Inhibition of aldose reductases from rat and bovine lenses by flavonoids

Flavones: Six Selected Flavones and Their Related Signaling Pathways That Induce Apoptosis in Cancer

Cancer is a horrific disease that, to date, has no cure. It is caused by various factors and takes many lives. Apoptosis is a programmed cell death mechanism and if it does not function correctly in cancer cells, it can lead to severe disease. There are various signaling pathways for regulating apoptosis in cancer cells. Flavonoids are non-artificial natural bioactive compounds that are gaining attention as being capable of for inducing apoptosis in cancer cells. Among these, in this study, we focus on flavones. Flavones are a subclass of the numerous available flavonoids and possess several bioactive functions. Some of the most reported and well-known critical flavones, namely apigenin, acacetin, baicalein, luteolin, tangeretin, and wogonin, are discussed in depth in this review. Our main aim is to investigate the effects of the selected flavones on apoptosis and cell signaling pathways that contribute to death due to various types of cancers.

Development of Aldose Reductase Inhibitors for the Treatment of Inflammatory Disorders and Cancer: Current Drug Design Strategies and Future Directions

Aldose Reductase (AR) is an enzyme that converts glucose to sorbitol during the polyol pathway of glucose metabolism. AR has been shown to be involved in the development of secondary diabetic complications due to its involvement in causing osmotic as well as oxidative stress. Various AR inhibitors have been tested for their use to treat secondary diabetic complications, such as retinopathy, neuropathy, and nephropathy in clinical studies. Recent studies also suggest the potential role of AR in mediating various inflammatory complications. Therefore, the studies on the development and potential use of AR inhibitors to treat inflammatory complications and cancer besides diabetes are currently on the rise. Further, genetic mutagenesis studies, computer modeling, and molecular dynamics studies have helped design novel and potent AR inhibitors. This review discussed the potential new therapeutic use of AR inhibitors in targeting inflammatory disorders and cancer besides diabetic complications. Further, we summarized studies on how AR inhibitors have been designed and developed for therapeutic purposes in the last few decades.

A Simple, Enzymatic Biotransformation Method Using Fresh Green Tea Leaves Efficiently Generates Theaflavin-Containing Fermentation Water That Has Potent Physiological Functions in Mice and Humans

The polyphenolic compound theaflavin, the main red pigment in black tea, possesses many beneficial properties, such as fat-reducing and glucose-lowering capabilities. To produce theaflavin-containing fermentation water on a large scale, we have developed a simple, inexpensive, and selective enzymatic biotransformation method to obtain sufficient levels from fresh green tea leaves. Subsequent administration of theaflavin-containing fermentation water to obese mice on a high-fat diet inhibited body weight gain, decreased casual blood glucose and fasting blood glucose levels, and lowered mesenteric and total fat composition. To note, there were no significant differences observed in food consumption between the experimental and control (water without theaflavin) mice groups. Next, we investigated the effect of this water on blood glucose levels in healthy humans and found that it significantly inhibited blood glucose levels. Thus, we showed that theaflavin-containing fermentation water can be efficiently generated from fresh green tea leaves and demonstrated its significantly potent effects in vivo.

Dietary flavonoid aglycones and their glycosides: Which show better biological significance?

The dietary flavonoids, especially their glycosides, are the most vital phytochemicals in diets and are of great general interest due to their diverse bioactivity. The natural flavonoids almost all exist as their O-glycoside or C-glycoside forms in plants. In this review, we summarized the existing knowledge on the different biological benefits and pharmacokinetic behaviors between flavonoid aglycones and their glycosides. Due to various conclusions from different flavonoid types and health/disease conditions, it is very difficult to draw general or universally applicable comments regarding the impact of glycosylation on the biological benefits of flavonoids. It seems as though O-glycosylation generally reduces the bioactivity of these compounds - this has been observed for diverse properties including antioxidant activity, antidiabetes activity, anti-inflammation activity, antibacterial, antifungal activity, antitumor activity, anticoagulant activity, antiplatelet activity, antidegranulating activity, antitrypanosomal activity, influenza virus neuraminidase inhibition, aldehyde oxidase inhibition, immunomodulatory, and antitubercular activity. However, O-glycosylation can enhance certain types of biological benefits including anti-HIV activity, tyrosinase inhibition, antirotavirus activity, antistress activity, antiobesity activity, anticholinesterase potential, antiadipogenic activity, and antiallergic activity. However, there is a lack of data for most flavonoids, and their structures vary widely. There is also a profound lack of data on the impact of C-glycosylation on flavonoid biological benefits, although it has been demonstrated that in at least some cases C-glycosylation has positive effects on properties that may be useful in human healthcare such as antioxidant and antidiabetes activity. Furthermore, there is a lack of in vivo data that would make it possible to make broad generalizations concerning the influence of glycosylation on the benefits of flavonoids for human health. It is possible that the effects of glycosylation on flavonoid bioactivity in vitro may differ from that seen in vivo. With in vivo (oral) treatment, flavonoid glycosides showed similar or even higher antidiabetes, anti-inflammatory, antidegranulating, antistress, and antiallergic activity than their flavonoid aglycones. Flavonoid glycosides keep higher plasma levels and have a longer mean residence time than those of aglycones. We should pay more attention to in vivo benefits of flavonoid glycosides, especially C-glycosides.

Construction of explicit models to correlate the structure and the inhibitory activity of aldose reductase: Flavonoids and sulfonyl-pyridazinones as inhibitors

The correlation between binding energies and bioactivities is the core of structure-based computer-aided drug design. However, many models to address this correlation are still strongly system-dependent at current stage. We constructed two explicit models to correlate the binding energies with the inhibitory activities of flavonoids and sulfonyl-pyridazinones as inhibitors of aldose reductase. The introduction of multiple complex states comprised of protein, coenzyme, substrate, and inhibitor can remarkably improve the correlation coefficients, compared with that using single complex state. Recombination of energy terms from complex structures and molecular descriptors of inhibitors can further improve the correlation. The explicit models provide correlation coefficients of 0.90 and 0.92 for flavonoids and sulfonyl-pyridazinones, respectively. These models also steadily present the contribution from each energy term and the favorite of protein-inhibitor complex states. Meanwhile, we also observed that some inhibitors can accommodate alternative sites out of the conserved binding pocket at the presence/absence of coenzyme and substrate. It is responsible for the remarkable change in the binding energies and thus significantly influences the correlation between the structures and the inhibitory activities. Overall, this work presents a rational way to construct reliable explicit models through the combination of multiple physically accessible complex states, even though each of them only bears marginal information related to their activities.

Esculetin, a Coumarin Derivative, Inhibits Aldose Reductase Activity in vitro and Cataractogenesis in Galactose-Fed Rats

Naturally occurring coumarin compounds have received substantial attention due to their pharmaceutical effects. Esculetin is a coumarin derivative and a polyphenol compound that is used in a variety of therapeutic and pharmacological strategies. However, its effect on aldose reductase activity remains poorly understood. In this study, the potential beneficial effects of esculetin on lenticular aldose reductase were investigated in galactose-fed (GAL) rats, an animal model of sugar cataracts. Cataracts were induced in Sprague-Dawley (SD) rats via a 50% galactose diet for 2 weeks, and groups of GAL rats were orally treated with esculetin (10 or 50 mg/kg body weight). In vehicle-treated GAL rats, lens opacification was observed, and swelling and membrane rupture of the lens fiber cells were increased. Additionally, aldose reductase was highly expressed in the lens epithelium and superficial cortical fibers during cataract development in the GAL rats. Esculetin reduced rat lens aldose reductase (RLAR) activity in vitro, and esculetin treatment significantly inhibited lens opacity, as well as morphological alterations, such as swelling, vacuolation and liquefaction of lens fibers, via the inhibition of aldose reductase in the GAL rats. These results indicate that esculetin is a useful treatment for galactose-induced cataracts.

Phenolic Compounds from the Leaves and Twigs of Osteomeles schwerinae That Inhibit Rat Lens Aldose Reductase and Vessel Dilation in Zebrafish Larvae

Three new phenolic biphenyl derivatives (1-3) and one new lignan glycoside (4) were isolated from the leaves and twigs of Osteomeles schwerinae. The structures of the new compounds were established by spectroscopic data interpretation. The inhibitory effects of 1-4 on rat lens aldose reductase in vitro were examined, and compounds 1-3 markedly inhibited the enzyme with IC50 values of 3.8 to 13.8 μM. In addition, the effects of these isolates on the dilation of hyaloid-retinal vessels induced by high glucose (HG) in zebrafish larvae were investigated. Compound 1 was the most effective in reducing HG-induced dilation of hyaloid-retinal vessels.

Cyanogenetic glycosides and simple glycosides from the linseed meal

Three new cyanogenetic triglycosides linustatins A-C (1-3), and two new simple glycosides linustatins D and E (4 and 5) were isolated from the 70% ethanol extract of flaxseed meal (Linum usitatissimum L.). Their structures were elucidated on the basis of spectroscopic analysis and chemical evidence. All of the isolates showed moderate activities against aldose reductase and weak activities against α-glucosidase, DPP-IV, and FBPase at the same concentrations as the positive control drugs.

WITHDRAWN: Flavonoid glycosylation and biological benefits

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Hyptis verticillata Jacq: a review of its traditional uses, phytochemistry, pharmacology and toxicology

ETHNOPHARMACOLOGICAL RELEVANCE

Hyptis verticillata Jacq. (Lamiaceae) (John Charles) is an important medicinal plant with a long history of traditional use, originating in Central America and now extending from Florida to Colombia and across the Caribbean. Records of its earliest use date back to the ancient Mayan and Aztec cultures of Mesoamerica. There is no indication that this plant is being used outside of the Americas.

AIM OF THE REVIEW

This review aims to provide a comprehensive overview of the traditional use, phytochemistry, pharmacological activity and toxicology of Hyptis verticillata and to highlight the opportunities for greater development of the plant's medicinal properties at a local and international level.

MATERIALS AND METHODS

An extensive and systematic review of the literature was undertaken and all relevant abstracts and full-text articles analysed and included in the review.

KEY FINDINGS

A wide range of traditional uses are cited in the literature, from internal uses for conditions affecting the respiratory system, digestive tract and gynaecological system to external uses for conditions affecting the skin and musculoskeletal system. Pharmacological studies to date have demonstrated significant activity which support the traditional use of the plant as an antiinflammatory, antimicrobial, antisecretory agent and hormone modulator. In addition studies have identified anti-cancer, acaricidal, insecticidal and molluscicidal activity. No clinical trials had been completed at the time of this review. A number of key phytochemicals have been isolated, identified and published to date including: 17 lignans; 4 triterpenes; 11 diterpenes, 3 sesquiterpenes, 3 monoterpenes, 2 flavonoids, 1 polyphenol and 1 alkaloid. Nine of these phytochemicals are novel to Hyptis verticillata. Plant extracts and isolated phytochemicals exhibit a broad range of activities that include: antimitotic; antiproliferative; cytotoxic; antioxidant; antiinflammatory; antibacterial; antifungal; antiviral; anti-HIV; antisecretory; hepatoprotective; insecticidal and acaricidal.

CONCLUSIONS

Hyptis verticillata is a medicinal plant with current widespread traditional use in the Americas that warrants further research, clinical trials and product development to fully exploit its medicinal value.

Aldose reductase inhibitory activity of compounds from Zea mays L

Aldose reductase (AR) inhibitors have a considerable therapeutic potential against diabetes complications and do not increase the risk of hypoglycemia. Through bioassay-guided fractionation of an EtOH extract of the kernel from purple corn (Zea mays L.), 7 nonanthocyanin phenolic compounds (compound 1-7) and 5 anthocyanins (compound 8-12) were isolated. These compounds were investigated by rat lens aldose reductase (RLAR) inhibitory assays. Kinetic analyses of recombinant human aldose reductase (rhAR) were performed, and intracellular galactitol levels were measured. Hirsutrin, one of 12 isolated compounds, showed the most potent RLAR inhibitory activity (IC(50), 4.78 μ M). In the kinetic analyses using Lineweaver-Burk plots of 1/velocity and 1/substrate concentration, hirsutrin showed competitive inhibition against rhAR. Furthermore, hirsutrin inhibited galactitol formation in rat lens and erythrocytes sample incubated with a high concentration of galactose; this finding indicates that hirsutrin may effectively prevent osmotic stress in hyperglycemia. Therefore, hirsutrin derived from Zea mays L. may be a potential therapeutic agent against diabetes complications.

Liquid chromatography-tandem mass spectrometry analysis allows the simultaneous characterization of C-glycosyl and O-glycosyl flavonoids in stingless bee honeys

The analysis of the phytochemicals present in stingless bee honey samples has been a difficult task due to the small amounts of samples available and to the complexity of the phytochemical composition that often combines flavonoid glycosides and aglycones. Honey samples produced in Venezuela from Melipona species were analyzed using a combination of solid-phase extraction and HPLC-DAD-MSn/ESI methodologies with specific study of the fragment ions produced from flavonoid glycosides. The analyses revealed that flavonoid glycosides were the main constituents. The honey samples analyzed contained a consistent flavonoid pattern composed of flavone-C-glycosides, flavonol-O-glycosides and flavonoid aglycones. The HPLC-DAD-MSn/ESI analysis and the study of the fragment ions obtained allowed the characterization and quantification for the first time of five apigenin-di-C-glycosides, and ten quercetin, kaempferol and isorhamnetin O-glycosides (di- and tri- glycosides), and the aglycones pinobanksin, quercetin, kaempferol and isorhamnetin in the different samples. This is the first report of flavonoid-C-glycosides in honey. The results show that the content of flavonoid-glycosides (mean values of 2712 μg/100 g) in stingless bee honeys is considerably higher than the content of flavonoid aglycones (mean values of 315 μg/100 g). This differs from previous studies on Apis mellifera honeys that consistently showed much higher aglycone content and smaller flavonoid glycoside content. The occurrence of relevant amounts of flavonoid glycosides, and particularly C-glycosides, in stingless bee honeys could be associated with their putative anticataract properties.

Natural flavonoids as potential multifunctional agents in prevention of diabetic cataract

Cataract is one of the earliest secondary complications of diabetes mellitus. The lens is a closed system with limited capability to repair or regenerate itself. Current evidence supports the view that cataractogenesis is a multifactorial process. Mechanisms related to glucose toxicity, namely oxidative stress, processes of non-enzymatic glycation and enhanced polyol pathway significantly contribute to the development of eye lens opacity under conditions of diabetes. There is an urgent need for inexpensive, non-surgical approaches to the treatment of cataract. Recently, considerable attention has been devoted to the search for phytochemical therapeutics. Several pharmacological actions of natural flavonoids may operate in the prevention of cataract since flavonoids are capable of affecting multiple mechanisms or etiological factors responsible for the development of diabetic cataract. In the present paper, natural flavonoids are reviewed as potential agents that could reduce the risk of cataract formation via affecting multiple pathways pertinent to eye lens opacification. In addition, the bioavailability of flavonoids for the lens is considered.

3D-QSAR (CoMFA and CoMSIA) and pharmacophore (GALAHAD) studies on the differential inhibition of aldose reductase by flavonoid compounds

Inhibitory activities of flavonoid derivatives against aldose reductase (AR) enzyme were modelled by using CoMFA, CoMSIA and GALAHAD methods. CoMFA and CoMSIA methods were used for deriving quantitative structure-activity relationship (QSAR) models. All QSAR models were trained with 55 compounds, after which they were evaluated for predictive ability with additional 14 compounds. The best CoMFA model included both steric and electrostatic fields, meanwhile, the best CoMSIA model included steric, hydrophobic and H-bond acceptor fields. These models had a good predictive quality according to both internal and external validation criteria. On the other hand, GALAHAD was used for deriving a 3D pharmacophore model. Twelve active compounds were used for deriving this model. The obtained model included hydrophobe, hydrogen bond acceptor and hydrogen bond donor features; it was able to identify the active AR inhibitors from the remaining compounds. These in silico tools might be useful in the rational design of new AR inhibitors.

Inhibitory effect of rhetsinine isolated from Evodia rutaecarpa on aldose reductase activity

Aldose reductase inhibitors have considerable potential for the treatment of diabetic complications, without increased risk of hypoglycemia. Search for components inhibiting aldose reductase led to the discovery of active compounds contained in Evodia rutaecarpa Bentham (Rutaceae), which is the one of the component of Kampo-herbal medicine. The hot water extract from the E. rutaecarpa was subjected to distribution or gel filtration chromatography to give an active compound, N2-(2-methylaminobenzoyl)tetrahydro-1H-pyrido[3,4-b]indol-1-one (rhetsinine). It inhibited aldose reductase with IC(50) values of 24.1 microM. Furthermore, rhetsinine inhibited sorbitol accumulation by 79.3% at 100 microM. These results suggested that the E. rutaecarpa derived component, rhetsinine, would be potentially useful in the treatment of diabetic complications.

QSAR prediction of inhibition of aldose reductase for flavonoids

We performed a predictive analysis based on quantitative structure-activity relationships (QSAR) of an important property of flavonoids, which is the inhibition (IC(50)) of aldose reductase (AR). The importance of AR inhibition is that it prevents cataract formation in diabetic patients. The best linear model constructed from 55 molecular structures incorporated six molecular descriptors, selected from more than a thousand geometrical, topological, quantum-mechanical, and electronic types of descriptors. As a practical application, we used the obtained QSAR model to predict the AR inhibitory effect of newly synthesized flavonoids that present 2-, 7-substitutions in the benzopyrane backbone.

Orally administered epigallocatechin gallate attenuates light-induced photoreceptor damage

EGCG, a major component of green tea, has a number of properties which includes it being a powerful antioxidant. The purpose of this investigation was to deduce whether inclusion of EGCG in the drinking water of albino rats attenuates the effect of a light insult (2200lx, for 24h) to the retina. TUNEL-positive cells were detected in the outer nuclear layer of the retina, indicating the efficacy of the light insult in inducing photoreceptor degeneration. Moreover, Ret-P1 and the mRNA for rhodopsin located at photoreceptors were also significantly reduced as well as the amplitude of both the a- and b-waves of the electroretinogram was also reduced showing that photoreceptors in particular are affected by light. An increase in protein/mRNA of GFAP located primarily to Müller cells caused by light shows that other retinal components are also influenced by the light insult. However, antigens associated with bipolar (alpha-PKC), ganglion (Thy-1) and amacrine (GABA) cells, in contrast, appeared unaffected. The light insult also caused a change in the content of various proteins (caspase-3, caspase-8, PARP, Bad, and Bcl-2) involved in apoptosis. A number of the changes to the retina caused by a light insult were significantly attenuated when EGCG was in the drinking water. The reduction of the a- and b-waves and photoreceptor specific mRNAs/protein caused by light were significantly less. In addition, EGCG attenuated the changes caused by light to certain apoptotic proteins (especially at after 2 days) but did not appear to significantly influence the light-induced up-regulation of GFAP protein/mRNA. It is concluded that orally administered EGCG blunts the detrimental effect of light to the retina of albino rats where the photoreceptors are primarily affected.

Inhibitors of aldose reductase and advanced glycation end-products formation from the leaves of Stelechocarpus cauliflorus R.E. Fr

Two dihydroflavonol glycosides, engeletin and astilbin, were isolated from an EtOAc extract of the leaves of Stelechocarpus cauliflorus R.E. Fr. (Annonaceae). The inhibitory activity of engeletin against a recombinant human aldose reductase (IC50 value=1.16 microM) was twice that of quercetin as a positive control (2.48 microM), and 23 times greater than that of astilbin (26.7 microM). Engeletin inhibited the enzyme uncompetitively. Astilbin was about as potent as the positive control, quercetin, in its inhibition of advanced glycation end-products formation. These flavonoids displayed therapeutic potential in the prevention and treatment of diabetic complications.

Inhibitory effects of Zingiber officinale Roscoe derived components on aldose reductase activity in vitro and in vivo

Ginger (Zingiber officinale Roscoe) continues to be used as an important cooking spice and herbal medicine around the world. Scientific research has gradually verified the antidiabetic effects of ginger. Especially gingerols, which are the major components of ginger, are known to improve diabetes including the effect of enhancement against insulin-sensitivity. Aldose reductase inhibitors have considerable potential for the treatment of diabetes, without increased risk of hypoglycemia. The assay for aldose reductase inhibitors in ginger led to the isolation of five active compounds including 2-(4-hydroxy-3-methoxyphenyl)ethanol (2) and 2-(4-hydroxy-3-methoxyphenyl)ethanoic acid (3). Compounds 2 and 3 were good inhibitors of recombinant human aldose reductase, with IC50 values of 19.2 +/- 1.9 and 18.5 +/- 1.1 microM, respectively. Furthermore, these compounds significantly suppressed not only sorbitol accumulation in human erythrocytes but also lens galactitol accumulation in 30% of galactose-fed cataract rat model. A structure-activity relationship study revealed that the applicable side alkyl chain length and the presence of a C3 OCH3 group in the aromatic ring are essential features for enzyme recognition and binding. These results suggested that it would contribute to the protection against or improvement of diabetic complications for a dietary supplement of ginger or its extract containing aldose reductase inhibitors.

HNE-dependent molecular damage in diabetic nephropathy and its possible prevention by N-acetyl-cysteine and oxerutin

Accumulation of Advanced Lipoxidation End-products (ALE), such as MDA- and HNE-protein adducts, and Advanced Glycation End-products, such as carboxymethyl-lysine (CML), are probably involved in the development of diabetic nephropathy. In this study the effect of some antioxidant treatments (oxerutin, N-acetylcysteine, taurine and N-acetylcysteine+taurine) on kidney lipoxidative damage has been evaluated by immunohistochemistry in streptozotocined rats. Diabetic rats showed marked glomerular positivity for ALE, while the samples from Control rats were negative. All treatments except taurine were able to protect the glomeruli from ALE accumulation; the failure of taurine may be due to residual oxidative properties of its derivatives. These data are consistent with those of our previous study, which showed that all the antioxidants used except taurine protected the glomeruli from diabetes-induced enlargement, increased apoptotic rate, decreased cell density and CML accumulation. These data attest to a role of glycoxidative and lipoxidative damage in diabetes-dependent damage of the kidney, and indicate that specific antioxidants can prevent or attenuate diabetic nephropathy.

Comparative trial of N-acetyl-cysteine, taurine, and oxerutin on skin and kidney damage in long-term experimental diabetes

This study analyzes the effect of chronic treatment with different antioxidants (N-acetyl-cysteine [NAC], taurine, a combination of NAC and taurine, and oxerutin) on long-term experimental diabetes induced by streptozotocin in rats. Glycoxidative damage was evaluated in the skin; glomerular structural changes were studied with morphometry and immunohistochemistry. Oxerutin treatment and the combined NAC plus taurine treatment resulted in reduced accumulation of collagen-linked fluorescence in skin in comparison with untreated diabetic rats. All treatments except taurine reduced glomerular accumulation of N(epsilon)-(carboxymethyl)lysine and protected against the increase in glomerular volume typical of diabetes; furthermore, the apoptosis rate was significantly decreased and the glomerular cell density was better preserved. Glycoxidative markers in the skin turned out to be good indicators of the glomerular condition. The findings that emerged from our study support the hypothesis that glomerular damage in diabetes can be prevented or at least attenuated by supplementation with specific antioxidants. Treatment with oxerutin and combined treatment with NAC plus taurine gave the most encouraging results, whereas the results of taurine-only treatment were either negligible or negative and therefore suggest caution in the use of this molecule in single-drug treatment courses.

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).

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.

Biotransformation of squamulosone by Curvularia lunata ATCC 12017

Squamulosone (aromadendr-1(10)-en-9-one), isolated in large quantity from the plant Hyptis verticillata Jacq. (Labiatae), was incubated with the fungus Curvularia lunata ATCC 12017 in two different growth media. Six metabolites were isolated from each medium. with five of the products being common to both fermentations. All seven metabolites are novel. The insecticidal activity of these aromadendranes was evaluated against the sweet potato weevil Cylas formicarius elegantus.

1-Benzopyran-4-one antioxidants as aldose reductase inhibitors

Starting from the inhibitory activity of the flavonoid Quercetin, a series of 4H-1-benzopyran-4-one derivatives was synthesized and tested for inhibition of aldose reductase, an enzyme involved in the appearance of diabetic complications. Some of the compounds obtained display inhibitory activity similar to that of Sorbinil but are more selective than Quercetin and Sorbinil with respect to the closely related enzyme, aldehyde reductase, and also possess antioxidant activity. Remarkably, these compounds possess higher pKa values than carboxylic acids, a characteristic which could make the pharmacokinetics of these compounds very interesting. Molecular modeling investigations on the structures of inhibitors bound at the active site of aldose reductase were performed in order to suggest how these new inhibitors might bind to the enzyme and also to interpret structure-activity relationships.

Inhibition of aldose reductase by maesanin and related p-benzoquinone derivatives and effects on other enzymes

A naturally occurring p-benzoquinone derivative, maesanin, inhibited porcine lens aldose reductase. Systematic investigation of related p-benzoquinone derivatives revealed that 2,5-dihydroxy-p-benzoquinone was a potent inhibitor of aldose reductase and aldehyde reductase but had no effect on NADH oxidase. Kinetic analysis showed this p-benzoquinone exhibited uncompetitive inhibition against DL-glyceraldehyde and noncompetitive inhibition against NADPH.

Inhibitory activity and mechanism of inhibition of the N-[[(4-benzoylamino)phenyl]sulfonyl]amino acid aldose reductase inhibitors

A series of substituted N-[[(4-benzoylamino)phenyl]sulfonyl]amino acids (BAPS-amino acids) were synthesized by established methods, and the stereochemistry of the products was confirmed by HPLC analysis after chiral derivatization. When tested against aldose reductase (alditol:NADP+ oxidoreductase; EC 1.1.1.21; ALR2) isolated from rat lens, all of the BAPS-amino acids were determined to be significantly more inhibitory than the corresponding N-(phenylsulfonyl)amino acids. Structure-inhibition and enzyme kinetic analyses suggest that the BAPS-amino acids inhibit ALR2 by a mechanism similar to the N-(phenylsulfonyl)amino acids. However, multiple inhibition analyses indicate that the increased inhibitory activity of the BAPS-amino acids is a result of interaction with multiple sites present on ALR2. Enzyme specificity studies with several of the BAPS-amino acids demonstrated that these compounds do not produce significant inhibition of other nucleotide-requiring enzymes including aldehyde reductase (alcohol: NADP+ oxidoreductase; EC 1.1.1.2; ALR1).

The purification and properties of aldose reductase from rat ovary

Aldose reductase has been highly purified from rat ovary to apparent homogeneity, as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme proved to be a monomeric protein with a molecular weight of about 39,900. The enzyme catalyzed the NADPH-dependent reduction of a number of aromatic and aliphatic aldehydes as well as aldo-sugars. The enzyme was potently inhibited by p-chloro-mercuribenzoate and a commercially developed aldose reductase inhibitor, M79175. The result of an immunoinhibition study, using antibody against the purified enzyme, indicated that the enzyme was responsible for more than 50% of the overall catalytic activity of D-glucose reduction in rat ovarian cytosol. Western blotting analysis revealed that immunoreactive proteins to anti-ovarian aldose reductase antibody were present in adrenal gland, various reproductive tissues, brain, lung, and heart of rats. Furthermore, ovarian tissues of various species contained immunoreactive proteins, though in small amounts. The enzyme was primarily localized in the granulosa cells and oocytes of all stages of follicular development during the estrous cycle, though it was also found in the corpora lutea cells in the pregnant rats.

Isolation and characterization of cDNA clones encoding aldose reductase

The action of aldose reductase has been implicated in the etiology of a variety of diabetic complications affecting the visual system. However, very little is known regarding the structure and functional organization of the genes encoding this key enzyme. In the present study, we have isolated and characterized complementary DNA clones encoding bovine lens aldose reductase. Nucleotide sequencing of four independently isolated clones was used to establish a 1154 nucleotide composite cDNA sequence. The cDNA sequence encodes 296 amino acids of the aldose reductase primary structure, and contains an additional 261 nucleotides of apparently untranslated sequence downstream from the coding region. No nucleotide sequence differences were found among the four independently isolated aldose reductase cDNA clones. The aldose reductase amino acid sequence deduced from the cDNA shows high homology to that reported for aldose reductase of the rat lens. Significant similarities are also evident between bovine lens aldose reductase and both human liver aldehyde reductase and frog lens rho-crystallin.

Bovine lens aldose reductase: identification of two enzyme forms

Two structurally different forms of bovine lens aldose reductase have been identified. Freshly prepared lens extracts contain an unactivated "b form" (ARb) which is sensitive to inhibition by Sorbinil. Upon incubation of the extracts with oxygen radical generating systems, ARb is converted to a more active "a form" (ARa), which is not inhibited by Sorbinil. ARa and ARb were purified to electrophoretic homogeneity.

Effects of 3,3'-di-O-methylquercetin on guinea-pig isolated smooth muscle

The effects of the flavone 3,3'-di-O-methylquercetin (DOMQ) have been examined and compared with those of quercetin, on guinea-pig isolated ileum, trachea, and main pulmonary artery (MPA). Except for transient contractions induced by low concentrations (10(-8)-3 x 10(-6) M), DOMQ and quercetin (up to 3 x 10(-4) M) caused reduction of the tone and the phasic contractions of the ileum. A23187 reversed the inhibitory effects of quercetin but not those of DOMQ. DOMQ and quercetin caused concentration-dependent relaxation of the trachea and the adrenaline-contracted MPA. DOMQ shifted to the right the concentration-effect curves induced by acetylcholine on the ileum and the trachea, and by adrenaline on MPA and those induced by CaCl2 on ileum, trachea and MPA. DOMQ also inhibited the contractions induced, in Ca2+-free EGTA-containing buffer, by histamine on ileum and by adrenaline on MPA. These observations suggest that DOMQ inhibits Ca2+ influx, Ca2+ release from intracellular stores and, more likely, Ca2+ binding to intracellular receptor proteins.

In vitro modification of bovine lens aldose reductase activity

Bovine lens aldose reductase can be activated in crude extracts upon incubation at 37 degrees C at relatively high ionic strength. This phenomenon shows a seasonal occurrence, the enzyme being susceptible to activation only in lenses of animals sacrified in summer. Systems generating oxygen activated species induce the enzyme activation, whereas scavengers of "oxygen radicals" preserve the activated state of the enzyme. Glutathione and other thiol compounds appear to prevent the enzyme activation.

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.