Structure-activity correlation of flavonoids for inhibition of bovine lens aldose reductase

To clarify the structure-activity correlation of flavonoids for inhibition of aldose reductase, about fifty flavonoid compounds were screened. The presence of hydrophobic substituents on the A ring and hydrophilic substituents on the B ring of the flavonoid skeleton was suggested to improve the potency of inhibitory activity. The activities of extracts of Scutellaria baicalensis, Andrographis paniculata and Gutierrezia microcephala are also described.     

Effect of magnesium lithospermate B on urinary excretion of arachidonate metabolites in rats with renal failure

The effect of magnesium lithospermate B isolated from Salviae miltiorrhizae Radix on excretion of urinary arachidonate metabolites was examined in both normal rats and those given adenine. Urinary excretion of prostaglandin E2 (PGE2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) decreased while urinary thromboxane B2 (TXB2) excretion increased markedly with the progression of renal failure. Rats administered magnesium lithospermate B showed an increase of urinary PGE2 excretion at the 6th and 12th days. Excretion of 6-keto-PGF1 alpha also showed a significant increase on the 6th and 12th days in rats with renal failure induced by the administration of adenine. However, these effects were lower than the corresponding values in normal rats. In addition, urinary PGE2 and 6-keto-PGF1 alpha excretions showed no appreciable difference in rats that exhibited progressive renal failure with continuation of the adenine administration period, as shown on the 18th and 24th days. There were no significant changes in TXB2 excretion between the control and magnesium lithospermate B-treated groups throughout the experimental period.     

Novel quercetin derivatives: synthesis and screening for anti-oxidant activity and aldose reductase inhibition

The direct acylation of quercetin (I) with 3-chloro-2,2-dimethylpropanoyl chloride (II) gives a complex reaction mixture. The synthesis of different acylated quercetin with from mono- to tetra-O-substituted functions was achieved in a simple procedure wherein the yield of isomers depended on the stoichiometric ratio of reagents. The crude reaction mixtures were analysed (LC-MS) and compared with the isolated products. Unambiguous structural characterisation of isomeric quercetin derivatives was confirmed by NMR analysis. In addition, the quercetin dimer can be obtained in a high yield in the simple procedure. The anti-oxidant activity and aldose reductase inhibition of the compounds were screened with the aim of providing bi-functional remedies to treat diabetic complications and other diseases where oxidative stress and the polyol pathway are key etiological factors.     

A combinatorial access to 1,5-benzodiazepine derivatives and their evaluation for aldose reductase inhibition

Aryldiazepinothiophenones 4 were prepared from the reaction of o-phenylenediamines with acetone in the presence of 2-mercaptocarboxylic acids along with thiazolobenzodiazepines 6, thiazolobenzimidazoles 7 and 1,5-benzodiazepines 5, which were obtained as by-products. The benzodiazepinothiophenones 4a-d and the benzodiazepines 5a-d were also isolated from the reaction of o-phenylenediamines 1a-c with phorone. Structural assignments of the new compounds as well as complete assignment of ¹H and ¹³C NMR signals were based on the analysis of their ¹H and ¹³C NMR (1D and 2D), IR, MS and elemental analysis data. Compounds 4 were evaluated for aldose reductase inhibition and also as antioxidants.     

姜黄素及其衍生物对醛糖还原酶的抑制作用

高血糖条件下,多元醇代谢通路（图1）被激活是糖尿病并发症发生与发展的重要原因之一。     

Contribution of prostaglandins to the renal responses to magnesium lithospermate B isolated from salviae miltiorrhizae radix

The involvement of prostanoids in the improvement of adenine-induced renal failure in rats by magnesium lithospermate B was studied. After intraperitoneal administration of magnesium lithospermate B to renal failure rats, the levels of glomerular filtration rate, renal plasma flow and renal blood flow were increased. Urinary excretions of prostaglandin E2 (PGE2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in renal failure rats were increased by the administration of magnesium lithospermate B, while that of thromboxane B2 had no effect. Pretreatment with indomethacin abolished the improving effect of magnesium lithospermate B on renal function concomitantly with markedly suppressed urinary excretion of prostanoids. These results suggest that the increased formation of PGE2 and 6-keto-PGF1 alpha might contribute to the improvement of adenine-induced renal failure in rats by magnesium lithospermate B.     

Characterization of aldose reductase and aldehyde reductase from the medulla of rat kidney

Aldose reductase and aldehyde reductase from the medulla of the rat kidney have been purified to homogeneity by using affinity chromatography, gel filtration and chromatofocusing. The molecular weights of aldose reductase and aldehyde reductase by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis were found to be 37000 and 39000, respectively. The isoelectric points of aldose reductase and aldehyde reductase were found to be 5.4 and 6.2 by chromatofocusing, respectively. The major differences of amino acid compositions between both enzymes were found in serine, alanine and aspartic acid. Substrate specificity studies showed that aldose reductase utilized aldo-sugars such as D-glucose and D-galactose, but aldehyde reductase did not use them. The Km values of aldose reductase for various substrates were lower than those of aldehyde reductase. Aldose reductase utilized both reduced nicotinamide adenine dinucleotide phosphate (NADPH) and reduced nicotinamide adenine dinucleotide (NADH) as coenzymes, whereas aldehyde reductase utilized only NADPH. The presence of the sulfate ion resulted in a dramatic activation of aldose reductase whereas it did not affect aldehyde reductase activity. These enzymes were strongly inhibited by the known aldose reductase inhibitors. However, aldose reductase was more susceptible than aldehyde reductase to inhibition by the aldose reductase inhibitors.     

Rapid and simple determination of aldose reductase and sorbitol dehydrogenase

Rapid and well-reproducible methods were developed for the determination of aldose reductase and sorbitol dehydrogenase. The aldose reductase activity measurement is based on photometric o-toluidine aldose back-measurement, which is widely used in laboratories for the quantitative determination of glucose. The spectrophotometric method based on the quantitative decrease in NADH proved suitable for the measurement of sorbitol dehydrogenase activity.Both methods could well be employed for the measurement of the aldose reductase and sorbitol dehydrogenase activities of normal and diabetic tissue homogenizates, and for the comparison of the measured values.     

Studies on aldose reductase inhibitors from natural products. IV. Constituents and aldose reductase inhibitory effect of Chrysanthemum morifolium, Bixa orellana and Ipomoea batatas.

The hot water extracts of Chrysanthemum morifolium, Bixa orellana and Ipomoea batatas, were found to have potent inhibitory activity towards lens aldose reductase (AR). Ellagic acid (4) was isolated from C. morifolium and I. batatas, isoscutellarein (7) from B. orellana and 3,5-dicaffeoylquinic acid (10) from I. batatas, respectively, as potent inhibitors.     

Docking and molecular dynamics study on the inhibitory activity of coumarins on aldose reductase

In order to explore the inhibitory mechanism of coumarins toward aldose reductase (ALR2), AutoDock and Gromacs software were used for docking and molecular dynamics studies on 14 coumarins (CM) and ALR2 protease. The docking results indicate that residues TYR48, HIS110, and TRP111 construct the active pocket of ALR2 and, besides van der Waals and hydrophobic interaction, CM mainly interact with ALR2 by forming hydrogen bonds to cause inhibitory behavior. Except for CM1, all the other coumarins take the lactone part as acceptor to build up the hydrogen bond network with active-pocket residues. Unlike CM3, which has two comparable binding modes with ALR2, most coumarins only have one dominant orientation in their binding sites. The molecular dynamics calculation, based on the docking results, implies that the orientations of CM in the active pocket show different stabilities. Orientation of CM1 and CM3a take an unstable binding mode with ALR2; their conformations and RMSDs relative to ALR2 change a lot with the dynamic process. While the remaining CM are always hydrogen-bonded with residues TYR48 and HIS110 through the carbonyl O atom of the lactone group during the whole process, they retain the original binding mode and gradually reach dynamic equilibrium.     

Potentiating effect of converting enzyme inhibitor captopril to the renal responses of magnesium lithospermate B in rats with adenine-induced renal failure

The renal responses of magnesium lithospermate B were investigated in the presence or absence of pretreatment with the converting enzyme (kininase II) inhibitor, captopril, in rats with adenine-induced renal failure. Magnesium lithospermate B (10 mg/kg body weight) caused a marked increase in the levels of the renal functional parameters (glomerular filtration rate, renal plasma flow and renal blood flow), accompanied by significant increases in urinary excretions of prostaglandin E2 (PGE2), kallikrein, sodium and creatinine. The administration of magnesium lithospermate B in combination with captopril (2 mg/kg body weight, 2 times) caused a further increase in renal functional parameters, urinary sodium and creatinine excretions. However, the kallikrein activity was similar to the control level. There were no significant changes between urinary PGE2 following magnesium lithospermate B alone, or in combination with captopril. In addition, angiotensin converting enzyme activity did not change following the administration of magnesium lithospermate B alone, but was significantly decreased in rats given captopril, both alone and in combination with magnesium lithospermate B. The captopril administration group (captopril alone or in combination with magnesium lithospermate B) showed a significant decrease in blood pressure. From these results, it seems that the combination of magnesium lithospermate B and captopril induces a further increase in renal function by improving the renal circulatory state.     

Synthesis and in vitro evaluation of botryllazine B analogues as a new class of inhibitor against human aldose reductase

Botryllazine B analogues of diverse substitution patterns have been prepared, and their in vitro inhibitory activities against recombinant human aldose reductase (h-ALR2) evaluated. Among the 15 compounds tested, 6-(4-aminophenyl)-2-(4-hydroxyphenyl)carbonylpyrazine (7b) proved to be the most potent inhibitor, with IC₅₀=0.91 μM. Kinetic analyses of 7b and botryllazine B (1) revealed that these inhibitors exhibit an unprecedented mixed-type inhibition on h-ALR2 with respect to the substrate d,l-glyceraldehyde, in the presence of NADPH at inhibitor concentrations near the IC₅₀ values.     

Inhibitory effects of 2'-hydroxychalcones on rat lens aldose reductase and rat platelet aggregation

Inhibitory effects of synthetic 2'-hydroxychalcone derivatives on rat lens aldose reductase (RLAR) and on platelet aggregation were investigated for the prevention or the treatment of chronic diabetic complications. 5'-chloro-4,2'-dihydroxychalcone (8) and 5'-chloro-3,2'-dihydroxychalcone (27) exhibited a potent inhibitory effect on rat platelet aggregation induced by ADP (IC50=0.10 and 0.06 mg/ml, respectively) and collagen (IC50=44 and 16 microg/ml, respectively) but showed relatively weak inhibitory activities on RLAR.     

Structural requirements of flavonoids and related compounds for aldose reductase inhibitory activity

The methanolic extracts of several natural medicines and medicinal foodstuffs were found to show an inhibitory effect on rat lens aldose reductase. In most cases, flavonoids were isolated as the active constituents by bioassay-guided separation, and among them, quercitrin (IC(50)=0.15 microM), guaijaverin (0.18 microM), and desmanthin-1 (0.082 microM) exhibited potent inhibitory activity. Desmanthin-1 showed the most potent activity, which was equivalent to that of a commercial synthetic aldose reductase inhibitor, epalrestat (0.072 microM). In order to clarify the structural requirements of flavonoids for aldose reductase inhibitory activity, various flavonoids and related compounds were examined. The results suggested the following structural requirements of flavonoid: 1) the flavones and flavonols having the 7-hydroxyl and/or catechol moiety at the B ring (the 3',4'-dihydroxyl moiety) exhibit the strong activity; 2) the 5-hydroxyl moiety does not affect the activity; 3) the 3-hydroxyl and 7-O-glucosyl moieties reduce the activity; 4) the 2-3 double bond enhances the activity; 5) the flavones and flavonols having the catechol moiety at the B ring exhibit stronger activity than those having the pyrogallol moiety (the 3',4',5'-trihydroxyl moiety).     

Synthesis and aldose reductase inhibitory activities of benzyl 2-oxazolecarbamate analogues.

Various analogues of benzyl 5-phenyl-2-oxazolecarbamate (1a) were synthesized, and the structure-activity relationship of these analogues as aldose reductase inhibitor was studied. The carbamate group was necessary for the inhibitory activity. The introduction of an alkyl group at the C-4 position of 1a enhanced the inhibitory activity, however, the N-carboxymethyl group on the carbamate moiety counteracted to a hydrophobic interaction between the alkyl group at the C-4 position and the enzyme molecule.