The bacterial flora of α-Gal knockout mice express the α-Gal epitope comparable to wild type mice

A Review of Applied Aspects of Dealing with Gut Microbiota Impact on Rodent Models

The gut microbiota (GM) affects numerous human diseases, as well as rodent models for these. We will review this impact and summarize ways to handle this challenge in animal research. The GM is complex, with the largest fractions being the gram-positive phylum Firmicutes and the gram-negative phylum Bacteroidetes. Other important phyla are the gram-negative phyla Proteobacteria and Verrucomicrobia, and the gram-positive phylum Actinobacteria. GM members influence models for diseases, such as inflammatory bowel diseases, allergies, autoimmunity, cancer, and neuropsychiatric diseases. GM characterization of all individual animals and incorporation of their GM composition in data evaluation may therefore be considered in future protocols. Germfree isolator-housed rodents or rodents made virtually germ free by antibiotic cocktails can be used to study diverse microbial influences on disease expression. Through subsequent inoculation with selected strains or cocktails of microbes, new "defined flora" models can yield valuable knowledge on the impact of the GM, and of specific GM members and their interactions, on important disease phenotypes and mechanisms. Rodent husbandry and microbial quality assurance practices will be important to ensure and confirm appropriate and research relevant GM.

Faecal and caecal microbiota profiles of mice do not cluster in the same way

Polymerase chain reaction (PCR)-based denaturation gradient gel electrophoresis (DGGE) is currently being used for characterizing the composition of the gut microbiota (GM) of mice in order to better control the study variation arising from the GM. At present, faeces are commonly sampled from live animals, while caecum is most commonly sampled from terminated animals. However, there is no knowledge whether the composition at the one site is representative for the other. In this study C57BL/6 mice were observed from the age of four weeks until the age of 10 weeks. Faeces were sampled weekly. Caecum was sampled surgically under anaesthesia and with subsequent ampicillin treatment at the age of six weeks and again after euthanasia at the age of 10 weeks. Faecal and caecal microbiota profiles were determined using DGGE and subjected to subsequent cluster analysis. The mice subjected to surgical caecal sampling clustered separately for two weeks after termination of antibiotics after which they again clustered with the non-surgically sampled mice. Faecal and caecal profiles clustered separately at the age of six weeks, but not at the age of 10 weeks. There were no correlations between faecal or caecal profiles at six or 10 weeks of age, respectively. It is concluded that faecal and caecal microbiota profiles are not representative of each other in mice. Therefore, it is recommendable in studies to sample from several sites specifically decided in relation to the specific model of a study.

Anti-Gal titers in healthy adults and inflammatory bowel disease patients

INTRODUCTION

ALPHA-GAL is a glycoconjugate present on cell membranes of mammals and bacteria but not humans who display anti-Gal antibodies (AB) in high titers provoked by the commensal gut flora. In the present study, we sought to determine the longitudinal course of alpha-Gal specific AB titers of all isotypes over 8 weeks among healthy adult subjects. Furthermore, we hypothesized that inflammatory bowel disease (IBD) patients display increased anti-Gal titers.

MATERIALS AND METHODS

We drew serum from healthy probands (n=20) weekly for 8 weeks and obtained plasma samples of from patients suffering from Crohn's disease (n=20) and ulcerative colitis (n=20). We measured anti-Gal ABs of all isotypes and total immunoglobulin (Ig) content using an enzyme-linked immunosorbent assay technique. For statistical evaluation of the longitudinal titers, we calculated confidence intervals for the slopes of a random intercept model, comparing variances between and within the probands. For group comparisons, we performed paired student t-tests and Pearson correlations.

RESULTS

Alpha-Gal specific IgG, IgM, IgD, and IgA titers remained unvaried within a narrow range upon longitudinal observation. Most probands did not display alpha-Gal specific IgE ABs. Crohn's disease patients showed highly increased alpha-Gal-specific IgA titers compared with control subjects (P<.01).

CONCLUSION

Apart from IgE, alpha-Gal-specific ABs of all isotypes remained constant over longer time periods in healthy subjects. Thus, significant titer changes actually represent increased antigen exposure and a specific anti-alpha-Gal response. Crohn's disease patients display increased anti-Gal IgA titers compared with healthy controls, which reflects a chronically impaired mucosal gut barrier in this patient cohort.

Time to include the gut microbiota in the hygienic standardisation of laboratory rodents

The gut microbiota (GM) composition and its impact on animal experiments has become currently dramatically relevant in our days: (1) recent progress in metagenomic technologies, (2) the availability of large scale quantitative analyses to characterize even subtle phenotypes, (3) the limited diversity of laboratory rodent GM due to strict barriers at laboratory animal vendors, and (4) the availability of up to 300.000 different transgenic mouse strains from different sources displaying a huge variety in their GM composition. In this review the GM is described as a variable in animal experiments which need to be reduced for scientific as well as ethical reasons, and strategies how to implement this in routine diagnostic procedures are proposed. We conclude that we have both enough information available to state that the GM has an essential impact on animal models, as well as the methods available to start dealing with these impacts.

Manipulation of the gut microbiota in C57BL/6 mice changes glucose tolerance without affecting weight development and gut mucosal immunity

Inflammatory diseases such as type 2 diabetes (T2D) in humans and mice are under the influence of the composition of the gut microbiota (GM). It was previously demonstrated that treating Lep(ob) mice with antibiotics improved glucose tolerance. However, wild type C57BL/6J mice may also exhibit plasma glucose intolerance reminiscent of human T2D. We hypothesized that antibiotic treatment in C57BL/6 mice would have an impact on glucose tolerance without affecting weight and gut immunology. When compared to mice treated with erythromycin or the controls, treatment for five weeks with ampicillin improved glucose tolerance without significantly affecting the weight or the number of gut mucosal regulatory T cells, tolerogenic dendritic cells or T helper cells type 1. 16S rRNA gene based denaturing gradient gel electrophoresis profiles clearly clustered according to treatment and showed that antibiotic treatment reduced GM diversity. It is concluded that antibiotic treatment changes glucose metabolism as well as the composition of the GM in C57BL/6 mice, and that this does not seem to be correlated to weight development in the mice.

Glucose intolerance in a xenotransplantation model: studies in alpha-gal knockout mice

Xenotransplantation holds the promise of replacing failing human organs with organs of animal origin. Transplantation of pancreatic islets from pigs to humans might restore glucose homeostasis and offer diabetic patients considerable improvement in their quality of life. The alpha-gal epitope, present in all mammals except humans, apes and Old World monkeys, is a decisive obstruction to successful xenotransplantation of vascularized organs as the reaction of alpha-gal-bearing endothelia with natural alpha-gal antibodies in the human blood mediates hyperacute rejection of the xenograft. Alpha-galactosyl transferase knockout mice (alpha-GT KO) develop cataract, but no other lesions have been established in these mice. Here we report for the first time that alpha-GT KO mice have impaired glucose tolerance (p<0.001) and decreased insulin sensitivity (p<0.0001). Homeostasis model assessment shows impaired beta-cell function (p<0.05). Similar physiological changes have not been examined in the alpha-galactosyl transferase pig. However, an association between alpha-galactosyl transferase knockout and impaired beta-cell function could have critical importance for islet xenotransplantation.