Effects of antioxidants on nerve and vascular dysfunction in experimental diabetes

Identification of bolegrevilol B and C as novel antioxidant compounds in Suillus grevillei mushroom

Suillus grevillei is a popular species of mushroom available worldwide. In this study, we isolated compounds, bolegrevilol B and bolegrevilol C, from the mushroom and observed their potent lipid peroxidation-inhibiting activity. The structures of bolegrevilol B and bolegrevilol C were elucidated as 3-geranylgeranyl-1,2,4-trihydroxybenzene and 3-geranylgeranyl-1,2-dihydroxy-4-methoxybenzene, respectively, through high-resolution electrospray ionization mass spectrometry (-) and 1D and 2D nuclear magnetic resonance analyses. Bolegrevilol B and C inhibited lipid peroxidation and exhibited IC50 values of 2.0 ± 0.29 µm and 1.0 ± 0.13 µm, respectively. Furthermore, bolegrevilol B and C demonstrated potent neuroprotective activities in neuronal hybridoma N18-RE-105 cells against L-glutamate toxicity (EC50 of 1.8 ± 1.7 n m and 7.2 ± 6.9 n m, respectively). Bolegrevilol B was found in nature for the first time, and, to the best of our knowledge, this is the first study to report the antioxidant activities of bolegrevilol B and C.

The Effect of Alpha-Lipoic Acid in the Treatment of Chronic Subjective Tinnitus through the Tinnitus Handicap Inventory Scores

BACKGROUND AND OBJECTIVES

Tinnitus affects millions of adults. Many therapies, including complementary and alternative medicine and tinnitus retraining therapies, have been trialed, but an effective option, particularly for chronic subjective tinnitus (CTS), is still lacking.

MATERIALS AND METHODS

This study investigated the effects of alpha-lipoic acid (600 mg. per day for two months) on two groups of patients using a questionnaire. One group (A) was affected by tinnitus associated with likely cochlear dysfunction and metabolic syndrome, and the other (B) was composed of subjects with acoustic nerve lesions. All the patients were asked to complete the Italian version of the tinnitus handicap inventory (THI) to determine the overall degree of perceived annoyance at the beginning and end of therapy. Pure tone averages for speech frequencies and for high frequencies were computed, and psychoacoustic pitch and loudness matches were determined for each subject before and after treatment.

RESULTS

The pure tone audiometry, pitch, loudness, and THI scores of both groups were reported. In group A, statistically significant differences were observed for the "functional" and "emotional" subscales. The total score of THI and the loudness of tinnitus were also significantly reduced. No statistically significant differences were observed in group B.

CONCLUSIONS

These findings suggest a possible contribution of the antioxidant effect to the organ of Corti in subjects with metabolic syndrome and CST.

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

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

Tridax procumbens Ameliorates Streptozotocin-Induced Diabetic Neuropathy in Rats via Modulating Angiogenic, Inflammatory, and Oxidative Pathways

Tridax procumbens (TP) is a traditional Indian therapeutic plant and was evaluated for its blood glucose lowering abilities, as well as for its ability to curb diabetic neuropathy (DN). Administrating 45 mg/kg body weight of streptozotocin (STZ) intraperitoneally for four weeks, DN was induced in Wistar rats. After the rats' tails were clipped, the blood glucose levels were measured. Body weight and urine volume were also assessed. Oxidative stress makers such as superoxide dismutase (SOD), thiobarbituric acid reactive substances (TBARS), catalase (CAT), inflammatory cytokines for instance tumor necrosis factor (TNF)-α, and interleukin (IL)-1β were estimated. Further, protein kinase C (PKC-β) and vascular endothelial growth factor (VEGF) were also estimated as angiogenic markers. Behavioral parameters were also evaluated by using cold allodynia using acetone test, hot allodynia using Eddy's hot plate, grip strength test using Rota rod, and hyperalgesia test using Tail flick technique. The statistical assessment of findings was done employing one-way (ANOVA) analysis of variance, and subsequently Turkey as post hoc with GraphPad Prism software package. The ingestion of TP for 1 month in DN rats stemmed in a substantial decline in blood glucose concentrations matched to nontreated rats with DN. There had been a considerable improvement in DN as evident from the finding from biochemical markers. The serum level of antioxidant defense enzymes was significantly increased, while the activities of TBARS had been substantially reduced in the TP treated rats with DN. TP averted DN-triggered surge levels of TNF-α and IL-6 in the serum. Further, PKC-β and VEGF concentrations had been also reduced by the treatment TP. The findings of this research demonstrated that the restorative impact of TP on DN rats might be linked to the anti-inflammatory and antioxidative antiangiogenic retorts.

Influence of intermittent fasting on prediabetes-induced neuropathy: Insights on a novel mechanistic pathway

Aims

Peripheral neuropathy (PN) is correlated with obesity and metabolic syndrome. Intermittent fasting (IF) has been described as the cornerstone in the management of obesity; however, its role in prediabetic complications is not well elucidated. Cytochromes P450 Monooxygenases (CYP450) are major sources of Reactive Oxygen Species (ROS) that orchestrate the onset and development of diabetic complications. One of the CYP-metabolites, Expoxyecosatetraenoic Acids (EETs), are considered to be negative regulators of ROS production. In this study, we elucidated the role of IF on ROS production and investigated its influence on prediabetes-induced PN.

Methods

C57/BL6 control mice, prediabetic, prediabetic that underwent alternate day fasting with different diet composition, and prediabetic mice treated with EET-metabolizing sEH-inhibitor, AUDA. Body mass composition, metabolic, behavioral, and molecular tests were performed.

Results

High-fat diet (HFD) led to an increase in NADPH-induced ROS production; that was due to an alteration in the epoxygenase pathway assessed by the decrease in CYP1a1/1a2 expression. IF reinstated the homeostatic levels of EETs in HFD-fed mice. Moreover, treatment with AUDA mimicked the beneficial effect observed with IF.

Conclusion

IF and EETs bioavailability have a protective role in prediabetes-induced PN, suggesting a novel interventional strategy in the management of prediabetes and its associated complications.

Evidence from a Systematic Review and Meta-Analysis Pointing to the Antidiabetic Effect of Polyphenol-Rich Plant Extracts from Gymnema montanum, Momordica charantia and Moringa oleifera

In vitro and animal model studies are of great interest for selecting new phytochemicals, including polyphenols with antioxidative properties, as candidates for antidiabetic drugs. This review provides evidence from a critical literature data analysis on the effects of plant extract supplementation in diabetes mellitus management. We considered and meta-analyzed the efficacy of oral supplementation of plant extracts in animal model studies and examined physiological and oxidative stress parameters. Finally, 23 articles were included in the meta-analysis, revealing three plants with experimentally confirmed in vivo and in vitro antidiabetic properties: Gymnema montanum, Momordica charantia and Moringa oleifera. The following parameter changes resulted from an investigation of the supplementation: reduced oxidative stress, decreased insulin resistance, increased insulin release, reduced adiposity, and a modulatory effect on glycolysis and gluconeogenesis, as well as attenuation of diabetes-associated weight loss, reduced fasting blood glucose and lowered oxidative status. A comparison of Gymnema montanum versus Glybenclamide revealed the superiority of extracts over drug administration in some aspects. Although the analyzed extracts are promising candidates for antidiabetic treatment, there is much inconsistent data in the literature. Therefore, ultimate references for using these compounds in the prevention of diabetes are currently not applicable.

Treatment for Diabetic Peripheral Neuropathy: What have we Learned from Animal Models?

INTRODUCTION

Animal models have been widely used to investigate the etiology and potential treatments for diabetic peripheral neuropathy. What we have learned from these studies and the extent to which this information has been adapted for the human condition will be the subject of this review article.

METHODS

A comprehensive search of the PubMed database was performed, and relevant articles on the topic were included in this review.

RESULTS

Extensive study of diabetic animal models has shown that the etiology of diabetic peripheral neuropathy is complex, with multiple mechanisms affecting neurons, Schwann cells, and the microvasculature, which contribute to the phenotypic nature of this most common complication of diabetes. Moreover, animal studies have demonstrated that the mechanisms related to peripheral neuropathy occurring in type 1 and type 2 diabetes are likely different, with hyperglycemia being the primary factor for neuropathology in type 1 diabetes, which contributes to a lesser extent in type 2 diabetes, whereas insulin resistance, hyperlipidemia, and other factors may have a greater role. Two of the earliest mechanisms described from animal studies as a cause for diabetic peripheral neuropathy were the activation of the aldose reductase pathway and increased non-enzymatic glycation. However, continuing research has identified numerous other potential factors that may contribute to diabetic peripheral neuropathy, including oxidative and inflammatory stress, dysregulation of protein kinase C and hexosamine pathways, and decreased neurotrophic support. In addition, recent studies have demonstrated that peripheral neuropathy-like symptoms are present in animal models, representing pre-diabetes in the absence of hyperglycemia.

CONCLUSION

This complexity complicates the successful treatment of diabetic peripheral neuropathy, and results in the poor outcome of translating successful treatments from animal studies to human clinical trials.

Antioxidant p-terphenyl compounds in the mushroom Boletopsis leucomelas (PERS.) FAYOD and how they change via cooking

Antioxidant compounds in the mushroom Boletopsis leucomelas (PERS.) FAYOD were isolated using chromatographic methods, and their structures were determined via detailed analyses using high-resolution atmospheric pressure chemical ionization mass spectrometry and nuclear magnetic resonance. We identified five known p-terphenyl compounds (Bl-I, Bl-II, Bl-III, cycloleucomelon-leukopentaacetat, and Bl-IV) and one p-terphenyl new compound (Bl-VI); we determined the complete structure of cycloleucomelon-leukopentaacetat in this study. All these compounds possess potent lipid peroxidation-inhibiting activities. We further investigated changes in their chemical structures and antioxidant activities by applying heat (grilling, boiling, and microwave heating), and proved the production of two known p-terphenyl compounds (BI-V and boletopsin A) and one new p-terphenyl compound (BI-VII) via deacetylation of the original p-terphenyl compounds for the first time. We also found that DPPH radical scavenging activity was enhanced upon moderate heat cooking (boiling and microwave heating) due to changes in p-terphenyl compounds.

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.

Analysis of the effect of probucol-mecobalamin tablets combination on oxidative stress in patients with diabetic peripheral neuropathy

OBJECTIVE

This research aimed to observe the effect of probucol combined with mecobalamin tablets on oxidative stress in patients with diabetic peripheral neuropathy (DPN).

METHODS

In this prospective study, 104 patients with DPN who were treated in our hospital were included, from August 2018 to January 2020. They were divided into groups of combination (n = 52) and control (n = 52) by using a random number table. All patients took mecobalamin tablets after meals for 3 months (1 tablet/time, 3 times/d). On this basis, patients in the combination group took probucol for 3 months (4 tablets/time, 2 times/d). The observation indicators were the Toronto Clinical Scoring System (TCSS)(symptom, sensory, and reflex scores), nerve conduction velocity[sensory nerve conduction velocity (SNCV) and motor nerve conduction velocity(MNCV) of the common peroneal nerve and median nerve], oxidative stress indicators[superoxide dismutase(SOD), malondialdehyde(MDA), glutathione peroxidase(GSH-Px) and catalase(CAT)], clinical efficacy and adverse reactions.

RESULTS

There was no significant difference in the symptom scores, sensory scores, reflex scores, and total scores between the two groups before treatment (p > 0.05), while these four indicators of the combination group were significantly lower than that in the control group after treatment (p < 0.05). These four indicators of the two groups after treatment were significantly lower than before treatment (p < 0.05). There was no significant difference in the SNCV and NMCV of the common peroneal nerve and median nerve between the two groups before treatment (p > 0.05), while the indicators of the combination group were significantly higher than that of the control group (p < 0.05) after treatment, and these indicators of the two groups after treatment were significantly higher than that before treatment (p < 0.05). There was no significant difference in SOD, MDA, GSH-Px, and CAT between the two groups before treatment (p > 0.05). After treatment, the SOD, GSH-Px, and CAT in the combination group were significantly higher than that in the control group (p < 0.05), while the MDA in the combination group was significantly lower than that in the control group (p < 0.05). After treatment, the SOD, GSH-Px, and CAT in the two groups were significantly higher than that before treatment (p < 0.05), while the MDA was lower (p < 0.05). The clinical efficacy of the combination group was significantly better than that of the control group (94.23 % vs 78.85 %, p＜0.05) after treatment. There was no significant difference in the incidence of total adverse reactions between the two groups (3.85 % vs 5.77 %, p > 0.05).

CONCLUSION

The therapeutic effect of probucol combined with mecobalamin tablets for patients with DPN was significant, which could effectively improve the oxidative stress response of patients and was worthy of clinical promotion.

Interfascicular Gliding Dysfunction Relation with Focal Neuropathy in Diabetic Patients with Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS), a common neuropathy of the upper limb, is highly prevalent in diabetic patients. Recent findings indicate that changes in median nerve elasticity and its gliding characteristics may contribute to the development of CTS. Normally, each nerve should be able to adapt to the positional changes by passive movement relative to the surrounding tissues. This ability is provided by a gliding apparatus around the nerve trunk in the surrounding soft tissue. The fascicles of nerve trunks can also glide against each other (interfascicular gliding). Sonoelastography indicates that nerve elasticity is decreased in patients with CTS compared to healthy patients. Moreover, decreased nerve elasticity in diabetes mellitus type II is associated with increased neuropathy, especially in peripheral nerves. Biomechanical factors, oxidative stress, and microvascular defects are also observed in diabetic neuropathy and account for different complications. A reduction in the elasticity of peripheral nerves may be related to decreased interfascicular gliding because of the biomechanical changes that occur in neuropathy. Surgical treatments, including nerve release and reduction of carpal tunnel pressure, improve peripheral gliding but do not resolve disease symptoms completely. According to the evidence, interfascicular gliding dysfunction is the most important factor in the pathogenesis of CTS in diabetic patients. Available evidence suggests that biomechanical variations affect interfascicular gliding more than peripheral gliding in diabetic patients. Decreased nerve elasticity is strongly correlated with decreased interfascicular gliding. It is further hypothesized that the concurrent use of antioxidants and pharmacological treatment (neuroprotection) such as alpha lipoic acid with carpal tunnel release in diabetic patients may alleviate the interfascicular gliding dysfunction and improve median neve elasticity. Decreased nerve elasticity and interfascicular gliding dysfunction play significant roles in the pathogenesis of CTS in diabetic patients.

Ginseng Extracts, GS-KG9 and GS-E3D, Prevent Blood-Brain Barrier Disruption and Thereby Inhibit Apoptotic Cell Death of Hippocampal Neurons in Streptozotocin-Induced Diabetic Rats

Type 1 diabetes mellitus is known to be linked to the impairment of blood–brain barrier (BBB) integrity following neuronal cell death. Here, we investigated whether GS-KG9 and GS-E3D, bioactive ginseng extracts from Korean ginseng (Panax ginseng Meyer), inhibit BBB disruption following neuronal death in the hippocampus in streptozotocin-induced diabetic rats showing type 1-like diabetes mellitus. GS-KG9 and GS-E3D (50, 150, or 300 mg/kg, twice a day for 4 weeks) administered orally showed antihyperglycemic activity in a dose-dependent manner and significantly attenuated the increase in BBB permeability and loss of tight junction proteins. GS-KG9 and GS-E3D also inhibited the expression and activation of matrix metalloproteinase-9 and the infiltration of macrophages into the brain parenchyma, especially into the hippocampal region. In addition, microglia and astrocyte activation in the hippocampus and the expression of proinflammatory mediators such as tnf-α, Il-1β, IL-6, cox-2, and inos were markedly alleviated in GS-KG9 and GS-E3D-treated group. Furthermore, apoptotic cell death of hippocampal neurons, especially in CA1 region, was significantly reduced in GS-KG9 and GS-E3D-treated groups as compared to vehicle control. These results suggest that GS-KG9 and GS-E3D effectively prevent apoptotic cell death of hippocampal neurons by inhibiting BBB disruption and may be a potential therapy for the treatment of diabetic patients.

Ameliorative Effects Of N-Acetylcysteine As Adjunct Therapy On Symptoms Of Painful Diabetic Neuropathy

Purpose

Painful diabetic neuropathy (PDN) is a variant of diabetic peripheral neuropathy which is highly prevalent and distressing in diabetic patients. Despite its high burden, the optimal treatment of PDN has remained a clinical challenge. To explain the emergence and maintenance of PDN, increasing attention has been focused on dimensions of inflammation and oxidative toxic stress (OTS). Accordingly, the aim of this study was to investigate the effects of oral N-acetylcysteine (NAC), an agent with known anti-oxidant and anti-inflammatory effects, as an adjunct therapy in patients suffering from PDN.

Patients and methods

113 eligible patients with type 2 diabetes suffering from PDN were randomly assigned to either the pregabalin + placebo or pregabalin + NAC group for 8 weeks (pregabalin at a dose of 150 mg per day, NAC and matched placebo at doses of 600 mg twice a day). Mean pain score was evaluated at baseline, week 1, 2, 4, 6, and 8 of the study based on the mean 24 hr average pain score, using an 11-point numeric rating scale (NRS). As secondary efficacy measures, mean sleep interference score (SIS) resulting from PDN, responder rates, Patient Global Impression of Change (PGIC), Clinical Global Impression of Change (CGIC), and safety were also assessed. Additionally, serum levels of total antioxidant capacity (TAC), total thiol groups (TTG), catalase activity (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), nitric oxide (NO), and malondialdehyde (MDA) were assessed at baseline and at the end of the study.

Results

Ninety patients completed the eight-week course of the study. The decrease in mean pain scores and mean sleep interference score in pregabalin + NAC group was greater in comparison with pregabalin + placebo group (p value<0.001 in both conditions). Moreover, more responders (defined as ≥50% reduction in mean pain score from baseline to end-point) were observed in the pregabalin + NAC group, in comparison with pregabalin + placebo group (72.1% vs 46.8%). More improvement in PGIC and CGIC from baseline to the end of the study was reported in pregabalin + NAC group. Oral NAC had minimal adverse effects and was well tolerated in almost all patients. Furthermore, in respect to OTS biomarkers, adjuvant NAC significantly decreased serum level of MDA and significantly increased serum levels of SOD, GPx, TAC, and TTG.

Conclusion

The pattern of results suggests that compared to placebo and over a time period of 8 weeks, adjuvant NAC is more efficacious in improving neuropathic pain associated with diabetic neuropathy than placebo. Ameliorative effects of NAC on OTS biomarkers demonstrated that NAC may alleviate painful symptoms of diabetic neuropathy, at least in part by its antioxidant effects.

Functional and Structural Changes of the Blood-Nerve-Barrier in Diabetic Neuropathy

The incidence of diabetes mellitus is approaching global epidemic proportions and should be considered a major health-care problem of modern societies in the twenty-first century. Diabetic neuropathy is a common chronic complication of diabetes and, although an adequate glycemic control can reduce the frequency of diabetic neuropathy in type 1 diabetes, the majority of type 2 diabetic patients will develop this complication. The underlying cellular and molecular mechanisms are still poorly understood, preventing the development of effective treatment strategies. However, accumulating evidence suggests that breakdown of the blood-nerve barrier (BNB) plays a pivotal pathophysiological role in diabetic neuropathy. In the present review, we highlight the structural and functional significance of the BNB in health and disease, focusing on the pathological molecular events leading to BNB dysfunction in diabetic neuropathy. In addition, we discuss potential molecular targets involved in BNB homeostasis that may pave the way toward novel therapeutic strategies for treating diabetic neuropathy.

Mitochondrial dysfunction contribute to diabetic neurotoxicity induced by streptozocin in mice: protective effect of Urtica dioica and pioglitazone

INTRODUCTION

Uncontrolled chronic hyperglycemia in diabetic patients could result in various complications, including neurotoxicity. Urtica dioica L. (UD) is known for its hypoglycemic and antioxidant effects. In this study, we evaluated the efficacy of UD and pioglitazone (PIO) in reduction of neurotoxicity and oxidative stress in streptozocin-induced diabetic mice.

MATERIALS AND METHODS

Male mice were divided into seven groups: control, diabetic, dimethyl sulfoxide-treated control, PIO-treated, UD-treated, UD-PIO-treated, and vitamin E-treated. For induction of diabetes, streptozocin was injected in a single dose (65 mg/kg, i.p.). All treatments were performed for 5 weeks. Neurotoxicity was evaluated through hot plate and formalin test. Then, animals were killed, brain tissue was separated and the mitochondrial fraction was isolated with different centrifuge technique. Also, oxidative stress markers (reactive oxygen species, lipid peroxidation, protein carbonyl, glutathione) were measured in brain. Mitochondrial function was evaluated by MTT test in brain isolated mitochondria.

RESULTS

Elevation of oxidative stress markers and mitochondrial damage were observed in diabetic mice compared to control group. Administration of PIO and UD ameliorated the oxidative stress and mitochondrial damage (p < 0.05) in diabetic mice. Also increase in pain score was shown in diabetic mice that treatment with UD and PIO diminished elevation of pain score in diabetic mice. Interestingly, simultaneous administration of PIO and UD showed synergism effect in attenuation of oxidative stress and hyperglycemia.

CONCLUSION

UD showed a therapeutic potential for the attenuation of oxidative stress and diabetes-induced hyperglycemia that can be considered as co-treatment in treatment of diabetic neurotoxicity.

Addressing Stem Cell Therapeutic Approaches in Pathobiology of Diabetes and Its Complications

High morbidity and mortality of diabetes mellitus (DM) throughout the human population is a serious threat which needs to be addressed cautiously. Type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) are most prevalent forms. Disruption in insulin regulation and resistance leads to increased formation and accumulation of advanced end products (AGEs), which further enhance oxidative and nitrosative stress leading to microvascular (retinopathy, neuropathy, and nephropathy) and macrovascular complications. These complications affect the normal function of organ and tissues and may cause life-threatening disorders, if hyperglycemia persists and improperly controlled. Current and traditional treatment procedures are only focused on to regulate the insulin level and do not cure the diabetic complications. Pancreatic transplantation seemed a viable alternative; however, it is limited due to lack of donors. Cell-based therapy such as stem cells is considered as a promising therapeutic agent against DM and diabetic complications owing to their multilineage differentiation and regeneration potential. Previous studies have demonstrated the various impacts of both pluripotent and multipotent stem cells on DM and its micro- and macrovascular complications. Therefore, this review summarizes the potential of stem cells to treat DM and its related complications.

Traumatic brain injury, diabetic neuropathy and altered-psychiatric health: The fateful triangle

Traumatic brain injury is a detrimental medical condition particularly when accompanied by diabetes. There are several comorbidities going along with diabetes including, but not limited to, kidney failure, obesity, coronary artery disease, peripheral vascular disease, hypertension, stroke, neuropathies and amputations. Unlike diabetes type 1, diabetes type 2 is more common in adults who simultaneously suffer from other comorbid conditions making them susceptible to repetitive fall incidents and sustaining head trauma. The resulting brain insult exacerbates current psychiatric disorders such as depression and anxiety, which, in turn, increases the risk of sustaining further brain traumas. The relationship between diabetes, traumatic brain injury and psychiatric health constitutes a triad forming a non-reversible vicious cycle. At the proteomic and psychiatric levels, cellular, molecular and behavioral alterations have been reported with the induction of non-traumatic brain injury in diabetic models such as stroke. However, research into traumatic brain injury has not been systematically investigated. Thus, in cases of diabetic neuropathy complicated with traumatic brain injury, utilizing fine structural and analytical techniques allows the identification of key biological markers that can then be used as innovative diagnostics as well as novel therapeutic targets in an attempt to treat diabetes and its sequelae especially those arising from repetitive mild brain trauma.

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

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

The aetiology of neuropathy in experimental diabetes

Most information on the aetiology of experimental diabetic neuropathy comes from studies on rodent models, particularly the streptozotocin-diabetic rat. The major factor that impairs small and large nerve fibre function is a decrease in nerve and ganglion perfusion. This leads to reduced conduction velocity, increased resistance to ischaemic conduction failure, blunted regenerative capacity, painful neuropathy, and autonomic nerve dysfunction. Hyperglycaemia, altered lipid metabolism and reduced insulin action combine to cause adverse metabolic effects on vasa nervorum, vascular endothelium being a notable target. The resultant reduced vasodilation and increased vasoconstriction causes endoneurial hypoxia. Oxidative stress is of primary importance, due to increased production of reactive oxygen species from a plethora of intra- and extracellular sources. Advanced glycation and carbonyl stress play a supporting role, as does essential fatty acid dysmetabolism. These mechanisms are associated with alterations in cell signalling mediated by protein kinases, nuclear factor Kappa B and poly (ADP-ribose) polymerase.

Vascular Impairment of Epineurial Arterioles of the Sciatic Nerve: Implications for Diabetic Peripheral Neuropathy

This article reviews the impact of diabetes and its treatment on vascular function with a focus on the reactivity of epineurial arterioles, blood vessels that provide circulation to the sciatic nerve. Another focus is the relationship between the dysregulation of neurovascular function and diabetic peripheral neuropathy. Diabetic peripheral neuropathy is a debilitating disorder that occurs in more than 50 percent of patients with diabetes. The etiology involves metabolic, vascular, and immunologic pathways besides neurohormonal growth factor deficiency and extracellular matrix remodeling. In the light of this complex etiology, an effective treatment for diabetic peripheral neuropathy has not yet been identified. Current opinion postulates that any effective treatment for diabetic peripheral neuropathy will require a combination of life style and therapeutic interventions. However, a more comprehensive understanding of the factors contributing to neurovascular and neural dysfunction in diabetes is needed before such a treatment strategy can be developed. After reading this review, the reader should have gained insight into the complex regulation of vascular function and blood flow to the sciatic nerve, and the impact of diabetes on numerous elements of vascular reactivity of epineurial arterioles of the sciatic nerve.

Naringenin neutralises oxidative stress and nerve growth factor discrepancy in experimental diabetic neuropathy

OBJECTIVES

Present study aims to investigate the ameliorative effects of naringenin (NG) on experimentally induced diabetic neuropathy (DN) in rats.

METHODS

Diabetes was induced by single intraperitoneal injection of streptozotocin (STZ, 60  g/kg). Naringenin (25 and 50 mg/kg/day) treatment was started 2 weeks after the diabetes induction and continued for five consecutive weeks. Pain threshold behaviour tests were performed at the end of the treatment. Serum levels of glucose, insulin and pro-inflammatory cytokines were assessed. In sciatic tissues, markers oxidative stress, cytokines and neurotrophic factors were measured.

RESULTS

NG treatments showed significant decrease in paw-withdrawal (P < 0.01) and tail-flick latency (P < 0.01). The drug attenuated the diabetic-induced changes in serum glucose, insulin and pro-inflammatory cytokines including tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and interleukin-6 (IL-6). In sciatic nerve, the diabetic-induced alterations in interleukins and oxidative stress biomarkers were significantly attenuated by NG. Decreased sciatic expressions of insulin growth factor (IGF) and nerve growth factor (NGF) in diabetic rats were also ameliorated by NG. Diabetes-induced dysregulated levels of nitric oxide (NO), thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH), activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) were ameliorated by NG. Histological analysis showed that NG corrected the altered sciatic changes in diabetic animals.

DISCUSSION

We suggest that neuro-protective effect of NG molecules in sciatic nerve of diabetic rats, through its anti-diabetic as well as antioxidant and anti-inflammatory properties.

Deletion of Protein Tyrosine Phosphatase 1B (PTP1B) Enhances Endothelial Cyclooxygenase 2 Expression and Protects Mice from Type 1 Diabetes-Induced Endothelial Dysfunction

Protein tyrosine phosphatase 1B (PTP1B) dephosphorylates receptors tyrosine kinase and acts as a molecular brake on insulin signaling pathway. Conditions of metabolic dysfunction increase PTP1B, when deletion of PTP1B protects against metabolic disorders by increasing insulin signaling. Although vascular insulin signaling contributes to the control of glucose disposal, little is known regarding the direct role of PTP1B in the control of endothelial function. We hypothesized that metabolic dysfunctions increase PTP1B expression in endothelial cells and that PTP1B deletion prevents endothelial dysfunction in situation of diminished insulin secretion. Type I diabetes (T1DM) was induced in wild-type (WT) and PTP1B-deficient mice (KO) with streptozotocin (STZ) injection. After 28 days of T1DM, KO mice exhibited a similar reduction in body weight and plasma insulin levels and a comparable increase in glycemia (WT: 384±20 vs. Ko: 432±29 mg/dL), cholesterol and triglycerides, as WT mice. T1DM increased PTP1B expression and impaired endothelial NO-dependent relaxation, in mouse aorta. PTP1B deletion did not affect baseline endothelial function, but preserved endothelium-dependent relaxation, in T1DM mice. NO synthase inhibition with L-NAME abolished endothelial relaxation in control and T1DM WT mice, whereas L-NAME and the cyclooxygenases inhibitor indomethacin were required to abolish endothelium relaxation in T1DM KO mice. PTP1B deletion increased COX-2 expression and PGI₂ levels, in mouse aorta and plasma respectively, in T1DM mice. In parallel, simulation of diabetic conditions increased PTP1B expression and knockdown of PTP1B increased COX-2 but not COX-1 expression, in primary human aortic endothelial cells. Taken together these data indicate that deletion of PTP1B protected endothelial function by compensating the reduction in NO bioavailability by increasing COX-2-mediated release of the vasodilator prostanoid PGI₂, in T1DM mice.

Antioxidant strategies in the management of diabetic neuropathy

Chronic hyperglycaemia (an abnormally high glucose concentration in the blood) resulting from defects in insulin secretion/action, or both, is the major hallmark of diabetes in which it is known to be involved in the progression of the condition to different complications that include diabetic neuropathy. Diabetic neuropathy (diabetes-induced nerve damage) is the most common diabetic complication and can be devastating because it can lead to disability. There is an increasing body of evidence associating diabetic neuropathy with oxidative stress. Oxidative stress results from the production of oxygen free radicals in the body in excess of its ability to eliminate them by antioxidant activity. Antioxidants have different mechanisms and sites of actions by which they exert their biochemical effects and ameliorate nerve dysfunction in diabetes by acting directly against oxidative damage. This review will examine different strategies for managing diabetic neuropathy which rely on exogenous antioxidants.

Neuroprotective effects of Gymnema sylvestre on streptozotocin-induced diabetic neuropathy in rats

The application of traditional medicine for diabetes and associated complications, such as diabetic neuropathy (DN), has received increasing attention. The aim of the present study was to investigate the potential ameliorative effect of Gymnema sylvestre (Gs) in a rat model of DN. Diabetes was induced via a single intraperitoneal injection of streptozotocin (STZ; 60 mg/kg). Treatment with Gs extract (50 or 100 mg/kg/day) began two weeks following the administration of STZ and was continued for five weeks. Pain threshold behavior tests were performed subsequent to the five-week Gs treatment period. In addition, the serum levels of glucose, insulin and proinflammatory cytokines, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6, were determined. Furthermore, the sciatic tissue levels of nitric oxide, thiobarbituric acid reactive substances and reduced glutathione were determined, as well as the activity levels of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase. Levels of insulin-like growth factor (IGF), nerve growth factor (NGF), TNF-α, IL-1β and IL-6 were also assessed in the sciatic tissue. In addition, the sciatic nerve tissue samples were analyzed for histopathological alterations. The diabetic rats exhibited apparent reductions in the paw-withdrawal (31%; P<0.01) and tail-flick latencies (38%; P<0.05). Furthermore, the diabetic rats demonstrated an evident elevation in serum and sciatic levels of proinflammatory cytokines. Measured oxidative stress biomarkers were significantly altered in the sciatic nerve tissue of the diabetic rats. Treatment with Gs attenuated diabetes-induced modifications with regard to the levels of serum glucose, insulin and proinflammatory cytokines. In the sciatic nerve tissue, the diabetes-induced alterations in IL levels and oxidative stress biomarkers were significantly improved in the Gs-treated rats. Furthermore, the reduction in the sciatic tissue expression levels of IGF and NGF was also ameliorated by Gs treatment. Histological analysis indicated that Gs corrected the sciatic tissue in the diabetic rats. Therefore, the results demonstrated that the neuroprotective effect of Gs may be associated with the inhibitory effect on the excessive activation of inflammatory molecules and oxidative stress mediators.

Sildenafil ameliorates long term peripheral neuropathy in type II diabetic mice

Diabetic peripheral neuropathy is a common complication of long-standing diabetes mellitus. To mimic clinical trials in which patients with diabetes enrolled have advanced peripheral neuropathy, we investigated the effect of sildenafil, a specific inhibitor of phosphodiesterase type 5 enzyme, on long term peripheral neuropathy in middle aged male mice with type II diabetes. Treatment of diabetic mice (BKS.Cg-m+/+Lepr^db/J, db/db) at age 36 weeks with sildenafil significantly increased functional blood vessels and regional blood flow in the sciatic nerve, concurrently with augmentation of intra-epidermal nerve fiber density in the skin and myelinated axons in the sciatic nerve. Functional analysis showed that the sildenafil treatment considerably improved motor and sensory conduction velocities in the sciatic nerve and peripheral thermal stimulus sensitivity compared with the saline treatment. In vitro studies showed that mouse dermal endothelial cells (MDE) cultured under high glucose levels exhibited significant down regulation of angiopoietin 1 (Ang1) expression and reduction of capillary-like tube formation, which were completely reversed by sildenafil. In addition, incubation of dorsal root ganglia (DRG) neurons with conditioned medium harvested from MDE under high glucose levels suppressed neurite outgrowth, where as conditional medium harvested from MDE treated with sildenafil under high glucose levels did not inhibit neurite outgrowth of DRG neurons. Moreover, blockage of the Ang1 receptor, Tie2, with a neutralized antibody against Tie2 abolished the beneficial effect of sildenafil on tube formation and neurite outgrowth. Collectively, our data indicate that sildenafil has a therapeutic effect on long term peripheral neuropathy of middle aged diabetic mice and that improvement of neurovascular dysfunction by sildenafil likely contributes to the amelioration of nerve function. The Ang1/Tie2 signaling pathway may play an important role in these restorative processes.

Febuxostat ameliorates diabetic renal injury in a streptozotocin-induced diabetic rat model

BACKGROUND

Oxidative stress and inflammation are known to play central roles in the development of diabetic nephropathy (DN). Febuxostat is a novel non-purine xanthine oxidase (XO)-specific inhibitor developed to treat hyperuricemia. In this study, we investigated whether febuxostat could ameliorate DN via renoprotective mechanisms such as alleviation of oxidative stress and anti-inflammatory actions.

METHODS

Male Sprague-Dawley rats were divided into three groups: a normal group, a diabetes group (DM group), and a febuxostat-treated diabetes group (DM+Fx group). We administered 5 mg/kg of febuxostat to experimental rats for 7 weeks and evaluated clinical and biochemical parameters and XO and xanthine dehydrogenase (XDH) activity in hepatic tissue. The degree of oxidative stress and extent of inflammation were evaluated from urine samples and renal tissue collected from each group.

RESULTS

Diabetic rats (DM and DM+Fx groups) had higher blood glucose and kidney weight relative to body weight than normal rats. Albuminuria was significantly reduced in febuxostat-treated diabetic rats compared with untreated diabetic rats. Quantitative analysis showed that hepatic XO and XDH activities were higher in the DM groups, but decreased after treatment with febuxostat. Urinary 8-OHdG concentrations and renal cortical nitrotyrosine also indicated reduced oxidative stress in the DM+Fx group relative to the DM group. The number of ED-1-stained cells in the glomerulus and tubule of diabetic renal tissue decreased in febuxostat-treated diabetic rats relative to that of non-treated diabetic rats. Diabetic rats also expressed higher transcript levels of inflammatory genes (E-selectin and VCAM-1), an inflammation-induced enzyme (COX-2), and inflammatory mediators (ED-1 and NF-κB) than control rats; expression of these genes was significantly reduced by treatment with febuxostat.

CONCLUSIONS

Febuxostat prevents diabetic renal injury such as albuminuria. This renoprotective effect appears to be due to attenuation of the inflammatory and oxidative effects of diabetes-induced renal damage through inhibition of XO and XDH activities.

Biology of diabetic neuropathy

More than half of all patients with diabetes develop neuropathic disorders affecting the distal sensory and/or motor nerves, or autonomic or cranial nerve functions. Glycemic control can decrease the incidence of neuropathy but is not adequate alone to prevent or treat the disease. This chapter introduces diabetic neuropathy with a morphological description of the disease then describes our current understanding of metabolic and molecular mechanisms that contribute to neurovascular dysfunctions. Key mechanisms include glucose and lipid imbalances and insulin resistance that are interconnected via oxidative stress, inflammation, and altered gene expression. These complex interactions should be considered for the development of new treatment strategies against the onset or progression of neuropathy. Advances in understanding the combined metabolic stressors and the novel study of epigenetics suggest new therapeutic targets to combat this morbid and intractable disease affecting millions of patients with type 1 or type 2 diabetes.

Neuroinflammation and oxidative stress in diabetic neuropathy: futuristic strategies based on these targets

In Diabetes, the chronic hyperglycemia and associated complications affecting peripheral nerves are one of the most commonly occurring microvascular complications with an overall prevalence of 50-60%. Among the vascular complications of diabetes, diabetic neuropathy is the most painful and disabling, fatal complication affecting the quality of life in patients. Several theories of etiologies surfaced down the lane, amongst which the oxidative stress mediated damage in neurons and surrounding glial cell has gained attention as one of the vital mechanisms in the pathogenesis of neuropathy. Mitochondria induced ROS and other oxidants are responsible for altering the balance between oxidants and innate antioxidant defence of the body. Oxidative-nitrosative stress not only activates the major pathways namely, polyol pathway flux, advanced glycation end products formation, activation of protein kinase C, and overactivity of the hexosamine pathway, but also initiates and amplifies neuroinflammation. The cross talk between oxidative stress and inflammation is due to the activation of NF- κ B and AP-1 and inhibition of Nrf2, peroxynitrite mediate endothelial dysfunction, altered NO levels, and macrophage migration. These all culminate in the production of proinflammatory cytokines which are responsible for nerve tissue damage and debilitating neuropathies. This review focuses on the relationship between oxidative stress and neuroinflammation in the development and progression of diabetic neuropathy.

Mechanisms of diabetic neuropathy: Schwann cells

As ensheathing and secretory cells, Schwann cells are a ubiquitous and vital component of the endoneurial microenvironment of peripheral nerves. The interdependence of axons and their ensheathing Schwann cells predisposes each to the impact of injury in the other. Further, the dependence of the blood-nerve interface on trophic support from Schwann cells during development, adulthood, and after injury suggests these glial cells promote the structural and functional integrity of nerve trunks. Here, the developmental origin, injury-induced changes, and mature myelinating and nonmyelinating phenotypes of Schwann cells are reviewed prior to a description of nerve fiber pathology and consideration of pathogenic mechanisms in human and experimental diabetic neuropathy. A fundamental role for aldose-reductase-containing Schwann cells in the pathogenesis of diabetic neuropathy, as well as the interrelationship of pathogenic mechanisms, is indicated by the sensitivity of hyperglycemia-induced biochemical alterations, such as polyol pathway flux, formation of reactive oxygen species, generation of advanced glycosylation end products (AGEs) and deficient neurotrophic support, to blocking polyol pathway flux.

Pathogenesis of diabetic neuropathy: focus on neurovascular mechanisms

Neuropathies of the peripheral and autonomic nervous systems affect up to half of all people with diabetes, and are major risk factors for foot ulceration and amputation. The aetiology is multifactorial: metabolic changes in diabetes may directly affect neural tissue, but importantly, neurodegenerative changes are precipitated by compromised nerve vascular supply. Experiments in animal models of diabetic neuropathy suggest that similar metabolic sequelae affect neurons and vasa nervorum endothelium. These include elevated polyol pathway activity, oxidative stress, the formation of advanced glycation and lipoxidation end products, and various pro-inflammatory changes such as elevated protein kinase C, nuclear factor κB and p38 mitogen activated protein kinase signalling. These mechanisms do not work in isolation but strongly interact in a mutually facilitatory fashion. Nitrosative stress and the induction of the enzyme poly (ADP-ribose) polymerase form one important link between physiological stressors such as reactive oxygen species and the pro-inflammatory mechanisms. Recently, evidence points to endoplasmic stress and the unfolded protein response as forming another crucial link. This review focuses on the aetiopathogenesis of neurovascular changes in diabetic neuropathy, elucidated in animal studies, and on putative therapeutic targets the majority of which have yet to be tested for efficacy in clinical trials.

Impaired nerve fiber regeneration in axotomized peripheral nerves in streptozotocin-diabetic rats

Aim/Introduction

Impaired nerve fiber regeneration is a salient feature of diabetic neuropathy. Its pathogenesis is still unclear. We attempted to characterize the structure of regenerated myelinated fibers after transection in streptozotocin‐diabetic rats.

Materials and Methods

Streptozotocin‐diabetic rats underwent transection of the sciatic nerve. Two and 4 weeks post‐axotomy, regenerated myelinated fibers of the cut end and fibers at its proximal site were morphometrically examined. Non‐diabetic control rats with axotomy were also examined for comparison.

Results

At 4 weeks post‐axotomy, diabetic rats showed an increased myelinated fiber density and total fiber number with a trend toward reduced fiber size at the cut end compared with those in control rats. The average number of myelin lamellae relative to axonal size in regenerated fibers at the cut end was significantly reduced in diabetic rats compared with that in control rats. The proximal site showed a reduced size of fibers and axons in both diabetic and control rats to a similar extent compared with those in a non‐axotomized state. At 2 weeks post‐axotomy, these findings were less apparent.

Conclusions

The nerves of diabetic rats when axotomized undergo impaired regeneration characterized by increased fiber density with hypomyelination.

Effect of iridoid glucoside on plasma lipid profile, tissue fatty acid changes, inflammatory cytokines, and GLUT4 expression in skeletal muscle of streptozotocin-induced diabetic rats

The present study was designed to examine the antihyperlipidaemic potential of iridoid glucoside isolated from Vitex negundo leaves in STZ-induced diabetic rats. The levels of cholesterol (TC), triglycerides, lipoproteins, free fatty acids, phospholipids, fatty acid composition, proinflammatory cytokines, muscle glycogen content, and glucose transporter 4 (GLUT4) expression were estimated in control and diabetic rats. Oral administration of iridoid glucoside at a dose of 50 mg/kg body weight per day to STZ-induced diabetic rats for a period of 30 days resulted in a significant reduction in plasma and tissue (liver and kidney) cholesterol, triglycerides, free fatty acids, and phospholipids. In addition, the decreased plasma levels of high-density lipoprotein-cholesterol and increased plasma levels of low density lipoprotein- and very low density lipoprotein-cholesterol in diabetic rats were restored to near normal levels following treatment with iridoid glucoside. The fatty acid composition of the liver and kidney was analyzed by gas chromatography. The altered fatty acid composition in the liver and kidney of diabetic rats was also restored upon treatment with iridoid glucoside. Moreover, the elevated plasma levels of proinflammatory cytokines and decreased levels of muscle glycogen and GLUT4 expression in the skeletal muscle of diabetic rats were reinstated to their normal levels via enhanced secretion of insulin from the remnant β cells of pancreas by the administration of iridoid glucoside. The effect produced by iridoid glucoside on various parameters was comparable with that of glibenclamide, a well-known antihyperglycemic drug.

Cell therapy for diabetic neuropathy using adult stem or progenitor cells

Diabetic neuropathy (DN) is the most common and disabling complication of diabetes that may lead to foot ulcers and limb amputations. Despite widespread awareness of DN, the only effective treatments are glucose control and pain management. A growing body of evidence suggests that DN is characterized by reduction of vascularity in peripheral nerves and deficiency in neurotrophic and angiogenic factors. Previous studies have tried to introduce neurotrophic or angiogenic factors in the form of protein or gene for therapy, but the effect was not significant. Recent studies have shown that bone marrow (BM)-derived stem or progenitor cells have favorable effects on the repair of cardiovascular diseases. Since these BM-derived stem or progenitor cells contain various angiogenic and neurotrophic factors, these cells have been attempted for treating experimental DN, and turned out to be effective for reversing various manifestations of experimental DN. These evidences suggest that cell therapy, affecting both vascular and neural components, can represent a novel therapeutic option for treatment of clinical DN.

n5-STZ Diabetic Model Develops Alterations in Sciatic Nerve and Dorsal Root Ganglia Neurons of Wistar Rats

One experimental model of diabetes mellitus (DM) similar to type II DM, called n5-STZ, is obtained by a single injection (via i.p.) of streptozotocin (STZ) in the 5th day of life of newborn rats. The present investigation aimed to characterize alterations in excitability of rat peripheral neurons in n5-STZ model. n5-STZ DM was induced, and electrophysiological evaluation was done at 12th week of rat life. Rats developed glucose intolerance, sensory alteration, and hyperglycemia or near-normoglycemia (21.2 ± 1.6 and 7.4 ± 0.4 mmol/L). In near-normoglycemia group the significant electrophysiological alteration observed was decreased in amplitude of 2nd wave (2nd component, conduction velocity: 48.8 m/s) of compound action potential (CAP) of sciatic nerve. For hyperglycemic rats, decreased excitability, amplitude, and conduction velocity of 2nd CAP component of sciatic nerve were found; a depolarization of resting potential (4-5 mV) and reduction in maximum ascendant and descendant inclinations of action potential were found in DRG neurons but no alteration on Na⁺ current (I_Na⁺). Thus, n5-STZ rats develop alterations in excitability which were related to glycemic levels but were not likely attributable to changes on I_Na⁺. Our data confirm that n5-STZ model is a useful model to study type II DM.

Emerging therapy for diabetic neuropathy: cell therapy targeting vessels and nerves

Diabetic neuropathy (DN), the most common complication of diabetes, frequently leads to foot ulcers and may progress to limb amputations. Despite continuous increase in incidence, there is no clinical therapy to effectively treat DN. Pathogenetically, DN is characterized by reduced vascularity in peripheral nerves and deficiency in angiogenic and neurotrophic factors. We will briefly review the pathogenetic mechanism of DN and address the effects and the mechanisms of cell therapies for DN. To reverse the changes of DN, studies have attempted to deliver neurotrophic or angiogenic factors for treatment in the form of protein or gene therapy; however, the effects turned out to be very modest if not ineffective. Recent studies have demonstrated that bone marrow (BM)-derived cells such as mononuclear cells or endothelial progenitor cells (EPCs) can effectively treat various cardiovascular diseases through their paracrine effects. As BM-derived cells include multiple angiogenic and neurotrophic cytokines, these cells were used for treating experimental DN and found to reverse manifestations of DN. Particularly, EPCs were shown to exert favorable therapeutic effects through enhanced neural neovascularization and neuro-protective effects. These findings clearly indicate that DN is a complex disorder with pathogenetic involvement of both vascular and neural components. Studies have shown that cell therapies targeting both vascular and neural elements are shown to be advantageous in treating DN.

Thymosin β4 promotes the recovery of peripheral neuropathy in type II diabetic mice

Peripheral neuropathy is one of the most common complications of diabetes mellitus. Using a mouse model of diabetic peripheral neuropathy, we tested the hypothesis that thymosin β4 (Tβ4) ameliorates diabetes-induced neurovascular dysfunction in the sciatic nerve and promotes recovery of neurological function from diabetic peripheral neuropathy. Tβ4 treatment of diabetic mice increased functional vascular density and regional blood flow in the sciatic nerve, and improved nerve function. Tβ4 upregulated angiopoietin-1 (Ang1) expression, but suppressed Ang2 expression in endothelial and Schwann cells in the diabetic sciatic nerve. In vitro, incubation of Human Umbilical Vein Endothelial Cells (HUVECs) with Tβ4 under high glucose condition completely abolished high glucose-downregulated Ang1 expression and high glucose-reduced capillary-like tube formation. Moreover, incubation of HUVECs under high glucose with conditioned medium collected from Human Schwann Cells (HSCs) treated with Tβ4 significantly reversed high glucose-decreased capillary-like tube formation. PI3K/Akt signaling pathway is involved in Tβ4-regulated Ang1 expression on endothelial and Schwann cells. These data indicate that Tβ4 likely acts on endothelial cells and Schwann cells to preserve and/or restore vascular function in the sciatic nerve which facilitates improvement of peripheral nerve function under diabetic neuropathy. Thus, Tβ4 has potential for the treatment of diabetic peripheral neuropathy.

Reactive oxygen and nitrogen species in pathogenesis of vascular complications of diabetes

Macrovascular and microvascular diseases are currently the principal causes of morbidity and mortality in subjects with diabetes. Disorders of the physiological signaling functions of reactive oxygen species (superoxide and hydrogen peroxide) and reactive nitrogen species (nitric oxide and peroxynitrite) are important features of diabetes. In the absence of an appropriate compensation by the endogenous antioxidant defense network, increased oxidative stress leads to the activation of stress-sensitive intracellular signaling pathways and the formation of gene products that cause cellular damage and contribute to the vascular complications of diabetes. It has recently been suggested that diabetic subjects with vascular complications may have a defective cellular antioxidant response against the oxidative stress generated by hyperglycemia. This raises the concept that antioxidant therapy may be of great benefit to these subjects. Although our understanding of how hyperglycemia-induced oxidative stress ultimately leads to tissue damage has advanced considerably in recent years, effective therapeutic strategies to prevent or delay the development of this damage remain limited. Thus, further investigation of therapeutic interventions to prevent or delay the progression of diabetic vascular complications is needed.

Analysis of myosin-V immunoreactive myenteric neurons from arthritic rats

CONTEXT

The inflammatory response itself and the consequent oxidative stress are able to promote neurodegeneration. So, it is possible that enteric nervous system is affected by inflammatory diseases threatening quality of life of patients. However, gastrointestinal symptoms of arthritis are usually attributed to anti-inflammatory drugs rather than neural damage.

OBJECTIVE

To confirm if the general population of myenteric neurons from the ileum and jejunum of rats is affected by arthritis.

METHODS

Twenty Holtzmann rats, 58-day-old male, were used and divided in four groups: control group (C30), arthritic group (Art30), older control group (C60) and older arthritic group (Art60). At 58 days old, the animals in groups Art30 and Art60 received an injection of the complete Freund's adjuvant in order to induce arthritis. The whole-mount preparations of ileum and jejunum were processed for myosin-V immunohistochemistry. Quantitative and morphometric analyses were performed.

RESULTS

Groups Art30 and Art60 presented, respectively, a reduction of 2% and 6% in intestinal area when compared to their control groups. No significant differences were observed in general neuronal density among the four groups (P>0.05). Group C60 presented a reduction of 14.4% and 10.9% in mean neuronal cell body area when compared to group C30 (P<0.05), for the ileum and jejunum, respectively. The other groups had a similar mean neuronal cell body area (P>0.05).

CONCLUSION

Arthritis does not promote quantitative or morphological damages in general myenteric population. However, studies in progress have revealed some significant alterations in myenteric neurons subpopulations (nitrergic and VIP-ergic neurons).

17β-estradiol protects Schwann cells against H2O2-induced cytotoxicity and increases transplanted Schwann cell survival in a cervical hemicontusion spinal cord injury model

Schwann cell (SC) transplantation is a promising repair strategy after spinal cord injury (SCI); however, a large number of SCs do not survive following transplantation. Previous studies have shown that 17β-estradiol (E2) protects several cell types against cytotoxicity. Thus, this study evaluated the protective potential of E2 on SCs in vitro and investigated the effect of E2 on transplanted SC survival in a rat model of SCI. Primary SC cultures were found to robustly express estrogen receptors (ER) and incubation with E2 protected SCs against hydrogen peroxide-induced cell death. This protection was not inhibited by the ER antagonist ICI 182,780, suggesting that genomic signaling is not necessary for protection. In a subsequent experiment, cervical hemicontusion SCI was induced in male rats followed by sustained administration of E2 or placebo. Eight days after SCI, SCs were transplanted into the injury epicenter. E2 treatment significantly increased the number of surviving labeled transplanted SCs evaluated 7 days after transplantation. These data demonstrate that E2 protects SCs against oxidative stress and improves transplanted SC survival, which suggests that E2 administration may be an intervention of choice for enhancing survival of transplanted SCs after SCI.

Chronic treatment of silymarin improves hyperalgesia and motor nerve conduction velocity in diabetic neuropathic rat

The effect of chronic silymarin (SM) treatment on hyperalgesia, sciatic motor nerve conduction velocity (MNCV) and oxidative stress in streptozotocin (STZ)-diabetic neuropathic rat was evaluated. Rats were divided into control, diabetic, SM-treated control and diabetic, and sodium salisylate (SS)-treated control and diabetic. SM was administered daily at a dose of 100 mg/kg for two months. Finally, hyperalgesia and sciatic MNCV and oxidative stress markers were assessed. Diabetic rats showed a significant deficit in MNCV and markedly exhibited chemical and thermal hyperalgesia, indicating development of diabetic neuropathy. Antioxidant enzyme superoxide dismutase (SOD) level significantly reduced and malondialdehyde (MDA) level significantly increased in diabetic rats compared to control rats; SM treatment significantly ameliorated the alteration in MNCV, hyperalgesia, MDA level and antioxidant enzyme SOD in diabetic rats. These results clearly suggest the potential effect of SM in prevention and treatment of diabetic neuropathy.