Defining conditions for the co-culture of Caco-2 and HT29-MTX cells using Taguchi design

Introduction: The co-culture of Caco-2 and HT29 cells for testing intestinal drug and nutrient transport and metabolism provides the presence of both absorptive and goblet cells, both of which have different culture requirements for optimal growth and function. The research on the co-culture of Caco-2 and HT29 cells is very limited in respect to refining specific conditions that reduce intra- and inter-laboratory variations. In the present study we reported conditions that enable reproducible results to be obtained for drug permeability using in vitro co-culture of Caco-2 and HT29-MTX based on Taguchi experimental design. Methods: The selection of four factors that specified cell culture conditions, namely culture medium, seeding time, seeding density, and Caco-2:HT29-MTX ratio on TEER value and individual permeability coefficients of propranolol, ketoprofen and furosemide was established. Based on the selected conditions for co-culture, we also confirmed the functionality of the final chosen culture condition using nitric oxide as an indicator of intestinal inflammation. Results: Choice of cell culture time and culture medium represented two of the most important factors that affected TEER values and the permeability coefficients of the model drugs. On the other hand, the seeding density and the Caco-2:HT29-MTX ratio exerted no significant influence on TEER values and the drug permeability coefficients. No absolute optimal cell culture condition could be obtained for all drugs; however subsequent confirmation experiments concluded that excellent precision for TEER values and drug permeability coefficients was obtained from the two operators using the following combination of conditions, namely an initial seeding density of 1 x 10(5) Caco-2 and HT29-MTX cells/cm(2) at a ratio of 9:1, followed by a 21 day culture time in MEM medium. Finally, functionality of the co-culture model system using the above selected in vitro conditions resulted in comparable nitric oxide synthesis to that of a Caco-2 cell monolayer. Discussion: Taguchi experimental design enabled us to define a combination of in vitro culture conditions that resulted in excellent operator reproducibility for determining drug permeability coefficients in a Caco-2 and HT29-MTX co-culture system. Moreover, the selected conditions used in co-culture of absorptive and goblet intestinal cells did not compromise the synthesis of nitric oxide, an indicator of inflammation, measured in Caco-2 monolayers. (C) 2010 Elsevier Inc. All rights reserved.