Kinetics of inhibition of platelet calpain II by human kininogens

Is there a role for bradykinin in cerebral malaria pathogenesis?

Malaria is a parasitic disease of global health significance and a leading cause of death in children living in endemic regions. Although various Plasmodium species are responsible for the disease, Plasmodium falciparum infection accounts for most severe cases of the disease in humans. The mechanisms of cerebral malaria pathogenesis have been studied extensively in humans and animal malaria models; however, it is far from being fully understood. Recent discoveries indicate a potential role of bradykinin and the kallikrein kinin system in the pathogenesis of cerebral malaria. The aim of this review is to highlight how bradykinin is formed in cerebral malaria and how it may impact cerebral blood-brain barrier function. Areas of interest in this context include Plasmodium parasite enzymes that directly generate bradykinin from plasma protein precursors, cytoadhesion of P. falciparum infected red blood cells to brain endothelial cells, and endothelial cell blood-brain barrier disruption.

Plasmin-mediated cleavage of high-molecular-weight kininogen contributes to acetaminophen-induced acute liver failure

Acetaminophen (APAP)-induced liver injury is associated with activation of coagulation and fibrinolysis. In mice, both tissue factor-dependent thrombin generation and plasmin activity have been shown to promote liver injury after APAP overdose. However, the contribution of the contact and intrinsic coagulation pathways has not been investigated in this model. Mice deficient in individual factors of the contact (factor XII [FXII] and prekallikrein) or intrinsic coagulation (FXI) pathway were administered a hepatotoxic dose of 400 mg/kg of APAP. Neither FXII, FXI, nor prekallikrein deficiency mitigated coagulation activation or hepatocellular injury. Interestingly, despite the lack of significant changes to APAP-induced coagulation activation, markers of liver injury and inflammation were significantly reduced in APAP-challenged high-molecular-weight kininogen-deficient (HK-/-) mice. Protective effects of HK deficiency were not reproduced by inhibition of bradykinin-mediated signaling, whereas reconstitution of circulating levels of HK in HK-/- mice restored hepatotoxicity. Fibrinolysis activation was observed in mice after APAP administration. Western blotting, enzyme-linked immunosorbent assay, and mass spectrometry analysis showed that plasmin efficiently cleaves HK into multiple fragments in buffer or plasma. Importantly, plasminogen deficiency attenuated APAP-induced liver injury and prevented HK cleavage in the injured liver. Finally, enhanced plasmin generation and HK cleavage, in the absence of contact pathway activation, were observed in plasma of patients with acute liver failure due to APAP overdose. In summary, extrinsic but not intrinsic pathway activation drives the thromboinflammatory pathology associated with APAP-induced liver injury in mice. Furthermore, plasmin-mediated cleavage of HK contributes to hepatotoxicity in APAP-challenged mice independently of thrombin generation or bradykinin signaling.

The contact activation and kallikrein/kinin systems: pathophysiologic and physiologic activities

The contact activation system (CAS) and kallikrein/kinin system (KKS) are older recognized biochemical pathways that include several proteins that skirt the fringes of the blood coagulation, fibrinolytic, complement and renin-angiotensin fields. These proteins initially were proposed as part of the hemostatic pathways because their deficiencies are associated with prolonged clinical assays. However, the absence of bleeding states with deficiencies of factor XII (FXII), prekallikrein (PK) and high-molecular-weight kininogen indicates that the CAS and KKS do not contribute to hemostasis. Since the discovery of the Hageman factor 60 years ago much has been learned about the biochemistry, cell biology and animal physiology of these proteins. The CAS is a pathophysiologic surface defense mechanism against foreign proteins, organisms and artificial materials. The KKS is an inflammatory response mechanism. Targeting their activation through FXIIa or plasma kallikrein inhibition when blood interacts with the artificial surfaces of modern interventional medicine or in acute attacks of hereditary angioedema restores vascular homeostasis. FXII/FXIIa and products that arise with PK deficiency also offer novel ways to reduce arterial and venous thrombosis without an effect on hemostasis. In summary, there is revived interest in the CAS and KKS due to better understanding of their activities. The new appreciation of these systems will lead to several new therapies for a variety of medical disorders.

Kininogens are antithrombotic proteins In vivo

Kininogens have recently been shown to possess antiadhesive, anticoagulant, and profibrinolytic properties and can inhibit platelet activation at low thrombin concentrations. To test whether kininogens have antithrombotic properties in vivo, we devised a model of limited arterial injury confined to removal of the endothelium. Brown-Norway Katholiek strain rats with an absence of low- and high-molecular-weight kininogen due to a single point mutation, A163T, were compared in the thrombosis model to the wild-type animals, which were otherwise genetically identical. Despite an equivalent vascular injury, the mean time (+/-SEM) for a 90% decrease in flow measured by laser Doppler was 38.4+/-17 minutes in the kininogen-deficient rats compared with 194+/-29 minutes in the wild-type animals (P<0.002). The degree of vascular injury was the same. No evidence for disseminated intravascular coagulation (decrease in factor V, antithrombin, or fibrinogen) or excessive fibrinolysis (elevation of fibrinogen degradation products) was found in either group of animals. The results suggest that kininogens have antithrombotic properties at low concentrations of thrombin and that inhibitory peptides derived from kininogen may constitute a new antithrombotic strategy.

High Molecular Weight Kininogen Regulates Prekallikrein Assembly and Activation on Endothelial Cells: A Novel Mechanism for Contact Activation

The consequences of assembling the contact system of proteins on the surface of vascular cells has received little study. We asked whether assembly of these proteins on the surface of cultured human endothelial cells (HUVECs) results in the activation of prekallikrein (PK) and its dependent pathways. Biotinylated PK binds specifically and reversibly to HUVECs in the presence of high molecular weight kininogen (HK) (apparent Kd of 23 ± 11 nmol/L,Bmax of 1.7 ± 0.5 × 107 sites per cell [mean ± SD, n = 5 experiments]). Cell-associated PK is rapidly converted to kallikrein. Surprisingly, the activation of cell-associated HK•PK complexes is entirely independent of exogenous factor XII (Km = 30 nmol/L,Vmax = 12 ± 3 pmol/L/min in the absencevKm = 20 nmol/L,Vmax = 9.2 ± 2.1 pmol/L/min in the presence of factor XII). Rather, kallikrein formation is mediated by an endothelial cell-associated, thiol protease. Cell-associated HK is proteolyzed during the course of prekallikrein activation, releasing kallikrein from the surface. Furthermore, activation of PK bound to HK on HUVECs promotes kallikrein-dependent activation of pro-urokinase, resulting in the formation of plasmin. These results indicate the existence of a previously undescribed, factor XII-independent pathway for contact factor activation on HUVECs that regulates the production of bradykinin and may contribute to cell-associated plasminogen activation in vivo.

High Molecular Weight Kininogen Regulates Prekallikrein Assembly and Activation on Endothelial Cells: A Novel Mechanism for Contact Activation

The consequences of assembling the contact system of proteins on the surface of vascular cells has received little study. We asked whether assembly of these proteins on the surface of cultured human endothelial cells (HUVECs) results in the activation of prekallikrein (PK) and its dependent pathways. Biotinylated PK binds specifically and reversibly to HUVECs in the presence of high molecular weight kininogen (HK) (apparent Kd of 23 ± 11 nmol/L,Bmax of 1.7 ± 0.5 × 107 sites per cell [mean ± SD, n = 5 experiments]). Cell-associated PK is rapidly converted to kallikrein. Surprisingly, the activation of cell-associated HK•PK complexes is entirely independent of exogenous factor XII (Km = 30 nmol/L,Vmax = 12 ± 3 pmol/L/min in the absencevKm = 20 nmol/L,Vmax = 9.2 ± 2.1 pmol/L/min in the presence of factor XII). Rather, kallikrein formation is mediated by an endothelial cell-associated, thiol protease. Cell-associated HK is proteolyzed during the course of prekallikrein activation, releasing kallikrein from the surface. Furthermore, activation of PK bound to HK on HUVECs promotes kallikrein-dependent activation of pro-urokinase, resulting in the formation of plasmin. These results indicate the existence of a previously undescribed, factor XII-independent pathway for contact factor activation on HUVECs that regulates the production of bradykinin and may contribute to cell-associated plasminogen activation in vivo.

p-Benzoquinone, a reactive metabolite of benzene, prevents the processing of pre-interleukins-1 alpha and -1 beta to active cytokines by inhibition of the processing enzymes, calpain, and interleukin-1 beta converting enzyme

Chronic exposure of humans of benzene affects hematopoietic stem and progenitor cells and leads to aplastic anemia. The stromal macrophage, a target of benzene toxicity, secretes interleukin-1 (IL-1), which induces the stromal fibroblast to synthesize hematopoietic colony-stimulating factors. In a mouse model, benzene causes an acute marrow hypocellularity that can be prevented by the concomitant administration of IL-1 alpha. The ability of benzene to interfere with the production and secretion of IL-1 alpha was tested. Stromal macrophages from benzene-treated mice were capable of the transcription to the IL-1 alpha gene and the translation of the message but showed an inability to process the 34-kDa pre-IL-1 alpha precursor to the 17-kDa biologically active cytokine. Treatment of normal murine stromal macrophages in culture with hydroquinone (HQ) also showed an inhibition in processing of pre-IL-1 alpha. Hydroquinone is oxidized by a peroxidase-mediated reaction in the stromal macrophage to p-benzoquinone, which interacts with the sulfhydryl (SH) groups of proteins and was shown to completely inhibit the activity of calpain, the SH-dependent protease that cleaves pre-IL-1 alpha. In a similar manner, HQ, via peroxidase oxidation to p-benzoquinone, was capable of preventing the IL-1 beta autocrine stimulation of growth of human B1 myeloid tumor cells by preventing the processing of pre-IL-1 beta to mature cytokine. Benzoquinone was also shown to completely inhibit the ability of the SH-dependent IL-1 beta converting enzyme. Thus benzene-induced bone marrow hypocellularity may result from apoptosis of hematopoietic progenitor cells brought about by lack of essential cytokines and deficient IL-1 alpha production subsequent to the inhibition of calpain by p-benzoquinone and the prevention of pre-IL-1 processing.

Thrombin-induced platelet aggregation is inhibited by the heptapeptide Leu271-Ala277 of domain 3 in the heavy chain of high molecular weight kininogen

The ability of kininogens to modulate thrombin-induced aggregation of human platelets has been assigned to domain 3 (D3) in the common heavy chain coded for by exons 7, 8, and 9 of kininogen gene. We expressed each of the exons 7, 8, and 9, and various combinations as glutathione S-transferase fusion proteins in Escherichia coli. Each of the exon products 7 (Lys236-Gln292), 9 (Val293-Gly328), and 8 (Gln329-Met357), and their combinations were evaluated for the ability to inhibit thrombin induced platelet aggregation. Only products containing exon 7 inhibited platelet aggregation induced by thrombin with an IC50 of > 20 microM. A deletion mutant of exon 7 product, polypeptide 7A product (Lys236-Lys270) did not block thrombin-induced platelet aggregation, while 7B product (Thr255-Gln292) and 7C product (Leu271-Gln292) inhibited aggregation. These findings indicated that the inhibitory activity is localized to residues Leu271-Gln292. Peptides Phe279-Ile283 and Phe281-Gln292 did not block thrombin, and Asn275-Phe279 had only minimal inhibitory activity. A heptapeptide Leu271-Ala277 inhibited thrombin-induced aggregation of platelets with an IC50 of 65 microM. The effect is specific for the activation of platelets by thrombin but not ADP or collagen. No evidence for a thrombin-kininogen complex was found, and neither HK nor its derivatives directly inhibited thrombin activity. Knowledge of the critical sequence of kininogen should allow design of compounds that can modulate thrombin activation of platelets.

Inhibitory and antiadhesive properties of human kininogens

Each of 11 exons of the human kininogen gene has the potential to code for different functional activities of the molecule in both bradykinin formation and interactions with platelets, neutrophils and endothelial cells. Our recent studies have localized amino acid sequences in exon 4 product and exon 5 product in domain 2, which bind and inhibit platelet calpain, respectively. Furthermore, we have shown that the exon 7 product expressed in domain 3 contains a decapeptide which interacts with thrombospondin on activated platelets, and a distinct septapeptide which inhibits thrombin-induced activation of platelets. Exon 8 and 9 products cooperate to inhibit cathepsins B and H. Domain 3 also contains a cell binding site for neutrophils, as does domain 5. Fine mapping of both cell binding domains has been performed by several groups of investigators for neutrophils, endothelial cells and platelets. The cell binding domain in D5 overlaps with the anionic surface binding subdomain of D5. The monomeric structure of kininogen assures that it will function as an antiadhesive protein, unlike dimeric fibrinogen. High molecular weight kininogen competes with fibrinogen binding to neutrophils and platelets. We have also fine mapped the domains for binding of kininogen (domain 6) to prekallikrein 'apple' domains 1 and 4. Kininogens can serve as proinflammatory proteins by releasing bradykinin, but cleaved kininogens exhibit antiadhesive and anti-inflammatory properties.

Hybrids of chicken cystatin with human kininogen domain 2 sequences exhibit novel inhibition of calpain, improved inhibition of actinidin and impaired inhibition of papain, cathepsin L and cathepsin B

Chicken cystatin and human kininogen domain 2 are members of the cystatin superfamily of protein-type cysteine proteinase inhibitors. They show structural and functional similarities, but only human kininogen domain 2 inhibits calpain. Using recombinant chicken cystatin as a scaffold for hybrid cassette analysis, the known reactive-site regions (N-terminus, first hairpin loop and second hairpin loop) were substituted by the corresponding sequences of human kininogen domain 2 in a single and combined manner. Seven hybrids were expressed, purified to homogeneity, characterized protein-chemically, and their inhibition of papain, actinidin, human cathepsin B, human cathepsin L and calpain (80-kDa subunit of rabbit skeletal muscle calpain II and porcine erthrocyte calpain 1) was determined. Strong but temporary inhibition of calpain by chicken cystatin hybrids carrying the N-terminus alone (variant sc1-KD2) or the N-terminus together with the first hairpin loop (variant sc1/2-KD2) was observed; hybrids of the second hairpin loop (sc3-KD2, sc1/3-KD2, sc2/3-KD2, sc1/2/3-KD2) were less strong calpain inhibitors. These data indicate that the inhibiton of calpain by human kininogen domain 2 requires the correct conformation and combination of several contact sites, and suggest that the N-terminus and the first hairpin loop play a major role in this ensemble. Remarkably, hybrid sc2-KD2 exhibited 5 or 150 times stronger inhibition of actinidin compared to native chicken cystatin or to proteolytically isolated human kininogen domain 2, respectively. This indicates an important role of the first hairpin loop of cystatins in the interaction with actinidin. Along with the impaired inhibition of cathepsin L, papain, actinidin, cathepsin B and calpain by the hybrids sc1/3-KD2, sc2/3-KD2 and sc1/2/3-KD2, these results support our hypothesis that all three predicted contact regions of kininogen domain 2 contribute to binding in the active-site clefts of papain-like enzymes in a finely balanced manner.

Inhibition of the conversion of pre-interleukins-1 alpha and 1 beta to mature cytokines by p-benzoquinone, a metabolite of benzene

Chronic exposure of humans to benzene causes severe bone marrow cell depression leading to aplastic anemia. Marrow stromal macrophage dysfunction and deficient interleukin-1 production has been reported for patients with severe aplastic anemia. The stromal macrophage, a target of benzene toxicity, is involved in hematopoietic regulation through the synthesis of several cytokines including interleukin-1, which is required for production by stromal fibroblasts of a number of cytokines required for the survival of hematopoietic progenitor cells. We have previously demonstrated that hydroquinone, a major toxic metabolite of benzene in marrow, prevents the proteolytic conversion of 31 kDa pre-interleukin-1 alpha to the 17 kDa cytokine by calpain in purified murine stromal macrophages. Furthermore, stromal macrophages from benzene-treated mice produce the 31 kDa pre-interleukin-1 alpha when stimulated in culture with endotoxin, but cannot convert the precursor to interleukin-1 alpha. In this report, we show that 1,4-benzoquinone, the oxidation product of hydroquinone in the cell, causes a concentration-dependent inhibition of highly purified human platelet calpain with an IC50 of 3 microM. Hydroquinone also inhibits the processing of pre-interleukin-1 beta by interleukin-1 beta convertase. The addition of 2 microM hydroquinone to B1 cells that undergo autocrine stimulation by interleukin-1 beta resulted in the cessation of autocrine cell growth and interleukin-1 beta secretion into the culture medium, as determined by Western immunoblots of the culture supernatants. Purified converting enzyme treated with 3 microM benzoquinone was incapable of converting 31 kDa recombinant pre-interleukin-1 beta to the 17 kDa mature cytokine as analyzed by polyacrylamide gel electrophoresis and Western immunoblotting. These findings support our observations in a mouse model that benzene-induced bone marrow cell depression results from a lack of interleukin-1 alpha subsequent to an inhibition by benzoquinone of calpain, the protease required for converting pre-interleukin-1 alpha to active cytokine. The results may provide a basis for studying benzene-induced aplastic anemia in a mouse model.

Evaluation of a microassay for human kininogens as cysteine protease inhibitors

Several methods have been described for the identification and quantification of kininogens based on both immunochemical and functional characteristics. This article presents a rapid, cheap and simple microplate assay of kininogens based on their ability to inhibit cysteine proteases. The target enzyme papain is activated by cysteine HCl and the activated enzyme will be inhibited by added kininogens. The residual enzyme activity that is not inhibited in this reaction subsequently hydrolyzes the added substrate, S-2302, generating a yellow color that is read in a microplate reader at 405 nm. This method is very sensitive, the smallest amount of kininogen that causes significant inhibition of papain is established to be 0.01 micrograms. As a quantitative method, the assay performs accurately when approximately 0.1 micrograms of low molecular weight kininogen or high molecular weight kininogen is added to the test system. The within-run coefficient of variation (%) of the method was 1.7% when the inhibition of papain was in the range 45-70% and the day to day variation as low as 2.3% when performed with a papain inhibition of 80%. Applications of the method are presented, studying chromatographic separated kininogens in plasma, ascites, and urine.

Structure and functions of human kininogens

Evidence has accumulated over the past three decades implicating plasma kininogens in numerous inflammatory processes. Delineation of the detailed biochemistry and, more recently, the molecular biology of the human kininogens has resulted in a deeper understanding of the structure-function correlations of the human kininogens. Studies of alterations of human kininogens in disease states have yielded information about the mechanisms of their involvement in inflammatory states. Here, Raul DeLa Cadena and Robert Colman summarize kininogen function in relation to structure and diagnostic and therapeutic potential.