Ethanol and PTZ effects on siRNA-mediated GABAB1 receptor: down regulation of intracellular signaling pathway in prenatal rat cortical and hippocampal neurons

Antidotal effects of thymoquinone against neurotoxic agents

Several plants which contain the active component thymoquinone (TQ) have been traditionally used in herbal medicine to treat various diseases. Several studies indicated the protective effects of TQ against neurotoxic agents. The present study was aimed to highlight the protective effects of TQ against neurotoxic agents. For this reason, the literature from 1998 to 2017 regarding the protective effects of TQ against neurotoxic agents and their involvement mechanisms has been studied. The present review suggests the protective effects of TQ against neurotoxic agents in experimental models. More clinical trial studies are however needed to confirm the antidotal effects of TQ in human intoxication.

Anti-Neuroinflammatory Property of Phlorotannins from Ecklonia cava on Aβ25-35-Induced Damage in PC12 Cells

Alzheimer disease (AD) is a neurodegenerative disorder characterized by excessive accumulation of amyloid-beta peptide (Aβ) and progressive loss of neurons. Therefore, the inhibition of Aβ-induced neurotoxicity is a potential therapeutic approach for the treatment of AD. Ecklonia cava is an edible brown seaweed, which has been recognized as a rich source of bioactive derivatives, mainly phlorotannins. In this study, phlorotannins including eckol, dieckol, 8,8'-bieckol were used as potential neuroprotective candidates for their anti-apoptotic and anti-inflammatory effects against Aβ25-35-induced damage in PC12 cells. Among the tested compounds, dieckol showed the highest effect in both suppressing intracellular oxidative stress and mitochondrial dysfunction and activation of caspase family. Three phlorotannins were found to inhibit TNF-α, IL-1β and PGE₂ production at the protein levels. These result showed that the anti-inflammatory properties of our compounds are related to the down-regulation of proinflammatory enzymes, iNOS and COX-2, through the negative regulation of the NF-κB pathway in Aβ25-35-stimulated PC12 cells. Especially, dieckol showed the strong anti-inflammatory effects via suppression of p38, ERK and JNK. However, 8,8'-bieckol markedly decreased the phosphorylation of p38 and JNK and eckol suppressed the activation of p38. Therefore, the results of this study indicated that dieckol from E. cava might be applied as a drug candidate for the development of new generation therapeutic agents against AD.

Neuroprotective effect of osmotin against ethanol-induced apoptotic neurodegeneration in the developing rat brain

Fetal alcohol syndrome is a neurological and developmental disorder caused by exposure of developing brain to ethanol. Administration of osmotin to rat pups reduced ethanol-induced apoptosis in cortical and hippocampal neurons. Osmotin, a plant protein, mitigated the ethanol-induced increases in cytochrome c, cleaved caspase-3, and PARP-1. Osmotin and ethanol reduced ethanol neurotoxicity both in vivo and in vitro by reducing the protein levels of cleaved caspase-3, intracellular [Ca²⁺]_cyt, and mitochondrial transmembrane potential collapse, and also upregulated antiapoptotic Bcl-2 protein. Osmotin is a homolog of adiponectin, and it controls energy metabolism via phosphorylation. Adiponectin can protect hippocampal neurons against ethanol-induced apoptosis. Abrogation of signaling via receptors AdipoR1 or AdipoR2, by transfection with siRNAs, reduced the ability of osmotin and adiponectin to protect neurons against ethanol-induced neurodegeneration. Metformin, an activator of AMPK (adenosine monophosphate-activated protein kinase), increased whereas Compound C, an inhibitor of AMPK pathway, reduced the ability of osmotin and adiponectin to protect against ethanol-induced apoptosis. Osmotin exerted its neuroprotection via Bcl-2 family proteins and activation of AMPK signaling pathway. Modulation of AMPK pathways by osmotin, adiponectin, and metformin hold promise as a preventive therapy for fetal alcohol syndrome.

Anthocyanins protect against ethanol-induced neuronal apoptosis via GABAB1 receptors intracellular signaling in prenatal rat hippocampal neurons

Here, we investigated the possible involvement of gamma-aminobutyric acid B1 receptor (GABAB1R) in mediating the protective effects of black soybean anthocyanins against ethanol-induced apoptosis in prenatal hippocampal neurons because GABARs are known to play an important role in the development of central nervous system. Treatments were performed on primary cultures of prenatal rat hippocampal neurons transfected with or without GABAB1R small interfering RNA (siRNA). The results showed that, when ethanol treatment was followed by anthocyanins treatment, cellular levels of proapoptotic proteins such as Bax, activated caspase-3, and cleaved poly (ADP-ribose) polymerase 1 (PARP-1) were decreased, and the cellular level of the antiapoptotic protein Bcl-2 was increased compared to treatment with ethanol alone. Furthermore, the effects of ethanol on cellular levels of GABAB1R and its downstream signaling molecules such as protein kinase A, calcium/calmodulin-dependent protein kinase II (CaMKII), and phosphorylated cAMP response element binding protein were diminished or reversed by anthocyanins treatment. The ability of anthocyanins to reverse the effects of ethanol on cellular levels of Bax, Bcl-2, active caspase-3, cleaved PARP-1, GABAB1R, and CaMKII were abrogated in cells transfected with GABAB1R siRNA. In a GABAB1R-dependent manner, anthocyanins also inhibited the ability of ethanol to elevate intracellular free Ca(2+) level and increase the proportion of cells with low mitochondrial membrane potential in the population. Cell apoptosis assay and morphological studies also confirmed the neuroprotective effect of anthocyanins against ethanol via GABAB1R. Our data suggest that GABAB1R plays an important role in the neuroprotective effects of anthocyanins against ethanol.

γ-Aminobutyric acid type B (GABAB) receptor expression is needed for inhibition of N-type (Cav2.2) calcium channels by analgesic α-conotoxins

α-Conotoxins Vc1.1 and RgIA are small peptides isolated from the venom of marine cone snails. They have effective anti-nociceptive actions in rat models of neuropathic pain. Pharmacological studies in rodent dorsal root ganglion (DRG) show their analgesic effect is mediated by inhibition of N-type (Ca(v)2.2) calcium channels via a pathway involving γ-aminobutyric acid type B (GABA(B)) receptor. However, there is no direct demonstration that functional GABA(B) receptors are needed for inhibition of the Ca(v)2.2 channel by analgesic α-conotoxins. This study examined the effect of the GABA(B) agonist baclofen and α-conotoxins Vc1.1 and RgIA on calcium channel currents after transient knockdown of the GABA(B) receptor using RNA interference. Isolated rat DRG neurons were transfected with small interfering RNAs (siRNA) targeting GABA(B) subunits R1 and R2. Efficient knockdown of GABA(B) receptor expression at mRNA and protein levels was confirmed by quantitative real time PCR (qRT-PCR) and immunocytochemical analysis, respectively. Whole-cell patch clamp recordings conducted 2-4 days after transfection showed that inhibition of N-type calcium channels in response to baclofen, Vc1.1 and RgIA was significantly reduced in GABA(B) receptor knockdown DRG neurons. In contrast, neurons transfected with a scrambled nontargeting siRNA were indistinguishable from untransfected neurons. In the HEK 293 cell heterologous expression system, Vc1.1 and RgIA inhibition of Ca(v)2.2 channels needed functional expression of both human GABA(B) receptor subunits. Together, these results confirm that GABA(B) receptors must be activated for the modulation of N-type (Ca(v)2.2) calcium channels by analgesic α-conotoxins Vc1.1 and RgIA.

Neuroprotection with metformin and thymoquinone against ethanol-induced apoptotic neurodegeneration in prenatal rat cortical neurons

Background

Exposure to ethanol during early development triggers severe neuronal death by activating multiple stress pathways and causes neurological disorders, such as fetal alcohol effects or fetal alcohol syndrome. This study investigated the effect of ethanol on intracellular events that predispose developing neurons for apoptosis via calcium-mediated signaling. Although the underlying molecular mechanisms of ethanol neurotoxicity are not completely determined, mitochondrial dysfunction, altered calcium homeostasis and apoptosis-related proteins have been implicated in ethanol neurotoxicity. The present study was designed to evaluate the neuroprotective mechanisms of metformin (Met) and thymoquinone (TQ) during ethanol toxicity in rat prenatal cortical neurons at gestational day (GD) 17.5.

Results

We found that Met and TQ, separately and synergistically, increased cell viability after ethanol (100 mM) exposure for 12 hours and attenuated the elevation of cytosolic free calcium [Ca²⁺]_c. Furthermore, Met and TQ maintained normal physiological mitochondrial transmembrane potential (Δψ_M), which is typically lowered by ethanol exposure. Increased cytosolic free [Ca²⁺]_c and lowered mitochondrial transmembrane potential after ethanol exposure significantly decreased the expression of a key anti-apoptotic protein (Bcl-2), increased expression of Bax, and stimulated the release of cytochrome-c from mitochondria. Met and TQ treatment inhibited the apoptotic cascade by increasing Bcl-2 expression. These compounds also repressed the activation of caspase-9 and caspase-3 and reduced the cleavage of PARP-1. Morphological conformation of cell death was assessed by TUNEL, Fluoro-Jade-B, and PI staining. These staining methods demonstrated more cell death after ethanol treatment, while Met, TQ or Met plus TQ prevented ethanol-induced apoptotic cell death.

Conclusion

These findings suggested that Met and TQ are strong protective agents against ethanol-induced neuronal apoptosis in primary rat cortical neurons. The collective data demonstrated that Met and TQ have the potential to ameliorate ethanol neurotoxicity and revealed a possible protective target mechanism for the damaging effects of ethanol during early brain development.

Effects of pentoxifylline and H-89 on epileptogenic activity of bucladesine in pentylenetetrazol-treated mice

The present study shows interactive effects of pentoxifylline (PTX) as a phosphodiesterase (PDE) inhibitor, H-89 as a protein kinase A (PKA) inhibitor and bucladesine (db-cAMP) as a cAMP agonist on pentylenetetrazol (PTZ)-induced seizure in mice. Different doses of pentoxifylline (25, 50, 100 mg/kg), bucladesine (50, 100, 300 nM/mouse), and H-89 (0.05, 0.1, 0.2 mg/100g) were administered intraperitoneally (i.p.), 30 min before intravenous (i.v.) infusion of PTZ (0.5% w/v). In combination groups, the first and second components were injected 45 and 30 min before PTZ infusion. In all groups, the control animals received an appropriate volume of vehicle. Single administration of PTX had no significant effect on both seizure latency and threshold. Bucladesine significantly decreased seizure latency and threshold only at a high concentration (300 nM/mouse). Intraperitoneal administration of H-89 (0.2 mg/100g) significantly increased seizure latency and threshold in PTZ-treated animals. All applied doses of bucladesine in combination with PTX (50 mg/kg) caused a significant reduction in seizure latency. Pretreatment of animals with PTX (50 and 100 mg/kg) attenuated the anticonvulsant effect of H-89 (0.2 mg/100g) in PTZ-exposed animals. H-89 (0.05, 0.2 mg/100g) prevented the epileptogenic activity of bucladesine (300 nM) with significant increase of seizure latency and seizure threshold. In conclusion, we showed that seizure activities were affected by pentoxifylline, H-89 and bucladesine via interactions with intracellular cAMP and cGMP signaling pathways, cyclic nucleotide-dependent protein kinases, and related neurotransmitters.

Vitamin C protects against ethanol and PTZ-induced apoptotic neurodegeneration in prenatal rat hippocampal neurons

Exposure to alcohol during brain development may cause a neurological syndrome called fetal alcohol syndrome, characterized by pre- and postnatal growth deficiencies, craniofacial anomalies, and evidence of CNS dysfunction. The objective of this study was to evaluate pentylenetetrazol (PTZ) and ethanol effects on Bax, Bcl-2 expression, which further induced activation of caspase-3, release of cytochrome-c from mitochondria, and to observe the protective effects of vitamin C (vit-C) against PTZ and ethanol-induced apoptotic neurodegeneration in primary-cultured neuronal cells at gestational day 17.5. Apoptotic neurodegeneration and neuroprotective effect of vit-C were measured by using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay, Western blot analysis, which further conformed by the measurement of mitochondrial membrane potential using JC-1 detection kit and immunofluorescence analysis. The results showed that PTZ and ethanol produced extensive Bax-dependent caspase-9 and caspase-3 activation and caused neuronal apoptosis. Furthermore, the cotreatment of vit-C along with ethanol and PTZ showed significantly decreased expression of Bax, caspase-9, caspase-3, cytochrome-c, and significantly increased expression of antiapoptotic Bcl-2 protein when compared with control group. Our findings indicate that PTZ and ethanol activate an intrinsic apoptotic death program in neurons that is likely to contribute to the neuropathologic effects in fetal alcohol exposure, and vit-C can prevent some of the deleterious effects of PTZ and ethanol on the developing brain. The available experimental evidence and the safety of vit-C in pregnancy suggest the experimental use of ascorbic acid as a new and effective protective agent ethanol and PTZ-induced apoptotic neurodegeneration.

Neuroprotective effect of vitamin C against the ethanol and nicotine modulation of GABA(B) receptor and PKA-alpha expression in prenatal rat brain

Prenatal ethanol exposure has various deleterious effects on neuronal development and can induce various defects in developing brain, resulting in fetal alcohol syndrome (FAS). gamma-Aminobutyric acid (GABA(B)) receptor (R) is known to play an important role during the development of the central nervous system (CNS). Our study was designed to investigate the effect of ethanol (100 mM), nicotine (50 microM) (for 30 min and 1 h), vitamin C (vitC, 0.5 mM), ethanol plus vitC, and nicotine plus vitC on expression level of GABA(B1), GABA(B2)R, and protein kinase A-alpha (PKA) in prenatal rat cortical and hippocampal neurons at gestational days (GD) 17.5. The results showed that, upon ethanol and nicotine exposure, GABA(B1) and GABA(B2)R protein expression increased significantly in the cortex and hippocampus for a short (30 min) and long term (1 h), whereas only GABA(B2)R subunit was decreased upon nicotine exposure for a long term in the cortex. Furthermore, PKA expression in cortex and hippocampus increased with ethanol exposure during short term, whereas long-term exposure results increased in cortex and decreased in hippocampus. Moreover, the cotreatment of vitC with ethanol and nicotine showed significantly decreased expression of GABA(B1), GABA(B2)R, and PKA in cortex and hippocampus for a long-term exposure. Mitochondrial membrane potential, Fluoro-jade-B, and propidium iodide staining were used to elucidate possible neurodegeneration. Our results suggest the involvement of GABA(B)R and PKA in nicotine and ethanol-mediated neurodevelopmental defects and the potential use of vitC as a effective protective agent for FAS-related deficits.