Accurate measurement of extended half-life and unmodified factor VIII low levels with one-stage FVIII assays is dependent on the matrix of calibration curves.

INTRODUCTION: The monitoring of factor VIII (FVIII) replacement therapy relies on the accurate measurement of FVIII activity over a large concentration range. However, unexplained overestimation of low FVIII levels has recently been reported with extended half-life recombinant FVIIIs. AIM: The objective of this study was to confirm previous publications indicating that the reagents used to generate the calibration curves determine the accuracy of the measurement of low FVIII levels. METHODS: We generated FVIII calibration curves with FVIII-deficient plasmas or a commercial diluent buffer. We then measured FVIII levels in FVIII-deficient plasma spiked with plasma FVIII, a full-length recombinant FVIII (Advate® , Shire, Brussels, Belgium) and two extended half-life recombinant FVIIIs (Elocta® , Swedish Orphan Biovitrum, Woluwe Saint-Lambert, Belgium and Afstyla® , CSL Behring, Mechelen, Belgium). FVIII levels were also analyzed in spiked samples prediluted two- and fourfold, either in diluent buffer or in FVIII-deficient plasma to evaluate parallelism. RESULTS: Coagulation times of calibration curves generated with diluent buffer were longer than those with FVIII-deficient plasmas. This resulted in an overestimation of FVIII levels lower than 25 IU/dL in spiked samples and in detection of FVIII activity (≥1 IU/dL) in FVIII-deficient plasma. Predilution of samples with diluent buffer rather than with FVIII-deficient plasma also led to discordant results. CONCLUSION: Our data confirm that the generation of calibration curves by dilution in FVIII-deficient plasma is crucial for the accurate measurement of low FVIII levels. When serial dilutions of samples are analyzed, predilution in FVIII-deficient plasma is required to respect the parallelism criteria. These methods should be more generally implemented for coagulation instruments.

Optimization of the detection of inhibitory autoantibodies against the VWF-cleaving protease ADAMTS13 with an automated chemiluminescent ADAMTS13 activity immunoassay.

INTRODUCTION: Acquired thrombotic thrombocytopenic purpura is a rare disease associated with the production of autoantibodies against the VWF-cleaving protease ADAMTS13. The detection of these antibodies is made difficult by the instability of ADAMTS13 in citrated plasma and the time-consuming ADAMTS13 assays. The aim of our study was to evaluate the optimal conditions for detecting anti-ADAMTS13 inhibitory antibodies with the novel automated chemiluminescent immunoassay HemosILR AcuStar ADAMTS13 Activity assay. METHODS: The parallelism between the AcuStar ADAMTS13 calibration curve and ADAMTS13 concentrations in serially diluted citrated plasma was evaluated after 2 hours incubation at 25°C, 37°C, or 37°C after addition of Ca2+ to preserve the activity of the metalloprotease. Using Bethesda assays based on the 3 incubation procedures and the HemosILR AcuStar ADAMTS13 Activity assay, the inhibitor titers were determined in patients' samples with ADAMTS13 antibodies and compared with those determined using the TechnozymR ADAMTS13 activity ELISA. RESULTS: The criterion of parallelism was respected for the 3 incubation methods over the range of ADAMTS13 concentrations relevant for the detection of ADAMTS13 inhibitor antibodies in a Bethesda assay. In agreement with this observation, all the incubation methods permitted the accurate detection and quantification of inhibitory anti-ADAMTS13 antibodies in the samples from patients with acquired thrombotic thrombocytopenic purpura. CONCLUSION: Incubation of plasma samples with normal plasma at 25°C, 37°C, or 37°C after addition of Ca2+ can be used in a Bethesda assay for quantifying the inhibitory activity of antibodies interfering with ADAMTS13 in the chemiluminescent HemosILR AcuStar ADAMTS13 Activity assay.

Selective homocysteine-lowering gene transfer attenuates pressure overload-induced cardiomyopathy via reduced oxidative stress.

UNLABELLED: Plasma homocysteine levels predict heart failure incidence in prospective epidemiological studies. We evaluated whether selective homocysteine-lowering gene transfer beneficially affects cardiac remodeling and function in a model of pressure overload-induced cardiomyopathy induced by transverse aortic constriction (TAC). Female C57BL/6 low-density lipoprotein receptor (Ldlr (-/-)) cystathionine-ß-synthase (Cbs (+/-)) mice were fed standard chow (control mice) or a folate-depleted, methionine-enriched diet to induce hyperhomocysteinemia (diet mice). Three weeks after initiation of thisdiet, mice were intravenously injected with 5 × 10(10) viral particles of an E1E3E4-deleted hepatocyte-specific adenoviral vector expressing Cbs (AdCBS), with the same dose of control vector, or with saline buffer. TAC or sham operation was performed 2 weeks later. AdCBS gene transfer resulted in 86.4 % (p < 0.001) and 84.6 % (p < 0.001) lower homocysteine levels in diet sham mice and diet TAC mice, respectively. Mortality rate was significantly reduced in diet AdCBS TAC mice compared to diet TAC mice during a follow-up period of 8 weeks (hazard ratio for mortality 0.495, 95 % CI 0.249 to 0.985). Left ventricular hypertrophy (p < 0.01) and interstitial myocardial fibrosis (p < 0.001) were strikingly lower in control TAC mice and diet AdCBS TAC mice compared to diet TAC mice. Diastolic function in diet AdCBS TAC mice was similar to that of control TAC mice and was significantly improved compared to diet TACmice. AdCBS gene transfer potently reduced oxidative stress as evidenced by a reduction of plasma TBARS and a reduction of myocardial 3-nitrotyrosine-positive area (%). In conclusion, selective homocysteine lowering potently attenuates pressure overload-induced cardiomyopathy via reduced oxidative stress. KEY MESSAGE: Plasma homocysteine levels predict heart failure incidence in epidemiological studies. Transverse aortic constriction (TAC) induces pressure overload. Selective homocysteine-lowering gene therapy reduces mortality after TAC. Selective homocysteine lowering attenuates cardiac hypertrophy and fibrosis after TAC. Decreased homocysteine levels enhance diastolic function and lower oxidative stress.