Structure of Aldehyde Reductase Holoenzyme in Complex with the Potent Aldose Reductase Inhibitor Fidarestat: Implications for Inhibitor Binding and Selectivity

Identification of a Selective SCoR2 Inhibitor That Protects Against Acute Kidney Injury

Acute kidney injury (AKI) is associated with high morbidity and mortality, and no drugs are available clinically. Metabolic reprogramming resulting from the deletion of S-nitroso-coenzyme A reductase 2 (SCoR2; AKR1A1) protects mice against AKI, identifying SCoR2 as a potential drug target. Of the few known inhibitors of SCoR2, none are selective versus the related oxidoreductase AKR1B1, limiting therapeutic utility. To identify SCoR2 (AKR1A1) inhibitors with selectivity versus AKR1B1, analogs of the nonselective (dual 1A1/1B1) inhibitor imirestat were designed, synthesized, and evaluated. Among 57 compounds, JSD26 has 10-fold selectivity for SCoR2 versus AKR1B1 and inhibits SCoR2 potently through an uncompetitive mechanism. When dosed orally to mice, JSD26 inhibited SNO-CoA metabolic activity in multiple organs. Notably, intraperitoneal injection of JSD26 in mice protected against AKI through S-nitrosylation of pyruvate kinase M2 (PKM2), whereas imirestat was not protective. Thus, selective inhibition of SCoR2 has therapeutic potential to treat acute kidney injury.

CADD Studies in the Discovery of Potential ARI (Aldose Reductase Inhibitors) Agents for the Treatment of Diabetic Complications

The lack of currently available drugs for treating diabetes complications has stimulated our interest in finding new Aldose Reductase inhibitors (ARIs) with more beneficial biological properties. One metabolic method uses aldose reductase inhibitors in the first step of the polyol pathway to control excess glucose flux in diabetic tissues. Computer-aided drug discovery (CADD) is key in finding and optimizing potential lead substances. AR inhibitors (ARI) have been widely discussed in the literature. For example, Epalrestat is currently the only ARI used to treat patients with diabetic neuropathy in Japan, India, and China. Inhibiting R in patients with severe to moderate diabetic autonomic neuropathy benefits heart rate variability. AT-001, an AR inhibitor, is now being tested in COVID-19 to see how safe and effective it reduces inflammation and cardiac damage. In summary, these results from animal and human studies strongly indicate that AR can cause cardiovascular complications in diabetes. The current multi-center, large-scale randomized human study of the newly developed powerful ARI may prove its role in diabetic cardiovascular disease to establish therapeutic potential. During the recent coronavirus disease (COVID-19) outbreak in 2019, diabetes and cardiovascular disease were risk factors for severely negative clinical outcomes in patients with COVID19. New data shows that diabetes and obesity are among the strongest predictors of COVID-19 hospitalization. Patients and risk factors for severe morbidity and mortality of COVID- 19.

Novel Hydroxychalcone-Based Dual Inhibitors of Aldose Reductase and α-Glucosidase as Potential Therapeutic Agents against Diabetes Mellitus and Its Complications

We designed a novel series of bifunctional inhibitors of α-glucosidase and aldose reductase (ALR2) based on the structure of hydroxychalcone. The two enzymes relate to blood glucose level and anomalously elevated polyol pathway of glucose metabolism under hyperglycemia, respectively. Most compounds in the series exhibited a potent inhibitory activity for both enzymes, and a significant antioxidant property was shown. Further in vivo studies of 11j and 14d using streptozotocin (STZ)-induced diabetic rats as a model found that 11j achieved not only good antihyperglycemic and glucose tolerance effect in a dose-dependent manner (p < 0.01) but also showed effective inhibition of polyol pathway. 14d significantly suppressed the maltose-induced postprandial glucose elevation. Additionally, they effectively improved lipid metabolisms and restored an antioxidant ability. Therefore, the two compounds may be promising agents for the prevention and treatment of diabetic complications.

Identification of 9H-purin-6-amine derivatives as novel aldose reductase inhibitors for the treatment of diabetic complications

A series of 9H-purin-6-amine derivatives as aldose reductase (ALR) inhibitors were designed and synthesized. Most of these derivatives, having a C6-substituted benzylamine side chain and N9 carboxylic acid on the core structure, were found to be potent and selective ALR inhibitors, with submicromolar IC₅₀ values against ALR2. Particularly, compound 4e was the most active with an IC₅₀ value of 0.038 μM, and it was also proved to be endowed with excellent inhibitory selectivity. The structure-activity relationship and molecular docking studies highlighted the importance of the carboxylic acid head group along with different halogen substituents on the C6 benzylamine side chain of the 9H-purin-6-amine scaffold for the construction of strong and selective ALR inhibitors.

β-Aldehyde ketones as dual inhibitors of aldose reductase and α-glucosidase with antioxidant properties

The synthesized β-aldehyde ketone compounds have strong biological activity because of their ionizable hydroxyl groups.

Overview of human 20 alpha-hydroxysteroid dehydrogenase (AKR1C1): Functions, regulation, and structural insights of inhibitors

Human aldo-keto reductase family 1C1 (AKR1C1) is an important enzyme involved in human hormone metabolism, which is mainly responsible for the metabolism of progesterone in the human body. AKR1C1 is highly expressed and has an important relationship with the occurrence and development of various diseases, especially some cancers related to hormone metabolism. Nowadays, many inhibitors against AKR1C1 have been discovered, including some synthetic compounds and natural products, which have certain inhibitory activity against AKR1C1 at the target level. Here we briefly reviewed the physiological and pathological functions of AKR1C1 and the relationship with the disease, and then summarized the development of AKR1C1 inhibitors, elucidated the interaction between inhibitors and AKR1C1 through molecular docking results and existing co-crystal structures. Finally, we discussed the design ideals of selective AKR1C1 inhibitors from the perspective of AKR1C1 structure, discussed the prospects of AKR1C1 in the treatment of human diseases in terms of biomarkers, pre-receptor regulation and single nucleotide polymorphisms, aiming to provide new ideas for drug research targeting AKR1C1.

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.

Role of Cys-298 in specific recognition of glutathione by aldose reductase

Aldose reductase (AR) is an NADPH-dependent oxidoreductase that is well-studied for its role in Diabetes Mellitus. Glutathione conjugated aldehydes are efficiently catalysed by AR. We have employed molecular dynamics simulations to investigate the dynamics of a glutathione analog, γ-glutamyl-S-(1,2-di-carboxyethyl)-cysteinyl-glycine (DCEG), into the binding pocket of AR. Study revealed that backbone nitrogens of Ala-299 and Leu-300 form a tiny pocket gated by thiol group of Cys-298. The glycine moiety of DCEG was able to displace the thiol group of Cys-298 to make hydrogen bond interactions with backbone of Ala-299, Leu-300, and Leu-301. This study provides the details of the dynamic interactions of DCEG in the binding pocket of AR, and shall aid in the design/discovery of differential inhibitors against AR.Communicated by Ramaswamy H. Sarma.

Virtual screening of epalrestat mimicking selective ALR2 inhibitors from natural product database: auto pharmacophore, ADMET prediction and molecular dynamics approach

Epalrestat is the only effective aldose reductase (ALR2) inhibitor available in the market for the treatment of diabetic neuropathy. Clinical effectiveness of epalrestat in diabetic neuropathy encouraged us to develop some more ALR2 inhibitors with a better therapeutic profile. Herein, we utilized the pharmacophoric features of epalrestat to search some novel ALR2 inhibitors from an InterBioScreen database of natural compounds. ADME and PAINS filters were applied to provide drug-likeness and to remove toxicophores from the screened hits. The pharmacophoric features of 4-hydroxy-2-nonenal (HNE), a well-known substrate of ALR1, were also explored to identify selective ALR2 inhibitors. The structure-based analysis was then adopted to find out the molecules showing interactions with ALR2 which are crucial for their therapeutic activity. These interaction patterns and binding modes were compared with that of epalrestat. Molecular dynamics (MD) analysis was also carried out to get more insight into the interactions of screened hits in the catalytic domain of ALR2. Additionally, the top hits were docked and simulated with aldehyde reductase (ALR1) to determine their selectivity for ALR2 over ALR1. Overall, five hits including STOCKIN-44771, STOCKIN-46041, STOCKIN-59369, STOCKIN-69620 and STOCKIN-88220 were found to possess a good therapeutic profile in terms of key interactions, binding energies and drug-likeness. Two hits, STOCKIN-46041 and STOCKIN-59369, were identified as the most selective ALR2 inhibitors when assessed their selectivity profile.Communicated by Ramaswamy H. Sarma.

(5-Hydroxy-4-oxo-2-styryl-4H-pyridin-1-yl)-acetic Acid Derivatives as Multifunctional Aldose Reductase Inhibitors

As rate-limited enzyme of polyol pathway, aldose reductase (ALR2) is one of the key inhibitory targets for alleviating diabetic complications. To reduce the toxic side effects of the inhibitors and to decrease the level of oxidative stress, the inhibitory selectivity towards ALR2 against detoxicating aldehyde reductase (ALR1) and antioxidant activity are included in the design of multifunctional ALR2 inhibitors. Hydroxypyridinone derivatives were designed, synthesized and evaluated their inhibitory behavior and antioxidant activity. Notably, {2-[2-(3,4-dihydroxy-phenyl)-vinyl]-5-hydroxy-4-oxo-4H-pyridin-1-yl}-acetic acid (7l) was the most potent, with IC50 values of 0.789 μM. Moreover, 7l showed excellent selectivity towards ALR2 with selectivity index 25.23, which was much higher than that of eparlestat (17.37), the positive control. More significantly, 7l performed powerful antioxidative action. At a concentration of 1 μM, phenolic compounds 7l scavenged DPPH radical with an inhibitory rate of 41.48%, which was much higher than that of the well-known antioxidant Trolox, at 11.89%. Besides, 7l remarkably suppressed lipid peroxidation with a rate of 88.76% at a concentration of 100 μM. The binding mode derived from molecular docking proved that the derivatives were tightly bound to the activate site, suggesting strongly inhibitory action of derivatives against ALR2. Therefore, these results provided an achievement of multifunctional ALR2 inhibitors capable with potency for both selective ALR2 inhibition and as antioxidants.

Dihydrobenzoxazinone derivatives as aldose reductase inhibitors with antioxidant activity

Dihydrobenzoxazinone based design and synthesis produced two series of compounds as aldose reductase (ALR2) inhibitor candidates. In particular, phenolic residues were embodied into the compounds for the combination of strengthening the inhibitory acitvity and antioxidant ability to retard the progression of diabetic complications. Most of the derivatives with styryl side chains exhibited excellent activities on selective ALR2 inhibition with IC₅₀ values ranging from 0.082 to 0.308 μM, and {8-[2-(4-hydroxy-phenyl)-vinyl]-2-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl}-acetic acid (3a) was the most potent. More significantly, most of dihydrobenzoxazinone compounds revealed not only good inhibitory effect on ALR2, but also showed powerful antioxidant activity. Notably, phenolic compound 3a was even comparable to the well-known antioxidant Trolox, confirming that the C8 p-hydroxystyryl substitution was key structure of lowering oxidative stress. Therefore, these results provided an achievement of multifunctional ALR2 inhibitors possessing capacities for both ALR2 inhibition and as antioxidants.

Functional characterization of an aldose reductase (bmALD1) obtained from the silkworm Bombyx mori

We describe a new member of the aldo-keto reductase (AKR) superfamily in the silkworm Bombyx mori. On the basis of its amino acid sequence and phylogenetic tree, this AKR belongs to the AKR1B family and has been designated as bmALD1. In the current study, recombinant bmALD1 was overexpressed, purified to homogeneity and kinetically characterized. We discovered that bmALD1 uses NADPH as a coenzyme to reduce carbonyl compounds such as DL-glyceraldehyde, glucose and 2-nonenal. No NADH-dependent activity was detected. To the best of our knowledge, bmALD1 is only the third AKR characterized in silkworm which, given its substrate specificity, could play a major role in glucose metabolism and antioxidant reactions. Our data provide an increased understanding of insect AKR function.

Opportunities for Tapping into Three-Dimensional Chemical Space through a Quaternary Carbon

A quaternary carbon bears four other carbon substituents or combination of four non-hydrogen substituents at four vertices of a tetrahedron. The spirocyclic quaternary carbon positioned at the center of a bioactive molecule offers conformational rigidity, which in turn reduces the penalty for conformational entropy. The quaternary carbon is a predominant feature of natural product structures and has been associated with more effective and selective binding to target proteins compared to planar compounds with a high sp² count. The presence of a quaternary carbon stereocenter allows the exploration of novel chemical space to obtain new molecules with enhanced three-dimensionality. These characteristics, coupled to an increasing awareness to develop sp³-rich molecules, boosted utility of quaternary carbon stereocenters in bioactive compounds. It is hoped that this Perspective will inspire the chemist to utilize quaternary carbon stereocenters to enhance potency, selectivity, and other drug-like properties.

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.

Identification of quinoxalin-2(1H)-one derivatives as a novel class of multifunctional aldose reductase inhibitors

Aim: Targeting aldose reductase and oxidative stress with quinoxalin-2(1 H)-one derivatives having a 1-hydroxypyrazole head as the bioisosteric replacement of carboxylic acid. Methodology & results: Aldose reductase inhibition, selectivity and antioxidant potency of all the synthesized compounds were evaluated, and binding modes were studied by molecular docking. Most of the derivatives showed potent and selective aldose reductase inhibition, and among them 13d was the most active (IC50 = 0.107 μM), suggesting success of the bioisosteric strategy. Phenolic 3,4-dihydroxyl compound 13f showed strong antioxidant ability even comparable to that of the well-known antioxidant Trolox. Conclusion: The present study identified the excellent bioisostere of the 1-hydroxypyrazole head group along with phenolic hydroxyl and vinyl spacer in C3 side chain on constructing quinoxalinone-based multifunctional aldose reductase inhibitors.

Designing of acyl sulphonamide based quinoxalinones as multifunctional aldose reductase inhibitors

A series of quinoxalinone scaffold-based acyl sulfonamides were designed as aldose reductase inhibitors and evaluated for aldose reductase (ALR2)/aldehyde reductase (ALR1) inhibition and antioxidation. Compounds 9b-g containing styryl side chains at C3-side exhibited good ALR2 inhibitory activity and selectivity. Of them, 9g demonstrated the most potent inhibitory activity with an IC₅₀ value of 0.100 μM, and also exhibited excellent antioxidant activity, even comparable to the typical antioxidant Trolox. Compounds 9 had higher lipid-water partition coefficients relative to the carboxylic acid compounds 8, indicating that they may have better lipophilicity and membrane permeability. Structure-activity relationship (SAR) studies found that acyl trifluoromethanesulfonamide group at N1 and the C3-dihydroxystyryl side chain were the key structure for improving the aldose reductase inhibitory activity and antioxidant activity.

Exploring the interactional details between aldose reductase (AKR1B1) and 3-Mercapto-5H-1,2,4-triazino[5,6-b]indole-5-acetic acid through molecular dynamics simulations

Aldose reductase (AKR1B1) has been considered as a significant target for designing drugs to counteract the development of diabetic complications. In the present study, molecular dynamics (MD) simulations and molecular mechanics generalized Born surface area (MM-GB/SA) calculations were performed to make sure which tautomer is the preferred one among three tautomeric forms (Mtia1, Mtia2, and Mtia3) of 3-Mercapto-5H-1,2,4-triazino[5,6-b]indole-5-acetic acid (Mtia) for binding to AKR1B1. The overall structural features and the results of calculated binding free energies indicate that Mtia1 and Mtia2 have more superiority than Mtia3 in terms of binding to AKR1B1. Furtherly, the local active site conformational characteristics and non-covalent interaction analysis were identified. The results indicate that the combination of Mtia2 and AKR1B1 is more stable than that of Mtia1. Furthermore, two extra hydrogen bonds between AKR1B1 and Mtia2 are found with respect to Mtia1. In addition, Mtia2 makes slightly stronger electrostatic interaction with the positively charged nicotinamide group of NADP⁺ than Mtia1. Based on the results above, Mtia2 is the preferred tautomeric form among the three tautomers. Our study can provide an insight into the details of the interaction between AKR1B1 and Mtia at the atomic level, and will be helpful for the further design of AKR1B1 inhibitors.

Pcal_1311, an alcohol dehydrogenase homologue from Pyrobaculum calidifontis, displays NADH-dependent high aldehyde reductase activity

Genome sequence of Pyrobaculum calidifontis, a hyperthermophilic archaeon, harbors three open-reading frames annotated as alcohol dehydrogenases. One of them, Pcal_1311, does not display a significantly high homology with any of the characterized alcohol dehydrogenases. Highest homology of 38% was found with the characterized counterpart from Geobacillus stearothermophilus. To examine the biochemical properties of Pcal_1311, we have cloned and functionally expressed the gene in Escherichia coli. Purified recombinant Pcal_1311 catalyzed the NAD(H)-dependent oxidation of various alcohols and reduction of aldehydes, with a marked preference for substrates with functional group at the terminal carbon. Highest activity for the oxidation reaction (3 μmol min^-1 mg^-1) was found with 1,4-butanediol and for the reduction reaction (150 μmol min^-1 mg^-1) with glutaraldehyde. Both the oxidation and reduction activities increased with the increase in temperature up to 80 °C. Recombinant Pcal_1311 was highly stable and retained more than 90% activity even after incubation of 180 min at 90 °C. In addition to the thermostabilty, Pcal_1311 was highly stable in the presence of known denaturants including urea and guanidine hydrochloride. The high stability, particularly thermostability, and the NADH-dependent aldehyde reduction activity make Pcal_1311 a unique member in the alcohol dehydrogenase family.

Synthesis and Functional Evaluation of Novel Aldose Reductase Inhibitors Bearing a Spirobenzopyran Scaffold

Background:

Aldose reductase, the first enzyme of the polyol pathway, is the key determinant for the pathogenesis of long term diabetic complications. Accordingly, its inhibition represents the major therapeutic strategy to treat this kind of pathologies.

Objectives:

In this work we describe the synthesis and the functional evaluation of a number of spiro-oxazolidinone and spiro-morpholinone acetic acid derivatives, and their benzyloxy analogs, developed as aldose reductase inhibitors.

Results:

Most of them proved to inhibit the target enzyme, showing IC₅₀ values in the micromolar/low micromolar range. SARs observed among the three different series allowed to highlight their key pharmacophoric elements, thus creating sound basis for the design of novel and more effective inhibitors.

Conclusion:

Although further substitution patterns are needed, the novel compounds here proposed represent a good starting point for the development of novel and effective ARIs.

Structure based comprehensive modelling, spatial fingerprints mapping and ADME screening of curcumin analogues as novel ALR2 inhibitors

Aldose reductase (ALR2) inhibition is the most legitimate approach for the management of diabetic complications. The limited triumph in the drug development against ALR2 is mainly because of its close structural similarity with the other members of aldo-keto reductase (AKR) superfamily viz. ALR1, AKR1B10; and lipophilicity problem i.e. poor diffusion of synthetic aldose reductase inhibitors (ARIs) to target tissues. The literature evidenced that naturally occurring curcumin demonstrates relatively specific and non-competitive inhibition towards human recombinant ALR2 over ALR1 and AKR1B10; however β-diketone moiety of curcumin is a specific substrate for liver AKRs and accountable for it’s rapid in vivo metabolism. In the present study, structure based comprehensive modelling studies were used to map the pharmacophoric features/spatial fingerprints of curcumin analogues responsible for their ALR2 specificity along with potency on a data set of synthetic curcumin analogues and naturally occurring curcuminoids. The data set molecules were also screened for drug-likeness or ADME parameters, and the screening data strongly support that curcumin analogues could be proposed as a good drug candidate for the development of ALR2 inhibitors with improved pharmacokinetic profile compared to curcuminoids due to the absence of β-diketone moiety in their structural framework.

Aldo-Keto Reductase Family 1 Member B10 Inhibitors: Potential Drugs for Cancer Treatment

Cytosolic NADPH-dependent reductase AKR1B10 is a member of the aldo-keto reductase (AKR) superfamily. This enzyme is normally expressed in the gastrointestinal tract. However, it is overexpressed in many solid tumors, such as hepatocarcinoma, lung cancer and breast cancer. AKR1B10 may play a role in the formation and development of carcinomas through multiple mechanisms including detoxification of cytotoxic carbonyls, modulation of retinoic acid level, and regulation of cellular fatty acid synthesis and lipid metabolism. Studies have suggested that AKR1B10 may be a useful biomarker for cancer diagnosis and a potential target for cancer treatment. Over the last decade, a number of AKR1B10 inhibitors including aldose reductase inhibitors (ARIs), endogenous substances, natural-based derivatives and synthetic compounds have been developed, which could be novel anticancer drugs. This review provides an overview on related articles and patents about AKR1B10 inhibitors, with a focus on their inhibition selectivity and mechanism of function.

2D-DIGE proteomic analysis identifies new potential therapeutic targets for adrenocortical carcinoma

Adrenocortical carcinoma (ACC) is a rare aggressive tumor with poor prognosis when metastatic at diagnosis. The tumor biology is still mostly unclear, justifying the limited specificity and efficacy of the anti-cancer drugs currently available. This study reports the first proteomic analysis of ACC by using two-dimensional-differential-in-gel-electrophoresis (2D-DIGE) to evaluate a differential protein expression profile between adrenocortical carcinoma and normal adrenal. Mass spectrometry, associated with 2D-DIGE analysis of carcinomas and normal adrenals, identified 22 proteins in 27 differentially expressed 2D spots, mostly overexpressed in ACC. Gene ontology analysis revealed that most of the proteins concurs towards a metabolic shift, called the Warburg effect, in adrenocortical cancer. The differential expression was validated by Western blot for Aldehyde-dehydrogenase-6-A1,Transferrin, Fascin-1,Lamin A/C,Adenylate-cyclase-associated-protein-1 and Ferredoxin-reductase. Moreover, immunohistochemistry performed on paraffin-embedded ACC and normal adrenal specimens confirmed marked positive staining for all 6 proteins diffusely expressed by neoplastic cells, compared with normal adrenal cortex.

In conclusion, our preliminary findings reveal a different proteomic profile in adrenocortical carcinoma compared with normal adrenal cortex characterized by overexpression of mainly metabolic enzymes, thus suggesting the Warburg effect also occurs in ACC. These proteins may represent promising novel ACC biomarkers and potential therapeutic targets if validated in larger cohorts of patients.

How does curcumin work with poor bioavailability? Clues from experimental and theoretical studies

Curcumin is a natural product with multiple biological activities and numerous potential therapeutic applications. However, its poor systemic bioavailability fails to explain the potent pharmacological effects and hinders its clinical application. Using experimental and theoretical approaches, we compared curcumin and its degradation products for its biological activities against Alzheimer's disease (AD), including the superoxide anion radical (O2(.-))-scavenging activity, Aβ fibrils (fAβ) formation-inhibiting activity, and enzymatic inhibition activity. We showed that compared to the parent compound curcumin, the degradation products mixture possessed higher O2(.-)-scavenging activity and stronger inhibition against fAβ formation. The docking simulations revealed that the bioactive degradation products should make important contribution to the experimentally observed enzymatic inhibition activities of curcumin. Given that curcumin is readily degraded under physiological condition, our findings strongly suggested that the degradation products should make important contribution to the diverse biological activities of curcumin. Our novel findings not only provide novel insights into the complex pharmacology of curcumin due to its poor bioavailability, but also open new avenues for developing therapeutic applications of this natural product.

Identification of novel pyrazole–rhodanine hybrid scaffolds as potent inhibitors of aldose reductase: design, synthesis, biological evaluation and molecular docking analysis

A series of novel pyrazole–rhodanine derivatives was designed, synthesized, and biologically evaluated for their potential inhibitory effect on both aldehyde reductase (ALR1) and aldose reductase (ALR2).

Plant aldo-keto reductases (AKRs) as multi-tasking soldiers involved in diverse plant metabolic processes and stress defense: A structure-function update

The aldo-keto reductase (AKR) superfamily comprises of a large number of primarily monomeric protein members, which reduce a broad spectrum of substrates ranging from simple sugars to potentially toxic aldehydes. Plant AKRs can be broadly categorized into four important functional groups, which highlight their roles in diverse plant metabolic reactions including reactive aldehyde detoxification, biosynthesis of osmolytes, secondary metabolism and membrane transport. Further, multiple overlapping functional aspects of plant AKRs including biotic and abiotic stress defense, production of commercially important secondary metabolites, iron acquisition from soil, plant-microbe interactions etc. are discussed as subcategories within respective major groups. Owing to the broad substrate specificity and multiple stress tolerance of the well-characterized AKR4C9 from Arabidopsis thaliana, protein sequences of all the homologues of AKR4C9 (A9-like proteins) from forty different plant species (Phytozome database) were analyzed. The analysis revealed that all A9-like proteins possess strictly conserved key catalytic residues (D-47, Y-52 and K-81) and belong to the pfam00248 and cl00470 AKR superfamilies. Based on structural homology of the three flexible loops of AKR4C9 (Loop A, B and C) responsible for broad substrate specificity, A9-like proteins found in Brassica rapa, Phaseolus vulgaris, Cucumis sativus, Populus trichocarpa and Solanum lycopersicum were predicted to have a similar range of substrate specificity. Thus, plant AKRs can be considered as potential breeding targets for developing stress tolerant varieties in the future. The present review provides a consolidated update on the current research status of plant AKRs with an emphasis on important functional aspects as well as their potential future prospects and an insight into the overall structure-function relationships of A9-like proteins.

Synthesis of optically pure (S)-2-amino-5-arylpent-4-ynoic acids by Sonogashira reactions and their potential use as highly selective potent inhibitors of aldose reductase

A new and convenient synthesis of optically pure (S)-2-amino-5-[aryl]pent-4-ynoic acids (alkynylated amino acids) is reported.

Benzothiazolyl substituted iminothiazolidinones and benzamido-oxothiazolidines as potent and partly selective aldose reductase inhibitors

Two new series of oxothiazolidine benzoate and acetate derivatives were synthesized and evaluated as aldehyde reductase (ALR1) and aldose reductase (ALR2) inhibitors.

Discovery of new selective human aldose reductase inhibitors through virtual screening multiple binding pocket conformations

Aldose reductase reduces glucose to sorbitol. It plays a key role in many of the complications arising from diabetes. Thus, aldose reductase inhibitors (ARI) have been identified as promising therapeutic agents for treating such complications of diabetes, as neuropathy, nephropathy, retinopathy, and cataracts. In this paper, a virtual screening protocol applied to a library of compounds in house has been utilized to discover novel ARIs. IC50's were determined for 15 hits that inhibited ALR2 to greater than 50% at 50 μM, and ten of these have an IC50 of 10 μM or less, corresponding to a rather substantial hit rate of 14% at this level. The specificity of these compounds relative to their cross-reactivity with human ALR1 was also assessed by inhibition assays. This resulted in identification of novel inhibitors with IC50's comparable to the commercially available drug, epalrestat, and greater than an order of magnitude better selectivity.

X-ray structure of the V301L aldo-keto reductase 1B10 complexed with NADP(+) and the potent aldose reductase inhibitor fidarestat: implications for inhibitor binding and selectivity

Only one crystal structure is currently available for tumor marker AKR1B10, complexed with NADP(+) and tolrestat, which is an aldose reductase inhibitor (ARI) of the carboxylic acid type. Here, the X-ray structure of the complex of the V301L substituted AKR1B10 holoenzyme with fidarestat, an ARI of the cyclic imide type, was obtained at 1.60Å resolution by replacement soaking of crystals containing tolrestat. Previously, fidarestat was found to be safe in phase III trials for diabetic neuropathy and, consistent with its low in vivo side effects, was highly selective for aldose reductase (AR or AKR1B1) versus aldehyde reductase (AKR1A1). Now, inhibition studies showed that fidarestat was indeed 1300-fold more selective for AR as compared to AKR1B10, while the change of Val to Leu (found in AR) caused a 20-fold decrease in the IC50 value with fidarestat. Structural analysis of the V301L AKR1B10-fidarestat complex displayed enzyme-inhibitor interactions similar to those of the AR-fidarestat complex. However, a close inspection of both the new crystal structure and a computer model of the wild-type AKR1B10 complex with fidarestat revealed subtle changes that could affect fidarestat binding. In the crystal structure, a significant motion of loop A was observed between AR and V301L AKR1B10, linked to a Phe-122/Phe-123 side chain displacement. This was due to the presence of the more voluminous Gln-303 side chain (Ser-302 in AR) and of a water molecule buried in a subpocket located at the base of flexible loop A. In the wild-type AKR1B10 model, a short contact was predicted between the Val-301 side chain and fidarestat, but would not be present in AR or in V301L AKR1B10. Overall, these changes could contribute to the difference in inhibitory potency of fidarestat between AR and AKR1B10.

Understanding the binding of daunorubicin and doxorubicin to NADPH-dependent cytosolic reductases by computational methods

The anthracycline anticancer agents daunorubicin (DAUN) and doxorubicin (DOX) are reduced by different NADPH-dependent cytosolic reductases into their corresponding alcohol metabolites daunorubicinol (DAUNol) and doxorubicinol (DOXol), which have been implicated in the development of chronic cardiomyopathy. To better understand the individual importance of each enzyme in the reduction and to provide deeper insight into the binding at atomic level we performed molecular docking and dynamics simulations of DAUN and DOX into the active sites of human carbonyl reductase 1 (CBR1) and human aldehyde reductase (AKR1A1). Such simulations evidenced a different behavior between the reductases with respect to DAUN and DOX suggesting major contribution of CBR1 in the reduction. The results are in agreement with available experimental data and for each enzyme and anthracycline pair provided the identification of key residues involved in the interactions. The structural models that we have derived could serve as a useful tool for structure-guided drug design studies.

Progresses in the pursuit of aldose reductase inhibitors: the structure-based lead optimization step

Aldose reductase (ALR2) is a crucial enzyme in the development of the major complications of diabetes mellitus. Very recently it has been demonstrated that the ARL2 inhibitor, fidarestat, significantly prevents inflammatory signals (TNF-α, LPS) that cause cancer (colon, breast, prostate and lung), metastasis, asthma, and other inflammatory diseases. Currently, fidarestat is in phase III clinical trial for diabetic neuropathy and was found to be safe. Thus the finding of novel, potent ARL2 inhibitors is today more than in the past in great demand as they can pave the way for a novel therapeutic approach for a number of diseases besides the diabetes. Herein, starting from the virtual screening-derived ALR2 inhibitor S12728 (1), a rational receptor-based lead optimization has been undertaken. The design and synthetic efforts here reported led to the discovery of several new compounds endowed with low micromolar/submicromolar activities.