Introduction
Severe acute pancreatitis (SAP) remains a life-threatening condition. There is no licensed medication for AP treatment. The inflammatory injury in SAP involves complex networks. Cyclooxygenase-2 (COX-2) is an inducible enzyme generated by immediate-early response genes after organismal injury. Normal pancreas does not express COX-2. Previous studies reported that pancreatic tissue rapidly expresses COX-2 during SAP [1-6]. In the mouse model of AP induced after systemic knockout of ptgs2 (COX-2 gene), pancreatic inflammation and lung injury in the pancreas were significantly reduced [4]. The single-center randomized controlled trial has demonstrated that early administration of selective COX-2 inhibitors (parecoxib sequential with celecoxib) in high-risk patients for SAP reduced the occurrence of SAP by approximately 47% and lowered local complications such as pancreatic necrosis by nearly 45% [7]. Recently, a well-designed multicenter randomized controlled trial validated the significant efficacy and safety of parecoxib sequential with imrecoxib in prevention and treatment of SAP [8], providing high-level favorable evidence for early anti-inflammatory intervention with COX-2 inhibitors. However, there is still a lack of theoretical support for the optimal timing of clinical intervention with selective COX-2 inhibitors.
Aims & Methods
This study aimed to clarify the cells COX-2 inhibitors target on and reveal the underline mechanism of COX-2 inhibitors in the treatment of SAP. A rat SAP model was established via retrograde infusion of sodium taurocholate and treated with the selective COX-2 inhibitor parecoxib. Endothelial cell-specific ptgs2 (COX-2 gene) knockout mice were used for genetic validation. Histopathology, immunohistochemistry, and transmission electron microscopy were employed to assess pancreatic injury, inflammation and ultrastructural changes. In vitro studies utilized TNF-α-stimulated human umbilical vein endothelial cells (HUVECs) treated with parecoxib or transfected with a ptgs2 overexpression plasmid. Transcriptomic analysis, molecular biology techniques, assays for mitochondrial function and cellular senescence were performed.
Results
COX-2 was specifically expressed in pancreatic microvascular endothelia, not in acinar cells, during SAP. Parecoxib intervention or genetic ablation of endothelial ptgs2 significantly improved survival rates, attenuated pancreatic necrosis, hemorrhage and inflammatory cell infiltration. This was associated with reduced neutrophil recruitment, decreased expression of adhesion molecules (VCAM-1, ICAM-1) and chemokines (CXCL1, CXCL2 and CXCL8), and suppression of the NF-κB pathway. Furthermore, COX-2 inhibition protected endothelia from TNF-α-induced dysfunction, mitigating markers of cellular senescence (p21, p16, p53 and phosphorylated γ-H2A.X) and preserving mitochondrial membrane potential by reducing mitochondrial permeability transition pore opening. Consequently, microvascular thrombosis and parenchymal necrosis were markedly reduced.
Conclusion
Over-expression of COX-2 in pancreatic endothelia at the onset of AP may deteriorate AP through attraction of a great number of neutrophils, pancreatic endothelial senescence, degeneration of mitochondria and thrombosis formation in pancreatic microcirculation. Down-regulation of COX-2 expression with COX-2 inhibitors as early as possible may be benefit for prevention and treatment of SAP.
References
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