Prostanoid receptors in human uterine myocytes: the effect of reproductive state and stretch

Distribution and Function of Prostaglandin E2 Receptors in Mouse Uterus: Translational Value for Human Reproduction

Prostaglandin (PG) E analogs are used clinically to ripen the cervix and induce labor. However, selective receptor agonists may have potential to improve induction response rates or manage unwanted uterine hypercontractility in conditions such as dysmenorrhea and preterm labor. To characterize their therapeutic value, PGE₂ analogs were used to investigate the functional E-type prostanoid (EP) receptor population in isolated human uterus. Responsiveness in mouse tissues was also examined to validate its use as a preclinical model. Uterine samples were obtained from mice at dioestrus (n = 12), term gestation (n = 14), and labor (n = 12) and from the lower uterus of women undergoing hysterectomy (n = 12) or Caesarean section (n = 18). Vehicle and agonist effects were assessed using superfusion and immersion techniques. PGE₂ evoked predominant excitatory responses in mouse and relaxation in human tissues. Selective EP₄ agonists inhibited tissue activity in both nonpregnant species, while the EP₂ mimetic CP533536 also attenuated uterine contractions throughout gestation. The uterotonic effects of the EP_3/1 agonist sulprostone were more pronounced than the EP₁ agonist ONO-D1-004, corresponding to abundant EP₃ receptor expression in all samples. The contractile phenotype in mouse compared with human uteri may relate to regional differences as well as high expression of EP₃ receptor transcripts. Similarities in nonpregnant and gestational tissues across species suggest that EP₃ may represent a valuable translational drug target for preventing uterine hypercontractility by employing a selective antagonist. SIGNIFICANCE STATEMENT: This research validates the use of nonpregnant mice for preclinical drug discovery of uterine EP receptor targets. To determine the utility of novel drugs and delivery systems at term pregnancy and labor, pharmacological agents interacting with EP₃ receptors have clear translational value.

Comparative analysis of myometrial and vascular smooth muscle cells to determine optimal cells for use in drug discovery

Novel therapeutic regulators of uterine contractility are needed to manage preterm labor, induce labor and control postpartum hemorrhage. Therefore, we previously developed a high-throughput assay for large-scale screening of small molecular compounds to regulate calcium-mobilization in primary mouse uterine myometrial cells. The goal of this study was to select the optimal myometrial cells for our high-throughput drug discovery assay, as well as determine the similarity or differences of myometrial cells to vascular smooth muscle cells (VSMCs)-the most common off-target of current myometrial therapeutics. Molecular and pharmacological assays were used to compare myometrial cells from four sources: primary cells isolated from term pregnant human and murine myometrium, immortalized pregnant human myometrial (PHM-1) cells and immortalized non-pregnant human myometrial (hTERT-HM) cells. In addition, myometrial cells were compared to vascular SMCs. We found that the transcriptome profiles of hTERT-HM and PHM1 cells were most similar (r = 0.93 and 0.90, respectively) to human primary myometrial cells. Comparative transcriptome profiling of primary human myometrial transcriptome and VSMCs revealed 498 upregulated (p ≤ 0.01, log2FC≥1) genes, of which 142 can serve as uterine-selective druggable targets. In the high-throughput Ca²⁺-assay, PHM1 cells had the most similar response to primary human myometrial cells in OT-induced Ca²⁺-release (E_max = 195% and 143%, EC₅₀ = 30 nM and 120 nM, respectively), while all sources of myometrial cells showed excellent and similar robustness and reproducibility (Z' = 0.52 to 0.77). After testing a panel of 61 compounds, we found that the stimulatory and inhibitory responses of hTERT-HM cells were highly-correlated (r = 0.94 and 0.95, respectively) to human primary cells. Moreover, ten compounds were identified that displayed uterine-selectivity (≥5-fold E_max or EC₅₀ compared to VSMCs). Collectively, this study found that hTERT-HM cells exhibited the most similarity to primary human myometrial cells and, therefore, is an optimal substitute for large-scale screening to identify novel therapeutic regulators of myometrial contractility. Moreover, VSMCs can serve as an important counter-screening tool to assess uterine-selectivity of targets and drugs given the similarity observed in the transcriptome and response to compounds.

Clinical Insights for Cervical Ripening and Labor Induction Using Prostaglandins

Cervical ripening is often the first component of labor induction and is used to facilitate the softening and thinning of the cervix in preparation for labor. Common methods used for cervical ripening include both mechanical (e.g., Foley or Cook catheters) and pharmacologic (e.g., prostaglandins) methods. The choice of method(s) for ripening should take into account the patient's medical and obstetric history, clinical characteristics, and risk of adverse effects if uterine tachysystole were to occur. In this narrative review, we highlight the differences between the prostaglandins dinoprostone and misoprostol with respect to pharmacology and pharmacokinetics, efficacy, and potential safety concerns. Practical guidance on choosing an appropriate prostaglandin agent for cervical ripening and labor induction is provided via the use of clinical vignettes. Considering the advantages and disadvantages of each preparation allows clinicians to individualize treatment, depending on the indications for induction and unique characteristics of each patient.

Molecular mechanisms regulating the vascular prostacyclin pathways and their adaptation during pregnancy and in the newborn

Prostacyclin (PGI(2)) is a member of the prostanoid group of eicosanoids that regulate homeostasis, hemostasis, smooth muscle function and inflammation. Prostanoids are derived from arachidonic acid by the sequential actions of phospholipase A(2), cyclooxygenase (COX), and specific prostaglandin (PG) synthases. There are two major COX enzymes, COX1 and COX2, that differ in structure, tissue distribution, subcellular localization, and function. COX1 is largely constitutively expressed, whereas COX2 is induced at sites of inflammation and vascular injury. PGI(2) is produced by endothelial cells and influences many cardiovascular processes. PGI(2) acts mainly on the prostacyclin (IP) receptor, but because of receptor homology, PGI(2) analogs such as iloprost may act on other prostanoid receptors with variable affinities. PGI(2)/IP interaction stimulates G protein-coupled increase in cAMP and protein kinase A, resulting in decreased [Ca(2+)](i), and could also cause inhibition of Rho kinase, leading to vascular smooth muscle relaxation. In addition, PGI(2) intracrine signaling may target nuclear peroxisome proliferator-activated receptors and regulate gene transcription. PGI(2) counteracts the vasoconstrictor and platelet aggregation effects of thromboxane A(2) (TXA(2)), and both prostanoids create an important balance in cardiovascular homeostasis. The PGI(2)/TXA(2) balance is particularly critical in the regulation of maternal and fetal vascular function during pregnancy and in the newborn. A decrease in PGI(2)/TXA(2) ratio in the maternal, fetal, and neonatal circulation may contribute to preeclampsia, intrauterine growth restriction, and persistent pulmonary hypertension of the newborn (PPHN), respectively. On the other hand, increased PGI(2) activity may contribute to patent ductus arteriosus (PDA) and intraventricular hemorrhage in premature newborns. These observations have raised interest in the use of COX inhibitors and PGI(2) analogs in the management of pregnancy-associated and neonatal vascular disorders. The use of aspirin to decrease TXA(2) synthesis has shown little benefit in preeclampsia, whereas indomethacin and ibuprofen are used effectively to close PDA in the premature newborn. PGI(2) analogs have been used effectively in primary pulmonary hypertension in adults and have shown promise in PPHN. Careful examination of PGI(2) metabolism and the complex interplay with other prostanoids will help design specific modulators of the PGI(2)-dependent pathways for the management of pregnancy-related and neonatal vascular disorders.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Recovery of orbital fat pad prolapsus and deepening of the lid sulcus from topical bimatoprost therapy: 2 case reports and review of the literature

OBJECTIVES

To report 2 cases of resolution of orbital fat pad prolapsus and deepening of the lid sulcus caused by topical bimatoprost therapy, and to review the literature.

METHODS

This was a retrospective, observational chart review.

RESULTS

A 54-year-old man with normotensive glaucoma presented with recovery of left lower lid orbital fat pad prolapsus, deepening of the lid sulcus, and iris color and eyelash changes 8 months after initiation of bimatoprost therapy in his left eye (OS). After stopping bimatoprost, his eyelashes and the lower lid orbital fat pad partially regained their natural appearance at 2 months and 4 months, respectively. However, there was no improvement of the left upper eyelid deepening and the iris hyperpigmentation, even after 30 months. A 75-year-old man with unilateral pseudoexfoliative glaucoma had been treated with bimatoprost OS. Three months after initiation of the therapy, his examination showed recovery of the inferior and superomedial orbital fat pad prolapsus, a deep and prominent upper lid sulcus with eyelash changes, and iris hyperpigmentation OS. Five months after discontinuation of bimatoprost, the eyelashes and superomedial orbital fat pad improved. Twenty-four months later, the inferior orbital fat pad partially got its natural appearance back, but the upper lid sulcus was slightly more deep and prominent than the fellow right eye. There was no alteration in iris hyperpigmentation.

CONCLUSION

Clinicians and patients should be aware of these possible effects of topical bimatoprost therapy. These adverse effects may not be completely reversible after discontinuation of the medication.

Prostanoid DP receptor (PTGDR) variants in mothers with post-coital associated preterm births: preliminary observations

OBJECTIVE

To describe prostanoid DP receptor (PTGDR) variants in women with preterm births who admitted to coital activity (CA) within 24 h of labor.

STUDY DESIGN

To achieve >80% statistical power, a pilot case-control study compared 24 premature births from mothers with CA (Group 1), 30 mothers of premature infants who did not have CA (Group 2 non-coital activity) and 95 non-coital activity mothers with term births (Group 3 controls). Four functional PTDGR single nucleotide polymorphisms (SNPs) were evaluated: T-549C, C-441/T, T-197C and G+1044A. PHASE 2.0.2 and SAS 9.2 were used for analysis.

RESULT

All SNPs were in Hardy-Weinberg equilibrium in controls. The C-441/T genotype frequency was significantly increased among Group 1 women relative to Group 2 and 3 women (odds ratio (OR): 30.1, 95% confidence interval (CI) 6.9-191 and 25.7 95%CI 25.7-not computible, respectively). Of the possible haplotypes among the groups, the TCTG haplotype (T-549C, C-441/T, T-197C and G+1044A) was significantly more frequent in Group 1 women compared with the control groups (OR 53.4, 95%CI 10.3-554.8).

CONCLUSIONS

A differential genomic pattern of PTGDR polymorphisms was identified in a sub-set of mothers which was associated with an increased risk of post-coital preterm birth.

Possible dual roles for prostacyclin in human pregnancy and labor

During pregnancy, the muscular layer of the uterine wall known as the myometrium, which is composed mainly of smooth muscle cells, is maintained in a state of relative quiescence. A switch from myometrial quiescence to myometrial activation is required to establish uterine contractions during labor. Researchers have long been perplexed by the fact that the major prostaglandin produced by the uterus just prior to labor, prostacyclin, is a smooth muscle relaxant. In this issue of the JCI, Fetalvero et al. provide data that they propose explains this paradox, at least in part (see the related article beginning on page 3966). The authors examined uterine tissue from pregnant women near term and found that prostacyclin stimulation, which raises cAMP levels that were previously thought to affect only myometrial quiescence, can promote myometrial activation over time by increasing the expression of a select group of proteins thought to be indicative of a uterine contractile state.

Periorbital changes associated with topical bimatoprost

PURPOSE

To describe periorbital changes induced by chronic topical therapy with daily bimatoprost 0.03% (Lumigan, Allergan Inc., Irvine, CA, U.S.A.).

METHODS

A clinical investigation of 5 nonconsecutive patients with unilateral glaucoma treated daily with topical bimatoprost 0.03% for up to 4 years prior to presentation.

RESULTS

In eyes treated with bimatoprost 0.03% the authors noted periorbital fat atrophy, deepening of the upper eyelid sulcus, relative enophthalmos, loss of the lower eyelid fullness, and involution of dermatochalasis compared with the fellow untreated eye. By inspecting old photographs the authors confirmed that these unilateral changes were not present prior to starting bimatoprost. In addition, these changes were partially reversible after discontinuation of the medication, whenever that was possible. In 2 cases imaging studies confirmed the clinical impression that these findings were not related to primary orbital pathology.

CONCLUSIONS

Physicians and patients should be aware of the potential of bimatoprost 0.03% to produce periorbital changes.

Amniotic fluid prostaglandin concentrations increase before the onset of spontaneous labor at term

OBJECTIVES

The role of prostaglandins (PGs) in the onset of human parturition has been controversial. Specifically, some investigators have proposed that PGs are the consequence rather than the cause of labor. An important question is whether or not amniotic fluid (AF) PG concentrations increase before the onset of labor in humans.

METHODS

The concentrations of PGs were determined in AF obtained from 167 singleton pregnant women with intact membranes. Patients were divided into four groups: (1) preterm not in labor (gestational age 15-36 weeks, n = 65); (2) term not in labor (n = 68); (3) spontaneous labor at term with cervical dilatation < 4 cm (n = 25); (4) spontaneous labor at term with cervical dilatation > or = 4 cm (n = 9). AF was obtained by transabdominal amniocentesis or collected at the time of cesarean delivery. All patients met the following criteria: (1) normal pregnancy outcome; (2) clear AF; (3) no significant medical or obstetric complications such as diabetes mellitus, preeclampsia, preterm birth, fetal growth restriction, or major congenital malformations; and (4) no significant neonatal complications. The concentrations of PGE2 and PGF2a in AF were determined by enzyme-linked immunosorbent assay (ELISA). Non-parametric analysis was performed.

RESULTS

(1) AF PG concentrations remained unchanged with advancing gestation until 36 weeks of gestation; (2) however, an abrupt increase in AF PG concentrations was observed before the onset of labor at term; (3) among cases without labor at term, the median AF PGF2a concentration increased with advancing gestation; (4) the presence of labor and the degree of cervical dilatation were significantly associated with a higher concentration of PGF2a.

CONCLUSIONS

An abrupt increase in AF PG concentrations (25-fold for PGF2a) occurs before the onset of spontaneous labor at term in humans; these observations suggest that PGs increase prior to the onset of labor and contradict the claim that an increase in PG concentrations is the consequence of labor.