High affinity of protocatechuic acid to human serum albumin and modulatory effects against oxidative stress and inflammation in alveolar epithelial cells: Modulation of pulmonary fibrosis

Protocatechuic acid (PCA), C7H6O4, has been shown to possess potential antioxidant properties. But its interaction with the main plasma carrier protein, human serum albumin (HSA), as well as its antioxidant mechanism remains largely unknown. It has been shown that induced pulmonary fibrosis can be modulated through mitigating epithelial apoptosis mediated by the prohibition of oxidative stress. Therefore, in this study, the interaction of PCA and HSA was explored by spectroscopy, calorimetry (DSC), as well as molecular docking studies. Also, the protective effects of PCA against lipopolysaccharide (LPS)-induced cytotoxicity and oxidative stress were evaluated by MTT, ROS, ELISA, real-time PCR, and western blot assays. It was shown that under the interaction of HSA with PCA a spontaneous interaction occurs with the contribution of hydrophobic forces, which results in the formation of a stable complex. Cellular assays showed that PCA reduced LPS-induced cytotoxicity in human type II alveolar epithelial cells (AECs) through mitigation of ROS production, release and gene expression of TNf-α and IL-1β as pro-inflammatory mediators, and caspase-3 gene and protein as an apoptotic factor. Also, it was shown that PCA can reduce the expression of NF-κB at the protein level, indicating a possible inhibition of pulmonary fibrosis via regulating the NF-κB signaling pathway. In conclusion, PCA could be a promising therapeutic agent for the control of oxidative stress in AECs which is an important factor in redox modulatory therapy, while its pharmacodynamics can be modulated by interaction with HSA.