Interleukin-6 attenuates the development of experimental diabetes-related neuropathy

Update on Biomarkers of Chronic Inflammatory Processes Underlying Diabetic Neuropathy

There is an increasing prevalence of diabetes mellitus (DM), particularly type 2 DM (T2DM), and its associated complications. T2DM is linked to insulin resistance, chronic inflammation, and oxidative stress, which can lead to both macrovascular and microvascular complications, including peripheral diabetic neuropathy (PDN). Inflammatory processes play a key role in the development and progression of T2DM and its complications, with specific markers like C-reactive protein (CRP), interleukins (ILs), and tumor necrosis factor (TNF)-α being associated with increased risk. Other key inflammatory markers such as nuclear factor kappa B (NF-κB) are activated under hyperglycemic and oxidative stress conditions and contribute to the aggravation of PDN by regulating inflammatory gene expression and enhancing endothelial dysfunction. Other important roles in the inflammatory processes are played by Toll-like receptors (TLRs), caveolin 1 (CAV1), and monocyte chemoattractant protein 1 (MCP1). There is a relationship between vitamin D deficiency and PDN, highlighting the critical role of vitamin D in regulating inflammation and immune responses. The involvement of macrophages in PDN is also suspected, emphasizing their role in chronic inflammation and nerve damage in diabetic patients. Vitamin D supplementation has been found to reduce neuropathy severity, decrease inflammatory markers, and improve glycemic control. These findings suggest that addressing vitamin D deficiency could offer therapeutic benefits for PDN. These molecular pathways are critical in understanding the pathogenesis of DM complications and may offer potential biomarkers or therapeutic targets including anti-inflammatory treatments, vitamin D supplementation, macrophage phenotype modulation, and lifestyle modifications, aimed at reducing inflammation and preventing PDN. Ongoing and more extensive clinical trials with the aim of investigating anti-inflammatory agents, TNF-α inhibitors, and antioxidants are needed to advance deeper into the understanding and treatment of painful diabetic neuropathy.

Neuroprotective Effects of Sodium-Glucose Cotransporter-2 (SGLT2) Inhibitors (Gliflozins) on Diabetes-Induced Neurodegeneration and Neurotoxicity: A Graphical Review

Diabetes is a chronic endocrine disorder that negatively affects various body systems, including the nervous system. Diabetes can cause or exacerbate various neurological disorders, and diabetes-induced neurodegeneration can involve several mechanisms such as mitochondrial dysfunction, activation of oxidative stress, neuronal inflammation, and cell death. In recent years, the management of diabetes-induced neurodegeneration has relied on several types of drugs, including sodium-glucose cotransporter-2 (SGLT2) inhibitors, also called gliflozins. In addition to exerting powerful effects in reducing blood glucose, gliflozins have strong anti-neuro-inflammatory characteristics that function by inhibiting oxidative stress and cell death in the nervous system in diabetic subjects. This review presents the molecular pathways involved in diabetes-induced neurodegeneration and evaluates the clinical and laboratory studies investigating the neuroprotective effects of gliflozins against diabetes-induced neurodegeneration, with discussion about the contributing roles of diverse molecular pathways, such as mitochondrial dysfunction, oxidative stress, neuro-inflammation, and cell death. Several databases-including Web of Science, Scopus, PubMed, Google Scholar, and various publishers, such as Springer, Wiley, and Elsevier-were searched for keywords regarding the neuroprotective effects of gliflozins against diabetes-triggered neurodegenerative events. Additionally, anti-neuro-inflammatory, anti-oxidative stress, and anti-cell death keywords were applied to evaluate potential neuronal protection mechanisms of gliflozins in diabetes subjects. The search period considered valid peer-reviewed studies published from January 2000 to July 2023. The current body of literature suggests that gliflozins can exert neuroprotective effects against diabetes-induced neurodegenerative events and neuronal dysfunction, and these effects are mediated via activation of mitochondrial function and prevention of cell death processes, oxidative stress, and inflammation in neurons affected by diabetes. Gliflozins can confer neuroprotective properties in diabetes-triggered neurodegeneration, and these effects are mediated by inhibiting oxidative stress, inflammation, and cell death.

Is metformin neuroprotective against diabetes mellitus-induced neurodegeneration? An updated graphical review of molecular basis

Diabetes mellitus (DM) is a metabolic disease that activates several molecular pathways involved in neurodegenerative disorders. Metformin, an anti-hyperglycemic drug used for treating DM, has the potential to exert a significant neuroprotective role against the detrimental effects of DM. This review discusses recent clinical and laboratory studies investigating the neuroprotective properties of metformin against DM-induced neurodegeneration and the roles of various molecular pathways, including mitochondrial dysfunction, oxidative stress, inflammation, apoptosis, and its related cascades. A literature search was conducted from January 2000 to December 2022 using multiple databases including Web of Science, Wiley, Springer, PubMed, Elsevier Science Direct, Google Scholar, the Core Collection, Scopus, and the Cochrane Library to collect and evaluate peer-reviewed literature regarding the neuroprotective role of metformin against DM-induced neurodegenerative events. The literature search supports the conclusion that metformin is neuroprotective against DM-induced neuronal cell degeneration in both peripheral and central nervous systems, and this effect is likely mediated via modulation of oxidative stress, inflammation, and cell death pathways.

Potential Roles of Anti-Inflammatory Plant-Derived Bioactive Compounds Targeting Inflammation in Microvascular Complications of Diabetes

Diabetes mellitus (DM) is a group of metabolic disorders, the characteristics of which include chronic hyperglycemia owing to defects in insulin function, insulin secretion, or both. Inflammation plays a crucial role in DM pathogenesis and innate immunity in the development of microvascular complications of diabetes. In addition, hyperglycemia and DM mediate a proinflammatory microenvironment that can result in various microvascular complications, including diabetic nephropathy (DNP), diabetic neuropathy (DN), and diabetic retinopathy (DR). DNP is a major cause of end-stage renal disease. DNP can lead to albuminuria, decreased filtration, mesangium expansion, thickening of the basement membrane, and eventually renal failure. Furthermore, inflammatory cells can accumulate in the interstitium and glomeruli to deteriorate DNP. DN is another most prevalent microvascular complication of DM and the main cause of high mortality, disability, and a poor quality of life. DNs have a wide range of clinical manifestations because of the types of fiber dysfunctions and complex structures of the peripheral nervous system. DR is also a microvascular and multifactorial disease, as well as a major cause of visual impairment globally. Pathogenesis of DR is yet to be fully revealed, however, numerous studies have already confirmed the role of inflammation in the onset and advancement of DR. Despite evidence, and better knowledge regarding the pathogenesis of these microvascular complications of diabetes, there is still a deficiency of effective therapies. Bioactive compounds are mainly derived from plants, and these molecules have promising therapeutic potential. In this review, evidence and molecular mechanisms regarding the role of inflammation in various microvascular complications of diabetes including DNP, DN, and DR, have been summarized. The therapeutic potential of several bioactive compounds derived from plants in the treatment of these microvascular complications of diabetes has also been discussed.

Polyphenols target miRNAs as a therapeutic strategy for diabetic complications

MiRNAs are a large group of non-coding RNAs which participate in different cellular pathways like inflammation and oxidation through transcriptional, post-transcriptional, and epigenetic regulation. In the post-transcriptional regulation, miRNA interacts with the 3'-UTR of mRNAs and prevents their translation. This prevention or dysregulation can be a cause of pathological conditions like diabetic complications. A huge number of studies have revealed the association between miRNAs and diabetic complications, including diabetic nephropathy, cardiomyopathy, neuropathy, retinopathy, and delayed wound healing. To address this issue, recent studies have focused on the use of polyphenols as selective and safe drugs in the treatment of diabetes complications. In this article, we will review the involvement of miRNAs in diabetic complications' occurrence or development. Finally, we will review the latest findings on targeting miRNAs by polyphenols like curcumin, resveratrol, and quercetin for diabetic complications therapy.

Changes in phrenic nerve compound muscle action potential in streptozotocin-induced diabetic rats

PURPOSE

To evaluate the phrenic nerve compound muscle action potential (CMAP) in rats after diabetes mellitus (DM) induction.

METHODS

Twenty DM animals (intravenous streptozotocin, 45 mg.kg^-1) and 25 controls underwent CMAP analysis before and 30, 60 and 90 days after DM induction.

RESULTS

Amplitude (mV) progressively declined in DM group after 30 (Mean difference (MD): -0.915, 95 % Confidence interval (CI) -1.580 to -0.250, p < 0.01), 60 (MD: -1.122, 95 % CI -1.664 to -0.581, p < 0.001) and 90 days (MD: -2.226, 95 % CI -3.059 to -1.393, p < 0.001); as well as the area (mV.ms) after 30 (MD: -3.19, 95 % CI -5.94 to -0.44, p < 0.05), 60 (MD: -3.94, 95 % CI -6.24 to -1.64, p < 0.001) and 90 days (MD: -8.64, 95 % CI -12.08 to -5.21, p < 0.001). Transient differences were observed in latency and duration at 60 days.

CONCLUSIONS

The progressive changes in phrenic nerve CMAP observed during DM suggest a decrement in axonal function rather than substantial demyelination.

Interleukin-6 potentiates endurance training adaptation and improves functional capacity in old mice

BACKGROUND

Interventions to preserve functional capacities at advanced age are becoming increasingly important. So far, exercise provides the only means to counteract age-related decrements in physical performance and muscle function. Unfortunately, the effectiveness of exercise interventions in elderly populations is hampered by reduced acceptance and compliance as well as disuse complications. We therefore studied whether application of interleukin-6 (IL-6), a pleiotropic myokine that is induced by skeletal muscle activity and exerts broad systemic effects in response to exercise, affects physical performance and muscle function alone or in combination with training in aged mice.

METHODS

Sedentary old male mice (Sed+Saline, n = 15) were compared with animals that received recombinant IL-6 (rIL-6) in an exercise-mimicking pulsatile manner (Sed+IL-6, n = 16), were trained with a moderate-intensity, low-volume endurance exercise regimen (Ex+Saline, n = 13), or were exposed to a combination of these two interventions (Ex+IL-6, n = 16) for 12 weeks. Before and at the end of the intervention, mice underwent a battery of tests to quantify endurance performance, muscle contractility in situ, motor coordination, and gait and metabolic parameters.

RESULTS

Mice exposed to enhanced levels of IL-6 during endurance exercise bouts showed superior improvements in endurance performance (33% more work and 12% greater peak power compared with baseline), fatigue resistance in situ (P = 0.0014 vs. Sed+Saline; P = 0.0199 vs. Sed+IL-6; and P = 0.0342 vs. Ex+Saline), motor coordination (rotarod performance, P = 0.0428), and gait (gait speed, P = 0.0053) following training. Pulsatile rIL-6 treatment in sedentary mice had only marginal effects on glucose tolerance and some gait parameters. No increase in adverse events or mortality related to rIL-6 treatment was observed.

CONCLUSIONS

Administration of rIL-6 paired with treadmill running bouts potentiates the adaptive response to a moderate-intensity low-volume endurance exercise regimen in old mice, while being safe and well tolerated.

Advances About Immunoinflammatory Pathogenesis and Treatment in Diabetic Peripheral Neuropathy

Most diabetic patients develop diabetic peripheral neuropathy (DPN). DPN is related to the increase of inflammatory cells in peripheral nerves, abnormal cytokine expression, oxidative stress, ischemia ,and pro-inflammatory changes in bone marrow. We summarized the progress of immune-inflammatory mechanism and treatment of DPN in recent years. Immune inflammatory mechanisms include TNF-α, HSPs, PARP, other inflammatory factors, and the effect of immune cells on DPN. Treatment includes tricyclic antidepressants and other drug therapy, immune and molecular therapy, and non-drug therapy such as exercise therapy, electrotherapy, acupuncture, and moxibustion. The pathogenesis of DPN is complex. In addition to strictly controlling blood glucose, its treatment should also start from other ways, explore more effective and specific treatment schemes for various causes of DPN, and find new targets for treatment will be the direction of developing DPN therapeutic drugs in the future.

Aging and the immune response in diabetic peripheral neuropathy

A large proportion of older individuals with diabetes go on to develop diabetic peripheral neuropathy (DPN). DPN is associated with an increase in inflammatory cells within the peripheral nerve, activation of nuclear factor kappa-light-chain-enhancer of activated B cells and receptors for advanced glycation end products/advanced glycation end products pathways, aberrant cytokine expression, oxidative stress, ischemia, as well as pro-inflammatory changes in the bone marrow; all processes that may be exacerbated with age. We review the immunological features of DPN and discuss whether age-related changes in relevant immunological areas may contribute to age being a risk factor for DPN.

Emerging Roles of microRNAs as Biomarkers and Therapeutic Targets for Diabetic Neuropathy

Diabetic neuropathy (DN) is the most prevalent chronic complication of diabetes mellitus. The exact pathophysiological mechanisms of DN are unclear; however, communication network dysfunction among axons, Schwann cells, and the microvascular endothelium likely play an important role in the development of DN. Mounting evidence suggests that microRNAs (miRNAs) act as messengers that facilitate intercellular communication and may contribute to the pathogenesis of DN. Deregulation of miRNAs is among the initial molecular alterations observed in diabetics. As such, miRNAs hold promise as biomarkers and therapeutic targets. In preclinical studies, miRNA-based treatment of DN has shown evidence of therapeutic potential. But this therapy has been hampered by miRNA instability, targeting specificity, and potential toxicities. Recent findings reveal that when packaged within extracellular vesicles, miRNAs are resistant to degradation, and their delivery efficiency and therapeutic potential is markedly enhanced. Here, we review the latest research progress on the roles of miRNAs as biomarkers and as potential clinical therapeutic targets in DN. We also discuss the promise of exosomal miRNAs as therapeutics and provide recommendations for future research on miRNA-based medicine.

Evolving concepts on the role of dyslipidemia, bioenergetics, and inflammation in the pathogenesis and treatment of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most widespread and disabling neurological conditions, accounting for half of all neuropathy cases worldwide. Despite its high prevalence, no approved disease modifying therapies exist. There is now a growing body of evidence that DPN secondary to type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) represents different disease processes, with T2DM DPN best understood within the context of metabolic syndrome rather than hyperglycemia. In this review, we highlight currently understood mechanisms of DPN, along with their corresponding potential therapeutic targets. We frame this discussion within a practical overview of how the field evolved from initial human observations to murine pathomechanistic and therapeutic models into ongoing and human clinical trials, with particular emphasis on T2DM DPN and metabolic syndrome.

Injury-induced gp130 cytokine signaling in peripheral ganglia is reduced in diabetes mellitus

Neuropathy is a major diabetic complication. While the mechanism of this neuropathy is not well understood, it is believed to result in part from deficient nerve regeneration. Work from our laboratory established that gp130 family of cytokines are induced in animals after axonal injury and are involved in the induction of regeneration-associated genes (RAGs) and in the conditioning lesion response. Here, we examine whether a reduction of cytokine signaling occurs in diabetes. Streptozotocin (STZ) was used to destroy pancreatic β cells, leading to chronic hyperglycemia. Mice were injected with either low doses of STZ (5×60mg/kg) or a single high dose (1×200mg/kg) and examined after three or one month, respectively. Both low and high dose STZ treatment resulted in sustained hyperglycemia and functional deficits associated with the presence of both sensory and autonomic neuropathy. Diabetic mice displayed significantly reduced intraepidermal nerve fiber density and sudomotor function. Furthermore, low and high dose diabetic mice showed significantly reduced tactile touch sensation measured with Von Frey monofilaments. To look at the regenerative and injury-induced responses in diabetic mice, neurons in both superior cervical ganglia (SCG) and the 4th and 5th lumbar dorsal root ganglia (DRG) were unilaterally axotomized. Both high and low dose diabetic mice displayed significantly less axonal regeneration in the sciatic nerve, when measured in vivo, 48h after crush injury. Significantly reduced induction of two gp130 cytokines, leukemia inhibitory factor and interleukin-6, occurred in diabetic animals in SCG 6h after injury compared to controls. Injury-induced expression of interleukin-6 was also found to be significantly reduced in the DRG at 6h after injury in low and high dose diabetic mice. These effects were accompanied by reduced phosphorylation of signal transducer and activator of transcription 3 (STAT3), a downstream effector of the gp130 signaling pathway. We also found decreased induction of several gp130-dependent RAGs, including galanin and vasoactive intestinal peptide. Together, these data suggest a novel mechanism for the decreased response of diabetic sympathetic and sensory neurons to injury.

Neuroprotective effects of chronic administration of levetiracetam in a rat model of diabetic neuropathy

OBJECTIVE

Diabetic neuropathy (DNP) is a frequent and serious complication of diabetes mellitus (DM) that leads to progressive and length-dependent loss of peripheral nerve axons. The purpose of the present study is to assess the neuroprotective effects of levetiracetam (LEV) on DNP in a streptozotocin (STZ)-induced DM model in rats.

METHODS

Adult Sprague-Dawley rats were administered with STZ (60mg/kg) to induce diabetes. DNP was confirmed by electromyography (EMG) and motor function test on 21st day following STZ injection. Study groups were assigned as follows; Group 1: Naïve control (n=8), Group 2: DM+1mL/kg saline (n=12), Group 3: DM+300mg/kg LEV (n=10), Group 4: DM+600mg/kg LEV (n=10). LEV was administered i.p. for 30 consecutive days. Then, EMG, motor function test, biochemical analysis (plasma lipid peroxides and total anti-oxidant capacity), histological and immunohistochemical analysis of sciatic nerves (TUNEL assay, bax, caspase 3, caspase 8 and NGF) were performed to evaluate the efficacy of LEV.

RESULTS

Treatment of diabetic rats with LEV significantly attenuated the inflammation and fibrosis in sciatic nerves and prevented electrophysiological alterations. Immunohistochemistry of sciatic nerves showed a considerable increase in bax, caspase 3 and caspase 8 and a decrease in NGF expression in saline-treated rats whereas LEV significantly suppressed apoptosis markers and prevented the reduction in NGF expression. Besides, LEV considerably reduced plasma lipid peroxides and increased total anti-oxidant capacity in diabetic rats.

CONCLUSIONS

The results of the present study suggest that LEV may have therapeutic effects in DNP through modulation of anti-oxidant and anti-apoptotic pathways.

Inflammation as a Therapeutic Target for Diabetic Neuropathies

Diabetic neuropathies (DNs) are one of the most prevalent chronic complications of diabetes and a major cause of disability, high mortality, and poor quality of life. Given the complex anatomy of the peripheral nervous system and types of fiber dysfunction, DNs have a wide spectrum of clinical manifestations. The treatment of DNs continues to be challenging, likely due to the complex pathogenesis that involves an array of systemic and cellular imbalances in glucose and lipids metabolism. These lead to the activation of various biochemical pathways, including increased oxidative/nitrosative stress, activation of the polyol and protein kinase C pathways, activation of polyADP ribosylation, and activation of genes involved in neuronal damage, cyclooxygenase-2 activation, endothelial dysfunction, altered Na(+)/K(+)-ATPase pump function, impaired C-peptide-related signaling pathways, endoplasmic reticulum stress, and low-grade inflammation. This review summarizes current evidence regarding the role of low-grade inflammation as a potential therapeutic target for DNs.

Interleukin 6 and cognitive dysfunction

The interleukin-6 (IL-6) is a pleiotropic cytokine that plays a key role in interaction between immune and nervous system. Although IL-6 has neurotrophic properties and beneficial effects in the CNS, its overexpression is generally detrimental, adding to the pathophysiology associated with CNS disorders. The source of the increase in peripheral IL-6 remains to be established and varies among different pathologies, but has been found to be associated with cognitive dysfunction in several pathologies. This comprehensive review provides an update summary of the studies performed in humans concerning the role of central and peripheral IL-6 in cognitive dysfunction in dementias and in other systemic diseases accompained by cognitive dysfuction such as cardiovascular, liver disease, Behçet's disease and systemic lupus erythematosus. Further research is needed to correlate specific deficits in IL-6 and its receptors in pathologies characterized by cognitive dysfunction and to understand how systemic IL-6 affects high cerebral function in order to open new directions in pharmacological treatments that modulate IL-6 signalling.

Experimental diabetes in neonatal mice induces early peripheral sensorimotor neuropathy

Animal models of diabetes do not reach the severity of human diabetic neuropathy but relatively mild neurophysiological deficits and minor morphometric changes. The lack of degenerative neuropathy in diabetic rodent models seems to be a consequence of the shorter length of the axons or the shorter animal life span. Diabetes-induced demyelination needs many weeks or even months before it can be evident by morphometrical analysis. In mice myelination of the peripheral nervous system starts at the prenatal period and it is complete several days after birth. Here we induced experimental diabetes to neonatal mice and we evaluated its effect on the peripheral nerve 4 and 8 weeks after diabetes induction. Neurophysiological values showed a decline in sensory nerve conduction velocity at both time-points. Morphometrical analysis of the tibial nerve demonstrated a decrease in the number of myelinated fibers, fiber size and myelin thickness at both time-points studied. Moreover, aldose reductase and poly(ADP-ribose) polymerase activities were increased even if the amount of the enzyme was not affected. Thus, type 1 diabetes in newborn mice induces early peripheral neuropathy and may be a good model to assay pharmacological or gene therapy strategies to treat diabetic neuropathy.

Transplantation of Stem Cells Obtained from Murine Dental Pulp Improves Pancreatic Damage, Renal Function, and Painful Diabetic Neuropathy in Diabetic Type 1 Mouse Model

Diabetes mellitus (DM) is one of the most common and serious chronic diseases in the world. Here, we investigated the effects of mouse dental pulp stem cell (mDPSC) transplantation in a streptozotocin (STZ)-induced diabetes type 1 model. C57BL/6 mice were treated intraperitoneally with 80 mg/kg of STZ and transplanted with 1 × 106 mDPSCs or injected with saline, by an endovenous route, after diabetes onset. Blood and urine glucose levels were reduced in hyperglycemic mice treated with mDPSCs when compared to saline-treated controls. This correlated with an increase in pancreatic islets and insulin production 30 days after mDPSC therapy. Moreover, urea and proteinuria levels normalized after mDPSC transplantation in diabetic mice, indicating an improvement of renal function. This was confirmed by a histopathological analysis of kidney sections. We observed the loss of the epithelial brush border and proximal tubule dilatation only in saline-treated diabetic mice, which is indicative of acute renal lesion. STZ-induced thermal hyperalgesia was also reduced after cell therapy. Three days after transplantation, mDPSC-treated diabetic mice exhibited nociceptive thresholds similar to that of nondiabetic mice, an effect maintained throughout the 90-day evaluation period. Immunofluorescence analyses of the pancreas revealed the presence of GFP+ cells in, or surrounding, pancreatic islets. Our results demonstrate that mDPSCs may contribute to pancreatic β-cell renewal, prevent renal damage in diabetic animals, and produce a powerful and long-lasting antinociceptive effect on behavioral neuropathic pain. Our results suggest stem cell therapy as an option for the control of diabetes complications such as intractable diabetic neuropathic pain.

Comparative study of peripheral neuropathy and nerve regeneration in NOD and ICR diabetic mice

The non-obese diabetic (NOD) mouse was suggested as an adequate model for diabetic autonomic neuropathy. We evaluated sensory-motor neuropathy and nerve regeneration following sciatic nerve crush in NOD males rendered diabetic by multiple low doses of streptozotocin, in comparison with similarly treated Institute for Cancer Research (ICR) mice, a widely used model for type I diabetes. Neurophysiological values for both strains showed a decline in motor and sensory nerve conduction velocity at 7 and 8 weeks after induction of diabetes in the intact hindlimb. However, amplitudes of compound muscle and sensory action potentials (CMAPs and CNAPs) were significantly reduced in NOD but not in ICR diabetic mice. Morphometrical analysis showed myelinated fiber loss in highly hyperglycemic NOD mice, but no significant changes in fiber size. There was a reduction of intraepidermal nerve fibers, more pronounced in NOD than in ICR diabetic mice. Interestingly, aldose reductase and poly(ADP-ribose) polymerase (PARP) activities were increased already at 1 week of hyperglycemia, persisting until the end of the experiment in both strains. Muscle and nerve reinnervation was delayed in diabetic mice following sciatic nerve crush, being more marked in NOD mice. Thus, diabetes of mid-duration induces more severe peripheral neuropathy and slower nerve regeneration in NOD than in ICR mice.

Early changes of LIFR and gp130 in sciatic nerve and muscle of diabetic mice

Peripheral neuropathy is a common complication of diabetes mediated by alterations of growth factors. Members of the neuropoietic cytokine family, which include IL-6, LIF, and CNTF among others, have been shown to be important regulators of peripheral nerves and the muscles that they innervate. To investigate their potential role in diabetic nerve and muscle, we studied the expression of the shared receptor subunits, LIFR and gp130 in a mouse model of streptozotocin (STZ)-induced diabetes. The results of Western blotting and densitometric analysis showed that both LIFR and gp130 protein expression were increased in diabetic sciatic nerve compared to control mice at early time points following STZ injection. In diabetic gastrocnemius muscle, LIFR and gp130 were increased from 3 days to 24 weeks following STZ injection. In contrast, both LIFR and gp130 protein expression were decreased in diabetic soleus muscle at 3-days post-injection. Our results suggest that hyperglycemia results in changes to nerve and muscle soon after the onset of diabetes and that cytokines may play a role in this process.

Date fruit extract is a neuroprotective agent in diabetic peripheral neuropathy in streptozotocin-induced diabetic rats: a multimodal analysis

Background. To study the effects of an aqueous extract of date fruit (Phoenix dactylifera L. Arecaceae) diet on diabetic polyneuropathy (DPN) in streptozotocin- (STZ-) induced diabetic rats. Methods. The effects of a date fruit extract (DFE) diet on diabetic neuropathy in STZ-induced diabetic rats were evaluated and compared with a nondiabetic control group, diabetic control group (sham), and vehicle group with respect to the following parameters: open field behavioral test, motor nerve conduction velocity (MNCV), and morphological observations. Results. In the model of STZ-induced of diabetic neuropathy, chronic treatment for 6 weeks with DFE counteracted the impairment of the explorative activity of the rats in an open field behavioral test and of the conduction velocity of the sciatic nerve (MNCV). In addition, pretreatment with DFE significantly reversed each nerve diameter reduction in diabetic rats. Conclusion. DFE treatment shows efficacy for preventing diabetic deterioration and for improving pathological parameters of diabetic neuropathy in rats, as compared with control groups.

Interleukin-6, a mental cytokine

Almost a quarter of a century ago, interleukin-6 (IL-6) was discovered as an inflammatory cytokine involved in B cell differentiation. Today, IL-6 is recognized to be a highly versatile cytokine, with pleiotropic actions not only in immune cells, but also in other cell types, such as cells of the central nervous system (CNS). The first evidence implicating IL-6 in brain-related processes originated from its dysregulated expression in several neurological disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. In addition, IL-6 was shown to be involved in multiple physiological CNS processes such as neuron homeostasis, astrogliogenesis and neuronal differentiation. The molecular mechanisms underlying IL-6 functions in the brain have only recently started to emerge. In this review, an overview of the latest discoveries concerning the actions of IL-6 in the nervous system is provided. The central position of IL-6 in the neuroinflammatory reaction pattern, and more specifically, the role of IL-6 in specific neurodegenerative processes, which accompany Alzheimer's disease, multiple sclerosis and excitotoxicity, are discussed. It is evident that IL-6 has a dichotomic action in the CNS, displaying neurotrophic properties on the one hand, and detrimental actions on the other. This is in agreement with its central role in neuroinflammation, which evolved as a beneficial process, aimed at maintaining tissue homeostasis, but which can become malignant when exaggerated. In this perspective, it is not surprising that 'well-meant' actions of IL-6 are often causing harm instead of leading to recovery.

The role of cytokines in Guillain-Barré syndrome

Cytokines play an important role in the pathogenesis of autoimmune diseases including Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN). In this article, we reviewed the current knowledge of the role of cytokines such as TNF-α, IFN-γ, IL-1β, IL-6, IL-12, IL-18, IL-23, IL-17, IL-10, IL-4 and chemokines in GBS and EAN as unraveled by studies both in the clinic and the laboratory. However, these studies occasionally yield conflicting results, highlighting the complex role that cytokines play in the disease process. Efforts to modulate cytokine function in GBS and other autoimmune disease have shown efficiency indicating that cytokines are important therapeutic targets.

Effects of interleukin-6 treatment on neurovascular function, nerve perfusion and vascular endothelium in diabetic rats

AIM

Interleukin-6 (IL-6), a member of the neuropoietic cytokine family, participates in neural development and has neurotrophic activity. Recent research has also indicated actions to improve vasa nervorum function in diabetes. Both these facets are potentially relevant for treatment of diabetic neuropathy. The aim of this study was to determine whether IL-6 treatment corrected changes in neurovascular function in streptozotocin-induced diabetic rats.

METHODS

After 1 month of diabetes, rats were given IL-6 for 1 month. The rats were subjected to sensory testing and measurements of nerve conduction velocities and nerve blood flow by hydrogen clearance microelectrode polarography. Further groups were used to study responses of the isolated gastric fundus and renal artery. Results were statistically analysed using ANOVA and post hoc tests.

RESULTS

Diabetic rats showed mechanical hyperalgesia, thermal hyperalgesia, and tactile allodynia. The former was unaffected by IL-6 treatment, whereas the latter two measures were corrected. Immunohistochemical staining of dorsal root ganglia for IL-6 did not reveal any changes with diabetes or treatment. The results showed that 22 and 17.4% slowing of sciatic motor and saphenous sensory nerve conduction velocities, respectively, with diabetes were improved by IL-6. Sciatic endoneurial perfusion was halved by diabetes and corrected by IL-6. A 40.6% diabetic deficit in maximal non-adrenergic, non-cholinergic relaxation of gastric fundus to nerve stimulation was unaffected by IL-6. Renal artery endothelium-dependent relaxation was halved by diabetes, the endothelium-derived hyperpolarizing factor (EDHF) component being severely attenuated. IL-6 did not affect nitric oxide-mediated vasorelaxation, but markedly improved EDHF responses.

CONCLUSIONS

IL-6 improved aspects of small and large nerve fibre and vascular endothelium dysfunction in diabetic rats. The functional benefits related to increased nerve blood flow via an EDHF mechanism, and IL-6 could have therapeutic potential in diabetic neuropathy and vasculopathy, which should be further evaluated.

Peripheral neuropathy in chronic obstructive pulmonary disease

The aim of this study was to evaluate the frequency and characteristics of peripheral nervous system involvement in chronic obstructive pulmonary disease and its relation with proinflammatory cytokines such as TNF-alpha, IL-6, IGF-1 and CRP. Forty chronic obstructive pulmonary disease patients with a mean age 62.8 +/- 5.5 years and 33 healthy controls with a mean age of 61.8 +/- 7.4 were included into this study. All subjects were evaluated with standard motor and sensory nerve conduction studies. Serum TNF-alpha, IL-6, CRP and IGF-1 were measured. The muscle strengths of three muscle groups (knee extensors, shoulder abductors and flexors) were assessed with a hand-held dynamometer. Peripheral neuropathy was detected at 15% of chronic obstructive pulmonary disease patients. Ulnar motor and sensory nerves, left sural nerve distal latencies were found significantly prolonged than healthy volunteers (p = 0.011), peroneal nerve conduction velocities was found lower in patients than in healthy controls (p = 0.021), tibial nerve amplitudes was found lower in patients than healthy controls (p = 0.046). CRP and TNF-alpha were found significantly higher in chronic obstructive pulmonary disease patients and IGF-1 was found significantly lower in chronic obstructive pulmonary disease patients. There was no correlations between proinflammatory cytokines, CRP and electrophysiological findings. Left sural nerve's sensory nerve action potential amplitude was correlated positively with FEV(1)% (r = 0.425; p = 0.009). Muscle strength at the shoulder and knee were significantly reduced in patients with COPD when compared with controls. The frequency of neuropathy was higher in chronic obstructive pulmonary disease when compared with the healthy controls. Chronic obstructive pulmonary disease patients have subclinical peripheral nerve involvements.

The neuroprotective effects of progesterone on experimental diabetic neuropathy in rats

This study was conducted to investigate the neuroprotective effects of progesterone (PROG) on electrophysiological and histomorphometrical alternation in STZ-induced diabetic neuropathy starting from 4 weeks after the diabetic induction. Thirty adult male Sprague-Dawley rats were randomly divided into 3 groups (with 10 rats in each), control (nondiabetic), untreated diabetic and diabetic PROG-treated. Diabetes was induced in adult male rats by a single dose injection of streptozotocin (STZ, 55 mg kg(-1), i.p.). In the PROG-treated group, 4 weeks after induce of diabetes; rats were treated with PROG (8 mg kg(-1), i.p., every two days) for 6 weeks. Diabetic rats showed a significant reduction in motor nerve conduction velocity (MNCV), mean myelinated fibers (MFs) diameter, axon diameter and myelin sheath thickness in the sciatic nerve after 6 weeks. In the untreated diabetic group endoneurial edema was observed in sciatic nerve and the numbers of MFs with infolding into the axoplasm, irregularity of fibers, myelin sheath with unclear boundaries and alteration in myelin compaction were also increased. Long-term treatment with PROG increased MNCV significantly and prevented all these abnormalities in treated diabetic rats. Our findings indicated that PROG as a therapeutic approach can protect neurophysiologic and histomorphologic alterations induced by peripheral diabetic neuropathy.

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.

Serum interleukin-6 in patients with burning mouth syndrome and relationship with depression and perceived pain

Objective. To examine alteration of serum interleukin-6 and its clinical significance in burning mouth syndrome (BMS) patients. Methods. 48 BMS patients and 31 healthy controls participated in the study. Serum interleukin-6 was measured by means of ELISA. Hamilton rating scale of depression (HRSD) and visual analogue scale (VAS) were used to quantitiate depressive status and pain levels of subjects, respectively. Results. 15 (31%) patients displayed substantial depressive symptoms (HRSD ≧ 16). HRSD scores of patients were significantly higher than controls and positively correlated to their VAS values (P = .002). Serum interleukin-6 in patients was much lower than controls and negatively correlated to their VAS values (P = .011). However, no significant relations were found between interleukin-6 and HRSD scores (P = .317). Conclusions. Serum interleukin-6 in patients with burning mouth syndrome is decreased and negatively correlated to chronic pain. Both psychological and neuropathic disorders might act as precipitating factors in BMS etiopathogenesis.