A Short History of the Consideration of Sex Differences in Biomedical Research - Lessons for the In Vitro Community from Animal Models and Human Clinical Trials.

In recent decades, it has become clear that in many fields - such as drug development, particularly with regard to drug dosage and specific disease treatment - the sex of a patient must be taken into consideration, in view of the fact that male and female physiology and pathophysiology show many differences of practical concern. While, in the last decade or so, considerable efforts have been undertaken to consider the sex of the animals during the planning of experiments, this topic has just started to be acknowledged in in vitro studies. Cells in such studies seem mainly to be used according to their availability, without considering the sex of the original donor. Even when such information is available, experimental data are reported without overtly detailing this information. In recent years, the increasing complexity of in vitro models (e.g. stem cell-based, 3-D cultures, organoids, or organ-on-a-chip technologies) has contributed to systems that better resemble the human in vivo situation. However, the issue of the sex of the experimental organisms being used has not yet been properly taken up by the cell culture community. Thus, alongside the increasing complexity of multicell-type models, we now see in vitro models that incorporate cells from both male and female origin - this representing, in fact, a genetic chimaera. Here, we aim to discuss where we are currently, with respect to considering the sex of any animals or humans used in experiments, and we try to identify what is lacking in the cell culture field, in order to help facilitate change.

Metabolic activation of nonpolar sediment extracts results in enhanced thyroid hormone disrupting potency.

Traditional sediment risk assessment predominantly considers the hazard derived from legacy contaminants that are present in nonpolar sediment extracts, such as polychlorinated biphenyls (PCBs), dioxins, furans (PCDD/Fs), and polyaromatic hydrocarbons (PAHs). Although in vivo experiments with these compounds have shown to be thyroid hormone disrupting (THD), in vitro their THD potency is not observed in nonpolar sediment extracts. This is hypothesized to be due to the absence of in vitro biotransformation which will result in bioactivation of the lipophilic compounds into THD hydroxyl metabolites. This study reveals that indeed metabolically activated nonpolar contaminants in sediments can competitively bind to thyroid hormone transport proteins. Sediment fractions were incubated with S9 rat microsomes, and the metabolites were extracted with a newly developed method that excludes most of the lipids to avoid interference in the applied nonradioactive 96-well plate TTR competitive binding assay. Metabolic activation increased the TTR binding potency of nonpolar fractions of POP-polluted sediments up to 100 times, resulting in potencies up to 240 nmol T4 equivalents/g sediment equivalent (nmol T4-Eq/g SEQ). This demonstrates that a more realistic in vitro sediment THD risk characterization should also include testing of both polar and medium polar sediment extracts for THD, as well as bioactivated nonpolar sediment fractions to prevent underestimation of its toxic potency.

Policy relevant results from an expert elicitation on the health risks of phthalates.

BACKGROUND: The EU 6th Framework Program (FP)-funded Health and Environment Network (HENVINET) aimed to support informed policy making by facilitating the availability of relevant knowledge on different environmental health issues. An approach was developed by which scientific agreement, disagreement, and knowledge gaps could be efficiently identified, and expert advice prepared in a way that is usable for policy makers. There were two aims of the project: 1) to apply the tool to a relevant issue; the potential health impacts of the widely used plasticizers, phthalates, and 2) to evaluate the method and the tool by asking both scientific experts and the target audience, namely policy makers and stakeholders, for their opinions. METHODS: The tool consisted of an expert consultation in several steps on the issue of phthalates in environmental health. A diagram depicting the cause-effect chain, from the production and use of phthalates to potential health impacts, was prepared based on existing reviews. This was used as a basis for an online questionnaire, through which experts in the field were consulted. The results of this first round of consultation laid the foundation for a new questionnaire answered by an expert panel that, subsequently, also discussed approaches and results in a workshop. One major task of the expert panel was to pinpoint priorities from the cause-effect chain according to their impact on the extent of potential health risks and their relevance for reducing uncertainty. The results were condensed into a policy brief that was sent to policy makers and stakeholders for their evaluation. RESULTS: The experts agreed about the substantial knowledge gaps within the field of phthalates. The top three priorities for further research and policy action were: 1) intrauterine exposure, 2) reproductive toxicology, and 3) exposure from medical devices. Although not all relevant information from the cause-effect chain is known for phthalates, most experts thought that there are enough indications to justify a precautionary approach and to restrict their general use. Although some of the experts expressed some scepticism about such a tool, most felt that important issues were highlighted. CONCLUSIONS: The approach used was an efficient way at summarising priority knowledge gaps as a starting point for health risk assessment of compounds, based on their relevance for the risk assessment outcome. We conclude that this approach is useful for supporting policy makers with state-of-the-art scientific knowledge weighed by experts. The method can assist future evidence-based policy making.

Safety assessment of titanium dioxide (E171) as a food additive.

The present opinion deals with an updated safety assessment of the food additive titanium dioxide (E 171) based on new relevant scientific evidence considered by the Panel to be reliable, including data obtained with TiO2 nanoparticles (NPs) and data from an extended one-generation reproductive toxicity (EOGRT) study. Less than 50% of constituent particles by number in E 171 have a minimum external dimension < 100 nm. In addition, the Panel noted that constituent particles < 30 nm amounted to less than 1% of particles by number. The Panel therefore considered that studies with TiO2 NPs < 30 nm were of limited relevance to the safety assessment of E 171. The Panel concluded that although gastrointestinal absorption of TiO2 particles is low, they may accumulate in the body. Studies on general and organ toxicity did not indicate adverse effects with either E 171 up to a dose of 1,000 mg/kg body weight (bw) per day or with TiO2 NPs (> 30 nm) up to the highest dose tested of 100 mg/kg bw per day. No effects on reproductive and developmental toxicity were observed up to a dose of 1,000 mg E 171/kg bw per day, the highest dose tested in the EOGRT study. However, observations of potential immunotoxicity and inflammation with E 171 and potential neurotoxicity with TiO2 NPs, together with the potential induction of aberrant crypt foci with E 171, may indicate adverse effects. With respect to genotoxicity, the Panel concluded that TiO2 particles have the potential to induce DNA strand breaks and chromosomal damage, but not gene mutations. No clear correlation was observed between the physico-chemical properties of TiO2 particles and the outcome of either in vitro or in vivo genotoxicity assays. A concern for genotoxicity of TiO2 particles that may be present in E 171 could therefore not be ruled out. Several modes of action for the genotoxicity may operate in parallel and the relative contributions of different molecular mechanisms elicited by TiO2 particles are not known. There was uncertainty as to whether a threshold mode of action could be assumed. In addition, a cut-off value for TiO2 particle size with respect to genotoxicity could not be identified. No appropriately designed study was available to investigate the potential carcinogenic effects of TiO2 NPs. Based on all the evidence available, a concern for genotoxicity could not be ruled out, and given the many uncertainties, the Panel concluded that E 171 can no longer be considered as safe when used as a food additive.

Time-dependent effects of perfluorinated compounds on viability in cerebellar granule neurons: Dependence on carbon chain length and functional group attached.

The toxicity of long chained perfluoroalkyl acids (PFAAs) has previously been reported to be related to the length of the perfluorinated carbon chain and functional group attached. In the present study, we compared the cytotoxicity of six PFAAs, using primary cultures of rat cerebellar granule neurons (CGNs). Two perfluoroalkyl sulfonic acids (PFSAs, chain length C6 and C8) and four perfluoroalkyl carboxylic acids (PFCAs, chain length C8-C11) were studied. These PFAAs have been detected in human blood and the brain tissue of mammals. The cell viability trypan blue and MTT assays were used to determine toxicity potencies (based on LC50 values) after 24h exposure (in descending order): perfluoroundecanoic acid (PFUnDA)≥perfluorodecanoic acid (PFDA)>perfluorooctanesulfonic acid potassium salt (PFOS)>perfluorononanoic acid (PFNA)>perfluorooctanoic acid (PFOA)>perfluorohexanesulfonic acid potassium salt (PFHxS). Concentrations of the six PFAAs that produced equipotent effects after 24h exposure were used to further explore the dynamics of viability changes during this period. Therefore viability was assessed at 10, 30, 60, 90, 120 and 180min as well as 6, 12, 18 and 24h. A difference in the onset of reduction in viability was observed, occurring relatively quickly (30-60min) for PFOS, PFDA and PFUnDA, and much slower (12-24h) for PFHxS, PFOA and PFNA. A slight protective effect of vitamin E against PFOA, PFNA and PFOS-induced reduction in viability indicated a possible involvement of oxidative stress. PFOA and PFOS did not induce lipid peroxidation on their own, but significantly accelerated cumene hydroperoxide-induced lipid peroxidation. When distribution of the six PFAAs in the CGN-membrane was investigated using NanoSIMS50 imaging, two distinct patterns appeared. Whereas PFHxS, PFOS and PFUnDA aggregated in large hotspots, PFOA, PFNA and PFDA showed a more dispersed distribution pattern. In conclusion, the toxicity of the investigated PFAAs increased with increasing carbon chain length. For molecules with a similar chain length, a sulfonate functional group led to greater toxicity than a carboxyl group.

New approaches to assess the transthyretin binding capacity of bioactivated thyroid hormone disruptors.

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl-ethers (PBDEs) are metabolized into hydroxylated metabolites (OH-PCBs/PBDEs), which can disrupt the thyroid hormone homeostasis. Binding of these metabolites to transport proteins such as transthyretin (TTR) is an important mechanism of their toxicity. Several methods to quantify the competitive thyroxine (T(4)) displacement potency of pure metabolites exist. However, quantification of the potency of in vitro metabolized PCBs and PBDEs has drawbacks related to the coextraction of compounds disturbing the T(4)-TTR competitive binding assay. This study identifies and quantifies the major coextractants namely cholesterol, saturated and nonsaturated fatty acids (SFA and NSFA) at levels above 20 nmol per mg equivalent protein following various extraction methods. Their TTR binding potency was analyzed in a downscaled, nonradioactive fluorescence displacement assay. At concentration factors needed for TTR competitive binding, at least 10µM of these coextracts is present, whereas individual SFA and NSFA disturb the assay from 0.3µM. The effectiveness of the in vitro metabolism and extraction of the model compounds CB 77 and BDE 47 was chemically quantified with a newly developed chromatographic method analyzing silylated derivatives of the OH-metabolites and coextractants. A new method to selectively extract metabolites and limit coextraction of disturbing compounds to less than 5 nmol per mg equivalent protein is presented. It is now possible to make a dose-response curve up to 50% inhibition with bioactivated CB 77 and BDE 47. The toxic potencies of bioactivated persistent organic pollutants (POPs) should be taken into account to prevent serious underestimation of their hazard and risk.