Inhibitors of platelet aggregation and blood coagulation isolated from the human placenta

Levels of alpha-fetoprotein during pregnancy and early infancy in normal and disease states

Alpha-fetoprotein (AFP) was 1 of the first serum protein markers to serve in the dual capacities of tumor marker and fetal defect marker, ie, an oncofetal protein, in the clinical laboratory. Although the serum-marker capacity of AFP has long been used, less is known of the fluid compartments of this oncofetal protein during fetal and perinatal development. In this review, the biologic activities of AFP are discussed in light of its presence in the various biologic fluid compartments: fetal serum, amniotic fluid, cord blood, urine, and maternal serum. AFP concentrations within the biologic fluids are considered in the context of gestational age, sex, body weight, and anatomic location. Discussion follows concerning the relationships and roles of AFP in various developmental disorders such as hypothyroidism, folate deficiencies, autoimmune disorders, acquired immunodeficiency disorder (AIDS), congenital heart defects, cystic fibrosis, preeclampsia/hypertension, and platelet aggregation disorders. Based on its presence in so many types of birth defects, malformations, and congenital anomalies, AFP can be seen to serve as a form of molecular "duct tape" during pregnancy and postnatal development.

A convenient method for preparation of the calcium ion-binding protein annexin V

This study presents a novel method for the production and purification of annexin V using cation exchange chromatography in the presence of calcium ions at neutral or alkaline pH. This method enables the handling of a large quantity of sample at one time without deterioration of the adsorption capacity of the cation exchange carrier by contaminating proteins, as well as the production of the calcium ion-binding protein annexin V with high purity on an industrial scale from both recombinant products and native products.

Monoclonal anti-annexin V antibody inhibits trophoblast gonadotropin secretion and induces syncytiotrophoblast apoptosis

The pathogenic role of anti-annexin V antibodies remains unclear. Anti-annexin V antibodies are frequently associated with higher incidences of intrauterine fetal loss, preeclampsia, and arterial and venous thrombosis. The present study investigated the in vitro ability of anti-annexin V antibody to bind human trophoblast cells, to affect trophoblast gonadotropin secretion and invasiveness, and to induce placental apoptosis. Cytotrophoblast cells were dispersed in Ringer bicarbonate buffer containing trypsin and DNase I, filtered, and layered over a Percoll gradient in Hanks balanced salt solution. In the case of monoclonal anti-annexin V antibody, the highest binding was found when the cells displayed the greatest amount of syncytium formation. Anti-annexin V antibody, but not its negative control, induced trophoblast apoptosis and significantly reduced trophoblast gonadotropin secretion. These findings suggest that recognition by anti-annexin V antibody of adhered annexin V on trophoblast cell structures might represent a potential pathogenic mechanism by which these antibodies can cause defective placentation.

Adsorption of anti-annexin V using dextran sulfate bound cellulose beads

Anti-annexin V (Anx V) antibodies are detected in SLE patients and patients with habitual fetal loss or preeclampsia. Several case reports have indicated that recurrent abortion based on antiphospholipid syndrome (APS) could be successfully treated with immunoadsorption by using dextran sulfate (DS) columns. The purpose of this study is to clarify whether or not anti-Anx V is also adsorbed by DS-bound cellulose beads. Sera from anti-Anx V-positive patients were mixed with DS-bound cellulose beads in vitro, and the titers of anti-Anx V were measured both before and after incubation. The anti-Anx V titers significantly decreased after incubation. The Anx V also bound to bovine serum albumin-conjugated DS immobilized on microtiter plates. The results of the present study lend support to the basic rationale for immunoadsorption therapy using DS columns in the treatment of habitual abortion closely associated with anti-Anx V antibodies.

Localization of the apoptosis-inducing activity of lupus anticoagulant in an annexin V-binding antibody subset

Lupus anticoagulant (LAC) is associated with arterial and venous thrombosis, thrombocytopenia, and recurrent fetal loss. We have reported previously that plasma with LAC activity induces apoptosis in endothelial cells and binds annexin V (Nakamura, N., Y. Shidara, N. Kawaguchi, C. Azuma, N. Mitsuda, S. Onishi, K. Yamaji, and Y. Wada. 1994. Biochem. Biophys. Res. Commun. 205:1488-1493). In this study, we separated two IgG antibody fractions, one with and one without affinity for annexin V, from 10 patients with LAC. LAC and apoptotic activities were localized in the annexin V-binding fraction in all 10 patients. DNA fragmentation was dose-dependent, paralleling the amount of IgG added to the human umbilical vein endothelial cell culture medium, and was inhibited by preincubation with annexin V. Removal of the antiphospholipid antibodies from patient IgG with phospholipid liposomes did not abolish the apoptosis-inducing activities or binding to annexin V. These results imply that patients with LAC often have antibodies that do not bind phospholipids and are responsible for the induction of apoptosis in endothelial cells.

An ADPase-like substance in placental extracts

The inhibitory effect of human placenta on ADP-induced platelet aggregation was examined. Placental extracts were purified by chromatography and gel filtration. The eluted fractions were subjected to affinity chromatography with Bestatin AH-Sepharose to obtain a more purified substance. A substance markedly inhibited platelet aggregation induced by ADP, and also exhibited high placental leucine aminopeptidase (P-LAP) activity. Preincubation of sample with ADP abolished the platelet aggregatory effect. Thin-layer chromatography (TLC) analysis revealed that the substance hydrolyzed ADP to AMP. The potent anti-platelet aggregating activity of placental extracts appears to be due to ADPase-like action. This action may be one of the controlling factors of hemostasis in fetoplacental circulation.

Primary structure of human placental anticoagulant protein

The primary structure of human placental anticoagulant protein was determined by a combination of amino acid and nucleotide sequencing techniques. The carboxymethylated protein was digested with cyanogen bromide, and the resulting peptides were separated by gel filtration and high-performance liquid chromatography. A total of 239 out of 319 amino acid residues were identified from 7 cyanogen bromide fragments. A full-length cDNA clone encoding placental anticoagulant protein was isolated from a human placenta cDNA library. This clone was 1.6 kilobases long and contained a translation initiation site coding for methionine, 957 nucleotides encoding for the mature protein, a stop codon, a poly(A) recognition site, and a poly(A) tail. Analysis of the tryptic-blocked peptide that originated from the NH2-terminus of the protein showed that the terminal methionine was removed and the adjacent alanine residue was acetylated by posttranslational events. Placental anticoagulant protein is composed of 319 amino acids with acetylalanine as the NH2-terminus and has a high degree of sequence identity with lipocortins I and II. It contains four internal repeats, each including a sequence corresponding to a putative Ca2+-dependent phospholipid binding site. Placental anticoagulant protein is a member of the lipocortin/calpactin family.