Fragrance inhalation toxicity assessment: a proactive testing strategy using ex vivo precision cut lung slices (PCLuS) for the prioritization of selected aroma ingredients candidates for in vivo testing.

Objective: To date, exposure thresholds for fragrance chemicals are most often extrapolated from oral administration data. Due to limited inhalation toxicity data, the potentially high exposure levels toward fragrances - especially in air care applications - are sometimes perceived as potentially critical. Herein, we assessed the potential inhalation toxicity of various commonly used fragrances with main focus on respiratory tract effects.

Methods: 19 high volume fragrances were screened for their cytotoxic potential by using rat precision cut lung slices (PCLuS). Based on the screening data, chemicals were categorized into low, mid, and high cytotoxicity groups. From these groups, five fragrances were selected for further in vivo investigation. In a 14-day inhalation study, male 7-week old Wistar rats were exposed to geraniol, geranyl acetate, citral, L-menthol, and p-tert-butyl-alpha-methylhydro-cinnamic aldehyde (BMHCA) to investigate the respiratory and sensory irritation potential.

Results: Ex vivo screening allowed for a preliminary classification of the cytotoxic potential, facilitating the selection of candidates for in vivo inhalation assessments. Local respiratory irritation was observed for liquid aerosol fractions of citral and geraniol, but not for other substances or vapor only exposure. Overall, no systemic effects related to treatment were observed. Sensory irritation was only observed for citral and BMHCA but not for other fragrance chemicals.

Discussion: While PCLuS and further model development could not fully replace animal testing at this stage, this study's findings contribute to the reduction and refinement according to 3 R principles and might serve as a foundation for future testing strategies aiming toward a complete replacement.