Abstract
Vitamin B12 (cobalamin) is an essential cofactor in the one-carbon metabolism. One-carbon metabolism is a set of complex biochemical reactions, through which methyl groups are utilised or generated, and thus plays a vital role to many cellular functions in humans. Low levels of cobalamin have been associated to metabolic/reproductive pathologies. However, cobalamin status has never been investigated in morbid obesity in relation with the reduced semen quality. We analysed the cross-sectional data of 47-morbidly-obese and 21 lean men at Careggi University Hospital and evaluated total cobalamin (CBL) and holotranscobalamin (the active form of B12; holoTC) levels in serum and semen. Both seminal and serum concentrations of holoTC and CBL were lower in morbidly obese compared to lean men, although the difference did not reach any statistical significance for serum holoTC. Seminal CBL and holoTC were significantly higher than serum levels in both groups. Significant positive correlations were observed between seminal holoTC and total sperm motility (r = 0.394, p = 0.012), sperm concentration (r = 0.401, p = 0.009), total sperm number (r = 0.343, p = 0.028), and negative correlation with semen pH (r = −0.535, p = 0.0001). ROC analysis supported seminal holoTC as the best predictor of sperm number (AUC = 0.769 ± 0.08, p = 0.006). Our findings suggest that seminal rather than serum levels of holoTC may represent a good marker of semen quality in morbidly obese subjects.
Highlights
B12 is a water-soluble vitamin synthesized only in bacteria [1]
Nutrients 2019, 11, 1540 vitamin is crucial for homeostasis and growth as it acts as a coenzyme for the synthesis of methionine, a precursor of S-adenosyl methionine which provides the methyl groups for the methylation processes of macromolecules such as DNA, lipids, proteins, and neurotransmitters acting in the one-carbon-metabolism [3,4]
Around 10%–30% of circulating CBL is bound to the carrier transcobalamin in a complex named holotranscobalamin, which is considered the bioactive vitamin B12 [5]
Summary
B12 (cobalamin, CBL) is a water-soluble vitamin synthesized only in bacteria [1]. Around 10%–30% of circulating CBL is bound to the carrier transcobalamin in a complex named holotranscobalamin (holoTC), which is considered the bioactive vitamin B12 [5]. HoloTC has been proposed to represent a better marker than CBL of the vitamin deficiency status [6,7,8]. Another metabolic marker inversely associated with cobalamin is methylmalonic acid used to detect CBL deficiency at tissue levels [6], it is not routinely available for clinical testing
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