Peroxisome proliferator-activated receptor-γ and thymic stromal lymphopoietin are involved in the pathophysiology of childhood coeliac disease

The Versatile Role of Peroxisome Proliferator-Activated Receptors in Immune-Mediated Intestinal Diseases

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that sense lipophilic molecules and act as transcription factors to regulate target genes. PPARs have been implicated in the regulation of innate immunity, glucose and lipid metabolism, cell proliferation, wound healing, and fibrotic processes. Some synthetic PPAR ligands are promising molecules for the treatment of inflammatory and fibrotic processes in immune-mediated intestinal diseases. Some of these are currently undergoing or have previously undergone clinical trials. Dietary PPAR ligands and changes in microbiota composition could modulate PPARs' activation to reduce inflammatory responses in these immune-mediated diseases, based on animal models and clinical trials. This narrative review aims to summarize the role of PPARs in immune-mediated bowel diseases and their potential therapeutic use.

The Emerging Role of Innate Lymphoid Cells (ILCs) and Alarmins in Celiac Disease: An Update on Pathophysiological Insights, Potential Use as Disease Biomarkers, and Therapeutic Implications

Celiac disease (CD) is an intestinal disease that develops in genetically predisposed individuals and is triggered by the ingestion of gluten. CD was considered a Th1-disease. Today, the role of Th17, IL-21, and IL-17A lymphocytes is well known. Inflammation is regulated by the activity of gluten-specific CD4+ T lymphocytes that produce pro-inflammatory cytokines, including IFN-γ, TNF-α, and IL-21, perpetuating the Th1 response. These cytokines determine an inflammatory state of the small intestine, with consequent epithelial infiltration of lymphocytes and an alteration of the architecture of the duodenal mucosa. B cells produce antibodies against tissue transglutaminase and against deamidated gliadin. Although the role of the adaptive immune response is currently known, the evidence about the role of innate immunity cells is still poorly understood. Epithelial damage determines the release of damage-associated molecular patterns (DAMPs), also known as alarmins. Together with the intestinal epithelial cells and the type 1 innate lymphoid cells (ILC1s), alarmins like TSLP, IL-33, and HMGB1 could have a fundamental role in the genesis and maintenance of inflammation. Our study aims to evaluate the evidence in the literature about the role of ILCs and alarmins in celiac disease, evaluating the possible future diagnostic and therapeutic implications.

The Association of Inflammatory Gut Diseases with Neuroinflammatory and Auditory Disorders

Disorders such as inflammatory bowel disease (IBD) and celiac disease (CeD) result in intestinal hyperpermeability or 'leaky' gut. The increased permeability of the intestinal barrier allows microbial metabolites, toxins, and pathogens to infiltrate the bloodstream and extraintestinal tissues, causing systemic inflammation. Despite differences in aetiology and pathophysiology, IBD and CeD share several extraintestinal manifestations such as neuroinflammation, neurological and psychiatric manifestations, and sensorineural hearing loss (SNHL). This narrative review focuses on the association between intestinal hyperpermeability with the brain and inner ear diseases. We postulate that the microbial metabolites and pathogens released from the gut increase the permeability of natural barriers, such as the blood-brain barrier (BBB) and blood-labyrinth barrier (BLB). The barrier breakdown allows the spreading of inflammatory processes to the brain and inner ear, leading to disease.

Dietary Gluten and Neurodegeneration: A Case for Preclinical Studies

Although celiac disease (CD) is an autoimmune disease that primarily involves the intestinal tract, mounting evidence suggests that a sizeable number of patients exhibit neurological deficits. About 40% of the celiac patients with neurological manifestations have circulating antibodies against neural tissue transglutaminase-6 (tTG6). While early diagnosis and strict adherence to a gluten-free diet (GFD) have been recommended to prevent neurological dysfunction, better therapeutic strategies are needed to improve the overall quality of life. Dysregulation of the microbiota-gut-brain axis, presence of anti-tTG6 antibodies, and epigenetic mechanisms have been implicated in the pathogenesis. It is also possible that circulating or gut-derived extracellular structures and including biomolecular condensates and extracellular vesicles contribute to disease pathogenesis. There are several avenues for shaping the dysregulated gut homeostasis in individuals with CD, non-celiac gluten sensitivity (NCGS) and/or neurodegeneration. In addition to GFD and probiotics, nutraceuticals, such as phyto and synthetic cannabinoids, represent a new approach that could shape the host microbiome towards better prognostic outcomes. Finally, we provide a data-driven rationale for potential future pre-clinical research involving non-human primates (NHPs) to investigate the effect of nutraceuticals, such as phyto and synthetic cannabinoids, either alone or in combination with GFD to prevent/mitigate dietary gluten-induced neurodegeneration.

Brain Opioid Activity and Oxidative Injury: Different Molecular Scenarios Connecting Celiac Disease and Autistic Spectrum Disorder

Celiac Disease (CD) is an immune-mediated disease triggered by the ingestion of wheat gliadin and related prolamins from other cereals, such as barley and rye. Immunity against these cereal-derived proteins is mediated by pro-inflammatory cytokines produced by both innate and adaptive system response in individuals unable to adequately digest them. Peptides generated in this condition are absorbed across the gut barrier, which in these patients is characterized by the deregulation of its permeability. Here, we discuss a possible correlation between CD and Autistic Spectrum Disorder (ASD) pathogenesis. ASD can be induced by an excessive and inappropriate brain opioid activity during the neonatal period. Cereal-derived peptides produced in celiac patients cross the blood-brain barrier and bind to endogenous opioid receptors interfering with neurotransmission and generating deleterious effects on brain maturation, learning and social relations. Moreover, an increase in oxidative stress and a decrease in the antioxidant capacity, as well as an extended mitochondrial impairment in the brain, could represent a possible connection between ASD and CD. Therefore, we critically discuss the proposed relationship between ASD and CD and the possible usefulness of a gluten-free diet in ASD patients.

Thymic stromal lymphopoietin levels are increased in patients with celiac disease

Thymic stromal lymphopoietin (TSLP) is a cytokine produced by epithelial cells in the lungs, skin, and intestinal mucosa and is involved in several physiological and pathological processes. In this study, we evaluated serum TSLP levels in patients with celiac disease (CD). The prospective study was conducted at a gastroenterology outpatient clinic between March 2018 and August 2018. Eighty-nine participants aged between 18 and 75 years were classified into following groups: 22 patients with newly diagnosed CD; 20 patients with CD who were compliant with a gluten-free diet (GFD); 32 patients with CD who were not compliant with a GFD; and 15 healthy controls. Demographic characteristics, disease duration, and selected biochemical and hematologic parameters were recorded and compared between groups. Median serum TSLP levels were 1193.65 pg/mL (range: 480.1-1547.1) in newly diagnosed CD patients, 110.25 pg/mL (range: 60.3-216.7) in CD patients who were compliant with a GFD, 113.1 pg/mL (range: 76.3-303.4) in CD patients who were not compliant with a GFD, and 57 pg/mL (range: 49-67.8) in healthy controls. Overall, there was a significant difference in serum TSLP levels between groups (p = 0.001). Patients with newly diagnosed CD had the highest serum TSLP levels. There was no significant difference in serum TSLP levels between patients with CD who were and were not compliant with a GFD. TSLP appears to be involved in the pathogenesis of CD. Further studies are required to determine if the TSLP signaling pathway can be used in the treatment of CD.

CD1a-Expressing Monocytes as Mediators of Inflammation in Ulcerative Colitis

BACKGROUND

CD1a-expressing CD14+ monocytes have been identified as inducers of autoreactive T cells. In this study, the link between inflammatory and metabolic signals and CD1a-expressing monocytes in vitro and in vivo was examined, and CD1a was evaluated as a potential therapeutic target for treatment of ulcerative colitis (UC).

METHODS

Peripheral blood mononuclear cells (PBMCs) from UC patients and non-UC donors were incubated with phosphatidylcholine (PC) for 2 and 7 days and subjected to flow cytometric analysis. Triacylglycerol (TAG) and cholesterol levels and frequencies of CD14+ CD1a+ monocytes were determined in a mouse model of UC that is based on NOD/scid IL2Rγnull mice reconstituted with PBMCs from UC patients (NSG-UC). NSG-UC mice were treated with anti-CD1a antibodies. Response to treatment was determined by clinical and histological scores, flow cytometric analysis of human leucocytes from the spleen and colon, and expression levels of TGFß1, HGF, IFNγ, and TARC.

RESULTS

Incubation of PBMCs with PC resulted in an increase of the frequency of CD1a+ CD14+ monocytes at the expense of CCR2-, CD86-, and TSLPR-expressing CD14+ monocytes. CD1a+ CD14+ monocytes induced the activation of CD4+ T cells and differentiation of Th cells. In vivo, TAG and cholesterol levels increased upon inflammation and correlated positively with CD14+ CD1a+ monocytes. NSG-UC mice benefitted from treatment with anti-CD1a antibodies, as indicated by a reduced histological score and reduced frequencies of CD1a+ CD14+ monocytes in the colon and spleen of mice.

CONCLUSION

CD1a-expressing monocytes might act as sensors and mediators of inflammation in UC. Mice benefitted from treatment with anti-CD1a antibodies.