Effect of a highly selective plasma-kallikrein synthetic inhibitor on contact activation relating to kinin generation, coagulation and fibrinolysis

The contact system proteases play disparate roles in streptococcal sepsis

Sepsis causes an activation of the human contact system, an inflammatory response mechanism against foreign surfaces, proteins and pathogens. The serine proteases of the contact system, factor XII and plasma kallikrein, are decreased in plasma of septic patients, which was previously associated with an unfavorable outcome. However, the precise mechanisms and roles of contact system factors in bacterial sepsis are poorly understood. We, therefore, studied the physiological relevance of factor XII and plasma kallikrein in a mouse model of experimental sepsis. We show that decreased plasma kallikrein concentration in septic mice is a result of reduced mRNA expression plasma prekallikrein gene, indicating that plasma kallikrein belong to negative acute phase proteins. Investigations regarding the pathophysiological function of contact system proteases during sepsis revealed different roles for factor XII and plasma kallikrein. In vitro, factor XII decelerated bacteria induced fibrinolysis, whereas plasma kallikrein supported it. Remarkably, depletion of plasma kallikrein (but not factor XII) by treatment with antisense-oligonucleotides, dampens bacterial dissemination and growth in multiple organs in the mouse sepsis model. These findings identify plasma kallikrein as a novel host pathogenicity factor in Streptococcus pyogenes sepsis.

Plasma Kallikrein Inhibitors in Cardiovascular Disease: An Innovative Therapeutic Approach

Plasma prekallikrein is the liver-derived precursor of the trypsin-like serine protease plasma kallikrein, and circulates in plasma bound to high molecular weight kininogen. Plasma prekallikrein is activated to plasma kallikrein by activated factor XII or prolylcarboxypeptidase. Plasma kallikrein regulates the activity of multiple proteolytic cascades in the cardiovascular system such as the intrinsic pathway of coagulation, the kallikrein-kinin system, the fibrinolytic system, the renin-angiotensin system, and the complement pathways. As such, plasma kallikrein plays a central role in the pathogenesis of thrombosis, inflammation, and blood pressure regulation. Under physiological conditions, plasma kallikrein serves as a cardioprotective enzyme. However, its increased plasma concentration or hyperactivity perpetuates cardiovascular disease (CVD). In this article, we review the biochemistry and cell biology of plasma kallikrein and summarize data from preclinical and clinical studies that have established important functions of this serine protease in CVD states. Finally, we propose plasma kallikrein inhibitors as a novel class of drugs with potential therapeutic applications in the treatment of CVDs.

Plasma Kallikrein-Kinin system mediates immune-mediated renal injury in trichloroethylene-sensitized mice

Trichloroethylene (TCE) is a major environmental pollutant. An immunological response is a newly-recognized mechanism for TCE-induced kidney damage. However, the role of the plasma kallikrein-kinin system (KKS) in immune-mediated kidney injury has never been examined. This study aimed to explore the role of the key components of the KKS, i.e. plasma kallikrein (PK), bradykinin (BK) and its receptors B1R and B2R, in TCE-induced kidney injury. A mouse model of skin sensitization was used to explore the mechanism of injury with or without a PK inhibitor PKSI. Kidney function was evaluated by measuring blood urea nitrogen (BUN) and creatinine (Cr) in conjunction with histopathologic characterization. Plasma BK was determined by ELISA; Renal C5b-9 membrane attack complex was evaluated by immunohistochemistry. Expression of BK and PK in the kidney was detected by immunofluorescence. mRNA and protein levels of B1R and B2R were assessed by real-time qPCR and Western blot. As expected, numerous inflammatory cell infiltration and tubular epithelial cell vacuolar degeneration were observed in TCE-sensitized mice. Moreover, serum BUN and Cr and plasma BK were increased. In addition, deposition of BK, PK and C5b-9 were observed and B1R and B2R mRNA and proteins levels were up-regulated. Pre-treatment with PKSI, a highly selective inhibitor of PK, alleviated TCE-induced renal damage. In addition, PKSI attenuated TCE-induced up-regulation of BK, PK and its receptors and C5b-9. These results provided the first evidence that activation of the KKS contributed to immune-mediated renal injury induced by TCE and also helped to identify the KKS as a potential therapeutic target for mitigating chemical sensitization-induced renal damage.

Type 2 diabetes elicits lower nitric oxide, bradykinin concentration and kallikrein activity together with higher DesArg(9)-BK and reduced post-exercise hypotension compared to non-diabetic condition

This study compared the plasma kallikrein activity (PKA), bradykinin concentration (BK), DesArg(9)-BK production, nitric oxide release (NO) and blood pressure (BP) response after moderate-intensity aerobic exercise performed by individuals with and without type 2 diabetes. Ten subjects with type 2 diabetes (T2D) and 10 without type 2 diabetes (ND) underwent three sessions: 1) maximal incremental test on cycle ergometer to determine lactate threshold (LT); 2) 20-min of constant-load exercise on cycle ergometer, at 90% LT and; 3) control session. BP and oxygen uptake were measured at rest and at 15, 30 and 45 min post-exercise. Venous blood samples were collected at 15 and 45 minutes of the recovery period for further analysis of PKA, BK and DesArg(9)-BK. Nitrite plus nitrate (NOx) was analyzed at 15 minutes post exercise. The ND group presented post-exercise hypotension (PEH) of systolic blood pressure and mean arterial pressure on the 90% LT session but T2D group did not. Plasma NOx increased ~24.4% for ND and ~13.8% for T2D group 15 min after the exercise session. Additionally, only ND individuals showed increases in PKA and BK in response to exercise and only T2D group showed increased DesArg(9)-BK production. It was concluded that T2D individuals presented lower PKA, BK and NOx release as well as higher DesArg(9)-BK production and reduced PEH in relation to ND participants after a single exercise session.

Peptidase inhibitors in the MEROPS database

The MEROPS website (http://merops.sanger.ac.uk) includes information on peptidase inhibitors as well as on peptidases and their substrates. Displays have been put in place to link peptidases and inhibitors together. The classification of protein peptidase inhibitors is continually being revised, and currently inhibitors are grouped into 67 families based on comparisons of protein sequences. These families can be further grouped into 38 clans based on comparisons of tertiary structure. Small molecule inhibitors are important reagents for peptidase characterization and, with the increasing importance of peptidases as drug targets, they are also important to the pharmaceutical industry. Small molecule inhibitors are now included in MEROPS and over 160 summaries have been written.

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.

Natural and engineered kallikrein inhibitors: an emerging pharmacopoeia

The kallikreins and kallikrein-related peptidases are serine proteases that control a plethora of developmental and homeostatic phenomena, ranging from semen liquefaction to skin desquamation and blood pressure. The diversity of roles played by kallikreins has stimulated considerable interest in these enzymes from the perspective of diagnostics and drug design. Kallikreins already have well-established credentials as targets for therapeutic intervention and there is increasing appreciation of their potential both as biomarkers and as targets for inhibitor design. Here, we explore the current status of naturally occurring kallikrein protease-inhibitor complexes and illustrate how this knowledge can interface with strategies for rational re-engineering of bioscaffolds and design of small-molecule inhibitors.

TNF-alpha and IL-1beta mediate inflammatory hypernociception in mice triggered by B1 but not B2 kinin receptor

Kinin receptors are involved in the genesis of inflammatory pain. However, there is controversy concerning the mechanism by which B(1) and B(2) kinin receptors mediate inflammatory hypernociception. In the present study, the role of these receptors on inflammatory hypernociception in mice was addressed. Mechanical hypernociception was detected with an electronic pressure meter paw test in mice and cytokines were measured by ELISA. It was observed that in naïve mice a B(2) (d-Arg-Hyp(3), d-Phe(7)-bradykinin) but not a B(1) kinin receptor antagonist (des-Arg(9)-[Leu(8)]-bradykinin, DALBK) inhibited bradykinin- and carrageenin-induced hypernociception. Bradykinin-induced hypernociception was inhibited by indomethacin (5 mg/kg) and guanethidine (30 mg/kg), while not affected by IL-1ra (10 mg/kg) or antibody against keratinocyte-derived chemokine (KC/CXCL-1, 500 ng/paw) or in TNFR1 knockout mice. By contrast, in previously lipopolysaccharide (LPS)-primed mouse paw, B(1) but not B(2) kinin receptor antagonist inhibited bradykinin hypernociception. Furthermore, B(1) kinin receptor agonist induced mechanical hypernociception in LPS-primed mice, which was inhibited by indomethacin, guanethidine, antiserum against TNF-alpha or IL-1ra. This was corroborated by the induction of TNF-alpha and IL-1beta release by B(1) kinin receptor agonist in LPS-primed mouse paws. Moreover, B(1) but not B(2) kinin receptor antagonist inhibited carrageenin-induced hypernociception, and TNF-alpha and IL-1beta release as well, in LPS-primed mice. These results suggest that in naïve mice the B(2) kinin receptor mediates inflammatory hypernociception dependent on prostanoids and sympathetic amines, through a cytokine-independent mechanism. On the other hand, in LPS-primed mice, the B(1) kinin receptor mediates hypernociception by a mechanism dependent on TNF-alpha and IL-1beta, which could stimulate prostanoid and sympathetic amine production.

Increase in kinins on post-exercise hypotension in normotensive and hypertensive volunteers

Post-exercise hypotension is an important event for blood pressure regulation, especially in hypertensive individuals. Although post-exercise hypotension is a well-known phenomenon, the mechanism responsible is still unclear. The kallikrein-kinin system is involved in blood pressure control, but its role in post-exercise hypotension has not yet been investigated. Thus, the purpose of this study was to investigate the involvement of the vasodilators bradykinin and des-Arg(9)-BK and kallikrein activity in post-exercise hypotension promoted by 35 min of cycle ergometer (CE) or circuit weight-training (CWT) bouts in normotensive and hypertensive individuals. A significant decrease in mean arterial pressure at 45 and 60 min after CE and 45 min after CWT was observed in normotensive individuals. Hypertensive values of mean arterial pressure were significantly reduced at 45 and 60 min after CE and at 60 min after CWT. Before exercise, plasma bradykinin concentrations and kallikrein activity were higher in hypertensive compared to normotensive volunteers. Kinin levels increased in the groups evaluated at the end of the training period and 60 min post-exercise. These data suggest that the kallikrein-kinin system may be involved in post-exercise hypotension in normotensive and hypertensive individuals subjected to CE and CWT bouts.

Role of the kallikrein-kinin system in Ang-(1-7)-induced vasodilation in mesenteric arterioles of Wistar rats studied in vivo-in situ

Angiotensin-(1-7) [Ang-(1-7)], exerts a variety of actions in the cardiovascular system, with an important effect being vasodilation. In this work, we investigated the relationship between the vasodilatory activity of Ang-(1-7) and the kallikrein-kinin system. Intravital microscopy was used to study the vasodilation caused by Ang-(1-7) in the mesenteric vascular bed of anesthetized Wistar rats. The topical application of Ang-(1-7) caused vasodilation of mesenteric arterioles that was reduced by A-779, JE 049 and peptidase inhibitors (aprotinin, SBTI, PKSI 527, E-64, PMSF). These results indicated that the vasodilation induced by Ang-(1-7) in the mesenteric arterioles of Wistar rats was heavily dependent on the activation of kallikrein and subsequent kinin formation.

Synergistic antithrombotic effect of a combination of NO donor and plasma kallikrein inhibitor

The aim of the present study was to investigate the effect of a NO donor (GSNO) and a plasma kallikrein inhibitor (PKSI-527) alone and in combination on global haemostatic status. A new in vitro test was employed which allows the measurement of both platelet function and spontaneous thrombolysis. Sixteen healthy young and 18 elderly volunteers were enrolled in this study. When GSNO (1 mM) or PKSI-527 (20 microM) was added to native human blood, platelet reactivity was significantly inhibited in both age groups. The combination of GSNO and PKSI-527 had additive inhibitory effect on platelets. Addition of either GSNO or PKSI-527 to blood samples did not significantly affect spontaneous thrombolysis, while added together, spontaneous thrombolysis was significantly enhanced. The thrombolysis enhancing effect was more prominent in elderly subjects. Our present findings suggest that the combination of NO donor and plasma kallikrein inhibitor may have clinical antithrombotic potential.

Blarina toxin, a mammalian lethal venom from the short-tailed shrew Blarina brevicauda: Isolation and characterization

Venomous mammals are rare, and their venoms have not been characterized. We have purified and characterized the blarina toxin (BLTX), a lethal mammalian venom with a tissue kallikrein-like activity from the submaxillary and sublingual glands of the short-tailed shrew Blarina brevicauda. Mice administered BLTX i.p. developed irregular respiration, paralysis, and convulsions before dying. Based on the amino acid sequence of purified protein, we cloned the BLTX cDNA. It consists of a prosequence and an active form of 253 aa with a typical catalytic triad of serine proteases, with a high identity with tissue kallikreins. BLTX is an N-linked microheterogeneous glycoprotein with a unique insertion of 10 residues, L(106)TFFYKTFLG(115). BLTX converted kininogens to kinins, which may be one of the toxic pathogens, and had dilatory effects on the blood vessel walls. The acute toxicity and proteolytic activity of BLTX were strongly inhibited by aprotinin, a kallikrein inhibitor, suggesting that its toxicity is due to a kallikrein-like activity of the venom.

Isolation of plasma kallikrein by high efficiency affinity chromatography and its characterization

We established a simple method for the purification of human plasma kallikrein (PK) by affinity chromatography and characterized it by analytical reverse phase-HPLC and Time of Flight Mass Spectroscopy (TOF-MS). The affinity resin (PKSI-Toyopearl) was synthesized using a selective synthetic inhibitor of plasma kallikrein (PKSI-527) as a ligand. The resin was found to have the highest efficiency in PK purification when the coupling ratio of PKSI-527 per resin was 9-14 micromol/g. PK was purified 466-fold with a yield of 83% from acetone-activated human plasma by affinity chromatography. The purity of PK thus obtained was confirmed by reverse phase-HPLC with a linear gradient of acetonitrile. The molecular weight of the purified PK was determined to be 86,151 by TOF-MS.

Development of plasma kallikrein selective inhibitors

During the course of the development of active center-directed plasmin inhibitors, it was found that N-(trans-4-aminomethylcyclohexanecarbonyl)-lysine-4-methoxycarb onylanilide inhibited plasma kallikrein more potently than other enzymes such as plasmin, urokinase, and thrombin, although the inhibitory activity was not as potent and enzyme selectivity not as high. Based on studies of structure-activity relationship, we designed and synthesized the plasma kallikrein selective inhibitor, N-(trans-4-aminomethylcyclohexanecarbonyl)-phenylalanine-4-carboxy methyl- anilide (Tra-Phe-APAA). Tra-Phe-APAA inhibited plasma kallikrein with a Ki value of 0.81 microM, while it inhibited glandular kallikrein, plasmin, urokinase, tissue plasminogen activator, factor Xa, factor XIIa, and thrombin with Ki values of > 500, 390, 200, > 500, > 500 > 500, and > 500 microM, respectively. We designated Tra-Phe-APAA as PKSI-527. Using PKSI-527 as an affinity ligand, we synthesized a new affinity gel (PKSI-Toyopearl) and employed it for the rapid purification of plasma kallikrein from human plasma. Human plasma activated with kaolin after acid treatment was applied to a PKSI-527-Toyopearl column. Adsorbed protein was eluted with 50 mM glycinehydrochloric acid buffer (pH 3.0). Plasma kallikrein was purified 181-fold with a yield of 85% from the kaolin-activated plasma.

Effects of a highly selective synthetic inhibitor of plasma kallikrein on disseminated intravascular coagulation in rats

We found a new, highly selective plasma kallikrein inhibitor, trans-4-aminomethyl-cyclohexanecarbonylphenylalanine 4-carboxymethylanilide hydrochloride, called PKSI-527 in our laboratories. This study was conducted to evaluate PKSI-527, on thromboplastin (TP)- and endotoxin (LPS)-induced disseminated intravascular coagulation (DIC) in rats. PKSI-527 was infused intravenously at 0.1 mg/kg/min for 250 min. Three of the parameters of the coagulation and fibrinolysis system, fibrinogen level, platelet counts and fibrin(ogen) degradation products (FDP) level were assayed. PKSI-527 prevented the change in the coagulation and fibrinolysis system in LPS-induced DIC, however it was not clearly effective in TP-induced DIC. The parameters of organ failure, such as serum glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), creatine phosphokinase (CPK), lactate, blood urea nitrogen and beta-glucuronidase, were assayed. Although the changes in the fibrinogen level, platelet counts and FDP level were almost the same in both models, the parameters of organ failure apparently increased in LPS-induced DIC more so than in TP-induced DIC. PKSI-527 significantly suppressed the increases in GOT and GPT in LPS-induced DIC. These results indicate that plasma kallikrein may play a significant role in LPS-induced DIC. Therefore, PKSI-527, as a synthetic plasma kallikrein inhibitor may be a valuable tool to explore the mechanism of DIC and the accompanying organ failure.

Antithrombotic effects of orally active synthetic antagonist of activated factor X in nonhuman primates

BACKGROUND

Since activated factor X (FXa) has a central role in hemostasis and thrombosis, it is an attractive target for antithrombotic strategies. Accordingly, we evaluated the relative antihemostatic and antithrombotic effects of an orally active amidinoaryl propanoic acid inhibitor of FXa, APAP, in baboons.

METHODS AND RESULTS

With a two-component thrombogenic device that induced the concurrent formation of both arterial-type platelet-rich and venous-type fibrin-rich thrombus when interposed in chronic exteriorized arteriovenous (AV) femoral shunts flowing at 40 mL/min, thrombus formation was compared for oral versus parenteral APAP by measurement of 111In-platelet deposition, 125I-fibrin accumulation, thrombotic obstruction of flow, and circulating levels of blood biochemical markers of thrombosis. The direct infusion of APAP (120 micrograms/min) into AV shunts proximal to thrombogenic devices for 1 hour achieved local drug levels of 4.3 +/- 0.4 mg/L and substantially reduced the accumulation of platelets and fibrin in the formation of venous-type fibrin-rich thrombus (P < .01) but not in the formation of platelet-rich arterial-type thrombus (P > .1). APAP was subsequently removed from plasma with plasma clearance rates of T50 alpha of 6.3 minutes and T50 beta of 99 minutes. The oral administration of APAP (50 mg/kg) produced peak plasma levels of 3.7 +/- 1.4 micrograms/mL at 30 minutes and gradually declining plasma levels over about 6 to 8 hours, with bioavailability estimated to be approximately 5% to 12%. Oral APAP decreased platelet deposition (P < .01) and fibrin accumulation (P < .05) in venous-type thrombus but failed to decrease platelet or fibrin accumulation in arterial-type thrombus (P > .1 in both cases). Oral and infused APAP prolonged the activated partial thromboplastin time and prevented thrombus-dependent elevations in plasma fibrinopeptide A, thrombin-antithrombin III complex, beta-thromboglobulin, and platelet factor 4 levels. Additionally, APAP produced dose-dependent inhibition of FXa bound to thrombus on segments of vascular graft interposed in exteriorized AV shunts for 15 minutes.

CONCLUSIONS

An oral synthetic antagonist of FXa, APAP, inhibits the formation of venous-type fibrin-rich thrombus by inactivating bound and soluble FXa without impairing platelet hemostatic function.

Effects of a highly selective plasma kallikrein inhibitor on collagen-induced arthritis in mice

A study was conducted to evaluate the effects of a new, highly selective plasma kallikrein inhibitor, PKSI-527, on collagen-induced arthritis (CIA) in mice. PKSI-527 or indomethacin was administered daily intraperitoneally from day 20 postimmunization. Clinical evaluation was performed, and two of the components of the kallikrein-kinin system, high-molecular-weight (HMW) kininogen and plasma prekallikrein, were assayed. PKSI-527, as well as indomethacin, reduced the severity of arthritis significantly. PKSI-527, but not indomethacin, restored consumed components of the kallikrein-kinin system. These results suggest that PKSI-527 suppresses CIA by modifying the kallikrein-kinin system and PKSI-527 as a synthetic plasma kallikrein inhibitor would be a valuable tool to study the mechanism of inflammation of arthritic diseases.

A finding of highly selective synthetic inhibitor of plasma kallikrein; its action to bradykinin generation, intrinsic coagulation and experimental DIC

We found a novel and highly selective synthetic inhibitor of plasma kallikrein (PK), called PKSI-527; the Ki value was 0.81 microM. PKSI-527 inhibited the bradykinin (BK) generation induced by kaolin and prolonged partial thromboplastin time (PTT). PKSI-527 prevented the decrease of fibrinogen (Fg) levels due to i.v. injection of ellagic acid in mice and ameliorated the endotoxin (ET)-induced DIC in rats.