Gastrointestinal neuroimmune disruption in a mouse model of Gulf War illness

Implication of the enteric glia in the IBS-like colonic inflammation associated with endometriosis

BACKGROUND

Endometriosis is a complex gynecological disorder characterized by the ectopic growth of endometrial tissue. Symptoms of endometriosis are known to impair the quality of life of patients, and among these are found dysmenorrhea, chronic pelvic pain, and gastrointestinal (GI) issues. GI issues such as painful bowel movements, bloating and constipation or diarrhea, are one of the common reasons for misdiagnosis with irritable bowel syndrome (IBS). Enteric glial cells (EGC) are known to play a role in pain associated with IBS, and reactive gliosis has been reported in patients with IBS, but the role of EGC in endometriosis has yet to be elucidated. We hypothesized that endometriosis will induce reactive gliosis, with increased expression of the glial fibrillary acidic protein (GFAP) and S100B, in the myenteric plexus of colonic sections in an animal model of endometriosis.

METHODS

In the present study animal experiments were employed to explore the impact of endometriosis on the gastrointestinal tract. Using a surgically induced endometriosis rat model, we collected ileal and colonic segments for analysis. We used H&E to assess microscopic damage in colon and ileum, immunofluorescence to measure GFAP and S100B expression in the colon, and toluidine blue staining to measure mast cell infiltration in colon and ileum. Immunofluorescence images were captured using confocal microscope and analyzed using ImageJ software.

RESULTS

All endometriosis animals developed vesicles. These animals had a significant increase in the colonic macroscopic damage compared to Sham and Naïve controls. Colonic and ileal sections didn't show statistical differences in microscopic damage between groups, yet endometriosis ileum had significantly increased mast cell infiltration compared to Naïve. GFAP immunostaining showed significantly increased integrated density in endometriosis when compared to Sham or Naïve, while no statistical difference was found in S100B integrated density between groups.

CONCLUSIONS

We conclude that endometriosis can alter GI homeostasis by inducing colon inflammation, reactive gliosis, and ileal mast cell infiltration. Taken together this suggests endometriosis can mimic IBS histopathology beyond the symptomatology, reinforcing this disease's complexity and the need to treat it beyond the gynecological setting.

Contributions of the gut microbiota to Gulf War Illness susceptibility: Findings from a mouse model

AIMS

In light of the evidence supporting a significant role of the gut microbiome in Gulf War Illness (GWI) pathology, we sought to examine its contribution to GWI susceptibility in a mouse model. We also aimed to identify bacterial taxa and microbially-derived metabolites associated with disease susceptibility.

MAIN METHODS

Male mice receiving pyridostigmine bromide (PB) orally, and controls were evaluated for symptoms of GWI at 8 weeks post-treatment. The Kansas criteria were adapted to assess behaviors associated with the following domains: gastrointestinal alterations, pain, mood, cognitive function, skin and respiratory disturbances. PB-treated subjects were classified into susceptible (GWI-S) or resilient (GWI-R). The status of the gut microbiome was assessed via analyses of the 16S rRNA gene and microbial-derived metabolites were evaluated with metabolomics tools.

KEY FINDINGS

Our results indicate that application of the Kansas criteria to behavioral outcomes in PB-treated mice resulted in a GWI susceptibility rate of ~35 %, similar to the one reported in humans. The composition and structure of the gut microbiome was different in GWI-S subjects compared to both control and GWI-R mice at 8 weeks but differences in microbial community structure were observed prior to PB treatment between GWI-R and GWI-S mice. GWI-S subjects exhibited a pattern of differentially abundant bacterial taxa and microbial metabolites.

SIGNIFICANCE

To our knowledge, this is the first preclinical report in which a stratification by susceptibility to GWI and its association with the gut microbiome is described. In light of the research conundrum that vulnerability to GWI represents, the use of tools that could provide further insight into this complex factor should be considered.

Crisis in the gut: navigating gastrointestinal challenges in Gulf War Illness with bioengineering

Gulf War Illness (GWI) is characterized by a wide range of symptoms that manifests largely as gastrointestinal symptoms. Among these gastrointestinal symptoms, motility disorders are highly prevalent, presenting as chronic constipation, stomach pain, indigestion, diarrhea, and other conditions that severely impact the quality of life of GWI veterans. However, despite a high prevalence of gastrointestinal impairments among these veterans, most research attention has focused on neurological disturbances. This perspective provides a comprehensive overview of current in vivo research advancements elucidating the underlying mechanisms contributing to gastrointestinal disorders in GWI. Generally, these in vivo and in vitro models propose that neuroinflammation alters gut motility and drives the gastrointestinal symptoms reported in GWI. Additionally, this perspective highlights the potential and challenges of in vitro bioengineering models, which could be a crucial contributor to understanding and treating the pathology of gastrointestinal related-GWI.

Recent Research Trends in Neuroinflammatory and Neurodegenerative Disorders

Neuroinflammatory and neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), traumatic brain injury (TBI) and Amyotrophic lateral sclerosis (ALS) are chronic major health disorders. The exact mechanism of the neuroimmune dysfunctions of these disease pathogeneses is currently not clearly understood. These disorders show dysregulated neuroimmune and inflammatory responses, including activation of neurons, glial cells, and neurovascular unit damage associated with excessive release of proinflammatory cytokines, chemokines, neurotoxic mediators, and infiltration of peripheral immune cells into the brain, as well as entry of inflammatory mediators through damaged neurovascular endothelial cells, blood-brain barrier and tight junction proteins. Activation of glial cells and immune cells leads to the release of many inflammatory and neurotoxic molecules that cause neuroinflammation and neurodegeneration. Gulf War Illness (GWI) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are chronic disorders that are also associated with neuroimmune dysfunctions. Currently, there are no effective disease-modifying therapeutic options available for these diseases. Human induced pluripotent stem cell (iPSC)-derived neurons, astrocytes, microglia, endothelial cells and pericytes are currently used for many disease models for drug discovery. This review highlights certain recent trends in neuroinflammatory responses and iPSC-derived brain cell applications in neuroinflammatory disorders.

Enteric glia promote visceral hypersensitivity during inflammation through intercellular signaling with gut nociceptors

Inflammation in the intestines causes abdominal pain that is challenging to manage. The terminals of sensory neurons innervating the gut are surrounded by glia. Here, using a mouse model of acute colitis, we found that enteric glia contribute to visceral pain by secreting factors that sensitized sensory nerves innervating the gut in response to inflammation. Acute colitis induced a transient increase in the production of proinflammatory cytokines in the intestines of male and female mice. Of these, IL-1β was produced in part by glia and augmented the opening of the intercellular communication hemichannel connexin-43 in glia, which made normally innocuous stimuli painful in female mice. Chemogenetic glial activation paired with calcium imaging in nerve terminals demonstrated that glia sensitized gut-innervating nociceptors only under inflammatory conditions. This inflammatory, glial-driven visceral hypersensitivity involved an increased abundance of the enzyme COX-2 in glia, resulting in greater production and release of prostaglandin E2 that activated EP4 receptors on sensory nerve terminals. Blocking EP4 receptors reduced nociceptor sensitivity in response to glial stimulation in tissue samples from colitis-model mice, and impairing glial connexin-43 reduced visceral hypersensitivity induced by IL-1β in female mice. The findings suggest that therapies targeting enteric glial-neuron signaling might alleviate visceral pain caused by inflammatory disorders.

Stimulator of interferon genes (STING) expression in the enteric nervous system and contributions of glial STING in disease

BACKGROUND

Appropriate host-microbe interactions are essential for enteric glial development and subsequent gastrointestinal function, but the potential mechanisms of microbe-glial communication are unclear. Here, we tested the hypothesis that enteric glia express the pattern recognition receptor stimulator of interferon genes (STING) and communicate with the microbiome through this pathway to modulate gastrointestinal inflammation.

METHODS

In situ transcriptional labeling and immunohistochemistry were used to examine STING and IFNβ expression in enteric neurons and glia. Glial-STING KO mice (Sox10CreERT2+/- ;STINGfl/fl ) and IFNβ ELISA were used to characterize the role of enteric glia in canonical STING activation. The role of glial STING in gastrointestinal inflammation was assessed in the 3% DSS colitis model.

RESULTS

Enteric glia and neurons express STING, but only enteric neurons express IFNβ. While both the myenteric and submucosal plexuses produce IFNβ with STING activation, enteric glial STING plays a minor role in its production and seems more involved in autophagy processes. Furthermore, deleting enteric glial STING does not affect weight loss, colitis severity, or neuronal cell proportions in the DSS colitis model.

CONCLUSION

Taken together, our data support canonical roles for STING and IFNβ signaling in the enteric nervous system through enteric neurons but that enteric glia do not use these same mechanisms. We propose that enteric glial STING may utilize alternative signaling mechanisms and/or is only active in particular disease conditions. Regardless, this study provides the first glimpse of STING signaling in the enteric nervous system and highlights a potential avenue of neuroglial-microbial communication.

Dysbiosis in gastrointestinal pathophysiology: Role of the gut microbiome in Gulf War Illness

Gulf War Illness (GWI) has been reported in 25%-35% of veterans returned from the Gulf war. Symptoms of GWI are varied and include both neurological and gastrointestinal symptoms as well as chronic fatigue. Development of GWI has been associated with chemical exposure particularly with exposure to pyridostigmine bromide (PB) and permethrin. Recent studies have found that the pathology of GWI is connected to changes in the gut microbiota, that is the gut dysbiosis. In studies using animal models, the exposure to PB and permethrin resulted in similar changes in the gut microbiome as these found in GW veterans with GWI. Studies using animal models have also shown that phytochemicals like curcumin are beneficial in reducing the symptoms and that the extracellular vesicles (EV) released from gut bacteria and from the intestinal epithelium can both promote diseases and suppress diseases through the intercellular communication mechanisms. The intestinal epithelium cells produce EVs and these EVs of intestinal epithelium origin are found to suppress inflammatory bowel disease severity, suggesting the benefits of utilizing EV in treatments. On the contrary, EV from the plasma of septic mice enhanced the level of proinflammatory cytokines in vitro and neutrophils and macrophages in vivo, suggesting differences in the EV depending on the types of cells they were originated and/or influences of environmental changes. These studies suggest that targeting the EV that specifically have positive influences may become a new therapeutic strategy in the treatment of veterans with GWI.

Self-reported gastrointestinal disorders among veterans with gulf war illness with and without posttraumatic stress disorder

BACKGROUND

Gulf War Illness (GWI) is a chronic, multi-symptom disorder affecting 25%-32% of Gulf War veterans. Veterans with GWI disproportionately suffer from gastrointestinal (GI) disorders. Given the increasing evidence supporting a gut-brain axis, we explore the relationship between post-traumatic stress disorder (PTSD), GWI, and self-reported GI disorders among GW veterans.

METHODS

Veterans from the Gulf War Era Cohort and Biorepository responded to a mail-based survey (N = 1058). They were stratified by GWI (Centers for Disease Control definition) and PTSD status. This yielded three groups: GWI-, GWI+/PTSD-, and GWI+/PTSD+. Multivariable logistic regression adjusting for demographic and military characteristics examined associations between GWI/PTSD groups and GI disorders. Results were expressed as adjusted odds ratios (aOR) with 95% confidence intervals (95% CI).

KEY RESULTS

The most frequently reported GI disorders were irritable bowel syndrome (IBS), gastroesophageal reflux disease (GERD), and colon polyps (CP). The GWI+/PTSD+ group had a higher odds of these disorders than the GWI+/PTSD- group (aOR_IBS  = 3.12, 95% CI: 1.93-5.05; aOR_GERD  = 2.04, 95% CI: 1.44-2.90; aOR_CP  = 1.85, 95% CI: 1.23-2.80), which had a higher odds of these disorders than the GWI- group (aOR_IBS  = 4.38, 95% CI: 1.55-12.36; aOR_GERD  = 2.51 95% CI: 1.63-3.87; aOR_CP  = 2.57, 95% CI: 1.53-4.32).

CONCLUSIONS & INFERENCES

GW veterans with GWI and PTSD have significantly higher odds of specific self-reported GI disorders than the other groups. Given the known bidirectional influences of the gut and brain, these veterans may benefit from a holistic healthcare approach that considers biopsychosocial contributors to the assessment and management of disease.

Chemical exposures and suspected impact on Gulf War Veterans

Gulf War Illness (GWI) encompass a spectrum of maladies specific to troops deployed during the Persian Gulf War (1990-1991). There are several hypothesized factors believed to contribute to GWI, including (but not limited to) exposures to chemical agents and a foreign environment (e.g., dust, pollens, insects, and microbes). Moreover, the inherent stress associated with deployment and combat has been associated with GWI. While the etiology of GWI remains uncertain, several studies have provided strong evidence that chemical exposures, especially neurotoxicants, may be underlying factors for the development of GWI. This mini style perspective article will focus on some of the major evidence linking chemical exposures to GWI development and persistence decades after exposure.

Experimental Models of Gulf War Illness, a Chronic Neuropsychiatric Disorder in Veterans

Gulf War illness (GWI) is a chronic multifaceted condition with debilitating pain and fatigue, as well as sleep, behavioral, and cognitive impairments in war veterans. Currently, there is no effective treatment or cure for GWI; therefore, there is a critical need to develop experimental models to help better understand its mechanisms and interventions related to GWI-associated neuropsychiatric disorders. Chemical neurotoxicity appears to be one cause of GWI, and its symptoms manifest as disruptions in neuronal function. However, the mechanisms underlying such incapacitating neurologic and psychiatric symptoms are poorly understood. The etiology of GWI is complex, and many factors including chemical exposure, psychological trauma, and environmental stressors have been associated with its development. Attempts have been made to create GWI-like symptomatic models, including through chronic induction in mice and rats. Here, we present a brief protocol of GWI in rats and mice, which exhibit robust neuropsychiatric signs and neuropathologic changes reminiscent of GWI. This article provides a guide to working protocols, application of therapeutic drugs, outcomes, troubleshooting, and data analysis. Our broad profiling of GWI-like symptoms in rodents reveals features of progressive morphologic and long-lasting neuropsychiatric features. Together, the GWI model in rodents shows striking consistency in recapitulating major hallmark features of GWI in veterans. These models help identify mechanisms and interventions for GWI. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Experimental induction of Gulf War illness in rats Support Protocol 1: Monitoring of Gulf War illness signs and neuroimaging analysis in rats Basic Protocol 2: Experimental induction of Gulf War illness in mice Support Protocol 2: Monitoring of Gulf War illness signs and neuropathology analysis in mice.

Household based-pyrethroids on adult zebrafish (Danio rerio) exert behavioral and cholinergic changes in different brain regions

Pyrethroid-based insecticides are largely used for mosquito control. These compounds have household and agricultural applications with different formulations. Two important compounds used as household insecticides are prallethrin and transfluthrin, both from the pyrethroid chemical group. With the mode of action centered on sodium channels, pyrethroids keep the ionic sodium channels open for a long time causing the death of the insect by nervous hyperexcitability. Given the increased use of household insecticides by humans and the incidence of disease outbreaks with unknown etiology such as autism spectrum disease, schizophrenia, and Parkinson's disease we investigate some physiological inputs of these compounds on zebrafish. In this study, we evaluated the social interaction, shoaling formation, and anxiety-like behavior of zebrafish exposed chronically to transfluthrin- and prallthrin-based insecticides (T-BI and P-BI). In addition, we quantified the activity of the enzyme acetylcholinesterase (AChE) in different brain regions. We observed that both compounds caused anxiolytic behavior and reduced shoaling formation and social interaction. Their behavioral biomarkers indicated a harmful ecological effect on the specie as well as a possible impact of these compounds on autism spectrum disorder (ASD) and schizophrenia (SZP). In addition, the AChE activity would change its activity in different brain regions modulating the anxiety-like behavior and social behavior in zebrafish. We conclude that P-BI and T-BI make us alert about the relationship of these compounds with nervous diseases related to cholinergic signaling.

Acute Exposure to Pyridostigmine Bromide Disrupts Cholinergic Myenteric Neuroimmune Function in Mice

Gulf War Illness (GWI) results from chemical exposure during the Gulf War, with notable impacts on gastrointestinal motility. Due to the limited demographic impacted by this ailment, an in-depth investigation of the GWI has yielded little regarding the underlying pathophysiological mechanisms. Here, the hypothesis that exposure to pyridostigmine bromide (PB) results in severe enteric neuro-inflammation, that cascades to disruptions in colonic motility, is tested. The analyses are performed on male C57BL/6 mice that are treated with physiologically similar doses of PB given to GW veterans. When colonic motility is assessed, GWI colons have significantly reduced forces in response to acetylcholine or electrical field stimulation. GWI is also accompanied by high levels of pro-inflammatory cytokines and chemokines, associated with increased numbers of CD40⁺ pro-inflammatory macrophages within the myenteric plexus. Enteric neurons responsible for mediating colonic motility reside within the myenteric plexus, and PB exposure reduced their numbers. Significant smooth muscle hypertrophy is also observed due to increased inflammation. Together, the results show that PB exposure caused functional and anatomical dysfunction, promoting impaired motility within the colon. Achieving a greater understanding of the mechanisms of GWI will allow more refinement in therapeutic options that improve veterans' quality of life.

A review of chemical warfare agents linked to respiratory and neurological effects experienced in Gulf War Illness

Over 40% of veterans from the Persian Gulf War (GW) (1990-1991) suffer from Gulf War Illness (GWI). Thirty years since the GW, the exposure and mechanism contributing to GWI remain unclear. One possible exposure that has been attributed to GWI are chemical warfare agents (CWAs). While there are treatments for isolated symptoms of GWI, the number of respiratory and cognitive/neurological issues continues to rise with minimum treatment options. This issue does not only affect veterans of the GW, importantly these chronic multisymptom illnesses (CMIs) are also growing amongst veterans who have served in the Afghanistan-Iraq war. What both wars have in common are their regions and inhaled exposures. In this review, we will describe the CWA exposures, such as sarin, cyclosarin, and mustard gas in both wars and discuss the various respiratory and neurocognitive issues experienced by veterans. We will bridge the respiratory and neurological symptoms experienced to the various potential mechanisms described for each CWA provided with the most up-to-date models and hypotheses.

Host gut resistome in Gulf War chronic multisymptom illness correlates with persistent inflammation

Chronic multisymptom illness (CMI) affects a subsection of elderly and war Veterans and is associated with systemic inflammation. Here, using a mouse model of CMI and a group of Gulf War (GW) Veterans' with CMI we show the presence of an altered host resistome. Results show that antibiotic resistance genes (ARGs) are significantly altered in the CMI group in both mice and GW Veterans when compared to control. Fecal samples from GW Veterans with persistent CMI show a significant increase of resistance to a wide class of antibiotics and exhibited an array of mobile genetic elements (MGEs) distinct from normal healthy controls. The altered resistome and gene signature is correlated with mouse serum IL-6 levels. Altered resistome in mice also is correlated strongly with intestinal inflammation, decreased synaptic plasticity, reversible with fecal microbiota transplant (FMT). The results reported might help in understanding the risks to treating hospital acquired infections in this population.

Long-Term Anxiety-Like Behavior and Microbiota Changes Induced in Mice by Sublethal Doses of Acute Sarin Surrogate Exposure

Anxiety disorder is one of the most reported complications following organophosphorus (OP) nerve agent (NA) exposure. The goal of this study was to characterize the long-term behavioral impact of a single low dose exposure to 4-nitrophenyl isopropyl methylphosphonate (NIMP), a sarin surrogate. We chose two different sublethal doses of NIMP, each corresponding to a fraction of the median lethal dose (one mild and one convulsive), and evaluated behavioral changes over a 6-month period following exposure. Mice exposed to both doses showed anxious behavior which persisted for six-months post-exposure. A longitudinal magnetic resonance imaging examination did not reveal any anatomical changes in the amygdala throughout the 6-month period. While no cholinesterase activity change or neuroinflammation could be observed at the latest timepoint in the amygdala of NIMP-exposed mice, important modifications in white blood cell counts were noted, reflecting a perturbation of the systemic immune system. Furthermore, intestinal inflammation and microbiota changes were observed at 6-months in NIMP-exposed animals regardless of the dose received. This is the first study to identify long-term behavioral impairment, systemic homeostasis disorganization and gut microbiota alterations following OP sublethal exposure. Our findings highlight the importance of long-term care for victims of NA exposure, even in asymptomatic cases.

Gene-Toxicant Interactions in Gulf War Illness: Differential Effects of the PON1 Genotype

About 25-35% of United States veterans who fought in the 1990-1991 Gulf War report several moderate or severe chronic systemic symptoms, defined as Gulf War illness (GWI). Thirty years later, there is little consensus on the causes or biological underpinnings of GWI. The Gulf War Era Cohort and Biorepository (GWECB) was designed to investigate genetic and environmental associations with GWI and consists of 1343 veterans. We investigate candidate gene-toxicant interactions that may be associated with GWI based on prior associations found in human and animal model studies, focusing on SNPs in or near ACHE, BCHE, and PON1 genes to replicate results from prior studies. SOD1 was also considered as a candidate gene. CDC Severe GWI, the primary outcome, was observed in 26% of the 810 deployed veterans included in this study. The interaction between the candidate SNP rs662 and pyridostigmine bromide (PB) pills was found to be associated with CDC Severe GWI. Interactions between PB pill exposure and rs3917545, rs3917550, and rs2299255, all in high linkage disequilibrium in PON1, were also associated with respiratory symptoms. These SNPs could point toward biological pathways through which GWI may develop, which could lead to biomarkers to detect GWI or to better treatment options for veterans with GWI.

Persistent exercise fatigue and associative learning deficits in combination with transient glucose dyshomeostasis in a GWI mouse model

Aims:

To characterize exercise fatigue, metabolic phenotype and cognitive and mood deficits correlated with brain neuroinflammatory and gut microbiome changes in a chronic Gulf War Illness (GWI) mouse model. The latter have been described in an accompanying paper [1].

Main methods:

Adult male C57Bl/6N mice were exposed for 28 days (5 days/week) to pyridostigmine bromide: 6.5 mg/kg, b.i.d., P.O. (GW1) or 8.7 mg/kg, q.d., P.O. (GW2); topical permethrin (1.3 mg/kg in 100% DMSO) and N,N-diethyl-meta-toluamide (DEET 33% in 70% EtOH) and restraint stress (5 min). Exercise, metabolic and behavioral endpoints were compared to sham stress control (CON/S).

Key findings:

Relative to CON/S, GW2 presented persistent exercise intolerance (through post-treatment (PT) day 161), deficient associative learning/memory, and transient insulin insensitivity. In contrast to GW2, GW1 showed deficient long-term object recognition memory, milder associative learning/memory deficit, and behavioral despair.

Significance:

Our findings demonstrate that GW chemicals dose-dependently determine the presentation of exercise fatigue and severity/type of cognitive/mood-deficient phenotypes that show persistence. Our comprehensive mouse model of GWI recapitulates the major multiple symptom domains characterizing GWI, including fatigue and cognitive impairment that can be used to more efficiently develop diagnostic tests and curative treatments for ill Gulf War veterans.

Gastrointestinal problems, mechanisms and possible therapeutic directions in Gulf war illness: a mini review

By its nature, Gulf war illness (GWI) is multisymptomatic and affects several organ systems in the body. Along with other symptoms, veterans who suffer from GWI commonly report chronic gastrointestinal issues such as constipation, pain, indigestion, etc. However, until recently, most attention has been focused on neurological disturbances such as cognitive impairments, chronic fatigue, and chronic pain among affected veterans. With such high prevalence of gastrointestinal problems among Gulf war (GW) veterans, it is surprising that there is little research to investigate the mechanisms behind these issues. This review summarizes all the available works on the mechanisms behind gastrointestinal problems in GWI that have been published to date in various databases. Generally, these studies, which were done in rodent models, in vitro and human cohorts propose that an altered microbiome, a reactive enteric nervous system or a leaky gut among other possible mechanisms are the major drivers of gastrointestinal problems reported in GWI. This review aims to draw attention to the gastrointestinal tract as an important player in GWI disease pathology and a potential therapeutic target.

Host gut microbiome and potential therapeutics in Gulf War Illness: A short review

AIMS

Since our troops had returned from the first Persian Gulf War in 1990-91, the veterans have reported chronic multisymptomatic illness widely referred to as Gulf War Illness (GWI). We aim to review the current directions of GWI pathology research in the context of chronic multisymptomatic illness and its possible gut microbiome targeted therapies. The veterans of Gulf War show symptoms of chronic fatigue, cognitive deficits, and a subsection report of gastrointestinal complications.

METHOD

Efforts of finding a suitable treatment regimen and clinical management remain a challenge. More recently, we have shown that the pathology is connected to alterations in the gut microbiome, and efforts of finding a suitable regimen for gut-directed therapeutics are underway. We discuss the various clinical interventions and summarize the possible effectiveness of gut-directed therapies such as the use of short-chain fatty acids (SCFA), phenolic compounds, and their metabolites, use of probiotics, and fecal microbiota transfer.

SIGNIFICANCE

The short review will be helpful to GWI researchers to expand their studies to the gut and find an effective treatment strategy for chronic multisymptomatic illness.

Emerging role of glutamate in the pathophysiology and therapeutics of Gulf War illness

Gulf War illness (GWI) is a chronic and multi-symptomatic disorder affecting veterans who served in the Gulf War. The commonly reported symptoms in GWI veterans include mood problems, cognitive impairment, muscle and joint pain, migraine/headache, chronic fatigue, gastrointestinal complaints, skin rashes, and respiratory problems. Neuroimaging studies have revealed significant brain structure alterations in GWI veterans, including subcortical atrophy, decreased volume of the hippocampus, reduced total grey and white matter, and increased brain white matter axial diffusivity. These brain changes may contribute to or increase the severities of the GWI-related symptoms. Epidemiological studies have revealed that neurotoxic exposures and stress may be significant contributors to the development of GWI. However, the mechanism underlying how the exposure and stress could contribute to the multi-symptomatic disorder of GWI remains unclear. We and others have demonstrated that rodent models exposed to GW-related agents and stress exhibited higher extracellular glutamate levels, as well as impaired structure and function of glutamatergic synapses. Restoration of the glutamatergic synapses ameliorated the GWI-related pathological and behavioral deficits. Moreover, recent studies showed that a low-glutamate diet reduced multiple symptoms in GWI veterans, suggesting an important role of the glutamatergic system in GWI. Currently, growing evidence has indicated that abnormal glutamate neurotransmission may contribute to the GWI symptoms. This review summarizes the potential roles of glutamate dyshomeostasis and dysfunction of the glutamatergic system in linking the initial cause to the multi-symptomatic outcomes in GWI and suggests the glutamatergic system as a therapeutic target for GWI.

Exercise and pyridostigmine prevents gastric emptying delay and increase blood pressure and cisplatin-induced baroreflex sensitivity in rats

Cisplatin treatment induces an autonomic dysfunction and gastrointestinal and cardiovascular disorders. Physical exercise as well as pyridostigmine treatment induces improves in the autonomic nervous system. In the current study, we investigated the effect of physical exercise and pyridostigmine treatment on gastrointestinal and cardiovascular changes in cisplatin-treated rats. Rats were divided into groups: Saline (S), Cisplatin (Cis), Exercise (Ex), Cisplatin+Exercise (Cis+Ex), Pyridostigmine (Pyr), and Cisplatin+Pyridostigmine (Cis+Pyr). We induced gastrointestinal dysmotility by administering 3 mg kg-1 of cisplatin once week for 5 weeks. The Ex was swimming (1 h per day/5 days per week for 5 weeks with 5% b.w.). GE was evaluated through the colorimetric method of fractional red phenol recovery 10 min after feeding. Pyr groups received 1.5 mg kg-1, p.o. or concomitant Cis treatment. Moreover, gastric contraction in vitro and hemodynamic parameters such as MAP, HR, and evoked baroreflex sensitivity were assessed, as well as sympathetic and parasympathetic tone and intrinsic heart rate (IHR). Cis decrease GE vs. saline (p<0.05). Cis+Ex or Cis+Pyr prevented (p<0.05) decrease in GE vs. Cis rats. Cis decreased (p<0.05) gastric responsiveness in vitro vs. saline. Cis+Ex or Cis+Pyr prevented this phenomenon. Cis treatment increase MAP and decrease in HR (p<0.05) vs saline. Cis+Ex or Cis+Pyr attenuated (p<0.05) both alterations. Cis increased sympathetic tone and decreased vagal tone and IHR (p<0.05) vs. the saline. Cis+Ex or Cis+Pyr prevented those effects vs. the Cis group. In conclusion, physical exercise and pyridostigmine treatment improves autonomic dysfunction and prevented GE delay and changes in hemodynamic parameters, baroreflex sensitivity, and cardiac autonomic control in cisplatin-treated rats.

A role for neuroimmune signaling in a rat model of Gulf War Illness-related pain

More than a quarter of veterans of the 1990-1991 Persian Gulf War suffer from Gulf War Illness (GWI), a chronic, multi-symptom illness that commonly includes musculoskeletal pain. Exposure to a range of toxic chemicals, including sarin nerve agent, are a suspected root cause of GWI. Moreover, such chemical exposures induce a neuroinflammatory response in rodents, which has been linked to several GWI symptoms in rodents and veterans with GWI. To date, a neuroinflammatory basis for pain associated with GWI has not been investigated. Here, we evaluated development of nociceptive hypersensitivity in a model of GWI. Male Sprague Dawley rats were treated with corticosterone in the drinking water for 7 days, to mimic high physiological stress, followed by a single injection of the sarin nerve agent surrogate, diisopropyl fluorophosphate. These exposures alone were insufficient to induce allodynia. However, an additional sub-threshold challenge (a single intramuscular injection of pH 4 saline) induced long-lasting, bilateral allodynia. Such allodynia was associated with elevation of markers for activated microglia/macrophages (CD11b) and astrocytes/satellite glia (GFAP) in the lumbar dorsal spinal cord and dorsal root ganglia (DRG). Additionally, Toll-like receptor 4 (TLR4) mRNA was elevated in the lumbar dorsal spinal cord, while IL-1β and IL-6 were elevated in the lumbar dorsal spinal cord, DRG, and gastrocnemius muscle. Demonstrating a casual role for such neuroinflammatory signaling, allodynia was reversed by treatment with either minocycline, the TLR4 inhibitor (+)-naltrexone, or IL-10 plasmid DNA. Together, these results point to a role for neuroinflammation in male rats in the model of musculoskeletal pain related to GWI. Therapies that alleviate persistent immune dysregulation may be a strategy to treat pain and other symptoms of GWI.

Pyridostigmine bromide exposure creates chronic, underlying neuroimmune disruption in the gastrointestinal tract and brain that alters responses to palmitoylethanolamide in a mouse model of Gulf War Illness

Gulf War Illness (GWI) is a chronic multisymptom illness that includes gastrointestinal disorders. Although the exact etiology of GWI is unknown, exposure to the drug pyridostigmine bromide (PB) is considered a major factor. Exposure to PB drives enteric neuroinflammation, promotes immunosuppression, and alters physiological functions of the colon in the short term but whether exposure to PB is sufficient to promote long term dysfunction is not known. Here, we tested whether exposure to PB is sufficient to drive long term changes that reflect GWI, and whether the endogenous anti-inflammatory mediator palmitoylethanolamide (PEA) is sufficient to reduce the detrimental effects of PB in the gut and brain of mice. Exposure to PB alone was not sufficient to cause major changes in neuromuscular transmission but did drive major changes by altering the effects of PEA. Calcium imaging data show that the mechanisms responsible include a shift in receptor signaling mediated by TRPV1, endocannabinoids, and peroxisome proliferator-activated receptors alpha (PPARα). Additional mechanisms include the development of glial reactivity and changes in enteric neurochemical coding and survival. PB and PEA caused major shifts in pro-inflammatory cytokines/chemokines in the brain and colon that persisted up to 5 months following exposure. Many of the effects of PB and PEA exhibit significant sex differences. Together, these results highlight novel mechanisms whereby PB promotes long-lasting changes in nervous system and immune function by inducing occult neuroplasticity that is revealed by subsequent exposure to unrelated drugs in a sex dependent manner.

Assessing the Beneficial Effects of the Immunomodulatory Glycan LNFPIII on Gut Microbiota and Health in a Mouse Model of Gulf War Illness

The microbiota’s influence on host (patho) physiology has gained interest in the context of Gulf War Illness (GWI), a chronic disorder featuring dysregulation of the gut–brain–immune axis. This study examined short- and long-term effects of GWI-related chemicals on gut health and fecal microbiota and the potential benefits of Lacto-N-fucopentaose-III (LNFPIII) treatment in a GWI model. Male C57BL/6J mice were administered pyridostigmine bromide (PB; 0.7 mg/kg) and permethrin (PM; 200 mg/kg) for 10 days with concurrent LNFPIII treatment (35 μg/mouse) in a short-term study (12 days total) and delayed LNFPIII treatment (2×/week) beginning 4 months after 10 days of PB/PM exposure in a long-term study (9 months total). Fecal 16S rRNA sequencing was performed on all samples post-LNFPIII treatment to assess microbiota effects of GWI chemicals and acute/delayed LNFPIII administration. Although PB/PM did not affect species composition on a global scale, it affected specific taxa in both short- and long-term settings. PB/PM elicited more prominent long-term effects, notably, on the abundances of bacteria belonging to Lachnospiraceae and Ruminococcaceae families and the genus Allobaculum. LNFPIII improved a marker of gut health (i.e., decreased lipocalin-2) independent of GWI and, importantly, increased butyrate producers (e.g., Butyricoccus, Ruminococcous) in PB/PM-treated mice, indicating a positive selection pressure for these bacteria. Multiple operational taxonomic units correlated with aberrant behavior and lipocalin-2 in PB/PM samples; LNFPIII was modulatory. Overall, significant and lasting GWI effects occurred on specific microbiota and LNFPIII treatment was beneficial.

Development of muscle atrophy and loss of function in a Gulf-War illness model: underlying mechanisms

Gulf War illness (GWI) afflicts military personnel who served during the Persian Gulf War and is notable for cognitive deficits, depression, muscle pain, weakness, intolerance to exercise, and fatigue. Suspect causal agents include the chemicals pyridostigmine (PB), permetrim (PM) and N,N-diethyl-m-toluamide (DEET) used as protectants against insects and nerve gases. No pre-clinical studies have explored the effects on skeletal muscle (SkM). Young male rats were provided PB, PM and DEET at equivalent human doses and physical restraint (to induce stress) for 3 weeks followed a 3-week recovery. GWI gastrocnemius weight was ~ 35% lower versus controls, which correlated with decreases in myofiber area, limb strength, and treadmill time/distance. In GWI rats, SkM fiber type relative abundance changed towards slow type I. Muscle wasting pathway proteins were upregulated while those that promote growth decreased as did mitochondrial endpoints and muscle ATP levels. Proteomic analysis of SkM also documented unique alterations in mitochondrial and metabolic pathways. Thus, exposure to GWI chemicals/stress adversely impacts key metabolic pathways leading to muscle atrophy and loss of function. These changes may account for GWI Veterans symptoms.

TLR Antagonism by Sparstolonin B Alters Microbial Signature and Modulates Gastrointestinal and Neuronal Inflammation in Gulf War Illness Preclinical Model

The 1991 Persian Gulf War veterans presented a myriad of symptoms that ranged from chronic pain, fatigue, gastrointestinal disturbances, and cognitive deficits. Currently, no therapeutic regimen exists to treat the plethora of chronic symptoms though newer pharmacological targets such as microbiome have been identified recently. Toll-like receptor 4 (TLR4) antagonism in systemic inflammatory diseases have been tried before with limited success, but strategies with broad-spectrum TLR4 antagonists and their ability to modulate the host-microbiome have been elusive. Using a mouse model of Gulf War Illness, we show that a nutraceutical, derived from a Chinese herb Sparstolonin B (SsnB) presented a unique microbiome signature with an increased abundance of butyrogenic bacteria. SsnB administration restored a normal tight junction protein profile with an increase in Occludin and a parallel decrease in Claudin 2 and inflammatory mediators high mobility group box 1 (HMGB1), interleukin-1β (IL-1β), and interleukin-6 (IL-6) in the distal intestine. SsnB also decreased neuronal inflammation by decreasing IL-1β and HMGB1, while increasing brain-derived neurotrophic factor (BDNF), with a parallel decrease in astrocyte activation in vitro. Mechanistically, SsnB inhibited the binding of HMGB1 and myeloid differentiation primary response protein (MyD88) to TLR4 in the intestine, thus attenuating TLR4 downstream signaling. Studies also showed that SsnB was effective in suppressing TLR4-induced nod-like receptor protein 3 (NLRP3) inflammasome activation, a prominent inflammatory disease pathway. SsnB significantly decreased astrocyte activation by decreasing colocalization of glial fibrillary acid protein (GFAP) and S100 calcium-binding protein B (S100B), a crucial event in neuronal inflammation. Inactivation of SsnB by treating the parent molecule by acetate reversed the deactivation of NLRP3 inflammasome and astrocytes in vitro, suggesting that SsnB molecular motifs may be responsible for its anti-inflammatory activity.

Acetylcholinesterase inhibitor exposures as an initiating factor in the development of Gulf War Illness, a chronic neuroimmune disorder in deployed veterans

Gulf War Illness (GWI) is a chronic multi-symptom disorder, characterized by symptoms such as fatigue, pain, cognitive and memory impairment, respiratory, skin and gastrointestinal problems, that is experienced by approximately one-third of 1991 Gulf War veterans. Over the nearly three decades since the end of the war, investigators have worked to elucidate the initiating factors and underlying causes of GWI. A significant portion of this research has indicated a strong correlation between GWI and exposure to a number of different acetycholinesterase inhibitors (AChEIs) in theater, such as sarin and cyclosarin nerve agents, chlorpyrifos and dichlorvos pesticides, and the anti-nerve agent prophylactic pyridostigmine bromide. Through studying these exposures and their relationship to the symptoms presented by ill veterans, it has become increasingly apparent that GWI is the likely result of an underlying neuroimmune disorder. While evidence indicates that AChEIs are a key exposure in the development of GWI, particularly organophosphate AChEIs, the mechanism(s) by which these chemicals instigate illness appears to be related to "off-target", non-cholinergic effects. In this review, we will discuss the role of AChEI exposure in the development and persistence of GWI; in particular, how these chemicals, combined with other exposures, have led to a chronic neuroimmune disorder. This article is part of the special issue entitled 'Acetylcholinesterase Inhibitors: From Bench to Bedside to Battlefield'.

Dysbiosis-Associated Enteric Glial Cell Immune-Activation and Redox Imbalance Modulate Tight Junction Protein Expression in Gulf War Illness Pathology

About 14% of veterans who suffer from Gulf war illness (GWI) complain of some form of gastrointestinal disorder but with no significant markers of clinical pathology. Our previous studies have shown that exposure to GW chemicals resulted in altered microbiome which was associated with damage associated molecular pattern (DAMP) release followed by neuro and gastrointestinal inflammation with loss of gut barrier integrity. Enteric glial cells (EGC) are emerging as important regulators of the gastrointestinal tract and have been observed to change to a reactive phenotype in several functional gastrointestinal disorders such as IBS and IBD. This study is aimed at investigating the role of dysbiosis associated EGC immune-activation and redox instability in contributing to observed gastrointestinal barrier integrity loss in GWI via altered tight junction protein expression. Using a mouse model of GWI and in vitro studies with cultured EGC and use of antibiotics to ensure gut decontamination we show that exposure to GW chemicals caused dysbiosis associated change in EGCs. EGCs changed to a reactive phenotype characterized by activation of TLR4-S100β/RAGE-iNOS pathway causing release of nitric oxide and activation of NOX2 since gut sterility with antibiotics prevented this change. The resulting peroxynitrite generation led to increased oxidative stress that triggered inflammation as shown by increased NLRP-3 inflammasome activation and increased cell death. Activated EGCs in vivo and in vitro were associated with decrease in tight junction protein occludin and selective water channel aquaporin-3 with a concomitant increase in Claudin-2. The tight junction protein levels were restored following a parallel treatment of GWI mice with a TLR4 inhibitor SsnB and butyric acid that are known to decrease the immunoactivation of EGCs. Our study demonstrates that immune-redox mechanisms in EGC are important players in the pathology in GWI and may be possible therapeutic targets for improving outcomes in GWI symptom persistence.

The Gut-Microbiome in Gulf War Veterans: A Preliminary Report

Gulf War Illness (GWI) is a chronic multi-symptom disorder affecting the central nervous system (CNS), immune and gastrointestinal (GI) systems of Gulf War veterans (GWV). We assessed the relationships between GWI, GI symptoms, gut microbiome and inflammatory markers in GWV from the Boston Gulf War Illness Consortium (GWIC). Three groups of GWIC veterans were recruited in this pilot study; GWV without GWI and no gastrointestinal symptoms (controls), GWV with GWI and no gastrointestinal symptoms (GWI-GI), GWV with GWI who reported gastrointestinal symptoms (GW+GI). Here we report on a subset of the first thirteen stool samples analyzed. Results showed significantly different gut microbiome patterns among the three groups and within the GWI +/-GI groups. Specifically, GW controls had a greater abundance of firmicutes and the GWI+GI group had a greater abundance of the phyla bacteroidetes, actinobacteria, euryarchaeota, and proteobacteria as well as higher abundances of the families Bacteroidaceae, Erysipelotrichaceae, and Bifidobacteriaceae. The GWI+GI group also showed greater plasma levels of the inflammatory cytokine TNF-RI and they endorsed significantly more chemical weapons exposure during the war and reported significantly greater chronic pain, fatigue and sleep difficulties than the other groups. Studies with larger samples sizes are needed to confirm these initial findings.