Rhein attenuates severe acute pancreatitis-associated intestinal injury through PPARγ regulating macrophage activation.

BACKGROUND: Severe acute pancreatitis (SAP) often leads to life-threatening multiorgan dysfunction, with intestinal barrier failure being a key driver of systemic inflammation. Although Rhein shows efficacy in SAP, its mechanism for protecting against pancreatitis-associated intestinal injury remains unclear. This study aimed to elucidate the mechanism of Rhein in pancreatitis-associated intestinal injury (PAII), with a focus on intestinal macrophage polarization and peroxisome proliferator-activated receptor γ (PPARγ) signaling.

METHODS: SAP was induced in male C57BL/6J mice by intraperitoneal injections of cerulein and lipopolysaccharide (LPS). Pancreatic and intestinal histopathology were assessed by hematoxylin and eosin staining using both paraffin and frozen sections. The expression of PPARγ, NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome components, and macrophage polarization markers was examined by real-time quantitative polymerase chain reaction (RT-qPCR), Western blotting, and immunofluorescence. RT-qPCR was also used to quantify the messenger RNA (mRNA) levels of pro-inflammatory cytokines (interleukin [ IL ]- 1β , IL-6 , tumor necrosis factor [ TNF ]- α , mono-cyte chemoattractant protein-1 [ MCP-1 ]) and the anti-inflammatory cytokine IL-10 in colonic tissues. Reactive oxygen species (ROS) levels in colonic tissues were detected by dihydroethidium staining. Serum levels of lipopolysaccharide were measured by enzyme-linked immunosorbent assay (ELISA). For in vitro mechanistic studies, primary bone marrow-derived macrophages isolated from C57BL/6J mice were stimulated with LPS and interferon-γ to induce M1 macrophage polarization, with or without Rhein treatment.

RESULTS: SAP-induced intestinal injury was characterized by downregulated PPARγ, NLRP3 inflammasome hyperactivation, and dominant M1 macrophage polarization. Rhein restored PPARγ, suppressed NLRP3, and reduced secretion of key M1-sustaining cytokines ( IL-6 , IL-1β , and TNF - α ). This attenuated the proinflammatory milieu, indirectly facilitating an M1-to-M2 phenotypic shift. All benefits were abolished by PPARγ antagonism.

CONCLUSION: Rhein alleviates pancreatitis-associated intestinal injury by activating PPARγ, which suppresses the NLRP3 inflammasome and downstream proinflammatory cytokine cascade, thereby modulating macrophage polarization. The PPARγ-NLRP3 axis is a crucial regulatory pathway and potential therapeutic target in SAP.