyl ditelluride [(PhTe)(2)]. Ebselen was the most potent inhibitor of LDH. A maximal inhibitory effect was obtained at 2 µM to LDH purified and at 20 µM to LDH from heart and liver homogenates. Moreover, (PhSe)(2), followed by (PhTe)(2), also presented a significant inhibitory effect on LDH activity. DL-dithiothreitol (DTT) was able to revert the inhibition of LDH induced by all compounds tested, confirming the involvement of essential thiol groups on LDH inhibition by organochalcogens. In conclusion, our results show that liver and heart LDH may be a possible target for the toxicity of organochalcogens at relative low concentrations. Our results also indicate that the use of LDH, as a marker of cell viability, may be biased by a direct inhibitory effect of ebselen or other chalcogenides on LDH, resulting in false protection in an in vitro system.

Methylmercury and diphenyl diselenide interactions in Drosophila melanogaster: effects on development, behavior, and Hg levels.

Methylmercury (MeHg) is a highly toxic environmental pollutant which binds with a high affinity to selenol groups. In view of this, seleno-compounds have been investigated as MeHg antidotes. In the present study, we evaluated the effects of the co-exposure to MeHg and the seleno-compound diphenyl diselenide (PhSe)2 on Drosophila melanogaster. We measured the survival rate, developmental survival, locomotor ability, reactive oxygen species (ROS) production, and Hg levels in D. melanogaster exposed to MeHg and/or (PhSe)2 in the food. Exposure to MeHg caused a reduction in the survival rate, developmental survival, and locomotion in D. melanogaster. In addition, MeHg increased the ROS production and mercury levels in flies. The co-exposure to MeHg and (PhSe)2 did not prevent the toxic effects of MeHg in D. melanogaster. On the contrary, the co-exposure enhanced the toxic effects on the locomotor ability and developmental survival. This effect may be explained by the fact that the co-exposure increased the Hg levels in body when compared to flies exposed only to MeHg, suggesting that MeHg and (PhSe)2 interaction may increase Hg body burden in D. melanogaster which could contribute for the increased toxicity observed in the co-exposure.

Ovotoxicants 4-vinylcyclohexene 1,2-monoepoxide and 4-vinylcyclohexene diepoxide disrupt redox status and modify different electrophile sensitive target enzymes and genes in Drosophila melanogaster.

The compounds 4-vinylcyclohexene 1,2-monoepoxide (VCM) and 4-Vinylcyclohexene diepoxide (VCD) are the two downstream metabolites of 4-vinylcyclohexene (VCH), an ovotoxic agent in mammals. In addition, VCM and VCD may be found as by-products of VCH oxidation in the environment. Recently, we reported the involvement of oxidative stress in the toxicity of VCH in Drosophila melanogaster. However, it was not possible to determine the individual contributions of VCM and VCD in VCH toxicity. Hence, we investigated the toxicity of VCM and VCD (10-1000 µM) in flies after 5 days of exposure via the diet. Our results indicated impairments in climbing behaviour and disruptions in antioxidant balance and redox status evidenced by an increase in DCFH oxidation, decreases in total thiol content and glutathione-S-transferase (GST) activity in the flies exposed to VCM and VCD (p<0.05). These effects were accompanied by disruptions in the transcription of the genes encoding the proteins superoxide dismutase (SOD1), kelch-like erythroid-derived cap-n-collar (CNC) homology (ECH)-associated protein 1 (Keap-1), mitogen activated protein kinase 2 (MAPK-2), catalase, Cyp18a1, JAFRAC 1 (thioredoxin peroxidase 1) and thioredoxin reductase 1 (TrxR-1) (p<0.05). VCM and VCD inhibited acetylcholinesterase (AChE) and delta aminolevulinic acid dehydratase (δ-ALA D) activities in the flies (p<0.05). Indeed, here, we demonstrated that different target enzymes and genes were modified by the electrophiles VCM and VCD in the flies. Thus, D. melanogaster has provided further lessons on the toxicity of VCM and VCD which suggest that the reported toxicity of VCH may be mediated by its transformation to VCM and VCD.

Co-exposure of the organic nanomaterial fullerene C60 with benzo[a]pyrene in Danio rerio (zebrafish) hepatocytes: evidence of toxicological interactions.

Compounds from the nanotechnology industry, such as carbon-based nanomaterials, are strong candidates to contaminate aquatic environments because their production and disposal have exponentially grown in a few years. Previous evidence shows that fullerene C60, a carbon nanomaterial, can facilitate the intake of metals or PAHs both in vivo and in vitro, potentially amplifying the deleterious effects of these toxicants in organisms. The present work aimed to investigate the effects of fullerene C60 in a Danio rerio (zebrafish) hepatocyte cell lineage exposed to benzo[a]pyrene (BaP) in terms of cell viability, oxidative stress parameters and BaP intracellular accumulation. Additionally, a computational docking was performed to investigate the interaction of the fullerene C60 molecule with the detoxificatory and antioxidant enzyme πGST. Fullerene C60 provoked a significant (p<0.05) loss in cellular viability when co-exposed with BaP at 0.01, 0.1 and 1.0 µg/L, and induced an increase (p<0.05) in BaP accumulation in the cells after 3 and 4h of exposure. The levels of reactive oxygen species (ROS) in the cells exposed to BaP were diminished (p<0.05) by the fullerene addition, and the increase of the GST activity observed in the BaP-only treated cells was reduced to the basal levels by co-exposure to fullerene. However, despite the potential of the fullerene molecule to inhibit π GST activity, demonstrated by the computational docking, the nanomaterial did not significantly (p>0.05) alter the enzyme activity when added to GST purified extracts from the zebrafish hepatocyte cells. These results show that fullerene C60 can increase the intake of BaP into the cells, decreasing cell viability and impairing the detoxificatory response by phase II enzymes, such as GST, and this latter effect should be occurring at the transcriptional level.