Investigation of thrombin concentration at the time of clot formation in simultaneous thrombin and fibrin generation assays.

Thrombin generation (TG) and fibrin clot formation represent the central process of blood coagulation. Up to 95% of thrombin is considered to be generated after the clot is formed. However, this was not investigated in depth. In this study, we conducted a quantitative analysis of the Thrombin at Clot Time (TCT) parameter in 5758 simultaneously recorded TG and clot formation assays using frozen plasma samples from commercial sources under various conditions of activation. These samples were supplemented with clotting factor concentrates, procoagulant lipid vesicles and a fluorogenic substrate and triggered with tissue factor (TF). We found that TCT is often close to a 10% of thrombin peak height (TPH) yet it can be larger or smaller depending on whether the sample has low or high TPH value. In general, the samples with high TPH are associated with elevated TCT. TCT appeared more sensitive to some procoagulant phenotypes than other commonly used parameters such as clotting time, TPH or Thrombin Production Rate (TPR). In a minority of cases, TCT were not predicted from TG parameters. For example, elevated TCT (above 15% of TPH) was associated with either very low or very high TPR values. We conclude that clotting and TG assays may provide complementary information about the plasma sample, and that the TCT parameter may serve as an additional marker for the procoagulant potential in plasma sample.

Comparative Thrombin Generation in Animal Plasma: Sensitivity to Human Factor XIa and Tissue Factor.

Preclinical evaluation of drugs in animals helps researchers to select potentially informative clinical laboratory markers for human trials. To assess the utility of animal thrombin generation (TG) assay, we studied the sensitivity of animal plasmas to triggers of TG, human Tissue Factor (TF), and Activated Factor XI (FXIa). Pooled human, mouse, rat, guinea pig, rabbit, bovine, sheep, and goat plasmas were used in this study. TF- or FXIa-triggered TG and clotting were measured via fluorescence and optical density, respectively. Thrombin peak height (TPH) and time (TPT), clot time (CT), and fibrin clot density (FCD) were all analyzed. The trigger low and high sensitivity borders (LSB and HSB) for each assay parameter were defined as TF and FXIa concentrations, providing 20 and 80% of the maximal parameter value, unless the baseline (no trigger) value exceeded 20% of the maximal, in which case, LSB was derived from 120% of baseline value. Normal human samples demonstrated lower TPH HSB than most of the animal samples for both TF and FXIa. Animal samples, except mice, demonstrated lower TPT LSB for FXIa versus humans. Most rodent and rabbit samples produced baseline TG in the absence of TG triggers that were consistent with the pre-activation of blood coagulation. FCD was not sensitive to both TF and FXIa in either of the plasmas. Animal plasmas have widely variable sensitivities to human TF and FXIa, which suggests that optimization of trigger concentration is required prior to test use, and this complicates the extrapolation of animal model results to humans.

Thrombogenic potential of picomolar coagulation factor XIa is mediated by thrombin wave propagation.

Inhibitors of coagulation factor XIa (FXIa) are currently being investigated as potential anticoagulant therapies. We hypothesize that circulating FXIa could be a potential target for these therapies. Using previous analyses of FXIa impurities in immune globulin products involved in thrombotic adverse events, we estimated that picomolar levels of FXIa can be thrombogenic. In an in vitro clot-growth assay, 0.1-3 pM of FXIa did not, by itself, activate clotting but increased the size of growing clots. Spatio-temporal reconstruction of thrombin activity inside the clot revealed that FXIa's effect was limited to the clot-plasma interface, in which FXIa produced a taller than standard wave of thrombin. Factor-depleted plasma and a panel of selective anti-FXIa antibodies showed that exogenous FXIa effects are (1) blocked by anti-FXIa antibodies, (2) independent of FXI activation inside the clot, and (3) larger than the contribution of in situ FXIa. In a thrombin generation (TG) assay, picomolar FXIa did not initiate TG but rather promoted TG triggered by tissue factor or thrombin, suggesting that the effect of FXIa on the thrombin wave is mediated by the elevation of thrombin-triggered TG. In circulating bovine blood, low doses of human FXIa did not initiate clotting but increased the size of stenosis-triggered thrombi. FXIa injection in mice enhanced TG in plasma for at least 6 hours ex vivo, confirming the persistence of circulating FXIa. Our findings suggest that picomolar levels of circulating FXIa may not be able to initiate thrombosis but can facilitate thrombus growth through the facilitation of TG inside the clot.

Thrombin generation test based on a 96-channel pipettor for evaluation of FXIa procoagulant activity in pharmaceuticals.

Thrombin generation (TG) assays are used widely to investigate both diseases and drugs that impact thrombosis and bleeding. TG assays were also instrumental in the identification of thrombogenic impurities in immune globulin products, which were associated with thrombotic adverse events in patients. TG assays are therefore now used by quality control laboratories of plasma derivative drug manufacturers and regulatory agencies responsible for the safety testing and release of immune globulin products. In this protocol, we describe a robust and sensitive version of the TG assay for quantitative measurement of thrombogenic activity in immune globulin products. Compared with the version of the assay commonly used in clinical laboratories that compares individual patient plasma samples with normal donor samples, our TG assay is suitable for quick (170-260 min) semiautomated analysis of multiple drug samples against the World Health Organization international standard for factor XIa. Commercially available reagents can be used for the assay, and it does not require specialized equipment. The protocol can be easily adapted for the measurement of the procoagulant activity of other biopharmaceuticals, e.g., coagulation factors.

Detecting factor XIa in immune globulin products: Commutability of international reference materials for traditional and global hemostasis assays.

BACKGROUND: Activated coagulation factor XIa (FXIa) is an impurity and primary source of procoagulant activity in thrombosis-implicated immune globulin (IG) products. Several assays, of varying quality and precision are used to assess FXIa-like procoagulant activity in units relevant to their respective principles. OBJECTIVES: To advance unified reporting, we sought to employ the World Health Organization reference reagents (RRs) to present the results of differing methodologies in units of FXIa activity and rank the sensitivity and robustness of these methodologies. METHODS: RR 11/236 served as a calibrator in several FXIa-sensitive blood coagulation tests: two commercial chromogenic FXIa assays (CAs); a nonactivated partial thromboplastin time (NaPTT); an in-house fibrin generation (FG) assay; an in-house thrombin generation (TG) assay; and an assay for FXIa- and kallikrein-like proteolytic activities based on cleavage of substrate SN13a. Some assays were tested in either normal or FXI-deficient plasma. RESULTS: Each method demonstrated a sigmoidal dose-response to RRs. NaPTT was the least sensitive to FXIa and the least precise; our in-house TG was the most sensitive; and the two CAs were the most precise. All methods, except for SN13a, which is less specific for thrombotic impurities, gave comparable (within 20% difference) FXIa activity assignments for IG lots. CONCLUSIONS: Purified FXIa reference standards support quantitation of FXIa levels in IG products in all tested assay methodologies. This should help to standardize the measurement of thrombotic potentials in IG products and prevent products exhibiting high procoagulant activity from distribution for patient use. Further research is needed to address the effect of IG product-specific matrixes on assay performance.

Combined thrombogenic effects of vessel injury, pregnancy and procoagulant immune globulin administration in mice.

BACKGROUND: Pregnant women are at increased risk of thrombotic adverse events. Plasma derived immune globulin (IG) products, which are used in pregnancy for various indications, may contain procoagulant impurity activated coagulation factor XI (FXIa). Procoagulant IG products have been associated with increased thrombogenicity but their effect in pregnancy is unknown. METHODS: Late pregnant (gestation days 17-20) or early lactation (days 1-3) and control female mice were treated with IGs supplemented with human FXIa then subjected to ferric chloride (FeCl3) vessel injury. Occlusion of blood vessel was assessed by recording blood velocity in the femoral vein for 20 min using doppler ultrasound laser imaging. FXIa dose was selected by the ability to increase thrombin generation in mouse plasma in vitro. RESULTS: FXIa produced robust thrombin generation in mouse plasma ex vivo. Following FeCl3 injury, pregnant and non-pregnant mice receiving IG + FXIa exhibited faster reduction of blood velocity in femoral vein compared to IG alone or untreated controls. In vitro, thrombin generation in plasma samples collected after thrombosis in FXIa-treated animals was elevated and could be reduced by anti-FXI antibody. CONCLUSIONS: Our results suggest that intravenously-administered FXIa may contribute to thrombosis at the site of vascular injury in both pregnant and non-pregnant animals.

G2019S-LRRK2 mutation enhances MPTP-linked Parkinsonism in mice.

Parkinson's disease (PD) is a common neurodegenerative disease with a heterogeneous etiology that involves genetic and environmental factors or exogenous. Current LRRK2 PD animal models only partly reproduce the characteristics of the disease with very subtle dopaminergic neuron degeneration. We developed a new model of PD that combines a sub-toxic MPTP insult to the G2019S-LRRK2 mutation. Our newly generated mice, overexpressing mutant G2019S-LRRK2 protein in the brain, displayed a mild, age-dependent progressive motor impairment, but no reduction of lifespan. Cortical neurons from G2019S-LRRK2 mice showed an increased vulnerability to stress insults, compared with neurons overexpressing wild-type WT-LRRK2, or non-transgenic (nTg) neurons. The exposure of LRRK2 transgenic mice to a sub-toxic dose of MPTP resulted in severe motor impairment, selective loss of dopamine neurons and increased astrocyte activation, whereas nTg mice with MPTP exposure showed no deficits. Interestingly, mice overexpressing WT-LRRK2 showed a significant impairment that was milder than for the mutant G2019S-LRRK2 mice. L-DOPA treatments could partially improve the movement impairments but did not protect the dopamine neuron loss. In contrast, treatments with an LRRK2 kinase inhibitor significantly reduced the dopaminergic neuron degeneration in this interaction model. Our studies provide a novel LRRK2 gene-MPTP interaction PD mouse model, and a useful tool for future studies of PD pathogenesis and therapeutic intervention.

Subvisible Particle Content, Formulation, and Dose of an Erythropoietin Peptide Mimetic Product Are Associated With Severe Adverse Postmarketing Events.

Peginesatide (Omontys(®); Affymax, Inc., Cupertino, CA) was voluntarily withdrawn from the market less than a year after the product launch. Although clinical trials had demonstrated the drug to be safe and efficacious, 49 cases of anaphylaxis, including 7 fatalities, were reported not long after market introduction. Commercialization was initiated with a multiuse vial presentation, which differs in formulation from the single-use vial presentation used in phase 3 studies. Standard physical and chemical testing did not indicate any deviation from product specifications in either formulation. However, an analysis of subvisible particulates using nanoparticle tracking analysis and flow imaging revealed a significantly higher concentration of subvisible particles in the multiuse vial presentation linked to the hypersensitivity cases. Although it is unknown whether the elevated particulate content is causally related to these serious adverse events, this report illustrates the utility of characterizing subvisible particulates not captured by conventional light obscuration.

Immune globulins and same-day thrombotic events as recorded in a large health care database during 2008 to 2012.

BACKGROUND: Thrombotic events (TEs) are rare and serious adverse events after administration of immune globulin (IG) products. Our study evaluated the occurrence of same-day TEs for different IG products and ascertained potential risk factors. STUDY DESIGN AND METHODS: This retrospective cohort study utilized HealthCore's Integrated Research Database (HIRD) to assess individuals exposed to IGs during 2008 to 2012. IG products were identified using recorded procedure codes and TEs were ascertained using ICD-9-CM diagnosis codes. The unadjusted same-day TE rates (per 1000 persons exposed) were estimated overall and by IG products, age, and sex. Multivariable logistic regression analyses were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for same-day TEs by IG products. RESULTS: Of 14,944 individuals exposed to IG products, 233 (15.6 per 1000 persons) had TE diagnosis code(s) recorded on the same-day as the IG exposure. Compared to Gammagard Liquid, Gammaplex (OR, 20.96; 95% CI, 2.45-179.33) and Vivaglobin (OR, 2.74; 95% CI, 1.19-6.32) users had a significantly increased same-day TE risk. Elevated, but nonsignificant TE risks were identified for Octagam, Gamunex, Privigen, and Lyophilized IG(s). An increased TE risk was also found with older age (≥45 years), prior TEs, and other health conditions. CONCLUSION: Our claims-based cohort study suggests a potentially elevated TE risk with different IG products and shows importance of recipient factors such as older age, previous TE, hypercoagulable state(s), and other health conditions. The results of this study suggest the need for continuous evaluation of procoagulant activity and manufacturing processes for IG products to further assure their safety.

Hyperimmune globulins and same-day thrombotic adverse events as recorded in a large healthcare database during 2008-2011.

Thrombotic events (TEs) are rare serious complications following administration of hyperimmune globulin (HIG) products. Our retrospective claims-based study assessed occurrence of same-day TEs following administration of HIGs during 2008-2011 and examined potential risk factors using HealthCore's Integrated Research Database (HIRD(SM) ) and laboratory testing of products' procoagulant Factor XIa activity by U.S. Food and Drug Administration. Multivariable regression was used to estimate same-day TE risk for different products. Of 101,956 individuals exposed to 23 different HIG product groups, 86 (0.84 per 1,000 persons) had a TE diagnosis code (DC) recorded on the same day as HIG administration. Unadjusted same-day TE DC rates (per 1,000 persons) ranged from 0.4 to 148.9 for different products. GamaSTAN S/D IG >10 cc had statistically significantly higher same-day TE DC risk compared to Tetanus IG (OR = 57.57; 95% CI = 19.72-168.10). Increased TE risk was also observed with older age (≥45 years), prior thrombotic events, and hypercoagulable state(s). Laboratory investigation identified elevated Factor XIa activity for GamaSTAN S/D, HepaGam B, HyperHep B S/D, WinRho SDF, HyperRHO S/D full dose, and HyperTET S/D. Our study, for the first time, identified increase in the same-day TE DC risk with GamaSTAN S/D IG >10 cc and suggests potentially elevated TE risk with other HIGs.

Correction of microplate location effects improves performance of the thrombin generation test.

BACKGROUND: Microplate-based thrombin generation test (TGT) is widely used as clinical measure of global hemostatic potential and it becomes a useful tool for control of drug potency and quality by drug manufactures. However, the convenience of the microtiter plate technology can be deceiving: microplate assays are prone to location-based variability in different parts of the microtiter plate. METHODS: In this report, we evaluated the well-to-well consistency of the TGT variant specifically applied to the quantitative detection of the thrombogenic substances in the immune globulin product. We also studied the utility of previously described microplate layout designs in the TGT experiment. RESULTS: Location of the sample on the microplate (location effect) contributes to the variability of TGT measurements. Use of manual pipetting techniques and applications of the TGT to the evaluation of procoagulant enzymatic substances are especially sensitive. The effects were not sensitive to temperature or choice of microplate reader. Smallest location effects were observed with automated dispenser-based calibrated thrombogram instrument. Even for an automated instrument, the use of calibration curve resulted in up to 30% bias in thrombogenic potency assignment. CONCLUSIONS: Use of symmetrical version of the strip-plot layout was demonstrated to help to minimize location artifacts even under the worst-case conditions. Strip-plot layouts are required for quantitative thrombin-generation based bioassays used in the biotechnological field.

Development and characterization of a new Parkinson's disease model resulting from impaired autophagy.

Parkinson's disease (PD) is a progressive neurodegenerative disease caused by the interaction of genetic and environmental factors. However, the etiology of PD remains largely unknown. Macroautophagy is known to play an essential role in the degradation of abnormal proteins and organelles. Furthermore, the loss of autophagy-related (Atg) genes results in neurodegeneration and abnormal protein accumulation. Since these are also pathologic features of Parkinson's disease, the conditional impairment of autophagy may lead to improved animal models for the study of PD. Using transgenic mice expressing Cre recombinase under the control of either the dopamine transporter or the engrailed-1 promoters, we generated mice with the conditional deletion of Atg7 in the dopamine neurons of the substantia nigra pars compacta, other regions of the midbrain, and also the hindbrain. This conditional impairment of autophagy results in the age-related loss of dopaminergic neurons and corresponding loss of striatal dopamine, the accumulation of low-molecular-weight α-synuclein, and the presence of ubiquitinated protein aggregates, recapitulating many of the pathologic features of PD. These conditional knock-out animals provide insight into the process of autophagy in Parkinson's disease pathology.

Synphilin-1 attenuates neuronal degeneration in the A53T alpha-synuclein transgenic mouse model.

Genetic alterations in alpha-synuclein cause autosomal dominant familial Parkinsonism and may contribute to sporadic Parkinson's disease (PD). Synphilin-1 is an alpha-synuclein-interacting protein, with implications in PD pathogenesis related to protein aggregation. Currently, the in vivo role of synphilin-1 in alpha-synuclein-linked pathogenesis is not fully understood. Using the mouse prion protein promoter, we generated synphilin-1 transgenic mice, which did not display PD-like phenotypes. However, synphilin-1/A53T alpha-synuclein double-transgenic mice survived longer than A53T alpha-synuclein single-transgenic mice. There were attenuated A53T alpha-synuclein-induced motor abnormalities and decreased astroglial reaction and neuronal degeneration in brains in double-transgenic mice. Overexpression of synphilin-1 decreased caspase-3 activation, increased beclin-1 and LC3 II expression and promoted formation of aggresome-like structures, suggesting that synphilin-1 alters multiple cellular pathways to protect against neuronal degeneration. These studies demonstrate that synphilin-1 can diminish the severity of alpha-synucleinopathy and play a neuroprotective role against A53T alpha-synuclein toxicity in vivo.

ATF3 plays a protective role against toxicity by N-terminal fragment of mutant huntingtin in stable PC12 cell line.

Huntington's disease is a progressive neurodegenerative disorder caused by a polyglutamine expansion near the N-terminus of huntingtin. The mechanisms of polyglutamine neurotoxicity, and cellular responses are not fully understood. We have studied gene expression profiles by short oligo array using an inducible PC12 cell model expressing an N-terminal huntingtin fragment with expanded polyglutamine (Htt-N63-148Q). Mutant huntingtin Htt-N63 induced cell death and increased the mRNA and protein levels of activating transcription factor 3 (ATF3). Mutant Htt-N63 also significantly enhanced ATF3 transcriptional activity by a promoter-based reporter assay. Overexpression of ATF3 protects against mutant Htt-N63 toxicity and knocking down ATF3 expression reduced Htt-N63 toxicity in a stable PC12 cell line. These results indicated that ATF3 plays a critical role in toxicity induced by mutant Htt-N63 and may lead to a useful therapeutic target.

Mutant huntingtin N-terminal fragments of specific size mediate aggregation and toxicity in neuronal cells.

Huntingtin proteolysis is implicated in Huntington disease pathogenesis, yet, the nature of huntingtin toxic fragments remains unclear. Huntingtin undergoes proteolysis by calpains and caspases within an N-terminal region between amino acids 460 and 600. We have focused on proteolytic steps producing shorter N-terminal fragments, which we term cp-1 and cp-2 (distinct from previously described cp-A/cp-B). We used HEK293 cells to express the first 511 residues of huntingtin and further define the cp-1 and cp-2 cleavage sites. Based on epitope mapping with huntingtin-specific antibodies, we found that cp-1 cleavage occurs between residues 81 and 129 of huntingtin. Affinity and size exclusion chromatography were used to further purify huntingtin cleavage products and enrich for the cp-1/cp-2 fragments. Using mass spectrometry, we found that the cp-2 fragment is generated by cleavage of huntingtin at position Arg(167). This site was confirmed by deletion analysis and specific detection with a custom-generated cp-2 site neo-epitope antibody. Furthermore, alterations of this cleavage site resulted in a decrease in toxicity and an increase in aggregation of huntingtin in neuronal cells. These data suggest that cleavage of huntingtin at residue Arg(167) may mediate mutant huntingtin toxicity in Huntington disease.

Acute kidney injury leads to inflammation and functional changes in the brain.

Although neurologic sequelae of acute kidney injury (AKI) are well described, the pathogenesis of acute uremic encephalopathy is poorly understood. This study examined the short-term effect of ischemic AKI on inflammatory and functional changes of the brain in mice by inducing bilateral renal ischemia for 60 min and studying the brains 24 h later. Compared with sham mice, mice with AKI had increased neuronal pyknosis and microgliosis in the brain. AKI also led to increased levels of the proinflammatory chemokines keratinocyte-derived chemoattractant and G-CSF in the cerebral cortex and hippocampus and increased expression of glial fibrillary acidic protein in astrocytes in the cortex and corpus callosum. In addition, extravasation of Evans blue dye into the brain suggested that the blood-brain barrier was disrupted in mice with AKI. Because liver failure also leads to encephalopathy, ischemic liver injury was induced in mice with normal renal function; neuronal pyknosis and glial fibrillary acidic protein expression were not increased, suggesting differential effects on the brain depending on the organ injured. For evaluation of the effects of AKI on brain function, locomotor activity was studied using an open field test. Mice subjected to renal ischemia or bilateral nephrectomy had moderate to severe declines in locomotor activity compared with sham-operated mice. These data demonstrate that severe ischemic AKI induces inflammation and functional changes in the brain. Targeting these pathways could reduce morbidity and mortality in critically ill patients with severe AKI.

Tiagabine is neuroprotective in the N171-82Q and R6/2 mouse models of Huntington's disease.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by chorea, incoordination, and shortened life-span, and by huntingtin inclusions and neurodegeneration. We previously screened the 1040 FDA-approved compounds from the NINDS compound library and found that a compound, nipecotic acid, significantly reduced mutant huntingtin aggregations and blocked cell toxicity in an inducible cell model of HD. Because nipecotic acid does not cross the blood-brain barrier (BBB), we studied its analogue, tiagabine, which is able to cross the BBB, in both N171-82Q and R6/2 transgenic mouse models of HD. Tiagabine was administered intraperitoneally at 2 and 5 mg/kg daily in HD mice. We found that tiagabine extended survival, improved motor performance, and attenuated brain atrophy and neurodegeneration in N171-82Q HD mice. These beneficial effects were further confirmed in R6/2 HD mice. The levels of tiagabine at effective doses in mouse serum are comparable to the levels in human patients treated with tiagabine. These results suggest that tiagabine may have beneficial effects in the treatment of HD. Because tiagabine is an FDA-approved drug, it may be a promising candidate for future clinical trials for the treatment of HD.

N-terminal proteolysis of full-length mutant huntingtin in an inducible PC12 cell model of Huntington's disease.

Proteolytic cleavage of mutant huntingtin may play a key role in the pathogenesis of Huntington's disease; however the steps in huntingtin proteolysis are not fully understood. Huntingtin was shown to be cleaved by caspases and calpains within a region between 460-600 amino acids from the N-terminus. Two smaller N-terminal fragments produced by unknown protease have been previously described as cp-A and cp-B. To further investigate the huntingtin proteolytic pathway, we used an inducible PC12 cell model expressing full-length huntingtin with either normal or expanded polyglutamine. This cell model recapitulates several steps of huntingtin proteolysis: proteolysis mediated by caspases within the region previously mapped for caspase cleavage, and cleavage generating two novel N-terminal fragments (cp-1 approximately 90-105 residues long and cp-2 extending beyond 115-129 epitope of huntingtin). Interestingly, the deletion of amino acids 105-114 (mapped previously as a cleavage site for cp-A) failed to affect the production of cp-1 or cp-2. Therefore, we conclude that these new fragments are distinct from previously described cp-A and cp-B. We demonstrate that cp-1 and cp-2 fragments are produced and accumulate within nuclear and cytoplasmic inclusions prior to huntingtin-induced cell toxicity, and these fragments can be formed by caspase-independent proteolytic cleavage of huntingtin in PC12 cells. In addition, inhibition of calpains leads to decreased subsequent degradation of cp-1 and cp-2 fragments, and accelerated formation of inclusions. Further delineation of huntingtin cleavage events may lead to novel therapeutic targets for HD.