Limited role of kininogen in the host response during gram-negative pneumonia-derived sepsis

The versatile role of the contact system in cardiovascular disease, inflammation, sepsis and cancer

The human contact system consists of plasma proteins, which - after contact to foreign surfaces - are bound to them, thereby activating the zymogens of the system into enzymes. This activation mechanism gave the system its name - contact system. It is considered as a procoagulant and proinflammatory response mechanism, as activation finally leads to the generation of fibrin and bradykinin. To date, no physiological processes have been described that are mediated by contact activation. However, contact system factors play a pathophysiological role in numerous diseases, such as cardiovascular diseases, arthritis, colitis, sepsis, and cancer. Contact system factors are therefore an interesting target for new therapeutic options in different clinical conditions.

Sex-specific differences in plasma levels of FXII, HK, and FXIIa-C1-esterase inhibitor complexes in community acquired pneumonia

Sex-dependent differences in immunity and coagulation play an active role in the outcome of community-acquired pneumonia (CAP). Contact phase proteins act at the crossroads between inflammation and coagulation thus representing a point of convergence in host defense against infection. Here, we measured the levels of factor XII (FXII), FXIIa-C1 esterase inhibitor (C1INH) complexes, and high molecular weight kininogen (HK) in plasma of CAP patients and correlated them to clinical disease severity. Levels of FXIIa-C1INH/albumin ratio were elevated, irrespective of sex, in plasma of CAP patients (n=139) as compared to age-matched donors (n=58). No simultaneous decrease in FXII levels, indicating its consumption, was observed. Stratification by sex revealed augmented FXII levels in plasma of CAP women as compared to sex-matched donors yet no apparent differences in men. This sex-specific effect was, however, attributable to lower FXII levels in female donors relative to men donors. Plasma estradiol levels mirrored those for FXII. Levels of HK/albumin ratio were decreased in CAP plasma as compared to donors, however, after stratification by sex, this difference was only observed in women and was related to higher HK/albumin values in female donors as opposed to male donors. Finally, strong negative correlation between plasma levels of HK/albumin ratio and CAP severity, as assessed by CRB65 score, in males and females was observed. Our study identifies sex-dependent differences in plasma levels of the contact phase proteins in elderly subjects that may contribute to specific clinical outcomes in CAP between men and women.

Kinins and Their Receptors in Infectious Diseases

Kinins and their receptors have been implicated in a series of pathological alterations, representing attractive pharmacological targets for several diseases. The present review article aims to discuss the role of the kinin system in infectious diseases. Literature data provides compelling evidence about the participation of kinins in infections caused by diverse agents, including viral, bacterial, fungal, protozoan, and helminth-related ills. It is tempting to propose that modulation of kinin actions and production might be an adjuvant strategy for management of infection-related complications.

Kininogen supports inflammation and bacterial spreading during Streptococccus Pyogenes Sepsis

BACKGROUND

High-molecular-weight kininogen is a cofactor of the human contact system, an inflammatory response mechanism that is activated during sepsis. It has been shown that high-molecular-weight kininogen contributes to endotoxemia, but is not critical for local host defense during pneumonia by Gram-negative bacteria. However, some important pathogens, such as Streptococcus pyogenes, can cleave kininogen by contact system activation. Whether kininogen causally affects antibacterial host defense in S. pyogenes infection, remains unknown.

METHODS

Kininogen concentration was determined in course plasma samples from septic patients. mRNA expression and degradation of kininogen was determined in liver or plasma of septic mice. Kininogen was depleted in mice by treatment with selective kininogen directed antisense oligonucleotides (ASOs) or a scrambled control ASO for 3 weeks prior to infection. 24 h after infection, infection parameters were determined.

FINDINGS

Data from human and mice samples indicate that kininogen is a positive acute phase protein. Lower kininogen concentration in plasma correlate with a higher APACHE II score in septic patients. We show that ASO-mediated depletion of kininogen in mice indeed restrains streptococcal spreading, reduces levels of proinflammatory cytokines such as IL-1β and IFNγ, but increased intravascular tissue factor and fibrin deposition in kidneys of septic animals.

INTERPRETATION

Mechanistically, kininogen depletion results in reduced plasma kallikrein levels and, during sepsis, in increased intravascular tissue factor that may reinforce immunothrombosis, and thus reduce streptococcal spreading. These novel findings point to an anticoagulant and profibrinolytic role of kininogens during streptococcal sepsis.

FUNDING

Full details are provided in the Acknowledgements section.

Prekallikrein - an emerging therapeutic target for Klebsiella pneumoniae infection?†

Klebsiella pneumoniae is a Gram-negative bacterium that is increasingly difficult to treat due to the emergence of multidrug resistant strains. In a recent article, Ding et al demonstrate that prekallikrein depletion in mice followed by intranasal instillation of K. pneumoniae leads to a reduced bacterial burden and prolonged host survival, together with evidence of reduced distant organ damage. These effects are apparently independent of the role of prekallikrein in the contact system, and are associated with transcriptional changes relevant to innate immunity in the lung, established prior to infection. This study highlights the importance of further investigating the role of prekallikrein and other contact cascade components in host defence to counter K. pneumoniae (and perhaps other pathogens), with an overall aim of identifying potential therapeutic targets relevant to pulmonary infection with such resistant pathogens. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Prekallikrein inhibits innate immune signaling in the lung and impairs host defense during pneumosepsis in mice

Prekallikrein (PKK, also known as Fletcher factor and encoded by the gene KLKB1 in humans) is a component of the contact system. Activation of the contact system has been implicated in lethality in fulminant sepsis models. Pneumonia is the most frequent cause of sepsis. We sought to determine the role of PKK in host defense during pneumosepsis. To this end, mice were infected with the common human pathogen Klebsiella pneumoniae via the airways, causing an initially localized infection of the lungs with subsequent bacterial dissemination and sepsis. Mice were treated with a selective PKK‐directed antisense oligonucleotide (ASO) or a scrambled control ASO for 3 weeks prior to infection. Host response readouts were determined at 12 or 36 h post‐infection, including genome‐wide messenger RNA profiling of lungs, or mice were followed for survival. PKK ASO treatment inhibited constitutive hepatic Klkb1 mRNA expression by >80% and almost completely abolished plasma PKK activity. Klkb1 mRNA could not be detected in lungs. Pneumonia was associated with a progressive decline in PKK expression in mice treated with control ASO. PKK ASO administration was associated with a delayed mortality, reduced bacterial burdens, and diminished distant organ injury. While PKK depletion did not influence lung pathology or neutrophil recruitment, it was associated with an upregulation of multiple innate immune signaling pathways in the lungs already prior to infection. Activation of the contact system could not be detected, either during infection in vivo or at the surface of Klebsiella in vitro. These data suggest that circulating PKK confines pro‐inflammatory signaling in the lung by a mechanism that does not involve contact system activation, which in the case of respiratory tract infection may impede early protective innate immunity. © 2019 Authors. Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

A Dynamic Variation of Pulmonary ACE2 Is Required to Modulate Neutrophilic Inflammation in Response to Pseudomonas aeruginosa Lung Infection in Mice

Angiotensin-converting enzyme 2 (ACE2) is a potent negative regulator capable of restraining overactivation of the renin-angiotensin system, which contributes to exuberant inflammation after bacterial infection. However, the mechanism through which ACE2 modulates this inflammatory response is not well understood. Accumulating evidence indicates that infectious insults perturb ACE2 activity, allowing for uncontrolled inflammation. In the current study, we demonstrate that pulmonary ACE2 levels are dynamically varied during bacterial lung infection, and the fluctuation is critical in determining the severity of bacterial pneumonia. Specifically, we found that a pre-existing and persistent deficiency of active ACE2 led to excessive neutrophil accumulation in mouse lungs subjected to bacterial infection, resulting in a hyperinflammatory response and lung damage. In contrast, pre-existing and persistent increased ACE2 activity reduces neutrophil infiltration and compromises host defense, leading to overwhelming bacterial infection. Further, we found that the interruption of pulmonary ACE2 restitution in the model of bacterial lung infection delays the recovery process from neutrophilic lung inflammation. We observed the beneficial effects of recombinant ACE2 when administered to bacterially infected mouse lungs following an initial inflammatory response. In seeking to elucidate the mechanisms involved, we discovered that ACE2 inhibits neutrophil infiltration and lung inflammation by limiting IL-17 signaling by reducing the activity of the STAT3 pathway. The results suggest that the alteration of active ACE2 is not only a consequence of bacterial lung infection but also a critical component of host defense through modulation of the innate immune response to bacterial lung infection by regulating neutrophil influx.

The plasma contact system as a modulator of innate immunity

PURPOSE OF REVIEW

The contact system is a plasma protease cascade, which activates the proinflammatory kallikrein-kinin system and the procoagulant intrinsic coagulation pathway. Recent advances demonstrating the novel functions of this system as a key player of innate immune system will be introduced in the present review.

RECENT FINDINGS

The role of the contact system is to initiate and participate in pathophysiological responses to injury, mainly the processes of coagulation and inflammation. The past few years have seen substantial progress, showing a new role of this system in regulation of innate immunity. The relationship between high-molecular-weight kininogen and lipopolysaccharide (LPS) has been investigated and a new function of high-molecular-weight kininogen has been identified as the critical LPS carrier supporting endotoxemia. In contrast, the role of high-molecular-weight kininogen in Klebsiella pneumoniae sepsis is limited. Coagulation factor XII (FXII) plays a detrimental role in murine wound healing and host defense against K. pneumoniae sepsis. In the pathogenesis of arthritis and colitis, the activation of plasma kallikrein and downstream cleavage of high-molecular-weight kininogen and release of bradykinin constitutes a critical pathway in the innate immune mechanism, whereas FXII is not important.

SUMMARY

Current findings indicate that the plasma contact system functions as an important constituent of innate immune system, contributing to the pathogenesis of the immunological and infectious diseases.

Bradykinin receptor deficiency or antagonism do not impact the host response during gram-negative pneumonia-derived sepsis

BACKGROUND

Kinins are short peptides with a wide range of proinflammatory properties that are generated from kininogens in the so-called kallikrein-kinin system. Kinins exert their biological activities through stimulation of two distinct receptor subtypes, the kinin or bradykinin B1 and B2 receptors (B1R, B2R). Acute challenge models have implicated B1R and B2R in the pathogenesis of sepsis. However, their role in the host response during sepsis originating from the lung is not known.

RESULTS

To determine the role of B1R and B2R in pneumonia-derived sepsis, B1R/B2R-deficient mice and wild-type mice treated with the B1R antagonist R-715 or the B2R antagonist HOE-140 were studied after infection with the common gram-negative pathogen Klebsiella pneumoniae via the airways. Neither B1R/B2R deficiency nor B1R or B2R inhibition influenced bacterial growth at the primary site of infection or dissemination to distant body sites. In addition, B1R/B2R deficiency or inhibition did not impact local or systemic inflammatory responses during Klebsiella induced pneumosepsis.

CONCLUSIONS

These data argue against an important role for kinins in the host response to pneumonia-derived sepsis caused by a clinically relevant pathogen.

Kininogen deficiency or depletion reduces enhanced pause independent of pulmonary inflammation in a house dust mite-induced murine asthma model

High-molecular-weight kininogen is an important substrate of the kallikrein-kinin system. Activation of this system has been associated with aggravation of hallmark features in asthma. We aimed to determine the role of kininogen in enhanced pause (Penh) measurements and lung inflammation in a house dust mite (HDM)-induced murine asthma model. Normal wild-type mice and mice with a genetic deficiency of kininogen were subjected to repeated HDM exposure (sensitization on days 0, 1, and 2; challenge on days 14, 15, 18, and 19) via the airways to induce allergic lung inflammation. Alternatively, kininogen was depleted after HDM sensitization by twice-weekly injections of a specific antisense oligonucleotide (kininogen ASO) starting at day 3. In kininogen-deficient mice HDM induced in Penh was completely prevented. Remarkably, kininogen deficiency did not modify HDM-induced eosinophil/neutrophil influx, T helper 2 responses, mucus production, or lung pathology. kininogen ASO treatment started after HDM sensitization reduced plasma kininogen levels by 75% and reproduced the phenotype of kininogen deficiency: kininogen ASO administration prevented the HDM-induced increase in Penh without influencing leukocyte influx, Th2 responses, mucus production, or lung pathology. This study suggests that kininogen could contribute to HDM-induced rise in Penh independently of allergic lung inflammation. Further research is warranted to confirm these data using invasive measurements of airway responsiveness.

Inhibition of the extrinsic or intrinsic coagulation pathway during pneumonia-derived sepsis

Pneumonia is the most frequent cause of sepsis, and Klebsiella pneumoniae is a common pathogen in pneumonia and sepsis. Infection is associated with activation of the coagulation system. Coagulation can be activated by the extrinsic and intrinsic routes, mediated by factor VII (FVII) and factor XII (FXII), respectively. To determine the role of FVII and FXII in the host response during pneumonia-derived sepsis, mice were treated with specific antisense oligonucleotide (ASO) directed at FVII or FXII for 3 wk before infection with K. pneumoniae via the airways. FVII ASO treatment strongly inhibited hepatic FVII mRNA expression, reduced plasma FVII to ~25% of control, and selectively prolonged the prothrombin time. FXII ASO treatment strongly suppressed hepatic FXII mRNA expression, reduced plasma FXII to ~20% of control, and selectively prolonged the activated partial thromboplastin time. Lungs also expressed FVII mRNA, which was not altered by FVII ASO administration. Very low FXII mRNA levels were detected in lungs, which were not modified by FXII ASO treatment. FVII ASO attenuated systemic activation of coagulation but did not influence fibrin deposition in lung tissue. FVII ASO enhanced bacterial loads in lungs and mitigated sepsis-induced distant organ injury. FXII inhibition did not affect any of the host response parameters measured. These results suggest that partial inhibition of FVII, but not of FXII, modifies the host response to gram-negative pneumonia-derived sepsis.