A Narrative Review of Protective Effects of Natural Compounds Against Lipopolysaccharide-Induced Injuries

Lipopolysaccharide (LPS) is a large amphipathic glycoconjugate molecule in the cell wall of Gram-negative bacteria. This bacterial endotoxin binds to toll-like receptor 4 (TLR4) and stimulates the inflammatory reactions and oxidative stress. The current paper presents the protective effects of natural compounds against LPS-induced injuries. The relevant findings were extracted from PubMed, Web of Science, Scopus, and Google Scholar databases from the beginning of 2005 until the end of September 2023 were employed. The results of in vitro and in vivo studies indicated that thymoquinone, crocin, carvacrol, and quercetin effectively attenuated LPS-induced damages via lowering the level of inflammatory cytokines and free radicals. These natural compounds could also amplify the antioxidant defense against LPS by increasing the activity of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT). In addition, a part of the protective effects of these phytochemicals against detrimental impacts of LPS is attributed to their ability to downregulate the TLR4 expression and to inhibit the NF-kappa B signaling pathway. Briefly, the protective effects of natural compounds mentioned in current review against LPS-caused damages mainly are mediated by their anti-inflammatory and antioxidant activities.