From inflammation to cytotoxicity: exposure pattern-dependent responses to alumina nanoparticles and dissolved hydrochloric acid in a human alveolar-capillary barrier model at the air-liquid interface.
TL;DR
It is shown that exposure pattern critically shapes alveolar-capillary responses, supporting human air-liquid interface co-culture models for mechanistic inhalation toxicology, and the contribution of potential gas-particle interactions occurring in combustion plumes could not be evaluated.
Abstract
Combustion of composite solid propellants generates complex aerosols containing metallic nanoparticles (NPs) and acidic gases, raising concerns about inhalation toxicity. Here, we investigated the effects of alumina (Al₂O₃) NPs, alone or combined with hydrochloric acid (HCl), in a human alveolar-capillary barrier (ACB) model exposed at the air-liquid interface. The model consisted of hAELVi alveolar epithelial cells co-cultured with HPMEC-ST1.6R pulmonary microvascular endothelial cells and exposed using a Vitrocell Cloud system under acute or repeated scenarios. Deposited Al₂O₃ NPs doses corresponding to low-to-high alveolar exposure scenarios were 0.007, 1.35 ± 0.1 and 2.3 ± 0.2µg/cm², with or without HCl at 1.37mM. Barrier integrity, viability, inflammatory and remodeling mediators, oxidative stress and DNA damage were assessed 24h after the final exposure. The co-culture formed a tight functional barrier with high transepithelial electrical resistance, low permeability and organized junctional protein expression. Acute exposure to the highest Al₂O₃ NPs dose induced a compartment-specific inflammation-related response, based on the biomarkers investigated, with increased IL-1α, IL-8, IL-1β, CCL2, DKK1 and angiogenin, without cytotoxicity or barrier disruption. Repeated exposure shifted the response toward moderate cytotoxicity at the highest dose, with viability decreasing to 77% for Al₂O₃ NPs alone and 66% for Al₂O₃ NPs with HCl, while permeability remained unchanged. No significant oxidative stress or γ-H2AX-associated DNA damage was detected. HCl co-exposure did not enhance Al₂O₃ NPs toxicity. However, because HCl was administered in dissolved form prior to nebulization, the contribution of potential gas-particle interactions occurring in combustion plumes could not be evaluated and the results should not be interpreted as evidence for or against synergistic effects arising from gas-particle interactions occurring in combustion plumes. These findings show that exposure pattern critically shapes alveolar-capillary responses, supporting human air-liquid interface co-culture models for mechanistic inhalation toxicology.