Increased activated protein C-protein C inhibitor complex level in patients positive for lupus anticoagulant

Relative remission rates of Janus kinase inhibitors in comparison with adalimumab in patients with active rheumatoid arthritis: a network meta-analysis

OBJECTIVES

The relative remission rates of tofacitinib, baricitinib, upadacitinib, and filgotinib compared with those of adalimumab were assessed in patients with rheumatoid arthritis (RA) who responded poorly to methotrexate (MTX).

METHODS

We performed a Bayesian network meta-analysis to combine direct and indirect evidence from randomized controlled trials (RCTs) to examine the Disease Activity Score in 28 joints with C‑reactive protein (DAS28-CRP), the Clinical Disease Activity Index (CDAI), the Simplified Disease Activity Index (SDAI), and the Boolean remission of tofacitinib, baricitinib, upadacitinib, filgotinib, and adalimumab in RA patients with inadequate responses to MTX.

RESULTS

Four RCTs, comprising 3507 patients, met the inclusion criteria. The filgotinib 200 mg + MTX and upadacitinib 15 mg + MTX groups showed a significantly higher DAS28-CRP < 2.6 than adalimumab 40 mg + MTX. Upadacitinib 15 mg + MTX showed a significantly higher CDAI (≤ 2.8) than adalimumab 40 mg + MTX (odds ratio [OR]: 1.62; 95% credible interval [CrI]: 1.16-2.29). The ranking probability based on the surface under the cumulative ranking curve (SUCRA) indicated that upadacitinib 15 mg + MTX had the highest probability of being the best treatment as it achieved a CDAI ≤ 2.8, followed by filgotinib 200 mg + MTX, baricitinib 4 mg + MTX, tofacitinib 5 mg + MTX, and adalimumab 40 mg + MTX. The Boolean remission showed the same distribution pattern as that of the CDAI ≤ 2.8. Upadacitinib 15 mg + MTX showed a significantly higher SDAI ≤ 3.3 than adalimumab 40 mg + MTX (OR: 1.62; 95% CrI: 1.16-2.28). SUCRA ranking based on SDAI ≤ 3.3 indicated that upadacitinib 15 mg + MTX had the highest probability of being the best treatment for achieving an SDAI ≤ 3.3, followed by baricitinib 4 mg + MTX, filgotinib 200 mg + MTX, tofacitinib 5 mg + MTX, and adalimumab 40 mg + MTX.

CONCLUSIONS

In RA patients with an inadequate response to MTX, remission rates with JAK inhibitors were significantly higher; there is evidence for differences in efficacy regarding remission among the different JAK inhibitors.

Comparative Efficacy and Safety of Janus Kinase Inhibitors and Secukinumab in Patients with Active Ankylosing Spondylitis: A Systematic Review and Meta-Analysis

BACKGROUND

Janus kinase (JAK) inhibitors and secukinumab have been demonstrated to be effective treatments for ankylosing spondylitis (AS). However, there have been no head-to-head trials comparing the effectiveness and safety characteristics of JAK inhibitors with secukinumab. This study aimed to evaluate the relative effectiveness and safety of JAK inhibitors and secukinumab in patients with active AS.

SUMMARY

A Bayesian network meta-analysis was conducted using direct and indirect data from randomized controlled trials (RCTs) that examined the efficacy and safety of tofacitinib 5 mg, upadacitinib 15 mg, filgotinib 200 mg, and secukinumab 150 mg in patients with active AS who had a poor response or intolerance to nonsteroidal anti-inflammatory drugs (NSAIDs) and were tumor necrosis factor (TNF) inhibitor-naïve. Data from six RCTs comprising 937 patients were analyzed. The Assessment of SpondyloArthritis International Society 20 (ASAS20) response rates were significantly higher in the JAK inhibitors and secukinumab groups than in the placebo group. The surface under the cumulative ranking curve (SUCRA)-based ranking probability based on the ASAS20 response rate suggested that tofacitinib 5 mg had the highest likelihood of being the best treatment for achieving the ASAS20 response rate, followed by filgotinib 200 mg, upadacitinib 15 mg, secukinumab 150 mg, and placebo. The SUCRA-based ranking probability based on the ASAS20 response rate suggested that tofacitinib 5 mg had the highest likelihood of being the best treatment for achieving the ASAS40 response rate, followed by upadacitinib 15 mg, secukinumab 150 mg, filgotinib 200 mg, and placebo.

KEY MESSAGES

Tofacitinib 5 mg was the most effective treatment for AS, whereas JAK inhibitors and secukinumab 150 mg were effective treatments in patients with active AS who had a poor response or intolerance to NSAIDs and were TNF inhibitor-naïve.

Relative efficacy and safety of Janus kinase inhibitors for the treatment of active psoriatic arthritis: a network meta-analysis

OBJECTIVE

To determine the relative effectiveness and safety of Janus kinase (JAK) inhibitors in active psoriatic arthritis (PsA) patients.

MATERIALS AND METHODS

A Bayesian network meta-analysis was performed using data from randomized controlled trials (RCTs) to evaluate the effectiveness and safety of upadacitinib 30 mg, upadacitinib 15 mg, tofacitinib 10 mg, tofacitinib 5 mg, and filgotinib 200 mg in active PsA patients.

RESULTS

Five RCTs including 2539 patients fulfilled the inclusion criteria. The surface under the cumulative ranking curve (SUCRA) revealed that filgotinib 200 mg had the highest probability of reaching a 20% American College of Rheumatology (ACR20) response rate, followed by upadacitinib 30 mg, upadacitinib 15 mg, tofacitinib 10 mg, tofacitinib 5 mg, and placebo. Upadacitinib 30 mg had the highest probability of achieving the ACR50 and ACR70 response rates, followed by upadacitinib 15 mg, filgotinib 200 mg, tofacitinib 10 mg, tofacitinib 5 mg, and placebo. The SUCRA rating based on the Psoriasis Area and Severity Index response rate of at least 75% (PASI75) showed that tofacitinib 10 mg had the highest probability of achieving this response, followed by upadacitinib 15 mg, filgotinib 200 mg, tofacitinib 5 mg, and placebo. Safety analyses evaluated adverse events (AEs) and serious adverse events (SAEs), but no statistically relevant differences were found.

CONCLUSION

Based on the ACR response rates, filgotinib 200 mg and upadacitinib 30 mg were the most effective, whereas tofacitinib 10 mg was the most effective treatment for PsA based on PASI75. However, treatment options were similar with regard to AEs and SAEs.

Comparative efficacy and safety of tofacitinib, baricitinib, upadacitinib, and filgotinib in active rheumatoid arthritis refractory to biologic disease-modifying antirheumatic drugs

OBJECTIVE

The relative efficacy and tolerability of tofacitinib, baricitinib, upadacitinib, and filgotinib were assessed in patients with rheumatoid arthritis (RA) with inadequate responses to biologic disease-modifying antirheumatic drugs (bDMARDs).

METHODS

We performed a Bayesian network meta-analysis to combine direct and indirect evidence from randomized controlled trials (RCTs) to examine the efficacy and safety of tofacitinib, baricitinib, upadacitinib, and filgotinib in RA patients with inadequate responses to bDMARDs.

RESULTS

Four RCTs comprising 1399 patients met the inclusion criteria. Tofacitinib, baricitinib, upadacitinib, and filgotinib achieved significant American College of Rheumatology 20% (ACR20) responses versus placebo. The ranking probability based on the surface under the cumulative ranking curve (SUCRA) indicated that upadacitinib 15 mg had the highest probability of being the best treatment for achieving the ACR20 response rate, followed by filgotinib 200 mg, baricitinib 4 mg, filgotinib 100 mg, tofacitinib 5 mg, and placebo. The ranking in SUCRA based on the ACR50 response rate indicated that baricitinib 4 mg had the highest probability of achieving the ACR50 response rate, followed by filgotinib 200 mg, tofacitinib 5 mg, upadacitinib 15 mg, filgotinib 100 mg, and placebo. Tofacitinib 5 mg showed a significantly higher ACR70 response rate than filgotinib 100 mg and upadacitinib 15 mg. Tofacitinib 5 mg, filgotinib 200 mg, and placebo showed a significantly lower serious adverse event rate than upadacitinib 15 mg.

CONCLUSION

Tofacitinib, baricitinib, upadacitinib, and filgotinib were effective treatment options for RA patients with an inadequate response to bDMARDs but with different efficacy and safety profiles.

Comparative effectiveness and safety of non-tumour necrosis factor biologics and Janus kinase inhibitors in patients with active rheumatoid arthritis showing insufficient response to tumour necrosis factor inhibitors: A Bayesian network meta-analysis of randomized controlled trials

WHAT IS KNOWN AND OBJECTIVE

Both biologic and Janus kinase (JAK) inhibitor therapies have demonstrated substantial effectiveness in placebo-controlled studies in patients with active rheumatoid arthritis (RA) showing inadequate responses to tumour necrosis factor (TNF) inhibitors. The purpose of this study was to determine the relative effectiveness and safety of non-TNF biologics and JAK inhibitors in patients with RA showing insufficient response to TNF inhibitors.

METHODS

A Bayesian network meta-analysis incorporating direct and indirect data from randomized controlled trials (RCTs) was used to investigate the effectiveness and safety of non-TNF biologics (abatacept, rituximab, tocilizumab, salirumab and sirukumab) and JAK inhibitors (tofacitinib, baricitinib, upadacitinib and filgotinib) in patients with RA showing insufficient response to TNF inhibitors.

RESULTS

Nine RCTs, evaluating 3577 patients for 12 weeks fulfilled the inclusion requirements. JAK inhibitors and non-TNF biologics achieved a significant American College of Rheumatology 20% (ACR20) response relative to the placebo. The ranking probability based on the surface under the cumulative ranking curve (SUCRA) showed that JAK inhibitor treatment was most likely to achieve the highest ACR20 response rate, followed by non-TNF biologics and placebo. The ACR50 rate displayed similar patterns as the ACR20 response rate, but non-TNF biologics have a higher value than JAK inhibitors based on the ACR70 response rate. Adverse events did not reach statistical significance nor did serious adverse events when looking at safety over 12 weeks. The confidence intervals overlap, and there is no clinical significance to these safety data, even compared with placebo.

WHAT IS NEW AND CONCLUSION

Both non-TNF biologics and JAK inhibitors have similar effects in patients with active RA that are refractory to anti-TNF treatment, and there were no differences with regard to safety among the treatments.

Janus kinase inhibitors for treating active ankylosing spondylitis: a meta-analysis of randomized controlled trials

OBJECTIVE

In this study, we aimed to assess the safety and efficacy of Janus kinase (JAK) inhibitors in patients with ankylosing spondylitis (AS).

METHODS

We conducted a Bayesian network meta-analysis using direct and indirect data from randomized controlled trials (RCTs), and examined the safety and efficacy of JAK inhibitors in active AS patients exhibiting inadequate response or intolerance to two or more non-steroidal anti-inflammatory drugs (NSAIDs).

RESULTS

RCTs included a total of 406 patients (203 experimental subjects and 203 controls) from three studies on upadacitinib, filgotinib, and tofacitinib. Assessment of SpondyloArthritis International Society 20% improvement (ASAS20), ASAS40, and ASAS5/6 responses were significantly higher in the JAK inhibitor group than in the placebo group. Other efficacy outcomes, such as ASAS partial remission, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI50), Ankylosing Spondylitis Disease Activity Score (ASDAS), Spondyloarthritis Research Consortium of Canada (SPARCC) Magnetic Resonance Imaging (MRI) scores, and Bath Ankylosing Spondylitis Functional Index (BASFI) were also significantly higher in the JAK inhibitor group compared to the placebo group. The JAK inhibitors significantly improved disease activity (ASAS partial remission, BASDAI50, ASDAS), function (BASFI), and MRI outcomes (SPARCC MRI spine). However, the incidence of adverse events (AEs) and serious adverse events (SAEs), and the rate of withdrawal attributed to AEs did not differ between the JAK inhibitor and placebo groups.

CONCLUSION

JAK inhibitors were effective in active AS patients exhibiting an inadequate response or intolerance to two or more NSAIDs, without the risk of SAEs; this suggests that based on our data, studies are warranted to further investigate the use of JAK inhibitors for treating AS.

Comparative study of the efficacy and safety of tofacitinib, baricitinib, upadacitinib, and filgotinib versus methotrexate for disease-modifying antirheumatic drug-naïve patients with rheumatoid arthritis

An assessment of the relative efficacy and tolerability of tofacitinib, baricitinib, upadacitinib, and filgotinib compared to those of methotrexate (MTX) was performed in disease-modifying antirheumatic drug (DMARD)-naive patients with rheumatoid arthritis (RA). We performed a Bayesian network meta-analysis to combine direct and indirect evidence from randomized controlled trials (RCTs) so as to examine the efficacy and safety of tofacitinib, baricitinib, upadacitinib, filgotinib, and MTX in DMARD-naïve RA patients. Four RCTs comprising 2185 patients met the inclusion criteria. The ranking probability based on the surface under the cumulative ranking curve (SUCRA) indicated that upadacitinib 15 mg had the highest probability of achieving the American College of Rheumatology 20% (ACR20) response rate, followed by baricitinib 4 mg, tofacitinib 5 mg, filgotinib 200 mg, and MTX. Tofacitinib, baricitinib, upadacitinib, and filgotinib treatments achieved significantly higher ACR50 and ACR70 responses compared to MTX. Tofacitinib 5 mg had the highest probability of achieving the ACR50 and ACR70 response rates, followed by upadacitinib 15 mg, baricitinib 4 mg, filgotinib 200 mg, and MTX. The safety analysis based on serious adverse events, adverse events (AEs), and withdrawals due to AEs revealed no statistically significant differences between the respective intervention groups. In conclusion, tofacitinib, baricitinib, upadacitinib, and filgotinib were effective treatment options for DMARD-naïve RA patients, suggesting a difference in efficacy and safety among the different JAK inhibitors.

Comparative efficacy and safety of tofacitinib, baricitinib, upadacitinib, filgotinib and peficitinib as monotherapy for active rheumatoid arthritis

WHAT IS KNOWN AND OBJECTIVE

Several clinical trials have attempted to evaluate the efficacy and safety of tofacitinib, baricitinib, upadacitinib, filgotinib and peficitinib as monotherapy in patients with active rheumatoid arthritis (RA), but their relative efficacy and safety as monotherapy remain unclear due to the lack of data from head-to-head comparison trials. The relative efficacy and safety of tofacitinib, baricitinib, upadacitinib, filgotinib and peficitinib as monotherapy for rheumatoid arthritis (RA) were assessed.

METHODS

We performed a Bayesian network meta-analysis to combine direct and indirect evidence from randomized controlled trials (RCTs) and examine the efficacy and safety of tofacitinib, baricitinib, upadacitinib, filgotinib and peficitinib as monotherapy relative to placebo in patients with RA.

RESULTS AND DISCUSSION

Five RCTs comprising 1547 patients met the inclusion criteria. Compared with placebo, tofacitinib, baricitinib, upadacitinib, filgotinib and peficitinib as monotherapy showed a significantly higher American College of Rheumatology 20% (ACR20) response rate. Peficitinib 150 mg monotherapy showed the highest ACR20 response rate (odds ratio, 17.24.39; 95% credible interval, 6.57-51.80). The ranking probability based on the surface under the cumulative ranking curve indicated that peficitinib 150 mg had the highest probability of being the best treatment for achieving the ACR20 response rate, followed by peficitinib 100 mg, filgotinib 200 mg, filgotinib 100 mg, tofacitinib 5 mg, upadacitinib 15 mg, baricitinib 4 mg and placebo. However, the number of patients who experienced serious adverse events did not differ significantly between the JAK inhibitors, except for tofacitinib 5 mg, and placebo.

WHAT IS NEW AND CONCLUSION

All five JAK inhibitors-tofacitinib, baricitinib, upadacitinib, filgotinib and peficitinib-were efficacious monotherapy interventions for active RA, and differences were noted in their efficacy and safety in monotherapy.

Comparison of the efficacy and safety of tofacitinib and upadacitinib in patients with active rheumatoid arthritis: A Bayesian network meta-analysis of randomized controlled trials

OBJECTIVES

The relative efficacy and safety of tofacitinib and upadacitinib were assessed in patients with rheumatoid arthritis (RA) with an inadequate response to conventional synthetic (cs) or biologic (b) disease-modifying anti-rheumatic drugs (DMARDs).

METHOD

We performed a Bayesian network meta-analysis to combine direct and indirect evidence from randomized controlled trials (RCTs) to examine the efficacy and safety of tofacitinib and upadacitinib in combination with methotrexate (MTX) in RA patients with an inadequate cs- or b-DMARD response.

RESULTS

Nine RCTs including 5794 patients met the inclusion criteria. There were 15 pairwise comparisons including 10 direct comparisons of 6 interventions. Upadacitinib 15 mg + MTX and upadacitinib 30 mg + MTX were among the most effective treatments for active RA with an inadequate cs- or b-DMARD response, followed by tofacitinib 10 mg + MTX, tofacitinib 5 mg + MTX, and adalimumab + MTX. Ranking probability based on the surface under the cumulative ranking curve (SUCRA) indicated that upadacitinib 15 mg + MTX and upadacitinib 30 mg + MTX had the highest probability of being the best treatment in terms of the American College of Rheumatology 20 response rate (SUCRA = 0.820, 0.762), followed by tofacitinib 10 mg + MTX (SUCRA = 0.623), tofacitinib 5 mg + MTX (SUCRA = 0.424), adalimumab + MTX (SUCRA = 0.371), and placebo + MTX (SUCRA = 0.001). No significant differences were observed in the incidence of serious adverse events after treatment with tofacitinib + MTX, upadacitinib + MTX, adalimumab + MTX, or placebo + MTX.

CONCLUSIONS

In RA patients with an inadequate response to cs- or b-DMARDs, upadacitinib 15 mg + MTX and upadacitinib 30 mg + MTX were the most efficacious interventions and were not associated with significant risks of serious adverse events.

The multi-functional serpin, protein C inhibitor: beyond thrombosis and hemostasis

Protein C inhibitor (PCI) is a member of the serine protease inhibitor (serpin) family. PCI was initially found to be an inhibitor of activated protein C, and later shown to be a potent inhibitor of blood coagulation and fibrinolysis such as that mediated by urokinase type-plasminogen activator. Therefore, the protein came to be known as plasminogen activator inhibitor-3. It also inhibits proteases involved in fertilization. PCI is broadly conserved, and is found in human, rhesus monkey, cow, rabbit, rat, mouse and chicken. The human PCI gene is located on chromosome 14q32.1 in a cluster of genes encoding related serpins. Sp1- and AP2-binding sites in the 5'-flanking region act as promoter and enhancer, respectively, for its expression in the liver. PCI mRNA is expressed in many organs in primates, but only in the reproductive organs in rodents. Recent studies using transgenic mice expressing the human gene have suggested that PCI is also involved in regulation of lung remodeling, tissue regeneration, vascular permeability, proteolysis in the kidney and tumor cell invasion. A protease inhibitor-independent activity of PCI, the prevention of anti-angiogenesis and metastasis of tumor cells, has also been observed. Thus, PCI is a unique multi-functional serpin playing diverse roles in the thrombosis and hemostasis in multiple organs and tissues of a variety of species.

Protein C inhibitor directly and potently inhibits activated hepatocyte growth factor activator

BACKGROUND

Hepatocyte growth factor (HGF) plays an important role in tissue repair and regeneration. HGF activator (HGFA), a factor XIIa-like serine protease, activates HGF precursor to HGF. The precursor of HGFA, proHGFA, is activated by thrombin generated at sites of tissue injury. It is known that protein C inhibitor (PCI), an inhibitor of activated protein C (APC), also inhibits thrombin-thrombomodulin (TM) complex.

OBJECTIVES

In the present study we evaluated the effect of PCI on thrombin-catalyzed proHGFA activation in the presence of TM, and on HGFA activity.

RESULTS

PCI did not inhibit thrombin-TM-mediated proHGFA activation, but it directly inhibited activated HGFA by forming an enzyme inhibitor complex. The second-order rate constants (m(-1) min(-1)) of the reaction between HGFA and PCI in the presence or absence of heparin (10 U mL(-1)) were 4.3 x 10(6) and 4.0 x 10(6), respectively. The inhibition of HGFA by PCI resulted in a significant decrease of HGFA-catalyzed activation of HGF precursor. Exogenous HGFA added to normal human plasma formed a complex with plasma PCI, and this complex formation was competitively inhibited by APC in the presence of heparin, but very weakly in the absence of heparin. We also demonstrated using recombinant R362A-PCI that Arg362 residue of PCI is important for HGFA inhibition by PCI as judged from the three-dimensional structures constructed using docking models of PCI and HGFA or APC.

CONCLUSION

These observations indicate that PCI is a potent inhibitor of activated HGFA, suggesting a novel function for PCI in the regulation of tissue repair and regeneration.

High prevalence of anti-prothrombin antibody in patients with deep vein thrombosis

The present study was designed to determine the prevalence of lupus anticoagulant (LA) antibody and several antibodies for antiphospholipid syndrome (APS) in patients with deep vein thrombosis (DVT)/pulmonary embolism (PE) (n = 48), cerebral thrombosis (CT, n = 30), systemic lupus erythematosus (SLE, n = 22), and idiopathic thrombocytopenic purpura (ITP, n = 30). The presence of antibodies was examined by using the respective ELISA kits. LA was positive in 38.6% of patients with DVT/PE, suggesting that LA is one of the most important risk factors in DVT/PE. The highest prevalence of anti-beta(2) glycoprotein I (beta(2)GPI) IgG was in CT and SLE, followed by DVT, and none in ITP and healthy volunteers (control, n = 40), suggesting that it is related to thrombosis, particularly arterial thrombosis. The highest prevalence of anti-prothrombin (aPT) IgG antibody was in DVT, followed by CT and SLE, and none in ITP and the control, suggesting that it is related to thrombosis, especially venous thrombosis. The highest prevalence of antiphospholipid (aPL) IgG was in DVT, CT, and SLE, but 0% in ITP and control. On the other hand, aPL IgM, anti-annexin V IgG, and anti-annexin V IgM were positive in patients both with and without thrombosis, suggesting that they are not related to thrombosis. Our results indicated that among the anti-phospholipid antibodies, LA is the most sensitive marker for APS while anti-beta(2)GPI IgG, aPT IgG, and aPL IgG are risk factors for thrombosis. In particular, aPT IgG is a significant marker for DVT/PE.

Coagulation tests and anti-phospholipid antibodies in patients positive for lupus anticoagulant

We examined activated partial thromboplastin time, kaolin clotting time, mixing with normal plasma in kaolin clotting time, dilute Russell's viper venom time, dilute Russell's viper venom time at high lipid concentrations, anti-phospholipid antibodies, and anti-cardiolipin-beta2-glycoprotein I complex antibody in 135 patients with prolongation of activated partial thromboplastin time and diagnosed 86 patients positive for lupus anticoagulant. The sensitivity of activated partial thromboplastin time and dilute Russell's viper venom time/dilute Russell's viper venom time-high lipid concentrations ratio for lupus anticoagulant were markedly high, but the specificity of activated partial thromboplastin time for lupus anticoagulant was not markedly high. The specificity, but not the sensitivity, of kaolin clotting time-mixing with normal plasma in kaolin clotting time was markedly high. In summary, dilute Russell's viper venom time to dilute Russell's viper venom time-high lipid concentrations ratio gave high sensitivity as well as specificity, being the only assay to confirm this. Of the patients positive for lupus anticoagulant, 25% were positive for anti-phospholipid antibodies and 17% were positive for anti-cardiolipin-beta2-glycoprotein I complex antibody. Of the lupus anticoagulant-positive patients with thrombosis, 45% were positive for anti-phospholipid antibodies, 35% were positive for anti-cardiolipin-beta2-glycoprotein I complex antibody, 60% were positive for both anti-phospholipid antibodies and anti-cardiolipin-beta2-glycoprotein I complex antibody, and only 17% were negative for anti-phospholipid antibodies and anti-cardiolipin-beta2-glycoprotein I complex antibody. These findings suggest that lupus anticoagulant can be diagnosed by dilute Russell's viper venom time/dilute Russell's viper venom time-high lipid concentrations ratio, and that thrombosis in lupus anticoagulant-positive may be predictable from both anti-phospholipid antibodies and anti-cardiolipin-beta2-glycoprotein I complex antibody. Plasma tissue type plasminogen activator level in lupus anticoagulant patients was significantly increased, and plasma tissue type plasminogen activator and fibrin-D-dimer levels in lupus anticoagulant-positive patients with thrombosis were significantly higher than in those without thrombosis, suggesting that the diagnosis of thrombosis by hemostatic markers might be important in lupus anticoagulant.

Synthesis and Ultrastructural Localization of Protein C Inhibitor in Human Platelets and Megakaryocytes

The occurrence of protein C inhibitor (PCI) in human platelets and megakaryocytes was analyzed. As judged from enzyme-linked immunosorbent assays (ELISAs), PCI was present in platelets at a concentration of 160 ng/2 × 109 cells. Its specific activity was 5 times higher than that of plasma PCI. Consistently, mainly the 57-kD form (active PCI) and some high molecular weight (Mr) forms, but no bands corresponding to cleaved PCI, were detected when platelet lysates were immunoprecipitated with monoclonal anti-PCI-IgG and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. The localization of PCI in platelets was studied by immunofluorescence histochemistry and immunotransmission electron microscopy: PCI was detected in  granules, in the open canalicular system, and on the plasma membrane. At these sites, colocalization with plasminogen activator inhibitor-1 was seen. Studies were performed to clarify whether platelet PCI is endogenously synthesized or taken up from plasma. Internalization of biotinylated-PCI was analyzed using platelets in suspension and gold-labeled streptavidin for visualization of incorporated biotin. Dose- and time-dependent uptake of PCI was found. PCI mRNA was detected in platelets by reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blotting, as well as in megakaryocytes by in situ hybridization of human bone marrow cryosections. We therefore conclude that platelets contain a functionally active PCI pool that is derived from both endogenous synthesis as well as internalization.

Synthesis and Ultrastructural Localization of Protein C Inhibitor in Human Platelets and Megakaryocytes

The occurrence of protein C inhibitor (PCI) in human platelets and megakaryocytes was analyzed. As judged from enzyme-linked immunosorbent assays (ELISAs), PCI was present in platelets at a concentration of 160 ng/2 × 109 cells. Its specific activity was 5 times higher than that of plasma PCI. Consistently, mainly the 57-kD form (active PCI) and some high molecular weight (Mr) forms, but no bands corresponding to cleaved PCI, were detected when platelet lysates were immunoprecipitated with monoclonal anti-PCI-IgG and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. The localization of PCI in platelets was studied by immunofluorescence histochemistry and immunotransmission electron microscopy: PCI was detected in  granules, in the open canalicular system, and on the plasma membrane. At these sites, colocalization with plasminogen activator inhibitor-1 was seen. Studies were performed to clarify whether platelet PCI is endogenously synthesized or taken up from plasma. Internalization of biotinylated-PCI was analyzed using platelets in suspension and gold-labeled streptavidin for visualization of incorporated biotin. Dose- and time-dependent uptake of PCI was found. PCI mRNA was detected in platelets by reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blotting, as well as in megakaryocytes by in situ hybridization of human bone marrow cryosections. We therefore conclude that platelets contain a functionally active PCI pool that is derived from both endogenous synthesis as well as internalization.

Aberrations of the tissue factor pathway in patients positive for lupus anticoagulant

To evaluate the relationship between the tissue factor (TF) pathway and lupus anticoagulant (LA), in the present study, we measured the plasma levels of TF antigen and TF pathway inhibitor (TFPI) antigen in patients positive for LA. Plasma TF and TFPI levels in LA-positive patients were significantly higher than levels in healthy volunteers (p < 0.01). In LA-positive patients, there were no significant differences in plasma TF and TFPI levels between patients with and without thrombosis. In patients with thrombosis, there was no significant difference in the plasma TF level between LA-positive and LA-negative patients; however, the plasma TFPI level in LA-positive patients was significantly lower than that in LA-negative patients (p < 0.01). We also examined the TF pathway in human umbilical venous endothelial cells (HUVEC) incubated with plasma of LA-positive patients, LA-negative patients, and healthy volunteers. TF activity was significantly higher (p < .05) in HUVECs incubated with the plasma of LA-positive patients than in cells incubated with the plasma of the other two groups (p < .01). However, there was no significant difference in TFPI antigen levels among the media of HUVECs incubated with the plasma of all groups. The viability of HUVEC incubated with the plasma of LA-positive patients with thromboses, LA-positive patients without thromboses, and LA-negative patients with thromboses were significantly lower than that of HUVECs incubated with the plasma of healthy volunteers (p < .01). These findings suggest that abnormalities of the TF pathway plays an important role in the mechanism of hypercoagulability in LA-positive patients. LA may affect vascular endothelial cells causing thrombogenesis.

Protein C inhibitor secreted from activated platelets efficiently inhibits activated protein C on phosphatidylethanolamine of platelet membrane and microvesicles

Protein C inhibitor (PCI) was detected in human platelets (2.9 ng/10(9) cells) and megakaryocytic cells (1.5 ng/10(6) cells). PCI mRNA was also detected in both platelets and megakaryocytic cells using nested polymerase chain reaction. PCI was found to be located in the alpha-granules of resting platelets. Approximately 30% of the total amount of PCI in platelets was released after stimulation with ADP, collagen, adrenalin, thrombin, or thrombin receptor-activating peptide. Secreted PCI was detected on the surface of activated platelets and phospholipid microvesicles. PCI secreted from thrombin receptor-activating peptide-stimulated platelets inhibited activated protein C (APC) efficiently. PCI significantly inhibited APC in the presence of phospholipid vesicles prepared using rabbit brain cephalin (RBC) or a mixture of 40% phosphatidylethanolamine (PE), 20% phosphatidylserine (PS), and 40% phosphatidylcholine (PC) with a second order rate constant of 1.0 x 10(6) M-1.min-1. Of these phospholipids, PE was critical for this inhibition. The dissociation constants of the binding of APC or PCI to solid phase phospholipids showed that APC binds more preferably to PE than to RBC or PS, and PCI to PE or RBC than to PS or PC. PCI binding to solid phase phospholipids depended on the presence of PE. RBC- or PE-bound PCI inhibited APC significantly but only weakly the gamma-carboxyglutamic acid domainless APC. The gamma-carboxyglutamic acid fragment of protein C suppressed the PCI-mediated inhibition of APC on solid phase RBC or PE. Most of the APC.PCI complex formed on solid phase RBC or PE was released into the soluble phase. These findings suggest that PCI secreted from activated platelets binds preferably to PE of platelet membrane and microvesicles and that it inhibits phospholipid-bound APC efficiently.

Plasma-activated factor VII level in patients positive for lupus anticoagulant

We examined plasma levels of activated factor VII (F VIla) in 50 patients positive for lupus anticoagulant (LA), in 83 patients negative for LA, and in 10 healthy volunteers as controls. Plasma F VIIa was present in healthy volunteers; its level was significantly increased, compared to the level in the controls, in patients with thrombosis, collagen diseases, and disseminated intravascular coagulation (DIC), suggesting that it reflected a thrombotic state. Plasma F VIIa was correlated with thrombin-antithrombin complex (TAT) in patients negative for LA but showed no such correlation in those positive for LA. Plasma F VIIa was negatively correlated with activated partial thromboplastin time (APTT) in patients positive for LA, but not in those negative for LA, suggesting that LA could inhibit the F VIIa assay system. Plasma F VIIa level was significantly increased in patients with thrombotic diseases; however, in patients positive for LA, it is possible that increased plasma F VIIa level may not be correlated with thrombogenicity.

The lupus anticoagulant/antiphospholipid syndrome

Lupus anticoagulants and anticardiolipin antibodies have been strongly associated with the risk of thrombosis, recurrent fetal loss, thrombocytopenia, and a number of other clinical manifestations that together have been referred to as the antiphospholipid syndrome. Despite growing evidence of the significance of this relationship, the pathogenetic mechanisms involved are largely unknown. Recent data suggest strongly that lupus anticoagulants (LACs) and anticardiolipin antibodies (ACAs) are antibodies to protein-phospholipid complexes rather than to phospholipids, as had originally been thought, and that other protein-phospholipid complexes, not recognized by standard assays for LACs or ACAs, may also exist in patients with the antiphospholipid syndrome. Although very recent experimental data may lead to new therapeutic approaches in this syndrome, at present we can only deal with the thrombotic risk by the use of long-term anticoagulation. This chapter reviews current methods of diagnosis, concepts of pathogenesis, and the basis for an approach to anticoagulation in patients at risk for thrombosis or other manifestations of the antiphospholipid syndrome.