Molekulare Mechanismen der Toxizität und Kanzerogenität des Mykotoxins Ochratoxin A
Final Report Abstract
Ochratoxin A (OTA), a mycotoxin and important food contaminant, is one of the most potent rodent renal carcinogens studied to date. Although controversial results regarding OTA genotoxicity have been published, it is now widely accepted that OTA is not a mutagenic, DNA-reactive carcinogen. Instead, recent data suggested that OTA may promote genomic instability and tumorigenesis through interference with cell division. The aims of this work were to provide further evidence for and understanding of disruption of mitosis by OTA. Specifically, we were interested to understand if aberrant mitosis occurs as a result of direct interference with microtubuli polymerisation / depolymerisation or rather through modulation of key mitotic protein kinases, such as Cdk1cdc2/cyclin B1 and aurora kinases. Further questions adressed involved target-organ /cell-type specificity and evidence for a threshold, below which adverse effects do not occur, to support human risk assessment. OTA did not inhibit microtubule assembly in a cell free polymerization assay at relevant concentrations, suggesting that OTA may disrupt mitosis through mechanisms other than direct binding to tubulin. In rats treated with OTA under conditions of carcinogenicity, aberrant expression of key regulators of mitosis linked to chromosomal instability was observed specifically in the kidney, the target organ of OTA carcinogenicity, and these changes localized to the straight segment of the proximal tubule epithelium, from which tumors in rats arise. Although expression changes were not confirmed in vitro, suggesting that overexpression in vivo may be a secondary event to compensate the initial insult, altered expression of mitotic regulators, which participate in spindle assembly, centrosome maturation and separation, chromosome segregation and cytokinesis, is nonetheless considered to play an important role in OTA carcinogenicity, particularly as several of these genes found to be altered in repsonse to OTA are frequently overexpressed in tumors where they are associated with chromosomal instability, aneuploidy, and poor prognosis in tumor patients. In vitro analysis further revealed centrosomal aberrations and metaphases with abnormally condensed chromatin and prematurely separated sister chromatids. These changes were accompanied by increased phosphorylation of core histones. Since histone phosphorylation at mitosis is thought to initate chromosome condensation and segregation by allowing loading of condensin and subsequent removal of cohesin, which provides sister chromatid cohesion, aberrant condensation and sister chromatid segregation in OTA treated cells may be the result of increased histone phosphorylation. Although the precise mechanism as to how OTA functions to perturb the intricate and tightly controlled process of mitosis remains to be elucidated, results from this study provided further support for a mechanism of OTA carcinogenicity involving interference with the mitotic machinery and subsequent chromosome segregation errors, accompanied by an increased risk of aneuploidy acquisition and subsequent tumor formation. In view of human risk assessment of OTA in food, it is important to emphasize that the dose-response of the transcriptional changes in rat kidney in vivo was in perfect agreement with the dose-response for nephrotoxicity, BrdU labeling and indeed, tumor formation after chronic treatment, thereby confirming the non-linearity of the dose-response and providing further support for a thresholded mechanism of OTA carcinogenicity.
Publications
- Modulation of cell adhesion and signal transduction by Ochratoxin A in human kidney epithelial cells. DGPT, Mainz, 2005. Archives of Pharmacology 371, Supplement 1, 454
Rached, E., Dekant, W., and Mally, A.
- Molekulare Mechanismen der Toxizität und Kanzerogenität des Mykotoxins Ochratoxin A. Landesforschungsschwerpunkt „Lebensmittel und Gesundheit: Mykotoxine“, Universität Karlsruhe, Karlsruhe 2006
Mally, A.
- Ochratoxin A blocks metaphase-anaphase transition, resulting in apoptosis and aberrant exit from mitosis. Society of Toxicology 45th Annual Meeting, San Diego, California, 2006. The Toxicologist, Supplement to Toxicological Sciences 90, 963
Mally, A., Rached, E., and Dekant, W.
- Ochratoxin A toxicity and carcinogenicity. International Symposium on recent advances in balkan endemic nephropathy, Zagreb 2006
Mally, A. and Dekant, W.
- Ochratoxin A: apoptosis and aberrant exit from mitosis due to perturbation of microtubule dynamics? Toxicol Sci. 2006; 92(1): 78-86
Rached E, Pfeiffer E, Dekant W, and Mally A
- Disruption of sister chromatid cohesion and mitosis by Ochratoxin A. 29th Mycotoxin-Workshop, Fellbach 5/2007
Müller, K., Pepe, G., Bekteshi, M., Rached, E., Dekant, W., Mosesso, P., and Mally, A.
- Modulation of the expression of genes involved in cell cycle control and regulation of mitosis by ochratoxin A in vivo. 29th Mycotoxin- Workshop, Fellbach 5/2007
Adler, M., Müller, K., Rached E., Dekant, W., and Mally, A.
- Molecular Mechanism of Ochratoxin A carcinogenicity. Gordon Research Conference on Mycotoxins and Phycotoxins, Waterville, Maine 6/2007
Mally, A.
- Ochratoxin A as a potential etiologic factor in endemic nephropathy: lessons from toxicity studies in rats. Food Chem Toxicol. 2007; 45(11): 2254-60
Mally A, Hard GC, and Dekant W
- Ochratoxin A carcinogenicity: time- and dose-dependent increase in renal cell proliferation in male F344 rats. DGPT, Mainz, 2007. Archives of Pharmacology
Rached, E., Hard, G.C., Blumbach, K., Weber, K., Draheim, R., Steger, U., Dekant, W., and Mally, A.
- Ochratoxin A carcinogenicity: Time- and dose-dependent increase in renal cell proliferation in male F344 rats. Society of Toxicology 46th Annual Meeting, Charlotte, 2007. The Toxicologist, Supplement to Toxicological Sciences 91
Rached, E., Hard, G.C., Blumbach, K., Weber, K., Draheim, R., Özden, S., Steger, U., Dekant, W., and Mally, A.
- Ochratoxin A: 13 week oral toxicity and cell proliferation in male Fischer F344/N rats. Toxicol Sci. 2007; 97(2):288-98
Rached E, Hard GC, Blumbach K, Weber K, Draheim R, Lutz, WK, Özden S, Steger U, Dekant W, and Mally A
- Ochratoxin A: 13-Week Oral Toxicity and Cell proliferation in Male Fischer F344/N Rats. 29th Mycotoxin-Workshop, Fellbach, 5/2007
Rached E., Hard, G.C., Blumbach, K., Weber, K., Draheim, R., Özden, S., Steger, U., Dekant, W., Mally, A.
- Untersuchungen zum Mechanismus der kanzerogenen Wirkung von Ochratoxin A. GdCh-Vortragsreihe, TU Kaiserslautern, 6/2007
Mally, A.
- Aberrant expression of key regulators of mitosis and chromosome segregation in rat kidney following exposure to ochratoxin A. Society of Toxicology 47th Annual Meeting, Seattle, 2008. The Toxicologist, Supplement to Toxicological Sciences
Adler, M., Müller, K., Rached, E., Dekant, W., and Mally A.
- Evaluation of putative biomarkers of nephrotoxicity after exposure to ochratoxin a in vivo and in vitro. Toxicol Sci 2008, 103, 371-381
Rached, E., Hoffmann, D., Blumbach, K., Weber, K., Dekant, W., and Mally, A.
- Modulation of key regulators of mitosis linked to chromosomal instability as an early event in ochratoxin A carcinogenicity. 7th Congress of the Toxicology in Developing Countries, 6.-10.9.2009, Sun City, South Africa
Mally, A.
- Modulation of key regulators of mitosis linked to chromosomal instability is an early event in ochratoxin A carcinogenicity. Carcinogenesis, 2009; 30(4):711-9
Adler, M., Müller, K., Rached, E., Dekant, W., Mally, A.
- Mycotoxins and the kidney: Modes of Action for Renal Tumor Formation by Ochratoxin A in Rodents. Mol. Nutr. Food Res. 2009, 53, 467 - 478
Mally, A and Dekant, W
