Chronic voluntary ethanol consumption induces favorable ceramide profiles in selectively bred alcohol-preferring (P) rats

10.1371/journal.pone.0139012PLoS ONE109e013901

Chronic Voluntary Ethanol Consumption Induces Favorable Ceramide Profiles in Selectively Bred Alcohol-Preferring (P) Rats

<div><p>Heavy alcohol consumption has detrimental neurologic effects, inducing widespread neuronal loss in both fetuses and adults. One proposed mechanism of ethanol-induced cell loss with sufficient exposure is an elevation in concentrations of bioactive lipids that mediate apoptosis, including the membrane sphingolipid metabolites ceramide and sphingosine. While these naturally-occurring lipids serve as important modulators of normal neuronal development, elevated levels resulting from various extracellular insults have been implicated in pathological apoptosis of neurons and oligodendrocytes in several neuroinflammatory and neurodegenerative disorders. Prior work has shown that acute administration of ethanol to developing mice increases levels of ceramide in multiple brain regions, hypothesized to be a mediator of fetal alcohol-induced neuronal loss. Elevated ceramide levels have also been implicated in ethanol-mediated neurodegeneration in adult animals and humans. Here, we determined the effect of chronic voluntary ethanol consumption on lipid profiles in brain and peripheral tissues from adult alcohol-preferring (P) rats to further examine alterations in lipid composition as a potential contributor to ethanol-induced cellular damage. P rats were exposed for 13 weeks to a 20% ethanol intermittent-access drinking paradigm (45 ethanol sessions total) or were given access only to water (control). Following the final session, tissues were collected for subsequent chromatographic analysis of lipid content and enzymatic gene expression. Contrary to expectations, ethanol-exposed rats displayed substantial reductions in concentrations of ceramides in forebrain and heart relative to non-exposed controls, and modest but significant decreases in liver cholesterol. qRT-PCR analysis showed a reduction in the expression of sphingolipid delta(4)-desaturase (<i>Degs2</i>), an enzyme involved in <i>de novo</i> ceramide synthesis. These findings indicate that ethanol intake levels achieved by alcohol-preferring P rats as a result of chronic voluntary exposure may have favorable vs. detrimental effects on lipid profiles in this genetic line, consistent with data supporting beneficial cardioprotective and neuroprotective effects of moderate ethanol consumption.</p></div

Mean (±SEM) g/kg ethanol intake (A), ml/kg ethanol and water intake (B), and ethanol preference (ratio of ethanol consumed to total fluid intake; C) in selectively bred alcohol-preferring (P) rats across all 15 session blocks of ethanol exposure (45 sessions total) in an intermittent-access 20% ethanol drinking paradigm. Individual session data were averaged in 3-session blocks prior to analysis.

<p>Mean (±SEM) g/kg ethanol intake (A), ml/kg ethanol and water intake (B), and ethanol preference (ratio of ethanol consumed to total fluid intake; C) in selectively bred alcohol-preferring (P) rats across all 15 session blocks of ethanol exposure (45 sessions total) in an intermittent-access 20% ethanol drinking paradigm. Individual session data were averaged in 3-session blocks prior to analysis.</p

Mean (±SEM) Optical Density Values by Lipid and Treatment Condition for Each Tissue Type.

<p>† indicates significant difference (<i>P</i> < 0.05) between ethanol and control within tissue type.</p><p>Mean (±SEM) Optical Density Values by Lipid and Treatment Condition for Each Tissue Type.</p

Levels of ceramides (A) and cholesterol (B) for each tissue type (represented as percent control) in selectively bred alcohol-preferring (P) rats exposed for 13 weeks to a 20% ethanol intermittent access drinking paradigm or given access to water alone (non-exposed control).

<p>Percent control = ((mean optical density value for ethanol/mean optical density value for control) × 100). *Significant difference between ethanol and control within tissue type (<i>P</i><0.05).</p

mRNA levels for genes encoding sphingolipid metabolic enzymes were determined in control and ethanol-exposed (EtOH) forebrain tissues by qRT-PCR.

<p>Expression was normalized to control rats. Error bars represent standard deviation. N = 4, *<i>P</i><0.05, # = not detectable.</p

Metabolite damage and its repair or pre-emption

It is increasingly evident that metabolites suffer various kinds of damage, that such damage happens in all organisms, and that cells have dedicated systems for damage repair and containment. Firstly, chemical biology is demonstrating that diverse metabolites are damaged by side-reactions of ‘promiscuous’ enzymes or by spontaneous chemical reactions, that the products are useless or toxic, and that the unchecked buildup of these products can be devastating. Secondly, genetic and genomic evidence from pro- and eukaryotes is implicating a network of novel, conserved enzymes that repair damaged metabolites or somehow pre-empt damage. Metabolite (i.e. small molecule) repair is analogous to macromolecule (DNA and protein) repair and appears from comparative genomic evidence to be equally widespread. Comparative genomics also implies that metabolite repair could be the function of many conserved protein families lacking known activities. How – and how well – cells deal with metabolite damage impacts fields ranging from medical genetics to metabolic engineering