Huanglian Jiedu Decoction improves the"central-peripheral"inflammatory microenvironment and enhances the cognitive function of APP/PS1 mice by inhibiting the activation of NLRP3 inflammasome mediated by gut microbiota.

Background: Huanglian Jiedu Decoction (HLJDD) is a representative formula for clearing heat and removing toxins, and some basic studies indicated that it can improve the learning cognitive ability of Alzheimer's disease (AD) mice, but the underlying molecular mechanism of its improvement in AD mice is still unclear, therefore, this paper delves into the mechanism of HLJDD to improve AD.

Purpose: This study aims to investigate whether HLJDD can improve the "central-peripheral" inflammatory microenvironment in APP/PS1 mice, and to explore its relationship with gut microbiota and NLRP3 inflammatory vesicles activation.

Materials and methods: In this paper, the fingerprint of HLJDD was established by high-performance liquid chromatography (HPLC) and the components of HLJDD were characterized by ultra-performance liquid chromatography-time-of-flight mass spectrometry (UPLC-O-TOF/MS). The potential signaling pathways of HLJDD against AD were preliminarily investigated through network pharmacology. Behavioral assessment, histopathological staining, immunofluorescence staining, immunohistochemical staining, and detection of central and peripheral inflammatory factors were used to explore the improvement of AD by HLJDD, in addition to which we examined the gut microbiota and expression of relevant inflammatory proteins.

Results: In this study, 137 chemical constituents, including flavonoids, terpenoids, and alkaloids, were first identified in HLJDD by HPLC fingerprinting and UPLC-Q-TOF/MS. In addition, 49 components were found in the brain tissue of APP/PS1 mice and 48 components were found in the plasma of APP/PS1 mice. Network pharmacology concluded that the relevant pathways for HLJDD treatment of AD include inflammatory pathways. We found that HLJDD was effective in improving the learning memory ability of APP/PS1 mice by in vivo mouse behavioral performance. Histopathological results showed that HLJDD had the effect of reducing AD-like pathological damage, and also found that HLJDD could significantly reduce the proportion of M1 type microglia and A1 type astrocytes, and increase the proportion of M2 type microglia and A2 type astrocytes, and the treatment of HLJDD also suppressed the infiltration of CD4⁺ and CD8⁺ T-cells in the brain, and inhibited Aβ deposition and reduced the expression of inflammatory factors in the brain, and alleviated central neuroinflammation. In addition, it was also found that HLJDD was able to reduce the expression of inflammatory factors in the peripheral blood and inhibit the peripheral immune response, and the results of gut microbiota also showed changes in gut microbiota after HLJDD treatment and verified the expression of inflammatory vesicle-associated proteins in the intestines, with significant upregulation of the expression of NLRP3, caspase-1, and ASC proteins in the model group, and significant downregulation of ZO-1 and occludin proteins, and reversal of the above changes after HLJDD intervention.

Conclusion: Therefore, it is hypothesized that HLJDD improves the "central-peripheral" inflammatory microenvironment in APP/PS1 mice by inhibiting the activation of NLRP3 inflammatory vesicles mediated by gut microbiota.