Pavlovic Kasja, Krako Jakovljevic Nina, Isakovic Andjelka M, Ivanovic Tijana, Markovic Ivanka, Lalic Nebojsa M
Clinic for Endocrinology, Diabetes and Metabolic Diseases, University Clinical Center of Serbia, Belgrade, Serbia.
Faculty of Medicine, Institute of Medical and Clinical Biochemistry, University of Belgrade, Belgrade, Serbia.
Front Pharmacol. 2022 Jul 6;13:930308. doi: 10.3389/fphar.2022.930308. eCollection 2022.
Metformin is an oral antidiabetic agent that has been widely used in clinical practice for over 60 years, and is currently the most prescribed antidiabetic drug worldwide. However, the molecular mechanisms of metformin action in different tissues are still not completely understood. Although metformin-induced inhibition of mitochondrial respiratory chain Complex I and activation of AMP-activated protein kinase have been observed in many studies, published data is inconsistent. Furthermore, metformin concentrations used for studies and their pharmacological relevance are a common point of debate. The aim of this study was to explore the effects of different metformin concentrations on energy metabolism and activity of relevant signaling pathways in C2C12 muscle cells . In order to determine if therapeutic metformin concentrations have an effect on skeletal muscle cells, we used micromolar metformin concentrations (50 µM), and compared the effects with those of higher, millimolar concentrations (5 mM), that have already been established to affect mitochondrial function and AMPK activity. We conducted all experiments in conditions of high (25 mM) and low glucose (5.5 mM) concentration, in order to discern the role of glucose availability on metformin action. According to our results, micromolar metformin treatment did not cause Complex I inhibition nor AMPK activation. Also, cells cultured in low glucose medium were more sensitive to Complex I inhibition, mitochondrial membrane depolarization and AMPK activation by millimolar metformin, but cells cultured in high glucose medium were more prone to induction of ROS production. In conclusion, even though suprapharmacological metformin concentrations cause Complex I inhibition and AMPK activation in skeletal muscle cells , therapeutic concentrations cause no such effect. This raises the question if these mechanisms are relevant for therapeutic effects of metformin in skeletal muscle.
二甲双胍是一种口服抗糖尿病药物，已在临床实践中广泛应用60多年，目前是全球处方量最大的抗糖尿病药物。然而，二甲双胍在不同组织中的作用分子机制仍未完全明确。尽管许多研究观察到二甲双胍可抑制线粒体呼吸链复合体I并激活AMP激活的蛋白激酶，但已发表的数据并不一致。此外，用于研究的二甲双胍浓度及其药理学相关性也是一个常见的争论点。本研究的目的是探讨不同浓度二甲双胍对C2C12肌肉细胞能量代谢及相关信号通路活性的影响。为了确定治疗浓度的二甲双胍是否对骨骼肌细胞有影响，我们使用了微摩尔浓度的二甲双胍（50 μM），并将其效果与已证实可影响线粒体功能和AMPK活性的更高的毫摩尔浓度（5 mM）进行比较。我们在高糖（25 mM）和低糖（5.5 mM）浓度条件下进行了所有实验，以了解葡萄糖可利用性对二甲双胍作用的影响。根据我们的结果，微摩尔浓度的二甲双胍处理并未导致复合体I抑制或AMPK激活。此外，在低糖培养基中培养的细胞对毫摩尔浓度二甲双胍引起的复合体I抑制、线粒体膜去极化和AMPK激活更敏感，但在高糖培养基中培养的细胞更容易诱导ROS产生。总之，尽管超药理浓度的二甲双胍会导致骨骼肌细胞中的复合体I抑制和AMPK激活，但治疗浓度并不会产生这种效果。这就提出了一个问题，即这些机制是否与二甲双胍在骨骼肌中的治疗作用相关。
