Comparative pulmonary toxicity of cadmium chloride on monoculture and co-culture of an in vitro alveolar barrier model

Cadmium is an industrial and environmental pollutant. It is partially accumulated in the lung and toxicity includes acute inflammatory effects, chronic edema, and bronchitis, as well as cancer. The lung epithelium represents the first barrier to be crossed by the inhaled metal compounds. The main goal of our study was to investigate the comparative toxicity of cadmium chloride using the established in vitro alveolar type II monoculture (NCI H441) and co-culture with the human pulmonary microvascular endothelial (HPMEC-ST1.6R) cell line. Monocultures and co-cultures grown on trans-well inserts for 11–13 days were exposed to CdCl2 from the apical and the basolateral side at concentrations up to 800 μM for 24 h. Following exposure, the effects of CdCl2 on the alveolar barrier formation (TEER), cytotoxicity (NRU), inflammation (IL-8 production), and expression of stress related genes Metalothionein 1X (MT1X), Heme oxygenase 1 (HMOX1), and Heat shock protein 70KDA (HSP70) using RT-PCR, were investigated. The basolateral exposure revealed higher impairment of barrier function and cell viability than the apical exposure in both monocultures and co-cultures. The quantification of IL-8 in the supernatants of monocultures and co-cultures showed enhanced release of the pro-inflammatory marker. The expressions of MT1X, HSP70, and HMOX1 were also increased in both in vitro models. The in vitro alveolar co-culture barrier model was found more sensitive to the examined parameters than the in vitro alveolar monoculture barrier model.