Untargeted Metabolomics Identifies Altered Cardiac Metabolite and Gene Expression Patterns in Late Preterm Growth-Restricted Newborn Lambs

Fetal growth restriction (FGR) may impair early postnatal cardiopulmonary function by limiting the heart’s ability to shift from glycolytic to fatty acid metabolism. We investigated whether the cardiac metabolic milieu is altered in newborn FGR lambs compared to control lambs 24 hours after birth. Twin-bearing ewes at 89 days gestation (d; term=148d) underwent single umbilical artery ligation to induce FGR or sham surgery (control). Lambs were delivered late preterm at 136d (~0.92 gestation) and monitored for 24 hours before postmortem tissue collection. Left ventricles were snap-frozen for untargeted metabolomics analysis via liquid chromatography/mass spectroscopy (LC-MS) and RT-qPCR, or fixed for immunohistochemical analysis. FGR lambs had lower body weights at birth (2.7 ± 0.3 vs. 4.3 ± 0.2; p=0.0002) and at 24 hours (2.7 ± 0.2 vs. 4.4 ± 0.2; p<0.0001) compared to controls. LC-MS identified 14 significantly altered metabolites in FGR hearts, with upregulated peptide and uric acid metabolism and downregulated lipid, carnitine and serotonin metabolism (fold change from control >1.5, p<0.05). RT-qPCR identified higher gene expression of long-chain fatty acid transport proteins SLC27A6 and ACADL, and lower gene expression of serotonin receptor HTR4. No differences in the gene expression of carnitine metabolism ( CPT1A, CPT1B) or uric acid metabolism ( XDH, HPRT1, GDA, PNP) were observed. Serotonin (5-hydroxytryptamine; 5-HT) density was reduced in FGR hearts (p=0.048). These findings suggest early shifts in postnatal cardiac metabolic adaptations in FGR lambs, particularly in lipid and serotonin pathways, and provide a foundation for future studies exploring the functional consequences of these changes.