Effect of Branched-Chain Amino Acid Supplements on Pancreatic Development in Preterm Lambs

Abstract

Background: Babies born preterm frequently receive nutritional supplements after birth to support growth and development. Both preterm birth and rapid early growth are associated with adverse metabolic outcomes. Targeted nutritional supplements are needed to enhance organ development and function without excessive weight gain. Branched-chain amino acids (BCAA) are essential nutrients for the development of the endocrine pancreas, especially β-cells. Hypothesis: Postnatal nutritional supplementation with BCAA will promote pancreatic development after preterm birth without excessive weight gain. Methods: Preterm-born lambs (137-days of gestation, labour induced with dexamethasone) were randomised to receive daily oral BCAA supplements (leucine, isoleucine, and valine, ratio 2:1:1), calorie-equivalent maltodextrin, or volume-equivalent water for two weeks after birth. Term-control lambs (induced at 147-days) received volume-equivalent water. Weight, morphometry, and milk intake were measured. At 12-months of age, an hyperglycaemic clamp (HGC) with arginine-challenge was performed to assess pancreatic function. Plasma concentrations of insulin and glucagon were measured using ELISA. Ten days after HGC, pancreatic tissues were collected for immunohistochemistry to measure islet number and composition. Tissues were multi-labelled with antibodies against insulin, glucagon, somatostatin, Ki67, and caspase-3. Antibodies were visualized using the Vslide scanner system. Groups were compared using ANOVA with Tukey post-hoc test. Results: BCAA supplements did not affect postnatal growth or milk intake. During HCG, baseline plasma glucose concentration was similar among groups; but higher in Maltodextrin-males than Maltodextrin-females (P=0.03). Baseline insulin concentrations were similar among groups, but higher in males than females (P=0.04). BCAA-males had higher insulin-to-glucose ratio (5-minutes post glucose infusion) than BCAA (P=0.01), Term (P=0.02) and Maltodextrin (P=0.04) females. Insulin sensitivity and insulin secretory response to arginine-challenge were similar among groups. Glucagon concentrations were highest in Maltodextrin-females throughout the clamp. There was no difference among groups or between sexes in insulin-, glucagon- or somatostatin-positive-area, β-, α-, or δ-cell number, or islet area and number. β-, α-, δ-cell-mass and islet mass were greater in males than females (P=0.008, P=0.01, P=0.003, and P=0,004, respectively). Ki67-proliferating cells and caspase-3-apoptotic cells were similar amongst groups and between sexes. Conclusions: Preterm birth and BCAA supplements did not alter endocrine pancreas morphology, but sex-specific interactions between nutritional supplements and islet cell function in preterm groups indicate that nutritional interventions after preterm birth may also need to be sex-specific.