Maillot-Marechal, E. | bioRxiv Science

bioRxiv2023

A screening strategy based on two zebrafish eleuthero-embryo OECD test guidelines for the hazard assessment of chemicals: case of some bisphenol substitutes

The use of efficient screening strategies for the hazard assessment of chemicals is a current challenge to support regulatory requirements. Herein, we combined two eleuthero-embryo assays, a refined Fish Embryo Toxicity assay (OECD TG 236) and the EASZY assay (OECD TG 250), both using transgenic (tg) (cyp19a1b:GFP). The simultaneous performance of both assays provides complementary information about the acute toxicity, developmental effects, and estrogenic activity. A refined EASZY assay is however necessary to obtain accurate EC50. In this work we compared bisphenol A (BPA) and ten of its substitutes. In the refined FET, most of the selected bisphenols were more toxic than BPA, induced developmental effects on zebrafish embryos, some being identified as teratogenic compounds (BPF, BPS-MAE, BPC Cl, 4,4ODP), and ten of them induced GFP intensity. Endocrine activity of the BPs was further investigated in the EASZY assay at concentrations that do not affect the survival and the hatching rates or induce developmental toxicity based on the target concentrations used as previously defined in the refined FET. All bisphenols elicited an estrogenic activity with the notable exception of TCBPA. Most BPs were more estrogenic than BPA, acted as agonist ligands of zfER{beta}2 as shown in zebrafish-specific in vitro reporter gene assay and functional zfERs were required to induce brain aromatase. Interestingly, BPS-MAE and BPS-MPE behave as pro-estrogens as they were unable to transactivate zebrafish ER{beta}2 in vitro but induced brain aromatase in vivo. Overall, the implementation of the zebrafish eleuthero embryo-based screening strategy efficiently provided relevant data contributing to their environmental hazard. It also provides further evidence that bisphenols modulate cyp19a1b expression during early brain development whom potential short and long-term adverse effects need to be addressed. SYNOPSISa zebrafish eleuthero embryo-screening strategy based on OECD TGs was implemented for an efficient hazard assessment of bisphenols revealing that most of them are more toxic and/or estrogenic than BPA

pharmacology and toxicology↗

bioRxiv2019

Repeated exposure to nanosecond high power pulsed microwaves increases cancer incidence in rat

High-power microwaves are used to inhibit electronics of threatening military or civilian vehicles. This work aims to assess health hazards of high-power microwaves and helps define hazard threshold levels of modulated radiofrequency exposures such as those emitted by the first generations of mobile phones. Rats were exposed to the highest possible field levels, under single acute or repetitive exposures for eight weeks. Intense microwave electric fields at 1 MV/m of nanoseconds duration were applied from two sources at different carrier frequencies of 10 and 3.7 GHz. The repetition rate was 100 pps, and the duration of train pulses lasted from 10 s to twice 8 min. The effects were studied on the central nervous system, by labelling brain inflammation marker GFAP and by performing different behavioural tests: rotarod, T-maze, beam-walking, open-field, and avoidance test. Long-time survival was measured in animals repeatedly exposed, and anatomopathological analysis was performed on animals sacrificed at two years of life or at death if earlier. One group was sham exposed. Few effects were observed on behaviour. With acute exposure, an avoidance reflex was shown at very high, thermal level (22 W/kg); GFAP was increased some days after exposure. Most importantly, with repeated exposures, survival time was 4-month shorter in the exposed group, with eleven animals exhibiting a large sub-cutaneous tumour, compared to two in the sham group. A residual X-ray exposure was also present in the beam (0.8 Gy), which is not a bias for the observed result. High power microwaves below thermal level in average, can increase cancer incidence and decrease survival time in rats, without clear effects on behaviour. The parameters of this effect need to be explored further, and a more precise dosimetry to be performed.

biophysics↗