The development and characterization of theophylline and budesonide co-encapsulated poly (lactic acid) (PLA) nanoparticles

Inhaled drug delivery is ideal for treatment of asthma and chronic obstructive pulmonary disease (COPD) as it allows a local action of the medication at the disease site. Biodegradable polymeric nanoparticles which might allow extended/sustained release of inhaled drugs are synthesized using various methods however; these do not permit high encapsulation efficiency for hydrophilic drugs. The aim of the project was to test the hypothesis that it was possible to develop an efficient method for the co-encapsulation of a hydrophilic and lipophilic drug (theophylline and budesonide respectively) into nanoparticles. In order to improve the loading efficiency of both hydrophilic and hydrophobic drugs, a modified double emulsification solvent diffusion (DESD) method was developed and both co-encapsulated and mono-encapsulated nanoparticles (containing either drug) were synthesized. Improved loading efficiency, studied using high performance liquid chromatography (HPLC), for both drugs was obtained. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) showed that particles were in the sub-micron range (150-400 nm). Measurement of zeta potential showed that the particles had a negative surface charge and additionally Fourier-transform infra-red (FT-IR) spectroscopy confirmed that this was due to the polymer and no drug was adsorbed on the external surface of the nanoparticles. Resemblance of nanoparticles thermograms, obtained using differential scanning calorimetry (DSC), to those of the polymer alone suggested successful encapsulation of the drugs. Stability studies of the drug encapsulated nanoparticles conducted at different temperatures indicated that storage conditions of 2-8°C over a period of 6 months showed minimal changes in the particle size, zeta potential and morphological characteristics of the nanoparticles. Storage (of the nanoparticles) at 40°C over the course of 6 months resulted in larger variations on the particle size and zeta potential but also loss of morphological features of the nanoparticles, suggestive of changes in the polymer state at this temperature. Franz diffusion cells were used to study the release of drugs from the nanoparticles over 24 hours at room temperature and at 37oC. The results showed that release of theophylline and budesonide from nanoparticles was biphasic and sustained compared to release of drug from solutions containing an equivalent concentration of drug. The effect of the nanoparticles on the viability of airway epithelial cells was studied using a human bronchial epithelial cell line (16HBE14o-) using a 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay. The nanoparticles had no significant effect ii on cell viability except at the highest concentration of the suspension studied (5 mg/mL) (P <0.05). The permeability of 16HBE14o- cells, cultured at an air-liquid interface, to theophylline and budesonide applied in solution and as mono-encapsulated and co-encapsulated nanoparticles was studied. The nanoparticles and drug solutions did not affect the tight junctions of the cells and similar to the results obtained in the Franz diffusion cells, both drugs crossed the cells more slowly when applied as nanoparticles in comparison to the solutions. To study deposition of the nanoparticles; nebulized suspensions of the nanoparticles in de-ionized water and dry powder formulations using different grades of lactose were compared. The prepared formulations were studied using a multi-stage liquid impinger (MSLI). The results indicated that drug deposition was greatest in stages 1 and 2 of the MSLI where particle size was greater than 6. 8μm from the dry powder formulations in contrast to deposition throughout the five stages of the MSLI from the nebulized suspension. Morphological assessment of the dry powder formulations using SEM showed nanoparticles adhered to the lactose but also included nanoparticles in the absence of lactose and vice versa. In conclusion, theophylline and budesonide nanoparticles were successfully formulated using PLA by application of the DESD method. Nanoparticles possessed desired physicochemical properties including submicron size range and negatively charged surface; however a higher loading efficiency of the hydrophobic drug was obtained despite modifications to the DESD method. Low toxicity of the nanoparticles to human bronchial epithelial cells and sustained release over a period of 24 hours was achieved. Nanoparticles were delivered successfully in the target site at a desired particle size range when formulated as nebulized suspensions.