Effect of α-linolenic acid on streptozotocin-induced diabetic retinopathy indices in vivo

Correlation between omega-3 intake and the incidence of diabetic retinopathy based on NHANES from 2005 to 2008

AIMS

To identify correlations between omega-3 intake and incidence of diabetic retinopathy (DR).

METHODS

This was a cross-sectional study using data from participants over age 40 in the National Health and Nutrition Examination Survey (NHANES) 2005-2008. Metrics included participants' intake of omega-3 fatty acids, specifically three types of representative polyunsaturated fatty acids, DR prevalence, and demographic characteristics. Multiple logistic regression models were used to assess the relationship between omega-3 intake and DR.

RESULTS

Of the 1243 participants included in this study, omega-3 intake was lower in patients with DR relative to those without DR. Of the three polyunsaturated fatty acids within the omega-3 fatty acid family that we focused on, participants without DR consumed more docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) than those with DR. In contrast, there was no significant difference in the intake of eicosapentaenoic acid (EPA). Higher omega-3 intake was associated with a decreased risk of DR. In a crude model, the odds ratio (OR) was 0.548 (95% CI 0.315, 0.951; p = 0.033). In the fully adjusted model of omega-3 (model II), the adjusted OR was 0.525 (95% CI 0.306, 0.901; p = 0.021). DPA and DHA were also associated with a decreased risk of DR. In the full adjustment model (model II) of DPA and DHA, the adjusted ORs were 0.0002 (95% CI 0.000, 0.166; p = 0.014) and 0.293 (95% CI 0.105, 0.819; p = 0.020). Subgroup analysis showed that the protective effect of omega-3 against DR was more significant in younger patients (p value = 0.015).

CONCLUSIONS

In this cross-sectional study of the U.S. general population, we found that increased intake of omega-3 and its components, specifically DPA and DHA were negatively associated with DR incidence. This suggests that omega-3 may be a potential protective factor for DR and may help to prevent or delay the onset and progression of DR.

ASCEND-Eye: Effects of Omega-3 Fatty Acids on Diabetic Retinopathy

PURPOSE

Preclinical studies support a protective role for omega-3 fatty acids (FAs) on diabetic retinopathy (DR), but these observations have not been confirmed in randomized trials. We present randomized evidence for the effects of omega-3 FAs on DR outcomes.

DESIGN

A substudy of the A Study of Cardiovascular Events iN Diabetes (ASCEND) double-blind, randomized, placebo-controlled trial of 1 g omega-3 fatty acids (containing 460 mg eicosapentaenoic acid and 380 mg docosahexaenoic acid) daily for the primary prevention of serious cardiovascular events, in 15 480 UK adults at least 40 years of age, with diabetes.

PARTICIPANTS

Fifteen thousand four hundred eighty adults at least 40 years of age from the United Kingdom with diabetes from the ASCEND cohort.

METHODS

Linkage to electronic National Health Service Diabetic Eye Screening Programme records in England and Wales and confirmation of participant-reported eye events via medical record review. Log-rank and stratified log-rank methods were used for intention-to-treat analyses of time until the main outcomes of interest.

MAIN OUTCOME MEASURES

The primary efficacy endpoint was time to the first postrandomization recording of referable disease, a composite of referable retinopathy (R2 or R3a/s) or referable maculopathy (M1) based on the grading criteria defined by the United Kingdom National Screening Committee. Secondary and tertiary outcomes included the referable disease outcome stratified by the severity of DR at baseline, any progression in retinopathy grade, and incident diabetic maculopathy.

RESULTS

Linkage data were obtained for 7360 participants (48% of those who were randomized in ASCEND). During their mean follow-up of 6.5 years, 548 participants (14.8%) had a referable disease event in the omega-3 FAs group, compared with 513 participants (13.9%) in the placebo group (rate ratio, 1.07; 95% confidence interval, 0.95-1.20; P = 0.29). There were no statistically significant between-group differences in the proportion of events for either of the secondary or tertiary outcomes.

CONCLUSIONS

Representing the largest prospective test of its kind to date, these data exclude any clinically meaningful benefits of 1 g daily omega-3 FAs on DR.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Diabetic retinopathy and the role of Omega-3 PUFAs: A narrative review

Diabetes mellitus has been a major cause of concern for the past few decades. As the number of diabetic patients increases, so too does the occurrence of its complications. Diabetic retinopathy (DR) is one of these and constitutes the most common cause of blindness amongst working-age individuals. Chronic exposure to a hyperglycaemic environment remains the driving force of a cascade of molecular events that disrupt the microvasculature of the retina and if left untreated can lead to blindness. In this review, we identify oxidative stress as a major implication in the pathway to the development of DR and speculate that it plays a central role especially in the early stages of the disease. Cells lose their antioxidant capacity under a hyperglycaemic state, free radicals are formed and eventually apoptosis ensues. The polyol pathway; advanced glycation end-product formation; the protein kinase C pathway, and the hexosamine pathway are found to contribute to the increase in oxidative stress observed in diabetic patients. We also investigate the use of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) in DR. These molecules possess antioxidant and anti-inflammatory properties and have been previously investigated for use in other ocular pathologies with promising results. In this review we present the latest findings in pre-clinical and clinical studies for the use of ω-3 PUFAs in DR. We hypothesise that ω-3 PUFAs could be beneficial for DR in ways of reducing the oxidative stress and limiting the progression of the disease that threatens the eyesight of the patient, in conjunction with conventional therapy.

Chemical Constituents and Hypoglycemic Mechanisms of Dendrobium nobile in Treatment of Type 2 Diabetic Rats by UPLC-ESI-Q-Orbitrap, Network Pharmacology and In Vivo Experimental Verification

This study aimed to systematically explore the chemical constituents of D. nobile and its hypoglycemic effect by UPLC-ESI-Q-Orbitrap, network pharmacology and in vivo experiment. The chemical constituents of D. nobile were qualitatively analyzed, and the hypoglycemic compounds were quickly identified. Network pharmacological analysis and molecular docking technique were applied to assist in the elucidation of the hypoglycemic mechanisms of D. nobile. A type 2 diabetic mellitus (T2DM) rat model was established using the HFD and STZ method for in vivo experimental verification, and these T2DM rats were treated with D. nobile extract and D. nobile polysaccharide for two months by gavage. The results showed that a total of 39 chemical constituents of D. nobile, including alkaloids, bibenzyls, phenanthrenes and other types of compounds, were identified. D. nobile extract and D. nobile polysaccharide could significantly ameliorate the body weight, hyperglycemia, insulin resistance, dyslipidemia and morphological impairment of the liver and pancreas in the T2DM rats. α-Linolenic acid, dihydroconiferyl dihydro-p-coumarate, naringenin, trans-N-feruloyltyramine, gigantol, moscatilin, 4-O-methylpinosylvic acid, venlafaxine, nordendrobin and tristin were regarded as the key hypoglycemic compounds of D. nobile, along with the hypoglycemic effect on the PI3K-AKT signaling pathway, the insulin signaling pathway, the FOXO signaling pathway, the improvement of insulin resistance and the AGE-RAGE signaling pathway. The Western blotting experiment results confirmed that D. nobile activated the PI3K/AKT pathway and insulin signaling pathway, promoted glycogen synthesis via regulating the expression of glycogen synthase kinase 3 beta (GSK-3β) and glucose transporter 4 (GLUT4), and inhibited liver gluconeogenesis by regulating the expression of phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6 phosphatase (G6pase) in the liver. The results suggested that the hypoglycemic mechanism of D. nobile might be associated with liver glycogen synthesis and gluconeogenesis, contributing to improving insulin resistance and abnormal glucose metabolism in the T2DM rats.

Dietary Intake and Diabetic Retinopathy: A Systematic Review of the Literature

Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus. The evidence connecting dietary intake and DR is emerging, but uncertain. We conducted a systematic review to comprehensively summarize the current understanding of the associations between dietary consumption, DR and diabetic macular edema (DME). We systematically searched PubMed, Embase, Medline, and the Cochrane Central Register of Controlled Trials between January 1967 to May 2022 for all studies investigating the effect of diet on DR and DME. Of the 4962 articles initially identified, 54 relevant articles were retained. Our review found that higher intakes of fruits, vegetables, dietary fibers, fish, a Mediterranean diet, oleic acid, and tea were found to have a protective effect against DR. Conversely, high intakes of diet soda, caloric intake, rice, and choline were associated with a higher risk of DR. No association was seen between vitamin C, riboflavin, vitamin D, and milk and DR. Only one study in our review assessed dietary intake and DME and found a risk of high sodium intake for DME progression. Therefore, the general recommendation for nutritional counseling to manage diabetes may be beneficial to prevent DR risk, but prospective studies in diverse diabetic populations are needed to confirm our findings and expand clinical guidelines for DR management.

Beneficial Actions of Essential Fatty Acids in Streptozotocin-Induced Type 1 Diabetes Mellitus

The essential fatty acids (EFA), n3 alpha-linolenic acid (ALA), and n6 linoleic acid (LA) are of benefit in diabetes mellitus, but their mechanisms of action are unknown. We, therefore, examined the effects of EFAs on the metabolism, gut microbiota, and inflammatory and retinal histopathology indices in streptozotocin (STZ)-induced type 1 diabetes mellitus (T1DM) animals, and we assessed the levels of vitreal lipoxin A4 (LXA4)-derived from LA-in subjects with diabetic retinopathy (DR). STZ-induced T1DM rats received LA or ALA 100 μg/day intraperitoneally on alternate days for 21 days, and their blood glucose; lipid profile; plasma, hepatic, and retinal fatty acid profiles (by gas chromatography); retinal histology; activities of hepatic and retinal desaturases; and inflammatory markers (by qRT-PCR) were evaluated. Gut microbiota composition was assayed by 16S rDNA sequencing technology of the fecal samples, and their short-chain fatty acids and bile acids were assayed by gas chromatography, liquid chromatography coupled with tandem mass spectrometry, respectively. The human vitreal fatty acid profiles of subjects with proliferative DR and LXA4 levels were measured. LA and ALA significantly improved the plasma glucose and lipid levels; increased the abundance of Ruminococcaceae (the ALA-treated group), Alloprevotella, Prevotellaceae_Ga6A1_group, Ruminococcaceae_UCG_010, and Ruminococcus_1 (the LA-treated group) bacteria; enhanced acetate and butyrate levels; and augmented fecal and hepatic concentrations of cholic acid, chenodeoxycholic acid, and tauro ursodeoxycholic acid in ALA- and LA-treated animals. Significant STZ-induced decreases in plasma LA, gamma-linolenic acid, arachidonic acid, and ALA levels reverted to near normal, following LA and ALA treatments. Significant changes in the expression of desaturases; COX-2, 5-LOX, and 12-LOX enzymes; and cytokines in T1DM were reverted to near normal by EFAs. DR subjects also had low retinal LXA4 levels. The results of the present study show that ALA and LA are of significant benefit in reversing metabolism, gut microbiota, and inflammatory and retinal index changes seen in T1DM, suggesting that EFAs are of benefit in diabetes mellitus.

The Effect of Diet and Lifestyle on the Course of Diabetic Retinopathy-A Review of the Literature

Diabetes is a major social problem. As shown by epidemiological studies, the world incidence of diabetes is increasing and so is the number of people suffering from its complications. Therefore, it is important to determine possible preventive tools. In the prevention of diabetic retinopathy, it is essential to control glycemia, lipid profile and blood pressure. This can be done not only by pharmacological treatment, but first of all by promoting a healthy lifestyle, changing dietary habits and increasing physical activity. In our work, we present a review of the literature to show that physical exercise and an adequate diet can significantly reduce the risk of diabetes and diabetic retinopathy.

The review of alpha-linolenic acid: Sources, metabolism, and pharmacology

α-linolenic acid (ALA, 18:3n-3) is a carboxylic acid composed of 18 carbon atoms and three cis double bonds, and is an essential fatty acid indispensable to the human body. This study aims to systematically review related studies on the dietary sources, metabolism, and pharmacological effects of ALA. Information on ALA was collected from the internet database PubMed, Elsevier, ResearchGate, Web of Science, Wiley Online Library, and Europe PMC using a combination of keywords including "pharmacology," "metabolism," "sources." The following findings are mainly contained. (a) ALA can only be ingested from food and then converted into eicosapentaenoic acid and docosahexaenoic acid in the body. (b) This conversion process is relatively limited and affected by many factors such as dose, gender, and disease. (c) Pharmacological research shows that ALA has the anti-metabolic syndrome, anticancer, antiinflammatory, anti-oxidant, anti-obesity, neuroprotection, and regulation of the intestinal flora properties. (d) There are the most studies that prove ALA has anti-metabolic syndrome effects, including experimental studies and clinical trials. (e) The therapeutic effect of ALA will be affected by the dosage. In short, ALA is expected to treat many diseases, but further high quality studies are needed to firmly establish the clinical efficacy of ALA.

Anti-Diabetic Effects of Isolated Lipids from Natural Sources through Modulation of Angiogenesis

BACKGROUND

Aberrant angiogenesis plays a fateful role in the development of diabetes and diabetic complications. Lipids, as a diverse group of biomacromolecules, are able to relieve diabetes through the modulation of angiogenesis.

OBJECTIVE

Owing to the present remarkable anti-diabetic effects with no or few side effects of lipids, the aim of this study was to assess the state-of-the-art research on anti-diabetic effects of lipids via the modulation of angiogenesis.

METHODS

To study the effects of lipids in diabetes via modulation of angiogenesis, we have searched the electronic databases including Scopus, PubMed, and Cochrane.

RESULTS

The promising anti-diabetic effects of lipids were reported in several studies. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil (FO) were reported to significantly induce neovasculogenesis in high glucose (HG)-mediated endothelial progenitor cells (EPCs) neovasculogenic dysfunction in type 2 diabetic mice. Linoleic acid, mono-epoxy-tocotrienol-α (MeT3α), and ginsenoside Rg1 facilitate wound closure and vessel formation. N-Palmitoylethanolamine (PEA), α-linolenic acid (ALA), omega-3 (ω3) lipids from flaxseed (FS) oil, ω-3 polyunsaturated fatty acids (PUFA), lipoic acid, taurine, and zeaxanthin (Zx) are effective in diabetic retinopathy via suppression of angiogenesis. Lysophosphatidic acid, alkyl-glycerophosphate, crocin, arjunolic acid, α-lipoic acid, and FS oil are involved in the management of diabetes and its cardiac complications. Furthermore, in two clinical trials, R-(+)-lipoic acid (RLA) in combination with hyperbaric oxygenation therapy (HBOT) for treatment of chronic wound healing in DM patients, as well as supplementation with DHA plus antioxidants along with intravitreal ranibizumab were investigated for its effects on diabetic macular edema.

CONCLUSION

Proof-of-concept studies presented here seem to well shed light on the anti-diabetic effects of lipids via modulation of angiogenesis.

Diet and risk of visual impairment: a review of dietary factors and risk of common causes of visual impairment

Age-related macular degeneration, diabetic retinopathy, cataract, and glaucoma remain the leading causes of visual impairment in developed nations, resulting in a substantial treatment burden on sufferers and health care systems. Despite significant advances in diagnostic testing and therapeutics, population-based strategies to reduce the burden of these diseases remain limited. However, there is some evidence that these diseases may share overlapping risk factors, particularly in regard to dietary intake and antioxidant status, and it is thus possible that dietary modification may reduce both the prevalence and severity of these conditions. In particular, dietary intake of green leafy vegetables, hyperglycemia/glycemia index, and omega-3 fatty acid intake, as well as overall dietary patterns, may affect risk of one or more of these conditions. In this review, we analyse the evidence for dietary intake and the association with these conditions, and provide insights into possible modifications that may thus simultaneously reduce the risk of visual impairment from multiple causes, including improving dietary intake of green leafy vegetables and reducing dietary glycemic index, both of which have been associated with a decreased risk of multiple causes of visual impairment.

Protective Effects and Molecular Signaling of n-3 Fatty Acids on Oxidative Stress and Inflammation in Retinal Diseases

Oxidative stress and inflammation play crucial roles in the development and progression of retinal diseases. Retinal damage by various etiologies can result in retinopathy of prematurity (ROP), diabetic retinopathy (DR), and age-related macular degeneration (AMD). n-3 fatty acids are essential fatty acids and are necessary for homeostasis. They are important retinal membrane components and are involved in energy storage. n-3 fatty acids also have antioxidant and anti-inflammatory properties, and their suppressive effects against ROP, DR, and AMD have been previously evaluated. α-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and their metabolites have been shown to alleviate retinal oxidative stress and inflammation involving various biological signaling pathways. In this review, we summarize the current understanding of the n-3 fatty acids effects on the mechanisms of these retinal diseases and how they exert their therapeutic effects, focusing on ALA, EPA, DHA, and their metabolites. This knowledge may provide new remedial strategies for n-3 fatty acids in the prevention and treatment of retinal diseases associated with oxidative stress and inflammation.

Molecular pathobiology of scleritis and its therapeutic implications

Scleritis and other autoimmune diseases are characterized by an imbalance in the levels of pro-inflammatory and anti-inflammatory molecules with the balance tilted more towards the former due to the failure of recognition of self. The triggering of inflammatory process could be ascribed to the presence of cytoplasmic DNA/chromatin that leads to activation of cytosolic DNA-sensing cGAS-STING (cyclic GMP-AMP synthase linked to stimulator of interferon genes) pathway and enhanced expression of NF-κB that results in an increase in the production of pro-inflammatory bioactive lipids. Bioactive lipids gamma-linolenic acid (GLA), dihomo-GLA (DGLA), prostaglandin E1 (PGE1), prostacyclin (PGI2) and lipoxin A4, resolvins, protectins and maresins have anti-inflammatory actions, bind to DNA to render it non-antigenic and are decreased in autoimmune diseases. These results suggest that efforts designed to enhance the production of anti-inflammatory bioactive lipids may form a new approach to autoimmune diseases. Local injection or infusion of lipoxins, resolvins, protectins and maresins or their precursors such as arachidonic acid may be exploited in the prevention and management of autoimmune diseases including scleritis, uveitis and lupus/rheumatoid arthritis.

Omega-3 fatty acids in prevention of diabetic retinopathy

OBJECTIVES

To review the competence of Omega-3 fatty acids in restricting the progression, thereby leading to prevention of diabetic retinopathy.

KEY FINDINGS

Owing to their anti-inflammatory and anti-angiogenic properties, Omega-3 fatty acids alleviate major aetiological agents. These fatty acids are renowned for their beneficial effects in various cardiovascular and other disorders; however, their potential to prevent the progression of diabetic retinopathy remains least explored.

SUMMARY

Utilizing this potential, we may develop effective prophylactic agents which markedly inhibit the advent of retinal angiogenesis and prevent the apoptosis of retinal endothelial and neuronal cells, thereby averting retinal degeneration, hence safeguarding diabetic patients from this sight-threatening complication.

Diabetic macular edema, retinopathy and age-related macular degeneration as inflammatory conditions

Diabetic macular edema (DME) and diabetic retinopathy (DR) are complications affecting about 25% of all patients with long-standing type 1 and type 2 diabetes mellitus and are a major cause of significant decrease in vision and quality of life. Age-related macular degeneration (AMD) is not uncommon, and diabetes mellitus affects the incidence and progression of AMD through altering hemodynamics, increasing oxidative stress, accumulating advanced glycation end products, etc. Recent studies suggest that DME, DR and AMD are inflammatory conditions characterized by a breakdown of the blood-retinal barrier, inflammatory processes and an increase in vascular permeability. Key factors that seem to have a dominant role in DME, DR and AMD are angiotensin II, prostaglandins and the vascular endothelial growth factor and a deficiency of anti-inflammatory bioactive lipids. The imbalance between pro- and anti-inflammatory eicosanoids and enhanced production of pro-angiogenic factors may initiate the onset and progression of DME, DR and AMD. This implies that bioactive lipids that possess anti-inflammatory actions and suppress the production of angiogenic factors could be employed in the prevention and management of DME, DR and AMD.

Dendrobium chrysotoxum Lindl. alleviates diabetic retinopathy by preventing retinal inflammation and tight junction protein decrease

Diabetic retinopathy (DR) is a serious complication of diabetes mellitus. This study aimed to observe the alleviation of the ethanol extract of Dendrobium chrysotoxum Lindl. (DC), a traditional Chinese herbal medicine, on DR and its engaged mechanism. After DC (30 or 300 mg/kg) was orally administrated, the breakdown of blood retinal barrier (BRB) in streptozotocin- (STZ-) induced diabetic rats was attenuated by DC. Decreased retinal mRNA expression of tight junction proteins (including occludin and claudin-1) in diabetic rats was also reversed by DC. Western blot analysis and retinal immunofluorescence staining results further confirmed that DC reversed the decreased expression of occludin and claudin-1 proteins in diabetic rats. DC reduced the increased retinal mRNA expressions of intercellular adhesion molecule-1 (ICAM-1), tumor necrosis factor α (TNFα), interleukin- (IL-) 6, and IL-1β in diabetic rats. In addition, DC alleviated the increased 1 and phosphorylated p65, IκB, and IκB kinase (IKK) in diabetic rats. DC also reduced the increased serum levels of TNFα, interferon-γ (IFN-γ), IL-6, IL-1β, IL-8, IL-12, IL-2, IL-3, and IL-10 in diabetic rats. Therefore, DC can alleviate DR by inhibiting retinal inflammation and preventing the decrease of tight junction proteins, such as occludin and claudin-1.

Potential role of polyunsaturated fatty acids in diabetic retinopathy

Diabetic retinopathy (DR) is a serious complication of long-standing diabetes mellitus. It affects about 25% of all patients with diabetes mellitus and causes a significant decrease in the quality of life. Despite many years of research, the exact pathway that leads to the development and progression of DR is not clear. Recent studies suggest that polyunsaturated fatty acids (PUFAs) and their metabolites could play a significant role in DR. There is evidence to suggest that an imbalance between pro- and anti-inflammatory eicosanoids and enhanced production of pro-angiogenic factors may initiate the onset and progression of DR. This implies that PUFAs and their metabolites that possess anti-inflammatory actions and suppress the production of angiogenic factors could be employed in the prevention and management of DR.