Additive protective effects of donepezil and nicotine against salsolinol-induced cytotoxicity in SH-SY5Y cells

Novel neuroprotective 5,6-dihydropyrido[2',1':2,3]imidazo[4,5-c]quinoline derivatives acting through cholinesterase inhibition and CB2 signaling modulation

A novel group of 5,6-dihydropyrido [2',1':2,3]imidazo [4,5-c]quinolines was prepared via a microwave assisted one-pot telescopic approach. The synthetic sequence involves the formation of an amine precursor of imidazo [1,2-a]pyridine via condensation and reduction under microwave irradiation. Subsequently, the Pictet-Spengler cyclisation reaction occurs with ketones (cyclic or acyclic) to obtain substituted 5,6-dihydropyrido [2',1':2,3]imidazo [4,5-c]quinolines in excellent yields. The compounds were tested as neuroprotective agents. Observed protection of neuron-like cells, SH-SY5Y differentiated with ATRA, in Parkinson's and Huntington's disease models inspired further mechanistic studies of protective activity against damage induced by 1-methyl-4-phenylpyridinium (MPP+), a compound causing Parkinson's disease. The novel compounds exhibit similar or higher potency than ebselen, an established drug with antioxidant activity, in the cells against MPP + -induced total cellular superoxide production and cell death. However, they exhibit a significantly higher capacity to reduce mitochondrial superoxide and preserve mitochondrial membrane potential. We also observed marked differences between a selected derivative and ebselen in terms of normalizing MPP + -induced phosphorylation of Akt and ERK1/2. The cytoprotective activity was abrogated when signaling through cannabinoid receptor CB2 was blocked. The compounds also inhibit both acetylcholine and butyrylcholine esterases. Overall the data show that novel 5,6-dihydropyrido [2',1':2,3]imidazo [4,5-c]quinoline have a broad cytoprotective activity which is mediated by several mechanisms including mitoprotection.

Donepezil-Loaded Nanocarriers for the Treatment of Alzheimer's Disease: Superior Efficacy of Extracellular Vesicles Over Polymeric Nanoparticles

Introduction

Drug delivery across the blood-brain barrier (BBB) is challenging and therefore severely restricts neurodegenerative diseases therapy such as Alzheimer's disease (AD). Donepezil (DNZ) is an acetylcholinesterase (AChE) inhibitor largely prescribed to AD patients, but its use is limited due to peripheral adverse events. Nanodelivery strategies with the polymer Poly (lactic acid)-poly(ethylene glycol)-based nanoparticles (NPs-PLA-PEG) and the extracellular vesicles (EVs) were developed with the aim to improve the ability of DNZ to cross the BBB, its brain targeting and efficacy.

Methods

EVs were isolated from human plasma and PLA-PEG NPs were synthesized by nanoprecipitation. The toxicity, brain targeting capacity and cholinergic activities of the formulations were evaluated both in vitro and in vivo.

Results

EVs and NPs-PLA-PEG were designed to be similar in size and charge, efficiently encapsulated DNZ and allowed sustained drug release. In vitro study showed that both formulations EVs-DNZ and NPs-PLA-PEG-DNZ were highly internalized by the endothelial cells bEnd.3. These cells cultured on the Transwell® model were used to analyze the transcytosis of both formulations after validation of the presence of tight junctions, the transendothelial electrical resistance (TEER) values and the permeability of the Dextran-FITC. In vivo study showed that both formulations were not toxic to zebrafish larvae (Danio rerio). However, hyperactivity was evidenced in the NPs-PLA-PEG-DNZ and free DNZ groups but not the EVs-DNZ formulations. Biodistribution analysis in zebrafish larvae showed that EVs were present in the brain parenchyma, while NPs-PLA-PEG remained mainly in the bloodstream.

Conclusion

The EVs-DNZ formulation was more efficient to inhibit the AChE enzyme activity in the zebrafish larvae head. Thus, the bioinspired delivery system (EVs) is a promising alternative strategy for brain-targeted delivery by substantially improving the activity of DNZ for the treatment of AD.

Salsolinol Induces Parkinson's Disease Through Activating NLRP3-Dependent Pyroptosis and the Neuroprotective Effect of Acteoside

Endogenous neurotoxin 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroiso-quinoline (Salsolinol, SAL) is a dopamine metabolite that is toxic to dopaminergic neurons in vitro and in vivo, and is involved in the pathogenesis of Parkinson's disease (PD). However, the molecular mechanism by which SAL induces neurotoxicity in PD remains challenging for future investigations. This study found that SAL induced neurotoxicity in SH-SY5Y cells and mice. RNA sequencing (RNAseq) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used to detect differentially expressed genes in SAL-treated SH-SY5Y cells. We found that NLR family pyrin domain-containing 3 (NLRP3)-dependent pyroptosis was enriched by SAL, which was validated by in vitro and in vivo SAL models. Further, NLRP3 inflammasome-related genes (ASC, NLRP3, active caspase 1, IL-1β, and IL-18) were increased at the mRNA and protein level. Acteoside mitigates SAL-induced neurotoxicity by inhibiting NLRP3 inflammasome-related pyroptosis in in vitro and in vivo PD models. In summary, the present study suggests for the first time that NLRP3-dependent pyroptosis plays a role in the pathogenesis of SAL-induced PD, and acteoside mitigates SAL-induced pyroptosis-dependent neurotoxicity in in vitro and in vivo PD models. The present results demonstrated a new mechanism whereby SAL mediates neurotoxicity by activating NLRP3-dependent pyroptosis, further highlighting SAL-induced pyroptosis-dependent neurotoxicity as a potential therapeutic target in PD.

Novel Dual AChE and ROCK2 Inhibitor Induces Neurogenesis via PTEN/AKT Pathway in Alzheimer's Disease Model

Alzheimer's disease (AD) is a progressive and complex neurodegenerative disease. Acetylcholinesterase inhibitors (AChEIs) are a major class of drugs used in AD therapy. ROCK2, another promising target for AD, has been associated with the induction of neurogenesis via PTEN/AKT. This study aimed to characterize the therapeutic potential of a novel donepezil-tacrine hybrid compound (TA8Amino) to inhibit AChE and ROCK2 protein, leading to the induction of neurogenesis in SH-SY5Y cells. Experiments were carried out with undifferentiated and neuron-differentiated SH-SY5Y cells submitted to treatments with AChEIs (TA8Amino, donepezil, and tacrine) for 24 h or 7 days. TA8Amino was capable of inhibiting AChE at non-cytotoxic concentrations after 24 h. Following neuronal differentiation for 7 days, TA8Amino and donepezil increased the percentage of neurodifferentiated cells and the length of neurites, as confirmed by β-III-tubulin and MAP2 protein expression. TA8Amino was found to participate in the activation of PTEN/AKT signaling. In silico analysis showed that TA8Amino can stably bind to the active site of ROCK2, and in vitro experiments in SH-SY5Y cells demonstrate that TA8Amino significantly reduced the expression of ROCK2 protein, contrasting with donepezil and tacrine. Therefore, these results provide important information on the mechanism underlying the action of TA8Amino with regard to multi-target activities.

Novel pentacyclic triterpenes exhibiting strong neuroprotective activity in SH-SY5Y cells in salsolinol- and glutamate-induced neurodegeneration models

Novel triterpene derivatives were prepared and evaluated in salsolinol (SAL)- and glutamate (Glu)-induced models of neurodegeneration in neuron-like SH-SY5Y cells. Among the tested compounds, betulin triazole 4 bearing a tetraacetyl-β-d-glucose substituent showed a highly potent neuroprotective effect. Further studies revealed that removal of tetraacetyl-β-d-glucose part (free triazole derivative 10) resulted in strong neuroprotection in the SAL model at 1 μM, but this derivative suffered from cytotoxicity at higher concentrations. Both compounds modulated oxidative stress and caspase-3,7 activity, but 10 showed a superior effect comparable to the Ac-DEVD-CHO inhibitor. Interestingly, while both 4 and 10 outperformed the positive controls in blocking mitochondrial permeability transition pore opening, only 4 demonstrated potent restoration of the mitochondrial membrane potential (MMP) in the model. Derivatives 4 and 10 also showed neuroprotection in the Glu model, with 10 exhibiting the strongest oxidative stress reducing effect among the tested compounds, while the neuroprotective activity of 4 was probably due recovery of the MMP.

Neurotoxicity of e-cigarettes

It appears that electronic cigarettes (EC) are a less harmful alternative to conventional cigarette (CC) smoking, as they generate substantially lower levels of harmful carcinogens and other toxic compounds. Thus, switching from CC to EC may be beneficial for smokers. However, recent accounts of EC- or vaping-associated lung injury (EVALI) has raised concerns regarding their adverse health effects. Additionally, the increasing popularity of EC among vulnerable populations, such as adolescents and pregnant women, calls for further EC safety evaluation. In this state-of-the-art review, we provide an update on recent findings regarding the neurological effects induced by EC exposure. Moreover, we discuss possible neurotoxic effects of nicotine and numerous other chemicals which are inherent both to e-liquids and EC aerosols. We conclude that in recognizing pertinent issues associated with EC usage, both government and scientific researchers must address this public health issue with utmost urgency.

Nicotine protects against manganese and iron-induced toxicity in SH-SY5Y cells: Implication for Parkinson's disease

Manganese (Mn) and iron (Fe) are trace elements that are essential for proper growth and physiological functions as both play critical role in a variety of enzymatic reactions. At high concentrations, however, they can be toxic and cause neurodegenerative disorders, particularly Parkinson-like syndromes. Nicotine, on the other hand, has been shown to have neuroprotective effects against various endogenous or exogenous toxins that selectively damage the dopaminergic cells. These cells include neuroblastoma-derived SH-SY5Y cells which express significant dopaminergic activity. However, practically no information on possible neuroprotective effects of nicotine against toxicity induced by trace elements is available. Therefore, in this study we investigated the effects of nicotine on toxicity induced by manganese or iron in these cells. Exposure of SH-SY5Y cells for 24 h to manganese (20 μM) or iron (20 μM) resulted in approximately 30% and 35% toxicity, respectively. Pretreatment with nicotine (1 μM) completely blocked the toxicities of Mn and Fe. The effects of nicotine, in turn, were blocked by selective nicotinic receptor antagonists. Thus, dihydro-beta erythroidine (DHBE), a selective alpha 4-beta 2 subtype antagonist and methyllycaconitine (MLA), a selective alpha7 antagonist, as well as mecamylamine, a non-selective nicotinic antagonist all dose-dependently blocked the protective effects of nicotine against both Mn and Fe. These findings provide further support for the potential utility of nicotine or nicotinic agonists in Parkinson's disease-like neurodegenerative disorders, including those that might be precipitated by trace elements, such as Fe and Mn. Moreover, both alpha4-beta2 and alpha7 nicotinic receptor subtypes appear to mediate the neuroprotective effects of nicotine against toxicity induced by these two trace metals.

Hormetic approaches to the treatment of Parkinson's disease: Perspectives and possibilities

Age-related changes in the brain reflect a dynamic interaction of genetic, epigenetic, phenotypic, and environmental factors that can be temporally restricted or more longitudinally present throughout the lifespan. Fundamental to these mechanisms is the capacity for physiological adaptation through modulation of diverse molecular and biochemical signaling occurring from the intracellular to the network-systemic level throughout the brain. A number of agents that affect the onset and progression of Parkinson's disease (PD)-like effects in experimental models exhibit temporal features, and mechanisms of hormetic dose responses. These findings have particular significance since the hormetic dose response describes the amplitude and range of potential therapeutic effects, thereby affecting the design and conduct of studies of interventions against PD (and other neurodegenerative diseases), and may also be important to a broader consideration of hormetic processes in resilient adaptive responses that might afford protection against the onset and/or progression of PD and related disorders.

Protective Effects of Donepezil Against Alcohol-Induced Toxicity in Cell Culture: Role of Caspase-3

Ethanol (EtOH) is one of the most frequently abused drugs with heavy health, economic, and societal burdens. Although moderate to low EtOH may have some neuroprotective effects, heavy EtOH consumption associated with high blood alcohol level (BAL) can be quite detrimental. The brain is particularly vulnerable to the damaging effects of high BAL, leading to neuronal loss, cognitive, and behavioral deficits. Although the exact causes of these detriments are not fully elucidated, it is believed that damage to the cholinergic system is at least partially responsible for the cognitive impairment. Thus, high BAL may result in selective apoptotic damage to the cholinergic neurons. Donepezil (DON), a centrally acting, reversible and non-competitive acetylcholinesterase (AChE) inhibitor, approved for use in Alzheimer's disease (AD), may also attenuate EtOH-induced cognitive impairment. Cognitive effects of DON might be due to an anti-apoptotic activity as some AChE inhibitors have been shown to have this property. The aim of this study was to determine whether DON might protect against EtOH-induced toxicity and whether such protection might be apoptotically mediated. We exposed the human neuroblastoma-derived, SH-SY5Y cells to a relatively high concentration of EtOH (500 mM) for 24 h and evaluated the effects of two concentrations of DON (0.1 and 1.0 μM) on alcohol-induced toxicity and caspase-3, an apoptotic marker. We found a dose-dependent protection of DON against EtOH-induced toxicity as well as dose-dependent attenuation of EtOH-induced increases in caspase-3 levels. Thus, DON may inhibit apoptosis as well as alcohol-induced toxicity.

Mechanistic evaluation of neuroprotective effect of estradiol on rotenone and 6-OHDA induced Parkinson's disease

BACKGROUND

The present study was intended to investigate the protective effect of estradiol against Parkinson's disease through the use of rotenone-induced neurotoxicity model.

METHODS

To define the effect on the behavioral function, Tail suspension test, morris water maize test and cylinder tests were performed. Several biochemical and histological markers related to Parkinson's disease was determined in animal and cell culture models. To evaluate the effect of estradiol on the cellular architecture in rotenone-induced brain tissue, the histopathological examination was carried out by using Haemotoxylin and Eosin staining. Moreover, estradiol effect was also been investigated for its protective effect against Parkinson's disease using cell culture model with use of brain endothelial cells. The flowcytometric analysis was carried out to measure apoptosis in cell culture model.

RESULTS

The abnormal level of antioxidant enzymes and lipid peroxidation were regulated toward the normal intensity under the influence of estradiol. Furthermore, intracellular ROS level and apoptosis were found to be reduced following estradiol treatment. During the 6-OHDA induced PD, the level of antioxidant marker such as GSH, ROS and TRAP, found to be significantly modulated by the estradiol.

CONCLUSION

In view of the above results, it may be suggested that the estradiol may be as a useful therapeutic agent against rotenone-induced neurotoxicity such as Parkinson's disease.

Neuroprotective effect of carnosine against salsolinol-induced Parkinson's disease

Carnosine is a dipeptide of β-alanine and histidine amino acids. It is widely present in muscle and brain tissues. Carnosine has been demonstrated to be an antioxidant agent that is beneficial in animals. Reactive oxygen species (ROS) and aldehydes are are generated from membrane fatty acid oxidation. The antioxidant potential and toxicity of salsolinol had been extensively studied in vivo and in vitro. The present study analyzed the protective effect of carnosine against Parkinson's disease in the salsolinol-induced rat brain and rat brain endothelial cells. Antioxidant and biochemical markers were determined in vitro and in vivo. Histopathological examination was completed in order to evaluate the protective effect of carnosine on the cellular architecture of salsolinol-induced brain tissue. In order to confirm the protective effect of carnosine further, it was also investigated at an in vitro level using rat brain endothelial cells. Fluorescence and confocal studies indicated reduced apoptosis in the endothelial cells of the rat brain tissue. Antioxidant enzymes and lipid peroxidation levels were renormalized following treatment with carnosine. In addition, carnosine treatment reduced mitochondria-derived ROS in the rat brain endothelial cells. These findings suggest that carnosine may be a therapeutic agent against salsolinol-induced Parkinson's.

Dose-dependent effect of Curcuma longa for the treatment of Parkinson's disease

Curcuma longa is a plant that belongs to the ginger family, Zingiberaceae. It has been used in Siddha medicine for thousands of years in Asia. Parkinson's disease (PD) is a degenerative disorder of the central nervous system that affects the motor system of the brain. Death of dopamine-producing cells in the substantia nigra leads to PD. Exposure to salsolinol, which is an endogenous neurotoxin, has been associated with damage to dopamine-producing cells. The present study assessed the toxicity of salsolinol in SH-SY5Y human neuroblastoma cells and subsequently investigated the neuroprotective potential of C. longa extract in salsolinol-induced toxic conditions in SH-SY5Y cells. Sulphorhodamine-B assay showed the protective effect of the anti-apoptotic effect of treated SH-SY5Y cells. Fluorescence microscopy and confocal laser scanning microscope analysis indicated the anti-apoptotic impact of the C. longa extract. Mitochondria-derived reactive oxygen species were reduced in C. longa extract-treated SH-SY5Y cells. Downregulated mRNA expression levels of p53, Bcl-2-associated X protein and caspase 3 were observed in the C. longa extract-treated SH-SY5Y cells. Caspase 3 activity was reduced in the C. longa extract-treated SH-SY5Y cells. In conclusion, the present findings demonstrated that solsolinol is neurotoxic to SH-SY5Y cells, and C. longa extract may be useful in the treatment of PD.

Duality of Antidepressants and Neuroprotectants

The co-morbidity of neuropsychiatric disorders, particularly major depressive disorder (MDD) with neurodegenerative diseases, in particular Parkinson's disease (PD) is now well recognized. Indeed, it is suggested that depressive disorders, especially in late life, may be an indication of latent neurodegeneration. Thus, it is not unreasonable to expect that deterrents of MDD may also deter the onset and/or progression of the neurodegenerative diseases including PD. In this review, examples of neuroprotective efficacy of established as well as prospective antidepressants are provided. Conversely, mood-regulating effects of some neuroprotective drugs are also presented. Thus, in addition to currently used antidepressants, ketamine, nicotine, curcumin, and resveratrol are discussed for their dual efficacy. In addition, potential neurobiological substrates for their actions are presented. It is concluded that pharmacological developments of mood-regulating or neuroprotective drugs can have cross benefit in co-morbid conditions of neuropsychiatric and neurodegenerative disorders and that inflammatory and neurotrophic factors play important roles in both conditions.

Low dose nicotine attenuates Aβ neurotoxicity through activation early growth response gene 1 pathway

Epidemiological studies indicate that smoking is negatively correlated with the incidence and development of Alzheimer's disease (AD). Nicotine was reported to be the active factor. However, the detailed mechanisms still remain to be fully elucidated. Early growth response gene 1 (EGR-1) plays important roles in several important biological processes such as promoting cell growth, differentiation, anti oxidative stress, and apoptosis, but few in the pathogenesis of AD. In the present study, we show that nicotine can activate the MAPK/ERK/EGR-1 signaling pathway partially through α7 nAChR. In addition, the up-regulation of EGR-1 by nicotine can also increase the phosphorylation of CyclinD1 which contributes to the attenuation of amyloid-β (Aβ(25-35)) -induced neurotoxicity. Although nicotine and Aβ(25-35) can activate EGR-1, the expression of EGR-1 is down-regulated following treatment with nicotine and Aβ(25-35). This study demonstrates that low dose nicotine attenuates Aβ(25-35)-induced neurotoxicity in vitro and in vivo through activating EGR-1 pathway.

Protective effects of curcumin against rotenone and salsolinol-induced toxicity: implications for Parkinson's disease

Parkinson's disease (PD) is a debilitating neurodegenerative disorder that results from the loss of or damage to dopaminergic cells in the substantia nigra. Exposure to either the pesticide rotenone or the endogenous neurotoxin salsolinol has been shown to mimic this dopaminergic cell loss. In this study, we first sought to determine whether combination of rotenone and salsolinol would result in an additive or synergistic toxicity. For this purpose we utilized SH-SY5Y cells, a human neuroblastoma cell line that is commonly used to model dopaminergic neurodegeneration. We then tested whether curcumin, a natural plant compound with known health benefits including potential neuroprotective properties, could also protect against rotenone and/or salsolinol-induced toxicity. Moreover, since apoptotic mechanism has been implicated in toxicity of these compounds the anti-apoptotic effect of curcumin was also evaluated. Our results indicate a synergistic toxicity of low concentrations of rotenone (1 and 5 µM) and salsolinol (25 and 50 µM) that was associated with apoptosis as determined by cell flow cytometry. There was also an increase in caspase-3 levels. Pretreatment with curcumin (1-µM) dose-dependently attenuated rotenone and/or salsolinol-induced toxicity and the associated apoptosis. These results suggest that exposure to a combination of rotenone and salsolinol may contribute to the pathology of PD, and that curcumin has a therapeutic potential in this disease.

Pinocembrin protects SH-SY5Y cells against MPP+-induced neurotoxicity through the mitochondrial apoptotic pathway

Pinocembrin (PB), the most abundant flavonoid in propolis, has been proven to have neuroprotective property against neurotoxicity in vivo and in vitro. Our recent study demonstrated the neuroprotective effect of PB against Aβ25-35-induced SH-SY5Y neurotoxicity. However, the mechanism as how PB can induce neuroprotection is not known. In the present study, we demonstrate here that PB abrogates the effects of the neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) which mimics Parkinson's disease (PD) with elevation of intracellular reactive oxygen species (ROS) level and apoptotic death. We found that pretreatment of SH-SY5Y cells with PB significantly reduced the MPP(+)-induced loss of cell viability, the generation of intracellular ROS, apoptotic rate, and the cleavage of caspase-3. PB strikingly inhibited MPP(+)-induced mitochondrial dysfunctions, including lowered membrane potential, decreased Bcl-2/Bax ratio, and the release of cytochrome c. Overall, these results suggest that PB is intimately involved in inhibiting MPP(+)-induced loss of mitochondrial function and induction of apoptosis that contributes toward neuronal survival. These data indicated that PB might provide a valuable therapeutic strategy for the treatment of PD.

Indenoindoles and cyclopentacarbazoles as bioactive compounds: synthesis and biological applications

Indenoindoles and their isomers cyclopentacarbazoles represent a wide class of synthetic and natural compounds. The great interest of these structures in (bio)organic chemistry is due to the use of various building blocks to get the elemental four ring structure. Depending on the synthetic route chosen, the chemists can achieve a large number of regioisomers. Each regioisomer can be considered as a template for specific functionalizations. Therefore, this mini-review aims (i) to present an overview on how to access this large family of heterocyclic compounds and (ii) to discuss their various biological applications and drug development in oncology (e.g. kinases), in CNS disorders (e.g. Alzheimer's disease), in endocrinology (e.g. hormone replacement therapy) and oxidative stress (e.g. organ preservation). Past and present works will be presented through the systems 6-5-5-6 and 6-5-6-5 (combination of 6-membered and 5-membered rings).

Biological activity of sym-triazines with acetylcholine-like substitutions as multitarget modulators of Alzheimer's disease

The bioactivities of two novel compounds (TAE-1 and TAE-2) that contain a sym-triazine scaffold with acetylcholine-like substitutions are examined as promising candidate agents against Alzheimer's disease. Inhibition of amyloid-β fibril formation in the presence of Aβ1-42, evaluated by Thioflavin T fluorescence, demonstrated comparable or improved activity to a previously reported pentapeptide-based fibrillogenesis inhibitor, iAβ5p. Destabilization of Aβ1-42 assemblies by TAE-1 and TAE-2 was confirmed by scanning electron microscopy imaging. sym-Triazine inhibition of acetylcholinesterase (AChE) activity was observed in cytosol extracted from differentiated human SH-SY5Y neuronal cells and also using human erythrocyte AChE. The sym-triazine derivatives were well tolerated by these cells and promoted beneficial effects on human neurons, upregulating expression of synaptophysin, a synaptic marker protein, and MAP2, a neuronal differentiation marker.

PACAP protects against salsolinol-induced toxicity in dopaminergic SH-SY5Y cells: implication for Parkinson's disease

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous 38 amino acid containing neuropeptide with various cytoprotective functions including neuroprotection. Administration of PACAP has been shown to reduce damage induced by ischemia, trauma, or exogenous toxic substances. Moreover, mice deficient in PACAP are more vulnerable to damaging insults. In this study, we sought to determine whether PACAP may also be protective against salsolinol-induced toxicity in SH-SY5Y cells and, if so, elucidate its mechanism(s) of action. Salsolinol (SALS) is an endogenous dopamine metabolite with selective toxicity to nigral dopaminergic neurons, which are directly implicated in Parkinson's disease (PD). SH-SY5Y cells, derived from human neuroblastoma cells, express high levels of dopaminergic activity and are used extensively as a model to study these neurons. Exposure of SH-SY5Y cells to 400 μM SALS for 24 h resulted in approximately 50 % cell death that was mediated by apoptosis as determined by cell flow cytometry and increases in caspase-3 levels. Cellular toxicity was also associated with reductions in brain-derived neurotrophic factor and phosphorylated cyclic AMP response element-binding protein. Pretreatment with PACAP dose-dependently attenuated SALS-induced toxicity and the associated apoptosis and the chemical changes. PACAP receptor antagonist PACAP6-38, in turn, dose-dependently blocked the effects of PACAP. Neither PACAP nor PACAP antagonist had any effect of its own on cellular viability. These results suggest the protective effects of PACAP in a cellular model of PD. Hence, PACAP or its agonists could be of therapeutic benefit in PD.

Salsolinol induced apoptotic changes in neural stem cells: amelioration by neurotrophin support

Salsolinol (SAL), a catechol isoquinoline has invited considerable attention due to its structural similarity with dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Its high endogenous presence in Parkinsonian brain implicated its possible association with the disease process. SAL is also present in alcohol beverages and certain food materials and can get access to brain especially in conditions of immature or impaired BBB. Besides this, the effect of SAL on neural stem cells (NSCs) which are potential candidates for adult neurogenesis and transplantation mediated rejuvenating attempts for Parkinson's disease (PD) brain has not been known so far. NSCs in both the cases have to overcome suppressive cues of diseased brain for their survival and function. In this study we explored the toxicity of SAL toward NSCs focusing on apoptosis and status of PI3K survival signaling. NSCs cultured from embryonic day 11 rat fetal brain including those differentiated to TH(+ve) colonies, when challenged with SAL (1-100μM), elicited a concentration and time dependent cell death/loss of mitochondrial viability. 10μM SAL on which significant mitochondrial impairment initiated was further used to study mechanism of toxicity. Morphological impairment, enhanced TUNEL positivity, cleaved caspase-3 and decreased Bcl-2:Bax suggested apoptosis. Sal toxicity coincided with reduced pAkt level and its downstream effectors: pCREB, pGSK-3β, Bcl-2 and neurotrophins GDNF, BDNF suggesting repressed PI3K/Akt signaling. Multiple neurotrophic factor support in the form of Olfactory Ensheathing Cell's Conditioned Media (OEC CM) potentially protected NSCs against SAL through activating PI3K/Akt pathway. This was confirmed on adding LY294002 the PI3K inhibitor which abolished the protection. We inferred that SAL exerts substantial toxicity toward NSCs. These findings will lead to better understanding of endogenous threats that might affect the fate of transplanted NSCs and their probable antidotes.

Neuroinflammation, neurodegeneration, and depression

Neurodegeneration and depression are two common co-morbid conditions, particularly within the aging population. Research has linked neuroinflammation as a major contributing factor to both of these diseases. The key to neuroinflammation effects on neurodegeneration and depression appears to lie within the dysregulation of the control and release of pro- and anti-inflammatory cytokines. This can come from an internal or external insult to the system, or from changes in the individual due to aging that culminate in immune dysregulation. The need to reduce neuroinflammation has led to extensive research into neuroprotectants. We discuss the efficacy found with nicotine, alcohol, resveratrol, curcumin, and ketamine. Our main focus will be on what research tells us about the connections between neuroinflammation, neurodegeneration, and depression, and the hope that neuroprotectants research gives people suffering from neurodegeneration and depression stemming from neuroinflammation. We will conclude by making suggestions for future research in this area.

Nicotine promotes survival of cells expressing amyloid precursor protein and presenilin: implication for Alzheimer's disease

Amyloid-β protein (Aβ) accumulation is one of the major hallmarks of Alzheimer's disease (AD) and plays a crucial role in its pathogenesis. Cellular models whereby amyloid precursor protein (APP) is highly expressed are commonly used to test the efficacy of novel neuroprotective compounds. In addition to Aβ, it is known that mutation in the protein presenilin contributes to early onset AD. Recently, a cellular neuroblastoma model where both APP and presenilin are expressed has become available. Since protective effects of nicotine against various neurotoxins have been observed, this study was designed to determine whether nicotine would also protect against cellular damage induced by APP or APP and presenilin. Wild type neuroblastoma (N2a) cell line, and those transfected with amyloid precursor protein (APP), and the combination of APP and presenilin were pretreated with various concentrations of nicotine and the survivability of the cells were determined by MTT assay. Nicotine dose dependently provided protection against cellular loss in all cell lines, with highest protection in the double transfected (44%) followed by single transfected (30%), and wild type (21%). The effects of nicotine in turn were blocked by mecamylamine, a non-selective nicotinic antagonist. These results suggest differential sensitivity of cell lines representing AD pathology to the protective effects of nicotine and provide further support of therapeutic potential of nicotinic agonists in at least a subtype of AD patients.

Protective effects of nicotine against aminochrome-induced toxicity in substantia nigra derived cells: implications for Parkinson's disease

Parkinson's disease is a debilitating progressive neurodegenerative disorder that results from the loss of or damage to dopaminergic cells containing neuromelanin in the substantia nigra (SN). The underlying neurodegenerative mechanism(s), however, remain elusive. Aminochrome, the precursor of neuromelanin is an endogenous substance capable of inducing selective neurotoxicity to dopaminergic neurons in SN. Nicotine, on the other hand, may offer protective effects against dopaminergic cell damage induced by various neurotoxins including MPTP and salsolinol. In this study, we sought to determine whether nicotine may also protect against aminochrome-induced toxicity in SN derived RCSN-3 cells. Exposure of RCSN-3 cells to a combination of aminochrome (50 μM) and dicoumarol (50 μM) for 48 h induced approximately 70 % cell death. Pretreatment with nicotine, dose-dependently blocked this toxicity. The effects of nicotine in turn were dose-dependently blocked by mecamylamine, a non-selective nicotinic receptor antagonist. These results suggest involvement of nicotinic receptors in protective effects of nicotine against aminochrome-induced toxicity and provide further evidence for possible therapeutic effects of nicotine or nicotinic agonists in Parkinson's disease.

Positive and negative effects of alcohol and nicotine and their interactions: a mechanistic review

Nicotine and alcohol are two of the most commonly abused legal substances. Heavy use of one drug can often lead to, or is predictive of, heavy use of the other drug in adolescents and adults. Heavy drinking and smoking alone are of significant health hazard. The combination of the two, however, can result in synergistic adverse effects particularly in incidences of various cancers (e.g., esophagus). Although detrimental consequences of smoking are well established, nicotine by itself might possess positive and even therapeutic potential. Similarly, alcohol at low or moderated doses may confer beneficial health effects. These opposing findings have generated considerable interest in how these drugs act. Here we will briefly review the negative impact of drinking-smoking co-morbidity followed by factors that appear to contribute to the high rate of co-use of alcohol and nicotine. Our main focus will be on what research is telling us about the central actions and interactions of these drugs, and what has been elucidated about the mechanisms of their positive and negative effects. We will conclude by making suggestions for future research in this area.

Toxic effects of low alcohol and nicotine combinations in SH-SY5Y cells are apoptotically mediated

It is well established that combination of heavy drinking and smoking has severe health consequences. However, at relatively low concentrations, both alcohol and nicotine may have beneficial effects including neuroprotection. Thus, protective effects of low alcohol concentration against beta-amyloid-induced toxicity in organotypic hippocampal slices and protective effects of nicotine against salsolinol-induced toxicity in human-derived neuroblastoma cells (SH-SY5Y) have been reported. In this study, we sought to determine whether alcohol might also be protective against salsolinol-induced toxicity in SH-SY5Y cells and whether the combination of low doses of alcohol and nicotine might have an additive or synergistic effect. Pre-exposure of SH-SY5Y cells to either ethanol (1 or 10 mM) or nicotine (20 or 50 μM) significantly attenuated salsolinol-induced toxicity. However, contrary to the expectation the combination of low doses of alcohol and nicotine not only did not provide any synergistic or additive protective effect, but exacerbated salsolinol-induced toxicity. Indeed, simple combination of low alcohol and nicotine resulted in significant toxicity in SH-SY5Y cells. This toxicity, reflected in a reduction in cell viability was associated with an increase in apoptosis as determined by caspase-3 measurement. These in vitro results suggest that combination of even low concentrations of alcohol and nicotine may activate apoptotic mechanisms that can lead to cell toxicity and detrimental consequences.

Effects of nicotine on depressive-like behavior and hippocampal volume of female WKY rats

The observed high incidence of smoking amongst depressed individuals has led to the hypothesis of 'self medication" with nicotine in some of these patients. The inbred Wistar-Kyoto (WKY) rats exhibit depressive-like characteristics as evidenced by exaggerated immobility in the forced swim test (FST). One aim of this study was to investigate whether nicotine may have an antidepressant-like effect in these animals. Moreover, because of human postmortem studies indicating a reduction of the hippocampus volume in depressed patients, it was of interest to determine whether such an anatomical anomaly may also be manifested in WKY rats and whether it would be affected by chronic nicotine treatment. Adult female WKY and their control Wistar rats were administered nicotine consecutively (0.2 mg/kg, i.p., once or twice daily for 14 days) and their activity in an open field, as well as their immobility in FST were assessed either 15 min or 18 h after the last injection. Another set of animals was treated twice daily with 0.2 mg/kg nicotine for 14 days and sacrificed on day 15 for stereological evaluation of the hippocampal volume. When tested 15 min after the last injection, once or twice daily nicotine exacerbated the immobility in the FST in WKY rats only. When tested 18 h after the last injection, only twice daily nicotine treatment resulted in less immobility in the FST in WKY rats. Open field locomotor activity was not affected by any nicotine regimen. WKY rats had significantly less hippocampal volume (approximately 20%) than Wistar rats which was not altered by nicotine. These findings further validate the use of WKY rats as an animal model of human depression and signify the importance of inherent genetic differences in final behavioral outcome of nicotine.