Determinants of plasma concentrations of perfluoroalkyl substances in pregnant Norwegian women

BACKGROUND

Perfluoroalkyl substances (PFASs) are widespread pollutants that have been associated with adverse health effects although not on a consistent basis. Diet has been considered the main source of exposure. The aim of the present study was to identify determinants of four plasma PFASs in pregnant Norwegian women.

METHODS

This study is based in the Norwegian Mother and Child Cohort Study (MoBa) conducted by the Norwegian Institute of Public Health. Our sample included 487 women who enrolled in MoBa from 2003 to 2004. A questionnaire regarding sociodemographic, medical, and reproductive history was completed at 17 weeks of gestation and a dietary questionnaire was completed at 22 weeks of gestation. Maternal plasma samples were obtained around 17 weeks of gestation. Plasma concentrations of four PFASs (perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorohexane sulfonate (PFHxS), and perfluorononanoate (PFNA)) were examined in relation to demographic, lifestyle, dietary, and pregnancy-related covariates. Predictors were identified by optimizing multiple linear regression models using Akaike's information criterion (AIC).

RESULTS

Parity was the determinant with the largest influence on plasma PFAS concentrations, with r(2) between 0.09 and 0.32 in simple regression models. In optimal multivariate models, when compared to nulliparous women, parous women had 46%, 70%, 19%, and 62% lower concentrations of PFOS, PFOA, PFHxS, and PFNA respectively (p<0.001 except for PFHxS, p<0.01). In all these models, duration of breastfeeding was associated with reduced PFAS levels. PFOA showed the largest reduction from breastfeeding, with a 2-3% reduction per month of breastfeeding in typical cases. Levels of PFOS, PFOA, and PFNA increased with time since most recent pregnancy. While pregnancy-related factors were the most important predictors, diet was a significant factor explaining up to 4% of the variance. One quartile increase in estimated dietary PFAS intake was associated with plasma PFOS, PFOA, PFHxS, and PFNA concentration increases of 7.2%, 3.3%, 5.8% and 9.8%, respectively, resulting in small, although non-trivial absolute changes in PFAS concentrations.

CONCLUSION

Previous pregnancies and breastfeeding duration were the most important determinants of PFASs in this sample of pregnant women.

145 CHARACTERIZATION OF THE PROTEIN ARGININE METHYLTRANSFERASE-DIMETHYLARGININE DIMETHYLAMINOHYDROLASE-NITRIC OXIDE AXIS DURING PORCINE EMBRYO DEVELOPMENT

Transcriptional deep sequencing analysis by Bauer et al. (2010) revealed a significant increase in expression of the arginine transporter SLC7A1 in in vitro–cultured porcine blastocysts compared with those cultured in vivo and this was corrected through supplemental arginine. This indicates an important role for arginine during porcine embryo development. Arginine is the precursor for nitric oxide (NO) production and previous work in mice and cattle has shown decreased development when embryos were cultured with a nitric oxide synthase (NOS) inhibitor. The NOS activity is inhibited by monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA) that are released during degradation of proteins methylated by protein arginine methyltransferases (PRMT). The enzyme dimethylarginine dimethylaminohydrolase (DDAH) is responsible for degrading MMA and ADMA in the cell. Therefore, the goal of this study was to investigate whether this PRMT-DDAH-NO axis exists in pre-implantation porcine embryos. To this end, expression of PRMT1, PRMT3, PRMT5, DDAH1 and endothelial NOS (NOS3) was analysed at different stages of embryonic development using real-time quantitative RT-PCR. In addition, the effect of supplemental arginine (1.69 mM) on the expression of the aforementioned genes was investigated. Production of NO in porcine embryos was also visualised using 4-amino-5-methylamino-2,7-difluorofluorescein diacetate (DAF-FM-DA). In vitro–fertilized porcine embryos were collected at the 4-cell and blastocyst stages. The RNA was isolated from pools of 18 to 20 embryos and cDNA, was synthesised using Superscript III (Invitrogen, Carlsbad, CA, USA). Real-time PCR analysis was performed and the mean fold change in gene expression from the reference gene YWHAG was analysed by t-test after a log transformation. Expression of PRMT3 and PRMT5 was significantly higher (P < 0.05) in blastocysts versus 4-cell embryos. Expression of PRMT1, however, was higher in 4-cell embryos (P < 0.05). The expression of DDAH1 was detected in 4-cell embryos, but DDAH1 became undetectable by the blastocyst stage. Previous microarray analysis in our laboratory by Whitworth et al. (2005 Biol. Reprod. 72(6), 1437–1451) also revealed a significant up-regulation of DDAH2 expression at the 4-cell stage versus blastocysts. Expression of NOS3 was undetectable in the 4-cell and blastocyst; however, NO was detected in 4-cell and blastocyst stage embryos by using DAF-FM-DA. This suggests that a different NOS may be acting in the porcine embryo. Addition of arginine did not have a significant effect on expression of the analysed genes. These results suggest that PRMT-DDAH regulated NO production may play a role during porcine embryo development. Understanding the PRMT-DDAH-NO axis and its regulation during embryonic development will further our ability to tailor in vitro culture so that it more appropriately mimics that of an in vivo environment. Funding was provided by NIH U42 RR18877.

Fecundability among women with type 1 and type 2 diabetes in the Norwegian Mother and Child Cohort Study

AIMS/HYPOTHESIS

We assessed the effects of type 1 diabetes and type 2 diabetes on fecundability (as manifest by increased time-to-pregnancy [TTP]) in a large cohort of pregnant women.

METHODS

This study is based on the Norwegian Mother and Child Cohort Study. Members of this large cohort were enrolled early in pregnancy and asked about TTP and other factors. Among the 58,004 women included in the analysis, we identified 221 cases of type 1 diabetes and 88 cases of type 2 diabetes using the Medical Birth Registry of Norway. A logistic analogue of the proportional probability model, a Cox-like discrete-time model, was used to compute fecundability odds ratios (FORs) and 95% CI for type 1 diabetes and type 2 diabetes, adjusted for maternal age and prepregnancy BMI.

RESULTS

Compared with non-diabetic women, the adjusted FOR for women with type 1 diabetes was 0.76 (95% CI 0.64-0.89) and the adjusted FOR for women with type 2 diabetes was 0.64 (95% CI 0.48-0.84). These FORs did not change substantively and remained statistically significant after excluding women with irregular menstrual cycles and accounting for cycle length.

CONCLUSIONS/INTERPRETATION

The results from the present study provide evidence of substantially decreased fecundability for women with type 1 and type 2 diabetes, even among those with a normal menstrual cycle.

381 PRODUCTION OF A TRANSGENIC PIGLET BY A NEW SPERM INJECTION TECHNIQUE

The technique for intracytoplasmic sperm injection (ICSI) has, until now, focused on scoring the tail of the sperm prior to catching and aspiration into the injection pipette. This is in spite of the fact that damage to the head would more closely simulate what occurs during normal fertilization. In addition, to aid in visualizing the injection process so that a reduced volume can be injected, the oocyte is generally centrifuged to clear a portion of the cytoplasm. Thus, with conventional ICSI, the sperm are immobilized with polyvinylpyrrolidone, repeatedly frozen and thawed, treated with DTT or Triton X-100, and severed between the head and tail; the oocyte is centrifuged or activated. All of the above treatments are designed to compensate for the intrinsic defects in conventional ICSI. Our objective was to use a modified ICSI procedure whereby aggressively motile sperm were captured onto the broken tip of an injection pipette and then injected into noncentrifuged oocytes. Damage to the head of the sperm occurred on the pipette or while pushed through the zona pellucida. These procedures are based on the work of Yong et al. 2003 Hum. Reprod. 18, 2390, where they achieved an improvement in development in vitro as compared to conventional methods. Ovaries were collected from prepubertal gilts, and oocytes were aspirated and matured in vitro. Sperm were collected from a transgenic boar carrying the green fluorescent protein (GFP) and frozen. After thawing, aggressively motile sperm were captured and injected through the zona pellucida and into the cytoplasm of the in vitro-matured oocytes. A total of 452 injected oocytes (43-171 oocytes per recipient) were surgically transferred into the oviduct of six surrogate gilts. Two gilts (33%) became pregnant. One gave birth to a healthy male piglet. GFP expression was observed in the nose and hooves by direct epifluorescent examination of the newborn piglet. This pattern of GFP expression is identical to that in non-ICSI-derived GFP pigs in this line. This result showed for the first time that this new sperm injection technique could be used for production of a viable transgenic piglet using in vitro-matured oocytes and frozen-thawed sperm.

254 DIFFERENTIAL TRANSCRIPTION AND CYSTOPLASMIC POLYADENYLATION ELEMENTS IN PORCINE GERMINAL VESICLE AND METAPHASE II OOCYTES

Identification of transcripts produced during porcine oocyte maturation is one of the first steps in defining pathways important to development. Practically, this information will aid in the refinement of in vitro culture processes, allowing for more efficient in vitro embryo production. To this end, mRNA was isolated from 50 in vitro-matured sow metaphase II stage oocytes (Bomed, Inc., Madison, WI, USA) (MIIs), 50 in vitro-matured gilt metaphase II-stage oocytes (MIIg), and 50 gilt germinal vesicle stage oocytes (GVO) by using the Dynabead® system (Dynal, Inc., Lake Success, NY, USA) and amplified by using the SMART system (Clontech, Palo Alto, CA, USA). The PCR products were ligated into a pSport vector and transformed into electro-competent E. coli. Colonies were randomly picked and sequenced at the University of Missouri DNA Core. Sequences were clustered with similar sequences derived from a larger expressed sequence tag (EST) project (http://genome.rnet.missouri.edu/Swine/) by using the tlcluster program developed at the University of Iowa. Following clustering, individual clusters in the cDNA libraries were compared by using Fisher's exact test (P < 0.01) to determine if they were differentially represented. Two sets of comparisons were performed, one between the MIIs and MIIg libraries, and another between the GVO library and the combination of both metaphase II libraries (MII). The number of clusters per number of clones in the library was 966/1668 (GVO), 458/820 (MIIg), and 158/819 (MIIs). There were 15/419 clusters that were different between the MIIs and MIIg libraries, and 26/1269 that were different between the MII and GVO libraries. Potential cytoplasmic polyadenylation elements (CPEs) identified from the literature were found in the GVO and MII libraries by using a custom pattern-matching program. Of the clusters with differential expression, 4/15 (MIIs vs. MIIg) and 7/26 (MII vs. GVO) contained CPEs. Table 1 contains a partial list of differentially expressed genes and the sequence of their cytoplasmic polyadenylation elements. Many genes were found to be differentially expressed in both (MII vs. GVO and MIIs vs. MIIg) comparisons. Collectively, these findings will facilitate the elucidation of important developmental pathways in swine and other animals. Table 1. Comparison of mRNA expression and cytoplasmic polyadenylation elements This work was partially funded by a University of Missouri Life Sciences Mission Enhancement grant and Food for the 21st Century.

Radiation hybrid comparative mapping between human chromosome 17 and porcine chromosome 12 demonstrates conservation of gene order

A comparative study of human chromosome 17 (HSA17) and pig chromosome 12 (SSC12) was conducted using both somatic cell hybrid panel (SCHP) and radiation hybrid (RH) panel analysis. Sequences from an expressed sequence tag (EST) project in pig reproduction were examined and six genes and ESTs originally believed to map to HSA17 were selected for this study. The genes/ESTs were TATA box binding protein-associated factor (TAF2N/RBP56), alpha-2-plasmin inhibitor (SERPINF2/PLI), H3 histone family 3B (H3F3B), aminopeptidase puromycin sensitive (NPEPPS), an expressed sequence tag (ESTMI015) and P311 protein (P311). The SCHP analysis mapped five genes/ESTs (TAF2N, H3F3B, SERPINF2, NPEPPS and ESTMI015) to SSC12q11-q15 and SSC12p11-p15 with 100% concordance, and assigned P311 to SSC2 (1/2q24)-q29 with 100% concordance. Radiation hybrid analysis of all six genes confirmed the SCHP mapping results, with average retention frequency of 25%. Recent human sequence data demonstrated that P311 is actually located on HSA5q. As HSA5q and SSC2q show conserved syntenic regions predicted from bi-directional painting, our P311 mapping data is consistent with these results. An expanded comparative SSC12 RH map integrating the five new type I markers and 23 previously mapped loci was established using a LOD score threshold of 4.8. The gene order of the five genes/ESTs on the SSC12 framework RH map (H3F3B-ESTMI015-NPEPPS-TAF2N-SERPINF2) is identical to the HSA17 GB4 map but with inversion of the map as conventionally drawn.