Ganglioside GM1 reduces ethanol induced phospholipase A2 activity in synaptosomal preparations from mice

Ganglioside GM1 and the Central Nervous System

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

Lentiviral-mediated knock-down of GD3 synthase protects against MPTP-induced motor deficits and neurodegeneration

Converging evidence demonstrates an important role for gangliosides in brain function and neurodegenerative diseases. Exogenous GM1 is broadly neuroprotective, including in rodent, feline, and primate models of Parkinson's disease, and has shown positive effects in clinical trials. We and others have shown that inhibition of the ganglioside biosynthetic enzyme GD3 synthase (GD3S) increases endogenous levels GM1 ganglioside. We recently reported that targeted deletion of St8sia1, the gene that codes for GD3S, prevents motor impairments and significantly attenuates neurodegeneration induced by 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The current study investigated the effects of GD3S inhibition on the neurotoxicity and parkinsonism induced by MPTP. Mice were injected intrastriatally with a lentiviral-vector-mediated shRNA construct targeting GD3S (shGD3S) or a scrambled-sequence control (scrRNA). An MPTP regimen of 18 mg/kg x 5 days reduced tyrosine-hydroxylase-positive neurons in the substantia nigra pars compacta of scrRNA-treated mice by nearly two-thirds. In mice treated with shGD3S the MPTP-induced lesion was approximately half that size. MPTP induced bradykinesia and deficits in fine motor skills in mice treated with scrRNA. These deficits were absent in shGD3S-treated mice. These results suggest that inhibition of GD3S protects against the nigrostriatal damage, bradykinesia, and fine-motor-skill deficits associated with MPTP administration.

Involvement of sphingolipids in ethanol neurotoxicity in the developing brain

Ethanol-induced neuronal death during a sensitive period of brain development is considered one of the significant causes of fetal alcohol spectrum disorders (FASD). In rodent models, ethanol triggers robust apoptotic neurodegeneration during a period of active synaptogenesis that occurs around the first two postnatal weeks, equivalent to the third trimester in human fetuses. The ethanol-induced apoptosis is mitochondria-dependent, involving Bax and caspase-3 activation. Such apoptotic pathways are often mediated by sphingolipids, a class of bioactive lipids ubiquitously present in eukaryotic cellular membranes. While the central role of lipids in ethanol liver toxicity is well recognized, the involvement of sphingolipids in ethanol neurotoxicity is less explored despite mounting evidence of their importance in neuronal apoptosis. Nevertheless, recent studies indicate that ethanol-induced neuronal apoptosis in animal models of FASD is mediated or regulated by cellular sphingolipids, including via the pro-apoptotic action of ceramide and through the neuroprotective action of GM1 ganglioside. Such sphingolipid involvement in ethanol neurotoxicity in the developing brain may provide unique targets for therapeutic applications against FASD. Here we summarize findings describing the involvement of sphingolipids in ethanol-induced apoptosis and discuss the possibility that the combined action of various sphingolipids in mitochondria may control neuronal cell fate.

A review of the interactions between alcohol and the endocannabinoid system: implications for alcohol dependence and future directions for research

Over the past fifty years a significant body of evidence has been compiled suggesting an interaction between the endocannabinoid (EC) system and alcohol dependence. However, much of this work has been conducted only in the past two decades following the elucidation of the molecular constituents of the EC system that began with the serendipitous discovery of the cannabinoid 1 receptor (CB1). Since then, novel pharmacological and genetic tools have enabled researchers to manipulate select components of the EC system, to determine their contribution to the motivation to consume ethanol. From these preclinical studies, it is evident that CB1 contributes the motivational and reinforcing properties of ethanol, and chronic consumption of ethanol alters EC transmitter levels and CB1 expression in brain nuclei associated with addiction pathways. These results are augmented by in vitro and ex vivo studies showing that acute and chronic treatment with ethanol produces physiologically relevant alterations in the function of the EC system. This report provides a current and comprehensive review of the literature regarding the interactions between ethanol and the EC system. We begin be reviewing the studies published prior to the discovery of the EC system that compared the behavioral and physiological effects of cannabinoids with ethanol in addition to cross-tolerance between these drugs. Next, a brief overview of the molecular constituents of the EC system is provided as context for the subsequent review of more recent studies examining the interaction of ethanol with the EC system. These results are compiled into a summary providing a scheme for the known changes to the components of the EC system in different stages of alcohol dependence. Finally, future directions for research are discussed.

Pharmacological actions of curcumin in liver diseases or damage

Since 1900 bc, several therapeutic activities have been attributed to the rhizomes of the plant Curcuma longa for a variety of diseases, including liver disorders. Curcumin, the main active compound obtained from this plant, was first isolated two centuries ago and its structure as diferuloylmethane was determined in 1910. Curcumin has shown anti-inflammatory, anti-oxidant, antifungal, antibacterial and anticancer activities. The pharmacological properties of curcumin were reviewed recently and focused mainly on its anticancer properties. However, its beneficial activity on liver diseases (known centuries ago, and demonstrated recently utilizing animal models) has not being reviewed in depth until now. The curcumin ability to inhibit several factors like nuclear factor-kappaB, which modulates several pro-inflammatory and profibrotic cytokines as well as its anti-oxidant properties, provide a rational molecular basis to use it in hepatic disorders. Curcumin attenuates liver injury induced by ethanol, thioacetamide, iron overdose, cholestasis and acute, subchronic and chronic carbon tetrachloride (CCl(4)) intoxication; moreover, it reverses CCl(4) cirrhosis to some extent. Unfortunately, the number of studies of curcumin on liver diseases is still very low and investigations in this area must be encouraged because hepatic disorders constitute one of the main causes of worldwide mortality.

Effects of ethanol on synthesis of prostaglandin F2α in bovine females

Ethanol stimulates the production of prostaglandins in many species. The purpose of this study was to verify the effect of ethanol on the production of prostaglandin F2α (PGF2α) and luteolysis in bovine females. In the first experiment, Holstein cows at day 17 of the oestrous cycle were treated with 100% ethanol (0.05 ml/kg of body weight, IV; n = 5), saline (0.05 ml/kg of body weight, IV; n = 4) or synthetic prostaglandin (150 μg of D-cloprostenol/cow, IM; n = 4). The plasma concentrations of 13, 14-dihydro-15-keto PGF2α (PGFM; the main metabolite of PGF2α measured in the peripheral blood) were assessed by radioimmunoassay (RIA). There was an acute release of PGFM in response to ethanol comparing to other treatments (p ≤ 0.05). However, only cows treated with PGF2α underwent luteolysis. In the second experiment, endometrial explants of cross-bred beef cows (n = 4) slaughtered at day 17 of the oestrous cycle were cultured for 4 h. During the last 3 h, the explants were cultured with medium supplemented with 0, 0.1, 1, 10 or 100 μl of 100% ethanol/ml. Medium samples were collected at hours 1 and 4 and concentrations of PGF2α were measured by RIA. Ethanol did not induce PGF2α production by the endometrium. In conclusion, ethanol does not cause luteolysis in cows because it stimulates production of PGF2α in extra-endometrial tissues.

Periconceptional alcohol consumption-induced changes in embryonic prostaglandin E levels in mouse organogenesis: modulation by nitric oxide

The mechanisms of the teratogenic effects of maternal alcohol consumption remain unclear. The aim of the present work was to study the organogenic PGE(2) levels and the modulation of PGE(2) levels by NO after periconceptional alcohol ingestion. Female mice were intoxicated with a 10% ethanol in drinking water before pregnancy and up to day 10 of gestation. The PGE(2) released from organogenic embryos was measured by radio immunoassay following incubation with or without the addition of either a NO donor or a NO synthase (NOS) inhibitor. In the ethanol-treated females, we found increased percentages of retarded embryos, associated with a significantly elevated resorption rate (p<0.05), very high quantities of morphologically abnormal E.10 embryos (p<0.001) and significantly increased PGE(2) release, as compared to the embryo parameters of control females. While in the control-derived E.10 embryos the NO donor produced significantly increased PGE(2) release, in the ethanol-derived embryos decreased quantities of PGE(2) were observed. L-NMMA inhibited PGE(2) release in both control and ethanol-derived embryos at different concentrations, whereas it decreased PGE(2) content in controls but not in ethanol-derived embryos. The periconceptional alcohol ingestion produced excessive PGE(2) release, decreased PGE(2) content and disruption of the regulatory NO-PGE(2) pathways. These PGs alterations may be related to delayed organogenesis and abnormal neural tube development after chronic periconceptional consumption of alcohol.

Ethanol-Inhibited [3H]Thymidine Incorporation via Protein Kinase C-p44/42 Mitogen-Activated Protein Kinase/Phospholipase A2Signal Pathway in Renal Proximal Tubule Cells

BACKGROUND

Ethanol exposure leads to changes of cell proliferation in a variety of cell types. However, how ethanol affects the proliferation of renal proximal tubule cells is not known.

METHODS

To examine the effect of ethanol on cell proliferation and its related signaling pathway, [H]thymidine incorporation, release of [H]arachidonic acid (AA), and Western blotting of protein kinase C (PKC)/mitogen-activated protein kinase (MAPK) were performed in primary cultured rabbit renal proximal tubule cells.

RESULTS

Ethanol inhibited [H]thymidine incorporation in a time- and dose-dependent manner. An inhibitory effect of ethanol on [H]thymidine incorporation was predominantly observed after 12 hr of treatment with 100 mM ethanol. Ethanol increased AA release and prostaglandin E2 production. In addition, ethanol-induced inhibition of [H]thymidine incorporation was blocked by phospholipase A2 inhibitors and was significantly blocked by PKC inhibitors. Indeed, ethanol induced a PKC translocation from the cytosolic to the membrane fraction. In addition, ethanol-induced inhibition of [H]thymidine incorporation was blocked by PD 98059 (a p44/42 MAPK inhibitor), but not by SB 203580 (a p38 MAPK inhibitor), and ethanol increased the phosphorylation of p44/42 MAPK. Results of phosphorylated p44/42 MAPK by ethanol were consistent with those of [H]thymidine incorporation and [H]AA-release experiments.

CONCLUSIONS

Ethanol inhibited [H]thymidine incorporation via PKC, p44/42 MAPK, and phospholipase A2 signaling pathways in primary cultured renal proximal tubule cells.

Neuromodulatory role of the endocannabinoid signaling system in alcoholism: an overview

The current review evaluates the evidence that some of the pharmacological and behavioral effects of ethanol (EtOH), including EtOH-preferring behavior, may be mediated through the endocannabinoid signaling system. The recent advances in the understanding of the neurobiological basis of alcoholism suggest that the pharmacological and behavioral effects of EtOH are mediated through its action on neuronal signal transduction pathways and ligand-gated ion channels, receptor systems, and receptors that are coupled to G-proteins. The identification of a G-protein-coupled receptor, namely, the cannabinoid receptor (CB1 receptor) that was activated by Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the major psychoactive component of marijuana, led to the discovery of endogenous cannabinoid agonists. To date, two fatty acid derivatives identified to be arachidonylethanolamide (AEA) and 2-arachidonylglycerol (2-AG) have been isolated from both nervous and peripheral tissues. Both these compounds have been shown to mimic the pharmacological and behavioral effects of Delta(9)-THC. The involvement of the endocannabinoid signaling system in the development of tolerance to the drugs of abuse including EtOH has not been known until recently. Recent studies from our laboratory have demonstrated for the first time the down-regulation of CB1 receptor function and its signal transduction by chronic EtOH. The observed down-regulation of CB1 receptor binding and its signal transduction results from the persistent stimulation of the receptors by the endogenous CB1 receptor agonists, AEA and 2-AG, the synthesis of which has been found to be increased by chronic EtOH treatment. This enhanced formation of endocannabinoids may subsequently influence the release of neurotransmitters. It was found that the DBA/2 mice, known to avoid EtOH intake, have significantly reduced brain-CB1-receptor function consistent with other studies, where the CB1 receptor antagonist SR141716A has been shown to block voluntary EtOH intake in rodents. Similarly, activation of the CB1 receptor system promoted alcohol craving, suggesting a role for the CB1 receptor gene in excessive EtOH drinking behavior and development of alcoholism. Ongoing investigations may lead to the development of potential therapeutic strategies for the treatment of alcoholism.

Reduced development of tolerance to the analgesic effects of morphine and clonidine in PKC gamma mutant mice

A variety of second messenger systems have been implicated in the intracellular mechanisms of tolerance development to the analgesic actions of morphine, a mu opioid, and clonidine, an alpha-2 adrenergic receptor agonist. Here, we studied mice that carry a null mutation in the gene encoding a neuronal specific isoform of protein kinase C (PKC), namely, PKC gamma. We used the tail-flick test to construct dose-response curves before and 4 days after chronic morphine (75-mg pellets, subcutaneously (s.c.)) or clonidine treatment (0.3mg/kg, s.c., twice daily). Baseline tail-flick latencies did not differ in PKC gamma mutant and wild-type mice (3-4s). Both morphine and clonidine produced a dose-dependent suppression of the tail-flick response with an ED(50) (effective dose resulting in a 50% reduction of the control response) value (2.0mg/kg for morphine and 0.1mg/kg for clonidine) that was similar for naive mutant and wild-type mice. In contrast, after 4 days of drug delivery, mutant mice showed significantly less rightward shift in the dose-response curve to morphine (six-fold for wild-type and three-fold for mutant mice) and to clonidine (five-fold for wild-type and no shift for the mutant mice). These results indicate that PKC gamma contributes to the development of tolerance to the analgesic effects of both morphine and clonidine. Chronic morphine treatment can also result in sensitization of spinal cord neurons and increased pain behaviors following a noxious insult. To assess the contribution of PKC gamma to this process, we studied the responses of wild-type and mutant mice to an intraplantar injection of formalin (a model of persistent pain) following chronic morphine treatment. Although morphine tolerance increased formalin-evoked persistent pain behavior and Fos-LI in wild-type mice, there was no difference between placebo- and morphine-treated mutant mice, suggesting that PKC gamma also contributes to chronic morphine-induced changes in nociceptive processing.

Fetal alcohol effects: mechanisms and treatment

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chair was Edward P. Riley. The presentations were (1) Does alcohol withdrawal contribute to fetal alcohol effects? by Jennifer D. Thomas and Edward P. Riley; (2) Brain damage and neuroplasticity in an animal model of binge alcohol exposure during the "third trimester equivalent," by Charles R. Goodlett, Anna Y. Klintsova, and William T. Greenough; (3) Ganglioside GM1 reduces fetal alcohol effects, by Basalingappa L. Hungund; and (4) Fetal alcohol exposure alters the wiring of serotonin system at mid-gestation, by F. Zhou, Y. Sari, Charles Goodlett, T. Powrozek, and Ting-Kai Li.

Red wine raises plasma HDL and preserves long-chain polyunsaturated fatty acids in rat kidney and erythrocytes

The effects of red wine and ethanol on plasma lipoproteins and the fatty acid composition of kidney lipids and erythrocytes phospholipids were studied. Lipid peroxidation is one of the main deleterious effects of oxidant attack on biomolecules, due to the disruption of the structural integrity of membranes. The vulnerability of the kidney to oxidative damage has been partly attributed to its high content of long-chain polyunsaturated fatty acids. Antioxidants, such as flavonoids, would be a means of reducing the risk of oxidative damage to membranes. Nutritional sources rich in antioxidants, including those provided by wine, are expected to attenuate the effects of oxidative challenges. Adult rats were fed red wine rich in flavonols, ethanol (125 ml/l), or alcohol-free red wine. The control group drank water. After 10 weeks, blood samples served to measure plasma lipoproteins and antioxidant capacity. Kidney lipids and erythrocyte phospholipids were extracted. The samples were assayed by GLC. Energy intake did not differ between all the groups, but the weight gain of the ethanol group was less than the other three groups. Blood HDL and triacylglycerols were increased by both ethanol and red wine. Ethanol decreased arachidonic and docosahexaenoic acids in both kidney lipids and erythrocyte phospholipids, as compared with either water, red wine or alcohol-free red wine groups. These results indicate that non-alcoholic components of red wine could contribute to avoiding the unfavourable effects of ethanol on plasma lipoproteins, kidney lipids and membrane erythrocyte phospholipids.

Ethanol and oxidative mechanisms in the brain

There is strong evidence showing that chronic and excessive ethanol consumption may enhance oxidative damage to neurons and result in cell death. Although not yet well understood, ethanol may enhance ROS production in brain through a number of pathways including increased generation of hydroxyethyl radicals, induction of CYP2E1, alteration of the cytokine signaling pathways for induction of iNOS and sPLA(2), and production of prostanoids through the PLA(2)/COX pathways. Since many neurodegenerative diseases are also associated with oxidative and inflammatory mechanisms in the brain, it would be important to find out whether chronic and excessive ethanol consumption may exacerbate the progression of these diseases. There is evidence that the polyphenolic antioxidants, especially those extracted from grape skin and seed, may protect the brain from neuronal damage due to chronic ethanol administration. Among the polyphenols from grapes, resveratrol seems to have unique antioxidant properties. The possible use of this compound as a therapeutic agent to ameliorate neurodegenerative processes should be further explored.

Phosphatidylethanol stimulates calcium-dependent cytosolic phospholipase A(2) activity of a macrophage cell line (RAW 264.7)

The synthesis of inflammation mediators produced from arachidonic acid is regulated primarily by the cellular concentration of free arachidonic acid. Since intracellular arachidonic acid is almost totally present as phospholipid esters, the concentration of intracellular arachidonic acid is primarily dependent on the balance between the release of arachidonic acid from membrane phospholipids and the uptake of arachidonic acid into membrane phospholipids. Cytosolic phospholipase A(2) is a calciumdependent enzyme that catalyzes the stimulus-coupled hydrolysis of arachidonic acid from membrane phospholipids. Following exposure of macrophages to various foreign or endogenous stimulants, cytosolic phospholipase A(2) is activated. Treatment with these compounds may also stimulate phospholipase D activity, and, in the presence of ethanol, phospholipase D catalyzes the synthesis of phosphatidylethanol. A cell-free system was used to evaluate the effect of phosphatidylethanol on cytosolic phospholipase A(2) activity. Phosphatidylethanol (0.5 microM) added to 1-stearoyl-2-[(3)H]-arachidonoyl-sn-glycero-3-phosphocholine vesicles stimulated cytosolic phospholipase A(2) activity. However, high concentrations (20-100 microM) of phosphatidylethanol inhibited cytosolic phospholipase A(2) activity. Phosphatidic acid, the normal phospholipase D product, also stimulated cytosolic phospholipase A(2) activity at 0.5 microM, but had an inhibitory effect on cytosolic phospholipase A(2) activity at concentrations of 50 and 100 microM. Ethanol (20-200 mM), the precursor of phosphatidylethanol, added directly to the assay did not alter cytosolic phospholipase A(2) activity. These results suggest that phosphatidylethanol alters the physical properties of the substrate, and at lower concentrations of anionic phospholipids the substrate is more susceptible to hydrolysis. However, at high concentrations, phosphatidylethanol either reverses the alterations in physical properties of the substrate or phosphatidylethanol may be competing as the substrate. Both interactions may result in lower cytosolic phospholipase A(2) activity.

Differential sensitivity of mouse neural crest cells to ethanol-induced toxicity

Neural crest cells (NCCs) have been identified as an important target population relative to ethanol-induced teratogenicity in both mouse and avian models. Additionally, whole embryo culture mouse models have shown strain-related differences in sensitivity to ethanol-induced damage following acute exposure during early NCC development. That differential sensitivity of NCCs may contribute to these strain differences has been unexplored. For this purpose, cultured NCCs from an inbred mouse strain (C57BL/6J; C57) that is more sensitive to ethanol-induced teratogenicity than an outbred strain (ICR) were compared. This study showed that the incidence of cell death was significantly higher for the C57 NCCs than those from the ICR strain at all ethanol concentrations tested, and as early as 12 hours after initial exposure to 100 mM ethanol. The lateral mobility of the membrane lipids was faster and the membrane GM1 content was lower in C57 cells than ICR cells both under control conditions and at all doses and times tested. Ethanol exposure resulted in significant increases in the membrane lipid lateral mobility, and decreases in the membrane GM1 content that occurred in a dose and time-dependent manner in the NCCs from both strains. A significant correlation was found between the GM1 content and lateral mobility of the membrane lipids, the lateral mobility of membrane lipids and cell viability, as well as the GM1 content and cell viability in the NCCs from both strains. These results suggest that different strain sensitivities to ethanol-induced teratogencity may lie, at least in part, in the interstrain differential response of the NCC population and that the vulnerability of the NCCs to ethanol-induced death may be related to their endogenous membrane GM1 content.

Gangliosides attenuate ethanol-induced apoptosis in rat cerebellar granule neurons

Ethanol significantly enhances cell death of differentiated rat cerebellar granule neurons on culture in a serum-free medium containing a depolarizing concentration of KCl (25 mM), 5 microM MK-801 (an NMDA receptor antagonist), and 20-200 mM ethanol for 1-4 days. Cell death augmented by ethanol was concentration- and time-dependent with neurons displaying hallmark apoptotic morphology and DNA fragmentation that correlated with the activation of cytosolic caspase-3. Inclusion of 5 microM MK-801 or 100 microM glycine in culture media did not alter rates of cell death indicating ethanol toxicity is mediated via an NMDA receptor-independent pathway. Preincubation with 50 microM gangliosides GM1, GD1a, GD1b or GT1b for 2 h, or preincubation with 10 microM LIGA20 (a semisynthetic GM1 with N-dichloroacetylsphingosine) for 10 min, attenuated caspase-3 activity and ethanol-induced cell death. Data show native gangliosides and a synthetic derivative are potently neuroprotective in this model of ethanol toxicity, and potentially serve as useful probes to further unravel the mechanisms relevant to neuronal apoptosis.

Chronic ethanol increases the cannabinoid receptor agonist anandamide and its precursor N-arachidonoylphosphatidylethanolamine in SK-N-SH cells

In an earlier study, we demonstrated that chronic ethanol (EtOH) exposure down-regulated the cannabinoid receptors (CB1) in mouse brain synaptic plasma membrane. In the present study, we investigated the effect of chronic EtOH on the formation of anandamide (AnNH), an endogenous cannabimimetic compound, and its precursor N-arachidonoylphosphatidylethanolamine (N-ArPE) in SK-N-SH cells that were prelabeled with [3H]arachidonic acid. The results indicate that exposure of SK-N-SH cells to EtOH (100 mM) for 72 h significantly increased levels of [3H]AnNH and [3H]N-ArPE (p < 0.05) (1.43-fold for [3H]AnNH and 1.65-fold for [3H]N-ArPE). Exposure of SK-N-SH cells to EtOH (100 mM, 24 h) inhibited initially the formation of [3H]AnNH at 24 h, followed by a progressive increase, reaching a statistical significance level at 72 h (p < 0.05). [3H]N-ArPE increased gradually to a statistically significant level after 48 and 72 h (p < 0.05). Incubation with exogenous ethanolamine (7 mM) and EtOH (100 mM, 72 h) did not result in an additive increase in the formation of [3H]AnNH. The formation of [3H]AnNH and [3H]N-ArPE by EtOH was enhanced by the Ca2+ ionophore A23187 or by the depolarizing agent veratridine and the K+ channel blocker 4-aminopyridine. Further, the EtOH-induced formation of [3H]AnNH and [3H]N-ArPE was inhibited by exogenous AnNH, whereas only [3H]AnNH formation was inhibited by the CB1 receptor antagonist SR141716A and pertussis toxin, suggesting that the CB1 receptor and G(i/o) protein mediated the regulation of AnNH levels. The observed increase in the levels of these lipids in SK-N-SH cells may be a mechanism for neuronal adaptation and may serve as a compensatory mechanism to counteract the continuous presence of EtOH. The present observation taken together with our previous results indicate the involvement of the endocannabinoid system in mediating some of the pharmacological actions of EtOH and may constitute part of a common brain pathway mediating reinforcement of drugs of abuse including EtOH.

Chronic ethanol administration down-regulates cannabinoid receptors in mouse brain synaptic plasma membrane

The effects of chronic ethanol (EtOH) consumption on the central nervous system may be related in part to its action on biological membranes by altering various receptor functions. In the current study, we examined the effects of chronic EtOH (4 day inhalation) on cannabinoid receptors (CB1) labeled with [3H]CP55,940 in synaptic plasma membranes (SPM) isolated from mouse brain. Our results indicate the presence of a high level of CB1 receptors in controls (Bmax=12.0+/-0.3 pmol mg-1 protein) which decreased significantly (-58%) in SPM from mouse brain chronically exposed to EtOH. This effect occurs without any changes in the receptor affinity (Kd=2. 3+/-0.3 nM for control and 2.9+/-0.3 nM for EtOH group, P>0.05). Dissociation kinetic results showed a dissociation rate constant (K-1) of 0.09+/-0.01 min-1 for control and this dissociation rate constant decreased significantly in the chronic EtOH treated mice brain (0.05+/-0.01 min-1, P<0.05). The competition studies with anandamide resulted in a substantial decrease in [3H]CP55,940 binding in both the control and EtOH group, with a decrease (P<0.05) in the Ki values in the SPM of chronic EtOH exposed mice. Hill transformation analysis showed an nH close to one in control (0. 92+/-0.01). This did not change significantly after chronic EtOH (0. 95+/-0.01) administration, which indicates the existence of a single class of receptor for [3H]CP55,940 binding in SPM from control and EtOH treated mice. The observed down-regulation of CB1 receptors by chronic EtOH may indicate the involvement of cannabinoid receptors in EtOH tolerance and dependence.

Effect of chronic ethanol exposure on mouse brain arachidonic acid specific phospholipase A2

The enzyme phospholipase A2 (PLA2), which catalyzes the hydrolysis of an ester bond at the sn-2 position of 1,2-sn-diacylglycerols, has been suggested to play an important role in regulating cellular functions. Although ethanol (EtOH)-induced activation of PLA2 activity was reported previously by us in mouse brain (Hungund et al., Neurochem Int 25: 321-325, 1994), its subcellular localization and biochemical properties have not been investigated. Therefore, in the present study, we examined the subcellular localization and characterization of EtOH-activated PLA2 activity in mouse brain. The results indicated that EtOH treatment decreased the specific activity of PLA2 for the first 48 hr, and then the activity increased and reached a peak level in both cytosol (1.6-fold) and membrane (1.7-fold) fractions at 96 hr of exposure. Specific activity was found to be higher in the membrane fraction than in the cytosol. Using differential density gradient centrifugation, subcellular localization of the membrane-associated PLA2 revealed that most of the EtOH-activated PLA2 specific activity was associated with the synaptic membrane (44%) followed by the nuclear membrane (13%). No significant increase in the PLA2 specific activity of mitochondrial and microsomal membranes was observed. No activity was detected in the myelin membrane. PLA2 specific activity of membranes from control and EtOH-exposed mouse brain exhibited preference for arachidonic acid over linoleic acid at the sn-2 position of glycero-3-phosphocholine (PC). No detectable PLA2 specific activity was found when PC containing oleic acid at the sn-2 position was used as a substrate. The present results also indicated that the PLA2 specific activity of membrane from control and EtOH-exposed mouse brain was insensitive to dithiothreitol, strongly stimulated by Ca2+, enhanced by glycerol, and inhibited by the cytosolic PLA2 (cPLA2) inhibitor methyl arachidonyl fluorophosphonate with an IC50 value of 3.33 microM. In summary, results suggest that the properties of EtOH-activated PLA2 activity found in mouse brain membrane fraction are similar to those of cPLA2 found in variety of cells, including mammalian brain.

Effects of acute and chronic ethanol exposure on fatty acid ethyl ester synthases in mouse cerebellar membranes

Fatty acid ethyl esters (FAEE), the products of esterification of fatty acids with ethanol (EtOH), are shown to cause organ injury in chronic alcohol abusers. Their formation is catalysed by the enzyme FAEE synthase which is present in both animal and human brain. In the present study, we investigated the effects of acute and chronic EtOH exposure on FAEE synthase activity in crude cerebellar membrane preparation of mice, using oleic, linoleic and arachidonic acids as substrates. The results indicate that FAEE synthase activity exists in synaptosomal membranes and the activity of this enzyme varied with various fatty acid substrates. The synthase activity was optimal in the membranes from the animals exposed acutely to EtOH when oleic acid was used as a substrate. A 14% increase in the incorporation of oleic acid was observed in the membranes from animals exposed to acute dose of EtOH. However, there was a 10% reduction in the synthase activity when arachidonic acid was used as a substrate in the membrane preparations from mice exposed chronically to EtOH. The results suggest that substrate specificity for FAEE synthase varied with the duration of exposure to EtOH.

The membrane disordering effect of ethanol on neural crest cells in vitro and the protective role of GM1 ganglioside

The teratogenic effect of ethanol appears to be related to excessive cell death in selected cell populations including craniofacial neural crest. Because there is a large body of evidence suggesting that a primary site of action of ethanol is at the membrane level, the current study was designed to examine and attempt to ameliorate ethanol-induced neural crest cell membrane changes that proceed cell death. To this end, neural crest cells were grown as primary cultures from mouse cranial neural tube be explants. In these cultured cells, the relationships between changes in membrane lipid lateral mobility (a measure of membrane fluidity) as determined using the technique of fluorescence recovery after photobleaching (FRAP), ethanol-induced cell death, and the protective role of GM1 ganglioside were examined. A dose-response study showed that treatment with 50, 100, 150, or 200 mM ethanol respectively, for 24 h was positively correlated with membrane lipid lateral mobility and negatively correlated with cell viability. Pre- or co-treatment of the cells with GM1 ganglioside diminished the ethanol-induced increases in membrane fluidity and decreases in cell viability. The results of this study suggest that change in membrane fluidity can account, in part, for ethanol-induced neural crest cell death and that the protection conferred by GM1 ganglioside may result from membrane stabilization and subsequent preservation of the biophysical properties and biological function of the ethanol-exposed cell membranes.

Effects of ethanol on the incorporation of free fatty acids into cerebral membrane phospholipids

Chronic ethanol exposure is known to affect deacylation-reacylation of membrane phospholipids (PL). In our earlier studies we have demonstrated that chronic exposure to ethanol (EtOH) leads to a progressive increase in membrane phospholipase A2 (PLA2) activity. In the current study, we investigated the effects of chronic EtOH exposure on the incorporation of different free fatty acids (FFAs) into membrane PL. The results suggest that the incorporation of fatty acids into four major PL varied from 9.6 fmol/min/mg protein for docosahexaenoic acid (DHA) into phosphatidylinositol (PI) to 795.8 fmol/min/mg protein for linoleic acid (LA) into phosphatidylcholine (PC). These results also suggest a preferential incorporation of DHA into PC; arachidonic acid (AA) into PI; oleic acid into phosphatidylethanolamine (PE) and PC;LA into PC and stearic acid into PE. Chronic EtOH exposure affected the incorporation of unsaturated fatty acid into PI, phosphatidylserine (PS) and PC. However, EtOH did not affect significantly the incorporation of any of the fatty acids (FA) studied into PE. No significant differences were observed with the stearic acid. It is suggested that acyltransferases may play an important role in the membrane adaptation to the injurious effects of EtOH.

Chronic inhibition of intracellular Ca2+ release or protein kinase C activation significantly reduces the development of morphine dependence

We have previously shown that chronic antagonism of metabotropic glutamate receptors in the brain attenuates naloxone-precipitated withdrawal symptoms in rats treated chronically with subcutaneous (s.c.) morphine. Several subtypes of metabotropic glutamate receptors are directly linked, through a guanine nucleotide regulatory protein, to the phosphatidylinositol (p.i.) second messenger system. In the present investigation, we assessed the effect of inhibiting the products of p.i. hydrolysis on the development of opioid dependence. Thus, concurrently with subcutaneous morphine, we infused intracerebroventricularly (i.c.v.) in rats, various doses of chelerythrine, which selectively inhibits the activation of protein kinase C, and thapsigargin, which inhibits the release of intracellular Ca2+ when given chronically. Both chelerythrine and thapsigargin reduced the severity of naloxone-precipitated abstinence symptoms when infused i.c.v. at a dose of 10 nmol/day. A single injection of either chelerythrine or thapsigargin immediately prior to the precipitation of withdrawal failed to decrease the severity of abstinence symptoms. Our results suggest that by chronically inhibiting activity of the phosphatidylinositol system, the development of morphine dependence can be attenuated.

Cortical cell plasma membrane alterations after in vitro alcohol exposure: prevention by GM1 ganglioside

Using choleratoxin/antitoxin immunohistochemistry, this study examined the effects of in vitro alcohol exposure on the morphology of cell plasma membranes in mixed fetal rat cortical cultures, and assessed the neuroprotective effects of exogenous monosialoganglioside (GM1). Gangliosides are involved in critical biological functions, including maintenance of membrane integrity. Plasma membranes are directly affected by alcohol exposure through multiple mechanisms. Results indicate that exposure to alcohol altered plasma membrane morphology as assessed by staining for the surface distribution of membrane GM1. Pretreatment with endogenous GM1 ameliorated the alcohol-induced alterations.

In utero ethanol exposure retards growth and alters morphology of cortical cultures: GM1 reverses effects

Ethanol, a developmental neurotoxin, alters plasma membranes' physicochemical properties affecting embryogenesis, cell migration, differentiation, and synaptogenesis. In a previous study using a model for fetal alcohol effects, GM1 ganglioside treatment was shown to reduce ethanol-induced accumulation of endogenous GM1 and fatty acid ethyl esters in rat fetuses. The present study was initiated to define further the in utero effects of ethanol and the capacity of GM1 treatment to ameliorate such effects. Wistar dams were exposed to ethanol (intragastrically) on gestation day (GD) 7 and GD8 and GD13 and GD14. GM1 ganglioside (10 mg/kg, im) was given 24 hr before ethanol administration. Cortical cultures were derived from GD15 and GD20 fetuses. GM1, which is highly localized on the cellular plasma membrane outer surface of CNS cells, was used as a marker molecule to assess cell integrity. Cholera toxin/antitoxin/fluorescence immunohistochemistry was used to localize GM1. Results indicate that the brief in utero exposure to ethanol affected cell growth and morphology. A marked retardation of cell development and arborization was observed as early as 24 hr after plating. Ethanol-exposed cells evidenced considerably altered GM1 localization. Such alterations likely reflect losses of membrane integrity. These in utero ethanol-induced pathologies are remarkably diminished in cultures derived from ethanol-exposed fetuses of dams treated with GM1.