N-3 polyunsaturated Fatty acids prevent diabetic retinopathy by inhibition of retinal vascular damage and enhanced endothelial progenitor cell reparative function

Genetic mechanisms of hemispheric functional connectivity in diabetic retinopathy: a joint neuroimaging and transcriptomic study

Background

DR represents a major cause of global vision loss; however, the genetic basis of functional homotopy,a critical neurobiological metric reflecting interhemispheric functional synchronization, remains largely unexplored. Emerging evidence suggests that DR patients exhibiting aberrant VMHC may potentially associate with distinct transcriptional profiles. These findings could provide novel mechanistic insights into the neuropathological substrates underlying DR-related visual and cognitive dysfunction.

Methods

Resting-state fMRI data from 46 DR patients and 43 HCs were analyzed to compute VMHC for assessing interhemispheric functional connectivity. Spatial transcriptomic-neuroimaging associations were examined using AHBA, revealing genes significantly correlated with VMHC alterations. Subsequent analyses included functional enrichment assessment and PPI network construction.

Results

DR patients demonstrated significantly lower VMHC in bilateral LING, PoCG, and PreCG versus controls, indicating impaired interhemispheric connectivity in visual-sensorimotor networks. VMHC variations spatially correlated with 4,000 genes (2,000 positive/negative each), enriched in transcriptional regulation, mitochondrial function, synaptic activity (BP/CC/MF), and lipid metabolism/N-glycan biosynthesis (KEGG). PPI network identified hub genes (ACTB/MRPL9/MRPS6,positive; H4C6/NDUFAB1/H3C12,negative) regulating mitochondrial dynamics, cytoskeleton, and epigenetics.

Conclusion

This study represents the first integration of fMRI and transcriptomics to elucidate the genetic determinants underlying VMHC disruption in DR. The findings demonstrate that impaired interhemispheric connectivity in DR involves complex interactions among genes regulating neurovascular, metabolic, and neurodegenerative pathways. These results significantly advance the understanding of neurological manifestations in DR and identify potential therapeutic targets for clinical intervention.

Nutrients and Natural Substances for Hypoglycemic Effects and Management in Diabetic Retinopathy

Diabetic retinopathy (DR) is a significant microvascular consequence of diabetes mellitus (DM), resulting in visual impairment and blindness. Controlling hyperglycemia is essential for avoiding and alleviating diabetic retinopathy. Nutrients and natural compounds possessing hypoglycemic characteristics present promising supplementary approaches to conventional therapies. This review assesses the influence of nutrients and natural substances on glycemic regulation and their possible effects on diabetic retinopathy.

GOAL

To investigate and consolidate knowledge about nutrients and natural compounds exhibiting hypoglycemic properties and their processes in the prevention and management of diabetic retinopathy.

APPROACHES

Extensive reviews were conducted on pertinent studies from databases including PubMed, Scopus, and Web of Science. Selection criteria encompassed papers that examined natural substances, nutrients, or dietary supplements exhibiting effects on blood glucose levels and pathways associated to diabetic retinopathy. Principal findings were encapsulated according to their mechanisms, efficacy, and safety.

OUTCOMES

Numerous foods, including omega-3 fatty acids, vitamin D, and polyphenols (e.g., curcumin, resveratrol), have hypoglycemic properties by improving insulin sensitivity and diminishing oxidative stress. Natural substances like berberine, quercetin, and flavonoids demonstrate analogous effects, influencing pathways associated with inflammation, advanced glycation end products (AGEs), and angiogenesis, which are critical factors in the evolution of diabetic retinopathy (DR). The synergistic benefits of integrating natural medicines with conventional antidiabetic medications may enhance glycemic control and reduce retinal damage. The safety profiles of these therapies are predominantly positive; nonetheless, clinical trials are still constrained in both breadth and scale.

CONCLUSIONS

Nutrients and natural compounds are promising supplementary approaches for glycemic regulation and the therapy of diabetic retinopathy. Additional research, encompassing extensive clinical studies, is required to substantiate their efficacy, determine optimal dose, and verify long-term safety. The use of these natural substances into clinical practice may improve comprehensive management of diabetes and associated consequences.

Elevated Very-Long-Chain Ceramides in the Vitreous Humor of Patients With Proliferative Diabetic Retinopathy

Purpose

To quantitate the levels of various ceramide species in the vitreous of patients with proliferative diabetic retinopathy (PDR) and to investigate the role of vitreal ceramides in the pathogenesis of PDR.

Study Design

A case control study.

Methods

We collected vitreous samples from 25 type 2 diabetes patients with PDR and 25 age- and sex-matched nondiabetic controls undergoing vitrectomy. The levels of ceramide species (C16:0, 18:0, 20:0, 22:0, 24:1, and 24:0) were measured by ultra-high-performance liquid chromatography-tandem mass spectrometry with positive electrospray ionization mode. The correlation of baseline characteristics, blood test data, and clinical manifestation of PDR were analyzed with vitreal ceramides levels.

Results

The total level of ceramides was substantially higher in the PDR group than the control group (18.626 ± 19.264 versus 3.524 ± 2.456 pmol/mg protein; P < 0.001). Among ceramides of various acyl chain lengths, the increases of very-long-chain (VLC) ceramides (C22-C24) were more drastic than those of long-chain ceramides (C16-C20). In the PDR group, VLC ceramide species accounted for 76.1%, whereas in the control group, C16 ceramide predominated at 40.5%. Based on the multivariate linear regression analysis, diagnosis of diabetes (β = 14.5751; P = 0.0327) and lower body mass index (β = -2.1396; P = 0.0173) were significantly associated with higher level of VLC ceramides. Intravitreal injection of anti-VEGF leads to insignificant reduction of VLC ceramides (P = 0.068).

Conclusions

Vitreal ceramide levels were elevated in diabetic subjects, especially the VLC species, which may contribute to the pathogenesis of diabetic retinopathy.

Effects of Selected Antioxidants on Electroretinography in Rodent Diabetic Retinopathy

Electroretinography (ERG) is a non-invasive technique for evaluating the retinal function in various ocular diseases. Its results are useful for diagnosing ocular disorders and assessing disease progression or treatment effectiveness. Since numerous studies are based on animal models, validating the ERG results from animals is pivotal. The first part of this paper presents basic information on the types of ERG tests used on rodents, and the second part describes the recorded functional changes in rodents' retinas when various antioxidant treatments for diabetic retinopathy were used. Our study showed that among the tests for diabetic retinopathy diagnosis in rodents, full-field ERG is accurate and the most commonly used, and pattern ERG and the photopic negative response of the flash ERG tests are rarely chosen. Furthermore, antioxidants generally protect retinas from functional losses. Their beneficial influence is expressed in the preserved amplitudes of the a- and b-waves and the oscillatory potentials. However, prolonging the drug exposure showed that the antioxidants could delay the onset of adverse changes but did not stop them. Future studies should concentrate on how long-term antioxidant supplementation affects the retinal function.

Retinal Docosahexaenoic Acid Is Significantly Reduced in Diabetic Humans and Mice: Possible Relationship to Diabetic Retinopathy

Purpose

The retina contains the highest concentration of the omega 3 fatty acid, docosahexaenoic acid (DHA), in the body. Although epidemiologic studies showed an inverse correlation between the consumption of omega 3 fatty acids and the prevalence of diabetic retinopathy, there are no data showing the effect of diabetes on retinal DHA in humans. In this study, we measured the DHA content of the retina in diabetic and non-diabetic humans as well as mice and determined the effect of diabetes on retinal thickness and function in mice.

Methods

Fatty acid composition was determined by gas chromatography/mass spectroscopy. Retinal thickness in mice was measured by optical coherence tomography and retinal function was measured by electroretinogram (ERG). Expression of selected genes involved in inflammation and lipid metabolism was determined by quantitative real-time PCR (qRT-PCR).

Results

We found a 40% reduction of DHA in peripheral retina and a 25% reduction in the macula of diabetic humans compared with nondiabetic controls. There was a 24% reduction in retinal DHA of type 2 diabetic mice (db/db) compared with the controls (db/+). The retinal thickness was significantly decreased in db/db mice, especially in the inner retina, and the ERG b-wave amplitudes were significantly attenuated. Increased expression of proinflammatory genes was observed in both human and mouse diabetic retinas.

Conclusions

Retinal DHA is reduced in diabetic humans and mice, which is associated with a thinning of retina and functional defects in diabetic mice. Enriching retinal DHA through diet may be beneficial in the prevention and treatment of diabetic retinopathy.

Diabetic retinopathy is a ceramidopathy reversible by anti-ceramide immunotherapy

Diabetic retinopathy is a microvascular disease that causes blindness. Using acid sphingomyelinase knockout mice, we reported that ceramide generation is critical for diabetic retinopathy development. Here, in patients with proliferative diabetic retinopathy, we identify vitreous ceramide imbalance with pathologic long-chain C16-ceramides increasing and protective very long-chain C26-ceramides decreasing. C16-ceramides generate pro-inflammatory/pro-apoptotic ceramide-rich platforms on endothelial surfaces. To geo-localize ceramide-rich platforms, we invented a three-dimensional confocal assay and showed that retinopathy-producing cytokines TNFα and IL-1β induce ceramide-rich platform formation on retinal endothelial cells within seconds, with volumes increasing 2-logs, yielding apoptotic death. Anti-ceramide antibodies abolish these events. Furthermore, intravitreal and systemic anti-ceramide antibodies protect from diabetic retinopathy in standardized rodent ischemia reperfusion and streptozotocin models. These data support (1) retinal endothelial ceramide as a diabetic retinopathy treatment target, (2) early-stage therapy of non-proliferative diabetic retinopathy to prevent progression, and (3) systemic diabetic retinopathy treatment; and they characterize diabetic retinopathy as a "ceramidopathy" reversible by anti-ceramide immunotherapy.

Understanding the Impact of Polyunsaturated Fatty Acids on Age-Related Macular Degeneration: A Review

Age-related Macular Degeneration (AMD) is a multifactorial ocular pathology that destroys the photoreceptors of the macula. Two forms are distinguished, dry and wet AMD, with different pathophysiological mechanisms. Although treatments were shown to be effective in wet AMD, they remain a heavy burden for patients and caregivers, resulting in a lack of patient compliance. For dry AMD, no real effective treatment is available in Europe. It is, therefore, essential to look for new approaches. Recently, the use of long-chain and very long-chain polyunsaturated fatty acids was identified as an interesting new therapeutic alternative. Indeed, the levels of these fatty acids, core components of photoreceptors, are significantly decreased in AMD patients. To better understand this pathology and to evaluate the efficacy of various molecules, in vitro and in vivo models reproducing the mechanisms of both types of AMD were developed. This article reviews the anatomy and the physiological aging of the retina and summarizes the clinical aspects, pathophysiological mechanisms of AMD and potential treatment strategies. In vitro and in vivo models of AMD are also presented. Finally, this manuscript focuses on the application of omega-3 fatty acids for the prevention and treatment of both types of AMD.

Emerging role of ferroptosis in diabetic retinopathy: a review

BACKGROUND

Diabetic retinopathy (DR) is a significant complication of diabetes and the primary cause of blindness among working age adults globally. The development of DR is accompanied by oxidative stress, characterised by an overproduction of reactive oxygen species (ROS) and a compromised antioxidant system. Clinical interventions aimed at mitigating oxidative stress through ROS scavenging or elimination are currently available. Nevertheless, these treatments merely provide limited management over the advanced stage of the illness. Ferroptosis is a distinctive form of cell death induced by oxidative stress, which is characterised by irondependent phospholipid peroxidation.

PURPOSE

This review aims to synthesise recent experimental evidence to examine the involvement of ferroptosis in the pathological processes of DR, as well as to explicate the regulatory pathways governing oxidative stress and ferroptosis in retina.

METHODS

We systematically reviewed literature available up to 2023.

RESULTS

This review included 12 studies investigating the involvement of ferroptosis in DR.

Study protocol of OmegaROP-2 prospective study: expression of placental fatty acid receptors in preterm newborns with retinopathy of prematurity

BACKGROUND

Incomplete vascularization of the retina in preterm infants carries a risk of retinopathy of prematurity (ROP). Progress in neonatal resuscitation in developing countries has led to the survival of an increasing number of premature infants, resulting in an increased rate of ROP and consequently in visual disability. Strategies to reduce ROP involve optimizing oxygen saturation, nutrition, and normalizing factors such as insulin-like growth factor 1 and n-3 long-chain polyunsaturated fatty acids (LC-PUFA). Our previous study, OmegaROP, showed that there is an accumulation or retention of docosahexaenoic acid (DHA) in mothers of infants developing ROP, suggesting abnormalities in the LC-PUFA placental transfer via fatty acid transporting proteins. The present study aims to better understand the LC-PUFA transport dysfunction in the fetoplacental unit during pregnancy and to find a novel target for the prevention of ROP development.

METHODS

The study protocol is designed to evaluate the correlation between the expression level of placental fatty acid receptors and ROP occurrence. This ongoing study will include 100 mother-infant dyads: mother-infant dyads born before 29 weeks of gestational age (GA) and mother-infant dyads with full-term pregnancies. Recruitment is planned over a period of 46 months. Maternal and cord blood samples as well as placental tissue samples will be taken following delivery. ROP screening will be performed using wide-field camera imaging according to the International Classification of ROP consensus statement.

DISCUSSION

The results of this study will have a tangible impact on public health. Indeed, if we show a correlation between the expression level of placental omega-3 receptors and the occurrence of ROP, it would be an essential step in discovering novel pathophysiological mechanisms involved in this retinopathy.

TRIAL REGISTRATION

NCT04819893.

Mendelian Randomization Analysis Reveals Causal Effects of Polyunsaturated Fatty Acids on Subtypes of Diabetic Retinopathy Risk

Polyunsaturated fatty acids (PUFAs) affect several physiological processes, including visual acuity, but their relationship with diabetic retinopathy (DR) remains elusive. The aim of this study was to determine whether PUFAs have a causal effect on DR. PUFAs- (total and omega-3 [FAw3] and omega-6 [FAw6] fatty acids and their ratio) and DR-associated single nucleotide polymorphisms derived from genome-wide association studies; sample sizes were 114,999 for fatty acids and 216,666 for any DR (ADR), background DR (BDR), severe non-proliferative DR (SNPDR), and proliferative DR (PDR). We hypothesized that the intra-body levels of PUFAs have an impact on DR and conducted a two-sample Mendelian randomization (MR) study to assess the causality. Pleiotropy, heterogeneity, and sensitivity analyses were performed to verify result reliability. High levels of PUFAs were found to be associated with reduced risk of both ADR and PDR. Moreover, FAw3 was associated with a decreased risk of PDR, whereas FAw6 demonstrated an association with lowered risks of both BDR and PDR. Our findings provide genetic evidence, for the first time, for a causal relationship between PUFAs and reduced DR risk. Consequently, our comprehensive MR analysis strongly urges further investigation into the precise functions and long-term effects of PUFAs, FAw3, and FAw6 on DR.

Improvement of retinal function in Alzheimer disease-associated retinopathy by dietary lysophosphatidylcholine-EPA/DHA

Alzheimer disease (AD) is the most prevalent cause of dementia in the elderly. Although impaired cognition and memory are the most prominent features of AD, abnormalities in visual functions often precede them, and are increasingly being used as diagnostic and prognostic markers for the disease. Retina contains the highest concentration of the essential fatty acid docosahexaenoic acid (DHA) in the body, and its deficiency is associated with several retinal diseases including diabetic retinopathy and age related macular degeneration. In this study, we tested the hypothesis that enriching retinal DHA through a novel dietary approach could ameliorate symptoms of retinopathy in 5XFAD mice, a widely employed model of AD. The results show that 5XFAD mice have significantly lower retinal DHA compared to their wild type littermates, and feeding the lysophosphatidylcholine (LPC) form of DHA and eicosapentaenoic acid (EPA) rapidly normalizes the DHA levels, and increases retinal EPA by several-fold. On the other hand, feeding similar amounts of DHA and EPA in the form of triacylglycerol had only modest effects on retinal DHA and EPA. Electroretinography measurements after 2 months of feeding the experimental diets showed a significant improvement in a-wave and b-wave functions by the LPC-diet, whereas the TAG-diet had only a modest benefit. Retinal amyloid β levels were decreased by about 50% by the LPC-DHA/EPA diet, and by about 17% with the TAG-DHA/EPA diet. These results show that enriching retinal DHA and EPA through dietary LPC could potentially improve visual abnormalities associated with AD.

OMEGA-3 FATTY ACIDS ARE ASSOCIATED WITH DECREASED PRESENCE AND SEVERITY OF DIABETIC RETINOPATHY: A Combined Analysis of MESA and GOLDR Cohorts

PURPOSE

Inflammation is associated with diabetic retinopathy development and progression, and previous studies have demonstrated that omega-3 polyunsaturated fatty acids have anti-inflammatory properties. Therefore, the goal of this study was to determine if omega-3 polyunsaturated fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are associated with decreased risk and severity of retinopathy in individuals with type 2 diabetes.

METHODS

In a combined population of 1,356 individuals with type 2 diabetes from the Multi-Ethnic Study of Atherosclerosis and Genetics of Latino Diabetic Retinopathy cohorts, odds ratios using logistic regression were determined to assess the association between polyunsaturated fatty acids and retinopathy.

RESULTS

In 1,356 participants with type 2 diabetes, individuals in the fourth quartile of DHA were 17% less likely to have retinopathy compared with the first quartile ( P = 0.009, CI: 0.72-0.95). Secondary analysis revealed 38% lower severity of retinopathy in individuals in the fourth quartile compared with the first quartile of DHA ( P = 0.006; CI: 0.44-0.87) and EPA + DHA ( P = 0.004; CI: 0.44-0.85). No significant associations were observed between EPA and retinopathy.

CONCLUSION

DHA is inversely associated with the presence and severity of diabetic retinopathy. Increased intake of dietary sources of DHA may provide some protection against retinopathy in individuals with type 2 diabetes and warrants more research as a preventative option.

Retinal Microvasculature and Neural Changes and Dietary Patterns in an Older Population in Southern Italy

BACKGROUND

Like other parts of the body, the retina and its neurovascular system are also affected by age-related changes. The rising age of populations worldwide makes it important to study the pathologies related to age and their potential risk factors, such as diet and eating habits. The aim of this study was to investigate the predictive power of food groups versus retinal features among noninstitutionalized older adults from Southern Italy using a machine learning approach.

METHODS

We recruited 530 subjects, with a mean age of 74 years, who were drawn from the large population of the Salus in Apulia Study. In the present cross-sectional study, eating habits were assessed with a validated food frequency questionnaire. For the visual assessment, a complete ophthalmic examination and optical coherence tomography-angiography analyses were performed.

RESULTS

The analyses identified 13 out of the 28 food groups as predictors of all our retinal variables: grains, legumes, olives-vegetable oil, fruiting vegetables, other vegetables, fruits, sweets, fish, dairy, low-fat dairy, red meat, white meat, and processed meat.

CONCLUSIONS

Eating habits and food consumption may be important risk factors for age-related retinal changes. A diet that provides the optimal intake of specific nutrients with antioxidant and anti-inflammatory powers, including carotenoids and omega-3 fatty acids, could have beneficial effects.

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.

Pigment epithelium-derived factor is an interleukin-6 antagonist in the RPE: Insight of structure-function relationships

Retinal and choroidal inflammatory lesions increase the levels of the pro-inflammatory cytokine interleukin-6 (IL-6). Pigment epithelium-derived factor (PEDF) has anti-inflammatory properties, but it is not known if it can prevent the production of IL-6 by the retinal pigment epithelium. To investigate the anti-inflammatory effects of PEDF in the RPE, we used human ARPE-19 cells stimulated with human recombinant tumor necrosis factor-alpha (TNF-α) to induce overexpression of the IL6 gene. We found that the viability of ARPE-19 cells decreased by 22% with TNF-α at 10 ng/ml, being drastically decreased at ≥50 ng/ml. TNF-α at 5-100 ng/ml elevated the production and secretion of IL-6 protein, as measured by ELISA. To challenge the TNF-α-mediated stimulation of IL-6, we used recombinant human PEDF protein. PEDF at 100 nM recovered the TNF-α-mediated loss of cell viability and repressed IL-6 gene expression as determined by RT-PCR. PEDF at 10-100 nM attenuated the IL-6 protein secretion in a dose dependent fashion (IC50 = 65 nM), being abolished with 100 nM PEDF. To map the region that confers the IL-6 blocking effect to the PEDF polypeptide, we used chemically synthesized peptides designed from its biologically active domains, pro-death 34-mer, and pro-survival 44-mer and 17-mer (H105A), to challenge the IL-6 overproduction. The pro-survival peptides recovered the TNF-α-mediated cell viability loss, and inhibited IL-6 secretion, while the 34-mer did not have an effect, suggesting a role for the pro-survival domain in blocking TNF-α-mediated cell death and IL-6 stimulation. Our findings position PEDF as a novel antagonistic agent of IL-6 production in RPE cells, underscoring its use for the management of retinal disease-related inflammation.

Implications of Diabetes-Induced Altered Metabolites on Retinal Neurodegeneration

Diabetic retinopathy (DR) is one of the major complications of diabetic eye diseases, causing vision loss and blindness worldwide. The concept of diabetic retinopathy has evolved from microvascular disease into more complex neurovascular disorders. Early in the disease progression of diabetes, the neuronal and glial cells are compromised before any microvascular abnormalities clinically detected by the ophthalmoscopic examination. This implies understanding the pathophysiological mechanisms at the early stage of disease progression especially due to diabetes-induced metabolic alterations to damage the neural retina so that early intervention and treatments options can be identified to prevent and inhibit the progression of DR. Hyperglycemia has been widely considered the major contributor to the progression of the retinal damage, even though tight control of glucose does not seem to have a bigger effect on the incidence or progression of retinal damage that leads to DR. Emerging evidence suggests that besides diabetes-induced hyperglycemia, dyslipidemia and amino acid defects might be a major contributor to the progression of early neurovascular retinal damage. In this review, we have discussed recent advances in the alterations of key metabolites of carbohydrate, lipid, and amino acids and their implications for neurovascular damage in DR.

INCREASED DIETARY INTAKE AND SERUM LEVELS OF ADVANCED GLYCATION END PRODUCTS (AGES) ARE ASSOCIATED WITH DIABETIC MACULAR EDEMA

Aim

Diabetic macular oedema (DME) can develop at all stages of diabetic retinopathy, causing visual impairment and blindness. Modern diets are high in advanced glycation end products (dAGEs), derived from processing methods, exerting a pivotal role in promoting diabetic retinopathy risk. In present study, we investigate the relationship between dietary and serum levels of AGEs and DME in type 2 diabetic subjects.

Methods

This case-control study was conducted between July 2018 and February 2019 on 50 case subjects with DME and 40 healthy controls without DM without DME. The sociodemographic characteristics, nutritional status, and anthropometric measurements were evaluated. The advanced glycation end products (AGEs) and receptor for AGEs (sRAGE) levels in serum were analysed.

Results

The AGEs levels of the DME group were higher than in the control group (p <0.05). sRAGE levels were higher in the DME group, but not statistically significant (p >0.05). The dietary intake of AGEs was higher in the DME group (p <0.05). It was found that an increase in neck circumference increased the risk of DME (p <0.001).

Conclusion

A positive correlation was found between DME and AGEs, dAGE, neck circumference, and waist circumference. For the validity of these results, studies, including controlled nutrition interventions, are needed.

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.

Lipids, hyperreflective crystalline deposits and diabetic retinopathy: potential systemic and retinal-specific effect of lipid-lowering therapies

The metabolically active retina obtains essential lipids by endogenous biosynthesis and from the systemic circulation. Clinical studies provide limited and sometimes conflicting evidence as to the relationships between circulating lipid levels and the development and progression of diabetic retinopathy in people with diabetes. Cardiovascular-system-focused clinical trials that also evaluated some retinal outcomes demonstrate the potential protective power of lipid-lowering therapies in diabetic retinopathy and some trials with ocular primary endpoints are in progress. Although triacylglycerol-lowering therapies with fibrates afforded some protection against diabetic retinopathy, the effect was independent of changes in traditional blood lipid classes. While systemic LDL-cholesterol lowering with statins did not afford protection against diabetic retinopathy in most clinical trials, and none of the trials focused on retinopathy as the main outcome, data from very large database studies suggest the possible effectiveness of statins. Potential challenges in these studies are discussed, including lipid-independent effects of fibrates and statins, modified lipoproteins and retinal-specific effects of lipid-lowering drugs. Dysregulation of retinal-specific cholesterol metabolism leading to retinal cholesterol accumulation and potential formation of cholesterol crystals are also addressed.

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.

Diabetic retinopathy and visual impairment in a Norwegian diabetic coast population with a high dietary intake of fish oils. An observational study

PURPOSE

To present retinal and visual findings in a Norwegian west coast diabetic population and to elucidate the effect of dietary intake of marine polyunsaturated fatty acids (PUFAs) on the development of diabetic retinopathy (DR).

METHODS

In an eye practice in an archipelago of 314 km², serving a population of about 40 000, we recorded the prevalence of visual impairment and DR in a referred diabetic population. 510 consecutive patients were included, 238 females and 272 males. 50 patients had type I and 460 had type II diabetes mellitus (DM). Self-reported medication, diet supplements, HbA1c and fish consumption were registered.

RESULTS

In the type I group, the median age was 44.5 and median DM duration 11.5 years [1-44]. 48% had photographic evidence of DR, 8 patients (16%) had proliferative retinopathy (PDR), and 6 patients (12%) had diabetic macular oedema (DME). All had best-corrected visual acuity (BCVA) of 0.5 (log MAR 0.3) or better in the best eye. In the type II group, the median DM duration was 8 years [1-53], and median age was 66. 98% had best eye BCVA at or better than 0.5 (log MAR 0.3) in the best eye.

CONCLUSION

None of the 510 patients had BCVA worse than 0.3 (log MAR 0.48) due to diabetic retinopathy. Compared to similar studies, we found a very low visual impairment rate. A possible protective effect of PUFA on the prevalence and progression of diabetic microangiopathy including retinopathy is discussed.

Key Role of 12-Lipoxygenase and Its Metabolite 12-Hydroxyeicosatetraenoic Acid (12-HETE) in Diabetic Retinopathy

PURPOSE

Abnormal lipid metabolism has been proved to be implicated in the complex pathogenesis of diabetic retinopathy (DR). 12-lipoxygenase (12-LOX) is a member of lipoxygenase family responsible for the oxygenation of cellular polyunsaturated fatty acids to produce lipid mediators which modulate cell inflammation. This review explores the role of 12-lipoxygenase and its products in the pathogenesis of DR.

METHODS

A comprehensive medical literature search was conducted on PubMed till September 2021.

RESULTS

Emerging evidence has demonstrated that 12-LOX and its main product 12- hydroxyeicosatetraenoic acid (12-HETE) activate retinal cells, especially retinal vascular endothelial cells, through the activation of NADPH oxidase and the subsequent generation of reactive oxygen species (ROS), mediating multiple pathological changes during DR. Genetic deletion or pharmacological inhibition models of 12-LOX in mice show protection from DR.

CONCLUSION

12-LOX and its product 12-HETE take important part in DR pathogenesis and show their potential as future therapeutic targets for DR. Further studies are needed on the specific mechanism including 12-LOX pathway related molecules, 12-HETE receptors and downstream signaling pathways.

Metabolomic comparison followed by cross-validation of enzyme-linked immunosorbent assay to reveal potential biomarkers of diabetic retinopathy in Chinese with type 2 diabetes

PURPOSE

To identify the biomarkers in the critical period of development in diabetic retinopathy (DR) in Chinese with type 2 diabetes using targeted and untargeted metabolomics, and to explore the feasibility of their clinical application.

METHODS

This case-control study described the differential metabolites between 83 Chinese type 2 diabetes mellitus (T2DM) samples with disease duration ≥ 10 years and 27 controls matched cases. Targeted metabolomics using high-resolution mass spectrometry with liquid chromatography was performed on plasma samples of subjects. The results were compared to our previous untargeted metabolomics study and ELISA was performed to validate the mutual differential metabolites of targeted and untargeted metabolomics on plasma. Multiple linear regression analyses were performed to adjust for the significance of different metabolites between groups.

RESULT

Mean age of the subjects was 66.3 years and mean T2DM duration was 16.5 years. By cross-validating with results from previous untargeted metabolomic assays, we found that L-Citrulline (Cit), indoleacetic acid (IAA), 1-methylhistidine (1-MH), phosphatidylcholines (PCs), hexanoylcarnitine, chenodeoxycholic acid (CDCA) and eicosapentaenoic acid (EPA) were the most distinctive metabolites biomarkers to distinguish the severity of DR for two different metabolomic approaches in our study. We mainly found that samples in the DR stage showed lower serum level of Cit and higher serum level of IAA compared with samples in the T2DM stage, while during the progression of diabetic retinopathy, the serum levels of CDCA and EPA in PDR stage were significantly lower than NPDR stage. Among them, 4 differential key metabolites including Cit, IAA, CDCA and EPA were confirmed with ELISA.

CONCLUSION

This is the first study to compare the results of targeted and untargeted metabolomics via liquid chromatography-mass spectrometry to find the serum biomarkers which could reflect the metabolic variations among different stages of DR in Chinese. The progression of DR in Chinese at different critical stages was related to the serum levels of specific differential metabolites, of which there is a significant correlation between DR progression and increased IAA and decreased Cit, hexanoylcarnitine, CDCA, and EPA. However, larger studies are needed to confirm our results. Based on this study, it could be inferred that the accuracy of targeted metabolomics for metabolite expression in serum is to some extent higher than that of untargeted metabolomics.

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.

Glucose-mediated de novo lipogenesis in photoreceptors drives early diabetic retinopathy

Diabetic retinopathy (DR) is an increasingly frequent cause of blindness across populations; however, the events that initiate pathophysiology of DR remain elusive. Strong preclinical and clinical evidence suggests that abnormalities in retinal lipid metabolism caused by diabetes may account for the origin of this disease. A major arm of lipid metabolism, de novo biosynthesis, is driven by elevation in available glucose, a common thread binding all forms of vision loss in diabetes. Therefore, we hypothesized that aberrant retinal lipid biogenesis is an important promoter of early DR. In murine models, we observed elevations of diabetes-associated retinal de novo lipogenesis ∼70% over control levels. This shift was primarily because of activation of fatty acid synthase (FAS), a rate-limiting enzyme in the biogenic pathway. Activation of FAS was driven by canonical glucose-mediated disinhibition of acetyl-CoA carboxylase, a major upstream regulatory enzyme. Mutant mice expressing gain-of-function FAS demonstrated increased vulnerability to DR, whereas those with FAS deletion in rod photoreceptors maintained preserved visual responses upon induction of diabetes. Excess retinal de novo lipogenesis—either because of diabetes or because of FAS gain of function—was associated with modestly increased levels of palmitate-containing phosphatidylcholine species in synaptic membranes, a finding with as yet uncertain significance. These findings implicate glucose-dependent increases in photoreceptor de novo lipogenesis in the early pathogenesis of DR, although the mechanism of deleterious action of this pathway remains unclear.

Nano-scale resolution of native retinal rod disk membranes reveals differences in lipid composition

Photoreceptors rely on distinct membrane compartments to support their specialized function. Unlike protein localization, identification of critical differences in membrane content has not yet been expanded to lipids, due to the difficulty of isolating domain-specific samples. We have overcome this by using SMA to coimmunopurify membrane proteins and their native lipids from two regions of photoreceptor ROS disks. Each sample's copurified lipids were subjected to untargeted lipidomic and fatty acid analysis. Extensive differences between center (rhodopsin) and rim (ABCA4 and PRPH2/ROM1) samples included a lower PC to PE ratio and increased LC- and VLC-PUFAs in the center relative to the rim region, which was enriched in shorter, saturated FAs. The comparatively few differences between the two rim samples likely reflect specific protein-lipid interactions. High-resolution profiling of the ROS disk lipid composition gives new insights into how intricate membrane structure and protein activity are balanced within the ROS, and provides a model for future studies of other complex cellular structures.

Fasting and fasting-mimicking treatment activate SIRT1/LXRα and alleviate diabetes-induced systemic and microvascular dysfunction

AIMS/HYPOTHESIS

Homo sapiens evolved under conditions of intermittent food availability and prolonged fasting between meals. Periods of fasting are important for recovery from meal-induced oxidative and metabolic stress, and tissue repair. Constant high energy-density food availability in present-day society contributes to the pathogenesis of chronic diseases, including diabetes and its complications, with intermittent fasting (IF) and energy restriction shown to improve metabolic health. We have previously demonstrated that IF prevents the development of diabetic retinopathy in a mouse model of type 2 diabetes (db/db); however the mechanisms of fasting-induced health benefits and fasting-induced risks for individuals with diabetes remain largely unknown. Sirtuin 1 (SIRT1), a nutrient-sensing deacetylase, is downregulated in diabetes. In this study, the effect of SIRT1 stimulation by IF, fasting-mimicking cell culture conditions (FMC) or pharmacological treatment using SRT1720 was evaluated on systemic and retinal metabolism, systemic and retinal inflammation and vascular and bone marrow damage.

METHODS

The effects of IF were modelled in vivo using db/db mice and in vitro using bovine retinal endothelial cells or rat retinal neuroglial/precursor R28 cell line serum starved for 24 h. mRNA expression was analysed by quantitative PCR (qPCR). SIRT1 activity was measured via histone deacetylase activity assay. NR1H3 (also known as liver X receptor alpha [LXRα]) acetylation was measured via western blot analysis.

RESULTS

IF increased Sirt1 mRNA expression in mouse liver and retina when compared with non-fasted animals. IF also increased SIRT1 activity eightfold in mouse retina while FMC increased SIRT1 activity and expression in retinal endothelial cells when compared with control. Sirt1 expression was also increased twofold in neuronal retina progenitor cells (R28) after FMC treatment. Moreover, FMC led to SIRT1-mediated LXRα deacetylation and subsequent 2.4-fold increase in activity, as measured by increased mRNA expression of the genes encoding ATP-binding cassette transporter (Abca1 and Abcg1). These changes were reduced when retinal endothelial cells expressing a constitutively acetylated LXRα mutant were tested. Increased SIRT1/LXR/ABC-mediated cholesterol export resulted in decreased retinal endothelial cell cholesterol levels. Direct activation of SIRT1 by SRT1720 in db/db mice led to a twofold reduction of diabetes-induced inflammation in the retina and improved diabetes-induced visual function impairment, as measured by electroretinogram and optokinetic response. In the bone marrow, there was prevention of diabetes-induced myeloidosis and decreased inflammatory cytokine expression.

CONCLUSIONS/INTERPRETATION

Taken together, activation of SIRT1 signalling by IF or through pharmacological activation represents an effective therapeutic strategy that provides a mechanistic link between the advantageous effects associated with fasting regimens and prevention of microvascular and bone marrow dysfunction in diabetes.

Metabolomics-based multidimensional network biomarkers for diabetic retinopathy identification in patients with type 2 diabetes mellitus

INTRODUCTION

Despite advances in diabetic retinopathy (DR) medications, early identification is vitally important for DR administration and remains a major challenge. This study aims to develop a novel system of multidimensional network biomarkers (MDNBs) based on a widely targeted metabolomics approach to detect DR among patients with type 2 diabetes mellitus (T2DM) efficiently.

RESEARCH DESIGN AND METHODS

In this propensity score matching-based case-control study, we used ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry system for serum metabolites assessment of 69 pairs of patients with T2DM with DR (cases) and without DR (controls). Comprehensive analysis, including principal component analysis, orthogonal partial least squares discriminant analysis, generalized linear regression models and a 1000-times permutation test on metabolomics characteristics were conducted to detect candidate MDNBs depending on the discovery set. Receiver operating characteristic analysis was applied for the validation of capability and feasibility of MDNBs based on a separate validation set.

RESULTS

We detected 613 features (318 in positive and 295 in negative ESI modes) in which 63 metabolites were highly relevant to the presence of DR. A panel of MDNBs containing linoleic acid, nicotinuric acid, ornithine and phenylacetylglutamine was determined based on the discovery set. Depending on the separate validation set, the area under the curve (95% CI), sensitivity and specificity of this MDNBs system were 0.92 (0.84 to 1.0), 96% and 78%, respectively.

CONCLUSIONS

This study demonstrates that metabolomics-based MDNBs are associated with the presence of DR and capable of distinguishing DR from T2DM efficiently. Our data also provide new insights into the mechanisms of DR and the potential value for new treatment targets development. Additional studies are needed to confirm our findings.

Lipid metabolism dysregulation in diabetic retinopathy

Lipid metabolic abnormalities have emerged as potential risk factors for the development and progression of diabetic complications, including diabetic retinopathy (DR). This review article provides an overview of the results of clinical trials evaluating the potential benefits of lipid-lowering drugs, such as fibrates, omega-3 fatty acids, and statins, for the prevention and treatment of DR. Although several clinical trials demonstrated that treatment with fibrates leads to improvement of DR, there is a dissociation between the protective effects of fibrates in the retina, and the intended blood lipid classes, including plasma triglycerides, total cholesterol, or HDL:LDL cholesterol ratio. Guided by these findings, plasma lipid and lipoprotein-independent mechanisms are addressed based on clinical, cell culture, and animal model studies. Potential retinal-specific effects of fatty acid oxidation products, cholesterol, and ceramide, as well as lipid-independent effects of PPAR alpha activation, are summarized based on the current literature. Overall, this review highlights promising potential of lipid-based treatment strategies further enhanced by the new knowledge of intraretinal lipids and lipoproteins in DR.

Association of n-6 PUFAs with the risk of diabetic retinopathy in diabetic patients

Diabetic retinopathy (DR), the most common microvascular complication of diabetes and leading cause of visual impairment in adults worldwide, is suggested to be linked to abnormal lipid metabolism. The present study aims to comprehensively investigate the relationship between n-6 polyunsaturated fatty acids (PUFAs) and DR. This was a propensity score matching based case-control study, including 69 pairs of DR patients and type 2 diabetic patients without DR with mean age of 56.7 ± 9.2 years. Five n-6 PUFAs were determined by UPLC-ESI-MS/MS system. Principle component regression (PCR) and multiple conditional logistic regression models were used to investigate the association of DR risk with n-6 PUFAs depending on independent training and testing sets, respectively. According to locally weighted regression model, we observed obvious negative correlation between levels of five n-6 PUFAs (linoleic acid, γ-linolenic acid, eicosadienoic acid, dihomo-γ-linolenic acid and arachidonicacid) and DR. Based on multiple PCR model, we also observed significant negative association between the five n-6 PUFAs and DR with adjusted OR (95% CI) as 0.62 (0.43,0.87). When being evaluated depending on the testing set, the association was still existed, and PCR model had excellent classification performance, in which area under the curve (AUC) was 0.88 (95% CI: 0.78, 0.99). In addition, the model also had valid calibration with a non-significant Hosmer-Lemeshow Chi-square of 9.44 (P = 0.307) in the testing set. n-6 PUFAs were inversely associated with the presence of DR, and the principle component could be potential indicator in distinguishing DR from other T2D patients.

Efficient Enrichment of Retinal DHA with Dietary Lysophosphatidylcholine-DHA: Potential Application for Retinopathies

Although decreased retinal docosahexaenoic acid (DHA) is a known risk factor for retinopathy, currently available omega-3 fatty acid supplements, which are absorbed as triacylglycerol (TAG), do not significantly enrich retinal DHA. We tested the hypothesis that lysophospahtidylcholine (LPC)-DHA which is absorbed as phospholipid, would efficiently increase retinal DHA because of the presence of LPC-specific transporter at the blood–retina barrier. In normal rats, LPC-DHA and di-DHA phosphatidylcholine (PC), which generates LPC-DHA during digestion, increased retinal DHA by 101% and 45%, respectively, but TAG-DHA had no significant effect at the same dose (40 mg/kg, 30 days). In normal mice, both sn-1 DHA LPC and sn-2 DHA LPC increased retinal DHA by 80%, but free DHA had no effect. Lipase-treated krill oil (which contains LPC-DHA and LPC-EPA (eicosapentaenoic acid), but not normal krill oil (which has little LPC), increased both retinal DHA (+76%) and EPA (100-fold). Fish oil, however, had no effect, whether lipase-treated or not. These studies show that retinal DHA can be efficiently increased by dietary LPC-DHA, but not by TAG-DHA or free DHA. Since DHA is known to be protective against retinopathy and other eye diseases, this study provides a novel nutraceutical approach for the prevention/treatment of these diseases.

Omega 3 Improves Both apoB100-containing Lipoprotein Turnover and their Sphingolipid Profile in Hypertriglyceridemia

CONTEXT

Evidence for an association between sphingolipids and metabolic disorders is increasingly reported. Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) improve apolipoprotein B100 (apoB100)-containing lipoprotein metabolism, but their effects on the sphingolipid content in lipoproteins remain unknown.

OBJECTIVES

In subjects with hypertriglyceridemia, we analyzed the effect of n-3 LC-PUFAs on the turnover apoB100-containing lipoproteins and on their sphingolipid content and looked for the possible association between these lipid levels and apoB100-containing lipoprotein turnover parameters.

METHODS

Six subjects underwent a kinetic study before and after n-3 supplementation for 2 months with 1 g of fish oil 3 times day containing 360 mg of eicosapentaenoic acid (EPA) and 240 mg of docosahexaenoic acid (DHA) in the form of triglycerides. We examined apoB100-containing lipoprotein turnover by primed perfusion labeled [5,5,5-2H3]-leucine and determined kinetic parameters using a multicompartmental model. We quantified sphingolipid species content in lipoproteins using mass spectrometry.

RESULTS

Supplementation decreased very low-density lipoprotein (VLDL), triglyceride, and apoB100 concentrations. The VLDL neutral and polar lipids showed increased n-3 LC-PUFA and decreased n-6 LC-PUFA content. The conversion rate of VLDL1 to VLDL2 and of VLDL2 to LDL was increased. We measured a decrease in total apoB100 production and VLDL1 production. Supplementation reduced the total ceramide concentration in VLDL while the sphingomyelin content in LDL was increased. We found positive correlations between plasma palmitic acid and VLDL ceramide and between VLDL triglyceride and VLDL ceramide, and inverse correlations between VLDL n-3 LC-PUFA and VLDL production.

CONCLUSION

Based on these results, we hypothesize that the improvement in apoB100 metabolism during n-3 LC-PUFA supplementation is contributed to by changes in sphingolipids.

Mitochondrial Ceramide Effects on the Retinal Pigment Epithelium in Diabetes

Mitochondrial damage in the cells comprising inner (retinal endothelial cells) and outer (retinal pigment epithelium (RPE)) blood-retinal barriers (BRB) is known to precede the initial BRB breakdown and further histopathological abnormalities in diabetic retinopathy (DR). We previously demonstrated that activation of acid sphingomyelinase (ASM) is an important early event in the pathogenesis of DR, and recent studies have demonstrated that there is an intricate connection between ceramide and mitochondrial function. This study aimed to determine the role of ASM-dependent mitochondrial ceramide accumulation in diabetes-induced RPE cell damage. Mitochondria isolated from streptozotocin (STZ)-induced diabetic rat retinas (7 weeks duration) showed a 1.64 ± 0.29-fold increase in the ceramide-to-sphingomyelin ratio compared to controls. Conversely, the ceramide-to-sphingomyelin ratio was decreased in the mitochondria isolated from ASM-knockout mouse retinas compared to wild-type littermates, confirming the role of ASM in mitochondrial ceramide production. Cellular ceramide was elevated 2.67 ± 1.07-fold in RPE cells derived from diabetic donors compared to control donors, and these changes correlated with increased gene expression of IL-1β, IL-6, and ASM. Treatment of RPE cells derived from control donors with high glucose resulted in elevated ASM, vascular endothelial growth factor (VEGF), and intercellular adhesion molecule 1 (ICAM-1) mRNA. RPE from diabetic donors showed fragmented mitochondria and a 2.68 ± 0.66-fold decreased respiratory control ratio (RCR). Treatment of immortalized cell in vision research (ARPE-19) cells with high glucose resulted in a 25% ± 1.6% decrease in citrate synthase activity at 72 h. Inhibition of ASM with desipramine (15 μM, 1 h daily) abolished the decreases in metabolic functional parameters. Our results are consistent with diabetes-induced increase in mitochondrial ceramide through an ASM-dependent pathway leading to impaired mitochondrial function in the RPE cells of the retina.

Retinopathy in a Diet-Induced Type 2 Diabetic Rat Model and Role of Epigenetic Modifications

Type 2 diabetes accounts for 90% of the population with diabetes, and these patients are generally obese and hyperlipidemic. In addition to hyperglycemia, hyperlipidemia is also closely related with diabetic retinopathy. The aim was to investigate retinopathy in a model closely mimicking the normal progression and metabolic features of the population with type 2 diabetes and elucidate the molecular mechanism. Retinopathy was evaluated in rats fed a 45% kcal as fat diet for 8 weeks before administering streptozotocin, 30 mg/kg body weight (T2D), and compared with age- and duration-matched type 1 diabetic rats (T1D) (60 mg/kg streptozotocin). The role of epigenetic modifications in mitochondrial damage was evaluated in retinal microvasculature. T2D rats were obese and severely hyperlipidemic, with impaired glucose and insulin tolerance compared with age-matched T1D rats. While at 4 months of diabetes, T1D rats had no detectable retinopathy, T2D rats had significant retinopathy, their mitochondrial copy numbers were lower, and mtDNA and Rac1 promoter DNA methylation was exacerbated. At 6 months, retinopathy was comparable in T2D and T1D rats, suggesting that obesity exaggerates hyperglycemia-induced epigenetic modifications, accelerating mitochondrial damage and diabetic retinopathy. Thus, maintenance of good lifestyle and BMI could be beneficial in regulating epigenetic modifications and preventing/retarding retinopathy in patients with diabetes.

Environmental Signals on Microglial Function during Brain Development, Neuroplasticity, and Disease

Recent discoveries on the neurobiology of the immunocompetent cells of the central nervous system (CNS), microglia, have been recognized as a growing field of investigation on the interactions between the brain and the immune system. Several environmental contexts such as stress, lesions, infectious diseases, and nutritional and hormonal disorders can interfere with CNS homeostasis, directly impacting microglial physiology. Despite many encouraging discoveries in this field, there are still some controversies that raise issues to be discussed, especially regarding the relationship between the microglial phenotype assumed in distinct contexts and respective consequences in different neurobiological processes, such as disorders of brain development and neuroplasticity. Also, there is an increasing interest in discussing microglial–immune system cross-talk in health and in pathological conditions. In this review, we discuss recent literature concerning microglial function during development and homeostasis. In addition, we explore the contribution of microglia to synaptic disorders mediated by different neuroinflammatory outcomes during pre- and postnatal development, with long-term consequences impacting on the risk and vulnerability to the emergence of neurodevelopmental, neurodegenerative, and neuropsychiatric disorders.

Characterizing the Retinal Phenotype in the High-Fat Diet and Western Diet Mouse Models of Prediabetes

We sought to delineate the retinal features associated with the high-fat diet (HFD) mouse, a widely used model of obesity. C57BL/6 mice were fed either a high-fat (60% fat; HFD) or low-fat (10% fat; LFD) diet for up to 12 months. The effect of HFD on body weight and insulin resistance were measured. The retina was assessed by electroretinogram (ERG), fundus photography, permeability studies, and trypsin digests for enumeration of acellular capillaries. The HFD cohort experienced hypercholesterolemia when compared to the LFD cohort, but not hyperglycemia. HFD mice developed a higher body weight (60.33 g vs. 30.17g, p < 0.0001) as well as a reduced insulin sensitivity index (9.418 vs. 62.01, p = 0.0002) compared to LFD controls. At 6 months, retinal functional testing demonstrated a reduction in a-wave and b-wave amplitudes. At 12 months, mice on HFD showed evidence of increased retinal nerve infarcts and vascular leakage, reduced vascular density, but no increase in number of acellular capillaries compared to LFD mice. In conclusion, the HFD mouse is a useful model for examining the effect of prediabetes and hypercholesterolemia on the retina. The HFD-induced changes appear to occur slower than those observed in type 2 diabetes (T2D) models but are consistent with other retinopathy models, showing neural damage prior to vascular changes.

Emerging Insights and Interventions for Diabetic Retinopathy

PURPOSE OF REVIEW

To introduce recent advances in the understanding of diabetic retinopathy and to summarize current and emerging strategies to treat this common and complex cause of vision loss.

RECENT FINDINGS

Advances in retinal imaging and functional analysis indicate that retinal vascular and neural pathologies exist long before the development of clinically visible retinopathy. Such diagnostics could facilitate risk stratification and selective early intervention in high-risk patients. Antagonists of the vascular endothelial growth factor pathway effectively reduce vision loss in diabetes and promote regression of disease severity. Promising new strategies to treat diabetic retinopathy involve novel systemic diabetes therapy and ocular therapies that antagonize angiogenic growth factor signaling, improve blood-retina barrier function and neurovascular coupling, modulate neuroretinal metabolism, or provide neuroprotection. Long considered a pure microvasculopathy, diabetic retinopathy in fact affects the neural and vascular retina as well as neurovascular communication. Emerging therapies include those that target neuroretinal dysfunction in addition to those modulating vascular biology.

Alteration of erythrocyte membrane polyunsaturated fatty acids in preterm newborns with retinopathy of prematurity

Extremely preterm infants are at high risk for retinopathy of prematurity (ROP), a potentially blinding disease characterized by abnormalities in retinal vascularization. Whereas animal studies revealed that n-3 polyunsaturated fatty acids (PUFAs) may be of benefit in preventing ROP, human studies conducted on preterm infants during the 1^st weeks of life showed no association between blood n-3 PUFA bioavailability and ROP incidence and/or severity, probably because of the influence of nutrition on the lipid status of infants. In the OmegaROP prospective cohort study, we characterized the erythrocyte concentrations of PUFAs in preterm infants aged less than 29 weeks gestational age (GA) without any nutritional influence. We show that GA is positively associated with the erythrocyte n-6 to n-3 PUFA ratio, and particularly with the ratio of arachidonic acid (AA) to docosahexaenoic acid (DHA), in infants with ROP. A time-dependent accumulation of AA at the expense of DHA seems to occur in utero in erythrocytes of preterm infants who will develop ROP, thus reinforcing previous data on the beneficial properties of DHA on this disease. In addition, preliminary data on maternal erythrocyte membrane lipid concentrations suggest modifications in placental transfer of fatty acids. Documenting the erythrocyte AA to DHA ratio at birth in larger cohorts might be useful to set up new prognostic factors for ROP.

Role of ω3 polyunsaturated fatty acids in diabetic retinopathy: a morphological and metabolically cross talk among blood retina barriers damage, autoimmunity and chronic inflammation

Vision disorders are one of the most serious complications of diabetes mellitus (DM) affecting the quality of life of patients and eventually cause blindness. The ocular lesions in diabetes mellitus are located mainly in the blood vessels and retina layers. Different retina lesions could be grouped under the umbrella term of diabetic retinopathies (DMRP).

We propose that one of the main causes in the etiopathogenesis of the DMRP consists of a progressive loss of the selective permeability of blood retinal barriers (BRB). The loss of selective permeability of blood retinal barriers will cause a progressive autoimmune process. Prolonged autoimmune injures in the retinal territory will triggers and maintains a low-grade chronic inflammation process, microvascular alterations, glial proliferation and subsequent fibrosis and worse, progressive apoptosis of the photoreceptor neurons.

Patients with long-standing DM disturbances in retinal BRBs suffer of alterations in the enzymatic pathways of polyunsaturated fatty acids (PUFAs), increase release of free radicals and pro-inflammatory molecules and subsequently incremented levels of vascular endothelial growth factor. These facts can produce retinal edema and photoreceptor apoptosis.

Experimental, clinical and epidemiological evidences showing that adequate metabolic and alimentary controls and constant practices of healthy life may avoid, retard or make less severe the appearance of DMRP. Considering the high demand for PUFAs ω3 by photoreceptor complexes of the retina, it seems advisable to take fish oil supplements (2 g per day). The cellular, subcellular and molecular basis of the propositions exposed above is developed in this article.

Synthesizer drawings the most relevant findings of the ultrastructural pathology, as well as the main metabolic pathways of the PUFAs involved in balance and disbalanced conditions are provided.

Analysis of sphingolipid composition in human vitreous from control and diabetic individuals

OBJECTIVE

Sphingolipids have a fundamental role in many cellular processes, and they have been implicated in insulin resistance and Diabetes Mellitus (DM) and its complications, including diabetic retinopathy (DR). Little is known about how bioactive sphingolipids relate to retinopathies in human DM. In this study, we analyzed the sphingolipid composition of type 2 diabetic (T2DM) and non-diabetic human vitreous samples.

METHODS

We conducted an observational study on post-mortem human vitreous samples from non-diabetic (Controls; n = 4; age: 71.6 ± 11.0 years, mean ± SD) and type 2 diabetic (T2DM; n = 9; age: 67.0 ± 9.2 years) donors to identify changes in sphingolipid composition. Samples were analyzed by a triple quadrupole mass spectrometer and individual sphingolipid species were identified and quantified using established protocols.

RESULTS

The total quantity (pmol/mg) of ceramide (Cer), lactosylceramide (Lac-Cer), and sphingomyelin (SM) were increased in type 2 diabetic vitreous samples. Among individual species, we found a general trend of increase in the longer chain species of ceramides, hexosylceramides (Hex-Cer), Lac-Cer, and SM.

CONCLUSIONS

This study shows the presence of measurable levels of sphingolipids in human vitreous. The results indicate changes in sphingolipid composition in the vitreous due to type 2 diabetes, which could be connected to the disease pathologies of the retina, retinal vessels, vitreous and the surrounding tissues.

Endothelial Regenerative Capacity and Aging: Influence of Diet, Exercise and Obesity

Background:

The endothelium plays an important role in cardiovascular regulation, from blood flow to platelet aggregation, immune cell infiltration and demargination. A dysfunctional endo-thelium leads to the onset and progression of Cardiovascular Disease (CVD). The aging endothelium displays significant alterations in function, such as reduced vasomotor functions and reduced angio-genic capabilities. This could be partly due to elevated levels of oxidative stress and reduced endothe-lial cell turnover. Circulating angiogenic cells, such as Endothelial Progenitor Cells (EPCs) play a significant role in maintaining endothelial health and function, by supporting endothelial cell prolifera-tion, or via incorporation into the vasculature and differentiation into mature endothelial cells. Howev-er, these cells are reduced in number and function with age, which may contribute to the elevated CVD risk in this population. However, lifestyle factors, such as exercise, physical activity obesity, and dietary intake of omega-3 polyunsaturated fatty acids, nitrates, and antioxidants, significantly af-fect the number and function of these circulating angiogenic cells.

Conclusion:

This review will discuss the effects of advancing age on endothelial health and vascular regenerative capacity, as well as the influence of diet, exercise, and obesity on these cells, the mecha-nistic links and the subsequent impact on cardiovascular health

Omega-3 from Flaxseed Oil Protects Obese Mice Against Diabetic Retinopathy Through GPR120 Receptor

The chronic and low-grade inflammation induced by obesity seem to be the “first hit” to retinopathy associated to diabetes type 2. Herein, we hypothesized that omega-3 fatty acids from flaxseed oil enriched diet disrupt the pro-inflammatory status in the retina, protecting against retinopathy development. For eight weeks under a high-fat diet (HF), several physiological parameters were monitored to follow the metabolic homeostasis disruption. After this period, mice were treated with a HF substituted in part of lard by flaxseed oil (FS) for another eight weeks. Food behavior, weight gain, glucose and insulin sensitivity, electroretinography, RT-qPCR and western blots were carried out. The HF was able to induce a pro-inflammatory background in the retina, changing IL1β and TNFα. VEGF, a master piece of retinopathy, had early onset increased also induced by HF. The FS-diet was able to decrease inflammation and retinopathy and improved retinal electro stimuli compared to HF group. GPR120 and GPR40 (G Protein-Coupled Receptors 120 and 40), an omega-3 fatty acid receptors, were detected in the retina for the first time. FS-diet modulated the gene expression and protein content of these receptors. Thus, unsaturated fatty acids protect the retina from diabetes type 2 mice model from disease progression.

Differential composition of DHA and very-long-chain PUFAs in rod and cone photoreceptors

Long-chain PUFAs (LC-PUFAs; C20-C22; e.g., DHA and arachidonic acid) are highly enriched in vertebrate retina, where they are elongated to very-long-chain PUFAs (VLC-PUFAs; C 28) by the elongation of very-long-chain fatty acids-4 (ELOVL4) enzyme. These fatty acids play essential roles in modulating neuronal function and health. The relevance of different lipid requirements in rods and cones to disease processes, such as age-related macular degeneration, however, remains unclear. To better understand the role of LC-PUFAs and VLC-PUFAs in the retina, we investigated the lipid compositions of whole retinas or photoreceptor outer segment (OS) membranes in rodents with rod- or cone-dominant retinas. We analyzed fatty acid methyl esters and the molecular species of glycerophospholipids (phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine) by GC-MS/GC-flame ionization detection and ESI-MS/MS, respectively. We found that whole retinas and OS membranes in rod-dominant animals compared with cone-dominant animals had higher amounts of LC-PUFAs and VLC-PUFAs. Compared with those of rod-dominant animals, retinas and OS membranes from cone-dominant animals also had about 2-fold lower levels of di-DHA (22:6/22:6) molecular species of glycerophospholipids. Because PUFAs are necessary for optimal G protein-coupled receptor signaling in rods, these findings suggest that cones may not have the same lipid requirements as rods.

Enteral Arg-Gln Dipeptide Administration Increases Retinal Docosahexaenoic Acid and Neuroprotectin D1 in a Murine Model of Retinopathy of Prematurity

Purpose

Low levels of the long chain polyunsaturated fatty acid (LCPUFA) docosahexaenoic acid (DHA) have been implicated in retinopathy of prematurity (ROP). However, oral DHA suffers from poor palatability and is associated with increased bleeding in premature infants. We asked whether oral administration of the neutraceutical arginine-glutamine (Arg-Glu) could increase retinal DHA and improve outcomes in a mouse model of oxygen-induced retinopathy (OIR).

Methods

Postnatal day 7 (P7) pups were maintained at 75% oxygen for 5 days and then returned to room air on P12. Pups were gavaged twice daily with Arg-Gln or vehicle from P12 to P17 and eyes were harvested for analysis on P17. Vaso-obliteration and vascular density were assessed on retinal flat mounts and preretinal neovascularization was assessed on retinal cross sections. Retinas were used for measurement of DHA and 10,17S-docosatriene (neuroprotectin D1, NPD1), a key DHA-derived lipid, and for analysis by reverse-phase protein array (RPPA).

Results

With Arg-Gln treatment, retinal DHA and NPD1 levels were increased in OIR pups. Arg-Gln reduced preretinal neovascularization by 39 ± 6% (P < 0.05) relative to vehicle control. This was accompanied by a restoration of vascular density of the retina in the pups treated with Arg-Gln (73.0 ± 3.0%) compared to vehicle (53.1 ± 3.4%; P < 0.05). Arg-Gln dipeptide restored OIR-induced signaling changes toward normoxia and was associated with normalization of insulin-like growth factor receptor 1 signaling and reduction of apoptosis and an increase in anti-apoptosis proteins.

Conclusions

Arg-Gln may serve as a safer and easily tolerated nutraceutical agent for prevention or treatment of ROP.

Loss of Angiotensin-Converting Enzyme 2 Exacerbates Diabetic Retinopathy by Promoting Bone Marrow Dysfunction

Angiotensin-converting enzyme 2 (ACE2) is the primary enzyme of the vasoprotective axis of the renin angiotensin system (RAS). We tested the hypothesis that loss of ACE2 would exacerbate diabetic retinopathy by promoting bone marrow dysfunction. ACE2^-/y were crossed with Akita mice, a model of type 1 diabetes. When comparing the bone marrow of the ACE2^-/y -Akita mice to that of Akita mice, we observed a reduction of both short-term and long-term repopulating hematopoietic stem cells, a shift of hematopoiesis toward myelopoiesis, and an impairment of lineage^- c-kit⁺ hematopoietic stem/progenitor cell (HS/PC) migration and proliferation. Migratory and proliferative dysfunction of these cells was corrected by exposure to angiotensin-1-7 (Ang-1-7), the protective peptide generated by ACE2. Over the duration of diabetes examined, ACE2 deficiency led to progressive reduction in electrical responses assessed by electroretinography and to increases in neural infarcts observed by fundus photography. Compared with Akita mice, ACE2^-/y -Akita at 9-months of diabetes showed an increased number of acellular capillaries indicative of more severe diabetic retinopathy. In diabetic and control human subjects, CD34⁺ cells, a key bone marrow HS/PC population, were assessed for changes in mRNA levels for MAS, the receptor for Ang-1-7. Levels were highest in CD34⁺ cells from diabetics without retinopathy. Higher serum Ang-1-7 levels predicted protection from development of retinopathy in diabetics. Treatment with Ang-1-7 or alamandine restored the impaired migration function of CD34⁺ cells from subjects with retinopathy. These data support that activation of the protective RAS within HS/PCs may represents a therapeutic strategy for prevention of diabetic retinopathy. Stem Cells 2018;36:1430-1440.

Vascular stem/progenitor cells: functions and signaling pathways

Vascular stem/progenitor cells (VSCs) are an important source of all types of vascular cells needed to build, maintain, repair, and remodel blood vessels. VSCs, therefore, play critical roles in the development, normal physiology, and pathophysiology of numerous diseases. There are four major types of VSCs, including endothelial progenitor cells (EPCs), smooth muscle progenitor cells (SMPCs), pericytes, and mesenchymal stem cells (MSCs). VSCs can be found in bone marrow, circulating blood, vessel walls, and other extravascular tissues. During the past two decades, considerable progress has been achieved in the understanding of the derivation, surface markers, and differentiation of VSCs. Yet, the mechanisms regulating their functions and maintenance under normal and pathological conditions, such as in eye diseases, remain to be further elucidated. Owing to the essential roles of blood vessels in human tissues and organs, understanding the functional properties and the underlying molecular basis of VSCs is of critical importance for both basic and translational research.

Models of retinal diseases and their applicability in drug discovery

INTRODUCTION

The impact of vision debilitating diseases is a global public health concern, which will continue until effective preventative and management protocols are developed. Two retinal diseases responsible for the majority of vision loss in the working age adults and elderly populations are diabetic retinopathy (DR) and age-related macular degeneration (AMD), respectively. Model systems, which recapitulate aspects of human pathology, are valid experimental modalities that have contributed to the identification of signaling pathways involved in disease development and consequently potential therapies. Areas covered: The pathology of DR and AMD, which serve as the basis for designing appropriate models of disease, is discussed. The authors also review in vitro and in vivo models of DR and AMD and evaluate the utility of these models in exploratory and pre-clinical studies. Expert opinion: The complex nature of non-Mendelian diseases such as DR and AMD has made identification of effective therapeutic treatments challenging. However, the authors believe that while in vivo models are often criticized for not being a 'perfect' recapitulation of disease, they have been valuable experimentally when used with consideration of the strengths and limitations of the experimental model selected and have a place in the drug discovery process.

Dietary intake and diabetic retinopathy: A systematic review

INTRODUCTION

The evidence linking dietary intake with diabetic retinopathy (DR) is growing but unclear. We conducted a systematic review of the association between dietary intake and DR.

METHODS

We systematically searched PubMed, Embase, Medline, and the Cochrane Central register of controlled trials, for publications between January 1967 and January 2017 using standardized criteria for diet and DR. Interventional and observational studies investigating micro- and macro-nutrient intakes; food and beverage consumptions; and dietary patterns were included. Study quality was evaluated using a modified Newcastle-Ottawa scale for observational studies, and the Cochrane collaboration tool for interventional studies.

RESULTS

Of 4265 titles initially identified, 31 studies (3 interventional, 28 Observational) were retained. Higher intakes of dietary fibre, oily fish, and greater adherence to a Mediterranean diet were protective of DR. Conversely, high total caloric intake was associated with higher risk of DR. No significant associations of carbohydrate, vitamin D, and sodium intake with DR were found. Associations of antioxidants, fatty acids, proteins and alcohol with DR remain equivocal.

CONCLUSIONS

Dietary fibre, oily fish, a Mediterranean diet and a reduced caloric intake are associated with lower risk of DR. Longitudinal data and interventional models are warranted to confirm our findings and better inform clinical guidelines.

COMBINED INTRAVITREAL RANIBIZUMAB AND ORAL SUPPLEMENTATION WITH DOCOSAHEXAENOIC ACID AND ANTIOXIDANTS FOR DIABETIC MACULAR EDEMA: Two-Year Randomized Single-Blind Controlled Trial Results

PURPOSE

To assess the 2-year effectiveness of intravitreal ranibizumab combined with a dietary supplement rich in docosahexaenoic acid (DHA) plus antioxidants in 62 patients with diabetic macular edema.

METHODS

In a randomized single-blind controlled study, 33 subjects (42 eyes) received intravitreal ranibizumab alone and 29 (34 eyes) combined with DHA (1,050 mg/day). Monthly ranibizumab (0.5 mg) was given for the first 4 months followed by on as-needed treatment.

RESULTS

At 24 months, the difference between groups in the decrease of central subfield macular thickness was significant in favor of the DHA supplementation group (95% confidence interval of the difference 7.20-97.656; P = 0.024), although improvement in best-corrected visual acuity measured in the Early Treatment Diabetic Retinopathy Study letters did not reach statistical significance (95% confidence interval 5.4-11.2, P < 0.66). At 24 months, gains of >5 and >10 letters were significantly higher in the DHA supplementation group as compared with controls when the worse and better seeing eyes were considered but other differences at 12 months and 24 months were not found.

CONCLUSION

Intravitreal ranibizumab combined with DHA supplementation reduced central subfield macular thickness after 2 years of follow-up as compared with ranibizumab alone in patients with diabetic macular edema. This anatomical improvement was accompanied by a trend for an amelioration of vision.