Oxygen Glucose Deprivation in Rat Hippocampal Slice Cultures Results in Alterations in Carnitine Homeostasis and Mitochondrial Dysfunction

Abstract

Mitochondrial dysfunction characterized by depolarization of mitochondrial membranes and the initiation of mitochondrial-mediated apoptosis are pathological responses to hypoxia-ischemia (HI) in the neonatal brain. Carnitine metabolism directly supports mitochondrial metabolism by shuttling long chain fatty acids across the inner mitochondrial membrane for beta-oxidation. Our previous studies have shown that HI disrupts carnitine homeostasis in neonatal rats and that L-carnitine can be neuroprotective. Thus, this study was undertaken to elucidate the molecular mechanisms by which HI alters carnitine metabolism and to begin to elucidate the mechanism underlying the neuroprotective effect of L-carnitine (LCAR) supplementation. Utilizing neonatal rat hippocampal slice cultures we found that oxygen glucose deprivation (OGD) decreased the levels of free carnitines (FC) and increased the acylcarnitine (AC): FC ratio. These changes in carnitine homeostasis correlated with decreases in the protein levels of carnitine palmitoyl transferase (CPT) 1 and 2. LCAR supplementation prevented the decrease in CPT1 and CPT2, enhanced both FC and the AC∶FC ratio and increased slice culture metabolic viability, the mitochondrial membrane potential prior to OGD and prevented the subsequent loss of neurons during later stages of reperfusion through a reduction in apoptotic cell death. Finally, we found that LCAR supplementation preserved the structural integrity and synaptic transmission within the hippocampus after OGD. Thus, we conclude that LCAR supplementation preserves the key enzymes responsible for maintaining carnitine homeostasis and preserves both cell viability and synaptic transmission after OGD.

l-Carnitine and Acetyl-l-carnitine Roles and Neuroprotection in Developing Brain

“…The carnitine shuttle is essential to prevent accumulation of long chain fatty acids and long chain acyl-CoAs which can be deleterious to cells [1, 43, 54]. The enzyme carnitine acetyltransferase (CAT) has a crucial role in the metabolic flexibility of cells, as it transfers a 2-carbon moiety from acetyl-CoA to L-carnitine, forming the membrane permeable compound acetyl-L-carnitine; this serves to regulate intracellular trafficking of carbons between mitochondria and cytosol [55].…”

“…An in vitro study by Rau et al [54] determined the effects of oxygen glucose deprivation (OGD) on carnitine homeostasis and synaptic activity in hippocampal slice cultures from 7 day old rat brain. Interestingly, OGD led to decreased levels of CPT I and CPT II protein, a corresponding decrease in free carnitine and an increase in the ratio of acylcarnitine to free carnitine [54].…”

Alternative mitochondrial electron transfer for the treatment of neurodegenerative diseases and cancers: Methylene blue connects the dots

“…For example, lipid rafts have been shown to influence the potency and efficacy of neurotransmitter receptors and transporters (Allen et al , 2007). lipid L-carnitine, its primary role appears to facilitate the transport of long chain fatty acids into mitochondria for β-oxidation cycle, has been indicated to be neuroprotective (Rau et al , 2012; Wang et al , 2007). Lipogenesis has been shown to regulate adult neural stem proliferation (Folmes et al , 2013; Knobloch et al , 2013).…”

Organotypic Hippocampal Slices as Models for Stroke and Traumatic Brain Injury

“…The increased presence of ROS and calcium within the mitochondria leads to lipid peroxidation and membrane damage [66]. Nitric oxide (NO) accumulates and reacts with superoxide anion to form peroxynitrite, which causes additional cell damage and leads to apoptotic and necrotic cell death [66,97]. Mitochondrial inhibitors (3-nitropropionic acid), compounds that induce glutathione depletion (l-buthionine-sulfoximine), and other reagents have been used to mimic the pathological process of ROS generation in OHSCs [66].…”