The retina as a window to early dysfunctions of Alzheimer's disease following studies with a 5xFAD mouse model.

Alzheimer's disease (AD) is a progressive neurodegenerative disease leading to neuronal dysfunctions with cognitive impairment. AD can affect visual pathways and visual cortex and result in various visual changes and problems. However, how early the visual dysfunctions occur in AD is still a matter of discussion. Here, we used electrophysiological techniques to show the presence of early anomalies in AD visual system. To this aim, we used a familial AD (FAD) model, the 5xFAD transgenic mouse, characterized by severe progressive amyloid pathology and cognitive deficits. We investigated the retina and primary visual cortex responsivity together with behavioral assessment of the visual acuity. Visual tests and recordings were conducted at different ages in 5xFAD mice, corresponding to different phases of neurodegeneration and beta amyloid accumulation. We showed that the visual system is impaired in 5xFAD mice. In particular, we found that the inner retina impairment precedes neuronal disorders in other brain areas and cognitive deficits. Thus, noninvasive retinal electrophysiology can provide a support for assessing early visual dysfunctions in AD.

Visual Evoked Potentials in Glaucoma and Alzheimer's Disease.

Visual responses to gratings alternating in contrast have been studied in humans and several mammalian species. Previous evidence from human patients and animal models of neurodegeneration has highlighted the importance to record simultaneously the pattern electroretinogram (P-ERG) and visual evoked cortical potentials (VEPs) to investigate retinal and post-retinal sites of neurodegeneration.In view of the increasing importance of research on experimental models of neurodegenerative diseases, we present here the parametric properties of visual evoked responses in animal models of glaucoma and Alzheimer's disease. Glaucoma and Alzheimer's disease (AD) are two distinct multifactorial neurodegenerative and progressive diseases, primarily affecting the elderly.

2-Acetyl-5-tetrahydroxybutyl imidazole (THI) protects 661W cells against oxidative stress.

Retinal degeneration and in particular retinitis pigmentosa (RP) is associated to ceramide (Cer) accumulation and cell death induction. Cer and sphingosine-1-phosphate (S1P) belong to the sphingolipids class and exert a pro-apoptotic and pro-survival activity, respectively. Our aim is to target sphingolipid metabolism by inhibiting S1P lyase that regulates one of the S1P degradation pathways, to reduce retinal photoreceptor damage. The murine 661W cone-like cell line was pretreated with THI, an inhibitor of S1P lyase and exposed to H2O2-induced oxidative stress. 661W cell viability and apoptosis were evaluated by Trypan Blue and TUNEL assay, respectively. Protein expression of mediators of the survival/death pathway (ERK1/2, Akt, Bcl-2, Bax) was analyzed by Western blotting. RT-PCR was performed to establish HO-1 transcript changes and LC-MS analysis to measure Cer intracellular content. THI rescues inhibitory H2O2-effect on 661W cell viability and impairs H2O2-induced apoptosis by increasing Bcl-2/Bax ratio. THI administration counteracts the oxidative stress effects of H2O2 on 661W cells by activating the Nrf2/HO-1 pathway, regulating ERK and Akt phosphorylation levels, and decreasing Cer intracellular content. We conclude that sphingolipid metabolism manipulation can be considered a therapeutic target to promote photoreceptor survival.

Synaptic Dysfunction in Alzheimer's Disease and Glaucoma: From Common Degenerative Mechanisms Toward Neuroprotection.

Alzheimer's disease (AD) and glaucoma are two distinct multifactorial neurodegenerative diseases, primarily affecting the elderly. Common pathophysiological mechanisms have been elucidated in the past decades. First of all both diseases are progressive, with AD leading to dementia and glaucoma inducing blindness. Pathologically, they all feature synaptic dysfunction with changes of neuronal circuitry, progressive accumulation of protein aggregates such as the beta amyloid (Aß) and intracellular microtubule inclusions containing hyperphosphorylated tau, which belongs to microtubule associated protein family. During an early phase of degeneration, both diseases are characterized by synaptic dysfunction and changes of mitogen-activated protein kinases (MAPK). Common degenerative mechanisms underlying both diseases are discussed here, along with recent results on the potential use of the visual system as a biomarker for diagnosis and progression of AD. Common neuropathological changes and mechanisms in AD and glaucoma have facilitated the transfer of therapeutic strategies between diseases. In particular, we discuss past and present evidence for neuroprotective effects of brain-derived neurotrophic factor (BDNF).

Natural grape extracts regulate colon cancer cells malignancy.

Natural dietary components are evolutionary-selected molecules able to control inflammation and cancerous transformation and progression. Because many studies assessed the beneficial properties of key molecules extracted from grapes, we aimed at investigating the properties of Liofenol™, a natural red wine lyophilized extract, devoid of alcohol and composed by a miscellaneous of components (polyphenols, flavonoids, anthocyanins). We proved that the colon cancer cell line HCT116 responded to Liofenol™ treatment by reducing their proliferation, in association with an increase of p53 and p21 cell cycle gate keepers. Liofenol™ increased dihydroceramides, sphingolipid mediators involved in cell cycle arrest and reduced proliferation rate. We observed a strong induction of antioxidant response, with the activation of the transcriptional factor Nrf2, involved in redox homeostasis and differentiation, without altering tumor sensitivity to chemotherapy. Liofenol™ induced an important morphology change in HCT116 cells, migration inhibition, undifferentiated stem/stem-like cells markers downregulation, and E-cadherin downregulation, interested in epithelia to mesenchymal malignant transition. We conclude that lyophilized grape extract, at dose comparable to putative dietary doses, can activate molecular pathways, involving Nrf2 signaling and the modulation of structural and signaling sphingolipid mediators that cooperate in promoting differentiation and reducing proliferation of digestive tract cancer cells.

BDNF prevents amyloid-dependent impairment of LTP in the entorhinal cortex by attenuating p38 MAPK phosphorylation.

The oligomeric form of the amyloid peptide Aß(1-42) is capable of perturbing synaptic plasticity in different brain areas. Here, we evaluated the protective role of brain-derived neurotrophic factor (BDNF) in beta amyloid (Aß)-dependent impairment of long-term potentiation in entorhinal cortex (EC) slices. We found that BDNF (1 ng/mL) supplied by perfusion was able to rescue long-term potentiation in Aß(1-42)-treated slices; BDNF protection was mediated by TrkB receptor as assessed by using the tyrosine kinase inhibitor K252a (200 nM). We also investigated the function of endogenous BDNF using a soluble form of TrkB receptor (TrkB IgG). Incubation of slices with TrkB IgG (1 µg/mL) increased the EC vulnerability to Aß. Finally, we investigated the effect of BDNF on the cell stress-kinase p38 mitogen-activated protein kinase (MAPK) in primary cortical cell cultures exposed to Aß(1-42). We found that Aß induces p38 MAPK phosphorylation, although pretreatment with BDNF prevented Aß-dependent p38 MAPK phosphorylation. This result was confirmed by an immunoassay in tissue extracts from EC slices collected after electrophysiology.

Conjunctivally Applied BDNF Protects Photoreceptors from Light-Induced Damage.

PURPOSE: To test whether the topical eye treatment with BDNF prevents the effects of continuous light exposure (LE) in the albino rat retina. METHODS: Two groups of albino rats were used. The first group of rats received an intraocular injection of BDNF (2 µL, 1 µg/µL) before LE, while the second group was treated with one single drop of BDNF (10 µL, 12 µg/µL) dissolved in different types of solutions (physiological solution, the polysaccharide fraction of Tamarind gum, TSP, and sodium carboxy methyl cellulose), at the level of conjunctival fornix before LE. The level of BDNF in the retina and optic nerve was determined by enzyme-linked immunosorbent assay. We recorded the flash electroretinogram (fERG) in dark adapted rats 1 week after LE. At the end of the recording session, the retinas were removed and labeled so that the number of photoreceptors nuclear rows and thickness of the outer nuclear layer was analyzed. RESULTS: Intravitreal injection of BDNF before LE prevented fERG impairment. Different ophthalmic preparations were used for topical eye application; the TSP resulted the most suitable vehicle to increase BDNF level in the retina and optic nerve. Topical eye application with BDNF/TSP before LE partially preserved both fERG response and photoreceptors. CONCLUSIONS: Topical eye treatment with BDNF represents a suitable, noninvasive tool to increase the retinal content of BDNF up to a level capable of exerting neuroprotection toward photoreceptors injured by prolonged LE. TRANSLATIONAL RELEVANCE: A collyrium containing BDNF may serve as an effective, clinically translational treatment against retinal degeneration.

Rescue of retinal function by BDNF in a mouse model of glaucoma.

Vision loss in glaucoma is caused by progressive dysfunction of retinal ganglion cells (RGCs) and optic nerve atrophy. Here, we investigated the effectiveness of BDNF treatment to preserve vision in a glaucoma experimental model. As an established experimental model, we used the DBA/2J mouse, which develops chronic intraocular pressure (IOP) elevation that mimics primary open-angle glaucoma (POAG). IOP was measured at different ages in DBA/2J mice. Visual function was monitored using the steady-state Pattern Electroretinogram (P-ERG) and visual cortical evoked potentials (VEP). RGC alterations were assessed using Brn3 immunolabeling, and confocal microscope analysis. Human recombinant BDNF was dissolved in physiological solution (0.9% NaCl); the effects of repeated intravitreal injections and topical eye BDNF applications were independently evaluated in DBA/2J mice with ocular hypertension. BDNF level was measured in retinal homogenate by ELISA and western blot. We found a progressive decline of P-ERG and VEP responses in DBA/2J mice between 4 and 7 months of age, in relationship with the development of ocular hypertension and the reduction of Brn3 immunopositive RGCs. Conversely, repeated intravitreal injections (BDNF concentration = 2 µg/µl, volume = 1 µl, for each injection; 1 injection every four days, three injections over two weeks) and topical eye application of BDNF eye-drops (12 µg/µl, 5 µl eye-drop every 48 h for two weeks) were able to rescue visual responses in 7 month DBA/2J mice. In particular, BDNF topical eye treatment recovered P-ERG and VEP impairment increasing the number of Brn3 immunopositive RGCs. We showed that BDNF effects were independent of IOP reduction. Thus, topical eye treatment with BDNF represents a promisingly safe and feasible strategy to preserve visual function and diminish RGC vulnerability to ocular hypertension.