4. Discussion
Lycorine, an alkaloid found in the bulbs of Lycoris Radiata, has been
proven to have anti-inflammatory effects(de Queiroz Souza et al., 2021;
Ge et al., 2020). ALI is a respiratory disease with a high fatality rate
that can be caused by a variety of reasons(L. Li et al., 2021; Zhu,
Wang, Xing, & Xiong, 2021). In this study, we performed many tests to
analyze whether lycorine has a protective effect on LPS-induced ALI in
mice(Qiu, Luo, & Fang, 2021; Yao, Xu, Jia, Li, & Wei, 2021; S. M. Zhu
et al., 2021). The results showed that lycorine significantly reduced
the degree of LPS-induced ALI. The results of pathological analysis and
molecular biological analysis proved that lycorine has a protective
effect on LPS-induced acute lung injury(Cui, Xu, Lv, & Guo, 2023).
Lipid rafts are signal transduction platforms on cell membranes. The
increase or decrease of lipid rafts will have a pronounced influence on
TLR4 (Amine, Benomar, & Taouis, 2021; da Cruz et al., 2021; Park, Cha,
Lee, Kim, & Choi, 2021)After LPS stimulation of lung tissues and cells,
TLR4 is recruited into lipid rafts to induce downstream signal
transduction(Y. Chen et al., 2020; Wei et al., 2016). It has shown that
TLR4 recruitment into lipid rafts can be inhibited using drugs by
interfering with lipid raft formation (cholesterol
consumption)(Dolganiuc, Bakis, Kodys, Mandrekar, & Szabo, 2006). It
reduces lipopolysaccharide-induced NF-κB activation and inflammatory
cytokine production(Kang et al., 2020; R. Xu et al., 2023; T. Xu, Cui,
Xu, Cao, & Guo, 2023). Our results show that lycorine can inhibit the
transfer of TLR4 to lipid rafts by decreasing the formation of lipid
rafts via consuming cholesterol. Next, we investigated the cause of
lycorine lowering cholesterol levels in lipid rafts. We used AutoDock
software to calculate the binding capacity of lycorine to LXRα. The
results showed that lycorine had an excellent combining ability with
LXRα. The results showed that LXRα plays a vital role in regulating
cholesterol homeostasis. LXRα mediates the expression of ABCA1 and ABCG
to regulate intracellular cholesterol levels.
We tested our hypothesis in cells that lycorine plays an
anti-inflammatory role by inhibiting the activation of the TLR4/NF-κB
signaling pathway through lipid rafts. The human non-small cell lung
cancer cell line (A549) is the primary constituent cell of lung tissue.
In this study, LPS stimulation of A549 induces the activation of the
TLR4/NF-κB signal pathway and promotes the secretion of inflammatory
cytokines, which play an essential role in the process of ALI. This is
similar to previous studies (Sivanantham et al., 2019). The results
showed that TNF-α, IL-1β, and IL-6 were significantly increased in ALI
of mice. We found that lycorine inhibits TNF-α, IL-1β, and IL-6
production in a dose-dependent manner. TLR4/NF-κB signal pathway plays a
crucial role in inducing cytokine production. Our results show that
lycorine inhibits LPS-induced cytokine production by inhibiting the
activation of the TLR4/NF-κB signal pathway.
Therefore, we examined the effects of lycorine on the activation of
LXRα, ABCA1, and ABCG. The results showed that lycorine induced the
expression of ABCA1 and ABCG by activating LXRα. Is this pathway related
to the anti-inflammatory effects of lycorine? We performed an LXRα
activity inhibition assay. The results showed that lycorine altered the
expression of ABCA1 and ABCG, membrane cholesterol levels, and
LPS-induced inflammatory when LXRα activity was inhibited. It confirmed
that inhibition of LXRα activity could reduce the anti-inflammatory
effect of lycorine. These results indicate that lycorine binding to LXRα
may promote the activation of LXRα. It confirmed that inhibition of LXRα
activity could reduce the anti-inflammatory effect of lycorine. Lycorine
depletes cholesterol by promoting the activation of LXRα. Cholesterol
depletion causes lipid raft instability. It inhibits TLR4 transport to
lipid rafts and LPS-induced inflammation.
In summary, our research shows that lycorine can inhibit the expression
of TNF-α, IL-1β, and IL-6 in A549 cells stimulated by LPS. The
anti-inflammatory mechanism of lycorine is related to the up-regulation
of the LXRα-ABCA1/ABCG pathway, which leads to the consumption of
cholesterol and reduces the transfer of TLR4 to lipid rafts thereby
inhibiting the inflammatory response induced by LPS.