Toxicology

Functional transepithelial transport measurements to detect nephrotoxicity in vitro using the RPTEC/TERT1 cell line Abstract The kidney is a frequent target for organ-specific toxicity as a result of its primary function in controlling body fluids, for example, via resorption of amino acids, peptides, nutrients, ions, xenobiotics and water from the primary urine as well as excretion of metabolic waste products and hydrophilic and amphiphilic xenobiotics. Compounds exhibiting dose-limiting nephrotoxicity include drugs from highly diverse classes and chemical structures, e.g., antibiotics (gentamicin), chemotherapeutics (cisplatin), immunosuppressants (cyclosporine A and tacrolimus) or bisphosphonates (zoledronate). All of these compounds elicit nephrotoxicity primarily by injuring renal proximal tubule epithelial cells (RPTECs). However, prediction of a compound's nephrotoxic potential in humans to support early unmasking of risk-bearing drug candidates remains an unmet challenge, mainly due to the complex kidney anatomy as well as pronounced inter- and intraspecies differences and lack of relevant and validated human in vitro models. Accordingly, we used the recently established human RPTEC/TERT1 cell line to carry out toxicity studies with a focus on impairment of functional characteristics, i.e., transepithelial electrical resistance (TEER), vectorial transport of water, cations, and anions. Results were compared to real-time cytotoxicity assessments using cellular impedance (xCELLigence assay) and the routine cell viability readout (MTT). As expected, most toxins caused exposure time- and concentration-dependent cytotoxicity. However, for some compounds (cyclosporine A and tacrolimus), transport processes were strongly impaired in absence of a concomitant decrease in cell viability. In conclusion, these data demonstrate that functional parameters are important, highly sensitive and meaningful additional readouts for nephrotoxicity assessment in human renal proximal tubule epithelial cells.

Role of microglial activation and neuroinflammation in neurotoxicity of acrylamide in vivo and in vitro Abstract Acrylamide, a soft electrophile, is widely used in the industry and laboratories, and also contaminates certain foods. Neurotoxicity and neurodegenerative effects of acrylamide have been reported in humans and experimental animals, although the underlying mechanism remains obscure. Activation of microglia and neuroinflammation has been demonstrated in various neurodegenerative diseases as well as other pathologies of the brain. The present study aimed to investigate the role of microglial activation and neuroinflammation in acrylamide neurotoxicity. Male 10-week-old Wistar rats were exposed to acrylamide by gavage at 0, 0.2, 2, or 20 mg/kg BW, once per day for 5 weeks. The results showed that 5-week exposure to acrylamide induced inflammatory responses in the cerebral cortex, evident by upregulated mRNA and protein expression of pro-inflammatory cytokines IL-1β, IL-6, and IL-18. Acrylamide also induced activation of microglia, indicated by increased expression of microglial markers, CD11b and CD40, and increased CD11b/c-positive microglial area and microglial process length. In vitro studies using BV-2 microglial cells confirmed microglial inflammatory response, as evident by time- (0–36 h; 50 μM) and dose- (0–500 μM; 24 h) dependent increase in mRNA expression of IL-1β and IL-18, as well as the inflammatory marker iNOS. Furthermore, acrylamide-induced upregulation of pro-inflammatory cytokines was mediated through the NLRP3 inflammasome pathway, as evident by increased expression of NLRP3, caspase 1, and ASC in the rat cerebral cortex, and by the inhibitory effects of NLRP3 inflammasome inhibitor on the acrylamide-induced upregulation of NLRP3, caspase 1, IL-1β, and IL-18 in BV-2 microglia.

Forensic evidence of sulfur mustard exposure in real cases of human poisoning by detection of diverse albumin-derived protein adducts Abstract We present the forensic analyses of plasma samples of human victims exposed to sulfur mustard (SM) in a crisis region in the Middle East in 2015. A few hours after exposure, poisoned persons showed typical signs and symptoms of percutaneous SM exposure including erythema and later on blisters and hardly healing skin wounds. Blood samples were collected 15 days after poisoning to be analyzed for the presence of long-lived protein-adduct biomarkers to verify SM poisoning. We applied a novel bioanalytical toolbox targeting four human serum albumin-derived biomarkers that were made accessible after plasma proteolysis. These adducts contained the SM-specific hydroxyethylthioethyl moiety either bound to the thiol group of a cysteine residue (C34*) or to the side-chain carboxylic group of a glutamic acid residue (E230*). Peptide biomarkers were produced from plasma of the victims using proteinase K (C34*PF), pronase (C34*P) and pepsin (AE230*VSKL and LQQC34*PFEDHVKL) for enzymatic protein cleavage. Separation and detection were carried out by selective micro-liquid chromatography–electrospray ionization high-resolution tandem mass spectrometry (µLC–ESI MS/HR MS). In addition to this site-specific adduct detection, a general approach after alkaline hydrolysis of the plasma protein fraction was applied. Liberated thiodiglycol (TDG) was derivatized with heptafluorobutyric anhydride and detected by gas chromatography–electron ionization mass spectrometry (GC–EI MS). The different bioanalytical methods yielded congruent results confirming SM poisoning for all patients who showed clinical signs and symptoms. This is the first time that real cases of SM poisoning were confirmed and presented by such a broad compilation of protein-derived biomarkers.

Selecting the dose metric in reverse dosimetry based QIVIVE

Behavioural and metabolomic changes from chronic dietary exposure to low-level deoxynivalenol reveal impact on mouse well-being Abstract The mycotoxin deoxynivalenol (DON) has a high global prevalence in grain-based products. Biomarkers of exposure are detectable in most humans and farm animals. Considering the acute emetic and chronic anorexigenic toxicity of DON, maximum levels for food and feed have been implemented by food authorities. The tolerable daily intake (TDI) is 1 µg/kg body weight (bw)/day for the sum of DON and its main derivatives, which was based on the no-observed adverse-effect level (NOAEL) of 100 µg DON/kg bw/day for anorexic effects in rodents. Chronic exposure to a low-DON dose can, however, also cause inflammation and imbalanced neurotransmitter levels. In the present study, we therefore investigated the impact of a 2-week exposure at the NOAEL in mice by performing behavioural experiments, monitoring brain activation by c-Fos expression, and analysing changes in the metabolomes of brain and serum. We found that DON affected neuronal activity and innate behaviour in both male and female mice. Metabolite profiles were differentiable between control and treated mice. The behavioural changes evidenced at NOAEL reduce the safety margin to the established TDI and may be indicative of a risk for human health.

Naturally occurring bisphenol F in plants used in traditional medicine Abstract Bisphenol F (BPF, 4-[(4-hydroxyphenyl)methyl]phenol) is a bisphenol that is structurally similar to bisphenol A (BPA). In response to consumer concern towards BPA, industry has started to substitute BPA for BPF and other bisphenol analogues in the production of epoxy resins and coatings for various applications. In 2016, it was reported that commercially sold mustard contained naturally occurring BPF. Here, the existing literature was reviewed to investigate whether other natural sources of BPF among edible plants exist, including their impact on human exposure to BPF. Coeloglossum viride var. bracteatum (rhizome), Galeola faberi (rhizome), Gastrodia elata (rhizome), Xanthium strumarium (seeds) and Tropidia curculioides (root) were found to contain naturally occurring BPF. Botanical extracts from these plants are used in traditional Chinese medicine. The highest values of BPF were recorded for G. elata and T. curculioides. Information on precise doses of the plant extracts used is scarce; however, for G. elata, also known as Tian Ma and available in powder form, a daily exposure of BPF from this source could theoretically amount up to 4.5 µg/kg body weight per day (based on a 70 kg body weight). Therefore, herbal products used in traditional Chinese medicine should be considered as a potential source contributing to the overall human exposure when assessing endocrine-active bisphenolic compounds.

Minor structural modifications of bisphenol A strongly affect physiological responses of HepG2 cells Abstract Bisphenols represent a large group of structurally similar compounds. In contrast to bisphenol A (BPA) and bisphenol S (BPS), however, toxicological data are usually scarce, thus making bisphenols an ideal candidate for read-across assessments. BPA, bisphenol C (BPC) and a newly synthesized bisphenol A/C (BPA/C) differ only by one methyl group attached to the phenolic ring. Their EC50 values for cytotoxicity and logPOW values are comparable. However, the estrogenic activities of these bisphenols are not comparable and among this group only BPC leads to a decrease of the mitochondrial membrane potential and ATP concentration in HepG2 cells. Conversely, the cell division rate was decreased by BPS, BPA, BPC and BPA/C at 10% toxicity (EC10). At lower concentrations, only BPC significantly affected proliferation. The pro-inflammatory cytokines TGFB1 and TNFwere significantly upregulated by BPC only, while SPP1 was upregulated by BPA, BPA/C and BPS. BPC led to the release of cytochrome c from mitochondria, indicating that this compound is capable of inducing apoptosis. In conclusion, the read-across approach revealed non-applicable in the case of the various structurally and physicochemically comparable bisphenols tested in this study, as the presence of one or two additional methyl group(s) attached at the phenol ring profoundly affected cellular physiology.

Integration of epidemiological findings with mechanistic evidence in regulatory pesticide risk assessment: EFSA experiences Abstract Toxicological risk assessment of plant protection products (PPP) is currently carried out with the principal input from regulatory toxicology studies following OECD test guidelines, with little input from epidemiological data. An EFSA-commissioned systematic review of pesticide epidemiological studies (Ntzani et al. in Literature review on epidemiological studies linking exposure to pesticides and health effects. EFSA supporting publication 2013:EN-497, 2013) revealed statistically significant associations, among others, between pesticide exposures, and Parkinson's disease and childhood leukemia. Thereafter, EFSA launched a project with a mandate for the plant protection products and their residues (PPR) Panel to set the ground for the use of epidemiological data in the risk assessment of pesticides, as requested by Regulation (EC) 1107/2009. The project culminated with the publication of two EFSA's scientific opinions on the potential contribution of experimental investigations and epidemiological studies in PPP risk assessment and with the scientific conference held on 20 November 2017, in Parma, Italy. The application of modern methodologies in exposure assessment, toxicology and epidemiology would improve the pesticide risk assessment process and support a mechanistic shift for the integration of these three disciplines under a novel paradigm in risk assessment. The application of the adverse outcome pathway (AOP) conceptual framework to this approach would contribute to gain insight into the biological plausibility of a hazard identified in epidemiological or experimental studies and would inform an Integrated Approach to Testing and Assessment (IATA) within a regulatory context.