Quality and Purity of L929 Cell Cultures: Isoenzyme Profiles As a Sensitive Marker of Cross-Contamination

Inappropriate handling of cells can generate modifications in the genomic DNA. The additional risk is cross-contamination. Isoenzyme analysis with gel agarose electrophoresis is a known, fast, and cheap technique for detection of species-specific isoforms of intracellular enzymes. The aim of the experimental work was to check if variations in the cell growth conditions can affect morphology and/or nuclear anomalies including micronuclei (MN) in the L929 cells; and to define how sensitive and selective is the classic gel agarose electrophoresis for analysis of isoforms of the selected enzymes to detect cross-contamination of L929 cultures with HeLa cells or with the related species, such as CHO-K1 cells, in the case of unavailability of the commercial kits. The experiments were done with use of the National Collection of Type Cultures clone 929 (L929)-mouse fibroblasts from subcutaneous connective tissue; HeLa-human cervix adenocarcinoma; and CHO-K1-epithelial-like hamster ovary cells. Cell morphology was evaluated with a light/fluorescence microscope. MN were determined with the cytokinesis-block micronucleus assay, and the isoenzyme analysis was performed using gel agarose electrophoresis. As shown, the overgrown cultures result in a significant increase of the MN in the L929 cells. The band patterns for lactate dehydrogenate, glucose-6-phosphate dehydrogenase, or malate dehydrogenase allow identification of the single L929, HeLa, or CHO-K1 cell line and to detect the cross-contamination, even up to 0.4%. There can be no exceptions from the recommended cell culture conditions in the passage scheme. The sensitivity of the gel agarose separation depends on the cells and on the type of enzyme tested and seems to be sufficient in a quick screening of the CHO-K1, L929, or HeLa cell cultures through the possible mutual contamination.