Differential Sphingolipid and Phospholipid Profiles in Alcohol and Nicotine‐Derived Nitrosamine Ketone‐Associated White Matter Degeneration

Abstract

Background Alcohol-mediated neurodegeneration is associated with white matter (WM) atrophy due to targeting of myelin and oligodendrocytes. However, variability in disease severity suggests co-factors contribute to WM degeneration. We examined the potential co-factor role of the tobacco-specific nitrosamine, nicotine-derived nitrosamine ketone (NNK), since smoking causes WM atrophy and most heavy drinkers consume tobacco products. Methods This 8-week study of Long Evans rats had 4 treatment groups: control; NNK-2 mg/kg, 3×/wk in Wks 3–8; ethanol (chronic-26% caloric + binge-2 g/kg, 3×/week in Wks 7–8); and ethanol+NNK. Exposure effects on WM lipid biochemical profiles and in situ distributions were examined using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) and tandem mass spectrometry. Results NNK mainly caused WM fiber degeneration and fiber loss, ethanol caused demyelination, and dual exposures had additive effects. Ethanol and ethanol+NNK decreased WM (including corpus callosum) and/or gray matter (hypothalamus, cortex, medial temporal) levels of several phosphatidylserine (PS), phosphatidylinositol (PI) and sphingolipid (sulfatide; ST) species, while NNK increased or had minimal effect on these lipids. Ethanol+NNK had broader and larger inhibitory effects on phospholipids and sulfatides than ethanol or NNK alone. Principle component analysis clustered control with NNK, and ethanol with ethanol+NNK groups, highlighting the independent ethanol-rather than NNK-driven responses. Conclusion Chronic ethanol exposures decreased several phospholipid and sphingolipid species in brain, while concomitant NNK exposures exacerbated these effects. These findings support our hypothesis that tobacco smoking is a pathogenic co-factor in alcohol-mediated WM degeneration.

Progressive white matter atrophy with altered lipid profiles is partially reversed by short-term abstinence in an experimental model of alcohol-related neurodegeneration

“…The proportions of sphingolipids (25%) and phospholipids (53%) and the spectra of sphingolipids (sulfatides, sphingomyelins, and lactosylceramides) and phospholipids (phosphatidylserines, phosphatidylinositols, phosphatidylethanolamines, plasmalogens, and phosphatidylglycerols) identified in WM are consistent with previous reports in which MALDI-TOF IMS was performed in the negative ionization mode (Nunez et al, 2016; O'Brien & Sampson, 1965; Yalcin et al, 2015). In contrast, other abundant lipids in myelin, including cholesterol, phosphatidylcholine, and sphingomyelin, which form protonated ([M+H] + ), sodiated ([M+Na] + ), or potassiated ([M+K] + ) adducts, were not detected because they are preferentially accessible via positive ionization mode mass spectrometry (Berry et al, 2011; Löhmann, Schachmann, Dandekar, Villmann, & Becker, 2010).…”

“…In contrast, other abundant lipids in myelin, including cholesterol, phosphatidylcholine, and sphingomyelin, which form protonated ([M+H] + ), sodiated ([M+Na] + ), or potassiated ([M+K] + ) adducts, were not detected because they are preferentially accessible via positive ionization mode mass spectrometry (Berry et al, 2011; Löhmann, Schachmann, Dandekar, Villmann, & Becker, 2010). These studies were focused on negative ionization mode MALDI-IMS to better characterize time-course effects of ethanol and abstinence on sulfatide expression, because previous reports suggested that sphingolipids were disproportionately targeted by alcohol exposure as well as other forms of WM degeneration (Roux et al, 2015; Yalcin et al, 2015). …”

“…Detailed methods have been described in previous reports (Yalcin & de la Monte, 2015). In brief, cryo-sections (8-µm thick) were thaw-mounted onto indium tin oxide (ITO)-coated slides (Delta Technologies, Loveland, CO), rinsed with 50-mM ammonium formate buffer (pH 6.4), and sublimed with 5-dehydroxybenzoic acid (DHB; Sigma-Aldrich Co, St. Louis, MO).…”

“…Given these varied and critical functions of myelin lipids, specialized analytical approaches are needed to gain a better understanding of how alcohol compromises WM integrity. Fortunately, recent advances in lipidomics now enable efficient in situ characterization of myelin lipid profiles in relation to disease, including experimental ARBD (Yalcin, Nunez, Tong, & de la Monte, 2015), without the need to generate tissue extracts (Roux et al, 2016, 2015; Wang, Jackson, Post, & Woods, 2008). We hypothesize that progressive ethanol-mediated WM atrophy and degeneration are associated with major alterations in myelin lipid composition, reflecting oligodendrocyte dysfunction, and that abstinence-induced recovery and restoration of WM integrity will at least in part normalize myelin lipid profiles.…”

Function of Thymosin Beta-4 in Ethanol-Induced Microglial Activation

“…Recently, it has become clear that chronic alcohol abuse results in immune activation in the CNS of neonatal to aged animals, and is believed to contribute to neurodegeneration [26][27][28]. In the developing brain, ethanol causes death of Purkinje neurons and cerebellar granule cell neurons of mice in vivo and in vitro [29,30].…”