Membranes Matter: Predicting Drug Toxicity

Abstract

2,4 dinitrophenol (DNP) is an artificial uncoupler of oxidative phosphorylation in mitochondria and was used in therapy against obesity in the mid-1930s. Due to severe side effects and even death cases DNP was prohibited for the therapeutic applications. A renewed interest for DNP originates from the intent to re-use it in small doses for the treatment of obesity, diabetes, hepatic steatosis and neuronal dysfunction. However, several aspects of its action mechanism in mitochondria are not understood. Considering an important role of membrane lipid composition for the mitochondrial uncoupling 1 , we compared the uncoupling effect of DNP in bilayer lipid membranes composed of (i) 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and cardiolipin (CL), which mimic inner mitochondrial membrane and (ii) DOPE-free membranes (DOPCþCL). Measurements of total membrane conductance, G, and membrane order parameter, S, revealed that DNP decreases G in concentration-dependent manner in DOPE-containing membranes. In contrast, S was more affected by DNP in DOPC-membranes. MD simulations revealed that (i) DNP-anions are localized in lipid headgroup region whereas protonated DNP were found to be shifted to the membrane centre as shown previously for fatty acids 2 , (ii) maxima of number density profiles for DNP-anion and DOPE overlap and (iii) the average distance between DNP-anion and DOPE headgroup corresponds to those of hydrogen bond. The molecular mechanism is discussed.