Role of neutrophils in the pathogenesis of acute inflammatory liver injury

Interaction of osteopontin with neutrophil alpha(4)beta(1) and alpha(9)beta(1) integrins in a rodent model of alcoholic liver disease

Previous studies from our laboratory have reported that osteopontin (OPN) mediated higher hepatic neutrophil infiltration makes female rats more susceptible to alcoholic steatohepatitis (ASH) than their male counterparts. The objective of the current work was to investigate the patho-mechanism by which OPN attracts the hepatic neutrophils in ASH. We hypothesized that OPN-mediated hepatic neutrophil infiltration is a result of signaling by N-terminal integrin binding motif (SLAYGLR) of OPN through its receptor alpha(9)beta(1) (VLA9) and alpha(4)beta(1) (VLA4) integrins on neutrophils. Compared to the males, females in the ASH group exhibited higher expression of alpha(4)beta(1) and alpha(9)beta(1) protein and mRNA and a significant decrease in the expression of these integrins was observed in rats treated with neutralizing OPN antibody. Immunoprecipitation experiments suggested the binding of OPN to alpha(4)beta(1) and alpha(9)beta(1) integrins. OPN-mediated neutrophil infiltration was also confirmed using Boyden chamber assays, and antibodies directed against alpha(4) and beta(1) integrins was found to significantly inhibit neutrophilic migration in vitro. In conclusion, these data suggest that SLAYGLR-mediated alpha(4)beta(1) and alpha(9)beta(1) integrin signaling may be responsible for higher hepatic neutrophil infiltration and higher liver injury in the rat ASH model.

Potential relationship between hepatobiliary osteopontin and peroxisome proliferator-activated receptor alpha expression following ethanol-associated hepatic injury in vivo and in vitro

Osteopontin (OPN) up-regulation is known to mediate hepatic inflammation in a rodent model of alcoholic liver disease (ALD) and alcohol ingestion is reported to inhibit hepatic peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activity leading to hepatic steatosis and inflammation. Therefore, the objective of this study was to investigate the potential relationship between the anti-inflammatory PPAR-alpha and proinflammatory OPN in rats and mice livers, and cell cultures of hepatocytes and biliary epithelium. Experiments were designed to evaluate the influence of ethanol (EtOH), lipopolysaccharide (LPS), and acetaldehyde (ACA) on OPN and PPAR-alpha expression levels in vivo (rats and mice) and in vitro (hepatocytes and biliary epithelium). Adult Sprague-Dawley rats and C57BL6 mice were fed EtOH-containing Lieber-DeCarli liquid diet for 6 weeks and injected with a single dose of LPS. A combination of EtOH and LPS treated rats and mice showed significant induction of hepatic OPN expression compared with the controls. Similarly, cells exposed to physiological doses of EtOH, LPS, a combination of EtOH and LPS, and ACA resulted in increased OPN protein and mRNA expression. Rats and mice in ALD model and cells treated with EtOH and ACA showed downregulation of PPAR-alpha mRNA. Also, DNA binding activity of PPAR-alpha to PPAR response element was significantly reduced following treatment. Overexpression of PPAR-alpha rescued the reduced PPAR-alpha activity and PPAR-alpha agonist, bezafibrate, elevated PPAR-alpha activity after treatment of EtOH, LPS, and ACA when cells were exposed by bezafibrate. To further delineate the potential relationship between OPN and PPAR-alpha, OPN(-/-) mice showed no change of PPAR-alpha mRNA level although wild-type mice showed downregulation of PPAR-alpha mRNA after EtOH treatment. In conclusion, the current study suggests that OPN is induced by EtOH and its metabolite ACA and opposite relationship likely exist between PPAR-alpha and OPN expression within the liver during ALD.

Matricellular proteins at the crossroad of inflammation and cancer

Some proteins of the extracellular matrix known as matricellular proteins have regulatory function in all aspects of physiological and pathological stroma rearrangement. Many aspects of their activity are related to inflammation and immune response suggesting their role in bridging inflammation and cancer.

Protective effects of magnesium isoglycyrrhizinate against carbon tetrachloride-induced acute liver injury in mice

AIM: To investigate the effect of magnesium isoglycyrrhizinate (MI) on acute liver injury induced by carbon tetrachloride (CCl₄) in mice and its relationship with the expression of nuclear factor kappa B (NF-κB) and intercellular adhesion molecule-1 (ICAM-1) in liver tissues.

METHODS: Thirty male Kunming mice (28 ± 2.2 g) were divided randomly into 3 groups: model group, normal control group and MI-treated group. The model of acute liver injury was established by intraperitoneal injection of 1% CCl₄ (0.1 mL/10 g). The mice in normal control group and MI-treated group were injected with sterile saline, and furthermore, the MI-treated mice were intraperitoneally injected with MI (15 mg/kg, once per day for five days) 15 min before CCl4 injection. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and tissue contents of malondialdehyde (MDA) and superoxide dismutase (SOD) were measured using biochemical method. SP immunohistochemistry was used to detect NF-κB and ICAM-1 expression. The pathological alterations were observed after HE staining.

RESULTS: The serum levels of AST, ALT and tissue content of MDA were significantly increased in model group as compared with those in normal control group (465.10 ± 35.90 kU/L vs 47.40 ± 4.13 kU/L; 582.37 ± 25.63 kU/L vs 116.06 ± 12.82 kU/L; 4.07 ± 0.38 nmol/mg vs 1.39 ± 0.03 nmol/mg; all P < 0.01), but tissue content of SOD was significantly decreased (29.71 ± 2.25 U/mg vs 87.02 ± 4.84 U/mg, P < 0.01). NF-κB and ICAM-1 were not expressed in normal control group, but obviously expressed in model group. In comparison with those in model group, the tissue expression of NF-κB and ICAM-1 in MI-treated group were decreased in concurrence with the alleviation of liver injury as well as a statistically significant decrease in AST (263.51 ± 22.89 kU/L), ALT (292.56 ± 26.01 kU/L) and MDA (2.17 ± 0.03 nmol/mg, P < 0.05) and increase in SOD (58.04 ± 2.56 U/mg, P < 0.01) in hepatic homogenate.

CONCLUSION: NF-κB and ICAM-1 are strongly expressed in acute liver injury in mice. MI can protect mice against CCl₄-induced acute liver injury by suppressing NF-κB activation and subsequent expression of ICAM-1.