The effects of metformin on simple obesity: a meta-analysis

Anti-obesity and metabolic benefits of metformin: Comparison of different delivery routes

Obesity is a severe public health problem. Healthy lifestyle interventions are commonly recommended for fighting obesity. But they are hard to follow and have low efficacy. Pharmacotherapy and surgery are of high efficacy but are beset with side effects. Browning subcutaneous white adipose tissue (WAT) is a practical and efficient approach for combating obesity. Metformin, a commonly used FDA-approved antidiabetic drug, is potent to induce browning of WAT through phosphorylation and activation of AMP-activated protein kinase. However, oral administration of metformin has low oral bioavailability, fast renal clearance, and low target specificity that limit metformin's application in browning WAT. Local and transdermal delivery of metformin directly to subcutaneous WAT using injection or microneedle (MN) in combination with iontophoresis (INT) may solve these problems. In this paper, we administered metformin to C57BL/6J obese mice using the following three routes: transdermal delivery (MN and INT), local injection into inguinal WAT (IgWAT, a type of subcutaneous WAT in mice), and oral gavage. The anti-obesity and metabolic effects of metformin via these delivery routes were determined and compared. As compared to local IgWAT injection and oral gavage delivery, transdermal delivery of metformin using MN and INT resulted in 9% lower body weight and 7% decrease in body fat% accompanied by improved energy metabolism and decreased inflammation through browning IgWAT in obese C57BL/6J mice. Transdermal delivery of metformin using MN and INT is an effective approach in browning subcutaneous WAT for combating obesity and improving metabolic health.

The effect of metformin on adipokines levels: A systematic review and meta-analysis of randomized-controlled trials

BACKGROUND

Considering the role of adipokine on diseases related to metabolic syndrome and even chronic diseases, it seems necessary to investigate effective interventions on these factors. This study aimed to comprehensively investigate the effects of metformin on adipokines.

METHODS

A comprehensive search was conducted in five databases using established keywords. The purpose of this search was to uncover controlled studies that have examined the impact of metformin on adipokines, specifically leptin, adiponectin, and resistin. The random-effects model analysis was used to provide pooled weighted mean difference and 95% confidence intervals.

RESULTS

Forty-nine studies were included in this article. The pooled findings showed that that the administration of metformin significantly decreases leptin (WMD: -3.06 ng/ml, 95 % CI: -3.81, -2.30, P < 0.001) and resistin (WMD: -1.27 µg/mL, 95 % CI: -2.22, -0.31, P = 0.009) levels in different populations compared to the control group. However, no significant effect of this antidiabetic drug on adiponectin levels was reported. The results obtained from the subgroup results in the present study also showed that metformin in people with a BMI greater than 30 kg/m2 compared to a BMI ≤ 30 kg/m2 causes a significant decrease in leptin levels and an increase in adiponectin levels. Also, metformin in lower doses (≤1500 mg/day) and younger people (<30 years) causes a significant increase in adiponectin levels.

CONCLUSIONS

In general, considering the role of adipokines on metabolic disease and even chronic disease, this drug can be used as a potentially useful drug, especially in obese people, to improve these factors.

Metformin: update on mechanisms of action and repurposing potential

Currently, metformin is the first-line medication to treat type 2 diabetes mellitus (T2DM) in most guidelines and is used daily by >200 million patients. Surprisingly, the mechanisms underlying its therapeutic action are complex and are still not fully understood. Early evidence highlighted the liver as the major organ involved in the effect of metformin on reducing blood levels of glucose. However, increasing evidence points towards other sites of action that might also have an important role, including the gastrointestinal tract, the gut microbial communities and the tissue-resident immune cells. At the molecular level, it seems that the mechanisms of action vary depending on the dose of metformin used and duration of treatment. Initial studies have shown that metformin targets hepatic mitochondria; however, the identification of a novel target at low concentrations of metformin at the lysosome surface might reveal a new mechanism of action. Based on the efficacy and safety records in T2DM, attention has been given to the repurposing of metformin as part of adjunct therapy for the treatment of cancer, age-related diseases, inflammatory diseases and COVID-19. In this Review, we highlight the latest advances in our understanding of the mechanisms of action of metformin and discuss potential emerging novel therapeutic uses.

Weight-centric treatment of type 2 diabetes mellitus

Background

Chronic non-communicable diseases (CNCD) represent a major cause of morbidity and mortality. Type 2 diabetes mellitus (T2DM) is one of the most prevalent CNCD that is associated with a significant medical and economic burden. One of the main modifiable risk factors of T2DM is obesity. Many medications used for T2DM can lead to weight gain, worsening one of the root causes of this disease.

Methods

In this clinical review, we study the effect of medications for T2DM on body weight. We used MEDLINE, Google scholar, PubMed, Scopus, and Embase databases to search for relevant studies between 1 January 1950 to 20 September 2022 in English language. Here, we review the most prescribed medications for T2DM and summarize their effect on patients' body weight. We will also present an expert opinion on a recommended weight-centric approach to treat T2DM.

Results

Multiple T2DM medications have been associated with weight gain. Insulin, sulfonylureas, thiazolidinediones and meglitinides may increase body weight. However, biguanides (e.g., metformin), glucagon-like peptide-1 agonists (e.g., semaglutide, liraglutide, tirzepatide), sodium-glucose cotransporter 2 inhibitors, and amylin analogs (e.g., pramlintide) are associated with significant weight loss. Dipeptidyl peptidase-4 inhibitors are considered weight neutral medications. Experts in the fields of endocrinology and obesity recommend utilizing a weight-centric approach when treating T2DM.

Conclusion

Considering the high prevalence and debilitating complication of T2DM, it is of utmost importance to shift from a weight gain approach (i.e., insulin, sulfonylureas) into a weight loss/neutral one (i.e., GLP-1 agonists, SGLT-2 inhibitors, metformin).

The ameliorating effects of metformin on disarrangement ongoing in gastrocnemius muscle of sarcopenic and obese sarcopenic mice

Sarcopenia and obese sarcopenia are increasingly prevalent chronic diseases with multifactorial pathogenesis, and no approved therapeutic drug to date. In the established sarcopenic mice models, muscle weakness, ectopic lipid deposition, and inflammatory responses in both serum and gastrocnemius muscle were observed, which were even deteriorated in obese sarcopenic models. With metformin intervention for 5 months, metformin exhibited benefits and restoring effects on gastrocnemius muscle of sarcopenic mice, but less effective on that of obese sarcopenic mice, as reflected in the increased percentage of muscle mass and enlarged fiber cross-sectional area, enhanced grip strength and exercise capacities, as well as the ameliorated ectopic lipid deposition and partially restored level of TNF-α, IL-1β, IL-6, MCP-1 and IL-1α, which may be via the activation of phospho-AMPKα (Thr172). The significant up-regulated mRNA and protein level of lipolysis related proteins like hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) may contribute to the ameliorated ectopic lipid deposition with metformin intervention. The uptake of free fatty acid may be also inhibited in obese sarcopenic mice with metformin administration, as reflected in down-regulated mRNA and protein level of fatty acid transporter CD36. Furthermore, NF-κB signaling pathway was involved in the anti-inflammatory effect of metformin. These findings suggest that metformin treatment may be conducive to the prevention of age-related sarcopenia by regulating lipid metabolism in skeletal muscle, i.e. enhanced lipolysis and attenuated hyper-inflammatory responses, which may be AMPK-dependent processes. Moreover, high-fat diet would aggravate the damage to ageing in skeletal muscles and reduced their reactivity to metformin.

Metformin combats obesity by targeting FTO in an m6A-YTHDF2-dependent manner

Obesity has become a health threat and hard enough to deal with. Evidences show that metformin could inhibit adipogenesis and combat obesity, while its mechanisms remain to be elucidated more comprehensively. In this study, we found that administration of metformin could combat obesity induced by high-fat diet (HFD), indicated by strikingly decreased body weight and weight of inguinal white adipose tissue (iWAT) and epidydimal white adipose tissue (eWAT) compared to the control group. Mechanically, we revealed that metformin could inhibit protein expression of FTO, leading to increased m⁶A methylation levels of cyclin D1 (Ccnd1) and cyclin dependent kinase 2 (Cdk2), two crucial regulators in cell cycle. Ccnd1 and Cdk2 with increased m⁶A levels were recognized by YTH m⁶A RNA binding protein 2 (YTHDF2), causing a YTHDF2-dependent decay and decreased protein expressions. In consequence, mitotic clonal expansion (MCE) process was blocked and adipogenesis was inhibited.

The Potential to Fight Obesity with Adipogenesis Modulating Compounds

Obesity is an increasingly severe public health problem, which brings huge social and economic burdens. Increased body adiposity in obesity is not only tightly associated with type 2 diabetes, but also significantly increases the risks of other chronic diseases including cardiovascular diseases, fatty liver diseases and cancers. Adipogenesis describes the process of the differentiation and maturation of adipocytes, which accumulate in distributed adipose tissue at various sites in the body. The major functions of white adipocytes are to store energy as fat during periods when energy intake exceeds expenditure and to mobilize this stored fuel when energy expenditure exceeds intake. Brown/beige adipocytes contribute to non-shivering thermogenesis upon cold exposure and adrenergic stimulation, and thereby promote energy consumption. The imbalance of energy intake and expenditure causes obesity. Recent interest in epigenetics and signaling pathways has utilized small molecule tools aimed at modifying obesity-specific gene expression. In this review, we discuss compounds with adipogenesis-related signaling pathways and epigenetic modulating properties that have been identified as potential therapeutic agents which cast some light on the future treatment of obesity.

Obesity Primer for the Practicing Gastroenterologist

With worsening of the obesity pandemic, gastroenterologists will see more patients with this chronic disease. Given the association between obesity and several gastrointestinal conditions and the interplay between obesity pathophysiology and gut hormones, gastroenterologists can play an important role in the management of this disease. Furthermore, because more patients undergo bariatric surgery, an understanding of postsurgical anatomy and medical and endoscopic management of bariatric surgical complications is essential. This article provides clinical tools for the assessment and management of obesity for the general gastroenterologist. Tables containing high-yield practical information are also provided for quick reference.

The Use of Metformin to Increase the Human Healthspan

Metformin is a safe, effective and useful drug for glucose management in patients with diabetes. However in recent years, more attention has been paid to the possibility of using metformin as an anti-aging drug. It was shown to significantly increase the lifespan in some model organisms and delay the onset of age-associated declines. The current review summarizes advances in clinical research on the potential role of metformin in the field of lifespan and healthspan extension. Growing amounts of evidence from clinical trials suggest that metformin can effectively reduce the risk of many age-related diseases and conditions, including cardiometabolic disorders, neurodegeneration, chronic inflammation and frailty. Metformin also holds promise as a drug that could be repurposed for chemoprevention or adjuvant therapy for certain types of cancer. Moreover, metformin induces autophagy by activation of AMPK and can thus be potentially used to promote heathspan by hormesis-like mechanisms. Although long-term intake of metformin is associated with low risk of adverse events, well-designed clinical trials are still required to uncover the potential use of this drug as a geroprotector.

Metformin-induced increases in GDF15 are important for suppressing appetite and promoting weight loss

Metformin is the most commonly prescribed medication for type 2 diabetes, owing to its glucose-lowering effects, which are mediated through the suppression of hepatic glucose production (reviewed in refs. ^1-3). However, in addition to its effects on the liver, metformin reduces appetite and in preclinical models exerts beneficial effects on ageing and a number of diverse diseases (for example, cognitive disorders, cancer, cardiovascular disease) through mechanisms that are not fully understood^1-3. Given the high concentration of metformin in the liver and its many beneficial effects beyond glycemic control, we reasoned that metformin may increase the secretion of a hepatocyte-derived endocrine factor that communicates with the central nervous system⁴. Here we show, using unbiased transcriptomics of mouse hepatocytes and analysis of proteins in human serum, that metformin induces expression and secretion of growth differentiating factor 15 (GDF15). In primary mouse hepatocytes, metformin stimulates the secretion of GDF15 by increasing the expression of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP; also known as DDIT3). In wild-type mice fed a high-fat diet, oral administration of metformin increases serum GDF15 and reduces food intake, body mass, fasting insulin and glucose intolerance; these effects are eliminated in GDF15 null mice. An increase in serum GDF15 is also associated with weight loss in patients with type 2 diabetes who take metformin. Although further studies will be required to determine the tissue source(s) of GDF15 produced in response to metformin in vivo, our data indicate that the therapeutic benefits of metformin on appetite, body mass and serum insulin depend on GDF15.

Polyglycolic acid sutures embedded in abdominal acupoints for treatment of simple obesity in adults: a randomized control trial

Background

Acupoint catgut embedding therapy characterized by acupoint, needle and catgut are superior to traditional acupuncture, due to exerting more comprehensive therapeutic efficacy. However, it is still deficient in clinical evidence for polyglycolic acid sutures, a novel biodegradable material instead of catgut, embedded for the treatment of simple obesity. In our study, we investigate the efficacy and related mechanism of polyglycolic acid sutures embedded in abdominal acupoints on simple obese persons by a randomized control trial.

Methods

A total of 51 eligible participators were randomly allocated to a polyglycolic acid sutures embedding therapy (PASET) group (n = 28) or control group (n = 23). Participators in PASET group received polyglycolic acid sutures alternatively embedded in abdominal I group and II group acupoints in odd and even number therapeutic courses, and participators in control group were required to perform lifestyle modification. The duration of the study was 10 weeks.

Results

It suggested that PASET significantly reduced weight, body mass index, hip circumference, waist circumference, waist/hip ratio, waist-to-height ratio and thickness of abdominal subcutaneous fat tissue compared with those before treatment (p < 0.01), but lifestyle modification only illustrated downward trend of weight (p < 0.05). Moreover, PASET group also improved the evaluated scores in aspects of physical function, self-esteem, public distress and sexual life, as well as decreased blood pressure, glycemia, low density lipoprotein, uric acid and the levels of tumor necrosis factor-alpha, interleukin-1β, and increased high density lipoprotein in comparison with those before treatment (p < 0.05), whose efficacies are superior to control group. Additionally, our results also indicate PASET is relative safe and its pain and discomfort can be tolerable.

Conclusions

PASET distinctly ameliorates anthropometric data and quality of life in obese population, which associates with improvements of metabolic profile and inflammatory response. Based on the advantageous actions, we think PASET is an effective therapeutic approach to simple obesity treatment.

Trial registration ChiCTR, ChiCTR1800015591. Registered 10 April 2018, http://www.chictr.org.cn/showproj.aspx?proj=23258

The Many Faces of Obesity and Its Influence on Breast Cancer Risk

Obesity is associated with increased risk of breast and other cancers. However, the complexity of the underlying mechanisms, together with the interplay of diet and physical activity—contributing to energy balance—and the role of adipose tissue, pose challenges to our understanding of the basis of this increased risk. Epidemiologic studies have documented a higher obesity prevalence in US black women compared to white women. Elucidation of the contribution of potential biological differences among racially distinct groups to their differences in breast cancer (BC) risk and mortality have been topics of considerable interest in recent years. The racial and ethnic variation in body fat distribution may account for at least part of the differences in breast cancer rates in these populations. Yet, while black women exhibit higher rates of obesity compared to white women, this does not translate directly into higher rates of BC. In fact, overall, BC in black women occurs with a lower incidence than BC in white women. Obesity is a known risk factor for postmenopausal breast cancer, and growing evidence suggests that abdominal obesity, also known as central obesity, may increase risk for triple negative breast cancer, which is more common in premenopausal women. The positive association of postmenopausal BC risk and specifically estrogen receptor (ER)-positive BC, is presumably due largely to accumulation of estrogen in the adipose tissue of the breast and other tissues. Of the two main types of adipose tissue—subcutaneous and visceral—visceral adipocytes are more active metabolically. Such adipose tissue harbors multiple molecular entities that promote carcinogenesis: endocrine molecules/hormones, immunologic factors, inflammatory cytokines, metabolic alterations, and other components of the microenvironment. Expression of these culpable entities is largely regulated by epigenetic mechanisms. The interrelationship between these entities and drivers of epigenetic alteration are critical to the regulation of pathways connecting obesity and cancer risk. Initiatives to counteract the carcinogenic effects of obesity have primarily involved modulation of energy balance by diet. However, targeting of specific molecular abnormalities characterizing adiposity offers an alternative approach to preventing cancer. Our goal in this review is to first discuss the major mechanisms contributing to the obesity-breast cancer link. We will also consider race, specifically black/white differences, as they relate to the association of obesity with breast cancer risk. Then we will enumerate strategies targeting these mechanisms to reduce BC risk, in large part by way of dietary interventions with potential to mitigate the cancer-promoting components of adiposity.

High Glucose Represses the Anti-Proliferative and Pro-Apoptotic Effect of Metformin in Triple Negative Breast Cancer Cells

Metformin, the most widely prescribed anti-diabetic drug, is shown to possess anti-cancer potential in treatment of cancers, including breast cancer; decreases breast cancer risk; and improves overall survival. However, reports suggest that higher glucose concentrations may negatively impact the anti-cancer efficacy of metformin. Therefore, we examined the anti-cancer potential of metformin in triple-negative breast cancer cells (TNBCs) exposed to different glucose (25 mM, 5.5 mM and zero glucose/glucose-starved) conditions. Our data indicates that a high glucose (25 mM) concentration (mimicking diabetes) significantly abrogated the effect of metformin on cell proliferation, cell death and cell cycle arrest in addition to loss of efficacy in inhibition of the mTOR pathway, a key metabolic pathway in TNBC cells. The mTOR pathway is activated in TNBCs compared to other subtypes of breast cancer, regulates the synthesis of proteins that are critical for the growth and survival of cancer cells and its activation is correlated to poor outcomes among TNBC patients, while also contributing to metastatic progression and development of resistance to chemotherapy/radiotherapy. Our studies were performed in two different types of TNBCs, MDA-MB-231 cells (mesenchymal stem cell-like (MSL)) and MDA-MB-468 (basal like-1 (BL-1)). Interestingly, lower concentrations of metformin (50, 100, 250, and 500 μM) significantly increased cell proliferation in 25 mM glucose exposed MDA-MB-231 cells, an effect which was not observed in MDA-MB-468 cells, indicating that the effective concentration of metformin when used as anti-cancer drug in TNBCs may have to be determined based on cell type and blood glucose concentration. Our data indicates that metformin treatment was most effective under zero glucose/glucose-starved conditions in MDA-MB-468 with a significant increase in the apoptotic population (62.3 ± 1.5%; p-value < 0.01). Under 5.5 mM glucose conditions in both MDA-MB-231 and MDA-MB-468 cells our data showed reduced viability of 73.56 ± 2.53%; p-value < 0.05 and 70.49 ± 1.68%; p-value < 0.001, respectively, along with a significant increase in apoptotic populations of both cell types. Furthermore, metformin (2 mM) inhibited the mTOR pathway and its downstream components under zero glucose/glucose-starved conditions indicating that using metformin in combination with agents that inhibit the glycolytic pathway should be more beneficial for the treatment of triple-negative breast cancers in diabetic individuals.