Diabetic neuropathy: pathogenesis and therapy

Effects of axonal ion channel dysfunction on quality of life in type 2 diabetes

OBJECTIVE

Pharmacological agents for diabetic peripheral neuropathy (DN) target a number of mechanisms, including sodium channel function and γ-aminobutyric acid-minergic processes. At present, prescription is undertaken on a trial-and-error basis, leading to prolonged medication trials and greater healthcare costs. Nerve-excitability techniques are a novel method of assessing axonal ion channel function in the clinical setting. The aim of this study was to determine the effects of axonal ion channel dysfunction on neuropathy-specific quality-of-life (QoL) measures in DN.

RESEARCH DESIGN AND METHODS

Fifty-four patients with type 2 diabetes mellitus underwent comprehensive neurologic assessment, nerve-conduction studies, and nerve-excitability assessment. Neuropathy severity was assessed using the Total Neuropathy Score. Neuropathy-specific QoL was assessed using a DN-specific QoL questionnaire (Neuropathy-Specific Quality of Life Questionnaire [NeuroQoL]). Glycosylated hemoglobin and BMI were recorded in all patients.

RESULTS

NeuroQoL scores indicated significant QoL impairment (mean 9.08 ± 5.93). Strength-duration time constant (SDTC), an excitability parameter reflecting sodium channel function, was strongly correlated with QoL scores (r = 0.545; P < 0.005). SDTC was prolonged in 48.6% of patients who experienced neuropathic symptoms. A significant correlation was also noted between SDTC and neuropathy severity (r = 0.29; P < 0.05). This relationship was strengthened when looking specifically at patients with clinically graded neuropathy (r = 0.366; P < 0.05).

CONCLUSIONS

The current study has demonstrated an association between markers of sodium channel function and QoL in DN. The study demonstrates that excitability techniques may identify patients in whom altered sodium channel function may be the dominant abnormality. The findings suggest that excitability techniques may have a role in clinical decision making regarding neuropathic treatment prescription.

Diabetic cardiovascular autonomic neuropathy: clinical implications

Diabetic cardiovascular autonomic neuropathy (DCAN), the impairment of the autonomic balance of the cardiovascular system in the setting of diabetes mellitus (DM), is frequently observed in both Type 1 and 2 DM, has detrimental effects on the quality of life and portends increased mortality. Clinical manifestations include: resting heart rate disorders, exercise intolerance, intraoperative cardiovascular lability, orthostatic alterations in heart rate and blood pressure, QT-interval prolongation, abnormal diurnal and nocturnal blood pressure variation, silent myocardial ischemia and diabetic cardiomyopathy. Clinical tests for autonomic nervous system evaluation, heart rate variability analysis, autonomic innervation imaging techniques, microneurography and baroreflex analysis are the main diagnostic tools for DCAN detection. Aldose reductase inhibitors and antioxidants may be helpful in DCAN therapy, but a regular, more generalized and multifactorial approach should be adopted with inclusion of lifestyle modifications, strict glycemic control and treatment of concomitant traditional cardiovascular risk factors, in order to achieve the best therapeutic results. In the present review, the authors provide aspects of DCAN pathophysiology, clinical presentation, diagnosis and an algorithm regarding the evaluation and management of DCAN in DM patients.

Effects of L-glutamine supplementation on the myenteric neurons from the duodenum and cecum of diabetic rats

CONTEXT

Peripheral neuropathy is one of the chronic complications of diabetes mellitus and is directly related to gastrointestinal consequences of the disease. Myenteric neurons are affected in some pathological conditions such as diabetic neuropathy. The imbalance between cellular antioxidants and free radicals, leading to an increase in oxidative stress, is considered one of the main factors responsible for neuronal damages in diabetes. Drugs that reduce the oxidative stress may play a significant role in the treatment of neurological complications of diabetes mellitus.

OBJECTIVE

To evaluate the effect of L-glutamine supplementation on the myenteric neurons from the cecum and duodenum of Wistar rats with streptozotocin-induced diabetes mellitus.

METHODS

The animals were divided in four groups (n = 5): non-treated normoglycemics, normoglycemics treated with L-glutamine, non-treated diabetics and diabetics treated with L-glutamine from the 4th day of diabetes induction on. The amino acid L-glutamine was added to their diet at 1%. Giemsa's technique was employed to stain the myenteric neurons. We determined the cell body area of 500 neurons in each group studied. The quantitative analysis was performed by sampling in an area of 16.6 mm² in the cecum and 3.6 mm² in the duodenum of each animal.

RESULTS

After the supplementation with L-glutamine in the duodenum, we observed a preservation of neuronal density in groups normoglycemic and diabetic (P<0.05). We also observed a preservation of the cell bodies area in diabetic animals (group treated with L-glutamine) (P<0.05). In the cecum, that preservation was not evident.

CONCLUSION

Supplementation with L-glutamine (1%) promoted a neuroprotective effect on the myenteric neurons from the duodenum of rats, both in terms of natural aging and of diabetes mellitus.

A comparative profile of methanol extracts of Allium cepa and Allium sativum in diabetic neuropathy in mice

Introduction:

Diabetic Neuropathy (DN) is a major microvascular complication of uncontrolled diabetes. This may result from increased oxidative stress that accompanies diabetes. Hence plants with antioxidant action play an important role in management of diabetes and its complications.

Materials and Methods:

This study was designed to evaluate preventive as well as curative effect of methanol extracts of outer scales and edible portions of two plants with established antioxidant action - Allium cepa and Allium sativum, in induced DN in albino mice. Mice were divided into control, diabetic and test extracts treated groups. Test extracts were administered daily at a dose of 200 mg/kg p.o. for 21 days, in the preventive group prior to onset of DN, and in the curative group after the onset of DN. Hyperalgesia and oxidative stress markers were assessed. STZ-diabetic mice showed a significant thermal hyperalgesia (as assessed by the tail-flick test), indicating development of DN.

Results:

Treatment with test extracts prevented loss in body weight, decreased plasma glucose level, and significantly ameliorated the hyperalgesia, TBARS, serum nitrite and GSH levels in diabetic mice.

Conclusion:

Methanol extract of outer scales of onion has shown most significant improvement; may be due to higher content of phenolic compounds in outer scales of A. cepa.

Duloxetine, pregabalin, and duloxetine plus gabapentin for diabetic peripheral neuropathic pain management in patients with inadequate pain response to gabapentin: an open-label, randomized, noninferiority comparison

OBJECTIVE

To determine whether duloxetine is noninferior to (as good as) pregabalin in the treatment of pain associated with diabetic peripheral neuropathy.

PATIENTS AND METHODS

We performed a 12-week, open-label study of patients with diabetic peripheral neuropathic pain who had been treated with gabapentin (≥ 900 mg/d) and had an inadequate response (defined as a daily pain score of ≥ 4 on a numerical rating scale [0-10 points]). The first patient was enrolled on September 28, 2006, and the last patient visit occurred on August 26, 2009. Patients were randomized to duloxetine monotherapy (n=138), pregabalin monotherapy (n=134), or a combination of duloxetine and gabapentin (n=135). The primary objective was a noninferiority comparison between duloxetine and pregabalin on improvement in the weekly mean of the diary-based daily pain score (0- to 10-point scale) at end point. Noninferiority would be declared if the mean improvement for duloxetine was no worse than the mean improvement for pregabalin, within statistical variability, by a margin of -0.8 unit.

RESULTS

The mean change in the pain rating at end point was -2.6 for duloxetine and -2.1 for pregabalin. The 97.5% lower confidence limit was a -0.05 difference in means, establishing noninferiority. As to adverse effects, nausea, insomnia, hyperhidrosis, and decreased appetite were more frequent with duloxetine than pregabalin; insomnia, more frequent with duloxetine than duloxetine plus gabapentin; peripheral edema, more frequent with pregabalin than with duloxetine; and nausea, hyperhidrosis, decreased appetite, and vomiting, more frequent with duloxetine plus gabapentin than with pregabalin.

CONCLUSION

Duloxetine was noninferior to pregabalin for the treatment of pain in patients with diabetic peripheral neuropathy who had an inadequate pain response to gabapentin.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00385671.

Geriatric conditions develop in middle-aged adults with diabetes

BACKGROUND

Geriatric conditions, collections of symptoms common in older adults and not necessarily associated with a specific disease, increase in prevalence with advancing age. These conditions are important contributors to the complex health status of older adults. Diabetes mellitus is known to co-occur with geriatric conditions in older adults and has been implicated in the pathogenesis of some conditions.

OBJECTIVE

To investigate the prevalence and incidence of geriatric conditions in middle-aged and older-aged adults with diabetes.

DESIGN

Secondary analysis of nationally-representative, longitudinal health interview survey data (Health and Retirement Study waves 2004 and 2006).

PARTICIPANTS

Respondents 51 years and older in 2004 (n=18,908).

MAIN MEASURES

Diabetes mellitus. Eight geriatric conditions: cognitive impairment, falls, incontinence, low body mass index, dizziness, vision impairment, hearing impairment, pain.

KEY RESULTS

Adults with diabetes, compared to those without, had increased prevalence and increased incidence of geriatric conditions across the age spectrum (p< 0.01 for each age group from 51-54 years old to 75-79 years old). Differences between adults with and without diabetes were most marked in middle-age. Diabetes was associated with the two-year cumulative incidence of acquiring new geriatric conditions (odds ratio, 95% confidence interval: 1.8, 1.6-2.0). A diabetes-age interaction was discovered: as age increased, the association of diabetes with new geriatric conditions decreased.

CONCLUSIONS

Middle-aged, as well as older-aged, adults with diabetes are at increased risk for the development of geriatric conditions, which contribute substantially to their morbidity and functional impairment. Our findings suggest that adults with diabetes should be monitored for the development of these conditions beginning at a younger age than previously thought.

Spinal astrocytic activation contributes to mechanical allodynia in a mouse model of type 2 diabetes

Diabetic neuropathic pain (DNP) plays a major role in decreased life quality of type 2 diabetes patients, however, the molecular mechanisms underlying DNP remain unclear. Emerging research implicates the participation of spinal glial cells in some neuropathic pain models. However, it remains unknown whether spinal glial cells are activated under type 2 diabetic conditions and whether they contribute to diabetes-induced neuropathic pain. In the present study, using a db/db type 2 diabetes mouse model that displayed obvious mechanical allodynia, we found that spinal astrocyte but not microglia was dramatically activated. The mechanical allodynia was significantly attenuated by intrathecally administrated l-α-aminoadipate (astrocytic specific inhibitor) whereas minocycline (microglial specific inhibitor) did not have any effect on mechanical allodynia, which indicated that spinal astrocytic activation contributed to allodynia in db/db mice. Further study aimed to identify the detailed mechanism of astrocyte-induced allodynia in db/db mice. Results showed that spinal activated astrocytes dramatically increased interleukin (IL)-1β expression which may induce N-methyl-D-aspartic acid receptor (NMDAR) phosphorylation in spinal dorsal horn neurons to enhance pain transmission. Together, these results suggest that spinal activated astrocytes may be a crucial component of mechanical allodynia in type 2 diabetes and "Astrocyte-IL-1β-NMDAR-Neuron" pathway may be the detailed mechanism of astrocyte-induced allodynia. Thus, inhibiting astrocytic activation in the spinal dorsal horn may represent a novel therapeutic strategy for treating DNP.

Immunohistochemical study of vasoactive intestinal peptide (VIP) enteric neurons in diabetic rats supplemented with L-glutamine

The purpose of this work was to study the area of the varicosities of nerve fibers of myenteric neurons immunoreactive to vasoactive intestinal peptide (VIP-IR) and of the cell bodies of VIP-IR submucosal neurons of the jejunum of diabetic rats supplemented with 2% L-glutamine. Twenty male rats were divided into the following groups: normoglycemic (N), normoglycemic supplemented with L-glutamine (NG), diabetic (D) and diabetic supplemented with L-glutamine (DG). Whole-mounts of the muscle tunica and the submucosal layer were subjected to the immunohistochemical technique for neurotransmitter VIP identification. Morphometric analyses were carried out in 500 VIP-IR cell bodies of submucosal neurons and 2000 VIP-IR varicosities from each group. L-Glutamine supplementation to the normoglycemic animals caused an increase in the areas of the cell bodies (8.49%) and varicosities (21.3%) relative to the controls (P < 0.05). On the other hand, there was a decrease in the areas of the cell bodies (4.55%) and varicosities (28.9%) of group DG compared to those of group D (P < 0.05). It is concluded that L-glutamine supplementation was positive both to normoglycemic and diabetic animals.

Incidence and evolution of oxaliplatin-induced peripheral sensory neuropathy in diabetic patients with colorectal cancer: a pooled analysis of three phase III studies

BACKGROUND

The purpose of this study was to determine whether the presence of diabetes mellitus (DM) influences the incidence, severity, and/or course of peripheral sensory neuropathy (PSN) after oxaliplatin (FOLFOX) therapy in patients with colorectal cancer (CRC).

METHODS

A retrospective pooled analysis incorporating three phase III studies was conducted: Multicenter International Study of Oxaliplatin, 5-Fluorouracil, and Leucovorin in the Adjuvant Treatment of Colon Cancer (MOSAIC) (adjuvant treatment; stage II/III colon cancer), EFC4584 (second-line treatment; metastatic CRC), and EFC2962 (first-line treatment; metastatic CRC). Patients were ineligible for the studies if they had known PSN (EFC4584) or PSN grade > or =1 (MOSAIC and EFC2962) at baseline. The incidence of PSN was evaluated retrospectively in patient subgroups with or without DM at baseline that received FOLFOX. Kaplan-Meier curves were used to assess the probability of PSN with increasing cumulative oxaliplatin dose.

RESULTS

Of 1587 patients enrolled across the three studies, 135 (8.5%) had DM at baseline. The incidence of PSN (non-DM/DM) was 45.0%/46.7% (grade 1), 28.6%/26.7% (grade 2), and 13.0%/12.6% (grade 3). The probability of PSN by cumulative dose of oxaliplatin was similar in DM and non-DM patients.

CONCLUSIONS

This retrospective analysis indicates that oxaliplatin-based therapy does not influence the incidence, severity, or time to onset of PSN in asymptomatic DM patients with CRC who meet eligibility criteria for clinical trials.

Peripheral gene transfer of glial cell-derived neurotrophic factor ameliorates neuropathic deficits in diabetic rats

Deprivation of neurotrophic factors contributes to the pathogenesis of diabetic neuropathy. However, the role of glial cell-derived neurotrophic factor (GDNF) in the pathogenesis of diabetic neuropathy remains unclear. The present study evaluated the pathogenic role of GDNF deficiency and the therapeutic potential of GDNF gene transfer for diabetic neuropathy. After injection of streptozotocin (STZ) for 2 weeks, diabetic rats displayed significant alteration in electrophysiological parameters, which was associated with structural changes and defective myelination in the sciatic nerves. The early diabetic neuropathy was accompanied by attenuation of the GDNF/GFRalpha1/Akt signaling cascade and depletion of sensory neuropeptides in the peripheral nerves. After detection of neuropathy, intramuscular GDNF gene transfer reversed the deficiency of GDNF/Akt signaling in the sciatic nerve and improved the neurological functions of diabetic rats. Moreover, GDNF gene delivery alleviated the axonal demyelination and restored the sensory neuropeptide levels in the sciatic nerve of diabetic rats. In summary, peripheral GDNF gene delivery ameliorates the diabetes-induced downregulation of the GDNF signaling complex in the peripheral nervous system and holds promises for treatment of diabetic neuropathy.

Clinical features and electrodiagnosis of diabetic peripheral neuropathy in the dysvascular patient

Diabetic peripheral neuropathy (DPN) is a common disorder that can lead to limb loss and death. Up to 50% of DPN patients can be asymptomatic. This fact contributes to making DPN the leading cause of lower limb amputation. The degree of heterogeneity in the clinical manifestations of DPN makes diagnosing this condition difficult. This article reviews the characteristics, diagnosis, electrodiagnosis, classification, pathogenesis, and treatment of DPN.

Vitamin E (alpha-tocopherol) supplementation in diabetic rats: effects on the proximal colon

Background

Neuropathy is one of the complications caused by diabetes mellitus which is directly related to the gastrointestinal manifestations of the disease. Antioxidant substances, such as vitamin E, may play an important role in the reduction of the neurological damage caused by diabetes mellitus. The aim of the present study was to determine whether vitamin E (α-tocopherol) at different concentrations induces any effects on the morphology of the intestinal wall and intrinsic innervation in the proximal colon of diabetic rats.

Methods

Thirty rats (90-day-old) were assigned to the following groups: N (normoglycemic), NE1 (normoglycemic supplemented with vitamin E 0.1%), NE2 (normoglycemic supplemented with vitamin E 2%), D (diabetic), DE1 (diabetic supplemented with vitamin E 0.1%), and DE2 (diabetic supplemented with vitamin E 2%). Animals received vitamin E supplementation for 120 days and were sacrificed when they were 210 days old. The proximal colon of each animal was subjected to histology to study the intestinal wall and goblet cells and processed for whole-mount preparations to morphoquantitatively determine the total myenteric population.

Results

Supplementation with vitamin E significantly reduced glycemia and glycated hemoglobin values and preserved the number of myenteric neurons in group DE2, without affecting intestinal area or thickness of the intestinal wall or muscular tunic.

Conclusion

Vitamin E (2%) influenced the glycemic parameters and had a neuroprotective effect on the total myenteric population, but the morphometric characteristics of the intestinal wall were unaffected.

Nerve decompression surgery as treatment for peripheral diabetic neuropathy: literature overview and awareness among medical professionals

Peripheral diabetic neuropathy (PDN) is one of the major complications arising in patients with diabetes. Since PDN is traditionally considered an irreversible disorder, treatment has been aimed to prevent the development of complications. In a novel concept, however, it is postulated that decompression surgery of the affected nerve may reverse the natural course of PDN. In this review, we will discuss experimental and human studies that addressed the value of nerve decompression surgery in PDN. Furthermore, we report on the awareness of this novel treatment strategy among medical professionals that are primarily involved in diabetes care.

Protective and therapeutic effects of swimming exercise training on diabetic peripheral neuropathy of streptozotocin-induced diabetic rats

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a typical complication of diabetes. No definitive treatment and prevention of DPN has been established, and very few data on the role of exercise training on DPN have been reported.

AIM OF THE STUDY

The protective and therapeutic effects of aerobic physical activity on the development of DPN in Type 1 were investigated.

METHODS

Rats were assigned to 5 groups: C (control), E (exercise), D (diabetic), DEx (exercise after diabetic), ExD (diabetic after exercise); C containing 10 animals and E, D, DEx, ExD containing 15 animals. Diabetes was induced with streptozotocin (STZ) (45 mg/kg, ip). Development of diabetes was confirmed by measuring blood glucose levels 2 days after STZ treatment. Body weights of all the animals were evaluated weekly throughout the experiment. Motor dysfunction defined by a significant increase in compound muscle action potential (CMAP) latency was recorded. The amplitude of CMAP which mainly reflects axonal dysfunction was also measured using standard techniques. Sciatic nerve morphometry and blood glucose levels were analyzed in all the groups.

RESULTS

Blood glucose level significantly increased 2 days after STZ injection. All diabetic rats showed decreased body weight compared to control rats. An increase in motor latency of CMAP and a decrease in amplitude of CMAP, indicative of neuropathy, were seen in STZ rats. On the completion of the study (the 56th day post-STZ), histological examination revealed significant myelin loss (thinner myelin) in sciatic nerves of STZ rats. Treatment with swimming exercise had no effect on glycemic control but restored body weight, CMAP amplitude, CMAP latency or motor dysfunction in the diabetic animals.

CONCLUSIONS

This study suggests that swimming exercise training has protective and therapeutic effects on DPN of STZ-induced diabetic rats.

Autonomic neuropathy precedes cardiovascular dysfunction in rats with diabetes

BACKGROUND

Our team previously demonstrated arterial stiffening and cardiac hypertrophy in type 2 diabetic rats at 8 but not 4 weeks after being administered streptozotocin (STZ) and nicotinamide (NA). The present study focused on investigating the effects of type 2 diabetes on cardiac autonomic nerve function in the STZ- and NA-treated animals, using modern spectral estimation technique.

DESIGN

An autoregressive process was performed to each detrended signal of heart rate and systolic blood pressure measured in the 4- and 8-week STZ-NA rats with anaesthesia. The power of low-frequency and high-frequency oscillations was automatically quantified with each spectral peak by computing the residuals. The closed-loop baroreflex gain was estimated using the square root of the ratio between heart rate and systolic blood pressure powers in the low-frequency band.

RESULTS

Compared with the age-matched controls, both the 4- and 8-week STZ-NA diabetic rats had significantly decreased low-frequency oscillations of heart rate but not systolic blood pressure variability, showing a decline in baroreflex gain (0.451 +/- 0.060 and 0.484 +/- 0.056 vs. 1.196 +/- 0.064 ms mmHg(-1), P < 0.05). On the other hand, the low frequency-high frequency power ratio of the heart period was also diminished in the two diabetic groups, indicating a shift in sympatho-vagal balance of the heart control (0.472 +/- 0.109 and 0.504 +/- 0.090 vs. 1.857 +/- 0.336, P < 0.05).

CONCLUSIONS

The cardiac autonomic dysfunction in the absence of any significant changes in vascular dynamics, 4 but not 8 weeks after induction of type 2 diabetes, suggests that the diabetic autonomic neuropathy may precede arterial stiffening and cardiac hypertrophy in the STZ- and NA-treated rats.

Clinical and nerve conduction studies in female patients with diabetic dermopathy

This study aims to assess the clinical and electrophysiological characteristics of diabetic polyneuropathy (PNP) in female patients. We investigated clinical and electrophysiological features in 175 female patients with diabetes mellitus to compare those with PNP only, diabetic dermopathy (DD), or diabetic foot (DF). Among clinical features, the loss of deep tendon reflexes, the presence of negative sensory symptoms, superficial sensory loss, and the loss of vibration sense were more common in DD patients than PNP patients. As compared with DD patients, the presence of skin atrophy, superficial and positive sensory symptoms were more common in DF patients. Neuropathic symptom and disability scores were significantly higher in DD and DF patients than PNP patients. In the electrophysiological studies, the only significant difference was observed in the mean distal latencies for ulnar nerves, which were longer in DD patients as compared with PNP patients, but similar between DD and DF patients. All other parameters failed to show significant difference among patients, though values for DD patients lied in between PNP and DF patients. Carpal tunnel syndrome was present in 45% of PNP patients, 63.8% of DD patients, and 50% of DF patients (P = 0.031). Our results suggest that female patients with diabetic dermopathy might have a more severe sensorial neuropathy than patients without these skin lesions.

Neuropatia autonômica: uma complicação de alto risco no diabetes melito tipo 1

O acometimento patológico do sistema nervoso no diabetes melito é muito amplo e, freqüentemente, bastante grave. A prevalência de neuropatia diabética atinge níveis elevados com a evolução temporal do diabetes, chegando, geralmente, a freqüências acima de 50% de lesão neurológica em diferentes grupos de pacientes analisados em nosso meio e no exterior. A lesão neurológica nesta situação patológica é extensa no organismo humano diabético, envolvendo amplamente todo o sistema nervoso periférico nos seus componentes sensitivo-motor e autonômico: com clínica característica e concordante com as hipóteses patogênicas de natureza metabólica e/ou microvascular. O sistema nervoso autonômico é o elemento fundamental na regulação da função da maior parte dos sistemas ou órgãos no organismo, portanto, a sua lesão pode trazer importantes alterações para as funções cardiovascular, respiratória, digestiva, urinária e genital, podendo influir na função vital de alguns desses órgãos ou sistemas. Este artigo aborda as alterações decorrentes da lesão do sistema nervoso autonômico, especialmente nos pacientes diabéticos tipo 1, procurando dimensionar o risco de morbimortalidade.

Interactions between microvascular and macrovascular disease in diabetes: pathophysiology and therapeutic implications

Convention partitions the complications of diabetes into two main subtypes. First are the diabetes-specific microvascular complications of retinopathy, nephropathy and neuropathy; second are the atherothrombotic macrovascular complications that account for the majority of premature deaths. Pathological interactions between microvascular and macrovascular complications, for example, nephropathy and macrovascular disease, are common. Similar mechanisms and shared risk factors drive the development and progression of both small and large vessel disease. This concept has therapeutic implications. Mounting evidence points to the need for multifactorial strategies to prevent vascular complications in subjects with diabetes and/or the metabolic syndrome. We advocate a combined therapeutic approach that addresses small and large vessel disease. Preferential use should be made of drug regimens that (i) maximize vascular protection, (ii) reduce the risk of iatrogenic vascular damage and (iii) minimize the increasing problem of polypharmacy.

Antiepileptic drugs in treatment of pain caused by diabetic neuropathy

Pain is frequent in diabetic neuropathy and is very hard to manage. Antiepileptic drugs have been used in treating pain for several decades. Their effectiveness has been described in different types of neuropathic pain, but when used as analgesics in painful diabetic neuropathy it still remains controversial. To clarify this effectiveness, a meta-analysis was performed to determine which antiepileptic drug had the best analgesic potential for managing pain in patients suffering from painful diabetic neuropathy. The search covered the Cochrane, MEDLINE, EMBASE, and LILACS databases, between January 1966 and September 2005. The following information was obtained from each article: criteria for diagnosing diabetic neuropathy, patients' age average, antiepileptic drug received and dose, sample size, duration of the disease and treatment follow-up, outcome measurement, evaluation of pain, and rescue medication. A combined 2.33 relative risk (95% confidence interval [CI] 1.88-2.88) was obtained; this result indicated that the antiepileptic drugs studied were effective for controlling pain in diabetic neuropathy. The corresponding necessary number to treat (NNT) values were established for evaluating which antiepileptic drug was most effective as an analgesic, according to our interests; pregabalin was shown to be the antiepileptic drug having the lowest NNT (NNT=3.24 and 95% CI 2.12-6.81) for achieving greater than 50% analgesia in patients suffering from painful diabetic neuropathy. Antiepileptic drugs are frequently used in the specific case of diabetic neuropathy; the combined result of this meta-analysis has demonstrated their analgesic benefit.

Therapeutic use of dextromethorphan: Key learnings from treatment of pseudobulbar affect

A variety of neurological conditions and disease states are accompanied by pseudobulbar affect (PBA), an emotional disorder characterized by uncontrollable outbursts of laughing and crying. The causes of PBA are unclear but may involve lesions in neural circuits regulating the motor output of emotional expression. Several agents used in treating other psychiatric disorders have been applied in the treatment of PBA with some success but data are limited and these agents are associated with unpleasant side effects due to nonspecific activity in diffuse neural networks. Dextromethorphan (DM), a widely used cough suppressant, acts at receptors in the brainstem and cerebellum, brain regions implicated in the regulation of emotional output. The combination of DM and quinidine (Q), an enzyme inhibitor that blocks DM metabolism, has recently been tested in phase III clinical trials in patients with multiple sclerosis and amyotrophic lateral sclerosis and was both safe and effective in palliating PBA symptoms. In addition, clinical studies pertaining to the safety and efficacy of DM/Q in a variety of neurological disease states are ongoing.

Effect of Early Nerve Release on the Progression of Neuropathy in Diabetic Rats

Diabetic neuropathy renders the peripheral nerves to be more susceptible to compression at potential entrapment sites. We evaluated the effects of "prophylactic" decompression procedures on the progression of diabetic neuropathy in an experimental model. Thirty diabetic Zucker rats were studied. Group I, II, and III rats were followed up for 12 weeks and IV, V, and VI rats for 24 weeks. Group III and VI rats served as short- and long-term controls without any surgical intervention. Group I and IV rats had tarsal tunnel release (TTR); group II and V rats had TTR and peroneal nerve release (PNR) procedures on their left legs. Nerve function was assessed by pinprick, toe spread tests, sciatic function index (SFI), somatosensory evoked potential (SSEP) analysis, and gastrocnemius muscle wet weight measurements.SFI analysis revealed a statistically significant difference between the combined TTR-PNR and nonoperative control groups at both short- and long-term follow-up (P </= 0.01). SSEP result analysis of operated left and nonoperated right sides revealed a statistically significant difference in P1 latency values at both short- and long-term follow-up (P < 0.05). We confirmed beneficial effects of decompression procedures at early onset of diabetes before the metabolic nerve injury advanced into an axonal loss.

Use of Tricyclic Antidepressants in Older Patients With Diabetic Peripheral Neuropathy

PURPOSE

To describe patterns of use of tricyclic antidepressants (TCAs) (eg, amitriptyline, nortriptyline) among older patients with diabetic peripheral neuropathy (DPN).

MATERIALS AND METHODS

Using a large, integrated, US health-insurance claims database, we identified all patients who received TCAs between January 1, 1999 and June 30, 2001 ("study period"). Among these persons, we then selected those who: (1) were aged >or=65 years as of the date of first receipt of a TCA during the study period; and (2) had one or more healthcare encounters with a diagnosis of DPN in the 30-day period immediately preceding date of first receipt of a TCA. We then examined the prevalence of selected comorbidities and concurrent use of medications which might render inappropriate the prescribing of TCAs, based on a listing of contraindications, warnings, and precautions found in the package inserts for these medications. Patterns of TCA prescribing were examined, based on information on paid claims.

RESULTS

There were 349 DPN patients, aged >or=65 years, who received TCAs. Mean age was 73.8 years, 55.9% were women, and 17.9% had diagnoses of depression. Most patients (84.0%) began therapy with amitriptyline. Almost one-half of study patients had indicators of potentially inappropriate TCA use, primarily cardiovascular comorbidities. Mean TCA dose among patients with and without these indicators was 23.3 (+/-13.4) mg and 25.4 (+/-15.3) mg, respectively (P=0.42).

CONCLUSIONS

The high prevalence of contraindications, warnings, or precautions and the low level of TCA exposure suggest that many older patients with DPN who receive TCAs may be inappropriately treated.

Neurotrophic modulation of myelinated cutaneous innervation and mechanical sensory loss in diabetic mice

Human diabetic patients often lose touch and vibratory sensations, but to date, most studies on diabetes-induced sensory nerve degeneration have focused on epidermal C-fibers. Here, we explored the effects of diabetes on cutaneous myelinated fibers in relation to the behavioral responses to tactile stimuli from diabetic mice. Weekly behavioral testing began prior to streptozotocin (STZ) administration and continued until 8 weeks, at which time myelinated fiber innervation was examined in the footpad by immunohistochemistry using antiserum to neurofilament heavy chain (NF-H) and myelin basic protein (MBP). Diabetic mice developed reduced behavioral responses to non-noxious (monofilaments) and noxious (pinprick) stimuli. In addition, diabetic mice displayed a 50% reduction in NF-H-positive myelinated innervation of the dermal footpad compared with non-diabetic mice. To test whether two neurotrophins nerve growth factor (NGF) and/or neurotrophin-3 (NT-3) known to support myelinated cutaneous fibers could influence myelinated innervation, diabetic mice were treated intrathecally for 2 weeks with NGF, NT-3, NGF and NT-3. Neurotrophin-treated mice were then compared with diabetic mice treated with insulin for 2 weeks. NGF and insulin treatment both increased paw withdrawal to mechanical stimulation in diabetic mice, whereas NT-3 or a combination of NGF and NT-3 failed to alter paw withdrawal responses. Surprisingly, all treatments significantly increased myelinated innervation compared with control-treated diabetic mice, demonstrating that myelinated cutaneous fibers damaged by hyperglycemia respond to intrathecal administration of neurotrophins. Moreover, NT-3 treatment increased epidermal Merkel cell numbers associated with nerve fibers, consistent with increased numbers of NT-3-responsive slowly adapting A-fibers. These studies suggest that myelinated fiber loss may contribute as significantly as unmyelinated epidermal loss in diabetic neuropathy, and the contradiction between neurotrophin-induced increases in dermal innervation and behavior emphasizes the need for multiple approaches to accurately assess sensory improvements in diabetic neuropathy.

Diabetes mellitus--overview

DM increases the risk of multiple complications including retinography, nephropathy, and atherosclerotic disease. Management strategies include management of the associated metabolic risk factors such has hyperglycemia, dyslipidemia, and hypertension. Additional management strategies include laser therapy for retinopathy and appropriate footwear to reduce the risk of lower extremity amputations.

How to better systematize the diagnosis of neuropathy?

Two attitudes can be proposed, one consisting of making a diagnosis of neuropathy, the other seeking to grade the stage that it has reached in order to give a prognosis and above all determine the right way in which to educate the patient. In order to do this, it is important for the diagnosis to be thorough. It should be based both on listening to what the patient has to say and examining him/her. It is vital to listen to the patient because the warning signs are discreet, yet very evocative, and they will be a great help in making a positive diagnosis. They should not be confused with signs of arterial damage. They should then be interpreted by means of clinical examination and the tools that are available, i.e. essentially monitoring the osteo-tendinous reflexes and sensory signs. The sensory signs can only be studied with high-quality instruments, i.e. either a monofilament of proven technical quality and that should be used with care in line with good clinical practice recommendations, or by using a graduated tuning fork, or a neuroesthesiometer which will make it possible to obtained graduated responses, not simply binary responses of the "yes/no" variety. A whole series of scores have been put forward combining both functional and physical signs, making it possible to try to quantify the stage reached and the extent of the neuropathy. It is only by using a thorough and regularly applied routine that we can progress to establishing a better prognosis and providing a better educational service for the patient.

Neuropathic pain: a practical guide for the clinician

Neuropathic pain, caused by various central and peripheral nerve disorders, is especially problematic because of its severity, chronicity and resistance to simple analgesics. The condition affects 2%-3% of the population, is costly to the health care system and is personally devastating to the people who experience it. The diagnosis of neuropathic pain is based primarily on history (e.g., underlying disorder and distinct pain qualities) and the findings on physical examination (e.g., pattern of sensory disturbance); however, several tests may sometimes be helpful. Important pathophysiologic mechanisms include sodium-and calcium-channel upregulation, spinal hyperexcitability, descending facilitation and aberrant sympathetic-somatic nervous system interactions. Treatments are generally palliative and include conservative nonpharmacologic therapies, drugs and more invasive interventions (e.g., spinal cord stimulation). Individualizing treatment requires consideration of the functional impact of the neuropathic pain (e.g., depression, disability) as well as ongoing evaluation, patient education, reassurance and specialty referral. We propose a primary care algorithm for treatments with the most favourable risk-benefit profile, including topical lidocaine, gabapentin, pregabalin, tricyclic antidepressants, mixed serotonin-norepinephrine reuptake inhibitors, tramadol and opioids. The field of neuropathic pain research and treatment is in the early stages of development, with many unmet goals. In coming years, several advances are expected in the basic and clinical sciences of neuropathic pain, which will provide new and improved therapies for patients who continue to experience this disabling condition.

VEGF 164 gene transfer by electroporation improves diabetic sensory neuropathy in mice

BACKGROUND

Diabetic neuropathy is the most common cause of peripheral neuropathy and a serious complication of diabetes. Vascular endothelial growth factor (VEGF) stimulates angiogenesis and has neurotrophic and neuroprotective activities. To examine the efficiency of VEGF 164 electro-gene therapy for neuropathy, intramuscular VEGF 164 gene transfer by electroporation was performed to treat sensory neuropathy in diabetic mice.

METHODS

VEGF 164 was overexpressed in the tibial anterior (TA) muscles of streptozotocin-induced diabetic mice with hypoalgesia, using a VEGF 164 plasmid injection with electroporation. From 2 weeks after electro-gene transfer, the nociceptive threshold was measured weekly using the paw-pressure test. The TA muscles, sciatic nerve, liver and spleen were histochemically examined at 4 weeks after electro-gene transfer.

RESULTS

Two weeks after electro-gene transfer into the bilateral TA muscles, the elevated nociceptive threshold was decreased to a normal level in all treated mice. Improvement of the hypoalgesia continued for 14 weeks. When the VEGF 164 plasmid was injected with electroporation into a unilateral TA muscle, recovery from hypoalgesia was observed in not only the ipsilateral hindpaw, but also the contralateral one, suggesting that VEGF circulates in the blood. No increase in the number of endoneurial vessels in the sciatic nerve was found in the VEGF 164 plasmid-electroporated mice.

CONCLUSIONS

These findings suggest that VEGF 164 electro-gene therapy completely recovered the sensory deficits, i.e. hypoalgesia, in the diabetic mice through mechanisms other than angiogenesis in the endoneurium of the peripheral nerve, and may be useful for treatment for diabetic sensory neuropathy in human subjects.

Exercise training can modify the natural history of diabetic peripheral neuropathy

BACKGROUND

Diabetes is the most important cause of peripheral neuropathy (DPN). No definitive treatment for DPN has been established, and very few data on the role of exercise training on DPN have been reported.

AIM OF THE STUDY

We sought to examine the effects of long-term exercise training on the development of DPN in both Types 1 and 2 diabetic patients.

PARTICIPANTS AND METHODS

Seventy-eight diabetic patients without signs and symptoms of peripheral DPN were enrolled, randomized, and subdivided in two groups: 31 diabetic participants [15 f, 16 m; 49+/-15.5 years old; body mass index (BMI)=27.9+/-4.7], who performed a prescribed and supervised 4 h/week brisk walking on a treadmill at 50% to 85% of the heart rate reserve (exercise group: EXE), and a control group of 47 diabetic participants (CON; 24 f, 23 m; 52.9+/-13.4 years old; BMI=30.9+/-8.4). Vibration perception threshold (VPT), nerve distal latency (DL), nerve conduction velocity (NCV), and nerve action potential amplitude (NAPA) in the lower limbs were measured.

RESULTS

We found significant differences on Delta (delta) in NCV for both peroneal and sural motor nerve between the EXE and CON groups during the study period (P<.001, for both). The percentage of diabetic patients that developed motor neuropathy and sensory neuropathy during the 4 years of the study was significantly higher in the CON than the EXE group (17% vs. 0.0%, P<.05, and 29.8% vs. 6.45%, P<.05, respectively). In addition, the percentage of diabetic patients who developed increased VPT (25 V) during the study was significantly higher in the CON than the EXE group (21.3% vs. 12.9%, P<.05). Change on Hallux VPT from baseline to the end of the study was significantly different between the EXE and CON groups (P<.05); no significant change in Malleolus VPT between the two groups occurred.

CONCLUSIONS

This study suggests, for the first time, that long-term aerobic exercise training can prevent the onset or modify the natural history of DPN.

ATP and norepinephrine contributions to sympathetic vasoconstriction of tail artery are altered in streptozotocin-diabetic rats

Sympathetic vasoconstriction is susceptible to diabetes, but contributions made by purinergic neurotransmission in this state have not been investigated. We aimed to evaluate sympathetic vasoconstriction contributions by ATP and norepinephrine in the tail artery from streptozotocin-diabetic rats by using isometric vascular rings. Tail arteries were isolated from rats made diabetic 3 mo earlier with streptozotocin (diabetic group), age-matched nondiabetic rats (nondiabetic injected), age-matched untreated animals (noninjected normal), and age-matched untreated animals in high glucose control Krebs solution (high glucose control). Responses to KCl (60 mM) or nerve stimulus trains of 1-100 impulses were identical in all groups. Electrical stimulation produced progressively greater contractions with increasing impulse numbers. These were partially reduced by suramin (100 microM, P2 antagonist), NF-279 (1 microM, P2X blocker), and phentolamine (2 microM, alpha-blocker). For purinergic antagonists, blockade was greater in diabetic vessels compared with that in others. No differential effect could be detected for phentolamine between groups. Bath-applied ATP (1 nM-1 mM) and norepinephrine (0.1 nM-100 microM) showed increased potency with diabetic group vessels. Desipramine (1 microM, norepinephrine reuptake inhibitor) potentiated neurally evoked responses in all groups equally and increased sensitivity to exogenous norepinephrine in a similar fashion. Histochemical labeling of sympathetic nerves with neuronal marker protein PGP-9.5 and a sympathetic nerve-specific antibody for tyrosine hydroxylase showed no reduction in diabetic innervation density. We demonstrate, for the first time, changes in contributions of ATP and norepinephrine in sympathetic responses of rat tail artery in diabetes, which cannot be accounted for by axonal degeneration or by changes in norepinephrine reuptake.

Use of tricyclic antidepressants in older patients with painful neuropathies

OBJECTIVE

To describe patterns of use of tricyclic antidepressants (TCAs) (e.g., amitriptyline, nortriptyline) in older patients with painful neuropathies.

RESEARCH DESIGN AND METHODS

Using a large US health insurance claims database, we identified all persons who: (1) received a TCA between 1 January 1999 and 30 June 2001, (2) were aged > or =65 years as of the date of their first prescription for a TCA during this period, and (3) had one or more health care encounters for the treatment of a painful neuropathy in the 30-day period immediately preceding their initial receipt of a TCA. We then examined the prevalence of selected comorbidities and/or concurrent use of medications that might render the prescribing of a TCA inappropriate, based on a listing of contraindications, warnings, and precautions found in the package inserts for these agents. Patterns of TCA use also were examined, based on information on paid claims.

RESULTS

A total of 1,732 patients met all inclusion and exclusion criteria for the study. Their mean age was 74.6 years; 60.3% were women. Amitriptyline was the most frequently prescribed TCA (79.4% of patients). Forty-one percent of study subjects receiving TCAs had conditions--primarily cardiovascular--that render the use of such agents potentially inappropriate. The mean daily dose of TCAs was universally low (about 23 mg).

CONCLUSIONS

The high prevalence of conditions rendering the use of TCAs potentially inappropriate, along with relatively low daily dosages, suggest that many older patients with painful neuropathies who are prescribed these agents may be suboptimally treated.

The prevalence of neuropathy and relationship with risk factors in diabetic patients: a single-center experience

OBJECTIVE

To determine the rate of distal symmetrical polyneuropathy (DSP) in patients with type 2 diabetes mellitus, to evaluate the role of history, neurological examination and the electrodiagnostic methods in the diagnosis of DSP, and to determine the association between electromyography-supported neuropathy (ESN), neuropathic complaints (NCs) and risk factors.

SUBJECTS AND METHODS

A total of 191 type 2 DM patients (109 female, 82 male; mean age 58.7 +/- 10 years) were recruited. The NCs were recorded. All patients had electromyographic (EMG) examinations. The relationship between ESN, NCs and risk factors were evaluated.

RESULTS

Of the 191 patients, 83 (43.5%) had DSP on EMG examinations and 92 (48.2%) patients suffered from NCs. Among the ESN patients, a significant relationship existed with HbA1(c) level, illness duration, smoking, male gender or insulin usage (p < 0.05) but not with age, hypertension, hypercholesterolemia or hypertriglyceridemia. The frequency of NCs was higher in patients with ESN. There was also a significant association between NCs and ESN (p < 0.05). The presence of NCs was not related to age, gender, smoking, hypertension, hypercholesterolemia and hypertriglyceridemia (p > 0.05) but NCs were correlated to HbA1(c) level, illness duration and insulin usage (p < 0.05).

CONCLUSION

Our data show that a strong association exists between the presence of DSP and illness duration, HbA1(c), smoking, thereby indicating that cessation of smoking and near normal glycemic control would be additional precautions to delay the beginning or progression of polyneuropathy.

Requirement of aldose reductase for the hyperglycemic activation of protein kinase C and formation of diacylglycerol in vascular smooth muscle cells

Activation of protein kinase C (PKC) has been linked to the development of secondary diabetes complications. However, the underlying molecular mechanisms remain unclear. We examined the contribution of aldose reductase, which catalyzes the first, and the rate-limiting, step of the polyol pathway of glucose metabolism, to PKC activation in vascular smooth muscle cells (VSMCs) isolated from rat aorta and exposed to high glucose in culture. Exposure of VSMCs to high glucose (25 mmol/l), but not iso-osmotic mannitol, led to an increase in total membrane-associated PKC activity, which was prevented by the aldose reductase inhibitors tolrestat or sorbinil or by the ablation of aldose reductase by small interfering RNA (siRNA). The VSMCs were found to express low levels of sorbitol dehydrogenase, and treatment with the sorbitol dehydrogenase inhibitor CP-166572 did not prevent high-glucose-induced PKC activation. Stimulation with high glucose caused membrane translocation of conventional (alpha, beta1, beta2, and gamma) and novel (delta and epsilon) isoforms of PKC. Inhibition of aldose reductase prevented membrane translocation of PKC-beta2 and -delta and delayed the activation of PKC-beta1 and -epsilon, whereas membrane translocation of PKC-alpha and -gamma was not affected. Treatment with tolrestat prevented phosphorylation of PKC-beta2 and -delta. High glucose increased the formation of diacylglycerol (DAG) and enhanced phosphorylation of phospholipase C-gamma1 (PLC-gamma1). Inhibition of aldose reductase prevented high glucose-induced DAG formation and phosphorylation of PLC-gamma1 and PLC-beta2 and -delta. Inhibition of phospholipid hydrolysis by D609, but not by the synthetic alkyl-1-lysophospholipid 1-O-octadecyl-2-O-methyl-rac-glycerophosphocholine, or edelfosine, prevented DAG formation. Treatment with sorbinil decreased the levels of reactive oxygen species in high-glucose-stimulated VSMCs. Hence, inhibition of aldose reductase, independent of sorbitol dehydrogenase, appears to be effective in diminishing oxidative stress and hyperglycemic changes in signaling events upstream to the activation of multiple PKC isoforms and PLC-gamma1 and may represent a useful approach for preventing the development of secondary vascular complications of diabetes.

Pharmacokinetics of dextromethorphan after single or multiple dosing in combination with quinidine in extensive and poor metabolizers

Dextromethorphan (DM) pharmacological properties predict that the widely used cough suppressant could be used to treat several neuronal disorders, but it is rapidly metabolized after oral dosing. To find out whether quinidine (Q), a CYP2D6 inhibitor, could elevate and prolong DM plasma profiles, 2 multiple-dose studies identified the lowest oral dose of Q that could be used in a fixed combination with 3 doses of DM. A multiple-dose study in healthy subjects with an extensive or a poor enzyme metabolizer phenotype evaluated the safety and pharmacokinetic profile of a selected fixed-dose combination (AVP-923). Study 1 randomized 46 healthy subjects, who were extensive CYP2D6 metabolizers, to receive 0, 2.5, 10, 25, 50, or 75 mg Q twice daily in combination with 30 mg DM for 7 days. Plasma and urine samples were collected after the first and last doses for the assay of DM, dextrorphan (DX), and Q. Study 2 randomized 65 healthy extensive CYP2D6 metabolizers to 8 groups given twice-daily 45- or 60-mg DM doses combined with 0, 30, 45, or 60 mg Q for 7 days. The effects of increasing Q were not different with doses greater than 25 mg, whereas lower doses showed a dose-related increase in plasma DM concentrations. Urinary ratios of DM/DX showed a Q dose- and time-related increase in the number of subjects converted to the poor metabolizer phenotype that reached 100% on day 3 of dosing with 25 mg Q. Results from both studies indicated that 25 to 30 mg Q is adequate to maximally suppress O-demethylation of DM. Study 3 evaluated 7 extensive metabolizers and 2 poor metabolizers given an oral capsule every 12 hours containing 30 mg Q combined with 30 mg DM. DM plasma AUC values increased in both groups of subjects during the 8-day study. The mean urinary metabolic ratio (DM/DX) increased at least 27-fold in extensive metabolizers by day 8. There was no effect of Q on urinary metabolic ratios in poor metabolizers. Safety evaluations, including electrocardiograms, indicated that the combination was well tolerated, with no difference between extensive and poor metabolizer phenotypes.

Effect of Glycemic Control on Electrophysiologic Changes of Diabetic Neuropathy in Type 2 Diabetic Patients

Diabetic neuropathy is a common complication of diabetes mellitus. Effective blood glucose control retards changes in nerve conduction velocity in type 1 diabetes. This study examined the relationship between glycemic control and electrophysiologic changes in diabetic neuropathy in 57 type 2 diabetic patients. Nerve conduction in the peroneal motor nerve, tibial motor nerve, and sural nerve were measured at study entry and at follow-up 24+/-3.12 months later. Changes in individual nerves are expressed as a percentage change (PC) and overall electrophysiologic changes are expressed as the sum of individual PCs. The PCs for peroneal motor nerve velocity, tibial motor nerve velocity, and sural nerve velocity were all lower in patients with a mean HbA1c of 8.5% or less compared with those in patients with a mean HbA1c of more than 8.5%, and SPCV (sum of PC in velocity) was significantly inversely correlated with mean HbA1c. However, there was no significant difference in SPCV in subjects with or without hypertension, hypertriglyceridemia, or low high-density lipoprotein cholesterol concentration. In conclusion, hyperglycemia is the most important etiology for electrophysiologic progression in type 2 diabetic patients. Furthermore, a mean HbA1c of more than 8.5% will result in significant deterioration in electrophysiology.

Risk factors for cardiac autonomic neuropathy in type 1 diabetes mellitus

AIMS/HYPOTHESIS

Cardiac autonomic neuropathy (CAN) is associated with increased morbidity and mortality in type 1 diabetes. Apart from glycaemic control, risk factors for CAN have not been extensively studied.

METHODS

As part of the EURODIAB Prospective Complications Study, CAN--defined as either a loss of heart rate variability or postural hypotension on standing--was assessed at baseline and follow-up (7.3+/-0.6 years from baseline) in patients with type 1 diabetes.

RESULTS

Follow-up measurements were available for 956 participants without CAN at baseline (age at baseline 31.3+/-8.9 years, duration of diabetes 13.5+/-8.3 years). During follow-up, 163 (17%) subjects developed CAN, yielding an incidence of 23.4 per 1,000 person-years. Blood pressure, weight, the presence of cardiovascular disease, albuminuria, distal symmetrical polyneuropathy (DSP) and retinopathy at baseline were associated with the incidence of CAN after adjustment for sex, duration of diabetes and HbA(1)c. In a multivariate regression model, baseline factors associated with an increased risk of developing CAN were age [odds ratio (OR)=1.3 per decade, 95% CI 1.1-1.7], HbA(1)c (OR=1.2 per percentage point, 95% CI 1.1-1.4), systolic blood pressure (OR=1.1 per 10 mmHg, 95% CI 1.0-1.3), feeling faint on standing (OR=2.0, 95% CI 1.2-3.2), DSP (OR=1.9, 95% CI 1.2-3.0) and retinopathy (OR=1.7, 95% CI 1.1-2.6).

CONCLUSION/INTERPRETATION

This study confirms the importance of exposure to hyperglycaemia as a risk factor for CAN. A small set of variables, including HbA(1)c, hypertension, DSP and retinopathy, predict the risk of CAN. Clinical trials are needed to address the impact of intensive antihypertensive treatment on CAN in type 1 diabetes.

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.

Antihyperalgesic effects of cizolirtine in diabetic rats: behavioral and biochemical studies

Although clinically well controlled at the metabolic level, type I diabetes resulting from an insufficient insulin secretion remains the cause of severe complications. In particular, diabetes can be associated with neuropathic pain which fails to be treated by classical analgesics. In this study, we investigated the efficacy of a novel non opioid analgesic, cizolirtine, to reduce mechanical hyperalgesia associated with streptozotocin (STZ)-induced diabetes, in the rat. Cizolirtine was compared to paroxetine, an antidepressant drug with proven efficacy to relieve painful diabetic neuropathy. Under acute conditions, cizolirtine (30 and 80 mg/kgi.p.) significantly increased paw withdrawal and vocalization thresholds in the paw pressure test in diabetic rats displaying mechanical hyperalgesia. The antihyperalgesic effects of cizolirtine persisted under chronic treatment conditions, since pre-diabetes thresholds were recovered after a two week-treatment with the drug (3 mg/kg/day, s.c.). In this respect, cizolirtine was as efficient as paroxetine (5 mg/kg per day, s.c.) which, however, was inactive under acute treatment conditions. Measurements of the spinal release of calcitonin gene-related peptide (CGRP) through intrathecal perfusion under halothane-anesthesia showed that acute administration of cizolirtine (80 mg/kg, i.p.) significantly diminished (-36%) the peptide outflow in diabetic rats suffering from neuropathic pain. This effect as well as the antihyperalgesic effect of cizolirtine were prevented by the alpha(2)-adrenoreceptor antagonist idazoxan (2 mg/kg, i.p.). These data suggest that the antihyperalgesic effect of cizolirtine in diabetic rats suffering from neuropathic pain implies an alpha(2)-adrenoceptor-dependent presynaptic inhibition of CGRP-containing primary afferent fibers.

Diabetic neuropathies

Diabetic neuropathy (DN) is a common complication of diabetes that often is associated with considerable morbidity and mortality. The epidemiology and natural history of DN is clouded with uncertainty because of confusion regarding the definition and measurement of this disorder. The recent resurgence of interest in the vascular hypothesis, oxidative stress, the neurotrophic hypothesis,and the possibility of the role of autoimmunity has opened up new avenues of investigation for therapeutic intervention. The ability to manage successfully the many different manifestations of diabetic neuropathy depends ultimately on success in uncovering the pathogenic processes underlying this disorder.

Unusual neurophysiological and immunological findings in myasthenia gravis: a case report

We describe the case of a male patient with ocular myasthenia gravis who developed a diabetic neuropathy similar to chronic inflammatory demyelinating polyradiculoneuropathy associated with transient generalized 'myokymic' discharges and distal weakness. He had antibodies against acetylcholine receptor and GQ1b ganglioside, but not anti-voltage-gated K(+) channel antibodies. Serial electrophysiological and immunological findings showed that diabetes was involved in the immune-mediated mechanism of peripheral neuropathy. We hypothesize that the concomitant appearance of distal motor weakness and decreased compound muscle action potentials upon repetitive nerve stimulation, together with increased distal motor latency and generalized peripheral nerve hyperexcitability, were all related to transient serum positivity to anti-GQ1b antibodies.

Lidocaine patch 5% with systemic analgesics such as gabapentin: a rational polypharmacy approach for the treatment of chronic pain

OBJECTIVE

To assess the effectiveness and safety of the lidocaine patch 5%, a targeted peripheral analgesic, in the treatment of postherpetic neuralgia, painful diabetic neuropathy, and low back pain patients with incomplete responses to their current analgesic treatment regimen containing gabapentin.

DESIGN

This was a 2-week, open-label, nonrandomized, multicenter pilot trial in the clinical setting. Patients with postherpetic neuralgia, painful diabetic neuropathy, or low back pain with partial responses (average daily pain intensity >4/10) to their current analgesic treatment regimen were included. Treatment consisted of daily application of up to four lidocaine patches to areas of maximal peripheral pain. Effectiveness was evaluated using the Brief Pain Inventory (BPI). Safety was assessed by adverse events, physical and neurologic examinations, vital signs, and clinical laboratory tests.

RESULTS

Significant improvements in BPI measures of pain intensity and pain relief were reported for all groups of patients after 2 weeks of lidocaine patch 5% treatment. Significant improvements in BPI measures of pain interference with general activity, mood, walking ability, normal work, relationships with others, sleep, and enjoyment of life were noted. The lidocaine patch 5% was found to be safe and well tolerated.

CONCLUSIONS

Results of this study highlight the potential advantages achieved with rational polypharmacy using a targeted peripheral analgesic, the lidocaine patch 5%, with centrally acting agents such as the anticonvulsant gabapentin. Controlled trials are warranted to further define the impact of such combination therapy.

Evaluation of orally active poly(ADP-ribose) polymerase inhibitor in streptozotocin-diabetic rat model of early peripheral neuropathy

AIMS/HYPOTHESIS

Poly(ADP-ribose) polymerase activation depletes NAD+ and high-energy phosphates, activates protein kinase C, and affects gene expression in various tissues. This study was designed to characterise the effects of the potent, orally active poly(ADP-ribose) polymerase inhibitor PJ34 in the Wistar rat model of early diabetic neuropathy.

METHODS

Control and streptozotocin-diabetic rats were maintained with or without PJ34 treatment (30 mg x kg(-1) x day(-1)) for two weeks, after two weeks without treatment. Endoneurial blood flow was assessed by hydrogen clearance; metabolites and high-energy phosphates were assayed by enzymatic spectrofluorometric methods; and poly(ADP-ribose) was detected by immunohistochemistry.

RESULTS

Blood glucose concentrations were increased to a similar extent in untreated and PJ34-treated diabetic rats compared with controls. Intense poly(ADP-ribose) immunostaining was observed in the sciatic nerve of diabetic rats, but not in other groups. Final sciatic motor nerve conduction velocity and digital sensory nerve conduction velocity were reduced by 24% and 22% respectively in diabetic rats compared with controls (p<0.01 for both), and both were 98% corrected by PJ34 (p<0.01 vs diabetic group for both). In contrast, with PJ34 treatment, nerve blood flow showed a modest (17%) increase, and vascular conductance showed a tendency to increase. Free mitochondrial and cytosolic NAD+:NADH ratios, assessed from the glutamate and lactate dehydrogenase systems, phosphocreatine concentrations, and phosphocreatine:creatine ratios were decreased in diabetic rats and essentially normalised by PJ34. In both untreated and PJ34-treated diabetic rats, nerve glucose, sorbitol and fructose were increased to a similar extent. PJ34 did not affect any variables in control rats.

CONCLUSIONS/INTERPRETATION

Short-term poly(ADP-ribose) polymerase inhibitor treatment reverses functional and metabolic abnormalities of early diabetic neuropathy. Complete normalisation of nerve blood flow is not required for correction of motor or sensory nerve conduction velocities, provided that a therapeutic agent can restore nerve energy state via direct action on Schwann cells.