Finding synergies for the 3Rs - Repeated Dose Toxicity testing: Report from an EPAA Partners' Forum.

The European Partnership for Alternative Approaches to Animal Testing (EPAA) convened a Partners' Forum on repeated dose toxicity (RDT) testing to identify synergies between industrial sectors and stakeholders along with opportunities to progress these in existing research frameworks. Although RTD testing is not performed across all industrial sectors, the OECD accepted tests can provide a rich source of information and play a pivotal role for safety decisions relating to the use of chemicals. Currently there are no validated alternatives to repeated dose testing and a direct one-to-one replacement is not appropriate. However, there are many projects and initiatives at the international level which aim to implement various aspects of replacement, reduction and refinement (the 3Rs) in RDT testing. Improved definition of use, through better problem formulation, aligned to harmonisation of regulations is a key area, as is the more rapid implementation of alternatives into the legislative framework. Existing test designs can be optimised to reduce animal use and increase information content. Greater use of exposure-led decisions and improvements in dose selection will be beneficial. In addition, EPAA facilitates sharing of case studies demonstrating the use of Next Generation Risk Assessment applying various New Approach Methodologies to assess RDT.

Derivation of an inhalation TTC for the workplace based on DNEL values reported under REACH.

The Threshold of Toxicological Concern (TTC) concept defines a generic tolerable exposure for chemicals of unknown toxicity below which the risk of adverse health effects is considered very small. The original concept was refined and extended over the years, based either on differentiated structural classes or on additional information on certain toxicological endpoints. Initially, the focus of the TTC application was only on systemic toxic effects after repeated oral intake and consisted of one value. However, under well-defined boundary conditions, a long-term systemic inhalation TTC could also serve as a cut-off criterion for occupational exposure in those cases where workers are exposed to very low levels of chemicals by inhalation contact and could therefore reduce the need to perform animal tests. Within the scope of the European REACH legislation, several thousand systemic long-term inhalation Derived No Effect Levels (DNELs) for workers have been published. By statistical evaluation of the DNEL distribution of 1876 chemicals and the resulting 99th percentiles, we propose an inhalation workplace TTC for systemic effects in the region of 50 µg/m3 (7 µg/kg body weight/day). Specific exclusion criteria apply for the discussed concept.

Interspecies extrapolation based on the RepDose database--a probabilistic approach.

Repeated dose toxicity studies from the RepDose database (DB) were used to determine interspecies differences for rats and mice. NOEL (no observed effect level) ratios based on systemic effects were investigated for three different types of exposure: inhalation, oral food/drinking water and oral gavage. Furthermore, NOEL ratios for local effects in inhalation studies were evaluated. On the basis of the NOEL ratio distributions, interspecies assessment factors (AF) are evaluated. All data sets were best described by a lognormal distribution. No difference was seen between inhalation and oral exposure for systemic effects. Rats and mice were on average equally sensitive at equipotent doses with geometric mean (GM) values of 1 and geometric standard deviation (GSD) values ranging from 2.30 to 3.08. The local AF based on inhalation exposure resulted in a similar distribution with GM values of 1 and GSD values between 2.53 and 2.70. Our analysis confirms former analyses on interspecies differences, including also dog and human data. Furthermore it supports the principle of allometric scaling according to caloric demand in the case that body doses are applied. In conclusion, an interspecies distribution animal/human with a GM equal to allometric scaling and a GSD of 2.5 was derived.