Studies of lipoproteins and fatty acids in maternal and cord blood of two racial groups in Trinidad

Frequency of fat mass and obesity-associated gene rs9939609 and peroxisome proliferator-activated receptor gamma 2 gene rs1801282 polymorphisms among Trinidadian neonates of different ethnicities and their relationship to anthropometry at birth

BACKGROUND

The fat mass and obesity-associated gene (FTO) rs9939609 and peroxisome proliferator-activated receptor gamma 2 gene (PPARG2) rs1801282 polymorphisms are type 2 diabetes mellitus susceptibility gene variants associated with obesity. This study examined whether these variants are associated with anthropometry at birth among a representative multi-ethnic sample of Trinidadian neonates.

METHODS

Cord blood was obtained from consecutive term live births and DNA was genotyped for FTO and PPARG2 variants using polymerase chain reaction. Associations between neonate anthropometry at birth and genotype frequency were assessed using the χ(2) test and linear regression.

RESULTS

Significant associations were observed between neonate ethnicity and PPARG2 (p = 0.005) and FTO (p = 0.017) variants: high-risk alleles were more prevalent among African than South Asian neonates for both variants. The allelic and genotypic frequencies for mixed neonates were between those for the African and those for the South Asian neonates. No significant relationship was observed between rs9939609 and rs1801282 and anthropometric measures. For both variants, the allelic and genotypic frequencies among the African and South Asian neonates mirrored those found elsewhere for similar ethnic groups.

CONCLUSIONS

Neonates of African ethnicity possess the highest frequency of rs9939609 and rs1801282 alleles and genotypes; this may be associated with ethnic differences in the risk of lifestyle diseases.

Distinct composition of human fetal HDL attenuates its anti-oxidative capacity

In human high-density lipoprotein (HDL) represents the major cholesterol carrying lipoprotein class in cord blood, while cholesterol is mainly carried by low-density lipoprotein in maternal serum. Additionally, to carrying cholesterol, HDL also associates with a range of proteins as cargo. We tested the hypothesis that fetal HDL carries proteins qualitatively and quantitatively different from maternal HDL. These differences then contribute to distinct HDL functionality in both circulations. Shotgun proteomics and biochemical analyses were used to assess composition/function of fetal and maternal HDL isolated from uncomplicated human pregnancies at term of gestation. The pattern of analyzed proteins that were statistically elevated in fetal HDL (apoE, proteins involved in coagulation, transport processes) suggests a particle characteristic for the light HDL2 sub-fraction. In contrast, proteins that were enriched in maternal HDL (apoL, apoF, PON1, apoD, apoCs) have been described almost exclusively in the dense HDL3 fraction and relevant to its anti-oxidative function and role in innate immunity. Strikingly, PON1 mass and activity were 5-fold lower (p<0.01) in the fetus, which was accompanied by attenuation of anti-oxidant capacity of fetal HDL. Despite almost equal quantity of CETP in maternal and fetal HDL, its enzymatic activity was 55% lower (p<0.001) in the fetal circulation, whereas LCAT activity was not altered. These findings indicate that maternally derived HDL differs from fetal HDL with respect to its proteome, size and function. Absence of apoA-1, apoL and PON1 on fetal HDL is associated with decreased anti-oxidative properties together with deficiency in innate immunity collectively indicating distinct HDLs in fetuses.

Lipoprotein concentrations in newborns are associated with allelic variations in their mothers

BACKGROUND

Factors determining lipoprotein concentrations in the fetus are not yet fully understood. We postulated that an important factor is the genetic make-up of the mother. In the present study, we examined the associations between the cord blood concentrations of lipoproteins of 525 newborns and the polymorphisms present in their mothers on the genes of apolipoprotein E (APOE*E2, *E3, *E4), apolipoprotein C-III (APOC3*C3238G also called APOC3*S2) and lipoprotein lipase (LPL*S447X).

RESULTS

Newborns born of mothers with APOE*E2 allele had significantly lower cord blood LDL-C (P < 0.01) and apoB (P < 0.01) and significantly higher cord blood HDL-C and apoA1 (all P-values < 0.03) compared to those born of mothers with APOE*E3E3 genotype. These associations were independent of the presence of APOE*E2 allele in the newborns. Similarly, APOC3*S2 in mothers was associated with significantly lower (all P < 0.001) cord blood LDL-C, apoB, HDL-C and apoA1. In contrast, LPL*S447X in mothers lowered significantly cord blood LDL-C and apoB only when LPL*S447X was present in newborns. Most of the effects of these maternal polymorphisms on the newborns were independent of the changes of maternal lipoproteins generated by these polymorphisms.

CONCLUSIONS

This is the first evidence that maternal genetic variations influence fetal lipoprotein concentrations, independent of the genetic status of the fetus and of the variations of maternal lipoprotein concentrations generated by these genetic variants. It suggests that proteic components of maternal lipoproteins strongly control the metabolism of maternal lipoproteins carried out at the surface of the placenta to assure the cholesterol delivery to the fetus.

Unique character and metabolism of high density lipoprotein (HDL) in fetus

Lipid and lipoprotein profiles, and enzymes for the lipid metabolism were compared between cord and adult blood. Consistent with previous reports, the major lipoprotein in cord blood was high-density lipoprotein (HDL), and that in adult blood was low-density lipoprotein (LDL). The level of apolipoprotein E (apo E) in cord blood was almost equivalent to that in adult blood, while other apolipoproteins and lipids were all lower than the adult level. In cord blood, apo E-rich HDL cholesterol represented more than 30% of total HDL cholesterol (around 11% in adult), and the concentration was about twice of that in adult blood. This apo E-rich HDL cholesterol was poorly esterified (E/T 56%) compared with that in adults (93%). The lecithin:cholesterol acyltransferase (LCAT) activity in cord blood was extremely low, while the activity and mass of cholesteryl ester transfer protein (CETP) were higher than those in adult blood. The apo E genotype did not show influences on total cholesterol, LDL cholesterol, total HDL cholesterol, and apo E rich HDL cholesterol levels in cord blood, as opposed to those in adult blood. The association of D442G mutation of the CETP gene with the increased HDL cholesterol in adult blood was not seen in cord blood. Rather, the mutation was associated with low total cholesterol and LDL cholesterol levels in cord blood. These results indicate that, in fetus, the character and metabolism of HDL, especially of apo E-rich HDL cholesterol, are distinct from those in adults.

Polymorphism of apolipoprotein E influences levels of serum apolipoproteins E and B in the human neonate

To gain more insight into the genetic vs. environmental influence of the apoE phenotypes on plasma lipoprotein variation we studied human umbilical cord sera at birth. Apolipoprotein E genetic phenotypes were determined in 110 individuals by immunoblotting and shown to be identical to the adult human isoforms with six phenotypes present and occurring at a similar frequency as reported previously for the adult population in the same area. Total serum cholesterol and triglyceride levels were low in the neonates and did not differ significantly between apoE phenotypes. On the other hand as in the adult, levels of apoE and B differed significantly between the phenotypes. ApoE was highest in individuals with the epsilon 2 allele and lowest in individuals expressing apoE4, and vice versa for apoB. We conclude that apoE phenotypes in human umbilical cord blood serum are already associated with pronounced differences in apoE and B levels in the newborn. The study demonstrates that the association of apoE and apoB levels with the apoE polymorphism occurs independently of significant enteral nutrition in the relatively constant in utero environment.

The association between apolipoprotein A-I and prostacyclin binding in human serum

The stability of Prostacyclin in human blood is dependent upon binding to circulating proteins. Although this binding has been considered to be primarily due to albumin, a recent report has suggested that apolipoprotein A-I is responsible. We compared prostacyclin binding to the concentration of albumin and apolipoprotein A-I in several groups of sera with known differences in the ability to bind prostacyclin. Our results indicate a strong correlation with albumin concentration but no correlation between binding and the concentration of apolipoprotein A-I. It appears that in the human circulation albumin concentration is the most important determinant of prostacyclin binding.

Dietary and other characteristics relevant for coronary heart disease in men of Indian, West Indian and European descent in London

The origins of the high standardized mortality ratio (SMR) for coronary heart disease (CHD) among Indians in Britain, and the low SMR for West Indian immigrants, have been explored by a community survey in London. Serum lipoproteins, plasma glucose, haemostatic factors and other putative risk characteristics were measured in 75 Indian, 64 European and 24 West Indian men aged 45-54 years. These represented 81% of men registered with a general practice and resident within a defined area. In 51 men, diet was assessed by 5-day weighed inventory. Plasma phospholipid fatty acids (PFA) were measured in 18 Indians and 19 Europeans with dietary records. The relatively high HDL and HDL2-cholesterol concentrations, low LDL-cholesterol concentration, reduced fat intake, increased ratio of dietary polyunsaturated/saturated fat, relatively frequent use of alcohol, and lack of obesity in West Indians accorded with their low SMR from CHD. By contrast, only the relatively low HDL and HDL2-cholesterol concentrations, infrequency of alcohol consumption, and lower proportion of PFA as n-3 fatty acids of marine origin afforded explanations for the high SMR of Indians. Hyperglycaemia appeared similarly prevalent in Indians and West Indians, but less common in Europeans. Of the haemostatic factors, West Indians had a relatively low VIIc (not statistically significant), while Indians had an increased platelet count and reduced platelet volume. Improved understanding of these ethnic differences in CHD mortality may depend upon elucidation of the contrasts in HDL-cholesterol concentration.