Shaoyao decoction alleviates DSS-induced colitis by inhibiting IL-17a-mediated polarization of M1 macrophages

Ethnopharmacological relevance: The efficacy of Shaoyao decoction (SYD), a traditional Chinese medicine prescription, in alleviating colonic mucosal inflammation in ulcerative colitis (UC) has been established. However, the specific mechanism underlying the therapeutic effects of SYD on UC is not clear.

Aim of study: In this study, we demonstrated the therapeutic effect of SYD on the polarization of M1 macrophages and elucidated the underlying mechanism.

Materials and methods: UC mice were induced with 3% DSS for one week and subsequently treated with SYD for another week. The composition of SYD was determined by HPLC. To assess the therapeutic efficacy of SYD, key parameters, including body weight changes, DAI scores, colon length, and histological alterations in colonic tissues, were monitored. ELISA was performed to quantify inflammatory cytokines, while Western blotting and immunofluorescence analyses were performed to quantify tight junction protein expression and M1 macrophage infiltration, respectively. Functional assessments focused on lysosomal activity and glucose oxidation in primary macrophages and RAW 264.7 cells exposed to LPS, IL-17A, and SYD using dedicated kits. To elucidate the mechanisms underlying the action of SYD, the data derived from TMT-based proteomics were analyzed to screen and predict its potential targets and regulated pathways.

Results: After treatment for seven days, SYD significantly mitigated colitis symptoms in mice, as determined by a decrease in body weight loss, an increase in colon length, and a decrease in disease activity index (DAI) score. The results of histopathological analysis showed substantial improvements in the integrity of colonic tissue. Additionally, SYD treatment significantly decreased the levels of proinflammatory cytokines, including IL-17A, IL-6, IL-1β, and TNF-α. This effect was accompanied by a reduction in the infiltration of CD86⁺ macrophages and restoration of occludin and ZO-1 levels, thus improving colonic mucosal permeability. SYD treatment also reversed the upregulation of Cathepsin (CTS) E, CTSS, lysosomal-associated membrane protein (LAMP)-1, and LAMP-2 expression observed in CD86⁺ macrophages and RAW 264.7 cells treated with IL-17A. These changes were accompanied by an increase in lysosomal acidification and the enzymatic activities of CTSE and CTSS, suggesting that SYD can restore lysosomal function. SYD also corrected the metabolic alterations in M1 macrophages, characterized by an increase in the extracellular acidification rate (ECAR) and a decrease in oxygen consumption rate (OCR). This was confirmed by a decrease in the ADP/ATP ratio, downregulation of pyruvate dehydrogenase kinase 4 (PDK4) and Lactate Dehydrogenase (LDH) expression, and a decrease in the concentrations of intracellular pyruvate and lactate. These findings showed that SYD promotes glucose oxidation in macrophages. The data derived from TMT-based proteomics showed that the PPAR pathway was a key target in regulating the polarization of M1 macrophages. SYD was also found to regulate the expression of the PPAR-α, PPAR-γ, and PPAR-δ proteins.

Conclusion: SYD inhibited the polarization of M1 macrophages induced by IL-17A. This effect occurred due to the restoration of lysosomal activity and glucose oxidation via activation of the PPAR/NF-κB pathway. Our findings provided novel insights into the mechanisms underlying the therapeutic effects of SYD in UC.

IL-17a; M1 macrophage polarization; PPAR/NF-κB pathway; Shaoyao decoction; Ulcerative colitis.