Caco-2 cells in culture synthesize and degrade dopamine and 5-hydroxytryptamine: A comparison with rat jejunal epithelial cells

Abstract

To explore the usefulness of Caco-2 cells in the study of intestinal dopaminergic and 5-hydroxytryptaminergic physiology, we have undertaken the study of aromatic L-amino acid decarboxylase (AADC), catechol-O-methyltransferase (COMT) and type A and B monoamine oxidase (MAO-A and MAO-B) activities in these cells using specific substrates. The activity of these enzymes was also evaluated in isolated rat jejunal epithelial cells. The results showed that V max values (in nmol mg protein −1 h −1) for AADC, using L-DOPA as the substrate, in rat jejunal epithelial cells (127.3 ± 11.4) were found to be 6-fold higher than in Caco-2 cells (22.5 ± 2.6). However, K m values in Caco-2 cells (1.24 ± 0.37 mM) were similar to those observed in rat jejuanl epithelial cells (1.30 ± 0.29 mM). Similar results were obtained when AADC activity was evaluated using L-5HTP as substrate; in rat jejunal epithelial cells V max values (in nmol mg prot −1 h −1) were found to be 5-fold that in Caco-2 cells (16.3 ± 1.0 and 3.0 ± 0.2, respectively), and K m values in Caco-2 cells (0.23 ± 0.08 mM) were again similar to those observed in rat intestinal epithelial cells (0.09 ± 0.03 mM). Caco-2 cells were not able to O-methylate dopamine, in contrast to rat jejunal epithelial cells (V max = 8.6 ± 0.4 nmol mg protein −1 h −1; K m = 516 ± 57 μM). V max values (in nmol mg protein −1 h −1) for type A and B MAO in Caco-2 cells (19.0 ± 0.6 and 5.4 ± 0.6, respectively) were found to be significantly lower (P < 0.05) than those in rat jejunal epithelial cells (46.9 ± 3.1 and 9.6 ± 1.2, respectively); however, no signifiant differences in the K m values were observed between Caco-2 and rat jejunal epithelial cells for both type A and B MAO. In conclusion, Caco-2 cells in culture are endowed with the synthetic and metabolic machinery needed to form and degrade DA and 5-HT, though, no COMT activity could be detected in these cells.