For ethical and regulatory reasons, in vitro tests for scoring potential toxicities of cosmetics are essential. A test strategy for investigating potential skin sensitization using two human keratinocytic and two human dendritic cell lines has been developed (Mehling et al. Arch Toxicol 86:1273–1295, 2012). Since prohaptens may be metabolically activated in the skin, information on xenobiotic metabolizing enzyme (XME) activities in these cell lines is of high interest. In this study, XME activity assays, monitoring metabolite or cofactor, showed the following: all three passages of keratinocytic (KeratinoSens® and LuSens) and dendritic (U937 und THP-1) cells displayed N-acetyltransferase 1 (NAT1) activities (about 6–60 nmol/min/mg S9-protein for acetylation of para-aminobenzoic acid). This is relevant since reactive species of many cosmetics are metabolically controlled by cutaneous NAT1. Esterase activities of about 1–4 nmol fluorescein diacetate/min/mg S9-protein were observed in all passages of investigated keratinocytic and about 1 nmol fluorescein diacetate/min/mg S9-protein in dendritic cell lines. This is also of practical relevance since many esters and amides are detoxified and others activated by cutaneous esterases. In both keratinocytic cell lines, activities of aldehyde dehydrogenase (ALDH) were observed (5–17 nmol product/min/mg cytosolic protein). ALDH is relevant for the detoxication of reactive aldehydes. Activities of several other XME were below detection, namely the investigated cytochrome P450-dependent alkylresorufin O-dealkylases 7-ethylresorufin O-deethylase, 7-benzylresorufin O-debenzylase and 7-pentylresorufin O-depentylase (while NADPH cytochrome c reductase activities were much above the limit of quantification), the flavin-containing monooxygenase, the alcohol dehydrogenase as well as the UDP glucuronosyl transferase activities.

EPA’s Office of Pesticide Programs (OPP) is committed to improving and transforming its approaches to pesticide human health and ecological risk assessment and management by increasing the efficiency and effectiveness of testing for risk assessment to inform decisions and to reduce the cost of the process both in dollars and animals. OPP is building on the ambitious NAS vision for Toxicity Testing in the 21st Century which calls for a shift toward the avoidance of significant perturbations of normal cellular pathways in exposed populations by using cell based assays to measure these perturbations, dose-response modeling organized around computational systems biology models of the circuitry underlying each toxicity pathway, and in vitro to in vivo extrapolations based on pharmacokinetic models to predict tissue concentrations under specific exposure conditions. OPP’s long-term goal is to move from a paradigm that involves requiring in vivo testing for “every possible adverse outcome” toward a hypothesis-driven paradigm where in vivo testing is targeted to the most likely hazards and risks of concern. Thus, rather than taking a one size fits all approach to toxicity testing OPP proposes a progressive, tiered-testing approach that starts with hazard-based hypotheses about the plausible toxicological and fate potential of a pesticide or group of pesticides based on their physical-chemical properties (e.g., using read-across and structure activity relationships [SARs] to examine toxicological potential). Existing exposure and toxicity information is then combined with refined exposure models, computational toxicological models (e.g., quantitative SARs or QSARs [(Q)SARs]), and diagnostic in vitro assays to narrow requirements for in vivo. Consistent with this view is the consideration of time and cost efficiencies associated with the generation and interpretation of toxicity and exposure data and the sound and responsible use of animals in testing. As the science evolves so too must the process to apply this information to predict the effects of concern in humans and non-humans well. Toxicity Test Validation in the 21st Century requires a hierarchical approach tailored to the purpose desired and based on an improved understanding of chemically-induced adverse outcome pathways to make the linkage between the molecular initiating event and an adverse outcome at the individual or population level. Approaches to accomplish this will be described in this talk with a particular emphasis on the evaluation of endocrine disruption. I-4-530 Use of Tox21 tools from screening and prioritization to risk assessment: When, how and what?