Acetyl-CoA carboxylase (ACC) activity is reduced, fatty acid oxidation is induced, and expression of lipogenic enzymes is suppressed - Phosphorylation and inactivation of ACC, as a result of AMPK activation,kserves to inhibit the proximal and rate-limiting step of lipogenesis. Reduced synthesis of the ACC product, malonyl-CoA, is also predicted to relieve inhibition of CPT-1, resulting in increased fatty acid oxidation. These effects are likely to contribute to metformin’s in vivo ability to lower triglycerides and VLDL.
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; Known target genes for SREBP-1, which include FAS and S14, are also downregulated in liver, further contributing to metformin’s effects to modulate circulating lipids and to reduce hepatic lipid synthesis and fatty liver. It should be noted that increased SREBP-1 is postulated as a central mediator of insulin resistance in DM2 and related metabolic disorders and that increased liver lipid content is implicated in hepatic insulin resistance
In isolated rat skeletal muscles, metformin stimulates glucose uptake coincident with AMPK activation. this effect is also additive with insulin (12). Thus, the observed association of increased glucose uptake and AMPK activation in isolated skeletal muscles suggests that metformin’s effect to augment muscle insulin action in vivo may be attributed to AMPK as well.
Metformin-mediated effects on hepatic glucose production contribute to its glucose-lowering efficacy. AMPK activation is required for inhibition of hepatocyte glucose production by metformin. Additional studies will be required to further elucidate precise mechanism(s) by which metformin-stimulated AMPK activation could result in inhibition of hepatic glucose production.