Hepatic leukocyte recruitment in a model of acute colitis

Alpha-1 acid glycoprotein reduces hepatic leukocyte recruitment in murine models of either early endotoxemia or early sepsis

OBJECTIVE

To characterize the effect of systemically administered AGP on early leukocyte recruitment in the livers of endotoxemic or septic mice and to determine whether this is influenced by LPS sequestration.

METHODS

Endotoxemia was induced in C57Bl/6 mice via intraperitoneal injection of LPS. Sepsis was induced in mice by cecal ligation and perforation. AGP (165 mg/kg) or saline (20 mL/kg) or HAS (200 mg/kg) was administered immediately after surgery or LPS injection and the hepatic microcirculation was examined by intravital microscopy at four hour.

RESULTS

Leukocyte adhesion in the PSV was reduced by treatment with AGP in mice subjected to either LPS or CLP protocols compared to either saline or HAS treatment. AGP-treated mice also had significantly higher sinusoidal flow in both models. Pre-incubation of LPS with AGP reduced the ability of LPS to recruit leukocytes to the liver microcirculation.

CONCLUSIONS

AGP was more effective in limiting hepatic inflammation and maintaining perfusion than saline or HAS, in both endotoxemic and septic mice. AGP sequestration of LPS may contribute to its anti-inflammatory effects.

Ulcerative colitis-induced hepatic damage in mice: studies on inflammation, fibrosis, oxidative DNA damage and GST-P expression

There exists a close relationship between ulcerative colitis and various hepatic disorders. The present study was aimed to evaluate the hepatocellular damage in experimental colitis model. Ulcerative colitis was induced in Swiss mice by cyclic treatment with 3% w/v dextran sulfate sodium in drinking water. The severity of colitis was assessed on the basis of disease activity index and colon histology. The effect of ulcerative colitis on the liver was assessed using various biochemical parameters, histological evaluation, sirius red staining, immunohistochemical staining with peroxisome proliferator-activated receptor γ, 8-oxo-7,8-dihydro-2'-deoxyguanosine and placental glutathione S-transferase, comet assay (alkaline and modified), Terminal Deoxynucleotidyl Transferase-mediated dUTP Nick End Labeling assay and western blot analysis to detect the protein expression of nuclear factor kappa B, cyclooxygenase-2, nuclear erythroid 2-related factor 2 and NADPH: quinone oxidoreductase-1. Dextran sulfate sodium induced severe colitis in mice as evident from an elevated disease activity index and histological abnormalities. Ulcerative colitis increased the permeability of colon as apparent from a significant reduction in the expression of tight junction protein, occludin. Further, the bacterial translocation assay as well as the analysis of lipopolysaccharide level revealed the existence of various bacterial species in the liver of ulcerative colitis-induced mice. There was a significant increase in the plasma alanine and aspartate transaminases and liver triglyceride levels, expression of peroxisome proliferator-activated receptor γ, inflammatory markers, oxidative stress, fibrosis, oxidative DNA damage and apoptosis in the liver of mice. Moreover, there was an increase in the expression of nuclear factor kappa B and cyclooxygenase-2 and a reduction in the expression of nuclear erythroid 2-related factor 2 and NADPH: quinone oxidoreductase-1 in the liver of severe ulcerative colitis-induced mice. The results of the present study provide evidence that ulcerative colitis is accompanied with hepatic damage in mice.

Contribution of gut bacteria to liver pathobiology

Emerging evidence suggests a strong interaction between the gut microbiota and health and disease. The interactions of the gut microbiota and the liver have only recently been investigated in detail. Receiving approximately 70% of its blood supply from the intestinal venous outflow, the liver represents the first line of defense against gut-derived antigens and is equipped with a broad array of immune cells (i.e., macrophages, lymphocytes, natural killer cells, and dendritic cells) to accomplish this function. In the setting of tissue injury, whereby the liver is otherwise damaged (e.g., viral infection, toxin exposure, ischemic tissue damage, etc.), these same immune cell populations and their interactions with the infiltrating gut bacteria likely contribute to and promote these pathologies. The following paper will highlight recent studies investigating the relationship between the gut microbiota, liver biology, and pathobiology. Defining these connections will likely provide new targets for therapy or prevention of a wide variety of acute and chronic liver pathologies.

The immunobiology of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease histologically characterized by the presence of intrahepatic and/or extrahepatic biliary duct concentric, obliterative fibrosis, eventually leading to cirrhosis. Approximately 75% of patients with PSC have inflammatory bowel disease. The male predominance of PSC, the lack of a defined, pathogenic autoantigen, and the potential role of the innate immune system suggest that it may be due to dysregulation of immunity rather than a classic autoimmune disease. However, PSC is associated with several classic autoimmune diseases, and the strongest genetic link to PSC identified to date is with the human leukocyte antigen DRB01*03 haplotype. The precise immunopathogenesis of PSC is largely unknown but likely involves activation of the innate immune system by bacterial components delivered to the liver via the portal vein. Induction of adhesion molecules and chemokines leads to the recruitment of intestinal lymphocytes. Bile duct injury results from the sustained inflammation and production of inflammatory cytokines. Biliary strictures may cause further damage as a result of bile stasis and recurrent secondary bacterial cholangitis. Currently, there is no effective therapy for PSC and developing a rational therapeutic strategy demands a better understanding of the disease.

A point mutation in the neu1 promoter recruits an ectopic repressor, Nkx3.2 and results in a mouse model of sialidase deficiency

SM/J is an inbred mouse strain with a complex phenotype including small body size, impaired immune response and a tissue-specific sialidase deficiency. We identified a regulatory mutation, (-519G-->A) within the neu1 promoter which in reporter assays resulted in significantly reduced transcription. This mutation generates a consensus binding site for Nkx3 family transcription repressors. Recombinant Nkx3.2 bound strongly to and preferentially repressed transcription of the mutant promoter. This tissue-specific deficiency results in a retarded immune response and modulates leukocyte recruitment. Examination of the hepatic microcirculation in mutant mice revealed increased rolling and decreased adhesion of leukocytes. Our findings support a significant role for lysosomal sialidase in inflammation and highlight the significance of repressor-recruitment in genetic disease.

Dextran sulphate sodium induces acute colitis and alters hepatic function in hamsters

Dextran sulphate sodium (DSS)-induced colitis in rodents is an experimental model for human inflammatory bowel disease (IBD). The aim of this study was to characterize the effect of DSS in hamster colon and liver. DSS (2-5%) was administrated in the drinking water for 4-6 days. Clinical symptoms were recorded daily, inflammatory and fatty acid-related metabolic markers were assessed in plasma, colon and liver. Six days of 3 or 5% DSS induced a severe wasting disease, whereas 2.5% DSS induced a colonic inflammation without severe systemic adverse effects. The systemic inflammatory response was characterized by an inverse production of albumin and the acute phase protein haptoglobin. The colonic inflammatory response was confined to the proximal colon, manifested by a high macroscopic inflammatory score, increased colon weight and expression of IL-1beta, IL-6 and iNOS, infiltration of inflammatory cells and epithelial disruption. In contrast, only a low/mild inflammatory response was observed in the distal colon of DSS-exposed hamsters. Significant hepatic-related metabolic alterations were also observed, with elevation of plasma triglycerides and increased liver expression of lipoprotein lipase and reduced expression of acyl-CoA oxidase and cytochrome P450A. Although liver weight was significantly reduced, no histopathological signs of inflammation or tissue damage were observed. In summary, hamsters exposed to 2.5% DSS for 6 days develop acute colitis resembling murine DSS-induced colitis. In addition, DSS-exposed hamster showed alterations in hepatic fatty acids metabolism resembling human IBD, suggesting that the model can potentially be used for target discovery and validation of hepatic-related metabolic alterations.

Inhalation of carbon monoxide prevents liver injury and inflammation following hind limb ischemia/reperfusion

The induction of heme oxygenase (HO), the rate limiting enzyme in the conversion of heme into carbon monoxide (CO) and biliverdin, limits liver injury following remote trauma such as hind limb ischemia/reperfusion (I/R). Using intravital video microscopy, we tested the hypothesis that inhaled CO (250 ppm) would mimic HO-derived liver protection. Hind limb I/R significantly decreased sinusoidal diameter and volumetric flow, increased leukocyte accumulation within sinusoids, increased leukocyte rolling and adhesion within postsinusoidal venules, and significantly increased hepatocyte injury compared with naive animals. Inhalation of CO alone did not alter any microcirculatory or inflammatory parameters. Inhalation of CO following I/R restored volumetric flow, decreased stationary leukocytes within sinusoids, decreased leukocyte rolling and adhesion within postsinusoidal venules, and significantly reduced hepatocellular injury following hind limb I/R. HO inhibition did not alter microcirculatory parameters in naive mice, but did increase inflammation, as well as increase hepatocyte injury following hind limb I/R. Inhalation of CO during HO inhibition significantly reduced such microcirculatory deficits, hepatic inflammation, and injury in response to hind limb I/R. In conclusion, these results suggest that HO-derived hepatic protection is mediated by CO, and inhalation of low concentrations of CO may represent a novel therapeutic approach to prevent remote organ injury during systemic inflammatory response syndrome, or SIRS.