Benzo[a]pyrene and tumor necrosis factor-α coordinately increase genotoxic damage and the production of proinflammatory mediators in alveolar epithelial type II cells.

Alveolar type II epithelial (AEII) cells regulate lung inflammatory response and, simultaneously, they are a target of environmental carcinogenic factors. We employed an in vitro model of rat AEII cells, the RLE-6TN cell line, in order to analyze the interactive effects of tumor necrosis factor-α (TNF-α), a cytokine which plays a key role in the initiation of inflammatory responses in the lung, and benzo[a]pyrene (BaP), a highly carcinogenic polycyclic aromatic hydrocarbon. TNF-α strongly augmented the formation of stable BaP diol epoxide-DNA adducts in AEII cells, which was associated with enhanced p53-Ser15 phosphorylation and decreased cell survival. The increased genotoxicity of BaP was associated with altered expression of cytochrome P450 (CYP) enzymes involved in its bioactivation, a simultaneous suppression of CYP1A1 and enhancement of CYP1B1 expression. Importantly, BaP and TNF-α acted synergistically to upregulate key inflammatory regulators in AEII cells, including the expression of inducible NO synthase and cyclooxygenase-2 (COX-2), and enhanced prostaglandin E2 production and expression of proinflammatory cytokines, such as TNF-α, interleukin-1β and interleukin-6. We observed that BaP and TNF-α together strongly activated p38 kinase, a principal regulator of inflammatory response. SB202190, a specific p38 inhibitor, prevented induction of both COX-2 and proinflammatory cytokines, thus confirming that p38 activity was crucial for the observed inflammatory reaction. Taken together, our data demonstrated, for the first time, that a proinflammatory cytokine and an environmental PAH may interact to potentiate both DNA damage and the inflammatory response in AEII cells, which may occur through coordinated upregulation of p38 activity.