Second trimester medical abortion with mifepristone and gemeprost: a review of 956 cases

Expression and roles of steroidogenic acute regulatory (StAR) protein in 'non-classical', extra-adrenal and extra-gonadal cells and tissues

The activity of the steroidogenic acute regulatory (StAR) protein is indispensable and rate limiting for high output synthesis of steroid hormones in the adrenal cortex and the gonads, known as the 'classical' steroidogenic organs (StAR is not expressed in the human placenta). In addition, studies of recent years have shown that StAR is also expressed in many tissues that produce steroid hormones for local use, potentially conferring some functional advantage by acting via intracrine, autocrine or paracrine fashion. Others hypothesized that StAR might also function in non-steroidogenic roles in specific tissues. This review highlights the evidence for the presence of StAR in 17 extra-adrenal and extra-gonadal organs, cell types and malignancies. Provided is the physiological context and the rationale for searching for the presence of StAR in such cells. Since in many of the tissues the overall level of StAR is relatively low, we also reviewed the methods used for StAR detection. The gathered information suggests that a comprehensive understanding of StAR activity in 'non-classical' tissues will require the use of experimental approaches that are able to analyze StAR presence at single-cell resolution.

Effects of parity and gestational age on second-trimester induction-abortion interval in combination with osmotic dilators and gemeprost

BACKGROUND

The true prognostic factors for induced medical abortion are unknown. We sought to investigate the effects of a patient's obstetric parameters on the induction-abortion interval in second-trimester medical abortion.

STUDY DESIGN

We studied 216 consecutive women. Pregnancy was terminated with cervical preparation using osmotic dilators followed by 1 mg vaginal gemeprost administered every 3 h for a maximum of five doses in the first 24 h. All variables are expressed in categorical form (parity, gestational age, maternal age and body mass index) and analyzed by the Cox proportional hazards model.

RESULTS

Parity ≥ 3 was associated with a shorter duration of the induction-abortion interval (adjusted hazards ratio 1.96; 95% confidence interval 1.13-3.40). A gestational age ≥ 16 weeks was associated with a longer duration of the induction-abortion interval (0.71; 0.52-0.98). No significant association was found in maternal age and body mass index.

CONCLUSIONS

In combination with osmotic dilators and gemeprost, gestational age and parity are independent factors that affected the induction to abortion interval of second-trimester medical abortion.

Post mortem magnetic resonance imaging in the fetus, infant and child: a comparative study with conventional autopsy (MaRIAS Protocol)

Background

Minimally invasive autopsy by post mortem magnetic resonance (MR) imaging has been suggested as an alternative for conventional autopsy in view of the declining consented autopsy rates. However, large prospective studies rigorously evaluating the accuracy of such an approach are lacking. We intend to compare the accuracy of a minimally invasive autopsy approach using post mortem MR imaging with that of conventional autopsy in fetuses, newborns and children for detection of the major pathological abnormalities and/or determination of the cause of death.

Methods/Design

We recruited 400 consecutive fetuses, newborns and children referred for conventional autopsy to one of the two participating hospitals over a three-year period. We acquired whole body post mortem MR imaging using a 1.5 T MR scanner (Avanto, Siemens Medical Solutions, Enlargen, Germany) prior to autopsy. The total scan time varied between 90 to 120 minutes. Each MR image was reported by a team of four specialist radiologists (paediatric neuroradiology, paediatric cardiology, paediatric chest & abdominal imaging and musculoskeletal imaging), blinded to the autopsy data. Conventional autopsy was performed according to the guidelines set down by the Royal College of Pathologists (UK) by experienced paediatric or perinatal pathologists, blinded to the MR data. The MR and autopsy data were recorded using predefined categorical variables by an independent person.

Discussion

Using conventional post mortem as the gold standard comparator, the MR images will be assessed for accuracy of the anatomical morphology, associated lesions, clinical usefulness of information and determination of the cause of death. The sensitivities, specificities and predictive values of post mortem MR alone and MR imaging along with other minimally invasive post mortem investigations will be presented for the final diagnosis, broad diagnostic categories and for specific diagnosis of each system.

Clinical Trial Registration

NCT01417962

NIHR Portfolio Number: 6794

Clinical guidelines. Labor induction abortion in the second trimester

Labor induction abortion is effective throughout the second trimester. Patterns of use and gestational age limits vary by locality. Earlier gestations (typically 12 to 20 weeks) have shorter abortion times than later gestational ages, but differences in complication rates within the second trimester according to gestational age have not been demonstrated. The combination of mifepristone and misoprostol is the most effective and fastest regimen. Typically, mifepristone 200 mg is followed by use of misoprostol 24-48 h later. Ninety-five percent of abortions are complete within 24 h of misoprostol administration. Compared with misoprostol alone, the combined regimen results in a clinically significant reduction of 40% to 50% in time to abortion and can be used at all gestational ages. However, mifepristone is not widely available. Accordingly, prostaglandin analogues without mifepristone (most commonly misoprostol or gemeprost) or high-dose oxytocin are used. Misoprostol is more widely used because it is inexpensive and stable at room temperature. Misoprostol alone is best used vaginally or sublingually, and doses of 400 mcg are generally superior to 200 mcg or less. Dosing every 3 h is superior to less frequent dosing, although intervals of up to 12 h are effective when using higher doses (600 or 800 mcg) of misoprostol. Abortion rates at 24 h are approximately 80%-85%. Although gemeprost has similar outcomes as compared to misoprostol, it has higher cost, requires refrigeration, and can only be used vaginally. High-dose oxytocin can be used in circumstances when prostaglandins are not available or are contraindicated. Osmotic dilators do not shorten induction times when inserted at the same time as misoprostol; however, their use prior to induction using misoprostol has not been studied. Preprocedure-induced fetal demise has not been studied systematically for possible effects on time to abortion. While isolated case reports and retrospective reviews document uterine rupture during second-trimester induction with misoprostol, the magnitude of the risk is not known. The relationship of individual uterotonic agents to uterine rupture is not clear. Based on existing evidence, the Society of Family Planning recommends that, when labor induction abortion is performed in the second trimester, combined use of mifepristone and misoprostol is the ideal regimen to effect abortion quickly and completely. The Society of Family Planning further recommends that alternative regimens, primarily misoprostol alone, should only be used when mifepristone is not available.

Midtrimester termination of pregnancy using gemeprost in combination with laminaria in women who have previously undergone cesarean section

AIM

We aimed to assess the efficacy and safety of midtrimester termination of pregnancy using gemeprost in combination with laminaria in women who had previously undergone cesarean section and in women who had not.

METHODS

Between January 1999 and December 2006, we carried out a retrospective study of termination of pregnancy at 12-21 weeks of gestation at the University of Tsukuba Hospital. Termination of pregnancy was carried out by three-step uterine cervical dilation using laminaria followed by vaginal administration of 1 mg gemeprost every 3 h for up to four doses over 24 h.

RESULTS

A total of 173 women underwent midtrimester termination of pregnancy. The women were categorized into two groups: those who had previously undergone cesarean section (n = 26) (previous cesarean section group) and those who had not (n = 147) (control group). Seven women had undergone cesarean section at least twice. The gemeprost dose administered was 2.8 +/- 1.4 mg for the previous cesarean section group and 2.4 +/- 1.6 mg for the control group (difference in doses not significant). Although abnormal vaginal bleeding (>500 mL) was more likely to occur in the previous cesarean section group than in the control group (odds ratio, 2.61; 95% confidence interval, 0.63-10.82), none of the woman required blood transfusion. Uterine rupture and failed abortion were not observed.

CONCLUSION

The efficacy and safety of our laminaria-gemeprost protocol for termination of pregnancy during the midtrimester are similar for women who have previously undergone cesarean section and those who have not.

Second trimester medical abortion with mifepristone-misoprostol and misoprostol alone: a review of methods and management

Second trimester abortions constitute 10-15% of all induced abortions worldwide but are responsible for two-thirds of major abortion-related complications. During the last decade, medical methods for second trimester induced abortion have been considerably improved and become safe and more accessible. Today, in most cases, safe and efficient medical abortion services can be offered or improved by minor changes in existing health care facilities. Second trimester medical abortion can be provided by a nurse-midwife with the back-up of a gynaecologist. Because of the potential for heavy vaginal bleeding and serious complications, it is advisable that second trimester terminations take place in a health care facility where blood transfusion and emergency surgery (including laparotomy) are available. This article provides basic information on regimens recommended for second trimester medical abortion. The combination of mifepristone and misoprostol is now an established and highly effective method for second trimester abortion. Where mifepristone is not available or affordable, misoprostol alone has also been shown to be effective, although a higher total dose is needed and efficacy is lower than for the combined regimen. Therefore, whenever possible, the combined regimen should be used. Efforts should be made to reduce unnecessary surgical evacuation of the uterus after expulsion of the fetus. Future studies should focus on improving pain management, the treatment of women with failed medical abortion after 24 hours, and the safety of medical abortion regimens in women with a previous caesarean section or uterine scar.

Patients’ obstetric history in mid-trimester termination of pregnancy with gemeprost: Does it really matter?

OBJECTIVE

The objective was to investigate the importance of previous obstetric history for termination of pregnancy in the second-trimester with gemeprost alone.

STUDY DESIGN

A consecutive series of 423 mid-trimester inductions of abortion at our teaching hospital was reviewed. Termination of pregnancy was carried out with 1mg of vaginal gemeprost every 3h up to three doses over a 24-h period, repeated the following day if necessary. Failed induction was defined as women undelivered by 96 h. The study population was then stratified by gestational age, parity, gravidity and previous uterine scars. Main outcome parameters were failed induction and complication rates. Statistical analysis was performed using the chi(2) test or Fisher's exact test for categorical data, and the t-test and linear regression for continuous variables.

RESULTS

No significant differences were found in the primary outcome parameters with regard to the obstetric parameters considered. The failed induction rate was 1.2% with an overall incidence of complications of 7.4%. Parity was the main factor that affected clinical response (time to abortion interval and number of pessaries).

CONCLUSION

Patients' obstetric history does affect the clinical response to gemeprost, but its safety and effectiveness are preserved. These data provide clinicians with important information for correct counselling.

Mid-trimester induced abortion: a review

Mid-trimester abortion constitutes 10-15% of all induced abortion. The aim of this article is to provide a review of the current literature of mid-trimester methods of abortion with respect to efficacy, side effects and acceptability. There have been continuing efforts to improve the abortion technology in terms of effectiveness, technical ease of performance, acceptability and reduction of side effects and complications. During the last decade, medical methods for mid-trimester induced abortion have shown a considerable development and have become safe and more accessible. The combination of mifepristone and misoprostol is now an established and highly effective method for termination of pregnancy (TOP). Advantages and disadvantages of medical versus surgical methods are discussed. Randomized studies are lacking, and more studies on pain treatment and the safety of any method used in patients with a previous uterine scar are debated, and data are scarce. Pain management in abortion requires special attention. This review highlights the need for randomized studies to set guidelines for mid-trimester abortion methods in terms of safety and acceptability as well as for better analgesic regimens.

Induction of second trimester abortion (12–20 weeks) with mifepristone and misoprostol: a review of 386 consecutive cases

DESIGN

A retrospective analysis of 386 women who underwent termination of pregnancy between 12 and 24 weeks' gestation.

METHODS

Each woman received 200 mg mifepristone orally followed by vaginal misoprostol 800 microg 36 to 48 h later. Three hours after the initial misoprostol administration, 400-microg doses of vaginal misoprostol were administered every 3 h, to a maximum of four doses in 24 h. If abortion failed, 200 mg mifepristone is given again 3 h after the last misoprostol dose, followed by 12 h of rest before vaginal misoprostol administration is repeated as per previous course of treatment.

RESULTS

Overall, 97.9% and 99.5% of the women aborted within 24 and 36 h, respectively. The median induction-to-abortion interval was 6.7 h (range: 1.4-73.8 h), and nulliparous women took significantly longer time to abort (6.0 h in multiparous women compared to 7.6 h in nulliparous women; p<.0001). One woman failed to abort within 48 h. Surgical evacuation of the uterus was performed in 5% of women for incomplete abortion or retained placenta. Multiparous women were less likely to need analgesic administration for pain relief, and to experience vomiting and diarrhea, than nulliparous women.

CONCLUSION

The combination of 200 mg mifepristone and vaginally administered misoprostol is a safe, effective and noninvasive regimen for termination of pregnancy between 12 and 20 weeks.

Labor induction abortion utilizing trilostane, a 3beta-hydroxysteroid dehydrogenase inhibitor

Labor induction abortion in the second trimester is a difficult problem in developing countries because antiprogestins are either not available or unaffordable. When prostaglandins are used alone for labor induction abortion without antiprogestin pretreatment, the induction to delivery interval and the treatment failure rate increase. Trilostane, an inhibitor of 3beta-hydroxysteroid dehydrogenase enzyme system, was given to 93 women between 13 and 19 weeks gestation. The trilostane dosage used was 120 mg twice daily for the first 24 h, and then 240 mg twice daily for the next 24 h. The women returned after 48 h for hospital admission. The women were randomized to three different misoprostol regimens: low-dose vaginal group (200 microg every 4 h), high-dose vaginal group (initial dose of 400 microg followed by 200 microg every 4 h) and vaginal-oral group (400 microg vaginally followed by 200 microg orally every 4 h). The median induction to abortion times were 17, 8.3 and 9.4 h, respectively. The latter two groups had significantly shorter induction to delivery times (p<.05). The most common side effects were a burning feeling in the face (47.7%) and nausea (13.3%). Overall, trilostane side effects were mild and self-limiting and did not interfere with therapy. In conclusion, trilostane can be given as out-patient therapy prior to admission for prostaglandin administration in labor induction abortion.

Use of mifepristone to ripen the cervix and induce labor in term pregnancies

OBJECTIVE

This study was undertaken to determine the efficacy of mifepristone for ripening the cervix and inducing labor in term pregnancies.

STUDY DESIGN

In a double-blind placebo-controlled dose-finding study, 346 women received 50, 100, 200, 400, or 600 mg of mifepristone or placebo. The main endpoint for efficacy was the number of patients in whom labor occurred between 12 and 45 and 54 hours after treatment or who had a Bishop score 6 or greater. Maternal and fetal tolerability was also studied.

RESULTS

No significant efficacy was observed whatever the dose of mifepristone. Mifepristone was well tolerated by the mother and fetus.

CONCLUSION

Mifepristone, at doses up to 600 mg, does not induce labor within 54 hours in patients with unfavourable cervical status.

Infection after medical abortion: A review of the literature

Medical abortion regimens have become widely used, but the frequency of infection after medical abortion is not well documented. This systematic review provides data on infectious complications after medical abortion. We searched Medline for articles written before July 2003 to determine the frequency of infection after medical abortion up to 26 weeks of gestation. We reviewed all articles and extracted data on the frequency of infection from 65 studies. The frequency of diagnosed and/or treated infection after medical abortion was very low (0.92%, N = 46,421) and varied among regimens. Results of this review confirm that, with respect to infectious complications, medical abortion is a safe and effective option for first- and second-trimester pregnancy termination. After accounting for regional variations in diagnosis, there is little difference in frequency of infection among the regimens reviewed. Future studies should report clear diagnosis and treatment standards for infection so that more precise information becomes available.

Methods for Induced Abortion

We describe present methods for induced abortion used in the United States. The most common procedure is first-trimester vacuum curettage. Analgesia is usually provided with a paracervical block and is not completely effective. Pretreatment with nonsteroidal analgesics and conscious sedation augment analgesia but only to a modest extent. Cervical dilation is accomplished with conventional tapered dilators, hygroscopic dilators, or misoprostol. Manual vacuum curettage is as safe and effective as the electric uterine aspirator for procedures through 10 weeks of gestation. Common complications and their management are presented. Early abortion with mifepristone/misoprostol combinations is replacing some surgical abortions. Two mifepristone/misoprostol regimens are used. The rare serious complications of medical abortion are described. Twelve percent of abortions are performed in the second trimester, the majority of these by dilation and evacuation (D&E) after laminaria dilation of the cervix. Uterine evacuation is accomplished with heavy ovum forceps augmented by 14-16 mm vacuum cannula systems. Cervical injection of dilute vasopressin reduces blood loss. Operative ultrasonography is reported to reduce perforation risk of D&E. Dilation and evacuation procedures have evolved to include intact D&E and combination methods for more advanced gestations. Vaginal misoprostol is as effective as dinoprostone for second-trimester labor-induction abortion and appears to be replacing older methods. Mifepristone/misoprostol combinations appear more effective than misoprostol alone. Uterine rupture has been reported in women with uterine scars with misoprostol abortion in the second trimester. Fetal intracardiac injection to reduce multiple pregnancies or selectively abort an anomalous twin is accepted therapy. Outcomes for the remaining pregnancy have improved with experience.

One- and 2-day mifepristone–misoprostol intervals are both effective in medical termination of second-trimester pregnancy

Termination of pregnancy because of fetal anomaly requires the utmost clinical sensitivity and individualized patient care. This study compared the efficacy of a 1-day mifepristone and misoprostol interval in medical termination of second-trimester pregnancy performed because of fetal anomaly with that of the standard 2-day interval among the first 100 women in each group. A 200 mg dose of mifepristone was used; 0.4 mg of misoprostol was administered vaginally at 3-h intervals until abortion occurred. When calculated from ingestion of mifepristone, the time to abortion was 28 h 25 min (28:25 h) [23:10-50:40 h; median (range)] and 52:43 h (45:55-83:15 h) (P < 0.0001) in the 1- and 2-day mifepristone-misoprostol groups respectively. However, following initiation of misoprostol administration, the time to abortion [7:25 h (1:00-23:15 h)] was longer (P < 0.05) in the 1-day interval group than in the 2-day interval group [6:20 h (0:45-36:30 h)]; by 12 h, 82 and 87% (n.s.) respectively of the subjects had aborted. The proportions of cases undergoing surgical evacuation of the uterus were 64 and 45% (P < 0.001), in the 1- and 2-day interval groups respectively. Thus both 1- and 2-day mifepristone-misoprostol intervals are valuable in termination of second-trimester pregnancy.

Midtrimester medical termination of pregnancy: a review of 1002 consecutive cases

We assessed the effectiveness, safety and factors that affected the outcome of midtrimester medical termination of pregnancy at 13-21 weeks gestation. Of the 1002 women, 3 took mifepristone and decided to continue with the pregnancy, with 999 women being compliant with the regimen. Of these, 2 women aborted prior to administration of misoprostol and 970 (97.1%) aborted successfully within five doses of misoprostol. Surgical intervention was necessary to complete the abortion process in 81 (8.1%) women. Women with no previous pregnancy (p = 0.02), no previous live birth (p = 0.0001) and gestations 17-21 weeks (p = 0.001) required more prostaglandin. Younger women (p = 0.0001) and women with a previous live birth (p = 0.001) were more likely to have a successful abortion. The induction abortion interval was significantly longer with increasing gestation [95% confidence interval (CI) difference in means: -2.52 to -0.89, p = 0.0001], increasing age (p = 0.0001) and no previous live birth (95% CI difference in means: -0.25 to -1.01, p = 0.0001). Surgical intervention was more likely to be required with increasing age (p = 0.008). Mifepristone in combination with misoprostol is a safe and effective regimen for midtrimester medical abortion with younger women and those with a previous live birth more likely to have a successful abortion.

Progesterone antagonists and progesterone receptor modulators: an overview

Since the original description of the structure of the antiprogestin, mifepristone, was published, numerous related compounds have been synthesized which may function as progesterone antagonists (PAs) or progesterone receptor modulators (PRMs). The latter are mixed agonists-antagonists. Both PAs and PRMs have therapeutic applications in female health care. Mifepristone is predominantly a PA and displays only minimum agonist activity in certain systems. Together with a prostaglandin, mifepristone can terminate pregnancies of less than 9 weeks duration, and it may also be used at later gestational ages. Mifepristone causes expulsion of the uterine contents following intrauterine fetal death. A mifepristone-prostaglandin combination has been shown to be very effective treatment in women with menses delay of 11 days or less. Many PAs and PRMs display antiproliferative effects in the endometrium. Serum estradiol levels however remain in the early to mid-follicular phase range. For this reason, they have application in the treatment of endometriosis and myoma without being associated with bone loss and hypoestrogenism. PRMs may also find application in the treatment of dysfunctional bleeding as well as an adjunct to estrogens in hormone replacement therapy in postmenopausal women. Many PAs have contraceptive potential by suppressing follicular development and blocking the LH surge. Low doses may also be potential contraceptives by retarding endometrial maturation without affecting ovulation or inducing bleeding. Mifepristone is an excellent agent for use as an emergency "postcoital" contraceptive. PAs may also be useful in IVF programs to prevent a premature LH surge and to delay the emergence of the implantation window. In addition to their use in women's health care, mifepristone and several other PAs are potent antiglucocorticoid agents and may be used to treat ACTH-independent Cushing's syndrome. They may also be used in the treatment of tumors containing steroid receptors and in other situations which require suppression of the ACTH-cortisol axis.

Medical abortion at 64 to 91 days of gestation: a review of 483 consecutive cases

OBJECTIVE

The purpose of this study was to assess the uptake and outcome of medical abortion in the late first trimester of pregnancy.

STUDY DESIGN

We conducted a review of the cases of 483 consecutive women in a university hospital who underwent medical abortion at 64 to 91 days of gestation and who used mifepristone that was followed 36 to 48 hours later by repeated doses of misoprostol.

RESULTS

A total of 891 abortions were carried out at 64 to 91 days of gestation from October 2000 to April 2002; of these, 483 cases (54.2%) were undertaken medically. Complete abortion occurred in 458 cases (94.8%). Efficacy decreased with advancing gestational age. Surgical evacuation was carried out in 1 woman (0.9%) at 9 to 10 weeks of gestation, in 8 women (5.3%) at 10 to 11 weeks of gestation, in 7 women (6.2%) at 11 to 12 weeks of gestation, and in 9 women (7.9%) at 12 to 13 weeks of gestation. Indications for surgery included ongoing pregnancy in 8 cases (1.7%), missed abortion in 3 cases (0.6%), incomplete abortion in 13 cases (2.7%), and emergency curettage for bleeding in 1 case (0.2%). The mean number of misoprostol doses used was 2.3; of those women who had a complete abortion, 152 women (32.6%) aborted within 4 hours of receiving the misoprostol. The mean induction to abortion interval was 5.5 hours; most cases (452; 93.6%) were treated as day cases.

CONCLUSION

Medical abortion between 64 and 91 days of gestation is effective and has a high uptake. Consideration should be given to extending the availability and choice of medical abortion to women in this gestational group.

Medical termination of pregnancy at 9-12 weeks of gestation

Current RCOG guidelines advise that surgical termination should be offered to those within the 9-12 weeks gestation band. While auditing the quality of services offered for termination of pregnancy in our unit, it became apparent that many women presenting at this gestation were requesting a medical method. There has been little clinical research into medical method of abortion at this gestation. The aim of the study was to assess the efficacy of medical methods of termination at 9-12 weeks gestation. A retrospective analysis of 25 cases who underwent medical termination using a regime of mifepristone followed 48 hours later by a course of vaginal gemeprost was undertaken. Complete abortion was achieved in 96% of cases; 92% of women required no more than two pessaries to achieve complete abortion. All but one patient was suitable for discharge on the same day. One woman underwent surgical evacuation in view of heavy bleeding. We conclude that medical TOP is a safe alternative to surgical method at 9-12 weeks' gestation.

A randomised study of misoprostol and gemeprost in combination with mifepristone for induction of abortion in the second trimester of pregnancy

OBJECTIVE

To compare the effectiveness of gemeprost and misoprostol as prostaglandins used in combination with mifepristone for induction of mid-trimester termination.

DESIGN

Randomised trial.

SETTING

Scottish teaching hospital.

SAMPLE

One hundred women undergoing abortion between 12 and 20 weeks.

METHODS

Each woman received 200 mg mifepristone and 36-48 hours later either 1 mg gemeprost vaginal pessary every 6 hours for 18 hours or 4 x 200 microg misoprostol tablets vaginally followed by 2 x 200 microg misoprostol tablets orally every 3 hours for 12 hours. Success was defined as the percentage of women aborted within 24 hours of the first administration of prostaglandin.

MAIN OUTCOME MEASURES

Prostaglandin-abortion interval and side effects.

RESULTS

There were no significant differences in median prostaglandin-abortion interval between gemeprost (6.6 hours 95% CI 6.0-10.7) and misoprostol (6.1 hours 95% CI 5.5-7.5) (P = 0.22). The cumulative abortion rates at 24 hours (96% vs 94%, respectively), the surgical evacuation rates (12% and 10%) and the incidence of vomiting, diarrhoea and pain were similar.

CONCLUSION

Two hundred milligrammes of mifepristone followed 36-48 hours later by either vaginal gemeprost or misoprostol is a highly effective way of inducing abortion in the second trimester of pregnancy.

Transcription of cholesterol side-chain cleavage cytochrome P450 in the placenta: activating protein-2 assumes the role of steroidogenic factor-1 by binding to an overlapping promoter element

Progesterone is essential to the sustenance of pregnancy in humans and other mammals. From the second trimester on, the human placenta is the sole origin of de novo synthesized steroid hormones. In mice, placentation at midgestation is accompanied by a temporal rise of steroid hormone synthesis commencing in the giant cells of the mouse trophoblast. In doing so, the giant trophoblasts, as any other steroidogenic cell, express high levels of the key steroidogenic enzyme, cholesterol side-chain cleavage cytochrome P450 (P450scc). Because steroidogenic factor 1 (SF-1), the transcription factor required for expression of P450scc in the adrenals and the gonads, is not expressed in the placenta, we hypothesized that placenta-specific nuclear factor(s) (PNF) assumes the role of SF-1 by binding to the same promoter region that harbors the SF-1 recognition site in the P450scc gene. To address this possibility, we used SCC1, a well conserved proximal region in the P450scc genes (-60/-32 in the rat gene) to purify PNF from human term placenta. Sequencing of the purified PNF revealed that it is the alpha isoform of the human activating protein-2 (AP-2alpha). Specific antibodies tested in EMSA confirmed that AP-2alpha is the predominant isoform that binds SCC1 in the human placenta, whereas AP-2gamma is the only mouse placental protein that binds this oligonucleotide. Functional studies showed that coexpression of the rat P450scc promoter (-378/+8 CAT) and AP-2 isoforms (alpha or gamma) in human embryonic kidney 293 cells results in a marked activation of chloramphenicol acetyltransferase (CAT) transcription that is dependent on an intact AP-2 motif, GCCTTGAGC. This motif conforms with consensus sequences previously determined for binding of the AP-2 alpha and gamma isoforms. Mutations of the AP-2 element ablated binding of AP-2 to SCC1, as well as severely diminished the promoter activity in primary mouse giant trophoblasts and human choriocarcinoma JAR cells. Collectively, these studies suggest that expression of placental P450scc is governed by AP-2 factors that bind to a cis-element that largely overlaps the sequence required for recognition of SF-1 in other steroidogenic tissues.