Maternal serum pregnancy-associated plasma protein-A concentration at 11-14 weeks of gestation and preeclampsia risk of women with common congenital anatomic uterine abnormalities

To evaluate maternal serum pregnancy-associated plasma protein-A (PAPP-A) levels at 11-14 weeks of gestation and preeclampsia risk in women with common congenital anatomic uterine abnormalities (AUAs). First trimester screening markers were compared between 12 AUA pregnancies, 60 age matched controls and 12 cases of early preeclampsia. PAPP-A level and birth weight were significantly lower in AUA compared to control and early preeclampsia group (p<.001). Preeclampsia was absent in the AUAs pregnancies group. Birth weight were similar in AUA group when we compared AUA and control group regarding weeks of gestation at delivery and lower but not significantly, when we compared AUA and early preeclampsia group. Our findings suggest that AUA pregnancies are associated with low first trimester maternal serum PAPP-A concentrations not predictive of susceptibility to preeclampsia.Impact statementWhat is already known on this subject? During first trimester screening for preeclampsia based on maternal pregnancy-associated plasma protein A (PAPP-A) levels, various parameters are used, such as the somatometric characteristics of pregnant woman, single or multiple pregnancy, smoking status, family history, diabetes, hypertension and measurement of blood pressure and uterine artery Dopplers.What do the results of this study add? Our pioneer study revealed that there is drastic difference in PAPP-A concentration in women with common anatomic uterine abnormalities (AUAs), in comparison with their age matched control women with normal uterus.What are the implications of these findings for clinical practice and further research? Based on our results, uterine anatomical deviations, is another factor which must be taken in account for preeclampsia risk calculation and further clinical consultation and follow up in those pregnancies. Lower PAPP-A levels in AUA cases is a weak predictor of susceptibility to preeclampsia and could be associated to smaller placental size rather than poor placentation and in future research the calculation of the uterine cavity functional dimension may lead to a more accurate clinical assessment.

Examination of the pregnancy-associated plasma protein-A assay on the Beckman Coulter Access® platform: suitability for use in first trimester Down's syndrome screening

Objective

To explore the clinical validity of the new Access® pregnancy-associated plasma protein-A (PAPP-A) assay for Down's syndrome screening.

Setting

Academic hospital.

Method

Residual serum samples ( n = 416) received for routine first trimester Down's syndrome screening (10-13 weeks) were retrieved from freezer storage and tested using two PAPP-A immunoassay methods. The new Access® assay was specifically compared, on a subset of these samples ( n = 194), with an assay proven to give acceptable Down's syndrome screening performance, the PerkinElmer (PE) AutoDELFIA method. Access® PAPP-A levels were examined in relation to gestational age and maternal weight, and were compared with the PE method by regression and Bland-Altman analyses.

Results

Access® PAPP-A assay results were highly correlated with the PE AutoDELFIA method ( r = 0.97). PAPP-A levels obtained using the Access® assay increased with advancing gestational age and were inversely related to maternal weight, as expected. The distribution of multiples of the median (MoM) values fit a log Gaussian distribution and the standard deviation of the log MoM (0.2331) matched published estimates. PAPP-A MoM levels in Down's syndrome pregnancies ( n = 6, median 0.30) showed the expected reduction.

Conclusion

Using an appropriate gestational age-specific median equation, the Access® PAPP-A assay is expected to perform acceptably in first trimester Down's syndrome screening.

A pilot study of the clinical relevance of the relationship between the serum level of pregnancy-associated plasma protein A and the degree of acute coronary syndrome

Serum levels of pregnancy-associated plasma protein-A (PAPP-A), high-sensitivity C-reactive protein (hs-CRP) and tumour necrosis factor-alpha (TNF-alpha) were measured in 70 patients with acute coronary syndrome (ACS), comprising 18 with unstable angina (UA), 37 with acute myocardial infarction (AMI) and 15 with stable angina (SA); 15 healthy controls were also included. Levels of PAPP-A were significantly higher in the UA and AMI groups than in the SA and control groups. Levels of PAPP-A were similar in the SA and control groups, and higher in the ACS patients who were cardiac troponin T-negative (comprising UA and AMI patients) than in the control and SA groups. Levels of hs-CRP and TNF-alpha were significantly higher in the SA group than in the control group, significantly higher in the UA group than in the SA and control groups, and significantly higher in the AMI group than in all other groups. Levels of PAPP-A in ACS patients were positively correlated with levels of hs-CRP and TNF-alpha. It would seem, therefore, that PAPP-A is associated with inflammation and might be used to detect plaque instability and rupture before an increase in cardiac troponin T is detectable.

Pregnancy-associated plasma protein-A, a marker for outcome in patients suspected for acute coronary syndrome

OBJECTIVES

To examine if pregnancy-associated plasma protein-A (PAPP-A) in patients with chest pain, could identify patients at risk for death or myocardial infarction.

DESIGN AND METHODS

Patients admitted with chest pain and both normal ECG and normal biomarkers were evaluated by serial measurement of PAPP-A. Main outcome measures were mortality and non-fatal myocardial infarction.

RESULTS

Median age of patients included (415) was 67years and 43% were women. The risk of death or non-fatal myocardial infarction after 3 months was 15% in the highest quartile of circulating PAPP-A compared with 3% in the lowest quartile (relative risk 3.7, p<0.01). Corresponding numbers after 1 year were 24% and 10% (relative risk 2.4, p=0.01).

CONCLUSION

In patients admitted with chest pain and both normal ECG and normal biomarkers PAPP-A seems to be valuable for predicting patients at high risk of death or non-fatal myocardial infarction.

Pregnancy associated plasma protein A, a novel, quick, and sensitive marker in ST-elevation myocardial infarction

Traditional biomarkers in acute coronary syndromes reflect myocardial necrosis but not the underlying arteriosclerotic disease. Pregnancy-associated plasma protein A (PAPP-A) is a new biomarker in acute coronary syndromes that detects vulnerable plaques in arteriosclerotic disease and identifies acute coronary syndromes earlier than traditionally used biomarkers. Information regarding circulating PAPP-A levels in patients with ST elevation myocardial infarctions (STEMIs) is limited and contradictory. The aim of the present study was to describe the presence and time-related pattern of circulating PAPP-A levels in patients with STEMIs. Consecutive patients (n = 354) referred for primary percutaneous intervention because of STEMI were included in the study. Blood samples for the analysis of PAPP-A, creatine kinase-MB (CKMB), and troponin T were drawn at admission and every 6 to 8 hours until biomarkers of myocardial necrosis were consistently decreasing. PAPP-A was measured using a newly developed sandwich enzyme-linked immunosorbent assay technique based on 2 monoclonal antibodies. In total, 1,091 PAPP-A, 1,049 troponin T, and 1,016 CKMB samples were analyzed. Mean PAPP-A values at admission were significantly higher in patients with STEMIs than in those with non-ST elevation myocardial infarctions or unstable angina pectoris (27.6 vs 12.2 mIU/L, p <0.01). In samples drawn <2 hours after admission, the sensitivity of PAPP-A was superior (93%) to that of CKMB (60%) and troponin T (61%). In conclusion, PAPP-A levels are elevated in >90% of patients presenting with STEMIs if measured <6 hours after the onset of symptoms or <2 hours of primary percutaneous coronary intervention. In the early stages of STEMI, PAPP-A seems to be a more sensitive marker of myocardial infarction than CKMB and troponin T.

Pregnancy-associated plasma protein A in non-cardiac conditions

OBJECTIVE

PAPP-A is a promising new marker in coronary heart disease. It is important to investigate its specificity in order to establish its clinical utility as a marker of coronary heart disease.

DESIGN AND METHODS

PAPP-A was measured within 24 h following hospital admission in 1448 consecutive patients admitted with diagnoses other than acute coronary syndromes.

RESULTS

PAPP-A was detectable (> or = 4.0 mIU/L) in 278 (19.2%) patients, among whom the mean level was 6.3 mIU/L (95% C.I., 6.1-6.5 mIU/L). The 95 and 99 percentiles for PAPP-A were 7.3 and 9.4 mIU/L, respectively. There was no difference in the mean PAPP-A of different diagnoses (p=0.33). None of the specific diagnoses known to influence established coronary markers appeared to influence the level of circulating PAPP-A.

CONCLUSION

PAPP-A is low in patients without known coronary heart disease. PAPP-A levels seem to be a potentially highly specific marker for heart disease.

Optimisation of sandwich ELISA based on monoclonal antibodies for the specific measurement of pregnancy-associated plasma protein (PAPP-A) in acute coronary syndrome

OBJECTIVES

PAPP-A has become the principal biochemical serum marker in first trimester screening for Down syndrome, the original data being based on results of a radioimmunoassay (RIA). Recent observations using sandwich ELISA technology have proposed PAPP-A as a potential marker in patients with acute coronary syndrome (ACS). The aims of the present study were to demonstrate (i) the importance of antibody specificity, (ii) the potential pitfalls in changing assay technology, (iii) the importance of strict definition of technology, and (iv) the application of a well-defined assay technology on sera from patients with ACS.

DESIGN AND METHODS

Candidate monoclonal antibodies (Mab) were identified by immunohistochemistry, Western blot and the absence of positive signals (ELISA) with normal, non-pregnant serum as antigen source. The ELISA technology was standardized against the original PAPP-A RIA and the WHO reference preparation (WHO 78/610). Results different from those obtained by the original RIA led to ELISA modifications with respect to dilution buffer and enzymatic digestion of the Mab.

RESULTS

The first generation ELISA revealed serum measurements from a pool of non-pregnant (n=103) individuals which, compared to the RIA, seemed to be false positive. The false positive reaction was abolished by addition of bovine serum (BS) to the dilution buffer. Subsequent analysis of individual sera (n=103) indicated that 7/103 were still false positive. This reaction was eliminated by introduction of F(ab')(2)-fragment of the indicator antibody. This modified ELISA revealed that serum PAPP-A levels in ACS were statistically significantly higher than in controls (p<0.001). Moreover, serum PAPP-A in ACS patients with ST-segment elevation (STEMI) were higher (p<0.001) compared to patients without ST-segment elevation (NSTEMI). Immunohistochemical analysis failed to identify PAPP-A in the atherosclerotic plaques.

Pregnancy associated plasma protein-A: ultrasensitive immunoassay and determination in coronary heart disease

OBJECTIVES

Markers of myocardial injury have been vital in the assessment of patients with coronary heart disease. Pregnancy associated plasma protein A (PAPP)-A is an insulin-like growth factor (IGF) binding protein (IGFBP)-4 protease and a potential early indicator of unstable angina. We developed an ultrasensitive enzyme-linked immunosorbent assay (ELISA) for PAPP-A and measured serum PAPP-A in patients with biochemical evidence of acute coronary syndrome.

DESIGN AND METHODS

Method development was based on pair-wise evaluation of a panel of antibodies and determination of PAPP-A specificity and sensitivity relative to those of a conventional method. Association of PAPP-A with myocardial damage was assessed in serum samples classified based on serum creatine kinase (CK)-MB or cardiac troponin-T levels.

RESULTS

Serum PAPP-A was significantly higher in samples with elevated CK-MB or troponin-T than in samples with normal CK-MB (p < 0.001). Marker-association studies showed strong correlation between PAPP-A and troponin-T (r = 0.59, p < 0.001) in a subset of troponin-T positive samples. Indications for both parallel as well as divergence in the expression of PAPP-A and troponin-T was also evident when serial timed samples available from a number of patients were analyzed.

CONCLUSIONS

The data are consistent with the conclusion that expression of PAPP-A is enhanced in patients with biochemical evidence of acute coronary syndrome and suggest strongly that demonstration of PAPP-A association with other cardiac markers might be influenced by their relative release dynamics (timing and duration). The availability of the ultrasensitive PAPP-A ELISA should facilitate systematic investigations of PAPP-A expression in this and other pathophysiological conditions that might involve altered expression of the IGF/PAPP-A system.

Double-monoclonal immunofluorometric assays for pregnancy-associated plasma protein A/proeosinophil major basic protein (PAPP-A/proMBP) complex in first-trimester maternal serum screening for Down syndrome

Four double-monoclonal time-resolved immunofluorometric assays (TrIFMAs) have been developed for the specific determination of pregnancy-associated plasma protein A/proeosinophil major basic protein (PAPP-A/proMBP) complex in first-trimester maternal serum samples. The assays have a functional sensitivity of &lt;4 mIU/L and a working range from 4 to 1000 mIU/L. These 4 assays, together with a polyclonal sandwich TrIFMA, were compared for their ability to discriminate between normal pregnancies (n = 149) and pregnancies carrying a Down syndrome fetus (n = 36) in maternal serum screening samples from gestational weeks 4–13. In 26 Down syndrome pregnancies from gestational weeks 7–12, the median PAPP-A multiples of the median concentration in controls (MoMs) determined by monoclonal antibody combinations 234–3/234–2*, 234–4/234–2*, 234–4/234–5*, and 234–5/234–6* were 0.35, 0.37, 0.42, and 0.44, respectively, whereas the median MoM determined by the polyclonal assay was 0.56. ROC curve analysis also showed that better overall diagnostic accuracy and detection rates were achieved by the monoclonal TrIFMAs than by the polyclonal TrIFMA. This report is the first to describe assays that specifically measure PAPP-A/proMBP complex without possible interference from other proMBP-containing complexes.

Time-resolved immunofluorometric assay of pregnancy-associated plasma protein A in maternal serum screening for Down's syndrome in first trimester of pregnancy

A low maternal serum concentration of pregnancy associated plasma protein-A (MS-PAPP-A) in the first trimester has been suggested as a marker for the presence of a Down's syndrome (DS) fetus. We developed a time-resolved immunofluorometric assay (TrIFMA) for PAPP-A with a sensitivity < 3.9 mIU/l. In the 7-12 gestational weeks interval the median multiples of the median (MoM) was 0.57 (95%-confidence interval; 0.47-0.99) in DS pregnancies (n = 29) and lower than in controls (n = 223) (P < 0.005). The efficiency of MS-PAPP-A alone was evaluated using empirical receiver-operator-characteristics (ROC) and a sensitivity of about 25% was found for a false-positive rate of about 10% in the 7-12 gestational weeks interval. In parameterized ROC analysis a sensitivity of 9% was found for a false-positive rate of 5%. The TrIFMA PAPP-A assay seems to fulfil the quality criteria for an assay to be used in large-scale serum screening for Down's syndrome.

Establishment and application of a normal range for nuchal translucency across the first trimester

Before chorionic villus sampling at 10-13 weeks' gestation, 453 women had the crown-rump length and nuchal translucency (NT) measured with transabdominal ultrasound. There were 19 aneuploid pregnancies (ten cases of trisomy 21, six of trisomy 18, one of 47 + marker, one 47,XXX, and one 45,X mosaic). Average NT was 1.7 mm (range 0-5 mm), correlating with the crown-rump length, but not maternal age. A static cut-off of 2.5 mm gave a false-positive rate of 1.3 per cent for crown-rump length between 30 and 35 mm, rising to 13 per cent in fetuses with a crown-rump length between 50 and 65 mm. This gave an overall false-positive rate of 5.5 per cent for a detection rate of 30 per cent for trisomy 21. Applying a dynamic action limit (95th centile), the false-positive rate remained at 5 per cent irrespective of the crown-rump length, detecting 30 per cent of trisomy 21 and 36.8 per cent of all aneuploidies. Raising the action limit to the 97.5th centile halved the false-positive rate (2.5 per cent), with no change in trisomy 21 detection and only a slight decrease in aneuploidy detection (31.6 per cent). Aneuploid fetuses showed normal first-trimester growth. NT increases with gestational age, making a dynamic action limit necessary to decrease the false-positive rate, while maintaining aneuploidy detection rates. Aneuploidy does not cause significant first-trimester growth retardation, enabling normal ranges for NT with crown-rump length to apply.

First-trimester biochemical screening for Down syndrome with the use of PAPP-A, AFP, and beta-hCG

Biochemical screening for Down syndrome (DS) is well established in the second trimester of pregnancy, but there is little information available on its value in the first trimester. This study describes our preliminary results with biochemical screening for DS in the first trimester of pregnancy in order to evaluate its efficacy at this time. Our study population, including 19 DS pregnancies, was evaluated using maternal serum levels of alpha-fetoprotein (AFP), beta-human chorionic gonadotropin (beta-hCG), and pregnancy-associated plasma protein A (PAPP-A). At a false positive rate (FPR) of 5 per cent, the detection rate (DR) for DS is 9 per cent for beta-hCG, 18 per cent for AFP, and 66 per cent for PAPP-A when considering these parameters individually. With different combinations of the analytes, the best detection rates are obtained with the association of PAPP-A and AFP (85 and 82 per cent DR for a 10 and 5 per cent FPR, respectively). Our data support the value of first-trimester biochemical screening for DS and that of PAPP-A as a single marker.

A sensitive enzyme immunoassay for pregnancy-associated plasma protein A (PAPP-A): a possible first trimester method of screening for Down syndrome and other trisomies

Pregnancy-associated plasma protein A (PAPP-A) is a large glycoprotein produced mainly by the trophoblast during pregnancy and released into the maternal circulation. Its biological function is unknown. In the second trimester i.e. when Down syndrome (DS) screening is routinely performed, the level of maternal serum PAPP-A was found to be within the normal range in pregnancies affected by fetal trisomy 21. However, PAPP-A was shown to be a potent marker for DS before 14 weeks of gestation. Only radioimmunoassays (RIAs) based on labelled antigen competition reached the required sensitivity for early pregnancy PAPP-A determinations; but they have a very short shelf life due to inherent tracer half-life and, in the case of PAPP-A, instability of the labelled antigen after three weeks. We describe a convenient and novel enzyme immunoassay (ELISA) with high sensitivity and a long shelf life.

Serum PAPP-A and free beta-hCG are first-trimester screening markers for Down syndrome

Serum measurements of pregnancy-associated plasma protein A (PAPP-A) and the free beta-human chorionic gonadotrophin (hCG) subunit were made in 13 women with Down syndrome (DS) pregnancies and six other women with fetal aneuploidy ascertained at chorionic villus sampling (CVS), as well as 89 women with contemporaneous normal control pregnancies. Median serum PAPP-A measurements (0.31 MOM, 95 per cent confidence interval (CI) 0.22-0.65 vs. normal 1.06, 95 per cent CI 0.89-1.20) were lower and free beta-hCG subunit measurements (1.13 MOM, 95 per cent CI 0.93-2.63 vs. normal 0.91, 95 per cent CI 0.79-1.03) were higher at statistically significant levels. Receiver operator characteristics (ROC) curves showed that the highest sensitivity for detection, 71.2 per cent (95 per cent CI 54.7-87.6 per cent), was for depressed PAPP-A levels; the combination of low serum PAPP-A levels, maternal age, and elevated free beta-hCG levels yielded a detection rate of 78.9 per cent (95 per cent CI 64.9-92.8 per cent) of the affected pregnancies at 8-12 weeks' gestation.

The relationship of uterine and umbilical Doppler resistance to fetal and placental protein synthesis in the second trimester

The relation of uteroplacental and umbilical Doppler resistance index (RI) to peripheral levels of alphafetoprotein (AFP), human chorionic gonadotrophin (hCG), human placental lactogen (HPL), Schwangerswaft protein (SP1), pregnancy-associated placental protein A (PAPP-A) and insulin-like growth factor binding protein 1 (IGP-BP1) at 16-24 weeks was established in a cross-sectional study of 183 unselected singleton pregnancies. There was an association between high values of uteroplacental RI and high hCG levels, and high umbilical RI values with high hCG and HPL levels. Thus, in the mid-trimester, the levels of some placental proteins seem to be related to placental resistance.

Serum PAPP-A levels are depressed in women with fetal Down syndrome in early pregnancy

The value of maternal serum pregnancy-associated plasma protein (PAPP)-A in screening for Down syndrome in early pregnancy was assessed using stored samples. Seventeen cases of Down syndrome and 66 unaffected control pregnancies were studied. The median PAPP-A level in the cases was 0.42 multiples of the expected value in controls (p < 0.0001). Eleven cases (65 per cent) had levels less than half the expected value compared with only six controls (9 per cent). A commercial assay kit is now needed so that prospective screening with this marker can begin.

The role of trophoblast dysfunction in the aetiology of miscarriage

OBJECTIVE

To investigate the endocrine changes associated with spontaneous miscarriage after fetal heart activity has been demonstrated.

DESIGN

Prospective study during the first trimester of pregnancy comparing the circulating levels of human chorionic gonadotrophin (hCG), Schwangerschaft protein 1 (SP-1), pregnancy-associated plasma protein A (PAPP-A), oestradiol (E2), and progesterone (P), and fetal growth (crown-rump length [CRL] and gestational sac volume [GSV]) in women who miscarried after the identification of fetal heart activity with those of normal singleton and twin pregnancies achieved following in vitro fertilisation (IVF) and embryo transfer (ET).

SETTING

The Assisted Conception Unit of King's College Hospital, London.

SUBJECTS

Nine women who miscarried after demonstration of fetal heart activity, 52 normal singleton and 22 normal twin pregnancies.

INTERVENTIONS

Weekly blood tests and ultrasound assessments of CRL and GSV.

RESULTS

Four fetuses (all singleton) died between 9 and 12 weeks gestation (Group 1), and seven (three singleton and two twin) died between 16 and 20 weeks gestation (Group 2). In Group 1, both fetal growth and placental function, as assessed by serial measurements of CRL and GSV, and of serum levels of PAPP-A, SP-1 and hCG respectively, were reduced before fetal death. In Group 2, while fetal growth was maintained in all but one case, placental function was reduced in 4 of 5 women.

CONCLUSION

These findings suggest that there may be a relationship between trophoblast dysfunction and some forms of miscarriage. Furthermore, the pattern of the reduction in the circulating levels of the placental proteins in later miscarriages suggests that the function of specific cell types may be impaired.

Molecular characterization of pregnancy-associated plasma protein-A by electrophoresis

Gradient polyacrylamide gel electrophoresis, isoelectric focusing and multidimensional immunoelectrophoretic techniques have been applied in order to physico-chemically characterize pregnancy-associated plasma protein-A (PAPP-A). By lectin affinity immunoelectrophoresis, PAPP-A contained sialic acid, glucose/mannose and N-acetyl-alpha-D-galactosamine. Immunoelectrophoretic analyses after incubation with various glycolases confirmed these findings and demonstrated that PAPP-A contained glucuronic acid, perhaps in chondroitin sulphate moities, thus indicating that PAPP-A may be a proteoglycan rather than a glycoprotein. Analysis by metal chelate and dye ligand affinity immunoelectrophoresis demonstrated many similarities between PAPP-A and alpha 2-macroglobulin (alpha 2M). However, unlike alpha 2M, PAPP-A did not form immunologically reactive complexes when incubated with proteases. Furthermore, as demonstrated by autoradiographic studies, PAPP-A did not contain internal thiolester groups, thus indicating that PAPP-A cannot inhibit proteases by molecular entrapment and, despite the homotetrameric molecular conformation, PAPP-A and alpha 2M may not have evolved from a common ancestral protein.

Pregnancy-associated protein-A does not improve predictability of pregnancy success or failure over human chorionic gonadotropin levels in early normal and abnormal pregnancy

In the present study we sought to compare levels of PAPP-A and hCG produced by different types of pregnancy: normal, ectopic, threatened abortion and molar pregnancy after evacuation. The gestations ranged from 13 to 122 days. Serum levels of both PAPP-A and hCG were measured and compared. Chi squares analysis were predictive only for increasing trends in hCG as well as decreasing trends of both hCG and PAPP-A. Analysis of variance and linear discriminant function used to evaluate results suggested that PAPP-A did not improve predictability of hCG. The values of PAPP-A levels for the postevacuation molar pregnancies barely exceeded the lower limit of detection; thus, no meaningful comparisons could be made.

Ultrasound and circulating placental protein measurements in complications of early pregnancy

Maternal serum levels of human chorionic gonadotrophin (hCG), Schwangerschaftsprotein 1 (SP1) and pregnancy-associated plasma protein A (PAPP-A) were measured in an unselected group of 624 women presenting with amenorrhoea and vaginal bleeding with or without abdominal pain to an emergency gynaecological ultrasound clinic. Abdominal sector scanning was used to assess uterine contents. Pregnancy was confirmed by ultrasound in 406 pregnancies. Histological confirmation was obtained in each case of pregnancy failure. A live fetus was demonstrated in 259 women of whom six subsequently miscarried; one of these had markedly depressed serum hCG and PAPP-A, but normal SP1 levels, and two had oligohydramnios. Of the 147 women without ultrasound evidence of fetal heart action 67 had a correct ultrasound diagnosis of anembryonic pregnancy. The predictive value of a depressed serum hCG level was 70% in this group, and 31% in samples taken at less than or equal to 7 weeks. The predictive value of a normal hCG level was 96%. In 34 women missed miscarriage was diagnosed readily by ultrasound; all but five had depressed hCG and PAPP-A levels. A clinical diagnosis of a complete or incomplete miscarriage was made in 45 women and easily confirmed by ultrasound. All of them had depressed hCG, SP1 and PAPP-A levels. These results indicate that the diagnostic value of ultrasound in threatened miscarriage is often better than that of biochemical tests.

Immunological heterogeneity of pregnancy-associated plasma protein-A (PAPP-A). Effects on the radioimmunoassay of PAPP-A

Pregnancy-associated plasma protein-A (PAPP-A) is a macromolecular glycoprotein produced by the trophoblast during pregnancy. Because the presence of PAPP-A in non-pregnant females is controversial, we re-evaluated our own radioimmunoassay technique for PAPP-A in the light of new observations about its immunological heterogeneity. Irrespective of the antibody (Geneva anti-PAPP-A or Dako anti-PAPP-A) the use of EDTA pregnancy plasma instead of pregnancy serum as a standard yielded different slopes of the standard curves and estimated significantly different amounts of PAPP-A in test samples. Moreover, highly purified tracers, isolated from maternal EDTA pregnancy plasma or pregnancy serum also produced significantly different results. So that the use of a tracer purified from EDTA plasma and EDTA pregnancy plasma as a standard will yield measurable levels of PAPP-A in non-pregnant female serum whereas the use of a tracer purified from maternal pregnancy serum and maternal pregnancy serum as a standard will not detect PAPP-A in the same samples. We conclude that, irrespective of the antiserum used, but depending on the biological origin of the tracer and the standard, different results will be obtained. PAPP-A is clearly immunologically heterogeneous, and the immunorecognition of PAPP-A will depend on whether or not blood coagulation has taken place.

Potential role of pregnancy-associated plasma protein-A in human reproduction

By radioimmunoassay, pregnancy-associated plasma protein-A (PAPP-A) was undetectable in matched follicular and luteal phase serum samples (n = 17) or in the peripheral circulation of normal males (n = 17). However, seminal plasma (91.5%), cervical mucus (100%) and pre-ovulatory follicular fluid (99.6%) were consistently PaPP-A positive. In addition to PAPP-A, four circulating protease inhibitors (PIs) were detected in pooled seminal plasma whereas pooled follicular fluid contained an additional six. Follicular concentrations of serum PIs were inversely related to molecular size. By contrast, PAPP-A formed a positive concentration gradient across the blood-reproductive tract barrier suggesting PAPP-A production within the reproductive tract. A minor proportion (1.7%) of ejaculated spermatozoa were coated with PAPP-A, as demonstrated by direct immunofluorescence. Since PAPP-A specifically inhibits leucocyte elastase, it is suggested that PAPP-A coated spermatozoa were "selected" to overcome localized phagocytic-proteolytic degradation. The physiological significance of these findings are discussed in relation to human reproduction.

A two-site immunoradiometric assay for human pregnancy-associated plasma protein A (PAPP-A) using monoclonal antibodies

A rapid, sensitive immunoradiometric assay has been developed for human pregnancy-associated plasma protein A (PAPP-A) using a purified mouse monoclonal antibody as the tracer and a rabbit polyclonal antibody to this protein in the solid-phase antibody preparation. The assay showed no measurable cross-reaction (less than 0.1%) against a range of purified human placental proteins, and a good correlation with a previously described radioimmunoassay procedure when tested on samples taken throughout normal human pregnancies. No PAPP-A-like immunological activity could be detected in sera from non-pregnant women, confirming the absence of this protein from the circulation outside pregnancy.

New placental proteins: chemistry, physiology and clinical use

In the past decade, several new placental proteins have been isolated and studied. The 'pregnancy-specific' beta 1-glycoprotein (SP1) is a major placental product with unusual physicochemical properties that has been extensively investigated, but its biological function remains uncertain. Pregnancy-associated plasma protein A (PAPP-A), a glycoprotein of mol. wt 400,000, has effects in vitro on the coagulation and complement cascades, probably by its properties of protease inhibition. Placental protein 5 (PP5) may be involved in the coagulation and fibrinolytic systems, and in follicle maturation and semen liquefaction. 'Placental protein 12' (PP12) is not a product of the placenta at all; it appears to be produced in the female genital tract under the influence of progesterone and may also be produced by proliferating liver cells. Further study may reveal new roles for these placental proteins beyond their traditional roles as tumour markers.

Comparison of different antibody preparations against pregnancy-associated plasma protein-A (PAPP-A) for use in localization and immunoassay studies

Four antibody preparations against pregnancy-associated plasma protein (PAPP-A) were compared in order to find an explanation for the contradictory results published on tissue localization, clinical usefulness and biological function of PAPP-A. One of the preparations studied was a rabbit anti-PAPP-A antiserum which has been offered for general scientific use (Bischof et al. 1979). Only the IgG fraction of anti-PAPP-A antisera which appeared to be monospecific and had been further absorbed with fetal connective tissue gave specific uniform staining of the cytoplasm of the syncytiotrophoblast exclusively. Circulating PAPP-A could not be detected by RIA employing this IgG preparation in the non-pregnant state, or before 18 days after conception. Circulating PAPP-A could be detected in all seven pregnant women studied within 4 weeks after conception. Identical results were obtained with a commercially available IgG fraction against PAPP-A.

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.

The prognostic value of HCG, PAPP-A, oestradiol-17 beta and progesterone in early human pregnancy

Four serum parameters were assayed weekly from the 4th to the 12th week of pregnancy and finally at 16 weeks, to assess their relative prognostic values for predicting pregnancy outcome. Of 85 pregnancies generated following treatment for infertility, 16 cases had blighted ova and subsequently aborted at a mean age of 9.9 +/- 0.5 weeks. Serum HCG concentrations differentiated (p less than 0.005) between ongoing pregnancies and blighted ova as early as the 4th week which was often several weeks in advance of clinical abortion. PAPP-A, oestradiol-17 beta and progesterone did not differentiate between the 2 groups until 7 weeks (p less than 0.005, p less than 0.001 and p less than 0.001 respectively). PAPP-A measurements detected ongoing pregnancies at week 4 (16.5 +/- 5 micrograms/l) but HCG remains the more sensitive diagnostic test. The lower limits of oestradiol-17 beta and progesterone for ongoing pregnancies were 670 pmol/l and 37 nmol/l respectively. The circulating concentrations of all 4 serum markers were unaffected by administration of medroxyprogesterone acetate from 6 to 16 weeks in both ongoing and aborting pregnancies.

Pregnancy-associated plasma protein-A concentrations in men with testicular and prostatic tumors

Pregnancy-associated plasma protein-A (PAPP-A) is a macromolecular glycoprotein produced during pregnancy by the trophoblast and the decidua. It is not specific to pregnancy, since immunoreactive PAPP-A is in the circulation of normal women and men and in seminal fluid. Immunohistochemically, PAPP-A is localized in some Leydig cells, in the epididymis, in the rete testis, and in seminal vesicles. This study was conducted to learn whether circulating levels of PAPP-A can be used as a marker for the monitoring of human testicular cancer. PAPP-A was increased only in certain nonseminomatous germ cell tumor [malignant teratoma undifferentiated (MTU) + seminoma, malignant teratoma intermediate (MTI)], but the overlap with the normal values was too big for PAPP-A to have any clinical significance. After orchidectomy or prostatectomy, PAPP-A decreased but the levels were were similar to those of normal men. In men, PAPP-A can be produced by certain nonseminomatous germ cell tumors, but its origin in disease-free males is probably not the testis or the prostate.

Binding of pregnancy-associated plasma protein-A (PAPP-A) to placental subfractions

Pregnancy-associated plasma protein-A (PAPP-A) has been shown to exert immunosuppressive effects both on complement and on lymphoblastogenesis. It was of interest to see whether this protein could bind to syncytiotrophoblast microvillous membranes since these represent the effective interface between fetal tissue and the immunocompetent mother. Placental subfractions were prepared according to established techniques. PAPP-A was purified from different sources (pregnancy serum and plasma, retroplacental serum, placental extracts) and labelled with radioactive iodine. It could be shown that radioactive PAPP-A, irrespective of its biological origin was primarily binding to brush border membrane preparations but that significant binding was also seen with plasma membrane preparations. The binding was specific since alpha 2-macroglobulin (a structurally related protein to PAPP-A) was unable to displace bound radioactive PAPP-A. Scatchard plot representation of the data indicated that the affinity of PAPP-A for its binding site was of the same order of magnitude as reported for the insulin or GnRH receptors of the trophoblast (Ka 2 10(7)-2.5 10(8) M-1). These results are in agreement with the immunohistochemical localization of PAPP-A on the trophoblast providing that the small binding to plasma membrane preparations is due to contamination.

Relation between pregnancy-associated plasma protein A (PAPP-A) in human peri-ovulatory follicle fluid and the collection and fertilization of human ova in vitro

In 42 patients, blood-free peri-ovulatory follicular fluid was aspirated from 86 follicles for estimation of pregnancy-associated plasma protein A (PAPP-A) and related to several variables associated with the fertilization of human ova in vitro. Follicle growth was stimulated by clomiphene citrate alone or in combination with human menopausal gonadotrophin (hMG) and ovulation was triggered by human chorionic gonadotrophin (hCG) except in six patients who had a spontaneous surge of luteinizing hormone (LH). PAPP-A was detected in 83 of the 86 follicles aspirated, ranging from 'undetectable' to 1044 micrograms/l. The concentration of PAPP-A was statistically significantly correlated with increasing follicle size, follicular oestradiol-17 beta concentration and oocyte recovery. At PAPP-A concentrations of greater than 200 micrograms/l, there was no correlation noted with the ability of the ovum to be fertilized, to cleave, or between PAPP-A levels in follicles from pregnant and non-pregnant cycles. There was no significant difference in the mean PAPP-A concentration for the two stimulation regimens, but concentrations were greater in follicular fluid from patients who surged spontaneously (P less than 0.001). It appears PAPP-A levels may provide an index of follicle maturity but not of the pregnancy potential of the ovum.

Monitoring of postimplantation embryo viability following successful in vitro fertilization and embryo transfer by measurement of placental proteins

Serum levels of pregnancy-associated plasma protein A (PAPP-A), human chorionic gonadotropin (hCG), and pregnancy-specific beta 1-glycoprotein (SP1) were measured in 21 women after successful in vitro fertilization and embryo transfer. Of the 21 pregnancies, 14, including 1 twin gestation, progressed successfully to term. The remaining seven, composed of tubal (n = 3), anembryonic (n = 1), and spontaneously aborted (n = 3) pregnancies, failed during the first half of pregnancy. Placental protein measurement was of no diagnostic value in the detection of anembryonic pregnancy. Similarly, measurement of hCG and SP1 could not readily distinguish tubal ectopic from normal intrauterine pregnancies. By contrast, the predictive value (38.9%) of a depressed PAPP-A level in conjunction with superior diagnostic sensitivity (70%) and relative risk factor (23.6) proved to be of greater diagnostic value in this potentially lethal condition. In the absence of ultrasonography, the biochemical diagnostic indices were comparable in the prediction of spontaneous abortion. However, in the presence of a live fetus, PAPP-A levels were consistently depressed (sensitivity, 91.7%) many weeks before pregnancy demise. The relative risk factor of depressed PAPP-A levels was 29 times greater than the risk associated with a depressed hCG level. These findings further demonstrate the potential diagnostic value of PAPP-A measurement for monitoring postimplantation embryo viability.

Monitoring of postimplantation embryo viability by measurement of PAPP-A, SP1, and hCG

After successful in vitro fertilization and embryo transfer, chorionic gonadotropin, pregnancy-specific beta 1-glycoprotein, and pregnancy-associated plasma protein-A were measured in serum samples collected serially from 21 patients. While 14 pregnancies, including one twin pregnancy, progressed successfully to term, the remaining seven pregnancies failed during the first half of gestation. This latter group consisted of three tubally implanted, one anembryonic, and three spontaneously aborted pregnancies. Circulating levels of hCG, SP1, and PAPP-A in the patient with an anembryonic pregnancy were within normal limits. Similarly, 90.5% of the serum samples obtained from women with tubal pregnancies showed hCG levels within normal limits. By contrast, only two of these samples had detectable PAPP-A, of which only one was within normal limits. Of the samples obtained from the patients who spontaneously aborted, including one patient with normal ultrasonic findings up to 48 hours prior to the event, 85.7% had PAPP-A concentration below the 10th percentile, whereas only 16.7% of these samples showed depressed hCG levels. These data suggest that PAPP-A measurement has great clinical potential in the management of compromised early pregnancies.

Pregnancy proteins in seminal plasma, seminal vesicles, preovulatory follicular fluid, and ovary

A number of proteins previously thought to be specific for the placenta or pregnancy have been identified in the fluids bathing both the oocyte and the sperm. In many cases their concentrations in follicular fluid and seminal plasma greatly exceeded those in the serum of nonpregnant women or men, and sometimes they even exceeded the levels in pregnancy sera. We report here the occurrence of PP5, PP12, PP14 and PAPP-A in follicular fluid and seminal plasma. In follicular fluid, the levels of PP5, PP12, and PAPP-A correlate with the estrogen concentration of the same fluid, and the PP12 and PAPP-A levels also bear a positive correlation to the progesterone concentration. The levels of PP12 and PAPP-A increase as the follicle grows, as do the levels of many steroid hormones. Therefore, the apparent correlations observed may be merely coincidental. However, circumstantial evidence from other reproductive organs indicates that the synthesis of PP12 and PAPP-A is stimulated by progesterone. Results of immunohistochemical staining show that PP12 and PAPP-A are localized in the luteinized granulosa cells and the corpus luteum. Previous studies indicate that PP5 and PAPP-A inhibit the action of proteolytic enzymes plasmin and elastase, which are believed to be involved in the mechanisms of ovulation. The study of the significance of these various placental proteins for human reproduction is only at its beginning. Clearly, elucidation of their function is the key to a more fundamental understanding of their role in the events governing ovulation and implantation.

Does ultrasound examination render biochemical tests obsolete in the prediction of early pregnancy failure?

Serum levels of fetal, placental and maternal hormones and proteins [alpha-fetoprotein (AFP), human chorionic gonadotrophin, human placental lactogen, schwangerschaftsprotein 1, pregnancy associated plasma protein-A (PAPP-A), oestradiol-17 beta, progesterone, pregnancy zone protein] were measured in 108 women with bleeding during the first half of pregnancy. Ultrasound examination at the time of each blood sampling revealed a fetal heart action on at least one occasion in 77 women. Spontaneous abortion occurred in 42 pregnancies, 31 of these showed no ultrasound sign of fetal life, whilst the fetal heart action was observed repeatedly until abortion in the remaining 11 women. Abnormally low levels of PAPP-A were most likely to indicate pregnancy failure, in particular if the fetal heart action was seen at the time of blood sampling. The predictive value, sensitivity and relative risk of a single depressed PAPP-A level were respectively 49, 89 and 41%, the predictive value of a normal result being 99%. With the exception of AFP, all other biochemical indices examined were consistently in the normal range in this group of women. If ultrasound findings were not considered, the biochemical indices were of comparable value in the prediction of spontaneous abortion. PAPP-A levels were uniformly depressed in all patients who spontaneously aborted, frequently weeks before this event, in the presence of a live fetus.

Seminal plasma levels of PAPP-A in normospermic and oligospermic men and tissue localization of PAPP-A in the male genital tract

Radioimmunoassay, gel filtration, isoelectric focusing, and immunoperoxidase methods were used to study the levels, properties, and localization of pregnancy-associated plasma protein A (PAPP-A) in the human seminal plasma and male genital tract. Seminal plasma specimens from 20 normospermic and 20 oligospermic men were studied. PAPP-A was found in 30 of 40 samples, the levels ranging from undetectable to 135 micrograms/liter (median 35 micrograms/liter) in the normospermic group and from undetectable to 111 micrograms/liter (median 21 micrograms/liter) in the oligospermic group. There was no significant difference in the PAPP-A levels between the two groups, and no correlation was observed between the seminal plasma PAPP-A levels and the volume of seminal plasma or the sperm count or the viability of spermatozoa. Serial dilutions of seminal plasma and PAPP-A standard yielded parallel dose-response curves, and incubation with seminal plasma did not result in any change in the elution pattern of [125I]PAPP-A in gel filtration. PAPP-A-immunoreactive material from seminal plasma eluted as two peaks, the major one corresponding to the elution volume of purified PAPP-A and the minor eluting more slowly. The isoelectric point of seminal plasma PAPP-A was 4.3-4.7 and that of term pregnancy serum was 4.2-4.6. In the immunoperoxidase staining, PAPP-A was seen in the epithelium of the prostate, seminal vesicle, and the ampullar part of the vas deferens but not in the testis, epididymis, proximal parts of vas deferens or urethra. The results confirm the occurrence of PAPP-A in the seminal plasma but do not suggest any clinical utility for seminal plasma PAPP-A measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

The development and validation of a radioimmunoassay for human pregnancy-associated plasma protein A (PAPP-A)

A specific and sensitive radioimmunoassay for human pregnancy-associated plasma protein A (PAPP-A) is described. This assay utilized tracer repurified by affinity chromatography on heparin-Sepharose. The most sensitive assay developed had a detection limit of 5 microliters PAPP-A in serum, and this protein could not be detected in sera from non-pregnant subjects. During pregnancy, mean circulating levels rose from 0.6 mg/l at 6 weeks gestation to 110 mg/l at term, and PAPP-A was detected in 44 of 101 umbilical blood samples. The use of the anticoagulants EDTA and acid citrate dextrose resulted in significantly different results in the plasma compared to the corresponding serum sample. PAPP-A was also measured in amniotic fluid.