At the 7th edition of the latest Spanish Society of Probiotics and Prebiotics (SEPyP)’s annual workshop, which was held on Seville (Spain) on January, 28-29th under the theme: “Probiotics, Prebiotics and Health: Scientific Evidence”, Paula Crespo took the time to speak with GMFH editors.
Paula Crespo Escobar, B.Sc., is a dietitian-nutritionist working with the Coeliac Disease and Digestive Immunopathology Research Group, Department of Pediatric Gastroenterology and Hepatology, La Fe University and Polytechnic Hospital, in Valencia (Spain). Escobar has participated in several national and international projects related to coeliac disease, such as the “Celiac Disease Genomic Environmental Microbiome and Metabolic Study” (CDGEMM), “Environmental risk factors associated with coeliac disease and other autoimmune diseases in people with a genetic susceptibility”, and PREVENTCD (from “prevent coeliac disease”).
Several studies point toward alterations of gut microbiota composition and function in coeliac disease (CD). Should the gut microbiota be considered a novel player in CD?
CD is a chronic inflammatory enteropathy caused by gluten, which is the trigger, in genetically predisposed people that carry disease susceptibility genes (HLA DQ2 and/or DQ8). This genetic predisposition is present in about 30-40% of the general population, however, only a small percentage of carriers (2-5%) develop CD. Moreover, patients with CD can develop this loss of tolerance to gluten at any time during their life, suggesting that additional environmental or host factors contribute to disease development.
In the recent past, the increase prevalence of the CD was associated with three main environmental factors: the amount and the timing of gluten introduction into the infant diet, in addition to the protective effect of breastfeeding. However, two recent large randomized controlled trials aimed at studying this hypothesis have shown that, in high-risk children, the timing of gluten introduction –delayed or early– as well as the duration of breastfeeding did not modify the risk of CD. Once again, these findings suggested that additional environmental factors or host factors are needed to trigger the disease development.
Actually, the additional factors that influence CD development are still unknown but, certainly, emerging evidence suggests that the gut microbiota is a novel player in CD. Indeed, some recent studies have demonstrated that CD patients have an altered faecal and duodenal microbiota composition compared with healthy subjects. Although the majority of these studies have been conducted using different methods, small sample sizes and patients of varying ages, making difficult to compare the results, the majority of these have reported an increase in the proportion of Gram negative bacteria –Bacteroides and E. coli– and low levels of Bifidobacteria and Lactobacilli, which have a protective and anti-inflammatory effect. Moreover, other studies have shown that CD patients with gastrointestinal symptoms have different microbiota composition when compared with controls and patients with dermatitis hepetiformis, suggesting that the microbiota could also play a role in the manifestation of the disease.
Therefore, these new findings suggest that the disease is associated with intestinal ‘dysbiosis’ and the question now is whether this imbalance in the microbiota composition precedes and promotes the disease onset or is a consequence of the disease. The true pathogenic role of the gut microbiota in CD development is still unknown and we will have to wait for the results of ongoing and future studies that are trying to link the altered microbiota in genetically at-risk subjects to later CD development.
What is the current knowledge about the modulation of gut microbiota by exogenous factors in order to improve the development of oral tolerance to gluten?
The current knowledge indicates that diet is one of the main drivers of gut microbiota composition and function. Therefore, modifying the diet could be possible to induce oral tolerance to gluten. Then, the reasoning is that introducing a small amount of gluten into the infant diet during a certain timeframe will induce the oral tolerance to gluten. In this line, two previous studies tested this hypothesis showing that at this time, it is not possible to improve the development of oral tolerance to gluten through the early introduction of gluten. Thus, it suggests that if it is not possible to induce oral tolerance to gluten early in life during the infant’s immune system development, it is unlikely it could be later on.
Other exogenous factors that have been hypothesized to modify the gut microbiota composition and thus, could improve oral tolerance are: the composition of breast milk, the mode of delivery (vaginally or by caesarean section), the ingestion of antibiotics and vaccinations. By now, there are no studies that consistently confirm this hypothesis, but the recent findings are encouraging to believe that in the future the oral tolerance to gluten may improve.
What is the effect of maternal diet on the composition of infants’ gut microbiota and reduction of CD risk?
The first years of life are paramount in establishing our endogenous gut microbiota, which is strongly affected by diet, among other things. Usually, the first food that we ingest is the breast milk whose composition is influenced, in turn, by the mother’s diet. Moreover, it is well-known that the transition from early infant feeding to complementary foods is a major determinant for gut microbiota development.
However, very few studies have addressed the influence of maternal diet on infant gut microbiota and the impact on CD risk. A recent study has investigated in a very small sample size whether breast milk composition differs in healthy mothers and mothers with CD, trying to identify additional factors determining CD risk. The study concluded that breast milk in celiac mothers has lower levels of immunoprotective compounds and Bifidobacterias as compared to breast milk of healthy mothers. The reduction in these components could theoretically diminish the protective effects of breast feeding on the child’s future risk of developing CD.
Conversely, the two previously cited randomized controlled trials established that neither the type of breast feeding nor the duration have a protective effect in CD development. Another study analysed whether the genotype is an independent factor influencing the early gut microbiota composition of healthy infants who are at risk of CD. Despite the small sample size, the authors reported that the genotype of these genetically at-risk infants influenced the early gut microbiota composition, identifying a higher proportion of Firmicutes and Proteobacterias in HLA-DQ2 positive children. This may mean that our microbiota composition is partially determined before we are born and the maternal diet could have a minimal effect on it.
Be that as it may, more studies that address the real role of maternal diet in the composition of infants’ gut microbiota and in reducing CD risk are needed.
When it comes to introducing gluten into the infant diet in order to reduce a child’s subsequent risk of developing CD, what are the recommendations? Should research on the interactions between dietary gluten and the gut microbiota affect these recommendations?
The current recommendations regarding gluten introduction are the same since 2008, and they are based on classical and observational studies.
The European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) recommends that it is prudent to avoid both early (less than 4 months of age) and late (7 or more months of age) gluten introduction and to introduce gluten while the infant is still being breastfed. Furthermore, the American Academy of Pediatrics (AAP) also based its recommendations on the observational studies, recommending that complementary foods can be introduced while the infant is being breastfed, between 4 to 6 months of age, without mentioning gluten specifically.
Thus, without doubt, it is time to develop new nutritional recommendations based on the recent findings and the better understanding of CD.
Does the gluten-free diet (GFD) have a proven lasting effect in terms of contributing to a gut microbiota restoration in CD patients?
Several studies have compared the gut microbiota of CD patients following a GFD with controls but, unfortunately, very few studies have longitudinally evaluated the effect of GFD in the gut microbiota composition in the same population for a long time. To date, the majority of the studies available have reported an incomplete restoration of the gut microbiota after following a GFD for at least two years, showing a reduction in the diversity of Lactobacillus and Bifidobacterium species and less abundant bacterial richness as compared to healthy samples. However, there are some perturbations in the gut microbiota, which seem to be normalized after long-term adherence to a GFD. On the contrary, other studies conducted with different methods and in paediatric populations, showed no differences in duodenal-associated microbiota between CD patients on GFD and controls, observing high concentrations of Streptococcus, Lactobacillus and Clostridium in both groups.
The reason why the GFD allows only a partial recovery of the gut microbiota in CD patients is still unclear but the main hypothesis is that there is a genetic influence on microbiota composition in CD patients which persists after following a GFD; also, it has been hypothesized that since gluten has a prebiotic action due to the fructans which contains, its absence in a GFD induces a change in the microbiota composition as compared to healthy subjects. However, more specific long-term studies aiming at evaluate the real impact of GFD on the gut microbiota composition, are needed to confirm these findings.
Adherence to a GFD is necessary for gut mucosal tissue recovery, but does it guarantee mucosal recovery in adults with CD years after diagnosis?
Yes, if they have a strict adherence to a GFD. In most cases, the method of assessing GFD adherence during the follow-up is the evaluation of serum CD-associated antibodies and the assessment of clinical symptoms. However, these levels of antibodies often decrease regardless of histological healing and GFD adherence. Moreover, the clinical symptoms improve immediately after beginning the GFD whereas the full mucosa tissue recovery is slower, but the patient can achieve this restoration if he or she rigorously follows the diet.
It is important to highlight that the disappearance of clinical symptoms and antibody negativity are not always synonymous with adherence and the good histological response to GFD.
What are the most relevant studies assessing the efficacy of probiotics in the context of CD? Is there research to support the ability of probiotics to treat symptoms associated with CD? Which strain(s) could be the most beneficial?
The potential use of probiotics in CD management is supported by the demonstrated intestinal dysbiosis associated with the disease, suggesting the possibility that these beneficial bacteria can help in maintaining and recovering gut barrier function.
Although data regarding this issue are encouraging, to date most of these data come from in vitro experimental models of CD; only a few studies have been conducted on humans. The three main randomized, double-blind placebo-controlled human intervention trials have tested three different strains. The first one studied the effect of Bifidobacterium infantis Natren Life Start (NLS) strain on untreated CD patients. The results showed that the probiotics did not modify the gut barrier function, which was the primary endpoint, probably due to an insufficient dose or the short time of administration; it did not improve diarrhoea or abdominal pain, nor modify the pro-inflammatory status, but improved gastrointestinal symptoms (indigestion and constipation) without statistical significance. However, it is noticeable that authors achieved other important secondary endpoints after the administration of the B. infantis NLS. They observed a significant reduction in the concentration of IgA tTG and IgA DPG antibodies in the intervention group but not in the placebo group. Moreover, the B. infatins NLS group also reported a significant improvement in some symptoms such as indigestion, constipation and, in some cases, in reflux.
A similar study evaluated the effect of Bifidobacterium longum CECT 7347 for 3 months in addition to a GFD in children newly diagnosed with CD. The results revealed that the probiotic intake was associated with a greater height percentile, a decrease in the levels of Bacteroides fragilis group as well as a reduction of CD3 T cells and an improvement of gastrointestinal symptoms in CD patients.
The last trial also evaluated the effect of combining the strains Bifidobacterium breve BR03 and Bifidobacterium breve B632 as compared to placebo in children with CD on a GFD. The results showed that the strains of Bifidobacterium breve decreased the production of pro-inflammatory cytokines in CD children.
Finally, another interesting study but not randomized, identified a noteworthy lack of Lactobacilli in CD children without symptoms. Thus, the researchers isolated five different Lactobacilli in the stools of healthy children and proposed Lactobacilli rhamnosus and Lactobacilli paracasei as potential probiotic strains due to their high resistance to gastrointestinal tract conditions.
Despite the promising studies that have demonstrated that the use of probiotics can improve the symptoms associated with CD, we have to take into account that it has been also demonstrated that after a correct adherence to GFD, the levels of antibodies decrease, the clinical symptoms improve immediately and the mucosa tissue is recovered. Therefore, the evidence regarding the use of probiotics in patients with CD is still insufficient to justify their use in clinical practice, at least with the objective of being an alternative treatment to the GFD.
In conclusion, the awareness and understanding of CD has improved in the last decades; despite that, we are still far from fully understanding disease pathogenesis and all factors involved in the disease onset, development and progression. The recent studies are very positive but we still need more well-designed studies to start to fit all pieces of the CD puzzle together. We have to study CD from a holistic point of view and not as a combination of different independent factors.