Metformin-Induced Mitochondrial Complex I Inhibition: Facts, Uncertainties, and Consequences

Mammalian target of differentiation-inducing factor-1 is mitochondrial malate dehydrogenase for activation of AMP-activated protein kinase and induction of mitochondrial fission

AIMS

Differentiation-inducing factor-1 (DIF-1) is a polyketide produced by Dictyostelium discoideum that inhibits growth and migration, while promoting the differentiation of Dictyostelium stalk cells through unknown mechanisms. DIF-1 localizes in stalk mitochondria. In addition to its effect on Dictyostelium, DIF-1 also inhibits growth and migration, and induces mitochondrial fission followed by mitophagy in mammalian cells, at least in part by activating AMP-activated protein kinase (AMPK). In a previous study, we found that DIF-1 binds to mitochondrial malate dehydrogenase (MDH2) and inhibits its activity in HeLa cells. In the present study, we investigated whether MDH2 serves as a pharmacological target of DIF-1 in mammalian cells.

MAIN METHODS

To examine the enzymatic activity of MDH, mitochondrial morphology, and molecular mechanisms of DIF-1 action, we conducted an MDH reverse reaction assay, immunofluorescence staining, western blotting, and RNA interference using mammalian cells such as human umbilical vein endothelial cells, human cervical cancer cells, mouse endothelial cells, and mouse breast cancer cells.

KEY FINDINGS

DIF-1 inhibited mitochondrial but not cytoplasmic MDH activity. Similar to DIF-1, LW6, an authentic MDH2 inhibitor, induced phosphorylation of AMPK, resulting in the phosphorylation of acetyl-CoA carboxylase (ACC) and the dephosphorylation of p70 S6 kinase with approximately the same potency. DIF-1 and LW6 induced mitochondrial fission. Furthermore, MDH2 knockdown using siRNA reproduced the DIF-1 action on the AMPK signaling and mitochondrial morphology. Conversely, an AMPK inhibitor prevented DIF-1-induced mitochondrial fission.

SIGNIFICANCE

We propose that MDH2 is a mammalian target of DIF-1 for the activation of AMPK and induction of mitochondrial fission.

Repurposing Metformin for the Treatment of Atrial Fibrillation: Current Insights

Metformin is an orally effective anti-hyperglycemic drug that despite being introduced over 60 years ago is still utilized by an estimated 120 to 150 million people worldwide for the treatment of type 2 diabetes (T2D). Metformin is used off-label for the treatment of polycystic ovary syndrome (PCOS) and for pre-diabetes and weight loss. Metformin is a safe, inexpensive drug with side effects mostly limited to gastrointestinal issues. Prospective clinical data from the United Kingdom Prospective Diabetes Study (UKPDS), completed in 1998, demonstrated that metformin not only has excellent therapeutic efficacy as an anti-diabetes drug but also that good glycemic control reduced the risk of micro- and macro-vascular complications, especially in obese patients and thereby reduced the risk of diabetes-associated cardiovascular disease (CVD). Based on a long history of clinical use and an excellent safety record metformin has been investigated to be repurposed for numerous other diseases including as an anti-aging agent, Alzheimer's disease and other dementias, cancer, COVID-19 and also atrial fibrillation (AF). AF is the most frequently diagnosed cardiac arrythmia and its prevalence is increasing globally as the population ages. The argument for repurposing metformin for AF is based on a combination of retrospective clinical data and in vivo and in vitro pre-clinical laboratory studies. In this review, we critically evaluate the evidence that metformin has cardioprotective actions and assess whether the clinical and pre-clinical evidence support the use of metformin to reduce the risk and treat AF.

New evidence: Metformin unsuitable as routine adjuvant for breast cancer: a drug-target mendelian randomization analysis

PURPOSE

The potential efficacy of metformin in breast cancer (BC) has been hotly discussed but never conclusive. This genetics-based study aimed to evaluate the relationships between metformin targets and BC risk.

METHODS

Metformin targets from DrugBank and genome-wide association study (GWAS) data from IEU OpenGWAS and FinnGen were used to investigate the breast cancer (BC)-metformin causal link with various Mendelian Randomization (MR) methods (e.g., inverse-variance-weighting). The genetic association between type 2 diabetes (T2D) and the drug target of metformin was also analyzed as a positive control. Sensitivity and pleiotropic tests ensured reliability.

RESULTS

The primary targets of metformin are PRKAB1, ETFDH and GPD1L. We found a causal association between PRKAB1 and T2D (odds ratio [OR] 0.959, P = 0.002), but no causal relationship was observed between metformin targets and overall BC risk (PRKAB1: OR 0.990, P = 0.530; ETFDH: OR 0.986, P = 0.592; GPD1L: OR 1.002, P = 0.806). A noteworthy causal relationship was observed between ETFDH and estrogen receptor (ER)-positive BC (OR 0.867, P = 0.018), and between GPD1L and human epidermal growth factor receptor 2 (HER2)-negative BC (OR 0.966, P = 0.040). Other group analyses did not yield positive results.

CONCLUSION

The star target of metformin, PRKAB1, does not exhibit a substantial causal association with the risk of BC. Conversely, metformin, acting as an inhibitor of ETFDH and GPD1L, may potentially elevate the likelihood of developing ER-positive BC and HER2-negative BC. Consequently, it is not advisable to employ metformin as a standard supplementary therapy for BC patients without T2D.

SGLT2-independent effects of canagliflozin on NHE3 and mitochondrial complex I activity inhibit proximal tubule fluid transport and albumin uptake

Beyond glycemic control, SGLT2 inhibitors (SGLT2is) have protective effects on cardiorenal function. Renoprotection has been suggested to involve inhibition of NHE3 leading to reduced ATP-dependent tubular workload and mitochondrial oxygen consumption. NHE3 activity is also important for regulation of endosomal pH, but the effects of SGLT2i on endocytosis are unknown. We used a highly differentiated cell culture model of proximal tubule (PT) cells to determine the direct effects of SGLT2i on Na+-dependent fluid transport and endocytic uptake in this nephron segment. Strikingly, canagliflozin but not empagliflozin reduced fluid transport across cell monolayers and dramatically inhibited endocytic uptake of albumin. These effects were independent of glucose and occurred at clinically relevant concentrations of drug. Canagliflozin acutely inhibited surface NHE3 activity, consistent with a direct effect, but did not affect endosomal pH or NHE3 phosphorylation. In addition, canagliflozin rapidly and selectively inhibited mitochondrial complex I activity. Inhibition of mitochondrial complex I by metformin recapitulated the effects of canagliflozin on endocytosis and fluid transport, whereas modulation of downstream effectors AMPK and mTOR did not. Mice given a single dose of canagliflozin excreted twice as much urine over 24 h compared with empagliflozin-treated mice despite similar water intake. We conclude that canagliflozin selectively suppresses Na+-dependent fluid transport and albumin uptake in PT cells via direct inhibition of NHE3 and of mitochondrial function upstream of the AMPK/mTOR axis. These additional targets of canagliflozin contribute significantly to reduced PT Na+-dependent fluid transport in vivo.NEW & NOTEWORTHY Reduced NHE3-mediated Na+ transport has been suggested to underlie the cardiorenal protection provided by SGLT2 inhibitors. We found that canagliflozin, but not empagliflozin, reduced NHE3-dependent fluid transport and endocytic uptake in cultured proximal tubule cells. These effects were independent of SGLT2 activity and resulted from inhibition of mitochondrial complex I and NHE3. Studies in mice are consistent with greater effects of canagliflozin versus empagliflozin on fluid transport. Our data suggest that these selective effects of canagliflozin contribute to reduced Na+-dependent transport in proximal tubule cells.

Alzheimer's disease and its treatment-yesterday, today, and tomorrow

Alois Alzheimer described the first patient with Alzheimer's disease (AD) in 1907 and today AD is the most frequently diagnosed of dementias. AD is a multi-factorial neurodegenerative disorder with familial, life style and comorbidity influences impacting a global population of more than 47 million with a projected escalation by 2050 to exceed 130 million. In the USA the AD demographic encompasses approximately six million individuals, expected to increase to surpass 13 million by 2050, and the antecedent phase of AD, recognized as mild cognitive impairment (MCI), involves nearly 12 million individuals. The economic outlay for the management of AD and AD-related cognitive decline is estimated at approximately 355 billion USD. In addition, the intensifying prevalence of AD cases in countries with modest to intermediate income countries further enhances the urgency for more therapeutically and cost-effective treatments and for improving the quality of life for patients and their families. This narrative review evaluates the pathophysiological basis of AD with an initial focus on the therapeutic efficacy and limitations of the existing drugs that provide symptomatic relief: acetylcholinesterase inhibitors (AChEI) donepezil, galantamine, rivastigmine, and the N-methyl-D-aspartate receptor (NMDA) receptor allosteric modulator, memantine. The hypothesis that amyloid-β (Aβ) and tau are appropriate targets for drugs and have the potential to halt the progress of AD is critically analyzed with a particular focus on clinical trial data with anti-Aβ monoclonal antibodies (MABs), namely, aducanumab, lecanemab and donanemab. This review challenges the dogma that targeting Aβ will benefit the majority of subjects with AD that the anti-Aβ MABs are unlikely to be the "magic bullet". A comparison of the benefits and disadvantages of the different classes of drugs forms the basis for determining new directions for research and alternative drug targets that are undergoing pre-clinical and clinical assessments. In addition, we discuss and stress the importance of the treatment of the co-morbidities, including hypertension, diabetes, obesity and depression that are known to increase the risk of developing AD.

Data-dependent and -independent acquisition lipidomics analysis reveals the tissue-dependent effect of metformin on lipid metabolism

INTRODUCTION

Despite the well-recognized health benefits, the mechanisms and site of action of metformin remains elusive. Metformin-induced global lipidomic changes in plasma of animal models and human subjects have been reported. However, there is a lack of systemic evaluation of metformin-induced lipidomic changes in different tissues. Metformin uptake requires active transporters such as organic cation transporters (OCTs), and hence, it is anticipated that metformin actions are tissue-dependent. In this study, we aim to characterize metformin effects in non-diabetic male mice with a special focus on lipidomics analysis. The findings from this study will help us to better understand the cell-autonomous (direct actions in target cells) or non-cell-autonomous (indirect actions in target cells) mechanisms of metformin and provide insights into the development of more potent yet safe drugs targeting a particular organ instead of systemic metabolism for metabolic regulations without major side effects.

OBJECTIVES

To characterize metformin-induced lipidomic alterations in different tissues of non-diabetic male mice and further identify lipids affected by metformin through cell-autonomous or systemic mechanisms based on the correlation between lipid alterations in tissues and the corresponding in-tissue metformin concentrations.

METHODS

A dual extraction method involving 80% methanol followed by MTBE (methyl tert-butyl ether) extraction enables the analysis of free fatty acids, polar metabolites, and lipids. Extracts from tissues and plasma of male mice treated with or without metformin in drinking water for 12 days were analyzed using HILIC chromatography coupled to Q Exactive Plus mass spectrometer or reversed-phase liquid chromatography coupled to MS/MS scan workflow (hybrid mode) on LC-Orbitrap Exploris 480 mass spectrometer using biologically relevant lipids-containing inclusion list for data-independent acquisition (DIA), named as BRI-DIA workflow followed by data-dependent acquisition (DDA), to maximum the coverage of lipids and minimize the negative effect of stochasticity of precursor selection on experimental consistency and reproducibility.

RESULTS

Lipidomics analysis of 6 mouse tissues and plasma allowed a systemic evaluation of lipidomic changes induced by metformin in different tissues. We observed that (1) the degrees of lipidomic changes induced by metformin treatment overly correlated with tissue concentrations of metformin; (2) the impact on lysophosphatidylcholine (lysoPC) and cardiolipins was positively correlated with tissue concentrations of metformin, while neutral lipids such as triglycerides did not correlate with the corresponding tissue metformin concentrations; (3) increase of intestinal tricarboxylic acid (TCA) cycle intermediates after metformin treatment.

CONCLUSION

The data collected in this study from non-diabetic mice with 12-day metformin treatment suggest that the overall metabolic effect of metformin is positively correlated with tissue concentrations and the effect on individual lipid subclass is via both cell-autonomous mechanisms (cardiolipins and lysoPC) and non-cell-autonomous mechanisms (triglycerides).

A case of exacerbated encephalopathy with stroke-like episodes and lactic acidosis triggered by metformin in a patient with MELAS

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a maternally inherited multisystemic disorder caused by mutations in mitochondrial DNA that result in cellular energy deficiency. MELAS affects the most metabolically active organs, including the brain, skeletal muscles, cochlea, retina, heart, kidneys, and pancreas. As a result, about 85% of carriers of m.3243A > G, the most common mutation in MELAS, develop diabetes by the age of 70. Although metformin is the most widely prescribed drug for diabetes, its usefulness in mitochondrial dysfunction remains controversial. Here, we present the case of a 32-year-old Korean patient diagnosed with MELAS who presented with exacerbated stroke-like episodes and lactic acidosis triggered by metformin.

Metformin: From Diabetes to Cancer-Unveiling Molecular Mechanisms and Therapeutic Strategies

Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin's role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement in survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin's bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

Understanding the variation in exercise responses to guide personalized physical activity prescriptions

Understanding the factors that contribute to exercise response variation is the first step in achieving the goal of developing personalized exercise prescriptions. This review discusses the key molecular and other mechanistic factors, both extrinsic and intrinsic, that influence exercise responses and health outcomes. Extrinsic characteristics include the timing and dose of exercise, circadian rhythms, sleep habits, dietary interactions, and medication use, whereas intrinsic factors such as sex, age, hormonal status, race/ethnicity, and genetics are also integral. The molecular transducers of exercise (i.e., genomic/epigenomic, proteomic/post-translational, transcriptomic, metabolic/metabolomic, and lipidomic elements) are considered with respect to variability in physiological and health outcomes. Finally, this review highlights the current challenges that impede our ability to develop effective personalized exercise prescriptions. The Molecular Transducers of Physical Activity Consortium (MoTrPAC) aims to fill significant gaps in the understanding of exercise response variability, yet further investigations are needed to address additional health outcomes across all populations.

A Dual Pharmacological Strategy against COVID-19: The Therapeutic Potential of Metformin and Atorvastatin

Metformin (MET) and atorvastatin (ATO) are promising treatments for COVID-19. This review explores the potential of MET and ATO, commonly prescribed for diabetes and dyslipidemia, respectively, as versatile medicines against SARS-CoV-2. Due to their immunomodulatory and antiviral capabilities, as well as their cost-effectiveness and ubiquitous availability, they are highly suitable options for treating the virus. MET's effect extends beyond managing blood sugar, impacting pathways that can potentially decrease the severity and fatality rates linked with COVID-19. It can partially block mitochondrial complex I and stimulate AMPK, which indicates that it can be used more widely in managing viral infections. ATO, however, impacts cholesterol metabolism, a crucial element of the viral replicative cycle, and demonstrates anti-inflammatory characteristics that could modulate intense immune reactions in individuals with COVID-19. Retrospective investigations and clinical trials show decreased hospitalizations, severity, and mortality rates in patients receiving these medications. Nevertheless, the journey from observing something to applying it in a therapeutic setting is intricate, and the inherent diversity of the data necessitates carefully executed, forward-looking clinical trials. This review highlights the requirement for efficacious, easily obtainable, and secure COVID-19 therapeutics and identifies MET and ATO as promising treatments in this worldwide health emergency.

Metformin increases 3-hydroxy medium chain fatty acids in patients with type 2 diabetes: a cross-sectional pharmacometabolomic study

Background

Metformin is a drug with a long history of providing benefits in diabetes management and beyond. The mechanisms of action of metformin are complex, and continue to be actively debated and investigated. The aim of this study is to identify metabolic signatures associated with metformin treatment, which may explain the pleiotropic mechanisms by which metformin works, and could lead to an improved treatment and expanded use.

Methods

This is a cross-sectional study, in which clinical and metabolomic data for 146 patients with type 2 diabetes were retrieved from Qatar Biobank. Patients were categorized into: Metformin-treated, treatment naïve, and non-metformin treated. Orthogonal partial least square discriminate analysis and linear models were used to analyze differences in the level of metabolites between the metformin treated group with each of the other two groups.

Results

Patients on metformin therapy showed, among other metabolites, a significant increase in 3-hydroxyoctanoate and 3-hydroxydecanoate, which may have substantial effects on metabolism.

Conclusions

This is the first study to report an association between 3-hydroxy medium chain fatty acids with metformin therapy in patients with type 2 diabetes. This opens up new directions towards repurposing metformin by comprehensively understanding the role of these metabolites.

Beneficial Effects of Low-Grade Mitochondrial Stress on Metabolic Diseases and Aging

Mitochondria function as platforms for bioenergetics, nutrient metabolism, intracellular signaling, innate immunity regulators, and modulators of stem cell activity. Thus, the decline in mitochondrial functions causes or correlates with diabetes mellitus and many aging-related diseases. Upon stress or damage, the mitochondria elicit a series of adaptive responses to overcome stress and restore their structural integrity and functional homeostasis. These adaptive responses to low-level or transient mitochondrial stress promote health and resilience to upcoming stress. Beneficial effects of low-grade mitochondrial stress, termed mitohormesis, have been observed in various organisms, including mammals. Accumulated evidence indicates that treatments boosting mitohormesis have therapeutic potential in various human diseases accompanied by mitochondrial stress. Here, we review multiple cellular signaling pathways and interorgan communication mechanisms through which mitochondrial stress leads to advantageous outcomes. We also discuss the relevance of mitohormesis in obesity, diabetes, metabolic liver disease, aging, and exercise.

Defining type 2 diabetes polygenic risk scores through colocalization and network-based clustering of metabolic trait genetic associations

BACKGROUND

Type 2 diabetes (T2D) is a heterogeneous and polygenic disease. Previous studies have leveraged the highly polygenic and pleiotropic nature of T2D variants to partition the heterogeneity of T2D, in order to stratify patient risk and gain mechanistic insight. We expanded on these approaches by performing colocalization across GWAS traits while assessing the causality and directionality of genetic associations.

METHODS

We applied colocalization between T2D and 20 related metabolic traits, across 243 loci, to obtain inferences of shared casual variants. Network-based unsupervised hierarchical clustering was performed on variant-trait associations. Partitioned polygenic risk scores (PRSs) were generated for each cluster using T2D summary statistics and validated in 21,742 individuals with T2D from 3 cohorts. Inferences of directionality and causality were obtained by applying Mendelian randomization Steiger's Z-test and further validated in a pediatric cohort without diabetes (aged 9-12 years old, n = 3866).

RESULTS

We identified 146 T2D loci that colocalized with at least one metabolic trait locus. T2D variants within these loci were grouped into 5 clusters. The clusters corresponded to the following pathways: obesity, lipodystrophic insulin resistance, liver and lipid metabolism, hepatic glucose metabolism, and beta-cell dysfunction. We observed heterogeneity in associations between PRSs and metabolic measures across clusters. For instance, the lipodystrophic insulin resistance (Beta - 0.08 SD, 95% CI [- 0.10-0.07], p = 6.50 × 10-32) and beta-cell dysfunction (Beta - 0.10 SD, 95% CI [- 0.12, - 0.08], p = 1.46 × 10-47) PRSs were associated to lower BMI. Mendelian randomization Steiger analysis indicated that increased T2D risk in these pathways was causally associated to lower BMI. However, the obesity PRS was conversely associated with increased BMI (Beta 0.08 SD, 95% CI 0.06-0.10, p = 8.0 × 10-33). Analyses within a pediatric cohort supported this finding. Additionally, the lipodystrophic insulin resistance PRS was associated with a higher odds of chronic kidney disease (OR 1.29, 95% CI 1.02-1.62, p = 0.03).

CONCLUSIONS

We successfully partitioned T2D genetic variants into phenotypic pathways using a colocalization first approach. Partitioned PRSs were associated to unique metabolic and clinical outcomes indicating successful partitioning of disease heterogeneity. Our work expands on previous approaches by providing stronger inferences of shared causal variants, causality, and directionality of GWAS variant-trait associations.

Kinetic Modeling of Hepatic Metabolism and Simulation of Treatment Effects

Mathematical modeling is a promising strategy to fill the experimentally unapproachable knowledge gaps about the relative contribution of various molecular processes to cellular metabolic function. To this end, we developed detailed kinetic models of the central metabolism of different cell types, comprising multiple metabolic functionalities. We used the model to simulate metabolic changes in several cell types under different experimental settings in health and disease. In this way, we show that it is possible to decipher and characterize the relative influence of various metabolic pathways and enzymes to overall metabolic performance and phenotype.Quantitative Systems Metabolism (QSM™) allows quantitative assessment of metabolic functionality and metabolic profiling based on proteomic data. Here, we describe the technique, namely, molecular resolved kinetic modeling, underlying QSM™. We explain the necessary steps for the generation of cell-specific models to functionally interpret proteomic data and point out some unresolved challenges and open questions.

Flavonoid-Phenolic Acid Hybrids Are Potent Inhibitors of Ferroptosis via Attenuation of Mitochondrial Impairment

Cinnamic acid, ferulic acid, and the flavonoids quercetin and taxifolin (dihydroquercetin) are naturally occurring compounds found in plants. They are often referred to as polyphenols and are known, among others, for their pharmacological effects supporting health through the inhibition of aging processes and oxidative stress. To improve their bioavailability, pharmacological activities, and safety, the creation of novel flavonoid-phenolic acid hybrids is an area of active research. Previous work showed that such hybridization products of phenolic acids and flavonoids enhanced the resilience of neuronal cells against oxidative stress in vitro, and attenuated cognitive impairment in a mouse model of Alzheimer's disease (AD) in vivo. Notably, the therapeutic effects of the hybrid compounds we obtained were more pronounced than the protective activities of the respective individual components. The underlying mechanisms mediated by the flavonoid-phenolic acid hybrids, however, remained unclear and may differ from the signaling pathways activated by the originating structures of the respective individual phenolic acids or flavonoids. In this study, we characterized the effects of four previously described potent flavonoid-phenolic acid hybrids in models of oxidative cell death through ferroptosis. Ferroptosis is a type of iron-dependent regulated cell death characterized by lipid peroxidation and mitochondrial ROS generation and has been linked to neurodegenerative conditions. In models of ferroptosis induced by erastin or RSL3, we analyzed mitochondrial (lipid) peroxidation, mitochondrial membrane integrity, and Ca2+ regulation. Our results demonstrate the strong protective effects of the hybrid compounds against ROS formation in the cytosol and mitochondria. Importantly, these protective effects against ferroptosis were not mediated by radical scavenging activities of the phenolic hybrid compounds but through inhibition of mitochondrial complex I activity and reduced mitochondrial respiration. Our data highlight the effects of flavonoid-phenolic acid hybrids on mitochondrial metabolism and further important mitochondrial parameters that collectively determine the health and functionality of mitochondria with a high impact on the integrity and survival of the neuronal cells.

Metformin-suppressed platelet's function in vitro: Possible relation to delayed or failure of platelet-rich fibrin preparation

Platelet-rich fibrin (PRF) is a popular autologous blood-derived biomaterial that is used in regenerative therapy. Owing to its simple preparation without additional factors, the PRF quality directly reflects the characteristics of individual blood samples. Antiplatelet or anticoagulant drugs can hamper the successful preparation of PRF. We recently observed similar phenomena in metformin-taking type-2 diabetics (T2DM). Thus, we hypothesized that metformin interferes with platelet function, thereby suppressing coagulation. For practical reasons, leukocyte- and platelet-rich plasma was prepared from healthy male donors (n = 9-15, age: 26-80 years) and treated with metformin (1-10 mM) for 24-72 h. Intrinsic and extrinsic coagulation activities were evaluated using prothrombin time (PT) and activated partial thromboplastin time (ATPP). Platelet adhesion and aggregation assays were performed using ADP stimulation. Among the parameters tested, APTT was the most sensitive and was significantly prolonged in the concentration range of 1-10 mM in a time- and concentration-dependent manner. Although obtained from healthy platelets and relatively higher concentrations of metformin, these findings suggest that metformin may induce further dysfunction of platelets to suppress intrinsic coagulation activity in T2DM patients, leading to failure of PRF preparation. This phenomenon may not have a severe impact on clinical diabetology or hematology. However, clinicians using PRF are recommended to be more sensitive to such information to avoid unexpected events in clinical settings.

NDUFA4 promotes the progression of head and neck paraganglioma by inhibiting ferroptosis

NDUFA4 is a component of respiratory chain-oxidative phosphorylation pathway. NDUFA4 is highly expressed in tumor tissues, but little is known about the function of NDUFA4 in head and neck paraganglioma (HNPGL). We examined NDUFA4 expression in tissues from 10 HNPGL patients and 6 controls using qRT-PCR and Western blotting. NDUFA4 knockdown PGL-626 cells were established by using lentivirus infection and puromycin screening. Cell viability, ATP production, lipid reactive oxygen species, and mitochondrial membrane potential assays were performed to investigate the ferroptotic effects in NDUFA4 deficiency HNPGL cancer cells. Xenograft mouse model was created to detect the synergetic antitumor action between NDUFA4 deficiency and Metformin. NDUFA4 was upregulated in tumor tissues of HNPGL patients. NDUFA4 knockdown impaired the assembly of mitochondrial respiratory chain complexes and decreased the production of ATP and reduced cancer cell viability. Mechanistically, NDUFA4 knockdown increased cell ferroptosis, which further promoted Metformin-induced ferroptosis in PGL-626 cells. Therefore, NDUFA4 deficiency enhanced Metformin-mediated inhibition of the HNPGL progression in mice. In conclusion, NDUFA4 promotes the progression of HNPGL, and NDUFA4 knockdown enhances Metformin-mediated inhibition of the HNPGL progression in a mouse model.

Sustained Nrf2 Overexpression-Induced Metabolic Deregulation Can Be Attenuated by Modulating Insulin/Insulin-like Growth Factor Signaling

The modulation of insulin/insulin-like growth factor signaling (IIS) is associated with altered nutritional and metabolic states. The Drosophila genome encodes eight insulin-like peptides, whose activity is regulated by a group of secreted factors, including Ecdysone-inducible gene L2 (ImpL2), which acts as a potent IIS inhibitor. We recently reported that cncC (cncC/Nrf2), the fly ortholog of Nrf2, is a positive transcriptional regulator of ImpL2, as part of a negative feedback loop aiming to suppress cncC/Nrf2 activity. This finding correlated with our observation that sustained cncC/Nrf2 overexpression/activation (cncCOE; a condition that signals organismal stress) deregulates IIS, causing hyperglycemia, the exhaustion of energy stores in flies' tissues, and accelerated aging. Here, we extend these studies in Drosophila by assaying the functional implication of ImpL2 in cncCOE-mediated metabolic deregulation. We found that ImpL2 knockdown (KD) in cncCOE flies partially reactivated IIS, attenuated hyperglycemia and restored tissue energetics. Moreover, ImpL2 KD largely suppressed cncCOE-mediated premature aging. In support, pharmacological treatment of cncCOE flies with Metformin, a first-line medication for type 2 diabetes, restored (dose-dependently) IIS functionality and extended cncCOE flies' longevity. These findings exemplify the effect of chronic stress in predisposition to diabetic phenotypes, indicating the potential prophylactic role of maintaining normal IIS functionality.

Aerobic exercise and metformin on intermuscular adipose tissue (IMAT): insights from multimodal MRI and histological changes in prediabetic rats

BACKGROUND

Physical exercise is the first-line intervention for prediabetes, and metformin is the most widely used oral insulin-sensitizing agent. Moreover, intermuscular adipose tissue (IMAT) directly affects insulin resistance by helping maintain glucose homeostasis. Here, we evaluated the effects of moderate aerobic exercise and/or metformin on histological IMAT parameters in non-streptozotocin-induced prediabetes.

METHODS

Male Wistar rats with prediabetes fed a high-fat diet and high-sugar drinks were randomly assigned to high-fat diet (PRE), metformin (MET), moderate aerobic exercise (EXE), combined therapy (EMC), or EMC + compound-c (EMA) groups for 4 weeks. Multimodal magnetic resonance imaging (MRI) was then performed, and tissue-specific inflammation and energy and lipid metabolism were evaluated in IMAT.

RESULTS

The EXE group had lower inflammatory factor levels, lipid metabolism, and mitochondrial oxidative stress, and shorter IMAT adipocyte diameters than the MET group. The MET group exhibited lower IL-1β and Plin5 expression than the PRE group. Furthermore, the IMAT of the EMC group had lower TNF-α and phosphorylated NF-κB levels and higher GLUT1 and GLUT4 expression than the PRE group. Multimodal MRI revealed significant changes in transverse-relaxation time 2, apparent diffusion coefficient, and fractional anisotropy values in the IMAT and muscles, as well as lower IMAT% values in the EXE and EMC groups than in the MET and PRE groups.

CONCLUSION

Moderate aerobic exercise training can effectively improve IMAT function and structure via the AMP-activated protein kinase pathway in prediabetes. Combining metformin with moderate aerobic exercise might elicit modest synergy, and metformin does not counterbalance the beneficial effects of exercise.

Dissecting the Role of Autophagy-Related Proteins in Cancer Metabolism and Plasticity

Modulation of autophagy as an anticancer strategy has been widely studied and evaluated in several cell models. However, little attention has been paid to the metabolic changes that occur in a cancer cell when autophagy is inhibited or induced. In this review, we describe how the expression and regulation of various autophagy-related (ATGs) genes and proteins are associated with cancer progression and cancer plasticity. We present a comprehensive review of how deregulation of ATGs affects cancer cell metabolism, where inhibition of autophagy is mainly reflected in the enhancement of the Warburg effect. The importance of metabolic changes, which largely depend on the cancer type and form part of a cancer cell's escape strategy after autophagy modulation, is emphasized. Consequently, pharmacological strategies based on a dual inhibition of metabolic and autophagy pathways emerged and are reviewed critically here.

Old drug, new tricks: the utility of metformin in infection and vaccination responses to influenza and SARS-CoV-2 in older adults

In the face of global pathogens such as influenza (flu) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), strategies beyond standard vaccines and virus-specific treatments are critically needed for older populations who are more susceptible to severe disease and death from these infections due to age-related immune dysregulation. Thus, complimentary therapeutics are needed to address the increased risk of complications and death in older adults. Metformin, an FDA approved diabetes drug, is an attractive therapeutic candidate to improve immune defenses and resilience in older adults facing viral challenge. Metformin is already a candidate anti-aging drug, but its benefits have potential to span beyond this and improve specific immune responses. Metformin can target multiple aging hallmarks as well as directly impact innate and adaptive immune cell subsets. Both retrospective and prospective studies have demonstrated metformin's efficacy in improving outcomes after SARS-CoV-2 or flu infections. Moreover, evidence from clinical trials has also suggested that metformin treatment can improve vaccination responses. In totality, these findings suggest that metformin can improve age-related declines in immunological resilience. Strategies to improve outcomes after infection or improve vaccine-induced protection are invaluable for older adults. Moreover, the ability to repurpose an already FDA approved drug has significant advantages in terms of necessary time and resources. Thus, metformin has great potential as a therapeutic to improve age-related immune dysregulation during flu and SARS-CoV-2 infections and should be further explored to confirm its ability to improve overall immunological resilience in older adults.

Topical metformin 30% gel in the treatment of acne vulgaris in women, a split face, placebo-controlled study

Acne vulgaris (AV), a widely common disorder, that negatively affects the quality of life. Metformin is a relatively safe, cheap and well tolerated drug that is widely used in the treatment of Diabetes. Systemic metformin has demonstrated promising results in treating acne, while topically it was studied for melasma and recalcitrant central centrifugal cicatricial alopecia. To study the safety and efficacy of topical metformin 30% in the treatment of AV. Twenty-seven female AV patients were asked to blindly apply metformin and placebo gels to either side of the face for 12 weeks. AV lesion count was performed at baseline, at each visit and 4 weeks after end of treatment. At the end of the treatment period, the treated side showed significant improvement of comedones, papules and nodules but not pustules. Although, lesions count increased 1 month after stopping treatment, comedones and papules numbers were still significantly less on the metformin side compared to placebo. No side effects were reported. The limited number of patients studied and the limited follow-up period. The metformin effect was not studied on cellular and molecular levels. Topical metformin nanoemulsion gel can be a promising safe and effective treatment of AV.

ADP-Fuse: A novel two-layer machine learning predictor to identify antidiabetic peptides and diabetes types using multiview information

Diabetes mellitus has become a major public health concern associated with high mortality and reduced life expectancy and can cause blindness, heart attacks, kidney failure, lower limb amputations, and strokes. A new generation of antidiabetic peptides (ADPs) that act on β-cells or T-cells to regulate insulin production is being developed to alleviate the effects of diabetes. However, the lack of effective peptide-mining tools has hampered the discovery of these promising drugs. Hence, novel computational tools need to be developed urgently. In this study, we present ADP-Fuse, a novel two-layer prediction framework capable of accurately identifying ADPs or non-ADPs and categorizing them into type 1 and type 2 ADPs. First, we comprehensively evaluated 22 peptide sequence-derived features coupled with eight notable machine learning algorithms. Subsequently, the most suitable feature descriptors and classifiers for both layers were identified. The output of these single-feature models, embedded with multiview information, was trained with an appropriate classifier to provide the final prediction. Comprehensive cross-validation and independent tests substantiate that ADP-Fuse surpasses single-feature models and the feature fusion approach for the prediction of ADPs and their types. In addition, the SHapley Additive exPlanation method was used to elucidate the contributions of individual features to the prediction of ADPs and their types. Finally, a user-friendly web server for ADP-Fuse was developed and made publicly accessible (https://balalab-skku.org/ADP-Fuse), enabling the swift screening and identification of novel ADPs and their types. This framework is expected to contribute significantly to antidiabetic peptide identification.

Preventing mitochondrial reverse electron transport as a strategy for cardioprotection

In the context of myocardial infarction, the burst of superoxide generated by reverse electron transport (RET) at complex I in mitochondria is a crucial trigger for damage during ischaemia/reperfusion (I/R) injury. Here we outline the necessary conditions for superoxide production by RET at complex I and how it can occur during reperfusion. In addition, we explore various pathways that are implicated in generating the conditions for RET to occur and suggest potential therapeutic strategies to target RET, aiming to achieve cardioprotection.

Gluconeogenesis Flux in Metabolic Disease

Gluconeogenesis is a critical biosynthetic process that helps maintain whole-body glucose homeostasis and becomes altered in certain medical diseases. We review gluconeogenic flux in various medical diseases, including common metabolic disorders, hormonal imbalances, specific inborn genetic errors, and cancer. We discuss how the altered gluconeogenic activity contributes to disease pathogenesis using data from experiments using isotopic tracer and spectroscopy methodologies. These in vitro, animal, and human studies provide insights into the changes in circulating levels of available gluconeogenesis substrates and the efficiency of converting those substrates to glucose by gluconeogenic organs. We highlight ongoing knowledge gaps, discuss emerging research areas, and suggest future investigations. A better understanding of altered gluconeogenesis flux may ultimately identify novel and targeted treatment strategies for such diseases.

Metformin is a metabolic modulator and radiosensitiser in rectal cancer

Resistance to neoadjuvant chemoradiation therapy, is a major challenge in the management of rectal cancer. Increasing evidence supports a role for altered energy metabolism in the resistance of tumours to anti-cancer therapy, suggesting that targeting tumour metabolism may have potential as a novel therapeutic strategy to boost treatment response. In this study, the impact of metformin on the radiosensitivity of colorectal cancer cells, and the potential mechanisms of action of metformin-mediated radiosensitisation were investigated. Metformin treatment was demonstrated to significantly radiosensitise both radiosensitive and radioresistant colorectal cancer cells in vitro. Transcriptomic and functional analysis demonstrated metformin-mediated alterations to energy metabolism, mitochondrial function, cell cycle distribution and progression, cell death and antioxidant levels in colorectal cancer cells. Using ex vivo models, metformin treatment significantly inhibited oxidative phosphorylation and glycolysis in treatment naïve rectal cancer biopsies, without affecting the real-time metabolic profile of non-cancer rectal tissue. Importantly, metformin treatment differentially altered the protein secretome of rectal cancer tissue when compared to non-cancer rectal tissue. Together these data highlight the potential utility of metformin as an anti-metabolic radiosensitiser in rectal cancer.

Why Metformin Should Not Be Used as an Oxidative Phosphorylation Inhibitor in Cancer Patients

BACKGROUND

Preclinical studies have suggested that metformin exerts antitumor effects on various types of cancers. However, the results of human clinical trials have been inconsistent.

SUMMARY

Metformin is widely considered to be a prime example of a clinically relevant compound that inhibits oxidative phosphorylation (OXPHOS). However, the efficacy of metformin in inhibiting OXPHOS in cancer patients remains uncertain. The available evidence suggests that the plasma concentration of metformin remains within the micromolar range when administered at therapeutic doses. While millimolar concentrations are necessary to inhibit complex I activity in isolated mitochondria, there is no evidence supporting the idea that metformin accumulates within the mitochondria. Metformin exerts a modest effect on the adenosine diphosphate to adenosine triphosphate (ATP) ratio, resulting in AMP-activated protein kinase activation, which promotes ATP-generating catabolic pathways and restores cellular energy balance.

KEY MESSAGES

The value of metformin as an OXPHOS inhibitor for cancer treatment is debatable, and caution should be exercised while using metformin for this purpose.

Synthesis and biological evaluation of novel pyrazole amides as potent mitochondrial complex I inhibitors

Targeting mitochondrial complex I (CI) is emerging as an attractive anticancer strategy, and CI inhibitor IACS-010759 has achieved breakthrough success. However, the narrow therapeutic index of IACS-010759 seriously hinders its further application. In this study, a series of novel pyrazole amides were designed and optimized based on IACS-010759, and their potential CI inhibitory effects were biologically evaluated. Among them, the maximum tolerated dose (MTD) values of SCAL-255 (compound 5q) and SCAL-266 (compound 6f) were 68 mg/kg, which was nearly 10 times that of IACS-010759 (6 mg/kg), showing good safety. In addition, SCAL-255 and SCAL-266 significantly inhibited the proliferation of HCT116 and KG-1 cells in vitro and exerted satisfactory inhibitory activity against KG-1 cells in vivo. These results suggested that the optimized compounds might serve as promising CI inhibitors against oxidative phosphorylation (OXPHOS)-dependent cancer, which merits further study.

Metformin ameliorates BMP2 induced adipocyte-like property in breast cancer cells

Neighboring adipocytes of tumor cells/cancer associated adipocytes supply many factors and fatty acids as fuel to cancer cells for inducing cancer progression and development. Epithelial breast cancer cells also differentiate into several cell types to meet various demands. This study reports that breast cancer cells exhibit inherent adipocyte-like property which is further enhanced in presence of BMP2. Antidiabetic metformin inhibits BMP2 induced adipocyte-like potential in breast cancer cells. Interestingly, breast cancer cells not only show lipid accumulation but also have ability to release lipid content. Thus, this study centers around the presence of the adipocyte cell-like property in breast cancer cells, the significance of BMP2 and metformin that may be explored in designing therapeutics against breast cancer.

The development and benefits of metformin in various diseases

Metformin has been used for the treatment of type II diabetes mellitus for decades due to its safety, low cost, and outstanding hypoglycemic effect clinically. The mechanisms underlying these benefits are complex and still not fully understood. Inhibition of mitochondrial respiratory-chain complex I is the most described downstream mechanism of metformin, leading to reduced ATP production and activation of AMP-activated protein kinase (AMPK). Meanwhile, many novel targets of metformin have been gradually discovered. In recent years, multiple pre-clinical and clinical studies are committed to extend the indications of metformin in addition to diabetes. Herein, we summarized the benefits of metformin in four types of diseases, including metabolic associated diseases, cancer, aging and age-related diseases, neurological disorders. We comprehensively discussed the pharmacokinetic properties and the mechanisms of action, treatment strategies, the clinical application, the potential risk of metformin in various diseases. This review provides a brief summary of the benefits and concerns of metformin, aiming to interest scientists to consider and explore the common and specific mechanisms and guiding for the further research. Although there have been countless studies of metformin, longitudinal research in each field is still much warranted.

Potential Role of the mTORC1-PGC1α-PPARα Axis under Type-II Diabetes and Hypertension in the Human Heart

Type-2 diabetes (T2DM) and arterial hypertension (HTN) are major risk factors for heart failure. Importantly, these pathologies could induce synergetic alterations in the heart, and the discovery of key common molecular signaling may suggest new targets for therapy. Intraoperative cardiac biopsies were obtained from patients with coronary heart disease and preserved systolic function, with or without HTN and/or T2DM, who underwent coronary artery bypass grafting (CABG). Control (n = 5), HTN (n = 7), and HTN + T2DM (n = 7) samples were analysed by proteomics and bioinformatics. Additionally, cultured rat cardiomyocytes were used for the analysis (protein level and activation, mRNA expression, and bioenergetic performance) of key molecular mediators under stimulation of main components of HTN and T2DM (high glucose and/or fatty acids and angiotensin-II). As results, in cardiac biopsies, we found significant alterations of 677 proteins and after filtering for non-cardiac factors, 529 and 41 were changed in HTN-T2DM and in HTN subjects, respectively, against the control. Interestingly, 81% of proteins in HTN-T2DM were distinct from HTN, while 95% from HTN were common with HTN-T2DM. In addition, 78 factors were differentially expressed in HTN-T2DM against HTN, predominantly downregulated proteins of mitochondrial respiration and lipid oxidation. Bioinformatic analyses suggested the implication of mTOR signaling and reduction of AMPK and PPARα activation, and regulation of PGC1α, fatty acid oxidation, and oxidative phosphorylation. In cultured cardiomyocytes, an excess of the palmitate activated mTORC1 complex and subsequent attenuation of PGC1α-PPARα transcription of β-oxidation and mitochondrial electron chain factors affect mitochondrial/glycolytic ATP synthesis. Silencing of PGC1α further reduced total ATP and both mitochondrial and glycolytic ATP. Thus, the coexistence of HTN and T2DM induced higher alterations in cardiac proteins than HTN. HTN-T2DM subjects exhibited a marked downregulation of mitochondrial respiration and lipid metabolism and the mTORC1-PGC1α-PPARα axis might account as a target for therapeutical strategies.

A triple-drug combination induces apoptosis in cervical cancer-derived cell lines

Introduction

Cervical cancer is a worldwide health problem due to the number of deaths caused by this neoplasm. In particular, in 2020, 30,000 deaths of this type of tumor were reported in Latin America. Treatments used to manage patients diagnosed in the early stages have excellent results as measured by different clinical outcomes. Existing first-line treatments are not enough to avoid cancer recurrence, progression, or metastasis in locally advanced and advanced stages. Therefore, there is a need to continue with the proposal of new therapies. Drug repositioning is a strategy to explore known medicines as treatments for other diseases. In this scenario, drugs used in other pathologies that have antitumor activity, such as metformin and sodium oxamate, are analyzed.

Methods

In this research, we combined the drugs metformin and sodium oxamate with doxorubicin (named triple therapy or TT) based on their mechanism of action and previous investigation of our group against three CC cell lines.

Results

Through flow cytometry, Western blot, and protein microarray experiments, we found TT-induced apoptosis on HeLa, CaSki, and SiHa through the caspase 3 intrinsic pathway, including the critical proapoptotic proteins BAD, BAX, cytochrome-C, and p21. In addition, mTOR and S6K phosphorylated proteins were inhibited in the three cell lines. Also, we show an anti-migratory activity of the TT, suggesting other targets of the drug combination in the late CC stages.

Discussion

These results, together with our former studies, conclude that TT inhibits the mTOR pathway leading to cell death by apoptosis. Our work provides new evidence of TT against cervical cancer as a promising antineoplastic therapy.

Metabolism-based targeting of MYC via MPC-SOD2 axis-mediated oxidation promotes cellular differentiation in group 3 medulloblastoma

Group 3 medulloblastoma (G3 MB) carries the worst prognosis of all MB subgroups. MYC oncoprotein is elevated in G3 MB tumors; however, the mechanisms that support MYC abundance remain unclear. Using metabolic and mechanistic profiling, we pinpoint a role for mitochondrial metabolism in regulating MYC. Complex-I inhibition decreases MYC abundance in G3 MB, attenuates the expression of MYC-downstream targets, induces differentiation, and prolongs male animal survival. Mechanistically, complex-I inhibition increases inactivating acetylation of antioxidant enzyme SOD2 at K68 and K122, triggering the accumulation of mitochondrial reactive oxygen species that promotes MYC oxidation and degradation in a mitochondrial pyruvate carrier (MPC)-dependent manner. MPC inhibition blocks the acetylation of SOD2 and oxidation of MYC, restoring MYC abundance and self-renewal capacity in G3 MB cells following complex-I inhibition. Identification of this MPC-SOD2 signaling axis reveals a role for metabolism in regulating MYC protein abundance that has clinical implications for treating G3 MB.

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.

Targeting the Host Mitochondria as a Novel Human Cytomegalovirus Antiviral Strategy

Human cytomegalovirus (HCMV) exploits host mitochondrial function to promote viral replication. HCMV gene products have been described to directly interact and alter functional or structural aspects of host mitochondria. Current antivirals against HCMV, such as ganciclovir and letermovir, are designed against viral targets. Concerns with the current antivirals include toxicity and viral resistance. Targeting host mitochondrial function is a promising alternative or complimentary antiviral approach as (1) drugs targeting host mitochondrial function interact with host targets, minimizing viral resistance, and (2) host mitochondrial metabolism plays key roles in HCMV replication. This review describes how HCMV alters mitochondrial function and highlights pharmacological targets that can be exploited for novel antiviral development.

Metformin induces mitochondrial fission and reduces energy metabolism by targeting respiratory chain complex I in hepatic stellate cells to reverse liver fibrosis

The activation and proliferation of hepatic stellate cells (HSCs) are critical processes for the treatment of liver fibrosis. It is necessary to identify effective drugs for the treatment of liver fibrosis and elucidate their mechanisms of action. Metformin can inhibit HSCs; however, no systematic studies demonstrating the effects of metformin on mitochondria in HSCs have been reported. This study demonstrated that metformin induces mitochondrial fission by phosphorylating AMPK/DRP1 (S616) in HSCs to decrease the expression of α-SMA and collagen. Additionally, metformin repressed the total ATP production rate, especially the production rate of ATP produced through mitochondrial oxidative phosphorylation, by inhibiting the enzymatic activity of complex I. Further analysis revealed that metformin strongly constrained the transcription of mitochondrial genes (ND1-ND6 and ND4L) that encode the core subunits of respiratory chain I. Upregulation of the mRNA expression of HK2 and GLUT1 slightly enhanced glycolysis. Additionally, metformin increased mitochondrial DNA (mtDNA) copy number to suppress the proliferation and activation of HSCs, indicating that mtDNA copy number can alter the fate of HSCs. In conclusion, metformin can induce mitochondrial fragmentation and low-level energy metabolism in HSCs, thereby suppressing HSCs activation and proliferation to reverse liver fibrosis.

Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes diagnosed after metformin-triggered stroke-like episodes

A 40-year-old man with sensorineural hearing loss and diabetes mellitus was hospitalized with acute-onset impaired consciousness and clumsiness in his left hand. He had been taking metformin for 4 months. A neurological examination revealed confusion and weakness in the left upper limb. Increased lactate levels were detected in the serum and cerebrospinal fluid. Magnetic resonance imaging revealed lesions in the right parietal and bilateral temporal lobes with a lactate peak in magnetic resonance spectroscopy. Finally, we made a genetic diagnosis of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes based on the detection of m.3243A>G. It is well-known that metformin should not be administered in patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes because metformin inhibits mitochondrial function and triggers stroke-like episodes. However, our patient was diagnosed with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes after metformin administration. Thus, we encourage physicians to exercise caution in the prescription of metformin in patients with short stature, sensorineural hearing loss, or young-onset diabetes mellitus because these patients may have undiagnosed mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes.

Metformin Impacts Human Syncytiotrophoblast Mitochondrial Function from Pregnancies Complicated by Obesity and Gestational Diabetes Mellitus in a Sexually Dimorphic Manner

Maternal obesity and gestational diabetes mellitus (GDM) are associated with placental dysfunction, small for gestational age (SGA) offspring, and programming of adult-onset disease. We examine how metformin, commonly used to treat type A2 GDM, affects placental metabolism as well as mitochondrial content and function. Syncytiotrophoblasts (STBs) were prepared from placentas of male and female fetuses collected at term cesarean section from lean (pre-pregnancy BMI < 25), obese (BMI > 30), and obese A2GDM women. Metformin treatment (0.001–10 mM) of STB caused no change in non-mitochondrial respiration but significant concentration-dependent (1 and 10 mM) decreases in basal, maximal, and ATP-linked respiration and spare capacity. Respiration linked to proton leak was significantly increased in STB of male A2GDM placentas at low metformin concentrations. Metformin concentrations ≥1 mM increased glycolysis in STB from placentas from lean women, but only improved glycolytic capacity in female STB. Whereas metformin had little effect on superoxide generation from male STB of any group, it gave a concentration-dependent decrease in superoxide generation from female STB of lean and obese women. Fewer mitochondria were observed in STB from obese women and male STB from lean women with increasing metformin concentration. Metformin affects STB mitochondrial function in a sexually dimorphic manner but at concentrations above those reported in maternal circulation (approximately 0.01 mM) in women treated with metformin for GDM.

Targeting Mitochondrial Metabolic Reprogramming as a Potential Approach for Cancer Therapy

Abnormal energy metabolism is a characteristic of tumor cells, and mitochondria are important components of tumor metabolic reprogramming. Mitochondria have gradually received the attention of scientists due to their important functions, such as providing chemical energy, producing substrates for tumor anabolism, controlling REDOX and calcium homeostasis, participating in the regulation of transcription, and controlling cell death. Based on the concept of reprogramming mitochondrial metabolism, a range of drugs have been developed to target the mitochondria. In this review, we discuss the current progress in mitochondrial metabolic reprogramming and summarized the corresponding treatment options. Finally, we propose mitochondrial inner membrane transporters as new and feasible therapeutic targets.

Effects of imeglimin on mitochondrial function, AMPK activity, and gene expression in hepatocytes

Imeglimin is a recently launched antidiabetic drug structurally related to metformin. To provide insight into the pharmacological properties of imeglimin, we investigated its effects on hepatocytes and compared them with those of metformin. The effects of imeglimin on mitochondrial function in HepG2 cells or mouse primary hepatocytes were examined with an extracellular flux analyzer and on gene expression in HepG2 cells by comprehensive RNA-sequencing analysis. The effects of the drug on AMPK activity in HepG2 cells, mouse primary hepatocytes, and mouse liver were also examined. Treatment of HepG2 cells or mouse primary hepatocytes with imeglimin reduced the oxygen consumption rate coupled to ATP production. Imeglimin activated AMPK in these cells whereas the potency was smaller than metformin. Bolus administration of imeglimin in mice also activated AMPK in the liver. Whereas the effects of imeglimin and metformin on gene expression in HepG2 cells were similar overall, the expression of genes encoding proteins of mitochondrial respiratory complex III and complex I was upregulated by imeglimin but not by metformin. Our results suggest that imeglimin and metformin exert similar pharmacological effects on mitochondrial respiration, AMPK activity, and gene expression in cultured hepatocytes, whereas the two drugs differ in their effects on the expression of certain genes related to mitochondrial function.

Data-dependent and -independent acquisition lipidomics analysis reveals the tissue-dependent effect of metformin on lipid metabolism

Introduction

Despite the well-recognized health benefits, the mechanisms and site of action of metformin remains elusive. Metformin-induced global lipidomic changes in plasma of animal models and human subjects have been reported. However, there is a lack of systemic evaluation of metformin-induced lipidomic changes in different tissues. Metformin uptake requires active transporters such as organic cation transporters (OCTs), and hence, it is anticipated that metformin actions are tissue-dependent. In this study, we aim to characterize metformin effects in non-diabetic male mice with a special focus on lipidomics analysis. The findings from this study will help us to better understand the cell-autonomous (direct actions in target cells) or non-cell-autonomous (indirect actions in target cells) mechanisms of metformin and provide insights into the development of more potent yet safe drugs targeting a particular organ instead of systemic metabolism for metabolic regulations without major side effects.

Objectives

To characterize metformin-induced lipidomic alterations in different tissues of non-diabetic male mice and further identify lipids affected by metformin through cell-autonomous or systemic mechanisms based on the correlation between lipid alterations in tissues and the corresponding in-tissue metformin concentrations.

Methods

Lipids were extracted from tissues and plasma of male mice treated with or without metformin in drinking water for 12 days and analyzed using MS/MS scan workflow (hybrid mode) on LC-Orbitrap Exploris 480 mass spectrometer using biologically relevant lipids-containing inclusion list for data-independent acquisition (DIA), named as BRI-DIA workflow followed by data-dependent acquisition (DDA), to maximum the coverage of lipids and minimize the negative effect of stochasticity of precursor selection on experimental consistency and reproducibility.

Results

Lipidomics analysis of 6 mouse tissues and plasma using MS/MS combining BRI-DIA and DDA allowed a systemic evaluation of lipidomic changes induced by metformin in different tissues. We observed that 1) the degrees of lipidomic changes induced by metformin treatment overly correlated with tissue concentrations of metformin; 2) the impact on lysophosphorylcholine and cardiolipins was positively correlated with tissue concentrations of metformin, while neutral lipids such as triglycerides did not correlate with the corresponding tissue metformin concentrations.

Conclusion

The data collected in this study from non-diabetic mice with 12-day metformin treatment suggest that the overall metabolic effect of metformin is positively correlated with tissue concentrations and the effect on individual lipid subclass is via both cell-autonomous mechanisms (cardiolipins and lysoPC) and non-cell-autonomous mechanisms (triglycerides).

Metformin improves fish sperm quality by regulating glucose uptake capacity during in vitro storage

A suitable additive for fish sperm storage in vitro is necessary for artificial reproduction. In this study, we evaluated the effects of different concentrations (100, 200, 400, and 800 µmol/L) of metformin (Met) on Schizothorax prenanti and Onychostoma macrolepis sperm under storage in vitro for 72 h. Compared with the control group, 400 µmol/L Met was more effective at improving the quality and fertilization capacity of S. prenanti sperm by increasing the adenosine triphosphate (ATP) content within the sperm. Further study found that Met stabilized the ATP level by enhancing the glucose uptake in S. prenanti sperm, and this effect might be associated with the activation of AMP-activated protein kinase (AMPK) in sperm. In this study, we also found that glucose could be absorbed by the sperm of S. prenanti, which was mainly accumulated in the midpiece of S. prenanti sperm, where mitochondria were located. In addition, Compound C significantly inhibited the beneficial effects of Met on the quality and glucose uptake capacity of S. prenanti sperm by inhibiting AMPK phosphorylation. These results revealed that AMPK played an important role in vitro sperm storage, and Met maintained ATP content and increased the storage time of S. prenanti sperm in vitro for 72 h, possibly due to Met enhanced glucose uptake capacity of sperm by activating AMPK. Similarly, the beneficial effects of Met on S. prenanti sperm were also found in O. macrolepis sperm, suggesting that Met may hold great promise for the practice of storing fish in vitro.

Metformin: A Promising Antidiabetic Medication for Cancer Treatment

Metformin is a widely used drug in patients with type 2 diabetes mellitus. Metformin inhibits hepatic gluconeogenesis and increases glucose utilization in peripheral tissues. In recent years, several studies have shown that metformin is a potential therapeutic agent against cancer, alone or combined with other anticancer treatments. Metformin mainly activates the AMPK complex and regulates intracellular energy status, inhibiting the mitochondrial respiratory chain complex I and reducing the production of reactive oxygen species. Other anticancer targets of metformin are specific transcription factors inhibiting cell proliferation, promoting apoptosis and reducing drug resistance. In addition, metformin modulates tumor cells' response to anticancer treatments, favoring the activity of T cells. In diabetic patients, metformin reduces the occurrence of cancer and improves the prognosis and efficacy of anticancer treatments. In this review, we provided a comprehensive perspective of metformin as an anticancer drug.

Evaluation of Genotoxicity and Toxicity of Annona muricata L. Seeds and In Silico Studies

Cancer is a multifactorial organic dysfunction for which great efforts are being devoted in searching for new treatments and therapeutic adjuvants. Annona muricata is a fruit that has promising activity against several types of cancer, as it contains acetogenins, the metabolite group associated with this action. Thus, the objective of this study was to evaluate, in experimental models, the toxic behavior of an extract and fraction rich in acetogenins from A. muricata seeds and study the acetogenin, Annonacin, in silico. Phytochemical characterization was made by thin layer chromatography, spectroscopy in the infrared region and nuclear magnetic resonance. Toxicity was evaluated by tests of Allium cepa and Artemia salina, and in silico studies using the SwissDock servers DockThor, PharmMapper, ADMETLab, PreADME, Osiris and ProTox. The extract and fraction showed genotoxic activity against meristematic cells of A. cepa, reducing the mitotic index; however, the extract produced great deleterious effects on the system, even causing cell necrosis. In A. Saline, the extract was more toxic than the fraction, but both samples were considered toxic. Annonacin was effectively linked to complex I, and presented different activities regarding toxicity. Thus, the results of this study are promising, highlighting the anticancer potential of acetogenins.

Targeting cancer-specific metabolic pathways for developing novel cancer therapeutics

Cancer is a heterogeneous disease characterized by various genetic and phenotypic aberrations. Cancer cells undergo genetic modifications that promote their proliferation, survival, and dissemination as the disease progresses. The unabated proliferation of cancer cells incurs an enormous energy demand that is supplied by metabolic reprogramming. Cancer cells undergo metabolic alterations to provide for increased energy and metabolite requirement; these alterations also help drive the tumor progression. Dysregulation in glucose uptake and increased lactate production via "aerobic glycolysis" were described more than 100 years ago, and since then, the metabolic signature of various cancers has been extensively studied. However, the extensive research in this field has failed to translate into significant therapeutic intervention, except for treating childhood-ALL with amino acid metabolism inhibitor L-asparaginase. Despite the growing understanding of novel metabolic alterations in tumors, the therapeutic targeting of these tumor-specific dysregulations has largely been ineffective in clinical trials. This chapter discusses the major pathways involved in the metabolism of glucose, amino acids, and lipids and highlights the inter-twined nature of metabolic aberrations that promote tumorigenesis in different types of cancer. Finally, we summarise the therapeutic interventions which can be used as a combinational therapy to target metabolic dysregulations that are unique or common in blood, breast, colorectal, lung, and prostate cancer.

Metformin Acutely Mitigates Oxidative Stress in Human Atrial Tissue: A Pilot Study in Overweight Non-Diabetic Cardiac Patients

Metformin, the first-line drug in type 2 diabetes mellitus, elicits cardiovascular protection also in obese patients via pleiotropic effects, among which the anti-oxidant is one of the most investigated. The aim of the present study was to assess whether metformin can acutely mitigate oxidative stress in atrial tissue harvested from overweight non-diabetic patients. Right atrial appendage samples were harvested during open-heart surgery and used for the evaluation of reactive oxygen species (ROS) production by means of confocal microscopy (superoxide anion) and spectrophotometry (hydrogen peroxide). Experiments were performed after acute incubation with metformin (10 µM) in the presence vs. absence of angiotensin II (AII, 100 nM), lipopolysaccharide (LPS, 1 μg/mL), and high glucose (Gluc, 400 mg/dL). Stimulation with AII, LPS, and high Gluc increased ROS production. The magnitude of oxidative stress correlated with several echocardiographic parameters. Metformin applied in the lowest therapeutic concentration (10 µM) was able to decrease ROS generation in stimulated but also non-stimulated atrial samples. In conclusion, in a pilot group of overweight non-diabetic cardiac patients, acute incubation with metformin at a clinically relevant dose alleviated oxidative stress both in basal conditions and conditions that mimicked the activation of the renin-angiotensin-aldosterone system, acute inflammation, and uncontrolled hyperglycemia.

Mechanism Underlying Metformin Action and Its Potential to Reduce Gastric Cancer Risk

Diabetes mellitus is associated with a high risk of developing gastric cancer (GC). Metformin, which is conventionally used to treat type 2 diabetes, induces AMP-activated protein kinase signaling and suppresses gluconeogenesis. Recent studies have reported that metformin is associated with beneficial effects in cancer prevention and treatment owing to its anti-tumor effects. This makes metformin a potential medication for GC therapy. However, contradicting reports have emerged regarding the efficacy of metformin in reducing the risk of GC. This review summarizes the impact of metformin on mitigating GC risk by analyzing clinical databases. The mechanism underlying the anti-tumor effect of metformin on GC is also discussed.

Metformin: Activation of 5′ AMP-activated protein kinase and its emerging potential beyond anti-hyperglycemic action

Metformin is a plant-based drug belonging to the class of biguanides and is known to treat type-2 diabetes mellitus (T2DM). The drug, combined with controlling blood glucose levels, improves the body’s response to insulin. In addition, trials have identified the cardioprotective potential of metformin in the diabetic population receiving the drug. Activation of 5′ AMP-activated protein kinase (AMPK) is the major pathway for these potential beneficial effects of metformin. Historically, much emphasis has been placed on the potential indications of metformin beyond its anti-diabetic use. This review aims to appraise other potential uses of metformin primarily mediated by the activation of AMPK. We also discuss various mechanisms, other than AMPK activation, by which metformin could produce beneficial effects for different conditions. Databases including PubMed/MEDLINE and Embase were searched for literature relevant to the review’s objective. Reports from both research and review articles were considered. We found that metformin has diverse effects on the human body systems. It has been shown to exert anti-inflammatory, antioxidant, cardioprotective, metabolic, neuroprotective, anti-cancer, and antimicrobial effects and has now even been identified as effective against SARS-CoV-2. Above all, the AMPK pathway has been recognized as responsible for metformin’s efficiency and effectiveness. Owing to its extensive potential, it has the capability to become a part of treatment regimens for diseases apart from T2DM.

Continuous extracorporeal clearance in metformin-associated lactic acidosis and metformin-induced lactic acidosis: a systematic review

INTRODUCTION

Metformin poisoning with lactic acidosis is an uncommon yet clinically serious condition related to the inhibition of normal aerobic metabolism. Toxicity may occur after an acute overdose although it is much more common after a systemic insult, such as acute kidney injury, in the setting of chronic use. Hemodialysis is currently the preferred extracorporeal treatment modality (Grade 1D evidence) although some patients may be too hemodynamically unstable to tolerate it. Continuous renal replacement therapy is considered an alternative if hemodialysis is unavailable but an evaluation of survival amongst this specific treatment class is lacking.

OBJECTIVES

To assess overall survival and provide an updated review of the toxicokinetic elimination parameters of patients receiving continuous renal replacement therapy for metformin poisoning.

METHODS

A comprehensive search was performed using the EMBASE and MEDLINE libraries from inception until November 30, 2021. Data was extracted and findings were summarized. Toxicokinetic parameters were analyzed and confirmed for accuracy when data permitted.

RESULTS

Eighty-three reports met inclusion criteria. These consisted of only low-quality evidence including 75 case reports, four case series, and four descriptive retrospective reviews. Overall survival among patients suffering from metformin toxicity who received continuous extracorporeal treatment was 85.8%. When stratified between metformin-induced lactic acidosis and metformin-associated lactic acidosis, survival was 75.0% and 87.4%, respectively. Available continuous renal replacement therapy toxicokinetic parameters were quite heterogeneous. Errors in previously published toxicokinetic calculations were noted in only two instances. The overall average and median peak metformin concentrations were 70.5 mg/L and 41.9 mg/L, respectively. The average and median extracorporeal clearance rates were 39.0 mL/min and 42.1 mL/min (range 9.0-58.7 mL/min). The average and median elimination half-life parameters were 27.5 h and median 23.0 h. Elimination half-life ranged from seven to 74 h. There was no meaningful relationship between peak metformin concentration and continuous extracorporeal treatment half-life at lower concentrations, though at very high concentrations (over 200 mg/L), there was a trend towards a half-life below 20 h. There is insufficient data to robustly evaluate overall survival in relation to the extracorporeal clearance rate. Finally, there was no relevant relationship between maximal lactate concentration and survival, nor nadir pH and survival, for patients with either type of metformin toxicity.

CONCLUSIONS

This retrospective systematic analysis of published cases treating metformin related lactic acidosis with continuous renal replacement therapy notes an overall slightly greater survival percentage compared to previous publications of individuals requiring any modality of renal replacement therapy. Because of publication bias, these results should be interpreted with caution and serve as hypothesis generating for future research. Prospective study focusing on the most clinically meaningful endpoint - survival - will help elucidate if continuous modalities are non-inferior to intermittent hemodialysis in metformin toxicity.

The role of AMP-activated protein kinase in GVHD-causing T cells

Allogeneic stem cell transplantation is a curative therapy for multiple hematologic disorders. However, this life-saving procedure is often complicated by acute graft-versus-host disease (GVHD), where donor T cells attack tissues in the recipient's skin, liver, and gastrointestinal tract. Previous research has demonstrated that GVHD-causing T cells undergo significant metabolic reprogramming during disease pathogenesis, with an increased reliance on oxidative metabolism. This dependence makes metabolic modulation a potential approach to treat and/or prevent GVHD. Here, we provide an overview on the metabolic changes adopted by allogeneic T cells during disease initiation, highlighting the role played by AMP-activated protein kinase (AMPK) and identifying ways in which these insights might be leveraged to therapeutic advantage clinically.