Effect of anticoagulants in colorimetric assay for basic carboxypeptidases

Procarboxypeptidase R deficiency causes increased lethality in concanavalin A-induced hepatitis in female mice

Carboxypeptidase R (CPR), also known as thrombin-activatable fibrinolysis inhibitor (TAFI), is an enzyme generated by proteolytic cleavage of its zymogen (proCPR). CPR removes the C-terminal arginine from inflammatory peptides such as C3a and C5a, bradykinin, enkephalin, and the thrombin-cleaved N-terminal fragment osteopontin (cleaved N-OPN). In the mouse model of concanavalin A (Con A)-induced immune-mediated fulminating hepatitis, cleaved N-OPN is one of the important peptides that induce the production of chemokines or cytokines. In the current study using proCPR deficient mice, we showed that injection of Con A into the mouse tail vein can induce a significantly higher lethality in proCPR-deficient female but not in male mice. Furthermore, a lack of CPR activity increased serum macrophage inflammatory protein-2 (MIP-2) and high-mobility group box 1 (HMGB1) levels after Con A injection. These in vivo findings suggest that CPR helps to protect against Con A-induced hepatitis.

Inactivation of the complement anaphylatoxin C5a by secreted products of parasitic nematodes

Given the importance of the complement anaphylatoxins in cellular recruitment during infection, the ability of secreted products from larval stages of Brugia malayi and Trichinella spiralis to influence C5a-mediated chemotaxis of human peripheral blood granulocytes in vitro was examined. Secreted products from B. malayi microfilariae almost completely abolished chemotaxis. This inhibition was blocked by phenylmethylsulphonyl fluoride, indicating the presence of a serine protease, which was subsequently shown to cleave C5a. In contrast, secreted products from T. spiralis infective larvae showed modest inhibition of C5a-mediated granulocyte chemotaxis, and this was blocked by potato carboxypeptidase inhibitor, an inhibitor of several metallocarboxypeptidases. Adult and larval stages of both parasites were demonstrated to secrete carboxypeptidases which cleaved hippuryl-L-lysine and hippuryl-L-arginine, and the T. spiralis enzyme was partially characterised. The data are discussed with reference to inflammation in parasitic nematode infection.

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.

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.

F(ab)'2-mediated neutralization of C3a and C5a anaphylatoxins: a novel effector function of immunoglobulins

High-dose intravenous immunoglobulin (IVIG) prevents immune damage by scavenging complement fragments C3b and C4b. We tested the hypothesis that exogenous immunoglobulin molecules also bind anaphylatoxins C3a and C5a, thereby neutralizing their pro-inflammatory effects. Single-cell calcium measurements in HMC-1 human mast cells showed that a rise in intracellular calcium caused by C3a and C5a was inhibited in a concentration-dependent manner by IVIG, F(ab)2-IVIG and irrelevant human monoclonal antibody. C3a- and C5a-induced thromboxane (TXB2) generation and histamine release from HMC-1 cells and whole-blood basophils were also suppressed by exogenous immunoglobulins. In a mouse model of asthma, immunoglobulin treatment reduced cellular migration to the lung. Lethal C5a-mediated circulatory collapse in pigs was prevented by pretreatment with F(ab)2-IVIG. Molecular modeling, surface plasmon resonance (SPR) and western blot analyses suggested a physical association between anaphylatoxins and the constant region of F(ab)2. This binding could interfere with the role of C3a and C5a in inflammation.

Elastase from activated human neutrophils activates procarboxypeptidase R

Carboxypeptidase R (EC 3.4.17.20; CPR) is an unstable basic carboxypeptidase found in fresh serum in addition to carboxypeptidase N (CPN) which is a stable enzyme. CPR in fresh serum is generated from its zymogen (proCPR) during coagulation by trypsin-like enzymes such as thrombin and thrombin/thrombomodulin complexes. Since removal of the C-terminal arginine abrogates the anaphylatoxin activity of C3a and C5a, CPR and CPN are regarded as anaphylatoxin inactivators. We report here that the culture supernatant of activated human neutrophils converts proCPR to CPR. Addition of an elastase specific inhibitor, N-methoxysuccinyl-Ala-Ala-Pro-Val-chloromethyl ketone (MSAAPVCK) to the supernatant of stimulated neutrophils completely inhibited activation of proCPR. On the other hand, a thrombin specific inhibitor, p-Nitrophenyl-p'-amidinophenyl-methanesulfonate hydrochloride (pNP-pAPMS) inhibited only 16% of proCPR activation by the neutrophil supernatant. Furthermore, purified elastase converted proCPR to CPR. Therefore, elastase can activate proCPR directly, or indirectly through activation of some proteases, which have been contaminating in reagents. Release of CPR generating enzymes from neutrophils should play an important role in regulation of excess inflammation.

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.