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Query: UMLS:C0030193 (pain)
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Rats developed tactile allodynia within days of the onset of diabetes and which persisted for up to 8 weeks. Allodynia was prevented by insulin therapy that maintained normoglycemia while established allodynia was reversed by insulin therapy and normoglycemia of days but not hours duration. Tactile allodynia persisted in diabetic rats that received enough insulin to maintain normal body and foot weights but remained hyperglycemic, whereas this therapy was sufficient to correct other nerve disorders in diabetic rats, including deficits of sensory and motor nerve conduction velocity, nerve blood flow and hyperalgesia during the formalin test. Treating diabetic rats with the aldose reductase inhibitor ICI 222155 did not prevent tactile allodynia. Tactile allodynia was of similar magnitude in diabetic rats and nerve injured control rats and diabetes did not alter the magnitude or time course of nerve injury-induced allodynia. Systemic lidocaine treatment alleviated tactile allodynia in nerve injured control rats and both sham-operated and nerve injured diabetic rats. The streptozotocin-diabetic rat develops tactile allodynia that appears to be related to prolonged periods of insulin deficiency or hyperglycemia and which is amenable to treatment with lidocaine. The model may be of use in investigating the efficacy of other potential therapeutic agents for treating painful diabetic neuropathy.
Pain 1996 Dec
PMID:Tactile allodynia and formalin hyperalgesia in streptozotocin-diabetic rats: effects of insulin, aldose reductase inhibition and lidocaine. 912 17

Diabetic polyneuropathy is the most frequent neuropathy in western countries. In Germany, there are 3.5 to 4 million diabetic patients. Diagnosis should rule out other polyneuropathies and assess two out of the five diagnostic criteria: neuropathic symptoms, neuropathic deficits, pathological nerve conduction studies, pathological quantitative sensory testing and pathological quantitative autonomic testing. So far, the pathophysiology of diabetic neuropathy remains to be fully understood. Among the various pathophysiological concepts are the Sorbitol-Myo-Inositol hypothesis attributing Myo-Inositol depletion to the accumulation of Sorbitol and Fructose, the concept of deficiency of essential fatty acids with reduced availability of gamma-linolenic-acid and prostanoids, the pseudohypoxia- and hypoxia-hypothesis attributing endothelial and axonal dysfunction and structural lesions to increased oxidative stress and free radical production. Obviously, the hyperglycemia induced generation of advanced glycation end products (AGEs) also contributes to structural dysfunctions and lesions. Elevated levels of circulating immune complexes and activated T-lymphocytes as well the identification of autoantibodies against vagus nerve or sympathetic ganglia support the concept of an immune mediated neuropathy. The reduction of neurotrophic factors such as nerve growth factor, neurotrophin-3 or insulin-like growth factors also seems to further diabetic neuropathy. The symmetrical, distally pronounced and predominantly sensory neuropathy is far more frequent than the symmetrical neuropathy with predominant motor weakness or the asymmetrical neuropathy. The painless neuropathy manifests with impaired light touch sensation, position sense, vibratory perception and diminished or absent ankle deep tendon reflexes. The painful sensory diabetic neuropathy primarily affects small nerve fibers and accounts for decreased temperature perception and paresthesias. The proximal, diabetic amyotrophy evolves subacutely or acutely, induces motor weakness of the proximal thigh and buttock muscles and is painful. Cranial nerve III-neuropathy is also painful and has an acute onset. Truncal radiculopathy follows the distribution of truncal roots and frequently causes intense pain. Autonomic neuropathy occurs with and without somatic neuropathy. The most important therapy is to attempt optimal blood glucose control, to reduce body weight and hyperlipidemia. Symptomatic therapy includes alpha-lipoic acid treatment, as the antioxidant seems to improve neuropathic symptoms. Aldose reductase inhibitors might reduce sorbitol and fructose production and normalize myo-inositol levels. However, there are no aldose reductase inhibitors available in Europe as yet. Evening primrose oil, containing gamma-linolenic acid, might improve nerve conduction velocities, temperature perception, muscle strength, tendon reflexes and sensory function. Substitution of nerve growth factor showed promising results in pilot studies but failed in a large-scale multicenter study. Symptomatic pain treatment can be achieved with tricyclic antidepressants, selective serotonin reuptake inhibitors, anticonvulsants such as carbamazepine, gabapentin or lamotrigine, or anti-arrhythmic drugs such as mexiletine. Topical capsaicin application should reduce neuropathic pain but also induces local discomfort in the beginning of therapy. Vasoactive substances, so far have not proven to be of major benefit in diabetic neuropathy. Physical therapy and thorough footcare are of primary importance and allow prevention of secondary complications such as foot amputations.
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PMID:[Diabetic somatic polyneuropathy. Pathogenesis, clinical manifestations and therapeutic concepts]. 1092 53

We previously reported that OT-7100 (5-n-butyl-7-(3,4,5-trimethoxybenzoylamino)pyrazolo[1,5-alpha]pyrimidine) had antinociceptive potency in various animal models. To further characterize this compound, the present study examined the effects of OT-7100 on mechanical hyperalgesia and motor nerve conduction velocity in streptozotocin-induced diabetic rats. OT-7100 significantly increased the nociceptive threshold in the diabetic rat in a dose-dependent manner. Gabapentin (anticonvulsant agent) and insulin strongly increased the nociceptive threshold but gabapentin increased it above normal levels. An aldose reductase inhibitor slightly increased the nociceptive threshold at a high dose. We also measured glucose levels and motor nerve conduction velocity in OT-7100-treated rats. Insulin decreased glucose levels but OT-7100 had no effect on glucose levels or on motor nerve conduction velocity. These results suggest that OT-7100 alleviates hyperalgesia in a diabetic neuropathy model in a different manner from gabapentin or aldose reductase inhibitor and may be a new treatment for the pain associated with peripheral nerve injury.
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PMID:Antinociceptive effect of the novel compound OT-7100 in a diabetic neuropathy model. 1171 Oct 35

Diabetic neuropathy is the most common peripheral neuropathy in western countries. Although every effort has been made to clarify the pathogenic mechanism of diabetic neuropathy, thereby devising its ideal therapeutic drugs, neither convinced hypotheses nor unequivocally effective drugs have been established. In view of the pathologic basis for the treatment of diabetic neuropathy, it is important to enhance nerve regeneration as well as prevent nerve degeneration. Nerve regeneration or sprouting in diabetes may occur not only in the nerve trunk but also in the dermis and around dorsal root ganglion neurons, thereby being implicated in the generation of pain sensation. Thus, inadequate nerve regeneration unequivocally contributes to the pathophysiologic mechanism of diabetic neuropathy. In this context, the research on nerve regeneration in diabetes should be more accelerated. Indeed, nerve regenerative capacity has been shown to be decreased in diabetic patients as well as in diabetic animals. Disturbed nerve regeneration in diabetes has been ascribed at least in part to all or some of decreased levels of neurotrophic factors, decreased expression of their receptors, altered cellular signal pathways and/or abnormal expression of cell adhesion molecules, although the mechanisms of their changes remain almost unclear. In addition to their steady-state changes in diabetes, nerve injury induces injury-specific changes in individual neurotrophic factors, their receptors and their intracellular signal pathways, which are closely linked with altered neuronal function, varying from neuronal survival and neurite extension/nerve regeneration to apoptosis. Although it is essential to clarify those changes for understanding the mechanism of disturbed nerve regeneration in diabetes, very few data are now available. Rationally accepted replacement therapy with neurotrophic factors has not provided any success in treating diabetic neuropathy. Aside from adverse effects of those factors, more rigorous consideration for their delivery system may be needed for any possible success. Although conventional therapeutic drugs like aldose reductase (AR) inhibitors and vasodilators have been shown to enhance nerve regeneration, their efficacy should be strictly evaluated with respect to nerve regenerative capacity. For this purpose, especially clinically, skin biopsy, by which cutaneous nerve pathology including nerve regeneration can be morphometrically evaluated, might be a safe and useful examination.
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PMID:Diabetic neuropathy and nerve regeneration. 1275 48

Painful diabetic neuropathy is a common distressing and challenging condition. The mechanism or mechanisms involved in its pathogenesis continue to elude clinical scientists. As with other conditions of painful distal symmetrical neuropathic conditions, pain relief involves the use of a variety of analgesic and neuroleptic drugs, aimed at reducing either central responses to painful stimuli or at dampening spontaneous irritability of affected neurons. More recently, several therapies directed at putative pathologic mechanisms specific to painful diabetic neuropathy have evolved. These include vasodilators, protein kinase C beta inhibition, antioxidants, and novel aldose reductase inhibitors. Preliminary clinical studies of these therapies have at present involved small numbers of patients; however, the results have been encouraging. This article considers the clinical aspects of diagnosis and management of chronic painful diabetic neuropathy, focusing on existing and newer therapies.
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PMID:New treatments for diabetic neuropathy: symptomatic treatments. 1461 41

We explored the specific impact of polyol pathway hyperactivity on dorsal root ganglia (DRG) using transgenic mice that overexpress human aldose reductase because DRG changes are crucial for the development of diabetic sensory neuropathy. Littermate mice served as controls. Half of the animals were made diabetic by streptozotocin injection and followed for 12 weeks. After diabetes onset, diabetic transgenic mice showed a significant elevation of pain sensation threshold after transient decrease and marked slowing of motor and sensory nerve conduction at the end of the study, while these changes were modest in diabetic littermate mice. Protein kinase C (PKC) activities were markedly reduced in diabetic transgenic mice, and the changes were associated with reduced expression of membrane PKC-alpha isoform that was translocated to cytosol. Membrane PKC-betaII isoform expression was contrariwise increased. Calcitonin gene-related peptide-and substance P-positive neurons were reduced in diabetic transgenic mice and less severely so in diabetic littermate mice. Morphometric analysis disclosed neuronal atrophy only in diabetic transgenic mice. Treatment with an aldose reductase inhibitor (fidarestat 4 mg x kg(-1) x day(-1), orally) corrected all of the changes detected in diabetic transgenic mice. These findings underscore the pathogenic role of aldose reductase in diabetic sensory neuropathy through the altered cellular signaling and peptide expressions in DRG neurons.
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PMID:Effects of polyol pathway hyperactivity on protein kinase C activity, nociceptive peptide expression, and neuronal structure in dorsal root ganglia in diabetic mice. 1556 56

Diabetic neuropathy is common, related to increased morbidity and mortality, and has no effective treatment at present. Interventions based on putative pathways thought to contribute to damage and repair of nerve fibres have yielded little success to date. Pain is a potentially debilitating manifestation of diabetic neuropathy and has many potential sites of origin and, hence, modulation. Its cause is unclear and it does not respond well to traditional pain therapies, proposed to mediate their benefits via multiple peripheral and central mechanisms. A better understanding of the mechanisms leading to nerve fibre degeneration and regeneration as well as pain has recently resulted in the development of a more targeted approach to the treatment of diabetic neuropathy. Thus, specific NMDA receptor antagonists and more specific neuronal serotonin and norepinephrine (noradrenaline) uptake inhibitors offer promise in the treatment of painful diabetic neuropathy. A number of treatments which include the aldose reductase inhibitors and neurotrophins have failed to reach the clinical arena. However, the antioxidant alpha-lipoic acid, as well as compounds which correct vascular dysfunction and hence neuropathy, such as ACE inhibitors and protein kinase C-beta inhibitors, have demonstrated more success.
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PMID:Current and future strategies for the management of diabetic neuropathy. 1598 43

A large number of neuroanatomical, neurophysiologic, and neurochemical mechanisms are thought to contribute to the development and maintenance of neuropathic pain (NP). As a result, a corresponding wide range of treatments have been employed to treat patients with NP, including antiepileptic drugs, opioid analgesics, tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, N-methyl-D-aspartate receptor antagonists, cholecystokinin receptor antagonists, adenosine, lipoic acid, cannabinoids, isosorbide dinitrate, dronabinol, capsaicin, protein kinase C inhibitors, aldose reductase inhibitors, and VR-1 receptor modulators. Many of these compounds are limited by marginal efficacy and clinically significant adverse events; few have been evaluated in well-controlled, large-scale clinical trials. At present, the only agents approved for the treatment of painful diabetic peripheral neuropathy and postherpetic neuralgia are lidocaine patches 5%, duloxetine, gabapentin, and pregabalin. Of these, only pregabalin is indicated for both conditions.
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PMID:New and emerging treatment options for neuropathic pain. 1677 59

Diabetic painful neuropathy (DPN) is one of the most common causes of neuropathic pain. The management of DPN consists of excluding other causes of painful peripheral neuropathy, maximising diabetic control and using medications to alleviate pain. The precise relationship between glycaemic control and the development and severity of DPN remains controversial. In this context, drugs such as aldose reductase inhibitors, ACE inhibitors, lipid-lowering agents and alpha-lipoic acid (thioctic acid) may have a useful role to play. There is also evidence that a successful pancreatic transplant may improve symptoms over time, but the mainstay of management continues to be symptomatic control of pain with drugs. Evidence from placebo-controlled studies has shown that opioids, antiepileptic and antidepressant drugs together with capsaicin are effective for alleviating DPN. Tramadol and oxycodone have been shown to be effective in studies of limited duration but their adverse effects, such as constipation and physical dependency, may limit their usefulness as a first-line treatment for DPN. Of the antidepressant drugs, the tricyclic antidepressants have been shown to be effective for alleviating DPN. These medications are widely used but their anticholinergic and sedative properties may not be well tolerated by patients. There is also good evidence that the serotonin-noradrenaline reuptake inhibitor antidepressant drugs venlafaxine and duloxetine are effective for treating DPN. However, venlafaxine may cause cardiac dysrhythmias, and patients using this medication require careful cardiac monitoring. Duloxetine appears to be less cardiotoxic and is licensed in the US and EU for alleviating DPN. The gabapentinoid group of drugs, gabapentin and pregabalin, appear to be the most evidence-based of the antiepileptic drugs for treating DPN. Large placebo-controlled studies have been performed with both of these agents. For many patients, it is still unclear what advantages pregabalin has over gabapentin for DPN. Until better evidence emerges, the potential availability of less expensive generic formulations of gabapentin, together with greater experience with its use, favour gabapentin as the main antiepileptic drug for alleviating DPN. Topiramate, lamotrigine, sodium valproate and oxcarbazepine have been shown to be effective in smaller studies but do not have the same evidence base as the gabapentinoid group of drugs. Of the newer antiepileptic drugs, lacosamide appears to be the most promising for alleviating DPN. Capsaicin has the best evidence base of all the topical agents, but local anaesthetic patches may also have a useful therapeutic role. It is not possible to nominate a single drug as the first-line treatment for DPN and there is evidence that a low-dose combination of two or more drugs rather than a single agent may provide better symptomatic relief with fewer adverse effects. Further studies are necessary to clarify the best combination(s) of treatment for DPN.
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PMID:Diabetic painful neuropathy: current and future treatment options. 1735 15

Diabetic peripheral neuropathy is the most common complication of long-standing diabetes mellitus which frequently results in clinically significant morbidities e.g. pain, foot ulcers and amputations. During its natural course it progresses from initial functional changes to late, poorly reversible, structural changes. Various interconnected pathogenetic concepts of diabetic neuropathy have been proposed based on metabolic and vascular factors, mostly derived from long-term hyperglycemia. These pathogenetic mechanisms have been targeted in several experimental and clinical trials. This review summarizes available, mainly morphological data from interventions designed to halt the progression or achieve the reversal of established diabetic neuropathy, which include the recovery of normoglycemia by pancreas or islet transplantation, polyol pathway blockade by aldose reductase inhibitors, mitigation of oxidative stress by the use of antioxidants or correction of abnormalities in essential fatty acid metabolism. Unfortunately, to date, no treatment based on pathogenic considerations has shown clear positive effects and thus early institution of optimal glycemic control remains the only available measure with proven efficacy in preventing or halting progression of diabetic neuropathy. Further experimental and clinical research employing objective reproducible parameters is clearly needed. Novel non-invasive or minimally invasive methods e.g. corneal confocal microscopy or epidermal nerve fiber counts may represent potentially useful instruments for the objective assessment of nerve damage and monitoring of treatment effects.
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PMID:Advanced Diabetic Neuropathy: A Point of no Return? 1748 38


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