“You should never assume. You know what happens when you assume. You make an ass out of you and me because that’s how it’s spelled.”
–Attributed to multiple individuals (but I heard this first when I watched Bad News Bears as a kid)
The increasing frequency of many conditions like inflammatory bowel disease cannot be explained by our genetics. The search for environmental triggers are ongoing. Broadly, the main suspects are dietary, antimicrobials, and pollutants. (Related blog post: Nutrition Week (Day 7) Connecting Epidemiology and Diet in Inflammatory Bowel Disease)
The latest concern is now Splenda:
“The Artificial Sweetener Splenda Promotes Gut Proteobacteria, Dysbiosis, and Myeloperoxidasse Reactivity in Crohn’s Disease-Like Ileitis” A Rodriguez-Palacios et al. Inflamm Bowel Dis 2018; 24: 1005-20. Editorial 1055-6 by B Chassaing and AT Gewirtz.
This highly technical study involved research in ileitis-prone SAMP mice and includes a huge amount of data and cool figures.
The authors note in their discussion: “The term ‘Western diets’ implies a proven shift of the microbiota that enhances the susceptibility to adherent-invasive E coli infections and intestinal inflammation in mice. In this study, we report similar findings due solely to the administration of a minor component of the diet.”
Some of the key points in the editorial:
- IBD has multigenic influences and “results from a general breakdown in the normally mutually-beneficial relationship between the intestine and the complex microbial community it harbors.”
- “New findings …that Splenda promotes microbiota dysbiosis in mice and exacerbates a hallmark of inflammation in ileitis-prone SAMP mice suggest that consumption of this synthetic sweetener may be a specific factor that contributes to development of IBD in persons genetically prone to this disorder.”
- Splenda has two main components: sucralose (sweetener) and maltodextrin (filler)
- Splenda did not “impact inflammatory markers in control mice, but rather increased such parameters in SAMP mice.”
- Splenda changed the microbiota in both control mice and SAMP mice, “particularly enrichment of gamma Proteobacteria, which are broadly associated with gut inflammatory diseases.”
- “Splenda may be relatively safe for the majority of the population but still represents a serious risk factor for those prone to developing IBD or other chronic inflammatory diseases.”
- Substances like sucralose which are primarily excreted in the feces (nonabsorbed) have generally been viewed as harmless. “Appreciation of the pivotal role of the microbiota in health questions the latter assumption.”
My take: I think the influences on the microbiota are difficult to tease out. Thus, this study (in mice) indicates —don’t assume that nonabsorbed agents are harmless
A recent study (SH Wong et al. Gastroenterol 2017; 153: 1621-33) highlights the potential role of the microbiota and colorectal cancer (CRC).
In this study, the stool from either patients with CRC or control patients was gavaged into mice twice a week for 5 weeks. One group of mice had received azoxymethane (AOM) which induces neoplasia and the other group were germ-free mice. Extensive studies involving immunohistochemistry, expresssion microarray, quantitative polymerase chain reaction, immunoblot, and flow cytometry.
- Conventional, AOM-treated mice who received gavage from patients with CRC had significantly higher proportions of high-grade dysplasia (P<.05) and macroscopic polyps (P<.01)
- Among the germ-free mice fed with stool from patients with CRC, there was a higher proportion of proliferating Ki-67-positve cells
- These findings correlated with more dysbiosis in the mice who received stool from patients with CRC and with upregulation of genes involved in cell proliferation, stemness, apoptosis, angiogenesis, and invasiveness
“This study provides evidence that the fecal microbiota from patients with CRC can promote tumorigenesis in germ-free mice and mice given a carcinogen.”
My take: This study shows that microbiota clearly influence the risk of CRC. I infer from this study that this could explain the potential healthy roles of diets with more fruits and vegetables, that promote healthier microbiota as well as the potential detrimental role of diets with more processed meats.
Related study: L Liu et al. Association between Inflammatory Diet Pattern and Risk of Colorectal Carcinoma Subtypes Classified by Immune Responses to Tumor Gastroenterol 2017; 153 1517-30. Using two databases from 2 prospective cohorts with followup of 124,433 participants, inflammatory diets had a higher risk of a colorectal cancer subtype.
Related blog posts:
Bright Angel Trail
A concise review (NJEM 2014; 371: 2526-28) quickly describes the latest science on microbiota, antibiotics, and obesity chiefly by summarizing the work of Cox LM et al (Cell 2014; 158: 705-21).
- In mice, studies have shown that low-dose penicillin in early life induces marked effects on body composition (eg. excessive weight gain) lasting into adulthood
- Prenatally administered penicillin to the mother and high-fat diet also induced fat mass of male mice.
- Gut microbiota transferred from penicillin-moderated flora mice (at 18 weeks) into the cecums of 3-week-old germ-free mice also resulted in excessive fat mass compared to controls who received gut microbiota transfer from control mice (who did not receive penicillin).
- “These results suggest that immunologic and metabolic changes are not caused by direct effects of antibiotics but rather by derived changes in the gut microbiota.”
- “It may even be speculated that in families in which obesity is a problem, specific antibiotic treatment at birth could reverse the adverse effect of obesogenic microbiota transferred from mother to infant during delivery.”
Take-home message: Understanding the microbes in our bodies may lead to much more than curing intestinal infections and intestinal maladies.
Related blog posts:
A recent study (J Pediatr 2014; 165: 23-9) confirmed the obvious: “early empiric antibiotic use in preterm infants is associated with lower bacterial diversity.” That being said, you still need the data and the specific changes are of importance.
This study examined the stools from 74 preterm infants (≤32 weeks gestational age) and determined how the microbiota changed in relation to no antibiotics (18% of cohort), brief antibiotics (1-4 days) (64% of cohort), or ‘intensive’ antibiotics (5-7 days) (18% of cohort). Empiric antibiotics consisted of ampicillin and gentamicin. Stools were analyzed with the 16s ribosomal DNA community profiling.
The key findings are graphically shown in Figure 1 with pie charts showing the relative abundance of 10 bacterial genera at week 1, week 2, and week 3 in each of the three groups.
- Those who received 5-7 days of antibiotics had the most changes in their microbiota with increased Enterobacter and lower bacterial diversity in the second and third weeks of life.
- In those who received no empiric antibiotics there was increasing bacterial diversity noted sequentially. These changes were not seen in either of the antibiotic groups. However, the group with brief antibiotic exposure returned to their baseline diversity by week 3.
- Infants receiving early antibiotics experienced more cases of necrotizing enterocolitis, sepsis and death than those who were not exposed to antibiotics (this was not proven to be casually-related).
Take-home message: This study proves that antibiotics change the microbiome in neonates and that neonates exposed to antibiotics may have complications as a result. Better biomarkers (with rapid turn around time) would allow more careful selection of which neonates need empiric antibiotics.
Related blog posts:
A recent study identifies a new biomarker for Crohn’s disease (CD) (Inflamm Bowel Dis 2014; 20: 1037-48).
The authors examined a cohort of 208 newly diagnosed pediatric CD and 43 non-IBD controls for ileal/rectal expression of FcγRIA mRNA. In addition, in a smaller cohort of 26 newly diagnosed CD patients, 83 established CD patients and 30 non-IBD controls the authors measured peripheral blood polymorphonuclear neutrophil (PMN) CD64 index.
- Ileal FcγRIA mRNA expression was significantly elevated in CD compared with non-IBD controls
- PMN CD64 was significantly elevated in CD compared with non-IBD controls and correlated with mucosal injury as measured by the simple endoscopic score for CD.
- Patients in clinical remission with a PMN CD64 <1 had a high rate of sustained remission (95%) whereas only 56% had sustained remission if PMN CD64 was >1.
Take-home point: This study shows in pediatrics, as in adults IBD patients, that PMN CD64 index is associated with mucosal inflammation; high levels are associated with clinical relapse. Serum biomarkers are likely to complement stool biomarkers like fecal calprotectin.
One other point the authors make: “studies have found that 57% to 59% of CD have concurrent IBS.” Thus, there is a need for biomarkers to distinguish whether patients with clinical symptoms are experiencing an inflammatory relapse.
Related blog post: Calprotectin: Part of diagnostic algorithm for IBD …
Two other studies in same issue:
“Alterations in the Intestinal Microbiome (Dysbiosis) as a Predictor of Relapse After Infliximab Withdrawal in Crohn’s disease” pages 978-86. N=33 CD patients. Key finding: “CD-associated dysbiosis, characterized by a decrease in Firmicutes, correlates with the time-to-relapse after infliximab withdrawal.”
“Tissue Studies in Screened First-degree Relatives Reveal a Distinct Crohn’s Disease Phenotype” pages 1049-56. N=38 asymptomatic relatives. Key finding: based on histologic scoring 61% were normal, 26% had minor lesions, and 13% had evidence of active disease. This study indicates that screening relatives may identify a subset with early biologic disease.
A recent editorial (NEJM 2013; 368: 1647-49) helps explain the link between diet, genes, and gut microbes. This editorial places in context a study, NEJM 2013; 368: 1575-84). “The investigators found than dietary choline is metabolized by gut microbes to trimethylamine (TMA), which in turn is absorbed into the host bloodstream and metabolized in the liver to trimethylamine-N-oxide (TMAO).” TMAO is thought to promote atherogenesis.
The study involved two phases. In the first, using mass spectrometry, before and after suppression of gut microbes with antibiotics, they showed that a phosphatidylcholine challenge increased all choline metabolites; however, antibiotic use suppressed the formation of TMAO.
In the second phase, they looked at fasting plasma TMAO in relation to cardiovascular events in more than 4000 participants who underwent elective coronary angiography. They identified an “independent, dose-dependent relationship between TMAO and the risk of a cardiovascular event.”
TMAO levels depend on the interaction between gut microbial production of TMAO which is affected by diet and by host genetic factors. The genetic factors are related to flavin-containing monooxygenases (FMO1 and FMO3); these enzymes oxidize TMA to TMAO are vary significantly in mice (and probably humans). With regard to diet, by limiting choline-rich foods (see links below regarding choline-rich foods) or by using probiotics, this may limit TMAO production and lower the risk of heart disease.
While these observations are intriguing, the mechanisms of TMAO in causing atherosclerosis and its primary function are unknown and much more information is needed to truly make these findings useful. It is possible that TMAO is simply a biomarker of other factors.
One aside, the editorial states that our gut microbes contain “at least 100 times as many genes as our own genome.”
Take-home message: TMAO is a new potentially modifiable risk factor for atherosclerotic disease.
Related blog links:
Other related links:
Maybe your mother was right –you should eat your vegetables! For a long time, it has been known that dietary changes can be used to treat Crohn’s disease. The specifics about what type of diet and the reasons for how diet promotes a healthy gastrointestinal tract are being unraveled. A person’s diet affects their microbiome; and, a number of recent articles have highlighted the microbiome in both functional and nonfunctional disorders (see below).
An even more fascinating article is in last week’s New England Journal of Medicine (NEJM 2012; 366: 181). This article discusses two publications which show how certain dietary components interact with intestinal immune receptors.
- Kiss EA et al. Science 2011 October 27 (Epub ahead of print).
- Li Y et al. Cell 2011; 147: 629-40.
This NEJM article implicates a typical ‘Western’ diet as a contributor to inflammatory bowel disease (IBD). However, a diet high in vegetables may prevent or reduce inflammation. One mechanism whereby vegetables affect the GI tract is through the AhR (aryl hydrocarbon) receptor. Some vegetables, like broccoli, cabbage, and brussel sprouts, are natural ligands for this receptor. A mouse model has shown that AhR deficiency “results in increased epithelial vulnerability, immune activation, and altered composition of the microbiota.” In addition, AhR is down-regulated in the intestinal tissue of persons with IBD. AhR ligands are associated with increased interleukin-22 which promotes intestinal integrity.
Additional work regarding the optimal diet are ongoing. There has been an interest in a ‘carbohydrate specific diet.’ This year’s NASPGHAN meeting (abstract #48) presented data on this diet from a retrospective study. This poster described five patients on monotherapy (diet alone) and at 6 months –good results in four patients (80%). A few prospective studies are underway; in fact, a prospective study with patients from our office will be presented at this year’s DDW. Initial results look promising (personal communication from lead investigator, Stan Cohen).
- -Gastroenterology 2010; 139: 1816, 1844. Microbiome & affect on IBD vs mucosal homeostasis.
- -J Pediatr 2010; 157: 240. Microbiota in pediatric IBD -increased E coli and decreased F praunsitzil in IBD pts.
- -Gastro 2011; 141: 28, 208. GM-CSF receptor (CD116) defective expression & function in 85% of IBD pts. n=52.
- -Scand J Gastro 2001; 36: 383-8. Elemental & polymeric diets successful in maintaining remission in ~43% of adults with complete steroid withdrawal.
- -Clin Gastro & Hepatology 2006; 4: 744. 10 weeks of exclusive modulen (along with clears) had 79% response rate (n=37). Better histologic response than steroids.
- -J Pediatr 2000; 136: 285. Nutritional treatment w polymeric diet is effective w/in 8 weeks in 32/37.
- -JPGN 2000; 31: 3 & 8. EN about as effective as steroids for primary Rx.
- -Can J Gastroenterol 1998; 12(8):544-49. Patients, diets and preferences in
a pediatric population with Crohn’s disease.
- -Gastroenterology 1988; 94:603-610. Chronic intermittent elemental diet improves growth failure in children with Crohn’s disease.
- -JPGN 1989; 8:8-12. Nutritional support for pediatric patients with inflammatory bowel disease.
- -J Pediatr 2000; 136: 285-91. The role of nutrition in treating pediatric Crohn’s disease in the new millennium.