Oscar Ratnoff: his contributions to the golden era of coagulation research

Blood-incompatibility in haemodialysis: alleviating inflammation and effects of coagulation

Blood-incompatibility is an inevitability of all blood-contacting device applications and therapies, including haemodialysis (HD). Blood leaving the environment of blood vessels and the protection of the endothelium is confronted with several stimuli of the extracorporeal circuit (ECC), triggering the activation of blood cells and various biochemical pathways of plasma. Prevention of blood coagulation, a major obstacle that needed to be overcome to make HD possible, remains an issue to contend with. While anticoagulation (mainly with heparin) successfully prevents clotting within the ECC to allow removal of uraemic toxins across the dialysis membrane wall, it is far from ideal, triggering heparin-induced thrombocytopenia in some instances. Soluble fibrin can form even in the presence of heparin and depending on the constitution of the patient and activation of platelets, could result in physical clots within the ECC (e.g. bubble trap chamber) and, together with other plasma and coagulation proteins, result in increased adsorption of proteins on the membrane surface. The buildup of this secondary membrane layer impairs the transport properties of the membrane to reduce the clearance of uraemic toxins. Activation of complement system-dependent immune response pathways leads to leukopenia, formation of platelet–neutrophil complexes and expression of tissue factor contributing to thrombotic processes and a procoagulant state, respectively. Complement activation also promotes recruitment and activation of leukocytes resulting in oxidative burst and release of pro-inflammatory cytokines and chemokines, thereby worsening the elevated underlying inflammation and oxidative stress condition of chronic kidney disease patients. Restricting all forms of blood-incompatibility, including potential contamination of dialysis fluid with endotoxins leading to inflammation, during HD therapies is thus still a major target towards more blood-compatible and safer dialysis to improve patient outcomes. We describe the mechanisms of various activation pathways during the interaction between blood and components of the ECC and describe approaches to mitigate the effects of these adverse interactions. The opportunities to develop improved dialysis membranes as well as implementation strategies with less potential for undesired biological reactions are discussed.

Adverse pregnancy outcomes and inherited thrombophilia

AIM

(1) To evaluate the prevalence of inherited thrombophilia in pregnant women with adverse pregnancy outcomes: intrauterine growth retardation (IUGR), preeclampsia (PE) and placental abruption. (2) To assess the impact of inherited thrombophilia on the nature of obstetric complications. (3) To assess levels of protein S, protein C, antithrombin III and homocysteine in pregnant women with adverse pregnancy outcomes.

SUBJECTS AND METHODS

The study comprised 162 pregnant women. The patients were divided into three test groups and one control group. In all 162 patients the following tests were completed: activated protein C resistance (APC-R), the level of free protein S, activity of protein C, antithrombin III and the level of homocysteine. The data were statistically analyzed via χ2 of independence or homogeneity test.

RESULTS

In 32 of 162 patients participating in clinical research thrombophilia was diagnosed (10 patients with APC-R, 21 patients with protein S deficiency, one patient with hyperhomocysteinemia): seven patients belonged to the control group and 25 patients had diagnosed adverse pregnancy outcomes (P=0.04). In 32 patients with diagnosed thrombophilia, level of protein S was decreased (P=0.04). Protein S deficiency was diagnosed, when level of protein S was lower than 30% in the second trimester and lower than 24% in the third trimester. The incidence of activated protein C resistance caused by the mutation of factor V Leiden was in six patients (5.9%) with adverse pregnancy outcomes, and in four patients (6.6%) from the control group. Results were not statistically significant. No protein C deficiency was diagnosed (diagnosis: level<60%), but in 50% of patients with thrombophilia level of protein C was over the norm (P=0.02). The level of antithrombin III was often decreased in patients with preeclampsia - (32.4%), then in the other patients - (17.2%) (P=0.04), but no patient was diagnosed with antithrombin III deficiency (diagnosis: level<60%).

CONCLUSIONS

Tests for thrombophilia should be carried out in women with adverse pregnancy outcomes in their history, who are planning pregnancy, to start anticoagulant prophylaxis. Our study supports the thesis that tests for thrombophilia should be carried out in women with a history of adverse pregnancy outcomes and who are planning a pregnancy to start anticoagulant prophylaxis.

Theories of Blood Coagulation

Although the concept of the coagulation cascade represented a significant advance in the understanding of coagulation and served for many years as a useful model, more recent clinical and experimental observations demonstrate that the cascade/waterfall hypothesis does not fully and completely reflect the events of hemostasis in vivo. The goal of this article is to review the evolution of the theories of coagulation and their proposed models to serve as a tool when reviewing the research and practice literature that was published in the context of these different theories over time.

Hageman factor, platelets and polyphosphates: early history and recent connection

  Platelet activation and blood coagulation are essential for hemostasis and contribute to a variety of other biological processes such as inflammation, complement activation and tissue repair. Factor (F)XII, originally called Hageman factor, plays an important role in the kallikrein-kinin system by activating prekallikrein. In the 1960s, a platelet activity that promoted FXII activation was identified but its biochemical nature remained unknown. Inorganic polyphosphates (poly P) are polymers that consist of many phosphate residues linked by phosphoanhydride bonds. These polymers exist in all living organisms. In bacteria, poly P is important for growth and survival. Recently, poly P has been identified in human platelet dense granules. Studied have shown that upon platelet activation and secretion, poly P activates FXII, indicating that it is most likely the elusive platelet FXII activator. Poly P also regulates coagulation and fibrinolysis. In this review, we focus on early studies of FXII and the identification of platelet FXII activation activity, and discuss recent findings of poly P in FXII activation and coagulation.

An updated concept of coagulation with clinical implications

BACKGROUND

Over the past century, a series of models have been put forth to explain the coagulation mechanism. The coagulation cascade/waterfall model has gained the most widespread acceptance. This model, however, has problems when it is used in different clinical scenarios. A more recently proposed cell-based model better describes the coagulation process in vivo and provides oral health care professionals (OHCPs) with a better understanding of the clinical implications of providing dental care to patients with potentially increased bleeding tendencies.

METHODS

The authors conducted a literature search using the PubMed database. They searched for key words including "coagulation," "hemostasis," "bleeding," "coagulation factors," "models," "prothrombin time," "activated partial thromboplastin time," "international normalized ratio," "anticoagulation therapy" and "hemophilia" separately and in combination.

CONCLUSIONS

The coagulation cascade/waterfall model is insufficient to explain coagulation in vivo, predict a patient's bleeding tendency, or correlate clinical outcomes with specific laboratory screening tests such as prothrombin time, activated partial thromboplastin time and international normalized ratio. However, the cell-based model of coagulation that reflects the in vivo process of coagulation provides insight into the clinical ramifications of treating dental patients with specific coagulation factor deficiencies.

CLINICAL IMPLICATIONS

Understanding the in vivo coagulation process will help OHCPs better predict a patient's bleeding tendency. In addition, applying the theoretical concept of the cell-based model of coagulation to commonly used laboratory screening tests for coagulation and bleeding will result in safer and more appropriate dental care.

Contact activation of blood-plasma coagulation

This opinion identifies inconsistencies in the generally-accepted surface biophysics involved in contact activation of blood-plasma coagulation, reviews recent experimental work aimed at resolving inconsistencies, and concludes that this standard paradigm requires substantial revision to accommodate new experimental observations. Foremost among these new findings is that surface-catalyzed conversion of the blood zymogen factor XII (FXII, Hageman factor) to the enzyme FXIIa (FXII [surface] --> FXIIa, a.k.a. autoactivation) is not specific for anionic surfaces, as proposed by the standard paradigm. Furthermore, it is found that surface activation is moderated by the protein composition of the fluid phase in which FXII autoactivation occurs by what appears to be a protein-adsorption-competition effect. Both of these findings argue against the standard view that contact activation of plasma coagulation is potentiated by the assembly of activation-complex proteins (FXII, FXI, prekallikrein, and high-molecular weight kininogen) directly onto activating surfaces (procoagulants) through specific protein/surface interactions. These new findings supplement the observation that adsorption behavior of FXII and FXIIa is not remarkably different from a wide variety of other blood proteins surveyed. Similarity in adsorption properties further undermines the idea that FXII and/or FXIIa are distinguished from other blood proteins by unusual adsorption properties resulting in chemically-specific interactions with activating anionic surfaces. IMPACT STATEMENT: This review shows that the consensus biochemical mechanism of contact activation of blood-plasma coagulation that has long served as a rationale for poor hemocompatibility is an inadequate basis for surface engineering of advanced cardiovascular biomaterials.