The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Thomas C Hohman - One of the best experts on this subject based on the ideXlab platform.
-
Molecular mechanism(s) of insulin action on the expression of the angiotensinogen gene in kidney proximal tubular cells.
Journal of the Renin-Angiotensin-Aldosterone System, 2020Co-Authors: Xiao-hua Wu, Thomas C Hohman, Xing Chen, Shao-ling Zhang, Li Pang, Catherine To, Tian-tian Wang, János G. Filep, John S.d. ChanAbstract:To investigate the molecular mechanism(s) of insulin action on the expression of the angiotensinogen (ANG) gene in kidney proximal tubular cells, we constructed a fusion gene, pOGH (hANG N1064/+27), containing the 5'-flanking regulatory sequence of the human ANG gene fused with the human growth hormone (hGH) gene as a reporter and stably integrated the fusion gene into the opossum kidney (OK) cell genomes. The level of expression of pOGH (hANG N-1064/+27) was quantified by the amount of immunoreactive hGH secreted into the medium. The addition of a high level of D(+)-glucose (25 mM) or phorbol 12-myristate 13-acetate (PMA, 10 -7 M) stimulated the expression of the fusion gene in OK cells. The stimulatory effect of glucose (25 mM) was blocked by insulin and Tolrestat (an inhibitor of aldose reductase). Tolrestat also inhibited the increase of cellular DAG and PKC activity stimulated by 25 mM glucose. While insulin did not affect the cellular DAG and PKC activity, it did block the stimulatory effect of high glucose (25 mM) and PMA on the expression of the fusion gene. Finally, PD98059 (an inhibitor of mitogen-activated protein kinase kinase (MEK)) enhanced the stimulatory effect of high levels of glucose and blocked the inhibitory effect of insulin on the expression of the fusion gene as well as on the phosphorylation of MEK and mitogen-activated protein kinase (MAPK). In contrast, Wortmannin (an inhibitor of phosphatidylinositol-3-kinase) did not block the inhibitory effect of insulin on the ANG gene expression. These studies demonstrate that the action of insulin, blocking the stimulatory effect of a high level of D(+)-glucose (25 mM) on the ANG gene expression is mediated, at least in part, via the 5'flanking region of the ANG gene and MAPK signal transduction pathway.
-
influence of Tolrestat on the defective leukocyte endothelial interaction in experimental diabetes
European Journal of Pharmacology, 2000Co-Authors: Jose Walber Miranda Costa Cruz, Thomas C Hohman, M A Oliveira, Zuleica Bruno FortesAbstract:One of the most devastating secondary complications of diabetes is the blunted inflammatory response that becomes evident even in the very early stages of poorly controlled diabetes mellitus. While the etiology of this diminished response is not clearly understood, it has been linked to a decrease in the respiratory burst of neutrophils, as well as a decrease in microvessel response to inflammatory mediators and defective leukocyte–endothelial interactions. Using video microscopy to visualize vessels of the internal spermatic fascia, we have characterized leukocyte–endothelial interactions in alloxan-induced diabetic and in galactosemic rats by quantitating the number of leukocytes rolling along the venular endothelium and the number of leukocytes sticking to the vascular wall after topical application of zymosan-activated plasma or leukotriene B4 (1 ng/ml), as well as after the application of a local irritant stimulus (carrageenan, 100 μg). We observed that while 33 days of alloxan-induced diabetes or 7 days of galactosemia had no effect on total or differential leukocyte counts and on the wall shear rate, both treatments significantly (P<0.001) reduced the number of leukocytes rolling along the venular endothelium by about 70% and the number of adhered leukocytes in postcapillary venules by 60%. These effects were not observed in diabetic and galactosemic animals treated with an aldose reductase inhibitor. The results suggest that impaired leukocyte–endothelial cell interactions are a consequence of an enhanced flux through the polyol pathway.
-
Probing the inhibitor‐binding site of aldose reductase with site‐directed mutagenesis
FEBS Journal, 1998Co-Authors: Thomas C Hohman, Ossama El-kabbani, Michelle H. Mcgowan, Michael S. Malamas, Tatiana Putilina, Yi-qun Wane, Deborah CarperAbstract:Aldose reductase (AR) has been implicated in the etiology of the secondary complications of diabetes, and enzyme inhibitors have been proposed as therapeutic agents. While effectively preventing the development of diabetic complications in animals, results from clinical studies of AR inhibitors have been disappointing, possibly due to poor potency in man. To assist in the design of more potent and specific inhibitors, crystallographic studies have attempted to identify enzyme-inhibitor interactions. Resolution of crystal complexes has suggested that the inhibitors bind to the enzyme active site and are held in place through hydrogen bonding and van der Waals interactions formed within two hydrophobic pockets. To confirm and extend these findings we quantified inhibitor activity with single, site-directed, mutant, human AR enzymes in which the apolar active-site residues tryptophan 20, −79, −111 and phenylalanine 115 were replaced with alanine or tyrosine, decreasing the potential for van der Waals interactions. Consistent with molecular models, the inhibitory activity of Tolrestat, Sorbinil and Zopolrestat decreased 800−2000-fold when tested with the mutant enzyme in which Trp20 was replaced with alanine. Further, alanine substitution for Trp111 decreased Zopolrestat's activity 400-fold, while mutations to Trp79 and Phe115 had little effect on the activity of any of the inhibitors. The alanine mutation at Trp111 had no effect on Tolrestat's activity but decreased the activity of Sorbinil by about 1000-fold. These latter effects were unanticipated based on the number of non-bonded interactions between the inhibitors, Tolrestat and Sorbinil, and Trp20 and Trp111 that have been identified in the crystal structures. In spite of these unexpected findings, our results are consistent with the hypothesis that AR inhibitors occupy the enzyme active site and that hydrophobic interactions between the enzyme and inhibitor contribute to inhibitor binding stability.
-
correction of nerve conduction and endoneurial blood flow deficits by the aldose reductase inhibitor Tolrestat in diabetic rats
Journal of The Peripheral Nervous System, 1998Co-Authors: M A Cotter, Norman E Cameron, Thomas C HohmanAbstract:Increased activation of the first half of the polyol pathway, the conversion of glucose to sorbitol by aldose reductase, has been implicated in aldose reductase inhibitor-preventable neurochemical changes that may contribute to the aetiology of diabetic neuropathy. Tolrestat has been used as a standard aldose reductase inhibitor to dissect out polyol pathway-dependent mechanisms in many experimental studies; however, doubt has been cast upon its ability to prevent nerve conduction velocity deficits in diabetic rats. Nerve dysfunction has also been linked to abnormal endoneurial blood flow and oxygenation via increased vasa nervorum polyol pathway flux. The aim of this study was to test whether Tolrestat could correct sciatic conduction velocity and perfusion defects in diabetic rats. Sciatic motor conduction velocity, 21% reduced by 1 month of streptozotocin-induced diabetes, was corrected by 23% and 84% with 1 month of Tolrestat treatment at doses of 7 and 35 mg/kg/day respectively. Endoneurial blood flow, 44-52% reduced by untreated diabetes, was within the nondiabetic range with high-dose Tolrestat treatment and the flow deficit was 39% corrected by the low dose. Sciatic sorbitol and fructose concentrations were approximately 13-fold and approximately 4-fold elevated by untreated diabetes. This was 32-50% attenuated by low-dose Tolrestat and sorbitol and fructose content was suppressed below the nondiabetic level by high dose treatment. A 58% nerve myo-inositol deficit was partially (32%) corrected by high-dose Tolrestat treatment. We conclude that Tolrestat restores defective conduction and blood flow in diabetic rats and is a good pharmacological tool for studies on polyol pathway effects in peripheral nerve.
-
the efficacy of Tolrestat in the treatment of diabetic peripheral neuropathy a meta analysis of individual patient data
Diabetes Care, 1996Co-Authors: Antonio Nicolucci, Jay G Graepel, Thomas C Hohman, Fabrizio Carinci, Frederick L Ferris, John M LachinAbstract:OBJECTIVE The aim of this meta-analysis was to review the existent evidence on the effectiveness of Tolrestat in the treatment of diabetic peripheral neuropathy. RESEARCH DESIGN AND METHODS Individual patient data on 738 subjects from the three randomized clinical trials published on this topic were analyzed using changes in motor nerve conduction velocities (NCVs) as endpoints. Nerves investigated included median, ulnar, tibial, and peroneal. RESULTS The pooled analysis of NCV taken as a continuous measurement showed a significant treatment effect, the magnitude of this benefit being approximately equal to 1 m/s for all the nerves investigated. When looking at the proportion of patients experiencing a loss of NCV of at least 1 or 2 m/s in at least two out of the four nerves investigated, it emerged that treatment reduced by > 40% the risk of such outcomes after adjusting for patients9 characteristics. The odds ratios relative to the placebo group were 1.82 (1.30–2.52) and 1.70 (1.15–2.48) for a decrease of 1 and 2 m/s, that is, placebo-treated patients have an 82 and 70% increased risk for a loss of nerve function of 1 and 2 m/s, respectively. No statistically significant difference in treatment effect emerged after stratification according to baseline motor NCV and glycated hemoglobin levels. CONCLUSIONS After a treatment duration ranging between 24–52 weeks, patients treated with Tolrestat had a reduced risk for developing nerve function loss compared with placebo-treated patients. Future long-term trials are needed to evaluate the impact of the treatment on more clinically meaningful endpoints such as the development of foot complications.
Adam F Cohen - One of the best experts on this subject based on the ideXlab platform.
-
Tolrestat pharmacokinetic and pharmacodynamic effects on red blood cell sorbitol levels in normal volunteers and in patients with insulin dependent diabetes
Clinical Pharmacology & Therapeutics, 1995Co-Authors: Jean M T Van Griensven, Soong T Chiang, Herman H. P. J. Lemkes, William J Jusko, Ria Kroon, Christian J Verhorst, Adam F CohenAbstract:Objectives To examine the effect of diabetes mellitus on the pharmacokinetics of Tolrestat and to investigate its effect on red blood cell sorbitol levels according to a new pharmacodynamic model for this class of drugs. Methods Single and multiple doses of Tolrestat (200 mg/twice a day) were administered to 12 patients with insulin-dependent (type I) diabetes and 12 healthy volunteers in an open parallel trial. Results Tolrestat disposition was characterized by first-order absorption and biexponential disposition: In normal subjects the terminal disposition half-life (t12) was 13 ± 3 hours (mean ± SD) and the apparent oral clearance (CL/F) was 48 ± 9 ml/hr/kg, similar to the values in patients with type I diabetes mellitus (t12 = 14 ± 4 hours; CL/F = 55 ± 10 ml/hr/kg). Red blood cell sorbitol concentrations, which declined because of Tolrestat's inhibition of aldose reductase, were characterized by an indirect-response model including a 50% inhibition constant (IC50) for production of sorbitol by aldose reductase. The removal of sorbitol (kout) was slower in patients with diabetes. The plasma IC50 averaged 2.0 ± 1.3 μg/ml in normal subjects and 2.5 ± 1.9 μg/ml in patients with diabetes. IC50 values expressed in free (unbound) concentrations (fu = 0.64%), which ranged from 12 to 16 ng/ml, were similar to the in vitro IC50 for inhibition of sorbitol accumulation in human red blood cells. Conclusions Tolrestat pharmacokinetics were similar in normal subjects and in patients with diabetes; however, the patients with diabetes had higher baseline sorbitol levels (11 versus 5 nmol/ml for normal subjects) and slower sorbitol efflux rates. The proposed biochemically realistic, dynamic model characterized well the red blood cell sorbitol response patterns after administration of single and multiple doses of Tolrestat. Clinical Pharmacology & Therapeutics (1995) 58, 631–640; doi:
Francesco Belfiore - One of the best experts on this subject based on the ideXlab platform.
-
In Vitro Inhibition of Glucose Phosphorylation by an Aldose-Reductase Inhibitor (Tolrestat) in Some Non–Insulin-Sensitive Rabbit Tissues
Journal of Diabetes and Its Complications, 1999Co-Authors: Silvia Iannello, Cavaleri A, Camuto M, Francesco BelfioreAbstract:Abstract We have previously demonstrated that in some non–insulin-sensitive tissues (capillaries of eel swimbladder Rete mirabile, and rabbit eye choroidocapillary lamina, optic nerve, retina, and lens) glucose phosphorylation increases with the increase in the concentration of glucose, a characteristic relevant to the hyperglycemia of diabetes. In the present research we demonstrate an effect of the aldose reductase inhibitor, Tolrestat, on the glucose-phosphorylating activity of rabbit lens and optic nerve, by assaying the enzyme activity of tissue homogenates (in the presence of 10 mmol/L glucose) without or with 10 min preincubation with increasing concentrations of Tolrestat (2, 4, and 8 μmol/L). In the lens, a 18% inhibition ( p p p
-
in vitro inhibition of glucose phosphorylation by an aldose reductase inhibitor Tolrestat in some non insulin sensitive rabbit tissues
Journal of Diabetes and Its Complications, 1999Co-Authors: Silvia Iannello, Massimo Camuto, Antonina Cavaleri, Francesco BelfioreAbstract:Abstract We have previously demonstrated that in some non–insulin-sensitive tissues (capillaries of eel swimbladder Rete mirabile, and rabbit eye choroidocapillary lamina, optic nerve, retina, and lens) glucose phosphorylation increases with the increase in the concentration of glucose, a characteristic relevant to the hyperglycemia of diabetes. In the present research we demonstrate an effect of the aldose reductase inhibitor, Tolrestat, on the glucose-phosphorylating activity of rabbit lens and optic nerve, by assaying the enzyme activity of tissue homogenates (in the presence of 10 mmol/L glucose) without or with 10 min preincubation with increasing concentrations of Tolrestat (2, 4, and 8 μmol/L). In the lens, a 18% inhibition ( p p p
-
In vitro inhibition of glucose phosphorylation by an aldose-reductase inhibitor (Tolrestat) in some non-insulin-sensitive rabbit tissues
Journal of Diabetes and its Complications, 1999Co-Authors: Silvia Iannello, Massimo Camuto, Antonina Cavaleri, Francesco BelfioreAbstract:We have previously demonstrated that in some non-insulin-sensitive tissues (capillaries of eel swimbladder Rete mirabile, and rabbit eye choroidocapillary lamina, optic nerve, retina, and lens) glucose phosphorylation increases with the increase in the concentration of glucose, a characteristic relevant to the hyperglycemia of diabetes. In the present research we demonstrate an effect of the aldose reductase inhibitor, Tolrestat, on the glucose-phosphorylating activity of rabbit lens and optic nerve, by assaying the enzyme activity of tissue homogenates (in the presence of 10 mmol/L glucose) without or with 10 min preincubation with increasing concentrations of Tolrestat (2, 4, and 8 μmol/L). In the lens, a 18% inhibition (p < 0.01) was observed in the presence of 8 μmol/L Tolrestat. In the optic nerve, a 12% (p < 0.05) and a 21% (p < 0.01) reduction was recorded at 4 and 8 μmol/L Tolrestat, respectively. Significant inverse correlations existed between the concentration of Tolrestat and the phosphorylation rate of glucose of rabbit lens and optic nerve. The dose-dependent inhibition of glucose phosphorylation observed by us suggests that the inhibitory action of Tolrestat on glucose metabolism extends beyond the well-known effects of this compound on the polyol pathway, and might contribute to the refraining action of Tolrestat on the development and progression of late diabetic complications in non-insulin- sensitive tissues. Copyright (C) 1999 Elsevier Science Inc.
Xiaoling Xu - One of the best experts on this subject based on the ideXlab platform.
-
Tolrestat acts atypically as a competitive inhibitor of the thermostable aldo keto reductase tm1743 from thermotoga maritima
FEBS Letters, 2020Co-Authors: Chenyun Zhang, Chao Wang, Zhiguo Wang, Jiejie Shen, Wanrong Tang, Xin Zhang, Xiaoling XuAbstract:Tolrestat and epalrestat have been characterized as noncompetitive inhibitors of aldo-ketone reductase 1B1 (AKR1B1), a leading drug target for the treatment of type 2 diabetes complications. However, clinical applications are limited for most AKR1B1 inhibitors due to adverse effects of cross-inhibition with other AKRs. Here, we report an atypical competitive binding and inhibitory effect of Tolrestat on the thermostable AKR Tm1743 from Thermotoga maritima. Analysis of the Tm1743 crystal structure in complex with Tolrestat alone and epalrestat-NADP(+) shows that Tolrestat, but not epalrestat, binding triggers dramatic conformational changes in the anionic site and cofactor binding pocket that prevents accommodation of NADP(+) . Enzymatic and molecular dynamics simulation analyses further confirm Tolrestat as a competitive inhibitor of Tm1743.
-
Tolrestat acts atypically as a competitive inhibitor of the thermostable aldo‐keto reductase Tm1743 from Thermotoga maritima
FEBS Letters, 2019Co-Authors: Chenyun Zhang, Chao Wang, Zhiguo Wang, Jiejie Shen, Wanrong Tang, Xin Zhang, Xiaoling XuAbstract:Tolrestat and epalrestat have been characterized as noncompetitive inhibitors of aldo-ketone reductase 1B1 (AKR1B1), a leading drug target for the treatment of type 2 diabetes complications. However, clinical applications are limited for most AKR1B1 inhibitors due to adverse effects of cross-inhibition with other AKRs. Here, we report an atypical competitive binding and inhibitory effect of Tolrestat on the thermostable AKR Tm1743 from Thermotoga maritima. Analysis of the Tm1743 crystal structure in complex with Tolrestat alone and epalrestat-NADP(+) shows that Tolrestat, but not epalrestat, binding triggers dramatic conformational changes in the anionic site and cofactor binding pocket that prevents accommodation of NADP(+) . Enzymatic and molecular dynamics simulation analyses further confirm Tolrestat as a competitive inhibitor of Tm1743.
Satish K. Srivastava - One of the best experts on this subject based on the ideXlab platform.
-
Contribution of Aldose Reductase to Diabetic Hyperproliferation of Vascular Smooth Muscle Cells
Diabetes, 2006Co-Authors: Sanjay Srivastava, Kota V. Ramana, Ravinder Tammali, Satish K. Srivastava, Aruni BhatnagarAbstract:The objective of this study was to determine whether the polyol pathway enzyme aldose reductase mediates diabetes abnormalities in vascular smooth muscle cell (SMC) growth. Aldose reductase inhibitors (Tolrestat or sorbinil) or antisense aldose reductase mRNA prevented hyperproliferation of cultured rat aortic SMCs induced by high glucose. Cell cycle progression in the presence of high glucose was blocked by Tolrestat, which induced a G0-G1 phase growth arrest. In situ, diabetes increased SMC growth and intimal hyperplasia in balloon-injured carotid arteries of streptozotocin-treated rats, when examined 7 or 14 days after injury. Treatment with Tolrestat (15 mg · kg−1 · day−1) diminished intimal hyperplasia and decreased SMC content of the lesion by 25%. Although Tolrestat treatment increased immunoreactivity of the lesion with antibodies raised against protein adducts of the lipid peroxidation product 4-hydroxy trans-2-nonenal, no compensatory increase in lesion fibrosis was observed. Collectively, these results suggest that inhibition of aldose reductase prevents glucose-induced stimulation of SMC growth in culture and in situ. Even though inhibition of aldose reductase increases vascular oxidative stress, this approach may be useful in preventing abnormal SMC growth in vessels of diabetic patients.
-
Activation of Nulcear Factor-κB by Hyperglycemia in Vascular Smooth Muscle Cells Is Regulated by Aldose Reductase
Diabetes, 2004Co-Authors: Kota V. Ramana, Sanjay Srivastava, Aruni Bhatnagar, Brian M. Friedrich, Satish K. SrivastavaAbstract:Activation of the polyol pathway has been linked to the development of secondary diabetic complications. However, the underlying molecular mechanisms remain unclear. To probe the contribution of this pathway, we examined whether inhibition of aldose reductase, which catalyzes the first step of the pathway, affects hyperglycemia-induced activation of the inflammatory transcription factor nuclear factor (NF)-κB. Treatment of vascular smooth muscle cells with the aldose reductase inhibitors Tolrestat and sorbinil prevented high-glucose–induced protein kinase C (PKC) activation, nuclear translocation of NF-κB, phosphorylation of IKK, and the increase in the expression of intracellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and aldose reductase. High-glucose–induced NF-κB activation was also prevented by the PKC inhibitors chelerythrine and calphostin C. Ablation of aldose reductase by small interference RNA (siRNA) prevented high-glucose–induced NF-κB and AP-1 activation but did not affect the activity of SP-1 or OCT-1. Stimulation with iso-osmotic mannitol activated NF-κB and increased the expression of aldose reductase but not ICAM-1 and VCAM-1. Treatment with aldose reductase inhibitors or aldose reductase siRNA did not affect mannitol-induced NF-κB or AP-1 activation. Administration of Tolrestat (15 mg · kg −1 · day −1 ) decreased the abundance of activated NF-κB in balloon-injured carotid arteries of diabetic rats. Collectively, these results suggest that inhibition of aldose reductase, which prevents PKC-dependent nonosmotic NF-κB activation, may be a useful approach for treating vascular inflammation caused by diabetes.
-
Aldose reductase regulates TNF-α-induced cell signaling and apoptosis in vascular endothelial cells
FEBS Letters, 2004Co-Authors: Kota V. Ramana, Aruni Bhatnagar, Satish K. SrivastavaAbstract:In this study, we examined the role of aldose reductase (AR) in regulating the cytotoxic effects of TNF-α on human umbilical vein endothelial cells. Inhibition of AR by sorbinil or Tolrestat prevented TNF-α-induced increase in Bax and Bak and the downregulation of Bcl-2. Inhibition of AR abrogated AP-1 DNA binding activity and prevented the activation of caspase-3, JNK, and p38 MAPK in cells stimulated by TNF-α. Exposure to TNF-α also induced apoptotic cell death, which was attenuated by AR inhibition or antisense ablation. These observations suggest that AR is a critical regulator of TNF-α-induced apoptotic signaling in endothelial cells.
-
Aldose reductase regulates TNF-alpha-induced cell signaling and apoptosis in vascular endothelial cells.
FEBS letters, 2004Co-Authors: Kota V. Ramana, Aruni Bhatnagar, Satish K. SrivastavaAbstract:In this study, we examined the role of aldose reductase (AR) in regulating the cytotoxic effects of TNF-alpha on human umbilical vein endothelial cells. Inhibition of AR by sorbinil or Tolrestat prevented TNF-alpha-induced increase in Bax and Bak and the downregulation of Bcl-2. Inhibition of AR abrogated AP-1 DNA binding activity and prevented the activation of caspase-3, JNK, and p38 MAPK in cells stimulated by TNF-alpha. Exposure to TNF-alpha also induced apoptotic cell death, which was attenuated by AR inhibition or antisense ablation. These observations suggest that AR is a critical regulator of TNF-alpha-induced apoptotic signaling in endothelial cells.
-
Involvement of cysteine residues in catalysis and inhibition of human aldose reductase. Site-directed mutagenesis of Cys-80, -298, and -303.
Journal of Biological Chemistry, 1992Co-Authors: J. Mark Petrash, Aruni Bhatnagar, Theresa M. Harter, Catherine S. Devine, Peter O. Olins, Satish K. SrivastavaAbstract:Abstract In order to study the potential role of cysteinyl residues in catalysis and inhibition of human aldose reductase, mutants containing cysteine to serine substitution at positions 80 (ALR2:C80S), 298 (ALR2:C298S), and 303 (ALR2:C303S) were constructed. Mutation of Cys298 resulted in the most profound changes, as ALR2:C298S displayed 4- to 5-fold elevation in K'm(NADPH), K'm(DL-glyceraldehyde), and kcat(DL-glyceraldehyde) relative to wild type aldose reductase as well as a 10-fold higher Ki for the aldose reductase inhibitor sorbinil. Wild type and mutant reductases were equally sensitive to Tolrestat, a structurally different reductase inhibitor. Carboxymethylation of the wild type enzyme or the C80S and C303S mutants led to a modest decrease in kcat as well as an increase in K'm(DL-glyceraldehyde) and Ki(sorbinil). These parameters were not significantly changed when ALR2:C298S was subjected to carboxymethylation. Lithium sulfate caused activation of ALR2:WT, C80S, and C303S but did not significantly affect the activity of ALR2:C298S. The differential sensitivity of wild type and mutant reductases to inhibition by sorbinil and Tolrestat, before and after carboxymethylation, indicates that these inhibitors bind at different sites. These results suggest that Cys-298 is present near the active site and constitutes a regulatory group which controls the catalytic activity and inhibitor sensitivity of the enzyme.
