Table 1.

Effects of Metformin on the Molecular Mechanisms of Hepatic Steatosis (De Novo Lipogenesis Reduction and Increased Fatty Acid β-Oxidation): Evidence from In Vivo Reports

Author (year)	Model (age)	Method	Metformin (dose/route/duration)	Effects of metformin	Interpretations
Studies showing effective intrahepatic lipid reduction by metformin
Fullerton et al. (2013)14	Male C57BL/6J mice (6 weeks old)	- HFD	- 50 mg/kg/day/IP/6 weeks - Starting after HFD for 12 weeks	↓ Hepatic lipogenesis, TG ↓ Malonyl CoA	Inhibitory phosphorylation of ACC by AMPK was essential for controlling lipid metabolism and metformin action.
		- ACC-DKI - HFD	- 50 mg/kg/day/IP/6 weeks - Starting after HFD for 12 weeks	↔ Hepatic lipogenesis, TG ↔ Malonyl CoA
Karavia et al. (2015)24	Male C57BL/6J mice (10–12 weeks old)	- Western diet	- 300 mg/kg/day/PO/18 weeks	↓ Hepatic TG, histologic steatosis ↑ P-AMPK/total AMPK	Metformin induced phosphorylation of AMPK.
Guo et al. (2018)22	Male C57BL/6J mice (3 weeks old)	- HFD	- 3 mg/kg/day/PO/5 weeks - Starting after HFD for 12 weeks	↓ Hepatic TG, TC ↑ p-AMPK/AMPK ↓ p-ACC/ACC	Metformin activated AMPK in vivo.
Huang et al. (2018)16	Male C57BL/6J mice (6 weeks old)	- HFD	- 250 mg/kg/day/PO/4 weeks then 500 mg/kg/day/PO/8 weeks - Starting after HFD for 14 weeks	↓ Hepatic TG, TC ↑ AMPK activity ↓ FAS, SCD1, SREBP-1c ↓ Hepatic ROCK1 activity	Metformin inactivated ROCK1, resulting in activation of AMPK signaling.
		- L-ROCK1-/- - HFD		↔ AMPK activity ↔ FAS, SCD1, SREBP-1c
Tang et al. (2016)23	Male C57BL/6J mice (4–6 weeks old)	- HFD	- 50 mg/kg/day/PO/15 days - Starting after HFD for 5 months	↓ Hepatic TG ↓ SREBP-1c, FAS, ACC-1 ↑ Hepatic LepR	Metformin dose-dependently enhanced hepatic leptin sensitivity.
			- 200 mg/kg/day PO/15 days - Starting after HFD for 5 months	↓ Hepatic TG ↓ SREBP-1c, FAS, ACC-1 ↑↑ Hepatic LepR
Stachowicz et al. (2012)38	Female C57BL/6J mice (8 weeks old)	- apoE-/-	- 10 mg/kg/day/PO/16 weeks	↑ SCAD, ECHD3, IPYR	Metformin up-regulated protein related fatty acid beta-oxidation.
Brandt et al. (2019)26	Female C57BL/6J mice (6–8 weeks old)	- Fat-fructose-and cholesterol-rich diet	- 300 mg/kg/day/PO/4 days	↓ Hepatic TG ↓ Liver NAS ↓ SREBP-1c ↔ FAS, ACC	Metformin improved liver histology and delayed the development of NAFLD.
			- 300 mg/kg/day/PO/6 weeks	↔ Hepatic TG ↓ Liver NAS ↔ SREBP-1c, FAS, ACC
Studies showing ineffective intrahepatic lipid reduction by metformin
Ford et al. (2015)15	Male C57BL/6J mice (8 weeks old)	- HFD	- 2.5 g/kg/day/PO/5 weeks - Starting after HFD for 5 weeks	↔ Hepatic TG ↔ p-ACC/ACC	Metformin had no effect on hepatic TG content and AMPK activation.
Sui et al. (2019)30	Male Zucker diabetic fatty rats (4–8 weeks old)	- fa/fa rats	- 50 mg/kg/day/PO/24 weeks	↑ Histologic fatty changes ↓ Total AMPK ↑ p-AMPK ↔ SCD1 ↓ G6PDX, HMGCS1, IGFBP1	Metformin promoted AMPK activation and correction of gene expression associated with LepR mutation.

ACC, acetyl-CoA carboxylase; ACC-DKI, ACC double knock-in mutation; AMPK, AMP-activated protein kinase; apoE^-/-, apolipoprotein E knock-out mutation; ECHD3, enoyl-CoA hydratase domain-containing protein 3; FAS, fatty acid synthase; G6PDX, glucose-6-phosphate dehydrogenase X-linked; HFD, high fat diet; HMGCS1, 3-hydroxy-3-methylglutaryl-coA synthase 1; IGFBP1, insulin-like growth factor-binding protein-1; IP, intraperitoneal route; IPYR, inorganic pyrophosphatase; LepR, leptin receptor; L-ROCK1^-/-, liver-specific ROCK1 deficient mice; NAFLD, nonalcoholic fatty liver disease; NAS, NAFLD activity score; p-ACC, phosphorylation of acetyl-CoA carboxylase; p-AMPK, phosphorylation of AMPK; PO, per os; ROCK1, Rho-kinase 1; SCAD, short-chain specific acyl-Co A dehydrogenase; SCD1, stearoyl-CoA desaturase-1; SREBP-1c, sterol regulatory element-binding protein 1; TC, total cholesterol contents; TG, triglyceride content; ↓, significant decrease; ↑, significant increase; ↔, no significant change.