Placental regulation of fatty acid delivery and its effect on fetal growth--a review

Relationship between plasma fatty acid profile and antioxidant vitamins during normal pregnancy

OBJECTIVE

To study the changes of plasma fatty acids and lipophilic vitamins during normal pregnancy.

DESIGN

Plasma fatty acid profile and the concentration of carotenoids, tocopherols and retinol were measured in healthy women at the first and third trimesters of pregnancy, at delivery, and in cord blood plasma.

RESULTS

Maternal plasma cholesterol and triglycerides increased from the first to the third trimester of gestation, while free fatty acids progressively increased from the first trimester through the third trimester to delivery, suggesting an enhanced lipolytic activity. Plasma levels of alpha- and gamma-tocopherols, lycopene and beta-carotene also progressively increased with gestation, but values in cord blood plasma were lower than in mothers at delivery. Retinol levels declined with gestational time and values in cord blood plasma were even lower. The proportion of total saturated fatty acids increased with gestation, and it further increased in cord blood plasma. Total n-9 fatty acids remained stable throughout pregnancy, and slightly declined in cord blood plasma, the change mainly corresponding to oleic acid. Total n-6 fatty acids declined with gestation and further decreased in cord blood plasma, and a similar trend was found for linoleic acid. However, arachidonic acid declined in women at the third trimester and at delivery as compared to the first trimester, but was enhanced in cord blood plasma. The proportion of total n-3 fatty acids remained stable throughout pregnancy at the expense of decreased alpha-linolenic acid at delivery but enhanced eicosapentaenoic acid, with small changes in docosahexaenoic acid. The proportion of these n-3 fatty acids was similar in cord blood plasma and maternal plasma at delivery.

CONCLUSIONS

Owing to the different placental transfer mechanisms and fetal capability to metabolize some of the transferred fatty acids and lipophilic vitamins, the fetus preserves the essential compounds to assure their appropriate availability to sustain its normal development and to protect itself from the oxidative stress of extrauterine life.

SPONSORSHIP

The studies reported herein have been carried out with financial support from the Commission of the European Communities, specific RTD programme 'Quality of Life and Management of Living Resources', QLK1-2001-00138 'Influence of Dietary Fatty Acids on the Pathophysiology of Intrauterine Foetal Growth and Neonatal Development' (PeriLip). It does not necessarily reflect its views and in no way anticipates the Commission's future policy in this area.

Modulatory effect of leptin on nitric oxide production and lipid metabolism in term placental tissues from control and streptozotocin-induced diabetic rats

Leptin production by placental tissues contributes to its circulating levels and functions. The diabetic pathology induces alterations in leptin levels. In the present study, leptin levels were evaluated in placental tissue from control and neonatal streptozotocin-induced (n-STZ) diabetic rats during late gestation. The effects of leptin levels on the generation of nitric oxide (NO), prostaglandin (PG) E2 production and lipid metabolism were examined. Leptin levels were diminished in placentas from n-STZ diabetic rats compared with controls (P < 0.01). These differences were also evident when leptin was evaluated immunohistochemically. Addition of leptin (1 nm) in vitro enhanced NO production in control (66%) and diabetic placentas (134%) by stimulating NO synthase activity (by 38% and 54%, respectively). The addition of leptin increased PGE2 production in placentas from control (173%) and diabetic rats (83%) and produced a 50% decrease in placental lipid levels (phospholipids, triacylglycerides, cholesterol and cholesteryl ester) without involving a reduction in de novo lipid synthesis. These data indicate that leptin enhances the production of placental NO and PGE2, vasoactive agents that modify placental blood flow, and that leptin stimulates placental lipid metabolism, probably generating more lipids for transfer to the fetus. In the diabetic rat, placental leptin was reduced, probably as a response to the maternal environment to locally regulate the transfer of nutrients to the developing fetus.

The lipid droplet-associated protein adipophilin is expressed in human trophoblasts and is regulated by peroxisomal proliferator-activated receptor-gamma/retinoid X receptor

Uptake and transplacental transfer of fatty acids is essential for fetal development. Human adipophilin and its murine ortholog adipocyte differentiation-related protein are lipid droplet-associated proteins that are implicated in cellular fatty acid uptake in adipocytes. The nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) stimulates lipid uptake by adipocytes and enhances differentiation of placental trophoblasts. We therefore hypothesized that adipophilin is expressed in human trophoblasts and that its expression is regulated by PPARgamma. We initially determined that adipophilin is expressed in human villous trophoblasts and that adipophilin expression is enhanced during differentiation of cultured primary term human trophoblasts. We also found that exposure of cultured human trophoblasts to the PPARgamma ligand troglitazone resulted in a concentration-dependent increase in adipophilin expression. We observed a similar increase with LG268, a ligand for retinoid X receptor (RXR), the heterodimeric partner of PPARgamma. Lastly, we demonstrated that ligand-activated PPARgamma and RXR stimulated the transcriptional activity of adipophilin promoter in CV-1 cells and in the placental JEG3 cell line. We conclude that the expression of adipophilin is enhanced during trophoblast differentiation and is up-regulated by ligand-activated PPARgamma/RXR. Enhanced adipophilin expression may contribute to fatty acid uptake by the placenta.

Analysis of FA contents in individual lipid fractions from human placental tissue

Data on FA contents in the human placenta are limited. Different methods have been used for the FA analysis, and only percentage results have been presented. We developed and evaluated a method for the determination of FA concentrations in placental tissue. Lipids were extracted from placental tissue with a chloroform/methanol mixture; and phospholipids (PL), nonesterified FA (NEFA), TG, and cholesterol esters (CE) were isolated by TLC. Individual lipid fractions were derivatized with methanolic hydrochloric acid, and the FAME were quantified by GC with FID. The CV of intra-assay (n = 8) of absolute concentrations were evaluated for FA showing a tissue content > 0.01 mg/g. CV ranges were 4.6-11.0% for PL, 6.4-9.3% for NEFA, 6.1-8.9% for TG, and 11.4-16.3% for CE. The relative FA composition across a term placenta indicated no differences between samples of central and peripheral locations of maternal and fetal site (CV 0.5-9.9%), whereas the absolute FA concentrations were only reproducible in the PL fraction (CV 7.0-12.8%). The method shows a reasonably high precision that is well suited for physiological and nutritional studies.

Human placental trophoblast cells express alpha-tocopherol transfer protein

Alpha-tocopherol transfer protein (alpha-TTP), a 30 kDa cytosolic protein first described to be present in the liver and important for alpha-tocopherol trafficking, plays a major role in maintaining alpha-tocopherol levels in plasma, while alpha-tocopherol is known as the major lipid-soluble antioxidant. Expression of alpha-TTP has not only been described in animal model liver, but also in diverse other tissues such as rat brain or pregnant mouse uterus, the latter finding stressing the importance of alpha-TTP for embryogenesis and foetal development. In this study, we report the identification of alpha-TTP in human liver by anti-human alpha-TTP monoclonal antibodies made in rat and the cellular localization of alpha-TTP in term human placenta. By immunohistochemistry, intense staining of alpha-TTP was seen in syncytiotrophoblast as well as in villous and invading extravillous cytotrophoblast, while basal decidual cells showed slighter, but present staining of alpha-TTP. Foetal vessel endothelium remained unstained. It is therefore suggested that alpha-TTP may play a major role in supplying alpha-tocopherol to the foetus prior to delivery and is likely involved in maintaining adequate alpha-tocopherol levels in the foetus.