Generation in plasma of a fast-acting inhibitor of plasminogen activator in response to endotoxin stimulation.

Abstract

Endotoxin producing bacteria cause disseminated intravascular coagulation (DIC); however, the mechanism of endotoxin action in man is still unclear. Impairment of the fibrinolytic system has been suggested as a contributing mechanism.A single injection of Escherichia coli lipopojysaccharide in rabbits resulted in a marked and prolonged increase of the levels of a fast-acting inhibitor of plasminogen activator (PAinhibitor) in plasma (from 3.9±0.7 to 41±13.2 U/ml after 3 h). Gel filtration studies indicated that inhibition of human tissue-type plasminogen activator (t-PA) by rabbit plasma is accompanied by a change in the elution profile of the activator compatible with the formation of an enzyme-inhibitor complex with an apparent molecular weight of 100,000. Injection of human t-PA (1,500 IU/kg body wt) in endotoxin treated animals resulted in very fast inhibition of t-PA and formation of a similar complex.The half-life of circulating PA-inhibitor activity in rabbits was about 7 min as estimated by donor receiver plasma transfusion experiments.Stimulation of cultured human endothelial cells with endotoxin resulted in enhanced rate of accumulation of PAinhibitor activity in the culture medium (two-to sevenfold increase). In five patients with septicemia, markedly increased levels of PA-inhibitor (14.3±15.5 U/ml) as compared with control subjects (13±0.7 U/ml) were observed in plasma.A very strong correlation (r = 0.98) was found between inhibition of t-PA and of urokinase in all conditions, suggesting that this fast-acting inhibitor reacts with both plasminogen activators.These data suggest that the appearance of this fast-acting PA-inhibitor is very sensitive to endotoxin stimulation. The marked increase in the level of PA-inhibitor in blood may contribute to the pathogenesis of DIC in septicemia.

Purification and characterization of natural and recombinant human plasminogen activator inhibitor‐1 (PAI‐1)

“…PAI-1 is a very potent and specific inhibitor of tissuetype plasminogen activator (t-PA) and urokinase [2,3], which rapidly inactivates t-PA in vivo [47]. Its exact physiopathological role in the regulation of in vivo fibrinolysis remains to be elucidated further [17, 18,481. PAI-1 has been isolated from several sources including bovine aorta endothelial cells [20] and several human tumor cell lines and cDNA has been expressed in E. coli and transiently in mammalian cells [5].…”

Stimulating effect of oxidized low density lipoproteins on plasminogen activator inhibitor-1 synthesis by endothelial cells.

“…43 It has also been reported that ox-LDL facilitate the uptake of endotoxin by human endothelial cells. 42 The presence of endotoxin in our preparations is unlikely, since heating ox-LDL totally suppressed the increase of PAI-1 synthesis by HUVEC.…”

“…43 While the effect of endotoxin is temperature-resistant, heating 50 /ig/ml ox-LDL protein for 15 minutes at 100°C completely suppressed the ability to stimulate PAI-1 synthesis, suggesting that endotoxin is not involved ( Table 2). This assumption is supported by the fact that no endotoxin was found with the Kabi-LAL endotoxin test.…”

Plasminogen activator inhibitor 1: Mechanisms of its synergistic regulation by growth factors

“…Clearance of PA-inhibitory activity from the circulation is rapid with measured half lives of 3.5 to 7 min (Colucci, Paramo et al 1985). Like other serpins, PAI-1 inhibits cognate proteases by mimicking their substrates, which results in the formation of an ester bond between the carboxyl group of serpin P1 residue and the hydroxyl group of the protease serine residue to produce a stable covalently linked inhibitor/protease inactive complex (De Taeye, ).…”

“…A major source of PAI-1 is liver because it is an acute phase protein ). Clearance of PAinhibitory activity from circulation is also rapid with measured half lives of 3.5 to 7 min (Colucci, Paramo et al 1985). Even the PAI-1 that is not cleared from the circulation has a limited half life of about 1-2 h due to its spontaneous conversion to an inactive latent conformer in which some of the primary recognition residues are incorporated into its largest β sheet (Mottonen, Strand et al 1992).…”