| Widespread occurrence of environmental pollutions has resulted in risks to public health and environmental safety. Nowadays, special attentions are paid to potential toxic effects to humans and mammals induced by some current use pesticides. Pyrethroids are characterized by their high efficacy to insects, low environmental mobility and relatively low mammalian toxicity. People and animals can easily come into contact with pyrethroids when they are released into the environment, and be exposed to them in several ways during daily life. Recent studies showed that some pyrethroids display different toxic effects and may possess health risks to humans and other mammals. As an important family of chiral pesticides, pyrethroids also show enantioselective toxicities to non-target organisms.Current studies of potential toxicities induced by pyrethroids mostly focus on individual toxic effect caused by the racemic form. Little attention has been given to the molecular mechanism of toxicity induced by a single enantiomer. In the present study, several common used chiral pyrethroids, represented by bifenthrin (BF), were chosen to evaluate immunotoxicity, reproductive endocrine disruption and liver injury in vitro and in vivo. Both the underlying mechanisms and enantioselectivity of toxicities were investigated using molecular biology methods. It is expected that both the results and approaches developed in the present study may be useful to achieve more comprehensive risk assessments of pyrethroids. The details of our study are as follows:(1) Risk assessment of man-made chemicals such as pesticides are mainly focused on parent compounds, and relatively little is known about their metabolites, especially with regard to target organ damages such as immunotoxicity. In the present study the immunotoxicity of five pyrethroids and three common metabolites was evaluated using an in vitro model by MTT assay, cytoflow and enzyme-linked immunosorbent assay (ELISA). Cell viability and apoptosis assays showed that both SPs and their metabolites possessed cytotoxicity to the monocytic cells. The aldehyde and acid derivatives were more effective than the other compounds at cytotoxicity, with inhibition of cell viability by 56.8 and 50.6% at 10-5mol/L, and induction of 8.52 and 8.81% cell apoptosis, respectively. Exposure to SPs and their metabolites also led to changes in the secretion levels of tumor necrosis factorα(TNFα) and interleukins (ILs), and again the metabolites showed stronger effects than the parent compounds. The aldehyde derivative upregulated IL-12p70 level by 1.87 fold and the alcohol and acid derivative increased the secretion of TNFα5.88 and 7.96 fold relative to the control group. In the in vitro model, the common metabolites of pyrethroids clearly exerted greater immunotoxic effects to monocytes than the intact parent compounds.(2) Based on the results that pyrethroids possessed immunotoxicity to monocytes, BF was chosen to evaluate both the mechanisms and enantioselectivity of immunotoxicity in vitro and in vivo. Results of the in vivo BALB/c mice model showed that, although there was no dysfunction in mouse spleen, intensive cytotoxicity and oxidative stress were induced in response to BF to disturb immune functions. Similar results displayed in the in vitro monocytes model and significant enantioselectivity existed in immunotoxicity induced by BF enantiomers. The two enantiomers could induce enantioselective immunotoxicity through generation of oxidative stress, disturbance of different apoptosis signaling pathways and causing cytotoxicity to monocytes. All the results revealed that BF possessed enantioselective immunotoxicity to non-target organisms.(3) Known as one kind of endocrine disrupting chemicals, pyrethroids could disrupt the signalling web of endocrine and reproductive systems and cause adverse reproductive effects in mammals and humans. In the present study, possible enantioselective interference of hormones in trophoblast to BF exposure was investigated. The JEG-3 choriocarcinoma cells were used as the in vitro model to study placental functions. The possible actions of BF on cell viability, hormone secretion and gene expressions were evaluated and interaction modes of BF enantiomers with estrogen receptorα(ERα) were further predicted by molecular modeling. After determination of the dose range of BF through MTT, results from hormone secretion and gene expression revealed that, BF could induce secretions of progesterone and human chorionic gonadotropin (hCG), upregulation of gonadotropin-releasing hormone (GnRH) and its receptor mRNA expression levels, in addition to significant alteration of steroidogenic gene expression. Both the racemic and enantiomeric BF could act partly through ER to disturb the balance of hormones in trophoblast. A consistent enantioselectivity with the rank order of S-BF> rac-BF> R-BF was showed in hormone disrupting. Using the molecular modeling, although no significant difference was found in flexibility and conformational change of ERa in complex with BF enantiomers, comparatively stronger binding affinity of S-BF to ERa than that of R-BF was revealed to partly explain for the enantioselectivity of BF.(4) The potential hepatotoxicity after exposed to low concentrations of pyrethroids and the mechanism remain unclear and could be easily overlooked if only the common clinical indicators of liver disease are examined. In the present study we evaluated the potential liver injury of BF and investigated the underlying mechanisms using BALB/c mice as an in vivo model. Changes in tissue histology, serum enzyme activities, cytotoxicity, oxidative stress, caspase activities and expression of genes related to apoptosis and metabolism were analyzed. Histological analyses and serum enzyme activities showed no obvious clinical evidence of liver damage. Cytotoxicity and oxidative stress were induced in response to BF. Exposure to BF also activated caspases and triggered mitochondrial apoptotic signal pathways in the mouse liver. The microarray results showed that BF could disturb the metabolic profile and extensively induce genes related to oxidative stress, including CYPs, GPXs, GSTs and kinases. In the in vivo model, BF induced liver injury through caspase-mediated mitochondrial-dependent cell death, a process that was closely related to oxidative stress, even in the absence of classical clinical biomarkers of liver dysfunction.Health risk assessment and environmental safety of the current use pesticides have become a hot issue of scientific researches. Results of the present study suggest that pyrethroids can exert different toxic effects via the processes of induction of oxidative stress, interference of signaling pathways, triggering apoptosis and finally possessing toxicities to different target organs. Enan(?)oselectivity exists commonly in potential toxicities of pyrethroids. It is suggested that more integrative health risk assessments of pyrethroids by considering the enantioselectivitive toxic effects at the levels of molecules, cells, and organisms are imperative. |
