Carbon monoxide produced by intrasinusoidally located haem-oxygenase-1 regulates the vascular tone in cirrhotic rat liver.
OBJECTIVE
Carbon monoxide (CO) produced by haem-oxygenase isoforms (HO-1 & HO-2) is involved in the regulation of systemic vascular tone. We aimed to elucidate the vasoregulatory role of CO in the microcirculation in normal and thioacetamide cirrhotic rat livers.


METHODS
Haem-oxygenase expression was examined by Western blot. Total HO enzymatic activity was measured spectrophotometrically. Sensitivity of hepatic stellate cells (HSCs) to CO-mediated relaxation was studied by a stress-relaxed-collagen-lattice model. To define the relative role of CO, the CO-releasing molecule CORM-2, the HO-inhibitor zinc protoporphyrin-IX and the HO-1 inducer hemin were added to an in situ liver perfusion set-up. The topography of vasoactive CO production was evaluated by applying different CO- and nitric oxide-trapping reagents in the liver perfusion set-up and by immunohistochemistry.


RESULTS
Western blot showed decreased expression of both HO isoenzymes (P<0.036 for HO-1; P<0.001 for HO-2) in cirrhotic vs normal rat livers, confirmed by the HO-activity assay (P=0.004). HSCs relaxed on exposure to CORM-2 (P=0.013). The increased intrahepatic vascular resistance (IHVR) of cirrhotic rats was attenuated by perfusion with CORM-2 (P=0.016) and pretreatment with hemin (P<0.001). Inhibition of HO caused a dose-related increase in IHVR in normal and cirrhotic liver. In normal liver, the haemodynamically relevant CO production occurred extrasinusoidally, while intrasinusoidally HO-1 predominantly regulated the microcirculation in cirrhotic livers.


CONCLUSIONS
We demonstrate a role for CO and HO in the regulation of normal and cirrhotic microcirculation. These findings are of importance in the pathophysiology of portal hypertension and establish CO/HO as novel treatment targets.
Van Landeghem
Lien
L
Department of Hepatology, University Hospital Gasthuisberg, KU Leuven, Belgium.
Laleman
Wim
W
Vander Elst
Ingrid
I
Zeegers
Marcel
M
van Pelt
Jos
J
Cassiman
David
D
Nevens
Frederik
F
D000818:Animals; D015153:Blotting, Western; D002248:Carbon Monoxide / Q000378:metabolism*; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D006427:Hemin; D006439:Hemodynamics / Q000502:physiology*; D055166:Hepatic Stellate Cells / Q000502:physiology; D008103:Liver Cirrhosis / Q000201:enzymology*; D008954:Models, Biological; D009942:Organometallic Compounds; D051381:Rats
D009942:Organometallic Compounds; C447082:tricarbonyldichlororuthenium (II) dimer; D006427:Hemin; D002248:Carbon Monoxide; D051547:Heme Oxygenase-1