Neonatal exendin-4 reduces growth, fat deposition and glucose tolerance during treatment in the intrauterine growth-restricted lamb

BACKGROUND IUGR increases the risk of type 2 diabetes mellitus (T2DM) in later life, due to reduced insulin sensitivity and impaired adaptation of insulin secretion. In IUGR rats, development of T2DM can be prevented by neonatal administration of the GLP-1 analogue exendin-4. We therefore investigated effects of neonatal exendin-4 administration on insulin action and β-cell mass and function in the IUGR neonate in the sheep, a species with a more developed pancreas at birth. METHODS Twin IUGR lambs were injected s.c. daily with vehicle (IUGR+Veh, n = 8) or exendin-4 (1 nmol.kg-1, IUGR+Ex-4, n = 8), and singleton control lambs were injected with vehicle (CON, n = 7), from d 1 to 16 of age. Glucose-stimulated insulin secretion and insulin sensitivity were measured in vivo during treatment (d 12–14). Body composition, β-cell mass and in vitro insulin secretion of isolated pancreatic islets were measured at d 16. PRINCIPLE FINDINGS IUGR+Veh did not alter in vivo insulin secretion or insulin sensitivity or β-cell mass, but increased glucose-stimulated insulin secretion in vitro. Exendin-4 treatment of the IUGR lamb impaired glucose tolerance in vivo, reflecting reduced insulin sensitivity, and normalised glucose-stimulated insulin secretion in vitro. Exendin-4 also reduced neonatal growth and visceral fat accumulation in IUGR lambs, known risk factors for later T2DM. CONCLUSIONS Neonatal exendin-4 induces changes in IUGR lambs that might improve later insulin action. Whether these effects of exendin-4 lead to improved insulin action in adult life after IUGR in the sheep, as in the PR rat, requires further investigation.Kathryn L. Gatford, Siti A. Sulaiman, Saidatul N. B. Mohammad, Miles J. De Blasio, M. Lyn Harland, Rebecca A. Simmons, Julie A. Owen

Effect of IUGR and neonatal exendin-4 on size at birth, postnatal growth and body composition in lambs.

<p>Neonatal growth rates are from d 0 to 16. NS: P>0.1, * different from CON (P<0.05), ? different from IUGR+Veh (P<0.05).</p

Effect of IUGR and neonatal exendin-4 treatment on in vivo metabolism in young lambs.

<p>Glucose tolerance (A), glucose-stimulated insulin secretion (B) and relative glucose-stimulated insulin secretion (C) were measured during an intravenous glucose tolerance test 14 days of age. CON (white circle, n = 7), IUGR+Veh (black circle, n = 8) and IUGR+Ex-4 (gray square, n = 8). Data are means ± SEM. * different from CON (P<0.05).</p

Effect of IUGR and neonatal exendin-4 on pancreas morphology and β-cell function.

<p>NS: P>0.1, * different from CON (P<0.05).</p

Effect of IUGR and neonatal exendin-4 treatment on in vitro insulin secretion from isolated islets in response to glucose and potassium chloride.

<p>CON (white bar, n = 5), IUGR+Veh (black bar, n = 5) and IUGR+Ex-4 (gray bar, n = 6). Data are means ± SEM. Specific contrasts: * P<0.05, ^# P<0.10.</p

Effect of IUGR and neonatal exendin-4 treatment on neonatal growth.

<p>Neonatal exendin-4 treatment reduced weight of twin IUGR lambs from 8 days of age (A), and abolished the negative relationship between birth weight and neonatal fractional growth rate (B). CON (white circle) and IUGR+Veh (black circle) lambs were treated once daily with vehicle (0.5% methanol in saline s.c.) and IUGR+Ex-4 (gray square) lambs were treated once daily with exendin-4 (1 nmol.kg⁻¹ s.c.). Data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056553#pone-0056553-g001" target="_blank">Figure 1A</a> are means ± SEM, and data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056553#pone-0056553-g001" target="_blank">Figure 1B</a> are individual animal outcomes. * different from CON (P<0.05), ? different from IUGR+Veh (P<0.05).</p

Impaired beta-cell function and inadequate compensatory increases in beta-cell mass after intrauterine growth restriction in sheep

Poor growth before birth increases the risk of non-insulin-dependent diabetes mellitus (NIDDM) and impairs insulin secretion relative to sensitivity. We investigated the effects of intrauterine growth restriction in sheep on insulin secretion, β-cell mass, and function from before birth to young adulthood and its molecular basis. Pancreas was collected from control and placentally restricted sheep as fetuses (d 143 gestation), lambs (aged 42 d), and young adults (aged 556 d), following independent measures of in vivo insulin secretion and sensitivity. β-Cells and islets were counted after immunohistochemical staining for insulin. In lambs, gene expression was measured by RT-PCR and expressed relative to 18S. β-Cell mass correlated positively with fetal weight but negatively with birth weight in adult males. Glucose-stimulated insulin disposition and β-cell function correlated negatively with fetal weight but positively with birth weight in adult males. Placental restriction increased pancreatic expression of IGF-II and IGF-I but decreased that of voltage-gated calcium channel, {alpha}1D subunit (CACNA1D) in lambs. In male lambs, pancreatic IGF-II and insulin receptor expression correlated strongly and positively with β-cell mass and CACNA1D expression with glucose-stimulated insulin disposition. Restricted growth before birth in the sheep does not impair insulin secretion, relative to sensitivity, before birth or in young offspring. IGF-II and insulin receptor are implicated as key molecular regulators of β-cell mass compensation, whereas impaired expression of the voltage-gated calcium channel may underlie impaired β-cell function after intrauterine growth restriction. With aging, the insulin secretory capacity of the β-cell is impaired in males, and their increases in β-cell mass are inadequate to maintain adequate insulin secretion relative to sensitivity