GM1 reduces infarct volume after focal cerebral ischemia

Pharmacological Manipulation of Trk, p75NTR, and NGF Balance Restores Memory Deficit in Global Ischemia/Reperfusion Model in Rats

Long-term memory impairment is reported in more than 50% of cardiac arrest survivors. Monosialoganglioside (GM1) provided neuroprotection in experimental models of stroke but failed to replicate its promise clinically for unknown reasons. GM1 stimulates the release of nerve growth factor (NGF), which is synthesized as a precursor protein (pro-NGF) that either mediates apoptosis through the p75 neurotrophin receptor (p75NTR) or is cleaved by the protease furin (FUR) to yield mature NGF, the latter supporting survival through tropomyosin kinase receptor (Trk). The flavanol epicatechin (EPI) inhibits p75NTR-mediated signaling and apoptosis by pro-NGF. The aim of the current work is to test whether these two drugs affect, or communicate with, each other in the setting of CNS injuries. Using the two-vessel occlusion model of global ischemia/reperfusion (I/R), we tested if pharmacological modulation of Trk, p75NTR, and NGF balance with GM1, EPI, and their combination, can correct the memory deficit that follows this insult. Finally, we tested if FUR insufficiency and/or p75NTR-mediated apoptosis negatively affect the neurotherapeutic effect of GM1. Key proteins for Trk and p75NTR, FUR, and both forms of NGF were assessed. All treatment regiments successfully improved spatial memory retention and acquisition. A week after the insult, most Trk and p75NTR proteins were normal, but pro/mature NGF ratio remained sharply elevated and was associated with the poorest memory performance. Pharmacological correction of this balance was achieved by reinforcing Trk and p75NTR signaling. GM1 increased FUR levels, while concomitant administration of EPI weakened GM1 effect on pro-survival Trk and p75NTR mediators. GM1 neuroprotection is therefore not limited by FUR but could be dependent on p75NTR. Graphical Abstract "."

Increased Expression of GM1 Detected by Electrospray Mass Spectrometry in Rat Primary Embryonic Cortical Neurons Exposed to Glutamate Toxicity

Neurons within different brain regions have varying levels of vulnerability to external stress and respond differently to injury. A potential reason to explain this may lie within a key lipid class of the cell's plasma membrane called gangliosides. These glycosphingolipid species have been shown to play various roles in the maintenance of neuronal viability. The purpose of this study is to use electrospray ionization mass spectrometry (ESI-MS) and immunohistochemistry to evaluate the temporal expression profiles of gangliosides during the course of neurodegeneration in rat primary cortical neurons exposed to glutamate toxicity. Primary embryonic (E18) rat cortical neurons were cultured to DIV (days in vitro) 14. Glutamate toxicity was induced for 1, 3, 6, and 24 h to injure and kill neurons. Immunofluorescence was used to stain for GM1 and GM3 species, and ESI-MS was used to quantify the ganglioside species expressed within these injured neurons. ESI-MS data revealed that GM1, GM2, and GM3 were up-regulated in neurons exposed to glutamate. Interestingly, using immunofluorescence, we demonstrated that the GM1 increase following glutamate exposure occurred in viable neurons, possibly indicating a potential intrinsic neuroprotective response. To test this potential neuroprotective property, neurons were pretreated with GM1 for 24 h prior to glutamate exposure. Pretreatment with GM1 conferred significant neuroprotection against glutamate-induced cell death. Overall, work from this study validates the use of ESI-MS for cell-derived gangliosides and supports the further development of lipid based strategies to protect against neuron cell death.

Abnormal cross-talk between mutant presenilin 1 (I143T, G384A) and glycosphingolipid biosynthesis

Mutations in the presenilin 1 (PS1) gene are associated with early onset familial Alzheimer's disease (FAD). In this study, we found that the expression of mutant-PS1 in stable transfectants of SH-SY5Y neuroblastoma cells results in a reduction of the biosynthesis and steady-state levels of glucosylceramide. As an in vivo corroboration of these data, there was a significant reduction of brain glucosylceramide and gangliosides in an animal model of FAD. In mutant-PS1-transfectants (I143T, G384A), immunocytochemistry disclosed a remarkable reduction of glucosylceramide synthase (GlcT-1)-like immunoreactivity in the cells when compared with those of mock- and wild-PS1 transfectants. Immunoprecipitation of GlcT-1 protein from mutant-PS1 transfectants demonstrated a marked reduction in GlcT-1 protein, but there was no reduction in the levels of GlcT-1 mRNA. Both coprecipitation and γ-secretase inhibition experiments suggest that mutant-PS1 seems to form a complex with GlcT-1 protein and to be involved in GlcT-1 degradation, which was never found in other cell types. Thus, mutations in the PS1 gene result in profound glycosphingolipids abnormalities by abnormal molecular interaction with GlcT-1.

Amyloid-β induced toxicity involves ganglioside expression and is sensitive to GM1 neuroprotective action

The effect of Aβ25-35 peptide, in its fibrillar and non-fibrillar forms, on ganglioside expression in organotypic hippocampal slice cultures was investigated. Gangliosides were endogenously labeled with D-[1-C(14)] galactose and results showed that Aβ25-35 affected ganglioside expression, depending on the peptide aggregation state, that is, fibrillar Aβ25-35 caused an increase in GM3 labeling and a reduction in GD1b labeling, whereas the non-fibrillar form was able to enhance GM1 expression. Interestingly, GM1 exhibited a neuroprotective effect in this organotypic model, since pre-treatment of the hippocampal slices with GM1 10 μM was able to prevent the toxicity triggered by the fibrillar Aβ25-35, when measured by propidium iodide uptake protocol. With the purpose of further investigating a possible mechanism of action, we analyzed the effect of GM1 treatment (1, 6, 12 and 24h) upon the Aβ-induced alterations on GSK3β dephosphorylation/activation state. Results demonstrated an important effect after 24-h incubation, with GM1 preventing the Aβ-induced dephosphorylation (activation) of GSK3β, a signaling pathway involved in apoptosis triggering and neuronal death in models of Alzheimer's disease. Taken together, present results provide a new and important support for ganglioside participation in development of Alzheimer's disease experimental models and suggest a protective role for GM1 in Aβ-induced toxicity. This may be useful for designing new therapeutic strategies for Alzheimer's treatment.

Plasminogen activator inhibitor type 1 derived peptide, EEIIMD, diminishes cortical infarct but fails to improve neurological function in aged rats following middle cerebral artery occlusion

Age is a primary risk factor in stroke that is often overlooked in animal studies. We contend that using aged animals yields insight into aspects of stroke injury and recovery that are masked, or not elicited, in younger animals. In this study, we examined effects of co-administration of a plasminogen activator inhibitor type 1 derived peptide, Glu-Glu-Iso-Iso-Met-Asp (EEIIMD), with tissue plasminogen activator (tPA) on infarct volume and functional outcome in aged rats following a transient middle cerebral artery occlusion. Results of our study showed aged (18-20 months) rats treated with EEIIMD along with tPA had reduced cortical infarction volume. However, aged rats showed no improvement in total infarction volume, edema formation, or functional outcome as compared to aged rats administered only tPA. Young adult rats (3-4 months) treated with EEIIMD showed significant improvement in cortical and total infarction volumes, edema formation, and functional outcome. Striatal infarction volume was unaffected by EEIIMD treatment in both young adult and aged rats. These findings emphasize that physiological differences exist between young adult and aged rats and suggest that taking aging processes into account when assessing stroke may improve our ability to discern which therapeutics can be translated from bench to bedside.

Chemokine receptors and neurotrophic factors: potential therapy against aids dementia?

Chemokine receptors, in particular, CXCR4 and CCR5, mediate human immunodeficiency virus type 1 (HIV-1) infection of immunocompetent cells and the apoptosis of these cells. However, the virus does not infect neurons. Yet through a variety of mechanisms, HIV promotes glial cell activation, synaptodendritic alterations, and neuronal loss that ultimately lead to motor and cognitive impairment. Chemokines and chemokine receptors are abundant in the adult central nervous system and play a role in neuronal apoptosis evoked by HIV proteins. Thus, reducing the availability of chemokine receptors may prevent the neuronal degeneration seen in HIV-positive patients. In this article, we present and discuss a recent experimental approach aimed at testing effective neuroprotective therapies against HIV-mediated neuronal degeneration.

Diet-induced changes in membrane gangliosides in rat intestinal mucosa, plasma and brain

OBJECTIVES

The objective of this study was to determine if dietary gangliosides induce changes in the ganglioside content of intestinal mucosa, plasma and brain and to identify where GM3 and GD3 are localized in the enterocyte membrane.

METHODS

Male 18-day-old Sprague-Dawley rats were fed a semipurified diet containing 20% (w/w) fat. The control diet contained triglyceride, reflecting the fat formulation of an existing infant formula. Two experimental diets were formulated by adding sphingomyelin (1% w/w of total fat) or a ganglioside-enriched lipid (0.1% w/w of total fat) to the control diet fat. The ganglioside fraction of ganglioside-enriched lipid diet contained more than 80% GD3. After 2 weeks of feeding, the total and individual ganglioside and cholesterol content was measured in small intestinal mucosa, plasma and brain.

RESULTS

The ganglioside-enriched lipid diet significantly increased total gangliosides in the intestinal mucosa, plasma and brain compared with the control diet. The ganglioside-enriched lipid diet significantly increased the level of GD3 (7.5% w/w) in the intestine compared with control (3.2% w/w) while decreasing the level of GM3, the major ganglioside in the intestine. The ratio of cholesterol to ganglioside in the intestinal mucosa, plasma and brain decreased significantly in rats fed the ganglioside-enriched lipid diet compared with controls. Confocal microscopy showed that GM3 is exclusively localized in the apical membrane of the enterocyte whereas GD3 is primarily localized in the basolateral membrane.

CONCLUSIONS

: The authors conclude that dietary ganglioside is absorbed in the small intestine and transported to different membrane sites, altering ganglioside levels in the intestinal mucosa, plasma and brain and thus possibly having the potential to change developing enterocyte function (and possibly that of other cell lines).

Acidosis enhances translocation of protein kinase C but not Ca(2+)/calmodulin-dependent protein kinase II to cell membranes during complete cerebral ischemia

Systemic hyperglycemia and hypercapnia severely aggravate ischemic brain damage when instituted prior to cerebral ischemia. An aberrant cell signaling following ischemia has been proposed to be involved in ischemic cell death, affecting protein kinase C (PKC) and the calcium calmodulin kinase II (CaMKII). Using a cardiac arrest model of global brain ischemia of 10 min duration, we investigated the effect of hyperglycemia (20 mM) and hypercapnia (pCO(2) 300 mmHg) on the subcellular redistribution of PKC (alpha, beta, gamma) and CaMKII to synaptic membranes and to the microsomes, as well as the effect on PKC activity. We confirmed the marked translocation of PKC and CaMKII to cell membranes induced by ischemia, concomitantly with a decrease in the PKC activity in both the membrane fraction and cytosol. Hyperglycemia and hypercapnia markedly enhanced the translocation of PKC-gamma to cell membranes while other PKC isoforms were less affected. There was no effect of acidosis on PKC activity, or on translocation of CaMKII to cell membranes. Our data strongly suggest that the enhanced translocation of PKC to cell membranes induced by hyperglycemia and hypercapnia may contribute to the detrimental effect of tissue acidosis on the outcome following ischemia.

Promotion of neuronal survival by GM1 ganglioside. Phenomenology and mechanism of action

The purpose of this article is to review recent findings regarding the mechanisms by which GM1 may mimic or potentiate certain actions of neurotrophic factors, including promotion of neuronal survival. It is proposed that the neuroprotective activity of GM1 is due, at least in part, to its ability to favor the dimerization of neurotrophic factor tyrosine kinases and thereby mimicking the action of their corresponding ligands. This may manifest both in the absence of ligand (thereby triggering a subset of neurotrophic-factor responses such as prevention of apoptosis) and in the presence of ligand (thereby potentiating responses to neurotrophic factors).

Gangliosides and neurotrophic growth factors in the retina. Molecular interactions and applications as neuroprotective agents

Polypeptide growth factors and gangliosides can both be considered as trophic agents involved in almost all stages of neural cell development, differentiation, survival, and pathology. In most cases their physiological roles are still not clear due to the considerable complexity in their regulation. Several growth factors [e.g., basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF)] and one species of ganglioside (GM1) have been shown to exert interactions with each other and also to exhibit neuroprotective effects against retinal ischemia in vivo and cerebral excitotoxicity in vitro. Different experimental models are used to investigate their relevance to ischemic and excitotoxic conditions in the retina, and it is shown that (1) both bFGF and EGF show very effective neuroprotection for rat retinal neurones exposed to toxic levels of glutamate or its nonphysiological agonist kainate in vitro; (2) GM1 (10(-5M) used under the same conditions does not afford protection; (3) retinal glial cells also suffer morphological perturbations following glutamate or kainate treatment, but this effect is dependent on neuron-glial interactions, indicating the existence of intermediate neuron-derived messenger molecules; (4) these glial changes can be corrected by posttreatment with either bFGF or EGF in vitro; (5) using an in vivo animal model involving anterior chamber pressure-induced ischemia in adult rats, it is shown that either pretreatment by intraperitoneal injection of GM1, or posttreatment by intraocular injection of the same ganglioside, reduces significantly histological damage to inner nuclear regions; and (6) in cultured retinal Müller glial cells the existence of molecular and metabolic interactions between both types of trophic factors is demonstrated. Hence both these groups of trophic molecules show interesting features for retinal ischemic treatment.

Growth factors and gangliosides as neuroprotective agents in excitotoxicity and ischemia

1. At least two different groups of molecules can be considered neurotrophic factors because they exert a variety of effects upon neural cells. The first consists of the numerous families of polypeptide growth factors known to take part in almost all stages of neural cell growth and functioning, including development, differentiation, survival and pathology. The second group also is characterized by extensive complexity of multiple forms, and consists of the sialic acid-containing glycosphingolipids or gangliosides. These molecules also take part in the transfer of information from the extracellular milieu to the cell interior, and, similarly to growth factors, are participants in such aspects as development, differentiation and functioning. 2. In this short overview, we consider the existing data on the neuroprotective effects of growth factors [e.g., basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and brain-derived neurotrophic factor] and one species of ganglioside (GM1) against retinal ischemia in vivo and cerebral excitotoxicity in vitro. 3. We used three different experimental models to investigate their relevance to ischemic and excitotoxic conditions in the retina and have shown that: (a) both bFGF and EGF show highly effective neuroprotection for rat retinal neurons exposed to toxic levels of glutamate or its nonphysiological agonist kainate in vitro (b) retinal glial cells suffer morphological perturbations after glutamate or kainate treatment, and this effect depends on neuron-glial interactions; (c) these glial changes can also be corrected by posttreatment with either bFGF or EGF in vitro; (d) with the use of an in vivo animal model involving anterior chamber pressure-induced ischemia in adult rats, either pretreatment by intraperitoneal injection of GM1 or posttreatment by intraocular injection of the same ganglioside significantly reduces histological damage to inner nuclear regions. 4. Hence both groups of trophic molecules show interesting features for retinal ischemic treatment.

Peptide growth factors but not ganglioside protect against excitotoxicity in rat retinal neurons in vitro

Glutamate is the major excitatory neurotransmitter in the retina, but excessive stimulation of its receptors leads to widespread neuronal stress and death. Both growth factors and gangliosides display important influences on responses to neuronal injury and degeneration. In this study, we have investigated the potential protective effects of two well characterized growth factors, epidermal and basic fibroblast growth factor (EGF and bFGF respectively), and the monosialoganglioside GM1, on cultured rat retinal neurons submitted to toxic levels of excitatory amino acids. Application of 1 mM glutamic acid reduced global neuronal viability by 80% when compared to control untreated cultures, whereas treatment with the glutamic acid agonist kainic acid (1 mM) led to specific, large decreases (75% reduction) in amacrine cell numbers. 24 h pretreatment with either EGF or bFGF (500 pM each) prevented the majority of excitatory amino acid-induced neuronal death, whereas similar treatment with 10(-5) M GM1 did not block neuronal degeneration. These findings demonstrate that EGF and bFGF act as neuroprotective agents against retinal excitotoxicity in vitro, whereas ganglioside GM1 is not effective in this particular paradigm.

Intravitreal injection of ganglioside GM1 after ischemia reduces retinal damage in rats

BACKGROUND AND PURPOSE

Gangliosides are normal components of cell membranes and contribute to structural rigidity and membrane function. They have been shown to protect against various insults in the brain. We have shown previously that GM1 administered intraperitoneally before the induction of retinal ischemia provides a protective effect. This study evaluates the protective effect of GM1 administered intravitreally after ischemia on retinal lesions.

METHODS

We induced retinal ischemia unilaterally in Long-Evans rats by increasing intraocular pressure to 160 mm Hg for 60 minutes. GM1 (20 microL x 10(-5) mol/L) or saline (20 microL) was injected into the vitreous 15 minutes after ischemia, and the postischemic survival time was either 8 or 15 days. The degree of retinal damage was assessed by histopathological study.

RESULTS

Retinal ischemia led to reductions in thickness and cell number, principally in the inner retinal layers (39% to 80%) and to a lesser extent in the outer retinal layers (26% to 45%). Postischemic treatment with intravitreally injected GM1 conferred significant protection against retinal ischemic damage after both 8 and 15 days of survival time. After 8 days of reperfusion, the ischemia-induced loss in overall retinal thickness was reduced by 15% and those of the inner nuclear and plexiform layers by 44% and 17%, respectively. Ischemic-induced ganglion cell and inner nuclear cell density losses were reduced by 37% and 27%, respectively. After 15 days of reperfusion, approximately the same statistically significant differences could be observed in comparison with the 15-day saline-injected group.

CONCLUSIONS

GM1 protects the rat retina from pressure-induced ischemic injury when given intravitreally after the insult. The protection provided by GM1 after initiation of retinal damage could be of therapeutic interest.

Neuronal apoptosis: current understanding of molecular mechanisms and potential role in ischemic brain injury

Apoptosis is a rediscovered mechanism of cell death crucial in normal development. Recent exploration of the genetic mechanisms of apoptosis has broadened our insight into the regulation of cell death in development as well as disease states. We present an overview on current understanding of the genetic molecular events in apoptosis in all, or most cell types, with emphasis on events observed in a well-characterized model of neuronal death in vitro. The second part of this article reviews recent studies in in vivo stroke models on the mechanism of cell death relevant to apoptosis after cerebral ischemia. Further delineation of the mechanisms of cell death, especially those that trigger apoptosis, is likely to redirect our approaches in the development of new therapeutic interventions for ischemic stroke.