Peganum harmala Polysaccharide Mitigates LPS-Induced Inflammatory Response in Macrophages by Activating Autophagy Pathway

Peganum harmala, a member of the Zygophyllaceae family, is known for its diverse biological activities, including anti-inflammatory properties. The mechanisms through which P. harmala polysaccharide (LTP) induces autophagy, however, remain largely unexplored. This study aims to elucidate the role of LTP in autophagy induction and its efficacy in mitigating inflammation within macrophages. Autophagosome formation was evaluated using GFP-LC3 vectors, and LC3-II levels induced by LTP were analyzed through laser scanning confocal microscopy. Western blotting assessed the expression of autophagy-related proteins and the phosphorylation state of p70S6K in NRK cells, treated both with and without LTP, alongside autophagy inducers and inhibitors. Additionally, RAW264.7 cells were treated with 1 μg/mL lipopolysaccharides (LPS), followed by Western blotting and ELISA assays to quantify inflammatory markers. The study's outcomes demonstrate that LTP facilitates an increase in autophagic activity, as evidenced by the enhanced expression of LC3-II and reduced levels of p62 in both NRK and RAW264.7 macrophages. This effect is mediated through the activation of the AMPK-mTOR signaling pathway, without inhibiting the autophagosome–lysosome fusion process. In vitro experiments with RAW264.7 cells treated with 1 μg/mL LPS showed that LTP markedly decreased the levels of TNF-α and IL-6. Our findings indicate that LTP effectively reduces inflammation in LPS-stimulated macrophages by promoting autophagy via an mTOR-dependent mechanism.