Interleukin-6 upregulates paraoxonase 1 gene expression via an AKT/NF-κB-dependent pathway

The aim of this study is to investigate the relationship between paraoxonase 1 (PON1) and atherosclerosis-related inflammation. In this study, human hepatoma HepG2 cell line was used as a hepatocyte model to examine the effects of the pro-inflammatory cytokines on PON1 expression. The results showed that IL-6, but not TNF-α and IL-1β, significantly increased both the function and protein level of PON1; data from real-time RT-PCR analysis revealed that the IL-6-induced PON1 expression occurred at the transcriptional level. Increase of IκB kinase activity and IκB phosphorylation, and reduction of IκB protein level were also observed in IL-6-treated HepG2 cells compared with untreated culture. This event was accompanied by increase of NF-κB-p50 and -p65 nuclear translocation. Moreover, treatment with IL-6 augmented the DNA binding activity of NF-κB. Furthermore, pharmacological inhibition of NF-κB activation by PDTC and BAY 11-7082, markedly suppressed the IL-6-mediated PON1 expression. In addition, IL-6 increased the levels of phosphorylated protein kinase B (PKB, AKT). An AKT inhibitor LY294002 effectively suppressed IKK/IκB/NF-κB signaling and PON1 gene expression induced by IL-6. Our findings demonstrate that IL-6 upregulates PON1 gene expression through an AKT/NF-κB signaling axis in human hepatocyte-derived HepG2 cell line.

Administration of rat acute-phase protein α(2)-macroglobulin before total-body irradiation initiates cytoprotective mechanisms in the liver

Previously, we showed that administration of the acute-phase protein α(2)-macroglobulin (α(2)M) to rats before total-body irradiation with 6.7 Gy (LD(50/30)) of X-rays provides the same level of radioprotection as amifostine. Here, we compare the cytoprotective effects of α(2)M and amifostine on rat liver. The potential of the liver to replenish cells destroyed by ionizing radiation was assessed by immunoblot analysis with antibody to proliferating cell nuclear antigen (PCNA). After irradiation, in unprotected rats PCNA decreased 6-fold from the basal level. In rats pretreated with either α(2)M or amifostine, PCNA was increased throughout a 4 week follow-up period, indicating that hepatocyte proliferation was unaffected. Since PCNA is an important component of the repair machinery, its increased expression was accompanied by significantly lower DNA damage in α(2)M- and amifostine-treated rats. At 2 weeks after irradiation, the Comet assay revealed a 15-fold increase in DNA damage in unprotected rats, while in α(2)M- and amifostine-treated rats we observed 3- and 4-fold rise in damage, respectively. The improved protection to DNA damage was supported by elevated activity of the antioxidant systems. Compared to untreated rats, pretreatments with α(2)M and amifostine led to similar increases in levels of the inflammatory cytokine IL-6 and the redox-sensitive transcription factor NFκB, promoting upregulation of MnSOD, the major component of the cell's antioxidant axis, and subsequent increases in Mn/CuZnSOD and catalase enzymatic activities. The results show that α(2)M induces protein factors whose interplay underlies radioprotection and support the idea that α(2)M is the central effector of natural radioprotection in the rat.

Up-regulation of hepatic heme oxygenase-1 expression by locally induced interleukin-6 in rats administered carbon tetrachloride intraperitoneally

We previously reported that interleukin-6 (IL-6) was locally produced in the early period after intraperitoneal (i.p.) or subcutaneous carbon tetrachloride (CCl4) administration, but not after oral (p.o.) administration. In the present study, we focused on the up-regulation of stress-inducible proteins induced by IL-6 after i.p. CCl4 administration. The expression of heme oxygenase-1 (HO-1) (EC 1.14.99.3) mRNA and protein were induced more in rats administered CCl4 via the i.p. route, compared with the p.o. route; however, expression of heat shock protein (HSP) 72 and HSP90 mRNA were increased to similar extents in both experimental groups. The induction of HO-1 mRNA and protein after i.p. CCl4 administration were significantly reduced after pretreatment with anti-rat IL-6 antibody. Activation of the signal transducer and activator of transcription factor 3 (STAT3), which promotes HO-1 expression, peaked together with plasma levels of IL-6 after i.p. CCl4 administration, suggesting that hepatic HO-1 expression was increased by IL-6 via the Janus kinase/STAT3 pathway. The present data indicate that hepatic HO-1 is up-regulated by endogenously produced IL-6, in addition to its up-regulation by heme derived from cytochrome P450 which has already been reported in rats administered i.p. CCl4. The up-regulation of hepatic HO-1 expression may reduce the tissue injury to livers caused by CCl4.

Interleukin-6 production by peritoneal mesothelial cells and its regulation by inflammatory factors in rats administered carbon tetrachloride intraperitoneally

We previously reported that a high level of interleukin-6 (IL-6), which is protective against CCl(4)-induced hepatotoxicity, is produced in the peritoneal cavity in the early period after ip carbon tetrachloride (CCl(4)) administration. The objective of this study was to identify the tissues and cells involved in IL-6 production and clarify the mechanisms underlying its regulation. IL-6 mRNA levels increased significantly in the serous membranes of the mesentery and peritoneum, but not in the parenchymal organs including liver, kidney and spleen, 3 h after ip CCl(4) administration. Peritoneal mesothelial cells (PMCs), a major cell population in serous membranes, were isolated from rat peritoneal walls by trypsin digestion and cultured with peritoneal exudate fluid (PEF) from CCl(4)-administered rats. PMCs produced a high level of IL-6 in the presence of PEF recovered 0.5 h after ip CCl(4) administration. Analyses of PEF revealed that the levels of prostaglandin E(2) (PGE(2)), histamine, IL-1alpha, IL-1beta and tumor necrosis factor-alpha (TNF-alpha) increased immediately after ip CCl(4) administration. These inflammatory factors, except for histamine, stimulated IL-6 production to varying degrees, in the following order: IL-1alpha>IL-1beta>TNF-alpha>>PGE(2). In summary, the present study indicates that the high level of IL-6 observed in the rat peritoneal cavity after ip CCl(4) administration is at least partially produced by PMCs stimulated cooperatively with IL-1alpha, IL-1beta, TNF-alpha and PGE(2). These inflammatory factors may be released from tissues or cells either stimulated or injured directly by CCl(4).

Early induced, high-level interleukin-6 expression in the rat peritoneal cavity into which a hepatotoxicant carbon tetrachloride was administered

IL-6 induction depending on the mode of carbon tetrachloride (CCl4) administration was investigated in rats. After the intraperitoneal (i.p.) administration of CCl4 in 50% corn oil at 1.0 ml/kg body weight, IL-6 level markedly increased in plasma and peaked at 4h. TNF-alpha and IL-1beta levels gradually increased, reaching the maximum at 24h. IL-10 level transiently peaked at 4h and then decreased, but later further increased, reaching the second peak at 24h. Plasma alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) activities peaked at 24h. As the vehicle-to-CCl4 ratio increased, the level of IL-6 decreased and the activities of ALT and SDH increased. After oral CCl4 administration, IL-6 was not significantly detected. IL-6 level in peritoneal exudate fluid (PEF) increased simultaneously with plasma IL-6 level after i.p. CCl4 administration, but the total amount of PEF IL-6 was 37-fold as much as that of plasma IL-6, in contrast to the result that the total amount of plasma IL-6 was 19-fold as much as that of PEF IL-6 after i.p. lipopolysaccharide administration. These results suggest that i.p. administration of CCl4 dissolved in a small amount of vehicle selectively induces a high production of IL-6 in the peritoneal cavity early after the administration. Since IL-6 is a protective cytokine against hepatotoxicity, its induction should be taken into consideration during analysis of data obtained using the CCl4-induced liver injury model.

Preventive effect of neutropenia on carbon tetrachloride-induced hepatotoxicity in rats

The preventive effect of neutropenia on carbon tetrachloride (CCl4)-induced hepatotoxicity was examined in rats. In rats treated once with CCl4 (1 ml kg(-1), i.p.), the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), indices of liver cell damage, and the hepatic activity of myeloperoxidase (MPO), an index of tissue neutrophil infiltration, increased at 6 h after the intoxication and further increased at 24 h. The liver of CCl4 -treated rats showed an increase in the concentration of thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation, and decreases in superoxide dismutase (SOD) activity and reduced glutathione (GSH) concentration at 6 h after the intoxication followed by a further increase in TBARS concentration and further decreases in SOD activity and GSH concentration at 24 h with increased xanthine oxidase (XO) activity at 24 h. Neutropenic treatment with anti-rat neutrophil antiserum (2 ml kg(-1), i.p.) at 0.5 h after CCl4 intoxication attenuated the increases in serum ALT and AST activities and hepatic MPO activity and TBARS concentration and the decreases in hepatic SOD activity and GSH concentration found at 6 and 24 h after CCl4 intoxication and the increase in hepatic XO activity found at 24 h after the intoxication. This neutropenia reduced the necrotic and degenerative changes with inflammatory cell infiltration in the liver cell of CCl4 -treated rats. These results indicate that neutropenia prevents CCl4 -induced hepatotoxicity in rats by attenuating the disruption of hepatic reactive oxygen species metabolism mediated by neutrophils accumulating in the liver tissue.