Cyto- and genotoxic potential of β-carotene and cleavage products under oxidative stress

Issue title: HNE and Further Lipid Peroxidation Products

Article type: Research Article

Authors: Alija, A.J. | Bresgen, N. | Sommerburg, O. | Langhans, C.D. | Siems, W. | Eckl, P.M.

Affiliations: Institute of Genetics and General Biology, University of Salzburg, Salzburg, Austria | Children's Hospital, University of Ulm, Germany | Children's Hospital, University of Heidelberg, Germany | Herzog-Julius Hospital for Rheumatology and Orthopedics, Bad Harzburg, Germany

Note: [] Address for correspondence: Peter M. Eckl, Department of Cell Biology, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria. Tel.: +43 662 8044 5782; Fax: +43 662 8044 144; E-mail: [email protected]

Abstract: Free radical attack on β-carotene results in the formation of high amounts of cleavage products with prooxidant activities towards subcellular organelles such as mitochondria, a finding which could provide an explanation for the contradictory results obtained with β-carotene in clinical efficacy and cancer prevention trials. Since primary hepatocytes proved to be very sensitive indicators for the genotoxic action of suspect mutagens/carcinogens we therefore investigated a β-carotene cleavage products mixture (CP), apo-8'-β-carotenal (apo-8') and β-carotene in the primary rat hepatocyte assay in the presence and absence of oxidative stress provided by hypoxia/reoxygenation (Hy/re). The endpoints tested were: the mitotic indices, the percentages of necrotic and apoptotic cells, micronucleated cells (MN), chromosomal aberrations (CA) and sister chromatid exchanges (SCE). The results obtained indicate a genotoxic potential of both CP and apo-8' already in the concentration range of 100 nM and 1 μM, i.e. at physiologically relevant levels of β-carotene and β-carotene breakdown products. In contrast, no significant cytotoxic effects of these substances were observed, nor did β-carotene induce significant cytotoxic or genotoxic effects at concentrations ranging from 0.01 up to 10 μM. However, when β-carotene is supplemented during oxidative stress induced by hypoxia/reoxygenation, a dose-dependent increase of CP is observed accompanied by increasing genotoxicity. Furthermore, when β-carotene cleavage products were supplied during oxidative stress significant additional increases of genotoxic effects were observed, the additional increases indicating an additive effect of both exposures. Summarizing, these results provide strong evidence that β-carotene breakdown products are responsible for the occurrence of carcinogenic effects found in the Alpha-Tocopherol Beta-carotene-Cancer prevention (ATBC) study and the beta-CArotene and RETinol Efficacy (CARET) Trial.

Keywords: β-Carotene, β-carotene breakdown products, oxidative stress, genotoxicity, hepatocytes

Journal: BioFactors, vol. 24, no. 1-4, pp. 159-163, 2005