Beta-glucogallin reduces the expression of lipopolysaccharide-induced inflammatory markers by inhibition of aldose reductase in murine macrophages and ocular tissues

Enzymatic synthesis of phenolic acid glucosyl esters to test activities on cholangiocarcinoma cells

While glycoside hydrolase family 1 (GH1) enzymes mostly catalyze hydrolysis reactions, rice Os9BGlu31 preferentially catalyzes transglycosylation to transfer a glucosyl moiety to another aglycone moiety to form a new glycosylated compound through a retaining mechanism. In this study, Os9BGlu31 was used to synthesize eight phenolic acid glucosyl esters, which were evaluated for activities in cholangiocarcinoma cells. The transglycosylation products of Os9BGlu31 wild type and its mutant variants were detected, produced on a milligram scale, and purified, and their structures were characterized by NMR spectroscopy. The transglycosylation products were evaluated by antioxidant and anti-proliferative assays, followed by an anti-migration assay for the selected phenolic acid glucosyl ester. Os9BGlu31 mutants produced higher yield and activity than wild-type enzymes on phenolic acids to produce phenolic acid glucosyl esters. Among these, gallic acid glucosyl ester (β-glucogallin) had the highest antioxidant activity and anti-proliferative activity in cholangiocarcinoma cells. It also inhibited the migration of cholangiocarcinoma cells. Our study demonstrated that rice Os9BGlu31 transglucosidase is a promising enzyme for glycosylation of bioactive compounds in one-step reactions and provides evidence that β-glucogallin inhibits cell proliferation and migration of cholangiocarcinoma cells. KEY POINTS: • Os9BGlu31 transglucosidases produced phenolic acid glucosyl esters for bioactivity testing. • Phenolic acid glucosyl esters were tested for cytotoxicity in cholangiocarcinoma cells. • β-Glucogallin displayed the highest inhibition of cholangiocarcinoma cell growth.

Aldose reductase is a potential therapeutic target for neurodegeneration

Neurodegeneration is a complex process involving various inflammatory mediators and cellular responses. Aldose reductase (AR) is a key enzyme in the polyol pathway, which converts glucose to sorbitol. Beyond its metabolic role, AR has also been found to play a significant role in modulating neuroinflammation. This review aims to provide an overview of the current knowledge regarding the involvement of AR inhibition in attenuating neuroinflammation and complications from diabetic neuropathies. Here, we review the literature regarding AR and neuropathy/neurodegeneration. We discuss the mechanisms underlying the influence of AR inhibitors on ocular inflammation, beta-amyloid-induced neurodegeneration, and optic nerve degeneration. Furthermore, potential therapeutic strategies targeting AR in neurodegeneration are explored. The understanding of AR's role in neurodegeneration may lead to the development of novel therapeutic interventions for other neuroinflammatory disorders.

Discussing pathologic mechanisms of Diabetic retinopathy & therapeutic potentials of curcumin and β-glucogallin in the management of Diabetic retinopathy

Diabetic retinopathy (DR) is a form of retinal microangiopathy that occurs as a result of long-term Diabetes mellitus (DM). Patients with Diabetes mellitus typically suffer from DR as a progression of the disease that may be due to initiation and dysregulation of pathways like the polyol, hexosamine, the AGE/RAGE, and the PKC pathway, which all have negative impacts on eye health and vision. In this review, various databases, including PubMed, Google Scholar, Web of Science, and Science Direct, were scoured for data relevant to the aforementioned title. The three most common therapies for DR today are retinal photocoagulation, anti-vascular endothelial growth factor (VEGF) therapy, and vitrectomy, however, there are a number of drawbacks and limits to these methods. So, it is of critical importance and profound interest to discover treatments that may successfully address the pathogenesis of DR. Curcumin and β-glucogallin are the two potent compounds of natural origin that are already being used in various nutraceutical formulations for several ailments. They have been shown potent antiapoptotic, anti-inflammatory, antioxidant, anticancer, and pro-vascular function benefits in animal experiments. Their parent plant species have been used for generations by practitioners of traditional herbal medicine for the treatment and prevention of various eye ailments. In this review, we will discuss about pathophysiology of Diabetic retinopathy and the therapeutic potentials of curcumin and β-glucogallin one of the principal compounds from Curcuma longa and Emblica officinalis in Diabetic retinopathy.

The Neuroimmune Regulation and Potential Therapeutic Strategies of Optic Pathway Glioma

Optic pathway glioma (OPG) is one of the causes of pediatric visual impairment. Unfortunately, there is as yet no cure for such a disease. Understanding the underlying mechanisms and the potential therapeutic strategies may help to delay the progression of OPG and rescue the visual morbidities. Here, we provide an overview of preclinical OPG studies and the regulatory pathways controlling OPG pathophysiology. We next discuss the role of microenvironmental cells (neurons, T cells, and tumor-associated microglia and macrophages) in OPG development. Last, we provide insight into potential therapeutic strategies for treating OPG and promoting axon regeneration.

Aldose reductase inhibition decelerates optic nerve degeneration by alleviating retinal microglia activation

As part of the central nervous system (CNS), retinal ganglion cells (RGCs) and their axons are the only neurons in the retina that transmit visual signals from the eye to the brain via the optic nerve (ON). Unfortunately, they do not regenerate upon injury in mammals. In ON trauma, retinal microglia (RMG) become activated, inducing inflammatory responses and resulting in axon degeneration and RGC loss. Since aldose reductase (AR) is an inflammatory response mediator highly expressed in RMG, we investigated if pharmacological inhibition of AR can attenuate ocular inflammation and thereby promote RGC survival and axon regeneration after ON crush (ONC). In vitro, we discovered that Sorbinil, an AR inhibitor, attenuates BV2 microglia activation and migration in the lipopolysaccharide (LPS) and monocyte chemoattractant protein-1 (MCP-1) treatments. In vivo, Sorbinil suppressed ONC-induced Iba1 + microglia/macrophage infiltration in the retina and ON and promoted RGC survival. Moreover, Sorbinil restored RGC function and delayed axon degeneration one week after ONC. RNA sequencing data revealed that Sorbinil protects the retina from ONC-induced degeneration by suppressing inflammatory signaling. In summary, we report the first study demonstrating that AR inhibition transiently protects RGC and axon from degeneration, providing a potential therapeutic strategy for optic neuropathies.

Kampo herbal ointments for skin wound healing

The management of skin wound healing problems is a public health issue in which traditional herbal medicines could play a determining role. Kampo medicine, with three traditionally used ointments, provides interesting solutions for these dermatological issues. These ointments named Shiunkō, Chuōkō, and Shinsen taitsukō all have in common a lipophilic base of sesame oil and beeswax from which herbal crude drugs are extracted according to several possible manufacturing protocols. This review article brings together existing data on metabolites involved in the complex wound healing process. Among them are representatives of the botanical genera Angelica, Lithospermum, Curcuma, Phellodendron, Paeonia, Rheum, Rehmannia, Scrophularia, or Cinnamomum. Kampo provides numerous metabolites of interest, whose content in crude drugs is very sensitive to different biotic and abiotic factors and to the different extraction protocols used for these ointments. If Kampo medicine is known for its singular standardization, ointments are not well known, and research on these lipophilic formulas has not been developed due to the analytical difficulties encountered in biological and metabolomic analysis. Further research considering the complexities of these unique herbal ointments could contribute to a rationalization of Kampo's therapeutic uses for wound healing.

Anti-inflammatory potential of turmeric, amla, and black pepper mixture against sepsis-induced acute lung injury in rats

Acute lung injury (ALI), is a severe inflammatory lung disease. We tested the prophylactic effect of a functional food mix comprising three anti-inflammatory plant products: turmeric, amla, and black pepper (TAB) against lipopolysaccharide (LPS)-induced ALI in rats. Two-month-old male Wistar rats were randomly divided into three groups: control (C), LPS (5 mg/kg), and LPS with TAB (TAB). After 6 h of LPS injection, the rats were sacrificed by cervical decapitation to collect the lung tissue. Results showed that TAB partially ameliorated LPS-induced increase in circulating inflammatory cytokines (TNFα and IL6) and significantly prevented lung histopathological changes. TAB also suppressed LPS-activated ER stress markers (GRP78, pIRE1, and CHOP) and apoptotic markers (caspase-3 and - 12) in the lung. The anti-inflammatory effects of the TAB support its potential use as an adjuvant to mitigate ALI. Importantly, TAB's ingredients have been used for centuries as part of the diet with limited or no toxic effects.

The Role of Aldose Reductase in Beta-Amyloid-Induced Microglia Activation

The occurrence of Alzheimer's disease has been associated with the accumulation of beta-amyloid (β-amyloid) plaques. These plaques activate microglia to secrete inflammatory molecules, which damage neurons in the brain. Thus, understanding the underlying mechanism of microglia activation can provide a therapeutic strategy for alleviating microglia-induced neuroinflammation. The aldose reductase (AR) enzyme catalyzes the reduction of glucose to sorbitol in the polyol pathway. In addition to mediating diabetic complications in hyperglycemic environments, AR also helps regulate inflammation in microglia. However, little is known about the role of AR in β-amyloid-induced inflammation in microglia and subsequent neuronal death. In this study, we confirmed that AR inhibition attenuates increased β-amyloid-induced reactive oxygen species and tumor necrosis factor α secretion by suppressing ERK signaling in BV₂ cells. In addition, we are the first to report that AR inhibition reduced the phagocytotic capability and cell migration of BV₂ cells in response to β-amyloid. To further investigate the protective role of the AR inhibitor sorbinil in neurons, we co-cultured β-amyloid-induced microglia with stem cell-induced neurons. sorbinil ameliorated neuronal damage in both cells in the co-culture system. In summary, our findings reveal AR regulation of microglia activation as a novel therapeutic target for Alzheimer's disease.

Molecular Cloning, Expression, and Functional Analysis of Glycosyltransferase (TbUGGT) Gene from Trapa bispinosa Roxb

Trapa bispinosa Roxb. is an economical crop for medicine and food. Its roots, stems, leaves, and pulp have medicinal applications, and its shell is rich in active ingredients and is considered to have a high medicinal value. One of the main functional components of the Trapa bispinosa Roxb. shell is 1-galloyl-beta-D-glucose (βG), which can be used in medical treatment and is also an essential substrate for synthesizing the anticancer drug beta-penta-o-Galloyl-glucosen (PGG). Furthermore, gallate 1-beta-glucosyltransferase (EC 2.4.1.136) has been found to catalyze gallic acid (GA) and uridine diphosphate glucose (UDPG) to synthesize βG. In our previous study, significant differences in βG content were observed in different tissues of Trapa bispinosa Roxb. In this study, Trapa bispinosa Roxb. was used to clone 1500 bp of the UGGT gene, which was named TbUGGT, to encode 499 amino acids. According to the specificity of the endogenous expression of foreign genes in Escherichia coli, the adaptation codon of the cloned original genes was optimized for improved expression. Bioinformatic and phylogenetic tree analyses revealed the high homology of TbUGGT with squalene synthases from other plants. The TbUGGT gene was constructed into a PET-28a expression vector and then transferred into Escherichia coli Transsetta (DE3) for expression. The recombinant protein had a molecular weight of 55 kDa and was detected using SDS-PAGE. The proteins were purified using multiple fermentation cultures to simulate the intracellular environment, and a substrate was added for in vitro reaction. After the enzymatic reaction, the levels of βG in the product were analyzed using HPLC and LC-MS, indicating the catalytic activity of TbUGGT. The cloning and functional analysis of TbUGGT may lay the foundation for further study on the complete synthesis of βG in E. coli.

Glucogallin Attenuates the LPS-Induced Signaling in Macrophages and Protects Mice against Sepsis

The anti-oxidant and anti-inflammatory effect of beta-glucogallin (BGG), a plant-derived natural product, was evaluated in both in vitro and in vivo studies. For the in vitro study, the ability of BGG pre-treatment to quench LPS-induced effects compared to LPS alone in macrophages was investigated. It was found that BGG pre-treatment showed a significant decrease in ROS, NO, superoxide, and pro-inflammatory cytokines (TNF-alpha, IL-4, IL-17, IL-1β, and IL-6) and increased reduced glutathione coupled with the restoration of mitochondrial membrane potential. Gene profiling and further validation by qPCR showed that BGG pre-treatment downregulated the LPS-induced expression of c-Fos, Fas, MMP-9, iNOS, COX-2, MyD88, TRIF, TRAF6, TRAM, c-JUN, and NF-κB. We observed that BGG pre-treatment reduced nuclear translocation of LPS-activated NF-κB and thus reduced the subsequent expressions of NLRP3 and IL-1β, indicating the ability of BGG to inhibit inflammasome formation. Molecular docking studies showed that BGG could bind at the active site of TLR4. Finally, in the LPS-driven sepsis mouse model, we showed that pre-treatment with BGG sustained toxic shock, as evident from their 100% survival. Our study clearly showed the therapeutic potential of BGG in toxic shock syndrome.

Novel Emblica officinalis extract containing β-glucogallin vs. metformin: a randomized, open-label, comparative efficacy study in newly diagnosed type 2 diabetes mellitus patients with dyslipidemia

The efficacy of Emblica officinalis extract (EOE) containing 10% β-glucogallin was compared against metformin in newly diagnosed subjects with diabetic dyslipidemia which is a significant factor in cardiovascular disease. Daily administration with EOE-1 g, EOE-2 g, or metformin 500 mg for 90 days significantly decreased fasting blood sugar and postprandial blood sugar (FBS and PPBS), hemoglobin A1c (HbA1c) and lipid levels in all three treatment groups. The FBS, PPBS and HbA1c were significantly lower in the EOE-2 g group compared with metformin and EOE-1 g groups. The reductions in LDL and TC in the EOE-2 g group were also significantly higher than in the EOE-1 g group and were comparable to the metformin group. No serious adverse effects were observed in any study participants. EOE-1 g and 2 g day^-1 are safe and potent antidiabetic agents, with comparable efficacy to the pharmaceutical drug, metformin. Supplementation with EOE-2 g day^-1 showed greater efficacy than metformin in reducing circulating glucose levels.

Physiological and Pathological Roles of Aldose Reductase

Aldose reductase (AR) is an aldo-keto reductase that catalyzes the first step in the polyol pathway which converts glucose to sorbitol. Under normal glucose homeostasis the pathway represents a minor route of glucose metabolism that operates in parallel with glycolysis. However, during hyperglycemia the flux of glucose via the polyol pathway increases significantly, leading to excessive formation of sorbitol. The polyol pathway-driven accumulation of osmotically active sorbitol has been implicated in the development of secondary diabetic complications such as retinopathy, nephropathy, and neuropathy. Based on the notion that inhibition of AR could prevent these complications a range of AR inhibitors have been developed and tested; however, their clinical efficacy has been found to be marginal at best. Moreover, recent work has shown that AR participates in the detoxification of aldehydes that are derived from lipid peroxidation and their glutathione conjugates. Although in some contexts this antioxidant function of AR helps protect against tissue injury and dysfunction, the metabolic transformation of the glutathione conjugates of lipid peroxidation-derived aldehydes could also lead to the generation of reactive metabolites that can stimulate mitogenic or inflammatory signaling events. Thus, inhibition of AR could have both salutary and injurious outcomes. Nevertheless, accumulating evidence suggests that inhibition of AR could modify the effects of cardiovascular disease, asthma, neuropathy, sepsis, and cancer; therefore, additional work is required to selectively target AR inhibitors to specific disease states. Despite past challenges, we opine that a more gainful consideration of therapeutic modulation of AR activity awaits clearer identification of the specific role(s) of the AR enzyme in health and disease.

Fundamentals of Diabetic Cataractogenesis and Promising Ways of its Pharmacological Correction

Cataracts in diabetes mellitus lead to decreased visual function and blindness. Cataract surgery for diabetes mellitus has limitations and complications. The search for effective means of conservative cataract therapy continues. The review presents the analysis of data from scientific sources, mainly for 2015–2020 using Internet resources (PubMed, Web of Science, Medline, eLibrary.Ru, Cyberleninka). In the work, diabetic cataractogenesis is presented as a sum of interrelated pathobiochemical processes. The main ones are the polyol pathway of glucose conversion, non-enzymatic glycation and oxidative modification of lens proteins, which are enhanced in diabetes mellitus. The lens has a high protein content. The formation of high molecular weight protein aggregates is of particular importance for the appearance of light scattering zones and a decrease in lens transparency. This review presents data on anti-cataract compounds that affect post-translational crystallin modification, prevent osmotic and oxidative stress in the lens, and exhibit antiglycation properties. This information shows that the search for means of pharmacological correction of cataractogenesis should be carried out among compounds with antioxidant and antiglycation activity. 

Antiglaucoma Potential of β-Glucogallin Is Mediated by Modulating Mitochondrial Responses in Experimentally Induced Glaucoma

BACKGROUND

The use of phytochemicals for the treatment of various bodily ailments has been in practice since ancient days. Even though in practice, scientific studies on the protective effect of β-glucogallin (BG) against glaucoma is limited.

OBJECTIVES

In the present study, the in vitro glaucoma model (hydrostatic pressure) using PC12 neuronal cells exposed to BG were used to elucidate its protective effects.

METHOD

The cultured cells were analyzed for the mitochondrial responses, oxidant-antioxidant status, and expression of caveolin-1, ANGPTL7, the glaucoma markers, and cytokines.

RESULTS

We demonstrated a significant increase in the expression of glial fibrillary acidic protein, ANGPTL7, with altered mitochondrial enzymes in glaucoma cells compared to the control. Moreover, cells predisposed to hydrostatic pressure demonstrated an increase in oxidative stress with augmented (p < 0.01) inflammatory cytokines such as IL-2, CXCR4, IL-6, IL-8, MCP-1, and TNF-α. On the other hand, cells pretreated with BG attenuated the reactive oxygen species levels with improved antioxidant enzymes. Simultaneously, the levels of inflammatory cytokines and ANGPTL7 proteins were found attenuated with restored mitochondrial responses in BG pretreated cells.

CONCLUSION

Thus, the results of the present study demonstrate that the use of BG on retinal cells against relieving the intraocular pressure may be a promising therapeutic for controlling the disease progression.

Potential effect of tropical fruits Phyllanthus emblica L. for the prevention and management of type 2 diabetic complications: a systematic review of recent advances

Phyllanthus emblica is a fruit widely consumed in subtropical areas, which is rich in polyphenols and other nutrients. There are increasing evidences that as a daily and nutritious fruit, it may have a positive role in controlling diabetic complications. According to the new study, its mechanisms include enhancing the functioning of insulin, reducing insulin resistance, activating the insulin-signaling pathway, protecting β-cells, scavenging free radicals, alleviating inflammatory reactions, and reducing the accumulation of advanced glycation end products. Owing to its few side effects, and low price, it should be easily accepted by patients and has potential for preventing diabetes. Taken together, Phyllanthus emblica may be an ideal fruit for controlling diabetic complications. This review highlights the latest findings of the role of Phyllanthus emblica in anti-diabetes and its complications, especially clarifies the molecular mechanism of the chemical components related to this effect, and prospects some existing problems and future research directions.

Standardized Emblica officinalis fruit extract inhibited the activities of α-amylase, α-glucosidase, and dipeptidyl peptidase-4 and displayed antioxidant potential

BACKGROUND

Emblica officinalis, known as amla in Ayurveda, has been used as a folk medicine to treat numerous pathological conditions, including diabetes. However, the novel extract of E. officinalis fruit extract (amla fruit extract, AFE, Saberry®) containing 100 g kg^-1 β-glucogallin along with hydrolyzable tannins has not yet been extensively studied for its antidiabetic potential.

OBJECTIVE

The aim of this study was to investigate the antidiabetic and antioxidant activities of AFE and its stability during gastric stress as well as its thermostability.

METHODS

The effect of AFE on the inhibition of pancreatic α-amylase and salivary α-amylase enzymes was studied using starch and yeast α-glucosidase enzyme using 4-nitrophenyl α-d-glucopyranoside as substrate. Further, 2,2-diphenyl-1-picrylhydrazyl radical scavenging and reactive oxygen species inhibition assay was performed against AFE.

RESULTS

AFE potently inhibited the activities of α-amylase and α-glucosidase in a concentration-dependent manner with half maximal inhibitory concentration (IC₅₀ ) values of 135.70 μg mL^-1 and 106.70 μg mL^-1 respectively. Furthermore, it also showed inhibition of α-glucosidase (IC₅₀ 562.9 μg mL^-1 ) and dipeptidyl peptidase-4 (DPP-4; IC₅₀ 3770 μg mL^-1 ) enzyme activities. AFE is a potent antioxidant showing a free radical scavenging activity (IC₅₀ 2.37 μg mL^-1 ) and protecting against cellular reactive oxygen species (IC₅₀ 1.77 μg mL^-1 ), and the effects elicited could be attributed to its phytoconstituents.

CONCLUSION

AFE showed significant gastric acid resistance and was also found to be thermostable against wet heat. Excellent α-amylase, α-glucosidase, and DPP-4 inhibitory activities of AFE, as well as antioxidant activities, strongly recommend its use for the management of type 2 diabetes mellitus. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Protective Effect of β-Glucogallin on Damaged Cataract Against Methylglyoxal Induced Oxidative Stress in Cultured Lens Epithelial Cells

BACKGROUND ß-glucogallin (GG) is one of the major plant polyphenolic antioxidants that have been associated with positive effects on human health and are crucial in the developing defense mechanism against the risk of diseases. However, reports on the protective mechanism of GG in lens epithelial cells are limited. MATERIAL AND METHODS ARPE-19 cells (a human retinal epithelial cell line) were exposed to methylglyoxal (MG) with or without GG to illuminate the protective role of GG in counteracting the cataract signaling. RESULTS Cells predisposed to MG demonstrated an increase in oxidative stress with augmented (P<0.01) inflammatory cytokines such as cyclooxygenase (COX)-2, chemokine receptor CXCR4, interleukin (IL)-6, IL-8, monocyte chemoattractant protein-1 (MCP-1), and intercellular adhesion molecule 1 (ICAM-1) genes. In addition, the expression of aldose reductase (AR) was increased to 2-fold with accumulated sorbitol in MG exposed cells compared to control. On the other hand, cells exposed to MG evidenced a 3-fold increase in RAGE (receptor for advanced glycation end products) and a 2-fold increase in NF-kappaB (nuclear factor kappa-light-chain-enhancer of activated B cells) expression compared to control cells. Intriguingly, lens epithelial cells pre-treated with GG attenuated the reactive oxygen species levels with improved antioxidant enzymes. Simultaneously, the levels of AR and other inflammatory cytokines were observed in the levels closer to control cells in GG pre-treated cells. CONCLUSIONS Thus, the results of the present investigation show that GG may be a potential drug for the prevention of cataract development and progression.

Vitamin K1 prevents diabetic cataract by inhibiting lens aldose reductase 2 (ALR2) activity

This study investigated the potential of vitamin K1 as a novel lens aldose reductase inhibitor in a streptozotocin-induced diabetic cataract model. A single, intraperitoneal injection of streptozotocin (STZ) (35 mg/kg) resulted in hyperglycemia, activation of lens aldose reductase 2 (ALR2) and accumulation of sorbitol in eye lens which could have contributed to diabetic cataract formation. However, when diabetic rats were treated with vitamin K1 (5 mg/kg, sc, twice a week) it resulted in lowering of blood glucose and inhibition of lens aldose reductase activity because of which there was a corresponding decrease in lens sorbitol accumulation. These results suggest that vitamin K1 is a potent inhibitor of lens aldose reductase enzyme and we made an attempt to understand the nature of this inhibition using crude lens homogenate as well as recombinant human aldose reductase enzyme. Our results from protein docking and spectrofluorimetric analyses clearly show that vitamin K1 is a potent inhibitor of ALR2 and this inhibition is primarily mediated by the blockage of DL-glyceraldehyde binding to ALR2. At the same time docking also suggests that vitamin K1 overlaps at the NADPH binding site of ALR2, which probably shows that vitamin K1 could possibly bind both these sites in the enzyme. Another deduction that we can derive from the experiments performed with pure protein is that ALR2 has three levels of affinity, first for NADPH, second for vitamin K1 and third for the substrate DL-glyceraldehyde. This was evident based on the dose-dependency experiments performed with both NADPH and DL-glyceraldehyde. Overall, our study shows the potential of vitamin K1 as an ALR2 inhibitor which primarily blocks enzyme activity by inhibiting substrate interaction of the enzyme. Further structural studies are needed to fully comprehend the exact nature of binding and inhibition of ALR2 by vitamin K1 that could open up possibilities of its therapeutic application.

Pharmacological properties of Rheum turkestanicum Janisch

Medicinal herbs have been increasingly used worldwide for diseases prevention and treatment. Rheum turkestanicum Janisch. is a perennial shrub of the Polygonaceae family. Genus Rheum includes more than 60 species growing around the world which are used in foods and traditional medicines. R. turkestanicum is believed to be able to improve different kinds of disorders including diabetes, hypertension, jaundice and cancer. In recent years, this medicinal plant has been a subject of many experimental studies to document its health-beneficial properties. These studies have revealed antidiabetic, anticancer, nephroprotective, cardioprotective, and hepatoprotective properties of R. turkestanicum. The presence of flavonoids (e.g. epicatechin and quercetin) and anthraquinones (e.g. chrysophanol, physcion, and emodin) in R. turkestanicum justifies its health-beneficial effects. Nevertheless, possible therapeutic applications and safety of this plant still need to be elucidated in further clinical studies.

Aldose reductase inhibition enhances lens regeneration in mice

After cataract surgery, epithelial cells lining the anterior lens capsule can transition to one of two divergent pathways, including fibrosis which leads to posterior capsular opacification (PCO), or lens fiber cell differentiation which leads to regeneration of lens material. We previously showed that the PCO response can be suppressed with aldose reductase (AR) inhibitors. In this present study we show that AR inhibition, both genetic and pharmacologic with Sorbinil, can augment the process of lens regeneration. Extracapsular lens extraction (ECLE) was carried out in C57BL/6 (WT), AR overexpression (AR-Tg), and AR knockout (ARKO) mice, and in some cases in mice treated with the AR inhibitor sorbinil. Whole eyes were harvested approximately 8 weeks after ECLE and evaluated by histological analysis and immunostaining for the fiber cell marker γ-crystallin. All eyes examined for lens regeneration were paraffin embedded for serial sectioning to produce three-dimensional reconstructed models of lens morphology and size. We observed that AR-null mice respond to ECLE by regenerating a lens-like structure with a circular shape and array of cell nuclei reminiscent of the lens bow region typical of the native mammalian lens. Although WT and AR-Tg eyes also produced some regenerated lens material after ECLE, their structures were consistently smaller than ARKO regenerated lenses. WT mice treated with sorbinil showed higher levels of lens regeneration after ECLE compared to WT mice, as assessed by size and three-dimensional morphology. Altogether, this study adds evidence for a critical role for AR in the response of lens epithelial cells to cataract extraction and lens regeneration.

Aldose Reductase Inhibition Prevents Development of Posterior Capsular Opacification in an In Vivo Model of Cataract Surgery

Purpose

Cataract surgery is a procedure by which the lens fiber cell mass is removed from its capsular bag and replaced with a synthetic intraocular lens. Postoperatively, remnant lens epithelial cells can undergo an aberrant wound healing response characterized by an epithelial-to-mesenchymal transition (EMT), leading to posterior capsular opacification (PCO). Aldose reductase (AR) inhibition has been shown to decrease EMT markers in cell culture models. In this study, we aim to demonstrate that AR inhibition can attenuate induction of EMT markers in an in vivo model of cataract surgery.

Methods

A modified extracapsular lens extraction (ECLE) was performed on C57BL/6 wildtype, AR overexpression (AR-Tg), and AR knockout mice. Immunofluorescent staining for the myofibroblast marker α-smooth muscle actin (α-SMA), epithelial marker E-cadherin, and lens fiber cell markers αA-crystallin and Aquaporin 0 was used to characterize postoperative PCO. Quantitative reverse transcription PCR (qRT-PCR) was employed to quantify postoperative changes in α-SMA, vimentin, fibronectin, and E-cadherin. In a separate experiment, the AR inhibitor Sorbinil was applied postoperatively and qRT-PCR was used to assess changes in EMT markers.

Results

Genetic AR knockout reduced ECLE-induced upregulation of α-SMA and downregulation of E-cadherin. These immunofluorescent changes were mirrored quantitatively in changes in mRNA levels. Similarly, Sorbinil blocked characteristic postoperative EMT changes in AR-Tg mice. Interestingly, genetic AR knockout did not prevent postoperative induction of the lens fiber cell markers αA-crystallin and Aquaporin 0.

Conclusions

AR inhibition prevents the postoperative changes in EMT markers characteristic of PCO yet preserves the postoperative induction of lens fiber cell markers.

Role of aldose reductase in diabetes-induced retinal microglia activation

Diabetes-induced hyperglycemia plays a key pathogenic role in degenerative retinal diseases. In diabetic hyperglycemia, aldose reductase (AR) is elevated and linked to the pathogenesis of diabetic retinopathy (DR) and cataract. Retinal microglia (RMG), the resident immune cells in the retina, are thought to contribute to the proinflammatory phenotype in the diabetic eye. However, we have a limited understanding of the potential role of AR expressed in RMG as a mediator of inflammation in the diabetic retina. Glycated proteins accumulate in diabetes, including Amadori-glycated albumin (AGA) which has been shown to induce a proinflammatory phenotype in various tissues. In this study, we investigated the ability of AGA to stimulate inflammatory changes to RMG and macrophages, and whether AR plays a role in this process. In macrophages, treatment with an AR inhibitor (Sorbinil) or genetic knockdown of AR lowered AGA-induced TNF-α secretion (56% and 40%, respectively) as well as cell migration. In a mouse RMG model, AR inhibition attenuated AGA-induced TNF-α secretion and cell migration (67% and 40%, respectively). To further mimic the diabetic milieu in retina, we cultured RMG under conditions of hypoxia and observed the induction of TNF-α and VEGF protein expression. Downregulation of AR in either a pharmacological or genetic manner prevented hypoxia-induced TNF-α and VEGF expression. In our animal study, increased numbers of RMG observed in streptozotocin (STZ)-induced diabetic retina was substantially lower when diabetes was induced in AR knockout mice. Thus, in vitro and in vivo studies demonstrated that AR is involved in diabetes-induced RMG activation, providing a rationale for targeting AR as a therapeutic strategy for DR.

Cataract Preventive Role of Isolated Phytoconstituents: Findings from a Decade of Research

Cataract is an eye disease with clouding of the eye lens leading to disrupted vision, which often develops slowly and causes blurriness of the eyesight. Although the restoration of the vision in people with cataract is conducted through surgery, the costs and risks remain an issue. Botanical drugs have been evaluated for their potential efficacies in reducing cataract formation decades ago and major active phytoconstituents were isolated from the plant extracts. The aim of this review is to find effective phytoconstituents in cataract treatments in vitro, ex vivo, and in vivo. A literature search was synthesized from the databases of Pubmed, Science Direct, Google Scholar, Web of Science, and Scopus using different combinations of keywords. Selection of all manuscripts were based on inclusion and exclusion criteria together with analysis of publication year, plant species, isolated phytoconstituents, and evaluated cataract activities. Scientists have focused their attention not only for anti-cataract activity in vitro, but also in ex vivo and in vivo from the review of active phytoconstituents in medicinal plants. In our present review, we identified 58 active phytoconstituents with strong anti-cataract effects at in vitro and ex vivo with lack of in vivo studies. Considering the benefits of anti-cataract activities require critical evaluation, more in vivo and clinical trials need to be conducted to increase our understanding on the possible mechanisms of action and the therapeutic effects.

Aldo-Keto Reductases: Multifunctional Proteins as Therapeutic Targets in Diabetes and Inflammatory Disease

Aldose reductase (AR) is an NADPH-dependent aldo-keto reductase that has been shown to be involved in the pathogenesis of several blinding diseases such as uveitis, diabetic retinopathy (DR) and cataract. However, possible mechanisms linking the action of AR to these diseases are not well understood. As DR and cataract are among the leading causes of blindness in the world, there is an urgent need to explore therapeutic strategies to prevent or delay their onset. Studies with AR inhibitors and gene-targeted mice have demonstrated that the action of AR is also linked to cancer onset and progression. In this review we examine possible mechanisms that relate AR to molecular signaling cascades and thus explain why AR inhibition is an effective strategy against colon cancer as well as diseases of the eye such as uveitis, cataract, and retinopathy.

Small molecules as therapy for uveitis: a selected perspective of new and developing agents

INTRODUCTION

Intraocular inflammation (uveitis) remains a significant burden of legal blindness. Because of its immune mediated and chronic recurrent nature, common therapy includes corticosteroids, disease-modifying anti-rheumatic drugs and more recently biologics as immune modulatory agents. The purpose of this article is to identify the role of new treatment approaches focusing on small molecules as therapeutic option in uveitis. Areas covered: A MEDLINE database search was conducted through February 2017 using the terms 'uveitis' and 'small molecule'. To provide ongoing and future perspectives in treatment options, also clinical trials as registered at ClinicalTrials.gov were included. Both, results from experimental as well as clinical research in this field were included. Since this field is rapidly evolving, a selection of promising agents had to be made. Expert opinion: Small molecules may interfere at different steps of the inflammatory cascade and appear as an interesting option in the treatment algorithm of uveitis. Because of their highly targeted molecular effects and their favorable bioavailability with the potential of topical application small molecules hold great promise. Nevertheless, a careful evaluation of these agents has to be made, since current experience is almost exclusively based on experimental uveitis models and few registered trials.

Characterization of Emodin as a Therapeutic Agent for Diabetic Cataract

Aldose reductase (AR) in the lens plays an important role in the pathogenesis of diabetic cataract (DC) by contributing to osmotic and oxidative stress associated with accelerated glucose metabolism through the polyol pathway. Therefore, inhibition of AR in the lens may hold the key to prevent DC formation. Emodin, a bioactive compound isolated from plants, has been implicated as a therapy for diabetes. However, its inhibitory activity against AR remains unclear. Our results showed that emodin has good selectively inhibitory activity against AR (IC50 = 2.69 ± 0.90 μM) but not other aldo-keto reductases and is stable at 37 °C for at least 7 days. Enzyme kinetic studies demonstrated an uncompetitive inhibition against AR with a corresponding inhibition constant of 2.113 ± 0.095 μM. In in vivo studies, oral administration of emodin reduced the incidence and severity of morphological markers of cataract in lenses of AR transgenic mice. Computational modeling of the AR-NADP(+)-emodin ternary complex indicated that the 3-hydroxy group of emodin plays an essential role by interacting with Ser302 through hydrogen bonding in the specificity pocket of AR. All the findings above provide encouraging evidence for emodin as a potential therapeutic agent to prevent cataract in diabetic patients.

Aldose reductase mediates retinal microglia activation

Retinal microglia (RMG) are one of the major immune cells in charge of surveillance of inflammatory responses in the eye. In the absence of an inflammatory stimulus, RMG reside predominately in the ganglion layer and inner or outer plexiform layers. However, under stress RMG become activated and migrate into the inner nuclear layer (INL) or outer nuclear layer (ONL). Activated RMG in cell culture secrete pro-inflammatory cytokines in a manner sensitive to downregulation by aldose reductase inhibitors. In this study, we utilized CX3CR1(GFP) mice carrying AR mutant alleles to evaluate the role of AR on RMG activation and migration in vivo. When tested on an AR(WT) background, IP injection of LPS induced RMG activation and migration into the INL and ONL. However, this phenomenon was largely prevented by AR inhibitors or in AR null mice, or was exacerbated in transgenic mice that over-express AR. LPS-induced increases in ocular levels of TNF-α and CX3CL-1 in WT mice were substantially lower in AR null mice or were reduced by AR inhibitor treatment. These studies demonstrate that AR expression in RMG may contribute to the proinflammatory phenotypes common to various eye diseases such as uveitis and diabetic retinopathy.

Aldose Reductase Mediates Transforming Growth Factor β2 (TGF-β2)-Induced Migration and Epithelial-To-Mesenchymal Transition of Lens-Derived Epithelial Cells

PURPOSE

Cataract surgery involves removal of lens tissue, but is associated with a high complication rate due to regrowth of residual lens epithelial cells to produce posterior capsule opacification (PCO) and diminished visual acuity. As inhibitors of aldose reductase (AR) have been shown to suppress markers of PCO, our studies were designed to identify a role for AR in the pathogenesis of PCO.

METHODS

Sorbinil-mediated AR inhibition was determined by measuring sorbitol accumulation. Cell migration was measured using both transwell and scratch assays. Proteins in the SMAD signaling pathway were measured by Western blotting. The interactions of AR and SMADs were demonstrated by co-immunoprecipitation (Co-IP) and proximity ligation assay (PLA). Epithelial-to-mesenchymal transition (EMT) expression was measured by Western blot and quantitative PCR (q-PCR). Matrix metalloproteinase (MMP)-2 and MMP-9 activities were measured in conditioned medium by zymography.

RESULTS

We observed that either Sorbinil-mediated AR inhibition or siRNA-mediated AR gene knockdown prevented migration of lens epithelial cells following exposure to TGF-β2. AR inhibition or AR knockdown reduced SMAD and MMP activation triggered by TGF-β2. In addition, we demonstrated AR inhibition or AR knockdown decreased TGF-β2-induced expression of EMT markers. Co-IP studies and PLA were used to demonstrate that AR and SMAD2 interact either directly or in close concert with additional factor(s) in a nonenzymatic manner.

CONCLUSIONS

This study demonstrates that AR participates in the response of lens epithelial cells to TGF-β2. Our studies raise the possibility that AR inhibition may be effective in preventing development of PCO by disrupting the TGF-β2/SMAD pathway.

Inhibition of ocular aldose reductase by a new benzofuroxane derivative ameliorates rat endotoxic uveitis

The study investigated the effects of the aldose reductase (AR) inhibitor benzofuroxane derivative 5(6)-(benzo[d]thiazol-2-ylmethoxy) benzofuroxane (herein referred to as BF-5m) on the biochemical and tissue alterations induced by endotoxic uveitis in rats. BF-5m has been administered directly into the vitreous, in order to assess the expression and levels of (i) inflammatory markers such as the ocular ubiquitin-proteasome system, NF-κB, TNF-α, and MCP-1; (ii) prooxidant and antioxidant markers such as nitrotyrosine, manganese superoxide dismutase (MnSOD), and glutathione peroxidase (GPX); (iii) apoptotic/antiapoptotic factors caspases and Bcl-xl; (iv) markers of endothelial progenitor cells (EPCs) recruitment such as CD34 and CD117. 5 μL of BF-5m (0.01; 0.05; and 0.1 μM) into the right eye decreased in a dose-dependent manner the LPS-induced inflammation of the eye, reporting a clinical score 1. It reduced the ocular levels of ubiquitin, 20S and 26S proteasome subunits, NF-κB subunits, TNF-α, MCP-1, and nitrotyrosine. BF-5m ameliorated LPS-induced decrease in levels of MnSOD and GPX. Antiapoptotic effects were seen from BF-5m by monitoring the expression of Bcl-xl, an antiapoptotic protein. Similarly, BF-5m increased recruitment of the EPCs within the eye, as evidenced by CD34 and CD117 antibodies.

Aldose reductase inhibition alleviates hyperglycemic effects on human retinal pigment epithelial cells

Chronic hyperglycemia is an important risk factor involved in the onset and progression of diabetic retinopathy (DR). Among other effectors, aldose reductase (AR) has been linked to the pathogenesis of this degenerative disease. The purpose of this study was to investigate whether the novel AR inhibitor, beta-glucogallin (BGG), can offer protection against various hyperglycemia-induced abnormalities in human adult retinal pigment epithelial (ARPE-19) cells. AR is an enzyme that contributes to cellular stress by production of reactive oxygen species (ROS) under high glucose conditions. A marked decrease in cell viability (from 100% to 78%) following long-term exposure (4 days) of RPE cells to high glucose (HG) was largely prevented by siRNA-mediated knockdown of AR gene expression (from 79% to 97%) or inhibition using sorbinil (from 66% to 86%). In HG, BGG decreased sorbitol accumulation (44%), ROS production (27%) as well as ER stress (22%). Additionally, we demonstrated that BGG prevented loss of mitochondrial membrane potential (MMP) under HG exposure. We also showed that AR inhibitor pretreatment reduced retinal microglia-induced apoptosis in APRE-19 cells. These results suggest that BGG may be useful as a therapeutic agent against retinal degeneration in the diabetic eye by preventing RPE cell death.

Aldose reductase inhibition prevents endotoxin-induced inflammatory responses in retinal microglia

PURPOSE

Retinal microglia become activated in diabetes and produce pro-inflammatory molecules associated with changes in retinal vasculature and increased apoptosis of retinal neurons and glial cells. We sought to determine if the action of aldose reductase (AR), an enzyme linked to the pathogenesis of diabetic retinopathy, contributes to activation of microglial cells.

METHODS

Involvement of AR in the activation process was studied using primary cultures of retinal microglia (RMG) isolated from wild-type and AR-null mice, or in mouse macrophage cultures treated with either AR inhibitors or small interfering RNA (siRNA) directed to AR. Inflammatory cytokines were measured by ELISA. Cell migration was measured using a transwell assay. Gelatin zymography was used to detect active matrix metalloproteinase (MMP)-9, while RMG-induced apoptosis of adult retinal pigment epithelium (ARPE-19) cells was studied in a cell coculture system.

RESULTS

Aldose reductase inhibition or genetic deficiency substantially reduced lipopolysacharide (LPS)-induced cytokine secretion from macrophages and RMG. Aldose reductase inhibition or deficiency also reduced the activation of MMP-9 and attenuated LPS-induced cell migration. Additionally, blockade of AR by sorbinil or through genetic means caused a reduction in the ability of activated RMG to induce apoptosis of ARPE-19 cells.

CONCLUSIONS

These results demonstrate that the action of AR contributes to the activation of RMG. Inhibition of AR may be a therapeutic strategy to reduce inflammation associated with activation of RMG in disease.

Tonicity-responsive enhancer binding protein regulates the expression of aldose reductase and protein kinase C δ in a mouse model of diabetic retinopathy

Recent studies revealed that Tonicity-responsive enhancer binding protein (TonEBP) directly regulates the transcription of aldose reductase (AR), which catalyzes the first step of the polyol pathway of glucose metabolism. Activation of protein kinase C δ (PKCδ) is dependent on AR and it has been linked to diabetic complications. However, whether TonEBP affects expressions of AR and PKCδ in diabetic retinopathy was not clearly shown. In this study, we used TonEBP heterozygote mice to study the role of TonEBP in streptozotocin (STZ)-induced diabetic retinopathy. We performed immunofluorescence staining and found that retinal expressions of AR and PKCδ were significantly reduced in the heterozygotes compared to wild type littermates, particularly in ganglion cell layer. To examine further the effect of TonEBP reduction in retinal tissues, we performed intravitreal injection of TonEBP siRNA and confirmed the decrease in AR and PKCδ levels. In addition, we found that a proapoptotic factor, Bax level was reduced and a survival factor, Bcl2 level was increased after injection of TonEBP siRNA, indicating that TonEBP mediates apoptotic cell death. In parallel, TonEBP siRNA was applied to the in vitro human retinal pigment epithelial (ARPE-19) cells cultured in high glucose media. We have consistently found the decrease in AR and PKCδ levels and changes in apoptotic factors for survival. Together, these results clearly demonstrated that hyperglycemia-induced TonEBP plays a crucial role in increasing AR and PKCδ levels and leading to apoptotic death. Our findings suggest that TonEBP reduction is an effective therapeutic strategy for diabetic retinopathy.

Design of an amide N-glycoside derivative of β-glucogallin: a stable, potent, and specific inhibitor of aldose reductase

β-Glucogallin (BGG), a major component of the Emblica officinalis medicinal plant, is a potent and selective inhibitor of aldose reductase (AKR1B1). New linkages (ether/triazole/amide) were introduced via high yielding, efficient syntheses to replace the labile ester, and an original two-step (90%) preparation of BGG was developed. Inhibition of AKR1B1was assessed in vitro and using transgenic lens organ cultures, which identified the amide linked glucoside (BGA) as a stable, potent, and selective therapeutic lead toward the treatment of diabetic eye disease.

Efficacy of quercetin derivatives in prevention of ulcerative colitis in rats

Reactive oxygen species has been implicated to contribute significantly to tissue injury associated with ulcerative colitis. Thus compounds with antioxidant properties could be potential therapeutic agents in this disease. Flavonoid compounds are known to possess antioxidative and antiinflammatory properties. Two derivatives of the flavonoid quercetin (Q), chloronaphthoquinone quercetin (CNC) and monochloropivaloyl quercetin (MCP), showed improved antioxidant properties and moreover, they efficiently inhibited aldose reductase activity in vitro. The aim of the work was to test the potential efficacy of quercetin and these synthetic derivatives in vivo in prevention of intestinal inflammation during ulcerative colitis in rats. Colitis was induced by intracolonic administration of acetic acid (4% solution). The control group received the same volume of saline. The vehicle dimethyl sulfoxide (DMSO) and the drugs Q, CNC or MCP were administered orally two hours and then one hour before the acetic acid or saline instillation. After 48 hours, the animals were sacrificed and the colon was weighed, measured and scored for visible damage. Acetic acid triggered an intense inflammatory response of the colon, characterised by haemorrhage, ulceration and bowel wall thickening. From the drugs tested, only CNC (2 × 50 mg/kg) effectively depressed inflammatory damage of the colon. The mechanism of this beneficial effect remains to be elucidated.

Development of aldose reductase inhibitors for the treatment of inflammatory disorders

INTRODUCTION

Accumulating evidence attributes a significant role to aldose reductase (ALR2) in the pathogenesis of several inflammatory pathologies. Aldose reductase inhibitors (ARIs) were found to attenuate reactive oxygen species (ROS) production both in vitro and in vivo. Thus, they disrupt signaling cascades that lead to the production of cytokines/chemokines, which induce and exacerbate inflammation. As a result, ARIs might hold a significant therapeutic potential as alternate anti-inflammatory drugs.

AREAS COVERED

The authors present a comprehensive review of the current data that support the central role of ALR2 in several inflammatory pathologies (i.e., diabetes, cancer, sepsis, asthma and ocular inflammation). Further, the authors describe the potential underlying molecular mechanisms and provide a commentary on the status of ARIs in this field.

EXPERT OPINION

It is important that future efforts focus on delineating all the steps of the molecular mechanism that implicates ALR2 in inflammatory pathologies. At the same time, utilizing the previous efforts in the field of ARIs, several candidates that have been proven safe in the clinic may be evaluated for their clinical significance as anti-inflammatory medication. Finally, structurally novel ARIs, designed to target specifically the proinflammatory subpocket of ALR2, should be pursued.