Development of a Plasma-Based Assay to Measure the Susceptibility of Factor V to Inhibition by the C-Terminus of TFPIα.

BACKGROUND: Factor V (FV) is proteolytically activated to FVa, which assembles with FXa in the prothrombinase complex. The C-terminus of tissue factor pathway inhibitor-α (TFPIα) inhibits both the activation and the prothrombinase activity of FV(a), but the pathophysiological relevance of this anticoagulant mechanism is unknown. FV Leiden (FVL) is less susceptible to inhibition by TFPIα, while overexpression of FV splicing variants with increased affinity for TFPIα (FV-short) causes bleeding. OBJECTIVE: This study aims to develop a plasma-based assay that quantifies the susceptibility of FV(a) to inhibition by the TFPIα C-terminus. MATERIALS AND METHODS: FV in highly diluted plasma was preactivated with FXa in the absence or presence of the TFPIα C-terminal peptide. After adding prothrombin, thrombin formation was monitored continuously with a chromogenic substrate and prothrombinase rates were obtained from parabolic fits of the absorbance tracings. TFPI resistance was expressed as the ratio of the prothrombinase rates with and without peptide (TFPIr). RESULTS: The TFPIr (0.25-0.34 in 45 healthy volunteers) was independent of FV levels. The TFPIr increased from normal individuals (0.29, 95% confidence interval [CI] 0.28-0.31) to FVL heterozygotes (0.35, 95% CI 0.34-0.37) and homozygotes (0.39, 95% CI 0.37-0.40), confirming TFPI resistance of FVL. Two individuals overexpressing FV-shortAmsterdam had markedly lower TFPIr (0.16, 0.18) than a normal relative (0.29), in line with the high affinity of FV-short for TFPIα. CONCLUSION: We have developed and validated an assay that measures the susceptibility of plasma FV to the TFPIα C-terminus. Once automated, this assay may be used to test whether the TFPIr correlates with thrombosis or bleeding risk in population studies.

Factor V Has Anticoagulant Activity in Plasma in the Presence of TFPIα: Difference between FV1 and FV2.

BACKGROUND: Activated factor V (FVa) is a potent procoagulant cofactor in the prothrombinase complex, whereas its precursor factor V (FV) stimulates the inhibition of factor Xa (FXa) by tissue factor pathway inhibitor-α (TFPIα), presumably by promoting TFPIα binding to phospholipids. Plasma FV comprises two glycosylation isoforms (FV1 and FV2) with low and high phospholipid-binding affinity, respectively. The FV1/FV2 ratio is increased in carriers of the FV R2 haplotype. OBJECTIVE: This article demonstrates the TFPIα-cofactor function of FV in plasma and compares FV1 and FV2. MATERIALS AND METHODS: Thrombin generation at low TF concentration was measured in FV-depleted plasma reconstituted with 0 to 100% FV, FV1 or FV2, and in 122 individuals genotyped for the R2 haplotype. The TFPIα-cofactor activities of FV1 and FV2 were also investigated in a model system of TFPIα-mediated FXa inhibition. RESULTS: In the FV titration, thrombin generation first increased (up to 5% FV) and then progressively decreased at higher FV concentrations. This anticoagulant effect of FV, which was also observed with FV2 but not with FV1, was largely abolished by anti-TFPIα antibodies, suggesting that it reflects TFPIα-cofactor activity of FV. In the model system of TFPIα-mediated FXa inhibition, FV2 was a more potent TFPIα-cofactor than FV1, in line with their respective phospholipid affinities. Accordingly, FV R2 carriers had higher thrombin generation than non-carriers, even after correction for demographics and plasma levels of coagulation factors and inhibitors. CONCLUSION: FV (and particularly its FV2 isoform) contributes to the TFPIα-dependent down-regulation of thrombin generation in plasma triggered with low TF.

Small volume plasma exchange for Guillain-Barré syndrome in resource-limited settings: a phase II safety and feasibility study.

OBJECTIVE: To assess the safety and feasibility of small volume plasma exchange (SVPE) for patients with Guillain-Barré syndrome (GBS). DESIGN: Non-randomised, single-arm, interventional trial. SETTING: National Institute of Neurosciences and Hospital, Dhaka, Bangladesh. PARTICIPANTS: Twenty adult (>18 years) patients with GBS presented within 2 weeks of onset of weakness who were unable to walk unaided for more than 10 m. INTERVENTIONS: SVPE involves blood cell sedimentation in a blood bag and removal of supernatant plasma after blood cells are retransfused. This procedure was repeated three to six times a day, for eight consecutive days. Fresh frozen plasma (FFP) and normal saline were used as replacement fluid. OUTCOME MEASURES: Serious adverse events (SAEs) were defined as severe sepsis and deep venous thrombosis related to the central venous catheter (CVC) used during SVPE. SVPE was considered safe if less than 5/20 patients experienced an SAE, and feasible if 8 L plasma could be removed within 8 days in at least 15/20 patients. RESULTS: Median patient age 33 years (IQR 23-46; range 18-55); 13 (65%) were male. Median Medical Research Council (MRC) sum score was 20 (IQR 0-29; range 0-36); three (15%) patients required mechanical ventilation. One patient developed SAE (severe sepsis, possibly related to CVC). The median plasma volume exchanged was 140 mL/kg (range 110-175) and removal of 8 L plasma was possible in 15 (75%) patients. Patients received a median 1 g/kg IgG via FFP although a substantial proportion of IgG was probably removed again by the SVPE sessions. GBS disability score improved by at least one grade in 14 (70%) patients 4 weeks after SVPE started. No patients died. CONCLUSION: SVPE seems a safe and feasible alternative treatment to standard plasma exchange (PE) or intravenous immunoglobulin (IVIg) for GBS; further studies of clinical efficacy in low-income and middle-income countries are warranted. TRIAL REGISTRATION NUMBER: NCT02780570.

Atypical Porcine Pestivirus: A Possible Cause of Congenital Tremor Type A-II in Newborn Piglets.

Congenital tremor type A-II in piglets has been regarded as a transmissible disease since the 1970s, possibly caused by a very recently-described virus: atypical porcine pestivirus (APPV). Here, we describe several strains of APPV in piglets with clinical signs of congenital tremor (10 of 10 farms tested). Piglets on a farm with no history of congenital tremor were PCR-negative for the virus. To demonstrate a causal relationship between APPV and disease, three gilts were inoculated via intramuscular injection at day 32 of pregnancy. In two of the three litters, vertical transmission of the virus occurred. Clinical signs of congenital tremor were observed in APPV-infected newborns, yet also two asymptomatic carriers were among the offspring. Piglets of one litter were PCR-negative for the virus, and these piglets were all without congenital tremors. Long-term follow up of farm piglets born with congenital tremors showed that the initially high viremia in serum declines at five months of age, but shedding of the virus in feces continues, which explains why the virus remains present at affected farms and causes new outbreaks. We conclude that trans-placental transmission of APPV and subsequent infection of the fetuses is a very likely cause of congenital tremor type A-II in piglets.

Inclusion body myositis. Clinical features and clinical course of the disease in 64 patients.

The clinical features of inclusion body myositis (IBM) were of minor importance in the design of consensus diagnostic criteria, mainly because of controversial views on the specificity of signs and symptoms, although some authors reported "typical" signs. To re-assess the clinical spectrum of IBM, a single investigator using a standard protocol studied a cohort of 64 patients cross-sectionally. Symptom onset was before the age of 50 years in 20% of cases. Only a few patients (14 %) started with weakness other than that of quadriceps, finger flexor or pharyngeal muscles. The sequence of power loss was erratic, but onset of symptoms with quadriceps weakness predicted an earlier onset of dysphagia in older patients (> or = 56 years) compared with younger ones (< 56 years) (p = 0.02). Despite widespread weakness patients had favourable scores on three commonly used function scales and they kept their employment. Complete wheel-chair dependency was rare (3 %). A dominant characteristic was the anatomical distribution of afflicted muscles: ventral extremity muscle groups were more affected than dorsal muscle groups and girdle muscles were least affected, the latter preserving postural stability. Ankylosis, especially in extension of the fingers,was frequently present. Together with the sparing of intrinsic hand muscles it was helpful in the preservation of many skillful movements. IBM has a unique distribution of muscle weakness. Ankylotic contractures are common. We feel that their joint impact on daily functioning is characteristic for the disease.

Timing and course of clinical response to intravenous immunoglobulin in chronic inflammatory demyelinating polyradiculoneuropathy.

OBJECTIVE: To investigate the timing, course, and clinical characteristics of the response to intravenous immunoglobulin in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). DESIGN: Data were extracted from the ICE trial, a randomized, double-blind, placebo-controlled trial of immune globulin intravenous, 10% caprylate/chromatography purified (IGIV-C). SETTING: Multiple international centers. PARTICIPANTS: One hundred seventeen individuals with CIDP. Intervention Treatment with IGIV-C (Gamunex, n = 59) or placebo (n = 58), with IGIV-C administered as a 2-g/kg loading dose followed by a 1-g/kg maintenance dose every 3 weeks, for up to 24 weeks. MAIN OUTCOME MEASURES: The primary efficacy parameter was an improvement of 1 or more points in adjusted Inflammatory Neuropathy Cause and Treatment (INCAT) disability score. Participants treated with IGIV-C were divided into subgroups based on meeting responder vs nonresponder definitions and by time to first improvement. RESULTS: Among 30 responders to IGIV-C, 14 (47%) patients had improved adjusted INCAT scores by week 3, and 16 (53%) patients improved at week 6 after a second infusion. Participants who improved by week 3 were more severely disabled at baseline than those who improved at 6 weeks. In patients who improved, the number of individuals reaching maximal improvement continued to increase during maintenance therapy for up to 24 weeks. For patients with first improvement by week 3, the change in dominant-hand grip strength over time tended to parallel the INCAT score. In patients with first improvement by week 6, however, the improvement in dominant-hand grip strength preceded initial improvement in INCAT score. CONCLUSIONS: Data suggest that treatment with 2 courses of IGIV-C administered 3 weeks apart may be required for initial improvement, and continued maintenance therapy may be necessary to achieve a maximal therapeutic response. Trial Registration clinicaltrials.gov Identifier: NCT00220740.