Decreased hepatic peroxisome proliferator-activated receptor-γ contributes to increased sensitivity to endotoxin in obstructive jaundice

Abstract

Aim: To investigate the role of hepatic peroxisome proliferator-activated receptor-γ (PPAR-γ) in increased susceptibility to endotoxin-induced toxicity in rats with bile duct ligation during endotoxemia.

Methods: Male Sprague-Dawley rats were subjected to bile duct ligation (BDL). Sham-operated animals served as controls. DNA binding were determined by polymerase chain reaction, Western blotting analysis, and electrophoretic mobility shift assay, respectively. BDL and sham-operated rats received a non-lethal dose of intraperitoneal lipopolysaccharide (LPS) injection (3 mg/kg, i.p.). Additionally, the potential beneficial effects of the PPAR-γ agonist rosiglitazone were determined in BDL and sham-operated rats treated with a non-lethal dose of LPS. Survival was assessed in BDL rats treated with a non-lethal dose of LPS and in sham-operated rats treated at a lethal dose of LPS (6 mg/kg, i.p.).

Results: PPAR-γ activity in rats undergoing BDL was significantly lower than in the sham-controls. Hepatic PPAR-γ gene expression was downregulated at both the mRNA and protein levels. In a parallel group, serum levels of pro-inflammatory cytokines were nearly undetectable in the sham-operated rats. When challenged with a non-lethal dose of LPS (3 mg/kg), the BDL rats had approximately a 2.4-fold increase in serum IL-6, a 2.7 fold increase in serum TNF-α, 2.2-fold increase in serum IL-1 and 4.2-fold increase in serum ALT. The survival rate was significantly lower as compared with that in sham-operated group. Additionally, rosiglitazone significantly reduced the concentration of TNF-α, IL-1β, IL-6 and ALT in sham-operated rats, but not in BDL rats, in response to LPS (3 mg/kg). Also, the survival was improved by rosiglitazone in sham-operated rats challenged with a lethal dose of LPS, but not in BDL rats, even with a non-lethal dose of LPS (3 mg/kg).

Conclusion: Obstructive jaundice downregulates hepatic PPAR-γ expression, which in turn may contribute to hypersensitivity towards endotoxin.

Keywords: Endotoxemia; Liver; Obstructive jaundice; Peroxisome proliferator-activated receptor-γ; Rosiglitazone.

Figure 1

Modified measurement of peroxisome proliferator-activated receptor-γ activation and expression upon bile duct ligation and consequent cholestasis. A: Electrophoretic mobility shift assay (top panel) of peroxisome proliferator-activated receptor (PPAR)-γ. DNA binding in nuclear extracts from liver, and relative densitometric analysis (lower panel). Data are expressed as mean ± SE (n = 3). ^aP < 0.05 for bile duct ligation (BDL) group vs sham group; B: PPAR-γ mRNA expression in the liver. PPAR-γ expression in the liver of BDL rats decreased significantly compared with the sham-group determined by quantitative real-time reverse transcription-polymerase chain reaction. Data are expressed as mean ± SE (n = 6). ^bP < 0.01 for BDL group vs sham group; C: Western blotting analysis (top panel) of PPAR-γ in nuclear extracts from liver, and relative densitometric analysis (lower panel, n = 3). Data are expressed as mean ± SE (n = 3). ^bP < 0.01 for BDL group vs sham group.

Figure 2

Survival rates of rats after administration of lipopolysaccharide (3 mg/kg, i.p.). The survival curve was estimated by the Kaplan-Meier method and the log-rank method was used to compare differences in survival rates between groups (n = 20). ^aP < 0.01 for bile duct ligation group vs sham group. BDL: Bile duct ligation; LPS: Lipopolysaccharide.

Figure 3

Effects of pretreatment with rosiglitazone (3 mg/kg, i.p.) on survival rates in rats after administration of lipopolysaccharide (6 mg/kg for sham-group and 3 mg/kg for bile duct ligation group, i.p.). The survival curve was estimated by the Kaplan-Meier method and the log-rank method was applied to compare differences in survival rates between groups (n = 20). Rosiglitazone pretreatment significantly improve the survival in sham + lipopolysaccharide (LPS) (6 mg/kg) group but not in bile duct ligation + LPS (3 mg/kg) group, ^aP < 0.05 vs sham + LPS group. BDL : Bile duct ligation; ROSI: Rosiglitazone.