Ganglioside potentiation of NGF-independent trophic agents on sensory ganglia

Does exogenous GM1 ganglioside enhance the effects of electrical stimulation in ameliorating degeneration after neonatal deafness?

This study examined the combined effects of administration of exogenous GM1 ganglioside and electrical stimulation on the cochlear nucleus (CN) of cats deafened neonatally by ototoxic drugs. Five normal hearing adult cats served as controls. Another 12 cats were deafened bilaterally by daily injections of neomycin sulfate (60 mg/kg) for 17-21 days after birth until auditory brainstem testing demonstrated profound hearing loss. Six of the deaf animals comprised the GM1 group, which received daily injections of GM1 ganglioside (30 mg/kg) for 28-38 days during the period after profound deafness was confirmed, and prior to receiving a cochlear implant. The non-GM1 group (n=6) received no treatment during this interim period. All the deafened animals underwent unilateral cochlear implantation at 6-9 weeks postnatal and received several months (mean duration, 32 weeks) of chronic electrical stimulation (4 h/day, 5 days/week). Stimulation was delivered by intracochlear bipolar electrodes, using electrical signals that were designed to be temporally challenging to the central auditory system. Results showed that in the neonatally deafened animals, both the GM1 and non-GM1 groups, the volume of the CN was markedly reduced (to 76% of normal), but there was no difference between the animals that received GM1 and those that did not. The cross sectional areas of spherical cell somata in both GM1 and non-GM1 groups also showed a highly significant reduction in size, to < or =75% of normal after neonatal deafening. Moreover, in both the GM1 and non-GM1 groups, the spherical cells in the CN ipsilateral to the implanted cochlea were significantly larger (6%) than cells in the control, unstimulated CN. Again, however, there was no significant difference between the GM1 group and the non-GM1 group in spherical cell size. These results contrast sharply with previous reports that exogenous GM1 prevents CN degeneration after neonatal conductive hearing loss and partially prevents spiral ganglion cell degeneration when administered immediately after ototoxic drug deafening in adult animals. Taken together, findings to date suggest that GM1 may be effective in preventing degeneration only if the GM1 is administered immediately at the time hearing loss occurs.

Adult human olfactory stem cells

The location of stem cells within the adult CNS makes them impractical for surgical removal and autologous transplantation. Their limited availability and histocompatibility issues further restrict their use. In contrast, olfactory neuroepithelium (ONe) located in the nasal passageways has a continuous regenerative capability and can be biopsied readily. To investigate the potential of human ONe to provide viable populations of pluripotent cells, ONe was harvested from cadavers 6-18 h postmortem, dissociated, plated and fed every 3-4 days. Heterogeneous populations of neurons, glia, and epithelia were identified with lineage-specific markers. After several weeks, 5-10% of the cultures produced a population of rapidly dividing cells, which in turn, produced neurospheres containing at least two subpopulations based on neuronal and glial specific antigens. Most contained one or more neuronal markers; a few were positive for A2B5 and/or GFAP. To determine if growth modulators would affect the neurosphere forming cells, they were exposed to dibutyryl-cAMP. The nucleotide reduced cell division and increased process formation. Although the cells had been passaged more than 70 times, their viability remained constant as shown by the MTT viability index. Donor age or sex were not limiting factors, because neurospheres have been established from cadavers of both sexes from 50 to 95 years old at time of death. The ex vivo expansion of these cells will provide a patient-specific population of cells for immunological, genetic and pharmacological evaluation. Our long-term goal is to determine the utility of these cells to facilitate CNS repair.

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).

Exogenous GM1 ganglioside effects on conductive and sensorineural hearing losses

Both CBA/J mice with neonatal cochlea removals and CBA/J mice with neonatal atresias of the external auditory meatus have significantly smaller ventral cochlear nucleus is greater in the mice with cochlea removals, but the soma area reduction is greater in the mice with external auditory meatus atresias. GM1 gangliosides were subcutaneously injected daily into a group of CBA/J mice with conductive hearing loss caused by neonatal removals of their left external auditory meatus, and into a group of CBA/J mice unilaterally deafened by left cochlea removals. In the mice with conductive hearing loss, the ganglioside treatment significantly ameliorated the atrophy of spiral ganglion neurons, ventral cochlear nucleus neurons, and ventral cochlear nucleus volume. In unilaterally deafened mice, the ganglioside treatment had no measurable effect on the atrophy of ventral cochlear nucleus neurons or of ventral cochlear volume. It is suggested that GM1 ganglioside treatment potentiates growth factors which sustain spiral ganglion integrity and that this sustained activity of the spiral ganglion in turn maintains the integrity of the cochlear nuclei.

Effects of age on GM1 ganglioside-induced recovery of concentrations of dopamine in the striatum in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

The effect of GM1 ganglioside on the recovery of concentrations of dopamine (DA) in the striatum, following administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was studied in mice of various ages. At the start of the study, the mice were 8 weeks, 6, 12 and 20 months old. Mice from each age group received MPTP for 5 days, followed by either GM1 ganglioside or saline for 4 or 8 weeks. Animals older than 8 weeks, that did not receive GM1 showed no spontaneous recovery of striatal levels of DA in the striatum, over either 4 or 8 weeks. Animals that received GM1 showed varied amounts of recovery of levels of DA in the striatum. The young animals (8 wk old) had the most pronounced effect from GM1. With increasing age, the magnitude of the effect of GM1 became attenuated and recovery had a longer latency. The results suggest that GM1 can be effective in at least partially restoring MPTP-depleted levels of DA in the striatum, even in aged mice.

Neurite-promoting activities of phosphatidylinositol and other lipids on fetal rat septal neurons in culture

Neurite-promoting activities of lipids were assessed using serum-free cultures of fetal rat septal neurons. The most potent one was phosphatidylinositol (PI), followed by PI 4-phosphate, phosphatidylserine, sphingomyelin, and phosphatidylcholine. The EC50 value for PI was 1.5 micrograms/ml (1.8 microM), and activity was maximal at 4 micrograms/ml (56% of total cells had neurites after 24 h). Cerebroside, sulfatide, and di- and triacylglycerols showed relatively low activities. Synthetic dipalmitoyl phosphatidylcholine was also active, with a maximal activity (47%) at 100 micrograms/ml, a finding implying that the unsaturated fatty acid moiety is not released and further used as substrate for the arachidonic acid cascade. Lysophospholipids, phosphatidylglycerol, and cardiolipin were rather cytotoxic and lacked activity, an observation suggesting that membrane perturbation is not responsible for the neurite-promoting activity. Treatment with a protein kinase C inhibitor, H-7, or an Na+,K(+)-ATPase inhibitor, ouabain, inhibited the PI-induced neurite outgrowth, but the cyclic AMP- and cyclic GMP-dependent protein kinase inhibitor HA1004 did not inhibit this activity, a result indicating that multiple elements (protein kinase C and Na+,K(+)-ATPase) are involved in the induction of neurites. Because phospholipids can be provided either as lipid vesicles or as lipoproteins produced by macrophages at regeneration sites, they may play an important role in the regeneration of certain populations of neurons.

Gangliosides: the relevance of current research to neurosurgery

Gangliosides are complex glycolipids found on the outer surface of most cell membranes: they are particularly concentrated in tissues of the nervous system. Gangliosides form part of the immunological identity of mammalian cells and are involved in a variety of cell-surface phenomena such as cell-substrate binding and receptor functions. In tumorous tissue, the ganglioside composition is altered, sometimes in direct proportion to the degree of malignancy. The literature on the glycosphingolipid composition and immunology of intracranial tumors is reviewed. Some gangliosides induce neuritogenesis and exhibit a trophic effect on nerve cells grown in vitro. In vivo, a particular ganglioside, GM1, reduces cerebral edema and accelerates recovery from injury (traumatic and ischemic) to the peripheral and central nervous systems of laboratory animals. Preliminary clinical studies have shown that treatment with gangliosides may have corresponding effects on lesions of the human peripheral nervous system. Gangliosides have not been tested in human subjects with brain injury.

Calcium regulation of neuronal differentiation: the role of calcium in GM1-mediated neuritogenesis

Cultures of mouse Neuro-2a neuroblastoma cells treated with 3-6 mM extracellular Ca2+ exhibited enhanced neurite extension characterized by increased neurite numbers and lengths. The ganglioside GM1 potentiated the effect of extracellular Ca2+ by increasing further the number and length of the neurites formed in response to exogenous Ca2+. Maximal neuritic numbers were achieved with 4 mM Ca2+ while the longest neurites were observed in medium containing 4-6 mM Ca2+. Stimulation of the Ca2+ influx with the ionophore A23187 or the amino acid taurine also enhanced neurite formation and GM1 potentiated these actions. Transmission electron microscopy revealed numerous microtubules and neurofilaments in neurites and microfilaments with the spine-like processes along fine neuritic branches and in the filopodia of growth cones. Neuritic varicosities and growth cones contained a variety of vesicles. All of these structures were increased in the presence of GM1 and were increased further by extracellular Ca2+ or A23187. The ability of GM1 to enhance neuritogenesis was diminished by EGTA or Ruthenium red. Similarly, the effect of GM1 was diminished or abolished by Ca2+ channel blockers such as CdCl2 or LaCl3. X-ray microprobe analysis revealed that GM1 alone enhanced intracellular levels of total ionic and membrane bound Ca2+, perhaps accounting for the increased neuritogenesis observed under conditions in which Ca2+ was manipulated. The present study suggest that the neuritogenic action of GM1 is Ca2+ dependent.

Rat dorsal root ganglion gangliosides during early development until senescence

The gangliosides of male rat dorsal root ganglia were studied during aging from the first day postnatally until senescence at 24 months. The ganglioside contents increased drastically until 12 months after birth and thereafter did not change considerably, and the increase pattern was in parallel with the increase of wet weight of the tissues. The major gangliosides of the dorsal root ganglia were GM3, LM1 (sialosyl-lactoneotetraosylceramide), unknown ganglioside X, GD1a, GD1b, GT1b and GQ1b. The most drastic changes in ganglioside composition were observed between the ages of postnatal day 1 and 1.5 months. The unknown ganglioside X (dominant at postnatal day I) decreased up to 1.5 months. In contrast, LM1, a minor ganglioside postnatal day 1, increased until 1.5 months of age. Except for these changes, the other gangliosides were present at almost constant ratios in the component profiles during aging until senescence.

Taurine-induced neuronal differentiation: the influence of calcium and the ganglioside GM1

Taurine-induced differentiation was examined in the murine neuroblastoma Neuro-2a cell line in the presence or absence of the monosialoganglioside GM1 and under conditions in which Ca2+ levels were manipulated. Taurine (4 mM), GM1 (200 micrograms/ml), or taurine with GM1 were applied to culture media that contained either various concentrations of Ca2+ or the Ca2+ ionophore A23187. Taurine or GM1 and taurine with GM1 increased the number of cells emitting neurites above that found for controls. A significant interaction was found between treatment (taurine, GM1 or taurine + GM1) and the manipulations of Ca2+ levels, affecting the number of neurites and producing changes on the neuritic and perikaryal surfaces. Treatment with both taurine and taurine + GM1 and the various concentrations of Ca2+ resulted in a significant increase in neurite elongation. The Ca2+ ionophore A23187 in the presence of taurine or taurine + GM1 caused neurites to grow longer than observed in media containing Ca2+, either in a low concentration (about 125 microM) or at 1-2 mM. Taurine-treated cultures in the presence of extracellular Ca2+ or A23187 were characterized by surfaces with numerous microvillar, spine-like projections. This effect was enhanced with GM1 and was less pronounced in the medium containing low levels of Ca2+. Transmission electron microscopy of the taurine-stimulated neurons revealed an excessive number of clear-core vesicles (40-200 nm in diameter) in perikarya, neurites and neuritic varicosities and growth cones. In addition, numerous aggregates of intermediate filaments were seen. They were most abundant in the taurine + GM1 treated cultures. The taurine + A23187 cultures also exhibited numerous microtubules within the elongated processes. The different neuritic patterns induced by taurine under conditions in which Ca2+ levels were manipulated and/or when cells were exposed to exogenous GM1 suggest that taurine's actions depend in part on Ca2+ flux.

Ganglioside function in the development and repair of the nervous system. From basic science to clinical application

Gangliosides play important roles in the normal physiological operations of the nervous system, in particular that of the brain. Changes in ganglioside composition occur in the mammalian brain not only during development, but also in aging and in several neuropathological situations. Gangliosides may modulate the ability of the brain to modify its response to cues or signals from the microenvironment. For example, cultured neurons are known to respond to exogenous ganglioside with changes characteristic of cell differentiation. Gangliosides can amplify the responses of neurons to extrinsic protein factors (neuronotrophic factors) that are normal constituents of the neuron's environment. The systemic administration of monosialoganglioside also potentiates trophic actions in vivo and improves neural responses following various types of injury to the adult mammalian central nervous system. The possible molecular mechanism(s) underlying the ganglioside effects may reflect an action in modulating ligand-receptor linked transfer of information across the plasma membrane of the cell.

Inhibition of conditioned media-mediated neuritogenesis of sensory ganglia by monoclonal antibodies to GM1 ganglioside

The monosialoganglioside GM1 can potentiate the neuritogenic activity of media conditioned by several cell types: neonatal glia, C6 glioma, embryonic chick heart or skeletal muscle and the rat myogenic line L6. To probe further the neuritogenic activity of conditioned media (CM), 5 mouse monoclonal antibodies (mAbs) against GM1, designated B6, C3, C4h2, D1 and D3 were incorporated individually into nutrient medium (NM) supplemented with CM prior to incubation with sensory ganglia. Nine-day embryonic chick dorsal root ganglia were explanted onto collagen-coated coverslips and incubated at 35 degrees C for 5 h in NM supplemented with 150 micrograms/ml GM1. After washing with NM, the explants were re-fed with NM + CM containing 20% mAb and cultured for an additional 43 h. The resultant neuritogenesis was evaluated microscopically by determining mean neurite number and length of randomly mixed cultures. The 5 antibodies differed in their capacities to inhibit CM-mediated neuritogenesis of these primed target cells. D1 and D3 were most effective in reducing neurite length and number produced by all sources of the CM, while C3 and C4h2 were intermediate in their inhibition of neurite initiation (number). The effect of B6 on neurite initiation and elongation was the least. The ability of these mAbs to inhibit neuritogenic activity of CM derived from both glial and myogenic tissue suggests that gangliosides play a basic role in neuronal development. The differing responses elicited by the individual mAbs may reflect a relationship between the structural complexity of the GM1 molecule and the neuritogenic mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)