Vascular heme oxygenase-1 induction suppresses microvascular thrombus formation in vivo.
OBJECTIVE
By heme degradation, heme oxygenase-1 (HO-1) provides endogenous carbon monoxide and bilirubin, both of which play major roles in vascular biology. The current study aimed to examine whether induction of HO-1 and its byproducts modulate the process of microvascular thrombus formation in vivo.


RESULTS
In individual microvessels of mouse cremaster muscle preparations, ferric chloride-induced thrombus formation was analyzed using intravital fluorescence microscopy. When mice were pretreated with an intraperitoneal injection of hemin, a HO-1 inducer, immunohistochemistry and Western blot protein analysis of cremaster muscle tissue displayed a marked induction of HO-1. In these animals, superfusion with ferric chloride solution induced arteriolar and venular thrombus formation, which, however, was significantly delayed when compared with thrombus formation in animals without HO-1 induction. The delay in thrombus formation in hemin-treated mice was completely blunted by tin protoporphyrin-IX, a HO-1 inhibitor, but not by copper protoporphyrin-IX, which does not inhibit the enzyme. Coadministration of the vitamin E analogue Trolox in HO-1-blocked animals almost completely restored the delay in thrombus formation, implying that, besides CO, the antioxidant HO pathway metabolite bilirubin mainly contributes to the antithrombotic property of HO-1. This was further supported by the fact that bilirubin was found as effective as hemin in delay of ferric chloride-induced thrombus formation. Animals with HO-1 induction revealed reduced P-selectin protein expression in cremaster muscle tissue, which most probably presented the molecular basis for delayed thrombus growth.


CONCLUSIONS
Local induction of HO-1 activity may be of preventive and therapeutic value for clinical disorders with increased risk of thrombotic events.
Lindenblatt
N
N
Department of Experimental Surgery, University of Rostock, Rostock, Germany.
Bordel
R
R
Schareck
W
W
Menger
M D
MD
Vollmar
B
B
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001663:Bilirubin / Q000502:physiology; D002712:Chlorides; D002839:Chromans / Q000494:pharmacology; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005290:Ferric Compounds / Q000633:toxicity; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051547:Heme Oxygenase-1; D006427:Hemin / Q000633:toxicity; D008297:Male; D008565:Membrane Proteins; D008665:Metalloporphyrins / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008833:Microcirculation; D018482:Muscle, Skeletal / Q000378:metabolism; D019007:P-Selectin / Q000096:biosynthesis / Q000235:genetics; D011524:Protoporphyrins / Q000494:pharmacology; D013927:Thrombosis / Q000139:chemically induced / Q000517:prevention & control*
D000975:Antioxidants; D002712:Chlorides; D002839:Chromans; D004791:Enzyme Inhibitors; D005290:Ferric Compounds; D008565:Membrane Proteins; D008665:Metalloporphyrins; D019007:P-Selectin; D011524:Protoporphyrins; D006427:Hemin; C032628:tin protoporphyrin IX; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse; D001663:Bilirubin; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; C024555:ferric chloride