Neuroglial and neuroblastoma cell lines are capable of metabolizing ethanol via an alcohol-dehydrogenase-independent pathway

Effects of Ethanol on Expression of Coding and Noncoding RNAs in Murine Neuroblastoma Neuro2a Cells

Excessive use of alcohol can induce neurobiological and neuropathological alterations in the brain, including the hippocampus and forebrain, through changes in neurotransmitter systems, hormonal systems, and neuroimmune processes. We aimed to investigate the effects of ethanol on the expression of coding and noncoding RNAs in a brain-derived cell line exposed to ethanol. After exposing Neuro2a cells, a neuroblastoma cell line, to ethanol for 24 and 72 h, we observed cell proliferation and analyzed up- and downregulated mRNAs and long noncoding RNAs (lncRNAs) using total RNA-Seq technology. We validated the differential expression of some mRNAs and lncRNAs by RT-qPCR and analyzed the expression of Cebpd and Rnu3a through knock-down of Cebpd. Cell proliferation was significantly reduced in cells exposed to 100 mM ethanol for 72 h, with 1773 transcripts up- or downregulated by greater than three-fold in ethanol-treated cells compared to controls. Of these, 514 were identified as lncRNAs. Differentially expressed mRNAs and lncRNAs were mainly observed in cells exposed to ethanol for 72 h, in which Atm and Cnr1 decreased, but Trib3, Cebpd, and Spdef increased. On the other hand, lncRNAs Kcnq1ot1, Tug1, and Xist were changed by ethanol, and Rnu3a in particular was greatly increased by chronic ethanol treatment through inhibition of Cebpd. Our results increase the understanding of cellular and molecular mechanisms related to coding and noncoding RNAs in an in vitro model of acute and chronic exposure to ethanol.

Single or combined exposure to chlorpyrifos and cypermethrin provoke oxidative stress and downregulation in monoamine oxidase and acetylcholinesterase gene expression of the rat's brain

The extensive uses of organophosphates and pyrethroids have made it necessary to investigate the neurotoxicity of their combination as they may implicate in the neurodegenerative syndromes. Monoamine oxidase-A (MAO-A) and acetylcholinesterase (AChE) gene expression in the rat brain were evaluated after independent and combined intoxications with chlorpyrifos and cypermethrin. Twenty-four mature male rats were equally distributed into four groups. The first one was kept as a control group, whereas the second, third and fourth were orally gavage with chlorpyrifos (16.324 mg/kg), cypermethrin (25.089 mg/kg) and their combination (9.254 mg/kg), respectively, for 4 weeks. As compared to the control group, intoxications with chlorpyrifos and/or cypermethrin revealed significant (P < 0.05) declines in the levels of brain neurotransmitters (dopamine and serotonin) plus the enzymatic activities of MAO-A, AChE and sodium-potassium adenosine triphosphatase. The mRNA genes expression of MAO-A and AChE have also confirmed the enzymatic actions. Moreover, the oxidative injury recorded as the levels of malondialdehyde and nitric oxide markedly increased (P < 0.01), while the total thiol content reduced and the histopathological outcomes have confirmed these impacts. In conclusion, chlorpyrifos and cypermethrin revealed antagonistic inhibitions on the brain MAO-A and AChE gene regulation through neurotransmission deteriorations and oxidative damage, which could describe their contributions in the neuropathological progressions.

Diallyl Sulfide: Potential Use in Novel Therapeutic Interventions in Alcohol, Drugs, and Disease Mediated Cellular Toxicity by Targeting Cytochrome P450 2E1

Diallyl sulfide (DAS) and other organosulfur compounds are chief constituents of garlic. These compounds have many health benefits, as they are very efficient in detoxifying natural agents. Therefore, these compounds may be useful for prevention/treatment of cancers. However, DAS has shown appreciable allergic reactions and toxicity, as they can also affect normal cells. Thus their use as in the prevention and treatment of cancer is limited. DAS is a selective inhibitor of cytochrome P450 2E1 (CYP2E1), which is known to metabolize many xenobiotics including alcohol and analgesic drugs in the liver. CYP2E1-mediated alcohol/drug metabolism produce reactive oxygen species and reactive metabolites, which damage DNA, protein, and lipid membranes, subsequently causing liver damage. Several groups have shown that DAS is not only capable of inhibiting alcohol- and drug-mediated cellular toxicities, but also HIV protein- and diabetes-mediated toxicities by selectively inhibiting CYP2E1 in various cell types. However, due to known DAS toxicities, its use as a treatment modality for alcohol/drug- and HIV/diabetes-mediated toxicity have only limited clinical relevance. Therefore, effort is being made to generate DAS analogs, which are potent and selective inhibitor of CYP2E1 and poor substrate of CYP2E1. This review summarizes current advances in the field of DAS, its anticancer properties, role as a CYP2E1 inhibitor, preventing agent of cellular toxicities from alcohol, analgesic drugs, xenobiotics, as well as, from diseases like HIV and diabetes. Finally, this review also provides insights toward developing novel DAS analogues for chemical intervention of many disease conditions by targeting CYP2E1 enzyme.

Regulation of cytochrome P450 2e1 expression by ethanol: role of oxidative stress-mediated pkc/jnk/sp1 pathway

CYP2E1 metabolizes ethanol leading to production of reactive oxygen species (ROS) and acetaldehyde, which are known to cause not only liver damage but also toxicity to other organs. However, the signaling pathways involved in CYP2E1 regulation by ethanol are not clear, especially in extra-hepatic cells. This study was designed to examine the role of CYP2E1 in ethanol-mediated oxidative stress and cytotoxicity, as well as signaling pathways by which ethanol regulates CYP2E1 in extra-hepatic cells. In this study, we used astrocytic and monocytic cell lines, because they are important cells in central nervous system . Our results showed that 100 mM ethanol significantly induced oxidative stress, apoptosis, and cell death at 24 h in the SVGA astrocytic cell line, which was rescued by a CYP2E1 selective inhibitor, diallyl sulfide (DAS), CYP2E1 siRNA, and antioxidants (vitamins C and E). Further, we showed that DAS and vitamin C abrogated ethanol-mediated (50 mℳ) induction of CYP2E1 at 6 h, as well as production of ROS at 2 h, suggesting the role of oxidative stress in ethanol-mediated induction of CYP2E1. We then investigated the role of the protein kinase C/c-Jun N-terminal kinase/specificity protein1 (PKC/JNK/SP1) pathway in oxidative stress-mediated CYP2E1 induction. Our results showed that staurosporine, a non-specific inhibitor of PKC, as well as specific PKCζ inhibitor and PKCζ siRNA, abolished ethanol-induced CYP2E1 expression. In addition, inhibitors of JNK (SP600125) and SP1 (mithramycin A) completely abrogated induction of CYP2E1 by ethanol in SVGA astrocytes. Subsequently, we showed that CYP2E1 is also responsible for ethanol-mediated oxidative stress and apoptotic cell death in U937 monocytic cell lines. Finally, our results showed that PKC/JNK/SP1 pathway is also involved in regulation of CYP2E1 in U937 cells. This study has clinical implications with respect to alcohol-associated neuroinflammatory toxicity among alcohol users.

Effect of ethanol on the metabolism of primary astrocytes studied by (13)C- and (31)P-NMR spectroscopy

Nuclear magnetic resonance was used as the primary technique to investigate the effect of ethanol (40, 80, and 160 mM) on the levels of high-energy phosphates, glycolytic flux, anaplerotic and oxidative fluxes to the tricarboxylic acid (TCA) cycle, the contribution of the pentose phosphate pathway (PPP), and the uptake and release of amino acids on primary cultures of rat astrocytes. On line (31)P-NMR spectroscopy showed that long-term exposure to ethanol caused a drop in the levels of ATP and phosphocreatine. The ratio between the fluxes through the pyruvate dehydrogenase and pyruvate carboxylase reactions also decreased, whereas the glycolytic flux and the ratio between formation of lactate and glucose consumption increased when cells were exposed to acute doses of ethanol. Flux through the pentose phosphate pathway was not affected. The uptake of cysteine and the release of glutamine were stimulated by ethanol, whereas the release of methionine was inhibited. Moreover, the fractional enrichment in serine was enhanced. The changes in the amino acid metabolism are interpreted as a response to oxidative stress induced by ethanol.

Histological distribution of class III alcohol dehydrogenase in human brain

The distributions of class III alcohol dehydrogenase (ADH), a glutathione-dependent formaldehyde dehydrogenase, and class I ADH in the human brain were examined immunohistochemically. The most intense immunostaining of class III ADH was observed in the dendrites and cytoplasm of cerebellar Purkinje cells. Scattered cerebral cortical neurons in layers IV and V, and some hippocampal pyramidal neurons were also immunopositive. The neuronal distribution of class III ADH resembled that of the vulnerable neurons in patients with hypoxic encephalopathy, which in view of the intense staining in the Purkinje cells, raises the possibility that this enzyme contributes to the hypoxia and cerebellar degeneration suffered by chronic alcoholics. Perivascular and subependymal astrocytes, which contribute to the maintenance of the cerebral cellular milieu and isolate the brain from the systemic circulation and cerebrospinal fluid, were also class III ADH positive. As the substrates of this enzyme include intrinsic toxic formaldehyde, inflammatory intermediate of 20-hydroxy-leukoteiene B4, and possibly ethanol, the distribution of class III ADH immunostaining indicates this enzyme contributes to the defence of the brain against degenerative processes. The finding that, unlike ependymal cells, subependymal astrocytes were class III ADH positive, suggests this enzyme may be useful for differentiating astrocytes and ependymal cells.

Ethanol metabolism by macrophages: possible role in organ damage

Macrophages and hepatocytes oxidize ethanol to acetate in vitro at comparable rates but by different biochemical pathways. Ethanol metabolism by macrophages is largely ADH-independent and mainly based on cytochrome P450 and on the extracellular release of superoxide anion radicals. There is also evidence that during ethanol metabolism, macrophages release more acetaldehyde extracellularly than hepatocytes; the high concentrations of acetaldehyde around macrophages may damage surrounding tissue cells. Some of this acetaldehyde forms unstable cytotoxic complexes with serum albumin and with erythrocytes. The superoxide anion radicals released by macrophages may not only oxidize ethanol to acetaldehyde but also react with and damage cells in their immediate vicinity. After exposure to ethanol, macrophage-depleted rodents show markedly reduced levels of cytotoxic acetaldehyde-albumin complexes in the blood and reduced levels of hydroxyethyl radicals in the bile compared to control animals, indicating that the generation of such potentially pathogenic molecules is, to a large extent, dependent on macrophage activity. Macrophage-depleted animals also show less early liver damage than control animals. The reduction in ethanol-induced liver damage in macrophage-depleted mice and rats may be due to a reduction or elimination of the generation of various Kupffer-cell-derived hepatotoxic substances, including acetaldehyde and reactive oxygen radicals, in such animals. These data suggest that ethanol metabolism by tissue macrophages may play an important role in mediating ethanol-related tissue damage.

Effects of ethanol on glucose transporter expression in cultured hippocampal neurons

Glucose transport was studied in primary hippocampal neuron cultures exposed to ethanol. Immunofluorescent staining with antibodies against neuron-specific enolase and glial fibrillary acidic protein identified approximately 95% of the cultured cells as neurons. Western blot analysis was conducted with polyclonal antisera to glucose transporter isoforms GLUT1 and GLUT3. As previously seen in astrocytes, GLUT1 protein was regulated by the culture medium glucose content. Exposure to 50 and 100 mM of ethanol for 5 hr induced dose-dependent reductions in GLUT1 and GLUT3 protein. In contrast, GLUT1 mRNA abundance was increased relative to controls under the same conditions. Glucose uptake, measured with the nonmetabolized analog, 2-deoxy-D-glucose, was reduced by 50 and 100 mM of ethanol in four experiments. These results indicate a direct effect of ethanol on neuronal glucose transporter expression, which may play a role in the neurotoxic effects of alcohol.

Macrophages are a major source of acetaldehyde in circulating acetaldehyde-albumin complexes formed after exposure of mice to ethanol

C57BL mice were depleted of macrophages by an intravenous injection of liposome-encapsulated dichloromethylene diphosphonate (DCMDP), and control mice were uninjected or injected with empty liposomes. One day after injection, a proportion of the DCMDP-treated and control mice was continuously exposed to ethanol vapor for 4 days. Albumin fractions were separated from the sera of both ethanol-unexposed and ethanol-exposed animals and tested for cytotoxicity against a monolayer of A9 cells using two indicators of cytotoxicity: detachment of adherent cells and a decrease in the ability of cells to reduce tetrazolium. The results show that, in mice exposed to ethanol, macrophages are a major source of the acetaldehyde in circulating cytotoxic acetaldehyde-albumin complexes and presumably also of free acetaldehyde.

Induction of herpes simplex virus type 1 immediate-early gene expression by a cellular activity expressed in Vero and NB41A3 cells after growth arrest-release

Infected cell protein 0 (ICP0), a major immediate-early regulatory protein of herpes simplex virus type 1 (HSV-1), activates expression of all classes of HSV genes as well as a variety of heterologous viral and cellular genes. Previous studies have shown that a cellular activity expressed maximally in Vero cells 8 h after release from growth arrest in the G0/G1 phase of the cell cycle can enhance plaque formation and gene expression of a mutant virus (7134) lacking both copies of the gene encoding ICP0 (W. Cai and P. Schaffer, J. Virol. 65:4078-4090, 1991). This observation suggests that the cellular activity can substitute for ICP0 to activate viral gene expression. To further characterize this cellular activity, Vero and NB41A3 (mouse neuroblastoma) cells were transfected at various times after release from growth arrest with promoter-chloramphenicol acetyltransferase (CAT) constructs containing promoters representing the major kinetic classes of HSV genes, and CAT activity was measured from 2 to 24 h postrelease. The results of these tests demonstrate that CAT expression from immediate-early promoter-CAT plasmids was enhanced 10- and 3-fold when Vero and NB41A3 cells were transfected at 6 and 2 h postrelease, respectively. In contrast, only low levels of immediate-early promoter-driven CAT activity were apparent when cells were transfected at later times postrelease. No significant stimulation of CAT activity was observed from promoter-CAT plasmids containing representative early or late HSV promoters or a heterologous viral (simian virus 40 early) promoter. Differences in the efficiency of uptake of plasmid DNA by cells at various times postrelease did not account for the observed differences in CAT expression. Unlike Vero cells, in which cell division resumed after release from growth arrest, division of NB41A3 cells did not resume. Rather, these cells displayed morphological features suggestive of a differentiated phenotype. Collectively, these findings demonstrate that a cellular activity expressed in Vero and NB41A3 cells after release from growth arrest can activate HSV gene expression by enhancing immediate-early gene expression.

Changes in brain MAO activity and glycogen levels upon chronic alcoholization of three successive generations of rats

Changes in neurobiological parameters were examined from early life (10 days post-natal) until late adulthood (8 months post-natal) in three successive generations of alcoholized rats. The mean daily consumption of alcohol by the 2nd and 3rd generation rats (7.40 +/- 0.22 and 7.70 +/- 0.20 g ethanol/kg body weight, respectively) was significantly greater than that of the 1st generation alcoholized group (4.26 +/- 0.33 g/kg). Brain/body weight ratios of alcoholized rats, 10 days post-natal, were significantly greater than controls, with 1st generation alcoholized rats presenting significantly greater brain/body weight ratios than those of the 2nd or 3rd generation, which tended toward control weights and ratios. This difference between alcoholized rats and controls persisted, although to a lesser extent, at 8 months post-natal. Glycogen content in the brains of rats of all alcoholized generations was significantly lower than in controls at 10 days post-natal, with a reversal of this situation in later life for 2nd and 3rd generation rats, which presented significantly greater cerebral glycogen levels than control or 1st generation alcoholized rats (which had an equivalent cerebral glycogen content). In 10-day-old rat pups, monoamine oxidase (MAO) activity in brain tissues had a tendency (mostly non-significant) to be greater in alcoholized rats than in controls, with a reversal of this situation, ie a statistically significant decrease in MAO activity in the 2nd and 3rd alcoholized generations with respect to controls, in 8-month-old rats. MAO activity in adrenal glands of alcoholized rats was greater than in controls at 10 days post-natal, and this difference persisted at 8 months.

Effect of ethanol on lipoprotein secretion in two human hepatoma cell lines, HepG2 and Hep3B

The two human hepatoma cell lines, HepG2 and Hep3B, have been demonstrated to metabolize ethanol efficiently even in the absence of alcohol dehydrogenase. By using specific metabolic inhibitors, it was found that the microsomal ethanol-oxidizing system (MEOS) plays a significant role in ethanol metabolism in these two cell lines. There is a strong positive correlation between the rates of ethanol metabolism and the total cytochrome P-450 levels in the hepatoma cells. The involvement of the cytochrome P-450 system was further supported by the induction of aniline p-hydroxylase activity after ethanol treatment. However, the 3- to 4-fold elevation in aniline p-hydroxylase activity was not accompanied by an increase in cytochrome P450IIE1 mRNA level. Exposure of HepG2 and Hep3B cells to ethanol resulted in an increase of accumulation of apoA-I (15%-45% over control) in a dose-dependent manner (from 5 to 50 mM) of ethanol over a 24-hr period. All other major apolipoproteins which included apo CII, apo CIII and apoE, with the exception of apoB, were not affected by these treatments. At a concentration of ethanol of 25 mM or greater, accumulation of apoB, VLDL and LDL triglyceride were increased by 20% to 25% over the control level. Elevation of HDL cholesterol (40%-70% over control) was observed when the cells were exposed to an ethanol concentration of > or = 10 mM. Metyrapone, which inhibited the MEOS, was capable of blocking the induction of apoAI caused by ethanol treatment.

Electrophysiological actions of acetate, a metabolite of ethanol, on hippocampal dentate granule neurons: interactions with adenosine

Acetate is the primary breakdown product of ethanol metabolism in the liver and has been found in the brain following ethanol ingestion in rats. Systemically administered acetate has been shown to cause motor impairment, an effect which is blocked by the adenosine receptor blocker, 8-phenyltheophylline (8-PT). The effects of sodium acetate were investigated in this study using intracellular recording techniques in rat hippocampal dentate granule cells, and were compared to the actions of ethanol and adenosine individually and in conjunction with 8-PT. Acetate hyperpolarized the membrane at 0.4-0.8 mM. The amplitude and duration of the postspike train afterhyperpolarization (AHP) were increased by acetate when the cell was repolarized to the control resting membrane potential. Comparable results were seen in voltage clamp. Acetate also decreased spike frequency adaptation. The effects of acetate were mimicked by adenosine (50 microM) and ethanol (20 mM). The ethanol effects occluded those produced by acetate. All of the effects of acetate, adenosine and ethanol could be inhibited with prior perfusion of 8-PT (1-10 microM). These data suggest that the actions of the major metabolite of ethanol, acetate, may be mediated by adenosine receptor activation.

Ethanol metabolism in rat brain homogenates by a catalase-H2O2 system

Homogenates of perfused rat brains incubated in the presence of ethanol (50-100 mM) and glucose (10 mM) were found to oxidize ethanol to acetaldehyde. The addition of glucose oxidase, a known hydrogen peroxide generator, to the incubation medium, significantly (P less than 0.05) increased the generation of acetaldehyde. The presence in the incubation medium of metyrapone, an inhibitor of cytochrome P450, or pyrazole, an alcohol dehydrogenase inhibitor, did not affect the levels of acetaldehyde obtained. Conversely, the presence of 3-amino-1,2,4-triazole, a known catalase inhibitor, induced a concentration-dependent reduction of the amount of acetaldehyde generated after incubation, even in the presence of glucose oxidase. Homogenates of perfused brains of rats treated with 3-amino-1,2,4-triazole or cyanamide (another H2O2-dependent catalase blocker) also showed a dose-dependent reduction of the acetaldehyde obtained. These findings support the notion that a catalase-mediated oxidation of ethanol is present in rat brain homogenates. It is suggested that this local oxidation of ethanol may have important biological implications. The data of both studies increase support for the notion that acetaldehyde is produced directly in the brain and that it may be the agent mediating some of the psychopharmacological properties of ethanol and be one of the factors determining the propensity of an animal to voluntarily consume ethanol.