Guinea pig Kupffer cells can be activated in vitro to an enhanced superoxide response. II. Involvement of eicosanoids

Reversible Kupffer cell suppression in biliary obstruction is caused by hydrophobic bile acids

BACKGROUND/AIM

Biliary obstruction is associated with suppressed Kupffer cell clearance of bacteria and intracellular bactericidal activity of the phagocytes. We studied the superoxide generation of Kupffer cell in biliary obstruction and after incubation with bile acids to elucidate the mechanism of impaired intracellular killing of these phagocytes.

METHODS

Kupffer cells were extracted from rats with common bile duct ligation or sham-operation. The extracted cells were tested for superoxide production immediately after extraction, 2 h and 24 h post-extraction. Superoxide generation from Kupffer cells after incubation with five bile acids (cholic acid, taurocholic acid, deoxycholic acid, chenodeoxycholic acid and ursodeoxycholic acid) at two different concentrations (0.1 mM and 1.0 mM) were also studied. Cell viability was monitored by trypan blue exclusion.

RESULTS

Kupffer cells extracted from common duct-ligated animals had significantly lower superoxide production (-1.37+/-0.24 nmol O2(-)/10(6) cells) compared to that from sham-operated rats (2.54+/-0.58 nmol O2(-)/10(6) cells) and non-operated rats (2.15+/-0.76 nmol O2(-)/10(6) cells) (p<0.05). After 2 h of resting in culture medium, these cells recovered significantly in superoxide production to 2.72+/-0.63 nmol O2(-)/10(6) cells (p<0.01). A dose-related reduction in superoxide production was demonstrated when Kupffer cells were incubated with bile acids. Hydrophobic bile acids (deoxycholic acid and chenodeoxycholic acid) caused more significant suppression than with hydrophilic bile acids (cholic acid, taurocholic acid, ursodeoxycholic acid). The drop in superoxide production after bile acid treatment was not due to cell death. Washing in Hank's balanced salt solution resulted in partial recovery of Kupffer cell superoxide production.

CONCLUSION

High blood levels of hydrophobic bile acids are likely to be the cause of impaired intracellular bactericidal activity of Kupffer cells in biliary obstruction.

Liver cytoprotection by prostaglandins

During the last decade intensive work on the relationships between the liver and the arachidonic acid cascade has greatly expanded our knowledge of this area of research. The liver has emerged as the major organ participating in the degradation and elimination of arachidonate products of systemic origin. The synthesis in the liver of arachidonate products derived from the cyclooxygenase, lipoxygenase and cytochrome P450 system pathways has been demonstrated. The participation of leukotriene B4 and cysteinyl-leukotrienes as mediators of liver damage and the possible therapeutic usefulness of prostaglandins (PGs) in acute liver injury has attracted the interest of clinicians. This article reviews the essential features regarding the role of arachidonate metabolites in liver disease and specially focuses on the cytoprotective effects on the liver displayed by PGE2, PGE1, PGI2 and synthetic PG analogs in experimental models of liver damage induced by ischemia-reperfusion injury, carbon tetrachloride, bacterial lipopolysaccharide and viral hepatitis and on the possible mechanisms underlying liver cytoprotection in these experimental models. The therapeutic usefulness of PGs in clinical practice is critically analyzed on the basis of available evidence in patients with fulminant hepatic failure and primary graft nonfunction following liver transplantation.

Prostanoid release of cultured liver sinusoidal endothelial cells in response to endotoxin and tumor necrosis factor. Comparison with umbilical vein endothelial cells

Vascular endothelial cells release prostanoids, especially prostacyclin, when properly stimulated. In addition to short acting stimuli like thrombin and histamine an increased prostanoid release occurs in the presence of endotoxin, interleukin 1 or tumor necrosis factor (TNF). The response of sinusoidal endothelial liver cells to such stimuli - probably important in hepatic inflammatory disease - is unknown. Sinusoidal endothelial liver cells from the guinea pig were isolated by centrifugal elutriation and investigated as confluent monolayers. Their prostanoid release in response to endotoxin and human recombinant TNF was determined by radioimmunoassays and compared to that obtained with cultured human umbilical vein endothelial cells. A pronounced time- and dose-dependent release of prostanoids was found with both cell types in response to endotoxin. In contrast to umbilical vein cells, liver endothelial cells produced not only large amounts of 6-keto-PGF1 alpha and some PGE2 but also thromboxane B2. Only umbilical vein endothelial cells responded to TNF with an increased 6-keto-PGF1 alpha release, emphasising the metabolic differences between both cell types.