How gut microbiota may impact ocular surface homeostasis and related disorders.

Changes in the bacterial flora in the gut, also described as gut microbiota, are readily acknowledged to be associated with several systemic diseases, especially those with an inflammatory, neuronal, psychological or hormonal factor involved in the pathogenesis and/or the perception of the disease. Maintaining ocular surface homeostasis is also based on all these four factors, and there is accumulating evidence in the literature on the relationship between gut microbiota and ocular surface diseases. The mechanisms involved are mostly interconnected due to the interaction of central and peripheral neuronal networks, inflammatory effectors and the hormonal system. A better understanding of the influence of the gut microbiota on the maintenance of ocular surface homeostasis, and on the onset or persistence of ocular surface disorders could bring new insights and help elucidate the epidemiology and pathology of ocular surface dynamics in health and disease. Revealing the exact nature of these associations could be of paramount importance for developing a holistic approach using highly promising new therapeutic strategies targeting ocular surface diseases.

Colorectal cancer, Vitamin D and microbiota: A double-blind Phase II randomized trial (ColoViD) in colorectal cancer patients.

BACKGROUND: Several studies suggest a role of gut microbiota in colorectal cancer (CRC) initiation and progression. Vitamin D (vitD) blood levels are also inversely correlated with CRC risk and prognosis. However, these factors' interplay remains unknown. METHODS: 74 CRC patients after standard treatment were randomized to 1-year 2000 IU/day vitD or placebo.  Baseline and post-treatment fecal microbiota for shotgun metagenomics sequencing was collected. Coda-lasso and Principal Component Analysis were used to select and summarize treatment-associated taxa and pathways. Associations between vitD and taxa/pathways were investigated with logistic regression. Mediation analysis was performed to study if treatment-associated taxa mediated the effect of supplementation on 25(OH)D levels. Cox proportional-hazards model was used for disease-free survival (DFS). RESULTS: 60 patients were analyzed. Change in alpha diversity (Shannon: p = 0.77; Simpson: p = 0.63) and post-treatment beta diversity (p = 0.70) were comparable between arms. Post-treatment abundances of 63 taxa and 32 pathways differed between arms. The 63 taxa also mediated the effect of supplementation on 25(OH)D (p = 0.02). There were sex differences in vitD levels, microbiota and pathways. Pathways of essential amino acids' biosynthesis were more abundant in supplemented women. Fusobacterium nucleatum presence at baseline was associated with worse DFS (p = 0.02). Those achieving vitD sufficiency (25(OH)D≥30 ng/ml) had lower post-treatment abundances (p = 0.05). Women were more likely to have F. nucleatum post-treatment (p = 0.02). CONCLUSIONS: VitD supplementation may contribute shaping the gut microbiota and the microbiota may partially mediate the effect of supplementation on 25(OH)D. The observed sex-specific differences highlight the necessity of including sex/gender as a variable in microbiome studies.

Can Postbiotics Represent a New Strategy for NEC?

Increasing evidence indicates that many of the health beneficial effects associated with the establishment of a symbiotic gut microbiota are driven by bacterial metabolic by-products.The term "postbiotics" indicates any soluble factor resulting from the metabolic activity of a live bacteria or any released molecule capable of providing health benefits through a direct or indirect mechanism.Alterations in preterm gut colonization associated with the intestinal barrier immaturity and the increased reactivity of the intestinal mucosa to colonizing bacteria have been implicated in the pathogenesis of necrotizing enterocolitis. Recent advances in the comprehension of the postbiotic biological effects and related mechanisms, some of them reviewed here, indicate that postbiotics may be a promising effective preventive strategy against necrotizing enterocolitis while avoiding the risk of administering live microorganisms to preterm infants that could translocate and cause infection. However, data from trials investigating the efficacy of postbiotics for the prevention of necrotizing enterocolitis in preterm infants are needed, and issues regarding their optimal regimen and start and duration of treatment need to be addressed.

Should probiotics be tested on ex vivo organ culture models?

The use of probiotic strains as nutritional supplements has been gaining ground in the last decade. As the mechanisms with which they modulate innate and adaptive immunity start to unravel, probiotics have repeatedly been suggested as potential treatment for a wide variety of diseases, including inflammatory bowel disease (IBD). However, even though the benefits of probiotic treatment for conditions like atopic dermatitis are well established, very limited clinical benefit has been obtained on IBD treatment. This could be due to the lack of suitable models on which to obtain valid pre-clinical data to select the most appropriate strain for a given condition. We recently described a newly developed model for the culture and apical stimulation of whole human intestinal mucosal explants. We showed that the tissue was only viable if incubated in an O(2) chamber, but it was possible to stimulate the tissue with bacteria in a conventional incubator. We used the new set-up to test three different Lactobacilli strains, none of which appeared to be benign on inflamed IBD mucosa.

Probiotic and postbiotic activity in health and disease: comparison on a novel polarised ex-vivo organ culture model.

BACKGROUND AND AIMS: Probiotics and their metabolic products, here called postbiotics, have been proposed as food supplements for a healthier intestinal homeostasis, but also as therapeutic aids in inflammatory bowel disease (IBD) with, however, very little clinical benefit. This may be due to the lack of reliable preclinical models for testing the efficacy of different strains. METHODS: The activity of three probiotic strains of Lactobacillus (or a postbiotic) was analysed and compared with a pathogenic strain of Salmonella on a novel organ culture system of human healthy and IBD intestinal mucosa developed in our laboratory. The system maintains an apical to basolateral polarity during stimulation due to the presence of a glued cave cylinder. The cylinder is detached at the end of the experiment and the tissue is processed for histology and immunohistochemistry. Cytokines released from the basolateral side are analysed. RESULTS: The model system provides several physiological characteristics typical of a mucosal microenvironment including the presence of an organised mucus layer and an apical to basolateral polarity. Polarised administration of bacteria is critical to control the ensuing immune response as it mimics the physiological entrance of bacteria. The authors show that probiotics are not always beneficial for the healthy host and can also be detrimental in inflamed IBD. This study shows that a potent postbiotic can protect against the inflammatory properties of invasive Salmonella on healthy tissue and also downregulate ongoing inflammatory processes in IBD tissue. CONCLUSIONS: Probiotics can have inflammatory activities in both healthy and IBD tissue. Valid preclinical data on proper model systems should therefore be obtained before specific probiotic strains enter the clinics, especially if administered during acute inflammatory responses. Postbiotics may be a safe alternative for the treatment of patients with IBD in the acute inflammatory phase.

Comparison of the immunomodulatory properties of three probiotic strains of Lactobacilli using complex culture systems: prediction for in vivo efficacy.

BACKGROUND: While the use of probiotics to treat or prevent inflammatory bowel disease (IBD) has been proposed, to this point the clinical benefits have been limited. In this report we analyzed the immunological activity of three strains of Lactobacillus to predict their in vivo efficacy in protecting against experimental colitis. METHODOLOGY/PRINCIPAL FINDINGS: We compared the immunological properties of Lactobacillus plantarum NCIMB8826, L. rhamnosus GG (LGG), L. paracasei B21060 and pathogenic Salmonella typhimurium (SL1344). We studied the stimulatory effects of these different strains upon dendritic cells (DCs) either directly by co-culture or indirectly via conditioning of an epithelial intermediary. Furthermore, we characterized the effects of these strains in vivo using a Dextran sulphate sodium (DSS) model of colitis. We found that the three strains exhibited different abilities to induce inflammatory cytokine production by DCs with L. plantarum being the most effective followed by LGG and L. paracasei. L. paracasei minimally induced the release of cytokines, while it also inhibited the potential of DCs to both produce inflammatory cytokines (IL-12 and TNF-alpha) and to drive Th1 T cells in response to Salmonella. This effect on DCs was found under both direct and indirect stimulatory conditions - i.e. mediated by epithelial cells - and was dependent upon an as yet unidentified soluble mediator. When tested in vivo, L. plantarum and LGG exacerbated the development of DSS-induced colitis and caused the death of treated mice, while, conversely L. paracasei was protective. CONCLUSIONS: We describe a new property of probiotics to either directly or indirectly inhibit DC activation by inflammatory bacteria. Moreover, some immunostimulatory probiotics not only failed to protect against colitis, they actually amplified the disease progression. In conclusion, caution must be exercised when choosing a probiotic strain to treat IBD.

The yin and yang of intestinal epithelial cells in controlling dendritic cell function.

Recent work suggests that dendritic cells (DCs) in mucosal tissues are "educated" by intestinal epithelial cells (IECs) to suppress inflammation and promote immunological tolerance. After attack by pathogenic microorganisms, however, "non-educated" DCs are recruited from nearby areas, such as the dome of Peyer's patches (PPs) and the blood, to initiate inflammation and the ensuing immune response to the invader. Differential epithelial cell (EC) responses to commensals and pathogens may control these two tolorogenic and immunogenic functions of DCs.