LPS exacerbates endothelin-1 induced activation of cytosolic phospholipase A2 and thromboxane A2 production from Kupffer cells of the prefibrotic rat liver.
OBJECTIVE
Thromboxane A2 (TXA2) has been suggested to play a significant role in the development of portal hypertension in fibrosis, and Kupffer cell (KC) derived TXA2 has been shown to mediate the hyperresponsiveness of the portal circulation to the vasoconstrictive actions of endothelin-1 (ET-1) during endotoxemia. The aim of this study was to determine whether the double stresses of prefibrotic changes and endotoxemia additively activate KC to increase release of TXA2 in response to ET-1, resulting in elevated portal resistance.


METHODS
One week Bile duct ligation (BDL) rats and sham-operated controls were subjected to isolated liver perfusions following LPS or saline for 6h. In a separate experiment, KC were isolated from BDL or sham rats and incubated with LPS or saline for 6h before the ET-1 treatment.


RESULTS
The double stresses of early fibrosis and LPS resulted in a greater sustained increase in portal pressure in response to ET-1 in BDL rats, and this increase correlated well with the much enhanced release of TXA2 in the perfusate. Media from the cultured KC showed significantly greater TXA2 release in response to ET-1 in BDL group than those in sham group, and LPS exacerbated this effect. Protein levels of cytosolic phospholipase A2 (cPLA2), cyclooxygenase-2, and thromboxane synthase were also significantly elevated in KC from BDL rats. ET-1 produced a marked increase in cPLA2 activation as measured by the phosphorylation of cPLA2 in KC of both BDL and sham groups. LPS greatly exacerbated the activation of cPLA2.


CONCLUSIONS
The data suggest that the double stresses additively activate KC with an upregulation of the key enzymes in the TXA2 biosynthesis and release increased amount of TXA2 via the augmented activation of cPLA2 in response to ET-1, which leads to the increased portal resistance and ultimately hepatic microcirculatory dysfunction.
Miller
Andrew M
AM
Department of Biology, University of North Carolina at Charlotte, 9201 University City Blvd, Charlotte, NC 28223, USA.
Masrorpour
Mina
M
Klaus
Christian
C
Zhang
Jian X
JX
D000818:Animals; D051546:Cyclooxygenase 2 / Q000032:analysis / Q000378:metabolism; D019332:Endothelin-1 / Q000494:pharmacology*; D004789:Enzyme Activation; D005355:Fibrosis; D054513:Group IV Phospholipases A2; D006975:Hypertension, Portal / Q000209:etiology* / Q000378:metabolism; D066298:In Vitro Techniques; D007728:Kupffer Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008099:Liver / Q000098:blood supply / Q000187:drug effects / Q000473:pathology; D008106:Liver Cirrhosis, Experimental / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008833:Microcirculation / Q000187:drug effects; D010741:Phospholipases A / Q000032:analysis / Q000378:metabolism; D054467:Phospholipases A2; D010766:Phosphorylation / Q000187:drug effects; D017082:Portal Pressure / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013928:Thromboxane A2 / Q000032:analysis / Q000378:metabolism*
D019332:Endothelin-1; D008070:Lipopolysaccharides; D013928:Thromboxane A2; D051546:Cyclooxygenase 2; D010741:Phospholipases A; D054513:Group IV Phospholipases A2; D054467:Phospholipases A2