The levels of plasma cholesterol in the human fetus throughout gestation

Characterization of lipoproteins and associated lipidome in very preterm infants: a pilot study

BACKGROUND

Preterm birth is associated with higher risks of suboptimal neurodevelopment and cardiometabolic disease later in life. Altered maternal-fetal lipid supply could play a role in such risks. Our hypothesis was that very preterm infants born with very low birth weight (VLBW) have altered lipidome and apolipoprotein profiles, compared with term infants.

METHODS

Seven mothers of VLBW infants born at <32 GA and 8 full-term mother-infant dyads were included. Cholesterol and triglycerides in lipoproteins were determined in maternal plasma and in the two blood vessels of the umbilical cord (vein (UV) and artery (UA)) following FPLC isolation. Apolipoprotein concentrations in lipoproteins and plasma lipidomic analysis were performed by LC-MS/MS.

RESULTS

We found higher cholesterol and VLDL-cholesterol in UV and UA and lower apolipoprotein A-I in HDL2 in UV in preterm neonates. Phosphatidylcholine (PC) containing saturated and monounsaturated fatty acids and specific sphingomyelin species were increased in UV and UA, whereas PC containing docosahexaenoic acid (DHA) was reduced in UV of VLBW neonates.

CONCLUSIONS

Lower DHA-PC suggests a lower DHA bioavailability and may contribute to the impaired neurodevelopment. Altered HDL-2, VLDL, and sphingomyelin profile reflect an atherogenic risk and increased metabolic risk at adulthood in infants born prematurely.

IMPACT

Lower ApoA-I in HDL2, and increased specific sphingomyelin and phosphatidylcholine containing saturated and monounsaturated fatty acid could explain the accumulation of cholesterol in umbilical vein in VLBW preterm neonates. Decreased phosphatidylcholine containing DHA suggest a reduced DHA availability for brain development in VLBW preterm infants. Characterization of alterations in fetal lipid plasma and lipoprotein profiles may help to explain at least in part the causes of the elevated cardiovascular risk known in people born prematurely and may suggest that a targeted nutritional strategy based on the composition of fatty acids carried by phosphatidylcholine may be promising in infants born very early.

Relationship between maternal and/or newborn cholesterol levels and neonatal septicemia: protocol for a Ugandan cohort of mother-newborn pairs

Background

Many aspects of microbial dissemination appear to vary with host cholesterol levels. Since neonatal septicemia remains a leading cause of newborn admissions and mortality in resource-limited settings, the contribution of abnormal cholesterol levels in maternal and/or newborn blood to the risk of neonatal septicemia and outcome requires elucidation. We aim to determine a relationship between maternal serum and neonatal cord blood cholesterol levels and neonatal septicemia.

Methods

This will be a mother-newborn pair cohort study. Approximately 353 pregnant women who are eligible and consent to participate in the study will have blood drawn for a lipid profile. Upon delivery, we will analyse the cord blood cholesterol of their newborns and follow them for 28 days to determine whether the infants develop clinical signs and symptoms suggestive of neonatal septicemia. Relative risk will be used to determine the association between cholesterol and newborn septicemia. Poisson regression will be used to estimate the relative risk (with 95% confidence intervals) of developing septicemia.

Discussion

Findings from our study will contribute evidence to support the inclusion of lipid profile screening for pregnant women and newborns. Our study will determine whether newborns with abnormal cholesterol or those born to mothers with abnormal cholesterol will require rigorous follow-up in neonatal clinics.

Adipose tissue development and lipid metabolism in the human fetus: The 2020 perspective focusing on maternal diabetes and obesity

During development, the human fetus accrues the highest proportion of fat of all mammals. Precursors of fat lobules can be found at week 14 of pregnancy. Thereafter, they expand, filling with triacylglycerols during pregnancy. The resultant mature lipid-filled adipocytes emerge from a developmental programme of embryonic stem cells, which is regulated differently than adult adipogenesis. Fetal triacylglycerol synthesis uses glycerol and fatty acids derived predominantly from glycolysis and lipogenesis in liver and adipocytes. The fatty acid composition of fetal adipose tissue at the end of pregnancy shows a preponderance of palmitic acid, and differs from the mother. Maternal diabetes mellitus does not influence this fatty acid profile. Glucose oxidation is the main source of energy for the fetus, but mitochondrial fatty acid oxidation also contributes. Indirect evidence suggests the presence of lipoprotein lipase in fetal adipose tissue. Its activity may be increased under hyperinsulinemic conditions as in maternal diabetes mellitus and obesity, thereby contributing to increased triacylglycerol deposition found in the newborns of such pregnancies. Fetal lipolysis is low. Changes in the expression of genes controlling metabolism in fetal adipose tissue appear to contribute actively to the increased neonatal fat mass found in diabetes and obesity. Many of these processes are under endocrine regulation, principally by insulin, and show sex-differences. Novel fatty acid derived signals such as oxylipins are present in cord blood with as yet undiscovered function. Despite many decades of research on fetal lipid deposition and metabolism, many key questions await answers.

Effect of gestational diabetes mellitus on newborn cholesterol metabolism

BACKGROUND AND AIMS

Impaired glucose metabolism during pregnancy may associate with changes in fetal cholesterol metabolism. We investigated if gestational diabetes mellitus (GDM) affects newborn cholesterol metabolism as determined by cord blood squalene and non-cholesterol sterols. Furthermore, we examined potential correlations between cord blood and maternal serum non-cholesterol sterols.

METHODS

Pregnant women at risk for GDM (BMI>30 kg/m²) were enrolled from maternity clinics in Finland. GDM was determined from the results of an oral glucose tolerance test. Serum samples were taken in the third trimester of pregnancy, and cord blood samples collected from their newborns at birth. Squalene and non-cholesterol sterols were analyzed from serum and cord blood by gas liquid chromatography. All women with GDM were in good glycaemic control.

RESULTS

The ratios of squalene and non-cholesterol sterols to cholesterol (100 × μmol/mmol of cholesterol) in cord blood did not differ between the infants born to mothers with GDM (n = 15) or mothers with normal glucose tolerance (n = 13). The ratios of sitosterol and campesterol to cholesterol in the cord blood correlated with the corresponding maternal serum ratios (r = 0.70, p < 0.0001) in both groups.

CONCLUSIONS

In obese women under good glycaemic control, GDM did not affect newborn cholesterol metabolism. Cord blood sitosterol and campesterol ratios to cholesterol correlated with the corresponding maternal serum ratios thus potentially reflecting maternal-fetal cholesterol transport.

Maternal and fetal lipid metabolism under normal and gestational diabetic conditions

Maternal lipids are strong determinants of fetal fat mass. Here we review the overall lipid metabolism in normal and gestational diabetes mellitus (GDM) pregnancies. During early pregnancy, the increase in maternal fat depots is facilitated by insulin, followed by increased adipose tissue breakdown and subsequent hypertriglyceridemia, mainly as a result of insulin resistance (IR) and estrogen effects. The response to diabetes is variable as a result of greater IR but decreased estrogen levels. The vast majority of fatty acids (FAs) in the maternal circulation are esterified and associated with lipoproteins. These are taken up by the placenta and hydrolyzed by lipases. The released FAs enter various metabolic routes and are released into fetal circulation. Although these determinants are modified in maternal GDM, the fetus does not seem to receive more FAs than in non-GDM pregnancies. Long-chain polyunsaturated FAs are essential for fetal development and are obtained from the mother. Mitochondrial FA oxidation occurs in fetal tissue and in placenta and contributes to energy production. Fetal fat accretion during the last weeks of gestation occurs very rapidly and is sustained not only by FAs crossing the placenta, but also by fetal lipogenesis. Fetal hyperinsulinemia in GDM mothers promotes excess accretion of adipose tissue, which gives rise to altered adipocytokine profiles. Fetal lipoproteins are low at birth, but the GDM effects are unclear. The increase in body fat in neonates of GDM women is a risk factor for obesity in early childhood and later life.

Relation of glucose control in diabetic pregnancy to fetal cholesterol homeostasis

OBJECTIVE

To determine the impact of maternal diabetic glucose control on fetal cholesterol homeostasis.

METHODS

Singleton pregnancies of 150 women complicated by gestational (n = 90) and pre-gestational (n = 60) diabetes were evaluated. Those with insulin-requiring diabetes had fasting blood glucose levels determined daily during the last 4 weeks of pregnancy and weekly fasting glucose values were obtained in those with A1 (diet-controlled) gestational diabetes. Umbilical cord venous serum was collected at delivery and total cholesterol levels were determined.

RESULTS

Among the 150 women, 69 had A1 gestational diabetes and 81 were insulin-requiring. Fasting glucose levels were inversely correlated (p < 0.001) to gestational age, regardless of diabetes classification. Umbilical serum cholesterol levels were inversely related (p < 0.002) to gestational age and weight, but did not vary according to diabetic classification. Among term infants (n = 110), umbilical serum cholesterol levels were inversely related to maternal fasting glucose levels at 4 weeks (p = 0.006) and 2 weeks (p = 0.006) before delivery.

CONCLUSION

Maternal hyperglycemia is associated with decreased plasma fetal cholesterol levels in term infants.

Cord blood lipoproteins and prenatal influences

PURPOSE OF REVIEW

Blood lipoprotein profiles in early life are known to be related to and predictive of those in adulthood, but little is known about their determinants. Genetic and environmental influences affect cord blood lipoproteins, but how this occurs and the relative contribution of these influences to the overall profile in healthy newborns remains uncertain.

RECENT FINDINGS

This review discusses findings from a range of earlier and more recent studies, and summarizes the key influences on cord blood lipoproteins. In particular, we review the potential contribution of maternal blood total cholesterol levels during pregnancy and the increased maternal transmission in newborns of mothers with diabetes.

SUMMARY

In cord blood, cholesterol levels are lower than in adults and the relative proportion present in HDL as opposed to LDL is much higher. The currently available evidence suggests that several factors influence the composition of cord blood lipoproteins. Although inheritance of major monogenic disorders can affect cord lipids in general, the genetic contribution appears to be minimal, although effects of the proprotein convertase subtilisin/kexine type 9 gene (PCSK9) need fuller exploration in this regard in certain ethnic groups. Evidence is summarized that maternal lipoprotein levels, particularly those due to diet or induced by pregnancy, influence cord lipid levels. Placental insufficiency and other conditions affecting fetal growth and the mode of delivery may also influence cord lipoprotein concentrations. How maternal glucose tolerance during pregnancy affects cord blood lipoproteins remains unclear. In view of increasing evidence that cardiovascular risk may have prenatal antecedents, this would seem to be an important area for further investigation.

Oxidative stress in the fetal circulation does not depend on mode of delivery

OBJECTIVE

We tested whether neonates are subject to oxidative stress by comparing the susceptibility of umbilical blood lipids with copper-induced peroxidation.

STUDY DESIGN

Umbilical arterial and venous blood samples were drawn from 32 pregnant women who delivered by elective cesarean section (CS) and from 32 pregnant women who delivered by spontaneous vaginal delivery (SVD) in a tertiary care center. Oxidative stress was evaluated by spectrophotometric monitoring of copper-induced peroxidation of serum samples.

RESULTS

The lag preceding lipid peroxidation in umbilical arterial blood was shorter than the lag in umbilical venous blood, irrespective of mode of delivery (14.0+/-1.8 vs 50.6+/-8.25 min, P=.0004 in SVD group; 17.7+/-1.6 vs 39.2+/-7.6 min, P=.006 in CS group).

CONCLUSION

Umbilical arterial lipids are more susceptible to peroxidation than umbilical venous lipids, indicating high oxidative stress in the fetal circulation irrespective of mode of delivery.

Plasma lecithin-cholesterol acyltransferase activity and cholesterol and phospholipid levels in premature newborn infants

Lecithin-cholesterol acyltransferase (LCAT) activity has been suggested to play an important role in the regulation of lipid metabolism. The present study was undertaken to examine any relationship between LCAT activity and altered cholesterol levels in plasma of full-term and preterm newborn infants. Plasma total, free and esterified cholesterol, total phospholipid and LCAT activity (cholesterol esterified, nmol/ml per h) were determined in placental cord blood. There was a significant negative relationship between total cholesterol levels and gestational age. The increased cholesterol with prematurity was due to both free and esterified cholesterol. There was also a significant negative relationship between LCAT activity and free cholesterol levels but not between LCAT activity and total cholesterol and esterified cholesterol levels. There was no relationship between esterified-to-free cholesterol ratio and LCAT activity. Total phospholipid was not significantly related to either gestational age or LCAT activity. This study suggests that reduced LCAT activity may be one of the factors that result in the accumulation of cholesterol in premature infants.

Plasma cholesterol and lipoprotein levels during fetal development and infancy

Intrauterine changes in plasma cholesterol and lipoprotein concentrations have been linked to the development of the adrenal gland (utilization of cholesterol) and liver (production of cholesterol by new synthesis). At term birth, racial and gender differences have been observed with white compared to black, and female compared to male, infants having higher cholesterol concentrations. Within hours of the beginning of oral feeding, total and LDL cholesterol rise significantly. Little further increase occurs after 7 days, and the concentration seen after this time is highly dependent upon the cholesterol and polyunsaturated fat content of the diet. By 12 months of age, investigators cease to find any effect of the milk source fed earlier in infancy on cholesterol and lipoproteins. This is not evidence that diet no longer influences cholesterol and lipoprotein concentrations, but only that individual lipid intakes are varied and difficult to quantitate. Cross-cultural comparisons of infants at this age in fact provide strong suggestive evidence that a large environmental component determines the circulating cholesterol and lipoprotein concentrations seen at one year and beyond.

Cord blood lipoprotein-cholesterol: relationship birth weight and gestational age of newborns

Umbilical plasma levels of lipoproteins-cholesterol were measured in 60 premature (less than 37 weeks), 60 small for gestational age (SGA, greater than 37 weeks), and 60 full term newborns (greater than 37 weeks) to ascertain the relationship between gestational age, infant's weight and concentration of plasma lipoprotein cholesterol. Umbilical levels of total cholesterol (TC), unesterified cholesterol (UC), low density lipoprotein cholesterol (LDL-C) and high density lipoprotein cholesterol (HDL-C) in premature newborns were significantly higher (P less than .001) than in term infants. The levels of TC, UC, HDL-C and very low density lipoprotein cholesterol (VLDL-C) were substantially higher (P less than .05) in umbilical cord plasma of SGA newborns than in cord plasma of full term newborns. Lecithin:cholesterol acyltransferase activity in cord plasma was indirectly assessed by measuring the ratio of esterified cholesterol to unesterified cholesterol (CE/UC). This ratio was significantly lower (P less than .01) in preterm and SGA than in full term newborns. In addition, plasma TC, UC, LDL-C and HDL-C levels were inversely correlated with gestational age of newborns. By contrast, CE/UC ratio had an inverse correlation with gestational age and HDL-C of the newborns. These findings suggest that the levels of TC in newborns are regulated by the uptake of LDL-C by the fetal adrenal and, additionally, by the lecithin:cholesterol acyltransferase (LCAT) activity of newborn plasma. Only by careful follow-up of hyperlipidemic neonates can the true incidence of familial hyperlipoproteinemia and the value of early diagnosis be assessed.

Fetal aortic cholesterol concentration and metabolism: relationship to plasma cholesterol and potential role of placental factors

The relationship of fetal plasma cholesterol levels to aortic free and esterified cholesterol concentration was determined in the rabbit during gestation. Plasma cholesterol levels (mg/dl) in early fetuses were markedly high and decreased at term. While aortic free cholesterol content increased with fetal age, cholesteryl ester concentration did not change significantly and no pathological accumulation was evident. This occurred despite high fetal aortic cholesterol esterification activity noted in earlier studies. We evaluated the potential effect of rabbit placental extracts on lipid metabolism and cellular proliferation in fetal aortic explants to explore the role of placental factors in affecting lipid metabolism. Labeled [14C]oleate and [3H]thymidine were used to investigate the rates of incorporation of (a) oleate into lipids, and (b) thymidine into DNA, respectively. Placental extracts at term (but not from 22 days gestation) significantly decreased oleate incorporation (P less than 0.05) into cholesteryl esters, phospholipids and diglycerides. This effect of placental extracts was noted both in absence or presence of serum in the culture medium, and was predominantly found in fraction of Mr greater than 100,000. [3H]Thymidine incorporation (dpm/g protein) into DNA was significantly decreased (P less than 0.01) by placental extracts. These studies suggest that placental extracts contain factor(s) influencing fetal aortic lipid metabolism in culture.

LDL receptors in bovine tissues assayed as the heparin-sensitive binding of 125I-labeled LDL in homogenates: relation between liver LDL receptors and serum cholesterol in the fetus and post term

The heparin-sensitive binding of 125I-labeled LDL in homogenates of bovine tissues was determined using a membrane filter assay. The binding fulfilled several criteria which have been established for the binding of LDL to its receptor, namely: saturability, dependence on Ca2+, sensitivity to proteolytic destruction and heat sensitivity. The adrenal cortex and the active corpus luteum exhibited the highest binding activity of the 22 different tissues assayed. Tissues from the central nervous system had low binding activity. Livers from fetal animals had higher binding than livers from young and adult animals and the binding of 125I-LDL to fetal liver homogenates showed an inverse correlation to the serum cholesterol levels, indicating that the LDL receptors in fetal liver may play a role in the regulation of the serum cholesterol level in the fetus during gestation. After birth, the binding of 125I-LDL to calf liver homogenates decreased to levels found in adult animals and this was paralleled by an increase of total serum cholesterol, suggesting that the rapid rise in serum cholesterol in mammals observed soon after birth may be caused by a decrease of the receptor-mediated catabolism of LDL in the liver.

Cholesterol synthesis by human fetal hepatocytes: effect of lipoproteins

The purpose of the present investigation was to determine the effect of various lipoproteins on the rate of cholesterol synthesis of human fetal liver cells maintained in culture. This was accomplished by measuring the rate of incorporation of tritium from tritiated water or carbon 14-labeled acetate into cholesterol in human fetal liver cells. Optimal conditions for each assay were determined. When human fetal liver cells were maintained in the presence of low-density lipoprotein, cholesterol synthesis was inhibited in a concentration-dependent fashion. Intermediate--density lipoprotein and very-low-density lipoprotein also suppressed cholesterol synthesis in human fetal liver cells. In contrast, high-density lipoprotein stimulated cholesterol synthesis in human fetal liver cells. The results of the present as well as our previous investigations suggest that multiple interrelationships exist between fetal liver cholesterol synthesis and lipoprotein-cholesterol utilization by the human fetal adrenal gland and that these processes serve to regulate the lipoprotein-cholesterol levels in fetal plasma.

Decline in the concentration of low-density lipoprotein-cholesterol in human fetal plasma near term

Fetal plasma levels of lipoprotein-cholesterol were quantified during the latter stages of normal human gestation to ascertain whether a relationship exists between fetal adrenal steroid production and the concentration of plasma lipoprotein-cholesterol. It was found that total cholesterol and low-density lipoprotein (LDL)-cholesterol levels in fetal plasma declined progressively from 33 to 42 weeks of gestation. At 41 to 42 weeks of gestation, the fetal plasma concentrations of total cholesterol (53 +/- 3 mg/dL, mean +/- SEM) and of LDL-cholesterol (28 +/- 2 mg/dL) were significantly lower (P less than 0.001) than those at 33 to 34 weeks of gestation (73 +/- 7 mg/dL and 49 +/- 6 mg/dL, respectively). However, there were no fluctuations in the plasma concentrations of high-density lipoprotein (HDL)-cholesterol during this period of fetal development. The fetal plasma levels of dehydroepiandrosterone sulfate (DS), the major secretory product of the fetal adrenals, rose significantly between 33 and 42 weeks of gestation. Since LDL-cholesterol is utilized as substrate for fetal adrenal steroidogenesis, it is suggested that the increasing rate of growth and steroid production by the fetal adrenals near term is causally related to the significant decline in the concentration of both LDL-cholesterol and total cholesterol in fetal plasma during normal human development.

Regulation of human fetal testicular secretion of testosterone: low-density lipoprotein-cholesterol and cholesterol synthesized de novo as steroid precursor

The results of the present investigation support the conclusion that low-density lipoprotein (LDL)-cholesterol facilitates androgen synthesis in human chorionic gonadotropin (hCG)-treated human fetal testicular tissue in vitro. Moreover, the number of LDL receptors and the rate of de novo synthesis of cholesterol are high during the period of active fetal testicular steroidogenesis and fall with advancing gestational age, suggestive of regulation by hCG.