Four-level levodopa adsorption on C60fullerene for transdermal and oral administration: a computational study

Abstract

After more than fifty years, the administration of levodopa (LDOPA), a prodrug that crosses the blood-brain barrier and is metabolized to dopamine in the central nervous system, remains the most effective treatment for Parkinson’s disease, despite the manifestation of significant side effects. The development of carrier systems to increase the rate of LDOPA crossing the blood-brain barrier, to achieve stable therapeutic plasma levels and minimize side effects, has been a challenge. Innovative nanosystems for delivering LDOPA are being tested for improved Parkinson's disease therapy. In particular, buckminsterfullerene C₆₀ is promising, due to its ability to penetrate through the skin and the gastrointestinal tract, as well as its biomedical applications to enhance drug delivery. Aiming to give theoretical support to attempts in developing levodopa preparations for transdermal and oral administration that may provide more continuous dopamine stimulation and fewer side effects, we present a computational study of levodopa adsorption on C₆₀ fullerene in the 2–8 pH range. The LDOPA state with COO⁻ and NH₃⁺ protonated (LDOPAc) is investigated, with classical molecular dynamics (CMD) and density functional theory (DFT) simulations being undertaken to describe the LDOPAc adsorption onto C₆₀ fullerene, LDOPAc@C₆₀. Annealing calculations were performed to explore the space of molecular configurations of LDOPAc@C₆₀ to obtain optimal geometries. From the DFT simulations, we found a four-level adsorption pattern, which is in agreement with the shell distribution of LDOPAc around C₆₀ that we have obtained from our CMD simulations. Four van der Waals-like interaction potentials, characteristic of the LDOPAc@C₆₀ adsorption levels were estimated, each one related to an –OH group, with energy minima varying from −0.35 eV to −0.73 eV, and centroid–centroid distances in the 6.5–8.8 Å range. Infrared absorption and Raman scattering spectra of the four adsorption configurations were evaluated, allowing us to determine vibrational signatures, which can be very useful in probing the existence of the four adsorption levels.