Selective increases of bifidobacteria in gut microflora improve high-fat-diet-induced diabetes in mice through a mechanism associated with endotoxaemia

Role of the gut microbiota in defining human health

The human superorganism is a conglomerate of mammalian and microbial cells, with the latter estimated to outnumber the former by ten to one and the microbial genetic repertoire (microbiome) to be approximately 100-times greater than that of the human host. Given the ability of the immune response to rapidly counter infectious agents, it is striking that such a large density of microbes can exist in a state of synergy within the human host. This is particularly true of the distal gastrointestinal (GI) tract, which houses up to 1000 distinct bacterial species and an estimated excess of 1 x 10(14) microorganisms. An ever-increasing body of evidence implicates the GI microbiota in defining states of health and disease. Here, we review the literature in adult and pediatric GI microbiome studies, the emerging links between microbial community structure, function, infection and disease, and the approaches to manipulate this crucial ecosystem to improve host health.

Host-microbial symbiosis in the vertebrate gastrointestinal tract and the Lactobacillus reuteri paradigm

Vertebrates engage in symbiotic associations with vast and complex microbial communities that colonize their gastrointestinal tracts. Recent advances have provided mechanistic insight into the important contributions of the gut microbiome to vertebrate biology, but questions remain about the evolutionary processes that have shaped symbiotic interactions in the gut and the consequences that arise for both the microbes and the host. Here we discuss the biological principles that underlie microbial symbiosis in the vertebrate gut and the potential of the development of mutualism. We then review phylogenetic and experimental studies on the vertebrate symbiont Lactobacillus reuteri that have provided novel insight into the ecological and evolutionary strategy of a gut microbe and its relationship with the host. We argue that a mechanistic understanding of the microbial symbiosis in the vertebrate gut and its evolution will be important to determine how this relationship can go awry, and it may reveal possibilities by which the gut microbiome can be manipulated to support health.

Gut microbiota in obesity and metabolic disorders

Obesity is a major public health issue as it is causally related to several chronic disorders, including type-2 diabetes, CVD and cancer. Novel research shows that the gut microbiota is involved in obesity and metabolic disorders, revealing that obese animal and human subjects have alterations in the composition of the gut microbiota compared to their lean counterparts. Moreover, transplantation of the microbiota of either obese or lean mice influences body weight in the germ-free recipient mice, suggesting that the gut ecosystem is a relevant target for weight management. Indigenous gut microbes may regulate body weight by influencing the host's metabolic, neuroendocrine and immune functions. The intestinal microbiota, as a whole, provides additional metabolic functions and regulates the host's gene expression, improving the ability to extract and store energy from the diet and contributing to body-weight gain. Imbalances in the gut microbiota and increases in plasma lipopolysaccharide may also act as inflammatory factors related to the development of atherosclerosis, insulin resistance and body-weight gain. In contrast, specific probiotics, prebiotics and related metabolites might exert beneficial effects on lipid and glucose metabolism, the production of satiety peptides and the inflammatory tone related to obesity and associated metabolic disorders. This knowledge is contributing to our understanding of how environmental factors influence obesity and associated diseases, providing new opportunities to design improved dietary intervention strategies to manage these disorders.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: the normal gut microbiota in health and disease

Mammals are metagenomic, in that they are composed not only of their own genome but also those of all of their associated microbes (microbiome). Individual variations in the microbiome influence host health and may be implicated in disease aetiology. Therefore, it is not surprising that decreased microbial diversity is associated with both obesity and inflammatory bowel disease. Studies in germ-free mice have demonstrated that the gut microbiota is required for development of diet-induced obesity as well as inflammatory diseases. However, the underlying molecular mechanism(s) for how the gut microbiota causes metabolic diseases is only beginning to be clarified. Furthermore, emerging data suggest that the gut microbiota may predispose or protect against other important diseases such as cardiovascular disease and diabetes.

Adapting functional genomic tools to metagenomic analyses: investigating the role of gut bacteria in relation to obesity

With the expanding availability of sequencing technologies, research previously centered on the human genome can now afford to include the study of humans' internal ecosystem (human microbiome). Given the scale of the data involved in this metagenomic research (two orders of magnitude larger than the human genome) and their importance in relation to human health, it is crucial to guarantee (along with the appropriate data collection and taxonomy) proper tools for data analysis. We propose to adapt the approaches defined for the analysis of gene-expression microarray in order to infer information in metagenomics. In particular, we applied SAM, a broadly used tool for the identification of differentially expressed genes among different samples classes, to a reported dataset on a research model with mice of two genotypes (a high density lipoprotein knockout mouse and its wild-type counterpart). The data contain two different diets (high-fat or normal-chow) to ensure the onset of obesity, prodrome of metabolic syndromes (MS). By using 16S rRNA gene as a genomic diversity marker, we illustrate how this approach can identify bacterial populations differentially enriched among different genetic and dietary conditions of the host. This approach faithfully reproduces highly-relevant results from phylogenetic and standard statistical analyses, used to explain the role of the gut microbiome in relation to obesity. This represents a promising proof-of-principle for using functional genomic approaches in the fast growing area of metagenomics, and warrants the availability of a large body of thoroughly tested and theoretically sound methodologies to this exciting new field.

Absence of intestinal microbiota does not protect mice from diet-induced obesity

The gut microbiota has been implicated in host nutrient absorption and energy homeostasis. We studied the influence of different diets on body composition in germ-free (GF) and conventional (CV) mice. GF and CV male adult C3H mice were fed ad libitum a semi-synthetic low-fat diet (LFD; carbohydrate-protein-fat ratio: 41:42:17; 19.8 kJ/g), a high-fat diet (HFD; 41:16:43; 21.4 kJ/g) or a commercial Western diet (WD; 41:19:41; 21.5 kJ/g). There was no difference in body weight gain between GF and CV mice on the LFD. On the HFD, GF mice gained more body weight and body fat than CV mice, and had lower energy expenditure. GF mice on the WD gained significantly less body fat than GF mice on the HFD. GF mice on both HFD and WD showed increased intestinal mRNA expression of fasting-induced adipose factor/angiopoietin-like protein 4 (Fiaf/Angptl4), but they showed no major changes in circulating Fiaf/Angptl4 compared with CV mice. The faecal microbiota composition of the CV mice differed between diets: the proportion of Firmicutes increased on both HFD and WD at the expense of the Bacteroidetes. This increase in the Firmicutes was mainly due to the proliferation of one family within this phylum: the Erysipelotrichaceae. We conclude that the absence of gut microbiota does not provide a general protection from diet-induced obesity, that intestinal production of Fiaf/Angptl4 does not play a causal role in gut microbiota-mediated effects on fat storage and that diet composition affects gut microbial composition to larger extent than previously thought.

Complex links between dietary lipids, endogenous endotoxins and metabolic inflammation

Metabolic diseases such as obesity are characterized by a subclinical inflammatory state that contributes to the development of insulin resistance and atherosclerosis. Recent reports also indicate that (i) there are alterations of the intestinal microbiota in metabolic diseases and (ii) absorption of endogenous endotoxins (namely lipopolysaccharides, LPS) can occur, particularly during the digestion of lipids. The aim of the present review is to highlight recently gained knowledge regarding the links between high fat diets, lipid digestion, intestinal microbiota and metabolic endotoxemia & inflammation.

A human volunteer study to assess the impact of confectionery sweeteners on the gut microbiota composition

Sweeteners are being sourced to lower the energetic value of confectionery including chocolates. Some, especially non-digestible carbohydrates, may possess other benefits for human health upon their fermentation by the colonic microbiota. The present study assessed non-digestible carbohydrate sweeteners, selected for use in low-energy chocolates, for their ability to beneficially modulate faecal bacterial profiles in human volunteers. Forty volunteers consumed a test chocolate (low-energy or experimental chocolate) containing 22·8 g of maltitol (MTL), MTL and polydextrose (PDX), or MTL and resistant starch for fourteen consecutive days. The dose of the test chocolates was doubled every 2 weeks over a 6-week period. Numbers of faecal bifidobacteria significantly increased with all the three test treatments. Chocolate containing the PDX blend also significantly increased faecal lactobacilli (P = 0·00 001) after the 6 weeks. The PDX blend also showed significant increases in faecal propionate and butyrate (P = 0·002 and 0·006, respectively). All the test chocolates were well tolerated with no significant change in bowel habit or intestinal symptoms even at a daily dose of 45·6 g of non-digestible carbohydrate sweetener. This is of importance not only for giving manufacturers a sugar replacement that can reduce energetic content, but also for providing a well-tolerated means of delivering high levels of non-digestible carbohydrates into the colon, bringing about improvements in the biomarkers of gut health.

Resistant starch improves insulin sensitivity in metabolic syndrome

AIMS

Diets rich in non-viscous fibre are linked to a reduced risk of both diabetes and cardiovascular disease; however, the mechanism of action remains unclear. This study was undertaken to assess whether chronic consumption of this type of fibre in individuals with the metabolic syndrome would improve insulin sensitivity via changes in ectopic fat storage.

METHODS

The study was a single-blind, randomized, parallel nutritional intervention where 20 insulin resistant subjects consumed either the fibre supplement (resistant starch) (40 g/day) or placebo supplement (0 g/day) for 12 weeks. Insulin sensitivity was measured by euglycaemic-hyperinsulinaemic clamp and ectopic fat storage measured by whole-body magnetic resonance spectroscopy.

RESULTS

Resistant starch consumption did not significantly affect body weight, fat storage in muscle, liver or visceral depots. There was also no change with resistant starch feeding on vascular function or markers of inflammation. However, in subjects randomized to consume the resistant starch, insulin sensitivity improved compared with the placebo group (P = 0.023). Insulin sensitivity correlated significantly with changes in waist circumference and fat storage in tibialis muscle and to a lesser extent to visceral-to-subcutaneous abdominal adipose tissue ratio.

CONCLUSION

Consumption of resistant starch improves insulin sensitivity in subjects with the metabolic syndrome. Unlike in animal models, diabetes prevention does not appear to be directly related to changes in body adiposity, blood lipids or inflammatory markers. Further research to elucidate the mechanisms behind this change in insulin sensitivity in human subjects is required.

The environment within: how gut microbiota may influence metabolism and body composition

Obesity, diabetes and consequently atherosclerotic vascular disease have become major health and public health issues worldwide. The increasing and staggering prevalence of obesity might not only be explained by nutritional habits or the reduction of energy expenditure through decreased physical activity. In addition, recent studies have focused on intestinal microbiota as environmental factors that increase energy yield from diet, regulate peripheral metabolism and thereby increase body weight. Obesity is associated with substantial changes in composition and metabolic function of gut microbiota, but the pathophysiological processes driving this bidirectional relationship have not been fully elucidated. This review discusses the relationships between the following: composition of gut microbiota, energy extracted from diet, synthesis of gut hormones involved in energy homeostasis, production of butyrate and the regulation of fat storage.

The impact of perinatal probiotic intervention on the development of overweight and obesity: follow-up study from birth to 10 years

BACKGROUND

The achievements in combating the increasing trend of overweight and obesity have thus far been inadequate. The recently discovered instrumental role of the gut microbiota in host metabolism may offer a novel target in the prevention and management of obesity.

OBJECTIVE

To evaluate the impact of perinatal probiotic intervention on childhood growth patterns and the development of overweight during a 10-year follow-up.

PATIENTS AND METHODS

Altogether 159 women were randomized and double-blinded to receive probiotics (1 × 10(10) colony-forming units of Lactobacillus rhamnosus GG, ATCC 53103) or placebo 4 weeks before expected delivery; the intervention extending for 6 months postnatally. Anthropometric measurements of the children were taken at the ages of 3, 6, 12 and 24 months and at 4, 7 and 10 years in 113 (72%) children.

RESULTS

The excessive weight gain was detected to be two-parted; the initial phase of excessive weight gain initiating during fetal period and continuing until 24-48 months of age and a second phase of excessive weight gain starting after the age of 24-48 months. The perinatal probiotic intervention appeared to moderate the initial phase of excessive weight gain, especially among children who later became overweight, but not the second phase of excessive weight gain, the impact being most pronounced at the age of 4 years (P=0.063, analysis of variance for repeated measures). The effect of intervention was also shown as a tendency to reduce the birth-weight-adjusted mean body mass index at the age of 4 years (P=0.080, analysis of covariance).

CONCLUSIONS

Early gut microbiota modulation with probiotics may modify the growth pattern of the child by restraining excessive weight gain during the first years of life. This novel observation calls for further epidemiological and clinical trials, with precise data on early growth patterns and on confounding factors influencing weight development.

Gut microbiota composition is associated with body weight, weight gain and biochemical parameters in pregnant women

Obesity is associated with complications during pregnancy and increased health risks in the newborn. The objective of the present study was to establish possible relationships between gut microbiota, body weight, weight gain and biochemical parameters in pregnant women. Fifty pregnant women were classified according to their BMI in normal-weight (n 34) and overweight (n 16) groups. Gut microbiota composition was analysed by quantitative real-time PCR in faeces and biochemical parameters in plasma at 24 weeks of pregnancy. Reduced numbers of Bifidobacterium and Bacteroides and increased numbers of Staphylococcus, Enterobacteriaceae and Escherichia coli were detected in overweight compared with normal-weight pregnant women. E. coli numbers were higher in women with excessive weight gain than in women with normal weight gain during pregnancy, while Bifidobacterium and Akkermansia muciniphila showed an opposite trend. In the whole population, increased total bacteria and Staphylococcus numbers were related to increased plasma cholesterol levels. Increased Bacteroides numbers were related to increased HDL-cholesterol and folic acid levels, and reduced TAG levels. Increased Bifidobacterium numbers were related to increased folic acid levels. Increased Enterobacteriaceae and E. coli numbers were related to increased ferritin and reduced transferrin, while Bifidobacterium levels showed the opposite trend. Therefore, gut microbiota composition is related to body weight, weight gain and metabolic biomarkers during pregnancy, which might be of relevance to the management of the health of women and infants.

Cholate-containing high-fat diet induces the formation of multinucleated giant cells in atherosclerotic plaques of apolipoprotein E-/- mice

OBJECTIVE

To determine the role of multinucleated giant cells (MGCs) in cardiovascular diseases.

METHODS AND RESULTS

MGCs are a hallmark of giant cell arteritis. They are also described in atherosclerotic plaques from aortic aneurysms and carotid and coronary arteries. Herein, we demonstrate that the cholate-containing Paigen diet yields many MGCs in atherosclerotic plaques of apolipoprotein E-/- mice. These mice revealed a 4-fold increase in MGC numbers when compared with mice on a Western or Paigen diet without cholate. Most of the MGCs stained intensively for cathepsin K and were located at fibrous caps and close to damaged elastic laminae, with associated medial smooth muscle cell depletion. During in vitro experiments, MGCs demonstrated a 6-fold increase in elastolytic activity when compared with macrophages and facilitated transmigration of smooth muscle cells through a collagen-elastin matrix. An elastin-derived hexapeptide (Val-Gly-Val-Ala-Pro-Gly [VGVAPG]) significantly increased the rate of macrophage fusion, providing a possible mechanism of in vivo MGC formation. Comparable to the mouse model, human specimens from carotid arteries and aortic aneurysms contained cathepsin K-positive MGCs.

CONCLUSIONS

Apolipoprotein E-/- mice fed a Paigen diet provide a model to analyze the tissue-destructive role of MGCs in vascular diseases.

Changes in intestinal bifidobacteria levels are associated with the inflammatory response in magnesium-deficient mice

Magnesium (Mg) deficiency is a common nutritional disorder that is linked to an inflammatory state characterized by increased plasma acute phase protein and proinflammatory cytokine concentrations. Recent studies have shown that changes in the composition of gut microbiota composition participate in systemic inflammation. In this study, therefore, we assessed the potential role of gut microbiota in intestinal and systemic inflammation associated with Mg deficiency in mice. For this purpose, mice were fed a control or Mg-deficient diet (500 mg vs. 70 mg Mg/kg) for 4 or 21 d. Compared with the mice fed the control diet, mice fed the Mg-deficient diet for 4 d had a lower gut bifidobacteria content (-1.5 log), a 36-50% lower mRNA content of factors controlling gut barrier function in the ileum (zonula occludens-1, occludin, proglucagon), and a higher mRNA content (by approximately 2-fold) in the liver and/or intestine of tumor necrosis factor-alpha, interleukin-6, CCAAT/enhancer binding protein homologous protein, and activating transcription factor 4, reflecting inflammatory and cellular stress. In contrast, mice fed the Mg-deficient diet for 21 d had a higher cecal bifidobacteria content compared with the control group, a phenomenon accompanied by restoration of the intestinal barrier and the absence of inflammation. In conclusion, we show that Mg deficiency, independently of any other changes in nutrient intake, modulates the concentration of bifidobacteria in the gut, a phenomenon that may time-dependently affect inflammation and metabolic disorders in mice.

Gut microbiota in human adults with type 2 diabetes differs from non-diabetic adults

BACKGROUND

Recent evidence suggests that there is a link between metabolic diseases and bacterial populations in the gut. The aim of this study was to assess the differences between the composition of the intestinal microbiota in humans with type 2 diabetes and non-diabetic persons as control.

METHODS AND FINDINGS

The study included 36 male adults with a broad range of age and body-mass indices (BMIs), among which 18 subjects were diagnosed with diabetes type 2. The fecal bacterial composition was investigated by real-time quantitative PCR (qPCR) and in a subgroup of subjects (N = 20) by tag-encoded amplicon pyrosequencing of the V4 region of the 16S rRNA gene. The proportions of phylum Firmicutes and class Clostridia were significantly reduced in the diabetic group compared to the control group (P = 0.03). Furthermore, the ratios of Bacteroidetes to Firmicutes as well as the ratios of Bacteroides-Prevotella group to C. coccoides-E. rectale group correlated positively and significantly with plasma glucose concentration (P = 0.04) but not with BMIs. Similarly, class Betaproteobacteria was highly enriched in diabetic compared to non-diabetic persons (P = 0.02) and positively correlated with plasma glucose (P = 0.04).

CONCLUSIONS

The results of this study indicate that type 2 diabetes in humans is associated with compositional changes in intestinal microbiota. The level of glucose tolerance should be considered when linking microbiota with metabolic diseases such as obesity and developing strategies to control metabolic diseases by modifying the gut microbiota.

Gut microbiota as a regulator of energy homeostasis and ectopic fat deposition: mechanisms and implications for metabolic disorders

PURPOSE OF REVIEW

To examine the role of gut microbiota in the regulation of host energy homeostasis and its role in the pathogenesis of obesity, diabetes and nonalcoholic fatty liver disease (NAFLD).

RECENT FINDINGS

Experimental models highlight several mechanisms connecting gut microbiota to host energy metabolism: increased energy harvesting from the diet, regulation of appetite through gut peptide, secretion, regulation of tissue-free fatty acid composition and uptake, storage and oxidation, modulation of intestinal barrier by glucagon-like peptide-2 secretion, activation of innate immunity and hepatic fibrogenesis through the lipopolysaccharide (LPS)-toll-like receptor-4 axis.Gut microbiota manipulation through antibiotics, prebiotics and probiotics yields encouraging results for the treatment of obesity, diabetes and NAFLD in animal models, but data in humans are currently scarce.

SUMMARY

Gut microbiota manipulation yielded encouraging results for the treatment of different metabolic disorders in experimental models. However, changing intestinal microbiota may be more difficult in free-living individuals compared to standardized laboratory models, and its long-term consequences are unknown. To safely and effectively change human gut microflora, future research should highlight the complex hormonal, immunomodulatory and metabolic mechanisms underlying microbiota-host interactions in different tissues and candidate treatments should be evaluated in well designed trials with patient-oriented end-points.

Probiotics and gut health: A special focus on liver diseases

Probiotic bacteria have well-established beneficial effects in the management of diarrhoeal diseases. Newer evidence suggests that probiotics have the potential to reduce the risk of developing inflammatory bowel diseases and intestinal bacterial overgrowth after gut surgery. In liver health, the main benefits of probiotics might occur through preventing the production and/or uptake of lipopolysaccharides in the gut, and therefore reducing levels of low-grade inflammation. Specific immune stimulation by probiotics through processes involving dendritic cells might also be beneficial to the host immunological status and help prevent pathogen translocation. Hepatic fat metabolism also seems to be influenced by the presence of commensal bacteria, and potentially by probiotics; although the mechanisms by which probiotic might act on the liver are still unclear. However, this might be of major importance in the future because low-grade inflammation, hepatic fat infiltration, and hepatitis might become more prevalent as a result of high fat intake and the increased prevalence of obesity.

Molecular characterisation of the faecal microbiota in patients with type II diabetes

The investigation provides molecular analyses of the faecal microbiota in type 2 diabetic patients. In order to characterise the gut microbiota in diabetic patients and to assess whether there are changes in the diversity and similarity of gut microbiota in diabetic patients when compared with healthy individuals, bacterial DNAs from 16 type 2 diabetic patients and 12 healthy individuals were extracted from faecal samples and characterised by PCR-denaturing gradient gel electrophoresis (DGGE) with primers specifically targeting V3 region of the 16S rRNA gene, as well as been sequenced for excised gel bands. The counts of Bacteroides vulgatus, Clostridium leptum subgroup and Bifidobacterium genus were assessed using quantitative PCR. By comparing species diversity profiles of two groups, we observed that there were no significant differences between diabetic and healthy group, although a few diabetic individuals (D6, D8) exhibited a remarkable decrease in species profiles. As for the similarity index, it was lower in inter-group than that in intra-group, which showed that the composition of gut microbiota in diabetic group might be changed due to diabetes status. Sequencing results also revealed that bacterial composition of diabetic group was different from that of the healthy group. B. vulgatus and Bifidobacterium genus were low represented in the microbiota of diabetic group, and the significant decrease was observed for Bifidobacterium by real-time PCR. Taken together, in this work we observed the characterisation of gut microbiota in diabetic patients, which suggests that the gut microbiota of diabetes patients have some changes associated with occurrence and development of diabetes.

Molecular characterisation of the faecal microbiota in patients with type II diabetes

The investigation provides molecular analyses of the faecal microbiota in type 2 diabetic patients. In order to characterise the gut microbiota in diabetic patients and to assess whether there are changes in the diversity and similarity of gut microbiota in diabetic patients when compared with healthy individuals, bacterial DNAs from 16 type 2 diabetic patients and 12 healthy individuals were extracted from faecal samples and characterised by PCR-denaturing gradient gel electrophoresis (DGGE) with primers specifically targeting V3 region of the 16S rRNA gene, as well as been sequenced for excised gel bands. The counts of Bacteroides vulgatus, Clostridium leptum subgroup and Bifidobacterium genus were assessed using quantitative PCR. By comparing species diversity profiles of two groups, we observed that there were no significant differences between diabetic and healthy group, although a few diabetic individuals (D6, D8) exhibited a remarkable decrease in species profiles. As for the similarity index, it was lower in inter-group than that in intra-group, which showed that the composition of gut microbiota in diabetic group might be changed due to diabetes status. Sequencing results also revealed that bacterial composition of diabetic group was different from that of the healthy group. B. vulgatus and Bifidobacterium genus were low represented in the microbiota of diabetic group, and the significant decrease was observed for Bifidobacterium by real-time PCR. Taken together, in this work we observed the characterisation of gut microbiota in diabetic patients, which suggests that the gut microbiota of diabetes patients have some changes associated with occurrence and development of diabetes.

The global diabetes epidemic as a consequence of lifestyle-induced low-grade inflammation

The recent major increase in the global incidence of type 2 diabetes suggests that most cases of this disease are caused by changes in environment and lifestyle. All major risk factors for type 2 diabetes (overnutrition, low dietary fibre, sedentary lifestyle, sleep deprivation and depression) have been found to induce local or systemic low-grade inflammation that is usually transient or milder in individuals not at risk for type 2 diabetes. By contrast, inflammatory responses to lifestyle factors are more pronounced and prolonged in individuals at risk of type 2 diabetes and appear to occur also in the pancreatic islets. Chronic low-grade inflammation will eventually lead to overt diabetes if counter-regulatory circuits to inflammation and metabolic stress are compromised because of a genetic and/or epigenetic predisposition. Hence, it is not the lifestyle change per se but a deficient counter-regulatory response in predisposed individuals which is crucial to disease pathogenesis. Novel approaches of intervention may target these deficient defence mechanisms.

Obesity and the human microbiome

PURPOSE OF REVIEW

Obesity was once rare, but the last few decades have seen a rapid expansion of the proportion of obese individuals worldwide. Recent work has shown obesity to be associated with a shift in the representation of the dominant phyla of bacteria in the gut, both in humans and animal models. This review summarizes the latest research into the association between microbial ecology and host adiposity, and the mechanisms by which microbes in the gut may mediate host metabolism in the context of obesity.

RECENT FINDINGS

Studies of the effect of excess body fat on the abundances of different bacteria taxa in the gut generally show alterations in the gastrointestinal microbiota, and changes during weight loss. The gastrointestinal microbiota have been shown to impact insulin resistance, inflammation, and adiposity via interactions with epithelial and endocrine cells.

SUMMARY

Large-scale alterations of the gut microbiota and its microbiome (gene content) are associated with obesity and are responsive to weight loss. Gut microbes can impact host metabolism via signaling pathways in the gut, with effects on inflammation, insulin resistance, and deposition of energy in fat stores. Restoration of the gut microbiota to a healthy state may ameliorate the conditions associated with obesity and help maintain a healthy weight.

Diversification of the gut symbiont Lactobacillus reuteri as a result of host-driven evolution

The vertebrate digestive tract, including that of humans, is the habitat to trillions of bacteria that are of significant importance to host biology and health. Although these communities are often postulated to have coevolved with their hosts, evidence is lacking, yet critical for our understanding of microbial symbiosis in vertebrates. To gain insight into the evolution of a gut symbiont, we have characterized the population genetic structure and phylogeny of Lactobacillus reuteri strains isolated from six different host species (human, mouse, rat, pig, chicken and turkey) using Amplified-Fragment Length Polymorphism (AFLP) and Multi-Locus Sequence Analysis (MLSA). The results revealed considerable genetic heterogeneity within the L. reuteri population and distinct monophyletic clades reflecting host origin but not provenance. The evolutionary patterns detected indicate a long-term association of L. reuteri lineages with particular vertebrate species and host-driven diversification. Results from a competition experiment in a gnotobiotic mouse model revealed that rodent isolates showed elevated ecological performance, indicating that evolution of L. reuteri lineages was adaptive. These findings provide evidence that some vertebrate gut microbes are not promiscuous, but have diversified into host-adapted lineages by a long-term evolutionary process, allowing the development of a highly specialized symbiosis.

Gut microbiota fermentation of prebiotics increases satietogenic and incretin gut peptide production with consequences for appetite sensation and glucose response after a meal

BACKGROUND

We have previously shown that gut microbial fermentation of prebiotics promotes satiety and lowers hunger and energy intake in humans. In rodents, these effects are associated with an increase in plasma gut peptide concentrations, which are involved in appetite regulation and glucose homeostasis.

OBJECTIVE

Our aim was to examine the effects of prebiotic supplementation on satiety and related hormones during a test meal for human volunteers by using a noninvasive micromethod for blood sampling to measure plasma gut peptide concentrations.

DESIGN

This study was a randomized, double-blind, parallel, placebo-controlled trial. A total of 10 healthy adults (5 men and 5 women) were randomly assigned to groups that received either 16 g prebiotics/d or 16 g dextrin maltose/d for 2 wk. Meal tolerance tests were performed in the morning to measure the following: hydrogen breath test, satiety, glucose homeostasis, and related hormone response.

RESULTS

We show that the prebiotic treatment increased breath-hydrogen excretion (a marker of gut microbiota fermentation) by approximately 3-fold and lowered hunger rates. Prebiotics increased plasma glucagon-like peptide 1 and peptide YY concentrations, whereas postprandial plasma glucose responses decreased after the standardized meal. The areas under the curve for plasma glucagon-like peptide 1 and breath-hydrogen excretion measured after the meal (0-60 min) were significantly correlated (r = 0.85, P = 0.007). The glucose response was inversely correlated with the breath-hydrogen excretion areas under the curve (0-180 min; r = -0.73, P = 0.02).

CONCLUSION

Prebiotic supplementation was associated with an increase in plasma gut peptide concentrations (glucagon-like peptide 1 and peptide YY), which may contribute in part to changes in appetite sensation and glucose excursion responses after a meal in healthy subjects.

Interactions between gut microbiota, host genetics and diet relevant to development of metabolic syndromes in mice

Both genetic variations and diet-disrupted gut microbiota can predispose animals to metabolic syndromes (MS). This study assessed the relative contributions of host genetics and diet in shaping the gut microbiota and modulating MS-relevant phenotypes in mice. Together with its wild-type (Wt) counterpart, the Apoa-I knockout mouse, which has impaired glucose tolerance (IGT) and increased body fat, was fed a high-fat diet (HFD) or normal chow (NC) diet for 25 weeks. DNA fingerprinting and bar-coded pyrosequencing of 16S rRNA genes were used to profile gut microbiota structures and to identify the key population changes relevant to MS development by Partial Least Square Discriminate Analysis. Diet changes explained 57% of the total structural variation in gut microbiota, whereas genetic mutation accounted for no more than 12%. All three groups with IGT had significantly different gut microbiota relative to healthy Wt/NC-fed animals. In all, 65 species-level phylotypes were identified as key members with differential responses to changes in diet, genotype and MS phenotype. Most notably, gut barrier-protecting Bifidobacterium spp. were nearly absent in all animals on HFD, regardless of genotype. Sulphate-reducing, endotoxin-producing bacteria of the family, Desulfovibrionaceae, were enhanced in all animals with IGT, most significantly in the Wt/HFD group, which had the highest calorie intake and the most serious MS phenotypes. Thus, diet has a dominating role in shaping gut microbiota and changes of some key populations may transform the gut microbiota of Wt animals into a pathogen-like entity relevant to development of MS, despite a complete host genome.

The microbiome and obesity: is obesity linked to our gut flora?

The human gut is a lush microbial ecosystem containing about 100 trillion microorganisms, whose collective genome, the microbiome, contains 100-fold more genes than the entire human genome. The symbiosis of our extended genome plays a role in host homeostasis and energy extraction from diet. In this article, we summarize some of the studies that have advanced the understanding of the microbiome and its effects on metabolism, obesity, and health. Metagenomic studies demonstrated that certain mixes of gut microbiota may protect or predispose the host to obesity. Furthermore, microbiota transplantation studies in germ-free murine models showed that the efficient energy extraction traits of obese-type gut flora are transmissible. The proposed methods by which the microbiome may contribute to obesity include increasing dietary energy harvest, promoting fat deposition, and triggering systemic inflammation. Future treatments for obesity may involve modulation of gut microbiota using probiotics or prebiotics.

Molecular crosstalk of probiotic bacteria with the intestinal immune system: clinical relevance in the context of inflammatory bowel disease

It is current knowledge that the intestinal microbiota plays a major role in the development and maintenance of intestinal health. Intestinal epithelial cells (IEC) constitute the interface between the gut lumen and the innate and adaptive immune system. To maintain intestinal homeostasis, the organized and diffuse compartments of the gut-associated lymphoid tissue have to process the continuously varying information at the interface between the luminal side and the host. Dysregulated intestinal immune responses towards commensal bacteria are an important factor in the pathogenesis of inflammatory bowel diseases (IBD). In contrast to the colitogenic effects of enteric bacteria, clinical and experimental studies showed that specific probiotic strains are protective in the context of chronic intestinal inflammation. Although the molecular understanding of bacteria-host interaction is improving, the anti-inflammatory mechanisms induced by these probiotic bacteria are just starting to be unraveled. The present review is meant to summarize and discuss the clinical relevance of probiotics, but it also seeks to give an overview about currently known probiotic mechanisms in the context of chronic intestinal inflammation with a focus on IEC.

Interplay between weight loss and gut microbiota composition in overweight adolescents

The aim of this study was to determine the influence of an obesity treatment program on the gut microbiota and body weight of overweight adolescents. Thirty-six adolescents (13-15 years), classified as overweight according to the International Obesity Task Force BMI criteria, were submitted to a calorie-restricted diet (10-40%) and increased physical activity (15-23 kcal/kg body weight/week) program over 10 weeks. Gut bacterial groups were analyzed by quantitative real-time PCR before and after the intervention. A group of subjects (n=23) experienced >4.0 kg weight loss and showed significant BMI (P=0.030) and BMI z-score (P=0.035) reductions after the intervention, while the other group (n=13) showed <2.0 kg weight loss. No significant differences in dietary intake were found between both groups. In the whole adolescent population, the intervention led to increased Bacteroides fragilis group (P=0.001) and Lactobacillus group (P=0.030) counts, and to decreased Clostridium coccoides group (P=0.028), Bifidobacterium longum (P=0.031), and Bifidobacterium adolescentis (P=0.044) counts. In the high weight-loss group, B. fragilis group and Lactobacillus group counts also increased (P=0.001 and P=0.007, respectively), whereas C. coccoides group and B. longum counts decreased (P=0.001 and P=0.044, respectively) after the intervention. Total bacteria, B. fragilis group and Clostridium leptum group, and Bifidobacterium catenulatum group counts were significantly higher (P<0.001-0.036) while levels of C. coccoides group, Lactobacillus group, Bifidobacterium, Bifidobacterium breve, and Bifidobacterium bifidum were significantly lower (P<0.001-0.008) in the high weight-loss group than in the low weight-loss group before and after the intervention. These findings indicate that calorie restriction and physical activity have an impact on gut microbiota composition related to body weight loss, which also seem to be influenced by the individual's microbiota.

Panorganismal gut microbiome-host metabolic crosstalk

Coevolution shapes interorganismal crosstalk leading to profound and diverse cellular and metabolic changes as observed in gut dysbiosis in human diseases. Here, we modulated a simplified gut microbiota using pro-, pre-, and synbiotics to assess the depth of systemic metabolic exchanges in mice, using a multicompartmental modeling approach with metabolic signatures from 10 tissue/fluid compartments. The nutritionally induced microbial changes modulated host lipid, carbohydrate, and amino acid metabolism at a panorganismal scale. Galactosyl-oligosaccharides reduced lipogenesis, triacylglycerol incorporation into lipoproteins and triglyceride concentration in the liver and the kidney. Those changes were not correlated with decreased plasma lipoproteins that were specifically induced by L. rhamnosus supplementation. Additional alteration of transmethylation metabolic pathways (homocysteine-betaine) was observed in the liver and the pancreas following pre- and synbiotic microbial modulation, which may be of interest for control of glucose metabolism and insulin sensitivity. Probiotics also reduced hepatic glycogen and glutamine and adrenal ascorbate with inferred effects on energy homeostasis, antioxidation, and steroidogenesis. These studies show the breadth and the depth of gut microbiome modulations of host biochemistry and reveal that major mammalian metabolic processes are under symbiotic homeostatic control.

The improvement of hypertension by probiotics: effects on cholesterol, diabetes, renin, and phytoestrogens

Probiotics are live organisms that are primarily used to improve gastrointestinal disorders such as diarrhea, irritable bowel syndrome, constipation, lactose intolerance, and to inhibit the excessive proliferation of pathogenic intestinal bacteria. However, recent studies have suggested that probiotics could have beneficial effects beyond gastrointestinal health, as they were found to improve certain metabolic disorders such as hypertension. Hypertension is caused by various factors and the predominant causes include an increase in cholesterol levels, incidence of diabetes, inconsistent modulation of renin and imbalanced sexual hormones. This review discusses the antihypertensive roles of probiotics via the improvement and/or treatment of lipid profiles, modulation of insulin resistance and sensitivity, the modulation of renin levels and also the conversion of bioactive phytoestrogens as an alternative replacement of sexual hormones such as estrogen and progesterone.

Antihypertensive properties of plant-based prebiotics

Hypertension is one of the major risk factors for cardiovascular disease. Although various drugs for its treatment have been synthesized, the occurring side effects have generated the need for natural interventions for the treatment and prevention of hypertension. Dietary intervention such as the administration of prebiotics has been seen as a highly acceptable approach. Prebiotics are indigestible food ingredients that bypass digestion and reach the lower gut as substrates for indigenous microflora. Most of the prebiotics used as food adjuncts, such as inulin, fructooligosaccharides, dietary fiber and gums, are derived from plants. Experimental evidence from recent studies has suggested that prebiotics are capable of reducing and preventing hypertension. This paper will discuss some of the mechanisms involved, the evidence generated from both in-vitro experiments and in-vivo trials and some controversial findings that are raised.

Top-down systems biology modeling of host metabotype-microbiome associations in obese rodents

Covariation in the structural composition of the gut microbiome and the spectroscopically derived metabolic phenotype (metabotype) of a rodent model for obesity were investigated using a range of multivariate statistical tools. Urine and plasma samples from three strains of 10-week-old male Zucker rats (obese (fa/fa, n=8), lean (fa/-, n=8) and lean (-/-, n=8)) were characterized via high-resolution 1H NMR spectroscopy, and in parallel, the fecal microbial composition was investigated using fluorescence in situ hydridization (FISH) and denaturing gradient gel electrophoresis (DGGE) methods. All three Zucker strains had different relative abundances of the dominant members of their intestinal microbiota (FISH), with the novel observation of a Halomonas and a Sphingomonas species being present in the (fa/fa) obese strain on the basis of DGGE data. The two functionally and phenotypically normal Zucker strains (fa/- and -/-) were readily distinguished from the (fa/fa) obese rats on the basis of their metabotypes with relatively lower urinary hippurate and creatinine, relatively higher levels of urinary isoleucine, leucine and acetate and higher plasma LDL and VLDL levels typifying the (fa/fa) obese strain. Collectively, these data suggest a conditional host genetic involvement in selection of the microbial species in each host strain, and that both lean and obese animals could have specific metabolic phenotypes that are linked to their individual microbiomes.

Critical role of Kupffer cells in the management of diet-induced diabetes and obesity

The aim of this study was to investigate the role of Kupffer cell in glucose metabolism and hepatic insulin sensitivity in mice. Both phagocytic activity and secretory capacity of Kupffer cells were blunted 24h after GdCl3 administration. Glucose tolerance--evaluated following an oral glucose tolerance test (OGTT)--was higher in GdCl3-treated mice whereas fasting insulinemia and HOMA-IR index decreased. The improvement of glucose tolerance and hepatic insulin signalling pathway after inhibition of Kupffer cells was supported by a lower hepatic gluconeogenic enzyme expression and a higher phosphorylation of Akt upon insulin challenge. Moreover, fasting hyperglycemia, insulin resistance and impaired glucose tolerance--induced by high fat (HF) diet--were improved through chronic administration of GdCl3. Interestingly, the inhibition of Kupffer cell exerted antiobesity effects in HF-fed mice, and lowered hepatic steatosis. Therefore, strategies targeting Kupffer cell functions could be a promising approach to counteract obesity and related metabolic disorders.

Intestinal microflora and metabolic diseases

Recent advances in molecular sequencing technology have allowed researchers to answer major questions regarding the relationship between a vast genomic diversity-such as found in the intestinal microflora-and host physiology. Over the past few years, it has been established that, in obesity, type 1 diabetes and Crohn's disease-to cite but a few-the intestinal microflora play a pathophysiological role and can induce, transfer or prevent the outcome of such conditions. A few of the molecular vectors responsible for this regulatory role have been determined. Some are related to control of the immune, vascular, endocrine and nervous systems located in the intestines. However, more important is the fact that the intestinal microflora-to-host relationship is bidirectional, with evidence of an impact of the host genome on the intestinal microbiome. This means that the ecology shared by the host and gut microflora should now be considered a new player that can be manipulated, using pharmacological and nutritional approaches, to control physiological functions and pathological outcomes. What now remains is to demonstrate the molecular connection between the intestinal microflora and metabolic diseases. We propose here that the proinflammatory lipopolysaccharides play a causal role in the onset of metabolic disorders.

Diet-induced metabolic improvements in a hamster model of hypercholesterolemia are strongly linked to alterations of the gut microbiota

The mammalian gastrointestinal microbiota exerts a strong influence on host lipid and cholesterol metabolism. In this study, we have characterized the interplay among diet, gut microbial ecology, and cholesterol metabolism in a hamster model of hypercholesterolemia. Previous work in this model had shown that grain sorghum lipid extract (GSL) included in the diet significantly improved the high-density lipoprotein (HDL)/non-HDL cholesterol equilibrium (T. P. Carr, C. L. Weller, V. L. Schlegel, S. L. Cuppett, D. M. Guderian, Jr., and K. R. Johnson, J. Nutr. 135:2236-2240, 2005). Molecular analysis of the hamsters' fecal bacterial populations by pyrosequencing of 16S rRNA tags, PCR-denaturing gradient gel electrophoresis, and Bifidobacterium-specific quantitative real-time PCR revealed that the improvements in cholesterol homeostasis induced through feeding the hamsters GSL were strongly associated with alterations of the gut microbiota. Bifidobacteria, which significantly increased in abundance in hamsters fed GSL, showed a strong positive association with HDL plasma cholesterol levels (r = 0.75; P = 0.001). The proportion of members of the family Coriobacteriaceae decreased when the hamsters were fed GSL and showed a high positive association with non-HDL plasma cholesterol levels (r = 0.84; P = 0.0002). These correlations were more significant than those between daily GSL intake and animal metabolic markers, implying that the dietary effects on host cholesterol metabolism are conferred, at least in part, through an effect on the gut microbiota. This study provides evidence that modulation of the gut microbiota-host metabolic interrelationship by dietary intervention has the potential to improve mammalian cholesterol homeostasis, which has relevance for cardiovascular health.

Metabolic activity of the enteric microbiota influences the fatty acid composition of murine and porcine liver and adipose tissues

BACKGROUND

Recent reports suggest that the metabolic activity of the gut microbiota may contribute to the pathogenesis of obesity and hepatic steatosis.

OBJECTIVE

The objective was to determine whether the fat composition of host tissues might be influenced by oral administration of commensal bifidobacteria previously shown by us to produce bioactive isomers of conjugated linoleic acid (CLA).

DESIGN

Murine trials were conducted in which linoleic acid-supplemented diets were fed with or without Bifidobacterium breve NCIMB 702258 (daily dose of 10(9) microorganisms) to healthy BALB/c mice and to severe combined immunodeficient mice for 8-10 wk. To ensure that the observations were not peculiar to mice, a similar trial was conducted in weanling pigs over 21 d. Tissue fatty acid composition was assessed by gas-liquid chromatography.

RESULTS

In comparison with controls, there was an increase in cis-9, trans-11 CLA in the livers of the mice and pigs after feeding with linoleic acid in combination with B. breve NCIMB 702258 (P < 0.05). In addition, an altered profile of polyunsaturated fatty acid composition was observed, including higher concentrations of the omega-3 (n-3) fatty acids eicosapentaenoic acid and docosahexaenoic acid in adipose tissue (P < 0.05). These changes were associated with reductions in the proinflammatory cytokines tumor necrosis factor-alpha and interferon-gamma (P < 0.05).

CONCLUSIONS

These results are consistent with the concept that the metabolome is a composite of host and microbe metabolic activity and that the influence of the microbiota on host fatty acid composition can be manipulated by oral administration of CLA-producing microorganisms.

Coffee, glucose homeostasis, and insulin resistance: physiological mechanisms and mediators

Epidemiological studies show coffee consumption to be correlated to large risk reductions in the prevalence of type 2 diabetes (T2D). Such correlations are seen with decaffeinated and caffeinated coffee, and occur regardless of gender, method of brewing, or geography. They also exist despite clear evidence showing that caffeine causes acute postprandial hyperglycemia and lower whole-body insulin sensitivity. As the beneficial effects of coffee consumption exist for both decaffeinated and caffeinated coffee, a component of coffee other than caffeine must be responsible. This review examines the specific coffee compounds responsible for coffee's effects on T2D, and their potential physiological mechanisms of action. Being plant-derived, coffee contains many beneficial compounds found in fruits and vegetables, including antioxidants. In fact, coffee is the largest source of dietary antioxidants in industrialized nations. When green coffee is roasted at high temperatures, Maillard reactions create a number of unique compounds. Roasting causes a portion of the antioxidant, chlorogenic acid, to be transformed into quinides, compounds known to alter blood glucose levels. Coffee consumption may also mediate levels of gut peptides (glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1), hormones intimately involved in the regulation of satiety and insulin secretion. Finally, coffee may have prebiotic-like properties, altering gut flora and ultimately digestion. In summary, it is evident that a better understanding of the role of coffee in the development and prevention of T2D has the potential to uncover novel therapeutic targets and nutraceutical formulations for the disease.

Intestinal microbiota during infancy and its implications for obesity

Obesity is a worldwide epidemic, threatening both industrialized and developing countries, and is accompanied by a dramatic increase in obesity-related disorders, including type 2 diabetes mellitus, hypertension, cardiovascular diseases, and nonalcoholic fatty liver disease. Recent studies have shown that the gut microbial community (microbiota) is an environmental factor that regulates obesity by increasing energy harvest from the diet and by regulating peripheral metabolism. However, there are no data on how obesogenic microbiotas are established and whether this process is determined during infancy. The sterile fetus is born into a microbial world and is immediately colonized by numerous species originating from the surrounding ecosystems, especially the maternal vaginal and fecal microflora. This initial microbiota develops into a complex ecosystem in a predictable fashion determined by internal (eg, oxygen depletion) and external (eg, mode of birth, impact of environment, diet, hospitalization, application of antibiotics) factors. We discuss how the gut microbiota regulates obesity and how environmental factors that affect the establishment of the gut microbiota during infancy may contribute to obesity later in life.

Lipid peroxidation is not a prerequisite for the development of obesity and diabetes in high-fat-fed mice

The mechanism, by which a high-fat (HF) diet could impair glucose metabolism, is not completely understood but could be related to inflammation, lipotoxicity and oxidative stress. Lipid peroxides have been proposed as key mediators of intracellular metabolic response. The purpose of the present study was to analyse, in mice fed with a HF diet, the possible association between obesity and glucose tolerance on the one hand, and between oxidative stress and lipid peroxidation on the other hand. The present results show that a HF diet (70 % energy as fat), v. a high-carbohydrate chow diet (control), increases body weight and fat mass development, and impairs glycaemia and insulinaemia within 4 weeks. It also promotes the expression of NADPH oxidase in the liver--signing both oxidative and inflammatory stress--but decreases thiobarbituric acid-reactive substances content in the liver as well as in epididymal, subcutaneous and visceral adipose tissues. HF diet, with elevated vitamin E content, induces high concentration of alpha-tocopherol in liver and adipose tissues, which contributes to the protection against lipid peroxidation. Thus, lipid peroxidation in key organs is not necessarily related to the development of metabolic disorders associated with diabetes and obesity.

Imbalances in faecal and duodenal Bifidobacterium species composition in active and non-active coeliac disease

Background

Gut bifidobacteria are believed to influence immune-related diseases. The objective of this study was to assess the possible relationships between the gut bifidobacteria composition and coeliac disease (CD) in children.

A total of 48 faecal samples (30 and 18 samples from active and no active CD patients, respectively) and 33 duodenal biopsy specimens of CD patients (25 and 8 samples from active and non-active CD patients, respectively) were analysed. Samples (30 faecal samples and 8 biopsies) from a control age-matched group of children were also included for comparative purposes. Gut Bifidobacterium genus and species were analyzed by real-time PCR.

Results

Active and non-active CD patients showed lower numbers of total Bifidobacterium and B. longum species in faeces and duodenal biopsies than controls, and these differences were particularly remarkable between active CD patients and controls. B. catenulatum prevalence was higher in biopsies of controls than in those of active and non-active CD patients, whereas B. dentium prevalence was higher in faeces of non-active CD patients than in controls. Correlations between levels of Bifidobacterium and B. longum species in faecal and biopsy samples were detected in both CD patients and controls.

Conclusion

Reductions in total Bifidobacterium and B. longum populations were associated with both active and non-active CD when compared to controls. These bacterial groups could constitute novel targets for adjuvant dietary therapies although the confirmation of this hypothesis would require further investigations.

Gut microbiota and pregnancy, a matter of inner life

More than a century ago, two Nobel Prizes in Physiology and Medicine were awarded to scientists who established the link between microbes and human health.