Metformin: From Research to Clinical Practice

Histone deacetylase functions and therapeutic implications for adult skeletal muscle metabolism

Skeletal muscle is a highly adaptive organ that sustains continuous metabolic changes in response to different functional demands. Healthy skeletal muscle can adjust fuel utilization to the intensity of muscle activity, the availability of nutrients and the intrinsic characteristics of muscle fibers. This property is defined as metabolic flexibility. Importantly, impaired metabolic flexibility has been associated with, and likely contributes to the onset and progression of numerous pathologies, including sarcopenia and type 2 diabetes. Numerous studies involving genetic and pharmacological manipulations of histone deacetylases (HDACs) in vitro and in vivo have elucidated their multiple functions in regulating adult skeletal muscle metabolism and adaptation. Here, we briefly review HDAC classification and skeletal muscle metabolism in physiological conditions and upon metabolic stimuli. We then discuss HDAC functions in regulating skeletal muscle metabolism at baseline and following exercise. Finally, we give an overview of the literature regarding the activity of HDACs in skeletal muscle aging and their potential as therapeutic targets for the treatment of insulin resistance.

Double benefit of metformin treatment: improved bladder function in cyclophosphamide-induced cystitis and enhanced cytotoxicity in cancer cells

Cyclophosphamide (CP) is a widely used anti-neoplastic drug; however, it leads to bladder dysfunction in the form of hemorrhagic cystitis that is a serious dose-limiting complication in cancer patients. We aimed to evaluate the protective effects of metformin (MET) in a mouse model of CP-related cystitis in parallel with its effect on CP-induced cytotoxicity in a breast cancer cell line, MDA-MB-231. Cystitis was induced by a single intraperitoneal injection of CP (300 mg/kg), and mice were administered MET, mesna, or vehicle treatment. 24 hours after cystitis induction, the bladders were removed for histopathological analysis and ex vivo evaluation of detrusor muscle contractility. The effect of MET on the cytotoxicity of CP in MDA-MB-231 cells was evaluated as the viability of the cells via MTT assay. Histopathological evaluation confirmed that CP induced a severe cystitis, and MET partially inhibited CP-induced bladder damage. Carbachol-evoked cholinergic contractions were significantly decreased in detrusor strips of mice injected with CP only compared to control (E_max=293.67± 20.00 vs. 497.79± 21.78 mg tension/mg tissue, respectively). In CP-injected mice, treatment with 100 mg/kg MET restored cholinergic contractions (E_max=473.72±62.61 mg tension/mg tissue). In MDA-MB-231 cells, MET decreased their viability, and the combination of MET and CP caused more decrease in cell viability as compared to CP alone (p<0.05), demonstrating that MET enhances the cytotoxicity of CP in these cancer cells. Our results indicate that MET has a strong potential as a therapeutic adjuvant to prevent CP-induced cystitis while enhancing the efficacy of CP.

Metformin Use Is Associated With Reduced Mortality in a Diverse Population With COVID-19 and Diabetes

Background

Coronavirus disease-2019 (COVID-19) is a growing pandemic with an increasing death toll that has been linked to various comorbidities as well as racial disparity. However, the specific characteristics of these at-risk populations are still not known and approaches to lower mortality are lacking.

Methods

We conducted a retrospective electronic health record data analysis of 25,326 subjects tested for COVID-19 between 2/25/20 and 6/22/20 at the University of Alabama at Birmingham Hospital, a tertiary health care center in the racially diverse Southern U.S. The primary outcome was mortality in COVID-19-positive subjects and the association with subject characteristics and comorbidities was analyzed using simple and multiple linear logistic regression.

Results

The odds ratio of contracting COVID-19 was disproportionately high in Blacks/African-Americans (OR 2.6; 95% CI 2.19-3.10; p<0.0001) and in subjects with obesity (OR 1.93; 95% CI 1.64-2.28; p<0.0001), hypertension (OR 2.46; 95% CI 2.07-2.93; p<0.0001), and diabetes (OR 2.11; 95% CI 1.78-2.48; p<0.0001). Diabetes was also associated with a dramatic increase in mortality (OR 3.62; 95% CI 2.11-6.2; p<0.0001) and emerged as an independent risk factor in this diverse population even after correcting for age, race, sex, obesity, and hypertension. Interestingly, we found that metformin treatment prior to diagnosis of COVID-19 was independently associated with a significant reduction in mortality in subjects with diabetes and COVID-19 (OR 0.33; 95% CI 0.13-0.84; p=0.0210).

Conclusion

Thus, these results suggest that while diabetes is an independent risk factor for COVID-19-related mortality, this risk is dramatically reduced in subjects taking metformin prior to diagnosis of COVID-19, raising the possibility that metformin may provide a protective approach in this high risk population.

Metformin enhances osteogenic differentiation of stem cells from human exfoliated deciduous teeth through AMPK pathway

Stem cells from human exfoliated deciduous teeth (SHEDs) are ideal seed cells in bone tissue engineering. As a first-line antidiabetic drug, metformin has recently been found to promote bone formation. The purpose of this study was to investigate the effect of metformin on the osteogenic differentiation of SHEDs and its underlying mechanism. SHEDs were isolated from the dental pulp of deciduous teeth from healthy children aged 6 to 12, and their surface antigen markers of stem cells were detected by flow cytometry. The effect of metformin (10-200 μM) treatment on SHEDs cell viability, proliferation, and osteogenic differentiation was analyzed. The activation of adenosine 5'-monophosphate-activated protein kinase (AMPK) phosphorylation Thr172 (p-AMPK) was determined by western blot assay. SHEDs were confirmed as mesenchymal stem cells (MSCs) on the basis of the expression of characteristic surface antigens. Metformin (10-200 μM) did not affect the viability and proliferation of SHEDs but significantly increased the expression of osteogenic genes, alkaline phosphatase activity, matrix mineralization, and p-AMPK level expression in SHEDs. Compound C, a specific inhibitor of the AMPK pathway, abolished metformin-induced osteogenic differentiation of SHEDs. Moreover, metformin treatment enhanced the expression of proangiogenic/osteogenic growth factors BMP2 and VEGF but reduced the osteoclastogenic factor RANKL/OPG expression in SHEDs. In conclusion, metformin could induce the osteogenic differentiation of SHEDs by activating the AMPK pathway and regulates the expression of proangiogenic/osteogenic growth factors and osteoclastogenic factors in SHEDs. Therefore, metformin-pretreated SHEDs could be a potential source of seed cells during stem cell-based bone tissue engineering.

Quantitative In Vivo Proteomics of Metformin Response in Liver Reveals AMPK-Dependent and -Independent Signaling Networks

Metformin is the front-line treatment for type 2 diabetes worldwide. It acts via effects on glucose and lipid metabolism in metabolic tissues, leading to enhanced insulin sensitivity. Despite significant effort, the molecular basis for metformin response remains poorly understood, with a limited number of specific biochemical pathways studied to date. To broaden our understanding of hepatic metformin response, we combine phospho-protein enrichment in tissue from genetically engineered mice with a quantitative proteomics platform to enable the discovery and quantification of basophilic kinase substrates in vivo. We define proteins whose binding to 14-3-3 are acutely regulated by metformin treatment and/or loss of the serine/threonine kinase, LKB1. Inducible binding of 250 proteins following metformin treatment is observed, 44% of which proteins bind in a manner requiring LKB1. Beyond AMPK, metformin activates protein kinase D and MAPKAPK2 in an LKB1-independent manner, revealing additional kinases that may mediate aspects of metformin response. Deeper analysis uncovered substrates of AMPK in endocytosis and calcium homeostasis.

Cellular toxicity of the metabolic inhibitor 2-deoxyglucose and associated resistance mechanisms

Most malignant cells display increased glucose absorption and metabolism compared to surrounding tissues. This well-described phenomenon results from a metabolic reprogramming occurring during transformation, that provides the building blocks and supports the high energetic cost of proliferation by increasing glycolysis. These features led to the idea that drugs targeting glycolysis might prove efficient in the context of cancer treatment. One of these drugs, 2-deoxyglucose (2-DG), is a synthetic glucose analog that can be imported into cells and interfere with glycolysis and ATP generation. Its preferential targeting to sites of cell proliferation is supported by the observation that a derived molecule, 2-fluoro-2-deoxyglucose (FDG) accumulates in tumors and is used for cancer imaging. Here, we review the toxicity mechanisms of this drug, from the early-described effects on glycolysis to its other cellular consequences, including inhibition of protein glycosylation and endoplasmic reticulum stress, and its interference with signaling pathways. Then, we summarize the current data on the use of 2-DG as an anti-cancer agent, especially in the context of combination therapies, as novel 2-DG-derived drugs are being developed. We also show how the use of 2-DG helped to decipher glucose-signaling pathways in yeast and favored their engineering for biotechnologies. Finally, we discuss the resistance strategies to this inhibitor that have been identified in the course of these studies and which may have important implications regarding a medical use of this drug.

METFORMIN USE IS ASSOCIATED WITH REDUCED MORTALITY IN A DIVERSE POPULATION WITH COVID-19 AND DIABETES

BACKGROUND

Coronavirus disease-2019 (COVID-19) is a growing pandemic with an increasing death toll that has been linked to various comorbidities as well as racial disparity. However, the specific characteristics of these at-risk populations are still not known and approaches to lower mortality are lacking.

METHODS

We conducted a retrospective electronic health record data analysis of 25,326 subjects tested for COVID-19 between 2/25/20 and 6/22/20 at the University of Alabama at Birmingham Hospital, a tertiary health care center in the racially diverse Southern U.S. The primary outcome was mortality in COVID-19-positive subjects and the association with subject characteristics and comorbidities was analyzed using simple and multiple linear logistic regression.

RESULTS

The odds ratio of contracting COVID-19 was disproportionately high in Blacks/African-Americans (OR 2.6; 95%CI 2.19-3.10; p<0.0001) and in subjects with obesity (OR 1.93; 95%CI 1.64-2.28; p<0.0001), hypertension (OR 2.46; 95%CI 2.07-2.93; p<0.0001), and diabetes (OR 2.11; 95%CI 1.78-2.48; p<0.0001). Diabetes was also associated with a dramatic increase in mortality (OR 3.62; 95%CI 2.11-6.2; p<0.0001) and emerged as an independent risk factor in this diverse population even after correcting for age, race, sex, obesity and hypertension. Interestingly, we found that metformin treatment was independently associated with a significant reduction in mortality in subjects with diabetes and COVID-19 (OR 0.33; 95%CI 0.13-0.84; p=0.0210).

CONCLUSION

Thus, these results suggest that while diabetes is an independent risk factor for COVID-19-related mortality, this risk is dramatically reduced in subjects taking metformin, raising the possibility that metformin may provide a protective approach in this high risk population.

Hepatic Glucose Output Inhibition by Mexican Plants Used in the Treatment of Type 2 Diabetes

De novo hepatic glucose production or hepatic gluconeogenesis is the main contributor to hyperglycemia in the fasting state in patients with type 2 diabetes (T2D) owing to insulin resistance, which leads to at least twice as much glucose synthesis compared to healthy subjects. Therefore, control of this pathway is a promising target to avoid the chronic complications associated with elevated glucose levels. Patients with T2D in the rural communities of Mexico use medicinal plants prepared as infusions that are consumed over the day between meals, thus following this rationale (consumption of the infusions in the fasting state), one approach to understanding the possible mechanism of action of medicinal plants is to assess their capacity to inhibit hepatic glucose production. Furthermore, in several of these plants, the presence of phenolic acids able to block the enzyme glucose-6-phosphatase (G6Pase) is reported. In the present work, extracts of Ageratina petiolaris, Bromelia karatas, Equisetum myriochaetum, Rhizophora mangle, and Smilax moranensis, which are Mexican plants that have been traditionally used to treat T2D, were assayed to evaluate their possible hepatic glucose output (HGO) inhibitory activity with a pyruvate tolerance test in 18-h fasted STZ-NA Wistar rats after oral administration of the extracts. In addition, the in vitro effects of the extracts on the last HGO rate-limiting enzyme G6Pase was analyzed. Our results showed that four of these plants had an effect on hepatic glucose production in the in vivo or in vitro assays. A. petiolaris and R. mangle extracts decreased glucose output, preventing an increase in the blood glucose levels and sustaining this prevented increase after pyruvate administration. Moreover, both extracts inhibited the catalytic activity of the G6Pase complex. On the other hand, even though S. moranensis and B. karatas did not exhibit a significant in vivo effect, S. moranensis had the most potent inhibitory effect on this enzymatic system, while the E. myriochaetum extract only inhibited hepatic glucose production in the pyruvate tolerance test. Because of the traditional method in which diabetic patients use plants, hepatic glucose production inhibition seems to be a mechanism that partially explains the common hypoglycemic effect. However, further studies must be carried out to characterize other mechanisms whereby these plants can decrease HGO.

Glucose-responsive Insulinoma with Insulin Hypersecretion Suppressed by Metformin

In type 2 diabetes mellitus, metformin suppresses excessive insulin secretion in relation to the intake of glucose. We herein report the case of a 45-year-old man with glucose-responsive insulinoma whose responsive hypoglycemia was alleviated by metformin. The patient had a history of a postprandial loss of consciousness, resulting in hospital admission. He refused surgery and diazoxide administration. A 75-g oral glucose tolerance test after metformin administration revealed the suppression of glucose-responsive insulin hypersecretion and responsive hypoglycemia. Pancreatic head duodenectomy was performed, which alleviated the symptoms. Metformin administration in patients with glucose-responsive insulinoma may therefore be effective for preventing responsive hypoglycemia and hyperinsulinemia.

Distinctive Roles of Sirtuins on Diabetes, Protective or Detrimental?

Dysregulation of metabolic pathways leads to type 2 diabetes, characteristic of high glucose concentration caused by insulin resistance. The histone deacetylases sirtuins exhibit remarkable enzymatic activities. Accumulating evidence indicates that sirtuins can be pharmacologically activated to ameliorate diabetes. Here, we evaluated different roles of sirtuins (SIRT1-SIRT7) in diabetes progression and described their involvement in metabolic pathways of skeletal muscle, adipose tissue and liver. The nuclear sirtuins, SIRT1, SIRT6, and SIRT7, regulate the activity of key transcription factors and cofactors in almost all tissues with the cellular responses to energy demands. The mitochondrial sirtuins, SIRT3, SIRT4, and SIRT5, regulate the activity of mitochondrial enzymes in response to fasting and calorie restriction. Moreover, genetic polymorphisms of SIRT1 and SIRT2 have been reported to associate with diabetes development. It's worth noting that SIRT1, SIRT2, SIRT3, and SIRT6 are positive regulators of insulin resistance in most cases. In the opposite, SIRT4 and SIRT7 inhibit insulin secretion and fatty acid oxidation. Identification of SIRT1 activators for diabetes has gained wide attention, such as metformin, resveratrol, and resveratrol derivatives. Randomized, prospective, and large-scale clinical trials are warrant to uncover the responsibilities of SIRTs modulators on diabetes progress.

Hypoglycemia and severe lactic acidosis in a dog following metformin exposure

Hypoglycemia and lactic acidosis are rare complications with metformin use in humans. As metformin is not commonly used in veterinary medicine, severe adverse effects secondary to exposure are not known. Awareness of potentially life‐threatening complications with metformin exposure is an important addition to the veterinary literature.

Defective insulin signaling and the protective effects of dimethyldiguanide during follicular development in the ovaries of polycystic ovary syndrome

It is established that the physiological effects of insulin are primarily mediated by the insulin signaling pathway. However, a defective insulin signaling is closely associated with the clinical manifestations of polycystic ovary syndrome (PCOS), which include excess androgen levels, insulin resistance and anovulation, and is involved in the pathophysiology of PCOS at the molecular level. Dimethyldiguanide (DMBG) has been widely employed to alleviate reproduction dysfunction in women with PCOS, however, the exact mechanism of this effect remains unclear. The objective of the present study was to investigate the effects of DMBG on the expression of the insulin signaling pathway in the ovaries of rats with PCOS, and to identify the potential underlying molecular mechanisms of these effects in PCOS. In the present study, a PCOS rat model was induced by letrozole, and successful establishment of the model was confirmed by examining ovarian histology and determining serum testosterone levels, by hematoxylin and eosin staining and ELISA, respectively. Subsequently, the expression of two key elements of insulin signaling, insulin receptor substrate (IRS)‑2 and phosphatidylinositol 3‑kinase (PI3K), was determined by immunohistochemistry and western blot analysis. The results demonstrated that IRS‑2 and PI3K expression was markedly decreased in PCOS ovaries, which was rescued by DMBG treatment. These results indicate that IRS‑2/PI3K signaling may be involved in the development of PCOS and the therapeutic effects of DMBG on PCOS. To further confirm the effects of DMBG on insulin signaling expression during this process, the expression of an additional two downstream proteins, phosphoinositide‑dependent kinase‑1 (PDK‑1) and the mammalian target of rapamycin (mTOR), was also investigated in the present study, and the results demonstrated that the expression of PDK‑1 and mTOR was significantly reduced in PCOS ovaries and increased following DMBG treatment, further indicating that altered insulin signaling may have an important role in the development and treatment of PCOS. In conclusion, the results of the present study indicate that the reduced expression of proteins involved in insulin signaling may contribute to the development of the clinical features of PCOS, and DMBG reverses reduced expression of insulin signaling components, by a mechanism that is yet to be determined, to attenuate certain symptoms of PCOS, such as obesity. To the best of our knowledge, the present study is the first to provide data regarding the detailed changes of insulin signaling during the development and treatment of PCOS, and may provide an important reference for clinical PCOS treatment.

Sirolimus and Metformin Synergistically Inhibits Colon Cancer In Vitro and In Vivo

We estimated the effect of various immunosuppressants (ISs) and metformin (M) to provide theoretical background of optimal therapeutic strategy for de novo colon cancer after liver transplantation (LT). Three colon cancer cell lines (HT29, SW620, and HCT116) were used in in vitro studies. HT29 was also used in BALB/c-nude mice animal models. Following groups were used in both in vitro and in vivo studies: sirolimus (S), tacrolimus (T), cyclosporin A (CsA), M, metformin/sirolimus (Met/S), metformin/tacrolimus (Met/T), and metformin/cyclosporin A (Met/CsA). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed and western blot analyses were performed for mTOR pathway proteins, apoptosis proteins, and epithelial-mesenchymal-transition (EMT) proteins. Tumor volume was measured for 4 weeks after inoculation. MTT-assay revealed significant cell viability inhibition in all 3 colon cancer cell lines in groups of S, M, and Met/S. Of note, group Met/S showed synergistic effect compare to M or S group. Western blot analysis showed significant low levels of all investigated proteins in groups of S and Met/S in both in vitro and in vivo experiment. Tumor growth was significantly inhibited only in the Met/S group. Combination of Met and S showed the most potent inhibition in all colon cancer cell lines. This finding might have application for de novo colon cancer.

Concentration-dependent metabolic effects of metformin in healthy and Fanconi anemia lymphoblast cells

Metformin (MET) is the drug of choice for patients with type 2 diabetes and has been proposed for use in cancer therapy and for treating other metabolic diseases. More than 14,000 studies have been published addressing the cellular mechanisms affected by MET. However, several in vitro studies have used concentrations of the drug 10-100-fold higher than the plasmatic concentration measured in patients. Here, we evaluated the biochemical, metabolic, and morphologic effects of various concentrations of MET. Moreover, we tested the effect of MET on Fanconi Anemia (FA) cells, a DNA repair genetic disease with defects in energetic and glucose metabolism, as well as on human promyelocytic leukemia (HL60) cell lines. We found that the response of wild-type cells to MET is concentration dependent. Low concentrations (15 and 150 µM) increase both oxidative phosphorylation and the oxidative stress response, acting on the AMPK/Sirt1 pathway, while the high concentration (1.5 mM) inhibits the respiratory chain, alters cell morphology, becoming toxic to the cells. In FA cells, MET was unable to correct the energetic/respiratory defect and did not improve the response to oxidative stress and DNA damage. By contrast, HL60 cells appear sensitive also at 150 μM. Our findings underline the importance of the MET concentration in evaluating the effect of this drug on cell metabolism and demonstrate that data obtained from in vitro experiments, that have used high concentrations of MET, cannot be readily translated into improving our understanding of the cellular effects of metformin when used in the clinical setting.

Metformin: Adjunct Therapy in Cancer Treatment

An employee undergoing cancer treatment was prescribed metformin, a medication used in the treatment of type 2 diabetes and currently used as adjunct therapy for cancer. Metformin’s anti-inflammatory properties inhibit tumor growth. It is speculated that cancer cells develop a metabolism that enhances aerobic glycolysis, which promotes cell growth and increases the need for glucose. Metformin decreases insulin in the blood, which decreases the amount of glucose available to cancer cells, thus starving the cells of nutrition, resulting in cell death. This case study explores the role of metformin in cancer treatment, with implications for occupational health nurses.

Autophagy and its link to type II diabetes mellitus

Autophagy, a double-edged sword for cell survival, is the research object on 2016 Nobel Prize in Physiology or Medicine. Autophagy is a molecular mechanism for maintaining cellular physiology and promoting survival. Defects in autophagy lead to the etiology of many diseases, including diabetes mellitus (DM), cancer, neurodegeneration, infection disease and aging. DM is a metabolic and chronic disorder and has a higher prevalence in the world as well as in Taiwan. The character of diabetes mellitus is hyperglycemia resulting from defects in insulin secretion, insulin action, or both. Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and failure of producing insulin on pancreatic beta cells. In T2DM, autophagy is not only providing nutrients to maintain cellular energy during fasting, but also removes damaged organelles, lipids and miss-folded proteins. In addition, autophagy plays an important role in pancreatic beta cell dysfunction and insulin resistance. In this review, we summarize the roles of autophagy in T2DM.