Studies on the significance of creatine for fetal and neonatal development

Abstract

Creatine is an amino acid derivative broadly known for its role in energy homeostasis, particularly for tissues with high and fluctuating energy demands. The creatine/phosphocreatine system has been extensively researched, and recently there has been a focus on understanding the importance of creatine in the developing brain. This is largely due to the discovery that severe depletion of cerebral creatine results in neurological and physical disability. As yet, very little is known about the creatine content of fetal organs, or the source of fetal creatine, and how this may change with advancing pregnancy. The studies described in this thesis were carried out in the spiny mouse, a precocial species that in comparison to conventionally used rodents, can be considered a more appropriate animal model for perinatal development in the human. The first study (Chapter 2) aimed to understand the significance of maternal creatine for the developing fetus, and to determine if the fetus developed the capacity to meet its own creatine requirement by the time of birth. We found that the placenta and fetal brain accumulated creatine over the second half of gestation. However, expression levels of the proteins and genes required for creatine synthesis suggested the placenta had no capacity for creatine synthesis, and the fetus showed a relatively low capacity for endogenous synthesis, until shortly before term. It was concluded that the fetus is almost completely reliant on a maternal source of creatine until as late as 0.9 of pregnancy in this species. In support of this, the gestational increase in creatine transporter expression in the placenta and fetal brain suggests an increase in the capacity for maternal-fetal transfer of creatine, and increased uptake of creatine by the developing brain. There is growing interest in creatine as a substance with neuroprotective properties. We assessed the potential for a maternal diet supplemented with creatine from mid-gestation to improve fetal and neonatal well-being following intrapartum hypoxia (Chapters 3 and 4). We developed a model of intrapartum hypoxia in the precocial spiny mouse that induced significant mortality, slowed postnatal growth in the 1-2 weeks after birth, and produced a pattern of brain injury 24 h after birth that is consistent with that seen in term human infants who survive birth-hypoxia. We found that a creatine supplemented maternal diet significantly increased placental and fetal reserves of creatine at term, specifically in the brain and heart. The offspring of these creatine-fed dams showed significantly reduced mortality and improved postnatal growth. The hypoxia-induced brain injury was almost completely ameliorated in offspring from creatine-fed dams; they showed significantly less lipid peroxidation in the brain, and fewer cells entering the apoptotic pathway in the cortical subplate, thalamus and piriform cortex. The studies in this thesis provide further evidence for the importance of creatine to the developing fetus, and also for its potential to protect the fetal brain from a later hypoxic insult. Future research should be directed at confirming these findings in larger animal models of late-gestation hypoxia, before optimizing a safe and efficient dose for recommendation to pregnant women classified as high risk for fetal hypoxia.