L-glutamine supplementation prevents myenteric neuron loss and has gliatrophic effects in the ileum of diabetic rats

Mechanisms of enteric neuropathy in diverse contexts of gastrointestinal dysfunction

The enteric nervous system (ENS) commands moment-to-moment gut functions through integrative neurocircuitry housed in the gut wall. The functional continuity of ENS networks is disrupted in enteric neuropathies and contributes to major disturbances in normal gut activities including abnormal gut motility, secretions, pain, immune dysregulation, and disrupted signaling along the gut-brain axis. The conditions under which enteric neuropathy occurs are diverse and the mechanistic underpinnings are incompletely understood. The purpose of this brief review is to summarize the current understanding of the cell types involved, the conditions in which neuropathy occurs, and the mechanisms implicated in enteric neuropathy such as oxidative stress, toll like receptor signaling, purines, and pre-programmed cell death.

Cancer-induced morphological changes in enteric glial cells in the jejunum of Walker-256 tumor-bearing rats

Cancer-induced cachexia is associated with systemic inflammation and gastrointestinal dysfunction. How changes to cells of the enteric nervous system contribute to gut dysfunction in tumor development and cancer cachexia is unknown. Here, we tested the hypothesis that changes to enteric glia, a type of peripheral glia that surround enteric neurons and regulate gut homeostasis, are associated with tumor development and that supplementing with the antioxidant L-glutathione is protective against the changes induced. Immunohistochemistry for neurons, enteric glial cells and immune cells was performed in whole-mount preparations and frozen histological sections of the jejunum from 20 Wistar rats, distributed in 4 groups: control, tumor of Walker-256, control administered with 1 % L-glutathione, and tumor of Walker-256 administered with 1 % L-glutathione. Morphoquantitative analyses were made using Image-Pro® Plus 4.5 and ImageJ® 1.43° software. Tumor development significantly reduced neuronal and glial cell populations in the myenteric and submucosal plexuses and enlarged glial cell body area in the submucosal plexus. In contrast, tumors increased glia in the jejunal mucosa and this effect was accompanied by B-lymphocyte recruitment. GSH-supplemented diet was not sufficient to protect against changes to neurons and glia in the submucosal plexus but was partially protective in the myenteric plexus. L-glutathione had no effect on physiological parameters of cachexia but was sufficient to preserve enteric glial cell density in the myenteric plexus. These results suggest that changes to both enteric neurons and glia likely contribute to the gastrointestinal effects of tumor development and that oxidative stress contributes to these effects in the enteric nervous system.

Is metformin neuroprotective against diabetes mellitus-induced neurodegeneration? An updated graphical review of molecular basis

Diabetes mellitus (DM) is a metabolic disease that activates several molecular pathways involved in neurodegenerative disorders. Metformin, an anti-hyperglycemic drug used for treating DM, has the potential to exert a significant neuroprotective role against the detrimental effects of DM. This review discusses recent clinical and laboratory studies investigating the neuroprotective properties of metformin against DM-induced neurodegeneration and the roles of various molecular pathways, including mitochondrial dysfunction, oxidative stress, inflammation, apoptosis, and its related cascades. A literature search was conducted from January 2000 to December 2022 using multiple databases including Web of Science, Wiley, Springer, PubMed, Elsevier Science Direct, Google Scholar, the Core Collection, Scopus, and the Cochrane Library to collect and evaluate peer-reviewed literature regarding the neuroprotective role of metformin against DM-induced neurodegenerative events. The literature search supports the conclusion that metformin is neuroprotective against DM-induced neuronal cell degeneration in both peripheral and central nervous systems, and this effect is likely mediated via modulation of oxidative stress, inflammation, and cell death pathways.

Brazil Nut (Bertholletia excelsa H.B.K) Retards Gastric Emptying and Modulates Enteric Glial Cells in a Dose-Dependent Manner

BACKGROUND

The role of food and nutrients in the regulation of enteric glial cell functions is unclear. Some foods influence enteric neurophysiology and can affect glial cell functions that include regulation of the intestinal barrier, gastric emptying, and colonic transit. Brazil nuts are the most abundant natural source of selenium, unsaturated fatty acids, fibers, and polyphenols.

OBJECTIVE

The study investigated the effects of a Brazil nut-enriched diet on enteric glial cells and gastrointestinal transit.

METHODS

Two-month-old male Wistar rats were randomized to a standard diet (control group, CG), standard diet containing 5% (wt/wt) Brazil nut (BN5), and standard diet containing 10% (wt/wt) Brazil nut (BN10) (n = 9 per group). After eight weeks, the animals underwent constipation and gastric emptying tests to assess motility. Evaluations of colonic immunofluorescence staining for glial fibrillary acidic protein (GFAP) and myenteric ganglia area were performed.

RESULTS

The BN5 group showed increased weight gain while the BN10 group did not (p < 0.0001). The BN10 group showed higher gastric residue amounts compared to the other groups (p = 0.0008). The colon exhibited an increase in GFAP immunoreactivity in the BN5 group compared to that in the other groups (p = 0.0016), and the BN10 group presented minor immunoreactivity compared to the CG (p = 0.04). The BN10 group presented a minor ganglia area compared to the CG (p = 0.0155).

CONCLUSION

The Brazil nut-enriched diet modified the gastric residual, colonic GFAP immunoreactivity, and myenteric ganglia area after eight weeks in healthy male Wistar rats.

Neuro-immune-metabolism: The tripod system of homeostasis

Homeostatic regulation of cellular and molecular processes is essential for the efficient physiological functioning of body organs. It requires an intricate balance of several networks throughout the body, most notable being the nervous, immune and metabolic systems. Several studies have reported the interactions between neuro-immune, immune-metabolic and neuro-metabolic pathways. Current review aims to integrate the information and show that neuro, immune and metabolic systems form the triumvirate of homeostasis. It focuses on the cellular and molecular interactions occurring in the extremities and intestine, which are innervated by the peripheral nervous system and for the intestine in particular the enteric nervous system. While the interdependence of neuro-immune-metabolic pathways provides a fallback mechanism in case of disruption of homeostasis, in chronic pathologies of continued disequilibrium, the collapse of one system spreads to the other interacting networks as well. Current review illustrates this domino-effect using diabetes as the main example. Together, this review attempts to provide a holistic picture of the integrated network of neuro-immune-metabolism and attempts to broaden the outlook when devising a scientific study or a treatment strategy.

Nutraceuticals and Enteric Glial Cells

Until recently, glia were considered to be a structural support for neurons, however further investigations showed that glial cells are equally as important as neurons. Among many different types of glia, enteric glial cells (EGCs) found in the gastrointestinal tract, have been significantly underestimated, but proved to play an essential role in neuroprotection, immune system modulation and many other functions. They are also said to be remarkably altered in different physiopathological conditions. A nutraceutical is defined as any food substance or part of a food that provides medical or health benefits, including prevention and treatment of the disease. Following the description of these interesting peripheral glial cells and highlighting their role in physiological and pathological changes, this article reviews all the studies on the effects of nutraceuticals as modulators of their functions. Currently there are only a few studies available concerning the effects of nutraceuticals on EGCs. Most of them evaluated molecules with antioxidant properties in systemic conditions, whereas only a few studies have been performed using models of gastrointestinal disorders. Despite the scarcity of studies on the topic, all agree that nutraceuticals have the potential to be an interesting alternative in the prevention and/or treatment of enteric gliopathies (of systemic or local etiology) and their associated gastrointestinal conditions.

Automatic chronic degenerative diseases identification using enteric nervous system images

Studies recently accomplished on the Enteric Nervous System have shown that chronic degenerative diseases affect the Enteric Glial Cells (EGC) and, thus, the development of recognition methods able to identify whether or not the EGC are affected by these type of diseases may be helpful in its diagnoses. In this work, we propose the use of pattern recognition and machine learning techniques to evaluate if a given animal EGC image was obtained from a healthy individual or one affect by a chronic degenerative disease. In the proposed approach, we have performed the classification task with handcrafted features and deep learning-based techniques, also known as non-handcrafted features. The handcrafted features were obtained from the textural content of the ECG images using texture descriptors, such as the Local Binary Pattern (LBP). Moreover, the representation learning techniques employed in the approach are based on different Convolutional Neural Network (CNN) architectures, such as AlexNet and VGG16, with and without transfer learning. The complementarity between the handcrafted and non-handcrafted features was also evaluated with late fusion techniques. The datasets of EGC images used in the experiments, which are also contributions of this paper, are composed of three different chronic degenerative diseases: Cancer, Diabetes Mellitus, and Rheumatoid Arthritis. The experimental results, supported by statistical analysis, show that the proposed approach can distinguish healthy cells from the sick ones with a recognition rate of 89.30% (Rheumatoid Arthritis), 98.45% (Cancer), and 95.13% (Diabetes Mellitus), being achieved by combining classifiers obtained on both feature scenarios.

Global Proteomic Profile Integrated to Quantitative and Morphometric Assessment of Enteric Neurons: Investigation of the Mechanisms Involved in the Toxicity Induced by Acute Fluoride Exposure in the Duodenum

The enteric nervous system is responsible for controlling the gastrointestinal tract (GIT) functions. Enteric neuropathies are highly correlated to the development of several intestinal disturbances. Fluoride (F) is extensively applied for dental health improvement and its ingestion can promote systemic toxicity with mild to severe GIT symptomatology and neurotoxicity. Although F harmful effects have been published, there is no information regarding noxiousness of a high acute F exposure (25 mg F/kg) on enteric neurons and levels of expression of intestinal proteins in the duodenum. Quantitative proteomics of the duodenum wall associated to morphometric and quantitative analysis of enteric neurons displayed F effects of a high acute exposure. F-induced myenteric neuroplasticity was characterized by a decrease in the density of nitrergic neurons and morphometric alterations in the general populations of neurons, nitrergic neurons, and substance P varicosities. Proteomics demonstrated F-induced alterations in levels of expression of 356 proteins correlated to striated muscle cell differentiation; generation of precursor metabolites and energy; NADH and glutathione metabolic process and purine ribonucleoside triphosphate biosynthesis. The neurochemical role of several intestinal proteins was discussed specially related to the modulation of enteric neuroplasticity. The results provide a new perspective on cell signaling pathways of gastrointestinal symptomatology promoted by acute F toxicity.

Quercetin increases bioavailability of nitric oxide in the jejunum of euglycemic and diabetic rats and induces neuronal plasticity in the myenteric plexus

Considering the antioxidant, neuroprotective, inflammatory and nitric oxide modulatory actions of quercetin, the aim of this study was to test the effect of quercetin administration in drinking water (40 mg/day/rat) on neuronal nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), overall population of myenteric neurons (HuC/D) and nitric oxide (NO) levels in the jejunal samples from diabetic rats. Male Wistar rats were distributed into four groups (8 rats per group): euglycemic (E), euglycemic administered with quercetin (E+Q), diabetic (D) and diabetic administered with quercetin (D+Q). Rats were induced to diabetes with streptozotocin (35mg/kg/iv) and, after 120 days, the proximal jejunum were collected and processed for immunohistochemical (VIP, nNOS and HuC/D) and chemiluminescence (quantification of tissue NO levels) techniques. Diabetes mellitus reduced the number of nNOS-IR (immunoreactive) (p <0.05) and HuC/D-IR (p <0.001) neurons, however, promoted an increased morphometric area of nNOS-IR neurons (p <0.001) and VIP-IR varicosities (p <0.05). In D+Q group, neuroplasticity effects were observed on HuC/D-IR neurons, accompanied by a reduction of cell body area of neurons nNOS- and VIP-IR varicosities (p <0.05). The NO levels were increased in the E+Q (p <0.05) and D+Q group (p <0.001) compared to the control group. In conclusion, the results showed that quercetin supplementation increased the bioavailability of NO in the jejunum in euglycemic and mitigate the effects of diabetes on nNOS-IR neurons and VIP-IR varicosities in the myenteric plexus of diabetic rats.

Chronic ingestion of deoxynivalenol-contaminated diet dose-dependently decreases the area of myenteric neurons and gliocytes of rats

BACKGROUND

Deoxynivalenol (DON), a mycotoxin produced by Fusarium spp., is commonly found in cereals ingested by humans and animals. Its ingestion is correlated with hepatic, hematologic, renal, splenic, cardiac, gastrointestinal, and neural damages, according to dose, duration of exposure and species. In this work, the effects of the ingestion of DON-contaminated diet at concentrations considered tolerable for human and animal intake were assessed.

METHODS

Male Wistar rats aging 21 days were allotted to five groups that were given, for 42 days, diets contaminated with different concentrations of DON (0, 0.2, 0.75, 1.75, and 2 mg kg^-1 of chow). Food ingestion, bodyweight, oxidative status and morphometric analyses of gliocytes, and neurons of jejunal myenteric ganglia were recorded.

KEY RESULTS

At these concentrations, there was no food rejection, decrease in bodyweight gain, changes in oxidative status, or loss of either neurons or gliocytes. However, DON decreased gliocyte area, general neuronal population, nitrergic, cholinergic and NADH-diaphorase positive subpopulations and, as a result, ganglion area.

CONCLUSIONS & INFERENCES

It was concluded that, even in the absence of visible effect, DON exposure reduces cell body area of gliocytes and neurons of the myenteric plexus of the rat jejunum.

Targeting the Enteric Nervous System to Treat Metabolic Disorders? "Enterosynes" as Therapeutic Gut Factors

The gut-brain axis is of crucial importance for controlling glucose homeostasis. Alteration of this axis promotes the type 2 diabetes (T2D) phenotype (hyperglycaemia, insulin resistance). Recently, a new concept has emerged to demonstrate the crucial role of the enteric nervous system in the control of glycaemia via the hypothalamus. In diabetic patients and mice, modification of enteric neurons activity in the proximal part of the intestine generates a duodenal hyper-contractility that generates an aberrant message from the gut to the brain. In turn, the hypothalamus sends an aberrant efferent message that provokes a state of insulin resistance, which is characteristic of a T2D state. Targeting the enteric nervous system of the duodenum is now recognized as an innovative strategy for treatment of diabetes. By acting in the intestine, bioactive gut molecules that we called "enterosynes" can modulate the function of a specific type of neurons of the enteric nervous system to decrease the contraction of intestinal smooth muscle cells. Here, we focus on the origins of enterosynes (hormones, neurotransmitters, nutrients, microbiota, and immune factors), which could be considered therapeutic factors, and we describe their modes of action on enteric neurons. This unsuspected action of enterosynes is proposed for the treatment of T2D, but it could be applied for other therapeutic solutions that implicate communication between the gut and brain.

Impaired Amino Acid and TCA Metabolism and Cardiovascular Autonomic Neuropathy Progression in Type 1 Diabetes

While diabetes is characterized by hyperglycemia, nutrient metabolic pathways like amino acid and tricarboxylic acid (TCA) cycle are also profoundly perturbed. As glycemic control alone does not prevent complications, we hypothesized that these metabolic disruptions are responsible for the development and progression of diabetic cardiovascular autonomic neuropathy (CAN). We performed standardized cardiovascular autonomic reflex tests and targeted fasting plasma metabolomic analysis of amino acids and TCA cycle intermediates in subjects with type 1 diabetes and healthy control subjects followed for 3 years. Forty-seven participants with type 1 diabetes (60% female and mean ± SD age 35 ± 13 years, diabetes duration 13 ± 7 years, and HbA_1c 7.9 ± 1.2%) had lower fumarate levels and higher threonine, serine, proline, asparagine, aspartic acid, phenylalanine, tyrosine, and histidine levels compared with 10 age-matched healthy control subjects. Higher baseline fumarate levels and lower baseline amino acid levels-asparagine and glutamine-correlate with CAN (lower baseline SD of normal R-R interval [SDNN]). Baseline glutamine and ornithine levels also associated with the progression of CAN (lower SDNN at 3 years) and change in SDNN, respectively, after adjustment for baseline HbA_1c, blood glucose, BMI, cholesterol, urine microalbumin-to- creatinine ratio, estimated glomerular filtration rate, and years of diabetes. Therefore, significant changes in the anaplerotic flux into the TCA cycle could be the critical defect underlying CAN progression.

Pathophysiology and management of diabetic gastroenteropathy

Polyneuropathy is a common complication to diabetes. Neuropathies within the enteric nervous system are associated with gastroenteropathy and marked symptoms that severely reduce quality of life. Symptoms are pleomorphic but include nausea, vomiting, dysphagia, dyspepsia, pain, bloating, diarrhoea, constipation and faecal incontinence. The aims of this review are fourfold. First, to provide a summary of the pathophysiology underlying diabetic gastroenteropathy. Secondly to give an overview of the diagnostic methods. Thirdly, to provide clinicians with a focussed overview of current and future methods for pharmacological and nonpharmacological treatment modalities. Pharmacological management is categorised according to symptoms arising from the upper or lower gut as well as sensory dysfunctions. Dietary management is central to improvement of symptoms and is discussed in detail, and neuromodulatory treatment modalities and other emerging management strategies for diabetic gastroenteropathy are discussed. Finally, we propose a diagnostic/investigation algorithm that can be used to support multidisciplinary management.

Effects of diabetes mellitus on myenteric neuronal density and sodium channel expression in the rat ileum

Diabetes mellitus (DM) may lead to gastrointestinal motility disorders. Rodent models of DM indicate the presence of morpho-functional abnormalities of the enteric nervous system. Here, we evaluated whether experimental DM can cause changes in the excitatory cholinergic fibers, neuronal density, and voltage-gated sodium channel (Nav) expression in the myenteric plexus of the ileum. After streptozotocin-induced hyperglycemia in female rats progressed for eight weeks, triple immunofluorescence labeling experiments revealed that the neuronal density in DM rats was significantly lower than that in control. On average, the density of total neurons reduced by 52.2% (p = 0.0001), cholinergic neurons by 50.0% (p = 0.0068), and nitrergic neurons by 54.8% (p = 0.0042). The number of neurons per ganglionic area was also significantly reduced (to 28.2% of total neurons, p = 0.0002; 27.7% of cholinergic neurons, p = 0.0002, and 32.1% of nitrergic neurons, p = 0.0016). Furthermore, the density of the cholinergic fibers at the surface of the longitudinal muscle was significantly reduced (DM: 24 ± 3%; p = 0.003, control: 41 ± 2%); however, western-blot analysis did not indicate a reduction in the expression of choline acetyltransferase (ChAT) in the DM group. The Nav1.6 isoform was detected in different myenteric neurons of the ileum. RT-qPCR data did not suggest an alteration of transcripts for ChAT, neuronal nitric oxide synthase, Nav1.3, Nav1.6, or Nav1.7. Our data support the view that chronic DM leads to a reduction of excitatory cholinergic fibers and neuronal density. However, changes in sodium channel expression pattern, which could cause neuronal dysfunction, were not detected.

Resveratrol promotes neuroprotection and attenuates oxidative and nitrosative stress in the small intestine in diabetic rats

Damages to the enteric nervous system caused by diabetes mellitus (DM) are frequently attributed to oxidative and nitrosative stress. We aimed to investigate the effect of Resveratrol (RSV) (10 mg/kg) on oxidative and nitrosative stress in the intestinal wall and morphoquantitative aspects of the myenteric plexus of the duodenum, jejunum and ileum in diabetic rats. Twenty-four rats were distributed into four groups (n = 6/group): control (C group), control treated with RSV (CR group), diabetic (D group), and diabetic treated with RSV (DR group) for 120 days. Immunohistochemical staining techniques for the general neuronal population, nitrergic and calretinin neuronal subpopulations, enteric glial cells and glial fibrillary acid protein were performed in the myenteric plexus. Furthermore, parameters of oxidative and nitrosative stress were analyzed in the intestinal wall. RSV attenuated oxidative and nitrosative stress and prevented neuronal loss and hypertrophy of the HuC/D-IR, nNOS-IR and CALR-IR neuronal subpopulations in the DR group compared with the D group (P < 0.05). In addition, RSV prevented the increase in glial fibrillary acid protein fluorescence in the DR group compared with the D (P < 0.05). These results suggest that RSV has antioxidant and neuroprotective effects in myenteric plexus in rats with experimental DM.

Enteric Glial Dysfunction Evoked by Apolipoprotein E Deficiency Contributes to Delayed Gastric Emptying

BACKGROUND AND AIM

Diabetes is the main cause of gastroparesis accompanying decreased neuronal nitric oxide synthase (nNOS) in myenteric ganglia of the stomach. Decreased nNOS expression in the stomach also results from defects in apolipoprotein E (ApoE), which is secreted by astrocytes and has neuroprotective effects on the central nervous system. However, the roles of ApoE and enteric glial cells on gastric motility are uncertain. In this study, ApoE and enteric glial cell alterations in gastroparesis were investigated.

METHODS

Type 2 diabetic (db/db) mice and ApoE-knockout mice were analyzed. Gastric emptying was measured using the ¹³C acetic acid breath test. Expression levels of the pan-neuronal marker, protein gene product 9.5 (PGP 9.5), and glial marker, glial fibrillary acidic protein (GFAP) were examined by immunohistochemistry. Neural stem cells (NSCs) were injected into the gastric antral wall of ApoE-knockout mice.

RESULTS

Delayed gastric emptying was observed in 27% of db/db mice with significant decreases in serum ApoE levels and GFAP expression in the gastric antrum. Gastric emptying was also delayed in ApoE-knockout mice, with a significant decrease in GFAP expression, but no change in PGP 9.5 expression. Transplantation of NSCs improved gastric emptying in ApoE-knockout mice through supplementation of GFAP-positive cells.

CONCLUSIONS

Our results suggest that decreased enteric glial cells in ApoE-knockout mice are crucial for development of delayed gastric emptying, and NSC transplantation is effective in restoring myenteric ganglia and gastric motility.

Glutamine up-regulates pancreatic sodium-dependent neutral aminoacid transporter-2 and mitigates islets apoptosis in diabetic rats

BACKGROUND

Glutamine aminoacid regulates insulin exocytosis from pancreatic β-cells. Liraglutide is a glucagon-like peptide-1 (GLP-1) analogue that has fascinated function in inhibiting β-cell apoptosis and preserving pancreatic β-cell mass. The present study investigated the benefit of adding glutamine to a regimen of liraglutide in diabetic rats focusing on their role in increasing insulin production and upregulation of the expression of sodium-dependent neutral aminoacid transporter-2 (SNAT2).

METHODS

In the present study, diabetes mellitus was induced in rats using streptozotocin (STZ, 50mg/kg, ip). Male rats were allocated into 5 groups, (i) vehicle group, (ii) STZ-diabetic rats, (iii) STZ-diabetic rats treated with liraglutide (150μg/kg, sc), (iv) STZ-diabetic rats treated with glutamine (po) and (v) STZ-diabetic rats treated with a combination of liraglutide and glutamine for four weeks. After finishing the therapeutic courses, the fasting blood glucose value was determined and rats were sacrificed. Pancreases were used for quantification of mRNA expression for SNAT2. Paraffin fixed samples were used for histologic staining and immunohistochemistry for insulin and apoptosis markers (activated caspase-3, BCL2 and BAX).

RESULTS

Treatment with liraglutide and/or glutamine enhanced insulin production and hence glycemic control in diabetic male rats with favorable effects on apoptosis markers. Treatment with glutamine and its combination with liraglutide significantly increased pancreatic expression of SNAT2 by approximately 30-35 folds.

CONCLUSION

Addition of glutamine to liraglutide regimen enhances the glycemic control and may have utility in clinical settings.

Diabetes-Related Induction of the Heme Oxygenase System and Enhanced Colocalization of Heme Oxygenase 1 and 2 with Neuronal Nitric Oxide Synthase in Myenteric Neurons of Different Intestinal Segments

Increase in hyperglycaemia-induced oxidative stress and decreased effectiveness of endogenous defense mechanisms plays an essential role in the initiation of diabetes-related neuropathy. We demonstrated that nitrergic myenteric neurons display different susceptibilities to diabetic damage in different gut segments. Therefore, we aim to reveal the gut segment-specific differences in the expression of heme oxygenase (HO) isoforms and the colocalization of these antioxidants with neuronal nitric oxide synthase (nNOS) in myenteric neurons. After ten weeks, samples from the duodenum, ileum, and colon of control and streptozotocin-induced diabetic rats were processed for double-labelling fluorescent immunohistochemistry and ELISA. The number of both HO-immunoreactive and nNOS/HO-immunoreactive myenteric neurons was the lowest in the ileal and the highest in the colonic ganglia of controls; it increased the most extensively in the ileum and was also elevated in the colon of diabetics. Although the total number of nitrergic neurons decreased in all segments, the proportion of nNOS-immunoreactive neurons colocalizing with HOs was enhanced robustly in the ileum and colon of diabetics. We presume that those nitrergic neurons which do not colocalize with HOs are the most seriously affected by diabetic damage. Therefore, the regional induction of the HO system is strongly correlated with diabetes-related region-specific nitrergic neuropathy.

Antioxidant Effects of the Quercetin in the Jejunal Myenteric Innervation of Diabetic Rats

Purpose

Enteric glial cells (EGCs) exert a critical role in the structural integrity, defense, and metabolic function of enteric neurons. Diabetes mellitus is a chronic disease characterized by metabolic disorders and chronic autonomic neuropathy. Quercetin supplementation, which is a potent antioxidant, has been used in order to reduce the effects of diabetes-induced oxidative stress. The purpose of this research was to investigate the effects of quercetin supplementation in the drinking water at a daily dose of 40 mg on the glial cells and neurons in the jejunum of diabetic rats.

Materials and methods

Twenty 90-day-old male adult Wistar rats were split into four groups: normoglycemic control (C), normoglycemic control supplemented with quercetin (Q), diabetic (D), and diabetic supplemented with quercetin (DQ). After 120 days, the jejunums were collected, and immunohistochemical technique was performed to label S-100-immunoreactive glial cells and HuC/D-immunoreactive neurons.

Results

An intense neuronal and glial reduction was observed in the jejunum of diabetic rats. Quercetin displayed neuroprotective effects due to reduced cell body areas of neurons and glial cells in Q and DQ groups compared to their controls (C and D groups). Interestingly, quercetin prevented the glial and neuronal loss with a higher density for the HuC/D-immunoreactive neurons (23.06%) and for the S100-immunoreactive glial cells (14.55%) in DQ group compared to D group.

Conclusion

Quercetin supplementation promoted neuroprotective effects through the reduction of neuronal and glial body areas and a slight prevention of neuronal and glial density reduction.

Experimental Cancer Cachexia Changes Neuron Numbers and Peptide Levels in the Intestine: Partial Protective Effects after Dietary Supplementation with L-Glutamine

Gastrointestinal dysmotility frequently occurs in cancer cachexia and may result from damage to enteric innervation caused by oxidative stress, especially due to glutathione depletion. We assessed the effect of dietary supplementation with 20 g/kg l-glutamine (a glutathione precursor) on the intrinsic innervation of the enteric nervous system in healthy and Walker 256 tumor-bearing Wistar rats during the development of experimental cachexia (14 days), in comparison with non-supplemented rats, by using immunohistochemical methods and Western blotting. The total neural population and cholinergic subpopulation densities in the myenteric plexus, as well as the total population and VIPergic subpopulation in the submucosal plexus of the jejunum and ileum, were reduced in cachectic rats, resulting in adaptive morphometric alterations and an increase in vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) expression, suggesting a neuroplastic response. l-glutamine supplementation prevented decrease in myenteric neuronal density in the ileum, morphometric alterations in the neurons and nerve fibers (in both the plexuses of the jejunum and ileum), and the overexpression of VIP and CGRP. Cancer cachexia severely affected the intrinsic innervation of the jejunum and ileum to various degrees and this injury seems to be associated with adaptive neural plasticity. l-glutamine supplementation presented partial protective effects on the enteric innervation against cancer cachexia, possibly by attenuating oxidative stress.

Desired and side effects of the supplementation with l-glutamine and l-glutathione in enteric glia of diabetic rats

BACKGROUND/AIMS

Enteric neuropathy associated with Diabetes Mellitus causes dysfunction in the digestive system, such as: nausea, diarrhea, constipation, vomiting, among others. The aim of this study was to compare the effects of supplementation with 2% l-glutamine and 1% l-glutathione on neurons and enteric glial cells of ileum of diabetic rats.

METHODS

Thirty male Wistar rats have been used according to these group distributions: Normoglycemic (N), Normoglycemic supplemented with l-glutamine (NG), Normoglycemic supplemented with l-glutathione (NGO), Diabetic (D), Diabetic supplemented with l-glutamine (DG) and Diabetic supplemented with l-glutathione (DGO). After 120days, the ileum was processed for immunohistochemistry of HuC/D and S100β. Quantitative and morphometric analysis have been performed.

RESULTS

Diabetic rats presented a decrease in the number of neurons when compared to normoglycemic animals. However, diabetes was not associated with a change in glial density. l-Glutathione prevented the neuronal death in diabetic rats. l-Glutathione increased a glial proliferation in diabetic rats. The neuronal area in diabetic rats increased in relation to the normoglycemics. The diabetic rats supplemented with l-glutamine and l-glutathione showed a smaller neuronal area in comparison to diabetic group. The glial cell area was a decreased in the diabetics. The diabetic rats supplemented with l-glutamine and l-glutathione did not have significant difference in the glial cell body area when compared to diabetic rats.

CONCLUSION

It is concluded that the usage of l-glutamine and l-glutathione as supplements presents both desired and side effects that are different for the same substance in considering normoglycemic or diabetic animals.

Differential effects in CGRPergic, nitrergic, and VIPergic myenteric innervation in diabetic rats supplemented with 2% L-glutamine

ABSTRACT The objective of this study was to investigate the effects of 2% L-glutamine supplementation on myenteric innervation in the ileum of diabetic rats, grouped as follows: normoglycemic (N); normoglycemic supplemented with L-glutamine (NG); diabetic (D); and diabetic supplemented with L-glutamine (DG). The ileums were subjected to immunohistochemical techniques to localize neurons immunoreactive to HuC/D protein (HuC/D-IR) and neuronal nitric oxide synthase enzyme (nNOS-IR) and to analyze varicosities immunoreactive to vasoactive intestinal polypeptide (VIP-IR) and calcitonin gene-related peptide (CGRP-IR). L-Glutamine in the DG group (i) prevented the increase in the cell body area of nNOS-IR neurons, (ii) prevented the increase in the area of VIP-IR varicosities, (iii) did not prevent the loss of HuC/D-IR and nNOS-IR neurons per ganglion, and (iv) reduced the size of CGRP-IR varicosities. L-Glutamine in the NG group reduced (i) the number of HuC/D-IR and nNOS-IR neurons per ganglion, (ii) the cell body area of nNOS-IR neurons, and (iii) the size of VIP-IR and CGRP-IR varicosities. 2% L-glutamine supplementation exerted differential neuroprotective effects in experimental diabetes neuropathy that depended on the type of neurotransmitter analyzed. However, the effects of this dose of L-glutamine on normoglycemic animals suggests there are additional actions of this beyond its antioxidant capacity.

Supplementation with L-Glutamine and L-Alanyl-L-Glutamine Changes Biochemical Parameters and Jejunum Morphophysiology in Type 1 Diabetic Wistar Rats

We evaluated the effects of the supplementation with L-glutamine and glutamine dipeptide (GDP) on biochemical and morphophysiological parameters in streptozotocin-diabetic rats. For this purpose, thirty animals were distributed into six groups treated orally (gavage) during thirty days: non diabetic rats (Control) + saline, diabetic + saline; Control + L-glutamine (248 mg/kg), Diabetic + L-glutamine (248 mg/kg), Control + GDP (400 mg/kg), Diabetic + GDP (400 mg/kg). Diabetes was induced by an intravenous injection of streptozotocin (60 mg/kg) and confirmed by fasting glucose ≥ 200 mg/dL. Physiological parameters, i.e., body mass, food intake, blood glucose, water intake, urine and faeces were evaluated during supplementation. After the period of supplementation, the animals were euthanized. The blood was collected for biochemical assays (fructosamine, transaminases, lipid profile, total protein, urea, ammonia). Moreover, the jejunum was excised and stored for morphophysiological assays (intestinal enzyme activity, intestinal wall morphology, crypt proliferative index, number of serotoninergic cells from the mucosa, and vipergic neurons from the submucosal tunica). The physiological parameters, protein metabolism and intestinal enzyme activity did not change with the supplementation with L-glutamine or GDP. In diabetic animals, transaminases and fructosamine improved with L-glutamine and GDP supplementations, while the lipid profile improved with L-glutamine. Furthermore, both forms of supplementation promoted changes in jejunal tunicas and wall morphometry of control and diabetic groups, but only L-glutamine promoted maintenance of serotoninergic cells and vipergic neurons populations. On the other hand, control animals showed changes that may indicate negative effects of L-glutamine. Thus, the supplementation with L-glutamine was more efficient for maintaining intestinal morphophysiology and the supplementation with GDP was more efficient to the organism as a whole. Thus, we can conclude that local differences in absorption and metabolism could explain the differences between the supplementation with L-glutamine or GDP.

Aqueous Extract of Agaricus blazei Murrill Prevents Age-Related Changes in the Myenteric Plexus of the Jejunum in Rats

This study evaluated the effects of the supplementation with aqueous extract of Agaricus blazei Murrill (ABM) on biometric and blood parameters and quantitative morphology of the myenteric plexus and jejunal wall in aging Wistar rats. The animals were euthanized at 7 (C7), 12 (C12 and CA12), and 23 months of age (C23 and CA23). The CA12 and CA23 groups received a daily dose of ABM extract (26 mg/animal) via gavage, beginning at 7 months of age. A reduction in food intake was observed with aging, with increases in the Lee index, retroperitoneal fat, intestinal length, and levels of total cholesterol and total proteins. Aging led to a reduction of the total wall thickness, mucosa tunic, villus height, crypt depth, and number of goblet cells. In the myenteric plexus, aging quantitatively decreased the population of HuC/D(+) neuronal and S100(+) glial cells, with maintenance of the nNOS(+) nitrergic subpopulation and increase in the cell body area of these populations. Supplementation with the ABM extract preserved the myenteric plexus in old animals, in which no differences were detected in the density and cell body profile of neurons and glial cells in the CA12 and CA23 groups, compared with C7 group. The supplementation with the aqueous extract of ABM efficiently maintained myenteric plexus homeostasis, which positively influenced the physiology and prevented the death of the neurons and glial cells.

Damage to enteric neurons occurs in mice that develop fatty liver disease but not diabetes in response to a high-fat diet

BACKGROUND

Disorders of gastrointestinal functions that are controlled by enteric neurons commonly accompany fatty liver disease. Established fatty liver disease is associated with diabetes, which itself induces enteric neuron damage. Here, we investigate the relationship between fatty liver disease and enteric neuropathy, in animals fed a high-fat, high-cholesterol diet in the absence of diabetes.

METHODS

Mice were fed a high-fat, high-cholesterol diet (21% fat, 2% cholesterol) or normal chow for 33 weeks. Liver injury was assessed by hematoxylin and eosin, picrosirius red staining, and measurement of plasma alanine aminotransaminase (ALT). Quantitative immunohistochemistry was performed for different types of enteric neurons.

KEY RESULTS

The mice developed steatosis, steatohepatitis, fibrosis, and a 10-fold increase in plasma ALT, indicative of liver disease. Oral glucose tolerance was unchanged. Loss and damage to enteric neurons occurred in the myenteric plexus of ileum, cecum, and colon. Total numbers of neurons were reduced by 15-30% and neurons expressing nitric oxide synthase were reduced by 20-40%. The RNA regulating protein, Hu, became more concentrated in the nuclei of enteric neurons after high-fat feeding, which is an indication of stress on the enteric nervous system. There was also disruption of the neuronal cytoskeletal protein, neurofilament medium.

CONCLUSIONS & INFERENCES

Enteric neuron loss and damage occurs in animals with fatty liver disease in the absence of glucose intolerance. The enteric neuron damage may contribute to the gastrointestinal complications of fatty liver disease.

Expression and possible role of IGF-IR in the mouse gastric myenteric plexus and smooth muscles

Insulin-like growth factor-I (IGF-I) and its receptor (IGF-IR) have tremendous trophic effects on the central, peripheral and enteric neurons. The loss of IGF-IR contributes to the development of diabetic gastroparesis. However, the nature and the function of the IGF-IR(+) cells in the gastric myenteric plexus remain unclear. In this study, anti-ChAT, anti-S100β or anti-c-KIT antibodies were used to co-label IGF-IR(+) cells and neurons, glial cells or interstitial cells of Cajal (ICCs), respectively. We also generated type 1 diabetic mice (DM) to explore the influence of impaired IGF-I/IGF-IR in the myenteric neurons. Results showed that IGF-IR was expressed in the epithelium, smooth muscles and myenteric plexi of the mouse stomach. Most of the IGF-IR(+) cells in the myenteric plexi were ChAT(+) cholinergic neurons, but not enteric glial cells and there were more IGF-IR(+) neurons and fibers in the gastric antrum than in the corpus. The IGF-IR(+)/ChAT(+) neurons and ICCs were closely juxtaposed, but distinctly distributed in the myenteric plexus, indicating a possible role for the IGF-IR(+)/ChAT(+) neurons in the mediation of gastric motility through ICCs. Moreover, the decrease of IGF-IR and cholinergic neurons in the myenteric plexi and smooth muscles of DM mice suggested that IGF-I/IGF-IR signaling might play a role in neuron survival and neurite outgrowth, as well as stem cell factor (SCF) production, which is required for the development of ICCs. Our results provide insights into the effects of IGF-I/IGF-IR signaling on the development of gastrointestinal motility disorders.

Is L-glutathione more effective than L-glutamine in preventing enteric diabetic neuropathy?

BACKGROUND

Diabetes and its complications appear to be multifactorial. Substances with antioxidant potential have been used to protect enteric neurons in experimental diabetes.

AIM

This study evaluated the effects of supplementation with L-glutamine and L-glutathione on enteric neurons in the jejunum in diabetic rats.

METHODS

Rats at 90 days of age were distributed into six groups: normoglycemic, normoglycemic supplemented with 2 % L-glutamine, normoglycemic supplemented with 1 % L-glutathione, diabetic (D), diabetic supplemented with 2 % L-glutamine (DG), and diabetic supplemented with 1 % L-glutathione (DGT). After 120 days, the jejunums were immunohistochemically stained for HuC/D+ neuronal nitric oxide synthase (nNOS) and vasoactive intestinal polypeptide (VIP). Western blot was performed to evaluate nNOS and VIP. Submucosal and myenteric neurons were quantitatively and morphometrically analyzed.

RESULTS

Diabetic neuropathy was observed in myenteric HuC/D, nNOS, and VIP neurons (p < 0.05). In the submucosal plexus, diabetes did not change nitrergic innervation but increased VIPergic neuronal density and body size (p < 0.05). Supplementation with L-glutathione prevented changes in HuC/D neurons in the enteric plexus (p < 0.05), showing that supplementation with L-glutathione was more effective than with L-glutamine. Myenteric nNOS neurons in the DGT group exhibited a reduced density (34.5 %) and reduced area (p < 0.05). Submucosal neurons did not exhibit changes. The increase in VIP-expressing neurons was prevented in the submucosal plexus in the DG and DGT groups (p < 0.05).

CONCLUSION

Supplementation with L-glutathione exerted a better neuroprotective effect than L-glutamine and may prevent the development of enteric diabetic neuropathy.

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.

Synchronized dual pulse gastric electrical stimulation induces activation of enteric glial cells in rats with diabetic gastroparesis

Objective. The aims of this study were to investigate the effects of synchronized dual pulse gastric electrical stimulation (SGES) on gastric motility in different periods for diabetic rats and try to explore the possible mechanisms of the effects. Methods. Forty-six rats were used in the study. Gastric slow waves were recorded at baseline, 7-14-day diabetes and 56-63-day diabetes before and after stimulation and the age-matched control groups. SGES-60 mins and SGES-7 days (60 mins/day) were performed to test the effects on gastric motility and to evaluate glial marker S100B expression in stomach. Results. (1) Gastric emptying was accelerated in 7-14-day diabetes and delayed in 56-63-day diabetes. (2) The S100B expression in 56-63-day diabetes decreased and the ultrastructure changed. (3) The age-associated loss of EGC was observed in 56-63-day control group. (4) SGES was able to not only accelerate gastric emptying but also normalize gastric slow waves. (5) The S100B expression increased after SGES and the ultrastructure of EGC was partially restored. The effect of SGES-7 days was superior to SGES-60 mins. Conclusions. Delayed gastric emptying due to the growth of age may be related to the EGC inactivation. The effects of the SGES on gastric motility may be associated with EGC activation.

High-fat diet ingestion correlates with neuropathy in the duodenum myenteric plexus of obese mice with symptoms of type 2 diabetes

Obesity and type 2 diabetes are increasing in prevalence at an alarming rate in developed and developing nations and over 50% of patients with prolonged stages of disease experience forms of autonomic neuropathy. These patients have symptoms indicating disrupted enteric nervous system function including gastric discomfort, gastroparesis and intestinal dysmotility. Previous assessments have examined enteric neuronal injury within either type 1 diabetic or transgenic type 2 diabetic context. This study aims to assess damage to myenteric neurons within the duodenum of high-fat diet ingesting mice experiencing symptoms of type 2 diabetes, as this disease context is most parallel to the human condition and disrupted duodenal motility underlies negative gastrointestinal symptoms. Mice fed a high-fat diet developed symptoms of obesity and diabetes by 4 weeks. After 8 weeks, the total number of duodenal myenteric neurons and the synaptophysin density index were reduced and transmission electron microscopy showed axonal swelling and loss of neurofilaments and microtubules, suggesting compromised neuronal health. High-fat diet ingestion correlated with a loss of neurons expressing VIP and nNOS but did not affect the expression of ChAT, substance P, calbindin and CGRP. These results correlate high-fat diet ingestion, obesity and type 2 diabetes symptoms with a loss of duodenal neurons, biasing towards those with inhibitory nature. This pathology may underlie dysmotility and other negative GI symptoms experienced by human type 2 diabetic and obese patients.

High-fat diet and age-dependent effects on enteric glial cell populations of mouse small intestine

Diabetes and obesity are increasing in prevalence at an alarming rate throughout the world. Autonomic diabetic neuropathy is evident in individuals that experience a long-standing diabetic disease state, and gastrointestinal (GI) dysmotility is thought to be the outcome of neuropathies within the enteric nervous system (ENS) of these patients. To date, an analysis of enteric glial cell population changes during diabetic symptoms has not been performed, and may bring insight into disease pathology and neuropathy, given glial cell implications in gastrointestinal and neuronal homeostasis. Diabetes and obesity were monitored in C57Bl/6J mice fed a 72% high-fat diet, and duodenal glial expression patterns were evaluated by immunohistochemistry and RT-PCR for S100β, Sox10 and GFAP proteins and transcripts, as well as transmission electron microscopy (TEM). The high-fat diet caused obesity, hyperglycemia and insulin resistance after 4 weeks. These changes were associated with a significant decline in the area density indices of mucosa-associated glial cell networks, evidenced by S100β staining at 8 and 20 weeks. All three markers and TEM showed that myenteric glial cells were unaffected by early and late disease periods. However, analysis of Sox10 transcript expression and immunoreactivity showed a diet independent, age-associated decline in glial cell populations. This is the first study showing that mucosal glia cell damage occurs during diabetic symptoms, suggesting that mucosal enteric glia injury may have a pathophysiological significance during this disease. Our results also provide support for age-associated changes in longitudinal studies of enteric glial cells.

New perspectives in the diagnosis and management of enteric neuropathies

Chronic disturbances of gastrointestinal function encompass a wide spectrum of clinical disorders that range from common conditions with mild-to-moderate symptoms to rare diseases characterized by a severe impairment of digestive function, including chronic pain, vomiting, bloating and severe constipation. Patients at the clinically severe end of the spectrum can have profound changes in gut transit and motility. In a subset of these patients, histopathological analyses have revealed abnormalities of the gut innervation, including the enteric nervous system, termed enteric neuropathies. This Review discusses advances in the diagnosis and management of the main clinical entities--achalasia, gastroparesis, intestinal pseudo-obstruction and chronic constipation--that result from enteric neuropathies, including both primary and secondary forms. We focus on the various evident neuropathologies (degenerative and inflammatory) of these disorders and, where possible, present the specific implications of histological diagnosis to contemporary treatment. This knowledge could enable the future development of novel targeted therapeutic approaches.

Diabetes-related alterations in the enteric nervous system and its microenvironment

Gastric intestinal symptoms common among diabetic patients are often caused by intestinal motility abnormalities related to enteric neuropathy. It has recently been demonstrated that the nitrergic subpopulation of myenteric neurons are especially susceptible to the development of diabetic neuropathy. Additionally, different susceptibility of nitrergic neurons located in different intestinal segments to diabetic damage and their different levels of responsiveness to insulin treatment have been revealed. These findings indicate the importance of the neuronal microenvironment in the pathogenesis of diabetic nitrergic neuropathy. The main focus of this review therefore was to summarize recent advances related to the diabetes-related selective nitrergic neuropathy and associated motility disturbances. Special attention was given to the findings on capillary endothelium and enteric glial cells. Growing evidence indicates that capillary endothelium adjacent to the myenteric ganglia and enteric glial cells surrounding them are determinative in establishing the ganglionic microenvironment. Additionally, recent advances in the development of new strategies to improve glycemic control in type 1 and type 2 diabetes mellitus are also considered in this review. Finally, looking to the future, the recent and promising results of metagenomics for the characterization of the gut microbiome in health and disease such as diabetes are highlighted.