Synthesis and biological evaluation of new epalrestat analogues as aldose reductase inhibitors (ARIs)

AKR1B1 drives hyperglycemia-induced metabolic reprogramming in MASLD-associated hepatocellular carcinoma

Background & Aims

The mechanism behind the progressive pathological alteration in metabolic dysfunction-associated steatotic liver disease/steatohepatitis (MASLD/MASH)-associated hepatocellular carcinoma (HCC) is poorly understood. In the present study, we investigated the role of the polyol pathway enzyme AKR1B1 in metabolic switching associated with MASLD/MASH and in the progression of HCC.

Methods

AKR1B1 expression was estimated in the tissue and plasma of patients with MASLD/MASH, HCC, and HCC with diabetes mellitus. The role of AKR1B1 in metabolic switching in vitro was assessed through media conditioning, lentiviral transfection, and pharmacological probes. A proteomic and metabolomic approach was applied for the in-depth investigation of metabolic pathways. Preclinically, mice were subjected to a high-fructose diet and diethylnitrosamine to investigate the role of AKR1B1 in the hyperglycemia-mediated metabolic switching characteristic of MASLD-HCC.

Results

A significant increase in the expression of AKR1B1 was observed in tissue and plasma samples from patients with MASLD/MASH, HCC, and HCC with diabetes mellitus compared to normal samples. Mechanistically, in vitro assays revealed that AKR1B1 modulates the Warburg effect, mitochondrial dynamics, the tricarboxylic acid cycle, and lipogenesis to promote hyperglycemia-mediated MASLD and cancer progression. A pathological increase in the expression of AKR1B1 was observed in experimental MASLD-HCC, and expression was positively correlated with high blood glucose levels. High-fructose diet + diethylnitrosamine-treated animals also exhibited statistically significant elevation of metabolic markers and carcinogenesis markers. AKR1B1 inhibition with epalrestat or NARI-29 inhibited cellular metabolism in in vitro and in vivo models.

Conclusions

Pathological AKR1B1 modulates hepatic metabolism to promote MASLD-associated hepatocarcinogenesis. Aldose reductase inhibition modulates the glycolytic pathway to prevent precancerous hepatocyte formation.

Impact and implications

This research work highlights AKR1B1 as a druggable target in metabolic dysfunction-associated steatotic liver disease (MASLD) and hepatocellular carcinoma (HCC), which could provide the basis for the development of new chemotherapeutic agents. Moreover, our results indicate the potential of plasma AKR1B1 levels as a prognostic marker and diagnostic test for MASLD and associated HCC. Additionally, a major observation in this study was that AKR1B1 is associated with the promotion of the Warburg effect in HCC.

Recent Studies of Nitrogen and Sulfur Containing Heterocyclic Analogues as Novel Antidiabetic Agents: A Review

The prevalence of diabetes mellitus is on the rise, which demands the identification of novel antidiabetic drugs. There is a need for safer and more effective alternatives because the therapy methods now available to manage diabetes have limits. Due to their diverse pharmacological characteristics, heterocyclic molecules with nitrogen and Sulfur atoms have become intriguing candidates in medicinal chemistry. These substances have a wide variety of structures that can be customized to target different pathways associated with diabetes and can affect important biological targets involved in glucose homeostasis. This review provides a thorough summary of the most recent studies on heterocyclic analogues of nitrogen and Sulfur as prospective antidiabetic agents. This review examines the variety of their structural forms, their methods of action, and assesses the results of preclinical and clinical investigations on their effectiveness and safety. Additionally, further optimization and development of innovative antidiabetic medications are highlighted, as well as the difficulties and prospects for the future in utilizing the therapeutic potential of these analogues. This study seeks to stimulate additional investigation and cooperation between researchers and medicinal chemists, promoting improvements in the creation of efficient and secure antidiabetic medicines to fulfill the needs in the management of diabetes.

Thiazolidinedione as a Promising Medicinal Scaffold for the Treatment of Type 2 Diabetes

BACKGROUND

Thiazolidinediones, also known as glitazones, are considered as biologically active scaffold and a well-established class of anti-diabetic agents for the treatment of type 2 diabetes mellitus. Thiazolidinediones act by reducing insulin resistance through elevated peripheral glucose disposal and glucose production. These molecules activate peroxisome proliferated activated receptor (PPARγ), one of the sub-types of PPARs, and a diverse group of its hybrid have also shown numerous therapeutic activities along with antidiabetic activity.

OBJECTIVE

The objective of this review was to collect and summarize the research related to the medicinal potential, structure-activity relationship and safety aspects of thiazolidinedione analogues designed and investigated in type 2 diabetes during the last two decades.

METHODS

The mentioned objective was achieved by collecting and reviewing the research manuscripts, review articles, and patents from PubMed, Science Direct, Embase, google scholar and journals related to the topic from different publishers like Wiley, Springer, Elsevier, Taylor and Francis, Indian and International government patent sites etc. Results: The thiazolidinedione scaffold has been a focus of research in the design and synthesis of novel derivatives for the management of type 2 diabetes, specifically in the case of insulin resistance. The complications like fluid retention, idiosyncratic hepatotoxicity, weight gain and congestive heart failure in the case of trosiglitazone, and pioglitazone have restricted their use. The newer analogues have been synthesized by different research groups to attain better efficacy and less side effects.

CONCLUSION

Thus, the potential of thiazolidinediones in terms of their chemical evolution, action on nuclear receptors, aldose reductase and free fatty acid receptor 1 is well established. The newer TZD analogues with better safety profiles and tolerability will soon be available in the market for common use without further delay.

Exploring the Divergent Reactivity of Vinyl Radicals Emanating from Alkynes and Thiols via Photoredox Catalysis

Organic chemistry has seen a surge in visible-light-driven transformations, which offer unique reaction pathways and access to new synthetic possibilities. We aim to provide a comprehensive understanding of state-of-the-art photo-mediated alkyne functionalization, with a focus on the reactive behavior of vinyl radicals. This review outlines our contributions to the field, including developing new methods for forming carbon-carbon and carbon-heteroatom bonds.

In silico study on antidiabetic and antioxidant activity of bioactive compounds in Ficus carica L

Hyperglycemia is one of the diagnostic issues in diabetes mellitus and is considered as a complex metabolic condition. It has been one of the most prevalent illnesses of the twenty-first century and still rising at an alarming rate across the globe and expected to impact 693 million individuals by 2045. Therefore, it is mandatory to develop more effective and safer treatments to manage diabetes. One of the ways to manage hyperglycemia is through inhibiting carbohydrate digestion and thereby lowering the glucose formation in the human body. The enzyme salivary amylase and pancreatic amylase is responsible for cleaving α-1,4-glucoside bond. Amylase inhibitors can lower blood glucose in diabetics by slowing digestion. Ficus carica is commonly known for its medicinal properties due to its various phytochemicals. In the present study, 10 phytochemicals present in F. carica compounds named, β-carotene, lutein, cyanidin-3-glucoside, gallic acid, luteolin, catechin, kaempferol, vanillic acid, peonidin-3-glucoside, and quercetin hydrate were taken to study their inhibition potential against pancreatic amylase and salivary amylase through molecular docking and molecular dynamics simulations. Further, density functional theory calculations are used to investigate the delocalization of electron density on the molecule as well as study ADME properties of the molecules take. A QSAR model has been developed using the binding energy obtained using molecular docking and thermodynamic parameters from DFT calculations.Communicated by Ramaswamy H. Sarma.

AKR1B1 inhibition using NARI-29-an Epalrestat analogue-alleviates Doxorubicin-induced cardiotoxicity via modulating Calcium/CaMKII/MuRF-1 axis

The clinical use of doxorubicin (Dox) is narrowed due to its carbonyl reduction to doxorubicinol (Doxol) implicating resistance and cardiotoxicity. Hence, in the present study we have evaluated the cardioprotective effect of AKR1B1 (or aldose reductase, AR) inhibitor NARI-29 (epalrestat (EPS) analogue) and its effect in the Dox-modulated calcium/CaMKII/MuRF1 axis. Initially, the breast cancer patient survival associated with AKR1B1 expression was calculated using Kaplan Meier-plotter (KM-plotter). Further, breast cancer, cardiomyoblast (H9c2), and macrophage (RAW 264.7) cell lines were used to establish the in vitro combination effect of NARI-29 and Dox. To develop the cardiotoxicity model, mice were given Dox 2.5 mg/kg (i.p.), biweekly. The effect of AKR1B1 inhibition using NARI-29 on molecular and cardiac functional changes was measured using echocardiography, fluorescence-imaging, ELISA, immunoblotting, flowcytometry, High-Performance Liquid Chromatography with Fluorescence Detection (HPLC-FD) and cytokine-bead array methods. The bioinformatics data suggested that a high expression of AKR1B1 is associated with significantly low survival of breast cancer patients undergoing chemotherapy; hence, it could be a target for chemo-sensitization and chemo-prevention. Further, in vitro studies showed that AKR1B1 inhibition with NARI-29 has increased the accumulation and sensitized Dox to breast cancer cell lines. However, treatment with NARI-29 has alleviated the Dox-induced toxicity to cardiomyocytes and decreased the secretion of inflammatory cytokines from RAW 264.7 cells. In vivo studies revealed that the NARI-29 (25 and 50 mg/kg) has prevented the functional, histological, biochemical, and molecular alterations induced by Dox treatment. Moreover, we have shown that NARI-29 has prevented the carbonyl reduction of Dox to Doxol in the mouse heart, which reduced the calcium overload, prevented phosphorylation of CaMKII, and reduced the expression of MuRF1 to protect from cardiac injury and apoptosis. Hence in conclusion, AKR1B1 inhibitor NARI-29 could be used as an adjuvant therapeutic agent with Dox to prevent cardiotoxicity and synergize anti-breast cancer activity.

Pivotal role of AKR1B1 in pathogenesis of colitis associated colorectal carcinogenesis

Identifying the target linking inflammation and oxidative stress to aggravate the disease progression will help to prevent colitis associated carcinogenesis. Since AKR1B1 overexpression is observed in inflammatory diseases and various cancers, we have investigated the role of AKR1B1 in colitis-associated colon carcinogenesis with the aid of epalrestat and its potent analogue NARI-29 (investigational molecule) as pharmacological probes. A TNF-α inducible NF-κB reporter cell line (GloResponse™ NF-κB-RE-luc2P HEK293) and dextran sodium sulfate (DSS) and 1,2 dimethyl hydrazine (DMH))-induced mouse model was used to investigate our hypothesis in vitro and in vivo. Clinically, an increased expression of AKR1B1 was observed in patients with ulcerative colitis. Our in vitro and in vivo findings suggest that the AKR1B1 modulated inflammation and ROS generation for the progression of colitis to colon cancer. AKR1B1 overexpression was observed in DSS + DMH-treated mice colons. Moreover, we could observe histopathological changes like immune cell infiltration, aberrant crypt foci, and tumour formation in DC groups. Mechanistically, we have witnessed modulation of the IKK/IκB/NF-κB and Akt/FOXO-3a/DR axis, increased inflammatory cytokines, increased expression of proliferative markers, Ki-67 and PCNA, and accumulation of β-catenin in the colon epithelium. However, pharmacological inhibition of AKR1B1 using NARI-29 or EPS has reversed the clinical, histopathological, and molecular alterations induced by DSS + DMH, confirming the obvious role of AKR1B1 in the promotion of colitis-associated carcinogenesis. In conclusion, our findings suggest that AKR1B1 targeted therapy could be a promising strategy for preventing CA-CRC and NARI-29 could be developed as a potent AKR1B1 inhibitor.

Molecular dissection of anti-colon cancer activity of NARI-29: special focus on H2O2 modulated NF-κB and death receptor signaling

Accumulating evidence attributes the role of aldose reductase (AR) in modulating ROS and inflammation which are the main factor responsible for cancer progression and drug resistance. Epalrestat is the only AR inhibitor being used in Asian countries. It did not make it to the markets of the USA and Europe due to marginal efficacy as an antioxidant and anti-inflammatory agent owing to difficulty reaching intracellular targets. In our previous studies, we attempted to synthesize the epalrestat analogs and reported that the compound 4-((Z)-5-((Z)-2-Cyano-3-phenylallylidene)-4-oxo-2-thioxothiazolidin-3-yl) benzoic acid named as NARI-29 has potent AR inhibition compared to epalrestat. In the current study, we aimed to find the effect of NARI-29 on ROS-induced cancer progression and TRAIL resistance in colon cancer in vitro models. In the first part of the study, we demonstrated that the NARI-29 has specific AKR1B1 inhibition and superior drug-like properties than epalrestat using bioinformatics tools. In the second part of the study, it was proven that NARI-29 has induced the hydrogen peroxide-triggered TRAIL-induced apoptosis in the colon cancer cells via modulating the AKR1B1/4HNE/FOXO3a/DR axis. The selective cytotoxicity of NARI-29 (10-fold) compared to epalrestat (4-fold) toward cancer cells is due to its differential ROS regulation and anti-inflammatory activities. Altogether, these data show that NARI-29 may be a potential candidate for AR inhibitors, which will be used to prevent colon cancer progression and as adjuvant therapy for preventing TRAIL resistance.

Aldose reductase and cancer metabolism: The master regulator in the limelight

It is strongly established that metabolic reprogramming mediates the initiation, progression, and metastasis of a variety of cancers. However, there is no common biomarker identified to link the dysregulated metabolism and cancer progression. Recent studies strongly advise the involvement of aldose reductase (AR) in cancer metabolism. AR-mediated glucose metabolism creates a Warburg-like effect and an acidic tumour microenvironment in cancer cells. Moreover, AR overexpression is associated with the impairment of mitochondria and the accumulation of free fatty acids in cancer cells. Further, AR-mediated reduction of lipid aldehydes and chemotherapeutics are involved in the activation of factors promoting proliferation and chemo-resistance. In this review, we have delineated the possible mechanisms by which AR modulates cellular metabolism for cancer proliferation and survival. An in-depth understanding of cancer metabolism and the role of AR might lead to the use of AR inhibitors as metabolic modulating agents for the therapy of cancer.

Rhodanine derivatives: An insight into the synthetic and medicinal perspectives as antimicrobial and antiviral agents

Rhodanine or 2-Thioxothiazolidin-4-one is a privileged heterocyclic compound offering a wide opportunity for structural modification, lead development, and modification. It is one of the highly decorated scaffolds in the drug discovery process. Rhodanine derivatives possess a plethora of biological activities due to their ability to interact with a diverse range of protein targets, which provide tremendous opportunities to discover new drugs with different modes of action. The most common strategy for developing novel rhodanine derivatives is the introduction of structurally diverse substituents at the C-5 or N-3, or both positions. Since the inception of Epralestat into the market in 1992, the exploration of rhodanine-3-acetic acids has led to the development of novel leads against different biological targets such as MRSA, HHV-6, Mycobacterial tuberculosis, dengue, etc. In the current pandemic era, some rhodanine compounds have been explored against SARS-CoV-2. In recent years, rhodanine and its derivatives have witnessed significant progress in developing new drug leads as potential antimicrobial and antiviral agents. Different synthetic methodologies and recent developments in the medicinal chemistry of rhodanine derivatives, including biological activities, their mechanistic aspects, structure-activity relationships, and in silico findings, have been compiled in the present review. This article will benefit the scientific community and offer perspectives on how these scaffolds as privileged structures might be exploited in the future for rational design and discovery of rhodanine-based bio-active molecules.

Moving toward a new horizon for the aldose reductase inhibitor epalrestat to treat drug-resistant cancer

Epalrestat (EPA) is a potent inhibitor of aldose reductases AKR1B1 and AKR1B10, used for decades in Japan for the treatment of diabetic peripheral neuropathy. This orally-active, brain-permeable small molecule, with a relatively rare and essential 2-thioxo-4-thiazolidinone motif, functions as a regulator intracellular carbonyl species. The repurposing of EPA for the treatment of pediatric rare diseases, brain disorders and cancer has been proposed. A detailed analysis of the mechanism of action, and the benefit of EPA to combat advanced malignancies is offered here. EPA has revealed marked anticancer activities, alone and in combination with cytotoxic chemotherapy and targeted therapeutics, in experimental models of liver, colon, and breast cancers. Through inhibition of AKR1B1 and/or AKR1B10 and blockade of the epithelial-mesenchymal transition, EPA largely enhances the sensitivity of cancer cells to drugs like doxorubicin and sorafenib. EPA has revealed a major anticancer effect in an experimental model of basal-like breast cancer and clinical trials have been developed in patients with triple-negative breast cancer. The repurposing of the drug to treat chemo-resistant solid tumors seems promising, but more studies are needed to define the best trajectory for the positioning of EPA in oncology.

Synthesis and aldose reductase inhibition effects of celecoxib derivatives containing pyrazole linked-sulfonamide moiety

In this article, we report the synthesis of Celecoxib derivatives containing the pyrazole-linked sulfonamide moiety. The enzyme inhibition effects of these derivatives on aldose reductase (AR) were also investigated. The IC₅₀ values of the pyrazole sulfonamide derivatives were determined to be in the range of 40.76-8.25 µM. Among the synthesized derivatives, the compound 16 showed the strongest inhibition effect against the AR enzyme, with an IC₅₀ value of 8.25 µM. Molecular docking studies were carried out to determine the interactions of the synthesized compounds with the AR enzyme, and ADMET studies were performed to assess the pharmacokinetic and drug-likeness properties.

Synthesis, Crystal Structures, Lipophilic Properties and Antimicrobial Activity of 5-Pyridylmethylidene-3-rhodanine-carboxyalkyl Acids Derivatives

The constant increase in the resistance of pathogenic bacteria to the commonly used drugs so far makes it necessary to search for new substances with antibacterial activity. Taking up this challenge, we obtained a series of rhodanine-3-carboxyalkyl acid derivatives containing 2- or 3- or 4-pyridinyl moiety at the C-5 position. These compounds were tested for their antibacterial and antifungal activities. They showed activity against Gram-positive bacteria while they were inactive against Gram-negative bacteria and yeast. In order to explain the relationship between the activity of the compounds and their structure, for selected derivatives crystal structures were determined using the X-ray diffraction method. Modeling of the isosurface of electron density was also performed. For all tested compounds their lipophilicity was determined by the RP-TLC method and by calculation methods. On the basis of the carried-out research, it was found that the derivatives with 1.5 N···S electrostatics interactions between the nitrogen atom in the pyridine moiety and the sulfur atom in the rhodanine system showed the highest biological activity.

Neuroprotective effects of oleuropein on retina photoreceptors cells primary culture and olive leaf extract and oleuropein inhibitory effects on aldose reductase in a diabetic model: Meriones shawi

Aldose reductase (AR) is an enzyme implicated in the development of diabetes complications among them diabetic retinopathy. Erythrocyte AR activity was measured in control and diabetic Meriones shawi, a type-2 diabetic model. We noticed an increase of AR activity in diabetic Meriones by comparison to controls. Olive leaf aqueous extract and oleuropein were tested for their inhibitory potential on AR activity. Both exerted a partial in-vitro inhibition effect which was higher with the olive leaf extract. The ex-vivo protective effect of oleuropein was tested in photoreceptors rod and Mcône retinal cells of Meriones shawi in hyperglycaemic conditions. Mixed retinal cells were cultured at 25 mM glucose for 5 days and treated with oleuropein. Cell viability was assessed using MTT test and trypan blue exclusion dye. Rod and Mcône Photoreceptors were characterised by immuno-cytochemistry. Oleuropein protected retinal cells against the toxic effect of glucose by improving the viability of photoreceptors.

Screening of potential antidiabetic phytochemicals from Gongronema latifolium leaf against therapeutic targets of type 2 diabetes mellitus: multi-targets drug design

Diabetes mellitus (DM) is the most predominant group of metabolic disorders wreaking havoc on the wellbeing of man, with type 2 diabetes mellitus (type 2 DM) accounting for most DM related cases. This study, hence, investigated the antidiabetic potential of Gongronema latifolium leaf fractionated compounds against proteins implicated in different molecular pathways related to the onset and progression of type 2 DM. A total of fifteen proteins that can act as type 2 DM therapeutic targets were identified from the literature and downloaded/modelled using respective repositories. After docking the compounds with the fifteen proteins, glycogen synthase kinase 3 beta (GSK 3β), glucagon-like peptide-1 receptor (GLP-1R) and human aldose reductase were chosen as the ideal targets due to their high binding affinities with the compounds. Subsequent in silico analysis like binding free energy, ADMET predictions using different servers, and machine-learning predictive models (QSAR) using kernel partial least square regression were employed to identify promising compounds against the three targets. The eleven identified compounds (Luteonin, Kampferol, Robinetin, Gallocatechin, Baicalin, Apigenin, Genistein, Rosmaric acid, Chicoric acid and Naringenin) formed stable complexes with the proteins, showed moderation for toxicity, drugability, GI absorptions and drug-drug interactions, though structure modifications may be needed for lead optimization. The predictive QSAR models with reliable correlation coefficient (R2) showed the potency of the compounds to act as inhibitors (pIC50) of aldose reductase and GSK 3β, and act as agonists (pEC50) of GLP-1R. Thus, this study experimental framework can be used to design compounds that can modulate proteins related to type 2 DM without inducing off-target effects.

Synthesis and Aldose Reductase Inhibition Effects of Novel N-Benzyl-4-Methoxyaniline Derivatives

In the current study, starting from 4-methoxyaniline, four Schiff bases were synthesized from benzaldehydes with Br and OMe. Corresponding N-benzylanilines and their derivatives were obtained from reductions (by NaBH₄ ) and substitutions (by acyl and tosyl chlorides) of these bases, respectively. The inhibitory effects of the sixteen compounds, twelve of which were novel compounds are examined. Then, we conducted molecular docking and binary QSAR studies to determine inhibitory-enzyme interactions of compounds that show an inhibitory effect. Our results reveal that methoxyanilline-derived compounds show good biological activities. The most active compound (22) has IC₅₀ values of 2.83 μM. These novel AR enzyme inhibitors may open new avenues for better AR inhibitors in the future.

Development of Aldose Reductase Inhibitors for the Treatment of Inflammatory Disorders and Cancer: Current Drug Design Strategies and Future Directions

Aldose Reductase (AR) is an enzyme that converts glucose to sorbitol during the polyol pathway of glucose metabolism. AR has been shown to be involved in the development of secondary diabetic complications due to its involvement in causing osmotic as well as oxidative stress. Various AR inhibitors have been tested for their use to treat secondary diabetic complications, such as retinopathy, neuropathy, and nephropathy in clinical studies. Recent studies also suggest the potential role of AR in mediating various inflammatory complications. Therefore, the studies on the development and potential use of AR inhibitors to treat inflammatory complications and cancer besides diabetes are currently on the rise. Further, genetic mutagenesis studies, computer modeling, and molecular dynamics studies have helped design novel and potent AR inhibitors. This review discussed the potential new therapeutic use of AR inhibitors in targeting inflammatory disorders and cancer besides diabetic complications. Further, we summarized studies on how AR inhibitors have been designed and developed for therapeutic purposes in the last few decades.

Synthesis, molecular modeling, selective aldose reductase inhibition and hypoglycemic activity of novel meglitinides

In the present study, a novel generation of selective aldose reductase ALR2 inhibitors with significant hypoglycemic activities was designed and modulated based on rhodanine scaffold joined to an acetamide linker in between two lipophilic moieties. The synthesis of the novel compounds was accomplished throughout simple chemical pathways. Molecular docking was performed on B-cell membrane protein SUR1, aldehyde reductase ALR1 and aldose reductase ALR2 active sites. Compounds 10B, 11B, 12B, 15C, 16C, 26F and 27F displayed the highest hypoglycemic activities with 80.7, 85.2, 87, 82.3, 83.5, 81.4 and 85.3% reduction in blood glucose levels, respectively. They were more potent than the standard hypoglycemic agent repaglinide with 65.4% reduction in blood glucose level. Compounds 12B and 15C with IC₅₀ 0.29 and 0.35 µM were more potent than the standard ALR2 inhibitor epalrestat with IC₅₀ 0.40 µM. They were selective towards ALR2 over ALR1 134 and 116 folds, respectively. Molecular docking studies matched with the in-vitro and in-vivo results to elucidate the dual activities of both compounds 12B and 15C as potent antagonists for ALR2 over ALR1 and good agonists for the SUR1 protein.

Aldose reductase and protein tyrosine phosphatase 1B inhibitors as a promising therapeutic approach for diabetes mellitus

Diabetes mellitus is a metabolic disease characterized by high blood glucose levels and usually associated with several chronic pathologies. Aldose reductase and protein tyrosine phosphatase 1B enzymes have identified as two novel molecular targets associated with the onset and progression of type II diabetes and related comorbidities. Although many inhibitors against these enzymes have already found in the field of diabetic mellitus, the research for discovering more effective and selective agents with optimal pharmacokinetic properties continues. In addition, dual inhibition of these target proteins has proved as a promising therapeutic approach. A variety of diverse scaffolds are presented in this review for the future design of potent and selective inhibitors of aldose reductase and protein tyrosine phosphatase 1B based on the most important structural features of both enzymes. The discovery of novel dual aldose reductase and protein tyrosine phosphatase 1B inhibitors could be effective therapeutic molecules for the treatment of insulin-resistant type II diabetes mellitus. The methods used comprise a literature survey and X-ray crystal structures derived from Protein Databank (PDB). Despite the available therapeutic options for type II diabetes mellitus, the inhibitors of aldose reductase and protein tyrosine phosphatase 1B could be two promising approaches for the effective treatment of hyperglycemia and diabetes-associated pathologies. Due to the poor pharmacokinetic profile and low in vivo efficacy of existing inhibitors of both targets, the research turned to more selective and cell-permeable agents as well as multi-target molecules.

Addressing selectivity issues of aldose reductase 2 inhibitors for the management of diabetic complications

Aldose Reductase 2 (ALR2), the rate-limiting enzyme of the polyol pathway, plays an important role in detoxification of some toxic aldehydes. Under hyperglycemia, this enzyme overactivates and causes diabetic complications (DC). Therefore, ALR2 inhibition has been established as a potential approach to manage these complications. Several ALR2 inhibitors have been reported, but none of them could reach US FDA approval. One of the main reasons is their poor selectivity over ALR1, which leads to the toxicity. The current review underlines the molecular connectivity of ALR2 with DC and comparative analysis of the catalytic domains of ALR2 and ALR1, to better understand the selectivity issues. This report also discusses the key features required for ALR2 inhibition and to limit toxicity due to off-target activity.

Substituted 2-thioxothiazolidin-4-one derivatives showed protective effects against diabetic cataract via inhibition of aldose reductase

In an effort to develop a new class of potent aldose reductase inhibitors against diabetic cataracts, a series of novel 2-thioxothiazolidine-4-one derivatives was synthesized in excellent yields via a facile synthetic route. These compounds were tested against aldehyde (ALR1) and aldose reductase (ALR2) enzymes, where they showed considerable inhibitory activity. Among the tested derivatives, compound 6e showed selective and excellent inhibition of ALR2 over ALR1. The experimental diabetes was induced by the intraperitoneal administration of streptozotocin in male Wistar rats. Compound 6e showed positive modulation of body weight, blood glucose, and blood insulin levels in diabetic rats. Compound 6e also showed ALR2 inhibition as evidenced by Western blot analysis in lens homogenates of Wistar rats having cataract. The docking study of 6e was also performed inside the active site of ALR2 to enumerate the key contacts for inhibitory activity.

In vitro studies of potent aldose reductase inhibitors: Synthesis, characterization, biological evaluation and docking analysis of rhodanine-3-hippuric acid derivatives

Inhibitors of aldose reductase are rate-limiting enzymes and could play a key role to prevent the complications of diabetes. In our attempt to develop novel inhibitors of aldose reductase, the derivatives of rhodanine-3-hippuric acid-pyrazole hybrid were synthesized and characterised by spectral data. The biological studies reveal that all the compounds show an excellent activity against ALR2 with IC₅₀ values ranging from 0.04 to 1.36 µM. Among these the synthesised compounds 6a-m, 6g and 6e showed specific inhibitory activity with IC₅₀ values of 0.04 and 0.06 µM respectively against ALR2 and found to be more potent than epalrestat (IC₅₀ = 0.87 μM), the only aldose reductase inhibitor currently used in the therapy. Molecular docking analysis using the AR-NADP⁺ complex as a receptor was performed with all the synthesized compounds. All the compounds exhibit a well-defined binding mode within the AR active site, similarly to previous described AR inhibitors, with the anion head group bound to the catalytic center, blocking thus its activity. By forming hydrogen bonds with Tyr48 and His110 of the protein from ALR2 (PDB ID: 2FZD), the compounds 6g and 6e interrupt the proton donation mechanism, which is necessary for the catalytic activity of ALR2.

Drug screening of rhodanine derivatives for antibacterial activity

Introduction: Bacteriological infections are a major risk to human health. These include all hospital and public-acquired infections. In drug discovery, rhodanines are privileged heterocyclic frameworks. Their derivatives possess strong anti-bacterial activity and some of them have shown potent activity against multidrug-resistant pathogens, both under in vitro and in vivo conditions. To treat multi-drug resistant pathogens, the development of novel potent drugs, with superior anti-bacterial efficacy, is paramount. One avenue which shows promise is the design and development of novel rhodanines.Areas covered: This review summarizes the status on rhodanine-based derivatives and their anti-bacterial activity, based on published research over the past six years. Furthermore, to facilitate the design of novel derivatives with improved functions, their structure-activity relationships are assessed with reference to their efficacy as anti-bacterial agents and their toxicity.Expert opinion: The pharmacological activity of molecules bearing a rhodanine scaffold needs to be very critically assessed in spite of considerable information available from various biological evaluations. Although, some data on structure-activity relationship frameworks is available, information is not adequate to optimize the efficacy of rhodanine derivatives for different applications.

Inhibition effects of quinones on aldose reductase: Antidiabetic properties

Diabetes mellitus is a chronic metabolic disease characterized by abnormal glucose metabolism. Aldose reductase (AR) is the first enzyme in the polyol pathway and converts glucose to sorbitol. It plays a vital role as a glucose reducing agent and is involved in the pathophysiology of diabetic complications. In this study, we purified AR from sheep kidney with a specific activity of 2.00 EU/mg protein and 133.33- fold purification After the purification of the AR enzyme, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed and the molecular weight of the enzyme was found approximately as 38 kDa. The inhibition effects of eight quinones were studied against AR. The quinones were potent inhibitors of AR with K_i values in the range of 0.07-20.04 μM. Anthraquinone showed the best potential inhibitory effects against AR. All compounds exhibited noncompetitive inhibition against AR. These compounds may be selective inhibitors of this enzyme. AR inhibition is an essential strategy for the attenuation and prevention of diabetic complications.

Current anti-diabetic agents and their molecular targets: A review

Diabetes mellitus is a medical condition characterized by the body's loss of control over blood sugar. The frequency of diagnosed cases and consequential increases in medical costs makes it a rapidly growing chronic disease that threatens human health worldwide. In addition, its unnerving statistical projections are perilous to both the economy of the nation and man's life expectancy. Type-I and type-II diabetes are the two clinical forms of diabetes mellitus. Type-II diabetes mellitus (T2DM) is illustrated by the abnormality of glucose homeostasis in the body, resulting in hyperglycemia. Although significant research attention has been devoted to the development of diabetes regimens, which demonstrates success in lowering blood glucose levels, their efficacies are unsustainable due to undesirable side effects such as weight gain and hypoglycemia. Over the years, heterocyclic scaffolds have been the basis of anti-diabetic chemotherapies; hence, in this review we consolidate the use of bioactive scaffolds, which have been evaluated for their biological response as inhibitors against their respective anti-diabetic molecular targets over the past five years (2012-2017). Our investigation reveals a diverse target set which includes; protein tyrosine phosphatase 1 B (PTP1B), dipeptidly peptidase-4 (DPP-4), free fatty acid receptors 1 (FFAR1), G protein-coupled receptors (GPCR), peroxisome proliferator activated receptor-γ (PPARγ), sodium glucose co-transporter-2 (SGLT2), α-glucosidase, aldose reductase, glycogen phosphorylase (GP), fructose-1,6-bisphosphatase (FBPase), glucagon receptor (GCGr) and phosphoenolpyruvate carboxykinase (PEPCK). This review offers a medium on which future drug design and development toward diabetes management may be modelled (i.e. optimization via structural derivatization), as many of the drug candidates highlighted show promise as an effective anti-diabetic chemotherapy.

Design, Synthesis and in Combo Antidiabetic Bioevaluation of Multitarget Phenylpropanoic Acids

We have synthesized a small series of five 3-[4-arylmethoxy)phenyl]propanoic acids employing an easy and short synthetic pathway. The compounds were tested in vitro against a set of four protein targets identified as key elements in diabetes: G protein-coupled receptor 40 (GPR40), aldose reductase (AKR1B1), peroxisome proliferator-activated receptor gama (PPARγ) and solute carrier family 2 (facilitated glucose transporter), member 4 (GLUT-4). Compound 1 displayed an EC₅₀ value of 0.075 μM against GPR40 and was an AKR1B1 inhibitor, showing IC₅₀ = 7.4 μM. Compounds 2 and 3 act as slightly AKR1B1 inhibitors, potent GPR40 agonists and showed an increase of 2 to 4-times in the mRNA expression of PPARγ, as well as the GLUT-4 levels. Docking studies were conducted in order to explain the polypharmacological mode of action and the interaction binding mode of the most active molecules on these targets, showing several coincidences with co-crystal ligands. Compounds 1–3 were tested in vivo at an explorative 100 mg/kg dose, being 2 and 3 orally actives, reducing glucose levels in a non-insulin-dependent diabetes mice model. Compounds 2 and 3 displayed robust in vitro potency and in vivo efficacy, and could be considered as promising multitarget antidiabetic candidates. This is the first report of a single molecule with these four polypharmacological target action.

Phytochemical profile, aldose reductase inhibitory, and antioxidant activities of Indian traditional medicinal Coccinia grandis (L.) fruit extract

Coccinia grandis (L.) fruits (CGFs) are commonly used for culinary purposes and has several therapeutic applications in the Southeast Asia. The aim of this work was to evaluate phytochemical profile, aldose reductase inhibitory (ARI), and antioxidant activities of CGF extract. The CGFs were extracted with different solvents including petroleum ether, dichloromethane, acetone, methanol, and water. The highest yield of total extractable compounds (34.82%) and phenolic content (11.7 ± 0.43 mg of GAE/g dried extract) was found in methanol extract, whereas water extract showed the maximum content of total flavonoids (82.8 ± 7.8 mg QE/g dried extract). Gas chromatography-mass spectroscopy (GC-MS) analysis of methanol and water extract revealed the presence of flavonoids, phenolic compounds, alkaloids, and glycosides in the CGFs. Results of the in vitro ARI activity against partially purified bovine lens aldose reductase showed that methanol extract of CGFs exhibited 96.6% ARI activity at IC₅₀ value 6.12 µg/mL followed by water extract 89.1% with the IC₅₀ value 6.50 µg/mL. In addition, methanol and water extracts of CGF showed strong antioxidant activities including ABTS^*+ scavenging, DPPH* scavenging, and hydroxyl radical scavenging. Our results suggest that high percentage of both flavonoids and phenolic contents in the CGFs are correlated with the ARI and antioxidant activities. The fruits of C. grandis are thus potential bifunctional agents with ARI and antioxidant activities that can be used for the prevention and management of DM and associated diseases.

Inhibition behaviours of some phenolic acids on rat kidney aldose reductase enzyme: an in vitro study

Aldose reductase (AR) inhibitors have vital importance in the treatment and prevention of diabetic complications. In this study, rat kidney AR was purified 19.34-fold with a yield of 3.49% and a specific activity of 0.88 U/mg using DE-52 Cellulose anion exchange chromatography, gel filtration chromatography and 2'5' ADP Sepharose-4B affinity chromatography, respectively. After purification, the in vitro inhibition effects of some phenolic acids (tannic acid, chlorogenic acid, sinapic acid, protocatechuic acid, 4-hydroxybenzoic acid, p-coumaric acid, ferulic acid, vanillic acid, syringic acid, α-resorcylic acid, 3-hydroxybenzoic acid and gallic acid) were investigated on purified enzyme. We determined IC50, Ki values and inhibition types of these phenolic acids. As a result, tannic and chlorogenic acid had a strong inhibition effect. On the other hand, gallic acid had a weak inhibition effect. In this study, all phenolic acids except for chlorogenic acid and p-coumaric acid showed non-competitive inhibition effects on rat kidney AR.

An efficient catalyst-free one-pot synthesis of primary amides from the aldehydes of the Baylis–Hillman reaction

Herein, a facile and efficient method for the preparation of allyl amides from the aldehydes of Baylis–Hillman adducts has been developed using a hydroxylamine/methanol system under a catalyst-free condition.

Novel tetrazoloquinoline-rhodanine conjugates: Highly efficient synthesis and biological evaluation

In search of new active molecules against Mycobacterium tuberculosis (MTB) H37Ra and Mycobacterium bovis BCG, a small focused library of rhodanine incorporated tetrazoloquinoline has been efficiently synthesized by using [HDBU][HSO4] acidic ionic liquid. The compound 3c found to be promising inhibitor of MTB H37Ra and M. bovis BCG characterized by lower MIC values 4.5 and 2.0 μg/mL, respectively. The active compounds were further tested for cytotoxicity against HeLa, THP-1, A549 and PANC-1 cell lines using MTT assay and showed no significant cytotoxic activity at the maximum concentration evaluated. Again, the synthesized compounds were found to have potential antifungal activity. Furthermore, to rationalize the observed biological activity data, the molecular docking study also been carried out against a potential target Zmp1 enzyme of MTB H37Ra, which revealed a significant correlation between the binding score and biological activity for these compounds. The results of in vitro and in silico study suggest that these compounds possess ideal structural requirement for the further development of novel therapeutic agents.

Hypervalent iodine catalysis for selective oxidation of Baylis–Hillman adducts via in situ generation of o-iodoxybenzoic acid (IBX) from 2-iodosobenzoic acid (IBA) in the presence of oxone

An efficient, eco-friendly protocol for selective oxidation of primary and secondary Baylis–Hillman alcohols to the corresponding carbonyl compounds in high yields has been developed with 2-iodosobenzoic acid (IBA).