Cloning and Sequence Determination of Human Placental Aldose Reductase Gene

Identification of 9H-purin-6-amine derivatives as novel aldose reductase inhibitors for the treatment of diabetic complications

A series of 9H-purin-6-amine derivatives as aldose reductase (ALR) inhibitors were designed and synthesized. Most of these derivatives, having a C6-substituted benzylamine side chain and N9 carboxylic acid on the core structure, were found to be potent and selective ALR inhibitors, with submicromolar IC₅₀ values against ALR2. Particularly, compound 4e was the most active with an IC₅₀ value of 0.038 μM, and it was also proved to be endowed with excellent inhibitory selectivity. The structure-activity relationship and molecular docking studies highlighted the importance of the carboxylic acid head group along with different halogen substituents on the C6 benzylamine side chain of the 9H-purin-6-amine scaffold for the construction of strong and selective ALR inhibitors.

Aldose Reductase: An Emerging Target for Development of Interventions for Diabetic Cardiovascular Complications

Diabetes is a leading cause of cardiovascular morbidity and mortality. Despite numerous treatments for cardiovascular disease (CVD), for patients with diabetes, these therapies provide less benefit for protection from CVD. These considerations spur the concept that diabetes-specific, disease-modifying therapies are essential to identify especially as the diabetes epidemic continues to expand. In this context, high levels of blood glucose stimulate the flux via aldose reductase (AR) pathway leading to metabolic and signaling changes in cells of the cardiovascular system. In animal models flux via AR in hearts is increased by diabetes and ischemia and its inhibition protects diabetic and non-diabetic hearts from ischemia-reperfusion injury. In mouse models of diabetic atherosclerosis, human AR expression accelerates progression and impairs regression of atherosclerotic plaques. Genetic studies have revealed that single nucleotide polymorphisms (SNPs) of the ALD2 (human AR gene) is associated with diabetic complications, including cardiorenal complications. This Review presents current knowledge regarding the roles for AR in the causes and consequences of diabetic cardiovascular disease and the status of AR inhibitors in clinical trials. Studies from both human subjects and animal models are presented to highlight the breadth of evidence linking AR to the cardiovascular consequences of diabetes.

A phenotype-directed chemical screen identifies ponalrestat as an inhibitor of the plant flavin monooxygenase YUCCA in auxin biosynthesis

Plant development is regulated by both synergistic and antagonistic interactions of different phytohormones, including a complex crosstalk between ethylene and auxin. For instance, auxin and ethylene synergistically control primary root elongation and root hair formation. However, a lack of chemical agents that specifically modulate ethylene or auxin production has precluded precise delineation of the contribution of each hormone to root development. Here, we performed a chemical genetic screen based on the recovery of root growth in ethylene-related Arabidopsis mutants with constitutive "short root" phenotypes (eto1-2 and ctr1-1). We found that ponalrestat exposure recovers root elongation in these mutants in an ethylene signal-independent manner. Genetic and pharmacological investigations revealed that ponalrestat inhibits the enzymatic activity of the flavin-containing monooxygenase YUCCA, which catalyzes the rate-limiting step of the indole-3-pyruvic acid branch of the auxin biosynthesis pathway. In summary, our findings have identified a YUCCA inhibitor that may be useful as a chemical tool to dissect the distinct steps in auxin biosynthesis and in the regulation of root development.

Structure optimization of tetrahydropyridoindole-based aldose reductase inhibitors improved their efficacy and selectivity

In our previous study, tetrahydropyridoindoles carboxymethylated in position 8 were identified as aldose reductase (ALR2) inhibitors with mild efficacy and selectivity yet with significant antioxidant activity. In the present study we proceeded with optimization of the tetrahydropyridoindole scaffold by shifting the carboxymethyl pharmacophore from position 8 to position 5, with the aim to improve the biological activity. Commercial databases were screened for the presence of tetrahydropyridoindoles carboxymethylated in position 5 and an experimental set of eight compounds was created. Mild inhibition characterized by IC₅₀ in micromolar range was recorded for compound 8 with the isopropyl substituent at the piperidine nitrogen (position 2). This alkylated tertiary nitrogen is characterized by a rather high basicity (pKa ∼ 10.4) with complete protonization at physiological pH. On the other hand, ALR2 inhibition activity of the low basicity derivatives 3-7 with an acyl substituted nitrogen in position 2 (pKa ∼ -1 to -3) was characterized with IC₅₀ values in low and medium nanomolar region. Docking into the binding site of human recombinant enzyme AKR1B1 performed for 3 revealed an interaction network responsible for the high affinity and selectivity. In ex vivo experiment, sorbitol accumulation in isolated rat eye lenses was significantly inhibited by 3 in the presence of high glucose, starting at a concentration as low as 0.1 μM. Moreover, in streptozotocin-induced diabetic rats, compound 3 administered intragastrically (i.g., 50 mg/kg/day) for five consecutive days significantly inhibited sorbitol accumulation in red blood cells and the sciatic nerve. Molecular obesity indices predicted along with water solubility point an excellent "lead-likeness" of compound 3, with prospects of further structure optimizations.

Identification of novel aldose reductase inhibitors based on carboxymethylated mercaptotriazinoindole scaffold

Fifteen compounds, sharing an indole-1-acetic acid moiety as a common fragment, were selected from commercial databases for testing aldose reductase inhibition. 3-Mercapto-5H-1,2,4-triazino[5,6-b]indole-5-acetic acid (13) was the most promising inhibitor, with an IC50 in the submicromolar range and high selectivity, relative to aldehyde reductase. The crystal structure of aldose reductase complexed with 13 revealed an interaction pattern explaining its high affinity. Physicochemical parameters underline the excellent "leadlikeness" of 13 as a promising candidate for further structure optimizations.

In vivo role of aldehyde reductase

BACKGROUND

Aldehyde reductase (AKR1A; EC 1.1.1.2) catalyzes the reduction of various types of aldehydes. To ascertain the physiological role of AKR1A, we examined AKR1A knockout mice.

METHODS

Ascorbic acid concentrations in AKR1A knockout mice tissues were examined, and the effects of human AKR1A transgene were analyzed. We purified AKR1A and studied the activities of glucuronate reductase and glucuronolactone reductase, which are involved in ascorbic acid biosynthesis. Metabolomic analysis and DNA microarray analysis were performed for a comprehensive study of AKR1A knockout mice.

RESULTS

The levels of ascorbic acid in tissues of AKR1A knockout mice were significantly decreased which were completely restored by human AKR1A transgene. The activities of glucuronate reductase and glucuronolactone reductase, which are involved in ascorbic acid biosynthesis, were suppressed in AKR1A knockout mice. The accumulation of d-glucuronic acid and saccharate in knockout mice tissue and the expression of acute-phase proteins such as serum amyloid A2 are significantly increased in knockout mice liver.

CONCLUSIONS

AKR1A plays a predominant role in the reduction of both d-glucuronic acid and d-glucurono-γ-lactone in vivo. The knockout of AKR1A in mice results in accumulation of d-glucuronic acid and saccharate as well as a deficiency of ascorbic acid, and also leads to upregulation of acute phase proteins.

GENERAL SIGNIFICANCE

AKR1A is a major enzyme that catalyzes the reduction of d-glucuronic acid and d-glucurono-γ-lactone in vivo, besides acting as an aldehyde-detoxification enzyme. Suppression of AKR1A by inhibitors, which are used to prevent diabetic complications, may lead to the accumulation of d-glucuronic acid and saccharate.

Human aldo-keto reductases 1B1 and 1B10: a comparative study on their enzyme activity toward electrophilic carbonyl compounds

Aldo-keto reductase family 1 member B1 (AKR1B1, 1B1 in brief) and aldo-keto reductase family 1 member B10 (AKR1B10, 1B10 in brief) are two proteins with high similarities in their amino acid sequences, stereo structures, and substrate specificity. However, these two proteins exhibit distinct tissue distributions; 1B10 is primarily expressed in the gastrointestinal tract and adrenal gland, whereas 1B1 is ubiquitously present in all tissues/organs, suggesting their difference in biological functions. This study evaluated in parallel the enzyme activity of 1B1 and 1B10 toward alpha, beta-unsaturated carbonyl compounds with cellular and dietary origins, including acrolein, crotonaldehyde, 4-hydroxynonenal, trans-2-hexenal, and trans-2,4-hexadienal. Our results showed that 1B10 had much better enzyme activity and turnover rates toward these chemicals than 1B1. By detecting the enzymatic products using high-performance liquid chromatography, we measured their activity to carbonyl compounds at low concentrations. Our data showed that 1B10 efficiently reduced the tested carbonyl compounds at physiological levels, but 1B1 was less effective. Ectopically expressed 1B10 in 293T cells effectively eliminated 4-hydroxynonenal at 5 μM by reducing to 1,4-dihydroxynonene, whereas endogenously expressed 1B1 did not. The 1B1 and 1B10 both showed enzyme activity to glutathione-conjugated carbonyl compounds, but 1B1 appeared more active in general. Together our data suggests that 1B10 is more effectual in eliminating free electrophilic carbonyl compounds, but 1B1 seems more important in the further detoxification of glutathione-conjugated carbonyl compounds.

AKR1B10 induces cell resistance to daunorubicin and idarubicin by reducing C13 ketonic group

Daunorubicin, idarubicin, doxorubicin and epirubicin are anthracyclines widely used for the treatment of lymphoma, leukemia, and breast, lung, and liver cancers, but tumor resistance limits their clinical success. Aldo-keto reductase family 1 B10 (AKR1B10) is an NADPH-dependent enzyme overexpressed in liver and lung carcinomas. This study was aimed to determine the role of AKR1B10 in tumor resistance to anthracyclines. AKR1B10 activity toward anthracyclines was measured using recombinant protein. Cell resistance to anthracycline was determined by ectopic expression of AKR1B10 or inhibition by epalrestat. Results showed that AKR1B10 reduces C13-ketonic group on side chain of daunorubicin and idarubicin to hydroxyl forms. In vitro, AKR1B10 converted daunorubicin to daunorubicinol at V(max) of 837.42±81.39nmol/mg/min, K(m) of 9.317±2.25mM and k(cat)/K(m) of 3.24. AKR1B10 showed better catalytic efficiency toward idarubicin with V(max) at 460.23±28.12nmol/mg/min, K(m) at 0.461±0.09mM and k(cat)/K(m) at 35.94. AKR1B10 was less active toward doxorubicin and epirubicin with a C14-hydroxyl group. In living cells, AKR1B10 efficiently catalyzed reduction of daunorubicin (50nM) and idarubicin (30nM) to corresponding alcohols. Within 24h, approximately 20±2.7% of daunorubicin (1μM) or 23±2.3% of idarubicin (1μM) was converted to daunorubicinol or idarubicinol in AKR1B10 expression cells compared to 7±0.9% and 5±1.5% in vector control. AKR1B10 expression led to cell resistance to daunorubicin and idarubicin, but inhibitor epalrestat showed a synergistic role with these agents. Together our data suggest that AKR1B10 participates in cellular metabolism of daunorubicin and idarubicin, resulting in drug resistance. These data are informative for the clinical use of idarubicin and daunorubicin.

Murine aldo-keto reductase family 1 subfamily B: identification of AKR1B8 as an ortholog of human AKR1B10

Aldo-keto reductase family 1 member B10 (AKR1B10), over-expressed in multiple human cancers, might be implicated in cancer development and progression via detoxifying cytotoxic carbonyls and regulating fatty acid synthesis. In the present study, we investigated the ortholog of AKR1B10 in mice, an ideal modeling organism greatly contributing to human disease investigations. In the mouse, there are three aldo-keto reductase family 1 subfamily B (AKR1B) members, i.e., AKR1B3, AKR1B7, and AKR1B8. Among them, AKR1B8 has the highest similarity to human AKR1B10 in terms of amino acid sequence, computer-modeled structures, substrate spectra and specificity, and tissue distribution. More importantly, similar to human AKR1B10, mouse AKR1B8 associates with murine acetyl-CoA carboxylase-α and mediates fatty acid synthesis in colon cancer cells. Taken together, our data suggest that murine AKR1B8 is the ortholog of human AKR1B10.

Aldose reductase and cardiovascular diseases, creating human-like diabetic complications in an experimental model

Hyperglycemia and reduced insulin actions affect many biological processes. One theory is that aberrant metabolism of glucose via several pathways including the polyol pathway causes cellular toxicity. Aldose reductase (AR) is a multifunctional enzyme that reduces aldehydes. Under diabetic conditions AR converts glucose into sorbitol, which is then converted to fructose. This article reviews the biology and pathobiology of AR actions. AR expression varies considerably among species. In humans and rats, the higher level of AR expression is associated with toxicity. Flux via AR is increased by ischemia and its inhibition during ischemia reperfusion reduces injury. However, similar pharmacological effects are not observed in mice unless they express a human AR transgene. This is because mice have much lower levels of AR expression, probably insufficient to generate toxic byproducts. Human AR expression in LDL receptor knockout mice exacerbates vascular disease, but only under diabetic conditions. In contrast, a recent report suggests that genetic ablation of AR increased atherosclerosis and increased hydroxynonenal in arteries. It was hypothesized that AR knockout prevented reduction of toxic aldehydes. Like many in vivo effects found in genetically manipulated animals, interpretation requires the reproduction of human-like physiology. For AR, this will require tissue specific expression of AR in sites and at levels that approximate those in humans.

Role of aldose reductase in TGF-beta1-induced fibronectin synthesis in human mesangial cells

Accumulation of glomerular extracellular matrix (ECM) may result in glomerulosclerosis. Several lines of evidence indicate a key role for transforming growth factor-beta1 (TGF-beta1) in glomerular ECM synthesis and degradation, such as fibronectin (FN). Aldose reductase (AR) was proven to be one of the TGF-beta1 responsive genes in cultured rat mesangial cells using the SSH-PCR method and there were positive correlation between the AR and TGF-beta1 in our previous studies. So we assumed that AR could regulate FN synthesis. In this study, we explored the role of AR in FN production and possible mechanism involved. The expression of AR, FN and c-Jun proteins were analyzed by Western blot and the activity of activator protein-1 (AP-1) was assessed by electrophoretic mobility shift assay (EMSA). Our results showed that AR could mediate the TGF-beta1-induced FN production, which may associate with AP-1 activation.

Unusual binding mode of the 2S4R stereoisomer of the potent aldose reductase cyclic imide inhibitor fidarestat (2S4S) in the 15 K crystal structure of the ternary complex refined at 0.78 A resolution: implications for the inhibition mechanism

The structure of human aldose reductase in complex with the 2 S4 R stereoisomer of the potent inhibitor Fidarestat ((2 S,4 S)-6-fluoro-2',5'-dioxospiro-[chroman-4,4'-imidazoline]-2-carboxamide) was determined at 15 K and a resolution of 0.78 A. The structure of the complex provides experimental evidence for the inhibition mechanism in which Fidarestat is initially bound neutral and then becomes negatively charged by donating the proton at the 1'-position nitrogen of the cyclic imide ring to the N2 atom of the catalytic His110.

Synthesis and activity of a new series of (Z)-3-phenyl-2-benzoylpropenoic acid derivatives as aldose reductase inhibitors

During the course of studies directed towards the discovery of novel aldose reductase inhibitors for the treatment of diabetic complications, we synthesized a series of new (Z)-3-phenyl-2-benzoylpropenoic acid derivatives and tested their in vitro inhibitory activities on rat lens aldose reductase. Of these compounds, (Z)-3-(3,4-dihydroxyphenyl)-2-(4-methylbenzoyl)propenoicacid (3k) was identified as the most potent inhibitor, with an IC50 of 0.49 microM. The theoretical binding mode of 3k was obtained by simulation of its docking into the active site of the human aldose reductase crystal structure.

Genetic restoration of aldose reductase to the collecting tubules restores maturation of the urine concentrating mechanism

To investigate the underlying causes for aldose reductase deficiency-induced diabetes insipidus, we carried out studies with three genotypic groups of mice. These included wild-type mice, knockout mice, and a newly created bitransgenic line that was homozygous for both the aldose reductase null mutation and an aldose reductase knockin transgene driven by the kidney-specific cadherin promoter to direct transgene expression in the collecting tubule epithelial cells. We found that from early renal developmental stages onward, urine osmolality did not exceed 1,000 mosmol/kgH2O in aldose reductase-deficient mice. The functional defects were correlated with significant renal cellular and structural abnormalities that included cell shrinkage, apoptosis, disorganized tubular and vascular structures, and segmental atrophy. In contrast, the transgenic aldose reductase expression in the bitransgenic mice largely but incompletely rescued urine concentrating capacity and significantly improved renal cell survival, cellular morphology, and renal structures. Together, these results suggest that aldose reductase not only plays important roles in osmoregulation and medullary cell survival but may also be essential for the full maturation of the urine concentrating mechanism.

Factorizing Selectivity Determinants of Inhibitor Binding toward Aldose and Aldehyde Reductases: Structural and Thermodynamic Properties of the Aldose Reductase Mutant Leu300Pro−Fidarestat Complex

Structure of the Leu300Pro mutant of human aldose reductase (ALR2) in complex with the inhibitor fidarestat is determined. Comparison with the hALR2-fidarestat complex and the porcine aldehyde reductase (ALR1)-fidarestat complex indicates that the hydrogen bond between the Leu300 amino group of the wild-type and the exocyclic amide group of the inhibitor is the key determinant for the specificity of fidarestat for ALR2 over ALR1. Thermodynamic data also suggest an enthalpic contribution as the predominant difference in the binding energy between the aldose reductase mutant and the wild-type. An additional selectivity-determining feature is the difference in the interaction between the inhibitor and the side chain of Trp219, ordered in the present structure but disordered (corresponding Trp220) in the ALR1-fidarestat complex. Thus, the hydrogen bond ( approximately 7 kJ/mol) corresponds to a 23-fold difference in inhibitor potency while the differences in the interactions between Trp219(ALR2) and fidarestat and between Trp220(ALR1) and fidarestat can account for an additional 10-fold difference in potency.

Interaction between the Polyol Pathway and Non-Enzymatic Glycation on Mesangial Cell Gene Expression

BACKGROUND/AIMS

Both activation of the polyol pathway and enhanced non-enzymatic glycation have been implicated in the pathogenesis of diabetic glomerulopathy. We investigated the interaction between these two pathways using normal mesangial cells (MCs) and transgenic (TG) MCs with elevated aldose reductase (AR) activity.

METHODS

TG mice with expression of the human AR (hAR) gene in kidney MCs were established. Mouse glomeruli and primary cultures of MCs from hAR TG and wild-type (WT) mice were studied regarding the changes in AR activity, transforming growth factor-beta1 (TGF-beta1) and type IV collagen mRNA and protein levels, in response to BSA modified by advanced glycation end-products (AGE-BSA).

RESULTS

Ex vivo addition of AGE-BSA increased AR activity, TGF-beta1 and type IV collagen mRNA levels in both WT and TG glomeruli, with greater rise in TG glomeruli. These increments were attenuated by zopolrestat, an AR inhibitor. In cultured MCs, AGE-BSA enhanced AR activity, TGF-beta(1) and type IV collagen mRNA and protein levels both in WT and TG MCs, again with greater increases in TG MCs. The AGE-induced enhancement in TGF-beta1 and type IV collagen expression were suppressed by either zopolrestat or transfection with an AR antisense oligonucleotide.

CONCLUSION

These data suggest that the activation of the polyol pathway by AGEs, more marked in genetic conditions with increased AR activity, may contribute to the pathogenesis of diabetic glomerulopathy, through enhancing mesangial cell expression of TGF-beta1 and type IV collagen.

High-Resolution Structures of Human Aldose Reductase Holoenzyme in Complex with Stereoisomers of the Potent Inhibitor Fidarestat: Stereospecific Interaction between the Enzyme and a Cyclic Imide Type Inhibitor

Structure determinations of human aldose reductase holoenzyme in complex with the 2S4R-,2R4S- and 2R4R-isomers of the potent inhibitor Fidarestat ((2S,4S)-6-fluoro-2',5'-dioxospiro[chroman-4,4'-imidazoline]-2-carboxamide) were carried out in order to elucidate the binding modes responsible for the differences in their inhibitory potencies. In the complex structure with the 2R4S-isomer the cyclic imide moiety formed hydrogen bonds with the side-chains of Trp111, Tyr48 and His110. In the attempt to determine the complex structure with the least potent 2R4R-isomer this ligand was not observed, and instead, the active site was simultaneously occupied by two citrate molecules (occupancies of 60% and 40%). In the case of 2S4R, the active site was occupied by a citrate molecule which anchors the 2S4R-isomer from its carbamoyl group. The structures of the complexes suggest that the differences in the interactions between the cyclic imide rings and carbamoyl groups of the compounds with residues His110, Trp111, Trp219 and Cys298 account for differences in their inhibitory potencies.

Probing the ultra-high resolution structure of aldose reductase with molecular modelling and noncovalent mass spectrometry

Aldose reductase, the first and rate-limiting enzyme of the polyol pathway, is a target for drug design for the treatment of diabetes complications. The structures of aldose reductase in complex with the cyclic imide inhibitors Fidarestat and Minalrestat were recently determined at ultra-high resolution (Proteins 2004, 55, 805). We have used the detailed structural information revealed at atomic resolution, including the assignment of protonation states for the inhibitors and active site residues, together with molecular modelling and noncovalent mass spectrometry to characterise the type and strength of the interactions between the enzyme and the inhibitors, and to attempt the design of novel potential inhibitors with enhanced binding energies of the complexes. The VC(50) values measured by mass spectrometry (accelerated voltage of ions needed to dissociate 50% of a noncovalent complex in the gas phase) for the aldose reductase inhibitors correlate with the IC(50) values (concentration of inhibitor giving 50% inhibition in solution) and with the electrostatic binding energies calculated between the active site residues Tyr48, His110 and Trp111 and the inhibitors, suggesting that electrostatic interactions play a major role in inhibitor binding. Our molecular modelling and design studies suggest that the replacement of the fluorine atom in Minalrestat's bromo-fluorobenzyl group with nitro, amide and carboxylate functional groups enhanced the predicted net binding energies of the complexes by 16%, 31% and 68%, respectively. When the carbamoyl group of Fidarestat was replaced with a nitro, 4-hydroxyl phenyl and carboxylate functional groups, the predicted net binding energies of the complexes were enhanced by 13%, 34% and 46%, respectively.

Ultrahigh resolution drug design. II. Atomic resolution structures of human aldose reductase holoenzyme complexed with fidarestat and minalrestat: Implications for the binding of cyclic imide inhibitors

The X-ray structures of human aldose reductase holoenzyme in complex with the inhibitors Fidarestat (SNK-860) and Minalrestat (WAY-509) were determined at atomic resolutions of 0.92 A and 1.1 A, respectively. The hydantoin and succinimide moieties of the inhibitors interacted with the conserved anion-binding site located between the nicotinamide ring of the coenzyme and active site residues Tyr48, His110, and Trp111. Minalrestat's hydrophobic isoquinoline ring was bound in an adjacent pocket lined by residues Trp20, Phe122, and Trp219, with the bromo-fluorobenzyl group inside the "specificity" pocket. The interactions between Minalrestat's bromo-fluorobenzyl group and the enzyme include the stacking against the side-chain of Trp111 as well as hydrogen bonding distances with residues Leu300 and Thr113. The carbamoyl group in Fidarestat formed a hydrogen bond with the main-chain nitrogen atom of Leu300. The atomic resolution refinement allowed the positioning of hydrogen atoms and accurate determination of bond lengths of the inhibitors, coenzyme NADP+ and active-site residue His110. The 1'-position nitrogen atom in the hydantoin and succinimide moieties of Fidarestat and Minalrestat, respectively, form a hydrogen bond with the Nepsilon2 atom of His 110. For Fidarestat, the electron density indicated two possible positions for the H-atom in this bond. Furthermore, both native and anomalous difference maps indicated the replacement of a water molecule linked to His110 by a Cl-ion. These observations suggest a mechanism in which Fidarestat is bound protonated and becomes negatively charged by donating the proton to His110, which may have important implications on drug design.

Structure of human aldose reductase holoenzyme in complex with statil: an approach to structure-based inhibitor design of the enzyme

Aldose reductase, a monomeric NADPH-dependent oxidoreductase, catalyzes the reduction of a wide variety of aldehydes and ketones to their corresponding alcohols. The X-ray structure of human aldose reductase holoenzyme in complex with statil was determined at a resolution of 2.1 A. The carboxylate group of statil interacted with the conserved anion binding site located between the nicotinamide ring of the coenzyme and active site residues Tyr48, His110, and Trp111. Statil's hydrophobic phthalazinyl ring was bound in an adjacent pocket lined by residues Trp20, Phe122, and Trp219, with the bromo-fluorobenzyl group penetrating the "specificity" pocket. The interactions between the inhibitor's bromo-fluorobenzyl group and the enzyme include the stacking against the side-chain of Trp111 as well as hydrogen bonding to residues Leu300 and Thr113. Based on the model of the ternary complex, the program GRID was used in an attempt to design novel potential inhibitors of human aldose reductase with enhanced binding energies of the complex. Molecular modeling calculations suggested that the replacement of the fluorine atom of statil with a carboxylate functional group may enhance the binding energies of the complex by 33%.

Polyol pathway and diabetic peripheral neuropathy

This chapter critically examines the concept of the polyol pathway and how it relates to the pathogenesis of diabetic peripheral neuropathy. The two enzymes of the polyol pathway, aldose reductase and sorbitol dehydrogenase, are reviewed. The structure, biochemistry, physiological role, tissue distribution, and localization in peripheral nerve of each enzyme are summarized, along with current informaiton about the location and structure of their genes, their alleles, and the possible links of each enzyme and its alleles to diabetic neuropathy. Inhibitors of pathway enzyme and results obtained to date with pathway inhibitors in experimental models and human neuropathy trials are updated and discussed. Experimental and clinical data are analyzed in the context of a newly developed metabolic odel of the in vivo relationship between nerve sorbitol concentration and metabolic flux through aldose reuctase. Overall, the data will be interpreted as supporting the hypothesis that metabolic flux through the polyol pathway, rather than nerve concentration of sorbitol, is the predominant polyol pathway-linked pathogeneic factor in diabetic preipheral nerve. Finally, key questions and future directions for bsic and clinical research in this area are considered. It is concluded that robust inhibition of metabolic flux through the polyol pathway in peripheral nerve will likely result in substantial clinical benefit in treating and preventing the currently intractable condition of diabetic peripheral neuropathy. To accomplish this, it is imperative to develop and test a new generation of "super-potent" polyol pathway inhibitors.

Overexpression of aldose reductase in liver cancers may contribute to drug resistance

We previously found that about 29% of human liver cancers overexpressed aldose reductase (AR) and about 54% of them overexpressed an AR-like gene called ARL-1 that has similar enzymatic activities to AR. Since these aldo-keto reductases can reduce a broad spectrum of substrates including cytotoxic aldehydes, we were interested to find out if these enzymes can contribute to the resistance of liver cancer chemotherapy by inactivating some of the anticancer drugs. HepG2 cells, a stable line of liver cells, were induced to overexpress AR by hypertonicity. Cells that were cultured in hypertonic medium became more resistant to daunorubicin, suggesting that overexpression of AR made the cells more resistant to this drug. This is confirmed by the fact that addition of AR inhibitor sensitizes the cells to this drug again. This information may be important for designing new drugs to treat this deadly disease.

Aldose and aldehyde reductases: correlation of molecular modeling and mass spectrometric studies on the binding of inhibitors to the active site

Aldose and aldehyde reductases are monomeric NADPH-dependent oxidoreductases that catalyze the reduction of a wide variety of aldehydes and ketones to their corresponding alcohols. The overall three-dimensional structures of the enzymes are composed of similar alpha/beta TIM-barrels, and the active site residues Tyr 50, His 113, and Trp 114 interacting with the hydrophilic heads of inhibitors are conserved. We have used molecular modeling and mass spectrometry to characterize the interactions between the enzymes and three aldose reductase inhibitors: tolrestat, sorbinil, and zopolrestat. Unlike the IC(50) values (concentration of inhibitor giving 50% of inhibition in solution), the Vc(50) values measured by mass spectrometry (accelerating voltage of ions needed to dissociate 50% of a noncovalent complex in the gas phase) for the two enzymes are similar, and they correlate with the electrostatic and hydrogen-bonding energies calculated between the conserved Tyr 50, His 113, and Trp 114 and the inhibitors. The results of our comparison agree with detailed structural information obtained by X-ray crystallography, suggesting that nonconserved residues from the C-terminal loop account for differences in IC(50) values for the two enzymes. Additionally, they confirm our previous assumption that the Vc(50) values reflect the enzyme-inhibitor electrostatic and hydrogen-bonding interactions and exclude the hydrophobic interactions.

A potent aldose reductase inhibitor, (2S,4S)-6-fluoro-2', 5'-dioxospiro[chroman-4,4'-imidazolidine]-2-carboxamide (Fidarestat): its absolute configuration and interactions with the aldose reductase by X-ray crystallography

The absolute configuration of the aldose reductase (AR) inhibitor, (+)-(2S,4S)-6-fluoro-2',5'-dioxospiro¿chroman-4, 4'-imidazolidine-2-carboxamide (fidarestat), was established indirectly by single-crystal X-ray analysis of (+)-(2S, 4S)-8-bromo-6-fluoro-2',5'-dioxospiro¿chroman-4, 4'-imidazolidine-2-carboxylic acid (1). The crystal structure of human AR complexed with fidarestat was determined, and the specific inhibition activity was discussed on the basis of the three-dimensional interactions between them. The structure clarified that fidarestat was located in the active site by hydrophilic and hydrophobic interactions and that the carbamoyl group of fidarestat was a very effective substituent for affinity to AR and for selectivity between AR and aldehyde reductase (AHR). Explanations for the differences between the observed activities of fidarestat and its stereoisomer 2 were suggested by computer modeling.

Cloning and characterization of two novel aldo-keto reductases (AKR1C12 and AKR1C13) from mouse stomach

In contrast to hepatic hydrosteroid dehydrogenases (HSDs) of the aldo-keto reductase family (AKR1C), little is known about a stomach one. From a mouse stomach cDNA library, we isolated two clones encoding proteins of 323 amino acid residues. They exhibited 93.2% amino acid sequence identity and 64-68% with any known HSDs. Recombinant proteins expressed in Escherichia coli reduced 9,10-phenanthraquinone with NAD(P)H as cofactor. The mRNAs were exclusively expressed in stomach, liver and ileum. The present study demonstrates that these proteins are new members of the HSD subfamily and they are named AKR1C12 and AKR1C13. Immunohistochemical analysis suggests that they are involved in detoxification of xenobiotics in the stomach.

Binding of aldose reductase inhibitors: correlation of crystallographic and mass spectrometric studies

Aldose reductase is a NADP(H)-dependent enzyme, believed to be strongly implicated in the development of degenerative complications of Diabetes Mellitus. The search for specific inhibitors of this enzyme has thus become a major pharmaceutic challenge. In this study, we applied both X-ray crystallography and mass spectrometry to characterize the interactions between aldose reductase and four representative inhibitors: AminoSNM, Imirestat, LCB3071, and IDD384. If crystallography remains obviously the only way to get an extensive description of the contacts between an inhibitor and the enzymatic site, the duration of the crystallographic analysis makes this technique incompatible with high throughput screenings of inhibitors. On the other hand, dissociation experiments monitored by mass spectrometry permitted us to evaluate rapidly the relative gas-phase stabilities of the aldose reductase-inhibitor noncovalent complexes. In our experiments, dissociation in the gas-phase was provoked by increasing the accelerating voltage of the ions (Vc) in the source-analyzer interface region: the Vc value needed to dissociate 50% of the noncovalent complex initially present (Vc50) was taken as a gas-phase stability parameter of the enzyme-inhibitor complex. Interestingly, the Vc50 were found to correlate with the energy of the electrostatic and H-bond interactions involved in the contact aldose reductase/inhibitor (Eel-H), computed from the crystallographic model. This finding may be specially interesting in a context of drug development. Actually, during a drug design optimization phase, the binding of the drug to the target enzyme is often optimized by modifying its interatomic electrostatic and H-bond contacts; because they usually depend on a single atom change on the drug, and are easier to introduce than the hydrophobic interactions. Therefore, the Vc50 may help to monitor the chemical modifications introduced in new inhibitors. X-ray crystallography is clearly needed to get the details of the contacts and to rationalize the design. Nevertheless, once the cycle of chemical modification is engaged, mass spectrometry can be used to select a priori the drug candidates which are worthy of further crystallographic investigation. We thus propose to use the two techniques in a complementary way, to improve the screening of large collections of inhibitors.

Identification and characterization of a novel human aldose reductase-like gene

We have identified a novel human protein that is highly homologous to aldose reductase (AR). This protein, which we called ARL-1, consists of 316 amino acids, the same size as AR, and its amino acid sequence is 71% identical to that of AR. It is more closely related to the AR-like proteins such as mouse vas deferens protein, fibroblast growth factor-regulated protein, and Chinese hamster ovary reductase, with 81, 82, and 83%, respectively, of its amino acid sequence identical to the amino acid sequence of these proteins. The cDNA of ARL-1 was expressed in Escherichia coli to obtain recombinant protein for characterization of its enzymatic activities. For comparison, the cDNA of human AR was also expressed in E. coli and analyzed in parallel. These two enzymes differ in their pH optima and salt requirement, but they act on a similar spectrum of substrates. Similar to AR, ARL-1 can efficiently reduce aliphatic and aromatic aldehydes, and it is less active on hexoses. While AR mRNA is found in most tissues studied, ARL-1 is primarily expressed in the small intestines and in the colon, with a low level of its mRNA in the liver. The ability of ARL-1 to reduce various aldehydes and the locations of expression of this gene suggest that it may be responsible for detoxification of reactive aldehydes in the digested food before the nutrients are passed on to other organs. Interestingly, ARL-1 and AR are overexpressed in some liver cancers, but it is not clear if they contribute to the pathogenesis of this disease.

Identification and characterization of multiple osmotic response sequences in the human aldose reductase gene

Aldose reductase (AR) has been implicated in osmoregulation in the kidney because it reduces glucose to sorbitol, which can serve as an osmolite. Under hyperosmotic stress, transcription of this gene is induced to increase the enzyme level. This mode of osmotic regulation of AR gene expression has been observed in a number of nonrenal cells as well, suggesting that this is a common response to hyperosmotic stress. We have identified a 132-base pair sequence approximately 1 kilobase pairs upstream of the transcription start site of the AR gene that enhances the transcription activity of the AR promoter as well as that of the SV40 promoter when the cells are under hyperosmotic stress. Within this 132-base pair sequence, there are three sequences that resemble TonE, the tonicity response element of the canine betaine transporter gene, and the osmotic response element of the rabbit AR gene, suggesting that the mechanism of osmotic regulation of gene expression in these animals is similar. However, our data indicate that cooperative interaction among the three TonE-like sequences in the human AR may be necessary for their enhancer function.

Purification, characterization and partial primary structure of morphine 6-dehydrogenase from rabbit liver cytosol

Morphinone, a toxic metabolite, was formed from morphine by NAD(P)-dependent morphine 6-dehydrogenase(s) in both the cytosol and microsomal fractions of the rabbit liver at pH 7.4. The enzyme activity in the cytosol fraction was about twice that in the microsomal fraction and NAD served as the preferred cofactor in both fractions. The enzyme in the cytosol fraction was purified to a homogeneous protein by the use of various chromatographic techniques. The enzyme is a monomeric protein with a molecular weight of 36,000 and an isoelectric point of 6.4. The enzyme had a dual cofactor specificity but NAD was more efficiently utilized than NADP. With NAD, the enzyme showed an optimal pH of 9.4, and the Km and Vmax values toward morphine were 0.72 mM and 0.59 unit/mg protein, respectively. The enzyme also exhibited a significant activity for morphine analogs having an unsaturated bond at C-7,8 (codeine, ethylmorphine, and normorphine), alicyclic alcohols (3-hydroxyhexobarbital, 1-indanol, and cyclohexene-2-ol) and benzenedihydrodiol. In the reverse reaction, the enzyme exhibited highly restricted specificity for o-quinones. Sulfhydryl re-agents and quercetin inhibited the enzyme but pyrazole, barbital, and indomethacin had little effect on the enzyme activity. Androstanes, lithocholic acid, and estradiol potently inhibited the enzyme in a competitive manner toward morphine binding. The partial amino acid sequence of the random peptides obtained by the proteolytic digestion of the enzyme, which comprised about 40% of the whole protein, revealed a significant homology to the corresponding regions in the members of the aldo-keto reductase family. These results therefore indicate that the present enzyme is a new and unique member of the aldo-keto reductase family.

Structure and function of 3 alpha-hydroxysteroid dehydrogenase

Mammalian 3 alpha-hydroxysteroid dehydrogenases (3 alpha-HSDs) inactivate circulating steroid hormones, and in target tissues regulate the occupancy of steroid hormone receptors. Molecular cloning indicates that 3 alpha-HSDs are members of the aldo-keto reductase (AKR) superfamily and display high sequence identity (> 60%). Of these, the most extensively characterized is rat liver 3 alpha-HSD. X-ray crystal structures of the apoenzyme and the E.NADP+ complex have been determined and serve as structural templates for other 3 alpha-HSDs. These structures reveal that rat liver 3 alpha-HSD adopts an (alpha/beta)8-barrel protein fold. NAD(P)(H) lies perpendicular to the barrel axis in an extended conformation, with the nicotinamide ring at the core of the barrel, and the adenine ring at the periphery of the structure. The nicotinamide ring is stabilized by interaction with Y216, S166, D167, and Q190, so that the A-face points into the vacant active site. The 4-pro-(R) hydrogen transferred in the oxidoreduction of steroids is in close proximity to a catalytic tetrad that consists of D50, Y55, K84, and H117. A water molecule is within hydrogen bond distance of H117 and Y55, and its position may mimic the position of the carbonyl of a 3-ketosteroid substrate. The catalytic tetrad is conserved in members of the AKR superfamily and resides at the base of an apolar cleft implicated in binding steroid hormone. The apolar cleft consists of a side of apolar residues (L54, W86, F128, and F129), and opposing this side is a flexible loop that contains W227. These constraints suggest that the alpha-face of the steroid would orient itself along that side of the cleft containing W86. Site-directed mutagenesis of the catalytic tetrad indicates that Y55 and K84 are essential for catalysis. Y55S and Y55F mutants are catalytically inactive, but still form binary (E.NADPH) and ternary (E.NADH.Testosterone) complexes; by contrast K84R and K84M mutants are catalytically inactive, but do not bind steroid hormone. The reliance on a Tyr/Lys pair is reminiscent of catalytic mechanisms proposed for other AKR members as well as for HSDs that belong to the short-chain dehydrogenase/reductase (SDR) family, in which Tyr is the general acid, with its pKa being lowered by Lys. Superimposition of the nicotinamide rings in the structures of 3 alpha-HSD (an AKR) and 3 alpha, 20 beta-HSD (an SDR) show that the Tyr/Lys pairs are positionally conserved, suggesting convergent evolution across protein families to a common mechanism for HSD catalysis. W86Y and W227Y mutants bind testosterone to the E.NADH complex, with effective increases in Kd of 8- and 20-fold. These data provide the first evidence that the side of the apolar cleft containing W86 and the opposing flexible loop containing W227 are parts of the steroid-binding site. Detailed mutagenesis studies of the apolar cleft and elucidation of a ternary complex structure will ultimately provide details of the determinants that govern steroid hormone recognition. These determinants could provide a rational basis for structure-based inhibitor design.

Chromosome 7q35 and susceptibility to diabetic microvascular complications

Aldose reductase (ALR2), the first enzyme of the polyol pathway, may plan an important role in the pathogenesis of diabetic microvascular complications. The gene coding for ALR2 has been localized to chromosome 7q35. Using an ALR2 probe in conjunction with the restriction endonuclease Bam-HI, we have investigated the ALR2 locus of 128 patients with type I diabetes. A significant decrease in the frequency of the 8.2 kilobase (kb) Bam-HI ALR2 genotype and 8.2 kb allele was found in patients with nephropathy (nephropaths) compared to those with retinopathy alone (retinopaths) (p < 0.05 and 0.25, respectively). We have previously shown that an RFLP of the T-cell antigen receptor constant beta-chain (TCRBC) locus, which is also localized to chromosome 7q35, is strongly associated with susceptibility to microvascular complications. The 128 patients were genotyped using the restriction endonuclease Bgl-II and a TCRBC probe. The 10/9.2-8.2 kb TCRBC-ALR2 genotype was significantly decreased in the nephropaths compared to the retinopaths (13.7% versus 43.6%, chi 2 = 10.1, p < 0.0025). The 10/9.2 and 9.2/9.2 kb TCRBC-ALR2 haplotypes were increased in the nephropaths compared to the retinopaths (32.5% versus 8.9% chi 2 = 10.9, p < 0.001). These results suggest that chromosome 7q35 harbors a gene(s) that is involved in the pathogenesis of microvascular complications. Interestingly, the gene coding for endothelial nitric oxide synthase has recently been localized to the same chromosomal region as ALR2.

Cell cycle effects of hypertonic stress on various human cells in culture

Long-term exposure to hypertonic (HT) culture media has been found to perturb the cell cycle and change gene expression in various animal cell types. A lower growth rate, with exit of cells from the cycling compartment has been observed previously in human transformed EUE cells. The aim of this study was to investigate if the kinetic changes after long-term HT stress, were typical of transformed cells or could be also found in primary cultures of normal cells. Human transformed cells from normal and neoplastic tissues, and normal human cells of epithelial and connective origin have been studied. After the incorporation of bromodeoxyuridine (BrdUrd), the frequency of S-phase cells was estimated by dual-parameter flow cytometry of DNA content versus BrdUrd immunolabelling; the total growth fraction was also estimated, after immunolabelling with an anti-PCNA antibody. We also investigated, by polyacrylamide gel electrophoresis, changes in the amount of a 35 kDa protein band, which increased in EUE cells grown in an HT medium, and which may be directly involved in cell resistance to hypertonicity. Lower BrdUrd labelling indices and higher frequencies of cells in the G0/1 range of DNA content were common features of all the cells in HT media, irrespective of their tissue of origin; other cycle phases may also be involved, depending on the cell type considered. The mechanisms by which cells cope with the HT environment could however differ, since only some cell types showed an increase of the 35 kDa stress protein found originally in HT EUE cells.

Presence of a closely related subgroup in the aldo-ketoreductase family of the mouse

Aldose reductase (alditol:NAD(P)+ 1-oxidoreductase), an enzyme implicated in the pathogenesis of various diabetic complications, catalyzes the reduction of a variety of aldehydes. From a mouse kidney library, we isolated aldose reductase cDNA that encodes a 316-amino-acid protein with approximately 97% identity to rat lens aldose reductase, approximately 69% identity to the mouse vas deferens protein and also approximately 69% identity to mouse fibroblast growth-factor-1-regulated protein. RNA-blot analysis demonstrated abundant expression of the enzyme transcript in the testis, skeletal muscle and kidney. However, a very low level of the transcript was detected in the sciatic nerve and lens, where abundant expression and involvement of the enzyme in diabetic complications were documented in other animals species. The isolated cDNA was expressed in Escherichia coli and the recombinant protein was purified to homogeneity by affinity chromatography and chromatofocusing. The expressed enzyme demonstrated reductase activity for various aldo sugars but not for the steroids. The enzyme reaction with DL-glyceraldehyde was, however, competitively inhibited by progesterone or 17 alpha-hydroxyprogesterone. The results not only indicate a unique tissue distribution and enzyme attribute of mouse aldose reductase, but also the presence of a closely related subgroup within the aldo-oxidoreductase superfamily in mouse tissues.

The role of polyols in the pathophysiology of hypergalactosemia

Cellular accumulation of galactitol has been suggested to cause the apparent dietary-independent, long-term complications in classic galactosemia. Experimental animals rendered hypergalactosemic by galactose feeding accumulate tissue galactitol, as well as millimolar quantities of galactose, and manifest biochemical, physiological and pathological abnormalities which are generally eliminated or curtailed by the concomitant administration of an aldose reductase inhibitor. This includes reduced cellular content of the cyclic polyol, myo-inositol, which like galactitol may function as an alternate intracellular osmolyte. However, the abnormalities detected in experimental galactosemic animals are more compatible with findings in experimental diabetes mellitus than in human galactosemia. Because patients with galactokinase deficiency fail to manifest the CNS and ovarian complications which characterize classic galactosemia, yet during long-term lactose restriction excrete comparable urinary quantities of galactitol, this polyol alone is not likely to play an important role during postnatal life in the pathogenesis of long-term complications. Notwithstanding, a role for either galactitol or myo-inositol in an intrauterine toxicity cannot be dismissed.

Secosteroid mechanism-based inactivators and site-directed mutagenesis as probes for steroid hormone recognition by 3 alpha-hydroxysteroid dehydrogenase

Rat liver 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD, EC 1.1.1.50) inactivates circulating androgens, progestins, and glucocorticoids. 3 alpha-HSD is a member of the aldo-keto reductase superfamily, and the X-ray structure of the apoenzyme shows the presence of an (alpha/beta)8 barrel [Hoog, S. S., Pawlowski, J. E., Alzari, P. M., Penning, T. M., & Lewis, M. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 2517-2521]. As yet, a three-dimensional structure of the ternary complex E.NADPH.steroid is unavailable. To identify regions of the enzyme involved in steroid hormone recognition, we have employed mechanism-based inactivators and site-directed mutagenesis. (3 RS)-1,10-Seco-5 alpha-estr-1-yne-3,17 beta-diol (1) and (17 RS)- 17-hydroxy-14,15-secoandrost-4-en-15-yn-3-one (3) are secosteroids which contain latent Michael acceptors (alpha,beta-unsaturated alcohols) at opposite ends of the steroid nucleus (at the C-3 and C-17 positions, respectively). It was found that compounds 1 and 3 inactivated 3 alpha-HSD only in the presence of NAD+. The requirement for cofactor implies that 1 and 3 are oxidized to the corresponding alpha,beta-unsaturated ketones for inactivation to occur. Chemically prepared 17 beta-hydroxy-1,10-seco-5 alpha-estr-1-yn-3-one (2) and 14,15-secoandrost-4-en-15-yne-3,17-dione (4), the presumed products of 1 and 3 oxidation, behaved as stoichiometric inactivators of 3 alpha-HSD. In the presence and absence of NAD+, 2 and 4 inactivated > 50% of the enzyme in 10 s or less.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of the gene encoding the major NAD(P)H-flavin oxidoreductase of the bioluminescent bacterium Vibrio fischeri ATCC 7744

The gene encoding the major NAD(P)H-flavin oxidoreductase (flavin reductase) of the luminous bacterium Vibrio fischeri ATCC 7744 was isolated by using synthetic oligonucleotide probes corresponding to the N-terminal amino acid sequence of the enzyme. Nucleotide sequence analysis suggested that the major flavin reductase of V. fischeri consisted of 218 amino acids and had a calculated molecular weight of 24,562. Cloned flavin reductase expressed in Escherichia coli was purified virtually to homogeneity, and its basic biochemical properties were examined. As in the major flavin reductase in crude extracts of V. fischeri, cloned flavin reductase showed broad substrate specificity and served well as a catalyst to supply reduced flavin mononucleotide (FMNH2) to the bioluminescence reaction. The major flavin reductase of V. fischeri not only showed significant similarity in amino acid sequence to oxygen-insensitive NAD(P)H nitroreductases of Salmonella typhimurium, Enterobacter cloacae, and E. coli but also was associated with a low level of nitroreductase activity. The major flavin reductase of V. fischeri and the nitroreductases of members of the family Enterobacteriaceae would thus appear closely related in evolution and form a novel protein family.

Is sorbitol dehydrogenase gene expression affected by streptozotocin-diabetes in the rat?

The polyol pathway, which comprises the enzymes aldose reductase and sorbitol dehydrogenase, is recognised to play a major role in the pathogenesis of diabetic complications. Although there has been extensive research on aldose reductase, the role of sorbitol dehydrogenase has been overlooked. This study examined the response of sorbitol dehydrogenase gene expression to streptozotocin-diabetes (STZ-diabetes) in the rat and whether these changes were reversed by insulin. STZ-diabetes increased testicular sorbitol dehydrogenase gene expression in a manner that was not reversible by insulin but had no effect on gene expression in kidney and brain. A secondary question was the relationship between sorbitol dehydrogenase and aldose reductase gene expression in STZ-diabetes. STZ-diabetes increased renal aldose reductase gene expression in a manner that was not reversible by insulin but had no effect on gene expression in the brain, testes and muscle. Thus, STZ-diabetes causes changes in sorbitol dehydrogenase gene expression which do not parallel those in aldose reductase, implying that expression of the two genes is not regulated via a common mechanism. Furthermore, changes in sorbitol dehydrogenase and aldose reductase gene expression cannot be fully explained on the basis of the osmoregulatory hypothesis, suggesting that regulation is mediated via mechanisms that are multifactorial and tissue-specific.

Aldose and aldehyde reductases from human kidney cortex and medulla

Aldose reductase and aldehyde reductase were purified to homogeneity from multiple samples of human kidney cortex and medulla. A single form of aldose reductase is expressed in kidney that is kinetically and immunochemically indistinguishable from aldose reductase expressed in other human tissues. The results support the conclusion that there is a single human aldose reductase, and that aldose reductase is expressed in a reduced form, characterized by high sensitivity to aldose reductase inhibitors and ability to catalyze the reduction of glucose. Aldose reductase is easily oxidized to a form that is insensitive to aldose reductase inhibitors and unable to catalyze the reduction of glucose. This form does not appear to exist in vivo, even in kidney from diabetics. There is wide variation in the level of expression of aldose reductase in kidney, especially in cortex. The immunochemically separate but similar aldehyde reductase is also expressed in kidney as a single enzyme indistinguishable from aldehyde reductase from other human tissues. Aldehyde reductase levels exceed those of aldose reductase, both in cortex and medulla.

Dihydrodiol dehydrogenase and its role in polycyclic aromatic hydrocarbon metabolism

Dihydrodiol dehydrogenase(s) (DD) have been implicated in the detoxication of proximate (trans-dihydrodiol) and ultimate carcinogenic (anti-diol-epoxide) metabolites of polycyclic aromatic hydrocarbons (PAHs). These activities are catalyzed by soluble hydroxysteroid dehydrogenases and/or by aldehyde reductases. Molecular cloning indicates tha these enzymes have a high degree of sequence identity with members of the aldo-keto reductase super family. Substrate specificity studies indicate that non-K-region trans-dihydrodiols are the preferred substrates and that anti-dio-epoxides are not oxidized by the enzyme. The products of the DD reaction are transient catechols which auto-oxidize to PAH-o-quinones. As a consequence of this auto-oxidation superoxide anion, hydrogen peroxide and semiquinone radicals are generated. Studies on the biotransformation of (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene indicate that in subcellular fractions from uninduced rat liver, DD plays a significant role in the metabolism of this proximate carcinogen. Thus, the formation of benzo[a]pyrene-7,8-dione is only superseded by the formation of tetraols which are derived from the anti-diol epoxide of benzo[a]pyrene [anti-BPDE;(+/-)-anti-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene]. PAH-o-quinones produced by DD can inactivate the enzyme. These PAH-o-quinones also vary in their reactivity towards cellular nucleophiles, their cytotoxicity and their genotoxicity. Non-bay region and methylated bay-region PAH-o-quinones generated by DD are the most reactive Michael acceptors, and are also the most cytotoxic in hepatoma cells. Cytotoxicity results from the 1e- redox-cycling of the PAH-o-quinone, concomittant production of superoxide anion and a subsequent alteration in redoxstate. PAH-o-quinones are also genotoxic thus [3H]-benzo[a]pyrene-7,8-dione readily forms deoxyguanosine-adducts with native calf-thymus DNA, i.e., to the same extent as anti-BPDE. The cytotoxic and genotoxic properties of PAH-o-quinones suggest that DD may initiate a hitherto unrecognized pathway of PAH activation.

Human kidney aldose and aldehyde reductases

Mounting experimental evidence links increased aldose reductase activity with diabetes-related kidney functional changes. To investigate the interrelationship of NADPH-dependent reductases in the human kidney, both aldose reductase and aldehyde reductase were purified from human kidney by a series of chromatographic procedures, including gel filtration on Sephadex G-100, affinity chromatography on Matrex Gel Orange A, and chromatofocusing on Mono P. Each purified enzyme appeared as a single band on polyacrylamide gel after electrophoresis or isoelectric focusing. Aldose reductase has a pI of 5.7 and apparent molecular weight of 37 kDa, calculated from SDS-polyacrylamide gel electrophoresis, while aldehyde reductase has a pI of 5.2 and molecular weight of 39 kDa. Similar molecular weights were also obtained by gel filtration, indicating that both aldose and aldehyde reductases are present as monomers in the human kidney. Aldehyde reductase is primarily localized in the cortex, while the medulla contains aldose reductase. Both enzymes displayed properties consistent with the general characteristics of aldose and aldehyde reductases obtained from either rat or dog kidney. Purified aldose reductase utilizes aldose sugars such as D-xylose, D-glucose, and D-galactose as substrates while aldehyde reductase preferentially reduces D-glucuronate and oxidizes L-gulonate to D-glucuronate. Despite the lower apparent affinity of aldehyde reductase for aldose sugars (approximately 20- to 100-fold less) both enzymes reduced D-xylose, D-glucose, and D-galactose to their respective sugar alcohols in in vitro incubation studies where the generated sugar alcohols were identified by gas chromatography. Both enzymes were also inhibited by aldose reductase inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)