Lipid environment determines the drug-stimulated ATPase activity of P-glycoprotein.

Abstract

P-glycoprotein (Pgp), also known as ABCB1 or multidrug resistance protein 1 (MDR1), is expressed in the luminal membrane of the intestine, liver, and kidney where it regulates the absorption, distribution, metabolism, and excretion (ADME) of a wide range of xenobiotic compounds and metabolites, and at the blood-brain where it protects the sanctuary from uptake of toxic compounds and enhances excretion of β-amyloid and metabolites. Its expression in cancer cells has been linked to multidrug resistance against many chemotherapeutic agents leading to ineffective treatment and relapse. Besides chemotherapeutic drugs, lipids have been suggested to be transported by themselves or co-transported with drugs by Pgp. Here we tested the hypothesis that the plasma membrane lipid composition modulates how drugs interact with Pgp and may greatly affect both the affinity of the transport substrates and its maximum activity. Our general approach was to test varieties of synthetic lipid mixtures starting with the bilayer-forming phosphatidylcholine (PC) and supplementing with phospholipids carrying different head groups as well as cholesterol. We present the first results of Pgp interactions with PC, phosphatidylethanolamine (PE), sphingomyelin (SM), and cardiolipin which we found to act as positive effectors and increase the apparent affinity for substrates and increase Vmax, while others acted as negative effectors and decreased Vmax. The impact on the substrate binding and translocation mechanisms of Pgp will be discussed. The long-term goal is to establish a stable source of synthetic phospholipid mixtures supplemented with cholesterol that mimic Pgp activity in its native environment in the human body.