Endocrine Abstracts

Introduction: Non-alcoholic fatty-liver disease and T2DM remain a global burden. Metformin is the first-line drug for T2DM that decreases glucose and lipid levels. However, prolonged metformin treatment decreases vitamin B12(B12), whereas low B12 is associated with obesity and dyslipidaemia. Clinical studies showed that metformin treatment increases circulating adiponectin and adiponectin improves NAFLD. Others suggested that metformin has no effect on intrahepatic triglyceride (TG) levels. We hypothesised that low B12 might impede metformin-induced intrahepatic lipid lowering effect. We tested this hypothesis and assessed whether low B12 impairs the beneficial effect of metformin on hepatic lipid metabolism and the potential underlying mechanisms.

Methods: HepG2 cells were cultured using custom-made B12 deficient EMEM-media and seeded with different concentrations of B12: 500nM(control), 1000pM(1nM), 100pM and 25pM(lowB12), followed by 24-hour metformin/adiponectin treatment. Western-blotting, RT-qPCR, total intracellular TG, radiochemical analysis of TG synthesis and seahorse mitochondria-stress assays were undertaken.

Results: In low-B12 hepatocytes, total intracellular TG and synthesized radiolabelled TG were increased. Regulators of lipogenesis-(SREBF1), cholesterol-(LDLR) and genes regulating lipogenesis, TG and cholesterol biosynthesis were increased. Genes regulating fatty acid oxidation-(FAO) and mitochondrial function were decreased. We also observed decreased pAMPKα and pACC levels. Following metformin treatment in low B12-hepatocytes, we found that the gene and protein expression of above targets were not alleviated. However, adiponectin independently decreased intrahepatic lipid levels even in low B12 conditions via upregulated pAMPKα and pACC levels. Combined adiponectin and metformin treatment ameliorated the low B12 effect and resulted in increased pAMPKα and pACC, with subsequent reduction in lipogenesis, increased FAO and mitochondria function.

Conclusion: Low B12 impaired the lipid lowering effect of metformin. Adiponectin independently decreased intrahepatic lipids even in low B12 conditions. Co-administration with adiponectin ameliorated the low B12 effect with metformin treatment and induced a higher intrahepatic lipid lowering effect.