Role of AMP-activated protein kinase in mechanism of metformin action
Metformin is a widely used drug for treatment of type 2 diabetes with no defined cellular mechanism of action. Its glucose-lowering effect results from decreased hepatic glucose production and increased glucose utilization. Metformin’s beneficial effects on circulating lipids have been linked to reduced fatty liver. AMP-activated protein kinase (AMPK) is a major cellular regulator of lipid and glucose metabolism. Here we report that metformin activates AMPK in hepatocytes; as a result, acetyl-CoA carboxylase (ACC) activity is reduced, fatty acid oxidation is induced, and expression of lipogenic enzymes is suppressed. Activation of AMPK by metformin or an adenosine analogue suppresses expression of SREBP-1, a key lipogenic transcription factor. In metformin-treated rats, hepatic expression of SREBP-1 (and other lipogenic) mRNAs and protein is reduced; activity of the AMPK target, ACC, is also reduced. Using a novel AMPK inhibitor, we find that AMPK activation is required for metformin’s inhibitory effect on glucose production by hepatocytes. In isolated rat skeletal muscles, metformin stimulates glucose uptake coincident with AMPK activation. Activation of AMPK provides a unified explanation for the pleiotropic beneficial effects of this drug; these results also suggest that alternative means of modulating AMPK should be useful for the treatment of metabolic disorders.
We thank Shiying Chen for characterizing anti-AMPK Ab’s, Marcie Donnelly for technical support related to animal studies, Mark Fraley for compound synthesis, and Georgianna Harris and Denis McGarry for helpful discussions and intellectual support.
See the related Commentary beginning on page 1105.
- 1. 2000IMS HEALTH’s National Prescription Audit Plus. http://www.ims-global.com.
- 2. Stumvoll M, Nurjhan N, Perriello G, Dailey G, Gerich JEMetabolic effects of metformin in non-insulin-dependent diabetes mellitus. N Engl J Med. 1995;333:550–554.
- 3. Wiernsperger NF, Bailey CJThe antihyperglycaemic effect of metformin: therapeutic and cellular mechanisms. Drugs. 1999;58:31–39.
- 4. Wu MS, et al Effect of metformin on carbohydrate and lipoprotein metabolism in NIDDM patients. Diabetes Care. 1990;13:1–8.
- 5. Schafer G. Biguanides. A review of history, pharmacodynamics and therapy. Diabete Metab. 1983;9:148–163.
- 6. Hundal RS, et al Mechanism by which metformin reduces glucose production in type 2 diabetes. Diabetes. 2000;49:2063–2069.
- 7. Hundal HS, Ramlal T, Reyes R, Leiter LA, Klip ACellular mechanism of metformin action involves glucose transporter translocation from an intracellular pool to the plasma membrane in L6 muscle cells. Endocrinology. 1992;131:1165–1173.
- 8. Galuska D, Nolte LA, Zierath JR, Wallberg-Henriksson HEffect of metformin on insulin-stimulated glucose transport in isolated skeletal muscle obtained from patients with NIDDM. Diabetologia. 1994;37:826–832.
- 9. Lin HZ, et al Metformin reverses fatty liver disease in obese, leptin-deficient mice. Nat Med. 2000;6:998–1003.
- 10. Hardie DG, Carling DThe AMP-activated protein kinase: fuel gauge of the mammalian cell? Eur J Biochem. 1997;246:259–273.
- 11. Winder WW, Hardie DGAMP-activated protein kinase, a metabolic master switch: possible roles in type 2 diabetes. Am J Physiol. 1999;277:E1–E10.
- 12. Hayashi T, Hirshman MF, Kurth EJ, Winder WW, Goodyear LJEvidence for 5′ AMP-activated protein kinase mediation of the effect of muscle contraction on glucose transport. Diabetes. 1998;47:1369–1373.
- 13. Merrill GF, Kurth EJ, Hardie DG, Winder WWAICA riboside increases AMP-activated protein kinase, fatty acid oxidation, and glucose uptake in rat muscle. Am J Physiol. 1997;273:E1107–E1112.
- 14. Goodyear LJAMP-activated protein kinase: a critical signaling intermediary for exercise-stimulated glucose transport? Exerc Sport Sci Rev. 2000;28:113–116.
- 15. Lochhead PA, Salt IP, Walker KS, Hardie DG, Sutherland C5-aminoimidazole-4-carboxamide riboside mimics the effects of insulin on the expression of the 2 key gluconeogenic genes PEPCK and glucose-6-phosphatase. Diabetes. 2000;49:896–903.
- 16. Foretz M, Carling D, Guichard C, Ferre P, Foufelle FAMP-activated protein kinase inhibits the glucose-activated expression of fatty acid synthase gene in rat hepatocytes. J Biol Chem. 1998;273:14767–14771.
- 17. Holmes BF, Kurth-Kraczek EJ, Winder WWChronic activation of 5′-AMP-activated protein kinase increases GLUT-4, hexokinase, and glycogen in muscle. J Appl Physiol. 1999;87:1990–1995.
- 18. Pollard, J.W., and Walker, J.M., editors1992. Basic cell culture protocols. Methods in Molecular Biology series, Volume 75. Humana Press Inc. Totowa, New Jersey, USA. 145–150.
- 19. Witters LA, Kemp BEInsulin activation of acetyl-CoA carboxylase accompanied by inhibition of the 5′-AMP-activated protein kinase. J Biol Chem. 1992;267:2864–2867.
- 20. Davies SP, Carling D, Hardie DGTissue distribution of the AMP-activated protein kinase, and lack of activation by cyclic-AMP-dependent protein kinase, studied using a specific and sensitive peptide assay. Eur J Biochem. 1989;186:123–128.
- 21. Mannaerts GP, Debeer LJ, Thomas J, DeSchepper PJMitochondrial and peroxisomal fatty acid oxidation in liver homogenates and isolated hepatocytes from control and clofibrate-treated rats. J Biol Chem. 1979;254:4585–4595.
- 22. Carling D, Clarke PR, Zammit VA, Hardie DG. Purification and characterization of the AMP-activated protein kinase. Copurification of acetyl-CoA carboxylase kinase and 3-hydroxy-3-methylglutaryl-CoA reductase kinase activities. Eur J Biochem. 1989;186:129–136.
- 23. Hayashi T, et al Metabolic stress and altered glucose transport: activation of AMP-activated protein kinase as a unifying coupling mechanism. Diabetes. 2000;49:527–531.
- 24. Sheng Z, Otani H, Brown MS, Goldstein JLIndependent regulation of sterol regulatory element-binding proteins 1 and 2 in hamster liver. Proc Natl Acad Sci USA. 1995;92:935–938.
- 25. Cusi K, DeFronzo RAMetformin: a review of its metabolic effects. Diabetes Reviews. 1998;6:89–131.
- 26. Wiernsperger NFMembrane physiology as a basis for the cellular effects of metformin in insulin resistance and diabetes. Diabetes Metab. 1999;25:110–127.
- 27. Sum CF, et al The effect of intravenous metformin on glucose metabolism during hyperglycaemia in type 2 diabetes. Diabet Med. 1992;9:61–65.
- 28. Wilcock C, Wyre ND, Bailey CJSubcellular distribution of metformin in rat liver. J Pharm Pharmacol. 1991;43:442–444.
- 29. Wilcock C, Bailey CJAccumulation of metformin by tissues of the normal and diabetic mouse. Xenobiotica. 1994;24:49–57.
- 30. Hermann LSMetformin: a review of its pharmacological properties and therapeutic use. Diabete Metab. 1979;5:233–245.
- 31. Sterne J, Duval D, Junien JLMetformin therapy. Research Clinical Forums. 1979;1:13.
- 32. Owen MR, Doran E, Halestrap APEvidence that metformin exerts its anti-diabetic effects through inhibition of complex 1 of the mitochondrial respiratory chain. Biochem J. 2000;348:607–614.
- 33. El-Mir MY, et al Dimethylbiguanide inhibits cell respiration via an indirect effect targeted on the respiratory chain complex I. J Biol Chem. 2000;275:223–228.
- 34. McGarry JD, Brown NF. The mitochondrial carnitine palmitoyltransferase system. From concept to molecular analysis. Eur J Biochem. 1997;244:1–14.
- 35. Shimomura I, et al Decreased IRS-2 and increased SREBP-1c lead to mixed insulin resistance and sensitivity in livers of lipodystrophic and ob/ob mice. Mol Cell. 2000;6:77–86.
- 36. Kakuma T, et al Leptin, troglitazone, and the expression of sterol regulatory element binding proteins in liver and pancreatic islets. Proc Natl Acad Sci USA. 2000;97:8536–8541.
- 37. Davies SP, Carling D, Munday MR, Hardie DG. Diurnal rhythm of phosphorylation of rat liver acetyl-CoA carboxylase by the AMP-activated protein kinase, demonstrated using freeze-clamping. Effects of high fat diets. Eur J Biochem. 1992;203:615–623.
- 38. McGarry JDWhat if Minkowski had been ageusic? An alternative angle on diabetes. Science. 1992;258:766–770.