Reversal of the Caspase-Dependent Apoptotic Cytotoxicity Pathway by Taurine from Lycium barbarum (Goji Berry) in Human Retinal Pigment Epithelial Cells: Potential Benefit in Diabetic Retinopathy

Natural plant medications for the treatment of retinal diseases: The blood-retinal barrier as a clue

BACKGROUND

Retinal diseases significantly contribute to the global burden of visual impairment and blindness. The occurrence of retinal diseases is often accompanied by destruction of the blood‒retinal barrier, a vital physiological structure responsible for maintaining the stability of the retinal microenvironment. However, detailed summaries of the factors damage the blood‒retinal barrier and treatment methods involving natural plant medications are lacking.

PURPOSE

To comprehensively summarize and analyze the protective effects of active substances in natural plant medications on damage to the blood-retina barrier that occurs when retinal illnesses, particularly diabetic retinopathy, and examine their medicinal value and future development prospects.

METHODS

In this study, we searched for studies published in the ScienceDirect, PubMed, and Web of Science databases. The keywords used included natural plant medications, plants, natural herbs, blood retinal barrier, retinal diseases, diabetic retinopathy, age-related macular degeneration, and uveitis. Chinese herbal compound articles, non-English articles, warning journals, and duplicates were excluded from the analysis.

RESULTS

The blood‒retinal barrier is susceptible to high glucose, aging, immune responses, and other factors that destroy retinal homeostasis, resulting in pathological changes such as apoptosis and increased vascular permeability. Existing studies have shown that the active compounds or extracts of many natural plants have the effect of repairing blood-retinal barrier dysfunction. Notably, berberine, puerarin, and Lycium barbarum polysaccharides exhibited remarkable therapeutic effects. Additionally, curcumin, astragaloside IV, hesperidin, resveratrol, ginsenoside Rb1, luteolin, and Panax notoginseng saponins can effectively protect the blood‒retinal barrier by interfering with distinct pathways. The active ingredients found in natural plant medications primarily repair the blood‒retinal barrier by modulating pathological factors such as oxidative stress, inflammation, pyroptosis, and autophagy, thereby alleviating retinal diseases.

CONCLUSION

This review summarizes a series of plant extracts and plant active compounds that can treat retinal diseases by preventing and treating blood‒retinal barrier damage and provides reference for the research of new drugs for treating retinal diseases.

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.

The modulation of cAMP/PKA pathway by asiaticoside ameliorates high glucose-induced inflammation and apoptosis of retinal pigment epithelial cells

Asiaticoside, the major bioactive constituent purified from Centella asiatica, is a pentacyclic triterpene saponin with sugar moieties (glucose-glucose-rhamnose). Its biological activities including anti-inflammation and antioxidant have been widely reported. This study aimed to investigate the role of asiaticoside in diabetic retinopathy (DR). Human retinal pigment epithelium (RPE) cells ARPE-19 were induced by high glucose. Then, cell survival rate, expression of inflammatory factors, oxidative stress, and apoptosis were measured by MTT method, western blot, oxidative stress detection kits and TUNEL respectively. To uncover the underlying mechanism, the levels of cyclic AMP (cAMP) and protein kinase A (PKA) were measured by Enzyme linked immunosorbent assay (ELISA) and PKA activities were detected by the Kemptide phosphorylation assay. Furthermore, cAMP inhibitor SQ22536 was also used to validate the mechanism. Asiaticoside suppressed the inflammation and apoptosis of ARPE-19 cells, and the activities of cAMP and PKA were inhibited upon HG induction while again released after further administration of asiaticoside. However, these effects were all abolished by SQ22536. In conclusion, we have demonstrated in this paper that asiaticoside ameliorates high glucose-induced inflammation and apoptosis of RPE cells by activating cAMP/PKA signaling pathway. asiaticoside-mediated activation of cAMP/PKA signaling pathway may serve as a potential target for the management of DR.

Fructus lycii: A Natural Dietary Supplement for Amelioration of Retinal Diseases

Fructus lycii (F. lycii) is an exotic "berry-type" fruit of the plant Lycium barbarum that is characterized by a complex mixture of bioactive compounds distinguished by their high antioxidant potential. F. lycii is used in traditional Chinese home cooking and in the Chinese Pharmacopeia as an aid to vision and longevity as well as a remedy for diabetes to balance "yin" and "yang" in the body for about two centuries. Although a myriad of bioactive compounds have been isolated from F. lycii, polysaccharides, carotenoids, flavonoids, and phenolics represent the key functional components of F. lycii. F. lycii has been shown to exhibit a wide range of biological activities in experimental settings including antioxidant, anti-inflammatory, antiapoptotic, and neuroprotective effects. Despite its medicinal role dating back to the eighteenth century in the Far East and robust evidence of beneficial effects on ocular health and retinal diseases originating mainly from studies in animal models, the role of F. lycii in the clinical management of retinal diseases is yet to be established. This article comprehensively reviews the literature germane to F. lycii and retinal diseases with particular emphasis on age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa, which are commonly seen in clinical practice.

Long Noncoding RNA MEG3 Inhibits Apoptosis of Retinal Pigment Epithelium Cells Induced by High Glucose via the miR-93/Nrf2 Axis

Diabetic retinopathy (DR) is the leading cause of visual impairment in developed nations. Though plasma microRNA-93 (miR-93) is associated with the risk of DR, the function and regulatory mechanism of miR-93 during DR remains unclear. Blood samples were collected from 12 DR patients and 12 healthy controls. Primary human retinal pigment epithelium (RPE) cells and ARPE-19 cells were cultured in 5 mmol/L or 33 mmol/L d-glucose medium. Long noncoding (lnc) RNA MEG3 and miR-93 expression was detected by real-time quantitative PCR. The effect of MEG3 and miR-93 on high glucose (HG)-induced apoptosis was detected by MTT and flow cytometry. IL-6 and tumor necrosis factor-α levels were detected by enzyme-linked immunosorbent assay. The relationships among MEG3, miR-93, and Nrf2 (also known as NFE2L2) were explored via dual-luciferase reporter assay. lncRNA MEG3 and Nrf2 were decreased and miR-93 was increased in blood samples of DR patients and HG-treated human RPE and ARPE-19 cells. Overexpression of miR-93 inhibited cell proliferation and promoted apoptosis, whereas overexpression of Nrf2 or MEG3 promoted proliferation and suppressed apoptosis and inflammation. In addition, MEG3 targeted miR-93 and down-regulated miR-93. Moreover, miR-93 directly targeted Nrf2 and negatively regulated Nrf2. This study suggests that lncRNA MEG3 depresses HG-induced apoptosis and inflammation of RPE via miR-93/Nrf2 axis, providing a novel perspective on the genesis and development of DR.

Protective effects of lycium barbarum polysaccharides on blood-retinal barrier via ROCK1 pathway in diabetic rats

Lycium barbarum polysaccharides (LBP) is commonly known as a traditional Chinese medicine, which has protective effects against diabetic complications in clinic, such as diabetic retinopathy (DR). Previous studies have revealed that Rho/ROCK pathway play an important role in DR development. However, the mechanism between LBP and DR remains unknown. This study aims to explore the clear mechanism of the protective effect of LBP in diabetic retinopathy. In this study, streptozocin (STZ, 45 mg/kg) was administered for diabetic rats modeling. Weight, blood glucose levels and blood lipid were measured to assess the metabolic changes by LBP on diabetic rats. Evans blue (EB) extravasation was determined to assess blood-retinal barrier (BRB) disruption. Hematoxylin and Eosin (HE) staining and immunohistochemistry assay were applied for retina morphology exploration. The membranous disks of retina were examined by transmission electron microscope. Further, high glucose condition was induced in choroidal-retinal endothelial cells (RF/6A). Western blotting was performed for P-Occludin, ROCK1 and P-MLC protein expression. The results indicated that the blood glucose levels, blood lipid and EB infiltration capacity were decreased while the weight was increased in LBP-treated diabetic rats compared with model rats. Moreover, LBP could thicken the overall retina, prevent the disturbance of photoreceptor cell membranous disks and inhibit pathological angiogenesis in diabetes. In addition, the decreased expression of P-Occludin and increased expression of RhoA-associated protein kinase (ROCK) or phosphorylated myosin light chain (P-MLC) were observed in retinal tissue of diabetic rats and high glucose induced by RF/6A cells, which could be rescued by LBP and/or Fasudil. LBP has the protective effects on blood-retinal barrier by regulating the Rho/ROCK signaling pathway in diabetic rats. LBP may be served as a Rho/ROCK inhibitor for the treatment of DR.

Taurine administration ablates sepsis induced diaphragm weakness

Infection induced diaphragm weakness is a major contributor to death and prolonged mechanical ventilation in critically ill patients. Infection induced muscle dysfunction is associated with activation of muscle proteolytic enzymes, and taurine is known to suppress proteolysis. We therefore postulated that taurine administration may prevent infection induced diaphragm dysfunction. The purpose of this study was to test this hypothesis using a clinically relevant animal model of infection, i.e. cecal ligation puncture induced sepsis (CLP). Studies were performed on (n = 5-7 mice/group): (a) sham operated controls, (b) animals with sepsis induced by CLP, (c) sham operated animals given taurine (75 mg/kg/d, intraperitoneally), and (d) CLP animals given taurine. At intervals after surgery animals were euthanized, diaphragm force generation measured in vitro, and diaphragm calpain, caspase and proteasomal activity determined. CLP elicited a large reduction in diaphragm specific force generation at 24 h (1-150 Hz, p < 0.001) and taurine significantly attenuated CLP induced diaphragm weakness at all stimulation frequencies (p < 0.001). CLP induced significant increases in diaphragm calpain, caspase and proteasomal activity; taurine administration prevented increases in the activity of all three pathways. In additional time course experiments, diaphragm force generation remained at control levels over 72 h in CLP animals treated with daily taurine administration, while CLP animals demonstrated severe, sustained reductions in diaphragm strength (p < 0.01 for all time points). Our results indicate that taurine administration prevents infection induced diaphragm weakness and reduces activation of three major proteolytic pathways. Because this agent is has been shown to be safe, non-toxic when administered to humans, taurine may have a role in treating infection induced diaphragm weakness. Future clinical studies will be needed to assess this possibility.

Nutraceuticals for the Treatment of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus and is characterized by degeneration of retinal neurons and neoangiogenesis, causing a severe threat to vision. Nowadays, the principal treatment options for DR are laser photocoagulation, vitreoretinal surgery, or intravitreal injection of drugs targeting vascular endothelial growth factor. However, these treatments only act at advanced stages of DR, have short term efficacy, and cause side effects. Treatment with nutraceuticals (foods providing medical or health benefits) at early stages of DR may represent a reasonable alternative to act upstream of the disease, preventing its progression. In particular, in vitro and in vivo studies have revealed that a variety of nutraceuticals have significant antioxidant and anti-inflammatory properties that may inhibit the early diabetes-driven molecular mechanisms that induce DR, reducing both the neural and vascular damage typical of DR. Although most studies are limited to animal models and there is the problem of low bioavailability for many nutraceuticals, the use of these compounds may represent a natural alternative method to standard DR treatments.

Curcumin inhibits high glucose‑induced inflammatory injury in human retinal pigment epithelial cells through the ROS‑PI3K/AKT/mTOR signaling pathway

Diabetic retinopathy (DR) is a retinal disease caused by metabolic disorders of glucose tolerance that can lead to irreversible blindness if not adequately treated. Retinal pigment epithelial cell (RPEC) dysfunction contributes to the pathogenesis of DR. In the present study the anti‑inflammatory effect of curcumin (CUR) was investigated in RPECs damaged by high glucose levels. RPEC treated with 30 mmol/l glucose was regarded as high glucose group, and cells treated with 24.4 mmol/l mannitol was set as equivalent osmolarity group. Cell Counting Kit‑8 assay was used to measure RPEC viability, the expression of phosphorylated (p)‑AKT and p‑mammalian target of rapamycin (mTOR) were assessed by western blot, and secretion of tumor necrosis factor (TNF)‑α, interleukin (IL)‑6 and IL‑1β in the culture medium was measured by ELISA. Intracellular reactive oxygen species (ROS) levels were measured by laser scanning confocal microscope. The present data indicated that, compared with mannitol treatment, high glucose treatment reduced RPEC viability, increased TNF‑α, IL‑6 and IL‑1β secretion, increased ROS formation and promoted phosphorylation of AKT and mTOR. The antioxidant N‑acetylcysteine, the phosphoinositide 3‑kinase (PI3K)/AKT inhibitor LY294002 and the mTOR inhibitor rapamycin ameliorated the effects of high glucose. In addition, pretreatment with 10 µmol/l CUR reduced secretion levels of TNF‑α, IL‑6 and IL‑1β, ROS formation and phosphorylation of AKT and mTOR. In conclusion, CUR inhibited high glucose‑induced inflammatory injury in RPECs by interfering with the ROS/PI3K/AKT/mTOR signaling pathway. The present study may reveal the molecular mechanism of CUR inhibition effects to high glucose‑induced inflammatory injury in RPEC.

Demystifying traditional Chinese medicines: Lycium barbarum as a model therapeutic

The practice of Traditional Chinese Medicine (TCM) focuses on holistic treatment of the body. This often includes preparation and application of medicinal herbs, either alone or in combination with other supplements. Lycium barbarum (LB), for example, is a commonly used herbal supplement in many Asian countries, being most well-known for improving kidney, liver, and eye health. It is also one of the most widely scientifically researched TCMs and a large body of literature is available describing its effects on various tissues and organ systems. In this perspective, we briefly expand upon how LB can be used as a model TCM in the systematic study of other herbal medicines, highlighting two of the primary barriers to their use in modern medicine worldwide.

Dual contribution of TRPV4 antagonism in the regulatory effect of vasoinhibins on blood-retinal barrier permeability: diabetic milieu makes a difference

Breakdown of the blood-retinal barrier (BRB), as occurs in diabetic retinopathy and other chronic retinal diseases, results in vasogenic edema and neural tissue damage, causing vision loss. Vasoinhibins are N-terminal fragments of prolactin that prevent BRB breakdown during diabetes. They modulate the expression of some transient receptor potential (TRP) family members, yet their role in regulating the TRP vanilloid subtype 4 (TRPV4) remains unknown. TRPV4 is a calcium-permeable channel involved in barrier permeability, which blockade has been shown to prevent and resolve pulmonary edema. We found TRPV4 expression in the endothelium and retinal pigment epithelium (RPE) components of the BRB, and that TRPV4-selective antagonists (RN-1734 and GSK2193874) resolve BRB breakdown in diabetic rats. Using human RPE (ARPE-19) cell monolayers and endothelial cell systems, we further observed that (i) GSK2193874 does not seem to contribute to the regulation of BRB and RPE permeability by vasoinhibins under diabetic or hyperglycemic-mimicking conditions, but that (ii) vasoinhibins can block TRPV4 to maintain BRB and endothelial permeability. Our results provide important insights into the pathogenesis of diabetic retinopathy that will further guide us toward rationally-guided new therapies: synergistic combination of selective TRPV4 blockers and vasoinhibins can be proposed to mitigate diabetes-evoked BRB breakdown.

Effects of Lycium barbarum on the Visual System

Lycium barbarum (wolfberry, gogi berry, gouqizi, ) is one of the most widely used Chinese herbal medicines (CHMs) and is also one of the most scientifically studied. Indeed, the polysaccharide component of this berry (LBP) has been shown to have antioxidant, antiinflammatory, antiexcitotoxic, and antiapoptotic properties. These properties make it a particularly useful treatment option for the ocular environment. Although there are a handful of studies investigating the use of LBP to treat diseases affecting the lens, the vast majority of the published literature investigating LBP in the visual system focus on the retina. In this chapter, we have described what is currently understood concerning the effects of LBP treatment on various retinal diseases, including glaucoma, ischemia/reperfusion, age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy. We then describe the functions attributed to LBP using other cellular contexts to elucidate the full mechanisms this CHM utilizes in the retina. By making connections between what is known about the function of LBP in a variety of tissues and its function as a therapy for retinal degenerative diseases, we hope to further emphasize the continued use of this CHM in clinical medicine in addition to providing a platform for additional study.

Chinese herbal drugs for the treatment of diabetic retinopathy

Objectives

To explore the various pharmacological actions and the molecular mechanisms behind them by which Chinese herbs tend to lower the risk of developing microvascular diabetic complications in retina and prevent its further progression.

Key findings

Several Chinese herbs, indeed, elicit potent anti-inflammatory, antioxidant, anti-angiogenic, anti-apoptotic, peroxisome proliferator-activated receptor-gamma receptor agonistic, platelet-activating factor antagonistic, aldose reductase inhibitory and various other beneficial pharmacological activities, required to counteract the pathological conditions prevalent in retina during diabetes.

Summary

Chinese herbs can potentially be used for the treatment/prevention of diabetic retinopathy owing to the virtue of numerous properties by which they alleviate several hyperglycaemia-induced pathological occurrences in retina. This would provide a natural and safe therapy for diabetic retinopathy, which currently is clinically limited to destructive techniques like laser photocoagulation and vitrectomy.

Neuro-protective Mechanisms of Lycium barbarum

Neuronal diseases, including retinal disorders, stroke, Alzheimer's disease, Parkinson's disease and spinal cord injury, affect a large number of people worldwide and cause heavy social and economic burdens. Although many efforts have been made by scientists and clinicians to develop novel drug and healthcare strategies, few of them received satisfactory outcomes to date. Lycium barbarum is a traditional homology of medicine and food in Chinese medicine, with the capability to nourish the eyes, liver and kidneys. Recent studies have also explored its powerful neuro-protective effects on a number of neuronal diseases. In the current review, we collected key recent findings regarding the neuro-protective effects and mechanisms of L. barbarum derivatives, primarily its polysaccharide (LBP) , in some common diseases of the nervous system. A comprehensive comparison with currently available drugs has also been discussed. In general, LBP is a promising neuronal protector with potent ameliorative effects on key pathological events, such as oxidative stress, inflammation, apoptosis and cell death with minimal side effects.

Management of diabetic complications: a chemical constituents based approach

ETHNOPHARMACOLOGICAL RELEVANCE

Long term hyperglycemia leads to development of complications associated with diabetes. Diabetic complications are now a global health problem without effective therapeutic approach. Hyperglycemia and oxidative stress are important components for the development of diabetic complications. Over the past few decades, herbal medicines have attracted much attention as potential therapeutic agents in the prevention and treatment of diabetic complications due to their multiple targets and less toxic side effects. This review aims to assess the current available knowledge of medicinal herbs for attenuation and management of diabetic complications and their underlying mechanisms.

MATERIAL AND METHODS

Bibliographic investigation was carried out by scrutinizing classical text books and peer reviewed papers, consulting worldwide accepted scientific databases (SCOPUS, PUBMED, SCIELO, NISCAIR, Google Scholar) to retrieve available published literature. The inclusion criteria for the selection of plants were based upon all medicinal herbs and their active compounds with attributed potentials in relieving diabetic complications. Moreover, plants which have potential effect in ameliorating oxidative stress in diabetic animals have been included.

RESULTS

Overall, 238 articles were reviewed for plant literature and out of the reviewed literature, 127 articles were selected for the study. Various medicinal plants/plant extracts containing flavonoids, alkaloids, phenolic compounds, terpenoids, saponins and phytosterol type chemical constituents were found to be effective in the management of diabetic complications. This effect might be attributed to amelioration of persistent hyperglycemia, oxidative stress and modulation of various metabolic pathways involved in the pathogenesis of diabetic complications.

CONCLUSION

Screening chemical candidate from herbal medicine might be a promising approach for new drug discovery to treat the diabetic complications. There is still a dire need to explore the mechanism of action of various plant extracts and their toxicity profile and to determine their role in therapy of diabetic complications. Moreover, a perfect rodent model which completely mimics human diabetic complications should be developed.

Cathepsin B contributes to autophagy-related 7 (Atg7)-induced nod-like receptor 3 (NLRP3)-dependent proinflammatory response and aggravates lipotoxicity in rat insulinoma cell line

Impairment of glucose-stimulated insulin secretion caused by the lipotoxicity of palmitate was found in β-cells. Recent studies have indicated that defects in autophagy contribute to pathogenesis in type 2 diabetes. Here, we report that autophagy-related 7 (Atg7) induced excessive autophagic activation in INS-1(823/13) cells exposed to saturated fatty acids. Atg7-induced cathepsin B (CTSB) overexpression resulted in an unexpected significant increase in proinflammatory chemokine and cytokine production levels of IL-1β, monocyte chemotactic protein-1, IL-6, and TNF-α. Inhibition of receptor-interacting protein did not affect the inflammatory response, ruling out involvement of necrosis. CTSB siRNA suppressed the inflammatory response but did not affect apoptosis significantly, suggesting that CTSB was a molecular linker between autophagy and the proinflammatory response. Blocking caspase-3 suppressed apoptosis but did not affect the inflammatory response, suggesting that CTSB induced inflammatory effects independently of apoptosis. Silencing of Nod-like receptor 3 (NLRP3) completely abolished both IL-1β secretion and the down-regulation effects of Atg7-induced CTSB overexpression on glucose-stimulated insulin secretion impairment, thus identifying the NLRP3 inflammasome as an autophagy-responsive element in the pancreatic INS-1(823/13) cell line. Combined together, our results indicate that CTSB contributed to the Atg7-induced NLRP3-dependent proinflammatory response, resulting in aggravation of lipotoxicity, independently of apoptosis in the pancreatic INS-1(823/13) cell line.