Glutamine and arginine affect Caco-2 cell proliferation by promotion of nucleotide synthesis

Objective: We tested our hypothesis that 1) the major effect of Gln is as a nitrogen donor, not an energy source, for nucleotides (NT) and 2) the supplementation of culture medium with arginine (Arg) decreases the flux of glutamine (Gln) for conversion to Arg, thus accelerating NT synthesis. Methods: Various concentrations of nucleosides (NS+NT) Gln, and glutamate (Glu) in culture were tested for their effect on Caco-2 cell proliferation. (Arg was tested in media with and without Gln to evaluate the Gln pathway. The incorporation of 15N from image-[5-15N]-Gln into NTs of DNA was measured under different NS + NT and Arg concentrations.) Results: The proliferation of Caco-2 cells was increased by NS + NT and Gln supplementation, but not by Glu. The effective concentration of NS + NT was 100-fold smaller than that of Gln. An Arg effect was observed only in the presence of Gln. The NT synthesis from Gln, as indicated by 15N incorporation from image-[5-15N]-Gln, was increased by Arg supplementation and decreased by NS + NT supplementation. Conclusion: These results support our hypothesis that the effects of Gln and Arg on Caco-2 cell proliferation are by the promotion of NT synthesis and that the major role of Gln is not energy supply.