Evaluating the performance of integrated approaches for hazard identification of skin sensitizing chemicals

The currently available animal-free methods for the detection of skin sensitizing potential of chemicals seem promising. However, no single method is able to comprehensively represent the complexity of the processes involved in skin sensitization. To ensure a mechanistic basis and cover the complexity, multiple methods should be integrated into a testing strategy, in accordance with the adverse outcome pathway that describes all key events in skin sensitization. Although current majority voting testing strategies have proven effective, the performance of individual methods is not taken into account. To that end, we designed a tiered strategy based on complementary characteristics of the included methods, and compared it to a majority voting approach. This tiered testing strategy was able to correctly identify all 41 chemicals tested. In terms of total number of experiments required, the tiered testing strategy requires less experiments compared to the majority voting approach. On the other hand, this tiered strategy is more complex due the number of different alternative methods required, and predicted costs are similar for both strategies. Both the tiered and majority voting strategies provide a mechanistic basis for skin sensitization testing, but the strategy most suitable for regulatory decision-making remains to be determined

Human relevance of an in vitro gene signature in HaCaT for skin sensitization

The skin sensitizing potential of chemicals is mainly assessed using animal methods, such as the murine local lymph node assay. Recently, an in vitro assay based on a gene expression signature in the HaCaT keratinocyte cell line was proposed as an alternative to these animal methods. Here, the human relevance of this gene signature is assessed through exposure of freshly isolated human skin to the chemical allergens dinitrochlorobenzene (DNCB) and diphenylcyclopropenone (DCP). In human skin, the gene signature shows similar direction of regulation as was previously observed in vitro, suggesting that the molecular processes that drive expression of these genes are similar between the HaCaT cell line and freshly isolated skin, providing evidence for the human relevance of the gene signature

Comparison of the molecular topologies of stress-activated transcription factors HSF1, AP-1, NRF2, and NF-kappa B in their induction kinetics of HMOX1

For cells, reacting aptly to changes in their environment is of critical importance. The protein Heme oxygenase-1 (HMOX1) plays a critical role as a guard of cellular homeostasis and is considered as a reliable indicator of cellular oxidative stress. A better understanding of the regulation of HMOX1 would assist to understand the physiological role of HMOX1 as well as to improve functional interpretation of the gene as a biomarker in for instance toxicogenomics. Remarkably, no less than four transcription factors are known to regulate the HMOX1 gene: HSF1, AP-1, NRF2, and NF-kB. To investigate induction kinetics of these transcription factors, we constructed mathematical simulation models for each of them. We included the topology of the known interactions of molecules involved in the activation of the transcription factors, and the feedback loops resulting in their down- regulation. We evaluate how the molecular circuitries associated with the different transcription factors differ in terms of their kinetics regarding HMOX1 induction, under different scenarios of acute and less acute stress. We also evaluate the combined effect of the four transcription factors on HMOX1 expression and the resulting alleviation of stress. Overall, the results support the assumption of different biological roles for the four transcription factors, with AP-1 being a fast acting general stress response protein at the expense of efficiency, and NRF2 being important for cellular homeostasis in maintaining low levels of oxidative stress. Keywords: Modelling; Gene regulatory network; Oxidative stress; Denatured protein; HMOX1; Network topology; Transcription facto