Ganglioside levels in hypoxic brains from neonatal and premature infants

Ganglioside GM1 and the Central Nervous System

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

Gangliosides in the Brain: Physiology, Pathophysiology and Therapeutic Applications

Gangliosides are glycosphingolipids highly abundant in the nervous system, and carry most of the sialic acid residues in the brain. Gangliosides are enriched in cell membrane microdomains ("lipid rafts") and play important roles in the modulation of membrane proteins and ion channels, in cell signaling and in the communication among cells. The importance of gangliosides in the brain is highlighted by the fact that loss of function mutations in ganglioside biosynthetic enzymes result in severe neurodegenerative disorders, often characterized by very early or childhood onset. In addition, changes in the ganglioside profile (i.e., in the relative abundance of specific gangliosides) were reported in healthy aging and in common neurological conditions, including Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis and epilepsy. At least in HD, PD and in some forms of epilepsy, experimental evidence strongly suggests a potential role of gangliosides in disease pathogenesis and potential treatment. In this review, we will summarize ganglioside functions that are crucial to maintain brain health, we will review changes in ganglioside levels that occur in major neurological conditions and we will discuss their contribution to cellular dysfunctions and disease pathogenesis. Finally, we will review evidence of the beneficial roles exerted by gangliosides, GM1 in particular, in disease models and in clinical trials.

Ontogenetic characteristics of behavior in rats subjected to hypoxia on day 14 or day 18 of embryogenesis

Physiological development, motor activity, and cognitive functions were studied in rats subjected to acute normobaric hypoxic hypoxia (3 h at an O2 concentration of 7%) at different stages of embryogenesis (days E14 or E18). Prenatal hypoxia was found to lead to delays in physiological development and the establishment of motor behavior during the first month of postnatal ontogenesis. These changes were more marked in rats subjected to hypoxia on day 14 of intrauterine development and disappeared with age. In adult rats, regardless of the timing of exposure to hypoxia (E14 or E18), learning ability was degraded and long-term and short-term memory were impaired. These results suggest that exposure to the pathogenic factor during the main period of neuroblast generation and migration (E14) was significant both for physiological development and the establishment of motor behavior in the animals and for the execution of the cognitive functions of the brain, while exposure during the period at which maturation and differentiation processes dominate in the brain (E18) was more significant in relation to the execution of cognitive functions.

Lactic acidosis stimulates ganglioside and ceramide generation without sphingomyelin hydrolysis in rat cortical astrocytes

Acidosis is a ubiquitous feature of cerebral ischemia, and triggers a cascade of biochemical events that results in neuronal injury. The purpose of this study was to evaluate the effects of lactic acidosis on the ganglioside composition, the ceramide and sphingomyelin (SM) levels in rat cortical astrocytes. Primary astrocyte cultures were exposed to lactic acid (pH 5.5) for 2, 5 and 17 h, and cell death was evaluated at each time point. Gangliosides, ceramides and SM were analyzed by high-performance thin layer chromatography. Lactic acidosis caused a progressive increase of both GM3 and GD3 gangliosides up to 5 h of treatment. However, at 17 h of acidosis, GM3 tented to return to the normal level whereas GD3 accumulated. Additionally, ceramides were gradually generated, whereas no significant decrease of SM occured for 17 h of acidosis. These results suggest that ceramides were not produced by the breakdown of SM and may be served as metabolic precursor for the biosynthesis of GM3 and GD3. Since these lipids are important messengers of the adaptative responses to stress, accumulation of sphingolipids triggered by lactic acid exposure of astrocytes might play an important role in determining the outcomes of injurious processes.

Neonatal hypoxia-ischemia reduces ganglioside, phospholipid and cholesterol contents in the rat hippocampus

Hypoxia-ischemia is a common cause of neonatal brain damage producing serious impact on cerebral maturation. This report demonstrates that rats submitted to hypoxia-ischemia present a marked decrease in hippocampal gangliosides, phospholipids and cholesterol contents as from 7 days after the injury. Although chromatographic profiles of the different ganglioside species (GM1, GD1a, GD1b, and GT1b) from the hippocampus of hypoxic-ischemic hippocampi groups (HI) were apparently unaffected, as compared with controls, there were quantitative absolute reductions in HI. The phospholipid patterns were altered in HI as from the 14th to the 30th day after the injury, where phosphatidylcholine (PC) quantities were higher than phosphatidylethanolamine (PE); additionally, the cardiolipin band was detected only in hippocampi of control adult rats. In general, the absolute quantities of phospholipids were lower in HI than in correspondent controls since 7th day after the injury. Considering that reported effects were maintained, we suggest they express a late biochemical response triggered by the neonatal hypoxic-ischemic episode; the consequences would be cell death and a delay on brain development, expressed by a reduction on synaptogenesis and myelinogenesis processes.

Ganglioside alterations in the central nervous system of rats chronically injected with methylmalonic and propionic acids

Neurological dysfunction and structural cerebral abnormalities are commonly found in patients with methylmalonic and propionic acidemia. However, the mechanisms underlying the neuropathology of these disorders are poorly understood. We have previously demonstrated that methylmalonic and propionic acids induce a significant reduction of ganglioside N-acetylneuraminic acid in the brain of rats subjected to chronic administration of these metabolites. In the present study, we investigated the in vivo effects of chronic administration of methylmalonic (MMA) and propionic (PA) acids (from the 6th to the 28th day of life) on the distribution and composition of gangliosides in the cerebellum and cerebral cortex of rats. Control rats were treated with the same volumes of saline. It was first verified that MMA and PA treatment did not modify body, cerebellum, or cortical weight, nor the ganglioside concentration in the cerebral cortex of the animals. In contrast, a significant reduction in total ganglioside content in the cerebellum of approximately 20-30% and 50% of control levels occurred in rats injected with MMA and PA, respectively. Moreover, chronic MMA and PA administration did not interfere with the ganglioside pattern in the cerebral cortex, whereas the distribution of individual gangliosides was altered in the cerebellum of MMA- and PA-treated animals. Rats injected with MMA demonstrated a marked decrease in GM1 and GD3, whereas chronic PA treatment provoked a significant reduction of all ganglioside species, with the exception of an increase in GM2. Since gangliosides are closely related to the dendritic surface and other neural membranes, indirectly reflecting synaptogenesis, these ganglioside abnormalities may be associated with the brain damage found in methylmalonic and propionic acidemias.

Effects of neonatal hypoxia/ischemia on ganglioside expression in the rat hippocampus

Neonatal Hypoxia-Ischemia (HI) triggers a cascade of biochemical events that result in neuronal injury, but the mechanisms underlying these processes are not completely understood, and information regarding the effect of HI on the synthesis of brain glycoconjugates is lacking. The present work evaluates the effects of neonatal HI on hippocampal ganglioside synthesis. Seven-day-old rat pups were exposed to HI for 2.5 h according to the modified Levine model and samples from hyppocampus were obtained at 30 min as well as at 1, 2 and 4 days later. The activity for synthesis of gangliosides was evaluated by determining the incorporation of N-acetyl [3H]neuraminc acid ([3H]NeuAc) into the endogenous gangliosides of Golgi membranes and by determining the activity of Sial-T2 (GD3 synthase) and GalNAc-T (GM2 synthase), the two enzymes acting on sialyllactosylceramide (GM3) at the branching point of synthesis of a- and b-ganglioside pathway. Northern blot experiments were also conducted to determine transcription levels of the mRNAs specific for these transferases. Neonatal HI caused a relative increase of in vitro [3H]NeuAc incorporation into endogenous lactosylceramide, which was most noticeable at 30 min and I day post-event and disappeared by day 2 and 4. The transient accumulation of [3H]GM3 correlated with decreases in the activities of GD3- and GM2 synthase measured at 30 min and at 1 day after the HI insult. No significant variations in the expression of the genes for these enzymes were observed. Results suggest that transient accumulation of GM3 may be due to post-translational events negatively modulating both GD3- and GM2 synthase activities.

Alterations in the ganglioside composition of rat cortical brain slices during experimental lactic acidosis: implications of an enzymatic process independent of the oxidative stress

Several in vitro studies have shown that lactic acidosis plays a role in brain damage by enhancing free radical formation and lipid peroxidation. The purpose of this study was to determine whether gangliosides are affected by lactic acid-induced oxidation in rat brain tissues. Cortical brain slices were incubated at 37 degrees C for 5 or 17 h in Krebs-Ringer buffer containing 20 mM lactic acid (final pH 5.5) previously equilibrated with 100% O2. Damage from lipid peroxidation was estimated by measurement of thiobarbituric acid-reactive substances (TBARS) and analysis of polyunsaturated fatty acids (PUFAs). Gangliosides were studied by high-performance thin-layer chromatography. Incubation with lactic acid induced overproduction of TBARS, whereas PUFAs were only slightly degraded, even after 17 h of incubation. However, the major modifications in the ganglioside profile occurred after 17 h of incubation. Gangliosides GD1a and GT1b decreased in conjunction with a substantial increase in the GM1 percentage. The addition of butylated-hydroxytoluene and desferrioxamine in the incubation medium, or incubation under 100% nitrogen, abolished TBARS production but not the ganglioside modifications, indicating that the change in ganglioside distribution was not related to oxidative stress induced by lactic acid. To investigate the possibility of an enzymatic process activated by the pH shift, slices were incubated with lactic acid in presence of 2,3-dehydro-2-deoxy-N-acetylneuraminic acid, a specific inhibitor of sialidase. In these conditions, no change in gangliosides profile occurred. These results demonstrate that sialidase is responsible for the alterations in the gangliosides composition of rat cortical brain slices during lactic acidosis.