Natural Compounds Regulate Macrophage Polarization and Alleviate Inflammation Against ALI/ARDS

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a pulmonary disease with high mortality associated with inflammation. During the development of ALI/ARDS, macrophages usually polarize toward M1 pro-inflammatory macrophages, promoting the inflammatory response in ALI/ARDS and aggravating lung tissue damage. Natural compounds with anti-inflammatory activity have achieved excellent results in the treatment of ALI/ARDS through different regulatory modes, including macrophage polarization. Of note, flavonoid, brevilin A, and tetrahydropalmatine play an important role in the treatment of ALI/ARDS by modulating the phenotypic polarization of macrophages and their pro-inflammatory cytokine expression in innate immune cells of the lung. Flavonoids are a kind of naturally occurring polyphenol compound, which has antioxidant and anti-inflammatory activities. Studies have found that some flavonoids can alleviate ALI/ARDS through inhibiting the expression of inflammatory cytokines in macrophages. Among them, 5-methoxyflavone, acacetin, grape seed proanthocyanidins, and luteolin can also regulate macrophage polarization. Therefore, the in-depth exploration of the regulatory mechanism of macrophages can lay the foundation for the application of flavonoids in alleviating inflammation-related lung injury. This review focuses on the macrophage polarization effects of different natural compounds and their potential anti-inflammatory mechanisms in the treatment of ALI/ARDS.