Analysis of absorption-enhancing mechanisms for combinatorial use of spermine with sodium taurocholate in Caco-2 cells

Previously, we reported that the combined use of spermine (SPM) and sodium taurocholate (STC) (SPM-STC) significantly improves the oral absorption of rebamipide (BCS class IV) and pulmonary absorption of interferon-alpha without any harmful histopathological changes in the gastrointestinal tract and lungs, respectively. In the present study, we examined the effect of SPM-STC on the transport of fluorescein isothiocyanate-labeled dextrans (FDs) across Caco-2 cell monolayers and attempted to clarify the mechanisms underlying the transport enhancement caused by SPM-STC. SPM-STC were found to significantly enhance the transport of FDs, while the treatment with SPM-STC was not harmful, and the decrease in transepithelial electrical resistance was transient and reversible. The voltage-clamp study clearly indicated that the opening of the paracellular route could be mainly responsible for the enhanced transport of FD-4. As for the mechanisms, it was found that SPM-STC caused a significant increase in membrane fluidity, which would lead to the enhanced transport of small-molecule drugs such as rebamipide. Since SPM-STC increased intracellular Ca2+ via Ca2+ uptake through Ca2+ channels and Ca2+ release from the endoplasmic reticulum stimulated by the IP3 pathway, the subsequent possible activation of the MLCK signaling pathway would have led to the contraction of the actin-myosin ring. The rearrangement of tight junction-constituting proteins induced through the MAPK pathway has also been suggested as a possible mechanism for opening tight junctions. Claudin-4, a key protein constituting the tight junction, merged with F -actin along with the plasma membrane, was significantly decreased, which would be at least partial structural evidence for the tight-junction opening.

Automated summary

The combined use of spermine and sodium taurocholate enhances the transport of fluorescein isothiocyanate-labeled dextrans across Caco-2 cell monolayers. This enhancement is achieved by increasing membrane fluidity, raising intracellular Ca2+ levels, and rearranging tight junction-constituting proteins. These findings provide insights into the mechanisms underlying the transport enhancement caused by spermine and sodium taurocholate.