Sorbitol Dehydrogenase Inhibitor Research Articles

In Silico Studies, Anti-oxidant Properties, Antisorbitol Dehydrogenase, Anti-alpha Amylase and Anti-gastrointestinal Cancer Potential of Violanthin as a Natural Compound.

In vitro studies have shown flavonoids to be effective antioxidants. Flavonoid C-glycosides have antioxidant properties, but there are very few data on their cellular antioxidant activity. The chemical activities of violanthin against alpha amylase and sorbitol dehydrogenase were investigated utilizing the molecular docking study. The anti-cancer activities of the compounds were evaluated against MKN45, AGS, and KATO III cell lines. The chemical activities of violanthin against some of the expressed surface receptor proteins (estrogen receptor, folate receptor, and CD44) in the mentioned cell lines were estimated using molecular docking calculations. 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) analyzes were performed to determine the effects of compound on cell viability levels. The results showed the possible interactions and their features at an atomic level. The docking scores indicated that violanthin has a significant binding affinity to the enzymes and proteins. IC50 values of violanthin for gastric cell lines (MKN45, AGS, KATO III) were 31.95±3.95, 53.06±6.02, 47.98±5.16 µM, respectively. For α-amylase and sorbitol dehydrogenase enzymes, IC50 values were 25.03 and 1.47 µM. Moreover, this compound formed strong contact with the enzymes and receptors. Therefore, violanthin could be a potential inhibitor for these enzymes and cancer cells. Several secondary problems of diabetes mellitus have been discovered to be prevented or treated with sorbitol dehydrogenase inhibitors.

Bazı İlaç ve Metallerin Keçi (Capra aegagrus hircus) Böbreğinde Aldoz Redüktaz ve Sorbitol Dehidrogenaz Enzimleri Üzerine Etkilerinin Araştırılması

The effects of some antibiotics and metals on goat (Capra aegagrus hircus) kidney aldose reductase (AR) and sorbitol dehydrogenase (SDH) activities were examined. For drugs and metals that exhibit inhibitory effect, Ki constants were calculated and inhibition types were determined by using Lineweaver-Burk curves. In our study, the highest inhibition showed ceftriaxone antibiotic in AR enzyme with an IC50 value of 0.0274 mM. More potent AR inhibitors can be synthesized from the ceftriaxone compound. This compound is followed by amikacin sulfate and ciproflaksasin compounds with IC50 values of 0.061 and 0.25 mM, respectively. The highest inhibition of metals showed Co+2 ion with IC50 value 0.000445 mM. This metal is followed by Fe+2 and Zn+2 with IC50 values of 0.0286 and 0.084 mM, respectively. In SDH enzyme, the highest inhibition showed rifamycin sodium antibiotic with an IC50 value of 0.016 mM. More potent SDH inhibitors can be synthesized from the rifamycin sodium compound. This compound is followed by ceftriaxone and cefuroxime compounds with IC50 values of 0.025 and 0.16 mM, respectively. The highest inhibition of metals showed Co+2 ion with IC50 value 0.00044 mM. This metal is followed by Fe+2 and Zn+2 with IC50 values of 0.009 and 0.16 mM, respectively.

Role of the Polyol Pathway in Locomotor Recovery and Wallerian Degeneration after Spinal Cord Contusion Injury.

Spinal cord contusion injury leads to Wallerian degeneration of axonal tracts, resulting in irreversible paralysis. Contusion injury causes perfusion loss by thrombosis and vasospasm, resulting in spinal cord ischemia. In several tissues, including heart and brain, ischemia activates polyol pathway enzymes—aldose reductase (AR) and sorbitol dehydrogenase (SDH)—that convert glucose to sorbitol and fructose in reactions, causing oxidative stress and tissue loss. We sought to determine whether activation of this pathway, which has been termed glucotoxicity, contributes to tissue loss after spinal cord contusion injury. We tested individual treatments with AR inhibitors (sorbinil or ARI-809), SDH inhibitor (CP-470711), superoxide dismutase mimetic (tempol), or combined sorbinil and tempol. Each treatment significantly increased locomotor recovery and reduced loss of spinal cord tissue in a standard model of spinal cord contusion in rats. Tissue levels of sorbitol and axonal AR (AKR1B10) expression were increased after contusion injury, consistent with activation of the polyol pathway. Sorbinil treatment inhibited the above changes and also decreased axonal swelling and loss, characteristic of Wallerian degeneration. Treatment with tempol induced recovery of locomotor function that was similar in magnitude, but non-additive to sorbinil, suggesting a shared mechanism of action by reactive oxygen species (ROS). Exogenous induction of hyperglycemia further increased injury-induced axonal swelling, consistent with glucotoxicity. Unexpectedly, contusion increased spinal cord levels of glucose, the primary polyol pathway substrate. These results support roles for spinal glucose elevation and tissue glucotoxicity by the polyol pathway after spinal cord contusion injury that results in ROS-mediated axonal degeneration.

Leafy vegetables inhibit activities of aldose reductase and sorbitol dehydrogenase in vitro

ABSTRACT One of the processes involved in pathogenesis of diabetic complications is the polyol pathway, which is catalyzed by the enzymes – aldose reductase and sorbitol dehydrogenase. Inhibition of one, or both, of these enzymes will shut down the polyol pathway ameliorating diabetic complications. Consumption of leafy vegetables is a dietary regime for management of diabetes mellitus and its complications. Inhibitory effects of leafy vegetables on activities of the polyol pathway enzymes aldose reductase and sorbitol dehydrogenase, and mode(s) of inhibition of these enzymes by the most effective plant were evaluated. Aqueous extract of leaves of African eggplant (Solanum macrocarpon L), bitter leaf (Vernonia amygdalina Del.), fluted pumpkin (Telfairia occidentalis Hook.) and clove basil leaf (Ocimum gratissimum L), were incubated with substrates (glucose and sorbitol) and enzymes, and their percent inhibition of enzymes determined spectrophotometrically. Due to low IC50 value, the aqueous extract of bitter leaf was used to assess kinetics of both enzymes. With exception of African eggplant, all plants displayed stronger inhibition of sorbitol dehydrogenase than aldose reductase. Vernonia amygdalina exhibited the lowest IC50 for aldose reductase (78.03 µg∙mL−1) and sorbitol dehydrogenase (22.17 µg∙mL−1). Vernonia amygdalina inhibited aldose reductase and sorbitol dehydrogenase in a noncompetitive, and mixed non-competitive manner, respectively. The V. amygdalina extract displayed potent inhibition of polyol pathway enzymes, and it needs to be determined if consumption affects the responses.

Carica papaya Linn. fruit extract inhibited the activities of aldose reductase and sorbitol dehydrogenase: possible mechanism for amelioration of diabetic complications

BackgroundDiabetes mellitus is a metabolic disorder which is associated with debilitating complications including eye disease, kidney disorder, and diabetic foot disease. One of the mechanisms implicated in the pathogenesis of diabetic complications is the polyol pathway. This study evaluated the inhibitory effect of aqueous extract of four tropical fruits, namely apple (Malus domestica Borkh.), banana (Musa paradisiaca Linn.), pawpaw (Carica papaya Linn.), and watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai), on the activities of polyol pathway enzymes (aldose reductase and sorbitol dehydrogenase).ResultsAll the fruits, with the exception of banana, displayed stronger inhibition of sorbitol dehydrogenase than aldose reductase which culminated in low IC50 for the inhibition of sorbitol dehydrogenase. Of the fruit extracts tested, pawpaw inhibited both aldose reductase and sorbitol dehydrogenase most effectively with IC50 of 150.78 μg/mL and 46.30 μg/mL, respectively. Lineweaver-Burk plot also revealed that the pawpaw extract inhibited aldose reductase competitively while sorbitol dehydrogenase was inhibited in a mixed non-competitive manner.ConclusionAqueous extract of pawpaw fruit effectively inhibited polyol pathway enzymes, and this may be attributed to rich nutritional and phytochemical composition of the fruit. Consequently, the consumption of pawpaw fruit may contribute to the amelioration of diabetic complications.

Search for non-acidic ALR2 inhibitors: Evaluation of flavones as targeted agents for the management of diabetic complications.

Diabetic complications (DC) follow multiple pathophysiological pathways and one of the key pathways is the polyol pathway which involves the metabolism of glucose via aldose reductase (ALR2) and sorbitol dehydrogenase (SDH). ALR2 inhibitors such as epalrestat has already been established as promising candidates for the management of DC. On the basis of pathophysiological understanding of polyol pathway, simultaneous inhibition of ALR2 and SDH may be expected to provide synergistic outcomes in the treatment strategies for DC. Thus, in this study, dual inhibitors of ALR2 and SDH were identified using pharmacophore-based virtual screening. For this purpose, the pharmacophore model for SDH (model ID: AAADH.343) was generated and validated. For screening against ALR2, the pharmacophore model (model ID: AADRR.1109) which was previously reported by our group was applied. Initially, flavones reported by our research group were screened by those two pharmacophore models to obtain hits with an optimum affinity for the catalytic domain of both ALR2 and SDH. Inhibitory potential of identified hits for ALR2 and SDH were then experimentally determined using enzymatic assays reported in the literature. Additional focus was laid on the selectivity of the designed molecules towards ALR2 over ALR1, thus evaluation against ALR1 was also performed. Overall, four molecules FLV-2, FLV-11, FLV-12, and FLV-15 were found to possess significant dual inhibitory activity against ALR2 and SDH, with selectivity over ALR1. Among them, FLV-2 displayed significant dual inhibitory potential with an IC50 value of 0.689±0.018µM and 0.174±0.003µM against ALR2 and SDH respectively with a selectivity index of 52.902 to ALR2 over ALR1.

Lens cholesterol biosynthesis inhibition: A common mechanism of cataract formation in laboratory animals by pharmaceutical products.

CJ-12,918, a 5-lipoxygenase (5-LO) inhibitor, caused cataracts during a 1-month safety assessment studies in rats whereas the structurally similar ZD-2138 was without effect. For CJ-12,918 analogs, blocking different sites of metabolic liability reduced (CJ-13,454) and eliminated (CJ-13,610) cataract formation in both rats and dogs. Using this chemical series as a test set, models and mechanisms of toxicity were first explored by testing the utility of ex vivo rat lens explant cultures as a safety screen. This model overpredicted the cataractogenic potential of ZD-2138 due to appreciably high lens drug levels and was abandoned in favor of a mechanism-based screen. Perturbations in lens sterol content, from a decline in lathosterol content, preceded cataract formation suggesting CJ-12,918 inhibited lens cholesterol biosynthesis (LCB). A 2-day bioassay in rats using ex vivo LCB assessments showed that the level of LCB inhibition was correlated with incidence of cataract formation in animal studies by these 5-LO inhibitors. Thereafter, this 2-day bioassay was applied to other pharmaceutical programs (neuronal nitric oxide synthase, sorbitol dehydrogenase inhibitor, squalene synthetase inhibitor and stearoyl-CoA desaturase-1 inhibitors/D4 antagonists) that demonstrated cataract formation in either rats or dogs. LCB inhibition >40% was associated with a high incidence of cataract formation in both rats and dogs that was species specific. Bioassay sensitivity/specificity were further explored with positive (RGH-6201/ciglitazone/U18666A) and negative (tamoxifen/naphthalene/galactose) mechanistic controls. This body of work over two decades shows that LCB inhibition was a common mechanism of cataract formation by pharmaceutical agents and defined a level of inhibition >40% that was typically associated with causing cataracts in safety assessment studies typically ≥1month.

High glucose concentration suppresses a SIRT2 regulated pathway that enhances neurite outgrowth in cultured adult sensory neurons

In peripheral nerve under hyperglycemic conditions high flux of d-glucose through the polyol pathway drives an aberrant redox state contributing to neurodegeneration in diabetic sensorimotor polyneuropathy (DSPN). Sirtuins, including SIRT2, detect the redox state via the NAD+/NADH ratio to regulate mitochondrial function via, in part, AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α). In adult dorsal root ganglia (DRG) sensory neurons mitochondrial dysfunction has been proposed as an etiological factor in dying-back neuropathy in diabetes. We tested the hypothesis that a high concentration of d-glucose depleted SIRT2 expression via enhancement of polyol pathway activity. We posited that this would lead to impaired mitochondrial function and suppression of neurite outgrowth in cultured sensory neurons. The use of dominant negative mutants or neurons from SIRT2 knockout (KO) mice to block SIRT2 signaling revealed that neurons derived from control or type 1 diabetic rodents required SIRT2 for optimal neurite outgrowth. Over-expression of WT-SIRT2 elevated neurite outgrowth in normal and diabetic cultures. SIRT2 protein isoforms 2.1 and 2.2 were reduced by 20–30% in DRG of type 1 diabetic mice (p < .05). After 72 h exposure to high d-glucose (25 mM vs 5 mM) cultured sensory neurons showed a significant 2-fold (p < .05) decrease in SIRT2 expression, P-AMPK, levels of respiratory Complexes II/III and respiratory capacity. DRG neurons expressed aldose reductase and the aforementioned deficits were prevented by treatment with aldose reductase inhibitors (lidorestat or sorbinil) or sorbitol dehydrogenase inhibitor (SDI-158). In cultures derived from type 1 diabetic rats treatment with SDI-158 elevated expression of SIRT2, P-AMPK/PGC-1α and neurite outgrowth (p < .05). SIRT2 KO neurons exhibited deficits in the LKB-1/AMPK/PGC-1α pathway and mitochondrial function. In cultured neurons the SIRT2 pathway enhances axonal outgrowth and this signaling axis encompassing activation of AMPK/PGC-1α is impaired in DSPN, in part, due to enhanced polyol pathway activity caused by hyperglycemia.

Sorbitol dehydrogenase inhibitor protects the liver from ischemia/reperfusion-induced injury via elevated glycolytic flux and enhanced sirtuin 1 activity.

Sorbitol dehydrogenase (SDH), a key enzyme of the polyol pathway, has recently been demonstrated to have an important role in mediating tissue ischemia/reperfusion (I/R) injury. The present study investigated how this enzyme may affect the ischemic liver and the mechanism underlying its effect. Firstly, C57BL/6 mice were subjected to oral administration of CP-470,711 (5 mg/kg body weight/day for five days) and 70% hepatic I/R. Next the present study further investigated the changes in liver function, histology, inflammation, apoptosis and necrosis; the cytosolic adenosine triphosphate (ATP) and nictotinamide adenine dinucleotide [NAD(H)] contents and the protein level of caspase 3 and sirtuin 1 (SIRT1). The data demonstrated that sorbitol dehydrogenase inhibitor (SDI)-administration significantly alleviated I/R-induced liver injury, palliated histological changes and lowered the level of hepatocyte apoptosis and necrosis. In addition, SDI-pretreatment in ischemic liver markedly maintained the cytosolic ATP and NAD(H) proportion, enhanced SIRT1 and suppressed the activation of caspase 3 at the protein level. The findings in the present study revealed that the flux through SDH may render the liver more vulnerable to I/R-induced injury and interventions targeting this enzyme may provide a novel adjunctive approach to protect from severe tissue injury following liver ischemia.

Inhibition of sorbitol dehydrogenase by nucleosides and nucleotides

Sorbitol dehydrogenase inhibitors have been found to prevent, or alleviate, various secondary complications of diabetes mellitus. In the present study, the effects of nucleosides and nucleotides on the rate of sorbitol oxidation catalyzed by the sheep liver enzyme were studied by steady-state kinetics at pH 7.4. Various such compounds, including ATP and the 2′-deoxy-analogues of ATP, ADP and AMP, reversibly inhibit enzyme activity by formation of enzyme–coenzyme-inhibitor ternary complexes. In each case, no deviations from linearity were seen in the double-reciprocal plots using sorbitol or NAD+ as the varied substrate and there was a linear relationship between inhibitor concentration and the observed inhibitory effects. Sorbitol was docked into a model of the sheep SDH-NAD+ complex based upon the structure of the human SDH-NAD+ holoenzyme. The resulting structure of the ternary complex of sheep SDH, NAD+ and sorbitol (PMDB ID code PM 0078068) shows that the reactive C-2 hydroxyl group of sorbitol is oriented toward the 4′-position of the nicotinamide moiety of the coenzyme, and that the adjacent primary hydroxyl group of sorbitol interacts with the catalytic zinc. The results indicate that the ribose moiety of the inhibitor structures is an important determinant for the observed effects. Specifically, the 2′-position of the ribose ring exerts an effect with respect to inhibitor potency.

Osmotic stress, not aldose reductase activity, directly induces growth factors and MAPK signaling changes during sugar cataract formation

In sugar cataract formation in rats, aldose reductase (AR) activity is not only linked to lenticular sorbitol (diabetic) or galactitol (galactosemic) formation but also to signal transduction changes, cytotoxic signals and activation of apoptosis. Using both in vitro and in vivo techniques, the interrelationship between AR activity, polyol (sorbitol and galactitol) formation, osmotic stress, growth factor induction, and cell signaling changes have been investigated. For in vitro studies, lenses from Sprague Dawley rats were cultured for up to 48 h in TC-199-bicarbonate media containing either 30 mM fructose (control), or 30 mM glucose or galactose with/without the aldose reductase inhibitors AL1576 or tolrestat, the sorbitol dehydrogenase inhibitor (SDI) CP-470,711, or 15 mM mannitol (osmotic-compensated media). For in vivo studies, lenses were obtained from streptozotocin-induced diabetic Sprague Dawley rats fed diet with/without the ARIs AL1576 or tolrestat for 10 weeks. As expected, lenses cultured in high glucose/galactose media or from untreated diabetic rats all showed a decrease in the GSH pool that was lessened by ARI treatment. Lenses either from diabetic rats or from glucose/galactose culture conditions showed increased expression of basic-FGF, TGF-β, and increased signaling through P-Akt, P-ERK1/2 and P-SAPK/JNK which were also normalized by ARIs to the expression levels observed in non-diabetic controls. Culturing rat lenses in osmotically compensated media containing 30 mM glucose or galactose did not lead to increased growth factor expression or altered signaling. These studies indicate that it is the biophysical response of the lens to osmotic stress that results in an increased intralenticular production of basic-FGF and TGF-β and the altered cytotoxic signaling that is observed during sugar cataract formation.

Inhibition of Partially Purified Sorbitol Dehydrogenase Activity From Sera of Patients With Type I Diabetes

In this research Sorbitol dehydrogenase (SDH) was partially purified from sera of patients with type I diabetes mellitus by dialysis and ion exchange chromatography step by step. One peak of SDH activity was obtained with specific activity of 40.065 unit/mg protein and with purification fold of 98.9 compared to crud enzyme. Inhibition of SDH was studied by Glibenclamide and Rosiglitazone drugs, the best concentration of both inhibiters was 6mM. The mechanism of SDH inhibition by using both drugs were noncompetitive. There is no change in Km value 100 mM. Vmax value without inhibitor was 22.175 but 13.634 and 14.615 unit/ml with Glibenclamide and Rosiglitazone respectively. Accordingly, the inhibition constant Ki was calculated and appeared 7mM for both inhibitors above. Finally, we propose that action of these drugs may contribute to decrease patients with type I diabetes complications through inhibition SDH which plays an important role in polyol pathway.

Pharmacokinetics, Pharmacodynamics, Tolerability, and Safety of a Novel Sorbitol Dehydrogenase Inhibitor in Healthy Participants

Increased glucose flux through the polyol pathway and the resultant oxidative stress is thought to be a major mechanistic contributor to microvascular diabetic complications. Inhibition of flux through this pathway can be blocked through inhibition of either of 2 enzymes, aldose reductase (AR) or sorbitol dehydrogenase (SDH). This report describes the pharmacokinetics, biomarker pharmacodynamics, and safety of CP-642,931, a potent and specific sorbitol dehydrogenase inhibitor (SDI). CP-642,931 was administered for 7 days to 57 healthy volunteers in doses ranging from 1 to 35 mg daily. After the 35-mg dose, CP-642,931 showed a t((1/2)) of 20.1 hours and t(max) at 0.5 to 1.25 hours. After a 35-mg dose, maximum inhibition of SDH was 91% (on days 1 and 7), and maximum serum sorbitol increase was 152-fold on day 7 compared to control. Five participants discontinued the study due to adverse events, including myalgia, muscle spasm, and muscle fatigue. All symptoms resolved in all but 1 participant, who continued to report intermittent muscle fasciculations upon follow-up. In conclusion, CP-642,931 is a potent and specific SDI that is rapidly absorbed through the oral route and effectively inhibits SDH. However, the drug is not well tolerated due to adverse neuromuscular effects.

Polyol pathway contributes to the acute hyperglycemia‐induced contractile dysfunction in perfused heart from rat

The polyol pathway, consisting of aldose reductase (AR) and sorbitol dehydrogenase (SDH), is an alternate metabolic route that converts excess glucose to fructose. Previously, inhibition of AR was found to protect diabetic mice hearts from contractile dysfunction, suggesting that the polyol pathway contributes to hyperglycemia‐induced contractile dysfunction. In this report we show that the polyol pathway also contributes to acute hyperglycemia‐induced cardiac contractile dysfunction. Isolated rat hearts were perfused with either Krebs' buffer containing 10 μM AR inhibitor, Fidarestat, or 1 μM SDH inhibitor, CP‐170,711, and subjected to acute hyperglycemia by perfusing with high glucose medium (33.3 mM) for 2 hours. We find that acute hyperglycemia‐induced contractile dysfunction of the isolated perfused hearts is improved by pharmacological inhibition of the polyol pathway. Under acute hyperglycemia, SERCA is inactivated by the tyrosine nitration, which is contributed by high level of peroxynitrite. However, the activity of NCX is increased, and the activation is probably contributed by reactive oxygen species. All these abnormalities were attenuated by treatment with ARI or SDI. Thus, during acute hyperglycemia, polyol pathway‐induced depletion of GSH and increased level of superoxide probably inactivate SERCA, and stimulate NCX, leading to the abnormalities in contractile function.

Polyol pathway impairs the function of SERCA and RyR in ischemic-reperfused rat hearts by increasing oxidative modifications of these proteins

A number of studies have shown that the polyol pathway, consisting of aldose reductase (AR) and sorbitol dehydrogenase (SDH), contributes to ischemia–reperfusion (I/R)-induced myocardial infarction due to depletion of ATP. In this report we show that the polyol pathway in I/R heart also contributes to the impairment of sacro/endoplasmic reticulum Ca2+-ATPase (SERCA) and ryanodine receptor (RyR), two key players in Ca2+ signaling that regulate cardiac contraction. Rat hearts were isolated and retrogradely perfused with either Krebs' buffer containing 1 μM AR inhibitor, zopolrestat, or 200 nM SDH inhibitor, CP-170,711, and challenged by 30 min of regional ischemia and 45 min of reperfusion. We found that post-ischemic contractile function of the isolated perfused hearts was improved by pharmacological inhibition of the polyol pathway. I/R-induced contractile dysfunction is most likely due to impairment in Ca2+ signaling and the activities of SERCA and RyR. All these abnormalities were significantly ameliorated by treatment with ARI or SDI. We showed that the polyol pathway activities increase the level of peroxynitrite, which enhances the tyrosine nitration of SERCA and irreversibly modifies it to form SERCAC674-SO3H. This leads to reduced level of S-glutathiolated SERCA, contributing to its inactivation. The polyol pathway activities also deplete the level of GSH, leading to decreased active RyR, the S-glutathiolated RyR. Thus, in I/R heart, inhibition of polyol pathway improved the function of SERCA and RyR by protecting them from irreversible oxidation.

Polyol Formation in Cell Lines of Rat Retinal Capillary Pericytes and Endothelial Cells (TR-rPCT and TR-iBRB)

The two most widely investigated animal models for diabetic retinopathy (DR) are the rat and dog. In dogs, aldose reductase (AR) is present only in retinal capillary pericytes and their destruction has been linked to polyol accumulation and resulting apoptosis. Since both rat capillary pericytes and endothelial cells have been reported to contain AR, the role of polyol pathway activity in capillary cell destruction has been investigated in rat retinal capillary pericyte (TR-rPCT) and endothelial (TR-iBRB) cells. TR-rPCT and TR-iBRB cell lines were recloned and their identities were reconfirmed by characteristic immunostaining. Cells were cultured up to 72 h in media containing 50 mM glucose or galactose with/without the AR inhibitors or a sorbitol dehydrogenase inhibitor (SDI) or with 30 mM 3-fluoro-3-deoxyglucose. Polyol levels were determined by HPLC or (19)F-NMR. Apoptosis was detected with TUNEL/DAPI staining. Smooth muscle actin is present only in pericytes while only endothelial cells stain for von Willebrand factor and accumulate acetylated low-density lipoprotein. AR is present in both cells but AR levels are lower in endothelial cells. Aldehyde reductase is also present in both cells. Cells cultured in 50 mM glucose or galactose show significant polyol accumulation in pericytes but endothelial cells show little accumulation of galactitol and no accumulation of sorbitol. Sorbitol accumulation in pericytes resulted in increased cellular permeability and increased TUNEL staining, which was reduced by AR inhibition. Although both rat retinal pericytes and endothelial cells contain AR, sorbitol accumulation and TUNEL staining primarily occur in pericytes and are inhibited by AR inhibitors.

Comparison of the effects of an aldose reductase inhibitor and a sorbitol dehydrogenase inhibitor on nerve function in streptozotocin-diabetic rat

Comparison of the effects of an aldose reductase inhibitor and a sorbitol dehydrogenase inhibitor on nerve function in streptozotocin-diabetic rat

Inhibitors of aldose reductase and sorbitol dehydrogenase mitigate hyperglycemia‐induced arteriolar dysfunction

Hyperglycemia by activating the polyol pathway elicits increases in intracellular sorbitol and fructose concentrations. Previously we showed that in isolated arterioles administration of sorbitol (10−7 M) elicited oxidative stress, which interferes with nitric oxide (NO) bioavailability and thus dilations. We hypothesized that an elevated level of fructose also contributes to the development of hyperglycemia‐induced dysfunction of microvessels. In isolated rat gracilis muscle arterioles (~150 μm at 80mmHg), high glucose treatment (25 mM for 30 min) reduced flow dependent dilation (max: 39 ±2 vs. 15 ±1 %), which was significantly reversed by an aldose reductase inhibitor, zopolrestat (max: 27±2 %) and partially by a sorbitol dehydrogenase inhibitor (SDI), CP‐470,711 (max: 23±3 %). Also, SDI ‐ in part ‐ restored dilations to flow in the presence of elevated sorbitol. Incubation of arterioles with fructose (10−4 M) reduced flow dependent dilations (max: 39±2 vs. 12±2 %), which were not further affected by inhibition of NO synthase by L‐NAME, but were partially reversed by SOD/CAT and PGH2/TXA2 receptor blocker SQ‐29548. Thus, we suggest that hyperglycemia ‐ by elevating intracellular sorbitol and fructose levels ‐ induces oxidative stress, which interferes with NO‐mediated dilations and promotes PGH2/TXA2 release. Thus the polyol pathway may contribute to the development of microvascular dysfunction in diabetes mellitus.(Grants: Hungarian SRF/OTKA T48376, K71591; HSC/ETT 364/2006 and AHA F. Aff. 0855910D, USA)

Polyol pathway and modulation of ischemia-reperfusion injury in Type 2 diabetic BBZ rat hearts.

We investigated the role of polyol pathway enzymes aldose reductase (AR) and sorbitol dehydrogenase (SDH) in mediating injury due to ischemia-reperfusion (IR) in Type 2 diabetic BBZ rat hearts. Specifically, we investigated, (a) changes in glucose flux via cardiac AR and SDH as a function of diabetes duration, (b) ischemic injury and function after IR, (c) the effect of inhibition of AR or SDH on ischemic injury and function. Hearts isolated from BBZ rats, after 12 weeks or 48 weeks diabetes duration, and their non-diabetic littermates, were subjected to IR protocol. Myocardial function, substrate flux via AR and SDH, and tissue lactate:pyruvate (L/P) ratio (a measure of cytosolic NADH/NAD+), and lactate dehydrogenase (LDH) release (a marker of IR injury) were measured. Zopolrestat, and CP-470,711 were used to inhibit AR and SDH, respectively. Myocardial sorbitol and fructose content, and associated changes in L/P ratios were significantly higher in BBZ rats compared to non-diabetics, and increased with disease duration. Induction of IR resulted in increased ischemic injury, reduced ATP levels, increases in L/P ratio, and poor cardiac function in BBZ rat hearts, while inhibition of AR or SDH attenuated these changes and protected hearts from IR injury. These data indicate that AR and SDH are key modulators of myocardial IR injury in BBZ rat hearts and that inhibition of polyol pathway could in principle be used as a therapeutic adjunct for protection of ischemic myocardium in Type 2 diabetic patients.

Gene deletion and pharmacological inhibition of aldose reductase protect against retinal ischemic injury

Retinal ischemic injury is common in patients with diabetes, atherosclerosis, hypertension, transient ischemia attack and amaurosis fugax. Previously, signs of ischemic stress, such as pericyte loss, blood–retinal barrier breakdown and neovascularization, which can lead to occlusion of retinal vessels, have been prevented in diabetic db/db mice with aldose reductase (AR) null mutation. To determine the role in retinal ischemic injury of AR and sorbitol dehydrogenase (SDH), the first and second enzymes in the polyol pathway, mice with deletion of AR (AR−/−) or SDH-mutation (SDH−/−), or C57BL/6N mice treated with AR or SDH inhibitors were subjected to transient retinal artery occlusion (2h of occlusion and 22h of reperfusion) by the intraluminal suture method. Neuronal loss and edema observed in wildtype (AR+/+) retinas after transient ischemia were prevented in the retinas of AR−/− mice or C57BL/6N mice treated with an AR inhibitor, Fidarestat. Fewer TUNEL-positive cells and smaller accumulations of nitrotyrosine and poly(ADP-ribose) were also observed in the retinas of AR−/− mice. However, SDH−/− mice and C57BL/6N mice treated with SDH inhibitor, CP-470,711, were not protected against ischemia-induced retinal damage. Taken together, AR contributes to retinal ischemic injury through increased edema and free radical accumulation. Therefore, AR inhibition should be considered for the treatment of retinal ischemic injury often observed in diabetic patients.