Combined neuroprotective action of adenosine A1 and cannabinoid CB1 receptors against NMDA-induced excitotoxicity in the hippocampus

Investigation on the neuroprotective effect of a cannabidiol-enriched non-psychotropic Cannabis sativa L. extract in an in vitro model of excitotoxicity

The purpose of this study was to evaluate the neuroprotective effect of a cannabidiol-enriched non-psychotropic Cannabis sativa L. extract (CSE) and its main constituents, cannabidiol and β-caryophyllene. An in vitro model of glutamate-induced neuronal excitotoxicity using SH-SY5Y cells was optimized. The impact of CSE on glutamate-impaired cell viability, brain-derived neurotrophic factor release, CB1 protein expression, and ERK levels was evaluated. The involvement of CB1 modulation was verified by the cotreatment with the CB1 antagonist AM4113. CSE was able to significantly protect SH-SY5Y from glutamate-impaired cell viability, and to counteract the changes in brain-derived neurotrophic factor levels, with a mechanism of action involving ERK modulation. Moreover, CSE completely reversed the reduction of CB1 receptor expression induced by glutamate, and the presence of the CB1 antagonist AM4113 reduced CSE effectiveness, suggesting that CBr play a role in the modulation of neuronal excitotoxicity. This work demonstrated the in vitro effectiveness of CSE as a neuroprotective agent, proposing the whole cannabis phytocomplex as a more effective strategy, compared to its main constituents alone, and suggested further investigations by using more complex cell models before moving to in vivo studies.

Adenosine Inhibits Cell Proliferation Differently in Human Astrocytes and in Glioblastoma Cell Lines

Glioblastoma (GBM) is the most common brain primary tumour. Hypoxic regions in GBM are associated to tumour growth. Adenosine accumulates in hypoxic regions and can affect cell proliferation and survival. However, how proliferating GBM cells respond/adapt to increased adenosine levels compared to human astrocytes (HA) is not clarified and was addressed in the present work. GBM cell lines and HA were treated for 3 days with test drugs. Thirty Adenosine (30 µM) caused a 43% ± 5% (P < 0.05) reduction of cell proliferation/viability in HA, through an adenosine receptor-independent mechanism, but had no effect in GBM cell lines U87MG, U373MG and SNB19. Contrastingly, inhibition of adenosine phosphorylation (using the adenosine kinase (ADK) inhibitor 5-iodotubercidin (ITU) (25 µM)), produced a strong and similar decrease on cell proliferation in both HA and GBM cells. The effect of adenosine on HA proliferation/viability was potentiated by 100 µM-homocysteine. Combined application of 30 µM-adenosine and 100 µM-homocysteine reduced the cell proliferation/viability in all three GBM cell lines, but this reduction was much lower than that observed in HA. Adenosine alone did not induce cell death, assessed by lactate dehydrogenase (LDH) release, both in HA and GBM cells, but potentiated the cytotoxic effect of homocysteine in HA and in U87MG and U373MG cells. Results show a strong attenuation of adenosine anti-proliferative effect in GBM cells compared to HA, probably resulting from increased adenosine elimination by ADK, suggesting a proliferative-prone adaptation of tumour cells to increased adenosine levels.

The Detrimental Action of Adenosine on Glutamate-Induced Cytotoxicity in PC12 Cells Can Be Shifted towards a Neuroprotective Role through A1AR Positive Allosteric Modulation

Glutamate cytotoxicity is implicated in neuronal death in different neurological disorders including stroke, traumatic brain injury, and neurodegenerative diseases. Adenosine is a nucleoside that plays an important role in modulating neuronal activity and its receptors have been identified as promising therapeutic targets for glutamate cytotoxicity. The purpose of this study is to elucidate the role of adenosine and its receptors on glutamate-induced injury in PC12 cells and to verify the protective effect of the novel A₁ adenosine receptor positive allosteric modulator, TRR469. Flow cytometry experiments to detect apoptosis revealed that adenosine has a dual role in glutamate cytotoxicity, with A_2A and A_2B adenosine receptor (AR) activation exacerbating and A₁ AR activation improving glutamate-induced cell injury. The overall effect of endogenous adenosine in PC12 cells resulted in a facilitating action on glutamate cytotoxicity, as demonstrated by the use of adenosine deaminase and selective antagonists. However, enhancing the action of endogenous adenosine on A₁ARs by TRR469 completely abrogated glutamate-mediated cell death, caspase 3/7 activation, ROS production, and mitochondrial membrane potential loss. Our results indicate a novel potential therapeutic strategy against glutamate cytotoxicity based on the positive allosteric modulation of A₁ARs.

Redox activation of excitatory pathways in auditory neurons as mechanism of age-related hearing loss

Age-related hearing (ARHL) loss affects a large part of the human population with a major impact on our aging societies. Yet, underlying mechanisms are not understood, and no validated therapy or prevention exists. NADPH oxidases (NOX), are important sources of reactive oxygen species (ROS) in the cochlea and might therefore be involved in the pathogenesis of ARHL. Here we investigate ARHL in a mouse model. Wild type mice showed early loss of hearing and cochlear integrity, while animals deficient in the NOX subunit p22^phox remained unaffected up to six months. Genes of the excitatory pathway were down-regulated in p22^phox-deficient auditory neurons. Our results demonstrate that NOX activity leads to upregulation of genes of the excitatory pathway, to excitotoxic cochlear damage, and ultimately to ARHL. In the absence of functional NOXs, aging mice conserve hearing and cochlear morphology. Our study offers new insights into pathomechanisms and future therapeutic targets of ARHL.

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Mice devoid of NADPH oxidase (NOX) activity are protected from age-related hearing loss.

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Cochlear NOX expression shows a similar pattern in mouse and human.

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NOX3, the predominant NOX isoform in the cochlea, is mostly expressed in auditory neurons.

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NOX-deficient auditory neurons show decreased transcription of glutamatergic pathway and are protected from excitotoxicity.

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NOX-mediated gene regulation within auditory neurons contributes to age-related hearing loss.

Adenosine inhibits human astrocyte proliferation independently of adenosine receptor activation

Brain adenosine concentrations can reach micromolar concentrations in stressful situations such as stroke, neurodegenerative diseases or hypoxic regions of brain tumours. Adenosine can act by receptor-independent mechanism by reversing the reaction catalysed by S-adenosylhomocysteine (SAH) hydrolase, leading to SAH accumulation and inhibition of S-adenosylmethionine (SAM)-dependent methyltransferases. Astrocytes are essential in maintaining brain homeostasis but their pathological activation and uncontrolled proliferation plays a role in neurodegeneration and glioma. Adenosine can affect cell proliferation, but the effect of increased adenosine concentration on proliferation of astrocytes is not clarified and was addressed in present work. Human astrocytes (HA) were treated for 3 days with test drugs. Cell proliferation/viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium assay and by cell counting. Cell death was evaluated by assessing lactate dehydrogenase release and by western blot analysis of αII-Spectrin cleavage. 30 µM-Adenosine caused a 40% ± 3% (p < .05, n = 5) reduction in cell proliferation/viability, an effect reversed by 2U/ml-adenosine deaminase, but unchanged in the presence of antagonists of any of the adenosine receptors. Adenosine alone did not induce cell death. 100 µM-Homocysteine alone caused 16% ± 3% (p < .05) decrease in HA proliferation. Combined action of adenosine and homocysteine decreased HA proliferation by 76% ± 4%, an effect higher (p < .05) than the sum of the effects of adenosine and homocysteine alone (56% ± 5%). The inhibitory effect of adenosine on HA proliferation/viability was mimicked by two adenosine kinase inhibitors and attenuated in the presence of folate (100 µM) or SAM (50-100 µM). The results suggest that adenosine reduces HA proliferation by a receptor-independent mechanism probably involving reversal of SAH hydrolase-catalysed reaction.

Therapeutic potential of cannabinoids as neuroprotective agents for damaged cells conducing to movement disorders

The basal ganglia (BG), an organized network of nuclei that integrates cortical information, play a crucial role in controlling motor function. In fact, movement disorders such as Parkinson's disease (PD) and Huntington's disease (HD) are caused by the degeneration of specific structures within the BG. There is substantial evidence supporting the idea that cannabinoids may constitute novel promising compounds for the treatment of movement disorders as neuroprotective and anti-inflammatory agents. This potential therapeutic role of cannabinoids is based, among other qualities, on their capacity to reduce oxidative injury and excitotoxicity, control calcium influx and limit the toxicity of reactive microglia. The mechanisms involved in these effects are related to CB1 and CB2 receptor activation, although some of the effects are CB receptor independent. Thus, taking into account the aforementioned properties, compounds that act on the endocannabinoid system could be useful as a basis for developing disease-modifying therapies for PD and HD.

Fructose-1,6-Bisphosphate Protects Hippocampal Rat Slices from NMDA Excitotoxicity

Effects of fructose 1,6-bisphosphate (F-1,6-P2) towards N-methyl-d-aspartate NMDA excitotoxicity were evaluated in rat organotypic hippocampal brain slice cultures (OHSC) challenged for 3 h with 30 μM NMDA, followed by incubations (24, 48, and 72 h) without (controls) and with F-1,6-P2 (0.5, 1 or 1.5 mM). At each time, cell necrosis was determined by measuring LDH in the medium. Energy metabolism was evaluated by measuring ATP, GTP, ADP, AMP, and ATP catabolites (nucleosides and oxypurines) in deproteinized OHSC extracts. Gene expressions of phosphofructokinase, aldolase, and glyceraldehyde-3-phosphate dehydrogenase were also measured. F-1,6-P2 dose-dependently decreased NMDA excitotoxicity, abolishing cell necrosis at the highest concentration tested (1.5 mM). Additionally, F-1,6-P2 attenuated cell energy imbalance caused by NMDA, ameliorating the mitochondrial phosphorylating capacity (increase in ATP/ADP ratio) Metabolism normalization occurred when using 1.5 mM F-1,6-P2. Remarkable increase in expressions of phosphofructokinase, aldolase and glyceraldehyde-3-phosphate dehydrogenase (up to 25 times over the values of controls) was also observed. Since this phenomenon was recorded even in OHSC treated with F-1,6-P2 with no prior challenge with NMDA, it is highly conceivable that F-1,6-P2 can enter into intact cerebral cells producing significant benefits on energy metabolism. These effects are possibly mediated by changes occurring at the gene level, thus opening new perspectives for F-1,6-P2 application as a useful adjuvant to rescue mitochondrial metabolism of cerebral cells under stressing conditions.

Novel Therapeutics in Glaucoma Management

BACKGROUND

Glaucoma is a progressive optic neuropathy characterized by retinal ganglion cell death and alterations of visual field. Elevated intraocular pressure (IOP) is considered the main risk factor of glaucoma, even though other factors cannot be ruled out, such as epigenetic mechanisms.

OBJECTIVE

An overview of the ultimate promising experimental drugs to manage glaucoma has been provided.

RESULTS

In particular, we have focused on purinergic ligands, KATP channel activators, gases (nitric oxide, carbon monoxide and hydrogen sulfide), non-glucocorticoid steroidal compounds, neurotrophic factors, PI3K/Akt activators, citicoline, histone deacetylase inhibitors, cannabinoids, dopamine and serotonin receptors ligands, small interference RNA, and Rho kinase inhibitors.

CONCLUSIONS

The review has been also endowed of a brief chapter on last reports about potential neuroprotective benefits of anti-glaucoma drugs already present in the market.

The endocannabinoid system, a novel and key participant in acupuncture's multiple beneficial effects

Acupuncture and its modified forms have been used to treat multiple medical conditions, but whether the diverse effects of acupuncture are intrinsically linked at the cellular and molecular level and how they might be connected have yet to be determined. Recently, an emerging role for the endocannabinoid system (ECS) in the regulation of a variety of physiological/pathological conditions has been identified. Overlap between the biological and therapeutic effects induced by ECS activation and acupuncture has facilitated investigations into the participation of ECS in the acupuncture-induced beneficial effects, which have shed light on the idea that the ECS may be a primary mediator and regulatory factor of acupuncture's beneficial effects. This review seeks to provide a comprehensive summary of the existing literature concerning the role of endocannabinoid signaling in the various effects of acupuncture, and suggests a novel notion that acupuncture may restore homeostasis under different pathological conditions by regulating similar networks of signaling pathways, resulting in the activation of different reaction cascades in specific tissues in response to pathological insults.

Chronic and acute adenosine A2A receptor blockade prevents long-term episodic memory disruption caused by acute cannabinoid CB1 receptor activation

Cannabinoid-mediated memory impairment is a concern in cannabinoid-based therapies. Caffeine exacerbates cannabinoid CB₁ receptor (CB₁R)-induced memory deficits through an adenosine A₁ receptor-mediated mechanism. We now evaluated how chronic or acute blockade of adenosine A_2A receptors (A_2ARs) affects long-term episodic memory deficits induced by a single injection of a selective CB₁R agonist. Long-term episodic memory was assessed by the novel object recognition (NOR) test. Mice received an intraperitoneal (i.p.) injection of the CB₁/CB₂ receptor agonist WIN 55,212-2 (1 mg/kg) immediately after the NOR training, being tested for novelty recognition 24 h later. Anxiety levels were assessed by the Elevated Plus Maze test, immediately after the NOR. Mice were also tested for exploratory behaviour at the Open Field. For chronic A_2AR blockade, KW-6002 (istradefylline) (3 mg/kg/day) was administered orally for 30 days; acute blockade of A_2ARs was assessed by i.p. injection of SCH 58261 (1 mg/kg) administered either together with WIN 55,212-2 or only 30 min before the NOR test phase. The involvement of CB₁Rs was assessed by using the CB₁R antagonist, AM251 (3 mg/kg, i.p.). WIN 55,212-2 caused a disruption in NOR, an action absent in mice also receiving AM251, KW-6002 or SCH 58261 during the encoding/consolidation phase; SCH 58251 was ineffective if present during retrieval only. No effects were detected in the Elevated Plus maze or Open Field Test. The finding that CB₁R-mediated memory disruption is prevented by antagonism of adenosine A_2ARs, highlights a possibility to prevent cognitive side effects when therapeutic application of CB₁R drugs is desired.

The Role of cGMP on Adenosine A 1 Receptor-mediated Inhibition of Synaptic Transmission at the Hippocampus

Both adenosine A₁ receptor and cGMP inhibit synaptic transmission at the hippocampus and recently it was found that A₁ receptor increased cGMP levels in hippocampus, but the role of cGMP on A₁ receptor-mediated inhibition of synaptic transmission remains to be established. In the present work we investigated if blocking the NOS/sGC/cGMP/PKG pathway using nitric oxide synthase (NOS), protein kinase G (PKG), and soluble guanylyl cyclase (sGC) inhibitors modify the A₁ receptor effect on synaptic transmission. Neurotransmission was evaluated by measuring the slope of field excitatory postsynaptic potentials (fEPSPs) evoked by electrical stimulation at hippocampal slices. N6-cyclopentyladenosine (CPA, 15 nM), a selective A₁ receptor agonist, reversibly decreased the fEPSPs by 54 ± 5%. Incubation of the slices with an inhibitor of NOS (L-NAME, 200 μM) decreased the CPA effect on fEPSPs by 57 ± 9% in female rats. In males, ODQ (10 μM), an sGC inhibitor, decreased the CPA inhibitory effect on fEPSPs by 23 ± 6%, but only when adenosine deaminase (ADA,1 U/ml) was present; similar results were found in females, where ODQ decreased CPA-induced inhibition of fEPSP slope by 23 ± 7%. In male rats, the presence of the PKG inhibitor (KT5823, 1 nM) decreased the CPA effect by 45.0 ± 9%; similar results were obtained in females, where KT5823 caused a 32 ± 9% decrease on the CPA effect. In conclusion, the results suggest that the inhibitory action of adenosine A₁ receptors on synaptic transmission at hippocampus is, in part, mediated by the NOS/sGC/cGMP/PKG pathway.