The Role and Mechanism of Metformin in Inflammatory Diseases

Metformin is a classical drug used to treat type 2 diabetes. With the development of research on metformin, it has been found that metformin also has several advantages aside from its hypoglycemic effect, such as anti-inflammatory, anti-aging, anti-cancer, improving intestinal flora, and other effects. The prevention of inflammation is critical because chronic inflammation is associated with numerous diseases of considerable public health. Therefore, there has been growing interest in the role of metformin in treating various inflammatory conditions. However, the precise anti-inflammatory mechanisms of metformin were inconsistent in the reported studies. Thus, this review aims to summarize various currently known possible mechanisms of metformin involved in inflammatory diseases and provide references for the clinical application of metformin.

Lysophosphatidylcholine induces adenosine release from macrophages via TRPM7-mediated mitochondrial activation

Even though macrophages have the potential to harm tissues through excessive release of inflammatory mediators, they play protective roles to maintain tissue integrity. In this study, we hypothesized that lysophosphatidylcholine (LPC), via G2A and A2B receptors, puts brakes on macrophages by the induction of adenosine release which could contribute to termination of inflammation. Mechanistically, LPC-induced PGE2 production followed by the activation of cAMP/protein kinase A (PKA) pathway which results in the activation of LKB1/AMPK signaling pathway leading to increasing Mg2+ influx concomitantly with an increase in mitochondrial membrane potential (MMP, Δψm) and ATP production. Then, ATP is converted to adenosine intracellularly followed by efflux via ENT1. In a parallel pathway, LPC-induced elevation of cytosolic calcium was essential for adenosine release, and Ca2+/calmodulin signaling cooperated with PKA to regulate ENT1 permeation to adenosine. Pharmacological blockade of TRPM7 and antisense treatment suppressed LPC-induced adenosine release and magnesium influx in bone marrow-derived macrophages (BMDMs). Moreover, LPC suppressed LPS-induced phosphorylation of connexin-43, which may counteract TLR4-mediated inflammatory response. Intriguingly, we found LPC increased netrin-1 production from BMDMs. Netrin-1 induces anti-inflammatory signaling via A2B receptor. In the presence of adenosine deaminase which removes adenosine in the medium, the chemotaxis of macrophages toward LPC was significantly increased. Hypoxia and metabolic acidosis are usually developed in a variety of inflammatory situations such as sepsis. We found LPC augmented hypoxia- or acidosis-induced adenosine release from BMDMs. These results provide evidence of LPC-induced brake-like action on macrophages by adenosine release via cellular magnesium signaling.

Metformin in cardiovascular diabetology: a focused review of its impact on endothelial function

As a first-line treatment for diabetes, the insulin-sensitizing biguanide, metformin, regulates glucose levels and positively affects cardiovascular function in patients with diabetes and cardiovascular complications. Endothelial dysfunction (ED) represents the primary pathological change of multiple vascular diseases, because it causes decreased arterial plasticity, increased vascular resistance, reduced tissue perfusion and atherosclerosis. Caused by “biochemical injury”, ED is also an independent predictor of cardiovascular events. Accumulating evidence shows that metformin improves ED through liver kinase B1 (LKB1)/5'-adenosine monophosphat-activated protein kinase (AMPK) and AMPK-independent targets, including nuclear factor-kappa B (NF-κB), phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt), endothelial nitric oxide synthase (eNOS), sirtuin 1 (SIRT1), forkhead box O1 (FOXO1), krüppel-like factor 4 (KLF4) and krüppel-like factor 2 (KLF2). Evaluating the effects of metformin on endothelial cell functions would facilitate our understanding of the therapeutic potential of metformin in cardiovascular diabetology (including diabetes and its cardiovascular complications). This article reviews the physiological and pathological functions of endothelial cells and the intact endothelium, reviews the latest research of metformin in the treatment of diabetes and related cardiovascular complications, and focuses on the mechanism of action of metformin in regulating endothelial cell functions.

Short-term Effects of Metformin on Cardiac and Peripheral Blood Cells Following Cecal Ligation and Puncture-induced Sepsis

AIM OF THE STUDY

Sepsis has well-documented inflammatory effects on cardiovascular and blood cells. This study is designed to investigate potential anti-inflammatory effects of metformin on cardiac and blood cells 12 and 24 h following cecal ligation and puncture (CLP)-induced sepsis.

METHODS

For the purpose of this study, 36 male Wistar rats were divided into six groups: two groups underwent CLP, two groups underwent CLP and received metformin, and two groups only received sham operations. 12 h later, 18 rats (half of rats in each of the three aforementioned groups) were sacrificed and cardiac and blood cells were harvested. Subsequently, 12 h later, the rest of the rats were euthanatized. In all harvested blood and cardiac cells, oxidative stress indicators, antioxidant properties, count of blood cells, neutrophil infiltration, percentage of weight loss and pathological assessment were conducted.

RESULTS

In our experiment, metformin elevated antioxidant levels, improved function of blood cells and percentage of weight loss. Moreover, in the groups which received metformin, oxidative stress and neutrophil infiltration markers were decreased significantly. Moreover, pathological investigations of cardiac cell injury were reduced in the metformin group.

CONCLUSIONS

Our findings suggest that in CLP induced sepsis model, metformin can improve the function of blood and cardiac cells through alleviating inflammation, improvement of anti-inflammation properties, and enhancement of blood profile, and all these effects are more pronounced after 24 h in comparison with 12 h after induction of sepsis.

An investigation into the pleiotropic activity of metformin. A glimpse of haemostasis

The most characteristic features of type 2 diabetes mellitus (T2DM) are hyperglycaemia and insulin resistance, however, patients with T2DM are at higher risk of cardiovascular disease (CVD) and atherosclerosis. Diabetes, frequently related to metabolic and vascular impairments, is also associated with thrombosis, increased blood coagulation and an imbalance between coagulation and fibrinolysis. Metformin is the most often used oral glucose-lowering agent; its beneficial properties include lowering insulin resistance, weight reduction and cardioprotection. Available data suggest that the advantageous properties of metformin stem from its favourable effects on endothelium, and anti-oxidative and anti-inflammatory properties. This paper reviews the favourable impact of metformin on endothelial function, with particular emphasis on the release of endogenous molecules modulating the state of the vascular endothelium and coagulation. It also summarizes the present knowledge on the influence of metformin on platelet activity and plasma haemostasis, including clot formation, stabilization and fibrinolysis. Its findings confirm that metformin should constitute first line therapy of T2DM subjects; however, more comprehensive methodical studies are required to discover the full potential of this drug.

Differential Regulation of LPS-Mediated VE-Cadherin Disruption in Human Endothelial Cells and the Underlying Signaling Pathways: A Mini Review

Endothelial cells lining the inner vascular wall form a monolayer that contributes to the selective permeability of endothelial barrier. This selective permeability is mainly regulated by an endothelium-specific adherens junctional protein, known as vascular endothelial-cadherin (VE-cadherin). In endothelial cells, the adherens junction comprises of VE-cadherin and its associated adhesion molecules such as p120, α-catenin, and β-catenin, in which α-catenin links cytoplasmic tails of VE-cadherin to actin cytoskeleton through β-catenin. Proinflammatory stimuli such as lipopolysaccharide (LPS) are capable of attenuating vascular integrity through the disruption of VE-cadherin adhesion in endothelial cells. To date, numerous studies demonstrated the disruption of adherens junction as a result of phosphorylation-mediated VE-cadherin disruption. However, the outcomes from these studies were inconsistent and non-conclusive as different cell fractions were used to examine the effect of LPS on the disruption of VE-cadherin. By using Western Blot, some studies utilized total protein lysate and reported decreased protein expression while some studies reported unchanged expression. Other studies which used membrane and cytosolic fractions of protein extract demonstrated decreased and increased VE-cadherin expression, respectively. Despite the irregularities, the results of immunofluorescence staining are consistent with the formation of intercellular gap. Besides that, the overall underlying disruptive mechanisms of VE-cadherin remain largely unknown. Therefore, this mini review will focus on different experiment approaches in terms of cell fractions used in different human endothelial cell studies, and relate these differences to the results obtained in Western blot and immunofluorescence staining in order to give some insights into the overall differential regulatory mechanisms of LPS-mediated VE-cadherin disruption and address the discrepancy in VE-cadherin expression.

A Review on The Protective Effects of Metformin in Sepsis-Induced Organ Failure

Despite advances in sepsis management, it remains a major intensive-care-unit (ICU) concern. From new prospective, positive effects of metformin, such as anti-oxidant and anti-inflammatory properties are considered potentially beneficial properties for management of septic patients. This article reviewed the potential ameliorative effects of metformin in sepsis-induced organ failure. Information were retrieved from PubMed, Scopus, Embase, and Google Scholar. Multi-organ damage, oxidative stress, inflammatory cytokine stimulation, and altered circulation are hallmarks of sepsis. Metformin exerts its effect via adenosine monophosphate-activated protein kinase (AMPK) activation. It improves sepsis-induced organ failure by inhibiting the production of reactive oxygen species (ROS) and pro-inflammatory cytokines, preventing the activation of transcription factors related to inflammation, decreasing neutrophil accumulation/infiltration, and also maintaining mitochondrial membrane potential. Studies reported the safety of metformin therapeutic doses, with no evidence of lactic acidosis, in septic patients.

Endothelial function and dysfunction: Impact of metformin

Cardiovascular and metabolic diseases remain the leading cause of morbidity and mortality worldwide. Endothelial dysfunction is a key player in the initiation and progression of cardiovascular and metabolic diseases. Current evidence suggests that the anti-diabetic drug metformin improves insulin resistance and protects against endothelial dysfunction in the vasculature. Hereby, we provide a timely review on the protective effects and molecular mechanisms of metformin in preventing endothelial dysfunction and cardiovascular and metabolic diseases.