Aldose reductase inhibitors from the fruiting bodies of Ganoderma applanatum

The isolation and characterization of rat lens aldose reductase (RLAR) inhibitors from the fruiting bodies of Ganoderma applanatum were conducted. Among the extracts and fractions from G. applanatum tested, the MeOH extract and EtOAc fraction were found to exhibit potent RLAR inhibition in vitro, their IC50 being 1.7 and 0.8 microg/ml, respectively. From the active EtOAc fraction, seven compounds with diverse structural moieties were isolated and identified as D-mannitol (1), 2-methoxyfatty acids (2), cerebrosides (3), daucosterol (4), 2,5-dihydroxyacetophenone (5), 2,5-dihydroxybenzoic acid (6), and protocatechualdehyde (7). Among them, protocatechualdehyde (7) was found to be the most potent RLAR inhibitor (IC50=0.7 microg/ml), and may be useful for the prevention and/or treatment of diabetic complications.     

Constituents from the fruiting bodies ofGanoderma applanatum and their aldose reductase inhibitory activity

Eight compounds were isolated from the fruiting bodies of Ganoderma applanatum, and were identified as 2-methoxyfatty acids (1), 5-dihydroergosterol (2), ergosterol peroxide (3) 3beta,7beta, 20,23xi-tetrahydroxy-11,15-dioxolanosta-8-en-26-oic acid (4), 7beta,20,23xi-trihydroxy-3,11,15-trioxolanosta-8-en-26-oic acid (5), cerevisterol (6), 7beta,23xi-dihydroxy-3,11,15-trioxolanosta-8,20E (22)-dien-26-oic acid (7), and 7beta-hydroxy-3,11,15,23-tetraoxolanosta-8,20E(22)-dien-26-oic acid methyl ester (8) by spectral analysis. All compounds were isolated for the first time from this fruiting bodies, and their effect on rat lens aldose reductase (RLAR) activity was tested. Among these eight compounds, ergosterol peroxide (3) was found to exhibit potent RLAR inhibition, its IC50 value being 15.4 microg/mL.     

Anti-platelet action of GU-7, a 3-arylcoumarin derivative, purified from glycyrrhizae radix

We have purified GU-7, a 3-arylcoumarin derivative, from glycyrrhizae radix, which is a crude drug of kampo herbal medicines. This was identified to be a new chemical compound and was found to have an anti-platelet action. GU-7 inhibited platelet aggregation, phosphorylation of 40K and 20K dalton proteins, inositol 1,4,5-trisphosphate production, intraplatelet calcium increase and phosphodiesterase activity in vitro. The data indicate that GU-7 inhibits platelet aggregation by increasing intraplatelet cAMP concentration. We have already reported the existence of aldose reductase inhibitors in some kampo medicines. In addition to the aldose reductase inhibiting action, anti-platelet action may also explain the mechanism by which kampo medicines are effective to diabetic neuropathy.     

Inhibitory effect of pyridyloxy- or phenoxylphenoxyalkanate derivatives on rat lens aldose reductase and rat platelet aggregation

The therapeutic potential of aldose reductase inhibitors for the prevention of the secondary complications of diabetes has been extensively reported. On the other hand, the hyperaggregability of platelets in diabetic patients has also been reported as a cause of chronic diabetic complications. The purpose of this study was to develop new compounds with these dual effects from pyridyloxy- or phenoxylphenoxyalkanate synthesized derivatives and examine the effect of their structure-activity relationships on the inhibition of rat lens aldose reductase (RLAR) as well as on platelet aggregation. 2-[4-(2,6-dichloro-3-methyl-phenoxy)-3-nitro-phenoxy]-propionic acid (3) exhibited the most potent inhibitory effect (IC(50) = 3.0 +/- 0.21 microM), comparable to tetramethylene glutaric acid (IC(50) = 6.1 +/- 0.2 microM), which is used as a positive control on RLAR, and showed potent inhibitory activities on rat platelet aggregation induced by ADP and collagen (IC(50) = 0.093 +/- 0.01 and 0.032 +/- 0.01 microM, respectively) comparable with aspirin (IC(50) = 0.15 +/- 0.05 and 0.047 +/- 0.01 microM, respectively), used as a positive control.     

Anthraquinones from the seeds of Cassia tora with inhibitory activity on protein glycation and aldose reductase

Nine anthraquinones, aurantio-obtusin (1), chryso-obtusin (2), obtusin (3), chryso-obtusin-2-O-beta-D-glucoside (4), physcion (5), emodin (6), chrysophanol (7), obtusifolin (8), and obtusifolin-2-O-beta-D-glucoside (9), isolated from an EtOAc-soluble extract of the seeds of Cassia tora, were subjected to in vitro bioassays to evaluate their inhibitory activity against advanced glycation end products (AGEs) formation and rat lens aldose reductase (RLAR). Among the isolates, compounds 6 and 8 exhibited a significant inhibitory activity on AGEs formation with observed IC(50) values of 118 and 28.9 microM, respectively, in an AGEs-bovine serum albumin (BSA) assay by specific fluorescence. Furthermore, compounds 6 and 8 inhibited AGEs-BSA formation more effectively than aminoguanidine, an AGEs inhibitor, by indirect AGEs-ELISA. N(epsilon)-Carboxymethyllysine (CML)-BSA formation was also inhibited by compounds 6 and 8. Whereas compounds 1, 4, and 6 showed a significant inhibitory activity on RLAR with IC(50) values of 13.6, 8.8, and 15.9 microM, respectively.     

Nigerloxin,a novel inhibitor of aldose reductase and lipoxygenase with Free radical scavenging activity from Aspergillus niger CFR-W-105

An enzyme inhibitor, nigerloxin, with inhibition against soy bean lipoxygenase-I (LOX-1), rat lens aldose reductase (RLAR) as well as free radical scavenging activity was isolated from the fermented wheat bran using Aspergillus niger CFR-W-105. Its chemical structure was identified as 2-amido-3-hydroxy-6-methoxy-5-methyl-4-(prop-1'-enyl) benzoic acid by NMR and GCEIMS data. The IC50 values against LOX-1 and RLAR were found to be 79 microM and 69 microM and ED50 against 1,1-diphenyl-2-picrylhydrazyl (DPPH) was 66 microM.     

Constituents of the flowers of Erigeron annuus with inhibitory activity on the formation of advanced glycation end products (AGEs) and aldose reductase

Seven phenolic compounds, caffeic acid (1), 4-hydroxybenzoic acid (2), 4-methoxybenzoic acid (3), protocatechuic acid (4), eugenol O-beta-D: -glucopyranoside (5), 3,6-di-O-feruloylsucrose (6), and 3,5-di-O-caffeoylquinic acid methyl ester (7), were isolated from an EtOAc-soluble partition of the flowers of Erigeron annuus. The structures of 1-7 were determined by spectroscopic data interpretation, particularly 1D and 2D NMR studies, and by comparison of their data with those published in the literature. All the isolates were subjected to in vitro bioassays to evaluate their inhibitory activities against the formation of advanced glycation end products (AGEs) and rat lens aldose reductase (RLAR). Of the compounds, 1, 6, and 7 exhibited potent inhibitory activities against the formation of AGEs. In the RLAR assay, compound 7 showed the most potent inhibitory activity.     

Inhibitory effects of isorhamnetin-3-O-beta-D-glucoside from Salicornia herbacea on rat lens aldose reductase and sorbitol accumulation in streptozotocin-induced diabetic rat tissues

The inhibitory effects of compounds from Salicornia herbacea (Chenopodiaceae) on rat lens aldose reductase (RLAR) and sorbitol accumulation in streptozotocin-induced diabetic rat tissues were investigated. The various fractions from the MeOH extract of S. herbacea were tested for their effects on RLAR in vitro. Among them, the EtOAc fraction was found to exhibit a potent RLAR inhibition (IC(50)=0.75 microg/ml), from which an active principle as a potent AR inhibitor was isolated and its chemical structure was elucidated as isorhamnetin-3-O-beta-D-glucoside (1) by spectral analysis. Compound 1 exhibited a potent RLAR inhibition in vitro, its IC(50) being 1.4 microM. Compound 1, when administered orally at 25 mg/kg in streptozotocin (STZ)-induced diabetic rats, caused not only a significant inhibition of serum glucose concentration but also sorbitol accumulation in the lenses, red blood cells (RBC), and sciatic nerves. These results indicate that compound 1 from S. herbacea is a leading compound for further study as a new drug for the prevention and/or treatment of diabetes and its complications.     

Inhibitory effect of chalcone derivatives on recombinant human aldose reductase

More than fifty chalcone derivatives were synthesized to examine structure-activity relationships against human aldose reductase. Certain 2',4'-dihydroxychalcone derivatives inhibited human aldose reductase activities, and 2',4',2, 4-tetrahydroxychalcone and 2',4',2-trihydroxychalcone showed potent inhibitory activity with IC50 values of 7.4x10(-9) M and 1.6x10(-7) M, respectively. On the other hand, cis-form chalcones, which were isomerized from the original trans-forms by irradiation of daylight in methanol solution, promoted the activity of human aldose reductase.     

Inhibitory activities of prenylated flavonoids from Sophora flavescens against aldose reductase and generation of advanced glycation endproducts

Important targets for the prevention and treatment of diabetic complications include aldose reductase (AR) inhibitors (ARIs) and inhibitors of advanced glycation endproduct (AGE) formation. Here we evaluate the inhibitory activities of prenylated flavonoids isolated from Sophora flavescens, a traditional herbal medicine, on rat lens AR (RLAR), human recombinant AR (HRAR) and AGE formation. Among the tested compounds, two prenylated chalcones--desmethylanhydroicaritin (1) and 8-lavandulylkaempferol (2)--along with five prenylated flavanones--kurarinol (8), kurarinone (9), (2S)-2'-methoxykurarinone (10), (2S)-3beta,7,4'-trihydroxy-5-methoxy-8-(gamma,gamma-dimethylally)-flavanone (11), and kushenol E (13) were potent inhibitors of RLAR, with IC50 values of 0.95, 3.80, 2.13, 2.99, 3.77, 3.63 and 7.74 microM, respectively, compared with quercetin (IC50 7.73 microM). In the HRAR assay, most of the prenylated flavonoids tested showed marked inhibitory activity compared with quercetin (IC50 2.54 microM). In particular, all tested prenylated flavonols, such as desmethylanhydroicaritin (1, IC50 0.45 microM), 8-lavandulylkaempferol (2, IC50 0.79 microM) and kushenol C (3, IC50 0.85 microM), as well as a prenylated chalcone, kuraridin (5, IC50 0.27 microM), and a prenylated flavanone, (2S)-7,4'-dihydroxy-5-methoxy-8-(gamma,gamma-dimethylally)-flavanone (12, IC50 0.37 microM), showed significant inhibitory activities compared with the potent AR inhibitor epalrestat (IC50 0.28 microM). Interestingly, prenylated flavonoids 1 (IC50 104.3 microg mL(-1)), 2 (IC50 132.1 microg mL(-1)), 3 (IC50 84.6 microg mL(-1)) and 11 (IC50 261.0 microg mL(-1)), which harbour a 3-hydroxyl group, also possessed good inhibitory activity toward AGE formation compared with the positive control aminoguanidine (IC50 115.7 microg mL(-1)). Thus, S. flavescens and its prenylated flavonoids inhibit the processes that underlie diabetic complications and related diseases and may therefore have therapeutic benefit.     

Spiro[fluoreneisothiazolidin]one dioxides: new aldose reductase and L-hexonate dehydrogenase inhibitors

The first examples of spiro[fluorene-9,4'- and -9,5'-isothiazolidin]one dioxides (1 and 2) were synthesized and screened for activity as aldose reductase and L-hexonate dehydrogenase inhibitors. Compared to compounds 1, and 9,5'-compounds 2, synthesized from fluorene-9-sulfonamides by alkylation at C(9) with ethyl bromoacetate followed by cyclization, were more active, but relatively nonselective, inhibitors of aldose reductase and L-hexonate dehydrogenase, with IC50 values for in vitro inhibition of both enzymes on the order of 10(-7)-10(-8) M. However, the isomeric 9,4'-compounds 1, prepared by alkylation of fluorene-9-carboxylic acid esters with bromo- or iodomethanesulfonamide followed by cyclization, were more selective inhibitors of L-hexonate dehydrogenase with IC50 values of about 10(-6) M.     

Biphenyl and biphenyl ether quinolizidine N-oxide alkaloids from Lagerstroemia indica L

Four new biphenyl and biphenyl ether quinolizidine N-oxide alkaloids, 5- EPI-dihydrolyfoline N-oxide (1), decamine N-oxide (2), lagerstroemine N-oxide (3), and lagerine N-oxide (4), were isolated from the aerial parts of Lagerstroemia indica, and their structures were established by extensive spectroscopic studies. In addition, the inhibitory effects of isolated compounds on rat lens aldose reductase (RLAR) were examined.     

Effects of BN 52063 and other agents inhibiting platelet-activating factor-induced contractile responses in rat portal vein

Platelet-activating factor (PAF-acether) is a potent agonist (EC50: 3.2 x 10(-8) M) of isolated rat portal vein. BN 52063 (composed of BN 52020, BN 52021 and BN 52022; molar ratio 2:2:1) specifically inhibits PAF-acether (10(-7) M) induced tone (IC50: 3.9 x 10(-5) M). Salbutamol (IC50: 3.1 x 10(-7) M), forskolin (IC50: 3.1 x 10(-6) M) and theophylline (IC50: 2.25 x 10(-4) M) are also effective in inhibiting PAF-acether-induced contractile responses and all excepting forskolin, show a certain specificity in this action. The basal myogenic activity of the rat portal vein is dose-dependently decreased by salbutamol (IC50: 1.2 x 10(-7) M), forskolin (IC50: 2.6 x 10(-6) M) and theophylline (IC50: 2.3 x 10(-4) M) whereas BN 52063 has no effect. The data suggest that rat portal veins possess specific PAF-acether receptors sensitive to BN 52063 and that PAF-acether effects could be inhibited by compounds which can bypass these putative receptors and modulate cAMP levels.     

Synthesis and in vitro aldose reductase inhibitory activity of compounds containing an N-acylglycine moiety

A number of N-benzoylglycines (6), N-acetyl-N-phenylglycines (7), N-benzoyl-N-phenylglycines (8), and tricyclic N-acetic acids (9-12) were synthesized as analogues of the N-acylglycine-containing aldose reductase inhibitors alrestatin and 2-oxoquinoline-1-acetic acid. Derivatives of 6, which represent ring-simplified analogues of alrestatin, are very weak inhibitors of aldose reductase obtained from rat lens, producing 50% inhibition only at concentrations exceeding 100 microM. Compounds of series 7 were designed as ring-opened analogues of the 2-oxoquinolines. While these derivatives are more potent than compounds of series 6 (IC50S of 6-80 microM), they are less active than the corresponding 2-oxoquinolines. Analogues of series 8 were designed as hybrid structures of both alrestatin and the 2-oxoquinoline-1-acetic acids. These compounds are substantially more potent than compounds of series 6 and 7 and display inhibitory activities comparable to or greater than alrestatin or the 2-oxoquinolines (IC50S of 0.1-10 microM). Of the rigid analogues of 8, the most potent derivative is benzoxindole (12) with an IC50 of 0.67 microM, suggesting that fusion of the two aromatic rings of 8 in a coplanar conformation may optimize affinity for aldose reductase in this series.     

Antidiabetic and aldose reductase activities of biflavanones of Garcinia kola

Kolaviron, a mixture of C-3/C-8 linked biflavonoids obtained from Garcinia kola produces significant hypoglycaemic effects when administered intraperitoneally to normal and alloxan diabetic rabbits at a dose of 100 mg kg-1. The fasting blood sugar in normoglycaemic rabbits was reduced from 115 mg/100 mL to 65 mg/100 mL after 4 h. In alloxan diabetic rabbits, the blood sugar was lowered from 506 mg/100 mL to 285 mg/100 mL at 12 h. The hypoglycaemic effects have been compared with those of tolbutamide. Kolaviron inhibited rat lens aldose reductase (RLAR) activity, with an IC50 value of 5.4 x 10(-6). The significance of these findings in the potential use of kolaviron as an antidiabetic agent is discussed.     

WF-2421, a new aldose reductase inhibitor produced from a fungus, Humicola grisea

WF-2421 is a novel aldose reductase inhibitor produced by Humicola grisea. WF-2421 was purified from the culture filtrate by successive ion exchange chromatography and the chemical structure was assigned to be alpha-formamido-5'-(2-formamido-1-hydroxyethyl)- beta,2',6-trihydroxy-3-biphenylpropanoic acid (1) on the basis of spectroscopic evidence. The IC50 value of WF-2421 was 3 x 10(-8) M against partially purified aldose reductase of rabbit lens.     

Isoflavonoids from the rhizomes of Belamcanda chinensis and their effects on aldose reductase and sorbitol accumulation in streptozotocin induced diabetic rat tissues

Aldose reductase, the key enzyme of the polyol pathway, is known to play important roles in the diabetic complication. The inhibitors of aldose reductase, therefore, would be potential agents for the prevention of diabetic complications. To evaluate active principles for the inhibition of aldose reductase from the rhizomes of Belamcanda chinensis, twelve phenolic compounds were isolated and tested for their effects on rat lens aldose reductase. As a result, isoflavones such as tectorigenin, irigenin and their glucosides were found to show a strong aldose reductase inhibition. Tectoridin and tectorigenin, exhibited the highest aldose reductase inhibitory potency, their IC50 values, being 1.08 x 10(-6) M and 1.12 x 10(-6) M, respectively, for DL-glyceraldehyde as a substrate. Both compounds, when administered orally at 100 mg/kg for 10 consecutive days to streptozotocin-induced diabetic rats, caused a significant inhibition of sorbitol accumulation in the tissues such as lens, sciatic nerves and red blood cells. Tectorigenin showed a stronger inhibitory activity than tectoridin. From these results, it is suggested that tectorigenin is attributed to be a promising compound for the prevention and/or treatment of diabetic complications.     

Selective irreversible inhibitors of aldose reductase.

A series of 5-substituted-1,3-dioxo-1H-benz[de]isoquinoline-2(3H)-acetic acid analogues have been examined as irreversible inhibitors of aldose reductase. The 5-alpha-bromoacetamide and 5-alpha-iodoacetamide analogues 5 and 6 gave irreversible inhibition of aldose reductase while the 5-alpha-chloroacetamide analogue 3 did not show this type of inhibition. Protection studies indicate that irreversible inhibitions are occurring at the inhibitor binding site. Comparative irreversible inhibition studies with rat lens aldose reductase (RLAR) and rat kidney aldehyde reductase (RKALR) indicate that 5-alpha-haloacetamide analogues 5 and 6 are much more effective inhibitors of RLAR.