Antithrombin prevents endotoxin-induced hypotension by inhibiting the induction of nitric oxide synthase in rats

Abstract

Antithrombin (AT) prevents Escherichia coli-induced hypotension in animal models of sepsis, and it further reduces the mortality of patients with septic shock. In the present study, we examined whether AT may prevent the endotoxin (ET)-induced hypotension by promoting the endothelial release of prostacyclin (PGI 2 ) in rats. Intravenous administration of AT (250 U/kg) prevented both hypotension and the increases in plasma levels of NO 2 ؊ / NO 3 ؊ in rats given ET. Lung expression of messenger RNA (mRNA) for tumor necrosis factor-␣ (TNF-␣) was transiently increased after ET administration, followed by the increases in lung tissue levels of TNF-␣. Both the lung activity of the inducible form of nitric oxide synthase (iNOS) and the lung expression of iNOS mRNA in animals administered ET were gradually increased after the TNF-␣ mRNA expression had peaked. Administration of AT significantly inhibited these increases. Neither DEGR-F.Xa, a selective inhibitor of thrombin generation, nor Trp 49 -modified AT, which is not capable of promoting the endothelial release of PGI 2 , showed any effects on these changes induced by ET. Administration of antirat TNF-␣ antibody produced effects similar to those induced by AT. Indomethacin pretreatment abrogated the effects induced by AT. Iloprost, a stable derivative of PGI 2 , produced effects similar to those of AT. These findings suggested that AT prevents the ET-induced hypotension by inhibiting the induction of iNOS through inhibiting TNF-␣ production. These effects of AT could be mediated by the promotion of endothelial release of PGI 2 and might at least partly explain the therapeutic effects for septic shock. IntroductionAntithrombin (AT) is an important serine protease inhibitor of the coagulation system. 1 Inhibition by AT of thrombin and the other serine proteases generated from the coagulation cascade is markedly accelerated by its interaction with the endothelial surface glycosaminoglycans (GAGs). 1 Patients with congenital AT deficiency and those with the variant AT that lacks affinity for GAGs develop thrombosis, showing the importance of the interaction of AT with the endothelial cell surface GAGs for regulation of the coagulation cascade. 2,3 AT has been shown to promote endothelial release of prostacyclin (PGI 2 ) by interacting with the endothelial surface GAGs in vitro 4,5 and in vivo. 6 PGI 2 potently inhibits platelet aggregation 7 and induces vasodilation, 8 thereby maintaining proper organ microcirculation. In addition, PGI 2 inhibits the endotoxin (ET)-induced monocytic production of tumor necrosis factor-␣ (TNF-␣). 9 TNF-␣ plays a role in the propagation of inflammation by activating neutrophils 10 and by inducing nitric oxide synthase (NOS). 11 Excessive production of NO by the inducible form of NOS (iNOS) plays critical roles in the pathophysiology of septic shock. 12 Septic shock, associated with infection with Gram-negative and Gram-positive bacteria and with fungus, is characterized by hypotension, organ dysfunction, and disseminated intravascular c...

Antithrombin reduces ischemia/reperfusion-induced renal injury in rats by inhibiting leukocyte activation through promotion of prostacyclin production

“…Consistent with this hypothesis, AT has been shown to inhibit pulmonary vascular injury and hypotension in rats challenged with lipopolysaccharide by inhibiting leukocyte activation through promotion of the endothelial release of PGI 2 . 11,12 In contrast to these reports, AT has been demonstrated to inhibit leukocyte activation directly. [13][14][15] These observations suggest that anti-inflammatory effects of AT may be mediated mainly by its direct inhibitory properties on leukocyte activation.…”

Tissue factor upregulation drives a thrombosis–inflammation circuit in relation to cardiovascular complications

“…239 The enhanced production and release of prostacyclin (PGI), an anti-inflammatory signal, diminishes LPS-induced TNF-and inducible NOS in preventing LPS-induced hypotension. 240 Apart from suppressing P-selectin expression to inhibit leukocyte rolling, 241 ATIII deactivates neutrophil chemotaxis towards IL-8. 242 In vivo, AT III exhibits a wide range of anti-inflammatory effects on human sepsis.…”

Thrombin Induces Nitric-oxide Synthase via Gα12/13-coupled Protein Kinase C-dependent I-κBα Phosphorylation and JNK-mediated I-κBα Degradation

“…The persistent NO production in septic patients may result from other unknown mediator(s) that are generated by LPS. The endogenous coagulation inhibitors reverse the vascular hyporeactivity induced by LPS (16,18). Protein C and ATIII have been studied extensively as the protective modulators of septic shock (47,48).…”

“…ATIII inhibits nuclear factor-B (NF-B) activation in monocytes and endothelial cells (17). In addition, it has been shown that ATIII prevents LPS-induced hypotension by inhibiting NOS induction in animals (18).…”