Effect of monosodium urate on NLRP3 inflammasome activation and the intervention effects of catechins

Autor: Jhih-Jia Jhang, 張至嘉
Rok vydání: 2016
Druh dokumentu: 學位論文 ; thesis
Popis: 104
Gouty arthritis is an inflammatory disease caused by an accumulation of monosodium urate (MSU) crystals in the joints. MSU is capable of activating the nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome, leading to interleukin-1β (IL-1β) secretion. Reactive oxygen species (ROS) is a major mediator of NLRP3/IL-1β axis. Although nuclear factor E2-related factor 2 (Nrf2) is recognized as a transcription factor that is involved in the response to oxidative stress, the effect of MSU on Nrf2 and on Nrf2-mediated antioxidant enzymes remains unclear. This study developed the experimental model of gouty inflammation, and we investigated the effects of MSU on IL-1β secretion and NLRP3 inflammasome activation in THP-1 cells and the role of Nrf2 on MSU-induced inflammation. Furthermore, this study investigated the protective effect and underlying mechanism of phytochemicals on MSU-induced inflammation in vivo and in vitro. Here, we showed that the THP-1 cells after treatment with MSU crystals significantly increased the release of IL-1β, NLRP3 inflammasome activation and ROS production. MSU also promoted the nuclear translocation of Nrf2 and activated the lysosome destabilizations. Moreover, the levels of heme oxygenase-1 (HO-1) expressions were up-regulated by MSU. MSU-induced IL-1β secretion and NLRP3 inflammasome activation were inhibited by knock-down of Nrf2 and using the HO-1 inhibitor, zinc (II) protoporphyrin IX (ZnPP). In addition, the HO-1 inhibition was able to increase the level of superoxide anion productions and the consumptions of glutathione. These findings suggest that Nrf2 and HO-1 mediate the redox homeostasis and interact with the pro-inflammatory elements in MSU-challenged THP-1 cells, thereby providing a new insight into how MSU-iduced gouty inflammation is mediated by specific mechanisms that are involved in the Nrf2-HO-1 antioxidant signaling pathway. C57BL/6 mice were peritoneally injected with MSU to investigate the effect of MSU on superoxide dismutase (SOD) activity and HO-1 expression. The results showed that MSU elevated neutrophil infiltration and neutrophil cytosolic factor 1 (NCF-1) expression. MSU increased NLRP3 protein expression level, IL-1β secretion and ROS generation. SOD activity was not affected by MSU, and HO-1 expression was ameliorated by MSU. These results suggest that MSU induce inflammatory responses and neutrophil infiltration, but SOD activity and HO-1 expression are not increased by MSU crystals in vivo. Treatment with agents that inhibit IL-1β secretion and NLRP3 activation has been implicated as a novel therapy for gout flare. A screening of phenolic compounds revealed that gallic acid and catechin exhibited the most potent free radical scavenging activities. Subcutaneous injection of gallic acid or catechin significantly reduced MSU-induced IL-1β and IL-6 secretion in C57BL/6 mice. However, only catechin inhibited MSU-induced IL-1β secretion and NLRP3 inflammasome activation in MSU-challenged THP-1 cells. MSU-triggered mitochondrial reactive oxygen species (MtROS) production and intracellular calcium levels were significantly decreased by treatment with catechin in THP-1 cells. Catechin treatment also up-regulated Bcl-2 levels and restored MSU-induced mitochondrial transmembrane potential impairment. These results indicate that the protective effects of catechin on MSU-induced IL-1β secretion are associated with modulation of mitochondrial damage. It also suggests that catechin has potential to protect gout attack by modulation of NLRP3 inflammasome activation. The effect of epigallocatechin gallate (EGCG) on MSU crystals-induced inflammation has further been investigated in this study. C57BL/6 mice received subcutaneous injection of EGCG or oral gavage of EGCG prior to the administration of intraperitoneal injection of MSU. The results demonstrated that EGCG inhibited MSU-stimulated neutrophils infiltration and NCF-1 expression level. The pro-inflammatory mediators, NLRP3 and IL-1β protein expressions, were reduced by EGCG administration. EGCG also suppressed the secretions of IL-1β, IL-6, monocyte chemoattractant protein-1 (MCP-1) and serum amyloid A (SAA) in mice. These results indicate that EGCG treatment ameliorates MSU-induced inflammation in mice. This study demonstrates that catechin and EGCG suppress MSU-induced inflammation via down-regulation of IL-1β secretion and NLRP3 inflammasome activation. The results suggest catechin and EGCG intakes are capable of preventing acute gout attack for gout individuals.
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