Effects of quercetin on diabetic retinopathy and its association with NLRP3 inflammasome and autophagy

Nutraceuticals for Diabetic Retinopathy: Recent Advances and Novel Delivery Systems

Diabetic retinopathy (DR) is a major vision-threatening disease among the working-age population worldwide. Present therapeutic strategies such as intravitreal injection of anti-VEGF and laser photocoagulation mainly target proliferative DR. However, there is a need for early effective management in patients with early stage of DR before its progression into the more severe sight-threatening proliferative stage. Nutraceuticals, natural functional foods with few side effects, have been proposed to be beneficial in patients with DR. Over the decades, many studies, either in vitro or in vivo, have demonstrated the advantages of a number of nutraceuticals in DR with their antioxidative, anti-inflammatory, neuroprotective, or vasoprotective effects. However, only a few clinical trials have been conducted, and their outcomes varied. The low bioavailability and instability of many nutraceuticals have indeed hindered their utilization in clinical use. In this context, nanoparticle carriers have been developed to deliver nutraceuticals and to improve their bioavailability. Despite its preclinical nature, research of interventive nutraceuticals for DR may yield promising information in their clinical applications.

Targeting autophagy with natural products as a potential therapeutic approach for diabetic microangiopathy

As the quality of life improves, the incidence of diabetes mellitus and its microvascular complications (DMC) continues to increase, posing a threat to people's health and wellbeing. Given the limitations of existing treatment, there is an urgent need for novel approaches to prevent and treat DMC. Autophagy, a pivotal mechanism governing metabolic regulation in organisms, facilitates the removal of dysfunctional proteins and organelles, thereby sustaining cellular homeostasis and energy generation. Anomalous states in pancreatic β-cells, podocytes, Müller cells, cardiomyocytes, and Schwann cells in DMC are closely linked to autophagic dysregulation. Natural products have the property of being multi-targeted and can affect autophagy and hence DMC progression in terms of nutrient perception, oxidative stress, endoplasmic reticulum stress, inflammation, and apoptosis. This review consolidates recent advancements in understanding DMC pathogenesis via autophagy and proposes novel perspectives on treating DMC by either stimulating or inhibiting autophagy using natural products.

Therapeutic Potential of Quercetin in Diabetic Neuropathy and Retinopathy: Exploring Molecular Mechanisms

Diabetes mellitus poses a significant health challenge globally, often leading to debilitating complications, such as neuropathy and retinopathy. Quercetin, a flavonoid prevalent in fruits and vegetables, has demonstrated potential therapeutic effects in these conditions due to its antioxidant, anti-inflammatory, and neuroprotective properties. This review summarizes and provides a comprehensive understanding of the molecular mechanisms underlying the efficacy of quercetin in ameliorating diabetic neuropathy and retinopathy. A thorough search was carried out across scientific databases, such as SciFinder, PubMed, and Google Scholar, to gather pertinent literature regarding the effect of quercetin on diabetic neuropathy and retinopathy till February 2024. Preclinical studies indicate that quercetin mitigates neuropathic pain, sensory deficits, and nerve damage associated with diabetic neuropathy by improving neuronal function, reducing DNA damage, regulating pro-inflammatory cytokines, enhancing antioxidant enzyme levels and endothelial function, as well as restoring nerve injuries. In diabetic retinopathy, quercetin shows the potential to preserve retinal structure and function, inhibiting neovascularization, preventing retinal cell death, reducing pro-inflammatory cytokines, and increasing neurotrophic factor levels. Moreover, through modulating key signaling pathways, such as AMP-activated Protein Kinase (AMPK) activation, Glucose Transporter 4 (GLUT 4) upregulation, and insulin secretion regulation, quercetin demonstrates efficacy in reducing oxidative stress and inflammation, thereby protecting nerve and retinal tissues. Despite promising preclinical findings, challenges, such as limited bioavailability, necessitate further research to optimize quercetin's clinical application in order to establish its optimal dosage, formulation, and long-term efficacy in clinical settings.

Tongqiao Mingmu formula alleviates retinal ganglion cell autophagy through PI3K/AKT/mTOR pathway

Glaucoma is a severe blindness-causing optic nerve disease characterized by a loss of retinal ganglion cells (RGCs). Previous studies have shown that the Tongqiao Mingmu (TQMM) formula can reduce retinal and optic nerve damage, but its mechanism of action requires further elucidation. In this study, an RGC injury model was prepared using glutamate and then treated with serum-containing drug from the TQMM formula (hereafter called "TQMM formula serum"). In the glutamate-induced RGC injury model, cell viability decreased with an increase in glutamate concentration, whereas the expression of autophagy-related biomarkers LC3 and Belicin-1 increased. An adenovirus transfection experiment revealed that glutamate markedly promoted autophagic flux in RGCs. Notably, TQMM formula serum inhibited the expression of autophagy-related biomarkers, reduced autophagy flux, and reversed the damage caused by glutamate to RGCs. Furthermore, the PI3K inhibitor LY294002 was used to intervene in the RGC autophagy model and was found to suppress the PI3K/AKT/mTOR pathway and enhance RGC autophagy. However, TQMM formula serum could generate an opposite effect and upregulate the expressions of the PI3K/AKT/mTOR pathway genes and proteins. In conclusion, the TQMM formula can prevent glutamate-induced autophagy in RGCs, possibly by activating the PI3K/AKT/mTOR pathway and reducing the expression of autophagy-related biomarkers LC3 and Belicin-1 to attenuate autophagy and maintain RGC viability.

Therapeutic effect of folic acid combined with decitabine on diabetic mice

AIM

To evaluate the therapeutic effect of folic acid combined with decitabine on diabetic mice.

METHODS

The diabetic model of db/db mice were randomly divided into model group, folic acid group, decitabine group, folic acid combined with decitabine group, and C57 mice as normal control group. The density of retinal blood vessels and retinal thickness were detected by fundus photography and optical coherence tomography, respectively. Pathological changes of retina were observed by hematoxylin-eosin (HE) staining. The homocysteine (Hcy) in serum was detected by enzyme linked immunosorbent assay (ELISA). TdT-mediated dUTP nick-end labeling (TUNEL) was used to detect apoptosis in retinal tissue. Evans blue dye was used to detect the permeability of retinal blood vessels. The platelet endothelial cell adhesion molecule-1 (CD31) and vascular endothelial growth factor receptor (VEGFR) protein were detected by Western blot. The 3-nitrotyrosine (3-NT) and 4-hydroxynonanine (4-HNE) were detected by immunohistochemistry.

RESULTS

The density of retinal blood vessels, retinal thickness, retinal vascular permeability and the proportion of apoptotic cells of retinal tissue in the model group increased significantly than control group (P<0.05). The Hcy in serum and the levels of CD31, VEGFR, 3-NT, and 4-HNE in retinal tissue increased significantly in the model group (P<0.01). Folic acid and decitabine both reversed these changes significantly, and the combination of the folic acid and decitabine worked best.

CONCLUSION

The combination of folic acid and decitabine has a more significant protective effect on the retina in diabetic mice.

The role of autophagy in the treatment of type II diabetes and its complications: a review

Type II diabetes mellitus (T2DM) is a chronic metabolic disease characterized by prolonged hyperglycemia and insulin resistance (IR). Its incidence is increasing annually, posing a significant threat to human life and health. Consequently, there is an urgent requirement to discover effective drugs and investigate the pathogenesis of T2DM. Autophagy plays a crucial role in maintaining normal islet structure. However, in a state of high glucose, autophagy is inhibited, resulting in impaired islet function, insulin resistance, and complications. Studies have shown that modulating autophagy through activation or inhibition can have a positive impact on the treatment of T2DM and its complications. However, it is important to note that the specific regulatory mechanisms vary depending on the target organ. This review explores the role of autophagy in the pathogenesis of T2DM, taking into account both genetic and external factors. It also provides a summary of reported chemical drugs and traditional Chinese medicine that target the autophagic pathway for the treatment of T2DM and its complications.

Effects of autophagy inhibitor 3-methyladenine on a diabetic mice model

AIM

To investigate the role of autophagy inhibitor 3-methyladenine (3-MA) on a diabetic mice model (DM) and the potential mechanism.

METHODS

Male C57BL/6J mice were randomly divided into a normal control group (NC group) and an DM group. DM were induced by multiple low-dose intraperitoneal injection of streptozotocin (STZ) 60 mg/kg·d for 5 consecutive days. DM mice were randomly subdivided into untreated group (DM group), 3-MA (10 mg/kg·d by gavage) treated group (DM+3-MA group) and chloroquine (CQ; 50 mg/kg by intraperitoneal injection) treated group (DM+CQ group). The fasting blood glucose (FBG) levels were recorded every week. At the end of experiment, retinal samples were collected. The expression levels of pro-apoptotic proteins cleaved caspase-3, cleaved poly ADP-ribose polymerase 1 (PARP1) and Bax, anti-apoptotic protein Bcl-2, fibrosis-associated proteins Fibronectin and type 1 collagen α1 chain (COL1A1), vascular endothelial growth factor (VEGF), inflammatory factors interleukin (IL)-1β and tumor necrosis factor (TNF)-α, as well as autophagy related proteins LC3, Beclin-1 and P62 were determined by Western blotting. The oxidative stress indicators 8-hydroxydeoxyguanosine (8-OHdG) and malondialdehyde (MDA) were detected by commercial kits.

RESULTS

Both 3-MA and CQ had short-term hypoglycemic effect on FBG and reduced the expression of VEGF and inflammatory factors IL-1β and TNF-α in DM mice. 3-MA also significantly alleviated oxidative stress indicators 8-OHdG and MDA, decreased the expression of fibrosis-related proteins Fibronectin and COL1A1, pro-apoptotic proteins cleaved caspase-3, cleaved PARP1, as well as the ratio of Bax/Bcl-2. CQ had no significant impact on the oxidative stress indicators, fibrosis, and apoptosis related proteins. The results of Western blotting for autophagy related proteins showed that the ratio of LC3 II/LC3 I and the expression of Beclin-1 in the retina of DM mice were decreased by 3-MA treatment, and the expression of P62 was further increased by CQ treatment.

CONCLUSION

3-MA has anti-apoptotic and anti-fibrotic effects on the retina of DM mice, and can attenuate retinal oxidative stress, VEGF expression and the production of inflammatory factors in the retina of DM mice. The underlying mechanism of the above effects of 3-MA may be related to its inhibition of early autophagy and hypoglycemic effect.

Effectiveness and safety of traditional Chinese medicine for diabetic retinopathy: A systematic review and network meta-analysis of randomized clinical trials

BACKGROUND

Diabetic retinopathy (DR) is currently recognized as one of the most serious diabetic microangiopathies and a major cause of adult blindness. Commonly used clinical approaches include etiological control, microvascular improvement, and surgical intervention, but they are ineffective and have many side effects. Oral Chinese medicine (OCM) has been used for thousands of years to treat DR and is still widely used today, but it is unclear which OCM is more effective for DR.

AIM

To estimate relative effectiveness and safety profiles for different classes of OCMs for DR, and provide rankings of the available OCMs.

METHODS

The search time frame was from the creation of the database to January 2023. RevMan 5.3 and Stata 14.0 software were used to perform the systematic review and Network meta-analyses (NMA).

RESULTS

A total of 107 studies and 9710 patients were included, including 4767 cases in the test group and 4973 cases in the control group. Based on previous studies and clinical reports, and combined with the recommendations of Chinese guidelines for the prevention and treatment of DR, 9 OCMs were finally included in this study, namely Compound Xueshuantong Capsules, Qiming Granules, Compound Danshen Dripping Pills, Hexue Mingmu Tablets (HXMM), Qiju Dihuang Pills (QJDH), Shuangdan Mingmu Capsules (SDMM), Danggui Buxue Decoction (DGBX), Xuefu Zhuyu Decoction and Buyang Huanwu Decoction. When these nine OCMs were analyzed in combination with conventional western medicine treatment (CT) compared with CT alone, the NMA results showed that HXMM + CT has better intervention effect on the overall efficacy of DR patients, HXMM + CT has better effect on improving patients' visual acuity, SDMM + CT has better effect on inhibiting vascular endothelial growth factor, DGBX + CT has better effect on reducing fundus hemorrhage area, HXMM + CT has better effect on reducing fasting blood glucose, and QJDH + CT has better effect on reducing glycated hemoglobin. When there are not enough clinical indicators for reference, SDMM + CT or HXMM + CT treatments can be chosen because they are effective for more indicators and demonstrate multidimensional efficacy.

CONCLUSION

This study provides evidence that combining OCMs with CT leads to better outcomes in all aspects of DR compared to using CT alone. Based on the findings, we highly recommend the use of SDMM or HXMM for the treatment of DR. These two OCMs have demonstrated outstanding efficacy across multiple indicators.

New Insights on Dietary Polyphenols for the Management of Oxidative Stress and Neuroinflammation in Diabetic Retinopathy

Diabetic retinopathy (DR) is a neurodegenerative and vascular pathology that is considered one of the leading causes of blindness worldwide, resulting from complications of advanced diabetes mellitus (DM). Current therapies consist of protocols aiming to alleviate the existing clinical signs associated with microvascular alterations limited to the advanced disease stages. In response to the low resolution and limitations of the DR treatment, there is an urgent need to develop more effective alternative therapies to optimize glycemic, vascular, and neuronal parameters, including the reduction in the cellular damage promoted by inflammation and oxidative stress. Recent evidence has shown that dietary polyphenols reduce oxidative and inflammatory parameters of various diseases by modulating multiple cell signaling pathways and gene expression, contributing to the improvement of several chronic diseases, including metabolic and neurodegenerative diseases. However, despite the growing evidence for the bioactivities of phenolic compounds, there is still a lack of data, especially from human studies, on the therapeutic potential of these substances. This review aims to comprehensively describe and clarify the effects of dietary phenolic compounds on the pathophysiological mechanisms involved in DR, especially those of oxidative and inflammatory nature, through evidence from experimental studies. Finally, the review highlights the potential of dietary phenolic compounds as a prophylactic and therapeutic strategy and the need for further clinical studies approaching the efficacy of these substances in DR management.

Antioxidant Activities of Natural Compounds from Caribbean Plants to Enhance Diabetic Wound Healing

Diabetic wound healing is a global medical challenge. Several studies showed that delayed healing in diabetic patients is multifactorial. Nevertheless, there is evidence that excessive production of ROS and impaired ROS detoxification in diabetes are the main cause of chronic wounds. Indeed, increased ROS promotes the expression and activity of metalloproteinase, resulting in a high proteolytic state in the wound with significant destruction of the extracellular matrix, which leads to a stop in the repair process. In addition, ROS accumulation increases NLRP3 inflammasome activation and macrophage hyperpolarization in the M1 pro-inflammatory phenotype. Oxidative stress increases the activation of NETosis. This leads to an elevated pro-inflammatory state in the wound and prevents the resolution of inflammation, an essential step for wound healing. The use of medicinal plants and natural compounds can improve diabetic wound healing by directly targeting oxidative stress and the transcription factor Nrf2 involved in the antioxidant response or the mechanisms impacted by the elevation of ROS such as NLRP3 inflammasome, the polarization of macrophages, and expression or activation of metalloproteinases. This study of the diabetic pro-healing activity of nine plants found in the Caribbean highlights, more particularly, the role of five polyphenolic compounds. At the end of this review, research perspectives are presented.

Effectiveness of targeting the NLRP3 inflammasome by using natural polyphenols: A systematic review of implications on health effects

Globally, inflammation and metabolic disorders pose serious public health problems and are major health concerns. It has been shown that natural polyphenols are effective in the treatment of metabolic diseases, including anti-inflammation, anti-diabetes, anti-obesity, neuron-protection, and cardio-protection. NLRP3 inflammasome, which are multiprotein complexes located within the cytosol, play an important role in the innate immune system. However, aberrant activation of the NLRP3 inflammasome were discovered as essential molecular mechanisms in triggering inflammatory processes as well as implicating it in several major metabolic diseases, such as type 2 diabetes mellitus, obesity, atherosclerosis or cardiovascular disease. Recent studies indicate that natural polyphenols can inhibit NLRP3 inflammasome activation. In this review, the progress of natural polyphenols preventing inflammation and metabolic disorders via targeting NLRP3 inflammasome is systemically summarized. From the viewpoint of interfering NLRP3 inflammasome activation, the health effects of natural polyphenols are explained. Recent advances in other beneficial effects, clinical trials, and nano-delivery systems for targeting NLRP3 inflammasome are also reviewed. NLRP3 inflammasome is targeted by natural polyphenols to exert multiple health effects, which broadens the understanding of polyphenol mechanisms and provides valuable guidance to new researchers in this field.

Quercetin effectively improves LPS-induced intestinal inflammation, pyroptosis, and disruption of the barrier function through the TLR4/NF-κB/NLRP3 signaling pathway in vivo and in vitro

Background

Inflammatory bowel diseases are characterized by the alterations of the mucosa and gastrointestinal physiology, and the core of these alterations is endothelial cells. Quercetin is a flavonoid presents in some traditional Chinese medicine, plants, and fruits. Its protective effects in several gastrointestinal tumors have been demonstrated, but its effects on bacterial enteritis and pyroptosis-related diseases have rarely been studied.

Objective

This study aimed to evaluate the effect of quercetin on bacterial enteritis and pyroptosis.

Design

In vitro experiments were performed using rat intestinal microvascular endothelial cells divided into seven groups: control group (no treatment), model group (10 μg/mL lipopolysaccharide (LPS)+1 mM adenosine triphosphate [ATP]), LPS group (10 μg/mL LPS), ATP group (1 mM ATP), and treatment groups (10 μg/mL LPS+1 mM ATP and 5, 10, and 20 μM quercetin). The expression of pyroptosis-associated proteins, inflammatory factors, tight junction proteins, and the percentage of late apoptotic and necrotic cells were measured. In vivo analysis was performed using specific pathogen-free Kunming mice pretreated with quercetin and the water extract of Cacumen Platycladi for 2 weeks followed by 6 mg/kg LPS on day 15. Inflammation in the blood and intestinal pathological changes were evaluated.

Results

Quercetin used in vitro significantly reduced the expression of Toll-like receptor 4 (TLR4), NOD-like receptor 3 (NLRP3), caspase-1, gasdermin D, interleukin (IL)-1β, IL-18, IL-6, and tumor necrosis factor-α. It also inhibited phosphorylation of nuclear factor-kappa B (NF-κB) p65 and increased cell migration and the expression of zonula occludens 1 and claudins, while reduced the number of late apoptotic cells. The in vivo results showed that Cacumen Platycladi and quercetin significantly reduced inflammation, protected the structure of the colon and cecum, and prevent fecal occult blood induced by LPS.

Conclusions

These findings suggested the ability of quercetin to reduce inflammation induced by LPS and pyroptosis through TLR4/NF-κB/NLRP3 pathway.

The ghrelin-GHSR-1a pathway inhibits high glucose-induced retinal angiogenesis in vitro by alleviating endoplasmic reticulum stress

Background

To investigate the effect of ghrelin, a brain-gut peptide hormone, on high glucose-induced retinal angiogenesis in vitro and explore its association with endoplasmic reticulum (ER) stress.

Methods

Human retinal microvascular endothelial cells (HRMECs) were first divided into control and high-glucose groups, and the mRNA and protein expression levels of the receptor for ghrelin [growth hormone secretin receptor 1a, (GHSR-1a)] in cells were determined. HRMECs were then treated with high glucose alone or in combination with ghrelin or siGHSR-1a, and cell viability, migration, tube formation and the expression of the ER stress-related proteins PERK, ATF4 and CHOP were detected. Finally, to clarify whether the effects of ghrelin are related to ER stress, tunicamycin, an inducer of ER stress, was used to treat HRMECs, and cell viability, cell migration, and tube formation were evaluated.

Results

GHSR-1a expression in HRMECs at both the mRNA and protein levels was inhibited by high-glucose treatment. Under high-glucose conditions, ghrelin promoted cell viability and inhibited migration and tube formation, which were blocked by siGHSR-1a treatment. Ghrelin inhibited the increases in the protein levels of p-PERK, ATF4 and CHOP induced by high-glucose treatment, and combination treatment with siGHSR-1a reversed this effect of ghrelin. When tunicamycin was added, the effects of ghrelin on cell viability, migration and tube formation were all weakened.

Conclusions

This study experimentally revealed that ghrelin can inhibit high glucose-induced retinal angiogenesis in vitro through GHSR-1a, and alleviation of ER stress may be one of the mechanisms underlying this effect.

Quercetin: an effective polyphenol in alleviating diabetes and diabetic complications

Various studies, especially in recent years, have shown that quercetin has beneficial therapeutic effects in various human diseases, including diabetes. Quercetin has significant anti-diabetic effects and may be helpful in lowering blood sugar and increasing insulin sensitivity. Quercetin appears to affect many factors and signaling pathways involved in insulin resistance and the pathogenesis of type 2 of diabetes. TNFα, NFKB, AMPK, AKT, and NRF2 are among the factors that are affected by quercetin. In addition, quercetin can be effective in preventing and ameliorating the diabetic complications, including diabetic nephropathy, cardiovascular complications, neuropathy, delayed wound healing, and retinopathy, and affects the key mechanisms involved in the pathogenesis of these complications. These positive effects of quercetin may be related to its anti-inflammatory and anti-oxidant properties. In this article, after a brief review of the pathogenesis of insulin resistance and type 2 diabetes, we will review the latest findings on the anti-diabetic effects of quercetin with a molecular perspective. Then we will review the effects of quercetin on the key mechanisms of pathogenesis of diabetes complications including nephropathy, cardiovascular complications, neuropathy, delayed wound healing, and retinopathy. Finally, clinical trials investigating the effect of quercetin on diabetes and diabetes complications will be reviewed.

Quercetin ameliorated cardiac injury via reducing inflammatory actions and the glycerophospholipid metabolism dysregulation in a diabetic cardiomyopathy mouse model

Quercetin has multiple protective effects against cardiometabolic diseases, but the biological mechanisms underlying the benefits in diabetic cardiomyopathy (DCM) are unclear. A mouse DCM model was established by high-fat diet...

Down-expression of the NLRP3 inflammasome delays the progression of diabetic retinopathy

The investigation aimed to evaluate the effects of Mcc950, an inhibitor of the NLRP3 inflammasome, on diabetic retinopathy (DR) mice. The general physiological condition of each group of mice was recorded. Retinal blood vessels were stained for observation of the density of blood vessels, and retinas were used for further morphological examination and fluorescent staining after the intravitreal injection of Mcc950. Mcc950 partially reversed hyperglycemia-induced vascular damage and had reduced histological changes compared to DR mice. IL-1β production in mice retinas in the diabetic model (DM) group increased, but pretreatment with Mcc950 significantly reversed these changes. Additionally, Mcc950 engineered reduced FITC dextran extravasation and vascular leakage. Therefore, it played an apparent protective role in DR and could be a new treatment strategy for DR.

Long-Term Oral Treatment with Non-Hypoglycemic Dose of Glibenclamide Reduces Diabetic Retinopathy Damage in the Goto-KakizakiRat Model

Diabetic retinopathy (DR) remains a major cause of vision loss, due to macular edema, retinal ischemia and death of retinal neurons. We previously demonstrated that acute administration of glibenclamide into the vitreous, or given orally at a non-hypoglycemic dose, protected the structure and the function of the retina in three animal models that each mimic aspects of diabetic retinopathy in humans. In this pilot study, we investigated whether one year of chronic oral glibenclamide, in a non-hypoglycemic regimen (Amglidia^®, 0.4 mg/kg, Ammtek/Nordic Pharma, 5 d/week), could alleviate the retinopathy that develops in the Goto-Kakizaki (GK) rat. In vivo, retinal function was assessed by electroretinography (ERG), retinal thickness by optical coherence tomography (OCT) and retinal perfusion by fluorescein and indocyanin green angiographies. The integrity of the retinal pigment epithelium (RPE) that constitutes the outer retinal barrier was evaluated by quantitative analysis of the RPE morphology on flat-mounted fundus ex vivo. Oral glibenclamide did not significantly reduce the Hb1Ac levels but still improved retinal function, as witnessed by the reduction in scotopic implicit times, limited diabetes-induced neuroretinal thickening and the extension of ischemic areas, and it improved the capillary coverage. These results indicate that low doses of oral glibenclamide could still be beneficial for the prevention of type 2 diabetic retinopathy. Whether the retinas ofpatients treated specifically with glibenclamideare less at risk of developing diabetic complications remains to be demonstrated.