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.     

The existence of aldose reductase inhibitors in some kampo medicines (Oriental herb prescriptions)

Traditionally in Japan, some kampo medicines which contain Glycyrrhizae radix (GR) and Paeoniae radix (PR) have long been used for the treatment of diabetic neuropathy. Since we have previously shown that GR und PR have potent aldose reductase inhibitory activities, we further investigated the constituents of these two. The boiled water extract of GR was applied to Sephadex LH-20 column chromatography and 6 fractions (Frs. A, B, Cs, Cp, D, and E) were obtained. Frs. Cp and D were retreated in the same manner and 7 pure compounds (GUs 1-7) were obtained. The boiled water extract of PR was fractionated with ethyl acetate followed by n-butanol and 3 fractions (Frs. 1-3) were collected. Fr. 1 was retreated in the same manner and 2 pure compounds (PRs 1 and 2) were obtained. Among the GU compounds, GU-2 was the most potent inhibitor of rat lens aldose reductase (RLAR) by inhibiting 86% at the concentration of 1.0 microgram/ml. The IC50 of GU-2 was 7.2 x 10(-7) M. Furthermore, GU-2 markedly inhibited sorbitol accumulation in human red blood cells, having an IC50 of 2.9 x 10(-5) M. GU-5 and PR-1 also inhibited RLAR (IC50: 5.6 x 10(-7) M and 6.3 x 10(-7) M, respectively). The structures of GU-2, GU-5, and PR-1 were identified as isoliquiritin, licuraside, and 1, 2, 3, 6-tetra-O-galloyl-beta-D-glucose, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis of flavonoids and their effects on aldose reductase and sorbitol accumulation in streptozotocin-induced diabetic rat tissues

Aldose reductase, the key enzyme of the polyol pathway, and oxidative stress are known to play important roles in the complications of diabetes. A drug with potent inhibition of aldose reductase and oxidative stress, therefore, would be a most promising drug for the prevention of diabetic complications. The purpose of this study was to develop new compounds with these dual-effects through synthesis of chalcone derivatives and by examining the structure-activity relationships on the inhibition of rat lens aldose reductase as well as on antioxidant effects. A series of 35 flavonoid derivatives were synthesized by Winget's condensation, oxidation, and reduction of appropriate acetophenones with appropriate benzaldehydes. The inhibitory activity of these derivatives on rat lens aldose reductase and their antioxidant effects, measured using Cu2+ chelation and radical scavenging activities on 1,1-diphenyl-picrylhydrazyl in-vitro, were evaluated. Their effect on sorbitol accumulation in the red blood cells, lenses and sciatic nerves of streptozotocin-induced diabetic rats was also estimated. Among the new flavonoid derivatives synthesized, those with the 2',4'-dihydroxyl groups in the A ring such as 2,4,2',4'-tetrahydroxychalcone (22), 2,2',4'-trihydroxychalcone (11), 2',4'-dihydroxy-2,4-dimethylchalcone (21) and 3,4,2',4'-tetrahydroxychalcone (18) were found to possess the highest rat lens aldose reductase inhibitory activity in-vitro, their IC50 values (concentration of inhibitors giving 50% inhibition of enzyme activity) being 1.6 x 10(-7), 3.8 x 10(-7), 4.0 x 10(-7) and 4.6 x 10(-7) M, respectively. All of the chalcones tested except 3, 18, 23 with o-dihydroxy or hydroquinone moiety showed a weak free radical scavenging activity. In the in-vivo experiments, however, compound 18 with o-dihydroxy moiety in the B ring showed the strongest inhibitory activity in the accumulation of sorbitol in the tissues. It also showed the strongest activity in transition metal chelation and free radical scavenging activity. Of the 35 4,2'-dihydroxyl and 2',4'-dihydroxyl derivatives of flavonoid synthesized, including chalcone, flavone, flavanone, flavonol and dihydrochalcone, some chalcone derivatives synthesized were found to possess aldose reductase inhibition and antioxidant activities in-vitro as well as inhibition in the accumulation of sorbitol in the tissues in-vivo. 3,4,2',4'-Tetrahydroxychalcone (18, butein) was the most promising compound for the prevention or treatment of diabetic complications.     

Development of potent aldose reductase inhibitors having a hydantoin structure

Seventeen hydantoin derivatives were tested as inhibitors of aldose reductase, an enzyme believed to participate in the initiation of diabetic complications. Nine compounds with high inhibitory activities (IC50 values against purified rat lens aldose reductase less than or equal to 1.06 X 10(-6)M) were tested further for their abilities to prevent sorbitol accumulation induced by exposure of excised rat lens and sciatic nerve to a high glucose concentration (50 mM). Seven active compounds among them inhibited sorbitol accumulation by about 50% or more at a concentration of 10(-5)M. These seven compounds were given orally to streptozotocin-induced diabetic rats at a dose of 50 mg/kg/day and were assessed for their abilities to prevent both sorbitol accumulation in two tissues (lens and sciatic nerve) and myo-inositol depletion in the sciatic nerve. 1-[(2,4,5-Trichlorophenyl)sulfonyl]hydantoin, 1-[(2,5-dichlorophenyl)sulfonyl]hydantoin, and 1-[(beta-naphthyl)sulfonyl]hydantoin were found to be the most effective: they inhibited sorbitol accumulation in the sciatic nerve completely and that in the lens by more than 92%. It is conceivable from this study that the three compounds are promising for further investigation targeted to the treatment of diabetic complications.     

Anti-platelet action of isoliquiritigenin, an aldose reductase inhibitor in licorice.

The mechanism was studied by which isoliquiritigenin, a new aldose reductase inhibitor purified from licorice (Glycyrrhizae radix), inhibits platelet aggregation. This new agent significantly inhibited the phosphorylation of 40,000- and 20,000-dalton proteins, and inhibited the formation of 12 (S)-hydroxy-5,8,10-heptadecatrienoic acid, 12-hydroxyeicosatetraenoic acid and thromboxane B2. The inhibitory effect of isoliquiritigenin on platelet aggregation in vitro was comparable to that of aspirin. Our findings may indicate that isoliquiritigenin elicits an anti-platelet action by inhibiting not only cyclooxygenase but also lipoxygenase or peroxidase activity in platelets. Isoliquiritigenin also showed an anti-platelet action in vivo. Isoliquiritigenin appears to be the only aldose reductase inhibitor with a significant anti-platelet action. Since the hyperaggregability of platelets has been implicated in the pathogenesis of diabetic complications, isoliquiritigenin may offer a unique benefit as an aldose reductase inhibitor.     

Novel, potent aldose reductase inhibitors: 3,4-dihydro-4-oxo-3-[[5-(trifluoromethyl)-2-benzothiazolyl] methyl]-1-phthalazineacetic acid (zopolrestat) and congeners

A new working hypothesis that there is a hitherto unrecognized binding site on the aldose reductase (AR) enzyme with strong affinity for benzothiazoles was pursued for the design of novel, potent aldose reductase inhibitors (ARIs). The first application of this hypothesis led to a novel series of 3,4-dihydro-4-oxo-3-(benzothiazolylmethyl)-1-phthalazineacetic+ + + acids. The parent of this series (207) was a potent inhibitor of AR from human placenta (IC50 = 1.9 x 10(-8) M) and was orally active in preventing sorbitol accumulation in rat sciatic nerve, in an acute test of diabetic complications (ED50 = 18.5 mg/kg). Optimization of this lead through medicinal chemical rationale, including analogy from other drug series, led to more potent congeners of 207 and culminated in the design of 3,4-dihydro-4-oxo-3-[[5-(trifluoromethyl)-2-benzothiazolyl] methyl]-1-phthalazineacetic acid (216, CP-73,850, zopolrestat). Zopolrestat was found to be more potent than 207, both in vitro and in vivo. Its IC50 against AR and ED50 in the acute test were 3.1 x 10(-9)M and 3.6 mg/kg, respectively. Its ED50s in reversing already elevated sorbitol accumulation in rat sciatic nerve, retina, and lens in a chronic test were 1.9, 17.6, and 18.4 mg/kg, respectively. It was well absorbed in diabetic patients, resulting in high blood level, showed a highly favorable plasma half-life (27.5 h), and is undergoing further clinical evaluation. An assortment of synthetic methods used for the construction of benzothiazoles, including an efficient synthesis of zopolrestat, is described. Structure-activity relationships in the new series are discussed.     

Presence of aldose reductase inhibitors in tea leaves

Water extract from commercial English tea has a potent inhibitory activity against human placenta aldose reductase (NADPH oxidoreductase, E.C.1.1.1.21.). Inhibitory activity was separated into five major fractions by one-step chromatography with a C-18 reverse phase column. The most active fraction was further subjected to reverse phase column chromatography. As a result, a well-known flavone-glycoside, isoquercitrin, was isolated as the most potent chemical. The inhibitory character of isoquercitrin for aldose reductase was a mix of uncompetitive and noncompetitive inhibitions, and its IC50 was 1 x 10(-6) M. In rat sciatic nerve tissue preparations, sorbitol accumulation in the presence of high concentrations of glucose (30 mM) was inhibited by 38% at 5 x 10(-4) M of isoquercitrin. The flavone-glycoside isoquercitrin is the active inhibitor of aldose reductase inhibitor present in English tea. Given the ability of aldose reductase inhibitors to prevent diabetic complications, an epidemiological study of the effect of tea consumption on the pathogenesis and progression of diabetic complications would be interesting.     

Pharmacological properties of fidarestat, a potent aldose reductase inhibitor, clarified by using sorbitol in human and rat erythrocytes

We examined the effect of fidarestat on the increase in sorbitol content in erythrocytes from healthy volunteers in vitro. Fidarestat inhibited the increase with an IC50 value of 18 nmol/l. A subsequent experiment showed that fidarestat had a similar inhibitory effect on the increase in sorbitol content in erythrocytes from diabetic patients. On the other hand, epalrestat, the only aldose reductase inhibitor used clinically, inhibited increase in sorbitol content at a concentration over 500-fold higher than fidarestat. Although the IC50 value of fidarestat was not affected by fasting plasma glucose, HbA1C, age, aldose reductase content or gender, there was a significant positive relationship between the IC50 value of epalrestat and fasting plasma glucose. In addition, in fidarestat (0.25-2 mg/kg)-treated diabetic rats, the inhibitory rate for erythrocyte sorbitol accumulation was well correlated with that for nerve sorbitol accumulation, which indicates that erythrocyte sorbitol is available for assessing the state of sorbitol pathway flux in target tissue after fidarestat administration. These results suggest that fidarestat potently inhibits the increase in sorbitol pathway flux in diabetic patients independent of various factors and that erythrocyte sorbitol is useful for its estimation.     

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 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.     

Potent, orally active aldose reductase inhibitors related to zopolrestat: surrogates for benzothiazole side chain.

A broad structure-activity program was undertaken in search of effective surrogates for the key benzothiazole side chain of the potent aldose reductase inhibitor, zopolrestat (1). A structure-driven approach was pursued, which spanned exploration of three areas: (1) 5/6 fused heterocycles such as benzoxazole, benzothiophene, benzofuran, and imidazopyridine; (2) 5-membered heterocycles, including oxadiazole, oxazole, thiazole, and thiadiazole, with pendant aryl groups, and (3) thioanilide as a formal equivalent of benzothiazole. Several benzoxazole- and 1,2,4-oxadiazole-derived analogues were found to be potent inhibitors of aldose reductase from human placenta and were orally active in preventing sorbitol accumulation in rat sciatic nerve, in an acute test of diabetic complications. 3,4-Dihydro-4-oxo-3-[(5,7-difluoro-2-benzoxazolyl)methyl]-1- phthalazineacetic acid (124) was the best of the benzoxazole series (IC50 = 3.2 x 10(-9) M); it suppressed accumulation of sorbitol in rat sciatic nerve by 78% at an oral dose of 10 mg/kg. Compound 139, 3,4-dihydro-4-oxo-3-[[(2-fluorophenyl)-1,2,4- oxadiazol-5-yl]methyl]-1-phthalazineacetic acid, with IC50 less than 1.0 x 10(-8) M, caused a 69% reduction in sorbitol accumulation in rat sciatic nerve at an oral dose of 25 mg/kg. The thioanilide side chain featured in 3-[2-[[3-(trifluoromethyl)phenyl]amino]-2-thioxoethyl]-3,4-dihydro - 4-oxo-1-phthalazineacetic acid (195) proved to be an effective surrogate for benzothiazole. Compound 195 was highly potent in vitro (IC50 = 5.2 x 10(-8) M) but did not show oral activity when tested at 100 mg/kg. Additional structure-activity relationships encompassing a variety of heterocyclic side chains are discussed.     

Inhibition of aldose reductases from rat and bovine lenses by flavonoids

Thirty flavones, four isoflavones and thirteen coumarins were tested as inhibitors of lens aldose reductase, which is believed to participate in the initiation of cataract formation in diabetes. Many were found to be potent inhibitors, and the two most potent ones were axillarin (5,7,3',4'-tetrahydroxy-3,6-dimethoxyflavone) and 6,3',4'-trihydroxy-5,7,8-trimethoxyflavone (LARI 1). These two flavones inhibited aldose reductase purified from rat lens with IC50 values of 2.6 X 10(8) and 3.6 X 10(8) M respectively. They also inhibited aldose reductase purified from bovine lens with IC50 values of 1.8 X 10(7) M. The potencies of the two compounds were superior to those of all the previously reported inhibitors of aldose reductase. Inhibition of rat and bovine lens aldose reductases by the two compounds was of a non-competitive type with DL-glyceraldehyde as the variable substrate. Some flavones including axillarin and LARI 1 were found to be poorly or scarcely inhibitory against several adeninenucleotide-requiring enzymes, which are involved in glycolysis and other metabolic reactions. These results obtained show that the two flavones have some features which may be required in clinically useful drugs for diabetic patients. All the potent inhibitors of the compounds tested had a flavone skeleton, one (or two free) hydroxyl(s) in ring C, and more than three hydroxyls (free or methylated) in ring A. The possible relationships of structures to inhibitory potencies of the compounds tested are discussed.     

Effects of novel aldose reductase inhibitors, M16209 and M16287, on streptozotocin-induced diabetic neuropathy in rats.

We investigated the effects of novel aldose reductase inhibitors, M16209 (1-(3-bromobenzo[b]furan-2-ylsulfonyl)hydantoin) and M16287 (1-(3-chlorobenzo[b]furan-2-ylsulfonyl)hydantoin), on neuropathy in streptozotocin-induced (STZ) diabetic rats. Both compounds (3-100 mg/kg per day, p.o.) dose dependently improved the decreased motor nerve conduction velocity in the sciatic nerve during a 14-day treatment period. These compounds also partially ameliorated the diabetes-induced histological changes in the sciatic nerve. A distinct increase in sorbitol content and a slight decrease in myo-inositol content was observed in the sciatic nerve of STZ diabetic rats, and the sorbitol accumulation was dose dependently suppressed by treatment with M16209 and M16287. Treatment started at an earlier period was more effective in the suppression of sorbitol accumulation. There was a significant correlation between motor nerve conduction velocity and nerve sorbitol content, whereas there was none between motor nerve conduction velocity and myo-inositol content. The present study indicates that M16209 and M16287 are potent aldose reductase inhibitors expected to be useful for the treatment of diabetic complications.     

Inhibition of aldehyde reductase by aldose reductase inhibitors

A broad group of structurally diverse aldose reductase inhibitors including flavonoids, carboxylic acids and hydantoins, have been examined for their ability to inhibit rat kidney aldehyde reductase (EC 1.1.1.19, EC 1.1.1.20) versus rat lens aldose reductase (EC 1.1.1.21). All aldose reductase inhibitors examined inhibited aldehyde reductase to some extent both in the reductive reaction as determined with glyceraldehyde as substrate and NADPH as coenzyme, and in the oxidative reaction where L-gulonic acid was oxidized to D-glucuronic acid in the presence of NADP+. Of the inhibitors examined, 2,7-difluorospirofluorene-9,5'-imidazolidine-2',4'-dion e (Al1576) was the most potent inhibitor requiring only concentrations in the 10(-8) M range to inhibit 50% of the in vitro activity of rat kidney aldehyde reductase (IC50 value), whereas 3-dioxo-1-H-benz[de]isoquinoline-2(3H)-acetic acid (alrestatin) was the least potent inhibitor requiring concentrations in the 10(-5) M range. Both the reductive and oxidative steps appeared equally inhibited by these aldose reductases inhibitors. Moreover, all compounds appeared to inhibit either crude or highly purified rat kidney aldehyde reductase to essentially the same extent. Marked differences in the selectivity of these inhibitors, expressed as the ratio of IC50 values for rat kidney aldehyde reductase versus rat lens aldose reductase with glyceraldehyde as substrate, were observed with selectivity for aldose reductase ranging from ca. 2-fold for Al1576 to 119-fold for 3-(4-bromo-2-fluorobenzyl-4-oxo-3-phthalazine-1-ylacetic acid (Ponalrestat). Kinetic and competition studies suggest that these inhibitors interact with aldehyde reductase at a common site that is not identical to either the substrate or nucleotide binding site. These results suggest that the inhibitor binding sites of rat kidney aldehyde reductase and aldose reductase contain several common characteristics.     

Inhibition of aldose reductase by phenylethanoid glycoside isolated from the seeds of Paulownia coreana

Aldose reductase (AR) inhibitors have considerable therapeutic potential against diabetic complications and do not increase the risk of hypoglycemia. Through bioassay-guided fractionation of the 70% acetone extract obtained from Paulownia coreana seeds, phenylpropanoid glycosides (compounds 1-4) and 5 phenolic compounds were isolated (compounds 5-9). Their structures were determined on the basis of spectroscopic analysis and comparison with reported data. All the isolates were subjected to in vitro bioassays to evaluate their inhibitory activities against recombinant human aldose reductase (rhAR) and sorbitol formation in human erythrocytes. Phenylethanoid glycosides showed more effective than the phenolic compounds in inhibiting rhAR. Among the compounds, isocampneoside II (3) was found to significantly inhibit rhAR with an IC(50) value of 9.72 μM. In kinetic analyses performed using Lineweaver-Burk plots of 1/velocity and 1/concentration of substrate, isocampneoside II (3) showed uncompetitive inhibition against rhAR. Furthermore, it inhibited sorbitol formation in a rat lens incubated with a high concentration of glucose; this finding indicated that isocampneoside II (3) may effectively prevent osmotic stress in hyperglycemia. Thus, the P. coreana-derived phenylethanoid glycoside isocampneoside II (3) may have a potential therapeutics against diabetic complications.     

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.     

In vivo activities of aldose reductase inhibitors having a 1-(arylsulfonyl)hydantoin structure

Two potent aldose reductase inhibitors, 1-[(2,5-dichlorophenyl)sulfonyl]hydantoin (Di-Cl-PSH) and 1-[beta-naphthyl)sulfonyl]hydantoin (beta-NSH), were tested for usefulness in the treatment of diabetic and galactosemic complications in animal experiments. Both drugs were effective for the treatment of diabetic neuropathy characterized by decreased motor nerve conduction velocity, that is, slowing of tail and sciatic-tibial motor nerve conduction velocities in streptozocin-induced diabetic rats was prevented during 3 weeks by intubating Di-Cl-PSH or beta-NSH at 50 mg/kg/day. Lenticular vacuole formation in rats fed a 30% galactose diet was blocked completely for at least 2 weeks by oral administration of Di-Cl-PSH or beta-NSH at both 30 and 100 mg/kg/day, whereas all of the eyes of vehicle-treated rats showed vacuole formation by day 4 on the galactose diet. The ED50 values of Di-Cl-PSH and beta-NSH for inhibition of sorbitol accumulation in the sciatic nerve and lens of streptozocin-induced diabetic rats were also estimated; the values of Di-Cl-PSH and beta-NSH were 1.1 and 3.4 mg/kg/day, respectively, for inhibition in the sciatic nerve and 4.8 and 16.0 mg/kg/day, respectively, for that in the lens. This study indicates that Di-Cl-PSH and beta-NSH have high potential for future clinical use as aldose reductase inhibitors.     

Synthesis and aldose reductase inhibitory activity of pyridazine derivatives possessing acetic acid group.

N-acetic acid and S-acetic acid derivatives of 5-arylidene pyridazines were synthesized for evaluation as new aldose reductase inhibitors. Intrinsic activity for each compound was assessed by measuring inhibition of enzymatic activity in an isolated pig lens enzyme preparation. All prepared compounds exhibited a significant in vitro aldose reductase inhibitory effect (10(-5) M less than or equal IC50 less than or equal to 10(-4) M). It was found that lipophilicity was important in increasing activity. Furthermore, this activity (log 1/IC50) could be correlated directly to a lipophilic parameter (log kw) for the whole data set.     

Inhibition of aldose reductase in five tissues of the streptozotocin-diabetic rat

For 22 days, streptozotocin-diabetic and normal rats were intubated once daily with ICI 105552 (1-(3, 4-dichlorobenzyl)-3-methyl-1, 2-dihydro-2-oxoquinol-4-ylacetic acid, sodium salt: 50 mg/kg body weight) an inhibitor of aldose reductase (EC 1.1.1.21), the first enzyme of the sorbitol pathway. Treatment with ICI 105552 affected neither glycaemia nor tissue glucose nor inositol concentrations yet reduced significantly the abnormal accumulations in diabetes of sorbitol in the lens (70% reduction), sciatic nerve (86%) and seminal vesicles with coagulating glands (S.V.C.G., 55%). ICI 105552 had no effect upon sorbitol accumulated in the diabetic kidney but it reduced the level in controls by 43%. The compound reduced the accumulation of sorbitol in diabetic retina by 58% although variation was too great for the decrease to be significant statistically. Treatment with ICI 105552 produced small (? 11%) yet statistically significant increases in the weights of the kidneys, and both liver and kidney weight/100 g residual body weight but did not affect the weights of the body, lens, retina or S.V.C.G. The importance of these findings for the development of potentially chemotherapeutic aldose reductase inhibitors is discussed.     

Effects of ellagic acid and 2-(2,3,6-trihydroxy-4-carboxyphenyl)ellagic acid on sorbitol accumulation in vitro and in vivo

Caesalpinia ferrea MART. (Leguminosae) called as Juca is one of the medicinal plants in Brazil used for diabetes. From the fruits of this plant, ellagic acid (EA) and 2-(2,3,6-trihydroxy-4-carboxyphenyl)ellagic acid (TEA) have been recently isolated as aldose reductase (AR) inhibitors. In this study, we examined to prove the inhibitory activity against AR of EA and TEA in vitro, and EA in vivo by measurement of the accumulation of sorbitol, which is the product of glucose reduction catalyzed by AR. TEA was not examined in vivo because of its shortage of yield from the fruits. EA and TEA significantly and dose-dependently inhibited sorbitol accumulation in erythrocytes, lens and sciatic nerve under incubating with glucose in vitro. EA at a dose of 75 mg/kg/d showed the most potent inhibition of sorbitol accumulation in erythrocytes, lens and sciatic nerve at 50, 75 and 100 mg/kg/d in vivo. These results suggest that the inhibitory activity of EA against AR causes to inhibit sorbitol accumulation by in vitro and in vivo experiments. EA is distributed in fruits and vegetables, so that taking them might be able to relieve diabetic complications.