The brain networks encoding visceral sensation in patients with gastrointestinal symptoms due to diabetic neuropathy

Central neuronal transmission in response to tonic cold pain is modulated in people with type 1 diabetes and severe polyneuropathy

AIMS

This study aimed to investigate cortical source activity and identify source generators in people with type 1 diabetes during rest and tonic cold pain.

METHODS

Forty-eight participants with type 1 diabetes and neuropathy, and 21 healthy controls were investigated with electroencephalography (EEG) during 5-minutes resting and 2-minutes tonic cold pain (immersing the hand into water at 2 °C). EEG power was assessed in eight frequency bands, and EEG source generators were analyzed using standardized low-resolution electromagnetic tomography (sLORETA).

RESULTS

Compared to resting EEG, cold pain EEG power differed in all bands in the diabetes group (all p < 0.001) and six bands in the controls (all p < 0.05). Source generator activity in the diabetes group was increased in delta, beta2, beta3, and gamma bands and decreased in alpha1 (all p < 0.006) with changes mainly seen in the frontal and limbic lobe. Compared to controls, people with diabetes had decreased source generator activity during cold pain in the beta2 and beta3 bands (all p < 0.05), mainly in the frontal lobe.

CONCLUSIONS

Participants with type 1 diabetes had altered EEG power and source generator activity predominantly in the frontal and limbic lobe during tonic cold pain. The results may indicate modulated central transmission and neuronal impairment.

Altered Resting Brain Functions in Patients With Irritable Bowel Syndrome: A Systematic Review

Background

The neural activity of irritable bowel syndrome (IBS) patients in the resting state without any intervention has not been systematically studied. The purpose of this study was to compare the resting-state brain functions of IBS patients with healthy controls (HCs).

Methods

The published neuroimage studies were obtained from electronic databases including PubMed, EMBASE, PsycINFO, Web of Science Core, CNKI Database, Wanfang Database, VIP Database, and CBMdisc. Search dates were from inception to March 14th, 2022. The studies were identified by the preidentified inclusion and exclusion criteria. Two independent reviewers compiled the studies and evaluated them for quality and bias.

Results

Altogether 22 fMRI studies were included in this review. The risk of bias of the included studies was generally low. The findings indicated that in IBS patients, increased or decreased brain areas were mostly associated with visceral sensations, emotional processing, and pain processing. According to brain network research, IBS may exhibit anomalies in the DMN, CEN, and emotional arousal networks. The fluctuations in emotion (anxiety, sadness) and symptoms in IBS patients were associated with alterations in the relevant brain regions.

Conclusion

This study draws a preliminary conclusion that there are insufficient data to accurately distinguish the different neurological features of IBS in the resting state. Additional high-quality research undertaken by diverse geographic regions and teams is required to reach reliable results regarding resting-state changed brain regions in IBS.

United European Gastroenterology (UEG) and European Society for Neurogastroenterology and Motility (ESNM) consensus on gastroparesis

BACKGROUND

Gastroparesis is a condition characterized by epigastric symptoms and delayed gastric emptying (GE) rate in the absence of any mechanical obstruction. The condition is challenging in clinical practice by the lack of guidance concerning diagnosis and management of gastroparesis.

METHODS

A Delphi consensus was undertaken by 40 experts from 19 European countries who conducted a literature summary and voting process on 89 statements. Quality of evidence was evaluated using grading of recommendations assessment, development, and evaluation criteria. Consensus (defined as ≥80% agreement) was reached for 25 statements.

RESULTS

The European consensus defined gastroparesis as the presence of symptoms associated with delayed GE in the absence of mechanical obstruction. Nausea and vomiting were identified as cardinal symptoms, with often coexisting postprandial distress syndrome symptoms of dyspepsia. The true epidemiology of gastroparesis is not known in detail, but diabetes, gastric surgery, certain neurological and connective tissue diseases, and the use of certain drugs recognized as risk factors. While the panel agreed that severely impaired gastric motor function is present in these patients, there was no consensus on underlying pathophysiology. The panel agreed that an upper endoscopy and a GE test are required for diagnosis. Only dietary therapy, dopamine-2 antagonists and 5-HT₄ receptor agonists were considered appropriate therapies, in addition to nutritional support in case of severe weight loss. No consensus was reached on the use of proton pump inhibitors, other classes of antiemetics or prokinetics, neuromodulators, complimentary, psychological, or more invasive therapies. Finally, there was consensus that gastroparesis adversely impacts on quality of life and healthcare costs and that the long-term prognosis of gastroparesis depends on the cause.

CONCLUSIONS AND INFERENCES

A multinational group of European experts summarized the current state of consensus on definition, symptom characteristics, pathophysiology, diagnosis, and management of gastroparesis.

Diabetic Neuropathy Influences Control of Spinal Mechanisms

PURPOSE

Comprehensive evaluation of the upstream sensory processing in diabetic symmetrical polyneuropathy (DSPN) is sparse. The authors investigated the spinal nociceptive withdrawal reflex and the related elicited somatosensory evoked cortical potentials. They hypothesized that DSPN induces alterations in spinal and supraspinal sensory-motor processing compared with age- and gender-matched healthy controls.

METHODS

In this study, 48 patients with type 1 diabetes and DSPN were compared with 21 healthy controls. Perception and reflex thresholds were determined and subjects received electrical stimulations on the plantar site of the foot at three stimulation intensities to evoke a nociceptive withdrawal reflex. Electromyogram and EEG were recorded for analysis.

RESULTS

Patients with DSPN had higher perception (P < 0.001) and reflex (P = 0.012) thresholds. Fewer patients completed the recording session compared with healthy controls (34/48 vs. 21/21; P = 0.004). Diabetic symmetrical polyneuropathy reduced the odds ratio of a successful elicited nociceptive withdrawal reflex (odds ratio = 0.045; P = 0.014). Diabetic symmetrical polyneuropathy changed the evoked potentials (F = 2.86; P = 0.025), and post hoc test revealed reduction of amplitude (-3.72 mV; P = 0.021) and prolonged latencies (15.1 ms; P = 0.013) of the N1 peak.

CONCLUSIONS

The study revealed that patients with type 1 diabetes and DSPN have significantly changed spinal and supraspinal processing of the somatosensory input. This implies that DSPN induces widespread differences in the central nervous system processing of afferent A-δ and A-β fiber input. These differences in processing may potentially lead to identification of subgroups with different stages of small fiber neuropathy and ultimately differentiated treatments.

United European Gastroenterology (UEG) and European Society for Neurogastroenterology and Motility (ESNM) consensus on gastroparesis

BACKGROUND

Gastroparesis is a condition characterized by epigastric symptoms and delayed gastric emptying (GE) rate in the absence of any mechanical obstruction. The condition is challenging in clinical practice by the lack of guidance concerning diagnosis and management of gastroparesis.

METHODS

A Delphi consensus was undertaken by 40 experts from 19 European countries who conducted a literature summary and voting process on 89 statements. Quality of evidence was evaluated using grading of recommendations assessment, development, and evaluation criteria. Consensus (defined as ≥80% agreement) was reached for 25 statements.

RESULTS

The European consensus defined gastroparesis as the presence of symptoms associated with delayed GE in the absence of mechanical obstruction. Nausea and vomiting were identified as cardinal symptoms, with often coexisting postprandial distress syndrome symptoms of dyspepsia. The true epidemiology of gastroparesis is not known in detail, but diabetes, gastric surgery, certain neurological and connective tissue diseases, and the use of certain drugs recognized as risk factors. While the panel agreed that severely impaired gastric motor function is present in these patients, there was no consensus on underlying pathophysiology. The panel agreed that an upper endoscopy and a GE test are required for diagnosis. Only dietary therapy, dopamine-2 antagonists and 5-HT4 receptor agonists were considered appropriate therapies, in addition to nutritional support in case of severe weight loss. No consensus was reached on the use of proton pump inhibitors, other classes of antiemetics or prokinetics, neuromodulators, complimentary, psychological, or more invasive therapies. Finally, there was consensus that gastroparesis adversely impacts on quality of life and healthcare costs and that the long-term prognosis of gastroparesis depends on the cause.

CONCLUSIONS AND INFERENCES

A multinational group of European experts summarized the current state of consensus on definition, symptom characteristics, pathophysiology, diagnosis, and management of gastroparesis.

Study protocol for a multicentre, randomised, parallel group, sham-controlled clinical trial investigating the effect of transcutaneous vagal nerve stimulation on gastrointestinal symptoms in people with diabetes complicated with diabetic autonomic neuropathy: the DAN-VNS Study

INTRODUCTION

A high proportion of people with diabetes experience gastrointestinal (GI) symptoms, which may be manifestations of diabetic autonomic neuropathy (DAN). The current treatment regime is ineffective and associated with major side effects. Transcutaneous vagal nerve stimulation (tVNS) is a new therapeutic option, which has been shown to increase GI motility and reduce inflammatory responses. As vagus is the main neuronal pathway for extrinsic coordination of GI secretion and motility, we hypothesise that tVNS will improve DAN-induced GI symptoms in subjects with diabetes.

METHODS AND ANALYSIS

The DAN-VNS study is a randomised multicentre clinical trial investigating the effect of short-term, high intensity as well as long-term, medium-intensity tVNS on GI symptom alleviation in 120 subjects with diabetes. The primary outcome consists of changes from baseline in subjective ratings of symptom severity. Secondary outcomes include changes in gastric motility and GI transit time measured by MRI and wireless motility capsule. Moreover, cardiovascular and sudomotor function, glycaemic control, brain sensory processing and presence of low-grade inflammation will be investigated as secondary outcome measures. Lastly, 15 responders of tVNS treatment will be included in an explorative, randomised, cross-over study, in which the acute endocrine and metabolic response to short-term tVNS will be investigated.

ETHICS AND DISSEMINATION

The study has been approved by the North Denmark Region Committee on Health Research Ethics (N-20190020). Results will be published in relevant international peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT04143269.

Gastrointestinal symptoms and cardiac vagal tone in type 1 diabetes correlates with gut transit times and motility index

BACKGROUND

Although gastrointestinal (GI) symptoms are common in diabetes, they frequently do not correlate with measurable sensorimotor abnormalities. The wireless motility capsule (WMC) measures pressure, temperature, and pH as it traverses the GI tract wherefrom transit times and motility indices are derived. The aim was to investigate whether GI symptoms correlate with changes in (a) segmental transit times, (b) segmental motility index, (c) cardiac vagal tone, or (d) presence/absence of peripheral neuropathy in type 1 diabetes.

METHODS

Gastrointestinal symptoms in 104 participants with type 1 diabetes were measured using Gastroparesis Cardinal Symptoms Index and Gastrointestinal Symptom Rating Scale. All underwent standardized WMC investigation measuring segmental transit time and motility. Cardiac vagal tone and presence of peripheral neuropathy were measured using electrocardiographic and nerve conduction velocity testing.

KEY RESULTS

Colonic transit time was correlated with postprandial fullness (P = .01) and constipation (P = .03), while decreased colonic motility index was correlated with diarrhea (P = .01) and decreased bloating (P < .05). Symptoms were not correlated with gastric or small bowel transit time or motility index. In participants with low cardiac vagal tone, gastric motility index (P < .01) and colonic transit time (P < .05) were increased, but not in those with peripheral neuropathy. Abdominal pain was decreased with both peripheral neuropathy (P = .04) and decreased cardiac vagal tone (P = .02).

CONCLUSIONS AND INFERENCES

This study supports the rationale for whole gut investigation, using not only transit times but incorporating contractility indices as well. Furthermore, a decreased parasympathetic modulation and an increased hyposensate state appear to be present in type 1 diabetes.

Peripheral, synaptic and central neuronal transmission is affected in type 1 diabetes

AIMS

We hypothesized that adults with type 1 diabetes and severe polyneuropathy have alterations in neuronal transmission at different anatomical levels. The aims were to investigate upstream sensory neuronal activation in terms of peripheral, spinal, precortical, and cortical transmission.

METHODS

48 participants with type-1 diabetes and polyneuropathy, and 21 age-matched healthy participants were included. Electrophysiological median nerve recordings were used to analyze peripheral transmission at Erb's point (P9-N11); spinal evoked potentials at Cv7 (P11-N14); subcortical evoked potentials at Oz (N14-P18); early cortical evoked potentials at CP5 (N20-P22); late cortical evoked potentials at C1 (N60-P80) and estimated cortical inter-peak latencies as measures of central conduction time.

RESULTS

In comparison to healthy, the presence of diabetes prolonged peripheral transmission at P9 and N11 (+0.49 ms, p = .000; +0.47 ms, p = .04, respectively), early cortical evoked potentials at CP5: N20 (+2.41 ms, p = .003) and P22 (+5.88 ms, p = .001) and cortical potentials at C1: N60 (+39.08 ms, p = .001) and P80 (+54.55 ms, p = .000) and central conduction time. Decreased amplitudes were shown peripherally (-2.13 μV, p = .000), spinally (-0.57 μV, p = .005) and pre-cortically (-0.22 μV, p = .004). In both healthy and people with diabetes increased central conduction time were associated with decreased parasympathetic tone (ρ = -0.52, p = .027; ρ = -0.35, p = .047, respectively).

CONCLUSION

Neuronal afferent transmission and brain responses were significantly impaired in diabetes and the presence of prolonged central conduction time is indicative of severe extensive neuronal damage. Trial registry number: EUDRA CT: 2013-004375-12; clinicaltrials.gov: NCT02138045.

Diabetic Gastroparesis

This review covers the epidemiology, pathophysiology, clinical features, diagnosis, and management of diabetic gastroparesis, and more broadly diabetic gastroenteropathy, which encompasses all the gastrointestinal manifestations of diabetes mellitus. Up to 50% of patients with type 1 and type 2 DM and suboptimal glycemic control have delayed gastric emptying (GE), which can be documented with scintigraphy, 13C breath tests, or a wireless motility capsule; the remainder have normal or rapid GE. Many patients with delayed GE are asymptomatic; others have dyspepsia (i.e., mild to moderate indigestion, with or without a mild delay in GE) or gastroparesis, which is a syndrome characterized by moderate to severe upper gastrointestinal symptoms and delayed GE that suggest, but are not accompanied by, gastric outlet obstruction. Gastroparesis can markedly impair quality of life, and up to 50% of patients have significant anxiety and/or depression. Often the distinction between dyspepsia and gastroparesis is based on clinical judgement rather than established criteria. Hyperglycemia, autonomic neuropathy, and enteric neuromuscular inflammation and injury are implicated in the pathogenesis of delayed GE. Alternatively, there are limited data to suggest that delayed GE may affect glycemic control. The management of diabetic gastroparesis is guided by the severity of symptoms, the magnitude of delayed GE, and the nutritional status. Initial options include dietary modifications, supplemental oral nutrition, and antiemetic and prokinetic medications. Patients with more severe symptoms may require a venting gastrostomy or jejunostomy and/or gastric electrical stimulation. Promising newer therapeutic approaches include ghrelin receptor agonists and selective 5-hydroxytryptamine receptor agonists.

Prevalence and predictors of small intestinal bacterial overgrowth in irritable bowel syndrome: a systematic review and meta-analysis

BACKGROUND

The reported prevalence of small intestinal bacterial overgrowth (SIBO) among individuals with irritable bowel syndrome (IBS) is highly variable. The aim of the study is to estimate the prevalence and identify predictors of SIBO in IBS.

METHODS

PubMed, Cochrane Library, and EMBASE through July 2017 were searched to identify studies evaluating the prevalence of SIBO in IBS. The pooled prevalence of SIBO among individuals with IBS and the pooled odds ratio (OR) of SIBO among those with IBS compared with healthy controls were calculated. Predictors of SIBO among IBS patients were also evaluated.

RESULTS

Fifty studies (8398 IBS, 1432 controls) met the inclusion criteria. Overall pooled prevalence of SIBO in IBS was 38% (95% CI 32-44) and was higher among individuals with IBS (OR 4.7, 95% CI 3.1-7.2) compared with controls. The pooled prevalence of SIBO in IBS was higher in studies diagnosed by breath tests (40%, 95% CI 33-46) compared with cultures (19%, 95% CI 8-30). Among those with IBS, female gender (OR 1.5, 95% CI 1.0-2.1), older age (standard mean difference 3.1 years, 95% CI 0.9-5.4), and IBS-diarrhea (OR 1.7, 95% CI 1.3-2.3) compared with other IBS subtypes increased the odds of SIBO; proton pump inhibitor (PPI) use (OR 1.1, 95% CI 0.7-1.7) was not associated with SIBO.

CONCLUSIONS

More than one-third of IBS patients tested positive for SIBO, and the odds of SIBO in IBS were increased by nearly fivefold. The prevalence of SIBO varied according to the diagnostic modality performed. Female gender, older age, and IBS-diarrhea, but not PPI use, were associated with SIBO among individuals with IBS.

Type 1 diabetic patients with peripheral neuropathy have pan-enteric prolongation of gastrointestinal transit times and an altered caecal pH profile

AIMS/HYPOTHESIS

We hypothesised that type 1 diabetic patients with established diabetic sensorimotor polyneuropathy (DSPN) would have segmental and/or pan-enteric dysmotility in comparison to healthy age-matched controls. We aimed to investigate the co-relationships between gastrointestinal function, degree of DSPN and clinical symptoms.

METHODS

An observational comparison was made between 48 patients with DSPN (39 men, mean age 50 years, range 29-71 years), representing the baseline data of an ongoing clinical trial (representing a secondary analysis of baseline data collected from an ongoing double-blind randomised controlled trial investigating the neuroprotective effects of liraglutide) and 41 healthy participants (16 men, mean age 49 years, range 30-78) who underwent a standardised wireless motility capsule test to assess gastrointestinal transit. In patients, vibration thresholds, the Michigan Neuropathy Screening Instrument and Patient Assessment of Upper Gastrointestinal Symptom questionnaires were recorded.

RESULTS

Compared with healthy controls, patients showed prolonged gastric emptying (299 ± 289 vs 179 ± 49 min; p = 0.01), small bowel transit (289 ± 107 vs 224 ± 63 min; p = 0.001), colonic transit (2140, interquartile range [IQR] 1149-2799 min vs 1087, IQR 882-1650 min; p = 0.0001) and whole-gut transit time (2721, IQR 1196-3541 min vs 1475 (IQR 1278-2214) min; p < 0.0001). Patients also showed an increased fall in pH across the ileocaecal junction (-1.8 ± 0.4 vs -1.3 ± 0.4 pH; p < 0.0001), which was associated with prolonged colonic transit (r = 0.3, p = 0.001). Multivariable regression, controlling for sex, disease duration and glycaemic control, demonstrated an association between whole-gut transit time and total GCSI (p = 0.02).

CONCLUSIONS/INTERPRETATION

Pan-enteric prolongation of gastrointestinal transit times and a more acidic caecal pH, which may represent heightened caecal fermentation, are present in patients with type 1 diabetes. The potential implication of delayed gastrointestinal transit on the bioavailability of nutrition and on pharmacotherapeutic and glycaemic control warrants further investigation.

TRIAL REGISTRATION

EUDRA CT: 2013-004375-12.

Integrity of central nervous function in diabetes mellitus assessed by resting state EEG frequency analysis and source localization

Diabetes mellitus (DM) is associated with structural and functional changes of the central nervous system. We used electroencephalography (EEG) to assess resting state cortical activity and explored associations to relevant clinical features. Multichannel resting state EEG was recorded in 27 healthy controls and 24 patients with longstanding DM and signs of autonomic dysfunction. The power distribution based on wavelet analysis was summarized into frequency bands with corresponding topographic mapping. Source localization analysis was applied to explore the electrical cortical sources underlying the EEG. Compared to controls, DM patients had an overall decreased EEG power in the delta (1-4Hz) and gamma (30-45Hz) bands. Topographic analysis revealed that these changes were confined to the frontal region for the delta band and to central cortical areas for the gamma band. Source localization analysis identified sources with reduced activity in the left postcentral gyrus for the gamma band and in right superior parietal lobule for the alpha1 (8-10Hz) band. DM patients with clinical signs of autonomic dysfunction and gastrointestinal symptoms had evidence of altered resting state cortical processing. This may reflect metabolic, vascular or neuronal changes associated with diabetes.

Ravages of Diabetes on Gastrointestinal Sensory-Motor Function: Implications for Pathophysiology and Treatment

Symptoms related to functional and sensory abnormalities are frequently encountered in patients with diabetes mellitus. Most symptoms are associated with impaired gastric and intestinal function. In this review, we discuss basic concepts of sensory-motor dysfunction and how they relate to clinical findings and gastrointestinal abnormalities that are commonly seen in diabetes. In addition, we review techniques that are available for investigating the autonomic nervous system, neuroimaging and neurophysiology of sensory-motor function. Such technological advances, while not readily available in the clinical setting, may facilitate stratification and individualization of therapy in diabetic patients in the future. Unraveling the structural, mechanical, and sensory remodeling in diabetes disease is based on a multidisciplinary approach that can bridge the knowledge from a variety of scientific disciplines. The final goal is to increase the understanding of the damage to GI structures and to sensory processing of symptoms, in order to assist clinicians with developing an optimal mechanics based treatment.

Assessment of the cardiovascular and gastrointestinal autonomic complications of diabetes

The global prevalence of diabetes mellitus is increasing; arguably as a consequence of changes in diet, lifestyle and the trend towards urbanization. Unsurprisingly, the incidence of both micro and macrovascular complications of diabetes mirrors this increasing prevalence. Amongst the complications with the highest symptom burden, yet frequently under-diagnosed and sub-optimally treated, is diabetic autonomic neuropathy, itself potentially resulting in cardiovascular autonomic neuropathy and gastrointestinal (GI) tract dysmotility. The aims of this review are fourfold. Firstly to provide an overview of the pathophysiological processes that cause diabetic autonomic neuropathy. Secondly, to discuss both the established and emerging cardiometric methods for evaluating autonomic nervous system function in vivo. Thirdly, to examine the tools for assessing pan-GI and segmental motility and finally, we will provide the reader with a summary of putative non-invasive biomarkers that provide a pathophysiological link between low-grade neuro inflammation and diabetes, which may allow earlier diagnosis and intervention, which in future may improve patient outcomes.

Understanding the sensory irregularities of esophageal disease

Symptoms relating to esophageal sensory abnormalities can be encountered in the clinical environment. Such sensory abnormalities may be present in demonstrable disease, such as erosive esophagitis, and in the ostensibly normal esophagus, such as non-erosive reflux disease or functional chest pain. In this review, the authors discuss esophageal sensation and the esophageal pain system. In addition, the authors provide a primer concerning the techniques that are available for investigating the autonomic nervous system, neuroimaging and neurophysiology of esophageal sensory function. Such technological advances, whilst not readily available in the clinic may facilitate the stratification and individualization of therapy in disorders of esophageal sensation in the future.

Impact of gut microbiota on diabetes mellitus

Various functions of the gut are regulated by sophisticated interactions among its functional elements, including the gut microbiota. These microorganisms play a crucial role in gastrointestinal mucosa permeability. They control the fermentation and absorption of dietary polysaccharides to produce short-chain fatty acids, which may explain their importance in the regulation of fat accumulation and the subsequent development of obesity-related diseases, suggesting that they are a crucial mediator of obesity and its consequences. In addition, gut bacteria play a crucial role in the host immune system, modulation of inflammatory processes, extraction of energy from the host diet and alterations of human gene expression. Dietary modulation of the human colonic microbiota has been shown to confer a number of health benefits to the host. Simple therapeutic strategies targeted at attenuating the progression of chronic low-grade inflammation and insulin resistance are urgently required to prevent or slow the development of diabetes in susceptible individuals. The main objective of this review is to address the pathogenic association between gut microbiota and diabetes, and to explore any novel related therapeutic targets. New insights into the role of the gut microbiota in diabetes could lead to the development of integrated strategies using probiotics to prevent and treat these metabolic disorders.

Brain changes in diabetes mellitus patients with gastrointestinal symptoms

Diabetes mellitus is a common disease and its prevalence is increasing worldwide. In various studies up to 30%-70% of patients present dysfunction and complications related to the gut. To date several clinical studies have demonstrated that autonomic nervous system neuropathy and generalized neuropathy of the central nervous system (CNS) may play a major role. This systematic review provides an overview of the neurodegenerative changes that occur as a consequence of diabetes with a focus on the CNS changes and gastrointestinal (GI) dysfunction. Animal models where diabetes was induced experimentally support that the disease induces changes in CNS. Recent investigations with electroencephalography and functional brain imaging in patients with diabetes confirm these structural and functional brain changes. Encephalographic studies demonstrated that altered insular processing of sensory stimuli seems to be a key player in symptom generation. In fact one study indicated that the more GI symptoms the patients experienced, the deeper the insular electrical source was located. The electroencephalography was often used in combination with quantitative sensory testing mainly showing hyposensitivity to stimulation of GI organs. Imaging studies on patients with diabetes and GI symptoms mainly showed microstructural changes, especially in brain areas involved in visceral sensory processing. As the electrophysiological and imaging changes were associated with GI and autonomic symptoms they may represent a future therapeutic target for treating diabetics either pharmacologically or with neuromodulation.

Impairments of the primary afferent nerves in a rat model of diabetic visceral hyposensitivity

Background

Diabetic neuropathy in visceral organs such as the gastrointestinal (GI) tract is still poorly understood, despite that GI symptoms are among the most common diabetic complications. The present study was designed to explore the changes in visceral sensitivity and the underlying functional and morphological deficits of the sensory nerves in short-term diabetic rats. Here, we compared the colorectal distension (CRD)-induced visceromotor response (VMR, an index of visceral pain) in vivo, the mechanosensitivity of colonic afferents ex vivo as well as the expression of protein gene product (PGP) 9.5 and calcitonin gene-related peptide (CGRP) in colon between diabetic (3–6 weeks after streptozotocin injection) and control (age-matched vehicle injection) rats.

Results

VMR was markedly decreased in the diabetic compared to the control rats. There was a significant decrease in multiunit pelvic afferent nerve responses to ramp distension of the ex vivo colon and single unit analysis indicated that an impaired mechanosensitivity of low-threshold and wide dynamic range fibers may underlie the afferent hyposensitivity in the diabetic colon. Fewer PGP 9.5- or CGRP-immunoreactive fibers and lower protein level of PGP 9.5 were found in the colon of diabetic rats.

Conclusions

These observations revealed the distinctive feature of colonic neuropathy in short-term diabetic rats that is characterized by a diminished sensory innervation and a blunted mechanosensitivity of the remnant sensory nerves.

Diabetes-related dysfunction of the small intestine and the colon: focus on motility

In contrast to gastric dysfunction, diabetes-related functional impairments of the small and large intestine have been studied less intensively. The gastrointestinal tract accomplishes several functions, such as mixing and propulsion of luminal content, absorption and secretion of ions, water, and nutrients, defense against pathogens, and elimination of waste products. Diverse functions of the gut are regulated by complex interactions among its functional elements, including gut microbiota. The network-forming tissues, the enteric nervous system) and the interstitial cells of Cajal, are definitely impaired in diabetic patients, and their loss of function is closely related to the symptoms in diabetes, but changes of other elements could also play a role in the development of diabetes mellitus-related motility disorders. The development of our understanding over the recent years of the diabetes-induced dysfunctions in the small and large intestine are reviewed in this article.

Macrophages in diabetic gastroparesis--the missing link?

BACKGROUND

Diabetic gastroparesis results in significant morbidity for patients and major economic burden for society. Treatment options for diabetic gastroparesis are currently directed at symptom control rather than the underlying disease and are limited. The pathophysiology of diabetic gastroparesis includes damage to intrinsic and extrinsic neurons, smooth muscle, and interstitial cells of Cajal (ICC). Oxidative damage in diabetes appears to be one of the primary insults involved in the pathogenesis of several complications of diabetes, including gastroparesis. Recent studies have highlighted the potential role of macrophages as key cellular elements in the pathogenesis of diabetic gastroparesis. Macrophages are important for both homeostasis and defense against a variety of pathogens. Heme oxygenase 1 (HO1), an enzyme expressed in a subset of macrophages has emerged as a major protective mechanism against oxidative stress. Activation of macrophages with high levels of HO1 expression protects against development of delayed gastric emptying in animal models of diabetes, while activation of macrophages that do not express HO1 are linked to neuromuscular cell injury. Targeting macrophages and HO1 may therefore be a therapeutic option in diabetic gastroparesis.

PURPOSE

This report briefly reviews the pathophysiology of diabetic gastroparesis with a focus on oxidative damage and how activation and polarization of different subtypes of macrophages in the muscularis propria determines development of delay in gastric emptying or protects against its development.

Diabetic gastroparesis: functional/morphologic background, diagnosis, and treatment options

The regulation of gastrointestinal motility mainly involves the smooth muscle, neural (extrinsic and intrinsic), and hormonal elements, the glial cells, and the interstitial cells of Cajal. An orchestrated function of all these components is required for the appropriate propulsive movement of the food in the gastrointestinal tract. Gastroparesis, a pathological slowing-down of gastric emptying, is a result of the damage to the tissue elements involved in the regulation of motility. Gastroparesis is one of the well-known complications of long-standing diabetes mellitus. Although it is rarely a life-threatening complication, it has a deteriorating effect on the quality of life, leads to unpredictable oscillation of the blood glucose level, and increases the time required for the absorption of food and medicines. This review describes the clinical characteristics of diabetic gastroparesis and summarizes the organic and functional motility abnormalities caused by this complication. Finally, the currently available and potential future therapeutic approaches are summarized.