HIV replication alters the composition of extrinsic pathway coagulation factors and increases thrombin generation

Abstract

Background: HIV infection leads to activation of coagulation, which may increase the risk for atherosclerosis and venous thromboembolic disease. We hypothesized that HIV replication increases coagulation potentially through alterations in extrinsic pathway factors.

Methods and results: Extrinsic pathway factors were measured among a subset of HIV participants from the Strategies for Management of Anti-Retroviral Therapy (SMART) trial. Thrombin generation was estimated using validated computational modeling based on factor composition. We characterized the effect of antiretroviral therapy (ART) treatment versus the untreated state (HIV replication) via 3 separate analyses: (1) a cross-sectional comparison of those on and off ART (n=717); (2) a randomized comparison of deferring versus starting ART (n=217); and (3) a randomized comparison of stopping versus continuing ART (n=500). Compared with viral suppression, HIV replication consistently showed short-term increases in some procoagulants (eg, 15% to 23% higher FVIII; P<0.001) and decreases in key anticoagulants (eg, 5% to 9% lower antithrombin [AT] and 6% to 10% lower protein C; P<0.01). The net effect of HIV replication was to increase coagulation potential (eg, 24% to 48% greater thrombin generation from computational models; P<0.01 for all). The pattern of changes from HIV replication was reversed with ART treatment and consistent across all 3 independent comparisons.

Conclusions: HIV replication leads to complex changes in extrinsic pathway factors, with the net effect of increasing coagulation potential to a degree that may be clinically relevant. The key influence of changes in FVIII and AT suggests that HIV-related coagulation abnormalities may involve changes in hepatocyte function in the context of systemic inflammation.

Trial registration: ClinicalTrials.gov NCT00027352.

Keywords: HIV infection; HIV replication; antiretroviral therapy; coagulation; inflammation; thrombin generation.

Figure 1.

Study design and sample flow diagram. ART indicates antiretroviral therapy; VS, viral suppression; DC, drug conservation.

Figure 2.

Schematic of the extrinsic pathway of coagulation represented in a mathematical model. The 2 pathways to initiate coagulation are shown: the primary extrinsic pathway (on the right), and the contact, intrinsic pathway (on the left). These multicomponent processes are illustrated as enzymes (open circles), inhibitors (hatched circles), zymogens (open boxes), or complexes (open ovals). The contact pathway has no known bleeding etiology associated with it and thus is considered accessory to hemostasis. The shaded area represents what kinetic reactions are included in our mathematical model. On injury to the vessel wall, tissue factor, the cofactor for the extrinsic tenase complex, is exposed to circulating factor VIIa and forms the extrinsic tenase complex. Factor IX and factor X are converted to their serine proteases, factor IXa (FIXa) and factor Xa (FXa), which then form the intrinsic tenase and the prothrombinase complexes, respectively—the combined actions of which lead to an explosive burst of the enzyme thrombin (IIa). In addition to its multiple procoagulant roles, thrombin also acts in an anticoagulant capacity when combined with the cofactor thrombomodulin in the protein Case complex. The protein Case reaction generates activated protein C (APC), which inactivates the cofactors factors Va and VIIIa, which then no longer support the respective procoagulant activities of the prothrombinase and intrinsic tenase complexes. The procoagulant response is also downregulated by the stoichiometric inhibitors tissue factor pathway inhibitor (TFPI) and antithrombin (AT). AT directly inhibits thrombin, FIXa, and factor Xa. FPA indicates fibrinopeptide A; FPB, fibrinopeptide B; mz‐IIa, meizothrombin.

Figure 3.

Comparisons of coagulation biomarkers between untreated and ART‐treated HIV infection in the SMART study. a, Baseline comparison (A) between participants off ART and on ART with suppressed HIV viral load. b, Randomized comparison (B) of deferring (DC group) versus starting (VS group) ART at 6 months among participants off ART at baseline. c, Randomized comparison (C) of stopping (DC group) versus continuing (VS group) ART at 2 months among participants on ART at baseline with suppressed HIV viral load. Plots include the relative differences in coagulation factor levels for the untreated versus ART‐treated states for the following comparisons: (A) at baseline between participants off vs on ART; (B) at 6 months for those off ART at baseline who were then randomized to deferred ART (untreated) vs start ART (ART treated); (C) at 2 months for those on ART at baseline who were then randomized to stop ART (untreated) vs continue ART (ART treated). Differences at baseline are presented from fully adjusted models, whereas differences from randomized comparisons are adjusted only for baseline level. Treatment differences are expressed as a percentage, error bars represent the 95% CI, and a positive percentage corresponds to a higher level in the untreated state. Factors used for modeling thrombin kinetics are delineated. Results consistently showed that HIV replication leads to increases in coagulation factors associated with inflammation (eg, FVIII, vWF), and decreases in coagulation factors predominantly synthesized in the liver (eg, FII, FVII, AT, protein C, and protein S), with no consistent effect on fibrinogen (which reflects inflammation but is synthesized by hepatocytes). To minimize the risk of false‐positive associations, we focused on the randomized comparisons B and C and emphasized differences that are significant in both. If a significance level corresponding to a Bonferroni adjusted Pvalue was used (0.05/13=0.0013), the following comparisons did not meet this threshold: TFPI in 3a, FVII in 3b, and fibrinogen in 3c. ART indicates antiretroviral therapy; SMART, Strategies for Management of Anti‐Retroviral Therapy; DC, drug conservation; VS, viral suppression; CI, confidence interval; vWF, von Willebrand factor; AT, antithrombin; TFPI, tissue factor pathway inhibitor.

Figure 4.

Computational modeling of thrombin kinetics among participants with untreated and ART‐treated HIV infection. Plots for computational modeling output of thrombin generation kinetics over time after a 5 pmol/L tissue factor stimulus are presented for: A, the baseline comparison between participants untreated (n=197) vs ART treated (n=475); B, the comparison at 6 months for those off ART at baseline who were then randomized to deferred ART (untreated; n=95) vs start ART (ART treated; n=102); C, the comparison at 2 months for those on ART at baseline who were then randomized to stop (untreated; n=232) vs continue (ART treated; n=243). The curves consistently demonstrate greater thrombin generation for untreated compared with ART‐treated participants. D, Levels for FVIII and AT from ART‐treated participants were substituted into the model in which remaining factors were from untreated participants at baseline. This demonstrates that differences in FVIII and AT account for a large degree of the differences in thrombin generation based on ART use. ART indicates antiretroviral therapy; AT, antithrombin; DC, drug conservation; VS, viral suppression.