Elastase from activated human neutrophils activates procarboxypeptidase R

Fibrinolytic Alterations in Sepsis: Biomarkers and Future Treatment Targets

Sepsis is a life-threatening condition which develops as a dysregulated immune response in the face of infection and which is associated with profound hemostatic disturbances and in the most extreme cases disseminated intravascular coagulation (DIC). In addition, the fibrinolytic system is subject to alterations during infection and sepsis, and impaired fibrinolysis is currently considered a key player in sepsis-related microthrombus formation and DIC. However, we still lack reliable biomarkers to assess fibrinolysis in the clinical setting. Furthermore, drugs targeting the fibrinolytic system have potential value in sepsis patients with severe fibrinolytic disturbances, but these are still being tested in the preclinical stage. The present review provides an overview of key fibrinolytic changes in sepsis, reviews the current literature on potential laboratory markers of altered fibrinolysis in adult sepsis patients, and discusses future perspectives for diagnosis and treatment of fibrinolytic disturbances in sepsis patients.

Structure-function relationships in thrombin-activatable fibrinolysis inhibitor

Thrombin-activatable fibrinolysis inhibitor (TAFI) is an important regulator in the balance of coagulation and fibrinolysis. TAFI is a metallocarboxypeptidase that circulates in plasma as zymogen. Activated TAFI (TAFIa) cleaves C-terminal lysine or arginine residues from peptide substrates. The removal of C-terminal lysine residues from partially degraded fibrin leads to reduced plasmin formation and thus attenuation of fibrinolysis. TAFI also plays a role in inflammatory processes via the removal of C-terminal arginine or lysine residues from bradykinin, thrombin-cleaved osteopontin, C3a, C5a and chemerin. TAFI has been studied extensively over the past three decades and recent publications provide a wealth of information, including crystal structures, mutants and structural data obtained with antibodies and peptides. In this review, we combined and compared available data on structure/function relationships of TAFI.

Fibrinolytic and coagulative activities of Yersinia pestis

The outer membrane protease Pla belongs to the omptin protease family spread by horizontal gene transfer into Gram-negative bacteria that infect animals or plants. Pla has adapted to support the life style of the plague bacterium Yersinia pestis. Pla has a β-barrel fold with 10 membrane-spanning β strands and five surface loops, and the barrel surface contains bound lipopolysaccharide (LPS) that is critical for the conformation and the activity of Pla. The biological activity of Pla is influenced by the structure of the surface loops around the active site groove and by temperature-induced LPS modifications. Several of the putative virulence-related functions documented for Pla in vitro address control of the human hemostatic system, i.e., coagulation and fibrinolysis. Pla activates human plasminogen to the serine protease plasmin and activates the physiological plasminogen activator urokinase. Pla also inactivates the protease inhibitors alpha-2-antiplasmin and plasminogen activator inhibitor 1 (PAI-1) and prevents the activation of thrombin-activatable fibrinolysis inhibitor (TAFI). These functions enhance uncontrolled fibrinolysis which is thought to improve Y. pestis dissemination and survival in the mammalian host, and lowered fibrin(ogen) deposition has indeed been observed in mice infected with Pla-positive Y. pestis. However, Pla also inactivates an anticoagulant, the tissue factor (TF) pathway inhibitor, which should increase fibrin formation and clotting. Thus, Pla and Y. pestis have complex interactions with the hemostatic system. Y. pestis modifies its LPS upon transfer to the mammalian host and we hypothesize that the contrasting biological activities of Pla in coagulation and fibrinolysis are influenced by LPS changes during infection.

Activated thrombin activatable fibrinolysis inhibitor (TAFIa) is associated with inflammatory markers in inflammatory bowel diseases TAFIa level in patients with IBD

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI) has been reported to be involved in the pathogenesis and progression of inflammatory bowel disease (IBD). Activated TAFI (TAFIa) attenuates fibrinolysis by cleaving C-terminal lysine residues thus down-regulating plasminogen activation. To date, no reports on TAFIa in IBD have been published.

METHODS

Plasma levels of TAFIa were measured using a functional assay in 55 consecutive patients with ulcerative colitis (UC) and 50 with Crohn's disease (CD). Associations of TAFIa with disease activity, hemostatic variables and inflammatory markers were assessed.

RESULTS

Plasma TAFIa was higher in CD patients than in those with UC. The disease activity correlated positively with TAFIa levels in the UC group, but not in the CD group. In UC patients, there were positive correlations of TAFIa with white blood cells, C-reactive protein and fibrinogen and an inverse correlation with albumin. In the CD group, a positive correlation was shown for C-reactive protein, fibrinogen and platelet count, while a negative correlation was noted for albumin.

CONCLUSIONS

This study is the first to show that TAFIa is increased in CD patients compared with UC and its levels are associated with inflammatory markers in both forms of IBD. These findings fit in the hypothesis that TAFIa may be a marker of active IBD, and in particular of active UC.

Evaluation of the profibrinolytic properties of an anti-TAFI monoclonal antibody in a mouse thromboembolism model

The enhancement of fibrinolysis constitutes a promising approach to treat thrombotic diseases. Activated thrombin activatable fibrinolysis inhibitor (TAFIa) attenuates fibrinolysis and is an attractive target to develop profibrinolytic drugs. TAFI can be activated by thrombin, thrombin/thrombomodulin, or plasmin, but the in vivo physiologic TAFI activator(s) are unknown. Here, we generated and characterized MA-TCK26D6, a monoclonal antibody raised against human TAFI, and examined its profibrinolytic properties in vitro and in vivo. In vitro, MA-TCK26D6 showed a strong profibrinolytic effect caused by inhibition of the plasmin-mediated TAFI activation. In vivo, MA-TCK26D6 significantly decreased fibrin deposition in the lungs of thromboembolism-induced mice. Moreover, in the presence of MA-TCK26D6, plasmin-α(2)-antiplasmin complexes in plasma of thromboembolism-induced mice were significantly increased compared with a control antibody, indicative of an acceleration of fibrinolysis through MA-TCK26D6. In this study, we show that plasmin is an important TAFI activator that hampers in vitro clot lysis. Furthermore, this is the first report on an anti-TAFI monoclonal antibody that demonstrates a strong profibrinolytic effect in a mouse thromboembolism model.

Thrombin-activatable fibrinolysis inhibitor is degraded by Salmonella enterica and Yersinia pestis

BACKGROUND

 Pathogenic bacteria modulate the host coagulation system to evade immune responses or to facilitate dissemination through extravascular tissues. In particular, the important bacterial pathogens Salmonella enterica and Yersinia pestis intervene with the plasminogen/fibrinolytic system. Thrombin-activatable fibrinolysis inhibitor (TAFI) has anti-fibrinolytic properties as the active enzyme (TAFIa) removes C-terminal lysine residues from fibrin, thereby attenuating accelerated plasmin formation.

RESULTS

 Here, we demonstrate inactivation and cleavage of TAFI by homologous surface proteases, the omptins Pla of Y. pestis and PgtE of S. enterica. We show that omptin-expressing bacteria decrease TAFI activatability by thrombin-thrombomodulin and that the anti-fibrinolytic potential of TAFIa was reduced by recombinant Escherichia coli expressing Pla or PgtE. The functional impairment resulted from C-terminal cleavage of TAFI by the omptins.

CONCLUSIONS

 Our results indicate that TAFI is degraded directly by the omptins PgtE of S. enterica and Pla of Y. pestis. This may contribute to the ability of PgtE and Pla to damage tissue barriers, such as fibrin, and thereby to enhance spread of S. enterica and Y. pestis during infection.

Targeted disruption of the gene encoding the murine small subunit of carboxypeptidase N (CPN1) causes susceptibility to C5a anaphylatoxin-mediated shock

Carboxypeptidase N (CPN) is a plasma zinc metalloprotease, which consists of two enzymatically active small subunits (CPN1) and two large subunits (CPN2) that protect the protein from degradation. Historically, CPN has been implicated as a major regulator of inflammation by its enzymatic cleavage of functionally important arginine and lysine amino acids from potent phlogistic molecules, such as the complement anaphylatoxins C3a and C5a. Because of no known complete CPN deficiencies, the biological impact of CPN in vivo has been difficult to evaluate. Here, we report the generation of a mouse with complete CPN deficiency by targeted disruption of the CPN1 gene. CPN1(-/-) mice were hypersensitive to lethal anaphylactic shock due to acute complement activation by cobra venom factor. This hypersensitivity was completely resolved in CPN1(-/-)/C5aR(-/-) but not in CPN1(-/-)/C3aR(-/-) mice. Moreover, CPN1(-/-) mice given C5a i.v., but not C3a, experienced 100% mortality. This C5a-induced mortality was reduced to 20% when CPN1(-/-) mice were treated with an antihistamine before C5a challenge. These studies describe for the first time a complete deficiency of CPN and demonstrate 1) that CPN plays a requisite role in regulating the lethal effects of anaphylatoxin-mediated shock, 2) that these lethal effects are mediated predominantly by C5a-induced histamine release, and 3) that C3a does not contribute significantly to shock following acute complement activation.

Thrombin-activatable Fibrinolysis Inhibitor Binds to Streptococcus pyogenes by Interacting with Collagen-like Proteins A and B

Regulation of proteolysis is a critical element of the host immune system and plays an important role in the induction of pro- and anti-inflammatory reactions in response to infection. Some bacterial species take advantage of these processes and recruit host proteinases to their surface in order to counteract the host attack. Here we show that Thrombin-activatable Fibrinolysis Inhibitor (TAFI), a zinc-dependent procarboxypeptidase, binds to the surface of group A streptococci of an M41 serotype. The interaction is mediated by the streptococcal collagen-like surface proteins A and B (SclA and SclB), and the streptococcal-associated TAFI is then processed at the bacterial surface via plasmin and thrombin-thrombomodulin. These findings suggest an important role for TAFI in the modulation of host responses by streptococci.

Thrombin-thrombomodulin connects coagulation and fibrinolysis: more than an in vitro phenomenon

Thrombin activatable fibrinolysis inhibitor (TAFI), when activated, forms a basic carboxypeptidase that can inhibit fibrinolysis. Potential physiologic activators include both thrombin and plasmin. In vitro, thrombomodulin and glycosaminoglycans increase the catalytic efficiency of TAFI activation by thrombin and plasmin, respectively. The most relevant (patho-) physiologic activator of TAFI has not been disclosed. Our purpose was to identify the physiologic activator of TAFI in vivo. Activation of protein C (a thrombin-thrombomodulin-dependent reaction), prothrombin, and plasminogen occurs during sepsis. Thus, a baboon model of Escherichia coli-induced sepsis, where multiple potential activators of TAFI are elaborated, was used to study TAFI activation. A monoclonal antibody (mAbTAFI/TM#16) specifically inhibiting thrombin-thrombomodulin-dependent activation of TAFI was used to assess the contribution of thrombin-thrombomodulin in TAFI activation in vivo. Coinfusion of mAbTAFI/TM#16 with a lethal dose of E coli prevented the complete consumption of TAFI observed without mAbTAFI/TM#16. The rate of fibrin degradation products formation is enhanced in septic baboons treated with the mAbTAFI/TM#16; therefore, TAFI activation appears to play a key role in the extent of fibrin(ogen) consumption during E coli challenge, and thrombin-thrombomodulin, in a baboon model of E coli-induced sepsis, appears to be the predominant activator of TAFI.

EF6265, a novel plasma carboxypeptidase B inhibitor, protects against renal dysfunction in rat thrombotic glomerulonephritis through enhancing fibrinolysis

BACKGROUND/AIM

Plasma carboxypeptidase B is a physiological fibrinolysis inhibitor. In the present study, the effects of EF6265, a novel specific plasma carboxypeptidase B inhibitor, on renal dysfunction in a rat thrombotic glomerulonephritis model were examined.

METHODS

The model was induced by injection of anti-glomerular basement membrane serum and lipopolysaccharide to rats. Renal microthrombosis was histologically evaluated by phosphotungstic acid-hematoxylin staining for fibrin thrombi. Renal dysfunction was evaluated on the basis of plasma levels of blood urea nitrogen as well as renal edemas and urine volume.

RESULTS

The glomerular microthrombi observed in a positive control group were significantly reduced after a short-term treatment (4 h) with EF6265 at a dose which enhanced fibrinolysis. The elevation of blood urea nitrogen and renal edema formation decreased, and the reduction of the urine volume improved after a long-term treatment (21 h) with EF6265. In addition, EF6265 had a protective activity against multiple organ dysfunction, because it reduced plasma lactate dehydrogenase and alanine aminotransferase levels and mortality in this model.

CONCLUSION

EF6265, which inhibits plasma carboxypeptidase B, showed a protective effect on thrombotic renal dysfunction in thrombotic glomerulonephritis through enhancing the fibrinolysis.

Complete inhibition of fibrinolysis by sustained carboxypeptidase B activity: the role and requirement of plasmin inhibitors

BACKGROUND

The antifibrinolytic effect of activated thrombin-activatable fibrinolysis inhibitor (TAFIa) and carboxypeptidase B (CPB) displays threshold behavior. When CPB was used to simulate conditions mimicking continuous TAFIa activity, it affected the lysis of plasma clots differently to clots formed from a minimal fibrinolytic system comprising fibrinogen, plasminogen and alpha(2)-antiplasmin. Whereas CPB saturably prolonged clot lysis in the purified system, the effect of CPB did not appear saturable in plasma clots.

METHODS

To rationalize this difference, we investigated the effects of alpha(2)-antiplasmin, alpha(2)-macroglobulin, antithrombin and aprotinin on CPB-mediated antifibrinolysis.

RESULTS

CPB alone prolonged fibrinolysis in a saturable manner and the efficacy of CPB increased with decreasing tissue-type plasminogen activator (t-PA) concentration. The inhibitors by themselves did not halt fibrinolysis and the potency of each inhibitor in the absence of CPB mirrored their solution-phase plasmin inhibitory potentials: alpha(2)-antiplasmin approximately equal to aprotinin >> alpha(2)-macroglobulin >> antithrombin. With both CPB and inhibitor present, a synergistic effect was observed. The antifibrinolytic sensitivity to CPB was related to the plasmin inhibitory potential of the inhibitor.

CONCLUSIONS

Fibrinolysis could be completely inhibited by alpha(2)-antiplasmin, alpha(2)-macroglobulin and antithrombin, but not aprotinin, in the presence of CPB, and occurred only when the irreversible inhibitor or pool of inhibitors were in excess of plasminogen. Western blot analysis indicated that the CPB-mediated shutdown of fibrinolysis was a result of plasminogen consumption prior to clot lysis. The CPB concentration required for fibrinolytic shutdown was dependent on t-PA concentration and the inhibitory potential of the irreversible inhibitor pool.

Chemoattractants, extracellular proteases, and the integrated host defense response

The host response to tissue injury and/or infection is dependent on the action of numerous extracellular proteases. Proteolytic cascades trigger blood clotting, fibrinolysis, and complement activation, while proteases released upon leukocyte degranulation are integral to the processes of inflammation and immunity. Modulation of effector protein activity by proteases provides a critical layer of posttranslational control that enables rapid enzymatic regulation of target proteins. This report reviews the emerging literature describing a novel class of proteolytic targets, leukocyte chemoattractants, and, in particular, chemerin, a dendritic cell and macrophage chemoattractant activated by serine proteases of the coagulation, fibrinolytic, and inflammatory cascades. As chemoattractants are critical for both systemic leukocyte positioning by triggering integrin activation and subsequent recruitment from circulation, and local intratissue leukocyte positioning via chemotaxis, modulation of attractant activities by proteases may have profound effects on the immune response.

Absence of thrombin-activatable fibrinolysis inhibitor protects against sepsis-induced liver injury in mice

Thrombin-activatable fibrinolysis inhibitor (TAFI), also known as carboxypeptidase R, has been implicated as an important negative regulator of the fibrinolytic system. In addition, TAFI is able to inactivate inflammatory peptides such as complement factors C3a and C5a. To determine the role of TAFI in the hemostatic and innate immune response to abdominal sepsis, TAFI gene-deficient (TAFI-/-) and normal wild-type mice received an i.p. injection with Escherichia coli. Liver TAFI mRNA and TAFI protein concentrations increased during sepsis. In contrast to the presumptive role of TAFI as a natural inhibitor of fibrinolysis, TAFI-/- mice did not show any difference in E. coli-induced activation of coagulation or fibrinolysis, as measured by plasma levels of thrombin-anti-thrombin complexes and D-dimer and the extent of fibrin depositions in lung and liver tissues. However, TAFI-/- mice were protected from liver necrosis as indicated by histopathology and clinical chemistry. Furthermore, TAFI-/- mice displayed an altered immune response to sepsis, as indicated by an increased neutrophil recruitment to the peritoneal cavity and a transiently increased bacterial outgrowth together with higher plasma TNF-alpha and IL-6 levels. These data argue against an important part for TAFI in the regulation of the procoagulant-fibrinolytic balance in sepsis and reveals a thus far unknown role of TAFI in the occurrence of hepatic necrosis.

Chemerin activation by serine proteases of the coagulation, fibrinolytic, and inflammatory cascades

Proteases function at every level in host defense, from regulating vascular hemostasis and inflammation to mobilizing the "rapid responder" leukocytes of the immune system by regulating the activities of various chemoattractants. Recent studies implicate proteolysis in the activation of a ubiquitous plasma chemoattractant, chemerin, a ligand for the G-protein-coupled receptor CMKLR1 present on plasmacytoid dendritic cells and macrophages. To define the pathophysiologic triggers of chemerin activity, we evaluated the ability of serum- and inflammation-associated proteases to cleave chemerin and stimulate CMKLR1-mediated chemotaxis. We showed that serine proteases factor XIIa and plasmin of the coagulation and fibrinolytic cascades, elastase and cathepsin G released from activated neutrophil granules and mast cell tryptase are all potent activators of chemerin. Activation results from cleavage of the labile carboxyl terminus of the chemoattractant at any of several different sites. Activation of chemerin by the serine protease cascades that trigger rapid defenses in the body may direct CMKLR1-positive plasmacytoid dendritic cell and tissue macrophage recruitment to sterile sites of tissue damage, as well as trafficking to sites of infectious and allergic inflammation.

TAFI and PAI-1 levels in human sepsis

BACKGROUND

Plasminogen activator inhibitor type-1 (PAI-1) is considered to be the main inhibitor of fibrinolysis in sepsis. However, the contribution of TAFI to the inhibition of fibrinolysis in sepsis is currently unknown.

METHODS

TAFI antigen and PAI-1 levels were measured in severe sepsis (n = 32) and septic shock (n = 8) patients. In addition, TAFI antigen levels had been determined in 151 controls.

RESULTS

Septic patients had significantly (p < 0.0001) decreased TAFI levels (median: 78.9% [range: 32.4-172.6]) as compared to controls (108.1% [35.9-255.4]). TAFI levels were equal in septic shock and severe sepsis (68.9% [32.4-172.6] vs. 82.5% [32.7-144.9], p = 0.987) as well as in survivors and non-survivors (87.1% [32.7-172.6] vs. 65.8% [32.4-129.5], p = 0.166). PAI-1 levels were significantly (705.5 ng/ml [131-5788]) higher in septic shock as in severe sepsis patients (316.5 ng/ml [53-1311], p = 0.016) and were equal in survivors and non-survivors (342 ng/ml [53-1311] vs. 413 ng/ml [55-5788], p = 0.231). TAT/PAP ratio (R((TAT/PAP))) reflecting the dysbalance between coagulation and fibrinolysis was calculated. R((TAT/PAP)) significantly increased with fatality and was significantly dependent on PAI-1, but not on TAFI. PAI-1 levels (570.5 ng/ml [135-5788]) and R((TAT/PAP)) (1.6 [0.3-6.1]) were significantly (p = 0.008 and p = 0.047) higher in patients with overt DIC as compared to patients without overt DIC (310 ng/ml [53-1128] and 0.6 [0.1-4.3]), whereas no difference was found for TAFI levels (68.9% [32.7-133.2] vs. 86.4% [32.4-172.6], p = 0.325).

CONCLUSIONS

Although inhibition in sepsis is mediated by both, PAI-1 might be involved early in the sepsis process, whereas TAFI might be responsible for ongoing fibrinolysis inhibition in later stages of sepsis.

Hepatitis induced by an IgM monoclonal antibody against procarboxypeptidase R

Procarboxypeptidase R (proCPR), also known as thrombin-activatable fibrinolysis inhibitor (TAFI), is present in plasma and can be activated to carboxypeptidase R (CPR) by trypsin-like enzymes such as thrombin and plasmin. CPR has the carboxypeptidase B-like activity that can inactivate the inflammatory peptides such as C5a by removing the C-terminal arginine and can interfere with fibrinolysis by removing C-terminal lysine residue of fibrin. In the present study, we conducted to produce monoclonal antibodies (mAbs) by using spleen cells from proCPR-deficient mice immunized by partially purified mouse proCPR. The mAbs obtained were IgM isotype and reacted with proCPR and interfered with activation of proCPR to CPR by thrombin-thrombomodulin complex. Some BALB/c mice implanted with the hybridoma died in 7 days, and intravenous injection of the mAb to BALB/c mice induced transient elevation of GOT and GPT in plasma although injection to the deficient mice did not. Furthermore, the histological features showed the focally lesions in liver tissue of BALB/c mice injected with the mAb. Since liver is the major site of proCPR synthesis, IgM mAb to proCPR should have induced local inflammation at the side resulting in induction of hepatitis.

Absence of Procarboxypeptidase R Induces Complement-Mediated Lethal Inflammation in Lipopolysaccharide-Primed Mice

Carboxypeptidase R (CPR) is a heat-labile enzyme found in serum in addition to stable carboxypeptidase N. CPR cleaves the C-terminal basic amino acids, arginine and lysine, from inflammatory peptides such as complement C3a and C5a, bradykinin, and enkephalin. This enzyme is generated from procarboxypeptidase R (proCPR), also known as thrombin-activatable fibrinolysis inhibitor, following cleavage by proteolytic enzymes such as thrombin, plasmin, and trypsin. We generated proCPR-deficient mice by knocking out exons 4 and 5 of the proCPR gene, which are regarded as essential for CPR function. At LPS challenge, there was virtually no difference in lethality among proCPR(+/+), proCPR(+/-), and proCPR(-/-) mice. However, challenge with cobra venom factor, which can activate and deplete almost all complement in vivo, induced a lethal effect on proCPR(-/-) mice following LPS sensitization which up-regulates C5a receptor expression. In contrast, proCPR(+/+) and proCPR(+/-) mice were able to tolerate the cobra venom factor challenge with the limited dose (30 U). Although carboxypeptidase N plays a role in inactivation of inflammatory peptides in vivo, CPR may also be important in the regulation of hyperinflammation.

Prevalence of inherited myeloperoxidase deficiency in Japan

The microbicidal activity of the myeloperoxidase (MPO)-hydrogen peroxide-halide system has been implicated as the most efficient, oxygen-dependent antimicrobial component of neutrophil host defense. Unexpectedly, individuals with MPO deficiency suffer few clinical consequences. In order to understand better the clinical impact of MPO deficiency, we surveyed several clinical hematology laboratories in Japan to assess the prevalence of MPO deficiency in the general population. MPO activity was determined by flow cytometry using the Technicon H series of automated systems. We identified 26 cases of complete MPO deficiency, prevalence 1 in 57,135, and 129 cases of partial deficiency, prevalence 1 in 17,501. The distribution of complete and partial deficiencies differed among the laboratories studied.

Preferential detection of pro-carboxypeptidase R by enzyme-linked immunosorbent assay

We generated two monoclonal antibodies (mAbs), 2A16 and 10G1, against pro-carboxypeptidase R (proCPR), also known as thrombin activatable fibrinolysis inhibitor (TAFI). By use of these mAbs, we developed a sandwich enzyme-linked immunosorbent assay (ELISA) system to detect proCPR. Since the amount of the antigen detectable by the ELISA was essentially the same in fresh plasma and serum incubated at 37 C for 1 hr, we concluded that the ELISA system detected not only proCPR, but also inactivated CPR generated from proCPR. However, an appreciable amount of proCPR remained unactivated in serum. For extensive activation of proCPR in plasma, thrombin and thrombomodulin complexes (TTM) can be used together with CaCl2. Following extensive conversion of proCPR to CPR by T-TM and CaCl2, converting plasma to serum (T-TM serum), antigenicity became undetectable by ELISA. Further analysis revealed that 2A16 reacts only with proCPR although 10G1 reacts with proCPR, active CPR and inactivated CPR. Therefore, we concluded that the ELISA system preferentially detects proCPR and not CPR. Our sandwich ELISA system utilizing 2A16 and 10G1 provides a suitable method for detecting proCPR and can be used to determine levels of proCPR in plasma samples from patients.

Modulation of procarboxypeptidase R (ProCPR) activation by complementary peptides to thrombomodulin

We designed complementary peptides (C-peptides) using a novel computer program (MIMETIC), which generates a series of peptides designed to interact with a target peptide sequence. Carboxypeptidase R (CPR) is an unstable basic carboxypeptidase found in fresh serum in addition to carboxypeptidase N (CPN) which is stable. CPR is generated from its precursor form (proCPR) by trypsin-like enzymes, and its activation is mediated by thrombin generated in the coagulation cascade. The efficiency of activation is enhanced approximately 1,200-fold when thrombin (T) is bound to thrombomodulin (TM). We attempted to generate C-peptides which recognize the T-binding site within TM assuming that some of these might interfere with the generation of T and TM complexes (T-TM). Among three peptides designed, two inhibited the enhancement in activation of proCPR by T in the presence of TM. One of the peptides at 16 microM reduced the activation of proCPR to the level obtained by T alone.

Distribution of rat C5a anaphylatoxin receptor

The anaphylatoxin, complement 5a (C5a), plays a key role in mediating various inflammatory reactions following complement activation. Several investigators have reported that C5a receptor (C5aR) is expressed in non-myeloid cells under certain conditions or in different cell lines. In our study, the abundance of C5aR-positive myeloid cells in rats depended on the organs examined. C5aR was usually expressed at the site of exposure to pathogens, such as in salivary gland or lung, and was up-regulated in liver in the inflammatory state induced by lipopolysaccharide (LPS) administration. Furthermore, the increased expression of C5aR antigen was not accompanied by an increase in C5aR mRNA in Kupffer cells following LPS challenge.

Heat stability of carboxypeptidase R of experimental animals

Carboxypeptidase N (CPN) and carboxypeptidase R (CPR) are present in fresh serum, and cleave C-terminal arginine or lysine residues from bioactive peptides such as anaphylatoxins and kinins resulting in regulation of peptide activity. Although CPN is present in the active form in plasma, CPR is generated from proCPR by trypsin-like enzymes such as thrombin. CPR regulates not only inflammatory peptides but also restricts fibrinolysis. To elucidate the complex role of CPN and CPR in vivo, studies in animal models will be essential. CPR of guinea pig, rat and rabbit decayed at 37 C rapidly as in the case of human CPR. However, at 25 C, CPR of those species decayed to some extent, although human serum CPR did not decay within 60 min. In the presence of thrombin inhibitor, CPR in the sera of animals tested decayed more rapidly than CPR in serum without thrombin inhibitor suggesting that additional generation of CPR may have been prevented during decay evaluation. However, human serum CPR decayed more rapidly in the absence of thrombin inhibitor indicating that thrombin may accelerate the decay in human serum.