Intestinal Hyperpermeability in Gulf War Veterans With Chronic Gastrointestinal Symptoms

Onset of Irritable Bowel Syndrome, Dyspepsia, Diarrhea, Bloating, and Constipation in Deployed Gulf War Veterans

An estimated 694,550 United States service members were actively deployed to the Persian Gulf from 1990-1991. Many veterans who were deployed developed Persian Gulf War Syndrome along with chronic gastrointestinal symptoms after returning from the Persian Gulf. Our objective in this study was to determine the phenotypic expression of gastrointestinal symptom complexes in previously healthy veterans who had been stationed in the Persian Gulf. One hundred and four consecutive veterans (88 males, 16 females) who had previously been deployed in 1990-91 were evaluated for their bowel habits and gastrointestinal symptoms. A workup was completed to find identifiable causes of their symptoms and all veterans were asked to do a modified version of the Bowel Disease Questionnaire symptom survey. None of the veterans reported gastrointestinal symptoms before deployment. During deployment to the Persian Gulf: 22 veterans (21%) developed irritable bowel syndrome; 17 (16%) developed dyspepsia; 50 (48%) developed diarrhea; 11 (11%) developed bloating; and 4 (4%) developed constipation. The results of the current study suggest that the development of irritable bowel syndrome, dyspepsia, diarrhea, bloating, and constipation is frequently seen in deployed Gulf War Veterans and the gastrointestinal symptoms commonly persist upon returning home. These novel findings are very important for currently deployed veterans who are serving in the Middle East and are at a high risk of developing gastrointestinal disorders.

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.

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.

Long COVID and the Neuroendocrinology of Microbial Translocation Outside the GI Tract: Some Treatment Strategies

Similar to previous pandemics, COVID-19 has been succeeded by well-documented post-infectious sequelae, including chronic fatigue, cough, shortness of breath, myalgia, and concentration difficulties, which may last 5 to 12 weeks or longer after the acute phase of illness. Both the psychological stress of SARS-CoV-2 infection and being diagnosed with COVID-19 can upregulate cortisol, a stress hormone that disrupts the efferocytosis effectors, macrophages, and natural killer cells, leading to the excessive accumulation of senescent cells and disruption of biological barriers. This has been well-established in cancer patients who often experience unrelenting fatigue as well as gut and blood–brain barrier dysfunction upon treatment with senescence-inducing radiation or chemotherapy. In our previous research from 2020 and 2021, we linked COVID-19 to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) via angiotensin II upregulation, premature endothelial senescence, intestinal barrier dysfunction, and microbial translocation from the gastrointestinal tract into the systemic circulation. In 2021 and 2022, these hypotheses were validated and SARS-CoV-2-induced cellular senescence as well as microbial translocation were documented in both acute SARS-CoV-2 infection, long COVID, and ME/CFS, connecting intestinal barrier dysfunction to disabling fatigue and specific infectious events. The purpose of this narrative review is to summarize what is currently known about host immune responses to translocated gut microbes and how these responses relate to fatiguing illnesses, including long COVID. To accomplish this goal, we examine the role of intestinal and blood–brain barriers in long COVID and other illnesses typified by chronic fatigue, with a special emphasis on commensal microbes functioning as viral reservoirs. Furthermore, we discuss the role of SARS-CoV-2/Mycoplasma coinfection in dysfunctional efferocytosis, emphasizing some potential novel treatment strategies, including the use of senotherapeutic drugs, HMGB1 inhibitors, Toll-like receptor 4 (TLR4) blockers, and membrane lipid replacement.

Prevalence of gastrointestinal disease in US Military Veterans under outpatient care at the Veterans Health Administration

Objectives:

There are currently no reliable estimates of the prevalence of gastrointestinal disease in the US Military Veterans. Hence, the study aims to determine its prevalence in military Veterans in the United States.

Methods:

This study utilized a retrospective, correlational design using a patient record database from the Department of Veteran’s Affairs. The participants in the study were Veterans diagnosed with gastrointestinal disease. Specific gastrointestinal diseases include more than 500,000 ambulatory care visits annually in the United States, which included peptic ulcer disease, gastroesophageal reflux disease, diverticular disease, ulcerative colitis, Crohn’s disease, irritable bowel syndrome, and functional dyspepsia, as well as the symptoms of constipation and nausea/vomiting. This study revealed the exact prevalence of gastrointestinal disease diagnosed in Veterans served in outpatient settings by the Veterans Health Administration and broke down this prevalence over time and by the Veteran period of service.

Results:

Findings revealed that gastrointestinal disease prevalence among Veterans varied according to their period of service.

Conclusions:

Findings may help improve screening for Veterans with this increased risk factor. However, further research should be performed to verify the prevalence of gastrointestinal disease in Veterans as compared to the general American population.

IL-17 and IL-17C Signaling Protects the Intestinal Epithelium against Diisopropyl Fluorophosphate Exposure in an Acute Model of Gulf War Veterans' Illnesses

Gulf War Veterans' Illnesses (GWI) encompasses a broad range of unexplained symptomology specific to Veterans of the Persian Gulf War. Gastrointestinal (GI) distress is prominent in veterans with GWI and often presents as irritable bowel syndrome (IBS). Neurotoxins, including organophosphorus pesticides and sarin gas, are believed to have contributed to the development of GWI, at least in a subset of Veterans. However, the effects of such agents have not been extensively studied for their potential impact to GI disorders and immunological stability. Here we utilized an established murine model of GWI to investigate deleterious effects of diisopropyl fluorophosphate (DFP) exposure on the mucosal epithelium in vivo and in vitro. In vivo, acute DFP exposure negatively impacts the mucosal epithelium by reducing tight junction proteins and antimicrobial peptides as well as altering intestinal microbiome composition. Furthermore, DFP treatment reduced the expression of IL-17 in the colonic epithelium. Conversely, both IL-17 and IL-17C treatment could combat the negative effects of DFP and other cholinesterase inhibitors in murine intestinal organoid cells. Our findings demonstrate that acute exposure to DFP can result in rapid deterioration of mechanisms protecting the GI tract from disease. These results are relevant to suspected GWI exposures and could help explain the propensity for GI disorders in GWI 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.

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.

Host Akkermansia muciniphila Abundance Correlates With Gulf War Illness Symptom Persistence via NLRP3-Mediated Neuroinflammation and Decreased Brain-Derived Neurotrophic Factor

Neurological disorders are commonly reported among veterans who returned from the Gulf war. Veterans who suffer from Gulf War illness (GWI) complain of continued symptom persistence that includes neurological disorders, muscle weakness, headaches, and memory loss, that developed during or shortly after the war. Our recent research showed that chemical exposure associated microbial dysbiosis accompanied by a leaky gut connected the pathologies in the intestine, liver, and brain. However, the mechanisms that caused the symptoms to persist even 30 years after the war remained elusive to investigators. In this study, we used a rodent model of GWI to investigate the persistence of microbiome alterations, resultant chronic inflammation, and its effect on neurotrophic and synaptic plasticity marker BDNF. The results showed that exposure to GW chemicals (the pesticide permethrin and prophylactic drug pyridostigmine bromide) resulted in persistent pathology characterized by the low relative abundance of the probiotic bacteria Akkermansia muciniphila in the gut, which correlated with high circulatory HMGB1 levels, blood-brain barrier dysfunction, neuroinflammation and lowered neurotrophin BDNF levels. Mechanistically, we used mice lacking the NLRP3 gene to investigate this inflammasome's role in observed pathology. These mice had significantly decreased inflammation and a subsequent increase in BDNF in the frontal cortex. This suggests that a persistently low species abundance of Akkermansia muciniphila and associated chronic inflammation due to inflammasome activation might be playing a significant role in contributing to chronic neurological problems in GWI. A therapeutic approach with various small molecules that can target both the restoration of a healthy microbiome and decreasing inflammasome activation might have better outcomes in treating GWI symptom persistence.

Gut permeability is affected by sex and increased in children with irritable bowel syndrome but not in functional abdominal pain

BACKGROUND

Gut permeability is increased in some children and adults with irritable bowel syndrome (IBS). We investigated whether this also is true for children with functional abdominal pain (FAP). We also determined whether sex affected permeability results.

METHODS

Sucrose, lactulose, mannitol, and sucralose were ingested after an overnight fast in well-phenotyped children with IBS (n = 95), FAP (n = 25), and healthy controls (HC) (n = 60). Urine was collected for 24 hours. Percent sucrose recovery was calculated based on the 0- to 3-hour collection; lactulose/mannitol ratio both on the 0- to 3-hour and 0- to 24-hour collections; and percent sucralose recovery on the 0- to 24-hours collection.

KEY RESULTS

Age was similar among the groups (P = .26). The lactulose/mannitol ratio was increased in IBS compared with HC at 0-3 and 0-24 hours (P = .023, P = .05, respectively). Percent sucralose recovery was greater in FAP than in HC (P = .045). No differences were noted among the groups in percent sucrose recovery. Taking sex into account, percent sucrose recovery was greater in girls with IBS vs HC girls (P = .008). The lactulose/mannitol ratio was greater in boys with IBS compared with HC boys at both time points (both P = .02). Percent sucralose recovery was greater in boys with IBS than in FAP or HC (both P < .001).

CONCLUSIONS AND INFERENCES

Sex is a critically important factor when measuring gut permeability. Boys with IBS have increased lactulose/mannitol ratios and percent sucralose recovery. Girls with IBS have increased percent recovery of sucrose. Children with FAP do not demonstrate abnormal gut 0permeability even taking sex into account.