Decreasing acidity in a series of aldose reductase inhibitors: 2-Fluoro-4-(1H-pyrrol-1-yl)phenol as a scaffold for improved membrane permeation.

Targeting long-term diabetic complications, as well as inflammatory pathologies, aldose reductase inhibitors (ARIs) have been gaining attention over the years. In the present work, in order to address the poor membrane permeation of previously reported ARIs, derivatives of N-phenylpyrrole, bearing groups with putative pKa≥7.4, were synthesized and evaluated for aldose reductase inhibitory activity. The 2-fluorophenol group proved the most promising moiety, and further modifications were explored. The most active compound (31), identified as a submicromolar inhibitor (IC50=0.443µM), was also selective against the homologous enzyme aldehyde reductase. Cross-docking revealed that 31 displays a peculiar interaction network that may be responsible for high affinity. Physicochemical profiling of 31 showed a pKa of 7.64, rendering it less than 50% ionized in the physiological pH range, with potentially favorable membrane permeation. The latter was supported from the successful inhibition of sorbitol formation in rat lenses and the ability to permeate rat jejunum.

Synthesis of derivatives of the keto-pyrrolyl-difluorophenol scaffold: some structural aspects for aldose reductase inhibitory activity and selectivity.

Seven novel ARIs (3a-c, 4a-c and 5) were synthesized with the implementation of an optimized and, partially, selective synthetic procedure, via a Friedel-Crafts acylation reaction. The synthesized ARIs have values of IC(50)(ALR2) ranging from 0.19µM (in case of compound 3b) to 2.3µM (in case of compound 4a), while the values of selectivity index towards ALR1 range from 1 (in case of compound 3b) to 238 (in case of compound 3a). Finally, we found out that the presence of an additional (secondary) aromatic area is not a prerequisite feature for ARI activity.

Glutathione-Hemin/Hematin Adduct Formation to Disintegrate Cytotoxic Oxidant Hemin/Hematin in Human K562 Cells and Red Blood Cells' Hemolysates: Impact of Glutathione on the Hemolytic Disorders and Homeostasis.

Hemin, an oxidized form of heme, acts as potent oxidant to regulate glutathione (GSH) content in pro-erythroid K562 nucleated cells, via activation of the KEAP1/NRF2 defensive signaling pathway. Moreover, GSH, as an essential metabolite, is involved in the regulation of cell-redox homeostasis and proposed to scavenge cytotoxic free heme, which is released from hemoglobin of damaged red blood cells (RBCs) during different hemolytic disorders. In the present study, we aimed to uncover the molecular mechanism by which GSH inhibits hemin-induced cytotoxicity (HIC) by affecting hemin's structural integrity in K562 cells and in RBC hemolysates. GSH, along with other thiols (cysteine, thioglycolic acid, and mercaptoethanol) altered the spectrum of hemin, while each of them co-added with hemin in cultures of K562 cells prevented HIC and growth arrest and markedly reduced the intracellular level of hemin. In addition, GSH endogenous levels served as a barrier to HIC in K562 cells, as shown by the depletion in GSH. LC-MS/MS analysis of the in vitro reaction between hemin and GSH revealed at least five different isomers of GSH-hemin adducts, as well as hydroxy derivatives as reaction products, which are characterized by unique mass spectra (MS). The latter allowed the detection of adducts in human RBC hemolysates. Based on these findings, we proposed a molecular mechanism via which GSH prevents HIC and structurally disintegrates heme. An analogous reaction was observed in RBC hemolysates via direct inter-reaction between hematin (ferric and hydroxide heme) released from hemoglobin and GSH. Overall, GSH-hematin adducts could be considered as novel entities of the human metabolome of RBCs in hemolytic disorders.

Structure-activity relations on [1-(3,5-difluoro-4-hydroxyphenyl)-1H-pyrrol-3-yl]phenylmethanone. The effect of methoxy substitution on aldose reductase inhibitory activity and selectivity.

Based on our previous work, we studied the effect of methoxy-substitution as well as the regioposition of the benzoyl-moiety of 4a [(1-(3,5-difluoro-4-hydroxyphenyl)-1H-pyrrol-3-yl)(phenyl)methanone]. On this basis, compounds 4b-c and 5a-c were synthesized and assayed for aldose and aldehyde reductase inhibitory activity. Furthermore, a 4,6-difluoro-5-hydroxyphenyl pattern (9) was studied, in order to verify the optimum position of the phenol-moiety. Compound 5b emerged as the most potent and selective inhibitor. Moreover, further assays proved 5b as a potent antioxidant and an inhibitor of sorbitol accumulation in isolated rat lenses. Combining the above attributes, 5b could serve as a lead compound targeted at long-term diabetes complications.

Substituted derivatives of indole acetic acid as aldose reductase inhibitors with antioxidant activity: structure-activity relationship.

Although multiple biochemical pathways are likely to be responsible for the pathogenesis of diabetic complications, substantial evidence suggests a key role for the polyol pathway and oxidative stress initiated by hyperglycemia. Thus aldose reductase, the first enzyme of the polyol pathway, has been identified as a potential target of pharmacological intervention to prevent diabetic complications. Aldose reductase inhibitors endowed with antioxidant activity would be dually beneficial. The aim of the study was to evaluate the structure-activity relationship of commercially available indole derivatives supported by the molecular modeling of their interaction with the enzyme aldose reductase from the viewpoint of the inhibitory effect on the enzyme and their antioxidant activity. The partially purified aldose reductase was prepared from rabbit eye lenses. In vitro inhibiton of the aldose reductase was determined by a conventional method. Antioxidant action of the compounds was documented in a DPPH test. Marked differences were recorded in the aldose reductase inhibition activities of 1- and 3-indole acetic acid derivatives. The interaction energies of the inhibitor vs. enzyme-NADP(+) complexes, calculated by computer aided molecular modeling, were in agreement with the higher inhibitory efficacy of 1-indole acetic acid in contrast with 3-indole acetic acid. The more efficient 1-indole acetic acid was proved to create stronger electrostatic interaction with NADP(+). However, the order of the antioxidant activities of the compounds studied was not in agreement with that of the inhibitory efficacies.

Drug-like Properties and Fraction Lipophilicity Index as a combined metric.

Fraction Lipophicity Index (FLI) has been developed as a composite drug-like metric combining log P and log D in a weighted manner. In the present study, an extended data set confirmed the previously established drug-like FLI range 0-8 using two calculation systems for log P/log D assessment, the freeware MedChem Designer and ClogP. The dataset was split into two classes according to the percentage of fraction absorbed (%FA) - class 1 including drugs with high to medium absorption levels and class 2 including poorly absorbed drugs. The FLI and FLI-C (ClogP based FLI) drug-like range covers 92 % and 91 % of class 1 drugs, respectively. Using MlogP, a narrower drug-like FLI-M range 0-7 was established, covering 91 % of class 1 drugs. The dependence of the degree of ionization to intrinsic lipophilicity within the FLI (FLI-C, FLI-M) drug-like range as well as the inter-relation between the other Ro5 properties (Mw, HD, HA) was explored to define drug-like / non-drug-like combinations as a safer alternative to single properties for drug candidates' prioritization. In this sense, we propose a combined metric of Mw and the number of polar atoms (Mw/NO) to account for both size and polarity. Setting the value 50 as cutoff, a distinct differentiation between class 1 and class 2 drugs was obtained with Mw/NO>50 for more than 70 % of class 1 drugs, while the opposite was observed for class 2 drugs.

Design and synthesis of novel series of pyrrole based chemotypes and their evaluation as selective aldose reductase inhibitors. A case of bioisosterism between a carboxylic acid moiety and that of a tetrazole.

Pyrrolyl-propionic and butyric-acid derivatives 1 and 2 were synthesized in order to study the effect of the variation of the methylene chain in comparison to the previously reported pyrrolyl-acetic acid compound I, which was found as potent aldose reductase inhibitor, while the pyrrolyl-tetrazole derivatives 3-5 were prepared as a non-classical bioisosteres of a carboxylic acid moiety. Also, pyrrolyl-tetrazole isomers 6 and 7 without an alkyl chain between the two aromatic rings were synthesized. The in vitro aldose reductase inhibitory activity of the prepared 1-7 compounds were estimated and compared with that of the initial compound (I). Overall, the data indicate that the presented chemotypes 6 and 7 are a promising lead compounds for the development of selective aldose reductase inhibitors, aiming to the long-term complications of diabetes mellitus.

Formation of novel N-acetylcysteine-hemin adducts abrogates hemin-induced cytotoxicity and suppresses the NRF2-driven stress response in human pro-erythroid K562 cells.

Heme (iron protoporphyrin IX), as the prosthetic group in hemoproteins, regulates vital cellular functions in human tissues. However, free heme released during hemolysis events promotes severe complications to millions of people worldwide. Over the years, thiols like glutathione (GSH) were known to antagonize heme toxicity. In this study, we have uncovered the underlying molecular mechanism by which N-acetylcysteine (NAC), a well-known thiol prevents hemin-induced cytotoxicity (HIC). Hemin-responsive human pro-erythroid K562 cells were employed to assess hemin intracellular accumulation and cytotoxicity at concentrations ≥50 µΜ, in cultures exposed only to hemin and/or both hemin and NAC. NAC inhibited the intracellular accumulation of hemin and prevented hemin-induced cell growth inhibition, cell death, oxidative stress, and accumulation of ubiquitinated proteins. Meanwhile, the activation of the NF-E2-related factor-2 (NRF2)-driven stress gene activation, a key element involved in HIC, was suppressed by NAC. A refined mechanism of the chemical reaction between NAC and hemin leading to adduct formation via a nucleophilic attack on hemin was uncovered for the first time by tandem mass spectrometry analysis (LC-MS/MS). Such thiol-hemin adducts acted as intermediates to mitigate HIC and to suppress hemin-induced NRF2-driven gene activation. Our findings support the concept that NAC-hemin adduct formation is the major novel molecular mechanism rather than the reactive oxygen species-scavenging capacity of thiols to protect cells from HIC. Our results imply that thiols and their derivatives can be of potential therapeutic value in hemolytic disorders.

Aldose reductase enzyme and its implication to major health problems of the 21(st) century.

Aldose reductase enzyme (ALR2) of the polyol metabolic pathway, apart from its role as detoxifying enzyme towards toxic aldehydes, osmoregulator in the kidney and regulator of sperm maturation, was first found to be implicated in the etiology of the long term diabetic complications. However, to date, emerging reports have suggested that under normal glucose concentration, ALR2 may be up-regulated by factors other than hyperglycemia and therefore be involved also in other pathological processes that have become major threats to human health in the 21(st) century. Such pathologies are a number of cardiac disorders, inflammation, mood disorders, renal insufficiency and ovarian abnormalities. In addition, ALR2 was found to be over-expressed in different human cancers such as liver, breast, ovarian, cervical and rectal cancers. Although several aldose reductase inhibitors (ARIs) have progressed to the clinical level, only one is currently on the market. Thus, attention is currently targeted to discover ARIs of distinct chemical structures, being neither hydantoin nor carboxylic acid derivatives. The present review focuses on the molecular mechanisms by which ALR2 is implicated in a number of pathologies, on various aspects concerning its catalytic mechanism and its active site, and on the main classes of ARIs that have been developed to date, as well as on reported (quantitive) structure-activity relationships. The presented data aim to support the notion that ARIs are of pharmacotherapeutic interest for the pharmaceutical community and highlight essential aspects for the development of efficient and potent ARIs.

Design and synthesis of N-(3,5-difluoro-4-hydroxyphenyl)benzenesulfonamides as aldose reductase inhibitors.

N-(3,5-Difluoro-4-hydroxyphenyl)benzenesulfonamide (4) and its derivatives 5-7 were prepared as putative bioisosteres of the previously reported aldose reductase inhibitors, which are the N-benzenesulfonylglycine derivatives I-IV. The in vitro aldose reductase inhibitory activity of the prepared compounds is higher than that of the respective glycine derivatives. Furthermore, the parent compound 4 reveals high antioxidant potential. Additionally, the intestine permeability of 4 is determined, and there is initial evidence that there is an operating influx mechanism. Overall, the data indicate that the presented chemotype could serve as a core structure for the design of putative pharmacotherapeutic agents, aiming to the long-term complications of diabetes mellitus.

Carboxymethylated pyridoindole antioxidants as aldose reductase inhibitors: Synthesis, activity, partitioning, and molecular modeling.

Starting from the efficient hexahydropyridoindole antioxidant stobadine, a series of carboxymethylated tetrahydro- and hexahydropyridoindole derivatives was synthesized and tested for the inhibition of aldose reductase, an enzyme involved in the etiology of diabetic complications. In vitro inhibiton of rat lens aldose reductase was determined by a conventional method. Kinetic analysis of (2-benzyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole-8-yl)-acetic acid (5b) and (2-phenethyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole-8-yl)-acetic acid (5c), the most potent compounds in this series with activities in micromolar range, showed uncompetitive inhibition. In addition to the importance of the acidic function, the inhibition efficacy was highly influenced by the steric conformation of the lipophilic aromatic backbone when comparing tetrahydro- and hexahydropyridoindole congeners. Selectivity with respect to the closely related aldehyde reductase was determined by measuring the corresponding inhibitory activities. Antioxidant action of the novel compounds was documented in a DPPH test and in a liposomal membrane model, oxidatively stressed by peroxyl radicals. The presence of a basicity center at the tertiary nitrogen, in addition to the acidic carboxylic function, predisposes these compounds to form double charged zwitterionic species, a characteristic which may remarkably affect their pH-lipophilicity profile. For compounds 5b and 5c, a maximal distribution ratio in a system comprised of 1-octanol/phosphate buffer was recorded near the neutral physiological pH, the region where the isoelectric point lies. Molecular docking simulations into the ALR2 active site performed for the zwitterionic species provided an explanation for the observed structure-activity relationships and the calculated parameters were in agreement with characteristic differences in the stereoelectronic profiles of the tetrahydro- versus hexahydropyridoindoles. 'Drug-likeness' of the novel aldose reductase inhibitors was assessed by applying the criteria of Lipinski's 'rule of five'.

The effect of aldose reductase inhibition by JMC-2004 on hyperglycemia-induced endothelial dysfunction.

OBJECTIVES: An increased glucose utilization by aldose reductase (ALR-2) has been implicated in the pathogenesis of diabetic vascular complications. In this process, several mechanisms are involved, including the depletion of cofactors required for the action of antioxidant enzymes or endothelial NO synthase. In this study, the effect of a novel ALR-2 inhibitor JMC-2004 on hyperglycemia-induced endothelial dysfunction was studied. METHODS: Bovine aortic endothelial cells (BAEC) were treated with glucose (30 mM), JMC-2004 (0.01mM), or glucose and JMC-2004 for 24 h. The cells were then stimulated with calcium ionophore A23187 after which NO production was measured electrochemically using a porphyrine-coated carbon NO electrode. Nitrite concentrations were determined in the cell supernatants. The peroxyl and hydroxyl radical-scavenging activity of JMC-2004 was measured with luminol-enhanced chemiluminescence. The expression of eNOS was determined by Western blotting. JMC-2004 IC50 for ALR-2 was determined colorimetrically with D-glyceraldehyde as a substrate. RESULTS: Incubating the cells with 30 mM glucose strongly diminished A23187- induced NO production. Treatment with JMC-2004 restored NO production by 40% without affecting eNOS expression. This effect was probably antioxidantindependent, since JMC-2004 did not have any antioxidant capacity. JMC-2004 exerted high selectivity towards ALR-2. CONCLUSIONS: ALR-2 inhibition with JMC-2004 was able to abolish hyperglycemia- induced endothelial dysfunction in bovine aortic endothelial cells.

Permeability characteristics of novel aldose reductase inhibitors using rat jejunum in vitro.

The aim of this study was to estimate in vivo permeability and bioavailability of epalrestat and newly synthesized compounds with possible therapeutic activity as aldose enzyme inhibitors (ARIs). For this purpose permeability in vitro using rat jejunum mounted in side-by-side diffusion cells was determined. Tested substances were found to be low and moderately permeable and some of them were also substrates for efflux transporters. It was shown, that the higher efflux for some derivatives was due to MRP-2, but not Pgp involvement. Tested ARIs do not share the same efflux transporter with epalrestat, the only ARI currently on the market in Japan. The most permeable compound, a 2,6-difluoro-4-pyrrol-1ylphenol derivative, is not a substrate for efflux transporters and would therefore be the most promising lead compound for further investigation of potent ARIs.

Substituted pyrrol-1-ylacetic acids that combine aldose reductase enzyme inhibitory activity and ability to prevent the nonenzymatic irreversible modification of proteins from monosaccharides.

Starting from the known inhibitory activity of (3-benzoylpyrrol-1-yl)acetic acid (I) and (2-benzoylpyrrol-1-yl)acetic acid (II), a series of 3-aroyl and 2,4-bis-aroyl derivatives (54-75) were synthesized and tested for inhibition of aldose reductase, an enzyme involved in the appearance of diabetic complications. It was found that a number of the tested compounds exhibited considerable activity in the micromolar range. Important structural features for the potent compounds is the presence of substituents with relatively low Hammett sigma values and/or moieties which increase their overall aromatic area. The most active derivative was the [2,4-bis(4-methoxybenzoyl)pyrrol-1-yl]acetic acid (75), with potency favorably compared to known ARIs such as tolrestat, epalrestat, zopolrestat, and fidarestat. Four selected derivatives were also evaluated for their ability to interfere with the oxidative modification of serum albumin in an in vitro experimental glycation model of diabetes mellitus. All of them showed considerable activity, comparable to the known inhibitor trolox. Our results, taken together, indicate that compound 75 combines favorably two biological activities directly connected to a number of pathological conditions related to the chronic diabetes mellitus.

[1-(3,5-difluoro-4-hydroxyphenyl)-1H-pyrrol-3-yl]phenylmethanone as a bioisostere of a carboxylic acid aldose reductase inhibitor.

[1-(3,5-Difluoro-4-hydroxyphenyl)-1H-pyrrol-3-yl]phenylmethanone (6) was synthesized as a putative bioisostere of the known aldose reductase (AR) inhibitor (3-benzoylpyrrol-1-yl)acetic acid (I). It was found that 6 is approximately 5 times more potent as an in vitro inhibitor of AR than I, with an IC(50) value in the submicromolar range. Furthermore, 6 showed considerable activity in an in vitro experimental glycation model of diabetes mellitus. Our results support the notion that 6 might become a useful lead structure.

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.

Novel aldose reductase inhibitors: a patent survey (2006--present).

INTRODUCTION: Initially studied for its central role in the pathogenesis of chronic diabetic complications, aldose reductase (ALR2) gains more attention over the years as its implication in inflammatory diseases is being established, along with the therapeutic potential of its inhibitors. AREAS COVERED: Reviewing the patents that were published since 2006, it is getting clear that the search for new chemical entities has subsided, giving rise to natural products and plant extracts with ALR2 inhibitory activity. Other aspects that were prominent were the search for proper forms of known inhibitors, in a way to improve their impaired physicochemical profile, as well as potential combination therapies with other compounds of pharmaceutical interest. On the spotlight were patents enhancing the therapeutic usage of aldose reductase inhibitors (ARIs) to various pathological conditions including cancer and inflammation-mediated diseases such as sepsis, asthma, and cancer. EXPERT OPINION: Although new chemical entities are scarcely registered and patented after many years of inconclusive clinical trials, the involvement of ALR2 to inflammatory pathologies might renew the interest in the field of ARIs.

Bis-pyrrolyl-tetrazolyl derivatives as hybrid polar compounds: A case of lipophilic functional bioisosterism with bis-acetamides.

Based on previous studies on bis-acetamides that act as hybrid polar compounds to induce leukemia cell differentiation, an attempt was made to bioisosterically replace the amide moiety with the lipophilic non-classical bioisostere tetrazole. A pyrrole group was also included in the molecule in order to retain the hydrogen bond donor capability. Thus, by linking the two polar ring systems with a highly lipophilic methylene chain compounds 2-4 were synthesized and assessed for their anti-proliferative activity in combination with their ability to induce murine erythroleukemia (MEL) cell differentiation. Furthermore, an initial investigation of the structure-activity relation points for the active compound 3 was undertaken by synthesizing compound 5 (a p-xylene analog) and compound 8 (a methylamidopyrrolyl analog). All compounds caused a dose-dependent inhibition of MEL cell growth but to a different extent. Compound 3 (1,6-bis[5-(1H-pyrrol-1-yl)-2H-tetrazol-2-yl]hexane) promoted erythroid differentiation in a fifty-fold lower concentration than hexamethylenebisacetamide (HMBA). Though induction of differentiation was to a lesser extent than HMBA, it caused accumulation of 80% Hb-producing cells as compared to that produced by HMBA, leading to differentiation-depended cell growth inhibition equal to that of HMBA after 96 h in culture. Compound 3 represents a potent inducer of hemoglobin gene activation in leukemic cells.

A diverse series of substituted benzenesulfonamides as aldose reductase inhibitors with antioxidant activity: design, synthesis, and in vitro activity.

We have previously reported the successful replacement of a carboxylic acid functionality with that of a difluorophenolic group on the known aldose reductase inhibitors (ARIs) of 2-(phenylsulfonamido)acetic acid chemotype. In the present work, based on bioisosteric principles, additional 2,6-difluorophenol and tetrazole, methylsulfonylamide, and isoxazolidin-3-one phenylsulfonamide derivatives were synthesized and tested in vitro in protocols primarily related to the long-term diabetic complications. Most of the compounds were found as ARIs at IC(50) < 100 µM, while the introduction of the 4-bromo-2-fluorobenzyl group in a phenylsulfonamidodifluorophenol structure resulted in a compound (4c) presenting a submicromolar inhibitory profile. However, the derivatives of tetrazole, methylsulfonylamine, and the (R)-enantiomer of isoxazolidin-3-one did not exhibit appreciable ARI activity. The selectivity of the active ARIs is also discussed. Furthermore, the synthesized compounds exhibited potent antioxidant potential (homogeneous and heterogeneous systems).

Nutritional overview on the management of type 2 diabetes and the prevention of its complications.

Diabetes mellitus is an increasing world health problem; particularly the prevalence of type 2 diabetes has assumed epidemic dimensions in Western industrialized societies. It is mainly the environmental, dietary and lifestyle behavioral factors that are the control keys in the progress of this disease. Several epidemiological studies have linked over nutrition and lack of physical activity with type 2 diabetes. Indeed, the excessive consumption of energy dense foods as source of carbohydrates and fats along with ineffective medical management has negative impact on controlling blood glucose levels and on insulin response. This usually leads to a hyperglycemic state, which is associated with the development of the devastating secondary complications. Dietary guidelines have always been important for people with diabetes mellitus. Nutrition management aims to improve health quality maintaining blood glucose levels in normal range so as to reduce the risk for diabetes complications. A well-balanced diet that provides the essential macro- and micro-nutrients is always an impaired need for a patient with diabetes. In this article nutrition recommendations will be displayed for the management of diabetes type 2 and the prevention of its complications. Particular emphasis will be given to the important role of micronutrients such as trace elements and vitamins as well as to the potentiality of some dietary agents to inhibit aldose reductase enzyme, implicated in the etiology of diabetes complications.