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.     

Relationships between structure and high-throughput screening permeability of peptide derivatives and related compounds with artificial membranes: application to prediction of Caco-2 cell permeability

To evaluate absorption of compounds across the membrane via a transcellular route, the permeability of peptide derivatives and related compounds was measured by the parallel artificial membrane permeation assay (PAMPA). The permeability coefficients by PAMPA were analyzed quantitatively using classical QSAR and Volsurf approaches with the physicochemical parameters. The results from both approaches showed that hydrogen bonding ability of molecules in addition to hydrophobicity at a particular pH were significant in determining variations in PAMPA permeability coefficients. The relationship between Caco-2 cell permeability and artificial lipid membrane permeability was then determined. The compounds were sorted according to their absorption pathway in the plot of the Caco-2 cell and PAMPA permeability coefficients.     

Synthesis and cytotoxic activities of beta-carboline amino acid ester conjugates

Beta-carboline represents a class of compounds with potent anti-tumor activity by intercalating with DNA. To further enhance the cytotoxic potency and bioavailability of beta-carboline, a series of novel beta-carboline amino acid ester conjugates were designed and synthesized, and the cytotoxic activities of these compounds were tested using a panel of human tumor cell lines. In addition, the membrane permeability of these compounds was evaluated in vitro using a Caco-2 cell monolayer model. The beta-carboline amino acid ester conjugates demonstrated improved cytotoxic activity compared to the parental beta-carbolines. In particular, the Lys/Arg conjugates were the most potent analogs with an IC(50) value of 4 and 1 microM against human cervical carcinoma cells. The low interaction energy of Arg conjugate based on molecular modeling may contribute to its enhanced cytotoxicity. Taken together, this study provided new insights into structure-activity relationships in the beta-carboline amino acid ester conjugates and identified the beta-carboline Lys/Arg conjugates as promising lead compounds for further in vivo biological and molecular evaluation.     

Enzymes in pancreatic islets that use NADP(H) as a cofactor including evidence for a plasma membrane aldehyde reductase.

Recent evidence of a pyruvate malate shuttle capable of transporting a large amount of NADPH equivalents out of mitochondria in pancreatic islets suggests that cytosolic NADP(H) plays a role in beta cell metabolism. To obtain clues about these processes the activities of several NADPH-utilizing enzymes were estimated in pancreatic islets. Low levels of pyrroquinolone quinone (PQQ) and low levels of enzyme activity that reduce PQQ were found in islets. Low activities of palmitoyl-CoA and stearoyl-CoA desaturases were also detected. Significant activities of glutathione reductase, aldose reductase (EC.1.1.1.21) and aldehyde reductase (EC.1.1.1.2) were present in islets. Potent inhibitors of aldehyde and aldose reductases inhibited neither glucose-induced insulin release nor glucose metabolism in islets indicating that these reductases are not directly involved in glucose-induced insulin reaction. Over 90% of aldose reductase plus aldehyde reductase enzyme activity was present in the cytosol. Kinetic and chromatographic studies indicated that 60-70% of this activity in cytosol was due to aldehyde reductase and the remainder due to aldose reductase. Aldehyde reductase-like enzyme activity, as well as aldose reductase immunoreactivity, was detected in rat islet plasma membrane fractions purified by a polyethylene glycol-Dextran gradient or by a sucrose gradient. This is interesting in view of the fact that voltage-gated potassium channel beta subunits that contain aldehyde and aldose reductase-like NADPH-binding motifs have been detected in plasma membrane fractions of islets [Receptors and Channels 7: 237-243, 2000] and suggests that NADPH might have a yet unknown function in regulating activity of these potassium channels. Reductases may be present in cytosol to protect the insulin cell from molecules that cause oxidative injury.     

Quantitative structure-activity analysis of 5-arylidene-2,4-thiazolidinediones as aldose reductase inhibitors

Design of aldose reductase (ALR2) inhibitors has received considerable attention. Aldose reductase inhibitors, when administered from the onset of hyperglycemia, prevent the progression of polyol accumulation-linked complications. The feasibility that inhibition of aldose reductase provides a pharmacologically direct treatment for diabetic complications that is independent of the control of blood sugar levels has spurred the development of structurally diverse aldose reductase inhibitors. In this work, we report quantitative structure-activity relationship (QSAR) analysis performed by 3D-QSAR analysis, Hansch analysis, and Fujita-Ban analysis on a series of 5-arylidene-2,4-thiazolidinediones as aldose reductase inhibitors. The 2D & 3D-QSAR models were generated using 18 compounds and Fujita-Ban analysis models were obtained using 23 compounds. The predictive ability of the resulting 2D and 3D models was evaluated against a test set of 5 compounds. Analyses of results from the present QSAR study inferred that 3rd position of the phenyl ring and acetic acid substitution at N-position of thiazolidinediones play a key role in the aldose reductase inhibitory activity.     

Discovery of new inhibitors of aldose reductase from molecular docking and database screening

Aldose reductase (ALR2) is a target enzyme for the treatment of diabetic complications. Owing to the limited number of currently available drugs for the treatment of diabetic complications, the discovery of new inhibitors of ALR2 that can potentially be optimized as drugs appears highly desirable. In this study, a molecular docking analysis of the structures of more than 127,000 organic compounds contained in the National Cancer Institute database was performed to find and score molecules that are complementary to ALR2. Besides retrieving several carboxylic acid derivatives, which are known to generally inhibit aldose reductase, docking proposed other families of putative inhibitors such as sulfonic acids, nitro-derivatives, sulfonamides and carbonyl derivatives. Twenty-five compounds, chosen as the highest-scoring representatives of each of these families, were tested as aldose reductase inhibitors. Five of them were found to inhibit aldose reductase in the micromolar range. For these active compounds, selectivity with respect to the closely-related aldehyde reductase was determined by measuring the corresponding inhibitory activities. The structures of the complexes between the new lead inhibitors and aldose reductase, here refined with molecular mechanics and molecular dynamics calculations, suggest that new pharmacophoric groups can bind aldose reductase very efficiently. In the case of the family of the nitro-derivative inhibitors, a class of particularly interesting compounds, a round of optimizations was performed with the synthesis and biological evaluation of a series of derivatives aimed at testing the proposed binding mode and at improving interaction with active site residues. Starting from a hit compound having an IC(50) of 42 microM, the most potent compound synthesized showed a 10-fold increase in inhibitory activity and 10-fold selectivity with respect to ALR1, and structure--activity relationships of the designed compounds were in agreement with the proposed mode of binding at the active site.     

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.     

Pyrazole inhibitors of HMG-CoA reductase: an attempt to dramatically reduce synthetic complexity through minimal analog re-design

An extraordinarily potent and hepatoselective class of HMG-CoA reductase inhibitors containing a pyrazole core was recently reported; however, its development was hampered by a long and difficult synthetic route. We attempted to circumvent this obstacle by preparing closely related analogs wherein the key dihydroxyheptanoic acid sidechain was tethered to the pyrazole core via an oxygen linker ('oxypyrazoles'). This minor change reduced the total number of synthetic steps from 14 to 7. Although the resulting analogs maintained much of the in vitro and cell activity of the pyrazoles, inferior in vivo activity precluded further development. Caco-2 cell permeability data suggest that enhanced cellular efflux of the oxypyrazoles relative to the pyrazoles may be responsible for the poor in vivo activity.     

The effect of oxidants on biomembranes and cellular metabolism

During the reductive process in the tissues, the aerobes generate a number of oxidants. Unless these oxidants are reduced, oxidative damage and cell death would occur. Oxidation of plasma membrane lipids leads to autocatalytic chain reactions which eventually alter the permeability of the cell. The role of oxidative damage in the pathophysiology of diabetic complications and ischemic reperfusion injury of myocardium, especially the changes in the channel activity which may lead to arrhythmia have been studied. Hyperglycemia activates aldose reductase which could efficiently reduce glucose to sorbitol in the presence of NADPH. Since NADPH is also aldose required by glutathione reductase for reducing oxidants, its diversion would lead to membrane lipid oxidation and permeability changes which are probably responsible for diabetic complications such as cataractogenesis, retinopathy, neuropathy etc. Antioxidants such as butylated hydroxy toluene (BHT) and also reductase inhibitors prevent or delay some of these complications. By using patch-clamp technique in isolated frog myocytes, we have shown that hydroxy radicals generated by ferrous sulfate and ascorbate as well as lipid peroxides such as t-butyl hydroperoxide facilitate the entry of Na⁺ by oxidizing Na⁺-channels. Increased intracellular Na⁺ leads to an increase in Na⁺/Ca²⁺ exchange. The increased Na⁺ concentration by itself may produce electrical disturbance which would result in arrhythmia. Increased Ca²⁺ may affect proteases and may help in the conversion of xanthine dehydrogenase to xanthine oxidase, consequently increased production of super oxide radicals. Increased membrane lipid peroxidation and other oxygen free-radical associated membrane damage in myocytes has been demonstrated.     

Structure-activity relationships of ganoderma acids from Ganoderma lucidum as aldose reductase inhibitors

A series of lanostane-type triterpenoids, known as ganoderma acids were isolated from the fruiting body of Ganoderma lucidum. Some of these compounds were identified as active inhibitors of the in vitro human recombinant aldose reductase. To clarify the structural requirement for inhibition, some structure–activity relationships were determined. Our structure–activity studies of ganoderma acids revealed that the OH substituent at C-11 is an important feature and the carboxylic group in the side chain is essential for the recognition of aldose reductase inhibitory activity. Moreover, double bond moiety at C-20 and C-22 in the side chain contributes to improving aldose reductase inhibitory activity. In the case of ganoderic acid C2, all of OH substituent at C-3, C-7 and C-15 is important for potent aldose reductase inhibition. These results provide an approach to understanding the structural requirements of ganoderma acids from G. lucidum for aldose reductase inhibitor. This understanding is necessary to design a new-type of aldose reductase inhibitor.     

In vivo metabolism of 3-deoxy-3-fluoro-D-glucose

Recent studies have demonstrated that 3-deoxy-3-fluoro-D-glucose (3-FG) is metabolized to 3-deoxy-3-fluoro-D-sorbitol (3-FS), via aldose reductase, and 3-deoxy-3-fluoro-D-fructose (3-FF), via the sorbitol dehydrogenase reaction with 3-FS, in rat cerebral tissue (Kwee, I. L., Nakada, T., and Card, P. J. (1987) J. Neurochem. 49, 428-433). However, the biochemistry of 3-FG in other mammalian organs has not been investigated making the application of 3-FG as a metabolic tracer uncertain. To address this issue we investigated 3-FG metabolism and distribution in isolated cell lines and in rabbit tissues in vivo with 19F NMR and gas chromatography-mass spectrometry. In general, the production of 3-FS is well correlated with the known distribution of aldose reductase in all the systems studied. Further metabolism of 3-FS to 3-FF was verified to occur in cerebral tissue. Surprisingly, two new fluorinated compounds were found in the liver and kidney cortex. These compounds are identified as 3-deoxy-3-fluoro-D-gluconic acid, which is produced via glucose dehydrogenase activity on 3-FG, and 3-deoxy-3-fluoro-D-gluconate-6-phosphate. Based on enzyme studies, it is argued that the 3-deoxy-3-fluoro-D-gluconate-6-phosphate is derived directly from 3-deoxy-3-fluoro-D-gluconic acid and not as a product of pentose phosphate activity. Direct oxidation and reduction are the major metabolic routes of 3-FG, not metabolism through glycolysis or the pentose phosphate shunt. Thus, 3-FG metabolism coupled with 19F NMR appears to be very useful for monitoring aldose reductase and glucose dehydrogenase activity in vivo.     

Development of novel pyrazolone derivatives as inhibitors of aldose reductase: An eco-friendly one-pot synthesis,experimental screening and in silico analysis

Aldose reductase is the key enzyme of polypol pathway leading to accumulation of sorbitol. Sorbitol does not diffuse across the cell membranes easily and therefore accumulates within the cell, causing osmotic damage which leads to retinopathy (cataractogenesis), neuropathy and other diabetic complications. Currently, aldose reductase inhibitors like epalrestat, ranirestat and fidarestat are used for the amelioration of diabetic complications. However, such drugs are effective in patients having good glycemic control and less severe diabetic complications. In present study we have designed novel pyrazolone derivative and performed eco-friendly synthesis approach and tested the synthesized compounds as potential inhibitors of aldose reductase activity. Additional in silico analysis in current study indicates presence of highly conserved chemical environment in active site of goat lens aldose reductase. The reported data is expected to be useful for developing novel pyrazolone derivatives as lead compounds in the management of diabetic complications.     

Design and synthesis of highly potent and selective (2-arylcarbamoyl-phenoxy)-acetic acid inhibitors of aldose reductase for treatment of chronic diabetic complications

Recent efforts to identify treatments for chronic diabetic complications have resulted in the discovery of a novel series of highly potent and selective (2-arylcarbamoyl-phenoxy)-acetic acid aldose reductase inhibitors. The compound class features a core template that utilizes an intramolecular hydrogen bond to position the key structural elements of the pharmacophore in a conformation, which promotes a high binding affinity. The lead candidate, example 40, 5-fluoro-2-(4-bromo-2-fluoro-benzylthiocarbamoyl)-phenoxyacetic acid, inhibits aldose reductase with an IC(50) of 30 nM, while being 1100 times less active against aldehyde reductase, a related enzyme involved in the detoxification of reactive aldehydes. In addition, example 40 lowers nerve sorbitol levels with an ED(50) of 31 mg/kg/d po in the 4-day STZ-induced diabetic rat model.     

On-bead combinatorial techniques for the identification of selective aldose reductase inhibitors

Aldose reductase (AKR1B1; ALR2; E.C. 1.1.1.21) is an NADPH-dependent carbonyl reductase which has long been associated with complications resulting from the elevated blood glucose often found in diabetics. The development of effective inhibitors has been plagued by lack of specificity which has led to side effects in clinical trials. To address this problem, a library of bead-immobilized compounds was screened against fluorescently labeled aldose reductase in the presence of fluorescently labeled aldehyde reductase, a non-target enzyme, to identify compounds which were aldose reductase specific. Picked beads were decoded via novel bifunctional bead mass spec-based techniques and kinetic analysis of the ten inhibitors which were identified using this protocol yielded IC50 values in the micromolar range. Most importantly, all of these compounds showed a preference for aldose reductase with selectivities as high as approximately 7500-fold. The most potent of these exhibited uncompetitive inhibition versus the carbonyl-containing substrate D/L-glyceraldehyde with a Ki of 1.16 microM.     

Comparison of in vitro models for the prediction of compound absorption across the human intestinal mucosa

Several in vitro assays have been developed to evaluate the gastrointestinal absorption of compounds. Our aim was to compare 3 of these methods: 1) the bio-mimetic artificial membrane permeability assay (BAMPA) method, which offers a high-throughput, noncellular approach to the measurement of passive transport; 2) the traditional Caco-2 cell assay, the use of which as a high-throughput tool is limited by the long cell differentiation time (21 days); and 3) The BioCoat high-throughput screening Caco-2 Assay System, which reduces Caco-2 cell differentiation to 3 days. The transport of known compounds (such as cephalexin, propranolol, or chlorothiazide) was studied at pH 7.4 and 6.5 in BAMPA and both Caco-2 cell models. Permeability data obtained was correlated to known values of human absorption. Best correlations (r = 0.9) were obtained at pH 6.5 for BAMPA and at pH 7.4 for the Caco-2 cells grown for 21 days. The Caco-2 BioCoat HTS Caco-2 Assay System does not seem to be adequate for the prediction of absorption. The overall results indicate that BAMPA and the 21-day Caco-2 system can be complementary for an accurate prediction of human intestinal absorption.     

Purification and characterization of the recombinant human aldose reductase expressed in baculovirus system

Large quantities of recombinant human aldose reductase were produced using Spodoptera frugiperda cells and properties of the enzyme were characterized. Direct purification of the recombinant aldose reductase by affinity column chromatography using Matrex gel orange A yielded a single 36 kDa band, similar in size to the purified human muscle aldose reductase, on a sodium dodecyl sulfate-polyacrylamide gel after silver staining. The isoelectric point of the recombinant enzyme was 5.85 which is identical to the human muscle aldose reductase. Following the treatment with an acylamino-acid releasing enzyme, the blocked NH2-terminal amino acid was identified to be acetylalanine. The successive NH2-terminal sequence and that of the COOH-terminal peptide concurred with the expected translated sequence. Kinetic analyses of the recombinant enzyme activity for various substrates and the cofactor, NADPH, demonstrated a good agreement with the previously reported kinetic data on the purified human aldose reductase. A high concentration of (NH4)2SO4 elicited a significant increase in both Km and Kcat for DL-glyceraldehyde as well as D-glucose. Although IC50 values for most of the aldose reductase inhibitors with recombinant enzyme were found to fall within the comparable range of those obtained with nonhuman mammalian enzymes, the IC50 value for epalrestat was more than 10-fold higher in the recombinant enzyme. These results indicate that the recombinant human aldose reductase expressed in the baculovirus system possesses structurally and enzymatically similar properties as those reported for the native human enzyme and should serve as a superior enzyme preparation to nonhuman mammalian enzymes for the screening of the efficacy and potency of newly developed aldose reductase inhibitors.     

Substituted indole-1-acetic acids as potent and selective CRTh2 antagonists-discovery of AZD1981

Novel indole-3-thio-, 3-sulfonyl- and 3-oxy-aryl-1-acetic acids are reported which are potent, selective antagonists of the chemoattractant receptor-homologous expressed on Th2 lymphocytes receptor (CRTh2 or DP2). Optimization required maintenance of high CRTh2 potency whilst achieving a concomitant reduction in rates of metabolism, removal of cyp p450 inhibition and minimization of aldose reductase and aldehyde reductase activity. High quality compounds suitable for in vivo studies are highlighted, culminating in the discovery of AZD1981 (22).     

Novel synthesis of nitro-quinoxalinone derivatives as aldose reductase inhibitors

A novel, non-acid series of nitroquinoxalinone derivatives was synthesized and tested for their inhibitory activity against aldose reductase as targeting enzyme. All active compounds displayed an 8-nitro group, and showed significant activity in IC₅₀ values ranging from 1.54 to 18.17 μM. Among them 6,7-dichloro-5,8-dinitro-3-phenoxyquinoxalin-2(1H)-one (7e), exhibited the strongest aldose reductase activity with an IC₅₀ value of 1.54 μM and a good SAR (structure–activity relationship) profile.     

Induction of aldose reductase in cultured human microvascular endothelial cells by advanced glycation end products

Accelerated formation and accumulation of advanced glycation end products, as well as increased flux of glucose through polyol pathway, have been implicated in the pathogenesis of diabetic vascular complications. We investigated effects of advanced glycation end products on the levels of aldose reductase mRNA, protein, and activity in human microvascular endothelial cells. When endothelial cells were cultured with highly glycated bovine serum albumin, aldose reductase mRNA in endothelial cells demonstrated concentration-dependent elevation. The increase in aldose reductase mRNA was accompanied by elevated protein expression and enzyme activity. Significant increase in the enzyme expression was also observed when endothelial cells were cultured with serum obtained from diabetic patients with end-stage renal disease. Pretreatment of the endothelial cells with probucol or vitamin E prevented the advanced glycation end products-induced increases in aldose reductase mRNA and protein. Electrophoretic mobility shift assays using the nuclear extracts of the endothelial cells treated with advanced glycation end products showed enhancement of specific DNA binding activity for AP-1 consensus sequence. These results indicate that accelerated formation of advanced glycation end products in vivo may elicit activation of the polyol pathway, possibly via augmented oxidative stress, and amplify endothelial cell damage leading to diabetic microvascular dysfunction.     

The effect of various liposome formulations on insulin penetration across Caco-2 cell monolayer

The aim of the study was to determine the penetration properties of various insulin containing liposome formulations through Caco-2 cell monolayer and to compare the in vitro test results with in vivo tests. The effect of sodium taurocholate as a penetration enhancer when it was added to the liposome formulation was also investigated. In vitro permeation experiments were performed in diffusion cells with the Caco-2 cell monolayer used as the membrane. Permeability values of various insulin containing liposome formulations through Caco-2 cells were determined (log k(insulin-solution) = -2.217 +/- 0.0723 cm.h(-1), log k(insulin-liposome) = -2.141 +/- 0.0625 cm.h(-1), log k(insulin-sodium tauroholate liposome)= -1.952 +/- 0.0623 cm.h(-1)). In vivo tests were performed in mice. Formulations were administered orally and blood glucose levels were determined and penetrations were compared with the Caco-2 cell experiment results. In conclusion, the permeability of insulin was increased across Caco-2 cell monolayer when the liposome sodium taurocholate (NaTC) formulation was used. The oral administration of insulin and NaTC incorporated liposomes significantly decreased blood glucose levels. Furthermore, it was shown that a high in vitro/in vivo correlation was observed using the Caco-2 cell monolayer model.