Review of dose setting for the extended one-generation reproductive toxicity studies (OECD TG 443): Considerations on ECHA's dose level selection recommendations.

During 2020, The European Chemicals Agency (ECHA) began evaluating the OECD Test Guideline 443: Extended One Generation Reproductive Toxicity Study (EOGRTS) to analyze specific aspects related to study design, conduct and toxicological findings. A significant outcome of this ECHA evaluation focused on adequate dose level selection. Subsequently, ECHA published recommendations for DART studies, however, these recommendations seemingly do not align with the principles of the 3Rs, animal welfare or human safety goals, specifically, regarding three aspects. First, the requirement to segregate testing for sexual function and fertility from the ability to produce normally developing offspring increases the risk of inadequate identification of postnatal hazards for development and sexual function and fertility, therefore failing human health protection goals. Second, the current ECHA high-dose level setting recommendations for EOGRTS exceed the MTD (Maximum Tolerated Dose), and therefore compromise the interpretation of the biological response relative to the intrinsic effect of the chemical under evaluation. Third, the combination of these aspects will result in an increase in the number of animals tested, increasing animal welfare concerns. This paper reflects the consensus of subject matter experts, professional, and scientific societies who have authored and signed on to this statement. The signatories encourage ECHA to adopt a revised science-driven approach to the dose selection criteria that strikes a balance between regulatory vigilance and scientific pragmatism.

Toxicological Assessment of Higher Olefins in OECD TG 422 Repeated Dose and Reproductive /Developmental Toxicity Screening Tests in Han Wistar Rats.

Higher olefins (HO) are used primarily as intermediates in the production of other chemicals, such as polymers, fatty acids, plasticizer alcohols, surfactants, lubricants, amine oxides, and detergent alcohols. The potential toxicity of five HO (i.e., 1-Octene, Nonene, Decene, Hexadecene, and 1-Octadecene) with carbon ranging from C8 to C18 was examined in a combined repeated dose and reproduction/developmental toxicity screening study (OECD TG 422). These five HO were administered to Han Wistar rats by gavage at 0 (controls), 100, 300, and 1000 mg/kg bw/day. As a group of substances, adaptive changes in the liver (liver weight increase without pathological evidence), as well as increased kidney weight in male rats, were observed in HO with carbon numbers from C8 to C10. The overall systemic no observed adverse effect level (NOAEL) for all HO was determined at 1000 mg/kg bw/day. In the reproductive/developmental toxicity assessment, offspring viability, size, and weights were reduced in litters from females treated with Nonene at 1000 mg/kg bw/day. The overall no observed effects level (NOEL) for reproductive toxicity was considered to be 300 mg/kg bw/day for Nonene and 1000 mg/kg bw/day for the other four HO, respectively. These data significantly enrich the database on the toxicity of linear and branched HO, allowing comparison with similar data published on a range of linear and branched HO. Comparisons between structural class and study outcome provide further supportive data in order to validate the read-across hypothesis as part of an overall holistic testing strategy.

An overview of the current challenges when using rabbits for prenatal developmental toxicity studies with consideration of the impact on data interpretation.

The rabbit prenatal developmental toxicity study is an international testing requirement for the identification and characterisation of the potential hazards of chemicals to human health. The importance of the rabbit for the detection of chemical teratogens is without question. However, the rabbit when used as a laboratory test species presents unique challenges affecting data interpretation. The purpose of this review is to identify the factors which may impact the behaviour of the pregnant rabbit and lead to significant inter-animal variability, confounding interpretation of maternal toxicity. Additionally, the importance of appropriate dose selection is discussed not least because of the conflicting guidance for identifying and defining acceptable maternal toxicity that lack reference to the rabbit in particular. The test guideline prenatal developmental toxicity study is often unable to distinguish between developmental effects as a consequence of maternal toxicity and those that are a direct effect of the test chemical on the offspring yet there is increasing pressure to use the highest possible dose levels to induce significant maternal toxicity which for the rabbit, a species little understood in toxicological terms and one that is highly susceptible to stress, is defined by very few endpoints. Interpretation of study data is further confounded by dose selection yet the developmental effects, even in the presence of maternal toxicity, are being used in Europe as the basis for classifying agents as reproductive hazards and the maternal effects are being used to define key reference values.

Assessment of the Intestinal Absorption of Higher Olefins by the Everted Gut Sac Model in Combination with In Silico New Approach Methodologies.

To reduce the number of animals and studies needed to fulfill the information requirements as required by Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (EC no. 1907/2006), a read-across approach was used to support approximately 30 higher olefins. This study aimed to assess the absorption potential of higher olefins through the gut wall as the experimentally determined bioavailability which would strengthen the read-across hypothesis and justification, reducing the need for toxicity studies on all of the higher olefins. The absorption potential of a series of higher olefins (carbon range from 6 to 28, with five configurations of the double bond) was determined in the in vitro everted rat small intestinal sac model and subsequently ranked. In addition, in silico approaches were applied to predict the reactivity, lipophilicity, and permeability of higher olefins. In the in vitro model, everted sacs were incubated in "fed-state simulated small intestinal fluid" saturated with individual higher olefins. The sac contents were then collected, extracted, and analyzed for olefin content using gas chromatography with a flame ionization detector. The C6 to C10 molecules were readily absorbed into the intestinal sacs. Marked inter-compound differences were observed, with the amount of absorption generally decreasing with the increase in carbon number. Higher olefins with ≥C14 carbons were either not absorbed or very poorly absorbed. In the reactivity simulation study, the reactivity is well described by the position of the double bond rather than the number of carbon atoms. In the lipophilicity and permeability analysis, both parameter descriptors depend mainly on the number of carbon atoms and less on the position of the double bond. In conclusion, these new approach methodologies provide supporting information on any trends or breakpoints in intestinal uptake and a hazard matrix based on carbon number and position of the double bond. This matrix will further assist in the selection of substances for inclusion in the mammalian toxicity testing programme.