Hexavalent chromium caused DNA damage repair and apoptosis via the PI3K/AKT/FOXO1 pathway triggered by oxidative stress in the lung of rat

Hexavalent chromium [Cr(VI)] is an occupational carcinogen that accumulates in the lungs and causes lung injury and even lung cancer. 36 SD male rats received inhalable intratracheal instillation of Cr(VI) (0.05, 0.25 mg Cr/kg) or the same volume (3 ml/kg) of normal saline weekly for 28 days (total 5 times). After 28 days of exposure, half of the rats in each group were sacrificed for investigation, and the rest stopped exposure and began to be self-repaired for two weeks. Histopathology analyses revealed that Cr(VI) induced slight dilatation and hemorrhage of perialveolar capillaries, pulmonary bronchodilation, and congestion with peripheral flaky-like necrosis accompanied by inflammatory cell infiltration, especially the 0.25 mg Cr/kg group. Cr(VI) exposure caused the increase of blood Cr, urinary Cr, MDA, urinary 8-hydroxy-2' -deoxyguanosine (8-OHdG), and the decrease of GSH and MDA, while two-week repair only reduced urinary Cr. Exposure to Cr(VI) significantly upregulated FOXO1 and downregulated p-AKT and p-FOXO1 for two weeks. PI3K in the 0.25 mg Cr/kg group was inhibited after two weeks of repair. Cr(VI) exposure mainly promoted GADD45a and CHK2 in the exposure group, promoted Bim, Bax/Bcl-2, and suppressed Bcl-2 and Bcl-xL in the repair group. These results demonstrate that Cr(VI) may induce DNA damage repair and apoptosis in the lung by activating the PI3K/AKT/FOXO1 pathway. Two-week repair may alleviate oxidative stress and DNA damage induced by Cr(VI) exposure but couldn't eliminate its effects. This study provides a new perspective for exploring the Cr(VI) induced lung cancer mechanism.