Acute and chronic effects of intravitreally injected beta-amyloid on the neurotransmitter system in the retina.

The potential cytotoxic effect of aggregated Abeta(1-42) to neurons that express classical neurotransmitters, including acetylcholine, gamma-amino butyric acid, catecholamines and serotonin was assessed. The cholinergic system has been the central focus of the therapeutic drug strategies in amyloid-depositing pathologies such as Alzheimer's disease. Aggregated Abeta(1-42) has a multisystem cytotoxic effect causing non-specific reduction in immunoreactivity, dysfunction, or loss of retinal nerve cells. The extent of this was investigated using immunocytochemistry, TUNEL staining for apoptosis, and measurement of cell density as well as retinal surface area. There was a differential acute and/or chronic effect of Abeta on choline acetyltransferase, gamma-aminobutyric acid and 5-tryptamine hydroxylase systems, observed with the increasing time course of 6h to 5 months, and a bilateral/systemic effect. In contrast, the overall pattern of catecholaminergic system, as revealed by tyrosine hydroxylase immunoreactivity of the retina, appears to have remained relatively unaffected by Abeta (however this may reflect neuronal loss due to reduction in the retinal surface). This is the first in vivo evidence in a CNS model to show that not only all major neurotransmitter systems are differentially affected by Abeta aggregates but the effect may vary from one transmitter system to another under the same experimental conditions in situ and in a dose- and time-dependent manner.

Analysis of neural potential of human umbilical cord blood-derived multipotent mesenchymal stem cells in response to a range of neurogenic stimuli.

We investigated the neurogenic potential of full-term human umbilical cord blood (hUCB)-derived multipotent mesenchymal stem cells (MSCs) in response to neural induction media or coculture with rat neural cells. Phenotypic and functional changes were assessed by immunocytochemistry, RT-PCR, and whole-cell patch-clamp recordings. Naive MSCs expressed both mesodermal and ectodermal markers prior to neural induction. Exposure to retinoic acid, basic fibroblast growth factor, or cyclic adenosine monophosphate (cAMP) did not stimulate neural morphology, whereas exposure to dibutyryl cAMP and 3-isobutyl-1-methylxanthine stimulated a neuron-like morphology but also appeared to be cytotoxic. All protocols stimulated increases in expression of the neural precursor marker nestin, but expression of mature neuronal or glial markers MAP2 and GFAP was not observed. Nestin expression increases were serum level dependent. Electrophysiological properties of MSCs were studied with whole-cell patch-clamp recordings. The MSCs possessed no ionic currents typical of neurons before or after neural induction protocols. Coculture of hUCB-derived MSCs and rat neural cells induced some MSCs to adopt an astrocyte-like morphology and express GFAP protein and mRNA. Our data suggest hUCB-derived MSCs do not transdifferentiate into mature functioning neurons in response to the above neurogenic protocols; however, coculture with rat neural cells led to a minority adopting an astrocyte-like phenotype.

Alterations in presenilin 1 processing by amyloid-beta peptide in the rat retina.

Accumulating evidence indicates that mutations in the presenilin 1 (PS1) gene are responsible for most cases of familial Alzheimer's disease (AD). Although its biological functions are not yet fully understood, it appears that PS1 plays a role in the processing and trafficking of the amyloid precursor protein (APP). However, little is known about factors that are involved in regulating the metabolism of PS1 especially in relation to AD pathology. In this study, we have examined the effect of optic nerve crush, intravitreal injection of the inflammatory agent lipopolysaccharide (LPS) or injection of amyloid beta(1-42) (A beta(1-42)) on the expression and processing of PS1 in the rat retina. We found that 48 h after injection of A beta(1-42) there was a dramatic alteration in the banding pattern of PS1 on Western blots, as indicated by marked changes in the levels of expression of some of its C- and N-terminal fragments in retinal homogenates. These results suggest an A beta(1-42)-induced potentiation of a non-specific stress-related but inflammation-independent alteration of processing of PS1 in this in vivo model.

Ergothioneine rescues PC12 cells from beta-amyloid-induced apoptotic death.

Beta-amyloid (Abeta) peptide is the major component of senile plaques and considered to have a causal role in the development and progression of Alzheimer's disease. There has been compelling evidence that Abeta-induced cytotoxicity is mediated through oxidative and/or nitrosative stress. Recently, considerable attention has been focused on dietary manipulation of oxidative and/or nitrosative damage. l-Ergothioneine (EGT; 2-mercaptohistidine trimethylbetaine) is a low-molecular-weight naturally occurring thiol compound of dietary origin that exists in the brain, liver, kidney, erythrocytes, ocular tissues, and seminal fluids of mammals. This water-soluble antioxidant has the ability to scavenge hydroxyl and peroxynitrite radicals as well as activated oxygen species, such as singlet oxygen. In this study, we investigated the effects of EGT on Abeta-induced oxidative and/or nitrosative cell death. Rat pheochromocytoma (PC12) cells treated with Abeta underwent apoptotic death as determined by positive in situ terminal end-labeling (TUNEL staining), decreased mitochondrial transmembrane potential, increased ratio of proapoptotic Bax to antiapoptotic Bcl-XL, elevated caspase-3 activity, and cleavage of poly(ADP-ribose) polymerase. EGT pretreatment attenuated Abeta-induced apoptosis in PC12 cells. Compared to N-acetyl-l-cysteine, which mainly scavenges reactive oxygen species, EGT effectively inhibited Abeta-induced cell death by suppressing peroxynitrite formation and subsequent nitration of protein tyrosine residues. The effects of EGT on the cytotoxicity induced by the nitric oxide donor sodium nitroprusside (SNP) and the peroxynitrite-generating 3-morpholinosydnonimine chlorhydrate (SIN-1) were compared. Whereas EGT significantly protected against SIN-1-mediated cell death, it barely affected the cytotoxicity induced by SNP. Thus EGT may attenuate apoptosis caused by Abeta, preferentially by eliminating peroxynitrite derived from the neurotoxic peptide. The importance of diet-derived antioxidants in the management of Alzheimer's disease and other neurodegenerative disorders is discussed.

Up-regulation of soluble amyloid precursor protein fragment secretion in the rat retina in vivo by metabotropic glutamate receptor stimulation.

Using the novel rat retinal-vitreal model we have investigated the effect of metabotropic glutamate receptor activation on amyloid precursor protein (APP) metabolism. The release of low mol. wt fragments of APP, at 15-23 kDa in particular, was markedly up-regulated by the metabotropic glutamate receptor agonist (1S,3R)-1-amino-1,3-cyclopentane dicarboxylic acid ((1S,3R)-ACPD) in a concentration- and time-dependent manner, and this response was blocked by the receptor antagonist (S)-alpha-methyl-4-caboxyphenylglycine ((S)-MCPG). These results, together with the observation of a lack of deleterious effects of (1S,3R)-ACPD on the retinal neurons, support a physiological role of metabotropic glutamate receptors in mediating the release of soluble APP fragments, an action which may have important functional and therapeutic implications for Alzheimer's disease.

Ergothioneine treatment protects neurons against N-methyl-D-aspartate excitotoxicity in an in vivo rat retinal model.

Injection of the glutamate agonist N-methyl-D-aspartate into the vitreous body of the rat eye resulted in a number of morphological changes in the retina. Most apparent was a dramatic reduction in the density and sizes of neurons accompanied by a decrease in amyloid precursor protein and glial fibrillary acidic protein immunoreactivity. Cell counts revealed that 81% of ganglion cells and 43% of non-ganglion cells were lost as a result of the treatment. However, in animals treated with the antioxidant ergothioneine, these figures dropped to 44 and 31%, respectively. Thus, ergothioneine appears to be neuroprotective in this system and the data suggest that antioxidants may provide a useful means of modulating glutamate-based toxicity.

The antioxidant cocktail, effective microorganism X (EM-X), protects retinal neurons in rats against N-methyl-D-aspartate excitotoxicity in vivo.

Injection of the glutamate agonist N-methyl-D-aspartate (NMDA) into the vitreous body of rats resulted in severe degeneration of neurons in the retina, with a loss of 81% of ganglion cells and 43% of non-ganglion cells. The cocktail EM-X is a novel antioxidant drink derived from ferment of unpolished rice, papaya and sea-weeds with effective microorganisms (EM-X). In animals treated with an intraperitoneal injection of EM-X, the loss of ganglion cells was reduced to 55% and that of non-ganglion cells to 34% when compared to untreated NMDA-injected retinas. Cell degeneration resulting from NMDA excitotoxicity, is thought to be mediated via oxidative stress mechanisms. The neuroprotective effect of the EM-X in this system is therefore likely to be due, at least in part, to its flavonoids, saponins, vitamin E and ascorbic content.

Neuroprotection by bioactive components in medicinal and food plant extracts.

Neurodegenerative diseases of the human brain comprise a variety of disorders that affect an increasing percentage of the population. Some of these are age dependent (e.g. Alzheimer's and Parkinson's diseases) and some are infection dependent, e.g. human immunodeficiency virus (HIV/AIDS). The vulnerable brain regions in HIV/AIDS individuals include the dentate nucleus in the cerebellum, the red nucleus, substantia nigra (SN) in the mid-brain, the subthalamic nucleus, thalamic fasciculus in the diencephalons, the globus pallidus and striatum (or neostriatum, which consists of caudate and putamen) in the forebrain. Lesion in these regions may lead to progressive dementia, which is similar to what is observed in Alzheimer's disease and Parkinson's disease. The entry of calcium into the cytoplasm of cells at concentrations that can activate oxidative enzymes such as phospholipase A(2) and xanthine oxidase, deplete cells of cysteine and glutathione, cause mitochondrial release of free radicals and cell death. Glutamate and its receptors are key molecular elements at the interface between neurons and glia. Dietary factors can modulate physiological functions (including brain function) thereby increasing the economic productivity of a population as a function of health. A greater understanding of the molecular mechanisms of neuroprotection, oxidative stress and immune function will facilitate definition of the prophylactic potentials of diet, nutritional/food supplements, medicinal plants and herbal extracts.

Targeting specific cell signaling transduction pathways by dietary and medicinal phytochemicals in cancer chemoprevention.

Natural phytochemicals derived from dietary sources or medicinal plants have gained significant recognition in the potential management of several human clinical conditions. Much research has also been geared towards the evaluation of plant extracts as effective prophylactic agents since they can act on specific and/or multiple molecular and cellular targets. Plants have been an abundant source of highly effective phytochemicals which offer great potential in the fight against cancer by inhibiting the process of carcinogenesis through the upregulation of cytoprotective genes that encode for carcinogen detoxifying enzymes and antioxidant enzymes. The mechanistic insight into chemoprevention further includes induction of cell cycle arrest and apoptosis or inhibition of signal transduction pathways mainly the mitogen-activated protein kinases (MAPK), protein kinases C (PKC), phosphoinositide 3-kinase (PI3K), glycogen synthase kinase (GSK) which lead to abnormal cyclooxygenase-2 (COX-2), activator protein-1 (AP-1), nuclear factor-kappaB (NF-κB) and c-myc expression. Effectiveness of chemopreventive agents reflects their ability to counteract certain upstream signals that leads to genotoxic damage, redox imbalances and other forms of cellular stress. Targeting malfunctioning molecules along the disrupted signal transduction pathway in cancer represent a rational strategy in chemoprevention. NF-κB and AP-1 provide mechanistic links between inflammation and cancer, and moreover regulate tumor angiogenesis and invasiveness, indicating that signaling pathways that mediate their activation provide attractive targets for new chemotherapeutic approaches. Thus cell signaling cascades and their interacting factors have become important targets of chemoprevention and phenolic phytochemicals and plant extracts seem to be promising in this endeavor.

Human umbilical cord blood-derived mesenchymal stem cells do not differentiate into neural cell types or integrate into the retina after intravitreal grafting in neonatal rats.

This study investigated the ability of mesenchymal stem cells (MSCs) derived from full-term human umbilical cord blood to survive, integrate and differentiate after intravitreal grafting to the degenerating neonatal rat retina following intracranial optic tract lesion. MSCs survived for 1 week in the absence of immunosuppression. When host animals were treated with cyclosporin A and dexamethasone to suppress inflammatory and immune responses, donor cells survived for at least 3 weeks, and were able to spread and cover the entire vitreal surface of the host retina. However, MSCs did not significantly integrate into or migrate through the retina. They also maintained their human antigenicity, and no indication of neural differentiation was observed in retinas where retinal ganglion cells either underwent severe degeneration or were lost. These results have provided the first in vivo evidence that MSCs derived from human umbilical cord blood can survive for a significant period of time when the host rat response is suppressed even for a short period. These results, together with the observation of a lack of neuronal differentiation and integration of MSCs after intravitreal grafting, has raised an important question as to the potential use of MSCs for neural repair through the replacement of lost neurons in the mammalian retina and central nervous system.

Rat neurosphere cells protect axotomized rat retinal ganglion cells and facilitate their regeneration.

We investigated the ability of a population of rat neural stem and precursor cells derived from rat embryonic spinal cord to protect injured neurons in the rat central nervous system (CNS). The neonatal rat optic pathway was used as a model of CNS injury, whereby retinal ganglion cells (RGCs) were axotomized by lesion of the lateral geniculate nucleus one day after birth. Neural stem and precursor cells derived from expanded neurospheres (NS) were transplanted into the lesion site at the time of injury. Application of Fast Blue tracer dye to the lesion site demonstrated that significant numbers of RGCs survived at 4 and 8 weeks in animals that received a transplant, with an average of 28% survival, though in some individual cases survival was greater than 50%. No RGCs survived in animals that received a lesion alone. Furthermore, labeled RGCs were also observed when Fast Blue was applied to the superior colliculus (SC) at 4 weeks, suggesting that neurosphere cells also facilitated RGC to regenerate to their normal target. Transplanted cells did not migrate or express neural markers after transplantation, and secreted several neurotrophic factors in vitro. We conclude that NS cells can protect injured CNS neurons and promote their regeneration. These effects are not attributable to cell replacement, and may be mediated via secretion of neurotrophic factors. Thus, neuroprotection by stem cell populations may be a more viable approach for treatment of CNS disorders than cell replacement therapy.

Umbilical cord blood mesenchymal stromal cells are neuroprotective and promote regeneration in a rat optic tract model.

Exploitation of the ability of stem cells to protect damaged neuronal tissue may be a more viable strategy than cell replacement for repair of the central nervous system (CNS). In this study we assessed the capacity of human umbilical cord blood (hUCB)-derived mesenchymal stromal cells (MSCs) to protect and promote regeneration of axotomised neurons within the rat optic system. The optic tract of neonatal rats was transected at the level of the lateral geniculate nucleus, and MSCs were introduced into the lesion site. MSCs survived well up to 2 weeks after grafting, and did not migrate significantly or differentiate. In the presence of MSC grafts, host axonal processes were found to be present in the lesion site, and there was stimulation of an endogenous neural precursor population. Four weeks after grafting, retrograde tracer experiments demonstrated that grafted MSCs, as well as cells of a human fibroblast line, exerted a neuroprotective effect, rescuing a significant percentage of axotomised retinal ganglion cells (RGCs). Further experiments with retrograde and anterograde tracers strongly indicated that MSCs could also promote re-growth of axotomised RGCs to their target, the superior colliculus (SC). Further analysis showed that hUCB-derived MSCs secreted several immunomodulatory and neurotrophic factors in vitro, including TGFbeta1, CNTF, NT-3 and BDNF, which are likely to play a role in neuroprotection. Our data indicate that hUCB-derived MSCs may be an easily accessible, widely available source of cells that can contribute towards neural repair through rescue and regeneration of injured neurons.

Differential effects of interleukin-1beta and S100B on amyloid precursor protein in rat retinal neurons.

PURPOSE: Interleukin-1beta (IL-1beta) and S100B calcium binding protein B (S100B) have been implicated in the pathogenesis of Alzheimer's disease. Both are present in and around senile plaques and have been shown to increase levels of amyloid precursor protein (APP) mRNA in vitro. However, it is not known how either of these substances affects APP in vivo. METHODS: We have studied the effects of IL-1beta and S100B on the expression and processing of APP using a retinal-vitreal model. We have also investigated the effect of amyloid beta peptide (Abeta) on APP in the same system and the regulation of S100B production by Abeta and IL-1beta from retinal glial cells. RESULTS: Retinal ganglion cells constitutively express APP. However, after intravitreal injection of IL-1beta or Abeta there was a marked reduction in APP levels as detected by Western blotting and IL-1beta produced a decrease in APP immunoreactivity (IR). Nissl staining showed that the integrity of the injected retinas was unchanged after injection. Two days after S100B injection, there was a small reduction in APP-IR but this was accompanied by the appearance of some intensely stained large ganglion cells and there was some up-regulation in APP holoprotein levels on Western blot. Seven days post-S100B injection, these large, highly stained cells had increased in number throughout the retina. Injection of Abeta and IL-1beta also caused an increase in S100B production within the retinal Müller glial cells. CONCLUSION: These results support the hypothesis that S100B (a glial-derived neurotrophic factor) and IL-1beta (a pro-inflammatory cytokine) can modulate the expression and processing of APP in vivo and so may contribute to the progression of Alzheimer's disease.

Glial and endothelial blood-retinal barrier responses to amyloid-beta in the neural retina of the rat.

The effects of an intravitreal or subretinal injection of soluble or aggregated forms of Abeta(1-42) on retinal nestin-immunoreactivity (-IR) and glial fibrillary acidic protein (GFAP)-IR in astrocytes and Müller glial cells and the integrity of the blood-retinal barrier (BRB) were tested in the in vivo rat vitreal-retinal model. Retinas were exposed for 1, 2, 3, 5 or 30 days. We present novel data demonstrating that aggregated Abeta(1-42) up-regulates nestin-IR in astrocytes and Müller cells, with a graded response directly related to the length of pre-injection aggregation time. Similar results were obtained with GFAP-IR, but the signal was weaker. An intravitreal injection of aggregated Abeta(1-42) led to VEGF-IR up-regulation, particularly in the GCL and to a lesser extent in the INL. VEGFR1-IR (Flt1) was also increased, particularly in Müller cells and this was accompanied by marked leakage of albumin into the retinal parenchyma of the injected eye, but not in the contralateral eye.

Developmental regulation and possible alternative cleavage of presenilin 1 in the rat retina.

Presenilin 1 (PS1) is a multitransmembrane protein well known for being mutated in most cases of familial Alzheimer's disease. Although its pathological effect is clear, its biological functions are not yet fully understood, but it appears to be involved in development and apoptosis. To investigate the role of PS1 in developmental processes we have studied the expression and proteolytic processing of this protein in the developing rat retina. PS1 appears to be developmentally regulated in the retina, and the pattern of PS1 immunoreactivity is consistent with a role in retinal lamination and pattern formation. Interestingly, no correlation was observed between PS1-positive cells and cells undergoing programmed cell death, suggesting that PS1 does not play a role in apoptosis occurring during this period. Moreover, we observed a change in the pattern of PS1 proteolytic fragments suggestive of a novel alternative cleavage site in the PS1 molecule.

The antioxidant cocktail effective microorganism X (EM-X) inhibits oxidant-induced interleukin-8 release and the peroxidation of phospholipids in vitro.

The antioxidant beverage EM-X is derived from the ferment of unpolished rice, papaya, and sea-weeds with effective microorganisms. Oxidative stress enhances the expression of proinflammatory genes, causing the release of the chemokine interleukin-8 (IL-8), which mediates a multitude of inflammatory events. Human alveolar epithelial cells (A549) were treated with H(2)O(2) (100 microM) or TNF-alpha (10ng/ml) alone or with the addition of EM-X (100 microl/ml), incubated for 20h, and the release of IL-8, measured using ELISA. EM-X inhibited the release of IL-8 at the transcriptional level in A549 cells. EM-X also decreased the iron/ascorbate dependent peroxidation of ox-brain phospholipids in a concentration dependent manner. A TEAC value of 0.10+/-0.05mM was obtained for EM-X, indicating antioxidant potential. We suggest that the anti-inflammatory and antioxidant properties of EM-X are dependent on the flavonoid contents of the beverage.

Amyloid-beta peptide is toxic to neurons in vivo via indirect mechanisms.

We have studied the neurotoxicity of amyloid-beta (Abeta) after a single unilateral intravitreal injection. Within the retina apoptotic cells were seen throughout the photoreceptor layer and the inner nuclear layer but not in the ganglion cell layer at 48 h after injection of Abeta(1-42) compared to vehicle control and control peptide. At 5 months, there was a significant reduction in total cell numbers in the ganglion cell layer in Nissl stained retinas. There was glial cell dysfunction with upregulation of glial fibrillary acidic protein and a reduction in the expression of Müller cell associated proteins in the injected retinas. These results suggest an indirect cytotoxic effect of Abeta on retinal neurons and an important role for dysfunction of Müller glia in mediating Abeta neurotoxicity.