The role of dyslipidemia in diabetic retinopathy

QiMing granules for diabetic retinopathy: a systematic review and meta-analysis of randomized controlled trials

Objective

This study aimed to assess the efficacy and safety of QiMing granules (QM) in the treatment of patients with diabetic retinopathy (DR).

Methods

We systematically searched multiple databases, including Pubmed, Embase, Web of Science, Cochrane Library, SinoMed, Chinese National Knowledge Infrastructure (CNKI), Wanfang database, and VIP database. Randomized controlled trials (RCTs) of QM in the treatment of DR were collected, and the search time limit was from the establishment of the database to 27 March 2024. Two independent researchers were involved in literature screening, data extraction, and bias risk assessment. The risk of bias in the included studies was assessed using the Risk of Bias Assessment tool for randomized controlled trials of Cochrane Collaboration 2.0 (RoB 2.0). The main outcomes were the overall efficacy, visual acuity, retinal circulation time, macular thickness. The secondary outcomes were the levels of triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and glycated hemoglobin (HbA1c). The adverse events was considered the safety outcome. Review Manager 5.4.1 and Stata 15.1 were used for meta-analysis. Data were pooled by random-effects or fixed-effects model to obtain the mean difference (MD), risk ratio (RR), and 95% confidence interval (CI).

Results

A total of 33 RCTs involving 3,042 patients were included in this study. Overall, we demonstrated that QM had a significant clinical effect on DR. QM alone was superior to conventional treatment (CT) in terms of overall efficacy [RR = 1.45, 95% CI: (1.34, 1.58), p < 0.00001, moderate certainty], retinal circulation time [MD = -0.56, 95% CI: (-1.01, -0.12), p = 0.01] and macular thickness [MD = -11.99, 95% CI: (-23.15, -0.83), p = 0.04]. QM plus CT was superior to CT in terms of overall efficacy [RR = 1.29, 95% CI: (1.24, 1.33), p < 0.00001], visual acuity [MD = 0.14, 95% CI: (0.11, 0.17), p < 0.00001], macular thickness [MD = -14.70, 95% CI: (-21.56, -7.83), p < 0.0001], TG [MD = -0.20, 95% CI: (-0.33, -0.08), p = 0.001, moderate certainty], TC [MD = -0.57, 95% CI: (-1.06, -0.07), p = 0.02], and LDL-C [MD = -0.36, 95% CI: (-0.70, -0.03), p = 0.03]. In terms of safety, the incidence of adverse events in the experimental group was less than that in the control group. The results of the GRADE evidence quality evaluation showed that the evidence quality of outcome indicators was mostly low.

Conclusion

QM can effectively improve overall efficacy, visual acuity, macular thickness, retinal circulation time, and reduce the levels of TG, TC, and LDL-C. However, due to the limited number of studies included, a small sample size, and a lack of high-quality literature, the possibility of publication bias cannot be excluded. Moreover, biases are present due to differences in study design, such as the absence of placebo use in the control group and a predominant use of combined intervention designs in the control group, along with deficiencies in allocation concealment and blinding methods. Therefore, more multi-center, large-sample, and rigorously designed studies are needed to substantiate this conclusion.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/#recordDetails, identifier CRD42023465165.

Diagnostic application in streptozotocin-induced diabetic retinopathy rats: A study based on Raman spectroscopy and machine learning

Vision impairment caused by diabetic retinopathy (DR) is often irreversible, making early-stage diagnosis imperative. Raman spectroscopy emerges as a powerful tool, capable of providing molecular fingerprints of tissues. This study employs RS to detect ex vivo retinal tissue from diabetic rats at various stages of the disease. Transmission electron microscopy was utilized to reveal the ultrastructural changes in retinal tissue. Following spectral preprocessing of the acquired data, the random forest and orthogonal partial least squares-discriminant analysis algorithms were employed for spectral data analysis. The entirety of Raman spectra and all annotated bands accurately and distinctly differentiate all animal groups, and can identify significant molecules from the spectral data. Bands at 524, 1335, 543, and 435 cm-1 were found to be associated with the preproliferative phase of DR. Bands at 1045 and 1335 cm-1 were found to be associated with early stages of DR.

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.

Statins as a risk factor for diabetic retinopathy: a Mendelian randomization and cross-sectional observational study

BACKGROUND

Diabetic retinopathy (DR) is the foremost cause of vision loss among the global working-age population, and statins are among the most frequently prescribed drugs for lipid management in patients with DR. The exact relationship between statins and DR has not been determined. This study sought to validate the causal association between statins usage and diabetic retinopathy.

METHODS

The summary-data-based Mendelian randomization (SMR) method and inverse-variance-weighted Mendelian randomization (IVW-MR) were used to identify the causal relationship between statins and DR via the use of expression quantitative trait loci (eQTL) data for 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) (31,684 blood samples), low density lipoprotein cholesterol-related GWAS data (sample size: 440,546), and DR-related GWAS data (14,584 cases and 176,010 controls). Additionally, a cross-sectional observational study based on the data from the National Health and Nutrition Examination Survey (NHANES) was conducted to supplement the association between DR and statins (sample size: 106,911). The odds ratios (ORs) with corresponding 95% confidence intervals (CIs) was employed to evaluate the results.

RESULTS

Based on the results of the MR analysis, HMGCR inhibitors were causally connected with a noticeably greater incidence of DR (IVW: OR = 0.54, 95% CI [0.42, 0.69], p = 0.000002; SMR: OR = 0.66, 95% CI [0.52, 0.84], p = 0.00073). Subgroup analysis revealed that the results were not affected by the severity of DR. The sensitivity analysis revealed the stability and reliability of the MR analysis results. The results from the cross-sectional study based on NHANES also support the association between not taking statins and a decreased risk of DR (OR = 0.54, 95% CI [0.37, 0.79], p = 0.001).

CONCLUSIONS

This study revealed that a significant increase in DR risk was causally related to statins use, providing novel insights into the role of statins in DR. However, further investigations are needed to verify these findings.

The role of statins in diabetic retinopathy

Diabetes mellitus is a growing global public health issue estimated to affect around 600 million people by 2040 [1]. It occurs in populations throughout the world, is increasing in both the developing world and high-income countries and also affects young, working-age people. Ocular involvement in diabetes occurs early in the disease and is present in over a third of diabetes mellitus Type 2 patients at the time of diagnosis. Blindness due to diabetic retinopathy (DR) remains a leading cause of adult-onset blindness, [1] which results from disruption of retinal vasculature, ischemia and its consequences and exudation causing macular edema. The prevalence of diabetic retinopathy is increasing at a greater rate than other causes of blindness including cataract, refractive errors, age-related macular degeneration and glaucoma. Compared to cataract and refractive error, management of diabetic retinopathy requires vast medical resources, including trained medical practitioners able to perform ocular injections and ophthalmologists for laser treatments and retinal surgery. This creates a significant burden on medical services as care for these patients lasts decades.

Generalized metabolic flux analysis framework provides mechanism-based predictions of ophthalmic complications in type 2 diabetes patients

Chronic metabolic diseases arise from changes in metabolic fluxes through biomolecular pathways and gene networks accumulated over the lifetime of an individual. While clinical and biochemical profiles present just real-time snapshots of the patients' health, efficient computation models of the pathological disturbance of biomolecular processes are required to achieve individualized mechanistic insights into disease progression. Here, we describe the Generalized metabolic flux analysis (GMFA) for addressing this gap. Suitably grouping individual metabolites/fluxes into pools simplifies the analysis of the resulting more coarse-grain network. We also map non-metabolic clinical modalities onto the network with additional edges. Instead of using the time coordinate, the system status (metabolite concentrations and fluxes) is quantified as function of a generalized extent variable (a coordinate in the space of generalized metabolites) that represents the system's coordinate along its evolution path and evaluates the degree of change between any two states on that path. We applied GMFA to analyze Type 2 Diabetes Mellitus (T2DM) patients from two cohorts: EVAS (289 patients from Singapore) and NHANES (517) from the USA. Personalized systems biology models (digital twins) were constructed. We deduced disease dynamics from the individually parameterized metabolic network and predicted the evolution path of the metabolic health state. For each patient, we obtained an individual description of disease dynamics and predict an evolution path of the metabolic health state. Our predictive models achieve an ROC-AUC in the range 0.79-0.95 (sensitivity 80-92%, specificity 62-94%) in identifying phenotypes at the baseline and predicting future development of diabetic retinopathy and cataract progression among T2DM patients within 3 years from the baseline. The GMFA method is a step towards realizing the ultimate goal to develop practical predictive computational models for diagnostics based on systems biology. This tool has potential use in chronic disease management in medical practice.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13755-023-00218-x.

Perilipin 2-positive mononuclear phagocytes accumulate in the diabetic retina and promote PPARγ-dependent vasodegeneration

Type 2 diabetes mellitus (T2DM), characterized by hyperglycemia and dyslipidemia, leads to nonproliferative diabetic retinopathy (NPDR). NPDR is associated with blood-retina barrier disruption, plasma exudates, microvascular degeneration, elevated inflammatory cytokine levels, and monocyte (Mo) infiltration. Whether and how the diabetes-associated changes in plasma lipid and carbohydrate levels modify Mo differentiation remains unknown. Here, we show that mononuclear phagocytes (MPs) in areas of vascular leakage in DR donor retinas expressed perilipin 2 (PLIN2), a marker of intracellular lipid load. Strong upregulation of PLIN2 was also observed when healthy donor Mos were treated with plasma from patients with T2DM or with palmitate concentrations typical of those found in T2DM plasma, but not under high-glucose conditions. PLIN2 expression correlated with the expression of other key genes involved in lipid metabolism (ACADVL, PDK4) and the DR biomarkers ANGPTL4 and CXCL8. Mechanistically, we show that lipid-exposed MPs induced capillary degeneration in ex vivo explants that was inhibited by pharmaceutical inhibition of PPARγ signaling. Our study reveals a mechanism linking dyslipidemia-induced MP polarization to the increased inflammatory cytokine levels and microvascular degeneration that characterize NPDR. This study provides comprehensive insights into the glycemia-independent activation of Mos in T2DM and identifies MP PPARγ as a target for inhibition of lipid-activated MPs in DR.

Hyperlipidemia and lipid-lowering therapy in diabetic retinopathy (DR): A bibliometric study and visualization analysis in 1993-2023

Background

Diabetic retinopathy (DR) is a common complication in diabetic patients. DR is also a neurodegenerative disease. Patients with hyperglycemia, hyperlipidemia, and hypertension are vulnerable to retinopathy development. While the roles of blood glucose and blood pressure in the development of retinopathy have been extensively studied, the relationship between body fat and DR pathogenesis and the impact of lipid-reducing drugs on DR has just emerged as a research hotspot in DR study. We aim to visualize the contributions and cooperation of reporters, organizations, and nations, in addition to the research hotspots and trends in DR-related lipid research from 1993 to 2023, by bibliometric analysis.

Methods

We extracted all publications about DR-related lipid research from 1993 to 2023 from the Web of Science Core Collection, and bibliometric features were studied using VOSviewer and the CiteSpace program.

Results

1402 documents were retrieved. The number of studies has risen consistently for three decades, from an average of 16.8/year in the 1990s to 28.8/year in the 2000s, 64.5/year in 2010s, and reached 112/year in 2020-2022, confirming they are hot research topic in the field. These reports were from 93 nations/regions, with the USA, China, Japan, Australia, and England taking the leading positions. Diabetes Research and Clinical Practice was the journal that published the most studies, and Diabetes Care was the most quoted. We identified 6979 authors, with Wong TY having the most papers and being the most commonly co-cited. The most popular keyword, according to our research, is diabetic retinopathy. Oxidative stress, diabetic macular edema (DME), lipid peroxidation, and other topics have often been investigated.

Conclusion

DR-related lipid research is conducted mainly in North America, Asia, Oceania, and Europe. Much study has centered on the relationship between lipid-lowering therapy and DR pathogenesis. These studies strongly support using lipid-reducing medications (fenofibrate, statins, and omega-3 PUFAs), combined with hyperglycemia and hypertension therapy, to prevent and treat DR. However, the impact of fenofibrate or statin on retinopathy is not correlated with their action on blood lipid profiles. Thus, more randomized clinical trials with primary endpoints related to DR in T1D or T2D are merited. In addition, the lipid biomarker for DR (lipid aldehydes, ALEs, and cholesterol crystals), the action of lipid-reducing medicines on retinopathy, the mechanism of lipid-lowering medications preventing or curing DR, and ocular delivery of lipid-lowering drugs to diabetic patients are predicted as the research focus in the future in the DR-related lipid research field.

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.

Lactucaxanthin Regulates the Cascade of Retinal Oxidative Stress, Endoplasmic Reticulum Stress and Inflammatory Signaling in Diabetic Rats

PURPOSE

The purpose of this study is to investigate the protective mechanism of lactucaxanthin against retinal angiogenesis in diabetic retinopathy.

METHODS

Streptozotocin-induced diabetic rats were orally gavaged with either lactucaxanthin or lutein (n=12/group) for 8 weeks. Serum and retina collected from euthanized rats were subjected to assess oxidative stress, ER stress and inflammatory response.

RESULTS

Lactucaxanthin administration was found to lower oxidative stress markers (protein carbonylation and lipid peroxidation) by augmenting antioxidant activity expression and ameliorated VEGF-A levels in diabetic group. Likewise, it suppressed the expression of ER stress (ATF4, ATF6, and XBP1), and inflammatory (TNF-α, IL-6, NF-κB, and ICAM-1) markers in diabetic retina. In addition, lactucaxanthin improved glucose tolerance and lipid profile under diabetic condition and suppressed the crosstalk between OS, ER stress, and inflammation.

CONCLUSION

Lactucaxanthin could be used as a promising therapeutic bioactive for treating DR condition, and retinal angiogenesis.

EXPERT OPINION

Limitation of the study includes the sample size and the duration of treatment. Despite these limitations, this study has revealed the potential of lactucaxanthin in treating eye related diabetic complications. To validate the results obtained from this study, clinical study must be performed to understand the relative benefit of lactucaxanthin in DR treatment.

Spleen Tyrosine Kinase Contributes to Müller Glial Expression of Proangiogenic Cytokines in Diabetes

Purpose

Neuroglial dysfunction occurs early in the progression of diabetic retinopathy. In response to diabetes or hypoxia, Müller glia secrete cytokines and growth factors that contribute to disease progression. This study was designed to examine common signaling pathways activated in Müller glia by both type 1 and pre-/type 2 diabetes.

Methods

RiboTag (Pdgfra-cre;HA-Rpl22) mice were used to compare the impact of streptozotocin (STZ) and a high-fat, high-sucrose (HFHS) diet on ribosome association of mRNAs in Müller glia by RNA sequencing analysis. Human MIO-M1 Müller cells were exposed to either hyperglycemic or hypoxic culture conditions. Genetic manipulation and pharmacologic inhibition were used to interrogate signaling pathways.

Results

Association of mRNAs encoding triggering receptor expressed on myeloid cells 2 (TREM2), DNAX-activating protein 12 kDa (DAP12), and colony stimulating factor 1 receptor (CSF1R) with ribosomes isolated from Müller glia was upregulated in both STZ diabetic mice and mice fed an HFHS diet. The TREM2/DAP12 receptor-adaptor complex signals in coordination with CSF1R to activate spleen tyrosine kinase (SYK). SYK activation was enhanced in the retina of diabetic mice and in human MIO-M1 Müller cell cultures exposed to hyperglycemic or hypoxic culture conditions. DAP12 knockdown reduced SYK autophosphorylation in Müller cells exposed to hyperglycemic or hypoxic conditions. SYK inhibition or DAP12 knockdown suppressed hypoxia-induced expression of the transcription factor hypoxia-inducible factor 1⍺ (HIF1⍺), as well as expression of vascular endothelial growth factor and angiopoietin-like 4.

Conclusions

The findings support TREM2/DAP12 receptor-adaptor complex signaling via SYK to promote HIF1α stabilization and increased angiogenic cytokine production by Müller glia.

Coadministration of Compound Danshen dripping pills and bezafibrate has a protective effect against diabetic retinopathy

Diabetic retinopathy (DR) is increasingly becoming a main complication of diabetes, and is difficult to cure. In our research, network pharmacology analysis suggested that both compound Danshen dripping pills (CDDP) and bezafibrate (BZF) have potential protective effects against DR and the two drugs may act synergistically. The pharmacological effects of the coadministration of CDDP and BZF were elucidated in db/db mice, which simulate DR. Fluorescein fundus angiography showed that coadministration attenuated vascular leakage. Optical coherence tomography and hematoxylin and eosin staining showed that coadministration improved retinal thickness better than CDDP monotherapy. In addition, cell fluorescence images of reactive oxygen species revealed that coadministration of CDDP and BZF had more potent effects against oxidative stress than CDDP monotherapy. Metabolomics analysis showed that coadministration reduced the ratio of oxidized glutathione to reduced glutathione further than CDDP monotherapy. Coadministration of CDDP and BZF may provide additional protective effects by resisting vascular leakage, increasing retinal thickness, and inhibiting inflammation and oxidative stress in DR.

Study on the Development of a Conceptual Framework to Identify the Risk Factors of Diabetic Retinopathy among Diabetic Patients: A Concept Paper

The most common complication of diabetes mellitus (DM) is diabetic retinopathy (DR). The control of DR risk factors is essential for the effective prevention of DR. There is currently a lack of research to guide DR-related research in Malaysia. This concept paper aimed to review published studies and propose a conceptual framework (CF) as a guide for future research to determine the prevalence of DR and its risk factors across DM patients. After a review of prior research, this study has presented a CF that takes into account these four key elements: the patient's sociodemographic characteristics, comorbidities, complications, and diabetes conditions, namely, the length of the disease and glycaemic control. In the suggested CF, ethnicity was highlighted as a crucial risk factor for DR across lower- to middle-income countries (LMIC) and multiracial countries. In order to guide future studies, scientific guidance is essential. The proposed CF would help future research to conduct scientific research related to DR. Also, the proposed CF was tailored to suit research across LMIC and multiracial countries.

Effect of cytokine-induced alterations in extracellular matrix composition on diabetic retinopathy-relevant endothelial cell behaviors

Retinal vascular basement membrane (BM) thickening is an early structural abnormality of diabetic retinopathy (DR). Recent studies suggest that BM thickening contributes to the DR pathological cascade; however, much remains to be elucidated about the exact mechanisms by which BM thickening develops and subsequently drives other pathogenic events in DR. Therefore, we undertook a systematic analysis to understand how human retinal microvascular endothelial cells (hRMEC) and human retinal pericytes (hRP) change their expression of key extracellular matrix (ECM) constituents when treated with diabetes-relevant stimuli designed to model the three major insults of the diabetic environment: hyperglycemia, dyslipidemia, and inflammation. TNFα and IL-1β caused the most potent and consistent changes in ECM expression in both hRMEC and hRP. We also demonstrate that conditioned media from IL-1β-treated human Müller cells caused dose-dependent, significant increases in collagen IV and agrin expression in hRMEC. After narrowing our focus to inflammation-induced changes, we sought to understand how ECM deposited by hRMEC and hRP under inflammatory conditions affects the behavior of naïve hRMEC. Our data demonstrated that diabetes-relevant alterations in ECM composition alone cause both increased adhesion molecule expression by and increased peripheral blood mononuclear cell (PBMC) adhesion to naïve hRMEC. Taken together, these data demonstrate novel roles for inflammation and pericytes in driving BM pathology and suggest that inflammation-induced ECM alterations may advance other pathogenic behaviors in DR, including leukostasis.

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.

Do different lipid components accelerate the pathogenesis and severity of Diabetic Retinopathy?

BACKGROUND

To assess the association of lipid and lipid-derived toxic molecules in pathogenesis and severity of diabetic retinopathy (DR) in type 2 diabetes mellitus (T2DM).

METHODS

The present cross-sectional study included 14 healthy individuals (HC) without T2DM, 22 T2DM subjects without DR (DNR), 24 T2DM subjects with mild non-proliferative DR (MNPDR), and 24 T2DM subjects with high-risk proliferative DR (HRPDR). All subjects underwent plasma and vitreous analysis for estimation of total lipid (TL), free fatty acid (FFA), lipid peroxides (LPOs) like malondialdehyde (MDA), 4-Hydroxy-noneal (HNE), the advanced lipoxidation end product (ALE) like Hexanoyl-lysine (HLY) and vascular endothelial growth factor (VEGF) following standard spectrophotometric and enzyme-linked immunosorbent assay (ELISA) methods respectively.

RESULTS

The concentration of TL, FFA, markers of lipid peroxidation and lipoxidation as well as VEGF in plasma and vitreous were found to be significantly elevated stepwise inT2DM subjects (HRPDR > MNPDR > DNR) compared to healthy controls (HC).Further, plasma conventional lipid components like total cholesterol (TCH), low density lipoprotein cholesterol (LDL-C) and triglycerides (TG), FFA and TL showed their significant positive correlations with vitreous level of different LPOs, ALE and VEGF in the DR group.

CONCLUSION

Total lipid and lipid-derived detrimental biomolecules ultimately result in increased secretion of VEGF and thus not only add as associated mediators in the pathogenesis of DR, these also accelerate the severity of microangiopathy in T2DM.

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.

Yiqi Tongluo Fang could preventive and delayed development and formation of diabetic retinopathy through antioxidant and anti-inflammatory effects

BACKGROUND

Yiqi Tongluo Fang (YQTLF) is an effective prescription for the treatment of diabetic retinopathy (DR), but its mechanism of action remains unclear.

METHOD

The content of YQTLF was determined using liquid and gas chromatography-mass spectrometry (LC-MS and GC-MS, respectively). Twenty-five Sprague Dawley (SD) rats were randomly selected as the normal control group. One hundred SD streptozotocin-induced diabetes (type 1) rats were randomly divided into diabetic control, diabetic+insulin+ calcium dobesilate (CaD), and diabetic+insulin+ YQTLF groups, with 25 rats in each group. Bodyweight level was measured every 2 weeks. After 12 weeks of gavage, the glucose levels, lipids, oxidative stress, inflammation, retinal histopathology, and the blood-retinal barrier were assessed in each group. The p38 MAPK pathway was changed to explore its internal mechanism. The measurement data were expressed as mean ± standard deviation, and different statistical methods were used according to a normal distribution, square error, or not.

RESULTS

A total of 1024 valid peaks were identified in YQTLF using GC-MS. YQTLF significantly lowered the fasting blood glucose levels in diabetic rats. YQTLF early inhibited changes in retinal histology, capillaries, cells, and tight junction proteins (such as ZO-1, occludin, claudin-5, and VE-cadherin) before the formation and development of DR. These findings correlated with the alleviation of glucolipid metabolism, inflammation, and oxidative stress. The lncRNA MALAT1 and the PRC 2/p38 MAPK-related pathway, such as the expression of EZH2, SUZ12, EED, p38 MAPK, MMP-9, and VEGFR, were also correlated.

CONCLUSION

We have demonstrated the molecular and cellular mechanisms underlying the preventive and delayed development and formation of DR. YQTLF prevents changes in dyslipidemia, retinal histology, capillaries, cells, and tight junction proteins. These protective effects appear to be linked to its antioxidant and anti-inflammatory effects, which prevent the activation of intracellular signaling pathways, such as the lncRNA MALAT1 and PRC 2/p38 MAPK-related pathway.

Common pathways in dementia and diabetic retinopathy: understanding the mechanisms of diabetes-related cognitive decline

Type 2 diabetes (T2D) is associated with multiple comorbidities, including diabetic retinopathy (DR) and cognitive decline, and T2D patients have a significantly higher risk of developing Alzheimer's disease (AD). Both DR and AD are characterized by a number of pathological mechanisms that coalesce around the neurovascular unit, including neuroinflammation and degeneration, vascular degeneration, and glial activation. Chronic hyperglycemia and insulin resistance also play a significant role, leading to activation of pathological mechanisms such as increased oxidative stress and the accumulation of advanced glycation end-products (AGEs). Understanding these common pathways and the degree to which they occur simultaneously in the brain and retina during diabetes will provide avenues to identify T2D patients at risk of cognitive decline.

Fustin ameliorates hyperglycemia in streptozotocin induced type-2 diabetes via modulating glutathione/Superoxide dismutase/Catalase expressions, suppress lipid peroxidation and regulates histopathological changes

Streptozotocin (STZ) 60 mg/kg, i.p.-induced diabetes in rat’s results into hyperglycemia, impaired oxidative stress, lipid profile, insulin levels and changes in body weight. Treatment with antihyperglycemics and antioxidants are accounted to produce favorable effect in this paradigm. Fustin, a flavonoid derived from Rhus verniciflua, extract of Rhus verniciflua reported to exhibit anti-hyperglycemic, antioxidant, anti-microbial, anti-arthritic effects, anti-obesity effects, antiplatelet effects and anti-cancer effects. However, no evidence is existing on effect of fustin on STZ-induction diabetes. Thus, we evaluated its effects against diabetes in STZ-induced rodents. Blood glucose, Insulin, lipid peroxidation (MDA), superoxide dismutase (SOD), catalase activity (CAT), glutathione (GSH) and lipid profile levels was assessed. After 30 days diabetes induction rodents showed a severe increased blood sugar level, MDA, high density lipid and decreased cholestrol, triglyceride, GSH, SOD, CAT, respectively.

Oppositely, treatment with fustin (50–100 mg/kg/p.o., two times daily, 30 days) enhanced blood glucose, lipid profile levels Insulin. Meanwhile, reduced MDA and enhanced GSH, SOD, and CAT in diabetic rats. Glibenclamide 5 mg/kg/p.o. also enhanced diabetes-induced complications and decreased oxidative stress. Further histopathology of pancreas confirms the protective effect fustin in STZ-induction diabetes in animals. In conclusion, the study revealed treatments with fustin avoid the changes in body weight, blood glucose, lipid profile and oxidative stress. As a results of these finding may lead to the growth of a choice of medicine for hyperglycemic in the future.

Updates on the Current Treatments for Diabetic Retinopathy and Possibility of Future Oral Therapy

Diabetic retinopathy (DR) is a complication of diabetes and one of the leading causes of vision loss worldwide. Despite extensive efforts to reduce visual impairment, the prevalence of DR is still increasing. The initial pathophysiology of DR includes damage to vascular endothelial cells and loss of pericytes. Ensuing hypoxic responses trigger the expression of vascular endothelial growth factor (VEGF) and other pro-angiogenic factors. At present, the most effective treatment for DR and diabetic macular edema (DME) is the control of blood glucose levels. More advanced cases require laser, anti-VEGF therapy, steroid, and vitrectomy. Pan-retinal photocoagulation for non-proliferative diabetic retinopathy (NPDR) is well established and has demonstrated promising outcomes for preventing the progressive stage of DR. Furthermore, the efficacy of laser therapies such as grid and subthreshold diode laser micropulse photocoagulation (SDM) for DME has been reported. Vitrectomy has been performed for vitreous hemorrhage and tractional retinal detachment for patients with PDR. In addition, anti-VEGF treatment has been widely used for DME, and recently its potential to prevent the progression of PDR has been remarked. Even with these treatments, many patients with DR lose their vision and suffer from potential side effects. Thus, we need alternative treatments to address these limitations. In recent years, the relationship between DR, lipid metabolism, and inflammation has been featured. Research in diabetic animal models points to peroxisome proliferator-activated receptor alpha (PPARα) activation in cellular metabolism and inflammation by oral fenofibrate and/or pemafibrate as a promising target for DR. In this paper, we review the status of existing therapies, summarize PPARα activation therapies for DR, and discuss their potentials as promising DR treatments.

Fustin Ameliorates Elevated Levels of Leptin, Adiponectin, Serum TNF-α, and Intracellular Oxidative Free Radicals in High-Fat Diet and Streptozotocin-Induced Diabetic Rats

Fustin is a prominent ingredient of Rhus verniciflua Stokes (Anacardiaceae) and has a wide range of pharmacological and clinical effects. The present study attempted to evaluate the antidiabetic potential of fustin in streptozotocin- and high-fat diet-induced diabetes in rats. The efficacy of fustin 50 mg/kg and 100 mg/kg/day p.o. was studied in 60% of total calories from fat as a high-fat diet along with single-dose administration streptozotocin (50 mg/kg, i.p.) experimentally induced diabetes in rats for 42 days. The mean body weight; blood glucose; and biochemical parameters such as lipid profile, total protein (TP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), insulin, leptin levels, adiponectin levels, glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) activity in serum were measured. The rats' weight was maintained in the fustin groups compared to the diabetic control group. Diabetes caused a significant increase in serum levels in blood glucose, lipid profile, MDA, TNF-α, ALT, and AST parameters and a decrease in serum insulin, adiponectin, leptin, GSH, SOD, and CAT compared to healthy rats. The treatment regimen with fustin (50 and 100 mg/kg) significantly restored all serum parameters in test groups. The present study found clinical evidence for the first time regarding the significant antidiabetic property of fustin, which could be a worthwhile candidate for the treatment of diabetes.

Potential Effects of Sweet Potato (Ipomoea batatas) in Hyperglycemia and Dyslipidemia-A Systematic Review in Diabetic Retinopathy Context

Hyperglycemia is a condition with high glucose levels that may result in dyslipidemia. In severe cases, this alteration may lead to diabetic retinopathy. Numerous drugs have been approved by officials to treat these conditions, but usage of any synthetic drugs in the long term will result in unavoidable side effects such as kidney failure. Therefore, more emphasis is being placed on natural ingredients due to their bioavailability and absence of side effects. In regards to this claim, promising results have been witnessed in the usage of Ipomoea batatas (I. batatas) in treating the hyperglycemic and dyslipidemic condition. Thus, the aim of this paper is to conduct an overview of the reported effects of I. batatas focusing on in vitro and in vivo trials in reducing high glucose levels and regulating the dyslipidemic condition. A comprehensive literature search was performed using Scopus, Web of Science, Springer Nature, and PubMed databases to identify the potential articles on particular topics. The search query was accomplished based on the Boolean operators involving keywords such as (1) Beneficial effect OR healing OR intervention AND (2) sweet potato OR Ipomoea batatas OR traditional herb AND (3) blood glucose OR LDL OR lipid OR cholesterol OR dyslipidemia. Only articles published from 2011 onwards were selected for further analysis. This review includes the (1) method of intervention and the outcome (2) signaling mechanism involved (3) underlying mechanism of action, and the possible side effects observed based on the phytoconstiuents isolated. The comprehensive literature search retrieved a total of 2491 articles using the appropriate keywords. However, on the basis of the inclusion and exclusion criteria, only 23 articles were chosen for further review. The results from these articles indicate that I. batatas has proven to be effective in treating the hyperglycemic condition and is able to regulate dyslipidemia. Therefore, this systematic review summarizes the signaling mechanism, mechanism of action, and phytoconstituents responsible for those activities of I. batatas in treating hyperglycemic based on the in vitro and in vivo study.

Characterizations of Hamster Retina as a Model for Studies of Retinal Cholesterol Homeostasis

Simple Summary

This work represents a comprehensive evaluation of hamster retina by state-of-the-art methodologies and provides evidence that hamsters may represent a better model for studies of retinal cholesterol maintenance than mice. The latter is an important finding, as disturbances in retinal cholesterol homeostasis are linked to age-related macular degeneration and diabetic retinopathy, which are blinding diseases.

Abstract

Cholesterol homeostasis in the retina, a sensory organ in the back of the eye, has been studied in mice but not hamsters, despite the latter being more similar to humans than mice with respect to their whole-body cholesterol maintenance. The goal of this study was to begin to assess hamster retina and conduct initial interspecies comparisons. First, young (3-month old) and mature (6-month old) Syrian (golden) hamsters were compared with 3- and 6-month old mice for ocular biometrics and retinal appearance on optical coherence tomography and fluorescein angiography. Of the 30 evaluated hamsters, seven had retinal structural abnormalities and all had increased permeability of retinal blood vessels. However, hamsters did not carry the mutations causing retinal degenerations 1 and 8, had normal blood glucose levels, and only slightly elevated hemoglobin A1c content. Cholesterol and six other sterols were quantified in hamster retina and compared with sterol profiles in mouse and human retina. These comparisons suggested that cholesterol turnover is much higher in younger than mature hamster retina, and that mature hamster and human retinas share similarities in the ratios of cholesterol metabolites to cholesterol. This study supports further investigations of cholesterol maintenance in hamster retina.

Circulating Biomarkers of Inflammation and Endothelial Activation in Diabetic Retinopathy

Inflammation and endothelial activation play a pivotal role in development and progression of diabetic retinopathy (DR), a vision-threatening complication of diabetes mellitus (DM) and the leading cause of blindness in the working age population. Easily accessible and validated biomarkers for DR early diagnosis and progression are required for use in clinical trials: here, we reviewed the available literature to understand the association of circulating levels of selected markers of inflammation and endothelial activation with the presence of nonproliferative and proliferative DR (NPDR and PDR) and investigate the relationship between their systemic and ocular levels. We additionally provide data synthesis and perform statistical analysis for interpretation of the collected evidence. CRP, IL-1β, IL-6, TNFα, sICAM1, and sVCAM1 circulating levels were increased in subjects with DM compared to healthy individuals. Moreover, TNFα and sVCAM1 showed increasing systemic levels with DR presence and severity; circulating CRP increased with the transition from no DR to NPDR, whereas IL-6 was increased in PDR compared to NDPR stages. The relationship between ocular and systemic concentrations of these proteins remained unclear due to the low number of studies with matched sampling. In conclusion, the available data supports the use of systemic biomarkers of inflammation and endothelial activation to identify DM status and DR severity. These systemic biomarkers are likely reflecting an overall state of inflammation and vascular activation in different tissues of the body, including the eyes. Prospective, longitudinal datasets are required to validate these biomarkers as predictors of early DR presence, of DR progression, or for disease monitoring.

Ten Years of Knowledge of Nano-Carrier Based Drug Delivery Systems in Ophthalmology: Current Evidence, Challenges, and Future Prospective

The complex drug delivery barrier in the eye reduces the bioavailability of many drugs, resulting in poor therapeutic effects. It is necessary to investigate new drugs through appropriate delivery routes and vehicles. Nanotechnology has utilized various nano-carriers to develop potential ocular drug delivery techniques that interact with the ocular mucosa, prolong the retention time of drugs in the eye, and increase permeability. Additionally, nano-carriers such as liposomes, nanoparticles, nano-suspensions, nano-micelles, and nano-emulsions have grown in popularity as an effective theranostic application to combat different microbial superbugs. In this review, we summarize the nano-carrier based drug delivery system developments over the last decade, particularly review the biology, methodology, approaches, and clinical applications of nano-carrier based drug delivery system in the field of ocular therapeutics. Furthermore, this review addresses upcoming challenges, and provides an outlook on potential future trends of nano-carrier-based drug delivery approaches in ophthalmology, and hopes to eventually provide successful applications for treating ocular diseases.

The potential of marine resources for retinal diseases: a systematic review of the molecular mechanisms

We rely on vision more than on any other sense to obtain information about our environment. Hence, the loss or even impairment of vision profoundly affects our quality of life. Diet or food components have already demonstrated beneficial effects on the development of retinal diseases. Recently, there has been a growing interest in resources from marine animals and plants for the prevention of retinal diseases through nutrition. Especially fish intake and omega-3 fatty acids have already led to promising results, including associations with a reduced incidence of retinal diseases. However, the underlying molecular mechanisms are insufficiently explained. The aim of this review was to summarize the known mechanistic effects of marine resources on the pathophysiological processes in retinal diseases. We performed a systematic literature review following the PRISMA guidelines and identified 107 studies investigating marine resources in the context of retinal diseases. Of these, 46 studies described the underlying mechanisms including anti-inflammatory, antioxidant, antiangiogenic/vasoprotective, cytoprotective, metabolic, and retinal function effects, which we critically summarize. We further discuss perspectives on the use of marine resources for human nutrition to prevent retinal diseases with a particular focus on regulatory aspects, health claims, safety, and bioavailability.

Statin reduces the incidence of diabetic retinopathy and its need for intervention: A systematic review and meta-analysis

Purpose:

We aimed to perform a systematic literature search on the latest evidence of the role of statin in reducing diabetic retinopathy and its need for intervention.

Methods:

A comprehensive search on cohort studies/clinical trials that assess statins and diabetic retinopathy up until August 2019 was performed. The outcome measured was the incidence of diabetic retinopathy and its need for intervention.

Results:

There were 558.177 patients from six studies. Statin was associated with a lower incidence of diabetic retinopathy (hazard ratio: 0.68 (0.55, 0.84), p < 0.001; I2: 95%). For the subtypes of diabetic retinopathy, statin lowers the incidence of proliferative diabetic retinopathy (hazard ratio: 0.69 (0.51, 0.93), p = 0.01; I2: 90%), non-proliferative diabetic retinopathy (hazard ratio: 0.80 (0.66, 0.96), p = 0.02; I2: 93%), and diabetic macular edema (hazard ratio: 0.56 (0.39, 0.80), p = 0.002; I2: 82%). Statin was associated with a reduced need for retinal laser treatment with a hazard ratio of 0.70 (0.64, 0.76) (p < 0.001; I2: 0%), intravitreal injection with a hazard ratio of 0.82 (0.79, 0.85) (p < 0.001; I2: 0%), and vitrectomy with a hazard ratio of 0.64 (0.48, 0.85) (p < 0.001; I2: 75%). Overall, statin was associated with a reduced need for intervention for diabetic retinopathy with a hazard ratio of 0.72 (0.64, 0.80) (p < 0.001; I2: 73%). The regression-based Egger’s test showed statistically significant small-study effects for non-proliferative diabetic retinopathy (p = 0.011) outcomes.

Conclusion:

Statin was associated with a decreased risk of diabetic retinopathy and its subtypes. Statin also reduced the need for intervention with retinal laser treatment, intravitreal injection, and vitrectomy.

Derivation and Validation of Essential Predictors and Risk Index for Early Detection of Diabetic Retinopathy Using Electronic Health Records

Diabetic retinopathy (DR) is a leading cause for blindness among working-aged adults. The growing prevalence of diabetes urges for cost-effective tools to improve the compliance of eye examinations for early detection of DR. The objective of this research is to identify essential predictors and develop predictive technologies for DR using electronic health records. We conducted a retrospective analysis on a derivation cohort with 3749 DR and 94,127 non-DR diabetic patients. In the analysis, an ensemble predictor selection method was employed to find essential predictors among 26 variables in demographics, duration of diabetes, complications and laboratory results. A predictive model and a risk index were built based on the selected, essential predictors, and then validated using another independent validation cohort with 869 DR and 6448 non-DR diabetic patients. Out of the 26 variables, 10 were identified to be essential for predicting DR. The predictive model achieved a 0.85 AUC on the derivation cohort and a 0.77 AUC on the validation cohort. For the risk index, the AUCs were 0.81 and 0.73 on the derivation and validation cohorts, respectively. The predictive technologies can provide an early warning sign that motivates patients to comply with eye examinations for early screening and potential treatments.

Combination of pathological and spectroscopic characterization to promote diagnosis of retinal pigment epithelium-Bruch's membrane complex in a diabetic rat model

Diabetic retinopathy (DR) is a common condition of diabetes, and approaches to detecting early DR using the unique characteristics of the retinal pigment epithelium-Bruch's membrane complex (RBC) have increasingly attracted attention. A diabetic model was established in Sprague-Dawley rats via streptozocin (STZ) injection for 1 (DM1) and 6 months (DM6), confirmed by weekly blood glucose measurement. Serum and retinal tissue-based advanced glycation endproducts (AGE) levels significantly elevated in diabetic rats, and RBC was evaluated by transmission electron microscopy and Raman spectroscopy. The results showed that whole Raman spectra and all marked band intensities could respectively achieve almost equal and accurate discrimination of all animal groups, along with the determination of important molecules from the band data. Further quantitative analyses indicated series of metabolic disturbance due to hyperglycemia were involved while the body self-regulation mechanism still played a role with different effects during the disease progression. Given this, Raman spectroscopy can reliably distinguish the early characterization of DR in addition to providing intrinsic key molecules that is sensitive to identify the early disease progression.

Reproducing diabetic retinopathy features using newly developed human induced-pluripotent stem cell-derived retinal Müller glial cells

Muller glial cells (MGCs) are responsible for the homeostatic and metabolic support of the retina. Despite the importance of MGCs in retinal disorders, reliable and accessible human cell sources to be used to model MGC-associated diseases are lacking. Although primary human MGCs (pMGCs) can be purified from post-mortem retinal tissues, the donor scarcity limits their use. To overcome this problem, we developed a protocol to generate and bank human induced pluripotent stem cell-derived MGCs (hiMGCs). Using a transcriptome analysis, we showed that the three genetically independent hiMGCs generated were homogeneous and showed phenotypic characteristics and transcriptomic profile of pMGCs. These cells expressed key MGC markers, including Vimentin, CLU, DKK3, SOX9, SOX2, S100A16, ITGB1, and CD44 and could be cultured up to passage 8. Under our culture conditions, hiMGCs and pMGCs expressed low transcript levels of RLPB1, AQP4, KCNJ1, KCJN10, and SLC1A3. Using a disease modeling approach, we showed that hiMGCs could be used to model the features of diabetic retinopathy (DR)-associated dyslipidemia. Indeed, palmitate, a major free fatty acid with elevated plasma levels in diabetic patients, induced the expression of inflammatory cytokines found in the ocular fluid of DR patients such as CXCL8 (IL-8) and ANGPTL4. Moreover, the analysis of palmitate-treated hiMGC secretome showed an upregulation of proangiogenic factors strongly related to DR, including ANG2, Endoglin, IL-1β, CXCL8, MMP-9, PDGF-AA, and VEGF. Thus, hiMGCs could be an alternative to pMGCs and an extremely valuable tool to help to understand and model glial cell involvement in retinal disorders, including DR.

miR-139-5p promotes neovascularization in diabetic retinopathy by regulating the phosphatase and tensin homolog

Pathological retinal neovascularization is a driver of the progression of diabetic retinopathy (DR). The present study sought to identify the microRNAs (miRNAs) that are differentially expressed during the progression of DR as well as to explore the specific regulatory mechanism of those miRNAs in retinal neovascularization. Using a microarray data set and a diabetic mouse model, it was determined that miR-139-5p was significantly upregulated during the progression of DR. The in vitro investigation revealed an elevation in the miR-139-5p level in both the high glucose (HG)-treated mouse retinal microvascular endothelial cells (mRMECs) and the HG-treated human RMECs (hRMECs). The miR-139-5p overexpression elevated cell migration, facilitated tube formation, and increased vascular endothelial growth factor (VEGF) protein level in the hRMECs. While the angiogenic effect of miR-139-5p overexpression was halted by an anti-VEGF antibody. Meanwhile, the miR-139-5p knockdown eliminated the VEGF-induced cell migration and tube formation in the hRMECs. The phosphatase and tensin homolog (PTEN) was the target gene of the miR-139-5p. PTEN overexpression removed the angiogenic effect of miR-139-5p overexpression, which led to reduced cell migration and tube formation. In the diabetic mice, the miR-139-5p antagomir effectively decreased the acellular capillaries and suppressed the formation of aberrant blood vessels in the retinal tissues. Taken together, miR-139-5p promotes retinal neovascularization by repressing PTEN expression.

Role of ceramides in the pathogenesis of diabetes mellitus and its complications

Diabetes mellitus (DM) is a systemic metabolic disease that affects 463 million adults worldwide and is a leading cause of cardiovascular disease, blindness, nephropathy, peripheral neuropathy, and lower-limb amputation. Lipids have long been recognized as contributors to the pathogenesis and pathophysiology of DM and its complications, but recent discoveries have highlighted ceramides, a class of bioactive sphingolipids with cell signaling and second messenger capabilities, as particularly important contributors to insulin resistance and the underlying mechanisms of DM complications. Besides their association with insulin resistance and pathophysiology of type 2 diabetes, evidence is emerging that certain species of ceramides are mediators of cellular mechanisms involved in the initiation and progression of microvascular and macrovascular complications of DM. Advances in our understanding of these associations provide unique opportunities for exploring ceramide species as potential novel therapeutic targets and biomarkers. This review discusses the links between ceramides and the pathogenesis of DM and diabetic complications and identifies opportunities for novel discoveries and applications.

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.

Nomogram Prediction Model for Diabetic Retinopathy Development in Type 2 Diabetes Mellitus Patients: A Retrospective Cohort Study

BACKGROUND

This study is aimed at investigating the systemic risk factors of diabetic retinopathy and further establishing a risk prediction model for DR development in T2DM patients.

METHODS

This is a retrospective cohort study including 330 type 2 diabetes mellitus (T2DM) patients who were followed up from December 2012 to November 2020. Multivariable cox regression analysis identifying factors associated with the hazard of developing diabetic retinopathy (DR) was used to construct the DR risk prediction model in the form of nomogram.

RESULTS

50.6% of participants (mean age: 58.60 ± 10.55) were female, and mean duration of diabetes was 7.09 ± 5.36 years. After multivariate cox regression, the risk factors for developing DR were age (HR 1.068, 95%Cl 1.021-1.118, P = 0.005), diabetes duration (HR 1.094, 95%Cl 1.018-1.177, P = 0.015), HbA1c (HR 1.411, 95%Cl 1.113-1.788, P = 0.004), albuminuria (HR 6.908, 95%Cl 1.794-26.599, P = 0.005), and triglyceride (HR 1.554, 95%Cl 1.037-2.330, P = 0.033). The AUC values of the nomogram for predicting developing DR at 3-, 4-, and 5-year were 0.854, 0.845, and 0.798.

CONCLUSION

Combining age, diabetes duration, HbA1c, albuminuria, and triglyceride, the nomogram model is effective for early recognition and intervention of individuals at high risk of DR development.

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.

Retina in a dish: Cell cultures, retinal explants and animal models for common diseases of the retina

For many retinal diseases, including age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy (DR), the exact pathogenesis is still unclear. Moreover, the currently available therapeutic options are often unsatisfactory. Research designed to remedy this situation heavily relies on experimental animals. However, animal models often do not faithfully reproduce human disease and, currently, there is strong pressure from society to reduce animal research. Overall, this creates a need for improved disease models to understand pathologies and develop treatment options that, at the same time, require fewer or no experimental animals. Here, we review recent advances in the field of in vitro and ex vivo models for AMD, glaucoma, and DR. We highlight the difficulties associated with studies on complex diseases, in which both the initial trigger and the ensuing pathomechanisms are unclear, and then delineate which model systems are optimal for disease modelling. To this end, we present a variety of model systems, ranging from primary cell cultures, over organotypic cultures and whole eye cultures, to animal models. Specific advantages and disadvantages of such models are discussed, with a special focus on their relevance to putative in vivo disease mechanisms. In many cases, a replacement of in vivo research will mean that several different in vitro models are used in conjunction, for instance to analyze and validate causative molecular pathways. Finally, we argue that the analytical decomposition into appropriate cell and tissue model systems will allow making significant progress in our understanding of complex retinal diseases and may furthermore advance the treatment testing.

Hyperreflective foci in diabetic macular edema with serous retinal detachment: association with dyslipidemia

AIMS

Hyperreflective foci (HF), detected in the retina of diabetic patients, suggest the presence of microglial activation and migration, while controversies still remain for the origin of HF to be precursors of hard exudates. We investigated the presence of HF and their association with dyslipidemia in serous retinal detachment (SRD)-type diabetic macular edema (DME).

METHODS

Forty-two eyes in 42 patients with diabetic retinopathy (DR) and 22 eyes in 22 patients with branch retinal vascular occlusion (BRVO) showing macular edema were included in this study. The medical records and OCT findings were retrospectively reviewed in patients with SRD-type DME and compared with those with BRVO. The mean number of HF, the mean choroidal thickness, and lipid profiles were analyzed and compared between groups.

RESULTS

The mean number of HF was significantly higher in DR group compared to BRVO group. Significant correlation of HF was noted with triglycerides (r = 0.523, P = 0.002). Triglycerides were significantly associated with HF by linear regression (β = 0.012, 95% CI 0.001-0.024, P = 0.034) and remained significantly associated by multiple linear regression (β = 0.014, 95% CI 0.003-0.025, P = 0.014).

CONCLUSIONS

HF on OCT of DME patients could be indicative of activated microglia. HF are associated with dyslipidemia, especially high triglycerides, suggesting inflammatory reaction from dyslipidemia in diabetic retina.

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.

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.

The Role of Lipoxidation in the Pathogenesis of Diabetic Retinopathy

Lipids can undergo modification as a result of interaction with reactive oxygen species (ROS). For example, lipid peroxidation results in the production of a wide variety of highly reactive aldehyde species which can drive a range of disease-relevant responses in cells and tissues. Such lipid aldehydes react with nucleophilic groups on macromolecules including phospholipids, nucleic acids, and proteins which, in turn, leads to the formation of reversible or irreversible adducts known as advanced lipoxidation end products (ALEs). In the setting of diabetes, lipid peroxidation and ALE formation has been implicated in the pathogenesis of macro- and microvascular complications. As the most common diabetic complication, retinopathy is one of the leading causes of vision loss and blindness worldwide. Herein, we discuss diabetic retinopathy (DR) as a disease entity and review the current knowledge and experimental data supporting a role for lipid peroxidation and ALE formation in the onset and development of this condition. Potential therapeutic approaches to prevent lipid peroxidation and lipoxidation reactions in the diabetic retina are also considered, including the use of antioxidants, lipid aldehyde scavenging agents and pharmacological and gene therapy approaches for boosting endogenous aldehyde detoxification systems. It is concluded that further research in this area could lead to new strategies to halt the progression of DR before irreversible retinal damage and sight-threatening complications occur.

Dyslipidemia in retinal metabolic disorders

The light‐sensitive photoreceptors in the retina are extremely metabolically demanding and have the highest density of mitochondria of any cell in the body. Both physiological and pathological retinal vascular growth and regression are controlled by photoreceptor energy demands. It is critical to understand the energy demands of photoreceptors and fuel sources supplying them to understand neurovascular diseases. Retinas are very rich in lipids, which are continuously recycled as lipid‐rich photoreceptor outer segments are shed and reformed and dietary intake of lipids modulates retinal lipid composition. Lipids (as well as glucose) are fuel substrates for photoreceptor mitochondria. Dyslipidemia contributes to the development and progression of retinal dysfunction in many eye diseases. Here, we review photoreceptor energy demands with a focus on lipid metabolism in retinal neurovascular disorders.

n-3 PUFA Supplementation Alters Retinal Very-Long-Chain-PUFA Levels and Ratios in Diabetic Animal Models

SCOPE

Long-chain (LC)-PUFAs act as precursors for the special class of retinal lipids known as very-long-chain (VLC)-PUFAs and the effect of diabetes on retinal VLC-PUFA levels is unexplored. In order to understand the supplemental effect of omega-3 (n-3) LC-PUFAs on decreasing levels of VLC-PUFAs due to diabetes, Nile rats, which develop diabetes spontaneously, and Akita mouse, a genetic diabetes model, are chosen.

METHODS AND RESULTS

Human retinal punches from donors are collected from an eye bank; lipids are extracted and analyzed to study the alterations in VLC-PUFAs and their omega-3/omega-6 (n-3/n-6) ratios. Nile rats are fed a high-fat diet to induce hyperglycemia, and then an n-3 PUFA-rich diet is fed to the experimental group for 2 months. Diabetic male Akita mice and WT mice are fed with 5% fish-oil mixed in with their chow for 2 months to observe the effect of n-3 PUFAs. Results indicate that VLC-PUFA levels are lower in human diabetic and retinopathic retinal punches compared to age-matched controls. With supplementation of n-3 PUFAs, there is a significant increase in n-3/n-6 VLC-PUFA ratios in both animal models compared to diabetic controls.

CONCLUSION

Dietary supplementation with n-3 LC-PUFAs helps to prevent progression of diabetes and associated retinopathy.

Sphingolipids as Emerging Mediators in Retina Degeneration

The sphingolipids ceramide (Cer), sphingosine-1-phosphate (S1P), sphingosine (Sph), and ceramide-1-phosphate (C1P) are key signaling molecules that regulate major cellular functions. Their roles in the retina have gained increasing attention during the last decade since they emerge as mediators of proliferation, survival, migration, neovascularization, inflammation and death in retina cells. As exacerbation of these processes is central to retina degenerative diseases, they appear as crucial players in their progression. This review analyzes the functions of these sphingolipids in retina cell types and their possible pathological roles. Cer appears as a key arbitrator in diverse retinal pathologies; it promotes inflammation in endothelial and retina pigment epithelium (RPE) cells and its increase is a common feature in photoreceptor death in vitro and in animal models of retina degeneration; noteworthy, inhibiting Cer synthesis preserves photoreceptor viability and functionality. In turn, S1P acts as a double edge sword in the retina. It is essential for retina development, promoting the survival of photoreceptors and ganglion cells and regulating proliferation and differentiation of photoreceptor progenitors. However, S1P has also deleterious effects, stimulating migration of Müller glial cells, angiogenesis and fibrosis, contributing to the inflammatory scenario of proliferative retinopathies and age related macular degeneration (AMD). C1P, as S1P, promotes photoreceptor survival and differentiation. Collectively, the expanding role for these sphingolipids in the regulation of critical processes in retina cell types and in their dysregulation in retina degenerations makes them attractive targets for treating these diseases.

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.

New potentials for 3-hydroxy-3-methyl-glutaryl-coenzymeA reductase inhibitors: Possible applications in retarding diabetic complications

The prevalence of diabetes mellitus is increasing all over the world and it is apparent that treatment of diabetic complications has the same importance as primary diabetes treatment and glycemic control. Diabetic complications occur as a result of prolonged hyperglycemia and its consequences, such as advanced glycation end products and reactive oxygen species. Impairment of lipid profile is also contributed to worsening diabetic complications. Therefore, it seems that the application of lipid-lowering agents may have positive effects on reversing diabetic complications besides glycemic control. Statins, a group of lipid-lowering compounds, have been shown to exert antioxidant, immunomodulatory, anti-inflammatory, and antiproliferative properties beyond their lipid-lowering effects. Furthermore, they have been reported to improve diabetic complications with different pathways. In this review, we will discuss the clinical importance, molecular biology of the most important microvascular/macrovascular diabetic complications, possible application of statins and their mechanism of action in retarding these complications.

Young Ossabaw Pigs Fed a Western Diet Exhibit Early Signs of Diabetic Retinopathy

Purpose

Recent clinical data suggest an increasing prevalence of obesity and type 2 diabetes in adolescents, placing them at high risk of developing diabetic retinopathy during adult working years. The present study was designed to characterize the early retinal and microvascular alterations in young Ossabaw pigs fed a Western diet, described as a model of metabolic syndrome genetically predisposed to type 2 diabetes.

Methods

Four-month-old Ossabaw miniature pigs were divided into two groups, lean and diet-induced obesity. Obese pigs were fed a Western diet with high-fat/high-fructose corn syrup/high-choleric content for 10 weeks. Blood and retina were collected for biochemical profiling, trypsin digest, flatmounts, Fluoro-Jade C staining, electron microscopy, quantitative PCR, immunohistochemistry, and Western blots.

Results

Young Ossabaw pigs had elevated fasting blood glucose after feeding on a Western diet for 10 weeks. Their retina showed disrupted cellular architecture across neural layers, with numerous large vacuoles seen in cell bodies of the inner nuclear layer. Microvessels in the obese animals exhibited thickened basement membrane, along with pericyte ghosts and acellular capillaries. The pericyte to endothelial ratio decreased significantly. Retina flatmounts from obese pigs displayed reduced capillary density, numerous terminal capillary loops, and string vessels, which stained collagen IV but not isolectin IB4. Quantitative PCR and Western blots showed significantly high levels of basement membrane proteins collagen IV and fibronectin in obese pigs.

Conclusions

This is the first study to describe the ultrastructural neuronal and vascular changes in the retina of young Ossabaw pigs fed a Western diet, simulating early signs of diabetic retinopathy pathogenesis.

Flavin Imbalance as an Important Player in Diabetic Retinopathy

The retina and RPE together constitute the most metabolically active ecosystem in the body, harboring high levels of flavins. Although diabetic patients have been reported to suffer from riboflavin deficiency and use of flavins as nutritional interventions to combat diabetic insult on other tissues have been investigated, such attempts have never been tested for the retina to avoid diabetic retinopathy. Furthermore, the role of flavins in pathophysiology of the retina and RPE has mostly been overlooked. Herein, we review the impact of flavins on various clinical manifestations of diabetic retinopathy and discuss possible ways to address them.

Diabetic Retinopathy-An Underdiagnosed and Undertreated Inflammatory, Neuro-Vascular Complication of Diabetes

Diabetes mellitus is a world-wide epidemic and diabetic retinopathy, a devastating, vision-threatening condition, is one of the most common diabetes-specific complications. Diabetic retinopathy is now recognized to be an inflammatory, neuro-vascular complication with neuronal injury/dysfunction preceding clinical microvascular damage. Importantly, the same pathophysiologic mechanisms that damage the pancreatic β-cell (e.g., inflammation, epigenetic changes, insulin resistance, fuel excess, and abnormal metabolic environment), also lead to cell and tissue damage causing organ dysfunction, elevating the risk of all complications, including diabetic retinopathy. Viewing diabetic retinopathy within the context whereby diabetes and all its complications arise from common pathophysiologic factors allows for the consideration of a wider array of potential ocular as well as systemic treatments for this common and devastating complication. Moreover, it also raises the importance of the need for methods that will provide more timely detection and prediction of the course in order to address early damage to the neurovascular unit prior to the clinical observation of microangiopathy. Currently, treatment success is limited as it is often initiated far too late and after significant neurodegeneration has occurred. This forward-thinking approach of earlier detection and treatment with a wider array of possible therapies broadens the physician's armamentarium and increases the opportunity for prevention and early treatment of diabetic retinopathy with preservation of good vision, as well the prevention of similar destructive processes occurring among other organs.

Retinal explant culture: A platform to investigate human neuro-retina

The retina is the tissue responsible for light detection, in which retinal neurons convert light energy into electrical signals to be transported towards the visual cortex. Damage of retinal neurons leads to neuronal cell death and retinal pathologies, compromising visual acuity and eventually leading to irreversible blindness. Models of retinal neurodegeneration include 2D systems like cell lines, disassociated cultures and co-cultures, and 3D models like organoids, organotypic retinal cultures and animal models. Of these, ex vivo human retinal cultures are arguably the most suitable models for translational research as they retain complex inter-cellular interactions of the retina and precisely mimic in-situ responses. In this review, we summarize the distinguishing features of the human retina which are important to preserve in experimental culture, the historical development of human retinal culture systems, the factors affecting ex vivo human retinal culture and the applications and challenges associated with current methods of human retinal explant culture.