sorbinil and Diabetes-Mellitus

Retinopathy is one of the most severe ocular complications of diabetes and is a leading cause of acquired blindness in young adults. The cellular components of the retina are highly coordinated but very susceptible to the hyperglycemic environment. The microvasculature of the retina responds to hyperglycemic milieu through a number of biochemical changes, including increased oxidative stress and polyol pathway, PKC activation and advanced glycation end product formation. Oxidative stress is considered as one of the crucial contributors in the pathogenesis of diabetic retinopathy, but oxidative stress appears to be highly interrelated with other biochemical imbalances that lead to structural and functional changes and accelerated loss of capillary cells in the retinal microvasculature and, ultimately, pathological evidence of the disease. One such potential connection that links oxidative stress to metabolic alterations is gyceraldehyde-3-phosphate dehydrogenase whose activity is impaired in diabetes, and that results in activation of other major pathways implicated in the pathogenesis of diabetic retinopathy. Alterations associated with oxidative stress offer many potential therapeutic targets making this an area of great interest to the development of safe and effective treatments for diabetic retinopathy. Animal models of diabetic retinopathy have shown beneficial effects of antioxidants on the development of retinopathy, but clinical trials (though very limited in numbers) have provided somewhat ambiguous results. Although antioxidants are being used for other chronic diseases, controlled clinical trials are warranted to investigate potential beneficial effects of antioxidants in the development of retinopathy in diabetic patients.

Topics: Aldehyde Reductase; Animals; Antioxidants; Diabetes Mellitus; Diabetic Retinopathy; Enzyme Inhibitors; Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+); Humans; Hyperglycemia; Imidazolidines; Mitochondria; Oxidative Stress; Retina; Signal Transduction

Recently, aldose reductase inhibitors (ARIs) have been registered in several countries for the improvement of glycaemic control. However, their efficacy is still controversial. ARIs inhibit the enhanced flux of glucose through the polyol pathway. As such, they can never be more effective than normoglycaemia, and so their potential benefits and limitations should be considered relative to the effects of prolonged euglycaemia. The clinical effects of ARIs can be put into perspective by assessing the effects of improved glycaemic control attained in randomised trials of intensive insulin treatment [such as the Diabetes Control and Complications Trial (DCCT)] and after pancreatic transplantation. Although direct comparison of these 3 interventions is hampered by differences in patient populations, duration and methods of follow-up and in the potency of ARIs, the effects of these 3 metabolic interventions and their course in time appear remarkably similar. For neuropathy, all 3 interventions induce an increase in average motor nerve conduction velocity of approximately 1 m/sec during the first months of treatment. At the same time, improvement of painful symptoms may occur. These changes probably largely represent a metabolic amelioration of the condition of the nerves. Around the second year of treatment with all 3 forms of metabolic improvement, an acceleration of nerve conduction of a similar magnitude occurs, with signs of structural nerve regeneration and some sensory recuperation. Experience with ARIs in nephropathy is still limited, but similar improvements in glomerular filtration rate and, less consistently, in urinary albumin excretion were found during short term normoglycaemia produced by all 3 forms of treatment. Comparison of a small number of studies, however, shows differences between intensive insulin regimens, pancreatic transplantation and ARIs in effects on retinopathy. Retinopathy often temporarily deteriorates in the early phases of improved glycaemic control, but this is not noted with ARIs. New microaneurysm formation was slightly reduced in a single long term study with the ARI sorbinil, but the preventive effects on the overall levels of retinopathy seemed less strong than in normoglycaemia trials of similar duration. However, the pharmacodynamic effects on inhibiting the polyol pathway differ among ARIs, and the half-life of the inhibiting effect of sorbinil may have been too short for a complete reduction of polyol pathway activity.

Topics: Adult; Aged; Aldehyde Reductase; Cross-Sectional Studies; Diabetes Mellitus; Diabetes Mellitus, Type 2; Diabetic Neuropathies; Humans; Imidazoles; Imidazolidines; Insulin; Islets of Langerhans Transplantation; Middle Aged; Naphthalenes; Pancreas Transplantation; Treatment Outcome

To update readers on research being conducted with the aldose reductase inhibitor (ARI) tolrestat in treating complications of diabetes mellitus. The article briefly describes early investigations with other ARIs and reviews the more recent studies of tolrestat. In addition, the article gives readers a simplified overview of the biochemical background pertinent to the use of these agents.. A MEDLINE search was performed to identify articles relating to the clinical use of, and research involving, the following ARIs: sorbinil, alrestatin, ponalrestat, and tolrestat. In addition, pharmaceutical manufacturers were contacted in an attempt to obtain data relating to ongoing investigations.. Review articles and clinical trials of sorbinil, alrestatin, and ponalrestat were included. Articles dealing with clinical trials of tolrestat were selected from the MEDLINE search. As there were only a few trials, all studies identified were included. No additional written data were available from the manufacturers.. ARIs, which when first introduced were proclaimed to be major advances in treating diabetic complications, have never produced the expected results. Problems with efficacy and toxicity relegated most of this class of agents to historical interest. One compound, tolrestat, has continued to be tested and has potential clinical application. To date, the extent of benefit that has been realized in tolrestat-treated patients is small to moderate. Improvements have occurred in paresthesia and neuropathy, but unfortunately, not in pain symptoms. Adverse effects have been minor and are primarily confined to elevations of hepatic alanine aminotransferase. Additional clinical trials are being conducted with this agent.. Tolrestat is the only one of the original ARIs still undergoing clinical trials. Results so far have been encouraging, but by no means definitive, for improvement in some aspects of diabetic neuropathy. Information from ongoing investigations is necessary before the true usefulness of tolrestat therapy can be determined.

Topics: Aldehyde Reductase; Clinical Trials as Topic; Diabetes Complications; Diabetes Mellitus; Humans; Imidazoles; Imidazolidines; Isoquinolines; Naphthalenes; Phthalazines

Aldose reductase inhibitors impede flux of glucose through the sorbitol pathway in diabetes mellitus. They therefore reduce the accumulation of the pathway metabolites, sorbitol and fructose, reduce the impact of the flux on the cofactors used by the pathway and reduce other derived phenomena, such as osmotic stress and myo-inositol depletion. As drugs, their targets are the chronic complications of diabetes--neuropathy, retinopathy, nephropathy and vasculopathy. In experimental models there is proof of activity against biochemical, functional and structural defects in all of the involved tissues, but we await full clinical verification of this potential.

Topics: Aldehyde Reductase; Animals; Cataract; Diabetes Complications; Diabetes Mellitus; Diabetic Angiopathies; Diabetic Nephropathies; Diabetic Neuropathies; Diabetic Retinopathy; Humans; Imidazoles; Imidazolidines

Topics: Aldehyde Reductase; Blood Glucose; Diabetes Complications; Diabetes Mellitus; Diabetic Nephropathies; Diabetic Neuropathies; Diabetic Retinopathy; Humans; Imidazoles; Imidazolidines; L-Iditol 2-Dehydrogenase; Naphthalenes; Phthalazines; Sugar Alcohol Dehydrogenases

Topics: Aldehyde Reductase; Animals; Binding Sites; Blood Glucose; Cataract; Chemical Phenomena; Chemistry; Corneal Diseases; Diabetes Complications; Diabetes Mellitus; Diabetic Angiopathies; Diabetic Nephropathies; Diabetic Neuropathies; Diabetic Retinopathy; Disease Models, Animal; Fluorenes; Galactose; Humans; Hydantoins; Imidazoles; Imidazolidines; Models, Molecular; Naphthalenes; Phthalazines; Rhodanine; Sorbitol; Structure-Activity Relationship; Substrate Specificity; Sugar Alcohol Dehydrogenases; Thiazolidines; Tissue Distribution

An increased prevalence of cataract is associated with diabetes. Biochemical studies of diabetic lenses have revealed a variety of metabolic abnormalities including changes in the levels of electrolytes, glutathione, nucleotides and sugars. Similar biochemical changes have also been observed in cataracts associated with galactosaemia, suggesting that these sugar cataracts have a common biochemical aetiology. The common biochemical factor found to initiate both types of sugar cataract is the formation of sugar alcohols (polyols) from either glucose or galactose by the enzyme aldose reductase (alditol: NADP+ 1-oxidoreductase, EC 1.1.1.21). Increased intracellular levels of these polar alcohols have a hyperosmotic effect which leads to lens fibre swelling, vacuole formation and subsequent opacification. The process of sugar cataract formation in animals can be prevented by inhibiting aldose reductase.

Topics: Aldehyde Reductase; Animals; Cataract; Diabetes Complications; Diabetes Mellitus; Diabetes Mellitus, Experimental; Galactose; Galactosemias; Glucose; Humans; Imidazoles; Imidazolidines; Intracellular Fluid; Lens, Crystalline; Mice; Osmosis; Rats; Sugar Alcohols

Aldose reductase inhibitors impede flux of glucose through the sorbitol pathway in diabetes mellitus. They therefore reduce the accumulation of the pathway metabolites, sorbitol and fructose, reduce the impact of the flux on the cofactors used by the pathway and reduce other derived phenomena, such as osmotic stress and myo-inositol depletion. As drugs, their targets are the chronic complications of diabetes--neuropathy, retinopathy, nephropathy and vasculopathy. In experimental models there is proof of activity against biochemical, functional and structural defects in all of the involved tissues, but we await full clinical verification of this potential.

Topics: Aldehyde Reductase; Animals; Cataract; Diabetes Complications; Diabetes Mellitus; Diabetic Angiopathies; Diabetic Nephropathies; Diabetic Neuropathies; Diabetic Retinopathy; Humans; Imidazoles; Imidazolidines

Photopic, 30-Hz, and foveal electroretinograms were measured in 19 diabetic patients in an experimental study of the effects of short-term Sorbinil (an aldose-reductase inhibitor) on retinal function. Patients were assigned in double-blind fashion to Sorbinil (250 mg/day) or placebo groups and were tested at the outset and after four weeks of therapy. Comparisons (t-test) between the Sorbinil and placebo groups failed to show significant effects of treatment on electroretinograms, although there was a significant correlation within the Sorbinil group between foveal recordings and red cell sorbitol at the end of treatment. Analysis showed that increased foveal electroretinograms were found in patients with low initial retinopathy but not in those with greater retinopathy. Eight patients continued Sorbinil treatment for one year. Again patients improving their foveal measurements had less initial retinopathy than those not improving. This difference was significant after one year of treatment but not at four weeks.

Topics: Adult; Aged; Diabetes Mellitus; Diabetic Retinopathy; Electroretinography; Erythrocytes; Humans; Imidazoles; Imidazolidines; Middle Aged; Osmolar Concentration; Photoreceptor Cells; Reaction Time; Time Factors; Visual Acuity

A considerable volume of animal pharmacologic data support the view that increased flux through the polyol pathway provides a unifying hypothesis for the major complications of diabetes. An extensive clinical program has been established to verify the extrapolation of the animal pharmacologic findings to man. Clinical data accumulated to date confirm the biochemical and electrophysiologic effects, and encouraging evidence of a drug effect in diabetic neuropathy and retinopathy has already been observed. In the large, controlled safety data base already available, the long-term clinical use of sorbinil is devoid of significant adverse effects in terms of both subjective side effects and laboratory parameters. The only clinically important adverse reaction reported to date has been a hypersensitivity reaction in the early weeks of therapy, which is similar to that seen with other hydantoins.

Topics: Aldehyde Reductase; Animals; Autonomic Nervous System Diseases; Blood Glucose; Clinical Trials as Topic; Diabetes Mellitus; Diabetic Neuropathies; Diabetic Retinopathy; Double-Blind Method; Humans; Imidazoles; Imidazolidines; Pain; Rats; Sorbitol; Sugar Alcohol Dehydrogenases

Two studies to investigate the penetration of the aldose reductase inhibitor, Sorbinil, were conducted. In the first study, 24 diabetic patients undergoing intracapsular extraction were randomised into three groups on a double masked basis. In the week immediately preceding the operation, all patients were requested to take two capsules daily before breakfast. Each capsule contained 200 mg Sorbinil, 100 mg Sorbinil, or a placebo. On measuring Sorbinil levels in lens, plasma and erythrocytes using HPLC, three clearly defined groups of patients were obtained. In one group no Sorbinil was detected, in the second group there were moderate levels of Sorbinil, while the third group had significantly higher levels of Sorbinil. The ratio of erythrocyte/plasma Sorbinil was 0.225, while the ratio for lens/plasma was 0.7, for both groups where Sorbinil was detected. In a second study, 20 patients were treated topically with a single dose of 0.5 mg ophthalmic Sorbinil at times ranging from 0-14 hr preoperatively. Sorbinil was detected in both lens and aqueous. Transport into the lens was complete within about 2 hr, and although aqueous levels were negligible after 6 hr, Sorbinil persisted up to 14 hr in the lens. Three out of 16 patients taking Sorbinil orally developed a maculopapular rash with pyrexia approximately 8 days after commencing the drug. No side effects were noted in any patients given the topical ophthalmic preparation.

Topics: Aged; Aldehyde Reductase; Aqueous Humor; Cataract Extraction; Chromatography, High Pressure Liquid; Diabetes Mellitus; Erythrocytes; Female; Fructose; Glucose; Humans; Imidazoles; Imidazolidines; Inositol; Lens, Crystalline; Male; Middle Aged; Sorbitol; Sugar Alcohol Dehydrogenases

To assess the potential role of polyol-pathway activity in diabetic neuropathy, we measured the effects of sorbinil--a potent inhibitor of the key polyol-pathway enzyme aldose reductase--on nerve conduction velocity in 39 stable diabetics in a randomized, double-blind, cross-over trial. During nine weeks of treatment with sorbinil (250 mg per day), nerve conduction velocity was greater than during a nine-week placebo period for all three nerves tested: the peroneal motor nerve (mean increase [+/- S.E.M.], 0.70 +/- 0.24 m per second, P less than 0.008), the median motor nerve (mean increase, 0.66 +/- 0.27, P less than 0.005), and the median sensory nerve (mean increase, 1.16 +/- 0.50, P less than 0.035). Conduction velocity for all three nerves declined significantly within three weeks after cessation of the drug. These effects of sorbinil were not related to glycemic control, which was constant during the study. Although the effect of sorbinil in improving nerve conduction velocity in diabetics was small, the findings suggest that polyol-pathway activity contributes to slowed nerve conduction in diabetics. The clinical applicability of these observations remains to be determined, but they encourage further exploration of this approach to the treatment or prevention of diabetic neuropathy.

Topics: Adult; Aged; Aldehyde Reductase; Diabetes Mellitus; Diabetic Neuropathies; Double-Blind Method; Drug Evaluation; Female; Glycated Hemoglobin; Humans; Imidazoles; Imidazolidines; Male; Median Nerve; Middle Aged; Motor Neurons; Neural Conduction; Peroneal Nerve; Random Allocation; Skin Temperature; Sugar Alcohol Dehydrogenases

Protein kinase C (PKC) and aldose reductase (AR) enzyme activities are increased in diabetes and complications are include retinopathy, nephropathy, and neuropathy. However, the relationship between PKC and AR and the underlying molecular mechanisms is still unclear. We aimed to evaluate the relationship between these two enzymes and clarify the underlying molecular mechanisms by the related signaling molecules. The effects of hyperglycemia and oxidative stress on AR and PKC enzymes and the signaling molecules such as nuclear factor-kappa B (NF-κB), inhibitor kappa B-alpha (IkB-α), total c-Jun, phospho c-Jun, and stress-activated protein kinases (SAPK)/Jun amino-terminal kinases (JNK) were evaluated in human retinal pigment epithelial cells (ARPE-19). AR, PKC protein levels, and related signaling molecules increased with hyperglycemia and oxidative stress. The AR inhibitor sorbinil decreased PKC expression and activity and all signaling molecule protein levels. Increased AR expression during hyperglycemia and oxidative stress was found to be correlated with the increase in PKC expression and activity in both conditions. Decreased expression and activity of PKC and the protein levels of related signaling molecules with the AR inhibitor sorbinil showed that AR enzyme may play a key role in the expression of PKC enzyme and oxidative stress during diabetes.

Topics: Aldehyde Reductase; Cell Line; Diabetes Mellitus; Diabetic Retinopathy; Enzyme Inhibitors; Epithelial Cells; Humans; Hyperglycemia; Imidazolidines; NF-kappa B; Oxidative Stress; Protein Kinase C; Retina; Retinal Pigment Epithelium; Signal Transduction

Pressure-induced vasodilation (PIV) allows skin blood flow to increase in response to locally applied pressure and may be protective against pressure ulcers. We previously showed that PIV was absent in 1-week diabetic mice exhibiting no neuropathy. Our aim was to determine whether the diabetes-induced PIV alteration could be prevented.. Diabetic mice received no treatment or a daily treatment with either sorbinil, alagebrium or alpha-lipoic acid (LPA) for 1 week. Laser Doppler flowmetry was used to evaluate PIV as well as endothelium-dependent vasodilation following iontophoretic delivery of acetylcholine (ACh). The effect of each treatment on oxidative stress was examined by plasma 8-isoprostane assay. LPA was the sole treatment to prevent both PIV and ACh vasodilation alterations, with a significant reduction of oxidative stress in diabetic mice. Both PIV and ACh-vasodilation were abolished in LPA-treated diabetic mice following injection of Nomega-nitro-L-arginine (p<0.05). In contrast, alagebrium and sorbinil prevented neither diabetes-induced PIV abolition nor endothelial alteration.. LPA treatment significantly reduced the oxidative stress and was able to preserve endothelial nitric oxide availability in the cutaneous microcirculation and then to preserve the PIV response in diabetic mice. LPA treatment could play a key role in limiting the risk of pressure-induced cutaneous ulcer during diabetes.

Topics: Acetylcholine; Aldehyde Reductase; Animals; Antioxidants; Biomarkers; Diabetes Mellitus; Dinoprost; Imidazolidines; Laser-Doppler Flowmetry; Male; Mice; Microcirculation; Nitric Oxide Synthase; Nitroarginine; Oxidative Stress; Pressure; Pressure Ulcer; Regional Blood Flow; Skin; Thioctic Acid; Vasodilation; Vasodilator Agents

Starting from the known inhibitory activity of (3-benzoylpyrrol-1-yl)acetic acid (I) and (2-benzoylpyrrol-1-yl)acetic acid (II), a series of 3-aroyl and 2,4-bis-aroyl derivatives (54-75) were synthesized and tested for inhibition of aldose reductase, an enzyme involved in the appearance of diabetic complications. It was found that a number of the tested compounds exhibited considerable activity in the micromolar range. Important structural features for the potent compounds is the presence of substituents with relatively low Hammett sigma values and/or moieties which increase their overall aromatic area. The most active derivative was the [2,4-bis(4-methoxybenzoyl)pyrrol-1-yl]acetic acid (75), with potency favorably compared to known ARIs such as tolrestat, epalrestat, zopolrestat, and fidarestat. Four selected derivatives were also evaluated for their ability to interfere with the oxidative modification of serum albumin in an in vitro experimental glycation model of diabetes mellitus. All of them showed considerable activity, comparable to the known inhibitor trolox. Our results, taken together, indicate that compound 75 combines favorably two biological activities directly connected to a number of pathological conditions related to the chronic diabetes mellitus.

Topics: Acetates; Aldehyde Reductase; Animals; Diabetes Mellitus; Enzyme Inhibitors; Female; Fructose; Male; Monosaccharides; Oxidation-Reduction; Proteins; Pyrroles; Rats; Rats, Inbred F344; Serum Albumin; Structure-Activity Relationship

The fate of dapsone hydroxylamine has been investigated in diabetic and normal human erythrocytes. In erythrocytes from four type 1 (insulin dependent) diabetic subjects, there was a significant decrease in dapsone hydroxylamine-mediated methaemoglobin formation compared with cells drawn from normal individuals (P < 0.01). However, the ability of the diabetic cells to detoxify the hydroxylamine to dapsone was not correspondingly reduced and was not different to normal cells. The initial rate of the accelerating effect of diethyl dithiocarbamate (DDC) on hydroxylamine-mediated methaemoglobin and dapsone formation was significantly reduced in diabetic compared with normal cells. There was no significant difference in hydroxylamine-dependent methaemoglobin formation between diabetic erythrocytes pretreated with either statil or sorbinil and untreated diabetic cells. Dapsone recovery in diabetic erythrocytes incubated with statil was not significantly different from statil-free incubations. However, in the presence of sorbinil, there was a marked reduction in dapsone formation at all four time points, (P < 0.001 at 15 min). Mean measured levels of glutathione did not differ significantly between the normal (380 +/- 30.9 mg/L; N = 8) and diabetic (349 +/- 58.7 mg/L; N = 8) volunteers. In summary, although diabetic erythrocytes were less sensitive to the effect of dapsone hydroxylamine-mediated methaemoglobin formation in comparison with normal cells, glutathione-dependent hydroxylamine reduction to dapsone was unaffected.

Topics: Dapsone; Diabetes Mellitus; Ditiocarb; Erythrocytes; Glutathione; Humans; Imidazoles; Imidazolidines; Methemoglobin; Models, Chemical; Oxidation-Reduction; Phthalazines; Temperature

Two methods are commonly used to measure sorbitol in mammalian tissues. The first uses sorbitol dehydrogenase for a coupled enzymatic reaction; unfortunately, other polyols are also substrates for this enzyme. The second uses gas-liquid chromatography (GLC) for separation of polyols and mass quantitation of sorbitol. A comparison of these two methods for the measurement of sorbitol in duplicate samples of lens, nerve, and erythrocytes indicates that GLC of polyol acetates consistently finds less sorbitol than measured by sorbitol dehydrogenase. Erythritol, threitol, ribitol, arabitol, and galactitol are polyols found in variable quantities in these tissues, which have a variable influence on the activity of sorbitol dehydrogenase and therefore alter sorbitol quantitation with this enzyme. Moreover, there is an unidentified substance(s) that reacts with sorbitol dehydrogenase which seems to increase in association with hyperglycemia in the lens and nerve, but not in erythrocytes. The quantity of this unknown substance(s) seems to be reduced by the aldose reductase inhibitor sorbinil in erythrocytes and to a lesser extent sciatic nerve and lens. Since enzymatic sorbitol quantitation in the lens, nerve, and erythrocytes is influenced by many known and unknown factors other than sorbitol, we recommend that GLC of polyol acetates be used to measure sorbitol in biologic tissues.

Topics: Aldehyde Reductase; Analysis of Variance; Animals; Chromatography, Gas; Diabetes Mellitus; Diabetes Mellitus, Experimental; Erythrocytes; Humans; Hyperglycemia; Imidazoles; Imidazolidines; L-Iditol 2-Dehydrogenase; Lens, Crystalline; Male; Rats; Rats, Inbred Strains; Sciatic Nerve; Sorbitol; Spectrometry, Fluorescence; Sugar Alcohols

The mechanism by which hyperglycaemia leads to diabetic complications has not been fully elucidated. Non-enzymatic glycosylation leads to considerable functional and structural alteration of proteins. Hyperglycaemia also induces changes in intracellular metabolites, particularly in the polyol pathway. Aldose reductase inhibitors, which block the polyol pathway, have been shown to prevent complications in animal models, and this provides the rationale for the large scale trials that are presently being conducted.

Topics: Aldehyde Reductase; Diabetes Complications; Diabetes Mellitus; Glycolysis; Glycosylation; Humans; Hyperglycemia; Imidazoles; Imidazolidines; Naphthalenes; Phthalazines; Rhodanine; Thiazolidines

Transition metal-catalysed oxidations have been implicated in the complications of diabetes. We report here that some experimental inhibitors of the enzyme aldose reductase (implicated in diabetes mellitus via its ability to catalyse glucose reduction to sorbitol) are also potent inhibitors of transition metal-catalysed ascorbate oxidation. The inhibition appears to be dependent upon the presence of a spirohydantoin group. It is conceivable that the copper- and iron-binding capacity of these compounds may contribute to some of their observed biological effects and may provide a starting point for a new generation of experimental drugs for the treatment of diabetes mellitus.

Topics: Aldehyde Reductase; Antioxidants; Ascorbic Acid; Copper; Diabetes Mellitus; Dose-Response Relationship, Drug; Fluorenes; Humans; Hydantoins; Imidazoles; Imidazolidines; Iron; Oxidation-Reduction; Structure-Activity Relationship

Topics: Aldehyde Reductase; Animals; Diabetes Mellitus; Flavonoids; Fructose; Glucose; Glutarates; Humans; Imidazoles; Imidazolidines; Sorbitol; Structure-Activity Relationship; Substrate Specificity

Sorbinil is a hydantoin aldose reductase inhibitor that has shown promise as therapy for patients with diabetic complications such as neuropathy and retinopathy. However, as many as 10% of patients receiving sorbinil have had adverse reactions characterized by fever, skin rash, and myalgia. Our previous studies of phenytoin suggested that susceptibility to reactions might result from an inherited detoxification defect. We did the current study to determine if sorbinil is metabolized to reactive intermediates and if cells from patients with a history of a reaction to sorbinil are appropriate for the in-vitro investigation of susceptibility. Microsome-generated metabolites of sorbinil (50 microM) were toxic to normal peripheral blood lymphocytes (7.9% +/- 0.3% dead cells [mean +/- SE]). Toxicity was increased in the presence of an epoxide hydrolase inhibitor (17.5% +/- 0.3% dead cells) and abolished by an inhibitor of cytochrome P-450. In contrast to cells from healthy controls and diabetics who tolerated sorbinil (7.9% +/- 0.7% and 7.8% +/- 0.4% dead cells, respectively), cells from the six patients who had sorbinil reactions showed significantly increased toxicity from metabolites of sorbinil and phenytoin (19.7% +/- 2.3% dead cells, P less than 0.001). Cells from three patients who had reactions to phenytoin were similarly sensitive to sorbinil metabolites (23.4% +/- 0.3% dead cells). We conclude that sorbinil is oxidatively metabolized to a potentially toxic intermediate. Certain patients may be at increased risk for developing hypersensitivity reactions. Development of this important new drug has been hampered by uncommon but potentially severe reactions. An increased understanding of the steps involved in the development of adverse reactions could lead to screening tests or to the development of safer compounds.

Topics: Adult; Animals; Biotransformation; Diabetes Mellitus; Drug Hypersensitivity; Female; Humans; Imidazoles; Imidazolidines; In Vitro Techniques; Lymphocytes; Male; Mice; Microsomes, Liver; Middle Aged; Phenytoin

We measured the alcohol sugars in sural nerves from 11 controls, 21 conventionally treated patients with diabetes and neuropathy, and 4 diabetics without neuropathy. The results were related to metabolic control and to clinical, neuropathological, and morphometric abnormalities in the nerves. The mean endoneurial glucose, fructose, and sorbitol values were higher in diabetic patients than in controls. Linear regression analysis revealed that nerve sorbitol content in the diabetics was inversely related to the number of myelinated fibers (P = 0.003). Mean nerve levels of myo-inositol were not decreased in the diabetic patients, with or without neuropathy, and were not associated with any of the neuropathological end points of diabetes. Our results indicate that myo-inositol deficiency is not part of the pathogenesis of human diabetic neuropathy, as had been hypothesized. Other accumulated alcohol sugars, however, were increased in diabetes and were associated with the severity of neuropathy. On repeat biopsy, six diabetics, treated for a year with the aldose reductase inhibitor sorbinil, had decreased endoneurial levels of sorbitol (P less than 0.01) and fructose (0.05 less than P less than 0.1), but unchanged levels of myo-inositol.

Topics: Adolescent; Adult; Aged; Aldehyde Reductase; Diabetes Mellitus; Diabetic Neuropathies; Erythrocytes; Female; Fructose; Glucose; Humans; Imidazoles; Imidazolidines; Inositol; Male; Middle Aged; Myelin Sheath; Nerve Regeneration; Nerve Tissue; Sorbitol; Sural Nerve

Topics: Aldehyde Reductase; Animals; Diabetes Complications; Diabetes Mellitus; Humans; Imidazoles; Imidazolidines; Sugar Alcohol Dehydrogenases

Topics: Aldehyde Reductase; Animals; Cataract; Diabetes Mellitus; Dogs; Glyceraldehyde; Humans; Imidazoles; Imidazolidines; L-Iditol 2-Dehydrogenase; Lens, Crystalline; Rabbits; Rats; Sugar Alcohol Dehydrogenases

A decade ago, we discovered that spirohydantoins are a novel class of aldose reductase inhibitors characterized by very potent in vivo activity. This important discovery resulted from a systematic screening effort for in vitro activity against aldose reductase isolated from bovine lens and subsequent testing of active compounds for in vivo activity in a streptozotocin-diabetic rat model, measuring inhibition of sorbitol formation in sciatic nerve. In this in vivo model, spirohydantoins were clearly more potent than all known carboxylic acid-type aldose reductase inhibitors. Structure-activity studies in the spirohydantoin class demonstrated that potent in vitro and in vivo activity were obtained when the spiro junction was adjacent to an aromatic ring and when this junction was part of a 5- or 6-membered ring system fused to the aromatic ring. Excellent in vitro and in vivo activity was achieved in 6-halogenated chromane derivatives with the spirohydantoin group attached in the 4-position. In this series, biologic activity is highly stereospecific and associated with the S configuration. Sorbinil, the S isomer of the 6-fluoro derivative in this series, is one such example: it is 30 times more potent than its R isomer in vitro (IC50 0.15 v 4.4 mumol/L) and 100 times more potent in vivo (ED50 0.25 mg/kg po v 25 mg/kg po).

Topics: Aldehyde Reductase; Animals; Chemical Phenomena; Chemistry; Diabetes Complications; Diabetes Mellitus; Diabetes Mellitus, Experimental; Imidazoles; Imidazolidines; Rats; Sciatic Nerve; Sorbitol; Sugar Alcohol Dehydrogenases

Based upon kinetic, structural, and immunologic properties, we have demonstrated that human tissues have three major forms of aldo-keto reductases: aldose reductase (AR), and aldehyde reductases I (AR I) and II (AR II). The proposed subunit compositions are AR, alpha; AR I, alpha-beta; and AR II, delta. Only AR can effectively reduce glucose to sorbitol. The beta subunits in AR I alter the substrate specificity of AR and prevent conformational changes required for the activation of alpha subunits. Partially purified AR (by DE-52) from human erythrocytes expresses biphasic kinetics with glucose and glyceraldehyde. The enzyme can be activated with glucose + glucose-6-P + NADPH and is strongly inhibited by sorbinil, alrestatin, and quercetrin, and by ADP, 2,3DPG, 1,3DPG, and 3PGA. The activated enzyme expresses monophasic kinetics with substrates (Km glucose less than 1 mmol/L) and is less susceptible to inhibition by synthetic AR inhibitors and phosphorylated intermediates. The enzyme from human brain, aorta, muscle, and ocular tissues was also activated under similar conditions. Erythrocyte enzyme was activated by incubation of blood with 30 to 50 mmol/L glucose. In diabetic subjects with blood sugar levels higher than 250 mg%, almost all the erythrocyte enzyme exists in the activated form. As demonstrated by enzyme-linked immunosorbent assay (ELISA), the increase in AR activity (in vivo and in vitro) was due to the activation of the enzyme and not to the de novo synthesis. In each case, the activation of the enzyme was confirmed by NADPH oxidation and the formation of proportionate amounts of sorbitol.

Topics: Aldehyde Reductase; Aorta; Brain; Diabetes Mellitus; Enzyme Activation; Erythrocytes; Eye; Glucose; Glyceraldehyde; Humans; Imidazoles; Imidazolidines; Muscles; NADP; Sugar Alcohol Dehydrogenases

Rats fed a high-galactose diet develop marked thickening of their retinal capillary basement membranes. The effect is prevented if the animals also receive the aldose reductase inhibitor sorbinil. The effect does not appear to be due to aldose reductase itself, since immunoreactive aldose reductase has not been found in the retinal microvasculature of the rat but rather to a related enzyme with similar substrate specificity. The detailed biochemical mechanism for basement membrane thickening is obscure, involving an alteration of the extracellular matrix, where aldose reductase and similar enzymes have not been described; osmotic damage to the microvascular cells, such as has been described following aldose reductase-induced sugar alcohol accumulation in lens epithelial cells, is not apparent in diabetic or galactosemic animals. It is possible that concentrations of intracellular sugar alcohols that do not substantially change the osmolarity of the cell cytosol alter intracellular enzyme activities. This, in turn, could affect the biosynthesis of extracellular matrix macromolecules, as suggested, for example, by the hypothesis of Rohrbach et al, based on studies of a basement membrane-producing tumor implanted in diabetic mice, which proposes that the hyperglycemia of diabetes mellitus causes a reduced synthesis of the heparan sulfate BM-1 proteoglycan with a subsequent overproduction of type IV collagen. This and other hypotheses of basement membrane thickening can be tested in diabetic or galactosemic rats, some of which receive aldose reductase inhibitors, or in retinal microvascular pericytes and endothelial cells grown in culture.

Topics: Aldehyde Reductase; Animals; Basement Membrane; Collagen; Diabetes Mellitus; Dogs; Female; Galactose; Galactosemias; Humans; Imidazoles; Imidazolidines; Mice; Microscopy, Electron; Rats; Rats, Inbred WKY; Retinal Vessels; Sugar Alcohol Dehydrogenases

Topics: Aldehyde Reductase; Body Water; Cataract; Collagen; Diabetes Complications; Diabetes Mellitus; Diabetic Neuropathies; Hand; Humans; Imidazoles; Imidazolidines; Joint Diseases; Models, Biological

Aldose reductase (alditol:NADP+ 1-oxidoreductase, EC 1.1.1.21) has been partially purified from human erythrocytes by DEAE-cellulose (DE-52) column chromatography. This enzyme is activated severalfold upon incubation with 10 microM each glucose 6-phosphate, NADPH, and glucose. The activation of the enzyme was confirmed by following the oxidation of NADPH as well as the formation of sorbitol with glucose as substrate. The activated form of aldose reductase exhibited monophasic kinetics with both glyceraldehyde and glucose (Km of glucose = 0.68 mM and Km of glyceraldehyde = 0.096 mM), whereas the native (unactivated) enzyme exhibited biphasic kinetics (Km of glucose = 9.0 and 0.9 mM and Km of glyceraldehyde = 1.1 and 0.14 mM). The unactivated enzyme was strongly inhibited by aldose reductase inhibitors such as sorbinil, alrestatin, and quercetrin, and by phosphorylated intermediates such as ADP, glycerate 3-phosphate, glycerate 1,3-bisphosphate, and glycerate 2,3-trisphosphate. The activated form of the enzyme was less susceptible to inhibition by aldose reductase inhibitors and phosphorylated intermediates.

Topics: Aldehyde Reductase; Diabetes Mellitus; Enzyme Activation; Erythrocytes; Glucose; Glyceraldehyde; Humans; Imidazoles; Imidazolidines; Isoquinolines; Kinetics; NADP; Quercetin; Sorbitol; Sugar Alcohol Dehydrogenases

Motor nerve conduction velocity was lower in streptozotocin-diabetic rats than in controls. Treatment with the aldose reductase inhibitor Sorbinil restored conduction velocity to normal. Diabetic rats had an increased concentration of sorbitol and reduced free inositol in sciatic nerve. Sorbinil corrected both defects. Inositol administration to diabetic rats also restored conduction velocity to normal. Genetically diabetic mice had reduced concentrations of inositol in sciatic nerve but fructose and sorbitol were normal. Glucose concentration was considerably increased.

Topics: Animals; Diabetes Mellitus; Fructose; Glucose; Imidazoles; Imidazolidines; Inositol; Male; Mice; Mice, Inbred C57BL; Neural Conduction; Rats; Rats, Inbred Strains; Sciatic Nerve; Sorbitol

Topics: Animals; Axons; Diabetes Mellitus; Diabetic Neuropathies; Fructose; Humans; Imidazoles; Imidazolidines; Neural Conduction; Rabbits; Schwann Cells; Sorbitol

Topics: Aldehyde Reductase; Animals; Cataract; Diabetes Mellitus; Humans; Imidazoles; Imidazolidines; L-Iditol 2-Dehydrogenase; Lens, Crystalline; Rats; Sorbitol; Sugar Alcohol Dehydrogenases