Molecular-weight-dependent, Anionic-substrate-preferential Transport of β-Lactam Antibiotics via Multidrug Resistance-associated Protein 4

beta-Lactam antibiotics have cerebral and peripheral adverse effects. Multidrug resistance-associated protein 4 (MRP4) has been reported to transport several P-lactam antibiotics, and its expression at the blood brain barrier also serves to limit their distribution to the brain. Therefore, the purpose of this study was to clarify the structure activity relationship of MRP4-mediated transport of beta-lactam antibiotics using MRP4-expressing Sf9 membrane vesicles. The transport activity was evaluated as MRP4-mediated transport per MRP4 protein [nL/(min.fmol MRP4 protein)] based on measurement of MRP4 protein expression by means of liquid chromatography-tandem mass spectrometry. Cefotiam showed the greatest MRP4-mediated transport activity [8.90 nL/(min.fmol MRP4 protein)] among the beta-lactam antibiotics examined in this study. Measurements of differential transport activity of MRP4 for various beta-lactam antibiotics indicated that (i) cephalosporins were transported via MRP4 at a greater rate than were penams, beta-lactamase inhibitors, penems, or monobactams; (ii) MRP4-mediated transport activity of anionic cephalosporins was greater than that of zwitterionic cephalosporins; and (iii) higher-molecular-weight anionic beta-lactam antibiotics showed greater MRP4-mediated transport activity than lower-molecular-weight ones, whereas zwitterionic beta-lactam antibiotics did not show molecular weight dependency of MRP4-mediated transport. These quantitative data should prove useful for understanding MRP-related adverse effects of beta-lactam antibiotics and their derivatives.