Microbial regulation of organismal energy homeostasis

Nondigestible Oligosaccharides with Anti-Obesity Effects

Obesity has an important influence on health conditions, causing a multitude of complications and comorbidities, and drug therapy is considered to be one of the treatment strategies. Nowadays, there is increasing interest in the study of intestinal microbiota regulation of obesity; also, an increasing number of agricultural and sideline products have been found to have anti-obesity potential. In the present review, we summarize an overview of current known and potential anti-obesity oligosaccharides and their molecular structures. We describe their anti-obesity potential activity and the molecular structure associated with this activity, the regulation of intestinal microbiota composition and its mechanism of action, including regulation of the short-chain fatty acid (SCFA) pathway and altering bile acid (BA) pathway. This review will provide new ideas for us to develop new anti-obesity functional foods.

The Two-Way Polyphenols-Microbiota Interactions and Their Effects on Obesity and Related Metabolic Diseases

Metabolic diseases can change the gut microbiota composition and function, and pathogenic bacteria contribute to the development of metabolic disorders. Polyphenols may act in the gut microbiota to favor the increase of beneficial bacteria and hamper the increase of pathogenic bacteria. In addition, the microbiota may act on polyphenols to increase their bioavailability. This two-way interactions between polyphenols and the gut microbiota could affect human metabolism and reduce cardiometabolic risk. Despite the possible benefits of polyphenols for human health through modulating the microbiome, studies are scarce, and present several limitations. This review provides an overview of the polyphenol-microbiota interactions and its effects on metabolic disorders.

Potential correlation between carbohydrate-active enzyme family 48 expressed by gut microbiota and the expression of intestinal epithelial AMP-activated protein kinase β

The expression of the carbohydrate-active enzyme family and related genes is known to be influenced by the response of intestinal microbiota to dietary changes. However, it is uncertain whether this is caused by variation in the intestinal microecology. In this study, metabolite analysis, 16S rDNA sequencing, metagenomics, and Western blotting were employed to investigate the effects of dietary intervention on the composition of gut microbiota and microbiota-mediated changes. The results showed that compared with the low fiber-fed group, the fiber diet-fed mice displayed a shift in gut microbiota composition to contain more members of phylum Bacteroidetes, accompanied by higher proportions of Akkermansia and typical probiotic Bifidobacterium. Moreover, correlations were found between microbial genes coding for carbohydrate-binding module family 48 (CBM48) and intestinal epithelial expression levels of AMPK β. This finding provides new insight for elucidating the contribution of dietary intervention through AMPK regulation linked to the microbial carbohydrate-binding family. PRACTICAL APPLICATIONS: The relationship suggested by these data will provide theoretical and applied foundations for the development of potential intervention targeting the interaction between gut microbiota and host health, particularly the use of dietary fiber as a medically relevant food. Additionally, a better understanding of the interactions between gut microbiota and intestinal epithelial will inform the development of gut microbiota intervention as a health-promoting procedure.

Exploring the Benefit of 2-Methylbutyric Acid in Patients Undergoing Hemodialysis Using a Cardiovascular Proteomics Approach

Short-chain fatty acids (SCFAs) can reduce pro-inflammatory parameters and oxidative stress, providing potential cardiovascular (CV) benefits. Although some evidence links SCFAs with host metabolic health via several biological mechanisms, the role of SCFA on CV disease in patients with kidney disease remains unclear. Herein, we investigate the association between a SCFA, 2-methylbutyric acid, and target CV proteomics to explore the potential pathophysiology of SCFA-related CV benefit in patients with kidney disease. Circulating 2-methylbutyric acid was quantified by high-performance liquid chromatography and 181 CV proteins by a proximity extension assay in 163 patients undergoing hemodialysis (HD). The associations between 2-methylbutyric acid and CV proteins were evaluated using linear regression analysis with age and gender, and multiple testing adjustment. The selected CV protein in the discovery phase was further confirmed in multivariable-adjusted models and evaluated by continuous scale association. The mean value of circulating 2-methylbutyric acid was 0.22 ± 0.02 µM, which was negatively associated with bone morphogenetic protein 6 (BMP-6) according to the false discovery rate (FDR) multiple testing adjustment method. The 2-methylbutyric acid level remained negatively associated with BMP-6 (β coefficient -1.00, 95% confidence interval -1.45 to -0.55, p < 0.001) after controlling for other CV risk factors in multivariable models. The cubic spline curve demonstrated a linear relationship. In conclusion, circulating 2-methylbutyric acid level was negatively associated with BMP-6, suggesting that this pathway maybe involved in vascular health in patients undergoing HD. However, further in vitro work is still needed to validate the translation of the mechanistic pathways.

Imbalance in the force: the dark side of the microbiota on stroke risk and progression

The composition of the gut microbiota depends on many factors, including our lifestyle, diet, metabolism, antibiotic use and hygiene. The contribution of these factors in shaping the gut microbiota and the subsequent effects on the prevention and development of stroke has been under intense investigation. Furthermore, several reports have uncovered the impact of stroke on intestinal dysfunction and gut dysbiosis, highlighting the delicate interplay between the brain, gut and microbiome following this acute brain injury. Despite our growing appreciation of the gut microbiota in shaping brain health, the immune system, host metabolism and disease progression, its therapeutic capability in stroke is yet to be fully exploited. This review will explore the microbiota-gut-brain axis in stroke, and examine the potential role of the gut microbiota in the onset, progression and recovery phase of stroke.

Prebiotics Fructo-, Galacto-, and Mannan-Oligosaccharide Do Not Protect against 5-Fluorouracil-Induced Intestinal Mucositis in Rats

BACKGROUND

Prebiotics selectively stimulate the growth of beneficial bacteria within the gastrointestinal tract, and have been investigated in human and animal studies for their capacity to improve intestinal health.

OBJECTIVE

We investigated the prebiotics fructo-oligosaccharide (FOS), galacto-oligosaccharide (GOS), and mannan-oligosaccharide (MOS) for their potential to alleviate intestinal damage in rats.

METHODS

Female Dark Agouti rats (6-8 wk old, 110-150 g) were allocated to 1 of the following treatment groups (n = 8/group): saline/water, saline/FOS, saline/GOS, saline/MOS, 5-fluorouracil (5FU)/water, 5FU/FOS, 5FU/GOS, and 5FU/MOS. Rats were pretreated with either 5% GOS, MOS, or FOS or vehicle (water) from day -12 to day 0. On day 0, rats received a single intraperitoneal injection of saline or 5FU. Metabolic data were recorded daily and all rats were killed on day 3. Histopathology was quantified in hematoxylin and eosin-stained sections. Intestinal sucrase and myeloperoxidase activity were quantified by biochemical assay. Fecal SCFAs-acetic, propionic, and butyric acid-were also measured. Statistical analysis was by repeated-measures, 2-factor ANOVA or Kruskal-Wallis and Mann-Whitney U test; P < 0.05 was considered statistically significant.

RESULTS

Body weight was significantly decreased in all treatment groups after 5FU injection, with no change in body weight observed in any prebiotic treatment group. Total food intake was lower by ≥7% in the GOS treatment group pre-5FU than in all other groups (P < 0.05). Ileal villus height was 18% higher in GOS-treated rats pre-5FU than in respective water controls (P < 0.05). Jejunal and ileal villus height and crypt depth were significantly decreased in all treatment groups after 5FU injection, with no prebiotic effect observed. SCFAs were differentially increased in prebiotic treatment groups compared with water-only controls (P < 0.05).

CONCLUSIONS

FOS, GOS, and MOS have differential effects in modifying small intestinal pathology and SCFA profiles in rats with healthy and damaged small intestinal mucosa.

Gut microbiota-derived succinate: Friend or foe in human metabolic diseases?

There is now a wealth of evidence showing that communication between microbiota and the host is critical to sustain the vital functions of the healthy host, and disruptions of this homeostatic coexistence are known to be associated with a range of diseases including obesity and type 2 diabetes. Microbiota-derived metabolites act both as nutrients and as messenger molecules and can signal to distant organs in the body to shape host pathophysiology. In this review, we provide a new perspective on succinate as a gut microbiota-derived metabolite with a key role governing intestinal homeostasis and energy metabolism. Thus, succinate is not merely a major intermediary of the TCA traditionally considered as an extracellular danger signal in the host, but also a by-product of some bacteria and a primary cross-feeding metabolite between gut resident microbes. In addition to maintain a healthy microbiome, specific functions of microbiota-derived succinate in peripheral tissues regulating host nutrient metabolism should not be rule out. Indeed, recent research point to some probiotic interventions directed to modulate succinate levels in the intestinal lumen, as a new microbiota-based therapies to treat obesity and related co-morbidities. While further research is essential, a large body of evidence point to succinate as a new strategic mediator in the microbiota-host cross-talk, which might provide the basis for new therapeutically approaches in a near future.

Intestinal Bacteroides sp. Imbalance Associated With the Occurrence of Childhood Undernutrition in China

Undernutrition (UN) is a worldwide concern affecting morbidity and mortality among children, but the safety and long-term efficacy of its current treatments remain controversial. Recent evidence showing the roles of the gut microbiome (GM) in nutrient absorption indicates its usefulness in alternative interventions to treat UN safely with sustainable amelioration. To enhance our understanding of the GM and childhood undernutrition, we deep sequenced the gut metagenomes of 65 children with moderate or severe undernutrition (UN group) and 61 healthy children (HC group) to identify associated taxa and genes using a two-stage validation scheme. At stage I, 54 UN patients and 51 healthy children were enrolled for the discovery of GM markers in UN children. The accuracy of the markers was then tested in an additional 11 UN patients and 10 healthy children at stage II. Compared to the HC group, the UN group had lower richness in microbial genes (P = 0.005, FDR = 0.005) and species (P = 0.002, FDR = 0.002). The distributions of bacterial genes enable the identification of 16 gene markers with which to discriminate UN patients with high accuracy [averaged areas under the receiver operating curve (AUC) = 0.87], including three Bacteroides uniformis genes that are responsible for the synthesis of iron transporters. We also identified four species markers that enable the UN patients to be confidently discriminated from the HC children (averaged AUC = 0.91), namely Bacteroides ovatus, Bacteroides uniformis, Bacteroides uniformis, and Bacteroides vulgatus. In addition, metabolic comparison showed significantly decreased isobutyric acid (P = 0.005, FDR = 0.017) and increased isovaleric acid (P = 0.006, FDR = 0.017) in UN patients. We also identified notable correlations between microbial species and short-chain fatty acids (SCFAs) and several nutritional indicators, including acetic acid and iron (r = 0.436, P = 0.029), butyric acid and iron (r = 0.422, P = 0.036), butyric acid and lymphocyte (r = -0.309, P = 0.011), and acetic acid and total protein (r = -0.303, P = 0.043). Taken together, the distinct features of gut microbiota in UN patients highlight the taxonomic and functional shift during the development of UN and provide a solid theoretical basis for intervention in childhood undernutrition through gut microbes.

Dietary short-chain fatty acid intake improves the hepatic metabolic condition via FFAR3

Fermented foods represent a significant portion of human diets with several beneficial effects. Foods produced by bacterial fermentation are enriched in short-chain fatty acids (SCFAs), which are functional products of dietary fibers via gut microbial fermentation. In addition to energy sources, SCFAs also act as signaling molecules via G-protein coupled receptors such as FFAR2 and FFAR3. Hence, dietary SCFAs in fermented foods may have a direct influence on metabolic functions. However, the detailed mechanism by dietary SCFAs remains unclear. Here, we show that dietary SCFAs protected against high-fat diet-induced obesity in mice in parallel with increased plasma SCFAs without changing cecal SCFA or gut microbial composition. Dietary SCFAs suppressed hepatic weight and lipid synthesis. These effects were abolished in FFAR3-deficient mice but not FFAR2-deficient. Thus, SCFAs supplementation improved hepatic metabolic functions via FFAR3 without influencing intestinal environment. These findings could help to promote the development of functional foods using SCFAs.

The Impact of Time of Day on Energy Expenditure: Implications for Long-Term Energy Balance

There is evidence to indicate that the central biological clock (i.e., our endogenous circadian system) plays a role in physiological processes in the body that impact energy regulation and metabolism. Cross-sectional data suggest that energy consumption later in the day and during the night is associated with weight gain. These findings have led to speculation that when, as well as what, we eat may be important for maintaining energy balance. Emerging literature suggests that prioritising energy intake to earlier during the day may help with body weight maintenance. Evidence from tightly controlled acute experimental studies indicates a disparity in the body's ability to utilise (expend) energy equally across the day and night. Energy expenditure both at rest (resting metabolic rate) and after eating (thermic effect of food) is typically more efficient earlier during the day. In this review, we discuss the key evidence for a circadian pattern in energy utilisation and balance, which depends on meal timing. Whilst there is limited evidence that simply prioritising energy intake to earlier in the day is an effective strategy for weight loss, we highlight the potential benefits of considering the role of meal timing for improving metabolic health and energy balance. This review demonstrates that to advance our understanding of the contribution of the endogenous circadian system toward energy balance, targeted studies that utilise appropriate methodologies are required that focus on meal timing and frequency.

Inter-organ communication: a gatekeeper for metabolic health

Multidirectional interactions between metabolic organs in the periphery and the central nervous system have evolved concomitantly with multicellular organisms to maintain whole-body energy homeostasis and ensure the organism's adaptation to external cues. These interactions are altered in pathological conditions such as obesity and type 2 diabetes. Bioactive peptides and proteins, such as hormones and cytokines, produced by both peripheral organs and the central nervous system, are key messengers in this inter-organ communication. Despite the early discovery of the first hormones more than 100 years ago, recent studies taking advantage of novel technologies have shed light on the multiple ways used by cells in the body to communicate and maintain energy balance. This review briefly summarizes well-established concepts and focuses on recent advances describing how specific proteins and peptides mediate the crosstalk between gut, brain, and other peripheral metabolic organs in order to maintain energy homeostasis. Additionally, this review outlines how the improved knowledge about these inter-organ networks is helping us to redefine therapeutic strategies in an effort to promote healthy living and fight metabolic disorders and other diseases.

Propionate alleviates high-fat diet-induced lipid dysmetabolism by modulating gut microbiota in mice

AIMS

The aims were to examine whether oral sodium propionate supplementation regulate lipid metabolism through modulating gut microbiota.

METHODS AND RESULTS

ICR male mice (26·98 ± 0·30 g) were randomly assigned to three groups (n = 10) and fed control diet (Con), high-fat diet (HFD) and HFD plus propionate (Pro) respectively. In this study, we found that HFD increased the weight of final body, inguinal white adipose tissues (iWAT), epididymal white adipose tissue (eWAT) and perirenal white adipose tissue (pWAT), as well as the adipocyte mean area of iWAT and eWAT in mice (P < 0·05), whereas sodium propionate treatment reduced the weight of iWAT and pWAT as well as adipocyte mean area of iWAT in mice fed a HFD (P < 0·05). Moreover, in the iWAT, the mRNA expression of lipogenesis genes, including peroxisome proliferator activated receptor γ, acetyl-CoA carboxylase and carnitine palmitoyl transferase-1β, was upregulated by HFD challenge (P < 0·05), and the elevation of these genes was nearly reversed to the level of control diet-fed mice by sodium propionate treatment. Meanwhile, sodium propionate treatment increased the hormone-sensitive lipase mRNA expression in the iWAT of HFD-fed mice (P < 0·05). High-throughput pyrosequencing of the 16S rRNA demonstrated that sodium propionate treatment significantly recovered the gut microbiota dysbiosis in HFD-fed mice, including the richness and diversity of microbiota and the ratio of Firmicutes to Bacteroidetes. Furthermore, the HFD-induced reductions in colonic levels of butyrate and valerate were reversed by sodium propionate treatment, which also normalized the serum LPS level seen in HFD-fed mice to the levels of the control diet-fed mice.

CONCLUSIONS

Collectively, these results indicated that sodium propionate treatment could improve lipid metabolism in HFD-fed mice, and the potential mechanisms might be via regulating gut microbiota.

SIGNIFICANCE AND IMPACT OF THE STUDY

We demonstrated for the first time that oral sodium propionate significantly improved HFD-induced dysbiosis of gut microbiota, indicating that the mitigative effect of propionate for HFD-induced lipid dysmetabolism might be mediated by gut microbiota in mice.

A protective mechanism of probiotic Lactobacillus against hepatic steatosis via reducing host intestinal fatty acid absorption

The gut microbiome has been known to contribute up to ~30% of the energy absorption of the host. Although various beneficial mechanisms of probiotics have been suggested for non-alcoholic fatty liver disease (NAFLD), whether and which probiotics impact the host's intestinal energy absorption have not yet been quantitatively studied. Here, we suggest a novel mechanism of probiotics against NAFLD, in which Lactobacillus rhamnosus GG, the most common probiotic, shares intestinal fatty acids and prevents the development of diet-induced hepatic steatosis. By using quantitative methods (radioactive tracers and LC-MS) under both in vitro and in vivo conditions, we found that bacteria and hosts competed for fatty acid absorption in the intestine, resulting in decreased weight gain, body fat mass, and hepatic lipid accumulation without differences in calorie intake and excretion in mice fed the probiotic bacteria.

Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study

Metabolic syndrome is characterized by a constellation of comorbidities that predispose individuals to an increased risk of developing cardiovascular pathologies as well as type 2 diabetes mellitus (T2DM)¹. The gut microbiota is considered as a new key contributor involved in the onset of obesity-related disorders². In humans, studies have provided evidence for a negative correlation between Akkermansia muciniphila abundance and overweight, obesity, untreated T2DM, or hypertension^3–8. As the administration of A.muciniphila has never been investigated in humans, we conducted a randomized double-blind placebo-controlled pilot study in overweight/obese insulin resistant volunteers, 40 were enroled and 32 completed the trial. The primary endpoints were on safety, tolerability and metabolic parameters (i.e., insulin resistance, circulating lipids, visceral adiposity, body mass). The secondary outcomes were the gut barrier function (i.e., plasma lipopolysacharrides (LPS) and gut microbiota composition. In this single-center study, we demonstrated that daily oral supplementation of 10¹⁰ bacteria either alive or pasteurized A.muciniphila for 3 months was safe and well tolerated. Compared to the Placebo, pasteurized A.muciniphila improved insulin sensitivity (+28.62±7.02%, P=0.002), reduced insulinemia (-34.08±7.12%, P=0.006) and plasma total cholesterol (-8.68±2.38%, P=0.02). Pasteurized A.muciniphila supplementation slightly decreased body weight (-2.27±0.92kg, P=0.091) as compared to the Placebo group, and fat mass (-1.37±0.82kg, P=0.092) and hip circumference (-2.63±1.14cm, P = 0.091) as compared to baseline. After 3 months of supplementation, A.muciniphila reduced the levels of relevant blood markers of liver dysfunction and inflammation while the overall gut microbiome structure was unaffected. In conclusion, this proof-of-concept study (NCT02637115) shows that the intervention was safe and well-tolerated and that the supplementation with A.muciniphila improves several metabolic paramaters.

Quantification of Fecal Short Chain Fatty Acids by Liquid Chromatography Tandem Mass Spectrometry-Investigation of Pre-Analytic Stability

Short chain fatty acids (SCFAs) are generated by the degradation and fermentation of complex carbohydrates, (i.e., dietary fiber) by the gut microbiota relevant for microbe⁻host communication. Here, we present a method for the quantification of SCFAs in fecal samples by liquid chromatography tandem mass spectrometry (LC-MS/MS) upon derivatization to 3-nitrophenylhydrazones (3NPH). The method includes acetate, propionate, butyrate, and isobutyrate with a run time of 4 min. The reproducible (coefficients of variation (CV) below 10%) quantification of SCFAs in human fecal samples was achieved by the application of stable isotope labelled internal standards. The specificity was demonstrated by the introduction of a quantifier and qualifier ions. The method was applied to investigate the pre-analytic stability of SCFAs in human feces. Concentrations of SCFA may change substantially within hours; the degree and kinetics of these changes revealed huge differences between the donors. The fecal SCFA level could be preserved by the addition of organic solvents like isopropanol. An analysis of the colon content of mice either treated with antibiotics or fed with a diet containing a non-degradable and -fermentable fiber source showed decreased SCFA concentrations. In summary, this fast and reproducible method for the quantification of SCFA in fecal samples provides a valuable tool for both basic research and large-scale studies.