Caloric content of Daphnia magna as reflect of propanil stress during a short-term exposure and its relationship to long-term responses.

The present study investigates energy stores changes in the aquatic invertebrate Daphnia magna following a 5-d exposure to propanil. Juveniles of D. magna were exposed to sublethal propanil concentrations (0.07, 0.10, 0.21 and 0.55 mgl(-1)) which were used previously to test their effect on reproduction, growth and survival (21 days test) of D. magna. Glycogen, total lipids, proteins, and dry weight were determined in control and exposed daphnids at 24, 48, 72, 96 and 120 h. Data were used to calculate caloric content as biomarker of propanil exposure. Results showed a depletion of energy reserves in D. magna exposed to the herbicide. At 120 h of exposure to the highest propanil concentration (0.5 mgl(-1)), the reduction in daphnid reserves were glycogen (28%), proteins (28%) and lipids (31%), and caloric content was reduced in 27%. On the other hand, we found a positive correlation between caloric content and the chronic parameters intrinsic rate of natural increase and offspring per female when daphnids were exposed for 120 h to the herbicide.

Fish tolerance to organophosphate-induced oxidative stress is dependent on the glutathione metabolism and enhanced by N-acetylcysteine.

Dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP) is an organophosphorus (OP) insecticide and acaricide extensively used to treat external parasitic infections of farmed fish. In previous studies we have demonstrated the importance of the glutathione (GSH) metabolism in the resistance of the European eel (Anguilla anguilla L.) to thiocarbamate herbicides. The present work studied the effects of the antioxidant and glutathione pro-drug N-acetyl-L-cysteine (NAC) on the survival of a natural population of A. anguilla exposed to a lethal concentration of dichlorvos, focusing on the glutathione metabolism and the enzyme activities of acetylcholinesterase (AChE) and caspase-3 as biomarkers of neurotoxicity and induction of apoptosis, respectively. Fish pre-treated with NAC (1 mmol kg(-1), i.p.) and exposed to 1.5 mg l(-1) (the 96-h LC85) of dichlorvos for 96 h in a static-renewal system achieved an increase of the GSH content, GSH/GSSG ratio, hepatic glutathione reductase (GR), glutathione S-transferase (GST), glutamate:cysteine ligase (GCL), and gamma-glutamyl transferase (gammaGT) activities, which ameliorated the glutathione loss and oxidation, and enzyme inactivation, caused by the OP pesticide. Although NAC-treated fish presented a higher survival and were two-fold less likely to die within the study period of 96 h, Cox proportional hazard models showed that hepatic GSH/GSSG ratio was the best explanatory variable related to survival. Hence, tolerance to a lethal concentration of dichlorvos can be explained by the individual capacity to maintain and improve the hepatic glutathione redox status. Impairment of the GSH/GSSG ratio can lead to excessive oxidative stress and inhibition of caspase-3-like activity, inducing cell death by necrosis, and, ultimately, resulting in the death of the organism. We therefore propose a reconsideration of the individual effective dose or individual tolerance concept postulated by Gaddum 50 years ago for the log-normal dose-response relationship. In addition, as NAC increased the tolerance to dichlorvos, it could be a potential antidote for OP poisoning, complementary to current treatments.

Increased recovery of brain acetylcholinesterase activity in dichlorvos-intoxicated European eels Anguilla anguilla by bath treatment with N-acetylcysteine.

Organophosphate (OP) pesticides are widely used as antiparasitic chemicals in finfish aquaculture. However, current antidotes cannot be applied to treat intoxicated fish. We showed in previous studies the importance of glutathione (GSH) metabolism in pesticide resistance of the European eel Anguilla anguilla L. The present work studied the effects of the antioxidant and glutathione pro-drug N-acetyl-L-cysteine (NAC) on the recovery of European eels exposed for 96 h to a sublethal concentration (0.17 mg l(-1); 20% of its 96 h LC50) of the OP pesticide dichlorvos (2,2-dichlorovinyl dimethyl phosphate; DDVP). This insecticide and acaricide decreased muscular GSH content and increased oxidised glutathione (GSSG), lowering the GSH:GSSG ratio, which is indicative of a condition of oxidative stress. Acetylcholinesterase (AChE) and glutathione reductase (GR) activities in the brain, which were biomarkers of neurotoxicity and oxidative stress, respectively, were also highly inhibited. Recovery in a 0.5 mM (81.6 mg l(-1)) NAC concentration ameliorated muscular GSH depletion, GSH:GSSG ratio, and the inhibition of brain AChE and GR activities. Hence, this is the first evidence of improved recovery of organophosphate-poisoned fish by bath treatments.