Molecular dynamics simulations of the interactions of medicinal plant extracts and drugs with lipid bilayer membranes

Several small drugs and medicinal plant extracts, such as the Indian spice extract curcumin, have a wide range of useful pharmacological properties that cannot be ascribed to binding to a single protein target alone. The lipid bilayer membrane is thought to mediate the effects of many such molecules directly via perturbation of the plasma membrane structure and dynamics, or indirectly by modulating transmembrane protein conformational equilibria. Furthermore, for bioavailability, drugs must interact with and eventually permeate the lipid bilayer barrier on the surface of cells. Biophysical studies of the interactions of drugs and plant extracts are therefore of interest. Molecular dynamics simulations, which can access time and length scales that are not simultaneously accessible by other experimental methods, are often used to obtain quantitative molecular and thermodynamic descriptions of these interactions, often with complementary biophysical measurements. This review considers recent molecular dynamics simulations of small drug-like molecules with membranes, and provides a biophysical description of possible routes of membrane-mediated pharmacological effects of drugs. The review is not exhaustive, and we focus on molecules containing aromatic ring-like structures to develop our hypotheses. We also show that some drugs and anesthetics may have an effect on the lipid bilayer analogous to that of cholesterol.