Differential effects of moderate chronic ethanol consumption on neurobehavior, white matter glial protein expression, and mTOR pathway signaling with adolescent brain maturation.

Background: Adolescent brains are highly vulnerable to heavy alcohol exposure. Increased understanding of how alcohol adversely impacts brain maturation may improve treatment outcomes.Objectives: This study characterizes short-term versus long-term effects of ethanol feeding on behavior, frontal lobe glial proteins, and mTOR signaling.Methods: Adolescent rats (8/group) were fed liquid diets containing 26% or 0% ethanol for 2 or 9 weeks, then subjected to novel object recognition (NOR) and open field (OF) tests. Frontal lobes were used for molecular assays.Results: Significant ethanol effects on OF performance occurred in the 2-week model (p < .0001). Further shifts in OF and NOR performance were unrelated to ethanol exposure in the 9-week models (p < .05 to p < .0001). Ethanol inhibited MAG1 (p < .01) and MBP (p < .0001) after 2 but not 9 weeks. However, both control and ethanol 9-week models had significantly reduced MAG1 (p < .001-0.0001), MBP (p < .0001), PDGFRA (p < .05-0.01), and PLP (p < .001-0.0001) relative to the 2-week models. GFAP was the only glial protein significantly inhibited by ethanol in both 2- (p < .01) and 9-week (p < .05) models. Concerning the mTOR pathway, ethanol reduced IRS-1 (p < .05) and globally inhibited mTOR (p < .01 or p < .001) in the 9- but not the 2-week model.Conclusions: Short-term versus long-term ethanol exposures differentially alter neurobehavioral function, glial protein expression, and signaling through IRS-1 and mTOR, which have known roles in myelination during adolescence. These findings suggest that strategies to prevent chronic alcohol-related brain pathology should consider the increased maturation-related vulnerability of adolescent brains.

Differential Early Mechanistic Frontal Lobe Responses to Choline Chloride and Soy Isoflavones in an Experimental Model of Fetal Alcohol Spectrum Disorder.

Fetal alcohol spectrum disorder (FASD) is the most common preventable cause of neurodevelopmental defects, and white matter is a major target of ethanol neurotoxicity. Therapeutic interventions with choline or dietary soy could potentially supplement public health preventive measures. However, since soy contains abundant choline, it would be important to know if its benefits are mediated by choline or isoflavones. We compared early mechanistic responses to choline and the Daidzein+Genistein (D+G) soy isoflavones in an FASD model using frontal lobe tissue to assess oligodendrocyte function and Akt-mTOR signaling. Long Evans rat pups were binge administered 2 g/Kg of ethanol or saline (control) on postnatal days P3 and P5. P7 frontal lobe slice cultures were treated with vehicle (Veh), Choline chloride (Chol; 75 µM), or D+G (1 µM each) for 72 h without further ethanol exposures. The expression levels of myelin oligodendrocyte proteins and stress-related molecules were measured by duplex enzyme-linked immunosorbent assays (ELISAs), and mTOR signaling proteins and phosphoproteins were assessed using 11-plex magnetic bead-based ELISAs. Ethanol's main short-term effects in Veh-treated cultures were to increase GFAP and relative PTEN phosphorylation and reduce Akt phosphorylation. Chol and D+G significantly modulated the expression of oligodendrocyte myelin proteins and mediators of insulin/IGF-1-Akt-mTOR signaling in both control and ethanol-exposed cultures. In general, the responses were more robust with D+G; the main exception was that RPS6 phosphorylation was significantly increased by Chol and not D+G. The findings suggest that dietary soy, with the benefits of providing complete nutrition together with Choline, could be used to help optimize neurodevelopment in humans at risk for FASD.

Rapid Alterations in Cerebral White Matter Lipid Profiles After Ischemic-Reperfusion Brain Injury in Fetal Sheep as Demonstrated by MALDI-Mass Spectrometry.

BACKGROUND: Perinatal ischemia-reperfusion (I/R) injury of cerebral white matter causes long-term cognitive and motor disabilities in children. I/R damages or kills highly metabolic immature oligodendroglia via oxidative stress, excitotoxicity, inflammation, and mitochondrial dysfunction, impairing their capacity to generate and maintain mature myelin. However, the consequences of I/R on myelin lipid composition have not been characterized. OBJECTIVE: This study utilized matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to assess alterations in cerebral supraventricular white matter myelin lipid profiles in a fetal sheep model of perinatal I/R. METHODS: Fetal sheep (127 days gestation) were studied after 30 minutes of bilateral carotid artery occlusion followed by 4 (n = 5), 24 (n = 7), 48 (n = 3), or 72 (n = 5) hours of reperfusion, or sham treatment (n = 5). White matter lipids were analyzed by negative ion mode MALDI-MS. RESULTS: Striking I/R-associated shifts in phospholipid and sphingolipid expression occurred over the 72-hour time course with most responses detected within 4 hours of reperfusion and progressing at the 48- and 72-hour points. I/R decreased expression of phosphatidic acid and phosphatidylethanol amine and increased phosphatidylinositol, sulfatide, and lactosylceramide. CONCLUSIONS: Cerebral I/R in mid-gestation fetal sheep causes rapid shifts in white matter myelin lipid composition that may reflect injury, proliferation, or recovery of immature oligodendroglia.

The Full Spectrum of Alzheimer's Disease Is Rooted in Metabolic Derangements That Drive Type 3 Diabetes.

The standard practice in neuropathology is to diagnose Alzheimer's disease (AD) based on the distribution and abundance of neurofibrillary tangles and Aß deposits. However, other significant abnormalities including neuroinflammation, gliosis, white matter degeneration, non-Aß microvascular disease, and insulin-related metabolic dysfunction require further study to understand how they could be targeted to more effectively remediate AD. This review addresses non-Aß and non-pTau AD-associated pathologies, highlighting their major features, roles in neurodegeneration, and etiopathic links to deficits in brain insulin and insulin-like growth factor signaling and cognitive impairment. The discussion delineates why AD with its most characteristic clinical and pathological phenotypic profiles should be regarded as a brain form of diabetes, i.e., type 3 diabetes, and entertains the hypothesis that type 3 diabetes is just one of the categories of insulin resistance diseases that can occur independently or overlap with one or more of the others, including type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease.

Neuroinflammation-Related Encephalopathy in an Infant Born Preterm Following Exposure to Maternal Diabetic Ketoacidosis.

A pregnant woman with new-onset type 1 diabetes and ketoacidosis delivered an infant at 28 weeks of gestation who died with multiple organ failure and severe cerebral vasculopathy with extensive hemorrhage, diffuse microgliosis, and edema. This illustrates that antenatal metabolic and inflammatory stressors may be associated with neonatal encephalopathy and cerebral hemorrhage.

Nonalcoholic Fatty Liver Disease and Diabetes Are Associated with Decreased CYP3A4 Protein Expression and Activity in Human Liver.

Nonalcoholic fatty liver disease (NAFLD) is a major cause of chronic liver disease in the Western population. We investigated the association of nonalcoholic fatty liver disease (NAFLD) and diabetes mellitus on CYP3A4 activity in human liver tissue from brain dead donors ( n = 74). Histopathologically graded livers were grouped into normal ( n = 24), nonalcoholic fatty liver (NAFL, n = 26), and nonalcoholic steatohepatitis (NASH, n = 24) categories. The rate of conversion of midazolam to its 1-hydroxy metabolite was used to assess in vitro CYP3A4 activity in human liver microsomes (HLM). A proteomics approach was utilized to quantify the protein expression of CYP3A4 and related enzymes. Moreover, a physiologically based pharmacokinetic (PBPK) model was developed to allow prediction of midazolam concentration in NAFL and NASH livers. CYP3A4 activity in NAFL and NASH was 1.9- and 3.1-fold ( p < 0.05) lower than normal donors, respectively. Intrinsic clearance (CLint) was 2.7- ( p < 0.05) and 4.1-fold ( p < 0.01) lower in donors with NAFL and NASH, respectively. CYP3A4 protein expression was significantly lower in NAFL and NASH donors ( p < 0.05) and accounted for significant midazolam hydroxylation variability in a multiple linear regression analysis (ß = 0.869, r2 = 0.762, P < 0.01). Diabetes was also associated with decreased CYP3A4 activity and protein expression. Both midazolam CLint and CYP3A4 protein abundance decreased significantly with increase in hepatic fat accumulation. Age and gender did not exhibit any significant association with the observed alterations. Predicted midazolam exposure was 1.7- and 2.3-fold higher for NAFL and NASH, respectively, which may result in a longer period of sedation in these disease-states. Data suggests that NAFLD and diabetes are associated with the decreased hepatic CYP3A4 activity. Thus, further evaluation of clinical consequences of these findings on the efficacy and safety of CYP3A4 substrates is warranted.

Altered temporal lobe white matter lipid ion profiles in an experimental model of sporadic Alzheimer's disease.

BACKGROUND: White matter is an early and important yet under-evaluated target of Alzheimer's disease (AD). Metabolic impairments due to insulin and insulin-like growth factor resistance contribute to white matter degeneration because corresponding signal transduction pathways maintain oligodendrocyte function and survival. METHODS: This study utilized a model of sporadic AD in which adult Long Evans rats administered intracerebral streptozotocin (i.c. STZ) developed AD-type neurodegeneration. Temporal lobe white matter lipid ion profiles were characterized by matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS). RESULTS: Although the lipid ion species expressed in the i.c. STZ and control groups were virtually identical, i.c. STZ mainly altered the abundances of various lipid ions. Correspondingly, the i.c. STZ group was distinguished from control by principal component analysis and data bar plots. i.c. STZ mainly reduced expression of lipid ions with low m/z's (less than 810) as well as the upper range m/z lipids (m/z 964-986), and increased expression of lipid ions with m/z's between 888 and 937. Phospholipids were mainly included among the clusters inhibited by i.c. STZ, while both sulfatides and phospholipids were increased by i.c. STZ. However, Chi-Square analysis demonstrated significant i.c. STZ-induced trend reductions in phospholipids and increases in sulfatides (P<0.00001). CONCLUSIONS: The i.c. STZ model of sporadic AD is associated with broad and sustained abnormalities in temporal lobe white matter lipids. The findings suggest that the i.c. STZ model could be used for pre-clinical studies to assess therapeutic measures for their ability to restore white matter integrity in AD.

Serum Insulin Levels Are Reduced by Intravenous Ghrelin Administration but Do Not Correlate with Alcohol Craving in Alcohol-Dependent Individuals.

BACKGROUND: Increasing evidence supports a role for appetite-regulating pathways like ghrelin, insulin, and leptin in alcoholism. We previously reported that intravenous (i.v.) exogenous ghrelin increases alcohol craving. We also reported i.v. ghrelin reduces endogenous serum leptin, whose levels, in turn, negatively correlated with alcohol craving. Exogenous ghrelin administration decreases insulin secretion both in vitro and in vivo experiments. This study tested the hypothesis that i.v. ghrelin may also decrease endogenous serum insulin levels in alcoholic individuals. Additionally, we explored possible correlations between serum insulin and alcohol craving, since a correlation between insulin and alcohol craving was previously reported. METHODS: This was a double-blind, placebo-controlled human laboratory study ( n =43). Non-treatment-seeking, alcohol-dependent, heavy drinkers were randomized to receive i.v. ghrelin or placebo, followed by an alcohol cue-reactivity procedure. RESULTS: There was a main effect for i.v. ghrelin, compared to placebo in reducing serum insulin ( P <.05). There was also a time effect ( P <.001) but not ghrelin x time interaction ( P >.05). We did not find a correlation between the reduction of serum insulin and alcohol craving ( P >.05). The change in serum insulin was consistent with a parallel reduction in serum connective-peptide in the ghrelin group compared with placebo, although this difference did not reach statistical significance ( P =.076). No similar effects were found for other glucose-regulating hormones analyzed i.e. glucagon, glucagon-like peptide-1, and gastric inhibitory peptide ( P s>.05). CONCLUSIONS: These findings indicate i.v. ghrelin administration has an effect on reducing serum insulin in alcohol-dependent individuals; however, the reduction of insulin did not correlate with changes in alcohol cue-elicited craving. We speculate that, unlike for leptin, the interactions between ghrelin and insulin relationship are limited at the peripheral level. However, mechanistic studies are needed to investigate this hypothesis.

Restoration of Wnt/ß-catenin signaling attenuates alcoholic liver disease progression in a rat model.

BACKGROUND & AIMS: Alcoholic liver disease (ALD) is characterized by the development of fatty liver, alcoholic hepatitis, fibrosis and cirrhosis. However, the underlying mechanism(s) associated with progression remains elusive. Pro-inflammatory cytokines have been implicated in ALD progression due to pro-apoptotic effects on hepatocytes. Wnt/ß-catenin signaling recently has been shown to promote inflammation and apoptosis, suggesting that activation of this signaling pathway may modulate ALD progression. The current study was designed to test whether pharmacological activation of Wnt/ß-catenin signaling altered ALD development and progression in a rat model. METHODS: Adult male Long Evans rats were fed with isocaloric liquid diets containing 0% or 37% ethanol for 8 weeks, and also treated with Wnt agonist during the last 3 weeks of the feeding regimen. Liver and blood samples were subjected to histology, TUNEL assay, immunoblot analysis, real-time quantitative PCR, and alanine transaminase (ALT) assay. RESULTS: Wnt/ß-catenin signaling was negatively correlated with Foxo3A expression and reduced steatosis, cellular injury and apoptosis in ALD rats. Mutation experiments demonstrated that Foxo3A was critical for modulating these effects. Activation of Wnt/ß-catenin signaling suppressed Foxo3A-induced apoptosis through upregulation of serum/glucocorticoid regulated kinase 1 (SGK1). Moreover, pharmacological restoration of Wnt/ß-catenin signaling reduced ALD progression in vivo. CONCLUSIONS: Wnt/ß-catenin signaling plays a protective role in ALD progression via antagonizing Foxo3A-induced apoptosis, and activation of the Wnt/ß-catenin signaling cascade attenuates ALD progression.

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

BACKGROUND: Alcohol-mediated neurodegeneration is associated with white matter (WM) atrophy due to targeting of myelin and oligodendrocytes. However, variability in disease severity suggests cofactors contribute to WM degeneration. We examined the potential cofactor role of the tobacco-specific nitrosamine, nicotine-derived nitrosamine ketone (NNK), because 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 weeks 3 to 8; ethanol (EtOH) (chronic-26% caloric + binge-2 g/kg, 3×/wk in weeks 7 to 8); and EtOH + NNK. Exposure effects on WM lipid biochemical profiles and in situ distributions were examined using matrix-assisted laser desorption/ionization imaging mass spectrometry and tandem mass spectrometry. RESULTS: NNK mainly caused WM fiber degeneration and fiber loss, EtOH caused demyelination, and dual exposures had additive effects. EtOH and EtOH + NNK decreased WM (including corpus callosum) and/or gray matter (hypothalamus, cortex, medial temporal) levels of several phosphatidylserine, phosphatidylinositol, and sphingolipid (sulfatide [ST]) species, while NNK increased or had minimal effect on these lipids. EtOH + NNK had broader and larger inhibitory effects on phospholipids and ST than EtOH or NNK alone. Principal component analysis clustered control with NNK, and EtOH with EtOH + NNK groups, highlighting the independent EtOH- rather than NNK-driven responses. CONCLUSIONS: Chronic EtOH 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 cofactor in alcohol-mediated WM degeneration.

Chronic Ethanol-Induced Impairment of Wnt/ß-Catenin Signaling is Attenuated by PPAR-δ Agonist.

BACKGROUND: The Wnt/ß-catenin pathway regulates liver growth, repair, and regeneration. Chronic ethanol (EtOH) exposure blunts normal liver regenerative responses, in part by inhibiting insulin/IGF signaling, and correspondingly, previous studies showed that EtOH-impaired liver regeneration could be restored by insulin sensitizer (proliferator-activated receptor [PPAR]-δ agonist) treatment. As Wnt/ß-catenin functions overlap and cross talk with insulin/IGF pathways, we investigated the effects of EtOH exposure and PPAR-δ agonist treatment on Wnt pathway gene expression in relation to liver regeneration. METHODS: Adult male Long Evans rats were fed with isocaloric liquid diets containing 0 or 37% EtOH for 8 weeks and also treated with vehicle or a PPAR-δ agonist during the last 3 weeks of the feeding regimen. The rats were then subjected to 70% partial hepatectomy (PH) and livers harvested at various post-PH time points were used to quantitate expression of 19 Wnt pathway genes using Quantigene 2.0 Multiplex Assay. RESULTS: EtOH broadly inhibited expression of Wnt/ß-catenin signaling-related genes, including down-regulation of Wnt1, Fzd3, Lef1, and Bcl9 throughout the post-PH time course (0 to 72 hours), and suppression of Wnt7a, Ccnd1, Fgf4, Wif1, Sfrp2, and Sfrp5 at 18- and 24-hour post-PH time points. PPAR-δ agonist treatments rescued the EtOH-induced suppression of Wnt1, Wnt7a, Fzd3, Lef1, Bcl9, Ccnd1, and Sfrp2 gene expression in liver, corresponding with the improvements in DNA synthesis and restoration of hepatic architecture. CONCLUSIONS: Chronic high-dose EtOH exposures inhibit Wnt signaling, which likely contributes to the impairments in liver regeneration. Therapeutic effects of PPAR-δ agonists extend beyond restoration of insulin/IGF signaling mechanisms and are mediated in part by enhancement of Wnt pathway signaling. Future studies will determine the degree to which targeted restoration of Wnt signaling is sufficient to improve liver regeneration and remodeling in the context of chronic EtOH exposure.

Differential Contributions of Alcohol and the Nicotine-Derived Nitrosamine Ketone (NNK) to Insulin and Insulin-Like Growth Factor Resistance in the Adolescent Rat Brain.

AIMS: Since epidemiologic studies suggest that tobacco smoke toxins, e.g. the nicotine-derived nitrosamine ketone (NNK) tobacco-specific nitrosamine, can be a co-factor in alcohol-related brain disease (ARBD), we examined the independent and additive effects of alcohol and NNK exposures on spatial learning/memory, and brain insulin/IGF signaling, neuronal function and oxidative stress. METHODS: Adolescent Long Evans rats were fed liquid diets containing 0 or 26% caloric ethanol for 8 weeks. During weeks 3-8, rats were treated with i.p. NNK (2 mg/kg, 3×/week) or saline. In weeks 7-8, ethanol groups were binge-administered ethanol (2 g/kg; 3×/week). In week 8, at 12 weeks of age, rats were subjected to Morris Water Maze tests. Temporal lobes were used to assess molecular indices of insulin/IGF resistance, oxidative stress and neuronal function. RESULTS: Ethanol and NNK impaired spatial learning, and NNK ± ethanol impaired memory. Linear trend analysis demonstrated worsening performance from control to ethanol, to NNK, and then ethanol + NNK. Ethanol ± NNK, caused brain atrophy, inhibited insulin signaling through the insulin receptor and Akt, activated GSK-3ß, increased protein carbonyl and 3-nitrotyrosine, and reduced acetylcholinesterase. NNK increased NTyr. Ethanol + NNK had synergistic stimulatory effects on 8-iso-PGF-2α, inhibitory effects on p-p70S6K, tau and p-tau and trend effects on insulin-like growth factor type 1 (IGF-1) receptor expression and phosphorylation. CONCLUSIONS: Ethanol, NNK and combined ethanol + NNK exposures that begin in adolescence impair spatial learning and memory in young adults. The ethanol and/or NNK exposures differentially impair insulin/IGF signaling through neuronal growth, survival and plasticity pathways, increase cellular injury and oxidative stress and reduce expression of critical proteins needed for neuronal function.

Differential Contributions of Alcohol and Nicotine-Derived Nitrosamine Ketone (NNK) to White Matter Pathology in the Adolescent Rat Brain.

AIM: Epidemiologic studies have demonstrated high rates of smoking among alcoholics, and neuroimaging studies have detected white matter atrophy and degeneration in both smokers and individuals with alcohol-related brain disease (ARBD). These findings suggest that tobacco smoke exposure may be a co-factor in ARBD. The present study examines the differential and additive effects of tobacco-specific nitrosamine (NNK) and ethanol exposures on the structural and functional integrity of white matter in an experimental model. METHODS: Adolescent Long Evans rats were fed liquid diets containing 0 or 26% ethanol for 8 weeks. In weeks 3-8, rats were treated with nicotine-derived nitrosamine ketone (NNK) (2 mg/kg, 3×/week) or saline by i.p. injection. In weeks 7-8, the ethanol group was binge-administered ethanol (2 g/kg; 3×/week). RESULTS: Ethanol, NNK and ethanol + NNK caused striking degenerative abnormalities in white matter myelin and axons, with accompanying reductions in myelin-associated glycoprotein expression. Quantitative RT-PCR targeted array and heatmap analyses demonstrated that ethanol modestly increased, whereas ethanol + NNK sharply increased expression of immature and mature oligodendroglial genes, and that NNK increased immature but inhibited mature oligodendroglial genes. In addition, NNK modulated expression of neuroglial genes in favor of growth cone collapse and synaptic disconnection. Ethanol- and NNK-associated increases in FOXO1, FOXO4 and NKX2-2 transcription factor gene expression could reflect compensatory responses to brain insulin resistance in this model. CONCLUSION: Alcohol and tobacco exposures promote ARBD by impairing myelin synthesis, maturation and integrity via distinct but overlapping mechanisms. Public health measures to reduce ARBD should target both alcohol and tobacco abuses.

Potential contributions of the tobacco nicotine-derived nitrosamine ketone (NNK) in the pathogenesis of steatohepatitis in a chronic plus binge rat model of alcoholic liver disease.

AIMS: Alcoholic liver disease (ALD) is linked to binge drinking and cigarette smoking. Heavy chronic ± binge alcohol, or low-level exposures to dietary nitrosamines cause steatohepatitis with insulin resistance and oxidative stress in animal models. This study examines hepatotoxic effects of sub-mutagenic exposures to tobacco-specific nitrosamine (NNK) in relation to ALD. METHODS: Long Evans rats were fed liquid diets containing 0 or 26% (caloric) ethanol (EtOH) for 8 weeks. In Weeks 3 through 8, rats were treated with NNK (2 mg/kg) or saline by i.p. injection, 3×/week, and in Weeks 7 and 8, EtOH-fed rats were binge-administered 2 g/kg EtOH 3×/week; controls were given saline. RESULTS: EtOH ± NNK caused steatohepatitis with necrosis, disruption of the hepatic cord architecture, ballooning degeneration, early fibrosis, mitochondrial cytopathy and ER disruption. Severity of lesions was highest in the EtOH+NNK group. EtOH and NNK inhibited insulin/IGF signaling through Akt and activated pro-inflammatory cytokines, while EtOH promoted lipid peroxidation, and NNK increased apoptosis. O(6)-methyl-Guanine adducts were only detected in NNK-exposed livers. CONCLUSION: Both alcohol and NNK exposures contribute to ALD pathogenesis, including insulin/IGF resistance and inflammation. The differential effects of EtOH and NNK on adduct formation are critical to ALD progression among alcoholics who smoke.

Therapeutic reversal of chronic alcohol-related steatohepatitis with the ceramide inhibitor myriocin.

Alcohol-related liver disease (ALD) is associated with steatohepatitis and insulin resistance. Insulin resistance impairs growth and disrupts lipid metabolism in hepatocytes. Dysregulated lipid metabolism promotes ceramide accumulation and oxidative stress, leading to lipotoxic states that activate endoplasmic reticulum (ER) stress pathways and worsen inflammation and insulin resistance. In a rat model of chronic alcohol feeding, we characterized the effects of a ceramide inhibitor, myriocin, on the histopathological and ultrastructural features of steatohepatitis, and the biochemical and molecular indices of hepatic steatosis, insulin resistance and ER stress. Myriocin reduced the severity of alcohol-related steatohepatitis including the abundance and sizes of lipid droplets and mitochondria, inflammation and architectural disruption of the ER. In addition, myriocin-mediated reductions in hepatic lipid and ceramide levels were associated with constitutive enhancement of insulin signalling through the insulin receptor and IRS-2, reduced hepatic oxidative stress and modulation of ER stress signalling mechanisms. In conclusion, ceramide accumulation in liver mediates tissue injury, insulin resistance and lipotoxicity in ALD. Reducing hepatic ceramide levels can help restore the structural and functional integrity of the liver in chronic ALD due to amelioration of insulin resistance and ER stress. However, additional measures are needed to protect the liver from alcohol-induced necroinflammatory responses vis-à-vis continued alcohol abuse.

Human alcohol-related neuropathology.

Alcohol-related diseases of the nervous system are caused by excessive exposures to alcohol, with or without co-existing nutritional or vitamin deficiencies. Toxic and metabolic effects of alcohol (ethanol) vary with brain region, age/developmental stage, dose, and duration of exposures. In the mature brain, heavy chronic or binge alcohol exposures can cause severe debilitating diseases of the central and peripheral nervous systems, and skeletal muscle. Most commonly, long-standing heavy alcohol abuse leads to disproportionate loss of cerebral white matter and impairments in executive function. The cerebellum (especially the vermis), cortical-limbic circuits, skeletal muscle, and peripheral nerves are also important targets of chronic alcohol-related metabolic injury and degeneration. Although all cell types within the nervous system are vulnerable to the toxic, metabolic, and degenerative effects of alcohol, astrocytes, oligodendrocytes, and synaptic terminals are major targets, accounting for the white matter atrophy, neural inflammation and toxicity, and impairments in synaptogenesis. Besides chronic degenerative neuropathology, alcoholics are predisposed to develop severe potentially life-threatening acute or subacute symmetrical hemorrhagic injury in the diencephalon and brainstem due to thiamine deficiency, which exerts toxic/metabolic effects on glia, myelin, and the microvasculature. Alcohol also has devastating neurotoxic and teratogenic effects on the developing brain in association with fetal alcohol spectrum disorder/fetal alcohol syndrome. Alcohol impairs function of neurons and glia, disrupting a broad array of functions including neuronal survival, cell migration, and glial cell (astrocytes and oligodendrocytes) differentiation. Further progress is needed to better understand the pathophysiology of this exposure-related constellation of nervous system diseases and better correlate the underlying pathology with in vivo imaging and biochemical lesions.

Conquering Insulin Network Dysfunctions in Alzheimer's Disease: Where Are We Today?

Functional impairments in the brain's insulin and insulin-like growth factor (IGF) signal transduction networks are recognized mediators of dysregulated energy metabolism, a major driver of the Alzheimer's disease (AD) neurodegeneration cascade. AD-associated insulin-deficient and insulin-resistant states mimic those of diabetes mellitus and affect all cell types in the brain. Besides accounting for abundant amyloid-ß and hyperphosphorylated tau lesions in AD, insulin/IGF pathway dysfunctions cause cortical atrophy, loss of synaptic plasticity, white matter myelin/oligodendrocyte degeneration, astrocyte and microglial neuroinflammation and oxidative stress, deficits in energy metabolism, mitochondrial dysfunction, and microvascular disease. These same neuropathological processes have been linked to cognitive impairment in type 2 diabetes mellitus, Parkinson's disease, and vascular dementia. Strategies to address metabolic mediators of cognitive impairment have been borrowed from diabetes and other insulin-resistant diseases and leveraged on preclinical AD model data. The repurposing of diabetes drugs led to clinical trials with intranasal insulin, followed by insulin sensitizers including metformin and peroxisome-proliferator-activated receptor agonists, and then incretin mimetics primarily targeting GLP-1 receptors. In addition, other glucose-lowering agents have been tested for their efficacy in preventing cognitive declines. The strengths and limitations of these approaches are discussed. The main conclusion of this review is that we have now arrived at a stage in which it is time to address long-term deficits in trophic factor availability and receptor responsiveness, signaling abnormalities that extend beyond insulin and include IGFs and interconnected pathways, and the need for multi-pronged rather than single-pronged therapeutic targeting to remediate AD and other forms of neurodegeneration.

Early-Stage Moderate Alcohol Feeding Dysregulates Insulin-Related Metabolic Hormone Expression in the Brain: Potential Links to Neurodegeneration Including Alzheimer's Disease.

Background: Alzheimer's disease (AD), one of the most prevalent causes of dementia, is mainly sporadic in occurrence but driven by aging and other cofactors. Studies suggest that excessive alcohol consumption may increase AD risk. Objective: Our study examined the degree to which short-term moderate ethanol exposure leads to molecular pathological changes of AD-type neurodegeneration. Methods: Long Evans male and female rats were fed for 2 weeks with isocaloric liquid diets containing 24% or 0% caloric ethanol (n = 8/group). The frontal lobes were used to measure immunoreactivity to AD biomarkers, insulin-related endocrine metabolic molecules, and proinflammatory cytokines/chemokines by duplex or multiplex enzyme-linked immunosorbent assays (ELISAs). Results: Ethanol significantly increased frontal lobe levels of phospho-tau, but reduced Aß, ghrelin, glucagon, leptin, PAI, IL-2, and IFN-γ. Conclusions: Short-term effects of chronic ethanol feeding produced neuroendocrine molecular pathologic changes reflective of metabolic dysregulation, together with abnormalities that likely contribute to impairments in neuroplasticity. The findings suggest that chronic alcohol consumption rapidly establishes a platform for impairments in energy metabolism that occur in both the early stages of AD and alcohol-related brain degeneration.

Agent Orange Herbicidal Toxin-Initiation of Alzheimer-Type Neurodegeneration.

Background: Agent Orange (AO) is a Vietnam War-era herbicide that contains a 1 : 1 ratio of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Emerging evidence suggests that AO exposures cause toxic and degenerative pathologies that may increase the risk for Alzheimer's disease (AD). Objective: This study investigates the effects of the two main AO constituents on key molecular and biochemical indices of AD-type neurodegeneration. Methods: Long Evans rat frontal lobe slice cultures treated with 250µg/ml of 2,4-D, 2,4,5-T, or both (D + T) were evaluated for cytotoxicity, oxidative injury, mitochondrial function, and AD biomarker expression. Results: Treatment with the AO constituents caused histopathological changes corresponding to neuronal, white matter, and endothelial cell degeneration, and molecular/biochemical abnormalities indicative of cytotoxic injury, lipid peroxidation, DNA damage, and increased immunoreactivity to activated Caspase 3, glial fibrillary acidic protein, ubiquitin, tau, paired-helical filament phosphorylated tau, AßPP, Aß, and choline acetyltransferase. Nearly all indices of cellular injury and degeneration were more pronounced in the D + T compared with 2,4-D or 2,4,5-T treated cultures. Conclusions: Exposures to AO herbicidal chemicals damage frontal lobe brain tissue with molecular and biochemical abnormalities that mimic pathologies associated with early-stage AD-type neurodegeneration. Additional research is needed to evaluate the long-term effects of AO exposures in relation to aging and progressive neurodegeneration in Vietnam War Veterans.

Dysregulated mTOR networks in experimental sporadic Alzheimer's disease.

Background: Beyond the signature amyloid-beta plaques and neurofibrillary tangles, Alzheimer's disease (AD) has been shown to exhibit dysregulated metabolic signaling through insulin and insulin-like growth factor (IGF) networks that crosstalk with the mechanistic target of rapamycin (mTOR). Its broad impact on brain structure and function suggests that mTOR is likely an important therapeutic target for AD. Objective: This study characterizes temporal lobe (TL) mTOR signaling abnormalities in a rat model of sporadic AD neurodegeneration. Methods: Long Evans rats were given intracerebroventricular injections of streptozotocin (ic-STZ) or saline (control), and 4 weeks later, they were administered neurobehavioral tests followed by terminal harvesting of the TLs for histopathological study and measurement of AD biomarkers, neuroinflammatory/oxidative stress markers, and total and phosphorylated insulin/IGF-1-Akt-mTOR pathway signaling molecules. Results: Rats treated with ic-STZ exhibited significantly impaired performance on Rotarod (RR) and Morris Water Maze (MWM) tests, brain atrophy, TL and hippocampal neuronal and white matter degeneration, and elevated TL pTau, AßPP, Aß, AChE, 4-HNE, and GAPDH and reduced ubiquitin, IL-2, IL-6, and IFN-γ immunoreactivities. In addition, ic-STZ reduced TL pY1135/1136-IGF-1R, Akt, PTEN, pS380-PTEN, pS2448-mTOR, p70S6K, pT412-p70S6K, p/T-pT412-p70S6K, p/T-Rictor, and p/T-Raptor. Conclusion: Experimental ic-STZ-induced sporadic AD-type neurodegeneration with neurobehavioral dysfunctions associated with inhibition of mTOR signaling networks linked to energy metabolism, plasticity, and white matter integrity.