Kallikrein inhibitors for angioedema: the progress of preclinical and early phase studies

INTRODUCTION

Hereditary angioedema (HAE) is a rare genetic disorder characterized by recurrent edema and predominantly caused by the dysregulation of the kinin-kallikrein system.

AREAS COVERED

This manuscript presents the results of preclinical and early clinical trials of newer drugs targeting the dysregulated kinin-kallikrein system. ATN-249 is an oral drug that has shown promising results in preclinical and Phase I studies, and good tolerability in the prophylactic treatment of attacks. KVD900 is also an oral agent developed for the on-demand treatment of HAE attacks. It has shown positive results in Phase I/II studies, with rapid absorption. The third drug, IONIS-PKKRx, is an antisense oligonucleotide targeting plasma prekallikrein mRNA. It has shown a dose-dependent reduction of plasma prekallikrein levels and proenzyme activation in Phase I/II studies, and has shown promising results. STAR-0215 is a long acting anti-activated kallikrein monoclonal antibody. A Phase 1a single ascending dose trial evaluated its safety, pharmacokinetics, and pharmacodynamics. Lastly, NTLA-2002 is an investigational gene-editing therapy.

EXPERT OPINION

The targeted treatment of the dysregulated kinin-kallikrein system with specific inhibitors is promising for the prevention of angioedema attacks. Ongoing phase III studies will provide further insight into the efficacy and long-term safety of these novel therapies, potentially expanding treatment options for HAE treatment.

Imbalance Between Angiotensin II and Kallikrein in Patients With ST-Segment Elevation Myocardial Infarction: A Case-Control Emergency Room Study

The present study aimed to investigate the balance between angiotensin II (Ang-II) and kallikrein (KLK1) in the pathogenesis of ST-segment elevation acute myocardial infarction (STEMI). The study included a total of 261 participants: 151 STEMI patients and 110 individuals with normal coronary arteries. The plasma levels of Ang-II and KLK1 were measured using enzyme-linked immunosorbent assays (ELISA). Multivariate logistic regression analysis indicated that the plasma levels of Ang-II, KLK1 and the ratio of Ang-II and KLK1 (Ang-II/KLK1) independently correlated with the presence of STEMI. Furthermore, we found independent associations between STEMI and smoking, cholesterol (CHO), high-density lipoprotein cholesterol (HDL-c), as well as age. The ratio of Ang-II/KLK1 correlated with the plasma level of the inflammatory cytokine, interleukin-6 (IL-6). Both Ang-II and KLK1 levels are significantly elevated in patients with STEMI. An increased Ang-II/KLK1 ratio may result in the over-activation of Ang-II and exacerbate the progression of STEMI(P = .046). In conclusion, we have demonstrated, for the first time, an Ang-II and KLK1 imbalance in patients with STEMI.

Berotralstat in hereditary angioedema due to C1 inhibitor deficiency: first real-world evidence from a Canadian center

Background

Hereditary angioedema due to C1 inhibitor deficiency is a rare genetic condition that causes recurrent swelling with consequent functional impairment and decreased quality of life. Long-term prophylaxis (LTP) to prevent angioedema episodes is a key component of disease management. Berotralstat, an oral, once-daily plasma kallikrein inhibitor, was approved for LTP by Health Canada in 2022.

Methods

We conducted a retrospective, real-world study investigating the effectiveness and adverse effects of berotralstat. Data on angioedema frequency, disease control, and adverse events were tabulated. Patient satisfaction with treatment was scored on a 5-point Likert scale, with 1 representing very unsatisfied and 5 representing very satisfied with therapy.

Results

From June, 2022 and May, 2023, 8 patients with HAE type 1 or type 2 received berotralstat. Effectiveness data were available for 7 patients who continued the drug for at least 3 months, 4 of whom switched to berotralstat from plasma-derived C1 inhibitor LTP. In these 7 patients, the average number of attacks per month decreased from 3.3 to 1.6 (p<0.05), representing a ~52% reduction in attack frequency. Median angioedema control test score numerically improved from 8 to 13 (p=0.0781). Of the 8 patients who received berotralstat, 3 reported no adverse effects and 5 experienced gastrointestinal side effects, which were mild and transient in 3 and led to discontinuation in 1. Average treatment satisfaction was between satisfied and very satisfied at 4.3.

Conclusion

Berotralstat is an effective agent for long-term prophylaxis in HAE. Most patients experienced no adverse effects or mild, transient gastrointestinal symptoms.

Proteolytic Activation of the Epithelial Sodium Channel (ENaC): Its Mechanisms and Implications

Epithelial sodium channel (ENaC) are integral to maintaining salt and water homeostasis in various biological tissues, including the kidney, lung, and colon. They enable the selective reabsorption of sodium ions, which is a process critical for controlling blood pressure, electrolyte balance, and overall fluid volume. ENaC activity is finely controlled through proteolytic activation, a process wherein specific enzymes, or proteases, cleave ENaC subunits, resulting in channel activation and increased sodium reabsorption. This regulatory mechanism plays a pivotal role in adapting sodium transport to different physiological conditions. In this review article, we provide an in-depth exploration of the role of proteolytic activation in regulating ENaC activity. We elucidate the involvement of various proteases, including furin-like convertases, cysteine, and serine proteases, and detail the precise cleavage sites and regulatory mechanisms underlying ENaC activation by these proteases. We also discuss the physiological implications of proteolytic ENaC activation, focusing on its involvement in blood pressure regulation, pulmonary function, and intestinal sodium absorption. Understanding the mechanisms and consequences of ENaC proteolytic activation provides valuable insights into the pathophysiology of various diseases, including hypertension, pulmonary disorders, and various gastrointestinal conditions. Moreover, we discuss the potential therapeutic avenues that emerge from understanding these mechanisms, offering new possibilities for managing diseases associated with ENaC dysfunction. In summary, this review provides a comprehensive discussion of the intricate interplay between proteases and ENaC, emphasizing the significance of proteolytic activation in maintaining sodium and fluid balance in both health and disease.

Human plasma kallikrein: roles in coagulation, fibrinolysis, inflammation pathways, and beyond

Human plasma kallikrein (PKa) is obtained by activating its precursor, prekallikrein (PK), historically named the Fletcher factor. Human PKa and tissue kallikreins are serine proteases from the same family, having high- and low-molecular weight kininogens (HKs and LKs) as substrates, releasing bradykinin (Bk) and Lys-bradykinin (Lys-Bk), respectively. This review presents a brief history of human PKa with details and recent observations of its evolution among the vertebrate coagulation proteins, including the relations with Factor XI. We explored the role of Factor XII in activating the plasma kallikrein-kinin system (KKS), the mechanism of activity and control in the KKS, and the function of HK on contact activation proteins on cell membranes. The role of human PKa in cell biology regarding the contact system and KSS, particularly the endothelial cells, and neutrophils, in inflammatory processes and infectious diseases, was also approached. We examined the natural plasma protein inhibitors, including a detailed survey of human PKa inhibitors' development and their potential market.

Mechanisms involved in hereditary angioedema with normal C1-inhibitor activity

Patients with the inherited disorder hereditary angioedema (HAE) suffer from episodes of soft tissue swelling due to excessive bradykinin production. In most cases, dysregulation of the plasma kallikrein-kinin system due to deficiency of plasma C1 inhibitor is the underlying cause. However, at least 10% of HAE patients have normal plasma C1 inhibitor activity levels, indicating their syndrome is the result of other causes. Two mutations in plasma protease zymogens that appear causative for HAE with normal C1 inhibitor activity have been identified in multiple families. Both appear to alter protease activity in a gain-of-function manner. Lysine or arginine substitutions for threonine 309 in factor XII introduces a new protease cleavage site that results in formation of a truncated factor XII protein (Δ-factor XII) that accelerates kallikrein-kinin system activity. A glutamic acid substitution for lysine 311 in the fibrinolytic protein plasminogen creates a consensus binding site for lysine/arginine side chains. The plasmin form of the variant plasminogen cleaves plasma kininogens to release bradykinin directly, bypassing the kallikrein-kinin system. Here we review work on the mechanisms of action of the FXII-Lys/Arg309 and Plasminogen-Glu311 variants, and discuss the clinical implications of these mechanisms.

Genetic Ablation and Pharmacological Blockade of Bradykinin B1 Receptor Unveiled a Detrimental Role for the Kinin System in Chagas Disease Cardiomyopathy

Chagas disease, the parasitic infection caused by Trypanosoma cruzi, afflicts about 6 million people in Latin America. Here, we investigated the hypothesis that T. cruzi may fuel heart parasitism by activating B1R, a G protein-coupled (brady) kinin receptor whose expression is upregulated in inflamed tissues. Studies in WT and B1R^-/- mice showed that T. cruzi DNA levels (15 days post infection-dpi) were sharply reduced in the transgenic heart. FACS analysis revealed that frequencies of proinflammatory neutrophils and monocytes were diminished in B1R^-/- hearts whereas CK-MB activity (60 dpi) was exclusively detected in B1R^+/+ sera. Since chronic myocarditis and heart fibrosis (90 dpi) were markedly attenuated in the transgenic mice, we sought to determine whether a pharmacological blockade of the des-Arg⁹-bradykinin (DABK)/B1R pathway might alleviate chagasic cardiomyopathy. Using C57BL/6 mice acutely infected by a myotropic T. cruzi strain (Colombian), we found that daily treatment (15-60 dpi) with R-954 (B1R antagonist) reduced heart parasitism and blunted cardiac injury. Extending R-954 treatment to the chronic phase (120-160 dpi), we verified that B1R targeting (i) decreased mortality indexes, (ii) mitigated chronic myocarditis, and (iii) ameliorated heart conduction disturbances. Collectively, our study suggests that a pharmacological blockade of the proinflammatory KKS/DABK/B1R pathway is cardioprotective in acute and chronic Chagas disease.

Peptides Derived from a Plant Protease Inhibitor of the Coagulation Contact System Decrease Arterial Thrombus Formation in a Murine Model, without Impairing Hemostatic Parameters

Several plant protein inhibitors with anticoagulant properties have been studied and characterized, including the Delonix regia trypsin inhibitor (DrTI). This protein inhibits serine proteases (trypsin) and enzymes directly involved in coagulation, such as plasma kallikrein, factor XIIa, and factor XIa. In this study, we evaluated the effects of two new synthetic peptides derived from the primary sequence of DrTI in coagulation and thrombosis models to understand the mechanisms involved in the pathophysiology of thrombus formation as well as in the development of new antithrombotic therapies. Both peptides acted on in vitro hemostasis-related parameters, showing promising results, prolonging the Partially Activated Thromboplastin Time (aPTT) and inhibited platelet aggregation induced by adenosine diphosphate (ADP) and arachidonic acid. In murine models, for arterial thrombosis induced by photochemical injury, and platelet-endothelial interactions monitored by intravital microscopy, both peptides at doses of 0.5 mg/kg significantly extended the time of artery occlusion and modified the platelet adhesion and aggregation pattern with no changes in bleeding time, demonstrating the high biotechnological potential of both molecules.

Safety Aspects and Rational Use of Lanadelumab Injections in the Treatment of Hereditary Angioedema (HAE): Clinical Insights

Hereditary angioedema (HAE) is a rare genetic disorder characterized by recurrent episodes of skin/mucosal swelling, and/or attacks of severe abdominal pain when it affects the gastrointestinal tract. The disease might be unexpectedly fatal when the upper airways are compromised. HAE clinical presentation, disease course and prognosis are associated with significant disease burden and severely impaired quality of life. Lanadelumab is a breakthrough therapy for the prevention of attacks in HAE type 1 and 2 patients. This revolutionary approach to administer a single subcutaneous injection (once every two to four weeks) and achieve complete disease control has dramatically improved patient care resulting in significant change in the life of affected families. Current data support the drug's tolerability in adult and adolescent patients without notable safety concerns in both clinical research and real-world settings. Rational use of prophylactic treatments of HAE searches for a socio-economic balance, taking into account the life-long course of the disease, the public health funds who pay the monetary price, and the patients who might need to receive the therapy for a period longer than investigated during the development program. In this review, we address the current evidence on lanadelumab's tolerability, highlighting aspects of the drug's rationale use in clinical practice. Further studies need to investigate whether this therapy might be appropriate in other forms of angioedema, such as idiopathic primary angioedema and HAE with normal C1 inhibitor. Future efforts must focus to improve modern drugs' accessibility in more countries. Although modern prophylactic options lessen the risk of fatal laryngeal attacks, patients must be equipped with reliable on-demand therapies and be trained how to use them as such a risk cannot be fully diminished with potentially life-threatening attacks occurring even in subjects with successful and stable long-term prophylaxis. Notwithstanding, further studies are needed to identify early responders from non-responders and develop therapies for the latter.

Blocking domain 6 of high molecular weight kininogen to understand intrinsic clotting mechanisms

Background

The contact system is initiated by factor (F) XII activation and the assembly of high molecular weight kininogen (HK) with either FXI or prekallikrein (PK) on a negatively charged surface. Overactivation of this system contributes to thrombosis and inflammation in numerous diseases. To develop effective therapeutics for contact system disorders, a detailed understanding of this pathway is needed.

Methods

We performed coagulation assays in normal human plasma and various factor‐deficient plasmas. To evaluate how HK‐mediated PK and FXI activation contributes to coagulation, we used an anti‐HK antibody to block access to domain 6 of HK, the region required for efficient activation of PK and FXI.

Results

FXI's binding to HK and its subsequent activation by activated FXII contributes to coagulation. We found that the 3E8 anti‐HK antibody can inhibit the binding of FXI or PK to HK, delaying clot formation in human plasma. Our data show that in the absence of FXI, however, PK can substitute for FXI in this process. Addition of activated FXI (FXIa) or activated PK (PKa) abolished the inhibitory effect of 3E8. Moreover, the requirement of HK in intrinsic coagulation can be largely bypassed by adding FXIa. Like FXIa, exogenous PKa shortened the clotting time in HK‐deficient plasma, which was not due to feedback activation of FXII.

Conclusions

This study improves our understanding of HK‐mediated coagulation and provides an explanation for the absence of bleeding in HK‐deficient individuals. 3E8 specifically prevented HK‐mediated FXI activation; therefore, it could be used to prevent contact activation‐mediated thrombosis without altering hemostasis.

Emerging drugs for the treatment of hereditary angioedema due to C1-inhibitor deficiency

INTRODUCTION

Hereditary angioedema due to C1-inhibitor (C1-INH-HAE) is a rare disease characterized by unpredictable swelling attacks that may be life-threatening when affecting the upper airways. Understanding the pathophysiology of HAE and the mechanism of bradykinin-mediated angioedema allowed the development of new therapies for the treatment of HAE: clinical trials are ongoing to expand the number of drugs available for on-demand treatment and prophylaxis.

AREAS COVERED

Authors discuss the products that have been used to treat this disease for many years and present the most recently marketed products and those which are under development.

EXPERT OPINION

Significant therapeutic progress has been made in HAE. In particular, drugs targeting specific molecules involved in the angioedema formation were developed and studies with new drugs are ongoing. In the coming years, more effective therapies with easier administration route options for on-demand treatment and long-term prophylaxis will be available to treat this disease and the variety of patients. Gene therapy strategies may offer a definitive treatment. High costs of current and new drugs may be a limiting factor for their availability, especially in developing countries.

Involvement of kallikrein-PAR2-proinflammatory pathway in severe trastuzumab-induced cardiotoxicity

Trastuzumab‐induced cardiotoxicity interferes with continued treatment in approximately 10% of patients with ErbB2‐positive breast cancer, but its mechanism has not been fully elucidated. In this study, we recruited trastuzumab‐treated patients with ≥30% reduction in left ventricular ejection fraction (SP) and noncardiotoxic patients (NP). From each of these patients, we established three cases of induced pluripotent stem cell‐derived cardiomyocytes (pt‐iPSC‐CMs). Reduced contraction and relaxation velocities following trastuzumab treatment were more evident in SP pt‐iPSC‐CMs than NP pt‐iPSC‐CMs, indicating the cardiotoxicity phenotype could be replicated. Differences in ATP production, reactive oxygen species, and autophagy activity were observed between the two groups. Analysis of transcripts revealed enhanced kallikrein5 expression and pro‐inflammatory signaling pathways, such as interleukin‐1β, in SP pt‐iPSC‐CMs after trastuzumab treatment. The kallilkrein5‐protease‐activated receptor 2 (PAR2)‐MAPK signaling pathway was more activated in SP pt‐iPSC‐CMs, and treatment with a PAR2‐antagonist suppressed interleukin‐1β expression. Our data indicate enhanced pro‐inflammatory responses through kallikrein5‐PAR2 signaling and vulnerability to external stresses appear to be the cause of trastuzumab‐induced cardiotoxicity in SP.

Omalizumab is not just an anti-immunoglobulin E

INTRODUCTION AND PURPOSE

The mechanism of omalizumab in urticaria is not literally known. Omalizumab may affect receptors on the mast cell surface in other ways, especially other than Fc epsilon RI.

MATERIALS AND METHODS

Thirty patients who were treated with omalizumab with the diagnosis of chronic urticaria were included in the study. For serum vasoactive intestinal peptide (VIP), kallikrein (KAL), and substance p (SP) values, 5 mL of blood was taken from the patients. These bloods were centrifuged for 5 min and stored at -80° until the levels were measured. The changes in values measured at baseline, third month, and sixth month were analyzed by Friedman test. A value of p < 0.05 was considered statistically significant results.

RESULTS

While SP, KAL, and VIP values increased continuously, it was observed that the D-dimer value decreased.

CONCLUSION

This study shows that omalizumab can affect mast cells other than IgE. To the best of our knowledge, this is the first study to show the relationship between omalizumab and VIP.

Both plasma basic carboxypeptidases, carboxypeptidase B2 and carboxypeptidase N, regulate vascular leakage activity in mice

BACKGROUND

Kallikrein is generated when the contact system is activated, subsequently cleaving high molecular weight kininogen to bradykinin (BK). BK binds to bradykinin receptor 2, causing vascular leakage. BK is inactivated by proteolysis by the plasma carboxypeptidase B2 and N (CPB2 and CPN). CPN is constitutively active but CPB2 is generated from its zymogen, proCPB2.

OBJECTIVES

Determine the role of CPB2 and CPN in the regulation of vascular leakage.

METHODS

Mice deficient in CPB2, CPN, or both (Cpb2-/- , Cpn-/- , and Cpb2-/- /Cpn-/- ) were compared with wild-type mice (WT) in a model of vascular leakage caused by skin irritation. In some experiments, mice were pretreated with antibodies that prevent activation of proCPB2.

RESULTS

Skin irritation increased vascular leakage most in Cpb2-/- /Cpn-/- , less in Cpb2-/- and Cpn-/- , and least in WT mice. There was no difference in vascular leakage without the challenge. Antibodies inhibiting activation of proCPB2 by plasmin, but not by the thrombin/thrombomodulin complex, increased vascular leakage to the level seen in Cpb2-/- mice. There was no change in levels of markers of coagulation and fibrinolysis.

CONCLUSIONS

Bradykinin is inactivated by both CPB2 and CPN independently. Plasmin is the activator of proCPB2 in this model. Mice lacking both plasma carboxypeptidases have more vascular leak than those lacking either alone. Although BK levels were not determined, BK is the likely substrate for CPB2 and CPN in this model.

Reviewing clinical considerations and guideline recommendations of C1 inhibitor prophylaxis for hereditary angioedema

BACKGROUND

Hereditary angioedema (HAE), a rare disease that is characterized by painful and recurring non-allergic swelling episodes, is caused by the deficiency or dysfunction of C1 inhibitor (C1INH) protein. A comprehensive HAE management plan may require long-term prophylaxis (LTP) in addition to on-demand treatment to help "normalize" patients' lives so that they may fully engage in work, school, family, and leisure activities.

AIM

The main objective of this narrative review is to provide an overview of updated guideline recommendations specific to LTP of HAE and discuss clinical considerations and pharmacologic management options, with a focus on C1INH.

MATERIALS AND METHODS

The authors reviewed relevant HAE literature for current recommendations regarding LTP and the role of C1NH.

RESULTS

Acute HAE attacks are treated with on-demand medication; however, there is a consensus that LTP should routinely be considered for risk reduction and prevention of future episodes. The 2017 World Allergy Organization/European Academy of Allergy and Clinical Immunology guidelines recommend that all patients with HAE be evaluated for LTP routinely and the 2020 HAE Association (HAEA) guidelines emphasize that the decision to use LTP should not be based on rigid criteria, but rather should be based on individual patient needs. Both guidelines recommend C1INH as first-line/preferred therapy for LTP in a range of patient types including adults, children/adolescents, and pregnant/lactating patients. The HAEA also recommends the kallikrein inhibitor, lanadelumab, as a first-line option for LTP. HAE pathway-specific agents for LTP have not been associated with notable safety concerns.

DISCUSSION

Plasma-derived C1INH has been available for 40+ years in Europe and impacts multiple targets within the HAE pathway. C1INH has been used for on-demand treatment and LTP. A subcutaneous formulation of plasma-derived C1INH is approved for LTP and produces functional C1INH activity levels consistently above the threshold needed for protection from HAE attacks. Other pathway-specific options for LTP include the plasma kallikrein inhibitors, lanadelumab-flyo and berotralstat, approved for adults and pediatric patients aged ≥12 years. C1INH is approved for adults and pediatric patients aged ≥6 years.

CONCLUSION

Assessing the need for LTP is vital in the ongoing dialogue between clinicians and patients, as both disease-related factors and patient preferences may change over time. Among available options for LTP, plasma-derived C1INH is the broadly recommended first-line option for LTP in patients with HAE, including pregnant/lactating women and pediatric patients (≥6 years).

Kallikrein augments the anticoagulant function of the protein C system in thrombin generation

BACKGROUND

Genetics play a significant role in coagulation phenotype and venous thromboembolism risk. Resistance to the anticoagulant activated protein C (APC) is an established risk for thrombosis. Herein, we explored the genetic determinants of thrombin generation (TG) and thrombomodulin (TM)-modulated TG using plasma from the Human Functional Genomics Project.

METHODS

Calibrated TG was measured both in absence and presence of TM using tissue factor as trigger. Genetic determinants of TG parameters and protein C pathway function were assessed using genome-wide single-nucleotide polymorphism (SNP) genotyping. Plasma samples were supplemented with purified apolipoprotein A-IV, prekallikrein, or kallikrein to test their influence on the anticoagulant function of TM and APC in TG.

RESULTS

Thrombin generation data from 392 individuals were analyzed. Genotyping showed that the KLKB1 gene (top SNP: rs4241819) on chromosome 4 was associated with the normalized sensitivity ratio of endogenous thrombin potential to TM at genome-wide level (nETP-TMsr, P = 4.27 × 10-8 ). In vitro supplementation of kallikrein, but not prekallikrein or apolipoprotein A-IV, into plasma dose-dependently augmented the anticoagulant effect of TM and APC in TG. Variations of rs4241819 was not associated with the plasma concentration of prekallikrein. Association between rs4241819 and nETP-TMsr was absent when TG was measured in presence of a contact pathway inhibitor corn trypsin inhibitor.

CONCLUSIONS

Our results suggest that kallikrein plays a role in the regulation of the anticoagulant protein C pathway in TG, which may provide a novel mechanism for the previously observed association between the KLKB1 gene and venous thrombosis.

Serum proteases prevent bacterial biofilm formation: role of kallikrein and plasmin

Biofilm formation is a general strategy for bacterial pathogens to withstand host defense mechanisms. In this study, we found that serum proteases inhibit biofilm formation by Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilus influenzae, and Bordetella pertussis. Confocal laser-scanning microscopy analysis revealed that these proteins reduce the biomass and alter the architecture of meningococcal biofilms. To understand the underlying mechanism, the serum was fractionated through size-exclusion chromatography and anion-exchange chromatography, and the composition of the fractions that retained anti-biofilm activity against N. meningitidis was analyzed by intensity-based absolute quantification mass spectrometry. Among the identified serum proteins, plasma kallikrein (PKLK), FXIIa, and plasmin were found to cleave neisserial heparin-binding antigen and the α-peptide of IgA protease on the meningococcal cell surface, resulting in the release of positively charged polypeptides implicated in biofilm formation by binding extracellular DNA. Further experiments also revealed that plasmin and PKLK inhibited biofilm formation of B. pertussis by cleaving filamentous hemagglutinin. We conclude that the proteolytic activity of serum proteases toward bacterial adhesins involved in biofilm formation could constitute a defense mechanism for the clearance of pathogens.

Cleavage of the vaspin N-terminus releases cell-penetrating peptides that affect early stages of adipogenesis and inhibit lipolysis in mature adipocytes

Vaspin expression and function is related to metabolic disorders and comorbidities of obesity. In various cellular and animal models of obesity, diabetes and atherosclerosis vaspin has shown beneficial, protective and/or compensatory action. While testing proteases for inhibition by vaspin, we noticed specific cleavage within the vaspin N-terminus and sequence analysis predicted cell-penetrating activity for the released peptides. These findings raised the question whether these proteolytic peptides exhibit biological activity.

We synthesized various N-terminal vaspin peptides to investigate cell-penetrating activity and analyse uptake mechanisms. Focusing on adipocytes, we performed microarray analysis and functional assays to elucidate biological activities of the vaspin–derived peptide, which is released by KLK7 cleavage (vaspin residues 21-30; VaspinN). Our study provides first evidence that proteolytic processing of the vaspin N-terminus releases cell-penetrating and bioactive peptides with effects on adipocyte biology. The VaspinN peptide increased preadipocyte proliferation, interfered with clonal expansion during the early stage of adipogenesis and blunted adrenergic cAMP-signalling, downstream lipolysis as well as insulin signalling in mature adipocytes.

Protease-mediated release of functional N-terminal peptides presents an additional facet of vaspin action. Future studies will address the mechanisms underlying the biological activities and clarify, if vaspin-derived peptides may have potential as therapeutic agents for the treatment of metabolic diseases.

Kinins and Kinin Receptors in Cardiovascular and Renal Diseases

This review addresses the physiological role of the kallikrein–kinin system in arteries, heart and kidney and the consequences of kallikrein and kinin actions in diseases affecting these organs, especially ischemic and diabetic diseases. Emphasis is put on pharmacological and genetic studies targeting kallikrein; ACE/kininase II; and the two kinin receptors, B1 (B1R) and B2 (B2R), distinguished through the work of Domenico Regoli and his collaborators. Potential therapeutic interest and limitations of the pharmacological manipulation of B1R or B2R activity in cardiovascular and renal diseases are discussed. This discussion addresses either the activation or inhibition of these receptors, based on recent clinical and experimental studies.

Exogenous pancreatic kininogenase protects against renal fibrosis in rat model of unilateral ureteral obstruction

Tissue kallikrein has protective function against various types of injury. In this study, we investigated whether exogenous pancreatic kininogenase (PK) conferred renoprotection in a rat model of unilateral ureteral obstruction (UUO) and H₂O₂-treated HK-2 cells in vitro. SD rats were subjected to UUO surgery, then PK (7.2 U/g per day, ip) was administered for 7 or 14 days. After the treatment, rats were euthanized; the obstructed kidneys were harvested for further examination. We found that PK administration significantly attenuated interstitial inflammation and fibrosis, and downregulated the expression of proinflammatory (MCP-1, TLR-2, and OPN) and profibrotic (TGF-β1 and CTGF) cytokines in obstructed kidney. UUO-induced oxidative stress, closely associated with excessive apoptotic cell death and autophagy via PI3K/AKT/FoxO1a signaling, which were abolished by PK administration. We further showed that PK administration increased the expression of bradykinin receptors 1 and 2 (B1R and B2R) mRNA and the production of NO and cAMP in kidney tissues. Coadministration with either B1R antagonist (des-Arg9-[Leu8]-bradykinin) or B2R antagonist (icatibant) abrogated the renoprotective effects of PK, and reduced the levels of NO and cAMP in obstructed kidney. In H₂O₂-treated HK-2 cells, addition of PK (6 pg/mL) significantly decreased ROS production, regulated the expression of oxidant and antioxidant enzymes, suppressed the expression of TGF-β1 and MCP-1, and inhibited cell apoptosis. Our data demonstrate that PK treatment protects against the progression of renal fibrosis in obstructed kidneys.

Development of an updated assay for prekallikrein activator in albumin and immunoglobulin therapeutics

Background

Prekallikrein activator (PKA) is a contaminating enzyme found in therapeutic albumin and immunoglobulin products. The level is commonly measured using methods such as that defined by the European Pharmacopoeia (Ph Eur) with traceability to the WHO International Standard for PKA. This method generally works well, but problems are sometimes observed.

Materials and methods

A simplified one‐step method has been developed to replace the existing Ph Eur two‐step method which consists of kallikrein generation followed by kallikrein measurement using a chromogenic substrate. Analysis of data from the one‐stage method is simplified by the use of a dedicated online app.

Results

The one‐stage method was validated against the current Ph Eur method using batches of albumin and immunoglobulins. Problem batches of immunoglobulins were investigated using the one‐stage method. Improved methodology using true initial rate determinations and use of acid‐treated prekallikrein substrate (PKS) helped understand and reduce artefactual results.

Conclusions

The one‐stage method and associated app streamline real‐time determination of PKA and promote good principles of enzyme assays to limit substrate depletion, while also conserving expensive PKS. Blanking steps and reproducibility are simplified.

Screening of chemical libraries in pursuit of kallikrein-5 specific inhibitors for the treatment of inflammatory dermatoses

Background Aberrant kallikrein activity is observed in a number of inflammatory dermatoses. Up-regulation of kallikrein-5 (KLK5) activity leads to uncontrolled skin desquamation and cleavage of proteinase-activated receptor-2 (PAR2), causing the release of pro-inflammatory cytokines and disruption of epidermal barrier function. This study aimed to identify KLK5-specific small molecule inhibitors which can serve as the foundation of a novel therapeutic for inflammatory skin disorders. Methods Five chemical libraries (13,569 compounds total) were screened against recombinant KLK5 using a fluorogenic enzymatic assay. Secondary validation was performed on the top 22 primary hits. All hits were docked in the KLK5 crystal structure to rationalize their potential interactions with the protein. Results A naturally occurring compound derived from the wood of Caesalpinia sappan (Brazilin) was identified as a novel KLK5 inhibitor (IC50: 20 μM, Ki: 6.4 μM). Docking suggests that the phenolic moiety of Brazilin binds in the S1-pocket of KLK5 and forms a H-bond with S195 side chain. KLK14 was also found to be susceptible to inhibition by Brazilin with a calculated IC50 value of 14.6 μM. Conclusions Natural KLK5 small molecule inhibitors such as Brazilin, are ideal for topical skin disease drug design and remain a promising therapeutic for severe cases of inflammatory skin disorders. Optimized KLK inhibitors may have increased efficacy as therapeutics and warrant further investigation.

Biophysical characteristics of dandruff-affected scalp categorized on the basis of sebum levels

BACKGROUND

Various sebum levels can be detected in dandruff-affected scalps. However, few studies have compared the biophysical characteristics of dandruff scalps categorized based on sebum levels.

AIMS

To investigate and compare the biophysical characteristics of dandruff-affected scalps categorized based on sebum levels.

METHODS

Fifty-four Korean women with dandruff and 30 healthy Korean women underwent physiological measurements, including evaluation of sebum and hydration levels, pH, and transepidermal water loss (TEWL) in the scalp. The levels of the biomarkers of interleukin-8 (IL-8) and kallikrein 5 (KLK5) and corneodesmosomes were investigated in the stratum corneum (SC) of the scalp.

RESULTS

Dandruff was categorized as dry (low-sebum, n = 25) or oily (high-sebum, n = 29) based on a sebum cutoff level of 97.82 μg/cm² . Both dry and oily dandruff-affected scalps showed significantly decreased hydration levels and increased pH and TEWL compared with healthy subjects, with hydration levels being lower in dry dandruff-affected scalps. IL-8 expression was significantly increased in the oily dandruff-affected scalp. In addition, both dry and oily dandruff-affected scalps showed significantly increased KLK5 levels in the SC, with the levels being higher in oily dandruff-affected scalps. Altered distribution of corneodesmosomes, present on the entire surface area of the corneocytes, was notable in oily dandruff-affected scalps.

CONCLUSION

The biophysical characteristics of the two types of dandruff represent the influence of different characteristics, including hydration levels, expression of IL-8 and KLK5, and corneodesmosome distribution. Thus, strategies to reduce dandruff levels should differ according to sebum levels.

Protease: Serpin complexes to assess contact system and intrinsic pathway activation

Mounting evidence suggests that a variety of disease states are pathophysiologically related to activation of the contact system in vivo. The plasma contact system is composed of a cascade of serine proteases initiated by surface activation of factor XII, which can then proceed through a procoagulant pathway by activating the intrinsic coagulation factor XI, or a proinflammatory pathway by activating prekallikrein. Serpins are the primary endogenous inhibitors of the contact system, which irreversibly inhibit their respective protease(s), forming a stable complex. We modified an existing assay strategy for detecting these complexes in plasma using ELISAs and determined the effect of preanalytical variation caused by anticoagulant selection and processing time. The assays were sensitive and specific to inherited deficiency of individual contact factors. We conclude that these assays are robust and represent a relatively simple approach to the assessment of contact factor activation in plasma samples.

Diabetes-induced upregulation of kallistatin levels exacerbates diabetic nephropathy via RAS activation

Kallistatin is an inhibitor of tissue kallikrein and also inhibits the Wnt pathway. Its role in diabetic nephropathy (DN) is uncertain. Here we reported that serum kallistatin levels were significantly increased in diabetic patients with DN compared to those in diabetic patients without DN and healthy controls, and positively correlated with urinary albumin excretion. In addition, renal kallistatin levels were significantly upregulated in mouse models of type 1 (Akita, OVE26) and type 2 diabetes (db/db). To unveil the effects of kallistatin on DN and its underlying mechanism, we crossed transgenic mice overexpressing kallistatin with OVE26 mice (KS‐tg/OVE). Kallistatin overexpression exacerbated albuminuria, renal fibrosis, inflammation, and oxidative stress in diabetes. Kallikrein activity was inhibited while the renin‐angiotensin system (RAS) upregulated in the kidney of KS‐tg/OVE mice compared to WT/OVE mice, suggesting a disturbed balance between the RAS and kallikrein‐kinin systems. As shown by immunostaining of endothelial makers, renal vascular densities were decreased accompanied by increased HIF‐1α and erythropoietin levels in the kidneys of KS‐tg/OVE mice. Taken together, high levels of kallistatin exacerbate DN at least partly by inducing RAS overactivation and hypoxia. The present study demonstrated a positive correlation between kallistatin levels and DN, suggesting a potential biomarker for prognosis of DN.

The matriptase-prostasin proteolytic cascade in dermatologic diseases

The proper development and function of skin and hair are dependent on proteolytic activities. Specifically, the matriptase-prostasin cascade is a series of proteolytic reactions in the epidermis integral to normal regulation of desquamation. An increasing amount of research describing this pathway has recently become available, and the importance of this pathway is exhibited by the association of genetic defects in this pathway with human diseases of the skin and hair. Given the relevance of this pathway to dermatology, we provide a review of the current understanding of its relevance to distinct clinical entities, including ichthyosis-hypotrichosis and Netherton syndromes.

Mechanisms of itching in mycosis fungoides: grade of itching correlates with eosinophil infiltration and kallikrein 5 expression

BACKGROUND

Mycosis fungoides (MF) is the most common variant of cutaneous T-cell lymphomas (CTCL). Itching can be a major symptom for patients with CTCL, however, itching associated with MF is not relieved by conventional therapy using anti-histamines, suggesting that histamine is not the main pruritogen. Therefore, the underlying mechanisms of itching in MF patients remain unclear.

OBJECTIVES

To investigate the clinical and histopathological features associated with MF-related itching.

MATERIALS AND METHODS

Skin sections from MF patients and healthy subjects were used for pathophysiological analysis and evaluation of protease activity. These results were compared with the degree of itching.

RESULTS

Of the MF patients, 40% did not report itching and 60% reported itching (moderate itching: 40%; strong itching: 20%). The number of eosinophils, but not mast cells, that infiltrated into skin was increased in the group with strong itching. In the skin of patients, both serine protease activity and immunoreactivity to kallikrein 5 (KLK5), a known itch mediator, increased relative to the grade of itching.

CONCLUSION

These results suggest that KLK5 and eosinophil infiltration may be involved in itching in patients with MF.

Lanadelumab for the treatment of hereditary angioedema

Introduction: Hereditary angioedema due to C1 inhibitor deficiency (C1-INH-HAE) is a rare yet still probably underdiagnosed clinical condition. Recurrent episodes of subcutaneous and sub-mucosal swelling may involve the skin, the gastrointestinal tract or even the upper airways, exposing the patients to the risk of death. With the aim of improving patients' quality of life, the therapeutic scenario has expanded over the years.Areas covered: The focus of the present review is lanadelumab, a fully human, κ-light-chain, monoclonal immunoglobulin G1 against plasma kallikrein, currently approved for long-term prophylaxis of C1-INH-HAE attacks in the USA and Canada and designated as an orphan drug by the European Medicines Agency.Expert opinion: Lanadelumab is able to inhibit plasma kallikrein with high selectivity and affinity. The subsequent phases of drug development and the ongoing open-label trial have proven its safety and efficacy. It overcomes some of the limitations of other drugs available for long-term prophylaxis, given the easy route of administration, the simple administration schedule and the possibility to tailor the treatment to each patient. Further studies are needed to test its efficacy also in other types of angioedema for which a central role of plasma kallikrein is envisaged.

Oral plasma kallikrein inhibitor BCX7353 for treatment of hereditary angioedema

Hereditary angioedema (HAE) is rare disorder caused by a SERPING1 gene mutation that triggers severe swelling of the skin and upper airway. Treatment options for HAE with deficient and dysfunctional C1-inhibitor are expanding to include small-molecule drugs that inhibit protein interactions in the kallikrein-kinin system. Discovered by BioCryst Pharmaceuticals, BCX7353 is a synthetic, once-daily, small molecule drug that can be taken as an oral capsule to treat HAE attacks and for prophylaxis. This article will summarize recent and current BCX7353 clinical trials. Overall, results indicate BCX7353 is a promising form of therapy with a rapid 1 h onset of action, long duration of action, and acceptable tolerance.

Potassium Intake Prevents the Induction of the Renin-Angiotensin System and Increases Medullary ACE2 and COX-2 in the Kidneys of Angiotensin II-Dependent Hypertensive Rats

In angiotensin II (Ang II)-dependent hypertensive rats there is an increased expression of proximal tubule angiotensinogen (AGT), collecting duct renin and angiotensin converting enzyme (ACE), which contributes to intratubular Ang II formation. Ang II acts on Ang II type 1 receptors promoting sodium retention and vasoconstriction. However concurrently, the ACE2-Ang-(1–7) axis and the expression of kallikrein and medullary prostaglandins counteract the effects of Ang II, promoting natriuresis and vasodilation. Human studies demonstrate that dietary potassium (K⁺) intake lowers blood pressure. In this report we evaluate the expression of AGT, ACE, medullary prorenin/renin, ACE2, kallikrein and cyclooxygenase-2 (COX-2) in Ang II-infused rats fed with high K⁺ diet (2%) for 14 days. Dietary K⁺ enhances diuresis in non-infused and in Ang II-infused rats. The rise in systolic blood pressure in Ang II-infused rats was attenuated by dietary K⁺. Ang II-infused rats showed increased renal protein levels of AGT, ACE and medullary prorenin and renin. This effect was attenuated in the Ang II + K⁺ group. Ang II infusion decreased ACE2 compared to the control group; however, K⁺ diet prevented this effect in the renal medulla. Furthermore, medullary COX-2 was dramatically induced by K⁺ diet in non-infused and in Ang II infused rats. Dietary K⁺ greatly increased kallikrein immunostaining in normotensive rats and in Ang II-hypertensive rats. These results indicate that a high K⁺ diet attenuates Ang II-dependent hypertension by preventing the induction of ACE, AGT and collecting duct renin and by enhancing medullary COX-2 and ACE2 protein expression in the kidney.

A review of kallikrein inhibitor lanadelumab in hereditary angioedema

Hereditary angioedema with C1 esterase inhibitor deficiency is a rare disorder characterized by unpredictable swelling of the face, larynx and gastrointestinal tract. Kallikreins are serine proteases that cleave kininogens to produce bradykinin leading to inflammation. A new prophylactic drug is lanadelumab (DX-2930, SHP-643), a recombinant, fully human IgG1 monoclonal antibody kallikrein inhibitor. Pharmacokinetics show a half-life of 14 days with a dose-dependent effect. Completed trials for lanadelumab include two Phase III studies with updated efficacy in preventing angioedema in hereditary angioedema patients. Ongoing data show the safety of the targeted therapy along with less frequent administration requirements. Information on long-term safety is still needed, as well as, further studies on the correlation of subcutaneous administered dosing requirements and severity of side effects.

Endothelial PAI-1 (Plasminogen Activator Inhibitor-1) Blocks the Intrinsic Pathway of Coagulation, Inducing the Clearance and Degradation of FXIa (Activated Factor XI)

Objective- Activation of coagulation FXI (factor XI) by FXIIa (activated factor XII) is a prothrombotic process. The endothelium is known to play an antithrombotic role by limiting thrombin generation and platelet activation. It is unknown whether the antithrombotic role of the endothelium includes sequestration of FXIa (activated factor XI) activity. This study aims to determine the role of endothelial cells (ECs) in the regulation of the intrinsic pathway of coagulation. Approach and Results- Using a chromogenic assay, we observed that human umbilical veins ECs selectively blocked FXIa yet supported kallikrein and FXIIa activity. Western blotting and mass spectrometry analyses revealed that FXIa formed a complex with endothelial PAI-1 (plasminogen activator inhibitor-1). Blocking endothelial PAI-1 increased the cleavage of a chromogenic substrate by FXIa and the capacity of FXIa to promote fibrin formation in plasma. Western blot and immunofluorescence analyses showed that FXIa-PAI-1 complexes were either released into the media or trafficked to the early and late endosomes and lysosomes of ECs. When baboons were challenged with Staphylococcus aureus to induce a prothrombotic phenotype, an increase in circulating FXIa-PAI-1 complex levels was detected by ELISA within 2 to 8 hours postchallenge. Conclusions- PAI-1 forms a complex with FXIa on ECs, blocking its activity and inducing the clearance and degradation of FXIa. Circulating FXIa-PAI-1 complexes were detected in a baboon model of S. aureus sepsis. Although ECs support kallikrein and FXIIa activity, inhibition of FXIa by ECs may promote the clearance of intravascular FXIa. Visual Overview- An online visual overview is available for this article.

Kallikrein-related peptidase 14 is the second KLK protease targeted by the serpin vaspin

Kallikrein-related peptidases KLK5, KLK7 and KLK14 are important proteases in skin desquamation and aberrant KLK activity is associated with inflammatory skin diseases such as Netherton syndrome but also with various serious forms of cancer. Previously, we have identified KLK7 as the first protease target of vaspin (Serpin A12). Here, we report KLK14 as a second KLK protease to be inhibited by vaspin. In conclusion, vaspin represents a multi-specific serpin targeting the kallikrein proteases KLK7 and KLK14, with distinct exosites regulating recognition of these target proteases and opposing effects of heparin binding on the inhibition reaction.

The miRNA-kallikrein interaction: a mosaic of epigenetic regulation in cancer

The kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases with trypsin- and chymotrypsin-like activities. Dysregulated expression and/or aberrant activation of KLKs has been linked to various pathophysiological processes, including cancer. Many KLKs have been identified as potential cancer biomarkers. microRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression by pairing to the 3' untranslated region (UTR) of complimentary mRNA targets. miRNAs are dysregulated in many cancers, including prostate, kidney and ovarian cancers. Several studies have shown that miRNAs are involved in the post-transcriptional regulation of KLKs. However, recent evidence suggests that miRNAs can also act as downstream effectors of KLKs. In this review, we provide an update on the epigenetic regulation of KLKs by miRNAs. We also present recent experimental evidence that supports the regulatory role of KLKs on miRNA networks. The potential diagnostic and therapeutic applications of miRNA-kallikrein interactions are also discussed.

Kallikrein-related peptidase 6 orchestrates astrocyte form and function through proteinase activated receptor-dependent mechanisms

Kallikrein-related peptidase 6 (Klk6) is the most abundant serine proteinase in the adult central nervous system (CNS), yet we know little regarding its physiological roles or mechanisms of action. Levels of Klk6 in the extracellular environment are dynamically regulated in CNS injury and disease positioning this secreted enzyme to affect cell behavior by potential receptor dependent and independent mechanisms. Here we show that recombinant Klk6 evokes increases in intracellular Ca2+ in primary astrocyte monolayer cultures through activation of proteinase activated receptor 1 (PAR1). In addition, Klk6 promoted a condensation of astrocyte cortical actin leading to an elongated stellate shape and multicellular aggregation in a manner that was dependent on the presence of either PAR1 or PAR2. Klk6-evoked changes in astrocyte shape were accompanied by translocation of β-catenin from the plasma membrane to the cytoplasm. These data are exciting because they demonstrate that Klk6 can influence astrocyte plasticity through receptor-dependent mechanisms. Furthermore, this study expands our understanding of the mechanisms by which kallikreins can contribute to neural homeostasis and remodeling and point to both PAR1 and PAR2 as new therapeutic targets to modulate astrocyte form and function.

Evaluation of a crystallographic surrogate for kallikrein 5 in the discovery of novel inhibitors for Netherton syndrome

The inhibition of kallikrein 5 (KLK5) has been identified as a potential strategy for treatment of the genetic skin disorder Netherton syndrome, in which loss-of-function mutations in the SPINK5 gene lead to down-regulation of the endogenous inhibitor LEKTI-1 and profound skin-barrier defects with severe allergic manifestations. To aid in the development of a medicine for this target, an X-ray crystallographic system was developed to facilitate fragment-guided chemistry and knowledge-based drug-discovery approaches. Here, the development of a surrogate crystallographic system in place of KLK5, which proved to be challenging to crystallize, is described. The biochemical robustness of the crystallographic surrogate and the suitability of the system for the study of small nonpeptidic fragments and lead-like molecules are demonstrated.

Tissue kallikrein regulates alveolar macrophage apoptosis early in influenza virus infection

Host cell proteases are involved in influenza pathogenesis. We examined the role of tissue kallikrein 1 (KLK1) by comparing wild-type (WT) and KLK1-deficient mice infected with influenza H3N2 virus. The levels of KLK1 in lung tissue and in bronchoalveolar lavage (BAL) fluid increased substantially during infection. KLK1 did not promote virus infectivity despite its trypsin-like activity, but it did decrease the initial virus load. We examined two cell types involved in the early control of pathogen infections, alveolar macrophages (AMs) and natural killer (NK) cells to learn more about the antiviral action of KLK1. Inactivating the Klk1 gene or treating WT mice with an anti-KLK1 monoclonal antibody to remove KLK1 activity accelerated the initial virus-induced apoptotic depletion of AMs. Intranasal instillation of deficient mice with recombinant KLK1 (rKLK1) reversed the phenotype. The levels of granulocyte-macrophage colony-stimulating factor in infected BAL fluid were significantly lower in KLK1-deficient mice than in WT mice. Treating lung epithelial cells with rKLK1 increased secretion of this factor known to enhance AM resistance to pathogen-induced apoptosis. The recruitment of NK cells to the air spaces peaked 3 days after infection in WT mice but not in KLK1-deficient mice, as did increases in several NK-attracting chemokines (CCL2, CCL3, CCL5, and CXCL10) in BAL. Chronic obstructive pulmonary disease (COPD) patients are highly susceptible to viral infection, and we observed that the KLK1 mRNA levels decreased with increasing COPD severity. Our findings indicate that KLK1 intervenes early in the antiviral defense modulating the severity of influenza infection. Decreased KLK1 expression in COPD patients could contribute to the worsening of influenza.

Imbalance in Renal Vasoactive Enzymes Induced by Mild Hypoxia: Angiotensin-Converting Enzyme Increases While Neutral Endopeptidase Decreases

Chronic hypoxia has been postulated as one of the mechanisms involved in salt-sensitive hypertension and chronic kidney disease (CKD). Kidneys have a critical role in the regulation of arterial blood pressure through vasoactive systems, such as the renin-angiotensin and the kallikrein-kinin systems, with the angiotensin-converting enzyme (ACE) and kallikrein being two of the main enzymes that produce angiotensin II and bradykinin, respectively. Neutral endopeptidase 24.11 or neprilysin is another enzyme that among its functions degrade vasoactive peptides including angiotensin II and bradykinin, and generate angiotensin 1-7. On the other hand, the kidneys are vulnerable to hypoxic injury due to the active electrolyte transportation that requires a high oxygen consumption; however, the oxygen supply is limited in the medullary regions for anatomical reasons. With the hypothesis that the chronic reduction of oxygen under normobaric conditions would impact renal vasoactive enzyme components and, therefore; alter the normal balance of the vasoactive systems, we exposed male Sprague-Dawley rats to normobaric hypoxia (10% O₂) for 2 weeks. We then processed renal tissue to identify the expression and distribution of kallikrein, ACE and neutral endopeptidase 24.11 as well as markers of kidney damage. We found that chronic hypoxia produced focal damage in the kidney, mainly in the cortico-medullary region, and increased the expression of osteopontin. Moreover, we observed an increase of ACE protein in the brush border of proximal tubules at the outer medullary region, with increased mRNA levels. Kallikrein abundance did not change significantly with hypoxia, but a tendency toward reduction was observed at protein and mRNA levels. Neutral endopeptidase 24.11 was localized in proximal tubules, and was abundantly expressed under normoxic conditions, which markedly decreased both at protein and mRNA levels with chronic hypoxia. Taken together, our results suggest that chronic hypoxia produces focal kidney damage along with an imbalance of key components of the renal vasoactive system, which could be the initial steps for a long-term contribution to salt-sensitive hypertension and CKD.

An exploration of bioactive peptides: My collaboration with Ervin G. Erdös

This paper provides a brief historical sketch of the science of biologically active peptides. It also offers the story of how Ervin G. Erdös, a pioneer in the study of metabolism of various peptides, influenced me through collaborations that span many years. I worked in Dr. Erdös's research laboratories in Oklahoma City, Dallas, and Chicago, and we shared research interests through visits across the Atlantic between the former Yugoslavia and the United States. Among other findings, we discovered angiotensin-converting enzyme in the retina, which opened up a new research direction for many scientists interested in serious ocular diseases. This tribute to my mentor paints a portrait of a man who, in addition to his dedication to science and his seminal discoveries about the metabolism of peptides, took the time to invest in training many young scientists. His fine personal qualities explain why all of those who worked with him hold him in such high regard.

Improving the understanding of plasma kallikrein contribution to arterial thrombus formation using two plant protease inhibitors

The purpose of antithrombotic therapy is the prevention of thrombus formation and/or its extension with a minimum risk of bleeding. The inhibition of a variety of proteolytic processes, particularly those of the coagulation cascade, has been reported as a property of plant protease inhibitors. The role of trypsin inhibitors (TIs) from Delonix regia (Dr) and Acacia schweinfurthii (As), members of the Kunitz family of protease inhibitors, was investigated on blood coagulation, platelet aggregation, and thrombus formation. Different from Acacia schweinfurthii trypsin inhibitor (AsTI), Delonix regia trypsin inhibitor (DrTI) is a potent inhibitor of FXIa with a K_iapp of 1.3 × 10^-9 M. In vitro, both inhibitors at 100 µg corresponding to the concentrations of 21 μM and 15.4 μM of DrTI and AsTI, respectively, increased approximately 2.0 times the activated partial thromboplastin time (aPTT) in human plasma compared to the control, likely due to the inhibition of human plasma kallikrein (huPK) or activated factor XI (FXIa), in the case of DrTI. Investigating in vivo models of arterial thrombus formation and bleeding time, DrTI and AsTI, 1.3 µM and 0.96 µM, respectively, prolonged approximately 50% the time for total carotid artery occlusion in mice compared to the control. In contrast to heparin, the bleeding time in mice treated with the two inhibitors did not differ from that of the control group. DrTI and AsTI inhibited 49.3% and 63.8%, respectively, ex vivo murine platelet aggregation induced by adenosine diphosphate (ADP), indicating that these protein inhibitors prevent arterial thrombus formation possibly by interfering with the plasma kallikrein (PK) proteolytic action on the intrinsic coagulation pathway and its ability to enhance the platelet aggregation activity on the intravascular compartment leading to the improvement of a thrombus.

Pericellular regulation of prostate cancer expressed kallikrein-related peptidases and matrix metalloproteinases by cell surface serine proteases

We provide evidence of a pericellular network of proteases that are elevated and co-expressed in prostate cancer. The network involves the membrane bound serine proteases hepsin and TMPRSS2, the secreted kallikrein-related peptidases KLK4 and KLK14, and the secreted matrix metalloproteinases MMP-3 and MMP-9. Western blot analysis of cell lysates, conditioned cell culture media, immunoprecipitates and cell surface proteins, demonstrates a network of interactions centred largely at the plasma membrane, with the Arg/Lys specific proteases hepsin and TMPRSS2 key regulators of the network. Our data demonstrate that like TMPRSS2, hepsin is able to autoactivate. Active hepsin degrades KLK4, generating a cell associated degradation product with corresponding reduction in levels of cell-free KLK4. In contrast hepsin activates KLK14. TMPRSS2 appears to cleave amino terminal to the KLK4 activation site such that it is available for further processing to generate the active KLK4 protease. In contrast with hepsin, TMPRSS2 degrades KLK14. In addition to these direct mechanisms of regulation, hepsin and TMPRSS2 indirectly modulate KLK4 activity by cleaving the KLK4-activating protease MMP-3. Hepsin and TMPRSS2 also activate MMP-9, which similar to MMP-3, associates with the cell surface. Interestingly our data also show that proteolysis occurs between the membrane spanning and catalytic domains of hepsin and TMPRSS2. Hepsin cleavage occurs via an autoproteolytic mechanism, whereas TMPRSS2 cleavage is mediated by KLK14. Hepsin and TMPRSS2 are not shed from the cell surface but proteolysis likely disrupts domains that regulate the proteolytic activity of these proteases. Immunocytochemical analyses demonstrate that hepsin and TMPRSS2 colocalize on the cell surface with the secreted serine proteases KLK4 and KLK14, only in membrane protrusions, suggesting that reciprocal proteolytic interactions occur in defined cellular structures that are important during cancer dissemination for cell migration, invasion and survival. Also of note, immunohistochemical analysis of serial sections of prostate tumor demonstrated significant overlapping expression of the six proteases in vivo. Collectively these data suggest the possibility that the novel proteolytic network identified by us, will be most important during active dissemination of prostate cancers, and that its disruption could inhibit metastasis.

Gene therapy for hypertension

INTRODUCTION

The control of hypertension and the resulting cardiovascular events is still insufficient. Thus, the search for novel means for blood pressure (BP) reduction remains worth further clinical and research attention. The advances in vector and construct design sketch the use of gene therapy in hypertension. Areas covered: We have searched for studies using gene therapy in hypertension reporting BP outcomes. We have identified 63 experimental studies demonstrating feasible targeting of the classical and new renin-angiotensin-aldosterone system, β1-adrenergic receptor, NO-cGMP axis, endothelin, natriuretic peptides, kallikrein system, cytochrome P-450 hydroxylase, oncogenes, growth factors, interleukins, angiopoietin-1, adrenomedullin or Klotho in small rodents. Expert opinion: The usual BP reduction was by 10-30 mmHg for up to several months. Some studies reported target organ damage attenuation or even survival prolongation. However, the concept did not reach the clinical phase, in contrast to other cardiovascular conditions. Increased gene transfection efficacy necessary for a systemic treatment, personalized identification of the implied aetiology from the multifactorial background and evidence from larger mammals are required for gene therapy to compete with the broad spectrum of current therapeutic options in hypertension. Until then, in the field of hypertension, gene modulation will provide a valuable research tool.

Modulation of the Plasma Kallikrein-Kinin System Proteins Performed by Heparan Sulfate Proteoglycans

Human plasma kallikrein-kinin system proteins are related to inflammation through bradykinin. In the proximity of its target cells, high molecular weight kininogen (H-kininogen) is the substrate of plasma kallikrein, which releases bradykinin from H-kininogen. Heparan sulfate proteoglycans (HSPGs) play a critical role in either recruiting kinin precursors from the plasma, or in the assembly of kallikrein-kinin system components on the cell surface. Furthermore, HSPGs mediate the endocytosis and activation of H-kininogen and plasma prekallikrein. In the presence of HSPGs (Chinese hamster ovary cell, CHO-K1, wild type cells) both heparin and heparan sulfate strongly inhibit the H-kininogen interaction with the cell membrane. H-kininogen is internalized in endosomal acidic vesicles in CHO-K1 but not in CHO-745 cells (mutant cells deficient in glycosaminoglycan biosynthesis). The endocytosis process is lipid raft-mediated and is dependent on caveolae. Both types of CHO cells do not internalize bradykinin-free H-kininogen. At pH 7.35, bradykinin is released from H-kininogen on the surface of CHO-745 cells only by serine proteases; however, in CHO-K1 cells either serine or cysteine proteases are found to be involved. The CHO-K1 cell lysate contains different kininogenases. Plasma prekallikrein endocytosis in CHO-K1 cells is independent of H-kininogen, and also prekallikrein is not internalized by CHO-745 cells. Plasma prekallikrein cleavage/activation is independent of glycosaminoglycans but plasma kallikrein formation is more specific on H-kininogen assembled on the cell surface through glycosaminoglycans. In this mini-review, the importance of HSPGs in the regulation of plasma kallikrein-kinin system proteins is shown.

Mast Cell Coupling to the Kallikrein-Kinin System Fuels Intracardiac Parasitism and Worsens Heart Pathology in Experimental Chagas Disease

During the course of Chagas disease, infectious forms of Trypanosoma cruzi are occasionally liberated from parasitized heart cells. Studies performed with tissue culture trypomastigotes (TCTs, Dm28c strain) demonstrated that these parasites evoke neutrophil/CXCR2-dependent microvascular leakage by activating innate sentinel cells via toll-like receptor 2 (TLR2). Upon plasma extravasation, proteolytically derived kinins and C5a stimulate immunoprotective Th1 responses via cross-talk between bradykinin B2 receptors (B2Rs) and C5aR. Awareness that TCTs invade cardiovascular cells in vitro via interdependent activation of B2R and endothelin receptors [endothelin A receptor (ET_AR)/endothelin B receptor (ET_BR)] led us to hypothesize that T. cruzi might reciprocally benefit from the formation of infection-associated edema via activation of kallikrein-kinin system (KKS). Using intravital microscopy, here we first examined the functional interplay between mast cells (MCs) and the KKS by topically exposing the hamster cheek pouch (HCP) tissues to dextran sulfate (DXS), a potent "contact" activator of the KKS. Surprisingly, although DXS was inert for at least 30 min, a subtle MC-driven leakage resulted in factor XII (FXII)-dependent activation of the KKS, which then amplified inflammation via generation of bradykinin (BK). Guided by this mechanistic insight, we next exposed TCTs to "leaky" HCP-forged by low dose histamine application-and found that the proinflammatory phenotype of TCTs was boosted by BK generated via the MC/KKS pathway. Measurements of footpad edema in MC-deficient mice linked TCT-evoked inflammation to MC degranulation (upstream) and FXII-mediated generation of BK (downstream). We then inoculated TCTs intracardiacally in mice and found a striking decrease of parasite DNA (quantitative polymerase chain reaction; 3 d.p.i.) in the heart of MC-deficient mutant mice. Moreover, the intracardiac parasite load was significantly reduced in WT mice pretreated with (i) cromoglycate (MC stabilizer) (ii) infestin-4, a specific inhibitor of FXIIa (iii) HOE-140 (specific antagonist of B2R), and (iv) bosentan, a non-selective antagonist of ET_AR/ET_BR. Notably, histopathology of heart tissues from mice pretreated with these G protein-coupled receptors blockers revealed that myocarditis and heart fibrosis (30 d.p.i.) was markedly and redundantly attenuated. Collectively, our study suggests that inflammatory edema propagated via activation of the MC/KKS pathway fuels intracardiac parasitism by generating infection-stimulatory peptides (BK and endothelins) in the edematous heart tissues.

New Tools to Study Contact Activation

The recent availability of a sensitive chromogenic method approach for determination of FXIa activity has been explored for designing sensitive methods for FXIIa and kallikrein, both using FXa formation as the read-out. For both enzymes the assay range 1–10 nmol/L provides a resolution of about 0.8 absorbance units with a total assay time of about 20 min. For studies on activation kinetics, subsampling and extensive dilution can be performed in MES–bovine serum albumin (BSA) buffer pH 5.7 for quenching of enzyme activity and with ensuing determination of FXa generation in a chromogenic FXIa method. Optionally, suitable inhibitors such as aprotinin and/or corn trypsin inhibitor may be included. The stability of FXIa, FXIIa, and kallikrein in MES–BSA buffer was shown to be at least 5 h on ice. In conclusion, the use of a sensitive chromogenic FXIa method either per se or in combination with MES–BSA buffer pH 5.7 are new and potentially valuable tools for the study of contact factor enzymes and their inhibitors. So far, dose–response studies of FXIIa and kallikrein have been limited to purified systems, and hence more data are required to learn whether these new methods might or might not be applicable to the determination of FXIIa and kallikrein activities in plasma.

Gingipains of Porphyromonas gingivalis Affect the Stability and Function of Serine Protease Inhibitor of Kazal-type 6 (SPINK6), a Tissue Inhibitor of Human Kallikreins

Periodontitis, a chronic inflammation driven by dysbiotic subgingival bacterial flora, is linked on clinical levels to the development of a number of systemic diseases and to the development of oral and gastric tract tumors. A key pathogen, Porphyromonas gingivalis, secretes gingipains, cysteine proteases implicated as the main factors in the development of periodontitis. Here we hypothesize that gingipains may be linked to systemic pathologies through the deregulation of kallikrein-like proteinase (KLK) family members. KLKs are implicated in cancer development and are clinically utilized as tumor progression markers. In tissues, KLK activity is strictly controlled by a limited number of tissue-specific inhibitors, including SPINK6, an inhibitor of these proteases in skin and oral epithelium. Here we identify gingipains as the only P. gingivalis proteases responsible for SPINK6 degradation. We further show that gingipains, even at low nanomolar concentrations, cleaved SPINK6 in concentration- and time-dependent manner. The proteolysis was accompanied by loss of inhibition against KLK13. We also mapped the cleavage by Arg-specific gingipains to the reactive site loop of the SPINK6 inhibitor. Moreover, we identified a significant fraction of SPINK6-sensitive proteases in healthy saliva and confirmed the ability of gingipains to inactivate SPINK6 under ex vivo conditions. Finally, we demonstrate the double-edge action of gingipains, which, in addition, can activate KLKs because of gingipain K-mediated proteolytic processing of the zymogenic proform of KLK13. Altogether, the results indicate the potential of P. gingivalis to disrupt the control system of KLKs, providing a possible mechanistic link between periodontal disease and tumor development.