Micropore filters for sterile filtration may leach toxic compounds affecting cell cultures (HL 60).

Reduction in HL-60 cell growth could be traced unexpectedly to sterile filtration procedures. To circumvent this problem, 11 available brands of micropore filters (five prepacked and six to be packed and autoclaved) were investigated with the aim of finding the least toxic product. Samples of 10 ml of RPMI 1640 medium with 10% fetal calf serum added were filtered through four filters of each brand to detect even small amounts of leached toxic compounds. HL-60 cells were cultured in these filtered media for three days and the results compared with cultures using unfiltered medium. A large variation in growth inhibition was found between the filters investigated, ranging from 0% to about 90%. The growth inhibition was due to leaching of toxic compounds, as revealed by viability test, reseeding, and direct microscopy. Adsorption of essential proteins to the micropore filters was found for only one of the filters investigated in this study.