Abstract/Summary

Cyclodextrins (CDs) and crown ethers (CEs) are widely recognized as host molecules being able to form inclusion complexes with various guest chemical molecules or metal ions, thereby enhancing their physicochemical properties. In this study, CDs and CEs were evaluated as solubility enhancers for haloperidol (HAL) and retinol (RE), with an emphasis on their effects on solubility, stability, permeability, and in vivo biological activity. For HAL, inclusion complexes were prepared by α-CD, β-CD, hydroxypropyl-β-CD (HP-β-CD), methyl-β-CD (ME-β-CD), and γ-CD, and characterized using Job’s plots, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD). α-CD, ME-β-CD, and HP-β-CD significantly (p＜0.05) increased HAL aqueous solubility through the formation of 1:1 inclusion complexes, while γ-CD had no effect and β-CD provided only modest enhancement. Pharmacological activity in planaria revealed that HAL induced reduced mobility (mimicking catalepsy) in mammals, whereas the presence of CDs lessened this mobility-reducing outcome, indicating altered bioavailability. Separately, 18-crown-6 and 12-crown-4 were used to prepare HAL/CE complexes by incubation. Both CEs improved HAL solubility several hundred-fold relative to pristine HAL, with 18-crown-6 further enhancing HAL permeation across cellulose membranes in Franz-type diffusion cells. The complexes displayed 1:1 stoichiometry, and CE toxicity was evaluated in planaria, Galleria mellonella larvae, and cell cultures. For RE, solubility studies with CDs and CEs (10–50 mg/mL) showed that CEs decreased solubility, whereas HP-β-CD and ME-β-CD markedly enhanced it via host–guest complexation. Photostability testing under 3550 lux natural light for 144 h demonstrated that HP-β-CD retained 51% of RE content, while RE/ME-β-CD complexes significantly (p ＜ 0.05) promoted tail regeneration in planaria compared to pure RE or control conditions. Collectively, these findings demonstrate that CDs and CEs can selectively enhance solubility, permeability, and stability of poorly soluble compounds, modulate in vivo pharmacological activity, and that planaria provides a simple, biologically relevant platform for early-stage screening of neuroactive and bioactive formulations.