Balfour R. Sartor

Gut microbiota induce IGF-1 and promote bone formation and growth

Significance New interventions are needed to improve bone health and reduce the risk for osteoporosis and fracture. Dysbiosis is increasingly linked to metabolic abnormalities, although the effect of the microbiota on skeletal health is poorly understood. Previous studies suggest microbiota are detrimental to bone by increasing resorption. In this report, we show that the gut resident microbiota promote bone formation, as well as resorption, with long-term exposure to microbiota resulting in net skeletal growth. Microbiota induce the hormone insulin-like growth factor 1 (IGF-1), which promotes bone growth and remodeling. Short-chain fatty acids (SCFAs), produced when microbiota ferment fiber, also induce IGF-1, suggesting a mechanism by which microbiota affect bone health. Manipulating the microbiome or its metabolites may afford opportunities to optimize bone health and growth. Appreciation of the role of the gut microbiome in regulating vertebrate metabolism has exploded recently. However, the effects of gut microbiota on skeletal growth and homeostasis have only recently begun to be explored. Here, we report that colonization of sexually mature germ-free (GF) mice with conventional specific pathogen-free (SPF) gut microbiota increases both bone formation and resorption, with the net effect of colonization varying with the duration of colonization. Although colonization of adult mice acutely reduces bone mass, in long-term colonized mice, an increase in bone formation and growth plate activity predominates, resulting in equalization of bone mass and increased longitudinal and radial bone growth. Serum levels of insulin-like growth factor 1 (IGF-1), a hormone with known actions on skeletal growth, are substantially increased in response to microbial colonization, with significant increases in liver and adipose tissue IGF-1 production. Antibiotic treatment of conventional mice, in contrast, decreases serum IGF-1 and inhibits bone formation. Supplementation of antibiotic-treated mice with short-chain fatty acids (SCFAs), products of microbial metabolism, restores IGF-1 and bone mass to levels seen in nonantibiotic-treated mice. Thus, SCFA production may be one mechanism by which microbiota increase serum IGF-1. Our study demonstrates that gut microbiota provide a net anabolic stimulus to the skeleton, which is likely mediated by IGF-1. Manipulation of the microbiome or its metabolites may afford opportunities to optimize bone health and growth.

Inflammation-associated adherent-invasive Escherichia coli are enriched in pathways for use of propanediol and iron and M-cell translocation.

Background:Perturbations of the intestinal microbiome, termed dysbiosis, are linked to intestinal inflammation. Isolation of adherent-invasive Escherichia coli (AIEC) from intestines of patients with Crohns disease (CD), dogs with granulomatous colitis, and mice with acute ileitis suggests these bacteria share pathoadaptive virulence factors that promote inflammation. Methods:To identify genes associated with AIEC, we sequenced the genomes of phylogenetically diverse AIEC strains isolated from people with CD (4), dogs with granulomatous colitis (2), and mice with ileitis (2) and 1 non-AIEC strain from CD ileum and compared them with 38 genome sequences of E. coli and Shigella. We then determined the prevalence of AIEC-associated genes in 49 E. coli strains from patients with CD and controls and correlated genotype with invasion of intestinal epithelial cells, persistence within macrophages, AIEC pathotype, and growth in standardized conditions. Results:Genes encoding propanediol utilization (pdu operon) and iron acquisition (yersiniabactin, chu operon) were overrepresented in AIEC relative to nonpathogenic E. coli. PduC (propanediol dehydratase) was enriched in CD-derived AIEC, correlated with increased cellular invasion, and persistence in vitro and was increasingly expressed in fucose-containing media. Growth of AIEC required iron, and the presence of chuA (heme acquisition) correlated with persistence in macrophages. CD-associated AIEC with lpfA154 (long polar fimbriae) demonstrated increased invasion of epithelial cells and translocation across M cells. Conclusions:Our findings provide novel insights into the genetic basis of the AIEC pathotype, supporting the concept that AIEC are equipped to exploit and promote intestinal inflammation and reveal potential targets for intervention against AIEC and inflammation-associated dysbiosis.

Development of an index to define overall disease severity in IBD

Background and aim Disease activity for Crohns disease (CD) and UC is typically defined based on symptoms at a moment in time, and ignores the long-term burden of disease. The aims of this study were to select the attributes determining overall disease severity, to rank the importance of and to score these individual attributes for both CD and UC. Methods Using a modified Delphi panel, 14 members of the International Organization for the Study of Inflammatory Bowel Diseases (IOIBD) selected the most important attributes related to IBD. Eighteen IOIBD members then completed a statistical exercise (conjoint analysis) to create a relative ranking of these attributes. Adjusted utilities were developed by creating proportions for each level within an attribute. Results For CD, 15.8% of overall disease severity was attributed to the presence of mucosal lesions, 10.9% to history of a fistula, 9.7% to history of abscess and 7.4% to history of intestinal resection. For UC, 18.1% of overall disease severity was attributed to mucosal lesions, followed by 14.0% for impact on daily activities, 11.2% C reactive protein and 10.1% for prior experience with biologics. Overall disease severity indices were created on a 100-point scale by applying each attributes average importance to the adjusted utilities. Conclusions Based on specialist opinion, overall CD severity was associated more with intestinal damage, in contrast to overall UC disease severity, which was more dependent on symptoms and impact on daily life. Once validated, disease severity indices may provide a useful tool for consistent assessment of overall disease severity in patients with IBD.

Systemic reactivation of otitis media with effusion in a rat model

OBJECTIVE: This study addresses the interaction of bacterial antigens, specifically peptidoglycan-polysaccharide (PG-PS) and lipopolysaccharide (LPS), in the induction and reactivation of mucoid middle ear effusions. METHODS: Twenty-seven rats underwent eustachian tube obstruction before inoculation of the middle ear bulla with PG-PS. Three weeks later, after resolution of all middle ear effusions, 6 rats were randomly selected and euthanized as the first control group (control I). The remaining 21 animals were randomly assigned to 3 groups that received intravenous injections of Krebs Ringer (control II), PG-PS, and LPS, respectively. These rats were euthanized 2 days after intravenous injection. Middle ear mucin production and histologic changes were measured in all animals. RESULTS: The mean concentrations of mucin were 0.94 ± 0.52 mg/mL, 0.41 ± 0.87 mg/mL, 16.33 ± 3.67 mg/mL, and 1.15 ± 0.41 mg/mL in the control I, control II, PG-PS, and LPS groups, respectively. Thus the mean concentration of mucin in the middle ear lavage samples was significantly greater in rats that were injected intravenously with PG-PS than in rats in other groups (P < 0.05). Histologic analyses demonstrated a greater degree of goblet cell hyperplasia in the PG-PS group than in other groups. CONCLUSIONS: This is the first animal model of recurring otitis media with effusion in which a systemic injection of PG-PS was used to reactivate a middle ear effusion in rats previously primed with a transtympanic injection of PG-PS. This study suggests that after otitis media with effusion has resolved, it may be reactivated by the presence of bacterial antigens and/or cytokines in the systemic circulation. (Otolaryngol Head Neck Surg 1999;121:7-12.)

An Animal Model for the Study of Genetic Predisposition in the Pathogenesis of Middle Ear Inflammation

Objectives Chronic otitis media with effusion (COME) is the most prevalent inflammatory disease in children and is associated with numerous adverse long‐term sequelae. Many factors have been associated with an increased risk of developing COME, one of which may be a genetic predisposition to the disease. To study the role that genetics play in the pathogenesis of COME, we used an animal model to compare the middle ear inflammatory responses in two different strains of rats (Lewis and Fisher).

The role of luminal bacteria in colitis: more than an antigenic drive

Recent studies provide compelling evidence that normal luminal bacteria are critically involved in the pathogenesis of experimental and clinical intestinal in ̄ammation [1,2]. For example, chronic colitis does not occur in germ-free (sterile) genetically engineered rats and mice [3±6], experimental intestinal in ̄ammation is attenuated by antibiotics, especially with anaerobic or broad spectra [7,8], and disease can be transferred by T lymphocytes reactive to luminal contents [9]. Similarly, the human idiopathic in ̄ammatory bowel diseases Crohn`s disease and ulcerative colitis respond to antibiotics [10,11], disease occurs in areas of highest bacterial concentrations, translocation of luminal bacteria and bacterial products is evident [12,13] and abnormally aggressive mucosal immune responses can be identi®ed to resident enteric bacteria [14,15]. Of considerable importance, not all indigenous luminal bacteria have equal capacities to induce in ̄ammation: some are aggressive, such as Bacteroides species in HLA B27 transgenic rats [4] and after direct injection of bacterial suspensions into the colonic wall of rats [16], some are neutral, such as Escherichia coli in HLA B27 transgenic rats [4]; and some are protective, such as Lactobacillus species in methotrexate-induced enterocolitis [17]. In this issue, GarciaLafuente and colleagues [18] provide further support for the in ̄uence of luminal bacteria in colitis by demonstrating that in ̄ammation induced by trinitrobenzene sulphonic acid (TNBS) is more aggressive in diverted colonic segments selectively colonized with six common enteric bacteria, including two Bacteroides strains, than in segments sterilized with vancomycin and imipenem. Despite the conclusive evidence that resident luminal bacteria contribute to intestinal in ̄ammation, the mechanisms by which normal enteric ̄ora induce and perpetuate the in ̄ammatory response remain uncertain. Several mechanisms have been proposed (Table 1), with the majority of evidence supporting direct stimulation of lamina propria macrophages, neutrophils and CD4 T lymphocytes by bacterial cell wall polymers [19], chemotactic peptides [20] and peptide antigens [9,21]. In addition to supporting this concept by demonstrating a greater degree of submucosal in ̄ammation in the bypassed colons of rats colonized with bacteria rather than those with sterile segments exposed to both TNBS and trinitrophenol (TNP), Garcia-Lafuente et al. [18] suggest that short-term bacterial colonization enhances colonic mucosal permeability to hydrophilic luminal compounds, thereby providing an additional mechanism of bacteria-induced injury. This study demonstrates that lumen to blood uptake of TNBS, a hydrophilic compound, is enhanced in the recolonized segment compared with the sterile segment, although transport of hydrophobic TNP is only minimally affected by bacterial colonization. Although bacterial alteration of TNBS resulting in enhanced absorptive properties is not conclusively excluded, there is no indication of altered migration of absorbed TNBS by HPLC. The authors postulate that increased mucosal permeability induced by luminal bacteria leads to enhanced exposure of epithelial cells and lamina propria effector cells to toxic TNBS, explaining the more extensive mucosal ulceration and eicosanoid secretion after bacterial colonization. In more physiological circumstances, bacterial enhancement of mucosal permeability could have important proin ̄ammatory consequences, such as accelerating the uptake of a number of phlogistic luminal compounds, including bacterial products [9,22] and dietary antigens [23]. This series of events could help explain the almost immediate in ̄ammation that develops in the bypassed ileum of Crohn`s disease patients after infusion of ileal luminal ef ̄uents [24]. Luminal bacteria can affect barrier function in a number of ways, each leading to the derangements observed by Garcia-Lafuente et al. [18]. Primary events include production of cytotoxins by certain E. coli [25,26], and Bacteroides fragilis [27] strains, mucin-degrading enzymes of Bacteroides vulgatus and enterococci [28], hyaluronidase by enterococci [29], and hydrogen sulphide by sulphatereducing anaerobes that blocks metabolism of short-chain fatty acids by colonic epithelial cells [30]. Whether the six bacterial species (which included Bacteroides strains and enterococci) used to colonize the bypassed colonic segment in Garcia-Lafuentes study can directly injure epithelial cells, degrade mucus, or destroy the basement membrane by these mechanisms remains to be determined. Potential secondary means of altering mucosal permeability are stimulation of chemokine production by epithelial cells in

Looking beyond symptoms and disease activity to define disease severity in inflammatory bowel disease: results of an IOIBD specialist panel

Looking beyond symptoms and disease activity to define disease severity in inflammatory bowel disease : results of an IOIBD specialist panel