Search PubMed⌕ Search

Biomedical subjects

P Kaufmann

Publications and source records attributed to P Kaufmann.

At least 253 records · Page 14Linked to original sources
PubMedDate not supplied

Interpretation of syncytial sprouts and bridges in the human placenta.

Human placental villi from normal and pathological material from the eighth to the 40th week of gestation were examined by light, scanning and transmission electron microscopy. Trophoblastic specializations--such as syncytial sprouts of early and late pregnancy, syncytial knots and syncytial bridges--were classified into proliferative and degenerative processes or artefacts caused by tangential sectioning. In early pregnancy and in diabetes mellitus most syncytial sprouts represent the initial phases in the development of villi. In late pregnancy, in particular in pre-eclampsia, most syncytial knots, sprouts and bridges are histological artefacts, caused by tangential sectioning of the trophoblastic surface. The chance of producing such artefacts is increased with increasing section thickness and with increasing branching and tortuosity of the villi. However, a small proportion of the syncytial knots, sprouts and bridges in the last-trimester placenta, those containing coarse pyknotic nuclei, are trophoblastic specializations of a probably degenerative character.

Chorionic Villi↗
PubMedDate not supplied

Cross-sectional features and three-dimensional structure of human placental villi.

Human placental villi from both normal and complicated pregnancies were examined by both light and scanning electron microscopy. The findings provide evidence that histological features such as syncytial sprouts, bridges, and a net-like arrangement of villi represent tangential sections of irregularly shaped villi rather than proliferative activity of the villous surface. Hence the two-dimensional appearance of paraffin and semithin sections has to be interpreted three-dimensionally in comparison with the respective scanning electron micrographs. In the light of these findings the various types of villous maldevelopment are summarized in a diagram which may be used as an aid for pathological diagnosis.

Chorionic Villi↗
PubMedDate not supplied

Aspects of human fetoplacental vasculogenesis and angiogenesis. I. Molecular regulation.

Patterns of fetoplacental angiogenesis vary during gestation and in association with certain pregnancy pathologies. In a set of three linked reviews, we provide a survey of current knowledge about the molecular regulation, cellular players, qualitative and quantitative morphological features of the vascularization of human placental villi. Here, an account is given of the role played by hypoxia-inducible factor in mediating the effects of oxygen on production of growth factor ligands and receptors which regulate angiogenesis and vessel maturation. However, it should be noted that, for the human placenta early in gestation, the normal (i.e. physiological) partial pressure of O(2)is low but this does not mean that the tissue is hypoxic. Thus, the mechanisms of regulating angiogenic growth factor production may differ at this time in comparison to those found later in gestation or in other tissues or organs. The vasculature in the placenta is plastic and changes markedly as gestation progresses. This is controlled by the complex interplay between physical factors and chemical factors including oxygen, growth factors and growth inhibitors. The companion reviews describe morphological features of normal and pathological development of the human placenta in the context of the factors discussed here.

Adult↗
PubMedDate not supplied

Aspects of human fetoplacental vasculogenesis and angiogenesis. II. Changes during normal pregnancy.

In this second review, we describe the main morphological events which accompany the development of the fetoplacental vascular system throughout normal human pregnancy and summarize findings on the expression of angiogenic growth factors and their receptors. Fetoplacental vasculogenesis starts at day 21 after conception by formation of haemangioblastic cords. In the following phase of branching angiogenesis (day 32 to week 25 post conception), haemangioblastic cords develop into a richly branched villous capillary bed with low fetoplacental blood flow impedance. This period is characterized by high placental levels of VEGF but moderate PlGF expression. In week 15, large centrally located villi show regression of peripheral capillary nets. In parallel, some remaining central capillaries acquire a tunica media and transform into arteries and veins. Beginning at about week 25 in the newly formed peripheral villi, angiogenesis switches from branching to non-branching and this period is accompanied by a steep drop in VEGF and a slower decline in PlGF expression. As a consequence of this switch, long poorly branched capillary loops are formed in the periphery of the fetoplacental vascular trees. These increase fetoplacental impedance but blood flow still increases due to rising fetal blood pressure. The possible interactions between (a). the biphasic development of intraplacental oxygen tensions, (b). changes in VEGF and PlGF levels and (c). developing vascular geometry are discussed. Special attention is given to the obvious discrepancy between sudden elevation of intervillous oxygen tensions which is not coincident with the appearance of angiogenic growth factor peaks and the switch from branching to non-branching angiogenesis. Finally, we deal with methods of quantifying aspects of angiogenesis in the villous vascular system and summarize the main findings during uncomplicated human pregnancy.

Adult↗
PubMedDate not supplied

Aspects of human fetoplacental vasculogenesis and angiogenesis. III. Changes in complicated pregnancies.

Patterns of fetoplacental angiogenesis vary not only during the course of a normal pregnancy but also in certain pregnancy pathologies. Here, we review some of the molecular and morphological events which occur in complicated pregnancies. The pregnancy complications are chosen in an attempt to represent the possible different origins (preplacental, uteroplacental, postplacental) of fetal hypoxia. Molecular events focus on reported changes in hypoxia-inducible factors, angiopoietins and the vascular endothelial, basic fibroblast and placenta growth factors and their receptors. Morphological changes focus on patterns of angiogenesis (branching and non-branching) and a consistent set of morphometric descriptors (covering measures of total capillary growth, villous capillarization and capillary size and shape in transverse section). Apart from some uncertainties due to lack of information, or failure to resolve fully the effects of intrauterine growth restriction and pre-eclampsia, alterations in the angiogenic growth factors and morphologies of capillaries and villi in different complicated pregnancies seem to conform reasonably well to those predicted by the fetal hypoxia paradigm. However, it is clear that future studies on the effects of different origins of fetal hypoxia should exercise more care in the choice and interpretation of relevant descriptors and take more account of the parallel effects of possible confounders. In addition, rather than comparing uncomplicated and complicated pregnancies only at term, more information about molecular and morphological events that occur throughout gestation would be extremely valuable. This includes further studies on changes in growth factor receptors, the less-well-documented angiogenic factors (e.g. angiogenin, angiostatin, endostatin) and the associations between endothelial cells and pericytes. A more integrated approach involving also parallel analysis of the effects of erythropoietin and other potential vasoactive factors on the behaviour and morphology of fetal vessels would be beneficial.

Adult↗
PubMedDate not supplied

Branching patterns of human placental villous trees: perspectives of topological analysis.

Topological analysis was applied to investigate the branching pattern of three specimens obtained from early human placenta (6, 9, and 16 weeks p.m.) reconstructed on the basis of semi-thin sections. Centripetal Horton-Strahler and centrifugal branching order nomenclature was used for topological description of the analysed tree-like structures. Bifurcation ratio and vertex ratio were determined for all three cases and were found to be relatively constant. It was shown that branching pattern is closely related to the model of random segment branching that implicates a high level of asymmetry and a small level of space limitation for branching. The significance of this approach for the analysis of development of the villous tree, for the analysis of mesenchymal villous heterogeneity, and for the estimation of physiological parameters for fetoplacental exchange is discussed. We suggest that topological analysis can lead to a new quantitative classification of branching patterns of the human placental villous trees in normal and pathologic pregnancies.

Chorionic Villi↗
PubMedDate not supplied

A three-dimensional study of the normal human placental villous core: II. Stromal architecture.

The three-dimensional architecture of the villous core of the chorionic villi has been studied in the human placenta throughout pregnancy by scanning electron microscopy, and compared with light microscopic and transmission electron microscopic, findings. Five different types of villi are recognizable: the mesenchymal villi are characterized by a network of tiny bundles of collagen fibrils, enmeshing mesenchymal cells, Hofbauer cells and vessels. The immature intermediate villi display a system of intercommunicating channels, parallel to the major axis of the villi. Within the channels, Hofbauer cells are present. The mature intermediate villi show narrow and short stromal channels, surrounded by a rather tight network of collagen fibrils. Large vessels and a highly compact network of collagen are typical of the stem villi. The terminal villi contain sinusoidally dilated capillaries and a small amount of connective tissue. These findings have numerous functional implications. They are particularly related both to the presence of the stromal channels which could facilitate the macrophagic and immunological task of the Hofbauer cells, and to the different types of villi, playing different roles in placental and fetal life, under normal and pathological conditions.

Chorionic Villi↗
PubMedDate not supplied

Fluid shift across the placenta: II. Fetomaternal transfer of horseradish peroxidase in the guinea pig.

The fetal side of the isolated guinea-pig chorio-allantoic placenta has been perfused with a fluid containing horseradish peroxidase. Electron micrographs show that protein is transferred across the fetal capillary endothelium via micropinocytosis as well as by transport through intercellular clefts. Under normal hydrostatic pressure no pinocytosis or other signs of fetomaternal protein transfer across the trophoblast have been observed. Instead, macrophages ingest the proteins that have reached the interstitial space between fetal endothelium and trophoblast. When the fetal venous pressure is raised up to 20 mmHg about 30 to 50 per cent of the arterial perfusion fluid, including proteins, is shifted into the maternal lacunae. In the beginning of this process slender tubules, and later on bag-like channels, appear that cross the trophoblast and probably connect lacunae and interstitium. The inner surface of the channels and the maternal lacunar surface are labelled by peroxidase. This indicates a fetomaternal transfer of proteins conveyed by the fluid shift. Protein transfer and fluid shift return to their previous levels when the fetal venous pressure is reduced. The size and number of channels are reduced but their structure and the reversibility of the events refute the possibility that they are of traumatic origin. It cannot be decided whether the channels are pre-existent but unrecognizable, or de-novo formations.

Animals↗
PubMedDate not supplied

Placental anatomy and diffusing capacity in guinea pigs following long-term maternal hypoxia.

To determine the relation of placental structure to placental diffusing capacity (DPCO), we exposed Hartley guinea pigs to 12 or 14 per cent O2 from day 15 of gestation to near term (64 days). At that time we measured DPCO and fetal body and placental weights. In addition, we used stereological techniques to measure placental parameters important to diffusing capacity. We also used a mathematical model with results from the stereological measurements to predict the diffusing capacity. In the first hypoxic group (E1), measured DPCO decreased 10.1 +/- 3.7 per cent, while that predicted was 2.4 per cent less than control. Total vascular volume decreased 6.6 +/- 3.6 per cent, while tissue volume and mean diffusion distance increased 10.2 +/- 5.6 per cent and 12.9 +/- 7.0 per cent, respectively. In the pair-fed animals, measured DPCO decreased 22.6 +/- 4.6 per cent, while that predicted was 20.0 per cent less than control. There were no significant stereological differences in this group. In the second (E2) hypoxic group, measured DPCO increased 27.2 +/- 7.4 per cent, while that predicted increased 38.2 per cent. For this same group, total vascular volume increased 11.7 +/- 3.0 per cent, and tissue volume and mean diffusion distance decreased 18.2 +/- 4.6 per cent and 17.8 +/- 3.8 per cent, respectively. These results demonstrate the dependence of placental diffusing capacity upon placental structure.

Animals↗
PubMedDate not supplied

The ultrastructure of the trophoblastic layer of the degu (Octodon degus) placenta: a re-evaluation of the 'channel problem'.

Previous studies on immersion-fixed specimens of the haemomonochorial labyrinthine chorioallantoic placenta of the degu have made visible channels or pores which completely crossed the trophoblastic layer; for the first time hints for an open connection between maternal blood spaces and fetal interstitium were demonstrated in a placenta. This important finding was re-evaluated by means of transmission electron microscopy paying particular attention to the influence of the mode of fixation and of ischaemic periods prior to fixation. Thirty placentae from seven near-term degu (estimated gestational age 80-90 days) were fixed at various times (5-45 min) after maternal death. Placentae were perfused in situ via the aorta/uterine arteries or the umbilical vein with 2.2 per cent phosphate-buffered glutaraldehyde (n = 7, ischaemic periods < 5-45 min) or lanthanum hydroxide/osmium tetroxide (n = 7, ischaemic periods < 5 min), or were immersion-fixed in 2.2 per cent phosphate-buffered glutaraldehyde (n = 16, ischaemic periods 10-45 min). In material with brief ischaemic periods (n = 3, 5-10 min) no open connections between the maternal blood lacunae and fetal interstitium could be detected. Instead, occasional foci of trophoblast reduced to a thickness of 0.1 micron were found. After ischaemic periods exceeding 10 min, the thin trophoblastic diaphragms had partly disappeared resulting in complete transtrophoblastic pores. It is likely, therefore, that visible trophoblastic pores or channels in the degu placenta are ischaemic artefacts. Application of lanthanum hydroxide from the fetal circulation showed that a branching system of membrane-lined tubules (15-50 nm wide) intruded the trophoblast from its basal side, as has been reported for the guinea-pig and human placenta. It remains to be investigated whether these invaginations belong to a continuous transtrophoblastic channel system.

Animals↗
PubMedDate not supplied

The distribution of macrophages in spiral arteries of the placental bed in pre-eclampsia differs from that in healthy patients.

Placental bed biopsies taken during caesarean section from 10 patients with pre-eclampsia and six healthy pregnancies were studied. We applied antibodies against cytokeratin and different macrophage markers to analyse the distribution of invasive extravillous trophoblast cells as compared to that of macrophages in myometrial segments of uteroplacental arteries. The data were evaluated quantitatively. We found a clear inverse relationship between local infiltration with macrophages and trophoblast invasion. In pre-eclampsia, vessel cross-sections prevailed which were characterized by large numbers of macrophages but a low degree of trophoblast invasion. In contrast, in normal third trimester pregnancies the respective arterial segments had a high degree of trophoblast invasion but were largely void of macrophages. These data suggest causal links between macrophages and inhibition of intra-arterial trophoblast invasion in pre-eclampsia.

Adult↗
PubMedDate not supplied

Phage display: a molecular tool for the generation of antibodies--a review.

Phage display comprises an array of methods, which can be used to display proteins on bacteriophages. We present in this article a summary of techniques, which can be used to express antibody libraries on bacteriophages. Since many researchers are more familiar with the conventional hybridoma technique for production of monoclonal antibodies we describe analogies and differences between these two techniques, both of which are used to reach comparable scientific objectives. We focus on the features which are specific to phage display techniques rather than for hybridoma techniques. These comprise the freedom to choose other animals than the mouse for immunization, the enormously large sample (up to 10(9) clones) which can be drawn and immortalized from a single immunized animal and the opportunity to enhance affinity of isolated antibodies by in vitro affinity maturation. The panning techniques, which are used to enrich specifically binding phage antibodies from the huge libraries are briefly summarized.

Animals↗
PubMedDate not supplied

Cell-cell-communication during placental development and possible implications for trophoblast proliferation and differentiation.

Since direct cell-cell-communication plays a crucial role in the coordination of proliferation and differentiation processes during development we have focused on the expression patterns of gap junctions and their functional implication in the human placenta. The gap junction protein connexin40 (Cx40) is expressed in the proximal extravillous trophoblast of cell islands and columns. In accordance with these observations, isolated trophoblast cells from first and second trimester placentae and choriocarcinoma cells (Jeg-3) reveal Cx40 expression. This channel is not only characteristic of the trophoblast cells along the invasive pathway but also of endothelial cells. To elucidate the functional role of this channel for proliferation and invasion, the non-coupled Jeg-3 cells have been transfected with Cx26, Cx40 and Cx43, respectively. In contrast to Cx40, the Cx26 channel was more potent in reducing proliferation and inducing differentiation indicated by hCG-beta secretion. Using the nude mouse model to study invasion properties of choriocarcinoma cells, we demonstrated that malignant trophoblast cells were able to invade host vessels and to replace endothelial cells. Upregulation of endogeneous connexin genes in tumours grown in nude mice enforces further experimental strategies to investigate the importance of the different channels to fake the cell biological program of endothelial cells.

Animals↗
PubMedDate not supplied

Endothelin A and B receptors change their expression levels during development of human placental villi.

Endothelin receptors have recently been found in non-vascular tissues including the human placenta. The present study investigated developmental changes in location and expression levels of endothelin A and B receptors (ETA-R, ETB-R) in human placentae and isolated trophoblast by comparing first and third trimester tissues. In the first trimester all cells and tissues were immunolabelled for ETA-R and ETB-R, whereas in third trimester placentae the syncytiotrophoblast (ETA-R, ETB-R) and macrophages (ETA-R) were unstained. Immunoblotting for both receptors revealed up to three bands at 33-35, 50 and 75 kDa, respectively, which were differentially present in the first and third trimester. Pre-adsorption of antibodies with oligopeptides used for antigen-generation weakened the immunoreactions. ETA-R protein levels decreased (P< 0.05) in total villous tissue and isolated trophoblast, whereas ETB-R was unchanged. ETB-R transcripts (RT-PCR) prevailed in both stages and tissues, but in contrast to the protein levels its preponderance decreased from first trimester to term in villous tissue (P< 0.01), because of a four to five-fold increase in ETA-R and only a two-fold (P< 0.05) increase in ETB-R mRNA levels (P< 0.01). We conclude that ET receptor location, intracellular processing and expression levels in human villous tissue change between the first and third trimester. This may reflect changing functions of ET-1 during placental development.

Abortion, Legal↗
PubMedDate not supplied

Characterization of trophoblast cell isolations by a modified flow cytometry assay.

The purity of isolated trophoblast cells is an important checkpoint in in vitro studies on the human placenta. Maintaining viability of primary cells for a prolonged period, or achieving cell proliferation in primary cell cultures, is often a matter of concern. In this paper we present a method for characterizing the purity of isolated trophoblast cells based on the expression of cytoskeletal proteins, as well as for assessing their cell cycle status, by flow cytometry. We show that after a simple permeabilization and fixation step in 70 per cent methanol, staining for cytokeratin 7 and vimentin could discriminate between trophoblast cells and contaminating populations. The method was applicable to trophoblast cells both from villous and extravillous origin. By staining the proliferation-related antigen Ki-67 and DNA, information was gained about the cell cycle status and viability of freshly isolated and cultured villous trophoblast cells. This method may help to quickly and quantitatively characterize preparations of isolated trophoblast, as well as to search for culture conditions favouring long-term survival and proliferation.

Cell Cycle↗
PubMedDate not supplied

Hypoxia favours necrotic versus apoptotic shedding of placental syncytiotrophoblast into the maternal circulation.

In the third trimester of normal pregnancy, the mother tolerates daily shedding of several grams of dying placental trophoblast into the maternal circulation. The balance between apoptotic and necrotic shedding is presently unknown. Since pre-eclampsia is characterized by an altered placental oxygenation and increased trophoblast shedding, we investigated the role of oxygen on the balance of apoptotic versus necrotic trophoblast shedding in vitro. We studied human trophoblast turnover in explanted villi from late first and third trimester placentas in low oxygen (2 per cent) and higher oxygen tensions (6 per cent and 18 per cent) for up to 72h. Trophoblast turnover including apoptosis and necrosis were assessed by histology, immunolocalization of Mib-1 (proliferation marker), Bcl-2 (apoptosis inhibitor), activated caspase 3 (apoptosis promoter), cytokeratin 18 neo-epitope formation (M30 antibody), TUNEL test (DNA degradation), and (3)H-cytidine and(3) H-uridine incorporations. Culture in 2 per cent oxygen increased cytotrophoblast proliferation and syncytiotrophoblast shedding by necrosis. The proteins necessary for execution of apoptosis were mostly retained in the cytotrophoblast due to lack of syncytial fusion. Culture in 6 per cent and 18 per cent oxygen reduced cytotrophoblast proliferation. Syncytial fusion occurred and activity of caspase 3 was found in the syncytiotrophoblast; the latter remained intact demonstrating physiologic turnover, including apoptotic shedding. We conclude that severe placental hypoxia favours necrotic rather than apoptotic shedding of syncytial fragments into the maternal circulation. Since uteroplacental ischaemia is a significant risk factor for pre-eclampsia, these findings may explain the link between reduced uteroplacental blood flow and the systemic clinical manifestations of this disease.

Adult↗
PubMedDate not supplied

Villous sprouting: fundamental mechanisms of human placental development.

There is increasing evidence that maldevelopment of the placental villous tree can play an important role in the pathogenesis of various pregnancy diseases. In this review we present the most recent advances of cellular and molecular mechanisms involved in the early formation of chorionic villi. In particular we focus our attention on the structural events during early villous sprouting leading to the formation of the mesenchymal villi which are the forerunners of all other villous types, i.e. immature intermediate villi, stem villi, mature intermediate villi and terminal villi. Early villous sprouting starts as 'hot spots' which are circumscribed areas consisting of highly proliferating cytotrophoblastic and stromal cells. The post-proliferative cytotrophoblastic cells fuse with the overlying syncytium leading to the formation of the trophoblastic sprouts. When villous mesenchyme invades the trophoblastic sprouts, the latter are transformed into villous sprouts. The vascularization of the villous sprouts leads to the formation of the mesenchymal villi, the most basic villous type. This process is repeated throughout pregnancy. We analyse the influence of various extracellular matrix molecules, e.g. tenascin and hyaluronic acid, on the formation of hot spots and mesenchymal villi as well as the transformation of the latter in other villous types. We present a critical survey on the data on vessel formation related to villous sprouting and morphogenesis of mesenchymal villi as well as the expression of various angiogenic factors and their receptors.

Chorionic Villi↗