Effect of ascorbic acid in vitro on lymphocyte reactivity to mitogens

Ascorbic acid does not modulate potassium currents in cultured human lymphocytes

BACKGROUND

Ascorbic acid (AA) is known to modulate lymphocyte function, but the mechanism of action is not clearly understood. As voltage-gated potassium currents play an important role in lymphocyte function, the effect of AA on voltage-gated potassium currents was studied.

METHODS

Peripheral blood mononuclear cells were cultured in the presence of increasing concentrations of AA (0, 0.125, 0.25, 0.5, and 1 mM). Potassium currents in resting lymphocytes were studied by whole cell patch clamp technique using a depolarizing protocol. Lymphocyte function was assessed by measuring interleukin-2 (IL-2) secretion after mitogenic stimulation by ELISA.

RESULTS

The mean current density of potassium currents recorded from cells cultured for 48 h in the presence of 0.125 mM AA was not significantly different from that of cells cultured in the absence of AA. There was about 50% inhibition of IL-2 secretion in cell cultures with 0.125 mM AA when compared to controls without AA. At higher concentrations of AA, the IL-2 secretion decreased further.

CONCLUSIONS

The results of the study indicate that the inhibition of lymphocyte function by AA in vitro may not be due to inhibition of potassium currents in the concentration tested.

Effect of dietary ascorbyl-2-phosphate on immune function after transport to a feeding facility

Effects of dietary ascorbyl-2-phosphate on immune function after a 210-km trip were measured in 18 Holstein heifers. After transport on d 0, 10 g of ascorbyl-2-phosphate each were added to the diets of 10 heifers, whereas eight heifers were fed a control diet. Plasma cortisol concentrations increased by an average of 25.6 microgram/ml on d 0 following transport, but by d 7 after transport had decreased to pretransport levels. Average daily gain was lower in heifers fed ascorbyl-2-phosphate from d 28 to 49 d after transport, but did not differ over the entire study. Feeding ascorbyl-2-phosphate maintained plasma ascorbate concentrations on d 7 post-transport, which decreased in control heifers. Plasma keyhole limpet hemocyanin antibody titers were significantly higher in control heifers from d 7 to 49. Mononuclear leukocyte proliferation responses were decreased on d 0 in lymphocytes stimulated by mitogens, with pokeweed mitogen-stimulated cells showing less of a response than cells stimulated by the other mitogens. In the absence of mitogens, dietary ascorbyl-2-phosphate increased basal 3H-methyl thymidine incorporation by cultured lymphocytes. Across diets and mitogens, lymphocytes treated with cortisol showed decreased 3H-methyl thymidine incorporation. Transportation acted as a stressor, as evidenced by the increased plasma cortisol levels at d 0 immediately after transport, but immunological effects were not apparent by d 7. Feeding ascorbyl-2-phosphate maintained plasma ascorbate concentrations on d 7, but had negative effects on immune responses posttransport.

Effects of ascorbic and dehydroascorbic acid on the multiplication of tumor ascites cells in vitro

The effects of AA and DHA on ATP C+ cell multiplication in vitro were studied by measuring incorporation of 3H thymidine into DNA. The results obtained demonstrate that both AA and DHA have the same effects: they favor cell multiplication at low doses and inhibit it at high doses. Experiments carried out with serial doses of both these substances revealed that AA is more efficient in determining both stimulating and inhibiting effects. The lesser efficiency of DHA may be attributed to its limited stability in culture medium. Studies on the effect of high doses of AA and DHA added to the culture medium in single or fractionated doses revealed that fractionated administration is more efficient in inhibiting cell multiplication than single administration.