Background: Microencapsulation of natural antioxidants in polymeric
systems represents a possible strategy for improving the oral bioavailability of compounds
that are otherwise poorly soluble.
Objective: α-lipoic acid (ALA) was microencapsulated with polymethacrylate polymers
(blends at various ratios of Eudragit® RS100 and RL100 resins).
Method: Microspheres were produced by solvent displacement of an ethanol cosolution
of ALA and polymers; the microsuspensions were then freeze-dried, using
trehalose as a cryoprotector. Microspheres were characterized in the solid state for
micromeritic properties and drug loading, as well as by infrared spectroscopy, powder
X-ray diffractometry and differential scanning calorimetry. The antioxidant activity
of free and encapsulated ALA was assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay.
Results: In vitro release studies, performed in simulated gastric (pH 1.2) and intestinal fluid (pH 6.8),
showed that, depending on polymer composition and drug-to-polymer ratio, ALA release can be slowed
down, compared to the dissolution pattern of the free drug. Solid-state characterization confirmed the
chemical stability of ALA in the microspheres, suggesting that ALA did not develop strong interactions
with the polymer and was present in an amorphous or a disordered-crystalline state within the polymer
network. As indicated by the DPPH assay, the microencapsulation of ALA in Eudragit® Retard matrices
did not alter its antioxidant activity.
Conclusion: ALA was effectively encapsulated in Eudragit® Retard matrices, showing a chemical stability
up to 6 months at room conditions and at 40°C. Moreover, since the drug maintained its antioxidant
activity in vitro, the potential application of these microparticulate systems for oral administration
would deserve further studies.