Efficacy of Metformin in Vitamin B12 Deficient Liver Cells

Objective: The anti-diabetic drug, metformin, is associated with progressive decrease in serum vitamin B12 levels whereas vitamin B12 deficiency is related to increased insulin resistance and dyslipidaemia by altered methylation. As the risk of vitamin B12 deficiency is increased among metformin users, it is of utmost importance to examine how metformin response in vitamin B12 deficient population.

Research design and methods: We investigated the cellular mechanism of metformin in vitamin B12 insufficient human hepatocellular cell line (HepG2). HepG2 was cultured in different vitamin B12 conditions (0, 10, 100, 1000 nM) for four passages over 24 days. Then, they were treated with metformin 2 mM for 24 h. Protein and RNA extracts were quantified for AMP-activated protein kinase (AMPK) and its downstream signals.

Results: In HepG2 culture, there was a decreased gene expression level of Fatty Acid Synthase (FAS) and 3-Hydroxy 3-Methylglutaryl CoA Reductase (HMGCR) enzymes in 1000 nM B12 compared to 0 nM B12 condition. In metformin-treated hepG2 cells, phosphorylations of AMPK and acetyl-CoA carboxylase (ACC) were increased in 1000 nM B12 compared to 0 nM B12 condition. Similarly, there was a decreased gene expression level of FAS and HMGCR with metformin activation and the effects was more pronounced in B12 supplemented cultures than 0 nM B12 condition.

Conclusion: Our preliminary results indicate that metformin phosphorylation of AMPK together with its downstream signals were reduced in low B12 differentiated hepatic cells. This noble finding highlights the importance of vitamin B12 sufficiency for full potency of metformin.