Characterization and applicability of a cytotoxicity assay determining growth inhibition after a 1-hour treatment with xenobiotics in human cell culture

In vitro cytotoxicity evaluation of plastic biomedical devices

Cytotoxic potential of four plastic biomedical devices (intravenous transfusion sets, IV sets; dextrose normal saline bottles, DNS bottles; Ringer lactate bottles, RL bottles; and Ryle's tubes) including 17 different brands was evaluated by investigating growth inhibition, percent survival, mitotic index and colony-forming ability (cfa) in L929, an adherent type mouse fibroblast cell line. Experimental sets were exposed with leachates of biomedical products in serum-free minimum essential medium (MEM) for 1 h at 37 degrees C in a CO2 incubator. After 1 h, medium was replaced with serum rich MEM containing essential amino acids and reincubated up to 96 h. Cells in serum-free MEM only were processed under identical conditions and served as the control. The leachates from all types of biomedical devices evaluated exhibited reduction in the growth and survival of the cell line in the first 12 h postexposure followed by their gradual recovery up to 96 h. A significant reduction in cell growth was apparent in the six brands of IV sets from 24 h onwards up to 36 h (59% growth inhibition). Though the cfa was also reduced in all the brands tested, the magnitude of reduction was less compared to growth inhibition. The results indicate that leachates of IV sets were more toxic compared to other biomedical devices screened, and growth inhibition assay was found to be more sensitive and suitable for cytotoxicity evaluation of biomedical devices.

The influence of GSTM1 null genotype on susceptibility to in vitro oxidative stress

From epidemiological studies, there is some evidence that genetic variation at the glutathione S-transferase (GST) loci GSTM1 influences individual susceptibility to disease associated with oxidative stress. The aim of this study was to elucidate the role of the GSTM1 genotype in protection against oxidant chemicals by comparing the sensitivity, genotoxicity and cytotoxicity of lymphocytes to benzo(a)pyrene (BaP)- and cumene hydroperoxide (CumOOH)-induced in vitro oxidative challenge. Malondialdehyde and protein carbonyl levels, and oxidation of 2',7'-dichlorofluorescin diacetate were used as biomarkers of oxidative stress in lymphocytes. Following supplementation with BaP or CumOOH, time-dependent increases were observed in the production of all the markers after incubation for 12-48 h. However, we could not find any differences between GSTM1 null and positive genotypes. Furthermore, dose or time response experiments indicated that GSTM1-deficient cells were not more sensitive than control cells to BaP-or CumOOH-induced cell killing and micronucleus formation, although they were hypersensitive to BaP-inhibited cellular growth. The results suggest that lymphocytes from individuals with the GSTM1 null genotype are not abnormally susceptible to in vitro induced oxidant challenge, when exposed to CumOOH.

Cytotoxicity and mutagenicity of a 2,4,6-trinitrotoluene (TNT) and hexogen contaminated soil in S. typhimurium and mammalian cells

The toxicity and mutagenicity of aqueous and organic extracts of soil contaminated with TNT, TNT metabolites and hexogen was determined in mammalian cell lines and in prokaryotic cells. The prokaryotic toxicity was determined via the colony forming ability of Salmonella typhimurium (strains TA 98 and TA 100). The same strains were used to test mutagenicity in the Ames test. The mammalian toxicity was analyzed in human fibroblasts by the inhibition of cell growth and cell viability (MTT assay). The mammalian mutagenicity was tested with the HPRT test in V79 cells (hamster lung). The aqueous soil extract did not reveal toxicity or mutagenicity in any of the tests performed. The DMSO/ethanol extract showed toxicity and mutagenicity in S. typhimurium. Thereby strain TA 98 was more sensitive than strain TA 100. In human fibroblasts cell growth was strongly inhibited, whereas no reduction of cell viability was found in the MTT test. Mutagenicity of the DMSO/ethanol extract of the soil was demonstrated in V79 cells.

Correlation of the lipophilicity of xenobiotics with their synergistic effects on DNA synthesis in human fibroblasts

The binary combination effects of DNA synthesis of human fibroblasts were investigated using 2,4-D with 15 xenobiotics of different chemical substance classes. Results were compared with previous investigations on cell growth. Each of the 15 chemicals tested at their no effect concentrations (NOEC's) increased the effects of 2,4-D on DNA synthesis. Thereby, the EC20 value of 2,4-D was reduced by approximately 40% in the combinations. The NOEC's of the xenobiotics used in the combinations varied by a factor of 1,600 and depended strongly on the lipophilicity of the agents combined with 2,4-D. A significant statistical correlation of r = 0.90 was found between the NOEC's of the 15 combined xenobiotics and their lipophilicity. The combination effects on DNA synthesis were similar to those on cell growth. The regression lines of the relationship between the NOEC's and lipophilicity in both assays showed only slight differences in the slopes. This is an additional confirmation of our hypothesis on a facilitated uptake of 2,4-D in the binary combinations.