Effect of tumor necrosis factor on cell proliferation kinetics and sister chromatid exchange frequency in human lymphocytes

Genetic toxicity of cytokines

Review of the literature shows that such cytokines as human interferons alpha and gamma, tumor necrosis factor alpha, epidermal growth factor and interleukin-2 may exhibit genotoxic properties in human peripheral blood lymphocyte cultures. For all above cytokines, except interleukin-2, parabolic-like relationship between the dose and the frequency of sister chromatid exchanges was found. Although the mechanisms of these genotoxic actions remain largely unknown, generation of free radicals or interaction with enzymes such as DNA topoisomerase II may be suspected. Human interferon alpha also may be considered as an antimutagenic compound in human cells. Human tumor necrosis factor alpha has been reported to enhance cytotoxicity and DNA fragmentation produced by DNA topoisomerase II-targeted anticancer drugs. At the same time, it has some radio- and chemoprotective properties in vitro and in vivo. Despite these facts, the question about genotoxicity of cytokines is not answered. Some problems must be resolved before receiving the final answer. First, much more cytokines must be tested for their genotoxic activity. Second, appropriate test-systems must be designed. Third, genotoxicity studies of cytokines must account for cytokine interaction in the cytokine network as well as for such cytokine-induced effects as cytotoxicity and apoptosis. Fourth, in each case, it is necessary to have experimental evidence that observed genotoxic effects were caused by cytokine under investigation and not by the other factors.

Chemical induction of interleukin-8, a proinflammatory chemokine, in human epidermal keratinocyte cultures and its relation to cytogenetic toxicity

Tumor promoters, proinflammatory cytokines, endotoxins, and protein synthesis inhibitors can modulate cell cycle kinetics of various cell types, stimulate production of reactive oxygen species, and induce keratinocytes to produce interleukin-8 (IL-8), a potent chemotactant for polymorphonuclear neutrophils and T lymphocytes. The aim of this study was to determine whether perturbations of cytogenetic responses correlated with the induction of IL-8 expression. Cultures of primary human keratinocytes were grown in serum-free medium with 5 mumol/L bromodeoxyuridine to label DNA and exposed either to phorbol-13-myristate-12-acetate (PMA) (0.0001-100 ng/ml), cycloheximide (CHX) (0.01-50 micrograms), lipopolysaccharide (0.1-100 micrograms/ml), tumor necrosis factor-alpha (TNF alpha) (3.13-50 ng/ml), or interleukin-1 alpha (IL-1 alpha) (1-182 pg/ml). Metaphase chromosome preparations were stained by a fluorescence-plus-Giemsa technique to differentiate sister chromatids. For IL-8 production, keratinocytes were grown to 70% confluency and then exposed to chemicals for 24 h. Immunoreactive IL-8 was quantitated from the supernatants by ELISA. With the exception of benzo(a)pyrene used as a positive control, none of the agents induced sister chromatid exchanges. However, PMA and TNF alpha induced IL-8 production that coincided with significant cell cycle inhibition. IL-1 alpha had no effect on cytogenetic endpoints, yet stimulated a 6.3-fold increase in IL-8. CHX inhibited cell cycle progression and mitotic activity at concentrations that were 200 times lower than required for IL-8 induction; however, puromycin (0.31-10 micrograms/ml), another protein synthesis inhibitor, did not induce IL-8. At all concentrations tested, TNF alpha reduced the mitotic index by approximately 45%, slowed cell cycle progression by approximately 3.5 h, and induced a flat, albeit large, IL-8 response at concentrations > or = 12.5 ng/ml. These agent-specific response patterns suggest that induction of IL-8 production is not always the inevitable result of cell cycle perturbations or genetic damage.

Modulation by novobiocin of sister-chromatid exchanges induced by tumor necrosis factor in human lymphocytes

The effect of the antibiotic novobiocin on human recombinant tumor necrosis factor (TNF)-induced sister-chromatid exchanges (SCEs) were examined in human peripheral blood lymphocytes. TNF, when introduced in a dose range of 10-1000 U/ml at the initiation of culture, was found to cause a significant increase in SCE frequency. The simultaneous addition of TNF and novobiocin (25 micrograms/ml) in the assay resulted in no increase of SCE frequency. Delayed (for 24 h) addition of novobiocin suppressed the induction of SCEs by 50, 100 and 500 U/ml but not by 1000 U/ml of TNF.