Intracerebroventricular metformin decreases body weight but has pro-oxidant effects and decreases survival

Metformin acts as a dual glucose regulator in mouse brain

Aims: Metformin improves glucose regulation through various mechanisms in the periphery. Our previous study revealed that oral intake of metformin activates several brain regions, including the hypothalamus, and directly activates hypothalamic S6 kinase in mice. In this study, we aimed to identify the direct effects of metformin on glucose regulation in the brain. Materials and methods: We investigated the role of metformin in peripheral glucose regulation by directly administering metformin intracerebroventricularly in mice. The effect of centrally administered metformin (central metformin) on peripheral glucose regulation was evaluated by oral or intraperitoneal glucose, insulin, and pyruvate tolerance tests. Hepatic gluconeogenesis and gastric emptying were assessed to elucidate the underlying mechanisms. Liver-specific and systemic sympathetic denervation were performed. Results: Central metformin improved the glycemic response to oral glucose load in mice compared to that in the control group, and worsened the response to intraperitoneal glucose load, indicating its dual role in peripheral glucose regulation. It lowered the ability of insulin to decrease serum glucose levels and worsened the glycemic response to pyruvate load relative to the control group. Furthermore, it increased the expression of hepatic G6pc and decreased the phosphorylation of STAT3, suggesting that central metformin increased hepatic glucose production. The effect was mediated by sympathetic nervous system activation. In contrast, it induced a significant delay in gastric emptying in mice, suggesting its potent role in suppressing intestinal glucose absorption. Conclusion: Central metformin improves glucose tolerance by delaying gastric emptying through the brain-gut axis, but at the same time worsens it by increasing hepatic glucose production via the brain-liver axis. However, with its ordinary intake, central metformin may effectively enhance its glucose-lowering effect through the brain-gut axis, which could surpass its effect on glucose regulation via the brain-liver axis.

Hormonal Regulation of Oxidative Phosphorylation in the Brain in Health and Disease

The developing and adult brain is a target organ for the vast majority of hormones produced by the body, which are able to cross the blood–brain barrier and bind to their specific receptors on neurons and glial cells. Hormones ensure proper communication between the brain and the body by activating adaptive mechanisms necessary to withstand and react to changes in internal and external conditions by regulating neuronal and synaptic plasticity, neurogenesis and metabolic activity of the brain. The influence of hormones on energy metabolism and mitochondrial function in the brain has gained much attention since mitochondrial dysfunctions are observed in many different pathological conditions of the central nervous system. Moreover, excess or deficiency of hormones is associated with cell damage and loss of function in mitochondria. This review aims to expound on the impact of hormones (GLP-1, insulin, thyroid hormones, glucocorticoids) on metabolic processes in the brain with special emphasis on oxidative phosphorylation dysregulation, which may contribute to the formation of pathological changes. Since the brain concentrations of sex hormones and neurosteroids decrease with age as well as in neurodegenerative diseases, in parallel with the occurrence of mitochondrial dysfunction and the weakening of cognitive functions, their beneficial effects on oxidative phosphorylation and expression of antioxidant enzymes are also discussed.

Early metformin treatment improves pancreatic function and prevents metabolic dysfunction in early overfeeding male rats at adulthood

NEW FINDINGS

What is the central question of this study? Studies reported the efficacy of metformin as a promising drug for preventing or treating of metabolic diseases. Nutrient stresses during neonatal life increase long-term risk for cardiometabolic diseases. Can early metformin treatment prevent the malprogramming effects of early overfeeding? What is the main finding and its importance? Neonatal metformin treatment prevented early overfeeding-induced metabolic dysfunction in adult rats. Inhibition of early hyperinsulinaemia and adult hyperphagia might be associated with decreased metabolic disease risk in these animals. Therefore, interventions during infant development offer a key area for future research to identify potential strategies to prevent the long-term metabolic diseases. We suggest that metformin is a potential tool for intervention.

ABSTRACT

Given the need for studies investigating the possible long-term effects of metformin use at crucial stages of development, and taking into account the concept of metabolic programming, the present work aimed to evaluate whether early metformin treatment might program rats to resist the development of adult metabolic dysfunctions caused by overnutrition during the neonatal suckling phase. Wistar rats raised in small litters (SLs, three pups per dam) and normal litters (NLs, nine pups per dam) were used as models of early overfeeding and normal feeding, respectively. During the first 12 days of suckling, animals from SL and NL groups received metformin, whereas the controls received saline injections. Food intake and body weight were monitored from weaning until 90 days of age, when biometric and biochemical parameters were assessed. The metformin treatment decreased insulin concentrations in pups from SL groups, and as adults, these animals showed improvements in glucose tolerance, insulin sensitivity, body weight gain, white fat pad stores and food intake. Low-glucose insulinotrophic effects were observed in pancreatic islets from both NL and SL groups. These results indicate that early postnatal treatment with metformin inhibits early overfeeding-induced metabolic dysfunctions in adult rats.

Mild Impairment of Mitochondrial OXPHOS Promotes Fatty Acid Utilization in POMC Neurons and Improves Glucose Homeostasis in Obesity

Mitochondrial oxidative phosphorylation (OXPHOS) and substrate utilization critically regulate the function of hypothalamic proopiomelanocortin (POMC)-expressing neurons. Here, we demonstrate that inactivation of apoptosis-inducing factor (AIF) in POMC neurons mildly impairs mitochondrial respiration and decreases firing of POMC neurons in lean mice. In contrast, under diet-induced obese conditions, POMC-Cre-specific inactivation of AIF prevents obesity-induced silencing of POMC neurons, translating into improved glucose metabolism, improved leptin, and insulin sensitivity, as well as increased energy expenditure in AIFΔPOMC mice. On a cellular level, AIF deficiency improves mitochondrial morphology, facilitates the utilization of fatty acids for mitochondrial respiration, and increases reactive oxygen species (ROS) formation in POMC neurons from obese mice, ultimately leading to restored POMC firing upon HFD feeding. Collectively, partial impairment of mitochondrial function shifts substrate utilization of POMC neurons from glucose to fatty acid metabolism and restores their firing properties, resulting in improved systemic glucose and energy metabolism in obesity.

Activation of AMPK by metformin improves withdrawal signs precipitated by nicotine withdrawal

Cigarette smoking is the leading cause of preventable disease and death in the United States, with more persons dying from nicotine addiction than any other preventable cause of death. Even though smoking cessation incurs multiple health benefits, the abstinence rate remains low with current medications. Here we show that the AMP-activated protein kinase (AMPK) pathway in the hippocampus is activated following chronic nicotine use, an effect that is rapidly reversed by nicotine withdrawal. Increasing pAMPK levels and, consequently, downstream AMPK signaling pharmacologically attenuate anxiety-like behavior following nicotine withdrawal. We show that metformin, a known AMPK activator in the periphery, reduces withdrawal symptoms through a mechanism dependent on the presence of the AMPKα subunits within the hippocampus. This study provides evidence of a direct effect of AMPK modulation on nicotine withdrawal symptoms and suggests central AMPK activation as a therapeutic target for smoking cessation.

Hypothalamic circuits regulating appetite and energy homeostasis: pathways to obesity

The ‘obesity epidemic’ represents a major global socioeconomic burden that urgently calls for a better understanding of the underlying causes of increased weight gain and its associated metabolic comorbidities, such as type 2 diabetes mellitus and cardiovascular diseases. Improving our understanding of the cellular basis of obesity could set the stage for the development of new therapeutic strategies. The CNS plays a pivotal role in the regulation of energy and glucose homeostasis. Distinct neuronal cell populations, particularly within the arcuate nucleus of the hypothalamus, sense the nutrient status of the organism and integrate signals from peripheral hormones including pancreas-derived insulin and adipocyte-derived leptin to regulate calorie intake, glucose metabolism and energy expenditure. The arcuate neurons are tightly connected to other specialized neuronal subpopulations within the hypothalamus, but also to various extrahypothalamic brain regions, allowing a coordinated behavioral response. This At a Glance article gives an overview of the recent knowledge, mainly derived from rodent models, regarding the CNS-dependent regulation of energy and glucose homeostasis, and illustrates how dysregulation of the neuronal networks involved can lead to overnutrition and obesity. The potential impact of recent research findings in the field on therapeutic treatment strategies for human obesity is also discussed.

Summary: This at a glance article gives an overview of the recent knowledge mainly derived from rodent models regarding the CNS-dependent regulation of energy and glucose homeostasis, and depicts how dysregulation of the involved neuronal networks promotes overnutrition and obesity.

Hypothalamic Mitochondrial Dysfunction as a Target in Obesity and Metabolic Disease

Mitochondria are important organelles for the adaptation to energy demand that play a central role in bioenergetics metabolism. The mitochondrial architecture and mitochondrial machinery exhibits a high degree of adaptation in relation to nutrient availability. On the other hand, its disruption markedly affects energy homeostasis. The brain, more specifically the hypothalamus, is the main hub that controls energy homeostasis. Nevertheless, until now, almost all studies in relation to mitochondrial dysfunction and energy metabolism have focused in peripheral tissues like brown adipose tissue, muscle, and pancreas. In this review, we highlight the relevance of the hypothalamus and the influence on mitochondrial machinery in its function as well as its consequences in terms of alterations in both energy and metabolic homeostasis.

Metformin, the aspirin of the 21st century: its role in gestational diabetes mellitus, prevention of preeclampsia and cancer, and the promotion of longevity

Metformin is everywhere. Originally introduced in clinical practice as an antidiabetic agent, its role as a therapeutic agent is expanding to include treatment of prediabetes mellitus, gestational diabetes mellitus, and polycystic ovarian disease; more recently, experimental studies and observations in randomized clinical trials suggest that metformin could have a place in the treatment or prevention of preeclampsia. This article provides a brief overview of the history of metformin in the treatment of diabetes mellitus and reviews the results of metaanalyses of metformin in gestational diabetes mellitus as well as the treatment of obese, non-diabetic, pregnant women to prevent macrosomia. We highlight the results of a randomized clinical trial in which metformin administration in early pregnancy did not reduce the frequency of large-for-gestational-age infants (the primary endpoint) but did decrease the frequency of preeclampsia (a secondary endpoint). The mechanisms by which metformin may prevent preeclampsia include a reduction in the production of antiangiogenic factors (soluble vascular endothelial growth factor receptor-1 and soluble endoglin) and the improvement of endothelial dysfunction, probably through an effect on the mitochondria. Another potential mechanism whereby metformin may play a role in the prevention of preeclampsia is its ability to modify cellular homeostasis and energy disposition, mediated by rapamycin, a mechanistic target. Metformin has a molecular weight of 129 Daltons and therefore readily crosses the placenta. There is considerable evidence to suggest that this agent is safe during pregnancy. New literature on the role of metformin as a chemotherapeutic adjuvant in the prevention of cancer and in prolonging life and protecting against aging is reviewed briefly. Herein, we discuss the mechanisms of action and potential benefits of metformin.

Hyperactive mTORC1 signaling is unaffected by metformin treatment in aged skeletal muscle

INTRODUCTION

Appropriate activation of growth signaling pathways, specifically mammalian target of rapamycin complex 1 (mTORC1), is central to muscle mass and metabolism. The goal of these studies was to examine the effects of metformin on mTORC1 signaling in aged skeletal muscle in an attempt to normalize growth signaling.

METHODS

Aged (23m) and young (3m) male mice were fed a low fat diet without or with 0.5% metformin for up to 8 weeks, then mTORC1-related signaling was examined in the plantar flexor complex.

RESULTS

Metformin had no significant effect on lowering body weight or muscle mass in aged animals, nor altered p70 S6 Kinase 1 (S6K1) and 4E-binding protein 1 (4E-BP1) phosphorylation. However, it significantly (P < 0.05) reduced body weight and lowered S6K1 and rpS6 phosphorylation in the young.

CONCLUSIONS

Collectively, these data suggest metformin is ineffective at normalizing growth signaling in aged skeletal muscle.