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 (10-50mM) showed an A_L type curve with a stability constant K_1:1=821M^-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±1.65μm and ∅_{DA:HP-β-CD-MS}=4.11±1.39μm, respectively. The zeta potential values of the microspheres were ζ_DA-MS=-7.85±0.32mV and ζ_{DA:HP-β-CD-MS}=-6.93±0.46mV. 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=43.29μM) against Vero cells (IC₅₀ of DA-MS=108.48μM and IC₅₀ of DA:HP-β-CD-MS=142.63μM).