Diabetes Volume 64, June 2015
1907
Yuichi Hattori,1 Kohshi Hattori,2 and Toshio Hayashi3
Pleiotropic Benefits of Metformin: Macrophage Targeting Its Anti-inflammatory Mechanisms Diabetes 2015;64:1907–1909 | DOI: 10.2337/db15-0090
(PMA). THP-1 cells are one of the most widely used models for investigating monocytic differentiation and subsequent biological functions of differentiated cells (11), although immortalized THP-1 cells may not always be of sufficient relevance to human macrophages. PMA treatment, which activates protein kinase C, can induce a greater degree of differentiation in THP-1 cells, as reflected by changes in morphology, adherence, phagocytosis, expression of surface markers, or the release of prostaglandin E and tumor necrosis factor-a (TNF-a) associated with macrophage differentiation (11,12). The differentiation of monocytes into macrophages is a pivotal step in the early immune response: In response to injury or inflammatory stimuli, migration of circulating monocytes into the inflamed tissues is accelerated, and subsequent differentiation into macrophages occurs rapidly. Upon differentiation, this maturation process allows the cells to actively participate in the inflammatory and immune responses. Thus, the ability of metformin to inhibit PMA-induced monocyte-to-macrophage differentiation in THP-1 cells discovered by Vasamsetti et al. (10) may serve as a novel mechanism underlying its anti-inflammatory actions. It must be kept in mind, however, that the inhibition of PMA-induced monocyte-tomacrophage differentiation was observed at a dose range of 0.5–2 mmol/L, which is much higher than the peak serum concentrations under clinically relevant dosing conditions (13). The study by Vasamsetti et al. (10) confirms that the inhibition by metformin of monocyte-to-macrophage differentiation was AMPK dependent. Furthermore, AMPKmediated signaling events in THP-1 cells are found to be downregulated in the presence of external stimuli, such as PMA and LPS (10). These observations suggest that AMPK may play a regulatory role in the differentiation
1Department of Molecular and Medical Pharmacology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan 2Anesthesiology and Pain Relief Center, University of Tokyo Hospital, Tokyo, Japan 3Department of Geriatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan
Corresponding author: Yuichi Hattori, [email protected]. © 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See accompanying article, p. 2028.
COMMENTARY
Metformin is a biguanide family member used in the treatment of type 2 diabetes and one of the most widely prescribed antidiabetes drugs. This drug increases the peripheral uptake of glucose, decreases hepatic glucose production, and reduces insulin resistance in liver and skeletal muscle. The exact molecular mechanisms responsible for its effect on glucose homeostasis are still not completely understood but may include the triggering of the AMPK pathway (1), although it has been indicated that the acute inhibitory effects of high doses of metformin on hepatic gluconeogenesis are independent of AMPK activation (2). Interestingly, experimental and clinical studies have shed new light on an array of potential benefits of metformin, not only in the treatment of diabetes. Notably, accumulating evidence suggests that the cardiovascular protective role of metformin is largely beyond its hypoglycemic action and is ascribed to pleiotropic effects (3–5). Previous studies have described the anti-inflammatory effects of metformin on different types of cells, including human vascular endothelial cells and smooth muscle cells (6,7). Recent reports have also demonstrated that metformin can attenuate lipopolysaccharide (LPS)-induced or oxidized LDL–induced proinflammatory responses in monocytes and macrophages (8,9). Although the crucial mechanisms underlying the anti-inflammatory effects of metformin remain to be fully elucidated, the current concept of atherosclerosis as an inflammatory disorder may imply that such anti-inflammatory properties could contribute, at least in part, to the anti-atherosclerotic effects of metformin beyond glucose lowering. In this issue of Diabetes, Vasamsetti et al. (10) demonstrate that metformin inhibits monocyte-to-macrophage differentiation in THP-1 cells, a human monocytic leukemia cell line, stimulated with phorbol myristate acetate
1908
Diabetes Volume 64, June 2015
Commentary
of monocytes into macrophages in response to stimulus inducers. Caution is required, however, in the AMPK activator/inhibitor used in this study because compound C can generate many off-target effects through inhibition of different protein kinases (14) and AICAR is a nonspecific activator of AMPK and has the potential to activate other AMP-sensitive enzymes (15). In this regard, it would have been better to use A-769662, a potent and reversible activator of AMPK that mimics the function of AMP on AMPKb-1 by allosteric activation and the inhibition of dephosphorylation of AMPK (16). Vasamsetti et al. (10) propose that metformin inhibits monocyte-to-macrophage differentiation by reducing STAT3 activity due to increased AMPK activation (Fig. 1). Indeed, metformin inhibited PMA-induced STAT3 phosphorylation in THP-1 cells in a concentration-dependent manner. Moreover, the STAT3 inhibitor stattic not only inhibited monocyte-to-macrophage differentiation but also reduced production of proinflammatory cytokines, such as TNF-a, in PMA-stimulated THP-1 cells. It should be noted, however, that the role of STAT3 in cytokine production by macrophages does not achieve a general agreement. Previous reports have shown that mice lacking STAT3deficient macrophages are characterized by excessive cytokine release (17,18).
Figure 1—A working model of the macrophage-targeting mechanism for the anti-inflammatory effects of metformin and its potentially beneficial outcomes. Based on the work of Vasamsetti et al. (10), the figure depicts how metformin can inhibit monocyte-tomacrophage differentiation. The anti-inflammatory mechanisms where macrophages are targeted in their differentiation/polarization may potentially contribute to the benefits of metformin in the prevention and/or treatment of vascular injury, atherosclerosis, certain cancers, and insulin resistance.
Macrophages exhibit marked phenotype heterogeneity. Phenotypically polarized macrophages are now generally termed proinflammatory M1 and anti-inflammatory M2. On the other hand, based on expression levels of Ly6C (Gr-1), an inflammatory monocyte marker, mouse monocytes subsets are grouped as Ly6C+ monocytes and Ly6C2 monocytes (19). In general terms, both human classical and intermediate monocytes exhibit inflammatory properties reminiscent of murine Ly6C+ monocytes, and human nonclassical monocytes show patrolling properties similar to those of murine Ly6C2 monocytes. Both human and mouse inflammatory monocytes express high levels of the chemokine receptor CCR2 and low levels of the chemokine receptor CX3CR1, whereas patrolling monocytes display a reverse pattern (20). The Ly6C+ monocyte–derived cells have been compared with M1 macrophages, while, in vascular inflammation, Ly6C2 monocytes are recruited to tissues and are more likely to differentiate into M2 macrophages, which secrete anti-inflammatory cytokines and contribute to tissue repair (21). Accordingly, how metformin can modulate the differentiation of Ly6C2 monocytes into M2 macrophages remains the subject of ongoing interesting studies. Previous work using murine bone marrow–derived macrophages and human monocyte-derived macrophages has revealed that activation of the AMPK signaling pathway suppresses proinflammatory responses and promotes macrophage polarization to an anti-inflammatory functional phenotype (22). The study by Vasamsetti et al. (10), together with the above report (22), suggests that metformin displays anti-inflammatory potentials at least in part by modulating macrophage differentiation and polarization. Macrophages are now emerging as an important player in the pathogenesis of insulin resistance. Thus, insulin resistance can result from a combination of altered functions of insulin-targeted tissues, adipocytes, skeletal muscles, and liver and the accumulation of inflammatory macrophages that are major sources of proinflammatory cytokines, such as TNF-a (23). Furthermore, several lines of evidence indicate that the presence of macrophages in tumors are more likely to contribute to cancer progression (24), and metformin may have a potential use in the treatment of different cancers in several clinical trials under way. Conclusively, the anti-inflammatory benefits of metformin targeting macrophage differentiation/polarization may help explain its usable value for prevention and/or treatment of vascular injury, atherosclerosis, certain cancers, and insulin resistance (Fig. 1). Duality of Interest. No potential conflicts of interest relevant to this article were reported.
References 1. Fullerton MD, Galic S, Marcinko K, et al. Single phosphorylation sites in Acc1 and Acc2 regulate lipid homeostasis and the insulin-sensitizing effects of metformin. Nat Med 2013;19:1649–1654
diabetes.diabetesjournals.org
2. Foretz M, Hébrard S, Leclerc J, et al. Metformin inhibits hepatic gluconeogenesis in mice independently of the LKB1/AMPK pathway via a decrease in hepatic energy state. J Clin Invest 2010;120:2355–2369 3. UK Prospective Diabetes Study (UKPDS) Group. Effect of intensive bloodglucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). Lancet 1998;352:854–865 4. Selvin E, Bolen S, Yeh HC, et al. Cardiovascular outcomes in trials of oral diabetes medications: a systematic review. Arch Intern Med 2008;168:2070– 2080 5. Forouzandeh F, Salazar G, Patrushev N, et al. Metformin beyond diabetes: pleiotropic benefits of metformin in attenuation of atherosclerosis. J Am Heart Assoc 2014;3:e001202 6. Hattori Y, Suzuki K, Hattori S, Kasai K. Metformin inhibits cytokine-induced nuclear factor kB activation via AMP-activated protein kinase activation in vascular endothelial cells. Hypertension 2006;47:1183–1188 7. Isoda K, Young JL, Zirlik A, et al. Metformin inhibits proinflammatory responses and nuclear factor-kappaB in human vascular wall cells. Arterioscler Thromb Vasc Biol 2006;26:611–617 8. Arai M, Uchiba M, Komura H, Mizuochi Y, Harada N, Okajima K. Metformin, an antidiabetic agent, suppresses the production of tumor necrosis factor and tissue factor by inhibiting early growth response factor-1 expression in human monocytes in vitro. J Pharmacol Exp Ther 2010;334:206–213 9. Kim J, Kwak HJ, Cha JY, et al. Metformin suppresses lipopolysaccharide (LPS)-induced inflammatory response in murine macrophages via activating transcription factor-3 (ATF-3) induction. J Biol Chem 2014;289:23246–23255 10. Vasamsetti SB, Karnewar S, Kanugula AK, Thatipalli AR, Kumar JM, Kotamraju S. Metformin inhibits monocyte-to-macrophage differentiation via AMPK-mediated inhibition of STAT3 activation: potential role in atherosclerosis. Diabetes 2015;64:2028–2041 11. Tsuchiya S, Kobayashi Y, Goto Y, et al. Induction of maturation in cultured human monocytic leukemia cells by a phorbol diester. Cancer Res 1982;42: 1530–1536
Hattori, Hattori, and Hayashi
1909
12. Schwende H, Fitzke E, Ambs P, Dieter P. Differences in the state of differentiation of THP-1 cells induced by phorbol ester and 1,25-dihydroxyvitamin D3. J Leukoc Biol 1996;59:555–561 13. Tucker GT, Casey C, Phillips PJ, Connor H, Ward JD, Woods HF. Metformin kinetics in healthy subjects and in patients with diabetes mellitus. Br J Clin Pharmacol 1981;12:235–246 14. Bain J, Plater L, Elliott M, et al. The selectivity of protein kinase inhibitors: a further update. Biochem J 2007;408:297–315 15. Towler MC, Hardie DG. AMP-activated protein kinase in metabolic control and insulin signaling. Circ Res 2007;100:328–341 16. Oakhill JS, Scott JW, Kemp BE. Structure and function of AMP-activated protein kinase. Acta Physiol (Oxf) 2009;196:3–14 17. Takeda K, Clausen BE, Kaisho T, et al. Enhanced Th1 activity and development of chronic enterocolitis in mice devoid of Stat3 in macrophages and neutrophils. Immunity 1999;10:39–49 18. Alonzi T, Newton IP, Bryce PJ, et al. Induced somatic inactivation of STAT3 in mice triggers the development of a fulminant form of enterocolitis. Cytokine 2004;26:45–56 19. Geissmann F, Jung S, Littman DR. Blood monocytes consist of two principal subsets with distinct migratory properties. Immunity 2003;19:71–82 20. Italiani P, Boraschi D. From monocytes to M1/M2 macrophages: phenotypical vs. functional differentiation. Front Immunol 2014;5:514 21. Woollard KJ, Geissmann F. Monocytes in atherosclerosis: subsets and functions. Nat Rev Cardiol 2010;7:77–86 22. Sag D, Carling D, Stout RD, Suttles J. Adenosine 59-monophosphateactivated protein kinase promotes macrophage polarization to an antiinflammatory functional phenotype. J Immunol 2008;181:8633–8641 23. Olefsky JM, Glass CK. Macrophages, inflammation, and insulin resistance. Annu Rev Physiol 2010;72:219–246 24. Solinas G, Germano G, Mantovani A, Allavena P. Tumor-associated macrophages (TAM) as major players of the cancer-related inflammation. J Leukoc Biol 2009;86:1065–1073
1907
Yuichi Hattori,1 Kohshi Hattori,2 and Toshio Hayashi3
Pleiotropic Benefits of Metformin: Macrophage Targeting Its Anti-inflammatory Mechanisms Diabetes 2015;64:1907–1909 | DOI: 10.2337/db15-0090
(PMA). THP-1 cells are one of the most widely used models for investigating monocytic differentiation and subsequent biological functions of differentiated cells (11), although immortalized THP-1 cells may not always be of sufficient relevance to human macrophages. PMA treatment, which activates protein kinase C, can induce a greater degree of differentiation in THP-1 cells, as reflected by changes in morphology, adherence, phagocytosis, expression of surface markers, or the release of prostaglandin E and tumor necrosis factor-a (TNF-a) associated with macrophage differentiation (11,12). The differentiation of monocytes into macrophages is a pivotal step in the early immune response: In response to injury or inflammatory stimuli, migration of circulating monocytes into the inflamed tissues is accelerated, and subsequent differentiation into macrophages occurs rapidly. Upon differentiation, this maturation process allows the cells to actively participate in the inflammatory and immune responses. Thus, the ability of metformin to inhibit PMA-induced monocyte-to-macrophage differentiation in THP-1 cells discovered by Vasamsetti et al. (10) may serve as a novel mechanism underlying its anti-inflammatory actions. It must be kept in mind, however, that the inhibition of PMA-induced monocyte-tomacrophage differentiation was observed at a dose range of 0.5–2 mmol/L, which is much higher than the peak serum concentrations under clinically relevant dosing conditions (13). The study by Vasamsetti et al. (10) confirms that the inhibition by metformin of monocyte-to-macrophage differentiation was AMPK dependent. Furthermore, AMPKmediated signaling events in THP-1 cells are found to be downregulated in the presence of external stimuli, such as PMA and LPS (10). These observations suggest that AMPK may play a regulatory role in the differentiation
1Department of Molecular and Medical Pharmacology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan 2Anesthesiology and Pain Relief Center, University of Tokyo Hospital, Tokyo, Japan 3Department of Geriatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan
Corresponding author: Yuichi Hattori, [email protected]. © 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See accompanying article, p. 2028.
COMMENTARY
Metformin is a biguanide family member used in the treatment of type 2 diabetes and one of the most widely prescribed antidiabetes drugs. This drug increases the peripheral uptake of glucose, decreases hepatic glucose production, and reduces insulin resistance in liver and skeletal muscle. The exact molecular mechanisms responsible for its effect on glucose homeostasis are still not completely understood but may include the triggering of the AMPK pathway (1), although it has been indicated that the acute inhibitory effects of high doses of metformin on hepatic gluconeogenesis are independent of AMPK activation (2). Interestingly, experimental and clinical studies have shed new light on an array of potential benefits of metformin, not only in the treatment of diabetes. Notably, accumulating evidence suggests that the cardiovascular protective role of metformin is largely beyond its hypoglycemic action and is ascribed to pleiotropic effects (3–5). Previous studies have described the anti-inflammatory effects of metformin on different types of cells, including human vascular endothelial cells and smooth muscle cells (6,7). Recent reports have also demonstrated that metformin can attenuate lipopolysaccharide (LPS)-induced or oxidized LDL–induced proinflammatory responses in monocytes and macrophages (8,9). Although the crucial mechanisms underlying the anti-inflammatory effects of metformin remain to be fully elucidated, the current concept of atherosclerosis as an inflammatory disorder may imply that such anti-inflammatory properties could contribute, at least in part, to the anti-atherosclerotic effects of metformin beyond glucose lowering. In this issue of Diabetes, Vasamsetti et al. (10) demonstrate that metformin inhibits monocyte-to-macrophage differentiation in THP-1 cells, a human monocytic leukemia cell line, stimulated with phorbol myristate acetate
1908
Diabetes Volume 64, June 2015
Commentary
of monocytes into macrophages in response to stimulus inducers. Caution is required, however, in the AMPK activator/inhibitor used in this study because compound C can generate many off-target effects through inhibition of different protein kinases (14) and AICAR is a nonspecific activator of AMPK and has the potential to activate other AMP-sensitive enzymes (15). In this regard, it would have been better to use A-769662, a potent and reversible activator of AMPK that mimics the function of AMP on AMPKb-1 by allosteric activation and the inhibition of dephosphorylation of AMPK (16). Vasamsetti et al. (10) propose that metformin inhibits monocyte-to-macrophage differentiation by reducing STAT3 activity due to increased AMPK activation (Fig. 1). Indeed, metformin inhibited PMA-induced STAT3 phosphorylation in THP-1 cells in a concentration-dependent manner. Moreover, the STAT3 inhibitor stattic not only inhibited monocyte-to-macrophage differentiation but also reduced production of proinflammatory cytokines, such as TNF-a, in PMA-stimulated THP-1 cells. It should be noted, however, that the role of STAT3 in cytokine production by macrophages does not achieve a general agreement. Previous reports have shown that mice lacking STAT3deficient macrophages are characterized by excessive cytokine release (17,18).
Figure 1—A working model of the macrophage-targeting mechanism for the anti-inflammatory effects of metformin and its potentially beneficial outcomes. Based on the work of Vasamsetti et al. (10), the figure depicts how metformin can inhibit monocyte-tomacrophage differentiation. The anti-inflammatory mechanisms where macrophages are targeted in their differentiation/polarization may potentially contribute to the benefits of metformin in the prevention and/or treatment of vascular injury, atherosclerosis, certain cancers, and insulin resistance.
Macrophages exhibit marked phenotype heterogeneity. Phenotypically polarized macrophages are now generally termed proinflammatory M1 and anti-inflammatory M2. On the other hand, based on expression levels of Ly6C (Gr-1), an inflammatory monocyte marker, mouse monocytes subsets are grouped as Ly6C+ monocytes and Ly6C2 monocytes (19). In general terms, both human classical and intermediate monocytes exhibit inflammatory properties reminiscent of murine Ly6C+ monocytes, and human nonclassical monocytes show patrolling properties similar to those of murine Ly6C2 monocytes. Both human and mouse inflammatory monocytes express high levels of the chemokine receptor CCR2 and low levels of the chemokine receptor CX3CR1, whereas patrolling monocytes display a reverse pattern (20). The Ly6C+ monocyte–derived cells have been compared with M1 macrophages, while, in vascular inflammation, Ly6C2 monocytes are recruited to tissues and are more likely to differentiate into M2 macrophages, which secrete anti-inflammatory cytokines and contribute to tissue repair (21). Accordingly, how metformin can modulate the differentiation of Ly6C2 monocytes into M2 macrophages remains the subject of ongoing interesting studies. Previous work using murine bone marrow–derived macrophages and human monocyte-derived macrophages has revealed that activation of the AMPK signaling pathway suppresses proinflammatory responses and promotes macrophage polarization to an anti-inflammatory functional phenotype (22). The study by Vasamsetti et al. (10), together with the above report (22), suggests that metformin displays anti-inflammatory potentials at least in part by modulating macrophage differentiation and polarization. Macrophages are now emerging as an important player in the pathogenesis of insulin resistance. Thus, insulin resistance can result from a combination of altered functions of insulin-targeted tissues, adipocytes, skeletal muscles, and liver and the accumulation of inflammatory macrophages that are major sources of proinflammatory cytokines, such as TNF-a (23). Furthermore, several lines of evidence indicate that the presence of macrophages in tumors are more likely to contribute to cancer progression (24), and metformin may have a potential use in the treatment of different cancers in several clinical trials under way. Conclusively, the anti-inflammatory benefits of metformin targeting macrophage differentiation/polarization may help explain its usable value for prevention and/or treatment of vascular injury, atherosclerosis, certain cancers, and insulin resistance (Fig. 1). Duality of Interest. No potential conflicts of interest relevant to this article were reported.
References 1. Fullerton MD, Galic S, Marcinko K, et al. Single phosphorylation sites in Acc1 and Acc2 regulate lipid homeostasis and the insulin-sensitizing effects of metformin. Nat Med 2013;19:1649–1654
diabetes.diabetesjournals.org
2. Foretz M, Hébrard S, Leclerc J, et al. Metformin inhibits hepatic gluconeogenesis in mice independently of the LKB1/AMPK pathway via a decrease in hepatic energy state. J Clin Invest 2010;120:2355–2369 3. UK Prospective Diabetes Study (UKPDS) Group. Effect of intensive bloodglucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). Lancet 1998;352:854–865 4. Selvin E, Bolen S, Yeh HC, et al. Cardiovascular outcomes in trials of oral diabetes medications: a systematic review. Arch Intern Med 2008;168:2070– 2080 5. Forouzandeh F, Salazar G, Patrushev N, et al. Metformin beyond diabetes: pleiotropic benefits of metformin in attenuation of atherosclerosis. J Am Heart Assoc 2014;3:e001202 6. Hattori Y, Suzuki K, Hattori S, Kasai K. Metformin inhibits cytokine-induced nuclear factor kB activation via AMP-activated protein kinase activation in vascular endothelial cells. Hypertension 2006;47:1183–1188 7. Isoda K, Young JL, Zirlik A, et al. Metformin inhibits proinflammatory responses and nuclear factor-kappaB in human vascular wall cells. Arterioscler Thromb Vasc Biol 2006;26:611–617 8. Arai M, Uchiba M, Komura H, Mizuochi Y, Harada N, Okajima K. Metformin, an antidiabetic agent, suppresses the production of tumor necrosis factor and tissue factor by inhibiting early growth response factor-1 expression in human monocytes in vitro. J Pharmacol Exp Ther 2010;334:206–213 9. Kim J, Kwak HJ, Cha JY, et al. Metformin suppresses lipopolysaccharide (LPS)-induced inflammatory response in murine macrophages via activating transcription factor-3 (ATF-3) induction. J Biol Chem 2014;289:23246–23255 10. Vasamsetti SB, Karnewar S, Kanugula AK, Thatipalli AR, Kumar JM, Kotamraju S. Metformin inhibits monocyte-to-macrophage differentiation via AMPK-mediated inhibition of STAT3 activation: potential role in atherosclerosis. Diabetes 2015;64:2028–2041 11. Tsuchiya S, Kobayashi Y, Goto Y, et al. Induction of maturation in cultured human monocytic leukemia cells by a phorbol diester. Cancer Res 1982;42: 1530–1536
Hattori, Hattori, and Hayashi
1909
12. Schwende H, Fitzke E, Ambs P, Dieter P. Differences in the state of differentiation of THP-1 cells induced by phorbol ester and 1,25-dihydroxyvitamin D3. J Leukoc Biol 1996;59:555–561 13. Tucker GT, Casey C, Phillips PJ, Connor H, Ward JD, Woods HF. Metformin kinetics in healthy subjects and in patients with diabetes mellitus. Br J Clin Pharmacol 1981;12:235–246 14. Bain J, Plater L, Elliott M, et al. The selectivity of protein kinase inhibitors: a further update. Biochem J 2007;408:297–315 15. Towler MC, Hardie DG. AMP-activated protein kinase in metabolic control and insulin signaling. Circ Res 2007;100:328–341 16. Oakhill JS, Scott JW, Kemp BE. Structure and function of AMP-activated protein kinase. Acta Physiol (Oxf) 2009;196:3–14 17. Takeda K, Clausen BE, Kaisho T, et al. Enhanced Th1 activity and development of chronic enterocolitis in mice devoid of Stat3 in macrophages and neutrophils. Immunity 1999;10:39–49 18. Alonzi T, Newton IP, Bryce PJ, et al. Induced somatic inactivation of STAT3 in mice triggers the development of a fulminant form of enterocolitis. Cytokine 2004;26:45–56 19. Geissmann F, Jung S, Littman DR. Blood monocytes consist of two principal subsets with distinct migratory properties. Immunity 2003;19:71–82 20. Italiani P, Boraschi D. From monocytes to M1/M2 macrophages: phenotypical vs. functional differentiation. Front Immunol 2014;5:514 21. Woollard KJ, Geissmann F. Monocytes in atherosclerosis: subsets and functions. Nat Rev Cardiol 2010;7:77–86 22. Sag D, Carling D, Stout RD, Suttles J. Adenosine 59-monophosphateactivated protein kinase promotes macrophage polarization to an antiinflammatory functional phenotype. J Immunol 2008;181:8633–8641 23. Olefsky JM, Glass CK. Macrophages, inflammation, and insulin resistance. Annu Rev Physiol 2010;72:219–246 24. Solinas G, Germano G, Mantovani A, Allavena P. Tumor-associated macrophages (TAM) as major players of the cancer-related inflammation. J Leukoc Biol 2009;86:1065–1073
