Effects of repeated Cr(VI) intratracheal instillation on club (Clara) cells and activation of nuclear factor-kappa B pathway via oxidative stress

•This is the first in vivo study investigating the effects of Cr(VI) exposure on club (Clara) cell, the expression of CC16 and its relationship with oxidative stress.•Club (Clara) cells were sensitive to repetitive Cr(VI) exposure via NF-κB up-regulation by reactive oxygen species generation during Cr reduction.•CC16 was supposed to be a peripheral biomarker of early lung injury produced by Cr(VI).•Oral Zn supplementation failed to alleviate Cr-induced club (Clara) cell damage and lung injury.

Hexavalent chromium [Cr(VI)] exposure is known to induce respiratory inflammation and contribute to lung cancer development, but little is known about its target cell type in lung. In the current study, we investigated the effects of repeated Cr(VI) intratracheal instillation on club (Clara) cells and club (Clara) cell secretory protein (CC16) in rats and explored whether the nuclear factor-kappa B (NF-κB) related pathway was involved. We also studied the role of orally delivered Zn against Cr-induced adverse health effects. For four weeks, sixty Sprague-Dawley male rats received weekly intratracheal instillation of potassium dichromate (K2Cr2O7) at 0, 0.063 and 0.630 mg Cr/kg with or without daily intragastric administration of zinc sulfate (ZnSO4) at 10 mg Zn/kg. Results showed that exposure to Cr(VI) significantly increased the organ coefficient of lung (organ weight as a percentage of body weight), albumin and total protein level in bronchoalveolar lavage fluid (BALF), indicating lung injury and compromised bronchoalveolar/blood barrier (BA/BB) integrity. With increasing Cr(VI) dose, the secretion of CC16 decreased in a dose-dependent manner, suggesting that CC16 can serve as a peripheral biomarker for club cell damage during early lung injury induced by Cr(VI). Increased expression of NF-κB were observed in club cells in both Cr-exposed groups, indicating upregulation of NF-κB, which can be induced by reactive oxygen species (ROS) generated by club cells during Cr reduction with repetitive Cr(VI) exposure. Cr-induced DNA damage was also observed, as significant increase of 8-OHdG was found with Cr exposure at 0.630 mg/kg week. Oral Zn supplementation did not alleviate changes in serum CC16 level under Cr(VI) exposure, indicating its failure in protecting against Cr(VI)-induced club cell damage.