Cadmium toxicity in a bronchial co-culture model

Cadmium is an industrial and environmental pollutant which can damage depending on the dose and route of exposure various organs including the lung.

After an explant-outgrowth culture of epithelial cells from small bronchi pure populations of primary isolated normal human bronchial epithelial cells (NHBE) were cultured with lung fibroblasts as bilayer on a 24-well HTS-Transwell filter plate. The cells were grown on a collagen type I and maintained at an air-liquid interface (ALI) by feeding basolaterally with medium. Barrier properties and morphological phenotype were compared over 31 days. The NHBE formed confluent layers, expressing functional tight junctions as measured by transepithelial electrical resistance (TER). In our study we tested the model for its applicability to investigate acute toxic effects at the human respiratory unit.

To determine if the treatment with the combination of cadmium influences the co-culture, cells were treated apically and basolaterally for 1h, 4h, 12h and 24h with cadmium in concentrations between 10µM to 500µM. TER decreased depending on the different concentrations in the first 4h up to 30% of the control. Cadmium displaces calcium and calcium measured in supernatants increased rapidly in both compartments. Immunfluorescence labelling showed that cadmium disrupts the epithelial cell-cell junctions. The fraction of apoptotic cells increased up to 30% of control over the incubation time measured with a TUNEL/H33342 dye mixture. After 24h cell death occurs both at low and high concentrations. Cadmium showed also an stimulatory effect on the proinflammatory cytokines IL-6 and IL-8.

In summary, cadmium induced significant changes in barrier functions, cytokine production and morphological structures.

These data indicate that our in vitro model reflects important characteristics of cadmium mediated cytotoxicity effects and can be used to explore lung toxicity.