In vivo and in vitro penetration of vitamins into human red blood cells

Abstract

The entry of vitamins in red cells after intravenous administration of multivitamins was determined in six healthy volunteers; as control, red cell samples from six volunteers were each incubated with vitamins. Except for some folates, ascorbate, vitamins A and E, all B-vitamin red cell titers increased after intravenous multivitamins. Oral administration of a lipid soluble ester of thiamin, thiamin propyldisulfide, penetrated the red cells better than intravenously administered thiamin hydrochloride or the pyrophosphate coenzyme. The most striking increases were seen with B₆, thiamin, and biotin. N⁵-formyl-tetrahydrofolate increased reduced folylpolyglutamates but no folate vitamer could increase any type of oxidized folates in red cells. After direct incubation, all vitamins, except for A and E, entered the red cell; in contrast to the results seen in vivo, ascorbate penetrated red cell suspensions. Phosphorylated thiamin and pyridoxal did not penetrate as well as their free bases. Thiamin propyldisulfide, nicotinic acid, pyridoxal hydrochloride, and cyanocobalamin entered the red cell better than other respective analogs. Red cells incubated with N⁵-formyl-tetrahydrofolate or N⁵-methyl-tetrahydrofolate showed large increments in the mono- and polyglutamates of N⁵-methyl-tetrahydrofolate. In vivo, most B-vitmains quickly concentrate in tissues and result in lower intracellular red cell vitamin titers than seen in vitro. In vitro, most vitamins seem to concentrate in red cells by diffusion and thus higher vitamin titers are attained in the cells with longer periods of incubation, whereas in vivo the avidity of other vitamin depots decreased availability of vitamins for red cells. We conclude that red cells, like plasma, are capable of transporting vitamins.