Glycated albumin modulates the contact system with implications for the kallikrein-kinin and intrinsic coagulation systems

BACKGROUND

Human serum albumin (HSA) is the most abundant plasma protein and is sensitive to glycation in vivo. The chronic hyperglycemic conditions in patients with diabetes mellitus (DM) induce a nonenzymatic Maillard reaction that denatures plasma proteins and forms advanced glycation end products (AGEs). HSA-AGE is a prevalent misfolded protein in patients with DM and is associated with factor XII activation and downstream proinflammatory kallikrein-kinin system activity without any associated procoagulant activity of the intrinsic pathway.

OBJECTIVES

This study aimed to determine the relevance of HSA-AGE toward diabetic pathophysiology.

METHODS

The plasma obtained from patients with DM and euglycemic volunteers was probed for activation of FXII, prekallikrein (PK), and cleaved high-molecular-weight kininogen by immunoblotting. Constitutive plasma kallikrein activity was determined via chromogenic assay. Activation and kinetic modulation of FXII, PK, FXI, FIX, and FX via in vitro-generated HSA-AGE were explored using chromogenic assays, plasma-clotting assays, and an in vitro flow model using whole blood.

RESULTS

Plasma obtained from patients with DM contained increased plasma AGEs, activated FXIIa, and resultant cleaved cleaved high-molecular-weight kininogen. Elevated constitutive plasma kallikrein enzymatic activity was identified, which positively correlated with glycated hemoglobin levels, representing the first evidence of this phenomenon. HSA-AGE, generated in vitro, triggered FXIIa-dependent PK activation but limited the intrinsic coagulation pathway activation by inhibiting FXIa and FIXa-dependent FX activation in plasma.

CONCLUSION

These data indicate a proinflammatory role of HSA-AGEs in the pathophysiology of DM via FXII and kallikrein-kinin system activation. A procoagulant effect of FXII activation was lost through the inhibition of FXIa and FIXa-dependent FX activation by HSA-AGEs.

Targeting Plasma Kallikrein With a Novel Bicyclic Peptide Inhibitor (THR-149) Reduces Retinal Thickening in a Diabetic Rat Model

Purpose

To investigate the effect of plasma kallikrein (PKal)-inhibition by THR-149 on preventing key pathologies associated with diabetic macular edema (DME) in a rat model.

Methods

Following streptozotocin-induced diabetes, THR-149 or its vehicle was administered in the rat via either a single intravitreal injection or three consecutive intravitreal injections (with a 1-week interval; both, 12.5 µg/eye). At 4 weeks post-diabetes, the effect of all groups was compared by histological analysis of Iba1-positive retinal inflammatory cells, inflammatory cytokines, vimentin-positive Müller cells, inwardly rectifying potassium and water homeostasis-related channels (Kir4.1 and AQP4, respectively), vascular leakage (fluorescein isothiocyanate-labeled bovine serum albumin), and retinal thickness.

Results

Single or repeated THR-149 injections resulted in reduced inflammation, as depicted by decreasing numbers and activation state of immune cells and IL-6 cytokine levels in the diabetic retina. The processes of reactive gliosis, vessel leakage, and retinal thickening were only significantly reduced after multiple THR-149 administrations. Individual retinal layer analysis showed that repeated THR-149 injections significantly decreased diabetes-induced thickening of the inner plexiform, inner nuclear, outer nuclear, and photoreceptor layers. At the glial-vascular interface, reduced Kir4.1-channel levels in the diabetic retina were restored to control non-diabetic levels in the presence of THR-149. In contrast, little or no effect of THR-149 was observed on the AQP4-channel levels.

Conclusions

These data demonstrate that repeated THR-149 administration reduces several DME-related key pathologies such as retinal thickening and neuropil disruption in the diabetic rat. These observations indicate that modulation of the PKal pathway using THR-149 has clinical potential to treat patients with DME.

Decreased plasma kallikrein activity is associated with reduced kidney function in individuals with type 1 diabetes

AIMS/HYPOTHESIS

Plasma kallikrein is the central mediator of the plasma kallikrein-kinin system, which is involved both in vascular control and thrombin formation cascades. The plasma kallikrein-kinin system has also been considered protective in pathological conditions, but the impact of plasma kallikreins on diabetic nephropathy remains unknown. The objective of this cross-sectional study was to explore the association of plasma kallikrein with diabetic nephropathy.

METHODS

We measured plasma kallikrein activity in 295 individuals with type 1 diabetes at various stages of diabetic nephropathy, and we tested the genetic association between the plasma kallikrein-kinin system and kidney function in 4400 individuals with type 1 diabetes.

RESULTS

Plasma kallikrein activity was associated with diabetes duration (p < 0.001) and eGFR (p < 0.001), and plasma kallikrein activity was lower with more advanced diabetic nephropathy, being lowest in individuals on dialysis. The minor alleles of the KNG1 rs5030062 and rs710446 variants, which have previously been associated with increased plasma pre-kallikrein and/or factor XI (FXI) protein levels, were associated with higher eGFR (rs5030062 β = 0.03, p = 0.01; rs710446 β = 0.03, p = 0.005) in the FinnDiane cohort of 4400 individuals with type 1 diabetes.

CONCLUSIONS/INTERPRETATION

Plasma kallikrein activity and genetic variants known to increase the plasma kallikrein level are associated with higher eGFR in individuals with type 1 diabetes, suggesting that plasma kallikrein might have a protective effect in diabetic nephropathy.

Theaflavin TF3 Relieves Hepatocyte Lipid Deposition through Activating an AMPK Signaling Pathway by targeting Plasma Kallikrein

Nonalcoholic fatty liver disease (NAFLD) is rapidly becoming the leading cause of chronic liver diseases throughout the world. The deficit of pharmacotherapy for NAFLD calls for an urgent need for a new drug discovery and lifestyle management. Black tea is the most popular and functional drink consumed worldwide. Its main bioactive constituent theaflavin helps to prevent obesity-a major risk factor for NAFLD. To find new targets for the development of effective and safe therapeutic drugs from natural plants for NAFLD, we found a theaflavin monomer theaflavin-3,3'-digallate (TF3), which significantly reduced lipid droplet accumulation in hepatocytes, and directly bound and inhibited the activation of plasma kallikrein (PK), which was further proved to stimulate adenosine monophosphate activated protein kinase (AMPK) and its downstream targets. Taken together, we proposed that the TF3-PK-AMPK regulatory axis is a novel mechanism of lipid deposition mitigation, and PK could be a new target for NAFLD treatment.

Factor XII truncation accelerates activation in solution

Essentials During contact system activation, factor XII is progressively cleaved by plasma kallikrein. We investigated the role of factor XII truncation in biochemical studies. Factor XII contains naturally occurring truncating cleavage sites for a variety of enzymes. Truncation of factor XII primes it for activation in solution through exposure of R353. SUMMARY: Background The contact activation system and innate immune system are interlinked in inflammatory pathology. Plasma kallikrein (PKa) is held responsible for the stepwise processing of factor XII (FXII). A first cleavage activates FXII (into FXIIa); subsequent cleavages truncate it. This truncation eliminates its surface-binding domains, which negatively regulates surface-dependent coagulation. Objectives To investigate the influence of FXII truncation on its activation and downstream kallikrein-kinin system activation. Methods We study activation of recombinant FXII variants by chromogenic assays, by FXIIa ELISA and western blotting. Results We demonstrate that FXII truncation primes it for activation by PKa in solution. We demonstrate this phenomenon in three settings. (i) Truncation at a naturally occurring PKa-sensitive cleavage site, R334, accelerates FXIIa formation in solution. A site-directed mutant FXII-R334A displays ~50% reduced activity when exposed to PKa. (ii) A pathogenic mutation in FXII that causes hereditary angioedema, introduces an additional plasmin-sensitive cleavage site. Truncation at this site synergistically accelerates FXII activation in solution. (iii) We identify new, naturally occurring cleavage sites in FXII that have so far not been functionally linked to contact system activation. As examples, we show that non-activating truncation of FXII by neutrophil elastase and cathepsin K primes it for activation by PKa in solution. Conclusions FXII truncation, mediated by either pathogenic mutations or naturally occurring cleavage sites, primes FXII for activation in solution. We propose that the surface-binding domains of FXII shield its activating cleavage site, R353. This may help to explain how the contact system contributes to inflammatory pathology.

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.

[Kallikrein-kinin system as a target for diabetic retinopathy treatment]

Multifactor etiology of diabetic retinopathy (DR) determines difficulty of understanding of pathogenesis and need of search of effective approaches to study key mechanisms of development of this microvascular complication of diabetes mellitus (DM). Significant achievements of the last years show the contribution of two proteolytic systems into pathogenesis of DR, that control vascular tone and permeability - kallikrein-kinin (KKS) and renin-angiotensin systems (RAS). Among new approaches to DR treatment one of the most appropriate is an influence on KKS by means of inhibiting kallikrein, that leads to reduction of retinal vascular permeability and allows to prevent the development of macula oedema and other consequences of vascular wall damage in DR.

Identification and characterisation of Kunitz-type plasma kallikrein inhibitors unique to Oxyuranus sp. snake venoms

As part of a wider study on Australian snake venom components, we have identified and characterised Kunitz-type protease inhibitors from the venoms of Oxyuranus scutellatus and Oxyuranus microlepidotus (Australian taipans) with plasma kallikrein inhibitory activity. Each inhibitor had a mass of 7 kDa and was purified from the venom as part of a protein complex. Mass spectrometry and N-terminal sequencing was employed to obtain amino acid sequence information for each inhibitor and a recombinant form of the O. scutellatus inhibitor, termed TSPI, was subsequently expressed and purified. TSPI was investigated for inhibition against a panel of 12 enzymes involved in haemostasis and estimates of the K(i) value determined for each enzyme. TSPI was found to be a broad spectrum inhibitor with most potent inhibitory activity observed against plasma kallikrein that corresponded to a K(i) of 0.057 ± 0.019 nM. TSPI also inhibited fibrinolysis in whole blood and prolonged the intrinsic clotting time. These inhibitors are also unique in that they appear to be found only in Oxyuranus sp. venoms.

Plasma kallikrein mediates retinal vascular dysfunction and induces retinal thickening in diabetic rats

OBJECTIVE

Plasma kallikrein (PK) has been identified in vitreous fluid obtained from individuals with diabetic retinopathy and has been implicated in contributing to retinal vascular dysfunction. In this report, we examined the effects of PK on retinal vascular functions and thickness in diabetic rats.

RESEARCH DESIGN AND METHODS

We investigated the effects of a selective PK inhibitor, ASP-440, and C1 inhibitor (C1-INH), the primary physiological inhibitor of PK, on retinal vascular permeability (RVP) and hemodynamics in rats with streptozotocin-induced diabetes. The effect of intravitreal PK injection on retinal thickness was examined by spectral domain optical coherence tomography.

RESULTS

Systemic continuous administration of ASP-440 for 4 weeks initiated at the time of diabetes onset inhibited RVP by 42% (P = 0.013) and 83% (P < 0.001) at doses of 0.25 and 0.6 mg/kg per day, respectively. Administration of ASP-440 initiated 2 weeks after the onset of diabetes ameliorated both RVP and retinal blood flow abnormalities in diabetic rats measured at 4 weeks' diabetes duration. Intravitreal injection of C1-INH similarly decreased impaired RVP in rats with 2 weeks' diabetes duration. Intravitreal injection of PK increased both acute RVP and sustained focal RVP (24 h postinjection) to a greater extent in diabetic rats compared with nondiabetic control rats. Intravitreal injection of PK increased retinal thickness compared with baseline to a greater extent (P = 0.017) in diabetic rats (from 193 ± 10 μm to 223 ± 13 μm) compared with nondiabetic rats (from 182 ± 8 μm to 193 ± 9 μm).

CONCLUSIONS

These results show that PK contributes to retinal vascular dysfunctions in diabetic rats and that the combination of diabetes and intravitreal injection of PK in rats induces retinal thickening.

Plasma kallikrein and diabetic macular edema

Recent proteomic studies have identified components of the kallikrein kinin system, including plasma kallikrein, factor XII, and kininogen, in vitreous obtained from individuals with advanced diabetic retinopathy. In rodent models, activation of plasma kallikrein in vitreous increases retinal vascular permeability; whereas inhibition of the kallikrein kinin system reduces retinal leakage induced by diabetes and hypertension. These findings suggest that intraocular activation of the plasma kallikrein pathway may contribute to excessive retinal vascular permeability that can lead to diabetic macular edema. The kallikrein kinin system contains two separate and independently regulated serine proteases that generate bradykinin peptides: plasma kallikrein and tissue kallikrein. Tissue kallikrein is expressed in the retina and ciliary body, where it has been implicated in exerting autocrine or paracrine effects via bradykinin receptors that are colocalized in these tissues. Emerging evidence suggests that plasma kallikrein inhibitors may provide a new therapeutic opportunity to reduce retinal vascular permeability.

Plasma Kallikrein and Angiotensin I-converting enzyme N- and C-terminal domain activities are modulated by the insertion/deletion polymorphism

Angiotensin I-converting enzyme (ACE) is recognized as one of the main effector molecules involved in blood pressure regulation. In the last few years some polymorphisms of ACE such as the insertion/deletion (I/D) polymorphism have been described, but their physiologic relevance is poorly understood. In addition, few studies investigated if the specific activity of ACE domain is related to the I/D polymorphism and if it can affect other systems. The aim of this study was to establish a biochemical and functional characterization of the I/D polymorphism and correlate this with the corresponding ACE activity. For this purpose, 119 male brazilian army recruits were genotyped and their ACE plasma activities evaluated from the C- and N-terminal catalytic domains using fluorescence resonance energy transfer (FRET) peptides, specific for the C-domain (Abz-LFK(Dnp)OH), N-domain (Abz-SDK(Dnp)P-OH) and both C- and N-domains (Abz-FRK(Dnp)P-OH). Plasma kallikrein activity was measured using Z-Phe-Arg-AMC as substrate and inhibited by selective plasma kallikrein inhibitor (PKSI). Some physiological parameters previously described related to the I/D polymorphism such as handgrip strength, blood pressure, heart rate and BMI were also evaluated. The genotype distribution was II n=27, ID n=64 and DD n=28. Total plasma ACE activity of both domains in II individuals was significantly lower in comparison to ID and DD. This pattern was also observed for C- and N-domain activities. Difference between ID and DD subjects was observed only with the N-domain specific substrate. Blood pressure, heart rate, handgrip strength and BMI were similar among the genotypes. This polymorphism also affected the plasma kallikrein activity and DD group presents high activity level. Thus, our data demonstrate that the I/D ACE polymorphism affects differently both ACE domains without effects on handgrip strength. Moreover, this polymorphism influences the kallikrein-kinin system of normotensive individuals.

Kallikrein modification with affinity to IgG present in higher amounts than normal in plasma from patients with Crohn's disease

This study presents immunological and functional evidence to suggest that the activation of prekallikrein (PK) in human plasma yields two modifications of kallikrein. One of these modifications showed amidolytic properties strongly deviating from those registered for the main part of the enzyme. The substrates were S-2302, Bz-Pro-Phe-Arg-pNA, S-2366 and S-2222. In PAGE immunoblots the PK heavy chain mAb 13G11 was found to detect the kallikrein 85 kD double band and bands with mol. weights of about 152 and 135 kD. Such a 152 kD band could be removed together with an IgG fraction on a Protein G column. In this study the kallikrein identity was confirmed by an estimation of the levels obtained in amidolytic assays of mixtures of normal plasma and plasma deficient in FXI, which in immunological assays showed a PK level of 140-150%, of normal. A comparison in amidolytic assays of normal plasma and plasma from patients with Crohn's disease showed that patients' plasma contained a significantly higher level than normal of modified kallikrein. An IgG removal procedure removed all modified kallikrein, and did not affect ordinary kallikrein levels.

A novel chromogenic peptide for prekallikrein/kallikrein determination

OBJECTIVE

To determine the Km, Vmax, and Ki of BOC-Leu-Ser-Thr-Arg-pNA (B3644) in the determination of kallikrein, and then to establish the procedure for plasma prekallikrein/kallikrein determination. Method Chromogenic substrate assays on a semi-auto spectrophotometer were employed.

RESULTS

The apparent activities of seven substrates: B3644, S2238, S2251, ChromozymPCa, T6140, ChromozymPK, and T1637, for porcine kallikrein were 0.788, 0.691, 0.659, 0.636, 0.438, 0.396, and 0.145, respectively, that of B3644 being the highest. Amidolysis caused by kaolin activated human normal plasma was independent of coagulation factors II, X, XI, and protein C, but dependent on prekallikrein and to some extent on factor XII. The kallikrein's, thrombin's, and plasmin's Km and Vmax for the B3644 were determined and calculated to be 235 micromol/L and 337 nmol x s(-1) x U(-1), 469 micromol/L and 63 nmol x s(-1) x U(-1), and 70 micromol/L and 358 nmol x s(-1) x U(-1), respectively. At the same time, the kallikrein, thrombin, and plasmin Ki values for antithrombin III (AT-III) or limabean trypsin inhibitor (LBTI) were detected to be 840 or 2.50. 32 or 0.32, and, 108 or 1.55 U/L, [d1] respectively. With B3644, the recovery percentages of kallikrein and kaolin activated plasma were 100%. Intra-assay CV values ranged from 2.3% to 4.6%. By using B3644 and introducing AT-III or LBLI into the determination system, an optimized procedure for prekallikrein/kallikrein determination was obtained. With this procedure, the mean percentage values of plasma prekallikrein in normal subjects, pregnant women (gestation > or =24 weeks), and in patients with hypertension, hepatic failure, or with advanced cancers were determined to be 113.5, 151.6 (P<0.01), 173.2 (P<0.01), 43.5 (P<0.005), and 88.7 (P<0.05), respectively.

CONCLUSION

B3644 was identified as a suitable substrate for the determination of plasma prekallkrein/kallikrein activity. A sensitive and reliable chromogenic substrate assay for human plasma prekallikrein was developed by using this novel substrate.

The plasma kallikrein-kinin system: its evolution from contact activation

The plasma kallikrein-kinin system consists of the proteins factor XII (FXII), prekallikrein (PK), and high molecular weight kininogen. It was first recognized as a surface-activated coagulation system that is activated when blood or plasma interacts with artificial surfaces. Although surface-activated contact activation occurs in vivo in the case of tissue destruction or a developing thrombus, the physiologic basis for the activation and function of this system has not been delineated. New investigations indicate that there is a proteolytic pathway on cells for PK activation independent of FXII. This pathway for PK with subsequent FXII activation indicates physiologic activities. These activities include blood pressure regulation and modulation of thrombosis risk independently of hemostasis. Furthermore, they include regulation of endothelial cell proliferation, angiogenesis and apoptosis through a cellular-based, outside-in signaling system. The present characterizations of this system, which incorrectly had been thought to initiate coagulation, represent an evolution of understanding in this field.

Cellular expression of plasma prekallikrein in human tissues

Plasma prekallikrein (PPK) is synthesised in hepatocytes and secreted into the blood, where it participates in the surface-dependent activation of blood coagulation, fibrinolysis, kinin generation and inflammation. Recently we demonstrated by quantitative RT-PCR that the human PPK gene is transcribed not only in the liver, but also in various non-hepatic human tissues at significant levels. However, up to now no reliable information is available concerning protein synthesis in the corresponding human tissues. Here we demonstrate by immunohistochemical studies that PPK or plasma kallikrein (PK) is localised in cells of different embryologically derived human tissues. In the human nephron, single cells of the distal tubules stained intensely, while the cytoplasm of cells forming proximal tubules and collecting ducts stained uniformly. PPK/PK was localised in hepatic epithelial cells of the liver, in cells of the pancreatic islet of Langerhans, in the interstitial Leydig cells of the testes, in the follicular and thecal granulosa cells of the ovary, and in the parotid gland, oesophagus, skin, respiratory tract, prostate and breast. We conclude that the cellular localisation of PPK/PK in multiple different progenitor-derived cells indicates specific cellular functions of this enzyme, in addition to its known function in the blood.

Heparin modulation of human plasma kallikrein on different substrates and inhibitors

The interplay of different proteases and glycosaminoglycans is able to modulate the activity of the enzymes and to affect their structures. Human plasma kallikrein (huPK) is a proteolytic enzyme involved in intrinsic blood clotting, the kallikrein-kinin system and fibrinolysis. We investigated the effect of heparin on the action, inhibition and secondary structure of huPK. The catalytic efficiency for the hydrolysis of substrates by huPK was determined by Michaelis-Menten kinetic plots: 5.12x10(4) M-1 s-1 for acetyl-Phe-Arg-p-nitroanilide, 1.40x10(5) M-1 s-1 for H-D-Pro-Phe-Arg-p-nitroanilide, 2.25x10(4) M-1 s-1 for Abz-Gly-Phe-Ser-Pro-Phe-Arg-Ser-Ser-Arg-Gln-EDDnp, 4.24x10(2)M-1 s-1 for factor XII and 5.58x10(2) M-1 s-1 for plasminogen. Heparin reduced the hydrolysis of synthetic substrates (by 2.0-fold), but enhanced factor XII and plasminogen hydrolysis (7.7- and 1.4-fold, respectively). The second-order rate constants for inhibition of huPK by antithrombin and C1-inhibitor were 2.40x10(2) M-1 s-1 and 1.70x10(4) M-1 s-1, respectively. Heparin improved the inhibition of huPK by these inhibitors (3.4- and 1.4-fold). Despite the fact that huPK was able to bind to a heparin-Sepharose matrix, its secondary structure was not modified by heparin, as monitored by circular dichroism. These actions may have a function in the control or maintenance of some pathophysiological processes in which huPK participates.

Inhibition of angiogenesis by cleaved high molecular weight kininogen (HKa) and HKa domain 5

High molecular weight kininogen (HK) is an abundant, multi-domain plasma protein that circulates in plasma primarily in its single chain form. Proteolytic cleavage of HK by plasma kallikrein releases the vasoactive nanopeptide bradykinin (BK), and converts HK into two-chain HK (HKa). BK appears to have pro-angiogenic activity, most likely mediated through binding to B1 and B2 receptors on endothelial cells. Conversely, HKa and its domain 5, but not (single chain) HK, have potent anti-angiogenic activity comparable to other endogenous angiogenesis inhibitors. The mechanism by which HKa exerts its anti-angiogenic activity remains controversial, but appears to involve binding to cell surface tropomyosin and induction of apoptosis of proliferating endothelial cells. A role for tropomyosin in mediating the anti-angiogenic signals of other anti-angiogenic proteins such as endostatin and histidine-proline-rich glycoprotein (HPRG) has also been reported. Here we review the physiological importance of high molecular weight kininogen in angiogenesis, with emphasis on the mechanism(s) by which this activity is mediated.

Plasminogen activation independent of uPA and tPA maintains wound healing in gene-deficient mice

Simultaneous ablation of the two known activators of plasminogen (Plg), urokinase-type (uPA) and the tissue-type (tPA), results in a substantial delay in skin wound healing. However, wound closure and epidermal re-epithelialization are significantly less impaired in uPA;tPA double-deficient mice than in Plg-deficient mice. Skin wounds in uPA;tPA-deficient mice treated with the broad-spectrum matrix metalloproteinase (MMP) inhibitor galardin (N-[(2R)-2-(hydroxamido-carbonylmethyl)-4-methylpentanoyl]-L-tryptophan methylamide) eventually heal, whereas skin wounds in galardin-treated Plg-deficient mice do not heal. Furthermore, plasmin is biochemically detectable in wound extracts from uPA;tPA double-deficient mice. In vivo administration of a plasma kallikrein (pKal)-selective form of the serine protease inhibitor ecotin exacerbates the healing impairment of uPA;tPA double-deficient wounds to a degree indistinguishable from that observed in Plg-deficient mice, and completely blocks the activity of pKal, but not uPA and tPA in wound extracts. These findings demonstrate that an additional plasminogen activator provides sufficient plasmin activity to sustain the healing process albeit at decreased speed in the absence of uPA, tPA and galardin-sensitive MMPs and suggest that pKal plays a role in plasmin generation.

Urokinase induced fibrinolysis in thromboelastography: a model for studying fibrinolysis and coagulation in whole blood

BACKGROUND

The contact system (CS) proteins, factor XII and prekallikrein are thought to have roles in blood coagulation and fibrinolysis. Recent research has suggested that the CS proteins might be more important in fibrinolysis and cell function than in coagulation. Most studies on fibrinolysis have used plasma or euglobulin assays, ignoring the influence of cellular elements of blood on the fibrinolytic process.

OBJECTIVE AND METHODS

In order to study both coagulation and fibrinolysis in whole blood (WB), we have developed a thromboelastography (TEG) assay to investigate both coagulation and fibrinolysis in the same blood sample. In this assay, named urokinase (UK) induced fibrinolysis in thromboelastography (UKIFTEG), TEG is performed on recalcified citrated WB in the presence of UK. Large variations in Ly60 (percentage lysis 60 min after clot formation) were obtained between different donors with the same UK concentration. The UKIFTEG assay was therefore performed using UK concentrations that gave Ly60 values in the approximate range of 20-40%.

RESULTS

The effect of CS activation was investigated in the presence or absence of celite (10 mg mL(-1) blood). Celite shortened the clotting time (CT), and increased Ly60 values. Factor XIIa (FXIIa) and plasma kallikrein (KK) produced concentration dependent reductions in CT (significant at concentrations of 1303 and 2600 ng mL(-1) blood, respectively) and increased Ly60 values (significant at concentrations of 652 and 1300 ng mL(-1) blood, respectively).

CONCLUSIONS

Our results show that CS activation and both FXIIa and KK produce reductions in clotting time and enhanced fibrinolysis in UKIFTEG.

Variability of biological effects of silicas: Different degrees of activation of the fifth component of complement by amorphous silicas

A biogenic and a pyrogenic amorphous silica were incubated in normal human plasma and compared on a per unit surface basis for their ability to split C5 molecules and yield small C5a peptides. Since C5a peptides induce selective chemotactic attraction of polymorphonuclear leukocytes (PMN), measurement of PMN-induced chemotaxis was used as an index of C5 activation. Though to a lesser extent than the crystalline forms, amorphous silicas can promote the cleavage of C5 protein and generation of C5a-like fragment. The biogenic silica, which differs from the pyrogenic variety in particle shape, level of contaminants, and degree of surface hydrophilicity, besides specific surface, induced a greater response. Both silicas activated C5 through a process which seems to involve multiple events similar to those induced by crystalline silica. C5 molecules are adsorbed and hydroxyl radicals are generated through Haber Weiss cycles catalyzed by the redox-active iron present at the particle surface either as trace impurities or chelated from plasma by silanol groups. In turn, these radicals convert native C5 to an oxidized C5-like form C5(H2O2). Finally, C5(H2O2) is cleaved by protease enzymatic action of plasma kallikrein activated by the same silica dusts, yielding a product, C5a(H2O2), having the same functional characteristic as C5a.

Expression, crystallization, and three-dimensional structure of the catalytic domain of human plasma kallikrein

Plasma kallikrein is a serine protease that has many important functions, including modulation of blood pressure, complement activation, and mediation and maintenance of inflammatory responses. Although plasma kallikrein has been purified for 40 years, its structure has not been elucidated. In this report, we described two systems (Pichia pastoris and baculovirus/Sf9 cells) for expression of the protease domain of plasma kallikrein, along with the purification and high resolution crystal structures of the two recombinant forms. In the Pichia pastoris system, the protease domain was expressed as a heterogeneously glycosylated zymogen that was activated by limited trypsin digestion and treated with endoglycosidase H deglycosidase to reduce heterogeneity from the glycosylation. The resulting protein was chromatographically resolved into four components, one of which was crystallized. In the baculovirus/Sf9 system, homogeneous, crystallizable, and nonglycosylated protein was expressed after mutagenizing three asparagines (the glycosylation sites) to glutamates. When assayed against the peptide substrates, pefachrome-PK and oxidized insulin B chain, both forms of the protease domain were found to have catalytic activity similar to that of the full-length protein. Crystallization and x-ray crystal structure determination of both forms have yielded the first three-dimensional views of the catalytic domain of plasma kallikrein. The structures, determined at 1.85 A for the endoglycosidase H-deglycosylated protease domain produced from P. pastoris and at 1.40 A for the mutagenically deglycosylated form produced from Sf9 cells, show that the protease domain adopts a typical chymotrypsin-like serine protease conformation. The structural information provides insights into the biochemical and enzymatic properties of plasma kallikrein and paves the way for structure-based design of protease inhibitors that are selective either for or against plasma kallikrein.

Conformational lability in serine protease active sites: structures of hepatocyte growth factor activator (HGFA) alone and with the inhibitory domain from HGFA inhibitor-1B

Hepatocyte growth factor activator (HGFA) is a serine protease that converts hepatocyte growth factor (HGF) into its active form. When activated HGF binds its cognate receptor Met, cellular signals lead to cell growth, differentiation, and migration, activities which promote tissue regeneration in liver, kidney and skin. Intervention in the conversion of HGF to its active form has the potential to provide therapeutic benefit where HGF/Met activity is associated with tumorigenesis. To help identify ways to moderate HGF/Met effects, we have determined the molecular structure of the protease domain of HGFA. The structure we determined, at 2.7 A resolution, with no pseudo-substrate or inhibitor bound is characterized by an unconventional conformation of key residues in the enzyme active site. In order to find whether this apparently non-enzymatically competent arrangement would persist in the presence of a strongly-interacting inhibitor, we also have determined, at 2.6 A resolution, the X-ray structure of HGFA complexed with the first Kunitz domain (KD1) from the physiological inhibitor hepatocyte growth factor activator inhibitor 1B (HAI-1B). In this complex we observe a rearranged substrate binding cleft that closely mirrors the cleft of other serine proteases, suggesting an extreme conformational dynamism. We also characterize the inhibition of 16 serine proteases by KD1, finding that the previously reported enzyme specificity of the intact extracellular region of HAI-1B resides in KD1 alone. We find that HGFA, matriptase, hepsin, plasma kallikrein and trypsin are potently inhibited, and use the complex structure to rationalize the structural basis of these results.

The Plasma and Tissue Kininogen-kallikrein-kinin System: Role in the Cardiovascular System

Bradykinin and Lys-bradykinin are potent peptide mediators implicated in several physiopathological effects in mammals. They act through activation of G-protein-coupled constitutive B(2) or inducible kinin B(1) receptors linked to signaling pathways involving increased intracellular Ca(++) concentrations and/or release of mediators including arachidonic acid metabolites, NO and EDHF. In the cardiovascular system, the kallikrein-kinin system exerts a fine control of vascular smooth muscle tone and arterial blood pressure, and plays a significant cardioprotective effect. This has been lately confirmed in experimental studies employing transgenic mice overexpressing human tissue kallikrein and animals with knockout of kinin B(1) and B(2) receptor gene. Disturbances in this system are associated with arterial hypertension, myocardial ischaemia and other clinical complications. Inhibitors of kininase II (angiotensin-converting enzyme) have been prescribed successfully to patients with cardiovascular diseases, but there is still a great interest in developing drugs or pharmacological strategies that augment the activity of kininogen-kallikrein-kinin system in pathological conditions. Delivery of adenovirus vector containing the human tissue kallikrein gene (gene kallikrein therapy) has emerged as a great potential to satisfy these conditions. This review provides a summary of plasma and tissue kallikrein-kinin system, focusing on the pharmacological properties, kinin receptors and drugs reported to interfere with their actions. The modulatory effects of the kallikrein-kinin system on cardiovascular system, particularly in regulating smooth muscle tone and arterial blood pressure and in preventing myocardium ischaemia have also been explored in the review.

Domain structure of bi-functional selenoprotein P

Human selenoprotein P (SeP), a selenium-rich plasma glycoprotein, is presumed to contain ten selenocysteine residues; one of which is located at the 40th residue in the N-terminal region and the remaining nine localized in the C-terminal third part. We have shown that SeP not only catalyses the reduction of phosphatidylcholine hydroperoxide by glutathione [Saito, Hayashi, Tanaka, Watanabe, Suzuki, Saito and Takahashi (1999) J. Biol. Chem. 274, 2866-2871], but also supplies its selenium to proliferating cells [Saito and Takahashi (2002) Eur. J. Biochem. 269, 5746-5751]. Treatment of SeP with plasma kallikrein resulted in a sequential limited proteolysis (Arg-235-Gln-236 and Arg-242-Asp-243). The N-terminal (residues 1-235) and C-terminal (residues 243-361) fragments exhibited enzyme activity and selenium-supply activity respectively. These results confirm that SeP is a bi-functional protein and suggest that the first selenocysteine residue is the active site of the enzyme and the remaining nine residues function as a selenium supplier.

Evidence that the prostate-specific antigen (PSA)/Zn2+ axis may play a role in human prostate cancer cell invasion

Prostate-specific antigen (PSA), which is used as a marker for the diagnosis and monitoring of prostate cancer, is a kallikrein protease which could potentially play a role in human prostate cancer cell invasion. Zinc ions are effective inhibitors of a number of proteases. The enzymatic activity of purified PSA was strongly inhibited by Zn(2+). The ability of LNCaP cells which express and secrete PSA to invade Matrigel was strongly suppressed by Zn(2+) at a concentration similar to that inhibiting the activity of purified PSA. Zn(2+) effectively inhibited the degradation of Matrigel by purified PSA. These results suggest that Zn(2+) in human prostate may suppress the invasion and metastasis of prostate cancer cells through the regulation of the proteolytic activity of PSA. Loss of inhibition of the proteolytic activity of PSA by Zn(2+) in prostate tumors could contribute to invasion.

Hepatic clearance of tissue-type plasminogen activator and plasma kallikrein in experimental liver fibrosis

We have previously shown that tissue-type plasminogen activator (tPA) and rat plasma kallikrein (RPK) share a common, but not unique, pathway for liver clearance.

AIM

To evaluate the hepatic clearance of both proteases in experimental liver fibrosis.

METHODS

The hepatic clearance of these proteases was studied in porcine serum-induced liver fibrosis using the isolated and perfused rat liver model. To better interpret the results, we also studied four other experimental groups: the turpentine oil-induced acute-phase response (AP group), AP group followed by GdCl3 administration (AP/Gd group), CCl4-induced cirrhosis (CCl4 group) and normal group.

RESULTS

The tPA clearance decreased significantly by both fibrotic and cirrhotic rat livers whereas the RPK clearance was not altered by the fibrotic rat liver. The hepatic clearance of tPA was reduced in the AP and AP/Gd groups; on the other hand, RPK clearance was increased in the AP group and, interestingly, this effect was neutralized by concomitant GdCl3 administration.

CONCLUSIONS

We observed that tPA and RPK clearances were affected differently by fibrosis as well as by different stimuli of the acute-phase response, despite the fact that they share a common hepatic clearance mechanism in normal livers, and they were equally affected in cirrhosis.

Engineering of a macromolecular scaffold to develop specific protease inhibitors

The specific inhibition of serine proteases, which are crucial switches in many physiologically important processes, is of value both for basic research and for therapeutic applications. Ecotin, a potent macromolecular inhibitor of serine proteases of the S1A family, presents an attractive scaffold to engineer specific protease inhibitors because of its large inhibitor-protease interface. Using synthetic shuffling in combination with a restricted tetranomial diversity, we created ecotin libraries that are mutated at all 20 amino acid residues in the binding interface. The efficacy of these libraries was demonstrated against the serine protease plasma kallikrein (Pkal). Competitive phage display selection yielded a Pkal inhibitor with an apparent dissociation equilibrium constant (K(i)*) of 11 pM, whereas K(i)* values for related proteases (such as Factor Xa (FXa), Factor XIa (FXIa), urokinase-type plasminogen activator (uPA), thrombin, and membrane-type serine protease 1 (MT-SP1)) were four to seven orders of magnitude higher. The adaptability of the scaffold was demonstrated by the isolation of inhibitors to two additional serine proteases, MT-SP1/matriptase and Factor XIIa.

Attenuated kinin release from human neutrophil elastase-pretreated kininogens by tissue and plasma kallikreins

Components of kinin-forming systems operating at inflammatory sites are likely to interact with elastase that is released by recruited neutrophils and may, at least temporarily, constitute the major proteolytic activity present at these sites. The aim of this work was to determine the effect of kininogen degradation by human neutrophil elastase (HNE) on kinin generation by tissue and plasma kallikreins. We show that the digestion of both low molecular mass (LK) and high molecular mass (HK) forms of human kininogen by HNE renders them essentially unsusceptible to processing by human urinary kallikrein (tissue-type) and also significantly quenches the kinin release from HK by plasma kallikrein. Studies with synthetic model heptadecapeptide substrates, ISLMKRPPGFSPFRSSR and SLMKRPPGFSPFRSSRI, confirmed the inability of tissue kallikrein to process peptides at either termini of the internal kinin sequence, while plasma kallikrein was shown to release the kinin C-terminus relatively easily. The HNE-generated fragments of kininogens were separated by HPLC and the fractions containing internal kinin sequences were identified by a kinin-specific immunoenzymatic test after trypsin digestion. These fractions were analyzed by electrospray-ionization mass spectrometry. In this way, multiple peptides containing the kinin sequence flanked by only a few amino acid residues at each terminus were identified in elastase digests of both LK and HK. These results suggest that elastase may be involved in quenching the kinin-release cascade at the late stages of the inflammatory reaction.

Mechanism of kinin release during experimental acute pancreatitis in rats: evidence for pro- as well as anti-inflammatory roles of oedema formation

1 Kinin B(2) receptor antagonists or tissue kallikrein (t-KK) inhibitors prevent oedema formation and associated sequelae in caerulein-induced pancreatitis in the rat. We have now further investigated the mechanism of kinin generation in the pancreas. 2 Kinins were elevated in the pancreatic tissue already before oedema formation became manifest. Peak values (421+/-59 pmol g(-1) dry wt) were reached at 45 min and remained elevated for at least 2 h; a second increase was observed at 24 h. Pretreatment with the B(2) receptor antagonist icatibant abolished kinin formation, while post-treatment was ineffective. 3 Total kininogen levels were very low in the pancreas of controls, but increased 75-fold during acute pancreatitis. This increase was absent in rats that were pretreated with icatibant. 4 During pancreatitis, t-KK-like and plasma kallikrein (p-KK)-like activity in the pancreas, as well as trypsinogen activation peptide (TAP) increased significantly. Icatibant pretreatment further augmented t-KK about 100-fold, while p-KK was significantly attenuated; TAP levels remained unaffected. 5 Endogenous protease inhibitors (alpha(1)-antitrypsin, alpha(2)-macroglobulin) were low in normal tissues, but increased 45- and four-fold, respectively, during pancreatitis. This increase was abolished when oedema formation was prevented by icatibant. 6 In summary, oedema formation is initiated by t-KK; the ensuing plasma protein extravasation supplies further kininogen and active p-KK to the tissue. Concomitantly, endogenous protease inhibitors in the oedema fluid inhibit up to 99% of active t-KK. Our data thus suggest a complex interaction between kinin action and kinin generation involving positive and negative feedback actions of the inflammatory oedema.

Properties of chemically oxidized kininogens

Kininogens are multifunctional proteins involved in a variety of regulatory processes including the kinin-formation cascade, blood coagulation, fibrynolysis, inhibition of cysteine proteinases etc. A working hypothesis of this work was that the properties of kininogens may be altered by oxidation of their methionine residues by reactive oxygen species that are released at the inflammatory foci during phagocytosis of pathogen particles by recruited neutrophil cells. Two methionine-specific oxidizing reagents, N-chlorosuccinimide (NCS) and chloramine-T (CT), were used to oxidize the high molecular mass (HK) and low molecular mass (LK) forms of human kininogen. A nearly complete conversion of methionine residues to methionine sulfoxide residues in the modified proteins was determined by amino acid analysis. Production of kinins from oxidized kininogens by plasma and tissue kallikreins was significantly lower (by at least 70%) than that from native kininogens. This quenching effect on kinin release could primarily be assigned to the modification of the critical Met-361 residue adjacent to the internal kinin sequence in kininogen. However, virtually no kinin could be formed by human plasma kallikrein from NCS-modified HK. This observation suggests involvement of other structural effects detrimental for kinin production. Indeed, NCS-oxidized HK was unable to bind (pre)kallikrein, probably due to the modification of methionine and/or tryptophan residues at the region on the kininogen molecule responsible for the (pro)enzyme binding. Tests on papain inhibition by native and oxidized kininogens indicated that the inhibitory activity of kininogens against cysteine proteinases is essentially insensitive to oxidation.

Fine mapping of the H-kininogen binding site in plasma prekallikrein apple domain 2

Plasma prekallikrein (PPK), the zymogen of the contact phase protease plasma kallikrein, forms a non-covalent complex with its substrate H-kininogen (HK). HK binds to cell surface proteoglycans, indirectly anchoring this bradykinin-generating protease to endothelial cells. The heavy chain of PPK consisting of four apple domains designated A1 to A4. Previous studies indicated that a major HK binding site on PPK is within the A2 domain, with additional contributions to binding provided by the N-terminal portion of Al and the central part of A4. To precisely map the relevant binding segments in A2, we employed a monoclonal anti-PPK antibody (PKH6) that binds to A2 and blocks HK-PPK complex formation with an apparent IC50 of 8 nM. Using recombinant A2 C-terminal deletion mutants, we mapped the target epitope of PKH6 to the N-terminal portion of A2, residues 92-153. C-terminal deletion of A2 to residue 145 resulted in a loss of PKH6 binding, as did proteolytic cleavage of A2 at Lys140-Arg141. A comparison of HK binding to various A2 deletion mutants revealed that the major HK binding site is localized to residues 145-153 in the central portion of A2, where it overlaps with the PKH6 epitope. This sequence is conserved in the A2 domain of the related protease factor XI, explaining the unusual strong cross-reactivity of PHK6 with factor XI, as well as the similar HK-binding characteristics of PPK and factor XI.

Assembly and activation of the plasma kallikrein/kinin system: a new interpretation

Understanding the importance and physiologic activity of the plasma kallikrein/kinin system (KKS) has been thwarted by the absence of an inclusive theory for its assembly and activation. The contact activation hypothesis describes the assembly and activation of this system in test tubes and disease states, but not under physiologic circumstances. Recent investigations have indicated a new cohesive hypothesis for understanding physiologic activation of this system. Prekallikrein (PK) and factor XI (FXI) through high molecular weight kininogen (HK) assemble on a co-localized, multiprotein receptor complex on endothelial cells that consists of at least cytokeratin 1 (CKI), gClqR, and urokinase plasminogen activator receptor (muPAR). When assembled on these proteins, prekallikrein becomes activated to kallikrein by the membrane-expressed enzyme prolylcarboxypeptidase (PRCP). Formed kallikrein then activates factor XII (FXII) for amplification of its activation and single chain urokinase. The plasma kallikrein/kinin system may serve as a physiologic counterbalance to the plasma renin angiotensin system (RAS) by lowering blood pressure and preventing thrombosis. Insights into the integrated role of these two systems may afford the development of novel therapeutic drugs to manage hypertension and thrombosis.

Glycosaminoglycans affect the action of human plasma kallikrein on kininogen hydrolysis and inflammation

Human plasma kallikrein (huPK) is a serine proteinase involved in many biological processes including those of the kallikrein-kinin system. The action of huPK on kininogen results in bradykinin (BK) release, a potent mediator of inflammatory responses. BK generation may be influenced by several agents, and the aim of this work was to investigate the effect of glycosaminoglycans (GAGs) on human high-molecular-weight kininogen (HK) hydrolysis by huPK and on inflammation. huPK was pre-incubated in the absence and presence of different GAGs, followed by the addition of kininogen. Bradykinin released at different times was measured by radioimmunoassay, and KM and kcat were calculated. Tuna and bovine dermatan sulfates, the most potent GAGs studied, reduced by 80% and 68%, respectively, the catalytic efficiency of huPK (control = 4. x 10(4) M(-1) s(-1) in BK release. The effect of bovine dermatan sulfate (BDS) on inflammatory response was studied in rat paw edema induced by carrageenin and hourly determined (1-4 h) by plethysmography. BDS significantly reduced the inflammatory response in the first and second hours of measurements (24% and 28%, respectively), p < 0.05. GAGs were shown to reduce bradykinin release "in vitro" and in an inflammation model. This reduction may play a role in the control or maintenance of some pathological and physiological processes.

Comparative effects of ACE inhibition and angiotensin II receptor blockade in the prevention of renal damage

Angiotensin II (Ang II) regulates a number of genes associated with progression of renal disease. The regulation of gene expression by Ang II occurs through specific receptors that are linked to changes in the activity of transcription factors within the nucleus of target cells. In particular, members of the nuclear factor-kappaB family of transcription factors are activated, which in turn fuels at least two autocrine reinforcing loops that amplify Ang II and tumor necrosis factor-alpha formation. Angiotensin converting enzymes (ACE) inhibitors and angiotensin antagonists (AIIAs) differ both pharmacokinetically and pharmacodynamically in patients with end-stage renal disease (ESRD). Several ACE inhibitors (such as captopril, enalapril and lisinopril) are dialyzable, whereas all of the AIIAs studied are not. Dose titration may be necessary when administering ACE inhibitors to patients with renal failure (ESRD), but is rarely a consideration when AIIAs are used.

Involvement of tissue kallikrein but not plasma kallikrein in the development of symptoms mediated by endogenous kinins in acute pancreatitis in rats

In order to investigate the mechanism of kinin release leading to vascular symptoms in acute interstitial-oedematous pancreatitis, the novel, selective inhibitors of tissue kallikrein, (2S,2'R)-2-(2'-amino-3'-(4'-chlorophenyl)propanoylamino)-N-(3-guanidinopropyl)-3-(1-naphthyl)propanoamide (FE999024, CH-2856), and of plasma kallikrein, (2'S,2"R)-4-(2'-(2"(carboxymethylamino)-3"-cyclohexyl-propanoylamino)-3'-phenyl-propanoylamino)piperidine-1-carboxamidin (FE999026, CH-4215), were used in experimental caerulein-induced pancreatitis in rats. Oedema formation and plasma protein extravasation during the 2 h infusion of caerulein were inhibited in a dose-dependent manner by i.p. pretreatment with FE999024 (7-60 micromol kg(-1)) while FE999026 had no effect at the same doses. Haemoconcentration and hypovolaemia associated with the pancreatic oedema formation during pancreatitis were significantly attenuated by FE999024 at a dose of 20 micro mol kg(-1). The reduction in circulating plasma volume was not affected by FE999026. Accumulation of amylase and lipase in the pancreas was dose-dependently reduced by FE999024 while enzyme activities in the blood serum were increased by FE999024 at 60 micromol kg(-1) indicating improved enzyme removal from the tissue. Enzyme activities in the tissue and in the blood remained unaffected by FE999026. FE999024 (20 micromol kg(-1)) largely inhibited increased tissue kallikrein-like activity in the pancreas during acute pancreatitis and also strongly attenuated influx of plasma kallikrein into the tissue. FE999026 (20 micromol kg(-1)) significantly inhibited plasma kallikrein-like activity in the pancreas but had no effect on tissue kallikrein-like activity. In conclusion, vascular kinin-mediated symptoms observed during oedematous pancreatitis in the rat are caused by the action of tissue kallikrein in the pancreas whereas an involvement of plasma kallikrein seems to be unlikely.

Activation of the tissue kallikrein-kinin system in stroke

Edema formation is a major problem in large ischemic infarcts, and the underlying breakdown of the blood-brain barrier is only incompletely understood. Here, we report that the tissue kallikrein-kinin system, which influences the permeability of the blood-brain barrier, is activated in stroke. In 22 patients with large infarcts in the territory of the middle cerebral artery, we found elevated plasma concentrations of the tissue kinin kallidin. The data suggest that further studies on a possible role of kinin receptor antagonists on edema after stroke are warranted.

Kallikrein-kinin system activation in Crohn's disease: differences in intestinal and systemic markers

OBJECTIVES

Observations in experimental models and in human ulcerative colitis suggest that activation of the kallikrein-kinin system plays a role in the pathogenesis of inflammatory bowel disease. The aim of this study was to assess activation of the plasma and tissue kallikrein-kinin system in Crohn's disease.

METHODS

We studied plasma inflammatory and contact system parameters in 36 patients with Crohn's disease and in 36 control subjects with noninflammatory GI diseases. We also obtained tissue samples from the involved intestine of 12 patients with Crohn's disease, and from normal peritumoral tissue (12 patients) and diverticulitis tissue (seven patients) as controls. Full-thickness sections were tested for intestinal tissue kallikrein reactivity with a specific antibody.

RESULTS

In Crohn's disease patients and controls, plasma levels of prekallikrein, factor XI, high molecular weight kininogen and its cleaved form were normal. Crohn's disease patients had significantly higher levels of antigen and functional Cl-inhibitor (+22%, +12%) than did controls (p = 0.005, p = 0.004). After surgical resection, antigen and functional Cl-inhibitor significantly decreased in Crohn's disease patients (-22%, -15%; p = 0.035, p = 0.006). Intestinal tissue kallikrein immunoreactivity was absent (75%) or weak (25%) in the goblet cells from Crohn's disease tissue sections but was normal in controls, with a highly significant difference in the staining score (p = 0.0001). Intestinal tissue kallikrein immunoreactivity in the interstitium was higher in Crohn's disease than in normal and diverticulitis samples (p = 0.0001 and p = 0.001, respectively).

CONCLUSIONS

Our observations suggest that intestinal tissue kallikrein is involved in the inflammatory process in Crohn's disease. The lack of contact system activation in peripheral blood might be related to the high plasma levels of Cl-inhibitor, the most important inhibitor of the contact system in the circulation.

Kallikreins and kininogens in saliva and plasma of patients presenting with rheumatoid arthritis

We evaluated the activities of salivary kallikrein and tissue/plasma kallikreins, and the plasma levels of high-molecular (HKg) and low-molecular (LKg) weight kininogens in patients with rheumatoid arthritis. The patients exhibited higher levels of the active salivary kallikrein compared to the controls. In contrast, the total salivary kallikrein activity of patients was not different from controls. In plasma from the patients, tissue kallikrein activity or plasma prekallikrein activity was not significantly different from the controls. Plasma HKg levels observed in patients were higher than in controls, whereas plasma LKg levels did not differ significantly from controls. Our results showed that most of the salivary kallikrein seen in patients is in its active form, suggesting the presence of systemic or local factors with the ability to activate salivary pro-kallikrein.

Activation of the kallikrein-kinin system by cardiopulmonary bypass in humans

We used cardiopulmonary bypass (CPB) as a model of activation of the contact system and investigated the involvement of the plasma and tissue kallikrein-kinin systems (KKS) in this process. Circulating levels of bradykinin and kallidin and their metabolites, plasma and tissue kallikrein, low and high molecular weight kininogen, and kallistatin were measured before, during, and 1, 4, and 10 h after CPB in subjects undergoing cardiac surgery. Bradykinin peptide levels increased 10- to 20-fold during the first 10 min, returned toward basal levels by 70 min of CPB, and remained 1.2- to 2.5-fold elevated after CPB. Kallidin peptide levels showed little change during CPB, but they were elevated 1.7- to 5.2-fold after CPB. There were reductions of 80 and 60% in plasma and tissue kallikrein levels, respectively, during the first minute of CPB. Kininogen and kallistatin levels were unchanged. Angiotensin-converting enzyme inhibition did not amplify the increase in bradykinin levels during CPB. Aprotinin administration prevented activation of the KKS. The changes in circulating kinin and kallikrein levels indicate activation of both the plasma and tissue KKS during activation of the contact system by CPB.

Bauhinia bauhinioides Plasma Kallikrein Inhibitor Interaction with Synthetic Peptides and Fluorogenic Peptide Substrates Related to the Reactive Site Sequence

A serine proteinase inhibitor was purified from Bauhinia bauhinioides seeds after extraction with 0.15M NaCl by ion-exchange column chromatography on DEAE-Sephadex, gel filtration on Superose 12 column, Mono Q chromatography or alternatively by affinity chromatography on trypsin- Sepharose. The inhibitor is a single polypeptide chain with molecular mass 20 kDa by gel filtration on Superose 12, but was resolved into two peaks by ion - exchange chromatography on Mono Q (FPLC system). The main eluted peak inhibits trypsin (Ki = 0.6 nM), plasma kallikrein (Ki = 0.35 nM), plasmin (Ki = 33.1 nM), and weakly chymotrypsin (Ki = 2,700 nM), being the most effective plasma kallikrein inhibitor isolated from Bauhinia seeds. Therefore, it was denominated Bauhinia bauhinioides kallikrein inhibitor (BbKI). Activity is thermolabile and on trypsin inhibition optimum pH is 8.0. BbKI displays high homology to other plant Kunitz inhibitors, except for the absence of disulfide bridges, and the only cysteine residue is at the C-terminal position (residue 154) characterizes a distinct member of the Kunitz family. The affinity of the inhibitor to trypsin was confirmed by adsorption to trypsin-Sepharose resin and by isolation of the trypsin-inhibitor complex by gel filtration. Peptides with variations around the reactive site of BbKI (GLPVRFESPLRINIIKESY) were synthesized containing a quenched fluorogenic group. Trypsin but not plasma kallikrein substrates, these peptides strongly inhibited plasma kallikrein.

A plasma kallikrein-dependent plasminogen cascade required for adipocyte differentiation

Here we show that plasma kallikrein (PKal) mediates a plasminogen (Plg) cascade in adipocyte differentiation. Ecotin, an inhibitor of serine proteases, inhibits cell-shape change, adipocyte-specific gene expression, and lipid accumulation during adipogenesis in culture. Deficiency of Plg, but not of urokinase or tissue-type plasminogen activator, suppresses adipogenesis during differentiation of 3T3-L1 cells and mammary-gland involution. PKal, which is inhibited by ecotin, is required for adipose conversion, Plg activation and 3T3-L1 differentiation. Human plasma lacking PKal does not support differentiation of 3T3-L1 cells. PKal is therefore a physiological regulator that acts in the Plg cascade during adipogenesis. We propose that the Plg cascade fosters adipocyte differentiation by degradation of the fibronectin-rich preadipocyte stromal matrix.

In vitro cleavage by asbestos fibers of the fifth component of human complement through free-radical generation and kallikrein activation

Chrysotile and crocidolite fibers incubated in normal human plasma (NHP) generated from the C5 component of complement C5a-type fragments that stimulated polymorphonuclear leukocyte (PMN) chemotaxis. Absorption of NHP with antiserum against C5a totally abolished neutrophil chemotactic activity. Asbestos fibers also produced C5a small peptides in the presence of ethylene glycol bis(beta-aminoethyl ether) N,N,N'N'-tetraacetic acid (EGTA) but not ethylene diamine tetraacetic acid (EDTA). Activation of C5 was significantly inhibited when asbestos fibers were pretreated with iron chelators such as sodium dithionite (DTN), deferoxamine (DFX), or ascorbate (AA). Concentration-related inhibition of C5 activation was also observed when asbestos fibers were added concurrently to plasma in the presence of DFX, 1,3-dimethyl-2-thiourea (DMTU), a strong hydroxyl scavenger, or aprotinin (APR), a specific protease inhibitor. Further, chrysotile and crocidolite significantly increased plasma kallikrein activity. Data demonstrate that asbestos-induced C5 activation plays a role in inflammatory reactions characteristic of asbestosis through mechanisms involving iron ions, hydroxyl radicals, and oxidized C5-ike fragments. The ferrous ions present at the asbestos fiber surface trigger this activation and catalyze, via Fenton reaction, the production of hydroxyl radicals, which in turn convert native C5 to an oxidized C5-like form. This product is then cleaved by kallikrein, activated by the same asbestos fibers, yielding an oxidized C5a with the same functional properties as C5a.

Activation of the plasma kallikrein/kinin system on endothelial cell membranes

For more than three decades, it has been known that the plasma kallikrein/kinin system becomes activated when exposed to artificial, negatively charged surfaces. The existence of an encompassing in vivo, negatively charged surface capable of activation of the plasma kallikrein/kinin system has, however, never been convincingly demonstrated. In this report, we describe current knowledge on how the proteins of the plasma kallikrein/kinin system assemble to become activated on cell membranes. On endothelial cells, the activation of the plasma kallikrein/kinin system is not initiated by factor XII autoactivation as seen on artificial surfaces. On endothelial cells, prekallikrein is activated by an antipain sensitive protease. Prekallikrein activation is dependent on the presence of high molecular weight kininogen and an optimal free Zn2+ concentration. Kallikrein generated on the surface of endothelial cell is capable of activating factor XII. Further, kallikrein formed on endothelial cell membranes is capable of cleaving its receptor and native substrate, high molecular weight kininogen, liberating bradykinin and the HK PK complex from the endothelial cell surface. Endothelial cell-associated kallikrein also is capable of kinetically favorable pro-urokinase and, subsequent, plasminogen activation.

[Kinin generation in acute and chronic airway inflammation]

OBJECTIVE

To investigate the kinin generation pathways in acute and chronic airway inflammation.

METHODS

BALF from patients with acute, chronic airway inflammation and healthy controls were collected. Kinins, Plasma kallikrein, alpha 2-macroglobulin and toluenesulphonyl-arginine methyl ester esterase activity (TAME-ea) in BALF were studied.

RESULTS

Kinins and TAME-ea values were significantly higher in the BALF of patients with acute and chronic airway inflammation than those in the controls, but there was no significant difference between acute and chronic groups; PK and alpha 2-M values were significantly higher in the acute group than the in chronic one. Gel filtration revealed the highest TAME-ea peak at about 800,000 in the acute group, corresponding with the first alpha 2-M peak, whereas at about 40,000 in chronic bronchitis. The inhibition test of the TAME-ea showed that the TAME-ea peak at 800,000 was mainly due to PK and the TAME-ea peak at 40,000 was mainly due to TK.

CONCLUSIONS

The results indicated that in acute airway inflammation kinins seem to be mainly generated by PK, whereas in chronic inflammation kininogenases other than PK--such as TK--seem to be more important.