Interaction of Salicylate and a Terpenoid Plant Extract with Model Membranes: Reconciling Experiments and Simulations

Abstract

We investigate the effects of two structurally similar small cyclic molecules: salicylic acid and perillic acid on a zwitterionic model lipid bilayer, and show that both molecules might have biological activity related to membrane thinning. Salicylic acid is a nonsteroidal antiinflammatory drug, some of the pharmacological properties of which arise from its interaction with the lipid bilayer component of the plasma membrane. Prior simulations show that salicylate orders zwitterionic lipid membranes. However, this is in conflict with Raman scattering and vesicle fluctuation analysis data, which suggest the opposite. We show using extensive molecular dynamics simulations, cumulatively >2.5 μs, that salicylic acid indeed disorders membranes with concomitant membrane thinning and that the conflict arose because prior simulations suffered from artifacts related to the sodium-ion induced condensation of zwitterionic lipids modeled by the Berger force field. Perillic acid is a terpenoid plant extract that has antiinfective and anticancer properties, and is extensively used in eastern medicine. We found that perillic acid causes large-scale membrane thinning and could therefore exert its antimicrobial properties via a membrane-lytic mechanism reminiscent of antimicrobial peptides. Being more amphipathic, perillic acid is more potent in disrupting lipid headgroup packing, and significantly modifies headgroup dipole orientation. Like salicylate, the membrane thinning effect of perillic acid is masked by the presence of sodium ions. As an alternative to sodium cations, we advocate the straightforward solution of using larger countercations like potassium or tetra-methyl-ammonium that will maintain electroneutrality but not interact strongly with, and thus not condense, the lipid bilayer.

Development of the CHARMM Force Field for Lipids

“…Analogous problems for other FF were recently summarized by Khandelia et al 38 Given the importance of ions in biological systems, this is a matter of concern. However, due to the additive approximation in the FF, the treatment of ions is inherently problematic.…”

Shedding light on the puzzle of drug-membrane interactions: Experimental techniques and molecular dynamics simulations

“…Therefore, Khandelia et al (2010) evaluated the influence of ions (Na + , K + and TMA + ) in MD simulations [82]. Specifically, the effect of salicylate on a DMPC membrane depended on the ion type, and the authors suggested that the presence of Na + masked the disordering effect of the drug in the previous simulation [82]. Recently, Venable et al (2013) revised the Lennard-Jones radii of ions in the CHARMM force field to calibrate the results to the experimental NMR deuterium order parameters, which minimized possible artefacts caused by the binding of ions to the lipid headgroups [83].…”

“…Therefore, Khandelia et al (2010) evaluated the influence of ions (Na + , K + and TMA + ) in MD simulations [82]. Specifically, the effect of salicylate on a DMPC membrane depended on the ion type, and the authors suggested that the presence of Na + masked the disordering effect of the drug in the previous simulation [82].…”

“…15 [82]. Therefore, Khandelia et al (2010) evaluated the influence of ions (Na + , K + and TMA + ) in MD simulations [82].…”

In Silico Identification of Plant-Derived Antimicrobial Peptides

“…Perillic acid is a terpenoid plant extract with antiinfective and anticancer properties, and is a small cyclic molecule structurally similar to salicylic acid. It is known to cause large-scale membrane thinning, a clearly possible antimicrobial activity through a membrane-lytic mechanism very close to that of AMPs (Khandelia et al, 2010). Indeed, also subproteins or subpeptides may be relevant to antimicrobial activity in silico prospection.…”