Reduced induction of anti-PF4/heparin antibody in RA patients after total knee arthroplasty

Virtual Screening of Protein Data Bank via Docking Simulation Identified the Role of Integrins in Growth Factor Signaling, the Allosteric Activation of Integrins, and P-Selectin as a New Integrin Ligand

Integrins were originally identified as receptors for extracellular matrix (ECM) and cell-surface molecules (e.g., VCAM-1 and ICAM-1). Later, we discovered that many soluble growth factors/cytokines bind to integrins and play a critical role in growth factor/cytokine signaling (growth factor-integrin crosstalk). We performed a virtual screening of protein data bank (PDB) using docking simulations with the integrin headpiece as a target. We showed that several growth factors (e.g., FGF1 and IGF1) induce a integrin-growth factor-cognate receptor ternary complex on the surface. Growth factor/cytokine mutants defective in integrin binding were defective in signaling functions and act as antagonists of growth factor signaling. Unexpectedly, several growth factor/cytokines activated integrins by binding to the allosteric site (site 2) in the integrin headpiece, which is distinct from the classical ligand (RGD)-binding site (site 1). Since 25-hydroxycholesterol, a major inflammatory mediator, binds to site 2, activates integrins, and induces inflammatory signaling (e.g., IL-6 and TNFα secretion), it has been proposed that site 2 is involved in inflammatory signaling. We showed that several inflammatory factors (CX3CL1, CXCL12, CCL5, sPLA2-IIA, and P-selectin) bind to site 2 and activate integrins. We propose that site 2 is involved in the pro-inflammatory action of these proteins and a potential therapeutic target. It has been well-established that platelet integrin αIIbβ3 is activated by signals from the inside of platelets induced by platelet agonists (inside-out signaling). In addition to the canonical inside-out signaling, we showed that αIIbβ3 can be allosterically activated by inflammatory cytokines/chemokines that are stored in platelet granules (e.g., CCL5, CXCL12) in the absence of inside-out signaling (e.g., soluble integrins in cell-free conditions). Thus, the allosteric activation may be involved in αIIbβ3 activation, platelet aggregation, and thrombosis. Inhibitory chemokine PF4 (CXCL4) binds to site 2 but did not activate integrins, Unexpectedly, we found that PF4/anti-PF4 complex was able to activate integrins, indicating that the anti-PF4 antibody changed the phenotype of PF4 from inhibitory to inflammatory. Since autoantibodies to PF4 are detected in vaccine-induced thrombocytopenic thrombosis (VIPP) and autoimmune diseases (e.g., SLE, and rheumatoid arthritis), we propose that this phenomenon is related to the pathogenesis of these diseases. P-selectin is known to bind exclusively to glycans (e.g., sLex) and involved in cell-cell interaction by binding to PSGL-1 (CD62P glycoprotein ligand-1). Unexpectedly, through docking simulation, we discovered that the P-selectin C-type lectin domain functions as an integrin ligand. It is interesting that no one has studied whether P-selectin binds to integrins in the last few decades. The integrin-binding site and glycan-binding site were close but distinct. Also, P-selectin lectin domain bound to site 2 and allosterically activated integrins.

Присуство на анти-ТФ4/хепарин антитела кај пациенти профилактички третирани со еноксапарин после ортопедски оперативен зафат

Хепарин-индуцираната тромбоцитопенија (ХИТ) е предизвикана од антитела кон тромбоцитниот фактор 4 (ТФ4)/хепарин комплексот. Таа значително го зголемува ризикот од крвавење и тромбоза кај пациентите, што е особено есенцијално во постоперативниот период. Во оваа студија ја проценуваме стапката на сероконверзија на анти-ТФ4/хепарин антителата кај пациенти со ревматоиден артритис и остеоартритис по имплантација на протеза на колк или колено лекувани профилактички со еноксапарин. Целта на истражувањето беш да се процени ризикот од хепарин-индуцирана тромбоцитопенија преку евалуација на индукцијата на анти-ТФ4/хепарин антителата кај пациенти со ревматоиден артритис и остеоартритис по имплантација на протеза на колена или колк, лекувани профилактички со еноксапарин. Материјал и методи: Беа испитани 36 пациенти, на возраст од 18 до 80 години, по имплантација на протеза на колк или колено, лекувани профилактички со еноксапарин. Пациентите беа поделени во две еднакви групи, односно пациенти со ревматоиден артритис (РА) и пациенти со остеоартритис (ОА). Пациентите беа следени за време на хоспитализацијата на Клиниката за ортопедски болести за појава на ХИТ. Во два наврата беше земена венска крв, од периферна вена, за имунолошки иследувања. Прв пат тоа беше направено пред почеток на лекување со еноксапарин, а втор пат постоперативно, 10 дена по оперативниот зафат. Беа нотирани демографски податоци, анти-ТФ4/хепарин антитела, седиментација на еритроцити (ESR), CRP, RF, CCP, ANA, појава на ХИТ. Резултати: Немаше сигнификантна разлика во вредностите на анти-ТФ4/хепарин кај пациентите со ОА и РА предоперативно. Стапката на анти-ТФ4/хепарин антитела кај пациентите со РА беше сигнификантно пониска од онаа кај пациентите со ОА (7,14% наспроти 27,27%, р=0,034). Немаше сигнификантна поврзаност на вредностите на анти-ТФ/4 антителото со вредностите на ESR, CRP, RF, CCP или ANA. Заклучок: Резултатите укажаа на намалена инциденција на анти-ТФ4/хепарин антитела кај пациентите со РА во споредба со оние со ОА. Ова укажува дека постои разлика во анти-ТФ4/хепарин имуниот одговор кај пациенти со РА наспроти оние со ОА, профилактички лекувани со еноксапарин, по ортопедски оперативен зафат за имплантација на протеза на колк или колено.

Factors predisposing to thrombosis after major joint arthroplasty

BACKGROUND

Total joint arthroplasty is one of the most common options for end stage osteoarthritis of major joints. However, we must take into account that thrombosis after hip/knee arthroplasty may be related to mutations in genes encoding for blood coagulation factors and immune reactions to anticoagulants [heparin-induced thrombocytopenia (HIT)/thrombosis]. Identifying and characterizing genetic risk should help to develop diagnostic strategies or modify anticoagulant options in the search for etiological mechanisms that cause thrombophilia following major orthopedic surgery.

AIM

To evaluate the impact of patients’ coagulation profiles and to study specific pharmacologic factors in the development of post-arthroplasty thrombosis.

METHODS

In 212 (51 male and 161 female) patients that underwent primary total hip arthroplasty (100) or total knee arthroplasty (112) due to osteoarthritis during a period of 1 year, platelet counts and anti-platelet factor 4 (PF4)/heparin antibodies were evaluated pre/postoperatively, and antithrombin III, methylenetetrahydrofolate reductase, factor V and prothrombin gene mutations were evaluated preoperatively. In a minimum follow-up of 3 years, 196 patients receiving either low-molecular-weight heparins (173) or fondaparinux (23) were monitored for the development of thrombocytopenia, anti-PF4/heparin antibodies, HIT, and thrombosis.

RESULTS

Of 196 patients, 32 developed thrombocytopenia (nonsignificant correlation between anticoagulant type and thrombocytopenia, P = 0134.) and 18 developed anti-PF4/heparin antibodies (12/173 for low-molecular-weight heparins and 6/23 for fondaparinux; significant correlation between anticoagulant type and appearance of antibodies, P = 0.005). Odds of antibody emergence: 8.2% greater in patients receiving fondaparinux than low-molecular-weight heparins. Gene mutations in factor II or V (two heterozygotes for both factor V and II) were identified in 15 of 196 patients. Abnormal low protein C and/or S levels were found in 3 of 196 (1.5%) patients, while all patients had normal levels of von Willebrand factor, lupus anticoagulant, and antithrombin III. Four patients developed HIT (insignificant correlation between thrombocytopenia and antibodies) and five developed thrombosis (two had positive antibodies and two were heterozygotes for both factor II & V mutations). Thrombosis was not significantly correlated to platelet counts or HIT. The correlation of thrombosis to antibodies, factor II, factor V was P = 0.076, P = 0.043, P = 0.013, respectively.

CONCLUSION

Screening of coagulation profile, instead of platelet monitoring, is probably the safest way to minimize the risk of post-arthroplasty thrombosis. In addition, fondaparinux can lead to the formation of anti-PF4/heparin antibodies or HIT.

Induction of anti-PF4/heparin antibodies after arthroplasty for rheumatic diseases

Heparin-induced thrombocytopenia (HIT) is an immune complication of heparin therapy caused by antibodies to complexes of platelet factor 4 (PF4) and heparin. These pathogenic antibodies against PF4/heparin bind and activate cellular FcγRIIa on platelets to induce a hypercoagulable state culminating in thrombosis. Recent studies indicate several conditions, including joint surgery, induce spontaneous HIT, which can occur without exposure to heparin. To determine the real-world evidences concerning the incidences of venous thromboembolism (VTE) after total joint arthroplasty for rheumatic disease, we conducted a multicenter cohort study (J-PSVT) designed to document the VTE and seroconversion rates of anti-PF4/heparin antibody in 34 Japanese National hospital organization (NHO) hospitals. J-PSVT indicated that prophylaxis with fondaparinux, not enoxaparin, reduces the risk of deep vein thrombosis in patients undergoing arthroplasty. Multivariate analysis revealed that dynamic mechanical thromboprophylaxis (intermittent plantar device) was an independent risk factor for seroconversion of anti-PF4/heparin antibodies, which was also confirmed by propensity-score matching. Seroconversion rates of anti-PF4/heparin antibodies were significantly reduced in rheumatoid arthritis (RA) patients compared with osteoarthritis (OA) patients, which may link with the findings that IgG fractions isolated from RA patients not OA patients contained PF4. Our study indicated that a unique profile of anti-PF4/heparin antibodies is induced by arthroplasty for rheumatic diseases.