The role of vitamin B12 deficiency on obesity, adipocytes and inflammation

Background: Obesity, considered a pandemic disease by the World Health Organization (WHO) is constantly increasing worldwide. Its prevalence has doubled since 1980 and the biggest rise is in the developing world. The change from traditional foods to highcalorie fast food and the more sedentary lifestyle is probably the main mechanism driving this rise of obesity. However, it is not known whether there is an interaction between underlying susceptibility and lifestyle/environmental changes that (for example though epigenetic programming) exacerbates this rate of rise in obesity. The increased availability of unhealthy highly processed food with poor nutritional value can lead to micronutrient deficiency resulting in profound metabolic changes. Micronutrients play an important role in the metabolism of macronutrients and their deficiency can bring about cellular dysfunction. Vitamin B12 (B12) is an essential micronutrient required for optimal hematopoietic, neurologic and other several metabolic reactions. Indeed, in the last decade, animal and clinical studies have revealed a correlation between B12 deficiency and adverse metabolic health profiles. In particular, B12 deficiency in pregnancy has been associated with maternal obesity, development of insulin resistance and dyslipidaemia. Furthermore, studies have also explored the effect of B12 on male infertility. Given the key metabolic role of adipose tissue (AT) in obesity, we hypothesised that B12 deficiency may adversely influence lipid synthesis and metabolism by the adipocytes leading to adipose tissue inflammation. We also hypothesised that low levels of circulating B12, particularly in the presence of obesity, might influence their intracellular levels in this key ‘metabolic tissue’ as well as in other biological fluids such as seminal fluid. If B12 deficiency adversely affects seminal quality/function, this may also provide evidence towards adverse epigenetic programming through the paternal route. Methods: To test these hypotheses, the human abdominal subcutaneous pre-adipocyte cell line (Chub-S7) and human abdominal subcutaneous primary pre-adipocytes were differentiated under different B12 concentrations and Human omental white adipose tissue (OmWAT) , subcutaneous white adipose tissue (ScWAT)and blood samples were collected from 106 pregnant women at delivery. Serum B12 and relevant metabolic risk factors were measured. Gene expression was performed by q-RTPCR, de novo triglyceride synthesis was quantified by radioactive tracing, s-oxidation, palmitate-induced oxygen consumption rate was determined using seahorse-XF analyser, and serum cytokine levels was evaluated with ELISA technique. To test the role of B12 in seminal fluid in obese xvi patients, we analysed the cross-sectional data of 47-morbidly-obese and 21 lean men. Total B12 and holotranscobalamin (the active form of B12; holoTC) levels in serum and semen has been evaluated. Results: Adipocytes cultured in decreasing extracellular B12 media concentrations resulted in progressively increased intracellular B12 and an increased gene expression of B12 receptor CD320 and transporter TCN2 has been shown in adipocytes cultured in low B12 and in ScWAT and OmWAT of B12 deficient pregnant women. Adipocytes cultured in low-B12 conditions showed significantly increased expression (P<0.01) of genes involved in triglyceride biosynthesis, a significantly decreased expression (P<0.01) of genes involved in s-oxidation and an increased expression (P<0.01) of pro-inflammatory cytokines. These data were also confirmed in the AT of B12-deficient pregnant women where an increase of cytokine secretion has been shown. Additionally, real-time fatty acid flux synthesis and fatty acid oxidation (FAO) induced by palmitate were significantly altered (P<0.05) in B12-deficient adipocytes. Furthermore, associations between B12 and metabolic related biochemical values has been found. Moreover, both seminal and serum concentrations of holoTC and B12 were lower in morbidly obese compared to lean men, although the difference did not reach any statistical significance for serum holoTC. Seminal B12 and holoTC were significantly higher than B12 and holoTC serum levels in both groups. Significant positive correlations were observed between seminal holoTC and total sperm motility, sperm concentration, total sperm number and negative correlation with semen pH.ROC analysis supported seminal holoTC as the best predictor of sperm number. Conclusion: Our study highlights that the increased lipogenesis, as well as impaired FAO and mitochondrial dysfunction in low B12, induce uncontrolled lipid accumulation in the AT leading to local increased inflammation in adipocytes and AT. Our data highlights that B12 deficiency has profound effects on adipocyte dysfunction, opening new insights into the pathogenesis of maternal obesity and the relevance of micronutrient supplementation for pregnant mothers. In addition to this, our findings suggest that paternal B12 levels might also important in adverse programming of the offspring, through poor seminal quality. While this is interesting and novel, it requires further work especially in fathers.