Intrauterine endotoxin infusion in rat pregnancy induces preterm delivery and increases placental prostaglandin F2alpha metabolite levels

Maternal Infection and Preterm Birth: From Molecular Basis to Clinical Implications

As the leading cause of neonatal morbidity and mortality, preterm birth is recognized as a major public health concern around the world. The purpose of this review is to analyze the connection between infections and premature birth. Spontaneous preterm birth is commonly associated with intrauterine infection/inflammation. The overproduction of prostaglandins caused by the inflammation associated with an infection could lead to uterine contractions, contributing to preterm delivery. Many pathogens, particularly Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis, Gardnerella vaginalis, Ureaplasma urealyticum, Mycoplasma hominis, Actinomyces, Candida spp., and Streptococcus spp. have been related with premature delivery, chorioamnionitis, and sepsis of the neonate. Further research regarding the prevention of preterm delivery is required in order to develop effective preventive methods with the aim of reducing neonatal morbidity.

Tools, techniques, and future opportunities for characterizing the mechanobiology of uterine myometrium

The myometrium is the smooth muscle layer of the uterus that generates the contractions that drive processes such as menstruation and childbirth. Aberrant contractions of the myometrium can result in preterm birth, insufficient progression of labor, or other difficulties that can lead to maternal or fetal complications or even death. To investigate the underlying mechanisms of these conditions, the most common model systems have conventionally been animal models and human tissue strips, which have limitations mostly related to relevance and scalability, respectively. Myometrial smooth muscle cells have also been isolated from patient biopsies and cultured in vitro as a more controlled experimental system. However, in vitro approaches have focused primarily on measuring the effects of biochemical stimuli and neglected biomechanical stimuli, despite the extensive evidence indicating that remodeling of tissue rigidity or excessive strain is associated with uterine disorders. In this review, we first describe the existing approaches for modeling human myometrium with animal models and human tissue strips and compare their advantages and disadvantages. Next, we introduce existing in vitro techniques and assays for assessing contractility and summarize their applications in elucidating the role of biochemical or biomechanical stimuli on human myometrium. Finally, we conclude by proposing the translation of "organ on chip" approaches to myometrial smooth muscle cells as new paradigms for establishing their fundamental mechanobiology and to serve as next-generation platforms for drug development.

Maternal Obesity and the Uterine Immune Cell Landscape: The Shaping Role of Inflammation

Inflammation is often equated to the physiological response to injury or infection. Inflammatory responses defined by cytokine storms control cellular mechanisms that can either resolve quickly (i.e., acute inflammation) or remain prolonged and unabated (i.e., chronic inflammation). Perhaps less well-appreciated is the importance of inflammatory processes central to healthy pregnancy, including implantation, early stages of placentation, and parturition. Pregnancy juxtaposed with disease can lead to the perpetuation of aberrant inflammation that likely contributes to or potentiates maternal morbidity and poor fetal outcome. Maternal obesity, a prevalent condition within women of reproductive age, associates with increased risk of developing multiple pregnancy disorders. Importantly, chronic low-grade inflammation is thought to underlie the development of obesity-related obstetric and perinatal complications. While diverse subsets of uterine immune cells play central roles in initiating and maintaining healthy pregnancy, uterine leukocyte dysfunction as a result of maternal obesity may underpin the development of pregnancy disorders. In this review we discuss the current knowledge related to the impact of maternal obesity and obesity-associated inflammation on uterine immune cell function, utero-placental establishment, and pregnancy health.

Microorganisms in the Placenta: Links to Early-Life Inflammation and Neurodevelopment in Children

Prenatal exposure to various stressors can influence both early and later life childhood health. Microbial infection of the intrauterine environment, specifically within the placenta, has been associated with deleterious birth outcomes, such as preterm birth, as well as adverse neurological outcomes later in life. The relationships among microorganisms in the placenta, placental function, and fetal development are not well understood. Microorganisms have been associated with perinatal inflammatory responses that have the potential for disrupting fetal brain development. Microbial presence has also been associated with epigenetic modifications in the placenta, as well other tissues. Here we review research detailing the presence of microorganisms in the placenta and associations among such microorganisms, placental DNA methylation, perinatal inflammation, and neurodevelopmental outcomes.

Clinical chorioamnionitis at term VII: the amniotic fluid cellular immune response

OBJECTIVES

1) To characterize the cellular composition of the amniotic fluid of patients diagnosed with clinical chorioamnionitis at term, as a function of the presence or absence of microorganisms determined by cultivation techniques, and 2) to characterize the cytokine production by white blood cells present in the amniotic fluid using flow cytometry-based techniques.

MATERIALS AND METHODS

Amniotic fluid samples from 20 women who had the diagnosis of clinical chorioamnionitis at term were analyzed using cultivation techniques (for aerobic and anaerobic bacteria as well as genital Mycoplasmas). Amniotic fluid IL-6 concentrations were determined by an enzyme-linked immunosorbent assay. Amniotic fluid leukocytes were visualized by using hematoxylin and eosin staining and immunofluorescence. Immunophenotyping of surface markers and cytokines was performed in amniotic fluid leukocytes using flow cytometry.

RESULTS

1) Neutrophils (CD45+CD15+ cells) were the most common leukocyte subset found in the amniotic fluid, followed by monocytes (CD45+CD14+ cells); other white blood cells (such as lymphocytes and natural killer cells) were scarce in the amniotic fluid; 2) the absolute counts of neutrophils and monocytes were significantly higher in patients with microorganisms found in the amniotic fluid than in those without detectable microorganisms, using cultivation techniques; 3) there was a significant correlation between the absolute counts of neutrophils and monocytes determined by flow cytometry (Spearman's correlation=0.97; P<0.001); 4) there was a significant correlation between the absolute white blood cell count determined with a hemocytometer chamber and by flow cytometric analysis (Spearman's correlation=0.88; P<0.001); and 5) the profile of cytokine expression differed between monocytes and neutrophils; while neutrophils predominantly produced TNF-α and MIP-1β, monocytes expressed higher levels of IL-1β and IL-1α.

CONCLUSION

Flow cytometry analysis of the amniotic fluid of patients with intra-amniotic infection and clinical chorioamnionitis at term demonstrated that neutrophils and monocytes are the most common cells participating in the inflammatory process. We have characterized, for the first time, the differential cytokine expression by these cells in this important complication of pregnancy.

Rosiglitazone Regulates TLR4 and Rescues HO-1 and NRF2 Expression in Myometrial and Decidual Macrophages in Inflammation-Induced Preterm Birth

INTRODUCTION

Elevated inflammation accounts for approximately 30% of preterm birth (PTB) cases. We previously reported that targeting the peroxisome proliferator-activated receptor gamma (PPARγ) pathway reduced the incidence of PTB in the mouse model of endotoxin-induced PTB. The PPARγ has proven anti-inflammatory functions and its activation via rosiglitazone significantly downregulated the systemic inflammatory response and reduced PTB and stillbirth rate by 30% and 41%, respectively, in our model. Oxidative stress is inseparable from inflammation, and rosiglitazone has a reported antioxidative activity. In the current study, we therefore aimed to evaluate whether rosiglitazone treatment had effects outside of inflammatory pathway, specifically on the antioxidation pathway in our model.

METHODS

Pregnant C57BL/6J mice (E16.5) were treated with phosphate-buffered saline (PBS), rosiglitazone (Rosi), lipopolysaccharide (LPS; 10µg in 200µL 1XPBS), or LPS + Rosi (6 hours after the LPS injection). The myometrial and decidual tissues were collected and processed for macrophage isolation using magnetic cell sorting and F4/80+ antibody. Expression levels of antioxidative factors- Nrf2 and Ho-1-along with the LPS receptor Tlr4 were quantified by quantitative polymerase chain reaction. The protein levels were assessed by immunofluorescence staining.

RESULTS

Both the decidual and myometrial macrophages from the LPS-treated animals showed significantly lowered expression of Ho-1 and Nrf2 and higher expression of Tlr4 when compared to the PBS control group. The macrophages from the animals in the LPS + Rosi group had significantly elevated expression of Ho-1 and Nrf2 and downregulated expression of Tlr4 when compared to the LPS group.

CONCLUSION

Rosiglitazone administration prevents PTB by downregulating inflammation and upregulating antioxidative response.

Interleukin (IL)-1 in rat parturition: IL-1 receptors 1 and 2 and accessory proteins abundance in pregnant rat uterus at term - regulation by progesterone

The role of interleukin-1 (IL-1), a pro-inflammatory cytokine, in parturition is typically noted by changes in its concentrations. Studying the expression of its receptor family, IL-1 receptor (IL-1R) 1, IL-1R2, IL-1R accessory protein (IL-1RAcP), and its predominantly brain isoform, IL-1RAcPb, during late gestation in the uterus in the Long-Evans rat is another. We assessed changes in their mRNA and protein relative abundance in the uterus and compared IL-1RAcP and IL-1RAcPb mRNA abundance in uterus, cervix, ovaries, placenta, and whole blood of Long-Evans rats during late gestation or in RU486 and progesterone-treated dams using quantitative real-time PCR and western immunoblotting. IL-1R1, IL-1RAcP, and IL-1RAcPb mRNA abundance significantly increased in the uterus at delivery whereas IL-1R2 mRNA abundance significantly decreased. IL-1R1 protein increased at term and IL-1R2 protein decreased at term compared to nonpregnant uteri. IL1-RAcPb mRNA abundance was less than IL-1RAcP, but in the lower uterine segment it was the highest of all tissues examined. RU486 stimulated preterm delivery and an increase in IL-1R1 mRNA abundance whereas progesterone administration extended pregnancy and suppressed the increase in IL-1R1. These data suggest that changes in uterine sensitivity to IL-1 occur during late gestation and suggest another level of regulation for the control of delivery. The roles for IL-1RAcP and IL-1RAcPb need to be determined, but may relate to different intracellular signaling pathways.

An imbalance between innate and adaptive immune cells at the maternal-fetal interface occurs prior to endotoxin-induced preterm birth

Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality worldwide. A transition from an anti-inflammatory state to a pro-inflammatory state in the mother and at the maternal-fetal interface has been implicated in the pathophysiology of microbial-induced preterm labor. However, it is unclear which immune cells mediate this transition. We hypothesized that an imbalance between innate and adaptive immune cells at the maternal-fetal interface will occur prior to microbial-induced preterm labor. Using an established murine model of endotoxin-induced PTB, our results demonstrate that prior to delivery there is a reduction of CD4+ regulatory T cells (Tregs) in the uterine tissues. This reduction is neither linked to a diminished number of Tregs in the spleen, nor to an impaired production of IL10, CCL17, or CCL22 by the uterine tissues. Endotoxin administration to pregnant mice does not alter effector CD4+ T cells at the maternal-fetal interface. However, it causes an imbalance between Tregs (CD4+ and CD8+), effector CD8+ T cells, and Th17 cells in the spleen. In addition, endotoxin administration to pregnant mice leads to an excessive production of CCL2, CCL3, CCL17, and CCL22 by the uterine tissues as well as abundant neutrophils. This imbalance in the uterine microenvironment is accompanied by scarce APC-like cells such as macrophages and MHC II+ neutrophils. Collectively, these results demonstrate that endotoxin administration to pregnant mice causes an imbalance between innate and adaptive immune cells at the maternal-fetal interface.

A Cross-Species Analysis of Animal Models for the Investigation of Preterm Birth Mechanisms

BACKGROUND

Spontaneous preterm birth is the leading cause of neonatal morbidity and mortality worldwide. The ability to examine the exact mechanisms underlying this syndrome in humans is limited. Therefore, the study of animal models is critical to unraveling the key physiologic mechanisms that control the timing of birth. The purpose of this review is to facilitate enhanced assimilation of the literature on animal models of preterm birth by a broad range of investigators.

METHODS

Using classical systematic and informatics search techniques of the available literature through 2012, a database of intact animal models was generated. Research librarians generated a list of articles using multiple databases. From these articles, a comprehensive list of Medical Subject Headings (MeSH) was created. Using mathematical modeling, significant MeSH descriptors were determined, and a MEDLINE search algorithm was created. The articles were reviewed for mechanism of labor induction categorized by species.

RESULTS

Existing animal models of preterm birth comprise specific interventions to induce preterm birth, as no animal model was identified that exhibits natural spontaneous preterm birth at an incidence comparable to that of the humans. A search algorithm was developed which when used results in a comprehensive list of agents used to induce preterm delivery in a host of animal species. The evolution of 3 specific animal models--sheep, mice, and rats--has demonstrated a clear shift in focus in the literature from endocrine to inflammatory agents of preterm birth induction.

CONCLUSION

The process of developing a search algorithm to provide efficient access to information on animal models of preterm birth illustrates the need for a more precise organization of the literature to allow the investigator to focus on distinctly maternal versus fetal outcomes.

A rat pup model of cerebral palsy induced by prenatal inflammation and hypoxia

Animal models of cerebral palsy established by simple infection or the hypoxia/ischemia method cannot effectively simulate the brain injury of a premature infant. Healthy 17-day-pregnant Wistar rats were intraperitoneally injected with lipopolysaccharide then subjected to hypoxia. The pups were used for this study at 4 weeks of age. Simultaneously, a hypoxia/ischemia group and a control group were used for comparison. The results of the footprint test, the balance beam test, the water maze test, neuroelectrophysiological examination and neuropathological examination demonstrated that, at 4 weeks after birth, footprint repeat space became larger between the forelimbs and hindlimbs of the rats, the latency period on the balance beam and in the Morris water maze was longer, place navigation and ability were poorer, and the stimulus intensity that induced the maximal wave amplitude of the compound muscle action potential was greater in the lipopolysaccharide/hypoxia and hypoxia/ischemia groups than in the control group. We observed irregular cells around the periventricular area, periventricular leukomalacia and breakage of the nuclear membrane in the lipopolysaccharide/hypoxia and hypoxia/ischemia groups. These results indicate that we successfully established a Wistar rat pup model of cerebral palsy by intraperitoneal injection of lipopolysaccharide and hypoxia.

Intrauterine infection and preterm labor

Preterm labor is defined as labor that begins before 37 completed weeks of pregnancy. More than 12% of infants born in the USA are preterm. At least 40% of preterm births are associated with intrauterine infection. Toll-like receptors (TLRs) are members of a family of cell-surface proteins responsible for recognition of a diverse spectrum of bacterial, viral and fungal pathogens. TLRs initiate the host innate (i.e. non-adaptive) immune response, inducing a proinflammatory cascade involving cytokines, chemokines, prostaglandins, and other effector molecules that result in the characteristic phenomena of labor, such as uterine contractions and rupture of fetal membranes. These cascades may also be activated by mechanisms that are not primarily infectious but are accompanied by inflammatory responses. Now that the molecular mechanisms linking infection and labor have been, to a large extent, elucidated, the challenge is to identify points of overlap with non-infectious causes of labor and to find intervention strategies that can minimize the negative impact of preterm delivery.

Horse species symposium: a novel approach to monitoring pathogen progression during uterine and placental infection in the mare using bioluminescence imaging technology and lux-modified bacteria

Uterine and placental infections are the leading cause of abortion, stillbirth, and preterm delivery in the mare. Whereas uterine and placental infections in women have been studied extensively, a comprehensive examination of the pathogenic processes leading to this unsatisfactory pregnancy outcome in the mare has yet to be completed. Most information in the literature relating to late-term pregnancy loss in mares is based on retrospective studies of clinical cases submitted for necropsy. Here we report the development and application of a novel approach, whereby transgenically modified bacteria transformed with lux genes of Xenorhabdus luminescens or Photorhabdus luminescens origin and biophotonic imaging are utilized to better understand pathogen-induced preterm birth in late-term pregnant mares. This technology uses highly sensitive bioluminescence imaging camera systems to localize and monitor pathogen progression during tissue invasion by measuring the bioluminescent signatures emitted by the lux-modified pathogens. This method has an important advantage in that it allows for the potential tracking of pathogens in vivo in real time and over time, which was hitherto impossible. Although the application of this technology in domestic animals is in its infancy, investigators were successful in identifying the fetal lungs, sinuses, nares, urinary, and gastrointestinal systems as primary tissues for pathogen invasion after experimental infection of pregnant mares with lux-modified Escherichia coli. It is important that pathogens were not detected in other vital organs, such as the liver, brain, and cardiac system. Such precision in localizing sites of pathogen invasion provides potential application for this novel approach in the development of more targeted therapeutic interventions for pathogen-related diseases in the equine and other domestic species.

Vaginal and oral microbes, host genotype and preterm birth

Preterm birth (PTB) is a leading cause of infant mortality and morbidity in the US and across the globe. Infection and associated inflammation are important initiators for PTB pathways; an estimated 40% of PTBs are attributed to amniochorionic-decidual or systemic inflammation. Historically, intrauterine infections have been implicated in PTB; recent evidence suggests that infections remote from the fetal site may also be causative. There is strong epidemiological evidence that bacterial vaginosis and periodontitis--two syndromes characterized by perturbations in the normal vaginal and oral bacterial microflora, respectively--are linked to infection-associated PTB. Oral and vaginal environments are similar in their bacterial microbiology; identical bacterial species have been independently isolated in periodontitis and bacterial vaginosis. Periodontitis and bacterial vaginosis also share many behavioral and sociodemographic risk factors suggesting a possible common pathophysiology. Genetic polymorphisms in host inflammatory responses to infection are shared between bacterial vaginosis, periodontitis and PTB, suggesting common mechanisms through which host genotype modify the effect of abnormal bacterial colonization on preterm birth. We review the state of knowledge regarding the risk of PTB attributable to perturbations in bacterial flora in oral and vaginal sites and the role of host genetics in modifying the risk of infection-related PTB. We posit that bacterial species that are common in perturbed vaginal and oral sites are associated with PTB through their interaction with the host immune system.

Evidence for participation of uterine natural killer cells in the mechanisms responsible for spontaneous preterm labor and delivery

OBJECTIVE

The purpose of this study was to determine in a mouse model whether uterine natural killer (uNK) cell cytotoxic activation induces infection/inflammation-associated preterm labor and delivery.

STUDY DESIGN

Wild type or interleukin (IL)-10(-/-) mice were injected intraperitoneally with lipopolysaccharide on gestational day 14. Mice were either killed for collection of uteroplacental tissue, spleen, and serum or allowed to deliver. Uteroplacental tissue was used for histology and characterization of uNK cells.

RESULTS

Low-dose lipopolysaccharide treatment triggered preterm labor and delivery in IL-10(-/-), but not wild type mice, in a manner independent of progesterone levels. Preterm labor and delivery in IL-10(-/-) mice was associated with an increased number and placental infiltration of cytotoxic uNK cells and placental cell death. Depletion of NK cells or tumor necrosis factor (TNF)-alpha neutralization in these mice restored term delivery. Furthermore, TNF-alpha neutralization prevented uNK cell infiltration and placental cell apoptosis.

CONCLUSION

The uNK cell-TNF-alpha-IL-10 axis plays an important role in the genesis of infection/inflammation-induced preterm labor/delivery.

Failure of E. coli bacteria to induce preterm delivery in the rat

Background

We sought to develop a model of bacterially induced preterm delivery in rats to parallel similar models in mice.

Methods

Female Sprague-Dawley rats on day 17 of gestation (normal term = 21–22 days) were inoculated into the uterus with either 2 × 10⁹ – 7 × 10¹⁰ killed E. coli organisms, 1 – 4 × 10⁸ live E. coli or sterile solution. These inoculations were made either via trans-cervical catheter or by direct intrauterine injection at laparotomy. Animals were then observed for delivery for variable periods up to term. Necropsies were performed and fetal viability was assessed.

Results

No rats delivered prematurely after bacterial exposure (27 animals observed for at least 48 hours), and all animals followed to term (n = 3) delivered live pups. No dams exhibited signs of systemic illness. There was a statistically significant but small negative effect of killed E. coli on fetal viability (100% of 80 fetuses from 6 control pregnancies and 93% of 182 fetuses from 14 bacterially-treated pregnancies were alive at necropsy, p = 0.014). Live bacteria had a larger effect on fetal viability, with only 64% of 14 fetuses, 47% of 28 fetuses and 32% of 31 fetuses surviving after trans-cervical administration of 7 × 10⁷, 2 × 10⁸ and 4 × 10⁸ E. coli, respectively.

Conclusion

Unlike mice, it has proven difficult to induce preterm labor in the rat using E. coli as a stimulating agent. The relevant literature is reviewed and hypotheses are offered to explain this phenomenon.

Direct interaction of surfactant protein A with myometrial binding sites: signaling and modulation by bacterial lipopolysaccharide

Surfactant protein A (SFTPA1), a member of the collagenous lectin (collectin) family, was first described as a major constituent of lung surfactant, but has recently also been found in the female genital tract. Various microorganisms colonize this area and may cause intrauterine infection or trigger preterm labor. We found that SFTPA1 was not produced in the uterus. Instead, it was immunodetected transiently in rat myometrium at the end (Days 19 and 21) of gestation, but not postpartum, and in cultured myometrial cells. Fluorescence microscopy showed that Texas Red-labeled SFTPA1 bound to myometrial cells. This result was confirmed by biochemical approaches. [(125)I]-SFTPA1 bound to two myometrial cell proteins (55 and 210 kDa). This interaction was dependent on the integrity of the collagenlike domain of SFTPA1. SFTPA1 rapidly activated mitogen-activated protein kinase 1/3 (MAPK1/3) in myometrial cells. Bacterial lipopolysaccharide (LPS), an agent known to trigger uterine contractions and preterm birth, also activated MAPK1/3. The prolonged treatment of myometrial cells with LPS or SFTPA1 upregulated PTGS2 (COX2) protein levels. The addition of rough-type LPS to SFTPA1 blocked the interaction of SFTPA1 with its binding sites and the activation of MAPK1/3 and PTGS2 by SFTPA1. Our data provide the first demonstration of a direct effect of SFTPA1 on rat myometrial cells and inhibitory cross talk between SFTPA1 and LPS signals, providing new insight into the mechanisms of normal and preterm parturition.

Prior Cesarean: A Contraindication to Labor Induction?

In 2004, cesarean rates were the highest ever in the United States. Simultaneously, the vaginal birth after cesarean (VBAC) rate fell, largely a result of reports of uterine rupture associated with VBAC attempts. This chapter reviews the efficacy and safety of VBAC associated with labor induction. Mechanical and pharmacologic methods of labor induction (notably misoprostol) are associated with increased maternal and perinatal morbidity compared with spontaneous VBAC attempts. However, the absolute risks remain low. Labor induction is not contraindicated in women with a prior cesarean but sound judgment, clinical precautions and specific consent are required.

Toll-like receptors and their role in the trophoblast

The aim of this review is to discuss the role of Toll-like receptors at the maternal-fetal interface and the capacity of trophoblast cells to initiate innate immune responses towards infection. The maternal-fetal interface represents an immunologically unique site that must promote tolerance to the allogenic fetus, whilst maintaining host defense against a diverse array of possible pathogens. Clinical studies have shown a strong association between certain complications of pregnancy and intrauterine infections. Therefore, innate immune responses against microorganisms at the maternal-fetal interface may have a significant impact on the success of a pregnancy. There is growing evidence that trophoblast cells are able to recognize and respond to pathogens through the expression of Toll-like receptors, an important part of innate immunity. This review will discuss the role of Toll-like receptors at the maternal-fetal interface, the potential for trophoblast cells to function as components of the innate immune system and the impact TLR-mediated trophoblast responses may have on pregnancy outcome.

Inflammatory-mediated model of cerebral palsy with developmental sequelae

OBJECTIVE

Cerebral palsy (CP) is characterized by motor deficits. There is increasing evidence that CP may result from inflammatory and infection-mediated white matter damage. Our objective was to develop an inflammatory model for CP based on chronic lipopolysaccharide (LPS) exposure with a recognizable phenotype in offspring.

STUDY DESIGN

On gestational days 15, 17, and 19 (approximately 28-36 wks human gestation; rat length of gestation is 21 days), pregnant rats were intracervically injected with 0.15 mg/kg LPS (in 0.1 mL saline) or 0.1 mL saline for controls. Neonatal tests for sensory-motor milestones were performed on postnatal days 1 to 21 (LPS n = 25; control n = 26). Adult males were tested at 8 weeks on open field and rotarod for motor activity. Immunohistochemistry studies were performed to assess olygodendrocyte (OL) damage. Statistical analysis included Mann-Whitney U and analysis of variance (ANOVA) with P < .05 considered significant.

RESULTS

Immunohistochemistry revealed a decrease in the immature OL marker PLP on day 21 (P = .03) in LPS-exposed offspring, and an increase of the mature OL marker CNP on day 21 and at 8 weeks (P < .01, P < .001). LPS-exposed offspring were delayed achieving 3 motor milestones: negative geotaxis (P < .05), cliff aversion (P < .01), and surface righting (P = .05). They were also delayed in eye opening (P < .01). There was no difference between the 2 groups for the other tests. There was a trend towards decreased mean speed in LPS-exposed adults in open field testing (P = .08), but no differences observed in rotarod testing.

CONCLUSION

Using an animal model for CP that mimics a chronic intrauterine inflammation that results in decreased levels of PLP, a marker for early oligodendrocytes consistent with white matter damage, we have demonstrated a phenotype relevant to the human CP manifestations in the neonatal period. Nevertheless, adult animals were able to compensate to the damage. Further refinement is needed to improve the understanding of pathogenesis, as well as allow for testing preventative therapies.

No phenotype associated with established lipopolysaccharide model for cerebral palsy

OBJECTIVE

Cerebral palsy (CP) is associated with childhood spasticity, seizures, and paralysis. Oligodendrocyte damage resulting in periventicular leukomalacia (PVL) in the developing brain has been implicated. Animal models of CP have used prenatal hypoxia and infection with histopathology of PVL as the end point. To evaluate whether this histologic end point is associated with a CP phenotype, we reproduced a lipopolysaccharide (LPS) model for PVL, 1 and evaluated developmental, behavioral, and motor outcomes.

STUDY DESIGN

On gestational day 15, Fischer 344 rats were intracervically injected with .1 mg/kg LPS (n = 5) or saline (n = 4). After delivery, evaluation for developmental milestones was performed on days 1 to 21 (LPS = 45; control = 30 pups). Males were also tested at 2.5 months using open-field, rotarod, and anxiety tests. On day 21, 2 pups/litter were perfused for immunohistochemistry, and stained with 2 oligodendrocyte antibodies: 2', d'-cyclic nucleotide phosphodiesterase (CNP), and myelin proteolipid protein (PLP) with relative densities of staining assessed using NIH Image software. Statistical analysis included Mann-Whitney U and analysis of variance (ANOVA).

RESULTS

LPS pups demonstrated decreased CNP (P = .04) and PLP (P = .06) staining, replicating the model. There was no difference seen in neonatal weight, righting, negative geotaxis, cliff aversion, rooting, forelimb grasp, audio startle, air righting, eye opening, and activity. Surprisingly, LPS-exposed neonatal rats mastered forelimb placement (P < .01) and surface righting (P = .02) earlier than control rats. There were no differences between adult groups in open field distance traveled (P = .8), open-field locomotion time (P = .6), rotarod (P = .6), or anxiety (P = .7).

CONCLUSION

Histologic evidence of white matter damage can be replicated using an LPS model for intrauterine inflammation. Significant phenotypic differences consistent with the motor and cognitive damage sequelae of such lesions (ie, CP) were not demonstrated. When evaluating animal models, it is important to assess not only biochemical markers for human disease, but also clinically relevant phenotypes.

Animal models of preterm birth

Preterm birth continues to pose a significant clinical dilemma and contributes to both acute and long-term neonatal morbidity. Despite efforts, the incidence of preterm birth has not decreased, partly because of our lack of understanding of the mechanisms that trigger parturition. Animal models are essential research tools for investigating the pathways that promote preterm parturition and for testing therapeutic interventions. Growing evidence correlates infection or inflammation with preterm birth. Consequently, many investigators have created animal models that reflect these findings. Current models of preterm parturition include diverse species, varying means of inducing an inflammatory or infectious state, and different routes of administration. Although each of these models can advance our knowledge, it is important to understand their advantages, disadvantages and unique characteristics. An understanding of such models will hopefully promote continued research that will ultimately lead to a decrease in preterm birth and an improvement in neonatal outcome.

Placental lesions caused by experimental infection of Sprague-Dawley rats with Mycoplasma pulmonis

PROBLEM

Sprague-Dawley (SD) rats infected during pregnancy with Mycoplasma pulmonis display adverse pregnancy outcomes that are similar to those observed in women with chorioamnionitis and may provide a good model system for this disease. The placental lesions caused by this microorganism, however, have not been thoroughly characterized.

METHOD OF STUDY

Rats were infected with 10(7) colony-forming units (CFU) M. pulmonis or vehicle control on gestation day (gd) 14 and were euthanized on gd 16-18. Tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 4 microm, and stained with hematoxylin and eosin (H & E). The slides were coded and examined by a blinded pathologist using light microscopy.

RESULTS

Infection with M. pulmonis was associated with necrosis of trophoblast giant cells at gd 18. Significantly more neutrophils were observed in the decidual region of the apex of the placenta in M. pulmonis infected animals. The vast majority of neutrophils, however, were observed in the decidua in the lateral regions of the placenta and in the adjacent endometrium.

CONCLUSIONS

Infection of SD rats with M. pulmonis resulted in histological placentitis similar to that described in deciduitis of humans and represents a good model system for investigations into the pathophysiology of intrauterine infection. The influx of neutrophils seems to migrate from the endometrium towards the lateral regions of the placenta near Reichert's membrane and the divergence of the parietal yolk sac.

Maternal and fetal inflammatory responses in unexplained fetal death

OBJECTIVE

The role of intra-amniotic infection in the etiology of fetal death has been proposed. This study was conducted to determine the prevalence of microbial invasion of the amniotic cavity (MIAC) and the frequency of maternal and/or fetal inflammation in patients presenting with a fetal death.

METHODS

A prospective study was conducted in patients with a fetal death. Amniocenteses were performed for clinical indications (karyotype), as well as to assess the microbiological and cytological state of the amniotic cavity. Fluid was cultured for aerobic and anaerobic bacteria and genital mycoplasmas. An amniotic fluid white blood cell count and glucose determinations were also performed. Histological examination of the placenta was conducted to identify a maternal inflammatory response (acute chorioamnionitis) or a fetal inflammatory response (funisitis).

RESULTS

This study included 44 patients with intrauterine fetal death. The median gestational age at diagnosis was 30.1 weeks (range 16.3-40.4 weeks). One patient had documented MIAC (1/44). Acute histological chorioamnionitis was found in 20.9% (9/43), but a fetal inflammatory response was observed in only 2.3% (1/43) of cases. One patient had a positive amniotic fluid culture for Streptococcus agalactiae (group B streptococcus).

CONCLUSION

Histological chorioamnionitis was present in 20.9% of cases, but MIAC could be demonstrated with conventional microbiological techniques in only one case. A fetal inflammatory response was nine times less frequent than a maternal inflammatory response (maternal 20.9% vs. fetal 2.3%, p = 0.008) in cases of fetal death.

Immunohistochemical distribution of Toll-like receptor 4 in term and preterm human placentas from normal and complicated pregnancy including chorioamnionitis

Recently discovered Toll-like receptors (TLRs) are essential for the induction of innate immune responses. One member of the TLR family, TLR4 mediates lipopolysaccharide (bacterial endotoxin)-induced inflammatory responses. Although the innate immune system appears to be important in the pathogenesis of infection-induced preterm delivery, the distribution of TLRs in human placenta is poorly understood. Here we investigated the expression of TLR4 protein in 43 human placentas obtained from normal and complicated pregnancies delivered in the second and third trimesters, using immunohistochemistry. TLR4 was localized to the extravillous trophoblasts, intermediate trophoblasts/X cells in the degenerative villi, and villous Hofbauer cells of all preterm and term placentas examined and to the inflammatory cells in placentas with chorioamnionitis (CAM). The villous Hofbauer cells of preterm CAM placentas demonstrated increased TLR4 immunoreactivity compared with those of preterm placentas without CAM or those of term placentas with or without CAM. These results suggest an important role of the villous Hofbauer cells in the activation of innate immune system in response to infectious pathogens in preterm placentas. Elucidation of biological functions of placental TLR4 under physiological conditions requires further investigation.

Bacterially-induced preterm labor and regulation of prostaglandin-metabolizing enzyme expression in mice: the role of toll-like receptor 4

Toll-like receptor 4 (TLR-4) is a critical mediator of the cellular response to lipopolysaccharide. Our purpose was to examine the role of TLR-4 in parturition and in the regulation of expression of prostaglandin synthase (cyclooxygenase [COX]-1 and COX-2) and 15-hydroxyprostaglandin dehydrogenase (PGDH) following exposure to heat-killed Escherichia coli (HKE) in pregnant mice. Inbred TLR-4-mutant C3H/HeJ mice and inbred normal C3HeB/FeJ mice on Day 14.5 of a 19- to 20-day gestation received intrauterine injection of either HKE or sterile vehicle (PBS). Preterm or term delivery was recorded for these animals. Tissues (myometrium, decidual caps, placentas, fetal membranes, and fetuses) were collected after injection of sterile vehicle or 5 x 109 HKE bacteria (n = 5 mice per strain per treatment per time point). The COX-1, COX-2, and PGDH gene expression was determined by semiquantitative reverse transcription-polymerase chain reaction. We found that 5 x 109 HKE induced preterm delivery in 100% of TLR-4-normal mice but in 0% of TLR-4-mutant mice. The HKE exposure up-regulated expression of COX-2, but not of COX-1, in maternal tissues in both mouse strains. The prostaglandin-catabolizing enzyme PGDH was down-regulated in myometrium, fetal membranes, and fetuses in control mice, but no change was observed in TLR-4-mutant mice after HKE treatment. These results demonstrate that a functional TLR-4 is essential for HKE-induced preterm labor and PGDH down-regulation but is not essential for HKE-induced COX-2 gene up-regulation. The TLR-4 may mediate bacterially induced preterm labor via regulation of prostaglandin degradation rather than prostaglandin synthesis.

Prenatal infection obliterates glutamate-related protection against free hydroxyl radicals in neonatal rat brain

Prenatal infection constitutes an important risk factor for brain injury, in both premature and full-term infants. Unfortunately, as the mechanisms involved are far from understood, no therapeutic strategy emerges to prevent the damage. We tested the hypothesis that administration of lipopolysaccharide (LPS) to gravid female rats enhanced glutamate-induced oxidative stress in brain of pups. A microdialysis probe was implanted into the striatum of 14-day-old animals and the release of hydroxyl radicals (.OH) in the perfusion medium was evaluated. Glutamate promoted a delayed.OH release in the offspring of dams given LPS, contrasting with the.OH decreases observed in control animals. A similar response occurred after infusion of (R,S)-3,5-dihydroxyphenylglycine (DHPG), a Group I metabotropic glutamate receptor (mGluR) agonist. This response was not consecutive to a remote activation of N-methyl-D-aspartate (NMDA) receptors, as it was unaffected by an NMDA receptor antagonist. Furthermore, the response to NMDA itself decreased in the offspring of dams given LPS. Massive amounts of DHPG, however, likely internalizing the mGlu receptor, still blunted the response to NMDA, as in controls. No quantitative variation occurred in mGluR1, mGluR5, or the NR1 subunit of the NMDA receptor between controls and neonates born from LPS-treated dams. Direct LPS injection into age-matched pups, by contrast, affected the response to neither glutamate nor DHPG. These results confirm that normally during perinatal development, the brain is protected from any oxidative stress resulting from excess glutamate, and the results support the hypothesis that maternal infection before delivery may lead to critical brain damage via the release of toxic free radicals.

Tocolytic activity of formoterol against premature delivery in mice

The tocolytic activity of formoterol (eformoterol), a long-acting potent beta(2)-adrenoceptor agonist, was assessed in pregnant mice, with determination of uterine effects on the 15th and 16th days of gestation. For examination in the lipopolysaccharide-induced premature delivery model, osmotic pumps filled with formoterol or saline solution were implanted subcutaneously under the back skin. The mice were sacrificed 18-20 h thereafter, and the numbers of fetuses in the uteri and the newborn were counted. The uteri, amniotic membranes and placenta were also rapidly removed for determination of IL-6 concentrations. Furthermore, the effect of formoterol on IL-6 secretion from mouse amnion cells was determined. Formoterol and ritodrine inhibited contraction responses of isolated mouse uteri and their intravenous administration resulted in lowered uterine motility. Lipopolysaccharide (30 microg mL(-1)/mouse) induced premature delivery, attributable to increased IL-6 secretion, and formoterol suppressed this. Doses of 5-500 microg/mouse thus reduced the number of prematurely delivered newborn, and 50 microg/mouse also depressed IL-6 secretion. On histopathologic analysis, the marked oedema and slight haemorrhage in the mouse cervix induced by lipopolysaccharide were reduced by administration of the beta(2)-adrenoceptor agonist. Neither formoterol (10(-7)-10(-5) M) nor ritodrine (10(-7)-10(-5) M) influenced spontaneous secretion of IL-6 in amnion cells. However, at 10(-7) and 10(-5) M, and 10(-6) and 10(-5) M, respectively, they inhibited lipopolysaccharide-induced IL-6 secretion and this inhibitory effect was competitively reversed by addition of ICI-118,551 (beta(2)-adrenoceptor antagonist), but not atenolol (beta(1)-adrenoceptor antagonist). These findings strongly suggest that formoterol can suppress premature delivery mediated by its actions on IL-6 secretion.

Lipopolysaccharide-binding protein in microbial invasion of the amniotic cavity and human parturition

OBJECTIVE

Lipopolysaccharide-binding protein (LBP) is an acute-phase protein of predominantly hepatic origin, capable of binding the lipid A fraction of bacterial lipopolysaccharide (LPS). The complex LBP-LPS binds to CD14, and has been implicated in the host response to gram-negative infection. The purpose of this study was to determine whether microbial invasion of the amniotic cavity (MIAC) and parturition (term and preterm) are associated with changes in the amniotic fluid concentration of LBP.

STUDY DESIGN

Amniotic fluid was retrieved by amniocentesis from 343 patients in the following groups: (1) those in mid-trimester with a subsequent normal pregnancy outcome (n = 84); (2) those in mid-trimester with a fetal loss after the procedure (n = 10); (3) those with preterm labor and intact membranes without MIAC who delivered at term (n = 36) or prematurely (n = 52), and those with preterm labor with MIAC (n = 26); (4) those with preterm premature rupture of membranes (PROM) with (n = 26) and without (n = 26) MIAC; and (5) those delivering at term with intact membranes in the absence of MIAC, in labor (n = 52) and not in labor (n = 31). The concentration of LBP in amniotic fluid was determined with a specific and sensitive immunoassay. Non-parametric statistics were used. A p value of < 0.05 was considered significant.

RESULTS

LBP was detected in 98% (335/343) of the amniotic fluid samples. MIAC was associated with a significant increase in amniotic fluid concentration of LBP in women with preterm labor and intact membranes, but not in preterm PROM. Spontaneous preterm parturition was associated with a significant increase in amniotic fluid concentration of LBP. Patients who had a spontaneous fetal loss after a mid-trimester amniocentesis had a significantly higher median amniotic fluid LBP concentration than those who had a mid-trimester amniocentesis and a normal perinatal outcome.

CONCLUSION

Preterm labor with MIAC and preterm parturition are associated with higher amniotic fluid concentrations of LBP than those with sterile amniotic fluid.

Effects of erythromycin on pregnancy duration and birth weight in lipopolysaccharide-induced preterm labor in pregnant rats

OBJECTIVE

The aim of this study was to investigate the effects of erythromycin on pregnancy duration and on live birth weight in lipopolysaccharide (LPS)-induced preterm labor model in rats.

STUDY DESIGN

Total of 60 pregnant rats on day 16 of gestation was intraperitoneally injected with 25 microg/kg LPS. Animals were randomly divided into six groups and 20mg/kg (n=10), 40 mg/kg (n=10), 60 mg/kg (n=10), 80 mg/kg (n=10), and 100mg/kg (n=10) erythromycin and equal volume of physiological saline (n=10) were given intraperitoneally. Injection of LPS-to-vaginal bleeding interval, vaginal bleeding-to-delivery interval, LPS injection-to-delivery interval was monitored and live birth weight of neonates was determined. Statistical analysis was performed using Kruskal-Wallis, Mann-Whitney U-test and Spearman correlation analysis.

RESULTS

Intraperitoneal injection of erythromycin to LPS-administered rats caused significant increase in latent period, labor period, total period and live birth weight in a dose dependent manner.

CONCLUSION

These data shows that erythromycin causes prolongation of pregnancy period and increases live birth weight in LPS-induced preterm labor of pregnant rats.