The concentration of collagen and the collagenolytic activity in the amnion and the chorion

Roles of Two Small Leucine-Rich Proteoglycans Decorin and Biglycan in Pregnancy and Pregnancy-Associated Diseases

Two small leucine-rich proteoglycans (SLRP), decorin and biglycan, play important roles in structural–functional integrity of the placenta and fetal membranes, and their alterations can result in several pregnancy-associated diseases. In this review, we briefly discuss normal placental structure and functions, define and classify SLRPs, and then focus on two SLRPs, decorin (DCN) and biglycan (BGN). We discuss the consequences of deletions/mutations of DCN and BGN. We then summarize DCN and BGN expression in the pregnant uterus, myometrium, decidua, placenta, and fetal membranes. Actions of these SLRPs as ligands are then discussed in the context of multiple binding partners in the extracellular matrix and cell surface (receptors), as well as their alterations in pathological pregnancies, such as preeclampsia, fetal growth restriction, and preterm premature rupture of membranes. Lastly, we raise some unanswered questions as food for thought.

Cross talk: Trafficking and functional impact of maternal exosomes at the Feto-maternal Interface under normal and pathologic states

Fetal cell-derived exosomes promote inflammation in uterine and cervical cells to promote labor and delivery. However, the effect of maternal exosomes on fetal cells is still not known. We tested the hypothesis that cervical cells exposed to infectious and oxidative stress (OS) signals produce exosomes that can induce inflammation at the feto-maternal interface (FMi). Exosomes isolated from medium samples from human ectocervical epithelial cells (Ecto), endocervical epithelial cells (Endo), and cervical stromal cells (Stroma) in normal cell culture (control) or exposed to infection or OS conditions were characterized based on morphology, size, quantity, expression of tetraspanin markers, and cargo proteins. Human decidual, chorion trophoblast (CTC), chorion mesenchymal (CMC), amnion mesenchymal (AMC), and amnion epithelial cells (AEC) were treated with control, LPS-, or OS-treated cervical exosomes. ELISA for pro-inflammatory cytokines and progesterone was done to determine the recipient cells' inflammatory status. Ecto, endo, and stroma released ∼110 nm, cup-shaped exosomes. LPS and OS treatments did not affect exosome size; however, OS significantly increased the number of exosomes released by all cervical cells. Cervical exosomes were detected by fluorescence microscopy in each target cell after treatment. Exosomes from LPS- and CSE-treated cervical cells increased the inflammatory cytokine levels in the decidual cells, CMC, AMC, and AEC. LPS-treated stromal cell exosomes increased IL-6, IL-8, and progesterone in CTC. In conclusion, infection and OS can produce inflammatory cargo-enriched cervical exosomes that can destabilize FMi cells. However, the refractoriness of CTC to exosome treatments suggests a barrier function of the chorion at the FMi.

Dynamic measurement of amnion thickness during loading by speckle pattern interferometry

INTRODUCTION

In previous studies on the mechanical parameters of amnions (AM), there is a limitation due to the lack of an accurate thickness measurement, which is an important parameter for determining AM-specific mechanical properties. As a bottleneck, the characterization of the basic mechanical properties of AM are greatly restricted, even with the proposal of fracture criteria.

METHOD

First, the initial thickness of the AM is estimated by the interpolated-volume-area method. Second, through combinations of our self-developed mini-biaxial tensile device with speckle pattern interferometry, this is the first time that researchers can accurately obtain the AM thickness at each transient moment in the process of loading.

RESULTS

Based on the experimental results, an accurate stress-strain curve could be obtained. Two important mechanical parameters-the fracture energy density and amnion rupture modulus-could be extracted as 0.184±0.036MPa and 108.57±17.32MPa, respectively. The fracture energy density and amnion rupture modulus provide objective criteria and a scientific basis for the evaluation of AM rupture.

DISCUSSION

The tensile stress-strain curve of a normal human amnion shows a distinct J-shape. This proves that the experimental results are basically reliable. Both important parameters --the fracture energy density and amnion rupture modulus, can be calculated from the stress-strain curve. Extracting these two parameters is critical for the evaluation and prediction of ROM, PROM and PPROM.

α-Lipoic acid blocks the GMCSF induced protease/protease inhibitor spectrum associated with fetal membrane weakening in-vitro

INTRODUCTION

We use an in-vitro human fetal membrane (FM) explant-based model to study inflammation-induced FM weakening, a prerequisite for PPROM. In this system, GMCSF is a critical intermediate, both necessary and sufficient for TNFα and thrombin induced FM weakening. α-Lipoic-acid (LA) blocks TNFα and thrombin, as well as GMCSF-induced weakening. Recently, we reported LA concomitantly blocks GMCSF-induction of MMPs 2, 9 and 10 and inhibition of TIMPs 1-3. The aim of this study was to show that LA blocks GMCSF-induced increases in additional proteases and reductions in additional protease inhibitors.

METHODS

FM fragments were cultured±LA and then±GMCSF. In other experiments, weak versus strong, fresh FM were cultured without additions. Fragments were strength tested and media analyzed by multiplex protein ELISA for proteases and protease inhibitors.

RESULTS

GMCSF induced FM weakening and concomitantly increased several Proteases (Cathepsin-S, Proteinase-3, Elastase-2) and decreased several protease inhibitors (NGAL, Cystatin-C, HE4 and Thrombospondin1). LA inhibited GMCSF-induced FM weakening and all enzymatic changes. Untreated weaker versus stronger regions of fresh FM showed comparable differences in proteases and protease inhibitor patterns to GMCSF-stimulated versus controls.

CONCLUSION

LA blocks GMCSF-induced human FM weakening and associated protease increases and inhibitor decreases. The GMCSF-induced spectrum of protease/protease-inhibitor changes is similar to that in the natural weak FM fragments. In concert with previously reported GMCSF-induced changes in MMPs & TIMPs, these other protease and protease-inhibitor changes presumably facilitate FM weakening and rupture. LA blocks these GMCSF effects and therefore may be a useful agent to prevent PPROM.

Rigid-bar loading on pregnant uterus and development of pregnant abdominal response corridor based on finite element biomechanical model

During pregnancy, traumas can threaten maternal and fetal health. Various trauma effects on a pregnant uterus are little investigated. In the present study, a finite element model of a uterus along with a fetus, placenta, amniotic fluid, and two most effective ligament sets is developed. This model allows numerical evaluation of various loading on a pregnant uterus. The model geometry is developed based on CT-scan data and validated using anthropometric data. Applying Ogden hyper-elastic theory, material properties of uterine wall and placenta are developed. After simulating the "rigid-bar" abdominal loading, the impact force and abdominal penetration are investigated. Findings are compared with the experimental abdominal response corridor, previously developed for a nonpregnant abdomen. "Response corridor" denotes a bounded envelope in response space, within which the system responses usually lie. Results show that at low abdominal penetrations (less than 45 mm), the pregnant abdomen response is highly compatible with the nonpregnant case. While, at large penetrations, the pregnant abdomen demonstrates stiffer behavior. The reason must be the existence of a fetus in the model. This reveals that the existing response corridors would not be reliable to be extended for a pregnant abdomen. Hence, response corridor development for a pregnant abdomen is a crucial task. In this study, a new fixed-back rigid-bar loading response corridor is proposed for a pregnant abdomen using the load-penetration behavior of the developed model. This model and response corridor can help to study the pregnant uterus response to environmental loading and investigate the injury risk to the uterus and fetus.

Influence of osmolarity and hydration on the tear resistance of the human amniotic membrane

The amnion is considered to be the load-bearing part of the fetal membranes. We investigated the influence of osmolarity of the testing medium and hydration on its fracture toughness. Mode I fracture tests revealed that physiological variations in the bath osmolarity do not influence the tear resistance of amnion, while larger changes, i.e. from physiological saline solution to distilled water, lead to a significant reduction of the fracture toughness. Uniaxial tensile tests on collagen hydrogels confirmed the reduction in toughness, suggesting that lower bath osmolarity triggers changes in the failure properties of single collagen fibers. Prenatal surgeries, in particular fetoscopic procedures with partial amniotic carbon dioxide insufflation, might result in dehydration of the amnion. Dehydration induced a brittle behavior; however, subsequent rehydration for 15 min resulted in a similar tear resistance as for the fresh tissue.

On the defect tolerance of fetal membranes

A series of mechanical experiments were performed to quantify the strength and fracture toughness of human amnion and chorion. The experiments were complemented with computational investigations using a 'hybrid' model that includes an explicit representation of the collagen fibre network of amnion. Despite its much smaller thickness, amnion is shown to be stiffer, stronger and tougher than chorion, and thus to determine the mechanical response of fetal membranes, with respect to both, deformation and fracture behaviour. Data from uniaxial tension and fracture tests were used to inform and validate the computational model, which was then applied to rationalize measurements of the tear resistance of tissue samples containing crack-like defects. Experiments and computations show that the strength of amnion is not significantly reduced by defects smaller than 1 mm, but the crack size induced by perforations for amniocentesis and fetal membrane suturing during fetal surgery might be larger than this value. In line with previous experimental observations, the computational model predicts a very narrow near field at the crack tip of amnion, due to localized fibre alignment and collagen compaction. This mechanism shields the tissue from the defect and strongly reduces the interaction of multiple adjacent cracks. These findings were confirmed through corresponding experiments, showing that no interaction is expected for multiple sutures for an inter-suture distance larger than 1 mm and 3 mm for amnion and chorion, respectively. The experimental procedures and numerical models applied in the present study might be used to optimize needle and/or staple dimensions and inter-suture distance, and thus to reduce the risk of iatrogenic preterm premature rupture of the membranes from amniocentesis, fetoscopic and open prenatal surgery.

Bioactivity and composition of a preserved connective tissue matrix derived from human placental tissue

There are a wide variety of extracellular matrices that can be used for regenerative purposes. Placental tissue-based matrices are quickly becoming an attractive option given the availability of the tissue source and the wide variety of bioactive molecules knows to exist in unprocessed placental tissues. As fresh placental tissues are seldom an option at the point of care, we examined both the composition and bioactivity of a commercially packaged flowable placental connective tissue matrix (FPTM) (BioECM^® , Skye Biologics, Inc.) that was preserved by the proprietary HydraTek^® process. The FPTM contained significant amounts of collagen and various growth factors such as bFGF, EGF, PDGF, KGF, and PIGF. In addition, it contained high levels of tissue inhibitors of metalloproteinases (TIMP-1 and 2) and molecules known to modulate the immune response including TGF-β and IL-4. In terms of its bioactivity, the FPTM displayed the ability (1) to suppress INF-γ secretion in activated T-cells nearly fourfold over control media, (2) to inhibit methicillin resistant Staphylococcus aureus (MRSA) and Staphylococcus saprophyticus proliferation, (3) to increase the migration of adipose-derived stem cells (ASCs) nearly threefold over control media and (4) to adhere to ASCs in culture. When ASCs were exposed to FPTM in culture, the cells maintained healthy morphology and showed no significant changes in the expression of five genes involved in tissue growth and repair as compared to culture in standard growth media. © 2018 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2731-2740, 2018.

Microstructure based prediction of the deformation behavior of soft collagenous membranes

The response of human amnion (HA) and bovine Glisson's capsule (GC) to uniaxial and biaxial tensile loading is analyzed on tissue (∼mm) and collagen fiber (∼μm) length scales. The mechanical behavior of the membranes is rationalized based on a discrete fiber network model that relates model parameters with microstructural features of the tissues. Parameters were first determined for GC based on the quantity and organization of collagen fibers in the tissue. Next, parameters for HA were defined by comparing the microstructures of the two membranes, which differ in fiber organization in that collagen forms μm-thick fiber bundles in GC while 50 nm-thin fibrils constitute the network in HA. The flexural behavior of these structures is phenomenologically represented in the model, indicating that shear forces are transmitted through fibrils within GC bundles, but to a much lesser extent than in a corresponding solid cross section. The model provides excellent predictions of the uniaxial and biaxial mechanical response, as well as of the progressive reorientation of fibers associated with uniaxial loading. The results are particularly relevant since model parameters were not obtained through a fitting procedure of the tissue's tension-stretch curve. Furthermore, simulations of representative in vivo deformation states indicated that a large part of the fibers are expected to be un-crimped under physiological loading conditions. Thus, the crimped shape of collagen fibers in the initial test configuration, and typically observed in histological analyses, might be a consequence of the contraction occurring when membranes are extracted from their environment in the body.

Differential Secretion of Matrix Metalloproteinase-2 and -9 After Selective Infection With Group B Streptococci in Human Fetal Membranes

OBJECTIVE

This study evaluated the secretions of zymogen and active forms of matrix metalloproteinase (MMP)-9 and MMP-2 and their specific inhibitors, TIMP-1 and TIMP-2 by fetal membranes stimulated with group B Streptoccocci (GBS).

METHODS

We used an in vitro experimental model that allowed us to estimate the individual contribution of the amnion (AM) and the choriodecidua (CHD) to the microbial insult. Membranes were obtained after delivery by elective cesarean delivery from women at 37 to 40 weeks of gestation without evidence of either active labor or intrauterine infection. Membranes were mounted in Transwell devices (Costar, New York, NY), physically separating the upper and lower chambers; 1 x 10(6) CFU of GBS was added to either AM or CHD and the secretions and gelatinolytic activity of MMP-2 and MMP-9 were measured in both compartments by enzyme-linked immunosorbent assay (ELISA) and zymography. TIMPs secretion was measured by ELISA. Both MMPs were immunolocalized in tissue sections.

RESULTS

The simultaneous stimulation at both sides was followed by increases of proMMP-9 (85.0 +/- 18.63 pg/mL) and proMMP-2 (4.10 +/- 1.90 ng/mL) in the CHD (P <.05). When only one side of the membrane was stimulated, the secretion level of proMMP-2 increased 2.3-fold and that of proMMP-9 2.5-fold in the CHD. The active forms of both enzymes did not change with any modality of stimulation. The secretion level of both TIMPs remained without significant changes. CHD and AM were positive for immunoreactive MMP-2 and MMP-9.

CONCLUSION

We propose that infection of fetal membranes with GBS is followed by active secretion of MMP and the CHD is the principal source of these mediators of extracellular matrix degradation.

Optical coherence tomography: A potential tool to predict premature rupture of fetal membranes

A fundamental question addressed in this study was the feasibility of preterm birth prediction based on a noncontact investigation of fetal membranes in situ. Although the phenomena of preterm birth and the premature rupture of the fetal membrane are well known, currently, there are no diagnostic tools for their prediction. The aim of this study was to assess whether optical coherence tomography could be used for clinical investigations of high-risk pregnancies. The thickness of fetal membranes was measured in parallel by optical coherence tomography and histological techniques for the following types of birth: normal births, preterm births without premature ruptures and births at full term with premature rupture of membrane. Our study revealed that the membrane thickness correlates with the birth type. Normal births membranes were statistically significantly thicker than those belonging to the other two groups. Thus, in spite of almost equal duration of gestation of the normal births and the births at full term with premature rupture, the corresponding membrane thicknesses differed. This difference is possibly related to previously reported water accumulation in the membranes. The optical coherence tomography results were encouraging, suggesting that this technology could be used in future to predict and distinguish between different kinds of births.

Fetal membranes structure and prelabour rupture

In most pregnancies labour begins at term in the presence of intact fetal membranes. Without intervention the membranes usually spontaneously rupture near the end of the first stage of labour. In 10% of pregnancies that deliver at term the fetal membranes fail to maintain their structural integrity and this results in their “prelabour rupture”, defined as spontaneous rupture of membranes at least one hour before the onset of labour. In 95–98% of these cases at term, labour is precipitated within 48 hours. Although preterm birth, defined as birth prior to 37 completed weeks of pregnancy, occurs in only 7–8% of all pregnancies, 40–60% of these deliveries are preceded by prelabour rupture of the fetal membranes.

Epidermal growth factor variations in amniotic membrane used for ex vivo tissue constructs

INTRODUCTION

The amniotic membrane (AM) is used for engineering ex vivo tissue constructs used in ocular surface reconstruction. Epidermal growth factor (EGF) content of the AM is believed to play a key role in supporting corneal epithelial cell expansion on AM. This study investigated EGF content in AM in relation to intra- and inter-donor variations and the effect of processing and preservation (handling).

METHODS

Fifteen human AM, both fresh and handled, were analyzed for EGF gene and protein expression by real-time polymerase chain reaction and ELISA, respectively.

RESULTS

EGF gene expression was predominantly seen in the AM epithelium (p<0.01). Similarly, EGF protein too was predominantly seen in the epithelial layer (p<0.01) for fresh and handled samples. EGF protein content varied between membranes (inter-donor) and at different sites within the same membrane (intra-donor). The highest EGF protein concentration was noted in the AM apical and mid-region epithelium. Significant EGF protein loss (p<0.01) was observed after handling.

CONCLUSION

There is a considerable variation in EGF content between and within donors. This is further affected by handling of the AM. Such variations could affect the clinical efficacy of tissue constructs. Current use of AM for ex vivo expansion of epithelial cells is not standardized and remains an area of concern.

Relation between mechanical properties and microstructure of human fetal membranes: an attempt towards a quantitative analysis

OBJECTIVE

We sought to measure the mechanical baseline behavior of fetal membranes in order to determine constitutive mechanical model parameters for fetal membranes, and to examine their relation to molecular correlates for mechanical function, i.e. collagen and elastin.

STUDY DESIGN

The uniaxial stress-strain response of nine human term fetal membranes was measured. Methods of nonlinear continuum mechanics were applied for the analysis of the stress-strain curves. Thickness of amnion and chorion were determined from histologic sections for each fetal membrane sample. Complementary biochemical analysis was performed to quantify the soluble collagen and soluble elastin components for each sample.

RESULTS

We report a straightforward histologic modality for measurements of amnion and chorion thickness. Average thickness of the amnion and chorion layers were 111+/-78 microm, and 431+/-113 microm, respectively, which are about twice larger than previously reported. The average content of acid-soluble elastin was 2.1% of wet weight and the one of pepsin/acetic acid-soluble collagen was 10.5% of dry weight. Our data show an inverse proportionality between soluble elastin and soluble collagen content. The low strain elastic modulus ranged between 10 and 25 kPa. Correlations were found between biochemical data and mechanical parameters: there is clearly a direct proportionality between small strain elastic modulus and elastin content. Further, a (less pronounced) direct correlation was observed also between soluble collagen content and the parameter governing the increase in stiffness at larger strains in the nonlinear mechanical model. The mechanical tests revealed a relatively low variability for samples from the same membrane but a large variation between donors. The proposed nonlinear model provides a good fit of the experimental data, with a coefficient of determination, R(2), typically in the range of 0.94. Membranes failure originated at the clamping points thus impairing the quantification of ultimate stress and strain. Thus, no correlation was found between maximum stress and collagen or elastin content.

CONCLUSIONS

This study provides a starting point for comprehensive quantitative analysis of the relationship between fetal membranes microstructure and their nonlinear deformation behavior. These insights could become useful in identifying potential medical interventions to prevent membranes rupture.

The biomechanics of amnion rupture: an X-ray diffraction study

Pre-term birth is the leading cause of perinatal and neonatal mortality, 40% of which are attributed to the pre-term premature rupture of amnion. Rupture of amnion is thought to be associated with a corresponding decrease in the extracellular collagen content and/or increase in collagenase activity. However, there is very little information concerning the detailed organisation of fibrillar collagen in amnion and how this might influence rupture. Here we identify a loss of lattice like arrangement in collagen organisation from areas near to the rupture site, and present a 9% increase in fibril spacing and a 50% decrease in fibrillar organisation using quantitative measurements gained by transmission electron microscopy and the novel application of synchrotron X-ray diffraction. These data provide an accurate insight into the biomechanical process of amnion rupture and highlight X-ray diffraction as a new and powerful tool in our understanding of this process.

Evidence of in vitro differential secretion of 72 and 92 kDa type IV collagenases after selective exposure to lipopolysaccharide in human fetal membranes

Premature rupture of chorioamniotic membranes complicated with intrauterine infection has been associated to degradation of extracellular matrix (ECM), which could explain local morphological changes. We used a culture system in which the chorioamniotic membranes form two independent chambers, allowing for the selective stimulation of either the amnion (AMN) and/or the choriodecidua (CHD) regions. Lipopolysaccharide (500 ng/ml) was added to the AMN and/or the CHD; secretions and gelatinolytic activity of matrix metalloproteinase (MMP)-2 and MMP-9 were measured in both compartments by enzyme-linked immunosorbent assay (ELISA) and zymography. Secretions of TIMP-1, TIMP-2 and TIMP-4 were measured by ELISA. Both metalloproteinases were immunolocalized in tissue sections. All stimulation modalities induced a similar proMMP-2 and proMMP-9 secretion pattern in the CHD with concentrations of 2.49 ng/ml and 90.91 pg/ml, respectively; the AMN showed no significant changes. The active forms of both enzymes did not change with any stimulation modality. TIMP-1, TIMP-2 and TIMP-4 secretions remained without significant changes (P = 0.41). ECM degradation and structural disarrangement were evident after stimulation. Secretion of proMMP-2 and proMMP-9 mainly in the CHD, presence of active forms associated to the tissue and minor changes in TIMPs secretion could favor ECM degradation and explain the weakening and thinning associated with the pathological rupture of chorioamniotic membranes.

Possible early prediction of preterm birth by determination of novel proinflammatory factors in midtrimester amniotic fluid

Interferon-gamma-inducible T cell-alpha chemoattractant (ITAC) is a chemokine, directing activated T lymphocytes toward sites of inflammation. ADAM-8 (A disintegrin and metalloprotease-8) is a glycoprotein expressed in cells promoting inflammation. Elastase, a protease targeting at the degradation of intra- or extracellular proteins, is inhibited by secretory leukocyte proteinase inhibitor (SLPI), which protects against microbial invasion. Adhesion molecules (soluble intercellular adhesion molecule--sICAM-1 and soluble vascular cell adhesion molecule-sVCAM--1) serve as markers of inflammation or tissue damage. We hypothesized that elevated midtrimester amniotic fluid concentrations of above substances, and decreased levels of SLPI could possibly be useful predictors of asymptomatic intra-amniotic inflammation and/or infection, eventually resulting in preterm labor and delivery. The study involved 312 women undergoing midtrimester amniocentesis. Thirteen cases, progressing to preterm delivery (<37 weeks), were matched with 21 controls (delivering >37 weeks) for age, parity, and gestational age at amniocentesis. Amniotic fluid levels of the above substances were measured by enzyme-linked immunosorbent assay (ELISA). Only amniotic fluid ITAC and ADAM-8 levels were significantly higher (P=0.005 and P < 0.02, respectively) in women delivering at <37 weeks than at >37 weeks. SLPI concentrations significantly increased in women going into labor without ruptured membranes irrespective of pre- or term delivery (P < 0.007, P < 0.001, respectively) and correlated with elastase (r=0.508, P < 0.002). In conclusion, elevated midtrimester amniotic fluid levels of ITAC and ADAM-8 could predict occult infections/inflammations, possibly resulting in preterm birth.

Investigation of midtrimester amniotic fluid factors as potential predictors of term and preterm deliveries

Aims. Our aim is to investigate, in 13 cases (delivering preterm) and 21 matched (for age, parity, and gestational age) controls (delivering at term), whether midtrimester amniotic fluid concentrations of elastase, secretory leukocyte proteinase inhibitor (SLPI), soluble intercellular adhesion molecule-1, and soluble vascular cell adhesion molecule predict asymptomatic intra-amniotic inflammation/infection and preterm labor. Results. Concentrations of all substances were not statistically different among mothers, delivering preterm or at term. SLPI concentrations significantly increased in women, going into labor without ruptured membranes, irrespective of pre- or term delivery (P < .007, P < .001, resp) and correlated with elastase (r = 0.508, P < .002). Conclusions. Midtrimester amniotic fluid SLPI concentrations significantly decrease when membrane rupture precedes pre- or full-term labor. However, none of the investigated substances predict preterm delivery.

Manufacture of a Cell-free Amnion Matrix Scaffold that Supports Amnion Cell Outgrowth In Vitro

We manufactured a cell-free extracellular matrix scaffolds in order to obtain a support material for amnion cell outgrowth, eventually being used for repair of prematurely ruptured fetal membrane. Human preterm or term amnion tissue was separated into its collagenous extracellular matrix and cell components. The acellular scaffold was explored for its capacity to support regrowth of isolated human amnion epithelial or mesenchymal cells in vitro. The outgrowth of amnion cells on and in the scaffold was investigated by scanning and transmission electron microscopy, and confocal laser scanning microscopy. Cell-free amnion matrix scaffolds demonstrated a porous collagen fiber network similar as in native amnion. Inoculation of acellular amnion scaffolds with human amnion cells revealed that its property to support amnion cell outgrowth was retained. Amnion epithelial and mesenchymal cells were found to grow into dense layers on the surface of the scaffold within 3-4 days and 7-8 days, respectively, and to some extent, invaded the scaffold during the culture period. Manufactured acellular amnion matrix retains structural and functional properties required for cell outgrowth in vitro. It may become useful to repair prematurely ruptured fetal membranes.

Labour induces increased concentrations of biglycan and hyaluronan in human fetal membranes

OBJECTIVE

The proteoglycan decorin stabilizes collagen whereas biglycan and hyaluronan disrupt well-organized collagen. The aim was to compare hyaluronan and proteoglycans in human fetal membranes obtained before and after spontaneous labour at term.

STUDY DESIGN

Prelabour samples of fetal membranes (N=9) were obtained from elective caesarean sections and regionally sampled from over the cervix (cervical membranes) and mid-zone samples between this area and the placental edge. Postlabour samples (N=11) were obtained from spontaneous vaginal delivery and also regionally sampled. Amnion and chorio-decidua were analysed separately. The proteoglycans decorin and biglycan were analysed using alcian blue precipitation, SDS polyacrylamide gel electrophoresis and immunostaining. Hyaluronan was analysed using a radioimmunoassay and by histochemistry. Collagen was measured by estimating hydroxyproline content.

RESULTS

In prelabour membranes the biglycan concentration (microg/mg wtw) in the cervical amnion was 40% lower than in the mid-zone amnion (P<0.05). After delivery the cervical amnion showed a twofold increase in biglycan (P<0.05), a 30% decrease in collagen (P<0.05), and a 50% decrease in decorin concentration (P<0.05). In mid-zone samples after delivery the concentrations of hyaluronan showed an increase form 1.0 to 4.9 microg/mg wtw (P<0.05). Histology demonstrated a gelatinous substance, which separated amnion and chorio-decidua, in particular at the cervical site. This gelatinous substance contained hyaluronan at a concentration of 3.0 microg/mg wtw.

CONCLUSION

It is well established that prelabour fetal membranes are considerably stronger than postlabour fetal membranes. Two features may explain this; a weakening of the amnion combined with a separation of amnion and chorio-decidua. The biomechanical changes are consistent with the decrease in collagen and decorin, and the increase in hyaluronan and biglycan demonstrated in this study. The separation of the membranes is caused by the formation of a gelatinous substance, rich in hyaluronan. The results indicate that the biomechanical changes are not merely secondary to the stress of labour but that an active maturation process is involved.

The Young's modulus of fetal preterm and term amniotic membranes

OBJECTIVE

To examine the Young's modulus of the human amniotic membranes, as well as its relationship to gestational age. To determine whether cellular and material-related parameters affect this modulus.

STUDY DESIGN

In a prospective study at the Obstetric outpatient clinic of the University Hospital Zurich Young's modulus, thickness and mesenchymal:epithelial cell ratio of amniotic membranes of preterm (N=23) and term (N=40) placentae were examined. Significance (P<0.05) was calculated with the Mann-Whitney two-sample rank sum test and Wilcoxon signed rank test, while correlations were made using the Spearman's correlation.

RESULTS

The Young's modulus of preterm amniotic membranes was significantly higher than that of term membranes. It varied within the same amniotic membrane. The thickness of the amnion in both preterm and term membranes did not differ significantly. The thinner the preterm and term amniotic membranes, the higher the Young's modulus was. There was no relation to the mesenchymal:epithelial cell ratio in the amnion.

CONCLUSIONS

Preterm amniotic membranes are stiffer than term amniotic membranes. Tentatively, we hypothesise that there may be a correlation between the extracellular matrix components and the elastic properties of the membrane.

Matrix metalloproteinase-8 is expressed in human chorion during labor

OBJECTIVE

The purpose of this study was to investigate the expression of matrix metalloproteinase-8 by human fetal membranes during labor.

STUDY DESIGN

Fetal membranes were obtained from women who underwent normal labor or elective cesarean delivery at term. Matrix metalloproteinase-8 levels in fetal membranes were determined by enzyme-linked immunosorbent assay and Western blot; the expression of the matrix metalloproteinase-8 gene was detected by reverse transcription-polymerase chain reaction. Immunohistochemistry and in situ hybridization was performed to localize matrix metalloproteinase-8 protein and messenger RNA in intact membranes.

RESULTS

Matrix metalloproteinase-8 protein levels were increased 5-fold in fetal membranes from labor compared with membranes that were obtained from cesarean delivery. Western blots confirmed the presence of matrix metalloproteinase-8 in protein extracts. Reverse transcription-polymerase chain reaction, in situ hybridization, and immunohistochemistry demonstrated that matrix metalloproteinase-8 messenger RNA and protein were expressed almost exclusively in the chorion after labor.

CONCLUSION

We conclude that matrix metalloproteinase-8 is produced primarily by chorionic cells in human fetal membranes and that the level of matrix metalloproteinase-8 protein and messenger RNA expression in fetal membranes increases during labor.

Neutrophil elastase and secretory leukocyte protease inhibitor in prelabor rupture of membranes, parturition and intra-amniotic infection

OBJECTIVE

Neutrophil elastase (NE), a multifunctional serine protease stored in azurophilic granules of mature neutrophils, is capable of intracellular degradation of proteins during phagocytosis and extracellular degradation of connective tissue during an inflammatory process. Secretory leukocyte protease inhibitor (SLPI) is a natural NE inhibitor present in amniotic fluid, fetal membranes and cervical mucus. An imbalance between NE and SLPI has been implicated as a mechanism of abnormal tissue destruction in chronic inflammatory diseases. The purpose of this study was to determine if parturition, premature rupture of the membranes (PROM) and microbial invasion of the amniotic cavity are associated with changes in amniotic fluid concentrations of NE and SLPI.

STUDY DESIGN

Amniotic fluid was retrieved by amniocentesis from 380 patients in the following groups: (1) preterm labor and intact membranes without microbial invasion of the amniotic cavity who delivered at term (n = 13) or prematurely (n = 26), and preterm labor with microbial invasion of the amniotic cavity (n = 9); (2) preterm PROM with (n = 34) and without (n = 51) microbial invasion of the amniotic cavity; and (3) term gestation without microbial invasion of the amniotic cavity with intact membranes not in labor (n = 63), in labor (n = 158), and with rupture of membranes not in labor (n = 26). Microbial invasion of the amniotic cavity was determined by a positive amniotic fluid culture for micro-organisms including aerobic, anaerobic and Mycoplasma species. NE and SLPI amniotic fluid levels were determined by highly specific and sensitive immunoassays.

RESULTS

Preterm PROM was associated with a significant increase in the amniotic fluid concentration of NE. Microbial invasion of the amniotic cavity was associated with a significant increase in the amniotic fluid concentration of NE in women with preterm labor and intact membranes, as well as in women with preterm PROM. Term and preterm parturition was associated with a significant increase in the amniotic fluid concentration of NE. In the absence of microbial invasion of the amniotic cavity, preterm and term PROM were associated with a significant reduction in the amniotic fluid concentration of SLPI.

CONCLUSION

Preterm PROM, microbial invasion of the amniotic cavity, and parturition at term and preterm are associated with a significant increase in the amniotic fluid concentration of NE. PROM is associated with a reduced amniotic fluid concentration of SLPI.

Identification of matrix metalloproteinase-9 in amniotic fluid and amniochorion in spontaneous labor and after experimental intrauterine infection or interleukin-1 beta infusion in pregnant rhesus monkeys

OBJECTIVE

The purpose of this study was to examine the roles of intrauterine infection, inflammation, and spontaneous labor on the expression of matrix metalloproteinase-9 in fetal membranes and amniotic fluid of late pregnant rhesus monkeys.

STUDY DESIGN

Pregnant rhesus monkeys with timed gestations were chronically catheterized to allow serial sampling of amniotic fluid before and during experimentally induced intrauterine inflammation. Six animals received group B streptococci into the chorionic-decidual space, and 4 animals received intra-amniotic interleukin-1 beta infusions (10 microg). Three additional animals were serially sampled by amniocentesis through late pregnancy until spontaneous term labor. Amniotic fluid samples were examined by zymography for matrix metalloproteinase-9 and -2 and Western immunoblot for matrix metalloproteinase-9 and -2 and tissue inhibitors of metalloproteinase-1 and -2. Fetal membranes were obtained at cesarean delivery during labor (before rupture), formalin fixed, and embedded in paraffin for immunocytochemistry of matrix metalloproteinase-9 and in situ hybridization of matrix metalloproteinase-9 messenger RNA. Tissues from 2 additional animals were collected as age-matched non-labor controls.

RESULTS

In amniotic fluid, the 92-kd latent matrix metalloproteinase-9 was detectable in late pregnancy and increased dramatically, followed by the appearance of the 83-kd active form before spontaneous term delivery. Amniotic fluid matrix metalloproteinase-2 levels (both latent and active forms) remained relatively constant throughout pregnancy and in labor. Both bacteria and interleukin-1 beta rapidly increased the signal of latent matrix metalloproteinase-9 without a consistent increase in the active form before the onset of labor. Chorionic-decidual inoculation of group B streptococci was followed by the expression of latent matrix metalloproteinase-9 before the appearance of group B streptococci in amniotic fluid or the onset of labor. Matrix metalloproteinase-2 increased to a new steady-state level or remained unchanged after group B streptococci inoculation or interleukin-1 beta infusion, respectively. Amniotic fluid tissue inhibitors of metalloproteinase-1 declined and tissue inhibitors of metalloproteinase-2 remained unchanged during early group B streptococci infection, after interleukin-1 beta infusion and on the day of spontaneous term labor. However, both tissue inhibitors of metalloproteinase-1 and -2 levels increased after preterm labor that was induced by group B streptococci. Immunocytochemistry localized matrix metalloproteinase-9 protein to amnion and chorion epithelial and mesenchymal cells and decidual stromal cells. Granular matrix metalloproteinase-9 staining was observed in the connective tissue layer of inflamed fetal membranes. In situ hybridization for messenger RNA confirmed the production of matrix metalloproteinase-9 by amnion and chorion.

CONCLUSION

Bacterial- and interleukin-1 beta-induced preterm labor and spontaneous term labor are preceded and accompanied by progressive increases in amniotic fluid matrix metalloproteinase-9 (92 kd) in rhesus monkeys. Amniotic fluid matrix metalloproteinase-9 may serve as a clinical marker for the onset of both preterm and term labor.

Proteoglycans and hyaluronan in human fetal membranes

OBJECTIVE

The aim of this study was to describe the distributions of major extracellular matrix components, such as proteoglycans, collagen and hyaluronan, in the fetal membranes at term.

STUDY DESIGN

Fetal membranes were obtained from elective cesarean deliveries at term. Guanidinium extracts were analyzed for proteoglycans with alcian blue precipitation, sodium dodecyl sulfate- polyacrylamide gel electrophoresis, and Western blotting and for hyaluronan with a radioimmunoassay. Collagen was measured by estimating hydroxyproline content. Tissue sections were immunostained for decorin and biglycan and stained for hyaluronan with a biotin-labeled hyaluronan-binding protein.

RESULTS

The fetal membranes contained predominantly smaller proteoglycans, such as biglycan and decorin. The amnion consisted of typical fibrous connective tissue with a high concentration of collagen. The amnion was dominated by decorin located in close connection with the collagen fibrils. The chorion was composed of a fibroblastic part containing collagen and decorin and a trophoblastic part mainly containing biglycan. In addition, large amounts of hyaluronan were found, especially in the amnion and in the decidual cell layers.

CONCLUSION

The distributions of proteoglycans, collagen, and hyaluronan in human fetal membranes may explain the biomechanical properties of this tissue. We suggest that changes in the relative proportions of these extracellular molecules are crucial for the proposed maturation process in the fetal membranes during the last weeks of pregnancy.

The hydroxyproline content of amnion and prelabour rupture of the membranes

OBJECTIVE

To determine whether prelabour rupture of the membranes is caused by a generalised reduction in amniotic collagen.

SETTING

Leeds General Infirmary, UK.

STUDY DESIGN

The hydroxyproline content of amnion from 55 women with prelabour rupture of the membranes was compared with that from 50 women whose membranes ruptured during labour and 28 women who were delivered by elective caesarean section.

RESULTS

No association was found between hydroxyproline content and the timing of membrane rupture. Hydroxyproline content was inversely correlated with gestation. The hydroxyproline content per cm(2) amnion was significantly increased in cases which had laboured. There was a strong correlation between the mechanical properties and the hydroxyproline content of amnion.

CONCLUSIONS

PROM is not associated with a generalised reduction in the hydroxyproline content of amnion.

Myofibroblast differentiation in the connective tissues of the amnion and chorion of term human fetal membranes-implications for fetal membrane rupture and labour

An area of the fetal membranes, within the rupture tear after spontaneous delivery at term, exhibits altered morphology compared to more distal sites. It is characterized by marked swelling of the amniotic and chorionic connective tissue layers, consistent with structural weakness, and a marked reduction of the thickness of both the cytotrophoblast and decidual layers. These features, albeit less extreme, have been identified in fetal membranes in the lower uterine pole in patients prior to labour. In this study of pre-labour, labour-affected and post-labour term fetal membranes, we report that these regions are associated with an alteration in the phenotype of the vimentin positive mesenchymal cell population of the chorionic connective tissue reticular layer, and are consistent with myofibroblastic differentiation, i.e. alpha-smooth muscle actin (alpha-sma) expression. In the reticular layer of the lower uterine pole biopsies in the labour-affected group the numbers and densities of alpha-sma immunoreactive positive cells were 17-fold (P=0.04) and 8.5-fold (P=0.02) higher than in mid-zone biopsies. After delivery, in rupture line biopsies the numbers and densities were 50-fold (P=0. 002) and 36-fold (P=0.003) higher compared to mid zone biopsies. The percentage of the vimentin positive population positive for alpha-sma was 2-5 per cent in mid-zone biopsies compared to 49 per cent (P=0.03) in the labour-affected 'cervical' biopsies and 69 per cent (P=0.05) in the rupture line biopsies. Within the tear sites, alpha-sma positive cells were also detected within the fibroblastic layer of the amniotic connective tissue. Although there was no significant difference between the numbers and density of alpha-sma cells in the reticular layers between mid and lower uterine pole biopsies in the pre-labour group, in a proportion of patients the biopsies were similar to labour-affected biopsies indicating that this alteration occurs prior to clinically apparent labour in these patients. The incidence of alpha-sma positive cells in the reticular layer correlated with morphological changes within the fetal membranes, for example thickness of reticular (r(2)=0.349, P=0.0006) and amniotic connective tissue layers (r(2)=0.389, P=0.0002). This suggests that cellular activities associated with myofibroblastic differentiation in the reticular layer of the chorion may be associated with the observed connective tissue changes, fetal membrane rupture and labour.

Local collagen turnover in human foetal membranes during full term vaginal delivery

OBJECTIVES

To investigate if changes in local metabolism of collagens type I and type III may contribute to the term rupture of the foetal membranes.

STUDY DESIGN

In extracts from membranes taken along the rupture line and near the site of the umbilical cord attachment to the placenta, we measured concentrations of specific markers of collagen synthesis, namely C-terminal propeptide of type I collagen (PICP) and N-terminal propeptide of type III collagen (PIIINP), as well as the concentration of the pyridinoline cross-linked C-terminal telopeptide of type I collagen (ICTP), which reflects the rate of collagen type I breakdown.

RESULTS

The mean concentrations of PICP and PIIINP did not differ statistically between the two examined groups of samples. The mean ICTP concentration was threefold higher in extracts prepared from samples taken near the rupture site, than from membranes derived from the proximity of the umbilical cord attachment.

CONCLUSIONS

Term rupture of foetal membranes is accompanied by increased local degradation of type I collagen fibrils at the rupture site, whereas the biosynthesis of collagen types I and III remains unchanged.

Urinary trypsin inhibitor suppresses the production of interstitial procollagenase/proMMP-1 and prostromelysin 1/proMMP-3 in human uterine cervical fibroblasts and chorionic cells

The mechanisms by which urinary trypsin inhibitor (UTI) prevents preterm premature rupture of fetal membrane and premature cervical ripening were investigated. We, therefore, examined the effects of UTI on the production of matrix metalloproteinases (MMPs) which closely participate in the breakdown of extracellular matrix in cultured human uterine cervical fibroblasts and human chorionic cells. UTI suppressed specifically the production of interstitial procollagenase/proMMP-1 and prostromelysin 1/proMMP-3 from both cells in a dose-dependent manner (0.32-1.28 microM). This suppression was accompanied by a decrease in steady-state levels of their mRNAs. These results indicate for the first time that UTI down-regulates the production of proMMP-1 and proMMP-3 accompanying with the decrease in the expression of their mRNAs, and therefore UTI actually participates in the maintenance of fetal membranes and/or uterine cervix by overall suppression of MMP production along with the known inhibitory actions towards serine proteinases.

The pathobiology of premature rupture of membranes

Premature rupture of membranes arises from what are likely multifaceted and multistep pathogenic pathways. Pathophysiological processes may involve both endogenous and exogenous fetal and maternal factors. This article reviews and analyzes information regarding, first, the form and function of fetal membranes; second, how membranes physically fail (rupture) at term and preterm gestations; and third, evaluates if we can reduce risks of rupture using physiological understanding and evidence-based clinical studies.

Increased matrix metalloproteinase activity and reduced tissue inhibitor of metalloproteinases-1 levels in amniotic fluids from pregnancies complicated by premature rupture of membranes

OBJECTIVES

It has been suggested that increased matrix metalloproteinases activity promotes the weakening of the amniochorion during normal and premature rupture of membranes. This study was designed to determine whether levels of matrix metalloproteinases and the tissue inhibitor of metalloproteinases-1 in amniotic fluid change in a pattern consistent with this hypothesis.

STUDY DESIGN

Gelatinolytic activity, measured by a soluble substrate assay and zymography, and the concentrations of tissue inhibitor of metalloproteinases-1 were estimated in amniotic fluid obtained from (1) normal early gestations, (2) normal term pregnancies with labor, (3) normal term pregnancies without labor, and (4) pregnancies complicated by premature rupture of membranes. The 92 kd type IV collagenase (matrix metalloproteinase-9) was also detected in amniotic fluid by Western blotting.

RESULTS

Matrix metalloproteinase activities were higher in amniotic fluid from normal term pregnancies with labor and pregnancies complicated by premature rupture of membranes than from early pregnancies and term gestations without labor. The amniotic fluid from term pregnancies with labor or pregnancies with premature rupture of membranes contained several gelatinases, as revealed by zymography. The major amniotic fluid gelatinolytic activity in premature rupture of membranes and term pregnancies with labor corresponded to matrix metalloproteinase-9. Tissue inhibitor of metalloproteinases-1 concentrations were highest in early-pregnancy amniotic fluid, followed by term gestation with labor, term gestation without labor, and premature rupture of membranes.

CONCLUSIONS

Normal labor and premature rupture of membranes are associated with increased levels of matrix metalloproteinases, particularly matrix metalloproteinase-9 in amniotic fluid. Premature rupture of membranes is associated with reduced levels of tissue inhibitor of metalloproteinases-1. The imbalance between matrix metalloproteinases and tissue inhibitor of metalloproteinases-1 in amniotic fluid may reflect a disorder that promotes premature rupture of membranes.

Secretory leukocyte protease inhibitor in the cervical mucus and in the fetal membranes

OBJECTIVE

The purpose was to determine the concentration of leukocyte elastase and SLPI in the cervical mucus plug, cervical tissue, fetal membranes, amniotic fluid and serum from pregnant women.

STUDY DESIGN

Samples were analysed using radioimmunoassay, immunodiffusion, immunohistological and enzyme assay techniques. Statistical comparisons were performed by the Mann-Whitney two-sample rank sum test.

RESULTS

Concentrations of SLPI and elastase in cervical tissue are significantly increased during pregnancy and after delivery. Very high concentrations of SLPI and elastase were found in the cervical mucus plug. The concentrations of SLPI and elastase in human fetal membranes are highest at the rupture site. The concentration of elastase in amnion from preterm delivery was significantly higher than in amnion from term deliveries.

CONCLUSION

The high molar ratio of SLPI/elastase in the cervical mucus plug suggests that inhibition of elastase is important during normal pregnancy. The role of SLPI may be protection of the fetal membranes and cervical tissue.

Structural characteristics of term human fetal membranes: a novel zone of extreme morphological alteration within the rupture site

OBJECTIVE

To determine the structural characteristics of the rupture site of term fetal membranes (amniochorion and decidua) that rupture spontaneously after the onset of labour.

DESIGN

Fourteen term fetal membranes were examined immediately after delivery at the light microscope level. Multiple samples were taken along the whole rupture site and long an axis between this site and placental edge. Morphometric analysis of the thickness of the constituent layers of the fetal membranes was performed.

SETTING

Leicester Royal Infirmary Maternity Hospital.

RESULTS

A restricted zone of extreme altered morphology, characterised by marked swelling and disruption of the connective tissue, thinning of the trophoblast layer and thinning or absence of decidua, was identified in the rupture site of all patients. Morphometric analysis of the thickness of membrane layers showed that these changes and the ratio between the thickness of the connective tissue layers and that of the trophoblast and decidua (termed fetal membrane morphometric index) were significant between the zone of extreme altered morphology and the rest of the membranes.

CONCLUSIONS

The morphological features of the zone of extreme altered morphology suggests that it represents an area of structural weakness of the membranes. Since this zone did not include the whole length of the rupture site, it is likely that it was present before membrane rupture and was generated during pregnancy. We hypothesise that the zone of extreme altered morphology represents the site of initial rupture after which the tear is transmitted through the membranes to produce the rupture site. It is possible that if these changes become more extreme, then prelabour membrane rupture may occur. Further characterisation of this zone may help to understand the mechanism of its genesis and its role in predisposing the fetal membranes to rupture.

Different biomechanical properties of human fetal membranes obtained before and after delivery

The aim of this study was to elucidate whether the mechanical properties of fetal membranes change during late pregnancy and labour. Membranes delivered by elective caesarean section in week 38 showed different load-strain curves to membranes obtained after spontaneous vaginal delivery at term. A major change in mechanical properties was a decrease in strength of the intact chorioamniotic membrane from 1.39 N to 0.98 N (width of biopsy 4 mm), mainly due to loss of strength of the amniotic component, from 1.27 N to 0.72 N. Moreover, the extensibility of the chorionic component (epsilon Fmax) increased after vaginal delivery from 0.42 to 0.54, resulting in a two-component behaviour of the intact chorioamniotic membrane and further decrease of strength. Based on these observations it is suggested that the amnion is attached to the chorion, act biomechanically in parallel and possess relatively high mechanical strength during pregnancy. After vaginal delivery the two membranes are separated, and pronounced changes are induced in their mechanical properties.

Human amniotic fluid modulation of collagenase production in cultured fibroblasts. A model of fetal membrane rupture

The participation of a mechanical factor as the only cause of rupture of fetal membranes during normal labor or premature rupture has been criticized, and the involvement of an enzymatic mechanism has been proposed. In this study we analyzed the effect of human amniotic fluids at different gestational ages on the collagenase synthesis of cultured fibroblasts. Our results show that term amniotic fluids are capable of inducing the synthesis of collagenase and other proteases in fibroblasts, as revealed by selective increases in collagenase activity and in immunoreactive collagenase. Nonterm amniotic fluids failed to do the same. This phenomenon is proposed as a model for studying the collagen degradation of fetal membranes during term gestation.

Biomechanical analysis of human chorioamniotic membranes

The biomechanical properties of human fetal membranes were analyzed by means of a materials testing machine. Special attention was paid to the biomechanical properties of the intact chorioamniotic membrane and the amniotic and chorionic components, separately, and thickness and storage of membrane samples. The load-strain and stress-strain relationships, and parameters calculated from the curves: extensibility, strength, elastic stiffness and failure energy, express the visco-elastic behavior of these membranes. The mechanical properties of the chorioamniotic membranes are determined by the interaction between the amniotic and chorionic components of the membrane. The strength of the intact chorioamniotic membrane, however, is primarily determined by the amniotic component, because the amniotic component is much less extensible. Thus, the chorionic component only contributes 10-15% of the strength when the amniotic component breaks. The chorionic component is twice as extensible as the amniotic component. Samples of fetal membranes can be stored at -70 degrees C, with no significant changes in the biomechanical properties. No significant differences were found between specimens, which were oriented in parallel with and at right angles to the placental edge. Small samples can be analysed and the localization of samples in relation to the placental edge and rupture site of the membranes can be standardized. The method is well suited for studies of premature rupture of fetal membranes.