The disappearance rate of pregnancy-associated plasma protein-A (PAPP-A) after the end of normal and abnormal pregnancies

PAPPA-mediated adipose tissue remodeling mitigates insulin resistance and protects against gestational diabetes in mice and humans

Pregnancy is a physiological state of continuous adaptation to changing maternal and fetal nutritional needs, including a reduction of maternal insulin sensitivity allowing for appropriately enhanced glucose availability to the fetus. However, excessive insulin resistance in conjunction with insufficient insulin secretion results in gestational diabetes mellitus (GDM), greatly increasing the risk for pregnancy complications and predisposing both mothers and offspring to future metabolic disease. Here, we report a signaling pathway connecting pregnancy-associated plasma protein A (PAPPA) with adipose tissue expansion in pregnancy. Adipose tissue plays a central role in the regulation of insulin sensitivity, and we show that, in both mice and humans, pregnancy caused remodeling of adipose tissue evidenced by altered adipocyte size, vascularization, and in vitro expansion capacity. PAPPA is known to be a metalloprotease secreted by human placenta that modulates insulin-like growth factor (IGF) bioavailability through prolteolysis of IGF binding proteins (IGFBPs) 2, 4, and 5. We demonstrate that recombinant PAPPA can stimulate ex vivo human adipose tissue expansion in an IGFBP-5- and IGF-1-dependent manner. Moreover, mice lacking PAPPA displayed impaired adipose tissue remodeling, pregnancy-induced insulin resistance, and hepatic steatosis, recapitulating multiple aspects of human GDM. In a cohort of 6361 pregnant women, concentrations of circulating PAPPA are inversely correlated with glycemia and odds of developing GDM. These data identify PAPPA and the IGF signaling pathway as necessary for the regulation of maternal adipose tissue physiology and systemic glucose homeostasis, with consequences for long-term metabolic risk and potential for therapeutic use.

The effect of heparin on pregnancy associated plasma protein-A concentration in healthy, non-pregnant individuals

OBJECTIVES

The objective of this study was to determine the differences in pregnancy associated plasma protein-A (PAPP-A) concentrations in heparin naive and heparin treated healthy men and non-pregnant women, to find a possible difference in different age groups, and to determine the response in PAPP-A concentration to repeated injections of unfractionated heparin.

DESIGN AND METHODS

Twenty-five healthy, non-pregnant volunteers divided into five groups (determined by gender and age) received 5000 IU unfractionated heparin intravenously. Five young men received an additional 5000 IU after 90 and 180 min. Blood samples to determine PAPP-A concentration and APTT were drawn at different time points.

RESULTS

Injection of heparin elicited increase in and rapid normalization of PAPP-A concentrations in all subjects. The group of 20-30-year-old never-pregnant women had lower responses than the individuals of the four other groups. The difference was not significant (p > 0.05). Repeated injections of heparin caused additional peaks in PAPP-A concentration of about the same sizes as the first peak. We observed an increase in time to normalization of PAPP-A concentration (from 75-90 min to 90-150 min) and APTT levels with repeated injections.

CONCLUSIONS

We observed a rapid normalization of PAPP-A. Our result has a great similarity to the half-life of unfractionated heparin. This result combined with the finding of equally sized peaks in PAPP-A concentration, and that all of this was found in healthy, non-pregnant individuals, suggests that heparin might compete for a binding-site on PAPP-A or with PAPP-A itself for a common receptor in healthy arterial vessels.

Pregnancy-associated plasma protein A (PAPP-A) and preeclampsia

Pregnancy-associated plasma protein A (PAPP-A) is a key regulator of insulin-like growth factor bioavailability essential for normal fetal development. In maternal blood, this protein increases with gestational age and then rapidly decreases after delivery. It is routinely used for Down syndrome screening in the first trimester of pregnancy, and its decrease compared to a normal pregnancy indicates an increased risk for both chromosomal anomalies and adverse pregnancy outcomes. It belongs to a group of biomarkers that predict later preeclampsia development, primarily early onset preeclampsia; however, it should be combined with a Doppler ultrasonography of the uterine artery (pulsatile index) and other biochemical and maternal factors to achieve a higher detection rate with an acceptable false positivity rate. Some studies have demonstrated an even more pronounced decrease of PAPP-A in the early second trimester of pregnancy in women who subsequently develop preeclampsia compared with women who do not develop preeclampsia. Conversely, during the last trimester of pregnancy, its concentration increases even more in patients with preeclampsia than in patients without. It is also detectable at very low levels in nonpregnant individuals, and a higher concentration indicates an adverse effect in patients with acute coronary syndromes or stable atherosclerotic disease and in patients with end-stage renal disease who are being treated with hemodialysis.

First Trimester Maternal Serum Screening Using Biochemical Markers PAPP-A and Free β-hCG for Down Syndrome, Patau Syndrome and Edward Syndrome

The first trimester screening programme offers a noninvasive option for the early detection of aneuploidy pregnancies. This screening is done by a combination of two biochemical markers i.e. serum free β-human chorionic gonadotrophin (free β-hCG) and pregnancy associated plasma protein A (PAPP-A), maternal age and fetal nuchal translucency (NT) thickness at 11 + 0-13 + 6 weeks of gestation. A beneficial consequence of screening is the early diagnosis or trisomies 21, 18 and 13. At 11 + 0-13 + 6 weeks, the relative prevalence of trisomies 18 and 13 to trisomy 21 are found to be one to three and one to seven, respectively. All three trisomies are associated with increased maternal age, increased fetal NT and decreased PAPP-A, but in trisomy 21 serum free β-hCG is increased whereas in trisomies 18 and 13 free β-hCG is decreased.

The disappearance rate of Schwangerschaftsprotein 1 in normal and pathological pregnancies

In six women with a normal vaginal delivery at term, in 12 women who had a suction curettage between 6 and 12 weeks gestation and in eight women with an ectopic pregnancy, the post-partum or the post-surgery decline in radioimmunoassayable SP1 was faster during the first 24 h after surgery or delivery than later, so that two half-lives were calculated. The first 'half-life' of about 20 h (0-24 h after delivery or surgery) was of the same order of magnitude in all groups studied and corresponded well to previously published values. The mean second 'half-life' (greater than 24 h after delivery or surgery) was significantly longer in term (72.2 h) and in ectopic pregnancies (64.1 h) than in first trimester pregnancies (45.5 h). These results might indicate that the metabolism of SP1 either changes during pregnancy or that the changing SP1 beta/SP1 alpha ratio during pregnancy markedly influences the levels of SP1 as measured by radioimmunoassay.

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.

Progesterone dependence and extratrophoblastic origin of pregnancy-associated plasma protein-A (PAPP-A) in early pregnancy

Pregnancy-associated plasma protein-A (PAPP-A) is a macromolecular glycoprotein produced in increasing concentration as pregnancy advances. PAPP-A is not specific to pregnancy since measurable levels have been found in non-pregnant females and in males. In non-pregnant females, PAPP-A is probably produced by the endometrium. The origin of PAPP-A in pregnant women is still controversial. In-vitro trophoblast and decidual explants both produce PAPP-A. So far, it is not known if the same applies to the in-vivo situation and to what extent these two tissues contribute to the circulating levels of PAPP-A. This study compares the circulating concentrations of PAPP-A and beta-hCG and progesterone in different pathological situations. In hydatidiform moles, beta-hCG levels are very high demonstrating an intense trophoblastic activity, whereas PAPP-A levels remain in the normal range. With spontaneous abortions, beta-hCG levels decline to very low values whereas PAPP-A continues to increase. These observations furnish indirect evidence for a major contribution to circulating PAPP-A levels by extratrophoblastic sites. Furthermore, PAPP-A levels decrease after administration of an anti-progesterone (RU486) either in-vivo or in-vitro. This is considered as a proof that PAPP-A levels in early pregnancy are progesterone dependent.