Salivary Microbiome in Pediatric and Adult Celiac Disease

Assessment of salivary microbiota profile as a potential diagnostic tool for pediatric celiac disease

The association between oral dysbiosis and celiac disease (CD) remains poorly understood, as does the impact of CD-associated dysbiosis on disease development or exacerbation. This study aims to investigate alterations in salivary microbial composition among children with CD. In this cross-sectional study, saliva samples from 12 children with active CD (A-CD group), 14 children with CD on a gluten-free diet (GFD), and 10 healthy control (HC) children were analyzed using DNA sequencing targeting the 16S ribosomal RNA. Both patients in A-CD and GFD groups showed a significant increase (p = 0.0001) in the Bacteroidetes phylum, while the Actinobacteria phylum showed a significant decrease (p = 0.0001). Notably, the Rothia genus and R.aeria also demonstrated a significant decrease (p = 0.0001) within the both CD groups as compare to HC. Additionally, the control group displayed a significant increase (p = 0.006) in R.mucilaginosa species compared to both CD patient groups. Distinct bacterial strains were abundant in the saliva of patients with active CD, indicating a unique composition of the salivary microbiome in individuals with CD. These findings suggest that our approach to assessing salivary microbiota changes may contribute to developing noninvasive methods for diagnosing and treating CD.

How the Microbiota May Affect Celiac Disease and What We Can Do

Celiac disease (CeD) is an autoimmune disease with a strong association with human leukocyte antigen (HLA), characterized by the production of specific autoantibodies and immune-mediated enterocyte killing. CeD is a unique autoimmune condition, as it is the only one in which the environmental trigger is known: gluten, a storage protein present in wheat, barley, and rye. How and when the loss of tolerance of the intestinal mucosa to gluten occurs is still unknown. This event, through the activation of adaptive immune responses, enhances epithelial cell death, increases the permeability of the epithelial barrier, and induces secretion of pro-inflammatory cytokines, resulting in the transition from genetic predisposition to the actual onset of the disease. While the role of gastrointestinal infections as a possible trigger has been considered on the basis of a possible mechanism of antigen mimicry, a more likely alternative mechanism appears to involve a complex disruption of the gastrointestinal microbiota ecosystem triggered by infections, rather than the specific effect of a single pathogen on intestinal mucosal homeostasis. Several lines of evidence show the existence of intestinal dysbiosis that precedes the onset of CeD in genetically at-risk subjects, characterized by the loss of protective bacterial elements that both epigenetically and functionally can influence the response of the intestinal epithelium leading to the loss of gluten tolerance. We have conducted a literature review in order to summarize the current knowledge about the complex and in part still unraveled dysbiosis that precedes and accompanies CeD and present some exciting new data on how this dysbiosis might be prevented and/or counteracted. The literature search was conducted on PubMed.gov in the time frame 2010 to March 2024 utilizing the terms "celiac disease and microbiota", "celiac disease and microbiome", and "celiac disease and probiotics" and restricting the search to the following article types: Clinical Trials, Meta-Analysis, Review, and Systematic Review. A total of 364 papers were identified and reviewed. The main conclusions of this review can be outlined as follows: (1) quantitative and qualitative changes in gut microbiota have been clearly documented in CeD patients; (2) intestinal microbiota's extensive and variable interactions with enterocytes, viral and bacterial pathogens and even gluten combine to impact the inflammatory immune response to gluten and the loss of gluten tolerance, ultimately affecting the pathogenesis, progression, and clinical expression of CeD; (3) gluten-free diet fails to restore the eubiosis of the digestive tract in CeD patients, and also negatively affects microbial homeostasis; (4) new tools allowing targeted microbiota therapy, such as the use of probiotics (a good example being precision probiotics like the novel strain of B. vulgatus (20220303-A2) begin to show exciting potential applications.

Celiac Disease: The Importance of Studying the Duodenal Mucosa-Associated Microbiota

There is increasing evidence indicating that changes in both the composition and functionality of the intestinal microbiome are closely associated with the development of several chronic inflammatory diseases, with celiac disease (CeD) being particularly noteworthy. Thanks to the advent of culture-independent methodologies, the ability to identify and quantify the diverse microbial communities residing within the human body has been significantly improved. However, in the context of CeD, a notable challenge lies in characterizing the specific microbiota present on the mucosal surfaces of the intestine, rather than relying solely on fecal samples, which may not fully represent the relevant microbial populations. Currently, our comprehension of the composition and functional importance of mucosa-associated microbiota (MAM) in CeD remains an ongoing field of research because the limited number of available studies have reported few and sometimes contradictory results. MAM plays a crucial role in the development and progression of CeD, potentially acting as both a trigger and modulator of the immune response within the intestinal mucosa, given its proximity to the epithelial cells and direct interaction. According to this background, this review aims to consolidate the existing literature specifically focused on MAM in CeD. By elucidating the complex interplay between the host immune system and the gut microbiota, we aim to pave the way for new interventions based on novel therapeutic targets and diagnostic biomarkers for MAM in CeD.

Probiotic formulations and gastro-intestinal diseases in the paediatric population: a narrative review

Background/Aim

Probiotics are live microbial supplements that improve the microbial balance in the host animal when administered in adequate amounts. They play an important role in relieving symptoms of many diseases associated with gastrointestinal tract, for example, in necrotizing enterocolitis (NEC), antibiotic-associated diarrhea, relapsing Clostridium difficile colitis, Helicobacter pylori infections, and inflammatory bowel disease (IBD). In this narrative review, the authors aim to evaluate the role of different probiotic formulations in treating gastrointestinal diseases in pediatric population aged 18 years or younger and highlight the main considerations for selecting probiotic formulations for use in this population.

Methodology

The authors searched PubMed and Clinicaltrials.gov from inception to 24th July 2022, without any restrictions. Using an iterative process, the authors subsequently added papers through hand-searching citations contained within retrieved articles and relevant systematic reviews and meta-analyses.

Results

The effectiveness of single-organism and composite probiotics in treating gastrointestinal disorders in pediatric patients aged 18 or under were analyzed and compared in this study. A total of 39 studies were reviewed and categorized based on positive and negative outcomes, and compared with a placebo, resulting in 25 studies for single-organism and 14 studies for composite probiotics. Gastrointestinal disorders studied included NEC, acute gastroenteritis (AGE), Acute Diarrhea, Ulcerative Colitis (UC), and others. The results show that probiotics are effective in treating various gastrointestinal disorders in children under 18, with single-organism probiotics demonstrating significant positive outcomes in most studies, and composite probiotics showing positive outcomes in all studies analyzed, with a low incidence of negative outcomes for both types.

Conclusion

This study concludes that single-organism and composite probiotics are effective complementary therapies for treating gastrointestinal disorders in the pediatric population. Hence, healthcare professionals should consider using probiotics in standard treatment regimens, and educating guardians can enhance the benefits of probiotic therapy. Further research is recommended to identify the optimal strains and dosages for specific conditions and demographics. The integration of probiotics in clinical practice and ongoing research can contribute to reducing the incidence and severity of gastrointestinal disorders in pediatric patients.

The Salivary Microbiome and Predicted Metabolite Production Are Associated with Barrett's Esophagus and High-Grade Dysplasia or Adenocarcinoma

BACKGROUND

Esophageal adenocarcinoma (EAC) is rising in incidence, and established risk factors do not explain this trend. Esophageal microbiome alterations have been associated with Barrett's esophagus (BE) and dysplasia and EAC. The oral microbiome is tightly linked to the esophageal microbiome; this study aimed to identify salivary microbiome-related factors associated with BE, dysplasia, and EAC.

METHODS

Clinical data and oral health history were collected from patients with and without BE. The salivary microbiome was characterized, assessing differential relative abundance of taxa by 16S rRNA gene sequencing and associations between microbiome composition and clinical features. Microbiome metabolic modeling was used to predict metabolite production.

RESULTS

A total of 244 patients (125 non-BE and 119 BE) were analyzed. Patients with high-grade dysplasia (HGD)/EAC had a significantly higher prevalence of tooth loss (P = 0.001). There were significant shifts with increased dysbiosis associated with HGD/EAC, independent of tooth loss, with the largest shifts within the genus Streptococcus. Modeling predicted significant shifts in the microbiome metabolic capacities, including increases in L-lactic acid and decreases in butyric acid and L-tryptophan production in HGD/EAC.

CONCLUSIONS

Marked dysbiosis in the salivary microbiome is associated with HGD and EAC, with notable increases within the genus Streptococcus and accompanying changes in predicted metabolite production. Further work is warranted to identify the biological significance of these alterations and to validate metabolic shifts.

IMPACT

There is an association between oral dysbiosis and HGD/EAC. Further work is needed to establish the diagnostic, predictive, and causal potential of this relationship.

The Immunomodulatory Role of Microbiota in Rheumatic Heart Disease: What Do We Know and What Can We Learn from Other Rheumatic Diseases?

Rheumatic heart disease (RHD) represents a serious cardiac sequela of acute rheumatic fever, occurring in 30-45% of patients. RHD is multifactorial, with a strong familial predisposition and known environmental risk factors that drive loss of immunological tolerance. The gut and oral microbiome have recently been implicated in the pathogenesis of RHD. Disruption of the delicate balance of the microbiome, or dysbiosis, is thought to lead to autoimmune responses through several different mechanisms including molecular mimicry, epitope spreading, and bystander activation. However, data on the microbiomes of RHD patients are scarce. Therefore, in this comprehensive review, we explore the various dimensions of the intricate relationship between the microbiome and the immune system in RHD and other rheumatic diseases to explore the potential effect of microbiota on RHD and opportunities for diagnosis and treatment.

Celiac Disease: Disease Models in Understanding Pathogenesis and Search for Therapy

Celiac disease is a complex polygenic systemic disorder caused by dietary gluten exposure that selectively occurs in genetically susceptible people. The potential celiac disease is defined by the presence of celiac disease-specific antibodies and compatible human leukocyte antigen but without histological abnormalities in duodenal biopsies. At present, the only treatment is lifelong adherence to a gluten-free diet. Despite its effectiveness, the diet is difficult to maintain due to its cost, availability of gluten-free foods, and hidden gluten. The need to develop non-dietary treatment methods is widely recognized, but this is prevented by the absence of a pathophysiologically relevant preclinical model. Nonetheless, in vitro and in vivo models have made it possible to investigate the mechanisms of the disease and develop new treatment approaches: The use of foods with neutralized gluten, microbiota correction, cocktails of specific endoproteinase, polymer gluten binders, specific inhibitors of transglutaminases and inflammatory cytokines, and a vaccine based on allergen-specific therapy.

Pathophysiology and immunogenetics of celiac disease

Celiac disease (CD) is a chronic inflammatory enteropathy caused by gluten (protein from wheat, rye and, barley) in genetically predisposed individuals carrying the HLA-DQ2/HLA-DQ8 genotype. This pathology has a multifactorial etiology in which HLA genes, the microbiome, gluten and, other environmental factors are involved in the development of the disease. Its pathogenesis involves both innate and adaptive immunity as well as upregulation of IL-15. The objective of this review is to examine the results of current studies on genetic and environmental variables to better understand the pathogenesis of this enteropathy. The complex etiology of celiac disease makes our understanding of the pathogenesis of the disease incomplete, and a better knowledge of the many genetic and environmental components would help us better understand the pathophysiology of celiac disease.

Current guidelines for the management of celiac disease: A systematic review with comparative analysis

BACKGROUND

Wheat and other gluten-containing grains are widely consumed, providing approximately 50% of the caloric intake in both industrialised and developing countries. The widespread diffusion of gluten-containing diets has rapidly led to a sharp increase in celiac disease prevalence. This condition was thought to be very rare outside Europe and relatively ignored by health professionals and the global media. However, in recent years, the discovery of important diagnostic and pathogenic milestones has led to the emergence of celiac disease (CD) from obscurity to global prominence. These modifications have prompted experts worldwide to identify effective strategies for the diagnosis and follow-up of CD. Different scientific societies, mainly from Europe and America, have proposed guidelines based on CD's most recent evidence.

AIM

To identify the most recent scientific guidelines on CD, aiming to find and critically analyse the main differences.

METHODS

We performed a database search on PubMed selecting papers published between January 2010 and January 2021 in the English language. PubMed was lastly accessed on 1 March 2021.

RESULTS

We distinguished guidelines from 7 different scientific societies whose reputation is worldwide recognized and representative of the clinical practice in different geographical regions. Differences were noted in the possibility of a no-biopsy diagnosis, HLA testing, follow-up protocols, and procedures.

CONCLUSION

We found a relatively high concordance between the guidelines for CD. Important modifications have occurred in the last years, especially about the possibility of a no-biopsy diagnosis in children. Other modifications are expected in the next future and will probably involve the extension of the non-invasive diagnosis to the adult population and the follow-up modalities.

The Role of HLA in the Association between IgA Deficiency and Celiac Disease

Selective IgA deficiency (SIgAD) is the most frequent primary immune defect. Since SIgAD is not characterized by relevant infectious issues in most cases, it is often diagnosed during the diagnostic work up of several and different autoimmune disorders, which are associated with this primary immune defect. The genetic background of SIgAD is complex and three HLA haplotypes resulted to be more frequently associated with it; in detail, two of them include HLA-DQB1^∗02 allelic variants, which are essential predisposing factors to develop Celiac Disease (CD). Here, we discuss the evidence regarding the role of HLA in the etiopathogenesis of SIgAD and its association with CD. Actually, the HLA region seems to play a modest role in the genetic predisposition to SIgAD and we may speculate that the association with the HLA-DQB1^∗02 alleles (or haplotypes including them) could derive from its link with CD. Indeed, SIgAD and some related immunological alterations are likely to predispose to several autoimmune diseases (with and despite different HLA backgrounds), including CD, which is relatively common and directly associated with the HLA-DQB1^∗02 allelic variants coding the DQ2 heterodimer. Further and specific studies are needed to make final conclusions in this regard.

Salivary Microbiota Is Significantly Less Diverse in Patients with Chronic Spontaneous Urticaria Compared to Healthy Controls: Preliminary Results

Background: Because of the important role in regulating the immune system, increasing evidence suggests a possible implication of gut microbiota in Chronic spontaneous urticaria (CSU). Although the oral cavity is the first site of contact between microbiota and the immune system, the association between salivary microbiota and CSU has not yet been reported. Objective: This case-control study aimed to compare differences in salivary microbiota between CSU patients and healthy controls (HC). Twenty-three participants—13 patients with CSU and 10 HC were enrolled; salivary microbiota was determined by molecular approach targeting 16S ribosomal RNA. Terminal restriction fragment length polymorphism (T-RFLP) analysis was performed. Results: Alpha diversity of salivary microbiota in CSU patients was significantly reduced compared to HC, resulting in alteration of the community composition. Species richness determined via the Shannon index was significantly reduced in the CSU group. Conclusion: Dysbiosis of salivary microbiota may contribute to a dysregulated immune system in the development of CSU. To our knowledge, this was the first study that reported an alteration in salivary microbiota composition in CSU patients.

Comparison of Microbial Populations in Saliva and Feces from Healthy and Celiac Adolescents with Conventional and Molecular Approaches after Cultivation on Gluten-Containing Media: An Exploratory Study

Microbes capable of metabolizing gluten are common in various parts of the intestinal tract. In this study, saliva and fecal samples were obtained from 10 adolescents (13–18 years of age), five of which had celiac disease (CD) and five of which were healthy volunteers (HV). Culture-enriched saliva and fecal samples were compared with molecular profiling, and microorganisms displaying lysis zones on gluten-containing media (i.e., gluten-degrading microorganisms; GDMs) were isolated. In total, 45 gluten-degrading strains were isolated, belonging to 13 genera and 15 species, including Candida albicans and Veillonella. GDMs were more common in HVs compared to CD patients and more diverse in saliva compared to feces. In saliva, GDMs showed partial overlap between HVs and CD patients. Bacterial communities in fecal samples determined with amplicon sequencing significantly differed between CD patients and HVs. Overall, 7–46 of all operational taxonomic units (OTUs) per sample were below the detection limit in the fecal samples but were present in the cultivated samples, and mainly included representatives from Lactobacillus and Enterococcus. Furthermore, differences in fecal short-chain fatty-acid concentrations between CD patients and HVs, as well as their correlations with bacterial taxa, were demonstrated.

Manipulation of the gut microbiome in gluten-intolerance

PURPOSE OF REVIEW

Gluten is a complex mixture of highly immunogenic glutamine- and proline-rich proteins found in some cereals. In celiac disease (CeD), gluten triggers an autoimmune response due to its interaction with the human leukocyte antigen heterodimers that confer the genetic risk. The involvement of gluten in other disorders has also been investigated, but its role beyond CeD is still unclear. Here, we review the most recent evidence of the involvement of gluten in diseases and the opportunities of manipulating the gut microbiota to treat or prevent gluten-related conditions.

RECENT FINDINGS

Most of the new studies have been conducted in the context of CeD, where important evidence has been gained on associations between the gut microbiota, genotype, and environmental factors such as breastfeeding and antibiotics. The role of the microbiota has been investigated in several prospective, observational and interventional studies with probiotics, which together showed that the gut microbiota could be targeted to ameliorate and aid in the prevention of CeD development.

SUMMARY

Several studies have evidenced how genetic and environmental factors influence the gut microbiome with consequences in CeD. These findings could inspire the development of microbiota modulation strategies to support the prevention or treatment of CeD.