Inhibition of the activation of Hageman factor (factor XII) by complement subcomponent C1q

Neonatal haemostatic parameters in correlation to gestational age and birth weight

INTRODUCTION

The aim of our study was to establish reference ranges for neonatal coagulation and fibrinolysis parameters and to investigate their relationship with gestational age (GA) and birth weight (BW).

METHODS

A single-centre prospective study was conducted in all healthy neonates born in our hospital during the study period, excluding those with maternal or neonatal disorders and diseases that affect haemostasis. The following parameters were measured: fibrinogen, prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT) as well as factors II, V, VII, VIII, IX, X, XI and XII, von Willebrand (vWF), protein C, free protein S, antithrombin (AT), activated protein C resistance (APCr), tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1).

RESULTS

Study population consisted of 327 neonates. Fibrinogen, AT III, proteins C and S, PAI-1, vWF and factors II, V, VIII, IX, XI and XII were positively correlated, while PT, aPPT, INR, APCr and tPA were negatively correlated with GA and BW. Proteins C and S, factors II, VIII, IX, XI and vWF, as well AT III and PAI-1 had a significant positive linear correlation with GA, while aPTT had a significant negative one. Fibrinogen, and factors V, VII and XII had a significant positive linear correlation with BW, while factor VIII, tPA, as well PT and INR had a significant negative one.

CONCLUSION

Fibrinogen, AT III, proteins C and S, PAI-1, vWF and factors II, V, VIII, IX, XI and XII increase with GA and BW.

Dysregulation of complement and coagulation pathways: emerging mechanisms in the development of psychosis

Early identification and treatment significantly improve clinical outcomes of psychotic disorders. Recent studies identified protein components of the complement and coagulation systems as key pathways implicated in psychosis. These specific protein alterations are integral to the inflammatory response and can begin years before the onset of clinical symptoms of psychotic disorder. Critically, they have recently been shown to predict the transition from clinical high risk to first-episode psychosis, enabling stratification of individuals who are most likely to transition to psychotic disorder from those who are not. This reinforces the concept that the psychosis spectrum is likely a central nervous system manifestation of systemic changes and highlights the need to investigate plasma proteins as diagnostic or prognostic biomarkers and pathophysiological mediators. In this review, we integrate evidence of alterations in proteins belonging to the complement and coagulation protein systems, including the coagulation, anticoagulation, and fibrinolytic pathways and their dysregulation in psychosis, into a consolidated mechanism that could be integral to the progression and manifestation of psychosis. We consolidate the findings of altered blood proteins relevant for progression to psychotic disorders, using data from longitudinal studies of the general population in addition to clinical high-risk (CHR) individuals transitioning to psychotic disorder. These are compared to markers identified from first-episode psychosis and schizophrenia as well as other psychosis spectrum disorders. We propose the novel hypothesis that altered complement and coagulation plasma levels enhance their pathways' activating capacities, while low levels observed in key regulatory components contribute to excessive activation observed in patients. This hypothesis will require future testing through a range of experimental paradigms, and if upheld, complement and coagulation pathways or specific proteins could be useful diagnostic or prognostic tools and targets for early intervention and preventive strategies.

Complement C1q Enhances Primary Hemostasis

The cross-talk between the inflammatory complement system and hemostasis is becoming increasingly recognized. The interaction between complement C1q, initiation molecule of the classical pathway, and von Willebrand factor (vWF), initiator molecule of primary hemostasis, has been shown to induce platelet rolling and adhesion in vitro. As vWF disorders result in prolonged bleeding, a lack of C1q as binding partner for vWF might also lead to an impaired hemostasis. Therefore, this study aimed to investigate the in vivo relevance of C1q-dependent binding of vWF in hemostasis. For this purpose, we analyzed parameters of primary and secondary hemostasis and performed bleeding experiments in wild type (WT) and C1q-deficient (C1qa^−/−) mice, with reconstitution experiments of C1q in the latter. Bleeding tendency was examined by quantification of bleeding time and blood loss. First, we found that complete blood counts and plasma vWF levels do not differ between C1qa^−/− mice and WT mice. Moreover, platelet aggregation tests indicated that the platelets of both strains of mice are functional. Second, while the prothrombin time was comparable between both groups, the activated partial thromboplastin time was shorter in C1qa^−/− mice. In contrast, tail bleeding times of C1qa^−/− mice were prolonged accompanied by an increased blood loss. Upon reconstitution of C1qa^−/− mice with C1q, parameters of increased bleeding could be reversed. In conclusion, our data indicate that C1q, a molecule of the first-line of immune defense, actively participates in primary hemostasis by promoting arrest of bleeding. This observation might be of relevance for the understanding of thromboembolic complications in inflammatory disorders, where excess of C1q deposition is observed.

Modulation of calcium-induced clot formation of human plasma by Malassezia furfur

The effect of Malassezia furfur on clot formation by human plasma was examined. The clotting time in the presence of M. furfur or Candida albicans was measured. M. furfur shortened the clotting time of calcium-induced clots by human plasma in a concentration-dependent manner. However, the protein content of the clots formed were not significantly different between the M. furfur-treated and the control group. The clotting time of clots triggered by thrombin or by placing plasma in glass tubes, which artificially activate the blood coagulation systems, were not affected by treatment with M. furfur. Moreover, acetone-treated M. furfur also shortens the calcium-induced clot formation time, while treatment with zymolyase, which causes decomposition of beta-glucan, did not shorten it. These results suggest that M. furfur activates the blood coagulation systems, and the beta-glucan portion of M. furfur plays a key role in shortening calcium-induced clot formation time.

Inhibition of the activation of hageman factor (factor XII) by eosinophils and eosinophilic constituents

Several syndromes characterized by striking eosinophilia may be complicated by thrombosis. The experiments described indicate that, paradoxically, eosinophils and certain of their constituents inhibit the activation of Hageman factor (HF, factor XII). In earlier studies, suspensions of mixed types of granulocytes, other nucleated peripheral blood cells, and platelets inhibited activation of Hageman factor by ellagic acid, glass, and sulfatides. After these cells were sedimented by centrifugation, the supernatant fluids were also inhibitory. No attempt had been made earlier to distinguish among different granulocytic species. In the present study, suspensions of eosinophils and the supernatant fluid after eosinophils had been separated by centrifugation inhibited activation of Hageman factor by ellagic acid. The protein concentration of that amount of supernatant fluid that inhibited activation by about half was 16 micrograms/ml, approximately the same as had been described for suspensions of peripheral blood mononuclear cells. Activation of Hageman factor by ellagic acid was also inhibited by certain constituents of eosinophils, including eosinophil peroxidase, eosinophil major basic protein and eosinophil cationic protein. Inhibition was not specific for ellagic acid-induced activation of Hageman factor, as inhibition was also observed with sulfatide-induced activation. Inhibition was presumably related to neutralization of the negative charge of activators of Hageman factor. Thus, bismuth subgallate, a particulate activator of Hageman factor, was no longer effective after it had been exposed to eosinophil cationic protein. The observations reported here raise the question of whether in vivo eosinophils modulate certain of the defense reactions ascribed to Hageman factor.

Endothelial cells produce a substance that inhibits contact activation of coagulation by blocking the activation of Hageman factor

Human umbilical vein endothelial cells (HUVECs) produce a property that impairs the generation of coagulant and amidolytic activity initiated when normal human plasma is exposed to glass. This inhibitory property blocks the adsorption of Hageman factor (factor XII) to glass, thereby preventing the activation of Hageman factor, but does not impair the coagulant or amidolytic activity of already activated Hageman factor (factor XIIa). This property in HUVEC lysates could be neutralized by a purified preparation of Hageman factor but not by purified prekallikrein or high molecular mass kininogen. A partially purified inhibitory fraction from cell lysates exhibited a single homogeneous band in SDS/PAGE of approximately 22.5 kDa. Inhibitory activity was also found in concentrates of conditioned media from HUVECs, which also impaired the binding of Hageman factor to a surface; it may not be identical with that found in cell lysates.

Inhibition of the activation of Hageman factor (factor XII) by human vascular endothelial cell culture supernates

The supernatant fluid (conditioned medium) of cultured human vascular endothelial cells inhibits activation of Hageman factor (factor XII), whether by ellagic acid, bovine brain sulfatides, or bismuth subgallate; inhibition appears to be a property of one or more proteins in the culture supernates. This phenomenon may contribute to maintaining the fluidity of circulating blood by inhibiting surface activation of the intrinsic pathway of coagulation.

Inhibition of the activation of Hageman factor (factor XII) by peripheral blood cells

Suspensions of peripheral blood mononuclear cells (PBMC), monocytes, T or B lymphocytes, platelets or granulocytes, and cell-depleted supernatant fluids of these suspensions inhibited activation of Hageman factor (HF, Factor XII) by ellagic acid, a property not shared by erythrocytes. PBMC also inhibited HF activation by glass or sulfatides. Contaminating platelets may have contributed to inhibition by PBMC. Elaboration of agents inhibiting HF activation required metabolically active cells. The inhibitor(s) in PBMC supernates were not identified with known agents, but had properties of a nonenzymatic protein. PBMC supernates did not contain fibrinogen, nor alter the thrombin, prothrombin, or partial thromboplastin times of normal plasma, amidolysis by activated plasma thromboplastin antecedent (Factor XIa) or activated Stuart factor (Factor Xa) or esterolysis by C1 (C1 esterase); they inhibited plasmin minimally. These experiments suggest that peripheral blood cells may impede intravascular coagulation. Whether this property helps maintain the fluidity of blood is unclear.