Prof. Dr. rer. nat. Irene Witte
Prof. Dr. rer. nat. Irene Witte
0441 / 48238
Zusammenfassung: Es werden gentoxische Kombinationswirkungen beschrieben, die zu einer erhöhten Krebsrate aufgrund von Umwelteinflüssen führen können. Dabei werden additive und synergistische Effekte, hervorgerufen durch Chemikalien, physikalische oder endogen gebildete Noxen berücksichtigt, sowie ihre Wechselwirkungen untereinander. Additive Kombinationswirkungen durch sehr ähnlich wirkende Chemikalien mit demselben Wirkort, sowie synergistische Wirkungen aufgrund von chemischen Reaktionen werden vergleichsweise als selten eingestuft. Synergistisch Ereignisse aufgrund von interaktiven Aktionen (unterschiedliche chemische Struktur, unterschiedlicher Wirkort) werden hingegen als häufige Kombinationswirkung angesehen. Hier spielt insbesondere die Zellmembran eine bedeutsame Rolle. Die Barrierefunktion der Zellmembranen gegenüber hydrophilen Xenobiotika kann durch verschiedene Mechanismen herabgesetzt werden, zum einen durch Membranschädigungen durch lipophile Verbindungen oder Tenside, zum Anderen durch das Einschleußen von Kanzerogenen mit Hilfe von Transportvehikeln (z. B. Nanopartikel), die eine hohe Bindungsfähigkeit für Xenobiotika besitzen. Die herausragende Rolle von Wasserstoffperoxid (H2O2) in gentoxischen Kombinationswirkungen wird dargestellt. Oxidativer Stress und somit auch H2O2 wird durch viele Chemikalien, physikochemisch wirkenden Noxen (Asbest, Nanopartikel, Holzstaub), physikalische Noxen (Lärm, elektromagnetische Felder,UV- und γ-Strahlen) und einige physiologische und psychische Prozesse erzeugt. Hinzu kommt, dass H2O2 in Anwesenheit anderer Xenobiotika verstärkt von der Zelle aufgenommen wird.
Abstract: The DNA damage by platinum cytostatics is thought to be the main cause of their cytotoxicity. Therefore the measurement of the DNA damage induced by cis- and carboplatin should reflect the sensitivity of cancer cells toward the platinum chemotherapeutics. DNA damage induced by cis- and carboplatin in primary cells of ovarian carcinomas was determined by the alkaline comet assay. In parallel, the reduction of cell viability was measured by the fluorescein diacetate (FDA) hydrolysis assay. While in the comet assay the isolated cells showed a high degree of DNA damage after a 24 h treatment, cell viability revealed no cytotoxicity after that incubation time. The individual sensitivities to DNA damage of 12 tumour biopsies differed up to a factor of about 3. DNA damage after a one day treatment with cis- or carboplatin correlated well with the cytotoxic effects after a 7 day treatment (r = 0,942 for cisplatin r = 0.971 for carboplatin). In contrast to the platinum compounds the correlation of DNA damage and cytotoxicity induced by adriamycin was low (r = 0,692), or did not exist for gemcitabine.The measurement of DNA damage induced by cis- and carboplatin is an accurate method to determine the in vitro chemosensitivity of ovarian cancer cells towards these cytostatics, because of its quickness, sensitivity, and low cell number needed.
Abstract: Early screening of drug candidates for genotoxicity typically includes an analysis for mutagenicity in bacteria and for clastogenicity in cultured mammalian cells. In addition, in recent years, an early assessment of photogenotoxicity potential has become increasingly important. Also, for screening purposes, expert computer systems can be used to identify structural alerts. In cases where structural alerts are identified, mutagenicity testing limited to bacteria can be conducted. The sequence of computer-aided analysis and limited testing using bacteria allows for screening a comparatively large number of drug candidates. In contrast, considerably more resources, in terms of supplies, technical time, and the amount of a test substance needed, are required when screening for clastogenic activity in mammalian cells. In addition, the relatively large percentage of false positive results for rodent carcinogenicity associated with clastogenicity assays is of considerable concern. As a consequence, mammalian cell-based alternatives to clastogenicity assays are needed for early screening of mammalian genotoxicity. The comet assay is a relatively fast, simple, and sensitive technique for the analysis of DNA damage in mammalian cells. This assay seems especially useful for screening purposes because false positives associated with excessive toxicity appear to occur less frequently, only relatively small amounts of a test compound are needed, and certain steps of the test procedure can be automated. Therefore, the in vitro comet assay is proposed as an alternative to cytogenetic assays in early genotoxicity/photogenotoxicity screening of drug candidates.
Abstract: Genotoxic combination effects of oxidative stress (induced by H2O2) and eight nongenotoxic environmental chemicals (4-chloroaniline, 2,3,4,6-tetrachlorophenol, lindane, 2,4-dichloroacetic acid (2,4-D), m-xylene, glyphosate, nitrilotriacetic acid and n-hexanol) were determined in human fibroblasts. Genotoxicity was measured quantitatively by the single cell gel electrophoresis assay. The nongenotoxic chemicals were used in non cytotoxic concentrations. H2O2 was used in concentrations producing low (50 microM) and no cytotoxicity (40 microM). All environmental chemicals acted in a synergistic way with H2O2 except DMSO which effectively inhibited H2O(2)-induced DNA damage. The most effective enhancers were 4-chloroaniline, 2,3,4,6-tetrachlorophenol, m-xylene, and n-hexanol. Synergistic effects of hexanol/H2O2 were still evident at a concentration of 0.09 noec (no observed effect concentration). In contrast to synergistic DNA damage in the cell antagonism was found measuring DNA breakage in isolated PM2 DNA. From the results we concluded that synergisms between H2O2 and nongenotoxic chemicals may be a general phenomenon which is not observed on the level of isolated DNA.
Abstract: The antioxidant propyl gallate (PG) induced single strand breaks in PM2 DNA at concentrations higher than 0.25 microM when it was combined with copper concentrations at 5 microM and above. In combination with 100 microM CuCl2, extensive double strand breakage was also observed. Neither PG alone nor CuCl2 showed any strand breaking properties. DNA strand breakage was inhibited by addition of catalase or the Cu(I) chelator neocuproine, indicating the involvement of H2O2 and a Cu(II)/Cu(I) redox cycle in the DNA damage. DNA damage of PG/Cu(II) was also observed in human fibroblasts. Using the alkaline elution technique concentrations of 0.15-0.5 mM PG induced DNA strand breaks in combination with 2.5 mM CuCl2, while the single substances did not show any effect. At these concentrations cell viability measured by the MTT assay was not reduced by more than 10%; however, cell growth was inhibited by PG in combination with Cu(II). This growth inhibition was apparently due to the DNA damage incurred by PG/Cu(II). The synergistic interaction between PG and Cu(II) is probably caused by a redox reaction between both compounds, whereby reactive species such as ROS are formed, which are responsible for the observed genotoxic and cytotoxic effects. Our results demonstrate that the antioxidative and cytoprotective properties of propyl gallate may change to prooxidative, cytotoxic and genotoxic properties in the presence of Cu(II).
Abstract: The cytotoxic combination effects of 2,4-D with 12 xenobiotics having different lipophilicity were investigated in human fibroblasts at their no effect concentrations (NOEC). Each of the chemicals tested in binary combinations enhanced the toxicity of 2,4-D. These synergistic combination effects were independent of the chemical structure of the test compounds. However, the NOEC’s of the xenobiotics used in the combinations varied by a factor of 10,000. For strongly lipophilic compounds the lowest NOEC’s were needed to induce synergistic cytotoxicity. A linear regression analysis of the concentrations (NOEC’s) of the 12 combined xenobiotics against their lipophilicity revealed a correlation with r = 0.96 for 11 agents. This close correlation may be explained by the membrane damaging properties of lipophilic compounds which enhance the uptake of hydrophilic agents.
Abstract: In the absence of light, tetracycline (TC) induced single- and double-strand breaks in PM2 DNA at micromolar concentrations in combination with CuCl2, whereas TC or CuCl2 alone had no effect. Strand break formation was completely suppressed by catalase and the specific Cu(I) scavenger neocuproine. The extent of strand break formation depended on the ratio of Cu(II):TC. At a ratio of > or = 2 most DNA damage was observed. The influence of the kind of Cu(II)/TC complexation on DNA strand break formation is discussed. The DNA damage in PM2 DNA provoked by TC/CuCl2 was indirectly detected also in human fibroblasts by the induction of DNA repair. The results are discussed with regard to human risk from TC/Cu(II).
Jacobi H, Witte I. (1991): Synergistic effects of U46 D fluid (dimethylammonium salt of 2,4-D) and CuCl2 on cytotoxicity and DNA repair in human fibroblasts. Toxicol Lett. 1991 58(2):159-67.
Abstract:The cytotoxicity of U46 D Fluid was tested in human fibroblasts after pretreatment with non-toxic or slightly toxic concentrations of CuCl2. While cell survival, colony-forming ability and protein synthesis were not affected by pretreatment with CuCl2, the inhibition of cell growth was enhanced as was inhibition of DNA synthesis. Synergistic effects of CuCl2 and U46 D Fluid were also detected on the induction of DNA repair measured by unscheduled DNA synthesis. While neither U46 D Fluid nor CuCl2 alone induced DNA repair, preincubation with CuCl2 followed by treatment with U46 D Fluid strongly provoked DNA repair.