Novel gut-based pharmacology of metformin in patients with type 2 diabetes mellitus

Metformin and Systemic Metabolism

Metformin can improve patients' hyperglycemia through significant suppression of hepatic glucose production. However, up to 300 times higher concentrations of metformin accumulate in the intestine than in the circulation, where it alters nutrient metabolism in intestinal epithelial cells and microbiome, leading to increased lactate production. Hepatocytes use lactate to make glucose at the cost of energy expenditure, creating a futile intestine-liver cycle. Furthermore, metformin reduces blood lipopolysaccharides and its initiated low-grade inflammation and increased oxidative phosphorylation in liver and adipose tissues. These metformin effects result in the improvement of insulin sensitivity and glucose utilization in extrahepatic tissues. In this review, I discuss the current understanding of the impact of metformin on systemic metabolism and its molecular mechanisms of action in various tissues.

Changes of saliva microbiota in the onset and after the treatment of diabetes in patients with periodontitis

The relationship between type 2 diabetes mellitus (T2DM) and oral microbiota is still insufficiently recognized. In the present study, we compared the salivary microbiome of nondiabetic individuals, treatment-naïve diabetic patients, and diabetic patients treated with metformin or a combination of insulin and other drugs. The α- and β-diversity demonstrated significant differences in the salivary microbiome between the nondiabetic people and patients with a history of diabetes, while little divergence was found among individuals with a history of diabetes. After characterizing the effects of periodontitis on the microbial composition of each group, the salivary microbiome of the treatment-naïve diabetic patient group was compared with that of nondiabetic people and the metformin/combined treatment groups. The results revealed changes in the contents of certain bacteria after both the onset and the treatment of diabetes; among these differential bacteria, Blautia_wexlerae, Lactobacillus_fermentum, Nocardia_coeliaca and Selenomonas_artemidis varied in all processes. A subsequent correlational analysis of the differential bacteria and clinical characteristics demonstrated that salivary microbes were related to drug treatment and certain pathological changes. Finally, the four common differential bacteria were employed for distinguishing the treatment-naïve diabetic patients from the nondiabetic people and the treated patients, with prediction accuracies of 83.3%, 75% and 75%, respectively.

The effect of exenatide on fasting bile acids in newly diagnosed type 2 diabetes mellitus patients, a pilot study

Background

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) demonstrated good glycemic efficacy in patients with type 2 diabetes mellitus (T2DM) recent years, whereas studies on GLP-1 RAs’ biliary effects were limited. Therefore, we aimed to assess the effect of exenatide on bile acids (BAs) and investigate the role of BAs in the glycemic control effect of exenatide.

Methods

Thirty-eight newly diagnosed T2DM participants without glucose-lowering drugs intake were recruited. Plasma total bile acids in fasting state (FTBAs) and other parameters were tested at baseline. Then exenatide were applied to the T2DM participants for 12 weeks. FTBAs and glycemic parameters were measured again after exenatide treatment, and correlation analysis between changes of FTBAs and glycemic parameters were conducted to investigate the role of BAs in the glycemic control effect of exenatide.

Results

The baseline FTBAs level of T2DM patients had no significance (3.84 ± 2.06 vs. 3.87 ± 2.89, P = 0.954) compared with healthy subjects. After 12-week exenatide treatment for the T2DM patients, FTBAs were decreased from 3.84 ± 2.06 μmol/L to 3.06 ± 1.27 μmol/L (P < 0.01). The correlation analysis showed that changes of FTBAs was positively correlated with changes of FPG (r = 0.355, P < 0.05).

Conclusions

Our results demonstrated a decreased FTBAs level after exenatide treatment for 12 weeks, without the interference of metformin and other glucose-lowering drugs. The reduction of FTBAs might not exert a positive role in the glycemic control effect of exenatide.

Trial registration

Trial registration number: NCT04303819. Registered in March 11, 2020 - Retrospectively registered.

Odd-numbered agaro-oligosaccharides alleviate type 2 diabetes mellitus and related colonic microbiota dysbiosis in mice

Agaro- and neoagaro-oligosaccharides with even-numbered sugar units possess a variety of biological activities. However, the effects of the odd-numbered oligosaccharides from Gracilaria agarose (OGAOs) on type 2 diabetes mellitus (T2DM) have not been reported. In this study, we aimed to evaluate the effects of OGAOs on anti-T2DM from different aspects. We found that OGAOs treatment could alleviate oxidative stress, inflammation, and the related hyperglycemia, insulin resistance, lipid accumulation, and obesity in high-fat diet (HFD) induced T2DM. Investigation of the underlying mechanism showed that colitis and colonic microbiota dysbiosis in T2DM mice were ameliorated after OGAOs treatment. First, OGAOs increased the expression of ZO-1, occludin, and AMPK, and suppressed the TLR4/MAPK/NF-κB pathway in colon indicating that OGAOs enhance intestinal integrity and conduct the anti-apoptosis effects to prevent the invasion of toxins and harmful microorganisms. Moreover, the relative abundance of Akkermansia was significantly upregulated in the gut microbiome of T2DM mice associated with a dramatic decrease of the relative abundance of Helicobacter, which are both beneficial for alleviating colitis and T2DM. In addition, Spearman's correlation analysis indicated that changes in the colonic microbiota could regulate oxidative stress, inflammation, and hyperlipidemia. In summary, the underlying mechanism of OGAOs on alleviating colitis and colonic microbiota dysbiosis in T2DM has been intensively studied, illustrating that OGAOs could be further developed as a potential pharmaceutical agent for T2DM.

Metabolic benefits of annatto-extracted tocotrienol on glucose homeostasis, inflammation, and gut microbiome

Emerging evidence suggests that the gut microbiome plays an important role in the pathophysiology of both obesity and type 2 diabetes mellitus. We previously reported that dietary annatto-extracted tocotrienol exerts beneficial effects by modulating inflammatory responses in mice fed a high-fat diet (HFD). The purpose of this study was to test the hypothesis that tocotrienol supplementation when combined with an HFD would result in an altered gut microbiota composition. For 14 weeks, forty-eight male C57BL/6J mice were assigned to 4 groups-low-fat diet, HFD, HFD supplemented with annatto-extracted tocotrienol at 800 mg/kg diet (AT), and HFD supplemented with metformin at 200 mg/kg diet. Glucose homeostasis was assessed by glucose and insulin tolerance tests, serum and pancreas insulin levels, and histological assessments of insulin and glucagon in pancreatic tissue. The concentrations of adipokines were measured in white adipose tissues. For the gut microbiome analysis, cecal content was collected, DNA was extracted, and 16S rRNA gene sequencing was performed. AT supplementation improved glucose homeostasis and lowered resistin, leptin, and interleukin-6 levels in white adipose tissue. Relative to the HFD group, AT-supplemented mice showed a decrease in the Firmicutes to Bacteroidetes ratio and had a lower abundance of Ruminococcus lactaris, Dorea longicatena, and Lachnospiraceae family. The relative abundance of Akkermansia muciniphila was increased in the AT group compared to the low-fat diet group. The association between the metabolic improvements and the identified bacterial taxa suggests a potential metabolic modulation caused by AT supplementation through the gut microbiota composition in mice fed an HFD.

Toxicomicrobiomics: The Human Microbiome vs. Pharmaceutical, Dietary, and Environmental Xenobiotics

The harmful impact of xenobiotics on the environment and human health is being more widely recognized; yet, inter- and intraindividual genetic variations among humans modulate the extent of harm, mostly through modulating the outcome of xenobiotic metabolism and detoxification. As the Human Genome Project revealed that host genetic, epigenetic, and regulatory variations could not sufficiently explain the complexity of interindividual variability in xenobiotics metabolism, its sequel, the Human Microbiome Project, is investigating how this variability may be influenced by human-associated microbial communities. Xenobiotic-microbiome relationships are mutual and dynamic. Not only does the human microbiome have a direct metabolizing potential on xenobiotics, but it can also influence the expression of the host metabolizing genes and the activity of host enzymes. On the other hand, xenobiotics may alter the microbiome composition, leading to a state of dysbiosis, which is linked to multiple diseases and adverse health outcomes, including increased toxicity of some xenobiotics. Toxicomicrobiomics studies these mutual influences between the ever-changing microbiome cloud and xenobiotics of various origins, with emphasis on their fate and toxicity, as well the various classes of microbial xenobiotic-modifying enzymes. This review article discusses classic and recent findings in toxicomicrobiomics, with examples of interactions between gut, skin, urogenital, and oral microbiomes with pharmaceutical, food-derived, and environmental xenobiotics. The current state and future prospects of toxicomicrobiomic research are discussed, and the tools and strategies for performing such studies are thoroughly and critically compared.

Mechanism of glucose-lowering by metformin in type 2 diabetes: Role of bile acids

Type 2 diabetes mellitus (T2DM) is an increasingly prevalent chronic condition, characterized by abnormally elevated blood glucose concentrations and, as a consequence, increased risk of micro- and macrovascular complications. Metformin is usually the first-line glucose-lowering medication in T2DM; however, despite being used for more than 60 years, the mechanism underlying the glucose-lowering action of metformin remains incompletely understood. Although metformin reduces hepatic glucose production, there is persuasive evidence that the gastrointestinal tract is crucial in mediating this effect, particularly via secretion of the incretin hormone glucagon-like peptide 1 (GLP-1). It is now well recognized that bile acids, in addition to their established function in fat digestion and absorption, are important regulators of glucose metabolism. Exposure of the small and large intestine to bile acids induces GLP-1 secretion, modulates the composition of the gut microbiota, and reduces postprandial blood glucose excursions in humans with and without T2DM. Metformin reduces intestinal bile acid resorption substantially, such that intraluminal bile acids may, at least in part, account for its glucose-lowering effect. The present review focuses on the conceptual shift in our understanding as to how metformin lowers blood glucose in T2DM, with a particular emphasis on the role of intestinal bile acids.

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.

Role of the Gut in Diabetic Dyslipidemia

Type 2 diabetes (T2D) is associated with increased risk of cardiovascular disease (CVD). In insulin resistant states such as the metabolic syndrome, overproduction and impaired clearance of liver-derived very-low-density lipoproteins and gut-derived chylomicrons (CMs) contribute to hypertriglyceridemia and elevated atherogenic remnant lipoproteins. Although ingested fat is the major stimulus of CM secretion, intestinal lipid handling and ultimately CM secretory rate is determined by numerous additional regulatory inputs including nutrients, hormones and neural signals that fine tune CM secretion during fasted and fed states. Insulin resistance and T2D represent perturbed metabolic states in which intestinal sensitivity to key regulatory hormones such as insulin, leptin and glucagon-like peptide-1 (GLP-1) may be altered, contributing to increased CM secretion. In this review, we describe the evidence from human and animal models demonstrating increased CM secretion in insulin resistance and T2D and discuss the molecular mechanisms underlying these effects. Several novel compounds are in various stages of preclinical and clinical investigation to modulate intestinal CM synthesis and secretion. Their efficacy, safety and therapeutic utility are discussed. Similarly, the effects of currently approved lipid modulating therapies such as statins, ezetimibe, fibrates, and PCSK9 inhibitors on intestinal CM production are discussed. The intricacies of intestinal CM production are an active area of research that may yield novel therapies to prevent atherosclerotic CVD in insulin resistance and T2D.

Effects of Metformin on the Gut Microbiota in Obesity and Type 2 Diabetes Mellitus

Metformin is a first-line treatment for type 2 diabetes mellitus (T2DM); however, its underlying mechanism is not fully understood. Gut microbiota affect the development and progression of T2DM. In recent years, an increasing number of studies has focused on the relationship between metformin and gut microbiota, suggesting that metformin might exert part of its hypoglycemic effect through these microbes. However, most of these results were not consistent due to the complex composition of the microbiota, the differences between species, the large variation between individuals, and the differences in experimental design, bringing great obstacle for our better understanding of the effects of metformin on the gut microbiota. Here, we reviewed the published papers concerning about the impacts of metformin on the gut microbiota of mice, rats, and humans with obesity or T2DM, and summarized the changes of gut microbiota composition caused by metformin and the possible underlying hypoglycemic mechanism which is related to gut microbiota. It was found that the proportions of some microbiota, such as phyla Bacteroidetes and Verrucomicrobia and genera Akkermansia, Bacteroides and Escherichia, were significantly affected by metformin in several studies. Metformin may exert part of hypoglycemic effects by altering the gut microbiota in ways that maintain the integrity of the intestinal barrier, promote the production of short-chain fatty acids (SCFAs), regulate bile acid metabolism, and improve glucose homeostasis.

Effects of Non-insulin Anti-hyperglycemic Agents on Gut Microbiota: A Systematic Review on Human and Animal Studies

Background: As growing evidence links gut microbiota with the therapeutic efficacy and side effects of anti-hyperglycemic drugs, this article aims to provide a systematic review of the reciprocal interactions between anti-hyperglycemic drugs and gut microbiota taxa, which underlie the effect of the gut microbiome on diabetic control via bug-host interactions. Method: We followed the PRISMA requirements to perform a systematic review on human vs. animal gut microbiota data in PubMed, SCOPUS, and EMBASE databases, and used Cochrane, ROBIN-I, and SYRCLE tools to assess potential bias risks. The outcomes of assessment were trends on gut microbiota taxa, diversity, and associations with metabolic control (e.g., glucose, lipid) following anti-hyperglycemic treatment. Results: Of 2,804 citations, 64 studies (17/humans; 47/mice) were included. In human studies, seven were randomized trials using metformin or acarbose in obese, pre-diabetes, and type 2 diabetes (T2D) patients. Treatment of pre-diabetes and newly diagnosed T2D patients with metformin or acarbose was associated with decreases in genus of Bacteroides, accompanied by increases in both Bifidobacterium and Lactobacillus. Additionally, T2D patients receiving metformin showed increases in various taxa of the order Enterobacteriales and the species Akkermansia muciniphila. Of seven studies with significant differences in beta-diversity, the incremental specific taxa were associated with the improvement of glucose and lipid profiles. In mice, the effects of metformin on A. muciniphila were similar, but an inverse association with Bacteroides was reported. Animal studies on other anti-hyperglycemic drugs, however, showed substantial variations in results. Conclusions: The changes in specific taxa and β-diversity of gut microbiota were associated with metformin and acarbose in humans while pertinent information for other anti-hyperglycemic drugs could only be obtained in rodent studies. Further human studies on anti-hyperglycemic drugs other than metformin and acarbose are needed to explore gut microbiota's role in their therapeutic efficacies and side effects.

Gluco-Metabolic Effects of Pharmacotherapy-Induced Modulation of Bile Acid Physiology

CONTEXT

The discovery and characterization of the bile acid specific receptors farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5) have facilitated a wealth of research focusing on the link between bile acid physiology and glucose metabolism. Modulation of FXR and TGR5 activation have been demonstrated to affect the secretion of glucagon-like peptide 1, insulin, and glucagon as well as energy expenditure and gut microbiota composition, with potential beneficial effects on glucose metabolism.

EVIDENCE ACQUISITION

A search strategy based on literature searches in on PubMed with various combinations of the key words FXR, TGR5, agonist, apical sodium-dependent bile acid transporter (ASBT), bile acid sequestrant, metformin, and glucose metabolism has been applied to obtain material for the present review. Furthermore, manual searches including scanning of reference lists in relevant papers and conference proceedings have been performed.

EVIDENCE SYNTHESIS

This review provides an outline of the link between bile acid and glucose metabolism, with a special focus on the gluco-metabolic impact of treatment modalities with modulating effects on bile acid physiology; including FXR agonists, TGR5 agonists, ASBT inhibitors, bile acid sequestrants, and metformin.

CONCLUSIONS

Any potential beneficial gluco-metabolic effects of FXR agonists remain to be established, whereas the clinical relevance of TGR5-based treatment modalities seems limited because of substantial safety concerns of TGR5 agonists observed in animal models. The glucose-lowering effects of ASBT inhibitors, bile acid sequestrants, and metformin are at least partly mediated by modulation of bile acid circulation, which might allow an optimization of these bile acid-modulating treatment modalities. (J Clin Endocrinol Metab XX: 00-00, 2019).

The Mechanism of Metabolic Influences on the Endogenous GLP-1 by Oral Antidiabetic Medications in Type 2 Diabetes Mellitus

Incretin-based therapy is now a prevalent treatment option for patients with type 2 diabetes mellitus (T2DM). It has been associated with considerably good results in the management of hyperglycemia with cardiac or nephron-benefits. For this reason, it is recommended for individuals with cardiovascular diseases in many clinical guidelines. As an incretin hormone, glucagon-like peptide-1 (GLP-1) possesses multiple metabolic benefits such as optimizing energy usage, maintaining body weight, β cell preservation, and suppressing neurodegeneration. However, recent studies indicate that oral antidiabetic medications interact with endogenous or exogenous GLP-1. Since these drugs are transported to distal intestine portions, there are concerns whether these oral drugs directly stimulate intestinal L cells which release GLP-1, or whether they do so via indirect inhibition of the activity of dipeptidyl peptidase-IV (DPP-IV). In this review, we discuss the metabolic relationships between oral antihyperglycemic drugs from the aspect of gut, microbiota, hormones, β cell function, central nervous system, and other cellular mechanisms.

Bile acids in glucose metabolism and insulin signalling - mechanisms and research needs

Of all the novel glucoregulatory molecules discovered in the past 20 years, bile acids (BAs) are notable for the fact that they were hiding in plain sight. BAs were well known for their requirement in dietary lipid absorption and biliary cholesterol secretion, due to their micelle-forming properties. However, it was not until 1999 that BAs were discovered to be endogenous ligands for the nuclear receptor FXR. Since that time, BAs have been shown to act through multiple receptors (PXR, VDR, TGR5 and S1PR2), as well as to have receptor-independent mechanisms (membrane dynamics, allosteric modulation of N-acyl phosphatidylethanolamine phospholipase D). We now also have an appreciation of the range of physiological, pathophysiological and therapeutic conditions in which endogenous BAs are altered, raising the possibility that BAs contribute to the effects of these conditions on glycaemia. In this Review, we highlight the mechanisms by which BAs regulate glucose homeostasis and the settings in which endogenous BAs are altered, and provide suggestions for future research.

Pharmacology of metformin - An update

Despite being a successful diabetes type 2 drug for more than a half-century in Europe, the mode of action of metformin is still debated. It is the purpose of this review to inform the reader about most recent findings for metformin with respect to its antidiabetic activity as well as proposed benefits beyond glucose control in humans. Clinical evidence now suggests that most of metformin benefits originate from its actions in the gut, involving hormone signaling by glucagon-like peptide 1 and peptide YY. Growth differentiation factor 15, also mainly produced in the gut, was first identified as a biomarker for metformin use but is now suggested to play a significant role in e.g. weight loss of prediabetics. The pharmacokinetics of the drug in humans as basis for pharmacodynamics, resulting in high tissue levels of the intestinal wall, including the colon, proven by biopsies, is presented. A critical survey of metformin actions on mitochondria, increasing the AMP/ATP ratio but also acting as a mild uncoupler, and of postulated new cellular targets (lysosomes) is included.

Urinary metabolomics analysis reveals the anti-diabetic effect of stachyose in high-fat diet/streptozotocin-induced type 2 diabetic rats

As a new platform of systems biology, metabolomics provides a powerful approach to discover therapeutic biomarkers and mechanism of metabolic disease. Type 2 diabetes mellitus (T2DM) is a global metabolic disease, thus, a urinary metabolomics profiling was analyzed to study the anti-diabetic effects and mechanism of stachyose (ST) on high-fat diet- and low dose streptozotocinc-induced T2DM rats. The results showed that ST treatment regulated the level of insulin, low-density lipoprotein cholesterol, and triglycerides, which demonstrates improvement in T2DM on ST treatment. Urinary samples from the ST and T2DM group were enrolled in metabolomics study, 21 differential metabolites were identified from urinary metabolomics analysis, indicating that the ST treatment partly exerted the anti-diabetes activity by regulating energy metabolism, gut microbiota changes and inflammation. A metabolomics strategy is both suitable and reliable for exploring the anti-diabetes effects and understanding the mechanisms of ST treatment against T2DM.

The Role of the Microbiome in Drug Response

The microbiome is known to regulate many aspects of host health and disease and is increasingly being recognized as a key mediator of drug action. However, investigating the complex multidirectional relationships between drugs, the microbiota, and the host is a challenging endeavor, and the biological mechanisms that underpin these interactions are often not well understood. In this review, we outline the current evidence that supports a role for the microbiota as a contributor to both the therapeutic benefits and side effects of drugs, with a particular focus on those used to treat mental disorders, type 2 diabetes, and cancer. We also provide a snapshot of the experimental and computational tools that are currently available for the dissection of drug-microbiota-host interactions. The advancement of knowledge in this area may ultimately pave the way for the development of novel microbiota-based strategies that can be used to improve treatment outcomes.

Additional Effect of Dietary Fiber in Patients with Type 2 Diabetes Mellitus Using Metformin and Sulfonylurea: An Open-Label, Pilot Trial

BACKGROUND

Metformin, sulfonylurea, and dietary fiber are known to affect gut microbiota in patients with type 2 diabetes mellitus (T2DM). This open and single-arm pilot trial investigated the effects of the additional use of fiber on glycemic parameters, insulin, incretins, and microbiota in patients with T2DM who had been treated with metformin and sulfonylurea.

METHODS

Participants took fiber for 4 weeks and stopped for the next 4 weeks. Glycemic parameters, insulin, incretins during mixed-meal tolerance test (MMTT), lipopolysaccharide (LPS) level, and fecal microbiota were analyzed at weeks 0, 4, and 8. The first tertile of difference in glucose area under the curve during MMTT between weeks 0 and 4 was defined as 'responders' and the third as 'nonresponders,' respectively.

RESULTS

In all 10 participants, the peak incretin levels during MMTT were higher and LPS were lower at week 4 as compared with at baseline. While the insulin sensitivity of the 'responders' increased at week 4, that of the 'nonresponders' showed opposite results. However, the results were not statistically significant. In all participants, metabolically unfavorable microbiota decreased at week 4 and were restored at week 8. At baseline, metabolically hostile bacteria were more abundant in the 'nonresponders.' In 'responders,' Roseburia intestinalis increased at week 4.

CONCLUSION

While dietary fiber did not induce additional changes in glycemic parameters, it showed a trend of improvement in insulin sensitivity in 'responders.' Even if patients are already receiving diabetes treatment, the additional administration of fiber can lead to additional benefits in the treatment of diabetes.

Role and effective therapeutic target of gut microbiota in NAFLD/NASH

Non-alcoholic fatty liver disease (NAFLD), the most prevalent chronic liver disease in the world, is affected by numerous extrinsic and intrinsic factors, including lifestyle, environment, diet, genetic susceptibility, metabolic syndrome and gut microbiota. Accumulating evidence has proven that gut dysbiosis is significantly associated with the development and progression of NAFLD, and several highly variable species in gut microbiota have been identified. The gut microbiota contributes to NAFLD by abnormal regulation of the liver-gut axis, gut microbial components and microbial metabolites, and affects the secretion of bile acids. Due to the key role of the gut microbiota in NAFLD, it has been regarded as a potential target for the pharmacological and clinical treatment of NAFLD. The present review provides a systematic summary of the characterization of gut microbiota and the significant association between the gut microbiota and NAFLD. The possible mechanisms of how the gut microbiota is involved in promoting the development and progression of NAFLD were also discussed. In addition, the potential therapeutic methods for NAFLD based on the gut microbiota were summarized.

Gut microbiota composition explains more variance in the host cardiometabolic risk than genetic ancestry

Cardiometabolic affections greatly contribute to the global burden of disease. The susceptibility to obesity, cardiovascular disease, and type-2 diabetes, conditions that add to the cardiometabolic syndrome (CMS), was associated with the ancestral genetic composition and gut microbiota. Studies explicitly testing associations between genetic ancestry and gut microbes are growing. We here examined whether the host genetic ancestry was associated with gut microbiota composition, and distinguished the effects of genetic ancestry and non-genetic factors on human cardiometabolic health. We performed a cross-sectional study with 441 community-dwelling Colombian mestizos from five cities spanning the Andes, Pacific, and Caribbean coasts. We characterized the host genetic ancestry by genotyping 40 ancestry informative markers; characterized gut microbiota through 16S rRNA gene sequencing; assessed diet intake, physical activity, cigarette, and medicament consumption; and measured cardiometabolic outcomes that allowed calculating a CMS risk scale. On average, each individual of our cohort was 67 ± 6% European, 21 ± 5% Native American and 12 ± 5% African. Multivariable-adjusted generalized linear models showed that individuals with higher Native American and African ancestries had increased fasting insulin, body mass index and CMS risk, as assessed by the CMS risk scale. Furthermore, we identified 21 OTUs associated to the host genetic ancestry and 20 to cardiometabolic health. While we highlight novel associations between genetic ancestry and gut microbiota, we found that the effect of intestinal microbes was more likely to explain the variance in CMS risk scale than the contributions of European, Native American and African genetic backgrounds.

Metformin and gut microbiota: their interactions and their impact on diabetes

The ratio of human to bacterial cells in the human body (microbiota) is around 1:1. As a result of co-evolution of the host mucosal immune system and the microbiota, both have developed multiple mechanisms to maintain homeostasis. However, dissociations between the composition of the gut microbiota and the human host may play a crucial role in the development of type 2 diabetes. Metformin, the most frequently administered medication to treat patients with type 2 diabetes, has only recently been suggested to alter gut microbiota composition through the increase in mucin-degrading Akkermansia muciniphila, as well as several SCFA-producing (short-chain fatty acid) microbiota. The gut microbiota of participants on metformin has exerted alterations in gut metabolomics with increased ability to produce butyrate and propionate, substances involved in glucose homeostasis. Thus, metformin appears to affect the microbiome, and an individual's metformin tolerance or intolerance may be influenced by their microbiome. In this review, we will focus on the effects of metformin in gut microbiota among patients with T2DM.

Variation in the Plasma Membrane Monoamine Transporter (PMAT) (Encoded by SLC29A4) and Organic Cation Transporter 1 (OCT1) (Encoded by SLC22A1) and Gastrointestinal Intolerance to Metformin in Type 2 Diabetes: An IMI DIRECT Study

OBJECTIVE

Gastrointestinal adverse effects occur in 20-30% of patients with metformin-treated type 2 diabetes, leading to premature discontinuation in 5-10% of the cases. Gastrointestinal intolerance may reflect localized high concentrations of metformin in the gut. We hypothesized that reduced transport of metformin via the plasma membrane monoamine transporter (PMAT) and organic cation transporter 1 (OCT1) could increase the risk of severe gastrointestinal adverse effects.

RESEARCH DESIGN AND METHODS

The study included 286 severe metformin-intolerant and 1,128 metformin-tolerant individuals from the IMI DIRECT (Innovative Medicines Initiative: DIabetes REsearCh on patient straTification) consortium. We assessed the association of patient characteristics, concomitant medication, and the burden of mutations in the SLC29A4 and SLC22A1 genes on odds of intolerance.

RESULTS

Women (P < 0.001) and older people (P < 0.001) were more likely to develop metformin intolerance. Concomitant use of transporter-inhibiting drugs increased the odds of intolerance (odds ratio [OR] 1.72, P < 0.001). In an adjusted logistic regression model, the G allele at rs3889348 (SLC29A4) was associated with gastrointestinal intolerance (OR 1.34, P = 0.005). rs3889348 is the top cis-expression quantitative trait locus for SLC29A4 in gut tissue where carriers of the G allele had reduced expression. Homozygous carriers of the G allele treated with transporter-inhibiting drugs had more than three times higher odds of intolerance compared with carriers of no G allele and not treated with inhibiting drugs (OR 3.23, P < 0.001). Use of a genetic risk score derived from rs3889348 and SLC22A1 variants found that the odds of intolerance were more than twice as high in individuals who carry three or more risk alleles compared with those carrying none (OR 2.15, P = 0.01).

CONCLUSIONS

These results suggest that intestinal metformin transporters and concomitant medications play an important role in the gastrointestinal adverse effects of metformin.

Metformin: Mechanisms in Human Obesity and Weight Loss

PURPOSE OF REVIEW

Metformin has multiple benefits for health beyond its anti-hyperglycemic properties. The purpose of this manuscript is to review the mechanisms that underlie metformin's effects on obesity.

RECENT FINDINGS

Metformin is a first-line therapy for type 2 diabetes. Large cohort studies have shown weight loss benefits associated with metformin therapy. Metabolic consequences were traditionally thought to underlie this effect, including reduction in hepatic gluconeogenesis and reduction in insulin production. Emerging evidence suggests that metformin-associated weight loss is due to modulation of hypothalamic appetite regulatory centers, alteration in the gut microbiome, and reversal of consequences of aging. Metformin is also being explored in the management of obesity's sequelae such as hepatic steatosis, obstructive sleep apnea, and osteoarthritis. Multiple mechanisms underlie the weight loss-inducing and health-promoting effects of metformin. Further exploration of these pathways may be important in identifying new pharmacologic targets for obesity and other aging-associated metabolic diseases.

Effects of metformin and alogliptin on body composition in people with type 2 diabetes

AIMS/INTRODUCTION

The aim of the present study was to investigate the effects of metformin and a dipeptidyl peptidase-4 inhibitor, alogliptin, on body composition in a 12-week randomized add-on trial in Japanese participants with type 2 diabetes.

MATERIALS AND METHODS

A total of 84 participants with poorly controlled type 2 diabetes undergoing antidiabetic therapy were randomly assigned to receive alogliptin (25 mg, once daily) or metformin (1,000 mg, twice daily) for 12 weeks. The primary efficacy end-point was body composition. The secondary end-points included factors associated with decreased bodyweight.

RESULTS

Compared with the baseline values, alogliptin significantly increased bodyweight (66.5 ± 19.2 to 67.6 ± 19.3 kg), body mass index (BMI; 25.4 ± 6.1 to 25.8 ± 6.3 kg/m2 ) and fat mass (20.3 ± 12.8 to 21.8 ± 14.5 kg), whereas metformin had no significant effect on body composition. Alogliptin was inferior to metformin in reducing bodyweight (0.84 ± 1.57 vs -0.35 ± 1.53 kg, P = 0.002), BMI (0.34 ± 0.69 to -0.15 ± 0.56 kg/m2 , P = 0.002) and fat mass (1.49 ± 5.06 vs -0.04 ± 1.81 kg, P = 0.042). BMI at baseline was associated with changes in bodyweight negatively in the metformin group and positively in the alogliptin group.

CONCLUSIONS

Metformin and alogliptin exert opposite effects on bodyweight in type 2 diabetes patients who are overweight. The higher the BMI, the more metformin reduces bodyweight and alogliptin increases weight.

Fecal Enterobacteriales enrichment is associated with increased in vivo intestinal permeability in humans

Type 2 diabetes (T2D) has been linked with increased intestinal permeability, but the clinical significance of this phenomenon remains unknown. The objective of this study was to investigate the potential link between glucose control, intestinal permeability, diet and intestinal microbiota in patients with T2D. Thirty‐two males with well‐controlled T2D and 30 age‐matched male controls without diabetes were enrolled in a case–control study. Metabolic parameters, inflammatory markers, endotoxemia, and intestinal microbiota in individuals subdivided into high (HP) and normal (LP) colonic permeability groups, were the main outcomes. In T2D, the HP group had significantly higher fasting glucose (P = 0.034) and plasma nonesterified fatty acid levels (P = 0.049) compared with the LP group. Increased colonic permeability was also linked with altered abundances of selected microbial taxa. The microbiota of both T2D and control HP groups was enriched with Enterobacteriales. In conclusion, high intestinal permeability was associated with poorer fasting glucose control in T2D patients and changes in some microbial taxa in both T2D patients and nondiabetic controls. Therefore, enrichment in the gram‐negative order Enterobacteriales may characterize impaired colonic permeability prior to/independently from a disruption in glucose tolerance.

Crosstalk between gut microbiota and antidiabetic drug action

Type 2 diabetes (T2D) is a disorder characterized by chronic inflated blood glucose levels (hyperglycemia), at first due to insulin resistance and unregulated insulin secretion but with tendency towards global spreading. The gut microbiota is recognized to have an influence on T2D, although surveys have not formed a clear overview to date. Because of the interactions between gut microbiota and host homeostasis, intestinal bacteria are believed to play a large role in various diseases, including metabolic syndrome, obesity and associated disease. In this review, we highlight the animal and human studies which have elucidated the roles of metformin, α-glucosidase inhibitors, glucagon-like peptide-1 agonists, peroxisome proliferator-activated receptors γ agonists, inhibitors of dipeptidyl peptidase-4, sodium/glucose cotransporter inhibitors, and other less studied medications on gut microbiota. This review is dedicated to one of the most widespread diseases, T2D, and the currently used antidiabetic drugs and most promising new findings. In general, the gut microbiota has been shown to have an influence on host metabolism, food consumption, satiety, glucose homoeostasis, and weight gain. Altered intestinal microbiota composition has been noticed in cardiovascular diseases, colon cancer, rheumatoid arthritis, T2D, and obesity. Therefore, the main effect of antidiabetic drugs is on the microbiome composition, basically increasing the short-chain fatty acids-producing bacteria, responsible for losing weight and suppressing inflammation.

Sotagliflozin, the first dual SGLT inhibitor: current outlook and perspectives

Sotagliflozin is a dual sodium-glucose co-transporter-2 and 1 (SGLT2/1) inhibitor for the treatment of both type 1 (T1D) and type 2 diabetes (T2D). Sotagliflozin inhibits renal sodium-glucose co-transporter 2 (determining significant excretion of glucose in the urine, in the same way as other, already available SGLT-2 selective inhibitors) and intestinal SGLT-1, delaying glucose absorption and therefore reducing post prandial glucose. Well-designed clinical trials, have shown that sotagliflozin (as monotherapy or add-on therapy to other anti-hyperglycemic agents) improves glycated hemoglobin in adults with T2D, with beneficial effects on bodyweight and blood pressure. Similar results have been obtained in adults with T1D treated with either continuous subcutaneous insulin infusion or multiple daily insulin injections, even after insulin optimization. A still ongoing phase 3 study is currently evaluating the effect of sotagliflozin on cardiovascular outcomes (ClinicalTrials.gov NCT03315143). In this review we illustrate the advantages and disadvantages of dual SGLT 2/1 inhibition, in order to better characterize and investigate its mechanisms of action and potentialities.

Dietary fibers as emerging nutritional factors against diabetes: focus on the involvement of gut microbiota

Diabetes mellitus (DM) increases the risk of cardiovascular diseases and other secondary complications, such as nephropathy, neuropathy, retinopathy, etc. The important risk factors for the pathogenesis of DM are aging, family history, sedentary lifestyle, unhealthy dietary habits, and obesity. Evidence from epidemiological studies also indicates that DM is characterized by specific alterations in the human gut microbiota (GM). GM transplantation in rodents and humans revealed that a specific GM constituent can be the cause and not just the consequence of the DM condition and complications. These findings suggest a potential role of GM in human health, disease prevention, and treatment. Dietary intervention studies using dietary fibers (DFs) suggested that modulation of the GM can suppress the metabolic risk markers in humans. However, a causal role of GM in such studies remains unexplored. Long-term follow-up studies disclosed that the diet rich in insoluble and non-viscous fibers are responsible for DF-mediated antidiabetic activities, while soluble and viscous fibers have little influence on DM despite having a profound impact on glycemia. However, general conclusions cannot be drawn simply based on these findings. Long-term follow-up studies are urgently required in this area to explore the therapeutic potential of different DFs in treating DM and to delineate the exact role of GM involvement. Here we review and discuss the signature of GM during DM, antidiabetic activity of metformin via GM modulation, DFs from different sources and their antidiabetic activity, and the possible role of GM involvement.

Pharmacologic and Nonpharmacologic Therapies for the Gut Microbiota in Type 2 Diabetes

The gut microbiota is an important regulator of host metabolism. Metagenome analyses have demonstrated that the gut microbiota differs between patients with type 2 diabetes and healthy subjects, and several studies have shown that impaired glucose metabolism is associated with decreased levels of butyrate-producing bacteria. Gut microbiota-produced metabolites, such as short-chain fatty acids, amino acid derivatives and secondary bile acids, participate in metabolic and immunologic processes and, hence, pose putative links between the gut microbiota and glucose homeostasis. Strategies to prevent and treat type 2 diabetes through manipulation of the gut microbiota are being developed. These include replacement of the gut microbiota by fecal transplantation, consumption of fibres to promote the function and growth of beneficial bacteria and treatment with probiotic bacterial strains. Furthermore, it has been shown that many drugs, including drugs used for treatment of diabetes, have major impacts on gut microbiota and, thereby, potentially on glucose metabolism. In particular, the commonly used drug metformin has been shown to influence the functional capacity of the gut microbiota, and recent evidence indicates that this may contribute to the antidiabetes effect of metformin.

Non-alcoholic fatty liver disease is associated with dysregulated bile acid synthesis and diarrhea: A prospective observational study

Background

Non-alcoholic fatty liver disease (NAFLD) may be associated with changes in bile acid (BA) metabolism. Hepatic BA production, measured by serum levels of the precursor 7α-hydroxy-4-cholesten-3-one (C4), is regulated by the farnesoid-X-receptor (FXR)-dependent ileal hormone fibroblast growth factor 19 (FGF19). Low FGF19 and high C4 are features of chronic BA diarrhea. Obeticholic acid, an FXR agonist, stimulates FGF19 and has shown therapeutic potential in both BA diarrhea and in NAFLD. We hypothesized there are associations of FGF19, C4 and BA diarrhea with NAFLD.

Methods and findings

127 patients with known NAFLD were recruited prospectively. Clinical features, including metformin use, markers of NAFLD severity and BA synthesis were analyzed. The overall incidence of chronic diarrhea was 25%, with features of BA diarrhea in 12%. FGF19 negatively correlated with C4 (r_s = -0.43, p = 0.001) and with alanine aminotransferase (r_s = -0.22, p = 0.03), but not with either NAFLD fibrosis or Fibroscan scores. High C4 was associated with a higher NAFLD fibrosis score (p < 0.05), and with diarrhea (p = 0.001). The median NAFLD fibrosis score was higher in those with diarrhea (p = 0.002). Metformin use, in 44% overall, was particularly associated with diarrhea (in 36% vs 17%, p = 0.02), and a lower median FGF19 (74 vs 105 pg/mL, p < 0.05).

Conclusions

Increased hepatic BA production and diarrhea, but not low FGF19, were associated with increased NAFLD fibrosis score, indicating dysregulation of the FXR-FGF19 axis and suggesting hepatic FGF19 resistance. Metformin use was an important factor in a subgroup, lowering FGF19, and resulting in bile acid diarrhea.

Higher Fecal Short-Chain Fatty Acid Levels Are Associated with Gut Microbiome Dysbiosis, Obesity, Hypertension and Cardiometabolic Disease Risk Factors

Fiber fermentation by gut microbiota yields short-chain fatty acids (SCFAs) that are either absorbed by the gut or excreted in feces. Studies are conflicting as to whether SCFAs are beneficial or detrimental to cardiometabolic health, and how gut microbiota associated with SCFAs is unclear. In this study of 441 community-dwelling adults, we examined associations of fecal SCFAs, gut microbiota diversity and composition, gut permeability, and cardiometabolic outcomes, including obesity and hypertension. We assessed fecal microbiota by 16S rRNA gene sequencing, and SCFA concentrations by gas chromatography/mass spectrometry. Fecal SCFA concentrations were inversely associated with microbiota diversity, and 70 unique microbial taxa were differentially associated with at least one SCFA (acetate, butyrate or propionate). Higher SCFA concentrations were associated with a measure of gut permeability, markers of metabolic dysregulation, obesity and hypertension. Microbial diversity showed association with these outcomes in the opposite direction. Associations were significant after adjusting for measured confounders. In conclusion, higher SCFA excretion was associated with evidence of gut dysbiosis, gut permeability, excess adiposity, and cardiometabolic risk factors. Studies assessing both fecal and circulating SCFAs are needed to test the hypothesis that the association of higher fecal SCFAs with obesity and cardiometabolic dysregulation is due to less efficient SCFA absorption.

Hypoglycemic Mechanism of the Berberine Organic Acid Salt under the Synergistic Effect of Intestinal Flora and Oxidative Stress

Both alterations to the intestinal microflora and chronic systemic inflammation predispose towards type 2 diabetes (T2D). Changes in the composition of the intestinal microflora are associated with glucose metabolism changes in rats with T2D. Here, we demonstrate that a berberine fumarate (BF) has a hypoglycemic effect by regulating the intestinal microflora and metabolism of diabetic rats. The T2D rats had disorders of glucose and lipid metabolism, an abnormal intestinal microflora, fewer butyrate-producing and probiotic-type bacteria, larger numbers of potentially pathogenic and sulfate-reducing bacteria, and tissue inflammation. Administration of berberine fumarate significantly ameliorated the metabolic disorder; increased the populations of Bacteroidetes, Clostridia, Lactobacillales, Prevotellaceae, and Alloprevotella; and reduced those of Bacteroidales, Lachnospiraceae, Rikenellaceae, and Desulfovibrio. In addition, it reduced inflammation, inhibiting the overexpression of TLR4 and p-JNK and increasing the expression of PI3K, GLUT2, and other proteins, which are closely related to oxidative stress, thereby promoting the metabolism of glucose.

Metformin-induced glucagon-like peptide-1 secretion contributes to the actions of metformin in type 2 diabetes

BACKGROUND

Metformin reduces plasma glucose and has been shown to increase glucagon-like peptide 1 (GLP-1) secretion. Whether this is a direct action of metformin on GLP-1 release, and whether some of the glucose-lowering effect of metformin occurs due to GLP-1 release, is unknown. The current study investigated metformin-induced GLP-1 secretion and its contribution to the overall glucose-lowering effect of metformin and underlying mechanisms in patients with type 2 diabetes.

METHODS

Twelve patients with type 2 diabetes were included in this placebo-controlled, double-blinded study. On 4 separate days, the patients received metformin (1,500 mg) or placebo suspended in a liquid meal, with subsequent i.v. infusion of the GLP-1 receptor antagonist exendin9-39 (Ex9-39) or saline. During 240 minutes, blood was sampled. The direct effect of metformin on GLP-1 secretion was tested ex vivo in human ileal and colonic tissue with and without dorsomorphin-induced inhibiting of the AMPK activity.

RESULTS

Metformin increased postprandial GLP-1 secretion compared with placebo (P = 0.014), and the postprandial glucose excursions were significantly smaller after metformin + saline compared with metformin + Ex9-39 (P = 0.004). Ex vivo metformin acutely increased GLP-1 secretion (colonic tissue, P < 0.01; ileal tissue, P < 0.05), but the effect was abolished by inhibition of AMPK activity.

CONCLUSIONS

Metformin has a direct and AMPK-dependent effect on GLP-1-secreting L cells and increases postprandial GLP-1 secretion, which seems to contribute to metformin's glucose-lowering effect and mode of action.

TRIAL REGISTRATION

NCT02050074 (https://clinicaltrials.gov/ct2/show/NCT02050074).

FUNDING

This study received grants from the A.P. Møller Foundation, the Novo Nordisk Foundation, the Danish Medical Association research grant, the Australian Research Council, the National Health and Medical Research Council, and Pfizer Inc.

Gut microbiota and inflammation in chronic kidney disease and their roles in the development of cardiovascular disease

The health and proper functioning of the cardiovascular and renal systems largely depend on crosstalk in the gut-kidney-heart/vessel triangle. Recent evidence suggests that the gut microbiota has an integral function in this crosstalk. Mounting evidence indicates that the development of chronic kidney and cardiovascular diseases follows chronic inflammatory processes that are affected by the gut microbiota via various immune, metabolic, endocrine, and neurologic pathways. Additionally, deterioration of the function of the cardiovascular and renal systems has been reported to disrupt the original gut microbiota composition, further contributing to the advancement of chronic cardiovascular and renal diseases. Considering the interaction between the gut microbiota and the renal and cardiovascular systems, we can infer that interventions for the gut microbiota through diet and possibly some medications can prevent/stop the vicious cycle between the gut microbiota and the cardiovascular/renal systems, leading to a decrease in chronic cardiovascular and renal diseases.

Gut microbiota and intestinal FXR mediate the clinical benefits of metformin

The anti-hyperglycemic effect of metformin is believed to be caused by its direct action on signaling processes in hepatocytes, leading to lower hepatic gluconeogenesis. Recently, metformin was reported to alter the gut microbiota community in humans, suggesting that the hyperglycemia-lowering action of the drug could be the result of modulating the population of gut microbiota. However, the critical microbial signaling metabolites and the host targets associated with the metabolic benefits of metformin remained elusive. Here, we performed metagenomic and metabolomic analysis of samples from individuals with newly diagnosed type 2 diabetes (T2D) naively treated with metformin for 3 d, which revealed that Bacteroides fragilis was decreased and the bile acid glycoursodeoxycholic acid (GUDCA) was increased in the gut. These changes were accompanied by inhibition of intestinal farnesoid X receptor (FXR) signaling. We further found that high-fat-diet (HFD)-fed mice colonized with B. fragilis were predisposed to more severe glucose intolerance, and the metabolic benefits of metformin treatment on glucose intolerance were abrogated. GUDCA was further identified as an intestinal FXR antagonist that improved various metabolic endpoints in mice with established obesity. Thus, we conclude that metformin acts in part through a B. fragilis-GUDCA-intestinal FXR axis to improve metabolic dysfunction, including hyperglycemia.

Gut microbiota and plasma metabolites associated with diabetes in women with, or at high risk for, HIV infection

BACKGROUND

Gut microbiota alteration has been implicated in HIV infection and metabolic disorders. The relationship between gut microbiota and diabetes has rarely been studied in HIV-infected individuals, who have excess risk of metabolic disorders.

METHODS

Our study during 2015-2016 enrolled predominantly African Americans and Hispanics in the Women's Interagency HIV Study. We studied 28 women with long-standing HIV infection under antiretroviral therapy and 20 HIV-uninfected, but at high risk of infection, women (16 HIV+ and 6 HIV- with diabetes). Fecal samples were analyzed by sequencing prokaryotic16S rRNA gene. Plasma metabolomics profiling was performed by liquid chromatography-tandem mass spectrometry.

FINDINGS

No significant differences in bacterial α- or β-diversity were observed by diabetes or HIV serostatus (all P > .1). Relative abundances of four genera (Finegoldia, Anaerococcus, Sneathia, and Adlercreutzia) were lower in women with diabetes compared to those without diabetes (all P < .01). In women with diabetes, plasma levels of several metabolites in tryptophan catabolism (e,g., kynurenine/tryptophan ratio), branched-chain amino acid and proline metabolism pathways were higher, while glycerophospholipids were lower (all P < .05). Results were generally consistent between HIV-infected and HIV-uninfected women, and no significant modification effects by HIV serostatus were observed (all P_interaction > 0.05). Anaerococcus, known to produce butyrate which is involved in anti-inflammation and glucose metabolism, showed an inverse correlation with kynurenine/tryptophan ratio (r = -0.38, P < .01).

INTERPRETATION

Among women with or at high risk for HIV infection, diabetes is associated with gut microbiota and plasma metabolite alteration, including depletion of butyrate-producing bacterial population along with higher tryptophan catabolism. FUND: NHLBI (K01HL129892, R01HL140976) and FMF.

Gut microbiome and type 2 diabetes: where we are and where to go?

Type 2 diabetes mellitus (T2D) is a highly prevalent metabolic disorder characterized by an imbalance in blood glucose level, altered lipid profile and high blood pressure. Genetic constituents, high-fat and high-energy dietary habits, and a sedentary lifestyle are three major factors that contribute to high risk of T2D. Several studies have reported gut microbiome dysbiosis as a factor in rapid progression of insulin resistance in T2D that accounts for about 90% of all diabetes cases worldwide. The gut microbiome dysbiosis may reshape intestinal barrier functions and host metabolic and signaling pathways, which are directly or indirectly related to the insulin resistance in T2D. Thousands of the metabolites derived from microbes interact with the epithelial, hepatic and cardiac cell receptors that modulate host physiology. Xenobiotics including dietary components, antibiotics and nonsteroidal anti-inflammatory drugs strongly affect the gut microbial composition and can promote dysbiosis. Any change in the gut microbiota can shift the host metabolism towards increased energy harvest during diabetes and obesity. However, the exact mechanisms behind the dynamics of gut microbes and their impact on host metabolism at the molecular level are yet to be deciphered. We reviewed the published literature for better understanding of the dynamics of gut microbiota, factors that potentially induce gut microbiome dysbiosis and their relation to the progression of T2D. Special emphasis was also given to understand the gut microbiome induced breaching of intestinal barriers and/or tight junctions and their relation to insulin resistance.

Drug pharmacomicrobiomics and toxicomicrobiomics: from scattered reports to systematic studies of drug-microbiome interactions

INTRODUCTION

Pharmacomicrobiomics and toxicomicrobiomics study how variations within the human microbiome (the combination of human-associated microbial communities and their genomes) affect drug disposition, action, and toxicity. These emerging fields, interconnecting microbiology, bioinformatics, systems pharmacology, and toxicology, complement pharmacogenomics and toxicogenomics, expanding the scope of precision medicine. Areas covered: This article reviews some of the most recently reported pharmacomicrobiomic and toxicomicrobiomic interactions. Examples include the impact of the human gut microbiota on cardiovascular drugs, natural products, and chemotherapeutic agents, including immune checkpoint inhibitors. Although the gut microbiota has been the most extensively studied, some key drug-microbiome interactions involve vaginal, intratumoral, and environmental bacteria, and are briefly discussed here. Additionally, computational resources, moving the field from cataloging to predicting interactions, are introduced. Expert opinion: The rapid pace of discovery triggered by the Human Microbiome Project is moving pharmacomicrobiomic research from scattered observations to systematic studies focusing on screening microbiome variants against different drug classes. Better representation of all human populations will improve such studies by avoiding sampling bias, and the integration of multiomic studies with designed experiments will allow establishing causation. In the near future, pharmacomicrobiomic testing is expected to be a key step in screening novel drugs and designing precision therapeutics.

Association of metformin administration with gut microbiome dysbiosis in healthy volunteers

BACKGROUND

Metformin is a widely used first-line drug for treatment of type 2 diabetes. Despite its advantages, metformin has variable therapeutic effects, contraindications, and side effects. Here, for the very first time, we investigate the short-term effect of metformin on the composition of healthy human gut microbiota.

METHODS

We used an exploratory longitudinal study design in which the first sample from an individual was the control for further samples. Eighteen healthy individuals were treated with metformin (2 × 850 mg) for 7 days. Stool samples were collected at three time points: prior to administration, 24 hours and 7 days after metformin administration. Taxonomic composition of the gut microbiome was analyzed by massive parallel sequencing of 16S rRNA gene (V3 region).

RESULTS

There was a significant reduction of inner diversity of gut microbiota observed already 24 hours after metformin administration. We observed an association between the severity of gastrointestinal side effects and the increase in relative abundance of common gut opportunistic pathogen Escherichia-Shigella spp. One week long treatment with metformin was associated with a significant decrease in the families Peptostreptococcaceae and Clostridiaceae_1 and four genera within these families.

CONCLUSIONS

Our results are in line with previous findings on the capability of metformin to influence gut microbiota. However, for the first time we provide evidence that metformin has an immediate effect on the gut microbiome in humans. It is likely that this effect results from the increase in abundance of opportunistic pathogens and further triggers the occurrence of side effects associated with the observed dysbiosis. An additional randomized controlled trial would be required in order to reach definitive conclusions, as this is an exploratory study without a placebo control arm. Our findings may be further used to create approaches that improve the tolerability of metformin.

Improved glycemic control with minimal systemic metformin exposure: Effects of Metformin Delayed-Release (Metformin DR) targeting the lower bowel over 16 weeks in a randomized trial in subjects with type 2 diabetes

Objective

Metformin use is restricted in patients with renal impairment due to potential excess systemic accumulation. This study evaluated the glycemic effects and safety of metformin delayed-release (Metformin DR), which targets metformin delivery to the ileum to leverage its gut-based mechanisms of action while minimizing systemic exposure.

Research designs and methods

Participants (T2DM [HbA1c 7–10.5%], eGFR ≥60 mL/min/1.73m², not taking metformin for ≥2 months) were randomized to QD placebo (PBO); QD Metformin DR 600, 900, 1200, or 1500 mg; or to single-blind BID Metformin immediate-release (IR) 1000 mg. The primary endpoint was change in HbA1c for Metformin DR vs. PBO at 16 weeks in the modified intent-to-treat (mITT) population (≥ 1 post-baseline HbA1c while on study drug), using a mixed-effects repeated measures model.

Results

571 subjects were randomized (56 years, 53% male, 80% white; BMI 32.2±5.5 kg/m²; HbA1c 8.6±0.9%; 51% metformin naive); 542 were in the mITT population. Metformin DR 1200 and 1500 mg significantly reduced HbA1c (-0.49±0.13% and -0.62±0.12%, respectively, vs. PBO -0.06±0.13%; p<0.05) and FPG (C_{average Weeks 4–16}: -22.3±4.2 mg/dL and -25.1±4.1 mg/dL, respectively vs. -2.5±4.2 mg/dL p<0.05). Metformin IR elicited greater HbA1c improvement (-1.10±0.13%; p<0.01 vs. Placebo and all doses of Metformin DR) but with ~3-fold greater plasma metformin exposure. Normalizing efficacy to systemic exposure, glycemic improvements with Metformin DR were 1.5-fold (HbA1c) and 2.1-fold (FPG) greater than Metformin IR. Adverse events were primarily gastrointestinal but these were less frequent with Metformin DR (<16% incidence) vs. Metformin IR (28%), particularly nausea (1–3% vs 10%).

Conclusion

Metformin DR exhibited greater efficacy per unit plasma exposure than Metformin IR. Future studies will evaluate the effects of Metformin DR in patients with type 2 diabetes and advanced renal disease.

Trial registration

Clinicaltrials.gov NCT02526524.

Effect of alive probiotic on insulin resistance in type 2 diabetes patients: Randomized clinical trial

BACKGROUND

Probiotics have beneficial effect on obesity related disorders in animal models. Despite a large number of animal data, randomized placebo-controlled trials (RCT) concluded that probiotics have a moderate effect on glycemic control-related parameters. However, effect of probiotics on insulin resistance are inconsistent.

AIM

In a double-blind single center RCT, effect of alive multistrain probiotic vs. placebo on insulin resistance in type 2 diabetes patient were assessed.

METHODS

A total of 53 patients met the criteria for inclusion. They were randomly assigned to receive multiprobiotic "Symbiter" (concentrated biomass of 14 probiotic bacteria genera Bifidobacterium, Lactobacillus, Lactococcus, Propionibacterium) or placebo for 8-weeks administered as a sachet formulation. The primary main outcome was the change HOMA-IR (homeostasis model assessment-estimated insulin resistance) which calculated using Matthews et al.'s equation. Secondary outcomes were the changes in glycemic control-related parameters, anthropomorphic variables and cytokines.

RESULTS

Supplementation with alive multiprobiotic for 8 weeks was associated with significant reduction of HOMA-IR from 6.85 ± 0.76 to 5.13 ± 0.49 (p = 0.047), but remained static in the placebo group. With respect to our secondary outcomes, HbA1c insignificant decreased by 0.09% (p = 0.383) and 0.24% (p = 0.068) respectively in placebo and probiotics groups. However, in probiotic responders (n = 22, patient with decrease in HOMA-IR) after supplementation a significant reduction in HbA1c by 0.39% (p = 0.022) as compared to non-responders was observed. In addition, from markers of chronic systemic inflammatory state only TNF-α and IL-1β changes significantly after treatment with probiotics.

CONCLUSION

Probiotic therapies modestly improved insulin resistance in patients with type 2 diabetes.

Postprandial glucose-lowering effect of premeal consumption of protein-enriched, dietary fiber-fortified bar in individuals with type 2 diabetes mellitus or normal glucose tolerance

AIMS/INTRODUCTION

Protein preload improves postprandial glycemia by stimulating secretion of insulin and incretin hormones. However, it requires a large dose of protein to produce a significant effect. The present study was carried out to investigate the postprandial glucose-lowering effect of a premeal protein-enriched, dietary fiber-fortified bar (PFB), which contains moderate amounts of protein, in individuals with type 2 diabetes mellitus or normal glucose tolerance (NGT).

MATERIALS AND METHODS

The participants (15 type 2 diabetes mellitus and 15 NGT) were randomly assigned to either a premeal or postmeal PFB group and underwent two mixed meal tolerance tests, 1 week apart in reverse order. Plasma levels of glucose, insulin, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide were measured.

RESULTS

During the mixed meal tolerance tests, the incremental area under the curve from 0 to 180 min of plasma glucose levels was lower with premeal PFB than with postmeal PFB in the type 2 diabetes mellitus (14,723 ± 1,310 mg min/dL vs 19,642 ± 1,367 mg min/dL; P = 0.0002) and NGT participants (3,943 ± 416 mg min/dL vs 4,827 ± 520 mg min/dL, P = 0.0296). In the type 2 diabetes mellitus participants, insulinogenic index and the incremental area under the curve from 0 to 180 min of plasma total glucagon-like peptide-1 levels were higher with premeal PFB than with postmeal PFB, but not in the NGT participants. There was no difference in postprandial glucose-dependent insulinotropic polypeptide levels between premeal and postmeal PFB in both groups.

CONCLUSIONS

Acute administration of premeal PFB decreased postprandial glucose excursion in both type 2 diabetes mellitus and NGT participants. In the type 2 diabetes mellitus participants, premeal PFB augmented the early-phase insulin secretion, possibly through enhancing glucagon-like peptide-1 secretion.

Inhalational supplementation of metformin butyrate: A strategy for prevention and cure of various pulmonary disorders

The management of chronic lung diseases such as cancer, asthma, COPD and pulmonary hypertension remains unsatisfactory till date, and several strategies are being tried to control the same. Metformin, a popular anti-diabetic drug has shown promising effects in pre-clinical studies and has been subject to several trials in patients with debilitating pulmonary diseases. However, the clinical evidence for the use of metformin in these conditions is disappointing. Recent observations suggest that metformin use in diabetic patients is associated with an increase in butyrate-producing bacteria in the gut microbiome. Butyrate, similar to metformin, shows beneficial effects in pathological conditions found in pulmonary diseases. Further, the pharmacokinetic data of metformin suggests that metformin is predominantly concentrated in the gut, even after absorption. Butyrate, on the other hand, has a short half-life and thus oral supplementation of butyrate and metformin is unlikely to result in high concentrations of these drugs in the lung. In this paper, we review the pre-clinical studies of metformin and butyrate pertaining to pathologies commonly encountered in chronic lung diseases and underscore the need to administer these drugs directly to the lung via the inhalational route.

Metformin: old friend, new ways of action-implication of the gut microbiome?

PURPOSE OF REVIEW

Gut dysbiosis was recently associated with the occurrence of type 2 diabetes (T2D). In addition to this finding, an increasing number of studies performed upon the last 5 years have also shown that metformin treatment leads to changes in gut bacterial composition in diabetic patients. This review focuses on the articles describing the effects of metformin on gut homeostasis (including the gut microbiota) and proposes potential mechanisms involved in those effects.

RECENT FINDINGS

Several human and animal studies emphasized that metformin alters the gut microbiota composition by enhancing the growth of some bacteria, such as Akkermansia muciniphila, Escherichia spp. or Lactobacillus and by decreasing the levels of some other ones like Intestinibacter. In-vitro studies also demonstrated a direct action of metformin on the growth of A. muciniphila and Bifidobacterium adolescentis. Moreover, in the intestines, metformin does not only improve the glucose uptake, but it also promotes the short-chain fatty acid (SCFA) production, protects the intestinal barrier and regulates the secretion of gut peptides SUMMARY: It is now clear that gut microbiota participates to the glucose-lowering effects of metformin in the context of diabetes. Further work is now needed to determine the exact mechanisms of action of the drug and to understand by which processes metformin is able to enhance the growth of some bacteria exhibiting beneficial effects for the host.

Actions of metformin and statins on lipid and glucose metabolism and possible benefit of combination therapy

Patients with diabetes type 2 have an increased risk for cardiovascular disease and commonly use combination therapy consisting of the anti-diabetic drug metformin and a cholesterol-lowering statin. However, both drugs act on glucose and lipid metabolism which could lead to adverse effects when used in combination as compared to monotherapy. In this review, the proposed molecular mechanisms of action of statin and metformin therapy in patients with diabetes and dyslipidemia are critically assessed, and a hypothesis for mechanisms underlying interactions between these drugs in combination therapy is developed.

Metformin and Autoimmunity: A "New Deal" of an Old Drug

Metformin (dimethyl biguanide) is a synthetic derivative of guanidine, isolated from the extracts of Galega officinalis, a plant with a prominent antidiabetic effect. Since its discovery more than 50 years ago, metformin represents a worldwide milestone in treatment of patients with type 2 diabetes (T2D). Recent evidence in humans indicates novel pleiotropic actions of metformin which span from its consolidated role in T2D management up to various regulatory properties, including cardio- and nephro-protection, as well as antiproliferative, antifibrotic, and antioxidant effects. These findings, together with ground-breaking studies demonstrating its ability to prolong healthspan and lifespan in mice, provided the basis for defining metformin as a potential antiaging molecule. Moreover, emerging in vivo and in vitro evidence support the novel hypothesis that metformin can exhibit immune-modulatory features. Studies suggest that metformin interferes with key immunopathological mechanisms involved in systemic autoimmune diseases, such as the T helper 17/regulatory T cell balance, germinal centers formation, autoantibodies production, macrophage polarization, cytokine synthesis, neutrophil extracellular traps release, and bone or extracellular matrix remodeling. These effects may represent a powerful contributor to antiaging and anticancer properties exerted by metformin and, from another standpoint, may open the way to assess whether metformin can be a candidate molecule for clinical trials involving patients with immune-mediated diseases. In this article, we will review the available preclinical and clinical evidence regarding the effect of metformin on individual cells of the immune system, with emphasis on immunological mechanisms related to the development and maintenance of autoimmunity and its potential relevance in treatment of autoimmune diseases.

The crosstalk of gut microbiota and chronic kidney disease: role of inflammation, proteinuria, hypertension, and diabetes mellitus

Chronic kidney disease (CKD) has been shown to result in profound changes in the composition and functions of the gut microbial flora which by disrupting intestinal epithelial barrier and generating toxic by-products contributes to systemic inflammation and the associated complications. On the other hand, emerging evidence points to the role of the gut microbiota in the development and progression of CKD by provoking inflammation, proteinuria, hypertension, and diabetes. These observations demonstrate the causal interconnection between the gut microbial dysbiosis and CKD. The gut microbiota closely interacts with the inflammatory, renal, cardiovascular, and endocrine systems via metabolic, humoral, and neural signaling pathways, events which can lead to chronic systemic inflammation, proteinuria, hypertension, diabetes, and kidney disease. Given the established role of the gut microbiota in the development and progression of CKD and its complications, favorable modification of the composition and function of the gut microbiome represents an appealing therapeutic target for prevention and treatment of CKD. This review provides an overview of the role of the gut microbial dysbiosis in the pathogenesis of the common causes of CKD including hypertension, diabetes, and proteinuria as well as progression of CKD.