The effect of phosphoramidon on inflammation-mediated preterm delivery in a mouse model

Repeated lipopolysaccharide exposure leads to placental endotoxin tolerance

PROBLEM

Placental infection induces increased levels of pro-inflammatory cytokines, which have been implicated in the pathogenesis of pre-term labor. Endotoxin tolerance is a phenomenon in which exposure to a dose of endotoxin makes tissue less responsive to subsequent exposures. The objective of our study was to determine whether repeated exposure to endotoxin will induce a tolerant phenotype in normal human second-trimester placental tissue.

METHODS OF STUDY

Human second-trimester placental explants from elective termination of pregnancy were cultured and exposed to endotoxin (LPS). After 24 hours, the media was collected for analysis, and the explants were re-exposed to LPS after adding fresh media for another 24 hours. This process was repeated for a total of 4 LPS doses. The media was collected from each day and analyzed for cytokine levels.

RESULTS

The first LPS treatment stimulated the secretion of the pro-inflammatory cytokines IL-1β and TNF-α. However, their production was significantly diminished with repeated LPS doses. Production of the anti-inflammatory cytokines, IL-1ra and IL-10, was also stimulated by the first LPS treatment, but secretion was more gradually and moderately decreased with repeated LPS doses compared to the pro-inflammatory cytokines. The ratios of the anti-inflammatory/pro-inflammatory mediators (IL-1ra/IL-1β and IL-10/TNF-α) indicate a progressively more anti-inflammatory milieu with repeated LPS doses.

CONCLUSION

Repeated LPS exposure of human second-trimester placental tissues induced endotoxin tolerance. We speculate that endotoxin tolerance at the maternal-fetal interface will protect the fetus from exaggerated inflammatory responses after repeated infectious exposure.

Inhibition of sphingosine kinase prevents lipopolysaccharide-induced preterm birth and suppresses proinflammatory responses in a murine model

Premature delivery occurs in 12% of all births, and accounts for nearly half of long-term neurological morbidity, and 60% to 80% of perinatal mortality. Despite advances in obstetrics and neonatology, the rate of premature delivery has increased approximately 12% since 1990. The single most common cause of spontaneous preterm birth is infection. Several lines of evidence have demonstrated the role of endothelin-1 as both a constrictor of uterine myometrial smooth muscle and a proinflammatory mediator. Endothelin-1 activates the phospholipase C pathway, leading to activation of protein kinase C and, in turn, sphingosine kinase (SphK). The inhibition of SphK has been recently shown to control the proinflammatory response associated with sepsis. We show herein, for the first time, that SphK inhibition prevents inflammation-associated preterm birth in a murine model. Rescue of pups from premature abortion with an SphK inhibitor occurs by suppression of the proinflammatory cytokines tumor necrosis factor α, Il-1β, and Il-6 and attenuation of polymorphonuclear inflammatory cells into the placental labyrinth. Moreover, we postulate that inhibition of SphK leads to suppression of endothelin-converting enzyme-1 expression, indicating the presence of an endothelin-converting enzyme 1/endothelin 1-SphK positive feedback loop. This work introduces a novel approach for the control of infection-triggered preterm labor, a condition for which there is no effective treatment.

N,N-dimethylacetamide regulates the proinflammatory response associated with endotoxin and prevents preterm birth

The proinflammatory response leads to various types of pathologic pathways, including the development of preterm birth. Preterm birth occurs in 12% of deliveries in the United States and causes more than 70% of perinatal morbidity and mortality. The most common cause of spontaneous preterm birth is intrauterine infection in the mother. There is accumulating evidence indicating that the release of proinflammatory cytokines plays a critical role in the pathogenesis of inflammation-associated premature delivery. We found that the common organic solvent, N,N-dimethylacetamide (DMA), prevents endotoxin-induced preterm birth in timed pregnant C57BL/6 embryonic day (E)15.5 mice and rescues their pups from spontaneous abortion at doses many-fold lower than those currently used clinically and in a dose-dependent fashion. We also provide histologic evidence that DMA suppresses the endotoxin-triggered proinflammatory response by significantly attenuating inflammatory cell infiltration of placental tissue. Furthermore, immunoblotting analysis of placental tissue harvested from our murine models revealed DMA-mediated regulation of expression of the proinflammatory cytokines IL-1β, tumor necrosis factor α, and IL-6, and increased expression of the regulatory inflammatory cytokine IL-10. By using in vitro studies, we provide evidence that DMA suppresses macrophage function and that this small molecule prevents nuclear translocation of nuclear factor-kB. These results suggest that DMA represents a newly discovered, nontoxic therapy for a broad range of inflammatory disorders.

Blockade of endothelin-1 with a novel series of 1,3,6-trisubstituted-2-carboxy-quinol-4-ones controls infection-associated preterm birth

Preterm birth (PTB) currently accounts for 13% of all births in the United States, with the leading cause of PTB being maternal infection. Endothelin-1, an extremely potent vasoconstrictor capable of increasing myometrial smooth muscle tone, has been shown to be up-regulated in the setting of infection in pregnancy, ultimately leading to PTB. In previous work, we have shown that infection-associated PTB is controlled in our murine model by using phospharamidon, an endothelin-converting enzyme-1 inhibitor; knocking down endothelin-converting enzyme-1 mRNA; or blocking the binding of endothelin-1 to the endothelin-A (ET(A)) receptor with either BQ-123 or with HJP-272, the 6-OH compound of our series of novel synthetic (ET(A)) receptor antagonists. In the current study, we show that HJP-272, a highly selective ET(A) receptor antagonist with an IC(50) of 70.1 nmol/L, binds in a noncompetitive manner to the ET(A) receptor. Additionally, we introduce n-propyl (HJP-286) and n-butyl (HJP-278) analogs of HJP-272. We find that the LD(50) of HJP-272, the analog in the series most effective in controlling preterm birth, is more than 20-fold higher than its therapeutic dose. Acute exposure to high doses of these compounds produces no histological changes in any organ, while chronic exposure produces only a rare hepatotoxic effect. These findings may be of clinical significance, as there is currently no FDA-approved therapy for women presenting with threatened preterm delivery.

Prevention of inflammation-associated preterm birth by knockdown of the endothelin-1-matrix metalloproteinase-1 pathway

Premature delivery occurs in 12% of all births, accounts for nearly half of neonatal morbidity and is increasing in frequency. Current therapeutic approaches to preterm delivery are ineffective and present serious risks to both the mother and fetus. Although there are multiple factors that contribute to the etiology of preterm birth, the single most common cause is infection. Recently, using cDNA microarray analysis of human placental tissue, we demonstrated that human placental matrix metalloproteinase-1 (MMP-1) is upregulated during labor. In a separate line of investigation, we have shown that blockade of endothelin-1 (ET-1) action through the use of an endothelin-converting enzyme-1 (ECE-1) inhibitor, an established commercially available endothelin receptor antagonist or a novel quinolone-derived endothelin receptor antagonist synthesized by our group also prevents preterm labor and delivery in a mouse model. We have now shown that induction of preterm labor with lipopolysaccharide in our mouse model is associated with increased levels of MMP-1. Furthermore, we showed that silencing the ECE-1/ET-1 pathway by using ECE-1 RNA interference prevents both the onset of preterm labor and upregulation of MMP-1. The data indicate that ET-1 and MMP-1 act in the same molecular pathway in preterm labor.

The matrix metalloproteases and endothelin-1 in infection-associated preterm birth

Preterm birth (PTB) is clinically defined as any delivery which occurs before the completion of 37 weeks of gestation, and is currently the most important problem in obstetrics. In the United States, PTB accounts for 12-13% of all live births, and, with the exception of fetuses suffering from anomalies, is the primary cause of perinatal mortality. While the risk factors for PTB are numerous, the single most common cause is intrauterine infection. As there is currently no FDA-approved therapy for infection-associated PTB, understanding the pathogenesis of preterm labor (PTL) and delivery should be given high priority. The matrix metalloproteinases (MMPs) are a family of enzymes that have been implicated in normal parturition as well as infection-triggered rupture of membranes and preterm birth. Several lines of evidence also suggest a role for endothelin-1 (ET-1) in infection-associated preterm delivery. This paper focuses on the evidence that the MMPs and ET-1 act in the same molecular pathway in preterm birth.

Can sulfasalazine prevent infection-mediated pre-term birth in a murine model?

PROBLEM

Sulfasalazine (SASP) blocks activation of nuclear factor-kappa B (NF-kappaB) in gestational tissues in vitro- one of the earliest signals in the inflammatory response. We hypothesized that the administration of SASP would reduce the rate of infection-mediated pre-term birth in a murine model.

METHOD

of study CD-1 mice (n = 40) were assigned on gestational day (gd) 14.5 to 1 of 3 treatments: (1) Sham infection and vehicle; (2) 10(4) CFU Escherichia coli and vehicle; or (3) 10(4) CFU E. coli and SASP (150 mg/Kg daily). Mice were observed twice daily and deliveries prior to gd 18.5 were considered pre-term.

RESULTS

Significantly more mice delivered prior to gd 18.5 when infected with 10(4) CFU E. coli than sham-infected mice (P < 0.001) and this effect was significantly reduced in mice also treated with SASP (P = 0.002). SASP also tended to increase litter size (P = 0.060) and significantly increased weight of pups born to dams with intrauterine infections (P = 0.001).

CONCLUSION

SASP reduced rates of pre-term delivery and improved pregnancy outcomes for mice infected with 10(4) CFU E. coli. This suggests that SASP has the potential to play a role in strategies to prevent pre-term birth in women.

Effect of the putative novel selective ETA-receptor antagonist HJP272, a 1,3,6-trisubstituted-2-carboxy-quinol-4-one, on infection-mediated premature delivery

Preterm birth (PTB), defined as any birth occurring before 37 weeks of gestation, occurs in only 12% of all births, yet accounts for nearly half of long-term neurological morbidity, and 60%-80% of perinatal mortality. The single most common cause of PTB is intrauterine infection. Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that is both upregulated by inflammatory cytokines and capable of increasing myometrial smooth muscle tone. We hypothesized, therefore, that ET-1 is a critical component of the parturition cascade in the setting of infection-associated PTB. In our previous work, we have shown that blockade of ET-1 synthesis through the use of the metalloproteinase inhibitor phosphoramidon results in control of preterm labor. In the current work, we showed that blockade of ET-1 action with 5-50 mg/kg i.p. 3-(3-carboxybenzyl)-1-((6-ethylbenzo[d][1,3]dioxol-5-yl)methyl)-6-hydroxy-4-oxo-1,4-dihydroquinoline-2-carboxylic acid (HJP272), a putative novel selective ETA-receptor antagonist (IC50, 70 nmol/L), prevents PTB induced with up to 50 mg/kg of i.p. lipopolysaccharide in a mouse model. This is the first report, to our knowledge, of control of infection-associated PTB with a specific ETA-receptor antagonist. The identification of a novel effective therapy for PTB could have important clinical implications.

The endothelin-converting enzyme-1/endothelin-1 pathway plays a critical role in inflammation-associated premature delivery in a mouse model

Premature delivery occurs in 12% of all births and accounts for nearly half of long-term morbidity. Current therapeutic approaches to preterm delivery are ineffective and present serious risks to both mother and fetus. The single most common cause of preterm birth is infection. Previous in vitro investigations have shown that endothelin-1 (ET-1) is induced by inflammatory cytokines and that it increases myometrial smooth muscle tone. Furthermore, we have previously shown that both the endothelin-converting enzyme-1 (ECE-1) inhibitor, phosphoramidon, as well as a novel ET-1 receptor A antagonist synthesized by our group, control premature delivery in a mouse model of inflammation-associated preterm delivery. In the current work, we show that levels of both ET-1 and ECE-1 are increased in gestational tissues in E16.5 mice induced to deliver prematurely after lipopolysaccharide administration. We also show that premature delivery is controlled by treatment with the selective endothelin receptor A antagonist BQ-123 in a dose-dependent manner. Finally, we show here for the first time that premature delivery can be controlled using RNA silencing, by hydrodynamic transfection of E15 mice with ECE-1 RNAi. Taken together, these data support a critical role for the ECE-1/ET-1 system in inflammation-associated premature delivery. The ability to control premature delivery by antagonizing or silencing the ECE-1/ET-1 system offers a novel approach to an unmet clinical need.

Phosphoramidon, an endothelin-converting enzyme inhibitor, attenuates lipopolysaccharide-induced acute lung injury

Phosphoramidon blocks the formation of endothelin-1 (ET-1), a proinflammatory mediator implicated in the pathogenesis of a variety of lung diseases. To determine whether phosphoramidon can ameliorate pulmonary inflammation, our laboratory undertook a series of experiments involving treatment of hamsters with either intraperitoneal (i.p.) or aerosolized phosphoramidon prior to induction of acute lung injury by intratracheal administration of lipopolysaccharide (LPS). The results indicate that phosphoramidon significantly reduces LPS-induced pulmonary inflammation as measured by lung histology, neutrophil content of bronchoalveolar lavage (BAL) fluid, percent tumor necrosis factor receptor 1 (TNFR1)-labeled BAL macrophages, and alveolar septal cell apoptosis. In additional experiments, i.p. administration of a novel endothelin A receptor anatgonist (HJP272) similarly decreased BAL neutrophils, whereas i.p. administration of either ET-1, or its precursor peptide, "big" ET-1, had the opposite effect. These findings support further evaluation of phosphoramidon and other ET-1 suppressors as potential treatments for human inflammatory lung disease.

PDE4 inhibition prevents preterm delivery induced by an intrauterine inflammation

The aim of this study was to explore the anti-inflammatory properties of phosphodiesterase-4 (PDE4) inhibitors in vivo and their potential ability to prevent inflammation-induced preterm delivery. Indeed, intrauterine inflammation is the major etiology of very preterm delivery, the leading cause of neonatal mortality and morbidity. Intrauterine injection of Escherichia coli LPS in 15-day-pregnant mice induced an increase of PDE4 activity and PDE4B expression at the maternofetal interface, a rise of amniotic fluid levels of TNF-alpha, IL-1beta, IL-6, and IL-10 and provoked massive preterm delivery and fetal demise. Selective PDE4 inhibition by rolipram prevented the rise in the proinflammatory cytokines. Following the nuclear translocation of the transcription factor NFkappaB, as a marker of cellular activation after the inflammatory challenge, showed a time-dependent sequential activation of the gestational tissues, from the uterine mesometrial to the fetal compartment, particularly in the glycogen-trophoblastic cells of the placenta. This activation was disrupted by PDE4 inhibition, and inflammation-induced preterm delivery and fetal demise were prevented. PDE4 selective inhibitors may thus represent a novel effective treatment to delay inflammation-induced preterm delivery and to prevent adverse outcomes in infants.

The molecular pathophysiology of bacterially induced preterm labor: insights from the murine model

Premature delivery, the most important problem in obstetrics in developed countries, continues to vex clinicians and researchers. Despite decades of investigation, the pathophysiology of premature labor is incompletely understood, and therapies or preventive strategies tailored to each of the many potential causes do not exist. The present review addresses one cause of prematurity, namely, intrauterine bacterial infection. Given the vastness of the literature for even this single etiology, we focus on the mouse as a model organism from which much can be learned about mammalian parturition. The underpinnings of bacterially induced labor are believed to involve a signaling cascade that begins with recognition of offending pathogens by cell-surface receptors (toll-like receptors). This cascade then operates through multiple branching and redundant pathways to bring about the changes within the gestational compartment that produce cervical ripening, labor, and ultimately delivery. The major challenge facing researchers is to understand the levels of complexity in the host response, so that prevention and treatment strategies may be sufficiently focused to minimize unwanted side effects, yet sufficiently broad to be effective. Given the complexity of the problem, this understanding can be aided by efficient model systems, of which one in vivo example is the mouse, an organism that shares with humans many similarities in the biochemical and molecular aspects of inflammation-induced preterm labor. We propose that tools with the power to assess simultaneously the myriad elements of the hypothesized signaling cascade (ie, genomic and proteomic technologies) are important components of the solution to the puzzle of parturition.