Mechanisms underlying metformin-induced secretion of glucagon-like peptide-1 from the intestinal L cell

Ashitaba Chalcone 4-Hydroxydericcin Promotes Glucagon-Like Peptide-1 Secretion and Prevents Postprandial Hyperglycemia in Mice

Certain polyphenols improve glucose tolerance by stimulating glucagon-like peptide-1 (GLP-1) secretion from intestinal L-cells. Ashitaba chalcones, 4-hydroxyderricin (4-HD), and xanthoangelol (XAG) have antihyperglycemic effects, but their molecular mechanism, including whether they promote GLP-1 secretion is unknown. This study investigates the 4-HD-induced GLP-1 secretory mechanisms and its anti-hyperglycemic effects. The secretory mechanisms were examined in STC-1 cells and antihyperglycemic effects in male ICR mice. In STC-1 cells, 4-HD, but not XAG, stimulated GLP-1 secretion through membrane depolarization and intracellular Ca2+ increase [Ca2+]i, via the L-type Ca2+ channel (VGCC). Verapamil and nifedipine, blockers of VGCC, and treatment in Ca2+-free buffer abolished 4-HD effects on [Ca2+]i and GLP-1 secretion. Moreover, 4-HD activated CaMKII and ERK1/2. Consistently, oral 4-HD suppressed postprandial hyperglycemia in mice and increased plasma GLP-1 and insulin levels, GLUT4 translocation, and activation of LKB-1 and Akt pathways in skeletal muscle. Furthermore, exendin 9-39, a GLP-1R antagonist, and compound C, an AMPK inhibitor, completely canceled the 4-HD-caused anti-hyperglycemic activities. 4-HD stimulated GLP-1 secretion through membrane depolarization coupled with [Ca2+]i increase via VGCC in L-cells and activated AMPK- and insulin-induced GLUT4 translocation in skeletal muscle. Thus, 4-HD possesses dual mechanisms for the prevention of hyperglycemia.

Modern-Day Therapeutics and Ongoing Clinical Trials against Type 2 Diabetes Mellitus: A Narrative Review

OBJECTIVES

Diabetes Mellitus (DM) is a global health concern that affects millions of people globally. The present review aims to narrate the clinical guidelines and therapeutic interventions for Type 2 Diabetes Mellitus (T2DM) patients. Furthermore, the present work summarizes the ongoing phase 1/2/3 and clinical trials against T2DM.

METHODS

A meticulous and comprehensive literature review was performed using various databases, such as PubMed, MEDLINE, Clinical trials database (https://clinicaltrials.gov/), and Google Scholar, to include various clinical trials and therapeutic interventions against T2DM.

RESULTS

Based on our findings, we concluded that most T2DM-associated clinical trials are interventional. Anti-diabetic therapeutics, including insulin, metformin, Dipeptidyl Peptidase-4 (DPP-4) inhibitors, Glucagon-Like Peptide-1 Receptor Agonists (GLP-1RAs), and Sodium- Glucose cotransporter-2 (SGLT-2) inhibitors are frontline therapeutics being clinically investigated. Currently, the therapeutics in phase IV clinical trials are mostly SGLT-2 inhibitors, implicating their critical contribution to the clinical management of T2DM.

CONCLUSION

Despite the success of T2DM treatments, a surge in innovative treatment options to reduce diabetic consequences and improve glycemic control is currently ongoing. More emphasis needs to be on exploring novel targeted drug candidates that can offer more sustained glycemic control.

A New Strategy for Obesity Treatment: Revealing the Frontiers of Anti-obesity Medications

Obesity dramatically increases the risk of type 2 diabetes, fatty liver, hypertension, cardiovascular disease, and cancer, causing both declines in quality of life and life expectancy, which is a serious worldwide epidemic. At present, more and more patients with obesity are choosing drug therapy. However, given the high failure rate, high cost, and long design and testing process for discovering and developing new anti-obesity drugs, drug repurposing could be an innovative method and opportunity to broaden and improve pharmacological tools in this context. Because different diseases share molecular pathways and targets in the cells, anti-obesity drugs discovered in other fields are a viable option for treating obesity. Recently, some drugs initially developed for other diseases, such as treating diabetes, tumors, depression, alcoholism, erectile dysfunction, and Parkinson's disease, have been found to exert potential anti-obesity effects, which provides another treatment prospect. In this review, we will discuss the potential benefits and barriers associated with these drugs being used as obesity medications by focusing on their mechanisms of action when treating obesity. This could be a viable strategy for treating obesity as a significant advance in human health.

Metformin: Diverse molecular mechanisms, gastrointestinal effects and overcoming intolerance in type 2 Diabetes Mellitus: A review

Metformin, the first line treatment for patients with type 2 diabetes mellitus, has alternative novel roles, including cancer and diabetes prevention. This narrative review aims to explore its diverse mechanisms, effects and intolerance, using sources obtained by searching Scopus, PubMed and Web of Science databases, and following Scale for the Assessment of Narrative Review Articles reporting guidelines. Metformin exerts it actions through duration influenced, and organ specific, diverse mechanisms. Its use is associated with inhibition of hepatic gluconeogenesis targeted by mitochondria and lysosomes, reduction of cholesterol levels involving brown adipose tissue, weight reduction influenced by growth differentiation factor 15 and novel commensal bacteria, in addition to counteraction of meta-inflammation alongside immuno-modulation. Interactions with the gastrointestinal tract include alteration of gut microbiota, enhancement of glucose uptake and glucagon like peptide 1 and reduction of bile acid absorption. Though beneficial, they may be linked to intolerance. Metformin related gastrointestinal adverse effects are associated with dose escalation, immediate release formulations, gut microbiota alteration, epigenetic predisposition, inhibition of organic cation transporters in addition to interactions with serotonin, histamine and the enterohepatic circulation. Potentially effective measures to overcome intolerance encompasses carefully objective targeted dose escalation, prescription of fixed dose combination, microbiome modulators and prebiotics, in addition to use of extended release formulations.

The role of glucagon-like peptide 1 in the postprandial effects of metformin in type 2 diabetes: a randomized crossover trial

AIMS

Although metformin is widely used for treatment of type 2 diabetes (T2D), its glucose-lowering mechanism remains unclear. Using the glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) antagonist exendin(9-39)NH2, we tested the hypothesis that postprandial GLP-1-mediated effects contribute to the glucose-lowering potential of metformin in T2D.

METHODS

In a randomized, placebo-controlled, double-blind, crossover study, 15 individuals with T2D (median HbA1c 50 mmol/mol [6.7%], body mass index 30.1 kg/m2, age 71 years) underwent, in randomized order, 14 days of metformin and placebo treatment, respectively. Each treatment period was preceded by 14 days without any glucose-lowering medicine and concluded by two 4 h mixed meal tests performed in randomized order and separated by >24 h with either continuous intravenous exendin(9-39)NH2 or saline infusion.

RESULTS

Compared to placebo, metformin treatment lowered fasting plasma glucose (mean of differences [MD] 1.4 mmol/L × min [95% CI 0.8-2.0]) as well as postprandial plasma glucose excursions during both saline infusion (MD 186 mmol/L × min [95% CI 64-307]) and exendin(9-39)NH2 infusion (MD 268 mmol/L × min [95% CI 108-427]). The metformin-induced improvement in postprandial glucose tolerance was unaffected by GLP-1R antagonization (MD 82 mmol/L × min [95% CI -6564-170]). Metformin treatment increased fasting plasma GLP-1 (MD 1.7 pmol/L × min [95% CI 0.39-2.9]) but did not affect postprandial GLP-1 responses (MD 820 pmol/L × min [95% CI -1750-111]).

CONCLUSIONS

Using GLP-1R antagonization, we could not detect GLP-1-mediated postprandial glucose-lowering effect of metformin in individuals with T2D. We show that 2 weeks of metformin treatment increases fasting plasma GLP-1, which may contribute to metformin's beneficial effect on fasting plasma glucose in T2D. Trial registration: Clinicaltrials.gov NCT03246451.

Update on Pediatric Anti-obesity Medications-Current Landscape and Approach to Prescribing

PURPOSE OF REVIEW

To review the current medical therapies available for treatment of obesity in children and adolescents less than 18 years old in the United States and outline the approach to their use.

RECENT FINDINGS

Obesity is a chronic disease with increasing prevalence in children and adolescents in the United States. Over the past few years, more FDA-approved medical treatments for obesity, such as GLP-1 receptor agonists, have emerged for patients less than 18 years old. Furthermore, there are medications with weight loss effects that can be used off-label for obesity in pediatric patients. However, access to many of these medications is limited due to age restrictions, insurance coverage, and cost. Medical options are improving to provide treatment for obesity in pediatric populations. FDA and off-label medications should be considered when appropriate to treat children and adolescents with obesity. However, further studies are needed to evaluate the efficacy and long-term safety of FDA-approved and off-label medications for obesity treatment in pediatric patients.

Research progress on Sirtuins (SIRTs) family modulators

Sirtuins (SIRTs) represent a class of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that exert a crucial role in cellular signal transduction and various biological processes. The mammalian sirtuins family encompasses SIRT1 to SIRT7, exhibiting therapeutic potential in counteracting cellular aging, modulating metabolism, responding to oxidative stress, inhibiting tumors, and improving cellular microenvironment. These enzymes are intricately linked to the occurrence and treatment of diverse pathological conditions, including cancer, autoimmune diseases, and cardiovascular disorders. Given the significance of histone modification in gene expression and chromatin structure, maintaining the equilibrium of the sirtuins family is imperative for disease prevention and health restoration. Mounting evidence suggests that modulators of SIRTs play a crucial role in treating various diseases and maintaining physiological balance. This review delves into the molecular structure and regulatory functions of the sirtuins family, reviews the classification and historical evolution of SIRTs modulators, offers a systematic overview of existing SIRTs modulation strategies, and elucidates the regulatory mechanisms of SIRTs modulators (agonists and inhibitors) and their clinical applications. The article concludes by summarizing the challenges encountered in SIRTs modulator research and offering insights into future research directions.

Understanding the action mechanisms of metformin in the gastrointestinal tract

Metformin is the initial medication recommended for the treatment of type 2 diabetes mellitus (T2DM). In addition to diabetes treatment, the function of metformin also can be anti-aging, antiviral, and anti-inflammatory. Nevertheless, further exploration is required to fully understand its mode of operation. Historically, the liver has been acknowledged as the main location where metformin reduces glucose levels, however, there is increasing evidence suggesting that the gastrointestinal tract also plays a significant role in its action. In the gastrointestinal tract, metformin effects glucose uptake and absorption, increases glucagon-like peptide-1 (GLP-1) secretion, alters the composition and structure of the gut microbiota, and modulates the immune response. However, the side effects of it cannot be ignored such as gastrointestinal distress in patients. This review outlines the impact of metformin on the digestive system and explores potential explanations for variations in metformin effectiveness and adverse effects like gastrointestinal discomfort.

Examining the clinical relevance of metformin as an antioxidant intervention

In physiological concentrations, reactive oxygen species play a vital role in regulating cell signaling and gene expression. Nevertheless, oxidative stress is implicated in the pathogenesis of numerous diseases and can inflict damage on diverse cell types and tissues. Thus, understanding the factors that mitigate the deleterious effects of oxidative stress is imperative for identifying new therapeutic targets. In light of the absence of direct treatment recommendations for reducing oxidative stress, there is a continuing need for fundamental research that utilizes innovative therapeutic approaches. Metformin, known for its multifaceted beneficial properties, is acknowledged for its ability to counteract the adverse effects of increased oxidative stress at both molecular and cellular levels. In this review, we delve into recent insights regarding metformin's antioxidant attributes, aiming to expand its clinical applicability. Our review proposes that metformin holds promise as a potential adjunctive therapy for various diseases, given its modulation of oxidative stress characteristics and regulation of diverse metabolic pathways. These pathways include lipid metabolism, hormone synthesis, and immunological responses, all of which may experience dysregulation in disease states, contributing to increased oxidative stress. Furthermore, our review introduces potential novel metformin-based interventions that may merit consideration in future research. Nevertheless, the necessity for clinical trials involving this drug remains imperative, as they are essential for establishing therapeutic dosages and addressing challenges associated with dose-dependent effects.

Association of Metformin Use with Iron Deficiency Anemia in Urban Chinese Patients with Type 2 Diabetes

BACKGROUND

Previous evidence yielded contradictory findings on the relationship between metformin and anemia. This study aims to assess whether metformin use is associated with iron-deficiency anemia (IDA) risk in patients with type 2 diabetes (T2D) in Beijing, China.

METHODS

Overall, 60,327 newly diagnosed T2D patients were included based on a historical cohort study design. The information pertaining to these patients was gathered from the Beijing Medical Claim Data for Employees Database. These patients were then categorized into the metformin and non-metformin groups and matched on a 1:1 propensity score based on their initial antidiabetic prescription. The Cox proportional hazards models were utilized to calculate the incidences and the hazard ratios (HRs).

RESULTS

The study enrolled 27,960 patients with type 2 diabetes, with 13,980 patients in each of the initial glucose-lowering prescription groups: metformin and non-metformin. During a median follow-up period of 4.84 years, 4832 patients developed IDA. The incidence of IDA was significantly lower in the metformin group (26.08/1000 person-years) than in the non-metformin group (43.20/1000 person-years). Among the three groups divided by the proportion of days covered by metformin, we found a negative correlation between the proportion of days covered by metformin and the risk of IDA. The risk of IDA in patients with a proportion of days covered by metformin of <20%, 20-79%, and ≥80% was 0.43 (0.38, 0.48), 0.37 (0.34, 0.42), and 0.91 (0.85, 0.98), respectively, compared to the non-metformin group. We also performed subgroup analyses and sensitivity analyses: the incidence of IDA in the metformin group was lower than that in the non-metformin group in all subgroups, and the protective effect was more significant in subgroups of patients aged ≥65, with Charlson comorbidity index (CCI) ≥2, and with gastric acid inhibitor use.

CONCLUSIONS

In Chinese patients with T2DM, metformin treatment was associated with a decreased risk of IDA admission, and this risk responded positively to the proportion of days covered by metformin. These findings suggest that metformin may have a pleiotropic effect on IDA in patients with type 2 diabetes. Our study has important clinical implications for the management of patients with diabetes and other conditions that increase the risk of IDA.

Pharmacological management of youth with type 2 diabetes and diabetic kidney disease: a comprehensive review of current treatments and future directions

INTRODUCTION

Diabetic kidney disease (DKD) is a leading cause of mortality in people with type 2 diabetes (T2D), and over 50% of individuals with youth-onset T2D will develop DKD as a young adult. Diagnosis of early-onset DKD remains a challenge in young persons with T2D secondary to a lack of available biomarkers for early DKD, while the injuries may still be reversible. Furthermore, multiple barriers exist to initiate timely prevention and treatment strategies for DKD, including a lack of Food and Drug Administration approval of medications in pediatrics; provider comfort with medication prescription, titration, and monitoring; and medication adherence.

AREAS COVERED

Therapies that have promise for slowing DKD progression in youth with T2D include metformin, renin-angiotensin-aldosterone system inhibitors, glucagon-like peptide-1 receptor agonists, sodium glucose co-transporter 2 inhibitors, thiazolidinediones, sulfonylureas, endothelin receptor agonists, and mineralocorticoid antagonists. Novel agents are also in development to act synergistically on the kidneys with the aforementioned medications. We comprehensively review the available pharmacologic strategies for DKD in youth-onset T2D including mechanisms of action, potential adverse effects, and kidney-specific effects, with an emphasis on published pediatric and adult trials.

EXPERT OPINION

Large clinical trials evaluating pharmacologic interventions targeting the treatment of DKD in youth-onset T2D are strongly needed.

Identification of Genipin as a Potential Treatment for Type 2 Diabetes

The prevalence of type 2 diabetes (T2D) has been rising dramatically in many countries around the world. The main signatures of T2D are insulin resistance and dysfunction of β-cells. While there are several pharmaceutical therapies for T2D, no effective treatment is available for reversing the functional decline of pancreatic β-cells in T2D patients. It has been well recognized that glucagon-like peptide-1 (GLP-1), which is an incretin hormone secreted from intestinal L-cells, plays a vital role in regulating glycemic homeostasis via potentiating glucose-stimulated insulin secretion and promoting β-cell function. We found that genipin, a natural compound from Elli, can directly target intestinal L-cells, leading to the secretion of GLP-1. Incubation of the cells with genipin elicited a rapid increase in intracellular Ca²⁺. Inhibition of PLC ablated genipin-stimulated Ca²⁺ increase and GLP-1 secretion, suggesting that genipin-induced GLP-1 release from cells is dependent on the PLC/Ca²⁺ pathway. In vivo, acute administration of genipin stimulated GLP-1 secretion in mice. Chronically, treatment with genipin via oral gavage at 50 mg/kg/day for 6 weeks reversed hyperglycemia and insulin resistance in high-fat-diet (HFD)-induced obese mice. Moreover, genipin alleviated the impaired lipid metabolism and decreased lipid accumulation in the liver of obese mice. These results suggest that naturally occurring genipin might potentially be a novel agent for the treatment of T2D and diet-induced fatty liver disease.

Evidence for Involvement of GIP and GLP-1 Receptors and the Gut-Gonadal Axis in Regulating Female Reproductive Function in Mice

Substantial evidence suggests crosstalk between reproductive and gut-axis but mechanisms linking metabolism and reproduction are still unclear. The present study evaluated the possible role of glucose-dependent-insulinotropic-polypeptide (GIP) and glucagon-like-peptide-1 (GLP-1) in reproductive function by examining receptor distribution and the effects of global GIPR and GLP-1R deletion on estrous cycling and reproductive outcomes in mice. GIPR and GLP-1R gene expression were readily detected by PCR in female reproductive tissues including pituitary, ovaries and uterine horn. Protein expression was confirmed with histological visualisation of incretin receptors using GIPR-Cre and GLP1R-Cre mice in which the incretin receptor expressing cells were fluorescently tagged. Functional studies revealed that female GIPR-/- and GLP-1R-/- null mice exhibited significantly (p < 0.05 and p < 0.01) deranged estrous cycling compared to wild-type controls, indicative of reduced fertility. Furthermore, only 50% and 16% of female GIPR-/- and GLP-1R-/- mice, respectively produced litters with wild-type males across three breeding cycles. Consistent with a physiological role of incretin receptors in pregnancy outcome, litter size was significantly (p < 0.001-p < 0.05) decreased in GIPR-/- and GLP-1R-/- mice. Treatment with oral metformin (300 mg/kg body-weight), an agent used clinically for treatment of PCOS, for a further two breeding periods showed no amelioration of pregnancy outcome except that litter size in the GIPR-/- group was approximately 2 times greater in the second breeding cycle. These data highlight the significance of incretin receptors in modulation of female reproductive function which may provide future targets for pharmacological intervention in reproductive disorders.

An olive-derived elenolic acid stimulates hormone release from L-cells and exerts potent beneficial metabolic effects in obese diabetic mice

Insulin resistance and progressive decline in functional β-cell mass are two key factors for developing type 2 diabetes (T2D), which is largely driven by overweight and obesity, a significant obstacle for effective metabolic control in many patients with T2D. Thus, agents that simultaneously ameliorate obesity and act on multiple pathophysiological components could be more effective for treating T2D. Here, we report that elenolic acid (EA), a phytochemical, is such a dual-action agent. we show that EA dose-dependently stimulates GLP-1 secretion in mouse clonal L-cells and isolated mouse ileum crypts. In addition, EA induces L-cells to secrete peptide YY (PYY). EA induces a rapid increase in intracellular [Ca²⁺]_i and the production of inositol trisphosphate in L-cells, indicating that EA activates phospholipase C (PLC)-mediated signaling. Consistently, inhibition of (PLC) or Gα_q ablates EA-stimulated increase of [Ca²⁺]_i and GLP-1 secretion. In vivo, a single dose of EA acutely stimulates GLP-1 and PYY secretion in mice, accompanied with an improved glucose tolerance and insulin levels. Oral administration of EA at a dose of 50 mg/kg/day for 2 weeks normalized the fasting blood glucose and restored glucose tolerance in high-fat diet-induced obese (DIO) mice to levels that were comparable to chow-fed mice. In addition, EA suppresses appetite, reduces food intake, promotes weight loss, and reverses perturbated metabolic variables in obese mice. These results suggest that EA could be a dual-action agent as an alternative or adjuvant treatment for both T2D and obesity.

Association of GLP1R Polymorphisms With the Incretin Response

CONTEXT

Polymorphisms in the gene encoding the glucagon-like peptide-1 receptor (GLP1R) are associated with type 2 diabetes but their effects on incretin levels remain unclear.

OBJECTIVE

We evaluated the physiologic and hormonal effects of GLP1R genotypes before and after interventions that influence glucose physiology.

DESIGN

Pharmacogenetic study conducted at 3 academic centers in Boston, Massachusetts.

PARTICIPANTS

A total of 868 antidiabetic drug-naïve participants with type 2 diabetes or at risk for developing diabetes.

INTERVENTIONS

We analyzed 5 variants within GLP1R (rs761387, rs10305423, rs10305441, rs742762, and rs10305492) and recorded biochemical data during a 5-mg glipizide challenge and a 75-g oral glucose tolerance test (OGTT) following 4 doses of metformin 500 mg over 2 days.

MAIN OUTCOMES

We used an additive mixed-effects model to evaluate the association of these variants with glucose, insulin, and incretin levels over multiple timepoints during the OGTT.

RESULTS

During the OGTT, the G-risk allele at rs761387 was associated with higher total GLP-1 (2.61 pmol/L; 95% CI, 1.0.72-4.50), active GLP-1 (2.61 pmol/L; 95% CI, 0.04-5.18), and a trend toward higher glucose (3.63; 95% CI, -0.16 to 7.42 mg/dL) per allele but was not associated with insulin. During the glipizide challenge, the G allele was associated with higher insulin levels per allele (2.01 IU/mL; 95% CI, 0.26-3.76). The other variants were not associated with any of the outcomes tested.

CONCLUSIONS

GLP1R variation is associated with differences in GLP-1 levels following an OGTT load despite no differences in insulin levels, highlighting altered incretin signaling as a potential mechanism by which GLP1R variation affects T2D risk.

Comparison of the Effectiveness of Once-Daily Alogliptin/Metformin and Twice-Daily Anagliptin/Metformin Combination Tablet in a Randomized, Parallel-Group, Open-Label Trial in Japanese Patients with Type 2 Diabetes

INTRODUCTION

The combination tablets of dipeptidyl peptidase-4 (DPP-4) inhibitors and metformin are used for both once-daily and twice-daily agents in Japan. If there is no difference in effectiveness between the once-daily and twice-daily DPP-4 inhibitor/metformin combination tablets, the once-daily agent is advantageous in terms of frequency of administration. The aim of this study was to compare the effectiveness of once-daily alogliptin/metformin combination tablet (alogliptin 25 mg/metformin 500 mg) and twice-daily anagliptin/metformin combination tablet low dose (LD) (anagliptin 100 mg/metformin 250 mg).

METHODS

Forty-eight Japanese patients with type 2 diabetes whose metformin administration of 250 mg twice daily had remained unchanged for at least 8 weeks, except when using DPP-4 inhibitors, glucagon-like peptide-1 receptor agonists, or insulin, were randomized to either the once-daily alogliptin/metformin combination tablet group or the twice-daily anagliptin/metformin combination tablet LD group. The primary endpoint was the difference in glycosylated hemoglobin (HbA1c) levels from baseline to week 12 of administration, whereas the secondary endpoints were fasting blood glucose, body mass index (BMI), and adherence.

RESULTS

Forty-four patients completed the study, and intention-to-treat analyses were performed. The adjusted mean value (standard error) for the change in HbA1c from week 0 to 12, was - 0.75 (0.109)% for the once-daily alogliptin/metformin combination tablet group and - 0.65 (0.109)% for the twice-daily anagliptin/metformin combination tablet LD group, with an intergroup difference of - 0.10% (95% confidence interval, CI - 0.407, 0.215). The upper limit of the bilateral 95% CI was 0.215%, below the 0.40% pre-defined as the non-inferiority margin. Fasting blood glucose, BMI, and adherence were not significantly different between the groups.

CONCLUSIONS

The once-daily alogliptin/metformin combination tablet was non-inferior to the twice-daily anagliptin/metformin combination tablet LD in Japanese patients with type 2 diabetes.

TRIAL REGISTRATION

University Hospital Medical Information Network Clinical Trial Registry (UMIN-CTR) (registration number: UMIN000034951).

Metformin: Is it a drug for all reasons and diseases?

Metformin was first used to treat type 2 diabetes in the late 1950s and in 2022 remains the first-choice drug used daily by approximately 150 million people. An accumulation of positive pre-clinical and clinical data has stimulated interest in re-purposing metformin to treat a variety of diseases including COVID-19. In polycystic ovary syndrome metformin improves insulin sensitivity. In type 1 diabetes metformin may help reduce the insulin dose. Meta-analysis and data from pre-clinical and clinical studies link metformin to a reduction in the incidence of cancer. Clinical trials, including MILES (Metformin In Longevity Study), and TAME (Targeting Aging with Metformin), have been designed to determine if metformin can offset aging and extend lifespan. Pre-clinical and clinical data suggest that metformin, via suppression of pro-inflammatory pathways, protection of mitochondria and vascular function, and direct actions on neuronal stem cells, may protect against neurodegenerative diseases. Metformin has also been studied for its anti-bacterial, -viral, -malaria efficacy. Collectively, these data raise the question: Is metformin a drug for all diseases? It remains unclear as to whether all of these putative beneficial effects are secondary to its actions as an anti-hyperglycemic and insulin-sensitizing drug, or result from other cellular actions, including inhibition of mTOR (mammalian target for rapamycin), or direct anti-viral actions. Clarification is also sought as to whether data from ex vivo studies based on the use of high concentrations of metformin can be translated into clinical benefits, or whether they reflect a 'Paracelsus' effect. The environmental impact of metformin, a drug with no known metabolites, is another emerging issue that has been linked to endocrine disruption in fish, and extensive use in T2D has also raised concerns over effects on human reproduction. The objectives for this review are to: 1) evaluate the putative mechanism(s) of action of metformin; 2) analyze the controversial evidence for metformin's effectiveness in the treatment of diseases other than type 2 diabetes; 3) assess the reproducibility of the data, and finally 4) reach an informed conclusion as to whether metformin is a drug for all diseases and reasons. We conclude that the primary clinical benefits of metformin result from its insulin-sensitizing and antihyperglycaemic effects that secondarily contribute to a reduced risk of a number of diseases and thereby enhancing healthspan. However, benefits like improving vascular endothelial function that are independent of effects on glucose homeostasis add to metformin's therapeutic actions.

A Planar Culture Model of Human Absorptive Enterocytes Reveals Metformin Increases Fatty Acid Oxidation and Export

BACKGROUND & AIMS

Fatty acid oxidation by absorptive enterocytes has been linked to the pathophysiology of type 2 diabetes, obesity, and dyslipidemia. Caco-2 and organoids have been used to study dietary lipid-handling processes including fatty acid oxidation, but are limited in physiological relevance or preclude simultaneous apical and basal access. Here, we developed a high-throughput planar human absorptive enterocyte monolayer system for investigating lipid handling, and then evaluated the role of fatty acid oxidation in fatty acid export, using etomoxir, C75, and the antidiabetic drug metformin.

METHODS

Single-cell RNA-sequencing, transcriptomics, and lineage trajectory was performed on primary human jejunum. In vivo absorptive enterocyte maturational states informed conditions used to differentiate human intestinal stem cells (ISCs) that mimic in vivo absorptive enterocyte maturation. The system was scaled for high-throughput drug screening. Fatty acid oxidation was modulated pharmacologically and BODIPY (Thermo Fisher Scientific, Waltham, MA) (B)-labeled fatty acids were used to evaluate fatty acid handling via fluorescence and thin-layer chromatography.

RESULTS

Single-cell RNA-sequencing shows increasing expression of lipid-handling genes as absorptive enterocytes mature. Culture conditions promote ISC differentiation into confluent absorptive enterocyte monolayers. Fatty acid-handling gene expression mimics in vivo maturational states. The fatty acid oxidation inhibitor etomoxir decreased apical-to-basolateral export of medium-chain B-C12 and long-chain B-C16 fatty acids, whereas the CPT1 agonist C75 and the antidiabetic drug metformin increased apical-to-basolateral export. Short-chain B-C5 was unaffected by fatty acid oxidation inhibition and diffused through absorptive enterocytes.

CONCLUSIONS

Primary human ISCs in culture undergo programmed maturation. Absorptive enterocyte monolayers show in vivo maturational states and lipid-handling gene expression profiles. Absorptive enterocytes create strong epithelial barriers in 96-Transwell format. Fatty acid export is proportional to fatty acid oxidation. Metformin enhances fatty acid oxidation and increases basolateral fatty acid export, supporting an intestine-specific role.

Comparison of the effectiveness and safety of insulin and oral hypoglycemic drugs in the treatment of gestational diabetes mellitus: a meta-analysis of 26 randomized controlled trials

OBJECTIVE

Oral hypoglycemic drugs for the treatment of gestational diabetes mellitus (GDM) are still controversial because they can pass through the placenta. The purpose of this meta-analysis is to evaluate the safety and effectiveness of oral hypoglycemic drugs.

METHODS

PubMed, Ovid Embase, Web of Science, and Cochrane databases were systematically searched (inception to 20 April 2021). Rev Man 5.0 was used to analyze the data. A random-effects model was used to compute the summary risk estimates.

RESULTS

There were 26 randomized controlled trials (RCTs) involving 4921 GDM patients which were included in this meta-analysis. Compared with metformin, insulin had a significant increase in the risk of preeclampsia (odds ratio [OR], 1.61; 95% confidence interval [CI], 1.06 to 2.45; I²=40%; p < .05), hypertension (OR, 1.42; 95% CI, 1.02 to 1.99; I²=0%; p < .05), hypoglycemia (OR, 3.93; 95% CI, 1.27 to 12.19; I²=0%; p < .05), neonatal hypoglycemia (OR, 1.92; 95% CI, 1.34 to 2.76; I²=41%; p < .0001), neonatal jaundice (OR, 2.70; 95% CI, 1.12 to 6.52; I²=0%; p < .05), and Neonatal Intensive Care Unit Admission (OR, 1.46; 95% CI, 1.09 to 1.95; I²=39%; p < .05), but the risk of neonatal macrosomia (OR, 1.67; 95% CI, 1.12 to 2.40; I²=0%; p < .05) and neonatal injury (OR, 0.70; 95% CI, 0.55 to 0.89; I²=0%; p < .01) is lower.

CONCLUSIONS

Metformin is comparable with insulin in glycemic control and neonatal outcomes and has the potential to replace insulin therapy in clinical practice. Glyburide is behind metformin and insulin, and more RCTs are needed to verify its safety.

Diabetes mellitus and Parkinson's disease: dangerous liaisons between insulin and dopamine

The relationship between diabetes mellitus and Parkinson's disease has been described in several epidemiological studies over the 1960s to date. Molecular studies have shown the possible functional link between insulin and dopamine, as there is strong evidence demonstrating the action of dopamine in pancreatic islets, as well as the insulin effects on feeding and cognition through central nervous system mechanism, largely independent of glucose utilization. Therapies used for the treatment of type 2 diabetes mellitus appear to be promising candidates for symptomatic and/or disease-modifying action in neurodegenerative diseases including Parkinson's disease, while an old dopamine agonist, bromocriptine, has been repositioned for the type 2 diabetes mellitus treatment. This review will aim at reappraising the different studies that have highlighted the dangerous liaisons between diabetes mellitus and Parkinson's disease.

Cardiovascular Effects of Incretin-Based Therapies: Integrating Mechanisms With Cardiovascular Outcome Trials

As the worldwide prevalence of diabetes and obesity continues to rise, so does the risk of debilitating cardiovascular complications. Given the significant association between diabetes and cardiovascular risk, the actions of glucose-lowering therapies within the cardiovascular system must be clearly defined. Incretin hormones, including GLP-1 (glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic polypeptide), are gut hormones secreted in response to nutrient intake that maintain glycemic control by regulating insulin and glucagon release. GLP-1 receptor agonists (GLP-1Ras) and dipeptidyl peptidase 4 inhibitors (DPP-4is) represent two drug classes used for the treatment of type 2 diabetes mellitus (T2DM) that improve glucose regulation through stimulating the actions of gut-derived incretin hormones or inhibiting their degradation, respectively. Despite both classes acting to potentiate the incretin response, the potential cardioprotective benefits afforded by GLP-1Ras have not been recapitulated in cardiovascular outcome trials (CVOTs) evaluating DPP-4is. This review provides insights through discussion of clinical and preclinical studies to illuminate the physiological mechanisms that may underlie and reconcile observations from GLP-1Ra and DPP-4i CVOTs. Furthermore, critical knowledge gaps and areas for further investigation will be emphasized to guide future studies and, ultimately, facilitate improved clinical management of cardiovascular disease in T2DM.

Management of Hyperglycemia in Older Adults with Type 2 Diabetes

The increasing incidence of type 2 diabetes in the general population as well as enhanced life expectancy has resulted in a rapid rise in the prevalence of diabetes in the older population. Diabetes causes significant morbidity and impairs quality of life. Managing diabetes in older adults is a daunting task due to unique health and psychosocial challenges. Medical management is complicated by polypharmacy, cognitive impairment, urinary incontinence, injurious falls, and persistent pain. Health care providers now have several traditional and contemporary pharmacologic agents to manage diabetes. Avoidance of hypoglycemia is critical; however, evidence-based guidelines are lacking due to the paucity of clinical trials in older adults. For many in this population, maintaining independence is more important than adherence to published guidelines to prevent diabetes complications. The goal of diabetes care in older adults is to enhance the quality of life without subjecting these patients to intrusive and complicated interventions. Recent technological advancements such as continuous glucose monitoring systems can have crucial supplementary benefits in the geriatric population.

New Aspects of Diabetes Research and Therapeutic Development

Both type 1 and type 2 diabetes mellitus are advancing at exponential rates, placing significant burdens on health care networks worldwide. Although traditional pharmacologic therapies such as insulin and oral antidiabetic stalwarts like metformin and the sulfonylureas continue to be used, newer drugs are now on the market targeting novel blood glucose-lowering pathways. Furthermore, exciting new developments in the understanding of beta cell and islet biology are driving the potential for treatments targeting incretin action, islet transplantation with new methods for immunologic protection, and the generation of functional beta cells from stem cells. Here we discuss the mechanistic details underlying past, present, and future diabetes therapies and evaluate their potential to treat and possibly reverse type 1 and 2 diabetes in humans. SIGNIFICANCE STATEMENT: Diabetes mellitus has reached epidemic proportions in the developed and developing world alike. As the last several years have seen many new developments in the field, a new and up to date review of these advances and their careful evaluation will help both clinical and research diabetologists to better understand where the field is currently heading.

The Hormetic Effect of Metformin: "Less Is More"?

Metformin (MTF) is the first-line therapy for type 2 diabetes (T2DM). The euglycemic effect of MTF is due to the inhibition of hepatic glucose production. Literature reports that the principal molecular mechanism of MTF is the activation of 5′-AMP-activated protein kinase (AMPK) due to the decrement of ATP intracellular content consequent to the inhibition of Complex I, although this effect is obtained only at millimolar concentrations. Conversely, micromolar MTF seems to activate the mitochondrial electron transport chain, increasing ATP production and limiting oxidative stress. This evidence sustains the idea that MTF exerts a hormetic effect based on its concentration in the target tissue. Therefore, in this review we describe the effects of MTF on T2DM on the principal target organs, such as liver, gut, adipose tissue, endothelium, heart, and skeletal muscle. In particular, data indicate that all organs, except the gut, accumulate MTF in the micromolar range when administered in therapeutic doses, unmasking molecular mechanisms that do not depend on Complex I inhibition.

Metformin Improves Autonomic Nervous System Imbalance and Metabolic Dysfunction in Monosodium L-Glutamate-Treated Rats

Metformin is an antidiabetic drug used for the treatment of diabetes and metabolic diseases. Imbalance in the autonomic nervous system (ANS) is associated with metabolic diseases. This study aimed to test whether metformin could improve ANS function in obese rats. Obesity was induced by neonatal treatment with monosodium L-glutamate (MSG). During 21-100 days of age, MSG-rats were treated with metformin 250 mg/kg body weight/day or saline solution. Rats were euthanized to evaluate biometric and biochemical parameters. ANS electrical activity was recorded and analyzed. Metformin normalized the hypervagal response in MSG-rats. Glucose-stimulated insulin secretion in isolated pancreatic islets increased in MSG-rats, while the cholinergic response decreased. Metformin treatment normalized the cholinergic response, which involved mostly the M3 muscarinic acetylcholine receptor (M3 mAChR) in pancreatic beta-cells. Protein expression of M3 mAChRs increased in MSG-obesity rats, while metformin treatment decreased the protein expression by 25%. In conclusion, chronic metformin treatment was effective in normalizing ANS activity and alleviating obesity in MSG-rats.

Efficacy and safety of the metformin-mazindol anorectic combination in rat

The current study investigates the anorectic interaction and safety of the mazindol-metformin combination in rats. Isobologram and interaction index were used to determine anorectic interaction between mazindol and metformin in the sweetened milk model. The safety profile of the mazindol-metformin combination was determined by measuring anxiety, blood pressure, hematic biometry and blood chemistry. An acute dose of mazindol and metformin administered per os, individually or as a mixture, has reduced the milk consumption in rats in a dose-dependent manner. Theoretical effective dose 40 (ED40t) did not differ from the experimental effective dose 40 (ED40e) obtained with the mazindol-metformin mixture in the anorexia experiments, by Student's t-test. In addition, the interaction index confirmed the additive anorectic effect between both drugs. A single oral dose of ED40e mazindol-metformin mixture induced anxiolysis in the elevated plus-maze test. Moreover, oral administration of mazindol-metformin combination for 3 months significantly decreased glycemia, but not blood pressure nor other parameters of hematic biometry and blood chemistry. Results suggest that mazindol-metformin combination exerts an additive anorectic effect, as well as anxiolytic and hypoglycemic properties. Mazindol-metformin combination might be useful in obese patients with anxiety disorders or diabetes risk factors.

Diets and drugs for weight loss and health in obesity - An update

Numerous combinations of diets and pharmacological agents, including lifestyle changes, have been launched to treat obesity. There are still ambiguities regarding the efficacies of different approaches despite many clinical trials and the use of animal models to study physiological mechanisms in weight management and obesity comorbidities, Here, we present an update on promising diets and pharmacological aids. Literature published after the year 2005 was searched in PubMed, Medline and Google scholar. Among recommended diets are low-fat (LF) and low-carbohydrate (LC) diets, in addition to the Mediterranean diet and the intermittent fasting approach, all of which presumably being optimized by adequate contents of dietary fibers. A basic point for weight loss is to adopt a diet that creates a permanently negative and acceptable energy balance, and prolonged dietary adherence is a crucial factor. As for pharmacological aids, obese patients with type 2 diabetes or insulin resistance seem to benefit from LC diet combined with a GLP-1 agonist, e.g. semaglutide, which may improve glycemic control, stimulate satiety, and suppress appetite. The lipase inhibitor orlistat is still used to maintain a low-fat approach, which may be favorable e.g. in hypercholesterolemia. The bupropion-naltrexone-combination appears promising for interruption of the vicious cycle of addictive over-eating. Successful weight loss seems to improve almost all biomarkers of obesity comorbidities. Until more support for specific strategies is available, clinicians should recommend an adapted lifestyle, and when necessary, a drug combination tailored to individual needs and comorbidities. Different diets may change hormonal secretion, gut-brain signaling, and influence hunger, satiety and energy expenditure. Further research is needed to clarify mechanisms and how such knowledge can be used in weight management.

Chemosensing in enteroendocrine cells: mechanisms and therapeutic opportunities

PURPOSE OF REVIEW

Enteroendocrine cells (EECs) are scattered chemosensory cells in the intestinal epithelium that release hormones with a wide range of actions on intestinal function, food intake and glucose homeostasis. The mechanisms by which gut hormones are secreted postprandially, or altered by antidiabetic agents and surgical interventions are of considerable interest for future therapeutic development.

RECENT FINDINGS

EECs are electrically excitable and express a repertoire of G-protein coupled receptors that sense nutrient and nonnutrient stimuli, coupled to intracellular Ca2+ and cyclic adenosine monophosphate. Our knowledge of EEC function, previously developed using mouse models, has recently been extended to human cells. Gut hormone release in humans is enhanced by bariatric surgery, as well as by some antidiabetic agents including sodium-coupled glucose transporter inhibitors and metformin.

SUMMARY

EECs are important potential therapeutic targets. A better understanding of their chemosensory mechanisms will enhance the development of new therapeutic strategies to treat metabolic and gastrointestinal diseases.

A Meta-Analysis of the Impact of Resveratrol Supplementation on Markers of Renal Function and Blood Pressure in Type 2 Diabetic Patients on Hypoglycemic Therapy

Evidence on the beneficial effects of resveratrol supplementation on cardiovascular disease-related profiles in patients with type 2 diabetes (T2D) is conflicting, while its impact on renal function and blood pressure measurements remains to be established in these patients. The current meta-analysis included randomized controlled trials (RCTs) reporting on the impact of resveratrol supplementation on markers of renal function and blood pressure in patients with T2D on hypoglycemic medication. Electronic databases such as MEDLINE, Cochrane Library, Scopus, and EMBASE were searched for eligible studies from inception up to June 2020. The random and fixed effects model was used in the meta-analysis. A total of five RCTs met the inclusion criteria and involved 388 participants with T2D. Notably, most of the participants were on metformin therapy, or metformin in combination with other hypoglycemic drugs such as insulin and glibenclamide. Pooled estimates showed that resveratrol supplementation in patients with T2D lowered the levels of fasting glucose (SMD: -0.06 [95% CI: -0.24, 0.12]; I2 = 4%, p = 0.39) and insulin (SMD: -0.08 [95% CI: -0.50, 0.34], I2 = 73%, p = 0.002) when compared to those on placebo. In addition, supplementation significantly lowered systolic blood pressure (SMD: -5.77 [95% CI: -8.61, -2.93], I2 = 66%, p = 0.02) in these patients. Although resveratrol supplementation did not affect creatinine or urea levels, it reduced the total protein content (SMD: -0.19 [95% CI: -0.36, -0.02]; I2 = 91%, p = 0.001). In all, resveratrol supplementation in hypoglycemic therapy improves glucose control and lowers blood pressure; however, additional evidence is necessary to confirm its effect on renal function in patients with T2D.

Design of G-protein-coupled bile acid receptor 1 (GPBAR1, TGR5) soft drugs with reduced gallbladder-filling effects

The G-protein-coupled bile acid receptor TGR5 agonists were widely developed in type 2 diabetes and gastrointestinal disorders, but were also full of challenges, due to the systemic on-targeted side effects, especially the gallbladder-filling effects. Here, to circumvent these risks, several TGR5 agonists with soft-drug designation had been designed and synthesized with the properties of rapid metabolized after drug effect. Among them, compound 19 showed negligible systemic exposure and favorable gallbladder safety on a 3-day continuous administration, providing a novel strategy for developing TGR5 agonists.

Probing the characteristics and biofunctional effects of disease-affected cells and drug response via machine learning applications

Drug-induced transformations in disease characteristics at the cellular and molecular level offers the opportunity to predict and evaluate the efficacy of pharmaceutical ingredients whilst enabling the optimal design of new and improved drugs with enhanced pharmacokinetics and pharmacodynamics. Machine learning is a promising in-silico tool used to simulate cells with specific disease properties and to determine their response toward drug uptake. Differences in the properties of normal and infected cells, including biophysical, biochemical and physiological characteristics, plays a key role in developing fundamental cellular probing platforms for machine learning applications. Cellular features can be extracted periodically from both the drug treated, infected, and normal cells via image segmentations in order to probe dynamic differences in cell behavior. Cellular segmentation can be evaluated to reflect the levels of drug effect on a distinct cell or group of cells via probability scoring. This article provides an account for the use of machine learning methods to probe differences in the biophysical, biochemical and physiological characteristics of infected cells in response to pharmacokinetics uptake of drug ingredients for application in cancer, diabetes and neurodegenerative disease therapies.

Intestine-selective reduction of Gcg expression reveals the importance of the distal gut for GLP-1 secretion

OBJECTIVE

Glucagon-like peptide-1 is a nutrient-sensitive hormone secreted from enteroendocrine L cells within the small and large bowel. Although GLP-1 levels rise rapidly in response to food ingestion, the greatest density of L cells is localized to the distal small bowel and colon. Here, we assessed the importance of the distal gut in the acute L cell response to diverse secretagogues.

METHODS

Circulating levels of glucose and plasma GLP-1 were measured in response to the administration of L cell secretagogues in wild-type mice and in mice with (1) genetic reduction of Gcg expression throughout the small bowel and large bowel (GcgGut-/-) and (2) selective reduction of Gcg expression in the distal gut (GcgDistalGut-/-).

RESULTS

The acute GLP-1 response to olive oil or arginine administration was markedly diminished in GcgGut-/- but preserved in GcgDistalGut-/- mice. In contrast, the increase in plasma GLP-1 levels following the administration of the GPR119 agonist AR231453, or the melanocortin-4 receptor (MC4R) agonist LY2112688, was markedly diminished in the GcgDistalGut-/- mice. The GLP-1 response to LPS was also markedly attenuated in the GcgGut-/- mice and remained submaximal in the GcgDistalGut-/- mice. Doses of metformin sufficient to lower glucose and increase GLP-1 levels in the GcgGut+/+ mice retained their glucoregulatory activity, yet they failed to increase GLP-1 levels in the GcgGut-/- mice. Surprisingly, the actions of metformin to increase plasma GLP-1 levels were substantially attenuated in the GcgDistalGut-/- mice.

CONCLUSION

These findings further establish the importance of the proximal gut for the acute response to nutrient-related GLP-1 secretagogues. In contrast, we identify essential contributions of the distal gut to (i) the rapid induction of circulating GLP-1 levels in response to pharmacological selective agonism of G-protein-coupled receptors, (ii) the increased GLP-1 levels following the activation of Toll-Like Receptors with LPS, and iii) the acute GLP-1 response to metformin. Collectively, these results reveal that distal gut Gcg + endocrine cells are rapid responders to structurally and functionally diverse GLP-1 secretagogues.

Dipeptidyl Peptidase-4 at the Interface Between Inflammation and Metabolism

Dipeptidyl peptidase-4 (DPP4) is a serine protease that rapidly inactivates the incretin peptides, glucagon-like peptide-1, and glucose-dependent insulinotropic polypeptide to modulate postprandial islet hormone secretion and glycemia. Dipeptidyl peptidase-4 also has nonglycemic effects by controlling the progression of inflammation, which may be mediated more through direct protein-protein interactions than catalytic activity in the context of nonalcoholic fatty liver disease (NAFLD), obesity, and type 2 diabetes (T2D). Failure to resolve inflammation resulting in chronic subclinical activation of the immune system may influence the development of metabolic dysregulation. Thus, through both its cleavage and regulation of the bioactivity of peptide hormones and its influence on inflammation, DPP4 exhibits a diverse array of effects that can influence the progression of metabolic disease. Here, we highlight our current understanding of the complex biology of DPP4 at the intersection of inflammation, obesity, T2D, and NAFLD. We compare and review new mechanisms identified in basic laboratory and clinical studies, which may have therapeutic application and relevance to the pathogenesis of obesity and T2D.

Flavone Hispidulin Stimulates Glucagon-Like Peptide-1 Secretion and Ameliorates Hyperglycemia in Streptozotocin-Induced Diabetic Mice

SCOPE

Loss of functional β-cell mass is central for the deterioration of glycemic control in diabetes. The incretin hormone glucagon-like peptide-1 (GLP-1) plays a critical role in maintaining glycemic homeostasis via potentiating glucose-stimulated insulin secretion and promoting β-cell mass. Agents that can directly promote GLP-1 secretion, thereby increasing insulin secretion and preserving β-cell mass, hold great potential for the treatment of T2D.

METHODS AND RESULTS

GluTag L-cells, INS832/13 cells, and mouse ileum crypts and islets are cultured for examining the effects of flavone hispidulin on GLP-1 and insulin secretion. Mouse livers and isolated hepatocytes are used for gluconeogenesis. Streptozotocin-induced diabetic mice are treated with hispidulin (20 mg kg^-1 day^-1 , oral gavage) for 6 weeks to evaluate its anti-diabetic potential. Hispidulin stimulates GLP-1 secretion from the L-cell line, ileum crypts, and in vivo. This hispidulin action is mediated via activation of cyclic adenosine monophosphate/protein kinase A signaling. Hispidulin significantly improves glycemic control in diabetic mice, concomitant with improved insulin release, and β-cell survival. Additionally, hispidulin decreases hepatic pyruvate carboxylase expression in diabetic mice and suppresses gluconeogenesis in hepatocytes. Furthermore, hispidulin stimulates insulin secretion from β-cells.

CONCLUSION

These findings suggest that Hispidulin may be a novel dual-action anti-diabetic compound via stimulating GLP-1 secretion and suppressing hepatic glucose production.

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.

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.

Canagliflozin Increases Postprandial Total Glucagon-Like Peptide 1 Levels in the Absence of α-Glucosidase Inhibitor Therapy in Patients with Type 2 Diabetes: A Single-Arm, Non-randomized, Open-Label Study

INTRODUCTION

To investigate canagliflozin-induced changes in postprandial total glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) levels in patients with type 2 diabetes mellitus (T2DM).

METHODS

Forty-five patients with T2DM who had inadequate glycemic control (glycated hemoglobin ≥ 6.5%) with diet and exercise alone (n = 15, drug naïve) and in combination with either a stable dose of the α-glucosidase inhibitor acarbose (n = 15) or metformin (n = 15) received canagliflozin, a sodium-glucose cotransporter 2 inhibitor, at 100 mg once daily for 12 weeks. The primary endpoint was the change from baseline to week 12 in postprandial glucose and plasma levels of total GLP-1 and GIP during a meal tolerance test (MTT).

RESULTS

Canagliflozin significantly reduced postprandial blood glucose (mean difference - 40.2 mg/mL at 60 min) and increased postprandial total GLP-1 (mean difference 1.8 pg/mL at 60 min) during an MTT. A transient reduction in the postprandial GIP level at only 30 min (mean difference - 80.3 pg/mL) during an MTT was observed. No changes in postprandial GLP-1 or GIP levels were seen after canagliflozin treatment as an add-on to acarbose in patients with T2DM. Acarbose treatment significantly decreased postprandial total GIP levels (P < 0.05) and tended to increase postprandial total GLP-1 levels (P = 0.07) compared to the other two treatments prior to canagliflozin.

CONCLUSION

Canagliflozin 100 mg increased postprandial total GLP-1 levels in the absence of acarbose, suggesting that it may upregulate GLP-1 secretion through delayed glucose absorption in the upper intestine, as with the α-glucosidase inhibitor.

TRIAL REGISTRATION

University Hospital Medical Information Network, UMIN000018345.

FUNDING

Mitsubishi Tanabe Pharma Corporation.

Effects of anagliptin on plasma glucagon levels and gastric emptying in patients with type 2 diabetes: An exploratory randomized controlled trial versus metformin

AIMS

Glucagon has an important role in glucose homeostasis. Recently, a new plasma glucagon assay based on liquid chromatography-high resolution mass spectrometry was developed. We evaluated the influence of a dipeptidyl peptidase-4 inhibitor (anagliptin) on plasma glucagon levels in Japanese patients with type 2 diabetes by using this new assay.

METHODS

Twenty-four patients with type 2 diabetes were enrolled in a prospective, single-center, randomized, open-label study and were randomly allocated to 4 weeks of treatment with metformin (1000 mg/day) or anagliptin (200 mg/day). A liquid test meal labeled with sodium [¹³C] acetate was ingested before and after the treatment period. Samples of blood and expired air were collected over 3 h. Plasma levels of glucose, glucagon, C-peptide, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured, and gastric emptying was also evaluated.

RESULTS

Twenty-two patients completed the study (metformin group: n = 10; anagliptin group: n = 12). Glycemic control showed similar improvement in both groups. In the anagliptin group, there was a slight decrease of the incremental area under the plasma concentration versus time curve for glucagon after the test meal (P = 0.048). In addition, the plasma level of active GLP-1 and GIP was increased, and plasma C-peptide was also increased versus baseline. Neither anagliptin nor metformin delayed gastric emptying.

CONCLUSIONS

In patients with type 2 diabetes maintained endogenous insulin secretion, anagliptin increased the plasma level of active GLP-1 and GIP in association with a slight stimulation of insulin secretion and slight inhibition of glucagon secretion, but did not delay gastric emptying. Clinical Trial Registry: University hospital Medical Information Network UMIN000028293.

Understanding the glucoregulatory mechanisms of metformin in type 2 diabetes mellitus

Despite its position as the first-line drug for treatment of type 2 diabetes mellitus, the mechanisms underlying the plasma glucose level-lowering effects of metformin (1,1-dimethylbiguanide) still remain incompletely understood. Metformin is thought to exert its primary antidiabetic action through the suppression of hepatic glucose production. In addition, the discovery that metformin inhibits the mitochondrial respiratory chain complex 1 has placed energy metabolism and activation of AMP-activated protein kinase (AMPK) at the centre of its proposed mechanism of action. However, the role of AMPK has been challenged and might only account for indirect changes in hepatic insulin sensitivity. Various mechanisms involving alterations in cellular energy charge, AMP-mediated inhibition of adenylate cyclase or fructose-1,6-bisphosphatase 1 and modulation of the cellular redox state through direct inhibition of mitochondrial glycerol-3-phosphate dehydrogenase have been proposed for the acute inhibition of gluconeogenesis by metformin. Emerging evidence suggests that metformin could improve obesity-induced meta-inflammation via direct and indirect effects on tissue-resident immune cells in metabolic organs (that is, adipose tissue, the gastrointestinal tract and the liver). Furthermore, the gastrointestinal tract also has a major role in metformin action through modulation of glucose-lowering hormone glucagon-like peptide 1 and the intestinal bile acid pool and alterations in gut microbiota composition.

Diabetes Mellitus and Colon Carcinogenesis: Expectation for Inhibition of Colon Carcinogenesis by Oral Hypoglycemic Drugs

The global deaths due to colorectal cancer and diabetes mellitus have increased by 57% and 90%, respectively. The relationship between various cancers and diabetes mellitus has been shown in multiple epidemiological studies. Hence, better management of diabetes mellitus is expected to reduce the risk of various cancers. This review focuses on colorectal cancer and aims to summarize recent findings on the antitumor effects of various oral hypoglycemic drugs on colorectal cancer and their estimated mechanisms. Of the seven classes of oral hypoglycemic agents, only metformin was found to have suppressive effects on colorectal cancer in both clinical and basic research. Clinical and basic researches on suppressing effects of glinides, dipeptidyl peptidase-4 inhibitors, thiazolidinedione, α-glucosidase inhibitors, and sodium glucose cotransporter-2 inhibitors against colon carcinogenesis have been insufficient and have not arrived at any conclusion. Therefore, further research regarding these agents is warranted. In addition, the suppressive effects of these agents in healthy subjects without diabetes should also be investigated.

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.

Which is better, high-dose metformin monotherapy or low-dose metformin/linagliptin combination therapy, in improving glycemic variability in type 2 diabetes patients with insufficient glycemic control despite low-dose metformin monotherapy? A randomized, cross-over, continuous glucose monitoring-based pilot study

AIMS/INTRODUCTION

The present study investigated the effect of high-dose metformin or low-dose metformin/linagliptin combination therapy on glycemic variability (GV) in type 2 diabetes patients with insufficient glycemic control despite low-dose metformin monotherapy in a cross-over study using continuous glucose monitoring.

MATERIALS AND METHODS

The present study was carried out with 11 type 2 diabetes outpatients (7% < glycated hemoglobin < 10%) receiving low-dose metformin monotherapy (500-1,000 mg). All patients were assigned to either metformin 1,500 mg monotherapy (HMET) or combination therapy of low-dose (750 mg) metformin and linagliptin 5 mg (LMET + dipeptidyl peptidase-4 [DPP4]). GV was evaluated by continuous glucose monitoring after >4 weeks of the initial treatment and again after cross-over to the other treatment. GV metrics were compared between the treatments using the Wilcoxon signed-rank test.

RESULTS

Of the continuous glucose monitoring-derived GV metrics for the HMET versus LMET + DPP4, mean glucose levels, standard deviations and mean amplitude of glucose excursions were not significantly different. Although the pre-breakfast glucose levels were not significantly different among the treatments (P = 0.248), the 3-h postprandial glucose area under the curve (>160 mg/dL) after breakfast was significantly larger with HMET versus LMET + DPP4 (9,550 [2,075-11,395] vs 4,065 [1,950-8,895]; P = 0.041).

CONCLUSIONS

A comparison of GV with HMET versus LMET + DPP4 suggested that LMET + DPP4 might reduce post-breakfast GV to a greater degree than HMET in type 2 diabetes patients receiving low-dose metformin monotherapy.

Metformin acutely lowers blood glucose levels by inhibition of intestinal glucose transport

Metformin is currently the most prescribed drug for treatment of type 2 diabetes mellitus in humans. It has been well established that long-term treatment with metformin improves glucose tolerance in mice by inhibiting hepatic gluconeogenesis. Interestingly, a single dose of orally administered metformin acutely lowers blood glucose levels, however, little is known about the mechanism involved in this effect. Glucose tolerance, as assessed by the glucose tolerance test, was improved in response to prior oral metformin administration when compared to vehicle-treated mice, irrespective of whether the animals were fed either the standard or high-fat diet. Blood glucose-lowering effects of acutely administered metformin were also observed in mice lacking functional AMP-activated protein kinase, and were independent of glucagon-like-peptide-1 or N-methyl-D-aspartate receptors signaling. [¹⁸F]-FDG/PET revealed a slower intestinal transit of labeled glucose after metformin as compared to vehicle administration. Finally, metformin in a dose-dependent but indirect manner decreased glucose transport from the intestinal lumen into the blood, which was observed ex vivo as well as in vivo. Our results support the view that the inhibition of transepithelial glucose transport in the intestine is responsible for lowering blood glucose levels during an early response to oral administration of metformin.

MARCH: factors associated with weight loss in patients with newly diagnosed type 2 diabetes treated with acarbose or metformin

INTRODUCTION

In this secondary analysis of the Metformin and AcaRbose in Chinese as the initial Hypoglycaemic treatment (MARCH) trial, we evaluated what demographic and clinical factors were associated with reduction in weight. We also assessed the effects of acarbose and metformin treatment on weight reduction.

MATERIAL AND METHODS

We analyzed the demographic and clinical laboratory values from the 784 patients with type 2 diabetes of the MARCH study who were treated for 48 weeks with acarbose or metformin. We determined the association of the different parameters with a weight reduction of ≥ 2 kg in patients using univariate and multivariate analysis.

RESULTS

In patients treated with acarbose, males were less likely than females to lose ≥ 2 kg of weight (p = 0.025). Higher baseline HbA_1c levels and lower decreases from baseline in fasting plasma glucose (FPG) levels after 48 weeks of treatment were negatively associated with losing ≥ 2 kg of weight (both, p < 0.05). Higher baseline glucagon AUC was also positively associated with reducing weight by ≥ 2 kg (p = 0.010). In patients treated with metformin, change from baseline in whole body insulin sensitivity increased the odds of having a weight reduction of ≥ 2 kg (p = 0.014).

CONCLUSIONS

This study found that for both acarbose and metformin, control of FPG significantly impacted weight loss. Baseline AUC for glucagon in patients treated with acarbose and an increase of whole body insulin sensitivity after 48 weeks of treatment with metformin were important factors for weight reduction.

Genistein enhances the secretion of glucagon-like peptide-1 (GLP-1) via downregulation of inflammatory responses

Glucagon-like peptide-1 (GLP-1) an incretin hormone, is known to regulate the glucose-mediated insulin secretion. However, reduction in the level of GLP-1 is considered to be a major cause for the reduction of GLP-1-dependent insulin secretory response. Genistein an isoflavone, is an important polyphenol and has wide range of therapeutic potentials, but its therapeutic effects alone and/or in combination with metformin on GLP-1 secretion have not been investigated yet. Hence, we aimed to investigate the stimulatory action of genistein in combination with metformin on GLP-1 via downregulation of inflammatory mediators, hyperlipidemia and hyperglycemia in alloxan-induced diabetic rats. Diabetes was induced in experimental rats by single administration of alloxan intraperitoneally. Metformin (50 mg/kg/day), genistein (20 mg/kg/day) and combination of genistein and metformin was administered in alloxan-induced diabetic rats. We found that genistein alone and/or in combination with metformin significantly increased the serum level (P < 0.01) and tissue content (P < 0.05) of GLP-1 in intestine when compared with that of metformin-treated animals. Similarly, genistein alone and/or in combination with metformin also resulted in normoglycemia (P < 0.001), glucose tolerance (P < 0.01), insulin sensitivity (P < 0.0001), hyperlipidemia (P < 0.01), liver and kidney function biomarkers (P < 0.01) as compared to that of metformin-treated experimental animals. Moreover, genistein alone and/or in combination with metformin also downregulated the inflammatory responses by decreasing the levels of interleuin-6, tumor necrosis factor-α and C-reactive protein in serum (P < 0.05) and intestine (P < 0.001) more efficiently as compared to that of metformin-treated experimental animals. The downregulation of inflammatory responses in intestine, was positively associated with increased secretion of GLP-1 from intestine. Histopathology of pancreas and intestine also showed that genistein significantly improved the deleterious effects of alloxan on pancreas and intestine. Hence, our work provides new insights on the synergistic effects of genistein and metformin on GLP-1 secretion. This may significantly improve the perception for proposing new GLP-1-based synergistic approaches for the treatment of diabetes mellitus.

Comparative Efficacy and Safety of Metformin, Glyburide, and Insulin in Treating Gestational Diabetes Mellitus: A Meta-Analysis

To compare the efficacy and safety of metformin, glyburide, and insulin in treating gestational diabetes mellitus (GDM), a meta-analysis of randomized controlled trials (RCTs) was conducted. PubMed, Embase, CINAHL, Web of Science, and Cochrane Library to November 13, 2018, were searched for RCT adjusted estimates of the efficacy and safety of metformin, glyburide, and insulin treatments in GDM patients. There were 41 studies involving 7703 GDM patients which were included in this meta-analysis; 12 primary outcomes and 24 secondary outcomes were detected and analyzed. Compared with metformin, insulin had a significant increase in the risk of preeclampsia (RR, 0.57; 95% CI, 0.45 to 0.72; P < 0.001), NICU admission (RR, 0.75; 95% CI, 0.64 to 0.87; P < 0.001), neonatal hypoglycemia (RR, 0.57; 95% CI, 0.49 to 0.66; P < 0.001), and macrosomia (RR, 0.68; 95% CI, 0.55 to 0.86; P < 0.05). To the outcomes of birth weight and gestational age at delivery, insulin had a significant increase when compared with metformin (MD, 114.48; 95% CI, 37.32 to 191.64; P < 0.01; MD, 0.23; 95% CI, 0.12 to 0.34; P < 0.001; respectively). Of the two groups between glyburide and metformin, metformin had lower gestational weight gain compared with glyburide (MD, 1.67; 95% CI, 0.26 to 3.07; P < 0.05). Glyburide had a higher risk of neonatal hypoglycemia compared with insulin (RR, 1.76; 95% CI, 1.32 to 2.36; P < 0.001). This meta-analysis found that metformin could be a safe and effective treatment for GDM. However, clinicians should pay attention on the long-term offspring outcomes of the relative data with GDM patients treated with metformin. Compared with insulin, glyburide had a higher increase of neonatal hypoglycemia. The use of glyburide in pregnancy for GDM women appears to be unclear.

Effects of metformin on metabolism of white and brown adipose tissue in obese C57BL/6J mice

BACKGROUND

To investigate effects of metformin on the regulation of proteins of white adipose tissue (WAT) and brown adipose tissue (BAT) in obesity and explore the underlying mechanisms on energy metabolism.

METHODS

C57BL/6J mice were fed with normal diet (ND, n = 6) or high-fat diet (HFD, n = 12) for 22 weeks. HFD-induced obese mice were treated with metformin (MET, n = 6). After treatment for 8 weeks, oral glucose tolerance test (OGTT) and hyperinsulinemic-euglycemic clamp were performed to evaluate the improvement of glucose tolerance and insulin sensitivity. Protein expressions of WAT and BAT in mice among ND, HFD, and MET group were identified and quantified with isobaric tag for relative and absolute quantification (iTRAQ) coupled with 2D LC-MS/MS. The results were analyzed by MASCOT, Scaffold and IPA.

RESULTS

The glucose infusion rate in MET group was increased significantly compared with HFD group. We identified 4388 and 3486 proteins in WAT and BAT, respectively. As compared MET to HFD, differential expressed proteins in WAT and BAT were mainly assigned to the pathways of EIF2 signaling and mitochondrial dysfunction, respectively. In the pathways, CPT1a in WAT, CPT1b and CPT2 in BAT were down-regulated by metformin significantly.

CONCLUSIONS

Metformin improved the body weight and insulin sensitivity of obese mice. Meanwhile, metformin might ameliorate endoplasmic reticulum stress in WAT, and affect fatty acid metabolism in WAT and BAT. CPT1 might be a potential target of metformin in WAT and BAT.

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.

Pleiotropic effects of metformin: Shaping the microbiome to manage type 2 diabetes and postpone ageing

Metformin is the first-choice therapy to lower glycaemia and manage type 2 diabetes. Continuously emerging epidemiological data and experimental models are showing additional protective effects of metformin against a number of age-related diseases (ARDs), e.g., cardiovascular diseases and cancer. This evidence has prompted the design of a specific trial, i.e., the Targeting Aging with Metformin (TAME) trial, to test metformin as an anti-ageing molecule. However, a unifying or prevailing mechanism of action of metformin is still debated. Here, we summarize the epidemiological data linking metformin to ARD prevention. Then, we dissect the deeply studied mechanisms of action explaining its antihyperglycemic effect and the putative mechanisms supporting its anti-ageing properties, focusing on studies using clinically pertinent doses. We hypothesize that the molecular observations obtained in different models with metformin could be indirectly mediated by its effect on gut flora. Novel evidence suggests that metformin reshapes the human microbiota, promoting the growth of beneficial bacterial species and counteracting the expansion of detrimental bacterial species. In turn, this action would influence the balance between pro- and anti-inflammatory circulating factors, thereby promoting glycaemic control and healthy ageing. This framework may reconcile diverse observations, providing information for designing further studies to elucidate the complex interplay between metformin and the metabiome harboured in mammalian body compartments, thereby paving the way for innovative, bacterial-based therapeutics to manage type 2 diabetes and foster a longer healthspan.