Infection, inflammation and the risk of cerebral palsy

Inhibition of Amniotic Interleukin-6 and Prostaglandin E2 Release by Ampicillin

OBJECTIVE

To test the effect of ampicillin on amniotic interleukin-6 (IL-6) and prostaglandin E2 (PGE2) release.

METHODS

In an in vitro study, IL-6 and PGE2 release from amnion-like Wistar Institute Susan Hayflick cells was assayed under basal conditions, as well as after incubation with ampicillin. In an in vivo study, amniotic fluid IL-6 was assayed in a total of 212 patients submitted to genetic amniocentesis during the 17th week of their singleton physiological pregnancy. The study population was subdivided as follows: 92 patients sampled before ampicillin administration, 70 patients sampled 4 hours after administration of 1 g ampicillin, and 50 patients sampled 12 hours after administration of 1 g ampicillin.

RESULTS

At doses ranging from 10-7 to 10-4 M, ampicillin decreased IL-6 release from Wistar Institute Susan Hayflick cells. The drug effect was already statistically significant (-30%; P <.05) at the lowest concentration tested (10-7 M), reaching the maximum (-50%) at 10-6 M after 4 hours of incubation. Moreover, ampicillin concentrations ranging from 10-7 to 10-4 M decreased PGE2 release from Wistar Institute Susan Hayflick cells; maximal inhibition was reached at 10-6 M after 4 hours (-40%; P <.05). Finally, IL-6 levels measured in amniotic fluid of patients sampled 4 hours after ampicillin administration proved strongly and significantly reduced when compared with those sampled either before or 12 hours after treatment (P <.001).

CONCLUSION

The capacity of ampicillin to directly decrease amniotic IL-6 and PGE2 release should be considered in the management of bacterial and nonbacterial inflammatory complications of pregnancy mediated by the cytokine and prostanoid interaction.

Does the risk of cerebral palsy increase or decrease with increasing gestational age?

BACKGROUND: It is generally accepted that the risk of cerebral palsy decreases with increasing gestational age of live born infants. However, recent studies have shown that cerebral palsy often has prenatal antecedents including congenital malformations, vascular insults and maternal infection. Cerebral palsy is therefore better viewed as occurring among fetuses, rather than among infants. We explored the epidemiologic implications of this change in perspective. METHODS: We used recently published data from Shiga Prefecture, Japan and from North-East England to examine the pattern of gestational age-specific rates of cerebral palsy under these alternative perspectives. We first calculated gestational age-specific rates of cerebral palsy as per convention, by dividing the number of cases of cerebral palsy identified among live births within any gestational age category by the number of live births in that gestational age category. Under the alternative formulation, we calculated gestational age-specific rates of cerebral palsy by dividing the number of cases of cerebral palsy identified among live births within any gestational age category by the number of fetuses who were at risk of being born at that gestation and being afflicted with cerebral palsy. RESULTS: Under the conventional formulation, cerebral palsy rates decreased with increasing gestational age from 63.9 per 1,000 live births at <28 weeks gestation to 0.9 per 1,000 live births at 37 or more weeks gestation. When fetuses were viewed as potential candidates for cerebral palsy, cerebral palsy rates increased with increasing gestational age from 0.08 per 1,000 fetuses at risk at <28 weeks gestation to 0.9 per 1,000 fetuses at risk at 37 or more weeks gestation. CONCLUSIONS: The fetuses-at-risk approach is the appropriate epidemiologic formulation for calculating the gestational age-specific rate of cerebral palsy from a causal perspective. It shows that the risk of cerebral palsy increases as gestational duration increases. This compelling view of cerebral palsy risk may help refocus research aimed at understanding and preventing cerebral palsy.

Patterns of cerebral inflammatory response in a rabbit model of intrauterine infection-mediated brain lesion

Although the fetal inflammatory response syndrome seems crucial to the association between intrauterine infection and white matter disease in human preterm infants, the underlying mechanisms remain unclear. Using our previously described rabbit model of cerebral cell death in the white matter and hippocampus induced by intrauterine Escherichia coli infection, we investigated inflammatory and astroglial responses in placenta and brain tissues, in correlation with cell death distribution. Brains and placentas were studied 12, 24, or 48 h following intrauterine inoculation of E. coli or saline (groups G12, G24, and G48). Diffuse monocyte-macrophage infiltrates positive for inducible nitric oxide synthase (i-NOS) were significantly more marked in G24 and G48 placentas than in controls. In the G48 fetuses with both diffuse cell death and focal periventricular white matter cysts mimicking cystic periventricular leukomalacia, a strong rabbit macrophage and inducible nitric oxide synthase immunostaining was observed at the border of these cystic lesions. In contrast, in the fetuses with only diffuse and significant cell death, no inflammatory or astroglial responses were detected in the white matter or hippocampus. Cell death was accompanied by i-NOS immunostaining in the hippocampus but not the white matter. Hippocampal cells positive for i-NOS usually displayed a neuronal phenotype. In this model, focal white matter cysts are accompanied by a robust inflammatory response, and diffuse cell death, which may mimic the white matter and hippocampal damage seen in very and extremely pre-term infants, occur in the absence of a detectable brain inflammatory response.

Chorioamnionitis: a risk factor for fetal and neonatal morbidity

Despite widespread use of drugs to arrest preterm labor, there has been no decrease in the numbers of low-birth-weight or preterm infants in the last 20 years. Evidence from many sources links preterm birth to symptomatic and subclinical infections. Recently, an increasing body of evidence has suggested that not only is subclinical infection responsible for preterm birth but also for many serious neonatal sequelae, including periventricular leukomalacia, cerebral palsy, respiratory distress and even bronchopulmonary dysplasia and necrotizing enterocolitis. Proxies of intrauterine infection include clinical chorioamnionitis, histological chorioamnionitis and intraamniotic increase in cytokines, which have been found to be associated with acute neonatal morbidity and mortality and, at least to some degree, with neurological impairment, chronic lung disease and thymus involution in the preterm infant. The infectious/inflammatory mechanisms involved are not fully understood, and the types of microbes and genetic features of host adaptive and innate immune responses need to be better characterized.

The epidemiology and causes of cerebral palsy

Cerebral palsy is the commonest physical disability in childhood, occurring in 2.0 to 2.5 per 1000 live births. Although the total number of children with cerebral palsy has remained stable or increased slightly since 1970, there has been a consistent rise in the proportion of cerebral palsy associated with preterm and very preterm births. Known causes of cerebral palsy--whether prenatal, perinatal or postnatal--must be distinguished from risk factors or associations. Much is known about such risk factors which, alone or in combination, may indirectly result in cerebral palsy. Causes and risk factors implicated in cerebral palsy are discussed in detail, together with directions for future research.

Neonatal cytokines and cerebral palsy in very preterm infants

To examine the relationship of cytokines in blood of very preterm neonates with later diagnosis of spastic cerebral palsy (CP) compared with infants of similar gestational age without CP, we measured concentrations of inflammatory cytokines and other substances in archived neonatal blood by recycling immunoaffinity chromatography. Subjects were surviving children born before 32 wk gestational age (GA) to women without preeclampsia, 64 with later diagnoses of CP and 107 control children. The initial analyses were augmented by measurement of 11 cytokines by a bead-based flow analytic system (Luminex) in an additional 37 children with CP and 34 control children from the same cohort. Concentrations of examined substances did not differ by presence of indicators of infection in mother, infant, or placenta. On ANOVA, concentrations of a number of cytokines were significantly related to neonatal ultrasound abnormalities (periventricular leukomalacia, ventricular enlargement, or moderate or severe germinal matrix hemorrhage). None of the substances measured either by immunoaffinity chromatography or flow analytic methods, including IL-1, -6, and -8 and tumor necrosis factor-alpha, was related to later diagnosis of CP or its subtypes. Inflammatory cytokines in neonatal blood of very premature infants did not distinguish those with later diagnoses of CP from control children.

Antenatal causes of cerebral palsy: associations between inherited thrombophilias, viral and bacterial infection, and inherited susceptibility to infection

Cerebral palsy rates of 2 in every 1,000 births have varied little over the last 40 years, despite improvements in obstetric care. In the past, cerebral palsy was thought to be due to poor obstetric care and management; however, epidemiological studies have refuted this, suggesting that there is usually an antenatal timing to the neuropathology of cerebral palsy. There are many known risk factors for cerebral palsy, including multiple gestation, prematurity, and low birth weight. Recently, intrauterine infection, maternal pyrexia, and the presence of thrombophilic disorders (thrombophilia) have been identified as major risk factors for subsequent cerebral palsy. This review examines the links between intrauterine infection, the fetal inflammatory response, and thrombophilia as possible causes of cerebral palsy. The interactions of viral or bacterial infections during pregnancy, normal or abnormal fetal cytokine responses, and hereditary fetal thrombophilias as antenatal causes of the neuropathology of cerebral palsy are now areas of research priority.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader will be able to describe the condition cerebral palsy, list the risk factors for the development of cerebral palsy, outline the ultrasound findings associated with cerebral palsy, and point out other conditions associated with cerebral palsy.

Chorioamnionitis and brain injury

The limited available evidence supports a strong association of chorioamnionitis with neonatal encephalopathy and CP in the term infant. The association of chorioamnionitis with depressed Apgar scores or neonatal seizures and with CP is equivocal in the preterm infant. Different study results may be related to differences in study populations, perhaps specifically to differences in susceptibility by stages of neurologic development as well as differences in gene frequencies associated with inflammation and thrombophilia. We require further understanding of the normal roles of cytokines in brain development, pregnancy, and inflammatory homeostasis before clinical interventions directed at cytokines, their receptors, or the inflammatory process are considered.

Pathogenesis of hypoxic-ischemic cerebral injury in the term infant: current concepts

Multiple, biochemical cascades contribute to the pathogenesis of neonatal hypoxic-ischemic brain injury. This article summarizes experimental evidence that supports the role of excitatory amino acids, calcium, free radicals, nitric oxide, proinflammatory cytokines, and bioactive lipids. Specific vulnerabilities that distinguish the response of the immature brain from that of the mature brain are highlighted. These include increased susceptibility to excitotoxicity and free radical injury, greater tendency to apoptotic death, and heightened vulnerability of developing oligodendrocytes. Available supportive evidence from human studies is also included. Implications for clinical neuroprotective strategies are discussed.

The epidemiology of cerebral palsy in term infants

Half of cerebral palsy (CP) arises in infants of normal birthweight; yet, many fewer studies seek to identify risk factors for CP in term and near-term infants than in those born very prematurely. There has been no net decrease in the prevalence of CP in term and near-term infants over recent decades. Potentially asphyxiating birth complications account for a small minority of CP cases. Recent studies suggest that disorders of coagulation and intrauterine exposure to infection or inflammation are associated with risk of CP, and that both can be accompanied by signs of neonatal encephalopathy, the best available predictor of CP in term neonates. Therapeutic interventions directed at preventing interruption of oxygen supply have not been shown to reduce the occurrence of CP. There have not yet been studies examining whether medical interventions directed at infection or coagulation disorder can reduce the frequency of CP.

Evidence for fetal involvement in the pathologic process of clinical chorioamnionitis

OBJECTIVE

Clinical and histologic chorioamnionitis have recently been identified as risk factors for cerebral palsy. Proinflammatory cytokines have been implicated in the mechanisms that are responsible for brain injury in cases of intrauterine infection. The purpose of this study was to determine whether clinical chorioamnionitis, which is a maternal syndrome, is associated with an elevation in the fetal plasma interleukin-6 (IL-6) that is indicative of fetal inflammation.

STUDY DESIGN

A cross-sectional study was designed to determine plasma concentrations of IL-6 in umbilical venous blood from patients with clinical chorioamnionitis (n = 26) and a control group (n = 111). Umbilical cord blood was obtained at the time of delivery. Plasma concentrations of IL-6 were measured with a sensitive and specific immunoassay. Nonparametric statistics were used for analysis.

RESULTS

Plasma concentrations of IL-6 were detectable in all samples of umbilical venous plasma. The median concentration of plasma IL-6 was higher in neonates born to mothers with clinical chorioamnionitis than in neonates born to mothers in the control group (clinical chorioamnionitis: median, 27.46 pg/mL; range, 1.3-5550.0 pg/mL; vs control: median, 2.13 pg/mL; range, 0.6-812.3 pg/mL; P <.001). Sixty-two percent of neonates (16/26) who were born to women with clinical chorioamnionitis had fetal plasma concentrations of IL-6 >11 pg/mL and 54% (14/26) had fetal plasma concentrations of IL-6 >18 pg/mL (these cutoff points have been used previously to define the fetal inflammatory response syndrome).

CONCLUSION

Umbilical vein plasma concentrations of interleukin-6 are elevated in the neonates who were born to mothers with clinical chorioamnionitis, which suggests that the inflammatory process that is responsible for the maternal syndrome of clinical chorioamnionitis frequently involves the human fetus.

Perinatal infection, fetal inflammatory response, white matter damage, and cognitive limitations in children born preterm

Only sparse information is available about a possible association between antenatal infection outside the brain and subsequent cognitive limitations among preterm infants. Based on published studies, we provide a theoretical schema that links them via the fetal inflammatory response and neonatal white matter damage. We conclude that the relationship between antenatal infection and cognitive limitations deserves much further attention by researchers interested in the prevention of this undesirable outcome of prematurity.

Models of white matter injury: comparison of infectious, hypoxic-ischemic, and excitotoxic insults

White matter damage (WMD) in preterm neonates is strongly associated with adverse outcome. The etiology of white matter injury is not known but clinical data suggest that ischemia-reperfusion and/or infection-inflammation are important factors. Furthermore, antenatal infection seems to be an important risk factor for brain injury in term infants. In order to explore the pathophysiological mechanisms of WMD and to better understand how infectious agents may affect the vulnerability of the immature brain to injury, numerous novel animal models have been developed over the past decade. WMD can be induced by antenatal or postnatal administration of microbes (E. coli or Gardnerella vaginalis), virus (border disease virus) or bacterial products (lipopolysaccharide, LPS). Alternatively, various hypoperfusion paradigms or administration of excitatory amino acid receptor agonists (excitotoxicity models) can be used. Irrespective of which insult is utilized, the maturational age of the CNS and choice of species seem critical. Generally, lesions with similarity to human WMD, with respect to distribution and morphological characteristics, are easier to induce in gyrencephalic species (rabbits, dogs, cats and sheep) than in rodents. Recently, however, models have been developed in rats (PND 1-7), using either bilateral carotid occlusion or combined hypoxia-ischemia, that produce predominantly white matter lesions. LPS is the infectious agent most often used to produce WMD in immature dogs, cats, or fetal sheep. The mechanism whereby LPS induces brain injury is not completely understood but involves activation of toll-like receptor 4 on immune cells with initiation of a generalized inflammatory response resulting in systemic hypoglycemia, perturbation of coagulation, cerebral hypoperfusion, and activation of inflammatory cells in the CNS. LPS and umbilical cord occlusion both produce WMD with quite similar distribution in 65% gestational sheep. The morphological appearance is different, however, with a more pronounced infiltration of inflammatory cells into the brain and focal microglia/macrophage ("inflammatory WMD") in response to LPS compared to hypoperfusion evoking a more diffuse microglial response usually devoid of cellular infiltrates ("ischemic WMD"). Furthermore, low doses of LPS that by themselves have no adverse effects in 7-day-old rats (maturation corresponding to the near term human fetus), dramatically increase brain injury to a subsequent hypoxic-ischemic challenge, implicating that bacterial products can sensitize the immature CNS. Contrary to this finding, other bacterial agents like lipoteichoic acid were recently shown to induce tolerance of the immature brain suggesting that the innate immune system may respond differently to various ligands, which needs to be further explored.

Increased FDG uptake in the ipsilesional sensorimotor cortex in congenital hemiplegia

The resting brain metabolism was estimated in six children suffering from a right congenital hemiplegia (CH) of subcortical origin. This estimate was based on the 18F-labeled 2-deoxy-2-fluoro-d-glucose (FDG) uptake measured by means of positron emission tomography and compared, using statistical parametric mapping (SPM99), with that of six control subjects. The contrast [CH children - Controls] showed that CH children had two loci of relatively higher FDG uptake. The larger voxel cluster was found in the ipsilesional hemisphere and comprised the primary motor and somatosensory cortices and left inferior parietal lobule. The other cluster was located in the contralesional hemisphere and encompassed the primary motor cortex, callosomarginal sulcus, and cingulate gyrus. The reverse contrast [Controls - CH children] showed that control subjects had a relatively higher FDG uptake bilaterally in the temporal and hippocampal gyri, the rostral part of the brain stem, the thalami, the putamen, and the superior frontal gyri. A crossed cerebellar diaschisis was not observed in CH children. This relatively higher FDG uptake in the ipsi- and contralesional motor areas of CH children stands out in contrast to the hypometabolism (diaschisis) frequently observed in adult stroke patients with a subcortical lesion. This increased FDG uptake in the disconnected ipsilesional motor areas may reflect a long-term adaptation leading, for example, to an increased synaptic density and/or activity or to a change in the density of glucose transporters.

Maternal periodontitis and prematurity. Part I: Obstetric outcome of prematurity and growth restriction

Oral Conditions and Pregnancy (OCAP) is a 5-year prospective study of pregnant women designed to determine whether maternal periodontal disease contributes to the risk for prematurity and growth restriction in the presence of traditional obstetric risk factors. Full-mouth periodontal examinations were conducted at enrollment (prior to 26 weeks gestational age) and again within 48 hours postpartum to assess changes in periodontal status during pregnancy. Maternal periodontal disease status at antepartum, using a 3-level disease classification (health, mild, moderate-severe) as well as incident periodontal disease progression during pregnancy were used as measures of exposures for examining associations with the pregnancy outcomes of preterm birth by gestational age (GA) and birth weight (BW) adjusting for race, age, food stamp eligibility, marital status, previous preterm births, first birth, chorioamnionitis, bacterial vaginosis, and smoking. Interim data from the first 814 deliveries demonstrate that maternal periodontal disease at antepartum and incidence/progression of periodontal disease are significantly associated with a higher prevalence rate of preterm births, BW < 2,500 g, and smaller birth weight for gestational age. For example, among periodontally healthy mothers the unadjusted prevalence of births of GA < 28 weeks was 1.1%. This was higher among mothers with mild periodontal disease (3.5%) and highest among mothers with moderate-severe periodontal disease (11.1%). The adjusted prevalence rates among GA outcomes were significantly different for mothers with mild periodontal disease (n = 566) and moderate-severe disease (n = 45) by pair-wise comparisons to the periodontally healthy reference group (n = 201) at P = 0.017 and P < 0.0001, respectively. A similar pattern was seen for increased prevalence of low birth weight deliveries among mothers with antepartum periodontal disease. For example, there were no births of BW < 1000 g among periodontally healthy mothers, but the adjusted rate was 6.1% and 11.4% for mild and moderate-severe periodontal disease (P = 0.0006 and P < 0.0001), respectively. Periodontal disease incidence/progression during pregnancy was associated with significantly smaller births for gestational age adjusting for race, parity, and baby gender. In summary, the present study, although preliminary in nature, provides evidence that maternal periodontal disease and incident progression are significant contributors to obstetric risk for preterm delivery, low birth weight and low weight for gestational age. These studies underscore the need for further consideration of periodontal disease as a potentially new and modifiable risk for preterm birth and growth restriction.

Cerebral white matter damage in the preterm infant: pathophysiology and risk factors

Based on clinical, epidemiologic, and experimental studies, the aetiology of white matter damage, specifically periventricular leukomalacia (PVL), is multifactorial and involves pre- and perinatal factors possibly including genetic factors, hypoxic-ischaemic insults, infection, excess cytokines, free radical production, increased excitatory amino acid release, and trophic factor deficiencies. The article summarizes research findings about the aetiology of white matter damage and cerebral palsy in preterm infants. The information is organized according to specific antecedents, for which we present epidemiological and neurobiological data. The most important prenatal factor appears to be intrauterine infection. We discuss the evidence supporting the hypothesis that the foetal inflammatory response contributes to neonatal brain injury and later developmental disability. We recently established an animal model of excitotoxic lesions in the developing mouse brain. Brain damage was induced by intra-cortical injections of ibotenate, a glutamatergic agonist. When administered on post-natal day 5 ibotenate induced the formation of white matter cysts. Our animal model could be used to further explore the mechanisms involved in the formation of PVL. Potentially preventive strategies will be discussed.