Treatment of diabetic polyneuropathy: Update 2006

Alpha-lipoic acid for diabetic peripheral neuropathy

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a frequent complication in people living with type 1 or type 2 diabetes. There is currently no effective treatment for DPN. Although alpha-lipoic acid (ALA, also known as thioctic acid) is widely used, there is no consensus about its benefits and harms.

OBJECTIVES

To assess the effects of alpha-lipoic acid as a disease-modifying agent in people with diabetic peripheral neuropathy.

SEARCH METHODS

On 11 September 2022, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase, and two clinical trials registers. We also searched the reference lists of the included studies and relevant review articles for additional references not identified by the electronic searches.

SELECTION CRITERIA

We included randomised clinical trials (RCTs) that compared ALA with placebo in adults (aged 18 years or older) and that applied the study interventions for at least six months. There were no language restrictions.

DATA COLLECTION AND ANALYSIS

We used standard methods expected by Cochrane. The primary outcome was change in neuropathy symptoms expressed as changes in the Total Symptom Score (TSS) at six months after randomisation. Secondary outcomes were change in neuropathy symptoms at six to 12 months and at 12 to 24 months, change in impairment, change in any validated quality of life total score, complications of DPN, and adverse events. We assessed the certainty of the evidence using GRADE.

MAIN RESULTS

Our analysis incorporated three trials involving 816 participants. Two studies included people with type 1 or type 2 diabetes, while one study included only people with type 2 diabetes. The duration of treatment was between six months and 48 months. We judged all studies at high risk of overall bias due to attrition. ALA compared with placebo probably has little or no effect on neuropathy symptoms measured by TSS (lower score is better) after six months (mean difference (MD) -0.16 points, 95% confidence interval (CI) -0.83 to 0.51; 1 study, 330 participants; moderate-certainty evidence). The CI of this effect estimate did not contain the minimal clinically important difference (MCID) of 0.97 points. ALA compared with placebo may have little or no effect on impairment measured by the Neuropathy Impairment Score-Lower Limbs (NIS-LL; lower score is better) after six months (MD -1.02 points, 95% CI -2.93 to 0.89; 1 study, 245 participants; low-certainty evidence). However, we cannot rule out a significant benefit, because the lower limit of the CI surpassed the MCID of 2 points. There is probably little or no difference between ALA and placebo in terms of adverse events leading to cessation of treatment within six months (risk ratio (RR) 1.48, 95% CI 0.50 to 4.35; 3 studies, 1090 participants; moderate-certainty evidence). No studies reported quality of life or complications associated with DPN.

AUTHORS' CONCLUSIONS

Our analysis suggests that ALA probably has little or no effect on neuropathy symptoms or adverse events at six months, and may have little or no effect on impairment at six months. All the studies were at high risk of attrition bias. Therefore, future RCTs should ensure complete follow-up and transparent reporting of any participants missing from the analyses.

Brain-Computer Interface to Deliver Individualized Multisensory Intervention for Neuropathic Pain

To unravel the complexity of the neuropathic pain experience, researchers have tried to identify reliable pain signatures (biomarkers) using electroencephalography (EEG) and skin conductance (SC). Nevertheless, their use as a clinical aid to design personalized therapies remains scarce and patients are prescribed with common and inefficient painkillers. To address this need, novel non-pharmacological interventions, such as transcutaneous electrical nerve stimulation (TENS) to activate peripheral pain relief via neuromodulation and virtual reality (VR) to modulate patients' attention, have emerged. However, all present treatments suffer from the inherent bias of the patient's self-reported pain intensity, depending on their predisposition and tolerance, together with unspecific, pre-defined scheduling of sessions which does not consider the timing of pain episodes onset. Here, we show a Brain-Computer Interface (BCI) detecting in real-time neurophysiological signatures of neuropathic pain from EEG combined with SC and accordingly triggering a multisensory intervention combining TENS and VR. After validating that the multisensory intervention effectively decreased experimentally induced pain, the BCI was tested with thirteen healthy subjects by electrically inducing pain and showed 82% recall in decoding pain in real time. Such constructed BCI was then validated with eight neuropathic patients reaching 75% online pain precision, and consequently releasing the intervention inducing a significant decrease (50% NPSI score) in neuropathic patients' pain perception. Our results demonstrate the feasibility of real-time pain detection from objective neurophysiological signals, and the effectiveness of a triggered combination of VR and TENS to decrease neuropathic pain. This paves the way towards personalized, data-driven pain therapies using fully portable technologies.

Long-Term Evaluation of Spinal Cord Stimulation in Patients With Painful Diabetic Polyneuropathy: An Eight-to-Ten-Year Prospective Cohort Study

OBJECTIVE

This study aimed to evaluate the long-term effects of spinal cord stimulation (SCS) in patients with painful diabetic polyneuropathy (PDPN).

MATERIALS AND METHODS

This prospective cohort study was the eight-to-ten-year follow-up of a previously performed pilot and randomized controlled trial on the effects of SCS in PDPN, initiated by the multidisciplinary pain center of Maastricht University Medical Center+. The study population consisted of a subgroup of patients who still used SCS treatment ≥ eight years after implantation (n = 19). Pain intensity scores (numeric rating scale [NRS]) during the day and night and data on secondary outcomes (ie, quality of life, depression, sleep quality) were reported during yearly follow-up consultations. Long-term efficacy of SCS was analyzed by comparing the most recently obtained data eight to ten years after implantation with those obtained at baseline.

RESULTS

Pain intensity, day and night, was significantly (p < 0.01) reduced by 2.3 (NRS 6.6-4.3) and 2.2 (NRS 6.8-4.6) points, respectively, when comparing the long-term data with baseline. Moreover, for > 50% of patients, the pain reduction was > 30%, which is considered clinically meaningful. No differences were found regarding the secondary outcomes.

CONCLUSION

This eight-to-ten-year follow-up study indicates that SCS can remain an effective treatment in the long term to reduce pain intensity in a subcohort of patients with PDPN who still had an SCS device implanted after eight years.

Exercise in the Prevention and Treatment of Type 2 Diabetes

Type 2 diabetes is a systemic, multifactorial disease that is a leading cause of morbidity and mortality globally. Despite a rise in the number of available medications and treatments available for management, exercise remains a first-line prevention and intervention strategy due to established safety, efficacy, and tolerability in the general population. Herein we review the predisposing risk factors for, prevention, pathophysiology, and treatment of type 2 diabetes. We emphasize key cellular and molecular adaptive processes that provide insight into our evolving understanding of how, when, and what types of exercise may improve glycemic control. © 2023 American Physiological Society. Compr Physiol 13:1-27, 2023.

Effect of Alpha-Lipoic Acid in the Treatment of Diabetic Neuropathy: A Systematic Review

Diabetic neuropathy is a clinical condition that can have a significant impact on quality of life, presenting as numbness, tingling, and burning in the extremities. Current treatment options focus on symptom alleviation and reducing exposure to risk factors as treating the pathophysiological causes of diabetic neuropathy remains a significant challenge. Novel studies have proposed that the use of antioxidants, including alpha-lipoic acid (⍺-lipoic acid), may represent a beneficial intervention for treating neuropathic pain in diabetic patients. This study aims to evaluate the effect of ⍺-lipoic acid in the treatment of diabetic neuropathy and determine its effectiveness in reducing the symptoms of diabetic neuropathy. To achieve our objective, PubMed, Scopus, and Web of Science databases were screened on March 3, 2022. Randomized controlled trials that investigated ⍺-lipoic acid treatment in diabetes mellitus patients with neuropathic pain and made an appropriate comparison were included. The reduction of neuropathic symptoms was the primary outcome, and the secondary outcome was the incidence of adverse events. Eight studies comprising 1,500 diabetic patients were evaluated in this systematic review. The findings were inconsistent among the literature concerning the effectiveness of ⍺-lipoic acid in the treatment of diabetic neuropathy, with three trials (37.5%) observing significant improvements in symptoms and five trials (62.5%) not observing any notable results. All studies found ⍺-lipoic acid to be a safe and tolerable intervention, with no reported adverse effects. The administration of ⍺-lipoic acid may result in symptom reduction and offers a safe and tolerable treatment option. However, there is limited evidence to support the beneficial outcomes of this approach. Further trials are warranted to corroborate or contradict the hypothesis that ⍺-lipoic acid is an effective intervention for the treatment of diabetic neuropathy.

Glucose-Related Traits and Risk of Migraine—A Potential Mechanism and Treatment Consideration

Migraine and glucose-related (glycaemic) traits (fasting glucose, fasting insulin, and type 2 diabetes) are common and complex comorbid disorders that cause major economic and social burdens on patients and their families. Studies on the relationship between migraine and glucose-related traits have yielded inconsistent results. The purpose of this review is to synthesise and discuss the information from the available literature on the relationship between fasting glucose, fasting insulin, and type 2 diabetes (T2D) with migraine. Publications on migraine and fasting glucose, migraine and fasting insulin, and migraine and T2D were identified from a PubMed and Google Scholar database search and reviewed for this article. Multiple publications have suggested that the comorbidity of migraine and glucose-related traits may have a similar complex pathogenic mechanism, including impaired glucose homeostasis, insulin resistance, reduced cerebrovascular reactivity, abnormal brain metabolism, shared genetic factors, neurotransmitters, and sex hormones. Furthermore, several studies have found a bi-directional link between migraine with insulin resistance and T2D. There is strong evidence for a biological association between migraine headache and glucose-related traits, and burgeoning evidence for shared genetic influences. Therefore, genetic research into these comorbid traits has the potential to identify new biomarkers and therapeutic targets and provide biological insight into their relationships. We encourage healthcare professionals to consider the co-occurrence of migraine with glucose-related traits in the evaluation and treatment of their patients.

Effects of Upregulation of TNFAIP3 on Diabetic Neuropathic Pain in Mice

Globally, diabetes has assumed epidemic proportions with the neuropathic complications attributed to the malady emerging as a substantial burden on patients and society. DNP has greatly affected the daily life of patients, the effect of traditional treatment methods is not ideal, and it is easy to produce drug resistance. This work is aimed at scrutinizing the effect of upregulating the expression of TNFAIP3 on diabetic neuralgia in mice. This work entailed ascertaining the effects of TNFAIP3 on a murine DNP system. This inspired us to observe the analgesic effect via high expression of lentivirus-mediated TNFAIP3 by intrathecal injection in the animal model to explore its regulatory impacts, symptom relief, and mechanistic role in pain. The results displayed an attenuation of hind paw pain hypersensitivity by LV-TNFAIP3 in the animals. The spinal cord and dorsal root ganglion of mice with neuropathic pain displayed an evident dip in TNFAIP3. Inhibition of the ERK/NF-κB signaling pathway employing LV-TNFAIP3 conspicuously suppressed this pathway while the diabetic pain hypersensitivity was quelled. This effect was also seen with insulin treatment evidently. In conclusion, according to the above analyses, the interaction between DNP and extracellular signal-regulated kinase signal transduction pathway is one of the key factors of pathogenesis.

A Comprehensive Review of Neuronal Changes in Diabetics

There has been an exponential rise in diabetes mellitus (DM) cases on a global scale. Diabetes affects almost every system of the body, and the nervous system is no exception. Although the brain is dependent on glucose, providing it with the energy required for optimal functionality, glucose also plays a key role in the regulation of oxidative stress, cell death, among others, which furthermore contribute to the pathophysiology of neurological disorders. The variety of biochemical processes engaged in this process is only matched by the multitude of clinical consequences resulting from it. The wide-ranging effects on the central and peripheral nervous system include, but are not limited to axonopathies, neurodegenerative diseases, neurovascular diseases, and general cognitive impairment. All language search was conducted on MEDLINE, COCHRANE, EMBASE, and GOOGLE SCHOLAR till September 2021. The following search strings and Medical Subject Headings (MeSH terms) were used: "Diabetes Mellitus," "CNS," "Diabetic Neuropathy," and "Insulin." We explored the literature on diabetic neuropathy, covering its epidemiology, pathophysiology with the respective molecular pathways, clinical consequences with a special focus on the central nervous system and finally, measures to prevent and treat neuronal changes. Diabetes is slowly becoming an epidemic, rapidly increasing the clinical burden on account of its wide-ranging complications. This review focuses on the neuronal changes occurring in diabetes such as the impact of hyperglycemia on brain function and structure, its association with various neurological disorders, and a few diabetes-induced peripheral neuropathic changes. It is an attempt to summarize the relevant literature about neuronal consequences of DM as treatment options available today are mostly focused on achieving better glycemic control; further research on novel treatment options to prevent or delay the progression of neuronal changes is still needed.

Comprehensive Assessment and Pharmacotherapy of Patients with Chronic Pain Syndrome Due to Diabetic Neuropathy and Postherpetic Neuralgia

Management of chronic pain, usually associated with comorbid conditions, remains challenging. General practitioners, together with multidisciplinary teams of specialists, play an important role in diagnosing and treating patients with chronic pain of different origin. This article outlines the main mechanisms underlying chronic nociceptive and neuropathic pain and describes some helpful techniques to initially evaluate and regularly monitor pain. Pharmacologic treatment options, including their benefits and adverse effects, with particular emphasis on the management of diabetic neuropathy and postherpetic neuralgia, commonly seen in the primary care practice setting, are presented. Chronic pain, regardless of its cause, is a disease syndrome and, as such, requires a comprehensive, individualised approach to each patient reaching beyond symptom control. Collaboration of physicians (general practitioners, diabetologists, neurologists, and pain specialists), pharmacists, and nurses in the management of patients with diabetic neuropathy and postherpetic neuralgia improves patient safety and contributes to better adherence to therapeutic regimens, which leads to more favourable outcomes and improved quality of life.

O-GlcNAc Transferase Is Essential for Sensory Neuron Survival and Maintenance

O-GlcNAc transferase (OGT) regulates a wide range of cellular processes through the addition of the O-GlcNAc sugar moiety to thousands of protein substrates. Because nutrient availability affects the activity of OGT, its role has been broadly studied in metabolic tissues. OGT is enriched in the nervous system, but little is known about its importance in basic neuronal processes in vivo Here, we show that OGT is essential for sensory neuron survival and maintenance in mice. Sensory neuron-specific knock-out of OGT results in behavioral hyposensitivity to thermal and mechanical stimuli accompanied by decreased epidermal innervation and cell-body loss in the dorsal root ganglia. These effects are observed early in postnatal development and progress as animals age. Cultured sensory neurons lacking OGT also exhibit decreased axonal outgrowth. The effects on neuronal health in vivo are not solely due to disruption of developmental processes, because inducing OGT knock-out in the sensory neurons of adult mice results in a similar decrease in nerve fiber endings and cell bodies. Significant nerve-ending loss occurs before a decrease in cell bodies; this phenotype is indicative of axonal dieback that progresses to neuronal death. Our findings demonstrate that OGT is important in regulating axonal maintenance in the periphery and the overall health and survival of sensory neurons.SIGNIFICANCE STATEMENT We show the importance of O-GlcNAc transferase (OGT) for sensory neuron health and survival in vivo This study is the first to find that loss of OGT results in neuronal cell death. Moreover, it suggests that aberrant O-GlcNAc signaling can contribute to the development of neuropathy. The sensory neurons lie outside of the blood-brain barrier and therefore, compared to central neurons, may have a greater need for mechanisms of metabolic sensing and compensation. Peripheral sensory neurons in particular are subject to degeneration in diabetes. Our findings provide a foundation for understanding the role of OGT under normal physiological conditions in the peripheral nervous system. This knowledge will be important for gaining greater insight into such disease states as diabetic neuropathy.

Aldo-Keto Reductase Family 1 Member B10 Inhibitors: Potential Drugs for Cancer Treatment

Cytosolic NADPH-dependent reductase AKR1B10 is a member of the aldo-keto reductase (AKR) superfamily. This enzyme is normally expressed in the gastrointestinal tract. However, it is overexpressed in many solid tumors, such as hepatocarcinoma, lung cancer and breast cancer. AKR1B10 may play a role in the formation and development of carcinomas through multiple mechanisms including detoxification of cytotoxic carbonyls, modulation of retinoic acid level, and regulation of cellular fatty acid synthesis and lipid metabolism. Studies have suggested that AKR1B10 may be a useful biomarker for cancer diagnosis and a potential target for cancer treatment. Over the last decade, a number of AKR1B10 inhibitors including aldose reductase inhibitors (ARIs), endogenous substances, natural-based derivatives and synthetic compounds have been developed, which could be novel anticancer drugs. This review provides an overview on related articles and patents about AKR1B10 inhibitors, with a focus on their inhibition selectivity and mechanism of function.

Promoted Interaction of Nuclear Factor-κB With Demethylated Purinergic P2X3 Receptor Gene Contributes to Neuropathic Pain in Rats With Diabetes

Painful diabetic neuropathy is a common complication of diabetes produced by mechanisms that as yet are incompletely defined. The aim of this study was to investigate the roles of nuclear factor-κB (NF-κB) in the regulation of purinergic receptor P2X ligand-gated ion channel 3 (P2X3R) plasticity in dorsal root ganglion (DRG) neurons of rats with painful diabetes. Here, we showed that hindpaw pain hypersensitivity in streptozocin-induced diabetic rats was attenuated by treatment with purinergic receptor antagonist suramin or A-317491. The expression and function of P2X3Rs was markedly enhanced in hindpaw-innervated DRG neurons in diabetic rats. The CpG (cytosine guanine dinucleotide) island in the p2x3r gene promoter region was significantly demethylated, and the expression of DNA methyltransferase 3b was remarkably downregulated in DRGs in diabetic rats. The binding ability of p65 (an active form of NF-κB) with the p2x3r gene promoter region and p65 expression were enhanced significantly in diabetes. The inhibition of p65 signaling using the NF-κB inhibitor pyrrolidine dithiocarbamate or recombinant lentiviral vectors designated as lentiviral vector-p65 small interfering RNA remarkably suppressed P2X3R activities and attenuated diabetic pain hypersensitivity. Insulin treatment significantly attenuated pain hypersensitivity and suppressed the expression of p65 and P2X3Rs. Our findings suggest that the p2x3r gene promoter DNA demethylation and enhanced interaction with p65 contributes to P2X3R sensitization and diabetic pain hypersensitivity.

Antineuropathic effect of 7-hydroxy-3,4-dihydrocadalin in streptozotocin-induced diabetic rodents

Background

Painful neuropathy is the most common and debilitating complication of diabetes and results in hyperalgesia and allodynia. Hyperglycemia clearly plays a key role in the development and progression of diabetic neuropathy. Current therapeutic approaches are only partially successful and they are only thought to reduce the pain associated with peripheral neuropathy. Some natural products offer combined antioxidant, anti-inflammatory and antinociceptive properties that may help to treat in a more integrative manner this condition. In this regard, the purpose of this study was to investigate the antineuropathic effect of 7-hydroxy-3,4-dihydrocadalin in streptozotocin-induced diabetic rats and mice without glucose control as well as the possible mechanism of action involved in this effect.

Methods

Rats and mice were injected with 50 or 200 mg/kg streptozotocin, respectively, to produce hyperglycemia. The formalin test and von Frey filaments were used to assess the nociceptive activity. Rota-rod was utilized to measure motor activity and malondialdehyde assay to determine anti-oxidative properties.

Results

After 3 weeks of diabetes induction, chemical hyperalgesia was observed in streptozotocin-injected rats. Oral acute administration of 7-hydroxy-3,4-dihydrocadalin (0.3–30 mg/kg) decreased in a dose-dependent manner formalin-evoked hyperalgesia in diabetic rats. In addition, methiothepin (non-selective 5-HT receptor antagonist, 1 mg/kg, i.p.) and ODQ (guanylyl cyclase inhibitor, 2 mg/kg, i.p.), but not naltrexone (opioid receptor antagonist, 1 mg/kg, s.c.), prevented 7-hydroxy-3,4-dihydrocadalin-induced antihyperalgesic effect. The anti-hyperalgesic effect of 7-hydroxy-3,4-dihydrocadalin was similar to that produced by pregabalin (10 mg/kg, p.o.). Furthermore, oral acute administration of 7-hydroxy-3,4-dihydrocadalin (30 mg/kg) reduced streptozotocin-induced changes in malondialdehyde concentration from plasma samples. Unlike pregabalin, 7-hydroxy-3,4-dihydrocadalin did not affect motor activity. Six weeks after diabetes induction, tactile allodynia was observed in the streptozotocin-injected rats. At this time, oral administration of 7-hydroxy-3,4-dihydrocadalin (30 mg/kg) or pregabalin (10 mg/kg) reduced in a similar way tactile allodynia in diabetic rats. Finally, chronic oral administration of 7-hydroxy-3,4-dihydrocadalin (30-300 mg/kg, 3 times/week, during 6 weeks), significantly prevented the development of mechanical hyperalgesia and allodynia in streptozotocin-induced diabetic mice.

Conclusions

Data suggests that 7-hydroxy-3,4-dihydrocadalin has acute and chronic effects in painful diabetic neuropathy. This effect seems to involve antioxidant properties as well as activation of 5-HT receptors and inhibition of guanylyl cyclase enzyme.

Electrical stimulation as an adjunctive treatment of painful and sensory diabetic neuropathy

BACKGROUND

The objective of this review is to evaluate the use of electrical stimulation to treat diabetic neuropathy. Application of electrical stimulation may provide a novel treatment option for large and small fiber neuropathy in persons with diabetes. Large and small nerve neuropathy alters pain, proprioception, touch perception, and motor function, which cause burning foot pain and serve as protective mechanisms from ulcerations.

METHODS

A content search for clinical trials involving electrical stimulation, neuropathy, and diabetes was conducted through PubMed. Randomized clinical trials and prospective studies with outcome measures affecting the lower extremity function were selected for review.

RESULTS

We identified eight studies in which electrical stimulation was used to treat diabetic neuropathy. Six studies evaluated small fiber neuropathy. Two studies evaluated patients with both small and large fiber neuropathy and reported significant improvement in vibration and monofilament testing and reduction in symptoms in the electrical stimulation treatment group. Six of the eight painful neuropathy studies identified significant improvement in symptoms. There were no studies that evaluated electrical stimulation to treated diabetic motor neuropathy, fall prevention or postural instability.

CONCLUSIONS

Electrical stimulation may be an effective alternative and adjunctive therapy to current interventions for diabetic peripheral neuropathy.

Meta-analysis of methylcobalamin alone and in combination with lipoic acid in patients with diabetic peripheral neuropathy

AIMS

To compare the efficacy and safety of daily lipoic acid (300-600 mg i.v.) plus methylcobalamin (500-1000 mg i.v. or im.) (LA-MC) with that of methylcobalamin alone (MC) on diabetic peripheral neuropathy (DPN).

METHODS

Electronic database were searched for studies published up to November 1, 2012 and study quality was assessed in duplicate. A random or a fixed effect model was used to analyse outcomes which were expressed as risk ratios (RRs) or mean difference (MD). I(2) statistic was used to assess heterogeneity.

RESULTS

Seventeen studies were included. Combined data from all studies showed that the LA-MC combination therapy was significantly superior to MC monotherapy (RR=1.47; 95% CI: 1.37-1.58). Superiority of the LA-MC combination was shown in nerve conduction velocity (NCV) with WMDs of 6.89 (95% CI: 4.24-9.73) for median motor nerve conduction velocity (MNCV), 5.24 (4.14-6.34) for median sensory nerve conduction velocity (SNCV), 4.34 (3.03-5.64) for peroneal MNCV, and 4.53 (3.2-5.85) for peroneal SNCV. There were no serious adverse events associated with treatment.

CONCLUSIONS

The results of the meta-analysis show that treatment with LA-MC for 2-4 weeks is associated with better outcomes in NCV and neuropathic symptoms relative to MC treatment. However larger well-designed studies are required to confirm this conclusion.

[Diabetic neuropathy]

These are the guidelines for diagnosis and treatment of diabetic neuropathy. This diabetic late complication comprises a number of mono- and polyneuropathies, plexopathies, radiculopathies and autonomic neuropathy. The position statement summarizes characteristic clinical symptoms and techniques for diagnostic assessment of diabetic neuropathy. Recommendations for the therapeutic management of diabetic neuropathy, especially for the control of pain in sensomotoric neuropathy, are provided.

Diabetes and alpha lipoic Acid

Diabetes mellitus is a multi-faceted metabolic disorder where there is increased oxidative stress that contributes to the pathogenesis of this debilitating disease. This has prompted several investigations into the use of antioxidants as a complementary therapeutic approach. Alpha lipoic acid, a naturally occurring dithiol compound which plays an essential role in mitochondrial bioenergetic reactions, has gained considerable attention as an antioxidant for use in managing diabetic complications. Lipoic acid quenches reactive oxygen species, chelates metal ions, and reduces the oxidized forms of other antioxidants such as vitamin C, vitamin E, and glutathione. It also boosts antioxidant defense system through Nrf-2-mediated antioxidant gene expression and by modulation of peroxisome proliferator activated receptors-regulated genes. ALA inhibits nuclear factor kappa B and activates AMPK in skeletal muscles, which in turn have a plethora of metabolic consequences. These diverse actions suggest that lipoic acid acts by multiple mechanisms, many of which have only been uncovered recently. In this review we briefly summarize the known biochemical properties of lipoic acid and then discussed the oxidative mechanisms implicated in diabetic complications and the mechanisms by which lipoic acid may ameliorate these reactions. The findings of some of the clinical trials in which lipoic acid administration has been tested in diabetic patients during the last 10 years are summarized. It appears that the clearest benefit of lipoic acid supplementation is in patients with diabetic neuropathy.

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

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

The roles of streptozotocin neurotoxicity and neutral endopeptidase in murine experimental diabetic neuropathy

We demonstrated that inhibition of neutral endopeptidase (NEP), a protease that degrades vaso- and neuroactive peptides, improves vascular and neural function in diabetic animal models. In this study we explored the role of NEP in neuropathy related to either insulin-deficient diabetes or diet-induced obesity using NEP deficient (−/−) mice. Initial studies showed that streptozotocin, in the absence of subsequent hyperglycemia, did not induce nerve conduction slowing or paw thermal hypoalgesia. Glucose disposal was impaired in both C57Bl/6 and NEP −/− mice fed a high fat diet. Thermal hypoalgesia and nerve conduction slowing were present in both streptozotocin-diabetic and high fat fed C57Bl/6 mice but not in NEP −/− mice exposed to either streptozotocin-induced diabetes or a high fat diet. These studies suggest that streptozotocin does not induce neurotoxicity in mice and that NEP plays a role in regulating nerve function in insulin-deficient diabetes and diet-induced obesity.

Alpha-lipoic Acid and diabetic neuropathy

Diabetic neuropathy presents a major public health problem. It is defined by the symptoms and signs of peripheral nerve dysfunction in diabetic patients, in whom other causes of neuropathy have been excluded. Pathogenetic mechanisms that have been implicated in diabetic neuropathy are: a) increased flux through the polyol pathway, leading to accumulation of sorbitol, a reduction in myo-inositol, and an associated reduced Na+-K+-ATPase activity, and b) endoneurial microvascular damage and hypoxia due to nitric oxide inactivation by increased oxygen free radical activity. Alpha-lipoic acid seems to delay or reverse peripheral diabetic neuropathy through its multiple antioxidant properties. Treatment with alpha-lipoic acid increases reduced glutathione, an important endogenous antioxidant. In clinical trials, 600 mg alpha-lipoic acid has been shown to improve neuropathic deficits. This review focuses on the relationship of alpha-lipoic acid and auto-oxidative glycosylation. It discusses the impact of alpha-lipoic acid on hyperglycemia-induced oxidative stress, and examines the role of alpha-lipoic acid in preventing glycation process and nerve hypoxia.

Nucleotide signaling and cutaneous mechanisms of pain transduction

Sensory neurons that innervate the skin provide critical information about physical contact between the organism and the environment, including information about potentially-damaging stimuli that give rise to the sensation of pain. These afferents also contribute to the maintenance of tissue homeostasis, inflammation and wound healing, while sensitization of sensory afferents after injury results in painful hypersensitivity and protective behavior. In contrast to the traditional view of primary afferent terminals as the sole site of sensory transduction, recent reports have lead to the intriguing idea that cells of the skin play an active role in the transduction of sensory stimuli. The search for molecules that transduce different types of sensory stimuli (mechanical, heat, chemical) at the axon terminal has yielded a wide range of potential effectors, many of which are expressed by keratinocytes as well as neurons. Emerging evidence underscores the importance of nucleotide signaling through P2X ionotropic and P2Y metabotropic receptors in pain processing, and implicates nucleotide signaling as a critical form of communication between cells of the skin, immune cells and sensory neurons. It is of great interest to determine whether pathological changes in these mechanisms contribute to chronic pain in human disease states such as complex regional pain syndrome (CRPS). This review discusses recent advances in our understanding of communication mechanisms between cells of the skin and sensory axons in the transduction of sensory input leading to pain.

The association between diabetes mellitus, glucose, and chronic musculoskeletal complaints. Results from the Nord-Trøndelag Health Study

Background

The relationship between diabetes mellitus (DM) and chronic musculoskeletal complaints (MSCs) is unclear. The aim of this study was to investigate the association between DM, non-fasting glucose and chronic MSCs defined as pain and/or stiffness ≥ 3 months during the past year in the general adult population.

Methods

The results were based on cross-sectional data from 64,785 men and women (aged ≥ 20 years) who participated in the Nord-Trøndelag Health Survey, which included 1,940 individuals with known DM. Associations were assessed using multiple logistic regression, estimating prevalence odds ratio (OR) with 95% confidence intervals (CIs).

Results

High non-fasting glucose was associated with a lower prevalence of chronic MSCs compared to a low glucose level. DM was associated with higher prevalence of chronic MSCs, in particular chronic widespread MSCs. In the multivariate analysis, adjusting for glucose level, BMI, age, gender and physical activity, chronic widespread MSCs was 1.6 times more likely (OR = 1.6, 95% CI 1.2–2.2) among individuals < 60 years of age with DM than among those without DM. The association between chronic widespread MSCs and DM was most evident among the group of individuals aged < 60 years with either type 2 DM or unclassified DM (OR = 1.8, 95% CI 1.3–2.5).

Conclusion

In this cross-sectional study a high non-fasting glucose was associated with lower prevalence of chronic MSCs. Among individuals with known DM chronic widespread MSCs were more likely.

Strategies for the diagnosis and treatment of neuropathic pain secondary to diabetic peripheral sensory polyneuropathy

This article proposes a strategy for the diagnosis and treatment of neuropathic pain due to diabetic peripheral sensory neuropathy, based on 15 years of experience in French pain-management centres and on the available literature. In the diabetic patient with chronic pain in the lower limbs, the first step in the diagnostic process is to identify the neuropathic origin of the pain. The second step is to evaluate the patient's medical history and make a rigorous baseline assessment of the neuropathic pain symptoms to determine an effective pain-management strategy. In the third step, adequate and well-tolerated treatment directed towards a variety of painful symptoms is selected, taking into account other co-morbidities such as anxiety and depression. This report reports on the clinical aspects of neuropathic pain exhibited by patients with diabetic sensory polyneuropathy, and the key factors in their diagnosis and treatment, based on the results of meta-analyses and on a recent expert consensus.

[Polyneuropathies in the elderly. Classification and thematic review]

The term polyneuropathy (PNP) is used to describe a group of entities affecting the peripheral nerves, due to external trauma or internal pathology. The prevalence of PNP in the elderly is between 5 and 10%. Despite the multiplicity of causes, the most common etiological factor is diabetes. PNP is characterized by a wide variety of symptoms, due to the multiple functions of nerves. Clinical manifestations range from sensory or motor deficit to inability to maintain gait and stability. Diagnosis is difficult in the elderly, and can be a challenge to the geriatrician in patients with functional impairment. The gold standard for diagnosis is electrophysiology testing. The present article describes the main PNP in the elderly based on the physiopathology of these diseases and provides a practical proposal for clinical classification.

Ranirestat: A Selective Aldose Reductase Inhibitor for Diabetic Sensorimotor Polyneuropathy

Objective:

To review the pharmacology, pharmacokinetics, clinical efficacy, and safety of ranirestat, an oral aldose reductase inhibitor with a unique chemical structure, as treatment of diabetic sensorimotor polyneuropathy in patients with diabetes mellitus.

Data Sources:

Primary literature and review articles were identified by searching MEDLINE (1950–June 2008), EMBASE (1991–June 2008), International Pharmaceutical Abstracts (1970–June 2008), and Google Scholar using the key terms ranirestat, AS-3201, SX-3030, aldose reductase inhibitors, diabetes mellitus, and peripheral neuropathy. Additional articles were identified from the bibliographies of the obtained literature.

Study Selection and Data Extraction:

Reviewed literature was restricted to available English-language articles. Preclinical and clinical trials were reviewed. One Phase 2 clinical trial and its extension study were identified. No data have yet been reported from Phase 3 trials that were conducted between 2004 and 2006.

Data Synthesis:

Ranirestat is a selective and reversible inhibitor of aldose reductase. Nerve damage is reduced by inhibiting this key enzyme in the polyol pathway, thus preventing the accumulation of sorbitol and fructose. Ranirestat has been compared with placebo in randomized, double-blind, controlled trials. Improvement in nerve function, sensation, and clinical grading scale were noted. Ranirestat was reported to be well tolerated.

Conclusions:

Ranirestat may offer a clinical advantage over current treatment modalities as the first agent to address one factor in the underlying cause of diabetic sensorimotor polyneuropathy. Further studies should be done on safety, efficacy, tolerability, and quality of life to determine how successful this agent will be in the treatment of diabetic sensorimotor polyneuropathy.

ACPE Universal Program Numbers:

407-000-08-056-H01-P (Pharmacists); 407-000-08-056-H01-T (Technicians)

Diabetic neuropathy: mechanisms to management

Neuropathy is the most common and debilitating complication of diabetes and results in pain, decreased motility, and amputation. Diabetic neuropathy encompasses a variety of forms whose impact ranges from discomfort to death. Hyperglycemia induces oxidative stress in diabetic neurons and results in activation of multiple biochemical pathways. These activated pathways are a major source of damage and are potential therapeutic targets in diabetic neuropathy. Though therapies are available to alleviate the symptoms of diabetic neuropathy, few options are available to eliminate the root causes. The immense physical, psychological, and economic cost of diabetic neuropathy underscore the need for causally targeted therapies. This review covers the pathology, epidemiology, biochemical pathways, and prevention of diabetic neuropathy, as well as discusses current symptomatic and causal therapies and novel approaches to identify therapeutic targets.

Early lipoic acid intake protects retina of diabetic mice

The aim of this study was to test the effect of lipoic acid treatment on the retina after a short diabetic insult. Diabetes was induced by alloxan and mice were divided into sub-groups; control, diabetic, diabetic+insulin and all groups received+/-lipoic acid (100 mg/kg body weight) for 3 weeks. GSH content, MDA concentration, GPx activity were measured and electroretinograms (ERG) were recorded. Early administration of lipoic acid to diabetic mice prevented the statistically significant decreases of GSH content and GPx activity and normalized MDA concentration. Moreover, lipoic acid restored electroretinogram b-wave amplitude of diabetic animals to control values. Lipoic acid has a protective effect on the diabetic retina.

The RAGE pathway: activation and perpetuation in the pathogenesis of diabetic neuropathy

The molecular mechanisms underlying loss of pain perception in diabetic neuropathy are poorly understood. Experimental diabetic neuropathy models recently provided evidence that engagement of the receptor for advanced glycation end products (RAGE) and RAGE-dependent sustained activation of the proinflammatory transcription factor nuclear factor kappa B might significantly contribute to reduced nociception. Most importantly, diabetes-induced loss of pain perception is largely prevented in RAGE-deficient mice compared to RAGE-bearing wild-type mice. Identifying RAGE-dependent inflammation as one pathomechanism underlying neuronal dysfunction might provide the basis for new therapeutic approaches.

Effect of C-peptide on diabetic neuropathy in patients with type 1 diabetes

Recent results indicate that proinsulin C-peptide, contrary to previous views, exerts important physiological effects and shows the characteristics of a bioactive peptide. Studies in type 1 diabetes, involving animal models as well as patients, demonstrate that C-peptide in replacement doses has the ability to improve peripheral nerve function and prevent or reverse the development of nerve structural abnormalities. Peripheral nerve function, as evaluated by determination of sensory nerve conduction velocity and quantitative sensory testing, is improved by C-peptide replacement in diabetes type 1 patients with early stage neuropathy. Similarly, autonomic nerve dysfunction is ameliorated following administration of C peptide for up to 3 months. As evaluated in animal models of type 1 diabetes, the improved nerve function is accompanied by reversal or prevention of nerve structural changes, and the mechanisms of action are related to the ability of C-peptide to correct diabetes-induced reductions in endoneurial blood flow and in Na⁺ K⁺-ATPase activity and modulation of neurotrophic factors. Combining the results demonstrates that C-peptide may be a possible new treatment of neuropathy in type 1 diabetes.

Treatment of painful neuropathy

PURPOSE OF REVIEW

With the aging of the population, treatment of painful neuropathies is becoming more and more important for neurological practice. This short review highlights recent findings and current problems.

RECENT FINDINGS

In addition to tricyclic antidepressants and gabapentin, the reliability of which is established, some drugs have more recently been demonstrated to be efficacious: major and minor opioids, pregabalin, and serotonin-noradrenaline-reuptake inhibitors. In contrast, some other drugs have yielded disappointing results: memantine, mexiletine, topiramate, and - very recently - lamotrigine. Three main questions are currently being debated. Notwithstanding their proven efficacy, should opioids be used in chronic noncancer pain? In which patients should serotonin-noradrenaline-reuptake inhibitors be preferred to tricyclic antidepressants? What is the difference between pregabalin and gabapentin? The whole field suffers from important limitations that make evidence-based medical data hard to translate in clinical practice: most clinical trials were and still are focused on two conditions only (diabetic neuropathy and postherpetic neuralgia) and studies on polytherapy are insufficient.

SUMMARY

A large variety of drugs are being tried in the treatment of painful neuropathy. Neurologists now have a wide choice. Recent publications can help in choosing the best treatment course.

Aldose reductase inhibitors for the treatment of diabetic polyneuropathy

BACKGROUND

Polyneuropathy, a common complication of diabetes mellitus, causes pain and sensory and motor deficits in the limbs, and is also an important independent predictor of foot ulceration. Inhibiting the metabolism of glucose by the polyol pathway using aldose reductase inhibitors is a potential mechanism to slow or reverse the neuropathy's progression.

OBJECTIVES

To assess the effects of aldose reductase inhibitors on the progression of symptoms, signs or functional disability in diabetic polyneuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Trials Register, MEDLINE (from January 1966 to May 2007), EMBASE (from January 1980 to May 2007) and LILACS (from 1982 to May 2007). We reviewed bibliographies of randomized trials identified, and contacted authors and experts in the field.

SELECTION CRITERIA

We included randomized controlled trials comparing an aldose reductase inhibitor with control, and lasting at least six months. The primary outcome measure was change in neurological function, measured in various ways, including strength testing, sensory examination, and composite scores of neurological examination. Secondary outcome measures were nerve conduction studies, neuropathic symptoms, quality of life, occurrence of foot ulcers and adverse effects.

DATA COLLECTION AND ANALYSIS

Trials included in the review were selected and assessed independently by at least two of us. Methodological criteria and study results were recorded on data extraction forms.

MAIN RESULTS

Thirty-two randomized controlled trials meeting the inclusion criteria were identified. Many had significant methodological flaws. Change in neurological function, our primary outcome measure, was assessed in 29 trials, but sufficient data for meta-analysis were only available in 13 studies, involving 879 treated participants and 909 controls. There was no overall significant difference between the treated and control groups (SMD -0.25, 95% CI -0.56 to 0.05), although one subgroup analysis (four trials using tolrestat) favored treatment. A benefit for neuropathic symptoms was suggested by a group of trials using a dichotomized endpoint (improvement or not), but this was contradicted by another group of trials which measured symptoms on a continuous scale. There was no overall benefit on nerve conduction parameters (27 studies) or foot ulceration (one study). Quality of life was not assessed in any of the studies. While most adverse events were infrequent and minor, three compounds had dose limiting adverse events that lead to their withdrawal from human use: severe hypersensitivity reactions with sorbinil, elevation of creatinine with zenarestat, and alteration of liver function with tolrestat.

AUTHORS' CONCLUSIONS

We found no statistically significant difference between aldose reductase inhibitors and placebo in the treatment of diabetic polyneuropathy. Any future clinical trials of aldose reductase inhibitors should be restricted to compounds proven to have substantial biological or preclinical advantages over previously tested agents.

Headache prevalence related to diabetes mellitus. The Head-HUNT Study

In patients with diabetes mellitus (DM), there are changes in vascular reactivity and nerve conduction that may be relevant for migraine pathophysiology. However, previous studies on the relationship between headache and DM have shown conflicting results. The aim of the present study was to investigate a possible association between headache and DM in a large population-based cross-sectional study. Associations were assessed in multivariate analyses, estimating prevalence odds ratios (ORs) with 95% confidence intervals (CIs). Prevalence OR of migraine was lower amongst persons with DM compared with those without DM, the OR being 0.4 (95% CI: 0.2-0.9) for type 1 and 0.7 (95% CI: 0.5-0.9) for type 2 DM. Furthermore, OR of headache were lower amongst those with duration of DM > or = 13 years compared with those who had got DM the last 3 years, OR 0.6 (95% CI: 0.4-0.9). The analyses revealed no clear associations between non-migrainous headache and DM. The reason for the inverse relationship between migraine and DM is unknown, but might be related to pathophysiological abnormalities in patients with DM that protect against migraine.