Novel antagonists of alcohol inhibition of l1-mediated cell adhesion: multiple mechanisms of action

The leaves of Crataeva nurvala Buch-Ham. modulate locomotor and anxiety behaviors possibly through GABAergic system

Background

Crataeva nurvala Buch-Hum is an indigenous herb, extensively used in traditional medicines of the South Asian countries to treat inflammation, rheumatic fever, gastric irritation, and constipation. Despite this wide range of uses, very little information is known regarding its effects on the central nervous system (CNS). Therefore, this study evaluated the neuropharmacological properties of methanolic extract of Crataeva nurvala leaves (MECN) using a number of behavioral models in animals. This study also identified potentially active phytochemicals in MECN.

Methods

Following MECN administration (at 50, 100 and 200 mg/kg; b.w.) the animals (male Swiss albino mice) were employed in hole-cross test (HCT), open field test (OFT), and rota-rod test (RRT) to evaluate sedative properties, where anxiolytic activities were investigated using elevated plus maze (EPM), light dark box (LDB), and marble burying test (MBT). The involvement of GABAergic system was evaluated using thiopental sodium (TS)-induced sleeping time determination test. Moreover, colorimetric phytochemical tests as well as GC/MS-MS were also conducted to define the phytochemical constituents of MECN.

Results

MECN possesses sedative properties indicated through the dose-dependent inhibition of locomotor activities of the animals in HCT and OFT and motor coordination in RRT. MECN also exhibited prominent anxiolytic properties through decreased burying behavior in MBT, increased time spent and transitions in open arm of EPM, and increased time spent in light compartment of LDB. In addition, the treatments potentiated TS-mediated hypnosis indicating a possible participation of GABAergic system in the observed sedative and anxiolytic activities. Phytochemical screening of MECN revealed 48 different compounds in it. We reviewed and conceive that the sedative and anxiolytic effects could be due to the presence of neuroactive compounds such as phytol, D-allose, and α-Tocopherol in MECN.

Conclusion

The present study showed that MECN possesses sedative and anxiolytic potential which could be beneficial in treatment of anxiety and insomnia associated with different psychological disorders.

Ethanol itself is a holoprosencephaly-inducing teratogen

Ethanol is a teratogen, inducing a variety of structural defects in developing humans and animals that are exposed in utero. Mechanisms of ethanol teratogenicity in specific defects are not well understood. Oxidative metabolism of ethanol by alcohol dehydrogenase or cytochrome P450 2E1 has been implicated in some of ethanol's teratogenic effects, either via production of acetaldehyde or competitive inhibition of retinoic acid synthesis. Generalized oxidative stress in response to ethanol may also play a role in its teratogenicity. Among the developmental defects that ethanol has been implicated in is holoprosencephaly, a failure to define the midline of the forebrain and midface that is associated with a deficiency in Sonic hedgehog pathway function. Etiologically, holoprosencephaly is thought to arise from a complex combination of genetic and environmental factors. We have developed a gene-environment interaction model of holoprosencephaly in mice, in which mutation of the Sonic hedgehog coreceptor, Cdon, synergizes with transient in utero exposure to ethanol. This system was used to address whether oxidative metabolism is required for ethanol's teratogenic activity in holoprosencephaly. We report here that t-butyl alcohol, which is neither a substrate nor an inhibitor of alcohol dehydrogenases or Cyp2E1, is a potent inducer of holoprosencephaly in Cdon mutant mice. Additionally, antioxidant treatment did not prevent ethanol- or t-butyl alcohol-induced HPE in these mice. These findings are consistent with the conclusion that ethanol itself, rather than a consequence of its metabolism, is a holoprosencephaly-inducing teratogen.

Alcohol Teratogenesis: Mechanisms of Damage and Strategies for Intervention

There are multiple mechanisms by which alcohol can damage the developing brain, but the type of damage induced will depend on the amount and developmental timing of exposure, along with other maternal and genetic factors. This article reviews current perspectives on how ethanol can produce neuroteratogenic effects by its interactions with molecular regulators of brain development. The current evidence suggests that alcohol produces many of its damaging effects by exerting specific actions on molecules that regulate key developmental processes (e.g., L1 cell adhesion molecule, alcohol dehydrogenase, catalase), interfering with the early development of midline serotonergic neurons and disrupting their regulatory-signaling function for other target brain structures, interfering with trophic factors that regulate neurogenesis and cell survival, or inducing excessive cell death via oxidative stress or activation of caspase-3 proteases. The current understanding of pathogenesis mechanisms suggests several strategic approaches to develop rational molecular prevention. However, the development of behavioral and biologic treatments for alcohol-affected children is crucial because it is unlikely that effective delivery of preventative interventions can realistically be achieved in ways to prevent prenatal damage in at-risk pregnancies. Toward that end, behavioral training that promotes experience-dependent neuroplasticity has been effective in a rat model of cerebellar damage induced by alcohol exposure during the period of brain development that is comparable to that of the human third trimester.

Effects of pre-natal alcohol exposure on hippocampal synaptic plasticity: Sex, age and methodological considerations

The consumption of alcohol during gestation is detrimental to the developing central nervous system (CNS). The severity of structural and functional brain alterations associated with alcohol intake depends on many factors including the timing and duration of alcohol consumption. The hippocampal formation, a brain region implicated in learning and memory, is highly susceptible to the effects of developmental alcohol exposure. Some of the observed effects of alcohol on learning and memory may be due to changes at the synaptic level, as this teratogen has been repeatedly shown to interfere with hippocampal synaptic plasticity. At the molecular level alcohol interferes with receptor proteins and can disrupt hormones that are important for neuronal signaling and synaptic plasticity. In this review we examine the consequences of prenatal and early postnatal alcohol exposure on hippocampal synaptic plasticity and highlight the numerous factors that can modulate the effects of alcohol. We also discuss some potential mechanisms responsible for these changes as well as emerging therapeutic avenues that are beginning to be explored.

Proceedings of the 2015 Annual Meeting of the Fetal Alcohol Spectrum Disorders Study Group

The 2015 Fetal Alcohol Spectrum Disorders Study Group (FASDSG) meeting was titled "Basic Mechanisms and Translational Implications." Despite decades of basic science and clinical research, our understanding of the mechanisms by which ethanol affects fetal development is still in its infancy. The first keynote presentation focused on the role of heat shock protein pathways in the actions of ethanol in the developing brain. The second keynote presentation addressed the use of magnetoencephalography to characterize brain function in children with FASD. The conference also included talks by representatives from several government agencies, short presentations by junior and senior investigators that showcased the latest in FASD research, and award presentations. An important part of the meeting was the presentation of the 2015 Henry Rosett award to Dr. Michael Charness in honor of his achievements in research on FASD.

Fetal Alcohol Spectrum Disorder: Potential Role of Endocannabinoids Signaling

One of the unique features of prenatal alcohol exposure in humans is impaired cognitive and behavioral function resulting from damage to the central nervous system (CNS), which leads to a spectrum of impairments referred to as fetal alcohol spectrum disorder (FASD). Human FASD phenotypes can be reproduced in the rodent CNS following prenatal ethanol exposure. Several mechanisms are expected to contribute to the detrimental effects of prenatal alcohol exposure on the developing fetus, particularly in the developing CNS. These mechanisms may act simultaneously or consecutively and differ among a variety of cell types at specific developmental stages in particular brain regions. Studies have identified numerous potential mechanisms through which alcohol can act on the fetus. Among these mechanisms are increased oxidative stress, mitochondrial damage, interference with the activity of growth factors, glia cells, cell adhesion molecules, gene expression during CNS development and impaired function of signaling molecules involved in neuronal communication and circuit formation. These alcohol-induced deficits result in long-lasting abnormalities in neuronal plasticity and learning and memory and can explain many of the neurobehavioral abnormalities found in FASD. In this review, the author discusses the mechanisms that are associated with FASD and provides a current status on the endocannabinoid system in the development of FASD.

Effect of lipid raft disruption on ethanol inhibition of l1 adhesion

Background

Alcohol causes fetal alcohol spectrum disorders in part by disrupting the function of the neural cell adhesion molecule L1. Alcohol inhibits L1-mediated cell–cell adhesion in diverse cell types and inhibits L1-mediated neurite outgrowth in cerebellar granule neurons (CGNs). A recent report indicates that ethanol (EtOH) induces the translocation of L1 into CGN lipid rafts and that disruption of lipid rafts prevents EtOH inhibition of L1-mediated neurite outgrowth. The same butanol–pentanol cutoff was noted for alcohol-induced translocation of L1 into lipid rafts that was reported previously for alcohol inhibition of L1 adhesion, suggesting that EtOH might inhibit L1 adhesion by shifting L1 into lipid rafts.

Methods

The NIH/3T3 cell line, 2A2-L1_s, is a well-characterized EtOH-sensitive clonal cell line that stably expresses human L1. Cells were treated with 25 mM EtOH, 5 μM filipin, or both. Lipid rafts were enriched in membrane fractions by preparation of detergent-resistant membrane (DRMs) fractions. Caveolin-1 was used as a marker of lipid rafts, and L1 and Src were quantified by Western blotting in lipid-raft-enriched membrane fractions and by immunohistochemistry.

Results

EtOH (25 mM) increased the percentage of L1, but not Src, in 2A2-L1_s membrane fractions enriched in lipid rafts. Filipin, an agent known to disrupt lipid rafts, decreased the percentage of caveolin and L1 in DRMs from 2A2-L1_s cells. Filipin also blocked EtOH-induced translocation of L1 into lipid rafts from 2A2-L1_s cells but did not significantly affect L1 adhesion or EtOH inhibition of L1 adhesion.

Conclusions

These findings indicate that EtOH does not inhibit L1 adhesion in NIH/3T3 cells by inducing the translocation of L1 into lipid rafts.

Two alcohol binding residues interact across a domain interface of the L1 neural cell adhesion molecule and regulate cell adhesion

Ethanol may cause fetal alcohol spectrum disorders (FASD) in part by inhibiting cell adhesion mediated by the L1 neural cell adhesion molecule. Azialcohols photolabel Glu-33 and Tyr-418, two residues that are predicted by homology modeling to lie within 2.8 Å of each other at the interface between the Ig1 and Ig4 domains of L1 (Arevalo, E., Shanmugasundararaj, S., Wilkemeyer, M. F., Dou, X., Chen, S., Charness, M. E., and Miller, K. W. (2008) Proc. Natl. Acad. Sci. U.S.A. 105, 371-375). Using transient transfection of NIH/3T3 cells with wild type (WT-L1) and mutated L1, we found that cysteine substitution of both residues (E33C/Y418C-L1) significantly increased L1 adhesion above levels observed for WT-L1 or the single cysteine substitutions E33C-L1 or Y418C-L1. The reducing agent β-mercaptoethanol (βME) reversibly decreased the adhesion of E33C/Y418C-L1, but had no effect on WT-L1, E33C-L1, or Y418C-L1. Thus, disulfide bond formation occurs between Cys-33 and Cys-418, confirming both the close proximity of these residues and the importance of Ig1-Ig4 interactions in L1 adhesion. Maximal ethanol inhibition of cell adhesion was significantly lower in cells expressing E33C/Y418C-L1 than in those expressing WT-L1, E33C-L1, or Y418C-L1. Moreover, the effects of βME and ethanol on E33C/Y418C-L1 adhesion were non-additive. The cutoff for alcohol inhibition of WT-L1 adhesion was between 1-butanol and 1-pentanol. Increasing the size of the alcohol binding pocket by mutating Glu-33 to Ala-33, increased the alcohol cutoff from 1-butanol to 1-decanol. These findings support the hypothesis that alcohol binding within a pocket bordered by Glu-33 and Tyr-418 inhibits L1 adhesion by disrupting the Ig1-Ig4 interaction.

Foetal Alcohol Spectrum Disorders and alterations in brain and behaviour

The term 'Foetal Alcohol Spectrum Disorders (FASD)' refers to the range of disabilities that may result from prenatal alcohol exposure. This article reviews the effects of ethanol on the developing brain and its long-term structural and neurobehavioural consequences. Brain imaging, neurobehavioural and experimental studies demonstrate the devastating consequences of prenatal alcohol exposure on the developing central nervous system (CNS), identifying specific brain regions affected, the range of severity of effects and mechanisms involved. In particular, neuroimaging studies have demonstrated overall and regional volumetric and surface area reductions, abnormalities in the shape of particular brain regions, and reduced and increased densities for white and grey matter, respectively. Neurobehaviourally, FASD consists of a continuum of long-lasting deficits affecting multiple aspects of cognition and behaviour. Experimental studies have also provided evidence of the vulnerability of the CNS to the teratogenic effects of ethanol and have provided new insight on the influence of risk factors in the type and severity of observed brain abnormalities. Finally, the potential molecular mechanisms that underlie the neuroteratological effects of alcohol are discussed, with particular emphasis on the role of glial cells in long-term neurodevelopmental liabilities.

Peptidergic agonists of activity-dependent neurotrophic factor protect against prenatal alcohol-induced neural tube defects and serotonin neuron loss

INTRODUCTION

Prenatal alcohol exposure via maternal liquid diet consumption by C57BL/6 (B6) mice causes conspicuous midline neural tube deficit (dysraphia) and disruption of genesis and development of serotonin (5-HT) neurons in the raphe nuclei, together with brain growth retardation. The current study tested the hypothesis that concurrent treatment with either an activity-dependent neurotrophic factor (ADNF) agonist peptide [SALLRSIPA, (SAL)] or an activity-dependent neurotrophic protein (ADNP) agonist peptide [NAPVSIPQ, (NAP)] would protect against these alcohol-induced deficits in brain development.

METHODS

Timed-pregnant B6 dams consumed alcohol from embryonic day 7 (E7, before the onset of neurulation) until E15. Fetuses were obtained on E15 and brain sections processed for 5-HT immunocytochemistry, for evaluation of morphologic development of the brainstem raphe and its 5-HT neurons. Additional groups were treated either with SAL or NAP daily from E7 to E15 to assess the potential protective effects of these peptides. Measures of incomplete occlusion of the ventral canal and the frequency and extent of the openings in the rhombencephalon were obtained to assess fetal dysraphia. Counts of 5-HT-immunostained neurons were also obtained in the rostral and caudal raphe.

RESULTS

Prenatal alcohol exposure resulted in abnormal openings along the midline and delayed closure of ventral canal in the brainstem. This dysraphia was associated with reductions in the number of 5-HT neurons both in the rostral raphe nuclei (that gives rise to ascending 5-HT projections) and in the caudal raphe (that gives rise to the descending 5-HT projections). Concurrent treatment of the alcohol-consuming dams with SAL prevented dysraphia and protected against the alcohol-induced reductions in 5-HT neurons in both the rostral and caudal raphe. NAP was less effective in protecting against dysraphia and did not protect against 5-HT loss in the rostral raphe, but did protect against loss in the caudal raphe.

CONCLUSIONS

These findings further support the potential usefulness of these peptides for therapeutic interventions in pregnancies at risk for alcohol-induced developmental deficits. Notably, the ascending 5-HT projections of the rostral raphe have profound effects in regulating forebrain development and function, and the descending 5-HT projections of the caudal raphe are critical for regulating respiration. Protection of the rostral 5-HT-system may help prevent structural and functional deficits linked to abnormal forebrain development, and protection of the caudal systems may also reduce the increased risk for sudden infant death syndrome associated with prenatal alcohol exposure.

An alcohol binding site on the neural cell adhesion molecule L1

Prenatal ethanol exposure causes fetal alcohol spectrum disorders (FASD) in part by disrupting the neural cell adhesion molecule L1. L1 gene mutations cause neuropathological abnormalities similar to those of FASD. Ethanol and 1-butanol inhibit L1-mediated cell-cell adhesion (L1 adhesion), whereas 1-octanol antagonizes this action. To test the hypothesis that there are alcohol binding sites on L1, we used 3-azibutanol and 3-azioctanol, the photoactivatable analogs of 1-butanol and 1-octanol, to photolabel the purified Ig1-4 domain of human L1 (hL1 Ig1-4). 3-Azibutanol (11 mM), like ethanol, inhibited L1 adhesion in NIH/3T3 cells stably transfected with hL1, whereas subanesthetic concentrations of 3-azioctanol (14 microM) antagonized ethanol inhibition of L1 adhesion. 3-Azibutanol (100-1,000 microM) and 3-azioctanol (10-100 microM) photoincorporated into Tyr-418 on Ig4 and into two adjacent regions in the N terminus, Glu-33 and Glu-24 to Glu-27. A homology model of hL1 Ig1-4 (residues 33-422), based on the structure of the Ig1-4 domains of axonin-1, suggests that Glu-33 and Tyr-418 hydrogen-bond at the interface of Ig1 and Ig4 to stabilize a horseshoe conformation of L1 that favors homophilic binding. Furthermore, this alcohol binding pocket lies within 7 A of Leu-120 and Gly-121, residues in which missense mutations cause neurological disorders similar to FASD. These data suggest that ethanol or selected mutations produce neuropathological abnormalities by disrupting the domain interface between Ig1 and Ig4. Characterization of alcohol agonist and antagonist binding sites on L1 will aid in understanding the molecular basis for FASD and might accelerate the development of ethanol antagonists.

Structural Constraints for Alcohol-Stimulated Ca2+ Release in Neural Crest, and Dual Agonist/Antagonist Properties of n-Octanol

BACKGROUND

Prenatal ethanol exposure is a leading cause of mental retardation. Alcohol damages susceptible neuronal populations through its alteration of signaling pathways that direct cellular activity and survival. In early neural crest cells, ethanol elicits an intracellular Ca2+ transient that is necessary and sufficient to cause apoptosis. We tested the hypothesis that ethanol's activity represents a saturable and selective effect of alcohols upon this pathway.

METHODS

Fura-2-loaded chick embryos, at the 3-somite stage, were exposed to n-alcohols ranging in size from ethanol (C2) to decanol (C10). Thereafter, Ca2+ mobilization was measured using Fura-2 and ratiometric imaging. Apoptosis was assessed using acridine orange uptake.

RESULTS

Ethanol caused the dose-dependent mobilization of intracellular Ca2+ within neural crest populations, with an EC50 of 52.0 mM. n-Alcohols displayed increasing potency for Ca2+ mobilization through pentanol. Hexanol and heptanol were inactive. Unexpectedly, micromolar n-octanol concentrations triggered significant Ca2+ release and apoptosis in a G-protein-dependent manner. Decanol was inactive. Coaddition of either octanol or decanol antagonized the ability of ethanol to stimulate Ca2+ release.

CONCLUSIONS

The selective, saturable effect of n-alcohols upon Ca2+ mobilization in neural crest is consistent with a hypothesis that ethanol stimulates these signals through specific interaction with one or more alcohol-binding sites on a target protein. Octanol may overcome structural constraints imposed upon C6 and C7 in interacting with this protein target; alternatively, it may interact through a unique binding site.

Synergistic effects of the peptide fragment D-NAPVSIPQ on ethanol inhibition of synaptic plasticity and NMDA receptors in rat hippocampus

The L1 cell adhesion molecule has been implicated in ethanol teratogenesis as well as NMDAR-dependent long-term potentiation (LTP) of synaptic transmission, a process thought to be critical for neural development. Ethanol inhibits LTP at least in part by interacting with NMDA receptors. Ethanol also inhibits L1-mediated cell adhesion in a manner that is prevented by an octapeptide, D-NAPVSIPQ (D-NAP), as well as long chain alcohols such as 1-octanol. Here we analyzed the effects of D-NAP and 1-octanol on ethanol modulation of LTP induced by theta burst stimulation in two subfields of the rat hippocampus, the dentate gyrus and area CA1. When theta burst stimulation was delivered in ethanol (50 mM), LTP was inhibited by about 50%. Surprisingly, when D-NAP (10(-7) M) and ethanol were co-applied or applied sequentially, LTP was completely absent. The effects of D-NAP were persistent, since delivery of a second theta burst stimulation following washout of D-NAP and ethanol elicited minimal plasticity. Application of D-NAP alone had no effect on LTP induction or expression. The synergistic effect of D-NAP on ethanol inhibition of LTP was concentration-dependent since D-NAP (10(-10) M) had an intermediate effect, while D-NAP (10(-13) M) had no effect on ethanol suppression of LTP. These observations were also replicated with a different ethanol antagonist, 1-octanol, in area CA1. To address the mechanisms underlying this long-lasting suppression of LTP, the sensitivity of pharmacologically isolated NMDAR extracellular field potentials to combinations of D-NAP and ethanol was determined. D-NAP (10(-7)M) alone had no effect on NMDA extracellular field potentials; however, the peptide significantly increased the inhibitory action of ethanol on NMDA extracellular field potential. The findings suggest that D-NAP and 1-octanol selectively interact with NMDA receptors in an ethanol-dependent manner, further implicating the L1 cell adhesion molecule in alcohol-related brain disorders.

Ethanol antagonist peptides: structural specificity without stereospecificity

Increasing evidence suggests that ethanol damages the developing nervous system partly by disrupting the L1 cell adhesion molecule. Ethanol inhibits L1-mediated cell adhesion, and compounds that antagonize this action also prevent ethanol-induced embryotoxicity. Two such compounds are the small peptides NAPVSIPQ (NAP) and SALLRSIPA (SAL). We showed previously that NAP and SAL antagonize ethanol inhibition of L1 adhesion at femtomolar to picomolar concentrations. Here we demonstrate that, despite this extraordinary potency, both NAP and SAL lack stereospecificity. d-NAP, a peptide composed entirely of d-amino acids, was an effective ethanol antagonist in NIH/3T3 cells transfected with human L1 and in the NG108-15 neural cell line. Interestingly, Ala-substituted derivatives of d-NAP demonstrate the same structure-activity relation as the corresponding derivatives of l-NAP. The Ser-Ile-Pro motif was important for the ethanol antagonist activity of d-NAP, l-NAP, and l-SAL, with Ile being the most critical element in all three. Like l-NAP, d-NAP effectively reduced ethanol-induced growth retardation in mouse whole embryo culture. The potential resistance of d-peptides to proteases makes d-NAP a potentially attractive agent for the prevention of fetal alcohol syndrome.

Differential effects of ethanol antagonism and neuroprotection in peptide fragment NAPVSIPQ prevention of ethanol-induced developmental toxicity

NAPVSIPQ (NAP), an active fragment of the glial-derived activity-dependent neuroprotective protein, is protective at femtomolar concentrations against a wide array of neural insults and prevents ethanol-induced fetal wastage and growth retardation in mice. NAP also antagonizes ethanol inhibition of L1-mediated cell adhesion (ethanol antagonism). We performed an Ala scanning substitution of NAP to determine the role of ethanol antagonism and neuroprotection in NAP prevention of ethanol embryotoxicity. The Ser-Ile-Pro region of NAP was crucial for both ethanol antagonism and protection of cortical neurons from tetrodotoxin toxicity (neuroprotection). Ala replacement of either Ser-5 or Pro-7 (P7A-NAP) abolished NAP neuroprotection but minimally changed the efficacy of NAP ethanol antagonism. In contrast, Ala replacement of Ile-6 (I6A-NAP) caused a decrease in potency (>2 logarithmic orders) with only a small reduction (<10%) in the efficacy of NAP neuroprotection but markedly reduced the efficacy (50%) and the potency (5 logarithmic orders) of NAP ethanol antagonism. Ethanol significantly reduced the number of paired somites in mouse whole-embryo culture; this effect was prevented significantly by 100 pM NAP or by 100 pM P7A-NAP, but not by 100 pM I6A-NAP. The structure-activity relation for NAP prevention of ethanol embryotoxicity was similar to that for NAP ethanol antagonism and different from that for NAP neuroprotection. These findings support the hypothesis that NAP antagonism of ethanol inhibition of L1 adhesion plays a central role in NAP prevention of ethanol embryotoxicity and highlight the potential importance of ethanol effects on L1 in the pathophysiology of fetal alcohol syndrome.