Thrombin activatable fibrinolysis inhibitor: Not just an inhibitor of fibrinolysis

OBJECTIVE

To review the activation of thrombin activatable fibrinolysis inhibitor (TAFI) and activity of activated TAFI (TAFIa) as it relates to the regulation of both fibrinolytic and proinflammatory substances.

DATA SOURCE

Published articles and reviews (from PubMed, published between 1962 and 2003) on experimental studies of coagulation, fibrinolysis, and inflammation.

DATA SYNTHESIS AND CONCLUSIONS

The principal physiologic role of TAFI is still a matter of debate. Although TAFI activation can result from proteolysis by a number of proteases, the most likely physiologic activators are thrombin (in complex with the cofactor thrombomodulin) and plasmin (in complex with polysaccharide cofactors). The activated enzyme, TAFIa, displays carboxypeptidase B-like activity and probably regulates both fibrinolysis and inflammation in response to injury and infection. At present, there is limited understanding of the role that TAFI plays in the interrelationships between coagulation, fibrinolysis, and inflammation. Although the potential therapeutic value of TAFIa inhibition/TAFI activation awaits further investigation, the data gathered to date suggest that, like activated protein C, TAFIa may play a pivotal role in regulating the crosstalk between coagulation, fibrinolysis, and inflammation.

Trypanosoma cruzi induces edematogenic responses in mice and invades cardiomyocytes and endothelial cells in vitro by activating distinct kinin receptor (B1/B2) subtypes

Trypanosoma cruzi, the protozoan that causes Chagas' heart disease, invades endothelial cells in vitro by activating the B2 kinin receptor (B2R). Here, we demonstrate that mice infected with trypomastigotes develop potent edema after treatment with the angiotensin-converting enzyme (ACE) (or kininase II) inhibitor captopril. Experiments performed with specific kinin receptor (B2R/B1R) antagonists and knockout mice revealed that the early-phase (3-h) edema is mediated by the constitutive B2R, whereas the late-phase (24-h) response depends on stimulation of the up-regulated B1R. Given previous evidence that parasite invasion of cells expressing B2R is potentiated by captopril, we investigated the prerequisites for in vitro infection of Chinese hamster ovary cells overexpressing either B1R or B2R, human umbilical vein endothelial cells activated by lipopolysaccharide, and neonatal rat cardiomyocytes. Our results indicate that captopril potentiates parasite invasion regardless of the kinin (B2/B1) activation pathways, whereas DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid (MGTA), an inhibitor of kininase I (carboxypeptidase M/N), selectively decreases parasite infectivity for B1R-expressing cells. These data suggest that formation of the B1R agonist, i.e., [des-Arg] kinins, critically depends on the processing action of kininase I, here proposed as a potential pathogenesis cofactor. Collectively, our data suggest that fluctuations in the levels of kininases may modulate parasite infectivity and pathological outcome in Chagas' disease.

Serum metabolism of bradykinin and des-Arg9-bradykinin in patients with angiotensin-converting enzyme inhibitor-associated angioedema

Angioedema (AE) associated with angiotensin-converting enzyme inhibitors (ACEi) is a rare, but potentially life-threatening adverse reaction. Several studies have suggested that bradykinin (BK) is responsible for ACEi-induced AE, but the mechanism remains unclear. We investigated the metabolism of BK and des-Arg9-BK in the serum of 20 patients with a history of ACEi-associated AE and 21 control (C) subjects. Synthetic BK was incubated with the sera for various periods of time and residual BK and generated des-Arg9-BK were quantified by specific and sensitive enzyme immunoassays. No significant difference of half-life (t1/2) of both BK and des-Arg9-BK could be measured between C subjects and patients with AE (AE) in absence of ACEi. However, an analysis according to the prolonged (+) or not (-) t1/2 of des-Arg9-BK allowed a new stratification of C subjects and AE patients in four subgroups. The preincubation of sera with enalaprilat at a concentration inhibiting ACE significantly prevented the rapid degradation of BK and des-Arg9-BK in these four subgroups. In presence of ACEi, a subgroup (50%) of AE patients (AE + ) had a particularly significant rise of the t1/2 of des-Arg9-BK. Once ACE was inhibited, the concentration or the nature of the ACEi had no significant effect on the t1/2 of des-Arg9-BK. However, a test dilution of AE + sera with a control (C) serum showed that an enzyme defect rather than a circulating inhibitor could be responsible for the abnormal metabolism of des-Arg9-BK when ACE is inhibited. In conclusion, half of the patients with ACEi-associated AE present in serum had an enzyme defect involved in the des-Arg9-BK metabolism leading to its accumulation. The B1 agonist could be responsible, at least in part, for the local inflammatory reaction associated with the AE.

[Basic (cleaving arginine and lysine residues) metallocarboxypeptidase of mammalian tissue: structure, properties and function]

The structure, physical, chemical and catalitical properties, functions and biological role of mammalian basic carboxypeptidases are observing. On the strength of the genetic and filogenic research data it is supposed the existence of a family of basic metal-dependent carboxypeptidases and the plan of it evolution is proposed. The connections between structure, localisation and function of this enzyme are discussed.

[Effect of bradykinin on airway epithelial ion transport and its modulation by endogenous peptidases]

To elucidate the effect of bradykinin (BK) on airway epithelial ion transport function and its modulation by endogenous peptidases, we studied the electrical properties of canine cultured tracheal epithelium under short-circuited conditions in vitro. Addition of BK to the mucosal side of Ussing chamber increased short-circuit current (SCC) in a dose-dependent manner, the maximal rise from the baseline value (delta SCC max) and the concentration required to produce a half-maximal effect being 7.1 +/- 0.7 microA/cm2 (p < 0.001) and 3.9 +/- 1.0 x 10(-7) M, respectively. This effect was greatly attenuated by the B2-receptor antagonist (D-Arg, Hyp3, Thi5,8, d-Phe7)-BK but not by the B1-receptor antagonist (Des-Arg9, Leu8)-BK. Blockade of angiotensin converting enzyme and aminopeptidase P by captopril and mercaptoethanol did not alter the BK-induced increase in SCC. On the other hand, phosphoramidon and MERGAPTA, inhibitors of neutral endopeptidase and carboxypeptidase N, respectively, strengthened the effect of BK. These results suggest that BK stimulates airway epithelial electrical properties through the activation of B2-receptor subtype, and that endogenous peptidases including neutral nedopeptidase and carboxypeptidase N may play a modulatory role in this action of BK.

Depressor action of bradykinin agonists relative to metabolism by angiotensin-converting enzyme, carboxypeptidase N, and aminopeptidase P

Bradykinin (BK) receptor agonists and antagonists contain modifications that confer resistance to specific peptidases. In control studies, rat plasma degraded BK (10.3 +/- 0.3 nmol/min/ml) via angiotensin-converting enzyme (ACE; EC 3.4.15.1; 5.2 +/- 0.3 nmol/min/ml), carboxypeptidase N (CPN; EC 3.4.17.3; 3.2 +/- 0.4 nmol/min/ml), aminopeptidase P (APP; EC 3.4.11.9; 0.6 +/- 0.2 nmol/min/ml), and other (unidentified) activity (2.1 +/- 0.6 nmol/min/ml). In contrast, BK agonist analogs were hydrolyzed more slowly due to selective resistance to these plasma peptidases. In addition to Lys-Lys-BK (B1087), which is partially resistant to ACE, [Hyp3,Phe8-r-Arg9]BK (B7642) was completely resistant to ACE, CPN, and the unidentified plasma activity (1.9 +/- 0.3 nmol/min/ml), and D-Arg0[Hyp3,Phe8-r-Arg9]BK (B7644) was resistant to all plasma hydrolysis, including APP (less than 0.2 nmol/min/ml). In vivo ACE-resistant B1087 exhibited a depressor potency and duration of action greater than BK and equivalent to that of BK in the presence of the ACE inhibitor enalapril. Although the B7642 and B7644 agonists were also more potent and longer acting than BK, the increases were no more than that seen for B1087, despite their additional resistance to CPN (B7642) and CPN and APP (B7644). The duration of action of these analogs was, however, increased after renal ligation. These data demonstrate the importance of ACE to the metabolism of circulating BK and BK analogs. In contrast, resistance to CPN and APP are not associated with further potentiation. Beyond ACE resistance, it is likely that the development of more potent, longer-acting BK agonists and antagonists will relate to other factors, such as renal processing independent of CPN and APP.

[Protaminase activity of plasma. III. Role of conversion enzyme (kininase II) in protaminase activity of plasma]

Kininase I (carboxypeptidase N) and kininase II (angiotensin converting enzyme) were isolated from human plasma by gel filtration on Sephadex G 200, then separated and partially purified by ion exchange chromatography. These two partially purified enzymic preparations allowed us to demonstrate that protamine underwent an extensive degradation only when both kininases acted simultaneously. The effects of CoCl2, an activator, and of several inhibitors, amongst which captopril, suggest that the same enzymatic system is responsible for the in vitro protaminasic activity of diluted unfractionated plasma.

Role of renal endopeptidase 24.11 in kinin metabolism in vitro and in vivo

The relative contributions of three kininases to total urinary kininase activity were determined by measuring the hydrolysis of kinins in the presence and absence of inhibitors of kininase I (2-mercaptomethyl-3-guanidinoethylthiopropanoic acid; MGTA), kininase II (captopril) and neutral endopeptidase 24.11 (NEP or enkephalinase A; phosphoramidon). Surprisingly, NEP was responsible for 68 +/- 2% (N = 18) of the total kininase in the rat while kininase I and II contributed only 9 +/- 0.4% and 23 +/- 1%, respectively. To study the effects of NEP inhibition on renal function, phosphoramidon (110 or 330 micrograms/hr/kg; N = 6) or saline (0.1 microliter/min; N = 6) was infused into rats. Urinary kinins, kininases, renal blood flow (RBF), glomerular filtration rate (GFR), UNaV, UKV and UV were measured during control, experimental and recovery periods. Phosphoramidon at the higher dose decreased total urinary kininase activity from 284 +/- 49 to 58 +/- 5 ng/min/kg (77%, P less than 0.01), and increased kinin excretion from 74 +/- 9 to 128 +/- 21 pg/min/kg (73%, P less than 0.02), UV from 72 +/- 10 to 82 +/- 10 microliters/min/kg (15%, P less than 0.01) and UNaV from 12 +/- 2 to 17 +/- 3 microEq/min/kg (37%, P less than 0.02), while BP, RBF, GFR and UKV did not change. 125I-Tyr0-bradykinin infused into the aorta did not appear in the urine intact during simultaneous phosphoramidon and captopril administration. This is the first demonstration of NEP having a major role in the catabolism of kinins. The increase in UNaV and UV after phosphoramidon administration may be due to the inhibition of intrarenal kinin destruction.

[Relationship between the kininase- and angiotensin- converting activity under normal conditions and in experimental myocardial infarct]

In rat experiments the depressor and pressor responses to kinins and angiotensins recorded in the carotid artery were compared as to the different methods of their administration. With intravenous injection, the responses to bradykinin and kallidin were lower, and to angiotensin I--higher, than with their intra-aortic administration. The responses to angiotensin II remain identical under these conditions. The administration of all the preparations against the background of 2,3-dimercaptopropanol (unithiol) resulted in levelling of the responses irrespective of the mode of administration. In experimental myocardial infarction induced in rats by ligation of the coronary artery a reduction of the kinin-destructing and an increase of the angiotensin-converting activity was noted in the early postinfarction period. The response of the peripheral vessels to angiotensin, bradykinin and noradrenaline is decreased, while that to isoproterenol remain unchanged. The obtained results support the concept of the existence of the kininase and angiotensin-converting activity connected with a common biochemical factor of pulmonary circulation. Changes in the proportion of these functions under normal conditions and in cases of pathological states are interpreted as a particular regulation mechanism of the vascular tone and arterial pressure.