Quercetin Improves Lipopolysaccharide-Induced Septic Liver Injury by Inhibiting the Activation of ROCK/NF-κB/NLRP3 Pathway

Abstract

Quercetin (QUE) is a common flavonoid compound, found in fruits and vegetables, with powerful anti-inflammatory and antioxidant properties. Nevertheless, the protective function and mechanisms of QUE in septic liver injury (SLI) caused by lipopolysaccharide (LPS) are still unknown. This study aimed to investigate the effect of QUE on SLI rats and the underlying mechanisms. Forty male Sprague-Dawley (SD) rats were randomly assigned into four groups (n = 10 per group): control group (CON), control + QUE group (CON + QUE), LPS group (LPS), and LPS + QUE group (LPS + QUE). Rats were administered intragastrically with QUE or normal saline for one week, and LPS was administered on the last day to induce the sepsis model. The results showed that QUE reduced aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in SLI rats (both p < 0.05). Additionally, histopathological analysis demonstrated that QUE alleviated the liver lesions in SLI rats. Furthermore, QUE also improved the oxidative stress and inflammatory responses, showing the decrease of malonaldehyde (MDA), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-18, and IL-6 and the increase of superoxide dismutase (SOD) in SLI rats (all p < 0.05). In addition, QUE decreased the expression of Toll-like receptor 4 (TLR4), phosphorylated myosin phosphatase target subunit (p-MYPT)-1, phosphorylated nuclear factor kappa-B (p-NF-κB), NOD-like receptor family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC), caspase-1, and cleaved-caspase-1 in liver (all p < 0.05). These results suggested that QUE could be able to treat SLI partly via stimulating the ROCK/NLRP3 pathway.

Keywords: NLRP3 inflammasome; lipopolysaccharide; quercetin; rho kinase (ROCK); septic liver injury.

FIGURE 1

The general structure of quercetin.

FIGURE 2

Quercetin had hepatic protection in SLI rats. (A) Serum ALT and AST activity. (B) Representative sections stained with HE (scale bar = 100 μm, 200×, scale bar = 50 μm, 400×). Arrows indicate inflammatory cells, and triangles indicate apoptotic cells. Serum and liver were obtained from the control group (CON), control + QUE group (CON + QUE), LPS group (LPS), and LPS + QUE group (LPS + QUE). Data were expressed as mean ± SEM (n = 10). **p < 0.01 and *p < 0.05 versus CON, ##p < 0.01 and #p < 0.05 versus LPS group.

FIGURE 3

Quercetin ameliorated the inflammatory responses and oxidative stress in SLI rats. (A) Levels of TNF‐α and IL‐6 in the serum and liver. (B) Representative histologic sections of reactive oxygen species (ROS) in four groups (scale bar = 100 μm, 200×). (C) Semi‐quantitative results of ROS. (D) MDA content and SOD activity in the liver and serum. Serum and liver were obtained from the control group (CON), control + QUE group (CON + QUE), LPS group (LPS), and LPS + QUE group (LPS + QUE). Data were expressed as mean ± SEM (n = 3–10). **p < 0.01 and *p < 0.05 versus CON, ##p < 0.01 and #p < 0.05 versus LPS group.

FIGURE 4

QUE inhibited the expression and activation of NLRP3 inflammasome in SLI rats. (A) Representative expression brands of NLRP3, ASC, caspase‐1, and cleaved caspase‐1. (B) Western blot bands' gray value. (C) Levels of IL‐1β and IL‐18 in the serum and liver. (D) Rat liver tissue stained with TUNEL (200×, scale bar = 100 μm). (E) Semi‐quantitative outcomes of apoptosis rate. Serum and liver were obtained from the control group (CON), control + QUE group (CON + QUE), LPS group (LPS), and LPS + QUE group (LPS + QUE). Data were expressed as mean ± SEM (n = 3–10). **p < 0.01 and *p < 0.05 versus CON, ##p < 0.01 and #p < 0.05 versus LPS group.

FIGURE 5

QUE suppressed the expression of TLR4/p‐MYPT/p‐NF‐κB in SLI rats. (A) Typical expression bands for TLR4, p‐MYPT‐1, and p‐NF‐κB. (B) Western blot bands' gray value. (C) Representative IHC images illustrating the nuclear translocation of p‐NF‐κB in liver tissue. Serum and liver were obtained from the control group (CON), control + QUE group (CON + QUE), LPS group (LPS) and LPS + QUE group (LPS + QUE). Data were expressed as mean ± SEM (n = 3). **p < 0.01 and *p < 0.05 versus CON, ##p < 0.01 and #p < 0.05 versus LPS group.