Differential effects of vitamin D3 vs vitamin D2 on cellular uptake, tissue distribution and activation of vitamin D in mice and cells

Abstract

To combat vitamin D deficiency, vitamin D₃ and vitamin D₂ are commonly used as a supplement or to fortify food sources. Human data show that the response of 25-hydroxyvitamin D (25(OH)D) to supplementation with vitamin D₃ is higher than to vitamin D₂. To elucidate the metabolic route of both vitamers, we conducted a study with vitamin D-depleted mice, which were allotted into three groups (n = 12) and received equal doses of either deuterated vitamin D₃, deuterated vitamin D₂ or both for 4 weeks. To further investigate the hepatic uptake and hydroxylation of both D-vitamers to 25(OH)D, we conducted cell culture experiments with murine and human hepatoma cells (Hepa1-6 and HepG2). The vitamin D metabolite concentrations in serum, tissues and cells were analyzed by LC-MS/MS or ELISA. In mice, vitamin D₂ resulted in lower serum and tissue concentrations of vitamin D (P < 0.001) than vitamin D₃, while the group which received both D-vitamers showed values in between. Interestingly, vitamin D₂ fed mice had 1.9-times and 2.9-times higher serum concentrations of total and free 25(OH)D (P < 0.001) than mice fed vitamin D₃, while the concentration of 1,25-dihydroxyvitamin D (1,25(OH)₂D) was 1.8-times lower (P < 0.001). The gene and protein expression of enzymes, involved in the hydroxylation and renal uptake of vitamin D remained largely unaffected by the D-vitamer. In contrast to the mice data, hepatoma cells preferred vitamin D₃ for 25-hydroxylation over vitamin D₂ (P < 0.001). In general, the formation of 25(OH)D was much more pronounced in human than in murine hepatoma cells (P < 0.001). To conclude, in contrast to humans, vitamin D₂ was more efficient in increasing 25(OH)D than vitamin D₃ in mice, although this difference was not caused by a preferential hydroxylation of vitamin D₂ in the liver. The metabolic routes of D₃ and D₂ in mice differ, showing lower circulating 1,25(OH)₂D and tissue vitamin D concentrations in D₂- than in D₃-fed mice.

Keywords: HepG2; Hepa1-6; Hepatoma cells; Mice; Vitamin D(2); Vitamin D(3).