Prolonged antibiotic treatment induces a diabetogenic intestinal microbiome that accelerates diabetes in NOD mice.

Accumulating evidence supports that the intestinal microbiome is involved in Type 1 diabetes (T1D) pathogenesis through the gut-pancreas nexus. Our aim was to determine whether the intestinal microbiota in the non-obese diabetic (NOD) mouse model played a role in T1D through the gut. To examine the effect of the intestinal microbiota on T1D onset, we manipulated gut microbes by: (1) the fecal transplantation between non-obese diabetic (NOD) and resistant (NOR) mice and (2) the oral antibiotic and probiotic treatment of NOD mice. We monitored diabetes onset, quantified CD4+T cells in the Peyer's patches, profiled the microbiome and measured fecal short-chain fatty acids (SCFA). The gut microbiota from NOD mice harbored more pathobionts and fewer beneficial microbes in comparison with NOR mice. Fecal transplantation of NOD microbes induced insulitis in NOR hosts suggesting that the NOD microbiome is diabetogenic. Moreover, antibiotic exposure accelerated diabetes onset in NOD mice accompanied by increased T-helper type 1 (Th1) and reduced Th17 cells in the intestinal lymphoid tissues. The diabetogenic microbiome was characterized by a metagenome altered in several metabolic gene clusters. Furthermore, diabetes susceptibility correlated with reduced fecal SCFAs. In an attempt to correct the diabetogenic microbiome, we administered VLS#3 probiotics to NOD mice but found that VSL#3 colonized the intestine poorly and did not delay diabetes. We conclude that NOD mice harbor gut microbes that induce diabetes and that their diabetogenic microbiome can be amplified early in life through antibiotic exposure. Protective microbes like VSL#3 are insufficient to overcome the effects of a diabetogenic microbiome.

Diets rich in n-6 PUFA induce intestinal microbial dysbiosis in aged mice.

Controversies have emerged regarding the beneficial v. detrimental effects of dietary n-6 PUFA. The alteration of the intestinal microbiota, a phenomenon termed dysbiosis, occurs during several chronic inflammatory diseases, but has not been well studied in an aged population. With present 'Western' diets predominantly composed of n-6 PUFA, we hypothesised that PUFA-rich diets cause intestinal dysbiosis in an aged population. C57BL/6 mice (aged 2 years) were fed a high-fat (40% energy), isoenergetic and isonitrogenous diet composed of rapeseed oil, maize oil or maize oil supplemented with fish oil. We examined ileal microbiota using fluorescence in situ hybridisation and stained tissues by immunofluorescence for the presence of immune cells and oxidative stress. We observed that feeding high-fat diets rich in n-6 PUFA promoted bacterial overgrowth but depleted microbes from the Bacteroidetes and Firmicutes phyla. This corresponded with increased body mass and infiltration of macrophages and neutrophils. Fish oil supplementation (rich in long-chain n-3 PUFA like DHA and EPA) restored the microbiota and inflammatory cell infiltration and promoted regulatory T-cell recruitment. However, fish oil supplementation was associated with increased oxidative stress, evident by the increased presence of 4-hydroxynonenal, a product of lipid peroxidation. These results suggest that an n-6 PUFA-rich diet can cause dysbiosis and intestinal inflammation in aged mice. However, while fish oil supplementation on an n-6 PUFA diet reverses dysbiosis, the combination of n-6 and n-3 PUFA, like DHA/EPA, leads to increased oxidative stress, which could exacerbate gastrointestinal disorders in the elderly.