Development and User Experiences of a Biopsychosocial Interprofessional Online Course on Persistent Somatic Symptoms.

Background: Communication between healthcare providers and patients with persistent somatic symptoms (PSS) is frequently hampered by mutual misunderstanding and dissatisfaction. Methods: We developed an online, interprofessional course to teach healthcare providers the knowledge, skills, and attitude they need to diagnose and treat PSS in a patient-centered manner based on the biopsychosocial model. The course consisted of six modules of 45-60 min. Each module contained different types of assignments, based on six cases: videos, discussion boards, reading assignments, polls, and quizzes. For this study, we included (1) medical residents, following the course as part of their residency training, and (2) healthcare providers (general practitioners, medical specialists, physiotherapists, nurses, and psychologists), following the course as continuing vocational training. Throughout the course, participants were asked to fill out online surveys, enquiring about their learning gains and satisfaction with the course. Results: The biopsychosocial approach was integrated across the modules and teached health care workers about recent insights on biological, psychological and social aspects of PSS. In total, 801 participants with a wide variety in clinical experience started the course; the largest groups of professionals were general practitioners (N = 400), physiotherapists (N = 124) and mental healthcare workers (N = 53). At the start of the course, 22% of the participants rated their level of knowledge on PSS as adequate. At the end of the course, 359 participants completed the evaluation questionnaires. Of this group, 81% rated their level of knowledge on PSS as adequate and 86% felt that following the course increased their competencies in communicating with patients with PSS (N = 359). On a scale from 1 to 10, participants gave the course a mean grade of 7.8 points. Accordingly, 85% stated that they would recommend the course to a colleague. Conclusion: Our course developed in a co-design process involving multiple stakeholders can be implemented, is being used, and is positively evaluated by professionals across a variety of health care settings.

Exploring temporal relationships among worrying, anxiety, and somatic symptoms.

OBJECTIVES: The role of anxiety symptoms in the development of functional somatic symptoms (FSS) is unknown. Somatic symptoms may be triggered by or give rise to anxiety symptoms. This study aimed to 1) explore interrelationships among within-day worrying, feeling anxious, and somatic symptoms, and 2) investigate the association between these interrelationships and overall level of FSS. METHODS: This study included 767 participants (83% females, mean age 39 years), who were recruited through an online crowdsourcing study in the Dutch general population. Somatic, and anxiety symptoms were reported thrice daily (6-h intervals) for 30 days using electronic diaries. FSS were assessed at baseline (PHQ-15). Temporal relationships among worrying, feeling anxious, and somatic symptoms were modeled using a multilevel vector autoregressive model. RESULTS: We observed large heterogeneity in the within-person interrelationships among worrying, feeling anxious and somatic symptoms. Averaged over participants, higher-than-usual somatic symptoms were associated with increases in levels of worrying six hours later (B = 0.017, 95% CI [0.006, 0.027]). At the between-person level, FSS levels predicted the persistence of feeling anxious (B = 0.230 95% CI [0.105, 0.350]) and the carry-over of worrying to feeling anxious over six-hours (B = 0.159, 95% CI [0.031, 0.283]). CONCLUSIONS: In contrast to what we expected, higher levels of somatic symptoms over multiple weeks were associated with the persistence and carry-over of within-day anxiety-related symptoms. One within-person association between psychological and somatic symptoms during the day was observed, suggesting that, over a time span of 6-h, anxiety symptoms relate to somatic symptoms only in a minority of people from the general population.

Clinical response correlates with 4-week postinjection ustekinumab concentrations in patients with moderate-to-severe psoriasis.

BACKGROUND: Cost-effective use of biologicals is important. As drug concentrations have been linked to clinical outcomes, monitoring drug concentrations is a valuable tool to guide clinical decision-making. A concentration-response relationship for ustekinumab at trough is uncertain owing to the contradictory results reported. OBJECTIVES: To investigate the relationship between 4-week postinjection ustekinumab concentrations and clinical response in patients with psoriasis. METHODS: Forty-nine patients with moderate-to-severe psoriasis treated with 45 mg or 90 mg ustekinumab every 12 weeks for ≥ 16 weeks were included. Ustekinumab serum concentrations and anti-ustekinumab antibodies were measured at week 4 after injection and disease severity was assessed by Psoriasis Area and Severity Index (PASI). RESULTS: At week 4 after injection, a significantly negative correlation was observed between ustekinumab concentrations and absolute PASI score up to 5·9 µg mL-1 (ρ = -0·357, P = 0·032). Ustekinumab concentrations were higher in optimal responders (PASI ≤ 2) than in suboptimal responders (PASI > 2) (4·0 vs 2·8 µg mL-1 , P = 0·036). The ustekinumab concentration threshold associated with optimal response was determined to be 3·6 µg mL-1 (area under the curve 0·71, sensitivity 86%, specificity 63%). Only one patient (2%) had anti-ustekinumab antibodies. Psoriatic arthritis was identified as an independent predictor of higher PASI scores and higher ustekinumab concentrations (P = 0·003 and P = 0·048, respectively). CONCLUSIONS: A concentration-response relationship at week 4 after injection was observed for patients with psoriasis treated with ustekinumab. Monitoring 4-week postinjection ustekinumab concentrations could timely identify underexposed patients who might benefit from treatment optimization. What's already known about this topic? Monitoring drug concentrations is a valuable tool that can guide clinical decision-making when drug concentrations are linked to clinical outcomes. The presence of a concentration-response relationship for ustekinumab at trough is still debated owing to the contradictory results reported. What does this study add? A concentration-response relationship at week 4 after injection for ustekinumab-treated patients with psoriasis was demonstrated. Monitoring 4-week postinjection ustekinumab concentrations could timely identify underexposed patients who might benefit from treatment optimization. Based on the findings of this study, a treatment algorithm for patients with a suboptimal response is proposed.

Individual variation in temporal relationships between exposure to radiofrequency electromagnetic fields and non-specific physical symptoms: A new approach in studying 'electrosensitivity'.

BACKGROUND: Everyday exposure to radiofrequency electromagnetic fields (RF-EMF) emitted from wireless devices such as mobile phones and base stations, radio and television transmitters is ubiquitous. Some people attribute non-specific physical symptoms (NSPS) such as headache and fatigue to exposure to RF-EMF. Most previous laboratory studies or studies that analyzed populations at a group level did not find evidence of an association between RF-EMF exposure and NSPS. OBJECTIVES: We explored the association between exposure to RF-EMF in daily life and the occurrence of NSPS in individual self-declared electrohypersensitive persons using body worn exposimeters and electronic diaries. METHODS: We selected seven individuals who attributed their NSPS to RF-EMF exposure. The level of and variability in personal RF-EMF exposure and NSPS were determined during a three-week period. Data were analyzed using time series analysis in which exposure as measured and recorded in the diary was correlated with NSPS. RESULTS: We found statistically significant correlations between perceived and actual exposure to wireless internet (WiFi - rate of change and number of peaks above threshold) and base stations for mobile telecommunications (GSM + UMTS downlink, rate of change) and NSPS scores in four of the seven participants. In two persons a higher EMF exposure was associated with higher symptom scores, and in two other persons it was associated with lower scores. Remarkably, we found no significant correlations between NSPS and time-weighted average power density, the most commonly used exposure metric. CONCLUSIONS: RF-EMF exposure was associated either positively or negatively with NSPS in some but not all of the selected self-declared electrohypersensitive persons.

Efficacy of switching to infliximab in patients with Crohn's disease with loss of response to adalimumab.

BACKGROUND AND STUDY AIMS: Anti-TNF monoclonal antibodies are a cornerstone in the treatment of Crohn's disease. Prospective data on switching from the subcutaneous and human adalimumab (ADM) to the intravenous and chimeric infliximab (IFX) are scarce. PATIENTS AND METHODS: In this prospective, observational, multicentre cohort study we included 21 patients with loss of response to ADM despite at least 4 consecutive weekly injections. Clinical response (CDAI drop≥70 points) and remission (CDAI≤150) were assessed after switching from ADM to IFX after 10 weeks, 6 and 12 months. Predictive factors of response/remission, the need for therapy intensification, discontinuation and safety were investigated. RESULTS: Short-term response and remission (10 weeks) were seen in 57% and 48% respectively. Mid- and long-term clinical response and remission were achieved in 40% and 25% after 6 months and in 45% and 20% after 12 months respectively. At 12 months, 81% still were on IFX. IFX therapy intensification was needed in half of the patients at 6 months and three quarter of patients at 12 months. Undetectable ADM trough levels (despite weekly injections) were a predictive factor for short-term response and remission to IFX. About half of the patients with response at week 10 maintained response at 6 and 12 months. CONCLUSIONS: Switching from ADM to IFX can be efficacious in patients with loss of response, in particular in case of undetectable ADM trough levels. The majority of patients however will need IFX therapy intensification during their first year of treatment.

Anti-infliximab antibody concentrations can guide treatment intensification in patients with Crohn's disease who lose clinical response.

BACKGROUND: The presence of antibodies towards infliximab (ATI) is associated with lower infliximab (IFX) trough concentrations and loss of response. IFX treatment intensification is effective for restoring response in most, but not all patients with Crohn's disease (CD). AIM: To compare outcome, pharmacokinetics and immunogenicity of treatment intensification strategies in patients with CD who lost clinical response to IFX. METHODS: A retrospective cohort study was conducted, including 103 patients with CD who lost clinical response during IFX maintenance therapy and therefore received a double dose IFX (10 mg/kg) and/or a next infusion after a shortened interval. IFX and ATI concentrations were measured in consecutive trough samples, just before (T0) and after (T+1) treatment intensification. RESULTS: Clinical response (physicians' global assessment) and biological response and remission (CRP) were restored in 63%, 42% and 24% of patients (evaluated at T+1). Treatment intensification increased IFX trough concentrations from 1.2 µg/mL [0.3-3.6] at T0 to 3.6 µg/mL [0.5-10.2] at T+1 (P < .0001). Using a drug tolerant assay, ATI were detected in the T0 sample of 47% of patients. ATI negatively impacted the achieved IFX trough concentration (Spearman r -0.57, P < .0001) and the probability of clinical response (P = 0.034) at T+1. When ATI were quantifiable but <282 ng/mL eq. at T0, combined interval shortening and dose doubling was more effective for restoring therapeutic IFX trough concentrations (≥3 µg/mL at T+1) than dose doubling alone, which in turn was more effective than interval shortening alone (P < .001). CONCLUSION: Antibodies towards infliximab can guide clinical decision-making on treatment intensification.

Amplified endogenous plasmin activity resolves acute thrombotic thrombocytopenic purpura in mice.

Essentials Plasmin is able to proteolyse von Willebrand factor. It was unclear if plasmin influences acute thrombotic thrombocytopenic purpura (TTP). Plasmin levels are increased during acute TTP though suppressed via plasmin(ogen) inhibitors. Allowing amplified endogenous plasmin activity in mice results in resolution of TTP signs. SUMMARY: Background Thrombotic thrombocytopenic purpura (TTP) is an acute life-threatening pathology, caused by occlusive von Willebrand factor (VWF)-rich microthrombi that accumulate in the absence of ADAMTS-13. We previously demonstrated that plasmin can cleave VWF and that plasmin is generated in patients during acute TTP. However, the exact role of plasmin in TTP remains unclear. Objectives Investigate if endogenous plasmin-mediated proteolysis of VWF can influence acute TTP episodes. Results In mice with an acquired ADAMTS-13 deficiency, plasmin is generated during TTP as reflected by increased plasmin-α2-antiplasmin (PAP)-complex levels. However, mice still developed TTP, suggesting that this increase is not sufficient to control the pathology. As mice with TTP also had increased plasminogen activator inhibitor 1 (PAI-1) levels, we investigated whether blocking the plasmin(ogen) inhibitors would result in the generation of sufficient plasmin to influence TTP outcome in mice. Interestingly, when amplified plasmin activity was allowed (α2-antiplasmin-/- mice with inhibited PAI-1) in mice with an acquired ADAMTS-13 deficiency, a resolution of TTP signs was observed as a result of an increased proteolysis of VWF. In line with this, in patients with acute TTP, increased PAP-complex and PAI-1 levels were also observed. However, neither PAP-complex levels nor PAI-1 levels were related to TTP signs and outcome. Conclusions In conclusion, endogenous plasmin levels are increased during acute TTP, although limited via suppression through α2-antiplasmin and PAI-1. Only when amplified plasmin activity is allowed, plasmin can function as a back-up for ADAMTS-13 in mice and resolve TTP signs as a result of an increased proteolysis of VWF.

Thrombin-activatable fibrinolysis inhibitor in human abdominal aortic aneurysm disease.

Essentials Patients with abdominal aortic aneurysms (AAA) develop dense clots that are resistant to lysis. This study explores the role of thrombin-activatable fibrinolysis inhibitor (TAFI) in human AAA. There is evidence of chronically increased TAFI activation in patients with AAA. TAFI may represent a pharmacological target for cardiovascular risk reduction in AAA. SUMMARY: Background Intra-luminal thrombosis is a key factor in growth of abdominal aortic aneurysms (AAAs). Patients with AAA form dense clots that are resistant to fibrinolysis. Thrombin-activatable fibrinolysis inhibitor (TAFI) has been shown to influence AAA development in murine models. Objective The aim of this study is to characterize the role of TAFI in human AAA. Methods Plasma levels of TAFI, TAFI activation peptide (TAFI-AP), activated/inactivated TAFI (TAFIa/ai) and plasmin-α2-antiplasmin complex were measured by ELISAs in patients with AAA (n = 202) and controls (n = 188). Results TAFIa/ai and TAFI-AP levels were higher in patients than controls (median [IQR], 20.3 [14.6-32.8] ng mL-1 vs. 14.2 [11.2-19.3] ng mL-1 and 355.0 [232.4-528.1] ng mL-1 vs. 248.6 [197.1-328.1] ng mL-1 ). TAFIa/ai was positively correlated with TAFI-AP (r = 0.164). Intact TAFI levels were not different between patients and controls (13.4 [11.2-16.1] µg mL-1 vs. 12.8 [10.6-15.4] µg mL-1 ). Plasmin-α2-antiplasmin was higher in AAA patients than controls (690.0 [489.1-924.3] ng mL-1 vs. 480.7 [392.6-555.3] ng mL-1 ). Conclusions The increase in TAFIa/ai and TAFI-AP suggests an increased TAFI activation in patients with AAA. Prospective studies are required to further elucidate the role of TAFI and fibrinolysis in AAA pathogenesis.

Dose de-escalation to adalimumab 40 mg every 3 weeks in patients with Crohn's disease - a nested case-control study.

BACKGROUND: Data on dose de-escalation in patients with Crohn's disease (CD) are limited. AIM: To evaluate outcomes of dose de-escalation from adalimumab (ADM) every other week (EOW) to every three weeks (ETW). METHODS: We selected patients with CD receiving maintenance therapy with ADM 40 mg ETW with serum levels (SL) available before and after dose de-escalation. Sex- and age-matched controls continuing ADM 40 mg EOW were identified. Patient reported outcome, C-reactive protein (CRP) and serum albumin were collected. RESULTS: Out of 898 patients, we identified 40 (11 male, median 37 years) who de-escalated to ADM 40 mg ETW for ADM-related adverse events (AE, n = 1), ADM SL >7 µg/mL (n = 8), or both (n = 31). Compared to controls, ADM SL dropped significantly within 4 months, without associated clinical or biochemical changes. In 53% of patients, dose de-escalation was associated with disappearance of AE (8/16 skin manifestation, 3/6 arthralgia, 5/7 frequent infectious episodes). During a median follow-up of 24 months, 65% of patients maintained clinical response, but 35% needed dose escalation back to ADM 40 mg EOW because of clinical relapse (n = 8), ADM SL <4 µg/mL (n = 2), or both (n = 4). CRP <3.5 mg/L at dose de-escalation was independently associated with dose escalation-free survival [odds ratio 6.28 (95% CI 1.83-21.59), P = 0.004]. We could not define a minimal ADM SL to consider or maintain dose de-escalation. CONCLUSIONS: Overall, 65% of patients who de-escalated to adalimumab 40 mg every 3 weeks remained in clinical remission for a median of 24 months. In 53% of patients, adalimumab-related adverse events disappeared after dose de-escalation. Regardless of adalimumab SL, disease remission should be assessed objectively prior to dose de-escalation.

Prognostic factors for long-term infliximab treatment in Crohn's disease patients: a 20-year single centre experience.

BACKGROUND: The long-term efficacy of infliximab in patients with Crohn's disease is suboptimal. AIM: To study prognostic factors for real-life long-term effcacy of infliximab in Crohn's disease. METHODS: All consecutive Crohn's disease patients treated with infliximab at a tertiary centre were retrospectively analysed. Only patients who received scheduled infliximab maintenance treatment were considered. Patient- and disease-related factors were used to identify independent predictors of infliximab failure-free survival using Cox proportional hazards regression. RESULTS: Of 1031 patients with Crohn's disease, 261 were eligible for inclusion. Median time on infliximab was 2.4 [IQR 1.4-4.7] years, and 65 (24.9%) patients experienced infliximab failure. Estimated 5-year infliximab failure-free survival was 65.9% (95% CI 58.3-73.5). Multivariate Cox regression identified disease duration ≥1 year (HR 2.5 (95% CI 1.2-5.2), P = 0.02), L1 disease location [HR 2.0 (1.1-3.5), P = 0.02], prior anti-TNF use [HR 2.3 (1.1-4.8), P = 0.03], haemoglobin <13.5 g/dL [HR 2.3 (1.2-4.4), P = 0.02], not using therapeutic drug monitoring [HR 8.0 (4.1-15.6), P = 1 × 10(-9) ], and first dose optimisation within first year [HR 3.7 (2.1-6.6), P = 5 × 10(-6) ] as independent predictors of infliximab failure-free survival. Stratifying patients into risk groups resulted in estimated 3-year infliximab failure-free survival rates ranging from 95.3% (94.2-96.4) to 26.3% (8.6-44.0) depending on the number of risk factors (P = 8 × 10(-13) ). CONCLUSIONS: This study identified several easy to obtain predictors of infliximab failure in patients with Crohn's disease, and these are in line with previous reports. Those with a high-risk profile for infliximab failure in whom infliximab initiation is considered, should be treated as early as possible making use of therapeutic drug monitoring.

Review article: pharmacological aspects of anti-TNF biosimilars in inflammatory bowel diseases.

BACKGROUND: Anti-tumour necrosis factor (anti-TNF) monoclonal antibodies have shown efficacy in inflammatory bowel diseases (IBD). As these therapies lose patent protection, biosimilar versions of the originator products are being developed, such as the infliximab biosimilar CT-P13; however, some uncertainty exists regarding their pharmacology in IBD. AIM: To review the literature on anti-TNF biosimilars focusing on pharmacokinetics, pharmacodynamic properties and comparative effectiveness, related to their use in IBD. METHODS: A PubMed literature search was performed using the following terms individually or in combination: 'biosimilars,' 'CT-P13,' 'Crohn's disease,' 'inflammatory bowel disease,' 'ulcerative colitis,' 'anti-TNFα therapy,' 'infliximab,' 'adalimumab,' 'pharmacokinetics,' 'immunogenicity.' RESULTS: Bioequivalence of CT-P13 and infliximab was shown in ankylosing spondylitis (AS) and therapeutic equivalence in rheumatoid arthritis (RA). Preliminary results of CT-P13 in IBD come from small post-marketing registries and case series with a relatively short-term follow-up period and suggest comparable efficacy and safety to infliximab. Inter- and intra-individual differences in exposure and response are well known for the original molecules but dosing regimens and concomitant medications are different for RA compared to IBD, limiting the ability to translate some of the pharmacology data in RA to IBD. Uncertainty exists about cross-reactivity of anti-drug antibodies and whether similar exposure-response relationships will be observed for biosimilars and efficacy thresholds for therapeutic drug monitoring can be used interchangeably. CONCLUSIONS: It is likely that biosimilars will be widely used for the treatment of IBD due to their cost savings and comparable efficacy. Nevertheless, robust post-marketing studies and pharmacovigilance are warranted in the coming years.

Ara h 1 protein-antibody dissociation study: evidence for binding inhomogeneities on a molecular scale.

The characterization of biomolecular interactions is essential when designing novel biosensors, since the interaction between the bioreceptor and the ligand determines important biosensing parameters such as sensitivity and selectivity. In this paper we study the interaction of the trimeric Ara h 1 protein with a monoclonal anti-Ara h 1 antibody by means of magnetic force-induced dissociation. The proteins were bound to magnetic particles and polystyrene surfaces by EDC/NHS reaction chemistry and by physisorption, respectively. Two different molecular configurations have been investigated, with either the Ara h 1 protein on the particles or the Ara h 1 protein on the polystyrene surface. A model with a Gaussian distribution of energy barriers for dissociation gives an adequate description for the measured multi-exponential decays. We hypothesize that distributions of molecular orientations as well as experimentally induced variations may underlay the observed distributions. The two molecular configurations show a different peak value of the energy distribution. Similarly, SPR experiments for two distinct configurations (either Ara h 1 protein on the surface, or anti-Ara h 1 antibody on the surface) also show clear differences in dissociation behavior. We hypothesize that the multivalency of the involved molecules leads to different modes of binding. The results of this work highlight the importance of molecular inhomogeneities when studying the interaction processes of biomolecular complexes.

Prior response to infliximab and early serum drug concentrations predict effects of adalimumab in ulcerative colitis.

BACKGROUND: Data for adalimumab in ulcerative colitis after prior use of infliximab are scarce. AIMS: To study adalimumab response rates and predictors of response in ulcerative colitis, including drug concentrations. METHODS: In this single centre cohort study 73 UC patients, previously exposed to infliximab, were assessed for response to adalimumab at weeks 12 and 52. Serum samples prior to week 12 were available and included in multivariate analysis to predict response. RESULTS: Overall clinical response at week 12 and 52 were 75% and 52%, respectively. Adalimumab was continued without need for dose escalation throughout year 1 in 16 patients, 22 needed dose escalation and 35 discontinued treatment within 1 year. Prior response to infliximab and early serum concentrations correlated with response. Receiver operator characteristic curve analysis yielded optimal adalimumab concentrations of 4.58 µg/mL for week 12 and 7.0 µg/mL for week 52. Independent predictors for response at week 12 were primary response to infliximab [odds ratio (OR) 8.33; 95% confidence interval (CI) 1.8-33.3; P = 0.006] and an adalimumab concentration ≥4.58 µg/mL at week 4 (OR 4.85; 95% CI 1.3-18.6; P = 0.009). Positive predictors for week 52 response were primary response to infliximab (OR 5.2; 95% CI 1.14-23.8; P = 0.034) and adalimumab concentration at week 4 of ≥7 µg/mL (OR 3.56; 95% CI 1.17-10.79; P = 0.025). CONCLUSION: Prior response to infliximab and high early adalimumab serum concentrations predict week 12 and year 1 responses to adalimumab in ulcerative colitis.

Identification of a novel, nanobody-induced, mechanism of TAFI inactivation and its in vivo application.

BACKGROUND: Down-regulation of fibrinolysis due to cleavage of C-terminal lysine residues from partially degraded fibrin is mainly exerted by the carboxypeptidase activity of activated thrombin-activatable fibrinolysis inhibitor (TAFIa). Recently, some intrinsic carboxypeptidase activity (i.e. zymogen activity) was reported for the proenzyme (TAFI); however, there is some discussion about its ability to cleave high molecular weight substrates. OBJECTIVE: We aimed to identify and characterize nanobodies toward mouse TAFI (mTAFI) that stimulate the zymogen activity and to test their effect in an in vitro clot lysis assay and an in vivo mouse thromboembolism model. METHODS AND RESULTS: Screening of a library of nanobodies toward mTAFI revealed one nanobody (VHH-mTAFI-i49) that significantly stimulates the zymogen activity of mTAFI from undetectable (< 0.35 U mg⁻¹) to 4.4 U mg⁻¹ (at a 16-fold molar ratio over mTAFI). The generated carboxypeptidase activity is unstable at 37 °C. Incubation of mTAFI with VHH-mTAFI-i49 revealed a time-dependent reduced activatability of mTAFI. Epitope mapping revealed that Arg227 and Lys212 are important for the nanobody/mTAFI interaction and suggest destabilization of mTAFI by disrupting the stabilizing interaction between the activation peptide and the dynamic flap region. In vitro clot lysis experiments revealed an enhanced clot lysis due to a reduced activation of mTAFI during clot formation. In vivo application of VHH-mTAFI-i49 in a mouse thromboembolism model decreased dose-dependently the fibrin deposition in the lungs of thromboembolism-induced mice. CONCLUSION: The novel, nanobody-induced, reduced activatability of mTAFI demonstrates to be a very potent approach to enhance clot lysis.

Monoclonal antibodies targeting the antifibrinolytic activity of activated thrombin-activatable fibrinolysis inhibitor but not the anti-inflammatory activity on osteopontin and C5a.

BACKGROUND: Recently, anti-thrombin-activatable fibrinolysis inhibitor (TAFI) mAbs selectively inhibiting plasmin-mediated TAFI activation were shown to stimulate fibrinolysis in vitro and in vivo, suggesting, in contrast to other findings, that plasmin-mediated TAFI activation plays an important role in fibrinolysis regulation. OBJECTIVE: To further characterize the effects of two plasmin-specific anti-TAFI mAbs (MA-TCK11A9 and MA-TCK26D6) on TAFI-dependent inhibition of fibrinolysis. METHODS AND RESULTS: Both mAbs inhibited plasmin-mediated but not thrombin/thrombomodulin-mediated TAFI activation, whereas neither inhibited the cleavage of hippuryl-arginine by activated TAFI (TAFIa). They stimulated tissue-type plasminogen activator-induced fibrinolysis in different clot lysis models through a TAFI-dependent mechanism, especially in the presence of thrombomodulin (TM), a condition in which TAFI is largely activated by the thrombin-TM complex. In a fibrinolysis-based TAFIa activity assay, both mAbs inhibited TAFIa, whereas other mAbs targeting thrombin-TM-mediated TAFI activation did not. The inhibition of TAFIa activity, however, was substrate-specific, because neither mAb inhibited the cleavage of thrombin-activated osteopontin and C5a by TAFIa, thus sparing the anti-inflammatory activity of TAFIa. CONCLUSIONS: Our anti-TAFI mAbs, by selectively inhibiting TAFIa activity on fibrin, may represent the prototype of a new class of TAFI inhibitors with improved pharmacologic activity.

Insights into thrombin activatable fibrinolysis inhibitor function and regulation.

Fibrinolysis is initiated when the zymogen plasminogen is converted to plasmin via the action of plasminogen activators. Proteolytic cleavage of fibrin by plasmin generates C-terminal lysine residues capable of binding both plasminogen and the plasminogen activator, thereby stimulating plasminogen activator-mediated plasminogen activation and propagating fibrinolysis. This positive feedback mechanism is regulated by activated thrombin activatable fibrinolysis inhibitor (TAFIa), which cleaves C-terminal lysine residues from the fibrin surface, thereby decreasing its cofactor activity. TAFI can be activated by thrombin alone, but the rate of activation is accelerated when in complex with thrombomodulin. Plasmin is also known to activate TAFI. TAFIa has no known physiologic inhibitors and consequently, its primary regulatory mechanism involves its intrinsic thermal instability. The rate of TAFI activation and stability of the active form, TAFIa, function in maintaining its concentration above the threshold value required to down-regulate fibrinolysis. Although all methods to quantify TAFI or TAFIa have their limitations, epidemiologic studies have indicated that elevated TAFI levels are correlated with an increased risk of venous thrombosis. Major efforts have been made to develop TAFI inhibitors that can either directly interfere with TAFIa activity or impair its activation. However, the anti-inflammatory properties of TAFIa might complicate the development and application of a TAFIa inhibitor that aims to increase the efficiency of thrombolytic therapy.