Phosphatidylethanol affects inositol 1,4,5-trisphosphate levels in NG108-15 neuroblastoma x glioma hybrid cells

Biochemical Mechanisms Associating Alcohol Use Disorders with Cancers

Simple Summary

Of all yearly deaths attributable to alcohol consumption globally, approximately 12% are due to cancers, representing approximately 0.4 million deceased individuals. Ethanol metabolism disturbs cell biochemistry by targeting the structure and function of essential biomolecules (proteins, nucleic acids, and lipids) and by provoking alterations in cell programming that lead to cancer development and cancer malignancy. A better understanding of the metabolic and cell signaling realm affected by ethanol is paramount to designing effective treatments and preventive actions tailored to specific neoplasias.

Abstract

The World Health Organization identifies alcohol as a cause of several neoplasias of the oropharynx cavity, esophagus, gastrointestinal tract, larynx, liver, or female breast. We review ethanol’s nonoxidative and oxidative metabolism and one-carbon metabolism that encompasses both redox and transfer reactions that influence crucial cell proliferation machinery. Ethanol favors the uncontrolled production and action of free radicals, which interfere with the maintenance of essential cellular functions. We focus on the generation of protein, DNA, and lipid adducts that interfere with the cellular processes related to growth and differentiation. Ethanol’s effects on stem cells, which are responsible for building and repairing tissues, are reviewed. Cancer stem cells (CSCs) of different origins suffer disturbances related to the expression of cell surface markers, enzymes, and transcription factors after ethanol exposure with the consequent dysregulation of mechanisms related to cancer metastasis or resistance to treatments. Our analysis aims to underline and discuss potential targets that show more sensitivity to ethanol’s action and identify specific metabolic routes and metabolic realms that may be corrected to recover metabolic homeostasis after pharmacological intervention. Specifically, research should pay attention to re-establishing metabolic fluxes by fine-tuning the functioning of specific pathways related to one-carbon metabolism and antioxidant processes.

Distribution of Phosphatidylethanol in Maternal and Fetal Compartments After Chronic Gestational Binge Alcohol Exposure

BACKGROUND

Phosphatidylethanol (PEth) is a promising biomarker for gestational alcohol exposure. Studies show PEth accumulation in maternal and fetal blood following alcohol exposure; however, distribution of specific PEth homologues (16:0/18:1, 16:0/18:2, 16:0/20:4) in maternal and fetal blood is unknown. Additionally, PEth levels in highly vulnerable FASD targets in maternal and fetal compartments remain unexplored. We hypothesized that all 3 major PEth homologues will be detectable in the maternal and fetal blood, the maternal uterine artery (a reproductive tissue that delivers oxygen and nutrients to fetoplacental unit), and fetal brain regions following gestational binge alcohol exposure and that homologue distribution profiles will be tissue-specific.

METHODS

Pregnant rats received once-daily orogastric gavage of alcohol (Alcohol; BAC 216 mg/dl@4.5g/kg/d; BAC 289 mg/dl@6g/kg/d) or iso-caloric maltose dextrin (Pair-fed control) from gestation days (GD) 5 to 20 or 21. Following chronic exposure, maternal and fetal tissues were analyzed for PEth homologue concentrations utilizing LC-MS/MS technology.

RESULTS

All 3 PEth homologues were detected in alcohol-exposed maternal blood, fetal blood, maternal uterine artery, and fetal brain regions (hippocampus, cerebral cortex, and cerebellum). In both maternal and fetal blood, respectively, PEth 16:0/18:2 was more abundant compared to 16:0/18:1 (p < 0.0001,~66%,↑; p = 0.0159, 20.4%↑) and 16:0/20:4 (p = 0.0072,~25%↑; p = 0.0187, 19.4%↑). Maternal PEth 16:0/20:4 was ~ 42% higher than 16:0/18:1 (p = 0.0015). Maternal PEth 16:0/18:2 and 16:0/20:4 were ~ 25%↑ and ~ 20%↑ higher than in fetal blood (p < 0.05). No homologue differences were detected in the maternal uterine artery. In all fetal brain regions, PEth 16:0/18:1 was significantly higher (p < 0.0001) than 16:0/18:2 (~48 to 78%↑) and 16:0/20:4 (~31 to 62%↑) concentrations. PEth 16:0/20:4 was ~ 18% higher than 16:0/18:1 (p < 0.05) in the fetal hippocampus and cortex.

CONCLUSION

All major PEth homologues were detected in maternal and fetal blood following chronic gestational binge alcohol exposure; homologue distribution profiles were tissue-specific. This study also provides insights into PEth accumulation in critical FASD targets, specifically the maternal uterine artery and fetal brain.

Mammalian phospholipase D: Function, and therapeutics

Despite being discovered over 60 years ago, the precise role of phospholipase D (PLD) is still being elucidated. PLD enzymes catalyze the hydrolysis of the phosphodiester bond of glycerophospholipids producing phosphatidic acid and the free headgroup. PLD family members are found in organisms ranging from viruses, and bacteria to plants, and mammals. They display a range of substrate specificities, are regulated by a diverse range of molecules, and have been implicated in a broad range of cellular processes including receptor signaling, cytoskeletal regulation and membrane trafficking. Recent technological advances including: the development of PLD knockout mice, isoform-specific antibodies, and specific inhibitors are finally permitting a thorough analysis of the in vivo role of mammalian PLDs. These studies are facilitating increased recognition of PLD's role in disease states including cancers and Alzheimer's disease, offering potential as a target for therapeutic intervention.

Nonoxidative ethanol metabolism in humans-from biomarkers to bioactive lipids

Ethanol is a widely used psychoactive drug whose chronic abuse is associated with organ dysfunction and disease. Although the prevalent metabolic fate of ethanol in the human body is oxidation a smaller fraction undergoes nonoxidative metabolism yielding ethyl glucuronide, ethyl sulfate, phosphatidylethanol and fatty acid ethyl esters. Nonoxidative ethanol metabolites persist in tissues and body fluids for much longer than ethanol itself and represent biomarkers for the assessment of ethanol intake in clinical and forensic settings. Of note, the nonoxidative reaction of ethanol with phospholipids and fatty acids yields bioactive compounds that affect cellular signaling pathways and organelle function and may contribute to ethanol toxicity. Thus, despite low quantitative contributions of nonoxidative pathways to overall ethanol metabolism the resultant ethanol metabolites have important biological implications. In this review we summarize the current knowledge about the enzymatic formation of nonoxidative ethanol metabolites in humans and discuss the implications of nonoxidative ethanol metabolites as biomarkers of ethanol intake and mediators of ethanol toxicity. © 2016 IUBMB Life, 68(12):916-923, 2016.

Polyphosphoinositide metabolism and Golgi complex morphology in hippocampal neurons in primary culture is altered by chronic ethanol exposure

AIMS

Ethanol affects not only the cytoskeletal organization and activity, but also intracellular trafficking in neurons in the primary culture. Polyphosphoinositide (PPIn) are essential regulators of many important cell functions, including those mentioned, cytoskeleton integrity and intracellular vesicle trafficking. Since information about the effect of chronic ethanol exposure on PPIn metabolism in neurons is scarce, this study analysed the effect of this treatment on three of these phospholipids.

METHODS

Phosphatidylinositol (PtdIns) levels as well as the activity and/or levels of enzymes involved in their metabolism were analysed in neurons chronically exposed to ethanol. The levels of phospholipases C and D, and phosphatidylethanol formation were also assessed. The consequence of the possible alterations in the levels of PtdIns on the Golgi complex (GC) was also analysed.

RESULTS

We show that phosphatidylinositol (4,5)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate levels, both involved in the control of intracellular trafficking and cytoskeleton organization, decrease in ethanol-exposed hippocampal neurons. In contrast, several kinases that participate in the metabolism of these phospholipids, and the level and/or activity of phospholipases C and D, increase in cells after ethanol exposure. Ethanol also promotes phosphatidylethanol formation in neurons, which can result in the suppression of phosphatidic acid synthesis and, therefore, in PPIn biosynthesis. This treatment also lowers the phosphatidylinositol 4-phosphate levels, the main PPIn in the GC, with alterations in their morphology and in the levels of some of the proteins involved in structure maintenance.

CONCLUSIONS

The deregulation of the metabolism of PtdIns may underlie the ethanol-induced alterations on different neuronal processes, including intracellular trafficking and cytoskeletal integrity.

Phosphatidylethanol accumulation promotes intestinal hyperplasia by inducing ZONAB-mediated cell density increase in response to chronic ethanol exposure

Chronic alcohol consumption is associated with increased risk of gastrointestinal cancer. High concentrations of ethanol trigger mucosal hyperregeneration, disrupt cell adhesion, and increase the sensitivity to carcinogens. Most of these effects are thought to be mediated by acetaldehyde, a genotoxic metabolite produced from ethanol by alcohol dehydrogenases. Here, we studied the role of low ethanol concentrations, more likely to mimic those found in the intestine in vivo, and used intestinal cells lacking alcohol dehydrogenase to identify the acetaldehyde-independent biological effects of ethanol. Under these conditions, ethanol did not stimulate the proliferation of nonconfluent cells, but significantly increased maximal cell density. Incorporation of phosphatidylethanol, produced from ethanol by phospholipase D, was instrumental to this effect. Phosphatidylethanol accumulation induced claudin-1 endocytosis and disrupted the claudin-1/ZO-1 association. The resulting nuclear translocation of ZONAB was shown to mediate the cell density increase in ethanol-treated cells. In vivo, incorporation of phosphatidylethanol and nuclear translocation of ZONAB correlated with increased proliferation in the colonic epithelium of ethanol-fed mice and in adenomas of chronic alcoholics. Our results show that phosphatidylethanol accumulation after chronic ethanol exposure disrupts signals that normally restrict proliferation in highly confluent intestinal cells, thus facilitating abnormal intestinal cell proliferation.

Phosphatidylethanol in Human Organs and Blood: A Study on Autopsy Material and Influences by Storage Conditions

OBJECTIVE

Phosphatidylethanol (PEth) is an abnormal phospholipid that is formed and accumulated in mammalian cells that have been exposed to ethanol. PEth has been proposed as a marker of ethanol abuse. This study was conducted to investigate the concentration of PEth in blood and organs obtained during the autopsy of alcoholics. In addition, we performed experiments on rat tissues and human blood to evaluate the effect of various storage conditions on PEth concentrations.

METHODS

Human tissues and blood from alcoholics and controls were obtained at autopsy and frozen at -20 degrees C until extraction. Blood from healthy donors was incubated with ethanol for 24 hr and thereafter either extracted directly or stored at room temperature, stored at 4 degrees C, frozen at -20 degrees C, or frozen in liquid nitrogen and stored at -80 degrees C before extraction. Rats were given intraperitoneal injections of ethanol and then killed, either while still intoxicated or when sober. Rat organs were homogenized and extracted directly, after a period of storage, and/or after freezing at -20 degrees C. PEth concentration was analyzed using HPLC and verified by mass spectrometry.

RESULTS

In all rat organs studied, PEth was formed during freezing at -20 degrees C with ethanol present. PEth concentrations of 9 to 205 mumol/liter were observed in the blood obtained at autopsy. The highest value was found in the case with the highest blood alcohol concentration (114 mmol/liter) at the time of death. In the experiments on human blood stored with ethanol present, PEth concentrations were not affected after 72 hr at 4 degrees C or after freezing in liquid nitrogen and storage at -80 degrees C for up to 144 hr but were slightly elevated after 24 hr at room temperature and at -20 degrees C. PEth was found in all organs obtained from the cadavers of alcoholics. Storage of organs at 4 degrees C for 24 hr with ethanol present had no effect on the PEth concentration. The PEth concentration was unaffected when no ethanol was present at the time of freezing.

CONCLUSIONS

The rat experiments indicated that the very high PEth concentrations found in the organs of the alcoholics were probably largely formed while the organs were frozen at -20 degrees C. Our data suggest that tissue material from bodies that were exposed to ethanol must be stored properly to obtain reliable results from subsequent analysis for PEth. Tissue should not be frozen at -20 degrees C but instead stored refrigerated until extraction, preferably within hours of autopsy, or frozen in liquid nitrogen and stored at -80 degrees C. Blood samples that contain ethanol can be stored refrigerated for up to 72 hr or frozen in liquid nitrogen and stored at -80 degrees C without affecting PEth levels.

MAP kinase signaling in diverse effects of ethanol

Chronic ethanol abuse is associated with liver injury, neurotoxicity, hypertension, cardiomyopathy, modulation of immune responses and increased risk for cancer, whereas moderate alcohol consumption exerts protective effect on coronary heart disease. However, the signal transduction mechanisms underlying these processes are not well understood. Emerging evidences highlight a central role for mitogen activated protein kinase (MAPK) family in several of these effects of ethanol. MAPK signaling cascade plays an essential role in the initiation of cellular processes such as proliferation, differentiation, development, apoptosis, stress and inflammatory responses. Modulation of MAPK signaling pathway by ethanol is distinctive, depending on the cell type; acute or chronic; normal or transformed cell phenotype and on the type of agonist stimulating the MAPK. Acute exposure to ethanol results in modest activation of p42/44 MAPK in hepatocytes, astrocytes, and vascular smooth muscle cells. Acute ethanol exposure also results in potentiation or prolonged activation of p42/44MAPK in an agonist selective manner. Acute ethanol treatment also inhibits serum stimulated p42/44 MAPK activation and DNA synthesis in vascular smooth muscle cells. Chronic ethanol treatment causes decreased activation of p42/44 MAPK and inhibition of growth factor stimulated p42/44 MAPK activation and these effects of ethanol are correlated to suppression of DNA synthesis, impaired synaptic plasticity and neurotoxicity. In contrast, chronic ethanol treatment causes potentiation of endotoxin stimulated p42/44 MAPK and p38 MAPK signaling in Kupffer cells leading to increased synthesis of tumor necrosis factor. Acute exposure to ethanol activates pro-apoptotic JNK pathway and anti-apoptotic p42/44 MAPK pathway. Apoptosis caused by chronic ethanol treatment may be due to ethanol potentiation of TNF induced activation of p38 MAPK. Ethanol induced activation of MAPK signaling is also involved in collagen expression in stellate cells. Ethanol did not potentiate serum stimulated or Gi-protein dependent activation of p42/44 MAPK in normal hepatocytes but did so in embryonic liver cells and transformed hepatocytes leading to enhanced DNA synthesis. Ethanol has a 'triangular effect' on MAPK that involve direct effects of ethanol, its metabolically derived mediators and oxidative stress. Acetaldehyde, phosphatidylethanol, fatty acid ethyl ester and oxidative stress, mediate some of the effects seen after ethanol alone whereas ethanol modulation of agonist stimulated MAPK signaling appears to be mediated by phosphatidylethanol. Nuclear MAPKs are also affected by ethanol. Ethanol modulation of nuclear p42/44 MAPK occurs by both nuclear translocation of p42/44 MAPK and its activation in the nucleus. Of interest is the observation that ethanol caused selective acetylation of Lys 9 of histone 3 in the hepatocyte nucleus. It is plausible that ethanol modulation of cross talk between phosphorylation and acetylations of histone may regulate chromatin remodeling. Taken together, these recent developments place MAPK in a pivotal position in relation to cellular actions of ethanol. Furthermore, they offer promising insights into the specificity of ethanol effects and pharmacological modulation of MAPK signaling. Such molecular signaling approaches have the potential to provide mechanism-based therapy for the management of deleterious effects of ethanol or for exploiting its beneficial effects.

Agonist-stimulated Ca2+ response in neutrophils from patients with primary alcoholism and alcoholized healthy subjects

The sensitivity of the inositol phosphate (IP)/Ca2+-second messenger generating system was assessed in neutrophils from healthy volunteers before and after ingestion of approximately 1%o ethanol for 2 h. In addition, isolated neutrophils from healthy subjects were incubated with ethanol in vitro. Furthermore, the sensitivity of the IP/Ca2+ system was evaluated in neutrophils from alcoholic patients in the state of active drinking, and after 2-3 weeks and 6 months of abstinence. EC50 values of the concentration-response curves obtained by agonist stimulation with formyl-methionyl-leucylphenylalanine (fMLP) of the intracellular Ca2+ accumulation were determined as an indicator of the sensitivity of the system. Ingestion of ethanol by healthy volunteers (both in the ex vivo and in vitro experiments) induced a rightward shift of the concentration-response curve (higher EC50 values) in neutrophils, indicating a reduced sensitivity to agonist stimulation evoked by ethanol. The sensitivity of the Ca2+ response in neutrophils from alcoholic patients decreased intraindividually after a period of 2-3 weeks of abstinence (higher EC50 values) and was at this time also significantly lower compared to a group of matched healthy controls In contrast, the maximal Ca2+ release induced by a saturating concentration of fMLP was increased after 2-3 weeks of abstinence, both intraindividually and in comparison to healthy controls. These alterations of the EC50 values and the maximal Ca2+ response were normalized after 6 months of abstinence. It is concluded that ethanol attenuates the sensitivity of the IP/Ca2+ system in neutrophils in healthy subjects. In neutrophils from alcoholic subjects complex alterations appear to persist up to several weeks, which are only normalized after a prolonged period of abstinence.

Increased levels of methylated intermediates of phosphatidylcholine lead to enhanced phospholipase D activity

Previous work from this laboratory and others has shown that neurotransmitters can activate phospholipase D. Unlike the phospholipase C that specifically hydrolyzes inositol-containing phospholipids, phospholipase D in neuronal tissue specifically hydrolyzes phosphatidylcholine. One route for the synthesis of phosphatidylcholine, is via methylation of phosphatidylethanolamine. Using an in vitro assay, we have previously shown that methylated intermediates are also good substrates for phospholipase D (1). In this manuscript we demonstrate that these intermediates are also substrates in the intact PC12 cells. Cells incubated with methyl and dimethylethanolamine incorporate more [3H]palmitic acid into the corresponding phospholipid, phosphatidyl-N-methylethanolamine and phosphatidyl-N,N-dimethylethanolamine. In these cells bradykinin causes a greater increase in [3H]phosphatidylethanol production. Elevated levels of [3H]phosphatidylcholine do not enhance bradykinin-stimulated [3H]phosphatidylethanol production, therefore, this effect is specific for the methylated intermediates. Finally, this effect is not due to some generalized enhancement of receptor coupling because incubation of the cells with methylethanolamine does not lead to an increase in bradykinin stimulated inositol phosphate production.

Ethanol inhibits the peak of muscarinic receptor-stimulated formation of inositol 1,4,5-trisphosphate in neuroblastoma SH-SY5Y cells

The effect of ethanol on muscarinic receptor-stimulated formation of inositol 1,4,5-trisphosphate was studied in human neuroblastoma SH-SY5Y cells. Stimulation with carbachol induced a biphasic increase of inositol 1,4,5-triphosphate with an initial peak after 10 sec declining to a plateau phase of elevation above basal levels, which was sustained for at least 5 min in the presence of agonist. The peak, but not the plateau phase, was concentration-dependently decreased by exposure to ethanol. Maximal inhibition was obtained within 30 sec of exposure to ethanol. Ethanol caused an increase in the EC50 value of carbachol for the initial rate of inositol 1,4,5-trisphosphate formation, measured after 10 sec of stimulation, from 98 microM in the absence to 196 microM in the presence of 100 mM ethanol. The potencies of pirenzepine and hexahydro-sila-difenidol hydrochloride for inhibiting [3H]quinuclidinyl benzilate binding and inositol 1,4,5-trisphosphate formation suggest that both phases are mediated via the muscarinic M1 receptor. Phorbol 12-myristate 13-acetate inhibited both phases of inositol 1,4,5-trisphosphate formation, whereas okadaic acid and modulators of cAMP-dependent protein kinase were without any effect. There was no inhibitory effect of ethanol when protein kinase C was inhibited by H7 and calphostin C, indicating that the ethanol effect is dependent on protein kinase C activity.

Phosphatidylethanol formation and degradation in brains of acutely and repeatedly ethanol-treated rats

The formation of the abnormal phospholipid phosphatidylethanol (PEth) was studied in hippocampus, cerebellum and cerebrum of rat brain after intraperitoneal ethanol administration. Prior to analysis by high performance thin layer chromatography PEth was purified. After one injection, PEth levels reached a maximum after 2 h and remained detectable for 14-24 h in all three regions. Repeated injections led to additional accumulation. Maximum in vivo levels of 30-50 nmol/g wet wt. were reached.

Agonist-stimulated and basal phosphatidylethanol formation in neutrophils from alcoholics

Phospholipase D has been shown to be a key enzyme in the signal transduction systems involved in neutrophil activation. In the presence of ethanol, the enzyme catalyzes a transphosphatidylation reaction through which phosphatidylethanol is formed instead of the normal product phosphatidic acid. The effects of ethanol on the formation of phosphatidylethanol and phosphatidic acid was studied in neutrophils from human alcoholics in vitro. Neutrophils were isolated and cellular lipids were labeled with [3H]oleate, whereafter the cells were preincubated with cytochalasin B. Subsequently, cells were stimulated with the chemotactic peptide formyl-Met-Leu-Phe in the presence of ethanol concentration ranging from 0 to 200 mM. In the presence of ethanol, both neutrophils from alcoholics and controls produced phosphatidylethanol, with a concomitant reduction of the production of phosphatidic acid. The amounts of phosphatidyl-ethanol and phosphatidic acid formed were dependent on the concentration of ethanol. In neutrophils from alcoholics, a higher apparent Km for the phospholipase D-mediated transphosphatidylation reaction was noted (58 mM ethanol compared with 28 mM in controls). The in vivo mass of phosphatidylethanol in recently drinking alcoholics was also analyzed in neutrophils. Measurable phosphatidyl-ethanol levels (average 5.6 pmol/10(8) neutrophils) were found in alcoholics up to 23 hr after the last intake of ethanol. Thus, in addition to the ethanol-induced changes in the normal production of phosphatidic acid, phosphatidylethanol accumulated in vivo in alcoholics may be expected to influence neutrophil function.

Long-term effects of intermittent versus continuous ethanol exposure on hippocampal synapses of the rat

The hippocampus is known to be very sensitive to a large spectrum of different neurotoxins including ethanol. Ethanol administered continuously or intermittently may affect the hippocampus in different ways. Intermittent administration of ethanol has many features in common with the low level electrical stimulation protocols which lead to the functional changes associated with the phenomenon of kindling. In this study, the differential effects of intermittent intraperitoneal ethanol injections (3 g/kg twice daily) and continuously administered ethanol in drinking water (20%) on hippocampal synapses in the rat were studied using ethanolic phosphotungstic acid staining and electron microscopy. After 1 month of intermittent exposure a significant reduction (18%) of synapses was seen in the stratum lucidum of the CA3 region. Continuously treated animals showed no significant change over this time despite a higher total ethanol intake. In the dentate gyrus, a compensatory increase in supragranular synaptic number was seen only in continuously treated animals. These findings demonstrate the sensitivity of synapses of the hippocampus to the presence of ethanol and the larger effects of peaking ethanol concentrations compared to more constant levels. These results emphasize the need to consider the differential effects of various types of ethanol consumption also on the human brain.

Developmental neurotoxicity of ethanol: further evidence for an involvement of muscarinic receptor-stimulated phosphoinositide hydrolysis

Various lines of evidence suggest that muscarinic receptor-stimulated phosphoinositide hydrolysis during postnatal development in the rat brain may play a relevant role in glial cell proliferation and neuronal differentiation. We have previously shown that administration of ethanol to developing rats during the brain growth spurt causes microencephaly and selectively decreases muscarinic receptor-stimulated phosphoinositide hydrolysis. In the present study we have investigated the sensitivity of the phosphoinositide system coupled to muscarinic receptors to ethanol inhibition during distinct stages of the brain growth spurt. Different groups of rats were treated for 3 days with ethanol (4 g/kg per day) on postnatal days 2-4 (initial), 6-8 or 10-12 (peak), 13-15 (final stage of the brain growth spurt). The results show that the period of maximal sensitivity to ethanol of muscarinic receptor-stimulated phosphoinositide hydrolysis coincides with the peak of the brain growth spurt and with the period of maximal efficacy of muscarinic receptor agonists to induce inositol phosphates accumulation. Interestingly, only when muscarinic receptor-stimulated phosphoinositide hydrolysis was inhibited, a significant reduction of brain weight was observed. The close parallel between inhibition of this second messenger response and reduction of brain weight suggests that the phosphoinositide system coupled to muscarinic receptors may represent a target for the neurotoxic effects of ethanol during this stage of brain development.

Contribution of phospholipases A2 and D to arachidonic acid liberation and prostaglandin D2 formation with increase in intracellular Ca2+ concentration in rat peritoneal mast cells

The contribution of phospholipases A2 (PLA2) and D (PLD) activation to arachidonic acid liberation and prostaglandin D2 (PGD2) formation was studied in stimulated rat peritoneal mast cells. Stimulation of the cells with ionomycin induced time-dependent and Ca(2+)-concentration-dependent increase in arachidonic acid liberation and PGD2 formation, and the Ca(2+)-dependent increase was especially remarkable at extracellular Ca2+ concentration higher than 200 microM. Staurosporine did not induce any effect on the arachidonic acid liberation, indicating that protein kinase C is not involved in the liberation. Addition of ethanol to the cells decreased the ionomycin-stimulated arachidonic acid liberation to 40% of the control, while it decreased the PGD2 formation almost completely, with the increase in phosphatidylethanol formation. Propranolol, a phosphatidate phosphohydrolase inhibitor, caused similar effects. p-Bromophenacyl bromide, a PLA2 inhibitor, inhibited partially the arachidonic acid liberation. The inhibition of the liberation by combination of p-bromophenacyl bromide and ethanol was additive and reached approximately 90%. Under the conditions used p-bromophenacyl bromide did not influence significantly the PLD activity assessed by the phosphatidylethanol formation. Histamine release was decreased by ethanol treatment to 35% of the control. These results suggest that more than half of the total arachidonic acid liberation is mediated by the sequential pathway of PLD/phosphatidate phosphohydrolase/diacylglycerol lipase and more than half of histamine release is also dependent on PLD activation, while the PGD2 formation is fully mediated by the pathway. PLA2 also contributes to arachidonic acid liberation but to a lower extent.

Adaptation of signal transduction in brain

Cell culture models were used to study the effects of long-term ethanol exposure on neuronal cells. Effects on phospholipase C and phospholipase D mediated signal transduction were investigated by assaying receptor-binding, G protein function, activities of lipases, formation of second messengers and c-fos mRNA. The signal transduction cascades displayed abnormal activities from 2 to 7 days of exposure which differed from the acute effects. Phosphatidylethanol formed by phospholipase D is an abnormal lipid that may harmfully affect nerve cell function.