Lactobacillus casei alters hPEPT1-mediated glycylsarcosine uptake in Caco-2 cells

Augmentation of the normal flora of the gastrointestinal tract with probiotic bacteria is currently under investigation as a therapeutic tool for several diseases. However, it is unknown whether probiotic bacteria such as Lactobacillus casei alter the expression and function of intestinal transport proteins such as hPEPT1. The effects of 24 and 48 h incubation of Caco-2 cells with 10(8)/L L. casei on the hPEPT1-mediated uptake rate of 20 micro mol/L [(3)H]glycylsarcosine were examined. Dipeptide uptake did not differ from the control at 24 h (15.9 +/- 2.4 vs. 11.5 +/- 1.4 cm.s(-1).mg protein(-1)); however, a significant increase in uptake occurred after 48 h of L. casei treatment (23.7 +/- 1.5 vs. 12.0 +/- 1.9 cm.s(-1).mg protein(-1); P = 0.005). hPEPT1 involvement was confirmed in experiments using excess substrate. Increased uptake of [(3)H]glycylsarcosine appeared to be the result of the direct interaction of the bacteria with Caco-2 cells because conditioned medium had no effect on dipeptide uptake. hPEPT1 mRNA levels did not differ at any time point. These results show that prolonged incubation of Caco-2 cells leads to increased hPEPT1 activity and that this occurs by a mechanism distinct from increased gene expression.