Molecular modeling and cytotoxicity of diffractaic acid: HP-β-CD inclusion complex encapsulated in microspheres

In this pioneer study, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was used to improve the solubility of the diffractaic acid (DA) via inclusion complex (DA:HP-β-CD). Subsequently, DA:HP-β-CD was incorporated into poly-ε-caprolactone (PCL) microspheres (DA:HP-β-CD-MS). Microspheres containing DA (DA-MS) or DA:HP-β-CD (DA:HP-β-CD-MS) were prepared using the multiple W/O/W emulsion-solvent evaporation technique. The phase-solubility diagram of DA in HP-β-CD (10-50 mM) showed an AL type curve with a stability constant K1:1 = 821 M−1. 1H NMR, FTIR, X-ray diffraction and thermal analysis showed changes in the molecular environment of DA in DA:HP-β-CD. The molecular modeling approach suggests a guest-host complex formation between the carboxylic moiety of both DA and the host (HP-β-CD). The mean particle size of the microspheres were ∅DA-MS = 5.23 ± 1.65 μm and ∅DA:HP-β-CD-MS = 4.11 ± 1.39 μm, respectively. The zeta potential values of the microspheres were ζDA-MS = −7.85 ± 0.32 mV and ζDA:HP-β-CD-MS = −6.93 ± 0.46 mV. Moreover, the encapsulation of DA:HP-β-CD into microspheres resulted in a more slower release (k2 = 0.042 ± 0.001; r2 = 0.996) when compared with DA-MS (k2 = 0.183 ± 0.005; r2 = 0.996). The encapsulation of DA or DA:HP-β-CD into microspheres reduced the cytotoxicity of DA (IC50 = 43.29 μM) against Vero cells (IC50 of DA-MS = 108.48 μM and IC50 of DA:HP-β-CD-MS = 142.63 μM).