Asbestos-exposed blood monocytes - Deoxyribonucleic acid strand lesions in co-cultured bronchial epithelial cells

Abstract

Objectives. In lungs of asbestos-exposed persons alveolar and interstitial macrophages are able to release genotoxic substances such as reactive oxygen intermediates. It is unknown whether reactive oxygen intermediates released by macrophages are able to induce DNA (deoxyribonucleic acid) strand lesions in neighboring bronchial epithelial cells. Methods. A co-culture (transwell) system was established which allows exposure of human blood monocytes cultured on a polycarbonate membrane within a distance of 1 mm of a monolayer of the bronchial epithelial cell line BEAS-2B. Results. Exposure of blood monocytes to chrysotile B (100 μg/106 cells) caused an up to 2.8-fold increase in DNA strand lesions in co-cultured BEAS-2B cells measured by alkaline elution when compared with the levels of control cells after 1, 3, 24, and 48 hours. The main DNA damage thus occurred as early as within 1 hour of incubation, corresponding to the time course of the release of reactive oxygen intermediates by blood monocytes determined by chemiluminescence. The maximum release of reactive oxygen intermediates (3.2-fold increase over control values) was measured after 30 minutes of exposure of blood monocytes to chrysotile B. The addition of catalase (200 U/ml) or desferoxamine (100 μM) to the culture medium blocked almost completely the induction of DNA strand lesions in this system (maximum 85%). Conclusions. Exposure of blood monocytes to chrysotile B results in an increase in the release of reactive oxygen intermediates and induces DNA strand lesions in neighboring bronchial epithelial cells.