Table 2.
Clinical, animal and cellular studies of metformin on macrophages associated with atherosclerotic diseases.
| Functions | Models or subjects | Mechanisms | Results | Conclusions |
|---|---|---|---|---|
| Inflammation | DM patients +metformin(n=498) or + Sulfonylurea(n=172), non-diabetic patients with congestive heart failure+metformin (n=20) or + Placebo (n=13) | ↓neutrophils to lymphocytes (NLR), ↓CCL11 |
↓inflammation in diabetic and non-diabetic patients | The anti-inflammatory effect of metformin has nothing to do with diabetes status. The study may accelerate the study of the effect of metformin in non-diabetic CVD (55). |
| PCOS (n = 83), Controls (n = 39), and PCOS+ metformin (n=21) | ↓ASAA | ↓intima-media | Metformin treatment can reduce serum ASAA in women with PCOS (57). | |
| ARDS mice Metformin (50 mg/kg) Alveolar macrophages (NR8383) cells, metformin (40 μg/mL) |
↓miR-138-5p ↑ SIRT1 ↓p-p38, p-ERK and p-NF-κB |
↓LPS-induced deaths ↓IL-6, IL-1β, IL-17 and TNF-α |
Metformin can reduce the LPS-induced lung damage via decreasing miR-138-5p expression, increasing the expression of its target gene SIRT1 and inhibiting MAPK pathway (58). | |
| LPS treated macrophages, metformin (10 mM) | ↑AMPK, ↓NF-κB |
↓CXCL10 and CXCL11 | Metformin inhibits LPS-stimulated chemokines expression via AMPK and NF-κB signaling pathways (53). | |
| ECs, macrophages and SMCs, Metformin (20 μM) | ↓PI3K-Akt ↓NF-κB |
↓IL-6 and IL-8 | Metformin can block NF-κB by inhibiting the PI3K-Akt pathway, thereby exerting a direct vascular anti-inflammatory effect (54). | |
| HFD fed rabbit, Metformin (200 mg/kg/day) monocytes, macrophages metformin (200 μg/mL) |
↓inflammatory cytokines and adhesion molecules | ↓AS ↓the adhesion of monocytes, inflammatory response of macrophages |
Metformin may inhibit the development of AS via inhibiting macrophage infiltration and inflammation (62). | |
| Inflammation | LPS-stimulated endotoxemia mice, metformin (250 or 500 mg/kg, twice daily), ob/ob mice (250 mg/kg, twice daily) LPS treated macrophages, metformin (0.5, 1, 2, 4 mM) |
↑AMPK and ATF3 NF-κB enrichment on TNF-α and IL-6 promoters caused by LPS were replaced by ATF3 |
↓TNF-α and IL-6 | AMPK activation and induction of ATF3 are potential mechanisms for metformin to exhibit anti-inflammatory effect in macrophages (113). |
| LPS induced macrophages, metformin (10 mM) | ↑AMPK ↓NF-κB |
↓CXCL10 and CXCL11, ↓IL-1 and IL-6 | Metformin reduces LPS-stimulated chemokine expression via AMPK and NF-κB signaling pathways (53). | |
| AGEs induced mouse BMDM Metformin (2μM) |
↑AMPK ↓NF-κB |
↓CD86) (M1 marker), ↑CD206 (M2 marker) and IL-10 |
Metformin partially reduces AGEs- stimulated the inflammatory response of mouse macrophages via AMPK activation and RAGE/NFκB pathway inhibition (114). | |
| HFD fed mice, metformin (150 mg/kg/d) LPS-induced BMDM, metformin (500 µM) |
↑AMPK ↓JNK1 and NF-κB |
↓liver steatosis ↓fat deposition ↓pro-inflammatory cytokines and lipogenic enzymes |
Metformin mainly prevents obesity-related NAFLD by directly reducing liver cell fat deposition and inhibiting the inflammatory response of liver cells and macrophages (115). | |
| Acetaminophen treated mice, metformin (350 mg/kg) HMGB1 treated macrophages, metformin (0.1~10 mM) |
Binds directly to the C-terminal acid tail of HMGB1. | ↓inflammatory response | Metformin inhibits inflammation via reducing the extracellular activity of HMGB1 (116). | |
| Inflammation | Neutrophils from patients with ARDS, metformin (500 µM/L) | ↑ AMPK Neutralization of HMGB1 in BAL fluid |
Neutralization of HMGB1 in BAL fluid or activation of AMPK in macrophages in BAL fluid improved cell swelling and NETs clearance. | Neutralizing HMGB1 or restoring AMPK activity with metformin represents a promising therapeutic strategy to reduce persistent lung inflammation of ARDS (117). |
| LPS-treated mice, metformin (50, 100 mg/kg), LPS-treated macrophages, metformin (1, 5, 10 mM) |
↑ AMPK ↓HMGB1. |
↓serum levels of HMGB1, IL-1β, TNF-α and myeloperoxidase activity in the lung. ↑the survival rate |
Metformin improves the survival rate of the lethal endotoxemia mouse model via inhibiting the release of HMGB1. AMPK activation is one of the mechanisms causing HMGB1 secretion inhibition (118). | |
| Methionine treated mice, Hcy treated macrophages, metformin (12.5, 25 and 50 μM) |
↑CSE expression | ↓levels of Hcy, TNF-α and IL-1β, | Metformin treatment reduces the harmful effects of methionine (63). | |
| Inflammasome | ATP treated macrophages, metformin (2 mM) bacterial sepsis mice, metformin (250 mg/kg) |
↑AMPK ↑inflammasomes |
↑mortality of mice with bacterial sepsis. ↑the activation of systemic inflammasomes (such as increased IL-1β level in blood and liver). |
These results indicate that AMPK signal transduction positively regulates ATP-cuased inflammasome activation and pyrophosphorylation in macrophages (72). |
| oxLDL treated macrophages, metformin (80μM) | ↑AMPK and PP2A, ↓NF-κB | ↓NLRP3 inflammasome | Metformin inhibited expression and activation of NLRP3 in oxLDL-induced macrophages via AMPK and PP2A (71). | |
| Inflammasome | Diabetic mice, Metformin (300 mg/kg/d) | ↓disorder of thioredoxin-1/thioredoxin interacting protein. ↓ROS and NLRP3 inflammasome |
↓metabolic disorders and AS | Metformin can inhibit the NLRP3 inflammasome activation in ApoE-/- mice and inhibit diabetes-accelerated AS, at least in part by activating AMPK and regulating thioredoxin-1/thioredoxin interacting protein (70). |
| Control (n=57), T2DM patients (n=47), Among 47 diabetic patients, 11 patients received metformin(500–1,000 mg/day). | ↑AMPK | ↓the maturation of IL-1β in MDM of T2DM patients | NLRP3 inflammasome is activated in MDM of T2DM patients, and metformin administration helps to regulate the activation of inflammasomes in T2DM (69). | |
| Oxidative stress | Macrophages (shPTEN cells), metformin (5 to 40 mM) | ↓Akt and ROS | ↓iNOS/NO and COX-2/PGE2,
↑apoptosis |
In shPTEN cells, Metformin can reduce the diffusion of inflammatory mediators and cell growth by inhibiting Akt activation and ROS production (78). |
| LPS treated Peripheral blood monocytes, metformin (0.02 and 2 mM) | ↑AMPK ↑ superoxide dismutase, glutathione peroxidase, catalase ↓malondialdehyde |
↓ROS and inflammatory cytokines (such as iNOS) | Metformin can improve diabetes by lowering blood glucose, reducing the oxidative stress, inflammatory cytokines, and inducing phenotypic changes of macrophages (79). | |
| macrophages, metformin (2-5 mM) | ↓Glutathione ↑paraoxonase 2 ↑ cellular ROS |
↓cholesterol content and biosynthesis rate Antioxidants decreased metformin-induced ROS and cancelled the inhibitory effect of cholesterol biosynthesis. |
The inhibitory effect of metformin on cholesterol biosynthesis is at least partially related to metformin-induced ROS in macrophages (81). | |
| macrophages, C2C12 skeletal muscle cells and HCT116 adenocarcinoma cells, Mito-Metformin | ↑calcineurin and Cn-dependent retrograde signaling pathway | ↑ ROS in mitochondria | The retrograde signal induced by Mito-Metformin is through the activation of the Ca2/Cn pathway (82). | |
| Foam cell formation | ApoE-/- mice fed with HFD, metformin(260 mg/kg) | ↑AMPK, ↑ABCA1 and ABCG1 in macrophages, ↑LCAT and SR-B1 in liver. ↑ M2 polarization ↑paraoxonase 1 ↓myeloperoxidase |
↑RCT ↓blood lipids peroxidation, ↓inflammatory cytokines expression ↓atherosclerotic plaque. |
AMPK activators promote the anti-atherosclerotic properties of HDL and attenuate AS (104). |
| 3-DG incubated macrophages, metformin (100 mM) | ↑the glycated HDL-mediated cholesterol efflux Exogenous HDL reduces the expression of ABCG1 mRNA and protein, but glycosylation makes HDL lose this effect. |
Glycated HDL particles cannot effectively act as ABCG1-mediated cholesterol efflux receptors. Metformin may be a drug candidate to improve cholesterol efflux (23). | ||
| LPS and oxLDL induced macrophages Metformin (100 or 200 μM/L) | ↓ ADRP | ↓LDs in the foam cells | Metformin can reduce the formation of THP-1 derived foam cells caused by LPS, decrease the ADRP expression and intracellular lipid accumulation (90). | |
| palmitic acid (PA) treated macrophages, Metformin (100, 250, 500μM) | ↓FOXO1 ↓FABP4 ↑ CPT-1. |
↓lipids accumulation in macrophages | Metformin reduces the lipids accumulation in macrophages via reducing FOXO1-mediated FABP4 transcription (91). | |
| oxLDL treated macrophages, metformin (15 μM) | ↑ABCG1 ↑ outflow of cholesterol to HDL ↑IL-10 secretion |
↓cholesterol accumulation and the formation of foam cell | The study highlights the therapeutic potential of metformin to target macrophage cholesterol efflux, which may reduce foam cell formation (89). | |
| Foam cell formation | ApoE-/- mice, Co-treatment with T317 and metformin (100 mg/day/kg) |
↓macrophages/foam cells in the arterial wall ↑ABCA1/ABCG1. Metformin activates AMPKα and reduces T317-stimulated hepatic LXRα activation and lipogenic gene expression. |
Co-administration increases the stability of the lesion block T317-caused fatty liver |
Co-administration of metformin and T317 can improve AS without activating adipogenesis, which indicates that this combination may be a new method to inhibit AS (92). |
| mouse BMDM and primary human MDMs, metformin (10 μM) | ↑AMPK ↑ATF1. |
Induced heme oxygenase and LXR jointly induce the Mhem phenotype. | Heme (10 μM) activates AMPK, and the downstream ATF1-induced heme oxygenase and LXR jointly induce the Mhem phenotype. (119). | |
| LPS induced macrophages, metformin (1-3 mM) | ↓NF-κB | apoE expression↑ | Metformin is a potential adjuvant in the treatment strategy of AS (120). | |
| HFD fed mice, metformin (250mg/kg) primary hepatocytes, metformin(0.5 mmol/L) |
↓multiple binding sites of phase 2 (transcription repressor) occupancy within ABCG5/8 site | ↑expression of ABCG5/8 and BSEP ↑initial clearance of 3H-cholesteryl ester HDL from the blood. |
Metformin may provide some support for cardiovascular benefits by increasing RCT, and AMPK activation inhibition may mediate anti-atherosclerotic effects by increasing ABCG5/8 expression (121). | |
| M1/M2 polarization | PBMCs were isolate from 30 normal-weight healthy adult volunteers, 30 obese volunteers, 20 obese newly diagnosed diabetic patients, as well as 30 metformin-treated obese diabetic patients. | ↑CD68 marker in obesity and in T2DM. ↓CD11b, CD11c, CD163 and CD169 in T2DM patients ↑TNFα, iNOS, IL-6, CD16, CD36, and CD206 in the T2DM Metformin restored TNFα, iNOS, IL-6, CD11c, CD36, CD169 and CD206 in T2DM patients to levels equivalent to those of lean volunteers. |
PBMCs in T2DM patients express a different pattern of phenotypic markers (represent metabolically activated macrophage (MMe)-like cells), which is not the pattern normally found in M1 or M2-like macrophages, and metformin can reduce circulating MMe-like cells (42). | |
| Olanzapine reated rats, metformin (300 mg/kg/day) | ↓body weight and IR, ↓macrophage polarization and pro-inflammatory factors. |
Metformin may reduce the IR caused by olanzapine by inhibiting the polarization and inflammation of macrophages in white AT (43). | ||
| M1/M2 polarization | HFD fed mice, metformin (300 mg/kg/d) In palmitate stimulated BMDM, metformin (2 mM) |
↑ AMPK, ↓IL-6 and TNF-α ↓CD11c and MCP1 (M1 markers) in AT ↓proportion of M1 macrophages, ↑the proportion of M2 macrophages |
Metformin can regulate the polarization of macrophages to anti-inflammatory M2 and improve low-grade inflammation in obesity by activating AMPK (23). | |
| Obese mice, metformin (300 mg/kg) | ↓SHP-1 and ↑insulin sensitivity. ↑anti-inflammatory macrophages AT |
↓CD80, CD86, TLR2, TLR4, NF-κB, STAT1 and other inflammatory markers ↓inflammation of AT |
Metformin exerts its insulin sensitization effect by inhibiting the activity and expression of SHP-1 (102). | |
| Ldlr-/- hyperlipidemia mice, metformin (in drinking water, 1mg/mL) Mouse BMDM, metformin (10 μM) |
↑AMPK/ATF1 ↑M2 marker genes, ↓ iNOS |
↓atherosclerotic lesions. ↑LXRβ, Hmox1, ApoE, ABCA1, PDGF and IGF1 |
metformin can activate the AMPK-ATF1-M2-like pathway in macrophages. These findings support the clinical trials of metformin in non-diabetic patients with high risk of AS (122). | |
| MCAO mice, metformin (50 mg/kg/day) |
↑ AMPK, microglia/macrophages tend to M2 phenotype |
↑ functional recovery, ↑neurogenesis and angiogenesis |
Chronic metformin treatment after stroke improves functional recovery through AMPK-induced M2 polarization (103). | |
| macrophages with/without LPS, metformin(1, 5, 10 mM) | ↑IL-4, IL-10, arginase 1 (Arg1) and lectin-1 (Mgl1) ↓Notch1, TNF-α, IL-1β and IL-6. |
Metformin regulates the M2 phenotype of RAW264.7 macrophages with/without LPS. The Notch1 signal may play a vital role (23). | ||
| Monocyte differentiation | Forty-four subjects with AMI and T2DM (metformin, n=21; short-acting insulin, n=23) | ↓Akt , | ↓sCD40L level | Metformin therapy in patients with AMI and T2DM can cause a faster decline in sCD40L, which may help improve the prognosis of this cohort (109). |
| Monocyte differentiation | HFD-fed ApoE-/- mice, metformin (260 mg/kg) | ↓CCR2 expression | ↓number of Ly6Chi monocytes in circulation as well as atherosclerotic plaques. | AMPK activation decreases the development of AS induced macrophages accumulation in ApoE-/- mice via reudcing the CCR2 expression, thereby preventing CCR2-induced migration of Ly6Chigh monocytes (123). |
| Ang-II induced ApoE-/- mice, Metformin (100 mg/kg/day) | ↑AMPK, ↓ STAT3 |
↓the infiltration of monocytes, ↓atherosclerotic plaques and aortic aneurysms |
AMPK activators reduce the differentiation of monocytes into macrophages by regulating AMPK-STAT3 axis (40). | |
| Apoptosis | oxLDL treated metformin, macrophages (0.1, 0.3, 0.5, 1 mM) | ↓scavenger receptors, including CD36 and SRA ↓expression of ER stress marker proteins (such as EIF2A and CHOP) ↓oxLDL-induced Δψm loss and cyto-c release. |
↓lipid uptake ↓the apoptosis of macrophages |
Metformin can prevent oxLDL-caused macrophage apoptosis and inhibit lipid uptake of macrophage (111). |
In this table, we describe that metformin plays a role in atherosclerosis by regulating monocyte/macrophage function, including cell function, objects, mechanisms, results and conclusions. ↑Represents increase or activation. ↓Represents to reducion or inhibition. The corresponding abbreviations are as follows: ABCA1, ATP-binding cassette transporter A1; ABCG1, ATP-binding cassette transporter G1;ADRP, adipose differentiation-related protein; AMPK, AMP-activated protein kinase; AGEs, advanced glycation end products; AMI, acute myocardial infarction; Ang-II, angiotensin II; ApoE, apolipoprotein E; ARDS, acute respiratory distress syndrome; ASAA, acute-phase serum amyloid A; AS, atherosclerosis; AT, adipose tissue; ATF3, transcription factor 3; BAL, bronchoalveolar lavage; BM, bone marrow; BMDM, bone marrow-derived macrophages; BSEP, bile salt export pump; CXCL10, C-X-C motif ligand; CCR2, CC chemokine receptor 2; CD, cluster of differentiation; CHOP, C/EBP homologous protein; CSE, cystathionine γ-lyase; COX-2, cyclooxygenase 2;CPT-1, carnitine palmitoyl transferase I; 3-DG, 3-deoxyglucosone; DM, diabetes mellitus; ECs, endothelial cells; EIF2A, eukaryotic translation initiation factor 2A; ERK, extracellular signal-regulated kinase; ER, endoplasmic reticulum; FABP4, fatty acid binding protein 4; FOXO1, forkhead box transcription factor O1; HFD, homocysteine (Hcy,; high-fat diet; HMGB1, high-mobility group box 1; Hmox1, Heme oxygenase 1; H2S, hydrogen sulfide; IGF1, insulin growth factor 1 IL, Interleukin; iNOS, inducible nitric oxide synthase; JNK1, c-Jun N-terminal kinase 1; LCAT, lecithin:cholesterol acyltransferase; Ldlr, low-density lipoprotein receptor; LPS, lipopolysaccharide; LXR, Liver X receptor; MAPK, mitogen activated protein kinase; MCAO, middle cerebral artery occlusion; MCP1, monocyte chemoattractant protein 1; MDMs, monocyte-derived macrophages; Δψm, mitochondrial membrane potential; NAFLD, non-alcoholic fatty liver disease; NETs, neutrophil extracellular traps; NF-κB, nuclear factor-κB nucleotide-binding oligomerisation domain receptor, pyrin domain containing (NLRP)3, the ratio of neutrophils to lymphocytes (NLR), NO, nitric oxide; oxLDL, oxidized low-density lipoprotein; PA, palmitic acid; PBMC, peripheral blood mononuclear cell; PCOS, Polycystic ovary syndrome; PDGF, platelet-derived growth factor; PGE2, prostaglandin E2; PI3K, phosphatidylinositol 3-kinase; AKT, protein kinase B; PMA, phorbol 12-myristate 13-acetate; PTEN, phosphatase and tensin homolog; RAGE, receptor for advanced glycation end products; ROS, reactive oxygen species; SH2, Src homology 2; domain-containing protein tyrosine phosphatase 1 (SHP-1); SIRT1, Sirtuin-1; SMCs, smooth muscle cells; SRA, scavenger receptor class A; SR-B1, scavenger receptor class B type 1; STAT, signal transducer and activator of transcription; TNF-α, tumor necrosis factor-α; TIP47, tail-interacting protein; TLR, Toll-like receptor.