Toxic effects of new ethyl-carbamates on the morphology, mortality and acetylcholinesterase activity of Eisenia foetida.

The toxicity of the ixodicidal carbamates ethyl-4-bromophenyl carbamate (LQM 919), ethyl-4-chlorophenyl carbamate (LQM 996) and propoxur on Eisenia foetida adults was evaluated to estimate their ecotoxic potential. The earthworm mortality and weight loss produced by the three evaluated carbamates showed a concentration-dependent effect (p < 0.0001) in the contact filter paper test (CFPT). In the artificial soil test (AST), mortality increased in relation to the exposure time (p < 0.0001) and the concentration (p < 0.01) of the carbamates. Only the earthworms exposed in the CFPT showed morphological alterations. According to the LC50 obtained in the CFPT, the three carbamates were classified as very toxic and, according to the LC50 obtained in the AST, the three carbamates were classified as highly toxic for E. foetida. The values of ki and kd indicated that LQM 919 and LQM 996 are weak inhibitors with lower affinity for the acetylcholinesterase of E. foetida than that of propoxur. The concentrations in the CFPT and AST at which 100% mortality was observed in E. foetida were 64- and 4-fold higher, respectively, than the egg hatching inhibitory concentration 99% reported for ticks.

Taenia hydatigena larvae vesicular concentrate reduces the egg shedding of Haemonchus contortus associated with the overexpression of abomasal cytokines in lambs.

The expression patterns of some cytokines were compared by RT-qPCR between lambs with and without Taenia hydatigena larvae vesicular concentrate (ThLVC) administration and subsequent infection with Haemonchus contortus. Lambs that received ThLVC prior to infection with H. contortus showed lower (p < 0.03) cumulative FEC (AUC = 18450 ± 3384) than infected lambs who did not receive ThLVC (AUC = 31081 ± 3277). Lambs infected with H. contortus, in general, overexpressed Th1 and Th2 cytokines in abomasal mucosa and abomasal lymph nodes, which seems to indicate a generalized and nonpolarized activation of the immune response by H. contortus. The main immunomodulatory effects of ThLVC were observed in the abomasal fundic region. The lambs that were given ThLVC prior to infection strongly overexpressed most of the studied cytokines representing the Th1 (IFNγ and IL2) and Th2 profiles (IL4, IL5, IL6 and IL10), proinflammatory cytokines (SOD1 and PRDX6) and IgE receptor; in contrast, lambs that were infected but did not receive ThLVC only moderately overexpressed IFNγ, IL4 and IL6. The absence of the significant overexpression of cytokines in lambs that only received ThLVC suggests that this derived from T. hydatigena does not have a stimulating effect per se; however, the presence of H. contortus did produce the highest expression (p < 0.01) cytokine profile among lambs that received ThLVC prior to infection compared to those who did not receive it, so its effect seems to be immunomodulatory and not only immunostimulatory.

Structure-Activity Relationship (SAR) and in vitro Predictions of Mutagenic and Carcinogenic Activities of Ixodicidal Ethyl-Carbamates.

Ethyl-4-bromophenyl-carbamate (LQM 919) and Ethyl-4-chlorophenyl-carbamate (LQM 996) are compounds that inhibit egg-laying and hatching of tick larvae that are resistant to conventional ixodicides. The structure-activity relationship (SAR) to get the endpoint predictions of mutagenicity and carcinogenicity of the LQM 919 and LQM 996 was performed and the absence of mutagenicity was confirmed by Ames test. SAR analysis show no structural alerts indicating the ability of ethyl-carbamates to bind biomolecules or estrogen receptors. Endpoint of mutagenicity with and without metabolic activation showed that the ethyl-carbamates were negative (p <0.05) for mutagenicity induction in strains TA97, TA98, TA102, TA1535, TA1537 and TA1538 of Salmonella typhimurium. Pre-incubation with different ethyl-carbamate concentrations did not increase the number of spontaneously reverting colonies; moreover, the compounds did not induce a concentration-dependent increase in the number of reverting colonies in any of the strains used. This confirmed the absence of mutagenic activity in this test system. Exogenous metabolic activation did not modify these observations; suggesting that no metabolites with mutagenic activity were present. The endpoint of carcinogenicity in rats were negative for LQM 919 (p <0.05,) and LQM 996 (p <0.001). The results of the present study strongly suggest that ethyl-carbamates do not represent a risk for cancer in mammals.

Acute oral and contact toxicity of new ethyl-carbamates on the mortality and acetylcholinesterase activity of honey bee (Apis mellifera).

The effects produced by the ethyl-carbamates: ethyl-4-bromophenyl carbamate (LQM 919) and ethyl-4-chlorophenyl carbamate (LQM 996) on the mortality and behavior of Apis mellifera were evaluated by the acute oral toxicity test and the acute contact toxicity test. The oral lethal dose, 50% of the ethyl-carbamates was >145.24 µg per bee, and the oral lethal dose, 50% of propoxur was 0.072 µg per bee. Therefore, according to the OECD criteria, the ethyl-carbamates were classified as relatively nontoxic orally; meanwhile, propoxur was classified as highly toxic orally. In the contact test, lethal concentrations 50% of the ethyl-carbamates were 4.83 and 2.23 µg/cm2 for LQM 919 and LQM 996, respectively; therefore, they were at least 10-fold less lethal (p < 0.05) than propoxur (0.22 µg/cm2). The ethyl-carbamates reduced the activity of A. mellifera acetylcholinesterase by up to 30%. The ki and kd values of both ethyl-carbamates were lower (p < 0.05) than those of propoxur and indicated that they are weak inhibitors and with low affinity to A. mellifera acetylcholinesterase, which along with the absence of behavioral alterations suggests that the mortality caused by ethyl carbamates is not related to damage to the nervous system. According to these results, the evaluated ethyl-carbamates can be considered a low ecotoxic risk for A. mellifera.

Oogenesis and embryogenesis inhibition induced by two new ethyl-carbamates in the cattle tick Rhipicephalus microplus.

The purpose of this work was to contribute to the understanding of the mechanism of action of two new ixodicides. The histological and ultrastructural alterations of Rhipicephalus microplus oocytes (San Alfonso strain) treated with two new ethyl-carbamates (ethyl-4-bromophenyl carbamate and ethyl-4-chlorophenyl carbamate) by the adult immersion test were evaluated by light microscopy and transmission electron microscopy. The effects of the carbamates on embryogenesis in eggs were evaluated by fluorescence microscopy using DAPI staining. Both ethyl-carbamates inhibited the maturation of most oocytes and induced a concentration-dependent decrease (r2  = 0.5, p < 0.05) in the embryonation percentage in the small number of eggs oviposited by treated ticks. Evident ultrastructural alterations were observed in the oocytes from ticks exposed to the ethyl-carbamates, including modification of the chorion structure, myelinic bodies and autophagic vacuoles that were associated with degenerated organelles (mitochondria, endoplasmic reticulum and yolk granules), nucleolus fragmentation and chromatin clumping in germinal vesicles. In conclusion, these ethyl-carbamates affect the reproductive potential of R. microplus due to their negative effects on oogenesis and their repercussions for embryonic development.