Background: Vitamin B12 (B12) is an essential micronutrient required for optimal hematopoietic, neurologic and other several metabolic reactions. Longitudinal studies and animal models showed that low maternal vitamin B12 deficiency is associated with the maternal obesity, development of insulin resistance and metabolic syndrome phenotype. Although the mechanisms underpinning metabolic disorders remain poorly defined, it has become increasingly clear that dysregulation of lipids and metabolic inflammation is associated with obesity and its comorbidities. Therefore, the aim of this study is to investigate the role of B12 in lipid regulation and inflammation in human adipocytes.
Methods: Human pre-adipocytes cell line (Chub-S7) and human primary pre-adipocytes were grown to confluence (day 0), differentiated in differentiation media for one week and maintained in nutrition media for next7 days (day 14). In order to analyse B12 deficiency effects, customized media with different concentrations of B12(25pM, 100pM, 1nM, 500nM) were used. On day 14,the condition media were collected and the cells were harvested for RNA and protein analysis, and stored at −80°C until use. Gene expression was performed by q-RTPCR and cytokine secretion was determined by ELISA. Cellular triglycerides (TG) synthesis was quantified using radioactive tracing technique by incorporation of 14C-oleate.
Results: Adipocytescultured in low vitamin B12 conditions showed significantly increased expression of genes involved in triglyceride synthesis such as Elongation Of Very Long Chain Fatty Acids Protein 6 (ELOLV6), Stearoyl-CoADesaturase(SCD), Glycerol-3-phosphateacyltransferases (GPAT), acylglycerolphosphateacyltransferase (AGPAT), phosphatidate phosphatase (LIPIN1), Diacylglycerol O-Acyltransferase 2 (DGAT2) and in lipid trafficking Fatty acid binding protein (FABP4). Cellular uptake of radio-labelled fatty acid (14C-oleate) for de novo TG biosynthesis assessed by scintillation was significantly higher in low B12 condition. In addition, we also observed that the gene expression of pro-inflammatory cytokines such as interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-18 (IL-18), transforming growth factor beta (TGF-β),monocyte chemoattractant protein-1 (MCP-1/CCL2) and IL1-beta secretion were significantly increased in low B12 conditions.