The effects of zenarestat, an aldose reductase inhibitor, on peripheral neuropathy in Zucker diabetic fatty rats

Discovery of extended product structural space of the fungal dioxygenase AsqJ

The fungal dioxygenase AsqJ catalyses the conversion of benzo[1,4]diazepine-2,5-diones into quinolone antibiotics. A second, alternative reaction pathway leads to a different biomedically important product class, the quinazolinones. Within this work, we explore the catalytic promiscuity of AsqJ by screening its activity across a broad range of functionalized substrates made accessible by solid-/liquid-phase peptide synthetic routes. These systematic investigations map the substrate tolerance of AsqJ within its two established pathways, revealing significant promiscuity, especially in the quinolone pathway. Most importantly, two further reactivities leading to new AsqJ product classes are discovered, thus significantly expanding the structural space accessible by this biosynthetic enzyme. Switching AsqJ product selectivity is achieved by subtle structural changes on the substrate, revealing a remarkable substrate-controlled product selectivity in enzyme catalysis. Our work paves the way for the biocatalytic synthesis of diverse biomedically important heterocyclic structural frameworks.

Multimodal Comparison of Diabetic Neuropathy in Aged Streptozotocin-Treated Sprague-Dawley and Zucker Diabetic Fatty Rats

The development and progression of diabetic polyneuropathy (DPN) are due to multiple mechanisms. The creation of reliable animal models of DPN has been challenging and this issue has not yet been solved. However, despite some recognized differences from humans, most of the current knowledge on the pathogenesis of DPN relies on results achieved using rodent animal models. The simplest experimental DPN model reproduces type 1 diabetes, induced by massive chemical destruction of pancreatic beta cells with streptozotocin (STZ). Spontaneous/transgenic models of diabetes are less frequently used, mostly because they are less predictable in clinical course, more expensive, and require a variable time to achieve homogeneous metabolic conditions. Among them, Zucker diabetic fatty (ZDF) rats represent a typical type 2 diabetes model. Both STZ-induced and ZDF rats have been extensively used, but only very few studies have compared the long-term similarities and differences existing between these two models. Moreover, inconsistencies have been reported regarding several aspects of short-term in vivo studies using these models. In this study, we compared the long-term course of DPN in STZ-treated Sprague-Dawley and ZDF rats with a multimodal set of readout measures.

Peripheral Neuropathy Phenotyping in Rat Models of Type 2 Diabetes Mellitus: Evaluating Uptake of the Neurodiab Guidelines and Identifying Future Directions

Diabetic peripheral neuropathy (DPN) affects over half of type 2 diabetes mellitus (T2DM) patients, with an urgent need for effective pharmacotherapies. While many rat and mouse models of T2DM exist, the phenotyping of DPN has been challenging with inconsistencies across laboratories. To better characterize DPN in rodents, a consensus guideline was published in 2014 to accelerate the translation of preclinical findings. Here we review DPN phenotyping in rat models of T2DM against the 'Neurodiab' criteria to identify uptake of the guidelines and discuss how DPN phenotypes differ between models and according to diabetes duration and sex. A search of PubMed, Scopus and Web of Science databases identified 125 studies, categorised as either diet and/or chemically induced models or transgenic/spontaneous models of T2DM. The use of diet and chemically induced T2DM models has exceeded that of transgenic models in recent years, and the introduction of the Neurodiab guidelines has not appreciably increased the number of studies assessing all key DPN endpoints. Combined high-fat diet and low dose streptozotocin rat models are the most frequently used and well characterised. Overall, we recommend adherence to Neurodiab guidelines for creating better animal models of DPN to accelerate translation and drug development.

Physiological and Pathological Roles of Aldose Reductase

Aldose reductase (AR) is an aldo-keto reductase that catalyzes the first step in the polyol pathway which converts glucose to sorbitol. Under normal glucose homeostasis the pathway represents a minor route of glucose metabolism that operates in parallel with glycolysis. However, during hyperglycemia the flux of glucose via the polyol pathway increases significantly, leading to excessive formation of sorbitol. The polyol pathway-driven accumulation of osmotically active sorbitol has been implicated in the development of secondary diabetic complications such as retinopathy, nephropathy, and neuropathy. Based on the notion that inhibition of AR could prevent these complications a range of AR inhibitors have been developed and tested; however, their clinical efficacy has been found to be marginal at best. Moreover, recent work has shown that AR participates in the detoxification of aldehydes that are derived from lipid peroxidation and their glutathione conjugates. Although in some contexts this antioxidant function of AR helps protect against tissue injury and dysfunction, the metabolic transformation of the glutathione conjugates of lipid peroxidation-derived aldehydes could also lead to the generation of reactive metabolites that can stimulate mitogenic or inflammatory signaling events. Thus, inhibition of AR could have both salutary and injurious outcomes. Nevertheless, accumulating evidence suggests that inhibition of AR could modify the effects of cardiovascular disease, asthma, neuropathy, sepsis, and cancer; therefore, additional work is required to selectively target AR inhibitors to specific disease states. Despite past challenges, we opine that a more gainful consideration of therapeutic modulation of AR activity awaits clearer identification of the specific role(s) of the AR enzyme in health and disease.

Addressing selectivity issues of aldose reductase 2 inhibitors for the management of diabetic complications

Aldose Reductase 2 (ALR2), the rate-limiting enzyme of the polyol pathway, plays an important role in detoxification of some toxic aldehydes. Under hyperglycemia, this enzyme overactivates and causes diabetic complications (DC). Therefore, ALR2 inhibition has been established as a potential approach to manage these complications. Several ALR2 inhibitors have been reported, but none of them could reach US FDA approval. One of the main reasons is their poor selectivity over ALR1, which leads to the toxicity. The current review underlines the molecular connectivity of ALR2 with DC and comparative analysis of the catalytic domains of ALR2 and ALR1, to better understand the selectivity issues. This report also discusses the key features required for ALR2 inhibition and to limit toxicity due to off-target activity.

3-Mercapto-5H-1,2,4-Triazino[5,6-b]Indole-5-Acetic Acid (Cemtirestat) Alleviates Symptoms of Peripheral Diabetic Neuropathy in Zucker Diabetic Fatty (ZDF) Rats: A Role of Aldose Reductase

Peripheral neuropathy is the most prevalent chronic complication of diabetes mellitus. Good glycemic control can delay the appearance of neuropathic symptoms in diabetic patients but it is not sufficient to prevent or cure the disease. Therefore therapeutic approaches should focus on attenuation of pathogenetic mechanisms responsible for the nerve injury. Considering the role of polyol pathway in the etiology of diabetic neuropathy, we evaluated the effect of a novel efficient and selective aldose reductase inhibitor, 3-mercapto-5H-1,2,4-triazino[5,6-b]indole-5-acetic acid (cemtirestat), on symptoms of diabetic peripheral neuropathy in Zucker Diabetic Fatty (ZDF) rats. Since the age of 5 months, male ZDF rats were orally administered cemtirestat, 2.5 and 7.5 mg/kg/day, for two following months. Thermal hypoalgesia was evaluated by tail flick and hot plate tests. Tactile allodynia was determined by a von Frey flexible filament test. Two-month treatment of ZDF rats with cemtirestat (i) did not affect physical and glycemic status of the animals; (ii) partially inhibited sorbitol accumulation in red blood cells and the sciatic nerve; (iii) markedly decreased plasma levels of thiobarbituric acid reactive substances; (iv) normalized symptoms of peripheral neuropathy with high significance. The presented findings indicate that inhibition of aldose reductase by cemtirestat is not solely responsible for the recorded improvement of the behavioral responses. In future studies, potential effects of cemtirestat on consequences of diabetes that are not exclusively dependent on glucose metabolism via polyol pathway should be taken into consideration.

Blockade of sigma 1 receptors alleviates sensory signs of diabetic neuropathy in rats

BACKGROUND

E-52862 (S1RA, 4-[2-[[5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]-morpholine), a novel selective sigma 1 receptor (σ1R) antagonist, has demonstrated efficacy in nociceptive and neuropathic pain models. Our aim was to test if σ1R blockade with E-52862 may modify the signs of neuropathy in Zucker diabetic fatty (ZDF) rats, a type 2 diabetes model.

METHODS

Mechanical and thermal response thresholds were tested on 7-, 13-, 14- and 15-week-old ZDF rats treated with saline or with E-52862 acutely administered on week 13, followed by sub-chronic administration (14 days). Axonal peripheral activity (skin-saphenous nerve preparation) and isolated aorta or mesenteric bed reactivity were analysed in 15-week-old ZDF rats treated with saline or E-52862 and in LEAN rats.

RESULTS

Zucker diabetic fatty rats showed significantly decreased thermal withdrawal latency and threshold to mechanical stimulation on week 13 compared to week 7 (prediabetes) and with LEAN animals; single-dose and sub-chronic E-52862 administration restored both parameters to those recorded on week 7. Regarding axonal peripheral activity, E-52862 treatment increased the mean mechanical threshold (77.3 ± 21 mN vs. 19.6 ± 1.5 mN, saline group) and reduced the response evoked by mechanical increasing stimulation (86.4 ± 36.5 vs. 352.8 ± 41.4 spikes) or by repeated mechanical supra-threshold steps (39.4 ± 1.4 vs. 83.5 ± 0.9). E-52862 treatment also restored contractile response to phenylephrine in aorta and mesenteric bed.

CONCLUSIONS

E-52862 administration reverses neuropathic (behavioural and electrophysiological) and vascular signs in the ZDF rat.

SIGNIFICANCE

Blockade of σ1R avoids the development of diabetic neuropathy in rats, and may represent a potentially useful therapeutic approach to peripheral neuropathies in diabetic patients. WHAT DOES THIS STUDY ADD?: This study presents evidences for the potential usefulness of sigma receptor blockade on diabetic neuropathy in rats. The methodology includes behavioural evidences, electrophysiological data and vascular-isolated models.

Diabetic complications in obese type 2 diabetic rat models

We overviewed the pathophysiological features of diabetes and its complications in obese type 2 diabetic rat models: Otsuka Long-Evans Tokushima fatty (OLETF) rat, Wistar fatty rat, Zucker diabetic fatty (ZDF) rat and Spontaneously diabetic Torii (SDT) fatty rat. Pancreatic changes with progression of diabetes were classified into early changes, such as islet hypertrophy and degranulation of β cells, and degenerative changes, such as islet atrophy and fibrosis of islet with infiltration of inflammatory cells. Renal lesions in tubuli and glomeruli were observed, and nodular lesions in glomeruli were notable changes in OLETF and SDT fatty rats. Among retinal changes, folding and thickening were interesting findings in SDT fatty rats. A decrease of motor nerve conduction velocity with progression of diabetes was presented in obese diabetic rats. Other diabetic complications, osteoporosis and sexual dysfunction, were also observed. Observation of bone metabolic abnormalities, including decrease of osteogenesis and bone mineral density, and sexual dysfunction, including hypotestosteronemia and erectile dysfunction, in obese type 2 diabetic rats have been reported.

Animal models of diabetes-induced neuropathic pain

Neuropathy will afflict over half of the approximately 350 million people worldwide who currently suffer from diabetes and around one-third of diabetic patients with neuropathy will suffer from painful symptoms that may be spontaneous or stimulus evoked. Diabetes can be induced in rats or mice by genetic, dietary, or chemical means, and there are a variety of well-characterized models of diabetic neuropathy that replicate either type 1 or type 2 diabetes. Diabetic rodents display aspects of sensorimotor dysfunction such as stimulus-evoked allodynia and hyperalgesia that are widely used to model painful neuropathy. This allows investigation of pathogenic mechanisms and development of potential therapeutic interventions that may alleviate established pain or prevent onset of pain.

Appropriateness of the Zucker Diabetic Fatty rat as a model for diabetic microvascular late complications

Male obese Zucker Diabetic Fatty (ZDF) rats develop type 2 diabetes around eight weeks of age, and are widely used as a model for human diabetes and its complications. The objective of the study was to test whether the complications manifested in the kidney and nerves of ZDF rats really correspond to human diabetic complications in their being related to the hyperglycaemic state. Four groups of ZDF rats were used. One lean (Fa/?) and one obese (fa/fa) untreated group served as non-diabetic and diabetic controls. In two further groups of obese (fa/fa) rats, diabetes was prevented by pioglitazone or delayed by food restriction. All rats were monitored up to 35 weeks of age with respect to their blood glucose, HbA1c and insulin levels, their kidney function (urinary glucose excretion, renal glucose filtration, glomerular filtration rate, albumin/creatinine ratio), and their nerve function (tactile and thermal sensory threshold and nerve conduction velocity). Pioglitazone prevented the development of diabetes, while food restriction delayed its onset for 8–10 weeks. Accordingly, kidney function parameters were similar to lean non-diabetic rats in pioglitazone-treated rats and significantly improved in food-restricted rats compared with obese controls. Kidney histology paralleled the functional results. By contrast, nerve functional evaluations did not mirror the differing blood glucose levels. We conclude that the ZDF rat is a good model for diabetic nephropathy, while alterations in nerve functions were not diabetes-related.

Electroacupuncture Zusanli (ST36) on Release of Nitric Oxide in the Gracile Nucleus and Improvement of Sensory Neuropathies in Zucker Diabetic Fatty Rats

The purpose of these studies was to examine the effects of electroacupuncture (EA) Zusanli (ST36) on release of nitric oxide (NO) in the gracile nucleus (GN) and determine if functional neuropathic changes were modified by EA ST36-induced NO in the nucleus in Zucker diabetic fatty (ZDF) rats. The foot withdrawal responses to mechanical, thermal and cold stimuli were measured before and after EA stimulation. A microdialysis probe was implanted in the GN and dialysate samples were collected 20 min before, during and after EA ST36. Total nitrate and nitrite (NO_x⁻) concentrations in the samples were quantified by using chemiluminescence. The baseline dialysate NO_x⁻ concentrations in the GN were decreased in ZDF rats compared to lean control (LC) rats (P < .05). In ZDF rats, dialysate NO_x⁻ releases in the GN were markedly increased during EA ST36, whereas in LC rats, the releases were moderately enhanced at 20–40 min after EA ST36. The withdrawal latencies to mechanical, cold and thermal stimuli were significantly improved 20 min after EA ST36 both in LC and ZDF rats, but not altered by non-acupoint stimulation. The withdrawal latencies to EA ST36 were further potentiated by 3-morpholinyl-sydnoneimine and inhibited by N^G-Propyl-l-arginine infused into the GN in ZDF rats (P < .05). These results show that EA ST36 increases NO release in the GN, and NO in the nucleus modifies withdrawal latencies to mechanical, cold, and thermal nociception stimuli. Data suggest that EA ST36 induces NO release in the GN, which contributes to improvement of sensory neuropathies in rats.

The involvement of aldose reductase in alterations to neurotrophin receptors and neuronal cytoskeletal protein mRNA levels in the dorsal root ganglion of streptozotocin-induced diabetic rats

Dorsal root ganglia (DRG) are recognized as one of the organs which are damaged in peripheral sensory diabetic neuropathy. In an experimental animal model, the alteration of the mRNA expression level of neurotrophins, their receptors and neuronal cytoskeletal protein have been reported. In this study, we examined whether these changes are improved by treatment with the aldose reductase inhibitor, zenarestat, in early-stage diabetic neuropathy of streptozotocin (STZ)-induced diabetic rats. Two weeks after the induction of diabetes mellitus by STZ treatment, zenarestat or a vehicle were given orally for two weeks. After the zenarestat treatment, the mRNA expression levels of neurotrophin receptors and neuronal cytoskeletal proteins in dorsal root ganglia were determined with a real-time polymerase chain reaction (PCR) method. Compared with the expression level of normal rats, a significant increase in Trk-C and Talpha1 alpha-tubulin and a decrease in neurofilament H mRNA expression level were observed in the DRG of STZ rats, while there were no significant changes in Trk-A, Trk-B, p75, neurofilament L, neurofilament M and betaIII tubulin mRNA expression. Zenarestat treatment significantly ameliorated the abnormal increase in Trk-C mRNA expression level. These data suggest that hyperactivation of the polyol pathway induces a deficit in neurotropism on peripheral sensory diabetic neuropathy.

Thirteen-month inhibition of aldose reductase by zenarestat prevents morphological abnormalities in the dorsal root ganglia of streptozotocin-induced diabetic rats

The dorsal root ganglia (DRG) have been identified as the target tissue in diabetic somatosensory neuropathy. It has been reported that, in the chronically diabetic state, DRG sensory neurons may undergo morphological changes. In this study, we examined the effect of zenarestat, an aldose reductase inhibitor, on the morphological derangement of the DRG and the sural nerve of streptozotocin-induced diabetic rats (STZ rats) over a 13-month period. The cell area of the DRG in STZ rats was smaller than that in normal rats. A decrease in fiber size was apparent in the sural nerve of the STZ rats, and the fiber density was greater. These morphological changes were reversed in zenarestat-treated STZ rats. The data suggest that, in peripheral sensory diabetic neuropathy, hyperactivation of the polyol pathway induces abnormalities not only in peripheral nerve fiber, but also in the DRG, which is an aggregate of primary sensory afferent cell bodies.

Distal degenerative sensory neuropathy in a long-term type 2 diabetes rat model

OBJECTIVE

Peripheral neuropathy associated with type 2 diabetes (DPN) is not widely modeled. We describe unique features of DPN in type 2 diabetic Zucker diabetic fatty (ZDF) rats.

RESEARCH DESIGN AND METHODS

We evaluated the structural, electrophysiological, behavioral, and molecular features of DPN in ZDF rats and littermates over 4 months of hyperglycemia. The status of insulin signaling transduction molecules that might be interrupted in type 2 diabetes and selected survival-, stress-, and pain-related molecules was emphasized in dorsal root ganglia (DRG) sensory neurons.

RESULTS

ZDF rats developed slowing of motor sciatic-tibial and sensory sciatic digital conduction velocity and selective mechanical allodynia with preserved thermal algesia. Diabetic sural axons, preserved in number, developed atrophy, but there was loss of large-calibre dermal and small-calibre epidermal axons. In diabetic rats, insulin signal transduction pathways in lumbar DRGs were preserved or had trends toward upregulation: mRNA levels of insulin receptor beta-subunit (IRbeta), insulin receptor substrate (IRS)-1, and IRS-2. The numbers of neurons expressing IRbeta protein were also preserved. There were trends toward early rises of mRNA levels of heat shock protein 27 (HSP27), the alpha2delta1 calcium channel subunit, and phosphatidylinositol 3-kinase in diabetes. Others were unchanged, including nuclear factor-kappaB (NF-kappaB; p50/p105) and receptor for advanced glycosylation endproducts (RAGE) as was the proportion of neurons expressing HSP27, NF-kappaB, and RAGE protein.

CONCLUSIONS

ZDF type 2 diabetic rats develop a distal degenerative sensory neuropathy accompanied by a selective long-term pain syndrome. Neuronal insulin signal transduction molecules are preserved.

A review of islet of Langerhans degeneration in rodent models of type 2 diabetes

Type 2 diabetes mellitus (TTDM) is characterized by progressive loss of glucose control through multifactorial mechanisms. The search for an understanding of TTDM has relied on animal models since the realization of the importance of the pancreas in controlling plasma glucose concentration. Rodent models of TTDM are developed to express hyperglycemia and not islet degeneration per se. Degeneration of the islets of Langerhans with beta-cell loss is secondary to insulin resistance and is regarded as the more important lesion. Despite this, differences between models are seen in the development and progression of islet degeneration. Assessing the differences between the models is important to appreciate the various aspects of TTDM and understand their advantages as well as their deficiencies. Relevant animal models of TTDM provide opportunities to investigate important physiological and cell biological processes that may ultimately lead to development of targeted therapies. This article reviews the importance, advantages, and limitations of rodent models of TTDM in relation to the histopathological changes that characterize islet degeneration. Pathophysiological mechanisms that contribute to islet degeneration are also discussed and are placed into the context of changes in islet histological appearances.

Oxidative injury and neuropathy in diabetes and impaired glucose tolerance

Clinical studies suggest that impaired glucose tolerance (IGT) is associated with the development of neuropathy. The aim of the current study was to determine if neuropathy developed in the female Zucker Diabetic Fatty (ZDF) rat, an animal model of IGT and type 2 diabetes. The ZDF rat develops impaired glucose tolerance (IGT) when fed a control diet, and frank diabetes when fed a high fat diet. Following 10 weeks of hyperglycemia, sensory nerve action potentials (SNAP) and compound motor action potentials (CMAP) were reduced and sensory conduction velocities were slowed (distal>proximal) in the tail and hind limb in ZDF animals with IGT and frank diabetes (p<0.01). Neuropathy was coupled with evidence of increased reactive oxygen species (ROS) and cellular injury in dorsal root ganglion (DRG) neurons from IGT animals. Our study supports the hypothesis that neuropathy develops in an animal model of IGT and is associated with evidence of oxidative injury in DRG and peripheral nerves.

Early diabetic neuropathy: Triggers and mechanisms

Peripheral neuropathy, and specifically distal peripheral neuropathy (DPN), is one of the most frequent and troublesome complications of diabetes mellitus. It is the major reason for morbidity and mortality among diabetic patients. It is also frequently associated with debilitating pain. Unfortunately, our knowledge of the natural history and pathogenesis of this disease remains limited. For a long time hyperglycemia was viewed as a major, if not the sole factor, responsible for all symptomatic presentations of DPN. Multiple clinical observations and animal studies supported this view. The control of blood glucose as an obligatory step of therapy to delay or reverse DPN is no longer an arguable issue. However, while supporting evidence for the glycemic hypothesis has accumulated, multiple controversies accumulated as well. It is obvious now that DPN cannot be fully understood without considering factors besides hyperglycemia. Some symptoms of DPN may develop with little, if any, correlation with the glycemic status of a patient. It is also clear that identification of these putative non-glycemic mechanisms of DPN is of utmost importance for our understanding of failures with existing treatments and for the development of new approaches for diagnosis and therapy of DPN. In this work we will review the strengths and weaknesses of the glycemic hypothesis, focusing on clinical and animal data and on the pathogenesis of early stages and triggers of DPN other than hyperglycemia.

Taurine reverses neurological and neurovascular deficits in Zucker diabetic fatty rats

Increased oxidative stress is implicated in the pathogenesis of diabetic peripheral neuropathy (DPN). However, the efficacy of antioxidant therapy on DPN complicating type 2 diabetes remains unexplored. We therefore determined the ability of the antioxidant taurine to reverse deficits of hind limb sciatic motor and digital sensory nerve conduction velocity (NCV), nerve blood flow (NBF), and sensory thresholds in hyperglycemic Zucker diabetic fatty (ZDF) rats. Experimental groups comprised lean nondiabetic (ND), ND treated with taurine (ND + T), untreated ZDF diabetic (D), and D rats treated with taurine (D + T). Compared to ND rats, 23%, 15% and 56% deficits of motor NCV, sensory NCV and NBF, respectively as well as thermal and mechanical hyperalgesia were reversed by taurine. An 84% deficit of dorsal root ganglion neuron calcitonin gene-related peptide in D rats was prevented by taurine. In summary, the antioxidant taurine reverses neurological and neurovascular deficits in experimental type 2 diabetes.

Amelioration of diabetic peripheral neuropathy by implantation of hematopoietic mononuclear cells in streptozotocin-induced diabetic rats

This study was performed in order to evaluate the angiogenic effect of implantation of either peripheral blood mononuclear cells (PBMNCs) or bone marrow mononuclear cells (BMMNCs) on diabetic peripheral neuropathy. Streptozotocin (50 mg/kg) was injected intravenously into 6-week-old male Lewis rats. Four weeks after the induction of diabetes, 6 x 10(7) of PBMNCs or 1 x 10(8) of BMMNCs were implanted into the left hindlimb muscle. Motor nerve conduction velocity (MNCV) was monitored before and after implantation. At the end of the experiment, bilateral nerve blood flow (NBF) was measured by laser Doppler and the number of vessels in the sciatic nerves quantified by Factor VIII staining of the sections. Diabetes resulted in an approximately 20% reduction (P < 0.01) in sciatic MNCV. Four weeks after implantation, MNCV was improved by 54% with PBMNCs and by 67% with BMMNCs (both P < 0.01). Moreover, the effects of implantation were almost abolished by administration of VEGF-neutralizing antibody. Sciatic NBF was reduced by approximately 50% by diabetes (P < 0.05). This reduction in perfusion was improved by 74% by implantation of PBMNCs and by 62% by implantation of BMMNCs (P < 0.05 and P < 0.01, respectively). These effects were observed only in the implanted limb. Immunohistochemical staining of sciatic nerve sections for Factor VIII showed no significant increase in the number of vessels in the sciatic nerve following implantation of either PBMNCs or BMMNCs. These data suggest that implantation of hematopoietic mononuclear cell fractions is associated with an improvement in MNCV as a result of arteriogenic effects in the sciatic nerve, and that VEGF may contribute to this effect. This improvement occurred in the absence of angiogenesis. Implantation of these cell fractions may therefore be a potential new therapeutic method for treating diabetic peripheral neuropathy.

Effects of Shenmai Huoxue Decoction on early diabetic peripheral neuropathy in rats

OBJECTIVE

To evaluate the effects of Shenmai Huoxue Decoction (SMHXD) on early diabetic peripheral neuropathy (DPN) in rats.

METHODS

The rats were randomly divided into 3 groups: normal group, diabetic model group and SMHXD-treated diabetic group. The diabetic rats were induced by streptozotocin (STZ) intraperitoneally. After the treatment, sensory nerve conduction velocity (SNCV) of caudal nerve was detected with evoked electromyography, and the activity of aldose reductase (AR) in erythrocytes and the concentration of endothelin (ET) in plasma were measured.

RESULTS

It was showed that the SNCV reduced significantly and the activity of AR in erythrocytes and the concentration of ET in plasma were increased significantly in diabetic group as compared with those in the normal group. The SNCV was increased, and the activity of AR in erythrocytes and the concentration of ET in plasma were improved significantly in SMHXD-treated diabetic group after the treatment.

CONCLUSION

The results indicate that SMHXD can alleviate the lesion of DPN in the early stage of diabetic rats.

Oxidative stress in the pathogenesis of diabetic neuropathy

Oxidative stress results from a cell or tissue failing to detoxify the free radicals that are produced during metabolic activity. Diabetes is characterized by chronic hyperglycemia that produces dysregulation of cellular metabolism. This review explores the concept that diabetes overloads glucose metabolic pathways, resulting in excess free radical production and oxidative stress. Evidence is presented to support the idea that both chronic and acute hyperglycemia cause oxidative stress in the peripheral nervous system that can promote the development of diabetic neuropathy. Proteins that are damaged by oxidative stress have decreased biological activity leading to loss of energy metabolism, cell signaling, transport, and, ultimately, to cell death. Examination of the data from animal and cell culture models of diabetes, as well as clinical trials of antioxidants, strongly implicates hyperglycemia-induced oxidative stress in diabetic neuropathy. We conclude that striving for superior antioxidative therapies remains essential for the prevention of neuropathy in diabetic patients.

Polyol pathway and diabetic peripheral neuropathy

This chapter critically examines the concept of the polyol pathway and how it relates to the pathogenesis of diabetic peripheral neuropathy. The two enzymes of the polyol pathway, aldose reductase and sorbitol dehydrogenase, are reviewed. The structure, biochemistry, physiological role, tissue distribution, and localization in peripheral nerve of each enzyme are summarized, along with current informaiton about the location and structure of their genes, their alleles, and the possible links of each enzyme and its alleles to diabetic neuropathy. Inhibitors of pathway enzyme and results obtained to date with pathway inhibitors in experimental models and human neuropathy trials are updated and discussed. Experimental and clinical data are analyzed in the context of a newly developed metabolic odel of the in vivo relationship between nerve sorbitol concentration and metabolic flux through aldose reuctase. Overall, the data will be interpreted as supporting the hypothesis that metabolic flux through the polyol pathway, rather than nerve concentration of sorbitol, is the predominant polyol pathway-linked pathogeneic factor in diabetic preipheral nerve. Finally, key questions and future directions for bsic and clinical research in this area are considered. It is concluded that robust inhibition of metabolic flux through the polyol pathway in peripheral nerve will likely result in substantial clinical benefit in treating and preventing the currently intractable condition of diabetic peripheral neuropathy. To accomplish this, it is imperative to develop and test a new generation of "super-potent" polyol pathway inhibitors.

Changes in endoneurial blood flow, motor nerve conduction velocity and vascular relaxation of epineurial arterioles of the sciatic nerve in ZDF-obese diabetic rats

BACKGROUND

We have previously reported that in streptozotocin-induced diabetic rats, reduction in endoneurial blood flow (EBF) and impairment of acetylcholine-mediated vascular relaxation of arterioles that provide circulation to the sciatic nerve precedes slowing of motor nerve conduction velocity (MNCV). However, in animal models of type 2 diabetes it is unknown whether slowing of MNCV is accompanied by vascular dysfunction.

METHODS

Using ZDF-lean and ZDF-obese diabetic rats we examined whether diabetes-induced slowing in MNCV was associated with a reduction in EBF and impaired vascular relaxation in epineurial arterioles of the sciatic nerve. We measured MNCV in the sciatic nerve using a non-invasive procedure, and sciatic nerve nutritive blood flow using microelectrode polarography. In vitro videomicroscopy was employed to quantify arteriolar diameter responses to acetylcholine in arterioles overlying the sciatic nerve.

RESULTS

MNCV and EBF in hyperglycemic (4-week duration) ZDF-obese diabetic rats were significantly decreased by 30% and 63%, respectively, compared to age-matched ZDF-lean rats. Acetylcholine elicited a dose-dependent dilation of epineurial vessels from ZDF-lean and ZDF-obese diabetic rats, although acetylcholine-induced dilation was significantly reduced in ZDF-obese diabetic rats. Determination of markers of oxidative stress provided ambiguous results. Superoxide levels were increased in epineurial vessels from ZDF-obese diabetic rats. Lens glutathione levels were decreased and serum thiobarbituric acid reactive substances increased in ZDF-obese diabetic rats but sciatic nerve conjugated diene and glutathione levels were not significantly different compared to ZDF-lean rats.

CONCLUSIONS

Diabetes causes a reduction in EBF and impairment in vascular relaxation in epineurial vessels in ZDF-obese diabetic rats. This impaired vascular response is associated with neural dysfunction.