Dynamic equilibrium between protein S and C4b binding protein is important for accurate determination of free protein S antigen

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.

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.

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.

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

Venous thromboembolism (VTE) incidence is rising rapidly in Japan with lifestyle westernization and aging. Deficiency of protein S, an important blood coagulation regulator, is a risk factor for VTE. Protein S deficiency prevalence in Asians is approximately 10 times that in Caucasians and that of protein S type II deficiency, associated with the protein S Tokushima mutation (K155E), is quite high in Japan. However, currently available methods for measuring protein S are not precise enough for detection of this deficiency. We developed a novel assay system for precise simultaneous determinations of total protein S activity and total protein S antigen level, using a general-purpose automated analyzer, allowing protein S-specific activity (ratio of total protein S activity to total protein S antigen level) to be calculated. Mean specific activity was 0.99 for samples from healthy individuals but 0.69 or less (mean-3SD) in protein S type II-deficient and warfarin-treated samples, but was 1.0 in an estrogen-treated sample with significantly decreased protein S antigen. Protein S gene analyses in healthy individuals with specific activity 0.69 or less revealed the K155E mutation in all three. These results show our new assay system to be an effective screening tool for protein S type II deficiency. This system can also be used in an automated analyzer, facilitating numerous sample measurements, and is, thus, applicable to regular medical checkups and diagnosing VTE. Such applications would potentially contribute to early detection of protein S type II deficiency, and, thereby, to thrombosis prevention.

Prothrombotic abnormalities in childhood ischaemic stroke

Childhood ischaemic stroke, incorporating arterial ischaemic stroke and cerebral sinus venous thrombosis, is associated with significant morbidity and mortality in children. The majority of cases in children present with well-recognised risk factors. The appreciation of the role prothrombotic abnormalities have in disease states is developing rapidly. Prothrombotic abnormalities are abnormalities of the coagulation system, fibrinolytic system, endothelial cells or platelets that lead to a reduced threshold for pathological thrombus formation. Our understanding of the role of prothrombotic abnormalities in childhood ischaemic stroke is increasing and has a direct bearing on the development of effective management and prevention strategies. We provide a brief background of prothrombotic abnormalities and review the available literature on prothrombotic markers in childhood ischaemic stroke. Overall, prothrombotic abnormalities have been identified in 20-50% of children presenting with AIS and 33-99% of children with cerebral sinus venous thrombosis. There appear to be a number of associations emerging including an increased frequency of factor V Leiden mutation, elevated lipoprotein (a), protein C deficiency and antiphospholipid antibodies in children presenting with arterial ischaemic stroke. The pathogenic role of prothrombotic abnormalities as predisposing to initial and recurrent childhood ischaemic stroke is becoming increasingly evident. The impact on treatment, however, will only be clarified with carefully designed, multi-institutional prospective studies.