The Association of Cigarette Smoke Exposure with Lung Cellular Toxicity and Oxidative Stress: the Protective Role of Crocin.

Cigarette smoke (CS) contains many free radicals and toxic chemicals. Nuclear erythroid-related factor-2 (Nrf2) is a transcriptional regulator of several phase II antioxidant genes, including glutamate-cysteine ligase (GCL). In this study, it was hypothesized that Crocin may mediate antioxidant signaling pathway to protect human lung epithelial cells against CS-mediated toxicity and oxidative stress via inducing glutathione (GSH) biosynthesis and activation of Nrf2 pathway. Alveolar epithelial cells (A549) were exposed to 1, 2.5 and 5% cigarette smoke extracts (CSE) with or without Crocin (500 μM). After 48 h exposure, the cytotoxicity, oxidant/antioxidant parameters and the Nrf2 pathway modification were assayed. Treatment of A549 cells with all concentrations of CSE dose dependently decreased cell viability, antioxidant levels, GCL and Nrf2 gene expression, which was associated with increased production of reactive oxygen species. Crocin not only restored CSE-depleted GSH levels by enhancing GCL expression via activation of Nrf2 but also quenched the CSE-generation and release of reactive oxygen species. Crocin attenuated CSE-mediated Nrf2 modifications, thereby inducing its nuclear accumulation associated with GCL gene transcription leading to enhanced GSH levels. By inducing GSH synthesis, Crocin attenuates CSE-mediated GSH depletion and protects cells against CSE-induced oxidative stress via Nrf2 pathway. These results may have implications in dietary modulation of natural antioxidants in treatment of pulmonary diseases.