Apolipoprotein E polymorphisms and spontaneous pregnancy loss in patients with endometriosis

The Role of ApoE Expression and Variability of Its Glycosylation in Human Reproductive Health in the Light of Current Information

Apolipoprotein E (ApoE), a 34-kDa glycoprotein, as part of the high-density lipoprotein (HDL), has antioxidant, anti-inflammatory and antiatherogenic properties. The variability of ApoE expression in the course of some female fertility disorders (endometriosis, POCS), and other gynecological pathologies such as breast cancer, choriocarcinoma, endometrial adenocarcinoma/hyperplasia and ovarian cancer confirm the multidirectional biological function of ApoE, but the mechanisms of its action are not fully understood. It is also worth taking a closer look at the associations between ApoE expression, the type of its genotype and male fertility disorders. Another important issue is the variability of ApoE glycosylation. It is documented that the profile and degree of ApoE glycosylation varies depending on where it occurs, the type of body fluid and the place of its synthesis in the human body. Alterations in ApoE glycosylation have been observed in the course of diseases such as preeclampsia or breast cancer, but little is known about the characteristics of ApoE glycans analyzed in human seminal and blood serum/plasma in the context of male reproductive health. A deeper analysis of ApoE glycosylation in the context of female and male fertility will both enable us to broaden our knowledge of the biochemical and cellular mechanisms in which glycans participate, having a direct or indirect relationship with the fertilization process, and also give us a chance of contributing to the enrichment of the diagnostic panel in infertile women and men, which is particularly important in procedures involved in assisted reproductive techniques. Moreover, understanding the mechanisms of glycoprotein glycosylation related to the course of various diseases and conditions, including infertility, and the interactions between glycans and their specific ligands may provide us with an opportunity to interfere with their course and thus develop new therapeutic strategies. This brief overview details some of the recent advances, mainly from the last decade, in understanding the associations between ApoE expression and some female and male fertility problems, as well as selected female gynecological diseases and male reproductive tract disorders. We were also interested in how ApoE glycosylation changes influence biological processes in the human body, with special attention to human fertility.

Increased ApoE Expression in Follicular Fluid and the ApoE Genotype Are Associated With Endometriosis in Chinese Women

More than 10% of women suffer from endometriosis (EMT) during their reproductive years. EMT can cause pain and infertility and requires further study from multiple perspectives. Previous reports have indicated that an increase inapolipoprotein E (ApoE) may be associated with a lower number of retrieved mature oocytes in older women, and an association between ApoE and spontaneous pregnancy loss may exist in patients with EMT. The purpose of this study was to investigate the existence of an increase in ApoE in follicular fluid (FF) and the possible relationship between ApoE and EMT in Chinese women. In the current study, 217 Chinese women (111 control subjects and 106 EMT patients) were included. The ApoE genotypes were identified by Sanger sequencing. We found that ApoE expression in FF was higher in patients with EMT than in the control group. In addition, a significant difference in ApoE4 carriers (ϵ3/ϵ4, ϵ4/ϵ4) was found between the control subjects and the patients with EMT. Furthermore, a nonparametric test revealed significant differences in the numbers of blastocysts and high-quality blastocysts, but not the hormone levels of FSH, LH, and E2, between the two groups. We also established a multifactor (BMI, high-quality blastocysts, and ϵ4) prediction model with good sensitivity for identifying patients who may suffer from EMT. Our results demonstrate that ApoE expression in FF is increased in EMT, the ApoE-ϵ4 allele is significantly linked to EMT, and a combined analysis of three factors (BMI, high-quality blastocysts, and ϵ4) could be used as a predictor of EMT.

Endometriosis and Risk of Adverse Pregnancy Outcomes

OBJECTIVE

To investigate the relationship between endometriosis and adverse pregnancy outcomes.

METHODS

Women between ages 25 and 42 years in 1989 (n=116,429) reported detailed information on pregnancies and reproductive health at baseline and every 2 years thereafter in the Nurses' Health Study II, a cohort study. In 2009, they completed a detailed, pregnancy-focused questionnaire. A total of 196,722 pregnancies were reported. Adverse pregnancy outcomes included spontaneous abortion, ectopic pregnancy, stillbirth, gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy (preeclampsia or gestational hypertension), preterm birth, and low birth weight. We estimated the relative risks (RRs) and 95% CIs of adverse pregnancy outcomes comparing pregnancies in women with and without a history of laparoscopically confirmed endometriosis using multivariable log-binomial regression, with generalized estimating equations to account for multiple pregnancies per woman.

RESULTS

Endometriosis was associated with a greater risk of pregnancy loss (spontaneous abortion: RR 1.40, 95% CI 1.31-1.49; ectopic pregnancy: RR 1.46, 95% CI 1.19-1.80). Endometriosis was also associated with a greater risk of GDM (RR 1.35, 95% CI 1.11-1.63) and hypertensive disorders of pregnancy (RR 1.30, 95% CI 1.16-1.45).

CONCLUSIONS

We observed an association between laparoscopically confirmed endometriosis and several adverse pregnancy outcomes. Future research should focus on the potential biological pathways underlying these relationships to inform screening or preventive interventions.

Endometriosis and Infertility: A Systematic Review

Endometriosis is one of the most common gynaecological conditions affecting 6% to 12% of women in the reproductive age group. It can be found in 35% to 45% of women who are trying to conceive and are infertile. Infertility is one of the most common problems associated with endometriosis. This review will look at the evidence that endometriosis may lead to infertility and the data looking at whether surgical correction of endometriosis may improve fertility outcomes.

Maternal apolipoprotein E genotype as a potential risk factor for poor birth outcomes: The Bogalusa Heart Study

OBJECTIVE

The objective of this study was to assess the association between apolipoprotein E (apoE) genotype and preterm birth (PTB) and small for gestational age (SGA).

STUDY DESIGN

ApoE phenotyping was performed on 680 women linked to 1065 births. Allele frequencies were compared and PTB and SGA risk was estimated using log-binomial regression.

RESULTS

The ɛ2 allele was more common in SGA births (P<0.01). SGA risk was increased among ɛ2 carriers compared with genotype ɛ3/ɛ3, though associations were attenuated following adjustment for maternal age, education, race, smoking and prenatal visits. Stronger associations were observed for term SGA (first birth: adjusted relative risk (aRR)=1.78, 95% confidence interval (CI) 1.06 to 2.98; any birth: aRR=1.52, 95% CI 0.96 to 2.40) and among whites specifically (first: aRR=2.88, 95% CI 1.45 to 5.69; any: aRR=2.75, 95% CI 1.46 to 5.22).

CONCLUSIONS

Associations between maternal apoE genotype and SGA may represent decreased fetal growth in women with lower circulating cholesterol levels.

Interaction of apolipoprotein E gene polymorphisms on miscarriage risk in black and white American women

OBJECTIVE

To evaluate whether [1] apolipoprotein E (APOE) polymorphisms can differentially regulate miscarriage risk and [2] whether this genotype effect could also be modulated by the race within populations.

DESIGN

Data were derived from the Coronary Artery Risk Development in Young Adults (CARDIA), a longitudinal study with black and white participants from four U.S.

SETTING

Not applicable.

PATIENT(S)

Women without miscarriages (controls) and women who miscarried at least once (cases).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

A group of women (n = 1,372) successfully followed for 25 years and with their APOE alleles identified were analyzed for miscarriage risk throughout their reproductive life. Additionally, a larger longitudinal analysis encompassing all the participants who had their APOE characterized (n = 2,140) was also performed for the association between APOE and miscarriage risk.

RESULT(S)

In white women followed up for 25 years, the odds ratio for miscarriage associated with APOE*2 allele presence was 1.61 (95% confidence interval, 1.04-2.50) compared with APOE*33 carriers. This was a race-dependent phenomenon as no associations between APOE alleles and miscarriage was observed in black women. Likewise, Cox regression analysis showed that cumulative miscarriage risk in white women was 37.2% in the APOE*2 carriers compared with 27.8% and 24.8% in APOE*33 and APOE*4 carriers, respectively. With APOE*33 as the reference, the age-adjusted hazard ratio associated with carrying the APOE*2 allele was 1.47 (95 confidence interval, 1.06-2.05).

CONCLUSION(S)

This variable miscarriage risk, produced by an interaction between genotype and race, may reconcile, at least partially, the conflicting reports of the association of APOE and miscarriage risk.

A prospective cohort study of endometriosis and subsequent risk of infertility

STUDY QUESTION

Is there a temporal relationship between endometriosis and infertility?

SUMMARY ANSWER

Endometriosis is associated with a higher risk of subsequent infertility, but only among women age <35 years.

WHAT IS KNOWN ALREADY

Endometriosis is the most commonly observed gynecologic pathology among infertile women undergoing laparoscopic examination. Whether endometriosis is a cause of infertility or an incidental discovery during the infertility examination is unknown.

STUDY DESIGN, SIZE, DURATION

This study included data collected from 58 427 married premenopausal female nurses <40 years of age from 1989 to 2005, who are participants of the Nurses' Health Study II prospective cohort.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Our exposure was laparoscopically confirmed endometriosis. Multivariate Cox proportional hazards regression models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for infertility risk (defined as attempting to conceive for >12 months) among women with and without endometriosis.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified 4612 incident cases of infertility due to any cause over 362 219 person-years of follow-up. Compared with women without a history of endometriosis, women with endometriosis had an age-adjusted 2-fold increased risk of incident infertility (HR = 2.12, 95% CI = 1.76-2.56) that attenuated slightly after accounting for parity. The relationship with endometriosis was only observed among women <35 years of age (multivariate HR <35 years = 1.77, 95% CI = 1.46-2.14; multivariate HR 35-39 years = 1.20, 95% CI = 0.94-1.53; P-interaction = 0.008). Risk of primary versus secondary infertility was similar subsequent to endometriosis diagnosis. Among women with primary infertility, 50% became parous after the endometriosis diagnosis, and among all women with endometriosis, 83% were parous by age 40 years.

LIMITATIONS, REASONS FOR CAUTION

We did not have information on participants' intentions to conceive, but by restricting the analytic population to married women we increased the likelihood that pregnancies were planned (and therefore infertility would be recognized). Women in our cohort with undiagnosed asymptomatic endometriosis will be misclassified as unexposed. However, the small proportion of these women are diluted among the >50 000 women accurately classified as endometriosis-free, minimizing the impact of exposure misclassification on the effect estimates.

WIDER IMPLICATIONS OF THE FINDINGS

This study supports a temporal association between endometriosis and infertility risk. Our prospective analysis indicates a possible detection bias in previous studies, with our findings suggesting that the infertility risk posed by endometriosis is about half the estimates observed in cross-sectional analyses.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the National Institutes of Health (grant numbers: UM1 CA176726, HD52473, HD57210, T32DK007703, T32HD060454, K01DK103720). We have no competing interests to declare.

Apolipoprotein E (ApoE) polymorphism is related to differences in potential fertility in women: a case of antagonistic pleiotropy?

The alleles that are detrimental to health, especially in older age, are thought to persist in populations because they also confer some benefits for individuals (through antagonistic pleiotropy). The ApoE4 allele at the ApoE locus, encoding apolipoprotein E (ApoE), significantly increases risk of poor health, and yet it is present in many populations at relatively high frequencies. Why has it not been replaced by natural selection with the health-beneficial ApoE3 allele? ApoE is a major supplier of cholesterol precursor for the production of ovarian oestrogen and progesterone, thus ApoE has been suggested as the potential candidate gene that may cause variation in reproductive performance. Our results support this hypothesis showing that in 117 regularly menstruating women those with genotypes with at least one ApoE4 allele had significantly higher levels of mean luteal progesterone (144.21 pmol l(-1)) than women with genotypes without ApoE4 (120.49 pmol l(-1)), which indicates higher potential fertility. The hormonal profiles were based on daily data for entire menstrual cycles. We suggest that the finding of higher progesterone in women with ApoE4 allele could provide first strong evidence for an evolutionary mechanism of maintaining the ancestral and health-worsening ApoE4 allele in human populations.

Characteristics of women with endometriosis from the USA and Puerto Rico

PURPOSE

To describe lifetime differences in clinical characteristics of women with endometriosis between the USA and Puerto Rico.

METHODS

A descriptive study using self-administered demographic and clinical questionnaires was undertaken. Women with self-reported surgically diagnosed endometriosis who completed questionnaires from the Endometriosis Association (EA), Wisconsin, USA (n = 4358) and the Endometriosis Research Program (ERP) in Puerto Rico (n = 878), were included in this study. We compared demographic, gynecological and clinical history, frequency of endometriosis-associated symptoms and co-morbidities.

RESULTS

Although both groups have similar symptomatology, EA respondents had significantly higher rates of chronic pelvic pain and incapacitating pain than ERP participants. EA respondents were significantly more likely to report a history of problems getting pregnant, heavy bleeding, and hysterectomy than ERP respondents. Miscarriages were more frequently reported by the ERP group. Co-morbidities such as allergies, chronic fatigue syndrome, and fibromyalgia were more prevalent in EA respondents, whereas asthma was significantly more frequent in participants from ERP.

CONCLUSIONS

Overall, women with endometriosis from the USA and Puerto Rico reported high rates of pain and infertility and a similar spectrum of symptoms. Those from the EA reported longer time to diagnosis, and diagnostic delays than those from the ERP, which may explain the observed increased in rates of endometriosis-related symptoms and co-morbidities in EA as compared to ERP.

Apolipoprotein E (Apo E) gene polymorphisms and recurrent pregnancy loss: a meta-analysis

BACKGROUND

Recently, a relationship between recurrent pregnancy loss (RPL) and Apolipoprotein E (Apo E) gene polymorphisms has been proposed. In order to investigate the real association between Apo E polymorphisms and RPL, our meta-analysis was carried out.

METHODS

We estimated the association with RPL risk under dominant and recessive models, in combination with the OR and RR with a 95% confidence interval (CI), which was used to assess the association between RPL and Apo E polymorphisms.

RESULTS

According to our criterion, there were 6 studies included. The dominant model used the E4/E3 group and the OR was 1.919 (95 %CI: 1.016-3.625, I(2) = 53.8%), the RR was 1.308 (95%Cl: 1.071-1.598) suggesting that carriers of the E4 allele would have a higher risk of causing spontaneous miscarriages. In addition, the OR was 0.727 (95%CI: 0.566-0.932, I(2) = 0.0%) and RR was 0.923 (95%CI: 0.867-0.982) in a fixed model for E3/E3 homozygotes versus other genotypes, suggesting that the Apo E3 polymorphism could be a protective factor. The OR was 1.365 (95% CI: 1.029-1.811, I(2) = 0 .0%) in a fixed model comparing the E2 allele with the E3 allele, suggesting that Apo E2 polymorphisms may contribute to RPL as a risk factor. Furthermore, after conducting sensitivity analysis in the E4/E3 group, the results showed this to be consistent and the OR was 2.249 (95%CI: 1.474-3.431).

CONCLUSIONS

There is a close association between RPL and Apo E gene polymorphisms. For RPL, the Apo E4 polymorphism could be a risk factor, the Apo E3 polymorphism may be a protective factor and the Apo E2 polymorphism may be another potential risk factor.

Low abundance plasma proteins in labour

Every year, millions of births worldwide are complicated by prematurity or difficult post-term deliveries, resulting in a high incidence of perinatal mortality and morbidity. Our poor understanding of human parturition is a key reason for our inability to improve the management of preterm and post-term birth. In this study, we used proteomic techniques to look into protein changes in placental blood plasma obtained from women before or after spontaneous or induced labour, with vaginal or caesarean section deliveries. Our aim was to understand the basic mechanisms of human parturition regardless of whether the signals that trigger labour are of maternal and/or fetal origin. We found proteins from 33 genes with significantly altered expression profiles in relation to mode of labour and delivery. Most changes in labour occurred in proteins associated with ‘immune and defence responses’. Although the signal transduction and regulation of these pathways varied among modes of delivery, hepatocyte nuclear factor 1 homeobox A emerged as a shared protein in the mechanism of labour. Moreover, several apolipoproteins such as apolipoprotein A-IV and APOE were found to change with labour, and these changes were also confirmed in maternal plasma. This study has identified significant protein changes in placental intervillous plasma with labour and has revealed several pathways related to human parturition.