Pharmacological Evaluations of Select Herbal Extracts on TLR7/8-induced Cytokine and Chemokine Production in Macrophage-like Cells

Abstract

Inflammation is an innate immune response triggered by harmful stimuli, such as pathogens, tissue injury, or toxins. The purpose is to eliminate the source of infection and initiate the healing process. However, an excessive acute inflammatory response can lead to severe and life-threatening complications, as seen during recent pandemics. In the context of viral infections, the activation of the TLR7/8 signaling pathway has been implicated in excessive cytokine secretion. In this study, we aimed to replicate the perturbed inflammatory environment resulting from the activation of the TLR7/8 specific agonists, imiquimod, and resiquimod. We utilized macrophage-like cells, as macrophages are the first responders during infections and secrete key pro-inflammatory cytokines (TNF-, IL-6, and IL-1{beta}) to recruit immune cells to the site of infection. Herbal medicines have been traditionally used for centuries to enhance respiratory immune function. In the present study, we employed a prophylactic approach, where macrophage-like THP1 cells, differentiated with PMA, were pre-treated with select herbal extracts/formulations prior to TLR7/8 activation in the presence of agonists. Several medicinal plants and formulations known for their therapeutic potential in respiratory ailments were investigated, including Withania somnifera, Tinospora cordifolia, Glycyrrhiza glabra, and AYUSH-64, an herbal formulation. The gene expression and corresponding secreted levels of various inflammatory mediators were measured using RT-PCR and ELISA methods, respectively, in treated and untreated differentiated THP1 cells induced with TLR7/8 agonists. Comparatively, the gene expression of inflammatory markers was significantly higher in resiquimod-induced cells than in imiquimod-treated cells. Notably, Withania somnifera demonstrated pronounced prophylactic efficacy compared to other herbs/formulations, as evidenced by reduction in expression of majority of investigated inflammatory marker genes.