van Hinsbergh V W, Kooistra T, van den Berg E A, Princen H M, Fiers W, Emeis J J
Gaubius Institute TNO, Leiden, The Netherlands.
Blood. 1988 Nov;72(5):1467-73.
The vascular endothelium plays an important role in fibrinolysis by producing tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI). The monokine tumor necrosis factor (human recombinant TNF) increased the production of PAI by cultured human endothelial cells from umbilical vein (twofold) and from foreskin microvessles (four to eight fold). This was demonstrated by titration of endothelial cell-conditioned medium with t-PA, by reverse fibrin autography, and by immunoprecipitation of [35S]PAI-1 by anti-PAI-1 IgG. TNF also induced a marked increase of PAI-1 messenger RNA (mRNA) in the cells. The stimulation of PAI activity by TNF was seen at 4 U/mL and reached a maximum at 500 U/mL. Human recombinant lymphotoxin and interleukin-1 (alpha and beta) also stimulated the production of PAI activity, while interleukin-6 was ineffective. Separate additions of TNF or interleukin-1 (IL-1) at optimal concentrations (500 U/mL and 5 U/mL, respectively) resulted in a comparable stimulation of PAI production by endothelial cells. The simultaneous addition of both mediators resulted in an additive effect. The effect of TNF could not be prevented by the addition of polymyxin B or by anti-IL-1 antibodies. Therefore, it is unlikely that TNF acts through the induction of IL-1 secretion by endothelial cells. Two hours after a bolus injection of 250,000 U/kg TNF into rats, a fivefold increase in circulating PAI levels was found. In the next ten hours, the levels returned to normal. Blood platelets do not significantly contribute to the increase in circulating PAI, because the number of platelets did not change after TNF injection and the amount of PAI in blood platelets is not sufficient for several hours during an increase in PAI activity. The acute phase reactants, fibrinogen and alpha 2-antiplasmin in rat plasma, were altered little if any two to 24 hours after injection of 250,000 U/kg TNF. In vitro, TNF did not change PAI production by human and rat hepatocytes in primary monolayer culture. Therefore, it is most likely that vascular endothelial cells contribute to the increased amount of circulating PAI induced by TNF in vivo. This increase in PAI activity might decrease fibrinolysis.
血管内皮通过产生组织型纤溶酶原激活物（t-PA）和纤溶酶原激活物抑制剂（PAI）在纤维蛋白溶解中起重要作用。单核因子肿瘤坏死因子（人重组TNF）可使培养的人脐静脉内皮细胞（增加两倍）和包皮微血管内皮细胞（增加四至八倍）的PAI产生增加。这通过用t-PA滴定内皮细胞条件培养基、反向纤维蛋白自显影以及用抗PAI-1 IgG免疫沉淀[35S]PAI-1来证实。TNF还可诱导细胞中PAI-1信使核糖核酸（mRNA）显著增加。TNF对PAI活性的刺激在4 U/mL时可见，在500 U/mL时达到最大值。人重组淋巴毒素和白细胞介素-1（α和β）也刺激PAI活性的产生，而白细胞介素-6则无效。分别以最佳浓度（分别为500 U/mL和5 U/mL）添加TNF或白细胞介素-1（IL-1）可导致内皮细胞对PAI产生的刺激相当。同时添加这两种介质会产生相加效应。添加多粘菌素B或抗IL-1抗体并不能阻止TNF的作用。因此，TNF不太可能通过诱导内皮细胞分泌IL-1来发挥作用。给大鼠静脉注射250,000 U/kg TNF推注剂量两小时后，循环中PAI水平增加了五倍。在接下来的十小时内，水平恢复正常。血小板对循环中PAI的增加贡献不大，因为TNF注射后血小板数量没有变化，且在PAI活性增加的数小时内血小板中的PAI量不足。注射250,000 U/kg TNF后两至24小时，大鼠血浆中的急性期反应物纤维蛋白原和α2-抗纤溶酶即使有变化也很小。在体外，TNF不会改变原代单层培养的人和大鼠肝细胞的PAI产生。因此，很可能是血管内皮细胞导致了TNF在体内诱导的循环中PAI量增加。PAI活性的这种增加可能会降低纤维蛋白溶解。
