Effect of metformin on glucose metabolism in the splanchnic bed

Metformin: Therapeutic profile in the treatment of type 2 diabetes

Metformin (dimethyl-biguanide) can claim its origins in the use of Galega officinalis as a plant treatment for symptoms ascribed to diabetes. Since the first clinical use of metformin as a glucose-lowering agent in 1957, this medicine has emerged as a first-line pharmacological option to support lifestyle interventions in the management of type 2 diabetes (T2D). It acts through multiple cellular pathways, principally in the gut, liver and muscle, to counter insulin resistance and lower blood glucose without weight gain or risk of overt hypoglycaemia. Other effects include improvements in lipid metabolism, decreased inflammation and lower long-term cardiovascular risk. Metformin is conveniently combined with other diabetes medications, can be prescribed in prediabetes to reduce the risk of progression to T2D, and is used in some regions to assist glycaemic control in pregnancy. Consistent with its diversity of actions, established safety profile and cost-effectiveness, metformin is being assessed for further possible clinical applications. The use of metformin requires adequate renal function for drug elimination, and may cause initial gastrointestinal side effects, which can be moderated by taking with meals or using an extended-release formulation. Thus, metformin serves as a valuable therapeutic resource for use throughout the natural history of T2D.

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.

Unveiling the potential pleiotropic effects of metformin in treating COVID-19: a comprehensive review

This review article explores the potential of metformin, a medication commonly used for type 2 diabetes, as an antiviral and anti-inflammatory agent in the context of coronavirus disease 2019 (COVID-19). Metformin has demonstrated inhibitory effects on the growth of SARS-CoV-2 in cell culture models and has shown promising results in reducing viral load and achieving undetectable viral levels in clinical trials. Additionally, metformin exhibits anti-inflammatory properties by reducing the production of pro-inflammatory cytokines and modulating immune cell function, which may help prevent cytokine storms associated with severe COVID-19. The drug's ability to regulate the balance between pro-inflammatory Th17 cells and anti-inflammatory Treg cells suggests its potential in mitigating inflammation and restoring T cell functionality. Furthermore, metformin's modulation of the gut microbiota, particularly changes in bacterial taxa and the production of short-chain fatty acids, may contribute to its therapeutic effects. The interplay between metformin, bile acids, the gut microbiome, glucagon-like peptide-1 secretion, and glycemic control has implications for the management of diabetes and potential interventions in COVID-19. By refreshing the current evidence, this review highlights the potential of metformin as a therapeutic option in the management of COVID-19, while also exploring its effects on the gut microbiome and immunometabolism.

Metformin and exercise effects on postprandial insulin sensitivity and glucose kinetics in pre-diabetic and diabetic adults

The potential interaction between metformin and exercise on glucose-lowering effects remains controversial. We studied the separated and combined effects of metformin and/or exercise on fasting and postprandial insulin sensitivity in individuals with pre-diabetes and type 2 diabetes (T2D). Eight T2D adults (60 ± 4 yr) with overweight/obesity (32 ± 4 kg·m-2) under chronic metformin treatment (9 ± 6 yr; 1281 ± 524 mg·day-1) underwent four trials; 1) taking their habitual metformin treatment (MET), 2) substituting during 96 h their metformin medication by placebo (PLAC), 3) placebo combined with 50 min bout of high-intensity interval exercise (PLAC + EX), and 4) metformin combined with exercise (MET + EX). Plasma glucose kinetics using stable isotopes (6,6-2H2 and [U-13C] glucose), and glucose oxidation by indirect calorimetry, were assessed at rest, during exercise, and in a subsequent oral glucose tolerance test (OGTT). Postprandial glucose and insulin concentrations were analyzed as mean and incremental area under the curve (iAUC), and insulin sensitivity was calculated (i.e., MATSUDAindex and OGISindex). During OGTT, metformin reduced glucose iAUC (i.e., MET and MET + EX lower than PLAC and PLAC + EX, respectively; P = 0.023). MET + EX increased MATSUDAindex above PLAC (4.8 ± 1.4 vs. 3.3 ± 1.0, respectively; P = 0.018) and OGISindex above PLAC (358 ± 52 vs. 306 ± 46 mL·min-1·m-2, respectively; P = 0.006). Metformin decreased the plasma appearance of the ingested glucose (Ra OGTT; MET vs. PLAC, -3.5; 95% CI -0.1 to -6.8 µmol·kg-1·min-1; P = 0.043). Metformin combined with exercise potentiates insulin sensitivity during an OGTT in individuals with pre-diabetes and type 2 diabetes. Metformin's blood glucose-lowering effect seems mediated by decreased oral glucose entering the circulation (gut-liver effect) an effect partially blunted after exercise.NEW & NOTEWORTHY Metformin is the most prescribed oral antidiabetic medicine in the world but its mechanism of action and its interactions with exercise are not fully understood. Our stable isotope tracer data suggested that metformin reduces the rates of oral glucose entering the circulation (gut-liver effect). Exercise, in turn, tended to reduce postprandial insulin blood levels potentiating metformin improvements in insulin sensitivity. Thus, exercise potentiates metformin improvements in glycemic control and should be advised to metformin users.

Advances in metformin for the treatment of non-alcoholic fatty liver disease in children

INTRODUCTION

The increased economic and social burdens for NAFLD worldwide make treating such a disease a significant public health issue. Metformin, a kind of insulin sensitizer generally used to treat type 2 diabetes, has been recently found to have efficacy on children's NAFLD in various areas such as glucolipid metabolism, intestinal bacterial metabolism, oxidative stress, and anti-inflammatory response. This article aims to provide an overview of the possible mechanisms of NAFLD in children and the potential therapeutic application of metformin.

AREAS COVERED

The Cochrane Library, PubMed, Scopus, and EMBASE database was systematically searched on 12 April 2022, using the keywords metformin; non-alcoholic fatty liver disease; and children to identify similar studies. An additional search for recently published research was performed in June 2020.

EXPERT OPINION

Although metformin has been proved to have an excellent therapeutic effect on children's NAFLD; we can still explore its potential impacts and mechanisms from different angles, such as combined medication. At the same time, we should also pay attention to its side effects.

Oral lactate slows gastric emptying and suppresses appetite in young males

BACKGROUND

Lactate serves as an alternative energy fuel but is also an important signaling metabolite. We aimed to investigate whether oral lactate administration affects appetite-regulating hormones, slows gastric emptying rate, and dampens appetite.

METHODS

Ten healthy male volunteers were investigated on two separate occasions: 1) following oral ingestion of D/L-Na-lactate and 2) following oral ingestion of isotonic iso-voluminous NaCl and intravenous iso-lactemic D/L-Na-lactate infusions. Appetite was evaluated by questionnaires and ad libitum meal tests were performed at the end of each study day. Gastric emptying rate was evaluated using the acetaminophen test.

RESULTS

Plasma concentrations of growth differential factor 15 (GDF15, primary outcome) increased following oral and iv administration of lactate (p < 0.001) with no detectable difference between interventions (p = 0.15). Oral lactate administration lowered plasma concentrations of acylated ghrelin (p = 0.02) and elevated glucagon like peptide-1 (GLP-1, p = 0.045), insulin (p < 0.001), and glucagon (p < 0.001) compared with iv administration. Oral lactate administration slowed gastric emptying (p < 0.001), increased the feeling of being "full" (p = 0.008) and lowered the "anticipated future food intake" (p = 0.007) compared with iv administration. Food intake during the ad libitum meal test did not differ between the two study days.

CONCLUSION

Oral lactate administration has a direct effect on the upper gastrointestinal tract, affecting gut hormone secretion, motility and appetite sensations which cannot be mediated through lactate in the systemic circulation alone. These data suggest that compounds rich in lactate may be useful in the treatment of metabolic disease.

CLINICAL TRIAL REGISTRY NUMBER

NCT0429981, https://clinicaltrials.gov/ct2/show/NCT04299815.

The Relationships between Gut Microbiota and Diabetes Mellitus, and Treatments for Diabetes Mellitus

Diabetes mellitus is considered to be a global epidemic. The combination of genetic susceptibility and an unhealthy lifestyle is considered to be the main trigger of this metabolic disorder. Recently, there has been increased interest in the roles of gut microbiota as a new potential contributor to this epidemic. Research, in recent years, has contributed to an in-depth characterization of the human microbiome and its associations with various diseases, including metabolic diseases and diabetes mellitus. It is known that diet can change the composition of gut microbiota, but it is unclear how this, in turn, may influence metabolism. The main objective of this review is to evaluate the pathogenetic association between microbiota and diabetes and to explore any new therapeutic agents, including nutraceuticals that may modulate the microbiota. We also look at several mechanisms involved in this process. There is a clear, bidirectional relationship between microbiota and diabetes. Current treatments for diabetes influence microbiota in various ways, some beneficial, but others with still unclear effects. Microbiota-aimed treatments have seen no real-world significant effects on the progression of diabetes and its complications, with more studies needed in order to find a really beneficial agent.

Integrated or Independent Actions of Metformin in Target Tissues Underlying Its Current Use and New Possible Applications in the Endocrine and Metabolic Disorder Area

Metformin is considered the first-choice drug for type 2 diabetes treatment. Actually, pleiotropic effects of metformin have been recognized, and there is evidence that this drug may have a favorable impact on health beyond its glucose-lowering activity. In summary, despite its long history, metformin is still an attractive research opportunity in the field of endocrine and metabolic diseases, age-related diseases, and cancer. To this end, its mode of action in distinct cell types is still in dispute. The aim of this work was to review the current knowledge and recent findings on the molecular mechanisms underlying the pharmacological effects of metformin in the field of metabolic and endocrine pathologies, including some endocrine tumors. Metformin is believed to act through multiple pathways that can be interconnected or work independently. Moreover, metformin effects on target tissues may be either direct or indirect, which means secondary to the actions on other tissues and consequent alterations at systemic level. Finally, as to the direct actions of metformin at cellular level, the intracellular milieu cooperates to cause differential responses to the drug between distinct cell types, despite the primary molecular targets may be the same within cells. Cellular bioenergetics can be regarded as the primary target of metformin action. Metformin can perturb the cytosolic and mitochondrial NAD/NADH ratio and the ATP/AMP ratio within cells, thus affecting enzymatic activities and metabolic and signaling pathways which depend on redox- and energy balance. In this context, the possible link between pyruvate metabolism and metformin actions is extensively discussed.

Metformin Stimulates Intestinal Glycolysis and Lactate Release: A single-Dose Study of Metformin in Patients With Intrahepatic Portosystemic Stent

The pharmacodynamic effects of metformin remain elusive, but several lines of evidence suggest a critical role of direct effects in the gastrointestinal (GI) tract. We investigated if metformin stimulates intestinal glucose metabolism and lactate release in the prehepatic circulation. We included eight patients with transjugular intrahepatic portosytemic stent in an open label study. Portal and arterialized peripheral blood was obtained before and 90 minutes after ingestion of 1,000 mg metformin. Metformin increased lactate concentrations by 23% (95% confidence interval (CI): 6-40) after 90 minutes in the portal vein. The plasma concentration of glucose, insulin, and C-peptide was higher in the portal vein compared with arterialized blood (P < 0.05, all) and was lowered at both sampling sites following metformin ingestion (P < 0.01, all). Plasma concentration of GLP-1 was 20% (95% CI: 2-38) higher in the portal vein at baseline and metformin increased the concentration with 11% (1.5 pM, P = 0.05). The median concentration of growth differentiation factor 15 was 10% (95% CI: 1-19) higher in the portal vein compared with arterialized blood. Ninety minutes after metformin administration, the median portal vein concentration increased to around 3,000 ng/mL with a mean portal/arterial ratio of 1.5 (95% CI: 1.2-1.8). Non-targeted metabolomics showed that metformin acutely affected benzoate-hippurate metabolism. A single-dose of metformin directly affects substrate metabolism in the upper GI tract in humans with direct stimulation of nonoxidative glucose metabolism. These data suggest glucose lowering effects of metformin can be intrinsically linked with the GI tract without hepatic uptake of the drug.

Metformin Benefits: Another Example for Alternative Energy Substrate Mechanism?

Since the UK Prospective Diabetes Study (UKPDS), metformin has been considered the first-line medication for patients with newly diagnosed type 2 diabetes. Though direct evidence from specific trials is still lacking, several studies have suggested that metformin may protect from diabetes- and nondiabetes-related comorbidities, including cardiovascular, renal, neurological, and neoplastic diseases. In the past few decades, several mechanisms of action have been proposed to explain metformin's protective effects, none being final. It is certain, however, that metformin increases lactate production, concentration, and, possibly, oxidation. Once considered a mere waste product of exercising skeletal muscle or anaerobiosis, lactate is now known to act as a major energy shuttle, redistributed from production sites to where it is needed. Through the direct uptake and oxidation of lactate produced elsewhere, all end organs can be rapidly supplied with fundamental energy, skipping glycolysis and its possible byproducts. Increased lactate production (and consequent oxidation) could therefore be considered a positive mechanism of action of metformin, except when, under specific circumstances, metformin and lactate become excessive, increasing the risk of lactic acidosis. We are proposing that, rather than considering metformin-induced lactate production as dangerous, it could be considered a mechanism through which metformin exerts its possible protective effect on the heart, kidneys, and brain and, to some extent, its antineoplastic action.

Metformin - its anti-cancer effects in hematologic malignancies

The main anti-diabetic effect of metformin mediated through stimulation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) is the inhibition of hepatic gluconeogenesis and triggering glucose uptake in skeletal muscles. Additionally, some new pathways, besides the AMPK activation, were discovered, that can explain wide-range properties of metformin. All these properties are now attracting the attention of researchers in the fields other than diabetes and the drug has been reported to have anti-cancer, immunoregulatory and anti-aging effects. Among others, the beneficial effects of metformin in hematological disorders like leukemias, lymphomas, and multiple myeloma were reported. Despite a great progress in therapy, these diseases are still incurable in most cases. Thus, there is an urgent need to discover novel, less toxic and more effective drugs especially for older or chemotherapy-resistant patients. In this review article, the current findings on the anti-cancer effect of metformin together with underlying possible mechanisms in blood cancers are discussed. However. to evaluate precisely these promising effects of metformin, more studies are required, because many of the published results are preclinical.

Inhibition of mitochondrial function by metformin increases glucose uptake, glycolysis and GDF-15 release from intestinal cells

Even though metformin is widely used to treat type2 diabetes, reducing glycaemia and body weight, the mechanisms of action are still elusive. Recent studies have identified the gastrointestinal tract as an important site of action. Here we used intestinal organoids to explore the effects of metformin on intestinal cell physiology. Bulk RNA-sequencing analysis identified changes in hexose metabolism pathways, particularly glycolytic genes. Metformin increased expression of Slc2a1 (GLUT1), decreased expression of Slc2a2 (GLUT2) and Slc5a1 (SGLT1) whilst increasing GLUT-dependent glucose uptake and glycolytic rate as observed by live cell imaging of genetically encoded metabolite sensors and measurement of oxygen consumption and extracellular acidification rates. Metformin caused mitochondrial dysfunction and metformin's effects on 2D-cultures were phenocopied by treatment with rotenone and antimycin-A, including upregulation of GDF15 expression, previously linked to metformin dependent weight loss. Gene expression changes elicited by metformin were replicated in 3D apical-out organoids and distal small intestines of metformin treated mice. We conclude that metformin affects glucose uptake, glycolysis and GDF-15 secretion, likely downstream of the observed mitochondrial dysfunction. This may explain the effects of metformin on intestinal glucose utilisation and food balance.

Clinical implications, diagnosis, and management of diabetes in patients with chronic liver diseases

Diabetes mellitus (DM) negatively affects the development and progression of chronic liver diseases (CLD) of various etiologies. Concurrent DM and CLD are also associated with worse clinical outcomes with respect to mortality, the occurrence of hepatic decompensation, and the development of hepatocellular carcinoma (HCC). Unfortunately, early diagnosis and optimal treatment of DM can be challenging, due to the lack of established clinical guidelines as well as the medical complexity of this patient population. We conducted an exploratory review of relevant literature to provide an up-to-date review for internists and hepatologists caring for this patient population. We reviewed the epidemiological and pathophysiological associations between DM and CLD, the impact of insulin resistance on the progression and manifestations of CLD, the pathogenesis of hepatogenic diabetes, as well as the practical challenges in diagnosis and monitoring of DM in this patient population. We also reviewed the latest clinical evidence on various pharmacological antihyperglycemic therapies with an emphasis on liver disease-related clinical outcomes. Finally, we proposed an algorithm for managing DM in patients with CLD and discussed the clinical and research questions that remain to be addressed.

The Association between Metformin Therapy and Lactic Acidosis

INTRODUCTION AND OBJECTIVES

There is increasing evidence to suggest that therapeutic doses of metformin are unlikely to cause lactic acidosis. The aims of this research were (1) to formally evaluate the association between metformin therapy and lactic acidosis in published case reports using two causality scoring systems, (2) to determine the frequency of pre-existing independent risk factors in published metformin-associated lactic acidosis cases, (3) to investigate the association between risk factors and mortality in metformin-associated lactic acidosis cases, and (4) to explore the relationship between prescribed metformin doses, elevated metformin plasma concentrations and the development of lactic acidosis in cases with chronic renal impairment.

METHODS

A systematic review was conducted to identify metformin-associated lactic acidosis cases. Causality was assessed using the World Health Organisation-Uppsala Monitoring Centre system and the Naranjo adverse drug reaction probability scale. Compliance to dosing guidelines was investigated for cases with chronic renal impairment as well as the association between steady-state plasma metformin concentrations prior to admission.

RESULTS

We identified 559 metformin-associated lactic acidosis cases. Almost all cases reviewed (97%) presented with independent risk factors for lactic acidosis. The prescribed metformin dose exceeded published guidelines in 60% of cases in patients with impaired kidney function. Metformin steady-state plasma concentrations prior to admission were predicted to be below the proposed upper limit of the therapeutic range of 5 mg/L.

CONCLUSIONS

Almost all cases of metformin-associated lactic acidosis reviewed presented with independent risk factors for lactic acidosis, supporting the suggestion that metformin plays a contributory role. The prescribed metformin dose, on average, exceeded the dosing recommendations by 1000 mg/day in patients with varying degrees of renal impairment but the predicted pre-admission plasma concentrations did not exceed the therapeutic range.

Intoxication à la metformine

La metformine, seul représentant disponible en France de la classe des biguanides, est un médicament antidiabétique largement prescrit. L’effet thérapeutique bénéfique du contrôle glycémique obtenu par inhibition de la néoglucogenèse est objectivé par une réduction de la morbimortalité chez les patients diabétiques de type 2. Néanmoins, la metformine affecte aussi le métabolisme du lactate en augmentant sa production par la cellule. Ainsi, l’effet secondaire le plus redouté est l’acidose lactique associée à la metformine (metformin-associated lactic acidosis [MALA]). Celle-ci est liée à une augmentation brutale de la concentration en metformine dans le sang et dans les tissus, que ce soit après ingestion d’une grande quantité de médicament ou plus souvent dans les suites d’une insuffisance rénale aiguë chez un patient traité au long cours. Dans ce contexte d’acidose métabolique majeure avec hyperlactatémie, la sévérité des défaillances d’organes conditionne le pronostic. La prise en charge thérapeutique est symptomatique avec recours précoce à une épuration extrarénale dans les formes sévères ou ne répondant pas au traitement initial. La prévention de la MALA repose avant tout sur le respect des contreindications de la metformine chez les patients diabétiques.

Mechanisms of action of metformin with special reference to cardiovascular protection

Management guidelines continue to identify metformin as initial pharmacologic antidiabetic therapy of choice for people with type 2 diabetes without contraindications, despite recent randomized trials that have demonstrated significant improvements in cardiovascular outcomes with newer classes of antidiabetic therapies. The purpose of this review is to summarize the current state of knowledge of metformin's therapeutic actions on blood glucose and cardiovascular clinical evidence and to consider the mechanisms that underlie them. The effects of metformin on glycaemia occur mainly in the liver, but metformin-stimulated glucose disposal by the gut has emerged as an increasingly import site of action of metformin. Additionally, metformin induces increased secretion of GLP-1 from intestinal L-cells. Clinical cardiovascular protection with metformin is supported by three randomized outcomes trials (in newly diagnosed and late stage insulin-treated type 2 diabetes patients) and a wealth of observational data. Initial evidence suggests that cotreatment with metformin may enhance the impact of newer incretin-based therapies on cardiovascular outcomes, an important observation as metformin can be combined with any other antidiabetic agent. Multiple potential mechanisms support the concept of cardiovascular protection with metformin beyond those provided by reduced blood glucose, including weight loss, improvements in haemostatic function, reduced inflammation, and oxidative stress, and inhibition of key steps in the process of atherosclerosis. Accordingly, metformin remains well placed to support improvements in cardiovascular outcomes, from diagnosis and throughout the course of type 2 diabetes, even in this new age of improved outcomes in type 2 diabetes.

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.

Metformin poisoning treated with high dose insulin dextrose therapy: a case series

Purpose

We describe the compassionate use of high dose insulin dextrose (HID) for life threatening metformin associated lactic acidosis (MALA) in four patients admitted to intensive care.

Methods

Patients presenting with refractory lactic acidosis believed to be secondary to metformin poisoning were included.High dose insulin dextrose at 0.5units/kg/hour was infused in 50% dextrose. Frequent blood gas analysis allowed titration of therapy. All patients also received continuous veno-venous haemofiltration.

Results

All four patients recovered to normal or near normal lactate and pH between 10 and 24 hours of therapy. Two patients had significant separation in time between initiation of HID and haemofiltration to suggest an independent effect of HID on improving pH and lactate.All patients had at least one episode of hypoglycaemia below 4.0 mmol/L with the lowest glucose in any patient during therapy being 3.0 mmol/L. All episodes were corrected with a dextrose infusion without sequelae.

Conclusions

Our study demonstrates that HID therapy appears to be safe in patients with suspected metformin poisoning. It also appears to work to drive down lactate, improve pH and patients' clinical condition. Further evidence is required to assess the effectiveness of HID therapy in the context of MALA.

Transient Blindness in a Patient with Severe Metformin-Associated Lactic Acidosis (MALA)

A 68-year-old man presented at the emergency room with sudden blindness. The day before, he had eaten sashimi and eel and drank alcohol for dinner. He experienced nausea, vomiting, and dizziness afterward. His medical history included hypertension and diabetes, and the latter was treated with metformin. Initial laboratory tests revealed severe metabolic acidosis (lactic acidosis). Massive hydration and intravenous sodium bicarbonate replacement therapies were initiated, but severe metabolic acidosis (lactic acidosis) did not resolve, in turn, leading to hemodialysis, which decreased metabolic acidosis. The patient's blindness improved, and his vision gradually recovered. As it is not easy to distinguish between blindness related to metformin-associated lactic acidosis (MALA) and blindness related to other causes, rapid correction of metabolic acidosis through hemodialysis might be helpful in differentiating this from of blindness from blindness related to other causes.

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.

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.

A Unique Case of Metformin-Associated Lactic Acidosis

Metformin-associated lactic acidosis [MALA] is a potentially fatal condition characterized by an elevation in serum lactate in patients with metformin exposure. An 82-year-old man with no prior renal history was brought to hospital after being found by his family in a confused state. He had a history of type 2 diabetes mellitus, and his medications included regular metformin. On arrival to our hospital he was conscious but confused and noted recent decreased oral intake. Initial investigations revealed severe acidemia (pH <6.75, undetectable bicarbonate), with elevated serum lactate, urea, creatinine, and hyperkalemia. He was treated with intravenous dextrose, crystalloids, and bicarbonate and underwent urgent hemodialysis. The patient responded well to supportive therapies and achieved full renal recovery one week after admission. He was discharged feeling well, with a new antihyperglycemic medication regimen. This case highlights the potential for life-threatening acidemia in cases of MALA. The case is further unique in that the patient was conscious and responded to questions on arrival, despite the serious metabolic disturbance, and recovered completely. From a safety standpoint, health care providers should advise and educate their patients about discontinuing metformin and other potentially harmful medications in the context of acute illness with volume contraction.

Pharmacokinetics of metformin in patients with gastrointestinal intolerance

AIMS

To assess potential causes of metformin intolerance, including altered metformin uptake from the intestine, increased anaerobic glucose utilization and subsequent lactate production, altered serotonin uptake, and altered bile acid pool.

METHODS

For this pharmacokinetic study, we recruited 10 severely intolerant and 10 tolerant individuals, matched for age, sex and body mass index. A single 500-mg dose of metformin was administered, with blood sampling at 12 time points over 24 hours. Blood samples were analysed for metformin, lactate, serotonin and bile acid concentrations, and compared across the phenotypes.

RESULTS

The intolerant individuals were severely intolerant to 500 mg metformin. No significant difference was identified between tolerant and intolerant cohorts in metformin pharmacokinetics: median (interquartile range [IQR]) peak concentration 2.1 (1.7-2.3) mg/L and 2.0 (1.8-2.2) mg/L, respectively (P = .76); time to peak concentration 2.5 hours; median (IQR) area under the curve (AUC)_0-24 16.9 (13.9-18.6) and 13.9 (12.9-16.8) mg/L*h, respectively (P = .72). Lactate concentration peaked at 3.5 hours, with mean peak concentration of 2.4 mmol/L in both cohorts (95% CI 2.0-2.8 and 1.8-3.0 mmol/L, respectively), and similar incremental AUC_0-24 in each cohort: tolerant cohort 6.98 (95% CI 3.03-10.93) and intolerant cohort 4.47 (95% CI -3.12-12.06) mmol/L*h (P = .55). Neither serotonin nor bile acid concentrations were significantly different.

CONCLUSIONS

Despite evidence of severe intolerance in our cohort, there was no significant difference in metformin pharmacokinetics or systemic measures of lactate, serotonin or bile acids. This suggests that metformin intolerance may be attributable to local factors within the lumen or enterocyte.

Metformin Alters Upper Small Intestinal Microbiota that Impact a Glucose-SGLT1-Sensing Glucoregulatory Pathway

The gut microbiota alters energy homeostasis. In parallel, metformin regulates upper small intestinal sodium glucose cotransporter-1 (SGLT1), but whether changes of the microbiota or SGLT1-dependent pathways in the upper small intestine mediate metformin action is unknown. Here we report that upper small intestinal glucose sensing triggers an SGLT1-dependent pathway to lower glucose production in rodents. High-fat diet (HFD) feeding reduces glucose sensing and SGLT1 expression in the upper small intestine. Upper small intestinal metformin treatment restores SGLT1 expression and glucose sensing while shifting the upper small intestinal microbiota partly by increasing the abundance of Lactobacillus. Transplantation of upper small intestinal microbiota from metformin-treated HFD rats to the upper small intestine of untreated HFD rats also increases the upper small intestinal abundance of Lactobacillus and glucose sensing via an upregulation of SGLT1 expression. Thus, we demonstrate that metformin alters upper small intestinal microbiota and impacts a glucose-SGLT1-sensing glucoregulatory pathway.

Drug Interactions of Metformin Involving Drug Transporter Proteins

Metformin is a most widely used medication all around the world to treat Type 2 diabetes mellitus. It is also found to be effective against various conditions including, Prediabetes, Gestational diabetes mellitus (GDM), Polycystic Ovarian Syndrome (PCOS), Obesity, Cancer, etc. It is a cationic drug and it depends Organic Cation Transporters (OCTs) and Multidrug and Toxin Extruders (MATEs) mostly for its pharmacokinetics movement. The probability of drug interaction increases with the number of concomitant medications. This article focuses the drug interactions of metformin and most of them are linked to the inhibition of OCTs and MATEs leading to increased plasma metformin concentrations and subsequent elevation of risk of Metformin Associated Lactic Acidosis (MALA). By identifying the drugs inhibiting OCTs and MATEs, the healthcare professionals can predict the drug interactions of metformin.

Metformin-associated lactic acidosis (MALA): Moving towards a new paradigm

Although metformin has been used for over 60 years, the balance between the drug's beneficial and adverse effects is still subject to debate. Following an analysis of how cases of so-called "metformin-associated lactic acidosis" (MALA) are reported in the literature, the present article reviews the pitfalls to be avoided when assessing the purported association between metformin and lactic acidosis. By starting from pathophysiological considerations, we propose a new paradigm for lactic acidosis in metformin-treated patients. Metformin therapy does not necessarily induce metformin accumulation, just as metformin accumulation does not necessarily induce hyperlactatemia, and hyperlactatemia does not necessarily induce lactic acidosis. In contrast to the conventional view, MALA probably accounts for a smaller proportion of cases than either metformin-unrelated lactic acidosis or metformin-induced lactic acidosis. Lastly, this review highlights the need for substantial improvements in the reporting of cases of lactic acidosis in metformin-treated patients. Accordingly, we propose a check-list as a guide to clinical practice.

Metformin: historical overview

Metformin (dimethylbiguanide) has become the preferred first-line oral blood glucose-lowering agent to manage type 2 diabetes. Its history is linked to Galega officinalis (also known as goat's rue), a traditional herbal medicine in Europe, found to be rich in guanidine, which, in 1918, was shown to lower blood glucose. Guanidine derivatives, including metformin, were synthesised and some (not metformin) were used to treat diabetes in the 1920s and 1930s but were discontinued due to toxicity and the increased availability of insulin. Metformin was rediscovered in the search for antimalarial agents in the 1940s and, during clinical tests, proved useful to treat influenza when it sometimes lowered blood glucose. This property was pursued by the French physician Jean Sterne, who first reported the use of metformin to treat diabetes in 1957. However, metformin received limited attention as it was less potent than other glucose-lowering biguanides (phenformin and buformin), which were generally discontinued in the late 1970s due to high risk of lactic acidosis. Metformin's future was precarious, its reputation tarnished by association with other biguanides despite evident differences. The ability of metformin to counter insulin resistance and address adult-onset hyperglycaemia without weight gain or increased risk of hypoglycaemia gradually gathered credence in Europe, and after intensive scrutiny metformin was introduced into the USA in 1995. Long-term cardiovascular benefits of metformin were identified by the UK Prospective Diabetes Study (UKPDS) in 1998, providing a new rationale to adopt metformin as initial therapy to manage hyperglycaemia in type 2 diabetes. Sixty years after its introduction in diabetes treatment, metformin has become the most prescribed glucose-lowering medicine worldwide with the potential for further therapeutic applications.

Metformin causes a futile intestinal-hepatic cycle which increases energy expenditure and slows down development of a type 2 diabetes-like state

OBJECTIVE

Metformin, the first line drug for treatment of type 2 diabetes, suppresses hepatic gluconeogenesis and reduces body weight in patients, the latter by an unknown mechanism.

METHODS

Mice on a high fat diet were continuously fed metformin in a therapeutically relevant dose, mimicking a retarded formulation.

RESULTS

Feeding metformin in pharmacologically relevant doses to mice on a high fat diet normalized HbA1c levels and ameliorated glucose tolerance, as expected, but also considerably slowed down weight gain. This was due to increased energy expenditure, since food intake was unchanged and locomotor activity was even decreased. Metformin caused lactate accumulation in the intestinal wall and in portal venous blood but not in peripheral blood or the liver. Increased conversion of glucose-1-¹³C to glucose-1,6-¹³C under metformin strongly supports a futile cycle of lactic acid production in the intestinal wall, and usage of the produced lactate for gluconeogenesis in liver.

CONCLUSIONS

The reported glucose-lactate-glucose cycle is a highly energy consuming process, explaining the beneficial effects of metformin given continuously on the development of a type 2 diabetic-like state in our mice.

18F-FDG uptake in the colon is modulated by metformin but not associated with core body temperature and energy expenditure

Purpose

Physiological colonic ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake is a frequent finding on ¹⁸F-FDG positron emission tomography computed tomography (PET-CT). Interestingly, metformin, a glucose lowering drug associated with moderate weight loss, is also associated with an increased colonic ¹⁸F-FDG uptake. Consequently, increased colonic glucose use might partly explain the weight losing effect of metformin when this results in an increased energy expenditure and/or core body temperature. Therefore, we aimed to determine whether metformin modifies the metabolic activity of the colon by increasing glucose uptake.

Methods

In this open label, non-randomized, prospective mechanistic study, we included eight lean and eight overweight males. We measured colonic ¹⁸F-FDG uptake on PET-CT, energy expenditure and core body temperature before and after the use of metformin. The maximal colonic ¹⁸F-FDG uptake was measured in 5 separate segments (caecum, colon ascendens,—transversum,—descendens and sigmoid).

Results

The maximal colonic ¹⁸F-FDG uptake increased significantly in all separate segments after the use of metformin. There was no significant difference in energy expenditure or core body temperature after the use of metformin. There was no correlation between maximal colonic ¹⁸F-FDG uptake and energy expenditure or core body temperature.

Conclusion

Metformin significantly increases colonic ¹⁸F-FDG uptake, but this increased uptake is not associated with an increase in energy expenditure or core body temperature. Although the colon might be an important site of the glucose plasma lowering actions of metformin, this mechanism of action does not explain directly any associated weight loss.

New insights into the anti-diabetic actions of metformin: from the liver to the gut

Metformin is established as the first-line therapy for type 2 diabetes (T2DM), but its mode of action remains elusive. Elucidation of the mechanisms underlying the anti-diabetic action of metformin may have the potential to optimise its glucose-lowering efficacy and lead to the development of agents acting on novel targets for the management of type 2 diabetes. Areas covered: This review highlights key pharmacokinetic features of metformin, summarises recent insights into its hepatic and gastrointestinal actions relevant to blood glucose homeostasis, and discusses the common gastrointestinal side effects of metformin. Literature concerning these areas was reviewed on PubMed. Expert commentary: The mechanisms by which metformin improves glycaemic control in type 2 diabetes are complex. Although novel hepatic pathways continue to be reported in preclinical studies, there is a lack of human evidence for most of these. Considering the fundamental role of the gastrointestinal tract in the regulation of blood glucose homeostasis and pleiotropic actions of metformin on several gastrointestinal targets relevant to glycaemic control, the gut is likely to represent at least as important a site of metformin action as the liver in the management of type 2 diabetes.

Metformin and the gastrointestinal tract

Metformin is an effective agent with a good safety profile that is widely used as a first-line treatment for type 2 diabetes, yet its mechanisms of action and variability in terms of efficacy and side effects remain poorly understood. Although the liver is recognised as a major site of metformin pharmacodynamics, recent evidence also implicates the gut as an important site of action. Metformin has a number of actions within the gut. It increases intestinal glucose uptake and lactate production, increases GLP-1 concentrations and the bile acid pool within the intestine, and alters the microbiome. A novel delayed-release preparation of metformin has recently been shown to improve glycaemic control to a similar extent to immediate-release metformin, but with less systemic exposure. We believe that metformin response and tolerance is intrinsically linked with the gut. This review examines the passage of metformin through the gut, and how this can affect the efficacy of metformin treatment in the individual, and contribute to the side effects associated with metformin intolerance.

A Fatal Case of Metformin-associated Lactic Acidosis

A 72-year-old woman with a history of type 2 diabetes mellitus was brought to the ER with metformin-associated lactic acidosis. She received continuous hemofiltration and hemodialysis, but the laboratory analyses showed no improvement. She died 11 hours after admission. Metformin is minimally bound to proteins and is readily dialyzable, but a prolonged period of dialysis is required, because metformin has a very large distribution volume and is distributed to multiple compartments. The peak blood metformin level was 432 mg/L in this case, which is one of the highest metformin concentrations ever reported, and eight hours of hemodialysis were not sufficient to reduce the serum level.

Prediction and validation of enzyme and transporter off-targets for metformin

Metformin, an established first-line treatment for patients with type 2 diabetes, has been associated with gastrointestinal (GI) adverse effects that limit its use. Histamine and serotonin have potent effects on the GI tract. The effects of metformin on histamine and serotonin uptake were evaluated in cell lines overexpressing several amine transporters (OCT1, OCT3 and SERT). Metformin inhibited histamine and serotonin uptake by OCT1, OCT3 and SERT in a dose-dependent manner, with OCT1-mediated amine uptake being most potently inhibited (IC50 = 1.5 mM). A chemoinformatics-based method known as Similarity Ensemble Approach predicted diamine oxidase (DAO) as an additional intestinal target of metformin, with an E-value of 7.4 × 10(-5). Inhibition of DAO was experimentally validated using a spectrophotometric assay with putrescine as the substrate. The Ki of metformin for DAO was measured to be 8.6 ± 3.1 mM. In this study, we found that metformin inhibited intestinal amine transporters and DAO at concentrations that may be achieved in the intestine after therapeutic doses. Further studies are warranted to determine the relevance of these interactions to the adverse effects of metformin on the gastrointestinal tract.

Therapeutic Use of Metformin in Prediabetes and Diabetes Prevention

People with elevated, non-diabetic, levels of blood glucose are at risk of progressing to clinical type 2 diabetes and are commonly termed 'prediabetic'. The term prediabetes usually refers to high-normal fasting plasma glucose (impaired fasting glucose) and/or plasma glucose 2 h following a 75 g oral glucose tolerance test (impaired glucose tolerance). Current US guidelines consider high-normal HbA1c to also represent a prediabetic state. Individuals with prediabetic levels of dysglycaemia are already at elevated risk of damage to the microvasculature and macrovasculature, resembling the long-term complications of diabetes. Halting or reversing the progressive decline in insulin sensitivity and β-cell function holds the key to achieving prevention of type 2 diabetes in at-risk subjects. Lifestyle interventions aimed at inducing weight loss, pharmacologic treatments (metformin, thiazolidinediones, acarbose, basal insulin and drugs for weight loss) and bariatric surgery have all been shown to reduce the risk of progression to type 2 diabetes in prediabetic subjects. However, lifestyle interventions are difficult for patients to maintain and the weight loss achieved tends to be regained over time. Metformin enhances the action of insulin in liver and skeletal muscle, and its efficacy for delaying or preventing the onset of diabetes has been proven in large, well-designed, randomised trials, such as the Diabetes Prevention Program and other studies. Decades of clinical use have demonstrated that metformin is generally well-tolerated and safe. We have reviewed in detail the evidence base supporting the therapeutic use of metformin for diabetes prevention.

AMP-activated protein kinase: a key regulator of energy balance with many roles in human disease

The AMP-activated protein kinase (AMPK) is a sensor of cellular energy status that regulates cellular and whole-body energy balance. A recently reported crystal structure has illuminated the complex regulatory mechanisms by which AMP and ADP cause activation of AMPK, involving phosphorylation by the upstream kinase LKB1. Once activated by falling cellular energy status, AMPK activates catabolic pathways that generate ATP whilst inhibiting anabolic pathways and other cellular processes that consume ATP. A role of AMPK is implicated in many human diseases. Mutations in the γ2 subunit cause heart disease due to excessive glycogen storage in cardiac myocytes, leading to ventricular pre-excitation. AMPK-activating drugs reverse many of the metabolic defects associated with insulin resistance, and recent findings suggest that the insulin-sensitizing effects of the widely used antidiabetic drug metformin are mediated by AMPK. The upstream kinase LKB1 is a tumour suppressor, and AMPK may exert many of its antitumour effects. AMPK activation promotes the oxidative metabolism typical of quiescent cells, rather than the aerobic glycolysis observed in tumour cells and cells involved in inflammation, explaining in part why AMPK activators have both antitumour and anti-inflammatory effects. Salicylate (the major in vivo metabolite of aspirin) activates AMPK, and this could be responsible for at least some of the anticancer and anti-inflammatory effects of aspirin. In addition to metformin and salicylates, novel drugs that modulate AMPK are likely to enter clinical trials soon. Finally, AMPK may be involved in viral infection: downregulation of AMPK during hepatitis C virus infection appears to be essential for efficient viral replication.

Dichloroacetate enhances apoptotic cell death via oxidative damage and attenuates lactate production in metformin-treated breast cancer cells

The unique metabolism of breast cancer cells provides interest in exploiting this phenomenon therapeutically. Metformin, a promising breast cancer therapeutic, targets complex I of the electron transport chain leading to an accumulation of reactive oxygen species (ROS) that eventually lead to cell death. Inhibition of complex I leads to lactate production, a metabolic byproduct already highly produced by reprogrammed cancer cells and associated with a poor prognosis. While metformin remains a promising cancer therapeutic, we sought a complementary agent to increase apoptotic promoting effects of metformin while attenuating lactate production possibly leading to greatly improved efficacy. Dichloroacetate (DCA) is a well-established drug used in the treatment of lactic acidosis which functions through inhibition of pyruvate dehydrogenase kinase (PDK) promoting mitochondrial metabolism. Our purpose was to examine the synergy and mechanisms by which these two drugs kill breast cancer cells. Cell lines were subjected to the indicated treatments and analyzed for cell death and various aspects of metabolism. Cell death and ROS production were analyzed using flow cytometry, Western blot analysis, and cell counting methods. Images of cells were taken with phase contrast microscopy or confocal microscopy. Metabolism of cells was analyzed using the Seahorse XF24 analyzer, lactate assays, and pH analysis. We show that when DCA and metformin are used in combination, synergistic induction of apoptosis of breast cancer cells occurs. Metformin-induced oxidative damage is enhanced by DCA through PDK1 inhibition which also diminishes metformin promoted lactate production. We demonstrate that DCA and metformin combine to synergistically induce caspase-dependent apoptosis involving oxidative damage with simultaneous attenuation of metformin promoted lactate production. Innovative combinations such as metformin and DCA show promise in expanding breast cancer therapies.

Efficacy and safety of metformin during pregnancy in women with gestational diabetes mellitus or polycystic ovary syndrome: a systematic review

BACKGROUND

Metformin is an effective oral anti-hyperglycemic agent that is widely used to manage diabetes mellitus type 2 in the general population and more recently, in pregnancy. However, as metformin crosses the placenta, its use during pregnancy raises concerns regarding potential adverse effects on the mother and fetus.

OBJECTIVE

(i) To provide background for the use of metformin during pregnancy through a narrative review and (ii) to critically appraise the published evidence on the efficacy and safety of using metformin during pregnancy through a systematic review.

RESULTS

Metformin appears to be effective and safe for the treatment of gestational diabetes mellitus (GDM), particularly for overweight or obese women. However, patients with multiple risk factors for insulin resistance may not meet their treatment goals with metformin alone and may require supplementary insulin. Evidence suggests that there are potential advantages for the use of metformin over insulin in GDM with respect to maternal weight gain and neonatal outcomes. Furthermore, patients are more accepting of metformin than insulin. The use of metformin throughout pregnancy in women with polycystic ovary syndrome reduces the rates of early pregnancy loss and preterm labor and protects against fetal growth restriction. There have been no demonstrable teratogenic effects, intra-uterine deaths or developmental delays with the use of metformin.

CONCLUSIONS

The publications reviewed in this paper support the efficacy and safety of metformin during pregnancy with respect to immediate pregnancy outcomes. Because there are no guidelines for the continuous use of metformin in pregnancy, the duration of treatment is based on clinical judgment and experience on a case-by-case basis.

Effects of chronic treatment with metformin on dipeptidyl peptidase-4 activity, glucagon-like peptide 1 and ghrelin in obese patients with Type 2 diabetes mellitus

AIMS

Studies investigating the acute effects of metformin have demonstrated actions on the incretin system and appetite regulatory hormones. There are limited data to support that these effects are sustained in the long term. We therefore studied the effects of chronic treatment with metformin on endogenous glucagon-like peptide 1, dipeptidyl peptidase-4 activity and active ghrelin (an orexigenic hormone) in obese patients with Type 2 diabetes mellitus.

METHODS

Eight subjects [six male, age 58.7 ± 2.6 years, BMI 41.1 ± 2.9 kg/m(2) , HbA(1c) 69 ± 6 mmol/mol (8.5 ± 0.5%), mean ± sem] with drug-naïve Type 2 diabetes were studied for 6 h following a standard mixed meal, before and after at least 3 months of metformin monotherapy (mean dose 1.75 g daily).

RESULTS

The area under the curve (AUC(0-6 h) ) for active glucagon-like peptide 1 was significantly higher on metformin (pre-metformin 1750.8 ± 640 pmol l(-1) min(-1) vs. post-metformin 2718.8 ± 1182.3 pmol l(-1) min(-1) ; P=0.01). The areas under the curves for dipeptidyl peptidase-4 activity and ghrelin were not significantly different pre- and post-treatment with metformin.

CONCLUSION

Three months or more of metformin monotherapy in obese patients with Type 2 diabetes was associated with increased postprandial active glucagon-like peptide 1 levels. The effects of metformin on the enteroinsular axis may represent yet another important mechanism underlying its glucose-lowering effects.

GLUT2 accumulation in enterocyte apical and intracellular membranes: a study in morbidly obese human subjects and ob/ob and high fat-fed mice

OBJECTIVE

In healthy rodents, intestinal sugar absorption in response to sugar-rich meals and insulin is regulated by GLUT2 in enterocyte plasma membranes. Loss of insulin action maintains apical GLUT2 location. In human enterocytes, apical GLUT2 location has not been reported but may be revealed under conditions of insulin resistance.

RESEARCH DESIGN AND METHODS

Subcellular location of GLUT2 in jejunal enterocytes was analyzed by confocal and electron microscopy imaging and Western blot in 62 well-phenotyped morbidly obese subjects and 7 lean human subjects. GLUT2 locations were assayed in ob/ob and ob/+ mice receiving oral metformin or in high-fat low-carbohydrate diet-fed C57Bl/6 mice. Glucose absorption and secretion were respectively estimated by oral glucose tolerance test and secretion of [U-(14)C]-3-O-methyl glucose into lumen.

RESULTS

In human enterocytes, GLUT2 was consistently located in basolateral membranes. Apical GLUT2 location was absent in lean subjects but was observed in 76% of obese subjects and correlated with insulin resistance and glycemia. In addition, intracellular accumulation of GLUT2 with early endosome antigen 1 (EEA1) was associated with reduced MGAT4a activity (glycosylation) in 39% of obese subjects on a low-carbohydrate/high-fat diet. Mice on a low-carbohydrate/high-fat diet for 12 months also exhibited endosomal GLUT2 accumulation and reduced glucose absorption. In ob/ob mice, metformin promoted apical GLUT2 and improved glucose homeostasis. Apical GLUT2 in fasting hyperglycemic ob/ob mice tripled glucose release into intestinal lumen.

CONCLUSIONS

In morbidly obese insulin-resistant subjects, GLUT2 was accumulated in apical and/or endosomal membranes of enterocytes. Functionally, apical GLUT2 favored and endosomal GLUT2 reduced glucose transepithelial exchanges. Thus, altered GLUT2 locations in enterocytes are a sign of intestinal adaptations to human metabolic pathology.

Increased F-18 FDG intestinal uptake in diabetic patients on metformin: a matched case-control analysis

PURPOSE

A matched case-control study was performed to assess the relationship between metformin use and the degree of F-18 fluorodeoxyglucose (FDG) bowel activity in diabetic patients.

MATERIALS AND METHODS

Seventy-seven diabetic patients referred to our department for a positron emission tomography/computed tomography study, including 45 on metformin, were compared with nondiabetic controls matched for sex, age, and body mass index. Positron emission tomography studies were obtained in a standard manner and reviewed in a blinded fashion. F-18 FDG uptake in the GI tract was evaluated quantitatively using maximal standardized uptake values and visually using a previously published semiquantitative scale.

RESULTS

F-18 FDG uptake in small and large bowel was significantly increased in metformin patients compared with nondiabetic controls both visually and quantitatively (all P < 0.0001), as well as compared with nonmetformin patients with diabetes. Control sites (liver, fat, muscle) showed similar uptake. Multiple regression analysis confirmed that metformin was the variable most strongly associated with bowel uptake.

CONCLUSION

Physiologic accumulation of F-18 FDG in bowel is increased in diabetic patients maintained on metformin.

Lactic acidosis induced by metformin: incidence, management and prevention

Lactic acidosis associated with metformin treatment is a rare but important adverse event, and unravelling the problem is critical. First, this potential event still influences treatment strategies in type 2 diabetes mellitus, particularly in the many patients at risk of kidney failure, in those presenting contraindications to metformin and in the elderly. Second, the relationship between metformin and lactic acidosis is complex, since use of the drug may be causal, co-responsible or coincidental. The present review is divided into three parts, dealing with the incidence, management and prevention of lactic acidosis occurring during metformin treatment. In terms of incidence, the objective of this article is to counter the conventional view of the link between metformin and lactic acidosis, according to which metformin-associated lactic acidosis is rare but is still associated with a high rate of mortality. In fact, the direct metformin-related mortality is close to zero and metformin may even be protective in cases of very severe lactic acidosis unrelated to the drug. Metformin has also inherited a negative class effect, since the early biguanide, phenformin, was associated with more frequent and sometimes fatal lactic acidosis. In the second part of this review, the objective is to identify the most efficient patient management methods based on our knowledge of how metformin acts on glucose/lactate metabolism and how lactic acidosis may occur (at the organ and cellular levels) during metformin treatment. The liver appears to be a key organ for both the antidiabetic effect of metformin and the development of lactic acidosis; the latter is attributed to mitochondrial impairment and subsequent adenosine triphosphate depletion, acceleration of the glycolytic flux, increased glucose uptake and the generation of lactate, which effluxes into the circulation rather than being oxidized further. Haemodialysis should systematically be performed in severe forms of lactic acidosis, since it provides both symptomatic and aetiological treatment (by eliminating lactate and metformin). In the third part of the review (prevention), the objective is to examine the list of contraindications to metformin (primarily related to renal and cardiovascular function). Diabetes is above all a vascular disease and metformin is a vascular drug with antidiabetic properties. Given the importance of the liver in lactate clearance, we suggest focusing on the severity of and prognosis for liver disease; renal dysfunction is only a prerequisite for metformin accumulation, which may only be dangerous per se when associated with liver failure. Lastly, in view of metformin's impressive overall effectiveness profile, it would be paradoxical to deny the majority of patients with long-established diabetes access to metformin because of the high prevalence of contraindications. The implications of these contraindications are discussed.

Glucose supply and insulin demand dynamics of antidiabetic agents

BACKGROUND

For microvascular outcomes, there is compelling historical and contemporary evidence for intensive blood glucose reduction in patients with either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM). There is also strong evidence to support macrovascular benefit with intensive blood glucose reduction in T1DM. Similar evidence remains elusive for T2DM. Because cardiovascular outcome trials utilizing conventional algorithms to attain intensive blood glucose reduction have not demonstrated superiority to less aggressive blood glucose reduction (Action to Control Cardiovascular Risk in Diabetes; Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation; and Veterans Affairs Diabetes Trial), it should be considered that the means by which the blood glucose is reduced may be as important as the actual blood glucose.

METHODS

By identifying quantitative differences between antidiabetic agents on carbohydrate exposure (CE), hepatic glucose uptake (HGU), hepatic gluconeogenesis (GNG), insulin resistance (IR), peripheral glucose uptake (PGU), and peripheral insulin exposure (PIE), we created a pharmacokinetic/pharmacodynamic model to characterize the effect of the agents on the glucose supply and insulin demand dynamic. Glucose supply was defined as the cumulative percentage decrease in CE, increase in HGU, decrease in GNG, and decrease in IR, while insulin demand was defined as the cumulative percentage increase in PIE and PGU. With the glucose supply and insulin demand effects of each antidiabetic agent summated, the glucose supply (numerator) was divided by the insulin demand (denominator) to create a value representative of the glucose supply and insulin demand dynamic (SD ratio).

RESULTS

Alpha-glucosidase inhibitors (1.25), metformin (2.20), and thiazolidinediones (TZDs; 1.25-1.32) demonstrate a greater effect on glucose supply (SD ratio >1), while secretagogues (0.69-0.81), basal insulins (0.77-0.79), and bolus insulins (0.62-0.67) demonstrate a greater effect on insulin demand (SD ratio <1).

CONCLUSION

Alpha-glucosidase inhibitors, metformin, and TZDs demonstrate a greater effect on glucose supply, while secretagogues, basal insulin, and bolus insulin demonstrate a greater effect on insulin demand. Because T2DM cardiovascular outcome trials have not demonstrated macrovascular benefit with more aggressive blood glucose reduction when using conventional algorithms that predominantly focus on insulin demand, it would appear logical to consider a model that incorporates both the extent of blood glucose lowering (hemoglobin A1c) and the means by which the blood glucose was reduced (SD ratio) when considering macrovascular outcomes.

Clearance of the high intestinal (18)F-FDG uptake associated with metformin after stopping the drug

PURPOSE

This study was done to determine whether interruption of metformin before (18)F-FDG PET/CT imaging could prevent the increased (18)F-FDG uptake in the intestine caused by this drug.

METHODS

Included in the study were 41 patients with known type 2 diabetes mellitus who were referred to our department for evaluation of various neoplastic diseases. Patients underwent two (18)F-FDG PET/CT scans, the first while they were on metformin and the second after they had stopped metformin. They stopped metformin and did not take any other oral antidiabetic medication starting 3 days before the second study and their blood glucose level was regulated with insulin when necessary to keep it within the range 5.55-8.33 mmol/l. FDG uptake was graded visually according to a four-point scale and semiquantitatively by recording the maximum standardized uptake value (SUVmax) in different bowel segments. A paired-samples t-test method was used to determine whether there was a significant difference between SUVmax measurements and visual analysis scores of the metabolic activity of the bowel in the PET/CT scans before and after stopping metformin.

RESULTS

Diffuse and intense (18)F-FDG uptake was observed in bowel segments of patients, and the activity in the colon was significantly decreased both visually and semiquantitatively in PET/CT scans performed after patients stopped metformin (p<0.05). There was a statistically significant decrease in activity in the small intestine on visual analysis (p<0.05), but semiquantitative measurements did not show a significant decrease in the SUVmax values in the duodenum or jejunum (p>0.05).

CONCLUSION

Metformin causes an increase in (18)F-FDG uptake in the bowel and stopping metformin before PET/CT study significantly decreased this unwanted uptake, especially in the colon, facilitating the interpretation of images obtained from the abdomen and preventing the obliteration of lesions.