Saffron (Crocus sativus L.) has been traditionally used in food preparation and as a medicinal plant. It currently has numerous therapeutic properties attributed to it, such as protection against ...ischemia, as well as anticonvulsant, antidepressant, anxiolytic, hypolipidemic, anti-atherogenic, anti-hypertensive, antidiabetic, and anti-cancer properties. In addition, saffron has remarkable beneficial properties, such as anti-apoptotic, anti-inflammatory and antioxidant activities, due to its main metabolites, among which crocin and crocetin stand out. Furthermore, increasing evidence underwrites the possible neuroprotective role of the main bioactive saffron constituents in neurodegenerative diseases, such as Parkinson's and Alzheimer's diseases, both in experimental models and in clinical studies in patients. Currently, saffron supplementation is being tested for ocular neurodegenerative pathologies, such as diabetic retinopathy, retinitis pigmentosa, age-related macular degeneration and glaucoma, among others, and shows beneficial effects. The present article provides a comprehensive and up to date report of the investigations on the beneficial effects of saffron extracts on the main neurodegenerative ocular pathologies and other ocular diseases. This review showed that saffron extracts could be considered promising therapeutic agents to help in the treatment of ocular neurodegenerative diseases.
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that causes degeneration of the lower and upper motor neurons and is the most prevalent motor neuron disease. This disease is ...characterized by muscle weakness, stiffness, and hyperreflexia. Patients survive for a short period of time from the onset of the disease. Most cases are sporadic, with only 10% of the cases being genetic. Many genes are now known to be involved in familial ALS cases and some of the sporadic ones. It has also been observed that, in addition to genetic factors, there are numerous molecular mechanisms involved in these pathologies, such as excitotoxicity, mitochondrial disorders, alterations in axonal transport, oxidative stress, accumulation of misfolded proteins, and neuroinflammation. This pathology affects the motor neurons, the spinal cord, the cerebellum, and the brain, but recently, it has been shown that it also affects the visual system, not only at the level of the oculomotor system but also at the retinal level, which is why the retina is being proposed as a possible biomarker of this pathology. This review includes the main aspects mentioned above related to ALS, such as the main genes involved, the most important molecular mechanisms that affect this pathology, its ocular involvement, and the possible usefulness of the retina as a biomarker.
Glaucoma is a neurodegenerative retinal disease characterized by irreversible loss of retinal ganglion cells (RGCs), leading to visual loss. Increased intraocular pressure (IOP) is the only risk ...factor for which treatment is available. However, other factors such as glial activation and dysfunction can also induce RGC death in glaucoma.
Astrocytes and Müller glia (macroglial cells) play important roles in neuronal activity by providing physical and metabolic support to neurons. In glaucoma, when tissue damage occurs, macroglial cells undergo reactive gliosis, to defend the nerve tissue against damage and attempt to maintain its homeostasis. However, alterations in the function of these cells could cause damage and even neuronal death. In reactive macrogliosis, cells undergo complex biochemical and functional remodelling and exhibit morphological changes characterized by cell body thickening, increased number and length of cell processes, increased cell number and up‐regulation of cytoskeletal components such as gliofibrillary acidic protein (GFAP), which is considered one of the main markers of this process and may act as antigen‐presenting cells by expressing major histocompatibility complex class II (MHC‐II). Reactivation of macroglia can initially be beneficial, as it increases their metabolic activity, increases the expression of antioxidant defence, and restores ion, water and neurotransmitter balance. However, if macroglia become chronic, it is detrimental by directly or indirectly damaging the tissue and preventing its repair. Astrocytes may act in concert with microglia during the inflammatory process, so inflammatory mediators produced by astrocytes can chronically activate microglial cells, contributing to neuronal death, and similarly, inflammatory mediators released by microglia can chronically activate astrocytes.
One of the most widely used models to elevate IOP is the unilateral laser‐induced ocular hypertension (OHT) model. Studies in this model have analysed the temporal pattern of RGC death and microglial cell activation at time points: 1, 3, 5, 8 and 15 days. Molecular changes in proinflammatory and anti‐inflammatory cytokines involved in the neuroinflammatory process, released by glial cells (microglia, astrocytes, and Müller cells) at the same time points mentioned above, have also been identified.
Given the close relationship between the activation of macroglia and microglia and their involvement in the death of RGCs in this pathology, the present work analysed how the activation of retinal macroglial cells occurred at different time points (1, 3, 5, 8 and 15 days) after the induction of OHT in an experimental model of laser‐induced OHT in mice. For this purpose, we have analysed the GFAP‐labelled retinal area, the intensity of GFAP labelling, and the expression of MHC‐II in both OHT eyes and normotensive contralateral eyes compared to naïve eyes.
In this study, in both OHT and contralateral eyes, macroglial cells showed morphological changes as well as in GFAP and MHC‐II expression at all time points analysed, being slightly more intense at 3–5 days, coinciding with the pattern of microglial activation previously studied, demonstrating this fact, a bilateral inflammatory process maintained over time in which microglia, astrocytes and Müller glia are involved.
Glaucoma is an age‐related neurodegenerative pathology, characterized by retinal ganglion cells (RGCs) death, which leads to irreversible blindness. Clinical studies have shown that one of the risk ...factors for glaucoma is high intraocular pressure (IOP). The only therapeutic strategy currently used in this pathology is the reduction of IOP, which does not always reverse neurodegeneration and stop the progression of the disease. However, there is another more important risk factor for glaucoma than IOP, which is aging. It has been observed that aging can increase the vulnerability of the central nervous system to damage. Changes that occur with aging can make RGCs more vulnerable to damage in the glaucomatous neurodegeneration process. The effects of oxidative stress and chronic exposure to light and inflammation mainly cause alterations in the retina due to aging.
In glaucomatous neurodegeneration, as in most neurodegenerative diseases, the immune system is involved. Glial cells are immune cells of the retina and optic nerve. When damage occurs, these cells respond quickly, becoming activated, to help restore tissue homeostasis and ensure the immune privilege of nerve tissue. In addition, with aging, a state of chronic parainflammation occurs, leading to the activation of the microglia and release of cytotoxic factors, such as TNF‐α, nitric oxide and other molecules, that which could significantly exacerbate glaucomatous neurodegeneration.
One of the main models for raising IOP is the unilateral model of laser‐induced ocular hypertension (OHT). Studies have analysed RGC death and the neuroinflammatory process (focusing on glial cell changes) in this unilateral laser‐induced OHT model in young adult mice. Considering that glaucoma is an age‐related pathology, and that age is the main risk factor, aged in these studies should have been considered a determinate factor.
We have used 15‐month‐old mice, which is the beginning point of the aging process of the mice, which is well established from 18 months. In this study, we found morphological signs of microglial activation and changes in the expression of MHCII, CD68 and P2RY12 in the naïve eyes of 15‐month‐old mice (early stage of aging), compared to young naïve adults.
On this study we have also analysed the microglial behaviour in response to an increase in IOP in 15‐month‐old mice in a unilateral laser‐induced OHT mouse model of both OHT and contralateral eyes. We also found microglial morphologic alterations and changes in the expression of MHCII, CD68 and P2RY12 in the eyes of 15‐month‐old OHT mice and in the eyes contralateral to them, compared to the eyes of young adult OHT mice and the eyes contralateral to them.
In neurodegenerative diseases associated with aging, such as glaucoma, the neuroinflammatory mechanisms induced by microglial cells have an important implication in the development of disease. The use of aging models to analyses the age‐related retinal pathologies could help to improve our understanding of the progression of these pathologies.
Signaling mediated by cytokines and chemokines is involved in glaucoma-associated neuroinflammation and in the damage of retinal ganglion cells (RGCs). Using multiplexed immunoassay and ...immunohistochemical techniques in a glaucoma mouse model at different time points after ocular hypertension (OHT), we analyzed (i) the expression of pro-inflammatory cytokines, anti-inflammatory cytokines, BDNF, VEGF, and fractalkine; and (ii) the number of Brn3a+ RGCs. In OHT eyes, there was an upregulation of (i) IFN-γ at days 3, 5, and 15; (ii) IL-4 at days 1, 3, 5, and 7 and IL-10 at days 3 and 5 (coinciding with downregulation of IL1-β at days 1, 5, and 7); (iii) IL-6 at days 1, 3, and 5; (iv) fractalkine and VEGF at day 1; and (v) BDNF at days 1, 3, 7, and 15. In contralateral eyes, there were (i) an upregulation of IL-1β at days 1 and 3 and a downregulation at day 7, coinciding with the downregulation of IL4 at days 3 and 5 and the upregulation at day 7; (ii) an upregulation of IL-6 at days 1, 5, and 7 and a downregulation at 15 days; (iii) an upregulation of IL-10 at days 3 and 7; and (iv) an upregulation of IL-17 at day 15. In OHT eyes, there was a reduction in the Brn3a+ RGCs number at days 3, 5, 7, and 15. OHT changes cytokine levels in both OHT and contralateral eyes at different time points after OHT induction, confirming the immune system involvement in glaucomatous neurodegeneration.
Alzheimer's disease (AD) is the most common type of dementia in the world. The main biomarkers associated with AD are protein amyloid-β (Aβ) plaques and protein tau neurofibrillary tangles, which are ...responsible for brain neuroinflammation mediated by microglial cells. Increasing evidence has shown that the retina can also be affected in AD, presenting some molecular and cellular changes in the brain, such as microglia activation. However, there are only a few studies assessing such changes in the retinal microglia in animal models of AD. These studies use retinal sections, which have some limitations. In this study, we performed, for the first time in a triple-transgenic AD mouse model (3xTg-AD), a quantitative morphometric analysis of microglia activation (using the anti-Iba-1 antibody) in retinal whole-mounts, allowing visualization of the entire microglial cell, as well as its localization along the extension of the retina in different layers. Compared to age-matched animals, the retina of 3xTg-AD mice presents a higher number of microglial cells and a thicker microglial cell body area. Moreover, the microglia migrate, reorient, and retract their processes, changing their localization from a parallel to a perpendicular position relative to the retinal surface. These findings demonstrate clear microglia remodeling in the retina of 3xTg-AD mice.
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Glaucoma is a neurodegenerative disease characterized by the loss of retinal ganglion cells (RGCs). An increase in the intraocular pressure is the principal risk factor but controlling ...this pressure does not always prevent glaucomatous damage, so other harmful factors would be implicated in this pathologic process. Several mechanisms have been proposed that leads to the RGC death in glaucoma, including glutamate excitotoxicity, aggregation of misfolded proteins, mitochondrial dysfunction, oxidative stress, neurotrophic deprivation, and neuroinflammation, among others. Therefore, early diagnosis of neurodegeneration, understanding of its pathogenic mechanisms, and the development of new neuroprotective therapies represent major challenges for treating this disease.
During the inflammatory process that occurs in glaucoma, retinal glial cells, both microglia and macroglia (Müller cells and astrocytes), become activated and release factors that can be neuroprotective in some cases and neurodegenerative in others. Cytokine‐ and chemokine‐mediated signalling engages in the neuroinflammatory process that leads to retinal ganglion cell (RGC) damage in glaucoma. Thus, a substance with anti‐inflammatory activity may protect against RGC degeneration.
Increasing evidence from both experimental models and clinical studies in patients supports the neuroprotective effect of saffron components in neurodegenerative conditions and in retinal neurodegenerative pathologies, due to its important anti‐inflammatory, anti‐apoptotic, and antioxidant properties.
This talk overviews the published studies that analysed the neuroprotective and anti‐inflammatory effects of saffron and its main components in both clinical trials and experimental models of glaucoma. All findings indicate that oral administration of saffron extract could be beneficial in glaucoma by decreasing the neuroinflammation associated with increased intraocular pressure, reducing microglial activation, regulating the production of proinflammatory cytokines, and preventing retinal ganglion cell death.
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Dravet syndrome (DS) is an epileptic encephalopathy caused by mutations in the Scn1a gene encoding the α1 subunit of the Nav1.1 sodium channel, which is associated with recurrent and ...generalized seizures, highly resistant to antiepileptic drugs, which is related to cognitive impairment, developmental delays, hyperactivity, dysautonomia, attention deficit, language impairment, autistic features, even leading to death. GABAergic interneurons are particularly affected, where the Nav1.1 channel is mainly located and the consequent imbalance between excitation and inhibition triggers brain hyperexcitability and seizures, altering the correct functioning of neural networks involved in cognitive processes.
Glial reactivity and neuroinflammatory processes have been shown to be present in childhood epileptic processes and therefore cytokines may exert a neuromodulatory role directly impacting neuronal excitability. Indeed, astrocytes have been documented to be involved in the pathogenesis of epilepsy, regulating neurotransmitter and ion concentrations.
In our experimental model of DS (Syn‐Cre/Scn1aWT/A1783V), inflammatory events in the prefrontal cortex and dentate gyrus of the hippocampus expressed as an increase in GFAP (astrocyte marker) and Iba‐1 (microglia marker) immunoreactivity have been observed, in addition to morphological changes compatible with activated astrocytes and microglia.
The retina is a projection of the brain, and in several pathologies affecting the central nervous system, such as neurodegenerative diseases, correlation between changes occurring in the brain and those occurring in the retina has been shown. Therefore, the analyse of the changes that may occur in retinal glial cells (astrocytes and microglia) in an experimental model of DS, and the correlation with the alterations observed in some specific cerebral areas of these animals could be good predictive and prognostic biomarkers for future treatment.
This study analyzes the retinal histological changes in glial cells (microglia and astrocytes), retinal ganglion cells (RGCs) and GABAergic amacrine cells in an experimental model of DS (Syn‐Cre/Scn1aWT/A1783V) compared to a control group at postnatal day (PND) 25. Retinal whole‐mounts were labelled with anti‐GFAP, anti‐Iba‐1, anti‐Brn3a and anti‐GAD65/67. Signs of microglial and astroglial activation and the number of Brn3a+ and GAD65+ 67+ cells were quantified. We found retinal activation of astroglial and microglial cells but not death of RGCs and GABAergic amacrine cells. These changes are similar to those found at the level of the hippocampus in the same experimental model in PND25, indicating a relationship between brain and retinal changes in DS. This suggests that the retina could serve as a possible biomarker in DS.
The neurodegenerative disease amyotrophic lateral sclerosis (ALS) affects the spinal cord, brain stem, and cerebral cortex. In this pathology, both neurons and glial cells are affected. However, few ...studies have analyzed retinal microglia in ALS models. In this study, we quantified the signs of microglial activation and the number of retinal ganglion cells (RGCs) in an SOD1G93A transgenic mouse model at 120 days (advanced stage of the disease) in retinal whole-mounts. For SOD1G93A animals (compared to the wild-type), we found, in microglial cells, (i) a significant increase in the area occupied by each microglial cell in the total area of the retina; (ii) a significant increase in the arbor area in the outer plexiform layer (OPL) inferior sector; (iii) the presence of cells with retracted processes; (iv) areas of cell groupings in some sectors; (v) no significant increase in the number of microglial cells; (vi) the expression of IFN-γ and IL-1β; and (vii) the non-expression of IL-10 and arginase-I. For the RGCs, we found a decrease in their number. In conclusion, in the SOD1G93A model (at 120 days), retinal microglial activation occurred, taking a pro-inflammatory phenotype M1, which affected the OPL and inner retinal layers and could be related to RGC loss.
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