In Vivo Clearance of Human Protein S in a Mouse Model

Thrombophilia Screening: Not So Straightforward

Although inherited thrombophilias are lifelong risk factors for a first thrombotic episode, progression to thrombosis is multifactorial and not all individuals with inherited thrombophilia develop thrombosis in their lifetimes. Consequently, indiscriminate screening in patients with idiopathic thrombosis is not recommended, since presence of a thrombophilia does not necessarily predict recurrence or influence management, and testing should be selective. It follows that a decision to undertake laboratory detection of thrombophilia should be aligned with a concerted effort to identify any significant abnormalities, because it will inform patient management. Deficiencies of antithrombin and protein C are rare and usually determined using phenotypic assays assessing biological activities, whereas protein S deficiency (also rare) is commonly detected with antigenic assays for the free form of protein S since available activity assays are considered to lack specificity. In each case, no single phenotypic assay is capable of detecting every deficiency, because the various mutations express different molecular characteristics, rendering thrombophilia screening repertoires employing one assay per potential deficiency, of limited effectiveness. Activated protein C resistance (APCR) is more common than discrete deficiencies of antithrombin, protein C, and protein S and also often detected initially with phenotypic assays; however, some centres perform only genetic analysis for factor V Leiden, as this is responsible for most cases of hereditary APCR, accepting that acquired APCR and rare F5 mutations conferring APCR will go undetected if only factor V Leiden is evaluated. All phenotypic assays have interferences and limitations, which must be factored into decisions about if, and when, to test, and be given consideration in the laboratory during assay performance and interpretation. This review looks in detail at performance and limitations of routine phenotypic thrombophilia assays.

Protein S Heerlen mutation heterozygosity is associated with venous thrombosis risk

Hereditary Protein S (PS) deficiency is a rare coagulation disorder associated with an increased risk of venous thrombosis (VT). The PS Heerlen (PSH) mutation is a rare S501P mutation that was initially considered to be a neutral polymorphism. However, it has been later shown that PSH has a reduced half-life in vivo which may explain the association of PSH heterozygosity with mildly reduced levels of plasma free PS (FPS). Whether the risk of VT is increased in PSH carriers remains unknown. We analyzed the association of PSH (rs121918472 A/G) with VT in 4,173 VT patients and 5,970 healthy individuals from four independent case-control studies. Quantitative determination of FPS levels was performed in a subsample of 1257 VT patients. In the investigated populations, the AG genotype was associated with an increased VT risk of 6.57 [4.06–10.64] (p = 1.73 10⁻¹⁴). In VT patients in whom PS deficiency was excluded, plasma FPS levels were significantly lower in individuals with PSH when compared to those without [72 + 13 vs 91 + 21 UI/dL; p = 1.86 10⁻⁶, mean + SD for PSH carriers (n = 21) or controls (n = 1236) respectively]. We provide strong evidence that the rare PSH variant is associated with VT in unselected individuals.

PROS1 genotype phenotype relationships in a large cohort of adults with suspicion of inherited quantitative protein S deficiency

Inherited protein S deficiency (PSD) is an established risk factor for venous thromboembolism (VTE). However, data are conflicting concerning risk of VTE associated with decreased free PS level (FPS) and information on PROS1 genotype-phenotype relationship is sparse. In a retrospective cohort of 579 patients with inherited type I/III deficiency suspicion, PROS1 genotyping was performed and the effect of genotype on FPS and on VTE risk was investigated. We found 116 (including 65 novel) detrimental mutations (DM) in 222 (type I/III in 194, type II in 28), PS Heerlen in 74, possibly non DM in 38 and no mutation in 245 subjects. Among DMs, type I/IIIDMs only were found in subjects with FPS< 30 %. Prevalence of type I/III DM decreased with increasing FPS level. Risk of VT associated with FPS level and genotype was studied in the 467 subjects with personal or family history of thrombosis. Only type I/IIIDM carriers presented with an increased risk of VTE [1.41 (95 %CI (1.05-1.89)] compared to subjects with no mutation. Among the group of type I/IIIDM heterozygotes and subjects with no mutation, the optimal FPS cut-off point for identifying subjects at increased VTE risk was searched for. We found that only subjects with FPS< 30 % and type I/IIIDM presented with an increased risk [1.48 (95 %CI 1.08-2.04)]. Our findings confirm the value of a cut-off FPS level for identifying subjects at increased VTE risk far below the lower limit of the normal range and suggest a place for PROS1 genotyping in PSD diagnosis strategy.

Heerlen polymorphism associated with type III protein S deficiency and factor V Leiden mutation in a Polish patient with deep vein thrombosis

Protein S is one of the major natural anticoagulants. A missense serine 501 to proline (S501P) Heerlen polymorphism is associated with reduced levels of free protein S. Heerlen polymorphism, especially when combined with other thrombophilia risk factors, can lead to thromboembolic complications. To our knowledge, we report here the first Polish case associated with heterozygous Heerlen polymorphism resulting in type III protein S deficiency, detected in a 50-year-old man with several thrombotic episodes of deep and superficial veins and a highly positive thrombotic family history. The patient also had factor V Leiden mutation and persistently elevated anticardiolipin antibodies. It seems that increased risk of thrombotic complications could be explained in the patient by a synergy between the effects of Heerlen polymorphism, factor V Leiden heterozygous status and antiphospholipid syndrome.

Elucidating the role of carbohydrate determinants in regulating hemostasis: insights and opportunities

Recent improvement in modern analytical technologies has stimulated an explosive growth in the study of glycobiology. In turn, this has lead to a richer understanding of the crucial role of N- and O-linked carbohydrates in dictating the properties of the proteins to which they are attached and, in particular, their centrality in the control of protein synthesis, longevity, and activity. Given their importance, it is unsurprising that both gross and subtle defects in glycosylation often contribute to human disease pathology. In this review, we discuss the accumulating evidence for the significance of glycosylation in mediating the functions of the plasma glycoproteins involved in hemostasis and thrombosis. In particular, the role of naturally occurring coagulation protein glycoforms and inherited defects in carbohydrate attachment in modulating coagulation is considered. Finally, we describe the therapeutic opportunities presented by new insights into the role of attached carbohydrates in shaping coagulation protein function and the promise of carbohydrate modification in the delivery of novel therapeutic biologics with enhanced functional properties for the treatment of hemostatic disorders.

Protein S inherited qualitative deficiency: novel mutations and phenotypic influence

BACKGROUND

Only a few mutations associated with qualitative protein S deficiency have already been described. Sensitivity and specificity for type II PROS1 mutations of commercially available reagents for measuring Protein S (PS) activity are not well established. Whether these mutations are significant risk factors for thrombosis remains an unresolved question.

METHODS

In order to address the first point, we present and discuss the results of PROS1 analysis performed in the 30 probands with type II PS-inherited deficiency suspicion and 35 relatives, studied in our laboratory between 2000 and 2008. In order to investigate the influence of type II mutations on the coagulability level, thrombin generation tests were performed on plasma from 102 PROS1 type II, type I/III or PS Herleen mutation heterozygous carriers and controls.

RESULTS

Mutations (12 novel, six already described) which probably explain the qualitative phenotype, were found in 27 (90%) out of the 30 probands studied. In relatives, 78% of heterozygotes presented with a type II phenotype. An APC resistance phenotype was documented in type II and type I/III defects heterozygous carriers; however, the effect of type II was milder than the effect of type I/III PS mutations.

CONCLUSIONS

A PS functional assay (Staclot PS, Stago) was efficient in screening for PROS1 type II defects, particularly in probands. A significant positive influence of type II mutations on ex vivo thrombin generation was demonstrated. However, whether these mutations increase the risk of venous thromboembolism requires further investigation.

A systems biology approach to understanding elevated serum alanine transaminase levels in a clinical trial with ximelagatran

Ximelagatran was developed for the prevention and treatment of thromboembolic conditions. However, in long-term clinical trials with ximelagatran, the liver injury marker, alanine aminotransferase (ALT) increased in some patients. Analysis of plasma samples from 134 patients was carried out using proteomic and metabolomic platforms, with the aim of finding predictive biomarkers to explain the ALT elevation. Analytes that were changed after ximelagatran treatment included 3-hydroxybutyrate, pyruvic acid, CSF1R, Gc-globulin, L-glutamine, protein S and alanine, etc. Two of these analytes (pyruvic acid and CSF1R) were studied further in human cell cultures in vitro with ximelagatran. A systems biology approach applied in this study proved to be successful in generating new hypotheses for an unknown mechanism of toxicity.

Macrophages contribute to the cellular uptake of von Willebrand factor and factor VIII in vivo

Von Willebrand factor (VWF) and factor VIII (FVIII) circulate in a tight noncovalent complex. At present, the cells that contribute to the removal of FVIII and VWF are of unknown identity. Here, we analyzed spleen and liver tissue sections of VWF-deficient mice infused with recombinant VWF or recombinant FVIII. This analysis revealed that both proteins were targeted to cells of macrophage origin. When applied as a complex, both proteins were codirected to the same macrophages. Chemical inactivation of macrophages using gadolinium chloride resulted in doubling of endogenous FVIII levels in VWF-null mice, and of VWF levels in wild-type mice. Moreover, the survival of infused VWF was prolonged almost 2-fold in VWF-deficient mice after gadolinium chloride treatment. VWF and FVIII also bound to primary human macrophages in in vitro tests. In addition, radiolabeled VWF bound to human THP1 macrophages in a dose-dependent, specific, and saturable manner (half-maximal binding at 0.014 mg/mL). Binding to macrophages was followed by a rapid uptake and subsequent degradation of the internalized protein. This process was also visualized using a VWF–green fluorescent protein fusion protein. In conclusion, our data strongly indicate that macrophages play a prominent role in the clearance of the VWF/FVIII complex.

Denaturing high-performance liquid chromatography mutation analysis in patients with reduced Protein S levels

BACKGROUND

Patients with congenital Protein S deficiency have increased risk of venous thromboembolism. However, Protein S levels show large intra-individual variation and the biochemical assays have low accuracy and a high interlaboratory variability. Genetic analysis might aid in a more precise diagnosis and risk estimation. The aim was to design a high-throughput genetic analysis based on denaturing high-performance liquid chromatography to identify sequence variations in the gene coding for Protein S.

PATIENTS

In total, 55 patients referred to the Section of Thrombosis and Haemostasis, Odense University Hospital, in the period 1998-2004 were included in the study.

RESULTS

Mutations were found in ten of the 55 patients: Six different variants were identified, of which four were not previously reported: One were a nonsense mutation substituting a glutamine with a stopcodon (c.790C>T) and the rest were missense mutations (c.932T>G; c.1367A>G; c.1378T>C). Furthermore, four patients carried the same mutation (c.1045G>A), while two carried the Heerlen mutation (c.1378T>C).

CONCLUSIONS

The reported method will be useful for rapidly detecting sequence variations in the gene coding for Protein S, giving a precise diagnosis and subsequently a better risk estimation.