Peripheral insulin resistance and impaired insulin signaling contribute to abnormal glucose metabolism in preterm baboons.

Premature infants develop hyperglycemia shortly after birth, increasing their morbidity and death. Surviving infants have increased incidence of diabetes as young adults. Our understanding of the biological basis for the insulin resistance of prematurity and developmental regulation of glucose production remains fragmentary. The objective of this study was to examine maturational differences in insulin sensitivity and the insulin-signaling pathway in skeletal muscle and adipose tissue of 30 neonatal baboons using the euglycemic hyperinsulinemic clamp. Preterm baboons (67% gestation) had reduced peripheral insulin sensitivity shortly after birth (M value 12.5 ± 1.5 vs 21.8 ± 4.4 mg/kg · min in term baboons) and at 2 weeks of age (M value 12.8 ± 2.6 vs 16.3 ± 4.2, respectively). Insulin increased Akt phosphorylation, but these responses were significantly lower in preterm baboons during the first week of life (3.2-fold vs 9.8-fold). Preterm baboons had lower glucose transporter-1 protein content throughout the first 2 weeks of life (8%-12% of term). In preterm baboons, serum free fatty acids (FFAs) did not decrease in response to insulin, whereas FFAs decreased by greater than 80% in term baboons; the impaired suppression of FFAs in the preterm animals was paired with a decreased glucose transporter-4 protein content in adipose tissue. In conclusion, peripheral insulin resistance and impaired non-insulin-dependent glucose uptake play an important role in hyperglycemia of prematurity. Impaired insulin signaling (reduced Akt) contributes to the defect in insulin-stimulated glucose disposal. Counterregulatory hormones are not major contributors.

Developmental regulation of key gluconeogenic molecules in nonhuman primates.

Aberrant glucose regulation is common in preterm and full-term neonates leading to short and long-term morbidity/mortality; however, glucose metabolism in this population is understudied. The aim of this study was to investigate developmental differences in hepatic gluconeogenic pathways in fetal/newborn baboons. Fifteen fetal baboons were delivered at 125 day (d) gestational age (GA), 140d GA, and 175d GA (term = 185d GA) via cesarean section and sacrificed at birth. Term and healthy adult baboons were used as controls. Protein content and gene expression of key hepatic gluconeogenic molecules were measured: cytosolic and mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-C and PEPCK-M), glucose-6-phosphatase-alpha (G6Pase-α), G6Pase-ß, fructose-1,6-bisphosphatase (FBPase), and forkhead box-O1 (FOXO1). Protein content of PEPCK-M increased with advancing gestation in fetal baboons (9.6 fold increase from 125d GA to 175d GA, P < 0.001). PEPCK-C gene expression was consistent with these developmental differences. Phosphorylation of FOXO1 was significantly lower in preterm fetal baboons compared to adults, and gene expression of FOXO1 was lower in all neonates when compared to adults (10% and 62% of adults respectively, P < 0.05). The FOXO1 target gene G6Pase expression was higher in preterm animals compared to term animals. No significant differences were found in G6Pase-α, G6Pase-ß, FOXO1, and FBPase during fetal development. In conclusion, significant developmental differences are found in hepatic gluconeogenic molecules in fetal and neonatal baboons, which may impact the responses to insulin during the neonatal period. Further studies under insulin-stimulated conditions are required to understand the physiologic impact of these maturational differences.

TGF-ß2, a protective intestinal cytokine, is abundant in maternal human milk and human-derived fortifiers but not in donor human milk.

OBJECTIVE: This study compared cytokines (in particular transforming growth factor [TGF]-ß2) and lactoferrin in maternal human milk (MHM), human-derived milk fortifier (HDMF), and donor human milk (DHM). MATERIALS AND METHODS: MHM was randomly collected from breastfeeding mothers who had no infectious illness at the time of milk expression. HDMF and DHM were products derived from human milk processed by Holder pasteurization. MHM samples were collected at different times (early/late) and gestations (preterm/term). Lactoferrin was analyzed by western blotting, and cytokines were quantified using commercial enzyme-linked immunosorbent assays. Significance was determined using analysis of variance. RESULTS: In the 164 samples analyzed, TGF-ß2 concentrations in HDMF and preterm MHM (at all collection times) were fivefold higher than in DHM (p<0.05). Early preterm MHM had levels of interleukin (IL)-10 and IL-18, 11-fold higher than DHM (p<0.05). IL-6 in DHM was 0.3% of the content found in MHM. IL-18 was fourfold higher in early MHM versus late MHM regardless of gestational age (p<0.05). Lactoferrin concentration in DHM was 6% of that found in MHM. CONCLUSIONS: Pasteurization decreases concentrations of most cytokines and lactoferrin in DHM. TGF-ß2, a protective intestinal cytokine, has comparable concentrations in HDMF to MHM despite pasteurization.

The ontogeny of the endocrine pancreas in the fetal/newborn baboon.

Erratic regulation of glucose metabolism including hyperglycemia is a common condition in premature infants and is associated with increased morbidity and mortality. The objective of this study was to examine histological and ultrastructural differences in the endocrine pancreas in fetal (throughout gestation) and neonatal baboons. Twelve fetal baboons were delivered at 125 days (d) gestational age (GA), 140d GA, or 175d GA. Eight animals were delivered at term (185d GA); half were fed for 5 days. Seventy-three nondiabetic adult baboons were used for comparison. Pancreatic tissue was studied using light microscopy, confocal imaging, and electron microscopy. The fetal and neonatal endocrine pancreas islet architecture became more organized as GA advanced. The percent areas of α-ß-δ-cell type were similar within each fetal and newborn GA (NS) but were higher than the adults (P<0.05) regardless of GA. The ratio of ß cells within the islet (whole and core) increased with gestation (P<0.01). Neonatal baboons, which survived for 5 days (feeding), had a 2.5-fold increase in pancreas weight compared with their counterparts killed at birth (P=0.01). Endocrine cells were also found in exocrine ductal and acinar cells in 125, 140 and 175d GA fetuses. Subpopulation of tissue that coexpressed trypsin and glucagon/insulin shows the presence of cells with mixed endo-exocrine lineage in fetuses. In summary, the fetal endocrine pancreas has no prevalence of a α-ß-δ-cell type with larger endocrine cell percent areas than adults. Cells with mixed endocrine/exocrine phenotype occur during fetal development. Developmental differences may play a role in glucose homeostasis during the neonatal period and may have long-term implications.