Evidence for genetic factors explaining the association between birth weight and low-density lipoprotein cholesterol and possible intrauterine factors influencing the association between birth weight and high-density lipoprotein cholesterol: analysis in twins

The PPARα/CYP4A14 bile acid pathway is associated with lipid metabolism disorders caused by low birth weight with high-fat diet

Purpose

To investigate possible mechanisms underlying the greater susceptibility of lipid metabolism disorders in low birth weight (LBW) mice fed with high-fat diets (HFDs).

Methods

LBW mice model was established by using the pregnancy malnutrition method. Male pups were selected from LBW and normal-birth weight (NBW) offspring at random. After 3 weeks of weaning, all offspring mice were fed with HFD. Serum triglycerides (TGs), cholesterol (TC), low density lipoprotein (LDL-C), total bile acid (TAB), non-esterified fatty acid (NEFA), and mice fecal bile acid profiles were measured. Lipid deposition in liver sections was visualized by Oil Red O staining. The weight ratio of liver, muscle, and adiposity was calculated. Tandem mass tag (TMT) combined with LC-MS/MS was used to determine the differentially expressed proteins (DEPs) of liver tissue in two groups. Bioinformatics was used for further analysis of DEPs to screen key target proteins, and then Western Blot (WB) and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were performed to validate the expressions of DEPs.

Results

LBW mice fed with HFD showed more severe lipid metabolism disorders in the childhood. In contrast to the NBW group, the serum bile acids and fecal ω-muricholic acid (ω-MCA) levels in the LBW group were significantly lower. LC-MS/MS analysis showed that downregulated proteins were associated with lipid metabolism, and further analysis found that these proteins are mainly concentrated in peroxisome proliferation-activated receptor (PPAR) and primary bile acid synthesis signaling pathways and are involved in cellular processes and metabolic processes through binding and catalytic functions. Bioinformatics analysis indicated that the level of Cytochrome P450 Family 46 Subfamily A Member 1 (CYP46A1), PPARα, key factors of cholesterol metabolism and bile acid synthesis, as well as downstream molecules Cytochrome P450 Family 4 Subfamily A Member 14 (CYP4A14), and Acyl-Coenzyme A Oxidase 2 (ACOX2) are markedly different in the liver of LBW individuals fed with HFD, and confirmed by WB and RT-qPCR.

Conclusion

LBW mice are more prone to dyslipidemia probably due to downregulated bile acid metabolism-related PPARα/CYP4A14 pathway, resulting in insufficient metabolism of cholesterol to bile acids, which, in turn, leads to elevated blood cholesterol.

Developmental origins of cardiometabolic health outcomes in twins: A systematic review and meta-analysis

BACKGROUND AND AIMS

Studies of twins can reduce confounding and provide additional evidence about the causes of disease, due to within-pair matching for measured and unmeasured factors. Although findings from twin studies are typically applicable to the general population, few studies have taken full advantage of the twin design to explore the developmental origins of cardiometabolic health outcomes. We aimed to systematically review the evidence from twin studies and generate pooled estimates for the effects of early-life risk factors on later-life cardiometabolic health.

METHODS AND RESULTS

An initial search was conducted in March 2018, with 55 studies of twins included in the review. Risk of bias was assessed using the Newcastle-Ottawa Scale, and eligible studies were included in a meta-analysis, where pooled estimates were calculated. Twenty-six studies analysed twins as individuals, and found that higher birthweight was associated with lower SBP (β = -2.02 mmHg, 95%CI: -3.07, -0.97), higher BMI (β = 0.52 kg/m², 95%CI: 0.20, 0.84) and lower total cholesterol (β = -0.07 mmol/L, 95%CI: -0.11, -0.04). However, no associations were reported in studies which adjusted for gestational age. Few of the included studies separated their analyses into within-pair and between-pair associations.

CONCLUSIONS

Early-life risk factors were associated with cardiometabolic health outcomes in twin studies. However, many estimates from studies in this review were likely to have been confounded by gestational age, and few fully exploited the twin design to assess the developmental origins of cardiometabolic health outcomes.

Associations between birth size and later height from infancy through adulthood: An individual based pooled analysis of 28 twin cohorts participating in the CODATwins project

BACKGROUND

There is evidence that birth size is positively associated with height in later life, but it remains unclear whether this is explained by genetic factors or the intrauterine environment.

AIM

To analyze the associations of birth weight, length and ponderal index with height from infancy through adulthood within mono- and dizygotic twin pairs, which provides insights into the role of genetic and environmental individual-specific factors.

METHODS

This study is based on the data from 28 twin cohorts in 17 countries. The pooled data included 41,852 complete twin pairs (55% monozygotic and 45% same-sex dizygotic) with information on birth weight and a total of 112,409 paired height measurements at ages ranging from 1 to 69 years. Birth length was available for 19,881 complete twin pairs, with a total of 72,692 paired height measurements. The association between birth size and later height was analyzed at both the individual and within-pair level by linear regression analyses.

RESULTS

Within twin pairs, regression coefficients showed that a 1-kg increase in birth weight and a 1-cm increase in birth length were associated with 1.14-4.25 cm and 0.18-0.90 cm taller height, respectively. The magnitude of the associations was generally greater within dizygotic than within monozygotic twin pairs, and this difference between zygosities was more pronounced for birth length.

CONCLUSION

Both genetic and individual-specific environmental factors play a role in the association between birth size and later height from infancy to adulthood, with a larger role for genetics in the association with birth length than with birth weight.

Lower birth weight is associated with alterations in dietary intake in adolescents independent of genetic factors: A twin study

BACKGROUND & AIMS

Lower birth weight is associated with an increased risk of cardiovascular and metabolic disease. These associations may, at least in part, be explained by alterations in dietary intake in later life. The aim of this study is to examine whether lower birth weight is associated with alterations in dietary intake in later life, and whether this association is due to intrauterine environmental or genetic factors.

METHODS

In this observational study birth weight and dietary intake were investigated in 78 dizygotic (DZ) and 94 monozygotic (MZ) adolescent same-sex twin subjects. Birth weight was obtained from the mothers. Dietary intake was assessed by two-day dietary records.

RESULTS

In the total group of twins, lower birth weight was associated with higher intake of saturated fat after adjustment for current weight (1.2 per cent of total energy intake (E%) per kg increase in birth weight, P < 0.01). Intra-pair analysis in all twin pairs demonstrated that twins with the lower birth weight had a 115 kcal higher total energy intake and a 0.7 E% higher saturated fat intake compared to their co-twins with the higher birth weight (P < 0.05). Intra-pair differences in birth weight were negatively associated with differences in energy intake and differences in intake of saturated fat after adjustment for differences in current weight (P = 0.07 and P < 0.05, respectively). Intra-pair differences in birth weight were positively associated with intra-pair differences in intake of dietary fibres (P < 0.05). These intra-pair differences and associations were similar for DZ and MZ twins (P for difference > 0.6).

CONCLUSIONS

Lower birth weight was related with higher intake of energy and saturated fat within twin pairs, and these associations were independent of zygosity, suggesting that the association between birth weight and alterations in dietary intake in later life is explained by intrauterine environmental rather than genetic factors.

Insulin-like growth factor-1 and lipoprotein profile in cord blood of preterm small for gestational age infants

Low birth weight was associated with cardiometabolic diseases in adult age. Insulin-like growth factor-1 (IGF-1) has a crucial role in fetal growth and also associates with cardiometabolic risks in adults. Therefore, we elucidated the association between IGF-1 level and serum lipids in cord blood of preterm infants. The subjects were 41 consecutive, healthy preterm neonates (27 male, 14 female) born at <37-week gestational age, including 10 small for gestational age (SGA) infants (<10th percentile). IGF-1 levels and serum lipids were measured in cord blood, and high-density lipoprotein cholesterol (HDLC), low-density lipoprotein cholesterol (LDLC) and very low-density lipoprotein triglyceride (VLDLTG) levels were determined by HPLC method. SGA infants had lower IGF-1 (13.1 ± 5.3 ng/ml), total cholesterol (TC) (55.0 ± 14.8), LDLC (21.6 ± 8.3) and HDLC (26.3 ± 11.3) levels, and higher VLDLTG levels (19.0 ± 12.7 mg/dl) than in appropriate for gestational age (AGA) infants (53.6 ± 25.6, 83.4 ± 18.9, 36.6 ± 11.1, 38.5 ± 11.6, 8.1 ± 7.0, respectively). In simple regression analyses, log IGF-1 correlated positively with birth weight (r = 0.721, P < 0.001), TC (r = 0.636, P < 0.001), LDLC (r = 0.453, P = 0.006), and HDLC levels (r = 0.648, P < 0.001), and negatively with log TG (r = -0.484, P = 0.002) and log VLDL-TG (r = -0.393, P = 0.018). Multiple regression analyses demonstrated that IGF-1 was an independent predictor of TC, HDLC and TG levels after the gestational age and birth weight were taken into account. In preterm SGA infants, cord blood lipids profile altered with the concomitant decrease in IGF-1 level.

Low birthweight and chronic kidney disease

Low birthweight reflects the congenital defects of organs, which is associated with chronic kidney disease through its direct influence on nephron number and function, also through related metabolic disease-induced kidney damage. We reviewed the current evidence regarding the role of low birthweight in the pathogenesis of chronic kidney disease.

Low-density lipoprotein profile changes during the neonatal period

OBJECTIVE

To investigate natural change of low-density lipoprotein (LDL) profile during the neonatal period and the impact of gestational age and birth weight on those changes.

STUDY DESIGN

We measured lipid composition in LDL fraction, LDL particle size and apolipoprotein B (apoB) concentration at birth, 5 days of age and 1 month of age in 63 healthy neonates that had 37 to 41-week gestational age.

RESULT

Low-density lipoprotein cholesterol and apoB concentrations increased from birth to 5 days of age, and the concentration persisted at 1 month in breast-fed and mixed-fed infants. However, in formula-fed infants, the concentration decreased at 1 month. At 5 days of age, neonates had larger and more triglyceride (TG)-rich LDL particles than at birth. At 1 month of age, LDL particles were smaller and more cholesterol rich than at 5 days of age. Single regression analyses showed that gestational age had influenced the LDL profile at birth and 5 days of age, while at 1 month milk determined the profile.

CONCLUSION

The number of LDL particles increased rapidly during the first 5 days of life, and the composition of LDL particles is modulated by TG content throughout the neonatal period. Gestational age and milk, rather than birth weight, determine postnatal changes in LDL profile.

Birthweight of offspring and mortality of parents: the Jerusalem perinatal study cohort

PURPOSE

We sought to examine the association between birthweight in offspring and mortality in their parents. Distinguishing between risks of outcomes in mothers from fathers potentially provides clues as to the relative roles of genetic versus nongenetic mechanisms underlying these associations.

METHODS

We studied total and cause-specific mortality in a population-based cohort of 37,718 mothers and 38,002 fathers whose offspring were delivered in West Jerusalem during 1964-1976, after an average follow-up of 34.12 years.

RESULTS

Hazard models controlling for sociodemographic and lifestyle characteristics indicated a U-shaped relationship between offspring's birthweight and overall mortality, deaths from coronary heart disease, circulatory and other non-neoplastic causes in their mothers. Greater rates of mortality from coronary heart disease were observed among mothers who gave birth to babies with low (hazard ratio [HR], 2.13; 95% confidence interval [CI], 1.40-3.25) and high birthweight (HR, 1.98; 95% CI, 1.36-2.88), as compared with mothers whose offspring weighed 2500-3999 g at birth. Adjustment for maternal pre-eclampsia slightly attenuated these results. Multivariate models indicated a negative linear relationship (HR, 0.95; 95% CI, 0.91-0.99) between offspring's birthweight and overall mortality in their fathers. Unlike the association in mothers, the relation was noted primarily with deaths from "other causes."

CONCLUSIONS

Birthweight of offspring is associated with parental mortality although the relation differs for fathers and mothers. These findings broaden previous observations that intra-uterine events have long-term consequences for adult health and support the need to explore genetic and/or environmental mechanisms underlying these associations.

The influence of birth weight and genetic factors on lipid levels: a study in adult twins

Twins can be used to investigate the biological basis for observed associations between birth weight and later disease risk, as they experiencein uterogrowth restriction compared with singletons, which can differ in magnitude within twin pairs despite partial or total genetic identity. In the present study, sixty monozygotic and seventy-one dizygotic same-sex twin pairs aged 19–50 years and eighty-nine singleton controls matched for age, gestational age, sex, maternal age and parity were recruited from an obstetric database. Associations between fasting lipid levels and birth weight were assessed by linear regression with adjustment for possible confounding factors. Twins were significantly lighter at birth but were not significantly different in adult height, weight or lipid levels from the singleton controls. There was a significant inverse association between birth weight and both total and LDL-cholesterol levels among singleton controls (−0·53mmol/l per kg (95% CI −0·97, −0·09),P=0·02 and −0·39mmol/l per kg (95% CI −0·76, −0·02),P=0·04, respectively), but there was no significant association between birth weight and lipid levels in either unpaired or within-pair analysis of twins. The results suggest that thein uterogrowth restriction and early catch-up growth experienced by twins does not increase the risk of an atherogenic lipid profile in adult life.

Characterisation of morbidity in a UK, hospital based, obesity clinic

AIM

To identify clinical features which predict those most at risk of co-morbidities within an obesity clinic.

METHODS

Children attending an obesity clinic had fasting glucose, insulin, and lipids measured prior to a standard oral glucose tolerance test (OGTT). History and examination established birth weight, family history of type 2 diabetes/obesity, pubertal status, and presence of acanthosis nigricans. Central and total fat mass was estimated by bio-impedance.

RESULTS

Of the 126 children evaluated, 10.3% (n = 13) had impaired glucose tolerance (IGT); the majority (n = 11) of these would not have been identified on fasting glucose alone. Those with IGT were more likely to have a parental history of type 2 diabetes (relative risk 3.5). IGT was not associated with acanthosis nigricans. Twenty five per cent (n = 19) of those evaluated (n = 75) had evidence of the "metabolic syndrome" (MS). HDL cholesterol and triglyceride levels were related to insulin sensitivity (HOMA-R); HDL cholesterol was also related to birth weight SDS. We observed a trend for those with MS to have a lower birth weight SDS. The severity of obesity did not influence the likelihood of IGT or MS.

CONCLUSIONS

Significant numbers of obese children have associated co-morbidities. Analysis of fasting blood glucose samples alone is not satisfactory to adequately evaluate glucose homoeostasis. The overall level of obesity does not predict co-morbidities. Special attention should be given to those with parental diabetes and a history of low birth weight who are more likely to have IGT and abnormal lipid profiles respectively.

Atherogenic lipid profile of Brazilian near-term newborns

Cardiovascular disease is the primary cause of death in Brazil. Recent studies have shown that low birth weight and preterm birth are linked to a higher prevalence of cardiovascular disease. The aim of the present study was to compare the levels of lipids and apolipoproteins and atherogenic indexes between term and near-term newborn infants. A sample of umbilical cord blood was obtained from 135 newborns (66 males) divided into two groups: 25 near-term neonates (35-36.6 weeks of gestational age) and 110 term neonates (37-42 weeks of gestational age). The total cholesterol concentrations were higher in the near-term neonates than in the term group (94.04 +/- 8.02 vs 70.42 +/- 1.63 mg/dl, P < 0.01), due to an increase in the LDL-cholesterol fraction in the near-term group (57.76 +/- 6.39 vs 34.38 +/- 1.29 mg/dl, P < 0.001). The atherogenic indexes (total cholesterol/HDL-cholesterol, LDL-cholesterol/HDL-cholesterol and apolipoprotein B/apolipoprotein A-I) were higher in the near-term group (P < 0.001, P < 0.001, and P < 0.05, respectively). The gestational age of the newborns was inversely correlated with total cholesterol and LDL-cholesterol, and also with the total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol indexes. These findings demonstrate that the lipid profile is worse in the group of near-term neonates compared with the term group. Future studies are needed to determine if this atherogenic profile in near-term neonates can affect body metabolism, increasing the risk for cardiovascular diseases in adult life.

Separating within and between effects in family studies: an application to the study of blood pressure in children

In epidemiology the analyses of family or twin studies do not always fully exploit the data, as information on differences between siblings is often used while between-families effect are not considered. We show how cross-sectional time-series linear regression analysis can be easily implemented to estimate within- and between-families effects simultaneously and how these effects can then be compared using the Hausman test. We illustrate this approach with data from the Uppsala family study on blood pressure in children with age ranging from 5.5 to 12.3 years for the younger and from 7.5 to 13.8 years for the older siblings. Comparing the effect of differences in birth weight on blood pressure within-family (in full siblings) and between-families (in unrelated children) allows us to study the contributions of fixed and pregnancy-specific maternal effects on birth weight and consequently on blood pressure. Our data showed a 0.88 mmHg decrease (95 per cent confidence interval: -1.7 to -0.03 mmHg) in systolic blood pressure for one standard deviation increase in birth weight between siblings within a family and 0.88 mmHg (95 per cent confidence interval: -1.6 to -0.2 mmHg) decrease in systolic blood pressure for one standard deviation increase in birth weight between unrelated children. These estimates were controlled for sex, age, pubertal stage, body size and pulse rate of the children at examination and for maternal body size and systolic blood pressure. The within- and between-families effects were not significantly different, p = 0.19, suggesting that fixed and pregnancy-specific factors have similar effects on childhood systolic blood pressure.

Low birth weight is associated with increased sympathetic activity: dependence on genetic factors

BACKGROUND

Low birth weight may be associated with high blood pressure in later life through genetic factors, an association that may be explained by alterations in sympathetic and parasympathetic activity. We examined the association of birth weight with cardiac pre-ejection period and respiratory sinus arrhythmia (indicators of cardiac sympathetic and parasympathetic activity, respectively) and with blood pressure in 53 dizygotic and 61 monozygotic adolescent twin pairs.

METHODS AND RESULTS

Birth weight of the twins was obtained from the mothers. Pre-ejection period and respiratory sinus arrhythmia were measured with electrocardiography and impedance cardiography at rest, during a reaction time task, and during a mental arithmetic task. In the overall sample, lower birth weight was significantly associated with shorter pre-ejection period at rest, during the reaction time task, and during the mental arithmetic task (P=0.0001, P<0.0001, and P=0.0001, respectively) and with larger pre-ejection period reactivity to the stress tasks (P=0.02 and P=0.06, respectively). In within-pair analyses, differences in birth weight were associated with differences in pre-ejection period at rest and during both stress tasks in dizygotic twin pairs (P=0.01, P=0.06, and P=0.2, respectively) but not in monozygotic twin pairs (P=0.9, P=1.0, and P=0.5, respectively). Shorter pre-ejection period explained approximately 63% to 84% of the birth weight and blood pressure relation.

CONCLUSIONS

Low birth weight is associated with increased sympathetic activity, and this explains a large part of the association between birth weight and blood pressure. In addition, our findings suggest that the association between birth weight and sympathetic activity depends on genetic factors.

The association between birth weight and plasma fibrinogen is abolished after the elimination of genetic influences

Low birth weight is associated with an increased risk of atherothrombosis, which may be related in part to the association between low birth weight and high plasma fibrinogen. The association between birth weight and fibrinogen may be explained by intrauterine, socio-economic or genetic factors. We examined birth weight and fibrinogen in 52 dizygotic and 56 adolescent monozygotic (genetically identical) twin pairs. The dizygotic but not the monozygotic twins with the lowest birth weight from each pair had a fibrinogen level that was higher compared with their co-twins with the highest birth weight [dizygotic twins: 2.62 +/- 0.46 g L(-1) vs. 2.50 +/- 0.41 g L(-1) (P = 0.04); monozygotic twins: 2.42 +/- 0.45 g L(-1) vs. 2.49 +/- 0.39 g L(-1) (P = 0.2)]. These findings suggest that the association between birth weight and plasma fibrinogen is abolished after the elimination of genetic influences and therefore that this association has genetic causes. Improvement of intrauterine nutrition may not lower fibrinogen levels in later life.

Clinical relevance of the biochemical, metabolic, and genetic factors that influence low-density lipoprotein heterogeneity

Traditional risk factors for coronary artery disease (CAD) predict about 50% of the risk of developing CAD. The Adult Treatment Panel (ATP) III has defined emerging risk factors for CAD, including small, dense low-density lipoprotein (LDL). Small, dense LDL is often accompanied by increased triglycerides (TGs) and low high-density lipoprotein (HDL). An increased number of small, dense LDL particles is often missed when the LDL cholesterol level is normal or borderline elevated. Small, dense LDL particles are present in families with premature CAD and hyperapobetalipoproteinemia, familial combined hyperlipidemia, LDL subclass pattern B, familial dyslipidemic hypertension, and syndrome X. The metabolic syndrome, as defined by ATP III, incorporates a number of the components of these syndromes, including insulin resistance and intra-abdominal fat. Subclinical inflammation and elevated procoagulants also appear to be part of this atherogenic syndrome. Overproduction of very low-density lipoproteins (VLDLs) by the liver and increased secretion of large, apolipoprotein (apo) B-100-containing VLDL is the primary metabolic characteristic of most of these patients. The TG in VLDL is hydrolyzed by lipoprotein lipase (LPL) which produces intermediate-density lipoprotein. The TG in intermediate-density lipoprotein is hydrolyzed further, resulting in the generation of LDL. The cholesterol esters in LDL are exchanged for TG in VLDL by the cholesterol ester tranfer proteins, followed by hydrolysis of TG in LDL by hepatic lipase which produces small, dense LDL. Cholesterol ester transfer protein mediates a similar lipid exchange between VLDL and HDL, producing a cholesterol ester-poor HDL. In adipocytes, reduced fatty acid trapping and retention by adipose tissue may result from a primary defect in the incorporation of free fatty acids into TGs. Alternatively, insulin resistance may promote reduced retention of free fatty acids by adipocytes. Both these abnormalities lead to increased levels of free fatty acids in plasma, increased flux of free fatty acids back to the liver, enhanced production of TGs, decreased proteolysis of apo B-100, and increased VLDL production. Decreased removal of postprandial TGs often accompanies these metabolic abnormalities. Genes regulating the expression of the major players in this metabolic cascade, such as LPL, cholesterol ester transfer protein, and hepatic lipase, can modulate the expression of small, dense LDL but these are not the major defects. New candidates for major gene effects have been identified on chromosome 1. Regardless of their fundamental causes, small, dense LDL (compared with normal LDL) particles have a prolonged residence time in plasma, are more susceptible to oxidation because of decreased interaction with the LDL receptor, and enter the arterial wall more easily, where they are retained more readily. Small, dense LDL promotes endothelial dysfunction and enhanced production of procoagulants by endothelial cells. Both in animal models of atherosclerosis and in most human epidemiologic studies and clinical trials, small, dense LDL (particularly when present in increased numbers) appears more atherogenic than normal LDL. Treatment of patients with small, dense LDL particles (particularly when accompanied by low HDL and hypertriglyceridemia) often requires the use of combined lipid-altering drugs to decrease the number of particles and to convert them to larger, more buoyant LDL. The next critical step in further reduction of CAD will be the correct diagnosis and treatment of patients with small, dense LDL and the dyslipidemia that accompanies it.