Potential therapeutic approaches to the treatment or prevention of diabetic neuropathy: evidence from experimental studies

Naringin Attenuates the Diabetic Neuropathy in STZ-Induced Type 2 Diabetic Wistar Rats

The application of traditional medicines for the treatment of diseases, including diabetic neuropathy (DN), has received great attention. The aim of this study was to investigate the ameliorative potential of naringin, a flavanone, to treat streptozotocin-induced DN in rat models. After the successful induction of diabetes, DN complications were measured by various behavioral tests after 4 weeks of post-induction of diabetes with or without treatment with naringin. Serum biochemical assays such as fasting blood glucose, HbA1c%, insulin, lipid profile, and oxidative stress parameters were determined. Proinflammatory cytokines such as TNF-α and IL-6, and neuron-specific markers such as BDNF and NGF, were also assessed. In addition, pancreatic and brain tissues were subjected to histopathology to analyze structural alterations. The diabetic rats exhibited increased paw withdrawal frequencies for the acetone drop test and decreased frequencies for the plantar test, hot plate test, and tail flick test. The diabetic rats also showed an altered level of proinflammatory cytokines and oxidative stress parameters, as well as altered levels of proinflammatory cytokines and oxidative stress parameters. Naringin treatment significantly improved these parameters and helped in restoring the normal architecture of the brain and pancreatic tissues. The findings show that naringin's neuroprotective properties may be linked to its ability to suppress the overactivation of inflammatory molecules and mediators of oxidative stress.

New horizons of biomaterials in treatment of nerve damage in diabetes mellitus: A translational prospective review

BACKGROUND

Peripheral nerve injury is a serious concern that leads to loss of neuronal communication that impairs the quality of life and, in adverse conditions, causes permanent disability. The limited availability of autografts with associated demerits shifts the paradigm of researchers to use biomaterials as an alternative treatment approach to recover nerve damage.

PURPOSE

The purpose of this study is to explore the role of biomaterials in translational treatment approaches in diabetic neuropathy.

STUDY DESIGN

The present study is a prospective review study.

METHODS

Published literature on the role of biomaterials in therapeutics was searched for.

RESULTS

Biomaterials can be implemented with desired characteristics to overcome the problem of nerve regeneration. Biomaterials can be further exploited in the treatment of nerve damage especially associated with PDN. These can be modified, customized, and engineered as scaffolds with the potential of mimicking the extracellular matrix of nerve tissue along with axonal regeneration. Due to their beneficial biological deeds, they can expedite tissue repair and serve as carriers of cellular and pharmacological treatments. Therefore, the emerging research area of biomaterials-mediated treatment of nerve damage provides opportunities to explore them as translational biomedical treatment approaches.

CONCLUSIONS

Pre-clinical and clinical trials in this direction are needed to establish the effective role of several biomaterials in the treatment of other human diseases.

Abnormal vibration perception threshold alters the gait features in type 2 diabetes mellitus patients

OBJECTIVE

It is generally believed that gait characteristics of diabetic neuropathic patients differ from those of non-diabetic ones. However, it is still unclear how the abnormal foot sensation influences the gait during walking in type 2 diabetes mellitus (T2DM). For the purpose of gaining a better insight into the alterations of detailed gait parameters and figuring out important aspects in the gait indexes by peripheral neuropathy in elder T2DM patients, we compared the gait features in participants with normal glucose tolerance (NGT) controls and diabetic individuals complicated by peripheral neuropathy or not.

SUBJECTS AND METHODS

Gait parameters were observed during the 10-m walk on flat land among different conditions of diabetes in 1,741 participants from three clinical centers. Subjects were divided into four groups: persons with NGT were taken as the control group; patients with T2DM included three subgroups: DM control (no chronic complications), DM-DPN (DM complicated by only peripheral neuropathy), and DM-DPN+LEAD (DM complicated by both neuropathy and artery disease). The clinical characteristics and gait parameters were assessed and compared among these four groups. Analyses of variance were employed to verify possible differences of gait parameters between groups and conditions. Stepwise multivariate regression analysis was performed to reveal possible predictors of gait deficits. Receiver operating characteristic (ROC) curve analysis was employed to find any discriminatory power of diabetic peripheral neuropathy (DPN) for the step time.

RESULTS

In participants burdened with DPN, whether complicated by lower extremity arterial disease (LEAD) or not, step time increased sharply (p < 0.05). Stepwise multivariate regression models showed that independent variables of gait abnormality were sex, age, leg length, vibration perception threshold (VPT), and ankle-brachial index (ABI) (p < 0.01). Meanwhile, VPT was a significant independent predictor of step time, spatiotemporal variability (SD_A), and temporal variability (SD_B) (p < 0.05). ROC curve analysis was explored to find the discriminatory power of DPN for the occurrence of increased step time. The area under the curve (AUC) value was 0.608 (95% CI: 0.562-0.654, p < 0.01), and the cutoff point was 538.41 ms accompanied by a higher VPT. A significant positive association was observed between increased step time and the highest VPT group [odds ratio (OR) = 1.83, 95% CI: 1.32-2.55, p< 0.01]. In female patients, this OR value elevated to 2.16 (95% CI: 1.25-3.73, p< 0.01).

CONCLUSIONS

In addition to sex, age, and leg length, VPT was a distinct factor that associated with altered gait parameters. DPN is associated with increased step time, and the step time increases with worsening VPT in type 2 diabetes.

Neuropathy and Quality of Life in Diabetic Continuous Ambulatory Peritoneal Dialysis Patients

Oiabetes mellitus is the commonest cause of end-stage renal failure and is associated with considerable morbidity. Neuropathy is one of the most serious complications of diabetes, linked to the incidence of nephropathy and retinopathy. The prevalence of neuropathy increases with age and duration of diabetes. Peripheral sensorimotor neuropathy is the main manifestation of neurological dam -age in diabetes, while autonomic neuropathy, a devastating complication, is also present in a large number of patients with long-term diabetes. Clinical features of autonomic neuropathy are mainly cardiovascular disorders and abnormal visceral function. One of the most important sequelae of neuropathy is the development of the insensitive foot at risk of ulceration, deformation, Charcot neuroarthropathy, and amputation. Prevention, education, and identification of the at-risk patient are the key elements in managing these severe complications. Oialysis, and mainly peritoneal dialysis, still remains the main renal replacement therapy for end-stage renal disease (ESRO) diabetic patients. It is obvious from many studies that diabetes and its complications are major risk factors associated with poorer survival rates, increased morbidity, and decreased quality of life. Few, if any, data are available specifically evaluating quality of life in continuous ambulatory peritoneal dialysis (CAPO) diabetic patients. Fewer data are available estimating the impact of neuropathy on the quality of life of such patients. Specific studies must be carried out to further investigate quality-of-life issues and neuropathy in this vulnerable group of patients.

Inhibition of miR-25 aggravates diabetic peripheral neuropathy

The hyperglycemia-induced enhanced oxidative stress is a key factor of diabetic peripheral neuropathy implicated in the pathogenesis of diabetic neuropathy, and microRNA may be involved, playing promotion or protection roles. In this study, we aimed to investigate the function of miR-25 during the development of oxidative/nitrative stress and in subsequent neurological problems. We detected the oxidative stress effects and expression of miR-25 on sciatic nerves from db/db diabetic model mice and analyzed the expression of related genes by qPCR and Western blotting. Interestingly, we observed increased reactive oxygen species (ROS) and Nox4 expression in db/db mice accompanied with reduced miR-25. MiR-25 inhibitor treatment increased nicotinamide adenine dinucleotide phosphate activity in Schwann cells, whereas miR-25 precursor overexpression led to opposite results. MiR-25 precursor reduced the activation of protein kinase C and decreased Nox4 expression at both mRNA and protein levels. Advanced glycation endproducts (AGEs) and the receptor for advanced glycation endproducts (RAGE) were increased in the serum and in the peripheral nerves obtained from diabetic mice, and miR-25 inhibitor treatment in Schwann cells from wt mice led to the same effect. However, miR-25 precursor transfection reduced AGEs and RAGE, and further reduced inflammatory factors that contribute to the pathological process of peripheral nerves. These findings, for the first time, indicate that miR-25 acts as a protection factor in diabetic neuropathy by downregulating AGE-RAGE and reducing nicotinamide adenine dinucleotide phosphate oxidase. miR-25 reduced protein kinase C-α phosphorylation to produce less reactive oxygen species in diabetic peripheral nerves, and therefore it played an important role in the regulation of oxidative/nitrative stress and in consequent neurological dysfunction.

New Horizons in Diabetic Neuropathy: Mechanisms, Bioenergetics, and Pain

Pre-diabetes and diabetes are a global epidemic, and the associated neuropathic complications create a substantial burden on both the afflicted patients and society as a whole. Given the enormity of the problem and the lack of effective therapies, there is a pressing need to understand the mechanisms underlying diabetic neuropathy (DN). In this review, we present the structural components of the peripheral nervous system that underlie its susceptibility to metabolic insults and then discuss the pathways that contribute to peripheral nerve injury in DN. We also discuss systems biology insights gleaned from the recent advances in biotechnology and bioinformatics, emerging ideas centered on the axon-Schwann cell relationship and associated bioenergetic crosstalk, and the rapid expansion of our knowledge of the mechanisms contributing to neuropathic pain in diabetes. These recent advances in our understanding of DN pathogenesis are paving the way for critical mechanism-based therapy development.

Mechanism of diabetic neuropathy: Where are we now and where to go?

Neuropathy is the most common complication of diabetes. As a consequence of longstanding hyperglycemia, a downstream metabolic cascade leads to peripheral nerve injury through an increased flux of the polyol pathway, enhanced advanced glycation end‐products formation, excessive release of cytokines, activation of protein kinase C and exaggerated oxidative stress, as well as other confounding factors. Although these metabolic aberrations are deemed as the main stream for the pathogenesis of diabetic microvascular complications, organ‐specific histological and biochemical characteristics constitute distinct mechanistic processes of neuropathy different from retinopathy or nephropathy. Extremely long axons originating in the small neuronal body are vulnerable on the most distal side as a result of malnutritional axonal support or environmental insults. Sparse vascular supply with impaired autoregulation is likely to cause hypoxic damage in the nerve. Such dual influences exerted by long‐term hyperglycemia are critical for peripheral nerve damage, resulting in distal‐predominant nerve fiber degeneration. More recently, cellular factors derived from the bone marrow also appear to have a strong impact on the development of peripheral nerve pathology. As evident from such complicated processes, inhibition of single metabolic factors might not be sufficient for the treatment of neuropathy, but a combination of several inhibitors might be a promising approach to overcome this serious disorder. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00070.x, 2010)

The effects of Ginkgo biloba extract (GBe) on axonal transport microvasculature and morphology of sciatic nerve in streptozotocin-induced diabetic rats

To evaluate the protective effects ofGinkgo biloba extract (GBe) which has antioxidant activity against peripheral neuropathy due to diabetes mellitus, slow axonal transport and morphology of sciatic nerve including endoneurial microvessels were examined in 12 rats with diabetes mellitus induced by streptozotocin (STZ, 60mg/kg, b.w., i.p.). Six of the diabetic rats were treated with 0.1 % of GBe for 6 weeks from one week after the STZ injection. Serum glucose and lipid peroxide levels in GBe-treated diabetic rats were significantly lower than those in untreated diabetic rats (p<0.01, respectively), though the serum glucose level was higher than that in the control rats. L-[(35)S] methionine pulse radiolabeling with subsequent gel fluorography demonstrated that mean velocities (Vmean) of actin and β-tubulin, i.e. slow component b (SCb) transport in untreated diabetic rats were significantly lower than those in control rats (p<0.05, respectively); mean diameter of axons in the former rats was significantly smaller than that in the latter (p<0.01). Vmean of actin transport in GBe-treated diabetic rats was significantly faster than that in untreated diabetic rats (p<0.05). Vmean of slow axonal transport was significantly correlated with mean diameter of axons in the three groups of rats combined (p<0.01). On electron microscopy, severe altered endoneurial microvessels decreasing in luminal area together with endothelial cell degeneration or hypertrophy, pericyte debris and basement membrane thickening were observed in untreated diabetic rats; on the other hand these findings were less prominent in the diabetic rats treated with GBe. It is suggested that GBe treatment may protect disturbed slow axonal transport and pathological alterations of peripheral nerve with abnormal endoneurial microvasculature from diabetes mellitus by antioxidant activity.

Neuroprotective effect of naringin by modulation of endogenous biomarkers in streptozotocin induced painful diabetic neuropathy

Diabetes mellitus is a serious debilitating epidemic affecting all social strata in developing as well as developed countries. Diabetic neuropathy is most common of secondary complications associated with diabetes mellitus and is characterized by slowing of nerve conduction velocity, elevated pain, sensory loss and nerve fiber degeneration. The aim of the present investigation was to evaluate the neuroprotective effect of naringin against streptozotocin (STZ) induced diabetic neuropathic pain in laboratory rats. Four weeks after intraperitoneal injection of STZ resulted in significant decrease in mechano-tactile allodynia, mechanical hyperalgesia, thermal hyperalgesia and motor nerve conduction velocity. Activity of endogenous antioxidant like superoxide dismutase as well as membrane bound inorganic phosphate enzyme was also found to be significantly decreased. It not only caused neural cell apoptosis but also enhanced lipid peroxide, nitrite, and inflammatory mediators' (TNF-α) level. Chronic treatment with naringin (40 and 80mg/kg) for 4 weeks significantly and dose dependently attenuated the decrease in level of nociceptive threshold, endogenous antioxidant and membrane bound inorganic phosphate enzyme. It also decreased the elevated levels of oxidative-nitrosative stress, inflammatory mediators as well as apoptosis in neural cells significantly and dose dependently. The important finding of the study is that, the naringin-insulin combination not only attenuated the diabetic condition but also reversed the neuropathic pain, whereas insulin or naringin alone only improved hyperglycemia but partially reversed the pain response in diabetic rats. Thus, naringin is a potential flavonone bearing antioxidant, antiapoptotic and disease modifying property acting via modulation of endogenous biomarker to inhibit diabetes induced neuropathic pain.

Effect of yogic exercise on super oxide dismutase levels in diabetics

Context:

Reactive oxygen species are known to aggravate disease progression. To counteract their harmful effects, the body produces various antioxidant enzymes, viz, superoxide dismutase, glutathione reductase etc. Literature reviews revealed that exercises help to enhance antioxidant enzyme systems; hence, yogic exercises may be useful to combat various diseases.

Aims:

This study aims to record the efficacy of yoga on superoxide dismutase, glycosylated hemoglobin (Hb) and fasting blood glucose levels in diabetics.

Settings and Design:

Forty diabetics aged 40–55 years were assigned to experimental (30) and control (10) groups. The experimental subjects underwent a Yoga program comprising of various Asanas (isometric type exercises) and Pranayamas (breathing exercises) along with regular anti-diabetic therapy whereas the control group received anti-diabetic therapy only.

Materials and Methods:

Heparinized blood samples were used to determine erythrocyte superoxide dismutase (SOD) activity and glycosylated Hb levels and fasting blood specimens collected in fluoride Vacutainers were used for assessing blood glucose.

Statistical Analysis Used:

Data were analyzed by using 2 × 2 × 3 Factorial ANOVA followed by Scheffe's posthoc test.

Results:

The results revealed that Yogic exercise enhanced the levels of Superoxide dismutase and reduced glycosylated Hb and glucose levels in the experimental group as compared to the control group.

Conclusion:

The findings conclude that Yogic exercises have enhanced the antioxidant defence mechanism in diabetics by reducing oxidative stress.

Sulodexide prevents peripheral nerve damage in streptozotocin induced diabetic rats

We investigated whether sulodexide has additional protective effects against peripheral nerve damage caused by microvascular dysfunction in a rat model of diabetes. Female Sprague-Dawley (SD) rats were divided into the following 4 groups (n=7-9/group): Normal, Normal+Sulodexide (sulodexide 10mg/kg), diabetic group, and diabetic+Sulodexide (sulodexide 10mg/kg). We assessed current perception threshold, skin blood flow, superoxide dismutase, and proteinuria in experimental rats after oral administration of sulodexide for 20 weeks. We also performed morphometric analysis of sciatic nerves and intraepidermal nerve fibers of the foot. Superoxide dismutase activity in the blood and sciatic nerve were increased significantly after sulodexide treatment in the diabetic group. Current perception threshold was reduced at 2000 Hz (633.3 ± 24.15 vs 741.2 ± 23.5 μA, P<0.05) and skin blood flow was improved (10.90 ± 0.67 vs 8.85 ± 0.49 TPU, P<0.05) in the diabetic+Sulodexide group compared with the diabetic group. The mean myelinated axon area was significantly larger (56.6 ± 2.2 vs 49.8 ± 2.7 μm(2), P<0.05) and the intraepidermal nerve fiber density was significantly less reduced (6.27 ± 0.24 vs 5.40 ± 0.25/mm, P<0.05) in the diabetic+Sulodexide group compared to the diabetic group. Our results demonstrate that sulodexide exhibits protective effects against peripheral nerve damage in a rat experimental model of diabetes. Therefore, these findings suggest that sulodexide is a potential new therapeutic agent for diabetic peripheral neuropathy.

Oxidative stress and antioxidant defense mechanisms linked to exercise during cardiopulmonary and metabolic disorders

Oxidative stress has been implicated in the pathophysiology of multiple human diseases, in addition to the aging process. Although various stimuli exist, acute exercise is known to induce a transient increase in reactive oxygen and nitrogen species (RONS), evident by several reports of increased oxidative damage following acute bouts of aerobic and anaerobic exercise. Although the results are somewhat mixed and appear disease dependent, individuals with chronic disease experience an exacerbation in oxidative stress following acute exercise when compared to healthy individuals. However, this increased oxidant stress may serve as a necessary “signal” for the upregulation in antioxidant defenses, thereby providing protection against subsequent exposure to prooxidant environments within susceptible individuals. Here we present studies related to both acute exercise-induced oxidative stress in those with disease, in addition to studies focused on adaptations resulting from increased RONS exposure associated with chronic exercise training in persons with disease.

Potencial terapêutico para a prevenção e tratamento da nefropatia e neuropatia diabéticas: evidências do uso do cilostazol

O cilostazol é um inibidor seletivo da fosfodiesterase tipo III com ação vasodilatadora, antiagregante plaquetária e antitrombótica. É considerada a droga de primeira escolha na claudicação intermitente devido à doença arterial obstrutiva periférica. Vários estudos demonstraram melhora significativa na distância percorrida na caminhada sem dor e na qualidade de vida, sem aumentar o risco de sangramento. Essas ações também foram verificadas em pacientes diabéticos, pois o cilostazol não afeta o metabolismo da glicose. Estudos, principalmente experimentais, têm mostrado resultados satisfatórios na melhora do fluxo sangüíneo neural, na atividade da bomba de sódio e potássio, na resistência à insulina e na microalbuminúria. Neste artigo, apresentamos uma revisão do uso do cilostazol na prevenção e no tratamento das complicações do diabetes mellitus, como nefropatia e neuropatia. Ressalta-se a necessidade do controle adequado dos níveis glicêmicos, da hipertensão arterial sistêmica e do tabagismo. Um maior número de estudos clínicos é necessário para melhor compreensão desses efeitos benéficos.

Omega-3 fatty acid effects on biochemical indices following cancer surgery

Epidemiological studies have indicated that a high intake of saturated fat and/or animal fat increases the risk of colon and breast cancer. Laboratory and clinical investigations have shown a reduced risk of colon carcinogenesis after alimentation with omega-3 fatty acids, as found in fish oil. Mechanisms accounting for these anti-tumor effects are reduced levels of PGE(2) and inducible NO synthase as well as an increased lipid peroxidation, or translation inhibition with subsequent cell cycle arrest. Further, omega-3 eicosapentaenoic acid is capable of down-regulating the production and effect of a number of mediators of cachexia, such as IL-1, IL-6, TNF-alpha and proteolysis-inducing factor. In patients with advanced cancer, it is possible to increase energy and protein intake via an enteral or parenteral route, but this seems to have little impact on progressive weight loss. Fish oil administration improved patients' conditions in cancer cachexia and during radio- and chemotherapy. In patients undergoing tumor resection surgery we observed improvement of liver and pancreas biochemical indices when omega-3 fatty acids were administered. This paper is a review of recent developments in the field of nutrition in cancer patients with emphasis on the acute phase response following cancer surgery and the beneficial aspects of fish oil administration.

Effect of aminoguanidine treatment on diabetes-induced changes in the myenteric plexus of rat ileum

The aim of this study was to investigate the ability of aminoguanidine (AG) to prevent diabetes-induced changes in nitric oxide synthase- (nNOS), vasoactive intestinal polypeptide- (VIP) and noradrenaline- (NA) containing nerves of the rat ileum using immunohistochemical and biochemical techniques. Diabetes was induced in adult male Wistar rats by a single intraperitoneal injection of streptozotocin (65 mg/kg). AG was administered in the drinking water to control (1.8 g/l) and diabetic (0.9 g/l) rats over a period of 8 weeks. Diabetes caused a significant increase in the thickness of nNOS-containing nerve fibres (p<0.001) in the circular muscle, in nNOS activity (p<0.05) and in the size distribution of nNOS-containing myenteric neurons (p<0.001). The thickness of VIP-containing nerve fibres was significantly greater (p<0.01) and there was a significant increase in varicosity size (p<0.01) and proportion of VIP-positive myenteric neurons (p<0.01) in diabetes. NA levels were significantly reduced (p<0.01) and the size of varicosities containing tyrosine hydroxylase (TH) was significantly increased (p<0.001) in diabetes. AG treatment completely or partially prevented the diabetes-induced increase in nNOS activity, in VIP-containing varicosity size, and in fibre width of both VIP- and nNOS-containing fibres in the circular muscle but had no effect on the diabetes-induced increase in nNOS-containing neuronal size or proportion of VIP-containing myenteric neurons. In contrast to VIP, AG treatment had no effect on the increase in TH-containing varicosity size in diabetes and also failed to prevent the decrease in NA levels induced by diabetes. These results indicate that AG treatment for neuropathy is not equally effective for all autonomic nerves supplying the ileum and that diabetes-induced changes in NA-containing nerves are particularly difficult to treat.

Saga of Renin-Angiotensin System and Calcium Channels in Hypertensive Diabetics: Does it Have a Therapeutic Edge?

Current understanding of the genesis of diabetic vascular disease suggests that vascular complications, such as atherosclerosis and hypertension, are associated with changes in structural and functional parameters. Experimental and epidemiological data suggest that activation of the renin-angiotensin-aldosterone system plays an important role in the development of micro- and macro-vascular complications. Most of the negative cardiovascular actions of angiotensin II are mediated through AT1 receptors, whereas the AT2 receptors mediate largely beneficial effects. Hence, compared to angiotensin converting enzyme inhibitors (ACEIs), selective AT1 receptor blockers (ARBs) should provide additional end organ protection via AT2 receptors activation. Although ACEIs are useful therapeutically, they are being currently displaced by ARBs. Enhanced calcium ion channel activity is reported in vascular smooth muscles from diabetic animal models. Clinical benefits of calcium channel blockers (CCBs) in diabetic hypertensive patients are controversial, but there is increasing experimental evidence for the beneficial effects of dihydropyridine-type CCBs. Although the treatment of hypertension in diabetics reduces cardiovascular and microvascular complications, the ideal strategy for treating hypertension in diabetics has not been well defined and warrants a combination approach. Only limited clinical data regarding the use of ARBs in combination with CCBs in diabetics are available. The experimental data suggest that combination of a CCB and an AT1 receptor blocker, or a hypothetical dual blocker of AT1 receptors as well as of calcium channels would be an ideal regimen. There is, however, no conclusive clinical evidence to support the combined use of these drugs. This review highlights the available experimental data that support the therapeutic benefits of this combination.

Diabetic neuropathies: features and mechanisms

Diabetic neuropathies include both focal neuropathies and diffuse polyneuropathy. Polyneuropathy, the most common of the diabetic neuropathies excluding focal entrapment, has not yet been explained by a single disease mechanism despite intensive investigation. A number of abnormalities appear to cascade into a 'vicious cycle' of progressive microvascular disease associated with motor, sensory and autonomic fiber loss. These abnormalities include excessive polyol (sugar alcohol) flux through the aldose reductase pathway, functional and structural alterations of nerve microvessels, nerve and ganglia hypoxia, oxidative stress, nonspecific glycosylation of axon and microvessel proteins, and impairment in the elaboration of trophic factors critical for peripheral nerves and their ganglia. While an initiating role for nerve ischemia in the development of polyneuropathy has been proposed, the evidence for it can be questioned. The role of sensory and autonomic ganglia in the development of polyneuropathy has had relatively less attention despite the possibility that they may be vulnerable to a variety of insults, particularly neurotrophin deficiency. Superimposed on the deficits of polyneuropathy is the failure of diabetic nerves to regenerate as effectively as nondiabetics. Polyneuropathy has not yet yielded to specific forms of treatment but a variety of new trials addressing plausible hypotheses have been initiated. This review will summarize some of the clinical, pathological and experimental work applied toward understanding human diabetic neuropathy and will emphasize ideas on pathogenesis.

Restoration of ultrastructural and biochemical changes in alloxan-induced diabetic rat sciatic nerve on treatment with Na3VO4 and Trigonella--a promising antidiabetic agent

Vanadium has been reported to have broad pharmacological activity both in vitro and in vivo. Vanadium compound, sodium orthovanadate, Na3VO4, is well known for its hypoglycaemic effects. However, Na3VO4 exerts these effects at relatively high doses (0.6 mg/ml) and exhibit several toxic effects. In the present study lower doses of Na3VO4 (0.2 mg/ml) are combined with Trigonella foenum graecum seed powder (TSP), another hypoglycaemic agent, to reduce its toxicity without compromising its antidiabetic potential. The efficacy of the lower doses of Na3VO4 has been investigated in restoring the altered glucose metabolism and histological structure in the sciatic nerves in 21 and 60 days alloxan diabetic rats. A portion of the glucose was found to be channelled from the normal glycolytic route to polyol pathway, evident by the reduced hexokinase activity and increased polyol pathway enzymes aldose reductase and sorbitol dehydrogenase activity causing accumulation of sorbitol and fructose in diabetic conditions. Ultrastructural observation of the sciatic nerve showed extensive demylination and axonal loss after eight weeks of diabetes induction. Blood glucose levels increased in diabetic rats were normalized with the lower dose of vanadium and Trigonella treatment. The treatment of the diabetic rats with vanadium and Trigonella prevented the activation of the polyol pathway and sugar accumulations. The sciatic nerves were also protected against the structural abnormalities found in diabetes with Trigonella foenum graecum as well as Na3VO4. Results suggest that lower doses of Na3VO4 may be used in combination with TSP as an efficient antidiabetic agent to effectively control the long-term complications of diabetes in tissues like peripheral nerve.

Prevention and partial reversal of diabetes-induced changes in enteric nerves of the rat ileum by combined treatment with alpha-lipoic acid and evening primrose oil

Treatment with alpha-lipoic acid (LA) or evening primrose oil (EPO), individually, fails to prevent diabetes-induced changes in enteric nerves. Since synergy between these treatments has been reported, the aim was to investigate the effectiveness of combined LA/EPO treatment. LA and EPO were administered in the diet (approximately 80 and 200 mg/kg/day, respectively) to control and diabetic (induced by streptozotocin, 65 mg/kg, i.p.) rats. For prevention, treatment started after 1 week and lasted 7 weeks. For reversal, treatment lasted 4 weeks and was initiated after 8 weeks. Nerves supplying the ileum containing vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and noradrenaline (NA) were examined immunohistochemically or biochemically. Diabetes caused a significant increase in VIP-containing cell bodies (p<0.001), decrease in NA content (p<0.01) and loss of CGRP-immunoreactivity. LA/EPO treatment totally prevented diabetes-induced changes in VIP (p<0.001) and CGRP and partially reversed (p<0.05) these changes once they had been allowed to develop. In contrast, treatment had no effect on diabetes-induced changes in NA-containing nerves. Therefore, LA and EPO are only effective at treating diabetes-induced changes in some enteric nerves when administered in combination. However, diabetes-induced changes in NA-containing nerves are resistant to treatment.

Novel inhibitors of advanced glycation endproducts

A number of natural or synthetic compounds as AGE inhibitors have been proposed, discovered or currently being advanced by others and us. We have identified two new classes of aromatic compounds; aryl- (and heterocyclic) ureido and aryl (and heterocyclic) carboxamido phenoxyisobutyric acids, and benzoic acid derivatives and related compounds, as potential inhibitors of glycation and AGE formation. Some of these novel compounds also showed "AGE-breaking" activities in vitro. Current evidence is that chelation of transition metals and/or trapping or indirect inhibition of formation of reactive carbonyl compounds are involved in the mechanisms of action of these novel AGE inhibitors and breakers. Here, we review the inhibitors of glycation and AGE-breakers published to date and present the results of our in vitro and in vivo investigations on a number of these novel AGE inhibitors. These AGE-inhibitors and AGE-breakers may find therapeutic use in the treatment of diseases that AGE formation and accumulation may be responsible for their pathogenesis such as diabetes, Alzheimer's, rheumatoid arthritis, and atherosclerosis.

Clinical trials for drugs against diabetic neuropathy: can we combine scientific needs with clinical practicalities?

Diabetic neuropathy is a chronic progressive disease accounting for considerable morbidity and reduced quality of life among patients with diabetes. Accumulating evidence suggests that the clinical and neurophysiological markers used to assess neuropathy not only predict the development of neuropathic foot ulceration, one of the most common causes for hospital admission and lower limb amputations, but are also predictors of increased mortality in diabetic patients. In addition to metabolic control, drug treatment of both incipient and clinically manifest diabetic neuropathy will be necessary for the years to come. Because 1-2% of the whole population in western societies may be affected, the search for effective drug treatment is not only a very important goal for the patient suffering from diabetic neuropathy and for the practicing physician, but also an economic task for both the health care systems and pharmaceutical companies. The validity of inferences about the clinical consequences of the use of any given agent to induce a specific pharmacologic effect will depend not only on the extent to which it affects the targeted biological phenomenon, but also on the extent to which all of the actions of the agent have been defined and the extent to which all affect the entire organism, alone and in concert. The ultimate test of the usefulness of a drug or device depends on the determination of outcomes, ideally in randomized clinical trials (RCTs) of sufficient scope and duration. The efficacy and safety of a variety of drugs based on the different pathogenetic hypotheses proposed have been evaluated in RCTs since the 1970s. However, the quality of RCTs published between 1981 and 1992 that evaluated the effects of medical treatment in diabetic polneuropathy was poor. Adequate designs for RCTs in diabetic neuropathy must consider the following criteria: type and stage of neuropathy, homogeneity of the study population, outcome measures (neurophysiological markers, intermediate clinical end points, ultimate clinical outcomes, quality of life), natural history, sample size, study duration, reproducibility of neurophysiological and intermediate end points, nonspecific effects of treatment, measures of treatment effect, the extent to which the overall trail result applies to individual patients (external validity), and the reporting of the RCTs. Trials focusing preferentially on patients with mild or moderate early stages of neuropathy over long periods of 3-5 years aimed at slowing or prevention, rather than reversal, using end point measures that have clinical and prognostic significance are most likely to produce meaningful results.

The effectiveness of treatments of diabetic autonomic neuropathy is not the same in autonomic nerves supplying different organs

The aim of the study was to investigate antioxidant (alpha-lipoic acid [LA]) and gamma-linolenic acid treatments in the prevention of changes in autonomic nerves induced in streptozotocin-diabetic rats. Autonomic nerves supplying the heart, penis, and gut were examined using immunohistochemical and biochemical techniques. LA and gamma-linolenic acid (present in evening primrose oil [EPO]) were administered as dietary supplements ( approximately 80 and 200 mg. kg(-1). day(-1), respectively). LA treatment prevented the diabetes-induced decrease of norepinephrine (NA) in the heart and of type I nitric oxide synthase (NOS-I) expression in erectile tissue of the penis but failed to prevent diabetes-induced changes in NA-, vasoactive intestinal polypeptide-, or calcitonin gene-related peptide-containing nerves supplying the ileum. LA partially prevented and EPO totally prevented the increase in NOS-I activity induced by diabetes in the ileum. EPO treatment failed to prevent any other diabetes-induced changes in the heart, penis, or ileum. These results demonstrate that, whereas LA treatment is more effective than EPO in preventing diabetes-induced changes in autonomic nerves, the effectiveness of LA treatment varies with the target organ studied. Diabetes-induced changes in nerves supplying the ileum are more resistant to treatment than those of the heart and penis.

Neurovascular disease, antioxidants and glycation in diabetes

People with diabetes are ten to fifteen times more likely to have a lower limb amputation (LLA) than non-diabetic individuals. Fifteen percent of people with diabetes will develop a foot ulcer during their lifetime, the rate of major amputation amongst diabetic individuals continues to rise, foot problems remain the commonest reason for diabetes-related hospitalisation and recurrence rates in patients with previous foot ulcers are 50% or more. Hyperglycaemia-induced oxidative stress has been shown to result in decreased nerve conduction velocity, and decreased endoneural blood flow-both precursors for neuropathy. Vitamin antioxidants have been shown to be effective therapy in experimental models in reducing free radical species and inhibiting the oxidative process in diabetes subjects. Little work has been published, however, regarding the dietary use of antioxidants from foods, and their specific effects on neurovascular disease and glycation within the diabetes population. Aetiological and prevention studies with dietary antioxidants from foods aimed at the complex nature of foot problems in diabetes are needed.

Pimagedine: a novel therapy for diabetic nephropathy

Hyperglycaemia is directly involved in causing long-term diabetic complications. The non-enzymatic glycation of proteins, yielding irreversible advanced glycation end products and advanced glycation end products-derived protein crosslinking, participates in the development of diabetic complications, such as diabetic nephropathy. Diabetic nephropathy is becoming a major medical problem with increasing numbers of these patients progressing to end stage renal disease, thus requiring renal replacement therapy. While several interventions may slow the development and progression of diabetic nephropathy, there is no effective treatment to prevent or reverse the disease. Pimagedine (aminoguanidine HCl) has been shown to be an effective agent in reducing the severity of the structural and functional alterations associated with experimental diabetic nephropathy. Preliminary studies suggest a beneficial effect of pimagedine in treating patients with diabetic nephropathy. In summary, these observations support a role for advanced glycation end products inhibitors, like pimagedine, in the management of diabetic nephropathy, either alone or in combination with other therapies.

The effect of insulin and sulodexide (Vessel Due F) on diabetic foot syndrome: pilot study in elderly patients

OBJECTIVE

To assess the efficacy of insulin plus sulodexide (a mixture of 80% heparin-like substances and 20% dermatan sulphate) on diabetic ulcers, and its influence on foot skin microcirculation and diabetic neuropathy.

RESEARCH DESIGN AND METHODS

Two groups of diabetic patients, suffering from severe neuropathy and ulceration, were randomly assigned to insulin (I) plus sulodexide (S) (n=12) or insulin plus placebo (P) (n=6) therapy, for 10 weeks. Laser Doppler assessment of foot skin flow (LDF), at rest and 30 or 60 s after arterial occlusion, and nerve conduction tests (sensorial evoked and motoric conduction potentials) have been evaluated in both groups.

RESULTS

Postischaemic flow was 2.5 times shorter in ulcerated vs. non-ulcerated feet in diabetic patients. A significant increase in flows after 30 and 60 s ischaemia was detected in both groups at the end of therapy (IS group, ulcerated foot, LDF=60 s: from 99.1+/-14.3 to 218.6+/-28.6 PU, P<.001. IP group=from 110.5+/-13.0 to 164.8+/-15.4 PU, P<.05). The length of reactive hyperaemia was higher in IS vs. IP group (IS: from 30.3+/-2.9 to 43.9+/-2.2 s, P<.001; IP: from 28.7+/-3.0 to 33.3+/-3.3 s, ns). Ninety-two percent of ulcers heals in a mean time of 46.4 days (IS group) vs. 83% and 63.0 days, respectively, in IP group. Nerve conduction studies have not demonstrated within- and between-group differences.

CONCLUSIONS

Sulodexide and insulin improve the postischaemic skin flow in ulcerated feet, without affecting nerve conduction tests. The effect of sulodexide results additive to insulin; it is clinically relevant, in the view of the possibility of reducing the time needed to completely heal ulcers. The ultimate validation of these preliminary results requires extensive trials.

The role of protein kinase C in the development of the complications of diabetes

Diabetes mellitus produces a state of chronic hyperglycemia which in turn leads to the development of severe complications including retinopathy, nephropathy, neuropathy, and atherosclerosis. Many different mechanisms have been put forward to attempt to explain how glucose elevations can damage these various organ systems. Protein kinase C activation is one of the sequelae of hyperglycemia and is thought to play a role in the development of diabetic complications. There are multiple mechanisms for its activation in the diabetic state and multiple downstream effects attributable to that activation. The role of protein kinase C activation in the development of the above-mentioned complications of diabetes is discussed in this chapter. In addition, the potential use of isoform-specific inhibitors of protein kinase C for the treatment of diabetic complications is proposed.

Physiological and morphometric analyses of neuropathy in sucrose-fed OLETF rats

To investigate the characteristic features of diabetic neuropathy in type 2 diabetes mellitus, Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of human type 2 diabetes mellitus, and non-diabetic Long-Evans Tokushima Otsuka (LETO) rats were fed with or without sucrose and/or an aldose reductase inhibitor, [5-(3-thienyl) tetrazol-1-yl] acetic acid (TAT), for 24 weeks, and physiological, biochemical and morphological assessments were performed. Sucrose administration caused remarkable hyperglycemia in OLETF rats but not in LETO rats. Sucrose-fed OLETF rats demonstrated delayed nerve conduction velocity, decreased coefficient of variation of R-R interval, reduced sciatic nerve blood flow, increased platelet aggregation activity, a lower concentration of erythrocyte 2,3-diphosphoglycerate, and decreased Na+/K+-ATPase activity in sciatic nerves, compared with the non-sucrose-fed OLETF and LETO rats. TAT prevented all these deficits except hyperglycemia. Sorbitol and fructose accumulation and myo-inositol depletion in tail nerves of sucrose-fed OLETF rats were ameliorated by TAT. Myelinated fiber size and density in sural nerves of sucrose-fed OLETF rats were decreased and increased, respectively, compared with non-sucrose-fed OLETF and LETO rats. These morphological abnormalities were normalized by TAT. These observations suggest that the sucrose-fed OLETF rat developed diabetic neuropathy not only electrophysiologically but also histologically, and that an aldose reductase inhibitor, TAT, possesses therapeutic value for the treatment of diabetic neuropathy.

Spinal cord stimulation in diabetic lower limb critical ischaemia: transcutaneous oxygen measurement as predictor for treatment success

OBJECTIVES

to evaluate whether transcutaneous oxygen tension (TcpO(2)) measurements could be used as a specific prognostic parameter in selecting diabetic patients for permanent device implantation.

METHODS

sixty consecutive diabetic patients (28 with autonomic neuropathy), classified as Fontaine stage III or IV, underwent spinal cord stimulation (SCS) for ischaemic pain, after failed conservative or surgical treatment. Pedal TcpO(2)on the dorsum of the foot and ankle-pressure Doppler measurements were performed before, and 2 and 4 weeks after implantation.

RESULTS

limb salvage and good pain relief were achieved in 35 patients, while in 12 partial pain relief and limb salvage for at least 6 months were obtained. In 13 patients the method failed and the ischaemic limbs were amputated. Only 3 of the 28 patients with neuropathy had any long-term benefit. Limb salvage was achieved in those patients with a significant increase in TcpO(2)within 2 weeks of stimulation. The stage of the neuropathy was inversely related to the success of SCS therapy. The ankle-brachial pressure index (ABPI) did not change after stimulation.

CONCLUSIONS

diabetic patients with significant increase of TcpO(2)and pain relief during a 2-week test period may be successfully treated by long-term SCS unless they have advanced autonomic neuropathy.

Autonomic nervous regeneration in acetic acid-induced ulcer from the viewpoint of synapse formation--effect of basic fibroblast growth factor and sofalcone in the rat

BACKGROUND

Monoclonal antibodies against GAP43 and synaptophysin, markers of regenerated nerves, have recently become available.

AIM

To investigate the regeneration of the autonomic nerves after acetic acid treatment, as well as the effect of recombinant basic fibroblast growth factor (bFGF-CS23) and sofalcone on reinnervation.

METHODS

Ulcers were induced by the direct application of 100% acetic acid to the serosal surface of the rat fundic stomach. Some rats were treated with bFGF-CS23 or sofalcone every 12 h after the acetic acid treatment. The immunohistochemical location of GAP43 and synaptophysin was observed by confocal laser microscopy, and the uptake sites of 14C-sofalcone were observed by autoradiography.

RESULTS

Both GAP43 and synaptophysin immunoreactivities surrounding microvessels were weak in the control group, whereas in the acetic acid-treated group, these immunoreactivities were increased. Treatment with bFGF-CS23 and sofalcone increased these immunoreactivities. The binding sites of sofalcone coincided with the location of regenerated nerves and surface mucous cells. The progenitors of the autonomic nerves were more abundant than expected.

CONCLUSION

Both bFGF and sofalcone seem to stimulate nerve regeneration.

Influence of tolrestat on the defective leukocyte-endothelial interaction in experimental diabetes

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 B(4) (1 ng/ml), as well as after the application of a local irritant stimulus (carrageenan, 100 microg). 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.

Does autonomic neuropathy influence spinal cord stimulation therapy success in diabetic patients with critical lower limb ischemia?

BACKGROUND

Spinal cord stimulation (SCS) improves microcirculatory blood flow and relieves diabetic neuropathic and ischemic pain, reducing the amputation rate in patients with peripheral arterial occlusive disease (PAOD). The purpose of this study was to evaluate whether the presence of autonomic neuropathy in diabetic patients with PAOD influences the success of SCS therapy.

METHODS

Sixty consecutive diabetic patients (15 with early and 13 with definite and/or combined autonomic neuropathy) with an ankle/brachial systolic pressure index (ABI) less than 0.20 +/- 0.08, underwent spinal cord stimulation after failed conservative or surgical treatment. The neuropathic status of the patients was evaluated before implantation and pedal TcpO2 measurements on the dorsum of the foot were performed.

RESULTS

Limb salvage and pain relief >75%, evaluated with the visual analogue scale, were achieved in 35 patients, whereas in 12 a partial success with pain relief >50% and limb salvage for at least 6 months were obtained. In 13 patients the method failed and the ischemic limbs were amputated. Among the 28 diabetic patients with autonomic neuropathy the treatment failed or resulted in only partial success in 25, whereas in all 32 patients without neuropathy limb salvage and pain relief >75% were achieved (p < 0.0001). Partial success in 10 patients with early neuropathy and in two with definite was achieved (p = 0.008), whereas in 11 patients with definite neuropathy and in two with early the method failed (p < 0.001). The stage of the neuropathy was inversely related to the success of SCS therapy, independent of the stage of the disease. The method's success was related to the presence of adequate paraesthesias and warm feeling in the painful area with size reduction of the trophic lesions.

CONCLUSIONS

Diabetic patients with peripheral arterial occlusive disease presenting with intractable pain may be successfully treated with spinal cord stimulation unless they have associated severe autonomic neuropathy.

Epidural spinal cord electrical stimulation in diabetic critical lower limb ischemia

Spinal cord stimulation (SCS) has been suggested to improve microcirculatory blood flow to relieve ischemic pain and to reduce amputation rate in patients with peripheral arterial occlusive disease (PAOD). The aim of this study was to evaluate the specific prognostic parameters in the prediction of successful SCS, in diabetic patients, performing a retrospective data analysis. To perform this evaluation, 64 diabetic patients (39 men, 25 women; mean age, 69 years) classified as Fontaine's stage III and IV, with PAOD, were treated with SCS for rest pain and trophic lesions with dry gangrene, after failed conservative or surgical treatment. In clinical controls, pedal transcutaneous oxygen tension (TcPO(2)), ankle/brachial blood pressure index (ABI), and toe pressure Doppler measurements were utilized to select and follow-up the patients. After 58 months of follow-up (range, 20-128 months), pain relief greater than 75% and limb salvage were achieved in 38 diabetic patients. A partial success was obtained in nine patients with pain relief greater than 50% and limb salvage for at least 6 months. The method failed in 17 patients or the device was removed due to technical problems, and the limb was amputated in these patients. TcPO(2) was assessed on the dorsum of the foot. Clinical improvement and SCS success were associated with increase of TcPO(2), before and after implantation. Limb salvage was achieved in the patients who had significant TcPO(2) increase within the 2 weeks of the testing period, independently of the stage of the disease. A TcPO(2) increase of more than 50% in the first 2 months after implantation was predictive of success, and was related to the presence of adequate paresthesias in the painful area during the trial period. TcPO(2) significantly increased after long-term follow-up in all patients with limb salvage (from 22.1 to 43.1 mm Hg in the rest pain patients, from 15.8 to 36.4 mm Hg in those with trophic lesions of less than 3 cm(2), and from 12.1 to 28.1 in those with trophic lesions of greater than 3 cm(2), (p < 0.01). ABI did not changed under stimulation. In diabetic patients with PAOD, the SCS increases the skin blood flow, is associated with significant pain relief, and could be proven an excellent alternative therapy, improving the life quality. Significant TcPO(2) increase within the 2-week test period, is a predictive index of therapy success and should be considered before the final decision in terms of cost effectiveness, before the permanent implantation.

Painful diabetic neuropathy

Chronic painful diabetic neuropathy causes symptoms that can last for many years and severely impair the quality of life of affected patients. This review describes the epidemiology, pathophysiology and treatment of chronic neuropathic pain. Particular emphasis is placed on a comprehensive review of the management of painful symptoms through a detailed review of the published literature using a variety of databases particularly Medline and EMBASE.

The effect of cadmium (Cd) treatment on somatosensory evoked potentials (SEPs) and conduction velocity in alloxane-induced diabetic rats: relation to lipid peroxidation

Fifty-two healthy Swiss male albino rats, aged three months, were divided into four groups: Control (C), diabetic (D), cadmium (Cd), and diabetic + Cd (D+Cd). Diabetes was induced in D and D+Cd groups by administration of alloxane (5 mg/100 g). Cd and D+Cd groups were injected with CdCl2 i.p. (2 mg/kg/week) for 2 months. Somatosensory evoked potentials (SEPs) of the four groups were recorded following left posterior tibial nerve (PTN) stimulation. The mean latencies of P1, N1, P2 and N2 components were prolonged in all experimental groups compared with the control group. P1N1 and N1P2 amplitudes were significantly decreased in Cd and D+Cd groups in comparison with the control group. P2N2 amplitude was significantly decreased in the Cd group compared with the control group. In addition, conduction velocities and action potential amplitudes were determined from the sciatic nerves. The means of peripheral conduction velocities and action potential amplitudes were decreased significantly in all the experimental groups in comparison with the control group. Thiobarbituric acid reactive substances (TBARS), an indicator of lipid peroxidation, were increased in the kidneys and sciatic nerves of all experimental groups compared with the control group. A significant increase in the TBARS level of the brain was found in the Cd and D+Cd groups.

Painful diabetic neuropathy

Chronic painful diabetic neuropathy can cause a variety of challenges, particularly in successful treatment. The pain, which can last for years, can severely impair quality of life. Management is difficult, although the careful use of drugs can be significantly beneficial. Tricyclic and anticonvulsant drugs may be effective, with a variety of drugs available as second line agents. Newer non-drug systems such as electrical spinal cord stimulation represent exciting possibilities for the future management of this most difficult diabetic syndrome.

Glucose-induced oxidative stress and programmed cell death in diabetic neuropathy

The Diabetes Control and Complications Trial (DCCT) established the importance of hyperglyemia and other consequences of insulin deficiency in the pathogenesis of diabetic neuropathy, but the precise mechanisms by which metabolic alterations produce peripheral nerve fiber damage and loss remain unclear. Emerging data from human and animal studies suggest that glucose-derived oxidative stress may play a central role, linking together many of the other currently invoked pathogenetic mechanisms such as the aldose reductase and glycation pathways, vascular dysfunction, and impaired neurotrophic support. These relationships suggest combinations of pharmacological interventions that may synergistically protect the peripheral nervous system (PNS) against the metabolic derangements of diabetes mellitus.

Oxidative stress in diabetic rats induced by streptozotocin: protective effects of melatonin

We have studied the effect of the administration of two doses of melatonin (melatonin 100 and melatonin 200 microg/kg bw) on diabetes and oxidative stress experimentally induced by the injection of streptozotocin (STZ) in female Wistar rats. STZ was injected as a single dose (60 mg/kg i.p. in buffered citrate solution, pH 4.0) and melatonin (melatonin 100, 100 microg/kg/day i.p.; melatonin 200, 200 microg/kg/day i.p.) beginning 3 days before diabetes induction and continuing until the end of the study (8 weeks). The parameters analysed to evaluate oxidative stress and the diabetic state were a) for oxidative stress, changes of lipoperoxides (i.e., malondialdehyde, MDA) in plasma and erythrocytes and the changes in reduced glutathione (GSH) in erythrocytes and b) for diabetes, changes in glycemia, lipids (triglycerides: TG; total cholesterol: TC; HDL-cholesterol, HDL-c), percentage of glycosylated hemoglobin (Hb%), and plasma fructosamine. The injection of STZ caused significant increases in the levels of glycemia, percentage of glycosylated hemoglobin, fructosamine, cholesterol, triglycerides, and lipoperoxides in plasma and erythrocytes, whereas it decreased the levels of HDL-c and the GSH content in erythrocytes. The melatonin 100 dose reduced significantly all these increases, except the percentage of glycosylated hemoglobin. With regard to the decreases of plasma HDL-c and GSH content in erythrocytes, this melatonin dose returned them to normal levels. The melatonin 200 dose produced similar changes, though the effects were especially noticeable in the decrease of glycemia (55% vs. diabetes), percentage of hemoglobin (P < 0.001 vs diabetes), and fructosamine (31% vs. diabetes). This dose also reversed the decreases of HDL-c and GSH in erythrocytes. Both doses of melatonin caused significant reduction of the percentage of glycosylated hemoglobin in those groups that were non-diabetic. These illustrate the protective effect of melatonin against oxidative stress and the severity of diabetes induced by STZ. In particular, this study confirms two facts: 1) the powerful antioxidant action of this pineal indole and 2) the importance of the severity of oxidative stress to maintain hyperglycemia and protein glycosylation, two pathogenetic cornerstones indicative of diabetic complications. Melatonin reduces remarkably the degree of lipoperoxidation, hyperglycemia, and protein glycosylation, which gives hope to a promising perspective of this product, together with other biological antioxidants, in the treatment of diabetic complications where oxidative stress, either in a high or in a low degree, is present.

Effect of aldose reductase inhibition on cardiovascular reflex tests in patients with definite diabetic autonomic neuropathy over a period of 2 years

The potential of the aldose reductase inhibitor tolrestat to ameliorate definite diabetic autonomic neuropathy (DAN), as defined by standard cardiovascular autonomic function tests, was evaluated in 35 patients over a period of 2 years, with repeated measurements at 3-month intervals. The effect of tolrestat (200 mg a day) was compared with that of placebo on 35 controls with diabetes mellitus, of similar age, gender, and glycemic control. In the placebo group, a significant deterioration of the indices, with the exception of Valsalva ratio, was recorded, while tolrestat induced a significant beneficial change in the values of most standard cardiovascular reflex tests, in comparison to baseline and placebo. The deep breathing tests (expiration-inspiration ratio, standard deviation, and mean circular resultant of R-R intervals), postural index, and postural hypotension were favorably affected. Three of 35 patients on tolrestat (8.6%) developed high transaminases levels (more than threefold the upper normal limit) and were withdrawn from the study. In conclusion, tolrestat improved autonomic nervous system function in patients with definite DAN, in comparison to baseline and placebo. The clinical importance of this finding needs further investigation.

Bimoclomol (BRLP-42) ameliorates peripheral neuropathy in streptozotocin-induced diabetic rats

A reduction in nerve conduction velocity and an increase in resistance to ischemic conduction failure are early signs of neural dysfunction in both diabetic patients and animal models of diabetes. The effect of Bimoclomol (BRLP-42), a drug under clinical development for the treatment of diabetic complications, on experimental peripheral neuropathy was examined in rats made diabetic by injection of streptozotocin. Daily oral doses of Bimoclomol (10 or 20 mg/kg) or control dose of gamma-linolenic acid (260 mg/kg), an agent with known neuropathy-improving effects, were administered for 3 months. Treatments began 1 day after diabetes induction to assess the prophylactic efficacy of Bimoclomol. Neuropathy was evaluated electrophysiologically by measuring motor and sensory nerve conduction velocities and resistance to ischemic conduction failure of sciatic nerve in vivo. Bimoclomol significantly reduced nerve conduction slowing and retarded the typical elevated ischaemic resistance due to streptozotocin-induced neuropathy, suggesting that the drug might be a useful treatment for diabetic peripheral neuropathies.

Electroretinogram in sucrose-fed diabetic rats treated with an aldose reductase inhibitor or an anticoagulant

To investigate the role of increased polyol pathway activity and hemodynamic deficits in the pathogenesis of diabetic retinopathy in non-insulin-dependent diabetes mellitus (NIDDM), Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of human NIDDM, were given water with or without 30% sucrose and some of them were fed laboratory chow containing 0.03% cilostazol, an anticoagulant, or 0.05% [5-(3-thienyl)tetrazol-1-yl] acetic acid monohydrate (TAT), an aldose reductase inhibitor, for 8 wk. Long-Evans Tokushima Otsuka (LETO) rats were used as nondiabetic controls. The peak latencies of oscillatory potentials of the electroretinogram in sucrose-fed OLETF rats were significantly prolonged compared with those in OLETF rats without sucrose feeding and LETO rats. There was a marked increase in platelet aggregability and a significant decrease in erythrocyte 2,3-diphosphoglycerate in sucrose-fed OLETF rats. Cilostazol significantly improved these parameters without changes in retinal levels of sorbitol and fructose. TAT, however, ameliorated all of these parameters. These findings confirm that the sucrose-fed OLETF rat is a useful animal model of retinopathy in human NIDDM and suggest that cilostazol improved diabetic retinopathy by modifying vascular factors, not by altering polyol pathway activity.

Age-dependent increase in ortho-tyrosine and methionine sulfoxide in human skin collagen is not accelerated in diabetes. Evidence against a generalized increase in oxidative stress in diabetes

The glycoxidation products Nepsilon-(carboxymethyl)lysine and pentosidine increase in skin collagen with age and at an accelerated rate in diabetes. Their age-adjusted concentrations in skin collagen are correlated with the severity of diabetic complications. To determine the relative roles of increased glycation and/or oxidation in the accelerated formation of glycoxidation products in diabetes, we measured levels of amino acid oxidation products, distinct from glycoxidative modifications of amino acids, as independent indicators of oxidative stress and damage to collagen in aging and diabetes. We show that ortho-tyrosine and methionine sulfoxide are formed in concert with Nepsilon-(carboxymethyl)lysine and pentosidine during glycoxidation of collagen in vitro, and that they also increase with age in human skin collagen. The age-adjusted levels of these oxidized amino acids in collagen was the same in diabetic and nondiabetic subjects, arguing that diabetes per se does not cause an increase in oxidative stress or damage to extracellular matrix proteins. These results provide evidence for an age-dependent increase in oxidative damage to collagen and support previous conclusions that the increase in glycoxidation products in skin collagen in diabetes can be explained by the increase in glycemia alone, without invoking a generalized, diabetes-dependent increase in oxidative stress.

Peripheral nerve regeneration through silicone chambers in streptozocin-induced diabetic rats

The silicone chamber model was used to evaluate peripheral nerve regeneration (PNR) in streptozocin (STZ)-induced diabetic rats. Diabetic and control animals underwent sciatic nerve transection and silicone chamber implantation establishing gaps of various lengths between the transected nerve ends. In animals with 5 and 10 mm gaps, diabetes was induced in experimental rats 1 week before surgery, and the animals were sacrificed 3 weeks after surgery. In animals with 8 mm gaps, diabetes induction occurred 3 days after surgery, and they were sacrificed after 7 weeks. Diabetic rats with 10 mm gaps demonstrated an impaired ability to form bridging cables, the initial step of regeneration through chambers. Morphometric studies of bridging cables between transected nerve ends demonstrated a significant reduction in the mean endoneurial area in diabetic animals with 5 and 8 mm gaps compared to controls. The number of regenerated myelinated axons in the chamber was significantly decreased in diabetic rats with 8 and 10 mm gaps. The mean myelinated fiber area in the regenerated cables of the diabetic group was significantly decreased with 5 mm gaps and significantly increased with 8 mm gaps compared to controls. Size-frequency histograms of regenerated myelinated fiber areas suggest a delay in the maturation of small caliber axons. Schwann cell migration across 5 mm gaps was examined with S-100 immunohistochemistry. The total distance of Schwann cell migration into cables from both proximal and distal ends was significantly reduced in diabetic animals. Characterization of PNR across gaps through silicone chambers in diabetic rats showed impairment in multiple aspects of the regenerative process, including cable formation, Schwann cell migration, and axonal regeneration.

Advanced glycation endproducts in ageing and Alzheimer's disease

Accumulation of advanced glycation endproducts (AGE) in the brain is a feature of ageing and degeneration, especially in Alzheimer's disease (AD). Increased AGE levels explain many of the neuropathological and biochemical features of AD such as extensive protein crosslinking (beta-amyloid and MAP-tau), oxidative stress and neuronal cell death. Oxidative stress and AGEs initiate a positive feedback loop, where normal age-related changes develop into a pathophysiological cascade. Combined intervention using antioxidants, metal chelators, anti-inflammatory drugs and AGE-inhibitors may be a promising neuroprotective strategy.