Novel ELISA for the specific detection of protease NEXIN-1 in human biological samples

Introduction

Serpin E2 or protease nexin‐1 (PN‐1) is a glycoprotein belonging to the serpin superfamily, whose function is closely linked to its ability to inhibit thrombin and proteases of the plasminergic system.

Objectives

In the absence of specific quantitative methods, an ELISA for the quantification of human PN‐1 was characterized and used in biological fluids.

Methods

The ELISA for human PN‐1 was developed using two monoclonal antibodies raised against human recombinant PN‐1. PN‐1 was quantified in plasma, serum, platelet secretion from controls and patients with hemophilia A and in conditioned medium of aortic tissue.

Results

A linear dose–response curve was observed between 2 and 35 ng/mL human PN‐1. Intra‐ and interassay coefficients of variation were 6.2% and 11.1%, respectively. Assay recoveries of PN‐1 added to biological samples were ≈95% in plasma, ≈97% in platelet reaction buffer, and ≈93% in RPMI cell culture medium. Levels of PN‐1 secreted from activated human platelets from controls was similar to that of patients with hemophilia A. PN‐1 could be detected in conditioned media of aneurysmal aorta but not in that of control aorta.

Conclusion

This is the first fully characterized ELISA for human serpin E2 level in biological fluids. It may constitute a relevant novel tool for further investigations on the pathophysiological role of serpin E2 in a variety of clinical studies.

Therapeutic drug monitoring in dermatology: the way towards dose optimization of secukinumab in chronic plaque psoriasis

Background

Despite the favourable efficacy profile of secukinumab, clinicians encounter varying clinical responses among patients potentially associated with under‐ and overdosing. As biologics are expensive, their rational use is crucial and evident. Therapeutic drug monitoring could guide clinicians in making decisions about treatment modifications.

Aim

In this multicentre, prospective study, we aimed to develop and validate a secukinumab immunoassay and searched for the therapeutic window in patients with psoriasis.

Methods

We determined secukinumab concentrations at trough in sera from 78 patients with psoriasis at multiple timepoints (Weeks 12, 24, 36, 48 and 52; after Week 52, measurements could be taken at an additional three timepoints) during maintenance phase, using an in‐house secukinumab immunoassay consisting of a combination of MA‐SEC66A2 as capture antibody and MA‐SEC67A9, conjugated to horseradish peroxidase, as detecting antibody. At each hospital visit, disease severity was assessed using the Psoriasis Area and Severity Index (PASI).

Results

After quantification, 121 serum samples were included for dose–response analysis. Based on a linear mixed‐effects model, secukinumab trough concentrations were found to decrease with increasing body mass index (BMI). Based on receiver operating characteristic (ROC) analysis, we concluded that the minimal effective secukinumab threshold was 39.1 mg/L in steady state, and that this was associated with a 92.7% probability of having an optimal clinical response (PASI ≤ 2 or reduction in PASI of ≥ 90%).

Conclusions

Monitoring and targeting a secukinumab trough concentration of 39.1 mg/L may be a viable treatment option in suboptimal responders. In patients with higher BMI, weight‐based dosing may be needed in order to prevent underdosing.

Endoscopic remission can be predicted by golimumab concentrations in patients with ulcerative colitis treated with the changed label

BACKGROUND

In 2018, the European Medicines Agency (EMA) replaced a fixed 50 mg every 4-week maintenance regimen of golimumab for ulcerative colitis (UC) patients weighing <80 kg with new, flexible dosing that allows reactive dose optimization to 100 mg if clinically needed. We analyzed the endoscopic remission rates and pharmacokinetics of this new dosing regimen in real-life settings.

METHODS

We prospectively recruited 30 consecutive (17 with body weight <80 kg) patients with UC who received golimumab with the new EMA label. The primary endpoint was endoscopic remission (Mayo ≤1) assessed by centrally-read endoscopy at week 14 and year 1. Golimumab concentrations, measured at nine prespecified timepoints, were correlated with endoscopic remission and identified cut-offs.

RESULTS

Endoscopic remission was achieved in 15/30 (50%) and 10/30 (33%) patients at week 14 and year 1, respectively. Reactive dose optimization to 100 mg maintenance was needed in 13/17 (76%) patients. Golimumab concentrations at week 6 predicted week 14 and year 1 endoscopic remission. Week 6 concentrations >10.7 µg/ml were a strong predictor for achievement and maintenance of endoscopic remission during the first year of treatment, while concentrations <5.1 µg/ml identified the opposite.

CONCLUSION

One-third of the patients reached and maintained endoscopic remission during the first year of golimumab treatment, but the need for dose optimization to 100 mg every 4 weeks of maintenance was high in patients weighing <80 kg. Golimumab concentrations <5.1 µg/ml at week 6 identified patients who are unlikely to reach and maintain endoscopic remission with the new, flexible EMA label.

Development and validation of immunoassays for monitoring of guselkumab and anti-guselkumab antibodies in patients with moderate-to-severe psoriasis

Therapeutic drug monitoring, which is the measurement of drug concentrations in the blood, is a useful tool to guide clinical decision-making and treatment adjustments, on the condition that drug concentrations are correlated with treatment response. For guselkumab, an anti-IL-23 monoclonal antibody for the treatment of moderate-to-severe psoriasis, such a concentration-response relationship could not yet be determined as no commercial assays for the quantification of this drug or antibodies against this drug are available. Therefore, the aim of this study was to develop and validate immunoassays for the quantification of guselkumab and anti-guselkumab antibodies according to the guidelines of the European Medicines Agency (EMA). A diverse panel of 20 highly specific anti-guselkumab monoclonal antibodies (MA-GUS) was generated of which eight revealed a neutralizing capacity of ≥65 %. At least seven different antibody clusters were identified based on their epitope binning profile. Using MA-GUS9F6 as the capture antibody and MA-GUS12G12 as the detection antibody, an ELISA was developed with a dose-response curve ranging from 0.08 to 5 ng/mL. The assay was specific, selective and could accurately and precisely quantify guselkumab concentrations in spiked healthy control serum and serum from guselkumab-treated psoriasis patients with a cut-off for quantification of 0.014 μg/mL. The presence of IL-23 in physiological concentrations or of non-neutralizing antibodies did not impact the quantification of guselkumab, while the presence of neutralizing antibodies did. Using MA-GUS12A9 as a calibrator, two anti-guselkumab antibody assays were developed to detect anti-guselkumab antibodies, which differ in the threshold for detection and quantification and the tolerance to the presence of guselkumab. Together, these validated immunoassays are essential to establish a concentration-response relationship and will allow the future implementation of therapeutic drug monitoring in moderate-to-severe psoriasis patients receiving guselkumab treatment.

Generation and characterization of monoclonal antibodies against the N-terminus of alpha-2-antiplasmin

Around 70% of circulating alpha-2-antiplasmin (α2AP), the main natural plasmin inhibitor, is N-terminally cleaved between residues Pro12 and Asn13 by antiplasmin-cleaving enzyme. This converts native Met-α2AP into the more potent fibrinolysis inhibitor Asn-α2AP. The Arg6Trp (R6W) polymorphism affects the N-terminal cleavage rate of Met-α2AP in a purified system, with ~8-fold faster conversion of Met(R6)-α2AP than Met(W6)-α2AP. To date, assays to determine N-terminally intact Met-α2AP in plasma have been limited to an ELISA that only measures Met(R6)-α2AP. The aim of this study was to generate and characterize monoclonal antibodies (mAbs) against Met(R6)-α2AP, Met(W6)-α2AP and all α2AP forms (total-α2AP) in order to develop specific Met(R6)-α2AP and Met(W6)-α2AP ELISAs. Recombinant Met(R6)-α2AP, Met(W6)-α2AP and Asn-α2AP were expressed in Drosophila S2 cells. Using hybridoma technology, a panel of 25 mAbs was generated against a mixture of recombinant Met(R6)-α2AP and Met(W6)-α2AP. All mAbs were evaluated for their specific reactivity using the three recombinant α2APs in one-site non-competitive ELISAs. Three mAbs were selected to develop sandwich-type ELISAs. MA-AP37E2 and MA-AP34C4 were selected for their specific reactivity against Met(R6)-α2AP and Met(W6)-α2AP, respectively, and used for coating. MA-AP15D7 was selected for its reactivity against total-α2AP and used for detection. With the novel ELISAs we determined Met(R6)-α2AP and Met(W6)-α2AP levels in plasma samples and we showed that Met(R6)-α2AP was converted faster into Asn-α2AP than Met(W6)-α2AP in a plasma milieu. In conclusion, we developed two specific ELISAs for Met(R6)-α2AP and Met(W6)-α2AP, respectively, in plasma. This will enable us to determine N-terminal heterogeneity of α2AP in plasma samples.

Immunoassays for the Quantitation of Porcine PAI-1 Antigen and Activity in Biological Fluid Samples

Two monoclonal antibody-based enzyme-linked immunosorbent assays (ELISAs) for the quantitation of porcine plasminogen activator inhibitor-1 (PAI-1) antigen and activity in plasma were constructed and validated. The intra-assay, interassay, and interdilution coefficients of variation were 4.3, 13, and 8%, respectively, for the antigen ELISA and 5, 16, and 11% for the activity assay. Assay recoveries, in the antigen ELISA, of either latent or active recombinant porcine PAI-1 (10 and 50 ng/ml) added to plasma were 86 ± 9% and 92 ± 22%, respectively, for the latent form and 89 ± 9% and 87 ± 7% for the active form (mean ± SD, n = 3 to 4). In the immunofunctional assay, recoveries for the same concentrations of active PAI-1 were 108 ± 16% and 92 ± 21%, respectively. In male porcine plasma the level of PAI-1 antigen was 31 ± 11 ng/ ml and the activity, 34 ± 16 ng/ml (mean ± SD, n = 10). In female plasma PAI-1 antigen levels were 20 ± 5.2 ng/ml and the PAI-1 activity 42 ± 17 ng/ml (n = 13). A linear correlation was found between PAI-1 antigen and activity levels in male (r = 0.60) and female (r = 0.70) plasma. Immunodepletion resulted in a decrease of >95% of the original PAI-1 antigen or activity levels. Incubation of plasma samples at 37° C for 16 h resulted in a significant decrease (70 to 85%) of PAI-1 activity. Under these conditions (37° C, 16 h) PAI-1 antigen levels remained unchanged in males whereas the response of the female samples in the PAI-1 antigen assay increased two-fold.

In lysed platelet-rich plasma males had 990 ± 470 ng/ml antigen and 160 ± 80 ng/ml activity and females, 920 ± 500 ng/ml antigen and 150 ± 98 ng/ml activity corresponding to 2.1 ± 0.77 fg PAI-1 antigen per platelet. Only 16% of PAI-1 released from platelets was found to be active. Linear correlations between PAI-1 antigen and activity were found for both males (r = 0.61) and females (r = 0.67).

The assays are both sensitive and specific and may, therefore, aid the elucidation of the pathophysiological role of PAI-1 in swine experimental models of atherosclerosis and other thrombotic disorders.

Variability in Golimumab Exposure: A 'Real-Life' Observational Study in Active Ulcerative Colitis

BACKGROUND AND AIMS

Golimumab has been approved recently to treat refractory moderate-to-severe ulcerative colitis [UC]. To date it is not clear why a considerable fraction of patients do not respond, or lose initial response, to golimumab therapy. Our aim was to investigate whether a low golimumab serum concentration and/or a positive anti-golimumab antibody status reduces the efficacy of this drug in patients with UC.

METHODS

Serum samples of 21 patients with moderate-to-severe UC were collected during the first 14 weeks of golimumab therapy. For measurement of golimumab serum concentrations, both a tumour necrosis factor [TNF]-coated enzyme-linked immunosorbent assay [ELISA] and a sandwich-type ELISA were developed. Anti-golimumab antibodies were measured using a bridging ELISA and a newly-developed drug-tolerant immunoassay. Clinical response and mucosal healing were assessed 14 weeks after start of treatment.

RESULTS

Out of 21 patients, 10 [48%] reached partial clinical response at Week 14. Median [interquartile range] serum golimumab concentration was significantly higher in partial clinical responders than in non-responders: 10.0 [7.8-10.5] µg/ml versus 7.4 [4.8-8.3] µg/ml at Week 2 [p = 0.035] and 5.1 [4.0-7.9] µg/ml versus 2.1 [1.8-4.2] µg/ml at week 6 [p = 0.037]. Four out of 21 UC patients developed anti-golimumab antibodies, detectable only using a drug-tolerant immunoassay, and three had a partial clinical response at that time. Clinical non-responders had a significantly more severe colitis, indicated by a higher endoscopic Mayo score at baseline compared with partial clinical responders [p = 0.048].

CONCLUSION

Adequate exposure to golimumab drives clinical response. A worse disease at baseline influences clinical response rate negatively.

Validation of a sample pretreatment protocol to convert a drug-sensitive into a drug-tolerant anti-infliximab antibody immunoassay

A meta-analysis revealed that up to 51% of patients treated with infliximab develop anti-drug Abs (ADA) which are associated with loss of response. Detection of ADA is strongly influenced by assay technique since drug-sensitive ADA assays are not able to detect ADA in the presence of drug and therefore underestimate ADA development. In addition, the lack of a calibrator antibody that can be used in a drug-sensitive and drug-tolerant assay hampers an adequate comparison among different assays. Here we present a sample pretreatment protocol to convert the bridging assay, originally developed as a drug-sensitive assay, into a drug-tolerant assay, allowing use of the same assay and calibrator antibody MA-IFX10F9. Using the sample pretreatment protocol, the bridging assay detects antibodies towards infliximab in samples containing up to 5-fold infliximab over anti-infliximab. Analysis of consecutive serum samples from infliximab treated patients revealed that the drug-tolerant assay detects ADA development up to 40 weeks earlier compared to the drug-sensitive assay. In conclusion, the sample pretreatment protocol can be implemented in various assay formats and allows determination of ADA in the presence of drug, providing the possibility for early treatment optimization. Copyright © 2016 John Wiley & Sons, Ltd.

Generation and characterization of a unique panel of anti-adalimumab specific antibodies and their application in therapeutic drug monitoring assays

A number of assays are currently available to support therapeutic drug monitoring of adalimumab. A complete characterization of the assays and comparison of different assays has not been performed. The aim of this study, therefore, is to generate and characterize of a panel of monoclonal antibodies towards adalimumab (MA-ADM); to use this panel to develop novel assays to determine adalimumab concentrations; to assess the impact of tumor necrosis factor (TNF) and (non-)neutralizing antibodies on adalimumab detection and to compare the performance of assays. In total, ten specific MA-ADM were generated of which four revealed a neutralizing potency of >78%. At least six different clusters were identified using principal component analysis. MA-ADM40D8 was selected as detecting antibody to determine adalimumab in the TNF-coated ELISA (A) and the MA-ADM28B8/MA-ADM40D8 antibody pair was chosen for use in the MA-coated ELISA (B). The impact of TNF and (non-) neutralizing antibodies was similar in both ELISAs. Finally, serum samples of adalimumab-treated Crohn's disease patients were collected and used for an external validation using the assay of Sanquin (C) and the apDia kit (D). All adalimumab assays showed excellent Pearson correlation: r=0.96 for A versus B, 0.96 for A versus C, 0.94 for A versus D, 0.97 for B versus C, 0.95 for B versus D and 0.94 for C and D. The excellent agreement with the two commercially available ELISAs allows harmonization of treatment algorithms in and between different hospitals/infusion centers.

Development and evaluation of monoclonal antibodies as probes to assess the differences between two tomato pectin methylesterase isoenzymes

The enzyme pectin methylesterase (PME) was purified from red ripe tomatoes (Lycopersicon esculentum) and through affinity chromatography two isoenzymes were fractionated (t1PME and t2PME). Further analysis of these two isoenzymes, both having a molar mass of 34.5kDa, revealed a difference in the N-terminal sequence and in amino acid composition. t1PME was identified as the major isoenzyme of PME in tomato fruit. In this study the aim was to develop a toolbox, consisting of monoclonal antibodies, that allows to gain insight into the in situ localization of PME in plant based food systems like tomatoes. A panel of six interesting monoclonal antibodies was raised against both isoenzymes, designated MA-TOM1-12E11, MA-TOM1-41B2, MA-TOM2-9H8, MA-TOM2-20G7, MA-TOM2-31H1 and MA-TOM2-38A11. The differences in epitopes between these monoclonal antibodies were determined using affinity tests towards denatured PME, cross-reactivity tests and inhibition tests. Characterization of these antibodies indicated an immunological difference between t1PME and t2PME, also revealing a conserved epitope on t2PME, carrot PME and strawberry PME. Different epitopes are recognized by the generated antibodies making them excellent probes for immunolocalization of PME by tissue printing. In tomato, t1PME and t2PME showed a pronounced co-localization, especially in the pericarp and the radial arms of the pericarp. Three of the generated antibodies could be used for immunolocalization of PME in carrots (Daucus carota L.), which was only present in the cortex and not in the vascular cylinder of carrots.

Development of sandwich-type ELISAs for the quantification of rat and murine thrombin activatable fibrinolysis inhibitor in plasma

BACKGROUND

Altered plasma levels of thrombin activatable fibrinolysis inhibitor (TAFI) are associated with a large number of pathologies. Rat and murine models are frequently used to study the pathophysiological role of TAFI in vivo but immunological tools to quantify rat and murine TAFI are lacking.

OBJECTIVE

The production of monoclonal antibodies (mAb) towards rat TAFI and the development of an ELISA for the quantification of rat and murine TAFI in plasma.

METHODS AND RESULTS

Monoclonal antibodies were raised in TAFI-deficient mice towards (activated) recombinant rat TAFI. Pair-wise testing of the mAb revealed three suitable ELISA combinations, namely RT36A3F5/RT30D8-HRP, RT36A3F5/RT82F12-HRP and RT82F12/RT36A3F5-HRP. All three ELISAs are highly specific for rat and murine TAFI. TAFI concentrations in the lower ng mL(-1) range can be determined in plasma samples with a high reproducibility. Comparing TAFI antigen levels measured by these ELISAs with TAFIa activity values determined by activity based assays revealed excellent correlations (R(2) > 0.98). The average antigen levels of 20 individual rat plasma samples were 16 +/- 2 microg mL(-1) using the RT36A3F5-RT30D8-HRP, 12 +/- 2 microg mL(-1) using the RT36A3F5-RT82F12-HRP and 21 +/- 2 microg mL(-1) using the RT82F12-RT36A3F5-HRP ELISA. The determined antigen levels in rat plasma are similar to the levels reported for human plasma.

CONCLUSIONS

We developed three highly specific and extremely sensitive sandwich-type ELISAs for the quantification of rat and murine TAFI in plasma. The described ELISAs will facilitate in vivo investigation on the pathophysiological role of TAFI.

Effect of improving flue gas cleaning on characteristics and immobilisation of APC residues from MSW incineration

The flue gas cleaning system of a MSW incinerator with a capacity of 350 kt/year was changed to improve the HCl elimination efficiency. Instead of the semi-wet operating spray reactor and subsequent baghouse, a two-step wet flue gas cleaning was added behind the baghouse. Elemental composition, X-ray powder diffraction patterns and TGA measurements showed that the resulting APC residue was totally different from the former residue. As a consequence, leaching characteristics of both residues also differed and another treatment was required prior to disposal. For the former residue, mainly leaching of Pb (>100 mg/l), necessitated treatment prior to landfilling. The lower alkalinity of the new residue resulted in a leachate pH of 9.7 and a Pb concentration of 0.8 mg/l. The leachate pH of the former residue was 12.4. The leaching of Pb and Zn increased above 100 mg/l when immobilising the new residue with cement. Better results were obtained when immobilising with micro silica. The high CaCl2 x 2H2O content of the new residue brought along clogging of the bag filter system. Adding 1.4% of CaO (or 1.9% of Ca(OH)2) to the residue already improved these inconveniences but again significantly changed the leaching behaviour of the residue.

Development of ELISAs measuring the extent of TAFI activation

OBJECTIVE

To date, quantitation of TAFI antigen levels has been mainly focused on "total" antigen levels and has been shown to yield ambiguous results because of the existence of different isoforms and various degrees of activation. Our objective was to develop assays that allow measuring the extent of TAFI activation.

METHODS AND RESULTS

A variety of enzyme-linked immunosorbent assays (ELISAs) were evaluated for their preferential reactivity toward TAFI before and after activation, and toward the recombinantly expressed activation peptide. Three ELISAs with distinct reactivities were selected: recognizing either exclusively nonactivated TAFI, the released activation peptide, or exclusively TAFIa (activated TAFI). Evaluation of TAFI activation during clot lysis revealed that decreases of TAFI levels are associated with increases of the released activation peptide and TAFIa levels. In addition, antigenic measurement of TAFIa parallels activity measured by chromogenic assay. Analyzing plasma samples revealed that subjects with hyperlipidemia had significantly higher plasma levels of both the activation peptide (109.2 versus 95.5; P<0.001) and TAFIa (112.1 versus 103.3; P=0.03), and not of TAFI antigen (92.5 versus 87.9; P=0.07) (results in % of plasma pooled from normolipidemic subjects).

CONCLUSIONS

ELISAs that allow to measure the extent of TAFI activation were developed. These ELISAs constitute more sensitive markers in studies on the relationship between TAFI and cardiovascular diseases.

Development of a genotype 325-specific proCPU/TAFI ELISA

OBJECTIVE

A Thr/Ile polymorphism at position 325 in the coding region of proCPU has been reported. Immunological assays, fully characterized (including genotype dependency), are required for the quantitation of proCPU levels.

METHODS AND RESULTS

We have generated a panel of monoclonal antibodies against human, plasma-derived proCPU. Two combinations exhibiting distinct reactivities were selected for measurement of proCPU in plasma. T12D11/T28G6-HRP yielded values of 10.1+/-3.1 microg/mL (mean+/-SD, n=86; normal donors), and T32F6/T9G12-HRP yielded values of 5.4+/-3.0 microg/mL. Grouping according to the 325 genotype demonstrated that T12D11/T28G6-HRP was independent to this polymorphism whereas T32F6/T9G12-HRP revealed a complete lack of reactivity with the Ile/Ile genotype (ie, 0.0+/-0.0, 4.2+/-1.7, and 7.3+/-2.9 microg/mL for the Ile/Ile, Ile/Thr, and Thr/Thr isoforms, respectively). Commercially available antigen assays appeared to be partially dependent on the 325 genotype (eg, 44+/-8.9% and 100+/-30% for the Ile/Ile and Thr/Thr isoforms, respectively).

CONCLUSIONS

Our data demonstrate that great care should be taken when evaluating proCPU antigen values as a putative causative agent or as a diagnostic risk marker for cardiovascular events.

The distal hinge of the reactive site loop and its proximity: a target to modulate plasminogen activator inhibitor-1 activity

The serpin plasminogen activator inhibitor type 1 (PAI-1) plays a regulatory role in various physiological processes (e.g. fibrinolysis and pericellular proteolysis) and forms a potential target for therapeutic interventions. In this study we identified the epitopes of three PAI-1 inhibitory monoclonal antibodies (MA-44E4, MA-42A2F6, and MA-56A7C10). Differential cross-reactivities of these monoclonals with PAI-1 from different species and sequence alignments between these PAI-1s, combined with the three-dimensional structure, revealed several charged residues as possible candidates to contribute to the respective epitopes. The production, characterization, and subsequent evaluation of a variety of alanine mutants using surface plasmon resonance revealed that the residues His(185), Arg(186), and Arg(187) formed the major sites of interaction for MA-44E4. In contrast, the epitopes of MA-42A2F6 and MA-56A7C10 were found to be conformational. The epitope of MA-42A2F6 comprises residues Lys(243) and Glu(350), whereas the epitope of MA-56A7C10 comprises residues Glu(242), Lys(243), Glu(244), Glu(350), Asp(355), and Arg(356). The participation of Glu(350), Asp(355), and Arg(356) provides a molecular explanation for the differential exposure of this epitope in the different conformations of PAI-1 and for the effect of these antibodies on the kinetics of the formation of the initial PAI-1-proteinase complexes. The localization of the epitopes of MA-44E4, MA42A2F6, and MA-56A7C10 elucidates two previously unidentified molecular mechanisms to modulate PAI-1 activity and opens new perspectives for the rational development of PAI-1 neutralizing compounds.

Identification of a target site in plasminogen activator inhibitor-1 that allows neutralization of its inhibitor properties concomitant with an allosteric up-regulation of its antiadhesive properties

The serpin plasminogen activator inhibitor-1 (PAI-1) has a dual function: 1) it plays an important role as a direct inhibitor of the plasminogen activation system, and 2) its interaction with the adhesive glycoprotein vitronectin suggests a role in tissue remodeling and metastasis, independent from its proteinase inhibitory properties. Unique to this serpin is the close association between its conformational and functional properties. Indeed, PAI-1 can occur in an active and a latent conformation, but both functions are exclusively present in the active conformation. We report here the epitope localization and functional effects of a monoclonal antibody (MA-124K1) that inhibits rat PAI-1 activity and simultaneously increases the binding of inactive PAI-1 to vitronectin (the affinity constant of PAI-1 for vitronectin is 2 x 10(7) m(-1) in the absence of MA-124K1 and 160 x 10(7) m(-1) in the presence of MA-124K1). To the best of our knowledge, this is the first monoclonal antibody dissociating the proteinase inhibitory properties from the vitronectin binding properties in PAI-1. Mutation of Glu(212) and/or Glu(220) in rat PAI-1 to Ala results in a strongly reduced affinity or absence of binding to MA-124K1. The three-dimensional structure of PAI-1 reveals that these residues constitute a conformational epitope close to the reactive-site loop and compatible with the effect of MA-124K1 on the inhibitory properties of PAI-1. However, the vitronectin binding site is localized at the opposite site of the molecule, indicating that the effect of MA-124K1 involves an allosteric modulation of the vitronectin binding site. Cell culture experiments revealed a significant reduction of cell attachment and migration in the presence of MA-124K1, providing evidence for the functional relevance of this antibody-mediated up-regulation of the vitronectin binding properties of PAI-1. In conclusion, a novel mechanism for interference with PAI-1 functions has been identified and is of importance in the modulation of cell migration and related events (e.g. tumor metastasis).

Immunoassays for the quantitation of porcine PAI-1 antigen and activity in biological fluid samples

Two monoclonal antibody-based enzyme-linked immunosorbent assays (ELISAs) for the quantitation of porcine plasminogen activator inhibitor-1 (PAI-1) antigen and activity in plasma were constructed and validated. The intra-assay, interassay, and interdilution coefficients of variation were 4.3, 13, and 8%, respectively, for the antigen ELISA and 5, 16, and 11% for the activity assay. Assay recoveries, in the antigen ELISA. of either latent or active recombinant porcine PAI-1 (10 and 50 ng/ml) added to plasma were 86 +/- 9% and 92 +/- 22%, respectively, for the latent form and 89 +/- 99% and 87 +/- 7% for the active form (mean +/- SD, n = 3 to 4). In the immunofunctional assay, recoveries for the same concentrations of active PAI-1 were 108 +/- 16% and 92 +/- 21%, respectively. In male porcine plasma the level of PAI-1 antigen was 31 +/- 11 ng/ ml and the activity, 34 +/- 16 ng/ml (mean +/- SD, n = 10). In female plasma PAI-1 antigen levels were 20 +/- 5.2 ng/ml and the PAI-1 activity 42 +/- 17 ng/ml (n = 13). A linear correlation was found between PAI-1 antigen and activity levels in male (r = 0.60) and female (r = 0.70) plasma. Immunodepletion resulted in a decrease of >95% of the original PAI-1 antigen or activity levels. Incubation of plasma samples at 37 degrees C for 16 h resulted in a significant decrease (70 to 85%) of PAI-1 activity. Under these conditions (37 degrees C, 16 h) PAI-1 antigen levels remained unchanged in males whereas the response of the female samples in the PAI-1 antigen assay increased two-fold. In lysed platelet-rich plasma males had 990 +/- 470 ng/ml antigen and 160 +/- 80 ng/ml activity and females, 920 +/- 500 ng/ml antigen and 150 +/- 98 ng/ml activity corresponding to 2.1 +/- 0.77 fg PAI-1 antigen per platelet. Only 16% of PAI-1 released from platelets was found to be active. Linear correlations between PAI-1 antigen and activity were found for both males (r = 0.61) and females (r = 0.67). The assays are both sensitive and specific and may, therefore, aid the elucidation of the pathophysiological role of PAI-1 in swine experimental models of atherosclerosis and other thrombotic disorders.

DSM-III-R and ICD-10 personality disorder features among women experiencing two types of self-reported homesickness: an exploratory study

This study investigated the intensity of DSM-III-R and ICD-10 personality disorder features among females experiencing self-reported homesickness. Three groups were compared: (a) a group of women experiencing chronic feelings of homesickness (CHS); (b) a group of women experiencing episodic attacks of homesickness, each time they go on holidays (EHS); and (c) a group of healthy control females, recruited from the general population (HC). This study aimed to investigate whether the homesick participants showed stronger features of personality pathology than the controls and whether those who report experiencing chronic feelings of homesickness showed stronger features of personality pathology than those who at the moment of testing were not in an actual state of homesickness. Glass effect sizes revealed that the DSM-III-R avoidant and dependent and the ICD-10 anxious and dependent traits were most strongly associated with either type of homesickness. Finally, CHS was particularly associated with passive-aggressive traits and EHS with sadistic traits. Based on the stories of 21 homesick women, a link between adverse attachment experiences in childhood and certain personality features on the one hand and homesickness on the other is tentatively suggested.

Correlation between oxidized low density lipoproteins and von Willebrand factor in chronic renal failure

An ELISA specific for a wide spectrum of oxidized apo B-100 in OxLDL was developed and applied to blood samples from 27 control subjects, 20 mild chronic renal failure (MCRF) patients, 21 severe chronic renal failure patients on conservative treatment (SCRF) and 56 severe chronic renal failure patients on maintenance hemodialysis (HEMO). Mean levels of OxLDL were 0.59 mg/dl in controls (95% CI, 0.52-0.66 mg/dl), and were 2.7-fold (p < 0.01), 3.1-fold (p < 0.001) and 5.4-fold (p < 0.001) higher in MCRF, SCRF and HEMO patients, respectively. Levels of von Willebrand factor, a marker of endothelial injury, were 100 percent in controls (95% CI, 90-110 percent), and were 1.5-fold (p = NS), 1.6-fold (p < 0.01) and 2.1-fold (p < 0.001) higher in MCRF, SCRF and HEMO patients, respectively. Multiple regression analysis revealed that the extent of renal failure (F = 14; p = 0.0004) accounted for a significant fraction of the variation in OxLDL levels, also after exclusion of patients with evidence of ischemic atherosclerotic disease (F = 21; p = 0.0001). After adjustment for the extent of renal failure, hemodialysis (F = 5.6; p = 0.021) and LDL cholesterol levels (F = 7.1, p = 0.0095) contributed significantly to the variation in OxLDL levels. Whereas the extent of renal failure contributed only marginally to the individual variations in vWF levels (F = 4.1; p = 0.048), these levels correlated significantly with plasma levels of OxLDL (F = 26; p = 0.0001). In conclusion, OxLDL increase progressively during the development of renal failure suggesting that the oxidation of LDL may be associated with endothelial injury and atherogenesis in these patients.

Correlation between Oxidized Low Density Lipoproteins and von Willebrand Factor in Chronic Renal Failure

An ELISA specific for a wide spectrum of oxidized apo B-100 in OxLDL was developed and applied to blood samples from 27 control subjects, 20 mild chronic renal failure (MCRF) patients, 21 severe chronic renal failure patients on conservative treatment (SCRF) and 56 severe chronic renal failure patients on maintenance hemodialysis (HEMO). Mean levels of OxLDL were 0.59 mg/dl in controls (95% Cl, 0.52-0.66 mg/dl), and were 2.7-fold (p <0.01), 3.1-fold (p <0.001) and 5.4-fold (p <0.001) higher in MCRF, SCRF and HEMO patients, respectively. Levels of von Willebrand factor, a marker of endothelial injury, were 100 percent in controls (95% Cl, 90-110 percent), and were 1.5-fold (p = NS), 1.6-fold (p <0.01) and 2.1-fold (p <0.001) higher in MCRF, SCRF and HEMO patients, respectively. Multiple regression analysis revealed that the extent of renal failure (F = 14; p = 0.0004) accounted for a significant fraction of the variation in OxLDL levels, also after exclusion of patients with evidence of ischemic atherosclerotic disease (F = 21; p = 0.0001). After adjustment for the extent of renal failure, hemodialysis (F = 5.6; p = 0.021) and LDL cholesterol levels (F = 7.1, p = 0.0095) contributed significantly to the variation in OxLDL levels. Whereas the extent of renal failure contributed only marginally to the individual variations in vWF levels (F = 4.1; p = 0.048), these levels correlated significantly with plasma levels of OxLDL (F=26; p=0.0001). In conclusion, atherogenic OxLDL increase progressively during the development of renal failure suggesting that the oxidation of LDL may be associated with endothelial injury and atherogenesis in these patients.

Phospholipid binding and lecithin-cholesterol acyltransferase activation properties of apolipoprotein A-I mutants

Recombinant human apolipoprotein A-I (apo A-I) and three deletion mutants: apo A-I(delta Leu44-Leu126), apo A-I(delta Glu139-Leu170), and apo A-I(delta Ala190-Gln243), purified from the periplasmic space of Escherichia coli, were studied. The rate of turbidity decrease following mixing of apo A-I(delta Ala190-Gln243) with dimyristoylphosphatidylcholine (DMPC) vesicles at 23 degrees C was 10-fold lower than that of the other apo A-I proteins, confirming that the carboxy-terminal region of apo A-I plays a role in rapid lipid binding. The Stokes radii of reconstituted high-density lipoproteins (rHDL), containing dipalmitoylphosphatidylcholine and cholesterol, were larger for the three apo A-I mutants [6.3 nm for apo A-I(delta Leu44-Leu126), 6.1 nm for apo A-I(delta Glu139-Leu170), and 6.5 nm for apo A-I(delta Ala190-Gln243)] than for intact apo A-I (5.0 nm). The mutant rHDL all contained 4 apo A-I molecules per particle as compared to 2 for intact apo A-I. Circular dichroism measurements revealed 8 alpha-helices per apo A-I molecule, 5 per apo A-I(delta Leu44-Leu126), 6 per apo A-I(delta Glu139-Leu170), and 4 per apo A-I(delta Ala190-Gln243) molecule as compared to predicted values of 8, 5, 6, and 6 alpha-helices, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Malondialdehyde-modified low density lipoproteins in patients with atherosclerotic disease

The murine monoclonal antibody mAb-1H11 raised against malondialdehyde (MDA)-modified LDL, was used to detect cross-reacting material in human atheromatous tissue and in plasma. MDA-modified LDL levels in plasma were 0.19 +/- 0.02 mg/dl (mean +/- SEM) in 44 control subjects, 0.24 +/- 0.02 mg/dl in 15 patients with chronic stable angina pectoris (P = NS vs LDL cholesterol matched controls), 1.4 +/- 0.1 mg/dl in 60 patients with acute myocardial infarction (P < 0.001 vs controls), and 0.86 +/- 0.11 mg/dl in 22 patients with carotid atherosclerosis (P < 0.001 vs controls). Modified LDL, isolated from pooled LDL of 10 patients, showed a higher electrophoretic mobility on agarose gels, a higher content of thiobarbituric acid reactive substances, and a higher cholesterol/protein ratio than native LDL and had a similar reactivity (antigen/protein ratio) in the assay as the in vitro MDA-modified LDL used for calibration. Its apo B-100 moiety was not fragmented. Uptake of this modified LDL by macrophages resulted in foam cell generation. In conclusion, elevated plasma levels of atherogenic MDA-modified LDL may be a marker for unstable atherosclerotic cardiovascular disease.

Stimulation with a monoclonal antibody (mAb4E4) of scavenger receptor-mediated uptake of chemically modified low density lipoproteins by THP-1-derived macrophages enhances foam cell generation

mAb4E4, a murine monoclonal antibody that is specific for acetylated LDL and malondialdehyde-treated LDL, binds specifically to modified LDL present in human atherosclerotic lesions. It is directed against an epitope that is poorly exposed in delipidated and solubilized apolipoprotein B-100 from modified LDL. mAb4E4, as well as its F(ab')2 and Fab fragments, enhanced the uptake of both acetylated LDL and malondialdehyde-treated LDL by THP-1-derived macrophages resulting in a sixfold increase of cytoplasmic cholesteryl ester levels. The increased uptake of modified LDL/mAb4E4 complexes did not occur via the Fc receptor and did not depend on aggregation of modified LDL particles. However, their uptake was inhibited by blocking the scavenger receptors with fucoidin or by downregulation of receptor expression with endotoxins or interferon-gamma, indicating that their uptake is mediated via these receptors. Thus, generation of autoimmune antibodies against modified LDL and subsequent endocytosis of soluble modified LDL/antibody complexes via scavenger receptors may enhance foam cell generation. This mechanism may contribute to the progression of atherosclerotic lesions.

Biochemical characterization of single-chain chimeric plasminogen activators consisting of a single-chain Fv fragment of a fibrin-specific antibody and single-chain urokinase

K12G0S32 is a 57-kDa recombinant single-chain chimeric plasminogen activator consisting of scFv-K12Go, a single-chain variable-region antigen-binding fragment (Fv) of the monoclonal antibody MA-15C5, which is specific for fragment D-dimer of human cross-linked fibrin, and a low-molecular-mass (33 kDa) urokinase-type plasminogen activator (u-PA-33k) containing amino acids Ala132-Leu411 (Holvoet, P., Laroche, Y., Lijnen, H. R., Van Cauwenberghe, R., Demarsin, E., Brouwers, E., Matthyssens, G. & Collen D. (1991) J. Biol. Chem. 266, 19717-19724). In addition, the Arg156-Phe157 thrombin-cleavage site in the u-PA moiety of K12G0S32 is removed by substitution of Phe157 with Asp. In the present study, the fibrinolytic potency of K12G0S32, determined in a system composed of a 125I-fibrin-labeled human plasma clot submerged in citrated plasma, was found to be only twofold higher than that of intact single-chain u-Pa (rscu-PA), but 17-fold higher than that of rscu-PA(M), a variant of rscu-PA in which the thrombin-cleavage site was removed by substitution of Phe157 with Asp. The fibrinolytic potency of K12G0S32T, with an intact thrombin-cleavage site, was 6-15-fold higher than that of rscu-PA. Conversion of 1 microM single-chain K12G0S32 or rscu-PA(M) into their two-chain derivatives with plasmin occurred at a rate of 1.0 +/- 0.15 nmol.min-1.nmol plasmin-1 and 0.85 +/- 0.074 nmol.min-1.nmol plasmin-1, compared to 14 +/- 2.3 nmol.min-1.nmol plasmin-1 and 18 +/- 2.6 nM.min-1.nmol plasmin-1 for K12G0S32T and rscu-PA, respectively. Purified fragment D-dimer of human cross-linked fibrin inhibited the fibrinolytic potency of single-chain K12G0S32T, but not of two-chain K12G0S32T, in a dose-dependent manner. Furthermore, the fibrinolytic potencies of two-chain K12G0S32 and K12G0S32T were not significantly higher than those of recombinant two-chain u-PA (rtcu-PA) or of rtcu-PA(M). These findings suggest that the 59-fold increase in fibrinolytic potency of K12G0S32T, relative to that of rscu-PA(M), is due both to targeting of the activator to the clot via the single-chain Fv fragment (sixfold increase) and to a more efficient conversion of single-chain K12G0S32T to its two-chain derivative (eightfold increase). Thus, targeting to clots by means of fibrin-specific antibodies results in a significant increase of the fibrinolytic potency of single-chain but not of two-chain u-PA.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of a chimeric plasminogen activator consisting of a single-chain Fv fragment derived from a fibrin fragment D-dimer-specific antibody and a truncated single-chain urokinase

An Mr 57,000 single-chain chimeric plasminogen activator, K12G0S32, consisting of a variable region fragment (Fv) derived from the fibrin fragment D-dimer-specific monoclonal antibody MA-15C5 and of a 33-kDa (amino acids Ala132 to Leu411) recombinant single-chain urokinase-type plasminogen activator (rscu-PA-33k) was studied. K12G0S32, secreted by infected Spodoptera frugiperda insect cells at a rate of 1.5 micrograms/10(6) cells/48 h, was purified to homogeneity by ion-exchange chromatography and gel filtration. It was obtained essentially as a single-chain molecule with a Ka = 5.5 x 10(9) M-1 for immobilized fragment D-dimer, similar to that of MA-15C5. The specific activity of both its single-chain and two-chain forms on fibrin plates was 100,000 IU/mg of urokinase-type plasminogen activator (u-PA) equivalent. Activation of plasminogen by two-chain K12G0S32 obeyed Michaelis-Menten kinetics with Km = 2.9 +/- 0.6 microM and a k2 = 3.7 +/- 0.6 s-1 (mean +/- S.D.; n = 3), as compared to Km = 12 microM and k2 = 4.8 s-1 for rtcu-PA-32k (recombinant low Mr two-chain u-PA consisting of amino acids Leu144 to Leu411). Single-chain K12G0S32 induced a dose- and time-dependent lysis of a 125I-fibrin-labeled human plasma clot immersed in citrated human plasma; 50% lysis in 2 h was obtained with 0.70 +/- 0.07 micrograms/ml (mean +/- S.D.; n = 5), as compared with 8.8 +/- 0.1 micrograms/ml for rscu-PA-32k (recombinant low Mr single-chain u-PA consisting of amino acids Leu144 to Leu411) (mean +/- S.D.; n = 3). With two-chain K12G0S32, 50% clot lysis in 2 h required 0.25 +/- 0.03 micrograms/ml (mean +/- S.D.; n = 3), as compared with only 0.62 +/- 0.04 micrograms/ml (mean +/- S.D.; n = 2) for rtcu-PA-32k. These results indicate that low Mr single-chain u-PA can be targeted to a fibrin clot with a single-chain Fv fragment of a fibrin-specific antibody, resulting in a 13-fold increase of the fibrinolytic potency of the single-chain form and a 2.5-fold increase of the potency of the two-chain form.

Dideoxycytidine alone and in an alternating schedule with zidovudine in children with symptomatic human immunodeficiency virus infection

OBJECTIVE

To determine whether a short course of 2',3'-dideoxycytidine (ddC) could provide safe antiretroviral activity in children with symptomatic human immunodeficiency virus infection and whether it could be used with azidothymidine (AZT, zidovudine). The goal was to maintain uninterrupted antiretroviral therapy while sparing AZT-related myelosuppression and ddC-related neuropathy.

METHODS

In a pilot study, we evaluated four dosage levels of ddC--0.015, 0.02, 0.03, and 0.04 mg/kg, given orally every 6 hours--in 15 children between 6 months and 13 years of age with Centers for Disease Control P2 (i.e., symptomatic) human immunodeficiency virus infection. Thirteen patients had not had any prior antiretroviral therapy; two patients had received and benefited from AZT, but dose-limiting neutropenia had developed. At each dosage level, ddC was given for 8 consecutive weeks and then stopped. After a 30-day rest, a schedule of ddC for 1 week was followed by 3 weeks of AZT therapy (180 mg/m2 every 6 hours); this alternating schedule was repeated for as long as tolerated. Age-appropriate psychometric testing was performed before the start of ddC therapy and after 8 weeks.

RESULTS

During the 8 weeks of therapy with ddC alone, no neutropenia or anemia was observed; 6 of 9 patients had decreases in p24 antigen levels, and 8 of 15 had an increased CD4 cell count. At the 0.04 mg/kg level, a rash developed in three patients; mild mouth sores developed in 9 of 15 patients. On the alternating ddC/AZT schedule, no neuropathy was observed.

CONCLUSIONS

2',3'-Dideoxycytidine has antiretroviral activity in some children and appears to be safe for short intervals. Longer courses of ddC at lower dosage levels, and schedules integrating ddC into combination regimens, deserve to be explored.