Efficacy of a 2-month dietary supplementation with polyunsaturated fatty acids in dry eye induced by scopolamine in a rat model

The Mediterranean Diet and Age-Related Eye Diseases: A Systematic Review

The Mediterranean diet (MD) is a healthy diet pattern that can prevent chronic age-related diseases, especially age-related eye diseases (AREDs) including cataract, glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR) and dry eye syndrome (DES). In this study, we systematically reviewed studies in the literature that had reported associations between adherence to the MD and the five above-mentioned AREDs. Randomized controlled trials as well as prospective and retrospective observational studies were included; 1164 studies were identified, of which 1, 2, 9, 2 and 4 studies met our eligibility criteria for cataract, glaucoma, AMD, DR, and DES, respectively. According to these studies, higher MD adherence was associated with reduced risks of incident DR, incident AMD and progression to late AMD, but whether early and neovascular AMD could be alleviated remained to be debated. The results regarding the effects of the MD on DES were mixed, with three studies reporting an associations between MD and decreased severity or incidence of DES, whereas one study reported the opposite. No significant associations were observed between the MD and cataract or glaucoma. Generally, convincing evidence suggested a protective effect of the MD against AMD and DR. However, the evidence for cataract, glaucoma, and DES was less conclusive, and high-quality studies are needed for comprehensive evaluations of the potential benefits of MD on these eye diseases.

Plasma Fatty Acids Pattern and Dry Eye Disease in the Elderly: The Montrachet Population-Based Study

(1) Background: To investigate the association between plasma fatty acids (FAs) and dry eye disease (DED) in an elderly population; (2) Methods: We conducted a population-based study, the Montrachet study, in individuals older than 75 years. DED was evaluated using the Schirmer I test without anesthesia, tear film breakup time (TFBUT) measurement and fluorescein corneal staining. Plasma FAs were measured in fasting blood using gas chromatography; (3) Results: A total of 740 subjects with a plasma measurement of 25 FAs were included in this study. The mean age was 82.2 ± 3.7 years, and 62.7% were women. DED was present in 35.0% of participants. We identified a plasma FAs pattern positively associated with DED, characterized by low polyunsaturated fatty acids (PUFAs), high monounsaturated fatty acids (MUFAs) and low saturated fatty acids (SFAs) levels. After adjustment for major confounders, individuals in the upper quartile of the FAs pattern scores compared with those in the lower quartile were more likely to present DED (OR 2.46 (95% CI 1.51-4.01), p = 0.001); (4) Conclusion: In this study, we found that a plasma FAs pattern characterized by low PUFAs, high MUFAs and low SFAs was significantly associated with DED in elderly participants.

Animal models of dry eye disease: Useful, varied and evolving (Review)

Dry eye disease (DED), which is a prevalent disease that still lacks successful treatment options, remains a major challenge in ophthalmology. Multiple animal models of DED have been used to decipher its pathophysiology and to develop novel treatments. These models use mice, rats, rabbits, cats, dogs and non-human primates. Each model assesses aspects of DED by focusing on elements of the lacrimal functional unit, which controls the homeostasis of the tear film. The present review outlines representative DED animal models and assesses their contribution to the study of DED. Murine models are the most extensively used, followed by rabbit models; the latter offer the advantage of larger eyes, a favorable biochemical profile for drug studies, experimental ease and relatively low cost, contrasting with non-human primates, which, although closer to humans, are not as accessible and are expensive. No comprehensive ‘ideal’ animal model encompassing all aspects of human DED exists nor is it feasible. Investigators often choose an animal model based on their experimental needs and the following four features of a given model: The size of the eye, its biochemical composition, the available research reagents and cost. As research efforts in DED expand, more refined animal models are needed to supplement the enormous contribution made to date by existing models.

Dietary n-3 PUFA Deficiency Increases Vulnerability to Scopolamine-Induced Cognitive Impairment in Male C57BL/6 Mice

BACKGROUND

DHA (22:6n-3), a long-chain n-3 PUFA, is essential for normal brain development and function. Our previous study demonstrated that DHA significantly improves scopolamine-induced dementia. However, there are no reports on the relation between n-3 PUFA deficiency and scopolamine-induced cognitive impairment.

OBJECTIVES

The aim of this study was to evaluate whether n-3 PUFA deficiency increases vulnerability to scopolamine-induced cognitive impairment.

METHODS

Male and female C57BL/6 mice were mated and fed an n-3 PUFA-adequate [containing 2.88% α-linolenic acid (ALA; 18:3n-3)] or -deficient (containing 0.09% ALA) diet for 2 consecutive generations. The corresponding second-generation male offspring were kept on the same diet as their mothers after weaning, and were randomly assigned to 2 subgroups at 7 wk of age, in which they were intraperitoneally injected with saline [fed n-3 PUFA-adequate (Con) or -deficient (Def) diet] or scopolamine [5 mg/kg body weight; fed n-3 PUFA-adequate (Sco) or -deficient (Def + Sco) diet] once per day for 7 d before killing. Behavioral performance was analyzed using the Morris Water Maze test. Fatty acid composition, protein expression, and indicators of cholinergic and oxidative stress in the brain were measured.

RESULTS

The Def group showed lower brain DHA (-63.7%, P ≤ 0.01) and higher n-6 PUFA (+65.5%, P ≤ 0.05) concentrations than the Con group. The Def + Sco group and the Sco group showed poorer spatial learning and memory (escape latency on the sixth day: +60.3% and +36.8%; platform crossings: -43.9% and -28.2%, respectively) and more obvious cholinergic dysfunction (acetylcholine: -47.6% and -27.7%, respectively), oxidative stress (glutathione peroxidase: -64.2% and -32.5%, respectively), apoptosis [B-cell lymphoma 2 (BCL2)-associated X protein/BCL2: +230.8% and +153.8%; phosphorylated P38/P38: +232% and +130%, phosphorylated c-Jun N-terminal kinase (JNK)/JNK: +104.5% and +58.8%, respectively], neuroinflammation (IL-1β: +317.6% and +95%, respectively), and neurodevelopmental delay (brain-derived neurotrophic factor: -54.4% and -7.25%, respectively) than their corresponding saline-treated controls.

CONCLUSIONS

Dietary n-3 PUFA deficiency significantly decreases brain DHA concentrations and increases vulnerability to scopolamine-induced cognitive impairment in C57BL/6 male mice.

The Protective Effect of Polyunsaturated Fatty Acids against Dry Eye Disease: A Literature Review

Dry eye disease (DED) is a common disease, and have an adverse effect the physical, functional, and psychological quality of life. It is a multifactorial disorder characterized by the loss of tear film homeostasis, in which self-perpetuating vicious cycle leads to deterioration of function and inflammation of the lacrimal functional unit. Hence, treatment strategies should be aimed at the interruption of the vicious inflammatory cycle and alleviation of ocular surface inflammation. Anti-inflammatory therapies have been shown to improve the signs and symptoms of the disease. Evidence indicates that polyunsaturated fatty acids (PUFAs) may contribute to reinforcement of innate anti-inflammatory mechanisms, and systemic and topical administration of PUFAs may help modulate ocular surface inflammation. In the present review, the authors will introduce the results of clinical and experimental studies to elucidate the mechanism, efficacy, and safety of systemic and topical supplementation with PUFAs as an alternative therapeutic strategy for DED. This review will also include discussion regarding current perspectives, including evidence-based recommendations and possible side effects of PUFAs supplementation. The review of the literature suggests that PUFAs supplementation can be a viable option for the treatment of DED, although further studies are needed for establishment of treatment guidelines.

Metabolomics approach to biomarkers of dry eye disease using 1H-NMR in rats

Dry eye disease (DED) is a chronic and progressive lesion on the ocular surface and induces symptoms, such as burning sensation, itchy eyes, heavy eyes, tired eyes, dry feeling, facial flushing, and blurred vision. The present study was performed to develop DED biomarkers using metabolomics in a rat model. DED was induced by injecting scopolamine and exposing rats to a dry condition. Scopolamine (12 mg/kg/day for 7 days) was subcutaneously injected to male Sprague-Dawley rats. The rats were placed in dry condition with air-flow and dehumidifier. Tear volume and tear breakup time (TBUT) were measured, and eyes were examined through fluorescein staining to assess DED. Mucosal damage and immune reactions were also determined. Plasma and urinary endogenous metabolites were determined using ¹H-NMR analysis. Compared with control tear and TBUT levels were significantly decreased in the DED group whereas corneal damage was significantly increased. The levels of interleukins (IL-6) and IL-1β significantly elevated in the cornea and lacrimal glands in the DED group. TNF-α was numerically increased but not significantly different between groups. Pattern recognition using principal component analysis (PCA) and orthogonal projections to latent structure-discriminant analysis (OPLS-DA) of the NMR spectra in global profiling revealed different clusters between DED and control groups. Target profiling demonstrated that PCA and OPLS-DA score plots were separated between DED and controls in plasma and urine. Subsequently, 9 plasma metabolites were selected to examine different clustering between groups, and 26 urinary metabolites were also selected. Plasma metabolites showed a non-significant rising tendency in the DED group. Urinary phenylalanine, phenylacetate, pantothenate, glycine, succinate, methanol, valine, propylene glycol, histidine, threonine, lactate, and acetate were significantly different between control and DED rats. These results may contribute to understanding the metabolic regulation that is involved in DED and might be useful for potential biomarkers related to DED in rats.

Effects of the re-esterified triglyceride (rTG) form of omega-3 supplements on dry eye following cataract surgery

Background/Aims

To evaluate the clinical outcomes of the systemic re-esterified triglyceride (rTG) form of omega-3 fatty acids in patients with dry eye symptoms after cataract surgery.

Methods

This prospective comparative cohort study comprised 66 patients complaining of new-onset non-specific typical dry eye 1 month after uncomplicated cataract surgery. Subjects were randomly allocated into control and omega-3 groups based on administration of the systemic rTG form of omega-3 fatty acids for 2 months, in addition to use of artificial teardrop. Ocular surface parameters (Schirmer’s test, tear break-up time, corneal staining score and matrix metalloproteinase-9 (MMP-9)) and subjective questionnaire results (Ocular Surface Disease Index (OSDI)) and Dry Eye Questionnaire [DEQ]) for dry eye were evaluated before and after omega-3 supplementation.

Results

Two months after omega-3 supplementation, the Oxford score was lower in the omega-3 group than in the control group. There was an improvement of subjective symptom scores of OSDI and DEQ in the omega-3 group (both p<0.05). The ratio of increasing MMP-9 level in the omega-3 group was lower than that in the control group (p=0.027).

Conclusion

The rTG form of omega-3 supplementation might be related to reduction of ocular surface inflammation rather than secretion of tears, and it might be effective for non-specific typical dry eye after uncomplicated cataract surgery.

Trial registration Number

NCT04411615.

Effectiveness of Mediterranean Diet Implementation in Dry Eye Parameters: A Study of PREDIMED-PLUS Trial

The purpose of this study is to evaluate the effect of a Mediterranean diet supplemented with extra virgin olive oil and nuts on dry eye parameters. The participants in this study were randomized into one of the two interventional arms: (1) a standard intervention group, a Mediterranean diet supplemented with extra virgin olive oil and nuts; and (2) an intensive intervention group, based on a hypocaloric Mediterranean diet and an intensive lifestyle program with physical activity and weight-loss goals. In both groups, common dry eye tests were conducted at baseline and after six months: the Ocular Surface Disease Index (OSDI), the Dry Eye Scoring System (DESS), tear break-up time (TBUT), the Schirmer's test, and the Oxford staining grade. Sixty-seven eyes were examined. After six months, dry eye parameters improved in both groups; differences between groups were favorable for the intensive intervention group. The implementation of a Mediterranean diet pattern was beneficial for the selected patients with dry eye, and could be beneficial for patients with dry eye in general. Behavioral support for diet adherence and the promotion of healthy lifestyles (exercise) and weight loss (calorie restriction) have an added positive effect.

Towards Lacrimal Gland Regeneration: Current Concepts and Experimental Approaches

Dry eye disease (DED) is a complex and multifactorial disease resulting in a continual cycle of tear hyperosmolarity and inflammation. Patients suffering from DED experience severe pain and visual impairments leading to a reduced quality of life. Aqueous-deficient dry eye (ADDE), mainly caused through a loss of functional lacrimal gland tissue, results in the most severe forms of DED. Despite a high prevalence, the current treatments remain palliative and may be insufficient to alleviate the symptoms. Consequently, investigations on experimental approaches for in situ lacrimal gland regeneration are of great clinical interest. This article reviews the current knowledge about processes involved in lacrimal gland regeneration, about lacrimal gland resident stem cells, and offers deductions about possible concepts for in situ lacrimal gland regeneration. Promising starting points might be the utilization of therapeutic proteins, such as bone morphogenetic protein 7, mesenchymal stem cells (MSC) or MSC-based treatments such as conditioned medium, lyophilized cell extracts or adult acinar cells. This review further summarizes current experimental approaches for the treatment of ADDE in animal models and patients. Approaches investigating side population stem cells, epithelial progenitor cells and MSC showed that the transplantation of these cells had therapeutic effects on ADDE. However, the most promising and best-studied experimental approach is the use of MSC for induction/enhancement of in situ lacrimal gland regeneration. Their immunomodulatory effects, low immunogenicity, promotion of tissue regeneration and involvement during spontaneous lacrimal regeneration are favorable traits for clinical applications. In addition, the efficacy and safety of allogeneic MSC transplantation have already been demonstrated in a small patient cohort.

The impact of sea buckthorn oil fatty acids on human health

The beneficial properties of fatty acids have been undervalued for several years. In contraposition, new studies reveal that fatty acids have an essential role for human health. The aim of the study is to demonstrate the clinical applications of fatty acids present in sea buckthorn oil. The composition of fatty acids found in sea buckthorn (Hippophae rhamnoides) oil is unique for this species, presenting a vast range of health benefits for humans and therefore it is highly valued by both biomedicine and the cosmetic industry. In this way, we will see the clinical effect of monounsaturated, polyunsaturated and saturated fatty acids that constitute sea buckthorn oil and how they contribute to the correct function of the organism. Despite there being studies that support the positive effects of sea buckthorn fatty acids, they are limited. Hence, most of the results obtained in this review are from studies of isolated fatty acids instead of fatty acids extracted from sea buckthorn oil. These facts permit to demonstrate the effect of sea buckthorn fatty acids separately but we lost the possibility of detecting a synergic effect of all of them. More studies are necessary to certify the clinical application of the fatty acids present in sea buckthorn oil as well as discovering possible synergies between them.

Effects of Polyunsaturated Fatty Acids on Nonspecific Typical Dry Eye Disease: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

To investigate the effects of polyunsaturated fatty acids (PUFAs) in patients with dry eye disease (DED), a multifactorial inflammatory disorder, we searched Cochrane Library, EMBASE, PubMed, and Web of Science for randomized clinical trials (RCTs) investigating the effect of PUFAs in patients with DED before March 2019. Two reviewers independently abstracted data of tear breakup time (TBUT), Schirmer’s test, osmolarity, and ocular surface disease index (OSDI). We conducted pairwise meta-analysis using means and standard deviations (SDs) in a random-effects model for continuous outcomes. Thirteen eligible RCTs with 1782 patients with nonspecific typical DED were included. Patients who received PUFA treatment without other eye medications exhibited greater improvements in TBUT (MD = 1.80; p = 0.001), Schirmer test scores (MD = 0.50; p < 0.001), osmolarity (MD = −15.95; p < 0.001), and OSDI scores (MD = −10.19; p < 0.001) than those who received placebo treatment. However, the effects of PUFAs on TBUT (p < 0.001) and OSDI scores (p = 0.03) weakened with treatment duration. PUFAs are effective in treating nonspecific typical DED, particularly as a short-term treatment, with relatively few adverse events. Therefore, in real-world clinical practice, PUFA supplements are worth being suggested to patients with nonspecific typical DED who are not concurrently using other topical or systematic eye medications.

Signaling pathways activated by resolvin E1 to stimulate mucin secretion and increase intracellular Ca2+ in cultured rat conjunctival goblet cells

Glycoconjugate mucin secretion from conjunctival goblet cells is tightly regulated by nerves and specialized pro-resolving mediators (SPMs) to maintain ocular surface health. Here we investigated the actions of the SPM resolvin E1 (RvE1) on cultured rat conjunctival goblet cell glycoconjugate secretion and intracellular [Ca2+] ([Ca2+]i) and the signaling pathways used by RvE1. Goblet cells were cultured from rat conjunctiva in RPMI medium. The amount of RvE1-stimulated glycoconjugate mucin secretion was determined using an enzyme-linked lectin assay with Ulex Europaeus Agglutinin 1 lectin. Cultured goblet cells were also incubated with the Ca2+ indicator dye fura 2/AM and [Ca2+]i was measured. Cultured goblet cells were incubated with inhibitors to phospholipase (PL-) C, D, and A2 signaling pathways. RvE1 stimulated glycoconjugate secretion in a concentration dependent manner and was inhibited with the Ca2+ chelator BAPTA. The Ca2+i response was also increased in a concentration manner when stimulated by RvE1. Inhibition of PLC, PLD, and PLA2, but not Ca2+/calmodulin-dependent kinase blocked RvE1-stimulated increase in [Ca2+]i and glycoconjugate secretion. We conclude that under normal, physiological conditions RvE1 stimulates multiple pathways to increase glycoconjugate secretion and [Ca2+]i. RvE1 could be an important regulator of goblet cell glycoconjugate mucin secretion to maintain ocular surface health.

Efficacy of nutritional supplementation with omega-3 and omega-6 fatty acids in dry eye syndrome: a systematic review of randomized clinical trials

PURPOSE

To critically appraise scientific evidence regarding the efficacy of nutritional supplementation with omega-3 and omega-6 fatty acids for the treatment of dry eye syndrome (DES).

METHODS

A systematic review of randomized clinical trials was performed. Two independent reviewers selected and analysed the scientific papers that met inclusion and exclusion criteria. Objective and subjective efficacy outcomes were assessed.

RESULTS

The trials involved a total of 2591 patients in fifteen independent studies. All studies were published between 2005 and 2015. The supplements used were mostly omega-3 and omega-6 in different proportions. Subjective improvement was measured using mainly Ocular Surface Disease Index (OSDI) test and Dry Eye Severity Score (DESS) test: significant differences in favour of the experimental group were found in seven of the studies. The objective amelioration was assessed by lacrimal function parameters: Tear break-up time (TBUT) significantly increased in nine studies and Schirmer's test in four studies.

CONCLUSION

We observed a discrete improvement in the parameters of tear function. Scientific evidence is not strong enough to systematically recommend the use of omega-3 and omega-6 fatty acids as a standalone treatment of DES independently from its aetiology. However, they could be considered as an effective alternative to topical treatment in patients with DES secondary to certain pathologies.

The role of systemic and topical fatty acids for dry eye treatment

Dry eye is a prevalent condition and one of the main reasons for patients to seek ophthalmic medical care. A low systemic level of omega fatty acids is a risk factor for dry eye disease (DED). There are two groups of essential fatty acids (EFAs): the omega-6 (n-6) family and the omega-3 (n-3) family. Humans evolved on a diet in which the n-6:n-3 ratio was approximately 1:1, however the current Western diet tends to be deficient in n-3 EFAs and this ratio is typically much higher (approaching 17:1). The metabolism of EFAs generates four new families of local acting mediators: lipoxins, resolvins, protectins, and maresins. These molecules have anti-inflammatory and pro-resolution properties. We present a critical overview of animal model studies and human clinical trials that have shown that dietary modification and oral supplementation could be complementary therapeutic strategies for the treatment of dry eye. Furthermore, we discuss preliminary results of the topical application of n-3 and n-6 EFAs because these molecules may act as natural anti-inflammatory agents with positive changes of the entire ocular surface system.

α-Melanocyte-stimulating hormone ameliorates ocular surface dysfunctions and lesions in a scopolamine-induced dry eye model via PKA-CREB and MEK-Erk pathways

Dry eye is a highly prevalent, chronic, and multifactorial disease that compromises quality of life and generates socioeconomic burdens. The pathogenic factors of dry eye disease (DED) include tear secretion abnormalities, tear film instability, and ocular surface inflammation. An effective intervention targeting the pathogenic factors is needed to control this disease. Here we applied α-Melanocyte-stimulating hormone (α-MSH) twice a day to the ocular surface of a scopolamine-induced dry eye rat model. The results showed that α-MSH at different doses ameliorated tear secretion, tear film stability, and corneal integrity, and corrected overexpression of proinflammatory factors, TNF-α, IL-1β, and IFN-γ, in ocular surface of the dry eye rats. Moreover, α-MSH, at 10(-4) μg/μl, maintained corneal morphology, inhibited apoptosis, and restored the number and size of conjunctival goblet cells in the dry eye rats. Mechanistically, α-MSH activated both PKA-CREB and MEK-Erk pathways in the dry eye corneas and conjunctivas; pharmacological blockade of either pathway abolished α-MSH's protective effects, suggesting that both pathways are necessary for α-MSH's protection under dry eye condition. The peliotropic protective functions and explicit signaling mechanism of α-MSH warrant translation of the α-MSH-containing eye drop into a novel and effective intervention to DED.

Application of the Cre/loxP Site-Specific Recombination System for Gene Transformation in Aurantiochytrium limacinum

The Cre/loxP site-specific recombination system was applied to Aurantiochytrium limacinum to obtain a transformant without the antibiotic resistance marker gene. First, the enhanced green fluorescent protein gene (egfp) and chloramphenicol resistance gene (Cmr), along with the two loxP loci, were integrated into the genome of A. limacinum OUC88 using 18S rDNA sequences as the homologous recombination sites. Then plasmid pSH65, containing a zeocin resistance gene (Bler) was transferred into A. limacinum OUC_CG. After induction with galactose, repeated passage in culture and PCR-based assessment, the pSH65 plasmid was lost and A. limacinum OUC_EG host was shown to no longer have resistance to 100 mg chloramphenicol/L or 5 mg zeocin/L. Through southern blotting and fluorescence detection, egfp was found to be integrated into the genome of A. limacinum OUC_EG, and EGFP was successfully expressed in the cells. The successful application of the Cre/loxP system demonstrates an experimental basis for genetic modification of A. limacinum so as to obtain transformed strains with no antibiotic resistance marker genes.

Essential fatty acids in the treatment of dry eye syndrome: A myth or reality?

Dry eye is a common condition that can severely impair the quality of life. Systemic and topical omega-3 fatty acids and omega-6 fatty acids have been used as treatment for patients with dry eye disease and showed promising results. Further multicenter randomized controlled trials are required in order to establish a standardized protocol for the treatment of dry eye syndrome with those essential fatty acids.

Anti-inflammatory effects of resolvin-D1 on human corneal epithelial cells: in vitro study

BACKGROUND

This study evaluated the anti-inflammatory effects of Resolvin-D1 (RV-D1) and its mechanism of action in human corneal epithelial (HCE) cells.

METHODS

HCE cells were incubated with different concentrations of RV-D1 for different time periods. Oleic acid (OA) and Dexamethasone (DM) served as negative and positive controls, respectively. Cells were stimulated with polyriboinosinic:polyribocytidylic acids (poly I:C). The protein contents and mRNA expression levels of Tumor necrosis factor-α (TNF-α), Interleukin (IL)-6, IL-1β and IL-8 were evaluated with multiplex fluorescent bead immunoassay (FBI) and real time-PCR, respectively. In addition, the expression of inhibitory factor-κBα (I-κBα) was evaluated with real time-PCR.

RESULTS

The protein level of pro-inflammatory cytokines TNF-α, IL-6, IL-1β and IL-8 significantly increased after stimulation with Poly I:C. RV-D1 treatment at concentration of 1 μM decreased the protein level of TNF-α to 20.76 ± 9.3% (P < 0.05), IL-6 to 43.54 ± 14.16% (P < 0.001), IL-1β to 46.73 ± 15.93% (P > 0.05) and IL-8 to 51.15 ± 13.01% (P < 0.05) compared with cells stimulated with poly I:C alone. Similarly, the mRNA levels of TNF-α, IL-6, IL-1β and IL-8 were significantly reduced after treatment with RV-D1. A highly significant dose response curve was demonstrated for RV-D1 treated HCE cells for TNF-α and IL-1β.DM treatment decreased the protein content for all of the pro-inflammatory cytokines, similar results were demonstrated at the mRNA level. The anti-inflammatory effects of RV-D1 were similar to those of DM for TNF-α, IL-6 and IL-8.

CONCLUSIONS

RV-D1 may serve as a potent anti-inflammatory agent in ocular surface inflammation, as evaluated in cultured HCE cells. The anti-inflammatory effects of RV-D1 were comparable to those of DM, and were mediated through nuclear factor kappa B (NF-κB) signal transduction.

Involvement of pigment epithelium-derived factor, docosahexaenoic acid and neuroprotectin D1 in corneal inflammation and nerve integrity after refractive surgery

Alterations in corneal innervations result in impaired corneal sensation, severe dry eye and damage to the epithelium that may in turn lead to corneal ulcers, melting and perforation. These alterations can occur after refractive surgery. We have discovered that pigment epithelium-derived factor (PEDF) plus docosahexaenoic acid (DHA or the docosanoid bioactive neuroprotectin D1 (NPD1)) induces nerve regeneration after corneal surgery that damages the stromal nerves. We found that PEDF is released from corneal epithelial cells after injury, and when DHA is provided to the cells it stimulates the biosynthesis of NPD1 by an autocrine mechanism. The combination of PEDF plus DHA also decreased the production of leukotriene B4 (LTB4), a neutrophil chemotactic factor, thereby decreasing the inflammation induced after corneal damage. These studies suggest that PEDF plus DHA and its derivative NPD1 hold promise as a future treatment to restore a healthy cornea after nerve damage.

Short-term long chain omega3 diet protects from neuroinflammatory processes and memory impairment in aged mice

Regular consumption of food enriched in omega3 polyunsaturated fatty acids (ω3 PUFAs) has been shown to reduce risk of cognitive decline in elderly, and possibly development of Alzheimer's disease. Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are the most likely active components of ω3-rich PUFAs diets in the brain. We therefore hypothesized that exposing mice to a DHA and EPA enriched diet may reduce neuroinflammation and protect against memory impairment in aged mice. For this purpose, mice were exposed to a control diet throughout life and were further submitted to a diet enriched in EPA and DHA during 2 additional months. Cytokine expression together with a thorough analysis of astrocytes morphology assessed by a 3D reconstruction was measured in the hippocampus of young (3-month-old) and aged (22-month-old) mice. In addition, the effects of EPA and DHA on spatial memory and associated Fos activation in the hippocampus were assessed. We showed that a 2-month EPA/DHA treatment increased these long-chain ω3 PUFAs in the brain, prevented cytokines expression and astrocytes morphology changes in the hippocampus and restored spatial memory deficits and Fos-associated activation in the hippocampus of aged mice. Collectively, these data indicated that diet-induced accumulation of EPA and DHA in the brain protects against neuroinflammation and cognitive impairment linked to aging, further reinforcing the idea that increased EPA and DHA intake may provide protection to the brain of aged subjects.

Ocular surface immunity: homeostatic mechanisms and their disruption in dry eye disease

The tear film, lacrimal glands, corneal and conjunctival epithelia and Meibomian glands work together as a lacrimal functional unit (LFU) to preserve the integrity and function of the ocular surface. The integrity of this unit is necessary for the health and normal function of the eye and visual system. Nervous connections and systemic hormones are well known factors that maintain the homeostasis of the ocular surface. They control the response to internal and external stimuli. Our and others' studies show that immunological mechanisms also play a pivotal role in regulating the ocular surface environment. Our studies demonstrate how anti-inflammatory factors such as the expression of vascular endothelial growth factor receptor-3 (VEGFR-3) in corneal cells, immature corneal resident antigen-presenting cells, and regulatory T cells play an active role in protecting the ocular surface. Dry eye disease (DED) affects millions of people worldwide and negatively influences the quality of life for patients. In its most severe forms, DED may lead to blindness. The etiology and pathogenesis of DED remain largely unclear. Nonetheless, in this review we summarize the role of the disruption of afferent and efferent immunoregulatory mechanisms that are responsible for the chronicity of the disease, its symptoms, and its clinical signs. We illustrate current anti-inflammatory treatments for DED and propose that prevention of the disruption of immunoregulatory mechanisms may represent a promising therapeutic strategy towards controlling ocular surface inflammation.

Efficacy of a new prescription-only medical food supplement in alleviating signs and symptoms of dry eye, with or without concomitant cyclosporine A

Purpose

To evaluate the effect of a new, prescription-only medical food supplement containing omega-3 and omega-6 essential fatty acids on dry eye signs and symptoms, with or without concomitant topical cyclosporine.

Methods

A total of 43 subjects were randomized and followed for 6 months. Group 1 (n = 23) was assigned to take two soft geltabs of the medical food supplement by mouth twice daily for 6 months. Group 2 (n = 20) was directed to take the medical food supplement in the same manner, along with topical cyclosporine, instilled twice daily during the last 3 months of the study. Subjects were evaluated at baseline, month 1, month 3, and month 6. Primary outcome measures included tear breakup time (TBUT), conjunctival staining, corneal staining, and change in subjective symptoms.

Results

Both groups had a statistically significant improvement in TBUT between baseline and month 6. In the food supplement only group, TBUT improved by 0.805 seconds from baseline to month 6. In the supplement/cyclosporine group, TBUT improved by 1.007 seconds from baseline. There was no statistically significant difference in TBUT between the two groups at baseline, month 3, or month 6. There were no significant differences in corneal or conjunctival staining between or within groups. Subjective symptoms were also improved in both groups.

Conclusion

Supplementation with the proper balance of omega-3 and omega-6 essential fatty acids improved TBUT and relieved patient symptoms. The addition of topical cyclosporine did not convey any statistically significant improvement in TBUT beyond that achieved by the supplement.

Resolvin E1 improves tear production and decreases inflammation in a dry eye mouse model

PURPOSE

Dry eye (DE) is a common ocular surface disease, particularly among women and the elderly, with chronic symptoms of eye irritation and, in severe cases, blurred vision. Several studies have shown that there is an inflammatory component in DE, although the pathogenesis is not thoroughly understood. Resolvin E1 (RvE1; RX-10001) is an endogenous mediator derived from the omega-3 polyunsaturated fatty acid eicosapentaenoic acid and is involved in inflammation resolution and tissue protection. Here we investigated the role of RvE1 in a DE mouse model.

METHODS

Thirteen- to 14-week-old female BALB/C mice were exposed to desiccating conditions. One week after DE exposure, animals were treated topically with drug or vehicle 4 times per day for an additional week. Controls were nontreated animals placed in a normal environment. Schirmer's test was performed before treatment initiation and at days 2 and 4 after treatment. Density of corneal epithelial cells was analyzed in vivo using the Rostock Cornea Module of the Heidelberg Retina Tomograph (HRT-II). Corneas were processed using Western blot analysis and immunofluorescence examination.

RESULTS

Schirmer's test showed a significant decrease in tear production in DE compared with controls. There was no change at 2 and 4 days after treatment with the vehicle, but a significant increase was observed at 2 and 4 days in the RvE1-treated group. The density of the superficial epithelial cells showed a significant decrease after DE compared with controls, which increased after 7 days of RvE1 treatment. Western blot analysis showed that α-smooth muscle actin and cyclooxygenase-2 (COX-2) expression were strongly upregulated after DE and decreased after 7 days of RvE1 treatment. Immunofluorescence confirmed strong positive staining of α-smooth muscle actin and COX-2 in stroma and/or in epithelia after DE, which decreased with RvE1 treatment. The percentage of infiltrating CD⁴+ T cells and CD11b+ cells decreased after RvE1 treatment when compared with DE.

CONCLUSION

RvE1 promotes tear production, corneal epithelial integrity, and a decrease in inflammatory inducible COX-2. In the stroma, RvE1 inhibits keratocyte transformation to myofibroblasts and lowers the number of monocytes/macrophages in this DE mouse model. These results suggest that RvE1 and similar resolvin analogs have therapeutic potential in the treatment of DE.

Docosahexaenoic acid, protectins and dry eye

PURPOSE OF REVIEW

To report recent data on the potential role of omega-3 fatty acids, in particular docosahexaenoic acid and its derivatives, in the treatment of dry eye syndrome.

RECENT FINDINGS

Dietary supplementation with polyunsaturated fatty acids yields positive results in the improvement of dry eye signs and symptoms. Although several studies have shown this, evidence is still lacking as to which fatty acid or what combination constitutes the most effective treatment. Studies show that treatment with alpha-linoleic acid reduces dry eye-induced inflammation. Eicosapentaenoic acid and docosahexaenoic acid derivatives, particularly resolvin E1 (RvE1) and neuroprotectin D1, appear to be responsible for docosahexaenoic acid's anti-inflammatory effect. This is supported in a study in which topical RvE1 resulted in decreased inflammation in a mouse dry eye model. Topical administration of pigment epithelium-derived factor in combination with docosahexaenoic acid accelerates the regeneration of corneal nerves after their damage during corneal surgery, promoting the return of sensitivity and reducing the signs of dry eye. This combined treatment also reduces objective signs of dry eye, such as rose bengal staining.

SUMMARY

No firm recommendations can be made regarding optimal dietary supplementation of essential fatty acids that benefit dry eye patients. On the basis of animal data and preliminary human studies, docosahexaenoic acid and its derivatives appear to be a safe, effective topical treatment for dry eye patients. This may result from their role in the resolution of inflammation and the regeneration of damaged corneal nerves.

No consequences of dietary n-3 polyunsaturated fatty acid deficiency on the severity of scopolamine-induced dry eye

PURPOSE

Epidemiological studies suggest that dietary n-3 polyunsaturated fatty acids (PUFAs) may protect against dry eye. This study aimed to evaluate whether a dietary deficiency in n-3 PUFAs may increase the severity of the pathology in a scopolamine-induced model of dry eye in the rat.

METHODS

Lewis rats of three consecutive generations were bred under a balanced diet or a diet deprived of n-3 PUFAs. Dry eye was experimentally induced by continuous scopolamine delivery in female animals from the third generation of both groups. After 10 days of treatment, the clinical signs of ocular dryness were evaluated in vivo using fluorescein staining. MHC II and the rat mucin rMuc5AC were immunostained on ocular sphere cryosections. The transcript levels of the pro-inflammatory cytokines interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α and interferon (IFN)-γ were quantified in the exorbital lacrimal glands (LG) and in the conjunctiva using reverse transcription followed by polymerase chain reaction. Lipids were extracted from the exorbital LG for fatty acid analysis of the phospholipids using gas chromatography.

RESULTS

When compared to control animals, the scopolamine treatment induced an increase in the cornea fluorescein staining score (from 0.5 ± 0.0 to 2.5 ± 1.0 arbitrary units (AU) for the balanced diet and from 1.2 ± 0.8 to 2.6 ± 0.5 AU for the n-3 PUFA-deficient diet); a decrease in rMuc5AC immunostaining in the conjunctival epithelium (-34% for the balanced diet and -23% for the n-3 PUFA-deficient diet); an increase in the LG transcript levels of TNF-α for the balanced diet and of TNF-α and IFN-γ for the deficient diet; an increase in the conjunctival transcript levels of IL-1β and IL-6 for the deficient diet; an increase in arachidonic acid (AA) and in the ∆5-desaturase index (ratio of AA to dihomo-gamma-linolenic acid) in the exorbital LG for both diets. When compared to the balanced diet, the n-3 PUFA-deficient diet induced an increase in the LG transcript levels of IL-6 for the control animals and of TNF-α for the control and dry eye animals as well as an increase in the conjunctival transcript levels of IL-6 for the dry eye animals. There was no significant diet difference in fluorescein staining, rMuc5AC, and MHC II immunostaining scores.

CONCLUSIONS

Our data suggest that an n-3 PUFA deficiency does not increase the severity of dry eye in a rat model of dry eye.

Oral sea buckthorn oil attenuates tear film osmolarity and symptoms in individuals with dry eye

Dry eye is a common condition that can severely impair the quality of life. We aimed to find out whether oral sea buckthorn (SB) oil, containing (n-3) and (n-6) fatty acids and antioxidants, affects dry eye. In this double-blind, randomized, parallel trial, 20- to 75-y-old women and men experiencing dry eye symptoms consumed 2 g of SB or placebo oil daily for 3 mo from fall to winter. One hundred participants were recruited and 86 completed the study. Clinical dry eye tests and symptom follow-ups were performed. Tear film hyperosmolarity is a focal factor in dry eye. There was a general increase in the osmolarity from baseline to the end of the intervention. Compared with the placebo group, the increase was significantly less in the SB group when all participants were included [intention to treat (ITT), P = 0.04] and when only participants consuming the study products for at least 80% of the intervention days were included [per protocol (PP), P = 0.02]. The maximum intensities of redness and burning tended to be lower in the SB group. In the ITT participants, the group difference was significant for redness (P = 0.04) but not for burning (P = 0.05). In the PP participants, the group difference was significant for burning (P = 0.04) but not for redness (P = 0.11). In conclusion, SB oil attenuated the increase in tear film osmolarity during the cold season and positively affected the dry eye symptoms.

Omega-3 fatty acids in dry eye and corneal nerve regeneration after refractive surgery

Dry eye (DE) is a multifactorial condition that affects the surface of the eye and induces an inflammatory response. Corneal nerves play an important role in the maintenance of a healthy ocular surface. Here we review corneal structure, nerve architecture, DE conditions, and nerve regeneration following corneal surgery and discuss how n-3 fatty acids affect the health of the cornea. Animal studies show that resolvins, compounds derived from eicosapentaenoic acid (EPA), increase tear volume and decrease inflammation induced by DE. After corneal surgery in rabbits, treatment with nerve growth factor (NGF) or pigment epithelial derived factor (PEDF) in conjunction with docosahexaenoic acid (DHA) increase nerve density and corneal epithelial cell proliferation. Increased synthesis of the novel docosanoid, neuroprotectin D1 (NPD1), was found in corneas after the animals were treated with PEDF and DHA. Topical application of these lipids derived from n-3 fatty acids could be useful in treating DE and prevent clinical complications such as cornea erosion and ulcerations.