The endothelial lining and its outer
lipid membrane are the first major barriers
drug molecules encounter upon
intravenous administration. Our previous work identified
lipid analogs that counteract plasma membrane barrier function for a series of amphiphilic drugs. For example, short-chain
sphingolipids (SCS), like
N-octanoyl-glucosylceramide, effectively elevated
doxorubicin accumulation in
tumor cells, both in vitro and in vivo, and in endothelial cells, whereas other (normal) cells remained unaffected. We hypothesize here that local
membrane lipid composition and the degree of
lipid ordering define SCS efficacy in individual cells. To this end, we study the differential effect of SCS on bovine aortic endothelial cells (BAEC) in its confluent versus proliferative state, as a model system. While their (plasma membrane) lipidome stays remarkably unaltered when BAECs reach confluency, their
lipids segregate to form apical and basolateral domains. Using probe NR12S, we reveal that
lipids in the apical membrane are more condensed/liquid-ordered. SCS preferentially attenuate the barrier posed by these condensed membranes and facilitate
doxorubicin influx in these particular membrane regions. We confirm these findings in MDCK cells and
artificial membranes. In conclusion, SCS-facilitated
drug traversal acts on condensed membrane domains, elicited by confluency in resting endothelium.