Early pregnancy prediction of spontaneous preterm birth before 32 completed weeks of pregnancy using plasma RNA: transcriptome discovery and initial validation of an RNA panel of markers

OBJECTIVE

To compare the second-trimester plasma cell-free (PCF) transcriptome of women who delivered at term with that of women with spontaneous preterm birth (sPTB) at or before 32 weeks of gestation and identify/validate PCF RNA markers present by 16 weeks of gestation.

DESIGN

Prospective case-control study.

SETTING

Academic tertiary care centre.

POPULATION

Pregnant women with known outcomes prospectively sampled.

METHODS

PCF RNAs extracted from women at 22-24 weeks of gestation (five sPTB up to 32 weeks and five at term) were hybridised to gene expression arrays. Differentially regulated RNAs for sPTB up to 32 weeks were initially selected based on P value compared with control (P < 0.01) and fold change (≥1.5×). Potential markers were then reordered by narrowness of distribution. Final marker selection was made by searching the Metacore™ database to determine whether the PCF RNAs interacted with a reported set of myometrial Preterm Initiator genes. RNAs were confirmed by quantitative reverse transcription polymerase chain reaction and tested in a second group of 40 women: 20 with sPTB up to 32 weeks (mean gestation 26.5 weeks, standard deviation ±2.6 weeks), 20 with spontaneous term delivery (40.1 ± 0.9 weeks) sampled at 16-19+5  weeks of gestation.

MAIN OUTCOME MEASURE

Identification of PCF RNAs predictive of sPTB up to 32 weeks.

RESULTS

Two hundred and ninety-seven PCR RNAs were differentially expressed in sPTB up to 32 weeks of gestation. Further selection retained 99 RNAs (86 mRNAs and 13 microRNAs) and five of these interacted in silica with seven Preterm Initiator genes. Four of five RNAs were confirmed and tested on the validation group. The expression of each confirmed PCF RNA was significantly higher in sPTB up to 32 weeks of gestation. In vitro study of the four mRNAs revealed higher expression in placentas of women with sPTB up to 32 weeks and the potential to interfere with myometrial quiescence.

CONCLUSIONS

The PCF RNA markers are highly associated with sPTB up to 32 weeks by 16 weeks of gestation.

TWEETABLE ABSTRACT

Women destined for spontaneous preterm birth can be identified by 16 weeks of gestation with a panel of maternal plasma RNAs.

The effect of an endothelin antagonist on blood pressure in a rat model of preeclampsia

OBJECTIVE

We attempted to determine the role of endothelin in a previously characterized animal model of preeclampsia by studying the effect of a specific endothelin antagonist, BQ123, on blood pressure.

STUDY DESIGN

A preeclampsia-like condition was induced by infusing pregnant rats with the nitric oxide synthase inhibitor N(G)-nitro-L -arginine methyl ester. Osmotic minipumps were inserted subcutaneously into timed pregnant Harlan-Sprague-Dawley rats on day 17 of pregnancy (term, 22 days). The pumps were loaded to continuously deliver either vehicle (control group) or N(G)-nitro-L -arginine methyl ester 50 mg/d, either alone or with BQ123 at 0.5 mg/d. In a similar but separate experiment, the dose of BQ123 was increased to 1 mg/d. Blood pressure was measured with the tail-cuff method before pump insertion and then daily until postpartum day 2.

RESULTS

Except for a decrease on the day after pump insertion, BQ123 0.5 mg/d had no significant effect on the hypertension induced by N(G)-nitro-L -arginine methyl ester. At the higher dose, however, BQ123 significantly attenuated the increase in blood pressure induced by N(G)-nitro-L -arginine methyl ester during most of the study period.

CONCLUSION

The effect of nitric oxide inhibition can be successfully attenuated by the use of an endothelin antagonist, thereby supporting the role of endothelin in the hypertension described with the preeclampsialike condition seen in pregnant rats.

The effect of indomethacin and prostacyclin agonists on blood pressure in a rat model of preeclampsia

OBJECTIVE

This study was designed to determine the effects of cyclooxygenase inhibition and prostacyclin agonists on the hypertension induced by nitric oxide synthase blockade in a previously characterized rat model of preeclampsia.

STUDY DESIGN

A condition similar to preeclampsia was induced by infusing pregnant rats with the nitric oxide synthase inhibitor N G -nitro- L -arginine methyl ester through subcutaneously implanted osmotic minipumps. Blood pressure was measured with the tail cuff method. In the first experiment the rats received either vehicle alone (control group), N G -nitro- L -arginine methyl ester (50 mg/d), indomethacin (0.1 mg/d), or N G -nitro- L -arginine methyl ester plus indomethacin beginning on day 17 of pregnancy. In the second experiment the rats received vehicle alone (control group), N G -nitro- L -arginine methyl ester (50 mg/d), or N G -nitro- L -arginine methyl ester plus iloprost (31 microgram/d). In a third experiment cicaprost (15 microgram/d) was substituted for iloprost.

RESULTS

Except for an increase on the day after insertion of the pump indomethacin had no significant effect on the hypertension induced by N G -nitro- L -arginine methyl ester. Both prostacyclin agonists (iloprost and cicaprost), however, attenuated the rise in blood pressure usually seen after N G -nitro- L -arginine methyl ester administration.

CONCLUSIONS

Nonselective inhibition of the cyclooxygenase enzymatic system does not influence the hypertension seen in the rat preeclampsia model induced by chronic nitric oxide deficiency. The hypertension in this model can be partially reversed with prostacyclin analogs.

Control and assessment of the uterus and cervix during pregnancy and labour

Preterm labour and resultant preterm birth are the most important problems in perinatology. Countless efforts have failed to establish a single effective treatment of preterm labour, partly because the mechanisms regulating the uterus and cervix during pregnancy are not well understood. New knowledge is needed to inhibit early progression of labour (uterine contractility and cervical ripening), and adequate quantitative tools to evaluate the uterus and cervix during pregnancy are lacking. In this review, we outline studies showing that the uterus (myometrium) and cervix pass through a conditioning step in preparation for labour. This step is not easily identifiable with present methods to assess the uterus or cervix. In the uterus, this seemingly irreversible step consists of changes in the electrical properties to make muscle more excitable and responsive to produce forceful contractions. In the cervix, the step consists of softening of the connective tissue components. Progesterone appears to have a dominant role in controlling both the uterus and cervix, as antiprogestins induce early, preterm conditioning leading to preterm labour. Apparently, nitric oxide (NO) also controls conditioning of the uterus and cervix. In the uterus, NO, in concert with progesterone, inhibits uterine contractility. At term, NO production by the uterus and placenta are decreased and allow labour to progress. In contrast, NO in the cervix increases at the end of pregnancy and it may be the final pathway for stimulating cervical ripening by activation of metalloenzymes. The progress of labour can be assessed non-invasively using electromyographic (EMG) signals from the uterus (the driving force for contractility) recorded from the abdominal surface. Uterine EMG bursts detected in this manner characterize uterine contractile events during human and animal pregnancy. A low uterine EMG activity, measured transabdominally throughout most of pregnancy, rises dramatically during labour. EMG activity also increases substantially during preterm labour in humans and rats. This method may be used one day to predict impending preterm labour and identify control steps and treatments. A quantitative method also assesses the cervix, using an optical device which measures collagen fluorescence in the cervix. The collascope estimates cervical collagen content from a fluorescent signal generated when collagen cross-links are illuminated with excitation light of about 340 nm. The system has proved useful in rats and humans at various stages of pregnancy, and indicates that cervical softening occurs progressively in the last one-third of pregnancy. In rats, collascope readings correlate with resistance measurements made in the isolated cervix, which may help to assess cervical function during pregnancy, and indicate control and treatments.

Changes in expression of the nitric oxide synthase isoforms in rat uterus and cervix during pregnancy and parturition

Nitric oxide (NO) is considered to be an important local mediator that suppresses uterine contractility in rats and rabbits during pregnancy until term. The aim of this study was to investigate the mRNA concentrations for the three isoforms of nitric oxide synthase (NOS) in rat uterus and cervix and to determine whether alterations occur in association with labour at term or preterm. RNA was isolated from full thickness uterine and cervical tissues from pregnant rats at various times during gestation, during labour at term or preterm and post partum. RNA was analysed using reverse transcription-polymerase chain reaction (RT-PCR) with a single set of amplimers specifically designed to detect all three isoforms of NOS. Three distinct PCR products were detected which corresponded to the expected sizes for endothelial (e)NOS, neuronal (b)NOS and inducible (i)NOS products (805, 521 and 428 bp respectively). In all tissues, the 428 bp product predominated and sequence analysis revealed this to be iNOS mRNA with a very close homology (97%) to the published sequence of rat iNOS. Densitometric analysis showed that uterine iNOS mRNA was increased during pregnancy, decreased on day 22 before labour and decreased further during labour at term. In contrast, cervical iNOS mRNA was low until delivery (day 22) when it increased and was dramatically elevated during labour. Similarly, 3 h after injection with the antiprogestin onapristone, iNOS mRNA was significantly decreased in the uterus (approximately 45%) and increased in the cervix (approximately 245%) when compared with controls. The mRNAs to bNOS and eNOS (corresponding to the 521 and 805 bp bands) were generally greatly reduced in quantity compared with the 428 bp product. The changes in these constitutive isoforms during gestation were minor compared with those in the inducible isoform. We conclude that the iNOS transcript is the most abundant NOS mRNA in the uterus as well as in the cervix and this probably indicates that the inducible NOS is the main isoform present in these tissues. The changes in iNOS mRNA at the end of pregnancy may play a role in the initiation of term labour and cervical ripening. Furthermore, the changes in expression of iNOS can be mimicked during preterm labour following antiprogesterone treatment, and may suggest that progesterone differentially controls the expression of iNOS in the uterus and cervix.

Contrasting effects of diethylenetriamine-nitric oxide, a spontaneously releasing nitric oxide donor, on pregnant rat uterine contractility in vitro versus in vivo

OBJECTIVE

The aim of the study was to investigate the in vitro (on tension) and in vivo (on intrauterine pressure) effects of a spontaneously releasing nitric oxide adduct, diethylenetriamine-nitric oxide, on rat uterine contractility.

STUDY DESIGN

Contractile responses to the nitric oxide donor diethylenetriamine-nitric oxide on isometric tension of rat uterine strips (in vitro) and on intrauterine pressure (in vivo) in anesthetized and conscious animals were quantified at late gestation and during preterm and term labor. Preterm labor was induced with the administration of a single injection of the antiprogestin onapristone (10 mg). All control animals were injected with diethylenetriamine, the parent compound, without nitric oxide.

RESULTS

The nitric oxide donor diethylenetriamine-nitric oxide relaxes rat uterine tissues when given in vitro during gestation (median effective dose 0.30 +/- 0.09 mmol/L) but fails to have an effect on uterine tissues from laboring term and preterm animals in the muscle bath. Intraperitoneal injection of the nitric oxide adduct in doses of 5 mg and 50 mg produced a significant and sustained decrease in intrauterine pressure in both delivering and nondelivering animals compared with intrauterine pressure values before administration. Analysis of intrauterine pressure levels at different time frames (before injection, immediately after injection, and after 30, 60, and 90 minutes) in anesthetized rats between days 19 and 21 of gestation shows that the dose of 5 mg diethylenetriamine-nitric oxide significantly (p < 0.05) decreased contractility starling at 30 minutes after administration. Similarly, during labor diethylenetriamine-nitric oxide (5 mg intraperitoneally) decreased contractility (p < 0.05) but only starting at 60 minutes after injection. However, with the dose of 50 mg diethylenetriamine-nitric oxide contractility was reduced 30 minutes (p < 0.05) after treatment during pregnancy (days 19 to 21). The same dose of diethylenetriamine-nitric oxide produced a greater relaxation immediately after intraperitoneal injection (p < 0.05) in the laboring group. Diethylenetriamine-nitric oxide (50 mg) also induced an earlier onset and greater relaxation in animals delivering preterm compared with nondelivering animals at the same stage of gestation. The intrauterine pressure maintained constant contractility levels throughout the 100-minute recording period in the control groups of anesthetized and conscious animals that were injected with diethylenetriamine at the equivalent doses. In the preterm laboring group the effects were similar in both anesthetized and conscious animals.

CONCLUSION

Although in vitro studies of uterine muscle show decreased inhibitory responses to nitric oxide donors during spontaneous term labor and preterm labor compared with tissues collected during late pregnancy (day 19), studies in vivo demonstrate that nitric oxide donors can decrease uterine contractility even more effectively during delivery. The results suggest that nitric oxide donors may act indirectly or that the fetal-placental unit increases the availability of nitric oxide in vivo. Therefore, despite what in vitro studies alone suggest, nitric oxide donor drugs may be very effective in suppressing either term or preterm labor.

Differential regulation of nitric oxide in the rat uterus and cervix during pregnancy and labour

The aim of this study was to determine if nitric oxide (NO) production and nitric oxide synthase (NOS) isoforms change within the uterus and cervix during pregnancy and labour either at term or preterm. NO production was compared in the rat uterus and cervix of non-pregnant and pregnant rats on days 18-22 prior to labour, day 22 during delivery, 1 day post-partum and after treatment with either 10 mg onapristone or progesterone. Uterine NO synthesis, reflected in nitrite production, increased during gestation (194.2 +/- 22.6 nmol/g on day 19) compared with the non-pregnant state (76.2 +/- 18.4 nmol/g, P < 0.05) and decreased during term labour and post-partum. Furthermore, injection of lipopolysaccharide (LPS) (100 micrograms/rat i.p.) on day 20 of gestation resulted in a significant increase in NO synthesis after 6 h. Conversely, cervical NO synthesis and nitrite production was low in the non-pregnant (65.1 +/- 9.2 nmol/g) and pregnant animals on days 18-22 of gestation (53.2 +/- 9.0 nmol/g on day 22, P > 0.05), but markedly increased during term labour (139 +/- 28.6 nmol/g, P < 0.05). Treatment with the antiprogestin onapristone suppressed uterine NO production and increased cervical production while continuous administration of progesterone from day 19 had the opposite effect. LPS produced a significant increase in cervical NO production in both the pregnant (8-fold) and non-pregnant (4-fold) states. All three known NOS isoforms (i.e., iNOS, nNOS and eNOS) were detected in the cervical samples but only two were present in the uterus (iNOs and eNOS). An increase in the presence of iNOS occurred during labour at term compared with cervices collected from day 19. This was contrary to the measurements of the isoform in the uterus. Also, there was a similar increase of nNOS in the cervix during labour. This isoform seemed absent in the uterus during gestation. No significant changes occurred in the abundance of eNOS in the cervix during labour at term compared with day 19. During preterm labour after onapristone, iNOS concentrations increased significantly in the cervix. In order to examine whether the NO pathway plays a role in cervical ripening, the effects of the nitric oxide synthesis inhibitor L-nitro-arginine methylester (L-NAME) on the duration of delivery and on cervical extensibility were also investigated. The duration of delivery was significantly prolonged in L-NAME-treated rats compared with the control group (2.4-fold). Moreover, cervical extensibility decreased significantly (1.7-fold) after in-vitro incubation with L-NAME (P < 0.005). We conclude that the NO system may have an active role in the cascade of processes involved in preparing the uterus and cervix for parturition.

Preterm birth in rats produced by the synergistic action of a nitric oxide inhibitor (NG-nitro-L-arginine methyl ester) and an antiprogestin (onapristone)

OBJECTIVE

The aim of this study was to determine whether inhibition of nitric oxide synthesis would affect the action of an antiprogesterone to provoke preterm labor.

STUDY DESIGN

Pregnant rats were continuously infused with NG-nitro-L-arginine methyl ester starting on day 16 of gestation. On day 17 of gestation groups of animals were injected subcutaneously with a single dose of either 3 or 30 mg/kg onapristone; animals were monitored for preterm labor and delivery for up to 48 hours.

RESULTS

Significant findings included the following results. (1) Combined treatment with NG-nitro-L-arginine methyl ester (50 mg per day) and low-dose onapristone (3 mg/kg) produced preterm labor, > 70% of the fetuses were delivered within 27 hours of treatment, whereas < 5% of the fetuses were delivered in the animals receiving either of these compounds alone. (2) NG-nitro-D-arginine methyl ester (50 mg per day) had no effect. (3) inhibition of nitric oxide by NG-nitro-L-arginine methyl ester also significantly increased the efficacy of high-dose onapristone (30 mg/kg) in preterm labor and delivery.

CONCLUSION

Treatment of pregnant rats with a combination of a nitric oxide inhibitor with onapristone significantly potentiated the ability of the antiprogesterone to induce preterm labor. The interaction of nitric oxide and progesterone may be required to maintain pregnancy.

Pre-eclampsia-like conditions produced by nitric oxide inhibition: effects of L-arginine, D-arginine and steroid hormones

The aim of this study was to establish that inhibiting nitric oxide (NO) production with NG-nitro-L-arginine methyl ester (L-NAME) results in high blood pressure conditions in chronically treated pregnant rats. To validate the model, the effects of L-arginine (the substrate for NO) and D-arginine (the stereoisomer of L-arginine which is not a substrate for NO synthesis) were studied on blood pressure and fetal weights. The effects of a progesterone agonist, promegestone (R5020) and 17 beta-oestradiol were also explored. The NO synthase inhibitor L-NAME was chronically infused s.c. into pregnant rats from day 17 of gestation, either alone or with the simultaneous infusion of L-arginine and injections of sex steroid hormones (promegestone and oestradiol), compounds that may act in the pathogenic pathways of pre-eclampsia. Systolic blood pressure was measured daily. Weight and mortality of pups were recorded immediately after delivery. Blood pressure was elevated significantly in rats treated with L-NAME for only 1 day following infusion; there was a consistent decline during the next 3 days of pregnancy followed by a dramatic and significant rise just prior to delivery and post-partum. Fetal weights were reduced significantly in the L-NAME-treated rats. Co-treatment of L-NAME-infused rats with L-arginine reversed both the increase in blood pressure and the decrease in fetal weights observed with L-NAME alone. R5020, but not oestradiol, also reduced blood pressure and increased fetal weights in the L-NAME-treated animals. NO appears to play essential roles in the regulation of blood pressure during pregnancy, as well as in fetal perfusion and fetal weights at delivery. This study also indicates that progesterone, and not oestrogen, may regulate the vascular adaptations during normal pregnancy. L-Arginine and progesterone agonists like promegestone may have beneficial effects on the high blood pressure levels and reduced fetal weights associated with pre-eclampsia.

Involvement of a nitric oxide-cyclic guanosine monophosphate pathway in control of human uterine contractility during pregnancy

OBJECTIVES

The aims of the study were to investigate whether a nitric oxide-cyclic guanosine monophosphate relaxation pathway is present in the human uterus and whether it differentially inhibits contractility during pregnancy and labor.

STUDY DESIGN

Myometrial strips were obtained from pregnant women who were either in labor or not in labor and from nonpregnant women. Nitrites and cyclic guanosine monophosphate production by the tissues and contractile responses to nitric oxide modifiers were measured.

RESULTS

Biochemical assays revealed that nitric oxide (nitrites) and cyclic guanosine monophosphate are generated by the human uterus. Cyclic guanosine monophosphate production by the uterus was increased by L-arginine (the substrate for nitric oxide) and diethylamine/nitric oxide (a nitric oxide donor) and decreased by nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase). Spontaneous contractility in vitro was increased by nitro-L-arginine methyl ester and decreased by diethylamine/nitric oxide, which furthermore produced a dose-dependent inhibition of contractility, and the median effective dose of inhibition in tissues from nonlaboring pregnant patients (1.5 +/- 0.4 mumol/L) is substantially lower than in tissues from laboring pregnant (21.7 +/- 7.4 mumol/L or nonpregnant (20.8 +/- 4.4 mumol/L) women. These studies show that the nitric oxide-cyclic guanosine monophosphate system exists in the human uterus and that it inhibits contractility. Furthermore, the relaxation responsiveness to nitric oxide is elevated during pregnancy and decreased during labor.

CONCLUSION

A nitric oxide-cyclic guanosine monophosphate relaxation pathway is present in the human uterus and may be responsible for maintaining uterine quiescence during pregnancy. A decrease in uterine relaxation responsiveness to nitric oxide at term may play a role in the initiation of labor.