In silico thrombin generation: Plasma composition imbalance and mortality in human immunodeficiency virus

Dysregulation of Protein S in COVID-19

Coronavirus Disease 2019 (COVID-19) has been widely associated with increased thrombotic risk, with many different proposed mechanisms. One such mechanism is acquired deficiency of protein S (PS), a plasma protein that regulates coagulation and inflammatory processes, including complement activation and efferocytosis. Acquired PS deficiency is common in patients with severe viral infections and has been reported in multiple studies of COVID-19. This deficiency may be caused by consumption, degradation, or clearance of the protein, by decreased synthesis, or by binding of PS to other plasma proteins, which block its anticoagulant activity. Here, we review the functions of PS, the evidence of acquired PS deficiency in COVID-19 patients, the potential mechanisms of PS deficiency, and the evidence that those mechanisms may be occurring in COVID-19.

Total Plasma Protein S Is a Prothrombotic Marker in People Living With HIV

BACKGROUND

HIV-1 infection is associated with multiple procoagulant changes and increased thrombotic risk. Possible mechanisms for this risk include heigthened expression of procoagulant tissue factor (TF) on circulating monocytes, extracellular vesicles, and viral particles and/or acquired deficiency of protein S (PS), a critical cofactor for the anticoagulant protein C (PC). PS deficiency occurs in up to 76% of people living with HIV-1 (PLWH). As increased ex vivo plasma thrombin generation is a strong predictor of mortality, we investigated whether PS and plasma TF are associated with plasma thrombin generation.

METHODS

We analyzed plasma samples from 9 healthy controls, 17 PLWH on first diagnosis (naive), and 13 PLWH on antiretroviral therapy (ART). Plasma thrombin generation, total and free PS, PC, C4b-binding protein, and TF activity were measured.

RESULTS

We determined that the plasma thrombin generation assay is insensitive to PS, because of a lack of PC activation, and developed a modified PS-sensitive assay. Total plasma PS was reduced in 58% of the naive and 38% of the ART-treated PLWH samples and correlated with increased thrombin generation in the modified assay. Conversely, plasma TF was not increased in our patient population, suggesting that it does not significantly contribute to ex vivo plasma thrombin generation.

CONCLUSION

These data suggest that reduced total plasma PS contributes to the thrombotic risk associated with HIV-1 infection and can serve as a prothrombotic biomarker. In addition, our refined thrombin generation assay offers a more sensitive tool to assess the functional consequences of acquired PS deficiency in PLWH.

Plasmatic Coagulation Capacity Correlates With Inflammation and Abacavir Use During Chronic HIV Infection

BACKGROUND

D-dimer concentrations in people living with HIV (PLHIV) on combination antiretroviral therapy (cART) are increased and have been linked to mortality. D-dimer is a biomarker of in vivo coagulation. In contrast to reports on D-dimer, data on coagulation capacity in PLHIV are conflicting. In this study, we assessed the effect of cART and inflammation on coagulation capacity.

SETTING

We explored coagulation capacity using calibrated thrombin generation (TG) and linked this to persistent inflammation and cART in a cross-sectional study including PLHIV with viral suppression and uninfected controls.

METHODS

We used multivariate analyses to identify independent factors influencing in vivo coagulation (D-dimer) and ex vivo coagulation capacity (TG).

RESULTS

Among 208 PLHIV, 94 (45%) were on an abacavir-containing regimen. D-dimer levels (219.1 vs 170.5 ng/mL, P = 0.001) and inflammatory makers (sCD14, sCD163, and high-sensitive C-reactive protein) were increased in PLHIV compared with those in controls (n = 56). PLHIV experienced lower TG (reflected by endogenous thrombin potential [ETP]) when compared with controls, after correction for age, sex, and antiretroviral therapy. Abacavir use was independently associated with increased ETP. Prothrombin concentrations were strongly associated with ETP and lower in PLHIV on a non-abacavir-containing regimen compared with those in controls, suggesting consumption as a possible mechanism for HIV-associated reduction in TG. D-dimer concentrations were associated with inflammation, but not TG.

CONCLUSIONS

Abacavir use was associated with increased TG and could serve as an additional factor in the reported increase in thrombotic events during abacavir use. Increased exposure to triggers that propagate coagulation, such as inflammation, likely underlie increased D-dimer concentrations found in most PLHIV.

Platelets in HIV: A Guardian of Host Defence or Transient Reservoir of the Virus?

The immune and inflammatory responses of platelets to human immunodeficiency virus 1 (HIV-1) and its envelope proteins are of great significance to both the treatment of the infection, and to the comorbidities related to systemic inflammation. Platelets can interact with the HIV-1 virus itself, or with viral membrane proteins, or with dysregulated inflammatory molecules in circulation, ensuing from HIV-1 infection. Platelets can facilitate the inhibition of HIV-1 infection via endogenously-produced inhibitors of HIV-1 replication, or the virus can temporarily hide from the immune system inside platelets, whereby platelets act as HIV-1 reservoirs. Platelets are therefore both guardians of the host defence system, and transient reservoirs of the virus. Such reservoirs may be of particular significance during combination antiretroviral therapy (cART) interruption, as it may drive viral persistence, and result in significant implications for treatment. Both HIV-1 envelope proteins and circulating inflammatory molecules can also initiate platelet complex formation with immune cells and erythrocytes. Complex formation cause platelet hypercoagulation and may lead to an increased thrombotic risk. Ultimately, HIV-1 infection can initiate platelet depletion and thrombocytopenia. Because of their relatively short lifespan, platelets are important signalling entities, and could be targeted more directly during HIV-1 infection and cART.

The Current State of HIV and Aging: Findings Presented at the 10th International Workshop on HIV and Aging

With increasing effectiveness of antiretroviral therapy, people with HIV (PWH) are living longer and the prevalence of older PWH continues to increase. Accordingly, PWH are experiencing an increased burden of age-related comorbidities. With this shifting demographics, clinicians and researchers face additional challenges in how to identify, address, and manage the complex intersections of HIV- and aging-related conditions. Established in 2009, the International Workshop on HIV and Aging brings together clinicians and researchers in cross-disciplinary fields along with community advocates and PWH to address the multidisciplinary nature of HIV and aging. This article summarizes plenary talks from the 10th Annual International Workshop on HIV and Aging, which took place in New York City on October 10 and 11, 2019. Presentation topics included the following: the burdens of HIV-associated comorbidities, aging phenotypes, community engagement, and loneliness; these issues are especially important for older PWH, considering the current COVID-19 pandemic. We also discuss broad questions and potential directions for future research necessary to better understand the interaction between HIV and aging.

In Silico Hemostasis Modeling and Prediction

Computational physiology, i.e., reproduction of physiological (and, by extension, pathophysiological) processes in silico, could be considered one of the major goals in computational biology. One might use computers to simulate molecular interactions, enzyme kinetics, gene expression, or whole networks of biochemical reactions, but it is (patho)physiological meaning that is usually the meaningful goal of the research even when a single enzyme is its subject. Although exponential rise in the use of computational and mathematical models in the field of hemostasis and thrombosis began in the 1980s (first for blood coagulation, then for platelet adhesion, and finally for platelet signal transduction), the majority of their successful applications are still focused on simulating the elements of the hemostatic system rather than the total (patho)physiological response in situ. Here we discuss the state of the art, the state of the progress toward the efficient "virtual thrombus formation," and what one can already get from the existing models.

Mathematical model of thrombin generation and bleeding phenotype in Amish carriers of Factor IX:C deficiency vs. controls

INTRODUCTION

Factor IX:C (FIX:C) levels vary in hemophilia B carriers even in pedigrees with a unifying genetic defect. Analyzing the balance between pro-and anticoagulants might increase our understanding of carriers' bleeding potential.

AIM

In this research study, we evaluated bleeding scores (BS) and a novel mathematical model of thrombin generation (TG) in Amish FIX:C deficient carriers and controls.

METHODS

Blood samples and BS were obtained from post-menarchal females, including 59 carriers and 57 controls from the same extended pedigree. Factors II, V, VII, VIII, IX, X, antithrombin, tissue factor pathway inhibitor and protein C were assayed to generate mathematical models of TG in response to 5pM tissue factor (TF) and for TF + thrombomodulin. BS was based on a modification of the MCMDM-1VWD scoring system.

RESULTS

Carriers had a lower mean FIX:C (68% vs. 119%), von Willebrand factor antigen (108 vs.133) and Tissue activatable fibrinolysis inhibitor (103 vs. 111) compared to controls; both groups had a similar mean BS. Carriers demonstrated significantly lower TG parameters on both mathematical models compared to controls. Carriers with FIX:C ≤ 50% had lower TG curves than those >50% but similar BS.

CONCLUSION

Thrombin generation showed significant differences between carriers and controls, between low (≤50%) and high (>50%) FIX:C carriers, and specifically in the TF + thrombomodulin model, between high FIX:C carriers and controls, although the BS were not different.

In silico thrombin generation: Plasma composition imbalance and mortality in human immunodeficiency virus

Background

Effective HIV treatment with antiretroviral therapy has prolonged survival and shifted causes of death to non-AIDS illnesses such as cardiovascular disease. We have shown that inflammation and HIV viral load associate with pro- and anticoagulant factor imbalances resulting in increased thrombin generation when mathematically modeled. We explore the hypothesis that factor compositional imbalance, corresponding to increased in silico thrombin generation, predicts mortality among HIV+ persons.

Methods

In a nested case-control study of HIV+ individuals on continuous antiretroviral therapy in two large trials, we evaluated cases (any non-violent mortality, n = 114) and matched controls (n = 318). Thrombin generation in response to a tissue-factor initiator for each individual was calculated by a mathematical model incorporating levels of factors (F)II, V, VII, VIII, IX, X, antithrombin, tissue factor pathway inhibitor, and protein C (PC) measured at study entry to the trials. In silico thrombin generation metrics included clot time, maximum rate (MaxR), maximum level (MaxL), and area under the curve (AUC).

Results

Levels of antithrombin and PC decreased, while FV and FVIII were higher in cases vs controls. This resulted in a more procoagulant phenotype with increased MaxR, MaxL, and AUC in cases compared to controls (P < 0.05 for all).

Conclusions

Antithrombin, FV, FVIII, and PC were the major contributors to the increased thrombin generation associated with mortality risk. Our results suggest that mortality in HIV is associated with an increase in in silico thrombin generation via altered balance of pro- and anticoagulant factors, likely due to an inflammatory response signal, and resulting coagulopathy.