Bacterial endotoxin and impaired fetal development

Disruption of female reproductive function by endotoxins

Endotoxemia can be caused by obesity, environmental chemical exposure, abiotic stressors and bacterial infection. Circumstances that deleteriously impact intestinal barrier integrity can induce endotoxemia, and controlled experiments have identified negative impacts of lipopolysaccharide (LPS; an endotoxin mimetic) on folliculogenesis, puberty onset, estrus behavior, ovulation, meiotic competence, luteal function and ovarian steroidogenesis. In addition, neonatal LPS exposures have transgenerational female reproductive impacts, raising concern about early life contacts to this endogenous reproductive toxicant. Aims of this review are to identify physiological stressors causing endotoxemia, to highlight potential mechanism(s) by which LPS compromises female reproduction and identify knowledge gaps regarding how acute and/or metabolic endotoxemia influence(s) female reproduction.

Escherichia coli and group B streptococcal infections in experimental animals

Small doses of Escherichia coli endotoxin or of viable E. coli caused only a mild illness in pregnant mice but severely impaired fetal development. After intravenous injection and after experimental renal infection E. coli multiplied in placental tissue, causing resorption of the conceptuses and sometimes fetal infection. It is suggested that in humans coliform bacteraemia sometimes results in abortion and premature delivery because of the placental damage brought about by E. coli and its abortifacient endotoxin. Isolates of group B streptococci from various sites in 175 patients varied markedly in their pathogenicity for mice, and pregnant animals were less susceptible to infection than non-pregnant. In late pregnancy streptococci multiplied rapidly in placental tissue, suggesting that the placenta may be a significant focus of infection at the time of delivery. After antibiotic treatment the majority of mice infected with a highly pathogenic strain died but the majority of those infected with a strain of low pathogenicity survived. Preliminary experiments suggest that guinea-pigs and rabbits may be useful for studying the role of maternally derived antibodies in protecting the neonate against group B streptococci.

Dietary zinc supplementation ameliorates LPS-induced teratogenicity in mice

Maternal infection during the first trimester of pregnancy has been associated with preterm birth, spontaneous abortion, growth retardation, and congenital anomalies. Previously, our group has shown that subcutaneous injection of zinc prevents endotoxin [lipopolysaccharide (LPS)]-induced teratogenicity. The purpose of this study was to investigate whether increasing or decreasing dietary zinc alters the teratogenic effects of LPS. Female C57BL6 mice were mated and fed diets containing 5, 35, or 100 mg/kg zinc. On gestational day (GD) 8, pregnant dams were injected with either LPS (0.5 mg/kg s.c.) or saline and killed on GD18. LPS-treated fetuses from dams fed 5 and 35 mg/kg zinc diet had a significantly higher number of abnormalities per litter (2- and 1- fold saline controls, respectively) compared with those from LPS + zinc supplemented dams, which were not significantly different from the saline control groups. The beneficial effect and importance of zinc was also reflected in the larger size of fetuses (weight and crown-rump length) from the LPS + zinc-supplemented treatment group. We have demonstrated that low dietary zinc during exposure to infection (i.e. LPS) in pregnancy augments the negative impact of LPS alone, and that dietary zinc supplementation throughout pregnancy ameliorates LPS-induced teratogenicity.

Zinc treatment prevents lipopolysaccharide-induced teratogenicity in mice

BACKGROUND

During pregnancy, exposure to lipopolysaccharide (LPS) can lead to abortion, preterm delivery, and teratogenicity. The mechanisms underlying these effects are unclear. Both LPS and ethanol are potent inducers of liver metallothionein (MT), a key Zn binding protein. The teratogenic effects of ethanol have been linked to MT-induced changes in maternal-fetal Zn homeostasis, leading tofetal deficiency. This study was designed to assess whether the teratogenic effects of LPS are also related to MT induction and changes in Zn homeostasis.

METHODS

Non-pregnant normal (MT +/+) and MT-null (MT -/-) mice were injected subcutaneously with 0.5 microg/gm LPS and killed over 48 hr. In MT +/+ mice, liver MT concentrations were elevated from 6 hr, and were maximal at 24 hr (30-fold basal), whereas liver Zn levels were also increased from 6 hr. Plasma Zn concentrations decreased by 80% at 6 hr, and were below normal between 6 and 24 hr. In MT -/- mice, plasma Zn levels were increased from basal between 6 and 16 hr. Dams were injected with LPS, saline, or LPS and ZnSO4 (2 microg/gm, MT +/+ only) on Day 8 of gestation (GDS), killed on GD18, and the fetuses examined for malformations.

RESULTS

External abnormalities were most prevalent in fetuses from MT +/+ dams exposed to LPS, where 34% of fetuses in each litterwere affected. MT +/+ dams treated with LPS and ZnSO4, and MT -/- dams treated with LPS had litters in which 5.4 and 4.8% of fetuses were abnormal respectively.

CONCLUSIONS

The findings of this study strongly support the hypothesis that LPS teratogenicity is mediated at least in part by MT-induced changes in maternal Zn homeostasis,which compromises fetal Zn supply.

From farm to table to brain: foodborne pathogen infection and the potential role of the neuro-immune-endocrine system in neurotoxic sequelae

The American diet is among the safest in the world; however, diseases transmitted by foodborne pathogens (FBPs) still pose a public health hazard. FBPs are the second most frequent cause of all infectious illnesses in the United States. Numerous anecdotal and clinical reports have demonstrated that central nervous system inflammation, infection, and adverse neurological effects occur as complications of foodborne gastroenteritis. Only a few well-controlled clinical or experimental studies, however, have investigated the neuropathogenesis. The full nature and extent of neurological involvement in foodborne illness is therefore unclear. To our knowledge, this review and commentary is the first effort to comprehensively discuss the issue of FBP induced neurotoxicity. We suggest that much of this information supports the role of a theoretical model, the neuro-immune-endocrine system, in organizing and helping to explain the complex pathogenesis of FBP neurotoxicity.

Effects of Escherichia coli and Porphyromonas gingivalis lipopolysaccharide on pregnancy outcome in the golden hamster

This report describes the effects of two gram-negative bacterial endotoxin (lipopolysaccharide [LPS]) preparations on hamster pregnancy outcome variables. Single intravenous challenges with Escherichia coli and Porphyromonas gingivalis LPS on day 8 of pregnancy produced dose-dependent effects on fetal weight malformation and fetal resorption with E. coli LPS having potent embryolethal effects. Premating maternal exposure to P. gingivalis produced embryolethal effects similar to those of E. coli. These data suggest that maternal exposure to P. gingivalis LPS prior to and during pregnancy can induce deleterious effects on the developing fetus.

Placental MHC class I antigen expression is induced in mice following in vivo treatment with recombinant interferon-gamma

Allogeneically pregnant mice (NFR/N (Swiss-derived) H2q x 57/B1 H2b) were injected daily from day 11 to 18 of gestation with recombinant rat interferon-gamma (IFN-gamma) and the effects on placental MHC antigen expression were evaluated by immunohistochemistry. The results demonstrated that a daily dose of 200,000 U/mouse induces a significant increase in placental MHC class I expression in the decidua and the basal zone spongiotrophoblast as well as the fetal mesenchyme, while the labyrinthine trophoblast was almost completely MHC negative. No significant induction of MHC class II antigen expression was observed in the placental tissue, with the exception of a few scattered cells. The MHC class II-inducing efficiency of the treatment protocol used was ascertained by staining maternal skin (ear), which proved to contain considerably elevated numbers of MHC class II-positive cells (mainly keratinocytes). The IFN-gamma treated group showed a higher incidence of fetal resorptions than the corresponding controls, but this was probably due to a non-specific toxic effect of the treatment as none of the sera analysed contained detectable amounts of anti-paternal antibodies, no infiltrating lymphocytes were detectable on histological examination of placental sections, and most of the IFN-gamma treated animals successfully completed their pregnancy.

Transplacental effects of endotoxemia on fetal mouse brain, bone, and placental tissue

Pregnant mice were given 0.005 mg endotoxin on day 10 of gestation or 0.0025 mg endotoxin on days 10 and 12. Pregnant mice treated with normal saline served as controls. On day 18 of pregnancy, fetuses and placentas were removed for microscopic and histological examination. The treated placentas had fibrin thrombi and hemorrhages in the labyrinth and spongiosa. Glycogen cells in the spongiosa were swollen. The long bones of experimental animals had few metaphyseal trabeculae, which also were disorganized, with an increase in the number of metaphyseal and diaphyseal osteoclasts. An increase in the number of necrotic neurons was observed in coronal sections of brains of experimental fetuses at the level of the trigeminal ganglion. To correlate the degree of neuronal necrosis with long-term behavioral effects, a behavioral test was performed on pups whose mothers were treated with endotoxin. The pups were tested at the age of 28 days and for the next 3 days for their audiogenic seizure response. The pups of the experimental groups were more sensitive to high sounds than the controls. Escherichia coli endotoxins seemed to have a significant teratogenic effect on mice, being more severe when endotoxin was given in divided doses to the pregnant animals. The widespread endothelial damage or the elevation of prostaglandin levels caused by endotoxins may have been responsible for these teratogenic effects.

Teratogenic effects of endotoxin on the golden hamster

Gram-negative urinary tract infections in pregnant women have been implicated as causes of maternal endotoxemia and a subsequent higher incidence of malformations in their offspring. A study was performed to evaluate the effects of endotoxin on the development of the golden hamster. Endotoxin was shown to be extremely embryolethal at higher doses and to produce several malformations at lower doses. The pregnant hamster and its developing embryos were observed to be far more sensitive to endotoxin than species examined by other investigators.

Studies on Escherichia coli vaccines: estimation of endotoxins in veterinary vaccines

Fifteen batches of E. coli vaccines for pigs, from three different manufacturers, were subjected to a quantitative form of the in vitro Limulus-amoebocyte-lysate (LAL) test for their free endotoxin content. A batch of vaccine associated with abortions in pregnant sows was found to contain a much higher level of free endotoxin than batches of vaccine not associated with abortion. The evidence of these assays suggests that they will be useful in the quality control of E. coli vaccines.