IGF-1 and Leptin Associate With Fetal HDL Cholesterol at Birth

Examination in Offspring of Mothers With Type 1 Diabetes

  1. Scott M. Nelson1,
  2. Dilys J. Freeman1,
  3. Naveed Sattar2,
  4. Frank D. Johnstone3 and
  5. Robert S. Lindsay2
  1. 1Department of Reproductive and Maternal Medicine, University of Glasgow, Glasgow, Scotland, U.K
  2. 2British Heart Foundation Glasgow Cardiovascular Research Centre, University of Glasgow, Glasgow, Scotland, U.K
  3. 3Department of Obstetrics and Gynecology, University of Edinburgh, Centre for Reproductive Biology, Edinburgh, U.K
  1. Address correspondence and reprint requests to Dr. Scott M. Nelson, Department of Reproductive and Maternal Medicine, Division of Developmental Medicine, University of Glasgow, Glasgow Royal Infirmary, 10 Alexandra Parade, Glasgow, G31 ER, U.K. E-mail: s.nelson{at}clinmed.gla.ac.uk

Abstract

OBJECTIVE— Offspring of mothers with type 1 diabetes (OT1DM) demonstrate increased fat deposition, hyperinsulinemia, and hyperleptinemia in utero. We examined the influence of maternal diabetes on cord lipids at birth and relationship to body composition, cord insulin, leptin, and other hormonal measures.

RESEARCH DESIGN AND METHODS— We performed an observational study measuring fetal, HDL, and LDL cholesterol; triglycerides; and nonesterified fatty acids (NEFAs) in a total of 139 OT1DM and 48 control subjects at birth and assessed cross-sectional relationships with birth weight, fetal insulin, leptin, adiponectin, and IGF-1.

RESULTS— Concentrations of total cholesterol (male OT1DM [mean ± SD] 1.49 ± 0.45 mmol/l and male control subjects 1.74 ± 0.33 mmol/l; P < 0.001), HDL cholesterol (0.53 ± 0.21 and 0.74 ± 0.19 mmol/l, respectively; P < 0.001), and NEFA (median 0.17 [interquartile range 2.30−2.95] and 0.21 [0.18–0.36], respectively; P < 0.001) were significantly lower in male OT1DM, with no significant differences in female subjects. Differences in male subjects were independent of mode of delivery. Cord lipids were unrelated to birth weight in OT1DM and did not show consistent relationships with fetal insulin. Unexpectedly, IGF-1 was a strong correlate of HDL cholesterol in control subjects (r = 0.40, P = 0.002) and OT1DM (r = 0.32, P < 0.001) but a negative correlate of triglycerides in control subjects (r = −0.48, P < 0.001) and OT1DM (r = −0.21, P = 0.004), with these relationships present in both sexes. In OT1DM, leptin was also independently correlated (negatively, P < 0.001) with HDL cholesterol in male and female subjects.

CONCLUSIONS— Maternal diabetes is associated with significant alterations in lipid levels in male fetuses. IGF-1, leptin, and male sex rather than insulin may be the major determinants of HDL cholesterol and triglycerides in utero.

There is increasing interest in how the intrauterine environment might influence cardiovascular and metabolic disease throughout life. In nondiabetic pregnancies, lower birth weight (1,2) (and smaller fetal abdominal circumference [3]) is associated with higher cord triglycerides and less consistently with lower HDL cholesterol (1,4) in addition to the well-described associations with increased risk of cardiovascular disease in adult life (5). Notably, much is still not known about the control or function of circulating fetal lipoproteins in utero. While free fatty acids cross the placenta, lipoproteins do not, and transfer of cholesterol is extremely limited (6). Oversupply of lipids, particularly nonesterified fatty acids (NEFAs), to the fetus have been proposed as a factor in promoting fetal adiposity (7,8). Maternal diabetes during pregnancy is associated with characteristic overgrowth of the fetus as well as marked hyperinsulinemia and hyperleptinemia, which is easily detectable in cord samples at birth (9). Offspring of mothers with type 2 diabetes are subject to in utero programming effects with increased risk of type 2 diabetes and obesity in childhood and early adulthood (10). In a single study, exposure to maternal type 1 diabetes in utero has also been associated with changes in lipids in childhood (11).

Given the preponderance of fetal macrosomia and fetal hyperinsulinemia in offspring of mothers with type 1 diabetes (OT1DM), this population represents an important opportunity to investigate the effects of fetal insulin and leptin on fetal lipids and to assess any potential interaction between fetal lipids and fetal growth. We assessed cholesterol, HDL cholesterol, triglycerides, VLDL cholesterol, LDL cholesterol, and total NEFA in cord blood of control subjects and OT1DM. We also assessed the relationship of cord lipids to birth weight, to measures of fetal adiposity, and, more broadly, to maternal glycemia (assessed by A1C), as well as to hormones in cord blood related to fetal carbohydrate metabolism, lipid metabolism, and growth (insulin, insulin propeptides, leptin, adiponectin, and IGF-1).

RESEARCH DESIGN AND METHODS

A comprehensive description of recruitment and exclusion criteria are available in the online appendix (available at http://dx.doi.org/10.2337/db07-0585) and previous publications (9,12,13).

Subjects and maternal and cord blood assays.

A total of 139 OT1DM and 48 control offspring were available for analysis. Maternal A1C and cord plasma insulin, 32–33 split proinsulin, proinsulin, leptin, IGF-1, and adiponectin were assayed centrally using a single laboratory and method as previously described (9,12,13). Plasma total cholesterol, triglycerides, VLDL cholesterol, HDL cholesterol, LDL cholesterol, and NEFAs were measured at a Centers for Disease Control and Prevention (Atlanta, GA) reference laboratory.

Statistical analysis.

Data were analyzed using Minitab 14 (State College, PA). In several cases, insulin, proinsulin, 32–33 split proinsulin, triglycerides, VLDL, NEFAs, and total–to–HDL cholesterol ratio measures were non–normally distributed, and unadjusted values are presented as median (interquartile range) and mean ± SD for normally distributed variables. Variables were logarithmically transformed to obtain normal distributions. Intergroup differences were assessed by unpaired t test or, where further explanatory variables were included, by general linear models. Spearman's correlation coefficients are reported. Step-wise logistic regression was performed using an α of P ≤ 0.15 for adding or removing predictors from the model.

RESULTS

Maternal and fetal characteristics.

Mothers with type 1 diabetes were of similar age and parity as control mothers (Table 1). OT1DM were delivered 2 weeks earlier than control offspring, with an increased number delivered by Caesarean section. Despite an earlier gestation at birth, OT1DM were heavier, with markedly increased weight in both male and female infants after adjustment for gestation at delivery. In keeping with this, birth weight in OT1DM was, on average, 2.0 SDs above that expected in the population and significantly greater than control subjects. Detailed anthropometric information was available on a subset of OT1DM. Offspring were of similar crown-rump and crown-heel length to control subjects but had increased triceps and subscapular skinfold thickness (Table 1).

TABLE 1

Characteristics of mothers with type 1 diabetes and their singleton offspring vs. control mothers and children

Fetal hormonal and lipid profiles in OT1DM and control subjects.

As previously reported for this cohort (9,12,13), maternal type 1 diabetes was associated with marked increases in absolute values of cord insulin, proinsulin, 32–33 split proinsulin, and leptin in both sexes (Table 2). Male OT1DM demonstrated a small decrease in fetal adiponectin compared with male control subjects and female OT1DM. Maternal diabetes was not associated with differences in IGF-1 (Table 2). Leptin or insulin propeptides were unrelated to mode of delivery (13), but insulin was higher in those delivered by elective Caesarean section (13). All differences between control subjects and OT1DM remained significant after adjustment for mode of delivery.

TABLE 2

Cord hormonal and lipid profiles of singleton OT1DM vs. control offspring

Mode of delivery (emergency vs. elective lower-uterine Caesarean section vs. vaginal or assisted delivery) did not influence circulating total cholesterol; triglycerides; or VLDL, LDL, or HDL cholesterol concentrations (data not shown). In contrast, NEFA concentrations were related to mode of delivery—being lower in babies delivered by Caesarean section—in both OT1DM (median vaginal 0.23 mmol/l [interquartile range 0.18–0.29], elective Caesarean section 0.15 mmol/l [0.12–0.18], and emergency Caesarean section 0.18 mmol/l [0.14–0.24]; P < 0.001) and control subjects (0.28 mmol/l [0.22–0.36], 0.18 mmol/l [0.14–0.21], and 0.20 mmol/l [0.14–0.30], respectively; P = 0.006).

In general, the effects of maternal diabetes on fetal lipids were restricted to male OT1DM, with lowest values of total, HDL, and LDL cholesterol levels and NEFAs in male OT1DM and an increased cholesterol–to–HDL cholesterol ratio compared with male control subjects and female OT1DM (Table 2). Notably, for HDL cholesterol and NEFA, while maternal diabetes was associated with significantly lower HDL cholesterol (P = 0.03) and NEFA (P = 0.001) levels, there were significant interactions (diabetes × sex: P = 0.001 and P = 0.04, respectively), with lowest values for HDL cholesterol and NEFAs in male OT1DM. Maternal diabetes did not significantly influence HDL cholesterol or NEFA levels in female OT1DM (P = 0.82 and P = 0.49, respectively). No significant interactions were observed for triglycerides and LDL and VLDL cholesterol levels.

Correlates of lipids with birth weight and hormonal measures in OT1DM and control subjects.

IGF-1 demonstrated consistent positive associations with HDL cholesterol and negative associations with triglycerides across male and female OT1DM and control subjects (Table 3). Several cord hormonal measures showed a number of other significant correlations; however, these were not consistent across different groups (Table 3). Importantly, fetal insulin failed to show consistent relationships with any of the fetal lipids, although a negative correlation with cord triglycerides was present in both male and female OT1DM. In OT1DM, leptin was negatively associated with HDL cholesterol in males (r = −0.41, P < 0.001) and females (r = −0.29, P = 0.02), although no relationships were observed in control subjects. Despite the relationship with leptin, fetal lipid profiles were not related to skinfolds or birth length in either sex of control subjects or OT1DM.

TABLE 3

Spearman's correlation coefficients (r) of cord lipids vs. birth weight and hormonal measures in cord blood at birth for male and female offspring of control mothers and mothers with type 1 diabetes

Multivariate analysis of independent correlates of fetal cord lipids in OT1DM and control subjects.

To examine potential hormonal associations with cord lipids, the relationship of HDL cholesterol, LDL cholesterol, triglycerides, and NEFAs to log insulin, log leptin, adiponectin, IGF-1, mode of delivery, and sex were examined using a step-wise regression model (Table 4). IGF-1 was a positive associate of HDL cholesterol and negative associate of triglycerides (control subjects and OT1DM). By contrast, leptin showed an inverse relationship (negative association with HDL cholesterol and positive with triglycerides) in OT1DM only (Table 4). Due to the strong correlation between birth weight and IGF-1, birth weight was added as a correlate in a second model. In this case, relationships of IGF-1 to HDL cholesterol and triglycerides remained significant in both control subjects and OT1DM. Notably IGF-1, similarly to HDL cholesterol, showed an interaction between diabetes and sex (diabetes × sex P = 0.05). Mode of delivery had a significant impact on NEFAs in control subjects and OT1DM. Male sex was associated with lower HDL cholesterol, LDL cholesterol, triglycerides, and NEFAs in OT1DM.

TABLE 4

Multivariate analysis of independent correlates of fetal cord lipids in OT1DM and control subjects

DISCUSSION

In this, the largest case-control study of its kind, we have tested whether maternal type 1 diabetes is associated with significant alteration in cord lipids in utero. We demonstrate a sex-specific reduction in HDL cholesterol and NEFAs, resulting in an increase in the cholesterol–to–HDL cholesterol ratio in male OT1DM. Second, we establish that leptin is an independent correlate of a reduced HDL cholesterol in OT1DM. Finally, our results identify an unexpectedly strong relationship of IGF-1 with HDL cholesterol and triglycerides in male and female control and diabetic OT1DM in utero; this relationship with IGF-1 may therefore contribute to the reduced HDL cholesterol observed in male OT1DM.

Cord lipids are only lower in male OT1DM. This may reflect a sex-specific programming interaction with maternal diabetes or, alternatively, mirror changes in leptin and IGF-1, major correlates of HDL cholesterol levels. Leptin has previously been shown to have a negative association with HDL cholesterol in obese children (14), and we demonstrate that this association is present in utero in OT1DM. Leptin is related to birth weight and particularly to fetal adiposity (correlation with skinfold thickness in this series: control r = 0.44, OT1DM r = 0.41 [9]). The negative relationship between HDL cholesterol and leptin may therefore reflect some indirect effect of fat mass or direct effect of leptin, and we cannot distinguish between these possibilities in this cross-sectional series. Adiponectin is positively associated with HDL cholesterol and negatively with fat mass in children (15). Notably, however, adiponectin, although lower in male OT1DM, was not an independent predictor of HDL cholesterol in OT1DM and of marginal significance in the control subjects. As such, adiponectin does not appear to provide a convincing link between HDL cholesterol and fat mass or leptin or provide an explanation for lower HDL cholesterol in male OT1DM.

Similarly, the striking positive relationship of IGF-1 and HDL cholesterol and negative relationship with triglycerides may reflect a primary relationship of HDL cholesterol and fat-free mass, as at least in childhood IGF-1 is closely related to fat-free mass (16). IGF-1 may also be exerting a more direct effect on HDL cholesterol in utero. In adult life, there is a positive association between IGF-1 and HDL cholesterol (17). Mechanistically, there are potential links between IGF-1 and HDL cholesterol through production and regulation of apolipoprotein M, a key component of pre–β-HDL, a subclass of lipid-poor apolipoproteins that serves as a key acceptor of peripheral cellular cholesterol (18). Apolipoprotein M is in turn reported to be regulated by insulin, leptin, and IGF-1 (19,20). Alternatively, it has been speculated that HDL cholesterol variations in diabetic pregnancies are due to enhanced cholesteryl ester transfer protein activity, thereby establishing an adult lipid profile prematurely (21). The consistent, strong, negative relationship between IGF-1 and triglycerides in OT1DM and control subjects may reflect increased uptake or alterations in fetal liver production of triglyceridess mediated by IGF-1 in utero. Our observation that IGF-1 rather than insulin is a major correlate of HDL cholesterol and that IGF-1 is significantly lower in male OT1DM is consistent with our proposal that IGF-1 metabolism may contribute to the regulation of HDL cholesterol.

Although recent data have emphasized the importance of fetal rather than maternal insulin in influencing placental genes (22) and thus placental function late in gestation, we do not demonstrate a major role for insulin in regulating fetal lipids. In adults, chronic (24-h) infusion of glucose and insulin is associated with a modest reduction in triglycerides and HDL cholesterol (∼10%), no change in LDL cholesterol, and marked (80%) reduction in free fatty acids (2325). While male OT1DM do have lower NEFAs, there is little relationship of fetal cord insulin with NEFAs, suggesting either that insulin is less active in control of NEFAs in utero or that compensatory mechanisms (such as increased placental transfer of NEFAs) are present. Admittedly, we rely on a single cord measure of NEFA and cannot distinguish between these possibilities. Nevertheless, it should be noted that cord insulin concentrations are often very high in this cohort (>300 pmol/l in 14% of OT1DM), and the lack of relationship of NEFAs and insulin do not support a direct effect of insulin.

Finally, it should be noted that within OT1DM, there is a positive relationship of maternal third-trimester A1C and fetal HDL cholesterol. In multivariate analysis, this relationship was not independent of cord leptin and IGF-1 (data not shown). Nevertheless, it suggests that the changes we observed may be influenced by maternal glycemia and therefore potentially modified by improvements in glycemic control.

In conclusion, maternal diabetes is associated with lower fetal lipids in male OT1DM, in particular HDL cholesterol (thus, significantly higher total–to–HDL cholesterol ratio). Perturbances in IGF-1 and leptin, rather than insulin, may be the major determinants of HDL cholesterol in utero. The long-term sequelae of these changes are unknown, but given the cardioprotective properties of HDL cholesterol if these alterations are perpetuated into later life, male offspring of mothers with diabetes may be at substantive risk of cardiovascular disease.

Acknowledgments

This study was supported by grants from the Chief Scientist Office of the Scottish Executive (K/MRS/50/C2726) and the GRI Research Endowment Fund (05REF007).

We acknowledge Dr. L. Cherry and Ann Brown, who expertly performed the lipid analysis, and the contributions of the different centers as previously noted (13).

Footnotes

  • Published ahead of print at http://diabetes.diabetesjournals.org on 31 July 2007. DOI: 10.2337/db07-0585.

    Additional information for this article can be found in an online appendix at http://dx.doi.org/10.2337/db07-0585.

    The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Received April 27, 2007.
    • Accepted July 24, 2007.

REFERENCES

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