Transport of micro-opioid receptor agonists and antagonist peptides across Caco-2 monolayer.

Milk is the source of beta-casomorphins--biologically active peptides with opioid activity--which are suspected to play various roles in the human body. The local influence of exogenous opioid peptides on gastrointestinal functions has been widely reported. After passing the gut barrier, beta-casomorphins may affect the functions of immunological system, as well as dopaminergic, serotoninergic and GABA-ergic systems in brain, regulate the opioid receptor development and elicit behavioral effects. However, possibilities and mechanisms of the intestinal transport of beta-casomorphins in human body in vivo have not been reported so far. In our research, the transepithelial transport of micro-opioid receptor agonists--human beta-casomorphin-5 and 7(BCM5, BCM7) and antagonist--lactoferroxin A (LCF A) have been investigated using Caco-2 monolayer. In order to determine the pathway of investigated peptide transport across Caco-2 monolayer, two directions of the transport (apical to basolateral and basolateral to apical) have been studied. All investigated peptides were transported across the human intestinal cell line Caco-2 and the curves of cumulative amount of transported peptides in time were linear in each case. In addition, the hydrolysis of beta-casomorphins during 60 min of experiment by dipeptidyl peptidase IV was observed. The data suggest the possibility of transport of opioid peptides derived from food across human intestinal mucosa.