Lipopolysaccharide (LPS) Up-Regulates the Expression of Haem Oxygenase-1 in Mouse Placenta

Inflammation-induced alterations in maternal-fetal Heme Oxygenase (HO) are associated with sustained innate immune cell dysregulation in mouse offspring

Heme oxygenase-1 (HO-1) is an evolutionarily conserved stress response enzyme and important in pregnancy maintenance, fetal and neonatal outcomes, and a variety of pathologic conditions. Here, we investigated the effects of an exposure to systemic inflammation late in gestation [embryonic day (E)15.5] on wild-type (Wt) and HO-1 heterozygous (Het, HO-1^+/-) mothers, fetuses, and offspring. We show that alterations in fetal liver and spleen HO homeostasis during inflammation late in gestation can lead to a sustained dysregulation of innate immune cell populations and intracellular myeloid HO-1 expression in the spleen through young adolescence [postnatal day 25] in mice.

Antenatal pentoxifylline therapy to prevent endotoxin-induced fetal injury in the preterm goat model

Objective:

Pentoxifylline (PTX) has immunomodulatory properties and is known to reduce sepsis-associated infant mortality. We aimed to evaluate maternal oral and intra-amniotic administration of PTX for the prevention of fetal inflammation and injury in a caprine model.

Materials and Methods:

Inflammation-mediated fetal injury was induced with maternal granulocyte-colony stimulating factor and intra-amniotic endotoxin at 0.76 of gestation in date-mated pregnant goats. Eight groups were formed (n=4 each): Control, fetal injury, oral 30 mg/kg/day and 60 mg/kg/day PTX for 15 days + fetal injury, intra-amniotic 400 mg/kg and 800 mg/kg estimated fetal weight single-dose PTX with and without fetal injury. Preterm delivery by hysterotomy was performed at 0.80 of gestation to evaluate the fetal and placental effects. Immunochemistry for various markers including interleukins, caspases, cyclooxygenases, vimentin, myelin basic protein, and surfactant proteins were carried out in the fetal lungs, fetal brain, and placenta. Fetal plasma and amniotic fluid interleukins were also evaluated. Kruskal-Wallis H test and Mann-Whitney U test were used for comparisons.

Results:

High-dose (60 mg/kg/day) maternal prophylactic oral treatment attenuated endotoxin-related histological injury and was related to low inflammatory marker expressions comparable to the controls (p>0.05 except cyclooxygenase 2). Following maternal oral administration, fetal plasma and amniotic fluid levels of the studied interleukins were also lower than the untreated endotoxin-exposed animals (p<0.05 for all comparisons). Intra-amniotic PTX was associated with inconsistent results and increased inflammatory markers in some fetuses.

Conclusion:

Oral PTX before preterm birth mitigates intrauterine inflammation with neuroprotective effects in the fetus. PTX can be considered as a candidate drug for fetal brain injury prevention in the preterm period.

Heme Oxygenase Protects against Placental Vascular Inflammation and Abortion by the Alarmin Heme in Mice

Both infectious as non-infectious inflammation can cause placental dysfunction and pregnancy complications. During the first trimester of human gestation, when palatogenesis takes place, intrauterine hematoma and hemorrhage are common phenomena, causing the release of large amounts of heme, a well-known alarmin. We postulated that exposure of pregnant mice to heme during palatogenesis would initiate oxidative and inflammatory stress, leading to pathological pregnancy, increasing the incidence of palatal clefting and abortion. Both heme oxygenase isoforms (HO-1 and HO-2) break down heme, thereby generating anti-oxidative and -inflammatory products. HO may thus counteract these heme-induced injurious stresses. To test this hypothesis, we administered heme to pregnant CD1 outbred mice at Day E12 by intraperitoneal injection in increasing doses: 30, 75 or 150 μmol/kg body weight (30H, 75H or 150H) in the presence or absence of HO-activity inhibitor SnMP from Day E11. Exposure to heme resulted in a dose-dependent increase in abortion. At 75H half of the fetuses where resorbed, while at 150H all fetuses were aborted. HO-activity protected against heme-induced abortion since inhibition of HO-activity aggravated heme-induced detrimental effects. The fetuses surviving heme administration demonstrated normal palatal fusion. Immunostainings at Day E16 demonstrated higher numbers of ICAM-1 positive blood vessels, macrophages and HO-1 positive cells in placenta after administration of 75H or SnMP + 30H. Summarizing, heme acts as an endogenous “alarmin” during pregnancy in a dose-dependent fashion, while HO-activity protects against heme-induced placental vascular inflammation and abortion.

Immune challenge-induced oxidative damage may be mitigated by biliverdin

An effective immune response results in the elimination of pathogens, but this immunological benefit may be accompanied by increased levels of oxidative damage. However, organisms have evolved mechanisms to mitigate the extent of such oxidative damage, including the production and mobilization of antioxidants. One potential mechanism of mitigating immune challenge-induced changes in oxidative physiology is increasing biliverdin production. Biliverdin is chemically an antioxidant, but within-tissue correlations between biliverdin concentration and oxidative damage have never been directly examined. To test how biliverdin tissue concentrations are associated with physiological responses to an immune challenge, we exposed northern bobwhite quail (Colinus virginianus) to one of four treatments: injection of a non-pathogenic antigen - either lipopolysaccharide or phytohemagglutinin, control injection of phosphate-buffered saline or a sham procedure with no injection. Twenty-four hours later, we quantified oxidative damage and triglyceride concentration in the plasma, and biliverdin concentration in the plasma, liver and spleen. We found that both types of immune challenge increased oxidative damage relative to both non-injected and vehicle-injected controls, but treatment had no effects on any other metric. However, across all birds, oxidative damage and biliverdin concentration in the plasma were negatively correlated, which is consistent with a localized antioxidant function of biliverdin. Additionally, we uncovered multiple links between biliverdin concentration, change in mass during the immune challenges and triglyceride levels, suggesting that pathways associated with biliverdin production may also be associated with aspects of nutrient mobilization. Future experiments that manipulate biliverdin levels or oxidative damage directly could establish a systemic antioxidant function or elucidate important physiological impacts on body mass maintenance and triglyceride storage, mobilization or transport.

Melatonin and endoplasmic reticulum stress: relation to autophagy and apoptosis

Endoplasmic reticulum (ER) is a dynamic organelle that participates in a number of cellular functions by controlling lipid metabolism, calcium stores, and proteostasis. Under stressful situations, the ER environment is compromised, and protein maturation is impaired; this causes misfolded proteins to accumulate and a characteristic stress response named unfolded protein response (UPR). UPR protects cells from stress and contributes to cellular homeostasis re-establishment; however, during prolonged ER stress, UPR activation promotes cell death. ER stressors can modulate autophagy which in turn, depending of the situation, induces cell survival or death. Interactions of different autophagy- and apoptosis-related proteins and also common signaling pathways have been found, suggesting an interplay between these cellular processes, although their dynamic features are still unknown. A number of pathologies including metabolic, neurodegenerative and cardiovascular diseases, cancer, inflammation, and viral infections are associated with ER stress, leading to a growing interest in targeting components of the UPR as a therapeutic strategy. Melatonin has a variety of antioxidant, anti-inflammatory, and antitumor effects. As such, it modulates apoptosis and autophagy in cancer cells, neurodegeneration and the development of liver diseases as well as other pathologies. Here, we review the effects of melatonin on the main ER stress mechanisms, focusing on its ability to regulate the autophagic and apoptotic processes. As the number of studies that have analyzed ER stress modulation by this indole remains limited, further research is necessary for a better understanding of the crosstalk between ER stress, autophagy, and apoptosis and to clearly delineate the mechanisms by which melatonin modulates these responses.

Heme oxygenase-1 is critically involved in placentation, spiral artery remodeling, and blood pressure regulation during murine pregnancy

The onset of pregnancy implies the appearance of a new organ, the placenta. One main function of the placenta is to supply oxygen to the fetus via hemoproteins. In this review, we highlight the importance of the enzyme heme oxygenase-1 (HO-1) for pregnancy to be established and maintained. HO-1 expression is pivotal to promote placental function and fetal development, thus determining the success of pregnancy. The deletion of the gene Hmox1 in mice leads to inadequate remodeling of spiral arteries and suboptimal placentation followed by intrauterine growth restriction (IUGR) and fetal lethality. A partial Hmox1 deletion leads to IUGR as well, with heterozygote and wild-type fetuses being born, but Hmox1 (-/-) significantly below the expected Mendelian rate. This strong phenotype is associated with diminished number of pregnancy-protective uterine natural killer (uNK) cells. Pregnant heterozygote females develop gestational hypertension. The protective HO-1 effects on placentation and fetal growth can be mimicked by the exogenous administration of carbon monoxide (CO), a product of heme catalyzed by HO-1. CO application promotes the in situ proliferation of uNK cells, restores placentation and fetal growth, while normalizing blood pressure. Similarly, HO-1 inhibition provokes hypertension in pregnant rats. The HO-1/CO axis plays a pivotal role in sustaining pregnancy and aids in the understanding of the biology of pregnancy and reveals a promising therapeutic application in the treatment of pregnancy complications.

Prostaglandins as negative regulators against lipopolysaccharide, lipoteichoic acid, and peptidoglycan-induced inducible nitric oxide synthase/nitric oxide production through reactive oxygen species-dependent heme oxygenase 1 expression in macrophages

Although prostaglandins (PGs) were reported to exert proinflammatory and anti-inflammatory effects in macrophages, their action mechanisms remain unclear. The effects of PGs including PGJ2 (J2), Δ-PGJ2 (Δ), 15-deoxy-Δ PGJ2 (15d), PGE2 (E2), and PGF2α (F2α) on lipopolysaccharide (LPS)-, lipoteichoic acid (LTA)-, and peptidoglycan (PGN)-induced inducible nitric oxide (NO) synthase (iNOS)/NO production by RAW264.7 macrophages were investigated. First, we found that induction of cyclooxygenase 2 (COX-2) protein occurred at a time earlier than that of heme oxygenase 1 (HO-1) protein, and the addition of the COX-2 inhibitor NS398 reduced HO-1 protein expression in LPS-, LTA-, and PGN-treated RAW264.7 macrophages. Incubation of RAW264.7 macrophages with the indicated PGs showed that J2, Δ, and 15d significantly induced HO-1 protein expression; however, E2 and F2α did not. Heme oxygenase 1 protein induced by J2, Δ, and 15d was inhibited by the transcriptional inhibitor, actinomycin (Act) D; the translational inhibitor, cycloheximide; and the antioxidant, N-acetyl cysteine (NAC). Increases in intracellular peroxide levels by J2, Δ, and 15d were detected via a 2',7'™-dichlorofluorescein diacetate (DCFH-DA) analysis, and they were prevented by the addition of NAC. In addition, J2, Δ, and 15d produced significant inhibition of LPS-, LTA-, and PGN-induced iNOS protein and NO production by RAW264.7 cells, in accordance with increased HO-1 protein expression. Reductions of LPS-, LTA-, and PGN-induced phosphorylated c-Jun N-terminal kinase, c-Jun protein, and activator protein 1 luciferase activity by J2, Δ, and 15d were identified, and the addition of the HO-1 inhibitor, tin protoporphyrin, reversed the inhibitory effects of Δ and 15d on LPS- and LTA-induced iNOS/NO, phosphorylated c-Jun N-terminal kinase, and c-Jun protein expressions by macrophages. Knockdown of HO-1 protein expression by HO-1 small interfering RNA blocked Δ and 15d inhibition of LPS- and LTA-induced events. Moreover, the compound, cyclopentenone (CP), which mimics the CP moiety of 15d, and its analog cyclohexenone were used, and cyclohexenone showed more potent induction of the HO-1 protein with effective inhibition of LPS-, LTA-, and PGN-induced iNOS/NO production than CP in macrophages. Reactive oxygen species-dependent HO-1 protein expression by PGs, which inhibited LPS-, LTA-, and PGN-induced iNOS/NO production, was identified in macrophages.

Melatonin alleviates lipopolysaccharide-induced placental cellular stress response in mice

Melatonin protects mice from lipopolysaccharide (LPS)-induced fetal death and intra-uterine growth retardation. Nevertheless, its molecular mechanism remains obscure. In the present study, we investigated the effects of melatonin on LPS-induced cellular stress in placenta. Pregnant mice were given with melatonin [5.0 mg/kg, intraperitoneal (i.p.)] 30 min before and 150 min after LPS (300 μg/kg, i.p.) on gestational day 15. Oxidative stress, endoplasmic reticulum (ER) stress, hypoxic stress, and heat stress in placenta were analyzed at 4 hr after LPS. As expected, maternal LPS administration resulted in placental glutathione (GSH) depletion and up-regulated the expression of placental antioxidative enzymes. In addition, LPS significantly increased the level of inducible nitric oxide synthase (iNOS) and enhanced the intensity of placental 3-nitrotyrosine residues. An ER stress, as determined by a decreased GRP78 expression, an obvious eIF2α and JNK phosphorylation, and an increased CHOP expression, were observed in placenta of pregnant mice injected with LPS. In addition, LPS significantly increased mRNA level of placental HIF-1α, VEGF, and ET-1, the markers of hypoxic stress. Heme oxygenase (HO)-1, a marker of heat stress, was also up-regulated in placenta of LPS-treated pregnant mice. Interestingly, LPS-induced placental oxidative stress, hypoxic stress, and ER stress were significantly alleviated when pregnant mice were given with melatonin, whereas melatonin had little effect on LPS-evoked placental HO-1 expression. In conclusion, maternally administered melatonin alleviates LPS-induced cellular stress in the placenta. Melatonin may be useful as pharmacological agents to protect the fetuses against LPS-induced intra-uterine fetal death and intra-uterine growth restriction.

Effects of prenatal infection on brain development and behavior: a review of findings from animal models

Epidemiological studies with human populations indicate associations between maternal infection during pregnancy and increased risk in offspring for central nervous system (CNS) disorders including schizophrenia, autism and cerebral palsy. Since 2000, a large number of studies have used rodent models of systemic prenatal infection or prenatal immune activation to characterize changes in brain function and behavior caused by the prenatal insult. This review provides a comprehensive summary of these findings, and examines consistencies and trends across studies in an effort to provide a perspective on our current state of understanding from this body of work. Results from these animal modeling studies clearly indicate that prenatal immune activation can cause both acute and lasting changes in behavior and CNS structure and function in offspring. Across laboratories, studies vary with respect to the type, dose and timing of immunogen administration during gestation, species used, postnatal age examined and specific outcome measure quantified. This makes comparison across studies and assessment of replicability difficult. With regard to mechanisms, evidence for roles for several acute mediators of effects of prenatal immune activation has emerged, including circulating interleukin-6, increased placental cytokines and oxidative stress in the fetal brain. However, information required to describe the complete mechanistic pathway responsible for acute effects of prenatal immune activation on fetal brain is lacking, and no studies have yet addressed the issue of how acute prenatal exposure to an immunogen is transduced into a long-term CNS change in the postnatal animal. Directions for further research are discussed.

Reactive oxygen species contribute to lipopolysaccharide-induced teratogenesis in mice

Lipopolysaccharide (LPS) has been associated with adverse developmental outcome, including embryonic resorption, fetal death and growth retardation, and preterm delivery. In the present study, we showed that an ip injection with LPS daily from gestational day (gd) 8 to gd 12 resulted in the incidence of external malformations. The highest incidence of malformed fetuses was observed in fetuses from dams exposed to 20 microg/kg LPS, in which 34.9% of fetuses per litter were externally malformed. In addition, 17.4% of fetuses per litter in 30 microg/kg group and 12.5% of fetuses per litter in 10 microg/kg group were externally malformed. Importantly, external malformations were also observed in fetuses from dams exposed to only two doses of LPS (20 microg/kg, ip) on gd 8, in which 76.5% (13/17) of litters and 39.1% of fetuses per litter were affected. LPS-induced teratogenicity seemed to be associated with oxidative stress in fetal environment, measured by lipid peroxidation, nitrotyrosine residues, and glutathione (GSH) depletion in maternal liver, embryo, and placenta. alpha-Phenyl-N-t-butylnitrone (PBN, 100 mg/kg, ip), a free radical spin-trapping agent, abolished LPS-induced lipid peroxidation, nitrotyrosine residues, and GSH depletion. Consistent with its antioxidant effects, PBN decreased the incidence of external malformations. Taken together, these results suggest that reactive oxygen species might be, at least partially, involved in LPS-induced teratogenesis.