We used TissUse's HUMIMIC Chip2 microfluidic model, incorporating reconstructed skin models and liver spheroids, to investigate the impact of consumer‐relevant application scenarios on the metabolic fate of the hair dye, 4‐amino‐2‐hydroxytoluene (AHT). After a single topical or systemic application of AHT to Chip2 models, medium was analysed for parent and metabolites over 5 days. The metabolic profile of a high dose (resulting in a circuit concentration of 100 μM based on 100% bioavailability) of AHT was the same after systemic and topical application to 96‐well EpiDerm™ models. Additional experiments indicated that metabolic capacity of EpiDerm™ models were saturated at this dose. At 2.5 μM, concentrations of AHT and several of its metabolites differed between application routes. Topical application resulted in a higher Cmax and a 327% higher area under the curve (AUC) of N‐acetyl‐AHT, indicating a first‐pass effect in the EpiDerm™ models. In accordance with in vivo observations, there was a concomitant decrease in the Cmax and AUC of AHT‐O‐sulphate after topical, compared with systemic application. A similar alteration in metabolite ratios was observed using a 24‐well full‐thickness skin model, EpiDermFT™, indicating that a first‐pass effect was also possible to detect in a more complex model. In addition, washing the EpiDermFT™ after 30 min, thus reflecting consumer use, decreased the systemic exposure to AHT and its metabolites. In conclusion, the skin–liver Chip2 model can be used to (a) recapitulate the first‐pass effect of the skin and alterations in the metabolite profile of AHT observed in vivo and (b) provide consumer‐relevant data regarding leave‐on/rinse‐off products.

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Levels of the cytokines interleukin-1-alpha, -1-beta, and -2 (IL-1-alpha, IL-1-beta, IL-2), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) were measured in the mitogen-stimulated whole blood cell cultures from 96 patients with Crohn's disease (48 untreated, 12 treated with sulfasalazine, 36 treated with corticosteroids), 74 patients with ulcerative colitis (21 untreated, 25 treated with sulfasalazine, 28 steroid treated), and 360 healthy controls. The cytokines were measured 4 days after induction by a sensitive immunoenzyme assay. In the blood cell cultures of the untreated and sulfasalazine treated patients with Crohn's disease and ulcerative colitis higher levels of TNF-alpha, IL-1-alpha and IL-1-beta were found whereas IL-2 production was decreased and IFN-gamma-production was not significantly different as compared to the controls. Leukocytes of the corticosteroid-treated patients with both diagnoses showed a lower production of all measured cytokines compared to the untreated patients. The same results were obtained, when the somewhat different counts of mononuclear cells in the peripheral blood of the patients and controls were taken into account. The elevated production of proinflammatory cytokines in the blood cell cultures suggests a systemic immune activation in patients with inflammatory bowel disease.

All cosmetic ingredients registered in Europe must be evaluated for their safety using non-animal methods. Microphysiological systems (MPS) offer a more complex higher tier model to evaluate chemicals. Having established a skin and liver HUMIMIC Chip2 model demonstrating how dosing scenarios impact the kinetics of chemicals, we investigated whether thyroid follicles could be incorporated to evaluate the potential of topically applied chemicals to cause endocrine disruption. This combination of models in the HUMIMIC Chip3 is new; therefore, we describe here how it was optimized using two chemicals known to inhibit thyroid production, daidzein and genistein. The MPS was comprised of Phenion® Full Thickness skin, liver spheroids and thyroid follicles co-cultured in the TissUse HUMIMIC Chip3. Endocrine disruption effects were determined according to changes in thyroid hormones, thyroxine (T4) and 3,3’,5-triiodothyronine (T3). A main part of the Chip3 model optimization was the replacement of freshly isolated thyroid follicles with thyrocyte-derived follicles. These were used in static incubations to demonstrate the inhibition of T4 and T3 production by genistein and daidzein over 4 days. Daidzein exhibited a lower inhibitory activity than genistein and both inhibitory activities were decreased after a 24 h preincubation with liver spheroids, indicating metabolism was via detoxification pathways. The skin-liver-thyroid Chip3 model was used to determine a consumer-relevant exposure to daidzein present in a body lotion based on thyroid effects. A “safe dose” of 0.235 μg/cm2 i.e., 0.047% applied in 0.5 mg/cm2 of body lotion was the highest concentration of daidzein which does not result in changes in T3 and T4 levels. This concentration correlated well with the value considered safe by regulators. In conclusion, the Chip3 model enabled the incorporation of the relevant exposure route (dermal), metabolism in the skin and liver, and the bioactivity endpoint (assessment of hormonal balance i.e., thyroid effects) into a single model. These conditions are closer to those in vivo than 2D cell/tissue assays lacking metabolic function. Importantly, it also allowed the assessment of repeated doses of chemical and a direct comparison of systemic and tissue concentrations with toxicodynamic effects over time, which is more realistic and relevant for safety assessment.