Neuropathology and pathogenesis of diabetic autonomic neuropathy

O-GlcNAcylation is crucial for sympathetic neuron development, maintenance, functionality and contributes to peripheral neuropathy

O-GlcNAcylation is a post-translational modification (PTM) that regulates a wide range of cellular functions and has been associated with multiple metabolic diseases in various organs. The sympathetic nervous system (SNS) is the efferent portion of the autonomic nervous system that regulates metabolism of almost all organs in the body. How much the development and functionality of the SNS are influenced by O-GlcNAcylation, as well as how such regulation could contribute to sympathetic neuron (symN)-related neuropathy in diseased states, remains unknown. Here, we assessed the level of protein O-GlcNAcylation at various stages of symN development, using a human pluripotent stem cell (hPSC)-based symN differentiation paradigm. We found that pharmacological disruption of O-GlcNAcylation impaired both the growth and survival of hPSC-derived symNs. In the high glucose condition that mimics hyperglycemia, hPSC-derived symNs were hyperactive, and their regenerative capacity was impaired, which resembled typical neuronal defects in patients and animal models of diabetes mellitus. Using this model of sympathetic neuropathy, we discovered that O-GlcNAcylation increased in symNs under high glucose, which lead to hyperactivity. Pharmacological inhibition of O-GlcNAcylation rescued high glucose-induced symN hyperactivity and cell stress. This framework provides the first insight into the roles of O-GlcNAcylation in both healthy and diseased human symNs and may be used as a platform for therapeutic studies.

Autonomic Cardiovascular Control in Health and Disease

Autonomic neural control of the cardiovascular system is formed of complex and dynamic processes able to adjust rapidly to mitigate perturbations in hemodynamics and maintain homeostasis. Alterations in autonomic control feature in the development or progression of a multitude of diseases with wide-ranging physiological implications given the neural system's responsibility for controlling inotropy, chronotropy, lusitropy, and dromotropy. Imbalances in sympathetic and parasympathetic neural control are also implicated in the development of arrhythmia in several cardiovascular conditions sparking interest in autonomic modulation as a form of treatment. A number of measures of autonomic function have shown prognostic significance in health and in pathological states and have undergone varying degrees of refinement, yet adoption into clinical practice remains extremely limited. The focus of this contemporary narrative review is to summarize the anatomy, physiology, and pathophysiology of the cardiovascular autonomic nervous system and describe the merits and shortfalls of testing modalities available. © 2023 American Physiological Society. Compr Physiol 13:4493-4511, 2023.

Oxidative Stress and Mitochondrial Dysfunction Associated with Peripheral Neuropathy in Type 1 Diabetes

Significance: This review highlights the many intracellular processes generating reactive oxygen species (ROS) in the peripheral nervous system in the context of type 1 diabetes. The major sources of superoxide and hydrogen peroxide (H₂O₂) are described, and scavenging systems are explained. Important roles of ROS in regulating normal redox signaling and in a disease setting, such as diabetes, contributing to oxidative stress and cellular damage are outlined. The primary focus is the role of hyperglycemia in driving elevated ROS production and oxidative stress contributing to neurodegeneration in diabetic neuropathy (within the dorsal root ganglia [DRG] and peripheral nerve). Recent Advances: Contributors to ROS production under high intracellular glucose concentration such as mitochondria and the polyol pathway are discussed. The primarily damaging impact of ROS on multiple pathways including mitochondrial function, endoplasmic reticulum (ER) stress, autophagy, and epigenetic signaling is covered. Critical Issues: There is a strong focus on mechanisms of diabetes-induced mitochondrial dysfunction and how this may drive ROS production (in particular superoxide). The mitochondrial sites of superoxide/H₂O₂ production via mitochondrial metabolism and aerobic respiration are reviewed. Future Directions: Areas for future development are highlighted, including the need to clarify diabetes-induced changes in autophagy and ER function in neurons and Schwann cells. In addition, more clarity is needed regarding the sources of ROS production at mitochondrial sites under high glucose concentration (and lack of insulin signaling). New areas of study should be introduced to investigate the role of ROS, nuclear lamina function, and epigenetic signaling under diabetic conditions in peripheral nerve.

Genetic and Epigenomic Modifiers of Diabetic Neuropathy

Diabetic neuropathy (DN), the most common chronic and progressive complication of diabetes mellitus (DM), strongly affects patients’ quality of life. DN could be present as peripheral, autonomous or, clinically also relevant, uremic neuropathy. The etiopathogenesis of DN is multifactorial, and genetic components play a role both in its occurrence and clinical course. A number of gene polymorphisms in candidate genes have been assessed as susceptibility factors for DN, and most of them are linked to mechanisms such as reactive oxygen species production, neurovascular impairments and modified protein glycosylation, as well as immunomodulation and inflammation. Different epigenomic mechanisms such as DNA methylation, histone modifications and non-coding RNA action have been studied in DN, which also underline the importance of “metabolic memory” in DN appearance and progression. In this review, we summarize most of the relevant data in the field of genetics and epigenomics of DN, hoping they will become significant for diagnosis, therapy and prevention of DN.

Levosimendan Prevents Memory Impairment Induced by Diabetes in Rats: Role of Oxidative Stress

BACKGROUND

Levosimendan is a calcium sensitizer and phosphodiesterase inhibitor that has potent antioxidant and anti-inflammatory activities.

OBJECTIVES

The aim of the current study is to investigate the potential protective effect of levosimendan on learning and memory impairment induced by diabetes.

METHODS

Adult Wister rats were randomly divided into four groups (n=15 rats/group): control, levosimendan, streptozotocin (STZ) induced diabetes, and levosimendan-STZ diabetes. Upon confirmation of the success of the STZ diabetic model, intraperitoneal levosimendan (100µg/kg/week) was administrated to the assigned groups for 4 weeks. Then, the radial arm water maze was used to evaluate spatial learning and memory. Oxidative stress biomarkers and brain-derived neurotrophic factor were evaluated in hippocampal tissues.

RESULTS

The results showed that Diabetes Mellitus (DM) impaired both short- and long- term memory (P<0.01), while levosimendan protected the animals from memory impairment. In addition, levosimendan prevented DM-induced reduction in the hippocampal levels of superoxide dismutase and glutathione peroxidase (P<0.05). Moreover, the administration of levosimendan prevented DM-induced increases in hippocampal thiobarbituric acid reactive substances level (P<0.05). Furthermore, levosimendan restored the ratio of reduced/oxidized glutathione (GSH/GSSG) in DM rats to that observed in the control group (P<0.05).

CONCLUSIONS

In summary, DM induced learning and memory impairment, and treatment with levosimendan impeded this impairment probably through preventing alterations in the antioxidant system in the hippocampus.

Muscarinic Toxin 7 Signals Via Ca2+/Calmodulin-Dependent Protein Kinase Kinase β to Augment Mitochondrial Function and Prevent Neurodegeneration

Mitochondrial dysfunction is implicated in a variety of neurodegenerative diseases of the nervous system. Peroxisome proliferator–activated receptor-γ coactivator-1α (PGC-1α) is a regulator of mitochondrial function in multiple cell types. In sensory neurons, AMP-activated protein kinase (AMPK) augments PGC-1α activity and this pathway is depressed in diabetes leading to mitochondrial dysfunction and neurodegeneration. Antimuscarinic drugs targeting the muscarinic acetylcholine type 1 receptor (M₁R) prevent/reverse neurodegeneration by inducing nerve regeneration in rodent models of diabetes and chemotherapy-induced peripheral neuropathy (CIPN). Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ) is an upstream regulator of AMPK activity. We hypothesized that antimuscarinic drugs modulate CaMKKβ to enhance activity of AMPK, and PGC-1α, increase mitochondrial function and thus protect from neurodegeneration. We used the specific M₁R antagonist muscarinic toxin 7 (MT7) to manipulate muscarinic signaling in the dorsal root ganglia (DRG) neurons of normal rats or rats with streptozotocin-induced diabetes. DRG neurons treated with MT7 (100 nM) or a selective muscarinic antagonist, pirenzepine (1 μM), for 24 h showed increased neurite outgrowth that was blocked by the CaMKK inhibitor STO-609 (1 μM) or short hairpin RNA to CaMKKβ. MT7 enhanced AMPK phosphorylation which was blocked by STO-609 (1 μM). PGC-1α reporter activity was augmented up to 2-fold (p < 0.05) by MT7 and blocked by STO-609. Mitochondrial maximal respiration and spare respiratory capacity were elevated after 3 h of exposure to MT7 (p < 0.05). Diabetes and CIPN induced a significant (p < 0.05) decrease in corneal nerve density which was corrected by topical delivery of MT7. We reveal a novel M₁R-modulated, CaMKKβ-dependent pathway in neurons that represents a therapeutic target to enhance nerve repair in two of the most common forms of peripheral neuropathy.

The Coming Age of Flavonoids in the Treatment of Diabetic Complications

Diabetes mellitus (DM), and its micro and macrovascular complications, is one of the biggest challenges for world public health. Despite overall improvement in prevention, diagnosis and treatment, its incidence is expected to continue increasing over the next years. Nowadays, finding therapies to prevent or retard the progression of diabetic complications remains an unmet need due to the complexity of mechanisms involved, which include inflammation, oxidative stress and angiogenesis, among others. Flavonoids are natural antioxidant compounds that have been shown to possess anti-diabetic properties. Moreover, increasing scientific evidence has demonstrated their potential anti-inflammatory and anti-oxidant effects. Consequently, the use of these compounds as anti-diabetic drugs has generated growing interest, as is reflected in the numerous in vitro and in vivo studies related to this field. Therefore, the aim of this review is to assess the recent pre-clinical and clinical research about the potential effect of flavonoids in the amelioration of diabetic complications. In brief, we provide updated information concerning the discrepancy between the numerous experimental studies supporting the efficacy of flavonoids on diabetic complications and the lack of appropriate and well-designed clinical trials. Due to the well-described beneficial effects on different mechanisms involved in diabetic complications, the excellent tolerability and low cost, future randomized controlled studies with compounds that have adequate bioavailability should be evaluated as add-on therapy on well-established anti-diabetic drugs.

Autonomic Nervous System Dysfunction: JACC Focus Seminar

Autonomic nervous system control of the heart is a dynamic process in both health and disease. A multilevel neural network is responsible for control of chronotropy, lusitropy, dromotropy, and inotropy. Intrinsic autonomic dysfunction arises from diseases that directly affect the autonomic nerves, such as diabetes mellitus and the syndromes of primary autonomic failure. Extrinsic autonomic dysfunction reflects the changes in autonomic function that are secondarily induced by cardiac or other disease. An array of tests interrogate various aspects of cardiac autonomic control in either resting conditions or with physiological perturbations from resting conditions. The prognostic significance of these assessments have been well established. Clinical usefulness has not been established, and the precise mechanistic link to mortality is less well established. Further efforts are required to develop optimal approaches to delineate cardiac autonomic dysfunction and its adverse effects to develop tools that can be used to guide clinical decision-making.

Brain-Derived Microparticles (BDMPs) Contribute to Neuroinflammation and Lactadherin Reduces BDMP Induced Neuroinflammation and Improves Outcome After Stroke

Microparticles (MPs, ~size between 0.1 and 1 mm) are lipid encased containers derived from intact cells which contain antigen from the parent cells. MPs are involved in intercellular communication and regulate inflammation. Stroke increases secretion of brain derived MP (BDMP) which activate macrophages/microglia and induce neuroinflammation. Lactadherin (Milk fat globule–EGF factor-8) binds to anionic phospholipids and extracellular matrices, promotes apoptotic cell clearance and limits pathogenic antigen cross presentation. In this study, we investigate whether BDMP affects stroke-induced neuroinflammation and whether Lactadherin treatment reduces stroke initiated BDMP-induced neuroinflammation, thereby improving functional outcome after stroke. Middle aged (8–9 months old) male C57BL/6J mice were subjected to distal middle cerebral artery occlusion (dMCAo) stroke, and BDMPs were extracted from ischemic brain 24 h after dMCAo by ultracentrifugation. Adult male C57BL/6J mice were subjected to dMCAo and treated via tail vein injection at 3 h after stroke with: (A) +PBS (n = 5/group); (B) +BDMPs (1.5 × 10⁸, n = 6/group); (C) +Lactadherin (400 μg/kg, n = 5/group); (D) +BDMP+Lactadherin (n = 6/group). A battery of neurological function tests were performed and mice sacrificed for immunostaining at 14 days after stroke. Blood plasma was used for Western blot assay. Our data indicate: (1) treatment of Stroke with BDMP significantly increases lesion volume, neurological deficits, blood brain barrier (BBB) leakage, microglial activation, inflammatory cell infiltration (CD45, microglia/macrophages, and neutrophils) into brain, inflammatory factor (TNFα, IL6, and IL1β) expression in brain, increases axon/white matter (WM) damage identified by decreased axon and myelin density, and increases inflammatory factor expression in the plasma when compared to PBS treated stroke mice; (2) when compared to PBS and BDMP treated stroke mice, Lactadherin and BDMP+Lactadherin treatment significantly improves neurological outcome, and decreases lesion volume, BBB leakage, axon/WM injury, inflammatory cell infiltration and inflammatory factor expression in the ischemic brain, respectively. Lactadherin treatment significantly increases anti-inflammatory factor (IL10) expression in ischemic brain and decreases IL1β expression in plasma compared to PBS and BDMP treated stroke mice, respectively. BDMP increases neuroinflammation and aggravates ischemic brain damage after stroke. Thus, Lactadherin exerts anti-inflammatory effects and improves the clearance of MPs to reduce stroke and BDMP induced neurological deficits.

Relationship between Systemic Vascular Characteristics and Retinal Nerve Fiber Layer Loss in Patients with Type 2 Diabetes

Retinal nerve fiber layer (RNFL) loss in diabetic patients is especially common regardless of diabetic retinopathy (DR). The correlations between nonglaucomatous RNFL loss and systemic characteristics in diabetic patients have aroused interests in many aspects. 167 subjects with type 2 diabetes who underwent evaluation for arterial stiffness and cardiovascular autonomic function using heart rate variability (HRV) were included in this study. Arterial stiffness was measured using cardio-ankle vascular index (CAVI) and ankle-brachial index (ABI). Multivariate regression analysis was performed to determine factors influencing the presence of RNFL loss according to age. Factors determining the superior location of diabetic RNFL loss were also investigated. CAVI were worse in patients with RNFL loss, especially in those with old age (≥50 yrs) (p = 0.037). Influential factor of RNFL defect in old group was ABI (p = 0.007). However, in young group (<50 yrs), HRV parameter (low-frequency/high-frequency ratio) determined the presence of RNFL loss (p = 0.040). Significant determinants of superior RNFL defect in old subjects were CAVI and ABI (p = 0.032 and p = 0.024). For young diabetic patients, autonomic dysfunction may have relationship with RNFL loss, but as patients get older, arterial stiffness could aggravate vascular autoregulation and diabetic RNFL loss. RNFL loss in diabetes may be correlated with systemic vascular conditions.

Increased Activation of the TRESK K+ Mediates Vago-Vagal Reflex Malfunction in Diabetic Rats

BACKGROUND & AIMS

Patients with diabetes have defects in the vagal afferent pathway that result in abnormal gastrointestinal function. We investigated whether selective increased activation of the 2-pore domain potassium channel TRESK (2-pore-domain weak inward-rectifying potassium channel-related spinal cord potassium channel) contributes to nodose ganglia (NG) malfunction, disrupting gastrointestinal function in diabetic rats.

METHODS

We conducted whole-cell current-clamp and single-unit recordings in NG neurons from diabetes-prone BioBreeding/Worcester rats and streptozotocin-induced diabetic (STZ-D) rats and compared them with control rats. NG neurons in rats or cultured NG neurons were exposed to pharmacologic antagonists and/or transfected with short hairpin or small interfering RNAs that reduced expression of TRESK. We then made electrophysiologic recordings and studied gastrointestinal functions.

RESULTS

We observed reduced input resistance, hyperpolarized membrane potential, and increased current threshold to elicit action potentiation in NG neurons of STZ-D rats compared with controls. NG neuron excitability was similarly altered in diabetes-prone rats. In vivo single-unit NG neuronal discharges in response to 30 and 60 pmol cholecystokinin octapeptide were significantly lower in STZ-D rats compared with controls. Reducing expression of the TRESK K+ channel restored NG excitability in vitro and in vivo, as well as cholecystokinin 8-stimulated secretion of pancreatic enzymes and secretin-induced gastrointestinal motility, which are mediated by vago-vagal reflexes. These abnormalities resulted from increased intracellular Ca2+ in the NG, activating calcineurin, which, in turn, bound to an nuclear factor of activated T cell-like docking site on the TRESK protein, resulting in neuronal membrane hyperpolarization.

CONCLUSIONS

In 2 rate models of diabetes, we found that activation of the TRESK K+ channel reduced NG excitability and disrupted gastrointestinal functions.

Glucotoxic Mechanisms and Related Therapeutic Approaches

Neuropathy is the earliest and commonest complication of diabetes. With increasing duration of diabetes, frequency and severity of neuropathy are worsened. Long-term hyperglycemia is therefore implicated in the development of this disorder. Nerve tissues require glucose energy to function and survive. Upon excessive glucose entry into the peripheral nerve, the glycolytic pathway and collateral glucose-utilizing pathways are overactivated and initiate adverse effects on nerve tissues. During hyperglycemia, flux through the polyol pathway, formation of advanced glycation end-products, production of free radicals, flux into the glucosamine pathway, and protein kinase C activity are all enhanced to negatively influence nerve function and structure. Suppression of these aberrant metabolic pathways has succeeded in prevention and inhibition of the development of neuropathy in animal models with diabetes. Satisfactory results were not attained, however, in patients with diabetes and further clinical trials are required. In this review, the author summarizes the hitherto proposed theories on the pathogenesis of diabetic neuropathy related to glucose metabolism and future prospects for the effective treatment of neuropathy.

Mitochondrial dysfunction in diabetic neuropathy: a series of unfortunate metabolic events

Diabetic neuropathy is a dying back neurodegenerative disease of the peripheral nervous system where mitochondrial dysfunction has been implicated as an etiological factor. Diabetes (type 1 or type 2) invokes an elevation of intracellular glucose concentration simultaneously with impaired growth factor support by insulin, and this dual alteration triggers a maladaptation in metabolism of adult sensory neurons. The energy sensing pathway comprising the AMP-activated protein kinase (AMPK)/sirtuin (SIRT)/peroxisome proliferator-activated receptor-γ coactivator α (PGC-1α) signaling axis is the target of these damaging changes in nutrient levels, e.g., induction of nutrient stress, and loss of insulin-dependent growth factor support and instigates an aberrant metabolic phenotype characterized by a suppression of mitochondrial oxidative phosphorylation and shift to anaerobic glycolysis. There is discussion of how this loss of mitochondrial function and transition to overreliance on glycolysis contributes to the diminishment of collateral sprouting and axon regeneration in diabetic neuropathy in the context of the highly energy-consuming nerve growth cone.

Neurorestorative Therapy of Stroke in Type 2 Diabetes Mellitus Rats Treated With Human Umbilical Cord Blood Cells

BACKGROUND AND PURPOSE

Diabetes mellitus is a high-risk factor for ischemic stroke. Diabetic stroke patients suffer worse outcomes, poor long-term recovery, risk of recurrent strokes, and extensive vascular damage. We investigated the neurorestorative effects and the underlying mechanisms of stroke treatment with human umbilical cord blood cells (HUCBCs) in type 2 diabetes mellitus (T2DM) rats.

METHODS

Adult male T2DM rats were subjected to 2 hours of middle cerebral artery occlusion (MCAo). Three days after MCAo, rats were treated via tail-vein injection with (1) PBS and (2) HUCBCs (5×10(6)), n=10 per group.

RESULTS

HUCBC stroke treatment initiated 3 days after MCAo in T2DM rats did not significantly decrease blood-brain barrier leakage (P=0.1) and lesion volume (P=0.078), but significantly improved long-term functional outcome and decreased brain hemorrhage (P<0.05) when compared with the PBS-treated T2DM MCAo control group. HUCBC treatment significantly promoted white matter remodeling as indicated by increased expression of Bielschowsky silver (axons marker), Luxol fast blue (myelin marker), SMI-31 (neurofilament), and Synaptophysin in the ischemic border zone. HUCBC promoted vascular remodeling and significantly increased arterial and vascular density. HUCBC treatment of stroke in T2DM rats significantly increased M2 macrophage polarization (increased M2 macrophage, CD163and CD 206; decreased M1 macrophage, ED1 and inducible nitric oxide synthase expression) in the ischemic brain compared with PBS-treated T2DM MCAo controls (P<0.05). HUCBC also significantly decreased proinflammatory factors, that is, matrix metalloproteinase 9, receptor for advanced glycation end products and toll-like receptor 4 expression in the ischemic brain.

CONCLUSIONS

HUCBC treatment initiated 3 days after stroke significantly increased white matter and vascular remodeling in the ischemic brain as well as decreased neuroinflammatory factor expression in the ischemic brain in T2DM rats and promoted M2 macrophage polarization. HUCBC reduction of neuroinflammation and increased vascular and white matter axonal remodeling may contribute to the HUCBC-induced beneficial effects in T2DM stroke rats.

Identification of proteins in hyperglycemia and stroke animal models

BACKGROUND

Stroke is a major cause of disability and death in adults. Diabetes mellitus is a metabolic disorder that strongly increases the risk of severe vascular diseases. This study compared changes in proteins of the cerebral cortex during ischemic brain injury between nondiabetic and diabetic animals.

METHODS

Adult male rats were injected with streptozotocin (40 mg/kg) via the intraperitoneal route to induce diabetes and underwent surgical middle cerebral artery occlusion (MCAO) 4 wk after streptozotocin treatment. Cerebral cortex tissues were collected 24 h after MCAO and cerebral cortex proteins were analyzed by two-dimensional gel electrophoresis and mass spectrometry.

RESULTS

Several proteins were identified as differentially expressed between nondiabetic and diabetic animals. Among the identified proteins, we focused on the following metabolism-related enzymes: isocitrate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, adenosylhomocysteinase, pyruvate kinase, and glucose-6-phosphate isomerase (neuroleukin). Expression of these proteins was decreased in animals that underwent MCAO. Moreover, protein expression was reduced to a greater extent in diabetic animals than in nondiabetic animals. Reverse transcription-polymerase chain reaction analysis confirmed that the diabetic condition exacerbates the decrease in expression of metabolism-related proteins after MCAO.

CONCLUSIONS

These results suggest that the diabetic condition may exacerbate brain damage during focal cerebral ischemia through the downregulation of metabolism-related proteins.

Lower urinary tract dysfunction in patients with peripheral nervous system lesions

The prevalence of lower urinary tract (LUT) dysfunction in peripheral nervous system (PNS) disorders is larger than in comparable control populations. This is particularly true for polyneuropathies with autonomic nervous system involvement, and for localized lesions with LUT innervation. LUT symptoms may be the guide to the diagnosis of processes localized in the lumbosacral spinal canal (as in cauda equina syndrome), and in the pelvis. Typical LUT dysfunctions (LUTD) caused by PNS involvement include bladder and sphincter hypoactivity with poor emptying, and incontinence. Paradoxically, bladder overactivity may also occur in pure PNS lesions. The acute cauda equina syndrome is an emergency requiring magnetic resonance imaging and surgery; in chronic neurogenic LUTD due to PNS involvement, the diagnosis of the lesion may be clarified by clinical neurophysiologic testing. Other important causes of neurogenic LUT dysfunction are perineoabdominal and pelvic surgeries. Surgeons are devising nerve-sparing techniques to prevent such major and often persistent complications in patients who are otherwise cured of the underlying disease. LUTD significantly affects the quality of life in patients and may lead to recurring urinary infections and upper urinary tract involvement. Thorough assessment of LUT function by urodynamics may be necessary in patients who are not improved by simple conservative measures.

Metabolic regulator LKB1 is crucial for Schwann cell-mediated axon maintenance

Schwann cells (SCs) promote axonal integrity independently of myelination by poorly understood mechanisms. Current models suggest that SC metabolism is critical for this support function and that SC metabolic deficits may lead to axonal demise. The LKB1-AMP-activated protein kinase (AMPK) kinase pathway targets several downstream effectors, including mammalian target of rapamycin (mTOR), and is a key metabolic regulator implicated in metabolic diseases. We found through molecular, structural and behavioral characterization of SC-specific mutant mice that LKB1 activity is central to axon stability, whereas AMPK and mTOR in SCs are largely dispensable. The degeneration of axons in LKB1 mutants was most dramatic in unmyelinated small sensory fibers, whereas motor axons were comparatively spared. LKB1 deletion in SCs led to abnormalities in nerve energy and lipid homeostasis and to increased lactate release. The latter acts in a compensatory manner to support distressed axons. LKB1 signaling is essential for SC-mediated axon support, a function that may be dysregulated in diabetic neuropathy.

Calcium signalling in sensory neurones and peripheral glia in the context of diabetic neuropathies

Peripheral sensory nervous system is comprised of neurones with their axons and neuroglia that includes satellite glial cells in sensory ganglia, myelinating, non-myelinating and perisynaptic Schwann cells. Pathogenesis of peripheral diabetic polyneuropathies is associated with aberrant function of both neurones and glia. Deregulated Ca(2+) homoeostasis and aberrant Ca(2+) signalling in neuronal and glial elements contributes to many forms of neuropathology and is fundamental to neurodegenerative diseases. In diabetes both neurones and glia experience metabolic stress and mitochondrial dysfunction which lead to deregulation of Ca(2+) homeostasis and Ca(2+) signalling, which in their turn lead to pathological cellular reactions contributing to development of diabetic neuropathies. Molecular cascades responsible for Ca(2+) homeostasis and signalling, therefore, can be regarded as potential therapeutic targets.

Temporal dystrophic remodeling within the intrinsic cardiac nervous system of the streptozotocin-induced diabetic rat model

Introduction

The pathogenesis of heart failure (HF) in diabetic individuals, called “diabetic cardiomyopathy”, is only partially understood. Alterations in the cardiac autonomic nervous system due to oxidative stress have been implicated. The intrinsic cardiac nervous system (ICNS) is an important regulatory pathway of cardiac autonomic function, however, little is known about the alterations that occur in the ICNS in diabetes. We sought to characterize morphologic changes and the role of oxidative stress within the ICNS of diabetic hearts. Cultured ICNS neuronal cells from the hearts of 3- and 6-month old type 1 diabetic streptozotocin (STZ)-induced diabetic Sprague-Dawley rats and age-matched controls were examined. Confocal microscopy analysis for protein gene product 9.5 (PGP 9.5) and amino acid adducts of (E)-4-hydroxy-2-nonenal (4-HNE) using immunofluorescence was undertaken. Cell morphology was then analyzed in a blinded fashion for features of neuronal dystrophy and the presence of 4-HNE adducts.

Results

At 3-months, diabetic ICNS neuronal cells exhibited 30% more neurite swellings per area (p = 0.01), and had a higher proportion with dystrophic appearance (88.1% vs. 50.5%; p = <0.0001), as compared to control neurons. At 6-months, diabetic ICNS neurons exhibited more features of dystrophy as compared to controls (74.3% vs. 62.2%; p = 0.0448), with 50% more neurite branching (p = 0.0015) and 50% less neurite outgrowth (p = <0.001). Analysis of 4-HNE adducts in ICNS neurons of 6-month diabetic rats demonstrated twice the amount of reactive oxygen species (ROS) as compared to controls (p = <0.001).

Conclusion

Neuronal dystrophy occurs in the ICNS neurons of STZ-induced diabetic rats, and accumulates temporally within the disease process. In addition, findings implicate an increase in ROS within the neuronal processes of ICNS neurons of diabetic rats suggesting an association between oxidative stress and the development of dystrophy in cardiac autonomic neurons.

Increased peripherin in sympathetic axons innervating plantar metatarsal arteries in STZ-induced type I diabetic rats

A common characteristic of axonopathy is the abnormal accumulation of cytoskeletal proteins. We recently reported that streptozotocin (STZ)-induced type 1 diabetes produced a change in the morphology of sympathetic nerve fibers supplying rat plantar metatarsal arteries (PMAs). Here we investigated whether these morphological changes are associated with axonal accumulation of the type III intermediate filament peripherin and the microtubule protein β-tubulin III, as both are implicated in axonal remodeling. PMAs from hyperglycemic STZ-treated rats receiving a low dose of insulin (STZ-LI) were compared with those from normoglycemic STZ-treated rats receiving a high dose of insulin (STZ-HI) and vehicle-treated controls. Western blotting revealed an increase in protein expression level for peripherin in PMAs from STZ-LI rats but no change in that for β-tubulin III. In addition, there was an increase in the number of peripherin immunoreactive nerve fibers in the perivascular nerve plexus of PMAs from STZ-LI rats. Co-labeling for peripherin and neuropeptide Y (a marker for sympathetic axons) revealed that peripherin immunoreactivity increased in sympathetic axons. None of these changes were detected in PMAs from STZ-HI rats, indicating that increased peripherin in sympathetic axons of STZ-LI rats is likely due to hyperglycemia and provides a marker of diabetes-induced nerve damage.

Diabetic neuropathy: an evaluation of the use of quercetin in the cecum of rats

AIM

To investigate the effect of quercetin supplementation on the myenteric neurons and glia in the cecum of diabetic rats.

METHODS

Total preparations of the muscular tunic were prepared from the ceca of twenty-four rats divided into the following groups: control (C), control supplemented with quercetin (200 mg/kg quercetin body weight) (CQ), diabetic (D) and diabetic supplemented with quercetin (DQ). Immunohistochemical double staining technique was performed with HuC/D (general population)/nitric oxide synthase (nNOS), HuC-D/S-100 and VIP. Density analysis of the general neuronal population HuC/D-IR, the nNOS-IR (nitrergic subpopulation) and the enteric glial cells (S-100) was performed, and the morphometry and the reduction in varicosity population (VIP-IR) in these populations were analyzed.

RESULTS

Diabetes promoted a significant reduction (25%) in the neuronal density of the HuC/D-IR (general population) and the nNOS-IR (nitrergic subpopulation) compared with the C group. Diabetes also significantly increased the areas of neurons, glial cells and VIP-IR varicosities. Supplementation with quercetin in the DQ group prevented neuronal loss in the general population and increased its area (P < 0.001) and the area of nitrergic subpopulation (P < 0.001), when compared to C group. Quercetin induced a VIP-IR and glial cells areas (P < 0.001) in DQ group when compared to C, CQ and D groups.

CONCLUSION

In diabetes, quercetin exhibited a neuroprotective effect by maintaining the density of the general neuronal population but did not affect the density of the nNOS subpopulation.

Cardiovascular autonomic dysfunction in non-obese diabetic mice

It is known that diabetes is associated with autonomic dysfunction; however, data about autonomic function in non-obese diabetic mice (NOD) remain scarce. We evaluated the autonomic profile of NOD mice. Female mice, 24-28 week old, were divided in two groups: NOD (n = 6) and control (n = 6, Swiss mice). NOD mice with glycemia ≥ 300 mg/dl were used. Heart rate variability (HRV) and arterial pressure variability (APV) in time and frequency domains, symbolic analysis of heart rate (HR) and baroreflex sensitivity were evaluated. HR and arterial pressure (AP) were similar between the groups; however, HRV (total variance of RR interval: NOD=21.07 ± 3.75 vs. C = 42.02 ± 6.54 ms(2)) and the vagal modulation index RMSSD were lower in NOD group (4.01 ± 0.32 vs. 8.28 ± 0.97 ms). Moreover, the absolute and normalized low-frequency (LF) components were also enhanced in NOD (normalized = 61.0 ± 4.0%) as compared to control mice (normalized = 20.0 ± 4.0%). Both the absolute and normalized high-frequency (HF) components were lower in NOD (normalized = 39.0 ± 4.0%) when compared to the control group (normalized = 80.0 ± 4.0). In the symbolic analysis the 0V pattern, an indication of sympathetic activity, was higher in NOD and 2 LV pattern, an indication of parasympathetic activity, was lower in the NOD than in the control group. Both bradycardic and tachycardic responses were decreased in NOD (3.01 ± 0.72 vs. 4.54 ± 0.36 bpm/mmHg and 2.49 ± 0.31 vs. C = 3.43 ± 0.33 bpm/mmHg) when compared to the control group. Correlation analysis showed negative correlations between vagal indexes (RMSSD, %HF and 2LV) and glycemic levels. In conclusion, NOD mice develop severe diabetes correlated with autonomic dysfunction.

The role of aberrant mitochondrial bioenergetics in diabetic neuropathy

Diabetic neuropathy is a neurological complication of diabetes that causes significant morbidity and, because of the obesity-driven rise in incidence of type 2 diabetes, is becoming a major international health problem. Mitochondrial phenotype is abnormal in sensory neurons in diabetes and may contribute to the etiology of diabetic neuropathy where a distal dying-back neurodegenerative process is a key component contributing to fiber loss. This review summarizes the major features of mitochondrial dysfunction in neurons and Schwann cells in human diabetic patients and in experimental animal models (primarily exhibiting type 1 diabetes). This article attempts to relate these findings to the development of critical neuropathological hallmarks of the disease. Recent work reveals that hyperglycemia in diabetes triggers nutrient excess in neurons that, in turn, mediates a phenotypic change in mitochondrial biology through alteration of the AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) signaling axis. This vital energy sensing metabolic pathway modulates mitochondrial function, biogenesis and regeneration. The bioenergetic phenotype of mitochondria in diabetic neurons is aberrant due to deleterious alterations in expression and activity of respiratory chain components as a direct consequence of abnormal AMPK/PGC-1α signaling. Utilization of innovative respirometry equipment to analyze mitochondrial function of cultured adult sensory neurons from diabetic rodents shows that the outcome for cellular bioenergetics is a reduced adaptability to fluctuations in ATP demand. The diabetes-induced maladaptive process is hypothesized to result in exhaustion of the ATP supply in the distal nerve compartment and induction of nerve fiber dissolution. The role of mitochondrial dysfunction in the etiology of diabetic neuropathy is compared with other types of neuropathy with a distal dying-back pathology such as Friedreich ataxia, Charcot-Marie-Tooth disease type 2 and human immunodeficiency virus-associated distal-symmetric neuropathy.

Niaspan increases axonal remodeling after stroke in type 1 diabetes rats

BACKGROUND AND OBJECTIVE

We investigated axonal plasticity in the bilateral motor cortices and the long term therapeutic effect of Niaspan on axonal remodeling after stroke in type-1 diabetic (T1DM) rats.

EXPERIMENTAL APPROACHES

T1DM was induced in young adult male Wistar rats via injection of streptozotocin. T1DM rats were subjected to 2h transient middle cerebral artery occlusion (MCAo) and were treated with 40 mg/kg Niaspan or saline starting 24 h after MCAo and daily for 28 days. Anterograde tracing using biotinylated dextran amine (BDA) injected into the contralateral motor cortex was performed to assess axonal sprouting in the ipsilateral motor cortex area. Functional outcome, SMI-31 (a pan-axonal microfilament marker), Bielschowsky silver and synaptophysin expression were measured. In vitro studies using primary cortical neuron (PCN) cultures and in vivo BDA injection into the brain to anterogradely label axons and terminals were employed.

RESULTS

Niaspan treatment of stroke in T1DM-MCAo rats significantly improved functional outcome after stroke and increased SMI-31, Bielschowsky silver and synaptophysin expression in the ischemic brain compared to saline treated T1DM-MCAo rats (p<0.05). Using BDA to anterograde label axons and terminals, Niaspan treatment significantly increased axonal density in ipsilateral motor cortex in T1DM-MCAo rats (p<0.05, n=7/group). Niacin treatment of PCN significantly increased Ang1 expression under high glucose condition. Niacin and Ang1 significantly increased neurite outgrowth, and anti-Ang1 antibody marginally attenuated Niacin induced neurite outgrowth (p=0.06, n=6/group) in cultured PCN under high glucose condition.

CONCLUSION

Niaspan treatment increased ischemic brain Ang1 expression and promoted axonal remodeling in the ischemic brain as well as improved functional outcome after stroke. Ang1 may partially contribute to Niaspan-induced axonal remodeling after stroke in T1DM-rats.

Selective responses of myenteric neurons to oxidative stress and diabetic stimuli

BACKGROUND

Diabetes has a differential effect on different subpopulations of myenteric neurons. Our aim was to investigate an in vitro model to examine the pathways underlying the development of nerve changes in diabetes.

METHODS

The proportions of neuronal cell bodies containing vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS) and calbindin relative to the pan-neuronal marker HuC/D were quantified in wholemount preparations of the myenteric plexus of adult rat ileum using double labeling immunohistochemistry. Preparations were maintained in culture for 24 h in the presence and absence of stimuli mimicking the diabetic environment including oxidative stress, carbonyl stress, high glucose and advanced glycation end products (AGEs). Data were compared with the effect of streptozotocin-induced diabetes in vivo. KEY RESULTS Only oxidative stress in vitro produced the same pattern as observed in diabetes with an increase in VIP-, decrease in nNOS-, and no change in calbindin-positive neurons. Carbonyl stress and high glucose caused an increase in VIP-containing neurons without affecting nNOS expression. In contrast, exposure to AGEs only caused a decrease in nNOS-positive neurons. Calbindin expression was unaffected by any of the stimuli. The effects of the stimuli were prevented by the antioxidant, α-lipoic acid, or the carbonyl scavenger, aminoguanidine.

CONCLUSIONS & INFERENCES

The results provide evidence that oxidative stress is the common factor in the development of neuronal changes in diabetes; however, the mechanism by which oxidative stress occurs depends on the individual subpopulation of myenteric neurons examined. The presence of calbindin appears to protect myenteric neurons against harmful stimuli.

Persistence of acidosis in alloxan-induced diabetic rats treated with the juice of Asystasia gangetica leaves

BACKGROUND

Diabetes mellitus is gradually becoming a global health burden leading to an increase in the search for herbal hypoglycemic agents as alternatives to synthetic ones. Asystasia gangetica is one of the herbs used in folklore system of medicine for managing hypoglycaemia associated with diabetes.

MATERIALS AND METHODS

The influence of the juice of A. gangetica leaf on alloxan-induced diabetic rats was assessed by treating diabetic rats with 25%, 50% and 75% fresh juice and glibenclamide for 5 weeks. Afterwards, the plasma concentrations of glucose, triacylglycerols, total cholesterol, high-density lipoprotein (HDL) cholesterol, thiobarbituric acid reactive substances and bicarbonate were assayed spectrophotometrically.

RESULTS

Treatment of the diabetic rats with the juice significantly (P < 0.05) reduced the elevated plasma levels of glucose to a level not significantly (P > 0.05) different from that of glibenclamide. The juice also significantly (P < 0.05) reduced the plasma lipid peroxidation and improved the lipid profile, as indicated by a significant (P < 0.05) reduction in the total cholesterol: HDL cholesterol ratio. However, there was a significant (P < 0.05) rise in the level of bicarbonate as result of the juice treatment from 28.15 ± 2.82 mmol/l in normal control to 60.83 ± 17.46 mmol/l in diabetic control and to 122.20 ± 34.68 mmol/l, 120.95 ± 35.09 mmol/l and 115.85 ± 11.79 mmol/l in 25%, 50% and 75% juice, respectively.

CONCLUSION

Therefore, this inability of A. gangetica to prevent acidosis detracts from the potential of its usefulness in managing diabetes.

Pharmacokinetics, pharmacodynamics, tolerability, and safety of a novel sorbitol dehydrogenase inhibitor in healthy participants

Increased glucose flux through the polyol pathway and the resultant oxidative stress is thought to be a major mechanistic contributor to microvascular diabetic complications. Inhibition of flux through this pathway can be blocked through inhibition of either of 2 enzymes, aldose reductase (AR) or sorbitol dehydrogenase (SDH). This report describes the pharmacokinetics, biomarker pharmacodynamics, and safety of CP-642,931, a potent and specific sorbitol dehydrogenase inhibitor (SDI). CP-642,931 was administered for 7 days to 57 healthy volunteers in doses ranging from 1 to 35 mg daily. After the 35-mg dose, CP-642,931 showed a t((1/2)) of 20.1 hours and t(max) at 0.5 to 1.25 hours. After a 35-mg dose, maximum inhibition of SDH was 91% (on days 1 and 7), and maximum serum sorbitol increase was 152-fold on day 7 compared to control. Five participants discontinued the study due to adverse events, including myalgia, muscle spasm, and muscle fatigue. All symptoms resolved in all but 1 participant, who continued to report intermittent muscle fasciculations upon follow-up. In conclusion, CP-642,931 is a potent and specific SDI that is rapidly absorbed through the oral route and effectively inhibits SDH. However, the drug is not well tolerated due to adverse neuromuscular effects.

Mitochondrial stress and the pathogenesis of diabetic neuropathy

Diabetic neuropathy is a major complication of diabetes that affects the sensory and autonomic nervous systems and leads to significant morbidity and impact on quality of life of patients. Mitochondrial stress has been proposed as a major mediator of neurodegeneration in diabetes. This review briefly summarizes the nature of sensory and autonomic nerve dysfunction and presents these findings in the context of diabetes-induced nerve degeneration mediated by alterations in mitochondrial ultrastructure, physiology and trafficking. Diabetes-induced dysfunction in calcium homeostasis is discussed at length and causative associations with sub-optimal mitochondrial physiology are developed. It is clear that across a range of complications of diabetes that mitochondrial physiology is impaired, in general a reduction in electron transport chain capability is apparent. This abnormal activity may predispose mitochondria to generate elevated reactive oxygen species (ROS), although experimental proof remains lacking, but more importantly will deleteriously alter the bioenergetic status of neurons. It is proposed that the next five years of research should focus on identifying changes in mitochondrial phenotype and associated cellular impact, identifying sources of ROS in neurons and analyzing mitochondrial trafficking under diabetic conditions.

Effects of insulin-like growth factor-1 (IGF-1) receptor signaling on rates of apoptosis in retina of dopamine beta hydroxylase (Dbh-/-) knockout mice

We have investigated whether insulin-like growth factor-1 (IGF-1) receptor signaling alters rates of apoptosis in dopamine beta-hydroxylase (Dbh(-/-)) knockout mice. Retinal lysates from Dbh(-/-) and their heterozygote littermates (Dbh(+/-)) were used to examine the role of norepinephrine in the regulation of IGF-1 receptor signaling and apoptosis in the retina. Western blot analysis was done for protein levels of total and phosphorylated IGF-1 receptor, insulin receptor substrate-1 (IRS-1), insulin receptor substrate-2 (IRS-2), and Akt. A caspase 3 ELISA and dopamine ELISA were done on retinal lysates. To verify which regions of the retina were undergoing apoptosis, TUNEL labeling was performed. No changes in dopamine were noted between the KO and heterozygote mice. IGF-1 receptor phosphorylation was significantly decreased in Dbh(-/-) mice as compared to their heterozygote littermates (P<0.05 vs. heterozygous mice). IRS-1 protein phosphorylation was significantly decreased in KO mice (P<0.05 vs. heterozygous mice), while no significant changes were noted in IRS-2 protein phosphorylation. Akt protein phosphorylation was also reduced in the KO mice, likely leading to increased cleaved caspase 3 levels. The increase in apoptosis in the Dbh(-/-) mice occurred predominantly in the inner retina. Our results suggest that IGF-1 receptor signaling is reduced in the retina of mice with dysfunctional adrenergic receptor signaling. The data also indicate that IGF-1 receptor signaling occurs primarily through IRS-1, rather than IRS-2. The reduction in Akt phosphorylation, likely through reduced IGF-1 receptor signaling, could explain the increase in cleaved caspase 3, leading to apoptosis. These results suggest that alterations in adrenergic receptor signaling modulate IGF-1 receptor signaling, which can regulate apoptosis in the retina.

Diabetic gastroparesis: diagnosis and management

Gastric emptying is frequently abnormal in patients with long-standing type 1 and type 2 diabetes mellitus. Symptoms commonly associated with disordered gastric emptying include nausea, vomiting, bloating and epigastric pain, while patients are also at risk of malnutrition, weight loss, impaired drug absorption, disordered glycaemic control and poor quality of life. Although often attributed to the presence of irreversible autonomic neuropathy, acute hyperglycaemia represents a potentially reversible cause of gastric dysfunction in diabetes. Scintigraphy represents the gold standard for measuring gastric emptying. The management of diabetic gastroparesis is less than optimal, partly because the pathogenesis has not been clearly defined. Treatment approaches include dietary modification and optimization of glycaemia, and the use of prokinetic drugs, while novel therapies such as gastric electrical stimulation are the subject of ongoing investigation.

Human cerebral neuropathology of Type 2 diabetes mellitus

The cerebral neuropathology of Type 2 diabetes (CNDM2) has not been positively defined. This review includes a description of CNDM2 research from before the 'Pubmed Era'. Recent neuroimaging studies have focused on cerebrovascular and white matter pathology. These and prior studies about cerebrovascular histopathology in diabetes are reviewed. Evidence is also described for and against the link between CNDM2 and Alzheimer's disease pathogenesis. To study this matter directly, we evaluated data from University of Kentucky Alzheimer's Disease Center (UK ADC) patients recruited while non-demented and followed longitudinally. Of patients who had come to autopsy (N = 234), 139 met inclusion criteria. These patients provided the basis for comparing the prevalence of pathological and clinical indices between well-characterized cases with (N = 50) or without (N = 89) the premortem diagnosis of diabetes. In diabetics, cerebrovascular pathology was more frequent and Alzheimer-type pathology was less frequent than in non-diabetics. Finally, a series of photomicrographs demonstrates histopathological features (including clinical-radiographical correlation) observed in brains of persons that died after a history of diabetes. These preliminary, correlative, and descriptive studies may help develop new hypotheses about CNDM2. We conclude that more work should be performed on human material in the context of CNDM2.

Increased basement membrane thickness, pericyte ghosts, and loss of retinal thickness and cells in dopamine beta hydroxylase knockout mice

Diabetes can cause damage to sympathetic nerves, and we have previously shown that experimental sympathectomy can produce capillary abnormalities in the retina similar to those seen in early diabetes. We postulate that the diabetes-induced loss of the sympathetic system, and at least in part the sympathetic neurotransmitter norepinephrine (NE), contributes to the development of retinal vascular and neural abnormalities in diabetes. Thus, we predict that non-diabetic animals that lack NE will develop microvascular and neural changes that are similar to those that are characteristic of diabetic retinopathy. To test this, retinas from non-diabetic dopamine beta hydroxylase (Dbh, Dbh(-/-)) knockout mice and their littermate controls were assessed for diabetic-like capillary and neural changes at 5 months of age. Genetic deletion of Dbh resulted in a significant decrease in retinal thickness and number of cells in the retinal ganglion cell layer (central retinal region). In addition, the number of pericyte ghosts and the basement membrane of retinal capillaries were significantly increased in the Dbh(-/-) mice. These results provide evidence that loss of sympathetic neurotransmission may contribute to the microvascular and neural changes of diabetic retinopathy. Restoration of sympathetic neurotransmission may be a new target for therapeutic intervention to inhibit the early phases of diabetic retinopathy.

Synaptic ultrastructural alterations anticipate the development of neuroaxonal dystrophy in sympathetic ganglia of aged and diabetic mice

Neuroaxonal dystrophy, a distinctive axonopathy characterized by marked enlargement of distal axons, is the hallmark pathologic alteration in aged and diabetic human prevertebral sympathetic ganglia and in corresponding rodent models. Neuroaxonal dystrophy is thought to represent the abnormal outcome of cycles of synaptic degeneration and regeneration; a systematic study of identified axon terminals in aged and diabetic prevertebral ganglia, however, has not previously been performed. We examined the initial changes that develop in presynaptic and postsynaptic elements in sympathetic ganglia of aged and diabetic mice and found numerous synaptic changes involving both presynaptic and postsynaptic elements. Early alterations in presynaptic axon terminal size, vesicle content, and morphology culminate in the development of anastomosing membranous tubulovesicular aggregates, accumulation of autophagosomes, and amorphous debris that form a continuum with progressively larger classically dystrophic swellings. Dendritic changes consist of the development of swellings composed of delicate tubulovesicular elements and mitochondriopathy characterized by increased numbers of small mitochondria and, exclusively in aged ganglia, megamitochondria. These results support the hypothesis that neuroaxonal dystrophy results from progressive changes in presynaptic axon terminals that likely involve membrane dynamics and which are accompanied by distinctive changes in postsynaptic dendritic elements.

Frequency and characteristics of extremely low accumulation of 123I-metaiodobenzylguanidine (MIBG) in patients with and without cardiovascular diseases

OBJECTIVE

Very low accumulation of 123I-metaiodobenzylguanidine (LoMIBG) in the human heart has been reported. This study assessed the frequency and characteristics of LoMIBG in the human heart.

METHODS

A total of 2212 patients (male/female ratio 1442/770, mean age 64 +/- 12 years) who underwent MIBG imaging were included. LoMIBG was defined as an initial heart-to-mediastinum (H/M) ratio of less than 1.4.

RESULTS

Of the 114 patients with LoMIBG, 2 patients were excluded because of taking imipramine. Patients with LoMIBG were older than those without LoMIBG (P < 0.0001). The main diagnosis and the number of patients with each disease were as follows: 28 of 410 coronary artery disease patients, 13 of 371 vasospastic angina patients, 3 of 86 various arrhythmias patients, 4 of 23 valvular heart disease patients, 9 of 101 dilated cardiomyopathy patients, 13 of 512 essential hypertension patients, 2 of 20 hypertrophic cardiomyopathy patients, 24 of 511 subjects without any definite disease (control), and 16 of 176 patients with miscellaneous diseases. When compared with patients without LoMIBG in each cardiovascular disease, LoMIBG patients had left ventricular function and frequency similar to critically ill patients. In the control group, the subjects with LoMIBG were significantly older (P < 0.0001) and had significantly higher HF (P < 0.03) and lower LF/HF (P < 0.001) than those without LoMIBG. In addition, the incidence of LoMIBG was significantly elevated in the elderly (P < 0.002).

CONCLUSIONS

LoMIBG occurred in patients both with various diseases and without obvious diseases. Aging may be one of the mechanisms contributing to LoMIBG, especially in patients without obvious diseases.

Structural remodeling of nucleus ambiguus projections to cardiac ganglia following chronic intermittent hypoxia in C57BL/6J mice

The baroreflex control of heart rate (HR) is reduced following chronic intermittent hypoxia (CIH). Since the nucleus ambiguus (NA) plays a key role in baroreflex control of HR, we examined whether CIH remodels vagal efferent projections to cardiac ganglia. C57BL/6J mice (3-4 months of age) were exposed to either room air (RA) or CIH for 3 months. Confocal microscopy was used to examine NA axons and terminals in cardiac ganglia following Fluoro-Gold (FG) injections to label cardiac ganglia, and microinjections of tracer DiI into the left NA to anterogradely label vagal efferents. We found that: 1) Cardiac ganglia were widely distributed on the dorsal surface of the atria. Although the total number of cardiac ganglia did not differ between RA and CIH mice, the size of ganglia and the somatic area of cardiac principal neurons (PNs) were significantly decreased (P < 0.01), and the size of the PN nuclei was increased following CIH (P < 0.01). 2) NA axons entered cardiac ganglia and innervated PNs with dense basket endings in both RA and CIH mice, and the percentage of innervated PNs was similar (RA: 50 +/- 1.0%; CIH: 49 +/- 1.0%; P > 0.10). In CIH mice, however, swollen cardiac axons and terminals without close contacts to PNs were found. Furthermore, varicose endings around PNs appeared swollen and the axonal varicose area around PNs was almost doubled in size (CIH: 163.1 +/- 6.4 microm(2); RA: 88 +/- 3.9 microm(2), P < 0.01). Thus, CIH significantly altered the structure of cardiac ganglia and resulted in reorganized vagal efferent projections to cardiac ganglia. Such remodeling of cardiac ganglia and vagal efferent projections provides new insight into the effects of CIH on the brain-heart circuitry of C57BL/6J mice.

Vitamin E supplementation in rats with experimental diabetes mellitus: analysis of myosin-V and nNOS immunoreactive myenteric neurons from terminal ileum

The effect of vitamin E (1 g/kg body weight) supplementation on myosin-V and neuronal nitric oxide synthase (nNOS) immunoreactive myenteric neurons from the ileum of diabetic rats was investigated in the present study. Forty animals were divided into the following groups: normoglycemics (N), normoglycemics treated with vitamin E (NE), diabetics (D), and diabetics treated with vitamin E (DE). Quantitative and morphometric analyses were performed. The area of the tertiary plexus was also determined. Diabetes produced a 24% reduction in the number of myosin-V neurons in group D compared with group N, an effect that was accompanied by an increase in the tertiary plexus area (P < 0.05). Neuronal density was 27% higher in group NE than group N (P < 0.05). Nitrergic neuronal density was not altered as a consequence of either diabetes or vitamin E treatment. Myosin-V and nNOS immunoreactive neuronal cell body area increased significantly in group NE. The area of myosin-V and nNOS myenteric neurons also increased in group D. Vitamin E treatment (group DE) increased only the size of nitrergic neurons. The present results suggest that vitamin E elicited a neuroprotective and neurotrophic effect on the natural aging process, but with regard to diabetes, vitamin E supplementation exerted a neurotrophic effect only on nitrergic neurons.

Effects of hyperglycemia on rat cavernous nerve axons: a functional and ultrastructural study

The present study explored parallel changes in the physiology and structure of myelinated (Adelta) and unmyelinated (C) small diameter axons in the cavernous nerve of rats associated with streptozotocin-induced hyperglycemia. Damage to these axons is thought to play a key role in diabetic autonomic neuropathy and erectile dysfunction, but their pathophysiology has been poorly studied. Velocities in slow conducting fibers were measured by applying multiple unit procedures; histopathology was evaluated with both light and electron microscopy. To our knowledge, these are the initial studies of slow nerve conduction velocities in the distal segments of the cavernous nerve. We report that hyperglycemia is associated with a substantial reduction in the amplitude of the slow conducting response, as well as a slowing of velocities within this very slow range (< 2.5 m/s). Even with prolonged hyperglycemia (> 4 months), histopathological abnormalities were mild and limited to the distal segments of the cavernous nerve. Structural findings included dystrophic changes in nerve terminals, abnormal accumulations of glycogen granules in unmyelinated and preterminal axons, and necrosis of scattered smooth muscle fibers. The onset of slowing of velocity in the distal cavernous nerve occurred subsequent to slowing in somatic nerves in the same rats. The functional changes in the cavernous nerve anticipated and exceeded the axonal degeneration detected by morphology. The physiologic techniques outlined in these studies are feasible in most electrophysiologic laboratories and could substantially enhance our sensitivity to the onset and progression of small fiber diabetic neuropathy.

Depletion of peptidergic innervation in the gastric mucosa of streptozotocin-induced diabetic rats

Autonomic neuropathy affecting the gastrointestinal system is a major presentation of diabetic neuropathy. Changes in the innervation of gastric mucosa or muscle layers can contribute to gastrointestinal symptoms. The present study investigated this issue by quantitatively analyzing the immunohistochemical patterns of the gastric innervation in rats with streptozotocin (STZ)-induced diabetes. In control rats, calcitonin gene-related peptide (CGRP) and substance P (SP) (+) nerve fibers appeared in the gastric mucosa and muscle layers. Double immunohistochemical staining showed that immunoreactivities for SP and CGRP were co-localized with a pan-neuronal marker protein gene product 9.5. Both SP (+) nerve fibers (p<0.001) and CGRP (+) nerve fibers (p<0.005) were decreased in the gastric mucosa within 4 weeks of diabetes; the reduction persisted throughout 24 weeks. Diabetic rats treated with insulin did not show decrease of SP or CGRP (+) fibers in the mucosa 4 weeks after STZ injection (p>0.05). There was no significant change in SP (+) nerve fibers (p>0.05) or CGRP (+) nerve fibers (p>0.05) of the gastric muscle layers. Reverse transcription-polymerase chain reaction (RT-PCR) showed that the expression levels of SP and CGRP mRNA in the thoracic dorsal root ganglia were similar between diabetic and control animals (p>0.05). Qualitative and quantitative ultrastructural examinations on the gastric mucosa documented unmyelinated nerve degeneration. These results suggest the existence of gastric sensory neuropathy in STZ-induced diabetes, and this pathology provides a foundation for understanding diabetic gastropathy.

Disrupted membrane homeostasis and accumulation of ubiquitinated proteins in a mouse model of infantile neuroaxonal dystrophy caused by PLA2G6 mutations

Mutations in the PLA2G6 gene, which encodes group VIA calcium-independent phospholipase A2 (iPLA(2)beta), were recently identified in patients with infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation. A pathological hallmark of these childhood neurodegenerative diseases is the presence of distinctive spheroids in distal axons that contain accumulated membranes. We used iPLA(2)beta-KO mice generated by homologous recombination to investigate neurodegenerative consequences of PLA2G6 mutations. iPLA(2)beta-KO mice developed age-dependent neurological impairment that was evident in rotarod, balance, and climbing tests by 13 months of age. The primary abnormality underlying this neurological impairment was the formation of spheroids containing tubulovesicular membranes remarkably similar to human INAD. Spheroids were strongly labeled with anti-ubiquitin antibodies. Accumulation of ubiquitinated protein in spheroids was evident in some brain regions as early as 4 months of age, and the onset of motor impairment correlated with a dramatic increase in ubiquitin-positive spheroids throughout the neuropil in nearly all brain regions. Furthermore accumulating ubiquitinated proteins were observed primarily in insoluble fractions of brain tissue, implicating protein aggregation in this pathogenic process. These results indicate that loss of iPLA(2)beta causes age-dependent impairment of axonal membrane homeostasis and protein degradation pathways, leading to age-dependent neurological impairment. iPLA(2)beta-KO mice will be useful for further studies of pathogenesis and experimental interventions in INAD and neurodegeneration with brain iron accumulation.

Degeneration of vagal efferent axons and terminals in cardiac ganglia of aged rats

Baroreflex control of the heart rate is significantly reduced during aging. However, neural mechanisms that underlie such a functional reduction are not fully understood. We injected the tracer DiI into the left nucleus ambiguus (NA), then used confocal microscopy and a Neurolucida Digitization System to examine qualitatively and quantitatively vagal efferent projections to cardiac ganglia of young adult (5-6 months) and aged (24-25 months) rats (Sprague Dawley). Fluoro-Gold was injected intraperitoneally to counterstain cardiac ganglionic principal neurons (PNs). In aged, as in young rats, NA axons projected to all cardiac ganglia and formed numerous basket endings around PNs in the hearts. However, significant structural changes were found in aged rats compared with young rats. Vagal efferent axons contained abnormally swollen axonal segments and exhibited reduced or even absent synaptic-like terminals around PNs, such that the numbers of vagal fibers and basket endings around PNs were substantially reduced (P < 0.01). Furthermore, synaptic-like varicose contacts of vagal cardiac axons with PNs were significantly reduced by approximately 50% (P < 0.01). These findings suggest that vagal efferents continue to maintain homeostatic control over the heart during aging. However, the marked morphological reorganization of vagal efferent axons and terminals in cardiac ganglia may represent the structural substrate for reduced vagal control of the heart rate and attenuated baroreflex function during aging.

Mechanisms of disease: the pathological basis of gastroparesis--a review of experimental and clinical studies

The pathogenesis of gastroparesis is complicated and poorly understood. This lack of understanding remains a major impediment to the development of effective therapies for this condition. Most of the scientific information available on the pathogenesis of gastroparesis has been derived from experimental studies of diabetes in animals. These studies suggest that the disease process can affect nerves (particularly those producing nitric oxide, but also the vagus nerve), interstitial cells of Cajal and smooth muscle. By contrast, human data are sparse, outdated and generally inadequate for the validation of data obtained from experimental models. The available data do, however, suggest that multiple cellular targets are involved. In practice, though, symptoms seldom correlate with objective measures of gastric function and there is still a lot to learn about the pathophysiology of gastroparesis. Future studies should focus on understanding the molecular pathways that lead to gastric dysfunction, in animal models and in humans, and pave the way for the development of rational therapies.

Long-term changes in sympathetic innervation in the corpus cavernosum of the STZ-diabetic rat

The noradrenaline (NA) concentration in the rat corpus cavernosum (CC) increased to approximately 350% of control values after about 8 weeks of hyperglycaemia induced by the intraperitoneal injection of streptozotocin (STZ) at 10 weeks of age. These changes were maintained for at least a further 32 weeks of hyperglycaemia and occurred without any significant change in the weight in the tissue. Smaller but significant increases in NA concentration occurred in the glans penis (GP) reaching 150-175% of the control levels during the period of prolonged hyperglycaemia. In contrast, there was no significant change in the NA concentration in the penile urethra. Measurements have also been made that relate to changes in the synthesis and reuptake of NA in the CC during the period during which high NA concentration is maintained. Immunohistochemical studies for the synthetic enzyme tyrosine hydroxylase in the CC indicate that the intensity of staining in the tissue had increased after 10, 20 and 32 weeks of hyperglycaemia, relative to the tissues from control animals. Dilated nerve fibres and engorged endings were present in the CC of the diabetic animals at these times. Reuptake of tritiated NA by the terminal axonal membranes in the CC was raised to 181% of control values after 12 weeks of hyperglycaemia (P<0.05), but later declined to values that are not significantly different from the control levels (after 26 and 64 weeks of hyperglycaemia). There are few studies of the effects of prolonged diabetes on functional aspects of sympathetic postganglionic neurones in the CC, and this paper suggests that the changes described represent remodelling of noradrenergic axonal terminals starting about after 8-10 weeks of hyperglycaemia; this delay in onset of the neuropathic changes is also a feature of type I diabetes in humans.

Innervation of the gastrointestinal tract: patterns of aging

The gastrointestinal (GI) tract is innervated by intrinsic enteric neurons and by extrinsic projections, including sympathetic and parasympathetic efferents as well as visceral afferents, all of which are compromised by age to different degrees. In the present review, we summarize and illustrate key structural changes in the aging innervation of the gut, and suggest a provisional list of the general patterns of aging of the GI innervation. For example, age-related neuronal losses occur in both the myenteric plexus and submucosal plexus of the intestines. These losses start in adulthood, increase over the rest of the life span, and are specific to cholinergic neurons. Parallel losses of enteric glia also occur. The extent of neuronal and glial loss varies along an oral-to-anal gradient, with the more distal GI tract being more severely affected. Additionally, with aging, dystrophic axonal swellings and markedly dilated varicosities progressively accumulate in the sympathetic, vagal, dorsal root, and enteric nitrergic innervation of the gut. These dramatic and consistent patterns of neuropathy that characterize the aging autonomic nervous system of the GI tract are candidate mechanisms for some of the age-related declines in function evidenced in the elderly.