Effects of lisinopril on streptozotocin-induced diabetic neuropathy in rats

Streptozotocin (STZ)-induced diabetic neuropathy in rats was monitored by measuring the motor nerve conduction velocity (MNCV) and histopathology of the tibial nerve. Pretreatment with lisinopril (2 mg/kg p.o., 5 days prior to STZ and continued for 10 weeks) significantly (p < 0.01) prevented deterioration of MNCV as compared to STZ-diabetic animals. Nerve sections from the lisinopril pretreated group revealed less structural damage as compared to STZ-diabetic rats. However lisinopril had no effect on blood sugar, i.e., it did not alter the diabetic state. It is concluded that lisinopril prevents the development of experimental diabetic neuropathy in STZ-induced diabetic rats.     

The effect of sorbinil, an aldose reductase inhibitor, on aortic function in control and streptozotocin-induced diabetic rats

1. The present study investigates the effect of treatment of 14-day streptozotocin-diabetic rats with the aldose reductase inhibitor, sorbinil, on changes ex vivo in aortic vasoconstriction and vasodilation. 2. Maximum contractile responses and aortic sensitivity to phenylephrine were significantly enhanced in aortae from 14-day diabetic rats, in accordance with our previous data. 3. Endothelium-dependent relaxations to carbachol were, in contrast, depressed, although endothelium-independent relaxations to forskolin and sodium nitroprusside were unaltered. 4. Sorbinil treatment of diabetic animals failed to prevent any of these diabetes-induced alterations in aortic function, and indeed exacerbated some of these alterations. In addition, sorbinil treatment caused altered aortic responses in control animals, which sometimes mirrored those found in diabetic animals. 5. It can be concluded that sorbinil may have actions in addition to, and independent of, polyol pathway inhibition. Thus, sorbinil may not be an effective tool for the investigation of aldose reductase inhibition within the vascular system of the rat.     

Effects of glucose, insulin or aldose reductase inhibition on responses to endothelin-1 of aortic rings from streptozotocin-induced diabetic rats.

1. This study investigated the constrictor responsiveness to endothelin-1 (ET-1, 0.1 nM-0.1 microM) of aortic rings (under 10 g resting tension in Krebs solution) from 2- and 6-week streptozotocin (STZ, 60 mg kg-1, i.v.)-induced diabetic rats and vehicle-treated control rats. 2. In aortae from 2- and 6-week STZ-treated rats, and their corresponding controls, removal of endothelium caused leftward shifts of ET-1 concentration-response curves without affecting maximum responses. 3. Maximum responses to ET-1 were reduced in aortae from both 2- and 6-week STZ-treated rats compared to those from control rats. Such reductions were still evident after removal of the endothelium. 4. Decreased responsiveness to ET-1 of aortae from 2-week STZ-treated rats was still evident after chronic treatment with the aldose reductase inhibitor epalrestat, but not after chronic insulin treatment or in aortae bathed in high glucose (30 mM) Krebs solution. 5. Decreased responsiveness to ET-1 of aortae from 6-week STZ-treated rats (compared with those from controls) was still evident after chronic epalrestat treatment and in high glucose Krebs solution. 6. These data suggest that the decreased responsiveness to ET-1 observed in aortae from 2- and 6-week STZ-induced diabetic rats is not due to abnormal activity of the polyol pathway. The altered responsiveness in aortae from 2-week diabetic rats (compared with those from control rats) may possibly be a manifestation of changes (adaptive or otherwise) which occur as a result of high glucose concentrations in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of a new aldose reductase inhibitor on diabetic complications in rats.

The effects of a new aldose reductase inhibitor, 7-fluoro-2-(N-methyl-N-carboxymethyl)sulfamoyl xanthone (BAL-ARI8, CAS 124066-40-6), on the diabetic complications of streptozotocin-induced diabetic rats were studied. The daily administration of BAL-ARI8 throughout the 8-week course of the experiment sharply decreased the sorbitol accumulation in the lens of the diabetic rats. The incidence of cataract formation was also reduced, being detected in only 45% of BAL-ARI8 treated animals, against the 100% of diabetic controls showing cataract after 8 weeks from diabetes onset. On the other hand, the serum glucose levels remained unchanged. In diabetic controls, there was about a 2.5-fold increase of the total protein urinary excretion during the 24 h. Treatment with BAL-ARI8 prevented up to 70% of this increase. Individual protein components were examined by polyacrylamide gel electrophoresis and quantitated by laser densitometric analysis. Diabetic-induced proteinuria primarily resulted from excretion of newly detected proteins with molecular weight in the range 30,000-60,000 D, together with an increase of albumin (25% of the total excretion) and the presence of new higher molecular weight proteins (greater than 66,000 D). BAL-ARI8 administration resulted in a shift of the protein profile back toward normality i.e. 73% of proteins with molecular weight below 30,000 D, 7.5% albumin and no proteins above 66,000 D. These results suggest that BAL-ARI8 may represent a therapeutic approach for the management of diabetic complications.     

醛糖还原酶抑制剂治疗糖尿病周围神经病变的临床观察

目的:观察醛糖还原酶抑制剂依帕司他治疗糖尿病周围神经病变(DPN)的疗效。方法:DPN患者90例,随机分为治疗组46例(口服依帕司他片),对照组44例(肌肉注射维生素B12),记录治疗前后患者的主观症状、体征及肌电图检查神经传导速度的改善情况。结果:经8周治疗后,证明依帕司他对糖尿病周围神经病变自觉症状、体征及周围神经传导速度的改善有较好疗效,其疗效优于对照组,两组疗效差异有显著性。结论:醛糖还原酶抑制剂依帕司他治疗糖尿病周围神经病变是一种安全、有效的药物。     

Computer-assisted design and synthesis of novel aldose reductase inhibitors

The design and synthesis of phenalene 26 (AY-31,358), an unsubstituted analogue of a tolrestat/ICI-105,552 computer-generated hybrid (7), are reported. Compound 7 was designed by the superimposition of the putative low-energy conformers of tolrestat (1) and ICI-105,552 (6). The more rigid aldose reductase inhibitor sorbinil (2) was used as a template to help discern a common pharmacophore in the three inhibitors. Compound 26 was synthesized as a model and was evaluated as an inhibitor of bovine lens aldose reductase. It was found to exhibit good in vitro activity as well as some in vivo activity in the nerve. It was expected that introduction of the trifluoromethyl and methoxy substituents would enhance the biological activity of model compound 26. As a result of a positive Ames test with 26, however, work has now been directed toward modifying the template in a way so as to eliminate the mutagenicity with retention of biological activity.     

Studies on WF-3681, a novel aldose reductase inhibitor. IV. Effect of FR-62765, a derivative of WF-3681, on the diabetic neuropathy in rats

Pharmacokinetic properties of WF-3681 and FR-62765 in rats were examined. FR-62765 showed higher peak concentrations in the plasma and higher concentrations in the sciatic nerve than WF-3681 when each compound was administered orally to rats. We therefore evaluated FR-62765 in rats with diabetic neuropathy. As a result, FR-62765 at 32 mg/kg/day administered for 3 weeks to streptozotocin-induced diabetic rats significantly prevented the accumulation of sorbitol in the sciatic nerve and the reduction of motor nerve conduction velocity in the tail. From these results it was concluded that the aldose reductase inhibitor FR-62765 might be a useful drug for diabetic neuropathy.     

Potential use of aldose reductase inhibitors to prevent diabetic complications

Reviewed are (1) the biochemical basis and pathophysiology of diabetic complications and (2) the structure-activity relationships, pharmacology, pharmacokinetics, clinical trials, and adverse effects of aldose reductase inhibitors (ARIs). ARIs are a new class of drugs potentially useful in preventing diabetic complications, the most widely studied of which have been cataracts and neuropathy. ARIs inhibit aldose reductase, the first, rate-limiting enzyme in the polyol metabolic pathway. In nonphysiological hyperglycemia the activity of hexokinase becomes saturated while that of aldose reductase is enhanced, resulting in intracellular accumulation of sorbitol. Because sorbitol does not readily penetrate the cell membrane it can persist within cells, which may lead to diabetic complications. ARIs are a class of structurally dissimilar compounds that include carboxylic acid derivatives, flavonoids, and spirohydantoins. The major pharmacologic action of an ARI involves competitive binding to aldose reductase and consequent blocking of sorbitol production. ARIs delay cataract formation in animals, but the role of aldose reductase in cataract formation in human diabetics has not been established. The adverse effects of ARIs include hypersensitivity reactions. Although the polyol pathway may not be solely responsible for diabetic complications, studies suggest that therapy with ARIs could be beneficial. Further research is needed to determine the long-term impact and adverse effects of ARIs in the treatment of diabetic complications.     

黄连素对糖尿病肾损伤大鼠肾功能、氧化应激、肾脏醛糖还原酶的影响

目的观察黄连素对链脲佐菌素诱导的糖尿病肾损伤大鼠肾功能保护作用,并从抗氧化应激、抑制肾脏醛糖还原酶活性及其基因表达等方面探讨黄连素抗糖尿病大鼠肾损伤的作用机制。方法用腹腔注射链脲佐菌素方法复制糖尿病大鼠肾损伤模型。随机分为正常对照组、模型对照组、黄连素组,每组10只。黄连素经口灌胃200 mg.kg-1.d-1,每周给药6 d,共12 wk。比较各组大鼠血糖、肾脏肥大指数(肾重/体重)、尿素氮(BUN)、血肌酐(Cr)、24h尿蛋白(UP24)等肾功能相关指标,比较各组血清超氧化物歧化酶(SOD)活性、脂质过氧化代谢产物丙二醛(MDA)含量、肾组织醛糖还原酶(AR)活性及其基因表达的改变。结果模型组大鼠血糖维持在较高水平、肾脏肥大指数、BUN、Cr、UP24等较正常组明显升高(P<0.05),血清SOD活性低下,MDA含量增加(P<0.05),肾脏AR活性与其基因表达明显升高(P<0.05)。黄连素组与模型组相比,能明显降低血糖、有效控制体重下降、明显改善肾脏肥大指数、BUN、Cr、UP24等指标(P<0.05),血清SOD活性增强,同时MDA含量减少(P<0.05),肾脏AR活性降低及AR mRNA水平下调(P<0.05)。结论对糖尿病肾损伤大鼠,黄连素在调节血糖的同时,可能通过提高机体抗氧化能力、减少肾脏AR活性与基因表达以抑制多元醇通路的激活发挥其肾功能的保护作用。     

Protective effects of bendazac lysine on diabetic peripheral neuropathy in streptozotocin-induced diabetic rats

1. Diabetic neuropathy is a many faceted complication of both type I and II diabetes. The aim of the present study was to investigate the effects of bendazac lysine (BDL), an anticataract drug, on experimental diabetic peripheral neuropathy (DPN) in rats. 2. Diabetes was induced in rats by intraperitoneal injection of 75 mg/kg streptozotocin (STZ) dissolved in 0.1 mol/L citrate buffer (pH 4.4). Bendazac lysine was administered to rats at doses of 50, 100 and 200 mg/kg twice a day for 12 weeks. 3. Diabetic rats without treatment showed hypopraxia, polydipsia, polyuria, slow weight gain, cataract, increased tail-flick threshold temperature, decreased motor nerve conduction velocity (nd induced pathological morphological changes of myelinated nerve fibres. All these symptoms were ameliorated in diabetic rats treated with BDL. Bendazac lysine ameliorated the blood glucose concentration, glycosylated haemoglobin levels and insulin levels in the plasma of diabetic rats, reduced aldose reductase activity in erythrocytes and advanced glycation end-products in both nerves and serum and increase the activity of glutathione peroxidase in the nerves and Na(+)/K(+)-ATPase in the nerves and erythrocytes. 4. Bendazac lysine exerts its protective effects against the progression of diabetic peripheral neuropathy in STZ-diabetic rats through multiple mechanisms and is a potential drug for the prevention of deterioration in DPN.     

Effects of aldose reductase inhibitors on antioxidant defense in rat and rabbit liver.

Aldose reductase has been implicated in the etiology of diabetic complications, atherosclerosis, and ischemia-reperfusion injury. Aldose reductase inhibitors are known to have species-dependent differences in biotransformation enzyme induction. Whether aldose reductase inhibitors, which have antioxidant potential, alter the oxidative stress pathway is unknown. This study has determined whether four daily ip treatments of either low (10 mg/kg) or high (50 mg/kg) doses of AL-1576 or AL-4114 alter the activities of the antioxidant defense enzymes catalase, glutathione reductase, glutathione peroxidase, superoxide dismutase, and the concentrations of reduced and oxidized glutathione in livers of normal rats and rabbits. There was no change in the concentration of thiobarbituric acid reactive substances in either rat or rabbit livers, indicating that lipid peroxidation was not increased by any treatment. Hepatic catalase, superoxide dismutase, and glutathione peroxidase activities and concentrations of reduced and oxidized glutathione were not significantly altered in rat, though glutathione reductase activity was increased after high doses of both drugs. However, in rabbit liver, glutathione reductase activity decreased in a dose-dependent manner after AL-4114 treatment, while superoxide dismutase and glutathione peroxidase activities decreased only after the low dose of AL-4114. Although AL-4114 and AL-1576 did not directly generate increased lipid peroxidation within normal rat and rabbit livers, some of the enzymes responsible for oxidative defense were altered, particularly in rabbit livers.     

Synthesis of flavonoids and their effects on aldose reductase and sorbitol accumulation in streptozotocin-induced diabetic rat tissues

Aldose reductase, the key enzyme of the polyol pathway, and oxidative stress are known to play important roles in the complications of diabetes. A drug with potent inhibition of aldose reductase and oxidative stress, therefore, would be a most promising drug for the prevention of diabetic complications. The purpose of this study was to develop new compounds with these dual-effects through synthesis of chalcone derivatives and by examining the structure-activity relationships on the inhibition of rat lens aldose reductase as well as on antioxidant effects. A series of 35 flavonoid derivatives were synthesized by Winget's condensation, oxidation, and reduction of appropriate acetophenones with appropriate benzaldehydes. The inhibitory activity of these derivatives on rat lens aldose reductase and their antioxidant effects, measured using Cu2+ chelation and radical scavenging activities on 1,1-diphenyl-picrylhydrazyl in-vitro, were evaluated. Their effect on sorbitol accumulation in the red blood cells, lenses and sciatic nerves of streptozotocin-induced diabetic rats was also estimated. Among the new flavonoid derivatives synthesized, those with the 2',4'-dihydroxyl groups in the A ring such as 2,4,2',4'-tetrahydroxychalcone (22), 2,2',4'-trihydroxychalcone (11), 2',4'-dihydroxy-2,4-dimethylchalcone (21) and 3,4,2',4'-tetrahydroxychalcone (18) were found to possess the highest rat lens aldose reductase inhibitory activity in-vitro, their IC50 values (concentration of inhibitors giving 50% inhibition of enzyme activity) being 1.6 x 10(-7), 3.8 x 10(-7), 4.0 x 10(-7) and 4.6 x 10(-7) M, respectively. All of the chalcones tested except 3, 18, 23 with o-dihydroxy or hydroquinone moiety showed a weak free radical scavenging activity. In the in-vivo experiments, however, compound 18 with o-dihydroxy moiety in the B ring showed the strongest inhibitory activity in the accumulation of sorbitol in the tissues. It also showed the strongest activity in transition metal chelation and free radical scavenging activity. Of the 35 4,2'-dihydroxyl and 2',4'-dihydroxyl derivatives of flavonoid synthesized, including chalcone, flavone, flavanone, flavonol and dihydrochalcone, some chalcone derivatives synthesized were found to possess aldose reductase inhibition and antioxidant activities in-vitro as well as inhibition in the accumulation of sorbitol in the tissues in-vivo. 3,4,2',4'-Tetrahydroxychalcone (18, butein) was the most promising compound for the prevention or treatment of diabetic complications.     

Selective irreversible inhibitors of aldose reductase.

A series of 5-substituted-1,3-dioxo-1H-benz[de]isoquinoline-2(3H)-acetic acid analogues have been examined as irreversible inhibitors of aldose reductase. The 5-alpha-bromoacetamide and 5-alpha-iodoacetamide analogues 5 and 6 gave irreversible inhibition of aldose reductase while the 5-alpha-chloroacetamide analogue 3 did not show this type of inhibition. Protection studies indicate that irreversible inhibitions are occurring at the inhibitor binding site. Comparative irreversible inhibition studies with rat lens aldose reductase (RLAR) and rat kidney aldehyde reductase (RKALR) indicate that 5-alpha-haloacetamide analogues 5 and 6 are much more effective inhibitors of RLAR.     

Permeability characteristics of novel aldose reductase inhibitors using rat jejunum in vitro.

The aim of this study was to estimate in vivo permeability and bioavailability of epalrestat and newly synthesized compounds with possible therapeutic activity as aldose enzyme inhibitors (ARIs). For this purpose permeability in vitro using rat jejunum mounted in side-by-side diffusion cells was determined. Tested substances were found to be low and moderately permeable and some of them were also substrates for efflux transporters. It was shown, that the higher efflux for some derivatives was due to MRP-2, but not Pgp involvement. Tested ARIs do not share the same efflux transporter with epalrestat, the only ARI currently on the market in Japan. The most permeable compound, a 2,6-difluoro-4-pyrrol-1ylphenol derivative, is not a substrate for efflux transporters and would therefore be the most promising lead compound for further investigation of potent ARIs.     

依帕司他对糖尿病大鼠肾脏醛糖还原酶活性、细胞凋亡及超微结构的影响

目的:研究醛糖还原酶(AR)、凋亡相关蛋白Bcl-2和Bax与糖尿病肾病的关系,探讨醛糖还原酶抑制剂(ARIs)依帕司他对糖尿病肾病的治疗作用。方法:雄性Wistar大鼠30只,随机平均分为3组:正常对照组、糖尿病模型组和依帕司他(10 mg.kg-1.d-1)治疗组,模型组和依帕司他组腹腔注射链脲佐菌素65 mg.kg-1诱发糖尿病。16周后,处死大鼠,分离晶体和肾脏,测定组织AR活性,观察Bcl-2和Bax的表达,取部分肾皮质电镜细胞计量、观察细胞凋亡的形态学变化。结果:与正常对照组相比,糖尿病模型组肾脏皮质AR活性明显升高(P<0.01),依帕司他治疗组AR活性明显较模型组降低(P<0.01),而血糖无明显变化。糖尿病模型组肾脏Bcl-2和Bax蛋白表达增加,依帕司他治疗组的Bcl-2蛋白表达较模型组增多,而Bax蛋白表达较模型组减少。透射电镜下见糖尿病模型组肾脏肾小管上皮细胞呈典型的凋亡形态学改变,依帕司他治疗组大鼠肾组织细胞凋亡改变明显减轻。糖尿病模型组肾小球基底膜增厚,系膜区域扩大,治疗组病变减轻。结论:AR过度激活可能通过促进Bcl-2和Bax蛋白的表达诱导细胞凋亡,而参与DN的发生与发展。依帕司他通过抑制醛糖还原酶活性,调节Bax和Bcl-2的表达抑制细胞凋亡,改善糖尿病大鼠肾脏结构与功能。     

Epalrestat: an aldose reductase inhibitor for the treatment of diabetic neuropathy

Diabetic neuropathy is one of the most common long-term complications in patients with diabetes mellitus, with a prevalence of 60-70% in the United States. Treatment options include antidepressants, anticonvulsants, tramadol, and capsaicin. These agents are modestly effective for symptomatic relief, but they do not affect the underlying pathology nor do they slow progression of the disease. Epalrestat is an aldose reductase inhibitor that is approved in Japan for the improvement of subjective neuropathy symptoms, abnormality of vibration sense, and abnormal changes in heart beat associated with diabetic peripheral neuropathy. Unlike the current treatment options for diabetic neuropathy, epalrestat may affect or delay progression of the underlying disease process. Data from experimental studies indicate that epalrestat reduces sorbitol accumulation in the sciatic nerve, erythrocytes, and ocular tissues in animals, and in erythrocytes in humans. Data from six clinical trials were evaluated, and it was determined that epalrestat 50 mg 3 times/day may improve motor and sensory nerve conduction velocity and subjective neuropathy symptoms as compared with baseline and placebo. Epalrestat is well tolerated, and the most frequently reported adverse effects include elevations in liver enzyme levels and gastrointestinal-related events such as nausea and vomiting. Epalrestat may serve as a new therapeutic option to prevent or slow the progression of diabetic neuropathy. Long-term, comparative studies in diverse patient populations are needed for clinical application.     

Effects of novel hydantoin derivatives with aldose reductase inhibiting activity on galactose-induced cataract in rats

Effects of novel aldose reductase inhibitors, M16209 (1-(3-bromobenzo[b]furan-2-ylsulfonyl)hydantoin) and M16287 (1-(3-chlorobenzo[b]furan-2-ylsulfonyl)hydantoin), on galactose-induced cataract formation in rats were investigated. Rats fed a 30% galactose diet developed lenticular opacity in the peripheral region by the 6th day of galactose feeding and showed gradual progression of opacity from the equator to the center of lenses. Histological study on the 15th day showed apparent lens fiber swelling and vacuolation predominantly in the equatorial and anterior cortical regions. Biochemical changes such as accumulation of galactitol, depletion of myo-inositol and decrease in glutathione (GSH) content in lenses preceded the appearance of opacity. Remarkable increase in NADPH content and decrease in NADP+ content, in addition to elevation of the ratio of Na+/K+, in lenses were also observed on the 15th day. Both M16209 and M16287 (10, 30 and 100 mg/kg/day, p.o.) dose-dependently ameliorated these morphological and biochemical changes except that restoration of myo-inositol content was incomplete. These results indicate that M16209 and M16287 can prevent galactose-induced cataract formation through amelioration of metabolic disorders and thus have high potential for clinical use in the treatment of some diabetic complications.     

The role of aldose reductase inhibitors in diabetic complications: recent trends

Pharmacological intervention of hyperglycemia-induced diabetic complications would be of great clinical significance since it is very difficult to maintain normoglycemia by any means in patients with diabetes mellitus. Several factors and pathways are involved in diabetic complications. One of the major contributory factors is aldose reductase. The beneficial effects of aldose reductase inhibitors in animal models have been reported. The clinical efficacy of these agents, however, is far from satisfactory and the reasons for this may vary. Recent advances in understanding the structure-based functioning, physiological and pathophysiological role of aldose reductase, the use of transgenic animal models and the abundant availability of human aldose reductase have greatly influenced the design and development of its inhibitors, which are highly selective, specific, potent and less toxic. Concurrently, other mechanisms involved in diabetic complications are being explored as targets for better therapeutic agents.     

Experimental validation and docking studies of flavone derivatives on aldose reductase involved in diabetic retinopathy, neuropathy, and nephropathy

The enzyme aldoreductase which plays an important role in pathogenesis of diabetic retinopathy, neuropathy, and nephropathy was purified from bovine lens, and its inhibitory activity was studied with the synthesized flavone derivatives 1-(2-hydroxyphenyl)ethanone as the starting material. Experimental study revealed that 2-chloroflavone shows less inhibitory activity of 60?C70% than other flavones used in the study. To validate experimental results computationally, docking studies of new flavone derivatives synthesized were performed with the enzyme aldose reductase, and the results indicate that 3-iodo, 4-methyl, 5-chloroflavone and 2-chloroflavone bind with higher and lesser affinities. Docking studies with site directed mutagenesis of Val47Ile, Tyr48His, Pro121Phe, Trp219Tyr, Cys298Ala, Leu300Pro, Ser302Arg, and Cys303Asp of the enzyme altered the inhibition activity of aldose reductase. The regression value (R ²) of 0.81 between the docking scores of the known inhibitors and the experimental logIC₅₀ indicates the reliability of the docking studies. Biological activity and carcinogenic properties predict that 3-iodo, 4-methyl, 5-chloroflavone is the best flavone inhibitor against aldose reductase.