Antigenic constituents in pregnancy plasma which are undetectable in normal non-pregnant female or male plasma

Structure-based mechanism of cysteine-switch latency and of catalysis by pappalysin-family metallopeptidases

Tannerella forsythia is an oral dysbiotic periodontopathogen involved in severe human periodontal disease. As part of its virulence factor armamentarium, at the site of colonization it secretes mirolysin, a metallopeptidase of the unicellular pappalysin family, as a zymogen that is proteolytically auto-activated extracellularly at the Ser54-Arg55 bond. Crystal structures of the catalytically impaired promirolysin point mutant E225A at 1.4 and 1.6 Å revealed that latency is exerted by an N-terminal 34-residue pro-segment that shields the front surface of the 274-residue catalytic domain, thus preventing substrate access. The catalytic domain conforms to the metzincin clan of metallopeptidases and contains a double calcium site, which acts as a calcium switch for activity. The pro-segment traverses the active-site cleft in the opposite direction to the substrate, which precludes its cleavage. It is anchored to the mature enzyme through residue Arg21, which intrudes into the specificity pocket in cleft sub-site S1'. Moreover, residue Cys23 within a conserved cysteine-glycine motif blocks the catalytic zinc ion by a cysteine-switch mechanism, first described for mammalian matrix metallopeptidases. In addition, a 1.5 Å structure was obtained for a complex of mature mirolysin and a tetradecapeptide, which filled the cleft from sub-site S1' to S6'. A citrate molecule in S1 completed a product-complex mimic that unveiled the mechanism of substrate binding and cleavage by mirolysin, the catalytic domain of which was already preformed in the zymogen. These results, including a preference for cleavage before basic residues, are likely to be valid for other unicellular pappalysins derived from archaea, bacteria, cyanobacteria, algae and fungi, including archetypal ulilysin from Methanosarcina acetivorans. They may further apply, at least in part, to the multi-domain orthologues of higher organisms.

Evaluation of Serum Pregnancy Associated Plasma Protein-A & Plasma D-Dimer in Acute Coronary Syndrome

INTRODUCTION

Acute coronary syndrome (ACS), a spectrum comprising unstable angina pectoris, ST Elevated Myocardial Infarction (STEMI) & Non ST Elevated Myocardial Infarction (NSTEMI) is the major cause of presentation in Emergency Department today. Though ECG and cardiac enzymes are used for diagnosis, they mislead the diagnosis sometimes and delay in treatment initiation. This leads us to search certain new parameters which reflect the pathophysiology of ACS. Markers of plaque stability like Pregnancy Associated Plasma Protein-A and D-Dimer, a marker of ongoing thrombosis are found to be better markers in early diagnosis.

AIM

To evaluate the diagnostic competence of PAPP-A and D-Dimer in acute coronary syndrome over CK-MB and to compare with the inflammatory marker High Sensitive C-Reactive Protein (hs-CRP) which is associated with atherosclerosis.

MATERIALS AND METHODS

Fifty patients presenting with acute onset of chest pain to Emergency Department with or without ECG changes served as cases and 50 healthy people served as controls. Serum PAPP-A is measured by Enzyme Linked Immunosorbent Assay (ELISA), D-Dimer and hs-CRP by using Latex Turbidimetry method.

RESULTS

A statistical significant difference of PAPP-A and D-Dimer was noted between the ACS and controls (p < 0.001) whereas CK-MB shows no much difference (p 0.09). Statistically significant positive correlation is noted between parameters.

CONCLUSION

PAPP-A marker of plaque instability and D-Dimer marker of ongoing thrombosis are raised in acute coronary syndrome and thus can be considered as one of the marker in ACS for diagnosis.

Performance of free β-human chorionic gonadotrophin (free β-hCG) and pregnancy associated plasma protein-A (PAPP-A) analysis between Delfia Xpress and AutoDelfia systems in The Netherlands

: The VU University Medical Center (VUmc) was the first hospital in the Netherlands to introduce the Delfia Xpress for the analysis of free β-human chorionic gonadotrophin (β-hCG) and pregnancy associated plasma protein-A (PAPP-A) in the first trimester screening program for Down syndrome. Since then, others have implemented this system. In this study, we tested the equality of measurements for free β-hCG and PAPP-A between Delfia Xpress systems and one AutoDelfia system.

: A total of 40 serum samples were aliquoted and stored at –20°C. Samples were analyzed by six Delfia Xpress systems and one AutoDelfia system over a time period of 2 years.

: The relationships between free β-hCG and PAPP-A were excellent for the different Delfia Xpress systems (r>0.99, p<0.0001). For PAPP-A, the agreement between the main system at VUmc and five other systems was linear with slopes between 0.99 and 1.06. Similarly, agreement for free β-hCG was linear with slopes between 0.99 and 1.09. Likewise, agreement for PAPP-A and free β-hCG was excellent for the AutoDelfia vs. the main Delfia Xpress at the VUmc (r>0.99, p<0.0001). For both PAPP-A and free β-hCG, the relationships were linear with slopes of 1.08 and 1.07.

: We demonstrate an excellent agreement for the analysis of PAPP-A and free β-hCG between Delfia Xpress systems and one AutoDelfia system.

Clin Chem Lab Med 2009;47:222–6.

Activity of ulilysin, an archaeal PAPP-A-related gelatinase and IGFBP protease

Human growth and development are conditioned by insulin-like growth factors (IGFs), which have also implications in pathology. Most IGF molecules are sequestered by IGF-binding proteins (IGFBPs) so that exertion of IGF activity requires disturbance of these complexes. This is achieved by proteolysis mediated by IGFBP proteases, among which the best characterised is human PAPP-A, the first member of the pappalysin family of metzincins. We have previously identified and studied the only archaeal homologue found to date, Methanosarcina acetivorans ulilysin. This is a proteolytically functional enzyme encompassing a pappalysin catalytic domain and a pro-domain involved in maintenance of latency of the zymogen, proulilysin. Once activated, the protein hydrolyses IGFBP-2 to -6 and insulin chain beta in vitro. We report here that ulilysin is also active against several other substrates, viz (azo)casein, azoalbumin, and extracellular matrix components. Ulilysin has gelatinolytic but not collagenolytic activity. Moreover, the proteolysis-resistant skeletal proteins actin and elastin are also cleaved, as is fibrinogen, but not plasmin and alpha1-antitrypsin from the blood coagulation cascade. Ulilysin develops optimal activity at pH 7.5 and strictly requires peptide bonds preceding an arginine residue, as determined by means of a novel fluorescence resonance energy transfer assay, thus pointing to biotechnological applications as an enzyme complementary to trypsin.

Substrate specificity of a metalloprotease of the pappalysin family revealed by an inhibitor and a product complex

Human pappalysin-1 is a multi-domain metalloprotease engaged in the homeostasis of insulin-like growth factors and the founding member of the pappalysin family within the metzincin clan of metalloproteases. We have recently identified an archaeal relative, ulilysin, encompassing only the protease domain. It is a 262-residue active protease with a novel 3D structure with two subdomains separated by an active-site cleft. Despite negligible overall sequence similarity, noticeable similarity is found with other metzincin prototypes, adamalysins/ADAMs and matrix metalloproteinases. Ulilysin has been crystallised in a product complex with an arginine-valine dipeptide occupying the active-site S(1') and S(2') positions and in a complex with the broad-spectrum hydroxamic acid-based metalloprotease inhibitor, batimastat. This molecule inhibits mature ulilysin with an IC(50) value of 61 microM under the conditions assayed. The binding of batimastat to ulilysin evokes binding to vertebrate matrix metalloproteases but is much weaker. These data give insight into substrate specificity and mechanism of action and inhibition of the novel pappalysin family.

Molecular Analysis of Ulilysin, the Structural Prototype of a New Family of Metzincin Metalloproteases

The metzincin clan encompasses several families of zinc-dependent metalloproteases with proven function both in physiology and pathology. They act either as broad spectrum protein degraders or as sheddases, operating through limited proteolysis. Among the structurally uncharacterized metzincin families are the pappalysins, of which the most thoroughly studied member is human pregnancy-associated plasma protein A (PAPP-A), a heavily glycosylated 170-kDa multidomain protein specifically cleaving insulin-like growth factor (IGF)-binding proteins (IGFBPs). Proulilysin is a 38-kDa archaeal protein that shares sequence similarity with PAPP-A but encompasses only the pro-domain and the catalytic domain. It undergoes calcium-mediated autolytic activation, and the mature protein adopts a three-dimensional structure with two subdomains separated by an active site cleft containing the catalytic zinc ion. This structure is reminiscent of human members of the adamalysin/ADAMs (a disintegrin and a metalloprotease) family of metzincins. A bound dipeptide yields information on the substrate specificity of ulilysin, which specifically hydrolyzes IGFBP-2 to -6, insulin, and extracellular matrix proteins but not IGFBP-1 or IGF-II. Accordingly, ulilysin has higher proteolytic efficiency and a broader substrate specificity than human PAPP-A. The structure of ulilysin represents a prototype for the catalytic domain of pappalysins.

Predictive value of hormone measurements in maternal and fetal complications of pregnancy

Intrauterine tissues (placenta, amnion, chorion, decidua) express hormones and cytokines that play a decisive role in maternal-fetal physiological interactions. The excessive or deficient release of some placental hormones in association with gestational diseases may reflect an abnormal differentiation of the placenta, an impaired fetal metabolism, or an adaptive response of the feto-placental unit to adverse conditions. This review is focused on the applicability of hormone measurements in the risk assessment, early diagnosis, and management of pregnancies complicated by Down's syndrome, fetal growth restriction, preeclampsia, preterm delivery, and diabetes mellitus. Combined hormonal tests or the combination of hormones and ultrasound may achieve reasonable sensitivity, but research continues to simplify the screening programs without sacrificing their accuracy. Only in a few instances is there sufficient evidence to firmly recommend the routine use of hormone tests to predict maternal and fetal complications, but the judicious use of selected tests may enhance the sensitivity of the risk assessment based solely on clinical and ultrasound examination.

First trimester screening for aneuploidy: serum biochemical markers

The article reviews screening for Down syndrome in the first trimester (8-13 gestational weeks) with maternal serum analytes. In the first trimester, 2 serum markers stand out: pregnancy-associated plasma protein-A, a large glycoprotein tetramer, and free beta-human chorionic gonadotropin (beta-hCG), 1 of the 2 subunits of the glycoprotein hormone hCG. Some data indicate that hCG itself may be as effective as free beta-hCG in the first trimester. Maternal serum levels of pregnancy-associated plasma protein-A are low and free beta-hCG are high (consensus multiple of the medians, 0.4 and 1.8, respectively) in Down syndrome pregnancy. The consensus estimate of screening performance by using pregnancy-associated plasma protein-A and free beta-hCG in combination with maternal age is 60% detection rate at a 5% false positive rate. This is similar to the screening performance of second trimester double markers, but not as good as the screening performance of second trimester triple or quad markers. For this reason, first trimester screening with serum markers alone cannot be recommended except in cases in which second trimester screening cannot be done.

Isolation and characterization of circulating complex between human pregnancy-associated plasma protein-A and proform of eosinophil major basic protein

The plasma protein previously known as pregnancy associated plasma protein-A (PAPP-A) and believed to contain only one kind of polypeptide chain has recently been shown to be a complex containing two different chains in equimolar amounts. One of the chains is now defined as the PAPP-A subunit, and the other has been identified as the proform of eosinophil major basic protein (proMBP) (Oxvig et al. (1993) J. Biol. Chem. 268, 12243-12246). A procedure for large scale preparation of the circulating complex (PAPP-A/proMBP) from pooled pregnancy serum is described. The amino acid and carbohydrate compositions of the isolated reduced and carboxymethylated PAPP-A (199 kDa) and proMBP subunits (38 kDa), and of the intact PAPP-A/proMBP have been determined. The PAPP-A and proMBP subunits contain 13.4% (w/w) and 38.6% (w/w) carbohydrate, respectively, and the intact complex contains 17.4% (w/w) carbohydrate. The PAPP-A subunit contains N-bound carbohydrate groups. In contrast, the proMBP subunit contains both N- and O-bound groups as well as glycosaminoglycan, previously found among plasma proteins only in inter-alpha-trypsin inhibitor and pre-alpha-trypsin inhibitor. It is shown that PAPP-A/proMBP can competitively inhibit human leucocyte elastase (KI = (5-10) x 10(-9) M) at an ionic strength of 0.075, but the inhibition is negligible at ionic strengths greater than 0.15. Human cathepsin G is also competitively inhibited (KI approx. 1 x 10(-6) M). The inhibition of both enzymes is most likely due to interactions with the glycosaminoglycan moiety of PAPP-A/proMBP. It is concluded that PAPP-A/proMBP is neither a potent nor a specific inhibitor of human leucocyte elastase.

Pregnancy-associated plasma protein A levels in maternal serum, extraembryonic coelomic and amniotic fluids in the first trimester

First trimester maternal serum levels of pregnancy-associated plasma protein A(PAPP-P) are reduced in women with a Down's syndrome pregnancy. We have examined the concentration of this molecule in the amniotic (AF) and extra-embryonic coelomic (EECF) fluids surrounding the developing fetus. Maternal serum levels of PAPP-A were elevated in all samples and steadily rose from a median of 480 mIU/1 at 8 weeks to a median of 6375 mIU/1 at 14 weeks gestation. Levels of PAPP-A were low in EECF and undetectable in the AF until 14 weeks gestation. This pattern of distribution is in contrast to that of most other trophoblast-associated antigens. This may reflect PAPP-A physiology and its specific production by the syncytiotrophoblast.

Immunohistochemical aspects of immunological cross-reaction and masking of epitopes for localization studies on pregnancy-associated plasma protein A

The influence of antibody absorption procedures and proteolytic pre-treatment of formaldehyde-fixed placental tissue on the localization of pregnancy-associated plasma protein A by immunoperoxidase technique was examined. Apparently monospecific IgG fraction of the anti-plasma protein applied directly on fixed tissue resulted in staining of connective tissue and a thin apical rim of the syncytiotrophoblast. Further absorption of the antibody with foetal connective tissue abolished this staining reaction. Pre-treatment of the fixed placental tissue with trypsin prior to application of the antibody, which had been absorbed with connective tissue, resulted in staining within the cytoplasm of the syncytiotrophoblast exclusively. Identical staining was seen when this IgG preparation was used directly on frozen placental tissue. The results point to the importance of the specificity of the antibody preparations and of proteolytic unmasking of epitopes when fixed tissues are used for localization studies of pregnancy-associated plasma protein A by immunoperoxidase technique.

Immunohistochemical localization of pregnancy-associated plasma protein A (PAPP-A) in placentae from normal and pre-eclamptic pregnancies

An immunohistochemical method was used to locate pregnancy-associated plasma protein A (PAPP-A) in the placenta and uterus. In addition to 10 placentae and basal plates from normal pregnancies, ranging in gestational age from 37 to 40 weeks, the following specimens were studied: three uteri obtained by hysterectomy during early pregnancy; and three placentae from patients with severe hypertensive pre-eclampsia. In early gestation, PAPP-A was localized in the villous cytotrophoblastic cell layer and the endometrial glands but was not found in the villous syncytiotrophoblast, the cytotrophoblastic cell columns or the decidual cells. On histochemical examination of placentae from cases of pre-eclampsia with hypertension, an increased number of villous cytotrophoblastic cells and so-called X-cells was observed. The monospecific antiserum to PAPP-A reacted strongly and evenly with the cytoplasm of these cells. The present study strongly suggests that the active production sites of PAPP-A are the villous cytotrophoblastic cells and the X-cells.

An immunochemical study of proteins with SP1 determinants in native and acidified pregnancy serum

The alpha and beta forms of the pregnancy-associated protein, SP1, have been studied in late pregnancy serum and in similar serum after acidification. In both sera only two forms of the protein, SP1 alpha and SP1 beta, could be found; both reacting with antisera against SP1. On gel chromatography these two forms could be separated, with the intermediate effluent containing a varying mixture of both proteins. Immunoelectrophoresis of the effluent fractions from gel chromatography showed rocket shaped immunoprecipitates whose morphology depended on the mixture of SP1 alpha and SP1 beta. Crossed immunoelectrophoresis confirmed that only two proteins could be defined with SP1 antisera; the front running protein having an alpha 2 electrophoretic mobility and a molecular weight of 430,000, while the slower moving component had the electrophoretic mobility of a beta 1 globulin and a molecular weight of 90,000.

Observations on the separation of SP1 alpha and SP1 beta by affinity chromatography

SP1 antigens in late pregnancy blood, in placental extracts and in acidified plasma have been purified on positive affinity chromatography columns with immobilized SP1 antiserum and on negative affinity columns with immobilized antihuman non-pregnancy serum. Both SP1 alpha and SP1 beta are bound by the positive column but only SP1 alpha is bound by the negative column. This is adduced as further support for the view that SP1 alpha is formed by the combination of SP1 beta with a protein present in non-pregnancy serum.

Heterogeneity of pregnancy-specific beta 1-glycoprotein following purification from maternal serum and partial characterization of a high-molecular-weight component

Pregnancy-Specific beta 1-Glycoprotein (PSB1G) has been purified from maternal serum by physico-chemical and immunochemical methods. Marked instability of the protein was noted after partial purification which correlated with hydroxylapatite chromatography of PSB1G. Three molecular heterogeneous forms were demonstrated by gel filtration on Sephacryl S-200 which were designated as PSB1G-I, II and III. Each of the latter purified materials displayed altered immunoelectrophoretic mobility, i.e., altered from beta 1 to gamma mobility. In immunodiffusion experiments PSB1G-I reacted in complete immunological identity with 'native' serum PSB1G whereas PSB1G-II and III reacted in partial identity with each of the latter, suggesting that they are dissociation and/or degradation products of the parent PSB1G. The apparent molecular weights of PSB1G-I, II and III as determined by gel filtration were 280 000, 69 000 and 23 000, respectively, PSB1G-I was selected for structural analysis on the basis of its immunological identity with 'native' antigen. SDS-PAGE studies of PSB1G-I with and without reducing agent strongly suggest that PSB1G-I and 'native' serum antigen are composed of two dissimilar subunits of equal molecular size which are bonded together by non-covalent linkage. One of the subunits appears to represent a single polypeptide chain, whereas the other subunit appears to be composed of two polypeptide chains of unequal size that are linked together by covalent bonds. Investigations are continuing towards confirmation of the proposed structural model of PSB1G-I by an alternate methodology of protein structure analysis.

Separation of two pregnancy-associated proteins with SP1 determinants and the conversion of SP1 beta to SP1 alpha

The alpha and beta forms of the pregnancy-associated protein, SP1 which have been previously identified in late pregnancy serum were found to be also present in the placenta. The alpha form was somewhat more difficult to extract, requiring the use of detergents in the extracting buffer. The two variants can be separated by ion exchange chromatography or by gel filtration and distinguished by the different shapes of the precipitation rockets on immunoelectrophoresis. The alpha variant appears to be the larger molecule on gel filtration. When solutions of SP1 are acidified to pH 2.5 the beta form is rapidly converted to the alpha form and the latter is slowly destroyed. It is suggested that SP1 alpha represents the combination of SP1 beta with some other protein present in the placenta and in the serum.

Development of radioimmunoassay for pregnancy-specific beta1-globulin and its measurement in serum of patients with trophoblastic and non-trophoblastic tumours

Levels of human pregnancy-specific or trophoblast-specific beta1-globulin (TBG) were measured by double-antibody radioimmunoassay (RIA) in 103 patients with trophoblastic tumours and in 114 patients with a variety of non-trophoblastic tumours. The sensitivity of RIA for TBG was about 1 ng per ml. Twenty healthy adult females and males had levels below 1 ng per ml. Using the RIA for measurement of TBG in sera which were selected from immunodiffusion-TBG-negative samples, we detected elevated TBG levels in 76.7% of cases with trophoblastic tumours and in 15% of different cases with non-trophoblastic malignancies. The diagnostic and prognostic significance of the measurement of TBG levels by RIA in patients with trophoblastic tumours is discussed.

Placental localization of human pregnancy--associated plasma proteins

Frozen sections of human placenta were examined for the presence of four human pregnancy proteins, pregnancy-associated plasma proteins A and C (PAPP-A and PAPP-C), human chorionic somatomammotropin (hCS), and pregnancy zone protein (PZP), by the indirect immunofluorescence technique. Monospecific rabbit antiserums to PAPP-A, PAPP-C and hCS all stained the trophoblast cytoplasm equivalently in a continuous layer, usggesting that the same trophoblast cells synthesize all three pregnancy proteins. In contrast, PZP was localized in blood vessel walls, parenchymal structures within the villous, as well as in the trophoblast cytoplasm. Its distribution in the latter was relatively inhomogeneous, tending to be more intense on the basement membrane side.

Relation of obstetric parameters to the concentrations of four pregnancy-associated plasma proteins at term in normal gestation

The relations between normal obstetric parameters and the maternal levels of four pregnancy-associated plasma proteins (PAPP) were studied, with the use of plasma samples taken from 187 normal pregnant women within seven days before delivery. PAPP-A levels were correlated with placental and newborn weights. The levels of this pregnancy protein was higher in primigravid women and in groups with higher diastolic blood pressure than in other groups. Women with extremely high PAPP-A concentrations were likely to have extremely large placental weight was not necessarily associated with a high PAPP-A level. PAPP-C was not correlated with placental or newborn weight. The relationship between PAPP-C and maternal age, as well as maternal weight, was significant by one but not in the other three statistical analyses employed. The pregnancy zone protein was found to be correlated with parity. In primigravid women, this protein additionally showed an inverse correlation with the placental weight. Human chorionic somatomammotropin was significantly related to placental weight and inversely related to maternal weight. Its relationship with newborn weight was best seen in primigravid subjects. Other parameters (systolic blood pressure, one- and five-minute Apgar scores, weeks of gestation, days before delivery, newborn sex, and newborn bilirubin level) were not related to any of these pregnancy proteins.

Human pregnancy-associated plasma proteins during the postpartum period

The plasma levels of four pregnancy-associated plasma proteins (PAPP's) and pregnancy zone protein (PZP) were studied in women after delivery of a single viable infant by gel immunodiffussion methods. Data from 89 random samples and 85 serial specimens from five women revealed that both PAPP-B and HPL (PAPP-D) disappeared within a day after delivery. PAPP-A showed a rapid drop in the first 2 or 3 days post partum and became nondetectable in 4 to 6 weeks, with a half-life of 3 to 4 days. PAPP-C had a sharp decrease by the second postpartum day and was not detected 3 to 4 weeks later, with a half-life of 1 to 2 days. None of the PAPP's was detected again during the rest of the 14 postpartum weeks studied. In contrast, the PZP showed a much slower decrease or even a temporary increase during the first 2 weeks post partum; it remained readily detectable over the entire 14 weeks studied.

Early detection of pregnancy-associated serum protein using antiserum to placental antigens

Antisera against human placental proteins were developed in goats and rabbits, using immunoadjuvants and a prolonged injection schedule. The antisera were absorbed with normal serum proteins and then tested in immunodiffusion against normal and pregnancy sera. Two bands of precipitation due to pregnancy antigens were observed in pregnancy sera as early as 18 days after conception. Detection of these antigens has possibilities for application as an early pregnancy test.

Measurement of pregnancy-associated plasma proteins during human gestation

Studies of four pregnancy-associated plasma proteins (PAPP's) were made on 206 plasma samples obtained from 175 pregnant women between 12 and 44 wk of gestation. The concentration of three PAPP's (A, C, and D) were assayed by quantitative crossed immunoelectrophoresis. They showed a gradual but small rate of increase during the 2nd trimester, which became more rapid in the 3rd trimester. PAPP-A continued to rise steadily during this period, while PAPP-C and PAPP-D (recently identified as human placental lactogen) tended to reach a plateau. Although PAPP-B could not be quantitated because of technical problems, it was detected in over 50% of the samples from the last 2 mo of gestation, but was almost never seen in those obtained during the 12th-28th wk of gestation. Various parameters were analyzed to determine their possible correlation with the PAPP levels during the last month of gestation. The race and age of the mother showed no influence on any of the PAPP's, while parity, sex of fetus, and infant birth weights appeared to affect the plasma concentration of some of the PAPP's. In the two instances studied, mothers of twins showed abnormally high PAPP levels.