title: Evaluation of Eudragit® Retard Polymers for the Microencapsulation of Alpha-Lipoic Acid.
abstract: 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).
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.forename: Tiziana M G
authors.initials: TM
authors.lastname: Pecora
authors.forename: Teresa
authors.initials: T
authors.lastname: Musumeci
authors.forename: Lucrezia
authors.initials: L
authors.lastname: Musumeci
authors.forename: Massimo
authors.initials: M
authors.lastname: Fresta
authors.affiliation: Department of Drug Sciences, University of Catania, Viale A. Doria, 6; I-95125 Catania, Italy.
authors.forename: Rosario
authors.initials: R
authors.lastname: Pignatello
mesh_terms: D000975:Antioxidants / Q000737:chemistry* / Q000528:radiation effects; D001713:Biphenyl Compounds / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D004339:Drug Compounding; D004355:Drug Stability; D008863:Microspheres; D010782:Photolysis; D010851:Picrates / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry* / Q000528:radiation effects; D033362:Powder Diffraction; D012995:Solubility; D008063:Thioctic Acid / Q000737:chemistry* / Q000528:radiation effects; D014466:Ultraviolet Rays; D014961:X-Ray Diffraction
chemical_list: D000975:Antioxidants; D001713:Biphenyl Compounds; D010851:Picrates; D011109:Polymethacrylic Acids; C038300:methylmethacrylate-methacrylic acid copolymer; D008063:Thioctic Acid; C004931:1,1-diphenyl-2-picrylhydrazyl