Induction of the multixenobiotic/multidrug resistance system in various cell lines in response to perfluorinated carboxylic acids.

The multixenobiotic resistance (closely related to multidrug resistance) system controls transport across the plasma membrane as a defense against toxic molecules. Multixenobiotic resistance system consists of an efflux pump, ABCB1 (also named P-glycoprotein, P-gp), and/or a molecule of the ABCC family (also named multiple resistance associated protein, MRP). ABCB1 is able to increase efflux of many low-molecular foreign molecules. Measuring system induction may be used as a biomarker of cell/organism exposure to foreign substances. Various established cell lines were tested for constitutive and induced multixenobiotic resistance proteins by Western blotting immunodetection. The pumping function was indirectly assayed with Rhodamine B by visualization of cell fluorescence in the presence of verapamil. Changes in ABC proteins were measured by flow cytometry after exposition to various perfluorinated carboxylic acids. MCF7 and HeLa cells were found to contain the highest constitutive level of both ABCB1 and ABCC1. HEK293 exhibited much less ABCB1 and no activity of pumping out Rhodamine B. The pumping activity was found to be related to the amount of the cell-type specific 170 kDa ABCB1 protein. An 8-day exposure to 10(-4) M perfluorononanoic acid resulted in about 2-2.5-fold increase of ABCB1 level. That was confirmed also for short times by flow cytometry of cells exposed to perfluorinated acids and its natural congeners. Both ABCB1- and ABCC1-related fluorescence increased along with the carbon chain in acids from C(6) up to C(9) and decreased for C(10). Measuring of multixenobiotic resistance changes in vitro induced by chemicals may be a convenient test for screening for their potential toxicity.