Epalrestat, an aldose reductase inhibitor, in diabetic neuropathy: An Indian perspective

Background:

A number of diabetic patients with diabetic neuropathy, in India, were treated with epalrestat, an aldose reductase inhibitor. In this study, more than 2000 patients with diabetic neuropathy, who were treated with epalrestat for 3-12 months, were analyzed to assess the efficacy and the adverse reactions of the drug.

Method:

We analyzed the subjective symptoms (spontaneous pain, numbness, coldness and hypoesthesia) and the nerve function tests (motor nerve conduction velocity, sensory nerve conduction velocity and vibration threshold).

Result:

The improvement rate of the subjective symptoms was 75% (slightly improved or better) and that of the nerve function tests 36%. Adverse drug reactions were encountered in 52 (2.5%) of the 2190 patients, none of which was severe.

Conclusion:

Although data are limited, it is strongly suggested that epalrestat is a highly effective and safe agent for the treatment of diabetic neuropathy.     

Effects of aldose reductase inhibitor treatment in diabetic polyneuropathy - a clinical and neurophysiological study.

The efficacy of treatment with an aldose reductase inhibitor (1,3-dioxo-1 H-benz-de-isoquinoline-2(3H)-acetic acid, AY-22,284, Alrestatin) on peripheral nerve function in diabetic polyneuropathy was assessed. Thirty patients with long-standing diabetes and slight to moderate neuropathy participated in the double-blind placebo trial. Clinical examination, sensory threshold determinations for vibratory, tactile and thermal stimuli, conduction velocity measurements and studies of automatic function were performed to evaluate the treatment. Significant differences favouring Alrestatin over placebo were found for many of the measured variables, whereas no changes occurred on placebo. The apparent improvement of neuropathy occurred despite persisting hyperglycaemia. The results indicate that aldose reductase inhibitor treatment may be of value in diabetic polyneuropathy, and provide support for the sorbitol pathway hypothesis of diabetic polyneuropathy.     

Impaired nerve regeneration in streptozotocin-diabetic rats. Effects of treatment with an aldose reductase inhibitor

Rats with streptozotocin-induced diabetes have a decreased rate of sciatic nerve regeneration. We studied the effects on this defect of treatment with the aldose reductase inhibitor, ponalrestat (25 mg/kg per day via an endogastric tube). The nerves of diabetic rats were crush-injured at 5 weeks of diabetes and regeneration evaluated 7 days later with the pinch-reflex test. Ponalrestat treatment was started at day 3 after streptozotocin injection and was continued for the whole experimental period, i.e. until 6 weeks of diabetes. The treatment prevented effectively the accumulation of sorbitol and fructose in the nerves of diabetic rats, but was without effect on the sciatic nerve regeneration (controls 21.8 +/- 1.2 mm/7 days (mean +/- SEM, n = 6), untreated diabetics 15.8 +/- 1.8 (n = 7), ponalrestat-treated diabetics 16.2 +/- 1.0 (n = 10]. The results indicate that there is no connection between increased sorbitol pathway flux and impaired regeneration in streptozotocin diabetic rats.     

Impaired regeneration and no amelioration with aldose reductase inhibitor in crushed unmyelinated nerve fibers of diabetic rats.

The regenerative ability of unmyelinated nerve fibers (UNFs) in diabetes and the effect of aldose reductase inhibitor (ARI) on it were ultrastructurally evaluated after sciatic nerve crush in control and untreated and tolrestat-treated streptozocin-induced diabetic rats. The density and number of UNFs were significantly increased in all groups at 5 weeks after the injury. The increase returned to the baseline level in control rats, but not in diabetic rats at 24 weeks. Although the axon size showed a marked decrease at 5 weeks and an incomplete recovery at 24 weeks in all groups, the recovery was significantly worse in diabetic than in control groups. Tolrestat did not have any effect on regeneration of UNFs in diabetes. These results suggest impaired regeneration of UNFs after nerve crush injury in diabetes and less therapeutic effect of ARI on it.     

Correction of nerve conduction and endoneurial blood flow deficits by the aldose reductase inhibitor, tolrestat, in diabetic rats

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 effect of an aldose reductase inhibitor (Sorbinil®) on diabetic neuropathy and neural function of the retina: a double-blind study

37 patients with diabetic neuropathy were randomized into 2 equal groups and given daily doses of 200 mg or 50 mg of Sorbinil - a potent aldose-reductase inhibitor - in a double-blind 4-week period between 2 periods on placebo. The purpose was to assess the role of the drug on various neurophysiological parameters and its clinical effect. No difference was shown either in the placebo periods compared to Sorbinil treatment or between the 2 groups on the neurophysiological parameters but there was a statistically significant effect on overall subjective well-being. The drug had no side-effects in the present study.     

Ultrastructural observations on myelinated fibres in experimental diabetes: effect of the aldose reductase inhibitor ponalrestat given alone or in conjunction with insulin therapy

Six groups of rats were studied over a 12-week period: onset and end controls, untreated diabetics, ponalrestat-treated diabetics, insulin-treated diabetics, and diabetics treated with ponalrestat and insulin. The concentrations of glucose, sorbitol and fructose significantly increased and that of myo-inositol significantly decreased in the sciatic nerve of untreated diabetic animals. Ponalrestat administration completely normalized sorbitol levels and partially corrected fructose and myo-inositol concentrations without altering nerve glucose levels. The biochemical abnormalities were also corrected in both the insulin-treated and insulin and ponalrestat-treated diabetic animals. Myelinated fibre cross-sectional areas and axonal areas were significantly less in the tibial nerve of diabetic animals as compared with age-matched controls. Insulin treatment partially corrected the reduction in fibre and axonal area but teased fibre preparations showed an excess of axonal degeneration as compared with controls, untreated diabetics and ponalrestat-treated diabetics. Ponalrestat given alone or in conjunction with insulin therapy did not correct the reduction in fibre or axonal area and single isolated fibres from diabetic animals treated with ponalrestat and insulin showed a marked excess of axonal degeneration, probably related to hypoglycaemia. The study fails to reveal any significant beneficial effect of aldose reductase inhibition on the structural abnormalities in peripheral nerve in experimental diabetes.     

Combined treatment with LDL-apheresis, chenodeoxycholic acid and HMG-CoA reductase inhibitor for cerebrotendinous xanthomatosis

The effects of combined treatment with low-density lipoprotein (LDL)-apheresis, chenodeoxycholic acid (CDCA) and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitor were studied in 2 patients with cerebrotendinous xanthomatosis. Patient 1 was initially treated with LDL-apheresis alone: serum cholestanol levels decreased by 50% after each apheresis, but returned to their initial levels within 2 weeks. After an addition of CDCA administration, the serum cholestanol levels steadily decreased, resulting in slight improvement of neurological symptoms. Patient 2 received a combined treatment with LDL-apheresis, CDCA and HMG-CoA reductase inhibitor. This combination showed less LDL-apheresis-dependent fluctuation and more rapid decrease of serum cholestanol levels than those in Patient 1, resulting in improvement and stabilization of the symptoms. Our results suggest that LDL-apheresis in combination with CDCA and HMG-CoA reductase inhibitor may have beneficial effects and can be one of the treatment options.     

Axonal transport and tissue contents of substance P in rats with long-term streptozotocin-diabetes. Effects of the aldose reductase inhibitor ‘statil’

This study examined the axonal transport of substance P-like immunoreactivity (SPLI) and its content in dorsal root ganglion, trigeminal ganglion, stomach and ileum of non-diabetic rats and two groups of rats with streptozotocin-induced diabetes of 9 months duration. One diabetic group received the aldose reductase inhibitor ‘Statil’ throughout the period of study. To reduce morbidity all diabetic animals were given twice-weekly injections of a long-acting insulin which restricted weight loss but did not prevent regular and severe hyperglycaemia. Axonal transport of SPLI was studied by measurement of accumulation at 12 h ligatures on the left sciatic nerve. There were no differences between the 3 groups either in the calculated anterograde and retrograde mean rates of accumulation (ranges 6.0 to 7.6 and 0.38 to 0.72 mm/h respectively) or mobile fractions of SPLI (means from 0.54 to 0.58). There were, however, marked reductions in anterograde and retrograde accumulations of SPLI in the constricted nerves of the ‘untreated’ diabetics (respectively 57 and 33% of controls;P < 0.01 for both). In the ‘Statil’-treated rats these deficits were attenuated (80 and 75% of controls). Diabetes also reduced the SPLI content of unligated sciatic nerve and trigeminal ganglion (65 and 75% of controls). ‘Statil’ prevented the deficit in the ganglion, but not in the nerve. ‘Statil’ treatment prevented themyo-inositol depletion and attenuated the sorbitol and fructose accumulation seen in the sciatic nerves of the untreated diabetic animals suggesting effective inhibition of aldose reductase in this tissue. The total SPLI content of the stomach and 1-cm segments of ileum were unaltered in the diabetic animals but due to the increased weights of these tissues the SPLI content per unit weight was reduced. These changes were unaffected by ‘Statil’.     

Sulforaphane enhances aquaporin-4 expression and decreases cerebral edema following traumatic brain injury

Brain edema, the infiltration and accumulation of excess fluid causing an increase in brain tissue volume, often leads to a rise in intracranial pressure and is a key contributor to the morbidity and mortality associated with traumatic brain injury (TBI). The cellular and molecular mechanisms contributing to the development/resolution of TBI-associated brain edema are poorly understood. Aquaporin-4 (AQP4) water channel is expressed at high levels in brain astrocytes, and the bidirectional transport of water through these channels is critical for the maintenance of brain water homeostasis. By using a rodent injury model, we show that TBI decreased AQP4 level in the injury core and modestly increased it in the penumbra region surrounding the core. Postinjury administration of sulforaphane (SUL), an isothiocyanate present in abundance in cruciferous vegetables such as broccoli, attenuated AQP4 loss in the injury core and further increased AQP4 levels in the penumbra region compared with injured animals receiving vehicle. These increases in AQP4 levels were accompanied by a significant reduction in brain edema (assessed by percentage water content) at 3 days postinjury. These findings suggest that the reduction of brain edema in response to SUL administration could be due, in part, to water clearance by AQP4 from the injured brain.     

Topical delivery of nerve growth factor for treatment of ocular and brain disorders

Neurotrophins are a family of proteins that support neuronal proliferation, survival, and differentiation in the central and peripheral nervous systems, and are regulators of neuronal plasticity. Nerve growth factor is one of the best-described neurotrophins and has advanced to clinical trials for treatment of ocular and brain diseases due to its trophic and regenerative properties. Prior trials over the past few decades have produced conflicting results, which have principally been ascribed to adverse effects of systemic nerve growth factor administration, together with poor penetrance of the blood-brain barrier that impairs drug delivery. Contrastingly, recent studies have revealed that topical ocular and intranasal nerve growth factor administration are safe and effective, suggesting that topical nerve growth factor delivery is a potential alternative to both systemic and invasive intracerebral delivery. The therapeutic effects of local nerve growth factor delivery have been extensively investigated for different ophthalmic diseases, including neurotrophic keratitis, glaucoma, retinitis pigmentosa, and dry eye disease. Further, promising pharmacologic effects were reported in an optic glioma model, which indicated that topically administered nerve growth factor diffused far beyond where it was topically applied. These findings support the therapeutic potential of delivering topical nerve growth factor preparations intranasally for acquired and degenerative brain disorders. Preliminary clinical findings in both traumatic and non-traumatic acquired brain injuries are encouraging, especially in pediatric patients, and clinical trials are ongoing. The present review will focus on the therapeutic effects of both ocular and intranasal nerve growth factor delivery for diseases of the brain and eye.     

黄芩苷对糖尿病患者红细胞醛糖还原酶活性及周围神经传导速度的影响

观察中药黄芩苷对糖尿病患者醛糖还原酶 (AR)活性抑制作用及对糖尿病神经病变影响。 37例糖尿病神经病变患者随机分为对照组 (18例 ,常规治疗 )和治疗组 (19例 ,常规治疗 黄芩苷 ) ,疗程 4周 ,治疗前后分别测定红细胞AR ,运动、感觉神经传导速度 ,膀胱残余尿量。上述指标治疗前二组相似 ,治疗后治疗组AR活性受到抑制 ,明显低于对照组 ,运动、感觉神经传导速度的改善明显高于对照 ,膀胱残余尿量亦显著少于对照组。黄芩苷可明显抑制AR活性 ,改善神经病变的指标 ,有助于糖尿病神经病变的治疗。     

Fine-structural localization of aldose reductase and ouabain-sensitive,K+-dependent p-nitro-phenylphosphatase in rat peripheral nerve

Summary Aldose reductase was visualized by light and electron microscopy using a goat anti-rat antibody with immunoperoxidase and immunogold, respectively. Ouabain-sensitive, K⁺-dependent, p-nitro-phenylphosphatase, a component of (Na⁺, K⁺)-ATPase, was localized at the electron microscopic level by enzyme histochemistry using p-nitro-phenylphosphate as substrate. In peripheral nerve, spinal ganglia and roots, the Schwann cell of myelinated fibers was the principal site of aldose reductase localization. Immunostaining was intense in the paranodal region and the Schmidt-Lanterman clefts as well as in cytoplasm of the terminal expansions of paranodal myelin lamellae and the nodal microvilli. Schwann cell cytoplasm of unmyelinated fibers were faintly labelled. Endoneurial vessel endothelia, pericytes and perineurium failed to bind appreciable amounts of aldose reductase antibody. However, mast cell granules bound antibody strongly. In contrast, p-nitro-phenylphosphatase reaction product was detected in the nodal axolemma, terminal loops of Schwann cell cytoplasm and the innermost layer of perineurial cells. In endothelial cells, reaction product was localized on either the luminal or abluminal, or on both luminal and abluminal plasmalemma. Endothelial vesicular profiles were often loaded with reaction product. Occasional staining of myelin and axonal organelles was noted. Mast cells lacked reaction product.Supported by the Veterans Administration Research Service, USPHS Grants NIH 14162 and NIH 18715, the California Affiliate of the American Diabetes Association and the Juvenile Diabetes Foundation International     

Apolipoprotein E4 enhances brain inflammation by modulation of the NF-kappaB signaling cascade

Apolipoprotein E4 (apoE4), the major genetic risk factor of Alzheimer's disease (AD), is associated with enhanced brain inflammation. Genome-wide gene expression profiling was employed to study the effects of apoE genotype on hippocampal gene expression in LPS-treated mice, transgenic for either apoE4 or the AD benign allele, apoE3. This revealed that the expression of inflammation-related genes following intracerebroventricular injection of LPS was significantly higher and more prolonged in apoE4 than in apoE3 transgenic mice. Clustering analysis revealed gene clusters which responded differently in apoE4 and apoE3 mice and were significantly enriched in NF-kappaB response elements. Direct measurement of NF-kappaB-regulated genes revealed that their extent of activation was greater in the apoE4 mice. Immunohistochemistry experiments revealed that microglial and NF-kappaB activation were more pronounced in apoE4 than in apoE3 mice. These findings suggest that the increased brain inflammation in apoE4 mice is related to disregulation of NF-kappaB signaling pathway.     

RNAi沉默AQP-4技术治疗胶质瘤性脑水肿的实验研究

目的 应用RNA干扰(RNAi)技术靶向沉默胶质瘤内水通道蛋白4(AQP -4)的表达,观察其对胶质瘤源性脑水肿的治疗效果.方法 构建靶向AQP-4的siRNA质粒,免疫荧光化学方法检测其对C6细胞AQP-4的沉默效果;建立SD大鼠颅内C6胶质瘤模型,分对照组、空载组、无义序列组和siRNA组;聚合酶链式反应和蛋白印迹方法分别检测第3、6、9、12天AQP-4的mRNA和蛋白水平;干/湿比重法和Evans蓝测定法检测不同时相脑组织含水量和血脑屏障通透性改变;比较动物生存期.结果 siRNA可沉默AQP-4表达;siRNA组脑组织水含量和血脑屏障通透性均明显低于对照组、空载组和无义序列组,动物生存期最长.结论 靶向AQP-4的RNAi技术可在一定程度上减轻胶质瘤性脑水肿的发生和发展,为胶质瘤脑水肿提供了一种新的治疗策略选择.     

Therapeutic potential of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors for the treatment of retinal and eye diseases

3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, generically termed statins, are widely prescribed for their cholesterol-lowering properties. In addition to lipid-lowering properties, statins have pleiotropic effects including anti-inflammatory, anti-apoptotic, and antiproliferative effects. Recently, data from experimental and observational studies have indicated that statins could also become a treatment option for diseases of the central nervous system (CNS). Many neurodegenerative diseases particularly affect the retina and other ocular structures and are the cause for blindness. This review, focused on recent clinical and experimental data, discusses known and putative mechanisms of statin actions underlying neuroprotective effects in relevant retinal and eye diseases. In addition, it presents evidence for the role of heat shock proteins (Hsps) as target of statin-mediated neuroprotective effects in ocular diseases.     

Expression of aldose reductase and sorbitol dehydrogenase genes in Schwann cells isolated from rat: effects of high glucose and osmotic stress

To investigate the polyol pathway activity in Schwann cells, we determined the mRNA levels of aldose reductase (AR) and sorbitol dehydrogenase (SDH) in cultured cells under hyperglycemic or hyperosmotic conditions using competitive RT-PCR technique. The expressions of AR and SDH mRNAs in Schwann cells were unaltered by high (30 mM) glucose content in the medium. On the other hand, osmotic stress elicited significant increases in AR mRNA without any effect on SDH mRNA expression. The levels of AR mRNA determined by this RT-PCR system were significantly correlated with AR activity, as well as the levels of sorbitol accumulated in Schwann cells cultured under hyperosmotic conditions. These findings suggest that in contrast to the induction of AR expression by osmotic stress, high glucose per se does not up-regulate expression of the enzymes constituting the polyol pathway in Schwann cells. The RT-PCR system developed in this study may be a useful tool in ascertaining the relative contributions of AR and SDH to the metabolic derangements leading to diabetic complications.     

Molecular scaffolds underpinning macroglial polarization: An analysis of retinal Müller cells and brain astrocytes in mouse

Key roles of macroglia are inextricably coupled to specialized membrane domains. The perivascular endfoot membrane has drawn particular attention, as this domain contains a unique complement of aquaporin‐4 (AQP4) and other channel proteins that distinguishes it from perisynaptic membranes. Recent studies indicate that the polarization of macroglia is lost in a number of diseases, including temporal lobe epilepsy and Alzheimer's disease. A better understanding is required of the molecular underpinning of astroglial polarization, particularly when it comes to the significance of the dystrophin associated protein complex (DAPC). Here, we employ immunofluorescence and immunogold cytochemistry to analyze the molecular scaffolding in perivascular endfeet in macroglia of retina and three regions of brain (cortex, dentate gyrus, and cerebellum), using AQP4 as a marker. Compared with brain astrocytes, Müller cells (a class of retinal macroglia) exhibit lower densities of the scaffold proteins dystrophin and α‐syntrophin (a DAPC protein), but higher levels of AQP4. In agreement, depletion of dystrophin or α‐syntrophin—while causing a dramatic loss of AQP4 from endfoot membranes of brain astrocytes—had only modest or insignificant effect, respectively, on the AQP4 pool in endfoot membranes of Müller cells. In addition, while polarization of brain macroglia was less affected by dystrophin depletion than by targeted deletion of α‐syntrophin, the reverse was true for retinal macroglia. These data indicate that the molecular scaffolding in perivascular endfeet is more complex than previously assumed and that macroglia are heterogeneous with respect to the mechanisms that dictate their polarization. © 2012 Wiley Periodicals, Inc.