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

Influence of novobiocin on <FONT FACE=Symbol>g</font>-irradiation G0-lymphocytes as analyzed by cytogenetic endpoints

Experiments with novobiocin (NB) post-treatment were performed to verify its effect on the frequencies of micronuclei (MN) and chromosomal aberrations (CA) induced by <FONT FACE="Symbol">g</font>-irradiation (0.75, 1.5 and 3.0 Gy) in human lymphocytes at G0-phase. The frequencies of MN significantly decreased by 44 and 50%, for the treatment with NB 50 µg/ml (30-min pulse) after radiation doses of 1.5 and 3.0 Gy, respectively. However, CA frequencies were not significantly affected. No significant effect on CA was observed when lymphocyte cultures were exposed to a single dose of 2.0 Gy at the G0-phase and posttreated with 25 µg/ml NB for three hours either immediately after irradiation (G0-phase) or after 24 h (S-phase). The significant suppressive effect of NB on MN frequencies supports the hypothesis that NB interaction with chromatin increases access to DNA repair enzymes.

Effects of a phytopreparation from Helleborus niger on immunocompetent cells in vitro

Extracts of Helleborus species are used as phytopreparations with immunostimulatory properties in Romanian traditional medicine. In Germany, Helleborus niger is used in homeopathy and as an adjuvant therapy in the treatment of tumor patients in anthroposophical medicine. In vitro application of an aqueous extract from Helleborus niger resulted in a slight induction of sister chromatid exchanges (SCE) in cultured peripheral blood mononuclear cells (PBMC) from healthy individuals, an effect associated with a slight increase of the [3H]thymidine uptake in the DNA of isolated lymphocytes. Since the cytokines interleukin (IL)-2 and tumor necrosis factor (TNF)-alpha were reported to increase the number of SCE, we measured the concentrations of these cytokines in the supernatants of cultured PBMC treated with the plant extract. Here, no significant changes were observed as compared with the controls, but a trend to higher supernatant concentrations of TNF-alpha in six out of ten individuals was noted. Compared with lymphocytes treated with the alkylating substance, cyclophosphamide, the increase of the SCE levels induced by the plant extract is weak. The relevance of this DNA destabilizing property remains to be clarified.

A new mechanism for DNA alterations induced by alpha particles such as those emitted by radon and radon progeny

The mechanism(s) by which alpha (alpha) particles like those emitted from inhaled radon and radon progeny cause their carcinogenic effects in the lung remains unclear. Although direct nuclear traversals by alpha-particles may be involved in mediating these outcomes, increasing evidence indicates that a particles can cause alterations in DNA in the absence of direct hits to cell nuclei. Using the occurrence of excessive sister chromatid exchanges (SCE) as an index of DNA damage in human lung fibroblasts, we investigated the hypothesis that alpha-particles may induce DNA damage through the generation of extracellular factors. We have found that a relatively low dose of alpha-particles can result in the generation of extracellular factors, which, upon transfer to unexposed normal human cells, can cause excessive SCE to an extent equivalent to that observed when the cells are directly irradiated with the same irradiation dose. A short-lived, SCE-inducing factor(s) is generated in alpha-irradiated culture medium containing serum in the absence of cells. A more persistent SCE-inducing factor(s), which can survive freeze-thaw and is heat labile is produced by fibroblasts after exposure to the alpha-particles. These results indicate that the initiating target for alpha-particle-induced genetic changes can be larger than a cell's nucleus or even a whole cell. How transmissible factors like those observed here in vitro may extend to the in vivo condition in the context of a-particle-induced carcinogenesis in the respiratory tract remains to be determined.

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.

Viscum album L. extracts reduce sister chromatid exchanges in cultured peripheral blood mononuclear cells

Increasing concentrations of Viscum album L. extracts were shown to significantly reduce sister chromatid exchange (SCE) frequency of phytohaemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMC) of healthy individuals. This decrease of SCE could not be explained either by changes in lymphocyte subpopulations, by cytostatic effects of the drug or by accelerated proliferation of PHA-stimulated PBMC. Currently, no other cells tested have shown this effect. One therapeutic effect of these anti-mutagenic drugs could be a stabilisation of mononuclear blood cell DNA.