Mechanism of Mesoporous Silica Nanoparticle Interaction with Hairy Root Cultures during Nanoharvesting of Biomolecules

Cellular uptake and expulsion mechanisms of engineered mesoporous silica nanoparticles (MSNPs) are important in their design for novel biomolecule isolation and delivery applications such as nanoharvesting, defined as using nanocarriers to transport and isolate valuable therapeutics (secondary metabolites) out of living plant organ cultures (e.g., hairy roots). Here, temperature-dependent MSNP uptake and recovery processes in hairy roots are examined as a function of surface chemistry. MSNP uptake into hairy roots and time-dependent expulsion are quantified using Ti content (present for biomolecule binding) and fluorescence spectroscopy of fluorescently tagged MSNPs, respectively. The results suggest that functionalization and surface charge (regulated by amine group attachment) play the biggest role in the effectiveness of uptake and recovery. Comparison of MSNP interactions with hairy roots at 4 and 23 °C shows that weakly charged MSNPs functionalized only with Ti are taken up and expelled by thermally activated mechanisms, while amine-modified positively charged particles are taken up and expelled mainly by direct penetration of cell walls. Amine-functionalized MSNPs move spontaneously in and out of plant cells by dynamic exchange with a residence time of 20 ± 5 min, suggesting promise as a biomolecule nanoharvesting platform for plant organ cultures.

Nanoharvesting of bioactive materials from living plant cultures using engineered silica nanoparticles

Plant secondary metabolites are valuable therapeutics not readily synthesized by traditional chemistry techniques. Although their enrichment in plant cell cultures is possible following advances in biotechnology, conventional methods of recovery are destructive to the tissues. Nanoharvesting, in which nanoparticles are designed to bind and carry biomolecules out of living cells, offers continuous production of metabolites from plant cultures. Here, nanoharvesting of polyphenolic flavonoids, model plant-derived therapeutics, enriched in Solidago nemoralis hairy root cultures, is performed using engineered mesoporous silica nanoparticles (MSNPs, 165 nm diameter and 950 m2/g surface area) functionalized with both titanium dioxide (TiO2, 425 mg/g particles) for coordination binding sites, and amines (NH2, 145 mg/g particles) to promote cellular internalization. Intracellular uptake and localization of the nanoparticles (in Murashige and Skoog media) in hairy roots were confirmed by tagging the particles with rhodamine B isothiocyanate, incubating the particles with hairy roots, and quenching bulk fluorescence using trypan blue. Nanoharvesting of biologically active flavonoids was demonstrated by observing increased antiradical activity (using 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay) by nanoparticles after exposure to hairy roots (indicating general antioxidant activity), and by the displacement of the radio-ligand [3H]-methyllycaconitine from rat hippocampal nicotinic receptors by solutes recovered from nanoharvested particles (indicating pharmacological activity specific to S. nemoralis flavonoids). Post-nanoharvesting growth suggests that the roots are viable after nanoharvesting, and capable of continued flavonoid synthesis. These observations demonstrate the potential for using engineered nanostructured particles to facilitate continuous isolation of a broad range of biomolecules from living and functioning plant cultures.

Microfluidic capillary zone electrophoresis mass spectrometry analysis of alkaloids in Lobelia cardinalis transgenic and mutant plant cell cultures

Application of a microfluidic CE* device for CZE-MS allows for fast, rapid, and in-depth analysis of large sample sets. This microfluidic CZE-MS device, the 908 Devices ZipChip, involves minimal sample preparation and is ideal for small cation analytes, such as alkaloids. Here, we evaluated the microfluidic device for the analysis of alkaloids from Lobelia cardinalis hairy root cultures. Extracts from wild-type, transgenic, and selected mutant plant cultures were analyzed and data batch processed using the mass spectral processing software MZmine2 and the statistical software Prism 8. In total 139 features were detected as baseline resolved peaks via the MZmine2 software optimized for the electrophoretic separations. Statistically significant differences in the relative abundance of the primary alkaloid lobinaline (C27 H34 N2 ), along with several putative "lobinaline-like" molecules were observed utilizing this approach. Additionally, a method for performing both targeted and untargeted MS/MS experiments using the microfluidic device was developed and evaluated. Coupling data-processing software with CZE-MS data acquisition has enabled comprehensive metabolomic profiles from plant cell cultures to be constructed within a single working day.

Interactions Between Ethanol and Dietary Fat in Determining Human Platelet Function

Platelet aggregation to collagen and ADP in vitro was assessed in the plasma of healthy human volunteers both before and after drinking 700 ml of white wine. This had no effect on platelet aggregation when compared with samples from the same individuals taken on a separate occasion without alcohol consumption. However, when alcohol was taken with a meal high in saturated fat, a significant inhibitory effect on platelet aggregation was observed when compared to the effect of the meal alone. There was no such interaction when the meal associated with alcohol ingestion contained mainly unsaturated fats. The fatty acid composition of plasma and platelet membranes from these volunteers showed a significantly increased proportion of saturated fats after the saturated fat meal. The concomitant ingestion of ethanol did not prevent this change. The concentration of alcohol in plasma achieved (c. 25 mM) may directly inhibit platelet aggregation when the platelet membrane content of saturated fats is high.

Inhibition of Platelet Aggregation by Ethanol in Vitro Shows Specificity for Aggregating Agent Used and Is Influenced by Platelet Lipid Composition

Ethanol at physiologically tolerable concentrations inhibited platelet aggregation in vitro in a relatively specific way, which may be influenced by platelet membrane lipid composition. Aggregation to collagen, calcium ionophore A23187 and thrombin (low doses) were often markedly inhibited by ethanol, adrenaline and ADP responses were little affected, and aggregation to exogenous arachidonic acid was actually potentiated by ethanol. Aggregation to collagen, thrombin and A23187 was inhibited more by ethanol in platelets enriched with saturated fatty acids than in those enriched with unsaturated fats. Platelets enriched with cholesterol showed increased sensitivity to ADP, arachidonate and adrenaline but this increase in cholesterol content did not appear to influence the inhibition by ethanol of platelet responses. The results suggest that ethanol may inhibit aggregation by an effect on membrane fluidity and/or calcium mobilization resulting in decreased activity of a membrane-bound phospholipase.

Adsorption and Recovery of Polyphenolic Flavonoids Using TiO2-Functionalized Mesoporous Silica Nanoparticles

Exploiting specific interactions with titania (TiO₂) has been proposed for the separation and recovery of a broad range of biomolecules and natural products, including therapeutic polyphenolic flavonoids which are susceptible to degradation, such as quercetin. Functionalizing mesoporous silica with TiO₂ has many potential advantages over bulk and mesoporous TiO₂ as an adsorbent for natural products, including robust synthetic approaches leading to high surface area, and stable separation platforms. Here, TiO₂-surface-functionalized mesoporous silica nanoparticles (MSNPs) are synthesized and characterized as a function of TiO₂ content (up to 636 mg TiO₂/g). The adsorption isotherms of two polyphenolic flavonoids, quercetin and rutin, were determined (0.05-10 mg/mL in ethanol), and a 100-fold increase in the adsorption capacity was observed relative to functionalized nonporous particles with similar TiO₂ surface coverage. An optimum extent of functionalization (approximately 440 mg TiO₂/g particles) is interpreted from characterization techniques including grazing incidence X-ray scattering (GIXS), high-resolution transmission electron microscopy (HRTEM), and nitrogen adsorption, which examined the interplay between the extent of TiO₂ functionalization and the accessibility of the porous structures. The recovery of flavonoids is demonstrated using ligand displacement in ethanolic citric acid solution (20% w/v), in which greater than 90% recovery can be achieved in a multistep extraction process. The radical scavenging activity (RSA) of the recovered and particle-bound quercetin as measured by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay demonstrates greater than 80% retention of antioxidant activity by both particle-bound and recovered quercetin. These mesoporous titanosilicate materials can serve as a synthetic platform to isolate, recover, and potentially deliver degradation-sensitive natural products to biological systems.

Target-directed discovery and production of pharmaceuticals in transgenic mutant plant cells

Plants are a source of complex bioactive compounds, with value as pharmaceuticals, or leads for synthetic modification. Many of these secondary metabolites have evolved as defenses against competing organisms and their pharmaceutical value is "accidental", resulting from homology between target proteins in these competitors, and human molecular therapeutic targets. Here we show that it is possible to use mutation and selection of plant cells to re-direct their "evolution" toward metabolites that interact with the therapeutic target proteins themselves. This is achieved by expressing the human target protein in plant cells, and selecting mutants for survival based on the interaction of their metabolome with this target. This report describes the successful evolution of hairy root cultures of a Lobelia species toward increased biosynthesis of metabolites that inhibit the human dopamine transporter protein. Many of the resulting selected mutants are overproducing the active metabolite found in the wild-type plant, but others overproduce active metabolites that are not readily detectable in non-mutants. This technology can access the whole genomic capability of a plant species to biosynthesize metabolites with a specific target. It has potential value as a novel platform for plant drug discovery and production, or as a means of optimizing the therapeutic value of medicinal plant extracts.

Novel multifunctional pharmacology of lobinaline, the major alkaloid from Lobelia cardinalis

In screening a library of plant extracts from ~1000 species native to the Southeastern United States, Lobelia cardinalis was identified as containing nicotinic acetylcholine receptor (nicAchR) binding activity which was relatively non-selective for the α4β2- and α7-nicAchR subtypes. This nicAchR binding profile is atypical for plant-derived nicAchR ligands, the majority of which are highly selective for α4β2-nicAchRs. Its potential therapeutic relevance is noteworthy since agonism of α4β2- and α7-nicAchRs is associated with anti-inflammatory and neuroprotective properties. Bioassay-guided fractionation of L. cardinalis extracts led to the identification of lobinaline, a complex binitrogenous alkaloid, as the main source of the unique nicAchR binding profile. Purified lobinaline was a potent free radical scavenger, displayed similar binding affinity at α4β2- and α7-nicAchRs, exhibited agonist activity at nicAchRs in SH-SY5Y cells, and inhibited [(3)H]-dopamine (DA) uptake in rat striatal synaptosomes. Lobinaline significantly increased fractional [(3)H] release from superfused rat striatal slices preloaded with [(3)H]-DA, an effect that was inhibited by the non-selective nicAchR antagonist mecamylamine. In vivo electrochemical studies in urethane-anesthetized rats demonstrated that lobinaline locally applied in the striatum significantly prolonged clearance of exogenous DA by the dopamine transporter (DAT). In contrast, lobeline, the most thoroughly investigated Lobelia alkaloid, is an α4β2-nicAchR antagonist, a poor free radical scavenger, and is a less potent DAT inhibitor. These previously unreported multifunctional effects of lobinaline make it of interest as a lead to develop therapeutics for neuropathological disorders that involve free radical generation, cholinergic, and dopaminergic neurotransmission. These include neurodegenerative conditions, such as Parkinson's disease, and drug abuse.

Animal Models for Medication Development and Application to Treat Fetal Alcohol Effects

Ethanol consumption during pregnancy can have lifelong consequences for the offspring, their family and society. Fetal alcohol spectrum disorders (FASD) include a range of physical and behavioral effects with the most significant impact occurring as a result of the effects of ethanol on the developing central nervous system (CNS). To date, there are no FDA approved drugs that have been tested that prevent/reduce or specifically treat the symptoms of FASD. There are several promising lines of research from rodent models aimed at reducing the neurotoxic effects of ethanol on the developing CNS or in treating the resulting behavioral impairments but these have not yet moved to clinical testing. The current review discusses some of the most promising targets for intervention and provides a review of the past and ongoing efforts to develop and screen pharmacological treatments for reducing the effects of prenatal ethanol exposure.

The Dietary Flavonoid Rhamnetin Inhibits Both Inflammation and Excitotoxicity During Ethanol Withdrawal in Rat Organotypic Hippocampal Slice Cultures

BACKGROUND

Ethanol (EtOH) causes neurotoxicity via several mechanisms including neuroinflammation (during EtOH exposure), and excitotoxicity (during EtOH withdrawal [EWD]). Alpha7 nicotinic acetylcholine receptor (nAChR) selective agonists have the potential to reduce both. The aim of this study was to evaluate the anti-inflammatory and neuroprotective potential of rhamnetin, a dietary flavonoid with alpha7 nAChR selective activity, in an in vitro model of EtOH-induced neurotoxicity.

METHODS

The anti-inflammatory and neuroprotective properties of rhamnetin were assessed in neonatal organotypic hippocampal slice cultures undergoing EWD (or not) and challenged with N-methyl-D-aspartate (NMDA) and/or lipopolysaccharide (LPS). Neurotoxicity was determined using propidium iodide uptake, and the inflammatory response was evaluated by measuring the release of tumor necrosis factor (TNF)-alpha (NO; quantified by ELISA) and nitric oxide (quantified by the Griess reaction) into culture media.

RESULTS

As predicted, rhamnetin reduced LPS-induced release of TNF-alpha and NO both under control conditions and during EWD. Additionally, rhamnetin had no effect on NMDA-induced neurotoxicity under control conditions, but significantly reduced NMDA toxicity during EWD. In contrast, rhamnetin had no effect on neurotoxicity induced by NMDA and LPS combined despite reducing TNF-alpha and NO levels under these conditions.

CONCLUSIONS

Rhamnetin is anti-inflammatory and neuroprotective during EWD and therefore has potential value in treating neurotoxicity caused by EtOH.

Altered relation between lipopolysaccharide-induced inflammatory response and excitotoxicity in rat organotypic hippocampal slice cultures during ethanol withdrawal

BACKGROUND

Ethanol (EtOH) causes neurotoxicity by several mechanisms including excitotoxicity and neuroinflammation, but little is known about the interaction between these mechanisms. Because neuroinflammation is known to enhance excitotoxicity, we hypothesized that neuroinflammation contributes to the enhanced excitotoxicity, which is associated with EtOH withdrawal (EWD). The aim of this study was to evaluate the lipopolysaccharide (LPS)-induced inflammatory response of cultured hippocampal tissue during EWD and its effects on the enhanced N-methyl-d-aspartate (NMDA) receptor-mediated excitotoxicity, which occurs at this time.

METHODS

Using a neonatal organotypic hippocampal slice culture (OHSC) model, we assessed the effects of NMDA and LPS (separately or combined) during EWD after 10 days of EtOH exposure. Neurotoxicity was assessed using propidium iodide uptake, and the inflammatory response was evaluated by measuring the release of tumor necrosis factor (TNF)-alpha (quantified by enzyme-linked immunosorbent assay) and nitric oxide (NO; quantified by the Griess reaction) into culture media. Furthermore, we explored the potential role of the microglial cell type using immortalized BV2 microglia treated with EtOH for 10 days and challenged with LPS during EWD.

RESULTS

As predicted, NMDA-induced toxicity was potentiated by LPS under control conditions. However, during EWD, the reverse was observed and LPS inhibited peak NMDA-induced toxicity. Additionally, LPS-induced release of TNF-alpha and NO during EWD was reduced compared to control conditions. In BV2 microglia, following EtOH exposure, LPS-induced release of NO was reduced, whereas TNF-alpha release was potentiated.

CONCLUSIONS

During EWD following chronic EtOH exposure, OHSC exhibited a desensitized inflammatory response to LPS and the effects of LPS on NMDA toxicity were reversed. This might be explained by a change in microglia to an anti-inflammatory and neuroprotective phenotype. In support, studies on BV2 microglia indicate that EtOH exposure and EWD do alter the response of these cells to LPS, but this cannot fully explain the changes observed in the OHSC. The data suggest that neuroinflammation and excitotoxicity do interact during EWD. However, the interaction is not as simple as we originally proposed. This in turn illustrates the need to assess the extent, importance, and relation of these mechanisms in models of EtOH exposure producing neurotoxicity.

A nicotinic receptor-mediated anti-inflammatory effect of the flavonoid rhamnetin in BV2 microglia

The alpha7 nicotinic acetylcholine receptor (nAChR) is a potential target in neuroinflammation. Screening a plant extract library identified Solidago nemoralis as containing methyl-quercetin derivatives that are relatively selective ligands for the alpha7 nAChR. Flavonoids are not known for this activity, so we screened a small library of pure flavonoids to confirm our findings. Some flavonoids, e.g. rhamnetin, displaced a selective alpha7 nAChR radioligand from rat brain membranes whereas similar structures e.g. sakuranetin, did not. To evaluate the contribution of this putative nAChR activity to the known anti-inflammatory properties of these flavonoids, we compared their effects on lipopolysaccharide induced release of inflammatory mediators from BV2 microglia. Both rhamnetin and sakuranetin reduced mediator release, but differed in potency (rhamnetin>sakuranetin) and the Hill slope of their concentration-response curves. For rhamnetin the Hill coefficient was >3.0 whereas for sakuranetin the coefficient was 1.0, suggesting that effects of rhamnetin are mediated through more than one mechanism, whereas sakuranetin has a single mechanism. nAChR antagonists decreased the Hill coefficient for rhamnetin toward unity, which suggests that a nAChR-mediated mechanism contributes cooperatively to its overall anti-inflammatory effect. In contrast nAChR antagonists had no effect on the potency or Hill coefficient for sakuranetin, but a concentration of nicotine (1μM) that had no effect alone, significantly increased the Hill coefficient of this flavonoid. In conclusion, the anti-inflammatory effects of rhamnetin benefit cooperatively from a nAChR-mediated mechanism. This action, together with potent free radical scavenging activity, suggests that flavonoids with alpha7 nAChR activity have therapeutic potential in neuroinflammatory conditions.

Improving the inhibitory activity of arylidenaminoguanidine compounds at the N-methyl-D-aspartate receptor complex from a recursive computational-experimental structure-activity relationship study

Using a combination of both the partial least squares (PLS) and back-propagation artificial neural network (ANN) pattern recognition methods, several models have been developed to predict the activity of a series of arylidenaminoguanidine analogs as inhibitory modulators of the N-methyl-D-aspartate receptor complex. This was done by correlating structural and physicochemical descriptors obtained from computation software with the experimentally observed [(3)H]MK-801 displacement ability of a small library of synthesized and in vitro screened arylidenaminoguanidines. Results for the generated PLS model were r(2)=0.814, rmsd=0.208, rCV(2)=0.714, loormsd=0.261. The ANN model was created utilizing the eleven descriptors from the PLS model for comparison. The quality of the ANN model (r(2)=0.828, rmsd=0.200, rCV(2)=0.721, loormsd=0.257) is similar to the PLS model, and indicates that the feature between the inputs and the output is majorly linear. These computational models were able to predict inhibition of the NMDA receptor complex by this series of compounds in silico, affording a predictive structure-based 'pre-screening' paradigm for the arylideneaminoguanidine analogs.

Natural Products Genomics: A novel approach for the discovery of anti-cancer therapeutics

Plants continue to retain some advantages over combinatorial chemistry as sources of novel compounds, for example, they can generate metabolites with a complexity beyond synthetic chemistry. However, this comes with its own problems in production and synthetic modification of these compounds. Natural Products Genomics (NPG) aims to access the plants own genomic capacity to increase yields, and modify complex bioactive metabolites, to alleviate these limitations. NPG uses a combination of gain of function mutagenesis and selection to a) mimic the evolution of novel compounds in plants, and b) to increase yields of known bioactive metabolites. This process is performed rapidly at the cell culture level in large populations of mutants. Two examples demonstrating proof of concept in Nicotiana tabacum (tobacco) and proof of application in the medicinal plant species Catharanthus roseus, are included to illustrate the feasibility of this approach. This biotechnology platform may alter the way in which plant drug discovery is perceived by the pharmaceutical industry, and provides an alternative to combinatorial chemistry for the discovery, modification and production of highly complex bioactive molecules.

Laboratory models available to study alcohol-induced organ damage and immune variations: choosing the appropriate model

The morbidity and mortality resulting from alcohol-related diseases globally impose a substantive cost to society. To minimize the financial burden on society and improve the quality of life for individuals suffering from the ill effects of alcohol abuse, substantial research in the alcohol field is focused on understanding the mechanisms by which alcohol-related diseases develop and progress. Since ethical concerns and inherent difficulties limit the amount of alcohol abuse research that can be performed in humans, most studies are performed in laboratory animals. This article summarizes the various laboratory models of alcohol abuse that are currently available and are used to study the mechanisms by which alcohol abuse induces organ damage and immune defects. The strengths and weaknesses of each of the models are discussed. Integrated into the review are the presentations that were made in the symposium "Methods of Ethanol Application in Alcohol Model-How Long is Long Enough" at the joint 2008 Research Society on Alcoholism (RSA) and International Society for Biomedical Research on Alcoholism (ISBRA) meeting, Washington, DC, emphasizing the importance not only of selecting the most appropriate laboratory alcohol model to address the specific goals of a project but also of ensuring that the findings can be extrapolated to alcohol-induced diseases in humans.

Reactive oxygen species regulate alkaloid metabolism in undifferentiated N. tabacum cells

Plants produce an immense number of natural products and undifferentiated cells from various plant tissues have long been considered an ideal source for their synthesis. However, undifferentiated plant cells often either lose their biosynthetic capacity over time or exhibit immediate repression of the required pathways once dedifferentiated. In this study, freshly prepared callus tissue was employed to further investigate the regulation of a natural product pathway in undifferentiated tobacco cells. Putrescine N-methyltransferase (PMT) is a pathway-specific enzyme required in nicotinic alkaloid production in Nicotiana species. Callus derived from transgenic Nicotiana tabacum plants harboring PMT promoter-GUS fusions were used to study factors that influence PMT expression. Under normal callus growth conditions in the presence of light and auxin, PMT promoter activity was strongly repressed. Conversely, dark conditions and the absence of auxin were found to upregulate PMT promoter activity, with light being dominant to the repressive effects of auxin. Since reactive oxygen species (ROS) are known by-products of photosynthesis and have been implicated in signaling, their involvement was investigated in transgenic callus by treatment with the ROS scavenger, dimethylthiourea, or catalase. Under highly repressive conditions for alkaloid synthesis, including normal culture conditions in the light, both ROS scavengers resulted in significant induction of PMT promoter activity. Moreover, treatment of callus with catalase resulted in the upregulation of PMT promoter activity and alkaloid accumulation in this tissue. These results suggest that ROS impact the regulation of the alkaloid pathway in undifferentiated cells and have implications for regulation of the pathway in other plant tissues.

Effects of mecamylamine on alcohol consumption and preference in male C57BL/6J mice

Alcohol and nicotine (in the form of tobacco) are 2 commonly used recreational drugs and studies show a high correlation between tobacco use and alcohol consumption. In the present study, using C57BL/6J mice, we investigated the ability of mecamylamine (a nicotinic antagonist) to reduce alcohol consumption and alcohol preference with free 24-hour access using a 2-bottle choice test drinking procedure. Male C57BL/6J mice were individually housed and acclimatized to 10% alcohol. Immediately following the last day of alcohol acclimatization, the mice (n = 5/group) received subcutaneous injections of mecamylamine (0.5, 1 and 2 mg/kg) or saline consisting of either intermittent (3 injections given every other day) or daily (injections on all 5 days) exposures. Fluid consumption (alcohol and water) was recorded daily. The results showed that mecamylamine significantly reduced alcohol consumption and alcohol preference in both phases of intermittent and daily drug exposures, while the total fluid consumption was unchanged. These results provide further support that mecamylamine is effective in reducing alcohol consumption and preference, and nicotinic-receptor-based drugs could further be explored as potential treatments for alcoholism.

Lobeline, a nicotinic partial agonist attenuates alcohol consumption and preference in male C57BL/6J mice

Lobeline is a partial nicotinic agonist and is currently being investigated as a therapeutic drug for several addictive disorders particularly for smoking cessation. The present study evaluated the effects of repeated (continuous and recurring) administration of lobeline on alcohol consumption (10% alcohol vs. water) and alcohol preference using a 2-bottle choice test procedure. Male C57BL/6J mice were individually housed and acclimatized to 10% alcohol. Immediately following the last day of alcohol acclimatization and attainment of consistent drinking pattern, mice (n=5/group) received subcutaneous injections of lobeline (3, 5, or 10 mg/kg) or saline. Groups received either repeated-recurring (3 injections, given every other day) or repeated-continuous (daily injections for 5 days) subcutaneous injections of lobeline. Fluid consumption (alcohol and water) was recorded daily. Results showed that lobeline significantly reduced alcohol consumption and alcohol preference during the repeated (recurring and continuous) administration phases, while total fluid consumption remained unchanged. These results provide support that nicotinic receptor based drugs may be useful as potential treatments for alcoholism.

Difluoromethylornithine (DFMO) reduces deficits in isolation-induced ultrasonic vocalizations and balance following neonatal ethanol exposure in rats

Neonatal ethanol (EtOH) exposure is associated with central nervous system dysfunction and neurotoxicity in rats. Increases in polyamine levels have been implicated as one underlying mechanism for some of EtOH's effects on the developing brain. In this study we addressed whether the inhibition of polyamine biosynthesis by alpha-difluoromethylornithine (DFMO) could reduce behavioral deficits induced by early EtOH exposure. Male and female rat pups received ethanol (6 g/kg/day EtOH i.g.), or isocaloric maltose (control) from postnatal days (PND) 1-8. On PND 8, animals were injected with either saline or DFMO (500 mg/kg, s.c.) immediately following the final neonatal treatment. Subjects were tested for isolation-induced ultrasonic vocalizations (USV) on PND 16; spontaneous activity in an open field apparatus on PND 20 and 21; and balance on PND 31. Animals exposed to EtOH neonatally displayed an increased latency to the first USV and reduced frequencies of USV, hyperactivity and preference for the center of the open field and poorer balance relative to controls. DFMO minimized these deficits in latency to the first USV and balance. These data provide further support that polyamines play a role in some of the functional deficits associated with EtOH exposure during early development and that reducing polyamine activity can improve outcome.

Alcohol withdrawal-induced hippocampal neurotoxicity in vitro and seizures in vivo are both reduced by memantine

BACKGROUND

The ethanol withdrawal (EWD) syndrome is typically treated using benzodiazepines such as diazepam. However there is concern that benzodiazepines may not prevent neurotoxicity associated with EWD. Antagonists of glutamate/N-Methyl-D-Aspartate receptors (NMDARs) such as MK801 have been shown to be effective against both EWD-induced neurotoxicity in vitro and seizures in vivo. However, most of these agents have adverse side effects. An exception is the moderate affinity NMDAR channel blocker memantine, used in Alzheimer's dementia. The present studies examined the ability of memantine to protect against EWD-related toxicity in vitro and seizures in vivo.

METHODS

Organotypic hippocampal slice cultures from neonatal rat pups were treated starting at 15 days in vitro with 100 mM ethanol for 10 days followed by a 24-hour EWD period. During the 24-hour EWD period cultures were treated with memantine (15 or 30 microM). MK801 (10 microM) was utilized as a positive control. For the in vivo studies, the ability of memantine (2, 5, 10, and 15 mg/kg) to reduce convulsions was analyzed in Swiss-Webster mice using the handling induced convulsion test paradigm.

RESULTS

In vitro studies demonstrated that memantine is effective at blocking EWD-induced neurotoxicity. In vivo experiments showed that memantine also significantly reduced convulsions induced by EWD in mice.

CONCLUSIONS

Memantine may be of therapeutic value during alcohol detoxification by virtue of its having neuroprotective effects in addition to anti-seizure activity. The potential role of memantine in treatment of alcoholism is deserving of further study.

Topiramate attenuates the stress-induced increase in alcohol consumption and preference in male C57BL/6J mice

Stress increases the risk for alcohol abuse and relapse behaviors. However, there are hardly any medications to counteract stress-induced alcoholism and relapse behaviors. The present study examined the effects of topiramate (intraperitoneal injections of 10, 20, and 30 mg/kg) in its ability to attenuate alcohol consumption on exposure to restraint stress in C57BL/6J mice on a 2-choice test procedure. Mice were either restrained for 1h/day for 5 successive days or left unrestrained. Subsequently, the effects of topiramate were studied in post-restraint days. Results showed that restrained animals increased alcohol consumption and alcohol preference significantly compared to control group on day 5. On post-restraint days, topiramate reduced alcohol consumption and alcohol preference on days 2-5 compared to saline. This experiment suggests that one mechanism of topiramate in reducing alcohol consumption and alcohol preference may involve an interaction with stress.

Acamprosate attenuates the handling induced convulsions during alcohol withdrawal in Swiss Webster mice

In the present study, we examined the effects of acamprosate for its ability to reduce handling induced convulsions (HICs) during alcohol withdrawal. Diazepam was used as a positive control. Swiss Webster male mice received three daily IP injections of alcohol (2.5 g/kg) or alcohol (2.5 g/kg)+methylpyrazole (4-MP) (9 mg/kg). (4-MP, being an alcohol dehydrogenase inhibitor slows down the breakdown of alcohol. 4-MP in combination with alcohol exhibits a dramatic increase in blood alcohol level compared to alcohol alone). Ten hours following the last alcohol injection, the mice were picked up by the tail and examined for their seizure susceptibility (HICs). Diazepam, a benzodiazepine known to reduce seizures during alcohol withdrawal, significantly reduced these HICs at doses of 0.25, 0.5 and 1 mg/kg (p's<0.001). Acamprosate, an anti-relapse compound used clinically in newly abstinent alcoholics, also reduced these HICs at doses of 100, 200 and 300 mg/kg (p's<0.05). This study supports the use of acamprosate during periods of alcohol withdrawal as well as during abstinence.

Age and gender differences in response to neonatal ethanol withdrawal and polyamine challenge in organotypic hippocampal cultures

BACKGROUND

Polyamines are synthesized and released in high concentrations during CNS development. These agents can potentiate N-methyl-D-aspartate receptor (NMDAR) function and appear to play an important role in CNS development. Previous work has shown that polyamine release is increased during ethanol withdrawal (EWD). This likely promotes NMDAR overactivity and contributes to neurotoxicity during EWD, however, little is known regarding such effects in early neonatal brain. The present study compared the effects of EWD and polyamine exposure on toxicity in hippocampal slice cultures derived from postnatal day 2 (PND 2) or postnatal day 8 (PND 8) day-old rats. Due to changes in NMDAR subtypes and response to polyamines, we predicted that slices taken from PND 2 pups would be more sensitive to EWD and polyamine challenge.

METHODS

Organotypic hippocampal slice cultures were obtained from neonatal rats either 2 or 8 days of age (PND 2 or PND 8). Five days after explantation, cultures were exposed to ETOH (50 mM- typically subthreshold for EWD induced cell death) for 10 days and then withdrawn from ETOH for 24-hour in the presence of 100 microM of the polyamine spermidine and/or 100 microM ifenprodil, an NMDAR antagonist that blocks the NMDAR that is the most sensitive to polyamine modulation. Cytotoxicity was measured after 24-hour by visualization of propidium iodide (PI) fluorescence.

RESULTS

There were clear age and gender-dependent differences in response to EWD and to polyamines. EWD produced significant increases in PI uptake in all subregions (CA1, CA3 and DG) of cultures derived from PND 2 pups, but not PND 8 pups. Exposure of cultures to spermidine for 24-hour also produced significant increases in cytotoxicity in all 3 regions of PND 2 cultures with no gender differences. In contrast, there were both gender and region-specific differences in response to spermidine in cultures from PND 8. While the CA1 region of both sexes displayed increased cytotoxicity following spermidine exposure, only females showed increased cytotoxicity in the CA3 region while the DG appeared relatively insensitive to spermidine. Exposure to spermidine during EWD produced enhanced toxicity in all 3 hippocampal subregions in tissue from both PND 2 and PND 8 rats and this was reduced or prevented by co-exposure to ifenprodil. Of interest, the PND 2 hippocampus was significantly more sensitive than the PND 8 hippocampus to the toxic effects of EWD and to spermidine during EWD in the DG and CA3 regions.

CONCLUSIONS

Hippocampal slice cultures derived from PND 2 rats were more sensitive to the toxic effects of both EWD and EWD + spermidine exposure than were those derived from PND 8 rats. These findings are similar to recent behavioral data collected from our lab showing greater sensitivity to ETOH's behavioral teratogenic effects when ETOH exposure in vivo occurred during the first postnatal week relative to the second postnatal week. Ifenprodil's ability to block the toxic effects of spermidine during EWD suggests that excess activity of NR2B subunits of the NMDAR contributed to the excitatory and cytotoxic effects of EWD plus spermidine. While no sex differences in toxicity were observed in cultures taken from pups during the first postnatal week, these data do suggest that later in neonatal life (i.e., the second postnatal week), the female hippocampus may be more sensitive to polyamine-induced neurotoxicity than males.

Topiramate (Topamax) reduces conditioned abstinence behaviours and handling-induced convulsions (HIC) after chronic administration of alcohol in Swiss-Webster mice

Topiramate has emerged as one of the promising drugs for the treatment of alcoholism and alcohol addiction. Recent studies have shown that topiramate reduces harmful drinking and initiates abstinence in humans, but little is known as to why this drug is effective.

AIMS

In the present study, we examined the effects of topiramate in reducing convulsions during alcohol withdrawal using a procedure called the handling-induced convulsion (HIC) test in male Swiss-Webster mice. In addition, we examined the ability of topiramate to reduce alcohol conditioned and anxiety related behaviours during conditioned abstinence using the elevated plus maze (EPM) test.

METHODS

HICs were examined 10 h after the 3rd daily alcohol (2.5 g/kg; 20% w/v)+4 methylpyrazole (4MP) (9 mg/kg) intraperitoneal (i.p.) injection with topiramate (0, 10 or 20 mg/kg ip) administered 30 min before testing. In the EPM, alcohol (1.75 g/kg; 20%, i.p.) or saline was administered daily for 9 days and subjects were immediately placed on the maze. Anxiety related behaviours included the amount of time spent and number of entries in the open or closed arms and grooming bouts, and conditioned behaviours including the stretched-attend posture were examined 24 h after the last day of alcohol injection.

RESULTS

Topiramate (10 and 20 mg/kg) significantly reduced HIC scores (P<0.05) compared to the alcohol/saline group. In the EPM, topiramate (20 mg/kg) reduced the stretched-attend postures (P<0.001) compared to the alcohol/saline group.

CONCLUSION

These findings suggest that topiramate reduces HICs during alcohol withdrawal and alcohol-conditioned behaviours during conditioned abstinence in Swiss-Webster mice.

Methamphetamine exposure antagonizes N-methyl-D-aspartate receptor-mediated neurotoxicity in organotypic hippocampal slice cultures

Glutamatergic systems have been increasingly recognized as mediators of methamphetamine's (METH) pharmacological effects though little is known about the means by which METH interacts with glutamate receptors. The present studies examined effects of METH (0.1-100 microM) on [3H]MK-801 binding to membranes prepared from adult rat cortex, hippocampus and cerebellum, as well as the neurotoxicity produced by 24-h exposure to N-methyl-D-aspartate (5-10 microM; NMDA) employing organotypic hippocampal slice cultures of neonatal rat. Co-incubation of [3H]MK-801 with METH (0.1-100 microM) did not reduce dextromethorphan (1 mM)-displaceable ligand binding. Exposure of slice cultures to NMDA for 24-h produced increases in uptake of the non-vital fluorescent marker propidium iodide (PI) of 150-500% above control levels, most notably, in the CA1 region pyramidal cell layer. Co-exposure to METH (>1.0 microM) with NMDA (5 microM) reduced PI uptake by approximately 50% in each subregion, though the CA1 pyramidal cell layer was markedly more sensitive to the protective effects of METH exposure. In contrast, METH exposure did not reduce PI uptake stimulated by 24-h exposure to 10 microM NMDA. Co-exposure to the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid (20 microM) prevented toxicity produced by exposure to 5 or 10 microM NMDA. These findings indicate that the pharmacological effects of short-term METH exposure involve inhibition of NMDA receptor-mediated neuronal signaling, not reflective of direct channel inhibition at an MK-801-sensitive site.

Potential Value of Changes in Cell Markers in Organotypic Hippocampal Cultures Associated With Chronic EtOH Exposure and Withdrawal: Comparison with NMDA-Induced Changes

BACKGROUND

Previous studies have shown that withdrawal from ethanol (EtOH) exposure induces neuronal damage, as indicated by propidium iodide (PI) uptake, in organotypic hippocampal slice cultures. This is prevented by MK801, suggesting that damage is "excitotoxic," resulting from activation of N-methyl-d-aspartate (NMDA) receptors by endogenous glutamate. To avoid reliance on a single indicator, and to enable assessment of recovery from the EtOH withdrawal (EWD) insult, we assessed changes in cell markers for neurons and glia, as well as cell division, following either EWD or NMDA challenge (as a positive control).

METHODS

Organotypic cultures from postnatal day (PND) 8 rats were cultured for 5 days before exposure to EtOH (mean concentration approximately 65 mM) for 10 days before EWD. Cultures of the same "days in vitro" age (DIV16) were exposed to NMDA (200 microM) for 1 hour. Neuronal injury was visualized using PI and indices of neurons, glia, or cell division were measured at intervals up to 10 days following the neurotoxic insults. Each time point and measurement used separate slice cultures, and these were treated as separate experiments with paired controls. Regional neuronal content was assessed by neuronal nuclear protein (NeuN) and calbindin D28k (Calb), glial content by glial fibrillary acidic protein (GFAP), and cell division by bromodeoxyuridine (BrdU) incorporation, all measured immunohistochemically.

RESULTS

Chronic exposure to EtOH was associated with a dramatic reduction in BrdU incorporation in all regions of cultures. Propidium iodide fluorescence in the CA1 region was elevated significantly after EWD and more so after NMDA challenge. Reduced immunoreactivity (IR) of NeuN and Calb suggested that loss of neurons resulted from the EWD insult. Bromodeoxyuridine incorporation was initially depressed even further by EWD, but had returned to control levels after 3 days. In contrast, following NMDA insult, BrdU incorporation was significantly and persistently elevated above control levels after 3 days. Glial fibrillary acidic protein was reduced immediately after both EWD and NMDA challenge. Several days after EWD, expression of neuronal and glial markers, although variable, had generally returned to control levels. In contrast, NeuN IR remained significantly reduced after NMDA challenge.

CONCLUSIONS

In general, the use of additional markers supports data obtained with PI uptake alone and suggests that neurons (and glia) are lost from the culture following EWD or NMDA challenge. These cell markers recover several days after EWD, but it is unclear whether functional recovery accompanies these changes. If the dramatic effect of EtOH exposure and EWD on BrdU incorporation reflects reduced neuro- and gliogenesis, it is likely that this adversely affects long-term recovery from EWD. Finally, some markers showed significant and consistent changes after EWD, whereas others did not. This information may facilitate the use of this model in evaluation of potential medications that protect against and/or promote recovery from neurotoxicity.

A 24 h corticosterone exposure exacerbates excitotoxic insult in rat hippocampal slice cultures independently of glucocorticoid receptor activation or protein synthesis

Elevations in circulating concentrations of glucocorticoids (GC) may increase the expression and/or sensitivity of ionotropic transmitter receptors in brain. For example, recent evidence suggests that acute and chronic GC exposure may alter the number and/or function of N-methyl-D-aspartate (NMDA)-type glutamate receptors, effects that may sensitize the brain to excitotoxic insults. The present studies examined the ability of short-term (24 h) corticosterone (CORT) exposure to potentiate NMDA-induced cytotoxicity in rat hippocampal slice cultures. Additional studies evaluated the role of mineralocorticoid (MR) and glucocorticoid receptor (GR) function, as well as de novo protein synthesis, in potentiation of toxicity by corticosterone exposure. Hippocampal slice cultures were exposed to NMDA (20 microM) for 24 h with cytotoxicity assessed by fluorescent detection of propidium iodide uptake. Exposure to NMDA caused significant propidium iodide uptake in each hippocampal region, while 24 h CORT (0.001-1 microM) exposure alone did not significantly increase propidium iodide uptake. Co-exposure of cultures to CORT and NMDA synergistically increased propidium iodide uptake in each hippocampal region, effects that were prevented by co-exposure to a non-toxic concentration of MK-801 (20 microM). In contrast, 24 h exposure with the MR antagonist spironolactone (1-10 microM), the GR antagonist RU-486 (1-10 microM), or the protein synthesis inhibitor cycloheximide (1 microM) failed to reduce the significant increase in propidium iodide uptake. These data suggest that relatively brief elevations in CORT levels may sensitize the hippocampus to injury independently of GC receptor activity and protein synthesis.

Corticosterone and dexamethasone potentiate cytotoxicity associated with oxygen-glucose deprivation in organotypic cerebellar slice cultures

Many patients display elevated levels of serum cortisol following acute ischemic stroke. Given that glucocorticoids may potentiate some forms of insult, these studies examined the effects of corticosterone or dexamethasone exposure on cytotoxicity following oxygen-glucose deprivation in the cerebellum, a brain region susceptible to stroke. In organotypic cerebellar slice cultures prepared from neonatal rat pups, 90-min of oxygen-glucose deprivation at 15 days in vitro resulted in significant cytotoxicity at 24-, 48-, and 72-h post-oxygen-glucose deprivation, as measured by uptake of propidium iodide. Exposure of cultures following oxygen-glucose deprivation to the antioxidant trolox (500 microM), but not to the glucocorticoid receptor antagonist RU486 (10 microM), completely blocked oxygen-glucose deprivation-induced cytotoxicity. Corticosterone (1 microM) or dexamethasone (10 microM) exposure alone did not significantly increase propidium iodide uptake above levels observed in control cultures. However, corticosterone or dexamethasone exposure after oxygen-glucose deprivation potentiated oxygen-glucose deprivation-mediated propidium iodide uptake at each time point. Trolox, as well as RU486, co-exposure of cultures to corticosterone or dexamethasone after oxygen-glucose deprivation abolished all cytotoxicity. In conclusion, these data demonstrated that glucocorticoid exposure modulated oxygen-glucose deprivation-mediated propidium iodide uptake, which likely involved glucocorticoid receptor activation and pro-oxidant effects.

Corticosterone Increases Damage and Cytosolic Calcium Accumulation Associated With Ethanol Withdrawal in Rat Hippocampal Slice Cultures

BACKGROUND

Evidence suggests that stress hormones (i.e., glucocorticoids) may be increased during acute or chronic consumption of ethanol and during withdrawal from ethanol consumption, effects that may contribute to the development of cognitive impairment. The goal of the current studies was to examine the hypothesis that increased glucocorticoid levels in conjunction with ethanol exposure and withdrawal may cause hippocampal damage.

METHODS

Organotypic hippocampal slice cultures were exposed to 50 mM ethanol for 10 days and withdrawn for 1 day. After withdrawal, cytotoxicity and cytosolic Ca2+ accumulation were measured using the nucleic acid stain propidium iodide and Calcium Orange, AM, respectively. Cultures were also treated with nontoxic concentrations of corticosterone (0.001-1 microM) during ethanol exposure and withdrawal or only during withdrawal. Additional cultures were coexposed to corticosterone and RU486 (0.1-10.0 microM), spironolactone (0.1-10.0 microM), or MK-801 (20 microM) during ethanol exposure and/or withdrawal.

RESULTS

Ethanol withdrawal did not increase propidium iodide fluorescence and cytosolic Ca2+ levels. However, significant increases in propidium iodide fluorescence and in cytosolic Ca2+ accumulation were observed in cultures when corticosterone (> or = 100 nM) was exposed during ethanol treatment and/or withdrawal. These effects of corticosterone on ethanol withdrawal were attenuated by RU486 and MK-801 but not by spironolactone coexposure.

CONCLUSIONS

This report demonstrated that corticosterone exposure during ethanol treatment and/or withdrawal resulted in significant hippocampal damage, possibly via activation of glucocorticoid receptors and enhancement of the glutamatergic cascade. The findings from these studies suggest that glucocorticoids contribute to the neuropathological consequences of alcohol dependence in humans.

Thiamine deficiency in the pathogenesis of chronic ethanol-associated cerebellar damage in vitro

Nutritional deficiencies associated with long-term ethanol consumption may cause neuronal damage in ethanol-dependent individuals. Thiamine deficiency, in particular, is thought to contribute to ethanol-associated cerebellar degeneration, although damage may occur in adequately nourished alcoholics. Thus, the present study examined the effects of thiamine depletion and ethanol exposure on cytotoxicity in rat cerebellum. Organotypic cerebellar slice cultures were treated starting at 25 days in vitro with 100 mM ethanol for 11 days or 10 days followed by a 24-h withdrawal period. This exposure paradigm has previously been shown in hippocampal slice cultures to result in spontaneous cytotoxicity upon ethanol withdrawal. Additional cerebellar cultures were exposed to the thiamine depleting agent pyrithiamine (10-500 microM) for 10 or 11 days, some in the presence of ethanol exposure or withdrawal. Other cultures were co-exposed to thiamine (1-100 microM), 500 microM pyrithiamine, and ethanol for 10 or 11 days. The results demonstrated that neither 11-day ethanol treatment nor withdrawal from 10-day exposure significantly increased cerebellar cytotoxicity, as measured by propidium iodide fluorescence. The 11-day treatment with 100 or 500 microM pyrithiamine significantly increased propidium iodide fluorescence approximately 21% above levels observed in control tissue. Cultures treated with both ethanol (11 days or 10 days plus withdrawal) and 500 microM pyrithiamine displayed a marked increase in cytotoxicity approximately 60-90% above levels observed in control cultures. Pyrithiamine and ethanol-induced cytotoxicity was prevented in cultures co-exposed to thiamine (10-100 microM) for the duration of pyrithiamine treatment. Findings from this report suggest that the cerebellum may be more sensitive to the toxic effects of thiamine deficiency, as compared with alcohol withdrawal, associated with alcohol dependence.

Choline exposure reduces potentiation of N-methyl-D-aspartate toxicity by corticosterone in the developing hippocampus

Exposure to high levels of glucocorticoids (GCs) may adversely affect neuronal viability, particularly in the developing hippocampus, via increased function or sensitivity of N-methyl-D-aspartate (NMDA)-type glutamate receptors. Conversely, choline supplementation in the developing brain may reduce the severity of subsequent insult. The present studies aimed to examine the extent to which short-term exposure to high concentrations of corticosterone would produce neuronal injury mediated by NMDA receptor activity. These studies also assessed the ability of choline to prevent this form of injury via interactions with nicotinic acetylcholine receptors (nAChRs) expressing the alpha7 subunit. Organotypic hippocampal slice cultures derived from neonatal rat were pre-treated for 72 h with corticosterone (100 nM) alone or with choline (0.1-10 mM), prior to a brief (1 h) NMDA exposure (5 microM). NMDA exposure produced significant cellular damage, reflected as increased fluorescence of the non-vital marker propidium iodide, in the CA1 region. While exposure to corticosterone alone did not produce damage, pre-treatment of cultures with corticosterone markedly exacerbated NMDA-induced toxicity. Pre-treatment with choline (> or =1 mM) alone or in combination with corticosterone markedly reduced subsequent NMDA toxicity, effects blocked by co-exposure to methyllycaconitine (100 nM), an antagonist active at nAChRs expressing the alpha7 subunit. These data suggest that even short-term exposure to high concentrations of GCs may adversely affect neuronal viability and that choline supplementation protects the brain from NMDA receptor-mediated damage, including that associated with hypercortisolemia.

Challenges to medications development in treating alcohol dependence: an international perspective

Few medications for treating alcohol dependence exist. Greater partnership is needed between academia and the pharmaceutical industry to develop, licence and market efficacious medications for treating alcohol dependence. Methodologies that span the divide between preclinical and large-scale clinical studies need to be developed in order to provide sufficient information on safety, toleration, drug-interaction profile and efficacy, with which to guide development decisions. Due to the heterogeneous nature of alcohol dependence, the effort of developing an efficacious medication is likely to be enhanced by clearer choices about the characteristics of the population. Careful consideration of potential mechanism of action of the putative therapeutic medication should enable the appropriate choice of drinking endpoint. The pharmaceutical industry in collaboration with academia might need to develop new approaches to determining appropriate treatment endpoints with regulatory bodies. The investment risk to industry should be appraised not only in terms of the rather poor results of previous marketing efforts but with a view to the opportunity to penetrate a potentially enormous and largely untapped market.

Hippocampal CA1 region neurodegeneration produced by ethanol withdrawal requires activation of intrinsic polysynaptic hippocampal pathways and function of N-methyl-D-aspartate receptors

Long-term intake of ethanol produces adaptive alterations in multiple transmitter systems in the hippocampal formation that likely contribute to ethanol withdrawal-induced seizure and excitotoxicity. The present studies were designed to examine the role of N-methyl-d-aspartate receptor activation and cytosolic Ca(2+) accumulation in the neurotoxic effects of ethanol withdrawal. Further, these studies investigated the role of hippocampal network excitation in promoting both Ca(2+) accumulation and neurotoxicity during ethanol withdrawal. Chronic, continuous (11 day) exposure to ethanol (91 mM starting concentration) did not produce neurotoxicity in any region of organotypic hippocampal explants, as measured by uptake of the non-vital fluorescent marker propidium iodide. Withdrawal from chronic (10 day) ethanol exposure was associated with rapid (30 min) and significant increases in intracellular Ca(2+), assessed by visualization of Calcium-Orange fluorescence, in each region of hippocampal explants. However, neurotoxicity was observed 24 h after initiation of withdrawal and was only seen in the cornu ammonis 1 (CA1) region. Exposure to MK-801 (20 microM) at the start of ethanol withdrawal markedly attenuated Ca(2+) entry in all regions, as well as, CA1 region neurodegeneration. Further, treatment of explants with tetrodotoxin (500 nM) as well as surgical transection of mossy fiber or Schaffer collateral projections immediately prior to ethanol withdrawal blocked both regional increases in Ca(2+) accumulation and CA1 neurotoxicity. These data suggest that neurodegeneration observed during ethanol withdrawal is dependent upon polysynaptic propagation of action potentials ("network excitation") and whole-hippocampal excitation of glutamatergic systems.

(−)-nicotine ameliorates corticosterone's potentiation of N-methyl-d-aspartate receptor-mediated cornu ammonis 1 toxicity

Hypercortisolemia, long-term exposure of the brain to high concentrations of stress hormones (i.e. cortisol), may occur in patients suffering from depression, alcoholism, and other disorders. This has been suggested to produce neuropathological effects, in part, via increased function or sensitivity of N-methyl-d-aspartate (NMDA)-type glutamate receptors. Given that cigarette smoking is highly prevalent in some of these patient groups and nicotine has been shown to reduce toxic consequences of NMDA receptor function, it may be suggested that nicotine intake may attenuate the neurotoxic effects of hypercortisolemia. To investigate this possibility, organotypic hippocampal slice cultures derived from rat were pre-treated with corticosterone (0.001-1 microM) alone or in combination with selective glucocorticoid receptor antagonists for 72-h prior to a brief (1-h) NMDA exposure (5 microM). Pre-treatment with corticosterone (0.001-1 microM) alone did not cause hippocampal damage, while NMDA exposure produced significant cellular damage in the cornu ammonis (CA)1 subregion. No significant damage was observed in the dentate gyrus or CA3 regions following NMDA exposure. Pre-treatment of cultures with corticosterone (0.1-1 microM) markedly exacerbated NMDA-induced CA1 and dentate gyrus region damage. This effect in the CA1 region was prevented by co-administration of the glucocorticoid receptor antagonist RU486 (>or=1 microM), but not spironolactone (1-10 microM), a mineralocorticoid receptor antagonist. In a second series of studies, both acute and pre-exposure of cultures to (-)-nicotine (1-10 microM) significantly reduced NMDA toxicity in the CA1 region. Co-administration of cultures to (-)-nicotine (1-10 microM) with 100 nM corticosterone prevented corticosterone's exacerbation of subsequent CA1 insult. This protective effect of (-)-nicotine was not altered by co-exposure of cultures to 10 microM dihydro-beta-erythroidine but was blocked by co-exposure to 100 nM methyllycaconitine, suggesting the involvement of nicotinic acetylcholine receptors possessing the alpha7* subunit. The present studies suggest a role for hypercortisolemia in sensitizing the hippocampal NMDA receptor system to pathological activation and indicate that prolonged nicotine exposure attenuates this sensitization. Thus, it is possible that one consequence of heavy smoking in those suffering from hypercortisolemia may be a reduction of neuronal injury and sparing of cellular function.

Neonatal ethanol exposure produces a hyperalgesia that extends into adolescence, and is associated with increased analgesic and rewarding properties of nicotine in rats

RATIONALE

Drug exposure during CNS development may alter subsequent dependence liability. We postulated that early alcohol exposure might produce persistent alterations in responses to noxious stimuli. Because relief of physical discomfort may be negatively reinforcing, changes in responses to noxious stimuli produced by early alcohol exposure may increase the rewarding properties of nicotine, a potent analgesic. Such factors may contribute to the high level of alcohol and nicotine co-abuse in humans.

OBJECTIVES

The purpose of this study was to determine whether neonatal ethanol exposure in rats altered responses to noxious stimuli, and whether nicotine would then be more rewarding to the alcohol-exposed offspring, perhaps via its analgesic actions.

METHODS

Neonatal rats received ethanol by gavage (5.0 or 6.5 g/kg) on postnatal days (PND) 9-13. An iso-caloric control group was also included. Rats were then tested to assess responsiveness to a mild noxious heat stimulus, as measured in the tail-flick assay (PND 14 and PND 28), for their response to acute analgesic injections of either nicotine or ethanol (PND 28), and for nicotine induced conditioned place preference (CPP) (PND 36).

RESULTS

Neonatal ethanol exposure produced hyperalgesia during the first 24 h after alcohol withdrawal (PND 14) that continued through PND 28. The analgesic effects of 12.5 microg/kg nicotine were enhanced approximately 2-fold in adolescent rats with previous ethanol histories, relative to controls. These ethanol-exposed rats also showed a significant CPP to nicotine, whereas controls showed no CPP.

CONCLUSIONS

Persistent decreases in tail-flick response latencies suggestive of hyperalgesia were observed following neonatal ethanol exposure in the rat. These changes were accompanied by increases in the analgesic and place-conditioning effects of nicotine in adolescence. If similar effects occur in humans, prenatal alcohol exposure may play a role in an increased risk for the rewarding effects and dependence liability of nicotine later in life.

The Neurotoxicity Induced by Ethanol Withdrawal in Mature Organotypic Hippocampal Slices Might Involve Cross-Talk Between Metabotropic Glutamate Type 5 Receptors and N-Methyl-d-Aspartate Receptors

BACKGROUND

We recently reported that the sodium salt of acamprosate (Na-acamprosate) demonstrates the characteristics of an antagonist at metabotropic glutamate type 5 receptors (mGluR5s) rather than at N-methyl-d-aspartate receptors (NMDARs). Because mGluR5s are able to enhance the function of NMDARs, this interplay may be involved in the dysregulation of glutamatergic transmission during ethanol withdrawal. The following studies use organotypic hippocampal slice cultures at a mature age to investigate the potential for this interplay in the neurotoxicity associated with withdrawal from long-term ethanol exposure.

METHODS

At 25 days in vitro, organotypic hippocampal slice cultures prepared from male and female 8-day-old rats were exposed to an initial concentration of 100 mM ethanol for 10 days before undergoing a 24-hr period of withdrawal. The effects of Na-acamprosate; 2-methyl-6-(2-phenylethenyl)pyridine (SIB-1893), a noncompetitive antagonist at mGluR5s; 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester, a noncompetitive antagonist at mGluR1s; dizocilpine (MK-801), a noncompetitive NMDAR antagonist; and staurosporine on the neurotoxicity induced by ethanol withdrawal were assessed by determining differences in propidium iodide uptake. Polypeptide levels of mGluR5s and the NR1 and NR2B subunits of NMDARs were also determined via Western blot analyses after 10 days of ethanol exposure.

RESULTS

Significant neurotoxicity was always evident in the CA1 hippocampal region after a 24-hr withdrawal period. This spontaneous neurotoxicity resulted from intrinsic changes induced by the long-term presence of ethanol. Na-acamprosate (200-1000 microM), SIB-1893 (200-500 microM), MK-801 (20 microM), and staurosporine (200 nM) were all neuroprotective. The polypeptide levels of mGluR5s and NR1 and NR2B subunits of NMDARs were all increased after ethanol exposure; however, the increase in mGluR5s did not achieve statistical significance.

CONCLUSIONS

From this model of long-term ethanol exposure and withdrawal, the functional interplay between mGluR5s and NMDARs might represent a novel target for the prevention of neurotoxicity associated with ethanol withdrawal.

Opposing effects of ethanol and nicotine on hippocampal calbindin-D28k expression

Long-term ethanol exposure produces multiple neuroadaptations that likely contribute to dysregulation of Ca(2+) balance and neurotoxicity during ethanol withdrawal. Conversely, nicotine exposure may reduce the neurotoxic consequences of Ca(2+) dysregulation, putatively through up-regulation of the Ca(2+)-buffering protein calbindin-D(28k). The current studies were designed to examine the extent to which 10-day ethanol exposure and withdrawal altered calbindin-D(28k) expression in rat hippocampus. Further, in these studies, we examined the ability of nicotine, through action at alpha(7)(*)-bearing nicotinic acetylcholine receptors (nAChRs), to antagonize the effects of ethanol exposure on calbindin-D(28k) expression. Organotypic cultures of rat hippocampus were exposed to ethanol (50-100 mM) for 10 days. Additional cultures were exposed to 500 nM (-)-nicotine with or without the addition of 50 mM ethanol, 100 nM methyllycaconitine (an alpha(7)*-bearing nAChR antagonist), or both. Prolonged exposure to ethanol (>/=50 mM) produced significant reductions of calbindin-D(28k) immunolabeling in all regions of the hippocampal formation, even at nontoxic concentrations of ethanol. Calbindin-D(28k) expression levels returned to near-control levels after 72 h of withdrawal from 10-day ethanol exposure. Extended (-)-nicotine exposure produced significant elevations in calbindin-D(28k) expression levels that were prevented by methyllycaconitine co-exposure. Co-exposure of cultures to (-)-nicotine with ethanol resulted in an attenuation of ethanol-induced reductions in calbindin-D(28k) expression levels. These findings support the suggestion that long-term ethanol exposure reduces the neuronal capacity to buffer accumulated Ca(2+) in a reversible manner, an effect that likely contributes to withdrawal-induced neurotoxicity. Further, long-term exposure to (-)-nicotine enhances calbindin-D(28k) expression in an alpha(7)* nAChR-dependent manner and antagonizes the effects of ethanol on calbindin-D(28k) expression.

Polyamines contribute to ethanol withdrawal-induced neurotoxicity in rat hippocampal slice cultures through interactions with the NMDA receptor

BACKGROUND

Several reports demonstrate that withdrawal from long-term ethanol exposure is associated with significant central nervous system neurotoxicity, produced at least in part by increased activity of N-methyl-d-aspartate receptors (NMDARs). Recent evidence suggests that elevations in the synthesis and release of the polyamines spermidine and spermine, which are known modulators of NMDARs, contribute to the increased activity of the receptor during ethanol withdrawal. Therefore, the goal of this investigation was to examine what role, if any, spermidine and spermine have in the generation of ethanol withdrawal-induced neurotoxicity.

METHODS

Neurotoxicity (measured as fluorescence of the cell death indicator propidium iodide, PI), glutamate release (measured by high-performance liquid chromatography analysis), and polyamine concentrations (by high-performance liquid chromatography) were measured in rat hippocampal slice cultures undergoing withdrawal from chronic (10 day) ethanol exposure (100 mM). In addition, the effects of the polyamine synthesis inhibitor di-fluoro-methyl-ornithine (DFMO, 0.1-100 nM) and NMDAR polyamine-site antagonists ifenprodil, arcaine, and agmatine (1 nM-100 microM) on ethanol withdrawal- and NMDA-induced neurotoxicity were measured.

RESULTS

Ethanol withdrawal significantly increased glutamate release (peaking at 18 hr with a 53% increase), increased concentrations of putrescine and spermidine (136% and 139% increases, respectively, at 18 hr), and produced significant cytotoxicity in the CA1 hippocampal region (56% increase in PI staining relative to controls) of the cultures. The cell death produced by ethanol withdrawal was significantly inhibited by ifenprodil (IC(50) = 14.9 nM), arcaine (IC(50) = 37.9 nM), agmatine (IC(50) = 41.5 nM), and DFMO (IC(50) = 0.6 nM). NMDA (5 microM) significantly increased PI staining in the CA1 region of the hippocampal cultures (365% relative to controls), but ifenprodil, arcaine, agmatine, and DFMO all failed to significantly affect this type of toxicity.

CONCLUSIONS

These data implicate a role for polyamines in ethanol withdrawal-induced neurotoxicity and suggest that inhibiting the actions of polyamines on NMDARs may be neuroprotective under these conditions.

Acamprosate inhibits the binding and neurotoxic effects of trans-ACPD, suggesting a novel site of action at metabotropic glutamate receptors

BACKGROUND

Several reported effects of acamprosate within the glutamatergic system could result from interactions with metabotropic glutamate receptors (mGluRs). The following experiments were performed to determine whether acamprosate could compete with trnas-ACPD (+/--1-aminocyclopentane-trans-1,3-dicarboxylic acid, an equimolecular mixture of 1S, 3R and 1R, 3S-ACPD and an agonist at both group I and group II mGluRs) sensitive binding sites and protect against trans-ACPD-induced neurotoxicity in organotypic hippocampal slice cultures.

METHODS

A P2 membrane preparation of cortices, cerebellums, and hippocampi of adult, male Sprague Dawley rats was used to determine the abilities of N-methyl-D-aspartic acid (NMDA) and trans-ACPD to displace [3H]glutamate in both the absence and the presence of the sodium salt of acamprosate (sodium mono N-acetyl homotaurine or Na-acamprosate). A comparison of the effects of 100 microM guanosine 5'-triphosphate on unlabeled glutamate, trans-ACPD, and Na-acamprosate was performed in the same paradigm. For the neurotoxicity studies, organotypic hippocampal slice cultures from male and female 8-day-old neonatal rats were exposed to either 500 microM -ACPD or 50 microM NMDA for 24 hr in normal culture medium containing serum on day 20 in vitro. The effects of Na-acamprosate and 2-methyl-6-(2-phenylethenyl)pyridine (SIB-1893), a noncompetitive antagonist at metabotropic type 5 receptors (mGluR5s), were assessed by determining differences in propidium iodide uptake as compared with neurotoxic challenges alone.

RESULTS

Na-acamprosate displaced 31% of [3H]glutamate but did not compete with NMDA for [3H]glutamate binding sites. Na-acamprosate displayed total competition with trans-ACPD. The presence of 100 microM guanosine 5'-triphosphate differentially altered the displacing capabilities of the two mGluR agonists, unlabeled glutamate and trans-ACPD, as compared with Na-acamprosate. Na-acamprosate (200-1000 microM) and SIB-1893 (20-500 microM) both were neuroprotective against trans-ACPD induced neurotoxicity that likely results from mGluR potentiation of NMDARs. In turn, Na-acamprosate and SIB-1893 had no direct effects on NMDA-induced neurotoxicity.

CONCLUSIONS

Na-acamprosate demonstrates the binding and functional characteristics that are consistent with a group I mGluR antagonist. The functional similarities between Na-acamprosate and SIB-1893 support an interaction of Na-acamprosate at mGluR5s. The neuroprotective properties of acamprosate and possibly its ability to reduce craving in alcohol-dependent patients may result from its alterations in glutamatergic transmission through mGluRs.

Neurotoxic effects of the human immunodeficiency virus type-1 transcription factor Tat require function of a polyamine sensitive-site on the N-methyl-D-aspartate receptor

Human immunodeficiency virus type-I (HIV-1) infection is often associated with neuronal loss in cortical and subcortical regions that may manifest as motor dysfunction and dementia. The function of the HIV-1 transcription protein Tat and subsequent activation of N-methyl-D-aspartate receptors (NMDAr) have been implicated in this form of neurodegeneration. However, it is unclear if Tat interacts directly with the NMDAr and the role of specific NMDAr subunit composition in mediating effects of Tat is also unclear. The present studies examined the ability of HIV-1 Tat1-72 protein (10 pM-1.0 microM) to displace [3H]MK-801 binding and to attenuate spermidine-induced potentiation of this binding in rat brain homogenate comprised of cerebellum, hippocampus, and cerebral cortex. The role of NMDAr polyamine-site function in the neurotoxic effects of Tat was determined using organotypic hippocampal slice cultures. Binding of [3H]MK-801 in adult rat brain homogenate was not reduced by Tat at concentrations below 1 microM. Tat potently inhibited the potentiation of [3H]MK-801 binding produced by co-exposure of membranes to the NMDAr co-agonist spermidine (IC(50)=3.74 nM). In hippocampal explants, Tat produced neurotoxicity in the CA3 and CA1 pyramidal cell layers, as well as in the dentate gyrus, that was significantly reduced by co-exposure to MK-801 (20 microM) and the NMDAr polyamine-site antagonist arcaine (10 microM). Exposure to the HIV-1 Tat deletion mutant (Tatdelta31-61) did not produce neurotoxicity in hippocampal explants. These data suggest that the neurotoxic effects of HIV-1 Tat are mediated, in part, by direct interactions with a polyamine-sensitive site on the NMDAr that positively modulates the function of this receptor.

Radioligand binding studies reveal agmatine is a more selective antagonist for a polyamine-site on the NMDA receptor than arcaine or ifenprodil

Ifenprodil, arcaine and agmatine have all been reported to inhibit the NMDA receptor by actions at polyamine-sites, however the specific sites with which these compounds interact is unknown. Here we used radioligand binding of [3H]MK-801 to a membrane preparation from rat cerebral cortex to investigate the interactions of these compounds with the NMDA receptor complex. In the absence of exogenous polyamines, agmatine reduced [3H]MK-801 binding only at concentrations over 500 micro M, as opposed to the putative polyamine-site antagonists arcaine and ifenprodil which directly reduce ligand binding at much lower concentrations (5 micro M) in the absence of polyamines. In our studies, all three compounds significantly reduced spermidine-potentiated [3H]MK-801 binding, however agmatine was the only compound effective at concentrations below those that produced direct inhibition of [3H]MK-801 binding. Under these conditions, agmatine had a K(i)=14.8 micro M for spermidine-potentiated [3H]MK-801 binding and displayed characteristics of a competitive antagonist. Agmatine, as well as ifenprodil and arcaine, also displaced [3H]spermidine from rat cortical membranes at concentrations similar to those that were effective at reducing spermidine-potentiated [3H]MK-801 binding. In conclusion, these data suggest that agmatine reduces the potentiating effects of polyamines by competitive antagonism at a specific site on the NMDA receptor complex, and that these actions of agmatine differ from those of ifenprodil and arcaine.

Nicotine exposure reduces N-methyl-D-aspartate toxicity in the hippocampus: relation to distribution of the alpha7 nicotinic acetylcholine receptor subunit

BACKGROUND

Exposure to nicotine has been shown to promote neuronal survival after excitotoxic insult to the brain. The role of specific nicotinic acetylcholine receptors (nAChRs) subtypes in mediating this effect is not well understood, however. Examination of distinct receptor subtypes in promoting neuronal survival is of importance not only in understanding the regulation of necrotic cell death but potentially in the development of novel pharmacological therapies that may reduce this form of neurodegeneration.

MATERIAL AND METHODS

The present studies examined the relationship between distribution of alpha7 subunit-bearing nAChRs, using autoradiographic imaging of [125I]alpha-bungarotoxin binding, and protective effects of nicotine against excitotoxic damage. Organotypic cultures of rat hippocampus were exposed to N-methyl-D-aspartate (NMDA; 200 microM) for 1 hour with or without (-)-nicotine (0.1-10 microM) and the alpha7 nAChR antagonist methyllycaconitine (MLA; 100 nM). Neuronal damage was assayed 24 hours later by observation of uptake of the non-vital fluorescent marker propidium iodide.

RESULTS

NMDA exposure produced significant neurotoxicity, particularly in pyramidal cell layers of CA3 and CA1, that was prevented by co-exposure to MK-801 (10 microM). Localization of the alpha7 subunit was varied with no binding observed in the dentate gyrus, low density in the CA3 and CA1 regions, and dense binding in the hilus. In all regions, co-exposure to (-)-nicotine (0.1-10.0 microM) significantly reduced (>30%) the cytotoxic consequences of NMDA insult. This protective effect was inhibited by co-exposure to MLA in the dentate and CA3, and to a lesser extent, CA1 regions.

CONCLUSIONS

The neuroprotective effect of nicotine against excitotoxicity, then, is not directly related to alpha7 subunit localization in the hippocampus.

Chronic nicotine exposure reduces N-methyl-D-aspartate receptor-mediated damage in the hippocampus without altering calcium accumulation or extrusion: evidence of calbindin-D28K overexpression

Neuronal accumulation of excess Ca2+ has been implicated in cellular death following several forms of physical and chemotoxic insult. Recent studies have suggested that exposure to agonists at brain nicotinic acetylcholine receptors reduces cytotoxic consequences of increased intracellular Ca2+ following some insults. In the present study, the ability of chronic exposure to (-)-nicotine to reduce cytotoxicity and attenuate increases in intracellular Ca2+ caused by exposure to N-methyl-D-aspartate were examined in organotypic cultures of rat hippocampus. Cultures were exposed to nicotine (0.1-10.0 microM) for five days prior to excitotoxic insult with N-methyl-D-aspartate. Exposure to N-methyl-D-aspartate produced concentration-dependent increases in both accumulation of 45Ca and in early and delayed cell death in the CA1, CA3 and dentate gyrus regions of cultures. The CA1 region of the hippocampus displayed the greatest sensitivity to cytotoxic effects of N-methyl-D-aspartate exposure; however, this regional difference was not associated with increased accumulation of 45Ca. Prior exposure to nicotine markedly attenuated N-methyl-D-aspartate-induced early and delayed cell death in each hippocampal region at concentrations as low as 0.1microM. However, nicotine did not alter the initial N-methyl-D-aspartate-stimulated influx of 45Ca or enhance extrusion of accumulated 45Ca measured at several time-points after insult. Five days of exposure to nicotine markedly increased immunoreactivity of the Ca2+ binding protein calbindin-D28K in each region of hippocampal cultures, effects reduced by mecamylamine co-exposure. These findings suggest that the potent protective effects of chronic nicotine exposure against neuronal overexcitation are not likely attributable to attenuations of Ca2+ accumulation, but are likely related to increased buffering of accumulated Ca2+.

Role of polyamines and NMDA receptors in ethanol dependence and withdrawal

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chair was John M. Littleton. The presentations were (1) Examination of ethanol spermine and acamprosate actions on native and recombinant NMDA receptors, by David Lovinger; (2) Ethanol inhibition of NMDA neurotoxicity on the polyamine site in cerebellar granule cells, by Sture Liljequist; (3) Alterations in expression of NMDA receptor subunits during ethanol exposure and withdrawal, by Raj Ticku; (4) Alterations in polyamine synthesis and release as a potential mechanism for ethanol dependence and withdrawal, by Izuru Matsumoto; (5) The role of polyamines in neurotoxicity induced by alcohol withdrawal in vitro, by John Littleton; and (6) Agmatine reduces some of the effects of "third trimester" alcohol exposure using a rodent model, by Susan Barron.

Endogenous indoles as novel polyamine site ligands at the N-methyl-D-aspartate receptor complex

High-throughput ligand displacement screens of a series of endogenous indoles revealed that tryptamine, serotonin and 5-methoxytryptamine readily displace [3H]spermidine and [3H]MK-801 from their respective binding sites in rat brain homogenate. These data, coupled with their potent inhibition of spermidine-potentiated [3H]MK-801 binding, suggest that certain endogenous indoles may act as ligands to one or more polyamine binding sites in the brain, including those on the N-methyl-D-aspartate receptor complex.