Role of eicosanoids in experimental alcoholic liver disease

Role of PGE2 in the development of pancreatic injury induced by chronic alcohol feeding in rats

BACKGROUND

Eicosanoids are known to modulate inflammation. Moreover, some studies report that endogenous prostaglandin E(2) (PGE(2)) protects the pancreas against injury. Therefore, we investigated its role in a rat model of chronic alcohol consumption.

METHODS

Rats were fed with 20% ethanol and a corn oil-supplemented diet using the interrupted alcohol feeding regimen (EI). Controls received water instead of ethanol (WI) or uninterruptedly ethanol (EU). After 13 mo, pancreas tissue was investigated morphologically, immunohistochemically and biochemically.

RESULTS

Pancreatic tissue was more severely injured in EI than in WI and EU (p < 0.05). Fibrogenesis (alpha-smooth muscle actin-positive cells, collagen types I and III) was increased in EI compared to WI (p < 0.05). In EI, mast cell numbers were increased, compared to WI, but decreased, compared to EU (p < 0.05). EI showed decreased PGE(2) and malondialdehyde contents compared to EU (p < 0.05) and decreased glutathione concentrations compared to WI (p < 0.05). PGE(2) content and fibrogenesis were inversely correlated in EU. The same correlation was detectable as a trend in all alcohol-fed rats.

CONCLUSION

The decrease in PGE(2) together with the increase in tissue damage and the inverse correlation between PGE(2) and fibrogenesis led us to suggest that endogenous PGE(2) plays a protective role in alcohol-induced injury in the pancreas.

Endotoxin, endotoxin-neutralizing-capacity, sCD14, sICAM-1, and cytokines in patients with various degrees of alcoholic liver disease

BACKGROUND

Chronic alcohol ingestion leads to endotoxemia which is believed to play an important role in the pathogenesis of alcoholic liver disease (ALD). The purpose of this study was to determine if chronic ethanol consumption, in addition to affecting plasma endotoxin and cytokines, also affects the endotoxin-neutralizing capacity (ENC), sCD14, and sICAM-1, in patients with ALD. A second aim was to identify correlations between these latter parameters, endotoxin, and cytokines, especially IL-10.

METHODS

Hospitalized patients with various degrees of ALD (n = 59), and 20 healthy volunteers were studied. Plasma endotoxin and ENC were determined using our kinetic Limulus amebocyte lysate test. Cytokines, sCD14, and sICAM-1 were measured by enzyme-linked immunosorbent assay.

RESULTS

Patients with ALD exhibited a mild endotoxemia (p < 0.01) and a marked decrease in ENC (p < 0.0002). TNF-alpha (p < 0.05), IL-6 (p < 0.0001), sICAM (p < 0.005), and sCD14 (p < 0.0005) were significantly elevated in all patients with ALD, and IL-10 (p < 0.05) in patients with cirrhotic ALD. With the exception of IL-10, the cytokines correlated with each other and with sICAM-1. No correlations occurred between endotoxin, ENC, and sCD14, and between these and the cytokines and sICAM-1. Elevated levels of endotoxin correlate with acute excessive alcohol ingestion. No gender differences were observed.

CONCLUSIONS

Acute alcohol intoxication rather than severe ALD results in significant endotoxemia. The limited capacity of plasma to neutralize endotoxin in liver injury seems to be an important factor in ALD which may be responsible for the release of endotoxin-induced mediators, such as cytokines, as well as s-ICAM-1, that are relevant in the pathogenesis of ALD.

A novel hepatointestinal leukotriene B4 receptor. Cloning and functional characterization

Leukotriene B(4) (LTB(4)) is a product of eicosanoid metabolism and acts as an extremely potent chemotactic mediator for inflammation. LTB(4) exerts positive effects on the immigration and activation of leukocytes. These effects suggest an involvement of LTB(4) in several diseases: inflammatory bowel disease, psoriasis, arthritis, and asthma. LTB(4) elicits actions through interaction with one or more cell surface receptors that lead to chemotaxis and inflammation. One leukotriene B(4) receptor has been recently identified (LTB(4)-R1). In this report we describe cloning of a cDNA encoding a novel 358-amino acid receptor (LTB(4)-R2) that possesses seven membrane-spanning domains and is homologous (42%) and genetically linked to LTB(4)-R1. Expression of LTB(4)-R2 is broad but highest in liver, intestine, spleen, and kidney. In radioligand binding assays, membranes prepared from COS-7 cells transfected with LTB(4)-R2 cDNA displayed high affinity (K(d) = 0.17 nm) for [(3)H]LTB(4). Radioligand competition assays revealed high affinities of the receptor for LTB(4) and LTB(5), and 20-hydroxy-LTB(4), and intermediate affinities for 15(S)-HETE and 12-oxo-ETE. Three LTB(4) receptor antagonists, 14,15-dehydro-LTB(4), LTB(4)-3-aminopropylamide, and U-75302, had high affinity for LTB(4)-R1 but not for LTB(4)-R2. No apparent affinity binding for the receptors was detected for the CysLT1-selective antagonists montelukast and zafirlukast. LTB(4) functionally mobilized intracellular calcium and inhibited forskolin-stimulated cAMP production in 293 cells. The discovery of this new receptor should aid in further understanding the roles of LTB(4) in pathologies in these tissues and may provide a tool in identification of specific antagonists/agonists for potential therapeutic treatments.

Eicosanoid production by adult Fasciola hepatica and plasma eicosanoid patterns during fasciolosis in sheep

Fasciola hepatica infection in sheep is known to cause anaemia, fever and elevated levels of liver enzymes. It was hypothesised that eicosanoids play a role in these pathophysiological changes, so the pattern of plasma eicosanoids during the course of acute and chronic fasciolosis was studied in sheep infected with a single dose of 800 F. hepatica metacercariae. Blood plasma was collected weekly until week 17 p.i. from infected sheep, and from uninfected controls. Adult F. hepatica were then recovered from bile ducts and incubated for production of ES products. Eicosanoids were determined by enzyme immuno-assay in blood plasma, fluke homogenates and ES products after chromatographic purification of the samples. Fever and anaemia were seen from 3 to 12 weeks p.i. and from 8 to 17 weeks p.i., respectively. Onset of fever was accompanied by elevated liver enzyme activities (aspartate amino transferase and gamma glutamyl transferase) in the plasma. In general, the plasma levels of prostaglandin E2 (PGE2), prostaglandin I2 (PGI2) and leukotriene B4 (LTB4) were reduced during the acute and chronic stages of the infection, whereas thromboxane B2 (TXB2) was reduced only at 8 weeks p.i. The TXB2/PGI2 ratio was increased in favour of TXB2 at 3 and 11 weeks p.i. Additionally, TXB2, PGI2, PGE2 and LTB4 were detected both in ES products and in homogenates of F. hepatica. It was concluded that eicosanoid depletion in the plasma is caused by parasite-induced liver damage. The changes in eicosanoid levels are highly correlated to the clinical signs of the disease. Changes in the pattern of host plasma eicosanoids during fasciolosis, as well as parasite-derived eicosanoids, may reflect or contribute to the pathology of the disease.

Thromboxane A2 analogue contracts predominantly the hepatic veins in isolated canine liver

Thromboxane A2 (TxA2) is a potent vasoconstrictor and has been implicated as a mediator of liver diseases such as ischemic-reperfusion injury. We determined the effects of TxA2 and the well-known hepatic venoconstrictor histamine, on the vascular resistance distribution and liver weight in isolated canine livers perfused with blood via the portal vein. The stable TxA2 (STA2; 20 micrograms, n = 5) and histamine (5 micrograms, n = 6) similarly increased the hepatic total vascular resistance, 2.5- and 2.4-fold, respectively. The increase in the hepatic venous resistance was significantly greater than that of the portal resistance (threefold vs. 1.9-fold for STA2; threefold vs. 1.8-fold for histamine). Predominant hepatic venoconstriction induced by both agents was confirmed in livers perfused in a reverse direction from the hepatic vein to the portal vein, as shown by marked precapillary vasoconstriction. STA2 transiently increased liver weight loss (-3.6 g/100 g liver weight), followed by a gradual weight gain (9.0 g/100 g). Histamine caused a progressive weight gain (9.1 g/100 g). In conclusion, similar to histamine, TxA2 constricts predominantly the hepatic vein in isolated canine livers.