Effects of acute dietary weight loss on postprandial plasma bile acid responses in obese insulin resistant subjects

Intermittent Fasting Improves Insulin Resistance by Modulating the Gut Microbiota and Bile Acid Metabolism in Diet-Induced Obesity

SCOPE

Adipose tissue macrophages (ATMs) are crucial in the pathogenesis of insulin resistance (IR). Intermittent fasting (IF) is an effective intervention for obesity. However, the underlying mechanism by which IF improves IR remains unclear.

METHODS AND RESULTS

Male C57BL/6J mice are fed chow-diet and high-fat diet (HFD) for 12 weeks, then is randomized into ad libitum feeding or every other day fasting for 8 weeks. Markers of ATMs and expression of uncoupling protein 1 (UCP-1) are determined. Gut microbiota and bile acids (BAs) are profiled using 16S rRNA sequencing and targeted metabolomics analysis. Results indicate that IF improves IR in HFD-induced obesity. IF decreases ATM infiltration, pro-inflammatory M1 gene expression, and promotes white adipose tissue (WAT) browning by elevating UCP-1 expression. IF restructures microbiota composition, significantly expanding the abundance of Verrucomicrobia particularly Akkermansia muciniphila, with the decrease of that of Firmicutes. IF increases the level of total BAs and alters the composition of BAs with higher proportion of 12α-hydroxylated (12α-OH) BAs. The changes in these BAs are correlated with differential bacteria.

CONCLUSION

The findings indicate that IF improves IR partially mediated by the interplay between restructured gut microbiota and BAs metabolism, which has implications for the dietary management in obesity.

Glycodeoxycholic acid as alternative treatment in 3β-hydroxy-Δ5-C27-steroid-oxidoreductase: a case report

Background

3β-hydroxy-Δ5-C27-steroid-oxidoreductase (3β-HSD) deficiency is a bile acid synthesis disorder that leads to the absence of normal primary bile acids and the accumulation of abnormal bile acids. This results in cholestatic jaundice, fat-soluble vitamin deficiency, acholic or fatty stools and failure to thrive. Bile acid supplementation is used to treat 3β-HSD-deficiency and its symptoms.

Methods

This report details the case of a 28-year-old woman diagnosed with 3β-HSD-deficiency, who was treated with glycine-conjugated deoxycholic acid (gDCA).

Results

gDCA treatment successfully restored normal bile acid levels, improved body weight by reducing fat malabsorption, and was well-tolerated with no observed liver problems or side effects.

Conclusions

As a potent FXR ligand, gDCA might exert its action through FXR activation leading to bile acid synthesis regulation.

Contribution of the microbiome for better phenotyping of people living with obesity

Obesity has reached epidemic proportion worldwide and in all ages. Available evidence points to a multifactorial pathogenesis involving gene predisposition and environmental factors. Gut microbiota plays a critical role as a major interface between external factors, i.e., diet, lifestyle, toxic chemicals, and internal mechanisms regulating energy and metabolic homeostasis, fat production and storage. A shift in microbiota composition is linked with overweight and obesity, with pathogenic mechanisms involving bacterial products and metabolites (mainly endocannabinoid-related mediators, short-chain fatty acids, bile acids, catabolites of tryptophan, lipopolysaccharides) and subsequent alterations in gut barrier, altered metabolic homeostasis, insulin resistance and chronic, low-grade inflammation. Although animal studies point to the links between an "obesogenic" microbiota and the development of different obesity phenotypes, the translational value of these results in humans is still limited by the heterogeneity among studies, the high variation of gut microbiota over time and the lack of robust longitudinal studies adequately considering inter-individual confounders. Nevertheless, available evidence underscores the existence of several genera predisposing to obesity or, conversely, to lean and metabolically health phenotype (e.g., Akkermansia muciniphila, species from genera Faecalibacterium, Alistipes, Roseburia). Further longitudinal studies using metagenomics, transcriptomics, proteomics, and metabolomics with exact characterization of confounders are needed in this field. Results must confirm that distinct genera and specific microbial-derived metabolites represent effective and precision interventions against overweight and obesity in the long-term.

The gut microbiota in obesity and weight management: microbes as friends or foe?

Obesity is caused by a long-term difference between energy intake and expenditure - an imbalance that is seemingly easily restored by increasing exercise and reducing caloric consumption. However, as simple as this solution appears, for many people, losing excess weight is difficult to achieve and even more difficult to maintain. The reason for this difficulty is that energy intake and expenditure, and by extension body weight, are regulated through complex hormonal, neural and metabolic mechanisms that are under the influence of many environmental factors and internal responses. Adding to this complexity, the microorganisms (microbes) that comprise the gut microbiota exert direct effects on the digestion, absorption and metabolism of food. Furthermore, the gut microbiota exerts a miscellany of protective, structural and metabolic effects both on the intestinal milieu and peripheral tissues, thus affecting body weight by modulating metabolism, appetite, bile acid metabolism, and the hormonal and immune systems. In this Review, we outline historical and recent advances in understanding how the gut microbiota is involved in regulating body weight homeostasis. We also discuss the opportunities, limitations and challenges of using gut microbiota-related approaches as a means to achieve and maintain a healthy body weight.

Changes in circulating bile acid subtypes in response to weight-loss diets are associated with improvements in glycemic status and insulin resistance: The POUNDS Lost trial

OBJECTIVE

Various primary and secondary bile acids (BAs) may play pivotal roles in glucose/insulin metabolism. We investigated whether changes in specific BA subtypes were associated with long-term changes in glucose and insulin sensitivity.

METHODS

This study included 515 adults with overweight or obesity who participated in a 2-year intervention study of weight-loss diets with different macronutrient intakes. Circulating primary and secondary unconjugated BAs and their taurine-/glycine-conjugates were measured at baseline and 6 months after the interventions. We analyzed associations of changes in BA subtypes with two-year changes in fasting glucose, insulin, and insulin resistance (HOMA-IR).

RESULTS

Greater decreases in primary and secondary BA subtypes induced by the interventions were significantly associated with greater reductions of fasting insulin and HOMA-IR at 6 months, showing various effects across the BA subtypes. The reductions of specific BA subtypes (chenodeoxycholate [CDCA], taurocholate [TCA], taurochenodeoxycholate [TCDCA], and taurodeoxycholate [TDCA]) were significantly related to improved glucose levels at 6 months. The initial (6-month) decreases in primary and secondary BA subtypes (glycochenodeoxycholate [GCDCA], TCDCA, and glycoursodeoxycholate [GUDCA]) were also significantly associated with long-term improvements in glucose and insulin metabolism over 2 years. We found significant interactions between dietary fat intake and changes in the BA subtypes for changes in glucose metabolism (Pinteraction < 0.05).

CONCLUSIONS

Weight-loss diet-induced changes in distinct subtypes of circulating BAs were associated with improved glucose metabolism and insulin sensitivity in adults with overweight or obesity. Dietary fat intake may modify the associations of changes in BA metabolism with glucose metabolism.

An Updated Perspective on the Dual-Track Model of Enterocyte Fat Metabolism

The small intestinal epithelium has classically been envisioned as a conduit for nutrient absorption, but appreciation is growing for a larger and more dynamic role for enterocytes in lipid metabolism. Considerable gaps remain in our knowledge of this physiology, but it appears that the enterocyte's structural polarization dictates its behavior in fat partitioning, treating fat differently based on its absorption across the apical versus the basolateral membrane. In this review, we synthesize existing data and thought on this dual-track model of enterocyte fat metabolism through the lens of human integrative physiology. The apical track includes the canonical pathway of dietary lipid absorption across the apical brush-border membrane, leading to packaging and secretion of those lipids as chylomicrons. However, this track also reserves a portion of dietary lipid within cytoplasmic lipid droplets for later uses, including the "second-meal effect," which remains poorly understood. At the same time, the enterocyte takes up circulating fats across the basolateral membrane by mechanisms that may include receptor-mediated import of triglyceride-rich lipoproteins or their remnants, local hydrolysis and internalization of free fatty acids, or enterocyte de novo lipogenesis using basolaterally absorbed substrates. The ultimate destinations of basolateral-track fat may include fatty acid oxidation, structural lipid synthesis, storage in cytoplasmic lipid droplets, or ultimate resecretion, although the regulation and purposes of this basolateral track remain mysterious. We propose that the enterocyte integrates lipid flux along both of these tracks in order to calibrate its overall program of lipid metabolism.

Gut microbiota-bile acid crosstalk contributes to the rebound weight gain after calorie restriction in mice

Calorie restriction (CR) and fasting are common approaches to weight reduction, but the maintenance is difficult after resuming food consumption. Meanwhile, the gut microbiome associated with energy harvest alters dramatically in response to nutrient deprivation. Here, we reported that CR and high-fat diet (HFD) both remodeled the gut microbiota with similar microbial composition, Parabacteroides distasonis was most significantly decreased after CR or HFD. CR altered microbiota and reprogramed metabolism, resulting in a distinct serum bile acid profile characterized by depleting the proportion of non-12α-hydroxylated bile acids, ursodeoxycholic acid and lithocholic acid. Downregulation of UCP1 expression in brown adipose tissue and decreased serum GLP-1 were observed in the weight-rebound mice. Moreover, treatment with Parabacteroides distasonis or non-12α-hydroxylated bile acids ameliorated weight regain via increased thermogenesis. Our results highlighted the gut microbiota-bile acid crosstalk in rebound weight gain and Parabacteroides distasonis as a potential probiotic to prevent rapid post-CR weight gain.

Caloric restriction is a common approach to weight reduction, however, weight regain is common. Here the authors report that caloric restriction reduces the abundance of Parabacteroides distasonis in the gut and alters serum bile acid (BA) profile, which contribute to weight regain in mice.

Changes in bile acid subtypes and long-term successful weight-loss in response to weight-loss diets: The POUNDS lost trial

BACKGROUND AND AIMS

Primary bile acids (BAs) are synthesized in the liver and secondary BAs result from intestinal microbial activity. Different subtypes of BAs may be involved in regulating adiposity and energy homeostasis. We examined how changes in circulating BA subtypes induced by weight-loss diets were associated with improvements in adiposity, regional fat deposition and energy metabolism among overweight and obese adults.

METHODS

The study included 551 subjects who participated in a 2-year weight-loss diet intervention trial. Circulating 14 BA subtypes (primary and secondary unconjugated BAs and their taurine-/glycine-conjugates) were measured at baseline and 6 months. Associations of changes in BAs with changes in weight, waist circumference, resting energy expenditure (REE), body fat composition and fat distribution were evaluated.

RESULTS

Greater decreases in primary BAs (cholate and chenodeoxycholate) and secondary BAs (deoxycholate and lithocholate) and their conjugates (except for glycolithocholate) were associated with more decreases in weight and waist circumference at 6 months (P_{-after-false-discovery-rate-correction} [P_FDR ] < .05). We found that changes in glycocholate and glycoursodeoxycholate were consistently associated with reductions of general and central adiposity, REE, whole-body fat and visceral adipose tissue (P_FDR  < .05). Further, the initial (6-month) changes in BA subtypes were differently predictive of successful weight loss over 2 years.

CONCLUSIONS

The decreases in primary and secondary BA subtypes after eating low-calorie weight-loss diets were significantly associated with improving adiposity, fat accumulation and energy metabolism, suggesting that specific BA subtypes would be predictive of long-term successful weight loss and individuals' response to the treatment of weight-loss diets.

Mechanisms of weight regain

Weight regain following weight loss is frequent problem that people with obesity face. This weight recidivism is often attributed to the lack of compliance with appropriate food habits and exercise. On the contrary, it is known that body weight and fat mass are regulated by numerous physiological mechanisms, far beyond voluntary food intake and physical exercise. Thus, the aim of this paper is to review the main peripheral and central mechanisms involved in weight regain. Gut hormone secretion profiles impact upon predisposition to weight regain according to an individual variability, although it is recognised a usual pattern of compensatory changes: a reduction in anorectic hormones secretion and an increase in orexigenic hormone. These changes lead to both increased appetite and reward value of food leading to increased energye intake. In addition, resting energy expenditure after weight loss is lower than expected according to body composition changes. This gap between observed and predicted energy expenditure following weight loss is named metabolic adaptation, which has been suggested to explain partly weight regain. This complicated scenario, beyond patient motivation, makes weight regain a challenge in long-term management interventions in patients with obesity.

Differential effects of a 40-hour fast and bile acid supplementation on human GLP-1 and FGF19 responses

Bile acids, glucagon-like peptide-1 (GLP-1), and fibroblast growth factor 19 (FGF19) play an important role in postprandial metabolism. In this study, we investigated the postprandial bile acid response in plasma and its relation to insulin, GLP-1, and FGF19. First, we investigated the postprandial response to 40-h fast. Then we administered glycine-conjugated deoxycholic acid (gDCA) with the meal. We performed two separate observational randomized crossover studies on healthy, lean men. In experiment 1: we tested 4-h mixed meal after an overnight fast and a 40-h fast. In experiment 2, we tested a 4-h mixed meal test with and without gDCA supplementation. Both studies measured postprandial glucose, insulin, bile acids, GLP-1, and FGF19. In experiment 1, 40 h of fasting induced insulin resistance and increased postprandial GLP-1 and FGF19 concentrations. After an overnight fast, we observed strong correlations between postprandial insulin and gDCA levels at specific time points. In experiment 2, administration of gDCA increased GLP-1 levels and lowered late postprandial glucose without effect on FGF19. Energy expenditure was not affected by gDCA administration. Unexpectedly, 40 h of fasting increased both GLP-1 and FGF19, where the former appeared bile acid independent and the latter bile acid dependent. Second, a single dose of gDCA increased postprandial GLP-1. Therefore, our data add complexity to the physiological regulation of the enterokines GLP-1 and FGF19 by bile acids.

Fibroblast Growth Factor 15/19: From Basic Functions to Therapeutic Perspectives

Discovered 20 years ago, fibroblast growth factor (FGF)19, and its mouse ortholog FGF15, were the first members of a new subfamily of FGFs able to act as hormones. During fetal life, FGF15/19 is involved in organogenesis, affecting the development of the ear, eye, heart, and brain. At adulthood, FGF15/19 is mainly produced by the ileum, acting on the liver to repress hepatic bile acid synthesis and promote postprandial nutrient partitioning. In rodents, pharmacologic doses of FGF19 induce the same antiobesity and antidiabetic actions as FGF21, with these metabolic effects being partly mediated by the brain. However, activation of hepatocyte proliferation by FGF19 has long been a challenge to its therapeutic use. Recently, genetic reengineering of the molecule has resolved this issue. Despite a global overlap in expression pattern and function, murine FGF15 and human FGF19 exhibit several differences in terms of regulation, molecular structure, signaling, and biological properties. As most of the knowledge originates from the use of FGF19 in murine models, differences between mice and humans in the biology of FGF15/19 have to be considered for a successful translation from bench to bedside. This review summarizes the basic knowledge concerning FGF15/19 in mice and humans, with a special focus on regulation of production, morphogenic properties, hepatocyte growth, bile acid homeostasis, as well as actions on glucose, lipid, and energy homeostasis. Moreover, implications and therapeutic perspectives concerning FGF19 in human diseases (including obesity, type 2 diabetes, hepatic steatosis, biliary disorders, and cancer) are also discussed.

The roles of bile acids and applications of microencapsulation technology in treating Type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disease characterized by the loss of glycemic control. Recent studies have shown significant inflammation and disturbed bile acid homeostasis, associated with T1DM. Bile acids are endogenously produced as a result of cholesterol catabolism in the liver and solely metabolized by gut microflora. This review investigates their potential oral delivery in T1DM using targeted delivery and encapsulation technologies. A sensitive and selective search was carried out using different search engines and databases. Keywords used included diabetes mellitus, bile acids and inflammation. To conclude, bile acids have a significant impact on diabetes symptoms and, when microencapsulated, may be used as an adjunct therapy to supplement T1DM treatment.

Role of Bile Acids in Metabolic Control

Bile acids are endocrine molecules that in addition to facilitating the absorption of fat-soluble nutrients regulate numerous metabolic processes, including glucose, lipid, and energy homeostasis. The signaling actions of bile acids are mediated through specific bile-acid-activated nuclear and membrane-bound receptors. These receptors are not only expressed by tissues within the enterohepatic circulation such as the liver and the intestine, but also in other organs where bile acids mediate their systemic actions. In this review, we discuss bile acid signaling and the interplay with the gut microbiota in the pathophysiology of obesity, type 2 diabetes, and non-alcoholic fatty liver disease, and the role of surgical and pharmacological interventions on bile acid profiles and metabolism.

Bile acids and bariatric surgery

Bariatric surgery, specifically Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), are the most effective and durable treatments for morbid obesity and potentially a viable treatment for type 2 diabetes (T2D). The resolution rate of T2D following these procedures is between 40 and 80% and far surpasses that achieved by medical management alone. The molecular basis for this improvement is not entirely understood, but has been attributed in part to the altered enterohepatic circulation of bile acids. In this review we highlight how bile acids potentially contribute to improved lipid and glucose homeostasis, insulin sensitivity and energy expenditure after these procedures. The impact of altered bile acid levels in enterohepatic circulation is also associated with changes in gut microflora, which may further contribute to some of these beneficial effects. We highlight the beneficial effects of experimental surgical procedures in rodents that alter bile secretory flow without gastric restriction or altering nutrient flow. This information suggests a role for bile acids beyond dietary fat emulsification in altering whole body glucose and lipid metabolism strongly, and also suggests emerging roles for the activation of the bile acid receptors farnesoid x receptor (FXR) and G-protein coupled bile acid receptor (TGR5) in these improvements. The limitations of rodent studies and the current state of our understanding is reviewed and the potential effects of bile acids mediating the short- and long-term metabolic improvements after bariatric surgery is critically examined.