Conserved shifts in the gut microbiota due to gastric bypass reduce host weight and adiposity

Pathways in microbe-induced obesity

Diet, host gene composition, and alterations in the intestinal microbiota can contribute to obesity. In microbe-induced obesity, metabolic changes stem from primary perturbation of the microbiota, consequent to modern changes in human biology. Microbiota disruption during early development can result in syndromes of metabolic dysfunction. We focus on the pathways involved in these interactions, particularly related to energy extraction and the role of inflammation in the metabolic phenotypes. Model physiologic systems and perturbations including gastric bypass surgery, pregnancy, and hibernation provide insight into the respective roles of the critical participants.

The absence of a microbiota enhances TSLP expression in mice with defective skin barrier but does not affect the severity of their allergic inflammation

Evidence is accumulating to suggest that our indigenous microbial communities (microbiota) may play a role in modulating allergic and immune disorders of the skin (Gallo and Nakatsuji, 2011; Macia et al., 2012). To examine the link between the microbiota and atopic dermatitis, we examined a mouse model of defective cutaneous barrier function with an atopic dermatitis-like disease due to loss of Notch signaling. Comparisons of conventionally-raised (CONV-R) and germ-free (GF) mice revealed a similar degree of allergic skin inflammation, systemic atopy, and airway hypersensitivity. GF mutant animals expressed significantly higher levels of thymic stromal lymphopoietin (TSLP), a major proinflammatory cytokine released by skin with defective barrier function, resulting in a more severe B-lymphoproliferative disorder that persisted into adulthood. These findings suggest a role for the microbiota in ameliorating stress signals released by keratinocytes in response to perturbation in cutaneous barrier function.

Quantifying the metabolic activities of human-associated microbial communities across multiple ecological scales

Humans are home to complex microbial communities, whose aggregate genomes and their encoded metabolic activities are referred to as the human microbiome. Recently, researchers have begun to appreciate that different human body habitats and the activities of their resident microorganisms can be better understood in ecological terms, as a range of spatial scales encompassing single cells, guilds of microorganisms responsive to a similar substrate, microbial communities, body habitats, and host populations. However, the bulk of the work to date has focused on studies of culturable microorganisms in isolation or on DNA sequencing-based surveys of microbial diversity in small-to-moderate-sized cohorts of individuals. Here, we discuss recent work that highlights the potential for assessing the human microbiome at a range of spatial scales, and for developing novel techniques that bridge multiple levels: for example, through the combination of single-cell methods and metagenomic sequencing. These studies promise to not only provide a much-needed epidemiological and ecological context for mechanistic studies of culturable and genetically tractable microorganisms, but may also lead to the discovery of fundamental rules that govern the assembly and function of host-associated microbial communities.

Roux-en-Y gastric bypass normalizes the blunted postprandial bile acid excursion associated with obesity

BACKGROUND

Bile acids (BAs) are nutrient-responsive hormones that modulate energy balance through cell surface and nuclear receptors. Postprandial plasma BAs have been found to be decreased in obesity.

OBJECTIVE

We aimed to determine whether meal-stimulated circulating BA levels are altered by Roux-en-Y gastric bypass (RYGB), an operation that modifies the neurohumoral determinants of food intake and energy expenditure to cause significant and durable weight loss.

DESIGN

Longitudinal study measuring fasting and postprandial plasma BAs before and after RYGB.

SUBJECTS

Five obese surgical patients and eight lean controls underwent frequent blood sampling after a standard liquid meal. Obese subjects were also tested at 1, 4 and 40 weeks after RYGB. Primary and secondary circulating BAs, as well as their glycine and taurine conjugates, were measured via reverse-phase high-performance liquid chromatography/mass spectroscopy.

RESULTS

We found that postprandial excursion of conjugated BAs was 52.4% lower in obese than in lean individuals by area-under-the-curve (AUC) analysis (378 vs 793 μmol min l(-1), respectively, P<0.05). By 40 weeks after RYGB, the meal-induced rise in conjugated BAs increased by 55.5% to the level of healthy lean controls (378 pre-op vs 850 μmol min l(-) post-op by AUC analyses, P<0.05). In contrast, postprandial concentrations of unconjugated BAs were similar in lean and obese individuals and were not affected by surgery.

CONCLUSION

In light of the growing evidence that BAs have key roles in glucose, lipid and energy homeostasis, the observation that RYGB normalizes the blunted postprandial circulating BA response in obesity suggests that BAs may contribute to the improvement in meal-related physiology seen after RYGB. Further studies are warranted to examine this hypothesis and to determine the degree to which an augmented BA response to nutrient ingestion may mediate the increased incretin response, brown adipose tissue activation and thermic effect of feeding that has been observed after this operation.