The importance of efflux transporters in CNS exposure to avermectin insecticides

PhDAvermectins are macrocyclic lactones insecticides, used as antihelminthics in humans and animals, since they have low human toxicity. There is a clear role for the efflux transporter mdr1 controlling CNS exposure to avermectins in polymorphic animal models, but the role of MDR1 in limiting human avermectin exposure is less well defined, although no such knockout MDR1 polymorphisms have been identified to date. The aim of this study was to characterise the kinetics of avermectin interactions with efflux transporters in the human SHSY5Y neuroblastoma cell line, and compare them with mouse isoforms expressed in N2a cells to determine the relevance of mouse data to human avermectin exposure. Protein and mRNA expression of human MDR1, MRP and mouse mdr1a were identified in the cell lines, similar to the blood-brain barrier except BCRP and bcrp were absent. Ki values for inhibition of MDR1 or MRP substrate efflux by avermectins did not differ significantly between human and mouse cells (P > 0.05); abamectin (MDR1 Ki = 0.95 ± 0.08μM; mdr1a Ki = 0.77 ± 0.25μM), emamectin benzoate (MDR1 Ki = 0.60 ± 0.07μM; mdr1a Ki = 0.56 ± 0.02μM) and ivermectin (MDR1 Ki = 0.24 ± 0.08μM; mdr1a Ki = 0.18 ± 0.02μM), but ivermectin has the highest affinity for inhibition of MDR1- and mdr1a-substrate efflux. Cytotoxicity was apparent for emamectin benzoate above 6μM, which is 100-fold higher than peak exposure concentrations, but not for abamectin or ivermectin. Expression levels of the chemokine genes SDF-2, AIMP1 and BDNF are candidates for biomarkers of avermectin exposure. These data show that SH-SY5Y cells are a good model in which to investigate avermectin exposure and to compare to mouse cells and have confirmed the involvement of MDR1 and MRP transporters. Avermectins are of global importance, so a greater understanding of mechanisms of human exposure is pertinent.Syngent

Biodiesel exhaust particle airway toxicity and the role of polycyclic aromatic hydrocarbons

Renewable alternatives to fossil diesel (FD) including fatty acid methyl ester (FAME) biodiesel have become more prevalent. However, toxicity of exhaust material from their combustion, relative to the fuels they are displacing has not been fully characterised. This study was carried out to examine particle toxicity within the lung epithelium and the role for polycyclic aromatic hydrocarbons (PAHs). Exhaust particles from a 20% (v/v) blend of FAME biodiesel had little impact on primary airway epithelial toxicity compared to FD derived particles but did result in an altered profile of PAHs, including an increase in particle bound carcinogenic B[a]P. Higher blends of biodiesel had significantly increased levels of more carcinogenic PAHs, which was associated with a higher level of stress response gene expression including CYP1A1, NQO1 and IL1B. Removal of semi-volatile material from particulates abolished effects on airway cells. Particle size difference and toxic metals were discounted as causative for biological effects. Finally, combustion of a single component fuel (Methyl decanoate) containing the methyl ester molecular structure found in FAME mixtures, also produced more carcinogenic PAHs at the higher fuel blend levels. These results indicate the use of FAME biodiesel at higher blends may be associated with an increased particle associated carcinogenic and toxicity risk

Grouping of UVCB substances with dose-response transcriptomics data from human cell-based assays

The application of in vitro biological assays as new approach methodologies (NAMs) to support grouping of UVCB (unknown or variable composition, complex reaction products, and biological materials) substances has recently been demonstrated. In addition to cell-based phenotyping as NAMs, in vitro transcriptomic profiling is used to gain deeper mechanistic understanding of biological responses to chemicals and to support grouping and read-across. However, the value of gene expression profiling for characterizing complex substances like UVCBs has not been explored. Using 141 petroleum substance extracts, we performed dose-response transcriptomic profiling in human induced pluripotent stem cell (iPSC)-derived hepatocytes, cardiomyocytes, neurons, and endothelial cells, as well as cell lines MCF7 and A375. The goal was to determine whether transcriptomic data can be used to group these UVCBs and to further characterize the molecular basis for in vitro biological responses. We found distinct transcriptional responses for petroleum substances by manufacturing class. Pathway enrichment informed interpretation of effects of substances and UVCB petroleum-class. Transcriptional activity was strongly correlated with concentration of polycyclic aromatic compounds (PAC), especially in iPSC-derived hepatocytes. Supervised analysis using transcriptomics, alone or in combination with bioactivity data collected on these same substances/cells, suggest that transcriptomics data provide useful mechanistic information, but only modest additional value for grouping. Overall, these results further demonstrate the value of NAMs for grouping of UVCBs, identify informative cell lines, and provide data that could be used for justifying selection of substances for further testing that may be required for registration

Biodiesel exhaust particle airway toxicity and the role of polycyclic aromatic hydrocarbons

Renewable alternatives to fossil diesel (FD) including fatty acid methyl ester (FAME) biodiesel have become more prevalent. However, toxicity of exhaust material from their combustion, relative to the fuels they are displacing has not been fully characterised. This study was carried out to examine particle toxicity within the lung epithelium and the role for polycyclic aromatic hydrocarbons (PAHs). Exhaust particles from a 20% (v/v) blend of FAME biodiesel had little impact on primary airway epithelial toxicity compared to FD derived particles but did result in an altered profile of PAHs, including an increase in particle bound carcinogenic B[a]P. Higher blends of biodiesel had significantly increased levels of more carcinogenic PAHs, which was associated with a higher level of stress response gene expression including CYP1A1, NQO1 and IL1B. Removal of semi-volatile material from particulates abolished effects on airway cells. Particle size difference and toxic metals were discounted as causative for biological effects. Finally, combustion of a single component fuel (Methyl decanoate) containing the methyl ester molecular structure found in FAME mixtures, also produced more carcinogenic PAHs at the higher fuel blend levels. These results indicate the use of FAME biodiesel at higher blends may be associated with an increased particle associated carcinogenic and toxicity risk