Neurophysiological changes in the central and peripheral nervous system of streptozotocin-diabetic rats. Course of development and effects of insulin treatment

Electrophysiological evidence of diabetes' impacts on central conduction recoveries in degenerative cervical myelopathy after surgery

OBJECTIVES

To assess the impact of diabetes mellitus (DM) on the postoperative motor and somatosensory functional recoveries of degenerative cervical myelopathy (DCM) patients.

METHODS

Motor and somatosensory evoked potentials (MEP and SSEPs) and modified Japanese Orthopedic Association (mJOA) scores were recorded in 27 diabetic (DCM-DM group) and 38 non-diabetic DCM patients (DCM group) before and 1 year after surgery. The central motor (CMCT) and somatosensory (CSCT) conduction time were recorded to evaluate the conductive functions of the spinal cord.

RESULTS

The mJOA scores, CMCT and CSCT improved (t test, p < 0.05) in both of the DCM-DM and DCM groups 1 year after surgery. The mJOA recovery rate (RR) and CSCT recovery ratio were significantly worse (t test, p < 0.05) in the DCM-DM group compared to the DCM group. DM proved to be a significant independent risk factor for poor CSCT recovery (OR = 4.52, 95% CI 2.32-7.12) after adjusting for possible confounding factors. In DCM-DM group, CSCT recovery ratio was also correlated with preoperative HbA1 level (R =  - 0.55, p = 0.003). Furthermore, DM duration longer than 10 years and insulin dependence were risk factors for lower mJOA, CMCT and CSCT recoveries among all DCM-DM patients (t test, p < 0.05).

CONCLUSIONS

DM may directly hinders spinal cord conduction recovery in DCM patients after surgery. Corticospinal tract impairments are similar between DCM and DCM-DM patients, but significantly worsened in chronic or insulin-dependent DM patients. The dorsal column is more sensitively affected in all DCM-DM patients. Deeper investigation into the mechanisms and neural regeneration strategies is needed.

Is diabetes the risk factor for poor neurological recovery after cervical spine surgery? A review of the literature

The poor prognosis of cervical spine surgery is mainly manifested as poor neurological recovery and the presence of new upper extremity dysfunction that promotes significant psychological and physiological burdens on patients. Many factors influence the prognosis of cervical spine surgery, including the age of patients, the time and mode of surgery, and the surgical technique used. However, in clinical studies, it has been observed that patients with diabetes have a higher probability of poor prognosis after surgery. Therefore, we review the pathophysiology of diabetic neuropathies and discuss its impact on cervical nerve system function, especially in cervical nerve roots and upper limb peripheral nerve conduction.

A Risk Calculator for the Prediction of C5 Nerve Root Palsy After Instrumented Cervical Fusion

BACKGROUND

C5 palsy is a common postoperative complication after cervical fusion and is associated with increased health care costs and diminished quality of life. Accurate prediction of C5 palsy may allow for appropriate preoperative counseling and risk stratification. We primarily aim to develop an algorithm for the prediction of C5 palsy after instrumented cervical fusion and identify novel features for risk prediction. Additionally, we aim to build a risk calculator to provide the risk of C5 palsy.

METHODS

We identified adult patients who underwent instrumented cervical fusion at a tertiary care medical center between 2013 and 2020. The primary outcome was postoperative C5 palsy. We developed ensemble machine learning, standard machine learning, and logistic regression models predicting the risk of C5 palsy-assessing discrimination and calibration. Additionally, a web-based risk calculator was built with the best-performing model.

RESULTS

A total of 1024 patients were included, with 52 cases of C5 palsy. The ensemble model was well-calibrated and demonstrated excellent discrimination with an area under the receiver-operating characteristic curve of 0.773. The following features were the most important for ensemble model performance: diabetes mellitus, bipolar disorder, C5 or C4 level, surgical approach, preoperative non-motor neurologic symptoms, degenerative disease, number of fused levels, and age.

CONCLUSIONS

We report a risk calculator that generates patient-specific C5 palsy risk after instrumented cervical fusion. Individualized risk prediction for patients may facilitate improved preoperative patient counseling and risk stratification as well as potential intraoperative mitigating measures. This tool may also aid in addressing potentially modifiable risk factors such as diabetes and obesity.

Surgical Procedures Required for Measurement Reduce Nerve Conduction Velocity: An In Vivo and In Vitro Comparative Study

Background: Although in vitro methods have disadvantages, they are still commonly used to measure nerve conduction velocity (NCV) in experimental studies. Therefore, this study was designed to demonstrate the effect of the surgical procedures required for in vitro methods on nerve fibers and the effect of in vivo and in vitro methods on the results of electrophysiological measurements.Methods: Rats were assigned to the in vivo (control-1, injury-1, and diabetic-1) and in vitro (control-2, injury-2, and diabetic-2) groups. The NCV and compound action potential amplitudes were measured, and the nerve fibers were histologically examined.Results: Damaged axons and myelin sheaths were observed in the control-2 group. The electrophysiological values of the in vitro groups were lower than those of the in vivo groups. Furthermore, these values were lower for the diabetic and injury groups than for the control groups.Conclusions: This study showed that the surgical procedures required for the in vitro method reduced the measured values. Owing to the previous and current disadvantages of the in vitro method, the in vivo method was more sensitive for the NCV measurement. Moreover, measurements can be performed using the current in vivo method for small nerve fibers.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Diabetes-induced auditory complications: are they preventable? a comprehensive review of interventions

Diabetes mellitus is a chronic metabolic disorder characterized by elevated blood glucose levels, which, over time, lead to major chronic complications in various organs of the body. A growing body of research suggests that diabetes could also result in degenerative changes in the auditory system. To date, several attempts have been made to prevent and reduce diabetes-induced auditory complications. Such attempts have generally focused on disease modifying as well as other pharmacological treatments involving several herbal and non-herbal agents such as vitamins C and E, rutin, resveratrol, coffee, trigonelline, Dioscorea nipponica, red ginseng, Pterostilbene Bofutsushosan, Daisaikoto, tolrestat, ACE inhibitors (enalapril), Ca antagonists (nimodipine), Lipo-prostaglandin E1, methylprednisolone, dexamethasone, and chlorogenic acid and also other strategies like acupuncture. However, there is no consensus about which are the most effective strategies for preventing and reducing auditory complications in diabetic patients with few side effects and maximum efficacy. This paper provides a comprehensive review of interventions for preventing and treating diabetes-induced auditory complications to help therapists.

Diabetes Mellitus-Related Dysfunction of the Motor System

Although motor deficits in humans with diabetic neuropathy have been extensively researched, its effect on the motor system is thought to be lesser than that on the sensory system. Therefore, motor deficits are considered to be only due to sensory and muscle impairment. However, recent clinical and experimental studies have revealed that the brain and spinal cord, which are involved in the motor control of voluntary movement, are also affected by diabetes. This review focuses on the most important systems for voluntary motor control, mainly the cortico-muscular pathways, such as corticospinal tract and spinal motor neuron abnormalities. Specifically, axonal damage characterized by the proximodistal phenotype occurs in the corticospinal tract and motor neurons with long axons, and the transmission of motor commands from the brain to the muscles is impaired. These findings provide a new perspective to explain motor deficits in humans with diabetes. Finally, pharmacological and non-pharmacological treatment strategies for these disorders are presented.

n-3 Fatty Acid and Its Metabolite 18-HEPE Ameliorate Retinal Neuronal Cell Dysfunction by Enhancing Müller BDNF in Diabetic Retinopathy

Diabetic retinopathy (DR) is a widespread vision-threatening disease, and neuroretinal abnormality should be considered as an important problem. Brain-derived neurotrophic factor (BDNF) has recently been considered as a possible treatment to prevent DR-induced neuroretinal damage, but how BDNF is upregulated in DR remains unclear. We found an increase in hydrogen peroxide (H₂O₂) in the vitreous of patients with DR. We confirmed that human retinal endothelial cells secreted H₂O₂ by high glucose, and H₂O₂ reduced cell viability of MIO-M1, Müller glia cell line, PC12D, and the neuronal cell line and lowered BDNF expression in MIO-M1, whereas BDNF administration recovered PC12D cell viability. Streptozocin-induced diabetic rats showed reduced BDNF, which is mainly expressed in the Müller glia cell. Oral intake of eicosapentaenoic acid ethyl ester (EPA-E) ameliorated BDNF reduction and oscillatory potentials (OPs) in electroretinography (ERG) in DR. Mass spectrometry revealed an increase in several EPA metabolites in the eyes of EPA-E-fed rats. In particular, an EPA metabolite, 18-hydroxyeicosapentaenoic acid (18-HEPE), induced BDNF upregulation in Müller glia cells and recovery of OPs in ERG. Our results indicated diabetes-induced oxidative stress attenuates neuroretinal function, but oral EPA-E intake prevents retinal neurodegeneration via BDNF in Müller glia cells by increasing 18-HEPE in the early stages of DR.

Gamma-aminobutyric acid-producing lactobacilli positively affect metabolism and depressive-like behaviour in a mouse model of metabolic syndrome

Metabolic and neuroactive metabolite production represents one of the mechanisms through which the gut microbiota can impact health. One such metabolite, gamma-aminobutyric acid (GABA), can modulate glucose homeostasis and alter behavioural patterns in the host. We previously demonstrated that oral administration of GABA-producing Lactobacillus brevis DPC6108 has the potential to increase levels of circulating insulin in healthy rats. Therefore, the objective of this study was to assess the efficacy of endogenous microbial GABA production in improving metabolic and behavioural outcomes in a mouse model of metabolic dysfunction. Diet-induced obese and metabolically dysfunctional mice received one of two GABA-producing strains, L. brevis DPC6108 or L. brevis DSM32386, daily for 12 weeks. After 8 and 10 weeks of intervention, the behavioural and metabolic profiles of the mice were respectively assessed. Intervention with both L. brevis strains attenuated several abnormalities associated with metabolic dysfunction, causing a reduction in the accumulation of mesenteric adipose tissue, increased insulin secretion following glucose challenge, improved plasma cholesterol clearance and reduced despair-like behaviour and basal corticosterone production during the forced swim test. Taken together, this exploratory dataset indicates that intervention with GABA-producing lactobacilli has the potential to improve metabolic and depressive- like behavioural abnormalities associated with metabolic syndrome in mice.

BDNF Alleviates Neuroinflammation in the Hippocampus of Type 1 Diabetic Mice via Blocking the Aberrant HMGB1/RAGE/NF-κB Pathway

Diabetes is a systemic disease that can cause brain damage such as synaptic impairments in the hippocampus, which is partly because of neuroinflammation induced by hyperglycemia. Brain-derived neurotrophic factor (BDNF) is essential in modulating neuroplasticity. Its role in anti-inflammation in diabetes is largely unknown. In the present study, we investigated the effects of BDNF overexpression on reducing neuroinflammation and the underlying mechanism in mice with type 1 diabetes induced by streptozotocin (STZ). Animals were stereotactically microinjected in the hippocampus with recombinant adeno-associated virus (AAV) expressing BDNF or EGFP. After virus infection, four groups of mice, the EGFP+STZ, BDNF+STZ, EGFP Control and BDNF Control groups, received STZ or vehicle treatment as indicated. Three weeks later brain tissues were collected. We found that BDNF overexpression in the hippocampus significantly rescued STZ-induced decreases in mRNA and protein expression of two synaptic plasticity markers, spinophilin and synaptophysin. More interestingly, BDNF inhibited hyperglycemia-induced microglial activation and reduced elevated levels of inflammatory factors (TNF-α, IL-6). BDNF blocked the increase in HMGB1 levels and specifically, in levels of one of the HMGB1 receptors, RAGE. Downstream of HMGB1/RAGE, the increase in the protein level of phosphorylated NF-κB was also reversed by BDNF in STZ-treated mice. These results show that BDNF overexpression reduces neuroinflammation in the hippocampus of type 1 diabetic mice and suggest that the HMGB1/RAGE/NF-κB signaling pathway may contribute to alleviation of neuroinflammation by BDNF in diabetic mice.

Suppressing Interferon-γ Stimulates Microglial Responses and Repair of Microbleeds in the Diabetic Brain

Microcirculatory damage is a common complication for those with vascular risk factors, such as diabetes. To resolve vascular insults, the brain's immune cells (microglia) must rapidly envelop the site of injury. Currently, it is unknown whether Type 1 diabetes, a condition associated with chronic immune system dysfunction, alters microglial responses to damage and what mechanisms are responsible. Using in vivo two-photon microscopy in adult male mice, we show that microglial envelopment of laser-induced cerebral microbleeds is diminished in a hyperglycemic mouse model of Type 1 diabetes, which could not be fully rescued with chronic insulin treatment. Microglia were important for vessel repair because reduced microglial accumulation in diabetic mice or near-complete depletion in healthy controls was associated with greater secondary leakage of the damaged vessel. Broadly suppressing inflammation with dexamethasone in diabetic mice but not healthy controls, significantly enhanced microglial responses to microbleeds and attenuated secondary vessel leakage. These enhancements were associated with changes in IFN-γ signaling because dexamethasone suppressed abnormally high levels of IFN-γ protein levels in brain and blood serum of diabetic mice. Further, blocking IFN-γ in diabetic mice with neutralizing antibodies restored normal microglial chemotaxic responses and purinoceptor P2ry12 gene expression, as well as mitigated secondary leakage. These results suggest that abnormal IFN-γ signaling disrupts microglial function in the diabetic brain, and that immunotherapies targeting IFN-γ can stimulate microglial repair of damaged vessels.SIGNIFICANCE STATEMENT Although Type 1 diabetes is an established risk factor for vascular complications, such as microbleeds, and is known to hinder wound healing in the body, no study has examined how diabetes impacts the brain's innate immune reparative response (involving cells called microglia) to vascular injury. Here we show that microglial responses to brain microbleeds were diminished in diabetic animals, which also exacerbated secondary leakage from damaged vessels. These impairments were related to abnormally high levels of the proinflammatory cytokine IFN-γ because reducing IFN-γ with immunosuppressant drugs or blocking antibodies helped restore normal microglial responses and repair of damaged vessels. These data highlight the use of IFN-γ modulating therapeutics to enhance vascular repair in at-risk populations.

Stroke Outcome and Determinants among Patients with and without Diabetes in a Tertiary Hospital in Ghana

BACKGROUND

Diabetes mellitus, a well-established independent risk factor for stroke, has varied association with stroke outcome from previous studies. This study investigated stroke outcome and determinants among patients with and without diabetes in a tertiary hospital in Ghana.

METHODS

A prospective study conducted among stroke patients with and without diabetes admitted in a Ghanaian tertiary hospital. Baseline clinical and biochemical data were documented. Functional stroke outcome was evaluated at 1, 3, and 6 months after stroke using the modified Rankin Scale.

RESULTS

Number of participants enrolled were 326 and 105 (32.20%) had diabetes. Higher proportions of diabetes patients had poor functional stroke outcome at 1, 3, and 6 months (79%, 75.23%, 73.33%) compared with those without diabetes (70.13%, 65.16, 61.99) (p>0.05). Stroke patients with diabetes had lower survival compared with those without diabetes (p=0.0745). Mortality at 6 months was more likely among ischaemic stroke patients with diabetes compared with those without diabetes (Odds Ratio 2.037; CI: 1.058-3.923). Determinants of poor functional stroke outcome for diabetes patients were older age (Adjusted Odds Ratio (AOR)-1.07; CI-1.03-1.12), female gender (AOR-3.74; CI-1.26-12.65), and pneumonia (AOR-11.32; CI-1.93-220.05) whereas the determinants for those without diabetes were unemployment (AOR-4.19; CI-1.24-19.50), speech abnormalities (AOR-1.99; CI1.08-3.73), and pneumonia (AOR-4.05; CI-1.83-9.77). High fasting plasma glucose (HR-1.15; CI-1.07-1.23), elevated temperature (HR-1.41; CI-1.11-1.79), and pneumonia (HR-2.25; CI-1.44-3.50) were determinants of low survival among all stroke patients.

CONCLUSION

Trends towards poorer functional outcome and reduced survival were found among Ghanaian stroke patients with diabetes compared with those without diabetes. Older age, female gender, pneumonia, elevated temperature, and fasting plasma glucose were determinants of adverse outcome in stroke patients with diabetes.

Neuroactive Steroids and Sex-Dimorphic Nervous Damage Induced by Diabetes Mellitus

Diabetes mellitus is a metabolic disease where improper glycaemic control may induce severe complications in different organs. In this review, we will discuss alterations occurring in peripheral and central nervous system of patients with type 1 (i.e., insulin dependent diabetes mellitus,) or type 2 diabetes (i.e., non-insulin dependent diabetes mellitus), as well as related experimental models. A particular focus will be on the role exerted by neuroactive steroids (i.e., important regulators of nervous functions) in the nervous damage induced by diabetes. Indeed, the nervous levels of these molecules are affected by the pathology and, in agreement, their neuroprotective effects have been reported. Interestingly, the sex is another important variable. As discussed, nervous diabetic complications show sex dimorphic features in term of incidence, functional outcomes and neuroactive steroid levels. Therefore, these features represent an interesting background for possible sex-oriented therapies with neuroactive steroids aimed to counteract nervous damage observed in diabetic pathology.

Integrated bioinformatic changes and analysis of retina with time in diabetic rats

Diabetic retinopathy (DR) is the most common chronic complication of diabetes. It can cause impaired vision and even blindness. However, the pathological mechanism of DR is still unknown. In the present study, we use bioinformatic analysis to reveal the pathological changes of early DR in a streptozotocin (STZ) induced diabetes rat model. The dataset GSE28831 was downloaded from the Gene Expression Omnibus (GEO) database. To clarify the pathological mechanism of early DR, genes which were up-regulated (UP group) or down-regulated (DOWN group) over time were identified. One hundred eighty six genes in the UP group and 85 genes in the DOWN group were defined. There were in total 28 Gene ontology (GO) terms with a P value lower than 0.05 in UP group, including astrocyte development, neutrophil chemotaxis, neutrophil aggregation, mesenchymal cell proliferation and so on. In the DOWN group, there were totally 14 GO terms with a P value lower than 0.05, including visual perception, lens development in camera-type eye, camera-type eye development, bicellular tight junction and so on. Signaling pathways were analyzed with all genes in the UP and DOWN groups, and leukocyte transendothelial migration and tight junction were selected. Protein–protein interaction (PPI) network was constructed and six hub genes Diras3, Actn1, Tssk6, Cnot6l, Tek and Fgf4 were selected with connection degree ≥5. S100a8, S100a9 and Tek may be potential targets for DR diagnosis and treatment. This study provides the basis for the diagnosis and treatment of DR in the future.

Effect of streptozotocin-induced diabetes on motor representations in the motor cortex and corticospinal tract in rats

Motor disorders in patients with diabetes are associated with diabetic peripheral neuropathy, which can lead to symptoms such as lower extremity weakness. However, it is unclear whether central motor system disorders can disrupt motor function in patients with diabetes. In a streptozotocin-induced rat model of type 1 diabetes, we used intracortical microstimulation to evaluate motor representations in the motor cortex, recorded antidromic motor cortex responses to spinal cord stimulation to evaluate the function of corticospinal tract (CST) axons, and used retrograde labeling to evaluate morphological alterations of CST neurons. The diabetic rats exhibited size reductions in the hindlimb area at 4 weeks and in trunk and forelimb areas after 13 weeks, with the hindlimb and trunk area reductions being the most severe. Other areas were unaffected. Additionally, we observed reduced antidromic responses in CST neurons with axons projecting to lumbar spinal segments (CST-L) but not in those with axons projecting to cervical segments (CST-C). This was consistent with the observation that retrograde-labeled CST-L neurons were decreased in number following tracer injection into the spinal cord in diabetic animals but that CST-C neurons were preserved. These results show that diabetes disrupts the CST system components controlling hindlimb and trunk movement. This disruption may contribute to lower extremity weakness in patients.

Neuroactive steroids and diabetic complications in the nervous system

Important complications of diabetes mellitus in the nervous system are represented by diabetic peripheral neuropathy and diabetic encephalopathy. In this context, an important link is represented by neuroactive steroids (i.e., steroids coming from peripheral glands and affecting nervous functionality as well as directly synthesized in the nervous system). Indeed, diabetes does not only affect the reproductive axis and consequently the levels of sex steroid hormones, but also those of neuroactive steroids. Indeed, as will be here summarized, the levels of these neuromodulators present in the central and peripheral nervous system are affected by the pathology in a sex-dimorphic way. In addition, some of these neuroactive steroids, such as the metabolites of progesterone or testosterone, as well as pharmacological tools able to increase their levels have been demonstrated, in experimental models, to be promising protective agents against diabetic peripheral neuropathy and diabetic encephalopathy.

Proximal Neuropathy and Associated Skeletal Muscle Changes Resembling Denervation Atrophy in Hindlimbs of Chronic Hypoglycaemic Rats

Peripheral neuropathy is one of the most common complications of diabetic hyperglycaemia. Insulin-induced hypoglycaemia (IIH) might potentially exacerbate or contribute to neuropathy as hypoglycaemia also causes peripheral neuropathy. In rats, IIH induces neuropathy associated with skeletal muscle changes. Aims of this study were to investigate the progression and sequence of histopathologic changes caused by chronic IIH in rat peripheral nerves and skeletal muscle, and whether such changes were reversible. Chronic IIH was induced by infusion of human insulin, followed by an infusion-free recovery period in some of the animals. Sciatic, plantar nerves and thigh muscle were examined histopathologically after four or eight weeks of infusion and after the recovery period. IIH resulted in high incidence of axonal degeneration in sciatic nerves and low incidence in plantar nerves indicating proximo-distal progression of the neuropathy. The neuropathy progressed in severity (sciatic nerve) and incidence (sciatic and plantar nerve) with the duration of IIH. The myopathy consisted of groups of angular atrophic myofibres which resembled histopathologic changes classically seen after denervation of skeletal muscle, and severity of the myofibre atrophy correlated with severity of axonal degeneration in sciatic nerve. Both neuropathy and myopathy were still present after four weeks of recovery, although the neuropathy was less severe. In conclusion, the results suggest that peripheral neuropathy induced by IIH progresses proximo-distally, that severity and incidence increase with duration of the hypoglycaemia and that these changes are partially reversible within four weeks. Furthermore, IIH-induced myopathy is most likely secondary to the neuropathy.

Effect of Salacia reticulata W. and Clitoria ternatea L. on the cognitive and behavioral changes in the streptozotocin-induced young diabetic rats

BACKGROUND

Diabetes mellitus (DM) of juvenile onset affects both the peripheral and central nervous systems (CNS). However, central effects are less documented and studied than peripheral deficits. Currently, the only feasible treatment available for type 1 DM (T1DM) is insulin which has its own limitations. Hence, an alternative therapy, especially a newer herbal formulation is very much the need of the time. The present study aimed to determine the effects of the alcoholic extracts of roots of the Salacia reticulata W. (SR) and Clitoria ternatea L. (CT) on cognitive and behavioral changes in juvenile diabetic rats.

METHODS

Diabetes was induced in 25-day-old Wistar rats by streptozotocin (50 mg/kg bw, IP). Animals were divided into seven groups (n=6). Rats were treated with root extracts of SR and CT (100 mg/kg BW each) for 30 days, from day 1 and day 20 of diabetes confirmation. Then, rats were tested in elevated plus maze (EPM) and Morris water maze (MWM).

RESULTS

A statistically significant (p<0.05) difference was observed between the SRCT group and diabetic groups of rats. Apart from decreasing FBS, the combined therapy also proved beneficial as nootropic agent in rats with early-onset diabetes. However, significant improvement is observed only in the learning and memory among preventive group, but not in the curative group.

CONCLUSIONS

SRCT, a herbal formula, when used in combination, has a more potent effect in preventing the deleterious effects of juvenile diabetes on cognitive and behavioral changes.

Administration of Zinc plus Cyclo-(His-Pro) Increases Hippocampal Neurogenesis in Rats during the Early Phase of Streptozotocin-Induced Diabetes

The effects of zinc supplementation on hippocampal neurogenesis in diabetes mellitus have not been studied. Herein, we investigated the effects of zinc plus cyclo-(His-Pro) (ZC) on neurogenesis occurring in the subgranular zone of dentate gyrus after streptozotocin (STZ)-induced diabetes. ZC (27 mg/kg) was administered by gavage once daily for one or six weeks from the third day after the STZ injection, and histological evaluation was performed at 10 (early phase) or 45 (late phase) days after STZ injection. We found that the proliferation of progenitor cells in STZ-induced diabetic rats showed an increase in the early phase. Additionally, ZC treatment remarkably increased the number of neural progenitor cells (NPCs) and immature neurons in the early phase of STZ-induced diabetic rats. Furthermore, ZC treatment showed increased survival rate of newly generated cells but no difference in the level of neurogenesis in the late phase of STZ-induced diabetic rats. The present study demonstrates that zinc supplementation by ZC increases both NPCs proliferation and neuroblast production at the early phase of diabetes. Thus, this study suggests that zinc supplemented with a histidine/proline complex may have beneficial effects on neurogenesis in patients experiencing the early phase of Type 1 diabetes.

Pain modulation from the brain during diabetic neuropathy: Uncovering the role of the rostroventromedial medulla

Diabetic neuropathy has a profound impact in the quality of life of patients who frequently complain of pain. The mechanisms underlying diabetic neuropathic pain (DNP) are no longer ascribed only to damage of peripheral nerves. The effects of diabetes at the central nervous system are currently considered causes of DPN. Management of DNP may be achieved by antidepressants that act on serotonin (5-HT) uptake, namely specific serotonin reuptake inhibitors. The rostroventromedial medulla (RVM) is a key pain control center involved in descending pain modulation at the spinal cord through local release of 5-HT and plays a peculiar role in the balance of bidirectional control (i.e. inhibitory and facilitatory) from the brain to the spinal cord. This review discusses recently uncovered neurobiological mechanisms that mediate nociceptive modulation from the RVM during diabetes installation. In early phases of the disease, facilitation of pain modulation from the RVM prevails through a triplet of mechanisms which include increase in serotonin expression at the RVM and consequent rise of serotonin levels at the spinal cord and upregulation of local facilitatory 5HT3 receptors, enhancement of spontaneous activity of facilitatory RVM neurons and up-regulation of the expression of transient receptor potential vanilloid type 1 (TRPV1) receptor. With the progression of diabetes the alterations in the RVM increase dramatically, with oxidative stress and neuronal death associated to microglia-mediated inflammation. In a manner similar to other central areas, like the thalamus, the RVM is likely to be a "pain generator/amplifier" during diabetes, accounting to increase DNP. Early interventions in DNP prevention using strategies that simultaneously tackle the exacerbation of 5-HT3 spinal receptors and of microglial RVM activity, namely those that increase the levels of anti-inflammatory cytokines, should be considered in the future of DNP treatment.

Diabetes and cervical myelopathy

Diabetes may affect the typical physical findings associated with cervical spondylotic myelopathy, as coexisting diabetic neuropathy may dampen expected hyperreflexia and also produce non-dermatomal extremity numbness. Most large studies of surgically treated diabetic patients with cervical spondylotic myelopathy have focused upon infection rates rather than exploring any differences in the presenting physical signs. We conducted a retrospective study of the pattern of presenting neurological signs and symptoms and of the clinical outcomes in 438 patients surgically treated for cervical spondylotic myelopathy, 79 of whom had diabetes. Compared with non-diabetic patients, those with diabetes were slightly older and had lower preoperative modified Japanese Orthopaedic Association (mJOA) scores. Those with diabetes also had a significantly higher incidence of hyporeflexia and a higher incidence of a positive Babinski sign, but there was no difference in the appearance of the Hoffman sign. The magnitude of mJOA improvement after surgery was comparable. We conclude that diabetes may alter the typical signs and symptoms of cervical spondylotic myelopathy and suggest that knowledge of the differences may aid in securing a prompt and accurate diagnosis.

Challenges and issues with streptozotocin-induced diabetes - A clinically relevant animal model to understand the diabetes pathogenesis and evaluate therapeutics

Streptozotocin (STZ) has been extensively used over the last three decades to induce diabetes in various animal species and to help screen for hypoglycemic drugs. STZ induces clinical features in animals that resemble those associated with diabetes in humans. For this reason STZ treated animals have been used to study diabetogenic mechanisms and for preclinical evaluation of novel antidiabetic therapies. However, the physiochemical characteristics and associated toxicities of STZ are still major obstacles for researchers using STZ treated animals to investigate diabetes. Another major challenges in STZ-induced diabetes are sustaining uniformity, suitability, reproducibility and induction of diabetes with minimal animal lethality. Lack of appropriate use of STZ was found to be associated with increased mortality and animal suffering. During STZ use in animals, attention should be paid to several factors such as method of preparation of STZ, stability, suitable dose, route of administration, diet regimen, animal species with respect to age, body weight, gender and the target blood glucose level used to represent hyperglycemia. Therefore, protocol for STZ-induced diabetes in experimental animals must be meticulously planned. This review highlights specific skills and strategies involved in the execution of STZ-induced diabetes model. The present review aims to provide insight into diabetogenic mechanisms of STZ, specific toxicity of STZ with its significance and factors responsible for variations in diabetogenic effects of STZ. Further this review also addresses ways to minimize STZ-induced mortality, suggests methods to improve STZ-based experimental models and best utilize them for experimental studies purported to understand diabetes pathogenesis and preclinical evaluation of drugs.

Metabolic Alterations Associated to Brain Dysfunction in Diabetes

From epidemiological studies it is known that diabetes patients display increased risk of developing dementia. Moreover, cognitive impairment and Alzheimer's disease (AD) are also accompanied by impaired glucose homeostasis and insulin signalling. Although there is plenty of evidence for a connection between insulin-resistant diabetes and AD, definitive linking mechanisms remain elusive. Cerebrovascular complications of diabetes, alterations in glucose homeostasis and insulin signalling, as well as recurrent hypoglycaemia are the factors that most likely affect brain function and structure. While difficult to study in patients, the mechanisms by which diabetes leads to brain dysfunction have been investigated in experimental models that display phenotypes of the disease. The present article reviews the impact of diabetes and AD on brain structure and function, and discusses recent findings from translational studies in animal models that link insulin resistance to metabolic alterations that underlie brain dysfunction. Such modifications of brain metabolism are likely to occur at early stages of neurodegeneration and impact regional neurochemical profiles and constitute non-invasive biomarkers detectable by magnetic resonance spectroscopy (MRS).

VEGF can protect against blood brain barrier dysfunction, dendritic spine loss and spatial memory impairment in an experimental model of diabetes

Clinical and experimental studies have shown a clear link between diabetes, vascular dysfunction and cognitive impairment. However, the molecular underpinnings of this association remain unclear. Since vascular endothelial growth factor (VEGF) signaling is important for maintaining vascular integrity and function, we hypothesized that vascular and cognitive impairment in the diabetic brain could be related to a deficiency in VEGF signaling. Here we show that chronic hyperglycemia (~8weeks) in a mouse model of type 1 diabetes leads to a selective reduction in the expression of VEGF and its cognate receptor (VEGF-R2) in the hippocampus. Correlating with this, diabetic mice showed selective deficits in spatial memory in the Morris water maze, increased vessel area, width and permeability in the dentate gyrus/CA1 region of the hippocampus and reduced spine densities in CA1 neurons. Chronic low dose infusion of VEGF in diabetic mice was sufficient to restore VEGF signaling, protect them from memory deficits, as well as vascular and synaptic abnormalities in the hippocampus. These findings suggest that a hippocampal specific reduction in VEGF signaling and resultant vascular/neuronal defects may underlie early manifestations of cognitive impairment commonly associated with diabetes. Furthermore, restoring VEGF signaling may be a useful strategy for preserving hippocampal-related brain circuitry in degenerative vascular diseases.

Neuroactive steroid treatment modulates myelin lipid profile in diabetic peripheral neuropathy

Diabetic peripheral neuropathy causes a decrease in the levels of dihydroprogesterone and 5α-androstane-3α,17β-diol (3α-diol) in the peripheral nerves. These two neuroactive steroids exert protective effects, by mechanisms that still remain elusive. We have previously shown that the activation of Liver X Receptors improves the peripheral neuropathic phenotype in diabetic rats. This protective effect is accompanied by the restoration to control values of the levels of dihydroprogesterone and 3α-diol in peripheral nerves. In addition, activation of these receptors decreases peripheral myelin abnormalities by improving the lipid desaturation capacity, which is strongly blunted by diabetes, and ultimately restores the myelin lipid profile to non-diabetic values. On this basis, we here investigate whether dihydroprogesterone or 3α-diol may exert their protective effects by modulating the myelin lipid profile. We report that both neuroactive steroids act on the lipogenic gene expression profile in the sciatic nerve of diabetic rats, reducing the accumulation of myelin saturated fatty acids and promoting desaturation. These changes were associated with a reduction in myelin structural alterations. These findings provide evidence that dihydroprogesterone and 3α-diol are protective agents against diabetic peripheral neuropathy by regulating the de novo lipogenesis pathway, which positively influences myelin lipid profile.

Effect of insulin-induced hypoglycaemia on the peripheral nervous system: focus on adaptive mechanisms, pathogenesis and histopathological changes

Insulin-induced hypoglycaemia (IIH) is a common acute side effect in type 1 and type 2 diabetic patients, especially during intensive insulin therapy. The peripheral nervous system (PNS) depends on glucose as its primary energy source during normoglycaemia and, consequently, it may be particularly susceptible to IIH damage. Possible mechanisms for adaption of the PNS to IIH include increased glucose uptake, utilisation of alternative energy substrates and the use of Schwann cell glycogen as a local glucose reserve. However, these potential adaptive mechanisms become insufficient when the hypoglycaemic state exceeds a certain level of severity and duration, resulting in a sensory-motor neuropathy with associated skeletal muscle atrophy. Large myelinated motor fibres appear to be particularly vulnerable. Thus, although the PNS is not an obligate glucose consumer, as is the brain, it appears to be more prone to IIH than the central nervous system when hypoglycaemia is not severe (blood glucose level ≤ 2 mm), possibly reflecting a preferential protection of the brain during periods of inadequate glucose availability. With a primary focus on evidence from experimental animal studies investigating nondiabetic IIH, the present review discusses the effect of IIH on the PNS with a focus on adaptive mechanisms, pathogenesis and histological changes.

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.

Alzheimer disease: An interactome of many diseases

Alzheimer Disease (AD) is an outcome as well as source of many diseases. Alzheimer is linked with many other diseases like Diabetes type 2, cholesterolemia, hypertension and many more. But how each of these diseases affecting other is still unknown to scientific community. Signaling Pathways of one disease is interlinked with other disease. But to what extent healthy brain is affected when any signaling in human body is disturbed is the question that matters. There is a need of Pathway analysis, Protein-Protein interaction (PPI) and the conserved interactome study in AD and linked diseases. It will be helpful in finding the potent drug or vaccine target in conscious manner. In the present research the Protein-Protein interaction of all the proteins involved in Alzheimer Disease is analyzed using ViSANT and osprey tools and pathway analysis further reveals the significant genes/proteins linking AD with other diseases.

Epidermal growth factor receptor inhibitor ameliorates excessive astrogliosis and improves the regeneration microenvironment and functional recovery in adult rats following spinal cord injury

BACKGROUND

Astrogliosis is a common phenomenon after spinal cord injury (SCI). Although this process exerts positive effects on axonal regeneration, excessive astrogliosis imparts negative effects on neuronal repair and recovery. Epidermal growth factor receptor (EGFR) pathway is critical to the regulation of reactive astrogliosis, and therefore is a potential target of therapeutics to better control the response. In this report, we aim to investigate whether blocking EGFR signaling using an EGFR tyrosine kinase specific inhibitor can attenuate reactive astrogliosis and promote functional recovery after a traumatic SCI.

METHOD

The astrocyte scratch injury model in vitro and the weight-drop SCI model in vivo were used as model systems. PD168393 was used to inhibit EGFR signaling activation. Astrocytic activation and phosphorylated EGFR (pEGFR) were observed after immunofluorescence staining and Western blot analysis. The rate of proliferation was determined by immunofluorescence detection of BrdU-incorporating cells located next to the wound. The levels of TNF-α, iNOS, COX-2 and IL-1β in the culture medium under different conditions were assayed by ELISA. Western blot was performed to semi-quantify the expression of EGFR/pEGFR, glial fibrillary acid protein (GFAP) and chondroitin sulfate proteoglycans (CSPGs). Myelin was stained by Luxol Fast Blue Staining. Cresyl violet eosin staining was performed to analyze the lesion cavity volume and neuronal survival following injury. Finally, functional scoring and residual urine recording were performed to show the rats' recovery.

RESULTS

EGFR phosphorylation was found to parallel astrocyte activation, and EGFR inhibitor PD168393 potently inhibited scratch-induced reactive astrogliosis and proinflammatory cytokine/mediator secretion of reactive astrocytes in vitro. Moreover, local administration of PD168393 in the injured area suppressed CSPGs production and glial scar formation, and resulted in reduced demyelination and neuronal loss, which correlated with remarkable hindlimb motor function and bladder improvement in SCI rats.

CONCLUSIONS

The specific EGFR inhibitor PD168393 can ameliorate excessive reactive astrogliosis and facilitate a more favorable environment for axonal regeneration after SCI. As such, EGFR inhibitor may be a promising therapeutic intervention in CNS injury.

Sweet memories: 20 years of progress in research on cognitive functioning in diabetes

This paper appears in a special issue of the European Journal of Pharmacology that commemorates the retirement of Professor Willem Hendrik Gispen as distinguished professor of Utrecht University and as editor of the European Journal of Pharmacology. The paper provides an overview of a research line on the impact of diabetes on cognition that we started together 20 years ago, and that continues to this day. I will report how we more or less stumbled upon this topic, that was understudied, but proved to be of definite clinical relevance. I will discuss how we tried to establish animal models, how developments from clinical and experimental studies from around the world led us to reconsider our concepts, and how findings from research on diabetic neuropathy, insulin signaling in the brain, Alzheimer's disease and dementia, and vascular disease and stroke converged and helped to create new ideas and refute others. This voyage has not ended yet, because the ultimate goal is to offer patients with diabetes treatment that can protect them against accelerated cognitive decline. Although this could take another 20 years, the research from Willem Hendrik and his group brought us an important step in the right direction.

Overexpression of conserved dopamine neurotrophic factor (CDNF) in astrocytes alleviates endoplasmic reticulum stress-induced cell damage and inflammatory cytokine secretion

Astrocyte damage and the disorders of cytokine secretion induced by endoplasmic reticulum stress (ERS) are crucial pathological processes in ischemic injury of the central nervous system (CNS), (e.g., ischemic reperfusion injury of the brain and spinal cord). ERS stimulates damage to astrocytes and the release of pro-inflammatory cytokines, which deteriorates CNS injury. This current study investigates whether the overexpression of conserved dopamine neurotrophic factor (CDNF) alleviates ER stress-induced cell damage and inflammatory cytokine secretion. We found that primary astrocytes showed both a successful transduction and a significant overexpression of CDNF protein following lentivirus application. Our results show that the percentage of LDH released as a result of ER stress was significantly lower in astrocytes with an overexpression of CDNF than in the control groups without CDNF overexpression, indicating that CDNF alleviates ER stress-induced astrocyte damage. The secretion and mRNA expression levels of pro-inflammatory cytokines were increased by tunicamycin, and this stimulation was significantly suppressed by an overexpression of CDNF, demonstrating that CDNF plays an important role in astrocyte inflammation and functioning by resisting ER stress. These findings suggest that primary astrocytes can be efficiently transduced with CDNF lentiviral vectors and that the overexpression of CDNF in astrocytes shows the potential to alleviate cell damage and proinflammatory cytokine secretion, which may represent a promising strategy for neuroprotection in the CNS.

Pioglitazone ameliorates memory deficits in streptozotocin-induced diabetic mice by reducing brain β-amyloid through PPARγ activation

AIM

To examine the effects of pioglitazone, a PPARγ agonist, on memory performance and brain amyloidogenesis in streptozotocin (STZ)-induced diabetic mice.

METHODS

ICR male mice were injected with STZ (150 mg/kg, iv) to induce experimental diabetes. Pioglitazone (9 and 18 mg·kg(-1)·d(-1), po) was administered for 6 weeks. Passive avoidance and Morris water maze (MWM) tests were used to evaluate cognitive function. The blood glucose and serum insulin levels were detected using the glucose oxidase method and an ELISA assay, respectively. β-amyloid (Aβ), β-amyloid precursor protein (APP), β-amyloid precursor protein cleaving enzyme 1 (BACE1), NF-κB p65, the receptor for advanced glycation end products (RAGE) and PPARγ in the brains were analyzed using Western blotting assays.

RESULTS

The STZ-induced diabetic mice characterized by hyperglycemia and hypoinsulinemia performed poorly in both the passive avoidance and MWM tests, accompanied by increased Aβ1-40/Aβ1-42, APP, BACE1, NF-κB p65 and RAGE levels and decreased PPARγ level in the hippocampus and cortex. Chronic pioglitazone treatment significantly ameliorated the memory deficits and amyloidogenesis of STZ-induced diabetic mice, and suppressed expression of APP, BACE1, RAGE and NF-κB p65, and activated PPARγ in the hippocampus and cortex. However, pioglitazone did not significantly affect blood glucose and insulin levels.

CONCLUSION

Pioglitazone ameliorates memory deficits in STZ-induced diabetic mice by reducing brain Aβ level via activation of PPARγ, which is independent of its effects on blood glucose and insulin levels. The results suggest that pioglitazone may be used for treating the cognitive dysfunction in type 1 diabetes mellitus.

Diabetes impairs cortical plasticity and functional recovery following ischemic stroke

Diabetics are at greater risk of having a stroke and are less likely to recover from it. To understand this clinically relevant problem, we induced an ischemic stroke in the primary forelimb somatosensory (FLS1) cortex of diabetic mice and then examined sensory-evoked changes in cortical membrane potentials and behavioral recovery of forelimb sensory-motor function. Consistent with previous studies, focal stroke in non-diabetic mice was associated with acute deficits in forelimb sensorimotor function and a loss of forelimb evoked cortical depolarizations in peri-infarct cortex that gradually recovered over several weeks time. In addition, we discovered that damage to FLS1 cortex led to an enhancement of forelimb evoked depolarizations in secondary forelimb somatosensory (FLS2) cortex. Enhanced FLS2 cortical responses appeared to play a role in stroke recovery given that silencing this region was sufficient to reinstate forelimb impairments. By contrast, the functional reorganization of FLS1 and FLS2 cortex was largely absent in diabetic mice and could not be explained by more severe cortical infarctions. Diabetic mice also showed persistent behavioral deficits in sensorimotor function of the forepaw, which could not be rescued by chronic insulin therapy after stroke. Collectively these results indicate that diabetes has a profound effect on brain plasticity, especially when challenged, as is often the case, by an ischemic event. Further, our data suggest that secondary cortical regions play an important role in the restoration of sensorimotor function when primary cortical regions are damaged.

Evaluation of metabolite changes in visual cortex in diabetic retinopathy by MR-spectroscopy

PURPOSE

To evaluate metabolite changes in the visual cortex of diabetic patients with nonproliferative or proliferative diabetic retinopathy by Magnetic Resonance Spectroscopy (MRS).

MATERIALS AND METHODS

15 normal subjects (group 1), 15 patients with diabetes who did not have diabetic retinopathy (group 2), 15 patients with nonproliferative diabetic retinopathy (NPDR) (group 3), and 15 patients with proliferative diabetic retinopathy (PDR) (group 4) were included in the study. Furthermore, diabetic patients were divided into two groups according to HbA1c levels (Group A: 20 patients, HbA1c <8%; Group B: 20 patients, HbA1c >8%). In all cases' left visual cortex, amounts of N-acetyl-aspartate (NAA), choline (Cho), and creatine (Cr) were measured by MRS. NAA/Cr, Cho/Cr, and NAA/Cho ratios were calculated. Furthermore, all cases' complete blood count (CBC) and biochemical parameters were evaluated.

RESULTS

There was no statistically significant difference for NAA/Cr, Cho/Cr, and NAA/Cho ratios between groups 1, 2, 3, and 4 (P>0.05). However there was a statistically significant difference for NAA/Cr and NAA/Cho ratios between groups A and B (P<0.05). There was no statistically significant difference for Cho/Cr ratio between groups A and B (P>0.05).

CONCLUSION

Although NAA/Cr and NAA/Cho ratios decrease in the visual cortex while diabetic retinopathy progresses, these decreases are not statistically significant. While HbA1c levels increase, the NAA concentration decreases in the visual cortex which indicates neuronal loss. The metabolite changes in the visual cortex are associated with acute events rather than chronic.

Effects of acute and chronic hyperglycemia on the neurochemical profiles in the rat brain with streptozotocin-induced diabetes detected using in vivo ¹H MR spectroscopy at 9.4 T

Chronic hyperglycemia could lead to cerebral metabolic alterations and CNS injury. However, findings of metabolic alterations in poorly managed diabetes in humans and animal models are rather inconsistent. We have characterized the cerebral metabolic consequences of untreated hyperglycemia from the onset to the chronic stage in a streptozotocin-induced rat model of diabetes. In vivo ¹H magnetic resonance spectroscopy was used to measure over 20 neurochemicals longitudinally. Upon the onset of hyperglycemia (acute state), increases in brain glucose levels were accompanied by increases in osmolytes and ketone bodies, all of which remained consistently high through the chronic state of over 10 weeks of hyperglycemia. Only after over 4 weeks of hyperglycemia, the levels of other neurochemicals including N-acetylaspartate and glutathione were significantly reduced and these alterations persisted into the chronic stage. However, glucose transport was not altered in chronic hyperglycemia of over 10 weeks. When glucose levels were acutely restored to euglycemia, some neurochemical changes were irreversible, indicating the impact of prolonged uncontrolled hyperglycemia on the CNS. Furthermore, progressive changes in neurochemical levels from control to acute and chronic conditions demonstrated the utility of ¹H magnetic resonance spectroscopy as a non-invasive tool in monitoring the disease progression in diabetes.

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.

[Analysis of gene expression profile of peripheral ganglia in early stage type Ⅱ diabetic rats]

Diabetic neuropathy (DN) is defined as the presence of symptoms and/or signs of peripheral nerve dysfunction in people with diabetes. The aim of this study is to screen differentially expressed genes in peripheral ganglia in early stage type Ⅱ experimental diabetic rats. We compared gene expression profiles of peripheral ganglia in type Ⅱ diabetic and nondiabetic rats based on Illumina® Sentrix® BeadChip arrays. The results showed that 158 out of a total of 12 604 known genes were significantly differentially expressed, including 87 up-regulated and 71 down-regulated genes, in diabetic rats compared with those in the nondiabetic rats. It is noted that some up-regulated genes are involved in the biological processes of neuronal cytoskeleton and motor proteins. In contrast, the down-regulated genes are associated with the response to virus\biotic stimulus\ other organism in diabetic rats. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the most significant pathway enriched in the changed gene set is metabolism (P < 0.001). These results indicated that metabolic changes in peripheral ganglia of diabetic rats could be induced by hyperglycemia. Hyperglycemia could change the expression of genes involved in neuronal cytoskeleton and motor proteins through immune inflammatory response, and then impair the structure and function of the peripheral ganglia.

High glucose-induced expression of inflammatory cytokines and reactive oxygen species in cultured astrocytes

Astrocyte activation plays important roles both in physiological and pathological process in the CNS. In the latter, the process is further aggravated by hyperglycemia, leading to diabetes complications of CNS. We report here that high glucose (HG) treatment stimulated astrocytic morphological alteration coupled with changes in glial fibrillary acidic protein (GFAP) and vimentin expression. Additionally, HG upregulated the expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), interleukin-4 (IL-4), and vascular endothelial growth factor (VEGF); however, its effects on transforming growth factor-β (TGF-β) expression were not evident. HG treatment induced increased production of reactive oxygen species (ROS) as well as activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator transcription 3 (STAT 3). HG-induced expression of TNF-α, IL-6, IL-1β, IL-4, and VEGF was blocked by ROS scavenger and inhibitors specific for NF-κB and STAT 3, respectively. The results suggest that the aforementioned multiple inflammatory cytokines and mediators that may be linked to the pathogenesis of the diabetes complications of CNS are induced by HG via the key signaling pathways.

Diabetes-induced myelin abnormalities are associated with an altered lipid pattern: protective effects of LXR activation

Diabetic peripheral neuropathy (DPN) is characterized by myelin abnormalities; however, the molecular mechanisms underlying such deficits remain obscure. To uncover the effects of diabetes on myelin alterations, we have analyzed myelin composition. In a streptozotocin-treated rat model of diabetic neuropathy, analysis of sciatic nerve myelin lipids revealed that diabetes alters myelin's phospholipid, FA, and cholesterol content in a pattern that can modify membrane fluidity. Reduced expression of relevant genes in the FA biosynthetic pathway and decreased levels of the transcriptionally active form of the lipogenic factor sterol-regulatory element binding factor-1c (SREBF-1c) were found in diabetic sciatic nerve. Expression of myelin's major protein, myelin protein zero (P0), was also suppressed by diabetes. In addition, we confirmed that diabetes induces sciatic nerve myelin abnormalities, primarily infoldings that have previously been associated with altered membrane fluidity. In a diabetic setting, synthetic activator of the nuclear receptor liver X receptor (LXR) increased SREBF-1c function and restored myelin lipid species and P0 expression levels to normal. These LXR-modulated improvements were associated with restored myelin structure in sciatic nerve and enhanced performance in functional tests such as thermal nociceptive threshold and nerve conduction velocity. These findings demonstrate an important role for the LXR-SREBF-1c axis in protection from diabetes-induced myelin abnormalities.

Reduced gap junctional communication among astrocytes in experimental diabetes: contributions of altered connexin protein levels and oxidative-nitrosative modifications

Experimental diabetes increases production of reactive oxygen-nitrogen species and inhibits astrocytic gap junctional communication in tissue culture and brain slices from streptozotocin (STZ)-diabetic rats by unidentified mechanisms. Relative connexin (Cx) protein levels were assessed by Western blotting using extracts from cultured astrocytes grown in high (25 mmol/liter) or low (5.5 mmol/liter) glucose for 2-3 weeks and STZ-diabetic rat brain. Chemiluminescent signals for diabetic samples were normalized to those of controls on the same blot and same protein load. Growth in high glucose did not alter relative Cx26 level, whereas Cx30 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were reduced by ∼30%, and Cx43 increased ∼1.9-fold. In the inferior colliculus of STZ-diabetic rats, Cx30 and Cx43 levels in three of four rats were half those of controls, whereas GAPDH and actin were unaffected. Diabetes did not affect levels of Cx30, Cx43, or GAPDH in cerebral cortex, but actin level rose 24%. Cx43 was predominantly phosphorylated in control and diabetic samples, so the reduced dye transfer is not due to overall dephosphorylation of Cx43. Astrocytic growth in high glucose reduced the dye-labeled area by 75%, but 10 min of treatment with dithiothreitol restored normal dye transfer. In contrast, nitric oxide donors inhibited dye transfer among astrocytes grown in low glucose by 50-65% within 1 hr. Thus, modifications arising from oxidative-nitrosative stress, not altered connexin levels, may underlie the reduced dye transfer among severely hyperglycemic cultured astrocytes, whereas both oxidative-nitrosative stress and regionally selective down-regulation of connexin protein content may affect gap junctional communication in the brains of STZ-diabetic rats.

The chronological characteristics of SOD1 activity and inflammatory response in the hippocampi of STZ-induced type 1 diabetic rats

Because it appears that oxidative stress and inflammation are implicated with disease pathogenesis in the diabetic brain, many researchers have used streptozotocin (STZ)-induced diabetic animals to study superoxide production and the effects of superoxide scavengers like Cu,Zn-superoxide dismutase (SOD1). However, many studies have been conducted without considering temporal changes after STZ injection. Interestingly, though SOD activities were not significantly different among the groups, SOD1 and 4-hydroxy-2-nonenal (4-HNE) immunoreactivities were significantly enhanced at 3 weeks after an STZ injection (STZ3w) versus only marginal levels in sham controls, whereas microglial activity was remarkably reduced in injected rats at this time. However, SOD1 immunoreactivity and microglial activities were only at the sham level at STZ4w. The present study provides important information concerning cell damage by ROS generated by STZ. Microglial response was found to be inactivated at STZ3w and neuronal cells (NeuN) showed a non-significant tendency to be reduced in number at STZ4w except in the dentate gyrus. We speculated that the above oxidative stress-related events should be accomplished at STZ3w in the brains of STZ-induced diabetes animal models. Therefore, the aim of the present study was to investigate chronological changes in SOD1 immunoreactivity associated with lipid peroxidation and inflammatory responses in the hippocampi of STZ-induced type I diabetic rats.

Global transcriptional programs in peripheral nerve endoneurium and DRG are resistant to the onset of type 1 diabetic neuropathy in Ins2 mice

While the morphological and electrophysiological changes underlying diabetic peripheral neuropathy (DPN) are relatively well described, the involved molecular mechanisms remain poorly understood. In this study, we investigated whether phenotypic changes associated with early DPN are correlated with transcriptional alterations in the neuronal (dorsal root ganglia [DRG]) or the glial (endoneurium) compartments of the peripheral nerve. We used Ins2(Akita/+) mice to study transcriptional changes underlying the onset of DPN in type 1 diabetes mellitus (DM). Weight, blood glucose and motor nerve conduction velocity (MNCV) were measured in Ins2(Akita/+) and control mice during the first three months of life in order to determine the onset of DPN. Based on this phenotypic characterization, we performed gene expression profiling using sciatic nerve endoneurium and DRG isolated from pre-symptomatic and early symptomatic Ins2(Akita/+) mice and sex-matched littermate controls. Our phenotypic analysis of Ins2(Akita/+) mice revealed that DPN, as measured by reduced MNCV, is detectable in affected animals already one week after the onset of hyperglycemia. Surprisingly, the onset of DPN was not associated with any major persistent changes in gene expression profiles in either sciatic nerve endoneurium or DRG. Our data thus demonstrated that the transcriptional programs in both endoneurial and neuronal compartments of the peripheral nerve are relatively resistant to the onset of hyperglycemia and hypoinsulinemia suggesting that either minor transcriptional alterations or changes on the proteomic level are responsible for the functional deficits associated with the onset of DPN in type 1 DM.

Hyperglycaemia and diabetes impair gap junctional communication among astrocytes

Sensory and cognitive impairments have been documented in diabetic humans and animals, but the pathophysiology of diabetes in the central nervous system is poorly understood. Because a high glucose level disrupts gap junctional communication in various cell types and astrocytes are extensively coupled by gap junctions to form large syncytia, the influence of experimental diabetes on gap junction channel-mediated dye transfer was assessed in astrocytes in tissue culture and in brain slices from diabetic rats. Astrocytes grown in 15–25 mmol/l glucose had a slow-onset, poorly reversible decrement in gap junctional communication compared with those grown in 5.5 mmol/l glucose. Astrocytes in brain slices from adult STZ (streptozotocin)-treated rats at 20–24 weeks after the onset of diabetes also exhibited reduced dye transfer. In cultured astrocytes grown in high glucose, increased oxidative stress preceded the decrement in dye transfer by several days, and gap junctional impairment was prevented, but not rescued, after its manifestation by compounds that can block or reduce oxidative stress. In sharp contrast with these findings, chaperone molecules known to facilitate protein folding could prevent and rescue gap junctional impairment, even in the presence of elevated glucose level and oxidative stress. Immunostaining of Cx (connexin) 43 and 30, but not Cx26, was altered by growth in high glucose. Disruption of astrocytic trafficking of metabolites and signalling molecules may alter interactions among astrocytes, neurons and endothelial cells and contribute to changes in brain function in diabetes. Involvement of the microvasculature may contribute to diabetic complications in the brain, the cardiovascular system and other organs.