Distinct patterns in the gut microbiota after surgical or medical therapy in obese patients

Type 2 diabetes mellitus-related environmental factors and the gut microbiota: emerging evidence and challenges

The gut microbiota is a group of over 38 trillion bacterial cells in the human microbiota that plays an important role in the regulation of human metabolism through its symbiotic relationship with the host. Changes in the gut microbial ecosystem are associated with increased susceptibility to metabolic disease in humans. However, the composition of the gut microbiota in those with type 2 diabetes mellitus and in the pathogenesis of metabolic diseases is not well understood. This article reviews the relationship between environmental factors and the gut microbiota in individuals with type 2 diabetes mellitus. Finally, we discuss the goal of treating type 2 diabetes mellitus by modifying the gut microbiota and the challenges that remain in this area.

Short-term impact of sucralose consumption on the metabolic response and gut microbiome of healthy adults

Sucralose is an artificial non-nutritive sweetener used in foods aimed to reduce sugar and energy intake. While thought to be inert, the impact of sucralose on metabolic control has shown to be the opposite. The gut microbiome has emerged as a factor shaping metabolic responses after sweetener consumption. We examined the short-term effect of sucralose consumption on glucose homeostasis and gut microbiome of healthy male volunteers. We performed a randomised, double-blind study in thirty-four subjects divided into two groups, one that was administered sucralose capsules (780 mg/d for 7 d; n 17) and a control group receiving placebo (n 17). Before and after the intervention, glycaemic and insulinaemic responses were assessed with a standard oral glucose load (75 g). Insulin resistance was determined using homeostasis model assessment of insulin resistance and Matsuda indexes. The gut microbiome was evaluated before and after the intervention by 16S rRNA sequencing. During the study, body weight remained constant in both groups. Glycaemic control and insulin resistance were not affected during the 7-d period. At the phylum level, gut microbiome was not modified in any group. We classified subjects according to their change in insulinaemia after the intervention, to compare the microbiome of responders and non-responders. Independent of consuming sucralose or placebo, individuals with a higher insulinaemic response after the intervention had lower Bacteroidetes and higher Firmicutes abundances. In conclusion, consumption of high doses of sucralose for 7 d does not alter glycaemic control, insulin resistance, or gut microbiome in healthy individuals. However, it highlights the need to address individual responses to sucralose.

Gut microbiota adaptation after weight loss by Roux-en-Y gastric bypass or sleeve gastrectomy bariatric surgeries

BACKGROUND

Gut microbiota could be involved in the metabolic improvement after surgery.

OBJECTIVE

The aim of the present study was to evaluate the short-term evolution of the gut microbiome after different bariatric surgery procedures and their functionality and relate it with obesity resolution.

SETTING

University hospital, Spain.

METHODS

We studied 28 patients with severe obesity; 14 underwent a Roux-en-Y gastric bypass (RYGB) and 14 underwent laparoscopic sleeve gastrectomy (SG). All patients were examined before and 3 months after the correspondent bariatric surgery. Gut microbiome profile was assessed by the sequencing of amplicons from the 16S rDNA gene by next-generation sequencing.

RESULTS

Gut microbiota profiles significantly differed between surgical procedures. RYGB suffered the largest changes in the microbiota population. SG and RYGB differed in their profiles with higher levels of Akkermansia, Eubacterium, Haemophilus, and Blautia for SG, while Veillonella, Slackia, Granucatiella, and Acidaminococcus occurred with greater levels in RYGB. RYGB microbiota changes were reflected also at the level of functionality, especially in pathways related to environmental adaptation. A biomarker discovery analysis revealed the genus Blautia as characteristic in SG, while Veillonella was of RYGB.

CONCLUSION

Our study shows a shift of the gut microbiome after a bariatric surgery in a procedure-related manner. Gut microbiome changes are related to the adaptation to the changing gut environment and could be related to the pH fluctuations.

Species Deletions from Microbiome Consortia Reveal Key Metabolic Interactions between Gut Microbes

The gut microbiome is a complex microbial community that plays a key role in human health. Diet is an important factor dictating gut microbiome composition. This is mediated by multiple microbe-microbe interactions that result in the fermentation of nondigestible carbohydrates and the production of short-chain fatty acids. Certain species play key metabolic roles in the microbiome, and their disappearance could result in dysbiosis. In this work, a synthetic consortium of 14 gut microbes was studied during the utilization of prebiotic inulin in batch bioreactors. Fermentations were repeated leaving one species out every time, in order to evaluate the impact of their elimination on the system. Substrate consumption, microbial composition, and metabolite production were determined. Single deletions never resulted in a complete loss of bacterial growth or inulin consumption, suggesting functional redundancy. Deletions of Bacteroides dorei and Lachnoclostridium clostridioforme resulted in lower biomass and higher residual inulin. The absence of B. dorei impacted the abundance of the other 10 species negatively. Lachnoclostridium symbiosum, a butyrate producer, appeared to be the most sensitive species to deletions, being stimulated by the presence of Escherichia coli, Bifidobacterium adolescentis, B. dorei, and Lactobacillus plantarum Conversely, bioreactors without these species did not show butyrate production. L. clostridioforme was observed to be essential for propionate production, and B. dorei for lactate production. Our analysis identified specific members that were essential for the function of the consortium. In conclusion, species deletions from microbial consortia could be a useful approach to identify relevant interactions between microorganisms and defining metabolic roles in the gut microbiome.IMPORTANCE Gut microbes associate, compete for, and specialize in specific metabolic tasks. These interactions are dictated by the cross-feeding of degradation or fermentation products. However, the individual contribution of microbes to the function of the gut microbiome is difficult to evaluate. It is essential to understand the complexity of microbial interactions and how the presence or absence of specific microorganisms affects the stability and functioning of the gut microbiome. The experimental approach of this study could be used for identifying keystone species, in addition to redundant functions and conditions that contribute to community stability. Redundancy is an important feature of the microbiome, and its reduction could be useful for the design of microbial consortia with desired metabolic properties enhancing the tasks of the keystone species.

Longitudinal changes of microbiome composition and microbial metabolomics after surgical weight loss in individuals with obesity

BACKGROUND

Some of the metabolic effects of bariatric surgery may be mediated by the gut microbiome.

OBJECTIVES

To study the effect of bariatric surgery on changes to gut microbiota composition and bacterial pathways, and their relation to metabolic parameters after bariatric surgery.

SETTINGS

University hospitals in the United States and Spain.

METHODS

Microbial diversity and composition by 16 S rRNA sequencing, putative bacterial pathways, and targeted circulating metabolites were studied in 26 individuals with severe obesity, with and without type 2 diabetes, before and at 3, 6, and 12 months after either gastric bypass or sleeve gastrectomy.

RESULTS

Bariatric surgery tended to increase alpha diversity, and significantly altered beta diversity, microbiota composition, and function up to 6 months after surgery, but these changes tend to regress to presurgery levels by 12 months. Twelve of 15 bacterial pathways enriched after surgery also regressed to presurgery levels at 12 months. Network analysis identified groups of bacteria significantly correlated with levels of circulating metabolites over time. There were no differences between study sites, surgery type, or diabetes status in terms of microbial diversity and composition at baseline and after surgery.

CONCLUSIONS

The association among changes in microbiome with decreased circulating biomarkers of inflammation, increased bile acids, and products of choline metabolism and other bacterial pathways suggest that the microbiome partially mediates improvement of metabolism during the first year after bariatric surgery.

HgS and Zuotai differ from HgCl2 and methyl mercury in intestinal Hg absorption, transporter expression and gut microbiome in mice

Mercury (Hg) is generally considered as a toxic metal; yet the biological outcomes of Hg-containing compounds are highly dependent upon their chemical forms. We hypothesize that mercury sulfide (HgS) is different from HgCl₂ and methylmercury (MeHg) in producing intestinal Hg absorption and disruption of gut microbiome. To test this hypothesis, mice were given orally with HgS (α-HgS, 30 mg/kg), Zuotai (β-HgS, 30 mg/kg), HgCl₂ (33.6 mg/kg, equivalent Hg as HgS), or MeHg (3.1 mg/kg, 1/10 Hg as HgS) for 7 days. Accumulation of Hg in the duodenum and ileum after HgCl₂ (30-40 fold) and MeHg (10-15 fold) was higher than HgS and Zuotai (~2-fold). HgCl₂ and MeHg decreased intestinal intake peptide transporter-1 and Ost-β, and increased ileal bile acid binding protein and equilibrative nucleoside transporter-1. The efflux transporters ATP-binding cassette sub-family C member-4 (Abcc4), Abcg2, Abcg5/8, and Abcb1b were increased by HgCl₂ and to a lesser extent by MeHg, while HgS and Zuotai had minimal effects. Bacterial DNA was extracted and subjected to 16S rDNA sequencing. Operational taxonomic unit (OTU) results showed that among the 10 phyla, HgS increased Firmicutes, Proteobacteria, while HgCl₂ increased Bacteroidetes, Cyanobacteria and decreased Firmicutes; among the 79 families, HgS increased Rikenellaceae, Lactobacillaceae, Helicobacteraceae, and decreased Prevotellaceae, while HgCl₂ increased Odoribacteraceae, Porphyromonadaceae, and decreased Lactobacillaceae; among the 232 genus/species, HgS and Zuotai affected gut microbiome quite differently from HgCl₂ and MeHg. qPCR analysis with 16S rRNA confirmed sequencing results. Thus, chemical forms of mercury are a major determinant for intestinal Hg accumulation, alterations in transporters and disruption of microbiome.

Lipopolysaccharide and inflammatory cytokines levels decreased after sleeve gastrectomy in Chinese adults with obesity

Obesity is linked to a low-grade systemic inflammation and lipopolysaccharide (LPS) is a key factor. Sleeve gastrectomy (SG) can significantly cause weight loss, but few reports have looked into the changes of LPS and inflammatory cytokines after surgery. To explore the potential short-term impact of SG on LPS and inflammatory cytokines and their relationship to early metabolic changes in obesity. 30 Chinese adults with obesity (BMI 39.37 ± 8.22 kg/m², 25 female) receiving SG were included in this study. Fasting blood samples were collected at baseline and 30 days after SG. Serum LPS markedly reduced from 336.50 (73.54, 500) pg/mL to 5.00 (5.00, 5.24) pg/mL at 1 month after SG (p < 0.05). There was a significant decrease in plasma IL-6, IL-8, and serum CRP after SG (all p < 0.05). Insulin resistance improved remarkably after surgery as displayed by reductions in fasting insulin level (FINS, p < 0.001), and HOMA-IR (p < 0.001). In addition, visceral fat area (VFA) decreased from 209.70 ± 39.96 cm² to 193.28 ± 43.68 cm² after SG (p < 0.001). LPS was positively correlated with FINS (r = 0.391, p = 0.033) and HOMA-IR (r = 0.38, p = 0.038) before SG. Meanwhile, VFA was positively associated with CRP (r = 0.388, p = 0.034) before surgery. When assessing 30-days postoperative changes, a positive correlation was found between the variations of LPS, IL-8 and the reduction of VFA. After multivariate analyses, only the reduced IL-8 level was independently associated with the reduction of VFA (p = 0.015). In conclusion, SG can significantly relieve the inflammation in obesity in the short term and LPS might be an earlier predictor of inflammatory changes after surgery.

Reversing Type 2 Diabetes: A Narrative Review of the Evidence

BACKGROUND

Type 2 diabetes (T2D) has long been identified as an incurable chronic disease based on traditional means of treatment. Research now exists that suggests reversal is possible through other means that have only recently been embraced in the guidelines. This narrative review examines the evidence for T2D reversal using each of the three methods, including advantages and limitations for each.

METHODS

A literature search was performed, and a total of 99 original articles containing information pertaining to diabetes reversal or remission were included.

RESULTS

Evidence exists that T2D reversal is achievable using bariatric surgery, low-calorie diets (LCD), or carbohydrate restriction (LC). Bariatric surgery has been recommended for the treatment of T2D since 2016 by an international diabetes consensus group. Both the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) now recommend a LC eating pattern and support the short-term use of LCD for weight loss. However, only T2D treatment, not reversal, is discussed in their guidelines.

CONCLUSION

Given the state of evidence for T2D reversal, healthcare providers need to be educated on reversal options so they can actively engage in counseling patients who may desire this approach to their disease.

Characterization of gut microbiota composition in HIV-infected patients with metabolic syndrome

The presence of metabolic syndrome (MS) per se or its separated components in HIV-infected patients contributes to an accelerated aging and increased cardiovascular risk. Gut microbiota (GM) dysbiosis has been linked with chronic inflammation associated with MS in a general non-infected population. However, no studies concerning GM have been performed in HIV-infected patients with MS. The aim of this study was to analyze bacterial translocation, inflammation, and GM composition in HIV-infected patients with and without MS. A total of 51 HIV-infected patients were recruited and classified according to the presence of MS (40 patients without MS and 11 with MS). Markers of bacterial translocation, inflammation, and cardiovascular risk were measured and GM was analyzed using 16S rRNA gene deep sequencing. No differences were observed among both HIV-infected groups in the bacterial translocation markers LBP and sCD14. A tendency to increase the inflammatory markers IL-6 (p = 0.069) and MCP-1 (p = 0.067) was observed in those patients suffering from MS. An increase in the cardiovascular risk markers PAI-1 (p = 0.007) and triglycerides/HDL cholesterol ratio (p < 0.0001) was also found in the MS group. No significant changes were observed at phylum level although a decrease in the abundance of seven genera and seven bacterial species, including some anti-inflammatory bacteria, was observed in HIV-infected patients with MS. To summarize, the presence of MS was not accompanied by major changes in GM, although the reduction observed in some anti-inflammatory bacteria may be clinically useful to develop strategies to minimize inflammation and its future deleterious consequences in these HIV-infected patients.

Gut microbiota and obesity: An opportunity to alter obesity through faecal microbiota transplant (FMT)

Obesity is a global pandemic with immense health consequences for individuals and societies. Multiple factors, including environmental influences and genetic predispositions, are known to affect the development of obesity. Despite an increasing understanding of the factors driving the obesity epidemic, therapeutic interventions to prevent or reverse obesity are limited in their impact. Manipulation of the human gut microbiome provides a new potential therapeutic approach in the fight against obesity. Specific gut bacteria and their metabolites are known to affect host metabolism and feeding behaviour, and dysbiosis of this biosystem may lead to metabolic syndrome. Potential therapies to alter the gut microbiota to treat obesity include dietary changes, supplementation of the diet with probiotic organisms and prebiotic compounds that influence bacterial growth, and the use of faecal microbiota transplant, in which gut microbiota from healthy individuals are introduced into the gut. In this review, we examine the growing scientific evidence supporting the mechanisms by which the human gut microbiota may influence carbohydrate metabolism and obesity, and the various possible therapies that may utilize the gut microbiota to help correct metabolic dysfunction.

Altered gut microbiome after bariatric surgery and its association with metabolic benefits: A systematic review

Bariatric surgery is currently the recommended therapy for significant weight reduction and remission of type 2 diabetes. Different types of bariatric surgery result in dramatic changes to gut bacteria but the contribution of such changes to the metabolic benefits achieved is still unclear. This systematic review of 14 clinical studies, incorporating 222 participants (146 patients with Roux-en-Y gastric bypass, 25 with sleeve gastrectomy, 30 with biliointestinal bypass, 7 with vertical banded gastroplasty, and 14 with an adjustable gastric band) reveals generally increased microbial diversity and gene richness after surgery. Major species-level changes include a decrease in the relative abundance of Faecalibacterium prausnitzii and increase in Escherichia coli. Decreases in the relative abundance of Firmicutes after sleeve gastrectomy and increases in Bacteroidetes and Proteobacteria after Roux-en-Y gastric bypass were seen. Microbial changes after surgery are discussed in the context of potential confounding effects of baseline diet, medications, and type 2 diabetes, with recommendations to consider these factors in future studies, to identify potentially causal associations with observed metabolic benefits.

Mechanisms underlying the weight loss effects of RYGB and SG: similar, yet different

The worldwide obesity epidemic continues unabated, adversely impacting upon global health and economies. People with severe obesity suffer the greatest adverse health consequences with reduced life expectancy. Currently, bariatric surgery is the most effective treatment for people with severe obesity, resulting in marked sustained weight loss, improved obesity-associated comorbidities and reduced mortality. Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB), the most common bariatric procedures undertaken globally, engender weight loss and metabolic improvements by mechanisms other than restriction and malabsorption. It is now clear that a plethora of gastrointestinal (GI) tract-derived signals plays a critical role in energy and glucose regulation. SG and RYGB, which alter GI anatomy and nutrient flow, impact upon these GI signals ultimately leading to weight loss and metabolic improvements. However, whilst highly effective overall, at individual level, post-operative outcomes are highly variable, with a proportion of patients experiencing poor long-term weight loss outcome and gaining little health benefit. RYGB and SG are markedly different anatomically and thus differentially impact upon GI signalling and bodyweight regulation. Here, we review the mechanisms proposed to cause weight loss following RYGB and SG. We highlight similarities and differences between these two procedures with a focus on gut hormones, bile acids and gut microbiota. A greater understanding of these procedure-related mechanisms will allow surgical procedure choice to be tailored to the individual to maximise post-surgery health outcomes and will facilitate the discovery of non-surgical treatments for people with obesity.

Differential composition of gut microbiota among healthy volunteers, morbidly obese patients and post-bariatric surgery patients

The modulation of the gut microbiota was recently deemed one of the mechanisms responsible for the excellent outcomes of bariatric surgery. However, to date, only few studies have assessed this, and they have high heterogeneity. In the present study, next-generation 16S ribosomal DNA amplicon sequencing was used to characterize the gut microbiota of healthy volunteers, as well as patients prior to and after sleeve gastrectomy (SG) or Roux-en-Y gastric bypass (RYGB). Significant differences in α diversity, β diversity and species were identified between the different groups/time-points. The results demonstrated excellent outcomes of SG and RYGB. The β diversity was lower in healthy volunteers compared with that in morbidly obese patients with or without type 2 diabetes mellitus. At 3 months after SG, the α diversity was increased and the β diversity was decreased. The abundance of certain species changed significantly after SG and RYGB. It was also revealed that the abundance of certain microbes was significantly correlated with the body mass index, fasting blood glucose and glycosylated haemoglobin. It may be concluded that bariatric surgery may cause obvious alterations in the gut microbiota and compared with healthy volunteers and obese patients without bariatric surgery, the microbiota composition of post-bariatric surgery has unique characteristics. However, studies with a larger cohort and longer follow-up may be required to confirm these results.

Cross-Regional View of Functional and Taxonomic Microbiota Composition in Obesity and Post-obesity Treatment Shows Country Specific Microbial Contribution

Gut microbiota has been shown to have an important influence on host health. The microbial composition of the human gut microbiota is modulated by diet and other lifestyle habits and it has been reported that microbial diversity is altered in obese people. Obesity is a worldwide health problem that negatively impacts the quality of life. Currently, the widespread treatment for obesity is bariatric surgery. Interestingly, gut microbiota has been shown to be a relevant factor in effective weight loss after bariatric surgery. Since that the human gut microbiota of normal subjects differs between geographic regions, it is possible that rearrangements of the gut microbiota in dysbiosis context are also region-specific. To better understand how gut microbiota contribute to obesity, this study compared the composition of the human gut microbiota of obese and lean people from six different regions and showed that the microbiota compositions in the context of obesity were specific to each studied geographic location. Furthermore, we analyzed the functional patterns using shotgun DNA metagenomic sequencing and compared the results with other obesity-related metagenomic studies, we observed that microbial contribution to functional pathways were country-specific. Nevertheless, our study showed that although microbial composition of obese patients was country-specific, the overall metabolic functions appeared to be the same between countries, indicating that different microbiota components contribute to similar metabolic outcomes to yield functional redundancy. Furthermore, we studied the microbiota functional changes of obese patients after bariatric surgery, by shotgun metagenomics sequencing and observed that changes in functional pathways were specific to the type of obesity treatment. In all, our study provides new insights into the differences and similarities of obese gut microbiota in relation to geographic location and obesity treatments.

Sleeve Gastrectomy: Metabolic Surgical Procedure of Choice?

Roux-en-Y gastric bypass and sleeve gastrectomy (SG) are fairly similar in terms of their long-term effects on excess body weight, cardiometabolic risk factors, and quality of life. However, SG appears to be a safer procedure with distinct metabolic advantages, which can be even better than gastric bypass in some aspects.

A comparison of rodent models of vertical sleeve gastrectomy

BACKGROUND

Although vertical sleeve gastrectomy (VSG) is fashioned in humans by applying multiple staple loads, rodent VSG is generally created through a single-staple load application.

OBJECTIVES

To investigate the impact of a 2-staple load VSG rat model more closely resembling the multistaple load operation done in humans on weight, metabolic outcomes, and the microbiome and how these compare with those obtained with the standard one-staple load model.

SETTING

University research facility, United States.

METHODS

High-fat diet-induced obese male rats were randomized to single-staple load VSG (VSG1), 2-staple load VSG (VSG2), or sham operation (Sham). Outcomes included weight and composition, food intake, glucose metabolism, lipids, bile acids, and intestinal microbiome. Statistical comparisons were performed using analysis of variance.

RESULTS

Both procedures resulted in substantial weight and body fat loss compared with Sham-treated animals. Weight loss was modestly greater for VSG2 compared with VSG1. Food intake was reduced in both procedures and accounted for the observed weight reduction. Glucose tolerance and plasma and hepatic lipid profiles were improved comparably in VSG1 and VSG2 relative to Sham. Bile acids were higher for VSG2 compared with Sham but not significantly different between VSG1 and VSG2. Neither procedure impacted intestinal microbiome richness and diversity compared with Sham across multiple intestinal sections. Colonic Actinobacteria was more abundant in VSG2 than in Sham. Relative abundances of bacterial phyla did not differ among VSG1, VSG2, and Sham across the remaining intestinal sections.

CONCLUSIONS

Although VSG1 or VSG2 offer effective and overall comparable platforms for the study of obesity, VSG2 resulted in superior weight loss.

Bile acids at the cross-roads of gut microbiome-host cardiometabolic interactions

While basic and clinical research over the last several decades has recognized a number of modifiable risk factors associated with cardiometabolic disease progression, additional and alternative biological perspectives may offer novel targets for prevention and treatment of this disease set. There is mounting preclinical and emerging clinical evidence indicating that the mass of metabolically diverse microorganisms which inhabit the human gastrointestinal tract may be implicated in initiation and modulation of cardiovascular and metabolic disease outcomes. The following review will discuss this gut microbiome-host metabolism axis and address newly proposed bile-mediated signaling pathways through which dysregulation of this homeostatic axis may influence host cardiovascular risk. With a central focus on the major nuclear and membrane-bound bile acid receptor ligands, we aim to review the putative impact of microbial bile acid modification on several major phenotypes of metabolic syndrome, from obesity to heart failure. Finally, attempting to synthesize several separate but complementary hypotheses, we will review current directions in preclinical and clinical investigation in this evolving field.