New quantitative total protein S-assay system for diagnosing protein S type II deficiency: clinical application of the screening system for protein S type II deficiency

Development of an assay using a modified coagulation factor V to measure protein S activity

BACKGROUND

Protein S (PS) is an anticoagulant that functions as a cofactor for activated protein C and the tissue factor pathway inhibitor. PS deficiency is a risk factor for venous thromboembolism. PS activity is commonly measured using clot-based assays involving fibrin and thrombin production, but improvements are needed.

OBJECTIVES

To develop a new assay for measuring plasma PS activity by quantifying the amount of activated coagulation factor (F)V cleaved by activated protein C.

METHODS

We designed a recombinant, modified FV (FVm) that mimicked FVa. We analyzed 160 purposively selected plasma samples from the Biobank of the National Cerebral and Cardiovascular Center.

RESULTS

The assay using mixed normal and PS-deficient plasma detected FVm cleavage in a PS concentration-dependent manner. The correlation between PS activity, measured using the FVm cleavage assay, and free PS antigen levels was relatively weak. We then sequenced all exons of PROS1 from 47 subjects with <60% activity in either the FVm cleavage assay or the clot-based assay. Nonsynonymous variants were identified in 12 of 24 subjects with <60% activity in both assays and in 2 of 7 subjects with <60% activity in the FVm cleavage assay alone. No variants were identified in 16 subjects with <60% activity in the clot-based assay alone. Unlike the clot-based assay, the FVm cleavage assay was not affected by the presence of rivaroxaban in the plasma.

CONCLUSION

An assay using the FVm substrate may be less susceptible to interference and provide a more accurate evaluation of plasma PS activity than clot-based assays.

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.

The effects of dienogest and combined oral contraceptives on protein S-specific activity in endometriosis patients

OBJECTIVE

One serious side effect of combined oral contraceptives (COCs) is venous thromboembolism. Reduced activity in activated protein C-related coagulation pathways is attributable to low protein S activity in one-third of Japanese patients with deep vein thrombosis. Herer, we quantified the behavior of protein S-specific activity in response to dienogest (DNG) and COCs using the protein S-specific activity assay system to explore its potential utility as a thrombosis marker.

STUDY DESIGN

This was a prospective cohort study. Female patients aged 20 - 49 years who were starting drug treatment for endometriosis using DNG or COCs were enrolled. Blood samples were taken before treatment and at the first, third, and sixth months of treatment. To analyze the primary endpoints, changes in total protein S antigen levels, total protein S activity, and protein S-specific activity from baseline to each time point were estimated using a linear mixed-effects model. All statistical analyses were performed in the SAS software version 9.4 (SAS Institute, Cary, NC). A two-sided P < 0.05 was considered statistically significant.

RESULTS

64 patients took DNG and 34 patients took COCs. Protein S-specific activity did not change significantly from baseline in the six months after treatment started in either group. In the DNG group, total protein S activity and total protein S antigen levels increased slightly from baseline levels after the treatment. The means for total protein S activity and total protein S antigen levels in the COC group remained within reference limits, but they both decreased markedly in the first month and stayed low. Protein S-specific activity in four women remaind below the reference limit throughout the whole study period, suggesting they may have potential protein S deficiencies.

CONCLUSION

The effects of DNG on protein S were negligible, though both total protein S activity and antigen levels decreased soon after COC treatment began and remained low. As there was no VTE event during the study, further studies with larger numbers of patients will be needed to confirm that protein S-specific activity can be a surrogate maker of VTE risk.

Effect on Plasma Protein S Activity in Patients Receiving the Factor Xa Inhibitors

AIMS

Measurement of protein S (PS) activity in patients taking direct oral anticoagulants (DOACs) using reagents based on a clotting assay results in falsely high PS activity, thus masking inherited PS deficiency, which is most frequently seen in the Japanese population. In this study, we investigated the effect of factor Xa (FXa) inhibitors on PS activity using the reagent on the basis of the chromogenic assay, which was recently developed in Japan.

METHODS

The study enrolled 152 patients (82 males and 70 females; the average age: 68.5±14.0 years) receiving three FXa inhibitors (rivaroxaban, edoxaban, and apixaban). PS activity was measured using the reagents on the basis of the clotting and chromogenic assays.

RESULTS

PS activity measured by the clotting assay reagents exhibited falsely high values depending on the plasma concentrations of FXa inhibitors in patients taking either rivaroxaban or edoxaban. However, none of the three FXa inhibitors affected PS activity when measured using the chromogenic assay.

CONCLUSION

In patients taking rivaroxaban or edoxaban, inherited PS deficiency is likely missed because the levels of PS activity measured using the reagents based on the clotting assay are falsely high. However, we report that three FXa inhibitors do not affect PS activity measured by the chromogenic assay. When measuring the levels of PS activity in patients undergoing DOACs, the principles of each reagent should be understood. Furthermore, plasma samples must be collected at the time when plasma concentrations of DOACs are lowest or the DOAC-Stop reagent should be used.

Reduced Activity of Protein S in Plasma: A Risk Factor for Venous Thromboembolism in the Japanese Population

The quantitative assay of protein S can help in rapidly identifying carriers of abnormal protein S molecules through a simple procedure (by determining the total protein S mass, total protein S activity, and protein S-specific activity in blood), without genetic testing. To clarify the relationship between venous thromboembolism (VTE) and protein S-specific activity, and its role in the diagnosis of thrombosis in Japanese persons, the protein S-specific activity was measured and compared between patients with thrombosis and healthy individuals. The protein S-specific activity of each participant was calculated from the ratio of total protein S activity to total protein S antigen level. Plasma samples were collected from 133 healthy individuals, 57 patients with venous thrombosis, 118 patients with arterial thrombosis, and 185 non-thrombotic patients. The protein S-specific activity of one-third of the patients with VTE was below the line of Y = 0.85X (−2 S.D.). Most protein S activities in the plasma of non-thrombotic patients were near the Y = X line, as observed in healthy individuals. In conclusion, it was clearly shown that monitoring protein S activity and protein S-specific activity in blood is useful for predicting the onset and preventing venous thrombosis in at least the Japanese population.

Comparative evaluation of reagents for measuring protein S activity: possibility of harmonization

Patients with congenital protein S (PS) deficiency show a hereditary predisposition for thrombosis, and PS deficiency is prevalent among Japanese populations. Diagnosis is based on symptoms of thrombosis and reduced PS activity. Three reagents that use different measurement principles for determining PS activity are available in Japan. This study aimed to confirm the possibility of harmonization of these three reagents to establish a universal standard for PS activity in Japanese populations. Commercial normal plasma and plasma samples obtained from healthy individuals and healthy pregnant women were tested at three facilities using three reagents for measuring PS: STA-Staclot Protein S (STA-PS), HemosIL Protein S (Clotting) (IL-PS), and a total PS assay (SNT-PS). The within-run precision of each reagent was good, as each had a coefficient of variation of ≤ 3.8%. The dilution linearity for each reagent was also good. The correlation coefficient was 0.94 for STA-PS vs. IL-PS, 0.93 for SNT-PS vs. STA-PS, and 0.90 for SNT-PS vs. IL-PS, indicating a good correlation. Although the three reagents available in Japan for measuring PS activity use different measurement methods, each showed good performance, and large differences were not observed between the obtained values. Harmonization among them appears possible.

Plasma phenotypes of protein S Lys196Glu and protein C Lys193del variants prevalent among young Japanese women

Protein S Tokushima (p.Lys196Glu) and two protein C gene variants (p.Arg189Trp, p.Lys193del) are hereditary thrombophilia in Japanese and Chinese populations, respectively; however, their diagnosis by plasma analyses is difficult because of the type II deficiency phenotype. Three gene variant genotypes were examined in young Japanese women (n = 231). Plasma total protein S activity and total protein S antigen levels were measured using a total protein S assay system, protein C and protein S activities by clot-based methods, and protein C and free protein S antigen levels by latex agglutination methods. protein S Tokushima (p.Lys196Glu) and protein C p.Lys193del variants were prevalent among participants with allele frequencies of 1.08 and 0.86%, respectively, whereas any carrier of protein C p.Arg189Trp variant was not identified. The plasma phenotype of the type II deficiency of protein S Tokushima heterozygotes was demonstrated by decreased total protein S activity with a normal total protein S antigen level; however, the protein C activities of protein C p.Lys193del heterozygotes were within reference intervals, whereas their protein C antigen levels were elevated. We compared the diagnostic accuracy of the total protein S activity/total protein S antigen ratio for identifying protein S Tokushima heterozygotes with that of the clot-based protein S activity/free protein S antigen ratio and found that sensitivity and specificity of 100% each was only achieved by the former. Protein S Tokushima and protein C p.Lys193del are prevalent among young Japanese women, and a plasma analysis using the total protein S assay system is more accurate than the clot-based protein S activity/free protein S antigen ratio for diagnosing protein S Tokushima carriers.

Evaluation of the plasma protein S dynamics during pregnancy using a total protein S assay: Protein S-specific activity decreased from the second trimester

AIM

The relationship between congenital protein S (PS) deficiency and complications during pregnancy remains unclear, partly due to the difficulty of precisely evaluating the PS level with conventional assays and the physiological decrease of PS during pregnancy. A new PS assay was developed to measure the total PS antigen and activity quantitatively and calculate PS-specific activity. This study aimed to evaluate the plasma PS dynamics during pregnancy using the new PS assay and establish the reference interval for pregnant women.

METHODS

A total of 253 pregnant women without a personal or family history of thromboembolism were recruited. Blood samples were obtained in the first, second and third trimesters and at one month post-partum. The total PS antigen, activity, and PS-specific activity were studied. Results were analyzed by the repeated measures single-factor anovas followed by a post-hoc test using Excel Statistics.

RESULTS

The mean ± standard deviation (IU/mL) of the total PS antigen levels in the first, second and third trimesters and 1 month post-partum were 0.67 ± 0.12, 0.67 ± 0.09, 0.68 ± 0.11 and 0.92 ± 0.13, respectively. The total PS activity (IU/mL) in the first, second and third trimesters and 1 month post-partum were 0.69 ± 0.14, 0.59 ± 0.10, 0.58 ± 0.12 and 0.87 ± 0.15, respectively. The PS-specific activity was within the normal range of nonpregnant women in the first trimester (1.02 ± 0.10) but decreased in the second and third trimesters (0.88 ± 0.09 and 0.85 ± 0.09, respectively) before increasing in the post-partum period (0.94 ± 0.08).

CONCLUSION

The total PS antigen and activity decrease throughout pregnancy, while the PS-specific activity decreases in the second and third trimesters.

Protein C and protein S deficiencies may be related to survival among hemodialysis patients

Background

Thrombophilia due to protein C (PC) and protein S (PS) deficiencies is highly prevalent among patients with stage 5 chronic kidney disease and is reported to arise due to extracorporeal circulation during hemodialysis (HD). This study aimed to evaluate the relationship between HD treatment and thrombophilia.

Methods

A total of 114 Japanese patients on maintenance HD (62 men, 52 women) were followed during 2008–2011. Their survival rates were compared against the duration of HD. Prior to each HD, coagulation/fibrinolysis parameters and PC and PS activities were measured using standard techniques. The patients were divided into two groups: Group 1, with PC and/or PS deficiencies (n = 32), and Group 2, without PC and PS deficiencies (n = 82). The influence of such deficiencies and duration of dialysis on survival was examined. Time-to-event analysis was applied using Kaplan-Meier estimates, and the log-rank test was proposed to test the equivalence of relative survival data. Hazard ratios and 95% confidence intervals (CI) were calculated.

Results

Of the 114 patients, 37 died (Group 1, 22; Group 2, 15). The hazard ratio (95% CI) was higher (p = 0.004) in Group 1 than Group 2. Gene analyses of PC and PS were performed in 14 patients from Group 1. No mutations in either protein were observed. We analyzed the causes of death in both groups; however, the estimated thrombophilia-related incidence of death could not be determined due to small sample size of HD patients.

Conclusions

Our results suggest that PC and PS deficiencies may be related to survival in HD patients. However, this finding warrants additional research.

Relationship between plasma protein S levels and apolipoprotein C-II in Japanese middle-aged obese women and young nonobese women

: Protein S, a nonenzymatic cofactor to activated protein C, presents in two forms in plasma, free form and in a complex with C4b-binding protein. The aim of this study was to determine the association of plasma protein S levels with the variables related to cardiovascular disease risk. The relationships between plasma protein S levels with lipids, inflammation markers, and adiposity were first examined on middle-aged obese women (n = 62), then on young nonobese women (n = 160) to verify the findings in the obese women. Total and free protein S antigen levels in middle-aged obese women, approximately half being in a postmenopausal state and suffered from dyslipidemia, correlated negatively with estradiol and positively with triglycerides, total cholesterol, LDL cholesterol, apoA-II, apoB, apoC-II, apoC-III, apoE, hemoglobin A1c, and protein C, whereas there was no correlation with HDL cholesterol, apoA-I, BMI, visceral fat area, blood pressure, or factor VII activity. Multiple linear regression analyses revealed that protein C, apoC-II, and fibrinogen were significant predictors of total protein S antigen levels, accounting for 51.9% of variance, and apoC-II as a singular significant predictor for free protein S antigen levels (12.3% of variance). In young nonobese women, most being normolipidemic, apoC-II was also selected as a significant predictor of total protein S antigen levels, but not of free protein S antigen levels. The positive relationship between plasma protein S levels and apoC-II, a key regulator of triglycerides hydrolysis, may contribute to the pathogenesis of increased concentrations of plasma protein S.

Gene analysis of six cases of congenital protein S deficiency and functional analysis of protein S mutations (A139V, C449F, R451Q, C475F, A525V and D599TfsTer13)

Congenital deficiency of protein S (PS), an anticoagulant factor, leads to venous thrombosis, with onset predominantly beginning in adolescence. In the present study, gene analysis of six unrelated Japanese families diagnosed with congenital PS deficiency identified five missense mutations in the PROS1 gene - c.757C>T (Ala139Val; A139V), c.1346 G>T (Cys449Phe; C449F), c.1352G>A (Arg451Gln; R451Q), c.1424G>T (Cys475Phe; C475F) and c.1574C>T (Ala525Val; A525V) - and one frameshift mutation, c.2135delA (Asp599ThrfsTer13; D599TfsTer13). C449F, R451Q, A525V and D599TfsTer13 are novel mutations. Results from ELISA to measure PS antigen levels in culture supernatant showed that the A139V variant was similar to wild-type, but other variants showed reductions when compared with wild-type. Results from pulse-chase analysis confirmed that the A139V variant exhibited secretion equivalent to wild-type, but for the other variants, there was no extracellular secretion, and it had nearly all been degraded inside the cell within six hours. Results from pulse-chase analysis using proteasome inhibitors also showed that intracellular degradation of mutant protein was inhibited. Activity of the A139V variant was decreased to 71% of wild-type, and the phospholipid binding capacity fell to as low as 45%. These results suggest that although the A139V variant has normal secretion, it has abnormal phospholipid binding capacity, and therefore causes type II PS deficiency, in which PS activity is decreased. It is also thought that with the other variants, misfolding due to amino acid mutations causes nearly all PS to be degraded intracellularly, therefore leading to type I PS deficiency.

Thrombosis Prediction Based on Reference Ranges of Coagulation-Related Markers in Different Stages of Pregnancy

Introduction:

Careful monitoring of the hypercoagulable state is required during pregnancy. However, coagulation and fibrinolysis markers are not fully utilized because there are no reference values reflective of coagulation and fibrinolysis dynamics during pregnancy, which differ from the nonpregnant state.

Methods:

Changes in antithrombin (AT), fibrinogen (Fbg), prothrombin fragment 1+2 (F1+2), thrombin–antithrombin complex (TAT), soluble fibrin (SF), D-dimer (DD), and protein S (PS) were investigated in healthy pregnant women, and reference ranges in the early, mid, late, and end stages of pregnancy were established.

Results:

The AT was essentially constant throughout pregnancy. The Fbg, F1+2, TAT, and DD increased significantly as pregnancy progressed. In contrast, SF did not show a significant increase throughout the entire pregnancy period. Total PS antigen and total PS activity showed a corresponding decrease from early gestation. When test data in 3 cases in which deep vein thrombosis or intrauterine fetal death occurred during pregnancy were compared to the established reference ranges, all of the cases had multiple markers with values that exceeded the reference ranges.

Conclusion:

Establishing reference ranges for each week could potentially make it possible to evaluate abnormalities of the coagulation and fibrinolysis systems during pregnancy. Of note, SF might be a useful marker that reflects thrombus formation during pregnancy. Larger-scale studies will be required to establish reference ranges for every gestational week.

Thrombophilia in East Asian countries: are there any genetic differences in these countries?

In recent years, genetic analyses of congenital deficiencies of three anticoagulant proteins, antithrombin, protein C (PC) and protein S (PS), in East Asian patients with venous thromboembolism (VTE) have greatly increased. The PS-K196E mutation is often identified in the Japanese population with an allelic frequency of 0.86 %, and a total of approximately 10,000 Japanese are estimated to be homozygotes. The heterozygotes show PS anticoagulant activities ranging from 40 to 110 %, and 16 % lower mean anticoagulant activity than that in wild-type individuals. Specific assay methods to identify carriers of this mutation have recently been developed. The mutation carriers are at risk of thrombosis during pregnancy but do not appear to be at risk for adverse pregnancy outcomes. To promote future research into this mutation and its relation to thrombosis, a thrombosis-prone mouse strain with the PS K196E mutation has been developed. We found the PS-K196E mutation and the heterozygous PS-deficiency in mice caused increased VTE, but did not cause aggravation of ischemic stroke, unlike factor V Leiden mutation. Importantly, the PS-K196E mutation is only identified in Japanese. This suggests that although East Asian populations including Japanese, Chinese, and Koreans are geographically and genetically close, the PS-K196E mutation seems to be Japanese-specific, suggesting that the mutation is a recent occurrence and fixed within the Japanese population. Some recurrent genetic mutations predisposing to VTE have been reported in Chinese and Korean populations. Although the genetic background for VTE is known to differ between populations with Caucasian descent and East Asian populations, some of the recurrent mutations differ even within the East Asian populations.

ELISA-Based Detection System for Protein S K196E Mutation, a Genetic Risk Factor for Venous Thromboembolism

Protein S (PS) acts as a cofactor for activated protein C in the plasma anticoagulant system. PS Lys196-to-Glu (K196E) mutation is a genetic risk factor for venous thromboembolism in Japanese individuals. Because of the substantial overlap in PS anticoagulant activity between KK (wild-type) and KE (heterozygous) genotypes, it is difficult to identify PS K196E carriers by measuring PS activity. Here, we generated monoclonal antibodies specific to the PS K196E mutant and developed a simple and reliable method for the identification of PS K196E carriers. We immunized mice with a keyhole limpet hemocyanin-conjugated synthetic peptide with Glu196. The hybridoma cells were screened for the binding ability of the produced antibodies to recombinant mutant EGF-like domains of PS (Ile117–Glu283). We obtained three hybridoma cell lines producing PS K196E mutation-specific antibodies. We established a sandwich enzyme-linked immunosorbent assay (ELISA) system in which the PS K196E mutation-specific monoclonal antibody was used as a detection antibody. We measured human plasma samples by using this system and successfully discriminated 11 individuals with the KE genotype from 122 individuals with the KK genotype. The ELISA system using the PS K196E mutation-specific antibody is a useful tool for the rapid identification of PS K196E carriers, who are at a higher risk for venous thromboembolism.

Activated protein C anticoagulant system dysfunction and thrombophilia in Asia

Thrombophilia that is common among Caucasians is caused by genetic polymorphisms of coagulation factor V Leiden (R506Q) and prothrombin G20210A. Unlike that in Caucasians, thrombophilia that is common in the Japanese and Chinese involve dysfunction of the activated protein C (APC) anticoagulant system caused by abnormal protein S and protein C molecules. Approximately 50% of Japanese and Chinese individuals who develop venous thrombosis have reduced activities of protein S. The abnormal sites causing the protein S molecule abnormalities are distributed throughout the protein S gene, PROS1. One of the most common abnormalities is protein S Tokushima (K155E), which accounts for about 30% of the protein S molecule abnormalities in the Japanese. Whether APC dysfunction occurs in other Asian countries is an important aspect of mapping thrombophilia among Asians. International surveys using an accurate assay system are needed to determine this.