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

Comprehensive mass spectrometry lipidomics of human biofluids and ocular tissues

Evaluating lipid profiles in human tissues and biofluids is critical in identifying lipid metabolites in dysregulated metabolic pathways. Due to various chemical characteristics, single-run lipid analysis has not yet been documented. Such approach is essential for analyzing pathology-related lipid metabolites. Age-related macular degeneration, the leading cause of vision loss in western countries, is emblematic of this limitation. Several studies have identified alterations in individual lipids but the majority are based on targeted approaches. In this study, we analyzed and identified approximately 500 lipid species in human biofluids (plasma and erythrocytes) and ocular tissues (retina and retinal pigment epithelium) using the complementarity of hydrophilic interaction liquid chromatography (HILIC) and reversed-phase chromatography (RPC), coupled to high-resolution mass spectrometry. For that, lipids were extracted from human eye globes and blood from 10 subjects and lipidomic analysis was carried out through analysis in HILIC and RPC, alternately. Furthermore, we illustrate the advantages and disadvantages of both techniques for lipid characterization. RPC showed greater sensitivity in hydrophobicity-based lipid separation, detecting diglycerides, triglycerides, cholesterol, and cholesteryl esters, whereas no signal of these molecules was obtained in HILIC. However, due to coelution, RPC was less effective in separating polar lipids like phospholipids, which were separated effectively in HILIC in both ionization modes. The complementary nature of these analytical approaches was essential for the detection and identification of lipid classes/subclasses, which can then provide distinct insights into lipid metabolism, a determinant of the pathophysiology of several diseases involving lipids, notably age-related macular degeneration.

GD3 synthase deletion alters retinal structure and impairs visual function in mice

Gangliosides are glycosphingolipids abundantly expressed in the vertebrate nervous system, and are classified into a-, b-, or c-series according to the number of sialic acid residues. The enzyme GD3 synthase converts GM3 (an a-series ganglioside) into GD3, a b-series ganglioside highly expressed in the developing and adult retina. The present study evaluated the visual system of GD3 synthase knockout mice (GD3s^-/- ), morphologically and functionally. The absence of b- series gangliosides in the retinas of knockout animals was confirmed by mass spectrometry imaging, which also indicated an accumulation of a-series gangliosides, such as GM3. Retinal ganglion cell (RGC) density was significantly reduced in GD3s^-/- mice, with a similar reduction in the number of axons in the optic nerve. Knockout animals also showed a 15% reduction in the number of photoreceptor nuclei, but no difference in the bipolar cells. The area occupied by GFAP-positive glial cells was smaller in GD3s^-/- retinas, but the number of microglial cells/macrophages did not change. In addition to the morphological alterations, a 30% reduction in light responsiveness was detected through quantification of pS6-expressing RGC, an indicator of neural activity. Furthermore, electroretinography (ERG) indicated a significant reduction in RGC and photoreceptor electrical activity in GD3s^-/- mice, as indicated by scotopic ERG and pattern ERG (PERG) amplitudes. Finally, evaluation of the optomotor response demonstrated that GD3s^-/- mice have reduced visual acuity and contrast sensitivity. These results suggest that b-series gangliosides play a critical role in regulating the structure and function of the mouse visual system.

Understanding Retinal Changes after Stroke

Stroke is the fifth leading cause of death and disability in the United States. According to World Heart Federation, every year, 15 million people suffer from stroke worldwide out of which nearly 6 million people die and another 5 million people are disabled. Out of many organs affected after stroke, one of them is eye. Majority of the stroke victims suffer vision loss due to stroke-induced retinal damage. However, stroke-induced retinal damage and microvascular changes have not been given paramount importance in understanding stroke pathophysiology and predicting its occurrence. Retinal imaging can be a very powerful tool to understand and predict stroke. This review will highlight the importance of retinal changes in predicting occurrence of stroke, major retinal changes, the relationship between retinal diseases and stroke and moreover, molecular mechanisms delineating the stroke induced-retinal changes and therapeutics associated with it.

Ganglioside Profiling of the Human Retina: Comparison with Other Ocular Structures, Brain and Plasma Reveals Tissue Specificities

Gangliosides make a wide family of glycosphingolipids, highly heterogeneous in both the ceramide moiety and the oligosaccharide chain. While ubiquitously expressed in mammalian tissues, they are particularly abundant in the brain and the peripheral nervous system. Gangliosides are known to play a crucial role in the development, maintenance and functional integrity of the nervous system. However, the expression and roles of gangliosides in the retina, although often considered as a window on the brain, has been far less studied. We performed an in-depth analysis of gangliosides of the human retina, especially using powerful LC/MS methods. We compared the pattern of ganglioside classes and ceramide molecular species of this tissue with other ocular structures and with brain and plasma in elderly human individuals. About a hundred of ganglioside molecular species among 15 distinct classes were detected illustrating the huge structural diversity of these compounds. The retina exhibited a very diverse ganglioside profile and shared several common features with the brain (prominence of tetraosylgangliosides, abundance of d20:1 long chain base and 18:0 fatty acid…). However, the retina stood out with the specific expression of GD3, GT3 and AcGT3, which further presented a peculiar molecular species distribution. The unique ganglioside pattern we observed in the human retina suggests that these ganglioside species play a specific role in the structure and function of this tissue. This lipidomic study, by highlighting retina specific ganglioside species, opens up novel research directions for a better understanding of the biological role of gangliosides in the retina.

Apprehending ganglioside diversity: a comprehensive methodological approach

Gangliosides (GGs) make a wide family of glycosphingolipids ubiquitously expressed in mammalian tissues and particularly abundant in the brain and nervous system. They exhibit a huge diversity due to structural variations in both their oligosaccharidic chain and ceramide moiety, which represent a real analytical challenge. Since their discovery in the 1940s, methods have persistently improved until the emergence of LC/MS, which offers a high level of specificity and sensitivity and is suitable with high-throughput profiling studies. We describe here a comprehensive approach relying on various techniques and aiming at fully characterizing GGs in biological samples. First, total GG content was determined by a biochemical assay. Second, GG class composition was assessed by high-performance thin-layer chromatography followed by colorimetric revelation. Then, ceramide types of GG classes were identified, and their relative quantification was performed thanks to the development of a powerful and reliable LC/MS method. Finally, ceramides were structurally characterized, and minor and less common GG classes were identified using high-resolution MS. These methods were applied to the rat retina to provide an exhaustive description of its GG composition, giving the base for a better understanding of the precise roles of GGs in this tissue.

Stroke in the eye of the beholder

The pathophysiological changes that occur during ischemic stroke can have a profound effect on the surrounding nerve tissue. To this end, we advance the hypothesis that retinal damage can occur as a consequence of ischemic stroke in animal models. We discuss the preclinical evidence over the last 3 decades supporting this hypothesis of retinal damage following ischemic stroke. In our evaluation of the hypothesis, we highlight the animal models providing evidence of pathological and mechanistic link between ischemic stroke and retinal damage. That retinal damage is closely associated with ischemic stroke, yet remains neglected in stroke treatment regimen, provides the impetus for recognizing the treatment of retinal damage as a critical component of stroke therapy.

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).

Retinal cholinergic and dopaminergic deficits of aged rats are improved following treatment with GM1 ganglioside

Selected cholinergic and dopaminergic markers were compared in the retina of aged (20-22-months-old) and young (3-months-old) rats before and after treatment with GM1 ganglioside. The dopaminergic markers, tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid were comparable in the young and aged animals and GM1 treatment did not alter them. In contrast, mazindol binding, a marker for the dopamine transporter, was diminished in the aged retina and treatment with GM1 restored binding to values found in the young animals. The cholinergic markers choline acetyltransferase and hemicholinium-3 binding, a marker for the high-affinity choline transport, were depressed in aged rats and GM1 corrected the deficits.

Neuroprotection in relation to retinal ischemia and relevance to glaucoma

Management of glaucoma is directed at the control of intraocular pressure (IOP), yet it is recognized now that increased IOP isjust an important risk factor in glaucoma. Therapy that prevents the death of ganglion cells is the main goal of treatment, but an understanding of the causes of ganglion cell death and precisely how it occurs remains speculative. Present information supports the working hypothesis that ganglion cell death may result from a particular form of ischemia. Support for this view comes from the fact that not all types of retinal ischemia lead to the pathologic findings seen in glaucomatous retinas or to cupping in the optic disk area. Moreover, in animal experiments in which ischemia is caused by elevated IOP, a retinal abnormality similar to that seen in true glaucoma is produced, whereas after occlusion of the carotid arteries a different pattern of damage is found. In ischemia, glutamate is released, and this initiates the death of neurons that contain ionotropic glutamate (NMDA) receptors. Elevated glutamate levels exist in the vitreous humor of patients with glaucoma, and NMDA receptors exist on ganglion cells and a subset of amacrine cells. Experimental studies have shown that a variety of agents can be used to prevent the death of retinal neurons (particularly ganglion cells) induced by ischemia. These agents are generally those that block NMDA receptors to prevent the action of the released glutamate or substances that interfere with the subsequent cycle of events that lead to cell death. The major causes of cell death after activation of NMDA receptors are the influx of calcium into cells and the generation of free radicals. Substances that prevent this cascade of events are, therefore, often found to act as neuroprotective agents. For a substance to have a role as a neuroprotective agent in glaucoma, it would ideally be delivered topically to the eye and used repeatedly. It is, therefore, of interest that betaxolol, a beta-blocker presently used to reduce IOP in humans, also has calcium channel-blocking functions. Moreover, experimental studies show that betaxolol is an efficient neuro protective agent against retinal ischemia in animals, when injected directly into the eye or intraperitoneally.

The potential of neuroprotection in glaucoma treatment

Visual field loss in glaucoma is due to death of retinal ganglion cells. Reducing or slowing down the loss of ganglion cells in glaucoma, a concept known as neuroprotection, would appear to be the only way forward. This does not imply that treatment of risk factors, such as elevated intraocular pressure, must not be continuously implemented. In this paper we point out that very little is known about the mechanisms of ganglion cell death in glaucoma and that data derived from studies on the "ideal animal model for glaucoma" must not be overemphasized. We also propose that the death processes of neurones in various diseases are fundamentally the same but vary in cause. Experimental data show that the death rate of neuronal populations is dependent on the impact of the insult and that neuroprotectants are more likely to benefit a patient in diseases in which the neurones die slowly, as in glaucoma, than in a disease in which the death of a set of neurones is rapid. We conclude that if a putative neuroprotectant can be administered in such a way that it reaches the retina in appropriate amounts and has insignificant side effects, it is likely to attenuate ganglion cell death and thus benefit the glaucoma patient.

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.

Effects of perfluorooctylbromide and vitamin E on ischemia induced retinal oxidative tissue damage

The aim of this study was to investigate the extent to which ischemia and reperfusion lead to oxidative damage of the retinal tissue and investigate how ischemic and reperfused retinal tissues react to the application of perfluorooctylbromide (PFOB) and, if this reaction can be influenced by protective drugs such as vitamin E (Vit.E). The experiments were performed with 60 male Wistar rats, divided into 12 groups using an established model of reversible ischemia and reperfusion of the globe. Grouping of animals was carried out according to different ischemia and reperfusion periods and different therapeutic regimens (PFOB, Vit.E). Treatment with PFOB and/or Vit.E was performed after 60 min of ischemia with 60 min of reperfusion. At the end of the experiments thiobarbituric acid reactive substances (TBARS) were determined in the retinal tissues and served as parameters of oxidative tissue damage. Ischemia of up to 60 min led to a significant increase in TBARS values. Ninety and 120 min of ischemia led to no further significant elevation compared to the 60 min or 90 min group. Following 60 min of ischemia, a reperfusion period of 15 min led to an increase in TBARS values that was significant (P<0.05) after 30 and 60 min. Addition of PFOB resulted in a further significant (P<0.05) increase in TBARS values as compared to the respective group without treatment. Vit. E alone did not change the values significantly compared to the respective group without treatment. However, the application of Vit.E in addition to PFOB led to a significant reduction in TBARS values. Ischemia resulted in severe oxidative retinal tissue damage, which increased during reperfusion. The reperfusion damage might be due to the known depletion of protecting substances such as vitamin E. Enhancement of oxygen supply by PFOB during reperfusion without any tissue protection leads to more severe damage. Thus, additional protection of the tissue by powerful antioxidants is necessary when providing oxygen for better tissue recovery.

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.