System biology of alcoholism: Understanding of the consequences of the metabolism in brain cells

Abstract

The addictive drug ethanol represents a serious universal health and social problem. Alcohol abuse and dependency have been increasing in many countries worldwide. Chronic use of alcohol leads to metabolic abnormalities and damage to the brain, which can result in severe cognitive dysfunction and addiction. Areas of the brain such as prefrontal cortex (PFC), the white matter, the hippocampus (HP), the cerebellum and the striatum are particularly vulnerable to the effects of alcohol. The striatum (ST), a region of brain closely associated with addiction mechanisms, is commonly divided into two regions, dorsal (DS) and ventral striatum (VS); the DS comprising caudate nucleus (CN) and putamen (P) while the VS is constituted mainly by nucleus accumbens (NAc). Neuroimaging analysis indicates that microstructural degradation is occurring in alcohol-affected brains and the abnormalities may be correlated with altered locomotor activity, aggressive behavior, changes in reward/aversion-related learning, deficient motor coordination, disturbances in procedural learning and memory. The NAc is strongly implicated in drug addiction but current evidence suggests that DS has also a significant role in this process. One of the aims of the project is to carry out comparative study of the sub-regions of human alcoholic striatum using two omics technologies (proteomics and metabolomics). There were no differences in the levels of dopamine (DA), 3,4-dihydrophenylacetic acid (DOPAC), serotonin (5HT), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (HIAA), histamine, L-glutamate (Glu), -aminobutyric acid (GABA), tyrosine (Tyr) and tryptophan (Tryp) between the DS (CN and P) and VS (NAc) in control brains. Choline (Ch) and acetylcholine (Ach) were higher and, norepinephrine (NE) is lower, in the VS Overall. Alcohol-affected ST had lower levels of neurotransmitters except for Glu (30% higher in the alcoholic ventral striatum). Ratios of DOPAC/DA and HIAA/5HT were higher in alcohol-affected ST indicating an increase in the DA and 5HT turnover. Glutathione was significantly reduced in all three regions of alcohol-affected ST. The pattern of changes of 13 neurometabolites in alcoholic sub-regions relative to their respective control was similar. In order to investigate correlations between the alcohol-related changes in metabolites and and altered protein expressions, the author has selected a single sub-region of ST for a global proteomics study. By analysing CN tissues, 25 unique proteins were found to be differently expressed in alcohol-affected tissue 9 relative to control. From the identified proteins two were dopamine-related proteins and one a GABA-synthesizing enzyme glutamate decarboxylase (GAD) 65. Two proteins that are related to apoptosis and/or neuronal loss (BiD and amyloid-β A4 precursor protein-binding family B member 3) were increased. These results suggest that neurotransmitter metabolism and systems possibly related to neuroprotective mechanisms in both the DS (CN and P) and the VS (NAc) are significantly influenced by long-term heavy alcohol intake associated with alcoholism. Amongst the mechanisms mediating the effects of alcohol oxidative stress may have produce a particularly significant impact and could make a strong contribution to the microstructural damage. It has been known that alcohol can have a particularly damaging effect on the PFC and the HP regions of the fetus/developing/adolescent brain. The change imparted at those stages of development could be irreversible resulting in lasting deficits in a range of personality traits and impacting decision making, memory and learning. The HP is a significant place of neurogenesis and a source of neural stem cell (NSC). These can differentiate into neurons, astrocytes and oligodendrocytes and constitute building blocks of the developing central nervous system. They can also contribute to brain repair at later stages of development and, possibly, even in adulthood. On current evidence, alcohol reduces neurogenesis but little or no tangible information is available on the actual biochemistry and/or the fate of NSC. In the present experiments, the NSC obtained from rat embryos were exposed to various concentrations of ethanol (25 to 100 mM) for up to 96 hours. The cell numbers were found to be reduced in the presence of ethanol but only at the higher concentrations (50 and 100 mM). There were no apparent dramatic changes in the morphology of the cells but the numbers of neuron-like (MAP2-positive) cells were reduced by ethanol in a dose-dependent manner. In proteome analysis of alcoholic cells, a total of 28 proteins were altered in 50 mM ethanol relative to ethanol-free control. Of these proteins some were constituents of cytoskeleton, others were involved in transcription/translation, energy metabolism, signal transduction and oxidative stress. Two of the proteins identified as altered were nucleophosmin (NPM) and dead-end protein homolog 1 (DND1). These were further studied by immunological techniques in cultured neurons and astrocytes. NPM decreased and DND1 increased in both alcohol affected neurons and astrocytes cells

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