Point of NO return for nitrergic nerves in diabetes: a new insight into diabetic complications

Constipation in DM are associated with both poor glycemic control and diabetic complications: Current status and future directions

Constipation is a major complications of diabetes mellitus. With the accelerating prevalence of diabetes worldwide and an aging population, there is considerable research interest regarding the altered function and structure of the gastrointestinal tract in diabetic patients. Despite current advances in hyperglycemic treatment strategies, the specific pathogenesis of diabetic constipation remains unknown. Patients with constipation, may be reluctant to eat regularly, which may worsen glycemic control and thus worsen symptoms associated with underlying diabetic bowel disease. This paper presents a review of the complex relationship between diabetes and constipation, exploring the morphological alterations and biomechanical remodeling associated with intestinal motility dysfunction, as well as alterations in intestinal neurons, cellular signaling pathways, and oxidative stress. Further studies focusing on new targets that may play a role in the pathogenesis of diabetic constipation may, provide new ideas for the development of novel therapies to treat or even prevent diabetic constipation.

Gut Region-Specific Interleukin 1β Induction in Different Myenteric Neuronal Subpopulations of Type 1 Diabetic Rats

Interleukin 1β (IL1β) is a pro-inflammatory cytokine that may play a crucial role in enteric neuroinflammation in type 1 diabetes. Therefore, our goal is to evaluate the effects of chronic hyperglycemia and insulin treatment on IL1β immunoreactivity in myenteric neurons and their different subpopulations along the duodenum-ileum-colon axis. Fluorescent immunohistochemistry was used to count IL1β expressing neurons as well as the neuronal nitric oxide synthase (nNOS)- and calcitonin gene-related peptide (CGRP)-immunoreactive myenteric neurons within this group. Tissue IL1β level was measured by ELISA in muscle/myenteric plexus-containing homogenates. IL1β mRNA was detected by RNAscope in different intestinal layers. The proportion of IL1β-immunoreactive myenteric neurons was significantly higher in the colon than in the small intestine of controls. In diabetics, this proportion significantly increased in all gut segments, which was prevented by insulin treatment. The proportion of IL1β-nNOS-immunoreactive neurons only increased in the diabetic colon, while the proportion of IL1β-CGRP-immunoreactive neurons only increased in the diabetic ileum. Elevated IL1β levels were also confirmed in tissue homogenates. IL1β mRNA induction was detected in the myenteric ganglia, smooth muscle and intestinal mucosa of diabetics. These findings support that diabetes-related IL1β induction is specific for the different myenteric neuronal subpopulations, which may contribute to diabetic motility disturbances.

Neural control of pancreatic peptide hormone secretion

Pancreatic peptide hormone secretion is inextricably linked to maintenance of normal levels of blood glucose. In animals and man, pancreatic peptide hormone secretion is controlled, at least in part, by input from parasympathetic (vagal) premotor neurons that are found principally in the dorsal motor nucleus of the vagus (DMV). Iatrogenic (insulin-induced) hypoglycaemia evokes a homeostatic response commonly referred to as the glucose counter-regulatory response. This homeostatic response is of particular importance in Type 1 diabetes in which episodes of hypoglycaemia are common, debilitating and lead to suboptimal control of blood glucose. Glucagon is the principal counterregulatory hormone but for reasons unknown, its secretion during insulin-induced hypoglycaemia is impaired. Pancreatic parasympathetic neurons are distinguishable electrophysiologically from those that control other (e.g. gastric) functions and are controlled by supramedullary inputs from hypothalamic structures such as the perifornical region. During hypoglycaemia, glucose-sensitive, GABAergic neurons in the ventromedial hypothalamus are inhibited leading to disinhibition of perifornical orexin neurons with projections to the DMV which, in turn, leads to increased secretion of glucagon.

Potential Therapeutic Effects of Natural Plant Compounds in Kidney Disease

Background: The blockade of the progression or onset of pathological events is essential for the homeostasis of an organism. Some common pathological mechanisms involving a wide range of diseases are the uncontrolled inflammatory reactions that promote fibrosis, oxidative reactions, and other alterations. Natural plant compounds (NPCs) are bioactive elements obtained from natural sources that can regulate physiological processes. Inflammation is recognized as an important factor in the development and evolution of chronic renal damage. Consequently, any compound able to modulate inflammation or inflammation-related processes can be thought of as a renal protective agent and/or a potential treatment tool for controlling renal damage. The objective of this research was to review the beneficial effects of bioactive natural compounds on kidney damage to reveal their efficacy as demonstrated in clinical studies. Methods: This systematic review is based on relevant studies focused on the impact of NPCs with therapeutic potential for kidney disease treatment in humans. Results: Clinical studies have evaluated NPCs as a different way to treat or prevent renal damage and appear to show some benefits in improving OS, inflammation, and antioxidant capacity, therefore making them promising therapeutic tools to reduce or prevent the onset and progression of KD pathogenesis. Conclusions: This review shows the promising clinical properties of NPC in KD therapy. However, more robust clinical trials are needed to establish their safety and therapeutic effects in the area of renal damage.

Dysregulation of nitric oxide synthases during early and late pathophysiological conditions of diabetes mellitus leads to amassing of microvascular impedement

Diabetes is a major killer worldwide and its unprecedented rise poses a serious threat to mankind. According to recent estimation, 387 million people worldwide are affected from the disease with a prevalence rate of 8.3 and 46.3 % still remains undiagnosed. Important characteristics of diabetes are abnormalities of the physiological signalling functions of reactive oxygen species and reactive nitrogen species. Increased oxidative stress contributes to the activation of stress-sensitive intracellular signalling pathways and the development of gene products that trigger cellular damage and contribute to the vascular complications of diabetes. Growing evidence from studies into many diseases suggests that the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure are correlated with oxidative stress. This leads to cell metabolism and cell-cell homeostasis to be complexly dysregulated. This review focuses to investigate the status of oxidative stress, nitric oxide and reactive species in early and diabetes. Significance of nitric oxide synthases Evidences has accumulated indicating that the generation of reactive oxygen species (oxidative stress) may play an important role in the etiology of diabetic complications thus attention was given on the reactive oxygen and reactive nitrogen species and their potential role in pathogenesis. Additionally, the therapeutic advances in diabetes management are included. Nanotechnology, statins and stem cell technology are some techniques which can be considered to have a possible future in the treatment sector of diabetes.

Role of sex hormones and their receptors on gastric Nrf2 and neuronal nitric oxide synthase function in an experimental hyperglycemia model

BACKGROUND

Gastroparesis, a condition of abnormal gastric emptying, is most commonly observed in diabetic women. To date, the role of ovarian hormones and/or gastric hormone receptors on regulating nitrergic-mediated gastric motility remains inconclusive.

AIM

The purpose of this study is to investigate whether sex hormones/their receptors can attenuate altered Nuclear factor (erythroid-derived 2)-like 2 (Nrf2), neuronal Nitric Oxide Synthase (nNOS) expression and nitrergic relaxation in gastric neuromuscular tissues exposed to in-vitro hyperglycemia (HG).

METHODS

Gastric neuromuscular sections from adult female C57BL/6 J mice were incubated in normoglycemic (NG, 5 mM) or hyperglycemic (30 mM or 50 mM) conditions in the presence or absence of selective estrogen receptor (ER) agonists (ERα /PPT or ERβ: DPN); or non-selective sex hormone receptor antagonists (ER/ICI 182,780, or progesterone receptor (PR)/ RU486) for 48 h. mRNA, protein expression and nitrergic relaxation of circular gastric neuromuscular strips were assessed.

RESULTS

Our findings in HG, compared to NG, demonstrate a significant reduction in ER, Nrf2, and nNOS expression in gastric specimens. In addition, in-vitro treatment with sex hormones and/or their agonists significantly (*p < 0.05) restored Nrf2/nNOSα expression and total nitrite production. Conversely, ER, but not PR, antagonist significantly reduced Nrf2/nNOSα expression and nitrergic relaxation.

CONCLUSIONS

Our data suggest that ER's can regulate nitrergic function by improving Nrf2/nNOS expression in experimental hyperglycemia.

Elevated pigment epithelium-derived factor induces diabetic erectile dysfunction via interruption of the Akt/Hsp90β/eNOS complex

AIMS/HYPOTHESIS

Diabetes mellitus erectile dysfunction (DMED) is a common complication of diabetes. The level of pigment epithelium-derived factor (PEDF) is significantly upregulated in the serum of individuals with obesity and diabetes. However, whether elevated PEDF levels contribute to DMED remains unknown. This study aimed to investigate the pathogenic role of PEDF and its related mechanism in DMED.

METHODS

We enrolled 65 men, of whom 20 were nondiabetic control participants, 21 participants with diabetes but without erectile dysfunction, and 24 with DMED. The International Index of Erectile Function (IIEF-5) questionnaire was administered to evaluate erectile function. Plasma PEDF in diabetic participants and streptozotocin (STZ)-induced diabetic animals was detected by ELISA. Erectile function was evaluated by measuring the intracavernous pressure (ICP) and the ICP/mean arterial pressure (MAP) ratio in STZ-induced diabetic rats treated with PEDF-neutralising antibody (PEDF-Ab), db/db mice treated with PEDF-Ab, and Pedf knockout mice with STZ-induced diabetes. The overexpression of PEDF was implemented by intraperitoneal injection of recombinant PEDF and intracavernous injection of PEDF-expressing adenovirus. A mechanistic study was performed by immunofluorescence staining, bimolecular fluorescence complementation (BiFC), immunoprecipitation and western blotting.

RESULTS

We found that the plasma level of PEDF was significantly higher in participants with DMED compared with diabetic counterparts without erectile dysfunction and nondiabetic controls. Interestingly, PEDF levels were negatively correlated with plasma nitrite/nitrate levels and erectile function in DMED patients and STZ-induced diabetic rats. Furthermore, overexpression of PEDF significantly suppressed ICP and endothelial nitric oxide synthase (eNOS) phosphorylation in control rats. In contrast, the PEDF-Ab and Pedf knockout ameliorated ICP and eNOS phosphorylation in diabetic rats and mice. Mechanistically, PEDF promoted the membrane translocation of Hsp90β and directly bound to the amino acid residues 341-724 of Hsp90β on the endothelial cell surface, subsequently blocking intracellular Hsp90β/Akt/eNOS complex formation and downregulating eNOS phosphorylation.

CONCLUSIONS/INTERPRETATION

These results indicate that elevated PEDF levels contribute to impaired erectile function by suppressing Hsp90β-mediated eNOS phosphorylation and that PEDF may represent a novel therapeutic target for diabetic erectile dysfunction. Graphical abstract.

Supplementation of 17β-Estradiol Normalizes Rapid Gastric Emptying by Restoring Impaired Nrf2 and nNOS Function in Obesity-Induced Diabetic Ovariectomized Mice

Gastroparesis (Gp) is a multifactorial condition commonly observed in females and is characterized by delayed or rapid gastric emptying (GE). The role of ovarian hormones on GE in the pathogenesis of obesity induced type 2 diabetes mellitus (T2DM) is completely unknown. The aims of our study are to investigate whether supplementation of 17β-estradiol (E2) or progesterone (P4) restores impaired nuclear factor erythroid 2-related factor 2 (Nrf2, an oxidative stress-responsive transcription factor) and nitric oxide (NO)-mediated gastric motility in ovariectomized (OVX) mice consuming a high-fat diet (HFD, a model of T2DM). Groups of OVX+HFD mice were administered daily subcutaneous doses of either E2 or P4 for 12 weeks. The effects of E2 and P4 on body weight, metabolic homeostasis, solid GE, gastric antrum NO-mediated relaxation, total nitrite levels, neuronal nitric oxide synthase (nNOSα), and its cofactor expression levels were assessed in OVX+HFD mice. HFD exacerbated hyperglycemia and insulinemia while accelerating GE (p < 0.05) in OVX mice. Exogenous E2, but not P4, attenuated rapid gastric emptying and restored gastric nitrergic relaxation, total nitrite levels, nNOSα, and cofactor expression via normalizing Nrf2-Phase II enzymes, inflammatory response, and mitogen-activated protein kinase (MAPK) protein expression in OVX+HFD mice. We conclude that E2 is beneficial in normalizing metabolic homeostasis and gastric emptying in obese, diabetic OVX mice consuming a fat-rich diet.

Role of neuronal nitric oxide synthase on cardiovascular functions in physiological and pathophysiological states

This review describes and summarizes the role of neuronal nitric oxide synthase (nNOS) on the central nervous system, particularly on brain regions such as the ventrolateral medulla (VLM) and the periaqueductal gray matter (PAG), and on blood vessels and the heart that are involved in the regulation and control of the cardiovascular system (CVS). Furthermore, we shall also review the functional aspects of nNOS during several physiological, pathophysiological, and clinical conditions such as exercise, pain, cerebral vascular accidents or stroke and hypertension. For example, during stroke, a cascade of molecular, neurochemical, and cellular changes occur that affect the nervous system as elicited by generation of free radicals and nitric oxide (NO) from vulnerable neurons, peroxide formation, superoxides, apoptosis, and the differential activation of three isoforms of nitric oxide synthases (NOSs), and can exert profound effects on the CVS. Neuronal NOS is one of the three isoforms of NOSs, the others being endothelial (eNOS) and inducible (iNOS) enzymes. Neuronal NOS is a critical homeostatic component of the CVS and plays an important role in regulation of different systems and disease process including nociception. The functional and physiological roles of NO and nNOS are described at the beginning of this review. We also elaborate the structure, gene, domain, and regulation of the nNOS protein. Both inhibitory and excitatory role of nNOS on the sympathetic autonomic nervous system (SANS) and parasympathetic autonomic nervous system (PANS) as mediated via different neurotransmitters/signal transduction processes will be explored, particularly its effects on the CVS. Because the VLM plays a crucial function in cardiovascular homeostatic mechanisms, the neuroanatomy and cardiovascular regulation of the VLM will be discussed in conjunction with the actions of nNOS. Thereafter, we shall discuss the up-to-date developments that are related to the interaction between nNOS and cardiovascular diseases such as hypertension and stroke. Finally, we shall focus on the role of nNOS, particularly within the PAG in cardiovascular regulation and neurotransmission during different types of pain stimulus. Overall, this review focuses on our current understanding of the nNOS protein, and provides further insights on how nNOS modulates, regulates, and controls cardiovascular function during both physiological activity such as exercise, and pathophysiological conditions such as stroke and hypertension.

Sodium nitrate preconditioning prevents progression of the neuropathic pain in streptozotocin-induced diabetes Wistar rats

Purpose

The purpose of the study was to evaluate the possible protective effects of low dose sodium nitrate preconditioning on the peripheral neuropathy in streptozotocin (STZ)-induced diabetic model.

Methods

Male Wistar rats were randomly divided into five groups: control (no intervention), control treated sodium nitrate (100 mg/L in drinking water), diabetic (no intervention), diabetic treated NPH insulin (2-4 U), and diabetic treated sodium nitrate (100 mg/L in drinking water). Diabetes was induced by intraperitoneal injection of STZ (60 mg/kg). All interventions were done for 60 days immediately following diabetes confirmation. Thermal and mechanical algesia thresholds were measured by means of hot-plate test, von Frey test, and tail-withdrawal test before the diabetic induction and after diabetes confirmation. At the end of the experiment, serum NOx level and serum insulin level were assessed. Blood glucose concentration and body weight have recorded at the base and duration of the experiment.

Results

Both hypoalgesia, hyperalgesia along with allodynia developed in diabetic rats. Significant alterations including, decrease in tail withdrawal latency (30th day), decreased mechanical threshold (60th day), and an increase in hot plate latency (61st day) were displayed in diabetic rats compared to control rats. Nitrate and insulin preconditioning produced protective effects against diabetes-induced peripheral neuropathy. Data analysis also showed a significant increase in glucose level as well as a considerable reduction in serum insulin and body weight of diabetic rats, which restored by both insulin and nitrate preconditioning.

Conclusion

Sodium nitrate preconditioning produces a protective effect in diabetic neuropathy, which may be mediated by its antihyperglycemic effects and increased serum insulin level.

Nitrergic Enteric Neurons in Health and Disease-Focus on Animal Models

Nitrergic enteric neurons are key players of the descending inhibitory reflex of intestinal peristalsis, therefore loss or damage of these neurons can contribute to developing gastrointestinal motility disturbances suffered by patients worldwide. There is accumulating evidence that the vulnerability of nitrergic enteric neurons to neuropathy is strictly region-specific and that the two main enteric plexuses display different nitrergic neuronal damage. Alterations both in the proportion of the nitrergic subpopulation and in the total number of enteric neurons suggest that modification of the neurochemical character or neuronal death occurs in the investigated gut segments. This review aims to summarize the gastrointestinal region and/or plexus-dependent pathological changes in the number of nitric oxide synthase (NOS)-containing neurons, the NO release and the cellular and subcellular expression of different NOS isoforms. Additionally, some of the underlying mechanisms associated with the nitrergic pathway in the background of different diseases, e.g., type 1 diabetes, chronic alcoholism, intestinal inflammation or ischaemia, will be discussed.

PARP inhibition in platinum-based chemotherapy: Chemopotentiation and neuroprotection

Cisplatin, carboplatin and oxaliplatin represent the backbone of platinum therapy for several malignancies including head and neck, lung, colorectal, ovarian, breast, and genitourinary cancer. However, the efficacy of platinum-based drugs is often compromised by a plethora of severe toxicities including sensory and enteric neuropathy. Acute and chronic neurotoxicity following platinum chemotherapy is a major constraint, contributing to dose-reductions, treatment delays, and cessation of treatment. Identifying drugs that effectively prevent these toxic complications is imperative to improve the efficacy of anti-cancer treatment and patient quality of life. Oxidative stress and mitochondrial dysfunction have been highlighted as key players in the pathophysiology of platinum chemotherapy-induced neuropathy. Inhibition of poly(ADP-ribose) polymerase (PARP), a nuclear enzyme activated upon DNA damage, has demonstrated substantial sensory and enteric neuroprotective capacity when administered in combination with platinum chemotherapeutics. Furthermore, administration of PARP inhibitors alongside platinum chemotherapy has been found to significantly improve progression-free survival in patients with breast and ovarian cancer when compared to those receiving chemotherapy alone. This review summarises the current knowledge surrounding mitochondrial damage and oxidative stress in platinum chemotherapy-induced neuropathy and highlights a potential role for PARP in chemopotentiation and neuroprotection.

Successful Midterm Management With an Herbal Decoction, Modified-Goshajinkigan (mGJG) for Non-Proliferative Diabetic Retinopathy: A Case Study

Diabetic retinopathy (DR) is one of the leading cause of blindness worldwide and the most common cause of blindness among the working population. Early treatment of the disease is essential to prevent severe visual loss among patients. But there are few therapeutic options available for early stage diabetic retinopathy. We present the case of an early stage diabetic retinopathy patient presented with retinal hemorrhages in the superior temporal area and disc hemorrhages of disc nasal area. The patient was diagnosed with mild NPDR on fundus examinations. After 6 months of taking modified-Goshaiinkigan (mGJG), the characteristic features of mild NPDR disappeared. Throughout three consecutive years of follow-ups, no evident lesions that could be diagnosed as DR were found during fundus examinations. Many components of mGJG have potential efficacy toward diabetic retinopathy. This study suggests that mGJG is a possible medication for early stage DR. Concerning the degenerative characteristics of DR, early management strategies are important in young DM patients and integrative care, such as in this case, are worth investigating further.

Diabetes-induced oxidative stress mediates upregulation of RhoA/Rho kinase pathway and hypercontractility of gastric smooth muscle

The pathogenesis of diabetes-associated motility disorders are multifactorial and attributed to abnormalities in extrinsic and intrinsic innervation, and a decrease in the number of interstitial cells of Cajal, and nNOS expression and activity. Here we studied the effect of hyperglycemia on smooth muscle function. Using smooth muscles from the fundus of ob/ob mice and of wild type (WT) mice treated with 30 mM glucose (HG), we identified the molecular mechanism by which hyperglycemia upregulates RhoA/Rho kinase pathway and muscle contraction. RhoA expression, Rho kinase activity and muscle contraction were increased, while miR-133a expression was decreased in smooth muscle of ob/ob mice and in smooth muscle treated with HG. Intraperitoneal injections of pre-miR-133a decreased RhoA expression in WT mice and reversed the increase in RhoA expression in ob/ob mice. Intraperitoneal injections of antagomiR-133a increased RhoA expression in WT mice and augmented the increase in RhoA expression in ob/ob mice. The effect of pre-miR-133a or antagomiR-133a in vitro in smooth muscle treated with HG was similar to that obtained in vivo, suggesting that the expression of RhoA is negatively regulated by miR-133a and a decrease in miR-133a expression in diabetes causes an increase in RhoA expression. Oxidative stress (levels of reactive oxygen species and hydrogen peroxide, and expression of superoxide dismutase 1 and NADPH oxidase 4) was increased in smooth muscle of ob/ob mice and in HG-treated smooth muscle. Treatment of ob/ob mice with N-acetylcysteine (NAC) in vivo or addition of NAC in vitro to HG-treated smooth muscle reversed the effect of glucose on the expression of miR-133a and RhoA, Rho kinase activity and muscle contraction. NAC treatment also reversed the decrease in gastric emptying in ob/ob mice. We conclude that oxidative stress in diabetes causes a decrease in miR-133a expression leading to an increase in RhoA/Rho kinase pathway and muscle contraction.

miR-223 contributes to the AGE-promoted apoptosis via down-regulating insulin-like growth factor 1 receptor in osteoblasts

miR-223 inhibits the advanced glycation end product (AGE)-promoted apoptosis in osteoblasts.

Advanced glycation end products (AGEs) have been confirmed to induce bone quality deterioration in diabetes mellitus (DM), and to associate with abnormal expression of miRNAs in DM patients or in vitro. Recently, miRNAs have been recognized to mediate the onset or progression of DM. In the present study, we investigated the regulation on miR-223 level by AGE-BSA treatment in osteoblast-like MC3T3-E1 cells, with real-time quantitative PCR assay. And then we examined the inhibition of insulin-like growth factor 1 receptor (IGF-1R) expression by miR-223, via targeting of the 3′ UTR of IGF-1R with real-time quantitative PCR, western blotting and luciferase reporter assay. Then we explored the regulation of miR-223 and IGF-1R levels, via the lentivirus-mediated miR-223 inhibition and IGF-1R overexpression in the AGE-BSA-induced apoptosis in MC3T3-E1 cells. It was demonstrated that AGE-BSA treatment with more than 100 μg/ml significantly up-regulated miR-223 level, whereas down-regulated IGF-1R level in MC3T3-E1 cells. And the up-regulated miR-223 down-regulated IGF-1R expression in both mRNA and protein levels, via targeting the 3′ UTR of IGF-1R. Moreover, though the AGE-BSA treatment promoted apoptosis in MC3T3-E1 cells, the IGF-1R overexpression or the miR-223 inhibition significantly attenuated the AGE-BSA-promoted apoptosis in MC3T3-E1 cells. In summary, our study recognized the promotion of miR-223 level by AGE-BSA treatment in osteoblast-like MC3T3-E1 cells. The promoted miR-223 targeted IGF-1R and mediated the AGE-BSA-induced apoptosis in MC3T3-E1 cells. It implies that miR-223 might be an effective therapeutic target to antagonize the AGE-induced damage to osteoblasts in DM.

Male accessory gland inflammation prevalence in type 2 diabetic patients with symptoms possibly reflecting autonomic neuropathy

Male accessory gland inflammation or infection (MAGI) is a potentially underdiagnosed complication of type 2 diabetes (DM2); specifically, we reported in a recent study that the frequency of MAGI was 43% among DM2 patients. In previous studies, we have demonstrated that diabetic autonomic neuropathy (DAN) is associated with a peculiar ultrasound characterization of the seminal vesicles (SVs) in DM2 patients. The aim of the present study was to evaluate the frequency of MAGI in two different categories of DM2 patients (i.e. patients with and without symptoms that possibly reflect DAN) and the respective ultrasound characterizations. Sixty DM2 patients with a mean (± s.e.m.) age of 42.0 ± 6.0 years (range: 34-47 years) were classified according to the presence or the absence of symptoms that could possibly reflect DAN (group A: DM2 with symptoms possibly reflecting DAN, n = 28 patients and group B: DM2 without symptoms possibly reflecting DAN, n = 32 patients). The patients in Group A exhibited a significantly higher frequency of MAGI compared with those in group B patients (P < 0.05); moreover, the Group A patients exhibited a significantly higher frequency of ultrasound signs suggestive of vesiculitis (P < 0.05). Finally, the concentrations of lymphocytes but not the concentrations of the leukocytes in the semen were significantly higher (P < 0.05) in group A compared with group B.

Advanced glycation end products induce endothelial-to-mesenchymal transition via downregulating Sirt 1 and upregulating TGF-β in human endothelial cells

In the present study, we examined the advanced glycation end products- (AGEs-) induced endothelial-to-mesenchymal transition (EndMT) in human umbilical vein endothelial cells (HUVECs). Results demonstrated that AGE-BSAs significantly reduced the cluster of differentiation 31 (CD 31) expression, whereas they promoted the expression of fibroblast-specific protein-1 (FSP-1), α-smooth muscle antibody (α-SMA), and collagen I at both mRNA and protein levels in HUVECs. And the AGE-BSAs also promoted the receptors for AGEs (RAGEs) and receptor I for TGF-β (TGFR I) markedly with a dose dependence, whereas the Sirt 1 was significantly downregulated by the AGE-BSA at both mRNA and protein levels. Moreover, the Sirt 1 activity manipulation with its activator, resveratrol (RSV), or its inhibitor, EX527, markedly inhibited or ameliorated the AGE-mediated TGF-β upregulation. And the manipulated Sirt 1 activity positively regulated the AGE-induced CD31, whereas it negatively regulated the AGE-induced FSP-1. Thus, Sirt 1 was confirmed to regulate the AGE-induced EndMT via TGF-β. In summary, we found that AGE-BSA induced EndMT in HUVECs via upregulating TGF-β and downregulating Sirt 1, which also negatively regulated TGF-β in the cell. This study implied the EndMT probably as an important mechanism of AGE-induced cardiovascular injury.

Potential role of nitric oxide synthase isoforms in pathophysiology of neuropathic pain

Neuropathic pain triggers a cascade of events in the sensory neurons. It is the main complication of diabetes after cardiovascular disease. Nitric oxide (NO) produced from nitric oxide synthases (NOS) is an important signaling molecule which is crucial for many physiological processes such as synaptic plasticity, neuronal survival, vasodilation, vascular homeostasis, immune regulation. Overproduction of NO due to changes in NOS isoforms level involves pathological processes such as neurotoxicity, septic shock and neuropathic pain. All three isoforms of NOS as well as their end product, NO have modulatory effect on neuropathic pain. Overactivation of the N-Methyl-D-Aspartate receptor and peroxynitrite formation results in high levels of neuronal NOS (nNOS) and endothelial NOS (eNOS) which suggest that nNOS and eNOS are critical for pain hypersensitivity. Inducible NOS induced in glia by inflammation due to activation of Tumor Necrosis Factor α, Calcitonin Gene Regulating Peptide, Mitogen Activated Protein Kinases, Extracellular signal Regulated Kinase, c-Jun N-terminal kinases can induce neuronal death. This review focuses on different nitric oxide synthases and their role in pathophysiology of neuropathic pain considering NOS as an important therapeutic target.

Hydroxyl fasudil, an inhibitor of Rho signaling, improves erectile function in diabetic rats: a role for neuronal ROCK

INTRODUCTION

The pathogenesis of diabetic erectile dysfunction (ED) includes neuropathy, but the molecular basis for neurogenic ED is incompletely understood. The RhoA/ROCK pathway has been implicated in diabetic neuropathy and in ED, but its role in diabetic neurogenic ED is not known.

AIMS

The aim of this study was to determine whether hydroxyl fasudil, a ROCK inhibitor, affects diabetic neuropathy-related ED.

METHODS

Type 1 diabetes mellitus was induced in male rats by streptozotocin (75 mg/kg, intraperitoneally). After 8 weeks, diabetic rats were administered hydroxyl fasudil, a selective ROCK inhibitor (10 mg/kg/day, intraperitoneally) or vehicle, for 4 weeks. Age-matched control, nondiabetic, rats were treated intraperitoneally for 4 weeks with saline. At week 12, after a 2 day washout, neuro-stimulated erectile function was evaluated. Major pelvic ganglia (MPG) were collected for Western blot analysis of RhoA, ROCK-1, ROCK-2, phospho (P)-AKT (Ser(473) ), and P-phosphatase and tensin homolog (P-PTEN) (Ser(380) /Thr(382/383) ).

MAIN OUTCOME MEASURES

Effect of ROCK inhibitor hydroxyl fasudil on erectile function and ROCK/P-AKT/P-PTEN pathway in the MPG of diabetic rats.

RESULTS

Erectile response was significantly (P < 0.05) reduced in diabetic rats compared with nondiabetic rats and was preserved (P < 0.05) in diabetic rats treated with hydroxyl fasudil. In diabetic rats, RhoA and ROCK-2 protein expressions in MPG were increased (P < 0.05) and remained increased in hydroxyl fasudil-treated rats. P-AKT (Ser(473) ) expression was decreased (P < 0.05), whereas P-PTEN (Ser(380) /Thr(382/383) ) expression was increased (P < 0.05) in MPG of diabetic rats compared with nondiabetic rats, and both were reversed (P < 0.05) in diabetic rats treated with hydroxyl fasudil.

CONCLUSION

Improved erectile function and restored P-AKT and P-PTEN in the MPG with hydroxyl fasudil treatment suggest the role of Rho signaling via PTEN/AKT pathway in neurogenic diabetic ED.

A spontaneous animal model of intestinal dysmotility evoked by inflammatory nitrergic dysfunction

Background and Aims

Recent reports indicate the presence of low grade inflammation in functional gastrointestinal disorders (FGID), in these cases often called “post-inflammatory” FGIDs. However, suitable animal models to study these disorders are not available. The Biobreeding (BB) rat consists of a diabetes-resistant (BBDR) and a diabetes-prone (BBDP) strain. In the diabetes-prone strain, 40–60% of the animals develop diabetes and concomitant nitrergic dysfunction. Our aim was to investigate the occurrence of intestinal inflammation, nitrergic dysfunction and intestinal dysmotility in non-diabetic animals.

Methods

Jejunal inflammation (MPO assay, Hematoxylin&Eosin staining and inducible nitric oxide synthase (iNOS) mRNA expression), in vitro jejunal motility (video analysis) and myenteric neuronal numbers (immunohistochemistry) were assessed in control, normoglycaemic BBDP and diabetic BBDP rats. To study the impact of iNOS inhibition on these parameters, normoglycaemic BBDP rats were treated with aminoguanidine.

Results

Compared to control, significant polymorphonuclear (PMN) cell infiltration, enhanced MPO activity, increased iNOS mRNA expression and a decreased ratio of nNOS to Hu-C/D positive neurons were observed in both normoglycaemic and diabetic BBDP rats. Aminoguanidine treatment decreased PMN infiltration, iNOS mRNA expression and MPO activity. Moreover, it restored the ratio of nNOS to Hu-C/D positive nerves in the myenteric plexus and decreased the abnormal jejunal elongation and dilation observed in normoglycaemic BBDP rats.

Conclusions

Aminoguanidine treatment counteracts the inflammation-induced nitrergic dysfunction and prevents dysmotility, both of which are independent of hyperglycaemia in BB rats. Nitrergic dysfunction may contribute to the pathophysiology of “low-grade inflammatory” FGIDs. Normoglycaemic BBDP rats may be considered a suitable animal model to study the pathogenesis of FGIDs.

Diabetic gastrointestinal motility disorders and the role of enteric nervous system: current status and future directions

BACKGROUND

Gastrointestinal manifestations of diabetes are common and a source of significant discomfort and disability. Diabetes affects almost every part of gastrointestinal tract from the esophagus to the rectum and causes a variety of symptoms including heartburn, nausea, vomiting, abdominal pain, diarrhea and constipation. Understanding the underlying mechanisms of diabetic gastroenteropathy is important to guide development of therapies for this common problem. Over recent years, the data regarding the pathophysiology of diabetic gastroenteropathy is expanding. In addition to autonomic neuropathy causing gastrointestinal disturbances the role of enteric nervous system is becoming more evident.

PURPOSE

In this review, we summarize the reported alterations in enteric nervous system including enteric neurons, interstitial cells of Cajal and neurotransmission in diabetic animal models and patients. We also review the possible underlying mechanisms of these alterations, with focus on oxidative stress, growth factors and diabetes induced changes in gastrointestinal smooth muscle. Finally, we will discuss recent advances and potential areas for future research related to diabetes and the ENS such as gut microbiota, micro-RNAs and changes in the microvasculature and endothelial dysfunction.

Diabetic gastroparesis: recent insights into pathophysiology and implications for management

Delayed gastric emptying affects a substantial proportion of patients with long-standing diabetes, and when associated with symptoms and/or disordered glycemic control, affects quality of life adversely. Important clinicopathological insights have recently been gained by the systematic analysis of gastric biopsies from patients with severe diabetic gastroparesis, which may stimulate the development of new therapies in the coming decade. Experience with prokinetic therapies and treatments, such as pyloric botulinum toxin injection and gastric electrical stimulation, has established that relief of symptoms does not correlate closely with acceleration of delayed gastric emptying, and that well-designed controlled trials are essential to determine the efficacy of emerging therapies.

Protection effect of endomorphins on advanced glycation end products induced injury in endothelial cells

Endomorphins (EMs) have a very important bridge-function in cardiovascular, endocrinological, and neurological systems. This study is to investigate the effects of EMs on the synthesis and secretion of vasoactive substances induced by advanced glycation end products in primary cultured human umbilical vein endothelial cells (HUVECs). Firstly, HUVECs were stimulated with AGEs-bovine serum albumin (AGEs-BSA), bovine serum albumin (BSA), or both AGEs-BSA and EMs together, respectively. Then, HUVEC survival rate was calculated by MTT assay, the levels of NO, endothelial nitric oxide synthase (eNOS), and inducible nitric oxide synthase (iNOS) were detected by colorimetric analysis, and the contents of endothelin-1 (ET-1) were detected by ELISA. The mRNA levels of eNOS and ET-1 were measured by RT-PCR. The expression of p38 mitogen-activated protein kinase (p38 MAPK) was detected by immunofluorescence assay. The results showed that the mRNA expression and secretion of eNOS were significantly enhanced after incubation with EMs compared to those with AGEs-BSA, while the secretion of NO and iNOS, mRNA expression, and secretion of ET-1 had opposite changes. The fluorescence intensity of p38MAPK in nuclear was decreased after pretreatment with EMs compared to incubation with AGEs-BSA. Conclusion. The present study suggests that EMs have certain protection effect on AGEs-BSA-induced injury in HUVEC.

Diabetic gastroparesis

BACKGROUND

Diabetic gastroparesis (DGP) is a gastric complication of diabetes mellitus that causes nausea, vomiting, early satiety, bloating and abdominal pain, in addition to significant morbidity.

SOURCES OF DATA

Original and review articles were reviewed through PubMed, including relevant guidelines from the European and American Neurogastroenterology Societies.

AREAS OF AGREEMENT

Diagnosis of DGP requires endoscopy and measurement of gastric emptying. Management requires prokinetic therapy, usually in addition to antinausea or other medications.

AREAS OF CONTROVERSY

The pathogenesis of DGP is poorly understood. Management strategies are highly variable. Growing points Prokinetic and neuromodulatory medications are in human clinical trials specifically for gastroparesis.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further understanding of the molecular pathology leading to DGP is required to potentially arrest the development of this serious diabetic complication. Evaluation of novel agents for use in DGP is sorely needed.

Neuroprotective effect of quercetin on the duodenum enteric nervous system of streptozotocin-induced diabetic rats

BACKGROUND

In diabetes mellitus (DM), hyperglycemia promotes changes in biochemical mechanisms that induce oxidative stress. Oxidative stress has been closely linked to adverse consequences that affect the function of the gastrointestinal tract caused by injuries to the enteric nervous system (ENS) that in turn cause neurodegeneration and enteric glial loss. Therapeutic approaches have shown that diet supplementation with antioxidants, such as quercetin, reduce oxidative stress.

AIMS

This work sought to evaluate neurons and enteric glial cells in the myenteric and submucosal plexuses of the duodenum in diabetic rats supplemented with quercetin.

METHODS

The duodenum of 24 rats, including a control group (C), control quercetin supplementation group (CQ), diabetic group (D), and diabetic quercetin supplementation group (DQ), were used to investigate whole mounts of muscular and submucosal layers subjected to immunohistochemistry to detect vasoactive intestinal peptide in the myenteric layer and double-staining for HuC-D/neuronal nitric oxide synthase (nNOS) and HuC-D/S100.

RESULTS

A reduction of the general neuronal population (HuC/D) was found in the myenteric and submucosal plexuses (p < 0.001) in the D and DQ groups. The nitrergic subpopulation (nNOS) decreased only in the myenteric plexus (p < 0.001), and glial cells decreased in both plexuses (p < 0.001) in the D and DQ groups. In diabetic rats, quercetin supplementation reduced neuronal and glial loss. Diabetes promoted an increase in the cell body area of both the general and nitrergic populations. Quercetin supplementation only prevented neuronal hypertrophy in the general population.

CONCLUSION

Supplementation with quercetin eased the damage caused by diabetes, promoting a neuroprotective effect and reducing enteric glial loss in the duodenum.

Pathophysiology of diabetic erectile dysfunction: potential contribution of vasa nervorum and advanced glycation endproducts

Erectile dysfunction (ED) due to diabetes mellitus remains difficult to treat medically despite advances in pharmacotherapeutic approaches in the field. This unmet need has resulted in a recent re-focus on the pathophysiology, in order to understand the cellular and molecular mechanisms leading to ED in diabetes. Diabetes-induced ED is often resistant to PDE5 inhibitor treatment, thus there is a need to discover targets that may lead to novel approaches for a successful treatment. The aim of this brief review is to update the reader in some of the latest development on that front, with a particular focus on the role of impaired neuronal blood flow and the formation of advanced glycation endproducts.

Poly(ADP-ribose) polymerase inhibition improves erectile function by activation of nitric oxide/cyclic guanosine monophosphate pathway in diabetic rats

INTRODUCTION

Endothelial dysfunction-induced abnormalities of the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway in the corpus cavernosum are thought to be the main factors involved in the pathogenesis of diabetes-induced erectile dysfunction (ED). Recent studies have shown that the poly(adenosine diphosphate ribose) polymerase (PARP) pathway plays a critical role in diabetic endothelial dysfunction.

AIM

  The aim of this study is to determine whether activation of the PARP pathway is involved in diabetic cavernosal endothelial dysfunction and abnormalities of the NO/cGMP pathway.

METHODS

Male Sprague-Dawley rats were randomly divided into three groups: age-matched controls, diabetic controls (DM), and the 3-aminobenzamide (3-AB, a PARP inhibitor)-treated diabetic group (DM+3-AB). Diabetes was induced by intraperitoneal injection of streptozotocin. Eight weeks after inducing diabetes, the DM+3-AB group was treated with 3-AB for 4 weeks.

MAIN OUTCOME MEASURES

Erectile function was assessed at 12 weeks after inducing diabetes by stimulating the cavernous nerve. Expression of poly(ADP-ribose), protein kinase B (Akt), phospho-Akt, endothelial nitric oxide synthase (eNOS), phospho-eNOS, and neuronal nitric oxide synthase (nNOS) were evaluated by Western blot. Cavernous NO generation and cGMP levels were also determined.

RESULTS

The DM group showed impaired erectile function and significantly increased PARP activity. Expression of total eNOS and nNOS, phospho-Akt, and eNOS decreased significantly in the DM group compared with those in the control group. In addition, cavernous NO generation and cGMP levels decreased significantly in the DM group compared with those in the control group. Treatment with 3-AB restored erectile function and significantly reversed all molecular alterations except decreased nNOS expression.

CONCLUSION

Overactivation of the PARP pathway in the corpus cavernosum of diabetic rats was involved in cavernosal endothelial dysfunction and abnormalities of the NO/cGMP pathway resulting in ED. These findings may be applied to develop novel therapies for patients with diabetic ED.

Advanced glycation end-products induce injury to pancreatic beta cells through oxidative stress

AIM

This study evaluated the direct effects of advanced glycation end-products (AGEs) on pancreatic β cells, including cellular viability, generation of reactive oxygen species (ROS) and insulin secretion, and also looked for the main source of ROS in INS-1 cells and the possible molecular mechanism(s) of cell injury by AGEs.

METHODS

INS-1 cells were cultured with 100, 200 and 500 mg/L of AGEs for specific periods of time. Cell apoptosis was determined by ELISA and real-time PCR assays. ROS were detected by DCFH-DA and MitoSOX Red probes with a flow cytometer, NADPH oxidase activity was measured by lucigenin chemiluminescence and MAPK phosphorylation was measured by Western blot tests.

RESULTS

Both cell apoptosis and ROS generation increased in AGE-treated cells in a dose-dependent way, and both the mitochondrial electron transport chain and NADPH oxidase pathway participated in ROS generation, although the role of the mitochondrial pathway was earlier and more important. AGEs exerted a toxic effect on insulin secretion that could be largely reversed by inhibiting ROS.

CONCLUSION

AGEs injured INS-1 cells by oxidative stress mainly through the mitochondrial pathway, although the JNK and p38 MAPK signaling pathways were also key modulators in ROS-mediated β-cell death.

The involvement of nitric oxide synthase neurons in enteric neuropathies

Nitric oxide (NO), produced by the neural nitric oxide synthase enzyme (nNOS) is a transmitter of inhibitory neurons supplying the muscle of the gastrointestinal tract. Transmission from these neurons is necessary for sphincter relaxation that allows the passage of gut contents, and also for relaxation of muscle during propulsive activity in the colon. There are deficiencies of transmission from NOS neurons to the lower esophageal sphincter in esophageal achalasia, to the pyloric sphincter in hypertrophic pyloric stenosis and to the internal anal sphincter in colonic achalasia. Deficits in NOS neurons are observed in two disorders in which colonic propulsion fails, Hirschsprung's disease and Chagas' disease. In addition, damage to NOS neurons occurs when there is stress to cells, in diabetes, resulting in gastroparesis, and following ischemia and reperfusion. A number of factors may contribute to the propensity of NOS neurons to be involved in enteric neuropathies. One of these is the failure of the neurons to maintain Ca(2+) homeostasis. In neurons in general, stress can increase cytoplasmic Ca(2+), causing a Ca(2+) toxicity. NOS neurons face the additional problem that NOS is activated by Ca(2+). This is hypothesized to produce an excess of NO, whose free radical properties can cause cell damage, which is exacerbated by peroxynitrite formed when NO reacts with oxygen free radicals.

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.

Gender bias in gastroparesis: is nitric oxide the answer?

Accumulating evidence suggests that gender-related differences are prominent in gastric motility functions in both health and disease. Women are more susceptible to gastroparesis than men. Though the mechanism(s) involved are not fully understood, impairment of the nitrergic system is one of the main factors responsible for the disease. Uncoupling of neuronal nitric oxide synthase (nNOS) causes a decreased synthesis of NO leading to a reduction in smooth muscle relaxation. Tetrahydrobiopterin (BH(4)) (an essential cofactor for nNOS) is a key regulator of nNOS activity for stomach dysfunction and gastroparesis. In addition, BH(4) has been shown to be a potent antioxidant and anti-inflammatory agent. Well established by results from our laboratory, a diminished intracellular (BH(4):total biopterin) ratio in diabetic female rats significantly impairs nNOS activity and function. Recent research has been focused on BH(4) biosynthesis and gastroparesis because reduced BH(4) cofactor levels can alter the production of NO by nNOS. Researchers are now paying more attention to the possibility of using BH(4) as a therapeutic strategy in gastroparesis. The purpose of this review is to provide an overview of the regulation and function of nNOS by sex hormones and BH(4) and its potential role in the treatment of gastroparesis.

Regional differences in neostigmine-induced contraction and relaxation of stomach from diabetic guinea pig

Delayed gastric emptying and autonomic neuropathy have been documented in patients with diabetes mellitus. Some medications used to treat delayed gastric emptying enhance release of acetylcholine from autonomic neurons to strengthen gastric contractions. Autonomic coordination among gastric regions may be altered in diabetes resulting in poor outcomes in response to prokinetic drugs. Fundus, antrum, and pylorus from STZ or control guinea pigs were treated with neostigmine to mimic release of acetylcholine from autonomic neurons by prokinetic agents. In diabetic animals, neostigmine-induced contractions were weaker in fundus and pylorus but similar in antrum. The muscarinic receptor antagonist 4-DAMP or the nicotinic receptor antagonist hexamethonium reduced neostigmine-induced contractions. Activation of presynaptic muscarinic receptors on nitrergic neurons was impaired in fundus and antrum from diabetic animals. Nerve-stimulated contractions and relaxations, number of nNOS myenteric neurons, and tissue choline content were reduced in fundus from diabetic animals. Despite reduced number of myenteric neurons, tissue choline content was increased in antrum from diabetic animals. Since cholinergic motility of each gastric region was affected differently by diabetes, prokinetic drugs that nondiscriminately enhance acetylcholine release from autonomic neurons may not effectively normalize delayed gastric emptying in patients with diabetes and more selective medications may be warranted.

Hepatocyte growth factor prevents advanced glycation end products-induced injury and oxidative stress through a PI3K/Akt-dependent pathway in human endothelial cells

AIMS

Advanced glycation end products (AGEs) trigger an oxidative reaction which then accelerates endothelial cell apoptosis; this is a critical event in the process of diabetic vascular complications. We previously demonstrated that hepatocyte growth factor (HGF) protects human endothelial cells against AGE-induced injury. The present study was designed to investigate the possible involvement of MAPK and PI3K/Akt signaling in the action of HGF.

MAIN METHODS

HUVECs were treated with AGEs in the presence or absence of HGF. For detection of apoptosis, the morphological Acridine Orange staining, flow cytometry, and caspase-3 activity assay were used. Generation of reactive oxygen species (ROS) and the change in mitochondrial membrane potential were measured using flow cytometry and fluorescence immune analysis. The activation of MAPK and Akt was assayed by Western blot.

KEY FINDINGS

HGF exerted its prosurvival effect by inhibiting the overproduction of intracellular ROS and the depolarization of mitochondrial membrane, induced by AGEs. HGF-induced survival correlated with Akt activity and was inhibited by the specific PI3K inhibitor. ERK also was activated by HGF and rescued cells from apoptosis, although the cytoprotective effect was less marked than for PI3K/Akt. HGF-mediated survival was independent of JNK and p38MAPK pathways. Furthermore, blocking the PI3K and Akt activities with PI3K inhibitors or transfection of HUVECs with the dominant-negative p85 or Akt effectively abolished the inhibition of the intracellular ROS production and mitochondrial damage.

SIGNIFICANCE

Our studies suggest that HGF, via PI3K/Akt signaling, prevents AGE-induced apoptosis and oxidative stress through the inhibition of mitochondrial damage in HUVECs.

Cardiac cholinergic NO-cGMP signaling following acute myocardial infarction and nNOS gene transfer

Myocardial infarction (MI) is associated with oxidative stress, which may cause cardiac autonomic impairment. We tested the hypothesis that acute MI disrupts cardiac cholinergic signaling by impairing nitric oxide (NO)-cGMP modulation of acetylcholine (ACh) release and whether the restoration of this pathway following cardiac neuronal NO synthase (nNOS) gene transfer had any bearing on the neural phenotype. Guinea pigs underwent four ligature coronary artery surgery (n = 50) under general anesthesia to induce MI or sham surgery (n = 32). In a separate group, at the time of MI surgery, adenovirus encoding nNOS (n = 29) or enhanced green fluorescent protein (eGFP; n = 30) was injected directly into the right atria, where the postganglionic cholinergic neurons reside. In vitro-evoked right atrial [3H]ACh release, right atrial NOS activity, and cGMP levels were measured at 3 days. Post-MI 24% of guinea pigs died compared with 9% in the sham-operated group. Evoked right atrial [3H]ACh release was significantly (P < 0.05) decreased in the MI group as was NOS activity and cGMP levels. Tetrahydrobiopterin levels were not significantly different between the sham and MI groups. Infarct sizes between gene-transferred groups were not significantly different. The nNOS transduced group had significantly increased right atrial [3H]ACh release, right atrial NOS activity, cGMP levels, and decreased cAMP levels. Fourteen percent of the nNOS transduced animals died compared with 31% mortality in the MI + eGFP group at 3 days. In conclusion, cardiac nNOS gene transfer partially restores the defective NO-cGMP cholinergic pathway post-MI, which was associated with a trend of improved survival at 3 days.

Characterization of myenteric neuropathy in the jejunum of spontaneously diabetic BB-rats

Decreased gastric expression and function of neuronal nitric oxide synthase (nNOS) has been proposed as a potential mechanism underlying diabetic gastroparesis. As gastric nNOS expression is vagally controlled, these changes might occur secondarily to vagal neuropathy. In addition, it is unclear whether other inhibitory neurotransmitters are also involved. We used the type 1 diabetic BioBreeding (BB)-rat model to study jejunal motor control and nNOS expression, which is independent of the vagus. Jejunal segments were used for in vitro contractility studies, and measurement of nNOS expression after 8 or 16 weeks of diabetes compared with age- and sex-matched controls. Unlike electrical field stimulation and acetylcholine (ACh)-induced contractions, non-adrenergic non-cholinergic (NANC) relaxations were significantly reduced in diabetic rats. In contrast to control rats, NANC relaxations in diabetic rats were N(omega)-nitro-L-arginine methyl ester (L-NAME) insensitive. Jejunal nNOS expression was significantly decreased in diabetic rats. Both in diabetic and in control animals, L-NAME resistant relaxations were sensitive to P(2)-receptor antagonists. In the jejunum of spontaneously diabetic rats, decreased nitric oxide responsiveness and decreased nNOS protein expression occur while purinergic transmission is unaffected. These findings indicate that nitrergic enteric neuropathy may be a primary dysfunction in diabetes, independent from vagal dysfunction.

Observations on a vestigial organ: a potential surrogate for enteric neuromesenchymal disease

Abnormalities of enteric nerves, interstitial cells of Cajal (ICC) and smooth muscle are often associated with severe gastrointestinal motility disorders. In this context, full-thickness biopsy of the gut may provide important diagnostic and prognostic clues as well as some possible therapeutic implications. Nonetheless, the unavoidable risk to further worsen prognosis evoked by laparotomy, and the unclear yield of histopathological analysis has hampered full-thickness gut sampling in patients with severe dysmotility. However, recent advances in minimally invasive surgery have refuelled enthusiasm in gastrointestinal neuromuscular pathology. In this issue of Neurogastroenterology and Motility, Miller et al. provide novel and exciting evidence that the appendix might be used as a surrogate tissue to analyse changes to enteric nerves, ICC and smooth muscle cells in patients with diabetic gastroenteropathy. The objective of this short review was to place this very important work in the context of current understanding of enteric neuromuscular dysfunction.

SOD2 protects neurons from injury in cell culture and animal models of diabetic neuropathy

Hyperglycemia-induced oxidative stress is an inciting event in the development of diabetic complications including diabetic neuropathy. Our observations of significant oxidative stress and morphological abnormalities in mitochondria led us to examine manganese superoxide dismutase (SOD2), the enzyme responsible for mitochondrial detoxification of oxygen radicals. We demonstrate that overexpression of SOD2 decreases superoxide (O(2)(-)) in cultured primary dorsal root ganglion (DRG) neurons and subsequently blocks caspase-3 activation and cellular injury. Underexpression of SOD2 in dissociated DRG cultures from adult SOD2(+/-) mice results in increased levels of O2-, activation of caspase-3 cleavage and decreased neurite outgrowth under basal conditions that are exacerbated by hyperglycemia. These profound changes in sensory neurons led us to explore the effects of decreased SOD2 on the development of diabetic neuropathy (DN) in mice. DN was assessed in SOD2(+/-) C57BL/6J mice and their SOD2(+/+) littermates following streptozotocin (STZ) treatment. These animals, while hyperglycemic, do not display any signs of DN. DN was observed in the C57BL/6Jdb/db mouse, and decreased expression of SOD2 in these animals increased DN. Our data suggest that SOD2 activity is an important cellular modifier of neuronal oxidative defense against hyperglycemic injury.

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.

Diabetes induces sex-dependent changes in neuronal nitric oxide synthase dimerization and function in the rat gastric antrum

Diabetic gastroparesis is a disorder that predominantly affects women. However, the biological basis of this sex bias remains completely unknown. In this study we tested the hypothesis that a component of this effect may be mediated by the nitrergic inhibitory system of the enteric nervous system. Age-matched male and female Sprague-Dawley rats were studied 8 or 12 wk after streptozotocin (55 mg/kg body wt ip)-induced sustained hyperglycemia and compared with controls. Solid gastric emptying (GE) studies were performed in all the groups. Changes in gastric antrum neuronal nitric oxide synthase (nNOS) mRNA and protein levels were analyzed by real-time PCR and Western immunoblotting, respectively. nNOS dimerization studies were performed using low-temperature SDS-PAGE. In vitro nitrergic relaxation (area under curve/mg tissue wt) was studied after the application of electric field stimulation in an organ bath. Changes in intragastric pressure (mmHg.s) in freely moving rats in the presence or absence of N(G)-nitro-l-arginine methyl ester (nitric oxide synthase inhibitor) were examined by an ambulatory telemetric method. After diabetes induction, GE is delayed in both male and female rats. However, diabetic females exhibited significant delayed GE than in diabetic males. Compared with male controls, gastric nNOS expression and nitrergic relaxation were substantially elevated in healthy female control rats, accompanied by significantly reduced intragastric pressure. The active dimeric form and dimer-to-monomer ratio of nNOSalpha were also higher in healthy females compared with male rats (P < 0.05). Diabetic females, but not males, showed significant (P < 0.05) impairment in both gastric nNOSalpha dimerization and nitrergic relaxation, accompanied by an increase in intragastric pressure. Our data provide evidence that females may have a greater dependency on the nitrergic mechanisms in health. Furthermore, diabetes seems to affect the nitrergic system to a greater extent in females than in males. Together, these changes may account for the greater vulnerability of females to diabetic gastric dysfunction.

Advanced glycation end products induce apoptosis in fibroblasts through activation of ROS, MAP kinases, and the FOXO1 transcription factor

Advanced glycation end products (AGEs) are elevated in aged and diabetic individuals and are associated with pathological changes associated with both. Previously we demonstrated that the AGE N(epsilon)-(carboxymethyl)lysine (CML)-collagen induced fibroblast apoptosis through the cytoplasmic and mitochondrial pathways and the global induction of proapoptotic genes. In the present study we investigated upstream mechanisms of CML-collagen-induced apoptosis. CML-collagen induced activation of the proapoptotic transcription factor FOXO1 compared with unmodified collagen. When FOXO1 was silenced, CML-collagen-stimulated apoptosis was reduced by approximately 75% compared with fibroblasts incubated with nonsilencing small interfering RNA, demonstrating the functional significance of FOXO1 activation (P < 0.05). CML-collagen but not control collagen also induced a 3.3-fold increase in p38 and a 5.6-fold increase in JNK(1/2) activity (P < 0.05). With the use of specific inhibitors, activation of p38 and JNK was shown to play an important role in CML-collagen-induced activation of FOXO1 and caspase-3. Moreover, inhibition of p38 and JNK reduced CML-collagen-stimulated apoptosis by 48 and 57%, respectively, and by 89% when used together (P < 0.05). In contrast, inhibition of the phosphatidylinositol 3-kinase/Akt pathway enhanced FOXO1 activation. p38 and JNK stimulation by CML-collagen was almost entirely blocked when formation of ROS was inhibited and was partially reduced by NO and ceramide inhibitors. These inhibitors also reduced apoptosis to a similar extent. Together these data support a model in which AGE-induced apoptosis involves the formation of ROS, NO, and ceramide and leads to p38 and JNK MAP kinase activation, which in turn induces FOXO1 and caspase-3.