Influence of macrophages and neutrophilic granulocyte-like cells on crystalline silica-induced toxicity in human lung epithelial cells

In many industrial activities, workers may be exposed by inhalation to particles that are aerosolized, To predict the human health hazard of these materials, we propose to develop a co-culture model (macrophages, granulocytes, and alveolar epithelial cells) designed to be more representative of the inflammatory pulmonary response occurring in vivo. Phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 cells were used as macrophages, All-trans retinoic acid (ATRA)-differentiated HL60 were used as granulocytes and A549 were used as epithelial alveolar type II cells. A crystalline silica sample DQ12 was used as a prototypical particle for its capabilities to induce DNA damage, inflammatory response, and oxidative stress in epithelial cells; its polyvinylpyridine-N-oxide (PVNO)-surface modified counterpart was also used as a negative particulate control. Cells in mono-, bi- or tri-culture were exposed to DQ12 or DQ12-PVNO for 24 h. DQ12 but not DQ12-PVNO induced a significant increase in DNA damage in A549 cells. The presence of differentiated THP-1 reduced the genotoxic effects of this crystalline silica sample. The exposure of A549 to DQ12 but not DQ12-PVNO induced a significant change in interleukin-8 (IL-8) protein levels which was exacerbated when differentiated THP-1, and HL-60, were added. In addition, while no production of TNFα was detected in the A549 monoculture, elevated levels of this cytokine were observed in the co-culture systems. This work shows that a cell culture model that takes into consideration the complexity of the pulmonary inflammatory response might be more dependable to study the toxicological properties of particles than "simple" monoculture models.