Campylobacters and impaired fetal development in mice

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.

Adverse pregnancy outcomes (APOs) and periodontal disease: pathogenic mechanisms

AIM

To evaluate the evidence on potential biological pathways underlying the possible association between periodontal disease (PD) and adverse pregnancy outcomes (APOs).

MATERIAL & METHODS

Human, experimental and in vitro studies were evaluated.

RESULTS

Periodontal pathogens/byproducts may reach the placenta and spread to the foetal circulation and amniotic fluid. Their presence in the foeto-placental compartment can stimulate a foetal immune/inflammatory response characterized by the production of IgM antibodies against the pathogens and the secretion of elevated levels of inflammatory mediators, which in turn may cause miscarriage or premature birth. Moreover, infection/inflammation may cause placental structural changes leading to pre-eclampsia and impaired nutrient transport causing low birthweight. Foetal exposure may also result in tissue damage, increasing the risk for perinatal mortality/morbidity. Finally, the elicited systemic inflammatory response may exacerbate local inflammatory responses at the foeto-placental unit and further increase the risk for APOs.

CONCLUSIONS

Further investigation is still necessary to fully translate the findings of basic research into clinical studies and practice. Understanding the systemic virulence potential of the individual's oral microbiome and immune response may be a distinctly different issue from categorizing the nature of the challenge using clinical signs of PD. Therefore, a more personalized targeted therapy could be a more predictive answer to the current "one-size-fits-all" interventions.

Adverse pregnancy outcomes (APOs) and periodontal disease: pathogenic mechanisms

AIM

To evaluate the evidence on potential biological pathways underlying the possible association between periodontal disease (PD) and adverse pregnancy outcomes (APOs).

MATERIAL & METHODS

Human, experimental and in vitro studies were evaluated.

RESULTS

Periodontal pathogens/byproducts may reach the placenta and spread to the foetal circulation and amniotic fluid. Their presence in the foeto-placental compartment can stimulate a foetal immune/inflammatory response characterized by the production of IgM antibodies against the pathogens and the secretion of elevated levels of inflammatory mediators, which in turn may cause miscarriage or premature birth. Moreover, infection/inflammation may cause placental structural changes leading to pre-eclampsia and impaired nutrient transport causing low birthweight. Foetal exposure may also result in tissue damage, increasing the risk for perinatal mortality/morbidity. Finally, the elicited systemic inflammatory response may exacerbate local inflammatory responses at the foeto-placental unit and further increase the risk for APOs.

CONCLUSIONS

Further investigation is still necessary to fully translate the findings of basic research into clinical studies and practice. Understanding the systemic virulence potential of the individual's oral microbiome and immune response may be a distinctly different issue from categorizing the nature of the challenge using clinical signs of PD. Therefore, a more personalized targeted therapy could be a more predictive answer to the current "one-size-fits-all" interventions.

Extrauterine listeriosis in the gravid mouse influences embryonic growth and development

Gravid mice and other rodents inoculated with Listeria monocytogenes typically fail to clear an intrauterine infection and either succumb or expel their intrauterine contents. We took advantage of this property to investigate the effects of an extrauterine infection on parameters of pregnancy success. Pregnant mice were selected for our study if they showed no clinical signs of listeriosis following oral inoculation at 7.5 gestational days (gd), and had no detectable intrauterine colony forming units (cfu) at near term (18.5 gd). The range of oral doses employed was 10⁶-10⁸ cfu per mouse for two listerial serotype strains (4nonb and 1/2a). At all doses, inoculation resulted in a decrease in average near-term (18.5 gd) fetal weight per litter compared to sham inoculated controls. Additionally, embryonic death (indicated by intrauterine resorptions) was exhibited by some inoculated mice but was absent in all sham inoculated animals. In parallel experiments designed to detect possible loss of placental function, gravid uteruses were examined histopathologically and microbiologically 96 h after oral inoculation. Placental lesions were associated with high (> 10⁶), but not low (< 10²) or absent intrauterine cfu. In vitro, mouse embryonic trophoblasts were indistinguishable from mouse enterocytes in terms of their sensitivity to listerial exposure. A model consistent with our observations is one in which products (host or bacterial) generated during an acute infection enter embryos transplacentally and influences embryonic survival and slows normal growth in utero.

Toll-like receptor 4 mediates intrauterine growth restriction after systemic Campylobacter rectus infection in mice

Campylobacter rectus is associated with fetal exposure and low birthweight in humans. C. rectus also invades placental tissues and induces fetal intrauterine growth restriction (IUGR) in mice, along with overexpression of Toll-like receptors (TLR4), suggesting that TLR4 may mediate placental immunity and IUGR in mice. To test this hypothesis we examined the effect of in vitro TLR4 neutralization on trophoblastic proinflammatory activity and studied the IUGR phenotype in a congenic TLR4-mutant mouse strain after in vivo C. rectus infection. Human trophoblasts were pretreated with TLR4 neutralizing antibodies and infected with C. rectus; proinflammatory cytokine production was assessed by cytokine multiplex assays. Neutralizing TLR4 antibodies significantly impaired the production of proinflammatory cytokines in trophoblastic cells after infection in a dose-dependent manner. We used a subcutaneous chamber model to provide a C. rectus challenge in BALB/cAnPt (TLR4(Lps-d) ) and wild-type (WT) females. Females were mated with WT or TLR4(Lps-d) males once/week; pregnant mice were infected at (E)7.5 and sacrificed at (E)16.5 to establish IUGR phenotypes. Maternal C. rectus infection significantly decreased fetal weight/length in infected WT when compared with sham WT controls (P < 0.05, analysis of variance). However, infected TLR4(Lps-d -/-) mice did not show statistically significant differences in fetal weight and length when compared with WT controls (P > 0.05). Furthermore, heterozygous TLR4(Lps-d +/-) fetuses showed IUGR phenotype rescue. We conclude that TLR4 is an important mediator of trophoblastic proinflammatory responses and TLR4-deficient fetuses do not develop IUGR phenotypes after C. rectus infection, suggesting that placental cytokine activation is likely to be mediated by TLR4 during low birthweight/preterm birth pathogenesis.

Characterization of the invasive and inflammatory traits of oral Campylobacter rectus in a murine model of fetoplacental growth restriction and in trophoblast cultures

Campylobacter species (C. jejuni, C. fetus) are enteric abortifacient bacteria in humans and ungulates. Campylobacter rectus is a periodontal pathogen associated with human fetal exposure and adverse pregnancy outcomes including preterm delivery. Experiments in pregnant mice have demonstrated that C. rectus can translocate from a distant site of infection to the placenta to induce fetal growth restriction and impair placental development. However, placental tissues from human, small-for-gestational age deliveries have not been reported to harbor C. rectus despite evidence of maternal infection and fetal exposure by fetal IgM response. This investigation examined the temporal relationship between the placental translocation of C. rectus and the effects on fetal growth in mice. BALB/c mice were infected at gestational day E7.5 to examine placental translocation of C. rectus by immunohistology. C. rectus significantly decreased fetoplacental weight at E14.5 and at E16.5. C. rectus was detected in 63% of placentas at E14.5, but not at E16.5. In in vitro trophoblast invasion assays, C. rectus was able to effectively invade human trophoblasts (BeWo) but not murine trophoblasts (SM9-1), and showed a trend for more invasiveness than C. jejuni. C. rectus challenge significantly upregulated both mRNA and protein levels of IL-6 and TNFalpha in a dose-dependent manner in human trophoblasts, but did not increase cytokine expression in murine cells, suggesting a correlation between invasion and cytokine activation. In conclusion, the trophoblast-invasive trait of C. rectus that appears limited to human trophoblasts may play a role in facilitating bacterial translocation and placental inflammation during early gestation.

Increased TLR4 expression in murine placentas after oral infection with periodontal pathogens

Maternal periodontitis has emerged as a putative risk factor for preterm births in humans. The periodontitis-associated dental biofilm is thought to serve as an important source of oral bacteria and related virulence factors that hematogenously disseminate and affect the fetoplacental unit; however the underlying biological mechanisms are yet to be fully elucidated. This study hypothesized that an oral infection with the human periodontal pathogens Campylobacter rectus and Porphyromonas gingivalis is able to induce fetal growth restriction, placental inflammation and enhance Toll-like receptors type 4 (TLR4) expression in a murine pregnancy model. Female Balb/C mice (n = 40) were orally infected with C. rectus and/or P. gingivalis over a 16-week period and mated once/week. Pregnant mice were sacrificed at embryonic day (E) 16.5 and placentas were collected and analyzed for TLR4 mRNA levels and qualitative protein expression by real-time PCR and immunofluorescence. TLR4 mRNA expression was found to be increased in the C. rectus-infected group (1.98 +/- 0.886-fold difference, P < 0.01, ANOVA) compared to controls. Microscopic analysis of murine placentas showed enhanced immunofluorescence of TLR4 in trophoblasts, mainly in the placental labyrinth layer. Also, combined oral infection with C. rectus and P. gingivalis significantly reduced the overall fecundity compared to controls (16.7% vs. 75%, infected vs. non-infected mice respectively, P = 0.03, Kaplan-Meier). The results supported an enhanced placental TLR4 expression after oral infection with periodontal pathogens. The TLR4 pathway has been implicated in the pathogenesis of preterm births; therefore the abnormal regulation of placental TLR4 may give new insights into how maternal periodontitis and periodontal pathogens might be linked to placental inflammation and preterm birth pathogenesis.

Campylobacter rectusMediates Growth Restriction in Pregnant Mice

BACKGROUND

Recent studies have suggested that subclinical infection may be an important cause of low birth weight. Campylobacters are important human pathogens, causing septicemia and occasionally abortion, premature labor, or severe perinatal infection. The potential role of oral species of Campylobacter in mediating adverse pregnancy outcomes in animal models has not yet been determined. Our objective was to determine the effects of Campylobacter rectus (C. rectus) infection on pregnancy outcomes in a mouse model.

METHODS

On embryonic day (E) 7.5, pregnant mice received a subcutaneous, intra-chamber challenge with live C. rectus at concentrations of 0, 10(7) or 10(9) colony forming units (CFU)/ml. They were sacrificed on E 16.5 and fetuses were evaluated for stage of development, weight, and crown-rump length.

RESULTS

Dams receiving C. rectus had more fetal resorptions after challenge with 10(7) or 10(9) CFU/ml (24.1% and 30.1%, respectively) than controls (9%). Higher numbers of growth-restricted fetuses were also observed in the C. rectus challenged groups (21%) as compared to controls (2.3%). Fetuses from dams challenged with 10(9) CFU/ml weighed less (0.49 +/- 0.05 g) and had shorter crown-rump lengths (14.69 +/- 0.56 mm) than controls (0.53 +/- 0.04 g; 15.54 +/- 0.63 mm). C. rectus was detected by polymerase chain reaction (PCR) in the placentas from both treated groups and in maternal liver tissues from the 10(9) CFU/ml challenged group.

CONCLUSIONS

Remote subcutaneous maternal C. rectus infection increases fetal resorptions and fetal growth restriction in a mouse model. The effects of an oral C. rectus infection on pregnancy remain to be determined.