Increased production of omega-3 fatty acids protects retinal ganglion cells after optic nerve injury in mice

Traumatic Optic Neuropathy: Update on Management

Traumatic optic neuropathy is one of the causes of visual loss caused by blunt or penetrating head trauma and is classified as both direct and indirect. Clinical history and examination findings usually allow for the diagnosis of traumatic optic neuropathy. There is still controversy surrounding the management of traumatic optic neuropathy; some physicians advocate observation alone, while others recommend steroid therapy, surgery, or both. In this entry, we tried to highlight traumatic optic neuropathy's main pathophysiologic mechanisms with the most available updated treatment. Recent research suggests future therapies that may be helpful in traumatic optic neuropathy cases.

Clinically relevant small-molecule promotes nerve repair and visual function recovery

Adult mammalian injured axons regenerate over short-distance in the peripheral nervous system (PNS) while the axons in the central nervous system (CNS) are unable to regrow after injury. Here, we demonstrated that Lycium barbarum polysaccharides (LBP), purified from Wolfberry, accelerated long-distance axon regeneration after severe peripheral nerve injury (PNI) and optic nerve crush (ONC). LBP not only promoted intrinsic growth capacity of injured neurons and function recovery after severe PNI, but also induced robust retinal ganglion cell (RGC) survival and axon regeneration after ONC. By using LBP gene expression profile signatures to query a Connectivity map database, we identified a Food and Drug Administration (FDA)-approved small-molecule glycopyrrolate, which promoted PNS axon regeneration, RGC survival and sustained CNS axon regeneration, increased neural firing in the superior colliculus, and enhanced visual target re-innervations by regenerating RGC axons leading to a partial restoration of visual function after ONC. Our study provides insights into repurposing of FDA-approved small molecule for nerve repair and function recovery.

Circulating fatty acids and risk of primary open-angle glaucoma: A mendelian randomization study

PURPOSE

The relationship between fatty acids (FAs) and glaucoma remains controversial despite several observational studies. We organized a mendelian randomization (MR) study to determine the genetic causal association between circulating FAs and primary open-angle glaucoma (POAG).

METHODS

The two-sample MR method was used to acquire causal estimates. Fourteen distinct single nucleotide polymorphisms (SNPs) of ten FAs were chosen as instrumental variables (IVs) at a genome-wide significance level (p < 5 × 10^-8). Summary statistics for POAG were available from a genome-wide association meta-analysis of 216,257 individuals of European ancestry (16,677 cases, 199,580 controls). The inverse-variance weighted (IVW) method was adopted to evaluate the causality of FAs and POAG. Multiple sensitivity analyses were applied to avoid pleiotropy.

RESULTS

The IVW method suggested no evidence to support causal effects of ten FAs on POAG. The odds ratio (OR) per one SD increment of each FA was OR_ALA = 1.64 (95% CI, 0.441-6.098, p = 0.46), OR_EPA = 0.815 (95% CI, 0.604-1.101, p = 0.182), OR_DPA = 0.896 (95% CI, 0.669-1.198, p = 0.458), OR_DHA = 1.014 (95% CI, 0.801-1.283, p = 0.91), OR_LA = 1.008 (95% CI, 0.971-1.045, p = 0.683), OR_AA = 0.993 (95% CI, 0.973-1.013, p = 0.483), OR_POA = 0.731 (95% CI, 0.261-2.048, p = 0.551), OR_OA = 1.048 (95% CI, 0.934-1.175, p = 0.425), OR_PA = 1.039 (95% CI, 0.903-1.196, p = 0.593), OR_SA = 0.967 (95% CI, 0.879-1.062, p = 0.477). Moreover, Sensitivity analysis indicated no pleiotropy.

CONCLUSION

This MR study does not support causal associations between ten FAs and POAG.

Traumatic optic neuropathy: a review of current studies

Traumatic optic neuropathy (TON) is a serious complication of craniofacial trauma that directly or indirectly damages the optic nerve and can cause severe vision loss. The incidence of TON has been gradually increasing in recent years. Research on the protection and regeneration of the optic nerve after the onset of TON is still at the level of laboratory studies and which is insufficient to support clinical treatment of TON. And, due to without clear guidelines, there is much ambiguity regarding its diagnosis and management. Clinical interventions for TON include observation only, treatment with corticosteroids alone, or optic canal (OC) decompression (with or without steroids). There is controversy in clinical practice concerning which treatment is the best. A review of available studies shows that the visual acuity of patients with TON can be significantly improved after OC decompression surgery (especially endoscopic transnasal/transseptal optic canal decompression (ETOCD)) with or without the use of corticosteroids. And new findings of laboratory studies such as mitochondrial therapy, lipid change studies, and other studies in favor of TON therapy have also been identified. In this review, we discuss the evolving perspective of surgical treatment and experimental study.

The Role of Dietary Nutrients in Peripheral Nerve Regeneration

Peripheral nerves are highly susceptible to injuries induced from everyday activities such as falling or work and sport accidents as well as more severe incidents such as car and motorcycle accidents. Many efforts have been made to improve nerve regeneration, but a satisfactory outcome is still unachieved, highlighting the need for easy to apply supportive strategies for stimulating nerve growth and functional recovery. Recent focus has been made on the effect of the consumed diet and its relation to healthy and well-functioning body systems. Normally, a balanced, healthy daily diet should provide our body with all the needed nutritional elements for maintaining correct function. The health of the central and peripheral nervous system is largely dependent on balanced nutrients supply. While already addressed in many reviews with different focus, we comprehensively review here the possible role of different nutrients in maintaining a healthy peripheral nervous system and their possible role in supporting the process of peripheral nerve regeneration. In fact, many dietary supplements have already demonstrated an important role in peripheral nerve development and regeneration; thus, a tailored dietary plan supplied to a patient following nerve injury could play a non-negotiable role in accelerating and promoting the process of nerve regeneration.

Protective Efficacy of a Dietary Supplement Based on Forskolin, Homotaurine, Spearmint Extract, and Group B Vitamins in a Mouse Model of Optic Nerve Injury

Glaucoma is a multifactorial blinding disease with a major inflammatory component ultimately leading to apoptotic retinal ganglion cell (RGC) death. Pharmacological treatments lowering intraocular pressure can help slow or prevent vision loss although the damage caused by glaucoma cannot be reversed. Recently, nutritional approaches have been evaluated for their efficacy in preventing degenerative events in the retina although mechanisms underlying their effectiveness remain to be elucidated. Here, we evaluated the efficacy of a diet supplement consisting of forskolin, homotaurine, spearmint extract, and vitamins of the B group in counteracting retinal dysfunction in a mouse model of optic nerve crush (ONC) used as an in vivo model of glaucoma. After demonstrating that ONC did not affect retinal vasculature by fluorescein angiography, we determined the effect of the diet supplement on the photopic negative response (PhNR) whose amplitude is strictly related to RGC integrity and is therefore drastically reduced in concomitance with RGC death. We found that the diet supplementation prevents the reduction of PhNR amplitude (p < 0.001) and concomitantly counteracts RGC death, as in supplemented mice, RGC number assessed immunohistochemically is significantly higher than that in non-supplemented animals (p < 0.01). Major determinants of the protective efficacy of the compound are due to a reduction of ONC-associated cytokine secretion leading to decreased levels of apoptotic markers that in supplemented mice are significantly lower than in non-supplemented animals (p < 0.001), ultimately causing RGC survival and ameliorated visual dysfunction. Overall, our data suggest that the above association of compounds plays a neuroprotective role in this mouse model of glaucoma thus offering a new perspective in inflammation-associated neurodegenerative diseases of the inner retina.

Fish oil treatment reduces chronic alcohol exposure induced synaptic changes

Alcohol addiction is a chronic neuropsychiatric disorder that represents one of the most serious global public health problems. Yet, currently there still lacks an effective pharmacotherapy. Omega-3 polyunsaturated fatty acids (N-3 PUFAs) have exhibited beneficial effects in a variety of neurological disorders, particularly in reversing behavioral deficits and neurotoxicity induced by prenatal alcohol exposure and binge drinking. In the present study, we investigated if fish oil, which is rich in N-3 PUFAs, had beneficial effects on preventing relapse and alleviating withdrawal symptoms after chronic alcohol exposure. Our results demonstrated that fish oil significantly reduced the chronic alcohol exposure-induced aberrant dendritic morphologic changes of the medium-sized spiny neurons in the core and the shell of nucleus accumbens. This inhibited the expression of AMPAR2-lacking AMPARs and their accumulation on the post synaptic membranes of medium-sized spiny neurons and eventually alleviated withdrawal symptoms and alcohol dependence. Our study therefore suggests that N-3 PUFAs are promising for treating withdrawal symptoms and alcohol dependence.

Further Evidence on Efficacy of Diet Supplementation with Fatty Acids in Ocular Pathologies: Insights from the EAE Model of Optic Neuritis

In the experimental autoimmune encephalomyelitis (EAE) mouse model of optic neuritis, we recently demonstrated that diet supplementation with a balanced mixture of fatty acids (FAs), including omega 3 and omega 6, efficiently limited inflammatory events in the retina and prevented retinal ganglion cell (RGC) death, although mechanisms underlying the efficacy of FAs were to be elucidated. Whether FAs effectiveness was accompanied by efficient rescue of demyelinating events in the optic nerve was also unresolved. Finally, the possibility that RGC rescue might result in ameliorated visual performance remained to be investigated. Here, the EAE model of optic neuritis was used to investigate mechanisms underlying the anti-inflammatory effects of FAs, including their potential efficacy on macrophage polarization. In addition, we determined how FAs-induced rescue of RGC degeneration was related to optic nerve histopathology by performing ultrastructural morphometric analysis with transmission electron microscopy. Finally, RGC rescue was correlated with visual performance by recording photopic electroretinogram, an efficient methodology to unravel the role of RGCs in the generation of electroretinographic waves. We conclude that the ameliorative effects of FAs were dependent on a predominant anti-inflammatory action including a role on promoting the shift of macrophages from the inflammatory M1 phenotype towards the anti-inflammatory M2 phenotype. This would finally result in restored optic nerve histopathology and ameliorated visual performance. These findings can now offer new perspectives for implementing our knowledge on the effectiveness of diet supplementation in counteracting optic neuritis and suggest the importance of FAs as possible adjuvants in therapies against inflammatory diseases of the eye.

Fatty Acids Dietary Supplements Exert Anti-Inflammatory Action and Limit Ganglion Cell Degeneration in the Retina of the EAE Mouse Model of Multiple Sclerosis

Optic neuritis is an acute inflammatory demyelinating disorder of the optic nerve (ON) and is an initial symptom of multiple sclerosis (MS). Optic neuritis is characterized by ON degeneration and retinal ganglion cell (RGC) loss that contributes to permanent visual disability and lacks a reliable treatment. Here, we used the experimental autoimmune encephalomyelitis (EAE) mouse model of MS, a well-established model also for optic neuritis. In this model, C57BL6 mice, intraperitoneally injected with a fragment of the myelin oligodendrocyte glycoprotein (MOG), were found to develop inflammation, Müller cell gliosis, and infiltration of macrophages with increased production of oncomodulin (OCM), a calcium binding protein that acts as an atypical trophic factor for neurons enabling RGC axon regeneration. Immunolabeling of retinal whole mounts with a Brn3a antibody demonstrated drastic RGC loss. Dietary supplementation with Neuro-FAG (nFAG^®), a balanced mixture of fatty acids (FAs), counteracted inflammatory and gliotic processes in the retina. In contrast, infiltration of macrophages and their production of OCM remained at elevated levels thus eventually preserving OCM trophic activity. In addition, the diet supplement with nFAG exerted a neuroprotective effect preventing MOG-induced RGC death. In conclusion, these data suggest that the balanced mixture of FAs may represent a useful form of diet supplementation to limit inflammatory events and death of RGCs associated to optic neuritis. This would occur without affecting macrophage infiltration and the release of OCM thus favoring the maintenance of OCM neuroprotective role.

Omega-3 fatty acids protect retinal neurons in the DBA/2J hereditary glaucoma mouse model

The purpose of this study was to evaluate the neuroprotective effects of omega-3 polyunsaturated fatty acid (ω3-PUFA) supplementation, alone or in combination with timolol eye drops, in a mouse model of hereditary glaucoma. DBA/2J mice (8.5-month-old) were assigned to an ω3-PUFAs + timolol, ω3-PUFAs only, timolol only, or an untreated group. Treated mice received a daily gavage administration of eicosapentaenoic acid (EPA) and docosahexaenoic acid and/or topical instillation of timolol (0.5%) once a day for 3 months. Blood was analysed regularly to determine ω3-PUFA levels and retinas were histologically analysed. Real-time PCR and Western blot were performed for retinal pro-inflammatory cytokines and macrophages. Blood arachidonic acid/EPA ratio gradually decreased and reached the desired therapeutic range (1-1.5) after 4 weeks of daily gavage with ω3-PUFAs in the ω3-PUFAs + timolol and ω3-PUFAs only groups. Retinal ganglion cell densities were significantly higher in the ω3-PUFAs + timolol (1303.77 ± 139.62/mm²), ω3-PUFAs only (768.40 ± 52.44/mm²) and timolol only (910.57 ± 57.28/mm²) groups than in the untreated group (323.39 ± 95.18/mm²). ω3-PUFA supplementation alone or timolol alone, significantly increased protein expression levels of M1 macrophage-secreted inducible nitric oxide synthase and M2 macrophage-secreted arginase-1 in the retina, which led to significant decreases in the expression levels of tumour necrosis factor-α (TNF-α). ω3-PUFA supplementation alone also resulted in significantly reduced expression of interleukin-18 (IL-18). ω3-PUFA + timolol treatment had no effect on the expression level of any of the aforementioned mediators in the retina. Supplementation with ω3-PUFAs has neuroprotective effect in the retinas of DBA/2J mice that is enhanced when combined with timolol eye drops. The continued inflammation following ω3-PUFAs + timolol treatment suggests that downregulation of IL-18 and TNF-α may not be the only factors involved in ω3-PUFA-mediated neuroprotection in the retina.

Long-Chain Omega-3 Fatty Acids Supplementation Accelerates Nerve Regeneration and Prevents Neuropathic Pain Behavior in Mice

Fish oil (FO) is the main source of long chain omega-3 polyunsaturated fatty acids (ω-3 PUFAs), which display relevant analgesic and anti-inflammatory properties. Peripheral nerve injury is driven by degeneration, neuroinflammation, and neuronal plasticity which results in neuropathic pain (NP) symptoms such as allodynia and hyperalgesia. We tested the preventive effect of an EPA/DHA-concentrate fish oil (CFO) on NP development and regenerative features. Swiss mice received daily oral treatment with CFO 4.6 or 2.3 g/kg for 10 days after NP was induced by partial sciatic nerve ligation. Mechanical allodynia and thermal hypernociception were assessed 5 days after injury. CFO 2.3 g/kg significantly prevented mechanical and thermal sensitization, reduced TNF levels in the spinal cord, sciatic MPO activity, and ATF-3 expression on DRG cells. CFO improved Sciatic Functional Index (SFI) as well as electrophysiological recordings, corroborating the increased GAP43 expression and total number of myelinated fibers observed in sciatic nerve. No locomotor activity impairment was observed in CFO treated groups. These results point to the regenerative and possibly protective properties of a combined EPA and DHA oral administration after peripheral nerve injury, as well as its anti-neuroinflammatory activity, evidencing ω-3 PUFAs promising therapeutic outcomes for NP treatment.

Low-dose DHA-induced astrocyte proliferation can be attenuated by insufficient expression of BLBP in vitro

Docosahexaenoic acid (DHA) is an n-3 long chain polyunsaturated fatty acid (PUFA) that is involved in a wide range of cellular processes in human cells. Brain lipid binding protein (BLBP) exhibits a high affinity for n-3 PUFAs, especially DHA, but the precise functional contributions of DHA and BLBP in astrocytes are not clear. We analyzed cell viability and the ratio of Ki67 positive cells after manipulating DHA and/or BLBP levels in cultured astrocytes, and found that low-dose DHA stimulated proliferation of astrocytes, whereas this proliferative effect could be attenuated by downregulation of BLBP. Moreover, we found that astrocyte proliferation was directly regulated by BLBP independently of DHA. Taken together, low-dose DHA-induced astrocyte proliferation was disturbed by insufficient BLBP; and besides acting as a fatty acid transporter, BLBP was also involved in the proliferation of astrocytes directly.

Reconnecting Eye to Brain

Although much is known about the regenerative capacity of retinal ganglion cells, very significant barriers remain in our ability to restore visual function following traumatic injury or disease-induced degeneration. Here we summarize our current understanding of the factors regulating axon guidance and target engagement in regenerating axons, and review the state of the field of neural regeneration, focusing on the visual system and highlighting studies using other model systems that can inform analysis of visual system regeneration. This overview is motivated by a Society for Neuroscience Satellite meeting, "Reconnecting Neurons in the Visual System," held in October 2015 sponsored by the National Eye Institute as part of their "Audacious Goals Initiative" and co-organized by Carol Mason (Columbia University) and Michael Crair (Yale University). The collective wisdom of the conference participants pointed to important gaps in our knowledge and barriers to progress in promoting the restoration of visual system function. This article is thus a summary of our existing understanding of visual system regeneration and provides a blueprint for future progress in the field.