Comparison of BaP-induced Mutagenesis in Monolayer and 3-Dimensional Culture Models

Objective: This study compares monolayer cultures to 3-dimensional culture models using mammary epithelial (MEC) and fibroblast cells (MFB) derived from a lacI Fischer rat. Cell culture models with 3-dimensional histo-architecture often show enhanced metabolic activities and are considered to be intermediate between monolayer cell cultures and in vivo.  We hypothesized that 3-dimensional cultures would show enhanced metabolism of the procarcinogen, benzo(a)pyrene (BaP) resulting in increased mutagenicity.  Also, we expected to see increased mutagenicity in MEC when cultured with MFB, as pilot studies indicated the MFB were more active. Using a trans-well with MEC and MFB on opposite sides, we expected interactions between MEC monolayers and MFB aggregates which could also lead to increased mutagenicity in the MEC.

Method: MEC were used as monolayers and MFB were used as monolayers, and aggregates (3D cultures) in an in vitro mutagenesis model.

Results: 1) 3-dimensional cell culture models did not show increased metabolism when compared to monolayers, 2) in co-culture, a 3:1 ratio of MEC: MFB showed increased mutagenicity compared to 9:1 or MEC alone, 3) in the Trans-well marginally increased mutagenicity in MEC was observed. Also, treatment of MEC monolayers with MFB aggregates resulted in increased mutagenicity of BaP compared to treatment with no aggregates.

Conclusion: Monolayers metabolized BaP better than the aggregates, perhaps due to their single layer architecture allowing better absorbance of BaP into cells. There was an increase in mutagenicity compared to MEC alone, when cells were co-cultured, however it can’t be concluded that the MFB’s act synergistically with MEC’s because there was no significant difference between 9:1 co-culture and MEC. Results from the Trans-well experiment were marginal, which made it difficult to conclude if aggregates interacted with MEC monolayers over a distance. We were able to establish conditions for future studies in the 3 types of assays.