RESUMEN
Neurones are dependent on their mitochondria to produce the necessary amounts of ATP for survival. Retinal ganglion cells (RGCs) have a particularly large number of mitochondria which-unlike neurones in the brain-are exposed to visual light of 400-850â¯nm. Here we demonstrate that short wavelength visual blue light negatively affects mitochondrial function, causing oxidative stress and decreased cell survival. In contrast, long wavelength red light enhances mitochondrial function to increase survival of cultured R28â¯cells and reduce the effects of blue light. Induction of retinal ischemia for 60â¯min in dark conditions caused a reduction in ATP levels accompanied by decreased RGC numbers in all areas of the retina. These effects were diminished when ischemia was induced with concomitant delivery of red light, and exacerbated when blue light was used. We conclude that while the levels of blue light that reach the human retina will be a fraction of those used in the present study, the chronic nature might, on a theoretical basis, be detrimental to RGC mitochondria which are already affected by conditions such as glaucoma. Our findings also show that exposing the retina to red light may be a therapeutic approach to supporting healthy mitochondrial functions as part of the treatment for retinal diseases in which these organelles are affected.
Asunto(s)
Luz , Mitocondrias/fisiología , Mitocondrias/efectos de la radiación , Células Ganglionares de la Retina/fisiología , Células Ganglionares de la Retina/efectos de la radiación , Animales , Línea Celular , Supervivencia Celular/fisiología , Supervivencia Celular/efectos de la radiación , Masculino , Ratas , Ratas Wistar , Retina/citología , Retina/fisiología , Retina/efectos de la radiaciónRESUMEN
The aim of the present studies was to characterise cell death following inhibition of mitochondrial complex I with rotenone in a transformed cell line (RGC-5 cells) and to examine the neuroprotective properties of the flavonoids genistein, epigallocatechin gallate (EGCG), epicatechin (EC) and baicalin. Rotenone-induced cell death of RGC-5 cells results in a generation of reactive oxygen species, a breakdown of DNA, the translocation of membrane phosphatidylserine, an up-regulation of haemoxygenase-1 and is unaffected by necrostatin-1 (inhibitor of necroptosis), z-VAD-fmk (pan caspase inhibitor) or NU1025 (PARP inhibitor) but attenuated with SP600125 (JNK inhibitor). Rotenone-induced toxicity of RGC-5 cells also caused an activation of mitogen-activated kinases indicated by an up-regulation and translocation into mitochondria of p-c-Jun, pJNK and pp38. Exposure of RGC-5 cells to rotenone does not affect apoptosis inducing factor or significantly stimulate caspase-3 activity. EGCG and EC both significantly blunt rotenone toxicity of RGC-5 cells at concentrations of 50 µM while genistein and baicalin were without effect. Significantly, genistein is approximately 20 times less efficacious than EGCG (IC(50) 2.5 µM) and EC (IC(50) 1.5 µM) at inhibiting sodium nitroprusside-induced lipid peroxidation. These studies show that rotenone toxicity of RGC-5 cells is neither necroptosis nor caspase-dependent apoptosis but involves the activation of mitogen-activated kinases and is inhibited by a JNK inhibitor, EGCG and EC. Genistein attenuates lipid peroxidation less efficaciously than EC and EGCG and does not affect rotenone toxicity of RGC-5 cells.
Asunto(s)
Caspasa 3/metabolismo , Flavonoides/farmacología , MAP Quinasa Quinasa 4/metabolismo , Células Ganglionares de la Retina/efectos de los fármacos , Rotenona/farmacología , Té/química , Proteínas Quinasas p38 Activadas por Mitógenos/metabolismo , Animales , Western Blotting , Línea Celular , Inmunohistoquímica , Etiquetado Corte-Fin in Situ , Peroxidación de Lípido , Especies Reactivas de Oxígeno/metabolismo , Células Ganglionares de la Retina/enzimologíaRESUMEN
AIMS: Deduce whether the isoflavone genistein blunts the effect of ischaemia to the retina. METHODS: Ischaemia was induced in rats by raising the intraocular pressure (120 mm Hg) for 50 min. Genistein (10 mg/kg) was injected intraperitoneally 1 h before and after ischaemia. Seven days after ischaemia, the level of mRNAs for neurofilament light (NF-L), caspase 3, caspase 8, glial fibrillary acidic protein (GFAP), poly-ADP ribose polymerase (PARP), Thy-1 and proteins (GFAP, NF-L, PARP) in whole retinas were determined. NF-L and tubulin proteins in optic nerves were also determined. Retinas were also processed for the localization of choline acetyltransferase (ChAT) and GFAP immunoreactivities. RESULTS: Ischaemia caused a significant reduction in ganglion cell proteins in the optic nerve (NF-L and tubulin) and retina (NF-L). Retinal Thy-1 (mRNA and protein) and NF-L (mRNA) were also reduced while mRNAs of caspase 3, caspase 8, PARP and GFAP (also protein) were increased. Changes in the mRNAs and proteins induced by ischaemia were significantly blunted by genistein with the exception of the increase in GFAP and PARP protein/mRNA levels. Ischaemia-induced changes in the localization of ChAT were also clearly attenuated by genistein treatment. CONCLUSIONS: Genistein blunts most of the damaging effects caused to the retina by ischaemia.
Asunto(s)
Genisteína/uso terapéutico , Presión Intraocular , Fitoestrógenos/uso terapéutico , Daño por Reperfusión/prevención & control , Enfermedades de la Retina/prevención & control , Animales , Caspasa 3/genética , Caspasa 8/genética , Ciclofilinas/genética , Modelos Animales de Enfermedad , Femenino , Técnica del Anticuerpo Fluorescente Indirecta , Proteína Ácida Fibrilar de la Glía/metabolismo , Inyecciones Intraperitoneales , Proteínas de Neurofilamentos/genética , Hipertensión Ocular/complicaciones , Hipertensión Ocular/genética , Poli Adenosina Difosfato Ribosa/genética , Proteínas/genética , ARN Mensajero/genética , Ratas , Ratas Wistar , Daño por Reperfusión/etiología , Daño por Reperfusión/genética , Enfermedades de la Retina/etiología , Enfermedades de la Retina/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Antígenos Thy-1/genéticaRESUMEN
The retina captures and converts light between 400-760 nm into electrical signals that are sent to the brain by way of the optic nerve and in the process helps to translate these electrical signals into what is known as vision. The same light that allows vision to occur is nevertheless also potentially toxic to retinal cells in certain situations. The shorter wavelengths of light are known to interact with chromophores in photoreceptors and pigment epithelial cells to cause oxidative stress and severe damage. Indeed it is generally accepted that short wavelength light effects is one cause for loss of photoreceptor function in age-related macular degeneration. Recent studies have demonstrated that light may be a contributing factor for the death of retinal ganglion cells in certain situations. Light as impinging on the retina, especially the short wavelength form, affect mitochondrial chromophores and can result in neurone death. Importantly ganglion cell axons within the eye are laden with mitochondria and unlike the outer retina are not protected from short wavelength light by macular pigments. It has therefore been proposed that when ganglion cell function is already compromised, as in glaucoma, then light impinging on their mitochondria might be a contributor to their eventual demise.
Asunto(s)
Luz , Mitocondrias/efectos de la radiación , Degeneración Retiniana , Envejecimiento/metabolismo , Animales , Homeostasis , Humanos , Retina/metabolismo , Retina/efectos de la radiaciónRESUMEN
Reduced neurotrophic support is one possible cause for retinal ganglion cells dying in glaucoma. Experiments were designed to investigate the effect of EP2 receptor agonist butaprost on transformed retinal ganglion (RGC-5) cells where reduced neurotrophic support was simulated by serum withdrawal. Cultures were analysed for cell viability, flow cytometry, reactive oxygen species and apoptosis. Western blot and immunohistochemistry were used to provide information for the occurrence of PGE(2) receptor-types. We demonstrated the existence of all four types of PGE(2) receptors in RGC-5 cells and exposure of cultures to butaprost resulted in an elevation of cAMP. Serum deprivation induced RGC-5 cell death was significantly attenuated by butaprost as well as by rolipram and forskolin where intracellular cAMP levels were increased. These data are of value in relation to the possible use of EP2 receptor agonists to reduce both elevated intraocular pressure and retinal ganglion cell death as occurs in glaucoma.
Asunto(s)
Receptores de Prostaglandina E/metabolismo , Células Ganglionares de la Retina/metabolismo , Alprostadil/análogos & derivados , Alprostadil/farmacología , Animales , Apoptosis/efectos de los fármacos , Línea Celular , Supervivencia Celular/efectos de los fármacos , Medio de Cultivo Libre de Suero/farmacología , Ratas , Especies Reactivas de Oxígeno/metabolismo , Receptores de Prostaglandina E/agonistas , Subtipo EP2 de Receptores de Prostaglandina E , Células Ganglionares de la Retina/efectos de los fármacosRESUMEN
The purpose of the present study was to determine whether the flavonoid, baicalin is effective at blunting the negative influence of ischemia/reperfusion to the rat retina in situ and of various insults to a transformed retinal ganglion cells (RGC-5 cells) in culture. Baicalin was administered intraperitoneally just before and after an ischemic insult to retina of one eye of a rat. Ischemia was delivered by raising the intraocular pressure above the systolic blood pressure for 50min. Seven days after ischemia, retinas were analysed for the localisation of various antigens. Retinal extracts were also analysed for various mRNAs. Moreover, the content of specific proteins was deduced in retinal and optic nerve extracts. Also, RGC-5 cells in culture were given one of three different insults, light (1000lx for 2 days), hydrogen peroxide (200microM H(2)O(2) for 24h) or serum deprivation (48h) where cell survival and reactive oxygen species (ROS) formation was assayed. Moreover, a lipid peroxidation assay was used to compare the antioxidant capacity of baicalin with the flavonoid, epigallocatechin gallate (EGCG). Ischemia/reperfusion to the retina affected the localisation of Thy-1 and choline acetyltransferase (ChAT) and the content of various proteins (optic nerve and retina) and mRNAs (retina). Importantly, baicalin statistically blunted most of the effects induced by ischemia/reperfusion. Only the increase in caspase-8 and caspase-3 mRNAs caused by ischemia/reperfusion were unaffected by baicalin treatment. Baicalin also attenuated significantly the negative insult of light, hydrogen peroxide and serum withdrawal to RGC-5 cells. In the lipid peroxidation studies, baicalin was also found to be equally effective as EGCG to act as an antioxidant. Significantly, the negative insult of serum withdrawal on RGC-5 cell survival was blunted by baicalin but not by EGCG revealing the different properties of the two flavonoids.
Asunto(s)
Flavonoides/farmacología , Hipoxia-Isquemia Encefálica/tratamiento farmacológico , Peroxidación de Lípido/efectos de los fármacos , Estrés Oxidativo/efectos de los fármacos , Daño por Reperfusión/tratamiento farmacológico , Células Ganglionares de la Retina/efectos de los fármacos , Animales , Caspasas/metabolismo , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/fisiología , Células Cultivadas , Colina O-Acetiltransferasa/metabolismo , Medio de Cultivo Libre de Suero/toxicidad , Peróxido de Hidrógeno/toxicidad , Hipoxia-Isquemia Encefálica/metabolismo , Hipoxia-Isquemia Encefálica/fisiopatología , Inyecciones Intraperitoneales , Peroxidación de Lípido/fisiología , Fármacos Neuroprotectores/farmacología , Estrés Oxidativo/fisiología , Estimulación Luminosa/efectos adversos , Ratas , Especies Reactivas de Oxígeno/metabolismo , Daño por Reperfusión/metabolismo , Daño por Reperfusión/fisiopatología , Células Ganglionares de la Retina/metabolismo , Antígenos Thy-1/metabolismoRESUMEN
Flupirtine has been shown to function as a neuroprotectant and is presently used in man to treat a number of conditions. The aim of this study was to investigate the specific antioxidant properties of flupirtine in relation to oxidant-induced damage to retinal photoreceptors. Initial in vitro studies on brain membranes showed that flupirtine was approximately 20 times more potent than trolox (vitamin E analogue) and 8 times more potent than metipranolol at attenuating lipid peroxidation caused by the nitric oxide donor, sodium nitroprusside (SNP). Subsequent immunohistochemical studies revealed that following an intraocular injection of SNP, retinal photoreceptors are the only retinal cell types that appear to be clearly affected. This was supported by electroretinogram (ERG) recordings which showed both the a- and b-wave amplitudes to be significantly reduced. Western blotting techniques showed that SNP caused a significant decrease in photoreceptor-specific markers (RET-P1, rhodopsin kinase), an increase in cleaved caspase-3, Bcl-2, and cleaved PARP proteins that are associated with apoptosis and no change in the ganglion cell specific marker, neurofilament (NF-L). This was supported by RT-PCR data where rhodopsin (photoreceptor specific) mRNA was reduced while Thy-1 and NF-L (ganglion cell specific) mRNAs were unaffected. In addition SNP caused an elevation of glial cell response mRNAs primarily associated with Müller cells (GFAP, CNTF, bFGF) as well as caspase-3 and Bcl-2. Importantly, when flupirtine was co-injected, the effects to the retina caused by SNP on retinal proteins and mRNAs were in most cases significantly blunted. The conclusion reached from this study is that flupirtine is a powerful antioxidant and when injected into the eye with SNP attenuates the detrimental influence of SNP to retinal photoreceptors. Since oxidative stress has been implicated in retinal diseases like age-related macular degeneration (AMD) this study provides "proof of principle" for the idea that flupirtine may help individuals suffering from such retinal diseases.
Asunto(s)
Aminopiridinas/metabolismo , Analgésicos/metabolismo , Fármacos Neuroprotectores/metabolismo , Donantes de Óxido Nítrico/metabolismo , Nitroprusiato/metabolismo , Células Fotorreceptoras/metabolismo , Células Fotorreceptoras/patología , Animales , Antihipertensivos/metabolismo , Antioxidantes/metabolismo , Caspasa 3/genética , Caspasa 3/metabolismo , Cromanos/metabolismo , Factor Neurotrófico Ciliar/genética , Factor Neurotrófico Ciliar/metabolismo , Relación Dosis-Respuesta a Droga , Electrorretinografía , Factor 2 de Crecimiento de Fibroblastos/genética , Factor 2 de Crecimiento de Fibroblastos/metabolismo , Proteína Ácida Fibrilar de la Glía/genética , Proteína Ácida Fibrilar de la Glía/metabolismo , Humanos , Etiquetado Corte-Fin in Situ , Peroxidación de Lípido , Metipranolol/metabolismo , Células Fotorreceptoras/citología , Proteínas Proto-Oncogénicas c-bcl-2/genética , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Ratas , Ratas Wistar , Rodopsina/genética , Rodopsina/metabolismo , Sustancias Reactivas al Ácido Tiobarbitúrico/metabolismoRESUMEN
BACKGROUND: Diabetes inhibits dark adaptation and both processes alter the electroretinogram (ERG) in similar ways. This study aimed to investigate the relationship between oscillatory potentials (OPs) and the b-wave during dark adaptation and to determine if this relationship changes during the development of diabetes. METHODS: Twenty-one rats were assigned to adaptation, control and diabetic groups. Rats were dark adapted for periods between 20 minutes and 4 hours, and ERGs recorded. Diabetes was induced with streptozotocin, and ERGs measured after 3, 6, 9 and 12 weeks after injection. RESULTS: Increasing periods of dark adaptation led to a logarithmic increase in the amplitude of the b-wave and the OPs. This was accompanied by a decrease in the peak times of the OPs and b-wave. Total OP amplitude and b-wave amplitude were linearly related, allowing an empirical OP constant to be developed to describe the relationship between the two parameters. Diabetes led to a progressive decrease in the amplitude and increase in the peak time of all waves. The OP constant decreased in a linear fashion with increasing duration of diabetes. CONCLUSIONS: It is argued that OP masking of the b-wave could explain previous inconsistencies in reported ERG changes in diabetes and that a slowing of dark adaptation does not account for these ERG changes. The report concludes that the OPs and b-wave amplitudes and latencies are intimately related in the normal retina and that this correlation is lost predictably during the development of diabetes.
Asunto(s)
Adaptación a la Oscuridad/fisiología , Diabetes Mellitus Experimental/fisiopatología , Retinopatía Diabética/fisiopatología , Retina/fisiopatología , Animales , Glucemia/metabolismo , Electrorretinografía , Masculino , Oscilometría , Enmascaramiento Perceptual/fisiología , Ratas , Ratas Wistar , Factores de TiempoRESUMEN
The aim of this investigation was to determine whether an ingredient of green tea, epigallocatechin gallate (EGCG) could attenuate oxidative stress-induced degeneration of the retina as occurs in age-related macular degeneration (AMD) and glaucoma. Initial in vitro studies on brain membranes showed that EGCG was approximately 10 times more potent than trolox (vitamin E analogue) at attenuating lipid peroxidation caused by the nitric oxide donor, sodium nitroprusside (SNP). Subsequent immunohistochemical studies revealed that following an intraocular injection of SNP retinal photoreceptors are affected. This was supported by electroretinogram (ERG) recordings which showed both the a- and b-wave amplitudes to be significantly reduced. RT-PCR and Western blotting techniques showed that SNP caused a significant decrease in photoreceptor-specific markers (RET-P1, rhodopsin kinase), an increase in the cell death marker caspase-3, and no change in the ganglion cell specific markers, neurofilament (NF-L) and Thy-1. Importantly, when EGCG was co-injected, the detrimental effects to the retina caused by SNP were significantly blunted. The conclusion reached from this study is that EGCG is a powerful antioxidant and when injected into the eye with SNP attenuated the detrimental influence of SNP to retinal photoreceptors. Since oxidative stress has been implicated in retinal diseases like AMD and glaucoma this study provides "proof of principle" for the idea that daily intake of EGCG may help individuals suffering from retinal diseases where oxidative stress is implicated.
Asunto(s)
Catequina/análogos & derivados , Fármacos Neuroprotectores/uso terapéutico , Estrés Oxidativo , Degeneración Retiniana/tratamiento farmacológico , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Caspasa 3/genética , Caspasa 3/metabolismo , Catequina/uso terapéutico , Colina O-Acetiltransferasa/metabolismo , Electrorretinografía/métodos , Regulación de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica/fisiología , Inmunohistoquímica/métodos , Etiquetado Corte-Fin in Situ/métodos , Peroxidación de Lípido/efectos de los fármacos , Proteínas de Neurofilamentos/genética , Proteínas de Neurofilamentos/metabolismo , Proteína Quinasa C/metabolismo , ARN Mensajero/metabolismo , Ratas , Degeneración Retiniana/etiología , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/métodos , Opsinas de Bastones/genética , Opsinas de Bastones/metabolismo , Rodopsinas Sensoriales/genética , Rodopsinas Sensoriales/metabolismo , Antígenos Thy-1/genética , Antígenos Thy-1/metabolismo , Ácido gamma-Aminobutírico/metabolismoRESUMEN
The authors propose that light entering the eye interacts with retinal ganglion cell (RGC) axon mitochondria to generate reactive oxygen intermediates (ROI) and that when these neurons are in an energetically low state, their capacity to remove these damaging molecules is exceeded and their survival is compromised. They suggest that in the initial stages of glaucoma, RGCs exist at a low energy level because of a reduced blood flow at the optic nerve head and that in the mitochondrial optic neuropathies (MONs), this results from a primary, genetic defect in aerobic metabolism. In these states RGCs function at a reduced energy level and incident light on the retina becomes a risk factor. Preliminary laboratory studies support this proposition. Firstly, the authors have shown that light is detrimental to isolated mitochondria in an intensity dependent manner. Secondly, light triggers apoptosis of cultured, transformed RGCs and this effect is exacerbated when the cells are nutritionally deprived. Detailed studies are under way to strengthen the proposed theory. On the basis of this proposal, the authors suggest that patients with optic neuropathies such as glaucoma or at risk of developing a MON may benefit from the use of spectral filters and reducing the intensity of light entering the eye.
Asunto(s)
Glaucoma/metabolismo , Luz/efectos adversos , Mitocondrias/efectos de la radiación , Enfermedades del Nervio Óptico/metabolismo , Células Ganglionares de la Retina/efectos de la radiación , Apoptosis/efectos de la radiación , Humanos , Mitocondrias/metabolismo , Disco Óptico/irrigación sanguínea , Enfermedades del Nervio Óptico/genética , Especies Reactivas de Oxígeno/metabolismo , Flujo Sanguíneo Regional , Células Ganglionares de la Retina/metabolismo , Factores de RiesgoRESUMEN
The aim of this work was to investigate the interrelated effects of glucose, nitric oxide (NO) and erythropoietin on neuronal survival in retinal cultures, thereby exploring the mechanism of neuronal death in the diabetic retina. Rat retinal cells were cultured in low (5 mM) or high (15 mM) glucose concentrations. After 9 days, cell viability was assessed by (3,4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and NO production was determined by the Griess reaction. Immunohistochemistry was used to quantify GABA-labelled neurones and cells staining for DNA breakdown. High or low glucose concentrations had no effect on basal NO production or the survival of neurones in culture, but treatment with N-nitro-L-arginine methyl ester reduced extracellular levels of NO and increased neuronal survival at both concentrations of glucose. Erythropoietin decreased cell death and NO levels, but only in cultures grown in low concentrations of glucose. It is concluded that erythropoietin's neurotrophic function in the retina is attenuated at glucose concentrations similar to those which occur in diabetes.
Asunto(s)
Eritropoyetina/farmacología , Glucosa/farmacología , Neuronas/metabolismo , Óxido Nítrico/biosíntesis , Retina/metabolismo , Animales , Muerte Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Citoprotección/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Inhibidores Enzimáticos/farmacología , Glucosa/metabolismo , NG-Nitroarginina Metil Éster/farmacología , Ratas , Retina/citología , Ácido gamma-Aminobutírico/biosíntesisRESUMEN
BACKGROUND: Experimental studies have yielded a wealth of information related to the mechanism of ganglion cell death following injury either to the myelinated ganglion cell axon or to the ganglion cell body. However, no suitable animal models exist where injury can be directed to the optic nerve head region, particularly the unmyelinated ganglion cell axons. The process of relating the data from the various animal models to many different types of optic neuropathies in man must, therefore, be cautious. RESULTS: Extensive studies on the isolated optic nerve have yielded valuable information on the way white matter is affected by ischaemia and how certain types of compounds can attenuate the process. Moreover, there are now persuasive data on how ganglion cell survival is affected when the ocular blood flow is reduced in various animal models. As a consequence, the molecular mechanisms involved in ganglion cell death are fairly well understood and various pharmacological agents have been shown to blunt the process when delivered before or shortly after the insult. CONCLUSIONS: A battery of agents now exist that can blunt animal ganglion cell death irrespective of whether the insult was to the ganglion cell body or the myelinated axon. Whether this information can be applied for use in patients remains a matter of debate, and major obstacles need to be overcome before the laboratory studies may be applied clinically. These include the delivery of the pharmacological agents to the site of ganglion cell injury and side effects to the patients. Moreover, it is necessary to establish whether effective neuroprotection is only possible when the drug is administered at a defined time after injury to the ganglion cells. This information is essential in order to pursue the idea that a neuroprotective strategy can be applied to a disease like glaucoma, where ganglion cell death appears to occur at different times during the lifetime of the patient.
Asunto(s)
Fármacos Neuroprotectores/uso terapéutico , Enfermedades del Nervio Óptico/tratamiento farmacológico , Nervio Óptico/efectos de los fármacos , Células Ganglionares de la Retina/efectos de los fármacos , Animales , Apoptosis/efectos de los fármacos , Apoptosis/fisiología , Axones/fisiología , Modelos Animales de Enfermedad , Glaucoma/tratamiento farmacológico , Glaucoma/fisiopatología , Humanos , Disco Óptico/efectos de los fármacos , Disco Óptico/fisiopatología , Nervio Óptico/fisiopatología , Enfermedades del Nervio Óptico/fisiopatología , Traumatismos del Nervio Óptico/tratamiento farmacológico , Traumatismos del Nervio Óptico/fisiopatología , Neuropatía Óptica Isquémica/tratamiento farmacológico , Neuropatía Óptica Isquémica/fisiopatología , Ratas , Células Ganglionares de la Retina/fisiologíaRESUMEN
In hypoxic or ischemic states, the receptors of the ganglion cells are overstimulated by release of neurotransmitters. Glutamate and GABA (gamma-aminobutyric acid) are the decisive neurotransmitters in the retina. It is presumed that the extent of cell death depends on the degree of depolarization, which in turn is determined by the amount of excitatory (glutamate) or inhibitory (GABA) receptors of the corresponding ganglion cell. The assumption is that the receptor profile of the individual ganglion cells determines the sensitivity of these cells to hypoxia or ischemia, i.e., the time up to cell death, and thus represents the underlying cause of the different rates of cell death in primary chronic open-angle glaucoma. Research on this receptor profile could be of pivotal importance for the approach to neuroprotective treatment of primary chronic open-angle glaucoma.
Asunto(s)
Glaucoma de Ángulo Abierto/metabolismo , Fármacos Neuroprotectores/uso terapéutico , Neurotransmisores/metabolismo , Neuropatía Óptica Isquémica/metabolismo , Neuropatía Óptica Isquémica/prevención & control , Degeneración Retiniana/metabolismo , Células Ganglionares de la Retina/metabolismo , Animales , Apoptosis/efectos de los fármacos , Glaucoma de Ángulo Abierto/complicaciones , Glaucoma de Ángulo Abierto/tratamiento farmacológico , Humanos , Hipoxia/etiología , Hipoxia/metabolismo , Hipoxia/prevención & control , Degeneración Nerviosa/etiología , Degeneración Nerviosa/metabolismo , Degeneración Nerviosa/prevención & control , Neuropatía Óptica Isquémica/etiología , Degeneración Retiniana/etiología , Degeneración Retiniana/prevención & control , Células Ganglionares de la Retina/efectos de los fármacos , Células Ganglionares de la Retina/patologíaRESUMEN
According to estimates made by WHO, approximately 105 million people are affected worldwide by glaucoma. This can be defined as progressive optic neuropathy with structural damage of the optic nerve head and death of retinal ganglion cells. Although elevated IOP is considered responsible for glaucoma, lowering the pressure often does not result in improvement. For this reason, other etiological factors are presumed, which are presented in the following contribution. The role of neuroprotective agents in the treatment of glaucoma is discussed. The pattern of ganglion cell death specific to glaucoma seems to suggest that certain ganglion cells could be more sensitive than others. The theory of "cumulative damage" in this case includes the hypothesis that the delayed onset of many neurodegenerative diseases such as glaucoma, Alzheimer's disease, or Parkinson's disease can be attributed to the age-related accumulation of toxic substances in the ganglion cells. On the contrary, the theory of "singular damage" is based on the assumption that certain ganglion cells are in a state of reduced homeostasis caused by the expression of so-called mutant response genes. Therapeutic approaches worthy of consideration based on their side effect profile and efficacy in animal trials, are presented.
Asunto(s)
Glaucoma de Ángulo Abierto/metabolismo , Fármacos Neuroprotectores/uso terapéutico , Neurotransmisores/metabolismo , Degeneración Retiniana/metabolismo , Células Ganglionares de la Retina/metabolismo , Animales , Apoptosis/efectos de los fármacos , Glaucoma de Ángulo Abierto/complicaciones , Glaucoma de Ángulo Abierto/tratamiento farmacológico , Humanos , Modelos Biológicos , Modelos Neurológicos , Degeneración Nerviosa/etiología , Degeneración Nerviosa/metabolismo , Degeneración Nerviosa/prevención & control , Degeneración Retiniana/etiología , Degeneración Retiniana/prevención & control , Células Ganglionares de la Retina/efectos de los fármacos , Células Ganglionares de la Retina/patologíaRESUMEN
The recreational use of the psychoactive drug, methamphetamine has increased markedly over the last three decades. It has long been known that this drug has detrimental effects upon the mammalian brain monoaminergic system, but the long- or short-term effects on the retina, a neurological extension of the central nervous system, have received little attention. The aim of this study was, therefore, to determine whether intraocular injection of methamphetamine (MA) is toxic to the healthy adult rat retina and to analyse its effects on the compromised retina after an injection of the ionotropic glutamate receptor agonist, kainate, which is known to cause retinal neuropathology. The equivalent of 1 mM (in the vitreous humour) MA and/or kainate (40 microM) were injected intravitreally. Flash electroretinograms (ERGs) were recorded before and 2 and 4 days after treatment. Five days after treatment, animals were killed and the retinas analysed either for the immunohistochemical localisation of various antigens or for electrophoresis/Western blotting. Some animals were kept for 19 days after treatment and the retinas analysed for tyrosine hydroxylase immunoreactivity. No differences could be found between vehicle- and MA-treated retinas with respect to the nature or localisation of either tyrosine hydroxylase immunoreactivity after 5 or 19 days or other antigens after 5 days. Moreover, the normal ERG and GFAP and calretinin protein antigens were unaffected by MA. Kainate treatment, however, caused a change in the ERGs after 2 and 4 days, an alteration in every antigen localised by immunohistochemistry and an increase in the retinal levels of calretinin and GFAP proteins. Significantly, the changes seen in the b-wave amplitude and implicit time of the ERG after 4 days and the increased level of GFAP protein after 5 days following kainate treatment were enhanced when MA was co-injected. Intravitreal injection of methamphetamine had no detectable detrimental effect on the normal adult rat retina but exacerbated the damaging effects of kainic acid. Such data suggest that a neurotoxic effect of MA may be more obviously illustrated when the tissue is already compromised as occurs in, for example, ischemia.
Asunto(s)
Estimulantes del Sistema Nervioso Central/toxicidad , Agonistas de Aminoácidos Excitadores/toxicidad , Ácido Kaínico/toxicidad , Metanfetamina/toxicidad , Retina/patología , Animales , Western Blotting , Estimulantes del Sistema Nervioso Central/administración & dosificación , Adaptación a la Oscuridad/fisiología , Sinergismo Farmacológico , Electrorretinografía , Ojo , Proteína Ácida Fibrilar de la Glía/metabolismo , Inmunohistoquímica , Inyecciones , Metanfetamina/administración & dosificación , Estimulación Luminosa , Ratas , Tirosina 3-Monooxigenasa/metabolismoRESUMEN
AIMS: To determine the effect of hypoglycaemia on ischaemic retinal injury. METHODS: Rat retinal cultures were incubated in varying concentrations of glucose while placed under standardised anoxic conditions, and the number of surviving GABA immunoreactive neurons was assessed using immunocytochemistry. Hypoglycaemia was induced in age and sex matched Wistar rats by an injection of rapid acting insulin. The blood, vitreous, and retinal glucose concentrations were measured using a hexokinase assay kit. Electroretinography, semiquantitative RT-PCR, and histology were used to compare the functional and structural retinal injury in these rats with the injury in appropriate controls after a period of pressure induced retinal ischaemia. RESULTS: Retinal cultures maintained in low glucose concentrations (<1 mM) had fewer surviving GABA immunoreactive neurons after an anoxic insult compared with retinal cultures maintained in 5 mM glucose. Hypoglycaemic rats had significantly lower vitreous glucose concentrations (0.57 (SEM 0.04) mM) than the control rats (3.1 (0.70) mM; p<0.001). The a-wave and b-wave amplitudes of the hypoglycaemic rats after 3 and 7 days of reperfusion were significantly lower than the amplitudes of the control rats. Furthermore, the level of Thy-1 mRNA (a retinal ganglion cell marker) was significantly lower in the hypoglycaemic group (p<0.001) and there was a corresponding exacerbation of structural injury compared with the controls. CONCLUSION: Hypoglycaemia causes a significant reduction in vitreous glucose levels and exacerbates ischaemic retinal injury.
Asunto(s)
Hipoglucemia/complicaciones , Isquemia/etiología , Enfermedades de la Retina/etiología , Enfermedad Aguda , Animales , Ciclofilinas/genética , Electrorretinografía , Glucosa/análisis , ARN Mensajero/análisis , Ratas , Ratas Wistar , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Antígenos Thy-1/genética , Cuerpo Vítreo/químicaRESUMEN
Glaucoma is a chronic optic neuropathy in which retinal ganglion cells die over a number of years. The initiation of the disease and its progression may involve an ischaemic-like insult to the ganglion cell axons caused by an alteration in the quality of blood flow. Thus, to effectively treat glaucoma it may be necessary to counteract the ischaemic-like insult to the region of the optic nerve head. Studies on the isolated optic nerve suggest that substances that reduce the influx of sodium would be particularly effective neuroprotectants. Significantly, of the presently used antiglaucoma substances, only beta-blockers can reduce sodium influx into cells. Moreover, they also reduce the influx of calcium and this would be expected to benefit the survival of insulted neurones. Betaxolol is the most effective antiglaucoma drug at reducing sodium/calcium influx. Our electroretinographic data indicated that topical application of levobetaxolol to rats attenuated the effects of ischaemia/reperfusion injury. Timolol was also effective but to a lesser extent. Based on these data we conclude that beta-blockers may be able to blunt ganglion cell death in glaucoma, and that levobetaxolol may be a more effective neuroprotectant than timolol because of its greater capacity to block sodium and calcium influx.
Asunto(s)
Betaxolol/uso terapéutico , Isquemia/tratamiento farmacológico , Retina/efectos de los fármacos , Intercambiador de Sodio-Calcio/antagonistas & inhibidores , Timolol/uso terapéutico , Animales , Betaxolol/farmacología , Calcio/antagonistas & inhibidores , Calcio/metabolismo , Glaucoma/tratamiento farmacológico , Glaucoma/metabolismo , Humanos , Isquemia/metabolismo , Retina/metabolismo , Sodio/antagonistas & inhibidores , Sodio/metabolismo , Intercambiador de Sodio-Calcio/metabolismo , Timolol/farmacologíaRESUMEN
The main aim of this study was to investigate whether intraocular injection of low concentrations of zinc (no greater than 10 microM) aid the survival of ganglion cells in the rat retina after excitotoxic (NMDA) and ischemia/reperfusion injuries. We also determined whether low amounts of zinc cause any detectable retinal toxicity. Intraocular injection of NMDA caused substantial reductions in the mRNA levels of the ganglion cell-specific markers Thy-1 and neurofilament light (NF-L). Co-injection of 0.1 or 1 nmol zinc neither diminished nor exacerbated the effect of NMDA on the levels of these mRNAs. Likewise, ischemia/reperfusion caused significant decreases in the levels of Thy-1 and NF-L mRNAs and in the b-wave amplitude of the electroretinogram. These effects were not counteracted by injection of zinc. Intraocular injection of NMDA caused marked toxicological effects in retinal glial cells, including upregulations of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), glial fibrial acidic protein (GFAP), basic fibroblast growth factor (FGF-2) and ciliary neurotrophic factor (CNTF). Interestingly, injection of 1 nmol zinc caused no changes in the levels of COX-2 and iNOS, yet produced similar, although quantitatively less pronounced, changes in FGF-2, GFAP and CNTF. The upregulations of FGF-2 and CNTF suggest that increasing zinc intake may benefit injured retinal neurons. However, this was not found to be the case in the present studies, perhaps due to the acute nature of the injury paradigms utilised.
Asunto(s)
Astringentes/farmacología , Retina/efectos de los fármacos , Células Ganglionares de la Retina/efectos de los fármacos , Sulfato de Zinc/farmacología , Animales , Muerte Celular , Supervivencia Celular/efectos de los fármacos , Factor Neurotrófico Ciliar/genética , Ciclooxigenasa 2 , Maleato de Dizocilpina/farmacología , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Electrorretinografía/instrumentación , Electrorretinografía/métodos , Agonistas de Aminoácidos Excitadores/toxicidad , Antagonistas de Aminoácidos Excitadores/farmacología , Ojo , Factor 2 de Crecimiento de Fibroblastos/genética , Factor 2 de Crecimiento de Fibroblastos/metabolismo , Proteína Ácida Fibrilar de la Glía/genética , Proteína Ácida Fibrilar de la Glía/metabolismo , Immunoblotting , Inmunohistoquímica , Isoenzimas/genética , N-Metilaspartato/toxicidad , Neuroglía/efectos de los fármacos , Óxido Nítrico Sintasa/genética , Óxido Nítrico Sintasa/inmunología , Óxido Nítrico Sintasa de Tipo I , Óxido Nítrico Sintasa de Tipo II , Prostaglandina-Endoperóxido Sintasas/genética , ARN Mensajero/biosíntesis , Ratas , Ratas Wistar , Daño por Reperfusión/genética , Daño por Reperfusión/metabolismo , Daño por Reperfusión/fisiopatología , Retina/citología , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Rodopsina/genética , Rodopsina/metabolismo , Antígenos Thy-1/genética , Factores de TiempoRESUMEN
The primary features of glaucomatous optic neuropathy are characteristic changes in the optic nerve head, a decrease in number of surviving ganglion cells and a reduction in vision. It is now generally accepted that a number of factors, including elevated intraocular pressure, could lead to the changes seen in the optic nerve head and to obtain a pharmacological means to treat the causes will vary from patient to patient. In contrast, a cascade of events have been proposed to explain how the changes in the optic nerve head may lead to the slow and differential death of ganglion cells in the disease. It is also proposed that drugs (neuroprotectants) influencing this cascade of events can attenuate ganglion cell death and lead to the treatment of all glaucoma patients.