Naveed Honarvar

Experience with local lymph node assay performance standards using standard radioactivity and nonradioactive cell count measurements

The local lymph node assay (LLNA) is the preferred test for identification of skin‐sensitizing substances by measuring radioactive thymidine incorporation into the lymph node. To facilitate acceptance of nonradioactive variants, validation authorities have published harmonized minimum performance standards (PS) that the alternative endpoint assay must meet. In the present work, these standards were applied to a variant of the LLNA based on lymph node cell counts (LNCC) run in parallel as a control with the standard LLNA with radioactivity measurements, with threshold concentrations (EC3) being determined for the sensitizers. Of the 22 PS chemicals tested in this study, 21 yielded the same results from standard radioactivity and cell count measurements; only 2‐mercaptobenzothiazole was positive by LLNA but negative by LNCC. Of the 16 PS positives, 15 were positive by LLNA and 14 by LNCC; methylmethacrylate was not identified as sensitizer by either of the measurements. Two of the six PS negatives tested negative in our study by both LLNA and LNCC. Of the four PS negatives which were positive in our study, chlorobenzene and methyl salicylate were tested at higher concentrations than the published PS, whereas the corresponding concentrations resulted in consistent negative results. Methylmethacrylate and nickel chloride tested positive within the concentration range used for the published PS. The results indicate cell counts and radioactive measurements are in good accordance within the same LLNA using the 22 PS test substances. Comparisons with the published PS results may, however, require balanced analysis rather than a simple checklist approach. Copyright

Assessment of Pre- and Pro-haptens Using Nonanimal Test Methods for Skin Sensitization

Because of ethical and regulatory reasons, several nonanimal test methods to assess the skin sensitization potential of chemicals have been developed and validated. In contrast to in vivo methods, they lack or provide limited metabolic capacity. For this reason, identification of pro-haptens but also pre-haptens, which require molecular transformations to gain peptide reactivity, is a challenge for these methods. In this study, 27 pre- and pro-haptens were tested using nonanimal test methods. Of these, 18 provided true positive results in the direct peptide reactivity assay (DPRA; sensitivity of 67%), although lacking structural alerts for direct peptide reactivity. The reaction mechanisms leading to peptide depletion in the DPRA were therefore elucidated using mass spectrometry. Hapten-peptide adducts were identified for 13 of the 18 chemicals indicating that these pre-haptens were activated and that peptide binding occurred. Positive results for five of the 18 chemicals can be explained by dipeptide formations or the oxidation of the sulfhydryl group of the peptide. Nine of the 27 chemicals were tested negative in the DPRA. Of these, four yielded true positive results in the keratinocyte and dendritic cell based assays. Likewise, 16 of the 18 chemicals tested positive in the DPRA were also positive in either one or both of the cell-based assays. A combination of DPRA, KeratinoSens, and h-CLAT used in a 2 out of 3 weight of evidence (WoE) approach identified 22 of the 27 pre- and pro-haptens correctly (sensitivity of 81%), exhibiting a similar sensitivity as for directly acting haptens. This analysis shows that the combination of in chemico and in vitro test methods is suitable to identify pre-haptens and the majority of pro-haptens.

Uterine adenocarcinoma in the rat induced by afidopyropen. An analysis of the lesion's induction, progression and its relevance to humans

ABSTRACT Afidopyropen is a novel insecticide that acts as a TRPV channel modulator in chordotonal organs of target insects. In two carcinogenicity studies with Fischer rats, an increased incidence of uterine adenocarcinomas was observed at 1000 and 3000 ppm. This finding prompted an investigation of the mechanism of the tumor formation as well as the relevance of this mechanism to humans. The mechanistic work took parallel paths: one path investigated the pharmacokinetic properties of the test substance at the doses where the tumors were found; while the second path examined the key mechanistic events that culminated in uterine adenocarcinomas. The results of the investigation indicated that the tumors only occurred at doses where excretion of test substance was saturated – indicating that homeostatic biological and/or physiological processes were overwhelmed. At the doses where these processes were overwhelmed, the test substance acted through a mechanism of dopamine agonism, triggering a cascade key events that resulted in uterine adenocarcinomas. An analysis of these mechanisms observed in rat showed that they are both quantitatively (pharmacokinetic mechanism) and qualitatively (dopamine agonism mechanism) not relevant to humans. Therefore the uterine adenocarcinomas observed in the rat associated with high doses of Afidopyropen are not expected to pose a carcinogenic risk to humans. HighlightsAfidopyropen induces rat uterine adenocarcinomas at high doses.Excretion of Afidopyropen was saturated at high doses.Dopamine agonism identified as MoA for induction of rat uterine adenocarcinomas.

Immunophenotyping does not improve predictivity of the local lymph node assay in mice

The local lymph node assay (LLNA) is a regulatory accepted test for the identification of skin sensitizing substances by measuring radioactive thymidine incorporation into the lymph node. However, there is evidence that LLNA is overestimating the sensitization potential of certain substance classes in particular those exerting skin irritation. Some reports describe the additional use of flow cytometry‐based immunophenotyping to better discriminate irritants from sensitizing irritants in LLNA. In the present study, the 22 performance standards plus 8 surfactants were assessed using the radioactive LLNA method. In addition, lymph node cells were immunophenotyped to evaluate the specificity of the lymph node response using cell surface markers such as B220 or CD19, CD3, CD4, CD8, I‐Aκ and CD69 with the aim to allow a better discrimination above all between irritants and sensitizers, but also non‐irritating sensitizers and non‐sensitizers. However, the markers assessed in this study do not sufficiently differentiate between irritants and irritant sensitizers and therefore did not improve the predictive capacity of the LLNA. Copyright