Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fibrin deposition is a common accompaniment of renal allograft rejection, indicating disruption of the normal physiologic balance between procoagulant and anticoagulant pathways. In vitro, tumor necrosis factor (TNF) induces endothelial expression of the procoagulant, tissue factor, and downregulation of thrombomodulin, a key component of the thrombomodulin/protein C (PC)/protein S (PS) pathway, which normally maintains an anticoagulant state by inactivating thrombin, preventing further thrombin formation by degrading factors Va and VIIIa, and decreasing plasminogen activator inhibitor activity. Raised levels of TNF were recently demonstrated within the blood of patients during episodes of renal allograft injection, and may be an early and discriminatory marker of rejection. This led us to investigate prospectively whether monitoring of serum TNF levels was of value clinically, and was associated with effects on circulating PC and PS levels, or alterations in intragraft thrombomodulin expression. Plasma samples (n = 454) were collected three times/week from all patients (n = 25) undergoing renal transplantation during a 9-month consecutive period, and assayed by ELISA and functional assays for TNF, PC, and free PS (FPS). Portions of renal biopsies, taken to evaluate episodes of acute deterioration of renal function, were evaluated by immunoperoxidase labeling for the presence and distribution of TNF, thrombomodulin, PC, PS, thrombin, fibrin, and factors V and VIII. Comparison of 78 plasma samples collected during 26 episodes of biopsy-proven acute cellular rejection with samples collected during periods of stable renal function (n = 349) showed that TNF levels rose significantly (390 +/- 242 pg/ml, p less than 0.01) above background levels 3 days before rising serum creatinine concentrations, and peaked (2,426 +/- 978 pg/ml) on the day of clinical rejection. PC-antigen (Ag) concentrations also decreased 3 days before rejection (68 +/- 13%, p less than 0.05), and were maximally depressed (49% +/- 16%, p less than 0.001) on the day of rejection. FPS levels were normal until the day before rejection (63% +/- 8%, p less than 0.01) and, like PC, were maximally depressed (43 +/- 10%) at rejection. Plasma TNF levels were significantly and inversely correlated with PC-Ag (p less than 0.001) and FPS (p less than 0.005) levels during rejection, regardless of whether such rejection episodes were steroid responsive or required OKT3 monoclonal antibody therapy. TNF, PC, and FPS levels were normal during episodes of cyclosporine toxicity and viral infection.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Tumor necrosis factor production during human renal allograft rejection is associated with depression of plasma protein C and free protein S levels and decreased intragraft thrombomodulin expression. 130 55

Thrombomodulin (TM), the endothelial cell surface receptor for thrombin-mediated activation of protein C and of its anticoagulant system, is involved in maintaining vascular nonthrombogenicity, and depressed TM activity may induce intravascular fibrin formation. TM antigen was previously found by immunohistochemical methods in rabbit glomeruli. We therefore attempted to identify the corresponding TM activity in isolated detergent-solubilized rat and human glomeruli. Like purified lung TM, rat glomeruli extracts accelerated the hydrolysis by activated protein C of the chromogenic substrate S-2238 in the presence of 10 nM thrombin, as determined by spectrophotometry. One mg glomerular protein promoted the formation of 681 +/- 115 nmol activated protein C, the equivalent of the amount generated by 845 ng of purified rabbit TM. TM activity correlated with the protein content of the glomerular extracts (r = 0.94). These extracts prolonged rat plasma activated partial thromboplastin time. Incubation of glomeruli with tumor necrosis factor-alpha (TNF) or E. coli lipopolysaccharide depressed their TM-like activity in a dose and time dependent manner. Incubation with TNF suppressed their anticoagulant activity. In human glomeruli, TM activity was also found at a level which corresponded to their TM antigen content, and was determined by ELISA with mouse monoclonal antibody. These results indicate that measurement of glomerular TM activity might help to clarify the mechanisms of intraglomerular fibrin deposition in renal diseases.
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PMID:Quantification and modulation of thrombomodulin activity in isolated rat and human glomeruli. 131 19

Hepatic veno-occlusive disease (VOD) is the most common life threatening complication of preparative-regimen-related toxicity for bone marrow transplantation (BMT). The frequency of VOD varies greatly, from 1-2% in centers performing pediatric BMT for thalassemia to over 50% in some centers doing BMT for hematologic malignancy. The term liver toxicity syndrome is a clinicopathologic definition which encompasses the range of histopathology within the hepatic venules and surrounding sinusoids and hepatocytes. These histologic abnormalities are statistically associated with a clinical syndrome of jaundice, ascites, and painful hepatomegaly developing early post-transplant. Newer modalities which may aid accuracy are transvenous liver biopsy along with determination of the gradient between the wedged and free hepatic venous pressures, and measurement of blood coagulatory components, particularly protein C levels. Analyses of clinical risk factors for VOD are confounded by lack of a clear hierarchy of risk when comparing heterogeneous patient populations, the methods of patient selection and choice of controls, and whether analysis is univariate or multivariate. Prospective multivariate analyses indicate that the risk of developing liver toxicity is independently correlated with intensity of conditioning therapy, pre-transplant viral hepatitis, use of antimicrobial therapy with acyclovir, amphotericin, or vancomycin (reflecting fever), and mismatched or unrelated allogeneic marrow grafts. These analyses plus morphologic and biochemical data support the hypothesis that VOD is caused by cytoreductive injury to hepatocytes and endothelium in zone three of the liver acinus, and in turn strongly influenced by factors which induce the release of tumor necrosis factor-alpha (TNF-alpha) leading to enhancement or activation of coagulation with obstruction of hepatic sinusoids and venules. Pharmacokinetic measurements of busulfan as a conditioning agent demonstrate a correlation between high steady-state busulfan levels and liver toxicity and suggest that safer and/or more efficacious plasma busulfan concentrations can be obtained by making individual dose adjustments and by changing the schedule of administration. Conservative therapy of severe VOD, including the use of peritoneal-pleural shunts for relief of ascites, is unsatisfactory. Results from prophylactic studies aimed at preventing VOD by heparin or prostaglandin E1 indicate considerable differences with toxicity and efficacy. Use of the TNF-alpha blocker, pentoxifylline, has also shown promise in lessening VOD. A statistical model which predicts patients likely to have an unfavorable outcome from VOD has been used to select premorbid patients for promising new therapeutic modalities, such as recombinant tissue plasminogen activator.
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PMID:Hepatic veno-occlusive disease--liver toxicity syndrome after bone marrow transplantation. 142 75

The levels of prothrombin fragment F1 + 2 were measured by a double antibody radioimmunoassay in blood samples collected into different anticoagulant solutions. We evaluated healthy males between the ages of 42 and 77, asymptomatic patients with hereditary deficiencies of protein C or protein S, and persons receiving tumor necrosis factor infusions. The results in specimens collected in an anticoagulant containing ACD, EDTA, adenosine, and 25 U/ml of heparin (a) were highly correlated with those collected in an anticoagulant containing a synthetic thrombin inhibitor, EDTA, and aprotinin (b). However, in asymptomatic patients with congenital antithrombin III deficiency, we found that the plasma levels of F1 + 2 in blood collected in anticoagulant (a) were usually substantially higher than those collected in anticoagulant (b). We determined that this phenomenon was not attributable to the venipuncture procedure itself, but rather appears to be due to the action of low concentrations of heparin in the presence of reduced blood levels of antithrombin III. Our data show that the previously documented elevations in plasma F1 + 2 levels in patients with congenital antithrombin III deficiency appear to be caused by the above in vitro anticoagulant effect, and that this population does not exhibit evidence of a prethrombotic state as defined by the F1 + 2 assay.
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PMID:Influence of anticoagulants used for blood collection on plasma prothrombin fragment F1 + 2 measurements. 178 Aug 6

Activated protein C is a plasma anticoagulant. For activated protein C to function as an anticoagulant, it must form a complex with protein S. Protein S anticoagulant activity is neutralized by formation of a reversible complex with C4b binding protein (C4bBP). C4bBP is an acute-phase plasma protein. When C4bBP levels increase, mass action forces the level of free protein S to decrease, giving rise to an acquired functional protein S deficiency. It has been proposed that these elevated C4bBP levels and the resultant acquired deficiency of protein S that occurs in inflammation could contribute to a hypercoagulable state. An experimental model to test this hypothesis was suggested by our previous studies that demonstrated that inhibition of protein C activation rendered baboons hypercoagulable in response to sublethal Escherichia coli infusion (J Clin Invest 79:918, 1987). We have extended these studies to examine the effect of inhibition of protein S activity with C4bBP in the host (baboon) response to infusion of sublethal concentrations of E coli organisms. Five sets of animals were studied: (1) those challenged with sublethal concentrations of E coli alone (0.4 x 10(10)/kg); (2) those supplemented only with C4bBP (20 mg/kg); (3) those challenged with the same level of E coli but supplemented with C4bBP (20 mg/kg); (4) those challenged with sublethal E coli and supplemented with C4bBP (20 mg/kg) and sufficient protein S (2.3 mg/kg) to fill the protein S binding sites on C4bBP; and (5) those challenged with lethal concentrations of E coli. Sublethal E coli infusion (group 1 animals) caused only an acute-phase response with no consumption of fibrinogen, detectable organ damage, or detectable tumor necrosis factor (TNF) in the plasma. C4bBP infusion (group 2 animals) resulted in no significant physiologic changes, no detectable plasma TNF, and little change in fibrinogen level. The group 3 animals, receiving both sublethal E coli and C4bBP, exhibited rapid consumption of fibrinogen, systemic organ damage, and detectable circulating TNF ultimately leading to death. The overall response of this group was very similar to the response of the group 5 animals receiving an LD100 dose of E coli. The group 4 animals, which were treated exactly as above except that C4bBP was supplemented with a slight excess of protein S, responded essentially like those that received sublethal E coli alone. These studies suggest that the elevation of C4bBP during an inflammatory response can contribute to fibrinogen consumption and vascular damage. This vascular damage may be associated with enhanced elaboration of cytokines like TNF.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:C4b-binding protein exacerbates the host response to Escherichia coli. 182 67

Thrombomodulin (TM), a critical component of the protein C anticoagulant pathway, has previously been localized to endothelial cells (EC), but not smooth muscle cells (SMC) of the blood vessel wall. We demonstrate that cultured rat, bovine, as well as human SMC, but not blood vessel wall smooth muscle tissue, possess significant functional levels of TM and TM mRNA. Cyclic adenosine monophosphate stimulates TM expression in cultured SMC, but not EC, while tumor necrosis factor suppresses TM expression in EC but not cultured SMC. We postulate that following acute or chronic EC injury, luminal SMC can express TM, and are therefore able to protect the damaged blood vessel from thrombosis.
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PMID:Expression of thrombomodulin by smooth muscle cells in culture: different effects of tumor necrosis factor and cyclic adenosine monophosphate on thrombomodulin expression by endothelial cells and smooth muscle cells in culture. 184 62

The procoagulant properties of cultured vascular endothelial cells are enhanced in response to inflammatory cytokines such as tumor necrosis factor-alpha (TNF). A major component of this response is a reduction in expression of thrombomodulin, a cell surface cofactor for the activation of protein C. Regulation of thrombomodulin expression by TNF has been reported to occur through multiple mechanisms. To determine the relative roles of transcriptional and posttranscriptional regulation, the effect of TNF on the turnover of thrombomodulin protein and mRNA was examined in human and bovine endothelial cells. Quantitative nuclease S1 protection assays showed a 70% to 90% reduction in thrombomodulin mRNA within 4 hours of the addition of 1.0 nmol/L TNF to the culture medium. The decrease in thrombomodulin mRNA resulted from inhibition of transcription, followed by rapid degradation of thrombomodulin transcripts (t1/2 less than or equal to 3 hours). In pulse-chase incubations, thrombomodulin synthesis decreased parallel with mRNA, but the rate of degradation of radiolabeled thrombomodulin was not significantly altered by TNF. Human thrombomodulin was degraded with a t1/2 of 8.2 +/- 2.4 hours (SD) or 7.5 +/- 1.3 hours (SD) in the absence or presence of TNF, respectively. We conclude that TNF acts primarily to inhibit thrombomodulin transcription. The subsequent decrease in activity results from the inherent instability of thrombomodulin mRNA and protein in these cells, and not from the regulation of thrombomodulin degradation.
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PMID:Regulation of thrombomodulin by tumor necrosis factor-alpha: comparison of transcriptional and posttranscriptional mechanisms. 184 63

Experimental models of deep venous thrombosis, heretofore, have not been available for laboratory studies. This investigation establishes a novel model of venous thrombosis by inhibiting the protein C system combined with venous stasis and subtle venous injury. Ten adolescent baboons were studied in pairs, with one animal receiving saline solution (B2, B4, B6, B8, B10) and one being exposed to thrombogenic reagents (B1, B3, B5, B7, B9). These reagents represented a combination of a monoclonal antibody (HPC4) to protein C, 1 to 4 mg/kg administered over 5 minutes, and tumor necrosis factor administered over 3 minutes at a dose of 150 micrograms/kg through a catheter placed into the left superficial femoral vein with distal ligation. To encourage stasis, a pediatric size blood pressure cuff was inflated to 40 mm Hg on the right thigh for 50 minutes of every hour during the first experimental day (day 1) in B5 to B10. The animals were observed for a 6-hour period on day 1 and then for an 11- to 15-day period until sacrifice. Hemodynamic and hematologic parameters were recorded along with duplex imaging of the iliac veins and inferior vena cava on a daily basis. Venography was performed on day 1, day 4, and the day of sacrifice. At sacrifice the entire iliac and vena caval system was carefully dissected, opened, and photographed. Experimental animals given the HPC4 and tumor necrosis factor developed left iliac vein thrombosis extending into the inferior vena cava. Duplex imaging, venography, and autopsy revealed that control animals receiving saline solution never developed comparable thrombus. Experimental subjects exhibited thrombus on duplex imaging by day 4 (B1), day 3 (B3), day 2 (B5), 120 minutes (B7), and 360 minutes (B9) after receiving HPC4 and tumor necrosis factor. Venograms performed on day 1 exhibited thrombus in B5, B7, and B9. The extent of thrombus, the timing of its occurrence, and its effect on the animals' left leg followed a dose-dependent relationship for the animals in which the occlusive blood pressure cuff was used. Significantly greater declines in blood pressure, white blood cell count, and platelet count were found in affected animals given HPC4 and tumor necrosis factor reagents as compared to control subjects. All affected animals demonstrated the appearance of fibrin split products and a markedly prolonged prothrombin time. This investigation, for the first time, establishes a reproducible model of deep venous thrombosis involving inhibition of protein C that will facilitate further laboratory studies on venous thrombosis.
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PMID:Deep venous thrombosis in the baboon: an experimental model. 194 66

A 38-year-old patient with cerebral P. falciparum malaria was admitted 12 days after a short trip to Kenya. The serum level of tumor necrosis factor (TNF-alpha) was elevated (251 pg/ml). In contrast, Protein C (plasma activity 36.1%; antigen concentration 31.7%) and protein C inhibitor 1 (activity 0.55 U/ml) levels were decreased. This suggested a state of functional activation of the clotting system which was confirmed by elevated levels (4.8 ng/ml) of circulating thrombin-antithrombin-III-complexes (TAT). Protein S (total and free) and coagulation factor IX levels were within normal range. Under successful antiparasitic therapy, TNF-alpha as well as protein C and protein C inhibitor 1 levels returned to baseline within one week. In the context of other studies that demonstrate procoagulant effects of TNF-alpha, it is remarkable that in the case of complicated P. falciparum malaria, an elevated concentration of TNF-alpha can be paralleled by a decreased plasma level of protein C and an increase in TAT suggesting a procoagulant state.
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PMID:[Malaria tropica with activation of blood coagulation and detection of tumor necrosis factor (NF-alpha) in serum]. 215 19

Endothelial cells play an important role in the regulation of thrombosis. Normal resting (i.e. unstimulated) endothelial cells exhibit antithrombotic activity. This property is due to an active participation of endothelial cells in the inhibition of platelet adhesion and aggregation, in the inhibition of thrombin generation, in the direct inactivation of thrombin, and in clot lysis through the fibrinolytic system. When endothelial cells are stimulated by cytokines such as tumor necrosis factor (TNF) or interleukin 1 (IL-1), they may switch to an active procoagulant state. On the one hand, thrombin generation can be regulated on the endothelial cell surface by thrombomodulin, which allows the activation by thrombin of protein C which subsequently acquires and expresses potent anticoagulant properties. On the other hand, after activation, the same endothelial cell can express tissue factor on its surface, which will lead to the triggering of the coagulation cascade resulting in the generation of thrombin. TNF has been shown both to induce tissue factor gene expression and to suppress transcription of the thrombomodulin gene in endothelial cells. Many cytokines induce tissue factor gene expression and procoagulant activity in the monocyte/macrophage lineage; they also stimulate adhesion of leukocytes to endothelial cells. Cytokines such as IL-1 or TNF can thus be characterized as important intercellular messengers during the onset of coagulation. The role of these compounds can be schematized as: 1) agents of the stimulation of endothelial cells by leukocytes, 2) agents of stimulation of leukocytes by endothelial cells, 3) localization of the coagulation response through the initiation of endothelial cell-leukocyte interactions. Pharmacological modulation of these responses is possible along two pathways: 1) inhibition of the activation of endothelial cells or leukocytes responsible for cytokine release, 2) inhibition of the cytokine-induced cellular activation responsible for potentiation of procoagulant activity.
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PMID:Modulation by cytokines of leukocyte-endothelial cell interactions. Implications for thrombosis. 217 56


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