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ABSTRACT: Cardiac autonomic neuropathy (CAN) is a relatively common and often devastating complication of diabetes. The major clinical signs are tachycardia, exercise intolerance, and orthostatic hypotension, but the most severe aspects of this complication are high rates of cardiac events and mortality. One of the earliest manifestations of CAN is reduced heart rate variability, and detection of this, along with abnormal results in postural blood pressure testing and/or the Valsalva maneuver, are central to diagnosis of the disease. The treatment options for CAN, beyond glycemic control, are extremely limited and lack evidence of efficacy. The underlying molecular mechanisms are also poorly understood. Thus, CAN is associated with a poor prognosis and there is a compelling need for research to understand, prevent, and reverse CAN. In this review of the literature we examine the use and usefulness of animal models of CAN in diabetes. Compared to other diabetic complications, the number of animal studies of CAN is very low. The published studies range across a variety of species, methods of inducing diabetes, and timescales examined, leading to high variability in study outcomes. The lack of well-characterized animal models makes it difficult to judge the relevance of these models to the human disease. One major advantage of animal studies is the ability to probe underlying molecular mechanisms, and the limited numbers of mechanistic studies conducted to date are outlined. Thus, while animal models of CAN in diabetes are crucial to better understanding and development of therapies, they are currently under-used.
Autonomic neuroscience: basic & clinical 04/2013; · 1.82 Impact Factor
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ABSTRACT: Dynamin-2-related centronuclear myopathy (DNM2-CNM) is a clinically heterogeneous muscle disorder characterized by muscle weakness and centralized nuclei on biopsy. There is little known about the muscle dysfunction underlying this disorder, and there are currently no treatments. In this study, we establish a novel zebrafish model for DNM2-CNM by transiently overexpressing a mutant version of DNM2 (DNM2-S619L) during development. We show that overexpression of DNM2-S619L leads to pathological changes in muscle and a severe motor phenotype. We further demonstrate that the muscle weakness seen in these animals can be significantly alleviated by treatment with an acetylcholinesterase inhibitor. Based on these results, we reviewed the clinical history of five patients with two different DNM2-CNM mutations (S619L and E368K) and found electrophysiological evidence of abnormal neuromuscular transmission in two of the individuals. All five patients showed improved muscle strength and motor function, and/or reduced fatigability following acetylcholinesterase inhibitor treatment. Together, our results suggest that deficits at the neuromuscular junction may play an important role in the pathogenesis of DNM2-CNM and that treatments targeting this dysfunction can provide an effective therapy for patients with this disorder.
Journal of Molecular Medicine 01/2013; · 4.67 Impact Factor
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ABSTRACT: Dynamin-2 (DNM2) is a large GTPase involved in clathrin-mediated endocytosis and related trafficking pathways. Mutations in human DNM2 cause two distinct neuromuscular disorders: centronuclear myopathy and Charcot-Marie-Tooth disease. Zebrafish have been shown to be an excellent animal model for many neurologic disorders, and this system has the potential to inform our understanding of DNM2-related disease. Currently, little is known about the endogenous zebrafish orthologs to human DNM2. In this study, we characterize two zebrafish dynamin-2 genes, dnm2 and dnm2-like. Both orthologs are structurally similar to human DNM2 at the gene and protein levels. They are expressed throughout early development and in all adult tissues examined. Knockdown of dnm2 and dnm2-like gene products resulted in extensive morphological abnormalities during development, and expression of human DNM2 RNA rescued these phenotypes. Our findings suggest that dnm2 and dnm2-like are orthologs to human DNM2, and that they are required for normal zebrafish development.
PLoS ONE 01/2013; 8(2):e55888. · 4.09 Impact Factor
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ABSTRACT: Multiple lines of evidence link the incidence of diabetes to the development of Alzheimer's disease (AD). Patients with diabetes have a 50 to 75% increased risk of developing AD. In parallel, AD patients have a higher than normal tendency to develop type 2 diabetes or impaired fasting glucose. Tau is the major component of neurofibrillary tangles, one of the hallmarks of AD pathology. The current study examined the effect of hyperglycemia on tau modification. Glucose treatment of rat embryonic cortical neurons results in concentration-dependent apoptosis and caspase-3 activation. These changes are well correlated with glucose time- and concentration-dependent tau cleavage. Aβ treatment induces tau cleavage and when added together with glucose, there is an additive effect on caspase activation, apoptosis, and tau cleavage. Tau cleavage is partially blocked by the caspase inhibitor, ZVAD. Cleaved tau displays a punctate staining along the neurites and colocalizes with cleaved caspase-3 in the cytoplasm. Both type 1 and type 2 diabetic mice display increased tau phosphorylation in the brain. In agreement with the effects of glucose on tau modifications in vitro, there is increased tau cleavage in the brains of ob/ob mice; however, tau cleavage is not observed in type 1 diabetic mouse brains. Our study demonstrates that hyperglycemia is one of major factors that induce tau modification in both in vitro and in vivo models of diabetes. We speculate that tau cleavage in diabetic conditions (especially in type 2 diabetes) may be a key link for the increased incidence of AD in diabetic patients.
Journal of Alzheimer's disease: JAD 12/2012; · 3.74 Impact Factor
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ABSTRACT: Diabetic neuropathy (DN) is the most common complication of diabetes and is characterized by distal-to-proximal loss of peripheral nerve axons. The idea of tissue-specific pathological alterations in energy metabolism in diabetic complications-prone tissues is emerging. Altered nerve metabolism in type 1 diabetes models is observed; however, therapeutic strategies based on these models offer limited efficacy to type 2 diabetic patients with DN. Therefore, understanding how peripheral nerves metabolically adapt to the unique type 2 diabetic environment is critical to develop disease-modifying treatments. In the current study, we utilized targeted LC/MS/MS to characterize the glycolytic and tricarboxylic acid (TCA) cycle metabolomes in sural nerve, sciatic nerve and dorsal root ganglia (DRG) from male type 2 diabetic mice (BKS.Cg-m+/+Leprdb; db/db) and controls (db/+). We report a depletion of glycolytic intermediates in diabetic sural nerve and sciatic nerve (glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate (sural nerve only), 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate, lactate) with no significant changes in DRG. Citrate and isocitrate TCA cycle intermediates were decreased in sural nerve, sciatic nerve and DRG from diabetic mice. Utilizing LC/ESI/MS/MS and HPLC methods, we also observed increased protein and lipid oxidation (nitrotyrosine; hydroxyoctadecadienoic acids, HODEs) in db/db tissue, with a proximal-to-distal increase in oxidative stress, with associated decreased aconitase enzyme activity. We propose a preliminary model, whereby the greater change in metabolomic profile, increase in oxidative stress, and decrease in TCA cycle enzyme activity may cause distal peripheral nerve to rely on truncated TCA cycle metabolism in the type 2 diabetes environment.
Journal of Endocrinology 10/2012; · 3.55 Impact Factor
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ABSTRACT: Dyslipidemia has been identified as an important pathogenic risk factor for diabetic neuropathy, but current animal models do not adequately reproduce the lipid profile observed in human diabetics (increased triglycerides with an elevated LDL-cholesterol and reduced HDL-cholesterol). High fat feeding of mice produces hyperlipidemia, but mice are resistant to increases in the LDL to HDL ratio, reducing the potential for peripheral lipid deposits to impact neuropathy, as is postulated to occur in human subjects. Genetic manipulations provide an alternative approach to reproducing a neuropathic plasma lipid profile. Based on findings from the atherosclerosis literature, we began with knockout of ApoE. Since knockout of ApoE alone only partially mimics the human diabetic lipid profile, we examined the impact of its combination with a well-characterized model of type 2 diabetes exhibiting neuropathy, the db/db mouse. We added further gene manipulations to increase hyperlipidemia by using mice with both ApoE and ApoB48 knockout on the ob/+ (leptin mutation) mice. In all of these models, we found that either the db/db or ob/ob genotypes had increased body weight, hyperlipidemia, hyperglycemia, and evidence of neuropathy compared with the control groups (db/+ or ob/+, respectively). We found that ApoE knockout combined with leptin receptor knockout produced a lipid profile most closely modeling human dyslipidemia that promotes neuropathy. ApoE knockout combined with additional ApoB48 and leptin knockout produced similar changes of smaller magnitude, but, notably, an increase in HDL-cholesterol. Our data suggest that the overall effects of ApoE knockout, either directly upon nerve structure and function or indirectly on lipid metabolism, are insufficient to significantly alter the course of diabetic neuropathy. Although these models ultimately do not deliver optimal lipid profiles for translational diabetic neuropathy research, they do present glycemic and lipid profile properties of value for future therapeutic investigations.
Experimental Neurology 10/2012; · 4.70 Impact Factor
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Academic medicine: journal of the Association of American Medical Colleges 10/2012; 87(10):1311-2. · 2.34 Impact Factor
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ABSTRACT: BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a fatal disorder involving the degeneration and loss of motor neurons. The mechanisms of motor neuron loss in ALS are unknown and there are no effective treatments. Defects in the distal axon and at the neuromuscular junction are early events in the disease course, and zebrafish provide a promising in vivo system to examine cellular mechanisms and treatments for these events in ALS pathogenesis. RESULTS: We demonstrate that transient genetic manipulation of zebrafish to express G93A-SOD1, a mutation associated with familial ALS, results in early defects in motor neuron outgrowth and axonal branching. This is consistent with previous reports on motor neuron axonal defects associated with familial ALS genes following knockdown or mutant protein overexpression. We also demonstrate that upregulation of growth factor signaling is capable of rescuing these early defects, validating the potential of the model for therapeutic discovery. We generated stable transgenic zebrafish lines expressing G93A-SOD1 to further characterize the consequences of G93A-SOD1 expression on neuromuscular pathology and disease progression. Behavioral monitoring reveals evidence of motor dysfunction and decreased activity in transgenic ALS zebrafish. Examination of neuromuscular and neuronal pathology throughout the disease course reveals a loss of neuromuscular junctions and alterations in motor neuron innervations patterns with disease progression. Finally, motor neuron cell loss is evident later in the disease. CONCLUSIONS: This sequence of events reflects the stepwise mechanisms of degeneration in ALS, and provides a novel model for mechanistic discovery and therapeutic development for neuromuscular degeneration in ALS.
Molecular Neurodegeneration 08/2012; 7(1):44. · 4.28 Impact Factor
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ABSTRACT: To compare and contrast the evidence for the effect of glucose control on the prevention of neuropathy in type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM).
In T1DM, multiple clinical trials have demonstrated a large benefit from enhanced glucose control, whereas the benefit in T2DM is much more modest. Epidemiologic and laboratory evidence exists to support factors other than hyperglycemia in the development of neuropathy including obesity, hypertension, dyslipidemia, inflammation, and insulin resistance.
T1DM neuropathy and T2DM neuropathy are fundamentally different. In T1DM, glucose control has a large effect on the prevention of neuropathy; therefore, future efforts should continue to concentrate on this avenue of treatment. In contrast, in T2DM, glucose control has a small effect on the prevention of neuropathy; as a result, more research is needed to define the underlying mechanisms for the development of neuropathy. Understanding these mechanisms may lead to novel therapeutic approaches to prevent or treat diabetic neuropathy.
Current opinion in neurology 08/2012; 25(5):536-41. · 5.43 Impact Factor
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ABSTRACT: Insulin-like growth factors (IGFs) play an integral role in development, growth, and survival. This article details the current understanding of the effects of IGFs in the peripheral nervous system (PNS) during health and disease, and introduces how the IGF system regulates PNS development and impacts growth and survival of PNS cells. Also discussed are implications of IGF signaling in neurodegeneration and the status and prospects of IGF therapies for PNS conditions. There is substantial support for the application of IGF therapies in the treatment of PNS injury and disease.
Endocrinology and metabolism clinics of North America 06/2012; 41(2):375-93, vii. · 3.56 Impact Factor
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ABSTRACT: Diabetic peripheral neuropathy is a prevalent, disabling disorder. The most common manifestation is distal symmetrical polyneuropathy (DSP), but many patterns of nerve injury can occur. Currently, the only effective treatments are glucose control and pain management. While glucose control substantially decreases the development of neuropathy in those with type 1 diabetes, the effect is probably much smaller in those with type 2 diabetes. Evidence supports the use of specific anticonvulsants and antidepressants for pain management in patients with diabetic peripheral neuropathy. However, the lack of disease-modifying therapies for diabetic DSP makes the identification of new modifiable risk factors essential. Growing evidence supports an association between components of the metabolic syndrome, including prediabetes, and neuropathy. Studies are needed to further explore this association, which has implications for the development of new treatments for this common disorder.
The Lancet Neurology 06/2012; 11(6):521-34. · 23.46 Impact Factor
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ABSTRACT: No United States-based clinical trials have attempted delivery of biological therapies directly to the spinal cord for treatment of amyotrophic lateral sclerosis (ALS) because of the lack of a meaningful US Food and Drug Administration-authorized cell candidate and a validated delivery approach.
To assess safety of delivery of a neural stem cell-based treatment into the upper lumbar segments of the ALS spinal cord in the first US Food and Drug Administration-authorized phase I trial.
Each microinjection series comprised 5 injections (10 μL/injection) separated by 4 mm. Each injection deposited 100,000 neural stem cells derived from a fetal spinal cord. Twelve patients were treated with either unilateral or bilateral injections. Group A, nonambulatory patients, underwent unilateral (n = 3) or bilateral (n = 3) lumbar microinjections. Groups B and C were ambulatory (n = 3 each) and, respectively, received unilateral or bilateral injections. Patients are followed clinically and radiologically to assess potential toxicity of the procedure.
Twelve patients have received a transplant. There was one instance of transient intraoperative somatosensory-evoked potentials depression. In the immediate postoperative period, there was 1 episode of urinary retention requiring Foley catheter reinsertion. By discharge, none had a documented motor function decrement. Two patients required readmission and reoperation for cerebrospinal fluid leak or suprafascial wound dehiscence (n = 1 each). Two deaths occurred at 8 and 13 months postsurgery; neither was related to the surgical transplant.
Our experience in 12 patients supports the procedural safety of unilateral and bilateral intraspinal lumbar microinjection. Completion of this phase I safety trial is planned by proceeding to cervical and combined cervical + lumbar microinjections in ALS patients.
Neurosurgery 05/2012; 71(2):405-16; discussion 416. · 2.79 Impact Factor
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ABSTRACT: Progress in developing treatments for diabetic neuropathy is slowed by our limited understanding of how disturbances in metabolic substrates - glucose and fatty acids - produce nerve injury. In this review, we present the current oxidative stress hypothesis and experimental data that support it. We identify weaknesses in our understanding of diabetes-disordered metabolism in the neurovascular unit, that is, in critical cell types of the microvascular endothelium, peripheral sensory neurons, and supporting Schwann cells. Greater understanding of peripheral nervous system bioenergetics may provide insight into new drug therapies or improvements in dietary interventions in diabetes or even pre-diabetes.
Journal of the Peripheral Nervous System 05/2012; 17 Suppl 2:10-4. · 2.80 Impact Factor
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ABSTRACT: To assess differences in excitatory (glutamate/glutamine or Glx) and inhibitory (γ-Aminobutyric acid or GABA) neurotransmitter levels using MR spectroscopy in pain processing regions of the brain in patients diabetic neuropathy (DN) and positive sensory symptoms and age-matched healthy control (HC) subjects.
Seven diabetic patients (5 males, 2 females, mean age = 57.0 ± 8.5 years) with confirmed DN and positive sensory symptoms and 7 age and sex matched HC subjects (mean age = 57.7 ± 3.2 years) underwent 3 Tesla MR spectroscopy. Glx and GABA levels were quantified in the right anterior and posterior insula, anterior cingulate cortex and right thalamus.
Mean Glx levels were significantly higher and mean GABA levels were significantly lower within the posterior insula in the DN patients compared to HC (P = 0.005 and 0.012 respectively).
This pilot data demonstrates an excitatory/inhibitory neurotransmitter imbalance in the brain of in patients with DN and positive sensory symptoms compared to pain free HC subjects.
Academic radiology 05/2012; 19(5):607-12. · 2.09 Impact Factor
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ABSTRACT: The DCCT/EDIC (Diabetes Control and Complications Trial/ Epidemiology of Diabetes Interventions and Complications) provides
a comprehensive characterization of the natural history of diabetic neuropathy in patients with type 1 diabetes and provides
insight into the impact of intensive insulin therapy in disease progression. The lessons learned about the natural history
of distal symmetrical polyneuropathy and cardiovascular autonomic neuropathy and the impact of glycemic control on neuropathy
are discussed in this review.
KeywordsDistal symmetrical polyneuropathy-Cardiovascular autonomic neuropathy-Nerve conduction studies-Heart rate variability studies-Glycemic control
Current Diabetes Reports 04/2012; 10(4):276-282. · 2.50 Impact Factor
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ABSTRACT: The contribution of oxidative stress to diabetic complications including neuropathy is widely known. Mitochondrial and cellular damage are associated with the overproduction of reactive oxygen species and decreased levels or function of the cellular antioxidant mitochondrial manganese superoxide dismutase (SOD2). We hypothesized that targeted SOD2 deletion in the peripheral nervous system using cre-lox technology under control of the nestin promoter would accelerate neuropathy in a type 2 model of diabetes, the BKS.db/db mouse. SOD2-deficient mice, however, demonstrated severe gait deformities and seizures and died by 20 days of age. Examination of SOD2 expression levels revealed that SOD2 was lost in brain and reduced in the spinal cord, but appeared normal in dorsal root ganglia and peripheral nerves in SOD2-deficient mice. These findings indicate incomplete targeted knockout of SOD2. Morphological examination revealed cortical lesions similar to spongiform encephalopathy in the brain of SOD2-deficient mice. No lesions were evident in the spinal cord, but changes in myelin within the sciatic and sural nerves including a lack of cohesion between layers of compact myelin were observed. Together, these results indicate that targeted neuronal SOD2 knockout using the nestin promoter results in severe central nervous system degeneration and perinatal lethality in mice. A specific peripheral nervous system-targeting construct is required to examine the consequences of SOD2 knockout in diabetic neuropathy.
Neuroscience 04/2012; 212:201-13. · 3.38 Impact Factor
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ABSTRACT: Advances in stem cell biology have generated intense interest in the prospect of transplanting stem cells into the nervous system for the treatment of neurodegenerative diseases. Here, we report the results of an ongoing phase I trial of intraspinal injections of fetal-derived neural stems cells in patients with amyotrophic lateral sclerosis (ALS). This is a first-in-human clinical trial with the goal of assessing the safety and tolerability of the surgical procedure, the introduction of stem cells into the spinal cord, and the use of immunosuppressant drugs in this patient population. Twelve patients received either five unilateral or five bilateral (10 total) injections into the lumbar spinal cord at a dose of 100,000 cells per injection. All patients tolerated the treatment without any long-term complications related to either the surgical procedure or the implantation of stem cells. Clinical assessments ranging from 6 to 18 months after transplantation demonstrated no evidence of acceleration of disease progression due to the intervention. One patient has shown improvement in his clinical status, although these data must be interpreted with caution since this trial was neither designed nor powered to measure treatment efficacy. These results allow us to report success in achieving the phase I goal of demonstrating safety of this therapeutic approach. Based on these positive results, we can now advance this trial by testing intraspinal injections into the cervical spinal cord, with the goal of protecting motor neuron pools affecting respiratory function, which may prolong life for patients with ALS.
Stem Cells 03/2012; 30(6):1144-51. · 7.78 Impact Factor
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ABSTRACT: Metabolic syndrome is a cluster of cardiovascular risk factors including obesity, diabetes and dyslipidemia. Insulin resistance (IR) is at the core of metabolic syndrome. In adipose tissue and muscle, IR results in decreased insulin signaling, primarily affecting downstream phosphatidylinositol 3-kinase (PI3K)/Akt signaling. It was recently proposed that neurons can develop hyperinsulinemia-induced IR, which in turn results in injury to the peripheral and central nervous systems and is probably pathogenic in common neurological disorders such as diabetic neuropathy and Alzheimer's disease (AD). This review presents evidence indicating that, similarly to insulin-dependent metabolically active tissues such as fat and muscle, neurons also develop IR and thus cannot respond to the neurotrophic properties of insulin, resulting in neuronal injury, subsequent dysfunction and disease states.
Trends in Endocrinology and Metabolism 03/2012; 23(3):133-41. · 8.11 Impact Factor
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ABSTRACT: Significant increases in National Institutes of Health (NIH) spending on medical research have not produced corresponding increases in new treatments and cures. Instead, laboratory discoveries remain in what has been termed the "valley of death," the gap between bench research and clinical application. Recently, there has been considerable discussion in the literature and scientific community about the causes of this phenomenon and how to bridge the abyss. In this article, the authors examine one possible explanation: Clinician-scientists' declining role in the medical research enterprise has had a dilatory effect on the successful translation of laboratory breakthroughs into new clinical applications. In recent decades, the percentage of MDs receiving NIH funding has drastically decreased compared with PhDs. The growing gap between the research and clinical enterprises has resulted in fewer scientists with a true understanding of clinical problems as well as scientists who are unable to or uninterested in gleaning new basic research hypotheses from failed clinical trials. The NIH and many U.S. medical schools have recognized the decline of the clinician-scientist as a major problem and adopted innovative programs to reverse the trend. However, more radical action may be required, including major changes to the NIH peer-review process, greater funding for translational research, and significantly more resources for the training, debt relief, and early career support of potential clinician-scientists. Such improvements are required for clinician-scientists to conduct translational research that bridges the valley of death and transforms biomedical research discoveries into tangible clinical treatments and technologies.
Academic medicine: journal of the Association of American Medical Colleges 03/2012; 87(3):266-70. · 2.34 Impact Factor
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ABSTRACT: The multidisciplinary approach to treatment of amyotrophic lateral sclerosis (ALS) has improved the overall care of patients suffering from this disease ( 1 , 2 ). This approach typically has included neurologists, physiatrists, occupational therapists, respiratory therapists and speech therapists. Dysphonia, dysarthria, and dysphagia are three of the most common bulbar manifestations of ALS, and are often the presenting symptoms in bulbar-onset patients. Despite this, otolaryngologists are often not included in ALS management until a tracheostomy is considered. The otolaryngologist can play an important role in early diagnosis and subsequent management of bulbar manifestations of ALS, and would be a valuable member of the multidisciplinary team.
Amyotrophic Lateral Sclerosis 02/2012; 13(2):229-32. · 3.40 Impact Factor
