Human Umbilical Artery as a New Approach Methodology (NAM) to assess thyroid-disruptive vascular effects of emerging contaminant mixtures

Thyroid hormone system disruption (THSD) is a significant public health concern and an EU research priority. Currently, no New Approach Methodologies (NAMs) are available in the OECD TG to assess THSD. Pregnant women are exposed daily to personal care products containing emerging contaminants, while contaminant interactions may further complicate chemical risk assessment. This work investigated the vascular effects of a mixture of UV filter octylmethoxycinnamate (OMC, 50µmol/L) and antimicrobial agent triclosan (TCS, 10µmol/L), under simulated hyperthyroidism conditions (T3, 6nmol/L). Human umbilical artery (HUA, n=4) was used for ex vivo organ bath experiments. Vascular homeostasis was assessed by serotonin (5-HT, 1µmol/L)-induced contraction and nifedipine (Nif, 1µmol/L)-induced relaxation. Results showed a significant increase (p=0.009) in Nif-induced relaxation in T3-exposed HUA (83.88 ± 2.33%) compared with the control group (62.73 ± 2.25%). Further, T3-exposed HUA treated with TCS exhibited a significant decrease in Nif-induced relaxation (55.52 ± 2.22%) compared with arteries exposed to a single T3- (83.88 ± 2.33%, p=0.005) and OMC-exposure (82.74 ± 2.76%, p=0.005) or OMC+TCS mixture (77.32 ± 3.11%, p=0.018). These findings highlight the T3-role in vascular tone modulation and vasorelaxation, suggesting signaling pathways beyond Ca2+ channels inhibition. Under simulated hyperthyroidism, vascular responses suggest differential modulation by TCS and OMC: OMC appear consistent with those elicited by T3, whereas TCS effects are compatible with predominant Ca2+ channel inhibition. In the mixture, vascular effects resemble those observed in OMC- and T3-exposed HUA, suggesting a possible contribution of OMC to the overall response. These hypotheses require further investigation. Overall, these proof-of-concept findings support the relevance of HUA as a NAM for THSD research. By preserving key physiological features and enabling ex vivo assessment of vascular responses, HUA represents a valuable tool for supporting human risk assessment of thyroid-disrupting chemicals.