The neuroprotective effect of dental pulp cells in models of Alzheimer`s and Parkinson`s disease

Aim of the present study was to investigate the neuroprotective effect of dental pulp cells (DPCs) in in vitro models of Alzheimer and Parkinson disease. Primary cultures of hippocampal and ventral mesencephalic neurons were treated for 24 h with amyloid beta (A beta(1-42)) peptide 1-42 and 6-OHDA, respectively. DPCs isolated from adult rat incisors were previously cultured in tissue culture inserts and added to the neuron cultures 2 days prior to neurotoxin treatment. Cell viability was assessed by the MTT assay. The co-culture with DPCs significantly attenuated 6-OHDA and A beta(1-42)-induced toxicity in primary cultures of mesencephalic and hippocampal neurons, and lead to an increase in neuronal viability in untreated cultures, suggesting a neurotrophic effect in both models. Furthermore, human dental pulp cells expressed a neuronal phenotype and produced the neurotrophic factors NGF, GDNF, BDNF, and BMP2 shown by microarray screening and antibody staining for the representative proteins. DPCs protected primary neurons in in vitro models of Alzheimer`s and Parkinson`s disease and can be viewed as possible candidates for studies on cell-based therapy.

Evaluation of estrogen neuroprotective effect on nigrostriatal dopaminergic neurons following 6-hydroxydopamine injection into the substantia nigra pars compacta or the medial forebrain bundle

Studies involving estrogen treatment of ovariectomized rats or mice have attributed to this hormone a neuroprotective effect on the substantia nigra pars compacta (SNpc) neurons. We investigated the effect of estradiol replacement in ovariectomized rats on the survival of dopaminergic mesencephalic cell and the integrity of their projections to the striatum after microinjections of 1 mu g of 6-hydroxydopamine (6-OHDA) into the right SNpc or medial forebrain bundle (MFB). Estradiol replacement did not prevent the reduction either in the striatal concentrations of DA and metabolites or in the number of nigrostriatal dopaminergic neurons following lesion with 1 mu g of 6-OHDA into the SNpc. Nevertheless, estradiol treatment reduced the decrease in striatal DA following injection of 1 mu g of 6-OHDA into the MFB. Results suggest therefore that estrogen protect nigrostriatal dopaminergic neurons against a 6-OHDA injury to the MFB but not the SNpc. This may be due to the distinct degree of lesions promoted in these different rat models of Parkinson`s disease.

Non-cell autonomous neuroprotective effect of carbon monoxide : microglia-to-neuron communication

RESUMO: A isquémia cerebral é uma das doenças mais predominantes a nivel mundial, sendo uma das principais causas de mortalidade e invalidez. Parte da propagação de dano no cérebro é causado por inflamação descontrolada, causada principalmente por disfunção da microglia. Desta forma, existe a necessidade de tentar desenvolver estratégias para melhor compreender e modular as acções destas células. O monóxido de carbono (CO), é uma molécula endógena com provas dadas como anti-neuroinflamatório em vários modelos. Assim, o principal objectivo do trabalho foi o estudo do CO como um modulador da acção da microglia, com principal foco dado à comunicação entre estas células e neurónios, tentando entender se existe um efeito neuroprotector por inibição da inflamação. Um protocolo de meio condicionado foi estabelecido usando as linhas celulares BV2 e SH-SY5Y, de microglia e neurónio. A molécula CORM-A1, que liberta expontaniamente CO, foi usada como método de entrega da molécula às celulas. Demonstrámos que o pre-tratamento de células BV2 com CORM-A1 gera neuroprotecção já que reduz a morte celular de neurónios SH-SY5Y quando são incubados com meio condicionado de microglia activada em conjunto com o pró-oxidante t-BHP (tert-butil hidroperóxido). Assim, considerámos que o CO promove neuroprotecção ao inibir as acções inflamatórias da microglia. O papel anti-inflamatório da molécula CORM-A1 foi confirmado quando se verificou que pré-tratamento desta molécula em microglia BV2 limita a secreção de TNF-α mas estimula a secreção de IL-10. Por último, a CORM-A1 induziu a expressão do receptor da microglia CD200R1, molécula que participa na comunicação neurónio-microglia e fundamental para a modulação das acções inflamatórias destas últimas. Em suma, o nosso trabalho reforçou as propriedades anti-neuroinflamatórias do CO e uma capacidade de modular viabilidade neuronal através do seu efeito a nível de comunicação célula-célula. ---------------------------- ABSTRACT: Brain ischemia is a widespread disease worldwide, being one of the main causes of mortality and permanent disability. A portion of the damage that ensues following the ischemic event is caused by unrestrained inflammation, which is mainly orchestrated by exacerbated microglial activity. Hence, developing strategies for modulating microglial inflammation is a major concern nowadays. The endogenous molecule carbon monoxide (CO) has been shown to possess anti-neuroinflammatory properties using in vitro and in vivo approaches. Thus, our objective was to study CO as modulator of microglial activity, in particular in what concerns their communication with neurons, by promoting neuronal viability and limiting inflammatory output of activated microglia. A conditioned media strategy was established with BV2 microglia and SH-SY5Y neurons as cell models. CO-releasing molecule A1 (CORM-A1), a compound that releases CO spontaneously, was used as method of CO delivery to cells. We found that CORM-A1 pre-treatment in BV2 cells yields neuroprotective results, as it limits cell death when SH-SY5Y neurons are challenged with conditioned media from LPS-activated microglia and the pro-oxidant t-BHP (tert-butyl-hydroperoxide). Thus, we assumed carbon monoxide promotes neuroprotection via inhibition of microglial inflammation, displaying a non-cell autonomous role. CORM-A1 pre-treatment limited inflammation by inhibiting BV2 secretion of TNF-α and stimulating IL-10 production. These results reinforce that CO’s anti-inflammatory role confers neuroprotection, as the alterations in these cytokines occur concurrently with the increase in SH-SY5Y viability. Finally, we showed for the first time that carbon monoxide promotes the expression of CD200R1, a microglial receptor involved in neuron-glia communication and modulation of microglia inflammation. Further studies are necessary to clarify this role. Altogether, other than just highlighting CO as an anti-inflammatory and neuroprotective molecule, this work set the foundation for disclosing its involvement in cell-to-cell communication.

Neuroprotective effect of ketamine/xylazine on two rat models of Parkinson's disease

There is a great concern in the literature for the development of neuroprotectant drugs to treat Parkinson's disease. Since anesthetic drugs have hyperpolarizing properties, they can possibly act as neuroprotectants. In the present study, we have investigated the neuroprotective effect of a mixture of ketamine (85 mg/kg) and xylazine (3 mg/kg) (K/X) on the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6-hydroxydopamine (6-OHDA) rat models of Parkinson's disease. The bilateral infusion of MPTP (100 µg/side) or 6-OHDA (10 µg/side) into the substantia nigra pars compacta of adult male Wistar rats under thiopental anesthesia caused a modest (~67%) or severe (~91%) loss of tyrosine hydroxylase-immunostained cells, respectively. On the other hand, an apparent neuroprotective effect was observed when the rats were anesthetized with K/X, infused 5 min before surgery. This treatment caused loss of only 33% of the nigral tyrosine hydroxylase-immunostained cells due to the MPTP infusion and 51% due to the 6-OHDA infusion. This neuroprotective effect of K/X was also suggested by a less severe reduction of striatal dopamine levels in animals treated with these neurotoxins. In the working memory version of the Morris water maze task, both MPTP- and 6-OHDA-lesioned animals spent nearly 10 s longer to find the hidden platform in the groups where the neurotoxins were infused under thiopental anesthesia, compared to control animals. This amnestic effect was not observed in rats infused with the neurotoxins under K/X anesthesia. These results suggest that drugs with a pharmacological profile similar to that of K/X may be useful to delay the progression of Parkinson's disease.

Neuroprotective effect of excitatory amino acid antagonist kynurenic acid in experimental bacterial meningitis

Sustained high-level exposure to glutamate, an excitatory amino acid neurotransmitter, leads to neuronal death. Kynurenic acid attenuates the toxic effects of glutamate by inhibition of neuronal excitatory amino acid receptors, including the N-methyl-D-aspartate subtype. To evaluate the role of glutamate in causing neuronal injury in a rat model of meningitis due to group B streptococci, animals were treated with kynurenic acid (300 mg/kg subcutaneously once daily) or saline beginning at the time of infection. Histopathologic examination after 24-72 h showed two distinct forms of neuronal injury, areas of neuronal necrosis in the cortex and injury of dentate granule cells in the hippocampus. Animals treated with kynurenic acid showed significantly less neuronal injury (P < .03) in the cortex and the hippocampus than did untreated controls. These results suggest an important contribution of glutamate to neurotoxicity in this animal model of neonatal meningitis.

Neuroprotective effect of cathodal transcranial direct current stimulation in a rat stroke model

Experimental focal brain ischemia generates in the penumbra recurrent depolarizations which spread across the injured cortex inducing infarct growth. Transcranial direct current stimulation can induce a lasting, polarity-specific, modulation of cortical excitability. To verify whether cathodal transcranial direct current stimulation could reduce the infarct size and the number of depolarizations, focal ischemia was induced in the rat by the 3 vessels occlusion technique. In the first experiment 12 ischemic rats received cathodal stimulation (alternating 15min on and 15min off) starting 45min after middle cerebral artery occlusion and lasting 4h. In the second experiment 12 ischemic rats received cathodal transcranial direct current stimulation with the same protocol but starting soon after middle cerebral artery occlusion and lasting 6h. In both experiments controls were 12 ischemic rats not receiving stimulation. Cathodal stimulation reduced the infarct volume in the first experiment by 20% (p=0.002) and in the second by 30% (p=0.003). The area of cerebral infarction was smaller in animals receiving cathodal stimulation in both experiments (p=0.005). Cathodal stimulation reduced the number of depolarizations (p=0.023) and infarct volume correlated with the number of depolarizations (p=0.048). Our findings indicate that cathodal transcranial direct current stimulation exert a neuroprotective effect in the acute phase of stroke possibly decreasing the number of spreading depolarizations. These findings may have translational relevance and open a new avenue in neuroprotection of stroke in humans.

The neuroprotective effect of pituitary adenylate cyclase-activating polypeptide on cerebellar granule cells is mediated through inhibition of the CED3-related cysteine protease caspase-3/CPP32

Caspase-3 knockout mice exhibit thickening of the internal granule cell layer of the cerebellum. Concurrently, it has been shown that intracerebral injection of pituitary adenylate cyclase-activating polypeptide (PACAP) induces a transient increase of the thickness of the cerebellar cortex. In the present study, we have investigated the possible effect of PACAP on caspase activity in cultured cerebellar granule cells from 8-day-old rat. Incubation of granule neurons with PACAP for 24 h promoted cell survival and prevented DNA fragmentation. Exposure of cerebellar granule cells to the specific caspase-3 inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp fluoromethylketone (Z-DEVD-FMK) for 24 h markedly enhanced cell survival and inhibited apoptotic cell death. Time-course studies revealed that PACAP causes a prolonged inhibition of caspase-3 activity without affecting caspase-1. Administration of graded concentrations of PACAP for 3 h induced a dose-dependent inhibition of caspase-3 activity. Incubation of granule cells with both dibutyryl-cAMP (dbcAMP) and phorbol 12-myristate 13-acetate (PMA) mimicked the inhibitory effect of PACAP on caspase-3. Cotreatment of cultured neurons with the protein kinase A inhibitor H89 and the protein kinase C inhibitor chelerythrine abrogated the effect of PACAP on caspase-3 activity. In contrast, the ERK kinase inhibitor U0126 did not affect the action of PACAP on caspase-3 activity. These data demonstrate that PACAP prevents cerebellar granule neurons from apoptotic cell death through a protein kinase A- and protein kinase C-dependent inhibition of caspase-3 activity.

Vascular endothelial growth factor: Direct neuroprotective effect in in vitro ischemia

Vascular endothelial growth factor (VEGF) is a hypoxia-inducible angiogenic peptide with recently identified neurotrophic effects. Because some neurotrophic factors can protect neurons from hypoxic or ischemic injury, we investigated the possibility that VEGF has similar neuroprotective properties. In HN33, an immortalized hippocampal neuronal cell line, VEGF reduced cell death associated with an in vitro model of cerebral ischemia: at a maximally effective concentration of 50 ng/ml, VEGF approximately doubled the number of cells surviving after 24 h of hypoxia and glucose deprivation. To investigate the mechanism of neuroprotection by VEGF, the expression of known target receptors for VEGF was measured by Western blotting, which showed that HN33 cells expressed VEGFR-2 receptors and neuropilin-1, but not VEGFR-1 receptors. The neuropilin-1 ligand placenta growth factor-2 failed to reproduce the protective effect of VEGF, pointing to VEGFR-2 as the site of VEGF's neuroprotective action. Two phosphatidylinositol 3′-kinase inhibitors, wortmannin and LY294002, reversed the neuroprotective effect of VEGF, implicating the phosphatidylinositol 3′-kinase/Akt signal transduction system in VEGF-mediated neuroprotection. VEGF also protected primary cultures of rat cerebral cortical neurons from hypoxia and glucose deprivation. We conclude that in addition to its known role as an angiogenic factor, VEGF may exert a direct neuroprotective effect in hypoxic-ischemic injury.

Neuroprotective Effect of Tauroursodeoxycholic Acid on N-Methyl-D-Aspartate-Induced Retinal Ganglion Cell Degeneration

Retinal ganglion cell degeneration underlies the pathophysiology of diseases affecting the retina and optic nerve. Several studies have previously evidenced the anti-apoptotic properties of the bile constituent, tauroursodeoxycholic acid, in diverse models of photoreceptor degeneration. The aim of this study was to investigate the effects of systemic administration of tauroursodeoxycholic acid on N-methyl-D-aspartate (NMDA)-induced damage in the rat retina using a functional and morphological approach. Tauroursodeoxycholic acid was administered intraperitoneally before and after intravitreal injection of NMDA. Three days after insult, full-field electroretinograms showed reductions in the amplitudes of the positive and negative-scotopic threshold responses, scotopic a- and b-waves and oscillatory potentials. Quantitative morphological evaluation of whole-mount retinas demonstrated a reduction in the density of retinal ganglion cells. Systemic administration of tauroursodeoxycholic acid attenuated the functional impairment induced by NMDA, which correlated with a higher retinal ganglion cell density. Our findings sustain the efficacy of tauroursodeoxycholic acid administration in vivo, suggesting it would be a good candidate for the pharmacological treatment of degenerative diseases coursing with retinal ganglion cell loss.

Exploring cinnamic acid scaffold: development of promising neuroprotective lipophilic antioxidants

New lipophilic hydroxycinnamic acid based derivatives were designed and synthesized and their antioxidant and neuroprotective activities evaluated. The chemical modification introduced in the cinnamic acid scaffold leads to compounds with amplified lipophilicity and in general with increased antioxidant activity when compared to natural models (caffeic and ferulic acids). The compounds did not display cytotoxicity and present a significant neuroprotective effect against 6-OH-DA induced damage to SH-SY5Y cells. Compound 6 stands out as an efficient radical scavenger and iron(II) chelator that ensures drug-like properties. Moreover, neuroprotection against oxidative damage was observed even at low concentration (1 μM). Therefore, compound 6 developed by a biology-oriented approach displays a combination of important features for a further optimization process that will generate a new effective antioxidant with therapeutic application for oxidative-stress-related events, namely neurodegenerative diseases.

A systematic review of existing data on long-term lithium therapy: neuroprotective or neurotoxic?

Lithium is an efficacious agent for the treatment of bipolar disorder, but it is unclear to what extent its long-term use may result in neuroprotective or toxic consequences. Medline was searched with the combination of the word 'Lithium' plus key words that referred to every possible effect on the central nervous system. The papers were further classified into those supporting a neuroprotective effect, those in favour of a neurotoxic effect and those that were neutral. The papers were classified into research in humans, animal and in-vitro research, case reports, and review/opinion articles. Finally, the Natural Standard evidence-based validated grading rationale was used to validate the data. The Medline search returned 970 papers up to February 2006. Inspection of the abstracts supplied 214 papers for further reviewing. Eighty-nine papers supported the neuroprotective effect (6 human research, 58 animal/in vitro, 0 case reports, 25 review/opinion articles). A total of 116 papers supported the neurotoxic effect (17 human research, 23 animal/in vitro, 60 case reports, 16 review/opinion articles). Nine papers supported no hypothesis (5 human research, 3 animal/in vitro, 0 case reports, 1 review/opinion articles). Overall, the grading suggests that the data concerning the effect of lithium therapy is that of level C, that is 'unclear or conflicting scientific evidence' since there is conflicting evidence from uncontrolled non-randomized studies accompanied by conflicting evidence from animal and basic science studies. Although more papers are in favour of the toxic effect, the great difference in the type of papers that support either hypothesis, along with publication bias and methodological issues make conclusions difficult. Lithium remains the 'gold standard' for the prophylaxis of bipolar illness, however, our review suggests that there is a rare possibility of a neurotoxic effect in real-life clinical practice even in closely monitored patients with 'therapeutic' lithium plasma levels. It is desirable to keep lithium blood levels as low as feasible with prophylaxis.

Phagocytosis of Photoreceptor Outer Segments by Transplanted Human Neural Stem Cells as a Neuroprotective Mechanism in Retinal Degeneration

Purpose. Transplantation of human central nervous system stem cells (HuCNS-SC) into the subretinal space of Royal College of Surgeons (RCS) rats preserves photoreceptors and visual function. To explore possible mechanism(s) of action underlying this neuroprotective effect, we performed a detailed morphologic and ultrastructure analysis of HuCNS-SC transplanted retinas. Methods. The HuCNS-SC were transplanted into the subretinal space of RCS rats. Histologic examination of the transplanted retinas was performed by light and electron microscopy. Areas of the retina adjacent to HuCNS-SC graft (treated regions) were analyzed and compared to control sections obtained from the same retina, but distant from the transplant site (untreated regions). Results. The HuCNS-SC were detected as a layer of STEM 121 immunopositive cells in the subretinal space. In treated regions, preserved photoreceptor nuclei, as well as inner and outer segments were identified readily. In contrast, classic signs of degeneration were observed in the untreated regions. Interestingly, detailed ultrastructure analysis revealed a striking preservation of the photoreceptor–bipolar–horizontal cell synaptic contacts in the outer plexiform layer (OPL) of treated areas, in stark contrast with untreated areas. Finally, the presence of phagosomes and vesicles exhibiting the lamellar structure of outer segments also was detected within the cytosol of HuCNS-SC, indicating that these cells have phagocytic capacity in vivo. Conclusions. This study reveals the novel finding that preservation of specialized synaptic contacts between photoreceptors and second order neurons, as well as phagocytosis of photoreceptor outer segments, are potential mechanism(s) of HuCNS-SC transplantation, mediating functional rescue in retinal degeneration.

Survival, differentiation, and neuroprotective mechanisms of human stem cells complexed with neurotrophin-3-releasing pharmacologically active microcarriers in an ex vivo model of Parkinson's disease

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Neuroprotective role of nutraceutical and phytochemical components

Neurodegenerative diseases (NDs) are characterized by a multifactorial etiology, in which oxidative stress and inflammation are the main causative factors. For this reason, increasing attention is being paid to the characterization and the identification of nutraceuticals and phytochemicals with intrinsic pleiotropic activity. Moreover, in a Circular Economy perspective, these natural compounds can be obtained also from renewable resources derived from the food industry by-products and can be used for both preventive and therapeutic purposes. The aim of this PhD program was to identify nutraceuticals and phytochemicals, both as extracts and pure compounds, and obtained from both plant and renewable sources, which due to their antioxidant and anti-inflammatory properties, were able to counteract cellular and molecular alterations that characterize NDs. Their neuroprotective potential has been evaluated in an in vitro model of neuroinflammation (the LPS-activated BV-2 microglial cell line), and/or in an in vitro model of neuronal oxidative stress (the neuron-like SH-SY5Y cell line differentiated with retinoic acid and exposed to H2O2). Four different projects, although deeply linked by the aforementioned common goal, have been discussed in this thesis: 1_ Impact of phenolic profile of different cherry cultivars on the potential neuroprotective effect in SH-SY5Y cells. 2_Anti-inflammatory activities of Spilanthol-rich essential oil from Acmella oleracea (L.). 3_Study of the anti-inflammatory activity of novel tacrine derivatives with lipids extracted from cashew nutshell liquid. 4_Coffee Silverskin (CSS) and Spent Coffee Grounds (SCG): coffee industry by-products as a promising source of neuroprotective agents. In general, it is, therefore, possible to conclude that the natural compounds studied in this thesis have been proven, due to their antioxidant and/or anti-inflammatory properties, to be valid preventive and therapeutic strategies for the treatment of NDs, to improve the life quality of these patients and of the general population by preventing and combating the onset of these deleterious diseases.

Effects of ascorbic acid supplementation in ileum myenteric neurons of streptozotocin-induced diabetic rats

The exacerbation of the oxidative stress and of the polyol pathway which impair damage myenteric plexus are metabolic characteristics of diabetes. The ascorbic acid (AA) is an antioxidant and an aldose reductase inhibitor, which may act as neuroprotector. The effects of AA supplementation on the density and cellular body profile area (CP) of myenteric neurons in STZ-induced diabetes in rats were assessed. Four groups with five animals each were formed: normoglycemic (C); diabetic (D); AA-treated diabetic (DS) and AA-treated normoglycemic (CS). Dosagen of 50mg of AA were given, three times a week, for each animal (group DS and CS). Ninety days later and after euthanasia, the ileum was collected and processed for the NADPH-diaphorase technique. There were no differences (P>0.05) in the neuronal density among the groups. The CP area was lower (P<0.05) in the DS and CS groups, with a higher incidence of neurons with a CP area exceeding 200µm² for groups C and D. The AA had no influence on the neuronal density in the ileum but had a neuroprotective effect, preventing the increase in the CP area and allowing a higher number of neurons with a CP area with less than 200µm².